international islamic university malaysia iium (international islamic university malaysia) engineering journal chief editor ahmad faris ismail, iium, malaysia. technical editor md. noor bin salleh, iium, malaysia. executive editor waqar asrar, iium, malaysia. associate editor anis nurashikin nordin, iium, malaysia. language editor lynn mason, iium, malaysia. copy editor hamzah mohd. salleh, iium, malaysia. editorial board members a.k.m nurul amin, iium, malaysia abdullah al-mamun, iium, malaysia abdumalik rakhimov, iium, malaysia amir akramin shafie, iium, malaysia erwin sulaeman, iium, malaysia hanafy omar, saudi arabia hazleen anuar, iium, malaysia konstantin khanin, university of toronto, canada luis le moyne, university of burgundy, france ma'an al-khatib, iium, malaysia md zahangir alam, iium, malaysia meftah hrairi, iium, malaysia mohammed konneh, iium, malaysia mohammad s. alam, university of south alabama, united states mustafizur rahman, national university singapore, singapore nurul fadzlin hasbullah, iium, malaysia ossama abdulkhalik, michigan technological university, united states rosminazuin ab. rahim, iium, malaysia aims & scope of iium engineering journal the iium engineering journal, published biannually, is a carefully refereed international publication of international islamic university malaysia (iium). contributions of high technical merit within the span of engineering disciplines; covering the main areas of engineering: electrical and computer engineering; mechanical and manufacturing engineering; automation and mechatronics engineering; material and chemical engineering; environmental and civil engineering; biotechnology and bioengineering; engineering mathematics and physics; and computer science and information technology are considered for publication in this journal. contributions from other areas of engineering and applied science are also welcomed. the iium engineering journal publishes contributions under regular papers, invited review papers, short communications, technical notes, and letters to the editor (no page charge). book reviews, reports of and/or call for papers of conferences, symposia and meetings, and advances in research equipment could also be published in iium engineering journal with minimum charges. referees’ network all papers submitted to iium engineering journal will be subjected to a rigorous reviewing process through a worldwide network of specialized and competent referees. each accepted paper should have at least two positive referees’ assessments. submission of a manuscript a manuscript should be submitted online to the iium-engineering journal website: journals.iium.edu.my/ejournal. further correspondence on the status of the paper could be done through the journal website and the e-mail addresses of the executive editor: waqar@iium.edu.my faculty of engineering, international islamic university malaysia (iium), p.o. box 10, 50728, kuala lumpur, malaysia. phone: (603) 6196 4482, fax: (603) 6196 4853. journals.iium.edu.my/ejournal mailto:waqar@iium.edu.my iium (international islamic university malaysia) engineering journal international advisory committee tibor czigany yiu-wing mai luis le moyne, isat, university of burgundy, france razi nalim, iupui, indianapolis, indiana, united states farzad ismail, usm, pulau pinang, malaysia ossama abdulkhalik, michigan technological university, united states a. anwar, united states abdul latif bin ahmad, malaysia hanafy omar, saudi arabia hany ammar, united states idris mohammed bugaje, nigeria k.b. ramachandran, india kunzu abdella, canada m mujtaba, united kingdom mohamed ai-rubei, ireland mohamed b trabia, united states mohammad s. alam, university of south alabama, united states m. nazmul karim, united states syed kamrul islam, united states published by: iium journal publication, international islamic university malaysia p.o. box 10, 50728 kuala lumpur, malaysia tel: 03 6207 3507/3503/3502, fax: (+603) 6196-6298 e-mail: journal_press@iium.edu.my website: http://journals.iium.edu.my printed by: perniagaan normahs no 3, 5 & 7, jalan 12/10, taman koperasi polis fasa 1, 68100 mukim batu, batu caves, kuala lumpur, malaysia. whilst every effort is made by the publisher and editorial board to see that no inaccurate or misleading data, opinion or statement appears in this journal, they wish to make it clear that the data and opinions appearing in the articles and advertisement herein are the responsibility of the contributor or advertiser concerned. accordingly, the publisher and the editorial committee accept no liability whatsoever for the consequence of any such inaccurate or misleading data, opinion or statement. microsoft word 178-990-1-ed-1 completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hayyan et al. 37 utilizing of 1-hexyl-1-methyl-pyrrolidinium bis (trifluoromethyl-sulfonyl) imide as medium for electrochemical generation of superoxide ion-radical maan hayyan 1,2 , farouq s. mjalli 1,3 , mohd ali hashim 1,2 and inas m. alnashef 4 1 university of malaya centre for ionic liquids (umcil), university of malaya, 50603 kuala lumpur, malaysia. 2 department of chemical engineering, university of malaya, 50603 kuala lumpur, malaysia 3 petroleum & chemical engineering department, sultan qaboos university, muscat 123, oman 4 chemical engineering department, king saud university, riyadh, saudi arabia. maan_hayyan@yahoo.com abstract: the superoxide ion-radical was generated and analysed electrochemically using cyclic voltammetry (cv) technique from oxygen dissolved in a room-temperature ionic liquid, 1-hexyl-1-methyl-pyrrolidinium bis (trifluoromethylsulfonyl) imide, at atmospheric pressure. it was found that the generated superoxide ion was stable which indicates its possible use for further useful applications. abstrak: ion radikal superoksida dihasil dan dianalisa secara elektrokimia menggunakan teknik voltammetri berkitar (cyclic voltammetry (cv)) daripada oksigen yang dilarutkan dalam larutan ionik pada suhu bilik, 1-hexyl-1-methyl-pyrrolidinium bis (trifluoromethylsulfonyl) imida, pada tekanan atmosfera. didapati bahawa ion superoksida yang terhasil adalah stabil. ini menunjukkan ia berkemungkinan berguna dalam aplikasi lain. keywords: superoxide ion; ionic liquid; cyclic voltammetry; pyrrolidinium 1. introduction ionic liquids are finding widespread use as alternative for conventional solvents in a variety of applications, including liquid–liquid extraction, fuel and solar cells, organometallic synthesis, electrochemical devices, capacitors, lubricants, stationary phases for chromatography; matrices for mass spectrometry, supports for the immobilization of enzymes, in separation technologies, as liquid crystals, templates for synthesis nanomaterials and materials for tissue preservation, in preparation of polymer–gel catalytic membranes, biphasic catalysis, and in generation of high conductivity materials. they have unique properties such as high electrical conductivity, wide temperature range of the liquid state, thermal stability, and low volatility. moreover, because of their intrinsic conductivity and wide electrochemical windows, they have been utilized in a wide range of electrochemical applications [1-8]. one of these important applications is utilizing ils as alternative media for the reduction of o2 into superoxide ion-radical (o2 •) [9-14]. alnashef et al. is the first team who has reported the evidence of the electrochemical generation of stable o2 • in the ionic liquid, [bmim][pf6] [10-11]. subsequently, other ils iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hayyan et al. 38 have been investigated comprising different structures of cations and anions such as trifluoromethylsulfonyl imide, tetrafluoroborate, hexafluorophosphate and chloroaluminate, combining with imidazolium, phsphnium or ammonium cations [9-17]. 2. experimental and materials scheme 1 shows the structures of the cation and anion that make up the il 1-hexyl-1methyl-pyrrolidinium bis (trifluoromethylsulfonyl) imide, [hmpyrr][n(tf)2], (for synthesis, merck) which selected for this study. the molecular weight is 452.44 g/mol, and the formula is (c13h24f6n2o4s2). scheme 1: the structure of [hmpyrr][n(tf)2]. cyclic voltammetry (cv) tests were performed in [hmpyrr][n(tf)2]. the il was dried overnight in a vacuum oven at 50 ° c. the electrochemistry was performed using potentiostat/galvanostat controlled by computer and data acquisition software. cvs can be conducted in a one compartment cell since the time of the experiment is relatively small to affect the ils. glassy carbon electrode (3 mm diameter) was used as working electrode, and platinum electrode was used as a counter electrode, while ag/agcl electrode was used as a reference electrode. all experiments were performed in a dry glove box under either an argon or helium atmosphere. prior to superoxide ion-radical generation, a nitrogen sparge was used while obtaining a background voltammogram. oxygen was then bubbled through the system for at least 30 minutes to allow sufficient solubilization. between consecutive cv runs, oxygen was bubbled briefly to refresh the system with oxygen and to remove any concentration gradients. nitrogen or oxygen sparging must be discontinued during the cv data acquisition. 3. results and discussion the electrochemical window (fig. 1), shows a wide potential range which indicates the feasibility of use this il for many electrochemical applications, one of them is electrochemical generation of o2 •, due to its stability at ± (-1) v the generation of o2 • occurs by reduction of o2. figure 1 illustrates that the potential range is about 5.67 v, this is can be attributed to the existence of pyrrolidinium cation and trifluoromethylsulfonyl anion, since this type of il proves its wide electrochemical window [18]. figure 2 shows the cyclic voltammograms for the one-electron reduction of o2 to o2 •. the reduction peak was found to be within (-1 to -1.4 v), table 1, from 9 mv/s till 144 mv/s. the presence of the backward peak (oxidation peak) confirms that the generated superoxide is stable. the negligible background cv in the presence of nitrogen indicates that the il is electrochemically stable in this range of potential (0 to -1.5 v). it can be stated in fig 2 the difference between the reduction and oxidation peaks changed with scan rate. this indicates that the electrochemical generation of the superoxide ion in the studied ils is not reversible. this is consistent with the electrochemistry of a kinetically irreversible soluble redox couple [19]. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hayyan et al. 39 potential vs. ag/agcl (v) -4 -3 -2 -1 0 1 2 3 4 c u rr e n t d e n s it y ( m a /c m 2 ) -1.0 -0.5 0.0 0.5 1.0 fig. 1: electrochemical window of [hmpyrr][n(tf)2]. potential vs. ag/agcl (v) -1.5-1.0-0.50.0 c u rr e n t d e n s it y ( m a /c m 2 ) -0.4 -0.2 0.0 0.2 0.4 0.6 144 mv/s 100 mv/s 81 mv/s 64 mvs 36 mv/s 9 mv/s background fig. 2: cvs for various scan rates (mv/s) with oxygen and nitrogen (background) in [hmpyrr][n(tf)2]. table 1: the current and potential of reduction peak in cvs. scan rate (mv/s) current peak (a) x10 -5 potential peak (v) 9 1.02 -1.019 36 2.60 -1.207 64 3.06 -1.254 81 3.40 -1.308 100 3.65 -1.342 144 4.38 -1.426 4. conclusion stable superoxide ion-radical was generated in [hmpyrr][n(tf)2]. cyclic voltammetry technique was used to investigate the stability of o2 •, the combined of pyrrolidinium cation with trifluoromethylsulfonyl anion were confirmed their capacity to be a good medium as ionic liquid for the electrochemical generation of o2 •. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hayyan et al. 40 acknowledgement the authors thank the university of malaya centre for ionic liquids (umcil) for supporting this research and the national plan for science, technology, and innovation in king saud university for their financial assistance through project no. 10-env1010-02. references [1] t. welton, room temperature ionic liquids: solvents for synthesis and catalysis, chem. rev. 99, 2071–2084, 1999. [2] p. wassersheid and t. welton, “ionic liquids in synthesis” wiley–vch, weinheim, 2003. [3] r. d. rogers, m. smiglak, a. melten, “the second evolution of ionic liquids: from solvents and separations to advanced materials-energetic examples from the ionic liquid”. accoun.chem. res. 40, 1182-1192, 2007. [4] z. zhengxi, g. a. o. xuhui, , y. li, “electrochemical properties of room temperature ionic liquids incorporating bf4 and tfsi anions as green electrolytes”. chinese science bulletin 50, 18, 2005. [5] f. endres, d. macfarlane, a. abbott, “electrodeposition from ionic liquids”, wiley-vch, 2008. [6] s. o'toole, s. pentlavalli, a. p. doherty, “behavior of electrogenerated bases in roomtemperature ionic liquids”. j. phys. chem. b, 111, pp. 9281-9287, 2007. [7] d. s. silvester, e. i. rogers, l. e. barrosse-antle, t. l. broder, r. g. compton, “the electrochemistry of simple inorganic molecules in room temperature ionic liquids”. journal of the brazilian chemical society 19, 611-620, 2008. [8] m. c. buzzeo, c. hardacre, r. g. compton, “extended electrochemical windows made accessible by room temperature ionic liquid/organic solvent electrolyte systems”. chemphyschem, 7, 176-180, 2006. [9] m. t. carter, c. l. hussey, s. k. d. strubinger, r. a. osteryoung, “electrochemical reduction of dioxygen in room-temperature imidazolium chloride-aluminum chloride molten salts”, inorg. chem., 30, 1149, 1991. [10] i. m. alnashef, m. l. leonard, m. c. kittle, m. a. matthews, j. w. weidner, “electrochemical generation of superoxide in room-temperature ionic liquids, electrochem”. solid-state lett. 4, d16, 2001. [11] i. m. alnashef , m. l. leonard, m. c. kittle, m. a. matthews, j. w. weidner, “superoxide electrochemistry in an ionic liquid”, ind. eng. chem. res. 41, 4475, 2002. [12] m. c. buzzeo, o. v. klymenko, j. d. wadhawan, c. hardacre, k. r. seddon, and r. g. compton, “voltammetry of oxygen in the room-temperature ionic liquids 1-ethyl-3methylimidazolium bis ((trifluoromethyl) sulfonyl) imide and hexyltriethylammonium bis ((trifluoromethyl) sulfonyl) imide: one-electron reduction to form superoxide. steady-state and transient behavior in the same cyclic voltammogram resulting from widely different diffusion coefficients of oxygen and superoxide”, j. phys. chem. a, 107, 8872, 2003. [13] y. katayama, h. onodera, m. yamagata, and t. miura, “electrochemical reduction of oxygen in some hydrophobic room-temperature molten salt systems”, j. electrochem. soc., 151, a59, 2004. [14] r. g. evans, o. v. klymenko, s. a. saddoughi, c. hardacre, and r. g. compton, “electroreduction of oxygen in a series of room temperature ionic liquids composed of group 15-centered cations and anions”. j. phys. chem. b, 108, 7878, 2004. [15] m. c. buzzeo, c. hardacre, and r. c. compton, “kinetic analysis of the reaction between electrogenerated superoxide and carbon dioxide in the room temperature ionic liquids 1ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and hexyltriethylammonium bis (trifluoromethylsulfonyl) imide”. anal. chem., 76, 4583 2004. [16] d. zhang, t. okajima, f. matsumoto, and t. ohsaka, “electroreduction of dioxygen in 1-nalkyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquids”. j. electrochem. soc., 151, d31, 2004. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hayyan et al. 41 [17] m. m. islam, t. imase, t. okajima, m. takahashi, y. niikura, n. kawashima, y. nakamura, and t. ohsaka, “stability of superoxide ion in imidazolium cation-based roomtemperature ionic liquids”. j. phys. chem. a, 113, 912–916, 2009. [18] y. katayama, k. sekiguchi, m. yamagata, and t. miura, “electrochemical behavior of oxygen/superoxide ion couple in 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide room-temperature molten salt”. j. electrochem. soc., 152, 8, e247-e250, 2005. [19] a. j. bard, l. r. faulkner, “electrochemical methods: fundamentals and applications”, wiley new york, 2001. microsoft word 185-788-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology shariful islam et al. 67 enhanced cancer cell (hela) killing efficacy of mixed αlpha and gamma iron oxide superparamagnetic nanoparticles under combined ac (alternating current) magnetic-field and photoexcitation md. shariful islam 1 , yoshihumi kusumoto 1* , md. abdulla al-mamun 1 and yuji horie 2 1 department of chemistry and bioscience, 2 department of electrical and electronics engineering, graduate school of science and engineering, kagoshima university, 1-21-35 korimoto, kagoshima 890-0065, japan. horie@eee.kagoshima-u.ac.jp; kusumoto@sci.kagoshima-u.ac.jp abstract: we synthesized mixed α and γ-fe2o3 nanoparticles and investigated their toxic effects against hela cells under induced ac (alternating current) magnetic-fields and photoexcited conditions at room temperature. the findings revealed that the cellkilling percentage was increased with increasing dose for all types of treatments. finally, 99% cancer cells were destructed at 1.2 ml dose when exposed to combined ac magnetic-field and photoexcited conditions (t3) whereas 89 and 83 % of hela cells were killed under only ac magnetic-field induced (t1) or only photoexcited (t2) condition at the same dose. abstrak: campuran α dan zarah γ-fe2o3 bersaiz nano disintesiskan dan kesan toksidnya terhadap sel hela dikaji dibawah aruhan medan magnet arus ulang-alik (alternating current (ac)) dan keadaan photoexcited (proses ransangan atom atau molekul suatu bahan dengan penyerapan tenaga sinaran) pada suhu bilik. penemuan mendedahkan bahawa peratusan sel yang musnah bertambah dengan pertambahan dos untuk semua jenis rawatan. akhirnya, 99% sel kanser dimusnahkan pada kadar dos 1.2ml setelah didedahkan terhadap kombinasi medan magnet ac dan keadaan photoexcited (t3) dimana 89% dan 83% sel hela dimusnahkan dengan hanya di bawah aruhan medan magnet ac (t1) atau hanya pada keadaan photoexcited (t2) pada kadar dos yang sama. keywords: cancer; hyperthermia; iron oxide nanoparticles; heat dissipation, cytotoxicity; hela cell 1. introduction preferential heating of certain organs or tissues to temperatures between 41 °c and 46 °c for cancer therapy is called " hyperthermia ". higher temperatures up to 56 °c, which yield widespread necrosis, coagulation or carbonization (depending on temperature) is called "thermo-ablation" [1]. magnetic iron oxide nanoparticles and their dispersions in various media have long been of scientific and technological interest. maghemite (γfe2o3) is biocompatible and therefore is one of the most extensively used biomaterials for different applications like cell separation, drug delivery in cancer therapy, magnetic induced hyperthermia, mri contrast agent, immunomagnetic separation and others [2]. hematite has been used as photocatalyst for the degradation of chlorophenol and azo dyes iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology shariful islam et al. 68 [3] whereas maghemite and magnetite/carbon composites have been found to be useful for reducing the amount of undesirable n2 in fuel oil [4]. superparamagnetic nanoparticles when exposed to an alternating magnetic field can be used to heat tumor cells to 4145 °c, where damage for normal tissues is reversible while the tumor cells are irreversibly damaged [5]. in an alternating magnetic field, induced currents are generated in metallic objects, and as a consequence, heat is generated in the metal. thus, when a magnetic fluid is exposed to an alternating magnetic field, the particles become powerful heat sources, destroying tumor cells since these cells are more sensitive to temperatures in excess of 41 °c than their normal counterparts [6]. in view of these, in this report we describe a method for the synthesis of superparamagnetic magnetite (fe3o4) nanoparticles with modification of the method as described by omoike [7]. then, fe3o4 was transferred into mixed α and γ-fe2o3 superparamagnetic nanoparticles with modification of the method as described by sun et al. [8]. in our study, as-synthesized mixed α and γ-fe2o3 nanoparticles were applied to hela cancer cell killing in different ways such as ac (alternating current) magneticfield induction (t1), photoexcitation (t2) and combination of both (t3) to evaluate their cancer cell-killing potentiality. 2. experimental 2.1 materials and methods typical syntheses of magnetic nanoparticles (mnps) were carried out by using the reaction between fe 2+ and fe 3+ in co-precipitation method [8]. in this experiment, chemicals used for synthesis of mnps were fecl3, hcl, 25% nh3 solution (wako pure chemical industries ltd., japan) and fecl2 (strem chemicals, newburyport). for hela cell culture, phosphate buffer saline (pbs), new born calf serum (nbs) (invitrogen corporation, gibco), enzyme trypsine-edta (gibco) solution, 0.5% trypan blue stain solution (nacalai tesque, inc., kyoto, japan) and minimum essential medium (mem) solution (sigma) were purchased and used as received. 2.2 synthesis and formation of mnps by co-precipitation method in a typical co-precipitation method, fecl3 (2.6 g) and fecl2 (1.3 g) were dissolved in nitrogen gas (n2) purged 2.0 m hydrochloric acid solution and magnetically stirred under a continuous flow of n2. the mixture was heated at 70°c for 30 min and again heated for another 5 min under a blanket of n2. ammonia was added drop by drop to precipitate the mnps and the black product formed was treated hydrothermally at 70°c for 30 min. the resulting nanoparticles were subsequently separated from the reaction media under a magnetic field and washed three times with millipore water before drying. finally the mnps were oven dried at 70°c for 3 h to get fe3o4. it is well known that fe3o4 can be oxidized to γ-fe2o3, which can be further transformed into α-fe2o3 at higher temperature [7]. in this report, we simply transferred the fe3o4 (fig. 1a) to mixed αand γ-fe2o3 superparamagnetic nanoparticles by annealing it at 400°c for 6 h in the presence of oxygen. 3. structure and magnetic characterization the as-synthesized mnps were characterized using xrd, fe-sem and tem. ac magnetic field induced heating capability of mnps were performed to observe the hyperthermia potentiality of the mixed α and γ-fe2o3 by dispersing the nanoparticles in distilled water as well as in a mem and magnetic hysteresis loops were measured by superconducting quantum interference device (squid, quantum design mpms-5). iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology shariful islam et al. 69 fig. 1: xrd patterns of fe3o4 (a) and mixed α and γ-fe2o3 (b) and particle size distribution of mixed α and γ-fe2o3 obtained from tem data with approximation by a normal distribution (inset). 4. in-vitro cytoxicity and anti-cancer assay hela cells provided by the riken brc through the national bio-resource project of the mext, japan were cultured in mem solution with 10% nbs in a humidified incubator with an atmosphere of 5% co2 in air at 37°c for 3 days. the in vitro cytotoxicity and anti-cancer effect of the mixed iron oxide nanoparticles against the hela cell line was evaluated by a trypan blue exclusion method [9]. in the experiment, the alternative current (ac) magnetic-field was created by using a magnetic oscillator with desired frequency and strength of 560 khz and 5.0 ka/m, respectively, and a xenon lamp (cermax 300-w lx300f, usa, ilc) with heat cut-off and band-pass filters (350–600 nm) with an average intensity of 30 mw cm -2 was used for the light irradiation on hela cells. the light power was measured by a spectroradiometer (model ls-100, eko instrument co. ltd.). a table rotator was used for the petri dish to ensure the homogeneous light irradiation on the cells and temperature increment for the every dish was measured by a digital thermometer (sato keiryoki, model sk-250wp іі-r). to investigate the cytotoxicity of synthesized nanomaterials, one dish was used as control without any nanomaterials and the other five dishes were treated with different doses, like 0.2, 0.4, 0.8, 1.0 and 1.2 ml of nanoparticles colloidal solution per 5 ml of mem solution where the actual colloidal solution concentration was 10 mg/ml. a haemocytometer was used to estimate the total number of viable cells. 5. results and discussion superparamagnetic fe3o4 nanoparticles prepared by the co-precipitation method had high crystallization and good magnetic properties. sem and tem images (fig. 2a, 2b) showed that the mean particle size was ca. 15 nm. the as-synthesized fe3o4 nanoparticles were transferred to mixed αand γ-fe2o3 superparamagnetic nanoparticles by annealing it iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology shariful islam et al. 70 at 400°c for 6 h in the presence of oxygen (fig. 1) with the high crystallinity and mean particle size of ca. 15 nm (in set in fig. 1, fig. 2c, 2d). fig. 2: sem images of fe3o4 (a) and mixed α and γ-fe2o3 (c) and tem images of fe3o4 (b) and mixed α and γ-fe2o3 (d), respectively. figure 1 shows x-ray diffraction (xrd) plots of the fe3o4 (a), mixed iron (iii) oxide (αand γ-fe2o3) (b) nanoparticles of optimum properties. heat dissipation of magnetic particles was evaluated by using an ac magnetic field generator. the heats generated from three distinct treatments (t1, t2 and t3) were evaluated by exposing various doses of mixed iron oxide mnps suspension dispersed in a mem to an ac magnetic field. the temperature increment of magnetite nanoparticles suspensions against different doses is shown in fig. 3. the results revealed that highest temperature increment was obtained 48.7 °c under combined ac magnetic-field induced and photoexcited (t3) conditions at dose of 1.2 ml whereas for only ac magnetic field induced (t1) or only photoexcited (t2) condition the temperature increment was 45.5 °c and 37.1°c, respectively. similar results were reported by atsumi et al. [10] that maximum heat dissipation was observed for the mnps suspension with an average particle diameter of 14 nm, synthesized by the coprecipitation method. the toxic effect of mixed iron oxide nanoparticles was obtained by counting the percentage of viable cells after all the treatments (fig. 4). the cancer cell viability was 59, 62 and 41 % for t1, t2 and t3, respectively, at a dose of 0.2 ml. similarly the findings (fig. 4) revealed the cell killing percentage was increased with increasing dose for all types of treatments. finally, 99% cancer cells were destructed at a dose of 1.2 ml when exposed to combined ac magnetic-field induced and photoexcited conditions (t3) whereas 89 and 83 % of hela cells were killed in only ac magnetic-field induced (t1) or only photoexcited (t2) condition at the same dose (fig. 4). however, instrumentation modeling of acmagnetic field and photoexcitation, for the first time used by us indicates that ca.15 nm (fig. 1, inset) mixed iron oxide mnps have maximum heating rates as well as cancer (hela) cell killing efficacy within the biologically safe frequency range. to the best of our understanding, the mechanism or reason for 99% hela cell killing under t3 condition can iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology shariful islam et al. 71 be ascribed to the combined or synergistic effect of ac magnetic-field induced hyperthermia and photocatalytic cytotoxicity. fig. 3: heat dissipation capability of mixed iron oxide nanoparticles under different conditions. fig. 4: cancer cell killing efficacy of mixed iron oxide nanoparticles under three distinct conditions. error bars are the standard errors. 6. conclusions we described the synthesis of superparamagnetic magnetite nanoparticles and the phase transfer to the mixed α and γ-fe2o3 phase which due to their uniformity and monodispersity appear ideal for ac-magnetic field induced hyperthermia applications. to the best of our knowledge, for the first time we studied the cytotoxicity of mixed α and γfe2o3 nanoparticles under the ac magnetic-field induced and photoirradiated conditions with almost 100% cancer cell killing efficacy. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology shariful islam et al. 72 acknowledgement the present work was partly supported by grant-in-aid for scientific research (b) (no.19360367) from japan society for the promotion of science (jsps) and grant-in-aid for jsps fellows (no.20·00083). the authors are very happy to acknowledge to assistant professor hirotaka manaka, department of electrical and electronics engineering, graduate school of science and engineering, kagoshima university, for the analysis of the hysteresis loops of the prepared nanomaterials. references [1] a. jordan, r. scholz, p. wust, h. fähling, r. felix, “magnetic fluid hyperthermia (mfh): cancer treatment with ac magnetic field induced excitation of biocompatible superparamagnetic nanoparticles”. journal of magnetism and magnetic materials, vol. 201, 413-419, 1999. [2] m. chirita, i. grozescu, “fe2o3 – nanoparticles, physical properties and their photochemical and photoelectrochemical applications”. chem. bull. "politehnica" univ. (timisoara), vol. 54, no.68, 1, 2009. [3] j. bandara, u. klehm, j. kiwi, “raschig rings-fe2o3 composite photocatalyst activate in the degradation of 4-chlorophenol and orange ii under daylight irradiation”. applied catalysis b: environmental, vol.76, 73-81, 2007. [4] m. brebu, m.a. uddin, a. muto, y. sakata, c. vasile, “catalytic degradation of acrylonitrile−butadiene−styrene into fuel oil 1. the effect of iron oxides on the distribution of nitrogen-containing compounds”. energy & fuels, vol. 15, 559-564, 2001. [5] t. neuberger, b. schopf, h. hofmann, m. hofmann, b. von rechenberg, “superparamagnetic nanoparticles for biomedical applications: possibilities and limitations of a new drug delivery system”. journal of magnetism and magnetic materials, vol. 293, no. 1, 483-496, 2005. [6] an-hui lu, e. l. salabas, s. ferdi, “magnetic nanoparticles: synthesis, protection, functionalization, and application”. angewandte chemie international edition, vol. 46, 1222-1244, 2007. [7] a. omoike, “synthesis and characterization of tannic acid functionalized magnetic nanoparticles”. acs symposium series 996, chapter 8, pp 90-107, 2008. [8] s. sun, h. zeng, d. b. robinson, s. raoux, p.m. rice, s. x. wang, g. li, “monodisperse mfe2o4 (m = fe, co, mn) nanoparticles”. journal of the american chemical society, vol. 126, no. 1, 273-279, 2004. [9] m. abdulla-al-mamun, y. kusumoto, a. mihata, m. s. islam, b. ahmmad, “plasmoninduced photothermal cell-killing effect of gold colloidal nanoparticles on epithelial carcinoma cells”. photochemical & photobiological sciences, vol. 8, 1125 -1129, 2009. [10] t. atsumi, b. jeyadevan, y. sato, k. tohji, “heating efficiency of magnetite particles exposed to ac magnetic field”. journal of magnetism and magnetic materials, vol. 310, 2841–2843, 2007. microsoft word 260 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 203 muslim views on organ transplant abdi o. shuriye department of science in engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. shuriye@iium.edu.my abstract: in islamic worldview human cadaver is considered holy and sacred as of the living person. the human dignity bestowed on all mankind applies and it is extended to the corpse. for this reason, in the muslim world at least, organ transplant has been contentious process. this paper is a study on the procedures and ethical implications of organ transplant. it evaluates the islamic views on the issue. abstrak: pada panndangan islam, mayat manusia adalah suci dan mulia sebagaimana orang yang masih hidup. atas sebab ini, pemindahan organ dalam dunia islam memerlukan proses yang teliti. kertas ini mengkaji prosedur dan implikasi etika pemindahan organ dari sudut pandangan islam. keywords: organ transplant; ethics; religion;muslim views 1. introduction an organ transplant is a surgical operation in which a failing or damaged organ in the human body is removed and replaced with a functioning one. the donated organ may be from a deceased donor, a living donor. the objective of this paper is to thrash out both cadaveric and living organ transplants. the significance of this research is that it studies the issue from the perspective of the qur’an [1]. the research contends that religious and ethical predicaments in organ transplantation relate to religious beliefs, organ donation process, organ allocation to recipients, and commercialization and shortages of human organs. 2. the nature and background of organ transplant originally the term organ is derived from a greek term organon which denotes tool or instrument. transplant as a term refers to move or transfer something to another place or situation, with some effort or upheaval [2]. specific usage of transplant refers to moving living tissue or an organ and implant them in another part of the body or in another body as it indicates the operation in which an organ or tissue is transplanted, or a person or a thing which has been moved to a new place or situation [3]. the combination of the two terms organ and transplantation, or organogenesis as it is also known, gives the meaning of moving part of the biological organism from certain place in the body to another place or from another person or animal to another. in other words organ transplant would mean taking an organ from one person through surgery and then placed into another person whose own organ has failed because of illness or injury. historically speaking, transplantation of living tissues and organs has begun in the nineteenth century; j.l. reverdin triumphantly described in 1869 skin grafts and c. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 204 tiersch systemized it. these were however, transplantations of tissue within the same patient. it was soon applied into the treatment of server burns and repair skin defects. however, in late 1880s treatment centres made certain attempts to test tissues by using skins of cadavers or of amputated limbs though there was no concrete result from such experiments. then by late 1930s, e. ullmann of vienna, experimented on autotransplantation of parts of the intestine in the heterotypic sites, which later marked the beginning of living organ transplantation [3, 4]. 3. the process of organ transplant obviously, in order for a candidate to receive an organ, a donor has to be available. in cases like bone marrow, some kidney transplants and a small number of liver transplants, the donor may be a person who shares the same compatibility of tissue and immune system responses that creates a match. when an organ becomes available for donation, the organ is offered to the candidate that is the best match, based on the criteria set by the given organization, including the waited period, medical history, and severity of the illness. note that once removed from the body, organs can only be stored for a short period of time. for the purpose of the process of kidney transplantation blood test be run for urea nitrogen, also urine output is necessary, this is done without neglecting the health status of the patient [3]. one of the methods to excise the renal from the donor is laparoscopy [5]. laparoscopy is done, under anesthetic condition, by making a small incision next to the navel. a laparoscope is passed through the peritoneum, a membranous sac lining the abdominal cavity. the abdomen is swelled by passing carbon dioxide or nitrous oxide gas into the peritoneal cavity. the organs are then, in this case, recovered from the donor [5]. in performing heart transplantation two current types of procedures are identified; the orthotopic and heterotopic approaches. the choice between these two procedures highly depends on the patients themselves and the time consumption for each approach differs from one patient to another [5]. the orthotopic procedure involves replacing the recipient’s heart with the donor’s. in other words, the recipient’s damaged heart will be excised and removed for good. the donor’s heart must be transplanted into the recipient within four to five hours after it is removed, preserved and packed [5]. the heterotopic procedure does not involve removing the original heart. instead, the new heart received from the donor will be placed next to the damaged heart and it will function in parallel with the recipient’s original heart. despite this advantage of having a ‘back-up’ heart, this procedure is still rarely done compared to the orthotopic approach [5]. liver transplantation procedure was first attempted on human by dr. thomas starzl in 1963 and it underwent improvements in subsequent years, especially with the discovery of a better and promising immunosuppressant therapy. the recent rate of survival has encouragingly increased up to 73 percent per year [3]. methods used to perform liver transplantation are similar to the heart transplantation approaches i. e. orthotopic and heterotopic, with the same notion of either dissecting and removing the recipient’s old liver or leaving it were it is and adding in a new liver to function in parallel with the old one. lung transplantation is also an old method. although dr. hardy successfully performed in 1963, the first single lung transplant, the possibility of developing lung transplants was still very low and vague, as complications arise from organ rejection, iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 205 infection and insufficient healing hindered further success [3]. in the process the patient may have to undergo several regular checks on respiratory systems to detect and control failures before any other complications occur. the damaged lung is normally removed by excising it from the main blood vessel attachments to the heart and bronchus [3]. 4. muslim view points on organ transplant one of the basic teachings of islam is the preservation and protection of human life from body to batin (inner) prohibiting murder and massacre and grievance against any one unlawfully. the almighty presaged muslims on the matter in the qur’an. “if a man kills a believer intentionally, his recompense is hell, to abide therein (forever): and the wrath and the curse of allah are upon him, and a dreadful penalty is prepared for him”. (qur’an, 4:93) under the islamic legal system therefore, the punishment of a murder of any human life pays a life price: “o you believe the law of equality is prescribed to you in cases of murder the free for the free, the slave for the slave, the women for the women. but if the brother of the slain makes any remission, then grant any reasonable demand. and compensate him with handsome gratitude. this is a concession and a mercy from your lord. after this, whoever exceeds the limits shall be in grave penalty”. (qur’an, 2:178) the qur’an also repetitively reminds its believers that humans are dignified, honored and favored over other creatures by allah; dignity of life and death therefore has to be preserved. “nor take life, which allah has made sacredexcept for justice cause. and if anyone is slain wrongfully, we have given his heir authority (to demand qisas or to forgive) but let him not exceed bounds in the matter of taking life, for he is helped (by the law”. (qur’an, 17:33) similarly the qur’an makes life sacred: “we have honored the sons of adam; provided them with transport on land and sea; given them fro sustenance things good and pure; and conferred on them special favors, above a great part of our creation”. ( qur’an, 17:70) manifestations of danger to human life such as violence, destruction and economic sanctions, are strictly prohibited. “o you who believe! eat not up your property among yourselves in vanities; but let there be among you traffic and trade by mutual good will: nor kill (or destroy) yourselves: for verily allah have been to you most merciful”. (qur’an, 4:29) in line with the qur’anic teachings, majority of the muslim scholars have invoked the principle of priority of saving human life and has permitted the organ transplant as a necessity to procure that noble end. nonetheless it is prohibited to violate, harm or mutilate the cadaver whether it is a muslim or a non-muslim. there are exceptions to this general rule especially in a case when there is a necessity (darurah). one question could be underscored that if the donor is alive he or she may undergo normal surgical operation iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 206 but can the body of a dead donor undergo surgical procedures? the assessment of the views of the muslim jurists may shed some light on the issue. muslim jurists hold diverse opinions on the aforementioned question. the maliki and hanbal schools maintain that it is impermissible to dissect a dead pregnant lady in order to retrieve the infant. the shafi‘i school of thought on the other hand allows dissection to be carried out. dissection to remove valuable items from the dead is also allowed according to the mainstream of muslim jurists, except the hanbali school [6]. maliki and hanbali’s opinion on pregnant lady to salvage the infant may not be relevant at this stage due to the technological development. a council consists of the scholars from the major muslim schools of law in britain had painstaking deliberated on the issue of organ transplant and concluded that: “the medical profession is the proper authority to define the signs of death. current medical knowledge considers brain death to be a proper definition of death. the council accepts brain-stem death as constituting the end of life for the purpose of organ transplant. the council supports organ transplant as a means of alleviating pain or saving life on the basis of the rules of shari’ah. muslims may carry donor cards. the next of kin of a dead person, in the absence of a donor card or an expressed wish of the dead person to donate his organs, may give permission to obtain organs from the body to save other people’s lives” [7]. in his work, fiqh al-islami wa adillatuh, wahba az-zuhaili insists that: “based on the ruling, which allows dissection on dead bodies in specific cases, any dissection or operation done on the dead body due to a significant necessity is allowable. for example, dissection for the knowledge of medicine and dissection in order to find the cause of death to convict criminals by which there are no other avenues to come to the truth (al-haq). these are based on the shari‘ah principle of establishing justice, adil, in any ruling given by the court, in order to avoid injustice, dhalim, from happening to the innocent or to ensure that the guilty do not escape from the punishment as a result of his crimes. even though such dissections are allowed, it should be done within necessary limits without overdoing it. besides, the sanctity of the dead body has to be respected and handled properly. after the investigation, bits and pieces should be gathered, suturing it up and finally shrouding the body should close the body. it is also allowable to perform any organ transplant such as the human heart or the eye. this must be with the condition that the donor is proven to be dead by a specialist in the field. this is because the priority is given to the living. the success of recovering vision for a human is a wonderful gift and is demanded by the shari‘ah” [8]. the permanent committee for legal rulings in the saudi kingdom concluded the following on dissection: 1. dissection to discern criminal act caused the death of the diseased is sanctioned. 2. dissection to identify contagious disease and finding methods of sojourning its spread is also endorsed. 3. dissection for educational and training purposes is authorized [9]. islam requires that the donor be mature and mentally sane, able to decide his or her destiny through free will and in full control and comprehension. the intention to trade an organ or exchange it with other organs is considered unlawful contract between donor and recipient, as humans should not put their body on the market. the life of the donor should not be in danger as a result of the organ removal. it is not permissible also to donate essential organs such as the brain, nervous system and other crucial parts even to the iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 207 donors’ loved ones. on this aspect muslim scholars are in agreement on the illegitimate nature of donating life to another person [9, 10]. muslim jurists also divided organ donors into two main groups, dead and a live, putting each category under certain conditions. on the living donor the aforementioned conditions such as being mature, sane, responsible and able to make personal decisions apply. on the organ from dead persons jurists have permitted taking certain organs from diseased body with the following conditions in place: 1. the deceased should have permitted before his or her death 2. it should not be for the purpose of commerce and pecuniary in an article entitled transplantation of cells of nervous system, specially the brian”, sheikh mohamad al-mukhtar, a contemporary muslim scholar, divided the donors into four categories: respected or honourable adults, minors, the foetus, and adults whose life is not protected by islam [11]. faith has also been made a factor in the discussion of muslim jurists on organ transplant. it appears there is consensus that transplant is permissible from one muslim to another and from a non-muslim to a muslim. transplanting muslim organs into those under muslim protection is however a matter subjected to some disagreement while the transplant of muslim organs into non-muslims is not permitted according to the mainstream of muslim jurists [11]. on the xenotransplantation, the halalicity of the organ is relevant. the qur’an prohibited muslims to make use of or benefit from non-halal organs. “forbidden to you (for good) are: dead meat, blood, on which hath been invoked the name of other than allah; that which hath been killed by strangling, or by a violent blow, or by a headlong fall, or by being gored to death; that which hath been (partly) eaten by a wild animal; unless you are able to slaughter it (in due form; that which is sacrificed on stone (altars); (forbidden) also id the division (of meat) by raffling with arrows: that is impiety”. (qur’an, 5:3) in another related verse the qur’an permits the use of the haramized organs on the basis of complelling necessity, (darurah): “he has only forbidden you what has died by itself, blood and pork, and anything that has been consecrated to something besides god. yet anyone who may be forced to do so, without craving or going too far, will have no offence held against him; for allah is forgiving, merciful” (qur’an, 2:173). 5. conclusion the research found that transplantation of living organs has begun in the nineteenth century and developed to be used in the treatment of server burns and repair skin defects. the researcher is of the opinion that the process of organ transplant has never been straightforward. it explained laparoscopy as a method used in the process of organ transplant. laparoscopy is done, under anesthetic condition, by making a small incision next to the navel. another procedure used is orthotopic procedure. it involves replacing the recipient’s heart with the donor’s. in other words, the recipient’s damaged heart will be excised and removed for good. the donor’s heart must be transplanted into the recipient within four to five hours after it is removed. nonetheless organ transplant involves ethical iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 208 and religious issues. one of the basic teachings of islam is the preservation and protection of human life from physical to psychological and from emotional to spiritual. references [1] al-qur’an al-karim [2] judy pearsall (ed), the new oxford dictionary of english, oxford, university press, 2001 [3] abdi o. shuriye, islamic ethical values on bioengineering practices: issues in genetic engineering. research management centre, iium, pp. xivxvi, 2006 [4] w.f. bynum and roy porter (eds.) companion encyclopedia of the history of the medicine, routledge, london, 1993 [5] the organ procurement and transplantation network. about donation: living donation, retrieved july 23, 2004, http://www.optn.org/about/donation/livingdonation [6] muhamad al-din, ad-dirar al-mukhtar, law publishing, lahor-pakistan, 1970 [7] http://www.islamicvoice.com. [8] wahab az-zuhaili, al-fiqh al-islamiyi wa adilatuhu, dar al-fikr, damascus, syria, 1989 [9] abdul aziz khalifah al-qussar, hukum tashrih al-insan, bayna al-shariati wal qa’nun, dar ibn hazmi, beirut, 1 st edition, 1999, p.80 [10] al-qussar, dr, abdul aziz khalifah, hukum tashrih al-insan, bayna al-shariati wal qa’nun, dar ibn hazmi, beirut, 1999, p. 88 [11] sheikh mohamad al-mukhtar, transplantation of cells of nervous system, specially the brian. majalah majama’ al-fiqh al-islami, the 6 th seminar of the majma’, pp.1747-1756 application of digital cellular radio for mobile location estimation iium engineering journal, vol. x, no. x, 200x jamaludin and faizal 178 green synthesis of silver nanoparticles using sago (metroxylon sagu) via autoclaving method aliyah jamaludin and che ku mohammad faizal* faculty of engineering technology, universiti malaysia pahang, 26300 gambang, pahang, malaysia. *corresponding author: mfaizal@ump.edu.my (received: 20th feb 2017; accepted: 29th dec 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.815 abstract: sago (metroxylon sagu) is a polysaccharide bio resource, which is biodegradable and low in toxicity that can be found in large scale in mukah, sarawak. a simple green method of synthesizing silver nanoparticles (agnps) has been developed using sago dissolved in water as the reducing agent. the mixture of dissolved sago and silver nitrate (agno3) were autoclaved at 121 °c for 20 minutes. the size, morphology and structures of the agnps formed in the sago solution were investigated through uvvis spectrophotemeter, xrd and fesem analysis. the synthesized agnps were spherical in shape and well distributed with average particle sizes of 19.3 ± 2.7 nm. abstrak: sago (pokok rumbia) adalah sumber bio polisakarida yang bioterurai dan rendah ketoksikan yang boleh didapati dalam skala yang besar di mukah, sarawak. satu kaedah hijau yang mudah untuk mensintesis nanopartikel perak telah dihasilkan dengan menggunakan sagu yang larut dalam air sebagai ejen penurunan. campuran sagu yang dilarutkan dan perak nitrat (agno3) telah autoklaf pada suhu 121°c selama 20 minit. saiz, morfologi dan struktur nanopartikel perak yang terhasil di dalam larutan sago telah disiasat melalui analisis spektrofotometer uv-vis, xrd dan fesem. nanopartikel perak yang dihasilkan adalah berbentuk bulat dengan purata saiz partikel 19.3 ± 2.7 nm. key words: green synthesis; silver nanoparticles; antibacterial; autoclaving; sago 1. introduction global problem associated with environmental concerns have resulted in wide approach of ‘green‘ method in most of activities worldwide. this awareness involves in most industries and have attracted many researches to work on ‘green‘ materials and methods applicable in varied of applications. one of the most critical field to be concerned about the manufacturing process is the medical field. therefore, researches are working and innovating the method and process in manufacturing the devices to be applied in biomedical-related field. some of the key issues that need to be focused is the utilization of nontoxic chemicals, environmentally benign solvents and renewable materials [1-2]. one of those field is the process of synthesizing nanoparticles to be applied as the antibacterial agent in medical application. silver nanoparticles (agnps) field of research has become the as the focus attention among other metal nanoparticles such as copper, zinc, titanium, magnesium and gold [3]. the applications of agnps involved in renewable energies, water treatment, cosmetics and biomedical devices [4]. one of the best properties of agnps is the antibacterial efficacy against bacteria, viruses and some other micro-organisms [5] . since iium engineering journal, vol. x, no. x, 200x jamaludin and faizal 179 decades ago, agnps have been applied as antibacterial agents in health industry, food storage, textile coatings and number of environmental applications [6]. generally, agnps can be synthesized through several methods such as chemical, physical, photochemical and biological synthesis. among those methods, chemical synthesis via chemical reduction method is the most frequently applied for the preparation of agnps in water or organic solvent. the silver ions (ag+) are reduced by the reducing agents such as borohydride, citrate and ascorbate. however, most of these reducing agents are highly reactive and non-environmetally friendly components [7]. therefore, the alternative synthesis routes have been developed through green methods to prepare agnps. green synthesis method is simpler and will minimize or eliminate the toxic waste.the preparation of agnps via green synthesis should be evaluated from the choices of the medium, no-toxic reducing agent and stabilizer material. generally, water is used as the environmental friendly solvent. meanwhile, glucose is widely used as a green reducing agent becuase of its chemical reaction rate which allows a compromise between the nuclei created and the growth of the agnps [8-9]. further, polysaccharide such as starch, chitosan and gums are used as the stabilizer in the preparation of agnps [4,10]. in some cases, polysaccharides serve as the reducing agent, capping agent and stabilizer. sago is a starch, a type of natural polymer available in nature. in malaysia, large scale commercial sago plantations are found in mukah, sarawak and beaufort, sabah. sago or scientifically named as metroxylon sago is a white, tasteless, and odourless natural polymer extracted from the pith of sago palm stems. the extracted sago is manufactured into powder or “pearl” form. currently, sago industry became one of the country’s important agricultural export commodities [11]. sago is traditionally cooked and eaten in various forms. it is also used commercially in making noodles and bread. however, the use of sago is not just limited to the food industry. sago is also used as a key material input in various industries, such as in the paper, plywood, and textile industries [12]. similar to other kind of starch, sago is also categorized as polysaccharides which consist of aldehyde groups. the presence of hydroxyl will facilitate the complexation of silver ions by electrostatic binding in the helical structure of polysaccharide [13-14]. therefore, these silver ions oxidize the hydroxyl groups to carbonyl groups, during which the silver ions are reduced to elemental silver as shown in equation (1) below. 𝐴𝑔𝑁𝑂3(𝑎𝑞) + 𝑅𝐶𝐻𝑂(𝑎𝑞) = 𝐴𝑔(𝑠) + 𝑅𝐶𝑂𝑂𝐻(𝑎𝑞) (1) therefore, sago is a great candidate to be utilize as the reducing agent to synthesize agnps. thus, the aim of this work is to eliminate the toxic waste by using sago as the reducing agent and also to simplify the method of synthesizing agnps via autoclaving method which is simple and quick. 2. material and methods silver nitrate (agno3, sigma-aldrich) of analytical reagent grade was used for the synthesis. sago powder was purchased from dhulau enterprise, putatan, sabah, malaysia. the materials were used without purification. all the solutions were prepared in deionized water. sago solutions were prepared by adding 0.4, 0.8, 1.2, 1.6 and 2.0 volume/weight percentage (w/v %) of sago powder into 50 ml deionized water. then, the sago solutions were mixed with 1mm of agno3 solution with mixture ratio of 1:1.5. the mixtures were autoclaved at 121 °c for 20 minutes to synthesize the agnps. the autoclave used in this work is as shown in figure 1. then, the agnps solution were characterized through uviium engineering journal, vol. x, no. x, 200x jamaludin and faizal 180 visible spectrometer within the wavelenght range of 400 – 800 nm to monitor the surface plasmon resonance. x-ray diffraction (xrd) analysis was carried out in 2θ range of 30 80° to confirm the crystal structure of the agnps. further, the size and morphology of the synthesized agnps were also characterized through field emission scanning electron microscope (fesem). fig. 1: autoclave machine used to synthesize agnps at 121 °c for 20 minutes. 3. results and discussion 3.1 uv-visible spectroscopy (uv-vis) analysis the presence of nanoparticles in liquid is commonly observed by using uv-vis spectroscopy. it is a sensitive and quick technique to confirm the formation of agnps by monitoring the absorption spectra and the wavelength. the range of wavelength for agnps must be in between 400-450 nm. physically, the colour changes of the agnps solution also indicated the formation of agnps. figure 2 (a) shows the absorption spectra of agnps solution with varies sago concentrations synthesized via autoclaving at 121 °c for 20 minutes. each of the solution exhibits absorption peak in the range of nanoparticles wavelength which are 411, 410, 408, 410 and 413 nm with increasing percentage of sago from 0.4 – 2.0 (w/v) %. however, only agnps solution with 1.2 (w/v) % of sago concentration did not show any peak around 330 nm as shown in the highlighted area in the figure. this result indicated that there were no aggregations of particles within the solution. figure 2 (b) shows a clearer view of the absorption and the wavelength of the agnps solution. the absorption of agnps solution showed a direct proportional increment to the concentration of sago. the higher the absorption is referred to the higher amount of agnps that have been formed. further, the wavelength is referred to the size of the agnps. larger agnps tend to agglomerate to minimize their higher surface energy. when agnps iium engineering journal, vol. x, no. x, 200x jamaludin and faizal 181 aggregate and the conduction electrons near each particle surface become delocalized and are shared amongst neighbouring particles. hence, the surface plasmon resonance shifts to lower energies, causing the absorption peaks shift to longer wavelengths. from the figure, agnps solution with 1.2 (w/v) % sago concentrations show the lowest wavelength at 408 nm which indicate the formation of smaller size agnps. physically, the colour changes of the agnps solution from translucent to light yellow as shown in figure 2 (c) also proved the formation of agnps. the colour changes may be due to the excitation of surface plasmon resonance and reduction of agno3[15].from this uv-vis analysis, it is proved that the aldehyde groups from sago have reduced the silver ions, to the elemantel silver [14]. the basic reduction mechanisme of silver ions by aldehyde group to elemantel silver is shown in equation (1). fig. 2: (a) the uv-vis absorption spectra of the synthesized agnps with varies sago concentration (b) wavelength and absorbance of agnps with varies sago concentration (c) the colour changes of the mixture before and after autoclaving process. 3.2 x-ray diffraction(xrd) analysis the crystal structure of the synthesized agnps were confirmed through xrd analysis. figure 3 shows the xrd pattern of the synthesized agnps with 1.2 (w/v) % of sago. the iium engineering journal, vol. x, no. x, 200x jamaludin and faizal 182 xrd spectrum shows the 2θ degree peaks at 38.38, 44.52, 64.72 and 77.83 corresponding to (111), (200), (220) and (311), respectively. peak (111) is more intense than the other planes which show broadening pattern because of the size of nanoparticles and the presence of premature ag lattice plane [16,17]. peak broadening is normally seen in crystallites smaller than 100 nm. nano particles have much less atoms hence the lattice sum is not able to converge to a diffraction line but broaden out. this condition complies with the terms of the scherrer equation where peak width is inversely proportional to crystallite size. the same xrd peaks of agnps synthesized using other starches have also been reported by hebeish et al. and ghaseminezhad et al. [18-19]. fig. 3: xrd pattern of the synthesized agnps using 1.2 (w/v) % sago. 3.3 field emission scanning electron microscope (fesem) analysis fesem images of the synthesized agnps are shown in figure 4 at different magnifications of 50000 and 150000 times, respectively. both figure 4 (a) and (b) reveal that the agnps are well dispersed and spherical in shape. the average particle size of the agnps is 19.3 ± 2.7 nm, calculated using imagej software.the size of these green synthesized agnps are comparable to the agnps that used pva,a synthetic polymer as the reducing agent produced by sagitha and coworkers [20]. 4. conclusion this work reports the green synthesis of agnps from agno3 using sago as the reducing agent. we have demostrated a simple, efficient, quick and green technique to produce agnps via autoclaving method. all the analysis through uv-vis, xrd and fesem have recorded comparable and promising results as other agnps synthesized using other methods. the size, morphological and particle distribution of these green synthesized agnps also proved that sago acts as a good reducing agent as other synthetic polymers. iium engineering journal, vol. x, no. x, 200x jamaludin and faizal 183 fig. 4: fesem images of the synthesized agnps with different maginifications (a) 50 000x and (b) 150 000x. acknowledgement the authors would like to thank universiti malaysia pahang for the financial assistance under the grant of rdu140346. references [1] fei x, jia m, du x, yang y, zhang r, shao z, zhao x, chen x. (2013) green synthesis of silk fibroin-silver nanoparticle composites with effective antibacterial and biofilm-disrupting properties. biomacromolecules, 14:4483–4488. [2] raveendran p, fu j, wallen sl. (2003) completely ‘green’ synthesis and stabilization of metal nanoparticles. journal of the american chemical society, 125:13940–13941. [3] moritz m, geszke-moritz m. (2013) the newest achievements in synthesis, immobilization and practical applications of antibacterial nanoparticles. chemical engineering journal, 228:596–613. [4] vigneshwaran n, nachane rp, balasubramanya rh, varadarajan p v. (2006) a novel one-pot ‘green’ synthesis of stable silver nanoparticles using soluble starch. carbohydrate research, 341:2012–8. [5] venkatpurwar v, pokharkar v. (2011) green synthesis of silver nanoparticles using marine polysaccharide: study of in-vitro antibacterial activity. materials letters, 65:999–1002. [6] abou el-nour kmm, eftaiha a, al-warthan a, ammar r a. a. (2010) synthesis and applications of silver nanoparticles. arabian journal of chemistry, 3:135–140. [7] cheviron p, gouanvé f, espuche e. (2014) green synthesis of colloid silver nanoparticles and resulting biodegradable starch/silver nanocomposites. carbohydrate polymers, 108:291–298. [8] vasileva p, donkova b, karadjova i, dushkin c. (2011) synthesis of starchstabilized silver nanoparticles and their application as a surface plasmon resonancebased sensor of hydrogen peroxide. colloids and surfaces a: physicochemical and engineering aspects, 382:203–210. iium engineering journal, vol. x, no. x, 200x jamaludin and faizal 184 [9] singh m, sinha i, mandal rk. (2009) role of ph in the green synthesis of silver nanoparticles. materials letters, 63:425–427. [10] xu w, jin w, lin l, zhang c, li z, li y, song r, li b. (2014) green synthesis of xanthan conformation-based silver nanoparticles: antibacterial and catalytic application. carbohydrate polymers, 101:961–7. [11] karim aa, nadiha mz, chen fk, phuah yp, chui ym, fazilah a. (2008) pasting and retrogradation properties of alkali-treated sago (metroxylon sagu) starch. food hydrocolloids, 22:1044–1053. [12] abd-aziz s. (2002) sago starch and its utilisation. journal of bioscience and bioengineering, 94:526–529. [13] gao x, wei l, yan h, xu b. (2011) green synthesis and characteristic of core-shell structure silver/starch nanoparticles. materials letters, 65:2963–2965. [14] kora aj, beedu sr, jayaraman a. (2012) size-controlled green synthesis of silver nanoparticles mediated by gum ghatti (anogeissus latifolia) and its biological activity. organic and medicinal chemistry letters, 2:17. [15] ahmed s, ahmad m, swami bl, ikram s. (2014) a review on plants extract mediated synthesis of silver nanoparticles for antimicrobial applications: a green expertise. journal of advanced research, 7:17–28. [16] venkatesham m, ayodhya d, madhusudhan a, veera babu n, veerabhadram g. (2012) a novel green one-step synthesis of silver nanoparticles using chitosan: catalytic activity and antimicrobial studies. applied nanoscience, 4:113–119. [17] zheng y, zhu y, tian g, wang a. (2015) in situ generation of silver nanoparticles within crosslinked 3d guar gum networks for catalytic reduction. international journal of biological macromolecules, 73:39–44. [18] hebeish a, el-rafie mh, el-sheikh ma, el-naggar me. (2013) nanostructural features of silver nanoparticles powder synthesized through concurrent formation of the nanosized particles of both starch and silver. journal of nanotechnology, 2013:1– 10. [19] ghaseminezhad sm, hamedi s, shojaosadati sa. (2012) green synthesis of silver nanoparticles by a novel method: comparative study of their properties. carbohydrate polymers, 89:467–72. [20] sagitha p, sarada k, muraleedharan k. (2016) one-pot synthesis of poly vinyl alcohol (pva) supported silver nanoparticles and its efficiency in catalytic reduction of methylene blue. trans nonferrous met soc china, 26:2693–2700. microsoft word 5-abdelrahman-iiumej32-27-2-o.k..doc iium engineering journal, vol. 2, no. 1, 2001 c. c. li et al. 39 preparation of active absorbent for flue gas desulfurization from coal bottom ash: effect of absorbent preparation variables chang chin li, lee keat teong, subhash bhatia and abdul rahman mohamed* school of chemical engineering, universiti sains malaysia, engineering campus,14300 nibong tebal, s. p. s., p. pinang, malaysia. chrahman@eng.usm.my abstract: an active absorbent for flue gas desulfurization was prepared from coal bottom ash, calcium oxide (cao) and calcium sulfate by hydrothermal process. the absorbent was examined for its micro-structural properties. the experiments conducted were based on design of experiments (doe) according to 23 factorial design. the effect of various absorbent preparation variables such as ratio of cao to bottom ash (a), hydration temperature (b) and hydration period (c) towards the bet (brunauer-emmett-teller) specific surface area of the absorbent were studied. at a cao to bottom ash ratio = 2, hydration temperature = 200 c and hydration period = 10 hrs, absorbent with a surface area of 90.1 m2/g was obtained. based on the analysis of the factorial design, it was concluded that factor a and c as well as the interaction of factors abc and bc are the significant factors that effect the bet surface area of the absorbent. a linear mathematical model that describes the relation between the independent variables and interaction between variables towards the bet specific surface area of the absorbent was also developed. analysis of variance (anova) showed that the model was significant at 1% level. key words : absorbent, bottom ash, design of experiments, desulfurization, surface area. 1. introduction in an effort to protect the environment, industrial operations are required to reduce its emission of air pollutants. an air pollutant recognized world wide is sulfur dioxide (so2). the primary source of so2 are from boilers running on solid and liquid fuels. this is due to the nature of the fuel, where the sulfur compound present in the fuel will react with the air to form so2 during combustion process in the boiler. therefore, in order to reduce the emission of so2, flue gas from the boiler has to be treated with appropriate yet affordable desulfurization technology before being emitted to the environment. presently, different types of flue gas desulfurization (fgd) units are being operated. a wet-type fgd unit based on a limestone-gypsum method is most widely used and suitable for large-scale boilers such as those installed in coal or oil-fired power stations. the wettype fgd process has many advantages and has been continuously improved in terms of efficiency and cost reduction. however, as the wet-type fgd process requires a large amount of water and a facility for wastewater treatment, researchers are currently shifting their focus towards developing a dry desulfurization process applicable to power stations in a region where water supply is not sufficient. calcium compounds, especially calcium silicate, shows high desulfurization activity in dry fgd processes, due to its high surface area. high surface area in calcium silicate exposed calcium ions in the absorbent for the reaction between so2 and calcium to occur. jozewicz and chang [1] reported that two factors were necessary in an absorbent for it to be readily react with so2 under the conditions encountered in a dry injection fgd process: (i) high absorbent surface area and (ii) amorphous surface structure. thus absorbent’s high surface area is one of the keys to good desulfurization activity. a number of studies have been carried out to prepare absorbents with high surface area (calcium silicate) from calcium hydroxide and coal fl y ash [1-6]. the absorbent prepared can achieve a high calcium (ca) utilization efficiency of 80%, which is much higher than the value of about 50% for the drytype duct injection process using calcium hydroxide as the so2 absorbent. however, the weakness of using absorbents prepared from calcium hydroxide and coal fly ash is the long period required for absorbent preparation, which might take up to 12 hrs. in this present study, the effects of substituting calcium hydroxide with calcium oxide and coal fly ash with coal bottom ash as the raw materials for preparation of the absorbent was investigated. the effect of various absorbent preparation variables such as hydration temperature, hydration period and ratio of cao to bottom ash towards the bet specific surface area of the absorbent were studied. design of experiments based on full factorial design of 23 was used in the present study to establish the significance of each independent variable and interaction between variables. a linear mathematical model that describes the relation between the independent variables and interaction between variables towards the bet specific surface area of the absorbent was also developed. iium engineering journal, vol. 2, no. 1, 2001 c. c. li et al. 40 2. material and methods the absorbent was prepared from calcium sulfate, calcium oxide and coal bottom ash. the calcium sulfate used was of reagent grade, calcium sulfate hemihydrate (bdh laboratory supplies, england), whereas the calcium oxide was of laboratory grade (bdh laboratory supplies, england). the coal bottom ash was supplied by kapar power plant of tenaga nasional berhad. the bottom ash was thoroughly sieved, to obtain average sizes smaller than 75 m. the bottom ash was of the following composition: sio2 42.0%, al2o3 19.0%, cao 4.6%, fe2o3 9.6%, mgo 2.1%, nao 1.6% and ignition loss 21.1%. standard procedure to prepare the absorbent was as follows. to prepare 20 g of the absorbent (dry weight), a mixture of coal bottom ash (50 % of the total used) and calcium oxide was mixed with 28 – 35 % of water at 70 c for 5 minutes. calcium sulfate (8 g) and the rest of the coal bottom ash were added into the slurry and the kneading were continued for 10 minutes. the kneaded materials were extruded to form pellets. the pellets were then subjected to hydrothermal treatment with steam at a specific temperature for a specific period of time followed by drying for 2 hours at 200 c. the dried pellets was then crushed and sieved through a 60 m mesh. the amount of chemicals used and experimental parameters are given in table 1. table 1: experimental design ; hydration parameters and results. solid code variables bet surface area (m2/g) cao/bottom ash ratio hydration temperature (c) hydration period (hrs) s1 1/1 100 3 6.6 s2 2/1 100 3 64.0 s3 1/1 200 3 19.7 s4 2/1 200 3 26.4 s5 1/1 100 10 28.8 s6 2/1 100 10 34.1 s7 1/1 200 10 17.9 s8 2/1 200 10 90.1 s9-i 1.5/1 150 6.5 43.5 s9-ii 1.5/1 150 6.5 40.5 s9iii 1.5/1 150 6.5 45.2 s9iv 1.5/1 150 6.5 42.8 the specific surface area of the absorbent was measured by the bet method using autosorb 1c quantachrome. prior to analyzing the sample, it was degassed at 200 c for at least 8 hrs. five-point method was used to estimate the surface area of the prepared absorbent. 3. results and discussion bet surface area for bottom ash, cao, s8 (maximum value of bet specific surface area) and commercial absorbents are given in table 2. the significant increase in the specific surface area of the hydrated coal bottom ash absorbent as compared to the raw materials suggests that the mixing of the above-shown reagents resulted in the formation of certain compounds with a relativel y higher surface area. the hydrated absorbent prepared has a mixture of cylindrical granular grains, which consists predominantly of some calcium aluminate silicate hydrates and cao. these calcium silicates compounds are the main component in absorbing so2. table 2 bet surface area of raw materials and hydrated absorbents. material bet surface area (m2 /g) uncalcined bottom ash 2.45 cao 1.52 prepared absorbent 90.1 commercial absorbent 64.3 the significant increase in the surface area of the hydrated absorbent also indicates a high structural porosity as compared to the regular cao. the high surface area of a solid absorbent is an important parameter in the solid-gas adsorption process as it may be one of the principal factors that determine the overall reactivity. hydration experiments’ based on doe [7] were employed according to 23 factorial design to produce eight different types of absorbent. these combinations allow the studying of the individual influences and their respective interactions of cao to bottom ash ratio, hydration temperature and hydration period towards the absorbents’ bet specific surface area obtained after hydration. table 1 shows the experimental design and the results obtained. four experiments (s9-i to s9-iv) at the center point of the experimental design were performed in order to determine the experimental error. in relation to the results of bet specific surface area, four main observations can be mentioned : (i) the obtained values range from 6.6 m2/g to 90.1 m2/g ; (ii) the highest value is 90.1 m2/g corresponding to the experiment s8 performed at the maximum levels of the hydration variables; cao to bottom ash ratio of 2:1, hydration temperature of 200oc and 10 hours of hydration period ; (iii) cao to bottom ash ratio has a significant positive effect on the specific surface area. higher cao to bottom ash ratio was discovered to result in higher specific surface area. this is most probabl y due to the variation in ph, the concentration and amounts of dissolved solids as increasing the cao to bottom ash ratio increases the total amount of dissolved solids and thus the amount of calcium silicate hydrate formed. the presence of crystallized compound, calcium silicate hydrates, also known as oyelite, is important because it contributes to the increase of specific surface area. as the calcium (ca) ion is the main component of oyelite, it is expected that more cao will bring about more of this hydrated compound. it is also known that alkalinity has a positive effect in creating a crystallized structure; and (iv) hydration period and temperature has mixed effects on the bet surface area. iium engineering journal, vol. 2, no. 1, 2001 c. c. li et al. 41 to study the significance of each independent variable and interaction between variables on the bet surface area, analysis on the factorial design based on the 23 full factorial design given in table 1 was carried out. the three variables studied in this experiment were coded as factor a for cao to bottom ash ratio, factor b for hydration temperature and factor c for hydration period. interaction between factors such as between hydration temperature and hydration period was coded as bc. for 2 level factorial design, the levels of each factor were coded as low or (-1) and high or (1). the coding for all the experiments is given in table 3. for un-replicated factorial design used in this work, a method attributed to daniel (1959) [8], which suggest the plotting of the effect of a factor on normal probability paper was used. from the probability plot, effects that are negligible are normally distributed, with mean zero and variance 2, and will fall along a straight line on this plot, while significant effects will have nonzero means and will not lie along the straight line. the average effect of a factor is defined as the change in response (bet surface area) produced by a change in the level of that factor, averaged over the levels of the other factors while the effect of interaction factors are given elsewhere [7]. the effects of the individual factors and interaction between factors were calculated based on the ‘yates’ algorithm [7] and tabulated in table 4. data for the probability plot is given in table 5 and the probability plot itself is given in fig. 1. table 3: coding system used in the factorial design. solid code factors coding for factors cao/bottom ash ratio hydration temperature (c) hydration period (hrs) a b c s1 1/1 100 3 -1 -1 -1 s2 2/1 100 3 1 -1 -1 s3 1/1 200 3 -1 1 -1 s4 2/1 200 3 1 1 -1 s5 1/1 100 10 -1 -1 1 s6 2/1 100 10 1 -1 1 s7 1/1 200 10 -1 1 1 s8 2/1 200 10 1 1 1 table 4: yates algorithm for calculating the effects of individual factors and interaction between factors. solid code factors bet surface area (m2/g) column (1) column (2) column (3) estimate of effect s1 (l)* 6.6 70.6 116.7 287.5 s2 a 64.0 46.1 170.8 141.5 35.4 s3 b 19.7 62.8 64.1 20.7 5.2 s4 ab 26.4 108.0 77.4 16.3 4.1 s5 c 28.8 57.4 -24.5 54.1 13.5 s6 ac 34.1 6.7 45.2 13.3 3.3 s7 bc 17.9 5.2 -50.7 69.7 17.4 s8 abc 90.1 72.2 67.0 117.7 29.4 *(l)all the factors are low table 5: tabulated data for the probability plot. order (j) factor effect (j-0.5)/7 7 a 35.4 0.929 6 abc 29.4 0.786 5 bc 17.4 0.643 4 c 13.5 0.500 3 b 5.2 0.357 2 ab 4.1 0.214 1 ac 3.3 0.071 fig. 1 ordered effects for the 23 factorial design from fig. 1, it is noted that factors a, abc, bc and c do not fall in a straight line. in other words, factor a and c as well as the interaction between factors bc and abc are the main variables that influence the bet surface area of the absorbent. a linear model was developed based on the four factors. the coefficient for the factors are taken from the values of the effect in table 4. the linear model for the bet surface area is given in eq. (1): surface area = abc 2 29.4 bc 2 17.4 c 2 13.5 a 2 35.4 35.9                          (1) where the value 35.9 m2/g is the average bet surface area for absorbents with solid code s1 to s8 and a, c, bc and abc are the factors which takes the value of 1 or –1 based on table 3. table 6 compares the actual values of response (bet specific surface area) with the predicted values obtained from the linear model given in eq. (1). it can be seen that the model predicts the bet surface area quite accurately with the absolute average percent deviation of less than 10%. to verify the significance of the model and the four main factors that affect the absorbent bet surface area, analysis of variance (anova) was used. table 7 presents the results of the analysis of variance calculated using design-expert 6.0.4 software. based on the results, it is showed that the model used is significant at 1% level. it is also shown that the fours factors used in the model are the significant factors at 1% level that affect the bet surface area of the absorbent. iium engineering journal, vol. 2, no. 1, 2001 c. c. li et al. 42 table 6: comparison between actual and predicted values for bet surface area. solid code actual (m2/g) predicted (m2/g) residual (m2/g) error (%) s1 6.6 5.5 1.1 16.7 s2 64.0 70.3 -6.3 9.8 s3 19.7 17.5 2.2 11.2 s4 26.4 23.4 3.0 11.4 s5 28.8 31.0 -2.2 7.6 s6 34.1 36.9 -2.8 8.2 s7 17.9 19.0 -1.1 6.1 s8 90.1 83.8 6.3 7.0 absolute average percent deviation 9.8 table 7: analysis of variance for the absorbent bet surface area. source of variance estimate of effects sum of squares degrees of freedom mean square fo a 35.4 2506.3 1 2506.3 69.4a c 13.5 367.2 1 367.2 10.2a bc 17.4 605.5 1 605.5 16.8a abc 29.4 1728.7 1 1728.7 47.9a model 5207.8 4 1301.9 36.1a residual 108.3 3 36.1 total 5316.1 7 a : significant at 1% level for further diagnostic checking of the model, the residual given in table 6 are plotted on a normal probability paper shown in fig. 2. the points on this plot lie reasonably close to a straight line, lending support to our conclusion that factors a and c as well as the interaction between factors bc and abc are the only significant factors that effect the bet surface area of the absorbent, and that the underlying assumptions of the analysis are satisfied. fig. 2 normal probability plot of residuals 4. conclusion an investigation established on the preparation of absorbent for dry-type flue gas desulfurization based on utilizing coal bottom ash has been carried out. the following conclusions can be deduced from the results ; (i) coal bottom ash exhibits a promising future as an absorbent of dry-type flue gas desulfurization and showed potential for highly effective absorbents to be produced commercially (ii) factor a, c and the interaction of factors abc and bc are the only significant factors that effect the bet surface area of the absorbents prepared from coal bottom ash, calcium oxide and calcium sulfate. acknowledgement we would like to thank universiti sains malaysia for funding this project under an irpa short term grant. references [1] w. jozewiez and j. c. s. chang, “evaluation of fdg injection sorbents and additives”, development of highly reactivity sorbents, vol. i. epa-600/7-89-006a, 1989. [2] a. garea, i. fernandez, j. r. viguri, m. i. ortiz, j. fernandez, m. j. renedo and j. a. irabien, “flyash/calcium hydroxide mixtures for so2 removal : structural properties and maximum yield”, chemical engineering journal, vol. 66, pp. 171-179, 1997. [3] y. li and m. sadakata, “study of gypsum formation for appropriate dry desulfurization process of flue gas”, fuel, vol. 78, pp. 1089-1095, 1999. [4] t. ishizuka, h. tsuchiai, t. murayama, t. tanaka and h. hattori, “preparation of active absorbent for dry-type flue gas desulfurization from calcium oxide, coal fly ash and gypsum”, ind. eng. chem. res., vol. 39, no. 5, pp. 1390-1396, 2000. [5] t. ishizuka, t. yamamoto, t. murayama, t. tanaka and h. hattori, “effect of calcium sulfate addition on the activity of the absorbent for dry flue gas desulfurization”, energy & fuels, vol. 15, no. 2, pp. 438-443, 2001. [6] j. fernandez, m. j. renedo, a pesquera and j. a. irabien, “effect of caso4 on the structure and use of ca(oh)2/fly ash sorbents for so2 removal”, powder technology, vol. 119, pp. 201-205, 2001. [7] d. c. montgomery, design and analysis of experiments, john wiley & sons, n.y., usa 1976. [8] c. daniel, “use of half-normal plots in interperating factorial two level experiments”, technometrics, vol. 1, pp. 311-324, 1959. nomenclature a significant at 1% level a ratio of cao to bottom ash abc interaction between ratio of cao to bottom ash, hydration temperature and hydration period b hydration temperature iium engineering journal, vol. 2, no. 1, 2001 c. c. li et al. 43 bet brunauer-emmett-teller bc interaction between hydration temperature and hydration period c hydration period doe design of experiment fgd flue gas desulfurization (l) all the factors are low biographies chang chin li obtained her b. sc. degree in chemical engineering from universiti sains malaysia in 2001. she is currently working with shell malaysia as a process engineer. her long term career plan is to carry out research work in the field of molecular engineering. lee keat teong obtained his b. sc. degree in chemical engineering from universiti sains malaysia in 2000. he is currently pursuing his ph.d also in chemical engineering at universiti sains malaysia under national science fellowship from the ministry of science, technology and environment, malaysia. his field of research is in air pollution control. prof. subhash bhatia joined the school of chemical engineering, universiti sains malaysia, perak branch campus, in 1995. he was full professor at the department of chemical engineering, indian institute of technology, kanpur (india). prof. bhatia was a visiting faculty at the university of queensland, australia from 1988 – 1989 and 1994 – 1995. his research interests are zeolite catalysis, chemical reaction engineering and environmental catalysis. he has written a book on zeolite catalysis that was published by crc press, usa and has published more than 75 papers at national and international journals. dr. abdul rahman mohamed obtained his ph.d. in chemical engineering from university of new hampshire. his research interest is mainly in the environmental issues with the emphasis in air pollution control. he is currently the dean and associate professor of the school of chemical engineering, universiti sains malaysia. dr. abdul rahman has conducted and completed numerous funded research projects and has published more than 80 papers at various international and national conferences and journals. iium engineering journal, vol. 2, no. 1, 2001 44 microsoft word 43-570-4-pra iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 1 spot welding copper–1%cr electrode tips produced via equal channel angular pressing l. b. hussain 1 , a.a. aljuboury 2 , m.a.m. gebril 3 , nurulakmal m. sharif 1 1 school of materials and mineral resources engineering, universiti sains malaysia, penang, malaysia 2 department of physics, garyounis university, benghazi, libya. 3 benghazi, libya abstract: a sharp 120 o equal channel angular pressing (ecap) following route bc was applied at room temperature to refine the grain sizes of pure copper and copper1%chromium alloy for spot welding electrode tips application. initially deformation behavior was investigated with the position using colorful plasticine as work piece followed by copper alloy. it was found that the deformation at the central part of the work piece is heavily sheared than the outer part. optical and scanning electron microscopy were used to study the progress of grain refining under the influence of rotation and number of passes during pressing. the influence of elongated fibrous nano grains on electrical conductivity and hardness were discussed. shear test of spot welded 303 stainless steel indicated that nano structural cu-1%cr electrode tips used showed a superior results compared to commercial electrodes. keywords: equal channel angular processing (ecap); spot welding; ultra-fine grains, conductivity, hardness. 1. introduction severe plastic deformation methods have been the subject of intensive investigations in recent years [1]. it has been proven to be available for producing materials of fine microstructure via a method where large strain can be introduced into a work piece by simple shear deformation without change in the cross sectional area [2-5]. ecap process, where two equal cross sectional channels intersect at an oblique angleφ and ψ indicates the angle occupied by the curved region at the point of intersection and lies between ψ =0 and φ−=ψ π [6]. a work piece of almost the same cross section is placed into one of the channels (vertical channel), and a plunger then extrudes it into the second channel. despite the unique capability of ecap, primarily it has not been widely used because the strain per pass through the die channels is not very large; therefore to obtain a desire high strain and microstructure by ecap, many passes are required. materials for spot welding electrodes should have sufficiently high thermal and electrical conductivities, and sufficiently low contact resistance, to prevent burning of the work piece surface or alloying of the electrode face with it and should have adequate strength to resist deformation at operating pressures and temperatures. electrode materials iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 2 have been classified by resistance welder manufacturers association (rwma) into two composition groups: copper-based alloys and refractory metal compositions. these classifications cover a wide range of resistance welding electrode materials to meet most applications [7]. in addition to these standard materials, there are a number of unclassified copper alloys and other materials that may be suitable for resistance welding electrodes. suitability will depend upon the application, although most requirements are met by materials that comply with rwma standards [8]. copper is used for electrodes because it has a low resistance and high thermal conductivity compared to most metals. unfortunately, when the electrodes get too hot, heat marks on the surface of work pieces can be formed. the electrodes also become susceptible to “mushrooming”. electrode mushrooming reduces their usable lifetime. an attempt to overcome this entire problem is to strengthen copper alloy which can be developed via nano structure. an attractive and viable approach or mechanism for improving the strength of copper is to introduce a fine cr structure into cu matrix, resulting in a dispersion-strengthened alloy. copper matrices containing fine dispersions are particularly attractive for their excellent combinations of thermal and electrical conductivities, strength retention at elevated temperature and overall micro structural stability. in the current study, the deformation behavior of plasticine mainly focused on understanding of local inhomogeneity, during the ecap process. in particular, the effect of friction conditions on the inhomogeneous deformation of the work piece is described. subsequently a nano fibrous structural copper chromium alloy can be produced. properties such as conductivity with low electrical resistance and hardness were also discussed. 2. materials and method a die with two intersecting channels of equal cross section is used. a work piece, in the form of a circular cross sections are produced by pressing the work piece in the vertical (entrance) die’s channel to fit within the entrance channel of an ecap die and it is then pressed through the die until it emerges from the exit channel. in this investigation, the pressing condition applied following route bc, in which after each pass the sample is rotated 90 o clockwise before performing the next pass. according to segal [9] the shear plane orientation changed with the number of passes and intersection of these shear planes develop an approximate uniform network into the material. therefore, an equiaxial and ultrafine structures with high angle grain boundaries are attained for route bc with lowest number of passes. thus, route bc is more effective and more suitable for grain refinement. therefore, for each pass the pressed work piece have to be removed from the die, rotate 90 o clockwise and re-insert into the die for the next pass. under these conditions, the deformation is achieved by simple shear. deformed by ecap, the work piece retains the same cross sectional area so that it is able to repeat the process to several cycles. therefore, every plastic strain could be accumulated in the sample. the materials used in the present investigation were plasticine, copper and copper1%cr alloy as work pieces of 10 mm diameter were subjected to ecap for several iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 3 extruding passes at room temperature through lubricated tool steel die. ecap die consisted of two channels at an angle of φ=90 o and ψ =0 o as shown in fig. 1. fig. 1: angles for equal channel angular pressing and ecaped workpiece. the plasticine was made from small equal and colorful plasticine pieces connected to each other under very low pressure to produce 10 mm cross section plasticine rod in order to simulate the grain structure of polycrystalline structures. the plasticine work pieces were photographed before extrusion through the die and after each required number of passes. then the deformed trend was investigated. pure copper (99.9%) 10 mm in diameter and 50 mm in length, and copper1%chromium alloy was prepared via melting and casting, the alloy was fully annealed at 850 o for 1 hr and subsequently machined to rods with dimensions of 10 mm in diameter and 50 mm in length for ecap. copper and copper-chromium samples were cut using diamond cutter at transverse and longitudinal directions with respect to pressing direction of plunger side and mounted for polishing and etching. scanning electron microscopy was conducted and the grain sizes ware observed and size was estimated directly from the grains that have a well-defined grain boundary. knoop micro hardness testing with 100 gm were applied at room temperature, the resulting impression was observed under a microscope and measured. the value of hardness was taken as the average of 10 measurement made on the surface of the sample. after the samples at transverse and longitudinal directions were cut, resistivity test was carried out. the test was accomplished by a four point probe. the samples were fabricated into truncated shape before weld test on stainless steel (304) was carried out on the electrodes. this work was done using the lathe machining; coolant is used to avoid the grain growth of samples due to heat generated during machining. the fabricated electrode tips should be fitted well into a modified holder, and the minimum face diameter of electrode with truncated shape was 5 mm. iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 4 shear test specimens were made from 304 stainless steel samples having dimensions of 0.7 mm thickness, 16 mm width and 50 mm length after surface polishing and cleaning by sand blasting to avoid any hindrance of the current passing. the foot press type spot welding machine was used in this project to joint stainless steel samples, and different welding parameters were used to weld the stainless steel samples to get the best welding property. 3. results and discussion it has been demonstrated that, providing the sample is constrained to fully fill the die channel and the die corner is sharp, on traveling through the die an element will be sheared abruptly by crossing the joint line between the two channels by an amount dependent on the die channel angle [2]. the difference in the deformation behavior within the plasticine sample where a deformation at the central part of the sample is heavily sheared than the outer part is attributed to two reasons. first, the asymmetry of the stress state, where the inner part of the entry side receives compressive stress due to the compression of the ramp, and the outer part of the entry side of the sample is in the tensile stress state since the outer part is elongated in the pressing direction ahead of and in the front part of the main deformation zone (fig. 2). second, the less sheared at the outer part is attributed to the friction effect between the sample and the die walls [10]. however, the friction will intensify the shear deformation of the surface elements since the friction operates in the reverse direction to that of the motion of the moving surface. evidently, the sample deformed in longitudinal fibrous with ultra fine structure in a cross section of the sample. after 12 passes clearly the structures has undergone a severe deformation and ultra fine structure can be seen in fig.1f. interestingly this deformation mechanism can be applied on copper and copper alloys for resistance spot welding applications. it may be obvious that hardness and conductivity can be improve since high conductivity and hardness are the critical factors to successful resistance spot welding (rsw) in robotic and automation industries. the initial grain size of pure copper is about 200 µm. the two groups were subjected to plastic deformation using the equal channel angular pressing (ecap) method. during ecap the direction and number of the billet passes through the channel are very important for microstructure refinement. therefore, samples were pressed through the die using a plunge, and when each pass is terminated, the samples were rotated about the longitudinal axis by 90º in the same direction after each consecutive pressing. this rotation procedure was designated as route bc and it led most expeditiously to a homogeneous equiaxedgrained structure in transverse toward the pressing [11, 12]. figures 3 (a) and (b) show the microstructure of pure cu and cu-1%cr alloy before and after ecap, respectively. it is observed that the pure copper sample shows defined equal axis grain, while cu-1%cr consisted of copper matrix with eutectic structure (fig. 3b). it was noted that the change of grains to elongated shape is distinct after four and seven passes of ecap (fig. 3c). it is interesting that the eutectic structure is also elongated and disperses as stringers in between the copper matrix. it was believed that deformation of the grain in the direction pressing lead to fibrous tiny grains. further passes lead to the iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 5 production of nano grains. however, microstructure of cu-1%cr after 7 passes in transverse direction showed equaxis and round eutectic grains (fig. 2c). (a) (b) (c) (d) (f) fig. 2: ecap plasticine sample (a) longitudinal simulated grain boundary before pressing, (b) cross section simulated grain boundary before pressing, (c) longitudinal cross section structure after one pass, (d) longitudinal cross section structure after 8 passes and (f) longitudinal cross section structure after 12 passes by using 120 o sharp die (top edgeinner ) and (bottom edge outer). x10 the knoop micro hardness measured on the surface of tip clearly indicates that the hardness of pure copper after ecap is higher than pure copper before ecap process (fig. 4). the hardness of copper-chromium was also improved by ecap process due to eca process which leads to formation of nano grains. it is believed that ecap processes enhanced and improved the hardness due to refinement of the grain, which leads to reduction in grain sizes within the submicron or nano range with boundaries having high angles of miss orientation. iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 6 (a) optical x1000 (b) optical x1000 (c) x1000 (d) x50000, marker 200 nm fig. 3: (a) microstructure of pure cu and (b) and (c) longitudinal cu-1%cr alloy before and after ecap respectively, the arrow indicates the direction of pressing (d) microstructure of cu-1%cr in transverse direction after 7 passes. 0 50 100 150 200 250 hardness (kg/mm2) pure cu befor ecap pure cu after ecap cu-1%cr before ecap cu-1%cr after ecap samples fig. 4: knoop hardness results of pure cu and cu-1%cr after and before ecap. iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 7 typically, comparison of iacs% was made between annealed copper to represent the commercial electrodes and cu-1%cr alloy after 4 passes. figure 5 shows the %iacs for standard annealed copper at 20 o c is 100%iacs and iacs% of cu-1%cr alloy after 4 passes. four probe resistivity results analysis indicated that the conductivity of cu –1%cr alloy in the ecap direction is improved by 10%, due to ecap processes which lead to formation of longitudinal grains with high angles which act as channels to help in carrying the charge carrier with less scattering. conductivity enhancement of cu-1%cr alloy after 4 passes ecap gives good indication to improve the resistance spot welding application beside the improvement of hardness. it has to be mentioned that after 4 passes the conductivity declined due to the presence of nano structure within the longitudinal direction which in turn acts as an obstacle in the current flow leading to increase the resistance. 94 96 98 100 102 104 106 108 110 112 pure cu cu-1% cr after ecap electrode % ia s c fig. 5: iacs% for pure cu no passes and cu-1%cr alloy after four passes. it was shown that shear strength values of welded stainless steel using cu-1%cr electrode tips after 4 passes of ecap compare to pure cu before ecap and after ecap, electrodes was improved by 25% for pure copper and 50% for cu-1%cr respectively. this is due to the hardness improvement and conductivity. in general the shear strength depends on both the tips contact area and the conductivity, large nugget area with low heat diffusivity leads to low shear stress. as the diameter of nugget increases with proper welding conditions, the load of failure increases and fracture takes place in one of the sheets around the periphery of the weld, leaving the nugget or slug attached to the other sheet (pull-out) failure. the failure leaving the nugget or slug attached to the other sheet interface is noted, which indicates that the diffusion due to the spot welding is good enough leading the shear to take place at heat affected zone circumference around the nugget. iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 8 in general cu-1%cr tips after ecap showed smaller tip diameter deformation during spot welding, in comparison with cu-1%cr produced tips before ecap, and pure copper tips, due to formation of nano grains that leads to higher hardness for cu-1%cr tips after ecap compared to cu-1%cr produced tips before ecap and pure copper tips. this may lead to longer life for cu-cr electrode tips produced by ecap than pure cu electrode tips produced without ecap, and cu-cr before ecap electrode tips. as a result, shear stress of welded stainless steel after ecap tips is higher than welded sample before ecap process tips. the electrode deformation occurred after each weld attempted. the trend of tips diameter deformation after ecap was less than that of tips produced before ecap. electrode tip diameter increases with a 100 weld number for tips produced before and after ecap for cu electrode tips. the change in diameter was observed to increase by 40% for electrodes without ecap application. figure 6 shows the complete feature of rsw for stainless steel welds using cu-1%cr electrode tips after 4 passes. nugget structure is well formed a thin area of heat-affected zone (haz) is observed around the nugget area, and indention of the outer surface of sheets was observed. this confirmed that the penetration or the depth that fusion extends into the outer work piece is in the accepted range (20 to 80%) of the work piece thickness. it showed high shear strength values of welded stainless steel using cu-1%cr electrode tips after 4 passes ecap compare to pure cu before ecap and after 4 passes ecap electrodes, this is due to the hardness improvement. typical shear failure rather detachment was observed, fig. 6b. (a) (b) fig. 6: (a) sem image that show the features of rsw of stainless steel welds by cu1%cr electrode tips after 4 passes which are structure of fusion zone (nugget) formation and very thin haz (x25). (b) maximum shear of spot welded stainless steel failure rather then detachment. iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 9 4. conclusions plasticine was used in order to understand more on the plastic deformation behavior of the polycrystalline material during the ecap process. it is clearly noticed, the lesser shear deformation zone occurrence near the surface which pass through the outer corner of the die is attributed to the fast move of the outer part of the material compared to the inner part of the material. this deformation mechanism leads to formation of nano fibrous structural grains. ecap produces nano elongated grain boundary with fine sub-grain for both cu and cu-1% cr ranging from 100 – 500 nm for four passes and less than 100 to 300 nm for seven passes respectively. the hardness of cu-1%cr was improved by ecap process compared to pure cu and cu-1%cr before ecap process due to formation of ultrafine and nano grains. after 4 passes in ecap process, the iacs % of cu-1% cr increased due to formation of longitudinal grains with high angles which act as channel to help in carrying the charge carrier. shear strength of welded stainless steel produced by cu-1% cr electrode tips after ecap process higher than that of tips produced before ecap process. on the other hand, the shear strength of stainless steel welds using cu-1% cr tips shows higher value than welding produced via cu tips before ecap process, and comparable to that produced via cu tips after ecap process. cu-1% cr electrode after ecap process showed less deformation in comparison with cu and cu-1% cr before ecap process. the complete features of rsw nugget for stainless steel welds using cu-1%cr electrode tips after ecap shows columnar grains and very thin area of heat affected zone (haz) and nugget formation with fewer defects for the joining of stainless steel welds using electrode tips are observed. references [1] s. j. oh, s. b kang, “analysis of the billet deformation during equal channel angular pressing”, mater. sci. eng. a343,107-117, 2003. [2] v. m. segal “material processing by simple shear”, mater.sci.eng. a197,157-164. 1995 [3] y.i. iwahashi, z. horita,. m. nemoto, t.g. langdon, “investigation of microstructural evolution during equal channel angular pressing “, acta. mater. vol.45 ,4733-4740,1997. [4] a. a. aljboury, l.b., hussain, n. m. sharif, m. z. addullah “the influence of plastic deformation via ecap on the hardness of 6061 al alloy”, um, kl, malaysia, paper 67, session 15, icramme 2005. [5] s. lee., a. utsunomiya, a. h.kamatsu, k. neishi, m.furukaw, z.horita, t.g. langdon,” influence of scandium and zirconium on grain stability and super plastic ductility in ultra fine grained al-mg alloys” acta. mater.,vol.50, 553-.560, 2002. [6] h. s. kim, finite element analysis of equal channel angular pressing using a round corner die” mater. sci. eng., a315, 122-128, 2001. [7] d. w. dickinson, resistance spot welding, metals handbook, nint edition, vol. 6, welding, brazing, and soldering, welding rolled research & development, republic steel corp. pp. 469, 493, 1983. iium engineering journal, vol. 9, no. 2, 2008 hussain et al. 10 [8] w. h. kearns, “welding handbook, resistance and solid state welding and others joining processes”, 7th edition, american welding society, 2501 northwest 7th street, miami, florida 33125, vol. 3, pp. 99,128,131,132(1980), [9] v.m segal., “equal channel angular extrusion: from macromechanics to structure formation”. mat. sci. eng. a271, 322–333. 1999. [10] y. wu, i. baker, “an experimental study of equal channel angular extrusion” scripta mater. vol. 37, 347-353, 1997. [11] a. shan, i.g. moon, h.s. jo, j.w. park “direct observation of shear deformation during equal channel angular pressing of pure aluminum”, scripta mater., vol. 41, 353-364, 1999. [12] y.i wahashi, j. wang, z. horita, m. nemoto, and t. g. langdon, “principle of equal channel angular pressing of ultra fine grained materials” scripta mater., vol.35, part 2, 143146,1996. microsoft word 180-994-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zainul abidin and anuar 43 comparison of the production of recombinant protein in suspension culture of cho cells in spinner flask and shake flask system zainul abidin. s.n.z and anuar. n department of chemical and process engineering, faculty of engineering, universiti kebangsaan malaysia, 43600 bangi, selangor. zakiah.zainul@yahoo.com abstract: chinese hamster ovary (cho) cells is one of the most widely used production host for the commercial production of biopharmaceuticals product. they have been extensively studied and developed, and today provide a stable platform for producing monoclonal antibodies and recombinant proteins. this study focused on the production of recombinant protein in suspension culture of cho cells in spinner flask and shake flask.the cho cells were transfected with dna plasmid containing lac z gene which codes for β-galactosidase. the β-galactosidase-expressing cho cells were adapted to suspension culture. the agitation speed for both spinner and shake flask were adjusted accordingly. the experiments were carried out in duplicate and samples were taken for cell count, determination of glucose consumption, lactate production and protein level by using biochemical assay. results showed that cell growth in spinner flask is more favorable than in shake flask. the cell concentration in spinner flask is 58% higher than in shake flask. on the other hand, specific activity of β-galactosidase is 25% higher in spinner flask compared to shake flask, at the same agitation speed. abstrak: sel ovari hamster china (chinese hamster ovary (cho)) digunakan secara meluas dalam hos pembiakan untuk tujuan komersil produk biofarmaseutikal. ia telah dikaji dan dibangunkan secara ekstensif, dan kini ia menyediakan landasan yang stabil untuk penghasilan antibodi monoklon dan protein rekombinan. kajian ini memfokuskan tentang penghasilan protein rekombinan menggunakan kultur ampaian sel cho di dalam kelalang putar dan kelalang goncang. sel cho dimasukkan dengan plasmid dna yang mengandungi gen lac z yang juga memberikan kod untuk β-galaktosidase. sel cho βgalaktosidase–terungkap dimasukkan ke dalam kultur ampaian. kelajuan agitasi untuk kedua-dua kelalang putar dan kelalang goncang disesuaikan dengan sewajarnya. eksperimen dijalankan menggunakan pendua dan sampel yang diambil untuk kiraan sel, penentuan penggunaan glukosa, penghasilan laktat dan aras protein dengan menggunakan cerakin biokimia. keputusan menunjukkan tumbesaran sel di dalam kelalang putar lebih menggalakkan daripada dalam kelalang goncang. kepekatan sel dalam kelalang putar adalah 58% lebih tinggi daripada dalam kelalang goncang. sebaliknya, pada kelajuan agitasi yang sama, aktiviti tertentu β-galaktosidase adalah 25% lebih tinggi dalam kelalang putar dibandingkan dengan kelalang goncang. keywords: chinese hamster ovary; β-galactosidase; spinner flask; shake flask 1. introduction in recent years, the number of recombinant proteins used for therapeutic applications has increased dramatically and outstanding importance. these demands have driven the development of a variety of improvements in protein expression technology, generally iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zainul abidin and anuar 44 concerning mammalian and microbial culture system. therefore, the need for recombinant proteins in fundamental research and for clinical applications is continually increasing. although other options are available, cultivated mammalian cells are often the primary choice for protein expression when functional protein folding and complex posttranslational modifications are required [1]. complex proteins that are impossible for bacteria, yeast or insect cells to produce can be achieved by using mammalian cells [2]. currently about 60% of all recombinant therapeutic proteins are produced in mammalian cells, mainly because of the ability of mammalian hosts to generate high-quality proteins that are similar in their biochemical properties to the naturally occurring human forms. this growing demand for high-quality recombinant therapeutics is driving the research and development of mammalian-cell-based manufacturing systems for enhanced production yields [3]. in industrial cell culture, chinese hamster ovary (cho) cells are commonly used as host for the production recombinant protein. they have been extensively studied and developed, and today provide a stable platforms for the production of recombinant therapeutic proteins and there are incentives to continuously improve the cell cultivation process [4]. cho cells have become the standard mammalian host cells used in the production of recombinant proteins, although mouse myeloma (ns0), baby hamster kidney (bhk), human embryonic kidney (hek-293) or human-retina-derived (perc6) cells are alternatives. all these cell lines have been adapted to grow in suspension culture and are well suited for scale-up in stirred tank bioreactors. however, cho cells are commonly employed as a host for producing various recombinant proteins for therapeutic applications [5]. the advantage of using cho and nso cells is that there are well-characterized platform technologies that allow for transfection, amplification and selection of highproducer clones [5]. however, cho cells are mainly dominating the mass production of recombinant protein products because of their capabilities for single-cell suspension growth [6]. the development of a stable cell line is a costly and time-consuming process, and this investment may be lost if the recombinant protein is not approved for clinical use [4]. when considering a process scale-up for larger production, attention should be given to the productivity and the product quality [5, 6]. classical cultivation apparatus at moderate scales is the glass spinner flask with a magnetically driven impeller for mixing. spinner flasks are less expensive and easier to handle than glass or stainless steel bioreactors. nevertheless, there is a considerable amount of work associated with their cleaning and sterilization [7]. many suspensionadapted cell lines can achieve densities of 1 to 2 x 10 6 cells ml -1 or higher in these spinner flasks [5]. fox (2003) stated that the major alternatives to spinner flask and bioreactors for culturing suspension mammalian cells are in suspension was agitated culture vessels such as erlenmeyer flasks operated on orbital shaker. in most research, shake flask has been choose and used as the first method in fundamental studies as well as in developing a larger scale fermentation process. shaken culture system are mostly developed for bacterial and fungal cultures, however applications for mammalian cell have also been reported since this system has been well established and proven to be very useful for initial culture experiments and screening purpose [9]. the purpose of the present work was to was to compare and to study the effectiveness of different cultivation vessels; spinner flasks and shake flasks for the growth and production of recombinant protein in chinese hamster ovary (cho) cell line. such iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zainul abidin and anuar 45 information will facilitate future optimization processes because mammalian cell have a highly individual character which will be highlighted by different glucose consumption, lactate production and sensitivity towards stress signal [8]. this study describes preliminary findings on the relationship between cell growth in agitated and shaker culture and production of β-galactosidase in cho cells. 2. materials and methods 2.1 cell line and medium the cell line used in this study was recombinant chinese hamster ovary (cho) cells [tf9(7)] obtained from mammalian cell culture laboratory of the national university of malaysia (ukm). the cell line was transfected with a dna fragment (plasmid) containing lac z gene which codes for an expression of β-galactosidase [10]. the cells expressed β galactosidase as the main protein product. cho cells were grown in rpmi 1640 (roswell park memorial institute) media containing 5% fetal bovine serum (gibco) and 1% penicillin streptomycin (gibco). the cells were cells were maintained in t-flask and incubated at 37c and 5% co2. 2.2 culture condition cultures were carried out in 500 ml wheaton spinner flask and erlenmeyer flasks with working volume of 200 ml, at 37°c in a 5% co2 incubator. the stirring and agitation speeds were adjusted at 60, 80, 100, and 120 rpm. the cell cultures were initiated at 2.5 x 10 5 cells ml -1 and were cultivated for 5 days. the spinner flask used bulb-shape glass magnetic impeller (wheaton) and the shake flask were shaken using incubator shaker (heidolph). the screw cap of the flask was hand-tightened during incubation. ph were adjusted as necessary by adding sterile naoh (1m) solution to raise the ph if the medium is acidic (yellow) or hydrochloric acid, hcl (1m) to reduce the ph if the medium is acidic (purple). all of the experiments were carried out in duplicate. 2.3 determination of cells growth and production samples (2 ml) were taken daily for cell count and for the measurement of glucose, lactate and protein production. 2.3.1 measurement of cell concentration and viability the cell viability was determined using the trypan-blue dye exclusion method using 0.04% trypan blue solution (sigma). the cells were counted in a fuchs rosenthal haemocytometer counting chamber by using inverted microscope. cell viability was expressed as the number of viable cells over the total number of cells. 2.3.2 glucose and lactate assays the sample were centrifuged at 1500 rpm for 5 min and supernatant was analyzed for glucose and lactate concentrations by using biochemistry analyzer (ysi 2700 select). 2.3.2 mtt assay mitochondrial activity of the cells was determined using mtt (3-(4, 5dimethylyhiazolil-2)-2, 5-diphenyl tetrazolium bromide (sigma) assay [11]. after cells were harvested, 100 µl cells suspensions were loaded into 96 wells plates. ten microliters of mtt (5 mg.ml -1 ) was loaded to each well of the plates, and incubated for 3 hours. the absorbance was measured by using micro-plate reader (versa max) at 595 nm. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zainul abidin and anuar 46 2.3.3 specific β-galactosidase activity assay specific β-galactosidase activity assay was measured in cell lysates using the betared β-galactosidase assay kit (novagene, usa) according to the manufacture’s instructions. samples were collected in tube and were spinned at 1500 rpm for 5 min. then the cells were rinsed with pbs once and 100 µ l of reportasol extraction buffer were added before respinned at 12000 rpm for 5 min. the supernatant was collected for β-galactosidase activity assay. according to the manufacture’s protocol, 5-50 µ l cell extraction and negative control were placed in 96 well plates and 145 µl of betared reaction buffer was added in each wells. the plates were incubated at 37°c. betared stop buffer was added to stop the reaction if the color changes to reddish. the results were measured at absorbance of 595 nm. in order to measure the total amount of protein concentration, dye binding quickstart bradford protein assay (bio-rad, usa) was carried out according to manufacturer’s protocol, by using bovine serum albumin (bsa, sigma) as the standard (bio-rad). in brief, standard (125-2000 mg.ml -1 ) and lysate were incubated with working reagent at room temperature for at least 5 min. the absorbance was measured at 595 nm by using bradford program on the biophotometer. 3. results and discussion cell growth and protein production were carried out in two different cultivation system; 500 ml spinner flask and 500 ml shake flask with working volume of 200 ml. the suspension cultures were started by filling 50% volume of the flasks with media to provide large headspace. this headspace was considered sufficient to supply oxygen to the cells, at least during the initial phases of growth, for cho cells typically seeded at a density of 2× 10 5 –3.5× 10 5 cells ml -1 [12-14]. in this experiment, the agitation speeds of the spinner flask were set at speed range of 60 rpm to 120 rpm. from the observations it showed that this condition has prevented both settling of cells and foaming of the growth medium. the spinner flask feature a bulb-shape glass impeller that rotates from a fixed position at the center of the flask, which provides a slow and gentle orbital movement for the susupension culture.mean while the shake flasks were shaken using an incubator shaker. results in fig. 1(a) and (b), show the cell concentration and percentage of viable in spinner flask at different agitation speed. the maximum number of viable cells was obtained at 60 rpm. cell density reached 1.84 x 10 6 cells ml -1 with 99.7% viability after 72 hours. whereas the lowest t cell concentration was achieved when culture was agitated at 100 rpm, with cell concentration and percentage viable cells 5.36 x 10 5 cells ml -1 and 79% respectively. this result showed that the cell concentration decrease as the agitation increased. the figures also showed that after 96 hours of cell cultivation, the cell growth rate has gradually has decreased until the end of the growth phase. figure 1 (c) shows the correlation between viability of cells and cellular growth and proliferation by using mtt assay. establishing a correlation between manual cell counts and metabolic kinetics was very challenging as the two types of measurement assess different aspects of physiological behavior of cultured cells [15]. it discovered that the cells viability was nearly similar with cellular growth. evaluation of glucose consumption versus cell density indicated that in all experiments performed, cell growth was limited by this nutrient as shown in fig. 1 (d). cell stopped growing when glucose depleted in the medium. the rate of lactate production is directly related to the rate of glucose consumption. the relation between the serum concentration in cultivation medium and glucose production and lactate production rates is highly dependent on the cell line applied [16]. this suggests that the cell growth is limited to depletion of nutrients and accumulation of toxic metabolites. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zainul abidin and anuar 47 the value of highest glucose concentration was approximately 2.70 g.l -1 and gradually decreases with the minimum concentration 0.01 g.l -1 . it shows that glucose consumption was consumed rapidly and was exhausted starting on day 2, which gradually decline until day 5. figure 1(e) shows lactate production and its accumulation and the final concentration achieved was 1.530 g/l. glucose consumption and lactate accumulation correlated well with the cell growth parameters. figure 1 (f) shows the value of specific activity β-galactosidase at different agitation speed. in spinner flask the best agitation speed was at 60 rpm in which cells reached maximum viable cell concentration of 1.84 x 10 6 cells ml -1 after 72 hours with maximum specific activity β-galactosidase of 21.9 miliunit mg -1 . at higher agitation speed, the value of specific β-galactosidase is lower than 1.0 milliunit mg -1 . these results indicated that the amounts of specific activity of βgalactosidase produced at various agitation speeds were very much depended on the cell growth and agitation speed. fig. 1: effect of different condition on the growth of recombinant cho cells as shown by the (a) cell viability (b) percentage of cell viability, (c) metabolic activity of cells (d) glucose consumption (e) lactate production (f) specific activity β-galactosidase in the culture media at different agitation speed in spinner flask. in order to compare cells cultivation, by using shake flask, this experiment was carried out at the same rate of agitation speed of 60 rpm to 120 rpm. 60 rpm has been choose as minimum agitation because at lower revolutions the cell will settle at the bottom of the flask meanwhile at agitation speed above 120 rpm agitation speed, the medium move too vigorously and cause cell death. from fig. 2 (a), it shows that different cell concentrations were obtained in shake flask at different agitation speed. the maximum cell concentration was established at 100 rpm with cell concentration of 1.07 x 10 6 cells ml -1 . the result also showed that the cell viability started to decrease after 60 hours of cultivation. percentage of viable cells shows that, agitation at100 rpm gave the best result iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zainul abidin and anuar 48 for viability of cells, which show 99% cell viable. however, at 120 rpm the cells viability started decreases in day 4 with only 25.5% viable cells. it shows that agitation speed of 120rpm is too vigorous for 200 ml volume in erlenmeyer flasks. at 60 and 80 rpm, the maximum value of total cells reached 7.24 x 10 5 cells ml -1 but viability started to decrease after 4 days of cultivation. figure 2 (d) and (e) show glucose consumption and lactate production in shake flask at different agitation speeds, the data shows that glucose was consumed rapidly and started to decrease in day 2 and gradually declined until day 5 same as in spinner flask. lactate production and accumulation reached final maximum concentrations of 1.565 g.l -1 . figure 2 (f) shows specific activity of β-galactosidase in shake flask, it shows stable protein production at 60 rpm, with maximum activity of 5.462 milliunit mg -1 . it is less compare to protein production in spinner flask. fig. 2: effect of different condition on the growth of recombinant cho cells as shown by the (a) cell viability (b) percentage of cell viability, (c) metabolic activity if cells (d) glucose consumption (e) lactate production (f) specific activity β-galactosidase in the culture media at different agitation speed in shake flask. 4. conclusion the agitations provided by spinner flask give better cell growth and higher protein production when compared to shake flasks. this study showed that shake flask is not suitable for culturing cho cells.. this might be due to high shear stress imposed in shake flask has affected the cell growth and viability. culture in spinner flasks shows better cell growth and higher enzyme production with specific enxyme activity β-galactosidase of 21.917 milliunit mg -1 at 60 rpm, compare to shake flask with only 5.462 milliunit mg -1 at same agitation speed. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zainul abidin and anuar 49 acknowledgement this study was supported by research university grant: ukm-gup-nbt-08-26-095 from, ministry of science, technology and innovation, malaysia. references [1] ryan. j.a., “growing more cells: a simple guide to small volume cell culture scale-up,” corning incorporated,” 2004 [2] woodside. s m. , bowen b. d. &. piret. j. m., “mammalian cell retention devices for stirred perfusion bioreactors”. cytotechnology,” vol 28, pp. 163–175, 1998. [3] matasci. m,. hacker. d. l, baldi. l , wurm. f. m., “. recombinant therapeutic protein production in cultivated mammalian cells: current status and future prospects,” drug discovery today: technologies, vol. 5, pp. 37–42, 2008. [4] girard p, jordan m, tsao m, wurm fm., “ small-scale bioreactor system for process development and optimization,” biochemical engineering, vol. 7, pp. 117–119, 2001. [5] schmidt, f.r., “optimization and scale up of inductrial fermentation process, “applied microbiology and biotechnology,” vol. 68, pp. 425-435, 2005 [6] wurm. f.m., “production of recombinant protein therapeutics in cultivated mammalian cells,” nature biotechnology, vol. 22, pp. 1393-1398, 2004. [7] ryan. j.a., “growing more cells: a simple guide to small volume cell culture scale-up,” corning incorporated,” 2004. [8] fox. s.r, patel. u.a, yap.m. g.s., wang. d.i c, “ maximizing interferon γ production by chinese hamster ovary cells through temperature shift optimization: experimental and modeling,” biotechnology and bioengineering, vol. 85, pp. 177-184, 2003. [9] matasci. m,. hacker. d. l, baldi. l , wurm. f. m., “. recombinant therapeutic protein production in cultivated mammalian cells: current status and future prospects,” drug discovery today: technologies, vol. 5, pp. 37–42, 2008. [10] saifudin. n. ibrahim.n, anuar. n., “optimization in trasnfection and stable production of in chinese hamster ovary cells,” biotechnology, vol 10(1), pp. 86-93, 2011 [11] mosmann, t., “rapid colorimetric assay for cellular growth and survival: application to proliferation and cytotoxicity assays,” journal of immunological methods, vol 65, pp. 55-63, 1983. [12] butler, m., “animal cell cultures: recent achievements and perspectives in the production of biopharmaceuticals,” applied microbiology and biotechnology, vol. 68, pp. 283-291, 2005. [13] jayapal, k. p., wlaschin, k. f., hu, w. s., yap, m. g. s., “recombinant protein therapeutics from cho cells-20 years and counting,” chem. eng. prog., vol. 103, pp. 40-47, 2007. [14] jesus. m.j.d and wurm. fm., “medium and process optimization for high yield, high density suspension cultures: from low throughput spinner flasks to high throughput milliliter,” bioprocess international, vol. 7, pp. 12–17, 2009. [15] tsao, y.s., cardoso, a.g., condon, g. g., voloch, m., lio, p., lagos j.c., kearns, b.g. & liu, z., “monitoring chinese hamster ovary cell culture by the analysis of glucose and lactate metabolism,” journal of biotechnolog, vol 118, pp.316-327, 2005. [16] hesham, a. e., abdeen, a., abdeen, s., elsayed, a. e., demellawy, m. & shereef, a., “serum concentration effects on the kinetics and metabolism of hela-s3 cell growth and cell adaptability for successful proliferation in serum free medium,” world applied sciences journal. vol. 6 (5), pp.608-615, 2009. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 usmanov and yusupov https://doi.org/10.31436/iiumej.v22i1.1497 energy and structure states of low-lying bands in 156gd pazlitdin nuritdinovich usmanov* and elmurod kuchkarboyevich yusupov department of physics, namangan engineering and technology institute, 160115 namangan, uzbekistan * corresponding author: usmanov1956.56@mail.ru (received: 3rd june 2020; accepted: 3rd september 2020; published on-line: 4th january 2021) abstract: the experimental results of the literary and electronic nuclear database for 156gd were summarized and analyzed. inertial parameters of rotating core were determined using the harris method. the theoretical values of energy and wave functions were calculated within the framework of a phenomenological model that takes into account coriolis mixing of state rotational bands. the calculated energy values were compared with existing experimental data, which were in good agreement. abstrak: hasil dapatan kajian melalui eksperimen pangkalan data nuklear dan elektronik bagi 156gd diringkaskan dan dianalisis. parameter inersia putaran berputar ditentukan menggunakan kaedah harris. nilai teori fungsi tenaga dan gelombang dikira dalam kerangka model fenomenologi yang mengambil kira campuran coriolis pada band putaran keadaan. nilai pengiraan tenaga dibandingkan dengan data eksperimen memberikan persetujuan yang baik. keywords: nuclei; energy; states; rotational bands; phenomenological model 1. introduction the gadolinium isotope with a mass a=156 is one of the most studied nuclei. the main reason is the large cross section ( , γ)n reaction in 156 gd , which provides big opportunities for studying the emission spectra in this reaction. full results on this nucleus are given in references [1,2]. several other nuclear processes supplement information on the levels and rotation bands in 156 gd . in the reaction of (α,2 )n data were obtained on the states of rotational bands with 1 0k  + = – to 26i + = , 2 0k  + = – to 14i + = , 3 0k  + = – to 10i + = , 4 0k  + = – to 6i + = , 5 0k  + = – to 4i + = , 1 2k  + = – to 15i + = and 2 2k  + = – to 4i + = . a wealth of experimental information was obtained as a result of studying the reaction ( , γ)n n [3]. based on the totality of the experimental data, one can think that for 156 gd all or almost all levels were found up to excitation energy of 2 mev. in 156 gd five rotational bands with π 0k + = are known. therefore, systematic study of the properties of these levels is very important to search the corresponding levels in the neighboring nuclei. 156 gd and 158 gd are the first nuclei in which a new type of excitation was discovered – collective states with π 1i + = [4]. at present, there have been several collective states experimentally observed in 156 gd with π 1i + = . their excitation energies and reduced probabilities ( 1)b m  are determined [5]. 167 iium engineering journal, vol. 22, no. 1, 2021 usmanov and yusupov https://doi.org/10.31436/iiumej.v22i1.1497 nonadiabaticity is observed in the energies and especially in the electromagnetic characteristics of the excited states of rotational bands with π 0k + = and π 2k + = of these nuclei [6-9]. in the present work, to explain these nonadiabatics, we use a phenomenological model that takes into account coriolis mixing of low–lying rotational bands [10, 11]. the energy levels and wave functions of the rotational band states are calculated. the nonadiabatics observed in the energies and wave functions of rotational states are discussed. more details of the phenomenological model used are given in ref. [10] and this model was also successfully applied to study the mixing of state bands of both positive and negative parity in [11-14]. 2. description of the model according to the phenomenological model of the nucleus [10], the hamilton operator has the following appearance: 2 rot , ( ) k k h h i h = + (1) , ' , ' rot , ' 1 ˆω δ ω ( ) χ( , ) k k k k k x k k h i k j k i k   = −   (2) rot rot ω ( ) ( )i de i di= – angular frequency of rotation of the core; к  − the head energies of the rotational bands; ˆ x k j k  – matrix element of coriolis interaction between the states of rotational bands; χ( , )i k – the coefficients are as follows: χ( ,0) 1i = , 1 2 2 χ( ,1) 1 ( 1) i i i = − + . the eigen wave function of the hamilton operator (1) has the following appearance:  2 ', , ' ' . ' ' ',0 2 1 2 (θ) gr, , 0 16π (θ) ( 1) (θ) 0 , 1 δ i k k i i k i m k k m k k k k i i i imk d k m d b d b + + + − − + =  +    + + −   +   (3) here , ' (θ) i m k d are generalized spherical functions; 0 is the vacuum for the k b + operators (in other words, the ground state of the nucleus in the intrinsic reference system); , i k k  are the amplitudes of mixing states of different bands with the same angular momentum i due to the coriolis interaction. eigen energies and wave functions of the rotational states are determined by diagonalization of the hamiltonian operator (2): σ , ' , , i i i k k k n n k n h  =  (4) the total energies of the states can be found by the following formula: rot ( ) ( ) ( ) k k e i e i i= + (5) there are different methods for determining the energy of the core rotational motion of the nucleus, for example, harris proposed to determine the following two-parameter formula [15]: 168 iium engineering journal, vol. 22, no. 1, 2021 usmanov and yusupov https://doi.org/10.31436/iiumej.v22i1.1497 3 0 rot 1 rot ( 1) ω ( ) ω ( )i i i i+ =  +  (6) 2 4 rot 0 rot 1 rot 1 3 ( ) ω ( ) ω ( ) 2 4 e i i i=  +  , here 0  and 1  – inertia parameters of the rotational core. 3. calculation and results according to bohr–mottelson and bengtsson–frauendorf, at small values of the spin of the nucleus, the rotational energy of the nucleus corresponds to the ground rotational states energy [16,17]. therefore, the inertial parameters of the core were determined by the harris method using the experimental energy states of ground band up to spin 8i  . table 1: values of the model parameters used in calculating level energies 0 1 12 ω 22 ω +ˆ0 11 νjx  + ˆ0 12 νjx   + ˆ0 13 νjx   + ˆ0 14 νjx   + ˆ0 15 νjx   + ˆ2 11 νjx +   + ˆ2 12 νjx +   33.3 169.47 1.076 1.739 0.416 0.45 0.25 0.91 0.42 0.40 0.1 note: 2 0 ( /mev) , 4 3 1 ( /mev ) are the inertial parameters of the rotating core (harris parameters), 1,22 ω (mev) are energies of the π 1,2 2k + = band heads, and ˆ x k j k  (mev) are the matrix elements of the coriolis interaction. figure 1 shows the values of the moment of inertia obtained by the harris method, which are compared with the effective values obtained using the following formula эфф эфф ( 1) ( ) ω ( ) i i i i +  = , here экс экс эфф ( 1) ( 1) ω ( ) 2 e i e i i + − − = (7) it can be seen from the comparison that there is a difference between them at high values of angular rotation frequency. i.e. at the large values of the total angular momentum i , deviations from the adiabatic theory are observed in the energies of the ground band. such nonadiabaticity is more pronounced in the energies of the vibration bands with 0k  + = and 2k  + = . to determine the causes of nonadiabaticity in the energies of the states of lowlying rotational bands, we use the phenomenological model presented above. the energy of the rotational motion of the nucleus, for the bands included in the basis of the hamiltonian operator (1), is considered the same and its values are determined by formula (6). the rotational motion at low frequencies is not related to its internal structure, i.e., the rotation of the nucleus does not affect the hamiltonian basic model (1). ground, five beta band ( 0k  + = ), two gamma 2k  + = and fifteen 1k   + = rotational bands are introduced in the hamiltonian model. the schrödinger equation of size (23x23) was solved. 169 iium engineering journal, vol. 22, no. 1, 2021 usmanov and yusupov https://doi.org/10.31436/iiumej.v22i1.1497 fig. 1: comparison of the values of the moments of inertia determined by the effective and harris method. the parameters of the model are determined in the following sequence: 1. for the head energies ωk of the ground π 1 ( 0 )k + = and π 0 n k + = bands are using the experimental values exp. ( 0) nk e i = because the head energies of these bands 0i = (in this case rotω (0) 0= ) and these states are not mixed by the coriolis forces; 2. the head energies ν1 ω of the π ν 1k + = bands found using their experimental values ν ν эксп 1 1 rot ω ( 1) ( 1);e i e i= = − = 3. the head energies 12 ω , 22 ω of the π 2k + = bands and 1,2 ˆ2 1 x j  +   are free parameters, their values were obtained by the least squares method, from the condition of better agreement of the theoretical energy of states with odd spins π 1 2k + = and π 2 2k + = rotational bands with the experimental data; 4. the parameters ˆ0 1 n x j  +   describing the coriolis interaction of the states of the π 0 n k = , and π 1k  + = bands are determined from the good agreement of the calculated theoretical energies of the states with even spins of the ground 1 (0 ) , π 2 3 4 5 0 , 0 , 0 , 0k + + + + = and π 1,2 2k + = of bands with experimental values. the selected numerical values of the model parameters are given in table 1. figure 2 shows the calculated energy values in the framework of the model which are compared with experimental results. 170 iium engineering journal, vol. 22, no. 1, 2021 usmanov and yusupov https://doi.org/10.31436/iiumej.v22i1.1497 fig. 2: comparison of theoretical and experimental energy values. the results of the comparison show that at small values of spin, the compatibility between them is good, and the difference increases with increasing spin. this difference suggests that additional effects must be taken into account when studying the properties of high-spin states. for example, it may be necessary to take into account the effect of the rotational motion of the nucleus on the intrinsic energy when the rotation of the nucleus is high. the wave functions of the states π 2 0k + = , π 3 0k + = , π 4 0k + = and π 1 2k + = bands obtained by solving the schrödinger equation (2) are present in tables 2, 3, 4 and 5 respectively. the hamiltonian basis includes 15 bands with π 1k  + = , but the table shows one component of 1 1k  + = . the components 1 i k  of the other π 1k  + = bands are determined using the following formula 1 1 1 1 1 1 ki i k k k         − = − . (8) in table 2, it can be seen that in the band with 2 0k  + = , the other components 20 i k  of the mixed bands increase with increasing spin i . this picture can be observed in other rotation bands. this result, which is due to coriolis interaction, is the main cause of the nonadiabatics manifested in the energy and electromagnetic characteristics of the exited states. 171 iium engineering journal, vol. 22, no. 1, 2021 usmanov and yusupov https://doi.org/10.31436/iiumej.v22i1.1497 table 2: the amplitude of the mixing of the base states 20 ψ i k + for 20k  + = band k i gr 02+ 03+ 04+ 05+ 11+ 21+ 22+ 2 -0.0052 0.9927 0.0261 0.0176 0.0068 0.0279 0.0927 0.0011 4 -0.0183 0.9516 0.0808 0.0599 0.0231 0.0555 0.2534 0.0043 6 -0.0385 0.8926 0.1404 0.1186 0.0460 0.0829 0.3496 0.0087 8 -0.0638 0.8353 0.1872 0.1815 0.0708 0.1068 0.3890 0.0135 10 -0.0922 0.7835 0.2177 0.2395 0.0942 0.1260 0.3988 0.0179 12 -0.1222 0.7378 0.2352 0.2884 0.1143 0.1404 0.3951 0.0216 14 -0.1529 0.6983 0.2440 0.3274 0.1306 0.1506 0.3859 0.0246 16 -0.1836 0.6645 0.2476 0.3577 0.1436 0.1576 0.3750 0.0270 18 -0.2141 0.6355 0.2482 0.3808 0.1537 0.1621 0.3639 0.0288 20 -0.2444 0.6106 0.2469 0.3984 0.1615 0.1649 0.3533 0.0302 table 3: the amplitude of the mixing of the base states 30 ψ i k + for 30k  + = band k i gr 02+ 03+ 04+ 05+ 11+ 21+ 22+ 2 -0.0025 -0.0275 0.9986 0.0118 0.0044 0.0161 -0.0183 0.0007 4 -0.0072 -0.0794 0.9923 0.0330 0.0122 0.0260 -0.0618 0.0023 6 -0.0120 -0.1374 0.9795 0.0549 0.0204 0.0319 -0.1110 0.0040 8 -0.0162 -0.1895 0.9625 0.0732 0.0272 0.0347 -0.1562 0.0054 10 -0.0194 -0.2321 0.9446 0.0872 0.0324 0.0356 -0.1938 0.0064 12 -0.0218 -0.2655 0.9278 0.0974 0.0362 0.0356 -0.2238 0.0072 14 -0.0236 -0.2916 0.9129 0.1050 0.0391 0.0350 -0.2476 0.0078 16 -0.0250 -0.3121 0.9001 0.1107 0.0412 0.0342 -0.2666 0.0082 18 -0.0260 -0.3285 0.8890 0.1151 0.0429 0.0333 -0.2819 0.0086 20 -0.0269 -0.3419 0.8795 0.1186 0.0442 0.0324 -0.2944 0.0088 table 4: the amplitude of the mixing of the base states 40 ψ i k + for 40k  + = band k i gr 02+ 03+ 04+ 05+ 11+ 21+ 22+ 2 -0.0119 -0.0347 -0.0239 0.9486 0.1105 0.1673 -0.0186 0.0396 4 -0.0302 -0.0952 -0.0675 0.8892 0.1910 0.2087 -0.0596 0.0546 6 -0.0471 -0.1625 -0.1199 0.8468 0.2258 0.2115 -0.1055 0.0569 8 -0.0604 -0.2265 -0.1744 0.8123 0.2393 0.2019 -0.1497 0.0566 10 -0.0698 -0.2812 -0.2257 0.7809 0.2427 0.1886 -0.1881 0.0554 12 -0.0760 -0.3249 -0.2708 0.7521 0.2414 0.1748 -0.2192 0.0539 14 -0.0798 -0.3584 -0.3090 0.7262 0.2379 0.1620 -0.2436 0.0524 16 -0.0822 -0.3838 -0.3408 0.7035 0.2337 0.1507 -0.2623 0.0510 18 -0.0836 -0.4030 -0.3671 0.6839 0.2294 0.1409 -0.2767 0.0497 20 -0.0844 -0.4177 -0.3890 0.6670 0.2254 0.1324 -0.2879 0.0486 172 iium engineering journal, vol. 22, no. 1, 2021 usmanov and yusupov https://doi.org/10.31436/iiumej.v22i1.1497 table 5: the amplitude of the mixing of the base states 12 ψ i k + for 12k  + = band k i gr 02+ 03+ 04+ 05+ 11+ 21+ 22+ 2 0.0021 0.0954 -0.0144 -0.0076 -0.0029 -0.0116 -0.9949 -0.0005 3 -0.0209 -0.9987 -0.0013 4 0.0052 0.2667 -0.0352 -0.0191 -0.0073 -0.0168 -0.9620 -0.0014 5 -0.0328 -0.9967 -0.0032 6 0.0070 0.3819 -0.0460 -0.0253 -0.0096 -0.0164 -0.9217 -0.0019 7 -0.0424 -0.9945 -0.0053 8 0.0078 0.4465 -0.0510 -0.0283 -0.0108 -0.0149 -0.8920 -0.0021 9 -0.0504 -0.9921 -0.0076 10 0.0082 0.4841 -0.0536 -0.0298 -0.0114 -0.0136 -0.8721 -0.0022 11 -0.0572 -0.9898 -0.0097 12 0.0085 0.5078 -0.0551 -0.0307 -0.0117 -0.0124 -0.8585 -0.0023 13 -0.0630 -0.9875 -0.0119 14 0.0087 0.5237 -0.0560 -0.0313 -0.0119 -0.0115 -0.8489 -0.0023 15 -0.0682 -0.9854 -0.0139 16 0.0088 0.5350 -0.0566 -0.0317 -0.0121 -0.0108 -0.8418 -0.0024 17 -0.0727 -0.9833 -0.0158 18 0.0089 0.5435 -0.0571 -0.0320 -0.0122 -0.0102 -0.8363 -0.0024 19 -0.0768 -0.9812 -0.0177 20 0.0089 0.5500 -0.0574 -0.0322 -0.0123 -0.0097 -0.8321 -0.0024 2 0.0021 0.0954 -0.0144 -0.0076 -0.0029 -0.0116 -0.9949 -0.0005 4. conclusion theoretical calculations were carried out for 156 gd nucleus in the framework of the phenomenological model taking into account coriolis mixing of low–lying rotation bands with positive parity. nonadiabaticities observed in the energies is explained by the coriolis mixing of low excited rotational states. to describe all the adiabatic rotational bands, the same moments of inertia have been used. the energy spectra of the positive parity states have been calculated. the results of calculation of energy spectra for ground π 1( 0 )k + = , π 20k + = , π 30k + = , π 40k + = , π 50k + = , π 12k + = , and π 22k + = band states is compared with the existing experimental data correspondingly and their compatibility is given. the mixing effects of the lower bands have been shown to be significant even at small spins. in the high spin states of ground band, the difference between the theory and experiment was observed. this may be due to the fact that for large values of the angular frequency of rotation of the nucleus, it is necessary to take into account the effects of rotation on intrinsic energy. the wave function of states of the rotational bands is calculated. the regularities of the change in the state components of the mixing bands are studied depending on the total angular momentum. 173 iium engineering journal, vol. 22, no. 1, 2021 usmanov and yusupov https://doi.org/10.31436/iiumej.v22i1.1497 acknowledgement this work has been financial supported by the committee for the coordination of the development of the science and technology under the cabinet of ministers of the republic of uzbekistan, fundamental grant “ot-f2-75” (2017-2021). references [1] reich cw. (2012) nuclear data sheets for a=156. 113: 2537-2840. [2] backlin a, hedin g, folgelberg b, et al. (1982) levels in 156gd studied in the ( , γ)n reaction. nucl. phys. a, 380: 189-260. [3] berzin yy, guseva tv, tamberg yy. (1983) investigation of 156gd in the reaction ( , γ)n izv. akad. nauk lat. ssr, ser. fiz. tekh. nauk. 1: 9-12. [4] bohle d, richter a, steffan w, et al. (1984) new magnetic dipole excitation mode studied in the heavy deformed nucleus 156gd by inelastic electron scattering. phys. lett. b 137: 27-31. [5] pitz hh, berg uep, heil rd, knaissl u, stock r. et al. (1989) systematic study of low-lying dipole excitations in 156,158,160gd by photon scattering. nucl. phys. a, 492: 411-425. [6] demidov а. м, govor l. i, kurkin v. а, mikhailov i. v. (2009) deexcitation of π 2 30 , 0 ,k + + = and 12 + levels by m1 transitions in nonspherical even–even nuclei. phys. at. nucl. 72(2): 201208. [7] demidov ам, govor li, kurkin vа, mikhailov iv. (2009) confrontation of nucleus deformation and multipole mixture parameters in 1(2 0 2 0 )n + + − transitions with rotational band structure for π 20k + = and π 30k + = . phys. at. nucl., 72(2): 209-213. [8] aprahamian a, lesher sr, stratman а. (2017) first excited 0+ states in deformed nuclei. bulg. j. phys. 44: 372--379. [9] aprahamian a, de haan rc, lesher sr, et al. (2018) lifetime measurements in 156gd. phys. rev. c., 98:034303. [10] usmanov p. n, mikhailov i. n. (1997) effects of nonadiabaticity of collective motion in eveneven deformed nuclei. phys. part. nucl. 28(4): 348-373. [11] usmanov pn, okhunov aa, salikhbaev us, vdovin ai. (2010) analysis of electromagnetic transitions in nuclei 176,178hf. phys. part. nucl. letters. 7(3):185–191. [12] usmanov pn, adam i, salikhbaev us, solnyshkin aa. (2010) theoretical analysis of experimental data on 160dy that were obtained in studying beta decay. phys. at. nucl. 73(12): 1990-1996. [13] usmanov pn, vdovin ai, solnyshkin aa, salikhbaev us. (2014) properties of оctupole vibrational bands in the 160dy nucleus. phys. at. nucl. 77(11): 1343-1349. [14] usmanov pn, vdovin ai, yusupov ek, salikhbaev us. (2019) phenomenological analysis of characteristics of rotational bands in 158,160gd isotopes. phys. part. nucl. letters. 19(6): 706-712. [15] harris sm. (1965) higher order corrections to the cranking model phys. rev. b 138(3): 509-513. [16] bohr a, mottelson b. (1977) nuclear structure, vol. 1,2. new york: benjamin [17] bengtsson r, frauendorf s. (1979) an interpretation of backbending in terms of the crossing of the ground state band with an aligned two–quasiparticle spectra band. nucl. phys., a 314: 27-36. 174 315 iium engineering journal, vol. 14, no. 1, 2013 zakaria et al. 43 total nitorgen content from earthworm (eisenia foetida) using the kjeldahl method zarina zakaria, alina rahayu mohamed, noor hasyierah mohd salleh and siti nursheela abu mansor school of bioprocess engineering, university malaysia perlis, 02600 arau, perlis. zarinaz@unimap.edu.my abstract: in the fish aquaculture management, fish feed is identified as a major problem. the high cost and scarcity of fishmeal in formulated feeds have led to the use of other protein sources such as earthworms and animal by-product. earthworm is an alternative source of protein to replace the fish meal in the fish feed formulation. in this study, total nitrogen content in the earthworm powder is determined using the kjeldahl method by employing the statistical software, full factorial design (ffd) which could provide the significant information about the studied parameters. the parameters are, the digestion time (min) and the volume of sulfuric acid (h2so4) (ml). from the analysis of variance (anova), the volume of h2so4 and the interaction between digestion time and the volume of h2so4 are found to be important parameters in the nitrogen determination process via the kjeldahl method. the highest nitrogen content obtained was 12.23%, when using 15 ml h2so4 and 60 mins of digestion time. the value of r2 is 0.9986, which shows that the selected parameters (the digestion time and the volume of h2so4) and its corresponding levels are highly correlated to the percentage nitrogen content in earthworm powder using the kjeldahl method. abstrak: dalam pengurusan akuakultur ikan, makanan telah dikenalpasti sebagai masalah utama. kos yang tinggi serta kekurangan sumber makanan telah menggalakkan pencarian sumber protein baru seperti cacing tanah dan hasil sampingan sembelihan haiwan ternakan. cacing adalah sumber protein alternatif menggantikan ramuan ikan (fish meal) dalam formulasi makanan ikan. dalam kajian ini, kandungan jumlah nitrogen dalam serbuk cacing tanah telah dianalisa menggunakan kaedah kjeldahl dengan menggunapakai perisian statistikal iaitu full factorial design (ffd) yang boleh memberikan maklumat yang penting berkenaan dengan parameter-parameter yang dikaji. parameter-parameter tersebut adalah masa pencernaan (min) dan isipadu asid sulfurik (h2so4) (ml). daripada analisa varian (anova), isipadu h2so4 dan interaksi antara masa pencernaan dan isipadu h2so4 telah dikenalpasti sebagai parameter-parameter utama dalam proses penentuan kandungan nitrogen melalui kaedah kjeldahl. kandungan nitrogen yang tertinggi diperolehi adalah 12.23% bila menggunakan 15 ml h2so4 dan 60 minit masa pencernaan. nilai r 2 adalah 0.9986 menunjukkan bahawa parameterparameter (masa pencernaan dan isipadu h2so4) dan aras yang dipilih mempunyai perkaitan langsung yang tinggi dengan kandungan nitrogen dalam serbuk cacing dengan menggunakan kaedah kjeldahl. keywords: nitrogen content;, earthworm; kjeldahl method 1. introduction the aquaculture sub-sector in malaysia is divided into marine aquaculture and freshwater aquaculture. for freshwater aquaculture, pond culture is the main system iium engineering journal, vol. 14, no. 1, 2013 zakaria et al. 44 employed [1].aquaculture is a prominent approach to increase the fish production to suffice fish available to the populace. it was reported that 1.43 million tonnes of fish catches last year, not including squids, prawns and oysters, are not enough to feed a population of 28.5 million [2]. under the third national agriculture policy, aquaculture production in malaysia is targeted to reach 600,000 tonnes annually by the year 2010, which include 200,000 tonnes freshwater fish. this multifold increase in production from its current level will place an increasing demand on the supplies of feed (formulated feed and trash feed), since the aquaculture sector is targeted at high value species such as grouper, snapper and penaeid prawn. these species require high inputs of fish protein in their feed [1]. the issue of fish feed is identified as major problem in the fish aquaculture management. the high cost and scarcity of fishmeal in formulated feeds has led to the use of other protein sources such as earthworms, insects, snail, mussels, maggot, frog, and plants in fish feeds [3].however, there are some problems related to the quality of protein sources for fish feed. the occurrence of leaching of total protein content and lipid which was low (<15%) in all fish silage pellets such as silage-poultry by-product meal was reported [4]. some small scale keli (clarias spp) or catfish breeders in malaysia prefer to use the animal by-product such as chicken gut as the fish meal to the catfish due to its low in price and easily available. however, this leads to the odour pollution around the fish pond and its nearby area. moreover, the tissue strength of fish meat was found to be low that it is only suitable for local use only. eisenia feotida or earthworm is viewed as possible alternative of protein source in fish meal. moreover, earthworms are being used as fish bait and this practice is common in fishing activity throughout malaysia. owing to their high reproductive rate, low feeding costs and ease of breeding in captivity, earthworms constitute an extremely interesting protein source for fish feed. mostly, earthworms with high protein are also used to feed chickens, pigs and as a dietary supplement for ornamental fish [5, 6]. the earthworm in dried or dehydrated form has protein content higher than other protein source such as fish meal, meat and bone meal, and soybean meal [7].moreover, eisenia feotida proteins were not toxic to a human cell line at low concentrations [8]. determination of protein content is an important measurement especially in biochemical analysis such as electrophoresis, immuno-analysis, molecular biology as well as other research applications [9]. the protein concentration can be determined by using different methods such as kjeldahl method, combustion method, bradford method, biuret method, lowry method, uv-visible spectroscopic method [9-13]. the kjeldahl method provides several advantages: it could work under appropriate conditions with analysis simultaneously. moreover, the distillation process is very fast and efficient [11]. on the other hand, biuret method is impractical because of the detection limit and large volumes of sample requirement [9].to the authors best knowledge, there has yet any papers published on the use of statistical tools (design expert software) in the determination of protein content in earthworm powder by employing the kjeldahl method of analysis. utilization of statistical tools like design expert software offers many advantages. design of experiment (doe) is an efficient tool in such a way that it could eliminate the time consuming phase which could not be achieved when using the conventional ofat (one-factor-at-a-time) method [14]. furthermore, the ofat method is inefficient, requires more experimentation than a factorial and unable to detect interactions between the parameters or factors [15]. factorial experiments through 2 k study are the only way to discover interactions between parameters [15]. a 2 k design is useful prior to response iium engineering journal, vol. 14, no. 1, 2013 zakaria et al. 45 surface study in order to conduct screening experiments to identify the important parameters that had effects on the process [16]. therefore, in consideration of this, the objectives of this paper are to screen the active parameters which are h2so4 volume (15-25 ml) and digestion time (40-60 min) that play significant roles in protein content determination in earthworm powder. these parameters were chosen since for standard operating procedure of kjeldahl, the minimum conditions are 25 ml and 60 min for h2so4 volume and digestion time respectively. full factorial design (ffd) was used to achieve the objective and consequently, the process conditions that would give the highest protein content in earthworm powder using the kjeldahl protein analysis could be obtained. 2. materials and methods 2.1 materials earthworm powder was purchased from local company. sodium hydroxide, h2so4, boric acid and the kjeldahl tablets were purchased from merck. 2.2 preparation for scrubber five liters of sodium hydroxide (8%) was prepared. the ph indicator (0.5 g bromothymol blue was dissolved in 500 ml ethanol (95%) and 500 ml distilled water was added to the solution) was made and added into the 8% of naoh. activated charcoal in granular form was installed at the scrubber unit (buchi scrubber b-414, switzerland). 2.3 preparation for digestion one gram of the earthworm powder was weighed on a nitrogen free paper before it was placed in a digestion tube. two kjeldahl tablets (10 g) were added to increase the speed of reaction in digestion process. h2so4 (98%) with varying volume was added and the sample was suspended by gently swirling the tube. additional blanks (without earthworm) were prepared. the digest system k-437 (buchi, switzerland) unit was preheated at 300 °c for 30 min. the digestion process was started from 300 o c up to 420°c with varying digestion time. after the sample was completely digested, it was cooled down to ambient temperature prior for distillation. 2.4 preparation for distillation one liter of boric acid (4%) with ph 4.65, 1 liter h2so4 (0.25 m) and 500 ml naoh (10%) were prepared. the cold sample was distilled using auto kjeldahl unit k-370 (buchi, switzerland). 2.5 preparation for titration once the distillation process was done, the distilled sample was titrated with 0.25 m sulfuric acid from kjelflex (buchi, switzerland) and stop once the colour became slight purple or ph 4.65. the volume of titrant used was recorded. 2.6 calculation of % nitrogen: for 0.25 m h2so4: %� � ���� �� – ������� �� � �.�� � ��.�� ������ ! "#�$�� ��� (1) iium engineering journal, vol. 14, no. 1, 2013 zakaria et al. 46 2.7 calculation of % protein: % protein = % nitrogen x empirical protein factor. a conversion factor (f) is used to convert the measured nitrogen concentration to a protein concentration. a conversion factor of 6.25 (equivalent to 0.16 g nitrogen per gram of protein) is used for many applications, however, this is only an average value, and each protein has a different conversion factor depending on its amino-acid composition [17]. 3. results and discussion a 2 level–two-factor-design 2 2 with digestion time, a (40-60 min) and volume of h2so4, b (15-25 ml) was employed (table 1). these 2 factors are used to view its correlation with the response (r1) which is the percentage of nitrogen content (% nitrogen). 2 2 with 7 centre points corresponds to 17 experimental runs were suggested. the results are obtained and tabulated in table 2. table 1: parameters under investigation. range and levels independent variables units symbols -1 0 +1 digestion time mins a 40 50 60 volume of h2so4 ml b 15 20 25 table 2: experimental results for earthworm protein. std run factor 1 a:time digestion (minute) factor 2 b:sulfuric acid (ml) response 1 ri (% nitrogen) 13 1 50.00 20.00 12.21 12 2 60.00 25.00 0.49 11 3 60.00 25.00 1.12 1 4 40.00 15.00 11.41 17 5 50.00 20.00 11.98 3 6 40.00 15.00 11.82 8 7 40.00 25.00 1.17 4 8 60.00 15.00 12.07 6 9 60.00 15.00 12.23 14 10 50.00 20.00 11.95 5 11 60.00 15.00 12.15 15 12 50.00 20.00 11.91 10 13 60.00 25.00 0.80 7 14 40.00 25.00 0.79 16 15 50.00 20.00 11.81 9 16 40.00 25.00 0.74 2 17 40.00 15.00 11.74 from the result, it clearly showed that the highest nitrogen content could be achieved at the centre point level for both of the involved parameters (run no 1, 5,10,12,15 in table iium engineering journal, vol. 14, no. 1, 2013 zakaria et al. 47 2). the lowest nitrogen contents were obtained at low and high level of digestion time against high volume of h2so4 (run no. 2, 3, 13, 14 and 16 in table 2). therefore, this indicated that at high level of h2so4, it could destroy the nitrogen content in the earthworm regardless of the digestion time. from the analysis of variance (anova) in table 3, the model f-value obtained is 2918.04 which imply that the model is statistically significant. the p-value < 0.0500 indicates that the model terms are significant. the p-value for factor a is 0.1154 which shows that the factor a is not significant; however the p-values for factor b and ab are 0.0001 and 0.0274 respectively which indicate that the factors b and ab are significant. moreover, the value of f-values for volume of h2so4 is the highest compared to other parameters. it can be inferred that the volume of h2so4 play an important role in the nitrogen determination process. the curvature f-value of 2637.10 implies that there is significant curvature (as measured by difference between the average of the center points and the average of the factorial points) in the design space. the results from anova was further supported by the r 2 value shown in table 4. the r 2 value of 0.9986 shows that the selected factors which are the digestion time and the volume of h2so4 and its corresponding levels are highly correlated to the percentage nitrogen content in earthworm powder using the kjeldahl method. table 3: anova for earthworm protein. source sum of squares degrees of freedom (df) mean square f value p-value prob> f model 14332.62 3 4777.54 2918.04 < 0.0001 significant a-digestion time 4.72 1 4.72 2.88 0.1154 not significant b-sulfuric acid volume 14317.59 1 14317.59 8744.95 < 0.0001 significant ab 10.31 1 10.31 6.30 0.0274 significant curvature 4317.56 1 4317.56 2637.10 < 0.0001 significant pure error 19.65 12 1.64 --- cor total 18669.83 16 ---- table 4: analysis of protein content in earthworm. std. dev. 1.28 r-squared 0.9986 mean 50.14 adj r-squared 0.9983 c.v. % 2.55 pred r-squared 0.9971 press 41.88 adeq precision 102.225 figure 1 shows the graph of half normal plot. point ab, a and b indicates the positive and negative effect for the factors. parameters that fall along the straight line are considered as the noise or error from replicates. factor b is the farthest from the noise with p-value< 0.0001, while factor ab with p-value of 0.0274 which is < 0.05 indicates that these 2 factors are significant. iium engineering journal, vol. 14, no. 1, 2013 zakaria et al. 48 fig. 1: graph of half normal plot. fig. 2: graph of slight interaction;●: 15 ml of h2so4;●:25 ml of h2so4. the interaction graph shows in fig. 2 is the relationship between the digestion time and the volume of h2so4 with its nitrogen yields. it shows the yield of nitrogen content against high level of h2so4 (25 ml) and low level of h2so4 (15 ml) together with the digestion time (40-60 min). for 15 ml h2so4, at 60 min then nitrogen yield is higher than the other one since a sufficient amount of h2so4 was used in digestion. however, the percentage of nitrogen content when using 25 ml h2so4 was lower because the excess amount of h2so4 results in the loss of nitrogen compound and caused excessive foaming that occurred during the digestion solution. iium engineering journal, vol. 14, no. 1, 2013 zakaria et al. 49 naturally, protein digests by pepsin into amino acid. besides enzyme, acid can be used to digest protein but in different manner. h2so4 originally used by the founder of this method and still being used for its efficacy. h2so4 is an oxidizing agent that reduced nitrogen in food into ammonia and other organic matter. as the organic material is oxidized the carbon content is converted to carbon dioxide and the hydrogen is converted into water. digestion is the most time consuming step and one of disadvantage of using kjeldahl method. however, this procedure has enabled the obtainment of nitrogen higher yield at shorter time and this is the advantage of this analysis. complete digestion was not achieved by using h2so4 alone. the combination of h2so4 and high temperature has produced better results. the use of concentrated h2so4 at high temperatures poses a considerable hazard. 4. conclusion the nitrogen content in the earthworm powder was statistically analysed using ffd through kjeldahl method. the statistical tool (ffd) employed in the study has shown that the volume of h2so4 (b) and the interaction between the digestion time and the volume of h2so4 (ab) are important parameters in the nitrogen determination process. the highest nitrogen content obtained was 12.23% when using 15 ml h2so4 and 60 mins of digestion time. the conversion of total nitrogen (protein and non-protein) will give a total of 76.465% crude protein. it was presume only small percentage of non-protein nitrogen existed in earthworm powder (1.5 – 2%) and still the value was higher than previously reported protein content in earthworm, 64.4–72.9% [18] and 62% [8]. therefore, it can be concluded that the determination of nitrogen content using the kjeldahl method and the statistical software (ffd) enabled the obtainment of the highest crude protein content in earthworm. this indicated that the kjeldahl method is a robust and fast technique to measure nitrogen content and the application of ffd could enable the appropriate conditions for each parameters involved. consequently, this could save time, chemicals and raw materials. since, the protein content of earthworm obtained was high, therefore earthworm proteins could be considered for use as a supplement in animal diets especially for fish cultivation. digestion time does not provide much effect to the experiment but yet need to be considered since the longer the digestion time, the temperature will increase. at higher temperature, nitrogen compounds are decomposed to elemental nitrogen, leading to nitrogen loss thus lowering the yield of protein content in earthworm. acknowledgement the authors gratefully acknowledge ministry of agriculture for the science fund (90060006) and school of bioprocess, university malaysia perlis for their financial support and facilities respectively. references [1] musa, che utama che, and ahmad adnan nuruddin. “trash fish production and national fish feed requirement in malaysia”, low value and trash fish in the asia-pacific region hanoi, vietnam. (2007): 107. [2] s. rahim and p. nambiar. “can’t count on bounty of the sea”. new straits times, 28 june. 2011.(date retrieved not mention) iium engineering journal, vol. 14, no. 1, 2013 zakaria et al. 50 [3] o.a. sogbesan, a.a.a. ugwumba, c.t. madu. “nutritive potentials and utilization of garden snail (limicolaria aurora) meat meal in the diet of clariasgariepinus fingerlings”, african journal of biotechnology, 5.20 (2003): 1999. [4] o.a. fagbenro, k. jauncey. “physical and nutritional properties of moist fermented fish silage pellets as a protein supplement for tilapia (oreochromisniloticus)”.. animal feed science and technology 71.1 (1998): 11-18. [5] j.r. sabine. “earthworms as a source of food and drugs” in earthwormecology from darwin to vermiculture. london: chapman and hall, (1986): 285-96. [6] k.f. shim, y.l chua. “studies on the protein requirement of the guppy poeciliareticulate”. journal of aquariculture and aquatic science,. 4 (1986): 79-84. [7] s.s. basa. “feed and feedstuffs for aquaculture use in philippines”. report for the workshop on shrimp and finfish feed development. fao corporate document repository,. (1989): 163. [8] a.l. medina, j.a.cova, r.a. vielma, p. pujic, m.p. carlos, j.v. torres.”immunological and chemical analysis of proteins from eiseniafoetida earthworm”. food and agricultural immunology, 15.3,4,25 (2003): 263. [9] b. okutucu, a. dincer, o.habib, f. zihnioglu. “comparison of five methods for determination of total plasma protein concentration”. journal of .biochemists and .biophysics .methods, 70 (2007): 709-11. [10] m.v-martinez, j. l-hernandez, m.a. l-yusty. “protein and amino acid contents in the crab, chionoecetesopilio”. food chemistry, 103 (2007): 1330-36. [11] k. khodabux, m.s.s.l.’omelette, s.j-laulloo, p. ramasami, p.rondeau. “chemical and near-infrared determination of moisture, fat and protein in tuna fishes”. food chemistry, 102 (2007): 669-75. [12] y.y. mosleh, s. paris-palacios, m.g.v. couderchet. “effects of the herbicide isoproturon on survival, growth rate and protein content of mature earthworms (lumbricusterrestris l.) and its fate in the soil”. applied soil ecology,. 23 (2003): 69-77. [13] s. metsämuuronen, m. mänttäri, m. nyström. “comparison of analysis methods for protein concentration and its use in uf fractionation of whey”.." desalination 283 (2011): 156-64. [14] y.l. pang, a.z. abdullah, s.bhatia. “optimization of sonocatalytic degradation of rhodamine b in aqueous solution in the presence of tio2 nanotubes using response surface methodology”. chemical engineering journal,.166 (2011): 873-80. [15] montgomery dc, runger gc: applied statistics and probability for engineers fifth edition, john wiley and sons, asia,. (2011): 558. [16] r myers, d.c. montgomery, c.m. anderson-cook. “response surface methodology, process and product optimization using designed experiments."”, john wiley and sons, (2011):73. [17] ministry of agriculture, fisheries and food .food standards committee report on novel protein foods, fsc/rep/62, hmso, london. (1975):82. [18] m.g. paoletti, e. buscardo, d.j. vander jagt, a. pastuszyn, l. pizzoferato, y-s huang, l.t chuang, m. millson, h. cerda, f.torres, r.h glew. proc. r. soc. lond. b . “nutrient content of earthworms consumed by ye'kuana amerindians of the alto orinoco of venezuela”,270. (2003): 249-57. iium engineering journal, vol. 14, no. 1, 2013 zakaria et al. 51 nomenclature h2so4 sulfuric acid ffd full factorial design uv-visible ultra-violet visible doe design of experiment ofat one-factor-at-a-time naoh sodium hydroxide r1 response 1 anova analysis of variance microsoft word 6-paper03 .doc iium engineering journal, vol. 1, no. 1, january 2000 h. a. el-motaafy 16 a proposed method for improving the performance of p-type gaas impatt h. a. el-motaafy ee dep., high technology institute (hti), ramadan-tenth city, cairo, egypt abstract: a special waveform is proposed and assumed to be the optimum waveform for p-type gaas impatts. this waveform is deduced after careful and extensive study of the performance of these devices. the results presented here indicate the superiority of the performance of the impatts driven by the proposed waveform over that obtained when the same impatts are driven by the conventional sinusoidal waveform. these results are obtained using a full-scale computer simulation program that takes fully into account all the physical effects pertinent to impatt operation. in this paper, it is indicated that the superiority of the proposed waveform is attributed to its ability to reduce the bad effects that usually degrade the impatt performance such as the space-charge effect and the drift-velocity dropping below saturation effect. the superiority is also attributed to the ability of the proposed waveform to improve the phase relationship between the terminal voltage and the induced current. key words: computer-aided design, gaas impatt, microwave engineering 1. introduction it is well known that the performance of n-type gaas impatt diodes is superior to that of p-type diodes [1-3]. this is attributed mainly to the velocity-field characteristic of electrons in the gaas material that has a negative-differential mobility region [1-3]. this allows the electrons to have higher velocities at the lower values of field encountered in the active region during the negative half cycle of operation. this is in contrast to holes whose velocity drops below the saturated drift velocity for the lower values of the field. since these effects are inherent in gaas material, it is only possible to improve the performance of p-type gaas impatts through modifying the microwave circuit where the diode is imbedded. since it has been previously reported that the performance of impatts could be improved if it is driven by a non-sinusoidal voltage waveform [4-6], the external circuit attached to the diode must be capable of supporting such waveforms. however, no comprehensive study has been conducted for determining the optimum waveform. in this paper, a systematic procedure for choosing the optimum waveform and designing the external microwave circuit is presented. a special waveform is proposed to be the optimum waveform for p-type gaas impatt. this proposition is supported by an extensive investigation of impatt operation. this investigation has been conducted using a full-scale computer simulation program that takes fully into account all the physical effects pertinent to impatt operation without resorting to approximations that limits the scope of its application. this program is a modified version of one described elsewhere [7]. the performance of a given impatt that is expected to be modest is studied when it is driven by this waveform and when it is driven by the conventional sinusoidal waveform. then the results obtained for the two cases are compared. the superiority of the proposed waveform (pwf) is demonstrated especially at higher values of the dc current density j dc . the pwf can be optimized further through optimizing its parameters. since the pwf is difficult to be realized practically, the performance of the impatt is studied when it is driven by the waveform v2. this waveform comprises only the first two harmonics of the proposed waveform. the performance in this case is found also to be much superior to the conventional case. 2. the proposed waveform the proposed waveform (vf) is shown in fig. 1 for the case where a2 = 90 v. in the first part of the cycle, 1, the height of the pwf is a1. in the second part, 2, the height is a2. in the negative half cycle the height is a3. the width of the transitions between the different parts is 1, 2, and 3. the waveform consisting of the first two harmonics of the proposed waveform denoted by v2 is shown in the same figure together with the conventional waveform (vc). the parameters of this waveform can be optimized according to the following guidelines that are deduced from our extensive study of impatt operation [1,2,7-10]: 1.  1 should be as small as possible to reduce the spread of transit times of charge carriers. 2.  2 should be as small as possible to increase the slope of the terminal voltage when crossing the breakdown level. this helps reduce the space charge effect and improve the phase delay provided by the avalanche process. 3. a1 should be null to reduce the power dissipation at the beginning of the rf cycle. 4. the choice of 2 and a2 is a compromise between the following factors: a. 2 should be minimized in order to reduce the spread of transit times of carriers. iium engineering journal, vol. 1, no. 1, january 2000 h. a. el-motaafy 17 b. a2 must be increased to reduce the space charge effect and the spread of transit times of carriers and to satisfy the breakdown condition. however, a2 must not be too high, lest the breakdown condition should be satisfied only by an excessive increase of the dc-breakdown voltage. this is attributed to the saturation of the ionization rates at the high values of electric field. c. the product 2 a2 must be as high as possible to enable the increase of a3, which improves the performance. 5. the choice of 3 and a3 is a compromise between the following factors: a. a3 must be sufficiently high in order to extract the maximum energy from the drifting carriers but must not be too high so as to cause the carrier drift velocity to drop below the saturated value. b. 3 must be reduced to delay the injection of the avalanche-generated packet (agp) in the drift region; but if 3 is excessively reduced, the conductance of the diode may become positive at some higher order harmonics. the effect of the parameter a2, and consequently a3, will be presented in this paper. 3. the results obtained for the chosen impatt the impatt whose performance will be studied is a gaas p-type one having a single-drift abrupt junction structure. the doping density in the drift region is -315 cm 105 and its width is 3.7 m  . the pwf has the following parameters: o 321 9 = =  , o721  , o902  , o1713  , v. 49.5 = a and v, 90 = 21a figures 2 and 3 show, respectively, the efficiency and the rf power density versus the dc current density j dc for the pwf and a sinusoidal signal of amplitude 70 v. the value of 70 v is chosen since it gives the best performance for the sinusoidal excitation at the highest values of j dc considered. figures 4 and 5 show the efficiency and the rf power for the waveform v2 consisting only of the first two harmonics of the pwf. the results indicate clearly the superiority of the proposed waveforms over the conventional sinusoidal signal especially at the higher values of the dc bias current where the efficiency becomes almost three times higher and the rf power six times higher for the pwf. this demonstrates the ability of the proposed waveforms to reduce considerably the space-charge effect. this is illustrated clearly in fig. 6, which shows the induced current ji for the proposed waveform and the sinusoidal signal at different values of the dc bias current for the pwf and the sinusoidal signal. it is clear that the major manifestation of the reduction of the space charge effect is the delay of the injection of the avalanche-generated packet in the drift region (dr). this means that the time delay provided by the avalanche process is increased. this contributes to the improvement of the performance. the performance is also improved by reducing the spread of the transit times of carriers. this causes the agp and consequently the peak of ji to be sharper, as the figures show. hence, ji has higher values for the pwf during the negative half cycle. this is attributed also to the reduction of the drift velocity dropping below the saturation (vdbs) effect. on the other hand, the shape and the values of the induced current in the negative half cycle are better for the proposed waveforms. this is attributed to the reduction of the spread of transit times of carriers for the pwfs. the reduction of the spread of transit times of carriers means that the generated pulse of holes will be more localized in both the time domain and the space. this is clearl y demonstrated in fig. 7 that shows the spatial distribution of the hole current density for the considered waveforms at different phase angles. as it is seen at the beginning of the rf cycle, some carriers from the previous cycle are still being extracted at the ohmic contact. the extraction of these carriers is carried out earlier for vf. hence, the start of the avalanche breakdown is considerably delayed for the proposed waveforms. this contributes to their better performance since the phase delay provided by the avalanche process is enhanced. the injection of the agp of holes is also delayed for the proposed waveform. correspondingly, the phase delay is increased. this effect considerabl y improves the performance. as the agp of holes drifts toward the ohmic contact it is dispersed by the effect of diffusion. this dispersion is enhanced by the spacecharge effect for vc. for vf, the dispersion is smaller. this is attributed to two facts: that the agp is sharper in both the space and the time domain, and the spacecharge effect is less significant for the pwf. the reduction of the spread of transit times means that the currents induced by the carriers have a better distribution of phase angles. consequently, the induced current will be higher. the drift-velocity dropping below saturation is less significant for vf. this causes almost all the holes to drift at the saturated velocity. hence, the induced current is higher and more flat for this waveform. this contributes to its better performance. figures 8 and 9 show the spatial distribution of the electron current (jn), and the spatial distribution of the electric field e at different phase angles for different values of dc current. by analyzing these results, it is clear that the agp, after being injected into the drift region, causes e to decrease behind it and to increase in its front. this effect becomes more significant as jdc increases. the decrease of the field behind the agp causes the avalanche generation to be suppressed earl y in the cycle, which reduces the spread of the transit times of the carriers and causes the peak of ji to be sharper. hence, the performance is improved. the increase of the field in the front of the agp suppresses the vdbs effect. hence, ji will have higher values during the negative half cycle and the efficiency is enhanced. the figures show also that ji is extremel y iium engineering journal, vol. 1, no. 1, january 2000 h. a. el-motaafy 18 small during the major portion of the positive half cycle for the pwf. this is attributed to the shape of the pwf and helps improve the efficiency. figures 10 and 11 show the effect of a2 on the performance of the p-type impatt. the increase of both the rf power and the efficiency with a2 is attributed mainly to the reduction of the space charge iium engineering journal, vol. 1, no. 1, january 2000 h. a. el-motaafy 19 -80 -60 -40 -20 0 20 40 60 80 100 120 -40 60 160 260 360 the phase angle, degrees th e v o lt a g e , v fig.1 the voltage waveforms vc, vf, and vs 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 dc current, ka/sq-cm. e f f ic ie n c y , % fig. 2 the efficiency versus dc current for vf and vc at f=9 g hz 0 10 20 30 40 50 60 70 80 0 2000 4000 dc current density, ka/sq-cm r f p o w e r d e n s it y , k w /s q c m . fig. 3 the rf power versus dc current for vf and vc 0 5 10 15 20 25 30 1 2 3 4 5 6 7 8 9 10 dc current density, ka/sq-cm e f f ic ie n c y , % fig. 4 the efficiency versus dc current density 0 10 20 30 40 50 60 70 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 dc current, ka/sq-cm r f p o w e r , k w /s q -c m fig. 5 rf power versus dc current for v2 and vc at f=9 g hz 0 1 2 3 4 5 6 7 8 9 0 90 180 270 360 phase angle in d u c e d c u r r e n t , k a /s q -c m . fig. 6a the induced current for vf and vc at jdc=3 ka/cm 2 iium engineering journal, vol. 1, no. 1, january 2000 h. a. el-motaafy 20 0 2 4 6 8 10 0 90 180 270 360 phase angl, degrees in d u c e d c u r r e n t , k a /s q -c m . fig. 6b the induced current for vf and vc at jdc=3.5 ka/cm2 0 2 4 6 8 10 12 0 90 180 270 360 phase angle in d u c e d c u r r e n t , k a /s q c m . fig. 6c the induced current for vf and vc at jdc=3.8 ka/cm2 0 2 4 6 8 10 12 0 90 180 270 360 phase angle. in d u c e d c u r r e n t , k a /s q -c m . fig. 6d the induced current for vf and vc at jdc=3.9 ka/cm2 -5 0 5 10 15 20 0 1 2 3 4 distance, um. h o le c u r r e n t , k a /s q -c m . fig. 7a the hole current versus distance for vf at jdc = 3.5 ka/cm2 -2 0 2 4 6 8 10 12 14 16 18 0 1 2 3 4 distance, um h o le c u r r e n t , k a /s q -c m fig. 7b the hole current versus distance for vc at jdc = 3.5 ka/cm2 -2 0 2 4 6 8 10 12 14 16 18 20 0 1 2 3 4 distance, um e le c t r o n c u r r e n t , k a /s q -c m . fig. 8a the electron current versus distance for vc at jdc = 3.5 ka/cm2 iium engineering journal, vol. 1, no. 1, january 2000 h. a. el-motaafy 21 -5 0 5 10 15 20 25 30 0 1 2 3 4 distance, um. e le c t r o n c u r r e n t , k a /s q -c m fig. 8b the electron current versus distance for vf at jdc = 3.5 ka/cm2 0 1 2 3 4 5 6 0 1 2 3 4 distance, um. e le c t r ic f ie ld , k v /s q -c m . fig. 9a the electric field versus distance for vc at jdc = 3.5 ka/cm2 0 1 2 3 4 5 6 7 0 1 2 3 4 distance, um. e le c t r ic f ie ld , k v /c m fig. 9b the electric field versus distance for vf at jdc = 3.5 ka/cm2 0 5 10 15 20 25 30 50 60 70 80 90 100 110 a2, v e f f ic ie n c y , % fig. 10 the efficiency versus a2 0 10 20 30 40 50 60 70 50 60 70 80 90 100 110 a2, v r f p o w e r , k w /s q -c m . fig. 11 the rf power versus a2 effect and the reduction of the spread of transit times of holes. since the increase of a2 causes a3 to increase, the improved performance is attributed also to the reduction of the minority carrier enhancement effect and to the fact that energy extracted in the dr increases with a2 and a3. the saturation and decrease of the power and the efficiency for the large values of a2 are attributed to the drift velocity dropping below saturation and the saturation of the ionization rates at higher electric fields. 4. the reasons leading to the superiority of the proposed waveforms the superiority of the performance of the impatts driven by the proposed waveforms is attributed to the following reasons: 1. the considerable reduction of the space charge effect. this is attributed to the high value of the slope of the terminal voltage when crossing the breakdown level and to the large value of this voltage in the time interval during which the avalanche breakdown takes place. iium engineering journal, vol. 1, no. 1, january 2000 h. a. el-motaafy 22 2. the generation of minority carriers in the drift region is diminished. this is attributed to the higher magnitude of rf voltage during the negative half cycle. 3. the phase delay provided by the avalanche process is increased. this is because both the start of this process and the injection of the agp in the drift region are delayed. this is attributed to the favorable shape of the proposed waveform and its ability to reduce both the space-charge effect and the minoritycarrier enhancement effect. therefore, the phase relationship between the terminal voltage and the induced current is improved. 4. the reduction of the spread of transit times of carriers. this is also attributed to the shape of the proposed waveform that helps reduce both the space charge effect and the minority carrier enhancement effect. the proposed waveform causes the carrier generation by the avalanche multiplication to be localized in the time and the space domains. 5. both the drift-velocity dropping below saturation and the depletion-layer width modulation effects are reduced. this is because of the higher optimum values of the operating dc bias current. 5. conclusion in this paper, the performance of the p-type gaas impatt is studied when it is driven by a proposed non-sinusoidal waveform. it is indicated that by using this waveform, the bad effects that usually degrade the impatt performance are reduced. these bad effects include the space-charge effect, the drift-velocity dropping below saturation effect, and the minoritycarrier enhancement effect. it is also illustrated that the proposed waveform helps increase the phase delay provided by the avalanche process and reduce the spread of transit times of carriers. all these factors contribute to the superiority of the proposed waveform over the conventional one. the performance is also studied when the p-type gaas impatt is driven by waveforms consisting only of the first two or three harmonics of the proposed waveform. in this case, the performance of the impatt is found superior to that obtained when the device is driven by the conventional waveforms. references [1] h. a. el-motaafy, ”a new physical explanation for the high-efficiency mode of operation of gaas impatt diodes”, seventh conference on solid-state science, cairo, april, 1984. [2] h. a. el-motaafy, “the modes of operations of gaas impatt diodes,” proceeding of the third national radio-science symposium, cairo, feb. 1985. [3] p. bauhahn and g. i. haddad, “ impatt device simulation and properties”, ieee trans. electron devices, vol. ed-24, jan., 1977. [4] k. mouthan, “two-frequency operation of the avalanche-transit-time oscillators”, proc. ieee (lett.), vol. 58, march 1970. [5] w. e. schroeder and g. i. haddad, “effect of harmonic and subharmonic signals on avalanche diode oscillator performance”, ieee trans. microwave theory tech., vol. mtt-18, june, 1970. [6] h. el-motaafy, “the optimum voltage for si-impatt diodes,” seventh conference on solid-state science, cairo, 1984. [7] h. el-motaafy, “full-scale computer simulation of trapatt diodes, “the third national radio-science symposium, cairo, 1985. [8] el-s. a. el-badawy, s. h. ibrahim, and h. a. elmotaafy, “analysis of low-high-low inp impatt reflection amplifiers”, antem’98, symposium on antenna and applied electromagnetics, aug. 9-12, 1998, ottawa, ontario, canada. [9] s. h. ibrahim, el-s. a. el-badawy, and h. a. elmotaafy, “analysis and design considerations of a proposed low-high-low inp distributed impatt diode”, icm’97, the international conference on microelectronics, oct., 1997, bandung, indonesia. [10] el-s. a. el-badawy, s. h. ibrahimh, and h. a. elmotaafy, “effect of the variation of the doping density on the performance of low-high-low inp impatt diodes”, 1977 north american radio science meeting (ieee ap-s, international symposium and ursi radio-science meeting, july, 1997, montreal, canada. biography dr. hosny ahmed el-motaafy was born in 1951, at cairo, egypt. he got his b.sc. and m.sc. degrees in electronic engineering in 1974 and 1979, respectively, from mtc (military technical college), cairo, egypt and his ph.d. from ensae (ecole nationale supérieure de l’aéronautique et de l’espace), toulouse france, in 1982. dr el-motaafy research interest is in microwave electronics and active integrated antennas where he has more than 70 publications. currently, he holds a position of associate professor at the “higher technological institute (hti)”, 10th of ramadan city, cairo, egypt. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 potential of low carbon nanotubes dosage on chromium removal from water nassereldeen ahmed kabbashi1*, firdaus abd-wahab1, warqaa muhammed bahaaddin2, lubna muhamed musa3, abdurahman nour hamid4, and isam yasseen qudsieh5 1 department of chemical engineering & sustainability, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2 department of environmental science, duhok polytechnic university, iraq. 3 department of horticultural sciences, faculty of agriculture, gezira university, sudan 4 faculty of chemical & natural resources engineering, universiti malaysia pahang, malaysia. 5 chemical engineering department, college of engineering, jazan university, p.o.box 706, jazan 45142, saudi arabia. * corresponding author: nasreldin@iium.edu.my (received: 5th december 2020; accepted: 31st december 2021; published on-line: 4th july 2022) abstract: this paper involves a method of eliminating hexavalent chromium (cr (vi)) from the synthetic water via a low dosage of carbon nanotubes (cnt). the ability of cnt to remove cr(vi) from synthetic water through the adsorption process was studied in batch experimentation. the findings revealed up to 100% elimination of cr(vi) in the 0.07 mg/l cr(vi) concentration. these excessive elimination proficiencies were credited to the powerful adsorption of chromium ions to the physical properties of the cnt. a pattern layout was created in these experimental runs in order to locate the ideal situation of the cr(vi) deletion from synthetic water. to accomplish the purposes of the experiment, there were 4 independent variables influencing several points, namely the cnt dosage, the ph of the water, the agitation speed, and the contact time. the statgraphics centurion xv software has been used to create the adsorption equivalence and to discover the major impacts to the elimination of cr(vi). the results show that the adsorption capability of the carbon nanotubes was considerably reliant on the ph of the cr(vi) solution, supported by the cnt dosage, the contact time, and the agitation speed. the expected optimization, using the adsorption equation, shows that a 1 mg cnt dosage with a ph=2, 120 minutes contact time, and moderate agitation rate at 150 rpm is the most optimal. abstrak: kajian ini melibatkan kaedah bagi menyingkirkan kromium (vi) dari air sintetik menggunakan karbon tiub nano berdos rendah. eksperimen kelompok dilakukan bagi menentukan keupayaaan karbon tiub nano menyingkirkan cr(vi) dari air sintetik melalui proses penjerapan. dapatan kajian menunjukkan cr(vi) telah disingkirkan sebanyak 100% dari kepekatan 0.07 mg/l cr(vi). kecekapan penyingkiran ini adalah disebabkan penjerapan ion-ion kromium yang kuat terhadap sifat fizikal nano tiub karbon tersebut. rekabentuk eksperimen telah dibina bagi menentukan peringkat optima penyingkiran cr(vi) dari air sintetik. bagi mencapai matlamat kajian, empat faktor yang terdiri daripada dos nano tiub karbon, ph air, kelajuan goncangan dan masa sentuhan diukur. perisian statgraphics centurion xv telah digunakan bagi mendapatkan nilai setara proses penjerapan dan kesan utama yang menyebabkan tersingkirnya cr(vi). dapatan kajian menunjukkan keupayaan penjerapan oleh nano tiub karbon sangat bergantung kepada ph larutan cr(vi), disusuli dengan dos nano tiub karbon masa sentuhan dan kelajuan goncangan. penjerapan optimum cr(vi) dapat dicapai pada tahap 10 iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 1 mg dos nano tiub karbon, larutan pada ph 2, masa sentuhan selama 120 minit dengan kelajuan goncangan sebanyak 150 rpm. keywords: statgraphics; low cnt dosage; polluted water; chromium 1. introduction carbon nanotubes (cnts) are new technology. they consist of cylinder-shaped carbon fragments and have various schemes that make them hypothetically beneficial in a wide range of functions in medicines, engineering, biotechnology, and other areas of materials science [1]. they demonstrate extraordinary strength and exceptional electrical properties. the characteristics of nanotubes are defined by their thickness and chiral angle, both of which depend on n and m [2]. the thickness, dt, is simply the length of the chiral vector divided by 4, and it has been found that dt = (ö3/p) ac-c (m 2 + mn + n2)1/2, (1) where ac-c is the space among neighboring carbon atoms in the flat sheet. in turn, the chiral angle is given by tan-1(ö3n/(2m + n)) (2) the existence of heavy metals in the environment is of prime concern because of their harmfulness to many life forms. various manufacturing practices produce aqueous wastes that contain heavy metal toxins. since the bulk of heavy metals do not break down into nontoxic end products, their concentrations must be decreased to appropriate amounts before the release of industrial effluents [3]. without extraction, the presence of these heavy metals could create threats to public health and disturb the visual quality of potable water. according to the world health organization (who), the metals of highest immediate alarm are chromium, aluminum, iron, manganese, nickel, cobalt, zinc, copper, mercury, cadmium, and lead. conventional methods for elimination of metals from industrial effluents involve solvent extraction, chemical precipitation, electrolytic extraction, dialysis, reverse osmosis, cementation, ion exchange, membrane filtration, adsorption and co-precipitation [4,5]. traditional chemical and physical treatment of low concentration, large volume wastes can be likely very costly [6]. consumptive processes, such as chemical precipitation, entail large capital and operating costs. awareness has therefore centered on non-consumptive techniques that involve ion-exchange and other sorption processes. the concept of using low-cost carbons and agricultural products and by-products for the removal of toxic metals from water has been examined by number of sources [7]. findings to evaluate the capability of scrap rubber to adsorb dissolved metal ions from water found it to be a reasonably effective adsorbent [8]. chromium removal in water treatment is a big challenge since the maximum limit concentration allowed in drinking water is only 0.1 ppm. chromium can be found in many oxidation forms; cr(vi) being the most toxic and soluble, and cr(iii) being the least toxic form of chromium [9]. conventionally, heavy metals are removed by techniques that produce hazardous chemical wastes and require post-treatment [10]. therefore, a wider interest has been shown in finding alternative methods to remove cr species from water to ensure sustainable and consumable water supply. in this premise, low carbon nanotube dosage will be used to remove chromium from water. the elimination of chromium from wastewater can be valuable in environmental research as the carbon nanotubes have comparatively low growth temperature, high yields, and high purities that can be attained and low cost [11]. in another study by el-shafey [12], he reported that chromium sorption 11 iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 was highly dependent on the initial ph value with reduction taking place in solutions with ph up to 7, showing sorption maxima in the ph range of 1.8–2.8 for the concentration range of 100–500 mg/l with an increase in the equilibrium ph. carbon dioxide evolved from the sorption media was determined. 2. methods for removal of cr(vi) a number of treatment techniques for the elimination of metal ions from water have been described here, with emphasis on ion exchange, reduction, electrochemical precipitation, electrodialysis, solvent extraction, evaporation, chemical precipitation, reverse osmosis and adsorption [13,14].the physical and chemical properties of cr(vi) are displayed in table 1. the cr(vi) concentration must be eliminated as it comes with deleterious effects to human health and is described as carcinogenic [15]. table 2 indicates numerous possible health impacts from human exposure to cr(vi). table 1: physical and chemical properties of cr(vi) parameter properties physical state liquid appearance orange odor none reported ph ~7 vapor pressure 14 mm hg @20 oc vapor density 0.7 evaporation rate >1 (ether=1) viscosity not available boiling point 212 °f freezing/melting point 32 °f decomposition temperature not available solubility soluble in water specific gravity/density 1.0 molecular formula solution molecular weight not available (source: atieh, 2010) table 2: impact of cr(vi) to human health type of exposure effect ingestion may affect kidneys and cause harm. may cause serious gastrointestinal tract irritation with nausea, vomiting, and possible burns. eye produces eye irritation and likely burns. skin may affect skin sensitization, an allergic reaction, which becomes obvious upon re-exposure to this material. contact may cause irritation and likely burns. lengthy skin contact may produce injury, especially if the skin is abraded. chronic long-time contact or repeated skin contact may affect sensitization dermatitis and likely destruction and/or ulceration. may cause respiratory tract cancer. may cause liver and kidney damage. chronic inhalation may cause nasal septum ulceration and perforation. inhalation may cause liver and kidney damage. may cause ulceration and perforation of the nasal septum if inhaled in excessive amounts. causes respiratory tract irritation with likely burns. (source: nomanbhay, 2005) 12 iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 2.1 formulation of the chromium stock solution the stock solution of 1000mg/l of cr (vi) ions was prepared using 2.829g k2cr2o7 salt or solids. new dilutions were applied for each study of the cr (vi) elimination which is 0.07mg/l, cnt dosage is from 0.1 to 1 mg, contact time is shown in table 2 as well as agitation speed. the ph of the solutions was modified using 0.1m hcl and 0.1m naoh and buffer was employed for keeping the ph of the solutions matching to the ph needed [2]. 2.2 the adsorption findings the adsorption capability of carbon nanotubes was established by the matrix design by setting the cr(vi) concentrations (0.07 mg/l) of 50 ml cr solution in 100 ml shake flasks, with several carbon nanotubes dosage (1 mg and 0.1 mg). the combination was stirred in a rotary shaker at different speeds (200 rpm, 150 rpm, 100 rpm and 50 rpm) supported by filtration making use of a syringe filter. the filtrate comprising the remaining concentration of cr(vi) was verified spectrophotometrically at 540 nm after complexation with 1,5 diphenylcarbazide [16]. for the purpose of rate of metal adsorption by carbon nanotubes, the supernatant was studied for remaining cr(vi) after the contact period of 10, 20, 30, 40, 60, 120 and 1440 minutes. the impact of ph on cr adsorption by carbon nanotubes was revealed at ph values of 2, 4, and 6. the impact of various dosages of carbon nanotubes were 0.1, 1 mg at 0.07 mg/l cr(vi) carbon nanotubes was selected. all the variable quantity is shown in table 3 below whereas fig. 1 confirms the overall summary of the cr(vi) elimination using carbon nanotubes. table 3: experimental system layout no. independent variables no. of levels description 1 cr(vi) concentration (mg/l) 1 0.07 2 ph 3 6, 4, 2 3 cnt dosage (mg) 4 1, 0.1 4 contact time (min) 7 10, 20, 30, 40, 60, 120, 1440 5 agitation speed (rpm) 4 50, 100, 150, 200 3. outcomes and analysis 3.1 consequences of variables on the cr (vi) elimination the results obtained showed that the chromium exhibits different types of phdependent equilibria in aqueous solution, cr(vi) is a highly toxic compound causing severe human health effects. for smaller ph (ph=2) values, cr3o10 and cr4o13 2varieties are created. the best possible original ph for the adsorption of hexavalent chromium onto carbon nanotubes was detected at ph=2. this implies the creation of more polymerized chromium oxide varieties with reduced ph. nearly 100% of cr(vi) ions were adsorbed from a solution of 0.07 mg/l [cr(vi)], at ph=2, while the adsorption was reduced by the alteration of the ph from 2 to 4 and 6 (as in fig. 1). the results showed that alcoholic groups are converted to carboxylic groups while reducing cr(vi) to cr(iv). the adsorption of metal ions varies on solution ph, which affects electrostatic attachment of ions to related metal groups. 13 iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 fig. 1: impact of ph on the adsorption of cr(vi) at 0.07 mg/l cr(vi) concentration. 3.2 impact of carbon nanotubes amount on chromium application the concentration of both the metal ions and the carbon nanotubes is a substantial component to be studied for efficient adsorption. the amount of adsorption is a function of the original intensity of ions. the carbon nanotubes were different from 10 mg, 5 mg, 1 mg and 0.1 mg and caused interaction with the cr(vi) solutions of 0.07 mg/l intensities. the concentration of the carbon nanotubes in the 50 ml solution is 2 mg/l for 0.1mg and 20 mg/l for 1 mg cnt. for 1 mg cnt, the elimination of chromium is successful and accomplished 100% elimination with ph=2, agitation speed of 150 rpm and 120 minutes, as displayed in fig. 2. fig. 2: impact of cnt amount on cr(vi) adsorption from solutions at 0.07 mg/l cr(vi). cr adsorbed vs ph 2, 93% 4, 50% 6, 36% 2, 100% 4, 57% 6, 43% 0% 20% 40% 60% 80% 100% 120% 0 2 4 6 8 ph c r a d s o rb e d ( % ) 0.1mg 1mg removal of cr(vi) (% ) vs cnt dosage (mg/l) 84% 86% 88% 90% 92% 94% 96% 98% 100% 102% 0 5 10 15 cnt dosage (mg) c r r e m o v a l (% ) cnt dosage (mg) 14 iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 3.3 impact of agitation speed the result of the agitation of the adsorption system in cr adsorption was observed at 200 rpm, 150 rpm, 100 rpm and 50 rpm of agitation. all agitation speeds were discovered to have positive impact to the adsorption process, as shown in fig. 3. agitation enables appropriate interaction among the metal ions in solution and the cnt binding sites and, by this means, supports efficient moving of chromium ions to the carbon nanotubes sites. at 100 rpm and 50 rpm, the adsorption speeds observed were discovered to be marginally smaller than that of 200 rpm and 150 rpm. these findings reveal that the interaction between solids and liquid is more efficient at 200 rpm and 150 rpm but a medium speed at 150 rpm is the safest. this remark, as in fig. 3, concurs with the earlier described biosorptive elimination of cr(vi) by the husk of bengal gram (cicer arientinum) [17]. fig. 3: impact of agitation speed (rpm) on cr(vi) adsorption, cr(vi) concentration=0.1 mg/l. 3.4 impact of contact time a deviation of contact times was studied to explore its impact on the elimination of cr (vi). figure 4 indicates that the reduction ratio improved with rising contact time. at 120 minutes of contact time, the elimination efficacy was almost 100%. this might be clarified by the rise of contact time causing a continuing reduction of cr (vi) until it achieved its stability. this outcome is coherent with the findings of gupta et al. [18], and junyapoon. [19] and binqiao ren et al. [20]. 3.5 modelling of data using statgraphic centurion xv software the pareto chart below (fig. 5) indicates each of the expected consequences in declining order of significance. the amount of each bar is proportionate to the standardized result, which is the expected outcome divided by its standard error. this is comparable to computing a t-statistic for each impact. the perpendicular line can be manipulated to decide which impacts are statistically significant. any bars which expand away from the line relate to impacts which are statistically significant at the 95.0% trust level. therefore, 5 consequences are significant. the largest effect is the ph, supported by time, dosage, speed and correlation among speed and ph. cr adsorbed (% ) vs agitation speed 77% 78% 79% 80% 81% 82% 83% 84% 85% 86% 87% 0 50 100 150 200 250 agitation speed c r a d s o rb e d ( % ) agitation speed 15 iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 fig. 4: impact of contact time on the adsorption of cr(vi) with [cr(vi)] = 0.07 mg/l. the r-squared statistic suggests that the model as equipped supports 51.8007% of the flexibility in percentage elimination. the adjusted r-squared statistic, which is more appropriate for assessing models with diverse numbers of independent variables, is 49.6985%. the standard error of the assessment reveals the standard deviation of the residuals to be 22.8074. the mean absolute error (mae) of 17.5874 is the average value of the remainders. the durbin-watson (dw) statistic tests the residuals to ascertain if there is any significant correlation established on the order in which they appear in the data file. since the p-value is greater than 5.0%, there is no hint of serial autocorrelation in the residuals at the 5.0% significance level. fig. 5: pareto chart analysis. the edges in fig. 6 signify the expected change in percentage elimination of cr (vi) as each factor is shifted from its low level to its high level, with all additional factors kept constant at a value halfway between their lows and their highs. note that all the factors with cr adsorbed vs contact time 0% 20% 40% 60% 80% 100% 120% 0 50 100 150 contact time (min) c r a d s o rb e d ( % ) 0.1mg 1mg 16 iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 significant main impacts have a better effect on the response which is the percentage elimination. from the pareto chart above, the adsorption equation model can be created as shown below: dosagecntphspeed timespeedphcradsorbed *89.1**0135.0 *013.0*14.0*06.1280.85(%)   note that the underlying model uses the form of a multiple linear regression model. each maintained main impact is incorporated in the model by itself, while the two-factor interface is represented by a cross product of speed and ph. the equation was outlined as illustrated in fig. 6. fig. 6: multiple linear regression results. r-squared = 64.1761 percent r-squared (adjusted for d.f.) = 63.6333 percent standard error of est. = 18.7668 mean absolute error = 14.2147 durbin-watson statistic = 0.950296 (p=0.0000) 4. conclusion the observations of the adsorption study on the capability of carbon nanotubes to eliminate cr(vi) reveals its possibility of usage to separate heavy metals from low concentration water. with 99.99% carbon nanotubes concentration, incredible properties, and structure, the elimination of cr(vi) was good and could accomplish up to 100% elimination. hence, the application of the carbon nanotubes to eliminate cr(vi) has been analysed in this experiment with four factors contributing namely the cnt dosage, the ph of the water, the agitation speed, and the contact time for the cr(vi) to be adsorbed with the carbon nanotubes. the experimental design that has been applied is the pattern design or the multilevel factorial. this experiment deals with one level of cr(vi) concentration, four levels of cnt 17 iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 dosage, three levels of ph, seven levels of contact time and four levels of agitation speed. there were 336 experimental runs that were done with 2 replicates, the optimum conditions for cr removal were reached by 1 mg cnt dosage, ph=2, 120 minutes of contact time, and a moderate agitation rate of 150 rpm. references [1] iijima s. (1991) helical microtubules of graphitic carbon. nature, 354: 56-58. [2] atieh ma, bakather oy, tawabini bs, bukhari aa, khaled m, alharthi m, fettouhi m, abuilaiwi fa. (2010) removal of chromium (iii) from water by using modified and nonmodified carbon nanotubes. j. nanomater. https://doi.org/10.1155/2010/232378. [3] el-sheikh ah. (2008) effect of oxidation of activated carbon on its enrichment efficiency of metal ions: comparison with oxidized and non-oxidized multi-walled carbon nanotubes. talanta, 75: 127-134. https://doi.org/10.1016/j.talanta.2007.10.039. [4] mishra s, bharagava rn. (2016) toxic and genotoxic effects of hexavalent chromium in environment and its bioremediation strategies. j. environ. sci. heal. part c environ. carcinog. ecotoxicol. rev., 34: 1-32. https://doi.org/10.1080/10590501.2015.1096883. [5] baig m, mehmood b, matin a. (2004) removal of chromium from industrial effluents by sand filtration. electron j env. agric food chem., 2. [6] lee ck, low ks, kek kl. (1995) removal of chromium from aqueous solution. bioresour. technol., 54: 183-189. https://doi.org/10.1016/0960-8524(95)00130-1. [7] mitra s, sarkar a, sen. s (2017) removal of chromium from industrial effluents using nanotechnology: a review. nanotechnol. environ. eng., 2. https://doi.org/10.1007/s41204017-0022-y. [8] baral ss, das sn, rath p. (2006) hexavalent chromium removal from aqueous solution by adsorption on treated sawdust. biochem. eng. j., 31: 216-222. https://doi.org/10.1016/j.bej.2006.08.003. [9] hummers ws, offeman re. (1958) preparation of graphitic oxide. j. am. chem. soc., 80: 1339. [10] wang k, et al. (2015) one-pot preparation of cross-linked amphiphilic fluorescent polymer based on aggregation induced emission dyes. colloids surfaces b biointerfaces., 126: 273279. https://doi.org/10.1016/j.colsurfb.2014.12.025. [11] dakiky m, khamis m, manassra a, mer’eb m. (2002) selective adsorption of cr(vi) in industrial adsorbents. adv. environ. res., 6: 533-540. [12] el-shafey ei. (2005) behaviour of reduction-sorption of chromium (vi) from an aqueous solution on a modified sorbent from rice husk. water. air. soil pollut., 163: 81-102. https://doi.org/10.1007/s11270-005-8136-4. [13] william pj. (1985) industrial wastewater treatment technology, 2nd ed, butterworthheinemann, london. [14] demirbas e, kobya m, senturk e, ozkan t. (2004) adsorption kinetics for the removal of chromium (vi) from aqueous solutions on the activated carbons prepared from agricultural wastes. water sa, 30: 533-539. https://doi.org/10.4314/wsa.v30i4.5106. [15] nomanbhay sm, palanisamy k. (2005) removal of heavy metal from industrial wastewater using chitosan coated oil palm shell charcoal. electron. j. biotechnol., 8: 43-53. https://doi.org/10.2225/vol8-issue1-fulltext-7. [16] eaton a, ramirez lm, haghani a. (2001) the erin brockovich factor-analysis of total and hexavalent chromium in drinking waters, awwa water qual. technol. conf. nashville, tn. [17] ahalya n, kanamadi rd, ramachandra tv. (2005) biosorption of chromium (vi) from aqueous solutions by the husk of bengal gram (cicer arientinum). electron. j. biotechnol., 8: 258-264. https://doi.org/10.2225/vol8-issue3-fulltext-10. [18] gupta vk, shrivastava ak, jain. n (2001) biosorption of chromium(vi) from aqueous solutions by green algae spirogyra species. water res., 35: 4079-4085. https://doi.org/10.1016/s0043-1354(01)00138-5. 18 iium engineering journal, vol. 23, no. 2, 2022 kabbashi et al. https://doi.org/10.31436/iiumej.v23i2.1717 [19] s. junyapoon, &s. weerapong. (2006) removal of hexavalent chromium from aqueous solutions by scrap iron filings. kmitl sci. tech. j., 6: 1-12. [20] ren b, zhang q, zhang x, zhao l, li h. (2018) biosorption of cr(vi) from aqueous solution using dormant spores of aspergillus niger. rsc adv., 8: 38157-38165. https://doi.org/10.1039/c8ra07084a. 19 microsoft word mamat20-final.doc iium engineering journal, vol. 1, no. 2, 2000 m. f. bin mamat et al. 1 effect of lithium chloride (licl) dopant on the performance of catalysts for the oxidative coupling of methane m. f. mamat, n. a. mohd zabidi, s. bhatia and m. h. a. megat ahmad school of chemical engineering, perak branch campus, universiti sains malaysia,31750 tronoh, perak, malaysia kkbhatia@kimia.eng.usm.my abstract: the present study reports effects of lithium chloride (licl) doping on mgo, la2o3, sno2, cao and zno catalysts. all the catalysts were prepared by the impregnation method. the catalysts were tested at reaction temperature of 775oc. the feed flow rate of methane, oxygen and nitrogen was carried out in the ratio of 3:1:2 giving a weight hourly space velocity (whsv) of 0.375 g.s/cm3. la2o3 showed the highest c2+ selectivity among the undoped catalysts. all the catalysts were doped with licl to compare their methane conversion, selectivity and product yield. the 2.0 mol% licl doped into la2o3 was the best catalyst formulation having achieved 46.7% of c2+ selectivity with ch4 conversion of 29.0% and the increase in selectivity was attributed to the presence of chlorine. hydrogen production was more pronounced for mgo based catalysts and believed to be generated by surfacecatalyzed reactions. key words: oxidative coupling, c2+ selectivity, hydrogen production, ethylene, chlorine 1. introduction direct conversion of methane to industrial organic compounds is particularly significant especially natural gas, where the major component is methane, is one of the most plentiful fossil fuels available. industry analysts estimate that the world holds enough readily recoverable natural gas to produce 500 billion barrels of synthetic crude [1]. perhaps triple that amount of gas can be found in coal seams, natural gas hydrates [2] and in formations that release the gas only slowly. crude oil is now the main source of chemicals and liquid fuels. however, with the continual depletion of crude oil reserve, the demand for natural gas as a source of chemicals and fuels would certainly increase [3]. one route is the direct dimerization of methane through the catalytic oxidative coupling of methane (ocm) process. the catalytic oxidative coupling of methane (ocm) is represented by the following equation: n4 2 4n-2y 2 y nch o c h yh o 2 + ® + (1) in most published works in this topic, n would have the optimum value of 2. oxidant other than o2, such as n2o and o3 have also been shown to facilitate the coupling reaction [4]. the hydrocarbon products are often reported as c2+ products, mostly ethane and ethylene as the major components with ethylene as the target product. c3 hydrocarbons are usually formed but at comparativel y low selectivity. in addition to these products, cox (co and co2) are also formed nonselectively. the conversion of ch4 to cox is undesirable since it represents a lower yield of hydrocarbons. the cox may also poison the surface of the catalyst. another important product from the reaction is hydrogen, which is also a valuable product especially in fuel cells, which is projected to become the main source of energy for automobiles [5]. a large number of compounds, mostly metal oxides has been tested and found capable of facilitating the oxidative coupling reaction. in most of the catalysts studied, reaction temperatures in the range of 700-900oc are needed and products consists of c2+ hydrocarbons, carbon monoxide, carbon dioxide and water are obtained. there appears to be an inverse relation between methane conversion and selectivity to c2 hydrocarbons, resulting in an upper limit of selectivity per pass through the reactor. indeed, investigation on the thermodynamic feasibility of the reactions, proposed that ethylene yield of 30 per cent is the highest that can be achieved [6]. in earlier studies, the goal of the applied research was often to maximize c2+ yield by varying composition of the catalyst, partial pressures of reactants, etc.; however, even in the best catalytic systems, the c2+ hydrocarbons concentration in the exit gas were quite low making it economically undesirable to extract c2+ from such a mixture. the more effective catalysts may be divided into five groups a) highly basic pure oxides, of which the early members of the lanthanide oxides series (excluding ceo2) are the best, b) group ia or iia ions supported on basic oxides (for example, li/mgo, ba/mgo and sr/la2o3), c) monophasic oxides, d) a few transition metal oxides that contain group ia ions, and e) any of these materials that are promoted with chloride ions. it is very unlikely that only a single type of site is responsible for the activation of methane as can be seen in the diversity of the catalysts used in the oxidative coupling reaction. it is difficult to determine the nature of the active sites as most characterization methods are iium engineering journal, vol. 1, no. 2, 2000 m. f. bin mamat et al. 2 applicable only at conditions far removed from those used in the actual catalytic reaction. nonetheless, rational hypothesis can be made concerning the species that might exist on the surface of the functioning catalysts. the addition of chloride ions to an oxidative coupling catalyst can have a marked effect on its properties, particularly with respect to the ethylene (c2h4) to ethane (c2h6) product ratio. the chloride may be introduced either initially as a part of the catalyst or through organo chlorine compounds, for instance ccl4, that are added to the reagents [7]. because chlorine is known to dehydrogenate c2h6 in the gas phase, it has been suspected that homogenous reactions may be responsible for the large c2h4/c2h6 ratios that are observed in these chlorine containing systems [8]. in this study, the effects of licl on different oxide catalysts such as mgo, la2o3, sno2, cao and zno are reported. 2. experimental catalysts were prepared through the wet impregnation method. powdered mgo (merck, extra high purity), la2o3 (fluka, purity 97%), cao(bdh), zno (merck, 99.0%) and sno2 (merck, 99.0%) were used directly from supplier's package without any treatment. for doping the catalysts with licl, desired amount of licl (merck, 98.0%) was dissolved in deionized water. the supports were then poured into the solution and stirred. the resulting paste was dried in an oven for 12 hrs at 110oc-120oc. the dried paste was then crushed to powder and calcined at 950oc for 4 hour. the calcined material was then pelletized at 5 tons/m2 for each 5 gm of catalyst. the pellet was then calcined again at 950oc for another 8 hrs. after calcination, the pellets were crushed and sieved to 40-60 mesh size. the same procedure was applied with the other dopant (li2co3, ajax, 99.5%) used before testing. the catalysts were tested in a stainless steel microreactor (o.d. 12.7 mm, i.d. 10.92 mm and length 600 mm) situated vertically in a tubular furnace (carbolite vst 12). the catalyst layer was placed in the center of the microreactor. the free space below and above the catalyst layer was filled with quartz particles (rdh) of 40-60 mesh size in order to minimize the dead volume of the reactor. methane (malaysian oxygen, purity 99.99%), oxygen (99.8%) and nitrogen (99.99%) were passed through the microreactor. flow of the gases was controlled using mass flow controllers (brooks 5850e for both nitrogen and oxygen and mks for methane). outlet gas flow rate was monitored using a gas flowmeter (alexander wright dm3 b). the gaseous products were analyzed using an on-line gas chromatograph (hewlett-packard 6890). porapaq n column was used to separate carbon dioxide, ethane, ethylene and propylene and molecular sieve 5a was used for separation of hydrogen, oxygen, carbon monoxide, nitrogen and methane. water, a by-product of the reaction, was trapped in a gas trap before gaseous product sampling was carried out. the gas chromatograph was calibrated using a standard gas mixture supplied by boc gases, u.k. the catalyst was first heated in o2 at a flow rate of 10 ml/min at 800oc for half an hour to oxidize adsorbed components. it was then cooled down to 700oc before mixture of reactants was fed through the microreactor with ch4:o2:n2 ratio of 3:1:2 giving a total flow rate of 240 ml/min. a 1.5 gm of catalyst was used for each experimental run. furnace temperature was adjusted to the desired reaction temperature. catalyst bed temperature was monitored using a chromel-alumel thermocouple inserted into the catalyst bed. once the bed temperature stabilized for 15 mins, the sample was drawn. the activity of the catalysts was expressed in terms of methane conversion, selectivity and yield for c2+ hydrocarbon and hydrogen. a carbon balance of 100+2% was obtained for every run over the catalysts. the conversion of methane or oxygen was defined as 4 2 4 2 4 2 x(ch or o ) moles ch or o conver t ed 100% moles ch or o fed = ´ (2) the selectivity for cn products was calculated as n n 4 s(c ) n moles c in product s 100% moles ch convert ed t o all product s = ´ ´ (3) the yield for cn product was given by n n 4 n moles c in pr oduct s y(c ) 100% moles ch fed ´ = ´ (4) the selectivity for h2 product was calculated as 2 2 4 s(h ) 2 moles h in product s 100% 4 moles ch convert ed t o all product s = ´ ´ ´ (5) the yield for h2 product was given by 2 n 4 2 moles h in pr oduct s y(c ) 100% moles ch fed ´ = ´ (6) 3. results in most of experimental runs, methane to oxygen mole ratio was more than 2. a 100% o2 conversion was achieved in most of experiments. figure 1 shows the methane conversion, selectivity and yield of c2+ hydrocarbons for undoped catalysts. la2o3 gives the highest activity in terms of selectivity and yield of c2+ hydrocarbons, which were 44.8% and 12.4% respectively, followed by mgo with 39.4% selectivity and yield of 11.3% of c2+ hydrocarbons. zno gave 18.8% selectivity of c2+ hydrocarbons and yield of 4.0%. catalytic performance of both sno2 and cao show that they are nonselective catalysts. all these results are in line with literature findings. both the la2o3 and mgo have been known to be good coupling catalysts especially when doped with alkaline earth oxides [9]. iium engineering journal, vol. 1, no. 2, 2000 m. f. bin mamat et al. 3 fig. 1 performance of undoped catalyst figure 2 shows the selectivity and yield of hydrogen for the undoped catalysts. mgo showed the highest activity with h2 selectivity of 19.1% and yield of 5.5%. compared to the selectivity and yield of hydrocarbons product, cao showed significant selectivity and yield of h2 relative to mgo. a selectivity of 12.0% and 2.7% yield of hydrogen were obtained. both sno2 and zno gave low activity to h2 formation. the ratios of c2h4/c2h6 and co/co2 are shown in figure 3. from these results, it appeared that higher c2+ selectivity leads to higher c2h4/c2h6 ratio, nevertheless a small degree of variation in catalytic activity among the catalysts was observed. mgo produced higher ethylene relative to ethane as compared to la2o3 even though la2o3 gave the highest selectivity to c2+ hydrocarbons. the c2h4/c2h6 ratio did not correlate with h2 selectivity and yield. fig. 2 activity of undoped catalyst for selectivity and yield of hydrogen production fig. 3 ethylene to ethane ratio and carbon monoxide to carbon dioxide ratio over undoped catalyst doping the catalysts with 1 mol% licl did not result in an apparent increase in terms of c2+ selectivity and yield for any of the catalysts except cao, as shown in figure 4. the c2+ selectivity of 1 mol% licl/cao increased much higher compared to the other catalysts but the methane conversion decreased. the c2+ selectivity increased from 7.6% to 17.2% wihile methane conversion dropped 22.8% to 18.8%. no marked changes in the measured parameters were observed for other 1 mol% licl doped catalysts. figure 5 shows the selectivity and yield of h2 on the 1 mol% licl doped catalysts. again, except for 1 mol% licl/cao, there are no significant changes in both the h2 selectivity and yield for the other catalysts. the h2 selectivity and yield for 1 mol% licl/cao catalysts decreased from 12.0% to 0.9% and from 2.7% to 0.2%, respectively. fig. 4 activity of 1 mol% of licl doped catalysts iium engineering journal, vol. 1, no. 2, 2000 m. f. bin mamat et al. 4 fig. 5 hydrogen production over 1 mol% licl doped catalyst figure 6 shows the ratios of c2h4/c2h6 and co/co2 against the 1 mol% licl doped catalysts. the presence of licl appears to have a conspicuous influence to the product ratios, especially doped mgo catalyst. the ratio of c2h4/c2h6 increased from 1.14 for mgo catalyst to 1.38 for 1 mol% licl/mgo whereas the co/co2 increased from 0.14 to 0.25. for the other catalysts, no significant changes were observed in c2h4/c2h6 ratio but the co/co2 ratio for cao and sno2 reduced markedly due to total oxidation to co2. because of its high selectitivity to c2+ hydrocarbons, both the la2o3 and mgo have been doped with 2 mol% licl. table 1 shows the results of these catalysts together with pure and 1 mol% licl doped catalysts for comparison purpose. fig. 6 products ratio over 1 mol% licl doped catalyst from table 1, increasing licl concentration on mgo resulted in a negative effect where the c2+ selectivity decreased from 39.6% for 1 mol% licl/mgo catalyst to 34.7% for 2 mol% licl/mgo. the conversion also decreased from 27.6% to 24.7%. the most marked change was observed on the c2h4/c2h6 ratio, which decreased from 1.38 to 0.29. this was observed when li2co3 was used as a precursor. the c2+ selectivity increased to 42.6% with methane conversion of 29.7%, resulting in c2+ yield of 12.7%. the c2h4/c2h6 ratio also increased to 1.5. all the other measured parameters were kept constant. for la2o3, doping it with 2 mol% licl caused an increase in c2+ selectivity and yield which were the highest among all the catalysts studied. table 1: catalytic activity of la2o3 and mgo based catalysts catalysts %ch4 conversion %c2+ hydrocarbons %c2+ yield %h2 selectivity %h2 yield c2h4/c2h6 co/co2 mgo 28.8 39.4 11.3 19.1 5.5 1.14 0.14 1 mol% licl/mgo 27.6 39.6 10.9 16.3 4.5 1.38 0.25 2 mol% licl/mgo 24.7 34.7 8.6 20.6 5.1 0.29 0.32 2 mol% li/mgo * 29.7 42.6 12.7 17.0 5.1 1.5 0.25 la2o3 27.7 44.8 12.4 15.8 4.4 0.95 0.11 1 mol% licl/la2o3 28.5 44.3 12.6 14.0 4.0 0.99 0.12 2 mol% licl /la2o3 29.0 46.7 13.5 15.5 4.5 1.05 0.10 2 mol% li/la2o3* 27.8 42.8 11.9 12.9 3.4 0.81 0.05 *prepared by using li2co3 as a precursor for li dopant iium engineering journal, vol. 1, no. 2, 2000 m. f. bin mamat et al. 5 the c2+ selectivity and yield of 2 mol% licl/la2o3 were 46.7% and 13.5%, respectively. the h2 selectivity and yield together with the c2h4/c2h6 and co/co2 ratios did not change significantly. the activity of 2 mol% licl/la2o3 also was better than 2 mol% li/la2o3 catalyst prepared by using li2co3 as the li dopant precursor, where the c2+ selectivity obtained was 42.8% with methane conversion of 27.8%. the conversion, yield and selectivity values were reproducible within experimental error of 5%. 4. discussions it is generally accepted that the oxidative coupling of methane to c2 hydrocarbons and subsequently to c3 and higher hydrocarbons is initiated by the generation of gas-phase methyl radicals [10]. this is accomplished through the abstraction of hydrogen atom from methane, which has been proposed as follows: s4 3ch o ch oh+ ® + (7) where the surface oxygen species, o-s is the active site. the ohwould be converted to water through subsequent reactions that regenerate the o-s with the help of gas-phase oxygen. ethane is formed via the coupling of methyl radicals in the gas phase, whereas ethylene is believed to be originated from the thermal dehydrogenation of ethane or the surface-catalyzed oxidative dehydrogenation of ethane. both co and co2 come from the gas-phase or surface catalyzed oxidation of methane, hydrocarbon intermediate species and hydrocarbons final product. the latter two may contribute more significantly than the former for this non-selective reactions [11]. the production of hydrogen may be invoked by these possible paths of consecutive reactions [12]: water gas-shift reaction (referred to as wgs) 2 2 2co h o co h+ ® + (8) thermal cracking of ethane 2 6 2 4 2c h c h h® + (9) steam reforming of hydrocarbons n 2n+ 2 2 2c h nh o nco (2n+ 1)h+ ® + (10) partial oxidation of hydrocarbons n 2n+ 2 2 2 1 c h no nco (n+ 1)h 2 + ® + (11) ethane dehydrogenation in the presence of steam is an un-catalyzed commercial process, whereas wgs and steam reforming of hydrocarbons do not proceed without a catalyst. partial oxidation can occur both thermally and catalytically. from the figures and table presented, it is noticeable that when the c2+ selectivity increases, the c2h4/c2h6 would also increase but not the h2 selectivity. this indicates that the catalytic oxidative dehydrogenation of ethane and the thermal dehydrogenation of ethane are the sources of ethylene and the water gas-shift reaction (eq. 8) is the main source of hydrogen production. the catalytic influence on these reactions is clearly shown by the differences in activity of cao and 1 mol% licl/cao. the relative importance of the catalytic oxidative dehydrogenation of ethane and the thermal dehydrogenation of ethane is, however, difficult to determine. the low co/co2 ratio recorded on all the catalysts indicates that the steam reforming of hydrocarbons (eq. 10) and the partial oxidation of hydrocarbons (eq. 11) do not proceed to a significant extent. the absence of steam reforming reaction is in line with kinetics observation by stansch[11] on la2o3/cao catalyst which stated that the reaction was not observed for reaction temperatures below 800oc but become significant above 800oc. this is because the reaction of c2+ hydrocarbons with water is much slower as compared with oxygen. investigation by hargreaves, et. al.[12] showed that partial oxidation of hydrocarbons was found to be the dominant route to h2 only at low oxygen conversion. in the present study, a 100% of oxygen conversion was achieved on all the catalysts system. for the catalysts studied, the positive influence of licl on la2o3 is much more pronounced. the increase in the c2h4/c2h6 ratio may indicate the participation of chlorine in dehydrogenating ethane in the gas phase. as the calcination and reaction temperature used in this study are relatively high, significant loss of chlorine from the catalyst may occur before and definitely after the reaction. this is believed to happen because of the evaporative nature of chlorine. during experimentation, chlorine may react with water vapors resulting in the formation of hcl. if chlorine induced dehydrogenation of ethane occurred, it is projected that mgo when doped with 2 mol% of licl should give a much higher c2h4/c2h6 ratio as compared to 1 mol% of licl/mgo. however, this is not the case in our present study. this suggests that other factor, which was influenced by the presence of cl plays a part in the catalyst selectivity. the negative effect of chlorine on mgo is proved further when li2co3 was used as a precursor to prepare 2 mol% li/mgo, and the c2+ selectivity increased together with the c2h4/c2h6 ratio. the presence of chlorine, however, possibly enhanced the c2h4/c2h6 ratio only at a much lower temperature. a study on licl/mgo catalyst showed the catalysts to be effective in increasing the ratio of c2h4/c2h6 up to 5 with c2 yield of 20% at 640oc[7]. for la2o3, higher doping concentration of licl gives a positive effect to the c2+ selectivity but the c2h4/c2h6 ratio remains to be similar. again, the presence of chlorine is the main factor in the increase of c2+ selectivity as doping the la2o3 with the same li concentration using li2co3 as the precursor do not give a similar result but a decrease in c2+ selectivity as observed. the different behavior of la2o3 and mgo based catalysts may be attributed to the influence of chlorine on the active sites of the catalysts. the chlorine seems to affect the catalysts activity more than that of lithium. iium engineering journal, vol. 1, no. 2, 2000 m. f. bin mamat et al. 6 5. conclusions results obtained show that the presence of licl has a marked influence on the activity of all the catalysts studied. the function of the chlorine atom is related more to the active sites on the surface of the catalysts rather than involved in facilitating ethylene formation via gas-phase dehydrogenation reaction of ethane, as previously suggested. it is also discovered that hydrogen is mainly produced through the water gasshift reaction. acknowledgements this research has been supported by universiti sains malaysia under long-term irpa grant (project no. 0202-05-7003). megat harun al rashid bin megat ahmad acknowledges ministry of science, technology and environment, malaysia for award of postgraduate scholarship. references [1] s. a. fouda, "liquid fuels from natural gas", scientific american, pp. 74-77, march 1998. [2] m. max, and w. dillon, "natural gas hydrate: a frozen asset?", chemistry and industry., pp. 16-18, january 2000. [3] g. j. hutchings, j. s. j. hargreaves, r.w. joyner and c. j. kiely, c. j., "towards understanding of methane coupling" chemtech, vol. 24, pp. 25-29, 1994. [4] a. g. anshits, e.v. kondratenko, e. n. voskresenskaya, l. i. kurteeva, and n. i., pavlenko, "the influence of o2 on oxidative coupling of methane over oxide catalysts using n2o as oxidant", catalysis today, vol. 46(2-3), pp. 211-216, 1998. [5] t. brousas, p. h. chiang, d. eng and m. stoukides, "technical and economic evaluation of a methane solid oxide fuel cell", ionics, vol. 1, pp. 328-337, 1995. [6] m. baerns, o. buyevskaya and l. mleczko, "direct conversion of methane to c2 hydrocarbons-is there a prospect for the future?", proceedings from the european applied research conference on natural gas-eurogas 94-sintef, trondheim, pp. 93-113, 1995. [7] j. h. lunsford, "the catalytic oxidative coupling of methane", angewandte chemie, vol. 34, pp. 970-980, 1995. [8] s. ahmed and j. b. moffat, "the oxidative coupling of methane on mn/sio2 and the effect of solidand gasphase doping", journal of catalysis, vol. 171, pp. 439448, 1999. [9] j. zaman, "oxidative processes in natural gas conversion", fuel processing technology, vol. 58, pp. 61-81, 1999. [10] n. w. cant, e. m. kennedy and p. f. nelson, "magnitude and origin of the deuterium kinetic isotope effect during methane coupling and related reactions over li/mgo catalysts", journal of physical chemistry, vol. 97, pp. 1445-1450, 1993. [11] z. stansch, l. mleczko and m. baerns, "comprehensive kinetics of oxidative coupling of methane over the la2o3/cao catalyst", industrial engineering and chemistry research, vol. 36, pp. 2568-2579, 1997. [12] j. s. j. hargreaves, j. g. hutchings and r. w., joyner, “hydrogen production in methane coupling over magnesium oxide”, natural gas conversion, elsevier, pp. 155-159, 1991. biographies muhammad fadzli bin mamat received his diploma in chemical engineering from universiti teknologi malaysia in 1993. he worked as a technician at mobil malaysia before furthering his study in chemical engineering at the school of chemical engineering, universiti sains malaysia. he carried out his final year project on the development of catalysts for the oxidative coupling of methane(ocm) under the supervision of dr. noor asmawati and graduated with honors recently. dr. noor asmawati binti mohd. zabidi received her b.s. in chemistry from nebraska wesleyan university, lincoln, usa in 1986. she carried out research in photocatalysis under the supervision of prof. timothy f. thomas at the university of missouri-kansas city, usa where she received her ph.d. in 1995. she has been a lecturer at the school of chemical engineering, universiti sains malaysia, perak branch campus since 1996. megat harun al rashid bin megat ahmad received his b.app.sc. in analytical chemistry from the school of chemical sciences, universiti sains malaysia in 1997. he conducted his msc. research project on the development of catalyst for the oxidative coupling of methane under the supervision of dr. noor asmawati and prof. subhash bhatia. previously he has undertaken research on the dpasv and dpp under the supervision of dr. sulaiman ab. ghani (usm), eia on tasik bera, pahang, malaysia (universiti malaya-wetlands international) and the determination of marker for p53 mutation for colon cancer research at the institute of medical research, malaysia. prof. subhash bhatia joined school of chemical engineering, universiti sains malaysia, perak branch campus, in 1995. he was a full professor at the department of chemical engineering, indian institute of technology, kanpur (india). prof. bhatia was a visiting faculty at the university of queensland, australia from 1988-89 and 1994-95. his research interests are zeolite catalysis, chemical reaction engineering and environmental catalysis. he has written a book on zeolite catalysis that was published by crc press, usa and has published more than 60 papers in national and international journals. iium engineering journal iium engineering journal, vol. 23, no. 2, 2022 zayan et al. https://doi.org/10.31436/iiumej.v23i2.2148 earlier denaturation of dna by using novel ternary hybrid nanoparticles jalal mohammed zayan1, akbar john2*, abdul khaliq rasheed3, batoul alallam4, mohammed khalid5, ahmad faris ismail1, bryan raveen nelson6 and hamzah mohd salleh7 1 department of mechanical engineering, international islamic university malaysia, kuala lumpur, malaysia. 2 institute of oceanography and maritime studies (inocem), kulliyyah of science, international islamic university malaysia, kuantan, malaysia. 3 department of new energy science and engineering, school of energy and chemical engineering, xiamen university malaysia. jalan sunsuria, bandar sunsuria, 43900 sepang, malaysia. 4 integrated medical center, advanced medical and dental institute,13200, malaysia. 5 graphene and advanced 2d materials research group, level 4, east wing nub, school of science and technology, sunway university, sunway city, petaling jaya, 47500, malaysia. 6 institute of topical biodiversity and sustainable development, universiti malaysia terengganu, 21030, kuala nerus, terengganu, malaysia. 7 international institute for halal research and training (inhart), international islamic university malaysia, kuala lumpur, malaysia * corresponding author: akbarhohn50@gmail.com (received: 10th july 2021; accepted: 1st november 2021; published on-line: 4th july 2022) abstract: two novel ternary hybrid nanoparticles (thnp) consisting of graphene oxide (go) and reduced graphene oxides (rgo) were added to samples of dna. the effect of the addition of nanoparticles on the thermal denaturation of dna samples was studied by measuring the absorbance using a temperature-controlled perkin elmer uv spectrophotometer. adding go-tio2-ag and rgo-tio2-ag nanoparticles lowered the denaturation temperature of template dna significantly. the nanoparticles affect the denaturation rate. the optimal go-tio2-ag and rgo-tio2-ag concentrations were found to be 5 × 10-2, which resulted in 86and 180-folds augmentation of dna denaturation (6.5 µg/ml), respectively, while it resulted in 2and 7-folds augmentation of dna denaturation (11.5 µg/ml), respectively, at temperature as low as 80 °c. the results indicated that rgo-tio2-ag nanoparticles exhibited significantly higher dna denaturation enhancement than rgo-tio2-ag nanoparticles, owing to their enhanced thermal conductivity effect. therefore, these nanoparticles could help to get improved pcr yield, hence enable amplification to be performed for longer cycles by lowering the denaturation temperatures. abstrak: dua ternar baru nanopartikel hibrid (thnp) mengandungi oksida grapen (go) dan oksida grapen yang dikurangkan (rgo) dan dimasukkan ke dalam sampel dna. kesan penambahan nanopartikel pada denaturasi termal pada sampel dna telah dikaji dengan mengukur penyerapan menggunakan kawalan-suhu perkin elmer uv spektrofotometer. penambahan go-tio2-ag dan rgo-tio2-ag nanopartikel telah mengurangkan suhu denaturasi pada templat dna dengan nyata. nanopartikel memberi kesan pada kadar denaturasi. kepekatan optimal go-tio2-ag dan rgo-tio2-ag didapati sebanyak 5 × 10-2, menyebabkan penambahan sebanyak 86dan 180-lipat pada dna denaturasi (6.5 µg/ml), masing-masing, sementara ia menyebabkan sebanyak 2dan 7237 iium engineering journal, vol. 23, no. 2, 2022 zayan et al. https://doi.org/10.31436/iiumej.v23i2.2148 lipat penambahan pada dna denaturasi (11.5 µg/ml), masing-masing, pada suhu serendah 80 °c. dapatan menunjukkan nanopartikel rgo-tio2-ag mempunyai kenaikan penambahan dna denaturasi nyata berbanding nanopartikel rgo-tio2-ag, disebabkan kesan kekonduksian penambahan suhu. oleh itu, nanopartikel ini dapat membantu bagi penambah baikan pengeluaran pcr, membolehkan penguatan dapat dilakukan dalam kitaran lebih lama dengan merendahkan suhu denaturasi. keywords: dna denaturation; polymerase chain reaction (pcr); nano-pcr; hybrid nanoparticles 1. introduction pcr is a widely used tool in molecular biotechnology to generate billions of copies of target dna from a single templet dna strand. this mechanism is the basis for detecting genetic mutation and disease diagnosis in various medical and omics applications. the pcr process involves three major stages: denaturation, annealing, and extension. these steps are performed by rapid heating and cooling of the samples to a specific temperature at the defined time. the denaturation is the first step of pcr which involves the unwinding of double-stranded dna into two single-stranded dna by applying heat [1,2]. from a thermodynamic perspective, the intricate arrangement and bonding of two adjacent base pairs in the dna (a, t, g, and c) is the most critical aspect for the stability of the dna double helix. therefore, the energy required to denature the dna should be equal to or greater than those bonding energies holding the base pairs. in genetics, pyrimidine/purine (yr) and a: t rich regions are less exposed to the stacking energies due to double hydrogen bonding than the g: c rich region with triple hydrogen bonds. therefore, the tatata sequence will melt readily once the reaction is heated to the denaturation temperature. denaturation or melting is modifying the molecular structure of the dna by breaking the weakening linkages of the dna. the application of heat to the dna sample increases the system's kinetic energy and entropy, leading to transitional and rotational movements between the dna helix causing a collision of the atoms and molecules with one another in the dna. these collisions reduce the strength of the hydrogen bonds, which eventually break, allowing a double-stranded dna helix to unwind into two single strands [3]. the initial denaturation step usually occurs at 94 °c to 98 °c for each amplification cycle depending on the optimal temperature for taq dna polymerase activity and the g-c content of the template dna used in the reaction. the denaturation temperature in a pcr assay is usually set at 95 °c, regardless of the characteristics of the dna template. therefore, the denaturation temperature may only vary the duration of the denaturation step instead of the temperature. hence, taq dna polymerase gradually inactivates under these conditions, and its half-life will be reduced from 130 min at 92.5 °c to 40 min 95 °c [4]. as the amplified product serves as a template in subsequent cycles, the taq dna polymerase activity might be limited later. moreover, some templates of double-stranded dna wind during a typical denaturation stage, while others will not unwind easily (e.g., dna templates of mammalian promoter gc-rich sequences are complicated to denature initially). increasing the temperature of the denaturation step by more than 95 °c can assist in enhancing denaturation, which may lead to better yield. however, biomolecules in pcr reactions are stressed when the denaturation temperature is excessively high. polymerases’ half-times will decrease by a factor of 3–9 between 95 °c and 100 °c, depending on enzyme type [5]. hence, dna polymerase activity could be improved by the judicious use of lower denaturation temperatures. 238 iium engineering journal, vol. 23, no. 2, 2022 zayan et al. https://doi.org/10.31436/iiumej.v23i2.2148 nanomaterial-assisted pcr technology has emerged to solve this problem by incorporating nanomaterials with excellent thermal conductivity into a pcr reaction [6]. this leads to enhanced dna denaturation and ultimately improves the pcr yield, as many researchers have studied in the past two decades [7]. in addition, some studies have proven the theory that by using nanoparticles as an additive, the dna denaturation process starts eventually at temperatures due to the excellent heat transfer property of the nanoparticles used in the pcr reaction [8]. for instance, graphene nanoflakes helped better heat dissipation, leading to enhanced dna denaturation during the first pcr step [9]. moreover, hexagonal boron nitride nanoparticles enhanced acanthamoeba dna yield at a lower denaturation temperature of 91.5 °c [10]. two novel ternary hybrid nanoparticles (thnp) consisting of graphene oxide (go) and reduced graphene oxides (rgo) were synthesized and characterized in a recent study [11]. they were coated with two other nanoparticles, silver (ag) and titanium dioxide (tio2). the potential use of go-tio2-ag and rgo-tio2-ag thnps as pcr enhancer additives is primarily discussed in this study. the primary target is the first step in the pcr reaction (dna denaturation step). the use of go-tio2-ag and rgo-tio2-ag nanoparticles is expected to lower the denaturation temperature template dna; this could help to get improved pcr yield of product, hence enables amplification to be performed for longer cycles. thnp of five different concentrations to two different concentrations of dna were used. the samples are investigated in a temperature-controlled spectrophotometer to check the absorbance of dna with thnp at different concentrations. 2. materials and methodology 2.1 synthesis of thnp the hydrothermal method was used to synthesize thnps as described in our previous study [11]. graphene oxide (go) was dispersed in deionized water at 1 mg/ml concentration using an ultrasonic stirring treatment for about two hours. a 10 ml by volume of titanium isopropoxide was mixed with 10 ml of isopropyl alcohol, and then the solution was added dropwise to 50 ml of go suspension. next, 10 ml of 0.2 m agno3 was added dropwise to the solution. the solution was stirred for two hours to ensure complete mixing and homogeneity. the ph of the solution was adjusted to 1.1, and then it was heated at 160 °c for 24 hours using a stainless steel autoclave lined with teflon. the product was washed with ethanol and then with water to remove all the remnants and unreacted ions and finally filtered. the resultant residue (go-tio2-ag nanocomposites) was dried at 80 °c. rgotio2-ag thnps was synthesized with the same procedure; however, ammonia and hydrazine were added to go suspension to remove oxygen molecules from go sheets and their functional groups. the characterization of thnp is described in our previous study [11]. 2.2 preparation of thnp-based nanofluids go-tio2-ag thnp were weighted using sartorius entris® balance and then dispersed in molecular biology-grade sterile/di water to make the final stock solution concentration of 5 x 10-2 wt % (sample a). next, the thnps were dispersed in ddh2o and then sonicated using ultrasound probe sonication for 2 min, followed by water bath sonication for about 4 hours to obtain a homogenous solution of nanofluids without sedimentation. the stock solution was then serially diluted for about four more concentrations, named concentration b(5x10-3)wt%, c(5x 0-4)wt%, d(5x10-5)wt%, and e(5x10-6)wt%. rgo-tio2-ag nanofluid was prepared in the same way. 239 iium engineering journal, vol. 23, no. 2, 2022 zayan et al. https://doi.org/10.31436/iiumej.v23i2.2148 2.3 dna isolation a salmon fish tissue sample was used as a template in this study. genomic dna was extracted and purified using dneasy blood & tissue kit (qiagen, hilden, germany) following the manufacturer's protocol. template concentration was ascertained using thermo qubit 3.0 fluorometer, and it was found to be 11.5 ng/μl and 6.5 ng/μl (a and b resp.) and stored at 4 °c for further use. 2.4 evaluation of dna denaturation by uv spectroscopy perkin elmer uv spectrophotometer was used to measure the absorbance of samples at 200-400 nm. the thermal denaturation experiments were carried out using two dna concentrations, named a (6.5 ng/μl) and b (11.5 ng/μl) in the presence and absence of the synthesized graphene-based ternary hybrid nanofluids (go-tio2-ag and rgo-tio2-ag) to determine the effect of nanoparticles on the early dna denaturation. five levels of concentrations, a(5x10-2)wt%, b(5x10-3)wt%, c(5x10-4)wt%, d(5x10-5)wt% and e(5x106)wt% were tested. the measurements were performed by mixing dna samples with the nanofluid at the ratio of 5:2 and then filled in a clean 5 mm spectrometer quartz cuvette cell. the absorbance was measured at various temperature ranges starting at 80 °c, with 2 °c increments, till 96 °c using the peltier system. 3. results and discussion 3.1 effects of thnps on dna denaturation the novel go-tio2-ag and rgo-tio2-ag ternary hybrid nanoparticles exhibited a superior enhancement of pcr and led to a 28.5% reduction of total cycles and enhanced the pcr yield 16.89-folds for go-tio2-ag and 15.75-folds for rgo-tio2-ag, compared to control in our earlier study [refer pcr manuscript]. in this study, the same ternary hybrid nanoparticles were added to two dna samples (samples a and b), and the absorbance is measured using a spectrophotometer. the absorbance (at 260 nm) of two dna samples (a:6.5 and b:11.5 ng/µl) with and without the synthesized graphene-based ternary hybrid nanofluids) at five concentration levels at various temperatures were measured as shown in fig 1. the absorbance of the dna in the presence of thnp can give us a deeper insight into the behavior of dna during the denaturation step. go-tio2-ag and rgo-tio2-ag thnp exhibited higher absorbance values than the control (without nanoparticles) over the measured temperature range (from 80 oc to 96 oc) in two different dna samples a and b with concentration, indicating early denaturation of dna even at temperatures as low as 80 °c. interestingly, the concentration of nanoparticles has an impact on the extent of dna denaturation. a more significant denaturation was exerted with the higher concentration of these nanoparticles than the lower one at all studied temperatures (fig. 1). when comparing the dna samples containing the nanoparticles, rgo-tio2-ag nanoparticles were significantly more effective than go-tio2-ag thnp at higher concentrations (5x10 -2) wt%. the absorbance of the dna samples containing 5x10-2 wt% go-tio2-ag nanoparticles was ∼86and ∼2-folds higher than the control dna samples at 80°c, for dna samples a and b, respectively, while the absorption in the presence of rgo-tio2-ag nanoparticles was ∼180and ∼7-folds higher than the control in dna samples a and b, respectively. moreover, dna was denatured earlier in the presence of rgo-tio2-ag nanoparticles at a concentration higher than c (5x10-4)wt%. at the same time, it was still earlier denatured in the presence of go-tio2-ag even at a concentration as low as e (5x10 -6) wt%. these results 240 iium engineering journal, vol. 23, no. 2, 2022 zayan et al. https://doi.org/10.31436/iiumej.v23i2.2148 indicate the importance of an optimal nanoparticle concentration for the maximal heat transfer effect. the earlier denaturation of the dna in the presence of the thnps could be due to the enhanced thermal conductivity of nanoparticles. the denaturation of double-stranded dna typically happens if the temperature exceeds 90 °c. as the kinetic energy and entropy of the reaction system increase, the transitional and rotational motions, which causes a collision of the atoms and molecules of the reagents, increase. these collisions reduce the strength of the hydrogen bonds, which eventually breaks, allowing a double-stranded dna helix to unwind into two single strands [12]. thus, the presence of nanoparticles enhances the dna’s denaturation due to the more excellent heat dissipation in the reaction mixture, which causes a collision of the atoms and molecules between nanoparticles, and pcr reagents [13]. thus, these results are proof that dna could be denatured earlier in the presence of thnps. furthermore, the percentage of enhancement that we achieved is significantly higher than previously published reports. fig. 1: near uv absorption spectra (260 nm) of dna in presence and absence of increasing concentration of go-tio2-ag and rgo-tio2-ag (5x10 -2 5x10-6 wt%) to determine the effect of nanoparticles on dna denaturation. to the left, a (6.5 ng/μl), and to the right, b (11.5 ng/μl) dna samples. the absorption spectra for go-tio2-ag and rgo-tio2-ag over 200 to 400 nm are presented side by side based on the concentration in figs. 2 and 3. it can be seen from fig 2, the strong absorption below 210 nm in the dna spectrum, at all temperatures, resulted from absorptions of phosphate groups and sugar parts. the second maximum dna absorption position was located at 260 nm due to dna base absorption. dna spectra had confirmed that the dna was denatured at temperature 92-94 °c as all spectra absorption at temperature ≤92 °c were significantly lower than that observed for spectra at temperature ≥ 94 °c. once the absorbance of uv light in the spectrophotometer has increased until it has completely melted or un-wound to two single strands, the denaturation can be determined. the absorbance will remain constant even if the temperature or heating is further increased. the hypochromic effect refers to the fact that single-strand dna absorbs 50 percent more uv light than double-strand dna before reaching the melting point. renaturation is the reversible process of denaturation, which occurs when the temperature is lowered below the melting point. the renaturation time can be used to calculate the repetitive fractions as well as the base composition [14]. the melting point, or tm, of different dna will vary depending on various factors such as the length of the dna strand, base composition, topological condition of dna, buffer composition, etc. compared to a longer strand of dna, a shorter dna strand will melt faster and more efficiently [15]. 80 82 84 86 88 90 92 94 96 0.0 0.2 0.4 0.6 0.8 1.0 1.2 a b s temperature ( 0 c) 2a 2b 2c 2d 2e 3a 3b 3c 3d 3e dna 80 82 84 86 88 90 92 94 96 0.0 0.2 0.4 0.6 0.8 1.0 1.2 a b s temperature ( 0 c) 2b 2c 2d 2e 3a 3b 3c 3d 3e dna 241 iium engineering journal, vol. 23, no. 2, 2022 zayan et al. https://doi.org/10.31436/iiumej.v23i2.2148 because many variables influence the melting point of dna, it is difficult to predict the exact melting temperature of a given dna sequence. fig. 2: (a), (b), (c), (d), and (e) are near uv absorption spectra of 6.5 ng/μl dna in presence and absence of go-tio2-ag samples of concentrations a(5x10 -2) wt%, b(5x10-3) wt%, c(5x10-4) wt%, d(5x10-5) wt% and e(5x10-6) wt%, respectively; (f), (g), (h), (i) and (j) are near uv absorption spectra of 6.5 ng/μl dna in presence and absence of rgo-tio2-ag samples of concentrations a(5x10 -2) wt%, b(5x10-3) wt%, c(5x10-4) wt%, d(5x10-5) wt% and e(5x10-6) wt%, respectively. (a) (a) (f) (b) (g) (c) (h) (d) (i) (e) (j) 242 iium engineering journal, vol. 23, no. 2, 2022 zayan et al. https://doi.org/10.31436/iiumej.v23i2.2148 fig. 3: (a), (b), (c), (d), and (e) are near uv absorption spectra of 11.5 ng/μl dna in presence and absence of go-tio2-ag samples of concentrations a(5x10 -2) wt%, b(5x10-3) wt%, c(5x10-4) wt%, d(5x10-5) wt% and e(5x10-6) wt%, respectively; (f), (g), (h), (i), and (j) are near uv absorption spectra of 11.5 ng/μl dna in presence and absence of rgo-tio2-ag samples of concentrations a(5x10 -2) wt%, b(5x10-3) wt%, c(5x10-4) wt%, d(5x10-5) wt% and e(5x10-6) wt%, respectively. 243 iium engineering journal, vol. 23, no. 2, 2022 zayan et al. https://doi.org/10.31436/iiumej.v23i2.2148 the shift in the dna absorption peak upon addition of go-tio2-ag reveals the interaction of the dna–thnps. the significant absorbance increase observed upon the addition of various concentrations of go-tio2-ag at temperature ≤ 92 °c indicates that the go-tio2-ag thnps augmented the denaturation of the double-stranded dna. however, and at a temperature ≥ 94° c, a higher dna denaturation was exhibited with the presence of at least 5x10-2 wt% of go-tio2-ag thnps. similar absorbance patterns can be seen for rgo-tio2-ag thnps spectra at all study concentrations except at a concentration of 5x10 2 wt%; their absorbance was significantly higher than that of go counterparts. additionally, rgo-tio2-ag nanoparticles did not enhance the denaturation at concentration 5x10-3 wt% to 5x10-6 wt%, indicating the importance of an optimal nanoparticle concentration for the maximal heat transfer effect. a similar absorption pattern was observed for dna samples a in the presence and absence of thnps; however, dna absorption peak shift upon thnps addition was more prominent. the dna denaturation was augmented at all concentrations of thnps except at 5x10-6 wt% and 5x10-5 wt% for go-tio2-ag and go-tio2-ag, respectively (fig. 3). moreover, there was a positive impact of go-tio2-ag thnps concentration on the denaturation. for instance, the absorption of the dna samples containing 5x10-2 wt% and 5x10-5 wt% go-tio2-ag nanoparticles was 4.0-, 1.99-folds, respectively, higher than the control a dna samples, and 54.64-, 20.57folds, respectively, higher than the control b dna samples, at 86 °c. thus, decreasing the concentration of go-tio2-ag thnps in dna samples, from 5x10 -2 wt% to 5x10-5 wt%, decreased the absorption significantly by 50% and 38% for dna samples a and b, respectively. on the other hand, reducing the concentration of rgo-tio2-ag thnps in the dna sample, from 5x10-2 wt% to 5x10-5 wt%, decreased the absorption by 3.4% for dna samples a and b, respectively. interestingly, at the lowest concentration of the thnp, their absorbance is negative, which indicates that the uv light passing through the dna samples in the presence of thnp gives out a greater intensity of light. therefore, it may have important significance. 4. conclusion the experiment has demonstrated the impact of adding the two novel ternary hybrid nanoparticles on dna denaturation. the rationale behind the use of graphene based thnps is its unique heat transfer properties. dna denaturation data showed that the enhancement of the dna denaturation was nanoparticle concentration-dependent. the higher concentrations exhibit the maximum enhancement of the dna denaturation owing to the enhanced thermal conductivity effect. rgo based thnp showed better results at higher concentrations compared to go-based thnp. we propose thnp can be effectively used to achieve early denaturation of dna samples. acknowledgements this research work was financially supported by a grant from the fundamental research grant scheme (frgs/1/2018/wab09/uiam/02/5), ministry of higher education, malaysia and a grant from the knowledge transfer and assimilation grant scheme 2021 (2-2/25/15/11-21), universiti malaysia terengganu (umt). we would also like to thank the reviewers for their constructive comments to improve this manuscript. 244 iium engineering journal, vol. 23, no. 2, 2022 zayan et al. https://doi.org/10.31436/iiumej.v23i2.2148 references [1] fu-ming sang, xin li, jia liu. (2017) development of nano-polymerase chain reaction and its application. chinese journal of analytical chemistry, 45(11): 1745-1753. [2] lorenz tc. (2012) polymerase chain reaction: basic protocol plus troubleshooting and optimization strategies. jove (journal of visualized experiments), 63: e3998. [3] ussery dw. (2013) dna denaturation, brenner’s encycl. genet. second ed., pp. 353-355. [4] shen c, yang w, ji q, maki h, dong a, zhang z. (2009) nanopcr observation: different levels of dna replication fidelity in nanoparticle-enhanced polymerase chain reactions. nanotechnology, 20(45): 455103. [5] cazzaniga g, songia s, biondi a. (2021) pcr technology to identify minimal residual disease. in leukemia stem cells (pp. 77-94). humana, new york, ny. [6] gabriel s, rasheed ak, siddiqui r, appaturi jn, fen lb, khan na. (2018) development of nanoparticle-assisted pcr assay in the rapid detection of brain-eating amoebae. parasitology research, 117(6): 1801-1811. [7] lin yc, wu hl. (2007) nano-pcr: breaking the bottom limit of the pcr denaturation temperature using nanogold. in transducers 2007. ieee international solid-state sensors, actuators and microsystems conference, pp. 391-394. [8] khaliq a, sonawane pj, sasi bk, sahu bs, pradeep t, das sk, mahapatra nr. (2010) enhancement in the efficiency of polymerase chain reaction by tio2 nanoparticles: crucial role of enhanced thermal conductivity. nanotechnology, 21(25): 255704. [9] khaliq a, kafafy r, salleh hm, faris wf. (2012) enhancing the efficiency of polymerase chain reaction using graphene nanoflakes. nanotechnology, 23(45) 455106. [10] rasheed ak, siddiqui r, ahmed smk, gabriel s, jalal mz, john a, khan na. (2020) hbn nanoparticle-assisted rapid thermal cycling for the detection of acanthamoeba. pathogens, 9(10): 824. [11] zayan m, rasheed ak, john a, muniandi s, faris a. (2021) synthesis and characterization of novel ternary hybrid nanoparticles as thermal additives in h2o. chemrxiv. doi:10.26434/chemrxiv.13710130.v1 [12] abbotts r, wilson dm. (2017) 3rd. coordination of dna single strand break repair. free radic biol med., 107: 228-244. doi: 10.1016/j.freeradbiomed.2016.11.039. [13] li a, zhou b, alves cs, xu b, guo r, shi x, cao x. (2016) mechanistic studies of enhanced pcr using pegylated pei-entrapped gold nanoparticles. acs applied materials & interfaces, 8(39): 25808-25817. [14] lee jy, lim hw, yoo si, zhang bt, park th. (2006) simulation and real-time monitoring of polymerase chain reaction for its higher efficiency. biochemical engineering journal, 29(12): 109-118. [15] bai y, cui y, paoli gc, shi c, wang d, shi x. (2015) nanoparticles affect pcr primarily via surface interactions with pcr components: using amino-modified silica-coated magnetic nanoparticles as a main model. acs applied materials & interfaces, 7(24): 13142-13153. 245 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 80 evaluation of the w-metric routing using rpl protocol in llns rosminazuin ab rahim*, abdallah m. awwad, aisha hasan abdalla and aliza aini md ralib department of electrical and computer engineering, kulliyyah of engineering, international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia. * corresponding author: rosmi@iium.edu.my (received: 31st march 2017; accepted: 17th oct 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.840 abstract: the current de-facto routing protocol over low power and lossy networks (lln) developed by the ietf working group (6lowpan), is named as routing protocol for low power and lossy networks (rpl). rpl in the network layer faces throughput challenges due to the potential large networks, number of nodes, and that multiple coexisting applications will be running in the same physical layer. in this study, a node metric for rpl protocol based on the node’s queue backlogs is introduced, which leads to a better throughput performance while maintaining the delay and the ability to use with different network applications. this metric depends on the length of packet queue of the nodes with the consideration of other link and node metrics, like etx or energy usage, leading to better load balancing in the network. to implement and evaluate the proposed metric compared to other rpl metrics, contikios and cooja simulator are used. extensive simulations have been carried out in a systematic way resulting in a detailed analysis of the introduced metric namely w-metric, expected transmission count (etx) and objective function zero (of0) that uses hop-count as a routing metric. the analysis and comparison are based on five performance parameters, which are throughput, packet delivery ratio (pdr), latency, average queue length, and power consumption. simulation results show that the introduced w-metric has a good performance compared to other rpl metrics with regards to performance parameters mentioned above. at the same time, the results show that its latency performance is comparable with other rpl routing metrics. in a sample simulation of 500 seconds with 25 nodes and with nodes sending packets periodically to the network root at a rate of 1 packet per 4 seconds, wmetric showed a very efficient throughput of 5.16 kbps, an increase of 8.2% compared to etx. results showed that it has a packet delivery ratio of 93.3%, which is higher compared to 83.3% for etx and 74.2% for of0. average queue length of 0.48 packet shows improvement of 15.8% better than etx. in addition, it exhibits an energy consumption of 5.16 mw which is 2.1% less than etx. overall, w-metric appears to be a promising alternative to etx and of0 as it selects routes that are more efficient by working on load balancing of the network and by considering the link characteristics. abstrak: protokol penghalaan de-facto semasa ke atas rangkaian kekuatan rendah dan lossy yang dibangunkan oleh kumpulan kerja ietf (6lowpan), dinamakan protokol penghalaan untuk kekuatan rendah dan rugi (rpl). rpl dalam lapisan rangkaian menghadapi cabaran throughput berikutan jangkaan rangkaian besar, bilangan nod dan aplikasi berganda bersama akan diproses dalam lapisan fizikal yang sama. dalam kajian ini, satu metrik nod untuk protokol rpl berdasarkan pada backend queue node diperkenalkan, yang membawa kepada prestasi yang lebih baik sambil mengekalkan kelewatan dan keupayaan untuk digunakan dengan aplikasi rangkaian yang berbeza. iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 81 metrik ini bergantung pada panjang packet queue dari node dengan pertimbangan metrik lain dan nodus lain, seperti etx atau penggunaan tenaga, yang mengarah kepada keseimbangan beban yang lebih baik dalam rangkaian. untuk melaksanakan dan menilai metrik yang dicadangkan berbanding metrik rpl lain, contikios dan cooja simulator telah digunakan. simulasi meluas telah dijalankan dengan cara yang sistematik yang menghasilkan analisis terperinci mengenai metrik yang diperkenalkan iaitu w-metrik, kiraan penghantaran dijangkakan (etx) dan fungsi objektif sifar (of0) yang menggunakan kiraan hop sebagai metrik penghalaan. analisis dan perbandingan adalah berdasarkan lima parameter prestasi, iaitu throughput, nisbah penghantaran paket (pdr), latency, panjang panjang antrian, dan penggunaan kuasa. hasil simulasi menunjukkan bahawa w-metrik yang diperkenalkan mempunyai prestasi yang lebih baik berbanding dengan metrik rpl lain berkaitan dengan parameter prestasi yang dinyatakan di atas. pada masa yang sama, hasil menunjukkan bahawa prestasi latency w-metrik adalah setanding dengan metrik penghalaan rpl yang lain. dalam simulasi sampel 500 saat dengan 25 nod dan dengan nod yang menghantar paket secara berkala ke akar rangkaian pada kadar 1 paket setiap 4 saat, w-metrik menunjukkan keluaran yang sangat efisien iaitu 5.16 kbps, peningkatan sebanyak 8.2% berbanding etx. keputusan menunjukkan bahawa ia mempunyai nisbah penghantaran paket 93.3%, yang lebih tinggi berbanding 83.3% untuk etx dan 74.2% untuk of0. purata panjang giliran 0.48 packet menunjukkan peningkatan 15.8% lebih baik daripada etx. di samping itu, ia mempamerkan penggunaan tenaga sebanyak 5.16 mw iaitu 2.1% kurang daripada etx. secara keseluruhan, w-metrik nampaknya menjadi alternatif yang berpotensi menggantikan etx dan of0 kerana ia memilih laluan yang lebih cekap dengan bekerja pada keseimbangan beban rangkaian dan dengan mempertimbangkan ciri-ciri pautan. keywords: iot; rpl; llns; queue backlog; objective function 1. introduction the internet is increasingly becoming an inevitable part of our lives and recently internet of things (iot) appeared as an important future scenario of the internet application. the number of computing and interconnected devices has grown exponentially within the last 2 decades, and it is expected to grow further. by the end of 2020, it is estimated that the world will have an approximate number of 50 billion connected devices [1-3]. the internet engineering task force (ietf) used the term, low power and lossy networks (llns) to refer to networks of different types of smart devices and sensors. these networks challenges include highly varying link quality, limited device memory, power, and recurrent link outage. in many environments, llns are emerging as a new deployment communication, like smart buildings, industrial automation, and for the majority of the envisioned iot [2]. conventional routing protocols fail to meet the llns requirements due to the mentioned limitations. the ietf working group has identified routing over low power and lossy networks (roll) as a solution for routing in this type of networks under particular deployment scripts. as a result, ipv6 routing protocol for low-power and lossy networks (rpl) is standardized in rfc 6550 to ensure ipv6 packets carried over ieee 802.4 is achievable, as well as to empower the usage of iot over wsn [4]. however, rpl in the network layer meets throughput challenges due to the potential huge network size, various coinciding applications in one physical network and the large amount of information and data created and imparted from the devices. rpl existing implementations mostly use either expected transmission count (etx) or hop-count routing metrics. etx measures the reliability of the link between two nodes. the etx link value expects the number of times to transmit a packet until it is successfully iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 82 delivered over that link. the weaker the link connecting two nodes, the higher the etx value and the greater the number of required retransmissions [5]. on the other hand, the objective function that uses hop-count metric calculates the path cost based on the number of hops between the node and the destination. the hop-count metric does not take into consideration the llns characteristics; therefore, it may choose a route that leads to bad throughput performance. in the same way, the etx metric is only concerned with the link loss [6]. researchers introduced a variety of extensions for rpl to tailor to the specific requirements of network applications including three multipath routing mechanisms based on rpl such as fast local repair (flr), energy load balancing (elb), and elb-flr, which is a combination of the first two as reported in [1]. results implied that this mechanism leads to better energy consumption and network lifetime. however, it didn’t lead to the improvement of the throughput performance. another research work used a backpressure routing protocol (backip) as a replacement for rpl routing protocol for data collection applications [7]. this protocol resulted in a better throughput performance, however it led to an increase in the potential end-to-end delay, limited applicability only to many-to-one communication, and a more complicated design compared to rpl. most of the studies related to rpl did not lead to the enhancement of throughput performance in lln networks. another study reported enhanced throughput performance of rpl using a back pressure approach, but simultaneously affecting other performance aspects [8]. the study introduced a routing metric for rpl protocol based on the node’s queue backlogs. the purpose of this metric was to enhance throughput performance of rpl protocol while maintaining the delay and preserving system resources such as the energy consumption. this metric depends on the length of the packet queue of the nodes with the consideration of other link and node metrics, like etx or energy usage, leading to better load balancing in the network. in [9], an investigation on the objective functions and related parameters which influence rpl performance is reported. a set of simulation runs using contiki operating system and cooja simulator is carried out. the rpl performance is evaluated in terms of packet delivery ratio (pdr), latency, energy consumption, and others that showed etx is a better routing metric compared to hop-counts. in this paper, investigation on the introduced routing metric, w-metric, as reported in [8] is compared to other rpl routing metrics like etx and of0: hop-count. this paper presents results of a simulation conducted using contikios and cooja simulator in terms of throughput, packet delivery ratio (pdr), latency, and power consumption. 2. background 2.1 determining routing protocol for low power and lossy network for ipv6 rpl builds and keeps up the network as a directed acyclic graph (dag), which can be isolated into many destination-oriented dags (dodags) [5]. rpl uses dodag information object (dio) control messages for the configuration process, support nodes to join the dodag, and then for parents’ selection. exchanging dodag information between nodes begins as soon as the rpl network starts through dio control messages. dag metric container defined in [5] used to carry needed routing constraints and metrics. iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 83 these metrics and constraints are used to determine the best path using the objective function (of). once the neighboring node receives a dio message, the rank is computed based on its parent’s rank and the cost to reach that parent. for the parent selection process, it is essential to choose an arrangement of the routing metrics that will influence routing choice for different dodags that is called an objective function (of). an of characterizes an arrangement of functions to compute rank, which is the relative separation of one node towards the root, and in addition to contrast neighbors with respect to the rank [6]. after receiving the dio message, the node joins the dag before sending the needed information such as dag-id, rank, routing metric, and of to its neighbors. hence, the rest of the nodes will join the dag after computing their ranks. this operation continues until the last node in the topology has computed its rank and joins the dag. path cost is a scalar value calculated as a function of the node or link characteristics through the end-to-end route from node toward the root [5]. when etx is used as a routing metric in rpl, then the path cost for node n towards dodag root(𝑃𝑎𝑡ℎ_𝐶𝑜𝑠𝑡(𝑖)) can be calculated as in eq. (1) and eq. (2) 𝑃𝑎𝑡ℎ_𝐶𝑜𝑠𝑡(𝑖) = 𝑅𝑎𝑛𝑘(𝑗) + 𝑅𝑎𝑛𝑘_𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 (1) 𝑅𝑎𝑛𝑘_𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 = etx𝑖→𝑗 ∗ 𝑀𝑖𝑛𝐻𝑜𝑝𝑅𝑎𝑛𝑘𝐼𝑛𝑐𝑟𝑒𝑎𝑠𝑒 (2) with 𝑗 as the preferred parent of 𝑖 and 𝑀𝑖𝑛𝐻𝑜𝑝𝑅𝑎𝑛𝑘𝐼𝑛𝑐𝑟𝑒𝑎𝑠𝑒 as a constant value. on the other hand, when the hop-count metric is used in the objective function, the path cost is equal to the number of hops from the node toward the root [6]. then, the path cost for node n (𝑃𝑎𝑡ℎ_𝐶𝑜𝑠𝑡(𝑖)) can be calculated as in eq. (3) with 𝑖𝑛𝑐𝑟𝑒𝑚𝑒𝑛𝑡 as a constant value. 𝑃𝑎𝑡ℎ_𝐶𝑜𝑠𝑡(𝑖) = 𝑅𝑎𝑛𝑘(𝑗) + 𝑖𝑛𝑐𝑟𝑒𝑚𝑒𝑛𝑡 (3) 2.2 queue backlog w-metric for rpl the motivation for this work is to define a routing metric that allows rpl to increase total network throughput and to achieve a better load balancing between nodes based on queue-backlogs. the queue-backlog 𝑄𝑖→𝑗 is the queue length of the neighboring’s queue in node 𝑖 that holds packets to be forwarded to its neighbor, node 𝑗. the general equation for calculating the weight of each link from a node to other nodes is described in eq. (4) [8]. 𝑊𝑖,𝑗 = 𝑥. 𝑄𝑖→𝑗 + 𝜃𝑖→𝑗 (4) where 𝜃𝑖→𝑗 is the corresponding cost of using the link (𝑖 → 𝑗), and 𝑥 is a constant parameter for penalty minimization by trading system queue occupancy. the queue length, 𝑄𝑖 is computed at each node. w-metric value will be recalculated as a moving average value as in eq. (5) whenever the queue length value or the used metric changes. 𝑊𝑖→𝑗 = 𝑝 ∗ 𝑊𝑖→𝑗 ^ + (1 − 𝑝) ∗ 𝑊𝑖→𝑗 (5) where p is a constant factor larger than zero and less than one and 𝑊𝑖→𝑗 ^ is the new value of 𝑊𝑖→𝑗, then update the metric container with the new value. rpl is set to calculate node rank based on the w-metric. on a path between a node 𝑉 and the root, w-metric is the summation of w-metric on each node along the path as in eq. (6). 𝑊𝑉,𝑇 = ∑ 𝑊𝑖→𝑗𝑓𝑜𝑟 𝑎𝑙𝑙 𝑛𝑜𝑑𝑒𝑠 𝑡ℎ𝑟𝑜𝑢𝑔ℎ (𝑉,𝑇)𝑃𝑎𝑡ℎ (6) iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 84 as a result, to route the packets from a node to the dodag root, a path with minimum wmetric value is selected. the usage of etx with w-metric leads to the calculation of the weight wi,j of the link 𝑖 → 𝑗 by a node 𝑖 towards a neighbor 𝑗 as follows in eq. (7): 𝑊𝑖,𝑗 = 𝑥 𝑄𝑖→𝑗 + 𝐸𝑇𝑋𝑖→𝑗 (7) 6. simulation setup in order to analyze and evaluate the performance of the introduced routing metric in comparison to other rpl routing metrics, a range of configuration settings have been considered. for this simulation, contikios and cooja simulators are used. a network topology consists of 25 tmote-sky nodes, which are the sensors sensing different aspects of the environment. nodes are randomly positioned in an area defined in fig. 1, with each grid square equal to 10 𝑚2. node 1 works as a sink (the root of the dodag) and the other 24 nodes as senders of upstream data packets periodically to the sink node. the total packet size of 120 bytes with transmitted power of zero dbm (or 31-contiki power level parameter) is identified. fig. 1: network topology used in simulation. for measuring the simulation time and the simulation stop time (after a certain needed time), a cooja plug-in feature, known as contiki test editor, is utilized. this feature creates a log file containing the output of all simulations and can be used for data analysis. for the purpose of introducing attenuation (greater “lossiness”) for the wireless medium with respect to the nodes relative distances, the cooja unit disk graph medium (udgm) is used. the udgm uses two range parameters for transmission range as well as for interference range with other radios. in addition, it defines another two parameters, which are successratio tx to model the loss at the sender and receiver-ratio rx to model the loss at the receiver side. the value of transmission ratio tx and reception ratio rx was set to lossfree (equal to 1). on the other hand, the transmission ratio tx was set as loss free to 100% with the reception ratio rx set to 90% for another set of simulations in order to model packet loss at the receiver side in the network. the operation mode of rpl is set to no-downward-traffic as the evaluation process of this study is only interested in using the multipoint-to-point communication. the iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 85 interference range is set to 120 m and the transmission range is set to 100 m. for different iterations of the proposed simulation tests, different values for the send interval are used in order to study the network throughput at different traffic levels and densities. table 1 presents the values of different network parameters used for this network topology and its set of simulations. table 1: simulation parameters parameter value transmitting power 0 dbm tx ratio 100% rx ratio 90%,100% transmission range 100 m interference range 120 m x factor for w-metric 1 p factor for w-metric 0.8 sending interval 4, 6 and 10 sec max_neighbor_queues 3 queuebuf_conf_num 8 client nodes 24 nodes simulation time 500 c 4. simulation results 4.1 network throughput throughput is the total data received at the root except duplicates and control packets to trace the throughput of all traffic flows. figure 2 shows network throughput at the root for w-metric as compared to etx and of0 for a send rate λ equal to 1 packet per 4 seconds. both transmission ratio tx and reception ratio rx are set to 100%. for simulation results presented in fig. 3, tx=100% and rx= 90% with a send rate of 1 packet per 4 seconds is used. figure 4 shows throughput for a simulation runs with tx=rx=100% and send rate of 1 packet per 10 seconds is considered. table 2 shows the average throughput of the network at the sink. from the mentioned figures and table, it is noted that w-metric has a better throughput performance compared to both of etx and of0 for different sending rates. the advantage of w-metrix over of0 is higher than that over etx. at lower sending rates throughput performance of the three metrics are very similar, however, as the sending rate increases, throughput difference also increases. table 2: send rate vs. average throughput per second (measured in kbps) setting w-metric (kbps) etx (kbps) of0 (kbps) send rate: 1 packet per 10 sec 2.147 2.140 2.140 send rate: 1 packet per 6 sec 3.390 3.300 3.310 send rate: 1 packet per 4 sec 5.160 4.770 4.290 send rate: 1 packet per 4 sec (lossy network) 4.900 4.480 3.900 iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 86 fig. 2: throughput of w-metric vs. etx vs. of0 at send rate of 1 packet per 4 sec. fig. 3: throughput of w-metric vs. etx vs. of0 at send rate of 1 packet per 4 sec (lossy). fig. 4: throughput of w-metric vs. etx vs. of0 at send rate of 1 packet per 10 sec. 4.2 packet delivery ratio the second performance evaluation metric is packet delivery ratio (pdr) which refers to the percentage of the number of packets successfully received at the root to the total number of packets sent from all the nodes. from table 3, w-metric has a packet delivery ratio that is slightly better than etx and of0 ratio at low send rate. however, it shows more improvement for higher send rates. on the other hand, etx also shows a better performance compared to of0. this proves the efficiency of w-metric compared to other rpl metrics. iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 87 the better performance of w-metric regarding pdr also refers to better load balancing and better route options. table 3: send rate vs. packet delivery ratio setting w-metric etx of0 send rate: 1 packet per 10 sec 99.97% 99.96% 99.96% send rate: 1 packet per 6 sec 98.80% 96.50% 97.10% send rate: 1 packet per 4 sec 93.30% 88.50% 80.50% send rate: 1 packet per 4 sec (lossy network) 88.60% 83.20% 72.00% 4.3 power consumption power consumption is considered to be one of the essential aspects of llns performance, as these devices need to work for years with limited power. for power consumption analysis, powertrace system is used. powertrace is a mechanism provided by contiki software for calculating the power consumption of low power wireless networks. as shown in table 4, w-metric has an advantage over both of etx and of0 for higher send rate. on the other hand, on lower and medium range rates, of0 shows a slightly better performance compared to w-metric and etx. however, of0 has the worst power consumption at high send rates due to higher number of retransmissions and the highly congested routes. because of the lossy nature of llns, the link quality changes frequently leading to frequent change in etx for the path. w-metric and etx can precisely reflect the link condition as both consider the path etx. on the other hand, of0 in path selection process does not consider the path etx as it only concerns on selecting the shortest path. consequently, the nodes will encounter more packet retransmissions, which results in more energy consumption. table 4: send rate vs. average power consumption (measured in mw) setting w-metric (mw) etx (mw) of0 (mw) send rate: 1 packet per 10 sec 2.164 2.282 2.057 send rate: 1 packet per 6 sec 3.264 3.268 3.139 send rate: 1 packet per 4 sec 5.162 5.276 5.494 send rate: 1 packet per 4 sec (lossy network) 6.009 6.370 6.713 4.4 delay performance the fourth performance metric evaluation is packet latency or end-to-end delay. the latency is defined as the total amount of time a packet needs to be transferred from the source node to the destination. latency is calculated as the average of all the packet latencies in the network from all nodes. figure 5 represents the cumulative distribution function (cdf) of the packets latency for the three metrics. it is noted that w-metric and etx have a similar latency performance and that both have a much better performance compared to of0. this is related to the fact that w-metric and etx considers the details of the link level when compute the best routes, while of0 only concerns about the hop-count separates the node and the root. table 5: send rate vs. average of maximum inter packet time iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 88 setting w-metric etx of0 average latency 2.89 sec 3.37 sec 5.46 sec send rate: 1 packet per 6 sec 3.264 3.268 3.139 fig. 5: cdf of the three routing metrics latencies. 5. conclusion in this paper, w-metric performance is evaluated using cooja simulator with contikios. the two objective functions in contikios, which use etx and of0 (hopcount), have been used for benchmarking. overall, w-metric shows a good performance compared to etx and of0. w-metric works on selecting more efficient routes by balancing the load of the network and taking into consideration the link characteristics, which leads to better throughput, pdr, and network latency. for power consumption, w-metric at high send rates had the best consumption resulting from selecting paths that lead to less radio collisions and re-transmissions through the network. on the other hand, of0 showed the best performance regarding power consumption in low and medium range send rates. for more enhancements on the w-metric, the suggested aspects in the next session can be investigated. there are many other aspects of w-metric design and performance need to be investigated as a future study. firstly, the context of this paper was limited to fixed nodes, but with mobile nodes, issues such as latency, pdr, and energy consumption become harder to optimize, making many aspects of routing in llns more difficult to manage. usual solutions for mobility depend on how frequently the routing information is updated; this is an important factor for llns that are limited in resources. hence, evaluation of w-metric on mobile nodes may offer valuable suggestions for more enhancements on this metric. secondly, memory utilization and routing table sizes are substantial parameters that need to be studied to be used with w-metric for further enhancements. acknowledgement the authors would like to acknowledge the support from the international islamic university malaysia and the ministry of higher education, malaysia, for the financial support in the form of a grant (research initiative grant scheme: rigs 16-083-0247). iium engineering journal, vol. 19, no. 2, 2018 ab rahim et al. 89 references [1] wang qh, kalantar-zadeh k, kis a, coleman jn, strano ms. (2012) electronics and optoelectronics of two-dimensional transition metal dichalcogenides. nature nanotechnology, 7(11):699-712. [2] passler r. (2001) dispersion-related assessments of temperature dependences for the fundamental band gap of hexagonal gan. j. applied physics, 90(8):3956-3964. [3] walukiewicz w, li sx, wu j, yu km, ager jw, haller ee, lu h, schaff wj. (2004) optical properties and electronic structure of inn and in-rich group iii-nitride alloys. j. crystal growth, 269:119-127. [4] cui k, fathololoumi s, kibria mg, botton ga, mi z. (2012) molecular beam epitaxial growth and characterization of catalyst-free inn/inxga1-xn core/shell nanowire heterostructures on si (111) substrates. nanotechnology, 23(8):085205. [5] incropera fp, dewitt dp, bergman tl, lavine as. (2011) introduction to heat transfer, 7th ed. [6] bejan a, kraus a. (2003) heat transfer handbook, usa. [7] the contiki operating system. available: http://www.contiki-os.org/index.html. [8] nori s, deora s, krishnamachari b. (2014) backip : backpressure routing in ipv6-based wireless sensor networks. usc ceng technical report ceng-2014-01. [9] sheng z, yang y, yu y, vasilakos a, mccann j, leung k. (2013) a survey on the ietf protocol suite for the internet of things: standards, challenges, and opportunities. ieee wireless communication, 20(6):91–98. http://www.contiki-os.org/index.html 299 iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 97 process modelling and debottlenecking study of a vaccine production nurul huda mohamed safri 1 , maizirwan mel 1 , dominic c.y. foo 2 , denny k.s. ng 2 and irene m.l. chew 3 1 bioprocess and molecular engineering research unit, department of biotechnology engineering, kulliyah of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. 2 department of chemical and environmental engineering, university of nottingham malaysia, jalan broga, 43500 semenyih, selangor, malaysia 3 school of engineering, monash university sunway campus, jalan lagoon selatan, 46150 bandar sunway, selangor, malaysia. maizirwan@iium.edu.my abstract: the main objective of this research work was to model and optimise the production of a locally-developed infectious coryza (ic) vaccine. the simulation work was performed using a commercially available batch process simulator superpro designer v5.5. six debottlenecking schemes were analysed using throughput analysis and cost to benefit ratio (cbr) when the annual production was set to increase by 100%. based on the economic analysis, the selected debottlenecking scheme has an annual predicted revenue of usd 240 million, with a gross margin of 9.13% and a return on investment (roi) of 46.12%. in addition, the payback period of the selected scheme is estimated to be within three years. abstrak: objektif utama dalam penyelidikan ini adalah untuk memodelkan dan mengoptimumkan hasil pembuatan vaksin tempatan coryza berjangkit. kerja simulasi ini dijalankan menggunakan alat simulasi super pro designer v5.5. sebanyak enam (6) skema khusus diujikaji menggunakan analisis pemprosesan dan kos kepada nisbah faedah (cbr) apabila pembuatan tahunan meningkat kepada 100%. berdasarkan analisis ekonomi yang telah dilakukan, sesuatu skema khusus yang dipilih mempunyai keuntungan sebanyak usd 240 juta dengan margin kasar 9.13% dan pulangan atas pelaburan (roi) sebanyak 46.12%. selain itu juga, tempoh pembayaran balik bagi skema yang dipilih dianggarkan dalam tempoh tiga(3) tahun. keywords: process simulation; modelling; debottlenecking; optimisation 1. introduction malaysia is one of the countries with the highest chicken consumption per capita in the world at 32 kg. some of the reasons for high chicken consumption are that chicken consumption is not against dietary prohibition or religious restrictions and chicken meat is a very low cost meat source in the country malaysia poultry and products annual 2006, 2006). therefore, the poultry industry in malaysia has grown from a backyard-type operation into a commercialised system in last 30 years. due to the rapid grow of the poultry industry, the poultry diseases has poses a threat to the viability and productivity of poultry farming. iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 98 infectious coryza (ic) disease is identified as one of the curses in the poultry industry worldwide [1]. ic is an acute respiratory disease of chickens which is caused by the bacterium known as haemophilus paragallinarum (hpg) [2]. chickens of all ages are susceptible to this type of disease. once the chickens are infected by this disease, the chickens get swollen eyes and nose, foul smelling discharges and sneezing. besides, the chickens’ feed and water intake are reduced significantly which eventually leads to weight lost and lower production of egg [3]. in order to prevent this disease, the breeders in malaysia normally administer vaccine which is imported from usa or japan to the chickens [3]. however, the imported vaccines do not cure the infected chickens because the emergence of variant local strains of hpg in the flocks [4]. in addition, the genetic makeup of local hpg strains is different from the standard hpg strains in the imported vaccines [5]. hence, producing ic vaccine from the local hpg strains is a better option to alleviate the ic disease problems in malaysia [6]. with an effective local-made ic vaccine, the dependency of malaysian breeders on the imported vaccines will be reduced. process modelling and simulation in pharmaceutical industries functions as methodologies and tools that can be used to evaluate alternatives and speed up the development effort which may immensely impact on the bottom line [7]. with the given production capacity, modeling and simulation tool such as superpro designer can be used to design and predict the feasibility of different production schemes [8]. for instance, kumaresan et al. presented an approach to model and optimise tongkat ali extract process via superpro designer [8]. based on the study, a base case was first generated on the overall process and then debottlenecking strategies were proposed [8]. besides that, detail economic analysis was also conducted. based on the similar approach, modelling of ic vaccine production using the batch process simulation tool superpro designer v5.5 is presented in this work. due to the production capacity is limited by the current operating condition and equipment setup, debottlenecking study is performed to increase in annual production. preliminary economic analysis is preformed to compare the debottlenecking schemes. figure 1 shows the process flowsheet for a typical ic vaccine production designed with superpro designer v5.5. the specifications for the major equipments used in the ic vaccine production are shown in table 1. in order to produce ic vaccine through fermentation process, the bacteria hpg is first prepared and transferred from a freezer (80°c) into a sterilized shake flask (p-1/sfr-101) contains media (nutrient and water). note that the preparation of hpg bacteria is excluded in this work. after 10 hours of prefermentation, the cultures were transferred to a 3 l seed fermentor (v-101), followed by a 30 l fermentor (v-103) and 300 l fermentor (v-104)., where the fermentation process is continued (see fig. 1). it is worth mentioning that the media for the fermentation processes was pre-prepared in a media blending tank (v-102), and sterilized (in p-4 and p-6/st-101) before it was transferred to the fermentors (v-103 and v-104) with the feed ratio of ten folds of the cultures feed. iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 99 2. infectious coryza (ic) vaccine production p-1 / sfr-101 300 ml inoculation p-2 / v-101 3 l fermentation w ater 1 hpg 1 w ater 2 nutrient 1 nutrient 2 p-5 / v-103 30 l fermentation p-7 / v-104 300 l fermentation p-3 / v-102 media blending tank w ater nutrient p-6 / st-101 heat sterilization p-4 / st-101 heat sterilization media p-7 media p-5 p-5 media p-7 media 3 l hpg 30 l hpg 300 ml hpg bacteria fermentation p-8 / ds-101 centrifugation 300 l hpg recovery and purification packaging vent out 1 vent out 2 vent out 3 vent out 4 media p-9 / v-105 kill tank pbs thimerosal cell paste p-11 / v-106 reactor tank alum10% p-12 / hg-101 homogenization antigen+adjuvan p-13 / v-107 storage vessel mixture p-14 / fl-101 filling vial vaccine product p-10 / mf-101 microfiltration inactive hpg filtrate concentrate fig. 1 process flowsheet of ic vaccine production (base case). table 1: major equipment specification for ic vaccine production. quantity procedure/ equipment specification fermentation section 1 p-1/sfr-101 volume = 500 ml 1 p-2/v-101 volume = 5 l 1 p-3/v-102 volume = 330 l 1 p-4/st-101 rated throughput of 1080 l/h (calculated based on design mode) 1 p-5/v-103 volume = 50 l 1 p-6/st-101 rated throughput of 1080 l/h (calculated based on design mode) 1 p-7/v-104 volume = 500 l recovery and purification section 1 p-8/ds-101 based on sigma factor 39627.55 m 2 (calculated based on design mode) 1 p-9/v-105 volume = 107.88 l (calculated based on design mode) 1 p-10/mf-101 0.45 µ m membrane pore size 1 p-11/v-106 volume = 77.96 l (calculated based on design mode) 1 p-12/hg-101 pumping efficiency of 70 % packaging section 1 p-13/v-107 volume = 77.94 l (calculated based on design mode) 1 p-14/fl-101 3000 entities/h (calculated based on design mode) iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 100 after the fermentation process, the cultures were harvested using a centrifuge (ds-101) and transferred to a kill tank (v-105) where the cultures were deactivated by adding thimerosal and phosphate buffer saline (pbs) [10]. next, the cultures were further concentrated by passing it through a microfiltration membrane (mf-101) with pore size of 0.45 µ m and 99.7% removal efficiency, before it was being transferred to a reactor tank (v-106) [11]. alum 10%, which acts as an adjuvant, was used an aid to the vaccine [12]. the adjuvant and antigen were homogenized in a homogenizer (hg-101) to ensure the same size particles. the mixture from the homogenizer was the final product and it was stored in a storage vessel (v-107) before it was sent for packing in filling machine (fl101).tables 2 and 3 summarise the process scheduling (sut: setup time; pt: process time; st: start time) for each unit operation and the details of the raw materials (amount; price) in the ic vaccine production. 3. bottleneck identification strategies based on the given information (tables 1 – 3) and flowsheet in fig.1, the process simulation of the based case is solved. the capital investment of the base case and the cost of production per unit are estimated as $18 million and $104.91, respectively. based on the selling of $115 per unit, the annual revenue is computed as $123 million with 2.51 years of payback period. table 2: scheduling summary for operations and procedures in the base case model. procedure/ equipment operation sut (mins) pt st p-1/sfr-101 charge nutrient 1 5 mins beginning of batch charge water 1 3 mins after nutrient 1 charge agitation 5 mins after water 1 charge charge hpg 1 3 mins after agitation fermentation 10 hours after hpg 1 charge transfer out 300 ml hpg to p-2 3 mins after fermentation p-2/v-101 charge nutrient 2 5 mins after 12 hours of batch operation charge water 2 3 mins after nutrient 2 charge agitation 8.4 mins after water 2 charge transfer in 300 ml hpg from p-1 master-slave with p-1 transfer out 300 ml hpg starts with transfer 300 ml in p-1 (to p-2) fermentation 6 hours after transfer in 300 ml hpg from p-1 transfer out 3 l hpg to p-5 3 mins after fermentation cip 15 mins after transfer out to p-3 iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 101 table 3 (continued): scheduling summary for operations and procedures in the base case model. procedure/ equipment operation sut (mins) pt st p-3/v-102 charge nutrient 20 calculated based on 600 l/h volumetric flowrate after 14.3 hours of batch operation charge water 20 calculated based on 600 l/h volumetric flowrate after charge nutrient agitation 10 mins after charge water transfer out media p-5 to p-4 20 calculated based on 600 l/h volumetric flowrate after agitation store 4.66 hours after transfer out media p-5 transfer out media p-7 to p-6 20 calculated based on 600 l/h volumetric flowrate after store cip 15 mins after transfer out media p-7 p-4/st-101 sterilize 15 mins starts with transfer out media p-5 in p-3 (to p-4) p-5/v-103 transfer in media p-5 from p-4 20 calculated based on 600 l/h volumetric flowrate after sterilize in p-4 transfer in 3 l hpg from p-2 master slave with p-2 transfer out 3 l hpg starts with transfer out 3 l hpg in p-2 (to p-5) fermentation 5 hours after transfer in 3 l hpg transfer out 30 l hpg to p-7 20 calculated based on 600 l/h volumetric flowrate after fermentation cip 15 mins after transfer out 30 l hpg p-6/st-101 sterilize 15 mins starts with transfer out media p-7 in p-3 (to p-6) p-7/v-104 transfer in media p-7 from p-6 20 calculated based on 600 l/h volumetric flowrate after sterilize in p-6 transfer in 30 l hpg from p-5 master slave with p-5 transfer out 30 l hpg starts with transfer out 30 l hpg in p-5 (to p-7) fermentation 4.5 hours after transfer in 30 l hpg transfer out broth to p8 master slave with p-8 centrifuge after fermentation cip 15 mins after transfer out broth iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 102 table 4 (continued): scheduling summary for operations and procedures in the base case model. procedure/ equipment operation sut (mins) pt st p-8/ds-101 centrifuge 60 mins starts with transfer out broth in p-7 (to p-8) cip 15 mins after centrifuge p-9/v-105 transfer in cell paste from p-8 master slave with p-8 centrifuge starts with centrifuge in p-8 charge pbs calculated based on 600 l/h flow rate after transfer in cell paste agitation 10 mins after charge pbs charge thimerosal calculated based on 600 l/h flow rate after agitation agitation 15 mins after charge thimerosal transfer out inactive hpg to p-10 20 calculated based on 600 l/h flow rate after agitation cip 15 mins after transfer out inactive hpg to p-10 p-10/mf-101 filtration 120 mins starts with transfer out inactive hpg in p-9 (to p10) cip 15 mins after filtration p-11/v-106 transfer in concentrate from p-10 20 master slave with p-10 filtration starts with filtration in p10 charge alum10% calculated based on 600 l/h flow rate after transfer in concentrate agitation 15 mins after charge alum10% transfer out antigen+adjuvant to p12 20 calculated based on 600 l/h flow rate after agitation cip 15 mins after transfer out antigen+adjuvant p-12/hg-101 homogenize 30 mins starts with transfer out product antigen+adjuvant in p-11 (to p-12) cip 15 mins after homogenize p-13/v-107 transfer in mixture from p-12 20 calculated based on 600 l/h flow rate starts with homogenize in p-12 transfer out product to p-13 20 calculated based on 600 l/h flow rate after transfer in mixture cip 15 mins after transfer out product p-14/fl-101 filling (fill level: 50 ml/bottle) 20 master slave with p-13 transfer out product starts with transfer out product in p-13 (to p-14) (sut: setup time; pt: process time; st: start time) iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 103 table 5: raw materials used in a single batch raw materials symbol approximation amount (kg/batch) price (usd/kg) aluminum hydroxide alum10% aluminum oxide 7.867 2.00 chicken serum chicken serum protein 8.481 207.15 glucose glucose glucose 50.886 25.14 haemophillusparagallinarum hpg biomass 0.032 0.00 disodium hydrogen phosphate na2hpo4 sodium hydrogen phosphate 25.443 85.14 nadh nadh protein 1.696 75,000.00 phosphate buffer saline pbs sodium chloride 38.701 14.29 peptone peptone protein 50.886 128.00 sodium chloride sodium chloride sodium chloride 32.228 8.57 thimerosal thimerosal ethyl benzene 0.013 10.17 water water water 7,318.739 0.02 as the increase of the demand of ic, the management decided to increase the production capacity by 100%. therefore, the current process is facing difficulties to meet the requirement. in order to overcome the problem, the process bottleneck is first identified. based on the set target, throughput analysis is first performed to identify the process bottlenecks, i.e. scheduling or size bottlenecks. generally, bottleneck could be caused by the limitation of equipment or resources such as utilities, labor and raw materials supply. based on the identified bottleneck, different debottlenecking schemes are proposed, and economic analysis is carried out for selection of the scheme with highest cbr. note that cbr is defined as the ratio of extra benefit to the extra cost as shown in equation (1) [7]. ��� � ���� �� ���� ���� � ��� � ���� (1) in order to increase the annual process throughput to 100%, three strategies are considered, i.e. increase of batch size (the amount of product produced per batch of operation), increase number of batches or increase of both batch size and number of batches. according to petrides et al., the scheduling bottleneck can be identified by tracking the total time consumed by each equipment within its cycle time [7]. the equipment with the longest cycle time is identified as the scheduling bottleneck, and this bottleneck will determine the maximum number of batches [12]. on the other hand, the size bottleneck of a process can be determined by calculating the capacity utilisation, uptime and combined utilisation of the various processing steps such as fermentation, centrifugation and filtration [10]. capacity utilisation of equipment is referred to the fraction of equipment capacity that is used during an operation. meanwhile, uptime is defined as ratio of equipment’s occupancy time over the plant cycle time. combined utilisation is the product of the capacity used and the uptime. this parameter clearly shows the time and capacity of particular equipment that is being used over the process. iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 104 fig. 2 the operation gantt chart (base case). figure 2 shows the operation gantt chart of the base case. as shown in fig. 2, it is noted that shake flask (sfr-101) is identified as the scheduling bottleneck due to its longest occupancy (10 hours) as compare to the other equipment. the next step is to identify the debottlenecking schemes as shown in the following section. 4. debottlenecking schemes to increase production after process bottleneck is identified, six debottlenecking schemes are proposed to increase the annual production of ic vaccine to 100%. as presented previously, shake flask (sfr-101) is identified as the scheduling bottleneck; hence, in order to increase the annual production, debottlenecking strategies should target to reduce the fermentation time in the shake flask. in order to reduce the fermentation time of shake flask (sfr-101), another set of 300 ml shake flask (sfr-102) that staggered the operation is considered. by staggering the shake flask the overall cycle time of shake flask is reduced by half. in this scheme (scheme 1), the annual throughput increased 39.48% as compared to the base case (1067 batches per year), while the cbr value is calculated at 0.74. this scheme provides a good debottlenecking alternative as the cost of shake flask is very low compared with the overall capital investment. since the annual throughput is only increased by 39.48%, the process needs to be further debottlenecked in order to achieve the targeted 100% increment. throughput analysis is next carried out for scheme 2, media bleeding tank (p3/v-102) is identified as the next scheduling bottleneck. hence, an additional media blending tank that operates in staggered mode is added. the annual throughput of this scheme is increased to 1136 batches, i.e. 48.5% increment from the base case. meanwhile, the cbr is determined as 0.77 which is slightly higher than scheme 1. iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 105 the throughput analysis is repeated on scheme 2 to generate scheme 3. in scheme 3 an additional 5 l fermentor (v-109) is added to operate in staggered mode with the current fermentor (v-101), after schemes 1 and 2 are considered. the annual throughput of this scheme is increased to 1141 batches, i.e. 49.2% increment from the base case. note that, the annual number of batches does not increase much as compare with scheme 2. meanwhile, the cbr of this scheme is same as scheme 2. thus, this scheme is not as attractive as compared to scheme 2. in scheme 4, throughput analysis reveals that the 500 l fermentor (v-104) emerges as the new process bottleneck due to its longest occupancy time due to its master slave relationship with centrifugation process and its long fermentation time. hence, an extra set of 500 l fermentor is added. based on the simulated result, the annual throughput for this scheme is increased to 1223 batches or 59.9% increment, and the cbr of this scheme is determined as 0.79. the 50 l fementor (v-103) is next identified as the new process bottleneck for scheme 4. in order to eliminate this process bottleneck, an additional 50 l fermentor is installed (scheme 5). the simulated result shows that the number of batches tremendously increased to 1492 and 95.03% increment from the base case, and the cbr is calculated as 0.86. it is worth noting that the cbr for scheme 5 is the highest cbr among all five debottleneck schemes. however, its annual production is yet to reach to 100%. bacteria fermentation p-1 / sfr-101 300 ml inoculation p-2 / v-101 3 l fermentation water 1 hpg 1 water 2 nutrient 1 nutrient 2 p-5 / v-103 30 l fermentation p-7 / v-104 300 l fermentation p-3 / v-102 media blending tank water nutrient p-6 / st-101 heat sterilization p-4 / st-101 heat sterilization media p-7 p-5 media p-7 media 30 l hpg (5) p-8 / ds-101 centrifugation 300 l hpg recovery and purification packaging vent out 1 vent out 2 vent out 3 vent out 4 media p-9 / v-105 kill tank pbs thimerosal cell paste p-11 / v-106 reactor tank alum10% p-12 / hg-101 homogenization antigen+adjuvan p-13 / v-107 storage vessel mixture p-14 / fl-101 filling vial vaccine product p-10 / mf-101 microfiltration inactive hpg filtrate concentrate p-1a / sfr-102 new shake flask nutrient 1a water 1a hpg 1a 300 ml hpg (1) p-2a / v-108 new 5 l fermentor nutrient 2a water 2a300 ml hpg (1a) 3 l hpg (2) p-3a / v-109 new media blending tank nutrient a water a p-5a / v-110 new 50 l fermentor p-7a / v-111 new 500 l fermentor p-6a / st-102 new heat sterilization p-4a / st-103 new heat sterilization s-101 p-7a media s-103 p-5a media s-105 s-106 30 l hpg (5a) fig. 3 debottlenecking scheme 6. scheme 6 is introduced where an additional heat steriliser is installed (see fig. 3). this equipment is operated in staggered mode with the existing heat steriliser. the annual throughput increases to 1530 batches from 765 batches in the base case. note that 100% increment of annual production is achieved. even though the cbr value for scheme 6 is computed as 0.85, which is slightly lower than that in scheme 5, this scheme fulfils the iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 106 objective of the debottlenecking study. the debottlenecking process is a continuous process as there is always a limitation of equipment for the overall production. after completing scheme 6, it is found that shake flask (p1/sfr-101) is once again becomes the new process bottleneck as it is now the longest process that limits the process cycle time. although debottlenecking is a continuous process, it stops when the scheme that achieves the company's target is achieved. for instance, in this case study, debottlenecking is stopped at scheme 6 as it met the 100% production rise as compared to the base case. table 4 shows the summary of all debottlenecking schemes as well as the base case. table 6: economic comparison of the base case study and debottlenecking strategy scenario % production increase (annual batches) annual throughput (vials) cost of investment ($) annual operating cost ($) annual revenue ($) unit production cost ($/vial) cbr base case 0 % (765) 1,074,395.354 18,202,250 112,710,857 123,555,466 104.9063 scheme 1 39.5% (1067) 1,498,535.742 22,184,430 156,633,492 172,331,610 104.5244 0.74 scheme 2 48.5% (1136) 1,595,441.990 23,429,706 166,728,627 183,475,829 104.5031 0.77 scheme 3 49.2 % (1141) 1,602,464.182 23,761,950 167,502,583 184,283,381 104.5281 0.77 scheme 4 59.9% (1223) 1,717,628.128 26,573,045 179,740,333 197,527,235 104.6445 0.79 scheme 5 95.0% (1492) 2,095,422.050 30,785,330 218,980,377 240,973,546 104.5042 0.86 scheme 6 100% (1530) 2,148,790.708 32,938,306 224,803,395 247,110,931 104.6186 0.85 5. conclusion in this work, process simulation tool is used to model and simulate the ic vaccine production. six debottleneck strategies are developed to increase the annual production to 100%. in this case study, scheme 6 is chosen as the best scheme to debottleneck the process because it fulfills the debottlecking objective, and with reasonable high cbr values. to further increase the profit of ic vaccine production, the company may consider producing their own chicken serum (due to its high cost) instead of sourcing from external supplier. references [1] rajurkar, gayatri, ashish roy, and mahendra mohan yadav. “an overview on epidemiologic investigations of infectious coryza.” veterinary world 2.10 (2009): 401403. [2] blackall, p. j., m. matsumoto, & r. yamamoto. “diseases of poultry.” lowa state: university press, (1997). [3] z “characterisation of haemophilus paragallinarum isolated in malaysia” j. vet. malaysia 3(1); 25-30. 3.1 (1991): 25-30. [4] blackall, p. j., l. e. eaves, & g. aus. “serotyping of haemophilus paragallinarumby the page scheme: comparison of the use of agglutination and hemagglutination-inhibition tests. “. avian diseases (1990): 643-45. [5] blackall, p. j. “infectious coryza: overview of the disease and new diagnostic options.” iium engineering journal, vol. 13 no. 1, 2012 mohamed safri et al. 107 clinical microbiology reviews. 12.4 (1999): 627-32. [6] mel, m., sarmidi, m.r., aziz, r.a., zain, z.m., and jamaluddin, a.a. “a study of the cell growth of haemophilus paragallinarum; optimization of ph and temperature.” proceeding 11th national biotechnology seminar, melaka. (1999): 151-153. [7] demetri petrides, alexandros koulouris, and charles siletti “throughput analysis and debottlenecking of biomanufacturing facilities, a job for process simulators.” . biopharm 15.8 (2002). [8] athimulam, a., kumaresan, s., foo, d. c. y., sarmidi, m. r. and aziz, r. a. “modelling and optimisation of eurycoma longifolia. water extract production, food and bioproduct processing.”. 84.2 (2006): 139-49. [9] intelligen, inc. (2005). superpro designer user’s guide (intelligen, inc., scotch plains, new jersey, usa). [10] mel, m., sarmidi, m.r., aziz, r.a., zain, z.m., and jamaluddin, a.a. “screening and optimization of haemophilus paragallinarum fermentation for coryza vaccine production.” proceeding regional chemical engineering symposium, nus singapore. (2000). [11] mel, m., sarmidi, m.r., aziz, r.a., zain, z.m., and jamaluddin, a.acoryza vaccine optimized in 16 l fermentor using bioengineering ferm control strategy. proceeding regional chemical engineering symposium, itb bandung indonesia, (2001). [12] mel, m., sarmidi, m.r., aziz, r.a., zain, z.m., jamaluddin, a.a. “development of coryza vaccine; optimisation and scale-up studies.” universiti teknologi malaysia: bioprocess engineering department. (2002). iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 effect of sterilization on mechanical and blood properties of medical grade polyvinyl chloride maryam poostchi and hamed bagheri* faculty of interdisciplinary sciences and technologies, tarbiat modares university,tehran,iran *corresponding author: hbagheri@modares.ac.ir (received: 5th january 2021; accepted: 16th april 2021; published on-line: 4th january 2022) abstract: the use of phthalates as a plasticizer in plasticized polyvinyl chloride (pvc) always poses the threat of migration of phthalates into the environment through medical equipment. phthalates can be used with natural-based plasticizers, such as epoxidized soybean oil (esbo) known as phthalate’s scavenger and pvc stabilizers. pvc formulations were characterized by different combinations of di (2-ethylhexyl) phthalate (dehp) 30-40% with 5% esbo. pvc flexibility increased significantly in the presence of esbo, without a change in strength (tensile test). the decrease of the tg temperature by adding esbo in differential scanning calorimetry indicated that esbo preserved dehp in the polymer. also, it was shown that the sterilization process with ethylene oxide, similar to esbo, decreased the tg of polymer. dehp migration was evaluated at a maximum level to the environment using the gas chromatography test. samples containing esbo showed less hemolysis. abstrak: penggunaan phthalates sebagai plasticizer dalam plastik polyvinyl chloride (pvc) selalu menimbulkan ancaman penghijrahan phthalates ke alam sekitar melalui peralatan perubatan. phthalates boleh digunakan dengan plasticizer berasaskan semula jadi, seperti minyak kacang soya epoxidized (esbo) yang dikenali sebagai pemulung phthalate dan penstabil pvc. formulasi pvc dicirikan oleh kombinasi yang berbeza di (2-ethylhexyl) phthalate (dehp) 30-40% dengan 5% esbo. fleksibiliti pvc meningkat dengan ketara di hadapan esbo, tanpa perubahan kekuatan (ujian tegangan). penurunan suhu tg dengan menambahkan esbo dalam calorimetri pengimbasan berbeza menunjukkan bahawa esbo mengekalkan dehp dalam polimer. juga, ditunjukkan bahawa proses pensterilan dengan etilena oksida, serupa dengan esbo, menurunkan tg polimer. penghijrahan dehp dinilai pada tahap maksimum ke lingkungan menggunakan uji kromatografi gas. sampel yang mengandungi esbo menunjukkan kurang hemolisis. keywords: di (2-ethylhexyl) phthalate, polyvinyl chloride, plasticizer, blood bag, epoxidized soybean oil 1. introduction in the years before 1970, glass bottles were used as containers for human blood preservation and were reused after cleaning and sterilization [1]. now containers are special plastic bags with appropriate properties that meet today’s needs regarding the maximum stability of the product and cell survival [2]. today, all blood containers are sterilized and disposable. blood bags used for blood preservation are made of polyvinyl chloride (pvc) [1–3]. pvc has a wider range of use in the construction and auto industries, as well as in the medical industry due to its characteristics, i.e. inert properties, transparency, easy sterilization, 282 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 compatibility with chemical compositions, and low cost [3–6]. semi-hard and soft pvc comprises numerous parts of plastic materials used in the medical industry. many sterilized disposable containers and tools, such as catheters, preservation bags for injecting fluids, medical tubes, preservation bags for blood and plasma, and dialysis equipment, are made of pvc. materials used in these tools, especially blood preservation bags and medical tubes, cannot be replaced with other polymers [7–10]. pvc is considered a hard polymer with high tg that is required to be plasticized for medical equipment, such as medical tubes and bags [11]. various plasticizers, such as phthalates, are utilized in pvc. phthalates are compounds formed as a result of phthalic acid esterification, which adds about 30-40% weight to pvc and plays a major role in its flexibility [9, 12]. di(2-ethylhexyl)-phthalate (dehp) is the most widely used plasticizer. most concerns are about the migration of dehp to the environment due to the non-covalent bond between dehp (phthalates) molecules and vinyl chlorides [5, 6, 10, 13–16]. epoxidized soybean oil (esbo) is an organic compound produced by soybean oil epoxidation [17]. the compound is used as a lubricant and stabilizer in pvc [5, 18–20]. food products preserved in glass containers are sealed with pvc films or linings. esbo is an additive used during pvc manufacture. esbo can resist the release of hcl molecules due to its bonding with chlorine atoms in pvc [6, 15, 20, 21]. the united states food and drug administration announced that the dehp study on lab animals did not prove the safe use of dehp for human beings. thus, dehp is used only for medical instruments with no continual contact with fluids in a patient’s body. furthermore, it is strongly advised not to utilize pvc–dehp containing medical instruments for vulnerable patients, such as infants and pregnant women. medical instrument manufacturing companies are also advised to remove dehp from their products [22]. sterilization is a major process in manufacturing medical tools. most soft pvc products should be sterilized before use. regarding the significance of the sterilization process in producing medical pvc tools, this study investigated the sterilization process effect on the migration of the plasticizer in the pvc bulk. the migration of the plasticizer probably increases due to special conditions in the sterilization process related to pressure and temperature. the present study mainly discussed how to modify pvc blood preservation bags and find suitable polymer compositions with higher safety, flexibility, and blood compatibility, as well as lower migration rate. the study also evaluated the effect of various factors, including sterilization with ethylene oxide gas and addition of secondary plasticizers, such as esbo, on the migration rate of plasticizers into the blood. we investigated certain properties of blood preservation bags and their stability and flexibility, including the release rate of plasticizers into the blood and blood compatibility (as clot formation for each pvc film with different percentages of plasticizers). 2. materials and methods 2.1 materials: the materials were used pvc s6058 with the k-value 60 manufactured by iranian petrochemical industries co., di-2 (ethylhexyl) phthalate manufactured by azar shimi co. (iran), 2,6-di-tert-butyl-4-methylphenol with vulkanox bht manufactured by lanxess (germany), esbo manufactured by mbt (south africa), ca-zn stearate manufactured by poorya exir co. (iran), chloroform with cas no. 3-66-67 and the molecular mass of 119.38g/mol manufactured by merck (germany), ethanol of 98% purity manufactured by 283 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 jahan khorram co. (iran), distilled water and physiologic serum manufactured by sepidaj pharmaceutical co. (iran), and sheep blood obtained from darvash co. (iran). 2.2 sample preparation: the plasticizer percentage of each sample (30-40%) was determined based on previous studies [16, 23, 24]. the three samples contained 30%, 35%, and 40% dehp. the test was also repeated with esbo, which was added as much as 5% to the samples four, five, and six as a secondary plasticizer (at the same dehp content). the number of samples along with their plasticizer contents is listed in table 2.1. the samples zero and seven were used as evidence samples; none of the two samples contained dehp, although the sample seven contained 5% esbo. table 2.1: percentage of each plasticizer was used in samples. secondary plasticizer (esbo) % primary plasticizer (dehp) % sample no. 0 0 0 0 30 1 0 35 2 0 40 3 5 30 4 5 35 5 5 40 6 5 0 7 after determining the plasticizer percentage in each sample, its component was measured in 100 units (phr), as shown in table 2.2. the weight of each sample was kept at 60g to fit the capacity of an internal mixer device. the fraction of each component, including pvc, a stabilizer, an antioxidant, a plasticizer, and esbo, was calculated based on 100 units(phr), as shown in table 2.2. table2.2: components of a sample weighing 60g sample no. composition sample no. composition 1 pvc+30%dehp (non-sterilized) 7 pvc+30%dehp (sterilized) 2 pvc+35%dehp (non-sterilized) 8 pvc+35%dehp (sterilized) 3 pvc+40%dehp (non-sterilized) 9 pvc+40%dehp (sterilized) 4 pvc+30%dehp+5%esbo (nonsterilized) 10 pvc+30%dehp+5%esbo (sterilized) 5 pvc+35%dehp+5%esbo (nonsterilized) 11 pvc+35%dehp+5%esbo (sterilized) 6 pvc+40%dehp+5%esbo (nonsterilized) 12 pvc+40%dehp+5%esbo (sterilized) 284 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 each sample was mixed with a w50 brabender mixer (germany) to obtain a homogeneous mixture. the mixing device was set at 160°c and 80 rpm, and the samples were mixed for two min. the sample without the plasticizer was selected as a control sample of zero migration. however, the sample was removed from the study because of its poor properties. sample films with 5mm thickness were prepared. hot pressing was conducted with a device manufactured by sanjesh baspar novin co. (iran), while cold pressing was performed with a device manufactured by toyo seiki (japan). each sample was fixed in two dumbbell-shaped casts where their dimensions were worked out according to iso 6621 standards—length 15cm, width 2cm, and thickness 3mm. the samples then underwent hot pressing at 165°c for four min under 60nm torque, followed by cold pressing (room temperature) for three min under 60nm torque. half of the dumbbell samples were sterilized to compare the characteristics before and after sterilization. each sample was put into a sterilized tank (jiangyin huaqing machinery, china) of 90% ethylene oxide gas at 50°c and 50kp for eight h. table 2.3 shows the composition of each prepared sample, including figures attributed to it, which were utilized later. table 2.3: sample nomenclature and abbreviations pvc dehp esbo ca-zn st bht sample no. gr phr gr phr gr phr gr phr gr phr 0 58.53 100 0 0 0 0 01.17 2 0.29 0.5 1 40.96 100 18.02 44 0 0 0.82 2 0.25 0.5 2 38.10 100 20.95 55 0 0 0.76 2 0.19 0.5 3 34.99 100 24.14 69 0 0 0.70 2 0.17 0.5 4 37.85 100 18.17 48 03.03 8 0.76 2 0.19 0.5 5 34.78 100 21.22 61 03.13 9 0.70 2 0.17 0.5 6 31.83 100 24.19 76 03.18 10 0.64 2 0.16 0.5 7 55.81 100 0 0 05.00 5 02.00 2 0.50 0.5 2.3 mechanical testing: both sterilized and non-sterilized samples underwent examination separately, based on iso-527 standards, using tcs2000 universal testing (gotech testing machines, taiwan). the study samples had an average thickness of 2.4mm and width of 10mm. 2.4 differential scanning calorimetry (dsc): differential scanning calorimetry (dsc) measurements were carried out on a dsc-1 unit manufactured by mettler toledo, switzerland. about 4-5mg of the polymer sample was sealed in an aluminum pan. the polymer sample was first heated to 130 °c at a rate of 10°c/min under nitrogen atmosphere for three min to erase the thermal history. then, it was cooled to -70°c at 285 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 a rate of 10°c/min for five min, and subsequently, heated to 130°c at a rate of 10°c/min. both the cooling and heating traces were recorded. 2.5 gas chromatography analysis (gc): 2.5.1 sample extraction all glassware was washed in 70% alcohol solutions and then put into the laboratory oven at 70°c for 15 min. the samples were cut in certain pieces using sterilized scissors and then put into a watch glass. the samples were weighed individually, and sterilized forceps were used to place the samples in an erlenmeyer flask immediately after it was filled with as much as 50cc chloroform solution. the samples were tapped, and the flask was placed in the oven at 25°c for 24 h. then, the flask was removed from the oven, and the pieces were taken out of the chloroform solution and put back in a watch glass. the pieces were again put into the oven at 70°c for 30 min to be dried. the solutions were preserved in other tapped dishes to be analyzed by gas chromatography. 2.5.2 preparation of standard solution dodecane, with the chemical formula c12h26, was utilized to prepare standard solutions. the solutions were prepared at 100, 200, and 500ppm concentrations. the 500ppm solution was more like the samples than the other two solutions. chromatography was performed on the cp3800 gas chromatograph manufactured by varian, usa. the injector temperature was set at 280°c with split-less mode, and the detector temperature was 300°c. the column was cp-sil 5 cb made from silica with an inner diameter of 0.25mm and a length of 25m. nitrogen-bearing gas at 40psi pressure and 1µl injection volume was applied to a flame ionization detector. the test was conducted with the following temperature condition passing through the liquid column: the initial temperature of 90°c was held for three min and increased at a heating rate of 15°c/min up to 280°c, which was held for five min. the total heating time was 20.67 min. 2.6 hemolysis test: the samples were cut into 1cm ˟ 1cm films with sterilized scissors and a knife under sterilized conditions. the cut films were added to 100 million red globules lacking serum. then, they were delivered to a container with 1 ml biological buffer using physiologic buffer and put in a shin saeng finetech rotary oven, (south korea) at 37°c for one h at 100rpm. after an hour, the samples were centrifuged at 10,000rpm for five min in a sigma3-30k centrifuge (atr, usa). the supernatant was tested using the wpa biowave ii spectrophotometer (biochrom, uk) at a 540nm wavelength to determine the released hemoglobin. 3. results and discussion 3.1 tensile test increasing the plasticizer to pvc led to increased flexibility (figs. 1a, b) by decreasing the tensile stress and increasing the maximum stain at break. considerable flexibility was observed in the samples 5 and 6 to which esbo was added, confirming the esbo plasticizer effect on pvc. 286 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 figure 3.1 mechanical properties of stretch pvc films evaluated: yield stress (a) and strain at breakpoint (b) before sterilization process. the stress-strain diagram demonstrated that ultimate stress decreased with increasing the plasticizer in the samples 1 to 6. furthermore, by adding esbo to the samples, ultimate stress decreased continually with increasing the plasticizer. both samples 2 and 4 with the same plasticizer content had different strains at break so that the maximum strain was 2% more in the sample 4 compared to the sample 2. the strain rate difference was insignificant in these samples due to the low plasticizer content. however, increasing the plasticizer content up to 40% led to a meaningful difference in the samples 3 and 5. in other words, replacing 5% dehp with 5% esbo increased the polymer strain from 156% to 257%. accordingly, esbo had higher plasticizing effect than dehp and its plasticizing characteristics in pvc. when a plasticizer (such as dehp) is added, its molecules will be placed in various sites between polymer chains. this helps pvc become more flexible and leads to a decrease in tg. the effect of plasticizers on tg is attributed to the increase in the free volume that enhances molecular mobility. although plasticizers reduce chain entanglement density, the length scale of the chain contributing to tg (~50 c-c bond) is smaller than the entanglement mw (~200 cc). it means that the chain entanglement density effect should not be considerable in typical plasticizer contents (~10-20%); unless one uses much higher plasticizer contents or coplasticizers such as esbo. all the samples represented similar behavior both before and after sterilization. the mechanical behavior of the samples after sterilization is shown in figure 3.2. the sterilization process did not have considerable effects on maximum strain at the break of the samples. the sample strains considerably increased after sterilization, indicating that sterilization tended to increase its flexibility. moreover, samples with 5% esbo better preserved their mechanical properties. 287 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 figure 3.2 mechanical properties of stretch pvc films evaluated; yield stress (a) and strain at breakpoint (b) after sterilization process. the results of mechanical testing after sterilization confirmed that the strain increased at the break of the polymer with the esbo plasticizer. the other plasticizers did not show such a maximum strain level at break. however, dehp showed maximum strain at break after sterilization. these results can be attributed to the fact that dehp molecules diffuse to polymer chains because of more heating during the sterilization process and lead to increasing the distance of polymer chains and thus increasing maximum strain at break. increasing dehp provides more void spaces between chains, leading to improving chain sliding against each other and increasing polymer flexibility. when esbo was added to the polymer, it caused higher increased molecular distances between pvc chains by the combined effect of esbo and dehp molecules. dehp was emplaced between pvc chains and, finally, increased polymer flexibility. actually esbo has a synergistic effect when used with dehp and increases the polymer flexibility. sarath josh et al. (2012) studied the temperature effect on the dehp migration and release in blood preservation bags and confirmed the increased dehp penetration index with increasing the temperature [25, 26]. in other words, dehp molecules were stabilized between pvc chains with increasing the temperature. during the sterilization process, the temperature increased to 60°c when ethylene oxide gas was penetrated to the polymer bulk. therefore, during the sterilization process, dehp molecules were better mixed with pvc molecules with increasing the temperature up to 60°c. the polymer was annealed, and its mechanical properties were improved. 3.2 dehp release from pvc 3.2.1 dsc analysis table 3.3 and figure 3.1 show the second heating dsc curves of the four samples. as shown in table 3.3, the tg temperature decreased with increasing esbo (table 3.1). accordingly, the tg temperature decreased 4°c in the sample 5 compared to the sample 2 and more than 13°c in the sample 11 compared to the sample 8. decreasing the tg temperature with increasing esbo indicates that esbo, used as a stabilizer for dehp, can be simultaneously used as a secondary plasticizer. furthermore, the 288 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 existence of esbo in the pvc polymer bulk not only stabilizes dehp into the pvc structure but also reduces the tg temperature in the samples. table 3.1 tg comparison in the samples 2, 5, 8 and 11 sample no. tstart ( oc) tfinal ( oc) tg ( oc) 2 -23.10 -4.73 -13.38 5 -37.50 -27.43 -17.09 8 -24.45 -5.13 -14.22 11 -31.27 -23.63 -27.29 the results showed that the tg temperature of the polymer decreased after sterilization because of more molecular diffusion of the plasticizer into the polymer bulk. the above findings are confirmed by the tensile test results, where the samples exhibited a higher maximum strain after sterilization. as shown in the mechanical test results, maximum strain at break increased with an increase in the plasticizer content. the dsc test results indicated that maximum strain at break increased by decreasing tg and increasing the free volume in the polymer chains. in other words, the dsc test results confirmed the tensile test results. a decrease in tg indicated an increase in the plasticizer effect on pvc because of the synergistic effect of esbo and the sterilization process (fig. 3.3). figure 3.3: dsc curve of the samples 2, 5, 8 and 11 3.2.2 gas chromatography test analysis the dehp concentration in the samples 8 and 11 was calculated to be 1333.4948 ppm and 1362.5368 ppm, respectively, with a difference of 30 ppm that can be neglected (fig. 3.4) 289 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 figure 3.4 chromatograms of samples 8 (a) and 11 (b). given the results in figure 3.4 showing the release rate of dehp into the extraction solution, it can be concluded that esbo has no role in the migration of dehp from the polymer bulk. 3.3 hemolysis analysis samples with hemolysis more than 2% are considered slightly hemolytic, according to analysis standards of medical tools. according to the results, the samples had no considerable hemolysis effect; maximum hemolysis was in the sample 7 at 3.3%, containing 30% dehp (fig. 3.5). however, it appears that adding esbo to pvc decreased the pvc hemolysis effect. thus, the sample 10 with 0.22% hemolysis percentage and the samples 11 and 12 with 0.88% hemolysis percentage were known as non-hemolytic samples, while the samples 7 and 8 were slightly hemolytic with 3.3% and 2% hemolysis percentages, respectively. therefore, the results indicated that the samples were non-hemolytic. haishima et al. demonstrated that pvc plasticizers, including a 6-carbon ring such as dehp, had an effective role in suppressing blood cell hemolysis [27]. moreover, miller et al. reported that adding small amounts of dehp to red blood cells reduced their hemolysis to 20%, which were preserved at 4°c for 35 days [28, 29]. the present study confirms these results. 290 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 figure 3.5 hemolysis of the samples 7 – 12 4. conclusion for more than 50 years, dehp has been used as a plasticizer in pvc in blood preservation bags and also in most medical tools. ethylene oxide sterilization is an essential process in manufacturing medical tools. the results of tensile tests and heat analysis on the samples demonstrated that 5% esbo led to dehp stabilization within the polymer structure and improved its mechanical properties with decreasing temperature (tg) and increasing polymer flexibility. moreover, sterilization using ethylene oxide gas improved mechanical properties of the samples. the results of the gas chromatography test on solutions extracted from the sterilized samples, both with and without esbo, indicated that esbo had no effect on the migration of dehp molecules into the non-polar environment. according to the hemolysis test results, dehp release into the blood was extremely low, as dehp is a non-polar molecule whereas blood is a polar one. moreover, all samples containing 5% esbo were non-hemolytic. finally, it can be summarized that sterilization has no significant effect on the migration of the plasticizer from the polymer bulk; however, its annealing effects help improve the mechanical properties of pvc medical tools. 291 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 references [1] van der meer pf, reesink hw, panzer s, wong j, ismay s, keller a, (2014) should dehp be eliminated in blood bags?. vox sang 106(2):176-95,doi: 10.1111/vox.12099. [2] dumont lj, baker s, dumont df, (2012)., exploratory in vitro study of red blood cell storage containers formulated with an alternative plasticizer. transfusion 20(7):1439-45, doi:10.1111/j.1537-2995.2011.03506.x. [3] chiellini f, ferri m, morelli a, dipaola l, latini g. (2013) perspectives on alternatives to phthalate plasticized poly(vinyl chloride) in medical devices applications. prog in polym science 38(7): 1067-1088, doi:10.1016/j.progpolymsci.2013.03.001. [4] hakkarainen m, (2003) new pvc materials for medical applications—the release profile of pvc/polycaprolactone–polycarbonate aged in aqueous environments. polym degrad stab 80(3):451-458, doi:10.1016/s0141-3910(03)00029-6. [5] coltro l, pitta jb, madaleno e, (2013) performance evaluation of new plasticizers for stretch pvc films. polym test 32(2):272-278, doi:10.1016/j.polymertesting.2012.11.009. [6] radaniel t, genay s, simon n, et al., (2014) quantification of five plasticizers used in pvc tubing through high performance liquid chromatographic-uv detection. j chromatogr b analyt technol biomed life sci 965:158-63, doi: 10.1016/j.jchromb.2014.06.027. [7] lamba nm, courtney jm, gaylor jd, lowe gd. (2000)in vitro investigation of the blood response to medical grade pvc and the effect of heparin on the blood response. biomater 21(1):89-96, doi:10.1016/s0142-9612(99)00145-3. [8] labed v, obeid h, ressayre k. (2013) effect of relative humidity and temperature on pvc degradation under gamma irradiation: evolution of hcl production yields. radiat phys chem 84:26-29, doi:10.1016/j.radphyschem.2012.06.052. [9] haishima y, matsuda r, hayashi y, hasegawa c, yagami t, tsuchiya t. (2004) risk assessment of di(2-ethylhexyl)phthalate released from pvc blood circuits during hemodialysis and pump-oxygenation therapy. int j pharm 274(1-2):119-29, doi:10.1016/j.ijpharm.2004.01.009. [10] al salloum h, saunier j. tfayli a. yagoubi n. (2016) studying dehp migration in plasticized pvc used for blood bags by coupling raman confocal microscopy to uv spectroscopy. mater sci eng c mater biol appl 61:56-62, doi: 10.1016/j.msec.2015.12.008. [11] khorasani mt, mirzadeh h. (2007) effect of oxygen plasma treatment on surface charge and wettability of pvc blood bag—in vitro assay. radiat phys chem 76(6):1011-1016, doi:10.1016/j.radphyschem.2006.10.002. [12] mankidy r., wiseman s. ma h, giesy jp. (2013) biological impact of phthalates. toxicol lett 217(1): 50-8, doi:10.1016/j.toxlet.2012.11.025. [13] wang q, storm bk. (2005) separation and analysis of low molecular weight plasticizers in poly(vinyl chloride) tubes. polym test 24(3):290-300, doi:10.1016/j.polymertesting.2004.12.002. [14] haishima y, seshimo f, higuch t, (2005) development of a simple method for predicting the levels of di(2-ethylhexyl) phthalate migrated from pvc medical devices into pharmaceutical solutions. int j pharm 298(1): 126-42, doi: 10.1016/j.ijpharm.2005.04.009. [15] zygoura pd, paleologos ek, kontominas mg. (2011) migration levels of pvc plasticisers: effect of ionising radiation treatment. food chem 128(1):106-13, doi: 10.1016/j.foodchem.2011.03.002. [16] burgos n, jiménez a. (2009) degradation of poly(vinyl chloride) plasticized with non-phthalate plasticizers under sterilization conditions. polym degrad stab 94(9):1473-1478, doi:10.1016/j.polymdegradstab.2009.05.004. [17] fankhauser-noti a, fiselier k, biedermann-brem s, grob, k. (2006) assessment of epoxidized soy bean oil (esbo) migrating into foods: comparison with esbo-like epoxy fatty acids in our normal diet. food chem toxicol 44(8):1279-86, doi: 10.1016/j.fct.2006.02.005. [18] karmalm p, hjertberg t, jansson a, dahl r. (2009) thermal stability of poly(vinyl chloride) with epoxidised soybean oil as primary plasticizer. polym degrad stab 94(12):2275-2281, doi:10.1016/j.polymdegradstab.2009.07.019. 292 iium engineering journal, vol. 23, no. 1, 2022 poostchi et al. https://doi.org/10.31436/iiumej.v23i1.1769 [19] yu by, lee ar, kwak sy. (2012) gelation/fusion behavior of pvc plastisol with a cyclodextrin derivative and an anti-migration plasticizer in flexible pvc. eur polym j 48(5):885-895, doi:10.1016/j.eurpolymj.2012.02.008. [20] bueno-ferrer c, garrigós mc, jiménez a. (2010) characterization and thermal stability of poly(vinyl chloride) plasticized with epoxidized soybean oil for food packaging. polym degrad stab 95(11):2207-2212, doi:10.1016/j.polymdegradstab.2010.01.027. [21] hammarling l, gustavsson h. svensson k, karlsson s, oskarsson a. (1998) migration of epoxidized soya bean oil from plasticized pvc gaskets into baby food. food addit contam 15(2):203-8, doi: 10.1080/02652039809374631. [22] sanco d. european commission, health & consumer protection directorate-general. opinion on medical devices containing dehp plasticised pvc 2002, doi: 10.2772/45179. [23] sunny mc, ramesh p, mohanan pv, george ke. (2010) metallocene based polyolefin: a potential candidate for the replacement of flexible poly (vinyl chloride) in the medical field. polym for advanced technologies 21(9):621-631, doi:10.1002/pat.1475. [24] al salloum h, saunier j, aymes-chodur c, barakat h, yagoubi n. (2015) impact of the nature and concentration of plasticizers on the ability of pvc to sorb drug. int j pharm 496(2):664-75, doi:10.1016/j.ijpharm.2015.11.004. [25] sarath josh mk, pradeep s. balachandran s, sudha devi r, vijayalakshmi amma ks, benjamin s. (2012). temperatureand solvent-dependent migrations of di(2-ethylhexyl) phthalate, the hazardous plasticizer from commercial pvc blood storage bag. j polym res 19(7), doi:10.1007/s10965-012-9915-4. [26] jérémy p et al (2019). new spe-lc-ms/ms method for the simultaneous determination in urine of 22 metabolites of dehp and alternative plasticizers from pvc medical devices, talanta, 198:377-389 [27] haishima y, kawakami t, hasegawa c, tanoue a, yuba t, isama k, matsuoka a, niimi s. (2014). screening study on hemolysis suppression effect of an alternative plasticizer for the development of a novel blood container made of polyvinyl chloride. j biomed mater res b appl biomater 102(4):721-8, doi: 10.1002/jbm.b.33052. [28] estep tn, pedersen ra, miller tj, stupar kr. (1984) characterization of erythrocyte quality during the refrigerated storage of whole blood containing di-(2-ethylhexyl) phthalate. blood 64(6): 1270-6, doi:10.1182/blood.v64.6.1270.1270 [29] amandine d et al. (2019). simultaneous determination of di(2-ethylhexyl) phthalate and diisononylcyclohexane-1,2-dicarboxylate and their monoester metabolites in four labile blood products by liquid chromatography tandem mass spectrometry, journal of pharmaceutical and biomedical analysis, 181:1-11, doi:10.1016/j.jpba.2019.113063. 293 microsoft word 200 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 7 kinematic analysis of tricept parallel manipulator mir amin hosseini 1 and hamid-reza mohammadai daniali 2 1 department of mechanical engineering, islamic azad university, ayatollah amoli branch, amol, iran. 2 department of mechanical engineering, babol university of technology, babol, iran. ma.hosseini@iauamol.ac.ir; mohammadi@nit.ac.ir abstract: parallel manipulators consist of fixed and moving platforms connected to each other with some actuated links. they have some significant advantages over their serial counterparts. while, they suffer from relatively small workspaces, complex kinematics relations and highly singular points within their workspaces. in this paper, forward kinematics of tricept parallel manipulator is solved analytically and its workspace optimization is performed. this parallel manipulator has a complex degree of freedom, therefore leads to dimensional in-homogeneous jacobian matrices. thus, we divide some entries of the jacobian by units of length, thereby producing a new jacobian that is dimensionally homogeneous. moreover, its workspace is parameterized using some design parameters. then, using ga method, the workspace is optimized subjects to some geometric constraints. finally, dexterity of the design is evaluated. abstrak: manipulator selari terdiri daripada platform tetap dan bergerak yang bersambung antara satu sama lain dengan beberapa pautan bergerak. manipulator selari mempunyai beberapa kebaikan tertentu dibandingkan dengan yang bersamaan dengannya. walaupun ia mempunyai ruang kerja yang sempit, hubungan kinematik kompleks dan titik tunggal tinggi dalam linkungan ruang kerjanya. dalam kajian ini, kinematik ke hadapan manipulator selari tricept diselesaikan secara analisa dan pengoptimuman ruang kerja dijalankan. manipulator selari ini mempunyai darjah kebebasan yang kompleks, yang menyebabkan ia mendorong kepada kehomogenan dimensi matriks jacobian. catatan jacobian dibahagikan kepada unit panjang, dimana ia menghasilkan jacobian baru yang homogen dimensinya. tambahan, ruang kerjanya diparameterkan dengan menggunakan beberapa parameter reka bentuk. kemudian, dengan kaedah ga, ruang kerja mengoptimakan subjek kepada beberapa kekangan geometrik. akhirnya, kecakatan reka bentuk dinilaikan. keywords: kinematic; workspace; singularity; tricept 1. introduction parallel manipulators are closed-loop mechanisms and consist of two main elements coupled through several limbs acting in parallel. one body is designated as fixed and is called base, while the other is regarded as movable and hence is called moving platform or end-effector (ee) of the manipulator. typically, the number of actuators is equal to the number of degrees of freedom (dof) of the manipulator. parallel manipulators have some significant advantages over their serial counterparts, such as more rigidity and accuracy, higher force and torque capacity and higher speed [1, iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 8 2]. on the other hand, they suffer from relatively small workspaces, complex kinematics relations and highly singular points within their workspaces. choosing a set of geometric parameters so as to achieve optimal performance is of vital significance in robotics research. among all kinematic measures, workspace is the most important index in the design of a parallel manipulator. in this paper, the workspace of tricept is parameterized using some design parameters. moreover, some geometric constraints are considered in the problem. because of nonlinear discontinuous behavior of the problem, ga is used here to optimize the workspace [3]. for the workspace of the manipulator, we evaluate local conditioning indices of the jacobian matrices, as well. this paper is organized as follows. as a case study, for tricept parallel manipulator with both rotational and translational dof, forward and inverse kinematics are derived analytically. moreover, its jacobian matrix is derived and its singularity is studied. finally, we optimize the workspace of the manipulator and evaluate its local conditioning index as a measure of dexterity. 2. tricept parallel manipulator tricept parallel manipulator, as depicted in fig. 1, with two rotational and one translational dof was introduced by neumann [4]. siciliano [5] studied the inverse kinematics and manipulability of tricept. fig. 1: tricept manipulator. the manipulator has three actuated limbs which connect the base to the moving platform. each of these limbs consists of a spherical – prismatic – spherical (sps) kinematic chain, where only the prismatic joint is actuated. alternatively, one of the spherical joints can be replaced by a universal joint with no side effect on the kinematic equations. in either case, as each of the actuated limbs has mobility of at least 6-dof, a passive prismatic–universal (pu) limb exists at the centre of the mechanism to constrain the mobility of the moving platform to 3-dof. when the moving platform is parallel to the base, the two revolute axes of the universal joint of the centre passive limb, are parallel with the base frame’s x and y-axes. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 9 moving and global frames, namely; {p (uvw)} and {o (xyz)}, are attached to the moving and base platforms, respectively. 2.1 inverse kinematic inverse kinematic problem is stated as: given a desired pose of the ee find the actuator lengths. considering fig. 1, one can write the following, in which the columns of the matrix are the position vectors of the spherical joints: 3 2 3 2 3c s s c s 0 0 0 0 c -s 0 0 0 0 2 2 -s c s c c c c s c s s c s c s s c s 2 23 2 3 2 3 s c s c s 2 2 s c c s c s c c s 23 2 3 2 3 a a a a a c c cd d d a a a a ad d d a ad d d a a a ad c d c θ ψ θ ψ θ ψ ψ θ θ ψ θ ψ θ ψ θ θ ψ θ ψ θ θ ψ θ ψ θ ψ ψ ψ ψ ψ θ θ ψ θ θ ψ θ ψ θ  − −           = − +                 + − + + − − + −= − − − − + + + + + a c s c c 2 a d cθ ψ θ ψ           − + +    (1) where a is the moving platforms radius. moreover, c and s stand for the cos and sin functions, respectively; c is the length of the passive prismatic actuator of the middle limb. the position vectors of the universal joints are grouped in the columns of matrix b as: 3 2 3 2 3 0 2 2 0 0 0 b b b b b  − −     = −        b (2) in which b is the radius of the base platform. according to eqs. (1) and (2) the actuator lengths can be calculated as the followings: (3) 1 2 2 2 2 3 3 3 3 a b bd q c d abc cdc c c sθ θ ψ ψ θ= + + + − + − 2 2 2 2 (4) 2 2 1 1 1 ( ) ( ) 3 3 2 3 3 3 2 ( ) 3 a b c s q c d ab c s s c bd s s cdc c ac c s ψ θ θ ψ θ ψ ψ θ θ ψ θ ψ = + + + − − + + + + + + 2 2 2 2 (5) 3 2 1 1 1 ( ) ( ) 3 3 2 3 3 3 2 ( ) 3 a b c s q c d ab c s s c bd s s cdc c ac c s ψ θ θ ψ θ ψ ψ θ θ ψ θ ψ = + + + − + + + − + + − 2 2 2 2 2.2 forward kinematic forward kinematic is stated as: given a set of actuator lengths find the pose of the ee. in eqs.(3-5), we substitute now the equivalent expressions for sψ and cψ given below: 2 tan( ) 2 t ψ = (6) 2 2 2 2 1 t s t ψ = + (7) iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 10 2 2 2 2 1 1 t c t ψ − = + (8) similarly, equivalent expressions for sθ and cθ yields: 1 tan( ) 2 t θ = (9) 1 2 1 2 1 t s t θ = + (10) 2 1 2 1 1 1 t c t θ − = + (11) substituting the values of sψ, cψ, sθ and cθ from eqs.(6-11) into eqs.(3-5), upon simplifications leads to the following equations for the limbs; 2 2 2 t t 0 ; for i 1, 2, 3 i i i m n l =+ + = (12) in which the parameters for the three limbs are defined as: (13) 2 2 1 1 12 1 2 1 1 1 2 ( )[( )( 2 ) 1 3 3 3 4 2 ( )( ) ( 2 )] 3 3 33 a b m t c d q ab cd t bd a b t c d q ab cd = + + + − + + + + + + + + − − − 2 2 2 2 2 2 2 2 (14) 1 0n = (15) 2 2 1 1 12 1 2 1 1 1 2 ( )[( )( 2 ) 1 3 3 3 -4 2 ( )( ) ( 2 )] 3 3 33 a b l t c d q ab cd t bd a b t c d q ab cd = + + + − + − + + + + + + − − + 2 2 2 2 2 2 2 2 (16) 2 2 2 1 22 1 2 1 2 1 2 ( )[( )( 2 ) 1 3 3 3 2 2 1 ( )( ) ( 2 )] 3 3 33 a b m t c d q ab cd t ac bd a b t c d q ab cd = + + + − + + + + − + + + + − + − 2 2 2 2 2 2 2 2 (17) 2 2 1 12 1 1 2 ( )[( )(2 2 ) ( )( ) (2 2 )] 1+ 3 ab n t bd ac t bd ac t = − + + + (18) 2 2 2 1 22 1 2 1 2 1 1 ( )[( )( 2 ) 1 3 3 3 2 2 2 ( )( ) ( 2 )] 3 3 33 a b l t c d q ab cd t ac bd a b t c d q ab cd = + + + − − − + + + + + + + − − + 2 2 2 2 2 2 2 2 (19) 2 2 3 1 32 1 2 1 2 1 2 ( )[( )( 2 ) 1 3 3 3 2 2 1 ( )( ) ( 2 )] 3 3 33 a b m t c d q ab cd t ac bd a b t c d q ab cd = + + + − + + + + − + + + + − + − 2 2 2 2 2 2 2 2 (20) 2 3 1 12 1 1 -2 ( )[( )( 2 2 ) ( )( ) ( 2 2 )] 1+ 3 ab n t bd ac t bd ac t = − + + + − − iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 11 (21) 2 2 3 1 32 1 2 1 2 1 1 ( )[( )( 2 ) 1 3 3 3 2 2 2 ( )( ) ( 2 )] 3 3 33 a b l t c d q ab cd t ac bd a b t c d q ab cd = + + + − − − + + + + + + + − − + 2 2 2 2 2 2 2 2 subtracting a ratio of equations (12) for the second and the third limbs leads to; (22) ( )2 23 2 2 2 2 2 2 3 2 3 2 3( ) 0m m t n t l m m t n t l+ + − + + = (23) ( )2 23 2 2 2 2 2 2 3 2 3 2 3( ) 0l m t n t l l m t n t l+ + − + + = then, one can write: 3 2 2 3 3 2 2 3 2 3 2 2 3 3 2 2 3 0 1 0 m n m n m l m l t l m l m l n l n − −      =      − −      (24) eliminating t2 from the foregoing equation yields: ( ) ( ) 23 2 2 3 3 2 2 3 3 2 2 3( ) 0m n m n l n l n m l m l− − + − = (25) recalling the above process for the first and the second limbs; the third and the first limbs lead to the following equations, respectively; ( ) ( ) 22 1 1 2 2 1 1 2 2 1 1 2( ) 0m n m n l n l n m l m l− − + − = (26) ( ) ( ) 23 1 1 3 3 1 1 3 3 1 1 3( ) 0m n m n l n l n m l m l− − + − = (27) equations (25-27) are univariate polynomials of degree eight and can be solved for t1. the common roots of these equations are the solutions sought. 3. jacobian and singularity analysis 3.1 jacobian matrix generally, the ee twist array and the actuators velocity vector are related as: x q =j x j q&& (28) in which jx and jq are the jacobians; x& is the three dimensional twist array; q& is the three dimensional actuator velocity vector as: (29) [ ] t c ψ θ=x &&& & (30) [ ] t 1 2 3 l l l=q & & && taking the first time derivatives of the i th limb vector close loop equation [5], yields; (31) ( )( )t tli li p i il+ × + =n c n ω r a d && rewriting the above equation for the three limbs leads to: iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 12 (32) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) 1 1 l1 1 l1 2 2 l2 2 l2 3 3 l3 3 l3 1 2 3 l z x y l z x y l z x y n n n c l l l ψ θ + × + × + × + × + × + × =                          r a d n r a d n r a d n r a d n r a d n r a d n && && && therefore, this equation can be written as a more general form of eq.(28), in which: (33) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) 1 1 l1 1 l1 2 2 l2 2 l2 3 3 l3 3 l3 l z x y l z x y l z x y x n n n + × + × + × + × + × + ×    =      r a d n r a d n r a d n r a d n r a d n r a d n j (34) 3 3q × =j i moreover, one can write eq.(28) as: (35) =x jq&& in which (36) 1 x − =j j 3.2 singularity analysis algebraically, singularity deals with the rank deficiency of the associated jacobian matrices. while geometrically, it is observed that the manipulator gains at least one additional uncontrollable dof or loses one or a few dof in singular points. the singularities encountered in parallel manipulators can be divided into three main groups [6]. the first type of singularity occurs when the manipulator reaches the boundary of its workspace. in such a configuration, different branches of the inverse kinematic problem meet, det( q j ) vanishes and one actuator does not produce any motion of the ee. at the second type of singularity, the ee can move in one or more directions and cannot resist against the force or torques in those directions while the actuators are locked. as opposed to the first one, this type of singularity occurs whenever different branches of the forward kinematic problem meet and det ( x j ) vanishes. the third type of singularity occurs in the case that both types of the foregoing singularities occur, simultaneously [6]. condition number of the jacobian matrix is an index to measure the distance from singularity. it will increase in the vicinity of the singular points. the inverse of this index, namely local conditioning index is commonly used for a measure of dexterity in robotic manipulators [7]. tricept has a complex degree of freedom; therefore its condition number depends on the singular values of the dimensional in-homogeneous jacobian. here, we divide the jacobian entries by units of length, thereby producing a new jacobian that is dimensionally homogeneous. by multiplying the associated entries of the twist array to the same length, iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 13 we made this array homogeneous, as well. this implies some sort of tradeoff between position and orientation components of the twist array. 3.3 weighted factor method dividing the second and the third columns of the jacobian matrix of eq. 28 by a length and multiply the second and the third coordinates of the twist vector to the same length [8] leads to the following dimensionally homogeneous relation: (37) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) 1 11 1 1 1 2 22 2 2 2 3 3 33 3 3 yx l z yx l z yx l z n l l c l n l l l l l l n l l ψ θ + ×+ × + ×+ × = + ×+ ×                                  ll ll ll r a d nr a d n r a d nr a d n r a d nr a d n && && && 4. workspace analysis in this section, we study the workspace of tricept manipulator based on combination of analytical method and numerical one. 4.1 algorithm in order to generate the workspace of tricept parallel manipulator, we divide the three dimensional ψ-θ-z workspace of the moving platform into a series of subworkspaces that are parallel to ψ-θ plane. then a numerical searching method is adopted to determine the boundary of the sub-workspaces. finally, the volume of workspace is calculated quantitatively. the searching method adopted here is similar to the one used in [9]. fig. 2: boundary points of a sub-workspace. in the particular sub-workspace at elevation zi (within the workspace), to determine the boundary of the sub-workspace one may find trajectories formed by the end of polar vector ρi rotating about z axis from 0 to 2π, (see fig. 2). when the boundary point in the direction of ρi is found as pi (ρcosα, ρsinα, zi); where ρi is the distance between zi and pi, α will be increased by ∆α, and the next point will be found, similarly. the determination of point pi is based on the inverse kinematics of the tricept. when searching the next boundary point pi+1, we set the initial value of ρi+1 as ρi, and judge whether point pi+1 is in iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 14 the range of workspace; if yes, then increase ρi+1, if not, then decrease ρi+1 until point pi+1 is on the boundary of the workspace. once the boundary points in the sub-workspace are all searched out, zi will be decreased by ∆z, and the new searching will be performed again. moreover, when α is increased by ∆α, the unit volume of the corresponding workspace can be expressed approximately as: 2 2 i dv z α πρ π ∆ = ∆ (38) therefore, the volume of the workspace can be calculated as: 2 1 2 max i min z 2 i z z 0 v z π α ρ α = = = ∆ ∆∑ ∑ (39) 4.2 geometric constraints there are some geometric constraints in the design process. these constraints are the upper and lower limits of actuators, spherical and universal joints, links lengths and platforms radiuses. it is simple to calculate the cone angle of joints (ζ) by using the geometric relations between actuators vector and ee pose. the geometric constraints of the tricept robot, is given in table 1. table 1: geometric constraints of the tricept manipulator. a (mm) b (mm) d (mm) ζ (deg) actuator (mm) 200300 300500 20200 ±60 400-750 5. ga optimization one of the drawbacks of parallel manipulators is their limited workspace volume. here, we apply genetic algorithm for workspace volume optimization. objective function: for achieving the desired workspace with maximum volume the objective function defined as follow: (40) max( )v v ∗ = where v and v ∗ are workspace volumes with unit of mm.rad 2 and workspace volume without considering any constraints (like conditioning index) respectively which can be estimated by the foregoing algorithm. all the parameters which play a role on the workspace volume are considered as the design parameters. they are the moving and base platform radiuses (a and b) and the upper part of passive link length (d). (41) [ ] t , ,a b d=λ iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 15 therefore, the problem can be stated as: (42) v * =max(v(d, ra, rb)) subject to: 1200< a < 300, 300 < b < 500, 20 <d <200 2400<actuator length(l)<750, -60< ζi<60 deg this optimization problem is solved by ga and leads to the data given in table 2, in which the maximum workspace is 944.2176 (mm.rad 2 ). moreover, the workspace is illustrated in fig. 3. table 2: optimization results for maximum workspace. b (mm) a (mm) d (mm) v * (mm.rad 2 ) no. of iteration 200 300.062 20 944.2176 51 fig. 3: maximum workspace. finally, we evaluate the distance from singularity by means of local conditioning index throughout the workspace of the tricept. this index for the optimized design of the table ii is within 0.57 and 0.61. moreover, the index for different elevations is depicted in fig. 4. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering hosseini and daniali 16 fig. 4: local conditioning index in different elevations. it is obvious from this figure that the design does not have any singular points within its workspace; therefore, it is well-conditioned. 6. conclusions in this paper the workspace optimization of tricept has been performed. this parallel manipulator has a complex degree of freedom and has leaded to dimensional inhomogeneous jacobian matrices. therefore, we divided some entries of the jacobian by units of length, thereby producing a new jacobian that is dimensionally homogeneous. by multiplying the associated entries of the twist array to the same length, we made this array homogeneous as well. for the platform, the workspace was parameterized using some design parameters. then, using ga method, the workspace was optimized subjects to some geometric constraints. moreover, the evaluation of local conditioning index revealed the dexterity of the design. references [1] j. angeles, “fundamentals of robotic mechanical systems,” new york, usa: springerverlag; 1997. [2] j.-p. merlet, “parallel robots,”kluwer academic publishers, 2000. [3] s.-d. stan, v. maties, r. balan and c. lapusan, “optimization of a hexapod micro parallel robot using genetic algorithms,” innovations and advanced techniques in systems, computing sciences and software engineering, pages 37-42, 2008. [4] k.-e. neumann. us patent 4,732,525, mar. 22, 1988. [5] b. siciliano, “the tricept robot: inverse kinematics, manipulability analysis and closed-loop direct kinematics algorithm,” robotica, vol. 17, no. 4, pp. 437445, 1999. [6] h. r. mohammadi daniali, p. j. zsombor-murray, and j. angeles, “singularity analysis of planar parallel manipulators” mechanism and machine theory, vol. 30, no. 5, pp. 665-678, 1995. [7] h. r. mohammadi daniali, p. j. zsombor-murray, and j. angeles, “the isotropic design of two general classes of planar parallel manipulators” journal of robotic systems, vol. 12, no. 12, pp. 795-805, 1995. [8] m.a. hosseini and h.r. m. daniali, “weighted local conditioning index of a positioning and orienting parallel manipulator”, unpublished. [9] j.a. carretero, r.p. podhorodeski, m.a. nahon and c.m. gosselin, “kinematic analysis and optimization of a new three degree-of freedom spatial parallel manipulator,” journal of mechanical design, vol 122, no. 1, pp. 17–24, 2000. microsoft word revised journal-iium46-3.doc iium engineering journal, vol.3 , no.1 , 2002 a.l. ahmad et al. 25 coagulation-sedimentation-extraction pretreatment methods for the removal of suspended solids and residual oil from palm oil mill effluent (pome) abdul latif ahmad, norliza ibrahim , suzylawati ismail and subhash bhatia school of chemical engineering, usm, engineering campus,14300 nibong tebal, pulau pinang tel: 04-5937788 fax: 04-5941013 chlatif@eng.usm.my abstract: suspended solids and residual oil removal in a liquid are relevant to numerous research areas and industry. the suspended solid cannot be removed completely by plain settling. large and heavy particles can settle out readily, but smaller and lighter particles settle very slowly or in some cases do not settle at all. because of this, it requires efficient physicalchemical pretreatment methods. our current research is to study the pretreatment methods in the removal of suspended solids and residual oil content in pome. preliminary analysis shows that pome contains 40,000 mg/l suspended solid and 4,000 mg/l oil and grease content that relatively very high compared to the maximum allowable limit by the malaysian department of environment which are only 400 mg/l and 50 mg/l respectively. the methods chosen were coagulationsedimentation method for suspended solids removal and solvent extraction for residual oil removal. jar test apparatus was used as the standard procedure for benchscale testing and alum was used as the coagulant. parameters studied were alum dosage, mixing time, mixing speed, sedimentation time and ph. for removal of residual oil, six different organic solvents; n-hexane, n-heptane, benzene, petroleum ether, pentane and petroleum benzene were used. for every solvent the effect of solvent ratio, mixing time, mixing speed and ph were analyzed. the results show that the optimum conditions in removal of suspended solid from pome were at ph 4.11, sedimentation time of 100 minutes and 150 rpm mixing speed with 1.5 hr mixing time. nhexane give the best performance in extracting residual oil from pome with solvent to pome ratio of 6:10. it was estimated about 0.54 grams of oil and grease can be extracted with optimum variables at ph 4, mixing speed of 200 rpm, and 20 minutes mixing time. key words: palm oil mill effluent, coagulation, suspended solid, residual oil, solvent extraction. 1. introduction palm oil mill effluent (pome) represented the highest by-products generated by palm oil mills, which is about 21 %. pome is a colloidal suspension of 95%-96% water, 0.6% 0.7% oil and 4%-5% total solids including 2%-4% suspended solids originated from the mixture of a sterilizer condensate, separator sludge and hydrocyclone wastewater [1]. the quantity of pome produced is about 60% for every tonne of fresh fruit bunches (ffb) processed. thus, an average of 30 tonnes ffb/hr mill in this country will generate about 18 – 19.5 tonnes effluent/hr [2]. with over 300 palm oil mills in malaysia, generation of large volumes of effluent could give significant impact to the environment since the characteristics of pome are extremely polluting with its high organic content. the characteristic of raw pome is shown in table 1[1]. the discharge of untreated pome into the river will undergo natural decomposition during which dissolved oxygen in the river water is rapidly depleted. this will certainly result in the decline or destruction of aquatic lives and deterioration of natural ecosystem. therefore pome requires a sound and efficient management system in utilization, treatment and disposal. table 1 characteristics of palm oil mill effluent.[1] parameter conc.* element conc.* ph 4.7 phosphorus 180 oil and grease 4,000 potassium 2,270 biochemical oxygen demand 25,000 magnesium 615 chemical oxygen demand 50,000 calcium 439 total solids 40,500 boron 7.6 suspended solids 18,000 iron 46.5 total volatile solids 34,000 manganese 2.0 ammoniacal nitrogen 35 copper 0.89 total nitrogen 750 zinc 2.3 *all parameters in mg/ l except ph. looking at the seriousness of environmental impact by palm oil industry, the government of malaysia has enacted the malaysian environmental quality act, 1974 and environmental quality (prescribed premises)(crude palm oil) regulations 1977. the malaysian department of environment, doe, has set the discharge standards for pome as shown in table 2 [3]. therefore, the palm oil industry faces the challenge of balancing the environmental protection, its economic viability and sustainable development. there is an urgent need to iium engineering journal, vol.3 , no.1 , 2002 a.l. ahmad et al. 26 find a way to preserve the environment of our country while keeping her economy healthy. table 2 parameter limits for watercourse discharge of pome [3] biochemical oxygen demand (bod) (mg/l) 100 suspended solids (mg/ l) 400 oil and grease (mg/ l) 50 ammoniacal nitrogen (mg/l) 150 total nitrogen (mg/l) 200 ph 5-9 bod – sample incubated for 3 days at 30 o c .several innovative treatment technologies have been developed and applied to palm oil mills to treat pome, and conventional biological treatments of anaerobic or facultative digestion are the most commonly used [4]. however, these biological treatment systems need proper maintenance and monitoring as the processes rely solely on microorganisms to break down the pollutants. the microorganisms are very sensitive to changes in the environment and thus great care has to be taken to ensure that a conducive environment is maintained for the microorganisms to thrive in. besides, it also generates vast amount of biogas. this biogas contains methane, carbon dioxide and trace amount of hydrogen sulphide where these gases are corrosive and odorous. besides the biological treatment, evaporation process has been suggested to treat pome [1]. by using pome containing 3-4 % total solids as feed, about 85 % of the water in the pome can be recovered as distillate. unfortunately energy requirement is a major constrain in this process. another physical treatment method, air-floatation systems was tested on a pilot plant scale. in this system, tiny, bubbles of air or oxygen are released in the effluent. in rising the surface of the effluent, this bubbles carry suspended solids to the surface where they are easily removed. however it was found to be very inefficient and unreliable [5]. full scale tests were carried out using centrifuge process. the suspended solids are separated from the liquid or concentrated by means of centrifuges but the system found to be unsatisfactory due to high wear rates and erratic operation [5]. treatment of palm oil mill effluent (pome) requires a sound and efficient system in facing the current challenge in compliance to the discharge standard regulation, environmental protection and economic viability. biological treatment systems are widely applied for treating pome however there are still some mills that fail to comply with the regulatory standard set by the malaysian department of environment (doe). therefore an alternative pome treatment system based on membrane separation technology is being studied and a promising result was observed. the proposed treatment consists of two stages of treatment; series of pretreatment processes (i.e. coagulation-sedimentationsolvent extraction) and membrane separation processes. 1.1 coagulation coagulation process can alter the suspended particles so that they can adhere to each other. during coagulation, a positive metal ion is added to water to reduce the surface charge to the point where the particles are not repelled from each other. chemicals (coagulant) are added to the water to bring the nonsettling particles together into larger, heavier masses of solids called floc [6]. technically, coagulation applies for the removal of colloidal particles or suspended solids. the most commonly used coagulants are [7]:  alum (aluminium sulfate), al2(so4)3.14h2o is the most common coagulant and is often used in conjunction with cationic polymers.  polyaluminium chloride, al(oh)x(cl)y, is efficient in some waters requiring less ph adjustment and producing less sludge.  ferric chloride, fecl3, may be more effective than alum in some application.  ferric sulfate, fe2(so4)3, is effective in some waters and more economical in some locations.  cationic polymers can be used alone as the primary coagulant or in conjunction with aluminum or iron coagulants. eilbeck and mattock [8] presented a list of common coagulants in treating wastewater from various industries such as food, textiles, pulp and paper. they found that aluminum sulphate was the most suitable coagulant. while a study carried out by lin et al. [9] found that coagulation using polyaluminum chloride (pac) and polymer (coagulation aid) was found to be effective as a pretreatment for partial removal of suspended solids, color and chemical oxygen demand of many industrial wastewaters. 1.2 solvent extraction solvent extraction method lately is the most powerful separation and purification tool in the process industries. it is used commercially in hydrometallurgy (including nuclear industry) and widely used within the chemical industry including organic chemical, petrochemical and pharmaceuticals. the principle is illustrated in a separatory funnel which contains two layers of liquids. one that is generally water (saq) and the other, generally, an organic solvent (sorg). normally the organic solvent has a lower density than water, but the opposite situation is also possible. a solute a, which is initially dissolved in only one of the two liquids, eventually distributes between the two phases. when this distribution reaches equilibrium, the solute is at concentration [a]aq in the aqueous layer and at concentration [a]org in the organic layer. the distribution ratio of the solute [10], d is defined as d = [a]org / [a]aq (1) “the total analytical concentration of the substance in the organic phase to its total analytical concentration in the aqueous phase, usually measured at equilibrium” [11], irresspective of whether the organic phase is the lighter or heavier one. iium engineering journal, vol.3 , no.1 , 2002 a.l. ahmad et al. 27 process efficiency will depend on the equilibrium distribution of the constituents between the wastewater and the extracting solvent and the kinetics of mass transfer between the two liquid phases. to increase efficiency, the solvent-to-waste ratio can be increased, or multiple extraction stages can be employed. solvent extraction has assumed importance in virtually all vegetable oil recovery plant. it recovers up to 98 percent of cottonseed oil. the soybean, which has low oil content, but whose physical structure is particularly suited to solvent extraction has been responsible for this development and solvent hexane is used for this purpose [12]. while in pharmaceutical industry, solvent extraction method is extensively used for purification and concentration of penicillin by utilizing n-butyl acetate or amyl acetate as solvent [10]. 2. material and methods 2.1 experimental materials pome was collected from felcra nasaruddin palm oil mill, ipoh, perak and cooled in a refrigerator from the temperature of 90oc to 0oc. technical grade alum [al2(so4)3. xh2o (x=13-16 h2o)] obtained from merck, germany, was used for the preparation of the alum solution. six technical grade solvents obtained from quicklab sdn. bhd. (perak); n-hexane, benzene, pentane, petroleum benzene, petroleum ether, and nheptane were used as solvents in solvent extraction process. in the present study, benzene has been chosen only to study its performance for comparison with other solvent, although benzene is known to be toxic and carcinogen. 2.2 experimental procedure 2.1.1. removal of suspended solid using coagulation and sedimentation process the jar test was performed using six beakers filled with 250 ml of pome and diluted with 750 ml of distilled water. 1 grams of aluminium sulphate (alum) equal to 1000 mg/l was added in each beaker. each beaker was mixed and flocculated uniformly using rapid mixing rate of 150 rpm for 10 minutes and slow mixing rate of 25 rpm for 20 minutes. the mixture was left to settle for 30 minutes. the parameters varied were alum dosage (1,000 – 7,000 mg/l), mixing speed (0 – 300 rpm), mixing time (0 – 3 hours), ph (4 – 9) and sedimentation time ( 0 – 420 minutes). 2.1.2. removal of residual oil using solvent extraction the experiments were conducted to evaluate the performance of six types of organic solvents, namely nhexane, benzene, petroleum benzene, petroleum ether, pentane and n-heptane in extracting residual oil from pome. it was performed using three beakers filled with 300 ml of pome. then, each beaker was filled with 60 ml of solvent and covered with an aluminum foil to prevent solvent evaporation and mixed in a flocculator for 5 minutes at the speed of 50 rpm. the mixture was left for another 5 minutes to let it separated into two phases. these two phases were then separated into two different beakers to be analyzed. in solvent extraction process, several parameters were varied. the variables were ratio of solvent to pome (2:10 – 10:10), mixing rate (50 – 250 rpm), mixing time (0 – 25 minutes) and ph of the sample (4 – 9). 3. analytical method after sedimentation, 5 ml of the supernatant sample was pipetted and diluted to 25 ml with distilled water. the samples were analyzed for turbidity using a 2100p turbidity meter (hach. company, colo, u.s.a.). this value was comparable to the concentration of suspended solids in sample. in order to determine the oil concentration in the treated sample, the extracted pome was transferred to a separating funnel. the pome container was rinsed with 30 ml of petroleum ether and solvent washings were added to the separating funnel. the mixture was shaken vigorously for 2 minutes and the layer was left for further separation for 5 minutes. the aqueous layer was drained into a sample container. the extraction was repeated with another two portion of 30 ml petroleum ether. the solvent layer was drained through a funnel containing a filter paper and 2 g anhydrous sodium sulphate, both of which have been solvent-rinsed, into a clean conical flask. the solvent was then distilled off using the rotary evaporator. the drying was completed in the oven at 103 oc for 5 to 10 minutes. the flask was cooled in a desiccator for about 30 min and weighed. the drying and cooling steps were repeated until the weight becomes constant to calculate the concentration of residual oil extracted. the experiment was repeated 3 times and the results were reproducible within an error of ± 5%. for determining the concentration of residual oil after the adsorption process, a calibration curve was made. this calibration correlates the concentration of residual oil with its absorbance. the concentration of residual oil was obtained from the solvent extraction process while its absorbance was measured by using a spectrophotometer (cecil 100 series) at a wavelength of 444 nm. the overall mass balance was verified by considering the removal efficiency at various stages in the process. 4. results and discussion 4.1 coagulation the figures presented below show the results of batch experimental procedure for five samples that were represented as a, b, c, d and e respectively. a) effect of alum dosage iium engineering journal, vol.3 , no.1 , 2002 a.l. ahmad et al. 28 the effect of alum dosage on the coagulation process is given in fig. 1. alum dosage was varied from 0 to 7,000 mg/l. while other parameters were kept constant at ph 4, 150 rpm for mixing rate, 10 minutes of mixing time and 30 minutes for sedimentation time. figure 2 shows a significant reduction in turbidity value with the increase in alum dosage until it reached the concentration of 4,000 mg/l. the turbidity reduced from 14,080 ntu to 1,615 ntu. the trend shows the increased in alum dosage leads to the reduction in turbidity. this phenomenon was explained by the chemical reaction during coagulation process [13] al3+ + 4h2o ⇌ al(oh)-4 + 4 h+ (2) whereby the turbidity of the sample were reduced due to the formation of the aluminium hydroxide flocs that settle to the bottom of the beaker. however, after reaching 4,000 mg/l point, the turbidity value almost reached steady state even with the increased of alum dosage. this result shows that the optimum coagulation will occur when the concentration of the alum is 4,000 mg/l. at this dosage, the zeta potential is zero and this is defined as the isoelectric point. zeta potential is used since it can represent the stability of the particle in the waste. at isoelectric point, almost all the particles charge have been neutralized by the high valence cations and this induce coagulation and precipitation. fig. 1: the effect of alum dosage on suspended solid removal from pome fig. 2: the effect of ph on suspended solid removal from pome b) effect of ph turbidity vs alum dosage 0 2000 4000 6000 8000 10000 12000 14000 16000 0 1000 2000 3000 4000 5000 6000 7000 alum dosage (mg/l) tu rb id ity (n tu ) a b c d e turbidity vs ph 0 500 1000 1500 2000 2500 3000 3500 4 5 6 7 8 9 ph t ur bi di ty ( n t u ) a b c d e iium engineering journal, vol.3 , no.1 , 2002 a.l. ahmad et al. 29 fig. 2 shows the effect of ph on flocculation process for the sample of pome. the value of ph were varied from ph 4 to ph 9 with constant parameters of alum dosage by 4,000 mg/l, 150 rpm mixing rate, 10 minutes mixing time and 30 minutes sedimentation time. it was observed that the best supernatant quality (low turbidity value) was obtained in acidic range, ph 4 to ph 6, while in neutral and alkaline range the turbidity value increased. this explained that in acidic range, particles in pome sample form an unstable suspension and coagulate among them. besides, the changes in ph value also give the effect of electric charges to the particles, whereby it influenced the particle stability [14]. the concentration of h+ ions and the density for negative ions on the surface of particles is low. thus particles become unstable and attraction forces in between particles keep increasing which lead to formation of bigger coagulant. while in alkaline range, the quality of the supernatant is poor since the particles form a stable suspensions and coagulation process is not very effective. in addition higher molecular weight of coagulant prevents the process for destabilized scattered particles. fig. 3: the effect of mixing speed on suspended solid removal from pome fig. 4: the effect of mixing time on suspended solid turbidity vs mixing speed 0 500 1000 1500 2000 2500 0 50 100 150 200 250 300 mixing speed (rpm) t ur bi di ty ( n t u ) a b c d e turbidity vs mixing time 0 500 1000 1500 2000 2500 0 0.5 1 1.5 2 2.5 3 mixing time (hr) t ur bi di ty ( n t u ) a b c d e iium engineering journal, vol.3 , no.1 , 2002 a.l. ahmad et al. 30 c) effect of mixing speed the effect of mixing speed on coagulation process is shown in fig. 3. in this experiment the mixing speed were varied from 0 to 300 rpm. other parameters were kept constant at ph 4, 4,000 mg/l of alum dosage, 10 minutes mixing time and 30 minutes of sedimentation time. it is obviously seen from the figure that slow mixing speed, range 0 to 100 rpm, is not critical for treating pome. however once the mixing speed is increased to 150 rpm, a dramatically reduction is shown in turbidity value. this is explained that within this mixing rate it provides a suitable condition for coagulation process. however, the turbidity value increases again when the mixing speed is increased. this phenomenon demonstrates that, too high mixing speed will break-up the flocs produced and give poor results on turbidity value. therefore from the results the optimum mixing speed is 150 rpm. d) effect of mixing time the effect of mixing time to the coagulation process is shown in fig. 4. this experiment was carried out under the constant parameters at ph 4, alum dosage of 4000 mg/l, 150 rpm of mixing speed and 30 minutes sedimentation time. the mixing time is varied from 0 to 3 hours. theoretically, mixing process give a chance to the particles contained in the pome to coagulate to each other. from the graph, the reduction in turbidity started once the mixing time is increase from 0 to 1.5 hours and this represent the condition where flocs are produced and settled to the bottom of the beaker. the turbidity value slightly increased after mixing time exceeded 1.5 hours. this shows that the reaction of coagulant agent and the particles are almost completed at 1.5 hours. removal from pome e) effect of sedimentation time the effect of sedimentation time is given in fig. 5. after the addition of 4,000 mg/l of alum dosage to the pome and proceed with mixing speed of 150 rpm for 1.5 hours of mixing time at ph 4, particles will attract to each other and flocs will be performed. from the graph it can be seen clearly that there is a drastic reduction in turbidity value once the sample is left for 0 to 100 minutes of sedimentation time. however the value become constant once it exceeds 100 minutes of sedimentation time. this result explained that almost all flocs produced after the coagulation and mixing process have settled to the bottom of the sludge layer after 100 minutes. the settling process is mainly affected by the gravity where heavier flocs will settle faster than dispersed particles. 4.2 solvent extraction all the figures presented show only the average value of repeating the experiment for five times of all the solvent. a) effect of solvent-pome ratio it is clear from fig. 6, that as the amount of solvent increases, the percentage of oil extracted also increases. but, after a certain point, the increment in the percentage of oil extracted becomes constant. even though more oil can be extracted continuously until the solvent-palm oil mill effluent ratio reaches 10:10, but the amount of oil extracted after the ratio of 4:10, are comparable for almost all the solvents. the straight line portion of the curve in the graph show that all the fatty acids content in pome has been extracted to the solvent. fig. 5: the effect of sedimentation time on suspended solid removal from pome turbidity vs sedimentation time 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 60 120 180 240 300 360 420 sedimentation time (minute) t ur bi di ty ( n t u ) a b c d e iium engineering journal, vol.3 , no.1 , 2002 a.l. ahmad et al. 31 fig. 6: the effect of solvent-pome ratio on extraction of residual oil from pome b) effect of mixing speed as shown in fig. 7, the rate of mass transfer increases with speed of mixing. therefore increasing the mixing speed will increase the value of oil extracted from the pome. the maximum extraction occurs at the speed of 200 rpm for all the solvents. as the speed of mixing increases, the chances for the molecules to meet one another becomes more and this makes the rate of extraction increases. however, after mixing speed of 200 rpm, the oil extracted becomes constant. this is because almost all fatty acids have been extracted from pome. increasing the speed after this stage will not result any further extraction of oil. c) effect of mixing time the oil extraction time of different solvents is shown in fig. 8. result on mixing time gives almost the same trend with the mixing speed. the oil extracted increased rapidly initially and reaching a constant value after 20 minutes. this is because, increasing the mixing time may not result further extraction of oil once equilibrium has been attained. therefore, it is obviously seen from the figure that the equilibrium can be achieved after 20 minutes of running the experiment. fig. 7: the effect of mixing speed on extraction of residual oil from pome 0.0500 0.1000 0.1500 0.2000 0.2500 0.3000 0 0.2 0.4 0.6 0.8 1 1.2 solvent:pome ratio o il ex tr ac te d (g ) n-hexane benzene pet. benzene pet. ether pentane n-heptane 0.0000 0.0500 0.1000 0.1500 0.2000 0.2500 0.3000 0 50 100 150 200 250 mixing speed (rpm) o il ex tr ac te d (g ) n-hexane benzene pet. benzene pet. ether pentane n-heptane iium engineering journal, vol.3 , no.1 , 2002 a.l. ahmad et al. 32 fig. 8: the effect of mixing time on extraction of residual oil from pome d) effect of ph for all the solvent used, the reading of oil extracted were low at ph ≤ 7 but reach maximum at ph 9 as shown in fig. 9. however it does not mean that the residual oil extraction is effective at ph 9 because, during studying the effect of ph for solvent extraction, naoh is being added to pome to increase the ph, however this activity will lead to the saponification process which means, the residual oil react or undergo hydrolysis with sodium hydroxide to produce glycerol and a fatty acid salt called soap which is more soluble in water rather than organic solvent. therefore, while determining the oil concentration in treated sample using petroleum ether, the weight of oil found to be less at ph 9 since the oil was hydrolyzed inside the pome and not being extracted to the solvent. thus utilizing the original ph of pome for residual oil extraction is preferred rather than adjusting the ph using strong acid or alkali to avoid hydrolysis reaction. fig. 9: the effect of ph on extraction of residual oil from pome 0.0000 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 4 7 9 ph o il ex tr ac te d (g ) n-hexane benzene pet. benzene pet. ether pentane n-heptane 0.0500 0.1000 0.1500 0.2000 0.2500 0.3000 0 5 10 15 20 25 mixing time (min) o il ex tr ac te d (g ) n-hexane benzene pet. benzene pet. ether pentane n-heptane iium engineering journal, vol.3 , no.1 , 2002 a.l. ahmad et al. 33 5. conclusions from the analysis result, it is clearly demonstrate that various parameters used in this experiment contribute their effect to the coagulation process. the optimum condition for suspended solids removal using a jar test process can be obtained at alum dosage of 4,000 mg/l at ph 4, mixing rate of 150 rpm and optimum mixing time of 1.5 hours. for sedimentation the optimum settling time is 100 minutes. at this optimum condition, the ntu reading was reduced from 14,080 ntu to 984 ntu whereby comparing to the calibration curve, the actual suspended solids content has been successfully reduced to 268 mg/l which is lower than the allowable limit by malaysian department of environment (doe) that is 400 mg/l. in solvent extraction, the optimum value of the solvent to pome ratio is 6:10 and mixing speed of 200 rpm for 20 minutes at original ph of pome, ph 4, was obtained with the oil concentration reduced from 1089 mg/l to 54 mg/l. references [1] a. n. ma, “environmental management for the palm oil industry”. palm oil developments, no. 30, pp. 1-10, 2000. [2] a. m. rusnani, a. n. ma, and e. hisham, “bod, tss and colour reduction of palm oil mill effluent using boiler fly ash”, porim bulletin, no. 39, pp. 25-31, 1999. [3] j. hanif, “natural rubber serum quality”, seminar hari alam sekitar pengurusan effluent kelapa sawit dan getah, melaka, 21 disember 1994. [4] s. k. quah, k. h. lim, d. gillies, b. j. wood, and j. kanagaratnam, “sime darby pome treatment and land application systems”, proceedings of regional workshop on palm oil mill technology and effluent treatment, porim, kuala lumpur, pp. 193-200, 1982. [5] s. mahabot and a.r. harun, effluent treatment system for felda’s palm oil mill, bahagian khidmat teknik, perbadanan kilang felda,kuala lumpur, 1990. [6] m.l. davis and d. a. cornwell, introduction to environmental engineering 2nd ed., mcgraw-hill, u.s.a, 1991. [7] g.m. wesner, water treatment plant design 3rd ed., u.s.a. : mcgraw-hill, 1998. [8] w. j. eilbeck and g. mattock, chemical processes in waste water treatment, england: ellis horwood limited. chapter 11, 1987. [9] s.h. lin, h.y. chan and h.g. leu, “treatment of wastewater effluent from an industrial park for agricultural irrigation”, desalination, no. 128, pp. 257267, 2000. [10] j. rydberg, introduction to solvent extraction, marcel dekker, new york, 1992. [11] h. freiser and g. h. nancollas, compendium of analytical nomenclature. definitive rules 1987. iupac, blackwell science publications, oxford, 1987. [12] t. a. george, shreve’s chemical process industries, fifth edition, mc.graw hill, singapore, pp. 508 – 528, 1984. [13] w.w. jr. eckenfelder, industrial water pollution water control, new york: mcgraw-hill, 1989. [14] s. rohrsetzer, i. paszli and f. csempesz, “colloid stability of electrostatically stabilized sols. part iii: the role of ph in hydration coagulation and peptization of sio2and al2o3sols”, colloid polym. sci., no. 276, pp. 260 – 266, 1998. biography of the authors associate prof. dr. abdul latif ahmad is currently the deputy dean (research and postgraduate study) at school of chemical engineering, engineering campus, universiti sains malaysia, nibong tebal, penang. he was born in selangor, malaysia in 1967. he received his b.eng. (chemical engineering), m.sc. (chemical engineering) and ph.d (membrane technology), all from university of wales, united kingdoms in 1990, 1991 and 1995 respectively. his area of research interest is membrane separation technology, synthesis and characterization toward the application of environmental monitoring and pollution control including water, wastewater and gas separation. norliza ibrahim was born in trengganu, malaysia in 1976. she received her b.eng. (chemical engineering) and m.sc. (chemical engineering) from universiti sains malaysia in 1999 and 2002 respectively. she is currently a lecturer at university of technology mara, shah alam. suzylawati ismail was born in penang, malaysia in 1973. she received her b.eng. (chemical engineering) from universiti sains malaysia in 1997 and currently pursuing her ph.d study in the area of environmental and membrane separation technology. subhash bhatia is currently the programme chairman (bioprocess and environment) at school of chemical engineering, engineering campus, universiti sains malaysia, nibong tebal, penang. he was born in pakistan in 1946. he received his b.eng. (chemical engineering) from hb technology institute, kanpur, india, m.sc. (chemical engineering) and ph.d (chemical engineering) at indian institute of technology, kanpur in 1971 and 1976 respectively. his area of research interest is reaction engineering and catalysis in particular zeolite catalyst. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 detection of traffic density with image processing using pin hole algorithm mochamad aditya irawanto, casi setianingsih* and budhi irawan computer engineering, school of electrical & engineering, telkom university, indonesia *corresponding author: setiacasie@telkomuniversity.ac.id (received: 6th july 2021; accepted:18th october 2021; published on-line: 4th january 2022) abstract: intelligent traffic monitors have developed and have become more attractive in recent years. a detection system in the monitoring traffic system is proposed using different algorithms. pin hole algorithm used to detect the car that passes the road (the studied area). a fixed camera mounted at a predetermined point is used with known height (of the camera), the intensity of the light, and the visibility of the camera. the classification process is important to know the traffic congestion status. the traffic congestion status will be sent to the server address already provided. in the congestion detection test, results were obtained with an accuracy value of 85% using the 64x64 grid division and obtaining good detection results for susceptible light intensity values between 5430 and 41379 lux with an accuracy value of between 60% and 90%. abstrak: sejak beberapa tahun ini, sistem pengawasan trafik pintar telah dibina dan terus berkembang luas. sistem pengesanan dalam sistem trafik pengawasan telah dicadangkan menggunakan pelbagai algoritma. algoritma lubang pin digunakan bagi mengesan kereta yang melalui jalan (kawasan kajian). kamera dipasang tetap pada titik tertentu iaitu dengan menyelaras ketinggian kamera, keamatan cahaya, dan kebolehlihatan kamera. proses klasifikasi sangat penting bagi menentukan status kesesakan trafik. status kesesakan trafik akan dihantar ke alamat pelayan yang telah disediakan. nilai ketepatan ujian pengesanan kesesakan yang diperoleh adalah 85% iaitu menggunakan pembahagi grid 64x64 dan dapatan kajian menunjukkan pengesanan yang baik bagi nilai keamatan cahaya antara 5430 dan 41379 lux dengan nilai ketepatan antara 60% dan 90%. keywords: intelligent traffic density; pin hole algorithm; congestion monitor; car detection; traffic details; image processing 1. introduction traffic lights with less efficient distribution can cause overcrowding at crossroads and can cause congestion that causes traffic jams to the detriment of road users [1]. congestion is a condition where there is a stagnant or interrupted flow of vehicles passing through the road due to the accumulation of vehicles exceeding the existing traffic capacity [2]. congestion problems are caused by a lack of available facilities and infrastructure such as road monitoring systems, road widths, traffic signs. generally, traffic monitoring systems that are running today still use traditional systems. the system used now is to use cameras installed at various points, which are monitored manually by the transportation agency. overall, this system can work well, detecting congestion in accordance with the 244 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 rules of the city of bandung in indonesia. it's just that congestion validation is still a bit challenging because there is no definite data comparison yet. pin hole algorithm was used to obtain the congestion status for traffic control on the toll road section. before that, the camera is fixed to take images (video) for the studied area, pre-processing of the image, contrast limited adaptive histogram equalization, edge detection, enhancement, then image segmentation and classification. the presented algorithm can work with different city roads. 2. related work to maximize the detection of traffic jams using image processing, according to previous research that has been done [3], several factors must be considered. the first is the camera settings. this setting is required to be able to determine the shooting results. the accuracy depends on many factors such as the width of the road, the height of the camera installation and the angle of the camera. the second is image segmentation. in object detection, before filtering using a certain algorithm, the initial process is to convert the data format. the data in mpeg form is converted to jpeg. in the form of jpeg format will be searching the edge value or background image, edge value is used to distinguish between road and object to be processed [4]. the edge value taking is done continuously in order to get perfect results [5]. detection of vehicle objects on a road segment to determine the status of traffic jams can use the pin hole algorithm [6]. pin hole algorithm works by using an ip camera. the result of detection from the camera will be mpeg4 which will be converted back into mjpeg to be processed to the next stage [7]. then the obtained image is filtered using a greyscale filter to determine the background value of the image. the background value is used to separate where the object is to be detected and which image is just the background of the image [7]. the picture shooting takes place within three minutes, and it is because if the image is taken less than three minutes sometimes still has data that is not yet valid and not perfect. then determined the parameters of the results in an emphasis on three parameters, namely the first parameter is the size of the image based on terms of connection, the speed of data as a data source. the second parameter is the large image download and the third parameter is the pixel pin hole size. another method that can be used in vehicle counting in traffic control is blob analysis [8]. the blob filter algorithm is able to detect congestion well. the steps required in this algorithm are as follows: 1. vehicle segmentation, settings in a location of picture shooting on camera. 2. background updating, define the background of the image by segmenting. 3. feature extraction and vehicle classification used to be able to define different objects when detecting images. 4. vehicle tracking is used to determine the amount of vehicle current based on the distance of each vehicle. 5. vehicle flow analysis and counting is used for the final count of the number of vehicles and the speed of the coming vehicle on the line. the output of this method is the number of vehicles outside the track with the average speed of the vehicle so that it can be concluded whether the situation can be said to be 245 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 stuck or not. this method also has an average accuracy value in three conditions of 90% with an estimated error of less than 5 km/hour. detecting traffic jams in the city in real-time with the help of a uav can be chosen as another alternative in analyzing traffic conditions. traffic data in the form of videos taken from drones is then detected using a deep learning algorithm, namely mask rcnn. several steps must be taken, namely, firstly counting the number of vehicles, and estimating the speed of the vehicle. second, estimate the geometric space for pixels in the image to perform vehicle recognition and tracking [9]. 3. research method 3.1 illustrations acquisition video is the process of taking the recording of toll road conditions taken with the *.mp4 video format then saved in a personal computer. the video acquisition is taken based on the entrance to the bandung city with the criteria of having one common goal and having multiple branches as an alternative way. the video acquisition was taken using gopro hero5 black with 720 pixels video quality and 1280 x 720 pixels resolution at 30 fps. the video acquisition is taken at the top of a person crossing the bridge (jpo) which is on a 5.1 m highway toll road. an illustration of video acquisition can be seen in fig. 1. fig. 1: illustration of video acquisition. 3.2 algorithm steps traffic congestion detection is achieved by many steps such as image acquisition from video acquisition, pre-processing on image, pin hole processing to perform vehicle calculation on image and result from classification. the process of the suggested algorithm can be described as follows: 3.2.1 image acquisition the image acquisition process is a step to get a sample image based on video recording. image captured with *.mp4 format and stored in *.png format. figure 2 shows the acquisition of the saved image with the format of *.png given region region of interest (roi) to detect congestion. roi is an area marked as the boundary area of toll roads that will be calculated using digital image processing. the original image that has been given the roi region can be seen in fig. 2. 246 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 fig. 2: image acquisition with roi. 3.2.2 pre-processing the pre-processing step is used to perform calculations by processing the image by combining filters in the image processing. the process that runs in this stage is like capturing the image of the video, changing the grayscale filter, inserting the image into the clahe filter, determining the border of the image, inserting the image into the low pass filter¸ and performing the image segmentation. a. greyscale greyscale is a color in pixels that are still between the range of black and white values 0-255 which means 0 is a value in black and 255 is white. gray degree in greyscale can be done by using digital image processing by adjusting the gray degree of the image using a threshold value. thresholding is the method used to be able to adjust the number of gray-degree values in digital images [10]. the colored image has a matrix value for each pixel in which each pixel has a value of red, green, and blue (r, g, b). to be able to change the color image into greyscale and set the gray degree using thresholding will be explained as follows • calculate the value of greyscale using the equation 𝑠 = 𝑟 ×𝑔 ×𝑏 3 (1) where s is greyscale value • calculate the value of thresholding using the equation 𝑥 = 𝑊 𝑏 (2) where 𝑥 is gray degree values after thresholding, w is gray degree values before thresholding, and b is the desired quantization values. the result of color image processing being the greyscale image can be seen in fig. 3. fig. 3: greyscale image result. 247 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 b. contras limited adaptive histogram equalization (clahe) clahe is a digital image processing process that improves image contrast by increasing contrast in local images by providing a maximum threshold value [11]. the clahe process functions to divide the local image contrast in a symmetrical grid called the area size. the image's division region size can be divided into sections such as cr for the corner region, br for border region¸ ir for the inner region [12]. the existence of the division of region sizes due to the division of the grid there are different characteristic values for each value of the neighborhood. the structure of region size can be seen in fig. 4. fig. 4: region size clahe. after dividing the local image into a symmetric grid, the calculation is performed by obtaining a new gray level on each local grid using the cumulative function distribution of histograms used in each local region (i, j). • calculates the distribution using an equation (𝑘) = (𝑁 −1) 𝑀 .∑ ℎ(𝑘);𝑛 = 1,2,3,…. ,𝑁 −1 𝑛 𝑘=0 (3) where m is the number of pixels, n is the greyscale value, and h(k) is the histogram on grey value. after calculating the distribution of cumulative function, then regional on local image give maximal threshold limit on the image using clahe. • calculates threshold limits using equations 𝛽 = 𝑀 𝑁 (1+ 𝑎 100 (𝑆𝑚𝑎𝑥 −1) (4) where m is wide of region size, n is greyscale value, and 𝑎 is minimum and maximum limit values of histograms ranging from 0-100. the result of image processing into clahe filter can be seen in fig. 5. fig. 5: clahe image result. 248 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 c. edge detection using canny method edge detection or abbreviated as ed is an object detection process in digital image processing that produces an edge output of the image object used to mark the detail part of the image [13]. ed is processed using canny method. the canny method is used because it produces a visible edge shape compared to robert, sobel, prewitt, and log methods after being processed using the global thresholding method [13]. ed in the process is done by giving gaussian filter greyscale image which then convoluted by using method of canny to get result of fine edge image. gaussian filter is done by using gaussian filter equation as follows [14]: • calculate gaussian filters using equations 𝐺(𝑥) = 1 √2𝜋𝜎2 𝑒 − 𝑥2+ 𝑦2 2𝜎2 (5) 𝜎 = standard deviation distribution (𝜎 = 1,4) e = exponential value (e = 2,71828183) (x,y) = the midpoint of the gaussian function • convolution with the canny method is done by equation 1 159 ( 2 4 5 4 2 4 9 12 9 4 5 12 15 12 5 4 9 12 9 4 2 4 4 4 2) (6) • calculate magnitude gradient using equation 𝐺 = |𝐺𝑋|+ |𝐺𝑦| (7) • determining the edges by using the equation 𝑞 = 𝑡𝑎𝑛−1 ( 𝐺𝑥 𝐺𝑦 ) (8) • gives the threshold value of the threshold to the ed by using equations 𝑔(𝑥,𝑦) = 𝑓(𝑥) = { 1, 𝑖𝑓 𝑇𝑚𝑖𝑛, ≤ 𝑓(𝑥,𝑦) ≤ 𝑇𝑚𝑎𝑥 0, 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 (9) the results from image processing in canny method can be seen in fig. 6. fig. 6: edge detection image result. 249 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 d. low pass filter using bilateral filter low pass filter is a method by using a filter type that passes low-frequency frequencies and dampens high-value frequencies in imagery [15]. in the process, lpf uses the bilateral filter method. the bf method is a noise reduction filter on the ash image and also maintains edge detection for smoother image results [16]. benefits of using the bilateral filter method include: • maintain edge detection while eliminating image disturbance and refining the resulting image • eliminate the opacity of the color image • an easy method to apply [16]. the bilateral filter method is calculated using the kernel filter equation 𝐾 = 1 𝐾𝑠𝑖𝑧𝑒.𝑤 𝑥 𝐾𝑠𝑖𝑧𝑒.ℎ ( 1 1 … 1 1 1 … 1 … … … … 1 1 … 1 ) (10) k = kernel bilateral filter ksize = wide of blur in the kernel w = width image h = high image the result of image processing in the bilateral filter can be seen in fig. 7. fig. 7: bilateral filter image result. e. image segmentation image segmentation is the process for recognition of objects in images and also feature extraction [13]. by doing image segmentation in the final stage, it will show the results of objects and backgrounds on the image. segmentation is done by assigning a threshold value (threshold) that applies to all parts of the input image. segmentation is done using the following equation 𝑔(𝑥,𝑦) = 𝑓(𝑥) = { 1, 𝑓(𝑥,𝑦) ≥ 𝑇𝑚𝑎𝑥 0, 𝑓(𝑥,𝑦) < 𝑇𝑚𝑎𝑥 (11) g(x,y) = image after thresholding f(x,y) = edge detection image result t = limit threshold value 250 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 fig. 8: segmentation image result. 3.2.3 pin hole algorithm processing determination of the area in the image is the process of determining the area by following the length and width of the toll road to be detected. after the image acquisition process, area masking is carried out by providing a detection area limit on the toll road section. the masking area is done by connecting the four coordinates in the image so that it becomes a 2d shape. then the detection area is calculated using the equation for the area of an irregular trapezoid. the preprocessed black and white image is divided into a small symmetrical grid (pin hole). the number of grids used is 8x8, 16x16, 32x32, 64x64 pixels. the process of dividing into a grid is done when inserting the clahe filter into the grayscale image. the next step is to find the centroid point (middle value) in the image in each grid area (pin hole). to calculate the vehicle capacity in the area to be detected, it can be done using background elimination (be) [17]. be is processed by eliminating everything that is considered, not including the object in the image so that the value of the object and the background of the image will be separated [17]. be can be done by first calculating the mean of the rgb value of the image with the p-value in the selected background image using equation 𝐵(𝑝) = ∑ 𝐼𝐵(𝑘,𝑝) 𝑛𝑘 (12) 𝐼𝐵(𝑘,𝑝) = pixel color value for point p in frame k then be from the process was calculated with equation 𝐷(𝑘,𝑝) = {𝐼𝐵(𝑘,𝑝) −𝐵 (𝑃)} (13) {.} = value euclidean distance between 𝐼𝐵 and 𝐼𝐵 after the be value is obtained, the image of the result of the process is only the centroid value of the object of the detected vehicle object. to obtain the value of congestion capacity in the area specified, then used equation 𝐺(𝑥) = 1− 𝐷(𝑘,𝑝) 𝐼𝐵(𝑘,𝑝) (14) g(x) = congestion value after doing the calculation on the input image, we will get the result of the number of centroid values contained in the box pin hole of the filled capacity of the box. 251 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 3.2.4 classification results classification is an advanced process of calculating the number of centroids from the pin hole area by grouping the calculation results into several categories determined based on the amount of capacity of the detected object. according to rudi herianto (2018), as the head of the satlatas bojongsoang unit, the congestion category can be grouped into 3, namely: a. traffic jam the jam status is used when the resulting value of the congestion capacity calculation reaches a value of more than 70%. b. crowded smoothly the current status is smoothly used when the value of the result of the congestion capacity calculation reaches a value of more than 10% and less than 70%. c. fluent the current status is used when the value of the calculation of congestion capacity reaches less than 10%. 4. results 4.1 testing the conversion of pixel values into meter units testing the conversion of pixel values into units of meters aims to see the effect of the results of the detection performed using imagery with the existing conditions significantly. to do this test needs to be done in several stages by taking several image samples that have a smooth and crowded classification smoothly. the stages that need to be done can be described as follows: a. determine the true value of the actual detection the actual detection area value is obtained by calculating the area of the road that is on the moh. toha toll road based on toll road geometry standard [18]. b. calculate the actual detection area the image roi is calculated using the formula of building a free trapezoidal space. where both sides of the trapezoid are the length of the toll road and the height of the trapezoid is the width of the toll road. c. calculate pixel area and conversion to meters calculating the area of pixels then converting them into meter units is done by calculating the area obtained from the image of the detection result into the equation 𝑎𝑟𝑒𝑎 = 𝐿𝑃 ×𝑑𝑝𝑖 ×𝑝𝑖𝑥𝑒𝑙 𝑡𝑜 𝑐𝑚 (15) dpi = dot per inch pixel to cm = 0.0264583333 cm d. determine the image scale value determine the value of the image scale by dividing the original area by the area of the pixel area converted into meters. it is helpful as a comparator value between the image of the detection result and the condition on the actual toll road. 252 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 based on the process of testing the conversion of pixel values to meters, the results are obtained for the actual detection area as shown in table 1. the result of the pixel value conversion to the unit meter can be seen in table 2. after getting each of the required values as in tables 1 and 2, conclusions can be drawn based on the sampling of the detected images. conclusions can be seen in table 3. table 1: wide actual toll roads no. explanation value 1. dpi 72 pixels per inch camera 2. actual toll road length 91 m 3. actual toll road width 10.5 m 4. actual toll road area 955.5 m2 table 2: scale and area of conversion no. area (pixels) area of conversion area (𝒎𝟐) actual toll road area (𝒎𝟐) conversion area scale with real area 1. 237900 pixels 4531.93 955.5 4:1 table 3: the final conversion result to the pixel value no pixel value value after conversion (𝒎𝟐) percentage of congestion area object area percentage of congestion classification area object area 1. 237900 17900 7.52% fluent 4531.93 340.9907 7.52% 2. 237900 34800 14.62% smoothly 4531.93 662.939 14.62% 4.2 pin hole grid testing the value of detection accuracy for 20 frames can be seen in fig. 9. pin hole grid test aims to see the effect of the number of pin hole boxes during the image segmentation process. this step is used to detect congestion when segmentation in the image entered in the clahe filter on the accuracy obtained in the process. clahe filter was used because the filter input image is divided into the symmetrical grid where the number of grids affects the pin hole's accuracy. a. image conformity results this test is done by running 5 different pin hole grid values, i.e., grid images 8x8, 16x16, 32x32, and 64x64 with the image without grid division. the grid value used for the original image and the segmentation image of the clahe filter results. the following results from the process can be seen in table 4. based on the segmentation image conformity using clahe filters with the original image in table 4, the results of segmentation images have a lot of noise due to the inadequate clahe filters caused by the small number of grids that cause excess calculation results when the process is done the histogram equalizer that causes the calculated vehicle object does not match the input 253 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 image. many noises in the results image are obtained in the image with a grid of 8x8, 16x16 and 32x32. fig. 9: value of accuracy to the number of grids. table 4: image conformity results no. grid amount results similar not similar original image clahe segmentation image 1. 0x0  2. 8x8  3. 16x16  4. 32x32  5. 64x64  55% 55% 55% 75% 85% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 8 x 8 16 x 16 32 x 32 no grid distribution image and non clahe filter 64 x 64 accuracy value against grid amount 254 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 a. image detection results this was done by comparing the detection value of the image with the correct value to get the accuracy value. the correct value is obtained from interviews conducted with mr. rudi herianto is the chief of the indonesian national police traffic department in bandung. 4.3 light intensity testing testing will be carried out by taking sample data on the results of recording traffic conditions on the toll road with different light intensity values. different light intensity values will be obtained by detecting at different times, i.e., morning, afternoon, evening, and night. after that, the comparison of results will be made based on the accuracy values obtained. from this stage, the conclusion will be drawn based on high accuracy values on the value of the light intensity obtained by concluding the vulnerable value of the appropriate light intensity to detect congestion. the results of this test can be seen in fig. 10. fig. 10: value accuracy of results based on light intensity. based on the graph in fig. 10, the value of light intensity affects the result of the accuracy value obtained from the detection of congestion. the difference in the value of accuracy obtained is based on several factors as follows: a. toll road conditions as seen in fig. 10 that the detection error that occurred on the toll road segment at light intensity is 11500 with an accuracy value of 0%. this is due to the detection of the image background as an object; after an analysis of the original image and the segmentation results obtained results that the error lies in the color of the uneven markers. b. car light although in fig. 10 the detection at night, the accuracy value reaches 100%, because the results of true values obtained from subjective opinions do not guarantee that the results are always correct. reflection of light from car lights is considered to have an excessive amount of light intensity from the specified threshold. therefore, the value of the excess light intensity is detected as an 0% 60% 90% 100% 0% 20% 40% 60% 80% 100% 120% 11500 41379 5430 93 value of results accuracy 255 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 object when image segmentation and is calculated in the search for congestion capacity values. 5. conclusion based on the results of the analysis of the testing scenario on the congestion detection system using image processing with pin hole algorithm, which is carried out on 5 toll roads that will enter the city of bandung, the following conclusions are obtained: 1. based on the conversion of pixel values into units of meter obtained results from the image of the sample taken that the area of detection value using the image of 237900 pixels equal to the area of 4531.93 m2 on the actual condition with a scale of 1:4 2. the congestion capacity for the classification results smoothly in the sample image will be the same value when the total object value of 340.9907 m is in the area of the detection area of 4531.93 m2 in the real condition. 3. the implementation of the system can produce an accuracy value of 85% by using symmetrical 64x64 grid images with an average computing time of 5 seconds. 4. the detection results are assessed in the light intensity range from 5.430 to 41.379 lux, assuming good road conditions. 5. the algorithm used still require modification with other algorithms in order to do detection at night. 6. based on the weather obtained when sampling is not so influential as long as the light intensity values obtained are still in the susceptible 5.430 to 41.379. 7. this system is helpful as an alternative to find the value of congestion capacity based on the number of vehicles that will enter the city of bandung through the highway. references [1] royani, tahere, haddadnia j, pooshideh mr. (2010) a simple method for calculating vehicle density in traffic images. in 6th ieee iranian conference on machine vision and image processing: october 2010; pp 1-4. [2] fibriliyanti, yanita, faradila lr, taqwa a. (2017) implementasi pengolahan citra dengan metode histogram of oriented gradient (hog) untuk pengaturan waktu pada traffic light berdasarkan deteksi kepadatan kendaraan. in prosiding snatif: 2017; pp 403-412. [3] directorate general of land transportation ministry of transportation republic of indonesia. (2008) technical instructions for the implementation of road equipment. jakarta. [4] nurhadiyatna a, hardjono b, wibisono a, sina i, jatmiko w, ma'sum ma, mursanto p. (2013) improved vehicle speed estimation using gaussian mixture model and hole filling algorithm. in 2013 ieee international conference on advanced computer science and information systems (icacsis): september 2013; pp 451-456. [5] kim ki, jung k, kim jh. (2002) color texture-based object detection: an application to license plate localization. in springer international workshop on support vector machines: august 2022; berlin, heidelberg. pp 293-309. [6] bas e, tekalp am, salman fs. (2007) automatic vehicle counting from video for traffic flow analysis. in 2007 ieee intelligent vehicles symposium: june 2007; pp 392-397. [7] mahatmaputra s, permata e, william. (2011) deteksi kemacetan lalu lintas melalui kamera menggunakan pin hole algorithm. comtech., 2:821-834. 256 iium engineering journal, vol. 23, no. 1, 2022 irawanto et al. https://doi.org/10.31436/iiumej.v23i1.2135 [8] cucchiara r, massimo p, paola m. (2000) image analysis and rule-based reasoning for a traffic monitoring system. ieee transactions on intelligent transportation systems, 1(2):119130. [9] chen th, lin yf, chen ty. (2007) intelligent vehicle counting method based on blob analysis in traffic surveillance. in second ieee international conference on innovative computing, informatio and control (icicic): september 2007; pp 238-238. [10] zhang h, liptrott m, bessis n, cheng j. (2019) real-time traffic analysis using deep learning techniques and uav based video. in 16th ieee international conference on advanced video and signal based surveillance (avss): september 2019; pp. 1-5. [11] saepudin d, rizal a. (2014) analisis contrast limited adaptive histogram equalization (clahe) dan region growing dalam deteksi gejala kanker payudara pada citra mammogram. jurnal elektro unika atma jaya., 7(1):15-28. [12] reza am. (2004) realization of the contrast limited adaptive histogram equalization (clahe) for real-time image enhancement. journal of vlsi signal processing systems for signal, image and video technology., 38(1):35-44. [13] junior ra, nurhasanah n, sanubary i. (2014) perbandingan penggunaan beberapa metode deteksi tepi pada pengolahan citra radiologi fraktur tulang. prisma fisika., 5(3):122-130. [14] triono p, murinto m. (2015) aplikasi pengolahan citra untuk mendeteksi fraktur tulang dengan metode deteksi tepi canny. jurnal informatika ahmad dahlan., 9(2):103-842. [15] panda dk, sukadev m. (2013) a gaussian mixture model with gaussian weight learning rate and foreground detection using neighbourhood correlation. in 2013 ieee asia pacific conference on postgraduate research in microelectronics and electronics (primeasia): december 2013; pp. 158-163. [16] tomasi c, manduchi r. (1998) bilateral filtering for gray and color images. in sixth ieee international conference on computer vision (ieee cat. no. 98ch36271): january 1998; pp. 839-846. [17] deswal s, gupta s, bhushan b. (2015) a survey of various bilateral filtering techniques. international journal of signal processing, image processing and pattern recognition., 8(3):105-120. [18] atkočiūnas e, blake r, juozapavičius a, kazimianec m. (2005) image processing in road traffic analysis. nonlinear analysis: modelling and control., 10(4):315-332. [19] the directorate general of directorate general of marga the ministry of public works and housing republic of indonesia. (2008) standar geometri jalan bebas hambatan untuk jalan tol. jakarta. 257 microsoft word 154-1275 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 45 optimum numbers of single network for combination in multiple neural networks modeling approach for modeling nonlinear system rabiatul adawiyah m.n. and zainal a. faculty of chemical engineering, universiti sains malaysia engineering campus, seri ampangan 14300 nibong tebal, seberang perai selatan, pulau pinang, malaysia. chzahmad@eng.usm.my abstract: this paper is focused on finding the optimum number of single networks in multiple neural networks combination to improve neural network model robustness for nonlinear process modeling and control. in order to improve the generalization capability of single neural network based models, combining multiple neural networks is proposed in this paper. by studying the optimum number of network that can be combined in multiple network combination, the researcher can estimate the complexity of the proposed model then obtained the exact number of networks for combination. simple averaging combination approach is implemented in this paper which is applied to nonlinear process models. it is shown that the optimum number of networks for combination can be obtained hence enhancing the performance of the proposed model. abstrak: karya ini memberi tumpuan kepada pencarian angka optimum untuk rangkaian tunggal dalam gabungan rangkaian neural pelbagai untuk meningkatkan kemantapan model kawalan dan model proses tidak linear. untuk meningkatkan keupayaan generalisasi model rangkaian tunggal, penggabungan rangkaian neural pelbagai telah dicadangkan dalam kertas kerja ini. kajian bilangan optimum rangkaian tungal yang boleh digabungkan dalam gabungan rangkaian pelbagai, penyelidik boleh menganggarkan kerumitan model yang dicadangkan. bilangan rangkaian yang tepat untuk gabungan juga boleh di kira. pendekatan gabungan purata yang mudah berdasarkan model proses tidak linear telah di kaji dalam kertas ini. bilangan optimum rangkaian untuk kombinasi yang keywords: neural network; multiple neural networks combination; nonlinear process; conic water tank 1. introduction artificial neural networks have been shown to be able to approximate any continuous non-linear functions and have been used to build data base empirical models for non-linear processes[1]. hence what is a neural network? according to haykin [2]:“a neural network is a massive parallel-distributed processor that has a natural capability for storing experiential knowledge and making it available for use. it resembles the brain in two respects knowledge is acquired by the networks through a learning process. interneuron connection strengths known as synaptic weights are used to store the knowledge.“ iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 46 furthermore, the main advantage of neural network based process models is that they are easy to build. this feature is particularly useful when modeling complicated processes where detailed mechanistic models are difficult to develop. however, a critical shortcoming of neural networks is that they often lack robustness unless a proper network training and validation procedure is used. robustness of the model can be defined as one of the baseline to judge the performance of the neural network models and it is really related to the learning or training classes as what bishop [3] described:“the importance of neural networks in this context is that they offer very powerful and very general framework for representing non-linear mappings from several input variables to several output variables, where the form of the mapping is governed by a number of adjustable parameters.“ there are a lot of factors that contributed to the successful research on neural networks and among them the two main factors are as follows. the first one is that neural networks are very powerful modeling tool capable of modeling extremely complex functions [1, 4, 5]. in particular, neural networks are non-linear models, which are very useful in modeling nonlinear systems that cannot be successfully modeled by linear models. the second main factor is that neural networks are easy to use and develop and they basically learn by examples. the neural network users gather representative data, and then invoke a training algorithm to automatically learn the structure of the data [6, 7, 8]. because of the advantages or the tremendous capability of neural networks, currently there are a lot of applications of neural networks in industry and business where neural networks are applied in signal processing, control, pattern recognition, medicine, speech processing and in business. in order to improve the robustness of neural networks a number of techniques have been developed lately like regularization [9] and the early stopping method[10]. ohbayashi[11] implemented the universal learning rule and second order derivatives to increase the robustness in neural network models. robustness is enhanced by minimizing the change in the values of criterion function caused by the small changes around nominal values of system parameters. lack of the robustness in individual neural networks is basically due to the over fitting of the models [12]. therefore combination of neural networks has come up and researchers concentrate on how over fitting can be avoided by improving the learning algorithm or by combining the neural networks. overfitting basically refers to the poor generalization of the networks due to fitting the noise in the data [13]. furthermore, the trained network might not minimize the error on the training data set because it has uncontrolled excess dynamics capability or because the training data itself is corrupted with noise. the representation capability of a neural network is determined by its size (number of neurons). if networks are too large they can find many solutions which fit the training set data exactly, but which contain high frequency dynamics is not present in the underlying function. when the data is corrupted with noise a second form of over fitting occurs. here the data itself contain high frequencies not present in the underlying function, with the result that minimizing the error on the data set will result in the networks fitting the noise. neural networks are related to the basic principle of brain [14] and try to mimic how brain works. they have been developed since 1940 after world war 2 when industrialization was growing rapidly. neural networks are generally structured in layers of which all the neurons are connected between the adjacent layers. as mentioned by iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 47 willis et al. [15], more accurate representation of the processes are required to ensure good process control performance especially in advance process control. therefore neural network models must be robust or stable when they are applied to new (unseen) data. even though neural network models are very powerful non-linear modeling tools, noises in the input data sometimes cause the model over-fitting. over-fitting and under fitting is the main problem in developing neural network models. in over-fitting, the error on the training data set is driven to a very small value, but when applied to unseen data, the network error is large and the generalization capability of the neural network is poor. while under fitting is due to that the neural network itself cannot cope with or fails to capture the relationship within the complex data [16]. therefore a lot of techniques have been introduced to improve the generalization capability of neural network models like regularization techniques [12, 13, 17], bayesian learning [8, 18] and also by using the parsimonious networks structure [19]. the most exceptional model for this approach is network pruning techniques and sequential orthogonal training techniques. a sequential orthogonal training technique gradually builds up a neural network model and avoids unnecessarily large networks structure [20]. among those approaches for improving neural network generalization, the combination of multiple neural networks seems to be very effective. therefore the multiple neural networks and combination of multiple neural networks is proposed in this paper with the aim of enhancing the single neural network robustness. the paper is organized as follows. section 2 presents the concept multiple neural networks and how its can be combined. section 3 presents the nonlinear process modeling for a nonlinear process. applications of the proposed technique to two case studies are given in section 4. finally, the last section concludes this paper. 2. multiple neural network the idea of multiple neural networks came up from wolpert [21] where he described about stacked generalization which is a technique for combining different representations to improve the overall prediction performance. it can also be described as an architecture of network consisting of several sub-models and a mechanism which combines the outputs of these sub-models [22]. there are several types of multiple neural networks but the underlying ideas are basically similar and the main difference is on how to create the submodels as shown in fig. 1. two major types of multiple neural networks are described here. the first category is multiple model neural networks [23, 24]. the training data are totally different in building the individual networks which can be built using different inputs in different regions of operation. the idea of this approach is to adapt different information by using different inputs, and by combining this information a better prediction can be obtained [22, 25]. the learning algorithm in each network can also be different and can be supervised or unsupervised methods. other multi model approach are introduced by jacobs [26] by using the ‘mixture of local expert’. then, jordan and jacobs[27] came up with the hierarchical mixture of neural networks. in this case they basically discuss about the supervised learning algorithm and how the divide and conquer method works. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 48 fig. 1: a multiple neural networks. some examples of multi model applications are in the field of pattern recognition where different models represent different image classification [28, 29]. medical application of multi models is presented by jerebko [30] where different classifications of polyps as single neural network models using different inputs are combined and better prediction rate is obtained. it has also been used in other medical fields like in diagnosis application and in detecting the lung cancer [31, 32]. multiple models have also been applied in time series forecasting [24]. in this case, each model forecasts a difference time series prediction or prediction horizon and this reduces the recursive prediction promoted to reducing the recursive error occurred in the long range prediction. it also shows that the multi network model performs better than single networks. the second category is to creating multiple models using the same training data but re-sampled or partitioned using particular algorithms [33, 34]. there are three main algorithms being used to re-sample or partition the training data which are bagging or bootstrap [34, 35] which is being used in this paper to create a multiple neural networks, adaboost [36, 37] and randomization [38]. the motivation of creating those different inputs or partitions is to create the effective network ensembles [39]. the bootstrap or bagging basically refers to replication of a training data set where the bootstrap algorithm re-samples the original training data set. some of the data samples may occur several times, and other may not occur in the sample at all. the individual training sets are independent and the neural networks can be trained in parallel. in this paper the data were resample using bootstrapping method. the development of computer capability also promoted the development of multiple neural networks. application of multiple neural networks will grow rapidly and become an important component of future research. this is also due to the various used of the neural networks and combining neural networks is one of the methods that increase the performance of network models. therefore, the objective of this paper is to study the optimum numbers of network that can be combined. the single network will be added one in a time to be combined until the optimum number of network is obtained based on the sum square error (sse) which is used the simple averaging method as shown below: 2.1 simples averaging iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 49 this method is the most common method in combining several model outputs with the weights fixed as shown below: nn2211 ŷw...ŷ w ŷ w ŷ +++= (1) where i ŷ is the network prediction from the ith network, n is the number of networks to be combined, ŷ is the final prediction output, and wi = 1/n is the weight for combining the ith network. the main disadvantage of this approach is that all the networks have the same contribution to the final prediction output even though some of the networks might have better predictions then others; consequently it might deteriorate the model. 3. nonlinear process modeling in this case study, the individual networks were trained by the levenberg-marquardt optimization algorithm with regularization and “early stopping”. the aggregated of single network are varies from 2 to 50 numbers of networks. if the number of networks is too small we might not get the optimum reduction of the sse in the combination. to accommodate systems with lag elements, while re-sampling the training and testing data using bootstrap re-sampling techniques, the training and testing were already in discrete time function, therefore, by re-sampling discrete time function, it will not affect the sequence of input-output mapping of the prediction. all weights and biases were randomly initialized in the range from –0.1 to 0.1. the individual networks are single hidden layer feed forward neural networks. hidden neurons use the sigmoid activation function whereas output layer neurons use the linear activation function. to cope with different magnitudes in the input and output data, all the data were scaled to zero mean and unit standard deviation. the data for neural network model building were divided into: 1) training data (for network training); 2) testing data (for cross-validation based network structure selection and early stopping); and 3) unseen validation data (for evaluation of the final selected model). in networks with fixed structure, network structures (numbers of hidden neurons) were determined through crossvalidation. networks with different numbers of hidden neurons were trained on the training data and tested on the testing data. the network with the lowest sse on the testing data is selected. in assessing the developed models, sse on the unseen validation data is used as the performance criterion. 3.1 case study: water tank level prediction figure 2 shows the model of conic water tank level apparatus. there is an inlet stream to the tank and an outlet stream from the tank. manipulating the inlet water flow rates will regulates the water tank level. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 50 fig. 2: conic water tank. o qq dt dv −= 1 (2) where, v is represents as volume of water in the tank (cm 3 ), q1 is inlet water flows rates (cm 3 /s) and qo is outlet water flows rates (cm 3 /s). the outlet water flow rate, qo, is related to the tank level, h, by the following equation: qo = hk (3) where k is constant for a fixed valve opening.the volume of water in the tank is related to the tank level by the following equation:       ++= 2 2 2 )(tan3tan θθ π hhr rhv (4) where r is the tank bottom radius and θ is the angle between the tank boundary and the horizontal plane. combining equations above, the following dynamics model for the tank level is obtained:       ++ − = 2 2 2 )(tantan 2 1 θθ hrh rn hkq dt dh (5) based on the above model, a simulation file is developed to simulate the process. the parameters used in the simulation are r = 10 cm, k = 34.77 cm 2.5/s and θ = 60. the sampling time is 10 second. the above equation indicates that the relationship between the inlet water flow rate and the water level in the tank is quite non-linear. the outlet valve characteristic showed that the static gain increased with tank level. the time constant of the processes increases with the tank level because the tank is of a conical shape. thus, both the static and dynamic characteristics of the process vary with the operating condition. all the building data are generated from the simulation program and noise with the distribution n (0, 0.7 cm) are added to simulated tank. the data was divided into three sections, which are training data, testing data and validation data respectively. outlet inlet iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 51 4. results and discussion in this case study, the input data to the neural network system will be divided into three sections (testing, training and validation). all these data have to be scaled before it can be use for analysis which is to normalize the data to zero mean and unity standard deviation. this is important since different input data have different magnitude or units. the dynamics model for tank level prediction is in the form of: [ ])1(),1()( 1 −−= ∧ tqthfth (6) where ∧ h represent the predicted tank level. the optimum number of hidden neuron has to be determined before the networks being used for training, testing and validation purpose. based on the analysis, the number of hidden neurons that came up with the least sse for the tank level model is used for other analysis in multiple neural networks. table 1 shows the results of sse for training and testing data for each trial while fig. 3 shows the plot of the results. from table 1 and fig. 3, the optimum number of nodes with minimum sse is 3 nodes with the value of sse 3.2668. hence, 3 nodes will be used for the tank level prediction analysis. table 1: sum square error (sse) for training and testing data for different no. of nodes for tank level prediction no. of nodes in hidden layer sse training data sse testing data sse (testing + training) 1 2.1703 1.6045 3.7748 2 1.7278 1.9299 3.6577 3 1.6273 1.6395 3.2668 4 1.6305 1.9049 3.5354 5 1.6074 1.8927 3.5001 6 1.6195 1.9123 3.5318 7 1.6376 1.9746 3.6122 8 1.6762 2.1139 3.7901 9 1.6329 2.2068 3.8397 10 1.7344 2.2205 3.9549 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 52 fig. 3: plot of total sse for (training + testing) data of tank level prediction versus number of nodes. after determined the number of nodes, the m-file for tank level prediction will be simulated to obtain the results of sum square error, sse and also mean sum square error, mean sse for neural networks system. the method of calculation of sse and mean sse in multiple neural networks are different. for sse in multiple networks, the predicted output value, yp for each network will be combined to obtain the mean predicted output value, p y . n y y n i ip p ∑ = = 1 , (7) where, n = number of network. this combined output value of p y will be used to compare with the true output value, y to obtained the sum square error, sse. 2 )( p yysse −= (8) for mean sse in multiple neural networks, the predicted output value, yp for each network will be used to compare with the true output value, y. this means the sum square error is obtained for each network in the multiple networks system. the mean value of sse for the networks will be determined and describe as mean sse. mean sse, n sse sse n i ip∑ = = 1 , (9) the results of sse and mean sse for tank level prediction are tabulate in table 2 and 3. while fig. 4 and fig. 5 show the plots of the results. 1 2 3 4 5 6 7 8 9 10 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 no. of nodes s s e ( t ra in in g + t e s ti n g ) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 53 table 2: results of sse for training, testing and validation data for tank level prediction. no. of networks sse training data sse testing data sse for (training + testing) sse validation data 1 1.6273 1.6395 3.2668 3.2311 5 1.6066 1.6948 3.3014 3.2922 10 1.5788 1.6224 3.2012 3.1671 15 1.5622 1.6219 3.1841 3.161 20 1.5642 1.6268 3.191 3.1554 25 1.5624 1.6123 3.1747 3.1387 30 1.5649 1.6062 3.1711 3.1363 35 1.5651 1.6019 3.167 3.1345 40 1.5626 1.5909 3.1535 3.1328 45 1.5629 1.5882 3.1511 3.1338 50 1.5627 1.5898 3.1525 3.1338 table 3: results of mean sse for training, testing and validation data for tank level prediction. no. of networks combined mean sse training data mean sse testing data mean sse (training + testing) data mean sse validation data 5 1.6967 1.7849 3.4816 3.5579 10 1.6826 1.716 3.3986 3.4317 15 1.6695 1.7153 3.3848 3.4075 20 1.6645 1.7126 3.3771 3.373 25 1.6615 1.6959 3.3574 3.3473 30 1.6595 1.6821 3.3416 3.3347 35 1.6586 1.6727 3.3313 3.308 40 1.6656 1.667 3.3326 3.349 45 1.6715 1.6687 3.3402 3.3615 50 1.6681 1.6659 3.334 3.354 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 54 fig. 4: plot of sse for (training + testing) data and validation data versus number of networks for tank level prediction. fig. 5: plot of mean sse for (training + testing) data and validation data versus number of networks for tank level prediction. from the results show in fig. 4, the sse for multiple neural networks are generally lower compare to single network. as compare to single network, the sse value increase when 5 networks is used for multiple networks system. beyond 10 networks, the sse values slowly decrease until almost steady at 35 networks. 0 5 10 15 20 25 30 35 40 45 50 3.1 3.15 3.2 3.25 3.3 3.35 no. of networks s u m s q u a re e rr o r (s s e ) training + testing validation 5 10 15 20 25 30 35 40 45 50 3.2 3.25 3.3 3.35 3.4 3.45 3.5 3.55 3.6 3.65 no. of networks m e a n s s e training + testing validation iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 55 from fig. 5, the mean sse also decrease with the increase in number of networks. the optimum number of networks with minimum mean sse for validation data achieve at 35 networks. the mean sse value for validation increase slightly when more than 35 networks are used. the overall results show that multiple neural networks provide good performance with lower sse compare to single network. the optimum number of network achieves at 35 networks. for further analysis, the plot of residual error of validation data for multiple (35) networks will be conducted. the result of plot is shown in fig. 6. fig. 6: plot of residual error of validation data for multiple neural networks for tank level prediction. the residual error is the difference between true output value, y and predicted output value, yp: residual error p yy −= (10) the true and predicted output values are rescaled to its original value (level, cm) before finding the residual error. from fig. 6, the residuals appear randomly scattered around zero indicating that the model describes the data well. the range of error is from -2.5 to 2.5 cm. there are total 199 sets of validation data use to compare with the predicted output values. to prove how well the multiple neural networks predict the output data, we can plot a graph to relate between the true and predicted output values. fig. 7 shows the results of the plot. the result of plots shows that the predicted output values were close to the true output values. the calculated correlation coefficient value r 2 for true and predicted output for fig. 7 for multiple networks is 0.9893. correlation coefficient is a normalized measure of linear relationship strength between two variables. the perfect fit will obtain a correlation coefficient value of 1. this means the results for the tank level prediction case study is close to the perfect fit value and indicate the multiple networks predict a good result. 0 20 40 60 80 100 120 140 160 180 200 -3 -2 -1 0 1 2 3 r e s id u a l e rr o r (c m ) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 56 fig. 7: plot of true output values versus predicted output values for multiple neural networks for tank level prediction. 5. conclusion as mention in earlier part that more accurate representation of neural networks is very crucial as it contributes to the improvement of model performance especially when it is applied to unseen data. therefore, major problem in modeling neural networks such as over fitting and under fitting can be avoided and generalization capability of the model can be enhanced. driven by such convincing result, a step has been taken into reaching the goal of modeling neural networks. one of the methods that have been utilized is by studying the optimum number of neural networks that eligible to be combined. by implementing the method, researcher can predict the intricacy of the model then finally obtained the best number of neural networks that should be combined. the overall result of this research has proposed 35 networks where the sse values reach the almost steady condition. the combination of 35 networks also has been proved be reliable since the result shows that the predicted output values closed to the true output values. acknowledgement this research is supported by universiti sains malaysia through ru grant 811106. references [1] hertz j, krogh a and palmer rg: introduction to the theory of neural computation. addison-wesley; 1991. [2] haykin s: neural networks. macmillan college publicating company; 1994 [3] bishop c: neural networks for pattern recognition.clarendon press; 1995 [4] grossberg s: neural networks and natural intelligence. mit press; 1988 [5] hinton g e: how neural networks learn from experience. scientifc american 1992, 267:144-151. [6] english e: mstacked generalisation and simulated evolution. biosystem 1996, 39: 3-18. [7] chen k, xu l and chi h: improved learning algorithm for mixture of expert in multiclass classification. neural networks 1999, 12: 1229 – 1252. [8] crucianu m, bone r and asselin de beauville jp: bayesian learning for re-current networks. neurocomputing 2001, 36: 235-242. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 57 [9] girosi f, jones m and poggio t: regularisation theory and neural networks architecture. neural computation 1995, 7:219-269. [10] morgan n and bourlard h: generalisation and parameter estimation in feedforward nets: some experiments. d. s. touretzkey (ed). in advances in neural information processing system 2,. san mateo ca, 1990, :630-637. [11] ohbayashi m, hirasawa k, toshimitsu k, murata j and hu j: robust control for non-linear system by universal learning networks considering fuzzy criterion and second order derivatives. in the proceeding ieee world congress on computational intelligence 1998. [12] caruana r, lawrence s and lee giles c: overfitting in neural networks: backpropagation, conjugate gradient and early stopping. neural information processing system 2000, 13:402-408. [13] mc loone s and irwin g: improving neural networks training solution using regularisation. neurocomnputing 2001, 37: 71-90. [14] patterson d w: artificial neural networks theory and application. prentice hall; 1996. [15] willis m j, di massimo c, montaque g a, tham m t and morris a j: artificial neural networks in process estimation and control. automatica 1992, 28 (6):1181-1187. [16] guyon x and yao j: on the underfitting and overfitting sets of model chosen by order selection criteria. journal of multivariate analysis 1999, 70:221-249. [17] hagiwara k and kuno k: regularisation learning and early stopping in linear networks. international joint conference on neural networks 2000, :511-516. [18] radford m n: bayesian learning for neural networks. statistics 1997, :118-183. [19] zhang j, morris a j and martin e b: long-term prediction models based on mixed order locally recurrent neural networks. computers and chemical engineering .1998, 22 (7-8): 1051-1063. [20] zhang j, morris a j, martin e b and kiparissides c: prediction of polymer quality in batch polymerisation reactors using robust neural networks. chemical engineering journal 1998, 69:135-143 [21] wolpert d h: stacked generalisation. neural networks 1992, 5:241-259. [22] eikens b and karim m n: process identification with multiple neural networks models. international journal of control 1999, 72(7/8):576-590. [23] chen l and narendra k s: intelligent control using multiple neural networks. international journal of adaptive control and signal processing 2003, 17:417-430. [24] nguyen h h and chan c w: multiple neural networks for a long term time series forecast. neural computation and application 2004, 13:90-98. [25] hashem s: optimal linear combination. neural networks 1997, 10(4):599-614. [26] jacobs r a m i j, nowlan s j and hinton, g e: adaptive mixture of local expert. neural computation 1991, 3:79-87. [27] jordan m i and jacobs r a: hierarchical mixtures of expert and the em algorithm. neural computation 1994, 6:191-214. [28] giacinto g and roli f: design oo effective neural network ensembles for image classification purposes. image and vision computing 2001, 19:699-707. [29] cho s b and lee j h: learning neural network ensemble for practical text classification. j. liu (ed). in lectures notes in computer science. berlin heidelberg, springer-verlag 2003, :1032-1036. [30] jerebko a k, malley j d, franaszek m and summers r m: multiple neural networks classification scheme for detection of colonic polyps in ct colonography data set. academic radiology 2003, 10(2):154-160. [31] hayashi y and setiono r: combining neural network prediction for medical diagnosis. computers in biology and medicine 2002, 32:237-246. [32] zhou z h, y b jiang and chen s f: lung cancer cell identification based on artificial neural networks ensembles. artificial inteligent in medicine 2002, 24:26-36. [33] zhang j: developing robust non-linear models through bootstrap aggregated neural networks. neurocomputing 1999, 25:93-113. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics rabiatul and zainal 58 [34] cunningham p, carney j and jacob s: stability problems with artificial neural networks and the ensembles solutions. artificial inteligent in medicine 2000, 20:217-225. [35] wehrens r, putter h and buyden l m c: the bootstrap: a tutorial,chemometrics and intelligent laboratory system 2000, 54:35-52. [36] schwenk h and bengio y: boosting neural networks. neural computation 2000, 12:18691887. [37] freund y and schapire r e: experiment with a new boosting algorithm. in the proceeding 13th international conference on machine learning 1996:148-156. [38] dietterich t g: an experimental comparison of three methods for constructing ensembles of decision trees: bagging, boosting, and randomization. machine learning 2000, 40(2):139 157. [39] sharkey a j c (eds): multi nets system. in combining artificial neural nets ensemble and modular. london: springer publication; 1999. iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 evaluation of ductility of reinforced concrete structures with shear walls having different thicknesses and different positions rifat resatoglu*and shahram jkhsi department of civil engineering, near east university, nicosia, northern cyprus * corresponding author: rifat.resatoglu@neu.edu.tr (received: 19th may 2020; accepted: 26th october 2021; published on-line: 4th july 2022) abstract: ductility is one of the main criteria in reinforced concrete (rc) structures. asce 7-10 seismic design code recognizes the importance of ductility in earthquakeresistant structures. the structures need to be designed to have sufficient strength and ductility for overall safety against earthquake forces. both the strength and the ductility are mutually associated to enhance structural seismic safety in this study. previous studies showed that a shear wall gives different performance based on its position in building structures. this paper presents the position of the shear walls and shear wall thicknesses effects on ductility. a total of 96 two-dimensional (2d) models are analyzed for this work using etabs software. the non-linear static analysis (pushover) method is used to analyze and design these rc building structures with shear walls. it is concluded that an increase in shear wall thickness causes a decrease in ductility values, and a decrease in ductility value will also occur when the shear wall position changes from edge to middle. abstrak: kemuluran adalah salah satu kriteria utama dalam struktur konkrit bertulang (rc). kod reka bentuk asce 7-10 seismik dunia menyedari pentingnya kemuluran dalam struktur tahan gempa. struktur perlu dibina bagi mencapai ketahanan kekuatan dan kemuluran yang mencukupi bagi keselamatan keseluruhan terhadap kekuatan gempa. kekuatan dan kemuluran dihubungkan bersama bagi meningkatkan keselamatan tahan gempa dalam kajian ini. kajian sebelumnya menunjukkan bahawa dinding ricih memberikan prestasi yang berbeza berdasarkan kedudukannya dalam struktur bangunan. kertas ini menunjukkan kedudukan dinding ricih dan ketebalan dinding ricih kesan pada kemuluran. sebanyak 96 model dua dimensi (2d) dianalisis dalam kajian ini menggunakan perisian etabs. kaedah analisis statik bukan linear (pushover) digunakan bagi menganalisis dan merancang struktur bangunan rc ini dengan dinding ricih. kesimpulannya peningkatan ketebalan dinding ricih menyebabkan penurunan nilai kemuluran, dan penurunan nilai kemuluran juga akan terjadi ketika posisi dinding ricih berubah dari tepi ke tengah. keywords: ductility; non-linear static analysis; earthquake design; pushover curve; shear wall 1. introduction according to past earthquakes, several reinforced concrete structures have either failed or sustained different degrees of destruction. overall, knowing the seismic efficiency of structures has been a question for science communities for a long time [1]. one of the most dangerous natural hazards is an earthquake that causes great losses of life and property damage [2]. 32 mailto:rifat.resatoglu@neu.edu.tr iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 earthquake-resistant structural system design depends on standardized seismic requirements to provide secure quality of life during massive earthquakes [3]. it is essential to build analytical modeling to evaluate the seismic behavior of current systems and to modify structural performance properties such as strength, stiffness, and deflection to betterdesired performance specifications [4]. the destruction depends not only on the scale of the earthquake but also on the form of the structural system. of utmost importance here, the dual system includes structural reinforced concrete frames with shear walls (mrfsw). dual structural frameworks are generally utilized as structural frameworks offering resistance to gravity and lateral forces [5]. in engineering structures, the concept of the formation of structural systems corresponds with the resistance to lateral forces of building structures. based upon the variety of stresses that may occur throughout the structural elements due to the implementation of forces, the widely utilized structural systems are divided into various groups [6]. the structural system formation is designed to work against longitudinal forces of gravity and lateral loads affected by wind or earthquake actions. gravity loads and lateral loads are the primary loads that are exposed to building structures [7]. shear walls are among the most widely applied systems in buildings to withstand lateral loads. implementing a shear wall is an effective solution to stiffen structural systems under lateral loads. the primary function of a shear wall is to increase the rigidity and strength of the building for lateral resistance [8]. shear walls are widely utilized as a longitudinal structural component across modern buildings to withstand the lateral loads caused by winds and earthquakes. if a reinforced concrete shear wall is built to become a ductile element, it already conducts forces significantly better. to increase the ductility of shear walls, the shear wall's general geometric measurements, the form and quantity of reinforcement, and the relation against the other components through the building support should be taken into consideration [9]. the location, number and curtailment of shear walls act an important factor for the soft story structures to displace during an earthquake. to minimize the negative influence of twisting in buildings, shear walls should be perfectly symmetrically positioned through plan [10]. the capacity of members or structural components that show displacement is generally indicated by the required ductility ratios, μ, in earthquake-resistant design. [11]. the ratio of maximum displacement identifies ductility proportion (∆m) to the related displacement at the beginning of yield (∆y) [12]. pushover analysis is a static non-linear technique that progressively raises the amount of the horizontal loads, preserving a specified distribution sequence throughout the height of the structure. pushover analysis, considering the maximum load and the peak inelastic deformation, will define a building's performance. influences of nonlinear static analysis can be modified once a mechanism of collapse has been formed. the primary benefit of pushover analysis is to obtain an over-strength estimation and provide a sense of the system's general ability to sustain inelastic displacement ductility [13]. nonlinear pushover analysis offers sufficient knowledge regarding the building's durability, deformation capability, the discovery of the yield displacement, and the ultimate displacement, which are all used to compute the building structure's ductility from dividing the maximum displacement by the displacement of the yield [14]. the pushover analysis assesses the structural system's predicted quality by measuring the structural system's strength and deflection. this approach computes the building's base shear capability and the performance stages of each building component against various degrees of earthquake force [15]. 33 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 2. objective of the study this present work aims to assess the rc structural buildings' ductility using various parameters with different thicknesses and different positions of shear walls. the research study evaluates the seismic assessment and the ductility of the 2d models of dual systems (mrfsw) using the pushover method. moreover, to evaluate the degree of impact on ductility value, different parameters such as span length, compressive strengths of concrete, number of stories, various thicknesses of the shear wall, and different positions of the shear wall are chosen. 3. literature review the effect of shear walls upon rc building structures' seismic efficiency is presented in this study. an estimate was made to assess losses in building structures, including suitable concrete and reinforced materials and shear walls besides beams and columns. these research findings will help select appropriate materials for structural buildings and shear walls in order to avoid destruction [16]. the impact of shear wall position in seismic resistance is defined [17]. the usage of the shear wall will efficiently decrease the displacement of the structure and story drifting. the shear walls' positioning in the centre of structures evenly provides an excellent performance that decreases the displacement and story-drift. shinde and raut [18] studied the varying shear wall thicknesses throughout similar buildings at various levels, preserving the places around similar positions and their impact upon multi-storied buildings' deformation. it is discovered, according to the findings, that the thickness already raises the rigidity, and by increasing the height and thickness, the deformation of shear walls decreases. the suitability of pushover analysis has been discussed for seismic evaluation of mid-rise to high-rise shear wall building structures and showed that pushover analysis understates the inner story drifts, especially those located on the top floors of building structures, and magnifies inelastic maximum roof displacement [19]. carrillo et al. [20] studied ductility for earthquake design of rc walls for low-rise houses. the study contrasts and explains rc walls' ductility value generally utilized in onefloor and two-floor houses. ductility capabilities in this research will be utilized to estimate the power modification and displacement amplification factors. the purpose of ductility throughout structural buildings is to guarantee that they have a specific amount of energy dispersion and deformation to prevent brittle destruction throughout the event of an earthquake [21]. considering the reaction of a structural framework to seismic behavior may be managed by limiting lateral displacements, the ductile approach should be designed [22]. the major energy absorbing component utilized by the current design technique to produce a ductile performance throughout a seismic loading cycle was plastic hinges. as per seismic design rules in current building codes, structures shall withstand minor to severe earthquakes without harm, at most without major damage or collapse [23]. throughout a large seism, the structure should get a low-cost resistance. plastic energy might be employed during the design by ground shaking a structure for efficiency assessment. the appropriate amount of ductility is crucial for rc structure collapse prevention [24]. venkatesh et al. [25] investigated the structural performance of rc moment-resisting frames with and without shear walls at various places to withstand seismic loads, as used in modern building techniques. in the condition of shear walls, the outcomes show higher resistance to horizontal loads. the impact of shear walls on the vulnerability of structures is 34 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 demonstrated in [26]. shear walls were examined for a g+8 story structure with and without shear walls. once compared to the models without the shear wall, the shear wall model showed a significant decline in horizontal displacement. because the structure's stiffness had increased, the displacement of the story had decreased. 4. methodology 4.1 introduction the analyzed rc dual system (mrfsw) is designed in accordance with asce 7-10 seismic design code. shear walls can minimize the lateral displacement of the building structures during the impact of earthquakes. the implementation of shear walls is a functionally effective solution for stiffening structures. the pushover analysis method is used to verify the yield displacement, maximum displacement, maximum base shear, and ductility ratio for 96 models with several thicknesses and positions of shear walls including various parameters such as span length, number of stories and compressive strengths of concrete. the location of the models is assumed to be in washington dc, united states of america. 4.2 material properties and details of models the material properties and details of the models are given below in table 1 and table 2, respectively. table 1: material properties of models table 2: details of 2d models parameters value number of stories (s) low (4), mid (8), and high-rise building (12) number of spans(n) 5 spans height of stories(h) typical story height (3.2m) and ground floor height (4m) span length(l) 5m, 5.5m, 6m, and 7m. positions of the shear wall. middle and edge thicknesses of shear wall 250mm and 300mm location of buildings washington dc, usa column section size for 4,8 and 12 stories 400mm*400mm, 400mm*650mm, and 400mm*800mm beam section sizes for 4,8 and 12 stories 350mm*400mm, 350mm*450mm, and 400mm*500mm material value compressive strength( 𝑓 ′𝑐) 250, 300 𝑘𝑔𝑓/𝑐𝑚2 𝐹𝑦 of reinforcement steel 420 𝑁/𝑚𝑚2. steel modulus of elasticity 200,000 𝑁/𝑚𝑚2 concrete modulus of elasticity 23500 and 25743 𝑁/𝑚𝑚2 unit weight of concrete 24 𝑘𝑁/𝑚3 live load 2 𝑘𝑁/𝑚2 super dead load 1.5 𝑘𝑁/𝑚2 masonry load 14 𝑘𝑁/𝑚 shear modulus, g 99847.2, 109377 𝑘𝑔𝑓/𝑐𝑚2 35 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 (a) edge (b) middle fig. 1: different positions of the shear wall. 4.3 seismic analysis methods every structure must be designed in a way to resist lateral forces including earthquakes [27]. in order to determine the performance and the maximum response of the structures, instead of the use of complicated nonlinear dynamic analysis, a nonlinear static analysis was employed, which is a simpler and quicker method for the estimation of the structural response. fig. 2: seismic analysis methods. 4.4 bilinear curve of pushover curve the request for a straightforward approach to estimate the non-linear analysis of a structure against earthquake loading is widely recognized as the pushover study. pushover curves illustrate the structure's nonlinear nature and a base shear deformed curve against the construction's lateral floor displacement. this method is dependent upon the principles of fema356, assuming equal regions underneath the primary curve and bilinear curves. a bilinear pushover curve has been constructed for every design building method and reflects various earthquake designs and building efficiency stages. so, each curve has been defined via 2 points: yields of capability and ultimate capacity. the maximal capacity was achieved after the general structural framework was developed as a total approach. a 15 percent reduction in strength occurred by failing specific components to reach the deformation linear nonlinear static (equivalent lateral load) static (pushover) dynamic (response spectrum) dynamic (time history) seismic analysis methods 36 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 capability. consequently, the strength referring to the optimum capacity does not always correlate with the actual highest power reported through the study. furthermore, the yield capability is not the building's power while the member's initial yield occurs. fig. 3: the bilinear curve of pushover curve [11]. 4.5 sample of the bilinear curve of capacity curve the ratio between the maximum displacement and linear displacement in a bilinear capacity curve is defined as the ductility factor. in order to estimate a bilinear curve from the capacity curve, the area under both curves must be identical. to determine the global yield point, the capacity curve is usually simplified as a bilinear curve that has the same area with respect to the axis of spectral displacement, which is referred to as the equal energy rule. the main intent for this procedure is to find the area under the pushover curve, which corresponds to the dissipated energy during earthquake, and it should be equal to the area under the bilinear curve. that area calculation is carried out using autocad, which is a commercial computer-aided design and drafting software application. these areas above the capacity curve and below the bilinear curve are shown in fig. 4. fig. 4: bilinear relationship of base shear versus roof displacement. thus, the pushover curve is exported from etabs to microsoft excel and is then transferred to autocad. in this stage, a horizontal line is drawn from 85% of the pushover 0 500 1000 1500 2000 2500 3000 3500 4000 0 100 200 300 400 500 600 700 b a se s h e a r ( k n ) displacement (mm) capacity curve bilinear curve ∆m=589.60mm∆y=195.13mm a2=58.52 a1=a2 a1=58.49 37 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 curve's maximum base shear. this line intersects the pushover curve and is passes it. another line is drawn from the coordinate centre and intersects with the drawn horizontal line. after that, the areas below the pushover curve and above the pushover curves are compared with each other, and the position of the second drawn line is changed until both areas are the almost equal. 5. results and discussions 5.1 results the results of yield displacement, maximum displacement, maximum base shear that were obtained from the pushover curve, and the ductility ratio calculated by dividing ∆𝑚 over ∆𝑦, as shown in equation (1), are summarized in table 3, table 4, and table 5 with compressive strength ( 𝑓 ′𝑐), 300 𝑘𝑔𝑓/𝑐𝑚2 for low-rise, mid-rise, and high-rise buildings, respectively. the equation for finding ductility ratio: µ= ∆𝑚 ∆𝑦 (1) table 3: results of pushover analysis and ductility values for low-rise (4-story) buildings 5.2 the effect of span length on ductility values ductility values of various span lengths are shown in tables 3, 4, and 5, and a comparison of ductility values with different span lengths is shown in fig. 5. this figure shows an increase in ductility value by 6%, 10%, and 31% caused by increasing the span length with 10%, 20%, and 40%, respectively. on the other hand, once span length increases, a reduction in yield displacement and an increase in maximum displacement can occur. the parameters used in this section are the shear wall position, which is located in the middle, and the number of stories, i.e., 4-story. 38 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 table 4: results of pushover analysis and ductility values for mid-rise (8-story) buildings table 5: results of pushover analysis and ductility values for high-rise (12-story) buildings fig. 5: the comparison between the ductility values for different span lengths in a 4-story building. 39 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 5.3 the effect of number of stories on ductility values in this section, the effect of the number of stories on ductility values is defined. ductility values of various numbers of stories are shown in tables 3, 4, and 5. the ductility value is increased by 33% by increasing the number of stories from 4 to 8 and by 71% from 4 to 12. this can be seen in fig. 6. the increment in the number of stories leads to increased yield displacement and ultimate displacement, which is how ductility value rises. parameters used in this section are: shear wall thickness = 300 mm, and shear wall position = middle. fig. 6: comparison of the values of ductility of different number of stories. 5.4 the effect of different thicknesses and positions of the shear wall on ductility values and capacity (pushover curve) the impact of different shear wall thicknesses and positions on ductility ratio is described in this section. table 3, 4 and 5 illustrate ductility rates with variations in different shear wall thicknesses and positions, respectively. as seen in fig. 7, as shear wall thickness increases from 250 mm to 300 mm, a decrease in ductility values will occur by 15%. increasing shear wall thicknesses from 250 mm to 300 mm caused an increment in yield displacement (∆𝑦) and a decrease in maximum displacement (∆𝑚) will occur that resulted in a reduction in ductility values. moreover, as shown in fig. 8, increasing shear wall thickness causes an increase in maximum base shear. as shown in fig. 9, when shear wall position changes from edge to middle, it causes a decrease in ductility value of 20 % and causes an increase in both yield displacement (∆𝑦), and ultimate displacement (∆𝑚). as shown in fig. 10, a change in shear wall position from edge to middle induces an increase in maximum base shear. 40 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 fig. 7: comparison between the values of ductility for different thicknesses of shear wall. fig. 8: the impact of the different thicknesses of the shear wall on the capacity (pushover) curve. fig. 9: comparison of the ductility values of different positions of shear wall. 41 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 fig. 10: the impact of the different positions of the shear wall on the capacity (pushover) curve. 6. conclusions in this paper, the two-dimensional dual system (mrfsw) has been studied. the models are designed with different thicknesses and shear wall positions to evaluate the ductility, maximum displacement, yield displacement, and maximum base shear. the summarized outcomes of this study are as follows:  increasing span length causes an increase in ductility value in low, mid, and highrise buildings. it has also been observed that by increasing the span length, there will be an increase in the yield displacement and maximum displacement.  by increasing the span length, it has been observed that the maximum base shear force decreases in all building models.  increasing the number of stories causes an increase in ductility value because the stiffness of the building will decrease by adding more floors.  when the shear wall thickness was increased from 250 mm to 300 mm, it was observed that there was a decrease in ductility values.  it has been observed that increasing shear wall thickness causes an increase in maximum base shear force.  the ductility rate is noticed to decrease by increasing the shear wall thickness.  when the shear wall position changes from edge to middle, it causes a reduction in ductility value.  by changing the shear wall position from the edge to the middle, an increase in both the yield displacement and the ultimate displacement has been found.  changing the shear wall position from edge to middle causes an increase in maximum base shear force for all story buildings. references [1] chou cc, tsai wj, chung pt. (2016) development and validation tests of a dual-core selfcentering sandwiched buckling-restrained brace (sc-sbrb) for seismic resistance. sciencedirect, 121(15): 30-41. [2] yön b, sayın e, onat o. (2017) earthquake and structural damages. earthquakes-tectonics, hazard and risk mitigation, 21(3): 319-339. 42 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 [3] furtado a, rodrigues h, arêde a, varum h, grubišić m, šipoš tk. (2018) prediction of the earthquake response of a three-story infilled rc structure. engineering structures, 171: 214235. [4] ravikumara hs, kulkarni sr, ks bna. (2015) study of plastic hinge formation in r.c frames with non-linear static analysis. an international journal of research in engineering and technology, 4(9): 179-182. [5] zerbin m, aprile a, spacone e. (2020) new formulation of ductility reduction factor of rc frame-wall dual systems for design under earthquake loadings. soil dynamics and earthquake engineering, 138: 106279. [6] rana en, rana s. (2014) structural forms systems for tall building structures. ssrg international journal of civil engineering, 1(4): 33-35. [7] esmaili o, epackachi s, samadzad m, mirghaderi sr. (2008) study of structural rc shear wall system in a 56-story rc tall building. the 14th world conference earthquake engineering. [8] madhu s. (2018) optimum location of shear walls in a r.c building. international journal of scientific & engineering research, 9(7): 2229-5518. [9] lovaraju k, balaji dk. (2015) effective location of shear walls on the performance of building frame subjected to earthquake load. international advanced research journal in science, engineering and technology, 2(1): 123-129. [10] rokanuzzaman m, farjana k, anik d, reza s. (2017) effective location of shear walls on the performance of building frame subjected to lateral loading. international journal of advances in mechanical and civil engineering, 4(6): 23-31. [11] vielma-perez jc, mulder mm. (2018) improved procedure for determining the ductility of buildings under seismic loads. revista internacional de métodos numéricos para cálculo y diseño en ingeniería, 34(1): 61-66. [12] mehta bb, vasani pc. (2014) ductility requirements for buildings. applied mechanics department, 216: 113-122. [13] khoshnoudian f, mestri s, abedinik f. (2011) proposal of lateral load pattern for pushover analysis of rc buildings. computational methods in civil engineering, 2(2): 169-183. [14] wang z, martinez-vazquez p, zhao b. (2020). pushover analysis of structures subjected to combined actions of earthquake and wind. engineering structures, 221: 111034. [15] kadid a, boumrkik a. (2008) pushover analysis of rc frame structure. asian journal of civil engineering, 9(1): 75-83. [16] ozkul t, kurtbeyoglu a, borekci m, zengin b, kocak a. (2019) effect of shear wall on seismic performance of rc frame buildings. engineering failure analysis, 100: 60-75. [17] tarigan j, manggala j, sitorus t. (2018) the effect of shear wall location in resisting earthquake. ms&e, 309(1): 012077. [18] shinde sb, raut nb. (2016) effect of change in thicknesses and height in shear wall on deflection of multistoried buildings. international journal of civil engineering and technology, 7(6): 587-591. [19] huang k, kuang js. (2010) on the applicability of pushover analysis for seismic evaluation of mediumand high-rise buildings. the structural design of tall and special buildings, 19: 573-588. [20] carrillo j, gonzález g, rubiano a. (2014) displacement ductility for seismic design of rc walls for low-rise housing. latin american journal of solids and structures, 11(4): 725-737. [21] xu, y. y., lin, z. r., & zhang, t. (2016). design features and significance of the ductile reinforced concrete frame structure. in design, manufacturing and mechatronics: proceedings of the 2015 international conference on design, manufacturing and mechatronics, 183-189. [22] sococol i, mihai p, olteanu-donţov i. (2019) ductility–concept for improving the seismic response for structural reinforced concrete frame systems. buletinul institutului politehnic din lasi. sectia constructii, arhitectura, 65(1): 17-30. [23] mantawy h. (2015) ductility of rc frame buildings subjected to the recent new zealand earthquakes. 5(1): 1–8. [24] skhakov r. (2003) seismic energy dissipation and ductility of rc elements section. in fifth national conference on earthquake engineering, 21(4): 22-32 43 iium engineering journal, vol. 23, no. 2, 2022 resatoglu and jkhsi https://doi.org/10.31436/iiumej.v23i2.2070 [25] venkatesh sv, bai hs, navanitha c. (2009) performance of rc frame with and without shear wall subjected to earthquake load. in proceedings of civil engineering conferenceinnovation without limits, 18(1): 19-21. [26] bongilwar r, harne vr, chopade a. (2018) significance of shear wall in multi-storey structure with seismic analysis. in iop conference series: materials science and engineering, 330(1): 12-17. [27] rathod sd, bhokare ss, dhiwar ps, shinde rn. (2017) comparative pushover analysis of rcc, steel and composite high rise building frame (g+11) using etabs. journal of information, knowledge, and research in civil engineering, 4(2): 88-94. 44 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 enhancement of the calorific value of empty fruit bunch (efb) by adding municipal solid waste as solid fuel in gasification process amadou dioulde donghol diallo, ma’an fahmi rashid alkhatib*, md. zahangir alam and maizirwan mel bioenvironmental engineering research centre (berc), department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia * corresponding author: maan@iium.edu.my (received: 3rd august 2020; accepted: 23rd january 2021; published on-line: 4th july 2021) abstract: empty fruit bunch (efb), a biomass-based waste, was deemed a potential replacement for fossil fuel. it is renewable and carbon neutral. the efficient management of this potential energy will help to deal with the problem associated with fossil fuels. however, a key parameter for evaluating the quality of raw material (efb) as a fuel in energy applications is the calorific value (cv). when this cv is low, then its potential utilization as feedstock will be restricted. to tackle this shortcoming, we propose to add municipal solid waste to enhance energetic value. thus, two major issues will be solved: managing solid residues and contributing an alternative energy source. this study aimed to investigate the possibility of mixing efb and municipal solid waste (msw) to make clean energy that is conscious of the environment (climate change) and sustainable development. the selected msw, comprising of plastics, textiles, foam, and cardboard, were mixed, with efb at various ratios. proximate analysis was used to determine moisture content, ash, volatiles, and fixed carbon, whilst elemental analysis, is used to determine chns/o for msw, efb and their various mixtures. the cv of each element was also measured. the research revealed a significant increase in the calorific value of efb by mixing it with msw according to msw/efb ratios: 0.25; 0.42; 0.66; 1.00 and 1.50 the corresponding calorific values in (mj/kg) were 19.77; 21.22; 22.67; 27.04 and 28.47 respectively. while the calorific value of pure efb was 16.86 mj/kg, the mixing of efb with msw promoted the increase in the cv of efb to an average of 23.83mj/kg. another potential environmental benefit of applying this likely fuel was the low chlorine (0.21 wt. % to 0.95 wt. %) and sulfur concentrations (0.041 wt. % to 0.078 wt.%). this potential fuel could be used as solid refuse fuel (srf) or refuse-derived fuel (rdf) in a pyrolysis or gasification process with little to no environmental effects. abstrak: tandan buah kosong (efb), sisa berasaskan biojisim, adalah berpotensi sebagai pengganti bahan bakar fosil. ia boleh diperbaharui dan karbon neutral. pengurusan berkesan pada potensi tenaga ini dapat membantu mengatasi masalah melibatkan bahan bakar fosil. namun, kunci parameter bagi menilai kualiti bahan mentah (efb) sebagai bahan bakar dalam aplikasi tenaga adalah nilai kalori (cv). apabila cv rendah, potensi menjadi stok suapan adalah terhad. sebagai penyelesaian, kajian ini mencadangkan sisa pepejal bandaran ditambah bagi meningkatkan nilai tenaga. oleh itu, dua isu besar dapat diselesaikan: mengurus sisa pepejal dan menambah sumber tenaga alternatif. kajian ini bertujuan mengkaji potensi campuran tandan buah kosong (efb) dan sisa pepejal bandaran (msw) bagi menghasilkan tenaga bersih dari 10 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 sudut persekitaran (perubahan iklim) dan pembangunan lestari. pemilihan msw, terdiri daripada plastik, tekstil, gabus dan kadbod, dicampurlan dengan pelbagai nisbah efb. analisis proksimat telah digunakan bagi mendapatkan kandungan kelembapan, abu, ruapan, dan karbon tetap, manakala analisis asas telah digunakan bagi mendapatkan chns/o bersama msw, efb dan pelbagai campuran lain. nilai kalori (cv) setiap elemen turut diukur. dapatan kajian menunjukkan penambahan ketara dalam nilai kalori efb dengan campuran bersama msw berdasarkan nisbah msw/efb 0.25; 0.42; 0.66; 1.00 dan 1.50 nilai kalori sepadan (mj/kg) adalah 19.77; 21.22; 22.67; 27.04 dan 28.47 masing-masing. manakala nilai kalori efb tulen adalah 16.86 mj/kg, campuran efb dan msw menunjukkan kenaikan cv dengan efb pada purata 23.83mj/kg. antara potensi semula jadi lain adalah dengan mencampurkan bahan bakar ini dengan kalori rendah (0.21 wt. % kepada 0.95 wt. %) dan kepekatan sulfur (0.041 wt. % kepada 0.078 wt.%). bahan bakar ini berpotensi sebagai bahan bakar pepejal sampah (srf) atau bahan bakar yang terhasil dari pepejal sampah (rdf) melalui proses pirolisis atau proses gasifikasi yang sedikit atau tiada kesan langsung terhadap persekitaran. keywords: municipal solid waste; empty fruit bunch; calorific value; energy; refuse derived fuel 1. introduction until now, fossil fuels account for almost 84% of global energy demand [1], and are the most reliable sources of energy. global production of solid waste increases with an increase in population, leading to environmental pollution [2-4]. according to massarutto [5] the world energy consumption in 2020 amounts to 196 terawatts (tw) of which 76 for electricity and 120 for heat, and that the potential production of energy from waste maybe double the actual figures. the production of solid waste in the world in 2011 amounted to 2 billion tons of waste during the year. and by 2025, it is estimated that there will be 2.2 billion tons of waste per year, after which 9.5 billion tons of waste will be produced per year in 2050 [3,6,7]. biomass gasification has a high potential for waste treatment compared to other existing techniques, such as soil filling, incineration, etc., because it can accept a wide range of inputs and may produce multiple useful products. biomass gasification is an intricate process involving the drying of the feedstock followed by pyrolysis, partial combustion of the intermediates, and finally gasification of the resulting products [7]. the calorific value (cv) is the key parameter for assessing the quality of the feedstock (efb) as fuel in energy applications. however, this calorific value for efb is low. in order to improve this calorific value, it must be mixed with other raw materials such as msw. municipal solid and biomass wastes are among the most sustainable sources of energy. vaish et al. [8], reported that the complexity and the increasing quantity of solid waste had made msw management a challenging task worldwide. biomass waste is abundant in many countries over the world, like malaysia, indonesia, guinea conakry, etc. among all, biomass waste offers significant opportunities for major, renewable, and suitable environmental-friendly energy sources. these residua, instead of being sent to landfill, could be valorized as a source of energy. another means to manage msw is by incineration. heavy metals like mercury (hg), cadmium (cd), arsenic (as), chromium (cr), and lead (pb), etc., contained in fly ash can cause air pollution by incineration of msw and soil and water pollution. the emissions of sox, nox, cox, and furans can pollute the environment likewise [2,9]. moreover, greenhouse gases (ghg) emissions should be reduced by the use of suitable technologies. the third-largest source of ghg is msw at almost 3-4% of the global anthropogenic methane, and 18% of global methane 11 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 emission came from total waste sectors [1]. as indicated in the study by vaish et al. [8] to achieve the goal of sustainable development, the problem of climate change, and other environmental challenges, must be tackled. msw is usually, managed through disposal at landfills, which experience severe environmental conditions, such as leachate, high salinity, and ghg generation [10]. sikarwar et al. [7] estimate that the production of electricity from fossils contributes to pollution and the emission of ghgs. solid residues are an alternative to provide environmentally friendly and sustainable energy, that is economically profitable when properly managed and processed [6,11,12]. solid refuse fuel (srf) and refuse-derived fuel (rdf), can be manufactured in the form of pellets, bricks, etc. it is easy to transport and could contribute to the reduction of pollution problems related to discharge and provides much-needed energy, especially for people suffering a shortage of fuels. previous studies had promoted srf and rdf technology, including its characteristics, composition, determination of high heating value, and other parameters [13-17]. in terms of thermal conversion, gasification is one of the many routes to produce clean and environmentally friendly fuel [18,19]. the synthesis gas production by gasification is a process of recovering energy from solid fuels using a high temperature. the quality of rdf depends primarily on the composition of the raw material such as plastic and heavy polymer containers, textiles, foam, etc., which are the basis for the increase in the heating value of fuel oil [13,20-22]. in other words, a higher calorific value is associated, with the content of paper/cardboard, plastic, etc., and their presence in high quantities at (40-80% w/w; weight by weight) can promote the reduction of emissions of co2. this study aims to improve the efb’s calorific value by adding specific amounts of msw. it could be a promising cleaner alternative solution to polluted fossil fuels. the study focused on the quality of the calorific value and special importance was given to reducing the environmental pollution. 2. materials and methods the data collected for this study was based on proximate and ultimate analysis of municipal solid waste and biomass, followed by a calorific value (cv) measurement. the analysis investigated the impact of moisture content, temperature, steam to biomass ratio, and particle size on gas composition, etc. adequate heating values make the material promising for applications such as gasification as rdf and srf technology [12,19]. 2.1 feed materials municipal solid and biomass wastes are abundant in malaysia; the estimated annual msw generated is about 13.68 mt per year, and about 1.17 kg average rate per capita per day of waste, while the amount of efb waste was estimated at 7.78 mt per year [17]. municipal solid waste (plastics, textile, paper/ cardboard, and foam) was collected at the gombak msw transportation station landfill and biomass waste (empty fruit bunch) was collected from sime darby research center at carey island, (selangor). the samples were ground to an average particle size of approximately 0.5 -1 mm, and 0.5-1 g were used as feed material. 12 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 2.2 preparation of municipal solid waste samples municipal solid and biomass waste had been selected as feedstock for the experiment. some samples (plastic, cardboard/paper, foam, and textile residue) were chosen and characterized. these components were selected because data and statistics from national solid waste management malaysia [17] indicated that they are the major constituents of msw. characterized samples were dried in the sun to remove moisture. the samples were prepared to a particle size at 0.5-1 mm for foam, plastic, textile, cardboard, and empty fruit bunch. following these sizes, each sample was weighed into a certain scale to determine the amount needed for mixing. then, five selected samples with different ratios were examined. 2.3 proximate analysis quantitative determination of moisture content, which has an impact on the calorific value; volatile matter, which represents the matter burns in a gaseous state; ash as inorganic waste material; and fixed carbon which amounts to the solid-state is determined using proximate analysis. 2.4 determination of moisture content moisture content is considered an important factor that affects the fuel property, seeing that it has an impact on the combustion behavior of the material and its stability. so, the moisture content is determined using astm e 871 standards by measuring the weight difference after heating the sample in the oven. it is done by weighing a known mass of the samples in an alumina crucible container and placing them in the oven at a set temperature of 105 oc for 1 hour. the difference in weight was recorded and calculated as a percentage of the sample weight. 2.5 determination of ash content the experimental procedure includes preparation of msw and efb mixed to a welldefined proportion, then the samples of sizes between 0.5 mm and 1 mm put in an alumina crucible. the muffle furnace linn high therm, type: (lm.212.26 db006031) was initially purged to remove gaseous combustibles in the furnace. the experiment is performed from ambient temperature up to the maximum temperature of 700 oc at a constant heating rate of 10 oc/min for 30 minutes (standard method astm d1102-84). the sample is then cooled in air, then in a desiccator, and finally weighed. 2.6 determination of volatile matter the experimental procedure includes preparation of msw and efb mixed to a welldefined proportion, then, the samples of sizes between 0.5 mm and 1 mm were put in an alumina crucible. the muffle furnace linn high therm, type: (lm.312.06 db004031) was initially purged to remove gaseous combustibles in a furnace. the experiment was performed from ambient temperature up to a maximum temperature of 925 oc at a constant heating rate of 10 oc/min, for seven minutes (standard method astm e872). then the sample was cooled in air, then in a desiccator, and weighed. finally, calculations were performed to determine the percentage of volatile matter in the samples. the fixed carbon determined through the difference of the sum of the others with the total sample. equations (1) and (2) are for the determination of fixed carbon and volatile matter, respectively. 13 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 fc= 1mcvmash (1) where: fc, is the fixed carbon in the msw and efb that remain in the char during the pyrolysis process after devolatilization. mc stands for moisture content, vm, volatile matter, and ash is the solid residue of msw and efb. the volatile matter (vm) is determined by the equation: vm= loss in weight of sample at 925±20˚c weight of sample taken ∗ 100 (2) all analyses were performed in duplicate. 2.7 ultimate analysis the ultimate analysis is used to determine the percentage of the following elements by standard methods, carbon (c), and hydrogen (h), by (astm e-777), nitrogen was performed by (astm e-778), chlorine, by (astm e776-87), and sulfur using (astm e-775). all these samples were analyzed in leco series 628 chns. oxygen was determined by subtracting the sum of all others cited above from the total of samples. 2.8 heating value to perform the calorific value of the msw and efb mixture, a parr 1341 oxygen bomb calorimeter was used for the analysis. it measures the energy released when the sample undergoes complete combustion in the presence of oxygen under a standard condition. 2.9 chemical composition of msw and efb the chemical composition of msw and efb is shown in table 1. table 2 illustrates the ratio of the msw and efb mixture. table 1: chemical composition of msw no components msw percentage (%) efb percentage (%) 1 c 52.96 41.2 2 h 6.58 6.36 3 o 36.78 47.70 4 n 0.65 0.74 5 s 0.028 0.09 6 cl 0.24 1.010 table 2: a mixing ratio of msw and efb samples no mixed elements wt.% 1 20 (msw) +80 (efb) 2 30 (msw) +70 (efb) 3 40 (msw) +60 (efb) 4 50 (msw) +50 (efb) 5 60 (msw) +40 (efb) 14 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 3. results and discussion the analyses of msw and efb were carried out individually and for their mixtures in predetermined proportions. then the calorific value was measured for each sample. figure 1 shows the results of the proximate analysis. the minimum value of volatile matter (2.96 wt.%) was found for efb, while the maximum amount (3.50 wt.%) belonged to msw. efb has the highest moisture and ash content (15.4 wt.% and 3.9 wt.% respectively) and the lowest held by msw (7.5 wt.% and 2.99 wt.% respectively). efb gasification would incur an additional cost for drying due to high moisture content. efb had the lowest fixed carbon value compared to msw (77.74 wt.% and 86 wt.% respectively). the higher fixed carbon, low moisture content, moderate volatile matter, and ash, thus resulting in higher heating value for msw. a similar result was reported by afzanizam et al. [23]. fig. 1: proximate analysis of msw and efb. the effect of the mixture (msw and efb) ratio on proximate analysis is shown in fig. 2. it can be seen that the msw and efb mixture of 60:40 % has the lowest ash (2.33 wt.%). the highest ash yield (4.22 wt.%), moisture content (12.43 wt.%), volatile matter (3.5 wt.%), and fixed carbon (92.03 wt.%) belong to (50:50; 20:80; 20:80 and 60:40 respectively). moreover, the moisture content and volatile matter decrease as the quantity of msw supplied in the mixture increases. also, ash, fixed carbon, and the calorific value increase proportionally with the increase of msw in the mixture. the ultimate analysis of pure msw and efb is shown in fig. 3. the msw has the highest percentage of carbon and hydrogen (52.96 wt.% and 6.56 wt.% respectively) and the lowest of oxygen and nitrogen (36.79 wt.% and 0.65 wt.% respectively). these two elements, carbon, and hydrogen are significant in the fuel because they increase the calorific value. similar findings were observed by [23,24]. the high quantity of carbon and hydrogen implies that this raw material could be used as a fuel in thermochemical energy conversion like pyrolysis and gasification for syngas production. it appears that carbon-hydrogen and calorific value increase with the elevation of the amount of msw in the mixture. in other words, the calorific value increases proportionally, with msw due to higher carbon and hydrogen content. in contrast, a small amount of nitrogen promotes the quality of the fuel, because it has no calorific value. the highest value of sulfur found in efb (0.0908 wt.%) followed by cardboard (0.0886 wt.%) and textile /foam (0.0594 wt.%) and the lowest in plastics (0.00751 wt.%) followed by 0 10 20 30 40 50 60 70 80 90 0 10 20 30 40 50 60 70 80 90 100 moisture content ash content volatile matter fixed carbon hhv h ig h h e a ti n g v a lu e (m j /k g ) c o m p o si ti o n ( w t. % ) msw efb 15 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 msw (0.0287 wt.%). sulfur also increases the value of fuel, but a large amount of sulfur leads to a smoky flame and it is harmful to the environment. fig. 2: proximate analysis of msw and efb mixture. fig. 3: ultimate analysis of msw and efb (inset: a zoom in for elemental composition of nitrogen and sulfur for the same materials). when the proportion of msw and efb is (50:50), carbon, and hydrogen got the highest values (52.50 wt.%) and (7.95 wt.%) respectively, while oxygen and nitrogen have the smallest concentration (34.71 wt.%, and 0.33 wt.% respectively) as seen in fig. 4. the comparison of carbon concentrations in fig. 3 and fig. 4 demonstrates a gain of 11 wt.% for efb, which was 41 wt. % for pure efb compared to 52 wt.% for msw and efb mixture of 50:50%. the carbon is one of the sources of the calorific value, the mix of msw and efb allows increasing the heating value of efb. besides, the calorific value of the mixture gradually increases from 19.77 mj/kg to 28.47 mj/kg, as the added amount of msw increases. it seems likely that these results are due, in fact, to the constituent elements of msw including carbon, and hydrogen in the plastics portions (72.84 wt.% and 9.46 wt.% respectively). figure 5 shows the gradual increase in the calorific value of the msw and efb mixture. 0 10 20 30 40 50 60 70 80 90 100 moisture content ash content volatile matter fixed carbon c o m p o si ti o n ( w t. % ) msw+efb: 20-80 msw+efb:30-70 msw+efb:40-60 msw+efb:50-50 msw+efb:60-40 0 0.2 0.4 0.6 0.8 nitrogen sulfur e le m e n ta l co m p o si ti o n (w t. % ) 16 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 fig. 4: ultimate analysis of msw and efb mixture (inset: a zoom in for elemental composition of nitrogen, chlorine and sulfur for the same materials). hydrogen sulfide reacts with metals to produce the corresponding metallic sulfide. thus, chlorine is deposited and poses a technical (i.e. corrosion of the wall of the device) and environmental problem during the gasification process. the concentration of chlorine in these samples varied from (0.154 wt.% cardboard to 1.010 wt.% efb). the average concentration of each component namely cardboard (0.154 wt.%), plastics (0.166 wt.%), textile and foam (0.531 wt.%), municipal solid waste (0.249 wt.%), and empty fruit bunch (1.010 wt.%) was measured. the finding shows the mixtures of efb and msw have high potential to produce rdf or srf fuel. based on the european standard en 15359, the components used in this study show that msw with 0.249 wt.% of cl, and 29.74 mj/kg as low heating value (lhv) is class 1, textiles (0.531 wt.% cl) class 2, efb (1.010 wt.% cl) and 15.09 mj/kg as low heating value (lhv) is class 3, thus the mixture efb and msw (0.21 wt.% cl), and (0.041 wt.% s) is class1 [16] as shown in table 3. the high heating value (hhv) can be converted into the low heating value (lhv) using the following formula: lhvi = hhvi – we. (9.hi +wi) (3) with lhvi : lhv of ith waste fraction, hhvi: hhv of ith waste fraction, we: standard heat of evaporation of water (2.441 mj/kg), hi: hydrogen content of ith waste fraction and wi : moisture content of ith waste fraction [12]. from the result of fig. 5, where the calorific value was expressed in hhv and the table 3 where the calorific value was expressed in lhv, formula (3) was used for the calculation of lhv. the mixture having a ratio of 60 (msw) and 40 (efb) has proven to be the best among others as it has the greatest calorific value (28.47 mj/kg) and lowest concentrations 0 10 20 30 40 50 60 carbon oxygen hydrogen nitrogen chlorine sulfur e le m e n ta l c o m p o si ti o n ( w t. % ) msw+ efb: 20-80 msw+ efb:30-70 msw+ efb:4060 msw+ efb:50-50 msw+ efb:60-40 0 0.2 0.4 0.6 0.8 1 1.2 nitrogen chlorine sulfur e le m e n ta l co m p o si ti o n (w t. % ) 17 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 of chlorine (0.21 wt.%) and sulfur (0.041 wt.%). thus, in terms of energy and environment, this mixture can be a promising raw material in the gasification process. compared to the european standard, the results of this study show that significant pollutant components such as mercury (hg), arsenic (as), bromine (br) are not found in these raw materials. sulfur (s) and chlorine are lower, hence their compliance with the environmental standard to be used as feedstock in the gasification process. furthermore, in this study, mercury is not found, being an added advantage for this promising fuel fig. 5: the high heating value of msw and efb mixture. table 3: waste classification criteria as srf, according to en 15359 [16] parameter unit classes current study 1 2 3 4 5 msw efb 60 (msw) + 40 (efb) lower heating value mj/kg ≥25 ≥ 20 ≥ 15 ≥ 10 ≥ 3 29.74 15.1 26.98 chlorine content %(w/w) ≤0.2 ≤ 0.6 ≤ 1.0 ≤ 1.5 ≤ 3 0.249 1.01 0.21 mercury content mg/mj ≤0.02 ≤0.03 ≤0.08 ≤0.15 ≤0.5 0 0 0 4. conclusions the goal of this investigation was to assess the efficacy of mixing municipal solid waste and biomass to improve the calorific value. the materials establish that the concentrations of carbon, hydrogen, nitrogen, and oxygen obtained from the analyses carried out are sufficient to produce a fuel of high calorific value. moreover, the environmental parameters (cl and s) are within the prescribed standards. these findings show that the calorific value (cv) of efb which is 16.86 mj/kg can be enhanced depending on the quantity of added msw and can reach up to 28.47mj/kg. this potential energy can be used as a raw material in a pyrolysis or gasification process with little to no environmental impacts. references [1] kumar a, samadder sr. (2017) a review on technological options of waste to energy for effective management of municipal solid waste. waste management, 69: 407-422. https:// doi.org/10.1016/j.wasman.2017.08.046 19.77 21.22 22.67 27.04 28.477 0.25 0.42 0.66 1 1.5 0 5 10 15 20 25 30 1 2 3 4 5 h ig h he at in g va lu e (m j/ kg ) msw and efb ratio heating value msw and efb ratio 18 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 liu z. (2019) gasification of municipal solid wastes: a review on the tar yields. energysources, part a: recovery, utilization and environmental effects, 41(11): 1296-1304. https://doi.org/10.1080/15567036.2018.1548508 19 [2] [3] lombardi l, carnevale e, corti a. (2014) a review of technologies and performances of thermal treatment systems for energy recovery from waste. waste management, 37: 26-44. https://doi.org/10.1016/j.wasman.2014.11.010 [4] makarichi l, jutidamrongphan w, techato k. (2018) the evolution of waste-to-energy incineration: a review. renewable and sustainable energy reviews, 91: 812–821. https://doi.org/10.1016/j.rser.2018.04.088 [5] massarutto a. (2014) economic aspects of thermal treatment of solid waste in a sustainable wm system. waste management. https://doi.org/10.1016/j.wasman.2014.08.024 [6] beyene hd, werkneh aa, ambaye tg. (2018) current updates on waste to energy (wte) technologies: a review. renewable energy focus, 24: 1-11. https://doi.org/10.1016/j.ref.2017.11.001 [7] sikarwar vs, zhao m, clough p, yao j, zhong x, memon mz, shah n, anthony ej, fennell ps. (2016) an overview of advances in biomass gasification. energy and environmental science, 9(10): 2939-2977. https://doi.org/10.1039/c6ee00935b [8] vaish b, sharma b, srivastava v, singh p, ibrahim mh, singh rp. (2019) energy recovery potential and environmental impact of gasification for municipal solid waste. biofuels, 10(1): 87-100. https://doi.org/10.1080/17597269.2017.1368061 [9] nobre c, gonçalves m, vilarinho c. (2019) a brief assessment on the application of torrefaction and carbonization for refuse derived fuel upgrading. lecture notes in electrical engineering, 505: 633-640. https://doi.org/10.1007/978-3-319-91334-6_86 [10] he p, chen l, shao l, zhang h, lü f. (2019) municipal solid waste (msw) landfill: a source of microplastics? evidence of microplastics in landfill leachate. water research, 159: 38-45. https://doi.org/10.1016/j.watres.2019.04.060 [11] brunner ph, rechberger h. (2015) waste to energy – key element for sustainable waste management. waste management, 37: 3-12. https://doi.org/10.1016/j.wasman.2014.02.003 [12] chol on, song ph, chol sy, hyok ry, nam ky. (2018) environmental effects a feasibility study of energy recovery of rdf from municipal solid waste. energy sources, part a: recovery, utilization, and environmental effects, 40(24): 2914-2922. https://doi.org/10.1080/15567036.2018.1514431 [13] de gisi s, chiarelli a, tagliente l, notarnicola m. (2018) energy, environmental and operation aspects of a srf-fired fluidized bed waste-to-energy plant. waste management, 73: 271-286. https://doi.org/10.1016/j.wasman.2017.04.044 [14] elisabete m, brás i, silva me. (2017) refuse derived fuel from municipal solid waste rejected fractionscase study the 15th international a symposium on district heating and cooling. energy procedia, 120: 349-356. https://doi.org/10.1016/j.egypro.2017.07.227 [15] farzad s, mandegari ma, görgens jf. (2016) a critical review on biomass gasification, cogasification, and their environmental assessments. biofuel research journal, 3(4): 483-495. https://doi.org/10.18331/brj2016.3.4.3 [16] garcés d, díaz e, sastre h, ordóñez s, gonzález-lafuente jm. (2015) evaluation of the potential of different high calorific waste fractions for the preparation of solid recovered fuels. waste management, 47(b): 164-173. https://doi.org/10.1016/j.wasman.2015.08.029 [17] hamzah, n., tokimatsu, k., & yoshikawa, k. (2019). solid fuel from oil palm biomass residues and municipal solid waste by hydrothermal treatment for electrical power generation in malaysia: a review. sustainability (switzerland), 11(4): 1-23. https://doi.org/10.3390/su11041060 [18] abdullah n, sulaiman f, taib rm. (2013) characterization of banana (musa spp.) plantation wastes as a potential renewable energy source. aip conference proceedings, 1528: 325-330. https://doi.org/10.1063/1.4803618 [19] aluri s, syed a, flick dw, muzzy jd, sievers c. (2018) pyrolysis and gasification studies of model refuse derived fuel (rdf) using thermogravimetric analysis. fuel processing technology, 179: 154-166. https://doi.org/10.1016/j.fuproc.2018.06.010 iium engineering journal, vol. 22, no. 2, 2021 diallo et al. https://doi.org/10.31436/iiumej.v22i2.1566 nizami as, shahzad k, rehan m, ouda okm, khan mz, ismail imi, almeelbi t, basahi j. m, demirbas a. (2017) developing waste biorefinery in makkah: a way forward to convert urban waste into renewable energy. applied energy, 186: 189-196. https://doi.org/10.1016/j.apenergy.2016.04.116 20 [20] [21] ouda okm, raza sa, nizami as, rehan m, al-waked r, korres ne. (2016) waste to energy potential: a case study of saudi arabia. renewable and sustainable energy reviews, 61: 328-340. https://doi.org/10.1016/j.rser.2016.04.005 [22] komilis d, kissas k, symeonidis a. (2014) effect of organic matter and moisture on the calorific value of solid wastes: an update of the tanner diagram. waste management, 34(2): 255. https://doi.org/10.1016/j.wasman.2013.09.023 [23] afzanizam n, nazri m, jaafar m, tung c, johan n. (2015) a review of palm oil biomass as a feedstock for syngas fuel technology. jurnal teknologi, 5: 13-18. [24] onoja e, chandren s, abdul razak fi, mahat na, wahab ra. (2018) oil alm (elaeis guineensis) biomass in malaysia: the present and future prospects. waste and biomass valorization, 10: 2099-2117. https://doi.org/10.1007/s12649-018-0258-1 microsoft word 3-dr farhat anwar-f.doc iium engineering journal, vol. 2, no. 2, 2001 f. anwar 13 application of digital cellular radio for mobile location estimation farhat anwar electrical and computer engineering department, kulliyyah of engineering, international islamic university. malaysia (iium), jalan gombak, 53100, kuala lumpur, malaysia. farhat@iiu.edu.my abstract: the capability to locate the position of mobiles is a prerequisite to implement a wide range of evolving its services. radiolocation has the potential to serve a wide geographical area. this paper reports an investigation regarding the feasibility of utilizing cellular radio for the purpose of mobile location estimation. basic strategies to be utilized for location estimation are elaborated. two possible approaches for cellular based location estimation are investigated with the help of computer simulation. their effectiveness and relative merits and demerits are identified. an algorithm specifically adapted for cellular environment is reported with specific features where mobiles, irrespective of their numbers, can locate their position without adversely loading the cellular system. key words: its, gsm, cellular radio, drgs, gps. 1. introduction intelligent transportation systems (its) is an umbrella term representing an evolving research field that addresses different aspects of road transportation related problems by offering new range of solutions with the help of state of the art information technology and advanced telecommunication facilities. in the context of its, information concerning mobile location is one of the basic requirements that is crucial to implement evolving services like dynamic route guidance system (drgs), fleet management, emergency vehicle dispatching etc. to name a few, although, the requirement for accuracy varies form application to application[1]. in case of route guidance and navigation there is a need for higher accuracy in location data, since guidance or navigation relies on the assumption of availability of reliable location data, otherwise a mobile could easily become lost by following a wrong route or taking a wrong turn. considering another application where vehicles could act as floating sensors providing information concerning traffic situations it has just experienced, demand for location accuracy could be a bit relaxed. even less accurate location data could be used for vehicular fleet management system where knowledge about a mobile's present location in terms of a street or road section or even area might be adequate enough depending on the particular demand. although satellite based global positioning systems (gps) can provide accurate positional information for mobile users there is considerable interest in assessing systems, which do not have to rely on gps. it is clear that global system for mobile communication (gsm) does have some estimate of the distance of a mobile from its serving base station (bs). the objective of this paper is to investigate to what extent the cellular infrastructure of the second generation (e.g. gsm) and future cellular phones could be used to estimate mobile location co-ordinates. in the following, an overview of different techniques that are used for locating a moving object is given in section-2. the feasibility of cellular radio based location system is addressed in section-3. section-4 elaborates the location estimation algorithm employed in this simulation-based investigation and the results are reported in section-5. and finally a conclusion is drawn in section-6. 2. mobile location finding techniques there are various methods that could be used to locate the position of a mobile. they could be broken down into three basic categories[2]: proximity systems, deadreckoning methods, and radio location methods (includes satellite based gps) it is possible to realize each of these basic categories through a multitude of different technical approaches and combinations of one or more of these categories are also receiving serious consideration[3]. 2.1 proximity systems: in these systems, proximity devices such as microwave or infrared beacons (e.g. auto guide project in london[4]), provide the location of mobiles by determining the relationship between the mobile and fixed locations strategically placed throughout the city. since beacons are positioned at known points in the road network, any passing mobile is able to update its position by interrogating the beacons[5]. as shown in fig. 1, the beacon service area only permits a mobile to retrieve information from that specific beacon. therefore, location accuracy directly depends on the size of this area and by reducing the area of operation higher location accuracy is achievable. iium engineering journal, vol. 2, no. 2, 2001 f. anwar 14 due to the functional requirement, a communication channel is needed between a mobile and the proximity device either to receive the broadcast message identifying the location (requiring a simple channel) or to interrogate for similar information (requiring a half or full duplex channel). since a mobile can only be located whenever it encounters proximity device, the frequency of positioning proximity devices will determine the continuity and accuracy of locating and monitoring mobiles. beacon service area a beacon service area b fig. 1: vehicular location fixing with proximity devices. s ta rt p resen t locatio n 2 km 1 km 1 k m 2 .3 km o n orth o 90 o 90 45 0 o fig. 2: vehicular location fixing with dead reckoning. 2.2 dead-reckoning method: this method relies on distance and heading sensors fitted to the mobile so that progress from a known starting position can be continually monitored and location, in terms of grid reference, can be updated as shown in fig. 2. unfortunately, many factors, such as changes in tire pressure, road conditions, surrounding man-made structures, e.g. metallic bridge, can greatly affect the distance and direction measurements. since, in the basic system, the computed location depends upon all previous location estimates, errors in location data tend to accumulate and can lead to sizeable positional errors. to compensate for this, the system must be updated and reinitialized on a regular basis. 2.3 radio location methods: this method involves direct measurements of radio signals traveling between a mobile and a number of fixed stations in an attempt to locate the mobile. in general, such methods use time or phase measurements to first determine the length or direction of the radio path and then use this to compute the location based upon known geometrical relationships. well-established radiolocation systems including gps (global positioning system) satellites, decca and loran-c, used in the air and sea, employ trilateration techniques. a b c d 1 d 2 d 3 vehic le fig. 3: vehicular location fixing with trilateration technique. 500 m 500 m a b c fig. 4: cellular radio as a proximity device. 0 20 40 60 80 100 0 0.2 0.4 0.6 0.8 1 1.2 1.4 distance in km l os s in d b a b c fig. 5: signal strength variation received by a mobile moving along a highway from three base stations (a, b, and c). iium engineering journal, vol. 2, no. 2, 2001 f. anwar 15 the trilateration technique generally employs the following two approaches. in the simple form of trilateration, the distance between the mobile and at least three stations is measured by determining the radio frequency travel time from the stations to the mobile and back to the stations. this requires that either two radio frequency channels be provided or the mobile be equipped with a transponder that would rebroadcast the signal at some fixed time increment following receipt of the incoming signal. this information is then relayed to a central location where the location determination is made. given the three distances d1, d2, and d3, the mobile is then located at the intersection of three circles of radius d1, d2, and d3 centered on station a, b, and c, respectively as shown in fig. 3. in an alternate approach, the differences between the arrival times of the various received signals could be measured and utilized. the time differences define hyperbolas with focal points at the stations. the intersection of the hyperbolas defines the mobile's location. at least three stations are required to resolve any ambiguity in location finding, though increasing the number of stations tends to decrease the error in the position estimate. since the radio channel (specifically the mobile radio channel) is quite hostile in comparison to other communication media, a two way transmission requirement of the first approach automatically introduces a greater potential for error in location data than the second approach where only one-way transmission is employed. the first approach also requires an interrogating (polling) signal followed by a response broadcast by a mobile which should be repeated to locate each and every individual mobile that needs to be located. therefore, the system has a capacity limit. interestingly the alternative approach seems to have unlimited capacity and could support an infinite number of mobiles. 3. feasibility of cellular radio based mobile location finding from the discussion of the preceding section it can be concluded that, for vehicular location finding an infrastructure of transmitter/receiver stations is a prerequisite for radio-location or proximity systems, or alternatively dead-reckoning could be used provided it is frequently reinitialized to prevent it from accumulating location error. the widespread deployment and availability of plmn infrastructure of base stations with limited processing capability automatically invokes huge interest to study their applicability for other services, specifically those that require a similar transceiver infrastructure. different features of cellular radio could also be investigated to realize new evolving applications. as an example, for efficient operation, tdma based cellular radio uses some kind of adaptive frame alignment. for example, in gsm the timing advance (ta) signal in the down link provides essential information for frame alignment which is used to set the up-link transmission time properly so that they could reach the base station in the proper time slot and avoid any overlapping in the adjacent slots[6]. this ta signal could be used as a measure of the distance between the mobile and the serving base-station. 3.1 cellular radio as a proximity system as previously discussed, a mobile could be located by acquiring information concerning its presence in the vicinity of electronic signposts. to get this information a communication link needs to be established, usually for a short time. normally in cellular radio operations, mobiles monitor the reception quality of the broadcast channel of all the neighboring base stations and the one with the strongest signal is selected as the serving base station. a mobile could be anywhere within a cell, and due to the very nature of the radio channel, the cell size and shape cannot be predicted accurately. therefore, with this approach it can only be possible to identify the presence of a mobile within the vicinity of a serving bs and the corresponding cell. system areas covered with macro or medium cells are generally large and might not be very useful but the prospect is much brighter where micro cells are employed, for example in an urban city center. considering a possible scenario as depicted in the fig. 4 where a road section is shown with three micro cells and each of the base stations are separated by 0.5 km. supposing a mobile is moving from cell a towards cell c. events are considered from the moment the mobile started its journey from the location of the base station a and the path-loss profile of the received signals from a, b, and c are monitored. assuming all three of the base stations are using same transmission power, existence of a line of sight propagation and employing inverse fourth power path loss formula[7] (l = 20.log f + 20.log d + 32.44 db) the received median path loss could be depicted graphically as in fig. 5. as can be seen, while the mobile is very close to a, it will select a as the serving bs due to strong signal received from a compared to other neighboring bss. therefore, the mobile under consideration could be located to be in cell a. when the mobile is midway between a and b the received signal strength from a and b is very close while signal from c is only around 10 db less. it should be mentioned that in the mobile environment signal fading of up to 20db is not uncommon[8]. the situation seems to improve as the mobile approaches base station b. the signal from b is quite distinct and more than 20 db higher than a and c as the distance between the mobile and the base station b becomes less than 100 meters. at this point, b could be easily selected as the serving bs by locating the mobile to be in cell b. the situation is quite similar when the mobile reaches the mid-point between b and c and it will be possible to select cell c when the mobile is less than 100 meters away from the base station c. from the preceding discussion it might be concluded that a mobile may be located while traveling through a micro cell and is less than 100 meters away from the specific base station. however, the presence of fading iium engineering journal, vol. 2, no. 2, 2001 f. anwar 16 will make it more difficult and in general it can only provide a rough idea about the location of a mobile. 3.2 cellular radio and dead-reckoning system a dead-reckoning system, as discussed previously, requires distance and direction of travel data to locate the current position of a mobile from the known starting position. the problem of error accumulation with distance, which is inherent to dead reckoning, could lead a mobile to become lost. this situation can be avoided or minimized by regularly correcting the position with some reliable and accurate location data. thus, the applicability of cellular radio to aid deadreckoning system will depend on the accuracy of the location estimation capability of cellular radio and it will be addressed in section 6 along with the discussion on simulation and results. 3.3 cellular radio and radio location system as discussed previously, the location of a vehicle or mobile could easily be calculated with the help of trilateration technique, for which the required parameters are: a) distance measures of the mobile from at least three reference points, b) location (co-ordinates) of each of these reference points in radiolocation systems, the distance parameters are obtained indirectly by measuring the travel time of radio signals from the mobile to each of the reference points (sensor stations). only tdma cellular radio of second generation and future third generation systems will be considered in this paper because of their inherent features which could possibly be exploited for estimating vehicular location relevant to its. two possible methods can be utilized with a cellular radio to find the distance parameters between a mobile and a base station. method 1 any signal transmitted from a mobile reaches the serving bs with some delay depending on the distance of separation between the mobile and the bs. in the case of a tdma system, the first signal received by the base station from a mobile will reach the intended time slot with a delay of twice the signal travel time between them. therefore, this delay could be used as the distance parameter for locating the mobile. cellular radio, like gsm, actually designates this time difference as timing advance (ta) and feeds this information back to the mobile. mobiles subsequently use this information to set the next (burst) transmission time earlier by ta, enabling further bursts from the mobile to reach the bs at the proper time slot, thus preventing any overlapping in the adjacent time slots. if a mobile is forced to access three or more of the basestations closely located around it and extract the individual ta values along with the co-ordinates of the corresponding base-stations, the position of the mobile could be calculated from these values using trilateration method. this scheme is depicted in fig.6. here a mobile with the intention to locate its position sends an access burst (ab1) to the serving base station bs1 that, in return, evaluates the timing advance parameter (ta1) and sends it to the mobile. repeating the same procedure, multiple timing advance parameters can be gathered from the neighboring bss. bs 1 bs 2 bs 3 ab1 ta1 ta3 ta2 ab2 ab3 base station : bs timing advance : ta access burst : ab fig. 6: using ta (timing advance) parameter for mobile to base station distance measurement. since the ta parameter is normally provided in number of bit periods, as in gsm, the accuracy in distance measurement will depend on the bit rate used. since signal arrival time is also subject to mobile environment induced error, effects such as delay spread could also degrade distance estimation accuracy. bs 1 bs 2 bs 3 base station : bs bs n t t t t 1 2 3 n signal reception time : t i fig. 7: location estimation with relative signal arrival time. iium engineering journal, vol. 2, no. 2, 2001 f. anwar 17 s1 s2 s3 sn v [x0,y0,t0] [x1,y1,t1] [x2,y2,t2] [x3,y3,t3] [xn,yn,tn] fig. 8: location estimation employing signal arrival time to known locations. method 2 this method requires all bss to be time synchronized. mobiles first use the control channel of the serving base station to synchronize their clock. then, the time of arrival of the control signals from the neighboring basestations are sequentially monitored and compared to the serving base-station. these signal arrival times will provide the necessary information regarding their relative distance from the mobile. now, knowing the location information of these base-stations (coordinates) the position of the mobile could easily be calculated from these values using trilateration method. the idea is demonstrated in fig.7. here, a mobile in a cell served by bs1 first synchronizes its internal clock with the base station. considering frame start time as the time reference, (for example), the mobile will sequentially scan all the neighboring base stations and their relative frame start times which will vary depending on the distance between the mobile and each surrounding base station. since all the base stations are considered as time synchronized with some reference clock, measurement of the frame start time performed by the mobile will be a relative measure of their distance. knowledge of the geographical location (coordinate) of all the neighboring base stations then leads to a set of equations of the form: 2 2( ) ( ) ( )i i ic t t x x y y     where c is the speed of light ti is the relative signal arrival time xi, yi is the co-ordinate of the i th base station. all that is now needed is to find the best or most likely value for x, y, and t which gives the location of the mobile. the geographical location parameter (glp) of the relevant base stations, in terms of some relevant coordinates, could be obtained in multiple ways, although broadcasting these information periodically by the base stations appears to be the best option because this approach avoids any dependency on the cellular system operation and the mobiles being served and offers, ideally, infinite service capacity. 4. implementation of location estimation algorithm the operational algorithm to find the estimated location of a mobile is elaborated in this section. in the ideal case, if it is possible to find the actual distance between the mobile and, at least, three neighboring base-stations. then the point of intersection of the three circles drawn from the base-stations taking these distance measures as the radius would give the actual location of the mobile. but, in the practical situations, there will be error in these distance measures and as a result it will be impossible to obtain a common point of intersection. there will be two points of intersection for each of the base-station pairs and, in the case of three base stations, there are six point altogether. it is now necessary to solve the problem of finding the location of the mobile and, probably, the best way is to find the most likel y location of the mobile. least square algorithm seems to be a good choice. an algorithm similar to[9] which has been specifically modified and adapted to be usable for cellular radio environment is investigated. here, the basic idea is to use the time of arrival of a signal at fixed stations (sensors), sent from the mobile, as the location data. the computational algorithm involves reducing the time-ofarrival data to an estimate of location. the particular class of algorithm uses the least-squares technique of fitting the location estimate to the raw time-of-arrival data. the original procedural setup could be easily explained by referring to fig.8. here, a vehicle v located at coordinates (x0, y0) starts transmitting a signal at time t0. a set of sensors {s1, s2, ..., sn} placed at co-ordinates (xi, yi) respectively receives this signal, delayed and distorted by multipath phenomena and noise. each station processes the received signal and forms an estimate ti of the time at which it started receiving the vehicle's signal. these estimates referred to a common time reference are relayed to the central processor. at the processor, the quantities 2 2( , , ) ( ) ( ) ( )i i i if x y t c t t x x y y      (1) where c is the speed of light, could all be made zero by proper choice of x, y, and t (i.e., x = x0, y = y0, t = t0), provided that the sensors estimates {ti} at the stations were correct. multipath and other time delay errors, however, cause the times ti to be in error by random amounts, perhaps by as much as several microseconds (each microsecond  300 meters). thus, using the observed ti in eq. (1), it will, in general, be impossible to pick (x,y,t) to make all fi = 0 simultaneously. the estimates ˆˆ ˆ( , , )x y t of 0 0 0( , , )x y t are therefore calculated in the least-squares sense and a computer based search is performed for x,y,t which minimizes, 2 1 ( , , ) ( , , ) n i i f x y t f x y t    (2) iium engineering journal, vol. 2, no. 2, 2001 f. anwar 18 once ˆˆ ˆ( , , )x y t have been found, t can be ignored and (x,y) used as an estimate of the vehicle's location. this least-squares approach is statistically more justifiable than the procedure of finding intersections of multiple circles or ellipses and then using least-squares methods on the reduced intersection data. for cellular applications, some modifications are made. first of all base stations are assumed to be time synchronized. the procedure starts with the mobile under consideration synchronizing with the serving base station. the control signal arrival time from this station is considered to be zero (as a reference) at first. then the mobile starts sequentially monitoring all the surrounding base stations one at a time and records their relative signal arrival time along with their location coordinates which could either be broadcast from the serving base station or from each of the individual base stations. these recorded parameters are then applied to the algorithm. 5. simulation and results according to engel’s study[10] the majority of errors in received signal arrival time are between zero and the total multipath spread. however with small but non-zero probability, the magnitude of the error can be many times the multipath spread. it has been suggested [8] that the delay spread is  0.5  sec. in a rural environment,  1  sec. for hilly terrain and  5  sec. for an urban environment. in this investigation all the aforementioned delay spreads are considered in a worstcase scenario. 5.1 location estimation employing ta parameters the impact of transmission bit rate on location error could be demonstrated by considering an ideal scenario where transmission environment induced errors (multipath delay) are not taken into consideration. here, the primarily error source is the way in timing advance (ta) is represented. in the simulation, tas are represented by integer number of bit periods and other parameters are, cell size (radius) = 10 km, cell cluster = 7 the relationship between the transmission bit rate and the average of the estimated location error of a mobile is shown in fig. 9. at 200 kbit/s the average location error is more than 300 m. increasing the bit rate gradually decreases the location error and at about 1.5 mb/s the average error is approximately 45 m. since, in the practical situation, the effect of transmission environment induced errors are unavoidable, the effect of multipath delay on signal reception time has also been considered. delay spreads of 0.5, 1, and 5 sec representing rural, hilly terrain, and urban environments are considered and the results are also shown in fig. 9 . in the case of rural environments, radial location error is around 300 m for 200 kbit/s transmission. location error gradually falls as the transmission rate is increased and at 1.5 mbit/s it is just over 50 m. for hilly regions, the location error profile is more or less the same at low bit rate. at 1.5 mbit/s it is around 80 m. in the case of urban environments, the average error in location estimation is quite high. at 900 kbits/sec this error is around 350 m and increasing the bit rate does not improve the situation. there are several disadvantages of using ta for vehicular location finding. errors are introduced in mobile to base station distance measurement due to the way tas are represented. since ta is given in integer number of transmission bit periods, it can only assume discrete values but this reduces the accuracy of distance measures and increases the error in location estimation. the operation of locating a mobile requires three or more random accesses to be made to different base stations and corresponding responses be received. therefore, number of mobiles in a cell and the frequency of location estimation procedure will impose a load on the serving cellular network, which may not be desirable. in normal operation, depending on the requirement, mobiles are allowed to access the serving base station. accessing base stations other than the serving one might require higher transmission power, which could introduce considerable co-channel interference. table 1: radial location error for a range of delay spread. delay spread (in micro seconds) 0.5 1.0 2.0 3.0 4.0 5.0 radial location error mean 33.48 71.17 138.03 205.94 268.91 332.67 standard deviation 16.26 31.92 65.1 102.28 123.8 173.8 iium engineering journal, vol. 2, no. 2, 2001 f. anwar 19 delay spread in micro sec. 0 50 100 150 200 250 300 350 400 450 500 200 500 800 1100 1400 bit rate (kbits/sec) a vg . l oc at io n er ro r ( m et er s) 0 0.5 1 5 fig. 9: location error due to a range of delay spread. de la y s p r e a d in mic r o s e c o n d s 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0 250 500 750 1000 ra d ia l lo c a tio n e s tima tio n e r r o r (me te r s ) p ro ba bi lit y 0 .5 1 2 3 4 5 fig. 10: probabilities of radial location error for a range of delay spread. 5.2 location estimation employing relative signal arrival (rsa) time the average radial location errors for different transmission environment are estimated with the aid of computer simulation and shown in fig.10 and table. 1. for a rural environment (with delay spread = 0.5) the estimated location error is 33.48 m which is quite encouraging. in this case the standard deviation is 16.26 m, which is quite narrow. in the case of a delay spread of 1 sec representing hilly terrain, average location error is around 71 m with a bit higher standard deviation of approximately 32 m. as expected, in the urban area with severe multipath problems the simulated experiment indicates average location error in the range of 332.67 m with quite a high standard deviation implying quite high error with wide fluctuation in estimation. the cumulative probability of location estimation error, as shown in fig. 11, provides much clearer understanding of the overall situation. it is evident that mobiles could almost always be located within 76 m radial distances in a rural environment. in the case of a hilly area, this has increased to 150 m. in an urban area the radial location error might be up to 900 m. delay spread 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 10 100 1000 radial location error (meters) % p ro ba bi lit y th at e rr or < a bs ci ss a 0.5 micro sec 1 micro sec 2 micro sec 3 micro sec 4 micro sec 5 micro sec fig. 11: location error probability comparison. 0 100 200 300 400 500 0.5 1 5 delay spread (micro-second) a vg . l oc at io n er ro r ( m et er s) ta rsa fig. 12: location error probability comparison. estimating the location of a mobile with relative signal reception time from the neighboring base station has many advantages. errors in the distance measurement between a mobile and surrounding base stations are minimized by avoiding discrete measurements as used iium engineering journal, vol. 2, no. 2, 2001 f. anwar 20 in ta, therefore achieving more accurate location estimation. this is clearly shown in fig. 12, where, for different signal delay spread, location error comparison between mobile location technique employing ta and mobile location technique employing rsa time is shown for reference cellular system with bit rate of 200 kbis/sec. there is no need for any dedicated bidirectional communication (i.e. random access) between a mobile and the neighboring base stations therefore avoiding any adverse loading effect on the serving cellular network. applying this location approach, it is possible to cater for infinite number of mobiles and any unwanted co-channel interference generation is avoided. location estimation accuracy is much higher than the alternative approach. the accuracy of positional information by cellular radio is not adequate for correcting the accumulation error of a dead-reckoning system, although this information can be used as a clue. if a digital road map is available in the vehicle, then location estimated via cellular radio could be used to isolate the probable area for searching and, by matching the movement profile of the mobile, it might be possible to recover it from a lost condition. 6. conclusion an investigation regarding the feasibility of employing cellular radio network for mobile location estimation has been reported in this paper. basic strategies to be utilized for location estimation are elaborated. two possible approaches for cellular based location estimation are investigated with the help of computer simulation. the results seem to contradict some recent publications where suggestions were made to use timing advance feature of gsm for locating mobiles. there are many disadvantages of using ta for vehicular location estimation as this requires multiple access attempts to be made by a mobile to number of base stations apart from the serving one. thus, higher transmission power will be needed which will eventually degrade the interference problem in the neighbouring base stations. a different strategy is suggested where the relative signal arrival times from different base stations may be utilized as a measure of their relative distance from a mobile. the prerequisite is time synchronisation of base stations, and mobile with the capability of detecting control signal arrival time from different base stations. the main feature of the strategy is that no additional overhead is imposed on the cellular systems and signal interference generation is avoided by eliminating the need for employing ta from the neighbouring cells. the accuracy of the mobile receiver to detect relative signal arrival time from the neighbouring base stations relative to the serving one will influence the estimation process. two-dimensional glp has been considered in the current study for simplicity. the effect of more realistic three-dimensional glp and corresponding location estimation accuracy needs further investigation. references [1] f. anwar, application of cellular radio in the field of rti, ph.d. thesis, department of electronic and electrical engineering, university of strathclyde, glasgow, u.k., 1995. [2] s. riter and j. mccoy, “automatic vehicle location an overview”, ieee transactions on vehicular technology, vol vt-26, no.1, february 1977. [3] j. m. sparman, “lisb route guidance and information system: first result of the field trial”, snv studiengesellschaft nahverkehr, berlin-33, auguste-viktoria-str. 62, west-germany, 1989. [4] i. catling and p. belcher, “autoguide electronic route guidance for london and the uk”, iee conference pablication number 299, february 1989. [5] j. walker, mobile information systems, arrec house inc., page 178-180. [6] m.r.l. hodges, “the gsm radio interface”, british telecom technology journal, vol 8, no 1, pp. 31-43, january 1990. [7] m.d. yacoub, foundations of mobile radio engineering, crc press, isbn 0-8493-8677-2. [8] r. steele, mobile radio communications, pentech press, london, isbn 07273-1406-8. [9] g.l. turin, jewell w.s., and johnston t.l.,”simulation of urban vehicle-monitoring systems”, ieee transactions on vehicular technology, vol. vt-21, no.1, february, 1972. [10] j. s. engel, “the effect of multiple transmission on the measured propagation delay of an fm signal”, ieee trans. veh. technol., vol. vt-18, pp. 44-52, may 1969. nomenclature its intelligent transportation systems gsm global system for mobile communication drgs dynamic route guidance system gps global positioning systems bs base station plmn public land mobile network ta timing advance ab access burst glp geographical location parameter rsa relative signal arrival biography farhat anwar was born in dhaka, bangladesh in 1963. he received his b.sc. and m.sc. degrees in applied physics and electronics from the university of dhaka in 1982 and 1983 respectively, and ph.d. from the university of strathclyde, glasgow, uk in 1996. he is currently an assistant professor at the department of electrical and computer engineering, international islamic university malaysia. he has 14 years of teaching and research experience. dr. anwar’s primary research interest is in the area of performance analysis of computer communication and mobile cellular networks. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 implementation of a machine learning algorithm for sentiment analysis of indonesia’s 2019 presidential election ghulam asrofi buntoro1*, rizal arifin1, gus nanang syaifuddiin1, ali selamat2,3, ondrej krejcar3, and hamido fujita4, 1faculty of engineering, universitas muhammadiyah ponorogo, indonesia 2malaysia-japan international institute of technology, universiti teknologi malaysia 3faculty of informatics and management, university of hradec kralove, czech republic 4faculty of software and information science, iwate prefectural university, iwate, japan *corresponding author: ghulam@umpo.ac.id (received: 3rd july 2020; accepted: 1st october 2020; published on-line: 4th january 2021) abstract: in 2019, citizens of indonesia participated in the democratic process of electing a new president, vice president, and various legislative candidates for the country. the 2019 indonesian presidential election was very tense in terms of the candidates' campaigns in cyberspace, especially on social media sites such as facebook, twitter, instagram, google+, tumblr, linkedin, etc. the indonesian people used social media platforms to express their positive, neutral, and also negative opinions on the respective presidential candidates. the campaigning of respective social media users on their choice of candidates for regents, governors, and legislative positions up to presidential candidates was conducted via the internet and online media. therefore, the aim of this paper is to conduct sentiment analysis on the candidates in the 2019 indonesia presidential election based on twitter datasets. the study used datasets on the opinions expressed by the indonesian people available on twitter with the hashtags (#) containing "jokowi and prabowo." we conducted data pre-processing using a selection of comments, data cleansing, text parsing, sentence normalization and tokenization based on the given text in the indonesian language, determination of class attributes, and, finally, we classified the twitter posts with the hashtags (#) using naïve bayes classifier (nbc) and a support vector machine (svm) to achieve an optimal and maximum optimization accuracy. the study provides benefits in terms of helping the community to research opinions on twitter that contain positive, neutral, or negative sentiments. sentiment analysis on the candidates in the 2019 indonesian presidential election on twitter using non-conventional processes resulted in cost, time, and effort savings. this research proved that the combination of the svm machine learning algorithm and alphabetic tokenization produced the highest accuracy value of 79.02%. while the lowest accuracy value in this study was obtained with a combination of the nbc machine learning algorithm and n-gram tokenization with an accuracy value of 44.94%. abstrak: pada tahun 2019 rakyat indonesia telah terlibat dalam proses demokrasi memilih presiden baru, wakil presiden, dan berbagai calon legislatif negara. pemilihan presiden indonesia 2019 sangat tegang dalam kempen calon di ruang siber, terutama di laman media sosial seperti facebook, twitter, instagram, google+, tumblr, linkedin, dll. rakyat indonesia menggunakan platfom media sosial bagi menyatakan pendapat positif, berkecuali, dan juga negatif terhadap calon presiden masing-masing. kampen pencalonan menteri, gabenor, dan perundangan hingga pencalonan presiden dilakukan melalui media internet dan atas talian. oleh itu, kajian ini dilakukan bagi menilai sentimen terhadap calon pemilihan presiden indonesia 2019 berdasarkan kumpulan data twitter. kajian ini menggunakan kumpulan data yang diungkapkan oleh rakyat indonesia yang terdapat di 78 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 twitter dengan hashtag (#) yang mengandungi "jokowi dan prabowo." proses data dibuat menggunakan pilihan komentar, pembersihan data, penguraian teks, normalisasi kalimat, dan tokenisasi teks dalam bahasa indonesia, penentuan atribut kelas, dan akhirnya, pengklasifikasian catatan twitter dengan hashtag (#) menggunakan klasifikasi naïve bayes (nbc) dan mesin vektor sokongan (svm) bagi mencapai ketepatan optimum dan maksimum. kajian ini memberikan faedah dari segi membantu masyarakat meneliti pendapat di twitter yang mengandungi sentimen positif, neutral, atau negatif. analisis sentimen terhadap calon dalam pemilihan presiden indonesia 2019 di twitter menggunakan proses bukan konvensional menghasilkan penjimatan kos, waktu, dan usaha. penyelidikan ini membuktikan bahawa gabungan algoritma pembelajaran mesin svm dan tokenisasi abjad menghasilkan nilai ketepatan tertinggi iaitu 79.02%. manakala nilai ketepatan terendah dalam kajian ini diperoleh dengan kombinasi algoritma pembelajaran mesin nbc dan tokenisasi n-gram dengan nilai ketepatan 44.94%. keywords: sentiment analysis; president; indonesia; naïve bayes classifier; support vector machine 1. introduction the turmoil resulting from organizing the 2019 indonesian general election, notably the presidential election, has been felt since last year. this has applied not only in the real world but also in cyberspace, mainly on social media sites such as twitter, instagram, facebook, etc., which people used to discuss their potential presidential candidates. the stages of the general election and presidential election in 2019 were announced by the indonesian general elections commission (kpu). the names of the presidential candidates had been widely discussed on social media as far back as the candidate registration phase in early 2019 by the indonesian kpu [1]. the virtual world is a world that is so free and difficult to control, where everyone is free to speak or give their opinion on their respective candidates. the opinions expressed by the public may be positive, neutral, or even negative. the world of information has developed so fast that there is now a significant amount of online media, from news information to social media or friendships, with social media including facebook, twitter, path, instagram, google+, and many more. twitter has a total of 330 million active users to date, while around 500 million tweets are made worldwide every day. there are around 100 million active daily users of twitter around the world [2]. social media is not only used as a means of friendship or for making friends but also for activities such as the promotion of merchandise or sale and purchase, up to political party promos or campaigns for regent, presidential, and legislative candidates. the team charged with ensuring a candidate for president or regional head, for example, will justify any means of campaigning for their candidate, as evidenced by the presence of many black campaigns during the campaign period [3], especially on social media against a candidate. today's campaign or imaging is not only done in the real world but also in the virtual world. social media, especially twitter, is now one of the most effective and efficient campaign venues. sentiment analysis continues to be used as part of opinion mining research. it is the process of understanding, extracting, and processing textual data automatically to obtain the sentiment information contained in an opinion sentence [4]. in this study, sentiment analysis was conducted with the aim of viewing and retrieving information pertaining to the opinions expressed by people in the indonesian language on twitter with regard to the candidates in the 2019 indonesian presidential election, whether those opinions were in the category of positive, neutral, or negative. to test the accuracy of the sentiment analysis in this study, we used two machine learning algorithms, namely 79 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 naïve bayes classifier (nbc) and support vector machine (svm) and 7 tokenizations including an alphabetic tokenizer, character n-gram tokenizer, unigram, bigram, trigram, n-gram, and word tokenizer. the result will enable us to see the accuracy of the machine learning methods nbc and svm[5] and 7 tokenizations including the alphabet tokenizer, character n-gram tokenizer, character tokenizer, unigram, bigram, trigram, n-gram, and word tokenizer for sentiment analysis of the 2019 indonesian presidential candidates. 2. related work sentiment analysis research used machine learning to classify turkish political news [6]. this research classified the sentiment toward turkish political news and determined whether the sentiment expressed was positive or negative. the different features of turkish political news were extracted with the machine learning algorithms of naïve bayes classifier (nbc), maximum entropy (me), and svm to produce a classification model. sentiment analysis was used to group texts according to their positive or negative orientation [7]. this paper explains the experimental results that apply svms to conduct benchmarking with standard datasets to train sentiment analysis classifiers. n-grams and different weighting schemes were used to extract the most classic features. this study also explores the chi-square weight feature to select informative features for the classification method. the results of this experimental analysis reveal that using the chi-square feature selection can significantly enhance classification accuracy. the main challenge for law enforcement in recent years has been the automatic detection of abusive language in online media [8]. first, we have developed a deep learning architecture that uses word frequency vectorization to implement the features above. second, we have proposed a method that, because it does not use pre-trained word embedding, is an independent language. third, we have conducted a comprehensive evaluation of our model using public datasets from labelled tweets and open-source implementations built using keras. the paper presents an ensemble classifier for detecting hate speech in short texts, such as opinion tweets used as corpus datasets [9]. our classification uses deep learning and combines a set of features related to user behaviour characteristics, such as the tendency to send rough messages as input to a combination of machine learning algorithms [10,11]. sentiment analysis research was carried out using a hybrid approach [12] with its research methods, including mining association rules, parsing dependencies, and sentiwordnet applied to solve this aspect-based sentiment analysis problem [13]. the performance of the research was evaluated using negative and racial domains and other benchmarks to evaluate the accuracy of aspect-based sentiment classification. 3. proposed methodology 3.1 tweet data collection crawling [14] carried out tweet data collection with r programming using r-studio from twitter. the data taken comprised only tweets in indonesian, which consisted of 5,000 tweets containing the jokowi keywords and 5000 tweets containing the prabowo keywords, to give a total of 10,000 tweets. the data were taken randomly from ordinary users of twitter (fig. 1). 80 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 fig. 1: proposed method of twitter sentiment analysis. figure 2 shows the coding of r language [15] that was used to crawl the data from twitter. the tweet data on jokowi comprised 5,000 tweets, which, along with examples of original tweets, featured lots of noise characterized by the presence of symbols and links. 81 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 fig. 2: crawling tweets of opinions about jokowi from twitter at r-studio. fig. 3: crawling tweets of opinion about prabowo from twitter at r-studio. figure 3 contains a coding of the r language for crawling data from twitter. also seen is the number of data tweets taken about prabowo, which numbered 5,000. the left-hand panes in figures 2 and 3 also contain examples of tweets in their original form and lots of noise from twitter with the presence of symbols and links. 3.2 data pre-processing the data pre-processing stage [16] in this study consisted of 4 steps, which are described as follows: a. selection of comments at this stage, comments were selected that contained the keywords of hashtags (#) jokowi and prabowo; any data that did not contain both were deleted. when crawling all comments with the hashtag, both will be taken even if they appear in the same sentence. then, during this process, the same comment will be deleted, even if it comes from a different twitter account, in order to find unique tweet data. 82 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 b. cleansing this process aimed to clean up any comments from twitter that were still dirty and contained a lot of noise. the opinion sentences obtained from twitter usually contained a certain level of noise, i.e., random errors or variants in measured variables; therefore, we had to eliminate and clean the noise. the items omitted were usually html characters, symbols, emoticon icons, hashtags (#), usernames (@username), url addresses (http://websitename.com), and email addresses (name@websitename.com). c. parsing the third data pre-processing step in this study was parsing [17]. the aim was to break the document into a string of words and then analyse the collection of words by separating them and determining the syntactic structure of each word. d. sentence normalization the aim of this step was to normalize the sentences taken from twitter; for example, a sentence containing the words gaul or alay [18] would be normalized so that the sentence or language of gaul and alay could be recognized as a language following kbbi (the great dictionary of the indonesian language) [19]. the normalization of sentences involved the following processes: • stretch punctuation and symbols other than the alphabet stretching punctuation involves inserting distance around the punctuation associated with words that come after or before. the aim is to avoid any punctuation and/or symbols other than those in the alphabet becoming one with the words during the tokenization process. • change to all lowercase letters • normalization of words. the rules in the normalization process are shown in table 1. table 1: rules for normalizing words normal / slang normal suffix –ny suffix –nya suffix –nk suffix –ng suffix –x suffix –nya suffix –z suffix –s suffix –dh suffix –t repeat words: sama2 repeat words: sama-sama spelling: oe alphabet: u spelling: dj alphabet: j • eliminate repeated letters when happy or upset, someone may write opinions based on their emotions; often, when expressing this in written form, they will repeat the same letter. for example: "kereeen" to express pleasure. repeated words like "kereeen" will be normalized to "cool". 3.3 tokenization after normalizing the sentence, it was then broken down into tokens [20] using a delimiter or space bar. the tokens used in this study are: 83 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 • alphabetic tokenizer: these tokens are formed only from adjacent alphabetical sequences, for example: aku, anak, asli, baik, bagus, cara, cinta, demi, engkau, enak, film • character n-gram tokenizer: this tokenizer divides the token into a one-word character; for example: pe, mi, lu, pe, mi, li, han, u, mum • unigram: this tokenizer divides the sentence into a token, with each token consisting of only one word; for example, "pemilu". • bigram: this tokenizer divides the sentence into a token, with each token consisting of two words; for example: "pemilihan umum”. • trigram: this tokenizer divides the sentence into a token, with each token consisting of three words; for example, “pemilihan umum indonesia". • n-gram tokenizer: this tokenizer divides the string into n-grams with the minimum and maximum number of grams as specified; for example, "pemilihan, pemilihan umum, pemilihan umum indonesia, aku, aku anak, aku anak indonesia" • word tokenizer: this tokenizer divides tokens from the basic words; for example, "aku, akun, akuntansi, alam, alami, alamiah" 3.4 determination of class attribute after pre-processing, the next stage in this research is to determine the class attribute. the class attribute used here is sentiment class; in this study, there are 3 class attributes [21], namely positive, neutral, and negative. the use of 3 class attributes provides a more detailed and accurate classification of public opinion toward a particular object. 3.5 load dictionary following the class attribute determination, the next step is to apply the lexicon-based method [22]. the dictionary used in this study comprises positive words (positive keywords), negative words (negative keywords), and negation words (negation keywords). the following is a sample dictionary and its contents: • positive keywords; for example, “amanah, ahli, jujur, adil, keren”. • negative keywords; for example, “apatis, benci, dosa, jahat, buruk”. • negation keywords; for example, “lebih, kurang, tidak, bukan”. • dictionary of slang conversion to kbba; for example, “cyg = sayang, lbh = lebih, krn = karena, jd = jadi, spt = seperti, ciyus = serius”. 3.6 determination of sentiment this is the process used for determining the sentiment (positive, neutral, or negative) in twitter data once the processing has been performed. the sentiment determining process used in this study consisted of the lexicon-based or dictionary-based method with python programming. in this study, we are using the positive and negative dictionary. the polarity score of an opinion word (p) will be 1 if the word is in the positive dictionary, meaning the word is positive. a word that is in neither the positive nor negative dictionary is worth 0, meaning it is neutral, while a word in the negative dictionary is worth -1, meaning it is negative [23]. the method for determining sentiment uses the sum formula n, namely the opinion polarity score of the word, plus p, that is the opinion commenting on the feature (f). after determining which words in a twitter opinion sentence are positive, neutral, or negative, the weight of the values contained in the sentence is then calculated by totalling the value of each opinion word. if the number of opinion words in the sentence is ≥ 1, then the sentiment value of the opinion sentence is positive; if the opinion value of the sentence 84 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 is 0, then the sentiment value of the opinion sentence is neutral, and if the opinion word value in the sentence is ≥ -1, then the sentiment value of the opinion sentence is negative. the determination of sentiment can be seen in table 2. table 2: determination of sentiment sentiment value positive ≥1 neutral 0 negative ≥-1 3.7 classification processes following the process for determining sentiment and having established the sentiment value of each opinion sentence using python programming, the next step is the sentiment classification process. the classification process uses the weka 3.8.3 machine learning tool [24], and the machine learning algorithms used in this study are nbc and svm. in the classification process, the data were tested using the 10-fold cross-validation method [25]. the method works by dividing the dataset into two, namely 10 parts with 9/10 parts used as training data and 1/10 parts used as testing data. the iteration process in the method can be run 10 times with a variety of training data and data testing using a combination of 10 parts of data. testing twitter dataset 1 2 3 4 5 6 7 8 9 10 fig. 4: illustration of 10-fold cross-validation. 3.8 evaluation of results the stages of evaluation in the study will examine the performance of accuracy, precision, and recall from the experiments that have been carried out. the results evaluation process is conducted using a confusion matrix [26] featuring as its indicators a true positive rate (tp rate), true negative rate (tn rate), false positive rate (fp rate), and false negative rate (fn rate). the tp rate is the percentage of the positive class that is successfully classified as a positive class, while the tn rate is the percentage of the negative class that is 85 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 successfully classified as a negative class. the fp rate is a negative class that is classified as a positive class, and the fn rate is a positive class that is classified as a negative class. table 3: confusion matrix predicted positive (a) neutral (b) negative (c) actual positive (a) aa ab ab neutral (b) ba bb bc negative (c) ca cb cc 4. experiment and results in this study, the dataset was derived from tweets of public opinion on the indonesian 2019 presidential candidates. the data were taken using the crawling method [27] with r programming using r-studio from twitter social media. the data taken were only tweets in indonesian, with the details of 5000 tweets containing jokowi’s keywords and 5,000 tweets containing prabowo’s keywords, giving a total of 10,000 tweets. the tweet data were taken randomly from both ordinary users and from the news media online on twitter. following the data pre-processing, tokenization, and class attribute determination steps, the dataset used for this study contained opinion sentences from twitter classified into their respective sentiment classes (positive, neutral, or negative) with python programming. the number of datasets is not the same as the amount of data taken because, during the data pre-processing, the same opinion sentence will be deleted to search for unique data, whereas when the data are being crawled, all opinion sentences will be taken even though the sentence is the same. table 4 contains the results of the determination of the sentiment class using the lexicon-based method [28] in python programming with three attribute classes, namely positive, neutral, and negative. table 4: results of determination of sentiment classes sentiment total positive 2688 neutral 4666 negative 2646 after determining the sentiment value of each opinion sentence, the opinion sentences are formed into a dataset using the attribute-relation file format (arff) [29] as the input for classifying data with weka. the tweet data were then classified or tested for accuracy using the nbc machine learning algorithms and svm with weka version 3.8.3 software. this study uses the 10-fold cross-validation method for the process of classifying or testing tweet data. in this process, the data are divided into 10 parts with 9/10 parts used for the training process and 1/10 parts used for the testing process. iteration takes place 10 times with variations in training and testing data using a combination of 10 parts of data. table 5 displays a comparison of the results from the nbc machine learning algorithm with svm. table 5: comparison of classification results* naïve bayes classifier (nbc) 86 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 *the precision and recall values are the average values of positive class values and negative classes the information in table 5 enables a comparison of the accuracy, precision, recall, tp rate, and tn rate values for each trial carried out with the nbc machine learning algorithm and svm. the columns contain the tokenization data used in this study while the rows contain the accuracy, precision, recall, tp rate, and tn rate values for each trial conducted. the process from data pre-processing to the determination of the sentiment class produced the dataset of this research, which was then used as the input in the classification process. the classification process was carried out with weka machine learning using the nbc machine learning algorithm and svm. the classification test process with 7 tokenizations produced values for accuracy, precision, recall, tp rate, and tn rate for each trial. fig. 5: accuracy level of different machine learning algorithms and tokenization methods. the blue and orange charts correspond to the naïve bayes classifier (nbc) and support vector machine (svm), respectively. from fig. 5, we can see that accuracy was tested in this study with two machine learning algorithms, namely nbc and svm, and the 7 tokenizations of alphabetic tokenizer, character n-gram tokenizer, unigram, bigram, trigram, n-gram, and word tokenizer. 0 10 20 30 40 50 60 70 80 90 alphabetic character n-gram unigram bigram trigram n-gram word naïve bayes classifier (nbc) support vector machine (svm) tokenization methods a cc u ra cy ( % ) tokenizer accuracy (%) precision (%) recall (%) tp rate (%) tn rate (%) alphabetic 49.94 52.5 49.9 51.4 50.5 character n-gram 51.81 54.4 51.8 53.7 51,7 unigram 50.11 52.6 50.1 53.3 48.4 bigram 50.51 61.2 50.5 79.7 25.3 trigram 55.98 68.5 56 21 20.3 n-gram 44.94 51.6 44.9 64.2 46 word 50.11 52.6 50.1 53.3 48.4 support vector machine (svm) tokenizer accuracy (%) precision (%) recall (%) tp rate (%) tn rate (%) alphabetic 79.02 79 79 73.8 70.3 character n-gram 58.47 59.20 58.50 55.70 64.40 unigram 78.9 78.9 78.9 73.2 70.8 bigram 69.21 72.1 69.2 51.5 48 trigram 61.21 71.7 61.2 30.1 31 n-gram 77.82 77.8 77.8 72.6 69.4 word 78.9 78.9 78.9 73.2 70.8 87 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 accuracy was one of the main parameters in the assessment of the sentiment analysis model used in this study. the formula for the value of accuracy was the amount of data that were successfully classified according to the class of sentiment for the entire amount of data classified. therefore, the greater the amount of data that were correctly classified according to the sentiment class, the higher the accuracy value. the highest accuracy value was obtained with respect to the combination of the svm and alphabetic tokenization machine learning algorithms, which had an accuracy value of 79.02%. in this study, machine learning methods such as the svm algorithm produced the highest accuracy because they work by recognizing word patterns. this machine learning algorithm is capable of easily recognizing and memorizing word patterns for a certain sentiment class in an opinion sentence. yet while it is easy to classify sentiment data correctly using these methods, alphabetic tokenization can improve accuracy by breaking a sentence into words, which enables the easy classification of sentences with sentiments. the lowest accuracy value in this study was obtained for the nbc machine learning algorithm with n-gram tokenization, which yielded an accuracy value of 44.94%. fig. 6: precision level of different machine learning algorithms and tokenization methods. the blue and orange charts correspond to the naïve bayes classifier (nbc) and support vector machine (svm), respectively. fig. 7: recall level of different machine learning algorithms and tokenization methods. the blue and orange charts correspond to the naïve bayes classifier (nbc) and support vector machine (svm), respectively. figure 6 shows that the highest precision value of 79% was obtained by the svm machine learning algorithm with alphabetic tokenization, while the lowest precision value 0 10 20 30 40 50 60 70 80 90 alphabetic character n-gram unigram bigram trigram n-gram word naïve bayes classifier (nbc) tokenization methods p re ci si o n ( % ) 0 10 20 30 40 50 60 70 80 90 alphabetic character n-gram unigram bigram trigram n-gram word naïve bayes classifier (nbc) support vector machine (svm) tokenization methods r e ca ll (% ) 88 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 of 55.1% came from the nbc machine learning algorithm with n-gram tokenization. in the figure 7, we can see that highest recall value of 79% was obtained with the svm machine learning algorithm and alphabetic tokenization, while the lowest recall value of 51.6% was obtained with the nbc machine learning algorithm with n-gram tokenization. the high precision values were obtained because the precision value formula was based on the number of positive classes that were correctly classified as a positive class divided by the total data classified as a positive class, whereas the recall value formula consisted of the number of positive classes that were correctly classified as positive classes divided by the number of actual positive classes. fig. 8: tp rate level of different machine learning algorithms and tokenization methods. the blue and orange charts correspond to the naïve bayes classifier (nbc) and support vector machine (svm), respectively. fig. 9: tn rate level of different machine learning algorithms and tokenization methods. the blue and orange charts correspond to the naïve bayes classifier (nbc) and support vector machine (svm), respectively. figure 8 displays the highest and lowest tp rate obtained using the nbc machine learning algorithm. the tp rate is a value denoting the amount of positive tweet data that were correctly classified according to the sentiment class, which in this case was positive. in contrast, the highest and lowest tn values were obtained using the svm machine learning algorithm as shown in fig. 9. the tn rate indicates the value of negative tweet 0 10 20 30 40 50 60 70 80 90 alphabetic character n-gram unigram bigram trigram n-gram word naïve bayes classifier (nbc) support vector machine (svm) tokenization methods t p r a te ( % ) 0 10 20 30 40 50 60 70 80 alphabetic character n-gram unigram bigram trigram n-gram word naïve bayes classifier (nbc) support vector machine (svm) tokenization methods t n r a te ( % ) 89 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 data that were correctly classified according to the sentiment class, which in this case was negative. from the research carried out, it can be seen that the model constructed delivered the greatest accuracy when using a combination of the svm machine learning algorithm and ngram tokenization, while the lowest accuracy value was obtained when testing using a combination of the nbc machine learning algorithm with trigram tokenization. the accuracy results produced were quite good; however, the model still made a number of mistakes when the classification process of the dataset with the distribution of sentiments was not as balanced as this study intended. the use of datasets with imbalanced distribution will lead to the incorrect classification of minority class data as majority class data [30], which results in a large value difference because most classifiers manage to correctly classify the majority class compared to the minor class [31]. 5. conclusions from the series of studies conducted, we can conclude that the sentiment analysis model built was suitable for use in determining the sentiment of public opinion on twitter with respect to the 2019 indonesian presidential candidates. the study aimed to test and determine which machine learning algorithms were suitable for the classification of public opinion on twitter, and also to test 7 suitable tokenizations and produce high accuracy when combined with the naïve bayes classifier (nbc) and support vector machine (svm) machine learning algorithms. the sentiment analysis revealed that there was much negative public sentiment on twitter aimed at the 2019 indonesian presidential candidates. the greatest accuracy value was obtained when using a combination of the svm machine learning algorithm and alphabetic tokenization, which yielded an accuracy value of 79.02%. the lowest accuracy value in this study was obtained for the nbc machine learning algorithm with n-gram tokenization, which had an accuracy value of 44.94%. this study has therefore demonstrated that the svm machine learning algorithm produces higher accuracy compared to the nbc machine learning algorithm. it is suggested that further research should endeavour to use more data and real-time data from both twitter and other social media sites such as facebook and youtube. acknowledgements this research was funded by universiti teknologi malaysia (utm) under research university grant vot-20h04, malaysia research university network (mrun) vot 4l876, and the fundamental research grant scheme (frgs) vot 5f073 supported under the ministry of education malaysia. the work is partially supported by the spev project, university of hradec kralove, fim, czech republic (id: 2103-2019), “smart solutions in ubiquitous computing environments” and by the project of excellence 2019/2205, faculty of informatics and management, university of hradec kralove. partial funding by universitas muhammadiyah ponorogo through the institute for research and public services (lppm) under the contract no. 115/vi.4/pn/2018 is also acknowledged. we are also grateful for the support of ph.d. students sebastien mambou and michal dobrovolny in consultations regarding application aspects. references [1] kpu portal publikasi pemilihan umum 2019. available: https://infopemilu.kpu.go.id/. [2] instagram by the numbers: stats, demographics & fun facts, omnicore agency, 2020. 90 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 available: https://www.omnicoreagency.com/instagram-statistics/. [3] januru l. (2016) analisis wacana black campaign (kampanye hitam) pada pilpres tahun 2014 di media kompas, jawa pos dan kedaulatan rakyat, natapraja, 4(2): 181-194. [4] indurkhya n, damerau fj. (2010) handbook of natural language processing, 2nd ed. chapman & hall/crc. [5] wagh b, n rw. (2016) sentimental analysis on twitter data using naive bayes, ijarcce, 5(12): 316-319. [6] yuret d, türe f. (2006) learning morphological disambiguation rules for turkish, proceedings of the human language technology conference of the north american chapter of the acl, pages 328–334. [7] zainuddin n, selamat a. (2014) sentiment analysis using support vector machine, in i4ct 2014 1st international conference on computer, communications, and control technology, proceedings, pages. 333–337. [8] pitsilis gk, ramampiaro h, langseth h. (2018) effective hate-speech detection in twitter data using recurrent neural networks, appl. intell., 48(12): 4730-4742. [9] pak a, paroubek p. (2010) twitter as a corpus for sentiment analysis and opinion mining, proc. 7th int. conf. lang. resour. eval. lr. 2010, pages. 1320–1326. [10] kolchyna, o., souza, t.t., treleaven, p., aste, t. (2015). twitter sentiment analysis: lexicon method, machine learning method and their combination. arxiv: computation and language. [11] nezhad zb, deihimi ma. (2019) a combined deep learning model for persian sentiment analysis, iium eng. j., 20(1): 129-139. [12] zainuddin n., selamat a., ibrahim r. (2016) improving twitter aspect-based sentiment analysis using hybrid approach. in: nguyen n.t., trawiński b., fujita h., hong tp. (eds) intelligent information and database systems. aciids 2016. lecture notes in computer science, vol 9621. springer, berlin, heidelberg. [13] zainuddin, n., selamat, a., ibrahim, r. (2018) hybrid sentiment classification on twitter aspect-based sentiment analysis. appl intell 48, 1218–1232. [14] purohit ns, angadi ab, bhat m, gull kc. (2015) crawling through web to extract the data from social networking site-twitter, 2015 natl. conf. parallel comput. technol. parcomptech 2015. [15] r: what is r?. available: https://www.r-project.org/about.html. [16] sammut c. (2011) genetic and evolutionary algorithms. in: sammut c., webb g.i. (eds) encyclopedia of machine learning. springer, boston, ma. [17] utomo fs, suryana n, azmi ms. (2020) stemming impact analysis on indonesian quran translation and their exegesis classification for ontology instances. iium eng. j., 21(1): 3350. [18] lutfiatun a, novitasari a, helfiyana a. (2018) bahasa alay pada chating di medsos remaja millenial ( bahasa alay vs remaja millenial ), prosiding senasbasa (seminar nasional bahasa dan sastra), pages. 34–41. [19] kbbi daring. available: https://kbbi.kemdikbud.go.id/ [20] weka_tokenizers: r/weka tokenizers in rweka: r/weka interface. available: https://rdrr.io/cran/rweka/man/weka_tokenizers.html. [21] jabreel m, moreno a. (2019) a deep learning-based approach for multi-label emotion classification in tweets, appl. sci., 9(6). [22] musto c, semeraro g, polignano m. (2014) a comparison of lexicon-based approaches for sentiment analysis of microblog, ceur workshop proc., 1314: 59-68. [23] buntoro ga. (2017) analisis sentimen calon gubernur dki jakarta 2017 di twitter, integer j. maret, 1(1): 32-41. [24] machine learning group department of computer science: university of waikato. available: https://www.cs.waikato.ac.nz/research/research-groups/machine-learning-group [25] wiley m, wiley jf. (2019) advanced r statistical programming and data models: analysis, machine learning, and visualization. apress media llc. [26] confusion matrix for your multi-class machine learning model. available: https://towardsdatascience.com/confusion-matrix-for-your-multi-class-machine-learning91 iium engineering journal, vol. 22, no. 1, 2021 buntoro et al. https://doi.org/10.31436/iiumej.v22i1.1532 model-ff9aa3bf7826. [27] hernandez-suarez a, sanchez-perez g, toscano-medina k, martinez-hernandez v, sanchez v, perez-meana h. (2018) a web scraping methodology for bypassing twitter api restrictions, pp. 1-7. [28] haniewicz k, rutkowski w, adamczyk m, kaczmarek m. (2013) towards the lexiconbased sentiment analysis of polish texts: polarity lexicon. [29] attribute-relation file format (arff). available: https://www.cs.waikato.ac.nz/~ml/weka/arff.html. [30] handling imbalanced datasets in machine learning towards data science. available: https://towardsdatascience.com/handling-imbalanced-datasets-in-machine-learning7a0e84220f28. [31] longadge r, dongre s. (2013) class imbalance problem in data mining review, int. j. comput. sci. netw., vol. 2, no 1. 92 1. introduction 2. related work 3. proposed methodology 4. experiment and results 5. conclusions acknowledgements references application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 experimental investigation of the influence of multi-recycling on the fracture behavior of post consumer high impact polystyrene from disposable cups evaluated by the j-integral approach hanan el bhilat1*, hassan mabchour2, houda salmi1, abdelilah hachim2 and khalid el had2 1 national higher school of electricity and mechanics, ensem, laboratory of control and mechanical characterization of materials and structures, casablanca, 20232, morocco. 2 institute of maritime studies, laboratory of materials and structures, casablanca, 20232, morocco. *corresponding author: h.elbhilat@ensem.ac.ma. (received: 11th november 2020; accepted: 5th september 2021; published on-line: 4thjanuary 2022) abstract: the aim of the present paper is to study the effect of multi-recycling on the fracture behavior of high impact polystyrene from disposable cups. after collecting and washing the material, it was subjected to six cycles of recycling. after each cycle, it was subjected to tensile tests to determine the r-curves. the theory of the j-integral contour has been used for the development of a characterization method of the fracture strength appropriate to the case of this non-linear elastoplastic polymer material. to this end, the method of multiple specimens (single edge notch tension sent) of thin thickness was used, by introducing cracks of the same lengths to several identical test pieces. the results suggested a slight decrease in crack resistance of recycled high impact polystyrene, especially during the first cycle, demonstrated by a comparison of jic values related to initiation of crack propagation. the fracture energy absorbed as a function of the cycles suggested a weakening within the material. abstrak: tujuan kajian ini adalah bagi mengkaji kesan tindak balas pada pelbagai peringkat-kitar semula ke atas kerapuhan polisterin berimpak tinggi pada cawan pakai buang. selepas mengumpul dan membasuh cawan ini, terdapat enam peringkat kitar semula. pada setiap peringkat, ianya akan melalui ujian tegangan bagi mendapatkan lengkung-r. teori kamiran-j kontur telah digunakan bagi mencipta kaedah khas bagi mengkaji kekuatan retakan bersesuaian bagi kes bahan polimer elastoplastik yang tidaklinear. sehingga kini, kaedah regangan tepi takuk tunggal (sent) telah digunakan pada spesimen berketebalan rendah, dengan menghasilkan keretakan sama panjang di permulaan kajian di buat pada pelbagai bahan uji yang serupa. dapatan kajian menunjukkan rintangan pada retakan telah berkurang sedikit pada polisterin kitar semula berimpak tinggi, terutama pada kitaran pertama, yang ditunjukkan pada nilai jic pada permukaan rambatan retakan awal. tenaga kerapuhan yang meresap pada setiap kitaran menunjukkan bahan telah melemah dari dalam. keywords: recycling; high impact polystyrene; fracture; j-integral; extrusion 268 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 1. introduction the 19th and 20th centuries marked the appearance of plastics. these new materials are the result of advances in petrochemicals and awakened a particularly strong interest in the aftermath of the second world war, a period during which the industry had to cope with the growing demand for raw materials. consequently, the various properties, ease of processing, and advantageous costs presented by these materials encourage their application in all fields of industrial production in order to meet the growing needs of consumers. the oil shock occurring in the 1970s marked the beginning of consumer polymers. however, this massive exploitation is not without consequences. indeed, the main drawback of polymeric materials lies in the fact that they are not biodegradable and thus create the problem of managing their industrial or consumer waste, which accumulates in a worrying manner. it is only in the last thirty years that the treatment of plastic waste has become a primary concern in preserving the environment. the recovery of plastic materials is then the subject of all attention, especially in the scientific world where many studies have looked at this global phenomenon. the general characteristics of plastic waste and recycled polymers, from a mechanical point of view, are established by the fact that they have undergone, during their previous uses, two major phenomena. on the one hand, used or recycled polymeric resins have experienced degradation due to aging (fatigue, temperature...), oxidation, or water absorption. this degradation is manifested by chain breaks and crosslinks occurring at the level of macromolecules. the consequence of these phenomena is the gradual deterioration of the thermomechanical properties of plastic materials [1-5]. on the other hand, pollution depending on the clean or dirty origin of the previous use of this waste can lead to a retention of impurities which influences, among other things, negatively, their thermal and mechanical properties. although these two factors are closely linked, their more or less extensive existence depends, of course, on the origin of the waste. for example, it makes perfect sense that industrial plastic waste undergoes very little degradation and has extremely low impurities. their existence and influence may even turn out to be negligible with regard to production waste (directly from polymerization reactors). too high temperatures or even too long a residence time could have a degradation effect [6-10]. that’s why this paper is only focused on the influence of multi-recycling on the fracture behavior of high impact polystyrene. high impact polystyrene (hips), is a specific polystyrene because of its opacity and above all, its impact resistance. it is also called impact polystyrene (sb). styrene is the basic element in the manufacture of polystyrene and its compatibility with other monomers and polymers makes it possible to imagine many styrenic compounds with various properties. hips is one of them. it incorporates 15 to 25% polybutadiene and is also obtained by grafting polybutadiene during the production of polystyrene. hips is an inexpensive plastic material that is easy to produce and shape. thus, it has a wide forming temperature range and is particularly suitable for thermoforming. in addition, it can have a glossy, satin or matte finish. it is also easily pigmentable; characteristics that make impact polystyrene widely used in various fields. it is used to manufacture displays, containers, toys, roof boxes, food packaging, etc. most of the scientific articles treating the influence of recycling on thermoplastics are interested in mechanical properties in particular: elongation at break, elastic limit, maximum stress and impact resistance. all of this data was determined by stress testing and pendulum impact testing in charpy and izod mode. also, various analyses with a scanning electron 269 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 microscope or even with an electronic transmission microscope have also been identified in certain works. the information found as a result of these tests was aimed at determining whether or not there was an improvement in mechanical properties [11-22]. however very limited studies have treated the elasto-plastic fracture behavior of post-costumer high impact polystyrene, especially in the case of multi-recycling. in this study, we investigated the effect of multi-recycling on the fracture behavior of high impact polystyrene from disposable cups, using the multi-specimen method that finds its application in elastoplastic fracture mechanics. a strained metal or polymer can undergo certain damage and alternations. this damage can lead, in some cases, to the appearance of macroscopic cracks. these cracks are often of sufficiently large size to satisfy the assumptions of continuity of the mechanics of a continuous medium. we can then place ourselves within the framework of fracture mechanics to characterize the harmfulness of this defect [23]. the goals of linear fracture mechanics are: the characterization of the stress fields and singular deformations at a crack point establishing the relationships between the crack point fields, the geometry of the test specimen and the overall field (measurable quantity) the energy conditions necessary for the (re)-initiating of the crack description of the crack propagation (stable or unstable) the determination of a critical size of the defects beyond which the failure (especially unstable) will be triggered initially, one will endeavor to present the cases where the factor ki: the factor of intensity of the stresses, and g the rate of restitution of energy, provide solutions in the understanding of the initiation mechanisms of polymers. in this paper, we will then be interested in the parameter j and its uses in fracture mechanics in the case where the material has a non-linear elastic behavior, which is the case of high impact polystyrene. unlike resilience, an integral characteristic depending on the experimental conditions, toughness is an intrinsic characteristic of materials and a quantity that can be used in design (like a young's modulus). the determination of the toughness is carried out on specimens notched by different theoretical approaches depending on the mechanical behavior of the material. indeed, for a brittle material, toughness is evaluated from the concepts of linear elastic fracture mechanics (lefm) while it is studied according to the concepts of elastoplastic fracture mechanics (post-yield fracture mechanics: pyfm) when the material is ductile. pyfm requires the introduction of the concept of cracking resistance curve or r curve. it was established by irwin [24] in order to characterize the resistance to slow cracking of materials with some ductility at the crack head. an r curve is a curve of variation of the toughness with the crack advance (δa). in general, a crack can start and then progress when a parameter (k, g, or j), representing the action of the external environment at the crack head, becomes equal to the resistance to cracking (kr, gr, or jr) of the material. in the case of a brittle material (lefm), the structure of the material and its resistance to cracking do not change during propagation due to the absence of plastic deformation at the crack head. on the other hand, in the case of a ductile material (pyfm), the progressive increase in the plastic deformation at the crack head during initiation and propagation causes an increase and then a stabilization of its resistance to cracking. the toughness of the material 270 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 can no longer be represented by a single critical parameter (kc or gc) but rather by an r curve (kr, gr or jr = f (δa)) (fig. 1). fig. 1: r curves in lefm and pyfm. rice [25] demonstrated that, in the case of a crack located in the xz plane and whose front is parallel to the axis z (fig. 2), the integral j (eq. (1)) is independent of contour γ and null when this contour is closed (there is no crack). we can consider that j represents the component of the energy flow crossing γ, due to the singularity related to the presence of the crack. 𝐽 = ׬ ቀ𝑊𝑑𝑦 − 𝑇𝑖 𝜕𝑢𝑖 𝜕𝑥 𝑑𝑠ቁ γ (1) with: w, the strain energy density, ti the outwardly oriented traction vector, ui, the displacement vector of the arc ds, s, the curvilinear abscissa on the contour γ, x, y and z the cartesian coordinates. fig. 2: illustration of the concept of integral j. note that w = ∫σij dεij, with σij and εij the stress and strain components, respectively. k r kc lefm 0 δa krmax k r kinit lefm 0 δa d s t⃗⃗ crack y x 271 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 j is calculated from the energy u necessary to propagate the crack (energy supplied by the external environment) (eq. (2)). 𝐽 = − 1 𝑏 𝑑𝑈 𝑑𝑎 (2) with “b”, the thickness of the specimen and “a” the crack length. from this equation (eq. (2)), begley and landes [26-28] have shown that j is identical to g in the case of a linearly elastic and brittle material and that j can be a criterion of rupture for elastoplastic materials. the crack is initiated when j reaches a critical value jic which is an intrinsic characteristic of the material. although jic's calculation methods are very controversial, the astm e813-81 standard that considers the case of metals seems to be applicable to polymers. this standard assumes that the curve j = f (δa) is a line and that jic corresponds to the intersection of this line with the blunt line (fig. 3) having for equation: 𝐽 = 2𝜎𝑦𝛥𝑎 (3) with σy being the stress at the tensile yield point of the material. on the other hand, the astm e 813-87 standard states that the curve j = f (δa) follows a power law of the form j = a.δa n and that jic corresponds to the value of j taken at the intersection of this curve with the straight line of eq. (4 )(fig. 3): 𝐽 = 2𝜎𝑦(𝛥𝑎 − 0,2𝑚𝑚) (4) fig. 3: method for determining jic according to astm e 813-81 (a) and astm e 813-87 (b). in practice, the procedure for obtaining j-r curves is identical to that used in lefm. to construct the j-r curves, it is necessary to perform the tests on multiple samples (7 minimum) up to different levels of deflection or crack opening. these tests will be followed by an optical measurement of the fracture surface in order to determine the actual crack advances. each test piece tested leads to the determination of a pair of values (j, ∆a), i.e. at a point on the j-r curve. next, we calculate the integral j. j = 2 σy δa j jic δa a j = 2 σ y (δa0,2mm) j jic δa b 272 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 2. materials and methods in this section, we present our experimental study, divided into two parts: the first is to study the effect of several extrusion/recycling cycles on the toughness properties of high impact polystyrene from disposable cups, mainly the j-δa curves. the second is devoted to the study of the effect of the six recycling cycles on the jic parameter then compare the results to virgin material. the work plan thus followed is presented below. the various experimental techniques used and their operating conditions, as well as the ways of using the results are also presented in this paper. 2.1 disposable cups recycling the high impact polystyrene disposable cups collected for this study by the recycling company have undergone mechanical recycling carried out at the level of the same recovery company. the process involves washing and then shredding the cups into small pellets. these pellets are then crushed using a grinder. the granulation (fig. 4) of the ground material obtained is carried out in a twin-screw granulating extruder by the material provider. fig. 4: hips granules and pellets from disposable cups. the extruder (leistritz) is equipped with a cylinder filter changer. the filtering system helps prevent unmelted granules or other impurities from entering the extrudate. the extrusion parameters are as follows: extrusion temperature: from 220 to 230 °c; screw speed: 35 rpm. a maximum injection pressure of 2,500 bars. the extrudates are cooled in a water tank before being transformed into granules using a cutter. these granules, considered to be the first cycle of extrusion, are then made into specimens destined for various thermo-mechanical tests by molding process as shown in fig. 5. the specimens obtained are treated in the same way and with the same conditions described above. these operations were repeated six times without any change under all conditions. therefore, the total number of extrusion cycles, to which the virgin resin is subjected, is equal to 6. 273 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 fig. 5: tests specimens according to iso 294-1 and iso 294-2. 2.2 choice of specimens for fracture behavior analysis the iso 13586 and astm d 5045 standards suggest that to evaluate the jic of a thermoplastic and thermosetting material, the tests must be carried out on ct (compact tension) specimens, or on sent (single edge notched tension) specimens. the dimensions of the test pieces are given by the standards. although the specifications and recommendations of the two standards iso 13586 and astm d 5045 are only applicable for linear fracture mechanics, the choice and sizing of specimens has been maintained by standard astm d 6068 for the determination of jr curves of elastoplastic polymer materials. in our experimental study, the jr curve of both virgin and recycled high impact polystyrene is drawn by adopting the operating mode described by the standard astm d 6068, but the general configuration of the test (type of test piece, experimental device, etc.) is identical to that performed in lefm (astm d 5045, iso 13586). the sent (fig. 6) specimens were molded by a sintesi molding machine. fig. 6: cracked tensile test piece on the side (sent). the last stage of preparation of the specimens is carried out using a razor blade. a precrack is introduced into the notched area of the specimen, the cutter blade of which, 0,4 mm thick, is changed after 5 specimens. the condition of the blade is essential to avoid residual stresses following this operation. un-notched sent specimens were machined for tests that correct the results obtained on notched and pre-cracked specimens. 80 10 δa 3 mm 274 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 2.3 test methodology and j-r curve the principle of the construction method of the experimental jr curve is to load a precracked specimen until an imposed displacement (displacement of the cross member), of the order of a few tenths of a millimeter, is reached with a fixed loading speed. the tensile tests were carried out using a zwickroell tensile machine with a 2,5 kn load cell. the fracture face is then optically examined to calculate the advance of the crack. consequently, two types of data are to be recovered on a test: the load displacement curve, which leads to calculate j. the fracture surfaces, which makes it possible to measure the crack advance δa. the crack advance measurements, being of very low values, were performed with ksm off-line measuring device that measures thinly cut cross sections (slices) of specimens, as shown in fig. 7. fig. 7: ksm off-line measuring device. thus, each specimen makes it possible to obtain a pair of values (j, δa) that represent a point on the j-r curve. this method, shown in fig. 8, (proposed by the astm d 6068) standard, provided that the loading speed adopted causes a clear and stable propagation of the crack. to ensure this condition, the iso 13586 standard recommends using, at a temperature of 23 ° c, a speed of 10 mm/min. the j integral is calculated from the area under the load displacement curve using grapher 14 software, which represents the total energy ut. a single tensile test is carried out on a non-notched sent specimen of the same size as the notched specimen. the unique load displacement curve from this test is used to calculate the indentation energy "ui" for each specimen. indeed, ui is the area under the curve between zero until the displacement corresponding to the maximum force applied to the notched and pre-cracked specimen. this amount of energy is dissipated by phenomena other than cracking. using ut and ui, j can be calculated for each test by eq. (5): 𝐽 = 𝜂(𝑈𝑇−𝑈𝑖) 𝑏(𝑤−𝑎0) (5) η is a geometrical dimensionless parameter. garcia et al [29] state that to calculate j of polymers, the factor η depends only on the ratio between the length of the crack and the width of the specimen (a0 / w). for the geometry of the test piece, clarke and landes [30] succeeded in obtaining an approximation of η through the formula: for ct specimens 275 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 𝜂 = 2 + 0,522 ቀ1 − 𝑎0 𝑤 ቁ (6) for sent specimens 𝜂 = 2 (7) 2.4 tests on sent specimens the sent specimens are loaded by applying a tensile force through the two symmetrical bores and a suitable mounting on the zwickroell tensile machine equipped with a 2,5 kn load cell. the test is stopped once the imposed displacement (u) is reached (fig. 8). the load-displacement curve is recovered and the cracking area is examined in the ksm instrument to facilitate the measurement of the different crack advance lengths δa. finally, the test piece is completely torn into two parts. fig. 8: variation of dissipated energy with constant displacement. eight restraints (u) are studied ranging from 2,5 mm to 10 mm. for displacements smaller than 2,5 mm, we did not observe an advance of the crack. the eight tries give us 8 points, with one or two extra specimens if needed. the standard requires a minimum of 7 points to draw the j-r curve. the maximum force and total energy are deduced and calculated from these curves. the values obtained are corrected by the indentation energy. so, j is calculated for each test specimen by applying eq. (5). the fracture areas of the two parts of the specimen are then observed. the depth of the pre-cracks (or initial crack) is not controlled during the preparation of the specimen, but measured precisely after each test under the ksm device. it is the average of three measurements of the distance between the notch tip and the crack tip. the distance between the final crack front and the initial crack front is measured at five equidistant points. the extension of the crack δa is the average of this value. the j-r curve given by the tensile tests on sent specimens is plotted. this curve characterizes the resistance to cracking of hips. the most useful information that can be p δu u du a a + δa p u 276 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 derived from this curve is the starting toughness jic, a characteristic of the material. it defines the initiation point of a crack. the astm e 813 standard recommends, for the calculation of jic, a graphic method that consists of shifting the blunt line to a δa = 0,2. jic is the intersection of this straight line with curve j. in addition to the blunt line method, some authors define jic, for polymer materials, as the value of the curve j δa which corresponds to an advanced 0,2 mm or 0,4 mm crack [31,32]. huand [32] asserted that j0,2 can also be taken as the characteristic value representative of crack initiation. 3. results and discussion a significant shift is noted between the j-r curve given by the tests on test pieces of virgin hips, and that obtained with recycled material. on the other hand, a slight decrease of jic is noticed amongst different cycles as shown in fig. 9 and fig. 10, thus demonstrating that the mechanical properties in terms of fracture energy, represented by the energy sufficient to initiate the fracture, decreases with the increase in the number of cycles performed. the material changes from a ductile state to a brittle state. embrittlement occurs abruptly by the combined effect of the drop in molar mass and the increase in crystallinity (entanglement), thus reducing the amorphous phase, which prevents crack growth within the material. through the number of recycling cycles, high impact polystyrene undergoes thermomechanical-chemical degradation inducing chain scissions, the molar weight decreases creating more chain ends. these extremities represent concentrates of fracture energy that absorb the energy and cannot propagate it any longer, initiating the fracture. in addition, a large difference in molecular mass produces a heterogeneous whole favoring fracture. the low number of entanglements that were the usual consolidation of high impact polystyrene propagates the tear easily creating the fracture while the fracture of virgin hips was relatively difficult. fig. 9: the j-δa curve of recycled hips during different cycles. 0 2 4 6 8 10 12 0 0.5 1 1.5 j (n /m m ) δa (mm) virgin cycle 1 cycle 2 cycle 3 cycle 4 cycle 5 cycle 6 277 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 fig. 10: the evolution of jic as a function of number of cycles. degradation during recycling/extrusion it is well known that extrusion is one of the most severe processes that a polymer can withstand [33], shear forces and high temperatures cause mechanical and thermal splitting of the polymer chain, resulting in the formation of end of chain radicals (initiation of propagation phenomenon) as shown in fig. 11. fig. 11: splitting of the polymer chains due to mechanical and thermal degradation. polymers are generally recycled in the molten state, at a temperature above the melting temperature but obviously well below the decomposition temperature. this does not prevent thermal and mechanical degradation from prevailing during the short implementation period (processing): thermal: the high friction shear can locally increase the temperature above the nominal processing temperature and chemical bonds can be thermally strained until they break. mechanical: when the rate of deformation of chemical bonds is much greater than the rate of relaxation of macromolecules, the activation energy of the fracture of the bonds and consequently the induced degradation time (ti), are reduced to the intensity of the applied stresses. the consequence of such degradation is the reduction in molar mass by 1/2, 1/4, or 1/8 of the initial molar mass [34], in fact, the molar mass of polymers plays a significant role in terms of durability. it has been generally recognized that high impact polystyrene becomes more stable when its molar mass increases or when the fraction of low masses decreases. shorter chains result in a greater number of chain ends. these ends provide elements very 0 0.5 1 1.5 2 2.5 3 3.5 4 virgin cycle 1 cycle 2 cycle 3 cycle 4 cycle 5 cycle 6 j ic ( n /m m ) 278 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 sensitive to aging and to degradation in general. they are even capable of locally catalyzing degradation reactions. a high molar mass induces the following properties: an increase in the entanglement rate (knots) which serves to counter the propagation of cracks in the material a drop in gas permeability and therefore a drop in the progression of reactive elements through the material [35]. our previous work [36] on characterizing of multi-recycled high impact polystyrene indicated an increase of the melt flow index as well as a decrease in molecular weight which supports the results of the present paper. 4. conclusion the study of the mechanical properties, in particular the fracture behavior of multirecycled high impact polystyrene from disposable cups, allowed us to specify the influence of the degradation phenomenon on the drop in jic values. mechanical degradations in the recycling/processing of polymers have been the least studied, no doubt because of their complexity; however, they play a very important role and their control is essential in the recycling operation. the growing demand from users for the quality and reliability of plastics, gives the study of degradation an increasingly important place, particularly from the perspective of recycling, which is becoming more and more inevitable. the multi-specimen method based on elastoplastic fracture mechanics, revealed a slight degradation in terms of fracture resistance, of the various recyclates, especially during the first cycle, this is explained by chain breaking, oxidation, and decreasing of the molar mass of high impact polystyrene. on the other hand, the present analysis strongly supports our previous work on the effect of multi-recycling on the material-flowing index as it showed an increase in melting flow index and therefore the decrease in viscosity with the number of recycling cycles. references [1] azwa zn,yousif bf,manalo ac, karunasena w. (2013), a review on the degradability of polymeric composites based on natural fibres, materials & design, 47(1): 424-442. https://doi.org/10.1016/j.matdes.2012.11.025 [2] celina m, linde e, brunson d, quintana a, giron n. (2019) overview of accelerated aging and polymer degradation kinetics for combined radiation-thermal environments, polymer degradation and stability,166 (1): 353-378. https://doi.org/10.1016/j.polymdegradstab.2019.06.007 [3] saikrishnan s, jubinville d, tzoganakis c, mekonnen tm. (2020) thermo-mechanical degradation of polypropylene (pp) and low-density polyethylene (ldpe) blends exposed to simulated recycling. polymer degradation and stability, 182(1). https://doi.org/10.1016/j.polymdegradstab.2020.109390 [4] ito m, nagai k. (2008) degradation issues of polymer materials used in railway field, polymer degradation and stability, 93(10): 1723-1735. https://doi.org/10.1016/j.polymdegradstab.2008.07.011 [5] verdu j. (2011) vieillissement chimique des plastiques : aspects généraux, techniques de l’ingénieur. https://www.techniques-ingenieur.fr/base-documentaire/archives-th12/archivesplastiques-et-composites-tiaam/archive-1/vieillissement-chimique-des-plastiques-aspectsgeneraux-am3151/ 279 https://www.techniques-ingenieur.fr/base-documentaire/archives-th12/archives-plastiques-et-composites-tiaam/archive-1/vieillissement-chimique-des-plastiques-aspects-generaux-am3151/ https://www.techniques-ingenieur.fr/base-documentaire/archives-th12/archives-plastiques-et-composites-tiaam/archive-1/vieillissement-chimique-des-plastiques-aspects-generaux-am3151/ https://www.techniques-ingenieur.fr/base-documentaire/archives-th12/archives-plastiques-et-composites-tiaam/archive-1/vieillissement-chimique-des-plastiques-aspects-generaux-am3151/ iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 [6] vranjes n, rek v. (2007) effect of epdm on morphology, mechanical properties, crystallization behavior and viscoelastic properties. macromolecular symposia, 258(1): 90100. https://doi.org/10.1002/masy.200751210 [7] kallel t, massardier-nageotte v, jaziri m, gérard j f, elleuch b. (2003) compatibilization of pe/ps and pe/pp blends. i. effect of processing conditions and formulation. journal of applied polymer science, 90(9): 2475-2484. https://doi.org/10.1002/app.12873 [8] lin y, marchand g r, hiltner a, baer e. (2011) adhesion of olefin block copolymers to polypropylene and high density polyethylene and their effectiveness as compatibilisers in blends. polymer, 52(7) :1635-1644. https://doi.org/10.1016/j.polymer.2011.02.012 [9] siddiqui m, antonakou e, redhwi h, achilias d. (2019) kinetic analysis of thermal and catalytic degradation of polymers found in waste electric and electronic equipment. thermochimica acta, 675 (1): 69-76. https://doi.org/10.1016/j.tca.2019.03.001. [10] sawaguchi t, sasaki d, takamura a. (2019) on the entanglement-based mechanism in thermal degradation of vinyl polymers, polymer degradation and stability, 169(1): 108990. doi: https://doi.org/10.1016/j.polymdegradstab.2019.108990. [11] hirayama d, clodoaldo s. (2018) morphologic and mechanical properties of blends from recycled acrylonitrile-butadiene-styrene and high-impact polystyrene, polymer, 135 (1): 271278. https://doi.org/10.1016/j.polymer.2017.12.038. [12] lin y, yakovleva v, chen h, hiltner a, baer e. (2009) comparison of olefin copolymers as compatibilizers for polypropylene and high-density polyethylene. journal of applied polymer science, 113(3): 1945-1952. https://doi.org/10.1002/app.30190 [13] zweifel h. (2000) plastics additives handbook munich. hanser. (5th edition) :900. [14] mehrabzadeh m, farahmand f. (2001) recycling of commingled plastics waste containing polypropylene, polyethylene, and paper. journal of applied polymer science. 80(13): 25732577. https://doi.org/10.1002/app.1367 [15] ku h, wang n, pattarachaiyakoop n, trada m. (2011) a review on the tensile properties of natural fiber reinforced polymers composites. composites, part b,42(4): 856-873. https://doi.org/10.1016/j.compositesb.2011.01.010 [16] grein c, gahleitner m, bernreitner k. (2012) mechanical and optical effects of elastomer interaction in polypropylene modification: ethylene-propylene rubber, poly-(ethylenecooctene) and styrene-butadiene elastomers. express polymer letters, 6(9): 688-696. doi: 10.3144/expresspolymlett.2012.74 [17] ubonnut l, thongyai s, praserthdam p. (2007) interfacial adhesion enhancement of polyethylene-polypropylene mixtures by adding synthesized diisocyanate compatibilizers. journal of applied polymer science,104(6): 3766-3773. https://doi.org/10.1002/app.25945 [18] radonjic g, gubeljak n. (2002) the use of ethylene/propylene copolymers as compatibilizers for recycled polyolefin blends. macromolecular material and engineering, 2(287): 122-132. https://doi.org/10.1002/1439-2054(20020201)287:2<122::aid-mame122>3.0.co;2-a [19] colbeaux a, kotek j, fenouillot f, taha m, wautier h, gérard j f. (2001) compatibilisation de mélanges polypropylène/polyéthylène par extrusion réactive. thèse doctorat insa lyon, 338 p. http://theses.insa-lyon.fr/publication/2001isal0058/these.pdf [20] almishal s, mohamed t, shazly m. (2020) experimental and statistical study of the effect of temperature and waste ratio on the mechanical properties and cost of polystyrene polypropylene plastic blends, heliyon, 6(6): e04166. https://doi.org/10.1016/j.heliyon.2020.e04166. [21] mehat nm, kamaruddin s. (2011) optimization of mechanical properties of recycled plastic products via optimal parameters using the taguchi methods. journal of materials processing technology, 211(12): 1989-1994. https://doi.org/10.1016/j.jmatprotec.2011.06.014 [22] krulis z, kokta v b, horak z, michalkova d, fortelny i. (2001) compatibilization as a procedure for recycling of commingled polyolefin waste. macromolecular materials and engineering, 286(3): 156-160. https://doi.org/10.1002/1439-2054(20010301)286:3<156::aid-mame156>3.0.co;2-j [23] ritchie r, liu d. (2021) chapter 2 foundations of fracture mechanics, introduction to fracture mechanics, elsevier: 3-9. https://doi.org/10.1016/b978-0-323-89822-5.00008-6. [24] irwin gr. (1957) analysis of stresses and strains near the end of a crack traversing a plate, journal of applied mechanics, 24:361-364. 280 https://doi.org/10.1002/app.12873 https://doi.org/10.1016/j.polymer.2011.02.012 https://doi.org/10.1016/j.tca.2019.03.001 https://doi.org/10.1016/j.polymdegradstab.2019.108990 https://doi.org/10.1016/j.polymer.2017.12.038 https://doi.org/10.1002/app.30190 https://doi.org/10.1002/app.1367 https://doi.org/10.1016/j.compositesb.2011.01.010 https://www.researchgate.net/deref/http%3a%2f%2fdx.doi.org%2f10.3144%2fexpresspolymlett.2012.74 https://doi.org/10.1002/app.25945 https://doi.org/10.1002/1439-2054(20020201)287:2%3c122::aid-mame122%3e3.0.co;2-a http://theses.insa-lyon.fr/publication/2001isal0058/these.pdf https://doi.org/10.1016/j.heliyon.2020.e04166 https://doi.org/10.1016/j.jmatprotec.2011.06.014 https://doi.org/10.1016/b978-0-323-89822-5.00008-6 iium engineering journal, vol. 23, no. 1, 2022 bhilat et al. https://doi.org/10.31436/iiumej.v23i1.1693 [25] rice jr. (1968) a path independent integral and approximate analysis of strain concentration by notches and cracks. journal of applied mechanics, 35(2):379-386. doi: 10.1115/1.3601206 [26] begley ja, landes jd. (1971) the effect of specimen geometry in jic. fracture toughness, american society of testing and materials, special technical publication, 514: 24-39. https://doi.org/10.1520/stp38817s [27] begley ja, landes jd. (1971) the j-integral as a fracture criterion. fracture toughness, american society of testing and materials, special technical publication, 514: 1-23. https://doi.org/10.1520/stp38816s [28] begley ja, landes jd. (1974) test results from j-lntegral studies: an attempt to establish a jic testing procedure. fracture analysis, american society for testing and materials, special technical publication, 560:170-186. https://doi.org/10.1520/stp33140s [29] brosa v, bernal c, frontini p. (1999) calibration of fracture mechanics parameters and j–r curve determination in polyethylene side-grooved arc-shaped specimens. eng. fract. mech,62(2-3): 231-248. https://doi.org/10.1016/s0013-7944(98)00094-0 [30] clarke g, landes j. (1979) evaluation of the j integral for the compact specimen. j. test. eval,7(5): 264-269. https://doi.org/10.1520/jte10222j [31] tancrez j, pabiot j, rietsch f. (1996) damage and fracture mechanisms in thermoplasticmatrix composites in relation to processing and structural parameters. compos. sci. technol, 56(7): 725-731. https://doi.org/10.1016/0266-3538(96)00013-9 [32] huang d. (1996) the application of fracture mechanics to materials selection. polym. eng. sci, 36(18): 2270-2274. https://doi.org/10.1002/pen.10625 [33] kumar s, singh r. (2003) primary and secondary recycling of thermosetting polymers: a review. reference module in materials science and materials engineering, 73(9): 1775. https://doi.org/10.1002/mame.200390005 [34] wrozynski rj, rubinsztajn m, potyrailo ra. (2004) evaluation of process degradation of polymer formulations utilizing high‐throughput preparation and analysis methods. macromolecular rapid communication, 2(1): 264-269. https://doi.org/10.1002/marc.200300167 [35] bartolomeo p. (2003) deriving a prediction of the life cycle of géosynthrtic polymers. bulletins des laboratoires des pont et chaussées, n°243-réf 4456, p.51. 281 https://www.researchgate.net/deref/http%3a%2f%2fdx.doi.org%2f10.1115%2f1.3601206 https://doi.org/10.1520/stp38817s https://doi.org/10.1520/stp38816s https://doi.org/10.1520/stp33140s https://doi.org/10.1016/s0013-7944(98)00094-0 https://doi.org/10.1520/jte10222j https://doi.org/10.1016/0266-3538(96)00013-9 https://doi.org/10.1002/pen.10625 https://doi.org/10.1002/mame.200390005 microsoft word 192 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 139 strategy and policy statements on green ict: an islamic perspective shihab a. hameed electrical and computer engineering department, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. shihab@iium.edu.my abstract: in this information and knowledge era; ict development and industry are growing very fast and associated with huge procurement force. today, the global society is facing serious challenges in improving environmental performance, particularly with climate change, global warming, and resource management. ict industry is widely contributing to the global economy associating with innovation, invention and rapid development of almost all the aspect of human life. on other hand; ict industry is responsible for global co2 emissions. global environmental problems are affecting directly many countries’ energy and industrial policies. the rapid increasing of ict usage means more energy consumption and more environmental problems and the estimated ict consumption of energy will be about 15% of the total consumption worldwide in 2020. therefore, many countries are establishing green ict policies which increase energy efficiency due to correspondence climate change. therefore, governments especially in developing and islamic countries need to adopt new strategic policies for efficient energy use in ict. this study presents the current environmental problems related to green ict and the efforts to solve it. several studies have warning from the current energy consumption paradigm, based on newly changed ict practices. this study provides guidelines for decision makers and ict professionals to enhance their work toward green ict and eliminating environmental problems. islamic viewpoint on environment and its protection is considered since it offers comprehensive, stable, and fair viewpoint that is based on main islamic sources; qur‘an and sunnah. hundreds of qur‘anic verses and prophet hadiths clarify (directly or indirectly) the right manner in dealing and protection of environment resources. this paper proposes a framework for strategy and policy statements of green ict based on islamic perspective to serve the world especially developing and islamic countries. abstrak: di era informasi dan komunikasi teknologi (ict) kini, pembangunan ict dan industri berkembang begitu pesat dan dikaitkan dengan daya membeli yang tinggi. hari ini, masyarakat dunia menghadapi cabaran dalam meningkatkan prestasi persekitaran, terutamanya dengan perubahan cuaca, pemanasan global, dan pengurusan sumber. industri ict merupakan penyumbang sebahagian besar daripada ekonomi global yang berkaitan dengan inovasi, reka cipta dan perkembangan pesat hampir semua aspek manusia. di sebaliknya pula, industri ict bertanggung jawab terhadap pelepasan co2 global. masalah persekitaran global secara langsung mempengaruhi polisi tenaga dan industri banyak negara. pembangunan pesat ict menyebabkan meningkatnya penggunaan tenaga dan pertambahan masalah persekitaran. penggunaan tenaga oleh ict dianggarkan mencapai jumlah 15% daripada jumlah penggunaannya di seluruh dunia pada tahun 2020. oleh itu, banyak negara yang membentuk polisi ict hijau supaya kecekapan tenaga dapat ditingkatkan seiring dengan perubahan cuaca. kerajaan terutamanya di negara-negara membangun dan negara islam lain haruslah mengamalkan polisi baru yang wajar agar tenaga digunakan secara efisien di bidang ict. kajian ini iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 140 membentangkan masalah persekitaran yang kini berkaitan dengan menhijaukan ict dan usaha-usaha untuk meyelesaikannya. beberapa kajian berbentuk peringatan berasaskan paradigma penggunaan tenaga terkini, berdasarkan kepada amalan terbaru ict yang dipinda. kajian memberikan garis panduan kepada pembuat-pembuat keputusan dan para professional ict untuk mempertingkatkan usaha mereka ke arah ict hijau dan menyelesaikan masalah alam sekitar. pandangan islam terhadap alam sekitar dan usaha melindunginya dipertimbangkan, memandangkan ianya memberi pendapat yang menyeluruh, stabil dan adil berdasarkan sumber-sumber islam iaitu quran dan sunnah. banyak ayat-ayat al-quran dan hadis-hadis memperjelaskan (secara langsung atau tidak langsung) cara yang betul dalam menangani dan melindungi sumber alam sekitar. kertas ini juga mencadangkan rangka kerja untuk pernyataan strategi dan polisi untuk menhijaukan ict berdasarkan perspektif islam dalam berkhidmat kepada dunia, terutamanya di negara-negara membangun dan negara-negara islam. keywords: green ict; ict professionals; strategy statement; environment problem; islamic perspective 1. introduction the rapid development in electrical, electronics information and communication technology leads to the huge production of such products. the strong procurement power for such products is mainly because of the big number of announcements in different media as well as reduction of products’ prices. this leads to the unwise behavior of customers in buying products regardless of their actual needs. the result is more consumption of energy in production and operating ict product, which lead to significant problems related to environment. climate change, green house gas ghg emission, and global warming are the key challenges facing global society since quarter of century. leaders, governmental and non-governmental organizations, universities and institutes, scientists, research centers and individual researchers work through different activities to face such challenges. these activities include: organizing summits, conferences, seminars, workshops, research projects, and other activities. they work toward finding efficient and effective solutions for better utilization and management for resources, improving environmental performance, and eliminate global warming. computers, computer-based applications, information technology, and communications become essential part and have tremendous effects on human life (directly or indirectly). the information and communication technology (ict) industry has a significant role and contribution to the global economy; but on the other hand ict is responsible for 2-3% of the global carbon footprint [1]. ict growth and usage increasing rapidly in the world; include many developing and muslim countries (asia and africa). the emerging economy and technological advances in many of the growing developing and islamic countries (malaysia, turkey, some arabian gulf countries (saudi arabia and uae), etc) as well as the two super population countries china and india (about 2.5 billions) leads to a rapidly increasing of global access of ict services. this will bring more environmental problems due to the sudden increment on the power request from the ict systems [2]. the increasing usage of ict equipments and the highly dependence on ict applications in almost all aspects of life; implies facing ict harmful affect on environment and other social aspects. sustainable existence of human and other creatures on earth requires that our future ict technologies must be inherently sustainable both by nature iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 141 and in usage [3]; but facing the main challenges related to global warming by co2 (green house gas, ghg) emission caused by global ict infrastructure. based on islamic resources qur‘an [4] and sunnah; all the universe created by allah swt and all its components and creatures are integrated and run in a consistent, accurate, balanced and perfect way. the human has a leading role in this universe as vicegerent of allah swt “allah the lord said to the angels: i will create a vicegerent on earth” [qur’an 2:30]. so human has to follow his lord rules and regulation to manage the universe and keep life stable and unharmed. to eliminate environmental problems we have to adopt an efficient strategy for green ict based on islamic perspective. 2. environmental problems: the role of ict in this information era, ict become the driving force to run almost all aspects of life. ict plays dual role in term of environmental problems (climate change and global warming). firstly is the consumption of power by ict equipment which leads to ghg or co2 emission, and secondly is using ict to enhance the efficiency of energy consumption in other sectors (industry, healthcare, education, etc). to understand the ict role in ghg or co2 emission; several analyses have been done on the economic impact of ict equipment on climate change and global warming. it shows that the ict industry co2 footprint is about to exceed than the aviation industry [5]. the growth rate of energy consumption and co2 emissions is doubling about every 5 years [6] and this rate can grow further. on the other hand we also have to know the contribution of ict applications in reducing co2 emission produced in other sectors. ict emissions are relatively little compared to other industries, but we have to know that it is almost the fastest growing sector in terms of usage and co2 emissions. ict industry could be one of the larger industry sources of green house gas emissions. it is estimated that ict industry consumes anywhere from 6-10% of the world's energy, and about half of these emissions are from personal computers and mobile phones [5]. ict industry has indirect contribution to co2 emission through its consumption of electrical power to run the ict electronic equipments and keep it cool, since every watt consumed by electronics equipments results in heat, which requires almost equal or greater amount of electricity for cooling ict equipment [7]. the big question is: did the ict technology improvements and better energy efficiency is enough while those savings are lost to greater consumption? [8]. the result shows that the improvements in efficiency have done little to reduce actual energy consumption since consumers take advantage of those gains to have more usage for ict equipments, drive bigger cars farther, or heat larger homes, etc [9]; this may result in greater ghg (co2) emissions. as such any strategy for the green ict infrastructure must undertake a systemic approach and should not assume that individual energy savings of either ict equipment or processes can necessarily result in overall global reduction in energy or co2 emissions [3]. improving efficiency of ict equipment or ict processes will lead to increase the energy efficiency directly. but we have to know that the technical solution in enhancing the efficiency of energy consumption is not enough unless it is integrated with enhancing and enriching the educational, cultural and ethical aspects of society to make people feel responsibility. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 142 the general understanding of ethics in islam can be express as a “set of moral principles and guidance that recognizes what is right behavior from what is wrong or what one should do or not”. qur’an and sunnah, show that all the muslims’ life should be guided by islamic ethics [10-13]. responsibility is an essential factor in islamic ethical principles, which is shown in many qur‘anic verses and prophet sunnah. islam specifies the responsibility for every people based on his role in life. prophet mohammed (peace and blessings upon him) said “every muslim is a shepherd (leader) and he is responsible for that which he shepherds”. although several countries and organizations have introduced green ict strategies or polices to address these issues but we still need for more efforts that respected islamic viewpoint. such strategy or policies will serve islamic world as well as others because of the universality, comprehensiveness, stability, and fairness of islamic principles. 3. green ict: energy consumption green environment, green life, and green ict are sample of the terms that become widely used in the last few years. green ict term has defined by several organizations, researches, and authors based on their viewpoint for the concept. samples of these meaning of green of ict are shown in this section. organization for economic cooperation and development oecd, which have 30 countries as members defined green ict as “ict to reduce environmental load and ict for using as a promoter to relieve social environment influence” [14]. the danish ministry of science technology and innovation defines green ict as “more environmentally friendly utilization of it and the use of sustainable it” [15]. ministry of economy, trade and industry in japan defined it as “saving in ict-related energy consumption and energy conservation through the use of ict” [16]. gartner defines green ict as “encompassing environmentally sustainable it and the use of it to contribute to environment preservation” [17]. other definition of green ict is “reduction of energy consumption and pollution of environment through it” [18]. malaysia green ict working group concept about green ict is “refers to conserving energy, using computing resources efficiently, reducing carbon emissions, appropriate handling of hazardous waste” [19]. however, we can add new definition for green ict as “the wise usage of ict to minimize the resources consumption and reduce ghg emission that leads to environment protection and better life”. ict energy consumption analysis shows that there are mainly five distinguish categories of equipment [20, 21] including data centers, pcs, nw equipments, tvs, and others. a summary description of these categories as: a) data center equipment, which comprises computing, storage and network equipment in data centers, but additional supporting equipment like heating ventilation and air conditioning and ups as well. b) pcs, which comprise both laptops and desktop computers. c) network equipment, which include switches, routers, modems and home gateways. network interface cards are not considered in this category as they are either accounted for in pcs or data centers. d) tvs, including additional equipment like dvd players. e) other devices like telephones, mobile phones, printers, fax machines, etc. an australian computer society acs published a report in 2010 about energy consumption and carbon footprint of ict usage in australia [22]. ict is responsible for nearly 2.7 percent of australia’s total carbon emissions. more significantly, it is directly iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 143 responsible for more than 7 per cent of all electricity generated in australia. these are significant figures, particularly given that australia is one of the largest carbon emitters per capita in the world. in 2009 australia’s ict users consumed 13.248 million kilowatt hours (kwh) of electricity, which caused 14.365 megatonnes (mt) of co2e (carbon dioxide equivalent) emissions. table 1 shows the energy consumption and ict carbon footprint in australia, 2009. table 1: energy consumption and ict carbon footprint in australia, 2009 [22]. kwh/ year co2e % of co2e total data centre 4,572,118 4,936,650 34.4 total other enterprise 2,989,078 3,223,620 22.4 total household 4,639,737 4,971,743 34.6 nw infrastructure 1,047,105 1,232,86 8.6 total 13,248,41 14,364,832 100.00 based on pickavet study on worldwide energy needs for ict [23] an analysis done for the worldwide electricity consumption of the equipment in these five categories for 2008 and their respective growth levels in order to predict a business as usual case for 2020. the analysis compared this with the global energy and electricity consumption levels as summarized in the following table 2 [24]. based on that main conclusion are summarized [20] as: the power consumption is fairly equally distributed between the different categories. this means that in order to realize large optimizations in the ict power consumptions, all these categories need to be tackled. it also implies that when evaluating solutions one should investigate the impact in all these areas. the analysis found that ict consumes about 7 % of the electricity consumption, which is fair fraction. however, this fraction will be double by 2020 in a business as usual scenario; so we have to find a suitable solution for this problem. studies, research work, and discussions shows that; although ict sector itself has clear contributes the global ghgs emission, but the reduction done in other sectors, which uses ict applications would be greater. a recent report by global e-sustainable initiative (gesi) estimates the use of icts can help reduce annual global ghgs emission 15 percent by 2020. the reduction corresponds to 7.8 billion tonnes of co2 equivalent [25]. table 2: world ict power consumption [24]. category power consumption 2008 (gw) growth rate (p.a.) 2020 prediction (gw) data centers 29 12% 113 pcs 30 7.5% 71 network equipment 25 12% 97 tvs 44 5% 79 other 40 5% 72 total 168 433 worldwide electricity 2350 2% 2970 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 144 ict fraction 7.15% 14.57% governments, organizations, universities, and industries have to pay attention to the role of icts in mitigating and adapting climate change, particularly ghgs emission: they need to improve environmental performance of ict sector as well as improve environmental performance by ict applications to other sectors [27]. the global green ict market shows fast growing. while the market is estimated to 0.5 billion dollars in 2008, it is expected to 4.8 billion dollars in 2013. 4. the concept of environment from islamic viewpoint islam is the last religion revealed by allah (god, almighty) as evident from the qur’an [4] ”this day, i have perfected your religion for you, completed my favour upon you, and have chosen for you islam as deen (religion” [qur‘an 5:3]. islam is basically based on two sources: the holy qur’an and the sunnah of prophet mohammed (pbuh). sunnah is mainly defined by muslim scholars as: “all what prophet mohammed (pbuh) says, acts, or agreed on”. people have to consider qur‘an as the highest standard that they should follow in their life and work. “verily this qur’an jdoth guide to that which is most right (or stable)” [qur’an 17:9]. the main objective of creating all mankind by god (allah swt) is to warship him; by developing and reconstructing the earth for the best (as vicegerent) through their good acting and deeds. allah swt said “i have only created jinn and human, that they may serve (worship) me” [qur’an 51:56]. since the proposed green ict strategy will be for used in several islamic countries; so we have to study the islamic viewpoint on environment based on quran and sunnah. several islamic authors and organizations have great effort in this topic. isesco has several studies one of them is related to environment in islam. studies shoes that environmental issues has increased today as skills have developed more quickly than wisdom and rationalism and as environmental problems have become a reality endangering human life both in the present and in the future. the situation could become worse unless human beings change their behavior to the better. it goes without saying that if human beings had abided by the teachings of islam, complied with its injunctions, and heeded its warnings, they would have avoided all the causes at the root of environmental problems. allah, sublime be his name, the creator of the human soul, knows what is good and what is bad for that very soul. almighty allah said in his holy book: “should he not know—he that created. and he is one that understands the finest mysteries (and) is well-acquainted (with them) “ [qur’an 67:14]. islam has tackled all environmental issues in a comprehensive manner, without going into the finest details. allah, most high, said: “ nothing have we omitted from the book “ [qur’an 6:38]. in another surah, he said: “then we (allah swt) put thee on the (right) way of religion: so follow thou that (way)“ [qur’an 45:18]. furthermore, in the hadith, the prophet has dealt with all of the topics that came up in the qur’an. allah said: “nor does he speak of (his own) desire. it is only a revelation revealed.“ [qur’an 53:3-4]. the isesco study on islam and environment discusses: iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 145 − the deals from an islamic viewpoint with the concept of environment as both a civilizational and natural reality. − highlights the signs of the divine miraculous and inimitable creation of nature. − addresses environmental issues and their causes as a result of the interaction of elements from the natural and cultural systems. it also sheds light on the opinion of the qur’an and the prophet on these problems. for had human beings abided by their faith and its regulations, they would have spared themselves all of these environmental problems. environment is defined as the sphere or context where human beings live. this includes all the natural and human phenomena [28] that affected humans and are affected by them and from which they get their means of subsistence such as food, clothing, medicine and shelter and wherein they exercise their relations with their human and nonhuman fellow creatures [29]. in a prominent environmentalist’s view [30]: “the environment is a set of conditions, substances and interactions taking place in any sphere where life exists“. − conditions include such climate elements as temperature, humidity, and light as well as cosmic states such as gravity. − substances comprise the earth and what is related to it like rock constituents, running water in rivers which fills the seas, and such life products as paper, fruits, wood, fur, meat and the like. − two kinds of interactions: physical interactions as chemical transformations and vital interactions related to the growth of living organisms. the scope of interactions can be local including the interaction between individuals and their surroundings. it can also be of wide scope as is the case with water circulation and the movements of wind. similarly, the sphere may be limited or may expand to include all the vital surroundings i.e. the sphere where life exists, that of the atmosphere, the hydrosphere and the lithosphere. this means that the environment is three-dimensional involving the ecological dimension, the socio-economic dimension, and the socio-cultural dimension (the system of values). 5. effort for green ict strategy the developed countries as well as some of the developing and muslim countries are increasing the investment in green ict as a new growing market but we need more contribution from others. we can summarize some of such effort for green ict strategy as: a korean effort in green ict strategy is shown in [18]. this study has significance as the base research for green ict policy making. it focuses on applying analytical hierarchy process. it considers priorities of primary goals to increase policy efficiency of green ict. malaysian green ict working group established in july 2010 to promote the usage of green ict in malaysia particularly the telecommunication industries [19]. its main mission is: set up a minimum green ict guidelines that can be used across industries; seeking sustainable ict industry development through eco-friendly technology; streamlining the effort of the private sectors and government to ensure green ict will become a standard; currently has more than 40 members and 3 active working threads (till nov 2010). there concept about green ict is: iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 146 − refers to conserving energy, using computing resources efficiently, reducing carbon emissions, appropriate handling of hazardous waste − driven by the desire to reduce cost, benefit the environment and be a good corporate citizen australian computer society acs works toward green ict strategy to help ict professionals reduce carbon dioxide emissions from ict equipment by developing a green ict policy outlining initiatives to reduce the organizations carbon footprint and guidelines on the safe disposal of old technology and leverage innovative technologies to reduce power consumption and lower carbon dioxide emissions [31]. the royal borough of kensington and chelsea, green ict strategy is based on strategic objectives include [32]: reduce the amount of energy consumed by our ict equipment; ensure equipment is turned off when not in use; reduce paper consumption; work with the change programs to identify the impact of the changes they propose. 6. framework for new strategic green ict policy although there are many attempts and efforts done to enhance the green ict performance and eliminate the ghg emission as well as adopting set of policies and strategies by several governments and organizations but there are still some weaknesses that we have to work on. this paper proposes a framework for new strategic green ict policies to eliminate the current environmental problems. this framework are represented in different layers starting from the ummah layer, state layer, until individual layer then the technical layer to show technically what we have to do to eliminate the harm on environment and get green ict. these layers include: a) the universal (ummah) layer: we have to define the main green ict strategy and policies to protect environment on international level (muslim ummah). this layer include the following steps: − define and adopt a unified and standard the high strategy for green ict for the whole ummah. − prepare a plan (with alternatives) and time schedule required to implement this strategy and have the mechanism to follow the implementation and adjust plan in emergency or critical cases. − having rules and regulations to easiest the implementation of the strategy and to have no conflict with other plans. − facilitate the cooperation between different countries to succeed in implementing the strategy b) the country layer: we have to define the main green ict strategy and policies for each country. this layer include the following steps: − define and adopt a unified and standard strategy and policies for green ict for the whole country. − prepare a plan (with alternatives) and time schedule required to implement the country strategy and policies and have the mechanism to follow the implementation and adjust plan in emergency or critical cases. − having rules and regulations to easiest the implementation of the country strategy and policies and to have no conflict with other plans. − facilitate implementation of strategic plan and policies by offering the suitable rules and regulations, budget, professional, education and training. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 147 − facilitate the cooperation between different ministries and organizations in the country to succeed in implementing the country green ict strategy and polices. − developed countries should participate in the main effort to solve environmental problems since they are responsible and highly contribute in creating such problem. c) education, research and training organizations layer: we have to define the role of educational institutes, research centers and training organization to understand and implement green ict and environment protection strategy and policies. − prepare a strategy to educate and train people to understand and implement green ict. − enrich the university programs, professional and training program with green ict concept and implementation to enhance society and human life. − prepare set of courses related to green ict (problem causes, proposed solutions, implementation and benefits). − support research activities in green ict and environmental protection. d) companies and production organizations layer: we have to define the role of companies and production organizations to understand and implement green ict and environment protection strategy and policies. so they have to get all their products in line with green ict. − prepare a strategy and policies to get high quality and environment friendly (green ict) products. − prepare an effective and efficient strategy and policies to collect, recycle and reuse of previously sold products. − prepare a suitable plans and time schedule for implementing and tracking the above strategy. − company strategy should be consistent with the country strategy for green ict. − prepare training for professional courses related to green ict. − company have to work based on ethical and moral principles in term of getting green ict and environment and not consider gaining money is the highest or the only target. e) ngo, social and islamic committees and organizations layer: we have to define the great role that the non-governmental organizations, social and islamic organizations and committees as well as the masjid (mosque) can play to explain the importance and warn from harmfulness related to green ict. − ngos, social and islamic committees and organizations (including masjid) have to prepare their strategy of work and prepare plan toward green ict and environment. − they have to importance of green environment and how to protect it. − show islamic viewpoint related to environment and its protection. − show the ethical aspects and its role in getting green ict and environment. f) human or individual layer: we have to define the great and key role of human to the success in adopting and implementing the green ict strategy and policies. − the role of human (as vicegerent of allah swt) in this universe. − the ethical aspect and moral behavior is an essential factor to succeed in green ict. − education and training to enhance human understanding for environmental problem and his role in having green ict and environment. g) technical layer: we have to define the technical aspects that we have to follow and implement it which can lead to green ict and environment protection. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 148 − more enhancement for data centers to get efficient energy consumption for servers, cooling system, and other operation environment. − using virtualization technology to reduce number of servers used. − disable screen savers and implement sleep mode in the time of inactivity for ict equipments. − using efficient and qualified nw and communication equipments and facilities. − using grid computing to replace most of the individual pcs. − shutting down all the unused pcs and laptops after office hours. − using timer to turn off the peripherals (printers, scanners, lcds, screens) automatically when unused for few minutes. − using an efficient and high quality equipment and power supply. − using default green printing (gray scale). − recycle toners cartridges and papers. h) developing a mathematical and statistical module to evaluate the performance of green ict. we have to specify and measure the factors that lead to environmental problem and its relation to green ict. 7. conclusion green ict and green environment are the main challenges in the 21 st century. ict became the driving force for the progress and development in all our life aspects. ict has significant role and participation in climate change and green house gas emission. ict industry has a tremendous role and contribution to the global economy but on the other side ict is responsible for 2-3% of the global carbon footprint. ict plays another significant role through ict applications in other sectors by efficient consumption of energy and high performance of sector. leaders, governments, organizations, universities, research centers, and individuals organize summits, conferences, projects, and other activities work toward less consumption of energy and less harmful. they have to find efficient and effective solutions for better utilization and management for resources, improving environmental performance, eliminate global warming. ict is an essential part of our life, which have significant effect on environment. the emerging economy and technological advances in developing and islamic countries as well as china and india will lead to rapidly increase the global access of ict services, which bring more environmental problems. the highly dependence on ict in all aspects of life implies facing its harmful affect on environmental and social aspects. so we have to eliminate the global warming by co2 or green house gas ghg emission caused by global ict infrastructure. this paper is a step toward adopting new green ict strategy and policies to eliminate environmental harms toward getting green environment. it shows the concept of environment and its protection from islamic viewpoint. this research work is initial framework and a stone within the solution of global environment destruction. it shows the required steps and guidance in each layer. following this frame work will lead to have green ict and a step towards green environment. references [1] postnote “ict and co2 emissions”, december 2008 number 319 [2] simon forge, “powering down: remedies for unsustainable ict”, foresight, journal, volume: 9 issue: 4, page: 3 21, 2007 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 149 [3] m. tahir riaz, josé m. gutiérrez, jens, m. pedersen, strategies for the next generation green ict infrastructure, 2 nd international symposium on applied sciences in biomedical and communication technologies isabel, 2010. ieeexplore.ieee.org/iel5/5367316/5373603/05373604.pdf. [4] the nobel qur’an, english translation of the meaning and commentary, king fahd complex for printing holy qur’an, ksa, 1417 h. [5] rich lechner , “an inefficient truth", global action plan, ibm, august 28, 2008 [6] phil mckenna, “can we stop the internet destroying our planet?”, new scientist, issue 2637, 03 january 2008 [7] santad, ijcsns, "visual basic software tool for ftth network management system" international journal of computer science and network security, vol.9 no.2, february 2009 [8] jeff rubin, the efficiency paradox, strategecon, cibc world markets, november 27, 2007 [9] don maclean, "icts, innovation and the challenge of climate change", international institute for sustainable development bill st. arnaud, chief research officer, canarie inc., may 2008 [10] abu da'ud sulayman ibn al-ash'ath al-sijistani al-izdi, “sunan abi da'ud”, bayrut : dar ibn hazm, 1997. [11] al bukhari muhammed bin ismail, “sahih al-bukhari”, bayrut : dar al-fikr, 1981 [12] al-ghazali muhammad, “khuluq al-muslim”, damascus : dar al-qalam, 2004. [13] al-ghazali abu hamed, “ihya' 'ulum al-din”, bayrut : dar al-ma’arifa, 1900. [14] oecd, “toward green ict strategies: assessing policies and programmes on ict and the environment”, organization for economic co-operation and development oecd, 2009. www.oecd.org/dataoecd/47/12/42825130.pdf [15] danish ministry of science technology and innovation(msti), “action plan for green it in denmark,” 2007. [16] s. h. park, “strategy to promote low carbon green growth based on ict,” national information society agency, 2009. [17] gartner, “gartner identifies the top 10 technologies for 2008,” 2008 [18] yong ho shim, ki youn kim, ji yeon cho, jin kyung park and bong gyou lee, strategic priority of green ict policy in korea: applying analytic hierarchy process, world academy of science, engineering and. technology, 58: 2009: www.waset.org/journals/waset/v58/v58-4.pdf [19] nur faezal elias, ict going green in malaysia, seminar by malaysian green ict working group, nov, 2010. [20] willem vereecken, ward van heddeghem, didier colle, mario pickavet and piet demeester, overall ict footprint and green communication technologies, proceedings of the 4th international symposium on communications, control and signal processing, isccsp 2010, limasbol, cyprus, 3-5 march 2010 [21] gartner research, conceptualizing "green it" and data centre power and cooling issues, 2007 [22] graeme philipson, the energy consumption and carbon footprint of ict usage in australia in 2010, australian computer society, 2010. [23] m. pickavet, w. vereecken, s. demeyer, p. audenaert, b. vermeulen, c. develder, d. colle, b. dhoedt, and p. demeester, "worldwide energy needs for ict: the rise of poweraware networking," in advanced networks and telecommunication systems, 2008. ants '08. 2nd international symposium on, dec. 2008, pp. 1-3. [24] international energy outlook 2009. energy information administration, 2009, ch. electricity, pp. 63-84 [25] global e-sustainability initiative, smart 2020:enabling the low carbon economy in the information age, 2008, available at : http://finance.gov.auipublications/ictreview/index.html iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering hameed 150 [26] seungdo kim1 , hyeon-kyeong kim2, hyoung jun kim3, climate change and icts, international telecommunications energy conference, intelec 2009, ieeexplore.ieee.org › conferences › telecommunications energy conf . [27] organization for economic co-operation and development/ directorate for science technology and industry/committee for information, computer and communications policy, towards green ict strategies, 2009. [28] michael allaby, a dictionary of environment, (london: macmillan , 1981). [29] mohammed sayyid jamil, addimoghrafia fittarbiyya assukkania, (cairo : dar gharib littiba’a wannashr, 1987) . [30] mohamed abdelafattah alqassas, al-‘insa’n wa qadaya al-bi’a : bahth kitab al-i’la’m alarabi waql-qada’ya al-bi’iyya, cairo : ma’ahad al-buhuth waddirasat, 1991. [31] australian computer society policy statement on green ict, aug 2007, www.acs.org.au [32] the royal borough of kensington and chelsea, green ict strategy: efficient, sustainable, responsible, december 2008, www.rbkc.gov.uk/environmentandtransport/.../idoc.ashx?docid..a2c4 microsoft word 2-bahatia iium-ej31-2-27-2 o.k..doc iium engineering journal, vol. 2, no. 1, 2001 f. a. a. twaiq et al. 13 catalytic cracking of palm oil over zeolite catalysts: statistical approach f. a. a. twaiq and s. bhatia* school of chemical engineering, universiti sains malaysia, engineering campus, 14300 nebong tebal, sps, pinang. chbhatia@eng.usm.my n. a. m. zabidi department of chemical engineering, universiti technologi petronas, sri iskandar 31750 tronoh, perak. abstract: the catalytic cracking of palm oil was conducted in a fixed bed micro-reactor over hzsm-5, zeolite  and ultrastable y (usy) zeolite catalysts. the objective of the present investigation was to study the effect of cracking reaction variables such as temperature, weight hourly space velocity, catalyst pore size and type of palm oil feed of different molecular weight on the conversion, yield of hydrocarbons in gasoline boiling range and btx aromatics in the organic liquid product. statistical design of experiment (doe) with 24 full factorial design was used in experimentation at the first stage. the nonlinear model and response surface methodology (rsm) were utilized in the second stage of experimentation to obtain the optimum values of the variables for maximum yields of hydrocarbons in gasoline boiling range and aromatics. the hzsm-5 showed the best performance amongst the three catalysts tested. at 623 k and whsv of 1 h-1, the highest experimental yields of gasoline and aromatics were 28.3 wt.% and 27 wt.%, respectively over the hzsm-5 catalyst. for the same catalyst, the statistical model predicted that the optimum yield of gasoline was 28.1 wt.% at whsv of 1.75 h-1 and 623 k. the predicted optimum yield of gasoline was 25.5 wt.% at 623 k and whsv of 1 h-1. key words: catalytic cracking, palm oil, zeolite, design of experiment, response surface methodology. 1. introduction the technology of catalytic cracking of triglycerides to produce fuels and other chemicals was investigated to find new sources of energy from plant oils[1]. canola oil, tall oil, jajoba oil, and other types of plant oils were converted to several types of hydrocarbons by hzsm-5, hydrogen-zeolite y, silica-alumina, h-mordenite and silica alumina-pillared clay catalysts, in the temperature range of 573  773 k[2]. direct upgrading of plant oils to fuels and chemicals could be of great help in local over production, and low international prices of agro products or higher prices of fossil fuels in isolated areas. shape selective zeolite catalysts can be used for converting palm oil to premium transportation fuels[3]. the shape selective zeolite catalyst used for catalytic cracking of canola oil was able to convert 60 – 95 wt.% of this oil to hydrocarbons in gasoline boiling range and light gases[4]. it has been reported that hzsm-5 gave mainly aromatic hydrocarbons from canola oil[5]. the properties of shape selective catalysts control the product distribution in the process, therefore, the choice of shape selective zeolite catalyst is an important factor[4]. activity and selectivity of these catalysts are governed by several factors such as acidity, pore size and distribution[2]. the conversion of palm oil to hydrocarbons in fuel range over different zeolite catalysts has been investigated by bhatia et al.[3]. the zeolites studied were hy, h-beta and hzsm-5. they have different characteristics, and are highly acidic cracking catalysts, the main difference was in the pore size dimensions[6]. statistical design of experiments were applied in the catalytic conversion of vegetable oils to fuel[5]. it was used to study the effects of operating conditions such as temperature, whsv and catalyst properties that have significant effects on the yield of selected products such as gasoline and aromatic hydrocarbons[7]. it has been reported that the type of catalyst, temperature and whsv are some of the main variables that affect the conversion and production of hydrocarbons in the gasoline boiling range[8]. the statistical model arises when the information available concerning a random process or system does not fully determine the probability model. the statistical model is typically taken to be the set of possible probability models. a mathematical linear model for conversion and yield of products can be obtained from the 2k factorial design. a model will describe the relation between the independent variables and the conversion of palm oil, gasoline and aromatics production. the models can predict the yields of product in terms of the significant variables in the process. these variables may be significant in one level of experimentation but negligible in another level as shown in the empirical model obtained from the design of experiment study[9]. the analysis of variance (anova) table partitions the total sample variability in an experimental design into components attributable to specific independent variables and interaction between independent variables[10]. iium engineering journal, vol. 2, no. 1, 2001 f. a. a. twaiq et al. 14 the non-linear model is required when curvature is found in the linear model to apply response surface method[11]. response surface methodology is closely related to univariate experimental design and it has broad applications in industrial statistics. response surface designs are usually used to justify a local linear approximation to the unknown function, then draw observation, and fit linear regression models of the desired responses to enable influence on the direction of steepest ascent[12]. to obtain the curvature effects, it would be necessary to consider an experimental design which would allow one to fit the experimental data to a nonlinear model[13]. when the vicinity of the maximum has been reached, the linearity in the model is enlarged to exclude quadratic and cross product terms, enabling estimation of the optimal location. the objectives of the present research are; (a) to study the effects of cracking reaction conditions on the conversion of palm oil to hydrocarbon products in the gasoline boiling point range; (b) to optimize the cracking reaction variables such as reaction temperature, weight hourly space velocity (whsv), pore size of zeolite catalyst and the feed molecular weight for higher production of hydrocarbons in the gasoline range and the aromatic hydrocarbons contents. 2. experimental 2.1 chemicals and catalysts two types of palm oil were used in the present investigation, refined, bleached and deodorized (rbd) palm olein and palm kernel oil, they were obtained from m/s golden agriculture oils sdn. bhd., butterworth – penang, malaysia, and m/s acidchem international sdn. bhd., butterworth – penang, malaysia, respectively. the chemical properties of the malaysian palm olein as fatty acid composition % (as methyl ester) was c12:0, 0.27; c14:0, 1.09; c16:0, 40.93; c18:0, 4.18; c18:1, 41.51; c18:2, 11.64; c18:3, 0.40; c20:0, 0.37 and palm kernel oil c6, 0.30; c8, 4.20; c10, 3.70; c12:0, 48.70; c14:0, 15.60; c16:0, 7.50; c18:0, 1.80; c18:1, 14.80; c18:2, 2.60; c18:3, 0.10 [14]. argon of 99.99 % purity was obtained from malaysian oxygen sdn. bhd., kuala lumpur and was used in the cracking of palm oil as a purge gas. three zeolite catalysts hzsm-5, zeolite  and usy of different pore size were used. the hzsm-5 zeolite (cbu 8070) and zeolite  (811bl-25) were supplied by p.q. corporation, kansas, usa. the ultrastable y (usy) zeolite was obtained from w. r. grace (s) ltd., grace division, asia pacific, singapore. the three zeolites were in powder form with particle size < 32m. the hzsm-5 and usy zeolites were calcined in a muffle furnace for 6 h at 773 k and zeolite  was calcined at 673 k prior to use. the properties of the catalysts are presented in table 1. table 1: chemical and physical characteristics of the zeolite catalyst si/al ratio pore size (nm) bet surface area (m2/g) acidity (mmol nh3) hzsm-5 50 0.540.56 390 0.55 zeolite  14 0.560.74 410 1.1 ultra stable y 7 0.80 520 0.91 2.2 procedure experiments were conducted in a stainless steel microreactor (155mm×10mm i.d.) fitted with a thermocouple fixed in the center of the catalyst bed[3]. one gram of calcined powder catalyst was loaded over 0.2g of quartz wool then covered with quartz wool and placed into the micro-reactor. the reactor was heated to the desired reaction temperature using an electrical vertical tube furnace. argon gas was allowed to flow at 0.2 l/h through the system for 1 h before feeding the palm oil into the reactor. the palm oil was fed by a syringe metering pump (cole-parmer) and was preheated to 573 k in a horizontal tube furnace to the reactor. the products were cooled by circulated water at 313 k in a condenser. the liquid products were collected in a glass sampler trap and the gaseous products separated in the trap were collected in a teflon sampling bag. the aqueous phase product was separated from the liquid product using a syringe. in order to estimate the quantity of the residual oil, the liquid product was distilled in a micro-distillation unit (buchi b580, gkr) at a temperature of 473 k under a vacuum of 5 pa. the distillate fraction was the organic liquid product (olp) and the pitch was the residual oil. 2.3 analysis of products the gaseous products were analyzed with a gas chromatograph (hewlett packard, model no. 5890 series ii) using a porapak q stainless steel column (90cm-length  3.15mm i.d.). the gc was equipped with both flame ionization detector (fid) and thermal conductivity detector (tcd). the analysis time was approximately 30 min for each injection. after normalizing the components, main molecular weight for the gases were calculated to determine the weight of the gaseous products. the fid was used to analyze the organic liquid products (olp) using a capillary glass column (petrocol dh 50.2, film thickness 0.5 m, 50m length and 0.2mm i.d.). the chromatogram was obtained for 90 min. the components were defined according to petroleum fuel boiling point ranges by injecting commercial samples of gasoline, kerosene, diesel and pure benzene, toluene and xylene. the spent catalyst was washed with hexane to determine the remaining residual oil over the catalyst. the coke formed on the catalyst during the cracking reaction was determined using a thermal gravimetric analyzer (perkin-elmer tga7). iium engineering journal, vol. 2, no. 1, 2001 f. a. a. twaiq et al. 15 3. results and discussion a fundamental part of statistics is concerned with the design of experiments to determine cause-effect relationship; the relationship with some response of the system is very important. for solving problem by statistical methods, a plan of the experiment must be set up that includes the method of collecting the data, the size of the sample and the method to solve the problem[12]. the full factorial design was used in the present investigation to assess the effect of the reaction parameters such as reaction temperature (t), weight hourly space velocity (whsv), zeolite catalyst pore size (cps) and feed molecular weight as the number of carbon atoms in the triglyceride molecule (nca) on the conversion of palm oil (pc), yield of hydrocarbons in gasoline boiling range (yg) and btx aromatic hydrocarbons (ya) in the liquid product. the conversion and yield of the desired product are defined as follows: conversion (wt .%) = gas olp w at er coke 100% p alm oil feed æ ö+ + + ÷ç ÷́ç ÷çè ø (1) yield of desired product (wt .%) = desired product 100% p alm oil feed æ ö÷ç ÷́ç ÷çè ø (2) 3.1 linear model the classical linear model in statistics assumes that observations are linearly related to the explanatory variables and are measured with independent, normal distributed error. the factorial design allows for examination of all main effects of the factors at any level and interactions between these factors[15]. the selection of the parameter intervals was based on the best operating conditions reported in the literature[8] and are presented in table 2. the 24 full factorial design was used in the first experimentation stage; with two levels for each factor. the experimental matrix for the sixteen experiments is shown in table 3. the significant variables and their effects on the responses have to be identified in order to study the effects of the reaction variables on the palm oil conversion (pc), yield of hydrocarbons in the gasoline boiling range (yg) and the yield of btx aromatic hydrocarbons (ya). in addition, one must also determines whether the interactions of these variables affect the responses. table 2: independent variables coded and real values used in the linear model factor temperature (t) weight hourly space velocity (whsv) catalyst pore size (cps) number of carbon atoms in the feed (nca) factor code a b c d unit k h-1 nm intervals 623723 14 0.540.80 38.551.0 table 3: experimental matrix of the 24 factorial design t whsv cps nca treatment combination pc , wt.% yg, wt.% ya, wt.% 623 1 0.54 38.5 l 98.89 29.25 26.64 723 4 0.80 51.0 abcd 57.61 11.68 1.79 723 1 0.80 51.0 acd 93.16 17.52 5.16 723 4 0.54 38.5 ab 83.73 19.53 15.51 723 1 0.80 38.5 ac 93.76 18.10 4.19 723 4 0.54 51.0 abd 86.05 24.40 20.29 623 1 0.54 51.0 d 99.01 28.29 27.06 723 4 0.80 38.5 abc 56.60 7.21 2.40 623 4 0.80 38.5 bc 28.65 1.64 1.10 623 4 0.80 51.0 bcd 28.34 3.83 1.73 723 1 0.54 51.0 ad 97.23 24.15 18.19 623 1 0.80 38.5 c 60.21 7.96 1.79 623 1 0.80 51.0 cd 53.20 7.33 2.16 723 1 0.54 38.5 a 98.33 22.48 19.23 623 4 0.54 51.0 bd 77.35 23.48 16.70 623 1 0.54 51.0 d 79.13 22.05 19.17 the four independent variables identified for this study were coded as t (a), whsv (b), cps (c) and nca (d). each variable is presented at two levels, the low level (-1) and the high level (+1). the sixteen experiments were performed in a random manner to minimize personal bias. figures 1, 2 and 3 present the normal probability plot for pc, yg and ya versus the estimated effect, respectively. based on this plot, all the effects that lie along the line are considered negligible; whereas the large effects are those which are far from the line. tables 4, 5 and 6 show the analysis of variance (anova) for the three responses, pc, yg and ya, iium engineering journal, vol. 2, no. 1, 2001 f. a. a. twaiq et al. 16 respectively. column 1 in these tables presents the main factors and its interactions and column 2 presents the estimated effect for each factor or interaction. the sum of squares presented in column 3 was calculated from the sum of squares of the significant factors and its interactions. the f-values are tabulated in column 6 and were compared to the critical f-values. the critical fvalues are shown in column 6 of table 6 as superscript values. the f-critical values were obtained from the percentage points tables of the fdistribution at 1% level reported in ref. [15]. regression analysis for the data was obtained from the factorial runs using the design-expert software (version 5.0). the coefficients for all the effects were obtained for pc, yg and ya and are presented in column 5. the anova shows that the linear model is significant for all the responses. fig. 1: normal probability plot of effects for the 24 factorial design for conversion of palm oil. fig. 2: normal probability plot of effects for the 24 factorial design for yield of gasoline. fig. 3: normal probability plot of effects for the 24 factorial design for yield of aromatics 3.1.1. influence of reaction variables on the responses factor d (feed molecular weight) and its interactions have no significant effect on the three responses, so it was neglected from the design. it was found that the conversion at different whsv’s and temperatures was almost identical with both types of feed. this result is in line with the reported results for the cracking of linear paraffins, in which conversion was constant when the carbon atoms in the chain were more than 25 for the linear hydrocarbons and greater than 35 for the nonlinear hydrocarbons[16]. palm oil conversion (pc): the effect of reaction temperature on the palm oil conversion was positive. the whsv has a negative effect on the conversion of palm oil in which the conversion decreased with increase in whsv. the cps also shows a negative effect on the conversion. it was observed that palm oil conversion did not increase with the increase of temperature over hzsm-5 catalyst having average pore size opening of 0.54 nm at the low level of whsv. the results are in line with the reported data for canola oil cracking[7]. the statistical model was applied to study the effect of whsv and temperature on the organic liquid products with different acid catalysts[7]. the selectivity of aromatics from canola oil was inline to those obtained from palm oil. this result indicates no real effect of the main factor itself, however there were significant effects on the interactions. the effect of the main factors should be neglected because the main factor has a positive effect on one level and negative effect at another level. in table 4, it is clear that the interaction ac has a positive effect, whereas the c factor has a negative effect. the f-value for the model was found to be significant at 1% level. iium engineering journal, vol. 2, no. 1, 2001 f. a. a. twaiq et al. 17 table 4: analysis of variance (anova) for conversion source of variance estimated effect sum of squares degree of freedom model coefficient f-value % contribution intercept 74.44 a 17.71 1254.93 1 8.85 41.6011.26 14.35 b -24.56 2413.27 1 -12.28 80.1011.26 27.66 c -30.98 3840.90 1 -15.49 127.5011.26 43.93 d -0.93 3.51 1 -0.46 0.1111.26 0.04 ab -0.08 0.03 1 -0.04 0.0011.26 0.00 ac 14.98 898.50 1 7.49 29.8011.26 10.27 ad 1.33 7.15 1 0.66 0.2311.26 0.08 bc -7.73 239.47 1 -3.86 7.9511.26 2.73 bd 1.21 5.88 1 0.60 0.2011.26 0.06 cd -0.81 2.64 1 -0.40 0.0911.26 0.03 abc -4.01 64.40 1 -2.00 0.0911.26 0.73 abd 0.03 0.00 1 0.01 0.0011.26 6.43 acd 0.61 1.50 1 0.30 0.0511.26 0.01 bcd 0.83 2.80 1 0.41 0.0911.26 0.03 abcd -1.28 6.63 1 -0.64 0.2211.26 0.07 model 8711.50 7 26.716.18 residuals 30.13 8 note: the critical f-values are shown as superscript in column 6. table 5: analysis of variance (anova) for gasoline yield source of variance estimated effect sum of squares degree of freedom model coefficient f-value % contribution intercept 1 a 1.33 2.66 1 28.35 5.909.65 2.3 b -2.58 -5.16 1 106.60 22.009.65 8.9 c -7.39 -14.78 1 874.68 181.009.65 73.0 d 0.78 1.56 1 9.76 2.009.65 0.8 ab 0.15 0.31 1 0.39 0.089.65 0.0 ac 2.89 5.78 1 133.98 27.809.65 11.1 ad 0.51 1.03 1 4.30 0.909.65 0.3 bc -0.74 -1.48 1 8.85 1.809.65 0.7 bd 0.85 1.71 1 11.73 2.409.65 0.9 cd -0.10 -0.21 1 0.18 0.049.65 0.0 abc -1.00 -2.01 1 16.20 3.309.65 1.3 abd 0.19 0.38 1 0.60 0.129.65 0.0 acd -0.21 -0.43 1 0.76 0.129.65 0.0 bcd 0.14 0.28 1 0.33 0.079.65 0.0 abcd 0.08 0.16 1 0.10 0.029.65 0.0 model 1143.62 4 59.155.67 residuals 53.23 11 note: the critical f-values are shown as superscript in column 6. iium engineering journal, vol. 2, no. 1, 2001 f. a. a. twaiq et al. 18 table 6: analysis of variance (anova) for aromatics yield source of variance estimated effect sum of squares degree of freedom model coefficient f-value % contribution intercept a -1.18 5.64 1 -0.59 0.568.86 0.40 b -3.21 41.28 1 -1.60 4.128.86 2.93 c -17.78 1265.58 1 -8.89 126.508.86 89.96 d 0.38 0.60 1 0.19 0.068.86 0.04 ab 1.51 9.15 1 0.75 0.908.86 0.65 ac 2.88 33.35 1 1.44 3.308.86 2.37 ad 0.66 1.75 1 0.33 0.178.86 0.12 bc 1.61 10.40 1 0.80 1.008.86 0.73 bd 0.18 0.14 1 0.09 0.008.86 0.00 cd -0.03 0.00 1 -0.02 0.008.86 0.00 abc -2.51 25.25 1 -1.25 2.508.86 1.79 abd 0.86 2.97 1 0.43 3.008.86 0.21 acd -0.81 2.64 1 -0.40 2.608.86 0.18 bcd -0.53 1.15 1 -0.26 0.108.86 0.08 abcd -1.31 6.89 1 -0.65 6.808.86 0.48 model 1265.58 1 10.328.86 residuals 141.24 14 note: the critical f-values are shown as superscript in column 6. yield of hydrocarbons in gasoline boiling range (yg): the reaction temperature has a low positive contribution on the production of hydrocarbons in the gasoline range and whsv has a negative effect on the yield of hydrocarbons. the pore size of the zeolite catalyst is the most important factor in the palm oil cracking process. the pore size of the zeolite has a large negative contribution on the yg. it is reported that the catalyst and whsv are the factors which control the production of the liquid products and reaction temperature has no effect on the selectivity of aliphatic hydrocarbons [7]. the values of yg decreased with increase of reaction temperature over hzsm-5 catalyst which indicates over-cracking. with large pore zeolite usy (0.8 nm), yg increased with increase of reaction temperature. this result is related to the significant effect of the interaction of ac which caused the hzsm5 catalyst to give higher yg at low temperature level, and the usy zeolite to give higher yg at high temperature level. the f-value for the model was found to be significant at 1% level and the linear model can predict the values for yg. yield of btx aromatics (ya): the reaction temperature and whsv and their interactions have no significant contribution to the yield of aromatics compared to that of the catalyst pore size. catalyst pore size (cps) of the zeolite was the only factor contributing to ya. the medium pore size presented in hzsm-5 zeolite shows the role of the pore dimension on the selectivity of the catalyst as selective for aromatic hydrocarbons. the role of the shape selectivity is obvious where the effect of reaction temperature is very little compared to the effect of the shape selectivity of the catalyst. the medium pore zeolite hzsm-5 was reported as selective for aromatics in the cracking of gas oil. hzsm-5 catalyst has been used as additive on fcc unit to improve the octane number of the gasoline [17]. in the literature, it is reported that addition of hzsm-5 catalyst used in the canola oil cracking combined with reaction temperature influenced the production of aromatic hydrocarbons in the process [7]. the selectivity of the catalyst is affected by variables such as the acidity of the catalyst and the shape of catalyst pore as well the location of the active sites in side the pores. the f-value for the model was found to be significant at 1% level. 3.2 nonlinear model to optimize the cracking reaction variables in the study range for greater yg and ya, higher polynomial degree model was required and response surface methodology (rsm) was used. to apply this model, an additional central level was added to the significant factors (t, whsv and cps) in the design to be a 33 full factorial design as shown in table 7. the low level was coded as 0, central level as 1 and the high level as 2 for each factor. zeolite  catalyst (pore size 0.560.74 nm) was used as the central level for the catalyst pore size factor in further experimentation. the total number of experiments was 27 and five repeated runs were performed at 673 k and 2.5 h-1 using zeolite  catalyst in order to estimate the experimental error. the experimental error was used to calculate the lack of fit test. the results of these experiments are presented in table 8. the analysis of variance (anova) for the 33 design is tabulated in table 9. the residual sum of squares was used to calculate the f-values. the fvalues for the models obtained from anova for the three responses are significant at 1 % level. the design-expert software was used to estimate the final quadratic equation for the three responses in terms of actual values of the factors. eqs. 3, 4 and 5 present the statistical quadratic models estimated from the significant effects and its interactions. iium engineering journal, vol. 2, no. 1, 2001 f. a. a. twaiq et al. 19 table 7: independent variables coded and real values used in the nonlinear model factor factor code unit low level (0) center level (1) high level (2) t a k 623 673 723 whsv b h-1 1 2.5 4 cps c nm 0.54 0.67 0.80 table 8: experimental matrix of the 33 factorial design t (k) whsv (h-1) cps (nm) treatment combination pc yg ya 623 1.0 0.54 000 99.0 28.3 27.0 623 1.0 0.67 001 82.2 22.0 3.5 623 1.0 0.80 002 53.2 7.3 2.2 623 2.5 0.54 010 80.3 26.6 21.1 623 2.5 0.67 011 65.0 19.1 4.5 623 2.5 0.80 012 45.3 5.2 1.1 623 4.0 0.54 020 77.4 23.5 16.7 623 4.0 0.67 021 51.2 15.6 8.4 623 4.0 0.80 022 28.3 3.8 1.7 673 1.0 0.54 100 96.9 20.5 16.0 673 1.0 0.67 101 82.2 22.0 3.5 673 1.0 0.80 102 61.0 13.7 2.5 673 2.5 0.54 110 89.6 25.6 21.9 673 2.5 0.67 111 76.6 19.6 4.7 673 2.5 0.80 112 51.0 13.0 2.5 673 4.0 0.54 120 78.7 17.3 13.2 673 4.0 0.67 121 64.0 16.4 4.3 673 4.0 0.80 122 29.6 4.3 1.0 723 1.0 0.54 200 97.2 24.2 18.2 723 1.0 0.67 201 95.7 18.4 6.6 723 1.0 0.80 202 93.2 17.5 5.2 723 2.5 0.54 210 91.6 22.9 17.2 723 2.5 0.67 211 88.2 26.3 5.7 723 2.5 0.80 212 70.7 14.3 5.1 723 4.0 0.54 220 86.0 24.4 20.3 723 4.0 0.67 221 77.2 16.3 9.1 723 4.0 0.80 222 57.6 11.7 1.8 repeated trials 673 2.5 0.67 111 75.0 21.0 4.8 673 2.5 0.67 111 73.0 20.5 5.2 673 2.5 0.67 111 76.5 19.6 4.7 673 2.5 0.67 111 72.5 18.0 5.5 673 2.5 0.67 111 73.0 18.6 5.1 the response surface methodology was used to predict the optimum values of the variables in the range studied. the maximum values of the responses obtained from statistical quadratic equations were plotted in three-dimensional graphs against reaction temperature (t) and weight hourly space velocity (whsv) for each zeolite catalyst. the three zeolites gave different response surface plots of conversion, yield of hydrocarbons in gasoline boiling range and yield of btx aromatics. figures 4, 5 and 6 show the response surface plots for conversion, yield of hydrocarbons in gasoline boiling range and yield of btx aromatics using hzsm-5 catalyst respectively. the maximum values of the responses were obtained from the statistical quadratic model. c 2 2 2 2 2 2 2 2 p = -2923.4 + 10.48 x 241.65 y + 5328.62 z 8.905e 3 x + 6.29 y + 628.1 z y + 0.43 x18.76 xz + 230.8 yz 1.6 e 4 x z 3.111e -3 xy 1.24 xz 6.64 y z 24.6 yz 0.27 xyz (3) 2 2 2 2 2 2 2 2 2 1818.97 5.53 73.57 2155.6 + 4.124 e-3 x + 6.29 y + 628.14 z 0.3xy 7.86xz + 43.29yz + 3.111e-4x 6.487 e -3x z778e -3xy + 1.15 xz + 1.51 y z + 5.59 yz 0 = +gy x y z .094xyz (4) a 2 2 2 2 2 2 2 2 y = 2279.73 4.89x 115.2y 3890.42z + 2.889e-3x 0.92y + 1367.12z + 0.074xy + 6.84xz + 270.34yz + 5.111e-5x y 3.385e-3x z 6.667e-4xy 1.18xz + 1.71y z 1 207.82yz 0.2xyz (5) where x is the temperature; y is the weight hourly space velocity and z is the catalyst pore size. table 9: analysis of variance (anova) for the three responses conversion, yield of gasoline and aromatics yield using the nonlinear model source of variance sum of squares degree of freedom mean square f-value pc mean 1.71  105 1 1.71  105 linear 9405 3 3135 298.65.42 quadratic 876 6 146 13.94.32 cubic 192 7 27 2.64.14 model 10472 16 655 62.4 residual 158 15 10.5 lack of fit 141 10 14.1 4.110.05 experimental error 17 5 3.4 yg mean 10422 1 10422 linear 960 3 320 61.55.42 quadratic 201 6 33 6.34.32 cubic 39 7 5.6 1.04.14 model 1199 16 75 14.4 residual 78 15 5.2 lack of fit 71 10 7.1 5.910.05 experimental error 6 5 1.2 ya mean 2283 1 2283 linear 1230 3 410 1085.42 quadratic 285 6 47.5 12.54.32 cubic 70 7 10 2.64.14 model 1583 16 99 26 residual 57 15 3.8 lack of fit 57 10 5.7 5710.05 iium engineering journal, vol. 2, no. 1, 2001 f. a. a. twaiq et al. 20 fig. 4: response surface plot for conversion of palm oil obtained from the nonlinear model over hzsm-5 catalyst. fig. 5: response surface plot for yield of gasoline obtained from the nonlinear model over hzsm-5 catalyst. fig. 6: response surface plot for yield of aromatics obtained from the nonlinear model over hzsm-5 catalyst. the optimum values obtained from the statistical model were:  for hzsm-5 catalyst, the optimum yield of gasoline was 28.1 wt.% at whsv of 1.75 h-1 and temperature 623 k with a conversion of 91.3 wt.%. the optimum yield of btx aromatics was 25.5 wt.% at temperature 623 k and whsv 1.0 h-1 with conversion 95.0 wt.%.  for zeolite  catalyst, the optimum yield of gasoline was 23.9 wt.% at temperature 723 k, 1.75 h-1 whsv at conversion 93.6 wt.%. the optimum yield of btx aromatics was 7.3 wt.% with conversion of 98.5 wt.% at 723 k and whsv of 1 h-1.  for usy zeolite catalyst, the optimum gasoline yield was 16.9 wt.% and yield of btx aromatics 7.3 wt.% at conversion of 85.7 wt.% at 723 k and whsv of 1 h-1. 4. conclusions  the medium pore size zeolite catalyst (hzsm-5) with the lowest acidity, gave the best performance among the three zeolite catalysts tested in terms of conversion, yield of gasoline and yield of btx aromatics.  type of palm oil feed did not affect the conversion or the production of gasoline.  the optimum values of reaction parameters were obtained using design of experiment (doe) coupled with response surface methodology (rsm).  the experimental values of the conversion, yield of gasoline and yield of btx aromatics were in good agreement with the values obtained from the proposed model. acknowledgement the financial support by the ministry of science, technology & environment, malaysian govt. under long term irpa grant (project: 03-02-05-7005) is gratefully acknowledged. references [1] s.p.r katikaneni,. j.d. adjaye, r.o. idem and n.n. bakhshi, “catalytic conversion of canola oil over potassium-impregnated hzsm-5 catalysts: c2-c4 olefin production and model reaction studies”, ind. eng. chem. res. 35, pp 3332 -3346 1996. [2] r.o. idem, s.p.r. katikaneni and n.n. bakhshi, “catalytic conversion of canola oil to fuels and chemicals: roles of catalyst acidity, basicity, and shape selectivity on product distribution”, fuel proc. tech. 51, pp 101-125, 1997. [3] s. bhatia, h.j. kee, l.m. lan and a.r. mohamed, “production of biofuel by catalytic cracking of palm oil: performance of different catalysts”, proc. biofuel, porim intl. biofuel and lubricant conf, kuala lumpur, pp 107-112, 1998. iium engineering journal, vol. 2, no. 1, 2001 f. a. a. twaiq et al. 21 [4] s.p.r. katikaneni, j.d. adjaye and n.n. bakhshi, “performance of aluminophosphate molecular sieve catalysts for production of hydrocarbons from woodderived and vegetable oils”, energy & fuels. 9, pp 1065-1078, 1995. [5] y.s. prasad, n.n. bakhshi, j.f. mathews and r.l. eager, “catalytic conversion of canola oil to fuels and chemical feedstocks. part i: effect of process conditions of the performance of hzsm-5 catalyst”. can. j. chem. eng. 64, pp 278-284, 1986. [6] s. bhatia, “zeolite catalysis principles and applications”, crc press inc boca raton, fl, usa, 1990. [7] j.d. adjaye, s.p.r. katikaneni, and n.n. bakhshi, “catalytic conversion of a biofuel to hydrocarbons: effect of mixtures of hzsm-5 and silica-alumina catalysts on product distribution”, fuel proc. tech. 48, pp 115-143, 1995. [8] t.y. leng, a.r. mohamed and s. bhatia, “production of fuels from catalytic conversion of palm oil: preliminary studies”, proc. reg. symp. chem. eng. 1, pp 75-81, 1997. [9] h. gonzalez, a. rodriguez, l. cendeno, j. ramirez and j. aracil, “isomerization of c8 aromatics over a pt/mordenite catalyst: a statistical model”, ind. eng. chem. res. 35, pp 3964-3972, 1996. [10] b. ghosh, d.c. agrawal and s. bhatia, “synthesis of zeolite a from calcined diatomaceous clay: optimization studies”, ind. eng. chem. res. 33, pp 2107-2110, 1994. [11] g.e.p. box, w.g. hunter and j.s. hunter, statistics for experimenters: an introduction to design, data analysis, and model building, john wiley & sons, new york, ny, usa, 1978. [12] w.g. cochran and g.m. cox, experimental designs, 2nd edn., john wiley & sons: singapore, 1957. [13] n. sanchez, m. martinez, and j. aracil, “selective esterification of glycerine to 1. glycerol monooleate 2. optimization studies”, ind. eng. chem. res. 36, pp 1529-1534, 1997. [14] t.s. tang, c.l. chong, m.s.a. yusoff and m.t. abgapor, “characteristics of superolein from the fraction of palm oil”, porim technology bulletin, 17, 1995. [15] d.c. montgomery, design and analysis of experiments, 3rd edn., john wiley & sons, new york, ny, usa, 1991. [16] j. abbot, and p.r. dunstan, “catalytic cracking of linear paraffins: effects of chain length”, ind. eng. chem. res. 36, pp 76 – 82, 1997. [17] j.m arandes, i. abajo, i fernandez, m.j. azkoiti and j. bilbao, ‘effect of hzsm-5 zeolite addition to fluid catalytic cracking catalyst. study in a laboratory reactor operating under industrial conditions. ind. eng. chem. res., 39, pp 1917 – 1924, 2000. list of symbols a factor code of temperature b factor code of whsv c factor code of catalyst pore size cps catalyst pore size (nm) d factor code of number of carbon atoms f-value the ratio of model mean square to the appropriate error mean square nca number of carbon atoms pc conversion of palm oil (wt.%) t temperature (k) usy ultrastable y zeolite whsv weight hourly space velocity (h-1) x actual temperature (k) y actual weight hourly space velocity (h-1) ya yield of btx aromatic hydrocarbons (wt.%) yg yield of hydrocarbons in gasoline boiling range (wt.%) z actual catalyst pore size (nm) biographies farouq twaiq received his b. sc. degree in chemical engineering from amman university college for applied engineering, amman, jordan, 1994. he worked as supervisor engineer in al-ryadh company for vegetable oil industries, 1994–1996. he received his m.sc. degree in 1998 and currently he is a ph.d. student in the school of chemical engineering at universiti sains malaysia under supervision of prof. s. bhatia. his research interests are in the synthesis and characterization of zeolite and molecular sieve composite materials and their applications as cracking catalysts. prof. subhash bhatia joined the school of chemical engineering, universiti sains malaysia, perak branch campus, in 1995. he was a full professor at the department of chemical engineering, indian institute of technology, kanpur (india). prof. bhatia was visiting faculty at the university of qeensland, australia from 1988 – 1989 and 1994 – 1995. his research interests are zeolite catalysis, chemical reaction engineering and environmental catalysis. he has written a book on zeolite catalysis that was published by crc press, usa and has published more than 75 papers in national and international journals. dr. noor asmawati binti mohd. zabidi received her bs. in chemistry from nebraska wesleyan university, lincoln, usa in 1986. she carried out research in photocatalysis under supervision of prof. timothy f. thomas at university of missouri-kansas city, usa where she received her ph.d. in 1995. she has been a lecturer at school of chemical engineering, universiti sains malaysia, perak branch campus from 1996– 2000. at present, she is a lecturer at universiti teknologi petronas, tronoh, perak. iium engineering journal, vol. 2, no. 1, 2001 22 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 classification of chest radiographs using novel anomalous saliency map and deep convolutional neural network mohd adli md ali1*, mohd radhwan abidin 2, nik arsyad nik muhamad affendi3, hafidzul abdullah1, daaniyal reesha rosman1, nu'man badrud'din1, faiz kemi1 and farid hayati1 1department. of physics, 2department of radiology, 3department of internal medicine, international islamic university malaysia, kuantan, malaysia *corresponding author: qunox@iium.edu.my (received: 27th august 2020; accepted: 30th january 2021; published on-line: 4th july 2021) abstract: the rapid advancement in pattern recognition via the deep learning method has made it possible to develop an autonomous medical image classification system. this system has proven robust and accurate in classifying most pathological features found in a medical image, such as airspace opacity, mass, and broken bone. conventionally, this system takes routine medical images with minimum pre-processing as the model's input; in this research, we investigate if saliency maps can be an alternative model input. recent research has shown that saliency maps' application increases deep learning model performance in image classification, object localization, and segmentation. however, conventional bottom-up saliency map algorithms regularly failed to localize salient or pathological anomalies in medical images. this failure is because most medical images are homogenous, lacking color, and contrast variant. therefore, we also introduce the xenafas algorithm in this paper. the algorithm creates a new kind of anomalous saliency map called the intensity probability mapping and weighted intensity probability mapping. we tested the proposed saliency maps on five deep learning models based on common convolutional neural network architecture. the result of this experiment showed that using the proposed saliency map over regular radiograph chest images increases the sensitivity of most models in identifying images with air space opacities. using the gradcam algorithm, we showed how the proposed saliency map shifted the model attention to the relevant region in chest radiograph images. while in the qualitative study, it was found that the proposed saliency map regularly highlights anomalous features, including foreign objects and cardiomegaly. however, it is inconsistent in highlighting masses and nodules. abstrak: perkembangan pesat sistem pengecaman corak menggunakan kaedah pembelajaran mendalam membolehkan penghasilan sistem klasifikasi gambar perubatan secara automatik. sistem ini berupaya menilai secara tepat jika terdapat tanda-tanda patologi di dalam gambar perubatan seperti kelegapan ruang udara, jisim dan tulang patah. kebiasaannya, sistem ini akan mengambil gambar perubatan dengan pra-pemprosesan minimum sebagai input. kajian ini adalah tentang potensi peta salien dapat dijadikan sebagai model input alternatif. ini kerana kajian terkini telah menunjukkan penggunaan peta salien dapat meningkatkan prestasi model pembelajaran mendalam dalam pengklasifikasian gambar, pengesanan objek, dan segmentasi gambar. walau bagaimanapun, sistem konvensional algoritma peta salien jenis bawah-ke-atas kebiasaannya gagal mengesan salien atau anomali patologi dalam gambar-gambar 234 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 perubatan. kegagalan ini disebabkan oleh sifat gambar perubatan yang homogen, kurang variasi warna dan kontras. oleh itu, kajian ini memperkenalkan algoritma xenafas yang menghasilkan dua jenis pemetaan saliensi anomali iaitu pemetaan kebarangkalian keamatan dan pemetaan kebarangkalian keamatan pemberat. kajian dibuat pada peta salien yang dicadangkan iaitu pada lima model pembelajaran mendalam berdasarkan seni bina rangkaian neural konvolusi yang sama. dapatan kajian menunjukkan dengan menggunakan peta salien atas gambar-gambar radiografi dada tetap membantu kesensitifan kebanyakan model dalam mengidentifikasi gambar-gambar dengan kelegapan ruang udara. dengan menggunakan algoritma grad-cam, peta salien yang dicadangkan ini mampu mengalih fokus model kepada kawasan yang relevan kepada gambar radiografi dada. sementara itu, kajian kualitatif ini juga menunjukkan algoritma yang dicadangkan mampu memberi ciri anomali, termasuk objek asing dan kardiomegali. walau bagaimanapun, ianya tidak konsisten dalam menjelaskan berat dan nodul. keywords: saliency mapping; chest radiograph; convolutional neural network 1. introduction the convolutional neural network (cnn) has become the de-facto choice for image classification and object detection. it has shown that the network model can achieve humanlevel accuracy, including for medical images. nevertheless, researchers are still finding ways to improve the classification performance with novel ideas. the majority of this research focuses on developing ever more complex and deep architecture. in this paper, we test the idea of changing the input typing rather than the model architecture. instead of using a regular medical image, the saliency map is proposed to be the alternative input. 1.1 introduction to saliency map itti et al. [1] introduced the concept of the saliency map in 1998. a saliency map is a numerical map that localizes an object (or objects) in an image that is deemed interesting (salient). in other words, the map emphasizes relevant features in an image while at the same time suppressing irrelevant features. saliency maps have been employed in many tasks, including image classification, object detection, and image segmentation [2,3]. methods for creating a salient map can be divided into the top-down and bottom-up approaches [4]. in the bottom-up approaches, the salient map is constructed based solely on the image's feature. features such as color mapping, contrast, edges, and objection placement are used to localize the image's salient region. famous bottom-up algorithms are binary normed gradient for objectness [5], the fine-grained [6], and spectral residual [7]. however, [8] stated that medical images produced by conventional modalities such as cxr, computer tomography (ct) scan, and ultrasound are mostly homogenous and possess very few color variants. in situations like this, most conventional bottom-up algorithms will fail to localize any salient object in the image; this is shown in fig. 4. contradicting the previous method, the top-down approach produces a salience map based on the task given. the algorithm takes external cues from a human or model feedback to construct the final salience map. this method is fast becoming the mainstream solution, especially for medical images, as it can produce precise salient region boundaries even in the presence of shades or reflections [9]. however, since the techniques are based on a supervised cnn model, from which it naturally inherits cnn dependencies. first, it requires a large number of annotated samples for training purposes. secondly, its development and deployment require access to accelerated hardware. these two requirements are an obstacle for the practical deployment of such technology in the medical 235 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 field, especially in malaysia. currently, malaysia lacks any open medical image dataset, and very few hospitals are equipped with, or have access to, accelerated hardware. 1.2 anomalous saliency mapping in this paper, we introduce a new algorithm called the xenafas algorithm that produces two novel anomalous saliency maps call intensity probability map (ipm) and weighted intensity probability map (wpm). different from the bottom-approach which only takes internal image cues, our approach takes cues from the probability mapping of a pixel's intensity relative to a cluster of similar images. however, it also does not require annotated samples or accelerated hardware to create the saliency map, which is practical in the context of malaysia's clinical settings. therefore, the algorithm can be considered as a middle ground between the bottom-up and top-down approach. we test the algorithm on a chest radiograph (cxr) dataset to see if the algorithm can create a salience region by highlighting pathological features such as air space opacities, masses, and foreign objects. 2. literature review for readers who want more information on the saliency map, ref [8] provides an extensive review of the subject matter. this paper's literature review will focus on the application of the saliency map in medical image analysis. the application of saliency in medical images can be separated into two categories, depending on when it is used. the majority of research only applied it post-training and solely for model interpretations; it is not actively involved in model training. for example, in [10], the saliency map produced by the class activation mappings (cam) [11] is used to validate the feature selected by the chexnext model for its classifications. similarly, in [12], a saliency map is created via the guided back-propagation method [13], which is then used to provide interpretability for model classification on breast cancer image classifications. research done by [14-16] also shows similar traits. however, it is vital to mention the finding by [17], in which the author demonstrated that most algorithms used to create this saliency map are inconsistent when repeated. among all algorithms, the gradcam [18] algorithm shows the most consistency. thus, the trustworthiness of using a saliency map to validate clinical cnn models is questionable. the second type of saliency map research actively uses it in the model training. for example, in [19], the saliency map in the form of an attention map reduces a model falsepositive rate. similar to a saliency map, the attention map produced by the attention gate (ag) algorithm suppresses irrelevant regions in the image. in [20], localization of pulmonary lesions in cxr images is achieved by extracting a saliency map from a cnn model. likewise, in [21], a saliency map is generated and used to detect polyps in capsule endoscopy. various bottom-up saliency algorithms are used for segmenting skin cancer in [22,23]. to the best of the authors' knowledge, there is yet a paper that examines the effect of using a saliency map as input for chest radiograph classification. therefore, in this paper, we tested the effect of using the proposed saliency map, ipm, and wpm, which will enhance the classification performance of the cnn model. in addition, we also test if the proposed saliency map successfully highlights all pathological features in a cxr image. for the interested reader, a review on the classification of cxr by supervised cnn models can be found from [24]. 236 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 3. methodology 3.1 the xenafas algorithm we proposed the xenafas method, an algorithm that indicates anomaly regions' location on a cxr image, based on the likelihood of a pixel's intensity (opacities) at a given location. the method starts with creating a control dataset. images for this dataset must be cherrypicked; avoiding images containing any form of anomalies. examples of anomalies include but are not limited to; any pathology, foreign body, extreme variation such as dextrocardia, rotated film, and patients in non-standard body positions. after the control dataset has been created, the images are clustered into several groups using the k-means algorithm. this step is needed to address the variation in patient body shape, image quality between x-ray machines, and the patient's body's orientation when the x-ray image is taken. the number of clusters, k, depends on the homogeneity of the images in the dataset. a good homogenous dataset will use a k value of 1–3, while a heterogeneous dataset will use a value between 7–10. next, the 2d pixel intensity distribution or probmat is created as shown in algorithm 1. fig. 1: the pseudocode for producing the probmat. there are several ways to create a non-parametric probability function; one of the most popular is to use the kernel density estimation method (kde). kde is easy to implement; however, computationally intensive when it is scaled to sample high-resolution images. a dataset with images with 256 by 256 resolution will need 65 536 kde modeling to create all the necessary probmat. this requirement will quickly exhaust the memory resource of a computer. additionally, there is no clear guideline on determining the appropriate bandwidth value of a kde model. we proposed another method as an alternative to kde. in this method, we first create a histogram of pixel intensity for all cxr images in the subcluster k, at a specific value of x and y. from the histogram, a discrete probability function can be obtained. a continuous function for all possible intensity values is approximate by combining the discrete probability function with cubic spline interpolation. the savitzky-golay filter was then applied to smooth the probability distribution function further. using this continuous probability function, it is now possible to create a matrix (probmat) representing the probability of all intensity values at any given location. pseudocode shown fig. 2 is used to create the anomalous saliency map. in this part, the probmat is used to produce the intensity 237 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 probability map (ipm) and weighted intensity probability map (wpm) for all cxr images. fig. 2: pseudocode to produce ipm and wpm saliency map. the wpm function is given by eq. (1), 𝑊(𝑥, 𝑦) = 𝑃(𝑖𝑥,𝑦 )𝑖𝑥,𝑦 (1) the weighted pixel intensity, 𝑊 at position 𝑥, 𝑦 is equal to the product of its intensity, 𝑖, and the intensity likelihood, 𝑃(), at the same locations. in wpm, the original pixel intensity acts as a weight for the likelihood. thus, only anomaly regions with high opacities will be shown in wpm; lucent anomalies will be suppressed. in visualizing ipm and wpm images, pixels with lower likelihood will have a higher intensity (appear brighter) than pixels with high likelihood. thus, a region that is marked brightly (highlighted) is a region that the algorithm considers to have anomaly features. one of the ipm and wpm images' fundamental weaknesses is that it suppresses anatomical landmarks. without anatomical landmarks, it is difficult to determine the location of an anomalous region relative to an organ. to solve this issue, we added ipm/wpm heatmap as a layer on top of the corresponding images. though, only regions that exceed the otsu threshold [25] are incorporated into the images. an example of ipm, wpm, infused-ipm (iipm) and infused-wpm (iwpm) is shown in fig. 5. for comparison purpose, fig. 4 shows the output of conventional bottom-up saliency mapping algorithms called fine-grained and spectral residual. the implementation of both these algorithms is taken from the opencv. 3.2 classification method this paper aims to test whether or not replacing cxr images with ipm and wpm will improve cnn's classification performance. thus, to ensure any performance changes are due to the input type and not the cnn architectures, only familiar deep cnn models are used. figure 3 shows the network architecture used, with the base model being mobilenet, densenet121, resnet50, vgg19 and xception [26-30]. the implementation of base model network architecture is taken from tensorflow (ver. 2) library and with the pre-trained weight from imagenet [31]. 238 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 fig. 3: classification network architecture. all models are trained with 100 epochs; however, an early stop is executed if there is no improvement in the loss value after ten epochs. all models were trained and tested on the google cloud platforms. we have chosen the regular classification metric performance for model validation: precision, sensitivity, receiver operating characteristic curve (roc-auc), and the area under the precision versus sensitivity curve (pr-auc). 3.3 dataset the dataset that is being used in this research is the google-nih dataset [32]. initially, nih provides the images while the labels are provided by google [33]. it is important to note that only labels for the test and validation dataset are provided from the source. to create the training dataset for this study, we split the original validation dataset into a new training and validation dataset with a ratio of 0.3. all datasets are imbalanced datasets. 3.4 qualitative validations to test the clinical relevance of the proposed algorithm, several normal and anomalous cxr images were selected, and the resulting ipm and wpm were examined qualitatively by a certified radiologist. anomalous cxr that was chosen includes images of a rotated film, foreign body, cardiomegaly, and masses. for model interpretation, the grad-cam [18] algorithm is used to visualize which region of the cxr is relevant to the model when making the class classification. 4. results and discussion 4.1 classification result table 1 shows several classification metrics obtained by various models and input-data types to classify the test dataset for air space opacity. while table 2 shows similar metrics for the classification of cxr images with masses/nodules. entries with the highest score for a particular metric is bolded. the result obtained is not particularly easy to decipher. the highest score in pr-auc, accuracy, and precision is obtained by resnet50+image, resnet50+iipm, and resnet50+iwmp, respectively. xception+image and vgg19+image do have a higher precision score, however, both results were rejected due to their sensitivity score being less than 0.5. this means the models falsely label the majority of positive samples. the model with the highest sensitivity score is vgg199+wpm, with a score of 0.930. however, the model precision is quite low, only 0.672, thus the next model, densenet121+iwpm, will be a better choice, having obtained 0.893 in sensitivity and 0.775 in precision. meanwhile, densenet121+image obtained the highest roc-auc score, 0.877. 239 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 table 1: classification performance of cnn models with different base models and input data type for the airspace opacity dataset. roc, pr, acc, pre, sen stand for roc-auc, precision-recall area under the curve, accuracy, precision, and sensitivity respectively. %∆ represents the percentage difference in score compared to the model with image as input input type rocauc %∆ pr-auc %∆ accuracy %∆ precision %∆ sensitivity %∆ mobilenetv2 image 0.844 0.883 0.770 0.814 0.781 ipm 0.824 -2.4 0.865 -2.1 0.754 -2.1 0.787 -3.3 0.789 1.0 wpm 0.801 -5.2 0.835 -5.4 0.670 -13.0 0.851 4.4 0.522 33.2 iipm 0.846 0.2 0.879 -0.5 0.767 -0.5 0.821 0.8 0.763 -2.3 iwpm 0.841 -0.3 0.873 -1.2 0.772 0.3 0.785 -3.6 0.834 6.9 densenet121 image 0.877 0.903 0.776 0.878 0.712 ipm 0.836 -4.7 0.874 -3.3 0.711 -8.4 0.878 -0.1 0.581 -18.3 wpm 0.820 -6.5 0.860 -4.8 0.736 -5.2 0.795 -9.5 0.733 3.0 iipm 0.873 -0.4 0.905 0.2 0.763 -1.7 0.877 -0.1 0.686 -3.6 iwpm 0.874 -0.3 0.904 0.1 0.788 1.5 0.775 11.8 0.893 25.4 xception image 0.856 0.890 0.683 0.921 0.495 ipm 0.809 -5.6 0.851 -4.4 0.736 7.8 0.757 17.9 0.803 62.1 wpm 0.797 -6.9 0.836 -6.1 0.729 6.7 0.797 13.5 0.714 44.1 iipm 0.835 -2.5 0.871 -2.1 0.732 7.2 0.856 -7.1 0.646 30.4 iwpm 0.841 -1.8 0.874 -1.8 0.723 5.7 0.876 -4.9 0.606 22.4 resnet50 image 0.873 0.907 0.784 0.881 0.725 ipm 0.838 -4.0 0.879 -3.1 0.757 -3.5 0.831 -5.7 0.728 0.4 wpm 0.829 -5.0 0.874 -3.7 0.759 -3.2 0.802 -9.0 0.775 6.9 iipm 0.870 -0.4 0.906 -0.2 0.790 0.6 0.872 -1.0 0.745 2.8 iwpm 0.867 -0.6 0.905 -0.3 0.743 -5.3 0.904 2.6 0.621 -14.3 vgg19 image 0.840 0.876 0.654 0.910 0.447 ipm 0.805 -4.2 0.860 -1.8 0.761 16.4 0.769 15.5 0.841 88.2 wpm 0.796 -5.3 0.843 -3.8 0.697 6.5 0.672 26.2 0.930 108. 3 iipm 0.858 2.2 0.894 2.1 0.760 16.1 0.875 -3.9 0.683 52.9 iwpm 0.845 0.6 0.887 1.3 0.760 16.1 0.852 -6.3 0.707 58.4 next, we analyze if using the proposed anomalous saliency mapping as input will result in a better classifier for the airspace opacity dataset. we are particularly interested if such change in input can boost the performance of shallower cnn models (mobilenetv2 and densenet121) to comparable performance of deeper cnn models (resnet50, vgg19 and xception). what is evident from the result, using the alternative data types as input enhances the model's sensitivity. for example, vgg19+wpm, which obtained the highest sensitivity, obtained a 108.3% improvement compared to vgg19+img. this sensitivity improvement is more apparent in deep cnn models (resnet50, vgg19, and xception) than shallower cnn models (mobilenetv2 and densenet121). 240 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 as one might expect, any improvement in sensitivity tends to reduce model precision. nevertheless, in most results, the degree of precision reduction is less than the degree of sensitivity gain. for example, the model xception+iipm obtained an increase of 30.4% in sensitivity while only reducing its precision by 7.1% compared to xception+image. the answer to which cnn model and input data type perform the best, depends on the purpose of the model. for screening purposes, then densenet121+iwpm will be the recommended model as it obtained the second-best sensitivity score while maintaining a reliable precision score. for precise clinical classification, then resnet50+iwmp is recommended. table 2: classification performance of cnn models with different base models and input data type for the mass/nodule dataset. roc, pr, acc, pre, sen stand for roc-auc, precision-recall area under the curve, accuracy, precision, and sensitivity respectively. %∆ represents the percentage difference in score compared to the model with image as input input type roc-auc %∆ pr-auc %∆ accuracy %∆ precision %∆ sensitivity %∆ mobilenetv2 image 0.588 0.194 0.709 0.209 0.336 ipm 0.568 -3.4 0.188 -3.2 0.729 2.8 0.201 -4.2 0.268 -20.2 wpm 0.588 0.0 0.204 5.2 0.755 6.5 0.206 -1.4 0.220 -34.3 iipm 0.577 -1.7 0.182 -6.4 0.805 13.4 0.194 -7.1 0.095 -71.7 iwpm 0.573 -2.4 0.192 -1.0 0.659 -7.2 0.188 -10.2 0.383 14.1 densenet121 image 0.606 0.199 0.739 0.228 0.308 ipm 0.587 -3.1 0.198 -0.6 0.716 -3.1 0.205 -10.1 0.308 0.0 wpm 0.607 0.3 0.209 4.9 0.541 -26.8 0.197 -13.8 0.664 115.4 iipm 0.619 2.2 0.215 7.9 0.669 -9.4 0.222 -2.8 0.478 54.9 iwpm 0.617 1.9 0.216 8.2 0.731 -1.0 0.241 5.7 0.366 18.7 xception image 0.637 0.231 0.702 0.227 0.410 ipm 0.587 -7.8 0.197 -14.7 0.633 -9.8 0.196 -13.8 0.464 13.2 wpm 0.575 -9.8 0.200 -13.5 0.611 -13.0 0.177 -22.0 0.437 6.6 iipm 0.602 -5.5 0.206 -10.6 0.737 5.0 0.213 -6.4 0.278 -32.2 iwpm 0.609 -4.5 0.210 -9.2 0.570 -18.7 0.192 -15.5 0.580 41.3 resnet50 image 0.643 0.242 0.689 0.225 0.437 ipm 0.644 0.2 0.268 11.0 0.631 -8.4 0.222 -1.3 0.580 32.6 wpm 0.619 -3.7 0.253 4.5 0.556 -19.3 0.199 -11.4 0.647 48.1 iipm 0.614 -4.5 0.210 -13.0 0.745 8.1 0.228 1.2 0.292 -33.3 iwpm 0.612 -4.7 0.222 -7.9 0.820 19.0 0.299 33.2 0.149 -65.9 vgg19 image 0.619 0.257 0.741 0.230 0.308 ipm 0.623 0.6 0.279 8.5 0.545 -26.4 0.195 -15.3 0.647 109.9 wpm 0.561 -9.3 0.194 -24.6 0.733 -1.1 0.206 -10.7 0.271 -12.1 iipm 0.620 0.1 0.245 -4.8 0.743 0.2 0.244 5.9 0.339 9.9 iwpm 0.628 1.4 0.260 1.0 0.752 1.5 0.248 7.7 0.319 3.3 it is worth noting that, since this dataset is imbalanced, the pr-auc score is more important than the roc-auc score. densenet121+iwpm also obtains a pr-auc score of 0.904, a 241 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 mere 0.003 less than the highest score, which is 0.907 by resnet50+image. in addition to obtaining a reliable classification score, it also has the advantage of requiring fewer computing resources than resnet50, vgg19, and xception. thus, it is more practical to be deployed in malaysian hospitals. in table 2, results show that all models failed to achieve acceptable classification performance for the mass/nodule testing-dataset. no model obtained a precision score of more than 0.5, meaning the majority of positive classifications were actually false. it is worth pointing out that all sensitivity scores for img input were lower than 0.5, thus all model missed the majority of the mass/nodule samples. only densenet121+wpm, resnet50+ wpm/ipm and vgg19+ipm manage to achieve a sensitivity score above 0.5. 4.2 qualitative assessment figure 4 shows the example of a saliency map produced by the fine grained and spectral residual algorithm, a conventional bottom-up algorithm. as shown in the figure, the fine grained failed to emphasize or suppress any feature in the image. conversely, the spectral residual suppressed almost all featured, making it impossible to extract any meaningful information from its saliency map. aligned with what was mentioned in [9], the conventional bottom-up saliency map algorithm cannot produce meaningful mapping for cxr images. fig. 4: the saliency map of a cxr image (a) produced by the fine grained, (b) and spectral residual (c) algorithms. fig. 5: a comparison between the original image and the corresponding ipm, wpm, iipm and iwpm for a patient in a normal (a-e) and rotated (f-j) position. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (a) image (b) ipm (c) wpm (d) iipm (e) iwpm (f) image (g) ipm (h) wpm (i) iipm (j) iwpm 242 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 figure 5(a) shows cxr images with no visible abnormalities; the resulting ipm and wpm are shown the fig. 5(b) and 5(c), respectively. there is no apparent region highlighted for the wpm image, implying that the algorithm does not identify any anomaly in the original cxr image. however, the perihilar region is incorrectly highlighted in the ipm image; this may suggest that the ipm may be over-sensitive in highlighting anomalies in cxr images. next, we examine how the algorithm processed cxr images taken for an incorrectly positioned patient, or for a rotated x-ray film. for example, in fig. 5(d), the patient's trachea is not located in the midline, suggesting that the patient may be rotated relative to the film. this orientation gives the appearance that the right lung is more lucent than the left. in the produced ipm image, the lucent region is highlighted, whereas wpm does not highlight this feature as wpm suppresses lucent anomalies. whether or not the cause of the right lung lucency is significant is still an anomaly from the imaging perspective. thus, the algorithm should highlight this anomaly as in the ipm image and then proceed to validate it by a radiologist. another feature that indicates that the patient is in an abnormal position is the presence of teeth in the cxr image. the anomaly is highlighted in the ipm and more evidently in the wpm image. teeth usually are not presented in a cxr, thus it is a form of anomaly that should be highlighted by a uas algorithm. however, the algorithm incorrectly highlighted the patient breasts; this error may have been caused by the lack of images containing breasts in the control dataset. fig. 6: chest radiograph with foreign body, (a) and (b). the resulting wpm images (c) and (d) clearly show the foreign bodies, arrow (1)-(4). figure 6(a) and 6(b) show cxr with foreign bodies, and the resulting wpm images are shown in fig. 6(c) and (d). in both wpm images, the foreign bodies (arrows) are highlighted clearly and are more apparent than in the original cxr images. the opacity of biological 243 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 matter around the foreign body is suppressed, making it appear lucent. with this result, it can be assumed that wpm images may help in identifying foreign objects in cxr. next, the algorithm capabilities in highlighting pathological changes are demonstrated. figure 7(a) shows a cxr with cardiomegaly, and it is highlighted clearly in both ipm, fig. 7(b) and wpm fig. 7(c) image. on the other hand, fig. 7(d) shows cxr with a homogenous opacity at the right lower lung zone that does not obscure the cardiac border. this feature is not highlighted in both ipm, fig. 7(e) and wpm, fig. 7(f) images. fig. 7: the cardiomegaly feature in (a) is clearly highlighted in the wpm (b) and ipm (c) image. however the generalized opacity feature in (d) is absent in the ipm (e) and wpm (f) images. additionally, the algorithm also frequently failed to highlight opacity due to mass and nodules. the single nodule in fig. 8(a) was not highlighted in the resulting wpm image, fig. 8(d). the same can also be said for the multiple nodule-like opacities at bilateral mid and lower lung zones, as shown in fig. 8(b). only some of the lung masses are highlighted in resulting wpm images, fig. 8(e). an example of a correctly highlighted lung mass is shown in fig. 8(c) and 8(f). 4.3 grad-cam results to meaningfully deploy a developed model in clinical use, it must show some degree of interpretability and the classification must be validated based on some biological markers. for this reason, we use the grad-cam, [18], to visualize which region on the input data is emphasized. figure 9(a) shows an example of cxr having airspace opacifications. figure 9(b)-(f) shows the output of the grad-cam algorithm for densenet121 models that were trained with different input data types. the only models that were trained using the wpm and iipm as input were correctly labeled the sample. 244 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 fig. 8: most of the lung nodules and masses in (a) and (b) failed to be highlighted in the resulting wpm images, (d) and (e). only lung masses in (c) were successfully highlighted in (f). fig. 9: output of the grad-cam algorithm for air space opacification dataset. regions that are marked red are regions that the densenet-121 deems important. an obvious pattern that emerges in fig. 9 is that models that received the original cxr image (image, iipm, and iwpm) as input tend to mark the lower-left diagram. on the other hand, the model that takes ipm and wpm tends to focus more on the lung and shoulder region. it is not exactly certain why the densenet121-ipm model incorrectly labeled the 245 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 image even though it correctly emphasized the lung region. one reason that can be attributed is the model emphasized the right lung more than the left lung. both models that correctly labeled the image, densenet121-wpm, and densenet121-iipm, emphasize the left lung region. even though densenet121-wpm also marked the left lung region; it emphasized more on the diagram, hence the wrong labeling. figure 10(a) shows a sample of cxr that is positive for mass. the location of the mass is in the left upper and lower lobe. figure 10(b)-(f) show the output result of the grad-cam algorithm for different resnet50 models that were trained by different input data types. models trained using images, iipm and iwpm, show similar marked regions; they extend from the left clavicle bone to the lung right middle lobe. for iipm and iwpm, the region does not cover any mass. thus, the model is falsely labeled as negative. resnet50+ipm correctly marked the left-upper lobe, and the mass contained in it. resnet50+wpm only weakly marked this region. no model correctly marked the mass at the left lower lobe. from the example of results shown in fig. 10, it can be concluded that the trained model failed to learn a mass feature. it also emphasizes the need for more effective feature extraction if we want to detect masses in cxr more accurately. fig. 10: output of the grad-cam algorithm for the mass/nodule dataset. regions that are marked red are regions that the resnet50 deems important. 5. conclusion in this paper, we introduce the xenafas algorithm, which creates the imp and wmp anomalous saliency mapping for cxr images. a qualitative study by a certified radiologist has shown that the algorithm can highlight most foreign objects and cardiomegaly in the cxr samples tested; however, it is inconsistent in highlighting masses and nodules. it has also been shown that using imp and wmp over regular cxr images increases the sensitivity of most cnn models that were tested. using the grad-cam algorithm, it has been demonstrated that by using the imp and wmp, the cnn model shifted its focus to a 246 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 more relevant cxr image region. the results obtained from the experiment conducted show that the imp and wmp can be an alternative to regular cxr images for future machine learning development. acknowledgement this work was supported by the malaysian ministry of higher education fundamental research grant scheme [grant no. frgs17-040-0606]. references [1] itti l, koch c, niebur e. (1998) a model of saliency-based visual attention for rapid scene analysis. ieee trans pattern anal mach intell. 20: 1254-1259. [2] liu n. and han j. (2016) dhsnet: deep hierarchical saliency network for salient object detection. in proceedings of the ieee conference on computer vision and pattern recognition; pp 678-686. [3] rahtu e, kannala j, salo m, heikkilä j. (2010) segmenting salient objects from images and videos. in european conference on computer vision; pp 366-379. [4] itti l, koch c. (2001). computational modelling of visual attention. nature reviews neuroscience, 2: 194-203. [5] cheng m-m, zhang z, lin w-y, torr p. (2014) bing: binarized normed gradients for objectness estimation at 300fps. in proceedings of the ieee conference on computer vision and pattern recognition; pp 3286-3293. [6] montabone s, soto a. (2010) human detection using a mobile platform and novel features derived from a visual saliency mechanism. image vis comput., 28: 391-402 [7] hou x, zhang l. (2007) saliency detection: a spectral residual approach. in ieee conference on computer vision and pattern recognition; pp 1-8. [8] borji a, cheng m-m, hou q, jiang h, li j. (2019) salient object detection: a survey. comput vis media; pp 1-34 [9] castillo jc, tong y, zhao j, zhu f rsna bone-age detection using transfer learning and attention mapping [http://noiselab.ucsd.edu/ece228_2018/reports/report6.pdf] [10] rajpurkar p, irvin j, ball rl, zhu k, yang b, mehta h, duan t, ding d, bagul a, langlotz cp, others. (2018) deep learning for chest radiograph diagnosis: a retrospective comparison of the chexnext algorithm to practicing radiologists. plos med., 15: e1002686 [11] zhou b, khosla a, lapedriza a, oliva a, torralba a. (2016) learning deep features for discriminative localization. in proceedings of the ieee conference on computer vision and pattern recognition; pp 2921o2929. [12] shen l, margolies lr, rothstein jh, fluder e, mcbride r, sieh w. (2019) deep learning to improve breast cancer detection on screening mammography. sci. rep., 9: 12495. [13] springenberg jt, dosovitskiy a, brox t, riedmiller m. (2015) striving for simplicity: the all convolutional, arxiv preprint arxiv:1412.6806 [14] ding y, sohn jh, kawczynski mg, trivedi h, harnish r, jenkins nw, lituiev d, copeland tp, aboian ms, mari aparici c, others. (2019) a deep learning model to predict a diagnosis of alzheimer disease by using 18f-fdg pet of the brain. radiology, 290: 456o464 [15] norman b, pedoia v, noworolski a, link tm, majumdar s. (2019) applying densely connected convolutional neural networks for staging osteoarthritis severity from plain radiographs. j. digit. imaging, 32: 471-477 [16] oh k, kim w, shen g, piao y, kang n-i, oh i-s, chung yc. (2019) classification of schizophrenia and normal controls using 3d convolutional neural network and outcome visualization. schizophr res., 212: 186-195 [17] arun nt, gaw n, singh p, chang k, hoebel kv, patel j, gidwani m, kalpathy-cramer j. (2020) assessing the validity of saliency maps for abnormality localization in medical imaging, arxiv preprint arxiv:200600063 cs 247 iium engineering journal, vol. 22, no. 2, 2021 md ali et al. https://doi.org/10.31436/iiumej.v22i2.1752 [18] selvaraju rr, cogswell m, das a, vedantam r, parikh d, batra d. (2017) grad-cam: visual explanations from deep networks via gradient-based localization. in proceedings of the ieee international conference on computer vision; pp 618-626. [19] schlemper j, oktay o, schaap m, heinrich m, kainz b, glocker b, rueckert d. (2019) attention gated networks: learning to leverage salient regions in medical images, arxiv preprint arxiv:180808114 cs [20] pesce e, withey sj, ypsilantis p-p, bakewell r, goh v, montana g. (2019) learning to detect chest radiographs containing pulmonary lesions using visual attention networks. med image anal, 53: 26-38 [21] deeba f, bui fm, wahid ka. (2020) computer-aided polyp detection based on image enhancement and saliency-based selection. biomed signal process control, 55: 101530. [22] fan h, xie f, li y, jiang z, liu j. (2017) automatic segmentation of dermoscopy images using saliency combined with otsu threshold. comput biol med, 85: 75-85 [23] khan ma, akram t, sharif m, saba t, javed k, lali iu, tanik uj, rehman a. (2019) construction of saliency map and hybrid set of features for efficient segmentation and classification of skin lesion. microsc res tech., 82: 741-763. [24] rahmat t, ismail a, aliman s. (2018) chest x-rays image classification in medical image analysis. appl med inform., 40: 63-73. [25] otsu n. (1979) a threshold selection method from gray-level histograms. ieee trans syst man cybern, 9: 62-66. [26] howard ag, zhu m, chen b, kalenichenko d, wang w, weyand t, andreetto m, adam h. (2017) mobilenets: efficient convolutional neural networks for mobile vision applications. arxiv preprint arxiv:170404861 [27] huang g, liu z, weinberger kq. (2016) densely connected convolutional networks. in proceedings of the ieee conference on computer vision and pattern recognition; pp 4700-4708 [28] he k, zhang x, ren s, sun j. (2016) deep residual learning for image recognition. in proceedings of the ieee conference on computer vision and pattern recognition; pp 770-778 [29] simonyan k, zisserman a. (2014) very deep convolutional networks for large-scale image recognition. arxiv preprint arxiv:14091556 [30] chollet f. (2016) xception: deep learning with depthwise separable convolutions. in proceedings of the ieee conference on computer vision and pattern recognition; pp 1251-1258 [31] deng j, dong w, socher r, li l-j, li k, fei-fei l. (2009) imagenet: a large-scale hierarchical image database. in: 2009 ieee conference on computer vision and pattern recognition; pp 248-255. [32] wang x, peng y, lu l, lu z, bagheri m, summers rm. (2017) chestx-ray8: hospital-scale chest x-ray database and benchmarks on weakly-supervised classification and localization of common thorax diseases. in proceedings of the ieee conference on computer vision and pattern recognition; pp 2097-2106 [33] majkowska a, mittal s, steiner df, reicher jj, mckinney sm, duggan ge, eswaran k, cameron chen p-h, liu y, kalidindi sr, et al. (2020) chest radiograph interpretation with deep learning models: assessment with radiologist-adjudicated reference standards and population-adjusted evaluation. radiology, 294: 421-431 248 1. introduction 2. literature review 3. methodology 4. results and discussion 5. conclusion acknowledgement references application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 influence of different percentage boiler ash-based geopolymer in laterite soil atiqah najwa zainuddin1*, mazidah mukri2, diana che lat1, roslizayati rosli1 and noor hidayu abdul rani3 1 faculty of civil engineering, universiti teknologi mara (uitm) johor branch, kampus pasir gudang, johor, malaysia 2 faculty of civil engineering, universiti teknologi mara (uitm) selangor, malaysia 3 faculty of chemical engineering, universiti teknologi mara (uitm) johor branch, kampus pasir gudang, johor, malaysia * corresponding author: atiqa387@uitm.edu.my (received: 23rd august 2020; accepted: 9th january 2021; published on-line: 4th july 2021) abstract: the waste generation of palm oil boiler ash has been one of its big problems as it is less used and deposited in landfills as a by-product. geopolymer is a new green technology that has been intensively studied in concrete applications. however, few studies on geopolymers have been conducted in soil applications. thus, this study investigated the influence of palm oil boiler ash-based geopolymer in laterite soil strength. different percentages, 5, 10, 15, and 20% of geopolymer mixtures, were added to laterite soil. the process of producing a geopolymer binder was performed by sieving boiler ash (150 µm), then mixing with sodium hydroxide (naoh) and sodium silicate (na2sio3) as an alkaline activator at a ratio of 1:2. this material effectiveness was tested through compaction test using a standard proctor, unconfined compressive strength, and the scanning electron microscope (sem). fifteen percent (15%) of geopolymer in laterite soil indicated the best-mixed design with a maximum dry density of 2.23 mg/m3 with a moisture content of 13.58%. the unconfined compressive strength test at curing times of zero, seven, and twenty-eight days on the ls-15.0 gpoba sample, show a slightly increased strength of 47, 58, and 76 kpa, respectively. the sem images proved that the geopolymer gel's development stabilized the soil structure from a loose structure to a denser soil structure. this study aims to investigate the influence of geopolymer in laterite soil. boiler ash as an alternative material in geotechnical applications was studied to understand and develop new green alternative materials to sustain the environment from industrial waste and to enhance laterite soil properties. abstrak: abu kelapa sawit adalah salah satu sisa utama yang terhasil dari industri kelapa sawit tetapi penggunaannya kurang dimanfaatkan dan dibuang ke tempat pembuangan sampah. teknologi hijau baru yang dikenali sebagai geopolimer telah dikaji secara intensif dengan kekuatan konkrit tetapi hanya sedikit kajian telah dibuat dalam penggunaan tanah. tujuan kajian ini adalah bagi mengesan geopolimer berasaskan abu kelapa sawit terhadap kekuatan tanah laterit. peratusan campuran geopolimer yang berbeza (0, 5, 10, 15 dan 20%) dicampur pada tanah laterit. bagi menghasilkan geopolimer, saiz 150 μm abu kelapa sawit disintesis dengan kombinasi bahan kimia natrium hidroksida (naoh) dan natrium silikat (na2sio3) pada nisbah 1:2 bagi semua campuran sebagai pengaktif alkali. ujian terhadap keberkesanan bahan adalah melalui proses ujian pemampatan menggunakan proktor standard, kekuatan pemampatan tidak terbatas, dan pengimbas mikroskop elektron (sem). berdasarkan dapatan ujian 67 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 pemadatan, 15% geopolimer di tanah laterit menunjukkan campuran terbaik dengan memberikan kepadatan pengeringan maksimum 2.23 mg/m3 pada kelembapan 13.58%. ujian kekuatan mampatan tidak terbatas pada masa pempolimeran sebanyak 0, 7 dan 28 hari diuji pada sampel ls-15.0gpoba bagi menguji kekuatan campuran. dapatan menunjukkan kekuatan geopolimer sedikit meningkat pada 47, 58 dan 76, masing-masing. imej sem membuktikan pengembangan gel geopolimer menstabilkan struktur tanah daripada struktur lopong kepada struktur tanah padat. oleh itu, abu kelapa sawit berasaskan geopolimer dan tanah laterit berpotensi sebagai alternatif bagi merawat tanah dalam aplikasi geoteknik dan berpotensi mengurangkan kadar kebolehtelapan. keywords: palm oil boiler ash; geopolymer; laterite soil; compaction compressive strength 1. introduction increased population is leading to higher demand in the construction industry and the growth of infrastructure. malaysia is the largest exporter of palm oil mill. the production of palm oil in malaysia has had a positive impact on sustained economic growth in the global market over the past four decades, and the annual production of palm oil in malaysia in the period of 2016–2020 has reached 15.4 million tons [1]. despite the apparent benefits, oil palm mills' production significantly contributes to environmental degradation [2]. production from palm oil processing for oil extraction generates waste such as palm kernel, nutshell, palm fiber, and empty fruit brunch. these wastes are incinerated and produce ashes at the boiler's lower compartment, known as boiler ash. it has now been revealed that the palm oil industry will produce 657,000 tons of waste at the end of december 2020 [3]. the wastes are either dumped to landfill or eventually exposed and contaminate the soil, creating a significant disposal issue and harming the environment [4]. nowadays, ordinary portland cement (opc) and lime have become the most common soil stabilizers used as additives to enhance soil properties. however, the use of ordinary portland cement (opc) is held responsible for some co2 emission during its production and has thus polluted the environment. several efforts are in progress to reduce ordinary portland cement as an additive material in soil stabilization to address global warming issues. studies are being conducted to find alternative and eco-friendly soil stabilizers from waste material to reduce co2 emission and decrease construction costs. therefore, in this study, boiler ash was introduced as an alternative by-product material in soil stabilizer by synthesizing it into geopolymer form. daviddovits [5] introduced a new green technology known as geopolymer to enhance mechanical properties and material strength in the construction industry. all the materials that contain si and al can be used as a constituent in geopolymer to be activated with alkali solution presence [6]. according to van jaarsveld et al. [7], the sio2 and al2o3 in the ash provide a rich source of si and al atoms as a source of aluminosilicate materials for producing geopolymers. xu et al. [8] investigated 16 natural al-si minerals and concluded that all the minerals are, to some extent, soluble in concentrated alkaline solution. according to daviddovits, geopolymerization is a reaction that consists of si-o-al and si-o-si bonds depending on the ability of alumina ion (6-fold or 4-fold coordination) to induce the crystallographer and chemical changes in silica backbone. in geopolymerization, a reaction three-dimensional techto-aluminosilicate framework called polysialate is shown in equation (1), where m is a cation (k, na, ca), n is the degree of polycondensation, and z is 1, 2, 3 or ≥3. in the sialates network, si-o-al bridge forms form the chain and ring of 68 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 sio4 and alo4 tetrahedra's cross-linked together with oxygen atoms. positive ions (na +, k+, ca2+) must balance the negative charge if al is in 4-fold coordination [7]. 𝑀𝑛[−(𝑆𝑖𝑂2)𝑧 − 𝐴𝑙𝑂2]𝑛 − 𝑤𝐻2𝑂 (1) previous researchers have investigated the application of geopolymer by using different waste materials, including sludge, fly ash, kaolin, risk husk, and slag [9-11]. the boiler ash contained the sum of sio2 and al2o3 about 44 to 55% which is the most required composition to produce geopolymer [12-13]. the researchers have systematically studied the effect of using different alkaline solutions, sodium hydroxide concentrations, curing times, temperatures, and sodium hydroxide and sodium silicate ratios [14-15]. duchesne et al. [16] in their study, proved that naoh presence in alkaline solution activated the reaction, dissolved si4+ and al3+, and produced smooth gel to fly ash. the presence of sodium silicate in the alkaline solution resulted in the rapid process of geopolymerization. khan et al. [17] agreed that the higher the percentage of fly ash-based geopolymer added, the higher the value of compressive strength. in one of his samples, 70% of compressive strength was achieved using fly ash geopolymer in cement compared to the use of ground granulated blast furnace slag (ggbs) in cement with only a 30% increase. the concentration of sodium hydroxide played an important role in dissolving the silica-alumina from the source material. in cement application, most of naoh's molarity is 8 to 16 m at curing days of seven to twenty-eight days. as agreed by emdadi et al. [18] in their study, compressive strength was intensively ranging from 10-14 m naoh. different molarity of naoh gives a different effect on geopolymer. in puertas et al. [19], a mixture of fly ash and naoh of 10 m was added to slag, resulting in compressive strength of approximately 50 mpa. investigation on the potential use of geopolymer of low calcium fly ash with different ratios of alkali activator, m1(0.5), m2(1.0), m3(1.5), m4(2.0), and m5(2.5), at curing time of three days gave compressive strength of 34.7, 61.6, 40.4, 40.5, and 22.3 mpa respectively. as agreed by skvara et al. [20] who observed the increasing ratio from 2 to 2.5, the compressive strength decreased due to the excess sodium silicate hindering water evaporation and structure formation. soil stabilization is a typical soil remediation method to improve the physical and chemical properties of low strength soil by mixing the potential raw materials as additives or processes. laterite soil is known to be very resistant to erosion. laterite soil can be demonstrated by the nature of its properties such as high shear strength, low infiltration capacity, and low clay content, making it an excellent geotechnical material [21]. ahmad sujeeth et al. [22] mentioned that laterite soil properties can easily change as it is exposed to air and water during construction. laterite soil is full of cavities and pores; therefore, it is crucial to select sufficient treatment in laterite soil to enhance soil strength and properties. marto et al. [23] stated that laterite is widely used and economically convenient in construction. hence, information on laterite properties is essential to design the geotechnical process's strength and durability in construction. in recent years, the stabilization technique has been studied using geopolymerization. the geopolymer has become an effective method because the geopolymer source is cheaper since it uses industrial waste and reduces environmental pollution. varied types of soil such as red mud soil, laterite soil, loess deposit, and sandblasting grit have been studied using a geopolymer to improve the soil properties [24-27]. thiha et al. [28] studied the shear parameter of three soil types at curing times of zero and seven days. naoh and na2sio3 were used as alkaline solutions and mixed with fly ash to produce a geopolymer. the ratio of fly ash-geopolymer to the soil was at 0.1. in the study, 69 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 soil with silty sand and high plasticity clay gave a higher soil strength than high plasticity silt at a curing time of seven days. moreover, geopolymer curing at seven days was higher at 30% at day zero. this was supported by wisam et al. [29] who made an extension of research to investigate naoh's different molarity (4, 6, 8, 10 and 12 m) in geopolymer technique. control soil samples displayed a ucs value of 77.9 kpa. alkali activation for soil-olivine mixture increased the strength of the mixture to 392.8, 421.4, 583.9 1082.8 and 904.3 kpa at 7 days, respectively. as a conclusion on this research, geopolymer reaction gives higher soil strength over time. alkaline activator dissolves the bonding of si-al-si from the source material and gains stronger atom bonding. further study on the long-term performance should be carried out on boiler ash to compare other raw materials’ effectiveness. nik et al. [30] studied the effectiveness of different percentages of class c fly ash geopolymer on the compaction effort used in a soil liner application. in their study, an investigation of compaction and a hydraulic conductivity test were conducted. based on the compaction test, 15% of the geopolymer gave optimum mdd, which led to a good hydraulic conductivity test. mdd 20% of the geopolymer decreased as the excess water in the geopolymer failed the geopolymerization. a few works have studied the use of geopolymer binder as material in soil improvement such as sludge, fly ash, kaolin, risk husk, and slag [9-11]. however, no malaysian works have used boiler ash as geopolymer source material. it is essential to carry out a study to understand and develop new green alternative materials to sustain the environment from industrial waste and convert it into alternative raw materials to enhance soil properties. this study investigates the potential of boiler ash as source material in producing a geopolymer to enhance laterite soil properties and sustain the environment. 2. methodology laboratory work was carried out in the faculty of civil engineering in uitm johor kampus pasir gudang, johor, malaysia. the total number of samples in this study was nine samples for chemical properties, sixteen samples for physical properties, five samples for compaction value, and three samples for unconfined compression test conductivity with a total of thirty-three samples. the sample number and sample definition of this analysis are shown in table 1. the best percentage of boiler-ash geopolymer added to laterite soil was investigated using five different percentages, (0, 5, 10, 15, and 20%). this percentage was determined based on the previous soil stabilization literature review [31-32]. table 1: soil descriptions no sample number soil description 1 ls p laterite soil + 0% poba geopolymer 2 ls – 5.0 gpoba laterite soil + 5.0% poba geopolymer 3 ls – 10.0 gpoba laterite soil + 10.0% poba geopolymer 4 ls – 15.0 gpoba laterite soil + 15.0% poba geopolymer 5 ls – 20.0 gpoba laterite soil + 20.0% poba geopolymer three stages of laboratory work were conducted to determine the physical properties. the atterberg test, ph test, particle density test, and shrinkage test followed the british standard bs 1377-2:1990. scanning electron machine (sem) was utilized at the faculty of chemical engineering, uitm johor kampus pasir gudang, and x-ray fluorescence at jabatan kimia utm skudai johor, covering the chemical properties test to determine the 70 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 soil structure of laterite soil mixed with geopolymer and the chemical composition in palm oil boiler ash. compaction and unconfined compression strength (uct) engineering tests were performed to investigate the reaction of soil strength to geopolymer. fig.1 shows the study flow chart in this study. fig 1: study flow chart. 2.1 materials in this study, laterite soil was mixed with a geopolymer to produce a good binder to enhance the properties of laterite soil. to generate a geopolymerization reaction, raw material from industrial waste known as palm oil boiler ash and alkaline activator (sodium hydroxide and sodium silicate) were mixed with a suitable mixed design as discussed below, thus generating a new green technology binder known as geopolymer. data of properties and soil strength at different percentages of boiler ashgeopolymer mixed in laterite soil were recorded. 2.1.1 laterite soil the laterite soil used was collected at a depth of 1.5 m, 100 m away from tanjung langsat landfill, pasir gudang, johor, malaysia. the gradation test was conducted using bs 1377: part 2:1990. fig. 2 shows the gradation chart of the laterite soil. from the sieve analysis test, the laterite soil used in this study consisted of about 25.98% of gravel, 35.55% of sand, and 38.47% of fine size grain and was classified under very “silty sand” as shown in table 2. the laterite soil had a specific gravity of 2.62. an atterberg limit test that was conducted on the laterite soil of sieve size 425 µm showed the result of the liquid limit (ll) of the soil was 58.61% and the plastic index (pi) was 6.15%. according to the unified soil classification system (uscs), this soil is classified as high plasticity (mh). the laterite soil in this study consisted of a high portion of silt compared to clay resulting in a low shear strength or low compressibility. this type of soil was therefore chosen in this study to investigate the effect of geopolymer palm oil (boiler ash) to enhance the mechanical and properties of laterite soil. geopolymer production boiler ash + alkaline activator (1:2) collecting sample laterite soil palm oil boiler ash (poba) soil sample on standard proctor test laterite soil + 0% geopolymer laterite soil + 5.0% geopolymer laterite soil + 10.0% geopolymer laterite soil + 15.0% geopolymer laterite soil + 20.0% geopolymer engineering test properties (unconfined compression test) -only for best % of geopolymer with high mdd value at curing time of: (0-day,7-day,28-day) chemical properties test • x-ray fluorescence test (xrf) • scanning electron machine test (sem) 71 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 fig. 2: grain size distribution of laterite soil. table 2: grading characteristics of the laterite soil composition of soil gravel % 25.98 sand % 35.55 silt % 25.81 clay (%) 12.66 gradation d60 (mm) 0.995 d50 (mm) 0.558 d30 (mm) 0.033 2.1.2 palm oil boiler ash (poba) palm oil boiler ash (poba) was sourced from teluk sengat palm oil mill, kota tinggi, johor. the palm oil boiler ash, as shown in fig.3, consisted of boiler ash that was obtained from the lower compartment of a palm oil boiler burning what consisted of large particles including nutshells and kernels. palm oil boiler ash is one of the industrial wastes from the burning of palm oil that creates disposal problems and causes soil contaminants as the waste is stored in landfills. the chemical composition of the palm oil boiler ash was determined using x-ray fluorescence (xrf), as shown in table 3. the higher content of silica could be the potential of a geopolymer. fig. 3: palm oil boiler ash (poba) in teluk sengat palm mill, johor. 72 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 table 3: chemical composition of laterite soil and boiler ash oxides sio2 al2o3 cao fe2o3 na2o mgo p2o5 k2o laterite soil (ls-p) palm oil boiler ash (poba) 56.0 43.9 30.3 4.55 0.381 13.1 9.54 4.11 3.27 2.45 0.290 12.5 based on table 3, the percentage of boiler ash was suitable to be a geopolymer source material as the percentage of silica was more than 40% [5]. in laterite soil, the silica-alumina comprised 30 percent to 60 percent content. however, the properties of laterite soil were complex such as shrinkage and low plastic index due to the presence of water. therefore, it was not sufficient for laterite soil alone without additives to be the source material for geopolymerization production. fig. 4 shows the size sample of the palm oil boiler ash at 150 µm used in this study. fig. 4: palm oil boiler ash passing 150 µm sieve size. 2.1.3 alkaline solution the alkaline activator used in this study was sodium hydroxide (naoh) in pellet form with 97% purity and sodium silicate (na2sio3), as shown in fig. 5. referring to thiha et al. [28], the concentration of sodium hydroxide (naoh) in this study was chosen to be 5 m. sodium silicate (na2sio3) was a liquid solution that consisted of 9.4% na2o, 30% sio2, and 60.5% h2o taken from chemical suppliers in johor. the ratio of sodium hydroxide (naoh) and sodium silicate (na2sio3) in the study was 1:2. 2.2 sample preparation the palm oil boiler ash was collected and ground to finer particles and sieved using 150 µm sieves and put in an oven at 80 oc for 24 hours to activate the silica content before being mixed with an alkaline activator. the fine particles of palm oil boiler ash were used to produce the geopolymerization reaction between palm oil boiler ash and alkaline solution at different mixed designs. the purpose of using an alkaline activator was to synthesize the chemical structure of palm oil boiler ash to produce a geopolymer. sodium hydroxide (naoh) and sodium silicate (na2sio3) were selected at a ratio of 1:2. the sodium hydroxide (naoh) pellets were prepared by diluting them with distilled water at a concentration of 5 m (molarity) to create an alkaline solution. the concentration of the sodium hydroxide solution (naoh) used was 5 m. for preparation of 1 m solution, 40 g naoh flakes were dissolved in water to prepare 1 liter of sodium hydroxide solution. thus, for preparation of 5 m, 200 g of naoh flakes were used. 73 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 fig. 5: (left) sodium hydroxide in pellet form; (right) sodium silicate in liquid form. during the preparation of naoh, precautions were taken to put the pellets into the distilled water and not the other way around as sodium hydroxide could react with moisture from the air and generate heat while dissolving and cause a fire near flammable material, as well as possible sparks that could come into contact with eyes or skin. the sodium silicate was poured into the naoh solution at a ratio of 1:2, stirred for 10 minutes, and left at room temperature for 24 hours to produce a better strength of mortar [12]. lastly, to produce the geopolymer binder, 80% of boiler ash and 20 % of alkaline solution were carefully mixed before being added to laterite soil at a different percentage of mixed design, as shown in fig. 6. after the geopolymer curing at ambient temperature for 24 hours, the geopolymer was mixed with laterite soil at a different percentage of 0, 5, 10, 15, and 20% as shown in fig. 7 the samples were then tested to determine the physical properties, chemical properties, compaction test, and soil strength using an unconfined compression test (uct) at zero, seven, and twenty-eight days of curing. fig 6: alkaline solution mixed with poba. fig 7: preparation of geopolymer mixed with laterite soil. 2.3 experimental design 2.3.1 compaction test five samples at different percentages of geopolymer (0, 5, 10, 15, and 20%) were prepared. the percentage of water required was added and mixed until a uniform consistency was achieved [30]. the standard proctor test as shown fig.9 was conducted in this study to determine the maximum dry density (mdd) and optimum moisture content (omc). the soil sample was dynamically compacted with a release of a steel hammer with a weight of 2.5 kg and 27 blows per each of three layers, falling freely 300 m with a 50 mm diameter of rammer. after compaction was conducted, samples were then trimmed to remove the excess soil, molded, and weighed. equation (2) and equation (3) show the calculation of the standard proctor test: 74 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 𝜌 = 𝑚2−𝑚1 𝑣 𝑀𝑔/𝑚3 (2) where: m1 = mass of mold and base m2= mass of soil and mold v = volume of mold then, dry density was calculated from the equation below: 𝜌 = ( 100 100+𝑤 )𝜌 𝑀𝑔/𝑚3 (3) the dry density was recorded to determine the optimum moisture content (omc) at the maximum dry density (mdd) to conduct an unconfined compression test (uct). 2.3.2 unconfined compression test (uct) fig. 8: uct machine. unconfined compressive strength is based on astm designation d2166. the size of samples in this test was 50 mm in diameter with 100 mm height based on the procedure in astm d2166. in this study, the investigation of unconfined strength was conducted for sample ls-15.0 gpoba measured at curing times of the compacted sample under ambient temperature. curing times of zero, seven, and twenty-eight days were chosen for this study. these samples were selected to determine the before and after reaction of the geopolymer towards laterite soil. also, ls-15.0 gpoba was chosen due to the best compaction obtained from mdd and omc results. the sample was mixed with water, based on moisture content resulting from the compaction test for ls15.0 gpoba. then, the samples were compacted in the mold with three (3) layers 10 tamping’s of compaction for each layer. the compressed samples at zero day were immediately diverted and installed for the uct test as shown in fig. 8. samples of seven and twenty-eight days were kept in a plastic bag and tightly sealed under ambient temperature based on curing times. when the sample reached its curing time, it was taken out and immediately run on the uct machine. in this test, all samples were sheared with the dry condition without submerging the sample into water. 75 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 3. results and discussion 3.1 physical properties of samples this study conducted laboratory investigations on different percentages of geopolymers to enhance the properties of laterite soil. this study aimed to determine the soil compaction and shear strength of geopolymer as additives in laterite soil. table 4 shows the physical properties of laterite soil. the properties and characteristics of laterite soil are important to be investigated for the future development of laterite soil. table 4: physical properties of different percentages of geopolymer in laterite soil soil description ls-p liquid limit (%) 58.61 plastic index (%) 6.15 specific gravity 2.62 ph 6.49 shrinkage 11.49 based on the experimental data collected, with the right percentage of boiler ash-based geopolymer added to laterite soil, it improves the properties of soil and enhances the soil strength. further investigation in the compaction test and soil strength was conducted as follows. 3.2 compaction test fig. 10 shows the compaction curve indicating maximum dry density (mdd) and optimum moisture content (omc) of all geopolymer percentages in laterite soil. based on the compaction curve produced, 0% of geopolymer in laterite soil gave a maximum dry density of 1.80 mg/m3 at 14.07% optimum moisture content. the adding of geopolymer at 5% and 10% showed increasing maximum dry densities of 1.88 mg/m3 and 1.90 mg/m3 and decreasing optimum moisture contents at 13.88% and 13.70%, respectively. the increase of moisture content was probably because of the reaction between laterite soil, and geopolymer led to the loss of water [27]. however, drastic increase can be seen of maximum dry density of 2.23 mg/m3 and decrease of optimum moisture content at 13.58% at 15.0 % of geopolymer in laterite which give positive results of geopolymerization reactions. 15.0 % of geopolymer in laterite soil indicated the optimum mixed design of geopolymer as a mixed design. the bonding created by alkaline solution and the subsequent isomorphous substitution of silica (si) has indeed increased the packing between the grains [32]. this result is supported by nik et al. [30] in their study on laterite soil and fly ash geopolymer mentioned, whereby geopolymer added in laterites soil showed an increment in dry density due to the action of alkaline attack which changed the soil mineral. in 20% of geopolymer, results gave a decreasing value of dry density of 1.71 mg/m3 and increasing optimum moisture content at 16.38%. this result happened due to the optimum and peak reaction achieved in 15.0 % of geopolymer in laterite soil. the structure of silica-alumina in geopolymerization was lost due to increased moisture content because of the rapid reaction between geopolymer and laterite soil, which led to the loss of water. this result is in good agreement with the noushini et al. [35] study of the behavior in laterite soil with sodium silicate-liquid stabilizer. based on the result obtained from this study in compaction parameters, the increased percentage of geopolymer added to laterite soil gives increasing mdd and decreasing omc. it was observed that the presence of a geopolymer in laterite 76 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 soil gave a strong relationship between moisture content and maximum dry density shows the compaction curve of tested samples. fig. 9: standard proctor machine and compaction sample. fig. 10: compaction curve of laterite soil with different percentages of geopolymer. 3.3 unconfined compression test (uct) soil compaction has direct effects on soil physical properties such as bulk density, strength, and porosity [36]. therefore, the ls-15.0 gpoba sample that gave the best value of maximum dry density (mdd) of 2.23 mg/m3 was directly chosen as the optimum percentage to determine the soil strength using an unconfined compression test (uct). in this study, the effect of compressive force on sample ls–15.0 gpoba was investigated at different curing times of zero, seven, and twenty-eight days. the samples were compacted under moisture content based on the compaction parameter of ls15.0 gpoba, which was 13.70%. the pieces were cured at ambient temperature (27°c to 30°c) reflecting the field conditions. the soil sample took on a hardened state after compacting. during the curing time, chemical reactions were expected to happen between the soil grain and the geopolymer molecules. table 5 shows the samples from lowest strength at zero day of curing (47 kpa) after seven days of curing (58 kpa). 0 0.5 1 1.5 2 2.5 0 5 10 15 20 25 30 35 d r y d e n si ty ( m g /m 3 ) moisture content (%) blank soil 5% poba + soil 10% poba + soil 15% poba + soil 20% poba + soil 77 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 fig. 11: (a) zero days, (b) seven days, (c) twenty-eight days of uct. the soil sample obtained after twenty-eight days achieved the highest compressive strength of 76 kpa. fig.12 showed a slight increase in compressive strength in increasing curing times of zero to twenty-eight days. the result is similar to previous studies [30,3738], where it shows the increment of compressive strength that proves the improvement of the geopolymerization process along the curing time. according to emdadi et al. [18] the form of aluminosilicate and alkaline influences the effect of compressive force in geopolymer. based on the result in this study, palm oil boiler ash (poba) that contains a high percentage of silica can be used as pozzolanic materials to enhance the shear strength of soils. the geotechnical technology using a geopolymer can be a potential study and practice in applying soil strength such as soil slope, embankment, and landfill soil liner. table 5: shear parameters of laterite soil with 15% of geopolymer at curing times of zero, seven, and twenty -nine days condition curing time (days) shear strength (kpa) ucs (kpa) 0 47 94 7 58 132 28 76 153 fig. 12: the comparison of soil strength (ls-15.0 gpoba) at zero, seven, and twenty-eight days of curing time. 0 10 20 30 40 50 60 70 80 0 7 28 c o m p re si v e s tr e n g th (k p a ) curing days a b c 78 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 3.2 microstructure of materials fig 13 shows the morphological features of plain laterite soil (ls-p) and fig 14 shows the laterite soil with 15% of geopolymer (ls.15.0 gpoba) at a curing time of zero days. the test was examined using scanning electron machine analysis using magnifying power 5000x at the faculty of chemical engineering in uitm johor campus, pasir gudang, johor, malaysia. as seen in fig. 13, the structure layered with larger voids led to low compressive strength. the microstructure of the laterite soil without geopolymer can be found to be loose and not uniform; cracks and pores are observed between soil particles. meanwhile, in fig. 14 some particles show popcorn type and spherical type. moreover, the structure of laterite soil with a geopolymer demonstrated a denser geopolymer matrix after the geopolymerization process with less pores compare to blank laterite. in the study by temujun et al. [39] the soil structure becomes compact causing higher packing density, low porosity in microstructure, and leading to higher strength. fig. 13: sem samples of plain laterite (ls-p). fig. 14: sem samples of laterite soil with 15% of geopolymer (ls.15.0 gpoba). pores pore/incomplete geopolymer geopolymer paste cracks 79 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 4. conclusion this paper examines the influence of geopolymers on the properties of laterite soil to be applied in the field of geotechnical application. the palm oil boiler ash combined with an alkaline solution at a constant ratio to form a geopolymer binder has shown to have a beneficial effect on compaction and high compressive strength by improving the properties of the laterite soil. based on the results of the study, the effective percentage of geopolymer in laterite soil was found at 15% that generated a maximum dry density of 2.23 mg/m3 at 13.58% optimum moisture content which gave a good compaction parameter leading to the high strength of soil properties. the uct was only conducted on the sample of ls.15.0 gpoba, which offered the highest mdd. samples were cured in a plastic bag at ambient temperature to suit field conditions at zero, seven, and twenty-eight days accordingly. based on the experimental data, the compressive strength of the geopolymer slightly increased as curing days increased on zero, seven, and twenty-eight and gave the strength of 47, 58, and 76kpa, respectively. based on sem test, it is apparent that it is due to the geopolymerization process that makes the sample harder and denser, which improves the soil strength. the sem images have proven that the development of geopolymer gel in laterite soil has stabilized the soil structure from a loose structure to a denser soil structure. thus, geopolymer-based palm oil boiler ash and laterite soil may be a potential by-product as an alternative to soil treatment in geotechnical applications that minimize porosity and potentially reduce permeability. acknowledgement the author would like to acknowledge the help of associate professor dr. ts. mazidah mukri as a post-graduate supervisor in this study. this work is also supported by the faculty of civil engineering and faculty of chemical engineering, uitm johor campus, pasir gudang for their facilities in the testing laboratory. references [1] hai tc, ng a, prudente c, pang c, tek choon yess, j. (2001) balancing the need for sustainable oil palm development and conservation: the lower kinabatangan floodplains experience. strategic directions for the sustainability of the oil palm industry, 53 pp. retrieved from http://assets.panda.org/downloads/balancingtheneed.pdf [2] abdullah n, sulaim f. (2013) the oil palm wastes in malaysia. in biomass now sustainable growth and use. intech. https://doi.org/10.5772/55302 [3] mangi,sa, ibrahim mhw, jamaluddin n, arshad mf, memon, fa, jaya rp, shahidan s. (2018) a review on potential use of coal bottom ash as a supplementary cementing material in sustainable concrete construction. international journal of integrated engineering, 10(9): 127-135. https://doi.org/10.30880/ijie.2018.10.09.006 [4] deraman lm, al bakri abdullah,mm, ming ly, hussin k, yahya z. (2015) a review on processing and properties of bottom ash based geopolymer materials. in key engineering materials, 660: 3-8. https://doi.org/10.4028/www.scientific.net/kem.660.3 [5] davidovits j. (2005) geopolymer, green chemistry and sustainable development solutions. in j. davidovits (ed.), proceedings of the world congress geopolymer 2005 (p. 236). institut geopolymere. [6] wattimena ok, antoni, hardjito d. (2017) a review on the effect of fly ash characteristics and their variations on the synthesis of fly ash based geopolymer. in aip conference proceedings, 1887: 020041. https://doi.org/10.1063/1.5003524 [7] h xu, van deventer jsj. (2000) the geopolymerisation of alumina-silicate minerals. int. j. miner. process., 59(3): 247-266. 80 https://doi.org/10.4028/www.scientific.net/kem.660.3 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 [8] van jaarsveld jgs, van deventer jsj, lorenzen l. (1997) potential use of geopolymeric materials to immobilize toxic metals: part i. theory and applications, miner. eng., 10(7): 659-669. [9] kanesan d, ridha s, rao p. (2017) formulation of geopolymer cement using mixture of slag and class f fly ash for oil well cementing. in iop conference series: materials science and engineering, 201: 012014. https://doi.org/10.1088/1757-899x/201/1/012014 [10] nanavati s, chetan nanavati s, jaywant lulla s, ranjeet singh a, bharat mehta d, mohan patel a, author c. (2017) a review on fly ash based geopolymer concrete. iosr journal of mechanical and civil engineering, 14(4): 12-16. https://doi.org/10.9790/1684-1404071216 [11] kabir sma, alengaram uj, jumaat mz, sharmin a, islam a. (2015) influence of molarity and chemical composition on the development of compressive strength in pofa based geopolymer mortar. advances in materials science and engineering, 2015: 647071 https://doi.org/10.1155/2015/647071. [12] yahya z, abdullah mmab, hussin k, ismail kn, razak ra, sandu av. (2015) effect of solids-to-liquids, na2sio3-to-naoh and curing temperature on the palm oil boiler ash (si + ca) geopolymerisation system. materials, 8(5): 2227-2242. https://doi.org/10.3390/ma8052227. [13] lopez e., vega-zamanillo a., calzada perez m.a., & hernandez-sanz a. (2015). bearing capacity of bottom ash and its mixture with soils. soils and foundations, 55, 529–535. https://doi.org/10.1016/j.sandf.2015.04.005 [14] jindal b. b. (2019). investigations on the properties of geopolymer mortar and concrete with mineral admixtures: a review. construction and building materials. elsevier ltd. https://doi.org/10.1016/j.conbuildmat.2019.08.025. [15] ma c. k, awan, a. z., & omar w. (2018). structural and material performance of geopolymer concrete: a review. construction and building materials. elsevier ltd. https://doi.org/10.1016/j.conbuildmat.2018.07.111. [16] duchesne j., duong l., bostrom t., & frost r. (2010). microstructure study of early in situ reaction of fly ash geopolymer observed by environmental scanning electron microscopy (esem). waste and biomass valorization, 1(3), 367–377. https://doi.org/10.1007/s1264910-9036-4. [17] khan, h., purohit, d., bagara, d., & pahadiya, h.s. (2016). geopolymer concrete with replacement of cement. international journal of engineering research & technology (ijert) 4-23. [18] emdadi, z., asim, n., amin, m. h., yarmo, m. a., maleki, a., azizi, m., & sopian, k. (2017). development of green geopolymer using agricultural and industrial waste materials with high water absorbency. applied sciences (switzerland), 7(5). https://doi.org/10.3390/app7050514. [19] puertas, f. & martıinez-ramıirez, s & alonso, s & vazquez, t. (2000). alkali-activated fly ash/slag cement strength behavior and hydration products. cement and concrete research. 301. 1625-1632. [20] skvara, f., kopecky, l., nemecek, j., & bittnar, z. (2006). microstructure of geopolymer materials based on fly ash. ceramics silikaty, 50(4), 208–215. [21] rosli, ros, nadiah. (2017). properties of laterite soils from sources near nibong tebal, malaysia. conference: icontes vistana hotel kuala lumpur https://www.researchgate.net/publication/324720622 [22] sujeeth, ahmed. (2015). an investigation into the geotechnical engineering properties of laterite soils in nilai, malaysia. 10.13140/rg.2.2.20036.04489. [23] marto, a., latifi, n., & sohaei, h. (2013). stabilization of laterite soil using gks soil stabilizer. electronic journal of geotechnical engineering, 18 c, 521–532. [24] parikshith, m. v., & sekhar, d. c. (2019). feasibility of fly-ash based geopolymer for soil stabilization. international journal of innovative technology and exploring engineering, 9(1), 4348–4351. https://doi.org/10.35940/ijitee.a5019.119119 [25] mukri, m., aziz, n. n. s., & khalid, n. (2018). geopolymer effect in modelling hydraulic conductivity for designing soil liner of laterite soil. international journal of civil engineering and technology, 9(7), 1962–1974. 81 https://doi.org/10.1088/1757-899x/201/1/012014 https://doi.org/10.1155/2015/647071 https://doi.org/10.3390/ma8052227 iium engineering journal, vol. 22, no. 2, 2021 zainuddin et al. https://doi.org/10.31436/iiumej.v22i2.1589 [26] liu, z., cai, c. s., liu, f., & fan, f. (2016). feasibility study of loess stabilization with fly ash-based geopolymer. journal of materials in civil engineering, 28(5). https://doi.org/10.1061/(asce)mt.1943-5533.0001490. [27] nikolic, i., zejak, r., radmilovic, v., blecic, d., & tadic, m. (2012). geopolymerization of fly ash as a possible solution for stabilization of used sandblasting grit. [28] thiha, s., lertsuriyakul, c., & phueakphum, d. (2018). shear strength enhancement of compacted soils using high-calcium fly ash-based geopolymer. international journal of geomate, 15(48), 1–9. https://doi.org/10.21660/2018.48.35692 [29] dheyab, w., ismael, z. t., hussein, m. a., & huat, b. b. k. (2019). soil stabilization with geopolymers for low cost and environmentally friendly construction. international journal of geomate, 17(63), 271–280. https://doi.org/10.21660/2019.63.8159 [30] nik ab aziz, n. n. s., mukri, m., hashim, s., & khalid, n. (2015). influence of compaction effort for laterite soil mix with geopolymer in designing soil liner. electronic journal of geotechnical engineering, 20(22), 12353–12364. [31] ahmad, f. h., mukri, m., & azmi, n. a. c. (2017). effectiveness of different percentage of bentonite in soil liner on interface shear strength with geosynthetic. international journal of applied engineering research, 12(7), 1360–1364. [32] ashraf, m. a., hossen, m. a., ali, m. a., & chakaraborty, b. p. (2018). stabilization of soil by mixing with different percentages of lime, 1–10. the 4th international conference on civil engineering for sustainable development [33] zhou, s. q., zhou, d. w., zhang, y. f., & wang, w. j. (2019). study on physicalmechanical properties and microstructure of expansive soil stabilized with fly ash and lime. advances in civil engineering. https://doi.org/10.1155/2019/4693757 [34] fattah, m., y., al-saidi, a., and jaber, m. (2014) consolidation properties of compacted soft soil stabilized with lime-silica fume mix. international journal of scientific & engineering research, 5, 1675-1682. [35] noushini, a., & castel, a. (2016). the effect of heat-curing on transport properties of low-calcium fly ash-based geopolymer concrete. construction and building materials, 112, 464–477. https://doi.org/10.1016/j.conbuildmat.2016.02.210. [36] nawaz, m. f., bourrié, g., & trolard, f. (2013). soil compaction impact and modelling. a review. agronomy for sustainable development, 33(2), 291–309. https://doi.org/10.1007/s13593-011-0071-8. [37] khale, d., & chaudhary, r. (2007). mechanism of geopolymerization and factors influencing its development: a review. journal of materials science, 42(3), 729–746. https://doi.org/10.1007/s10853-006-0401-4. [38] alvarez-ayuso, e., querol, x., plana, f., alastuey, a., moreno, n., izquierdo, m., barra, m. (2008). environmental, physical and structural characterization of geopolymer matrixes synthesized from coal (co-)combustion fly ashes. journal of hazardous materials, 154(1– 3), 175–183. https://doi.org/10.1016/j.jhazmat.2007.10.008 [39] temuujin, j., & van riessen, a. (2009). effect of fly ash preliminary calcination on the properties of geopolymer. journal of hazardous materials, 164(2–3), 634–639. https://doi.org/10.1016/j.jhazmat.2008.08.065. 82 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 251 numerical study of thermal characteristics of fuel oil-alumina and water-alumina nanofluid flow in a channel in the laminar flow hossein fatahian1*, hesamoddin salarian1, majid eshagh nimvari2 and esmaeel fatahian1 1 department of mechanical engineeing, nour branch, islamic azad university, nour, iran 2 faculty of engineeing, amol university of special modern technologies, amol, iran. * corresponding author: fatahianhossein@gmail.com (received: 27th july 2017; accepted:10th march 2018; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.857 abstract: the present study investigated the thermal effects of the use of nanoparticles in the fuel-oil and water-based fluids, as well as the numerical simulation of laminar flow of fuel-oil-alumina and the water-alumina nanofluids in a channel. a second order discretization method was used for solving equations and a simple algorithm was applied for pressure-velocity coupling using fluent. effect of nanoparticle volume fraction and particles size in different reynolds numbers (900≤re≤2100) on the convective heat transfer coefficient was studied. the simulation was conducted for three different volume fractions and particle sizes in the laminar flow under constant heat flux. the results showed that adding nanoparticles to the base fluid caused an increase in the thermal conductivity ratio of the fluid, which was observed to a greater degree in the fuel oil-alumina nanofluid than in the water-alumina nanofluid. the increase in nanoparticle volume fraction caused an increase in the convective heat transfer coefficient and the nusselt number of the nanofluids. the significant point of this study was that in the same volume fraction, the effect of adding alumina nanoparticles to the fuel-oil-based fluid had more effect than adding these particles to water-based fluid, while the effect of increasing the reynolds number in the water-alumina nanofluid on convective heat transfer coefficient was greater than the fuel-oil-alumina. also, in the same reynolds number and volume fraction with increasing size of nanoparticles, the value of the convective heat transfer coefficient was decreased. the results of this study can be used in refineries and petrochemical industries where the fuel-oil fluid flows in the channels. abstrak: kajian ini adalah bagi mengkaji kesan haba terhadap penggunaan bahan bakar-minyak dan cecair asas-air dalam nanopartikel, juga menjalankan simulasi pengiraan aliran laminar bahan bakar-minyak-alumina dan cecair-nano air-alumina dalam saluran. kaedah berasingan kelas kedua telah digunakan bagi menyelesaikan persamaan dan algoritma simple telah diaplikasikan dalam gandingan kelajuan-tekanan menggunakan fluent. kesan jumlah pecahan nanopartikel dan pelbagai bilangan saiz zarah dalam bilangan reynolds (900≤re≤2100) pada pekali pemindahan haba perolakan telah dikaji. simulasi telah dijalankan pada tiga pecahan isipadu berlainan dan pada zarah dalam aliran laminar dengan fluks haba tetap. hasil kajian menunjukkan bahawa dengan penambahan nanopartikel dalam cecair-asas menyebabkan peningkatan nisbah daya pengaliran haba cecair pada cecair-nano bahan bakar-minyak-alumina iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 252 melebihi daripada cecair-nano air-alumina. penambahan pada pecahan isipadu nanopartikel ini menyebabkan peningkatan pada nilai pekali pemindahan haba perolakan dan bilangan nusselt dalam cecair-nano. perkara penting dalam kajian ini adalah pada pecahan isipadu sama, kesan penambahan nanopartikel alumina kepada cecair berasaskan minyak mempunyai kesan yang lebih besar daripada penambahan zarah-zarah ini kepada cecair berasaskan air. pada masa sama, kesan peningkatan bilangan reynolds dalam cecair-nano air-alumina pada pekali pemindahan haba perolakan lebih besar daripada kesan peningkatan bahan bakarminyak-alumina. selain itu, pada bilangan reynolds yang sama dan dengan peningkatan saiz nanopartikel pecahan isipadu, nilai pekali pemindahan haba perolakan turut menurun. hasil kajian ini boleh digunakan dalam industri penapisan dan petrokimia di mana bahan bakar cecair minyak mengalir dalam saluran. keywords: blood rheology; blood rheology; non-newtonian fluids; shear-thinning behavior; thixotropy 1. introduction heat transfer is a vital process in all industries around the world. low thermal conductivity of conventional heat transfer fluids such as water, oil, and ethylene glycol mixture is a serious limitation in improving the performance and compactness of engineering equipment [1]. nowadays, new strategies are used in order to improve the effective heat transfer behaviors of such fluids. using particles of nanometer dimensions in liquids is one of these strategies that led to the production of nanofluids. the term ‘nanofluid’ refers to a two-phase mixture with the continuous phase generally being a liquid and the dispersed phase constituting ‘nanoparticles’ i.e. extremely fine metallic particles of size below 100 nm [2]. numerous studies have revealed the advantages of nanofluids over base fluids regarding higher thermal conductivity. a theoretical analysis of nanofluid flow was reported by prasher et al. [3]. they compared the pressure drop of base fluids and nanofluids when the heat transfer coefficient for both fluids was equal. literature exists [4-10] on single-phase nanofluids forced convection flow in such various geometries as flat plates, circular tubes, noncircular channels, annuli, and cross flow over circular tubes. the previous results have underscored the enhancement of heat transfer due to the presence of nanoparticles in the fluids. xuan and li [11] and xuan and roetzel [12] have identified two causes of improved heat transfer by nanofluids: the increased thermal dispersion due to the chaotic movement of nanoparticles that accelerates energy exchanges in the fluid and the enhanced thermal conductivity of nanofluids. on the other hand kelbinski et al. [13] studied four possible mechanisms that contribute to the increase in nanofluid heat transfer: brownian motion of the particles, molecular-level layering of the liquid/particle interface, heat transport in the nanoparticles, and nanoparticle clustering. similarly to wang et al. [14], they showed that the effects of the interface layering of liquid molecule and nanoparticle clustering could provide paths for rapid heat transfer. pak and cho [15] investigated the heat transfer performance of al2 o3-g and tio2 nanoparticles dispersed in water inside a horizontal tube. they observed that an increase in re number and particle concentration leads to an increase in nu number, but the convective heat transfer coefficient of nanofluid with 3% volume fraction decreases by 12% compared to the base fluid. li et al. [16,17] also experimentally studied the convective heat transfer of cuo/water nanofluid inside a horizontal tube with constant heat flux in both laminar and turbulent regimes. their studies showed that the suspended iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 253 nanoparticles enhanced the convectional heat transfer performance of the base fluid. sankar et al. [18] simulated the variation of the thermal conductivity in nanofluids using a molecular dynamics approach. zhao et al. [19] concluded that the addition of solid nanoparticles with high thermal conductivity and the phenomenon of micro convection, caused by a nonuniform shear stress in a nanofluids, are the main factors in the enhancement of heat transfer coefficients. khaled and vafai [20] investigated the effect of thermal dispersion on heat transfer enhancement of nanofluids. wen and ding [21] were first to develop a theoretical model to predict particle migration in pressure-driven laminar pipe flows of relatively dilute nanofluids. they showed that shear induced, viscosity gradient-induced, and concentration gradient-induced particle migration results in the large radial variation of particle distribution, viscosity, and thermal conductivity. maiga et al. [22] numerically studied the hydrodynamic and thermal behavior of turbulent flow in a tube using the al2o3/water nanofluid under the constant heat flux boundary condition. in their study, a new correlation is proposed to calculate the fully developed heat transfer coefficient for the nanofluid considered. rostamani et al. [23] simulated the turbulent flow of copper oxide (cuo), alumina (al2o3), and oxide titanium (tio2) nanofluids with different volume concentrations of nanoparticles flowing through a two-dimensional duct under constant heat flux condition. their results showed that the cuo/water and tio2/water nanofluids have the highest and lowest shear stress values, respectively, due to the higher viscosity of copper oxide (cuo) in comparison to other nanofluids. moghari et al. [24] numerically studied the pressure drop and thermal characteristics of al2o3-water nanofluid flow in horizontal annuli under constant heat flux boundary conditions applied to both inner and outer walls. they analyzed the effects of nanoparticle volume fraction, heat flux ratio, radius ratio, and grashof number on heat transfer and showed that nusselt number increases with the increase of nanoparticle volume fraction, heat flux, radius ratios, and grashof number. celik et al. [25] investigated laminar mixed convection in a two dimensional symmetrically and partially heated vertical channel and also noted that aluminum oxide/water nanofluid was considered as working fluid. their results showed that the use of nanoparticles in fluid increases heat transfer rate in the channels. also, the rate of increase depends on both the reynolds and the richardson numbers. in this study, two-dimensional laminar flow of fuel-oil-alumina and water-alumina nanofluids in a channel was conducted. the main reason for choosing fuel oil-alumina nanofluid was that nanoparticles are used as additives to engine oils in order to remove more heat from the high heat flux parts of engines [26, 27]. these additives also have shown anti wear and anti-friction characteristics due to their spherical shapes [28]. for this purpose the effect of nanoparticle volume fraction and particles size in different reynolds numbers (900≤re≤2100) on convective heat transfer coefficient has been studied. the simulation was conducted for three volume fractions of 1%, 3%, and 6% and particle size of 60 nm, 90 nm, and 150 nm under laminar flow with a constant thermal flux of 8846.4 w/m2. for validation, the results of this study had compared with the experimental data of anoop et al. [29] and numerical results of moraveji et al. [30]. 2. geometry and boundary conditions figure 1 shows the geometry of the channel [30]. the input side of the channel was considered as the inlet velocity boundary condition and the output side was considered as the outlet pressure boundary condition. a laminar flow regime was considered under boundary condition of constant temperature at the inlet and constant thermal flux was considered on the walls of channel. also, a no-slip boundary condition was considered on the walls. in this simulation, the flow regime was laminar and the analysis was done for iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 254 the reynolds numbers of 900≤re≤2100. the inlet temperature was 300 k and the constant thermal flux was 8846.4 w/m2 on the walls of channel. fig. 1: schematic geometry of channel [30]. 3. the basic governing equation on nanofluid flow finding the thermophysical properties of nanofluids is one of the most important issues in simulating the flow and heat transfer of nanofluids. among these properties, it can be noted that study results are significantly dependent on the actual values for the viscosity and thermal conductivity coefficient. the assumption of a single-phase model was considered and the simulation was carried out for the steady state of fluid flow in this channel. also, the conservation equations are shown respectively below including conservation of mass, conservation of momentum, and conservation of energy. 𝛻. (𝜌𝑛𝑓 𝑉) = 0 (1) 𝛻. (𝜌𝑛𝑓 𝑉𝑉) = −𝛻𝑃 + 𝛻. (𝜇𝑛𝑓 𝛻𝑉) (2) 𝛻. (𝜌𝑛𝑓 𝐶𝑉𝑇) = 𝛻. (𝑘𝑛𝑓 𝛻𝑇) (3) 4. equations of nanofluid properties for solving the conservation equations, determination of the thermophysical properties of nanofluids such as density, specific thermal coefficient, and thermal conductivity coefficient is required. in this study, different relations were proposed to determine these characteristics. 𝜌𝑛𝑓 = (1 − 𝜑)𝜌𝑓 + 𝜑𝜌𝑠 (4) (𝜌𝛽)𝑛𝑓 = (1 − 𝜑)(𝜌𝛽)𝑓 + 𝜑𝛽𝜌𝑠 (5) (𝜌𝐶𝑝)𝑛𝑓 = (1 − 𝜑)(𝜌𝐶𝑝)𝑓 + ( 𝜌𝐶𝑝)𝑠 (6) 𝛼𝑛𝑓 = 𝑘𝑛𝑓 ( 𝜌𝐶𝑝)𝑛𝑓 (7) where φ is the volume fraction of particle and the nf, f, and p indices represent the nanofluid, base fluid, and particle respectively. pak et al. [31] experimentally showed that eq. (4) is a precise definition of the nanofluid density. for solving the equations, the nanofluid thermophysical properties were required. density, volumetric expansion coefficient, heat capacity, and thermal diffusion coefficient of the nanofluid were calculated from the following relations [32] with the help of fluid and nanoparticle properties. for nanofluid viscosity, various relations were presented in the references where the brinkman relation [32] is more interesting for researchers than other relations. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 255 𝜇𝑛𝑓 = 𝜇𝑓 (1−𝜑)2.5 (8) several formulas were presented for nanofluid thermal conductivity coefficient but the formula presented by patel et al. [33] was used here. 𝑘𝑒𝑓𝑓 = 𝑘𝑓 [1 + 𝑘𝑠𝐴𝑠 𝑘𝑓𝐴𝑓 + 𝑐𝑘𝑠 𝑃𝑒 𝐴𝑠 𝑘𝑓𝐴𝑓 ] (9) in this relation, ks = 36 w/m.k is the thermal conductivity coefficient for alumina and kf = 0.6 w/m.k is the thermal conductivity coefficient for water. these properties with other required properties for water and alumina nanoparticles are presented in table 1. c is an experimental constant and equals to 36000 which is reported by santra et al. [34]. in this relation, the as/af ratio was calculated as follows: 𝐴𝑠 𝐴𝑓 = 𝑑𝑓 𝑑𝑠 ∅ 1−∅ (10) the diameter of the solid nanoparticles was 60 nm, 90 nm, and 150 nm. the following formula had used to calculate the molecular diameter [27]. 𝑑𝑓 = [ 6𝑀 𝑁𝜋𝜌𝑓 ] 1 3⁄ (11) where in this relation, m is the molecular mass of the base fluid and n is avogadro number which is equal to 6.022 × 10-23 mol-1. also in eqn. (9), pe was calculated as: 𝑃𝑒 = 𝑢𝑠𝑑𝑠 𝛼𝑓 (12) in this relation, us is the brownian motion velocity of the nanoparticles which is expressed by the following equation: 𝑢𝑠 = 2𝑘𝑏𝑇 𝜋𝜇𝑓𝑑𝑠 2 (13) where kb is boltzmann constant, kb = 1.3807 × 10 -23 j/k. the following equations were used to calculate the heat transfer coefficient and the nusselt number. 𝑁𝑢 = ℎ(𝑥)𝐷 𝑘 (14) ℎ(𝑥) = 𝑞" (𝑇𝑤(𝑥)−𝑇𝑓(𝑥) (15) where q”, d, k, tw and tf are the heat flux, diameter, fluid thermal conductivity, wall temperature, and film temperature along the wall in an axial position. the physical properties of alumina, water-based fluid and fuel-oil-based fluids such as density, specific heat, thermal conductivity coefficient, and viscosity are given in table 1. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 256 5. numerical method in this study, the second-order upwind method was used because it provides more accurate results. the coupling between velocity and pressure terms was handled using the semi-implicit method for pressure linked equations (simple) algorithm. the assumption of a single-phase model was considered and simulation was done for the steady-state flow of fluid in the channel. the general form of conservation equations is similar to ordinary fluids in the single-phase method but for the density, thermal conductivity, viscosity and specific heat, the apparent properties of the nanofluid were used. in this method, the slip between the base fluid and the nanoparticles was ignored and the effect of the presence of particles on the apparent properties was seen. table 1: the physical properties of alumina, fuel-oil-based fluid and water-based fluid µ [kg/m.s] k [w/m. k] cp [j/kg. k] ρ [kg/m3] properties 36 765 3600 alumina 0.048 0.12 1880 960 fuel-oil 0.001003 0.6 4182 998.2 water 6. grid independence in the present study, four different grids were generated for the channel in order to investigate the grid independence and the results for the four grids were compared. the numbers of nodes were 7590, 10263, 13728, and 25309 respectively, and these were used to calculate the heat transfer coefficient in terms of the reynolds number. then, for comparing the results with other grids, it was observed that there was little difference between the finest grid and the grid with 13728 nodes. therefore, in order to save calculation time, the grid with 13728 nodes was used to obtain the results. figure 2 shows the details of grid independence. fig. 2: grid independence study. 7. validation in general, experimental study of nanofluids is a very extensive research and there are multiple variables, the most important among them are thermal conductivity and viscosity. different researches had reported different values for these variables, as well as their dependence on each other or on other variables according to different experimental conditions. various relations, or mathematical models, were presented in this field that iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 257 indicated the same variety of results in the research. the experimental data of anoop et al. [29] and numerical results of moraveji et al. [30] were considered for validation in the present study which the changes of convective heat transfer coefficient were investigated based on the reynolds number (fig. 3). the geometry of the study of moraveji et al. [30] is the same as the experimental study of anoop et al. [29]. the results showed that the present study was in good agreement with the experimental data of anoop et al. [29] and numerical results of moraveji et al. [30]. fig. 3: comparing the changes of convective heat transfer coefficient based on the reynolds number with the experimental data of anoop et al. [29] and numerical results of moraveji et al. [30]. 8. results and discussion 8.1 the changes in the thermal conductivity ratio based on the percentages of the volume fraction of nanoparticles figure 4 shows the increase in thermal conductivity rate based on the volume fraction percentages of nanoparticles for water-alumina and fuel-oil-alumina nanofluids as calculated from the formula provided by patel et al. [33]. as can be seen, the thermal conductivity rate is greater than 1 for all nanofluids and it increases by increasing the volume fraction of nanoparticles [35]. the highest rate of increase is for the fuel-oilalumina nanofluid with a volume fraction of 6% and a particle size of 60 nm. it should be noted that the effective thermal conductivity of nanofluids depends on the thermal conductivity of solid particles and the base fluid, the volume fraction of the particle, particle shape, thickness, and thermal conductivity of the nano layer [36]. also, thermal conductivity depends on the particle size, nanoparticle density, and the combination of characteristics of the base fluid and the nanoparticles [37, 38]. fig. 4: the changes of thermal conductivity rate based on the percentages of the volume fraction of nanoparticles. 200 300 400 500 600 700 800 900 900 1100 1300 1500 1700 1900 h ( w /m 2 -k ) re present study-pure water anoop et al. [29]-pure water moraveji et al. [30]-pure water iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 258 8.2 the changes in the nusselt number based on the percentages of the volume fraction of nanoparticles figures 5, 6 and 7 show the changes in the nusselt number based on the reynolds number for the nanofluid with particles of 60 nm, 90 nm, and 150 nm in volume fractions of 1%, 3%, 6%, and base fluid (pure water). as can be seen, the nusselt number increases with the increasing reynolds number and increasing volume fraction of nanoparticles so that this increase is more remarkable at high reynolds numbers. this increase is very low for a volume fraction of 1% but a significant increase can be observed by increasing the nanoparticle density to 6%. the nusselt number increases about 16% in a volume fraction of 6% and at reynolds number of 2100 for nanofluid with particles of 60 nm compared to base fluid, for a nanofluid with particles of 90 nm, about 12% compared to base fluid and for nanofluid with particles of 150 nm, about 9% compared to base fluid. fig. 5: the changes in the nusselt number of water-based nanofluid with particles of 60 nm based on the reynolds number. fig. 6: the changes in the nusselt number of water-based nanofluid with particles of 90 nm based on the reynolds number. figures 8, 9 and 10 show the changes in the nusselt number based on the reynolds number for a nanofluid with particles of 60 nm, 90 nm, and 150 nm in volume fractions of 1%, 3%, 6%, and base fluid (fuel-oil). in these figures, the nusselt number increases significantly with increasing volume fraction of nanoparticles but it increases with a slight slope with increase in the reynolds number. this increase is very low for all particles, but a significant increase can be observed by increasing the nanoparticles density to 6%. in this way, the nusselt number increases about 56% in a volume fraction of 6% and at a 3 4 5 6 7 900 1100 1300 1500 1700 1900 2100 n u re pure water ϕ=1% ϕ=3% ϕ=6% 3 4 5 6 7 900 1100 1300 1500 1700 1900 2100 n u re pure water ϕ=1% ϕ=3% ϕ=6% iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 259 fig. 7: the changes in the nusselt number of water-based nanofluid with particles of 150 nm based on the reynolds number. fig. 8: the changes in the nusselt number of fuel-oil-based nanofluid with particles of 60 nm based on the reynolds number. fig. 9: the changes in the nusselt number of fuel-oil-based nanofluid with particles of 90 nm based on the reynolds number. reynolds number of 2100 for a nanofluid with particles of 60 nm compared to the base fluid, for a nanofluid with 90 nm particles, about 44% compared to base fluid, and for a nanofluid with particles of 150 nm about 33% compared to base fluid. 3 4 5 6 7 900 1100 1300 1500 1700 1900 2100 n u re pure water ϕ=1% ϕ=3% ϕ=6% 2 6 10 14 18 22 26 30 900 1100 1300 1500 1700 1900 2100 n u re fuel-oil ϕ=1% ϕ=3% ϕ=6% 4 8 12 16 20 24 900 1100 1300 1500 1700 1900 2100 n u re fuel-oil ϕ=1% ϕ=3% ϕ=6% iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 260 fig. 10: the changes in the nusselt number of fuel-oil-based nanofluid with particles of 150 nm based on the reynolds number. 8.3 effect of volume fraction of nanoparticles on convective heat transfer coefficient figures 11, 12 and 13 show the changes in the convective heat transfer coefficient based on the reynolds number for nanofluids with particles of 60 nm, 90 nm, and 150 nm of alumina with volume fractions of 1%, 3%, 6%, and base fluid (pure water). by increasing the nanoparticle density with particles of 60 nm, 90 nm, and 150 nm from 1% to 6% at the reynolds number of 2100, the convective heat transfer coefficient has its highest rate of increase. by comparing the figures, it can be found that convective heat transfer coefficient increases with the reduction of particle size. experiments showed that convective heat transfer coefficient increased by adding nanoparticles to the base fluid. the reasons for this increase are related to the increase in the turbulence of the vortices, the reduction of the boundary layer thickness, the inverse dispersion of suspended nanoparticles, the significant increase in the thermal conductivity and the thermal capacity of the fluid. [39]. as can be seen, the convective heat transfer coefficient increases significantly by increasing the reynolds number. regardless of the significant increase in convective heat transfer coefficient of a nanofluid with increasing reynolds number, it is observed that this coefficient increases simultaneously with a decrease in particle size for a constant reynolds number. the distance between the curves in fig. 13 is greater than fig. 11 and fig. 12. in the other words, the effect of particle size on the convective heat transfer coefficient of a nanofluid is greater at higher reynolds numbers in the present study. therefore, reducing particle size has a better effect on increasing the convective heat transfer coefficient of nanofluids at higher reynolds numbers. another point that can be derived from the figures is that by increasing the reynolds number and for constant sizes of nanoparticles, higher nanoparticle density is needed to achieve higher heat transfer coefficients but at lower reynolds numbers, the use of lower nanoparticle density also has a good effect on increasing heat transfer coefficient. 8 10 12 14 16 18 20 22 900 1100 1300 1500 1700 1900 2100 n u re fuel-oil ϕ=1% ϕ=3% ϕ=6% iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 261 fig. 11: the effect of particle volume fraction and reynolds number on convective heat transfer coefficient for particles of 60 nm. fig. 12: the effect of particle volume fraction and reynolds number on convective heat transfer coefficient for particles of 90 nm. fig. 13: the effect of particle volume fraction and reynolds number on convective heat transfer coefficient for particles of 150 nm. figure 14, 15 and 16 show the changes of convective heat transfer coefficient based on reynolds number for nanofluid with particles of 60 nm, 90 nm and 150 nm of alumina with volume fractions of 1%, 3%, 6%, and base fluid (fuel-oil). it can be seen that with the increase in the reynolds number, the convective heat transfer coefficient is increased with a slight slope. for example, the convective heat transfer coefficient is 723.23 at  = 6% and re=900 and it is 762.78 at  = 6%, and re=2100 for nanoparticles of 60 nm, which is increased by about 5%. the convective heat transfer coefficient increases with the increase of volume fraction of nanoparticles [34]. therefore, the increase in the convective heat 400 500 600 700 800 900 900 1100 1300 1500 1700 1900 2100 h ( w /m 2 -k ) re pure water ϕ=1% ϕ=3% ϕ=6% 400 500 600 700 800 900 900 1100 1300 1500 1700 1900 2100 h ( w /m 2 -k ) re pure water ϕ=1% ϕ=3% ϕ=6% 400 500 600 700 800 900 1100 1300 1500 1700 1900 2100 h ( w /m 2 -k ) re pure water ϕ=1% ϕ=3% ϕ=6% iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 262 transfer coefficient is observed to be about 55% at  = 6% and re=2100. the remarkable point is that at the same reynolds number and volume fraction, the amount of convective transfer heat transfer coefficient is decreased with the increase of the size of the nanoparticles. fig. 14: the effect of particle volume fraction and reynolds number on convective heat transfer coefficient for particles of 60 nm. fig. 15: the effect of particle volume fraction and reynolds number on convective heat transfer coefficient for particles of 90 nm. fig. 16: the effect of particle volume fraction and reynolds number on convective heat transfer coefficient for particles of 150 nm. 100 200 300 400 500 600 700 900 1100 1300 1500 1700 1900 2100 h (w /m 2 -k ) re fuel-oil ϕ=1% ϕ=3% ϕ=6% 100 200 300 400 500 600 700 900 1100 1300 1500 1700 1900 2100 h (w /m 2 -k ) re fuel-oil ϕ=1% ϕ=3% ϕ=6% 200 300 400 500 900 1100 1300 1500 1700 1900 2100 h (w /m 2 -k ) re fuel-oil ϕ=1% ϕ=3% ϕ=6% iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 263 8.4 effect of nanoparticle size on nusselt number figure 17 shows the changes in the nusselt number for a nanofluid with particles of 60 nm, 90 nm, and 150 nm with volume fraction of 1% and water-based fluid at reynolds numbers from 900 to 2100. it is concluded from the figures that smaller nanoparticles have a larger nusselt number than larger nanoparticles. so that it is increased about 20% at  = 1% and re=2100 for nanoparticles of 60 nm but it is increased about 15% for nanoparticles of 90 nm at  = 1% and re=2100 and for nanoparticles of 150 nm at  = 1% and re=2100, it is increased about 10% higher than the base fluid. also, the increase of reynolds number causes an increase in the nusselt number and the maximum amount of increase in the nusselt number is for nanoparticles of 60 nm is about 29%. fig. 17: comparing the changes in the nusselt number for a water-based nanofluid with particles of 60 nm, 90 nm, and 150 nm with a volume fraction of 1% and water-based fluid. figure 18 shows the changes of nusselt number for a nanofluid with particles of 60 nm, 90 nm, and 150 nm with volume fraction of 1% and fuel-oil-based fluid at reynolds numbers from 900 to 2100. as the reynolds number increases, the nusselt number increases with a slight slope. it is concluded from the figures that smaller nanoparticles have a larger nusselt numbers than larger nanoparticles. it is increased about 16% at  = 1% and re=2100 for nanoparticles of 60 nm but it is increased about 13% for nanoparticles of 90 nm at  = 1% and re=2100 and for nanoparticles of 150 nm at  = 1% and re=2100, it is increased about 7% higher than the base fluid. fig. 18: comparing the changes of nusselt number for fuel-oil-based nanofluid with particles of 60 nm, 90 nm, and 150 nm with a volume fraction of 1% and fuel-oil based fluid. 3.5 4 4.5 5 5.5 6 6.5 900 1100 1300 1500 1700 1900 2100 n u re pure water 60nm-ϕ=1% 90nm-ϕ=1% 150nm-ϕ=1% 11 12 13 14 15 16 900 1100 1300 1500 1700 1900 2100 n u re fuel-oil 60nm-ϕ=1% 90nm-ϕ=1% 150nm-ϕ=1% iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 264 8.5 effect of nanoparticle size on convective heat transfer coefficient figure 19 shows the changes of convective heat transfer coefficient for nanofluids with particles of 60 nm, 90 nm, and 150 nm with a volume fraction of 1% and water base fluid at reynolds numbers from 900 to 2100. it is quite obvious that nanofluids have higher convective heat transfer coefficient than the base fluid [29]. by increasing the reynolds number, the convective heat transfer coefficient increases with a large slope. also, smaller nanoparticles have larger nusselt numbers than larger nanoparticles. for example, it increases about 4% at  = 1% and re=2100 for nanoparticles of 60 nm, for nanoparticles of 90 nm at  = 1% and re=2100 it increases about 3% and for nanoparticles of 150 nm at  = 1% and re=2100 it increases about 2% than base fluid. the effect of the reynolds number on increasing the convective heat transfer coefficient is greater than the effect of nanoparticle size, so that the maximum amount of increase in convective heat transfer coefficient for nanoparticles of 60 nm and at a reynolds number of 2100 is about 28%. fig. 19: comparing the changes of convective heat transfer coefficient for water-based nanofluid with particles of 60 nm, 90 nm, and 150 nm with a volume fraction of 1% and water-based fluid. fig. 20: comparing the changes of convective heat transfer coefficient for fuel-oil base nanofluid with particles of 60 nm, 90 nm, and 150 nm with a volume fraction of 1% and fuel-oil based fluid. figure 20 shows the changes of convective heat transfer coefficient for nanofluids with particles of 60 nm, 90 nm and 150 nm with volume fractions of 1% and fuel-oil based 450 500 550 600 650 700 750 800 900 1100 1300 1500 1700 1900 2100 h ( w /m 2 -k ) re pure water 60 nm-ϕ=1% 90 nm-ϕ=1% 150 nm-ϕ=1% 300 315 330 345 360 375 390 405 900 1100 1300 1500 1700 1900 2100 h (w /m 2 -k ) re fuel-oil 60nm-ϕ=1% 90nm-ϕ=1% 150nm-ϕ=1% iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 265 fluids at reynolds numbers from 900 to 2100. by increasing the reynolds number, the convective heat transfer coefficient is increased and the slope of the increase in nanoparticles with smaller size is greater than in other cases. for example, it increases about 15% at  = 1% and re=2100 for nanoparticles of 60 nm but for nanoparticles of 90 nm at  = 1% and re=2100 it increases about 12% and for nanoparticles of 150 nm at  = 1% and re=2100 it increases about 7% compared to base fluid. 8.6 changes in the convective heat transfer coefficient based on axial position figure 21 shows the changes of nusselt number for a nanofluid with particles of 60 nm, 90 nm, and 150 nm with volume fraction of 1% and water base fluid based on the axial position. it is concluded from the figures that by increasing the axial position, convective heat transfer coefficient decreases so that the value of this coefficient in the inlet is more than the other parts [40], which is similar to the results of wen and ding [21] who studied nanofluid heat transfer in micro channels. this coefficient decreases significantly at the inlet of the channel and it decreases with a very small slope after 50% of the length of the channel. it is also observed that the nanofluid with smaller particles has a higher convective heat transfer coefficient than larger particles at the same axial position for a constant volume fraction. for example, convective heat transfer coefficient has decreased about 76% from the inlet to the outlet of the channel for particles of 60 nm. fig. 21: comparing the changes of convective heat transfer coefficient for water-based nanofluid with particles of 60 nm, 90 nm, and 150 nm with a volume fraction of 1% and water based fluid based on axial position. fig. 22: comparing the changes of convective heat transfer coefficient for fuel-oil-based nanofluid with particles of 60 nm, 90 nm, and 150 nm with a volume fraction of 1% and fuel-oil based fluid based on axial position. 400 600 800 1000 1200 1400 1600 1800 0.0 0.2 0.4 0.6 0.8 1.0 1.2 h ( w /m 2 -k ) x (m) pure water 60nm-ϕ=1% 90nm-ϕ=1% 150nm-ϕ=1% 320 340 360 380 400 420 440 0.0 0.3 0.6 0.9 1.2 h ( w /m 2 -k ) x (m) fuel-oil 60nm-ϕ=1% 90nm-ϕ=1% 150nm-ϕ=1% iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 266 figure 22 shows the changes of nusselt number for a nanofluid with particles of 60 nm, 90 nm, and 150 nm with volume fraction of 1% and fuel-oil base fluid based on the axial position. similar to water-based fluid, the value of the convective heat transfer coefficient in the inlet is more than the other parts [31]. also, this coefficient decreases by increasing the length of the channel but its reduction is not similar to the water-based fluid and it decreases with almost the same slope along the length of the channel. as it is clear, the amount of convective heat transfer is greater in nanoparticles with smaller sizes. 8.7 comparison of the changes of temperature at the end of the channel figures 23 and 24 show the changes in temperature at the end of the channel for water-alumina and fuel oil-alumina nanofluids at reynolds numbers of 900 and 2100 for a volume fraction of 6% and nanoparticles of 60 nm. nanofluids have heated through the channel wall, and their temperature is increased along the length of channel [30] so that a higher temperature is observed near the channel wall as compared to the other parts of the channel. little changes are observed at reynolds numbers of 900 and 2100 for fuel oilalumina nanofluid. also, the maximum temperature of nanofluid at a reynolds number of 900 is higher than at a reynolds number of 2100, because the convective heat transfer coefficient at higher reynolds numbers is higher than at low reynolds numbers [30]. fig. 23: the changes of temperature at the end of the channel for water-alumina nanofluid (60 nm-6%). fig. 24: the changes of temperature at the end of the channel for fuel oil-alumina (60 nm-6%). iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 267 9. conclusion in this study, convective heat transfer of fuel oil-alumina and water-alumina nanofluids flow in a channel in a laminar flow was conducted using fluent. the effects of nanoparticle volume fraction, nanoparticle size, axial position and the reynolds number on the convective heat transfer coefficient and the nusselt number were studied. the simulation was conducted for three volume fractions of 1%, 3% and 6% and particle sizes of 60 nm, 90 nm, and 150 nm in laminar flow with a constant thermal flux of 8846.4 w / m2 where the following results were obtained from this study:  increasing of the nanoparticle volume fraction causes an increase in the convective heat transfer coefficient and the nusselt number of the nanofluid.  the reynolds number has a significant effect on convective heat transfer coefficient of water-alumina nanofluid and increase of the reynolds number increases this coefficient. by increasing the reynolds number, convective heat transfer coefficient of fuel oil-alumina nanofluid slightly increases.  by increasing the axial position, the amount of convective heat transfer coefficient in both nanofluids decreases. it is also observed that in a constant volume fraction, a nanofluid with smaller particles has a higher convective heat transfer coefficient than larger particles in the same axial position.  according to the axial position, the amount of convective heat transfer coefficient at the inlet of the channel is more than in the other parts of the channel for wateralumina nanofluid and by increasing the axial position, this coefficient decreases with a large slope. the axial position of this coefficient is reduced with a large slope which the convective heat transfer coefficient decreases with almost the same slope along the channel for the fuel oil-alumina nanofluid.  the rate of thermal conductivity for all nanofluids is greater than 1 and this amount increases by increasing the volume fraction of nanoparticles so that the highest increase rate is for a fuel oil-alumina nanofluid in a volume fraction of 6% and a particle size of 60 nm.  the effect of the reynolds number on increasing the convective heat transfer coefficient for water-alumina nanofluid is more than the effect of nanoparticle size so that in a volume fraction of 1%, the highest increase rate for convective heat transfer coefficient is about 28% for nanoparticles of 60 nm and at a reynolds number of 2100. but for fuel oil-alumina nanofluid, the effect of increasing of the size of nanoparticles is greater than the effect of the increase in the reynolds number. the results of this study can be used in refineries and petrochemical industries where the fuel-oil fluid flows in channels. references [1] mirmasoumi s, behzadmehr a. (2008) numerical study of laminar mixed convection of a nanofluid in a horizontal tube using two-phase mixture model. applied thermal engineering, 28(7):717-727. [2] maı̈ga sb, nguyen ct, galanis n, roy g. (2004) heat transfer behaviors of nanofluids in a uniformly heated tube. superlattices and microstructures, 35(3):543-557. [3] prasher r, song d, wang j, phelan p. (2006) measurements of nanofluid viscosity and its implications for thermal applications. applied physics letters, 89(13):133-140. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 268 [4] bianco v, manca o, nardini s. (2011) numerical investigation on nanofluids turbulent convection heat transfer inside a circular tube. international journal of thermal sciences, 50(3):341-349. [5] bianco v, manca o, nardini s. (2010) numerical simulation of water/al2o3 nanofluid turbulent convection. advances in mechanical engineering, article id976254:1-10. [6] bianco v, nardini s, manca o. (2011) enhancement of heat transfer and entropy generation analysis of nanofluids turbulent convection flow in square section tubes. nanoscale research letters, 6(1):252-259. [7] corcione m, cianfrini m, quintino a. (2012) heat transfer of nanofluids in turbulent pipe flow. international journal of thermal sciences, 56(3):58-69. [8] rahimi-esbo m, ranjbar a. a, ramiar a, rahgoshay m, arya a. (2012) numerical study of the turbulent forced convection jet flow of nanofluid in a converging duct. numerical heat transfer, part a: applications, 62(1):60-79. [9] ghaffari o, behzadmehr a, ajam h. (2010) turbulent mixed convection of a nanofluid in a horizontal curved tube using a two-phase approach. international communications in heat and mass transfer, 37(10):1551-1558. [10] massoudi m, phuoc t x. (2012) remarks on constitutive modeling of nanofluids. advances in mechanical engineering, 4(1):90-105. [11] yimin x, li q. (2000) heat transfer enhancement of nanofluids. international journal of heat and fluid flow, 21(1):58-64. [12] yimin x, roetzel w. (2000) conceptions for heat transfer correlation of nanofluids. international journal of heat and mass transfer, 43(19):3701-3707. [13] keblinski p, phillpot sr, choi su, eastman ja. (2002) mechanisms of heat flow in suspensions of nano-sized particles (nanofluids). international journal of heat and mass transfer, 45(4):855-863. [14] wang x, xu x, choi su. (1999) thermal conductivity of nanoparticle-fluid mixture, journal of thermophysics and heat transfer, 13(2):474-480. [15] pak bc, cho yi. (1998) hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles. experimental heat transfer an international journal, 11(2):151-170. [16] li q, xuan y. (2002) convective heat transfer and flow characteristics of cu-water nanofluid. science in china series e: technological sciences, 45(4):408-416. [17] li q, xuan y, and wang j. (2003) investigation on convective heat transfer and flow features of nanofluids. journal of heat transfer, 125(2):151-155. [18] sankar n, mathew n, sobhan c b. (2008) molecular dynamics modeling of thermal conductivity enhancement in metal nanoparticle suspensions. international communications in heat and mass transfer, 35(7):867-872. [19] hao zn, zhao r, wang lr. (2005) analyses of physical mechanism and numerical simulation for micro-convection enhancement in the solid-liquid two phase flow, journal of engineering thermophysics, 26(1):656-658. [20] khaled a, vafai k. (2005) heat transfer enhancement through control of thermal dispersion effects. international journal of heat and mass transfer, 48(11):2172-2185. [21] dongsheng w, ding y. (2004) experimental investigation into convective heat transfer of nanofluids at the entrance region under laminar flow conditions. international journal of heat and mass transfer, 47(24):5181-5188. [22] maïga eb, sidi, nguyen ct, galanis n, roy g, maré t, coqueux m. (2006) heat transfer enhancement in turbulent tube flow using al2o3 nanoparticle suspension. international journal of numerical methods for heat & fluid flow, 16(3):275-292. [23] rostamani m, hosseinizadeh sf, gorji m, khodadadi jm. (2010) numerical study of turbulent forced convection flow of nanofluids in a long horizontal duct considering variable properties. international communications in heat and mass transfer, 37(10):1426-1431. [24] mokhtari r, talebi f, rafee r, shariat m. (2015) numerical study of pressure drop and thermal characteristics of al2o3–water nanofluid flow in horizontal annuli. heat transfer engineering 36(2):166-177. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 269 [25] celik h, mobedi m, manca o, buonomo b. (2018) enhancement of heat transfer in partially heated vertical channel under mixed convection by using al2o3 nanoparticles. heat transfer engineering, 39(3): 229-240. [26] battez a, hernández r, gonzález jl, fernández d, machado a, chou r, riba j. (2008) cuo, zro2 and zno nanoparticles as antiwear additive in oil lubricants. wear, 265(3):422428. [27] wu yy, tsui wc, liu tc. (2007) experimental analysis of tribological properties of lubricating oils with nanoparticle additives. wear, 262(7):819-825. [28] saeedinia m, akhavan-behabadi ma, razi p. (2012) thermal and rheological characteristics of cuo–base oil nanofluid flow inside a circular tube. international communications in heat and mass transfer, 39(1):152-159. [29] anoop kb, sundararajan t, das s k. (2009) effect of particle size on the convective heat transfer in nanofluid in the developing region. international journal of heat and mass transfer, 52(9):2189-2195. [30] moraveji m, darabi m, haddad mh, davarnejad r. (2011) modeling of convective heat transfer of a nanofluid in the developing region of tube flow with computational fluid dynamics. international communications in heat and mass transfer, 38(9):1291-1295. [31] pak bc, cho yi. (1998) hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles. experimental heat transfer an international journal, 11(2):151-170. [32] brinkman hc. (1952) the viscosity of concentrated suspensions and solutions. the journal of chemical physics, 20(4):571-571. [33] patel he, sundararajan t, pradeep t, dasgupta t, dasgupta n, das sk. (2005) a microconvection model for thermal conductivity of nanofluids. pramana, 65(5):863-869. [34] santra ak, sen s, chakraborty n. (2009) study of heat transfer due to laminar flow of copper-water nanofluid through two isothermally heated parallel plates. international journal of thermal sciences 48(2):391-400. [35] saeedinia m, akhavan-behabadi m a, and razi p. (2012) thermal and rheological characteristics of cuo–base oil nanofluid flow inside a circular tube. international communications in heat and mass transfer, 39(1):152-159. [36] murshed sms , leong kc, yang c. (2008) investigations of thermal conductivity and viscosity of nanofluids. international journal of thermal sciences, 47(5):560-568. [37] li s, eastman ja. (1999) measuring thermal conductivity of fluids containing oxide nanoparticles. journal of heat transfer, 121(2):280-289. [38] eastman ja, choi sus, li sh, yu w, thompson lj. (2001) anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles. applied physics letters, 78(6):718-720. [39] li q, xuan y, wang j. (2003) investigation on convective heat transfer and flow features of nanofluids. journal of heat transfer, 125(2):151-155. [40] jung jy, oh hs, kwak hy. (2009) forced convective heat transfer of nanofluids in microchannels. international journal of heat and mass transfer, 52(1):466-472. draft for iium journal publication iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 eye blink identification and removal from single-channel eeg using emd with energy threshold and adaptive filter lutfi aizat mohamed jefri, faridah abd rahman*, noreha abdul malik and farah nadia mohd isa dept. of electrical and computer engineering, international islamic university of malaysia, kuala lumpur, malaysia *corresponding author: faridah_ar@iium.edu.my (received: 7 april 2023; accepted: 31 may 2023; published on-line: 4 july 2023) abstract: electroencephalography (eeg) is a non-invasive method for measuring electrical activity in the brain, which reflects the underlying neural activity of the brain. in recent years, portable eeg devices become more ubiquitous in domestic uses, research and clinical applications due to their compact design and ease of use in various settings. like many other bio signal modalities, eeg devices are prone to the interference of physiological artifacts, mainly from eye blinking. however, since portable eegs are equipped with only a few channels at most or sometimes just contain a single channel, removing the eye blink artifact from the eeg data is a challenge. the conventional artifact removal method using source separation cannot be applied to a single-channel eeg signal. eye blink artifact removal is important because its spectrum overlaps with the eeg’s theta and delta frequency bands, which can be confused with brain activity. univariate-based removal method is compatible with eeg data with few channels. this paper presents a method to remove eye blink artifact based on single-channel eeg processing using empirical mode decomposition (emd) and adaptive noise cancellation (anc) system. by applying energy thresholds in emd, there is no need to incorporate emd with other methods to extract eye blink component accurately. anc is used to converge the extracted eye blink component for effective eye blink artifact removal with very minimal changes to affected eeg data. the proposed method was tested on simulated eeg signals, and the result showed a good root mean-square error (rmse) average value of the cleaned eeg (0.3211 ± 0.2738) and a high correlation coefficient (cc) average value of the cleaned eeg (0.9430 ± 0.0839). abstrak: electroensefalografi (eeg) adalah kaedah bukan invasif untuk mengukur aktiviti elektrik di dalam otak, yang mencerminkan aktiviti saraf dalam otak. kebelakangan ini, peranti eeg mudah alih menjadi lebih meluas dalam kegunaan domestik, penyelidikan dan aplikasi klinikal kerana reka bentuknya yang padat dan kemudahan penggunaan dalam pelbagai tetapan. seperti kebanyakan modaliti biosignal yang lain, peranti eeg terdedah kepada gangguan artifak fisiologi, terutamanya daripada kerdipan mata. walau bagaimanapun, memandangkan eeg mudah alih dilengkapi dengan paling banyak pun hanya beberapa saluran, atau kadangkala hanya satu saluran, mengalih keluar artifak kerdipan mata daripada data eeg adalah satu cabaran. kaedah penyingkiran artifak konvensional menggunakan pemisahan sumber tidak dapat digunakan pada alat eeg satu saluran. penyingkiran artifak kerdipan mata adalah penting kerana spektrumnya bertindih dengan jalur frekuensi teta dan delta eeg, maka boleh dikelirukan dengan aktiviti otak. kaedah penyingkiran berasaskan univariat adalah serasi untuk data eeg dengan saluran yang sedikit. kertas kerja ini membentangkan kaedah untuk membuang artifak kelipan mata berdasarkan pemprosesan eeg saluran tunggal menggunakan penguraian mod empirikal (emd) dan pembatalan bunyi adaptif (anc). dengan menggunakan ambang tenaga dalam emd, tiada 141 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 keperluan untuk menggabungkan emd dengan kaedah lain bagi mengekstrak komponen kerdipan mata dengan tepat. anc digunakan untuk menumpu komponen kerdipan mata yang diekstrak bagi penyingkiran artifak kerdipan mata yang berkesan dengan perubahan yang sangat minimum pada data eeg yang terjejas. kaedah yang dicadangkan telah diuji pada signal eeg yang disimulasi, serta hasilnya menunjukkan nilai purata ralat min kuasa dua purata (rmse) yang baik bagi eeg yang dibersihkan (0.3211±0.2738), dan nilai purata pekali korelasi (cc) yang baik bagi eeg yang dibersihkan (0.9430±0.0839). key words: adaptive filter, eye blink extraction, emd, energy thresholding, univariate processing 1. introduction electroencephalography (eeg) is one of the brain monitoring modalities that records electrical signals that originate from the neuronal activities across the cerebral cortex of the brain. these signals correspond to the higher level of the brain functions such as thinking, solving problems, memory, learning, feeling and processing emotions, intelligence, behavior regulation and body movement to some extent. as such, coupled with eeg equipment that is mainly easy to be used, there are many types of research on the matter related to the brain, utilizing eeg as a medium or small input data to analyze and explore the exactitude of a hypothesis and to synthesize solution for the objective of the research. for example, jacobsen et al. use eeg to study eeg’s beta power variability that corresponds to gait movement variability down the terrain [1]. the design of the eeg equipment is relatively of simpler implementation, making it possible to be miniaturized into a compact and portable eeg device [2]. likewise, the nature of portable eeg that is simpler and less cumbersome to be set up than medical-grade eeg, making it stand out for use. as such, the interest in incorporating the portable eeg device into brain related research and application development is becoming increasingly ubiquitous [3]–[5]. a review of different brands of portable eeg is also made of their respective efficacy on different domains of brain related study [6]. the application of eeg in research and domestic use is expected to remain ubiquitous. eeg signals propagate from the cerebral cortex, an outer layer of the brain, then across the meninges, skull, and scalp of the subject to the eeg electrodes, making them prone to contamination with other signals that are not of brain origin, which are called artifacts. these artifacts may be external, meaning they originate from the eeg equipment like electrical interference and alternating current artifact, or internal, meaning signals that originate from a physiological body such as electrooculogram (eog), electromyogram (emg) and electrocardiogram (ecg). although the internal artifacts are of physiological origin, these signals may not be desirable for brain-related analysis because they are not implicative to brain activity during the eeg recording session. hence, in most cases, artifacts need to be discarded in order to obtain clean, pure eeg data. unlike internal artifact, external artifacts contamination can be avoided by correct equipment set up. while internal artifacts prevention is accomplished by limiting the subject movements and making sure the subject is calm during eeg recording. likewise, there have been many techniques being proposed on how to remove these internal artifacts. nevertheless, eye blinks are considered one of the most pervasive artifacts contaminating the eeg signals. eye blink artifact is persistent in its presence during eeg recording even with restrictive and controlled experimental design. ultimately, there would be many scenarios where eye blink artifact removal comes in handy when it comes to eeg recording. therefore, with relation to portable eeg, the univariate-based eye blink removal method is preferred compared to the multivariate-based method. this is because the portable 142 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 eeg is only equipped with a few eeg channels. univariate refers to a single eeg channel use, while multivariate refers to the use of multiple eeg channels. the multivariate-based method generally needs a larger number of inputs as its performance is linearly proportional to the number of inputs. therefore, the univariate method is more effective than the multivariate method in processing eeg data retrieved from portable devices as it only needs one input to perform effectively. the univariate method also needs to be able to remove the eye blink without affecting the eeg component that is superimposed with the eye blink artifact while maintaining its quality of being straightforward in terms of implementation. in this paper, we propose a method of eye blink region identification using five samples window-mean and an energy thresholded-empirical mode decomposition (emd) to extract the eye blink component, coupled with recursive least-mean square (rls) adaptive filtering to remove the eye blinks from single-channel eeg. the proposed method aims to approximate the eye blinks artifact within the identified eye blink region with high similarity as a reference in the adaptive noise cancellation system. 2. related works in this section, a few univariate eye blink removal methods are briefly reviewed, along with the basis of the proposed technique is elaborated. these includes the eye blink detection method, eye blink component extraction and eye blink artifact filtering. 2.1 eeg eye blink artifact detection eye blink artifact is constituted of the overlapped frequency spectrum with eeg theta and delta frequency band (0.3 hz to 7 hz) that is indicated by 10 to 100 times bigger amplitudewise deflections within the eeg data [7]. occurrences of eye blink artifact contamination in eeg data can be traced by abrupt prominent eeg magnitude change. therefore is a foolproof way of detecting the eye blink artifact. this is because the propagation of potential from corneal-retinal dipole by the eye lid during eye blinking activity exhibits abrupt deflective spikes in eeg recording [8]. the specific eeg recording brand may influence the temporal characteristic of the deflections. for example, a voluntary eye blink artifact captured using an openbci amplifier, as shown in fig. 1. (a) has different morphology when compared to an eye blink artifact that is captured using g.tec amplifier in fig. 1. (b), and emotiv device in fig. 1. (c). fig. 1. example of voluntary eye blink captured in frontal channel of three different eeg devices (a) openbci, (b) g.tec cap-type device, (c) emotiv nevertheless, the consistency of the recorded eye blink artifact characteristic across any eeg equipment brand is shown temporally by the huge deflective spike in any eeg data that (a) (b) (b) (c) 143 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 contains the eye blink artifact. as such, most eye blink detection methods use amplitude-based quantification as means for non-eye blink and eye blink region segregation. this may be in terms of windowed amplitude mean as proposed by authors of [9], highest amplitude as reference for eye blink temporal span approximation as posited in [7], amplitude power, as demonstrated in [10], and amplitude energy as being presented in [11]. therefore, amplitude-based quantification is suitable to be incorporated in detecting the eeg segment of interest. for the proposed method in this paper, amplitude-based thresholding based on five samples window-mean is used to gauge the eeg data amplitude differences to dismiss the samples with amplitude lower than the threshold but retain the samples that are higher than the threshold to mark the eye blink region, as being demonstrated in [12]. this approach is independent of any assumption on the duration of the eye blinking activity to avoid including clean eeg region with the identified eye blink region or excluding any portion of the eye blink region. 2.2 eye blink component extraction decomposition-based univariate signal processing is a popular class of methods for eye blink removal. lately, singular spectrum analysis (ssa), with various implementation designs, has been proposed to remove eye blink artifact from a single eeg channel. however, the number of components or subspaces that an input can be composed into must be preset by mapping the single-channel eeg into a multivariate data matrix before decomposition by ssa is executed. subsequently, the appropriate workaround is introduced to ensure satisfactory eye blink component reconstruction. for example, maddirala et al. use hjorth mobility as a threshold to choose the ssa subspaces for the eye blink reconstruction [13]. while in [14], the eigenvalue ratio is used as the threshold to select the subspaces that correspond to the eye blink component for eye blink reconstruction. nevertheless, different temporal lengths of the recorded eeg and also possibly inconsistent morphology of the eye blink artifact due to different use of eeg devices may cause the variability on the suitable number of subspaces (m) to be preset for the signal decomposition that yields good component separation, which ultimately, causes variability to the threshold value for ssa subspaces selection. the ambiguity of the value that needs to be used in the parameters setting requires preparatory testing, which may complicate the implementation of the proposed methods. in contrast, emd may bypass this problem for its empirical way of decomposing a signal. therefore, emd is adaptable to variable eye blink morphology and eeg temporal length without any respective parameters’ adjustment. emd is a data-driven method that decomposes signals in the time domain by a sifting process. this process identifies all local extrema in the input signal, starting with those corresponding to the smallest oscillation period. then, the identified oscillatory mode is extracted, which also yields the intermediate residual, as shown in fig. 2. this oscillatory mode is called the intrinsic mode function (imf). the identified extrema are used to construct upper and lower envelopes before being averaged to find the mean envelope. the mean envelope is then subtracted from the signal to acquire the oscillatory mode that consists of a spectral that is higher than the spectral of the derived mean envelope. a thorough explanation of how emd operates is well presented by zeller et al. in [15]. generally, emd segregates signal components locally and separates the data into locally non-overlapping time scale components. from the decomposing eye blink region perspective, the first imf is extracted from the signal, the intermediate residual is produced, and the sifting process is iterated again using the intermediate residual to extract other imfs until it becomes a monotonic component. consequently, the later extracted imf has slower oscillatory characteristics than the former. 144 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 this shows that emd yields imf components that start with the highest oscillatory rate to the final monotonic residual. moreover, using the local extrema to derive the imf allows the derivation to be automatic and adaptive time-variant filtering, which results from imfs that exhibit non-stationarity nature with amplitude-frequency modulated (am/fm) characteristics. as such, the nature of emd sequential operations in filtering out imfs can be approximated as a dyadic filter. this is because, on average, the amount of the extrema is reduced by onehalf from an imf to the next imf. fig. 2. the simplified sifting process visualization. (a) extrema identification. (b) mean envelope construction. (c) first imf. (d) the residual, or the last imf. since the advent of emd, it has been integrated into the process of eog artifact removal and has subsequently been widely disseminated in the academic literature. in [16], the correlation coefficient (cc) between the summed up imfs with the true eeg component is used as an indicator for eye blink component presence, which is calculated after every time an imf is added up from the first imf. when the cc decreases to lower than 0.9, the latest imf that is added up is deemed to have eye blink component. hence, starting from that latest imf to the residual, the imfs are added up to reconstruct the eye blink component that can be used as a reference for adaptive noise cancellation (anc). however, this technique needs the ground truth pure eeg that is similar in its temporal features to the eeg within the eye blinkcontaminated data in order to calculate the cc value, which is counterproductive. while in [17], cc is also used between the artifactual eeg segment and the imfs. due to the scale of the eye blink component being larger than the eeg signal, the cc value obtained with imfs containing eye blink component is larger. the cc threshold of 0.5 is used to discriminate between imfs representing eeg and eye blink component, of which the imfs with cc that is larger than 0.5 will be discarded before reconstruction. this method is vulnerable to the loss of some eeg components, especially the one that lies within the delta band. in [18], the 95% confidence interval of log energy of fractional gaussian noise (fgn) is used as a threshold to select imfs representative of eog artifact. however, there is no workaround to deal with the 145 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 potential of emd’s mode-mixing effect which would possibly cause some eeg component removal along with the reconstructed eog. the ability of emd to decompose a signal into their respective oscillatory modes also makes it possible to employ multivariate data processing for a single eeg channel. for example, emd is incorporated with canonical correlation analysis (cca) in a way that the emd is made to produce partial separation of eye blink artifact from the eeg data. the cca is used to find the canonical weights that can be used to approximate the eye blink component that is free from eeg mixing [19]. nevertheless, emd can be utilized solely to extract the eye blink component without combining it with other techniques for its empirical method in decomposing the input signal. we proposed using five samples window-mean thresholding to identify the eye blink regions within the single-channel eeg. each identified region is then decomposed using emd to extract the eye blink component. thus, emd is used only upon the isolated region as decomposing a time series with the transient component, which in this case is the eye blink component, causes mode-mixing due to over-sifting that may be induced during imf derivation, as discussed by zeller et al. [15]. also, the emd used for the proposed method is as proposed by rato et al. [20], as its implementation addresses the problem of the emd in terms of extrema computation, extrema interpolation, boundary conditions and sifting criterion. 2.3 eye blink artifact removal adaptive filtering is a filter which receives reference input 𝑟1(𝑛) as its input impulse to find the least resultant error e(n) between the produced impulse response y(n) and the targeted component 𝑟2(𝑛). an adaptive filter can be represented as an impulse filter as the following eq. 1: y(n) = ∑ 𝑤𝑘 ∙ 𝑟1(𝑛 − 𝑘) 𝐿 𝑘 (1) the parameter l is the order of the filter, 𝑤𝐿 is the filter coefficient with span of l, 𝑟1(n) is the reference input and y(n) is the impulse response. the 𝑟1(n) is useful as it is the essential factor in producing the impulse response that is converged to the desired component 𝑟2(n) that is mixed with the input signal s(n). this is because the source of 𝑟1(n) comes from the same source as 𝑟2(𝑛). in the context of the interest, 𝑟1(n) and 𝑟2(𝑛) represent eye blink component. this means the eye blink component must be available to remove the respective eye blink artifact from the affected eeg segment. in this paper, the eye blink component is extracted from the identified eye blink region in noisy eeg signals, as opposed to relying on the eog channel which records the eye activities such as blinking and movement. the eye blink component extraction method is incorporated because of consideration for the ubiquity use of portable eeg in research and domestic uses. for the univariate method, eye blink removal is more plausible in its use of eeg data recorded using portable eeg devices as it only consists of a few eeg channels and many have no eog electrode. therefore, the eye blink removal method is designed to operate without the requirement for an eog channel by extracting the eye blink component from noisy eeg. this extracted eye blink component is used as the reference 𝑟1 in adaptive filtering. in adaptive filtering, 𝑟2(𝑛) removal is done by producing y(n) that is equivalent to the eye blink component within the eeg segment to not affect the eeg component during the removal. in order to find y(n), the error e(n) is used as feedback to assist the convergence of y(n). as shown in eq. 2, the e(n) is the difference between the y(n) and 𝑟2(𝑛) that is desired to 146 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 be as small as possible, as the smaller the e(n) results better converged y(n), as depicted in eq. 3. e(n) = 𝑟2(𝑛) – y(n) (2) e(n) ≈ 0, y(n+1) ≈ 𝑟2(n+1) (3) in order to cater for the next y(n) computation, the current e(n) is used as feedback into the adaptive algorithm. the adaptive algorithm optimizes the weight to converge the y(n+1) to 𝑟2(𝑛 + 1), as being described in the following: 𝑤𝑘(n+1) = 𝑤𝑘(𝑛) − 2 ∙ 𝜇 ∙ 𝑒(𝑛) ∙ 𝑟1(𝑛 − 𝑘) (4) the value of 𝜇 is between 0 and 1. y(n+1) = ∑ 𝑤𝑘 ∙ 𝑟1(𝑛 + 1 − 𝑘) 𝐿 𝑘 (5) the weight optimization in eq. 4 is based on the least mean square error (lms) algorithm. the 𝜇 parameter is a constant to ensure fast adaptation for 𝑤𝑘(n+1) that can converge y(n+1) to 𝑥2(𝑛) effectively. in this paper, recursive least mean square error (rls) is used for weight optimization because rls needs lesser n iteration counts or steps number to converge the y(n) to its respective 𝑟2(𝑛), hence a faster convergence rate. faster convergence impacts its output, especially when the input is of a short segment. this applies to the marked eye blink region as its temporal length may span at most by only 2 seconds. the rls algorithm is as the following: 𝑤𝑘(n+1) = 𝑤𝑘(𝑛) − 2 ∙ 𝜇 ∙ 𝑒(𝑛) ∙ 𝐾(𝑛) (6) k(n) is the filter coefficient vector given by eq. 7 as the following. 𝐾(𝑛) = 𝑃(𝑛)∙𝑟1(𝑛) 𝜆+ 𝑟1 𝑇(𝑛)∙𝑃(𝑛)∙𝑟1(𝑛) (7) p(k) is the inverse correlation matrix with its initialization as the following: p(0) = [ 𝛿−1 0 ⋯ 0 0 𝛿−1 ⋯ 0 ⋯ ⋯ ⋯ ⋯ 0 0 ⋯ 𝛿−1 ] (8) the parameter 𝛿 is the regulatory factor and the constant k is the length of the tap input vector. the p(k) adaptation is done as depicted by the following equation. p(n+1) = 𝜆−1 ∙p(n) −𝜆𝑛−1 ∙k(n)∙ 𝑢𝑇(𝑛) ∙p(n) (9) the fact that p(n) and k(n) need each other during the weight optimization is why it is called a recursive least mean square adaptive algorithm. 3. methodology the implementation of the proposed method is described in this section. fig. 3 illustrates the outline of the methodology in terms of the block diagram. firstly, the procedure for eeg dataset preparation is described. then, the eye blink region detection, eye blink component extraction and eye blink artifact removal are explained. finally, the performance metric is calculated upon the removal output accordingly with the original simulated eeg data that is juxtaposed with the performance metric from egambaram et al. [19] to prove the effectiveness of our method. 147 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 fig. 3. the block diagram of a methodology for our eye blink removal 3.1 eeg dataset preparation the eeg dataset used has been schemed to have an eeg component that can be ground truth data to assess the performance of the proposed method in preserving the brain-originated signals in the noisy eeg after eye blink artifact removal. thus, eeg data is simulated by superimposing the pure eeg data with eye blink artifact. the superimposition of eye blink artifact can be understood as a linear mix between two signals: x(t) = y(t) + z(t) (10) x(t) is the eye blink contaminated-eeg, while y(t) is the pure eeg component and z(t) is the eye blink artifact. the eeg data used in the experiment to assess the proposed technique is simulated in a way that it is possible to compare the performance metrics values, which is documented in [19]. exponential functions represent the eye blink components z(t) with different peak magnitudes that can be expressed mathematically as follows: 𝑍(𝑡) = ∑𝐴𝑒−(10𝑡−𝐵) 2 (11) a is the peak height ranges from 7 to 19 in magnitude and b is the temporal location of the peaks. fig. 4 (a) shows an example of the synthetic eye blink artifact. as for the eeg component, it is synthesized by using the pink noise for which its amplitude range between 0.0±3. fig. 4 (b) illustrates the synthetic eeg, y(t). in order to obtain a synthetic eye blink artifact contaminated-eeg, x(t), the synthetic eye blink component and synthetic eeg are added together as demonstrated by eq. 10. fig. 4 (c) depicts the synthetic x(t). this dataset is used to evaluate the equivalent performance metrics that later are used to compare with other emd-based technique proposed by egambaram et al. every unit of y(t), z(t) and the resultant x(t) are simulated with the length of 10 seconds at 256 sampling rate or 2560 samples. 3.2 eye blink region detection in order to extract the eye blink component, the eye blink regions and artifact-free regions within the eeg data need to be identified. the targeted processes only on the specified eeg regions not only reduce the computational requirement and time but also prevent the mode-mixing in the decomposed imfs during eye blink component extraction by emd. to be able to mark the eye blink region, amplitude thresholding is used to exploit the conspicuous difference of amplitude between pure eeg and eye blink artifact. in order to do so, the pure eeg maximum amplitude of the eye blink artifact-contaminated eeg needs to be ascertained beforehand. accordingly, eeg data that is recorded or prepared that corresponds to the pure eeg component in the eeg of interest is computed as its maximum amplitude. this maximum eeg data simulation eye blink region identification eye blink component extraction eye blink artifact removal performance metric calculation 148 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 amplitude value is a discriminatory factor in the eye blink artifact-contaminated eeg data. the following is a pseudocode to describe the steps in setting the amplitude threshold value: algorithm: finding the threshold for the deflection detection algorithm for each eeg data channel. input: array of pre-processed baseline eeg data, [data] output: threshold for deflection detection [𝑑𝑎𝑡𝑎𝑚𝑒𝑎𝑛] ← mean([eeg_data(1:5:end)]) [data]min ← min([𝑑𝑎𝑡𝑎𝑚𝑒𝑎𝑛]) [data]max ← max([𝑑𝑎𝑡𝑎𝑚𝑒𝑎𝑛]) [value]max ← max(abs([data]max), abs([data]min)) threshold ← [value]max +1 from this pseudocode, the mean of every five-sample window in the eeg data is used to determine the threshold instead of the individual sample because this window-mean can act like smoothing against the outlier amplitudes from eeg high frequency-component that may wrongly influence the determination for the suitable threshold value. if the value of the threshold is too high, it may bypass the eeg segment that contains an eye blink artifact (false negative), but if it is too low, it may include a clean eeg segment (false positive). fig. 5 (a) illustrates the threshold (red color) that discriminates the eye blink region and the clean eeg. in the case of eeg data used to test the proposed method, the synthetic eeg data y(t) is used to compute the amplitude threshold. fig. 4. (a) the simulated eye blink component z. (b) the simulated eeg component y. (c) the simulated eye blink contaminated-eeg x (a) (b) (c) 149 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 as shown in the last line of the pseudocode, the threshold value is concluded as the maximum value added by 1 to dismiss clean eeg data samples effectively during eye blink artifact detection. during the detection, as visualized by fig. 5 (b), the mean of every five samples is again computed and compared against the threshold to deem it as part of the eye blink region, as represented by an orange color or clean eeg samples (blue color) in a temporally successive manner. the detection by five-sample window-mean also helps to differentiate the five-sample segment whether it is a clean eeg sample or a contaminated eeg sample, more discretely. the whole eye blink region is considered to be detected completely when no more 5sample mean value is detected as an eye blink contaminated eeg segment for another 150 samples consecutively. before the detected eye blink-contaminated eeg samples are marked as a complete eye blink segment, the neighbouring samples at the beginning and end of the detected segment are included as part of the detected segment until the nearest zero-crossing is reached at both ends. at this point, an eye blink-region detection is complete. this is visualized in fig. 5 (c), which shows that, in orange color, a complete eye blink region is marked. then, the detection moves to the next five samples to detect another eye blink region. fig. 5. (a) the window-mean threshold (red line) is used to discriminate the eye blink region. (b) eye blink samples are detected (orange color). (c) the whole eye blink region is approximated by the nearest zero-crossing 3.3 eye blink component extraction after the eye blink region is detected, emd decomposes the segment. before the decomposition, the segment is segregated into its individual deflection, as shown in fig. 6 (b). to ensure smooth approximation of the envelope during sifting process, a constant 𝛼 is used as a factor for the mean envelope e(t) whenever the e(t) is subtracted from the signal x(t) or the intermediate residual 𝑟𝑛(𝑡) as the following: x(t) = x(t) − 𝛼 ∙ 𝑒(𝑡) (12) the constant 𝛼 value is between from 0 to 1. energy thresholding is deployed during imf derivation and as a stopping criterion. for imf derivation, qresol is used as an additional condition to derive an imf. the threshold qresol is as an energy ratio of which when the energy of the e(t) is qresol times lower than the energy of x(t) or 𝑟𝑛(𝑡), the imf is derived from the following: (a) (b) (c) 150 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 if qresol > energy of x(t)or rn(t) energy of e(t) , imf is derived. (13) threshold qresol aims to avoid constructing envelopes that introduce new components during imf derivation. as for the energy threshold for the stopping criterion, the ratio of x(t) or 𝑟𝑛(𝑡) to the new residual produced (𝑟𝑛+1(𝑡)), which is produced after an imf is derived, called threshold qresid. the decomposition stops when the value of qresid is lower than its set threshold: if qresid > energy of x(t)or rn(t) energy of rn+1(t) , the decomposition is stopped. (14) the incorporation of threshold qresid influences the decomposition by emd so that it does not produce a monotonic signal as its final residuum in a definitive manner like the original emd would. this behavior is useful when the objective of the decomposition is to extract low oscillatory components with specific temporal features. before the decomposition, the deflection segregation is done according to the zerocrossings between each deflection. deflection segregation allows the eye blink component to be extracted by emd without being fragmented across imfs due to over sifting. eye blink artifact morphology is independent of any mathematical basis. however, the individual deflection generally resembles a peak or valley with one extremum, which is consistent with the emd final residuum of which, after being generated, the decomposition stopped. hence, as illustrated in fig. 6 (c), the final residuum is a representative of the respective eye blink deflection instead of the monotonic signal, which ultimately can be used to reconstruct the eye blink component directly without the need to utilize other imfs for the process. fig. 6. (a) the identified eye blink region (orange line) is fed into emd. (b) the eye blink is segregated into its individual deflection. (c) emd decomposition. (d) eye blink component extraction. (e) eye blink artifact removal by anc. (f) the anc output is a cleaned signal. adaptive filtering deflection 1 deflection 2 deflection 3 deflection 1 deflection 2 deflection 3 imf 1 imf 2 imf 3 imf 4 imf 5 residual *used for reconstruction *reference channel *output *input channel (a) eye blink detection (b) deflections segmentation (c) emd decomposition (d) eye blink component reconstruction (f) output (e) eye blink removal 151 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 the consistency of this occurrence is important so that only residuum is needed for the eye blink component reconstruction instead of the inclusion of a deliberate selection of suitable imfs so that automatic eye blink component reconstruction is possible. in the proposed method, the residua are concatenated at their ends to form the respective eye blink component by means of spline interpolation, as visualized by fig 6 (d). this reconstructed eye blink component has a similar deflection shape as the respective eye blink artifact contained in the eeg segment and thus can be utilized as a reference channel for adaptive filtering to remove the eye blink artifact from the eeg segment. 3.4 eye blink artifact removal after the eye blink component is reconstructed, it is used as reference data r1(n), as shown in fig. 7. the block diagram of the proposed adaptive filter that is used as adaptive noise cancellation (anc) system is shown. the identified eye blink region is fed into the anc as primary input d(n). the rls-based algorithm is used in the adaptive filter to remove the eye blink artifact from the marked eeg segment. for the respective eeg segments that correspond to the eye blink affected eeg region, their length span ranges from 0.25 to 1.5 seconds. hence, 𝛿 value is set to be 0.99 and 𝜆 value to be 10 with a coefficient order of 2 to ensure efficient and stable impulse response convergence. fig. 7. anc structure 3.5 performance metric in order to measure the performance of the proposed method in removing the eye blink artifact, two data-centric measures are used on the processed eeg segments accordingly. the performance metrics are correlation coefficient (cc) and relative root-mean-square error (rmse). the values generated from these performance metrics indicate how well the processed eeg data is preserved. the cc and rmse are measured for the eeg component and eye blink component, respectively; between before and after being processed for eye blink artifact removal. the following are the mathematical descriptions of the performance metrics. the cc is measured as the following: 𝐶𝐶𝐸𝐸𝐺 = 𝑐𝑜𝑣(𝑌𝑝𝑖𝑛𝑘𝑛𝑜𝑖𝑠𝑒, 𝑌𝑜𝑢𝑡𝑝𝑢𝑡) 𝑠𝑡𝑑(𝑌𝑝𝑖𝑛𝑘𝑛𝑜𝑖𝑠𝑒)∗𝑠𝑡𝑑(𝑌𝑜𝑢𝑡𝑝𝑢𝑡) (15) 𝐶𝐶𝑒𝑦𝑒 𝑏𝑙𝑖𝑛𝑘 = 𝑐𝑜𝑣(𝑍𝑠𝑖𝑚𝑢𝑙𝑎𝑡𝑒𝑑, 𝑍𝑟𝑒𝑐𝑜𝑛𝑠𝑡𝑟𝑢𝑐𝑡𝑒𝑑) 𝑠𝑡𝑑(𝑍𝑠𝑖𝑚𝑢𝑙𝑎𝑡𝑒𝑑)∗𝑠𝑡𝑑(𝑍𝑟𝑒𝑐𝑜𝑛𝑠𝑡𝑟𝑢𝑐𝑡𝑒𝑑) (16) + + − adaptive filter weight update algorithm 𝑑(𝑛) = (𝑛) + 𝑟2(𝑛) eye blink region 𝑟1(𝑛) emdextracted eye blink component (𝑛) ≈ 𝑟2(𝑛) 𝑒(𝑛) ≈ 0 𝑑(𝑛) = (𝑛) + 𝑒(𝑛) 152 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 the rmse is measured as the following: 𝑅𝑀𝑆𝐸𝐸𝐸𝐺 = √ ∑ (𝑌𝑝𝑖𝑛𝑘𝑛𝑜𝑖𝑠𝑒(𝑡)− 𝑌𝑜𝑢𝑡𝑝𝑢𝑡(𝑡)) 2𝑛 𝑡=1 𝑛 (17) 𝑅𝑀𝑆𝐸𝑒𝑦𝑒 𝑏𝑙𝑖𝑛𝑘 = √ ∑ (𝑍𝑠𝑖𝑚𝑢𝑙𝑎𝑡𝑒𝑑(𝑡)− 𝑍𝑟𝑒𝑐𝑜𝑛𝑠𝑡𝑟𝑢𝑐𝑡𝑒𝑑(𝑡)) 2𝑛 𝑡=1 𝑛 (18) the variable 𝑋(𝑡)𝑠𝑖𝑚𝑢𝑙𝑎𝑡𝑒𝑑 is the simulated eye blink contaminated-eeg, 𝑌𝑝𝑖𝑛𝑘𝑛𝑜𝑖𝑠𝑒 is the simulated eeg component, 𝑌𝑜𝑢𝑡𝑝𝑢𝑡 is the cleaned simulated eeg component, 𝑍𝑠𝑖𝑚𝑢𝑙𝑎𝑡𝑒𝑑 is the simulated eye blink component and 𝑍𝑟𝑒𝑐𝑜𝑛𝑠𝑡𝑟𝑢𝑐𝑡𝑒𝑑 is reconstructed eye blink component. 4. results and discussion 4.1 eeg dataset structure the eeg dataset used to measure the performance metric is fully-simulated eeg data as described in subsection 3.1. this is done to compare the performance metrics with the eye blink removal technique proposed by egambaram et al. [19]. the generation of fully-simulated eeg for component y(t), z(t) and x(t) are iterated until 100 units are obtained. this total unit of eeg data is expedient to gauge the reliability of the performance metrics values in consistently proving the eye blink removal method of its level of performance. 4.2 proposed eye blink component extraction the extracted eye blink component is desired to be identical to its source. in this regard, a good eye blink component extraction is an eye blink component extraction with good precision of its features with the features of the original eye blink artifact. this is to ensure only the eye blink artifact is subtracted from the identified eeg segment during adaptive filtering. generally, correct eye blink component extraction is also important for any rejectionbased eye blink removal method, which includes the ica-based method. fig. 8 shows a sample of the reconstructed eye blink component (line in yellow colour) that being plotted in such a way that it can be compared with its respective eye blink reconstruction (line in blue colour). two windows each magnifies a simulated eye blink region that originates from the main plot. fig. 8. the simulated eye blink component and its eye blink reconstruction. 153 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 the result shown in table 1 contains the 𝐶𝐶𝑒𝑦𝑒 𝑏𝑙𝑖𝑛𝑘 and rmseeye blink values computed using the proposed eye blink component extraction method being juxtaposed with the respective performance metrics from the proposed fastemd-cca by egambaram et al. the better value in comparison is bolded for every measurement. table 1: performance metrics for eye blink component extraction between the proposed method and fastemd-cca. performance metrics emd-af (proposed method) fastemd-cca 𝐂𝐂𝐞𝐲𝐞 𝐛𝐥𝐢𝐧𝐤(𝝁 ± 𝝈) 𝟎.𝟗𝟗𝟏𝟓 ± 𝟎.𝟎𝟑𝟓𝟖 0.9754 ± 0.0055 𝐂𝐂𝐞𝐲𝐞 𝐛𝐥𝐢𝐧𝐤(95% ci) 0.9880-0.9950 0.9743-0.9765 𝐑𝐌𝐒𝐄𝐞𝐲𝐞 𝐛𝐥𝐢𝐧𝐤(𝝁 ± 𝝈) 𝟎.𝟐𝟗𝟔𝟎 ± 𝟎.𝟐𝟗𝟗𝟖 0.6580 ± 0.0776 𝐑𝐌𝐒𝐄𝐞𝐲𝐞 𝐛𝐥𝐢𝐧𝐤(𝟗𝟓% 𝑪𝑰) 0.2666-0.3253 0.6426-0.6734 the result above shows that the eye blink reconstruction using emd with spline interpolation resembles the original eye blink artifact better than the combination of emd with cca. its cc value evidences this is statistically higher than fastemd-cca, while the proposed method’s rmse is statistically lower than that resulting from fastemd-cca. hence, with appropriate energy thresholding for imf derivation (qresol) and as decomposition stopping criterion (qresid), emd is already substantial for excellent eye blink reconstruction. in the experimentation of implementing the emd based on rato et al. revision, 𝛼 value is set to 0.5 for smooth but relatively efficient e(t) formation regulation, qresid is set to 55 for satisfactory imf derivation and qresid is set to 57 for sufficient eye blink component extraction. fig. 6 shows a sample of the simulated eye blink contaminated-eeg (line in orange colour) with its respective eye blink reconstruction (line in blue colour). 4.3 proposed eye blink removal the extracted eye blink component is used to remove its eye blink source from its respective region. this can be done by means of component cancellation. in our proposed method, the extracted eye blink component is converged first by means of producing an appropriate impulse response using the rls weight adaptation algorithm. the impulse response is then used to cancel out the eye blink artifact from the marked region by anc. fig. 9 displays the original simulated eeg component (line in red colour) being overlapped with its cleaned counterpart (line with yellow colour) to visualize any differences between them. the cleaned eeg is the output of the proposed method. also, the eye blink-contaminated eeg (line with blue colour) is also plotted into the same graph to visualize the difference between it and the cleaned eeg. in the following, the results on the performance metrics indicating the degree of possible change that may occur on the ground truth eeg are tabulated in table 2. this degree of change is measured between the original simulated eeg data and the eeg data extracted after eye blink artifact removal performed by the proposed method. as for the metric, cc and rmse are also used. the better value in comparison is bolded for every measurement. a higher cc value, closer to 1, or if it is 1 itself reveals that the cleaned segment is nearly or perfectly similar with its original counterparts. the lower value of rmse points to a lower degree of difference between the cleaned segment and its original eeg component. 154 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 fig. 9. the original simulated eeg data (line with blue colour) and its respective component retrieved after eye blink removal (line with yellow colour). table 2: performance metrics for eye blink component removal between proposed method (emd-af) and fastemd-cca. performance metrics emd-af (proposed method) fastemd-cca 𝐂𝐂𝑬𝑬𝑮(𝝁 ± 𝝈) 𝟎.𝟗𝟒𝟑𝟎 ± 𝟎.𝟎𝟖𝟑𝟗 0.7478 ± 0.0687 𝐂𝐂𝑬𝑬𝑮(95% ci) 0.9348-0.9513 0.7341-0.7614 𝐑𝐌𝐒𝐄𝐄𝐄𝐆(𝝁 ± 𝝈) 𝟎.𝟑𝟐𝟏𝟏 ± 𝟎.𝟐𝟕𝟑𝟖 0.6580 ± 0.0776 𝐑𝐌𝐒𝐄𝑬𝑬𝑮(𝟗𝟓% 𝑪𝑰) 0.2942-0.3479 0.6426-0.6734 the cc obtained from egambaram et al. experimentation for the eeg component shows that its cc value dropped from the average of 0.9754, which is the cc obtained for the eye blink component, to 0.7478, which is the value that corresponds to the obtainment of ground truth eeg component after eye blink removal. this signifies that direct rejection of the eye blink artifact using its extracted eye blink component derived may cause distortion to the cleaned eeg segment. therefore, it is substantial to introduce a mechanism that ensures the extracted eye blink component is converged to its eye blink artifact within the respective eeg segment in order to minimize the distortion that may be caused after the removal process. adaptive filtering is serviceable on the matter of converging the extracted eye blink with the contained eye blink artifact. this is proven by the higher cc and lower rmse value for the cleaned eeg segment by the adaptive filtering utilization in the proposed method. fastemd is meant not completely to decompose the eeg segment. instead, it decomposes the respective eeg into a finite number of imfs set beforehand, assuming that the first three imfs are of eeg component and the remaining contains eye blink artifact. subsequently, after the imfs are divided into the non-artifactual and artifactual components, 155 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 they are added up to reconstruct into two components: non-artifactual and artifactual. the cca is later used to find the correlation between the two components to separate the eeg component that remains within the artifactual components. this paper intended to test the capability of emd in extracting the eye blink component that is similar in its temporal feature without being complemented by other data processing techniques. its heuristic approach in signal decomposition is the desirable quality that is expected to be harnessed in retrieving specific components. therefore, with an appropriate workaround to the emd, like energy thresholding, emd alone is effective for eye blink component reconstruction that is handy for its subsequent removal. 5. conclusion in this paper, we proposed the five samples-window mean as the basis for amplitude thresholding that was used to identify the eye blink region in the eye blinks-contaminated single-channel eeg. we demonstrated that incorporation of energy thresholds with emd decomposition to extract the eye blink deflections makes it possible to automate the eye blink reconstruction process. the identified eye blink region and extracted components are used as reference in rls-anc system to remove the eye blinks artifact in eye blink region while preserving the original eeg in eye blink-free region. the notable contribution of the proposed method is the utilization of the data-driven decomposition nature of emd to extract the eye blink deflections that is monumental in the eye blink component reconstruction. the proposed method is evaluated using synthetic eeg datasets, and results show better performance compared to existing fastemd-cca technique. the results show that the proposed method was successful in extracting eye blink components with high similarity to its simulated original waveforms and the removal of eye blink using anc was successful without altering or distorting the original eeg. the results also demonstrated that eeg components decomposition and separation using emd is sufficient for eye blink reconstruction without relying on the multivariate data processing methods that is significantly higher in complexity. in this study, eye blink identification and removal process were performed offline. for real time implementation, the routine for accommodating delay must be designed and incorporated adequately in distributive manner across the eeg recording and the eye blink removal process because the emd decomposition process is intrinsically sequential. nevertheless, the proposed method is a completely univariate eye blink removal method that extracts the eye blink component in an empirical manner which complements the adaptive denoising process for effective eye blink removal in a single eeg channel. acknowledgement this paper is funded by the ministry of higher education (mohe) malaysia through the research management centre, international islamic university malaysia (iium) under the fundamental research grant scheme frgs 1/2019 (ref: frgs/1/2019/tk04/uiam/02/14 – project id: frgs19-098-0707). references [1] artoni f, fanciullacci c, bertolucci f, panarese a, makeig s, micera s, chisari c. (2017). unidirectional brain to muscle connectivity reveals motor cortex control of leg muscles during stereotyped walking. neuroimage, 159:403–416. doi: 10.1016/j.neuroimage.2017.07.013. [2] mandekar s, holland a, thielen m, behbahani m, melnykowycz m (2022). advancing towards ubiquitous eeg, correlation of in-ear eeg with forehead eeg. sensors, 156 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 22(4):1568. https://doi.org/10.3390/s22041568 [3] lau-zhu a, lau mph, mcloughlin g (2019). mobile eeg in research on neurodevelopmental disorders: opportunities and challenges. dev cogn neurosci., 36:100635. doi: 10.1016/j.dcn.2019.100635. [4] nagar p and sethia d (2019). brain mapping based stress identification using portable eeg based device. 11th international conference on communication systems and networks (comsnets), 601–606. doi: 10.1109/comsnets.2019.8711009. [5] bhavnani s, parameshwaran d, sharma kk, mukherjee d, divan g, patel v and thiagarajan tc. (2022). the acceptability, feasibility, and utility of portable electroencephalography to study resting-state neurophysiology in rural communities. front. hum. neurosci, 16:802764. doi: 10.3389/fnhum.2022.802764. [6] sawangjai p, hompoonsup s, leelaarporn p, kongwudhikunakorn s, and wilaiprasitporn t. (2020). consumer grade eeg measuring sensors as research tools: a review. ieee sensors journal, 20(8):3996–4024. doi: 10.1109/jsen.2019.2962874. [7] shahbakhti m et al. (2021). vme-dwt: an efficient algorithm for detection and elimination of eye blink from short segments of single eeg channel. ieee transactions on neural systems and rehabilitation engineering, 29:408–417. doi: 10.1109/tnsre.2021.3054733. [8] iwasaki m, kellinghaus c, alexopoulos a v, burgess r c, kumar a n, han y h, lüders h o, and leigh r j. (2005). effects of eyelid closure, blinks, and eye movements on the electroencephalogram. clinical neurophysiology : official journal of the international federation of clinical neurophysiology, 116(4), 878–885. https://doi.org/10.1016/j.clinph.2004.11.001. [9] kanoga s, kanemura a, and asoh h. (2019). multi-scale dictionary learning for ocular artifact reduction from single-channel electroencephalograms. neurocomputing, 347:240– 250. doi: 10.1016/j.neucom.2019.02.060. [10] agarwal m and sivakumar r. (2019). blink: a fully automated unsupervised algorithm for eye-blink detection in eeg signals. 57th annual allerton conference on communication, control, and computing, allerton, 1113–1121. doi: 10.1109/allerton.2019.8919795. [11] g bhaskar n rao, anumala v s, peri p p and aneesh s. (2020). automatic detection and correction of blink artifacts in single channel eeg signals. international journal of advanced computer science and applications (ijacsa), 11(1). http://dx.doi.org/10.14569/ijacsa.2020.0110144 [12] jefri l a m, rahman f a, malik n a, and isa f n m. (2022). eye blink region detection in eeg using amplitude thresholding. 8th international conference on mechatronics engineering (icom 2022), 77–83. doi: 10.1049/icp.2022.2269. [13] maddirala a k and veluvolu k c. (2022). ssa with cwt and k-means for eye-blink artifact removal from single-channel eeg signals. sensors, 22(3). doi: 10.3390/s22030931. [14] maddirala a k and veluvolu k c. (2021). eye-blink artifact removal from single channel eeg with k-means and ssa. sci rep., 11(1). doi: 10.1038/s41598-021-90437-7. [15] zeiler a, faltermeier r, keck i r, tomé a m, puntonet c g, and lang e w. (2010). empirical mode decomposition an introduction. proceedings of the international joint conference on neural networks, 2010. doi: 10.1109/ijcnn.2010.5596829. [16] shahbakhti m, bavi m and eslamizadeh m. (2013). elimination of blink from eeg by adaptive filtering without using artifact reference. 2013 4th international conference on intelligent systems, modelling and simulation, 190-194, doi: 10.1109/isms.2013.106. [17] patel r, janawadkar m p r, sengottuvel s, gireesan k, and radhakrishnan t s. (2016). suppression of eye-blink associated artifact using single channel eeg data by combining cross-correlation with empirical mode decomposition. ieee sens j., 16(18):6947–6954. doi: 10.1109/jsen.2016.2591580. [18] molla m k i, rabiul islam m, tanaka t, and rutkowski t m. (2012). artifact suppression from eeg signals using data adaptive time domain filtering. neurocomputing, 97:297–308. 157 iium engineering journal, vol. 24, no. 2, 2023 jefri et al. https://doi.org/10.31436/iiumej.v24i2.2814 doi: 10.1016/j.neucom.2012.05.009. [19] egambaram a, badruddin n, asirvadam v s, begum t, fauvet e, and stolz c. (2020). fastemd–cca algorithm for unsupervised and fast removal of eyeblink artifacts from electroencephalogram. biomed signal process control, 57:2020. doi: 10.1016/j.bspc.2019.101692. [20] rato r t, ortigueira m d, and batista a g. (2008). on the hht, its problems, and some solutions. mech syst signal process, 22(6):1374–1394. doi: 10.1016/j.ymssp.2007.11.028. 158 microsoft word 179 completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hamad and abuidris 203 risk factors for prostate cancer patients among gezira state-central of sudan f.a. hamad1 and d.o. abuidris2 1 department of biochemistry, faculty of applied medical sciences, university of gezira, sudan. 2 department of oncology, national cancer institute, university of gezira, sudan. fatimaabubaker@yahoo.com abstract: the aim of this study is to assess the risk factors for prostate cancer among sudanese patients treated in national cancer institute (nci), gezira university, wadmedani, sudan. the study was performed on 268 prostate cancer patients, age ranging between 45-98 years. similar number of 268 persons (age and sex matched) was used as control group .the study period was from may-2006 to december-2009. data was collected from patients using a questionnaire which was filled in order to obtain information regarding: age, residence, tribe, education levels, occupation, marital status, stage of disease, family history and habits .the body mass index (bmi) was determined by anthropometrics measurements (weight and height). prostate cancer is the commonest cancer among male patients treated in the nci. the mean age of patients was 72.2±9.25. most of patients (73.9%) were over 66-years. family history is positive in 18 (6.7%) of the patients. rural inhabitants were 79.8% of all cases. the disease is equally distributed among different tribes. the illiteracy among cases is 39.1%. the commonest occupation was farming (60.1%). majority (90.7%) of the patients were married. most cases (85.4%) presented with stage ііі and іv. 73% of the patients had one or more of unhealthy habits (smoking, snuff and alcohol). the bmi was high in 6.9% of the patients. risk factors for prostate cancer in the study area, which may appear to have a high significant effect, were: the age, education level, occupation, unhealthy habits and the bmi. abstrak: tujuan kajian ini dijalankan ialah untuk menilai faktor-faktor risiko untuk kanser prostat di kalangan pesakit-pesakit yang dirawat di institut kanser kebangsaan (nci), universiti gezira, wadmedani, sudan. kajian dijalankan pada 268 pesakit kanser prostat, berumur di antara 45-98 tahun. jumlah bilangan pesakit yang sama iaitu seramai 268 orang (sama umur dan jantina) telah digunakan sebagai kumpulan kawalan. tempoh kajian ialah pada mei 2006 sehingga disember 2009. data diperolehi daripada pesakitpesakit dengan menggunakan boring soal selidik yang diisi untuk mendapatkan maklumat: umur, tempat tinggal, puak, taraf pendidikan, pekerjaan, status perkahwinan, peringkat penyakit, sejarah keluarga dan tabiat-tabiat. indeks jisim badan (bmi) telah ditentukan melalui pengukuran antropometri (berat dan ketinggian). kanser prostat ialah kanser yang paling banyak dihidapi pesakit-pesakit yang dirawat di nci. purata umur ialah 72.2±9.25. kebanyakan pesakit (73.9%) berumurlebih 66 tahun. sejarah keluarga ialah positif pada 18 (6.7%) pesakit. penduduk luar bandar ialah 79.8% daripada keseluruhan jumlah kes. penyakit ini terbahagi sama rata di antara puak-puak. kadar buta huruf di antara kes-kes ialah 39.1%. pekerjaan yang paling banyak ialah bertani (60.1%). majoriti (90.7%) pesakit telah berkahwin. kebanyakan kes-kes (85.4%) menghidapi peringkat iii dan iv penyakit. 73% daripada jumlah pesakit mempunyai satu atau lebih tabiat yang kurang sihat (merokok, menghidu, dan alkohol). 6.9% pesakit mempunyai indeks jisim badan (bmi) yang tinggi. faktor-faktor risiko untuk kanser prostat di dalam kawasan kajian yang menunjukkan kesan signifikan yang tinggi ialah: iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hamad and abuidris 204 umur, taraf pendidikan, pekerjaan, tabiat-tabiat kurang sihat dan indeks jisim badan (bmi). keywords: prostate cancer; body mass index; age; life-style; occupation; sudan 1. introduction worldwide, more than 670,000 men are diagnosed with prostate cancer every year, accounting for one in nine of all new cancers in males. recent incidence rates are heavily influenced by the availability of serum prostate specific antigen (psa) testing in the population and incidence varies far more than mortality.around 306,369 cases are diagnosed each year in europe. the lowest european rates are in southern and eastern europe, while the highest rates are found in scandinavia and northern european states [1]. prostate cancer is now the most commonly diagnosed cancer in men as well as the second leading cause of male cancer deaths and occurs in 1 out of 6 men [2]. the only fully established risk factors for prostate cancer are increasing age, africanamerican ethnicity, and family history of the disease. research has almost conclusively established a link for male hormones (androgens) in the causation of prostate cancer, but the effects of these hormones are not fully understood. although lifestyle factors (including diet and exercise) have been conclusively established as prostate cancer risk or protective factors, there is some evidence that a diet high in animal fat may account for differences noted in the incidence between different countries. however obesity has a high prevalence in patients with prostate cancer [3]. smoking and alcohol increased the risk of prostate cancer [4]. the “socioeconomic factors“ correlating to prostate cancer are population density, education, and income level [5]. farmers; certain occupations and industries with exposures to cadmium, herbicides, and fertilizers; and men with low occupational physical activity levels have elevated prostate cancer risk [6]. prostate cancer incidence increases dramatically with increasing age. although it is a very unusual disease in men younger than 50 years, rates increase exponentially thereafter [7]. prostate cancer increases faster with age than any other major cancer and, with an aging population, the burden of illness from prostate cancer will probably continue to increase in the future [2]. risk increases two to three times for men with a family history of prostate cancer in a first-degree relative. the risk appears to be higher if the relative is a brother rather than a father, suggesting that the disease is recessive or linked to the x chromosome [8]. risk is also increased if the affected relative is young or if more than one relative is affected [9]. the risk of developing and dying from prostate cancer is dramatically higher among blacks, is of intermediate levels among whites, and is lowest among native japanese [10-11]. black american men have higher rates of prostate cancer than white american men [10]. education is an important attribute guiding the selection of occupation. this, in turn, is a predictive factor for disposable income and many socioeconomic aspects of life, including residential and lifestyle factors. health conscious behaviour, such as seeking and affordability of healthy food and participation in health promotional and screening programs, relates to education and socioeconomic factors [12]. the incidence of prostate cancer correlates with population density, education, and income level [2]. the risk for prostate cancer was shown to have a much higher incidence within certain occupation ,such as farming, as well as amongst mechanics, newspaper workers, plumbers, and men in rubber manufacturing industries [2]. significant excess risks were seen for agriculture-related industries, soap and perfume manufacture, and leather iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hamad and abuidris 205 processing industries. significantly elevated standardized incidence ratios were observed amongst leather workers, and white-collar occupations [13]. several investigators have studied the history of men with prostate cancer in an effort to determine if sexual behaviour and/or fertility are related to the development of prostate cancer [2]. the men with prostate cancer were sexually active earlier and had more partners than the control group, but other evidence appears to indicate the opposite [14-16]. the cigarette smoking may be a risk factor for the development of prostate cancer. cadmium is a trace mineral found in cigarette smoke and alkaline batteries. people working in the welding and electroplating occupations are exposed to high levels of cadmium. cadmium exposure places an individual at greater risk for prostate cancer; cadmium increases the risk for prostate cancer by interacting with zinc. zinc is a necessary trace element in multiple intracellular metabolic pathways, and the prostate contains high amounts of zinc [2]. the body mass index (bmi) was calculated as weight in kilograms divided by the square of height in meters [17]. the world health organization (who) says that overweight and obesity are the most important known avoidable causes of cancer after tobacco. the obese patients had higher grade cancer and showed a trend toward having a more advanced pathologic stage [18]. the relationship between body mass index (bmi) and prostate cancer risk may be complex because obesity is associated with various hormonal factors and because the influence of bmi may differ according to whether the cancers are hereditary or sporadic [19] .obesity is associated with endocrine changes (e.g., increased estrogen and decreased testosterone in the blood) that have been implicated in the cause of prostate cancer [20]. dietary fat, previous ecologic studies have demonstrated a direct relationship between a country’s prostate cancer-specific mortality rate and average total calories from fat consumed by the country’s population [21-22].the relationship between other dietary factors and prostate cancer is complex. the risk increased with increasing dietary fat, animal fat and saturated and monounsaturated fat intake while approximately half of studies found no association between them and prostate cancer risk [23-24]. the men with the highest intake of dairy products and calcium were more likely to develop prostate cancer than men with the lowest intake. the advanced prostate cancer was the highest versus lowest intake categories of dairy products and the highest versus lowest intake categories of calcium [26]. no definitive links between prostate cancer and viruses have been established. the men with prostate cancer had higher titres of herpes virus and cytomegalovirus than did the control group in this study. the relationship between the risk for developing prostate cancer and a history of sexually transmitted disease remains unclear but appears tenuous [2].vasectomy may increase the risk for prostate cancer because of the observation that vasectomised men have higher levels of circulating testosterone. a study by sidney et al has found positive correlation between the number of years since vasectomy and prostate cancer risk. the relative risk for prostate cancer increased over time, with men who had a vasectomy 20 or more years in the past being the most at risk. there for vasectomy appears to confer an increased risk for the development of prostate cancer [2]. the history of benign prostatic hyperplasia carried a relative risk. a higher death rate from prostate cancer in men with a history of benign prostatic hyperplasia; however, the reasons for these findings remain unclear [2]. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hamad and abuidris 206 2. materials and methods the study covers all the 268 prostate cancer patients treated in the nci from may 2006 to december 2009. another 268 matched and not known to have prostate cancer persons from the main hospital attendants or the community were also chosen to form the control group. data was collected using a formal designed questionnaire. 2.1 questionnaire for each patient a questionnaire data form was filled, in order to obtain information regarding: age, residence, tribe, education level, occupation, marital status, habits and past medical history. date of diagnosis, stage of cancer and present complaints were also recorded. all questionnaires forms were filled by the first author. 2.2 anthropometric measurements weight, height and body mass index were measured. all patients' height and weight were taken. body mass index was obtained using weight over the square of height. readings were taken to the nearest 0.1 kg and 0.1 cm. 2.3 analysis statistical analysis was done using spss programmed under window (ibm) computer system. p value of < 0.05 is considered significant. 3. results most of the study patients, 202 (75.3%) were inhabitants of gezira state. the cases came from central and northern regions tribes and its distribution is similar to its normal census distribution. majority of the patients studied (85.4%) were diagnosed with stage ііі and iv disease (table 1). table 1: characteristics for prostate cancer patients (n=536). prostate cancer(n=268) control (n=268) frequency (%) state gezira 202 (75.3%) 268 (100%) 470 (87.7%) sinar 25.0 (9.3%) 25.0 (4.7%) al gadarf 21.0 (7.8%) 21.0 (3.9%) kurdfan 7.0 (2.6%) 7.0 (1.3%) kasla 6.0 (2.2%) 6.0 (1.1%) blue nile 4.0 (1.4%) 4.0 (0.7%) white nile 2.0 (0.74%) 2.0 (0.4%) al khartoum 1.0 (0.37%) 1.0 (0.2%) tribes northern tribes 97 (36.1%) 90 (33.6%) 187 (34.8%) middle tribes 104 (38.8%) 121 (45.2%) 225 (41.9%) western tribes 57 (21.2%) 49 (18.3%) 106 (19.8%) eastern tribes 10 (3.7%) 1 (0.37%) 11 (2.05%) southern tribes others 7 (2.6%) 7 (1.30%) stage stage іv 197 (73.5%) 197 (73.5%) stage ііі 32 (11.9%) 32 (11.9%) stage іі 5 (1.9%) 5 (1.9%) stage і 3 (1.1%) 3 (1.1%) unknown stage 31 (11.6%) 31 (11.6%) iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hamad and abuidris 207 more than 73.9 % of cases occur in men over 66 years, with the largest number being diagnosed in the age period between 66 76 years. in this study, 18 (6.7%) of the patients had positive family history. the majority of the patients were married, 243 (90.7%). among the study population 73% of cases had one or more of the unhealthy habits like smoking, snuff and/or alcohol consumption. strong association between unhealthy habits and prostate cancer was significant (p<0.000). more than 26% of the patients were snuffers (dipped tobacco usually under lips), 30% of were smokers, and 16% of the prostate cancer patients were alcohol drinkers. thirty nine percent of the patients were illiterate. χ 2 test performed on this group indicates that there is a significantly high association between the education level and prostate cancer (p <0.000). furthermore, 20.5% (55) of the patients were underweight with bmi (<18.5), and 93 (34.7%) of them were in normal weight with bmi (18.5-24.9), but 45 (16.9 %) of the patients had high bmi (≥25). χ 2 test performed on this data indicates that bmi has significant effects on prostate cancer with value of p<0.000 (table 2). occupations with low physical activity like office workers, drivers and teachers etc, represent more than 15% of all patients. however 60% (161) of the patients were farmer. χ 2 test performed on this data indicates that being a farmer or have an occupation with low physical activity has significant effect on prostate cancer (p<0.000). 4. discussion in this study, it was found that age is the strongest risk factor with a statistically high significant effect. prostate cancer is largely a disease of older men and is rare below the age of 45 years. this goes with the statements by kirby et. al. [27] , and parkin et. al. [28], they stated that prostate cancer incidence increases dramatically with increasing age. although it is a very unusual disease in men younger than 50 years, rates increase exponentially thereafter. the domination of gezira state inhabitants could be explained by the area, which nci drain. the effect of ethnicity was described by boring et al, who studied the incidence of clinical prostate cancer among different ethnic groups. african american men were found to have the highest incidence of prostate cancer, and asian and native american men have the lowest incidence [29]. in this study we can’t see effect of ethnicity probably because most of the study area population have similar origin. the family history findings agree with steinberg et al, who reported that approximately 15% of men with a diagnosis of prostate cancer will be found to have a first-degree male relative (e.g., brother, father) with prostate cancer, compared with approximately 8% of the u.s. population. approximately 9% of all prostate cancers may result from heritable susceptibility genes [30]. there is no significant association between sexual activity and prostate cancer, this agreed with kenneth et al, who said that marriage is often assumed to be synonymous with increased sexual activity, and fertility is often measured by the number of children a man admits to having fathered. it remains unclear if sexual activity has any relationship to prostate cancer risk [2]. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hamad and abuidris 208 table 2: risk factors for prostate cancer patients (n=536). prostate cancer (n=268) control (n=268) x 2 test age ≥45 ≤46 2 (0.74%) 266 (99.25%) 1 (0.37%) 267 (99.6%) sig (0.000) family history positive negative 18 (6.7%) 250 (93.2%) 268 (100%) sig (0.000) marital status married single widow divorce 243 (90.7%) 4 (1.4%)) 20 (7.5%) 1 (0.37%) 263(98.2%) 2 (0.75%) 3 (1.1%) ns residence rural urban 214 (79.8%) 54 (20.1%) 174 (65%) 94 (35%) ns unhealthy habits smoking alcohol snuff no habits 81 (30.2%) 43 (16%) 72 (26.8%) 143 (53.3%) 53 (19.8%) 5 (1.86%) 48 (18%) 185 (69%) sig (0.000) education levels illiterate kalwa primary secondary university above university 105 (39.1%) 68 (25.4%) 54 (20.1%) 28 (10.4%) 11 (4.1%) 2 (0.74%) 27(10.0%) 40(15%) 111(41.1%) 53(19.8%) 37(13.8%) sig (0.000) bmi underweight normal weight overweight pre-obese obese glass і obese glass іі obese glass ііі 55 (20.5%) 93 (34.7%) 30 (11.2%) 12 (4.5%) 3 (1.1%) 26 (9.7%) 131 (48.9%) 29 (10.8%) 88 (32.8%) 31 (11.6%) sig (0.000) occupations farmer worker office worker driver free job teacher mechanic nurse policeman engineer imam (mosque) 161 (60.0%) 39 (14.6%) 13 (4.8%) 18 (6.7%) 18 (6.7%) 9 (3.3%) 3 (1.1%) 3 (1.1%) 2 (0.75%) 1 (0.37%) 1 (0.37%) 31 (11.6%) 93 (34.7%) 37 (13.8%) 34 (12.7%) 20 (7.5%) 30 (11.2%) 8 (3.0%) 2 (0.75%) 8 (3.0%) 5 (1.9%) sig (0.000) a number of studies have found that cigarette smoking may be a risk factor for the development of prostate cancer. hsing and colleagues demonstrated relative risks of 1.8 and 2.1 for cigarette smoking and chewing tobacco, respectively [31]. also bagnardi et. al., found a significant increased risk for men drinking more than 50 g/day of alcohol, with a slightly higher risk for men consuming more than 100 g/day [32]. probably this study agrees with what has been published on the relation between tobacco/ alcohol and prostate cancer. the significance of literacy in this study agrees with baquet and colleagues from the national cancer institute, who investigated the incidence of prostate cancer with population density, education, and income level [33]. also this fact supported by kari iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hamad and abuidris 209 hemminki et. al., who reported that educational level, may influence the risk of cancer in many ways [12]. marjaana, published in 2001 that more than 35 studies on prostate cancer risk, most of it conclude that there is no association between prostate cancer risk and obesity. some report that obese men are at a higher risk than men of healthy weight, particularly for more aggressive tumors. one study found an increased risk among men with high waist-to-hip ratios, suggesting that abdomen fat may be a more appropriate measure of body size in relation to prostate cancer [34]. majority of the patients (79.8%) were from rural area. the later finding may only reflect the nature of this area where we find that most of inhabitants are living in rural area. the higher incidence of prostate cancer patients in agricultural communities reflects the effect of the problems that farmer suffer from, such as exposure to pesticides, engine exhausts, solvents, dust, animal fuels, and specific microbes, this agrees with reports from national cancer institute, usa [35]. on the other hand 14.6% of the prostate cancer patients were workers from different fields. kristan et al. published that many studies found moderate support for risk due to the following occupations: electrical power workers, water transport workers, aircraft fabricators, metal product fabricators, structural metal erectors, and railway transport workers. the following substances exhibited moderately strong associations: metallic dust, liquid fuel combustion products, lubricating oils and greases, and polyaromatic hydrocarbons from coal [36]. 5. conclusion the common potential risk factors, among study population, include: age, education level and positive family history. other factors include history of tobacco and alcohol consumption, bmi, and occupation. these findings are similar to the published literature. the dietary risk is not clear in sudanese prostate cancer patients, because the relationship between dietary factors and prostate cancer is complex. further research is needed to confirm these findings and identify specific exposures related to excess risk in some occupations and industries, including exposure to a variety of chemicals, such as pesticides, herbicides, fertilisers, solvents engine exhaust gases and organic dust and biological agents. references [1] j. ferlay, p. autier, m. boniol, m. heanue, m. colombet, and p. boyle. “estimates of the cancer incidence and mortality in europe”. ann. oncol., vol 18, no. 3, 581-92, 2007. [2] k.j. pienta and p.s. esper. “risk factors for prostate cancer”. ann. intern. med., vol 118, no. 10, 793-803, 1993. [3] e. giovannucci, e.b. rimm, y. liu, m. leitzmann, k. wu, m.j. stampfer, and w.c. willett. “body mass index and risk of prostate cancer in u.s. health professionals”. jnci journal of the national cancer institute, vol. 95, no. 16, 1240-1244, 2003. [4] h. grönberg, s.d. isaacs, and j.r. smith. “characteristics of prostate cancer in families potentially linked to the hereditary prostate cancer 1 (hpc1) locus”. jama vol. 278, no. 15, 1251-1255, 1997. [5] c.r. baquet, j.w. horm, t. gibbs, p. greenwald. “socioeconomic factors and cancer incidence among blacks and whites”. j natl cancer inst., vol. 83, 551-557, 1991. [6] s.s. wagner, a.p. chokkalingam, h.s.r. malker, b.j. stone, j.k. mclaughlin, and a.w. hsing. “occupation and prostate cancer risk in sweden”. journal of occupational & environmental medicine, vol 42, no. 5, 517-525, 2000. [7] epidemiological aspects. in: kirby rs, christmas tj, brawer mk: prostate cancer. london, england: mosby, 1996: pp 23-32. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hamad and abuidris 210 [8] monroe, k., et al. evidence of an x-linked or recessive genetic component to prostate cancer risk. nat med. vol 1, 827-829, 1995. [9] elo, j.p. and t. visakorpi. molecular genetics of prostate cancer. ann med. vol 33, no. 2, 130-141, 2001. [10] ries lag, eisner mp, kosary cl, et al., eds.: seer cancer statistics review, 1975-2002. bethesda, md: national cancer institute; 2005. also available online www.nci.gov. [11] bunker ch, patrick al, konety br, et al.: high prevalence of screening-detected prostate cancer among afro-caribbeans: the tobago prostate cancer survey. cancer epidemiol biomarkers prev 11 (8): 726-9, 2002. [12] kari hemminki and xinjun li. level of education and the risk of cancer in sweden. cancer epidemiology, biomarkers & prevention; 2003;796 vol. 12, 796–802. [13] sharma-wagner, sangeeta; chokkalingam, anand p., malker, hans s. r.; stone, b. j. ; mclaughlin, joseph k.; hsing, ann w. occupation and prostate cancer risk in sweden. journal of occupational & environmental medicine; 2000; 42(5):517-525. [14] honda gd, bernstein l, ross lk, greenland s, gerkins v, henderson b.vasectomy, cigarette smoking and age at first sexual intercourse as risk factors for prostate cancer in middle-aged men. br j cancer 1988; 57:326-31. [15] rotkin i. studies in the epidemiology of prostate cancer: expanded sampling. cancer treat rep 1977; 61:173-80. [16] ross r, deapen d, casagrande j, et al. a cohort study of mortality from cancer of the prostate in catholic priests. br j cancer 1981; 43:233-5. [17] timothy j. key, 2003. body mass index, serum sex hormones, and breast cancer risk in postmenopausal women. jnci journal of the national cancer institute 95(16):1218-1226. [18] motamedinia p, korets r, spencer ba, benson mc, mckiernan jm. body mass index trends and role of obesity in predicting outcome after radical prostatectomy.2008. [19] edward giovannucci, eric b. rimm, yan liu, michael leitzmann, kana wu, meir j. stampfer, walter c. willett. body mass index and risk of prostate cancer in u.s. health professionals. jnci journal of the national cancer institute; 2003; 95(16):1240-1244. [20] andersson so, wolk a, bergström r, adami ho, engholm g, englund a, nyrén o. body size and prostate cancer: a 20-year follow-up study among 135006 swedish construction workers. 1997; 5;89(5):385-9. [21] armstrong b, doll r: environmental factors and cancer incidence and mortality in different countries, with special reference to dietary practices. int j cancer; 1975; 15 (4): 617-31. [22] rose dp, connolly jm: dietary fat, fatty acids and prostate cancer. lipids; 1992; 27 (10): 798-803. [pubmed abstract] [23] optenberg sa, thompson im, friedrichs p, et al.: race. treatment, and long-term survival from prostate cancer in an equal-access medical care delivery system. jama; 1995; 274 (20): 1599-605. [24] wang y, corr jg, thaler ht, et al. decreased growth of established human prostate lncap tumors in nude mice fed a low-fat diet. j natl cancer inst; 1995; 87 (19): 1456-62. [pubmed abstract] [25] bairati i, meyer f, fradet y, et al.: dietary fat and advanced prostate cancer. j urol; 1998; 159 (4): 1271-5. [26] gao x, lavalley mp, tucker kl. prospective studies of dairy product and calcium intakes and prostate cancer risk: a meta-analysis. j natl cancer inst; 2005; 97 (23): 1768-77. [pubmed abstract] [27] kirby rs, christmas tj, brawer mk: prostate cancer. london, england: mosby. epidemiological aspects; 1996; 23-32. [28] parkin, d.m., et al. cancer incidence in five continents volume viii. iarc scientific publications. 2002; ed. vol. 155. lyon, france [29] boring cc, squires ts, tong t. cancer statistics. cancer; 1992; 42:19-39. [30] steinberg gd, carter bs, beaty th, et al. family history and the risk of prostate cancer. prostate ; 1990; 17 (4): 337-47. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology hamad and abuidris 211 [31] hsing aw, mclaughlin jk, schuman lm, bjelke e, gridley g, wacholder s, et al. diet, tobacco use, and fatal prostate cancer: results from the lutheran brotherhood cohort study. cancer res; 1990; 50:6836-40. [32] bagnardi, v., et al., a meta-analysis of alcohol drinking and cancer risk. br j cancer; 2001; 85(11): 1700-5. [33] baquet cr, horm jw, gibbs t, greenwald p. socioeconomic factors and cancer incidence among blacks and whites. j natl cancer inst; 1991; 83: 551-7. [34] marjaana lahti-koski . body mass index and obesity among adults in finland. publication of the national public health institute; 2001: 51. [35] national cancer institute .u.s.national institutes of health. prostate cancer prevention. risk factors for prostate cancer development.www.cancer.gov. [36] kristan j. aronson , , jack siemiatycki, ronald dewar and michel gérin. occupational risk factors for prostate cancer: results from a case-control study in montréal, québec, canada. american journal of epidemiology; 1996; vol. 143(4): 363-373. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 jarial et al. 56 anti-lipolytic activity and phytochemical screening ofchelianthesalbomarginata against pathogenic microorganisms rini jarial 1* , lakhveeer singh 1 , ab wahid zularisam 1 and shamsher singh kanwar 2 1 faculty of engineering technology, universiti malaysia pahang, lebuhrayatunrazak, 26300 gambang, pahang, malaysia. 2 department of biosciences, hpu summer hill shimla, 171005 india. *corresponding author:rini.is.jarial66@gmail.com (received: 27 th feb. 2017; accepted: 20 th sept. 2017; published on-line: 1 st dec. 2017) abstract:the aim of the present study is to evaluate the therapeutic properties of selected fern,chelianthusalbomarginata,and to identify its functional compounds. the methanolic fern-extract (mfe) of these ferns was assessed for anti-bacterial activities by measuring inhibition zones against a panel of pathogenic bacterial strains using an agar diffusion method. mfe at a concentration of 25 μg/ml showed marked anti-bacterial activity against all bacterial strains (6-23mm zone of inhibition) and was maximum against enterobacter sp. (23 mm). in addition, the mfe of c. albomarginatahad obtained the best mic values of 2.25µg/ml against s. aureus and enterobacter sp., respectively. the mfe also possessed good anti-lipolytic activity (66.5%) against porcine pancreatic lipase (ppl), and cholesterol oxidase inhibition (79%). this result showed that mfe of c. albomarginata,under optimal concentration, is not only a potent source of natural anti-oxidants and anti-bacterial agents but also possesses efficient cholesterol degradation and anti-lipolytic activities, that can be beneficial in body weight management. abstrak:tujuan kajian ini adalahbagi menilai ciri-ciri terapeutik paku-pakis terpilih, chelianthus albomarginata dan bagi mengenal pasti fungsi sebatian. aktiviti antibakteria pada ekstrak metanol pakis (mfe) ini telah dinilai dengan mengukur zon perencatan terhadap panel strain bakteria patogenik mengguna kaedah penyebaran agar. pada kepekatan 25 μg/ml, mfe menunjukkan aktiviti antibakteria yang paling ketara terhadap semua antigen bakteria (zon perencatan 6-23mm) dan maksimum terhadap enterobacter sp (23 mm). di samping itu, mfe c. albomarginata mempunyai nilai mic terbaik 2.25μg/ml terhadap s. aureus dan enterobacter sp., masing-masing. mfe juga menunjukkan aktiviti antilipolitik yang baik (66.5%) terhadap enzim lipase pankreas babi (ppl) dan kolesterol perencatan oksidase (79%). keputusan ini menunjukkan mfe c. albomarginata pada kepekatan optimum bukan sahaja sumber semula jadi antioksidamujarab dan antibakteria,malah turut mempunyai degradasi kolesterol berkesan dan aktiviti antilipolitik, iaitu bermanfaat bagi pengurusan berat badan. keywords:chelianthesalbomarginata; phytochemicals; anti-oxidant; antibacterial; antilipolytic 1. introduction chelianthesalbomarginata is a member of adiantaceae family, which can grow up to 60 cm in length. the ferns are naturally rich in phytochemicals and many types of iium engineering journal, vol. 18, no. 2, 2017 jarial et al. 57 valuable alkaloids, tannins, and flavonoids. ferns offer us bioactive molecules that may serve as safer therapeutics to combat existing new world diseases. the medicinal value of ferns has been known to many for more than 2000 years [1]. the screening of medicinally important fern extracts for antibacterial activity may be beneficial for humans and animal diseases [1]. people use traditional herbs to treat a variety of diseases including bacterial infections, but nowadays bacterial strains resistant most of the antibiotics and drugs [2] which cause approximately one-half of all death in world. plants are the only common sources of potentially valuable new drugs. this provokes us to assess ferns as a source of potential chemotherapeutic agents for antimicrobial and anti-lipolytic activity based on their ethnomedicinal properties. to date, no reports exist on the anti-lipolytic activity of ferns. the most common traditional use of ferns is to treat skin problems, wounds, fever, cough, reproductive problems, and also insect repellent [3]. the common diseases that could be treated by ferns include, ulcers (used fern stem juice), dysentery, and as protective medicine after childbirth [4]. with this knowledge, in the present study, the mfe of c. albomarginata was made and used to assay its biochemical constituents. other activities like anti-bacterial, anti lypolytic and mic activity against a panel of common human pathogenic bacterial strains. this could lead to new business ventures in pharmaceutical area as well as in commercial area and contribute to the bioeconomy. the anti-oxidant properties and anti-bacterial activities of a.veriens has been reported by several researchers [5] but here, the novelty of this study is to assess the effectiveness of mfe of c. albomarginatacontaining efficient cholesterol degradation and anti-lipolytic potential. 2. materials and methods 2.1 collection of ferns chelianthesalbomarginataferns were collected from the kuantan region and near the ump area was done on the basis of ethno medicinal properties mentioned in the literature [6]. 2.2preparation of fern tissue extracts fresh fern/plant material (whole plant) were washed under running tap water, air dried and then homogenized to fine powder. the powered preparations were stored in airtight glass vials. for preparing tissue extracts, 1.0g of air-dried powder was placed in 10 ml of methanol in a conical flask, plugged with cotton and the same was kept on a rotary shaker at 200 rpm for 48 h. the extract was filtered through whatman filter paper no.1 and the filtrate was centrifuged at 10,000 rpm at 4 o c for 15 min. the supernatant was collected and completely evaporated at room temperature. the left over mfe (methanolic fern extract) residue was dissolved in pbs (0.05 m phosphate buffer saline, ph 7.2) to reach a final concentration and was rendered sterilized by filtration (0.22 µm millipore filter).the filter-sterilized preparation of mfe obtained was kept at -70 o cin airtight vials for storage. 2.3 bacterial growth medium an appropriate amount of muller hinton medium (mh) and mh broth were bought from hi-media, mixed with distilled water, and then sterilized in an autoclave. the sterilized media were poured into petri dishes. the solidified plates were bored out with a sterile cork borer. the plates with wells were used for the antibacterial studies. iium engineering journal, vol. 18, no. 2, 2017 jarial et al. 58 2.4 assay for antimicrobial activity by well diffusion method antibacterial activities of the mfe preparations were tested using a well-diffusion method. the prepared culture plates were inoculated with different selected strains of bacteria using a streak plate method. wells were made on the agar surface with 6 mm cork borer. the mfe were poured into the well using a sterile auto pipette. the plates were incubated at 37ºc for 24 h for the bacterial growth to appear. the plates were observed for zone clearance around the wells. the zones of inhibition(s) around the well (in mm), including the well diameter, were recorded. the observations were taken in all 3 replicates and the average values ±sem were tabulated. a total of 12 bacterial strains that included staphylococcus aureus, klebsiella pneumonia, pseudomonas aeruginosa, salmonella paratyphi, shigellaflexerni, escherichia coli, staphylococcus citreus, enterobacter sp., salmonella typhimurium, streptococcus mutans, proteus vulgaris, and salmonella epidermis were employed to determine the antimicrobial activities of the mfe .the antibacterial activities of the mfe preparation were tested using a well-diffusion method. the petri plates containing mullerhinton (mh) agar were inoculated with different selected strains of bacteria using a surface spreading method. the uniform diameter (0.5 cm) wells were created in the mhagar plates with a sterile borer. the mfe was poured at different concentrations into each of the wells using an auto-pipette. the plates were incubated thereafter at 36.5 ± 0.5ºc for 24 h in order for bacterial growth and zone of clearance to appear. values less than 8 mm for the tested fern extracts were considered as not active against microorganisms [12]. 2.5 mic of mfe of chelianthes albomarginata selected bacterial strains the mic assay was performed in a 96-well micro-titer plate. for the mic assay, twelve wells in each of the rows of micro-titer plate were used; out of which last two wells were taken as control (no mfe was added). each of the 10 wells received 100 µl of the mh broth; except the 1 st well that received 200 µl of broth containing 500 µg/ml of the mfe. from the 1 st well, 100 µl of the mh-broth containing mfe was withdrawn with a sterile tip, and the same was transferred to the 100 µl of the broth in the 2 nd well. contents were mixed 4 times, then 100 µl of mh-broth was withdrawn from 2 nd well and was added to the 3 rd well. in this way, a range of 2-fold serial dilutions was prepared. the mh broth in each of the wells was inoculated with 2 µl of the pure bacterial culture and the content was mixed by 10 clockwise and 10 anti-clockwise rotations on a flat surface. the microtiter plate was incubated at 37 o c for 24 h. thereafter, the observations for growth of bacteria were visually made and mic of mfe for each of the test bacteria were recorded and expressed as µg/ml of mfe. 2.6 assay for cholesterol oxidase activity a previously reported [12] colorimetric method was used to assay the cholesterol oxidase activity in the mfe. approximately diluted commercial grade bacterial cholesterol oxidase (sigma chemical co., saint louis, usa) was employed to calibrate a reference profile using cholesterol as a substrate. one unit (u) of cholesterol oxidase activity was defined as the amount of enzyme capable of converting 1.0 µmole of cholesterol to 4-cholesten-3-one per minute at ph 7.5± 0.1 and at a temperature of 37 ± 1 ºc. 2.7 anti-lipase assay to 2.9 ml of tris-hcl buffer (0.1 m, ph 8.5), 80 µl of mfe of c.albomarginata was added. the reaction mixture was then incubated at 37oc in a water bath for 10 min to remove the turbidity then 80 µl of the substrate (p-npp, 20 mm) was added along with 20 iium engineering journal, vol. 18, no. 2, 2017 jarial et al. 59 µl of ppl. the reaction mixture was re-incubated at 55ocin a water-bath for 10 min. the reaction was stopped by chilling at -40oc. the amount of p-nitrophenol (p-np) released was measured at a410 (perkin elmer uv/vis spectrophotometer lambda 12) after bringing the tubes to room temperature. a standard curve of p-np was plotted at the selected concentration (10-100 µg/ml) vs. observed a410 values. 2.8 statistical analysis the results were expressed as the mean ± standard error of the mean (sem) for each group. statistical difference was evaluated using student’s t-test. results were observed to be highly significant at p<0.05 and p < 0.001. 3. results 3.1 anti-microbial activity of mfe the mfe of c. albomarginatashowed excellent activity against s. aureus with the average zone of inhibition of 24±0.5 mm, and s. epidermidis (22±0.5 mm), followed by marked antibacterial activities against salmonella paratyphi, salmonella typhi, and enterobacter sp. with zone of inhibition of 23.0±2.9, 23.0±1.5, and 22.0±1.5 mm respectively (fig. 1a-d). the least antibacterial activity of mfe was recorded against salmonella typhimurium (18.0±1.0 mm) in table 1. fig.1: anti-bacterial activity of mfe of c.albomarginataagainst selected microorganisms. inhibition zones for (a) shigella flexneri; (b)enterobacter sp.; (c) pseudomonas aeruginosa;(d) e.coli. table1: anti-bacterial activity of mfe of c.albomarginata against selected pathogenic bacteria organism inhibition zone (mean value in mm±sd) organism inhibition zone (mean value in mm±sd) pseudomonas aeruginosa 20.0± 1.0 enterobacter sp 22.0± 1.5 shigellaflexneri 23.0± 2.7 klebssiella pneumoniae 23.0± 1.9 escherichia coli 20.0± 0.5 staphylococcus aureus 24.0± 0.5 salmonella typhimurium 18.0± 1.0 streptococcus mutans 22.0± 1.0 salmonella paratyphi 23.0± 2.9 staphylococcus citreus 22.0± 1.0 salmonella typhi 23.0± 1.5 staphylococcus epidermidis 22.0± 0.5 iium engineering journal, vol. 18, no. 2, 2017 jarial et al. 60 3.2 mic as a measure of antibacterial activity of mfe the mic values of mfe ofc. albomarginatawere recorded against selected common pathogenic bacteria (table 2). the mle ofc. albomarginatahad the best mic values against s. aureus and enterobacter sp. (2.25 mg/ml; table 2). table2: mic of mfe of c. albomarginata againsta panel of common pathogenic strains organism mic (mg/ml) organism mic (mg/ml) pseudomonas aeruginosa 4.50 enterobacter sp 2.25 shigellaflexneri 4.50 klebssiella pneumoniae 4.50 escherichia coli 4.50 staphylococcus aureus 2.25 salmonella typhimurium 4.50 streptococcus mutans 4.50 salmonella paratyphi 4.50 staphylococcus citreus 4.50 salmonella typhi 4.50 staphylococcus epidermidis 4.50 3.3 anti-lipolytic assay and cholesterol oxidase activity of mfe lipase activity was assayed by the method [13] by measuring the micromoles of pnitrophenol released from pnitrophenyl palmitate. the mfe ofc.albomarginatawas found to possess 48.5% anti-lipolytic activity against ppl and 66.0% cholesterol oxidase activity. 4. discussion here we propose a sensitive and rapid method for screening the antimicrobial activity of c. albomarginata ferns. antibacterial activity obtained in this study with methanolic solvent was used for extraction. c. albomarginatarepresents a rich natural source of antimicrobial agents. plants are used medicinally in different countries and are important sources of many potent and powerful drugs. a wide range of medicinal plants (or their parts) are used to extract raw drugs and they possess varied medicinal properties [7,8]. in the present investigation, the methanolic plant extract of c. albomarginatawas formulated and studied for its anti-microbial activity against 12 common potentially pathogenic bacteria. the mfe of c. albomarginatashowed excellent activity against s. aureus with the average zone of inhibition of 24.0±0.5 mm (around 25mm). the results of this experiment revealed that the mfe of c. albomarginatais an effective antimicrobial agent for s. aureus [9] and reported that extracts of fern inhibited s. aureus, s epidermidis, salmonellatyphiincluding v. cholerae. in the present study, the mic values for mle were determined by micro-dilution method. the mfe of c. albomarginatahad the best mic values against s. aureus and enterobacter(2.25 µg/ml, respectively). a similar finding was reported for bordetella pertussis [9]. the aqueous extracts of pterisvitatta inhibited cariogenic streptococci, including s. mutans. the anti-bacterial activity against other harmful mouth flora has also been reported in patented literature [15]. a potentially valuable anti-cariogenic effect of ferns was suggested by inhibition of the synthesis of insoluble glucans by s. mutans. this includes flavonols, mainly quercetin, kaempferol, myricetin, and their glycosides. c.albomarginata has been shown to have a wide range of beneficial physiological and pharmacological effects. the use of ferns is clearly still a long way from clinical application, but there are promising leads in the dental context [10]. the concept of being able to exploit an antimicrobial agent which is a new chemical entity iium engineering journal, vol. 18, no. 2, 2017 jarial et al. 61 found in an abundantly available and renewable source is indeed an important achievement. the cholesterol degradation (cholesterol oxidase), as well as antioxidant activity, of mfe of ferns was studied by employing in vitro assay systems. the mfe of c. albomarginatashowed the best mic values against s. aureus and enterobacter sp. (2.25 mg/ml, respectively). there are some contradictions over precisely which bacterial species are inhibited by ferns, as previously [11] s. typhimurium and campylobacter jejuni have been reported to be both resistant and susceptible to methanolic extract of c. albomarginatathesedifferences in observations might be seen because of bacterial strain variation. our study also provided a strong evidence of the ability of the mfe of c. albomarginatato inhibit the activity of mammalian lipase (ppl) in vitro. the mfe showed (66%) anti-lipolytic activity against ppl as well as cholesterol oxidase inhibition of 66%. the present study thus indeed provided strong experimental evidence that the mfe of c. albomarginata is not only a potent source of natural anti-oxidants and anti-bacterial activities but also possesses efficient cholesterol degradation and anti-lipolytic potential. 5. conclusion mfe has potential to inhibit the growth of many common bacterial pathogens. there are still scanty studies on anti-bacterial properties of c. albomarginata or their biochemical constituents. it may be suggested that the plants/tea extracts may possess effective antimicrobial activities that may be explored in the management of common bacterial infectious diseases. c. albomarginatamay represent a new source of antimicrobial phytochemicals with stable biological activity that can extend a scientific base for the use of tea in modern medicine. the need for the screening of other known or unknown medicinal plants becomes more compelling because of indiscriminate/irrational use of potent antibiotics, many bacteria/microorganisms have developed genetic modification to overcome bactericidal/bacteriostatic effects of commonly used antibiotics. most of the diseases against which the lycophytes are said to have curative properties are caused by both gram-positive and gram-negative bacteria. the discovery of novel phyto-constituents that are likely to have least toxicity and/or undesired side-effects is a much desired event. finally, it could be concluded that the mfe of c. albomarginatanot only possessed strong to moderate anti-bacterial activities against 12 common pathogenic and opportunistic bacteria but also markedly effected the degradation of cholesterol in vitro as well as appeared to be an effective anti-lipolytic preparation. mfe of c. albomarginataappeared to be a potent source of natural anti-oxidants and anti-bacterial activities besides possessing efficient cholesterol degradation and anti-lipolytic potential that might be beneficial to improve human health. the active principles involved in this plant need to be purified and individually studied for their active antibacterial, anti-lipase and anti-cholesterol oxidase biochemical constituents. acknowledgement the study was funded by universiti malaysia pahang (ump) and the commonwealth fellowship ministry of malaysia. we are thankful to the anonymous reviewers for their valuable comments. references [1] nath k, bhattacharya m. (2016) antibacterial activity of rhizome extracts of four pteridophytesfromsouthernassam, north east india . asian journal of phytomedicine and clinical research, 4(1):1-5. iium engineering journal, vol. 18, no. 2, 2017 jarial et al. 62 [2] sofowara a. (1982) medicinal plants and traditional medicine in west africa john wiley and sons. 41 (2): 252256. [3] dongmo a, ndom n, massoma d, dzikouk g, fomani m, bissoue n, vierling w. (2003) vasodilating effect of the root bark extract of ficussaussureana on guinea pig aorta. pharmaceutical biology, 41(5):371-374. [4] mohan s, balamurugan v, salini s, rekha t. (2012) antioxidant and phytochemical potential of medicinal plant kalanchoepinnata.journal of chemical and pharmaceutical research, 4(1):197-202. . [5] marinova d, ribarova f, atanassova m. (2005) total phenolics and total flavonoids in bulgarian fruits and vegetables. j chemtechnol metall,40(1):255-260. [6] singh m, khare b, rawat a. (2008) antimicrobial activity of some important adiantum species used traditionally in indigenous systems of medicine . journal of ethnopharmacology, 115(2):327-329. [7] wang x, cao j, wu q. (2016) flavonoids, antioxidant potential, and acetylcholinesterase inhibition activity of the extracts from the gametophyte” and archegoniophore of marchantiapolymorpha l. molecules, 12(1):13-15. [8] trease r, evans w.pharmacognosy (2012) 15th edn. saunders, pp. 214-393. [9] just m,recsio c, giner r, cuellar d, marez s, bilia j. (1998) anti-inflammatory activity of usual lupanesaponins from bulerumfruiticescens. planta medica 121 (2) :404-407. [10] raj va, kumar v, singh p, kumar v. (2012) in vitro antimicrobial activity of kalanchoepinnata leaf lipids, journal of ethnopharmacology, 115 (3): 3-5 [11] singh s, jarial r, kanwar ss. (2013) therapeutic effect of herbal medicines on obesity: herbal pancreatic lipase inhibitors. woodpecker journal medical plants. 111 (2):053-065. [12] das s, mujib a, dey s. (1999) biotechnology of medicinal plants: recent advances and potential. first edition (uk992 publications, hyderabad, india) pp126-139. [13] winkler h, (1979) utilized this same method at frequencies less than 1 hz to examine the effects of strain amplitude. journal of ethnopharmacology, 112 (2):245249. microsoft word 187 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering khalifa et al. 123 ethical issues in monitoring and based tracking systems othman o. khalifa, jalel chebil, aisha-hassan abdallh and shihab hameed electrical and computer engineering department, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. khalifa@iim.edu.my abstract: monitoring and based tracking systems use a variety of technologies to record and monitor the activities of humans. this can increase the risks to the privacy and security of individuals. the amount of information gathered about individuals is growing through the proliferation of surveillance cameras, sensors; microchips and radio frequency identification rfid tags embedded in devices and products. advances in electronic technologies allow companies and government agencies to store and process large amounts of information about individuals. the internet provides the ultimate copier device, making this information easily available to millions. this paper highlights the ethical issues emerging with the new technologies in the monitoring and base tracking system. new regulations should be proposed to protect the individual privacy. abstrak: pemantauan dan sistem berasaskan pengesanan menggunakan pelbagai teknologi untuk merakam dan memantau aktiviti manusia. ini boleh meningkatkan risiko dari segi privasi dan keselamatan individu. jumlah maklumat yang dikumpulkan tentang individu berkembang melalui proliferasi pengawasan kamera, sensor; mikrocip dan tag frekuensi radio yang diletakkan di dalam peranti dan produk. kemajuan dalam teknologi elektronik membolehkan syarikat-syarikat dan agensi-agensi kerajaan menyimpan dan memproses sejumlah besar maklumat mengenai individu. internet menyediakan peranti salinan utama, menjadikan maklumat ini didapati dengan mudah. kajian ini memaparkan isu-isu etika yang baru muncul dengan teknologi baru dalam pemantauan dan sistem berasaskan pengesanan. peraturan baru perlu dicadangkan untuk melindungi privasi individu. keywords: privacy implications; tracking systems; ethical issues; rfid 1. introduction monitoring and based tracking systems are an emerging technology with significant potential benefits to domains requiring automatic retrieval of information about objects, such as packages, people, store merchandise, books in libraries, spare parts in repair depots, histories of objects through the manufacturing process, and many other applications. as the technology of monitoring and based tracking systems become more complex and affordable, it is becoming much easier to monitor and track people. as result, the issue of privacy of the individual becomes more serious since the available technologies make it easier for some abuser to invade the privacy of people. this study discusses the issue of privacy to three types of monitoring and iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering khalifa et al. 124 based tracking systems: radio frequency identification (rfid), global positioning system (gps), and closed circuit television (cctv). in this paper, sections 2 to 4 describe the rfid, gps and cctv systems technology used in monitoring and tracking system. the issue of privacy is also discussed. section 5 presents the islamic view for the privacy of the individual. the protection of privacy from the emerging new technology is discussed in section 6. finally, section 7 concludes the paper. 2. rfid technology there are rfid is an electronic tagging technology that allows an object, a place, or a person to be automatically identified at a distance using radio waves [1-2]. an rfid system can be composed of three subsystems: an rf subsystem, an enterprise subsystem, and inter-enterprise subsystem (national institute of standards and technology, 2007). the rf subsystem performs identification and related transactions using wireless communication. the enterprise subsystem contains computers running specialized software that can store, process, and analyze data acquired from rf subsystem transactions to make the data useful to a supported business process. the inter-enterprise subsystem connects enterprise subsystems when information needs to be shared across organizational boundaries. every rfid system includes an rf subsystem, which is composed of tags attached to or embedded in objects and readers that query the tags. the tags also referred to as transponders are small electronic devices that are affixed to objects or embedded in them. the components of the tag are: a microchip and an antenna. the typical tag size ranges from a postage stamp to a pager [3]. each tag has a unique identifier. important characteristics of tags include their identifier format, the source of their power, the radio frequencies over which they operate, their size and shape, and additional functionality they support, such as security features and connections to environmental sensors (national institute of standards and technology, 2007). the rfid reader is a device that wirelessly communicates with tags to identify the item connected to each tag and associate the tagged item with related data. both the tag and the reader are two-way radios, and each has an antenna and is capable of transmitting radio signals. 2.1 applications and benefits of rfid systems the rfid systems are used by the industry, the commercial companies and security. typical applications include labeling products for rapid checkout at a pointof-sale terminal, inventory tracking, animal tagging, timing marathon runners, smart card, smart passport, secure automobile keys, and access control for secured facilities [4][5]. in the commercial sector, rfid tags on products are used to manage inventories and supply chains. rfid employs a numbering scheme called electronic product code (epc) which can provide a unique identification for any physical object in the world. in addition, rfid tags identify lost items, and even keep tabs on people; the data carriers have assisted with surgeries, prevented the abduction of infants, and tracked teenagers on their way to school. 2.2 privacy threats from the rfid iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering khalifa et al. 125 privacy is a very important topic for consumer acceptance of technologies. the consequence for misusing the rfid technology may rise to privacy issues. rfid technology is so revolutionary that it offers less than ethical characters unprecedented opportunities for theft, covert tracking, and behavioral profiling. without the appropriate controls, attackers can perform unauthorized tag reading and clandestine location tracking of people or objects. rfid devices can be used to locate and monitor peoples without their permission; building up a detailed profile of a person based upon items in their possession; or even to impersonate individuals by replicating their rfid tags. criminals can also manipulate rfid-based systems (i.e. retail checkout systems) by either cloning rfid tags, modifying existing tag data, or by preventing rfid tags from being read in the first place. tag deactivation is a minimum requirement to fulfill privacy protection. in most cases, individuals present unique identification numbers in an authentication process, as evidence that they are who they claim to be. according to glasser et al.[14], “rfid does not violate privacy anymore than credit card and bar code use, unless intruders have access to readers and the associated databases.”. on the other hand, the tag or the reader can be hidden without the knowledge of the person. rfid tags could be hided affixed to people, goods and documents, and then used to monitor and track the movements of these items or collect a profile of the individual by aggregation of the tags in that individual’s possession. if rfid readers were secreted affixed into exit doors or other certain places, then the people dos know when tags in their belongs are being read, or for what for. rfid technologies are almost unique in their ability to impact personal privacy in any of the four ‘dimensions’ of privacy: • territorial privacy: rfid devices could be used to monitor the location of objects, collect data information about the items surround the individual, or track the movements of objects. • bodily privacy: rfid devices with built-in sensors could be used to monitor the health of an individual, or even be embedded in their skin to track their movements. • communications privacy: packages, a post letter could be tracked with an rfid tags and know the destination. • data privacy: rfid devices embedded in equipments are now commonly used as authentication mechanisms for computer users. these impacts raise many equations and concerns regarding privacy, on the other hand, peoples argue that rfid technologies may be used to protect peoples and goods. in other words, rfid technology could be used for better human life quality. the ethical element would be based upon: • respect confidentiality • don't "flame" • don't be anonymous • don't allow third party to access other's data • don't misrepresent or lie • follow government's general guidelines • consider presentation of message iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering khalifa et al. 126 3. global positioning systems a global positioning system (gps) uses a constellation of gps satellites that orbit the earth. these satellites broadcast messages on radio frequencies that consist of the time of the message and orbital information. a gps receiver measures the transit times of messages from four satellites to determine its distance from each satellite, and thereby calculate its location. this type of location data helps police with their investigations, such as tracking down a criminal or even someone who is lost or missing. they can act as a safety device to protecting your family and loved ones. location technology also helps locate stolen cars. the technology for these tracking devices is constantly improving. it can be of huge assistance to those navigating in unfamiliar territory. in the united states, law enforcement officials use gps technology to track criminal suspects and parolees without their awareness. for example, they may attach to the individual’s car a device such as track stick, which is a gps data logger integrated with google earth [1]. law enforcement officials argue that gps devices fall outside the scope of laws regulating wiretaps and similar forms of electronic surveillance because they do not record conversations [2]. some states have considered requiring gps devices on all motor vehicles, to track the distances that they travel. then states could collect taxes from motorists, in proportion to their mileage, to pay for the construction and maintenance of highways [3]. these vehicle mileage taxes would replace gasoline taxes, whose revenues will decline as the number of electric and hybrid-powered cars increases. gpss are used by businesses, such as package delivery services, to track employees who travel to multiple. the gps system has a number of major benefits. however, there is some potential that tracking data can be misused, and can be considered an invasion of privacy. with the advanced trend of gps technologies in wireless devices in order to accessorize them with navigation features [6], many raised equation about such information of using this technology. with accounts of law enforcement officials remotely activating mobile devices of suspects for audio surveillance [7], it is not hard to imagine that the gps data could also remotely and surreptitiously be read providing a ubiquitous surveillance device. the combination of motorists and mobile phone users form a huge majority of the urban population and citizens should not be victims of mass surveillance or privacy abuses based on location data. rigorous ethical and legislative safeguards need to be implemented to protect future abuses of individuals privacy in this context. location technologies are still in their nascent stages, therefore, from a technology point of view, it is important to dispel these privacy concerns right from the beginning, and focus on building in privacy protection within such systems so that as new applications become available, appropriate privacy measures are integral to them [6]. 4. closed circuit television (cctv) cctv cameras have become more advanced in recent years and it can now isolate and track identified targets, recognize number-plates, and eavesdrop on conversations. cctv has spread in the last few years. cctv cameras are now used not only on motorways, where you’ll receive warning about upcoming cameras, but also on cash machines, housing estates, and car parks [8]. the closed circuit television (cctv) is considered as a technical solution to security problems. it can assist effectively in preventing, detecting, and/or prosecuting crimes ranging from iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering khalifa et al. 127 major terrorism to minor vandalism. with the help of cctv, both public and private spaces can be made more secure. however cctv cameras were not only used to prevent crimes, it also been used by employers wishing to check up on staff or ensure that customer service is up to the standard. in addition, they are used to monitor certain group of people or race without their knowledge. this may be an intrusion on privacy. it is largely this potential problem with cctv that has been regulated against [9]. cctv is found anywhere. many has been permitted the use of cctv in public areas including shopping malls, motorways and housing estates. regulations require a sign providing information for contacting the camera operator wherever cctv is used in a public area. these signs should be made visible when you enter a camera-monitored area [8]. 5. information privacy: an islamic perspective as discussed earlier, tracking system technologies introduce new challenging privacy issues. protection of personal information has become rapidly important in term of privacy. the advance in technology creates new security challenges related to the protection of personal information. it also provides information about guidelines that address the collection, use and disclosure of personal information. privacy is an essential factor related to human right and freedom society. it is included in the foundation of the rule of law, patient confidentiality, lawyer-customer privilege, private property, and many other fields related to the autonomy of the individual. with the rapid development of new information and communication technologies in the 21 st century, the ability of the government and the private sector to collect, record and "mine" personal information has grown exponentially. the critical change related to the privacy happen after september 11, 2001 incident, where legislators struggle to balance security against civil liberties, privacy is likely to remain an important social and political issue. the reality shows that protection of personal information has become with very low priority compared to security aspects, which leads to sever unfair treated for many innocents. one of the critical issues related to using monitoring or tracking systems is the collection of personal information for an illegal or unethical purpose which is against privacy. islam is the last religion revealed to the world, which is comprehensive, fair, and lead to goodness in this life and the hereafter. the privacy is one of the essential factors in islamic life. several verses in quran as well as many saying from prophet mohammed (peace and blessings be upon him) mentioned directly or indirectly the importance of respecting the privacy of any person. allah swt request us to avoid suspicion, spy not on each other as shown in quran “o ye who believe! avoid suspicion as much (as possible): for suspicion in some cases is a sin: and spy not on each other nor speak ill of each other behind their backs. would any of you like to eat the flesh of his dead brother? nay ye would abhor it...but fear allah: for allah is oftreturning most merciful” (qur'an, 49:12). the general text of the qur’an on the prohibition of spying similarly means that all varieties of espionage are included. furthermore the qur’anic text on espionage is immediately preceded by an address to the believers to “avoid indulgence in suspicion, for surely suspicion in most cases is sinful, and spy not…” (qur’an, 49:12). espionage originates in suspicion, which is also to be avoided as far as possible, although the wording of the text is not as categorical on suspicion as it is on iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering khalifa et al. 128 spying. the text here seems to permit suspicion that is based on reasonable grounds [6]. the point, however, is that both are seen as a threat to personal dignity and a violation of the individual’s right to privacy. the prohibition of spying also includes opening of personal letters and confidential correspondence. this is, in fact, the subject of a hadith to the effect that “one who looks into the letter of his brother without his permission is like looking into the fire of hell.” (al-suyuti, al-jami assaghir, p. 165; ibn majah, al-adab al-shariyya, vol. 2, p. 166). 6. privacy protection new methods for ensuring customer and staff privacy have to be developed. any organization that pilots or implements the monitoring and based tracking systems may consider the consequences impact of the privacy aspects. organizations that using the monitoring systems may gained some benefits through the use of these technologies in applications such as stock control, safety, security, commitment and loyalty management. however, privacy advocates may cause many adversities which may affect the members of the organization. such problems could be avoided if the users avoid reputation damage and risk of legal action. therefore privacy related issues should be considered prior to implementing of any emerging technology. this is can be done through a risk management process, which should address a number of key questions including: these technology be affixed to items that may used beyond the control of the organization. is it necessary to keep or process privite information within these systems? is the consequence impact of a privacy incident outweighing the possible benefits arising from the use of technologies? can the organisation ensure that every member and sister organisation will keep the privacy of personal information, and use these systems in proper manner? since no amount of privacy or security measures that may control these systems, the abuse by authorised users may happens. an effective mechanism may be used to reduce the risk of privacy violation and protect both the individual and the organisation in the event of such problems. 7. conclusion privacy protection becomes increasingly harder as the technology becomes more widely deployed. it is often demanded, but rarely implemented. each time a new consumer technology is introduced, the protection of private data is seen as a burden to quick deployment. privacy problems in monitoring and based tracking systems, such as the information leakage, traceability and impersonation are a challenging issues. references [1] evsenkorkmaz and alp ustundag, standards, security & privacy issues about radio frequency identification (rfid), rfid burasia 1 st annaual conference, pp. 1-10, sept. 2007. [2] n. c. wu, m. a. nystrom, t. r. lin, and h. c. yu, challenges to rfid adoption management for the globale future, picmbt, vol. 2, pp. 618-623, july 2006. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering khalifa et al. 129 [3] razaq, wai tong luk, kam man shum, lee ming cheng, and kai ning yung, secondgeneration rfid, security & privacy. ieee, vol. 6, no. 4, pp. 21-27, july-aug. 2008. [4] juels, rfid security and privacy: a research survey, selected areas in communications, ieee journal, vol. 24, no. 2, pp. 381-394, feb. 2006. [5] klaus finkenzeller, rfid handbook, radio-frequency identification fundamentals and applications, wiley, 1999. [6] m. ohkubo, k. suzuki, and s. kinoshita, rfid privacy issues and technical challenges, communications of the acm, vol. 48, no. 9, pp. 66-71, sept. 2005. [7] juels, r. l. rivest, m. szydlo, the blocker tag: selective blocking of rfid tags for consumer privacy, in proceedings of 10th acm conference on computer and communications security (ccs’03), 2003. [8] muhammad usman iqbal, samsung lim, privacy implications of automated gps tracking and profiling”, ieee technology and society magazine ieee technol soc mag , vol. 29, no. 2, pp. 39-46, 2010. [9] mccullagh, d & broache, a 2006, fbi taps cell phone mc as eavesdropping tool , cnet news, viewed 10 april 2007, http://news.com.com/fbi+taps+cell+phone+mic+as+eavesdropping+tool/21001029_36140191.html [10] http://www.yourprivacy.co.uk/cctvsystems.html , viwd april 7, 2011. [11] ann rudinow sætnan, heidi mork lomell and carsten wiecek, “controlling cctv in public spaces: is privacy the (only) issue? reflections on norwegian and danish observations”, surveillance & society cctv special (eds. norris, mccahill and wood) 2(2/3): 396-414, 2004. [12] floerkemeier, r. schneider, m. langheinrich, scanning with purpose suppporting the fair information principles in rfid protocols, 2nd international symposium on ubiquitous computing systems ucs, 2004. [13] h. lee, j. kim, privacy threats and issues in mobile rfid, the first international conference on availability, reliability and security (ares '06), 2006. [14] j. kim, e. y. choi, d. h. lee, secure mobile rfid system against privacy and security problems, third international workshop on security, privacy and trust in pervasive and ubiquitous computing (secperu’07), 2007, pp. 67-72. [15] d.j. glasser, k.w. goodman, and n.g. einspruch, “chips, tags and scanners: ethical challenges for radio frequency identification,” ethics and information technology, vol. 9, no. 2, pp. 101-109, july 2007. [16] katherine albrecht, “rfid: tracking everything, everywhere”, http://www.michaeljournal.org/rfid.asp, viewed april 8, 2011. psg dynamic changes in methamphetamine abuse using recurrence quantification analysis iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. psg dynamic changes in methamphetamine abuse using recurrence quantification analysis ghasem sadeghi bajestani1 and sayyed majid mazinani2* 1research center for computational cognitive neuroscience – system & cybernetic laboratory, 2department of electrical engineering, imam reza international university, mashhad, iran. *corresponding authors: smajidmazinani@imamreza.ac.ir, g.sadeghi@imamreza.ac.i ir (received: 9th june 2018; accepted: 17th april 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.956 abstract: polysomnography (psg) is a standard approach based on comprehensive monitoring of cardiorespiratory signals during sleep. this study has been conducted on subjects with a record of methamphetamine abuse. the significance of this work is methamphetamine abuse detection and measurement without the use of blood tests. with regard to the nonlinear and chaotic dynamic of vital signals and the richness of psg, the tool employed to carry out the study is recurrence qualification analysis. the objective behind this is to observe and quantify nonlinear dynamic changes of vital signals caused by methamphetamine abuse. results reveal that: 1) chaotic signals, in other words, system complexity has decreased; 2) under the influence of methamphetamine, signal entropy has increased, bringing about the irregularity of the signals; 3) methamphetamine consumption prompts signal compression to overtake signal expansion which means signal information has declined. abstrak: polisomnografi (psg) adalah pendekatan piawai berdasarkan pengawasan menyeluruh signal kardiorespiratori ketika tidur. kajian ini telah dijalankan ke atas subjek yang mempunyai rekod salah guna methapitamin. kepentingan kajian ini adalah bagi mengesan salah guna methapitamin dan mengukurnya tanpa menggunakan ujian darah. dengan mengambil kira ketidak-linearan dan signal penting dinamik dan psg yang berharga, kaedah yang digunakan bagi menjalankan kajian ini adalah analisis kelayakan berulang. objektif di sebalik kajian ini adalah bagi melihat dan mengkuantiti perubahan dinamik tidak linear ke atas signal penting disebabkan salah guna methapitamin. hasil menunjukkan: 1) signal huru-hara, atau kata lain, kesulitan sistem telah berkurang; 2) di bawah pengaruh methapitamin, signal entropi telah bertambah, menjadikan signal tidak normal; 3) pengambilan methapitamin menyebabkan signal mampat mengambil alih signal kembang bermaksud informasi signal telah berkurang. keywords: sleep apnea; methamphetamine; chaos; recurrence qualification analysis; polysomnography 1. introduction sleep apnea is a common breathing disorder in sleep during which the individual’s breathing is disrupted. it lasts for several seconds or several minutes and occurs at least 5 times in an hour. sleep apnea results in serious health problems such as excessive daily drowsiness, nonrestorative sleep, depression, decrease in memory, and even serious cardiac arrhythmias. also, it has indirect effects on high blood pressure, brain stroke, and 79 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. myocardial infarction. fortunately, sleep apnea is a curable disorder. however, the majority of patients suffering from it, comprising 6 percent of the whole world population, remain undiagnosed [1,2]. polysomnography (psg) is a standard approach based on comprehensive monitoring of cardiorespiratory signals during sleep which is used to detect sleep apnea. in psg the following vital signals are simultaneously recorded: 1) eeg: electroencephalography; 2) eog: electrooculogram, 3) emg: electromyography; 4) ecg: electrocardiography; 5) air flow through the nose, stomach, and the chest; 5) snoring and oxygen-rich blood (spo). studying vital signals of the body yields valuable information on bodily behavior. in recent years, nonlinear methods of analyzing physiological signals have replaced traditional methods, such as fourier transport and wavelet transport. this is mainly because physiological rhythms of the body are nonlinear, chaotic, and unstable. in other words, the characteristics of physiological signals change with the passage of time and these changes are not regular. on the basis of the research carried out in this field, when a bodily disorder occurs, system behavior becomes more predictable and regular while system disorder decreases. in the past, to analyze sleep apnea, numerous research works were conducted on different organs of the body, particularly on the heart and its various parameters such as the number of heart beats. the human brain is the control center of every bodily activity while, on the other hand, the body’s metabolism influences the brain. accordingly, influential factors on metabolism (such as methamphetamine) affect the cerebral dynamic signals. this study is particularly conducted on subjects with a record of methamphetamine abuse. according to studies carried out on psg, especially on bodily behaviors during sleep, subjects with a record of methamphetamine abuse suffer from problems such as decrease in sleep time, nonrestorative sleep, decrease in the healthy functioning of the body, and an increase in mortality rate [3,4]. it is widely believed that sleep apnea is caused by narcotic drugs such as opium, heroin, and morphine. however, recent studies reveal that methamphetamine, too, can cause sleep apnea. in december 28, 2012, research was conducted on 535 people addicted to methamphetamine hydrochloride that revealed 40 subjects were experiencing apnea. the rate of apnea among the subjects was 7.48 percent [2]. 2. methodology 2.1 data collection this study is particularly conducted on subjects with a record of methamphetamine abuse. according to studies done on psg [5], and especially on physiological behaviors during sleep, subjects with a record of methamphetamine abuse suffer from problems such as decrease in sleep time, nonrestorative sleep, decrease in the healthy functioning of the body, and an increase in mortality rate [6]. to record psg and analyze sleep apnea, it is necessary to hospitalize the patient overnight. the data used in this study are stored in the sleep clinic at ibn sina hospital, mashhad, iran. to create this database, 13 subjects (aging 25±5) were asked to stay overnight in the hospital. all the signals were sampled at 256 hz which include a four-channeled eeg with four channels, a standard two-channeled eog, emg, ecg, heartbeat, chin movements, left and right leg movements, blood oxygen, respiration signals, snore signals, and thorax and abdominal signals. the database that we record for this research includes 13 subjects with 5 (control group) cg subjects whose health has been confirmed by a doctor and 8 (methamphetamine group) mg with a record of methamphetamine abuse. 80 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. 2.2 curve recurrence tools for analyzing data recurrence is a fundamental property of dynamic systems that can be exploited to determine the behavior of the system in the phase space [7]. recurrence as a scientific element was introduced by henry poincare in 1980. he was the first to prove that the three-body problem was chaotic and unsolvable. when working on the three-body problem, poincare stated that, irrespective of some exceptional trajectories whose occurrences were infinitely improbable, it could be shown that the system recurrently returns to a point very close to its starting point. in 1987, eckmann et al. [8,9] introduced the method of recurrence plots (rp) in order to concretize the recurrences in dynamic systems. let us assume that there is the trajectory (consisting of n points) of a system in its phase space. the system development is, therefore, described by a series of vectors that denote a trajectory in a virtual mathematical space. the corresponding recurrence curve, then, is based on the following recurrence matrix: (1) where n is the number of considered states of , considering the error distance ε. regarding the fact that the system does not exactly recur to a previously observed state, ε is essential. rp can be defined as follows: (2) where n is the number of calculated points, is the norm, and is the heaviside function (meaning that if x<1, then , and in other points ). to compute rp, a proper norm has to be chosen. the norms that are frequently exploited are l1, l2 norms (the euclidean norm), and the norm (maximum or supremum norm). since ε is fixed, , l1, and l2 find the most, the least, and the intermediate amount of neighbors respectively. to compute rp, is often used, because it computes fast and allows us to study rp features analytically. ε can have a fixed value or it can vary. choosing a proper ε is of great importance, because if ε is too small, there will be almost no rp, and if ε is too large, rp will experience too much disturbance, causing thicker and longer diagonal structures. some criteria for choosing ε are introduced: 1) a few percentage of the suggested maximum phase space diameter (usually less than 10 per cent of the mean) [9,10]. 2) taking into account the density of the recurrence points by seeking a scaling region in the density of the recurrence points [8]. 3) measuring a composition of real signals and observable noise with standard deviation (to get similar results in noise-free situations, ε needs to be chosen so that it is five times greater than the standard deviation: . this criterion, which is useful for de-noising, minimizes fragmentation and the thickness of the diagonal lines in accordance with the threshold [9]. 4) using constant density of the recurrence points: the fan method is suitable to be used for bodily signals since it does not necessitate the presence of soakers with similar volume and capacity to compare state space behaviors [10]. 81 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. 2.2.1 complexity criteria (recurrence qualification analysis rqa) to move beyond the visual impressions obtained from rps, several qualitative complexity criteria of small scale structures are presented in rps that are known as recurrence qualification analysis. on the basis of the density of the recurrence points, these measures include structures of diagonal lines of length l, meaning that the two trajectory segments were running tangentially within the neighboring distance of ε for l time units, and structures of vertical lines of length v, showing that the trajectory does not change considerably for v time units. 1) criteria based on recurrence density recurrence rate: the simplest criterion of recurrence curves is recurrence rate (rr) or recurrence percentage, which is calculated as in equation 3: (3) which is a measurement of the density of the recurrence points in rp. 2) criteria based on diagonal lines determinism: uncorrelated or weakly correlated processes with accidental relations or with chaotic behavior are the causes behind the formation of very short diagonals, while deterministic processes form longer diagonals and isolated recurrence points. the ratio of diagonal recurrence points (from minimum length lmin) to all recurrence points is introduced as the criterion of the system’s determinism. (4) the threshold excludes the lmin of diagonal lines that are formed by parallel movements in the phase space trajectory. for lmin = 1, determinism is equal to one. nevertheless, if lmin is too large, the histogram of p(1) can become scattered, and consequently, determinism’s reliability decreases. on the basis of the histogram, p(ε, l) of diagonal lines is l, that is (5) sometimes for reasons of simplicity, the symbol ε is eliminated from the rqa (that is, the average diagonal line length (l): it is the average time that two trajectory segments are close to each other and can, thus, be interpreted as the average prediction time. (6) where is the total number of diagonal lines. this criterion is related to the divergence of the phase space trajectory. the length of the longest diagonal line (lmax): another rqa criterion is taking into consideration the length of the longest diagonal line in the rp. 82 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. (7) the faster the segments of the trajectory diverge, the shorter the diagonal lines become. entropy: it refers to the shannon entropy with the probability of which is exploited to find a diagonal line with the exact length of l in the recurrence curve. (8) entropy shows the complexity of the rp with respect to diagonal lines. for instance, for uncorrelated noise, the value of the entropy is almost small, which points to its low complexity. 3. criteria based on vertical lines laminarity (lam): similar to determinism, it is the ratio of the vertical lines recurrence points to the total number of recurrence points. it is calculated as follows: (9) computing lam can be done only by those values of v that are greater than the minimal length vmin so that the effect of tangential movement declines. for maps, vmin = 2 is a good value. lam criterion illustrates the instances of laminar states in the system without describing the length of these laminar phases. if rp includes more single recurrence points than vertical structures, lam decreases. trapping time (tt): the average length of vertical structures is calculated as in the following equation: (10) which is referred to as trapping time. computing this criterion requires taking into consideration a minimal length vmin (as in lam). tt is the mean time that a system remains stable in a particular state. it can also estimate for how long a state can remain trapped. the length of the longest vertical line (vmin): it is similar to lmax in diagonal lines. (11) where ny is the absolute number of vertical lines. contrary to criteria based on diagonal lines, these criteria can detect chaos-chaos transitions. consequently, it allows intermittency for even short and non-stationary data series to be investigated. moreover, since measures that quantify the vertical structures for periodic dynamics are zero, it is easier to detect chaos-chaos transitions [11]. recurrence points of first type (t1): consider a special state like . then, assuming that 83 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. (12) fig. 1: recurrence points of the first type, each arrow is a trajectory. illustrates a set of recurrence points that includes the entire set of points in fig. 1. these recurrence points show a sequence in the order of their appearance on a trajectory. for instance, , where bi is the number of elements in . accordingly, the recurrence time of the first type (t1) is the average of all . it calculates the evolution of constructed state phases. recurrence points of the second type: these are the points that are entering from outside. in fig. 1 these points are shown by the black dots. this trajectory might stay within the neighborhood for some time, meaning that it forms a sequence of points represented by the open dots in fig. 1. these points are called sojourn points1. the recurrence time of the second type (t2) is the average of time difference between the neighboring black dots on a trajectory, which is the system’s required average time in order for it to recur to a particular state after eliminating the sojourn points. data sets are analyzed as in the diagram below. data recording (cg and mg) preprocessing (noise cancelling) processing (rqa) detection 3. results as mentioned earlier, the primary aim of rps is to concretize the trajectories in phase space, which is particularly beneficial to systems with large dimensions. with the passage of time, rps provide valuable insights into these systems because normal patterns in rps are related to special behaviors of the system. respiratory disruptions that last from 20 seconds to one minute usually occur intermittently in the space of 5 minutes or more. thus, respiratory dynamics occur periodically during sleep. as illustrated in fig. 2, the rp of cg subjects (the figure on the right) consists of ordered and regular vertical and diagonal lines. but in the rp of the mg, white areas in recurrence diagram denote sudden changes are observed in the dynamics. 1states of subsequent time may fall into the neighbourhood of the state at time i, pretending artificial recurrences (grey dots). this is called tangential motion and such points are referred to as sojourn points [10]. 84 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. fig. 2: eeg recurrence diagram from f4 electrode. on the right is (control group) cg and on the left is (methamphetamine group) mg. the recurrence diagram in fig. 2 is related to the eeg signal from channel f4 of the healthy subject and the one on the left belongs to the subject with a record of methamphetamine abuse. as it is illustrated, the figure on the right (the healthy subject) includes vertical and regular diagonal lines while in the rp of the patient, white zones or stripes indicate sudden changes in the dynamic. fig. 3: eeg recurrence signal diagram from lead electrode. on the right is (control group) cg and on the left is (methamphetamine group) mg. the recurrence diagram in fig. 3 is related to the eeg signal of the healthy subject and the subject with a record of methamphetamine abuse. as a result of methamphetamine abuse, the changeability of the (hrv) eeg signal has declined, and the ecg signal has changed from a chaotic state to a quasi-periodic state. as mentioned before, rqa refers to quantified values describing the structure of recurrence curves. normally, there are ten values used in rqa: recurrence rate (rr), determinism (det), maximum diagonal line length (lmax), maximum vertical line length (v), entropy of the distribution of the diagonal lines (entr), average length of diagonal lines (l), laminarity (lam), trapping time (tt), recurrence time of the first type (t1), and recurrence time of the second type (t2). in this study the proposed method to choose neighbors is fan (fixed amount of nearest neighbors). as it was discussed earlier, by choosing fan to compute recurrence plots, the determined threshold would change at every state, such that there exists a fixed number of recurrence points for each of the 85 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. rps. this indicates that an rp is always fixed. therefore, in this study, only nine measures of rqa are exploited as features. as illustrated in tables 1 and 2, the value of all the features of the normal subject is higher. this is due to the decrease of non-linear interrelations in normal subjects. it is also observed that mean and standard deviation in rr are fixed. most of the meaningful differences belong to l (the average length of diagonal lines), entr, and t2. l is the average time that two trajectory segments are close to each other, and can be interpreted as the mean prediction time. entropy is used to find a diagonal line of the exact length of l in the rp. entropy shows the complexity of rps with respect to diagonal lines (as shown in part 2-2-1 these parameters did not have units). table 1: mean and standard deviation of rp in eeg signal of c3 channel eeg3 rr det l lmax entr lam tt vmax t1 t2 mg mean 0.0980 0.9905 19.1365 966.5133 3.6213 0.9918 12.7628 64.0933 7.5694 106.326 var 0.0081 0.0814 3.5343 79.4451 0.3569 0.0815 1.8599 11.6621 0.8683 16.21226 cg mean 0.0980 0.9913 24.3466 966.5133 3.8809 0.9922 13.1054 59.0067 7.9481 116.3217 var 0.0081 0.0815 5.1310 79.4451 0.4263 0.0816 1.8817 11.4461 0.8310 17.59166 table 2: mean and standard deviation of rp in ecg signal eeg3 rr det l lmax entr lam tt vmax t1 t2 mg mean 0.0980 0.9905 23.8587 966.5133 3.7902 0.9924 15.8588 62.1000 7.9072 142.7364 var 0.0081 0.0814 2.8912 79.4451 0.3260 0.0816 1.4517 11.2577 0.7499 14.1170 cg mean 0.0980 0.9915 33.5127 966.0733 4.0865 0.9925 20.5995 72.6333 6.8875 167.8453 var 0.0081 0.0815 5.9778 79.5916 0.3663 0.0816 3.0648 11.5772 0.9024 22.9307 since apnea can cause disturbances in the balance and the regularity of the heart during sleep, using ecg signals to detect sleep apnea is very useful. furthermore, it is believed that the recurrence points derived from ecg signals are immune to the effects of the non-stationary nature of nonlinear time series. therefore, it can be used as a proper tool in detecting methamphetamine abuse. comparing tables 1 and 2 indicate that the change in ecg signal is more obvious in comparison with the eeg signal, meaning that methamphetamine (at least in the examined subjects) has a greater effect on the heart than on the brain. in other words, rqa reveals changes in the dynamics of heart signals more than it reveals changes in the brain signals. results point to palpable changes in the nonlinear dynamic of vital signals (especially heart and brain signals) caused by methamphetamine abuse. as a result of methamphetamine consumption, measures such as the average length of diagonal lines, entropy, and recurrence points of the second type are increased. this indicates that, firstly, due to methamphetamine consumption, the predictability of signals has increased. in other words, signal complexity has declined. secondly, as a result of methamphetamine consumption, signal entropy has grown. the increase of entropy brings about the increase of signal irregularity. thirdly, methamphetamine consumption occasions signal compression more than its expansion. this means that signal information has decreased. 3.1 statistical analysis in this study we have used t test statistical analysis. in independent samples, a t test is obtained by dividing the difference between the means of the samples and the standard deviation of the distribution of differences (known as the standard error of the difference). t test assumes that the data have been collected from normal distribution with equal variance. the result of this test is reflected in the p value. if p tends towards zero, it 86 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. becomes obvious that the zero hypothesis is rejected at the level of 5 per cent, and if it tends towards one, it will be against the zero hypothesis at the level of 5 per cent. fig. 4: recurrence enter (up figures) and l (down figures) parameters in f4 channel of eeg signal of mg (on the left) and cg (on the right). to compare the signals of normal subjects with those of the ones under the influence of methamphetamine abuse on psg signals, the above-mentioned measures, such as rr, determinism (det), maximum diagonal line length (lmax), maximum vertical line length (v), entropy of the distribution of the diagonal lines (entr), average length of diagonal lines (l), laminarity (lam), trapping time (tt), recurrence time of the first type (t1), and recurrence time of the second type (t2) are obtained, which identify signal behavior. then, t-test was used to investigate the degree of the meaningfulness of the difference in these measures both in normal subjects and in patients (table 3). this result is in accord with the ones we obtained directly from the nonlinear recurrence plots. the best measures that reveal the most differences between the two classes are l, entr, tt, and t2. these measures are formed based on diagonal and vertical lines, and show chaos-chaos [12] and chaos-order transitions respectively. 87 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. in table 3 the extracted p-value features are specified according to nonlinear values of 0.05. as it is seen, the l, entr, tt, t2 measures reveal the most differences between the two classes. these values show chaos-chaos and chaos-order transitions respectively. for example, l is the average time that two trajectory segments are close to each other and can, thus, be interpreted as the average prediction time and in all psg signals, we could see mg signals have deterministic behaviors and therefore show significant difference between cg and mg. table 3: p-value in comparing control group with the group affected by methamphetamine abuse feature signal rr det l maxl entr lam tt maxv t1 t2 eeg f3 1 0.9662 10 e -5 1 0.0105 0.9903 10 e -5 10e -5 10e -5 0.2472 f4 1 0.9621 10 e -5 1 0.0010 0.9911 10 e -5 10e -5 10e-5 0.3708 c3 1 0.9266 10 e -5 1 10e -5 0.9652 0.1139 0.0002 0.0001 10 e -5 c4 1 0.9280 10 e -5 1 10e -5 0.9652 0.1675 0.0004 0.0423 0.0007 o1 1 0.9513 10 e -5 1 10 e -5 0.9825 0.8043 0.0014 0.3677 0.3057 o2 1 0.9371 10 e -5 1 10 e -5 0.9671 10 e -5 0.0320 0.6149 10 e -5 eog e1 1 0.8349 10 e -5 1 10 e -5 0.9146 0.0001 0.8429 0.8225 010 e -5 e2 1 0.6880 10 e -5 0.4201 10 e -5 0.8220 10 e -5 0.1779 0.0032 010 e -5 ecg 1 0.9196 10 e -5 0.9618 10 e -5 0.9867 10 e -5 10 e -5 10 e -5 010 e -5 chin ( as psg protocol) 1 10 e -5 0.1332 0.0053 0.3072 10 e -5 0.0466 0.3182 0.1195 010 e -5 abdo ( as psg protocol) 1 10 e -5 10 e -5 10 e -5 10 e -5 0.8813 10 e -5 10 e -5 10 e -5 010 e -5 flow ( as psg protocol) 1 0.1060 10 e -5 1 10 e -5 0.9861 10 e -5 10 e -5 10 e -5 010 e -5 pflow ( as psg protocol) 1 10 e -5 10 e -5 10 e -5 10 e -5 0.6264 10 e -5 10 e -5 10 e -5 10 e -5 rleg ( as psg protocol) 1 0.0007 10 e -5 10 e -5 10 e -5 10 e -5 10 e -5 10 e -5 0.0793 10 e -5 lleg ( as psg protocol) 1 10 e -5 0.0014 10 e -5 10 e -5 10 e -5 10 e -5 0.0724 0.0652 10 e -5 hr 1 0.9972 0.1626 0.7422 0.1469 0.9979 0.2083 1 0.1737 0.7200 spo2 1 0.9975 0.0050 0.0005 10 e -5 0.9991 0.0093 1 0.0065 0.0274 snore 1 10 e -5 10 e -5 10 e -5 10 e -5 0.8350 0.2640 0.5546 0.0982 0.0181 thor ( as psg protocol) 1 0.9740 10 e -5 1 0.3218 0.9867 10 e -5 10 e -5 10 e -5 10 e -5 p-value less than 1e-4 4. conclusion methamphetamine abuse has increased dramatically during the past decade, this could be detected with psg signals without blood testing. methamphetamine abuse affects sleep and we could measure this with efficacy. rqa parameters show signals’ chaotic behaviors and this research displays that self-organization in psg signals are affected with methamphetamine abuse. 5. compliance with ethical standards 5.1 ethical approval all procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 helsinki declaration and its later amendments or comparable ethical standards. 5.2 informed consent informed consent was obtained from all individual participants included in the study. 88 iium engineering journal, vol. 20, no. 1, 2019 bajestani and mazianani. references [1] netsi e, santos is, stein a, barros fc, barros ajd, matijasevich a. (2017). a different rhythm of life: sleep patterns in the first 4 years of life and associated sociodemographic characteristics in a large brazilian birth cohort. sleep medicine, 37: 77-87. [2] goldberger al, amaral la, glass l, hausdorff jm, ivanov pc, mark rg, et al. (2000). physiobank, physiotoolkit, and physionet components of a new research resource for complex physiologic signals. circulation, 101: e215-e220. [3] valladares em, irwin mr. (2007). polysomnographic sleep dysregulation in cocaine dependence. the scientific world journal, 7: 213-216. [4] subasi a. (2013). classification of emg signals using pso optimized svm for diagnosis of neuromuscular disorders. computers in biology and medicine, 43: 576-586. [5] tkachenko n, singh k, abreu n, morse am, day c, fitzgerald k, et al. (2016). establishing a role for polysomnography in hospitalized children. pediatric neurology, 57: 39-45. [6] o'reilly c, gosselin n, carrier j, nielsen t. (2014). montreal archive of sleep studies: an open access resource for instrument benchmarking and exploratory research. journal of sleep research, 23: 628-635. [7] koebbe m, mayer-kress g. (1992). use of recurrence plots in the analysis of time-series data," in santa fe institute studies in the sciences of complexity-proceedings, pp. 361-361. [8] eckmann j-p, kamphorst so, ruelle d. (1987). recurrence plots of dynamical systems. epl (europhysics letters), 4: 973. [9] marwan n, wessel n, meyerfeldt u, schirdewan a, kurths j. (2002). recurrence-plotbased measures of complexity and their application to heart-rate-variability data. physical review e, 66: 026702. [10] marwan n, kurths j. (2004). cross recurrence plots and their applications. mathematical physics research at the cutting edge, cv benton editor, pp. 101-139. 89 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <feff005500740069006c0069006300650020006500730074006100200063006f006e0066006900670075007200610063006900f3006e0020007000610072006100200063007200650061007200200064006f00630075006d0065006e0074006f0073002000640065002000410064006f00620065002000500044004600200061006400650063007500610064006f007300200070006100720061002000760069007300750061006c0069007a00610063006900f3006e0020006500200069006d0070007200650073006900f3006e00200064006500200063006f006e006600690061006e007a006100200064006500200064006f00630075006d0065006e0074006f007300200063006f006d00650072006300690061006c00650073002e002000530065002000700075006500640065006e00200061006200720069007200200064006f00630075006d0065006e0074006f00730020005000440046002000630072006500610064006f007300200063006f006e0020004100630072006f006200610074002c002000410064006f00620065002000520065006100640065007200200036002e003000200079002000760065007200730069006f006e0065007300200070006f00730074006500720069006f007200650073002e> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 6-shehab iiuej 33-21-3 o.k..doc iium engineering journal, vol. 2, no. 1, 2001 s. a. hameed and a. a. abbasi 45 developing an intelligent generator for semi-actual test data s. a. hameed, a. m. a. al-abbasi centre of measurement and evaluation, university of bahrain,bahrin shihab@iiu.edu.my, amajid@iiu.edu.my abstract: the actual test data generation is one of the difficult and expensive parts of applying softwaretesting techniques. many of the current test data generators suffer from the reduction of user’s confidence in generated test data and testing process. this is because of focusing on developer and database administrator viewpoints regardless of users concerns and focusing on data type and structure regardless of meaning. this paper proposes a model of an intelligent generator for semi-actual test data with the aim of increasing users confidence in software testing. the model uses samples of real data as a resource data and a set of efficient generation techniques based on statistical methods such as permutations, combination, sampling, and statistical distributions. the selection of the suitable structure and generation technique is based on one of the intelligent soft computing techniques such as fuzzy logic, neural network, heuristic, or genetic algorithm. the generated test data is validated according to the data specifications then tested by one of the normality testing techniques to be close to the real world or environment of the testing processes. this model offers the ability of simulating real environments. keywords: software testing, test data generation, semi-actual data, intelligent generator, simulation. 1. introduction during the 1990’s, the primary challenge and goal of software engineering was the production of quality software and the reduction cost of computer-based solutions that can be implemented with software [1, 2]. to improve software quality, software testing is one of the essential tools. it is one of the complicated problems in the life cycle of software development, which is expensive (40-50% of the total software development cost) and labor intensive [3, 4]. software is now being applied in critical situations to control valuable machinery, handle money, and safeguard human lives. the failure in such situations can be disastrous; therefore there is much need for efficient software testing to reduce the risk of software [5, 6]. software testing requires set(s) of test data. the automation and improvement of test data generation will reduce the cost of software development and testing. unfortunately, automatic test data generation still faces many problems. these problems can be summarized as follows:  shortage and inefficiency of some test data generation techniques or tools.  duplicated or conflicting descriptions of the same or similar data items used in applications that have similar goals.  the generated data holds high ratio of meaningless items, which may not reflect the specifications, culture, and environment of the population under test.  using inefficient set of generation technique(s) based mainly on random number generator (rnd) or similar functions.  focusing on developer or database administrator viewpoints regardless of user concerns.  minimum participation of the user in test data generation process.  lack of user’s confidence in the generated test data, testing process, and consequently in application under test. to overcome these problems this paper proposes a model of an intelligent generator for semi-actual test data. it is an improvement on a previous work [7]. the proposed model uses intelligent, soft computing, approaches such as fuzzy logic, neural network, heuristic, or genetic algorithm [8] to provide approximate solutions to selected problems. these approaches are suitable for selecting the suitable data item’s structures and generation technique for the proposed model. the generated test data is then checked according to the normality test(s) to satisfy the required specifications. 2. goal and objectives the main goal is to generate suitable set(s) of semiactual test data to support the software testing process, and to improve user confidence in testing software applications. the function of this generator to:  generating different volumes, types, and structures of test data.  generate different sets of test data that contains high ratio of meaningful and semi-actual items, which reflects the specifications or environment of the population under test.  offer a unified description of meaningful data items to eliminate duplication or conflicting description of data items.  develop a set of efficient and powerful generation techniques based mainly on several statistical iium engineering journal, vol. 2, no. 1, 2001 s. a. hameed and a. a. abbasi 46 methods. these techniques offer good flexibility to the user to generate different types and structures of meaningful data.  offer a set of test normality techniques to insure the efficiency of the generated data.  use a suitable intelligent soft computing such as fuzzy logic, neural network, or genetic algorithm in selecting the suitable data item structure and data generation technique.  increase the user’s confidence in test data, testing, and application under test by allowing more participation to the user than recent test data generation tools; through the selection of the required list and its specifications, resource data and generation technique.  improve software industry by developing reliable software products. 3. test data generator modules the intelligent generator for semi-actual test data consists of many modules, which include: 3.1 setup specifications the setup specification is a very important preparation step before generation. the main activities of this step are shown in fig. 1, which can be summarized as:  specifying the required list to be generated from the mdi sub-library.  specifying, or selecting, the suitable list structure from mdi structures sublibrary using one of the intelligent selection techniques.  determining the list and fields specifications or selecting it from default specifications sub-library.  specifying the resource data or selecting it from default values sub-library.  specifying, or selecting, the suitable generation technique(s) using one of the intelligent selection techniques.  specifying the output file and device. this module reflects the interface between the user and the meaningful data generation model to setup the required list and its related specifications and restrictions. it offers good flexibility and participation to the different users to select or insert the requirements for generating list(s) of meaningful data. 3.2 data descriptions this module is used to offer a unified description for the meaningful data items, which are used by a set of applications that have the same or similar goal. the main steps for meaningful data description and library construction can be summarized as:  preparing a unified list by collecting all the data items and its related structures, from set of applications that have the same or similar goal, in a unified list(s).  sorting the unified list by sorting the contents of the unified list of data items.  eliminating duplicated items by selecting one data item from each set of duplicated items and deleting the others then links all structures for the deleted items into the selecting one.  eliminating similar items by selecting one item from each set of similar meaning items and deleting the others then linking all structures from the deleted items into the selected one. the produced data item called a pure list.  creating a md library by storing all data items in the pure list in a md items sub-library and the structures in md item structures sub-library. the result of this step is a meaningful data library, which contains:  meaningful data items (mdi) sub-library: contains a set of possible meaningful data items that could be generated by this model.  mdi structures sub-library: contains all possible structures for each element in the previous mdi sub-library. the user has the ability to modify the library contents according to the application goal and environment. the main advantage of this step is to eliminate the duplicated or conflicted description(s) for meaningful data items used by the similar applications. it is a step towards standardizing the data description used in such applications. 3.3 default specifications and values this module represents the second part of the meaningful data library. it consists of two optional components that includes a:  mdi default-specifications sub-library (optional): contains the default specifications of each element in the previous mdi sub-library.  mdi default samples sub-library (optional): contains the default values or samples for each simple type of the elements in the mdi sub-library. the importance of the defaults is to help the nonprofessional users in selecting the specifications and the values for the required data item. 3.4 sample of resource data the data generation process requires a set of resource data, which could be a sample of real data taken from the actual environment, set(s) of assumed data prepared by the expert or professional people who is working in the environment, default pre-saved data, pre-generated data, or sets of alphabets or boundary values data. resource data is an important factor in this model and affects the efficiency of the generated data. the model focuses on using a sample of real or assumed data as a main resource. this generates data reflecting the population’s specifications or cultures. the other resources of data are used as supporting resources. the resource data should validate according to data specifications used before by the generation engine. the main advantages of using a sample of real or assumed data as resource data can be concluded as increase: iium engineering journal, vol. 2, no. 1, 2001 s. a. hameed and a. a. abbasi 47  the ratio of meaningful (semi-actual) data, which reflects the specification, environment and culture of the population under test.  the user participation in software development and testing. this could support the current trend of giving more participation the user and to eliminate the developer or database administrator bias in selecting the test data.  the user confidence in test data, testing process and testing results. 3.5 generation techniques this module uses a set of efficient generation techniques based mainly on several statistical methods. it offers the ability to generate lists of meaningful data, which are of different structures and volumes. the techniques include permutation with replacement, permutation without replacement, permutation with partial replacement, and permutation from multiple groups. these different permutation techniques produces (nk), (n!/(n-k)!), ((n-1)k + (n-1)k+1), and (n1*n2*n3* ….) permutations respectively [9, 10]. besides the permutation techniques there are several statistical distributions, which include discrete binomial or multinomial distributions and continuous normal or gamma distributions, and sampling random, systematic, or sequential techniques [11, 12]. the generation procedures are supported by hashing, sorting and searching techniques [13, 14]. this set of generation techniques offers flexibility to the users to generate the suitable volume of data. the generated data could be numeric, character or boolean and representing simple, compound or composite structures. the selection of the suitable generation technique(s) is based on intelligent selection techniques. the generation techniques built as functions or routines are stored in a special library and ready when called by the generation engine. 3.6 generation engine the generation engine represents the main processing part in the md generation model. it generates the required list(s) of data based on the user setup to the list specifications and restrictions, which has been mentioned in setup step. this module uses information from md library, resource data, generation techniques, and output requirements to generate the required data. there are two main strategies used for data generation. the first one is called one phase strategy, which is suitable to generate all types of lists. it requires that all fields in the selected structure be of simple type so it uses sampling or permutation techniques directly to generate the data in one phase. the second strategy is the multiple-phases, which is suitable to generate composite lists by generating its components in many phases. the result of each phase will be used as resource data for the next phases. the generation will continue until the required list is produced. the main steps for the meaningful test data generation phases are shown in fig. 2, which can be summarized as: i. preparation phase:  select the required list to be generated.  select the suitable structure for the selected list, using one of the intelligent selection approaches.  setup list specifications.  setup field specifications for each field in the structure.  specify or insert the sample data for the field(s).  validate the sample data according to the field specifications.  store all specifications and sample data in temporary files to be used by the next phase. ii. generation phase:  read the preparation files.  call the main generation technique, according to one of intelligent selection approaches, to generate list of raw data.  filtering the raw list according to list specification.  testing the generated data according to the normality testing techniques.  customizing the generated list according to the customizing techniques to get the exact volume of data.  store the generated list on the specified output file within the specified output device. 3.7 validation and statistical test this module is responsible for validating the generated set(s) of data according to the list and field specifications. it is a descriptive testing of the generated data. the second type is statistical testing such as the normality testing and correlation coefficient. a common statistical technique judges whether an assumed model provides us with an adequate description of the observed data, it is a statistical test of the distributional assumptions built into the model. the power of any statistical test depends very much on the amount of information, which is available. the influence on the power is the detailed use of the data items, that is the nature of the test in terms of the criterion and the critical region. the tests for evaluating the assumed normality are [15]:  the wtest for normality  an approximate analysis of variance test for normality.  the probability plot correlation coefficient test for normality.  the d-test for normality. the multiple correlation coefficient (r) will reflect the measure of the linear association between the dependent variable y and the independent variables x1, x2, .., xk. 3.8 output this module is used to store the generated data in specified form, on the required output file and device according to specifications inserted by the user. the output device could be one of the i/o devices such as hard disk, floppy disk, cd, screen or printer. the importance of this module is to store the result in the required file and device for later usage. iium engineering journal, vol. 2, no. 1, 2001 s. a. hameed and a. a. abbasi 48 fig. 1: setup specifications for data item setup list & field specifications select list select list structure size of generated list (quantity) main generation technique different sequential, systematic, or random sampling, and statistical dist. from mdi structures sub-library (default) from md items sub-library margin + / supporting gen. technique is list has a primary key yes / from a list of output devices output device output file insert required list name select list type field type resource of sample data default sample / insert by user sample size integer, real, character, boolean lower & upper limits for numeric type only primary key type field format not-key, primary key, composite relational level relation with other fields relation field name restriction on the field constraint constant / variable field length for character type only relation with other lists relation field name list name relations & constraints include >, >=, <, <=, =, <> not-related, relational, multiple related iium engineering journal, vol. 2, no. 1, 2001 s. a. hameed and a. a. abbasi 49 . fig. 2: flow of semi-actual test data generator select required select list setup list specifications setup field(s) specifications select or insert sample data validate sample data store preparation phase results mdi sub-library mdi structures sub-library call main generation filtering raw generated list call seconded gt to customize raw output the generated results library of generation techniques (routines) preparatio n files intelligent selection fuzzy logic neural nw heuristic genetic algorithm validation mdi default specifications sub-library mdi default values sub-library normality test, correlation cof. iium engineering journal, vol. 2, no. 1, 2001 s. a. hameed and a. a. abbasi 50 fig. 3: generation of different levels of test data 4. constructing different levels of data to identify meaningful data there is a need for describing the different levels that represent the meaningful data. these levels could be classified mainly into single list, multiple dimension list, and integrated lists. 4.1 . single list level the single list is constructed from a set of records that have the same type and structure. the list will hold the type of its base record; therefore the lists are classified into a simple, similar compound, not-similar compound, composite and relational types. the following is a brief description of different structures of records:  simple record consists of one field of integer, real, character, or boolean type.  similar-compound record consists of duplicating the same simple field many times.  not similar-compound record consists of many simple fields but of different types.  composite record consists of aggregation of many simple, compound or composite fields.  relational record is a compound or composite record with a relationship(s) between some of its fields. the construction of different records is shown in fig. 3. 4.2 multiple-dimension list level this level is constructed from a collection of a set of the same type and structure lists. the table holds the same type of its base list, therefore the tables are classified into a simple, similar compound, not-similar compound, character numeric other symbols simple record data structure & specification compound record relational record relationships between fields alphabet sample of real-data set of semi-actual data record level composite record simple list compound list relational list list level composite list simple multi-d table compound multi-dim table relational multi-dim table multi-dim table level composite multi-dim table relationships between lists set of integrated lists iium engineering journal, vol. 2, no. 1, 2001 s. a. hameed and a. a. abbasi 51 composite, and relational. the generation of a multidimension table is done by repeating the process of generating a list for specific times according to the required table. 4.3 integrated or multiple related lists level some of the software applications, specially the relational database, contain related lists or tables because there is some relationship(s) between these lists. the generation of this type requires specifying the relationships between these lists in accordance to its usage in the generation process. 5. conclusion the proposed model that overcomes some of the current problems to improve the test data generation. it offers good flexibility of the users, specially experts or professionals, to insert or select the required list of data to be generated, its structure and specifications, its components and their specifications, the generation technique(s), and resource of sample data. the usage of more powerful generation techniques, which are based on statistical methods besides the usage of real or assumed sample of data will participate in generating test data that holds a high ratio of semi-actual and meaningful items. the generated data will reflect the specification or environment of population under test. the intelligent selection of data item’s structure and the generation technique will increase the model efficiency in selection, and increase total performance. the construction of meaningful data library will increase the efficiency of the test data generation process. the validation, normality test, and correlation coefficient will increase the efficiency and reliability on the generated data. the above results lead to increase the user confidence in the generated test data, testing process, testing result, and consequently in application under test. the ability of generating different types and structures of data taking in consideration the relationships between data fields will make this model suitable for generating test data for different applications specially the database applications, which are used in testing control systems. references [1] b. t. mynatt, software engineering with student project guidance. usa, prentice-hall international editions, 1990. [2] r. s. pressman, software engineering: a practitioner's approach. (4th ed.), singapore, mcgraw-hill book company, 1997. [3] r. c. ferguson and b. korel, “the chaining approach for software test data generation”. acm transactions on software engineering and methodology, 5(1), pp.63 – 86, 1996. [4] a. j. offutt, zhenyi j. zhenyi, j. pan, the dynamic domain reduction approach to test data generation. software practice and experience, to appear in 1999. [5] a. j. offutt, “an integrated automatic test data generation system. journal of systems integration”, 1(3), pp.391-409, 1991,. [6] s. a. hameed, a. deraman and a. hamdan, a framework for database test data generator, technical report ftsm / mei lt48, university kebangsaan malaysia, 1998. [7] s. a. hameed, meaningful test data generation based on statistical methods, ph.d. thesis, faculty of information science and technology, university kebangsaan malaysia, 2000. [8] l. h. tsoukalas and r.e. uhrig, fuzzy and neural approaches in engineering, usa, john wiley & sons, inc, 1997. [9] l. devore jay, probability and statistics for engineering and the sciences, us brooks / cole publishing company, 3rd edition, 1991. [10] w. hamming richard, the art of probability for scientists and engineers. usa, addison-wesley publishing company, 1991. [11] a. agresti and b. finlay, statistical methods for the social sciences. san francisco: dellen publishing company, 1986. [12] l. lapin lawrence, statistics meaning and methods, harcourt brace jovanovich inc, 1975 [13] m. a. weiss, data structures and algorithm analysis in c, 2nd ed., addison-wesley logman, inc, 1997. [14] c. a. shaffer, a practical introduction to data structures and algorithm analysis. international edition, prenticehall international, inc, 1997. [15] a. a. aziz, simulation systems for statistical tests, ph.d. thesis, university of essex, uk, 1987. biographies shihab a. hameed was asst. prof. at electrical & computer eng. department, faculty of engineering, iium university (currently in university of bahrain). he obtained his ph.d. from ukm university (malaysia) in software engineering / sw testing. he has over twenty year industrial and educational experience in software development and as academician. he has published many research papers both locally and internationally. abdulmajid a. al-abbasi was assoc. prof. at science in engineering department, faculty of engineering iium university. currently he is working at university of bahrain. he obtained his ph.d. from essex university (uk) in simulator systems, 1988. his research interests are random number generation and analysis. he has several research papers published internationally. iium engineering journal, vol. 2, no. 1, 2001 52 149 iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 1 convection heat transfer modeling of ag nanofluid using different viscosity theories m.ayatollahi, sh.nasiri and a.b. kasaeian faculty of new science & technology, university of tehran, iran. tehran, iran. alikasa20@gmail.com abstract: in this paper, the effects of adding nanoparticles (including ag) to a fluid media for improving free convection heat transfer were analysed. the free convective heat transfer was assumed to be in laminar flow regime, and the corresponding calculations and solutions were all done by the integral method. water, as a newtonian fluid, was considered as the base and all relevant thermo physical properties of the nanofluids were considered to be unvarying. the calculations performed and the graphs generated showed that, in general, the addition of nanoparticles to the fluid media resulted in an increment or improvement of its heat transfer coefficient. with increase in the concentration of the nanoparticles, the heat transfer rate of the fluid also increased. the increment in heat transfer is also dependent on the nanoparticles’ thermal conductivity and the viscosity theory which was utilized in the calculations. in this study, four different theories were used to calculate the viscosities of the nanofluids. the effects of viscosity on the nanofluids’ thermal conductivity were apparent from the calculations which were performed for nanoparticle concentrations of 4% or less. abstrak: kajian ini menganalisis kesan penambahan nanopartikel ag ke dalam media bendalir bagi tujuan pembaikkan pemindahan haba perolakan bebas. perolakan bebas diandaikan berada di zon aliran laminar, di mana penyelesaian dan pengiraan telah dilakukan mengunakan kaedah kamilan. air yang merupakan cecair newtonian, dianggap sebagai asas dan sifat terma fizikal nanocecair dianggapkan tidak berubah. mengikut pengiraan yang dilakukan dan graf yang diplotkan, umumnya penambahan nanopartikel kepada media bendalir menyebabkan peningkatan dan pengembangan pekali pemindahan haba. kadar pemindahan haba meningkat dengan nanopartikel. peningkatan pemindahan haba juga bergantung kepada pengalir haba nanopartikel dan teori kelikatan yang digunakan. di dalam kajian ini, empat jenis teori telah digunakan bagi pengiraan kelikatan nanopartikel. kesan kelikatan ke atas pengalir haba nanocecair sangat jelas kelihatan. kesemua pengiraan telah dilakukan ke atas kepekatan kurang dari 4%. keywords: ag nanofluid, heat transfer, natural convection 1. introduction optimization of heat transfer in the direction of achieving more efficiency needs concentration on the facilities scale-down and also increasing the heat transfer rate. the conductivity of some metallic particles, metallic oxides and nanotubes is much higher than the conductivity of liquids. according to the novel ideas, adding very tiny particles onto liquids (which makes nanofluids)may develop the heat transfer rate remarkably [1, 2]. it is obvious that using nanofluids and researches about that subject have been popularized during the recent years. the investigations about forced convection have been mostly iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 2 experimental and practical and the studies about the free convection heat transfer as experimental and theoretical have well grown simultaneously, for al2o3 with a volume fraction of 3% exhibits better enhancement than those for 4%or 5%, which is still lower than pure water [3]. the studies and experiments show that the forced convection heat transfer of nanofluids is dependent on reynolds number [4] although beside all the experimental activities about this subject, lack of sufficient information is absolutely evident [5]. different experiments and studies have been done on the improvement of free convection heat transfer and the results have been published by several papers [6, 7]. the nanoparticles concentrations highly effect on the convection heat transfer improvement, which is associated with increasing of heat transfer coefficient and the nanoparticles nusselt number theinfluence of shape of the nanopartice on heat transfer augmentation is simulatedusing an empirical shape of nano parameter which depicts the ratio of surface area to volume of the nanoparticles [8]. also, some other experimental researches have been done on ag/water which have appropriate agreement with the theoretical fundamentals [9, 10]. regarding the obtained results by the performed experimental works, it is crystal clear that the heat transfer coefficient (h) is directly dependent on k/δt where k is conductivity and δt is the thickness of thermal boundary layer. one of the main reasons for increasing the heat transfer rate of nanofluids comparing to the base fluid individually, is raising the heat transfer coefficient by adding nanoparticles. existence of numerous papers about nanofluids, verify the declaration [11, 12]. the amount of enhancement is dependent on the particle shape, particle type, particle size, particle concentration and kind of base fluid [13]. in the recent works, one can apparently understand that in addition to all the mentioned factors, viscosity is effective on heat transfer improvement and plays a significant role beside the nanoparticles conductivity [14]. for purpose of investigation of viscosity effect on heat transfer coefficient, four different models have been used in this paper. the modeling results have been compared with the similar experimental results. in principle, increasing of random movement of nanoparticles causes thermal conductivity enhancement in nanofluids [15]. in this study, an appropriate mechanical model has been chosen which is solved by integral solution methods. the results may be used for both states of uhf and uwt which can be applied for both laminar and turbulent regimes [16]. 2. mechanical model the applied model is a vertical plane which on free convection in laminar conditions occurs. according to fig. 1, two kinds of boundary conditions including uniform heat flux (uhf) and uniform wall temperature (uwt) may be used for this model. in reference to what was stated in the introduction, all fluid properties are assumed constant except viscosity. writing the continuity, momentum and energy equations in directions of x and y for steady-state conditions will help us to obtain the target equations. also the simultaneous solution of the following integrals, considering a four-power polynomial profile for velocity and temperature, leads to the following equations. continuity equation : ∂u/� ∂x� � ∂v/ ∂y � 0 (1) momentum equation: � � � u � � � v � � � gβ�t� � t�� � v (2) energy equation: � � � u � � � v � � � ��� �� �� (3) iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 3 fig. 1: temperature and velocity distribution of free convection boundary layer. using the integral solution and considering the mentioned profile for velocity and temperature, we would have: � u � βρωω ! "#$% &�η' � 3η) � 3η# � η* θ � �t � t∞� � ρ+ω #$ ,�η� ' � 2η� ) � 2η� � 1/ 0 (4) where, η � y ⁄ 3 4 1 and η� � y ∂�8 4 1 the relation between thermal boundary layer thickness and hydrodynamic boundary layer thickness may be shown as follows: ∂��9,��;< �9,�� (5) putting equation 4 into the following integrals and solving these two integrals simultaneously, � = udy �>? � = u#>@a? dy � gβbc = �t � t���<>�@a? dy � dbc e � � f�;? � 0 (6a) � = θdy �<>? � = �t � t��udy�∆>�@a? � �@a��@a e � �f� � 0 (6b) ω may be obtained as equation 7. (considering ∂/∂t=0 for steady-state conditions and lnpr = k) ω � 1.576 n 10o'k' � 4.227 n 10o)k) � 4.282 n 10o#k# � 0.1961k � 0 (7) according to what is observed, ω is a function of pr and pr is as a function of nanofluid viscosity, so the amount of ω is noticeably changed with pr. in this paper, different models of viscosity have been applied. different parameters are effective on a nanofluid viscosity which from, the particles shape and the shear exerted onto fluid are of the most significance [17]. regarding to the experimental and practical iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 4 researches, investigators have found that viscosity is dependent on the method of preparation of nanoparticle as well [18]. nanoparticles, because of very fine structure, make a stable and homogeneous state when solving in the base fluid. this, causes the nanofluids are considered similar to the base fluids as mono-phase. since, temperature raising causes increase in the nanoparticles mean diameter [19], temperature is taken constant in this paper for precise solution of the integrals. the mean diameter of nanoparticles is assumed to be 32-50 nm and the calculations have been done for uhf and uwt boundary conditions. after solving the integrals, the parameters are substituted in nu and the effects of ω changes on nu are investigated. the maxwell wasp model is chosen for nu calculations, which has agreement with the experimental results [20]. the average nusselt number along the wall may be obtained by the following equation [21]. nubcvvvvvv � w@avvvvvxyza (8) meanwhile, the average nusselt numbers are different for uhf and uwt boundary conditions. for uwt boundary condition [21]: nubcvvvvvv � '√\)∆@a ] ^_y_̀)abc_��d∆@ao\� grgc h ì (9) also, for uhf boundary condition [21]: nubcjvvvvvv � k\ l #^_y_̀#ac_��d∆@ao\�∆@a` grgcj m in (10) grbf * is the modified grashof number [21]: grgc j � ^opx`qza�za� (11) the boundary-layer change rate is f�∆� � d∆zan o\∆za`d∆@an o\∆@a` (12) the ε function (expressing the heat transfter performance) is [19] �%� � 100 uvβ_y_̀ ν_� f�∆�w α � 1x (13) α varies with different boundary conditions, α=1/5 for uhf and α=1/4 for uwt. also, the r index states the nanofluids/base fluids ratio. the nanoparticles concentration is shown by subscript f and we use the available relations for obtaining viscosity, constant temperature specific heat and β: ρbc � �1 � φ�ρbc � φρ{ (14) ,c{/bc � �1 � φ�,c{/gc � φ,c{ /{ (15) �ρβbc� � �1 � φ��ρβ�gc � φ�ρβ�{ (16) for the calculation of nanofluid conductivity, the wasp model has been used [20]: iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 5 k� � q}~#qzao#��qzaoq��q}~#qza~�,qzaoq}/ (17) as stated, for investigation of viscosity effects, four viscosity models have been used. the first model which is introduced for nanofluids, is the brinkman model [22]: µ� � µ@aµza � "�"o��n� (18) the second model is the model which was presented by einstein`s [23]: µ� � µ@aµza � �1 � 2.5φ� for φ � 0.05 (19) the third model has been presented by considering the brownian movement [24]: µ� � µ@aµza � 1 � 2.5φ � 6.17φ# (20) and the fourth model, which was presented by pak and cho, is as followings [25]: µ� � µ@aµza � 1 � 3.911φ � 533.9φ# (21) the calculations have been done for all of the mentioned viscosity models and for taking a better and more logical conclusion, temperature is taken around 22º c, the nanoparticles mean diameter is considered as 32-50 nm and the maximum concentration is assumed to be 4%. the results show the nusselt changes with viscosity models, particles size, grashof number for ag for both uhf and uwt boundary conditions. 3. results and discussion considering the assumptions mentioned in the previous part, the properties of ag were obtained. according to different gr numbers, volume fractions and viscosity models, the uhf and uwt nusselt numbers were obtained (tables 1-4). table 1: average nusselt number nanofluids (ag/water) model (i) nuuhf gr 10 3 10 4 10 5 ф=1 4.289 6.798 10.773 ф=2 4.409 6.987 11.074 ф=3 4.535 7.187 11.391 ф=4 4.661 7.387 11.585 nuuwt ф=1 6.051 10.760 19.135 ф=2 6.276 11.1599 19.845 ф=3 6.494 11.548 20.536 ф=4 6.722 11.954 21.257 iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 6 table 2: average nusselt number nanofluids (ag/water) model (ii) table 3: average nusselt number nanofluids (ag/water) model (iii) table 4: average nusselt number nanofluids (ag/water) model (iv) nuuhf gr 10 3 10 4 10 5 ф=1 4.435 6.639 10.773 ф=2 4.409 6.996 11.074 ф=3 4.535 7.109 11.391 ф=4 4.661 7.387 11.585 nuuwt ф=1 6.051 10.760 19.135 ф=2 6.276 11.599 19.845 ф=3 6.494 11.548 20.536 ф=4 6.722 11.954 21.257 nuuhf gr 10 3 10 4 10 5 ф=1 4.189 6.639 10.521 ф=2 4.412 6.992 11.082 ф=3 4.542 7.199 11.409 ф=4 4.673 7.406 11.738 nuuwt ф=1 5.948 10.577 18.8096 ф=2 6.316 11.231 19.972 ф=3 6.645 11.816 21.012 ф=4 6.7898 12.074 21.471 nuuhf gr 10 3 10 4 10 5 ф=1 4.053 6.423 10.1798 ф=2 3.972 6.296 9.978 ф=3 3.922 6.216 9.852 ф=4 3.873 6.138 9728 nuuwt ф=1 5.629 10.011 17.802 ф=2 5.450 9.692 17.235 ф=3 5.314 9.451 16.806 ф=4 5.184 9.129 16.393 iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 7 at gr = 10 5 (as the highest gr number), the graphs were depicted for ag in both uhf and uwt for a better demonstration and observing the viscosity models behavior (fig. 27). fig. 2: nusselt number versus volume fraction for different viscosity models at uhf (nanoparticle:ag /gr=10 3 ) fig. 3: nusselt number versus volume fraction for different viscosity models at uwt (nanoparticle ag/gr=10 3 ) fig. 4: nusselt number versus volume fraction for different viscosity models at uhf (nanoparticle:ag/gr=10 4 ). iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 8 fig. 5: nusselt number versus volume fraction for different viscosity models at uwt (nanoparticle ag /gr= 10 4 ) fig. 6: nusselt number versus volume fraction for different viscosity models at uhf (nanoparticle: ag/gr=10 5 ) fig. 7: nusselt number versus volume fraction for different viscosity models at uwt (nanoparticle: ag/gr=10 5 ) iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 9 4. conclusion the pak and cho viscosity model predicts a higher increase in viscosity when adding more nanoparticles and this behavior, causes nonconformity with the other models. for prediction of nanofluids (containing metal or metal oxide particles) free convection heat transfer , the brinkman model, the einstein model and the brownian movement model are proposed to be applied for précise calculations. the free convection heat transfer coefficients of ag nanofluid increase by increasing the nanoparticles volume fraction to 4%. thus for both the uwt and uhf surface thermal conditions, the examination of two viscosity models leads to constrasted conclusions. the use of the experimental correlation for the viscosity leads only to a weak enhancement (less than 1%) with a trend to a deterioration phenomenon with increasing the particle concentration in the considered range. references [1] drexler, erik . k., “engines of creation”., london: publisher not mention, 1990. [2] maxwell, clerk. j., “electricity and magnetism”. oxford:clarendon press, 1873. [3] nada, abu. e., chamkha j. ali.,, “effect of nanofluid variable properties on natural convection in enclosure”, international journal of thermal sciences 49. 479-91 (2010). [4] s.e.b. maїga, s.j. palm, c.t. nguyen, g. roy, n. galanis, “heat transfer enhancement by using nanofluids in forced convection flows”, international journal of heat and fluid flow 26. 530 (2005). [5] s.m. foutukian, m. esfahani, “experimental study of turbulent convective heat transfer and pressure drop of dilute cuo/water nanofluids inside a circular tube”, international journal of heat and mass transfer 37. 214-19 (2010). [6] y. xuan, q. li, “investigation on convective heat transfer and flow features of nanofliuds”, journal of heat transfer 33. 151 (2005). [7] d. wen, y. ding, “experimental investigation into convective heat transfer of nanofluids at entrance region under laminar flow conditions”, international journal of heat mass transfer 47. 5181 2004. [8] s.kumar et al. “analysis of flow and thermal field in nanofluid using a single phase thermal dispersion model”. applied mathematical modelling 34 573-92 [9] k.khanafer , k.vafai, marilyn lightstone, “bouyancy-driven heat transfer enchancement in two-dimensional enclosure utilizing nanofluids”,international journal of heat and mass transfer 46. 3693-53 (2003). [10] e.büyükögüt, “natural convection of water based nanofluids in inclined enclosure with heat source”, international journal of thermal sciences 48. 2063-73 (2009). [11] s.a putnam, d.g. cahill, p.v. b braun, “thermal conductivity of nanoparticle suspensions”, journal of applied physics 99 5 [12] y. ding, h. alias, d. wen, r.a. williams, “heat transfer of aqueous suspensions of carbon nanotubes , int. j. heat and mass transfer, vol. 49 pp. 240-250, 2006 [13] h.e. patel, s.k. das, t. sundararajan, a. s. nair, b. george, t. pradeep, “thermal conductivites of naked and monolayer protected metal nanoparticle based nanofluids. manifestation of anomalous enhancement and chemical effect”, applied physics letters 83 (14), 2931-2933 [14] h.ahmari, s.gh.etemad, “stability of nanofluids”, proceeding of 1st conference of nanotechnology in environments 1, iut974 [15] y. hang, h.s park, j.k. lee, w.h.jung, “thermal conductivity enhancement of nanofluids current”. applied physics, 61 667 [16] j.koo and c.kleinstreuer, “a new thermal conductivity model for nanofluids”, journal of nanoparticle research 6 577 (2004). iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 10 [17] j. buongiorno, l. w. hu, s. yip, “nanofluid coolants for advanced nuclear power plants”, nano technology workshop, mit, (2005). [18] d.p. kulkarni, d.k. das, r.s.vajjha, “application of nanofliuds in heating building and reducing pollution”, international journal applied energy 86 .2566-73 (2009). [19] s.k. das, n. putra, p. thiesen, w.roetzel, “ temperature dependence of thermal conductivity enhancement for nanofluids”, journal of heat transfer (asme)125: 567 (2003). [20] j.c. maxwell, “a treatise of electricity and magnestism”, third ed. clarendon oxford, p: 382, 1904. [21] g. polidori, s. fohanno, c. t. nguyen, “a note on heat transfer modeling of newtonian nanofluids in laminar free convection”, international journal of thermal science 46 739-44 [22] h. c. brinkman, “the viscosity of concentrated suspension and solutions”,. journal chemistry physics 20 571-81 [23] a. einstein, “investigation on the theory of brownian motion”, dover, new york, 1956. [24] d.orozeco, “hydrodynamic behavior of polar particle”,. 42375-396 [25] b.c. pak, y. cho, “hydrodynamic and heat transfer study of dispersed fluids with submission metallic oxide particle”, experiments heat transfer 11 151-70 iium engineering journal, vol. 13, no. 1, 2012 ayatollahi et al. 11 nomenclature �� prandtl number �� &� ��o"�o"* heat capacity � &� �o"�o"* thermal conductivity � viscosity ��� uniform heat flux ��� uniform wall temperature �&�#�o"* kinematic viscosity ¡� grashof number ¡� j¢£ modified grashof number ¤¥ nusselt number greek symbols δ� thermal boundary layer thicknesses δ dynamical boundary layer thicknesses ¨ volume fraction © volumetric expansion coefficient ª heat transfer performance α constant ω ratio of thermal boundary layer thickness (¬­ ) to that of the dynamical (δ� subscripts � nanoparticle ®¯ base fluid � nanofluid / base fluid rate application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 vehicle air conditioner (vac) control system based on passenger comfort: a proof of concept suroto munahar1, bagiyo condro purnomo1, muhammad izzudin1, muji setiyo1* and madihah mohd saudi2 1 department of automotive engineering, universitas muhammadiyah magelang, magelang 56172, indonesia 2 faculty of science and technology, universiti sains islam malaysia, bandar baru nilai 71800, nilai, negeri sembilan, malaysia * corresponding author: muji@unimma.ac.id (received: 28th january 2021; accepted: 5th april 2021; published on-line: 4thjanuary 2022) abstract: the air conditioning system (ac) in passenger cars requires precise control to provide a comfortable and healthy driving. in an ac system with limited manual control, the driver has to repeatedly change the setting to improve comfort. this problem may be overcome by implementing an automatic control system to maintain cabin temperature and humidity to meet passenger's thermal comfort. therefore, this paper presents the development of a laboratory-scale prototype air conditioning control system to regulate temperature, humidity and air circulation in the cabin. the experimental results show that the control system is able to control air temperature in the range of 21 °c to 23 °c and cabin air humidity between 40% to 60% in various simulated environmental conditions which indicate acceptance for comfort and health standards in the vehicle. in conclusion, this method can be applied to older vehicles with reasonable modifications. abstrak: sistem penyejuk udara (ac) pada kenderaan penumpang memerlukan ketepatan kawalan bagi menyediakan keselesaan dan kesejahteraan pemanduan. melalui sistem ac dengan kawalan manual terhad, pemandu perlu berulang kali mengubah penyesuaian latar bagi meningkatkan keselesaan. masalah ini dapat diatasi dengan menerapkan sistem kawalan automatik bagi menjaga suhu dan kelembapan kabin agar memenuhi keselesaan suhu penumpang. oleh itu, kajian ini merupakan pembangunan prototaip sistem kawalan ac skala laboratari bagi mengawal suhu, kelembapan dan peredaran udara dalam kabin. hasil eksperimen menunjukkan sistem kawalan ini mampu mengendali suhu udara pada kitaran 21 °c hingga 23 °c dan kelembaban udara kabin antara 40% hingga 60% pada pelbagai keadaan persekitaran simulasi yang menunjukkan penerimaan standard keselesaan dan kesejahteraan kenderaan. sebagai kesimpulan, cara ini dapat diaplikasi pada kenderaan lama dengan modifikasi bersesuaian. keywords: air conditioner; control system; humidity; temperature 1. introduction the vehicle air conditioner (ac) system was developed to provide passenger comfort. initially, the ac system was only used to regulate temperature but that is not enough anymore. although the thermal comfort of building occupants has been studied extensively, in-vehicle thermal comfort is continuously being developed due to its dynamics. since vehicles operate in a dynamic environment, therefore passenger comfort in the vehicle is very important to ensure people travel safely [1–3]. moreover, as climate change causes iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 temperature extremes, a study proposes to formulate new guidelines for car design based on passengers’ thermal comfort to avoid health impacts [4]. apart from temperature, to provide passenger comfort in the targeted cabin, humidity and air circulation speed are also important parts that must be considered [5,6]. humidity greatly affects health [7,8] and changes in extreme humidity lead to new disease symptoms [9]. maintaining humidity in the cabin can be done by opening the windows while driving [10]. however, in extreme weather such as summer, connecting cabin space with environment will add excessive load to air conditioning system. on the other hand, if the humidity is too low it can cause dehydration and endanger driving safety due to driving errors [11]. another method is to put phase change material (pcm) to control humidity and temperature in the car, but it works passively [12]. temperature-humidityair circulation speed is interrelated air property [13,14]. the speed of air circulation in vehicle air conditioners is generally controlled manually via a knob on the dashboard, except in modern cars equipped with sophisticated sensors. manual controls cannot provide good thermal comfort, as airspeed reset is based solely on feedback from the passenger or driver. therefore, air speed control in an ac system also needs to be developed. increasing passenger comfort in the cabin by maintaining temperature has been discussed extensively, both while the vehicle is running and when the vehicle is from a parking location [2,4,12,13,15]. however, the discussion on the integration of temperaturehumidity-air speed control systems based on effective human comfort is still very limited, except at the simulation stage [16-18]. therefore, this study aims to develop a specific air conditioning control system used in vehicles to adjust temperature-humidity-air speed based on effective human comfort (22 °c; 40% to 60% of relative humidity, rh). the lab-scale prototype is tested in a simulation room, conditioned to resemble real environmental conditions. furthermore, the room temperature was measured using a thermometer, humidity was evaluated by humidity meter, and the airflow meter was applied to estimate airflow. 2. method 2.1 system description room/cabin temperature temperature control heater, expansion valve, condenser fan, evaporator fan, compressor, water sprayer room/cabin temperature temperature sensor inputinput controller controller devices devices output output feedback feedback temperature loadtemperature load fig. 1: the block diagram of temperature control. the system developed is presented in fig. 1 and fig. 2. this system has five main blocks including the input, controller, devices, feedback, and output. temperature control uses a closed loops system, and the feedback mechanism uses a sensor. the prototype has five components, encompassing the heater, condenser fan, evaporator fan, expansion valve, and compressor. the confounding factor of temperature control is the heat load from the iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 outside. the humidity control system consists of a heater, water sprayer and humidity sensor to provide feedback. room/cabin humidity humidity control heater and water sprayer room/cabin humidity humidity sensor humidity loadhumidity load inputinput controller controller devicesdevices output output feedback feedback fig. 2: the block diagram of humidity control. 2.2 experiment set-up figure 3 shows the experimental set-up which includes the electronic control module (1), evaporator (2), compressor (3), condenser (4), and expansion valve (5). the specifications of each equipment are shown in table 1. the electronic control module (ecm) consists of a microcontroller, relay, and electronic circuits that are programmed based on the desired needs. the ecm works based on input from temperature and humidity sensors, and produces output to the water sprayer, condenser fan, evaporator fan, heater, and compressor. the performance mechanism of this air conditioning system follows the process shown in fig. 4. this figure shows a psychometric diagram used to explain the conditions of the cabin space. when the cabin room has a high temperature and humidity (at point 1), the ac system will regulate temperature and humidity in a condition of thermal comfort (point 3). process from point 1 to point 3 is a process of dehumidifying (1 to 2) and cooling (2 to 3). when a vehicle suddenly passes a highly cold temperatures area, the ac system will turn on the heater (r) to increase the temperature. likewise, when a vehicle suddenly passes through an immensely low humidity area, the ac system turns on the water sprayer which will spray water (in the form of fog) to increase the humidity in order to achieve thermal comfort conditions. table 1: specifications of the tools used in the study no parts specification 1. evaporator evaporator unit a3 toyota; denso 2. compressor type sd505 sd 505 universal model sanden, piston type, driven by a 220-volt ac motor with a power of 2 hp. 3. expansion valve tev type (thermo expansion valve) 4. temperature sensor sensor type ds18b20; wrapped in stainless steel pipe; dimensions 6 x 50 mm; cable length 100 cm; power supply 3-5.5v; temperature range -55 to + 125c; analog type 5. humidity sensor dimension: 28.2 x 13.1 x 10 mm; weight: 6 g; working voltage: 3v ~ 5.5v; output signal: digital signal; temperature measurement range: 40 ͦc to 80 c; accuracy: 0.5 °c; humidity range: 0 ~ 100%; rh accuracy: 2% 6. heater 12 volts 300 w with coil type heating element 7. simulation environment dimension: 1.5 x 1.5 x 3 m iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 fig. 3: set up experiment: 1-electronic control module (ecm); 2-evaporator; 3-compressor; 4-condenser; 5-expansion valve; t-temperature sensor; h-humidity sensor; w-water sprayer; and r-heater. fig. 4: psychometric chart of ac system. installation of heating sensors, water spray, temperature and humidity sensors are paired adjacent to the evaporator. the ecm input includes temperature and humidity iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 sensors, while the evaporator is mounted in series against the condenser and compressor. this prototype was tested during hot climates with a location in indonesia which has a longitude position of -7.520639969601074 and latitude 110.22739445901612. 2.3 logic rule of control system the control system has two subsystems to control temperature and humidity of cabin air as shown in fig. 5 and fig. 6. the logic rule of temperature control has a working structure as follows. if the temperature is below 16 °c, the programming statement is set to turn on the heater (r) and turn off the air conditioner but the evaporator fan is on (p1). the length of time the heater runs depends on the high and low temperature of the cabin space, so if the temperature of the cabin space is very low, it takes a longer heater lifetime to achieve thermal comfort. if the temperature of the cabin space is in the range of 17 to 20 °c, then the statement program is set to activate the ac compressor and heater with the evaporator fan at very low speed (p2). the statement program is set to turn on the evaporator fan in a very low position speed to reach a range of 21 to 24 °c (p3) and so on according to fig. 5. start air temperature design of control system embeded system if<16 o c if 17-20 o c if 21-24 o c p1 p2 p3 yes yes yes yes yes yes no no no no if 25-30 o c if 31-35 o c if >36 o c p4 p5 p6 yes yes yes yes yes yes no no no no end fig. 5: logic rule of temperature control system. start air humidity design of control system embeded system if>80% if 79-60% if 59-40% s1 s2 s3 yes yes yes yes yes yes no no no no if 39-30% if <20% s4 s5 yes yes yes yes no no no no end fig. 6: logic rule of humidity control system. the cabin temperature is set at 25 to 30 °c, where the programming statement turns on evaporator fan to medium speed position, condenser, and expansion valve are in position 2 (p2). furthermore, a cabin temperature of 31 to 35 °c requires the statement program to turn on the evaporator fan to high speed, while the condenser fan and expansion valve are iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 in position 3 (p3). in addition, cabin temperatures above 36 °c require the statement program to turn on a maximum high evaporator fan, while the condenser and expansion valve are in position 4 (p4). table 2 shows the various temperature control system statements. the condenser fan, compressor and magnetic coupling are connected in one line, so that if the magnetic coupling is on, condenser fan, the compressor will start. likewise, if the magnetic coupling turns off, the condenser fan, the compressor will shut off. table 2: statement of the air temperature control system no position functioning system 1. p1 • heater on • evaporator fan off • compressor off 2. p2 • heater on • evaporator fan on (min. low speed) • compressor on 3. p3 • heater off • evaporator fan on (low speed) • compressor on 4. p4 • heater off • evaporator fan on (medium speed) • compressor on 5. p5 • heater off • evaporator fan on (hight speed) • compressor on 6. p6 • heater off • evaporator fan on (max. high speed) • compressor on the humidity control system algorithm works with the following conditions. if the humidity in cabin space is more than 80%, the statement program is set to turn on the air conditioning system which aims to remove moisture in cabin space. if the air reads very dry (below 39%), water spray is activated to increase humidity. meanwhile, if the humidity reads at 40 to 60%, the sprinkler and heater are turned off. table 3 shows the humidity control system statements and algorithms. table 3: statement of the air humidity control system no position functioning system 1. s1 heater on 2. s2 heater on 3. s3 4. s4 sprayer in position 1 5. s5 sprayer in position 2 air temperature and humidity were measured in the cabin space, the lowest and highest values observed were 17 °c and 31 °c, respectively. meanwhile, the lowest and highest humidity data were obtained in the range of 20% and 84%. data is collected at 380 meters above sea level. temperature, air velocity, and humidity data were collected using a digital thermometer, airflow meter and humidity meter, respectively. iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 3. results and discussion 3.1 wiring diagram of developed prototype integrated control system for cabin room comfort has interconnected parts. the circuit which includes input, controller, actuator, output and feedback is characterized by a sequential working system. the lm 35 sensor is a temperature sensitive device that is known to produce analog signals. therefore, changes in temperature of simulation room can be detected based on modification of the resistance. the dht11 sensor is able to detect ambient air humidity by measuring amount of water vapor in simulation room. figure 7 shows the wiring diagram made. fig. 7: wiring diagram of the controller system. 3.2 air speed, temperature, and humidity measurement the automatic integration control system for room comfort was set at 22 °c, based on the effective comfort for humans [19], while the simulation room temperature was obtained from 31 °c. the temperature at the 21st minute has reached a precise setting, and period of decline is affected by thermal load. furthermore, airspeed is modified based on temperature previously achieved, as 7.8 m/s produced by evaporator fan is generated at 31°c. based on the evaluation, an automatic decline to 7 m/s was reported at 30°c, and 6.5 m/s was achieved after reaching 22 °c. the controller system subsequently maintains temperature in the range of 21 to 23 °c, and the results in fig. 8 show comparison between automatic and manual techniques. iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 fig. 8: temperature and airspeed at the highest temperature position. manually controlled air temperatures have several conditions, and 5.5 m/s is used as speed position of evaporator fan. furthermore, a decline in temperature requires a longer time compared to an automatic control system, as only 18 °c is reached within 30 minutes. this condition possibly occurs due to the presence of constant evaporator fan speed, which does not increase automatically, hence the need to achieve the addition of automatic comfort temperature. in addition, it was not possible for the manual control system to reach an effective position for humans (22 °c) in the 30th minute. data were collected at 17 °c, and under this condition, the controller turns on the heater. this subsequently generates heat in the simulation enviroment, while the airspeed assists in spreading the warm air emitted. furthermore, 20 °c was reached on the 20th minute, and then the control system turns off the heater, subsequently circulating the heat in order to maintain 22 °c. also, the system works to achieve an effective temperature for humans, and fig. 9 shows the simulation environment characteristics with the heater. the manually controlled systems require a speed of 5.5 m/s and only 18 °c is reached at the 30th minute. the temperature increase process tends to be slower because the manual controls are not integrated with the heater system. the performance characteristics of the temperature control system are successful in working in the range of 21 °c to 23 °c which is closer to human thermal comfort (effective temperature setting). fig. 9: temperature and airspeed at the lowest temperature position. 10 20 30 15 20 25 30 35 40 air temp. (automatic control) air speed (automatic control) temp. targeted air temp. (manual control) air speed (manual control) time (minute) t e m p e ra tu re ( o c ) 6 8 10 a ir s p e e d ( m /s ) 0 10 20 30 10 15 20 25 30 air temp. (automatic control) air speed (automatic control) effective temp. setting air speed (manual control) air temp. (manual control) time (minute) t e m p e ra tu re ( o c ) 6 8 10 6 8 10 a ir s p e e d ( m /s ) iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 air humidity data is obtained from simulation chamber at the highest condition of 90%, characterized by relatively large (wet) water vapor content. furthermore, the automatic control system turns on the heater to 60% position and aimed at achieving the simulation room dry out. the heated air with water vapor content is further removed from the room with a removal system, while the humidity decreases. meanwhile, the automatic system has the ability to maintain the humidity conditions at 40% to 60%. figure 10 shows the control system characteristics. the regulation data for air humidity in a manual system is obtained at around 90%, in order to turn on the heater. however, a slight decline was observed at 89% on the 30th minute, resulting from the opened ventilation. fig. 10: air humidity at the highest position. the air humidity is obtained at the lowest position (dry) in simulation room, using a humidity tester. therefore, the speed of achieving this condition is increased by exposing the environment to an initial draining process. this involves the removal of hot air, and new data is collected after reaching the least position (dry). the automatic control systems operated is then commenced at the initial lowest humidity level of 20%, where the water sprayer is turned on, and consequently emitting moist mist. therefore, the humidity slowly increases to 40%, where the sprayer is turned off. this controller system maintains ideal humidity conditions between 40% to 60%, and fig. 11 shows test results from the lowest humidity position. fig. 11: air humidity at the lowest position. iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 furthermore, the air humidity in a manual system is obtained data at 20% because of the inability to turn on the water sprayer. hence, there is a high difference between this application and an automatic system with the capacity to reduce and maintain effective humidity for humans. the script programming of the temperature control system is shown in appendix 1. 4. conclusion comprehensive conclusion was made based on the test results, which include: • in the aspect of room temperature, the control system data retrieved was in the highest position (hot), and the automatic control system was able to reduce the room temperature from 31 ºc to range from 21 °c to 23 °c in 21 minutes. this prototype works according to settings in effective temperature area to attain human comfort. however, the manual controllers only reach 27 °c in 21 minute, hence longer time is required to cool the room, and it is also difficult to achieve optimal temperatures for passengers. room control systems are tested from the lowest temperature position (cold), where automatic unit turns on heater in the simulation room. therefore, 17 °c is raised to the settings in range of 21 °c to 23 °c, and the speed temperature fluctuation is influenced by room volume and heater/ac control capacity. furthermore, effective temperatures are not reached in manual control systems because of the inability to warm up the room. • based on the data retrieved, the humidity control system was at the highest position (wet) at 90%. therefore, the automatic unit turns on the heater system to promote air vapor dryness and subsequent removal from the simulation room. this unit reduces humidity to a range of 40% to 60% (effective humidity for human comfort). meanwhile, the manual system is unable to cause a decline to the effective value for passengers due to the non-integration with the heater and sprayer. • based on the data retrieved, humidity control system was in the least position (dry), working at 20%. furthermore, automatic unit turns on water sprayer, subsequently leading to higher humidity up to the range of 40% to 60%. also, it is able to work according to the setting of humans effective comfort, both in terms of temperature and humidity regulation. however, this condition is not attainable by the manual controllers. this is a model study, and the automatic system created shows better work capacity than the manual, hence greater potential for application in the cabin rooms of real vehicles. the fluctuation rate of temperature and humidity is set based on the regulation capacity of the heater, air conditioner, and room volume. references [1] kristanto d, leephakpreeda t. (2017) sensitivity analysis of energy conversion for effective energy consumption, thermal comfort, and air quality within car cabin. energy procedia, 138: 552-557. https://doi.org/10.1016/j.egypro.2017.10.158 [2] danca p, nastase i, bode f, croitoru c, dogeanu a, meslem a. (2019) evaluation of the thermal comfort for its occupants inside a vehicle during summer. iop conference series: materials science and engineering, 595(1). https://doi.org/10.1088/1757899x/595/1/012027 [3] setiyo m, widodo n, purnomo bc, munahar s, rahmawan ma. (2019) harvesting cooling effect on lpg-fueled vehicles for mini cooler : a lab-scale investigation. indonesian journal of science & technology, 4(1): 39-47. https://doi.org/10.17509/ijost.v4i1.12834 https://doi.org/10.1016/j.egypro.2017.10.158 https://doi.org/10.1088/1757-899x/595/1/012027 https://doi.org/10.1088/1757-899x/595/1/012027 https://doi.org/10.17509/ijost.v4i1.12834 iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 [4] ravindra k, agarwal n, mor s. (2020) assessment of thermal comfort parameters in various car models and mitigation strategies for extreme heat-health risks in the tropical climate. journal of environmental management, 267: 110655. https://doi.org/10.1016/j.jenvman.2020.110655 [5] zhou x, lai d, chen, q. (2019) experimental investigation of thermal comfort in a passenger car under driving conditions. building and environment, 149: 109-119. https://doi.org/10.1016/j.buildenv.2018.12.022 [6] shahzad s, brennan j, theodossopoulos d, hughes b, calautit jk. (2016) the accuracy of thermal comfort zone, ashrae standard 55-2013. cibse technical symposium. http://hdl.handle.net/10545/620577 [7] zhai y, zhang y, zhang h, pasut w, arens e. (2015) human comfort and perceived air quality in warm and humid environments with ceiling fans. building and environment, 90: 178-185. https://doi.org/10.1016/j.buildenv.2015.04.003 [8] toftum j, anette sj, fanger po. (1998) upper limits for indoor air humidity to avoid uncomfortably humid skin. energy and buildings, 28: 1-13. https://doi.org/10.1016/s03787788(97)00017-0 [9] javadinejad s, dara r, jafary f. (2020) potential impact of climate change on temperature and humidity related human health effects during extreme condition. safety in extreme environments, 2: 189-195. https://doi.org/10.1007/s42797-020-00021-x [10] gładyszewska-fiedoruk k, teleszewski tj. (2020) modeling of humidity in passenger cars equipped with mechanical ventilation. energies, 13(11). https://doi.org/10.3390/en13112987 [11] watson p, whale a, mears sa, reyner la, maughan rj. (2015) mild hypohydration increases the frequency of driver errors during a prolonged, monotonous driving task. physiology and behavior, 147: 313-318. https://doi.org/10.1016/j.physbeh.2015.04.028 [12] afzal a, saleel ca, badruddin ia, khan tmy, kamangar s, mallick z, samuel od, soudagar mem. (2020) human thermal comfort in passenger vehicles using an organic phase change material– an experimental investigation, neural network modelling, and optimization. building and environment, 180: 107012. https://doi.org/10.1016/j.buildenv.2020.107012 [13] li cl, zhang x, chung sl. (2012) temperature and humidity control inside an automobile during heating period. journal of the chinese institute of engineers, transactions of the chinese institute of engineers, series a, 35(6): 641-654. https://doi.org/10.1080/02533839.2012.701853 [14] khatoon s, kim mh. (2020) thermal comfort in the passenger compartment using a 3-d numerical analysis and comparison with fanger’s comfort models. energies, 13(3). https://doi.org/10.3390/en13030690 [15] purnomo bc, setiawan ic, nugroho ha. (2020) study on cooling system for parked cars using mini air cooler and exhaust fan. automotive experiences, 3(2): 81-88. https://doi.org/10.31603/ae.v3i2.3801 [16] wang y, gao q, zhang t, wang g, jiang z, li y. (2017) advances in integrated vehicle thermal management and numerical simulation. energies, 10(10). https://doi.org/10.3390/en10101636 [17] brusey j, hintea d, gaura e, beloe n. (2018) reinforcement learning-based thermal comfort control for vehicle cabins. mechatronics, 50: 413-421. https://doi.org/10.1016/j.mechatronics.2017.04.010 [18] warey a, kaushik s, khalighi b, cruse m, venkatesan g. (2020) data-driven prediction of vehicle cabin thermal comfort: using machine learning and high-fidelity simulation results. international journal of heat and mass transfer, 148: 119083. https://doi.org/10.1016/j.ijheatmasstransfer.2019.119083 [19] buonocore c, de vecchi r, scalco v, lamberts r. (2020) thermal preference and comfort assessment in air-conditioned and naturally-ventilated university classrooms under hot and humid conditions in brazil. energy and buildings, 211: 109783. https://doi.org/10.1016/j.enbuild.2020.109783 https://doi.org/10.1016/j.jenvman.2020.110655 https://doi.org/10.1016/j.buildenv.2018.12.022 http://hdl.handle.net/10545/620577 https://doi.org/10.1016/j.buildenv.2015.04.003 https://doi.org/10.1016/s0378-7788(97)00017-0 https://doi.org/10.1016/s0378-7788(97)00017-0 https://doi.org/10.1007/s42797-020-00021-x https://doi.org/10.3390/en13112987 https://doi.org/10.1016/j.physbeh.2015.04.028 https://doi.org/10.1016/j.buildenv.2020.107012 https://doi.org/10.1080/02533839.2012.701853 https://doi.org/10.3390/en13030690 https://doi.org/10.31603/ae.v3i2.3801 https://doi.org/10.3390/en10101636 https://doi.org/10.1016/j.mechatronics.2017.04.010 https://doi.org/10.1016/j.ijheatmasstransfer.2019.119083 https://doi.org/10.1016/j.enbuild.2020.109783 iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 appendix 1: script programming const int temperaturelm35 = a0; float temperature, data; const int relay1 = 2 ; const int relay2 = 3 ; const int relay3 = 4 ; const int relay4 = 5 ; const int relay5 = 6 ; const int relay6 = 7 ; void setup() { serial.begin(9600); pinmode(temperaturelm35, input); pinmode(relay1, output); pinmode(relay2, output); pinmode(relay3, output); pinmode(relay4, output); pinmode(relay5, output); pinmode(relay6, output); } void loop() { data = analogread (temperaturelm35); temperature = data / 2.0408; serial.print("temperature: "); serial.print(temperature); serial.println(); delay(1000); if (temperature <= 16 ) //heater on { digitalwrite(relay1, high); digitalwrite(relay2, low); digitalwrite(relay3, low); digitalwrite(relay4, low); digitalwrite(relay5, low); digitalwrite(relay6, low); } else if ( temperature <= 20 )// very low speed { digitalwrite(relay1, high); digitalwrite(relay2, high); digitalwrite(relay3, low); digitalwrite(relay4, low); digitalwrite(relay5, low); digitalwrite(relay6, low); } else if( temperature <= 24)// low speed { digitalwrite(relay1, low); digitalwrite(relay2, low); digitalwrite(relay3, high); digitalwrite(relay4, low); digitalwrite(relay5, low); digitalwrite(relay6, low); } else if( temperature <= 30)// medium speed { digitalwrite(relay1, low); digitalwrite(relay2, low); digitalwrite(relay3, low); iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 digitalwrite(relay4, high); digitalwrite(relay5, low); digitalwrite(relay6, low); } else if ( temperature <= 35)// high speed { digitalwrite(relay1, low); digitalwrite(relay2, low); digitalwrite(relay3, low); digitalwrite(relay4, low); digitalwrite(relay5, high); digitalwrite(relay6, low); } else if ( temperature >= 36)// very high speed { digitalwrite(relay1, low); digitalwrite(relay2, low); digitalwrite(relay3, low); digitalwrite(relay4, low); digitalwrite(relay5, low); digitalwrite(relay6, high); } } meanwhile, the script embedded in the humidity control system is shown as follows = #include <dht.h> #define sensor a0 dht dht; int relay1= 2; int relay2= 3; int relay3= 4; void setup(){ serial.begin(9600); delay(500); pinmode(sensor, input); pinmode(relay1, output); pinmode(relay2, output); pinmode(relay3, output); } void loop(){ dht.read11(sensor); serial.print("air humidity = "); serial.print(dht.humidity); serial.println("% "); delay (1000); int sen = dht.humidity; if ( sen <= 20.00){ digitalwrite(relay1, high); digitalwrite(relay2, low); digitalwrite(relay3, low); } if ( sen <= 40.00){ digitalwrite(relay1, high); delay(500); digitalwrite(relay2, low); digitalwrite(relay3, low); else if ( sen <= 60.00){ digitalwrite(relay1, low); digitalwrite(relay2, low); digitalwrite(relay3, low); iium engineering journal, vol. 23, no. 1, 2022 munahar et al. https://doi.org/10.31436/iiumej.v23i1.1812 } else if ( sen <= 80.00){ digitalwrite(relay1, low); digitalwrite(relay2, low); digitalwrite(relay3, high); delay(500); } else if ( sen <= 100.00){ digitalwrite(relay1, low); digitalwrite(relay2, low); digitalwrite(relay3, high); } } microsoft word 7-paper print04yaser.doc iium engineering journal, vol. 1, no. 1, january 2000 y. m. a. khalifa and d. h. horrocks 22 analog circuits design automation tool using genetic algorithms y. m. a. khalifa electrical engineering department, university of north dakota, grand forks, nd 58202, usa d. h. horrocks school of engineering, cardiff university of wales, cardiff cf2 3tf, uk abstract: an investigation into the application of genetic algorithms (ga) for the design of electronic analog circuits is presented in this paper. in this paper an investigation of the use of genetic algorithms into the problem of analog circuits design is presented. in a single design stage, circuits are produced that satisfy specific frequency response specifications using circuit structures that are unrestricted and with component values that are chosen from a set of preferred values. the extra degrees of freedom resulting from unbounded circuit structures create a huge search space. it is shown in this paper that genetic algorithms can be successfully used to search this space. the application chosen is a lc all pass ladder filter circuit design. key words: computer-aided design, analog circuits, artificial intelligence. 1. introduction computer-aided design tools for analog circuits consist almost invariably of circuit analysis or simulation packages; no general-purpose analog circuit synthesis tools are available. conventional numerical optimization techniques can be used to obtain combinations of component values that satisfy given design specifications. in addition, conventional optimization techniques operate on circuits after having their desired responses approximated by a suitable polynomial, using ideal components with unrestricted values, and only operating on pre-defined circuit structures. the restrictions introduced by pre-defining the circuit structure waste extra degrees of freedom in the design process and can conceal many novel design structures that can satisfy the target response and at the same time enhance the design process. in previous papers, [1-6] ga were applied to fixed structure circuit designs to satisfy certain specifications. as mentioned earlier, the predetermination of the circuit structure required in conventional design techniques is a limiting factor when considering a powerful search technique such as ga. a few attempts have been made to include structure synthesis in genetically based optimization techniques such as genetic programming (gp) [7] and ga [8]. however, these techniques suffered huge delays and memory usage and needed to be used in conjunction with circuit analysis packages such as pspice [9]. there is still a need, however, for more efficient algorithms that are faster, self-sufficient and can function independently. this is particularly important in the development of new generations of analog programmable analog arrays (apaa) programming tools. in this paper an efficient ga technique for free structure analog circuit design is described. the paper is organized as follows. section 2 introduces the genetic algorithms in details. section 3 presents the ga implementation technique and chromosome structure, and section 4 discusses the least squared error evaluation technique used by ga. section 5 presents results for a number of analog filter design specifications that were generated by the ga. section 6 concludes the paper. 2. genetic algorithms genetic algorithm is an evolutionary algorithm which falls into the class of global optimization techniques. a number of different classifications of the existing global optimization techniques are described in [10]. however, in [11] a different classification is presented which would be more appropriate for the case considered here. it classified global optimization methods into two main categories, namely volume-oriented and path-oriented. in the volume-oriented method, an exhaustive search over the whole volume of the feasible region is conducted (e.g. grid search [12], monte-carlo methods [13]). while in the path-oriented method, the search starts from an arbitrary or specifically chosen point in the feasible region, and then follows one or more paths in the search for a global optimum. the path-oriented method is further divided into the prediction method and the exploration method. the prediction method uses a model of the objective function to predict the steps (e.g. tunneling methods [14]), while the exploration method (e.g. rotating coordinates [15]) does not. evolutionary algorithms, according to the above classification, fall mainly into the group of path-oriented exploration methods. during the optimization process, however, evolutionary methods can act to a lesser degree as predicting methods as well as volume-oriented methods. the most common of these evolutionary algorithms is genetic iium engineering journal, vol. 1, no. 1, january 2000 y. m. a. khalifa and d. h. horrocks 23 algorithm which has gained much importance in the last twenty years [16]. the field of genetic algorithms was founded by john holland in the early 1970's. in [17], holland emphasizes the ability of simple representations to encode complicated structures and the power of simple transformations to improve that structure. these representations are combined in what is called in biology a chromosome. a number of these chromosomes will constitute a population. syntactic operations are then used to alter and improve these coded solutions. holland described genetic algorithms [18] as a control structure with which these representations and operations could be managed in order to evolve bit strings that were well developed to the problem to be solved. as in natural evolution, the problem each individual chromosome faces is one of searching for beneficial adaptations to a complicated and changing environment. the knowledge that each individual gains is embodied within the chromosomes of a population. figure 1, shows a flowchart of a simple ga. 3. implementation 3.1 chromosome adaptation and structure in [1-3] the predetermination of the circuit structures has helped in reducing the chromosome length. this was achieved by incorporating the order of the chromosome genes into the node connections information. however, in the case of free structure circuit synthesis this technique cannot be used. in the case of free structure design, the solution space is much larger and the optimization process is composite. it involves the optimization of two different but highly correlated problems; the structure as well as the sizing of a circuit. hence, all specifications of the electrical circuit including the structure and the sizing of all the components should be included in the chromosome representation. the specifications of the electrical circuit include the number of components in the circuit, the type of each component and a list of connections between the components. circuit components can include a variety of different types of components, including resistors, capacitors, inductors, etc.. given the above information, the chromosome for each circuit comprises a number m of groups of equal bit lengths, and an extra group of bits representing the number of nodes in the circuit, figure 2. each gene in the chromosome specifies a component and contains four fields (i) type of component (l, c, etc.), (ii) a pointer to a menu containing component value, (iii) and (iv) circuit nodes to which the component is connected, see figure 4. it is generally desirable for a low cost design to use the least number of components. for this reason a null component, representing an open circuit, is introduced into the component type menu. evaluati on evaluation start yes no reproduction crossover mutation new population time out ? initial population terminator fig. 1 simple genetic algorithm 1 2 3gene#: m #nodes field 1 field 2 field 3 field 4 component type r-menu l-menu c-menunull connection node 1 connection node 2 value pointer fig. 2 chromosome structure. iium engineering journal, vol. 1, no. 1, january 2000 y. m. a. khalifa and d. h. horrocks 24 3.2 the design program the design program of the free structure circuit synthesis is briefly described in this section with pseudo code. on entry the user is required to supply the following input data: type of filter (low pass, high pass, band pass) 1 , min 2 , max  n, the maximum number of nodes. optional, and can be used to limit the search to a certain number of designs.  m, the maximum number of components (optional). the program execution is described in pseudo code in figure 3. fig. 3 pseudo code for a single generation evaluation the execution of the program starts by calculating n, maximum number of nodes. then genes representing elements are decoded one at a time, splitting them into four fields as explained in section 5.1. upon determining type, value and connection nodes, the component value is inserted in the corresponding nodal admittance matrix (nam) location according to rules in section 4. when all elements are decoded, contents of the resulting entries in nam are passed to the calculation function, in which lower-upper (lu) decomposition and solutions to the matrix equations are solved. the error and fitness evaluation functions are performed by means of least square error over a frequency design template specified as shown in the following section. 4. least squared error evaluation the error measured is defined as the difference between the specified response constraint, hupp ( ) and hlow ( ) , denoted by the shading in figure 4, where hupp ( ) is the upper boundary of the frequency response, and h low( ) is the lower boundary, and the actual response, ha ( ) , from the design represented by ga chromosomes. the actual frequency response, ha ( ) , will hence be prescribed by its unique combination of component values. therefore,  vnm lllcccrrrh ,...,,,,...,,,,...,,, 212121 fig. 4 design template for simplicity, all types of components will be declared as k. thus h becomes  qkkkh ,...,,, 21 (1) where q = m + n + v hence the error function will depend on the region it is applied for. for the pass band the error function would be ),...,,,( 21 qkkkerr  ),...,,,()( 21 qalow kkkhh   (2) while in the stop band the error function would be ),...,,,( 21 qkkkerr  ),...,,,()( 21 qaupp kkkhh   (3) the least-squares error criteria e is used as a performance index because of mathematical simplicity and ease of programming. the error is defined as  u l qkkkerre ),...,,,( 21 (4) substituting from (13) in (12), lse would be    u l qa kkkhhlse    221 ),...,,,()( (5) where h() is the boundary response )(upph or )(lowh . since the calculations must be performed for population_member = 0 to population_size, do determine n, number of nodes for gene_location = 1 to m, do decode fields 1,2,3 and 4 descale fields 3 and 4 according to n update nam end for for frequency_test_point = 0 to maximum, do lu decompose nam calculate response compare with template and find error end for end for magnitude db frequency pass transition band stop band band ripple hupp() hlow() iium engineering journal, vol. 1, no. 1, january 2000 y. m. a. khalifa and d. h. horrocks 25 numerically, the integration in eq. (5) will be replaced by summation. therefore,  2 1 21 ),...,,,()(   m i qa kkkhhlse  (6) where m is equally spaced frequency points assumed over the range of integration. this is chosen because of ease in programming. 4.1 specified weighted errors equation (6) gives equal weight for all frequency points within the range. this does not necessarily reflect the prescribed performance; for example, in the case of numerically small errors in the pass band. this numerically small error in the pass band will be more likely to affect the accuracy of a solution than a relatively larger error encountered in the stop band. hence, a weight function can be inserted in equation (6) to enable us to emphasize or de-emphasize the error in the various regions of the frequency spectrum [19]. therefore equation (6) can be modified to be   2 1 21 ),...,,,()()(   m i qa kkkhhwlse  (7) the weight function w() has been arbitrarily chosen to be two in the pass band region and unity in the stop band region. any other design weight functions can be easily applied instead. although the pass band will be characterized by a specific pass band ripple, the upper boundary of the response represents the maximum power transfer level, the claimed results of lc filter theory. therefore, testing only the suitability of the lower limit of the response would be sufficient as the upper limit will never be exceeded in the pass band [11]. in the stop band region, only the upper limit of the specified attenuation level needs to be considered, since any lower value of attenuation meets the specifications. the transition region is considered as a ‘don’t care’ region. thus it is sufficient to test just the pass band and the stop band for confirmations. the different frequency band boundaries are shown in figure 4. the fitness function is defined as the simple reciprocal of error as defined by eq. (7). this produces the desired characteristic that fitness is larger for better circuits with less error, and also causes increased fitness separation for groups of solutions that are near optimum. 4.2 performance improvements by controlling connection fields the number of nodes comprising the circuit is determined at the beginning of the decoding process to control the connection node numbers of the circuit components. the fields determining the connection nodes are decoded in a way to produce node numbers within n. this is achieved by scaling down the whole range of values of allowed node numbers to only that of n. this helps to avoid circuit structures that would have components connected to nodes that do not exist in the defined structure and which are hence unacceptable, and would be a total waste of time to evaluate. 5. results it is very difficult and nearly impossible to design a practical circuit that meets the exact or the piecewise linear specifications of a given design. therefore, t is a common practice for circuit designers to specify a band of permissible variations in the gain characteristics rather than specific values for the gain at each frequency grid point. in this implementation the desired design template is the starting point of the design process, whereas in conventional designs, polynomial approximation for the desired response is used [19]. this has the limitation of constraining the feasible solution to sets of design parameters that would satisfy the polynomial approximation. by designing directly from the template specifications a designer would avoid that extra degree of approximation a polynomial fitting would introduce. at the same time they provide an extra degree of freedom which would enlarge the solution space considerably to include any design that would reside within the design template without necessarily being represented by a polynomial. that would give genetic algorithms an advantage over conventional optimization methods for the credit it holds in investigating huge solution spaces, due to its nature. also the ga search starts from an arbitrary point in the solution space and need not have any prior knowledge of the feasible region of the required design. to illustrate the success of the above ga in designing filters with free topology, a number of design templates are specified upon which the ga are applied. a further design response is specified as a transfer function which the ga has successfully matched. in the cases of low and high pass design specifications, it is found that ga has provided solutions that have the conventional ladder structure circuits as well as some novel design structures, as will be seen in the next subsections. the flat losses of the circuit responses are left unconstrained. this is acceptable in many applications and the extra degree of freedom created tends to allow the ga to find more solutions. 5.1 low pass design three different low pass design specifications are considered. in the first, a pass band ripple of 1 db, minimum attenuation of -100 db at a transition ratio of 10. an average group of five solutions emerged; the frequency response of one of these solutions is plotted in figure 5. the circuit constructed by the ga is shown in figure 6. it is noticed that well known  and t ladder structures have also been generated by the ga. that could be due to the low sensitivity such structures have to small changes in component values. this feature will be discovered in ga as it approaches an acceptable solution. large changes in the frequency response in a iium engineering journal, vol. 1, no. 1, january 2000 y. m. a. khalifa and d. h. horrocks 26 solution that could be considered as a good one will most likely affect its performance negatively, and hence the ga will tend to move away from that solution to a more stable solution region. r=100  c=0.1 f l=1.0 mh c=0.18 f c=10 nf r=68  l=0.22 mh c=0.18  f i/p o/p fig. 6 genetically designed circuit with a pass band ripple of 1 db and stop band edge at -100 db. r=100  c=82 nf l=1.0 mh r=5.6  c=18 nf c=0.15  fr=470  c=0.15  fc=22 nf c=0.18 f o/pi/p fig. 7 genetically designed filter circuit with 0.5 db pass band ripple and -60 db stop band attenuation fig. 5 frequency response examples for low pass design template (a) pass-band and (b) stop band a tighter specification in the pass band is introduced, with a 0.5 db pass band ripple allowed and -60 db minimum attenuation at pass band edge normalized at 10 rad/sec. a group of five solutions also satisfied these specifications. a circuit structure of one of these is shown in figure 7. the frequency response for three of the resulting families of circuits are shown in figure 8 (a), (b), and (c). a third template of 0.2 db pass band ripple and stop band attenuation of -50 db with a transition ratio of 10 is also considered. a group of an average six solutions are generated. some of these solution’s frequency responses are plotted in figure 9. 5.2 high pass design the high pass filter design is done directly without having to use a low pass prototype and then perform frequency transformations. a design template of 1 db pass band ripple and attenuation of -60 db at the stop band edge with a transition ration of 10 is considered. four solutions, on average, emerged. two of these circuits are shown in figure 10. the frequency responses of the resulting circuits are shown in figure11. 6. conclusions this paper has presented a novel circuit design tool by using the ga strong search abilities in both the structure and sizing domain of a circuit design problem. a successful design of the chromosome structure has been obtained to include the full circuit specifications. 0 .0 1 -7 -7 .5 -8 -8 .5 -9 0 .5 1 pass band amplitude db  (10 rad/sec)5 (a) 0 .0 1 0 .1 1 0 -5 0 1 0 0 1 5 0 2 0 0 1 0 amplitude db  (10 rad/sec) 5 stop band edge (b) iium engineering journal, vol. 1, no. 1, january 2000 y. m. a. khalifa and d. h. horrocks 27 fig. 8 (a), (b) and (c) frequency responses for low pass design template with 0.5 db pass band ripple and -60 db stop band edge 0.01 10.5 10 -10.5 11 -11.5 12 a m p l i tud e d b  (10 ra d /se c) 5 p a ss b a n d 0.01 10.5 -10 10.5 -11 -11.5 -12 a m p l i tud e d b  (1 0 ra d /se c) 5 p a ss b a n d 0.01 0.1 1 10 0 10 20 30 40 50 60 70 a m p l i tu d e d b  (1 0 ra d /se c) 5 stop b a n d e d g e 0.01 0.1 1 10 00 -10 -20 -30 -40 -50 -60 -70 a m p l i tu de d b  (1 0 ra d/se c) 5 sto p b a n d e d g e 44 -44.5 45 -45.5 46 0.01 10.5 amplitude db  (10 rad/sec) 5 pass band 0.01 0.1 1 10 00 -40 -50 -60 -70 -80 -90 100 amplitude db  (10 rad/sec) 5 stop band edge (a) (b) (c) iium engineering journal, vol. 1, no. 1, january 2000 y. m. a. khalifa and d. h. horrocks 28 fig. 9 (a) and (b) frequency response for low pass design template with a 0.2 band pass ripple and -50 db stop band edge r=100  l=4.7 mh r=100  c=0.1  f l=1.0 mh l=1.0 mhl=1.0 mh r=39  l=0.47 mh i/p o /p r=100  l=1.0 mh l=0.47 mh r=39  c=100 n f c=56 nf r=0.15  c=0.1 f o/pi/p l=4.7 mh (a) (b) fig. 10 (a) and (b) genetically derived high pass filter circuit with 1db pass band ripple and attenuation of -60 db at the stop band edge 0 .0 1 -1 -1 .5 -2 -2 .5 -3 10 .5 amplitude db  (10 rad/sec) 5 pass band -41.5 -42.5 a m p l i tud e d b 0.01 -41 -42 -43 0.5 1  (1 0 ra d /se c) 5 p a ss ba n d 0 .0 1 0 .1 1 10 0 -2 0 -4 0 -6 0 amplitude db  (10 rad/sec) 5 stop band edge a m p l i tud e d b 0.01 0.1 1 10 40 -60 -80 -100 -120  (1 0 ra d /se c) 5 sto p b a nd e d g e (a) (b) iium engineering journal, vol. 1, no. 1, january 2000 y. m. a. khalifa and d. h. horrocks 29 fig. 11 genetically derived high pass filter circuit references [1] d. h. horrocks and y. m. a. khalifa,, "genetically derived filter circuits using preferred value components", proc. iee colloquium on analog signal processing, oxford, uk, pp 4/1-4/5, oct. 1994. [2] d. h. horrocks and y. m. a. khalifa,, "genetically evolved fdnr and leap-frog filters using preferred components values", proc. european conference on circuit theory and design, istanbul, turkey, pp 359362, aug. 1995. [3] d. h. horrocks and y. m. a. khalifa,, "genetic algorithm design of electronic analog circuits including parasitic effects", proc. first on-line workshop on soft computing (wsc1), nagoya university, japan, pp 71-78, aug. 1996. [4] d. h. horrocks and y. m. a. khalifa,, "evolutionary design of analog electronic circuits; current status", iee colloquium on analog signal processing, oxford, uk, pp 7/1-7/8, nov. 1996. [5] d. h. horrocks and y. m. a. khalifa, "rapid feasible region estimation for enhanced performance of genetically derived circuit design technique", proc. of the fourth ieee international conference on electronics, circuits and systems, cairo, egypt, dec. 1997. [6] y. m. a. khalifa and d. h. horrocks, "isomorphism elimination for the enhancement of genetically generated analog circuits", proc. of the international symposium on circuits and systems iscas’99, orlando, florida. usa, pp 314-317, june 1999. [7] j. r. koza, d. andre, f. h. bennet iii, and m. a. keane,”toward evolution of electronic animals using genetic programming”, proceeding of the first annual conference, stanford university, cambridge, july 2831, 1995. [8] j. b. grimbleby, “automatic synthesis of active electronic networks using algorithms”, iee genetic algorithms in engineering systems: innovations and applications, conference publication no. 446, pp103107, sep. 1997. [9] w. blume, “computer circuit simulation”, byte v 11 n 7, pp. 165-166, 168-170, jul 1986. [10] g. s. g. beveridge and g. schechter, optimization theory and practice, new york, mcgraw-hill, 1970. [11] k. ensor, g. bennet and w. peter, “stochastic optimization via grid search”, proc. mathematics of stochastic manufacturing systems, williamsburg, va, pp. 89-100, 1996. [12] j. p. c. kleijnen, statistical techniques in simulation, m. dekker, new york, 1974-75. [13] a. levy and v. s. gomez, “the tunnelling method applied to global optimization”, numerical optimization, pp. 213—244, 1984. [14] a. m. arthurs and j. t. lewis, “rotating co-ordinates in scattering theory”, proceedings of the royal society. series a. mathematical and physical, sciences a 269, pp 585-588, , 1962. [15] d. e. goldberg, genetic algorithms in search, optimization and machine learning, addison-wesley, reading ma usa, 1989. [16] j. holland, adaptation in natural and artificial systems, university of michigan, ann harbor, 1975. [17] l. davis, handbook of genetic algorithms, van nostrand reinhold, new york, pp. 36-38, 1991. [18] l. o. chua, computer-aided analysis of electronic circuits, prentice-hall, 1975. [19] g. c. times and j. w. lapatra, circuit synthesis and design, mcgraw-hill, new york, 1977. appendix direct construction of nodal admittance matrix and current source vector in the actual implementation of nodal analysis on digital computers, a direct method which avoids the complexity of constructing a and yb and performing the matrix multiplication is used [19]. amplitude db  (10 rad/sec) 5 pass band 2 6 10 -9 9.5 -10 10.5 -11 11.5 -12 amplitude db  (10 rad/sec) 5 stop band edge 0.01 0.1 1 10 0 20 40 60 80 -100 -120 -140 iium engineering journal, vol. 1, no. 1, january 2000 y. m. a. khalifa et al 30 the rules for forming the nodal equations by inspection can be stated as follows: 1. the diagonal entries of y are positive and y jj   admittances connected to node j (4) 2. the off diagonal entries of y are negative and are given by y jk   admittances connected between node j and k (5) 3. the jth entry of the right-hand-side vector j is: j j   current from independent sources entering node j (6) the above are useful when formulating network equations by hand as they enable us to write the equations on a node-by-node basis. for computer formulation, an element-by-element approach is preferable, as the equations are set up in a single scan of the element list. consider an element with admittance y connected between nodes j and k. let the current through this element be denoted by i with orientation from node j to node k. the current i will appear only in the kcl equations associated with nodes j and k, once with a positive sign and once with a negative sign kcl at node j: .........  i kcl at node k: .........  i let us now write the current i in terms of the voltage across the element, vj-vk, and the admittance. kcl at node j:   .........  vkjvy kcl at node k:   .........  vkjvy separating the term associated with the voltages, kcl at node j: ... ... ... ...   yv j yvk kcl at node k: ... ... ... ...   yv j yvk we thus find that admittance of a two terminal element connected between nodes j and k appears only in rows and columns j and k of y with a plus sign at locations (j , j) and (k,k) and with a negative sign at locations (j , k) and (k , j). symbolically, this is written as j k j k        yy yy (7) for the right-hand-side vector we note that an independent current source of value j connected between nodes j and k (oriented toward k) contributes to rows j and k of j as follows       j j k j (8) the symbolic representation (7) and (8) are the key to computerized formulation and will be extended to other kinds of elements. list of symbols and abbreviations max maximum attenuation in the pass-band mi n minimum attenuation in the stop-band  pass-band angular frequency edge  stop-band angular frequency edge a incident matrix e total error function err() error function at angular frequency  hupp() design template upper bound for the frequency response hlow() design template upper bound for the frequency response ha() actual frequency response of the resulting circuit i element current jn equivalent nodal current source vector kcl kirchof current law lu lower-upper matrix decomposition m maximum number of components in a chromosome n maximum number of nodes in a chromosome nam nodal admittance matrix method q total number of components in a circuit v element voltage yb branch admittance yn nodal admittance matrix yjj admittance connected to node j yjk admittance connected between node j and k biography yaser m. a. khalifa received his b. sc. degree from alexandria university, egypt, and his phd degree from cardiff university of wales in 1992 and 1997 respectively. dr. khalifa is currently an assistant professor at the department of electrical engineering at the university of north dakota, usa. dr. khalifa’s primary research interest is in the application of evolutionary algorithms in the design of analog and digital circuits. david h. horrocks obtained a b.sc. (hons) from the university of westminster, london, in 1962 and his ph.d. from the university of newcastle upon tyne, uk, in 1968 and then held a postdoctoral research post. since 1970, he has been on the faculty of cardiff university until his recent retirement. his research interests include analog and digital signal processing; ai techniques for electronic design, and low power signal processing. he is an author/co-author of two books, several patents and 100 research publications. he was co-recipient of the 1990/91 iee ambrose fleming premium journal paper award. microsoft word 214-1008-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jalal et al. 125 removal of nitrate and phosphate from municipal wastewater sludge by chlorella vulgaris, spirulina platensis and scenedesmus quadricauda 1 jalal k.c.a., 2 md. zahangir alam, 1 matin w.a., 1 kamaruzzaman b.y., 1 akbar j. and 3 toffazel hossain 1 department of biotechnology, kulliyyah of science, international islamic university malaysia, jalan sultan ahmad shah, bandar indera mahkota, 25200, kuantan pahang, malaysia. 2 department of biotechnology engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. 3 ministry of health and family welfare bangladesh. jkchowdhury@iium.edu.my abstract: nitrate and phosphorus in wastewater contribute to health and environmental threats as they are linked to illnesses as well as ecosystem disruption via algal blooms in contaminated water bodies. based on above perspectives a comparative study was conducted on three local freshwater microalgae:chlorella vulgaris, spirulina platensis and scenedesmus quadricauda to evaluate their effects on nitrate and phosphorus removal from municipal wastewater sludge (mws). algae performance in removing nitrate and phosphorus was evaluated by measuring nitrate and phosphorus content of mws incubated with the strains for 7 days. instantaneous readings were taken every 48 hours to determine periodic levels of the nutrients phosphate and nitrate. bod5 was also evaluated to identify the strain with the most robust growth that would demand for oxygen the most in the dark. spirulina platensis was shown as the most efficient microalgae to reduce nitrate in mws and the best-growing among the three strains, while chlorella vulgaris removed phosphorus the most effectively. thus spirulina and chlorella could be potential candidates by showing their intrinsic merit for the reduction of phosphate and nitrate in wastewater treatment. abstrak: nitrat dan fosforus dalam air sisa menggugat kesihatan dan mengancam alam sekitar memandangkan ia berkait dengan penyakit-penyakit serta gangguan terhadap ekosistem melalui pembiakan alga dalam air yang tercemar. berdasarkan perspektif di atas, satu kajian perbandingan telah dijalankan terhadap tiga mikro alga air tawar tempatan : chlorella vulgaris, spirulina platensis dan scenedesmus quadricauda untuk dinilai kesannya terhadap penyingkiran nitrat dan fosforus dari enap cemar air sisa bandaran (municipal wastewater sludge (mws)). kebolehan alga dalam penyingkiran nitrat dan fosforus dikaji dengan menyukat kandungan nitrat dan fosforus dalam mws yang dieramkan dengan strain ini selama 7 hari. bacaan serta-merta diambil setiap 48 jam untuk menentukan tahap berkala nutrien fosfat dan nitrat. bod5 juga dinilai untuk mengenal pasti strain yang membesar dengan cepat yang memerlukan bekalan oksigen paling banyak dalam gelap. spirulina platensis dikenal pasti sebagai mikro alga yang paling cekap dalam pengurangan nitrat dalam mws dan paling cepat tumbesarannya, manakala chlorella vulgaris menyingkir fosforus dengan paling berkesan. maka spirulina and chlorella berpotensi dalam mengurangkan fosfat dan nitrat dalam rawatan air sisa. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jalal et al. 126 keywords: chlorella vulgaris; spirulina platensis; scenedesmus quadricauda; nitrate; phosphate; wastewater 1. introduction generation of wastewater, alongside consumer waste, is characteristic of any human community. this liquid byproduct of human habitation is produced through the various uses of water in everyday life, discharging with it bodily waste, cleaning agents, disposed liquids, and discarded items among other things. in the environment, when these nutrients enter water bodies in high content, eutrophication ensues as photosynthetic algae thrive to explosive proportions, killing aquatic life through either oxygen and sunlight depletion, or massive contamination of the water with deadly phycotoxins. the presence of nitrate in drinking water also raises health concerns [1] particularly for its link to the blood disorder methemoglobinemia among bottle-fed infants (blue baby syndrome), as well as increased risk of specific cancers and adverse reproductive outcomes [2]. as such, nitrate and phosphorus in wastewater have been recognized as priority targets for removal, with maximum contaminant levels (mcl) set in place to regulate water quality. the u.s. environmental protection agency (epa) mcl of 10mg/l nitrate-nitrogen (nitrate-n) (equivalent to 45mg/l as nitrate), and the world health organization (who) guideline of 11mg/l nitrate-n (equivalent to 50mg/l as nitrate) in particular were prescribed for protection against infant methemoglobinemia. biological treatment of nitrate and phosphorus in wastewater have been widely studied, with various organisms namely bacteria, fungi, protozoa and microalgae identified as potent agents for their uptake. microalgae for one are interesting for study and application in this area for the attractive idea of ‘beneficial eutrophication’ at the treatment plant, which should ideally deplete the nutrients enough so that effluents discharged, would be cleaner and safer for the environment. additionally, microalgal use in wastewater treatment has also piqued researchers’ interest for the potential of using wastewater treatment plants to generate valuable, nutritious biomass for agricultural and aquacultural purposes. to date, lack of studies have been conducted on how local microalgal strains varies in efficiency of nutrient uptake from wastewater. the interest of this study is thus to compare the performance of these three malaysian freshwater microalgae in removing nitrate and phosphorus from local municipal wastewater. a) municipal wastewater as a source of nutrient pollution usepa [3] reported in its manual that the toilet use is the main source of nitrogen compared to basin, sink and appliance use (table 1). food waste disposal makes the second biggest source of wastewater nitrogen as per the context of the report, where food grinder use is widespread in the community. nitrate in wastewater is generally produced as an intermediate of nitrogen metabolism by microorganisms, beginning with ammonification of proteins or other nitrogen-containing compounds, followed by nitrification of ammonia into nitrite, and later, oxidation of nitrite into nitrate. based on the understanding nitrate accumulation becomes a concern in water quality management. contrary to nitrate, phosphorus levels do not fluctuate as much, with this nutrient persisting from early on alongside other forms of phosphorous compounds in the wastewater production line. the significant phosphorus content in wastewater is largely blamed on detergent use, where predetergent days saw only 3 to 4 mg/l of phosphorus in treated municipal wastewater compared to the 10 to 20 mg/l concentrations reported more recently. in addition to detergents, phosphorous compounds are also used for corrosion control in water supply as well as industrial cooling systems. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jalal et al. 127 table 1: typical pollutants of concern in effluent from onsite wastewater treatment systems (adapted from ‘on site wastewater treatment systems manual, 2002’). pollutant public health or water resource impacts pathogens parasites, bacteria, and viruses can cause communicable diseases through direct or indirect body contact or ingestion of contaminated water or shellfish. pathogens can be transported for significant distances in ground water or surface waters. nitrogen nitrogen is an aquatic plant nutrient that can contribute to eutrophication and dissolved oxygen loss in surface waters, especially in nitrogen-limited lakes, estuaries, and coastal embayments. algae and aquatic weeds can contribute trihalomethane (thm) precursors to the water column that might generate carcinogenic thms in chlorinated drinking water. excessive nitrate-nitrogen in drinking water can cause methemoglobinemia in infants and pregnancy complications. phosphorus phosphorus is an aquatic plant nutrient that can contribute to eutrophication of phosphorus-limited inland surface waters. high algal and aquatic plant production during eutrophication is often accompanied by increases in populations of decomposer bacteria and reduced dissolved oxygen levels for fish and other organisms. b) biological approaches to nitrate and phosphate removal various means of reducing the nutrient load of wastewater have been introduced and implemented, whether physicochemical or biological. alongside techniques like ion exchange, gas stripping, and breakpoint chlorination for nitrogen as well as coagulation/sedimentation by metal salt or lime for phosphorus [4], employment of biological agents proves to be an intriguing and attractive approach for researchers and investors alike. the attractiveness of this approach lies in its seemingly simple principle of letting natural, living agents capable of functioning and reproducing independently process the pollutants out of the wastewater. removal by bacteria is currently the best-explored, with most systems incorporating the approach relying on the role of resident bacteria in the nitrogen cycle to achieve their goals. not much difference is seen with biological phosphorus removal, as seen in most contributions to the literature which targeted and discussed both nutrients mutually. there was considerable success thus far, with significant reductions in nutrient levels of wastewater documented and reported in numerous cases, promising better prospects for water quality management. c) algae as an agent of waste removal alage are photosynthetic, pigment-producing, protein-rich microorganisms especially play vital role for treating wastewater treatment systems for their unique ability to generate their own carbon source and oxygen, greater visibility that aids growth monitoring, and high commercial value. these traits excellently complement their notable capacity in nitrogen and phosphorus uptake for synthesis of cellular proteins and other essential biomolecules. microalgae such as chlorella sp. and scenedesmus sp. are commonly sighted at treatment tanks, especially in warmer climates, naturally colonizing wastewater postsecondary treatment at high rate and possessing high nutrient removal capabilities [4]. in hong kong, tam and wong (1994) [5] investigated the feasibility of cultivating iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jalal et al. 128 chlorella pyrenoidosa in primary settled sewage for inorganic nutrient removal, and up to 80% of nitrogen was removed from the settled sewage, whereas phosphorus content was reduced to 1-2 mg/l following a week of culture. by cultivating the microalgae in suspension, the research setup allowed for greater mobility of these nutrient-removing agents within the substrate. a study on pitted four polar strains of mat-forming cyanobacteria-phormidium subfuscum, p. tenue, unidentified oscillatoria, and schizothrix calcicola-against a tropical strain, phormidium bohneri to assess their nutrient uptake in temperatures as low as 50ºc [6]. this high-latitude study also raised a significant point in its design: in order for biomass harvesting post-treatment to be more efficient, it is more preferable to employ species with a natural tendency to aggregate, such as epilithic or benthic filamentous cyanobacteria. based on above perspectives, this study was aimed to evaluate nitrate and phosphate reduction in mws used as a growth medium for the microalgal strains such as chlorella vulgaris and scenedesmus quadricauda both genera commonly found colonizing wastewater—as well as spirulina platensis, a matforming filamentous alga. 2. materials and methods 2.1 sludge collection sludge used as substrate for this research was collected from the indah water konsortium (iwk) wastewater treatment plant in titiwangsa, kuala lumpur. the sludge obtained from the gravity thickener at the facility was filtered on-site with a mesh and transferred into a polymer container for storage. 2.2 substrate preparation sludge was stored in a polymer container following collection and stored at 4ºc. for use as substrate, the collected sludge was diluted with distilled water to 20% the original concentration and transferred to 250 ml conical flasks (minireactors) for incubation. the substrate-containing minireactors (fig. 3.3) were then autoclaved at 121ºc. 2.3 algal strains culture chlorella vulgaris, spirulina platensis and scenedesmus quadricauda were purchased from university of malaya algae culture collection (umacc) for this research. c. vulgaris and s. quadricauda were suspended in bold’s basal medium (bbm) while s. platensis was grown in kosaric medium [7]. the purchased cultures were then maintained in an incubator-shaker at 150 rpm and 37ºc. 2.4 incubation ten milliliters from each strain was aseptically transferred into the sterilized minireactors in triplicates. the inoculated minireactors were then labeled as cv1, cv2, cv3 (c. vulgaris); sp1, sp2, sp3 (s. platensis); and sq1, sq2, sq3 (s. quadricauda) while sterile sludge was used as control. the mini reactors were incubated in the incubator shaker at 150 rpm and 37ºc with an electric bulb as the light source for one week. 2.5 data collection and analysis hach dr/2400 spectrophotometer was used for nitrate and phosphorus content analysis [8], [9]. nitrate detection (mg/l no3-n) was done using the chromotropic acid method, and for reactive phosphorus (orthophosphate) detection (mg/l po4 3), the phosver tm 3 method. absorbance for both tests was 410nm and 880 nm respectively. a sample from each mini reactor was collected every 48 hours, and nitrate and phosphorus iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jalal et al. 129 reading was taken using hach dr/2400 via steps outlined in the user manual. for both tests, reading was done three times on each sample for accuracy. 2.6 bod5 four 250 ml samples of wastewater sludge-one sterile and the others inoculated with an algal species each-were prepared for biochemical oxygen demand (bod) analysis following incubation. all samples were saturated with oxygen using an air pump, and the initial dissolved oxygen (do) level was taken using ysi 5000 do meter for each sample. after 5 days of incubation in the dark, the final do level was taken, and the difference between final and initial levels were recorded. 3. results and discussion 3.1 nitrate and phosphate removal by microalgae after a week of incubation in mws (ph 6, 37ºc, 150 rpm and 60 w light) and four periodic readings, changes were observed in the nitrate and phosphate content of the mini reactors. both nutrients displayed a general decrease in level within mini reactors inoculated with the three local strains (fig. 1 and fig. 2). cv, sp, sq and c refer to chlorella vulgaris, spirulina platensis, scenedesmus quadricauda, and control respectively. both phosphate and nitrate were reduced by 40 to 50 percent, assessed from the margin of change from the initial nitrate concentration to the lowest achieved concentration in any one of these mini reactors. spirulina platensis exhibited the largest reduction in nitrate content, followed by chlorella vulgaris, then scenedesmus quadricauda. sp mini reactors also displayed a steadier decrease in nitrate content, compared to cv and sq which exhibited fluctuations at different points in time. reduction in phosphate content was between 30-40% approximately, based on the margin of change from the initial concentration to the lowest achieved concentration in any of the three groups. cv minireactors displayed the largest reduction in phosphate, followed by the sq group, then sp. fig. 1: nitarte level in presence of different microalgae. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jalal et al. 130 fig. 2: phosphate level in presence of different microalgae. the nutrient-removing capability of microalgae—as explored and documented in various studies previously—was demonstrated yet again in the setup for this study. significant removal of nitrate and phosphorus from wms took place within the algal mini reactors, evidence of the biological activity of the three strains. the living cells drew much-needed nitrate and phosphorus from their wastewater environment for synthesis of amino acids, pigments, nucleic acids, atp, biochemical precursors etc. absence or limitation of these nutrients would otherwise lead to retardation in growth, metabolic efficiency, and ultimately survival in the environment. phycocyanin, an essential pigment in algal photosynthesis, has been reported to degrade more rapidly in nitrogen-limited cells and supplying cells with nitrogenous compounds would restore this pigment to healthy levels [10]. spirulina platensis was the leading species in phosphate and nitrate removal, as observed in the sp mini reactors’ steadier and steeper decline in nitrate content. table 2: removal of nitrate level in wastewater by using microalgae. days cv sp sq c 0 10.5 9.5 8.9 6.7 2 5.3 5.2 6.5 5.3 4 3.1 2.3 3.3 3.3 6 2.2 1.5 2.8 2.8 nitrate level reduced less in and compared to microalgae strains. as the control mws was kept sterile throughout incubation, this observation could be attributed to chemical oxidation of nitrogenous compounds like nitrite into nitrate [11]. algal cells in sp displayed greater efficiency in removing nitrate whether originally present or generated from chemical breakdown in the substrate throughout the study periods. this enhanced ability to remove nitrate is likely attributable to the tendency in spirulina platensis to aggregate and form mats. the intricate filamentous network of living cells with shared nitrate removal efficacy might have been advantageous for spirulina platensis over a more iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jalal et al. 131 unicellular distribution such as in chlorella vulgaris and scenedesmus quadricauda. in removing phosphorus on the other hand, chlorella vulgaris appeared more adept than its counterparts while spirulina platensis was slowest throughout the study periods (table 3). table 3: removal of phosphate level in waste water by using microalgae. days cv sp sq c 0 58.80 58.98 57.00 54.78 2 40.47 45.19 47.10 48.55 4 32.20 40.32 45.27 43.55 6 24.84 34.32 42.39 38.79 pre-culture conditions have been studied previously [12] and found to be a factor affecting phosphorus uptake in a cyanobacterial species, microcystis aeruginosa. m. aeruginosa pre-cultured in phosphorus-poor medium (starved) was observed to have a higher phosphorus uptake rate than those pre-cultured in well supplemented medium. a similar effect might have taken place with the cultured spirulina platensis, also a cyanobacterium, originating from a phosphorus-enriched medium (kosaric). the setback in spirulina platensis’ phosphorus removal in comparison with its counterparts was potentially attributable to its phosphorus-rich medium of origin, which might have reduced its phosphorus-uptake capacity [13]. 3.2 bod5 microalgae used were all photoautotrophic which did not require for organic carbon sources; hence oxygen demand calculated would correlate more with algal respiration [14] where the greater the oxygen uptake, the more likely for the strain to have grown substantially in the medium. s. platensis container was observed to have the highest bod5 among the three strains, followed by chlorella vulgaris and scenedesmus quadricauda. spirulina platensis was thus roughly evaluated as the best-growing in the mws medium compared to the other two. this is particularly interesting as spirulina platensis is not known to be as common in waste water environments as chlorella spp. and scenedesmus spp. another interesting study observed that spirulina platensis requires alkaline (ph 9) environments [14] yet the ph of the mws used as substrate ranged from 5.9 to 6.2. this slightly acidic ph of the mws did not seem to affect its growth as much, as seen from the better performance shown in nitrate removal and greater oxygen demand in respiration. 4. conclusion as the observations showed that spirulina platensis showed better efficiency than those of others in nitrate removal and overall growth, while chlorella vulgaris dominated in phosphorus removal. spirulina platensis’ exceptional performance in nitrate uptake was most likely contributed by the shared function of the aggregated cells and more robust growth. a delicate interaction of roles between cell die-offs and nitrate generation through chemical oxidation was suggested as the cause behind the slower nitrate removal by chlorella vulgaris and scenedesmus quadricauda. these findings have certainly shed light on the differences in value of employing different algal species in wastewater treatment. spirulina platensis and chlorella vulgaris have certainly proven to be leading species in iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jalal et al. 132 basic nutrient treatment of wastewater, and the health, environmental and commercial benefits cannot simply be ignored. furthermore these microalgae could be instrumental for the conversion of ‘waste to wealth’ in our environment. references [1] m. j. hill,. “nitrates and nitrites in food and water”. woodhead publishing.jennett, j. c., hassett, j. m. & smith, j. e. (1980). the use of algae to control heavy metals in the environment. environmental geochemistry and health. vol.2 (1):26-31, 1991. [2] m. h. ward, t. m. dekok, p. levallois, j. brender, g. gulis, b. t. nolan, and j. vanderslice,. “workgroup report: drinking-water nitrate and health-recent findings and research needs”. environmental health perspectives. vol. 113 (11): 1607-14. 2005. [3] us epa,. “onsite wastewater treatment systems manual”. 2002. office of water, office of research and development: u.s. environmental protection agency. [4] p. chevalier, d. proulx, p. lessard, w. f. vincent, and j. de la noue,. “nitrogen and phosphorus removal by high latitude mat-forming cyanobacteria for potential use in tertiary wastewater treatment”. journal of applied phycology. vol.12: 105-112, 2000. [5] n. f. y., tam., and wong, y.s. “feasibility of using chlorella pyrenoidosa in the removal of inorganic nutrients from primary settled sewage”. in s.m. phang, y.k. lee, m.a. borowitzka & b.a. whitton (eds.) algal biotechnology in asia-pacific region (pp. 291– 99). 1994. university of malaya: kuala lumpur. [6] phang, s. m. and chu, w. l. catalogue of strains. university of malaya algae culture collection: kuala lumpur. 1999. [7] a. d., eaton, l. s. clesceri, e. w. rice, and a. e. greenberg, and m. h. franson,. “standard methods for the examination of water & wastewater”., 2005. centennial edition. apha/awwa/wef. [8] l. e. bashan, j. p. hernandez, and y. bashan,. “microalgae growth-promoting bacteria as “helpers” for microalgae: a novel approach for removing ammonium and phosphorus from municipal wastewater. first international meeting on microbial phosphate solubilization. 2003. [9] hach,.“dr/2400 spectrophotometer procedure manual”. 2004. hach company:usa. [10] l. lishman., “the influence of substrate and temperature on biological nitrogen removal in wastewater treatment systems”. 1997. university of waterloo: canada. [11] i. m. rafiqul, k.c.a. jalal and m.z. alam., environmental factors for optimization of spirulina biomass in laboratory culture. biotechnology. vol. 4 (1): 19-22. 2005. [12] m. okada, r. sudo, and s. aiba., “phosphorus uptake and growth of blue-green alga, microcystis aeruginosa. biotechnology & bioengineering. vol.24 (1): 143-52. 2004. [13] m. a. aziz and w. j. ng,. “optimizing algal growth in treating wastewater effluents by activated algae-reactor”. in s.m. phang, y.k. lee, m.a. borowitzka & b.a. whitton (eds.) algal biotechnology in asia-pacific region. pp. 285–90. 1994. university of malaya: kuala lumpur. [14] i. s. m. rafiqul,. “growth and biochemical composition of spirulina platensis & s. fusiformis under different culture conditions”. 2004. phd thesis. kolej universiti sains & teknologi malaysia. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 bolad et al. 213 color recognition wearable device using machine learning for visualy impaired person tarek mohamed bolad , nik nur wahidah nik hashim* and noor hazrin hany mohamad hanif department of mechatronics engineering, kulliyyah of engineering, international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia. * corresponding author: niknurwahidah@iium.edu.my (received:6th june 2018; accepted: 13th oct 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.945 abstract: recognizing colors is a concerning problem for the visually impaired person. the aim of this paper is to convert colors to sound and vibration in order to allow fully/partially blind people to have a ‘feeling’ or better understanding of the different colors around them. the idea is to develop a device that can produce vibration for colors. the user can also hear the name of the color along with ‘feeling’ the vibration. two algorithms were used to distinguish between colors; rgb to hsv color conversion in comparison with neural network and decision tree based machine learning algorithms. raspberry pi 3 with open source computer vision (opencv) software handles the image processing. the results for rgb to hsv color conversion algorithm were performed with 3 different colors (red, blue, and green). in addition, neural network and decision tree algorithms were trained and tested with eight colors (red, green, blue, orange, yellow, purple, white, and black) for the conversion to sound and vibration. neural network and decision tree algorithms achieved higher accuracy and efficiency for the majority of tested colors as compared to the rgb to hsv. abstrak: membezakan antara warna adalah masalah yang merunsingkan terutamanya kepada mereka yang buta, separa buta atau buta warna. tujuan kertas penyelidikan ini adalah untuk membentangkan kaedah menukar warna kepada bunyi dan getaran bagi membolehkan individu yang buta, separa buta atau buta warna untuk mendapat ‘perasaan’ atau pemahaman yang lebih baik tentang warna-warna yang berbeza disekeliling mereka. idea yang dicadangkan adalah dengan membuat sebuah alat yang dapat menghasilkan getaran bagi setiap warna yang berbeza. disamping itu, pengguna juga dapat mendengar nama warna tersebut. algoritma yang digunakan untuk membezakan antara warna adalah penukaran warna rgb kepada hsv yang dibandingkan dengan rangkaian neural dan algoritma pembelajaran mesin berasaskan pokok keputusan. raspberry pi 3 bersaiz kad kredit dengan perisian open source computer vision (opencv) mengendalikan pemprosesan imej. hasil algoritma penukaran warna rgb kepada hsv telah dilakukan dengan tiga warna yang berbeza (merah, biru, dan hijau). tambahan pula, hasil rangkaian neural dan algoritma berasaskan pokok keputusan telah dilakukan dengan lapan warna (merah, hijau, biru, oren, kuning, ungu, putih, dan hitam) dengan penukaran warna tersebut kepada bunyi dan getaran. selain itu, hasil rangkaian neural dan algoritma berasaskan pokok keputusan mencapai hasil dapatan yang baik dengan ketepatan dan kecekapan yang tinggi bagi kebanyakan warna yang diuji berbanding rgb kepada hsv. keywords: colors; neural network; image processing; vibration; sound. iium engineering journal, vol. 19, no. 2, 2018 bolad et al. 214 1. introduction people with color blindness do not have the ability to distinguish between certain colors. in life, color blindness has variant negative impacts on the growth of individual patients. there are two types of color blindness, namely partial color blindness, in which the person could not distinguish certain colors, and full color blindness, where only white, grey, and black could be seen. according to the statistics, about 1 in 12 men (8%) and 1 in 200 women (0.5%) suffer from color blindness in the world. the most common form is red-green color blindness which affects men more than women [1]. distinguishing between colors has been a serious problem faced by blind and color blind people. problems can emerge in performing daily routine activities such as choosing and preparing food, gardening, driving a car, and selecting clothes. in addition, they are often limited in their ability to interact socially and have difficulty finding suitable employment as well. converting colors to sound and vibration is the proposed method to combat this problem. when we look at certain colors, they can impact our emotions. for example, the color red is usually associated with aggression, orange is seen as energetic, yellow is associated with happiness, and green with nature or natural elements. the proposed system will allow a user to feel different vibrations to represent these emotions and hear the name of the color through speakers/earphones. 2. previous work there is an extensive literature on color recognition, but only a few works on converting colors to sound or vibration. rashid et al. [2] proposed a wearable device that is able to identify colors and convert them to sound by speaking out the name of the color in two languages via wire or bluetooth headphone. the device was developed using an arduino nano microcontroller. as reported by cavaco et al. [3], color and light information could be converted into sound using a special software tool, sonarx that works in real time. this tool converts digital images into sound by mapping the hsv parameters of these image pixels into audio parameters. palsokar [4] suggested a system that provides color perception based on rgb-hsl of the captured color image through auditory substitution. rgb color in the audio signal color model is mapped to hsl. manaf and sari [5] designed and implemented a color-blind aid system. they developed finger interaction between the user and colored objects with a sound augmented reality concept. this work used two platforms: a windows embedded standard 2009 (wes2009) and a system based on windows phone 7. rini and thilagavathi [6] proposed a system that can recognize cloth patterns and colors by using a support vector machine (svm) algorithm. identifying the color can be done using a normalized histogram of each image in the hsi color model. the features that were obtained from the image were extracted using three descriptors: radon signature and wavelet sub-bands. there were training and testing for a dataset of 627 images of four different clothing pattern designs. trifanica, butean, moldoveanu and butean [7] demonstrated that colors could be perceived into vibration with the use of an xbox gamepad. iium engineering journal, vol. 19, no. 2, 2018 bolad et al. 215 3. methodology 3.1 rgb to hsv color conversion algorithm rgb and hsv are types of color space that describe how colors can be represented as tuples of numbers, normally as three values. for instance, rgb can be considered as the x, y, and z axes. rgb is a combination of red, green, and blue added together in many ways to reproduce array of colors that range from 0 to 255. hsv is cylindrical-coordinate representations of points in the rgb color space. it stands for hue, saturation and value. the difference between them is that hue represents color, which has an angle from 0 degrees to 360 degrees, saturation indicates the range of grey in the color space with range from 0 to 100% and value is the brightness of the color and varies with color saturation with a range from 0 to 100% too. the conversion was done using an image processing technique with pythontm programming language and opencv library. three colors were chosen in this algorithm: red, blue, and green. the first stage was identifying the range of each color. the rgb of red color is (255, 0, 0), blue color (0, 0, 255), and green color (0, 255, 0). the second stage was taking the maximum, m, of the three rgb values of each color, which are defined as: 𝑀𝑟 = 𝑚𝑎𝑥(𝑅, 𝐺, 𝐵) (1) 𝑀𝑏 = 𝑚𝑎𝑥(𝑅, 𝐺, 𝐵) (2) 𝑀𝑔 = 𝑚𝑎𝑥(𝑅, 𝐺, 𝐵) (3) the third stage was taking the minimum, m of the three rgb values of each color as follows: 𝑚𝑟 = 𝑚𝑖𝑛(𝑅, 𝐺, 𝐵) (4) 𝑚𝑏 = 𝑚𝑖𝑛(𝑅, 𝐺, 𝐵) (5) 𝑚𝑔 = 𝑚𝑖𝑛(𝑅, 𝐺, 𝐵) (6) finally, calculating the hsv values: v = m/255 (7) s = 1m/m if m > 0 (8) s = 0 if m = 0 (9) 𝐻 = 𝐶𝑜𝑠−1 { 1 2 [(𝑅 − 𝐺) + (𝑅 − 𝐵)] √(𝑅 − 𝐺)2 + (𝑅 − 𝐵)(𝐺 − 𝐵) } (10) where v, s, and h are value, saturation, and hue respectively. 3.2 artificial neural network based machine learning iium engineering journal, vol. 19, no. 2, 2018 bolad et al. 216 an artificial neural network is an information processing model that is inspired by the way biological neural networks function in the human brain. in this paper, multilayer perceptron (mlp) is used to train the dataset. mlp, also called feedforward neural network, consisted of more than one perceptron. they are composed of input layers (the dataset) that contain more than 1700 frames to receive the signal, an output layer that makes a decision or prediction about the inputs, and two hidden layers are between those two layers. mlp trains the input-output pairs and learns to model the correlation between those inputs and outputs. mlp is trained on the dataset that contains eight colors: red, blue, green, yellow, orange, purple, white, and black, depending on their rgb values. the purpose of neural network training is to minimize the output errors on a particular set of training data by adjusting the network weights, w. in this algorithm, opencv, tensorflow and scikit-learn libraries are used for training. figure 1 shows the neural network diagram. fig. 1: neural network diagram. 3.3 data preparation data preparation is essential for any training to ensure the dataset gives high performance and accuracy. reshaping the images was the first step in the preprocessing stage which adjusts the images height and width. each image contains three layers where each layer has the height of 64 pixels and width of 36 pixels. the total pixels for an image is 2304 pixels for one layer and 6912 pixels for the three layers of the image. the final step was to organize each image depending on the number of channels. typically there are three channels of data corresponding to the colors red, green, and blue (rgb). the pixel levels are usually [0,255]. 3.4 decision tree algorithm based machine learning the function of the decision tree is to create a training model that predicts the class or value of the target variables by learning decision rules inferred from the training dataset. the decision tree algorithm can be used for solving regression and classification problems. classification is used to classify rgb values for each frame of the dataset for the eight colors. 3.5 speech synthesizer pyttsx (pythontm text-to-speech x-platform) library in opencv is used to convert text to speech synthesizers. it uses different speech engines based on operating system. in this paper, ‘espeak’ engine is used to generate the speech, as it supports many languages. english language has been used in this paper to hear the color's name. 3.6 vibration iium engineering journal, vol. 19, no. 2, 2018 bolad et al. 217 the vibration actuator used in this system in a linear resonant actuator (lra) motor. this is the same vibration actuator that is used inside mobile phones. this lra is coupled with an ultrasonic sensor and will vibrate when it detects an object within a 5 cm distance and identifies its color. 4. system design in this paper, five main components are used in order to run the system. the components are a raspberry pi3 single board computer, a raspberry pi camera module with 5mp resolution, an ultrasonic sensor, an lra vibration motor, and earphones. the design of this system was divided into three parts. the first part is a hand index box that contains the raspberry pi camera, ultrasonic sensor, and a push button. the second box is attached to a stretching strap to which the vibration actuator is attached. the third part is the hand wrist box that includes the raspberry pi3 and a small breadboard. these parts are designed to be worn on the right hand. the prototype is shown in fig. 2. fig. 2: final prototype. figure 3 illustrates the block diagram describing the general system design. the ultrasonic sensor and the camera are the inputs of the system. the outputs are sound and vibration. the relationship between the inputs and the outputs is the image processing, which was done using the raspberry pi3. fig. 3: system block diagram. 5. results 5.1 rbg to hsv color detection a webcam camera was used in the beginning to detect just three colors: red, green, and blue. the image is converted to the rgb color space and then the equations of iium engineering journal, vol. 19, no. 2, 2018 bolad et al. 218 rgb to hsv conversion are applied to the image to identify the color. the experiment was done by using three different objects which are blue note, red bag, and green jacket. the system was able to identify the color of each object. the detection of the camera was from a distance of approximately 2 to 4 cm for each object. figure 4 shows the result of blue object with the hsv components. fig. 4: example of blue object detection using rgb to hsv. (a) hsv image, (b) hue, (c) saturation and (d) value. fifteen different objects with different materials and colors were tested at different conditions. each color was represented by five objects. the first group of five objects was tested in the indoor condition, the second group of five objects was tested outdoors, and the last group was tested beside an open window. distance was measured from 2 to 3 cm for each object. the result of color accuracy is shown in table 1. table 1: result of color accuracy using rgb to hsv color (% accuracy) conditions indoor outdoor beside open window red 20 60 60 green 100 60 60 blue 100 100 100 the intensity of light affected the detection of colored objects, especially the red colored objects. the accuracies of the five red objects for indoor, outdoor and window with distance of 2 cm were the lowest among the other colors, which were 20%, 60%, and 60% respectively. green and blue objects obtained high results as compared to the red color. it can be seen from the table that green produced the highest result within the indoor area but for outdoor area and area besides the open window produced 60% correct detection. ultimately, blue had the best results for all conditions with an accuracy of 100%. 5.2 machine learning color detection after using the neural network and decision tree algorithms to train the dataset, which included more than 1700 frames, the training was done by clustering each region of each frame based on rgb values for the eight colors. the experiment was conducted using a raspberry pi camera to classify the colors of 40 different objects in iium engineering journal, vol. 19, no. 2, 2018 bolad et al. 219 three different conditions as well. each color was tested on five different objects. figure 5 shows the accuracy of each color in three different areas. it is clear that most of the colors had good accuracy based on the neural network and decision tree algorithms. white and purple colors had low accuracy, particularly the white color, which was affected by the light. the accuracy was calculated as each object has 20% if it is the true color and 0% if it is the wrong color. inside and outside the room were the best areas for color recognition. however, for areas inside the room, beside the window and outside the room, the accuracy of the white color are 20%, 0%, and 0% respectively, which is considered the lowest accuracy among other colors. on the other hand, black color obtained 100% accuracy for all three areas, while green obtained 100% detection for area inside the room and 80% correct detection for the remaining two areas. to sum up, the objects with black and green colors are considered the best objects with the highest accuracy as compared to white and purple colors. fig. 5: histogram bin of color accuracy using machine learning algorithm. it is clear that most of the colors had good accuracy based on the neural network and decision tree algorithms. white and purple colors had low accuracy, particularly the white color, which was affected by the light. the accuracy was calculated as each object has 20% if it is the true color and 0% if it is the wrong color. inside and outside the room were the best areas for color recognition. however, for areas inside the room, beside the window and outside the room, the accuracy of the white color are 20%, 0%, and 0% respectively, which is considered the lowest accuracy among other colors. on the other hand, black color obtained 100% accuracy for all three areas, while green obtained 100% detection for area inside the room and 80% correct detection for the remaining two areas. to sum up, the objects with black and green colors are considered the best objects with the highest accuracy as compared to white and purple colors. 5.3 system setup and integration the last part of the experiment was connecting the rpi camera, earphones, ultrasonic sensor, and the vibration actuator to the rpi3 as follows. firstly, the camera was turned on. secondly, the ultrasonic, vibration, and the sound system were toggled on by the switch. from a user-experience, it can be very helpful to give additional feedback, such as a sound or vibration, to notify the user. if the measured distance is less than 5 cm, the pwm signal was set to 30 (for all 8 colors). however, if the distance is out of the range, the pwm signal iium engineering journal, vol. 19, no. 2, 2018 bolad et al. 220 was set to zero. the result of the sound and vibration were accurate based on the colors that were detected by the camera. the speech sound uses english language. figure 6 shows the steps and the overall system diagram. fig. 6: system setup. 6. conclusion hearing colors and ‘feeling’ emotions is the best way to permit color blind and blind people to distinguish between colors. nonetheless, the most important problem that was faced in this project is the lighting surrounding the objects that significantly affected the camera during the detection of the colors. the results shown above are divided into two sections: rgb to hsv color conversion algorithm and neural network with decision tree algorithms. the neural network and decision tree algorithms have shown good performance and high accuracy as compared with rgb to hsv color conversion in recognizing colors. in addition, the sound system and vibrations were verified on the system and the results were shown to be reliable and efficient. acknowledgement this work is supported by the iium research initiative grant scheme (rigs16-071-0235). references [1] ohkubo t, kobayashi k. (2008). a color compensation vision system for color-blind people. proceedings of the sice annual conference, 1286–1289. https://doi.org/10.1109/sice.2008.4654855 [2] rashid h, al-mamun asmr, sijanur m, robin r, ahasan m, reza smt. (2016). bilingual wearable assistive technology for visually impaired persons. https://doi.org/10.1109/meditec.2016.7835386 [3] cavaco s, mengucci m, henriquesh t, correia n, medeiros f. (2013). from pixels to pitches : unveiling the world of color for the blind. https://doi.org/10.1109/segah.2013.6665305 [4] palsokar a. (2016). a rgb-hsi conversion based model to map the colour perception into audio equivalent to assist visually impaired persons. https://doi.org/10.1109/iacc.2016.96 [5] manaf a, sari r. (2011). color recognition system with augmented reality concept and finger interaction. https://doi.org/10.1109/ictke.2012.6152389 [6] rini jj, thilagavati b. (2015). recognizing clothes patterns and colours for blind people using neural network, 1–5. https://doi.org/10.1109/iciiecs.2015.7193006 [7] trifanica a, butean a, moldoveanu a, butean d. (2015). gamepad vibration methods to help blind people perceive colors, 37–40. retrieved from https://www.researchgate.net/publication/283070958 microsoft word 135-pra iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 11 e-waste: ethical implications for education and research muaz hawari 1 and mohamed h. hassan 2 1 graduate student, electrical and computer engineering department, faculty of engineering, international islamic university malaysia 2 alexandria university, egypt, currently on leave at king abdulaziz university, jeddah, saudi arabia **this work was performed when the second author was on leave, faculty of engineering, international islamic university-malaysia mhmheg@yahoo.com abstract: “e-waste” is a popular, informal name for electronic products nearing the end of their “useful life”. this includes discarded computers, televisions, vcrs, stereos, copiers, fax machines, electric lamps, cell phones, audio equipment and batteries. ewastes are considered dangerous, as certain components of some of these electronic products contain materials; such as lead; that are hazardous, depending on their condition and density. if improperly disposed, e-wastes can leach lead and other substances into soil and groundwater posing a threat to human health and environment. many of these electronic products can be reused, refurbished, or recycled in an environmentally sound manner so that they are less harmful to the ecosystem. this paper highlights the types and hazards of e-wastes particularly the computers’ waste. the dimensions and ethicality of the problem in the third-world countries are reviewed. the needs for the appropriate management of e-waste and options that can be implemented are discussed. after reviewing the islamic concepts for environmental protection, ethical implications for curriculum development as well research directions are highlighted. elements for a course on e-waste as well as some across-the-curriculum topics are proposed. this is specially tailored to suit the faculty of engineering at the international islamic university-malaysia. keywords: e-waste, environment, ethics and education 1. introduction the life span of computers used to be decades, then years, and now often months. millions of computers, screens, and peripherals are being rendered obsolete after little more than a year of active use. just a small percentage of these are reaching the solid waste stream. most are stored in attics, garages, and warehouses because their owners are unwilling to throw away something they perceive to have so much value. most consumers are unaware of the toxic materials in the products they rely on for word processing, data management, and access to the internet, as well as for electronic games. in general, iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 12 computer equipment is a complicated assembly of more than 1,000 materials, many of which are highly toxic, such as chlorinated and brominated substances, toxic gases, toxic metals, biologically active materials, acids, plastics and plastic additives [1]. there are two root computer and electronic waste (hereafter, e-waste) problems: (1) the volume of computers and related e-waste improperly disposed of in landfills and (2) the toxicity of both the computer chip manufacturing process and the computer or cathode ray tube monitor (crt) itself as a waste product. e-waste contains significant quantities of toxic materials [1]. each computer or television display monitor contains an average of 4-8 pounds of lead. monitor glass contains about 20% lead by weight. about 70% of the heavy metals (including mercury and cadmium) found in landfills come from electronic equipment discards. these heavy metals and other hazardous substances found in electronics can contaminate groundwater and pose other environmental and public health risks. three methods of disposal are currently applied [2]: (1) incineration which generate and disperse contaminants and toxic substances, (2) open burning which releases many pollutants into environment, and (3) landfill where lead and mercury cause severe contamination in landfills besides these contaminations can spread to ground water resources. it is thus apparent that the environmental and health impacts are of serious concern. while computer waste is relatively valuable when delivered to a recycler, the high cost of transportation and handling generally makes it uneconomical. there is insufficient infrastructure to support increased recycling of crt/computer waste and few economic incentives to create one. what adds to the problem is that most developing nations lack awareness of the dangers posed by e-waste, as well as any e-waste collection and recycling or disposal systems or programs. 2. dimension of the problem the fundamental dynamism of computer manufacturing that has transformed life since the second half of the 20 th century, leads to rapid product obsolescence. the average computer platform has a lifespan of less than two years, and hardware and software companies, especially intel and microsoft, constantly generate new programs that fuel the demand for more speed, memory and power. today, it is frequently cheaper and more convenient to buy a new machine to accommodate the newer generations of technology than it is to upgrade the old. the dimension of this issue can be seen in the developing countries and the developed ones as explained below. interested reader may refer to references [2] and [3] for more data on e-waste problems in various countries. 2.1 developed countries three quarters of all computers ever bought in the u.s. are sitting in people’s attics and basements because they don’t know what to do with them. just to give an estimation of iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 13 the size of this issue, we will consider the following numbers in the u.s. as an example [4]. americans are buying more computers than people in any other nation. currently over 50% of u.s. households own a computer [4]. because of advances in chip technology, the life span of a computer has been reduced from perhaps 4-5 years to approaching 2 years or less. computer junking is also happening at a faster rate. the lifespan of computers is decreasing. in 1997 the average lifespan of a computer tower was 4-6 years and computer monitors 6-7 years. this has fallen to 2 years in 2005 [1, 5]. for the three years between 1997 and 1999, it is estimated that some 50 million u.s. computer towers had been dumped, burned, shipped abroad or stored to await eventual disposal [1]. a recent us study found that over 315 million computers became obsolete by the year 2004 [5]. recycling of computer monitors is no better. over 300 million computer monitors have been sold in the u.s. since 1980. yet, in 1997 only about 1.7 million monitors in the us were "recycled," the majority of which about 1 million monitors was shipped abroad to countries such as china or india. e-waste represents from two to five percent of the u.s. municipal solid waste stream. an estimated 300,000 tons of e-waste ended up in the u.s. landfills in 2000, and the problem is expected to grow four-fold in the near future. in 1998 only 6 percent of older computers were recycled compared to the numbers of new computers put on the market that year. in contrast, for major appliances such as washing machines, air conditioners, refrigerators, dryers, dishwashers and freezers, the proportion recycled in 1998 was about 70% of the number put on the market that year [5]. of the small number of computers that are recycled, more than three-quarters come from large-scale users of the equipment. individual users and small businesses contribute only a small fraction of the equipment that is recycled because no collection or recycling program is in place [5]. currently the cheapest e-waste recycling option in the u.s. is to send e-waste overseas. however, how it is used or disposed of there is largely unknown [5]. the district of guiyu in china, for example, has become an electronic trash junkyard, with pcs and peripherals forming mountains and overflowing into streets; with its people making a living stripping away pc parts with their bare hands. in the mean time, in the u.s., second hand dealers (thrift shops, salvation army, goodwill) and waste haulers or those in the recycling business are unsure about how to handle equipment they are receiving and what disposal options are legally available to them. additionally, with no certainty about market volume, infrastructure investment is risky. 2.2 developing countries in the developing countries, the dimension of the issue is not as drastic as it is in the developed countries. for example, malaysia has been putting a lot of effort to eradicate this problem before it gets persistent and out of control. the "recycle pc" campaign, spearheaded by the association of the computer and multimedia industry of malaysia (pikom) and waste management company alam flora sdn bhd [6], is picking up steam since its launch in march 2005. this campaign aims to create environmental awareness by encouraging the public and organizations to recycle pcs and their peripherals. between the period of march 10 and april 30, 2005, alam flora has collected 816 computers and peripherals. this includes 194 computer monitors, 147 central processing units (cpus) 428 printers, and 47 miscellaneous pc components [7]. iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 14 panasonic malaysia sdn bhd was among the first corporations to answer the call to recycle when it handed over 60 used pcs and laptops to alam flora within a week from launching the pc recycling campaign [6]. the japanese technology giant also pledged to donate more pcs to the recycle pc campaign each time it embarks on a pc upgrading exercise. alam flora has assigned collection points and recycling centers all over the country for people to drop off their old pcs to be recycled. in india however, the problem is worse. the developed countries use india as a drop point to dumb their e-waste in. india has no pc recycling program or at least not a wellknown one. almost 50% of the pcs sold in india are products from the secondary market and are re-assembled on old components. the remaining market share is covered by multinational manufacturers (30%) and indian brands (22%). pcs manufacturers are major contributors of e-waste. the waste consists of defective ic chips, motherboards, monitors and other peripheral items produced during the production process. waste also includes defective pcs under guarantee procured from consumers as replacement items [8]. it is worth mentioning that in india, the import of e-waste is legally prohibited. nevertheless, there are reports of e-waste imports from abroad. analyses by the ministry of environment showed no results concerning import of e-waste, but the ministry admits that a 100% control of the borders is not possible [8]. what complicates the problem is that computer waste, which does not have any resale or reuse value, is openly burnt or disposed off in landfills. in africa, nigeria is undergoing rapid and massive growth in cell phone and computer technology. the city of lagos in nigeria is believed to be representative of developments rapidly taking place in other port cities of africa. while no official figures exist, it is apparent that a very significant portion of this growth is fueled by the importation of second-hand equipment from rich developed countries. experts stated that 500 containers of used computers come into the port of lagos each month imported primarily from europe and north america [9]. many of the exporters were identified by institutional asset tags left on the equipment. additionally, private data from exported hard drive memory systems were extracted, raising questions about a new form of irresponsibility which is the privacy of information. while some of the imported material to lagos is fully functional and is directly re-used, or can be repaired, there is nevertheless a significant quantity of the imported computer equipment or parts, estimated by local experts to be between 25-75% that is considered junk. it is unmarketable due to either its lack of computing effectiveness, or due to the fact that it is un-economic to repair. local experts complain that of the estimated 500 40-foot containers shipped to lagos each month, as much as 75% of the imports are “junk” and are not economically repairable or marketable. consequently, this e-waste is being discarded and routinely burned in what the environmentalists call yet “another” cyber-age nightmare now landing on the shores of developing countries” [9]. because most of the exports/imports are not pre-tested for functionality, it is not possible to know whether these exports are legally defined as hazardous waste (i.e. requiring disposal whole or in part, and being hazardous) under the basel convention. from a regulatory standpoint, diligent enforcement discretion would demand testing be performed prior to allowing export. the basel convention is an international treaty that sets up controls, enforcement mechanisms, and requirements that signatories agree to follow, including preventing and monitoring illegal traffic in hazardous waste, promoting iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 15 cleaner technologies and production, and focusing specifically on helping developing nations [10]. 3. technical aspects and side effects of dumping ewaste to have an idea about the materials involved in the e-waste, the following table shows composition of a typical desktop pc weighing ~ 60 lbs [11]: name content (% of total weight) weight of material in computer (lbs.) use/contents plastics 22.9907 13.8 includes organics, oxides other than silica lead 6.2988 3.8 metal joining, radiation shield/crt, pwb aluminum 14.1723 8.5 structural, conductivity/housing, crt, pwb, connectors germanium 0.0016 < 0.1 semiconductor/pwb gallium 0.0013 < 0.1 semiconductor/pwb iron 20.4712 12.3 structural, magnetivity/(steel) housing, crt, pwb tin 1.0078 0.6 metal joining/pwb, crt copper 6.9287 4.2 conductivity/crt, pwb, connectors barium 0.0315 < 0.1 in vacuum tube/crt nickel 0.8503 0.51 structural, magnetivity/(steel) housing, crt, pwb zinc 2.2046 1.32 battery, phosphor emitter/pwb, crt tantalum 0.0157 < 0.1 capacitors/pwb, power supply indium 0.0016 < 0.1 transistor, rectifiers/pwb vanadium 0.0002 < 0.1 red phosphor emitter/crt beryllium 0.0157 < 0.1 thermal conductivity/pwb, connectors gold 0.0016 < 0.1 connectivity, conductivity/pwb, connectors iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 16 europium 0.0002 < 0.1 phosphor activator/pwb titanium 0.0157 < 0.1 pigment, alloying agent/(aluminum) housing ruthenium 0.0016 < 0.1 resistive circuit/pwb cobalt 0.0157 < 0.1 structural, magnetivity/(steel) housing, crt, pwb palladium 0.0003 < 0.1 connectivity, conductivity/pwb, connectors manganese 0.0315 < 0.1 structural, magnetivity/(steel) housing, crt, pwb silver 0.0189 < 0.1 conductivity/pwb, connectors antinomy 0.0094 < 0.1 diodes/housing, pwb, crt bismuth 0.0063 < 0.1 wetting agent in thick film/pwb chromium 0.0063 < 0.1 decorative, hardener/(steel) housing cadmium 0.0094 < 0.1 battery, glu-green phosphor emitter/housing, pwb, crt selenium 0.0016 0.00096 rectifiers/pwb niobium 0.0002 < 0.1 welding allow/housing yttrium 0.0002 < 0.1 red phosphor emitter/crt mercury 0.0022 < 0.1 batteries, switches/housing, pwb arsenic 0.0013 < 0.1 doping agents in transistors/pwb silica 24.8803 15 glass, solid state devices/crt,pwb 3.1 risks related to some toxic substances in pcs the following is a more detailed description of the hazards of e-waste based on the different material involved [11]. lead: lead can cause damage to the central and peripheral nervous systems, blood system and kidneys in humans. effects on the endocrine system have also been observed and its serious negative effects on children’s brain development have been well documented. lead accumulates in the environment and has high acute and chronic toxic effects on plants, animals and microorganisms [12]. iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 17 cadmium: cadmium compounds are classified as toxic with a possible risk of irreversible effects on human health. cadmium and cadmium compounds accumulate in the human body, particularly in kidneys. cadmium is absorbed through respiration but is also taken up with food. mercury: when inorganic mercury spreads out in the water, it is transformed to methylated mercury in the bottom sediments. methylated mercury easily accumulates in living organisms and concentrates through the food chain particularly via fish. methylated mercury causes chronic damage to the brain. hexavalent chromium: chromium vi can easily pass through membranes of cells and is easily absorbed producing various toxic effects within the cells. it causes strong allergic reactions even in small concentrations. asthmatic bronchitis is another allergic reaction linked to chromium vi. chromium vi may also cause dna damage [12]. plastics: it is estimated that the largest volume of plastics used in electronics manufacturing (at 26%) was polyvinyl chloride (pvc), which creates more environmental and health hazards than most other type of plastic. pvc is a difficult plastic to recycle and it contaminates other plastics in the recycling process. of more importance, however, the production and burning of pvc products generates dioxins and furans. brominated flame retardants: brominated flame-retardants are a class of brominated chemicals commonly used in electronic products as a means for reducing flammability. in computers, they are used mainly in four applications: in printed circuit boards, in components such as connectors, in plastic covers and in cables. they are also used in plastic covers of tv sets and in domestic kitchen appliances. various scientific observations indicate that polybrominated diphenylethers (pbde) might act as endocrine disrupters. research has revealed that levels of pbdes in human breast milk are doubling every five years and this has prompted concern because of the effect of these chemicals in young animals [13]. researchers in the us found exposure to polybrominated biphenyls (pbbs) may cause an increased risk of cancer of the digestive and lymph systems [14]. the presence of polybrominated flame-retardants in plastic makes recycling dangerous and difficult [15]. 4. islamic aspects of environmental protection islam is considered a comprehensive way of life whose teachings cover, directly or indirectly, every possible human relationship including that with the environment. these iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 18 teachings are primarily available in the revealed knowledge which comprises the qur’an and prophet muhammad’s tradition (sunnah). islam emphasizes strongly on preserving the environment. basically, the relationship between human beings and the environment is of three categories [16]: vicegerency: the human being in the islamic world-view is considered a vicegerent. in her/his capacity as a vicegerent, the human being is perceived as the trustee of the earth. she/he is not supposed to cause corruption in any form on earth (i.e. the environment). life on earth entails great responsibilities. it is a test with accountability. it is followed by either reward or punishment. subjection: the earth is made available for human use, without abuse or misuse. the circle of things available for the benefit of humanity is much greater than that of the environment. inhabitation: the qur’an, moreover, makes it clear that the earth is our habitat and that we are required to dwell on it, work it out and establish a balanced way of life without excesses or deficiencies. the meaning of inhabitation (i’mar) includes spreading and settling all over the earth, inhabiting every livable quarters, building …etc. in short, it includes every positive activity that would make life on earth prosperous. if an activity diverts humanity from the right path (i.e. against the shari`ah), then it cannot be considered as i`mar. the i`mar of the earth should be in areas and projects that could benefit humanity and not harm it. this means that projects and activities that destroy the environment are excluded. protecting the environment: it should be known that islam advocates the protection of the environment, though not in name, for the word ‘environment’ (bi’ah), along with its connotations, evolved in recent times [16]. the fact that to protect the environment is considered an act of worship does not mean that every component of the environment should be saved. in fact, it is sometimes to the contrary. the prophet, peace and blessings be upon him, stated that a person who uprooted a tree [which formed an obstacle] in the path of people, ended up in heavens. the islamic position forms a middle path between human behavior that has disregard to the environment and those who practically worship the environment. islam prohibited the cutting or destruction of trees and plants, and encouraged people to protect and increase plants for the great reward associated with that. in conclusion, protecting an environment is an essentiality in islam. the aims of the shari’ah are five: protection of religion, protection of life, protection of mind, protection of offspring, and protection of property. though protection of the environment is not included in the aims of the shari’ah, the environment encompasses all the other aims of the shari`ah. for if the situation of the environment keeps deteriorating, there will ultimately be no life, no property and no religion. the destruction of the environment prevents the human being from fulfilling the concept of vicegerency on earth. indeed, the iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 19 very existence of humanity is at stake here. excessive pollution might lead to sterility, deformities, abortion and chronic diseases. as far as protecting the mind or reason, the highly polluted industrial cities might not see the sun for long days resulting in deep depressions which affects the person’s ability to rationalize properly. certain radiation might also destroy the brain. the attempt to protect the property will also be in vain in the context of a highly polluted environment. there are already many rivers and lakes that are considered dead with no marine life. this is a direct result of acid rain which destroys also forests. it is worth mentioning that protecting the environment from an islamic point of view is one of the topics that are well established and the above analysis is not meant to be conclusive. interested reader may refer to other sources in the literature such as references [17] and [18]. 5. recommended actions in this section, some actions that can be adopted are reviewed. almost all of these actions have to be carried out simultaneously. some of them are targeted to create a wider awareness amongst the end-users. 5.1 the 3r initiative one approach to dealing with the e-waste problem is the 3r initiative which can be summarized as follows [19]: • reduce: attempt to reduce the amount of waste generated reduce/eliminate use of toxic substances like lead and mercury. • reuse: repeated use of items or parts of items which are still usable • recycle: use of waste itself as resource however, it has to be stressed that success depends on [19]: • public recognition of hazards involved in e-waste • organized collection and transportation of e-waste 5.2 binding purchasing with take-back product responsibility this is known as extended producer responsibility (epr). the aim of epr is to encourage producers to prevent pollution and reduce resource and energy use in each stage of the product life cycle through changes in product design and process technology. in its widest sense, producer responsibility is the principle that producers bear a degree of responsibility for all the environmental impacts of their products. this includes upstream impacts arising from the choice of materials and from the manufacturing process as well as the downstream impacts, i.e. from the use and disposal of products. epr focuses on the responsibility that producers are responsible for their products at the end of their useful iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 20 life (post-consumer stage). the model example of epr is product take-back where a producer takes back a product at the end of its useful life (i.e., when discarded) either directly or through a third party. other terms used are 'take-back', 'product liability' or 'life cycle product responsibility'. this has been implemented by hp companies in the u.s. [20]. hence, the producers have a great deal of responsibility to take back their products and recycle them at the end of the products’ operational lives. it puts full financial responsibility on producers to set up collection, recycling and disposal systems. 5.3 citizens' responsibility a great responsibility is placed on the citizen. the citizen has to feel responsible of whatever electronic gear that the end-user have at his or her house. the individual has to help the recycling organizations by giving them back the electronic devices after he or she is done with it. the end-user has to be aware of the dangers and risks that arise from dumping the electronic gears or storing them in their attics or backyards. the end-user should contact the local or state government representatives, explain to them why he or she is concerned and ask them to get involved in developing solutions. they could ban the land filling and incineration of electronic junk. they can help to promote computer re-use and recycling infrastructure. they can support extended producer responsibility (epr) for computer manufacturers. waste prevention is perhaps more preferred to any other waste management option including recycling. donating electronics for reuse extends the lives of valuable products and keeps them out of the waste management system for a longer time. reuse, in addition to being an environmentally preferable alternative, also benefits society. by donating used electronics, schools, non-profit organizations, and lower-income families can afford to use equipment that they otherwise could not afford. care should be taken while donating such items, i.e., the items should be in working condition. 5.4 encouraging reuse according to the basel action network (ban) [10], developing countries need help to create environmentally sound waste management systems. such efforts should not be part of continuing to stop exporting hazardous wastes to those countries, but rather as a necessity for any country that must deal with all kinds of wastes. 6. implications for curriculum development in the faculty of engineering, international islamic university malaysia (iium) in the era of globalization, certain ethical, social, and global aspects of the graduate engineer need to be enhanced [21]. this has important implications for education and research [22]. as explained before, this needs to be stressed from an islamic point of view. another motive for such ethical consideration is that accreditation by recognized bodies necessitates taking into consideration the ethical contents of the engineering programs [23]. iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 21 academic institutions have an important role in informing the students of the great environmental risks that could arise from the e-waste issue. usually, computer engineering graduates know little information (if any) about the material or chemical contents of a pc. may be it is none of their concern from a career point of view but nowadays every individual and engineer in particular has to be updated of the environmental issues arising from the various electronic devices they use daily. as such, educational institutions in muslim countries can play a role model in modifying their engineering curriculum to accommodate the e-waste problems. there are many ways for the universities to spread the awareness amongst the students and staff of this issue. workshops and seminars can be organized on a semester basis or at least annually. courses could be added to the engineering curriculum on solid waste management in general and e-waste management specifically. proposals for the faculty of engineering at the international islamic university malaysia regarding these issues are discussed below. 6.1 designing a course on e-waste a preliminary survey was done on universities syllabi for computer engineering programs. according to the authors’ knowledge, no university offers a course for computer engineering students about the materials contained within a pc and its harm as e-waste. in the faculty of engineering at international islamic university malaysia (iium), different courses could be added to the curriculum to help increase the awareness of this issue. as a start, a general course on solid waste management may be proposed. such a course could be adapted in the faculty of engineering, in different programs especially in the manufacturing and materials engineering department. for example, a course titled solid waste management and environmental health (envh 445) is taught at the university of washington (uw), in the u.s. the primary goal of this course is to provide students with a comprehensive understanding of solid waste management from an environmental/public health perspective. the learning objectives of the course aim at making the students able to: (1) identify and discuss the public health, regulatory, planning, technical, and economic principles that influence the solid waste management system within washington state, (2) describe appropriate methods to minimize the impact to the public’s health from solid waste related activities, (3) analyze the importance of an integrated solid waste handling system including source reduction, recycling and reuse, composting, land filling and combustion and (4) develop a more informed opinion on a variety of solid waste related issues. some of the topics covered are: public hazards and importance of laws and regulations, solid waste characterization and planning, source reduction/recycling in action, solid waste impact on global climate change, land filling, waste combustions, e-waste. 6.2 including e-waste topics using across-the-curriculum approach another approach is to include topics on waste management and e-wastes across the curriculum. for example, these topics may be included in the following courses: iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 22 course department mec4131 advanced materials engineering manufacturing & materials engineering bte3610 waste management and utilization biotechnology engineering since there is no such course in the electrical and computer engineering program, selected topics could be covered using seminars or workshops. another approach is to include elements of the e-waste problem in the course computer architecture and design (ece 3213). in the mean time, waste and e-waste topics may be the topics of final year projects where the students may perform literature surveys on the technical aspects of the problem or even address one of the alternative solutions as explained in the following section. during industrial training, the students may be advised to be alert to the problem and try to assess its dimensions in the different fields. finally, e-waste may be a good topic for a university outreach program undertaken by the students associations to educate the surrounding community on environmental issues. 7. implications for research and regulations e-waste processing in developing nations has only recently emerged as an important issue, thus relevant research remains scarce. the overarching issue of assessing and managing the environmental impacts of electronics, however, has a history of research and implementation, especially from the 1990’s [2]. specific areas that need science and technology inputs are [19]: • cleaner technologies such as those for waste minimization, recycling, recovery and treatment • environment friendly manufacturing processes (e.g. lead free soldering) • material flow analysis for benchmarking the performance review of industries • greening of supply chains of manufacturers of electronic components major events that have developed to service the research and implementation community are concerned with green electronics [2]. in the u.s., the flagship event is the “international symposium on electronics and the environment”, sponsored by ieee, and has been held annually since 1993. international participation in previous years was mainly from europe, but more recently presentations from japan and other asian countries have been on the increase. from 2003, a new annual event, “e-scrap”, has emerged as a new player in the field. it is more targeted towards industry and policymakers. in europe, the main event in the field is “electronics goes green”, which has been held in 2000 and 2004 in berlin. while there has been no regular event in japan focuses on electronics and iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 23 the environment specifically, the “international conference on ecobalance”, held biannually since 1994, and “international symposium on environmentally conscious design and inverse manufacturing”, held biannually since 1999, include much content related to electronics. 7.1 examining e-waste related regulations in its list of recommendations to combat illegal dumping of e-waste, the basel action network (ban) urges governments to pressure manufacturers to remove toxic chemicals from products as soon as possible. ban also calls on strict enforcement of the basel convention [10] and lauds australia for its efforts in that regard. australia requires full testing of electronic waste to certify that it complies with the basel convention before it is exported. the ban report on dumping in lagos calls the u.s. "the worst actor" among developed countries that perpetuate dumping of hazardous waste in developing nations. it is thus clear that there is a need to examine e-waste related regulations at the national level. regardless of the fact that this issue has legal background, engineers can help in identifying the technical aspects of the problem to the legal experts. 7.2 design of toxic and hazard free products many companies have shown they can design cleaner products. industry is making some progress to design cleaner products but there is a need to move beyond these projects and ensure that all products are upgradeable and non-toxic some examples of alternatives are [24]: (1) hewlett-packard company has developed a safe cleaning method for chips using carbon dioxide cleaning as a substitute for hazardous solvents. (2) printed circuit boards can be redesigned to use a different base material, which is self-extinguishing, thereby eliminating the need for flame-retardants. matsushita is accelerating efforts to eliminate toxic substances and develop more environmentally benign materials such as lead-free solder, non-halogenated lead wires and non-halogenated plastics. matsushita also developed the first lead-free solder for flow soldering applications and have recently launched, in japan, their first totally-recyclable television sets. sony corp has developed a lead-free solder alloy, which is usable in conventional soldering equipment. there is a range of lead-free solders now available. obviously, substitutes need to be proven for safety. (3) pressures to eliminate halogenated flame-retardants and design products for recycling have led to the use of metal shielding in computer housings. in 1998 ibm introduced the first computer that uses 100% recycled resin (pc/abs) in all major plastic parts for a total of 3.5 pounds of resin per product. toshiba is working on a modular upgradeable and customizable computer to cut down on the amount of product obsolescence. they are also developing a cartridge which can be rewritten without exchanging parts or modules allowing the customer to upgrade at low cost. iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 24 it is thus worth mentioning that efforts are under way to propose safe alternate materials. more funding as well as directed research is still needed along these directions. as mentioned before, this is a golden chance for research institutions in muslim countries to take the lead in relieving the environment from such problematic e-wastes. 8. conclusions while advances in technology continue to improve and enrich our lives, product lifecycles are getting shorter. this means an increasing stockpile of end-of-life equipment that needs to be managed. when discarded, much of this equipment ends up in landfills in developed countries or is exported to third world countries. electronic equipment contains harmful toxins which, when released into the environment, can contaminate water, land and air. while there are many ways to dispose of unwanted electronics, there are few guarantees that the resulting e-waste will be disposed of responsibly. this is a major issue, either in the developed countries due to the amounts generated or in developing countries due to lack of recycling systems. it is clearly unethical for the developed countries to dump their e-waste in developing ones. government control should be practiced to avoid such actions. citizens have a responsibility in spreading the awareness on this issue. engineers should be in the forefront since they master the technical background of the issue. a preliminary survey indicated that e-waste is hardly covered in engineering faculties worldwide. as such, academic institutions in muslim countries can play a role model in modifying their engineering curriculum to accommodate the e-waste problems. the islamic concepts of the need to protect the environment should be clearly spelled out in any course related to waste management in general and e-waste management specifically. e-waste management can be introduced as separate courses. related topics can be embedded in related courses, as well as as topics for final year projects. they can also be addressed during industrial training. more funding as well as directed research is still needed to find alternate materials to tackle the e-waste problems. this is a golden chance for research institutions in muslim countries to take the lead in relieving the environment from such hazards. technological issues that pose environmental threats need to be carefully examined. implications for education and research due to these technological aspects need to be done on a systematic basis especially for universities in muslim countries. references [1] environmental protection agency, “computer display industry and technology profile”, epa 744.r.98.005, december 1998. iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 25 [2] e. williams, international activities on e-waste and guidelines for future work, united nations university, in: third workshop on material cycles and waste management in asia, national institute of environmental sciences: tsukuba, japan (2005) [3] 2008 review of directive 2002/96 on waste electrical and electronic equipment (weee), united nations university, germany, august 2007 [4] http://www.crra.com/ewaste/articles/computers.html, retrieved march 2006, [5] national safety council, “electronic product recovery and recycling baseline report” washington, dc, 1999. [6] http://www.alamflora.com.my [7] z. karim, good start to pc recycling campaign, the star online, 9 june 2005. http://thestar.com.my [8] r. agarwal, rakesh ranjan and papiya sarkar, scrapping the hi-tech myth: computer waste in india, toxics link report, feb. 2003: http://www.toxicslink.org, retrieved august 2008. [9] the digital dump: exporting re-use and abuse to africa, basel action network, seattle, washington 98104 usa, 2005 [10] http://www.basel.int [11] microelectronics and computer technology corporation (mcc), electronics industry environmental roadmap. austin, tx: mcc, 1996. http://www.svtc.org. [12] lead background and national experience with reducing risk, compare risk reduction, monograph no 1, oecd paris, 1993. [13] persistent organic pollutants, swedish environmental protection agency, monitor 16, http://www.sciencedaily.com/releases/1998/08/980821085353.htm, retrieved january, 2006. available online:: http://nvv.sh.ateles.se/epages, [14] a. hoque et al, epidemiology, vol 9 (4), pp. 373-8, 1998. [15] k. brenner, formation of polybrominated dibenzofurans (pbdfs) and dioxins (pbdds) during extrusion production of a polybutylenetenerephtalate (pbtp)/glassfibre resin blended with decabromodiphenylether (pbdpe)/sb2o3; product and workplace analysais, 1986. [16] a. kutty , islam and environmental ethics, the islamic institute of toronto, canada, posted on http://www.islamonline.net, in june, 2007, retrieved august 2008. [17] m. abu-sway, towards an islamic jurisprudence of the environment, department of philosophy, al-quds university, jerusalem, posted on http://www.islamonline.net, in august, 2002 , retrieved august 2008. [18] f. de chatel, prophet mohammed: a pioneer of the environment, anthropologist of islamic culture, the netherlands, posted on http://www.islamonline.net, in february, 2003, retrieved august 2008. [19] s. banerjee, e-waste research and development issues, inae seminar on recycling for electronics and automotive, mumbai, india, september, 2007. [20] http://www.hp.com/hpinfo/newsroom/press/2002/020723a.html, retrieved january, 2006 [21] m. h. hassan, practical approach towards fulfillment of the ethical, social and global attributes of the graduate engineer, the 2005 regional conference on engineering education, johor, malaysia, december 12-13, 2005. iium engineering journal, vol. 9, no. 2, 2008 hawari and hassan 26 [22] m. h. hassan, integrating islamic concepts in the engineering curriculum. case study: faculty of engineering, iium, in: islamic engineering ethics: foundations, integration and practices, abdi shuriye et al (eds.), future text publications, selangor, malaysia, 2006. [23] w. h. abulfaraj and m. h. hassan, teaching and assessment of professional ethics in the nuclear engineering education according to the abet engineering criteria, 2007 american society of engineering education annual conference & exposition june 24-27, 2007 honolulu, usa. [24] international symposium on electronics and the environment, the institute of electrical and electronics engineers, may 11-13, danvers, 1999. microsoft word srfraz14-final-.doc iium engineering journal, vol. 1, no. 2, 2000 m. sarfraz and z. habib 1 rational cubics and conics representation: a practical approach m. sarfraz department of information & computer science, king fahd university of petroleum and minerals, kfupm # 1510, dhahran 31261, saudi arabia. sarfraz@ccse.kfupm.edu.sa z. habib national college of textile engineering, faisalabad, pakistan. zulfiqar_habib@hotmail.com abstract: a rational cubic spline, with one family of shape parameters, has been discussed with the view to its application in computer graphics. it incorporates both conic sections and parametric cubic curves as special cases. the parameters (weights), in the description of the spline curve can be used to modify the shape of the curve, locally and globally, at the knot intervals. the rational cubic spline attains parametric 2c smoothness whereas the stitching of the conic segments preserves visually reasonable smoothness at the neighboring knots. the curve scheme is interpolatory and can plot parabolic, hyperbolic, elliptic, and circular splines independently as well as bits and pieces of a rational cubic spline. key words: computer graphics, interpolation, spline, conic, rational cubic, 1. introduction piecewise rational cubic spline functions provide a powerful tool for designing of curves, surfaces and some analytic primitives such as conic sections that are widely used in engineering design and various computer graphics applications. these applications may be representing some font outline, round corner in an object, or it may be a smooth fit to a given data. several segments of curves, to compose a desired curve outline, can have different mathematical descriptions. for example, a font “s” when designed, appears to have straight lines, conics, and cubics as essential parts of its outline. single mathematical formulation for the precise definition of various types of geometry shapes is one of the major advantages of the rational cubic spline functions. this research describes the parametric 2c rational cubic spline representation possessing a family of shape control parameters. this family of shape parameters has been utilized to produce straight line segments, conics, and cubics. the features of maintaing some reasonable amount of continuity between conic and cubic arcs, estimated end derivatives, conic (circular, elliptical, parabolic, and hyperbolic) splines, and circular arcs for given radius or center, are further achievements in this research. there are many schemes in the literature for shape control using cubic interpolants. for brevity, the reader is referred to work done by various authors [1-14]. the presented curve scheme encompasses and extends the results of sarfraz et al. [10]. in sarfraz et al. [10], a 1c rational cubic spline with approximated derivatives at control points, was used but continuity between conic and cubic arcs was not discussed. intermediate point interpolation scheme and circular arcs, presented in jamaludin [7], are not practical as the space curves and exact circular arcs are not possible. in gregory et al. [4-5], end derivatives are based on the assumption of the user, which is not convenient. moreover, the conics were not discussed at all. we have estimated most suitable end derivatives for more pleasing results. in hoschek [4], rational quadratic spline is used for circular spline. we are using very simple technique using rational cubic spline for the same circular spline. in addition, the scheme has the following properties, which may lead to a more useful approach to curve and surface design in cagd:  the curve has 2c continuity between the rational cubic arcs and 1g continuity between cubic and conic arcs.  most suitable end derivatives are estimated.  the scheme is local, i.e. shape control parameters will not significantly affect the adjacent parts of the design curve.  any part of the rational cubic spline can be made conic (with exact circle and ellipse) or straight line using the same interpolant.  the method is suitable for space curves and hence can also be generalized to surfaces. the paper has been organized in such a way that a 2c parametric rational cubic spline scheme, together with determination of tangents at the knot points, is considered in section 2. analysis of the designing curve has been made in section 3. conditions for conics and straight line segments are given in section 4. the section 5 mentions about circular arcs. this section also iium engineering journal, vol. 1, no. 2, 2000 m. sarfraz and z. habib 2 covers all types of circular arcs in space. in section 6, we have presented a scheme to calculate end derivatives (tangents). for practical purposes, an algorithm has bee designed in section 7 where as the demonstration has been made in section 8. the section 9 concludes the paper. fig. 1 spline curves with various end conditions: (a) with distance based derivatives, (b)-(c) with exact derivatives. 2. the rational cubic spline let mif r , i = 0,1,...n, î be a given set of data points at the distinct knots it rî . also let m id rî , denote derivative values at the knots. define a parametric 0c piecewise rational cubic mp : r r ® as follows: ( ) ( ) ( ) ( ) , 0, 1, ...., 1, n tip t p ti m ti i nº = = (2.1) where ( ) ( ) ( ) ( ) ( )( ) 3 2 2 3 1 1 1 1 1 1 i i i i i i i n t f v w f q q q g q q g q + = + + + + + ( ) ( ) ( )2 21 1i im t q q q g q= + + , ( ) 1/ ,i i i iit t h h t tq += = . the following choice of control vertices 1 1 1 , 1 1 . 1 i i i i i i i i v f d w f d g g+ + üï= + ïï+ ïïýïï= + ïï+ ïþ (2.2) leads (2.1) to a 1c piecewise rational cubic hermite spline. the choice of parameters i > -1 g ensures a strictly positive denominator in the rational cubic. thus from bernstein bezier theory, the curve lies in the convex hull of the control points 1{ , , , }i i i if v w f + and is variation diminishing. for the construction of a 2c rational cubic spline in subsection 2.1, we need to manipulate second derivative of (2.1), which is as follows: ( ) ( )2ip t = ( ) ( ) ( ){ } ( ) ( ){ } 2 33 2 3 2 1 1 1 1 2 1 i i i i i i a b c e h q q q q q q g q q + + + + (2.3) where ( )( ) ( ) ( ) ( )( ) 1 1 1 1 1 , 3 , 3 , 1 , i i i ii i i ii i i i i i i i ii a d d d b d c d e d d d g g + + + + ü= + d + ïïïïï= d ïïïýï= d ïïïï= + d + ïïïþ (2.4) and ( )1 / .i i iif f h+d = (2.5) 2.1. estimation of tangent vectors there are different choices of the tangent vectors id at if , which can be opted for practical implementation for the computation of a curve with specific amount of smoothness. for 1c curve methods, some reasonable tangent approximation method can be used. the distance-based approximations are found reasonabl y good as far as pleasing smoothness is concerned. we, now, define the tangent vectors id at if . for open curves, the end conditions are defined as: ( ) ( ) ( ) ( ) 0 0 01 2 1 2 2 / 2 , 2 / 2.n n nn n d f f f f d f f f fü= ïïïýï= ïïþ (2.6) this choice will control the direction of the curve properly at the end segments. the tangents at the interior knots, for i = 1, 2,..., n-1 , are given by: ( ) ( )( )1 11i i i i ii id a f f a f f+= + (2.7) where 1 1 1 , 0, .. , .iii i ii i f f a i n f f f f + + = = + for closed curves, the end conditions are defined as: 1 1 1 1, ,n nf f f f+= = and the tangents at the interior knots are same as in (2.7) but 0, 1, ..., .i n= . the experiments have shown that the use of the distance-based approximated derivatives, corresponding to any control polygon (open or closed), provides visually pleasing output. figure 1(a) is the display of this derivative scheme for an "s" shaped data. for further details, the reader is referred to sarfraz et al. [10]. iium engineering journal, vol. 1, no. 2, 2000 m. sarfraz and z. habib 3 fig. 2 curvature plots of spline curves with exact derivatives: (a) with distance based end derivatives, (b) with conic compatible end derivatives. for a higher continuity than 1c , more complicated constraints are required to be fit. for example, for rational cubic spline, the constraints lead to a tridiagonal linear system of eq.s. this system is diagonally dominant and hence provides a unique solution. this system can be solved using some tridiagonal linear system solver like lu decomposition method. their details are as follows: 1c constraints (1) (1)( ) ( ), 1, ...,i ip t p t i n + -= = give 1 1 1( ) ,i ii i id f f dg -= and 2c constraints (2) (2)( ) ( ) , 1, .., 1i ip t p t i n + -= = lead to the following system of equations: ( ) ( )( )1 1 1 11 1i i i ii i i ih d h h h dg g++ + + 1 _ 1, 1, .., 1i ii i i ng g-= d + d = (2.8) for the need of graphical results, exact derivatives may be computed from (2.8) together with the end conditions in (2.6). figure 1(b) is the demonstration for this derivative scheme. the end conditions used here may not be appropriate for the objectives of this paper. therefore, a reasonable choice has been made in section 5, which demonstrates the "s" shaped data in fig. 1(c). the difference can be seen in fig. 2 demonstrating curvature plots of figures 1(b) and 1(c) in figures 2(a) and 2(b) respectively. 3. design curve analysis the parameters ig are mainly meant to be used freely to control the shape of the curve. at the same time, for the convenient of the designer, it is also required that the ideal geometric properties of the curve are not lost. the geometric properties, like variation diminishing, convex hull, and positivity, are the ones which need to be presented in the description of the design curve.  for the constraints, 1,i ig ³ " , it is very obvious that the rational cubic is characterized as of bernstein bezier form.  thus following the bernstein bezier theory, the piece of curve ( )ip t lies in the convex hull of { }1, , ,i i i if v w f + it also follows the variation diminishing property within the convex hull. that is any straight line crossing the control polygon of { }1, , ,i i i if v w f + does not cross the curve more than its control polygon. for the practical implementation, we choose i -1g ³ . the interval tension properties are apparent for the rational hermite form and are explained in the following subsections. 3.1. interval tension the interval shape property is obvious from the following limit behaviour. that is, the increase in the shape parameter in any interval tightens the curve towards the line segment joined by the control points. ( ) ( ) 10 1 i i i p t f f g q q +® = +lim . 3.2. global tension applying the interval property above successively, the design curve converges to the control polygon as the derivatives, either being distance-based or computed from the system of equations, are bounded. 4. conic and linear segments conic and straight line are the most important parts in designing which can be achieved through rational cubic interpolant, so that we can use the same interpolant for all types of curves. the procedure is as follows: let iu be taken as the point of intersection of tangents at if and 1if + (in case the tangents are parallel, i u can be taken as the point where the arc is desired to be splitted, for example, it may be the inflection or the middle point, etc.) then, we have: 1 , 1 1 i i i i i i ii i i f u v f u w g g g g + + üïï= ï+ ïïïý+ ïï= ïï+ ïïþ (4.1) it can be noted that the ratioanl cubic eq. (2.1) is the generalization of the following rational quadratic: iium engineering journal, vol. 1, no. 2, 2000 m. sarfraz and z. habib 4 ( ) ( ) ( ) ( ) ( ) ( ) 2 2 1 2 2 1 1 1 1 i i i i i f y f q t q ti q q q g q q q q g q ++ + º = + + , 0, 1, ...., 1,i n= (4.2) by raising the degree of (4.2), by multiplying the numerator and denominator by ( )1 q q+ , one can :obtain the following rational cubic form ( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( )( ) 3 2 2 3 1 3 2 2 3 1 1 1 1 1 1 1 1 1 1 i i i i i i i i i f v w f p t p ti q q q g q q g q q q q g q q g q ++ + + + + º = + + + + + , 0, 1, ...., 1,i n= (4.3) this form is similar to (2.1) as ( ) ( ) ( ) ( )( ) ( ) ( )3 2 22 3 21 1 1 1 1 1 1i i iiq q q g q q g q q q q g q+ + + + + = + + in a similar way, by degree raise, one can also observe that the rational quadratic (4.2) is the generalization of the following linear interpolant: ( ) ( ) ( ) 11 i il t l t f fi q q +º = + , 0, 1, ...., 1i n= (4.4) this linear interpolant will be used for the drawing of straight line segments later on.) hence, for conic section properties and choice of shape parameters, various conics are recovered depending upon the nature of weights (see [12]). that is, the ith arc will be:  parabolic if i > 2 g  hyperbolic if i > 2 g  elliptic if i > 2 g  straight line: i = 0 g (can be considered as a second method for straight line segment)  circular if  cos2i (4.5) where  is the angle between 1 iif f+ and i iu f and i i i iu f tm= + (4.6) where it is the unit vector along id and 2 1 1 ( ) 2( ). ii i i ii f f f f t m + + = (4.7) is determined by the condition 1i i i iu f u f += now we are imposing continuity conditions so that both segments can share same tangent direction at knot to ensure 1g continuity. for this we are changing the direction of exact derivatives with same magnitude. thus, to preserve continuity at fi, we take fig. 3 spline curves: (a) circular spline, (b) elliptic spline, (c) parabolic spline, (d) hyperbolic spline. 1 1 ( ) 1 1 i i i i i i i ii i d d u f u f w f d güïï= ïïïïýïï= ïï+ ïïþ (4.8) iium engineering journal, vol. 1, no. 2, 2000 m. sarfraz and z. habib 5 to achieve a straight line, one needs to replace iu with 1if + . similarly, for continuity at 1if + , we take ( )11 1 1 1 1 1 1 , 1 1 i ii i ii i i i i d d f u f u v f d g + + + + + + + + üïï= ïïïïýïïï= + ï+ ïïþ (4.9) and replacement of iu with if leads to a straight line. 5. circular arcs this section is devoted for the construction of circular arc. the cases, for a given radius and given center, are independently discussed in subsections 5.1 and 5.2 respectively. 5.1. circular arc for given radius let r be the given radius of the circular arc such that 1 2 iif fr + > (4.10) fig. 4 curvature plots of fig. 3: (a) circular spline, (b) elliptic spline, (c) parabolic spline, (d) hyperbolic spline. then, the center m can lie anywhere on the circle centered at ( )1 2 i if fn + + = , (4.11) and having radius b as follows: 2 12 2 iif fb r + æ ö÷ç ÷ç= ÷ç ÷ç ÷ç ÷è ø . (4.12) it will be preferred that it should lie on the plane passing through, 1,i if f + and ' iu , where ' iu is the intersection of 1 , i if f + id and 1id + . therefore circular arc should lie on the side of 'iu . let e1 be the rotation of fi+1 around n by an angle  on the plane passing through 1,i if f + and ' iu . where 090q = for anti-clockwise rotation and 090q = for clockwise rotation of circular arc. now 1 1 e n e e n = is a unit vector passing through n and perpendicular to 1 iif f+ . then m n be= + will be the center of the circular arc. let  be the angle between n m and -if m , then 2 cosig f= take = f f for anti clockwise rotation of circular arc. let t ¢ be the rotation of 1if + around if through angle  on the plane passing through 1,i if f + and iu ¢. then i i i t f t t f ¢= ¢ is a unit tangent vector at if . now use eq. (4.6) to find iu , eq. (4.1) to find control points iv and iw , eq. (4.8) for continuity at if , eq. (4.9) for continuity at 1if + and finally use rational cubic interpolant in eq. (2.1) for required circular arc. in this scheme, the radius r can be used as a shape control parameter. 5.2. circular arc for given center let m be the given center of the circular arc such that 1i im f f m+= let m ¢ be the rotation of m by if through angle q on the plane passing through 1,i if f + and m . where 090q = for clockwise rotation of circular arc and 090q = for anti-clockwise rotation. then i i i m f t m f ¢= ¢2n f is a unit tangent vector at if . let  be the angle between 1 iif f+ and it , therefore 2 cosig f= iium engineering journal, vol. 1, no. 2, 2000 m. sarfraz and z. habib 6 now use eq. (4.6) to find iu , eq. (4.1) to find control points iv and iw eq. (4.8) for continuity at if , eq. (4.9) for continuity at 1if + . finally, we use rational cubic interpolant, in eq. (2.1), for required circular arc. 6. end conditions a compatible choice, which is quite appropriate for the curve scheme of this paper, is presented here. for tangent at first point, let 0q be the angle between 01 f f and 02 f f . take 0 0q q= for anticlockwise rotation of points 0 1, f f and 2f . let t0 be the rotation of 1 f around 0 f by an angle 0q on the plane passing through 0 1, f f and 2f . then equation section 6 2 01 0 0 0 0 0 0 01 0 0 0 0 0 0 ( ) , 2( ). 2 , 3( ) 3 f f u f t f f t f u v d v f m m üïï= = + ïïïïýï+ ïï= = ïïïþ (6.1) where 0m is determined by the condition 0 0 0 1u f u f= and 0 0 & v d are taken from (4.1) & (2.3) respectively. fig. 5 (a) rational cubic spline with second last interval as circular arc piece, (b) the corresponding curvature plot. similarly for tangent at last point, let 0q be the angle between 1 nnf f and 2 nnf f . take n nq q= for anti-clockwise rotation of points 1,n nf f and 2nf . let nt be the rotation of 1nf around nf by an angle 0q on the plane passing through 1,n nf f and 2nf . then 2 1 1 1 1 1 1 1 1 ( ) , 2( ). 2 , 3( ) 3 nn n nn n n n nn n n n nn n f f u f t f f t f u w d f w m m-üïï= = + ïïïïýï+ ïï= = ïïïþ (6.2) where n-1 is determined by the condition 1 1 1nn n nu f u f-= and -1 & nnw d are taken from (4.1) & (2.3) respectively. fig. 6 (a) a rational cubic spline with 2nd interval as circular arc for radius 16r = , (b) the corresponding curvature plot. fig. 7 (a) a cubic spline with its 2nd interval as circular arc for center (0, 10, 2.5)m = , (b) the corresponding curvature plot. 7. algorithm in this section a high-level description of an algorithm for generating an interpolating curve, which modifies its shape interactively according to the proposals described in above sections, is given. the algorithm is presented in c-like pseudo code. //----construction of exact derivatives exactderivatives { calculate d[0] using (6.1); calculate d[n] using (6.2); find exact derivatives d[i], i=1..n-1, using (2.5). } //----to preserve continuity at f[i] & f[i+1] preservecontinuity iium engineering journal, vol. 1, no. 2, 2000 m. sarfraz and z. habib 7 { if (i > 0) // to preserve continuity at f[i] use eq. (4.8); if (i < n) // to preserve continuity at f[i+1] use eq. (4.9); } //----control points v[i], w[i] controlpoints { if (spline==’line’) use eq. (4.4); else if (spline==’conic’ || spline==’circular’) { use eq. (4.3); } else // for cubic spline use eq. (2.2); } //----circular, elliptic, parabolic and hyperbolic spline conicspline { calculate d[0] using (6.1); t[0] = (d[0]-f[0])/absvec(d[0]-f[0]); for (i=0; i<n; i++) { mu = sqrvec(f[i+1]-f[i]) / (2.0*dotprod(f[i+1]-f[i],t[i])); u = f[i] + mu*t[i]; d[i+1] = f[i+1] u; t[i+1] = d[i+1]/absvec(d[i+1]); if (spline== ‘circular’) gama[i] = 2.0*dotprod(f[i+1]-f[i],u-f[i]) / (absvec(f[i+1]-f[i])*absvec(u-f[i])); controlpoints; } } //----circular arc for ith segment circulararc { spline = ‘circular’; t[i] = d[i]/absvec(d[i]); mu = sqrvec(f[i+1]-f[i]) / (2.0*dotprod(f[i+1]f[i],t[i])); u = f[i] + mu*t[i]; gama[i] = 2.0*dotprod(f[i+1]-f[i],u-f[i]) / (absvec(f[i+1]-f[i])*absvec(u-f[i])); controlpoints; preservecontinuity; } //----circular arc for ith segment when radius is given circulararcforradius { spline = ‘circular’; n = (f[i]+f[i+1])/2.0; b = sqrt( sqr(radius) sqr(absvec(f[i]-f[i+1])/2.0) ); if (clockwise) angle = -pi/2.0; // for clockwise rotation of points else angle = pi/2.0; // for anti clockwise rotation of points ud = pointofintersection(f[i],d[i],f[i+1],d[i+1]; e = rotation(f[i+1],n,angle,ud); // rotation of f[i+1] about n through angle on the // plane of f[i+1], n & ud. e = (e-n)/absvec(e-n); m = n + b*e; phi = acos(dotprod(n-m,f[i]-m)/(absvec(nm)*absvec(f[i]-m))); gama[i] = 2.0*cos(phi); if (!clockwise) phi = -phi; // for anti clockwise rotation of points t = rotation(f[i+1],f[i],phi,m); // rotation of f[i+1] about f[i] through phi on the // plane of f[i+1], f[i] & m. t = (t-f[i])/absvec(t-f[i]); mu = sqrvec(f[i+1]-f[i]) / (2.0*dotprod(f[i+1]-f[i],t)); u = f[i] + mu*t; controlpoints; preservecontinuity; } //----circular arc for ith segment when center is given circulararcforcenter { spline = ‘circular’; if (clockwise) angle = pi/2.0; // for clockwise rotation of points else angle = -pi/2.0; // for anti clockwise rotation of points t = rotation(m,f[i],angle,f[i+1]); // rotation of m about f[i] through angle on the // plane of m, f[i] and f[i+1]. t = (t-f[i])/absvec(t-f[i]); phi = acos(dotprod(f[i+1]-f[i],t)/absvec(f[i+1]-f[i])); gama[i] = 2.0*cos(phi); mu = sqrvec(f[i+1]-f[i]) / (2.0*dotprod(f[i+1]-f[i],t)); u = f[i] + mu*t; controlpoints; preservecontinuity; } //----main body of the algorithm main() { read input data f[i] and shape control parameters gamma[i], i = 0..n; exactderivatives; // exact derivatives d[i], i = 0..n spline = ‘cubic’; for(i=0; i<n; i++) controlpoints; // control points v[i], w[i] for cubic spline //----conic spline (circular, elliptic, parabolic, hyperbolic) read nature of spline (circular, conic); if (spline != ‘circular’) read gama[i] for i = 0..n-1; conicspline; // control points v[i], w[i] for conic spline, i = 0..n-1. //----circular arc for ith segment read position i; circulararc; // control points v[i], w[i] for circular arc. //----circular arc for ith segment when radius is given read position i and radius; if (radius <= absvec(f[i]-f[i+1])/2.0) cout << “invalid radius” << “\n”; circulararcforradius; // control points v[i], w[i] for circular arc. //----circular arc for ith segment when center is given read position i and center m; if (abs(absvec(f[i]-m)-absvec(f[i+1]-m)) > 0.01) error("give correct center...."); circulararcforcenter; // control points v[i], w[i] for circular arc. //----straight line segment spline = ‘line’; controlpoints; // control points v[i], w[i] //----rational cubic spline for (i=0; i<n; i++) for(j=0; j<=20; j++) iium engineering journal, vol. 1, no. 2, 2000 m. sarfraz and z. habib 8 { t = j/20; calculate p(t) using (2.1); plot graph; } } // end of main algorithm. 8. demonstration the demonstration in this section has used derivative end conditions of section 5. figure 3 contains a block of conic splines where fig. 3(a) is circular spline, fig. 3(b) is elliptic spline, fig. 3(c) is parabolic spline, and fig. 3(d) is hyperbolic spline. fig. 4 represents the corresponding curvature plots of the curves in fig. 3. the demonstration of a rational cubic spline when it contains conic segments is made in fig. 5. figure 5(a) is a rational cubic spline with second last curve as circular spline, the corresponding curvature plot in fig. 5(b) verifies the result. the demonstration of the spline, where some circular arcs with specific radius are to be plotted, is given in fig. 6. the fig. 6(a) is a rational cubic spline with 2nd interval as circular arc for radius 16 r = where as the fig. 6(b) is its corresponding curvature plot. figure 7 demonstrates the circular arcs at some specific center. the fig. 7(a) is a cubic spline with its 2nd interval as circular arc for center (0, 10, 2.5) m = where as the fig. 7(b) is its corresponding curvature plot. 9. conclusion and future work we have described an interval controlled rational cubic interpolation scheme. the scheme offers a number of possible ways in which the shape of the corresponding curves may be altered by the users. it is therefore felt that such a scheme could be a useful addition to an interactive design package, with the user having enough control over the curve segments. the provision of the shape parameters, in the description of the piecewise rational functions, provides freedom to modify the shape in desirous regions in a stable manner. the rational spline scheme is meant for parametric curves and is capable of designing plane as well as space curves. it is an interpolatory rational spline scheme enjoying all the ideal geometric properties. it has features to produce all types of conic curves in such a way that the whole design curve may be produced as a circular, elliptic, parabolic, or a hyperbolic spline curve. in addition, the desired conic pieces may also be fitted within the rational cubic spline. overall smoothness of the rational cubic spline is 2c whereas the conics are stitched with 1g continuity. the curve scheme is extendable to surfaces and authors are lookng to publish it in a subsequent paper. some extra shape control parameters are also expected to be included to have some more degrees of freedom for designers. these shape parameters may be like point, interval, or biased shape control parameters used by various authors including nielson[8], foley[3], barsky[1], sarfraz[10-14], gregory et al[4-5]. acknowledgement the authors are thankful to the anonymous referees for their valuable comments and suggestions in the improvement of the manuscript. references [1] b. a. barsky, computer graphics and geometric modeling using beta-splines, springer-verlag, 1986. [2] g. farin, curves and surfaces for computer aided geometric design, academic press, 1988. [3] t. a. foley, “surface interpolation with tension controls using cardinal bases”, computer aided geometric design, vol. 6, pp. 97-109, 1989. [4] j. a. gregory, m. sarfraz, and p. k. yuen, “interactive curve design using c2 rational splines”, computers and graphics, vol. 18(2), 153-159, 1994. [5] j. a. gregory and m. sarfraz, “a rational spline with tension”, computer aided geometric design, vol. 7, 113, 1990. [6] j. hoschek, “circular splines”, computer-aided design, vol. 24, pp. 611-618 , 1992. [7] m. a. jamaludin, h. b. said, and a. a. majid, “shape control of parametric cubic curves”, proceedings of cad/graphics’ 95, china, spie proceedings series vol. 2644, pp. 128-133, 1995. [8] g. m. nielson, “rectangular -splines”, ieee computer graphics and applics. 6, 35-40, 1986. [9] l. piegl, and w. tiller, “the nurbs book”, springer, 1995. [10] m. sarfraz, z. habib and m. hussain, “piecewise interpolation for designing of parametric curves”, proceedings of ieee conference on information visualization, iv' 98, london, pp. 307-313, 1998. [11] m. sarfraz, m. hussain, and z. habib, “local convexity preserving rational cubic spline curves”, proceedings ieee conference on information visualization, iv' 97, london, pp. 211-218, 1997. [12] m. sarfraz, “curves and surfaces for cad using 2c rational cubic splines”, engineering with computers, vol. 11(2), pp. 94-102, 1995. [13] m. sarfraz, “designing of curves and surfaces using rational cubics”, computers and graphics, vol. 17(5), 529-538, 1993. [14] m. sarfraz, “a rational cubic spline with biased, point and interval tension”, computers and graphics, vol. 16, pp. 427-430, 1992. iium engineering journal, vol. 1, no. 2, 2000 m. sarfraz and z. habib 9 biography muhammad sarfraz received a ph.d. degree from brunei university in 1990. he is currently an associate professor and chairman of research committee in the department of information & computer science at king fahd university of petroleum and minerals. he has published around 90 journal and conference papers, edited seven proceedings of international conferences, given various keynotes and invited talks. his areas of interest are computer graphics, computer aided geometric design, font outline capture and representation, document & image processing, digitization of geometric models, scientific visualization, geometric modeling, surface reconstruction, geometric algorithms, error analysis, spline theory, computational geometry, spline wavelets, and genetic algorithms. he is member of ieee, acm, ams ivs, pms, isoss and is organizer of various international conferences. he has achieved various medals and awards in education and research. zulfiqar habib received his master degree from punjab university lahore, pakistan in 1990. he is currently a ph.d. student in the department of mathematics and computer science at kagoshima university, japan. his areas of interest are computer graphics, computer geometric design, surface reconstruction, geometric algorithms, error analysis, spline theory, and computational geometry. 318 iium engineering journal, vol. 14, no. 1, 2013 aminul islam 53 a technique for designing variation resilient subthreshold sram cell aminul islam department of electronics and communication engineering, birla institute of technology (deemed university), mesra, ranchi, jharkhand, india. aminulislam@bitmesra.ac.in abstract: this paper presents a technique for designing a variability aware subthreshold sram cell. the architecture of the proposed cell is identical to the standard read-decoupled 8-transistor (rd8t) sram cell with an exception that the access fets are replaced with transmission gates (tgs). in this work, different design metrics are assessed and compared with rd8t sram cell. the proposed design offers 2.14× and 1.75× improvement in tra (read access time) and twa (write access time) respectively compared with rd8t. it proves its robustness against process variations by featuring narrower spread in tra distribution (2.35×) and twa distribution (3.79×) compared with rd8t. the proposed bitcell offers 1.16× higher read current (iread) and 1.64× lower bitline leakage current (ileak) respectively compared with rd8t. it also shows its robustness by offering 1.34× (1.58×) tighter spread in iread (ileak) compared with rd8t. it exhibits 1.42× larger iread to ileak ratio. it shows 2.2× higher frequency at 250 mv with read bitline capacitance of 10 ff. besides, the proposed bitcell achieves same read stability and write-ability as that of rd8t at the cost of 3 extra transistors. the leakage power of the proposed design is close to that of rd8t. abstrak: kertas kerja ini membentangkan teknik merekabentuk sel bawah ambang sram yang bolehubah. senibina sel yang dicadangkan adalah sama dengan sel sram 8-transistor (rd8t) “pisahan-bacaan” piawai kecuali fet akses digantikan dengan sel pintu transmisi (tgs). di dalam kajian ini, beberapa metrik rekabentuk dinilai dan dibandingkan dengan sel rd8t sram. rekabentuk yang dicadangkan menawarkan peningkatan 2.14× dan 1.75× dalam tra (masa akses baca) dan twa (masa akses tulis) berbanding dengan rd8t. ia membuktikan kekukuhan variasi proses dengan menampilkan tebaran yang lebih sempit dalam pengagihan tra (2.35 ×) dan pengagihan twa (3.79 ×) berbanding dengan rd8t. sel-bit yang dicadangkan mempunyai arus baca 1.16 × lebih tinggi (iread) dan arus bocor bitline 1.64 × lebih rendah (ileak) berbanding dengan rd8t. ia juga membuktikan kekukuhan dengan menawarkan 1.34 × (1.58 ×) penyebaran sempit di iread (ileak) berbanding dengan rd8t dan nisbah iread / ileak 1.42 × lebih besar. ia menunjukkan kekerapan 2.2 × lebih tinggi pada 250 mv dengan kemuatan membaca bitline sebanyak 10 ff. selain itu, sel bit yang dicadangkan mencapai kestabilan membaca dan keupayaan menulis yang sama seperti rd8t dengan kos tambahan 3 transistor. kebocoran kuasa rekabentuk yang dicadangkan hampir sama dengan rd8t. keywords: variability; robust, subthreshold; random dopant fluctuation (rdf); read static noise margin (rsnm); write static noise margin (wsnm). 1. introduction due to severe increase in threshold voltage (vt) fluctuation caused by global and local process variations in ultra-short-channel devices, 6t sram cell and its variants cannot be operated at further scaled supply voltages without parametric and functional failure causing yield loss. single-ended 6t sram cell [1] suffers from iium engineering journal, vol. 14, no. 1, 2013 aminul islam 54 write delay. low power 6t sram cell [2] could reduce access delay and write power but could not improve stability. read-decoupled 8t (rd8t) proposed in [3-6], could improve rsnm (read static noise margin), but failed to improve variability significantly. battery operated mobile platforms such as pna, pda, cell phone, rfid tag, hearing aid, defibrillator, ipod, smartcard, smartphone, smartpen demand ultralow power sram to prolong battery life as sram is an integral part of all these platforms. subthreshold operation holds promise for ultralow power operation for these emerging applications. however, the design of robust sram is challenging in subthreshold regime due to more severe mismatch in device characteristics induced by process variability compared with superthreshold region [7, 8]. to circumvent process variation, robust and variation tolerant sram cell design technique capable of absorbing vt shift due to random dopant fluctuation (rdf), and variation in other device and process parameters (such as length, width, oxide thickness, sub-wavelength-lithography, etching, etc.) and still be able to perform expected functions need to be investigated. trade-off must generally be made in terms of area to achieve this goal. to solve process variation issues and minimum vdd operability in the face of extreme vt variation in ultrashort-channel devices at aggressively scaled technology node such as 16 nm, this paper proposes a transmission gate (tg)-based subthreshold 11t sram cell (hereafter called p11t) and compares its performance with standard read-decoupled 8-transistor sram cell (hereafter called rd8t). the remainder of this paper is organized as follows. section-2 presents the proposed design and its variability analysis. simulation results are discussed and compared in section-3. section-4 concludes the paper. 2. proposed tg-based 11t sram cell an attempt is made in this work to mitigate the impact of process, voltage and temperature (pvt) variations on design metrics of traditional rd8t sram cell by incurring minimum area penalty and retaining its dual port architecture. 2.1 cell sizing and array architecture as fluctuation in vt due to rdf exhibits an inverse dependence on square root of device area [9], it is apparent that the simplest solution to the variability problem is to use larger device area. therefore, the design metrics of the proposed design are compared with those of rd8t to demonstrate that the proposed design offers narrower spread in its design metrics even at iso-device area (device width over length (w/l) ratios are mentioned in figs. 1 and 2). the array architecture of rd8t [5] is applicable to the proposed sram array organization as well. an array can be optimized by the usage of peripheral circuits designed in lsdl (limited switch dynamic logic) [10] and gated diode sense amplifier [11] as was done in rd8t [5]. the proposed design utilizes one read port and one write port and does not require much architectural changes except adding a pfet (mp3, mp4, and mp5) in parallel with each access nfet, thereby making it an 11t sram cell. iium engineering journal, vol. 14, no. 1, 2013 aminul islam 55 fig. 1: proposed tg-based read-decoupled 11t sram cell (p11t). fig. 2: standard read-decoupled 8t sram cell (rd8t). two additional controls wwlb (write word line bar) and rwlb (read wordline bar) are required to switch the access pfets. they are non-overlapping complementary signal of wwl (write wordline) and rwl (read wordline) respectively. therefore, while accessing the cell, all relevant access fets are switched simultaneously on for reading or writing. during hold mode all access fets remain off. 2.2 current analysis of proposed design read current (iread) can be expressed analytically by solving kirchoff ’s current law at node qm (with internal node “qb” storing “1”), where current flows out through mn6 and flows in through mn5 and mp5. ).,( ),( ),( 6 5 5 qmdsqbgsmn rblqmdsrblrwlbgsmp qmrbldsqmrwlgsmnread vvvvi vvvvvvi vvvvvvii === −=−=+ −=−== (1) thus, iread is the sum of the currents imn5 and imp5 that passes through mn6 while discharging precharged rbl. the write-ability of a one half cell is determined by applying complementary signal to bl and blb. with bl = 1, iwrite is defined as a net current flowing out of internal node “qb” storing “1’ iium engineering journal, vol. 14, no. 1, 2013 aminul islam 56 ).,( ),( ),( ),( 1 3 3 1 qbdsqgsmn qbdsqbwwlbgsmp qbdswwlgsmn ddqbdsddqgsmpwrite vvvvi vvvvvi vvvvi vvvvvvii ==− =−=− ==− −=−== (2) since vq is usually small, the last term of iwrite is neglected. thus, iwrite is the difference in current between pull-up device resisting the write and access devices discharging the node “qb”. in the proposed p11t cell (fig. 1), the read current (iread), defined as rbl discharge current, is the summation of two currents flowing through nmos(mn5) and pmos(mp5) transistors of a transmission gate (tg) respectively. this summation of read current iread over two different transistors in parallel is primarily responsible for the lower value of variability in case of p11t. this averaging is impossible in case of standard rd8t due to the existence of only one access transistor. it is clear that the total current will remain almost constant in case parameters of mn5 and mp5 vary in opposite direction due to summation. it is highly unlikely that parameters of both mn5 and mp5 of tg will vary in the same direction because they are of different types and mp5 exists in a different nwell. moreover, it can be deduced that the current idp5 (through mp5) varies to stabilize the total read current, in case current idn5 (through mn5) varies due to rdf induced vt shift and vice versa. this can be understood by assuming that only the threshold voltage of mn5 of tg goes down due to rdf whereas the threshold voltage of mp5 remains unchanged. this increases the current through mn5 and the total current iread through tg and hence vqm rises quickly and vrbl falls rapidly. this rapid rise of vqm and fall of vrbl increases threshold voltages of mn5 and mp5 due to body effect respectively, thereby, reducing the current through both mn5 and mp5. this helps in reducing (stabilizing) the total current iread. similarly, if the threshold voltage of mn5 increases due to rdf or any other reasons, the current through mn5 and also the total current iread decrease and hence, vqm rises slowly and vrbl reduces gradually. this results in lower value of threshold voltages for both mn5 and mp5 due to less pronounced body effect compared with the first case. the lower value of threshold voltage increases the current through both mn5 and mp5, thereby, stabilizing the total current iread. the same explanation can be given in case the threshold voltage of mp5 varies due to rdf or any other reason. therefore, it can be concluded that iread in tg is much more stable compared to iread in nmos pass transistor. similar explanation can be given for stability of iwrite. 3. simulation result this section presents various design metrics which are estimated during monte carlo (mc) simulations in hspice using 16 nm cmos ptm [12]. 3.1 simulation set-up threshold voltage (vt) is assumed to have independent gaussian distribution with 3σ variation of 58% [13]. though, this itrs anticipation of 58% vt variation is quite aggressive, this value is selected to demonstrate that the proposed technique is still able to perform better than rd8t (however, 10% vt variation is also used for certain simulation setup, which is mentioned in relevant figures). authors in [14] showed that variation in cox (gate oxide capacitance) due to variation in l (channel length), w (width), and tox (oxide thickness) is negligibly small. it is to be noted that the effect of all parameter iium engineering journal, vol. 14, no. 1, 2013 aminul islam 57 variations can be translated into the effective variation in threshold voltage [15]. therefore, only 58% vt variation is applied taking itrs projection into consideration. itrs 2009 also anticipates temperature variation within the range from − 55 °c to 155 °c. therefore, standby power dissipation is measured over this temperature range. as per itrs 2009, expected variation in supply voltage is 10% in the future technology generations such as 16 nm [13]. hence, most of the design metrics are estimated by scaling the supply voltage from 400 mv down to 250 mv and below. the authors in [14] showed that a sample size of 2000 ensures a lower than 4% inaccuracy in the estimation of standard deviation. this work uses 5000 sample size while estimating design metrics with mc simulation [16]–[18] to achieve even higher accuracy. moreover, read and write access failure probabilities are assessed by mc simulations with 25000 run [16]. unless specified otherwise, all parameters are estimated under the above variation/simulation setup. 3.2 read current, read bitline leakage current and their variabilities in subthreshold, the ion/ioff ratio for nfet (pfet) in 16 nm technology becomes as low as 150 (170) @ 200 mv, which may be even lower in the face of process variation (see fig. 3) (this nominal value of ion to ioff ratio is obtained by simulating an nfet and pfet (w/l = 32 nm/16 nm) in 16 nm technology). this may result in read failure and impose a theoretical upper bound on the number of cells sharing a common bitline. the devices in read buffer of both designs are therefore up-sized to mitigate these issues in subthreshold operation. the higher ion to ioff ratio of pfet compared to nfet leverage the iread/ileak ratio in the proposed design (see fig. 3). fig. 3: on-current to off-current ratio of nfet and pfet (w/l = 32 nm/ 16 nm) in 16-nm technology. iread of both designs are estimated during simulation (see fig. 4). rd8t shows higher iread because the drive current of nfet is higher than pfet (~1.5× with w/l = 32 nm/ 16 nm). therefore, though the width of mp5 (2×w) and mn5 (1.5×w) in p11t taken together is (3.5×w) equal to that of mn5 in rd8t, their drive strength is not equal. however, improved iread variability is achieved in the proposed design due to the averaging effect of tg (see fig. 5). this improved variability in iread offers narrower spread in other design metrics of the proposed design. iium engineering journal, vol. 14, no. 1, 2013 aminul islam 58 fig. 4: read current of proposed bitcell (p11t) and standard rd8t. fig. 5: read current variability versus vdd. proposed bitcell (p11t) offers tighter spread in iread @ all considered supply voltages compared with rd8t. the proposed design offers lower rbl (read bitline) leakage current ileak (see fig. 6). it happens even though the pull-down stack (mn6) in read buffer has equal width (4×w) and the read buffer switch mn5 and mp5 forming tg in p11t taken together has equal width to that of mn5 in rd8t. this can be understood by conceiving the hot-carrier injection mechanism in short-channel devices. in a short-channel device, due to high electric field near the si/sio2 interface, electrons or holes can gain sufficient energy from the electric field to cross the interface potential barrier and enter the oxide layer. this effect is so called hot-carrier injection. the injection of electrons from si to sio2 is more likely than injection of holes, as electrons have lower effective mass than that of holes, and the barrier height for holes (4.5 ev) is more than that for electrons (3.1 ev) [19]. it can be observed that the long tail of the ileak distribution in case of rd8t extends to the right beyond that of p11t, which results in significant increase in ileak (see fig. 7). ileak distribution curves of p11t and rd8t cross at 1.3 na. based on the simulation data, the estimation shows that 18% of statistical samples in case of p11t have ileak higher than 1.3 na signifying higher column height because larger number of cells can be connected to rbl compared with rd8t (63% of statistical samples in case of rd8t have ileak higher than 1.3 na). iium engineering journal, vol. 14, no. 1, 2013 aminul islam 59 fig. 6: read bitline leakage current versus vdd. proposed bitcell (p11t) offers lower ileak @ all considered supply voltages compared with rd8t. fig. 7: impact of process variations on the bitline leakage current (ileak) in 16 nm technology with 3σ vt variation of 10% @ vdd = 0.25 v. fig. 8: ileak variability versus vdd. proposed bitcell (p11t) offers narrower spread in ileak @ all considered supply voltages proving its robustness. the proposed cell exhibits improved rbl leakage current variability compared to rd8t (see fig. 8). it shows its robustness by offering 1.34× and 1.58× tighter spread in iread and ileak respectively compared with rd8t @ 250 mv. higher iread to ileak ratio is highly expected in subthreshold sram design to achieve higher sense margin and column height. the proposed design exhibits higher iread to ileak ratio even in the face of severe vt variability mentioned in the simulation setup. it exhibits 1.42× higher iread to ileak ratio @ 250 mv implying its suitability in deep subthreshold operation (see fig. 9). iium engineering journal, vol. 14, no. 1, 2013 aminul islam 60 fig. 9: iread to ileak ratio versus vdd. proposed bitcell (p11t) offers higher ratio at all considered supply voltages signifying its suitability in deep subthreshold operation compared with rd8t. 3.3 read stability and write-ability rd8t/p11t isolates the storage nodes q and qb, resulting in rsnm free structure. and the operating margin, which is significantly improved, is set by the hold snm and the write margin. the read stability of sram cell (rsnm) relies on vdd. this is illustrated in fig. 10, which shows that rsnm gradually decreases with vdd scaling. the proposed design shows three roots even at vdd = 250 mv. this implies that the proposed bitcell can be operated in the subthreshold region at this voltage. rsnm vtcs of both cells, starting from 400 mv down to 250 mv have three distinct roots assuring its functionality as a bistable circuit in read and hold mode [8-9], [17-18], [20]. fig. 10: read static noise margin (rsnm) reduction with vdd scaling. it shows three roots even @ vdd = 250 mv with rsnm =45 mv, signifying its ability to function as a bistable circuit. the write-ability of a cell is measured using read and write vtcs as shown in fig. 11. the write vtc while writing “1” at qb is measured by sweeping vqb (see fig. 11, y-axis) with blb & wwl high and bl low while monitoring vq (see fig. 11, x-axis). this write iium engineering journal, vol. 14, no. 1, 2013 aminul islam 61 vtc is used in combination with the read vtc measured by sweeping vq (see fig. 11, xaxis) while monitoring vqb (see fig. 11, y-axis). the side length of the smallest square, that can be inscribed between the read and write vtcs of the same sram cell at the lower half of the curves, passed the trip voltage of inv1, represents wsnm [9], [17], [18], [21]. when wsnm falls below zero, write vtc intersects read vtc, indicating positive write margin and signifying write failure. wsnm of p11t and rd8t are illustrated in fig. 11 @ 250 mv. fig. 11: static voltage characteristics of sram cells during write operation in 16 nm process technology @ supply voltage vdd = 250 mv. 3.4 read/write access times and their variabilities the estimated result of tra (read access time or read delay) and its distribution is plotted in fig. 12. tra at vdd = 250 mv is also reported in table i. normalized values are reported in bracket. as observed from table i, the proposed design (p11t) exhibits 2.14× improvement in read delay compared with rd8t @ 250 mv. it offers 2.35× improvement in tra distribution @ 250 mv compared with rd8t, thereby proving its robustness against process variations. this improvement comes due to the use of tg in place of pass transistor in the read buffer. fig. 12: read delay and its variability versus vdd. iium engineering journal, vol. 14, no. 1, 2013 aminul islam 62 table 1: read access time and its spread @ vdd = 250 mv. sram std. dev. (s) mean (s) std. dev./mean p11t 8.179e-07 1.894e-07 (1) 4.32 (1) rd8t 4.101e-06 4.046e-07 (2.14) 10.14 (2.35) the estimated results of twa (write access time or write delay) and its distribution are plotted in fig. 13. twa at vdd = 250 mv are also reported in table ii. the values are normalized with respect to that of p11t and are reported in bracket. as observed from these simulation results, the proposed design offers 1.75× improvement in twa compared with rd8t @ 250 mv. it proves its robustness against process variations by featuring tighter spread (2.79×) in twa distribution compared with rd8t @ 250 mv. this improvement comes due to the pfets employed in tgs. fig. 13: write delay and its variability versus vdd. table 2: write access time and its spread at vdd = 250 mv. sram std. dev. (s) mean (s) std. dev./mean p11t 1.186e-08 3.980e-09 (1) 2.98 (1) rd8t 5.798e-08 6.981e-09 (1.75) 8.31 (2.79) 3.5 leakage power estimation the standby power consumption in an sram cell is more critical than dynamic power consumption, since the whole part of the cache remains idle most of the time except the row being accessed. leakage power is estimated when the cell is in hold mode. it is observed, that the standby power of the proposed design is close to that of rd8t at all temperatures ranging from − 55 °c to 155 °c (plot not shown). and standby power increases exponentially as the temperature is increased due to the subthreshold device behaviour. figure 14 shows leakage current (istandby) distribution of both designs in hold mode with 3σ threshold voltage (vt) variation of 10% @ vdd = 0.25 v. iium engineering journal, vol. 14, no. 1, 2013 aminul islam 63 fig. 14: impact of process variations on the leakage current (istandby) in hold mode in 16 nm technology with 3σ threshold voltage (vt) variation of 10% @ vdd = 0.25 v. 3.6 failure analysis read access and write access failure probability analyses are carried out to assess the practicability of both cells to function under subthreshold conditions (see fig. 15). the number of trials n = 25000 in mc simulations is set to achieve sufficient accuracy in the estimation of the access failure probability [16]. the probability of access failure is estimated as the ratio of the number of occurrence of read/write failure to the total number of experiments. it can be observed from the figure that the probabilities of both the access failures are lower in case of p11t compared to rd8t. this indicates that there will be a least number of faulty cells in case of p11t-based sram offering maximum yield in the subthreshold regime compared with rd8t. rd8t fails to improve writeability, though it offers good rsnm. in this analysis, it clearly exhibits its poor write-ability by showing higher write access failure probability although its write access nfets are up-sized to match with tgs in p11t. on the other hand, the proposed p11t, offers lower value of read access and write access failure probability. this is attributed to the fact that tg employs a pfet that is less velocity saturated and relatively stronger in subthreshold region. in particular, the proposed bitcell exhibits no read and write access failures even @ 205 mv, whereas rd8t shows read access failure of 0.2e-3 and write access failure of 0.2e-1 at the same supply voltage. thus, the proposed bitcell will provide voltage and dimension scaling advantages. low voltage operation will result in reduction of standby power (linearly, ddstandby v×i ) and dynamic power (quadratically, 2 ddl vc ) with reduced vdd. one should note that the failure mechanisms illustrated above are function of environmental parameters. hence the failure map of a cache will change if these parameters are altered. iium engineering journal, vol. 14, no. 1, 2013 aminul islam 64 fig. 15: read and write access failure probability of rd8t and p11t. proposed bitcell (p11t) exhibits much smaller read/write access failure probability offering maximum yield of sram based on it. it also signifies its suitability at deep subthreshold voltage compared to rd8t. 3.7 performance analysis figure 16 shows the operating frequency versus crbl plot @ vdd = 250 mv. the proposed bitcell achieves 2.2× higher frequency @ 250 mv with read bitline capacitance of 10 ff (equivalently 229 cells connected to rbl, neglecting contact and wire capacitance). higher frequency also implies that the column height using the proposed design will be higher. the shorter column height has negative impact on chip area. fragmentation of column incurs extra silicon area because of supply power grid distribution in the chip. thus, longer bitline is preferred to save chip area. to observe the effect of varying crbl on read delay variation, read delay variability versus crbl is plotted in fig. 17, which again shows that the proposed design is robust against process variation. fig. 16: operating frequency versus read bitline capacitance. iium engineering journal, vol. 14, no. 1, 2013 aminul islam 65 fig. 17: read delay variability versus read bitline capacitance. 3.8 area comparison the layout of both cells was drawn for fair area comparison (layout not shown). the proposed bitcell adds 20% area overhead compared to rd8t sram cell of [5]. although, the proposed cell-size expands by 20%, its overwhelming improvement in variability justifies the additional overhead. moreover, overall area penalty is less since more cells can be included on the bitline, which is evident from the previous performance analysis. 4. conclusion due to aggressive scaling of device dimensions, variability has become a metric of equal importance as snm (static noise margin) and wsnm (write static noise margin) in sram cell. this paper proposes a tg-based variability aware 11t sram cell. it analyzes the impact of pvt variations on its read access time, write access time, read current, bitline leakage current, and standby current. the results show significant improvement in most of the design parameters over standard rd8t sram cell demonstrating its robustness and functionality up to 250 mv and below. it mitigates impact of pvt variations mainly due to access tgs employed in the design. the proposed design is an attractive choice for application in scaled technology in subthreshold region in the presence of severe variation. references [1] jawar singh, dhiraj k. pradhan, simon hollis, and saraju p. mohanty. “a single ended 6t sram cell design for ultra-low-voltage applications”. ieice electronics express, 5.18 (2008): 750-55. [2] h. mizuno, and t. nagano. “driving source-line cell architecture for sub-1-v high-speed low-power applications”. ieee journal of. solid-state circuits, 31.4 (1996): 552-57. [3] k. takeda, y. hagihara, y. aimoto, m. nomura, y. nakazawa, t. ishii, and h. kobatake. “a read-staic-noise-margin-free sram cell for low-vdd and high-speed applications”. ieee journal of . solid-state circuits, 41.1 (2006): 113-21. [4] f. frustaci, p. corsonello, s. perri, and g. cocorullo. “techniques for leakage energy reduction in deep submicrometer cache memories”. ieee transitions . very large scale integration. (vlsi) 14.11 (2006): 1238-49. [5] . chang, r. k. montoye, y. nakamura, k. a. batson, r. j. eickemeyer, r. h. dennard, w. haensc, and d. jamsek. “an 8t-sram for variability tolerance and low-voltage operation in high-performance caches”. ieee journal of . solid-state circuits, . 43.4 (2008): 95663. iium engineering journal, vol. 14, no. 1, 2013 aminul islam 66 [6] t.-h. kim, j. liu, and c. h. kim. “a voltage”. ieee journal of . solid-state circuits, 44.6 (2009): 1785-95. [7] bo zhai, s. hanson, d. blaauw, and d. sylvester. “a variation-tolerant sub-200 mv 6-t subthreshold sram”. ieee journal of. solid-state circuits, 43.10 (2008): 2338-47. [8] a. islam, mohd. hasan, and tughrul arslan. "variation resilient subthreshold sram cell design technique". international journal of electronics, (2012): 1-15. [9] islam and mohd. hasan. “a technique to mitigate impact of process, voltage and temperature variations on design metrics of sram cell”. microelectronics reliability, 52.2 (2012): 405-11. [10] r. montoye, w. belluomini, h. ngo, c. mcdowell, j. sawada, t. nguyen, b. veraa, j. wagoner, and m. lee. “a double precision floating point multiply”. digest of technical papers 1.1 (2003): 336-37. [11] w. k. luk and r. h. dennard. “gated diode amplifiers”.. circuits and systems ii: express briefs, ieee transactions on 52.5 (2005): 266-270. [12] n, nimo group. "predictive technology model (ptm); nanoscale integration and modeling (nimo) group, arizona state university." (2007). [13] semiconductor industry association (sia), international technology roadmap for semiconductors 2009 edition. [online]. [14] m. alioto, g. palumbo, and m. pennisi. “understanding the effect of process variations on the delay static and domino logic”. very large scale integration (vlsi) systems, ieee transactions on 18.5 (2010): 697-710. [15] a.agarwal, b. c. paul, s. mukhopadhyay and k. roy. “process variation in embedded memories: failure analysis and variation aware architecture”. ieee journal of solid-state circuits, 40 (2005): 1804-14 [16] j. p. kulkarni, k. kim, and k. roy, “a 160mv robust schmitt trigger based subthreshold sram”. ieee journal of. solid-state circuits 42.10 (2007): 2303-13. [17] a.islam and mohd. hasan. “leakage characterization of 10t sram cell”. "electron devices, ieee transactions on 59.3 (2012): 631-38. [18] islam and mohd. hasan. "variability aware low leakage reliable sram cell design technique". microelectronics reliability, 52.6 (2012): 1247: 52. [19] y. taur and t. h. ning. “fundamentals of modern vlsi devices”. new york: cambridge university press, 2009. [20] bhavnagarwala, s. kosonocky, c. radens, y. chan, k. stawiasz, u. srinivasan, s. p. kowalczyk, and m. m. ziegler. “a sub-600 mv, fluctuation tolerant 65-nm cmos sram array with dynamic cell biasing”. ieee journal of . solid-state circuits,. 43.4 (2008): 946 55. [21] z. guo, a. carlson, l-t. pang, k. t. doung, t-j. k. liu, and b. nikolic “large-scale sram variability characterization in 45nm cmos”. ieee journal of . solid-state circuits, 44.11 (2009): 3174-92. microsoft word 202-1279 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics basuki et al. 117 mathematical modeling and numerical solution of iron corrosion problem based on condensation chemical properties basuki w. 1 , arif f. 2 and tri r. 2 1 department of mathematics, institut teknologi sepuluh nopember,surabaya, indonesia. 2 department of mathematics & industrial technology, jamber university-wijaya kusuma surabaya university ,jamber-surabaya, indonesia. b_widodo@matematika.its.ac.id abstract: corrosion process is a natural phenomenin that occurs with the various metals, where the corrosion process in electrochemical environment can be explained by using a galvanic cell. the iron corrosion process is based on the acidity degree (ph) of a condensation, iron concentration and condensation temperature of electrolyte. these are applied at electrochemistry cell. the iron corrosion process at this electrochemical cell also is able to generate electrical potential and electric current during the process. this paper considers how to build a mathematical model of iron corrosion based on electrical potential and electric current. the mathematical model further is solved using the finite element method. the iron corrosion model is built based on the iron concentration, condensation temperature, and iteration time applied. in the electric current density model, the current is generated between the cathode and anode poles and the iteration time applied. whereas the potential electric model, is based on the electric potential and the iteration time applied. the numerical results show that the part of iron sample, attacked by corrosion, is a function of time, depth difference, iron concentration, condensation temperature and the sum of reduced mass during corrosion process. abstrak: proses kakisan adalah kes semulajadi yang berlaku di pelbagai logam, di mana proses kakisan dalam elektrokimia boleh diterangkan dengan menggunakan sel galvani. proses pengaratan besi adalah berdasarkan kepada tahap keasidan (ph) daripada pemeluapan, kepekatan besi dan suhu pemeluapan elektrolit. sifat-sifat ini digunakan pada sel elektrokimia. proses pengaratan besi pada sel elektrokimia ini juga mampu menjana arus dan voltan elektrik. kertas ini menerangkan cara-cara membina model matematik untuk kakisan besi, arus dan voltan elektrik. model matematik ini diselesaikan dengan menggunakan kaedah unsur terhingga. model kakisan besi dibina berdasarkan kadar kepekatan besi, suhu pemeluapan, dan lelaran. ketumpatan arus elektrik berdasarkan jumlah arus elektrik yang ada tiang-tiang katod dan anod tiang pada setiap lelaran. manakala model potensi elektrik, berdasarkan pada kadar awal voltan elektrik pada masa lelaran. bacaan experimen menunjukkan bahawa bahagian anod tetap keras walaupun dikakis dan dipengaruhi oleh kepekatan besi dan suhu pemeluwapan dan jumlah jisim. keywords: iron corrosion; concentration of iron; electrochemical cell; finite element method. iium engineering journal, vol. 12, no. 6, 201 1. introduction iron is one of the most important m corrosion of iron happened naturally. rustiness can be described as a material ruination by action which embossing area, where resistance of a material on the rustiness depends on the numerous variables such [1]. the important aspect in a material rustiness is mass transport characteristic, that due to evacuation of temperature, migration and diffusion. the distribution character from the effects which are generated in an object depends on force sys itself object. a real rustiness case is a galvanic process with metal that works as an anode, a cathode and as one conductor for the electrons. the quantitative simulation of iron rustiness relates to possibility that deterioration forecasting of conglomerate stones are contain the iron item, thus here pointed to build a rustiness model as possible as free of context in physically and can be interfaced to a model of chemical reaction. this paper focuses on a mathematical modeling of an electro chemistries reaction that ta during corrosion process and the model then solved using finite element method, in which it is shown geometrically as an electrochemistry cell process. reduction-oxidation reaction in electrochemistry cell by using a pa based on the law of physical chemistry. 2. governing equation the important aspect in a material rustiness is mass transport characteristics, which are occurred because of temperature, migration and diffusion evacuation. these are appropriate with condensation mass i.e.: jk = –dk ck–c where : dk = diffusion constant ck = concentration in molar (moles/liter) zk = charge number f = faraday’s constant = the electric potential in the electrolyte r = gas constant t = absolute temperature this condensation mass further is transported by electrical field on molecular diffusion process [2]. for each type, the equation of transporta of accumulator acid, i.e.: + .[(– g journal, vol. 12, no. 6, 2011: special issue in science and ethics 118 introduction iron is one of the most important metals that has many benefits to the human iron happened naturally. rustiness can be described as a material ruination by action which embossing area, where resistance of a material on the rustiness depends such as material properties and environmental characteris the important aspect in a material rustiness is mass transport characteristic, that evacuation of temperature, migration and diffusion. the distribution character from the effects which are generated in an object depends on force system characteristic and a real rustiness case is a galvanic process with metal that works as an anode, a cathode and as one conductor for the electrons. the quantitative simulation of iron rustiness relates to possibility that deterioration forecasting of conglomerate stones are contain the iron item, thus here pointed to build a rustiness model as possible as free of context in physically and can be interfaced to a model of chemical reaction. this paper focuses on a mathematical modeling of an electro chemistries reaction that ta during corrosion process and the model then solved using finite element method, in which it is shown geometrically as an electrochemistry cell process. this paper illustrates the oxidation reaction in electrochemistry cell by using a partial differential model based on the law of physical chemistry. governing equation the important aspect in a material rustiness is mass transport characteristics, which are occurred because of temperature, migration and diffusion evacuation. these are ropriate with condensation mass jk of species k, as mentioned in planckck (1) = concentration in molar (moles/liter) = the electric potential in the electrolyte this condensation mass further is transported by electrical field on molecular diffusion process [2]. for each type, the equation of transportation can be written in a form ).ck]–dk 2 ck=sk (2) : special issue in science and ethics basuki et al. human society. iron happened naturally. rustiness can be described as a material ruination by action which embossing area, where resistance of a material on the rustiness depends as material properties and environmental characteristics the important aspect in a material rustiness is mass transport characteristic, that occur evacuation of temperature, migration and diffusion. the distribution character from tem characteristic and a real rustiness case is a galvanic process with metal that works as an anode, a cathode and as one conductor for the electrons. the quantitative simulation of iron rustiness relates to possibility that deterioration forecasting of conglomerate stones are contain the iron item, thus here pointed to build a rustiness model as possible as free of context in physically and can be interfaced to a model of chemical reaction. this paper focuses on a mathematical modeling of an electro chemistries reaction that taken place during corrosion process and the model then solved using finite element method, in which illustrates the rtial differential model the important aspect in a material rustiness is mass transport characteristics, which are occurred because of temperature, migration and diffusion evacuation. these are -nernst’s law, this condensation mass further is transported by electrical field on molecular tion can be written in a form iium engineering journal, vol. 12, no. 6, 201 where sk is ions production or ruination of type fe +2 ion because of rust forming. in this corrosion process case, it is taken place in the interface between electrodes and condensation of electrolyte. electrical tension can be obtained by considering the total electrical current and it disregards the neutrality electric condensation of electrolyte. newman (1996) explains that the power of the electrical current condensation mass constant change from iron. it can be formulated using the faraday’s law: a statement of electro-neutrality is that the electric current density is non is: . i = 0 inserting the expression (3) in equation (4), we obtain: . ( ) = 0 by using the planck–nernst’s law (1), we then end up with an equation for the electric potential, i.e.: notice that when the concentration gradients may be neglected, eq. (6) then reduces to the laplace’s equation, i.e.: 2 = 0. 3. boundary conditions by analyzing the electrochemistry, iron rustiness proc oxidation by the oxygen that comes from the air. figure electrolyses with (fe) iron electrode. in this condensation there are some species, for example h + and oh ions obtained from the result of h ion that come from electrode ionization. fe oh ions peripatetic towards positive pole [4]. (a) g journal, vol. 12, no. 6, 2011: special issue in science and ethics 119 is ions production or ruination of type k, for example in elimination case from ion because of rust forming. in this corrosion process case, it is taken place in the interface between electrodes and condensation of electrolyte. electrical tension can be obtained by considering the total electrical current and it disregards the neutrality electric condensation of electrolyte. newman (1996) explains that the power of the electrical current i ,in condensation of the electrolyte, is condensation mass constant change from iron. it can be formulated using the faraday’s neutrality is that the electric current density is non-divergent, that (4) pression (3) in equation (4), we obtain: ) = 0 (5) nernst’s law (1), we then end up with an equation for the electric = – ∑ dk 2 ck (6) notice that when the concentration gradients may be neglected, eq. (6) then reduces to the (7) boundary conditions by analyzing the electrochemistry, iron rustiness process is event of iron metal at comes from the air. figure 1 shows that h2o condensation electrolyses with (fe) iron electrode. in this condensation there are some species, for ions obtained from the result of h2o ionization as solvent and fe ion that come from electrode ionization. fe 2+ ions peripatetic towards negative pole and ions peripatetic towards positive pole [4]. (b) : special issue in science and ethics basuki et al. , for example in elimination case from ion because of rust forming. in this corrosion process case, it is taken place in the electrical tension can be obtained by considering the total electrical current and it disregards the neutrality electric condensation of electrolyte. newman (1996) explains that ,in condensation of the electrolyte, is flown in the condensation mass constant change from iron. it can be formulated using the faraday’s divergent, that nernst’s law (1), we then end up with an equation for the electric notice that when the concentration gradients may be neglected, eq. (6) then reduces to the ess is event of iron metal o condensation electrolyses with (fe) iron electrode. in this condensation there are some species, for ionization as solvent and fe 2+ ions peripatetic towards negative pole and iium engineering journal, vol. 12, no. 6, 201 fig. 1: (a) location of the anode and cath during the corrosion process takes place, it will entangle the reaction of reduction oxidation (redox) in electrolytic cell by using a partial di physical chemistry. newman (1996) explains that the only reaction takes place in anode is disconnection of metal. in this case, reaction of (fe) iron can be written as: (a)fe → fe 2+ where e 0 a is the standard potential of (a) reaction. the current density is produced by (a) reaction and it can be written by the butler ia = i0a . where : i0a = exchange current density of (a) reaction, th which the net current at the electrode is null (this value is obtained experimentally), άa = transfer coefficient for (a) reaction (this value is obtained experimentally, although a good estimate is 1/2), za = number of electrons participating in (a) reaction, ήa = overvoltage = äö − ea electrode and the electrolyte (soon after the electronic double layer) and e electrode potential at zero current. as only the species fe 2+ mass flux will be non-zero only. hence, once the density current is evaluated from eq. (2), we can use the faraday’s law to ev the fluxes are then used as boundary condition at the anode for the transport equation. further, the cathode pole, between the easiest matters experiences reduction is molecule so that happened reduction to h g journal, vol. 12, no. 6, 2011: special issue in science and ethics 120 location of the anode and cathode in a corrosion process (b) and a one dimensional galvanic cell. during the corrosion process takes place, it will entangle the reaction of reduction oxidation (redox) in electrolytic cell by using a partial differential model, based on law of physical chemistry. newman (1996) explains that the only reaction takes place in anode is disconnection of metal. in this case, reaction of (fe) iron can be written as: + 2e-, e 0 a = 0,44 (oxidation) (8) is the standard potential of (a) reaction. the current density is produced by (a) reaction and it can be written by the butler-volmer’s equation as: (9) exchange current density of (a) reaction, that is the current density evaluated , in which the net current at the electrode is null (this value is obtained experimentally), transfer coefficient for (a) reaction (this value is obtained experimentally, although a good estimate is 1/2), number of electrons participating in (a) reaction, a, where äö is the variation in potential between the electrode and the electrolyte (soon after the electronic double layer) and e electrode potential at zero current. 2+ are involved in the anode reaction, we can assume that its zero only. hence, once the density current is evaluated from eq. (2), we can use the faraday’s law to evaluate the mass flux: jfe2 + = jh+ = 0 ; on x = 0. (10) the fluxes are then used as boundary condition at the anode for the transport equation. further, the cathode pole, between the easiest matters experiences reduction is molecule so that happened reduction to h2o: : special issue in science and ethics basuki et al. ) and a oneduring the corrosion process takes place, it will entangle the reaction of reductionfferential model, based on law of physical chemistry. newman (1996) explains that the only reaction takes place in anode is is the standard potential of (a) reaction. the current density is produced by (a) at is the current density evaluated , in which the net current at the electrode is null (this value is obtained experimentally), transfer coefficient for (a) reaction (this value is obtained experimentally, , where äö is the variation in potential between the electrode and the electrolyte (soon after the electronic double layer) and ea is the are involved in the anode reaction, we can assume that its zero only. hence, once the density current is evaluated from eq. (2), the fluxes are then used as boundary condition at the anode for the transport equation. further, the cathode pole, between the easiest matters experiences reduction is h2o iium engineering journal, vol. 12, no. 6, 201 (b) 4h + + o 2 +4e the cathodes current density can once again be evaluated according to the butler volmer’s equation, by considering the (b) reaction only: ib = i0b where : i0b = exchange current density of (b) reaction, άb = transfer coefficient for (b) reaction, zb = number of electrons participating in (b) reaction, ήb = over voltage, with the negative sign it means that the flow of current proceeds from the electrode to the electrolyte, on the reverse of direction with respect to the axis. the boundary conditions for the transport equations (2) are obtained as before, by considering that only the h+ species are involved in the cathode reaction, and therefore only its mass flux will be non 4. initial conditions every condensation has degree of acidity (hydrogen ion exponent) influences to the corrosion process of a metal. svante arhenius comments that acid is a compound, which if it is dissolved in water then it will yield (h alkaline is a compound dissolved in water will yield (oh small fraction from (h2o) water molecules are dissociated in h amount are determined by the constant equilibrium from dissociation reaction , that is: h2o h concentration of (h + ) hydronium ion and (oh condensation generally very low but hardly determines characters of condensation, especially condensation in water. sorensen (1868 concept to avoid usage of a real sm the function of negative logarithm from the concentration of h condensation, and formulated as follows: ph = – log [ch with ch + is concentration from ion h equilibrium of pure water, applies: g journal, vol. 12, no. 6, 2011: special issue in science and ethics 121 +4e → 2h2o; e 0 b = 1,23 v. (11) the cathodes current density can once again be evaluated according to the butler volmer’s equation, by considering the (b) reaction only: , (12) exchange current density of (b) reaction, transfer coefficient for (b) reaction, number of electrons participating in (b) reaction, over voltage, with the negative sign it means that the flow of current proceeds from the electrode to the electrolyte, on the reverse of direction with respect to the axis. the boundary conditions for the transport equations (2) are obtained as before, by hat only the h+ species are involved in the cathode reaction, and therefore -zero: jfe2+ = 0 jh + = ; on x = l (13) initial conditions every condensation has degree of acidity (hydrogen ion exponent) influences to the corrosion process of a metal. svante arhenius comments that acid is a compound, which if it is dissolved in water then it will yield (h + ) hidronium ion. while alkaline is a compound dissolved in water will yield (oh ) hydroxide ion [4]. as known, a o) water molecules are dissociated in h + and oh amount are determined by the constant equilibrium from dissociation reaction , that is: o h + + oh (14) ) hydronium ion and (oh ) hydroxide ion in a liquid condensation generally very low but hardly determines characters of condensation, especially condensation in water. sorensen (1868-1939) further proposes ph and poh concept to avoid usage of a real small number [4]. according to sorensen ph and poh are the function of negative logarithm from the concentration of h + and oh condensation, and formulated as follows: h + ] dan poh = – log [coh ] (15) is concentration from ion h + and coh is concentration of oh equilibrium of pure water, applies: : special issue in science and ethics basuki et al. the cathodes current density can once again be evaluated according to the butler– with the negative sign it means that the flow of current proceeds from the electrode to the the boundary conditions for the transport equations (2) are obtained as before, by hat only the h+ species are involved in the cathode reaction, and therefore different and influences to the corrosion process of a metal. svante arhenius comments that acid is a ) hidronium ion. while xide ion [4]. as known, a and oh ions in the amount are determined by the constant equilibrium from dissociation reaction , that is: ) hydroxide ion in a liquid condensation generally very low but hardly determines characters of condensation, 1939) further proposes ph and poh all number [4]. according to sorensen ph and poh are and oh ions in a ion where at iium engineering journal, vol. 12, no. 6, 201 ph + poh = 14 those concentration of the ions expressed in a set of molar (m), where the molarity expresses that the various solu has ph = 7, so that concentration from both of good ions of h molar. smaller ph value of condensation hence level of the solution acidity excelsior and so do on the contrary. 5. results and discussion finite element method is one of approach method of numeric that bases on the problems at every part of element that is named by finite element. every problem that exists will be finalized with the quadratic approach, where element method has form of matrix equation: where: [k],[kt] = assemble matrix {r} = vector from node magnitude which [r] = assemble style parameter vector global matrix equation hereinafter will be finalized to time, where in this solution it will be used approach of finite difference with the crack global matrix compiler can be w if it is taken è = 1/2 hence will be obtained crack pattern: global matrix equation therefore will have a form of approach to time as follows: g journal, vol. 12, no. 6, 2011: special issue in science and ethics 122 + poh = 14 (16) those concentration of the ions expressed in a set of molar (m), where the molarity expresses that the various solute moles in every 1 condensation liter ( mol/liter). pure water has ph = 7, so that concentration from both of good ions of h + and oh ions equal to 10 molar. smaller ph value of condensation hence level of the solution acidity excelsior and results and discussion finite element method is one of approach method of numeric that bases on the problems at every part of element that is named by finite element. every problem that exists will be finalized with the quadratic approach, where the problem solving form finite element method has form of matrix equation: (17) where: = vector from node magnitude which unknown = assemble style parameter vector global matrix equation hereinafter will be finalized to time, where in this solution it will be used approach of finite difference with the crack-nicholson’s pattern. equation of global matrix compiler can be written down in the form of finite difference as: if it is taken è = 1/2 hence will be obtained crack-nicholson’s pattern, with approach global matrix equation therefore will have a form of approach to time as follows: : special issue in science and ethics basuki et al. those concentration of the ions expressed in a set of molar (m), where the molarity te moles in every 1 condensation liter ( mol/liter). pure water ions equal to 10 -7 molar. smaller ph value of condensation hence level of the solution acidity excelsior and finite element method is one of approach method of numeric that bases on the problems at every part of element that is named by finite element. every problem that the problem solving form finite global matrix equation hereinafter will be finalized to time, where in this solution it nicholson’s pattern. equation of ritten down in the form of finite difference as: nicholson’s pattern, with approach global matrix equation therefore will have a form of approach to time as follows: iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics basuki et al. 123 the numerical solution of those equations which will be visualized by using matlab 7.0 program. the result is shown in fig. 2: (a) (b) (c) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics basuki et al. 124 fig. 2: iron corrosion process based on difference time (a), concentration of iron (b), and temperature condensation (c). based on the obtained figure above, it can be determined that the relation of the longer time required. therefore, the chances that the happening of corrosion is substantially increase, and so do on the contrary. the concentration influence of iron towards the iron corrosion process is greater than the applied iron concentration. therefore, the possibility that the happening of iron corrosion increasingly increases and conversely. third factor that has an effect on is condensation temperature used, ever greater of temperature used hence possibility that the happening of corrosion exactly increasingly minimizes. the statement chimes in with planck-nernst law about mass transport and first faraday’s law where mass that’s yielded or reduced compares straight to time and concentration of metal that’s applied but proportional inversely with condensation temperature. numerical result of the electrical potential equation is also be visualized by using matlab 7.0 program and it is depicted in fig. 3: (a) (b) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics basuki et al. 125 fig. 3: electric potential based to time difference (a) and electric potential beginning (b). based on the above picture, i.e. fig. 3, which obtained for determinable electrical tension the relation of that longer time required hence level of electrical tension value of mean emerging at every node would increasingly increases, and so do on the contrary. the beginning electric potential influence that’s used smaller that’s applied hence electric potential average value also increasingly minimizes, and so does on the contrary. the statement chimes in with planck-nernst’s law about mass transport, where potential electric is compared straight to time. the electrical current also arises during the corrosion process at electrochemistry cell, in which the numerical results of those equations will be visualized in the form of figures by using the matlab 7.0 program. the results are shown in fig. 4: (a) (b) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics basuki et al. 126 fig. 4: electric current based to time difference (a) and condensation temperature (b). based on the fig. 4 that are obtained is known that longer time required hence electric current that emerges at every node increasingly declines, and so do on the contrary. temperature factor also influences to electrical current value that emerges during corrosion process to take place that is ever greater of condensation temperature used hence electric current happened at every node also increasingly increased where both of those relationships chimed in with faraday’s first law and mass transport planck-nernst’s law that is inversely proportional electric current to the time and it compares straight with the condensation temperature. 6. conclusion based on the numerical simulations which have made so it can be concluded that the inferential part of gristle metal part of functioning metal as anode support, in this case there is in the beginning of metal. if the time is longer applied hence part of metal experiencing impairment concentration by the end of iteration would increasingly long in meaning of gristle area corrosion to be longer so that metal mass that reduce by the corrosion more and more and so do on the contrary. the concentration factor of initial iron also influences to corrosion process, that is value excelsior concentration of iron used hence impairment concentration of iron by the end of iteration also increasingly long in meaning of area which gristle corrosion to be broader, so that number of masses that’s yielded for the concentration of larger ones has number of bigger reduced masses and so do on the contrary. temperature factor also influences to iron corrosion that is more high condensation temperature excelsior used in condensation of electrolyte hence degradation of concentration of increasingly short, in meaning of gristle area corrosion to be more minimizes, so that mass reduced that’s yielded to increasingly minimizes and so do on the contrary. at the electrical potential increasingly of time hence the potential electrical average value also increases, while ever greater of beginning electric potential that’s applied hence electric potential value which emerges at every node and electric potential average value also increases, and so do on the contrary. at electric current increasingly increasing of time hence electric current value which emerges that’s increasingly minimizes, while iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics basuki et al. 127 growing of condensation temperature of electrolyte used hence electric current value which emerges to increasingly, and so do on the contrary. acknowledgement we would like to thank the institut teknologi sepuluh nopember-surabaya indonesia, which give us a grant and chance to disseminate an intellectual output of our research. references [1] shifler d. a, “corrosion science”, physical science, vol. 47, 2005, pp. 2335–2352. [2] atkins p.w., physical chemistry, oxford university press, oxford, 1990 [3] newman, j. s., electrochemical systems, prentice-hall, englewood cliffs, new jersey, 1996. [4] sudarmo u., chemistry, erlangga, jakarta, 2006. microsoft word 29-408-1-pb.doc iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 151 multi-level sampling approach for continous loss detection using iterative window and statistical model mohd fo’ad rohani 1 , mohd aizaini maarof 1 , ali selamat 1 and houssain kettani 2 1 faculty of computer science and information systems, universiti teknologi malaysia, 81300 skudai, johor, malaysia 2 department of electrical and computer engineering and computer science, polytechnic university of puerto rico, p. o. box 192017, san juan, puerto rico 00919, usa e-mail: {foad, aizaini, aselamat}@utm.my, hkettani@pupr.edu abstract: this paper proposes a multi-level sampling (mls) approach for continuous loss of self-similarity (loss) detection using iterative window. the method defines loss based on second order self-similarity (soss) statistical model. the optimization method (om) is used to estimate self-similarity parameter since it is fast and more accurate in comparison with other estimation methods known in the literature. probability of loss detection is introduced to measure continuous loss detection performance. the proposed method has been tested with real internet traffic simulation dataset. the results demonstrate that normal traces have probability of loss detection below the threshold at all sampling levels. meanwhile, false positive detection can occur where abnormal traces have probability of loss that imitates normal behavior at sampling levels below 100 ms. however, the loss probability exceeds the threshold at sampling levels larger than 100 ms. our results show the possibility of detecting anomaly traffic behavior based on obtaining continuous loss detection monitoring. keywords: loss of self-similarity (loss), multi-level sampling, anomaly traffic detection, second order self-similarity, iterative window 1. introduction the advanced technology of attack tools and their availability on internet have increased network vulnerability to misuse and performance traffic problems. internet service providers are now faced with the challenging task to providing continuous network traffic monitoring system to ensure that security is well maintained. thus, the need for reliable monitoring of network anomaly traffic detection in ethernet network is crucial to ensure uninterrupted quality of service (qos) performance. this can be achieved by continuously detecting loss of self-similarity (loss) occurrences in network traffic when the packets are treated as a time series [1-4]. malicious traffic such as denial of service (dos) packets have tendency to contribute to the deviation from the self-similarity model [3, 4]. consequently, loss is detected [1-4] and a high percentage of loss detection will iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 152 alert a signal of poor qos performance [5, 6] due to the uncontrolled self-similarity structure. implementation of loss detection with second order self-similarity (soss) statistical model has been introduced in order to attain high speed and accuracy detection needs [2]. previous works in [1, 2] have used fixed sampling and fixed window to detect loss. however, fixed sampling is insufficient to reveal the self-similarity distribution error efficiently [7, 8]. on the other hand, dynamic window is needed for iterative loss detection in order to detect the present of anomaly traffic behavior continuously. in this work, we propose a continuous loss detection using iterative window and multi-level sampling (mls) approach. the optimization method (om) [9, 10] is used to estimate self-similarity parameter or known as hurst (h) value. we have evaluated the loss detection performance using probability of loss detection measurement. this paper is organized as follows: section 2 discusses in brief the self-similarity model and the estimation method of the parameter h. the proposed loss detection method is discussed in section 3 while the experimental and empirical analyses are presented in section 4. finally, our conclusion and future work are summarized in section 5. 2. soss model and estimation method 2.1 second order self-similarity statistical model and parameter estimation method let define a second-order stationary process { ( ), 0}x x t t  with constant mean  , finite variance 2 and autocorrelation ( )k as follow: 2 2[ ( )], [( ( ) )]e x t e x t     (1) 2( ) [( ( ) )( ( ) )] /k e x t x t k       (2) let ( ) ( ){ ( ), 0}m mx x t t  denote the aggregate process of x at aggregation level 0m  . thus, we have: ( ) ( 1) 1 1 ( ) ( ) , 0 mt m w m t x t x w t m      . (3) let ( ) ( )m k  and ( ) ( )m k denote the variance and autocorrelation function of ( )mx respectively. x is called exactly second-order self-similar (esoss) if ( ) ( ) ( ) m k k   for all 1m  . in esoss, the autocorrelation structure is preserved for all m such that: 2 2 21 ) [( 1) 2 ( 1) ] 2 k k k k            (4) where 0k  and 0 1  . x is called asymptotical second-order self-similar (asoss) if )lim (m m k  ~ 2 2 2 1 [( 1) 2 ( 1) ] 2 k k k          (5) where 0k  , 0m  and 0 1  . x is called long-range dependent (lrd) if its autocorrelation function satisfies: ( )k ck   where k   , 0c  and 0 1  . iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 153 there are several methods to estimate h. in this paper we use om that was developed in [9, 10] which was proven relatively fast and accurate compared to other methods such as the wavelet method. the om defines curve-fitting error (cfe) function as ek(β) such as: 2 1 1 ( ( ( ) ( )) 4 k k n k e k k k        (6) where ρ(k) denotes the autocorrelation function of the model with parameter β that we would like to fit the data to, ρn(k) is the sample autocorrelation function of the data, and k is the largest value of k such that it minimize the edge effect for the calculation of ρn(k). if the minimum of ek(β) is less than 10 -3 , then the data fits the model and the minimizer ̂ is picked to be the estimate of the parameter β [9]. 2.2 loss of self-similarity detection model let x(t) be a stochastic time series data with second order stationary property. the autocovariance decay of x(t) and aggregated x (m) (t) that follow esoss model can be written as in equation (7): , lim ( ) ( )m m k k k    ~ 0 c k  (7) where m is sampling level, k is correlation lag, co is constant and β is self-similarity parameter. equation (7) shows sampling level m does not play an important role in the autocorrelation process for exactly self-similarity model. nevertheless, the self-similarity processes can also be treated as processes x(j) in the class x of those stationary processes that feature an asymptotic decay in autocovariance [11]. thus, we should take into account esoss and asoss models concurrently in order to estimate the self-similarity parameter for normal and abnormal traffic correctly. to develop loss detection using both models; let denotes autocovariance, variance and autocorrelation for aggregated process x (m) (t) as shown in equation (8), (9) and (10): , lim ( )m m k k  ~ 1 c m k    (8) lim (0)m m   ~ 2 c m  (9) , , ( ) lim ( ) lim (0) m m mm k m k k k            ~ 1 2 c m k c m       ~ 3 c k  (10) where c1, c2 and c3 are constants. previous works in [9, 12, 13] have assumed normal internet traffic always follow esoss model where its characteristics can be described by equations (8) to (10). it is clearly shown in equation (10) that autocorrelation decay is not influenced by aggregation (m) parameter for normal traffic. in esoss model, the correlation lag (k) plays an important role to obtain high accuracy self-similarity parameter (β) estimation. iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 154 a high density of dos packet, such as in the presence of malicious traffic dos traffic, can produce self-similarity distribution error and disturbs internet traffic behavior. the normal characteristics of equations (8), (9) and (10) are disrupted. consequently, loss is detected. equation (11) shows that for abnormal traffic, the autocovariance and variance decay of 1 c m k    and 2 '( )c m  are not identically distributed. as a result, the characteristic of equation (11) deviates from normal self-similarity pattern as shown in equation (10). , , ( ) lim ( ) lim (0) m m m m k m k k k            ~ 1 2 ' ( ) c m c m k             ≄ 3 c k  (11) equations (10) and (11) demonstrate that aggregation (m) and correlation lag (k) are two parameters that need to be considered for estimating the cfe (or ek(β)) value in equation (6) correctly in order to improve loss detection accuracy. previous work in [2] had used om to estimate self-similarity parameter to detect anomaly traffic. their method is based on loss detection and their definition of normal traffic behavior as follows: l n h cf (12) where : [0.5,1] l h h  and n cf : cfe < threshold (at fixed sampling m). on the other hand, abnormal behavior defined as loss is detected at normal fixed sampling such as ' n cf where cfe threshold . nevertheless their technique has only considered fixed sampling such as 10ms or 100ms which is not sufficient to reveal the hidden self-similarity distribution error accurately. uncovering loss at multi-level sampling (mls) time scale was suggested in [7, 8] in order to reveal the hidden selfsimilarity distribution error effectively. we investigate multi-level sampling at micro sampling range that is below one second which known as engineering factor [14] for internet protocol design. we limit the value of correlation lag below five hundred in order to avoid longer time estimation in order to maintain high speed loss detection performance. 3. continous loss detection using iterative window and multi-level sampling approach we have considered a multi-level sampling approach with sampling level (m) in the range of 10ms_≤_m_≤_1000ms in order to investigate the proposed loss detection method [7, 8, 14]. we define iterative window as the window size is continuously incremented in a defined fixed size window denoted by δw. each of packet traces that accumulated at the current iterative window buffer is then being evaluated for loss detection occurrence. the proposed loss detection method has considered esoss and asoss models with their properties are described in equations (7), (10) and (11). meanwhile, the normal and abnormal traffic behavior has implemented definition based on equation (12) for each of fixed sampling traces in the mls structure. the procedure of continuous loss detection method consists of two processes that includes initializing iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 155 window and loss detection process. the initialization window is done to fulfill the minimum window size requirement before correct estimation of h [2] can be obtained. this involves window size that meets the cfe criterion below the threshold value. in addition, the definition of initialization window also considers normal lrd behavior such as shown in equation (12). the process of loss and soss detection can only be continued if the initialization window has been established. however, if initialization window fails (if) even though enough capturing time is given such as 30 minutes as used in [12, 13], we declare malicious traffic behavior is captured. the algorithm for initialization window process is shown in fig. 1. fig. 1: initialization window process. on the other hand, continuous loss and soss detection with iterative window is based on whether cfe_>_10 -3 for loss and cfe_≤_10 -3 for soss. similar to the process of initialization window procedure, the normal self-similarity behavior that follow soss model is also taken into account the normal lrd behavior as defined in equation (12). the loss detection algorithm is shown in fig. 2. fig. 2: loss and soss detection process. we introduce measurement probability of loss detection to assess the effectiveness of the proposed detection algorithm. thus, we define iterative window update in a continuous set stepsize, δw set window, w = w + δw while (w < wmax) estimate h and cfe if (cfe < threshold) && (0.5 < h < 1) inialization window success soss is detected proceed with loss detection else increment δw++ set w = w + δw end end if (w ≥ wmax) && (errcheck = 0) initialization window failed suspect suspicious behavior end while (w < wmax) increment δw++ update w=w+ δw estimate h and cfe if (cfe < threshold) && (0.5 < h <1) soss is detected else loss is detected end end iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 156 hunting mode as 1 2 3 { , , ,...., } i n w w w w w for 1, 2, 3,.....,i n . for each of the updated window wi, if loss is detected then we update loss window equal to wi or else update soss window with wi. suppose we have the updated loss and soss window as follows: 1 2 3 ( ) { , , ,...., } k loss i l l l l for 1, 2, 3,.....,i k and 1 2 3 ( ) { , , ,...., } m soss j s s s s for 1, 2, 3,.....,j m . then, we define the probability of loss (pl) and the probability of soss (ps) detection using equations (12) and (13): 1 1 1 ( ) k i l k m i j k j k l p p loss l s          , (12) 1 1 1 ( ) m i s k m i j k j k s p p soss l s         (13) there are three possible conditions for pl and ps value when we change the sampling level value from lower m to higher m as follows: i) pl < ps ii) pl = ps iii) pl > ps the first condition represents the normal behavior of internet traffic that dominated by self-similarity model and we refer this as near to normal. the smaller value of pl indicates the higher probability of internet traffic follows the normal soss model. the critical point occurs when both probability values are the same. at this point, loss and soss occurrences are equally detected and we refer this as critical point where pl and ps equal 0.5. on the other hand, the traffic behavior is treated as near to abnormal when the value of pl is larger than ps which shows self-similarity leakage is dominant. this condition is usually occurring at higher sampling level such as m is larger than 500 ms. at this condition, we can predict that the traffic is deviated from normal soss model and can be treated as contains suspicious or malicious packets traffic such as dos activities. 4. experiments and empirical analyses we have simulated the fsksmnet internet traffic traces collected on september 29, 2006 at faculty of computer science and information systems (fcsis) [7] in order to evaluate the proposed loss detection method. the network infrastructure consists of ten vlans with 100basefx fast ethernet backbone which is connected to university gigabit backbone. the simulation is divided into normal and abnormal traffic. normal traffic is defined as internet activities that strictly follow fcsis network policy. on the other hand, abnormal traffic contains simulated injection of dos flooding packets at controlled rate. each of simulation traces is about 30 minutes and the details are shown in table 1. fnet-1 and fnet-2 are normal traces while fnet-3 contains udp, tcp syn and tcp rst, while fnet-4 has tcp syn and udp flooding packets. in the experiments, we set correlation lag k equal 100 in order to ensure the elapse time for correlation process in the om iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 157 remains fast and optimize. if we set higher value of k, we need more sample size packets at the higher sampling level m in order to fulfill minimum window requirement as required in the proposed loss detection method. in the parameter estimation using om, the threshold value for estimated cfe is set to 10 -3 to obtain correct estimation h as used in [2, 9, 10]. we choose sampling level randomly equal 10ms, 50ms, 100ms, 200ms, 500ms, 700ms and 1000ms [7, 8, 14] to represent multi-level sampling structure in the experiments. table 1: fsksmnet dataset 2006 [7] fsksmnet-normal trace total packet fnet-1 ip=4197509: tcp(97.87%), udp(1.69%), icmp(0.12%), igmp(0.01%), others(0.31%) fnet-2 ip=7371721: tcp(92.17%), udp(0.93%), icmp(0.07%), igmp(0.004%), others(6.83%) fsksmnet-abnormal trace total packet fnet-3 ip=7468026: tcp(85.60%), udp(14.35%), icmp(0.04%), igmp(0.01%), others(0.005%) fnet-4 ip=9707011: tcp(69.17%), udp(30.77%), icmp(0.04%), igmp((0.005%), others(0.02%) the results of continuous loss detection for fsksmnet traces are shown in fig. 3 and fig. 4 respectively. fig. 3 illustrates loss detection for normal traces while fig. 4 for malicious traces. our simulation result shows zero probability of loss is detected at all sampling levels of m for normal trace fnet-1. the result demonstrates that the normal fnet-1 trace strictly follows esoss model as clearly shown in fig. 3(a). however, there is a tendency for normal internet activities that produce traffic behavior with a small portion of loss detection occurs at higher value of m such as above 500ms. this can be illustrated by normal trace fnet-2 in fig. 3(b). meanwhile, our result also demonstrates that loss is hardly detected for malicious traces fnet-3 at small value of m such as lower than 100ms as shown in fig. 4(a). however, the loss occurrence is revealed clearly at higher value of m such as larger than 100 ms. the results show that multi-level sampling approach can improve loss detection performance as illustrates in fig. 3 and fig. 4. the finding is agreed with previous results in [7, 8] where loss detection model is implemented by using the property of esoss and asoss models such as shown in equations (7), (10) and (11). iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 158 0 0.5 1 1.5 2 2.5 3 3.5 x 10 4 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 50ms100ms200ms500ms 700ms window p ro b a b il it y o f d e te c ti o n loss soss (a) 0 0.5 1 1.5 2 2.5 3 3.5 x 10 4 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 50ms100ms 200ms 500ms 700ms window p ro b a b il it y o f d e te c ti o n loss soss (b) fig. 3: loss detection for normal traces: fnet-1 (a) and fnet-2 (b). another indication for malicious or suspicious behavior presence in the traces is that the failure to obtain the initialized window as illustrated by abnormal trace fnet-4 in fig. 4(b). as shown in fig. 4(b), the algorithm is not able to obtain the initialized window or window initialization failed (if) when the value of m is larger than 100 ms. this is an additional alert signal that reveals the presence of abnormal traffic packets in the network despite the capability to imitate soss model behavior at lower sampling such as value of m is less than 100 ms. iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 159 0 0.5 1 1.5 2 2.5 3 3.5 x 10 4 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 50ms 100ms200ms500ms 700ms window p ro b a b il it y o f d e te c ti o n loss soss (a) 0 1 2 3 4 x 10 4 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 200ms 100ms 50ms 500ms 700ms window p ro b a b il it y o f d e te c ti o n if loss soss (b) fig. 4: loss detection for abnormal traces: fnet-3 (a) and fnet-4 (b). the probability of continuous loss detection for normal and abnormal traffic is shown in fig. 5. the loss probability for the normal fnet-1 trace is less than 0.1 for all values of m, which is much smaller than the threshold 0.5. similarly, the normal fnet-2 trace has probability of loss value less than 0.1 at sampling level m below 500 ms but increase slowly to 0.4 at higher value of m larger than 500 ms. however, the probability of loss for malicious traces fnet-3 and fnet-4 have similar patterns with fnet-2. they hide the self-similarity distribution error at value of m below 100 ms but the error is exposed clearly at value of m larger than 100 ms. the result in fig. 5 also illustrates that both malicious traces fnet-3 and fnet-4 have exceeded the critical probability of loss threshold at 0.5. this will give a clear alarm signal to network security analyst that a severe esoss leakage is occurred during the continuous loss detection process. we iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 160 define esoss leakage as in any level of m; there is at least one sampling level where loss can be detected. another word, the self-similarity leakage demonstrates the breach indication of esoss model property. our assumption is that if probability of loss value estimated below the threshold i.e. 0.5 l p  , then the traffic behavior will be dominated by soss model. otherwise, the majority of updated windows are detected with loss which alerts a large amount of esoss leakage occurrence. this can be shown in fig. 5 where fnet-3 and fnet-4 have critical esoss leakage warning compared to fnet-1 and fnet-2 at sampling level m larger than 100ms. thus, the probability of loss measurement can be used as a technique to reveal the abnormal traffic behavior in a continuous loss detection at multi-level sampling approach as illustrates in fig. 5. 0 10 50 100 200 500 700 1000 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 m-level ( ms ) t o ta l p r ( l o s s ) d e te c ti o n fnet-1 fnet-2 fnet-3 fnet-4 threshold fig. 5: probability of continuous loss detection. 5. conclusion and future work in this paper, we proposed a multi-level sampling approach for continuous loss of self-similarity (loss) detection monitoring using iterative window technique. the loss detection method is based on second order self-similarity statistical (soss) model while the optimization method (om) is used to estimate the self-similarity parameter. the proposed method uses cfe criterion and lrd behavior to detect loss. if the estimated cfe is not exceeding threshold value and h is in the range of lrd, then it is identified as soss detection. otherwise, loss is detected. the probability of loss introduced in this work can continuously measure loss detection performance. our simulation results show that at all sampling levels, normal traces is usually exhibit small probability of loss detection compared to probability of soss detection. on the other hand, there is a possibility for malicious traces to have probability of loss detection that imitate normal traffic behavior which normally occur at lower sampling level such as below 100ms. however, the probability of loss detection for abnormal traffic is clearly exposed when sampling level is larger than 100 ms. this is a promising approach to develop an improved continuous loss detection for anomaly traffic behavior monitoring based on soss model iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 161 and multi-level sampling approach. in future, we plan to implement continuous loss detection method using average value of multi-level sampling parameters such as average cfe and h in multi-level sampling structure. moreover, the approach can verify whether internet traffic traces are preserving or violating the self-similarity property based on esoss and asoss models in order to develop a reliable network traffic monitoring systems. acknowledgement this work was funded by universiti teknologi malaysia (utm) under the human resource development program. the authors are grateful to dr. sulaiman mohd noor at cict, utm and mr. firoz at unit it, fsksm for their help in preparing the simulation of fsksmnet 2006 datasets. references [1] w. h. allen and g. a. marin, "the loss technique for detecting new denial of service attacks," in southeastcon, 2004. proceedings. ieee, alabama, usa, 2004, pp. 302-309. [2] m. y. idris, a. h. abdullah, and m. a. maarof, "iterative window size estimation on self-similarity measurement for network traffic anomaly detection," international journal of computing & information sciences, vol. 2, pp. 83-91, 2004. [3] w. schleifer and m. mannle, "online error detection through observation of traffic self-similarity," in communications, iee proceedings-, 2001, pp. 38-42. [4] w. yan, e. hou, and n. ansari, "anomaly detection and traffic shaping under self-similar aggregated traffic in optical switched networks," in icctz003, 2003, pp. 378-381. [5] a. erramilli, o. narayan, and w. willinger, "experimental queueing analysis with long-range dependent packet traffic," networking, ieee/acm transactions on, vol. 4, pp. 209-223, 1996. [6] k. park, g. kim, and m. e. crovella, "effect of traffic self-similarity on network performance," in performance and control of network systems, dallas, tx, usa, 1997, pp. 296-310. [7] m. f. rohani, m. a. maarof, a. selamat, and h. kettani, "uncovering anomaly traffic based on loss of self-similarity behavior using second order statistical model," international journal computer science and network security, vol. 7, pp. 116-122, september 2007. [8] m. f. rohani, m. a. maarof, a. selamat, and h. kettani, "loss of self-similarity detection with second order statistical model and multi-level aggregation iium engineering journal, vol. 11, no. 2, 2010 mohd fo’ad rohani et al. 162 approach," in international conference on robotics, vision, information and signal processing (rovisp2007), 2007, pp. 152-156. [9] h. kettani, "a novel approach to the estimation of the long-range dependence parameter." vol. phd: university of wisconsin – madison, 2002. [10] h. kettani and j. a. gubner, "a novel approach to the estimation of the long-range dependence parameter," circuits and systems ii: express briefs, ieee transactions on, vol. 53, pp. 463-467, june 2006. [11] g. mazzini, r. rovatti, and g. setti, "on the aggregation of self-similar processes," ieice transactions fundamentals, vol. e88–a, pp. 2656 – 2663, october 2005. [12] w. e. leland, m. s. taqqu, w. willinger, and d. v. wilson, "on the self-similar nature of ethernet traffic," in acm sigcomm, 1993, pp. 183–193. [13] w. e. leland, m. s. taqqu, w. willinger, d. v. wilson, and m. bellcore, "on the self-similar nature of ethernet traffic (extended version)," ieee/acm transactions on networking, vol. 2, pp. 1-15, 1994. [14] c. d. cairano-gilfedder and r. g. clegg, "a decade of internet research -advances in models and practices," bt technology journal, vol. 23, pp. 115-128, october 2005. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 consolidation integrated buoyancy equation for soft ground improved with lightweight polyurethane foam diana che lat1*, ismacahyadi bagus mohamed jais2, nazri ali3, nor zurairahetty mohd yunus3, nor hibatul wafi nor zarin4 and atiqah najwa zainuddin1 1 faculty of civil engineering, universiti teknologi mara (uitm) johor, pasir gudang campus, 81750, masai, johor 2 faculty of civil engineering, universiti teknologi mara (uitm) selangor, shah alam campus, 40450, shah alam, selangor 3 school of civil engineering, faculty of engineering, universiti teknologi malaysia, 81310 johor bahru, johor 4 cawangan kejuruteraan cerun, jkr malaysia, jalan sultan salahuddin, 50582 kuala lumpur *corresponding author: dianacl@uitm.edu.my (received: 2nd january 2021; accepted: 30th october 2021; published on-line: 4thjanuary 2022) abstract: consolidation settlement occurs when a saturated soil is subjected to an increase in overburden pressure that causes a volume change in the soil. when a lightweight material is used as a ground improvement, the stress is reduced as the soft soil is partially removed and replaced by the lightweight material. in addition, the improved ground with lightweight material has a potential to uplift due to the buoyancy of lightweight material. the uplift force reduces the stress imposed on the underlying soil as it acts in the upward direction, thus further reducing the consolidation settlement. this study is executed to produce an alternative equation for consolidation settlement incorporating the buoyancy effect for lightweight polyurethane (pu) foam as a ground improvement method. a rowe cell consolidation laboratory test was conducted on untreated marine clay soil as well as on improved marine clay with different thicknesses of lightweight pu foam. validation of the laboratory test results was done by finite element analysis, plaxis 2d. the thickness of pu foam governs the buoyancy and the hydrostatic pressure of water displaced by pu foam, which is incorporated in the alternative equation. the alternative consolidation settlement equation is applicable for ground improved with lightweight polyurethane foam and found to be more economical and practical as the buoyancy is taken into account in the equation. abstrak: mendapan pengukuhan berlaku apabila tanah tepu mengalami peningkatan tekanan beban yang menyebabkan perubahan isipadu tanah. apabila bahan ringan digunakan sebagai penambahbaikan tanah, tekanan akan berkurang kerana sebahagian tanah lembut dikeluarkan dan diganti dengan bahan ringan. selain itu, tanah yang diperbaiki dengan bahan ringan berpotensi untuk terangkat ke atas keranan daya apung bahan ringan. daya angkat bahan ringan mengurangkan tekanan yang dikenakan ke atas tanah kerana daya bertindak ke arah atas, dan seterusnya megurangkan mendapan pengukuhan. kajian ini dijalankan untuk menghasilkan persamaan alternatif bagi mendapan pengukuhan dan digabungkan dengan kesan daya apung untuk busa poliuretena ringan (pu) sebagai kaedah penambahbaikan tanah. ujian makmal mendapan pengukuhan menggunakan peralatan rowe cell dilakukan pada tanah liat marin yang asal serta yang diperbaiki dengan ketebalan busa pu ringan yang berbeza. 1 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 pengesahan hasil ujian makmal dilakukan dengan analisis elemen terhingga, plaxis 2d. ketebalan busa pu mempengaruhi daya apung dan tekanan hidrostatik bagi kedalaman air yang disesarkan oleh busa pu dan digabungkan dalam persamaan alternatif. persamaan alternatif mendapan pengukuhan tersebut boleh digunapakai untuk pembaikan tanah menggunakan bahan ringan busa poliuretena dan didapati menjimatkan kos dan praktikal kerana keapungan diambilkira didalam persamaan tersebut. keywords: soft ground; consolidation settlement; buoyancy; polyurethane; lightweight 1. introduction construction on soft clay causes consolidation settlement of the soil due to increased overburden load and low permeability of clay soil. in order to reduce the overburden load, lightweight materials are proposed as a ground improvement for soft clay. some of the lightweight fill materials such as foamglass, sawdust and bark residue, foamed concrete, lightweight clay aggregate, shredded tires, floating bamboo and plastic bags [1,2] have been investigated as a ground improvement method. low et al. [3] proposed a new floating foundation system, namely a lightweight concrete infill buoyant system whereby plastic bags, used tires, and tubes were used as a lightweight material for foundation construction whilst bamboo and bakau were used to encapsulate the waste materials and form a composite floating foundation. on top of that, lightweight foams are also currently in demand due their ability to enable fast construction work with less manpower as the foam can be pre-fabricated in the factory. this study focuses on lightweight foam, namely polyurethane (pu) foam, as a ground improvement method. in 1937, dr. otto bayer was the first person to produce and investigate polyurethane [4]. polyurethane is a class of polymers with a mix of polyol (oh) and isocyanate (-nco) that react during polymerization of polyurethane [5-8]. nowadays, pu foams are recognized as one of the most crucial classes of polymers that transform the quality of human life [9]. it was predicted that the worldwide consumption of pu will be over 79 billion usd in 2021 [10]. as the demand increases, the sustainable production of pu foam is very crucial. polyol can be produced from bio-based oil and crude glycerol [11-13] whilst isocyanate can be produced from non-isocyanate material (nipu), which is non-petroleum based [14-17]. when this lightweight material is used as a ground improvement method on saturated soil, buoyancy of the material may cause uplift. excessive uplift may damage the structure founded on it [18]. the buoyancy is an upward force exerted by a fluid that acts on an immersed object. over two millennia ago, archimedes of syracuse [19] developed the archimedes’ principle, which states that “any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.” the buoyancy acting on an underground structure in either shallow or deep foundation was measured and compared with archimedes’ principle [20-22]. frydelund and aaboer [23] had reported on a few failure cases of embankment, which was founded on lightweight geofoam due to buoyancy. in 1987, the first lightweight geofoam, namely expanded polystyrene foam (eps) fill built-in norway, floated off during an unpredicted rainfall season and rising flood waters. in thailand, the unexpected water level washed away a road filled with eps. the geofoam experienced uplift during flooding as the weight of earthfill overlying the foam was inadequate. various methods have been proposed to prevent the effect of hydrostatic uplift pressure, such as providing adequate load overlying the foam, proper drainage underneath the foam and installation of ground anchors [24]. 2 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 consolidation settlement occurs when a saturated soil is subjected to an increase in overburden pressure that causes a soil volume change. the consolidation settlement reduces as the saturated soil is partially removed and replaced with the lightweight pu foam. in addition, the pu foam that is immersed in water as well as in saturated soil, produces a buoyant force that acts in an upward direction that might further reduce the consolidation settlement of the soil. therefore, the consolidation settlement considering the effect of buoyancy for the ground improved with pu foam is investigated in this study. 2. methodology the consolidation settlement test for untreated and treated soil samples with different thickness of pu foam was executed utilizing rowe cell. the rowe cell was developed at manchester university, uk by professor rowe [25]. the detailed description of the principles and practice of rowe cell testing are given in head [26]. in the rowe cell, the test sample is loaded hydraulically by water pressure acting on a flexible diaphragm. drainage of the sample can be controlled and pore water pressure is measured [27]. the advantages of rowe cell over oedometer test includes minimum vibration effects, measurable pore water pressure, as well as the execution of the saturation process [26]. rowe cell differs from oedometer as the load is applied continuously instead of incrementally. cell pressure, back pressure, and pore water pressure drainage line are attached on top and bottom part of the rowe cell apparatus as shown in fig. 1. fig.1: rowe cell apparatus. 2.1 rowe cell consolidation test on saturated marine clay with pu foam partial replacement the test procedure for rowe cell consolidation test on saturated clay is as shown in fig. 2. prior to the testing, the calibration of the rowe cell apparatus was performed according to bs1377-part 6:1990 [28] and head [26]. for sample preparation, one kilogram of oven dried soil sample was mixed with distilled water at 1.4 times the liquid limit to form a slurry before placing it into the rowe cell mould. the pu foam is produced by mixing polyol and isocyanate until it reacts, expands and hardens to form pu. next, the sample of soil is placed inside the mould followed by the replacement of pu foam on the soil sample. it was followed by the placement of the top cell which was attached to lvdt, load cell, and cell pressure. back pressure and pore pressure were attached to the bottom cell. the determination of consolidation and buoyancy behaviour of the clay soil improved with pu foam were carried out on a few samples of pu foam. 3 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 partial replacement of the soft clay with pu foam was done at shallow depth. thus, in this laboratory test, the thickness of soft clay was 25 mm whilst the thicknesses of pu foam were 5 mm, 10 mm, 15 mm and 20 mm which were equivalent to 20%, 40%, 60% and 80% of pu foam to initial soft clay thickness respectively. in general, there were two phases during the consolidation integrated buoyancy test: the saturation and consolidation phases. the saturation process was carried out by applying cell pressure and back pressure alternately until skempton’s degree of saturation value,  equalled or exceeded 0.95. during the consolidation process, the samples were tested in 150 mm diameter mould of rowe cell with the effective overburden pressure of 10, 20, 50, 100, 200 and 400 kpa. the test procedures are described in detail in bs1377-part 6:1990b for step-loading test using rowe cell [28]. all samples for four (4) different polyurethane foam thicknesses and untreated soil samples were tested and the data recorded using data system 7.2 (ds7) software by ele international. fig. 2: procedure of rowe cell consolidation test. 2.2 the validation of rowe cell test with finite element model plaxis 2d the validation of rowe cell laboratory test results was done with finite element model of plaxis 2d [29]. the finite element replicates the condition of pu foam construction at a shallow depth of road/walkway foundation and the typical cross-section is as shown in fig. 3. the material model used in the finite element analysis was a plane strain with 15 nodes with a standard fixities boundary. under long structure, the strain in the longitudinal direction will be zero (except at each end), therefore, strain takes places only in the plane of cross-section producing plane strain with effective volumetric modulus, k’ subject to effective young’s modulus, e’ and poisson’s ratio, v’ as in eq. (1): k’= e’/[2(1+v’)(1-2v’)] (1) the soft clay was in undrained condition as it is the most critical condition that the saturated clay experienced during and after construction due to very low permeability of the soil. however, the shear strength parameter input in soft-soil creep model in plaxis only allowed the use of effective shear strength parameter as the water is not supposed to resist any shear stress. the finite element model of the existing condition of the site before ground improvement is as shown in fig. 4 whilst fig. 5 shows the finite element model of the site after ground improvement with pu foam partial replacement at shallow depth of soft clay. table 1 shows the details of subsoil and pu properties used in the finite element model whilst fig. 6 shows the detailed cross-section for the ground improved with 1 m thickness of pu foam as an example. the effective shear strength parameters of the clay 4 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 were obtained from the consolidated undrained (cu) triaxial strength test whilst the properties of pu foam were obtained from the unconfined compressive strength test. the finite element model for the existing condition consisted of 2.5 m thick soft clay, followed by a hard layer of about 10 m thick. a layer of pu foam was used as a ground improvement method varying in thickness from 0.5 m, 1 m, 1.5 m and 2 m, which was equivalent to 20%, 40%, 60% and 80% of initial soft clay thickness, respectively. this was equivalent to the thickness of pu foam used in rowe cell consolidation test, as shown in table 2. the geotextile separator shown in figs. 4 and 5 functioned as a separator between soft clay and pu foam which did not contribute any strength, therefore, it was not modelled in plaxis. the fem analysis was executed for 5 years which is equivalent to 90% degree of consolidation based on the coefficient of consolidation, cv obtained for the clay sample. fig. 3: typical cross-section of pu foam construction at shallow depth of road foundation. fig. 4: cross-section of existing site in finite element model. fig. 5: cross-section of the site after ground improvement with pu foam partial replacement at shallow depth of soft clay. table 1: properties of soil and pu soft clay hard layer pu type unit undrained drained non-porous model soft soil creep mohr coulomb linear elastic unsat [kn/m³] 10 18 3 sat [kn/m³] 16 20 kx [m/day] 1.45e10-5 0.010 ky [m/day] 1.45e10-5 0.010 eref [kn/m²] 50000 30000  [-] 0.495 0.3 0.3 c’ref [kn/m²] 5 3 2 5 ’ [°] 23 22 18 30 * 0.093 * 0.041 * 0.0046 5 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 fig. 6: cross-section of improved ground with subsoil properties. table 2: the details of pu foam thickness in fem analysis and rowe cell laboratory test % pu foam to initial soft clay thickness pu foam thickness in rowe cell lab (mm) (initial soft clay thickness = 25 mm) pu foam thickness in fem (m) (initial soft clay thickness = 2.5 m) 20% 5 0.5 40% 10 1 60% 15 1.5 80% 20 2.0 3. results and discussion the condition of the pu foam before and after rowe cell test is shown in fig. 7. the pu foam did not show any distress or crack after the consolidation process, indicating that it was highly resistant to compression. therefore, pu foam is currently one of the best alternative ground improvement methods for soft soil because of its many advantages [3032]. the design of pu foam as a ground improvement takes into account the effect of buoyancy in the consolidation process. thus, the current consolidation settlement equation was modified to integrate the buoyancy effect of the pu foam. the buoyant force, fb acts in the opposite direction to the overburden load pressure (p) as shown in fig. 8. therefore, a buoyant force is able to reduce the consolidation settlement of the soft ground due to the increased load. fig. 7: conditions of pu foam before and after rowe cell consolidation test. fig. 8: buoyant force acting on pu foam at shallow depth of soft clay. from the rowe cell laboratory consolidation test as well as the finite element model, the compressibility index of the soil improvements with pu foam, ccpu for different thickness of pu foam were obtained. existing consolidation settlement as in eq. (2) is used to calculate the existing ground as well as improved ground based on the ccpu 6 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 obtained. however, the consolidation settlement equation based on the compressibility index, cc, of existing soft clay is more practical instead of ccpu, therefore, eq. (2) was modified to produce an alternative equation that incorporated the buoyant force, fb, and hydrostatic pressure at the pu foam area, uhpu, as in eq. (3). since pu foam is a lightweight material, the buoyant force is introduced by the weight of water that is displaced by the pu foam, fb, as in eq. (4) and this is in line with archimedes’ principle [19] and equivalent to the hydrostatic pressure at the pu foam area uhpu. the buoyant force acts in the opposite direction to the overburden load, and as the pu foam thickness increases, the buoyant force increases as more water is displaced by the pu foam in the saturated soil. therefore, a buoyant force is able to reduce the consolidation settlement of soft ground, . pu = 𝐶𝑐𝑝𝑢.𝐻 1+𝑒0 log [ 0 ′ +𝑝𝑢+ 0 ′ +𝑝𝑢 ] (2) the initial effective stress in the alternative equation of consolidation settlement integrated buoyancy for the ground improved with pu foam as in eq. (3) refers to the effective stress of the soft clay soil, o’, the stress from pu foam pu and the hydrostatic pressure at pu foam, uhpu. the increase in the effective stress refers to the applied load pressure,  and the buoyant force, fb, which acts in the opposite direction of the applied load pressure, . fig. 9 shows an example of the improved ground condition with the detailed parameters for elaboration on the alternative equation. the alternative equation applicable for normally consolidated soil with an overconsolidated ratio ocr value of 1. fig. 9: example of improved ground condition with detailed parameters for elaboration of the alternative equation.  = 𝐶𝑐𝐻 1+𝑒0 log [ 0 ′ +𝑝𝑢+𝑈ℎ𝑝𝑢+−𝐹𝑏 0 ′ +𝑝𝑢+𝑈ℎ𝑝𝑢 ]  = 𝐶𝑐𝐻 1+𝑒0 log [ 0 ′ +𝑝𝑢+ 0 ′ +𝑝𝑢+𝑈ℎ𝑝𝑢 ] (3) where: cc = compression index for marine clay soil h (m)= drainage path length eo = initial void ratio o’ (kpa)= initial effective stress pu (kpa)= stress from pu foam  (kpa) = the increase of overburden stress fb 7 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 fb (kn) = buoyant force per square meter area = weight of water displaced by pu foam (uhpu) fb = uhpu = w.tpu (4) figure 10 shows the relationship between load pressure and settlement for the ground improved with pu foam with 20% pu foam thickness to initial soft clay. the comparisons are made between the results of rowe cell consolidation laboratory test (%pu-lab), finite element model (%pu-fem), consolidation settlement integrated buoyancy equation (%pu new eq) and existing consolidation settlement equation (%pu ex eq). all the results show good agreement with each other with the difference tolerance less than 20% except for the existing consolidation equation whereby the settlement value is overpredicted and the tolerance is more than 20%. the results are also compared with the untreated soil sample based on rowe cell consolidation laboratory test and finite element model in the same graph. for untreated soil samples, the settlement value obtained from rowe cell laboratory test (soil only-lab) is very close to the finite element analysis results (soil only-fem). the settlement reduces with the ground improvement of 20% pu foam to initial soft clay thickness. a similar trend occurs for other thicknesses of pu foam of 40%, 50%, 60% and 80% as shown in figs. 11 to 14. fig. 10: load pressure and settlement relationship for untreated and improved soil sample (20% pu foam to initial soft clay depth) fig. 11: load pressure and settlement relationship for untreated and improved soil sample (40% pu foam to initial soft clay depth). 8 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 fig. 12: load pressure and settlement relationship for untreated and improved soil sample (50% pu foam to initial soft clay depth). fig. 13: load pressure and settlement relationship for untreated and improved soil sample (60% pu foam to initial soft clay depth). fig. 14: load pressure and settlement relationship for untreated and improved soil sample (80% pu foam to initial soft clay depth). all the samples of improved soil with pu foam indicate that the settlement value is overpredicted by the existing consolidation settlement equation. the existing equation does not take into consideration the buoyancy effect of the pu foam to the consolidation settlement of the ground. therefore, an alternative equation of consolidation settlement integrated buoyancy should be applied for improved ground with pu foam to avoid overprediction of settlement value thus more conservative and might increase the construction cost. figure 15 shows the combination of load pressure vs consolidation settlement for the soil improved with different thickness of pu foam ranging from 20% to 80% of pu foam to initial soft clay thickness as well as the untreated soil sample. the trend shows that the consolidation settlement reduces with the increase in pu foam -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 0 50 100 150 200 250 300 350 400 450 s e tt le m e n t (m m ) load pressure (kpa) soil only-lab soil only-fem 50% pu fem 50% pu lab 50%pu new eq 50% pu ex eq -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 0 50 100 150 200 250 300 350 400 450 s e tt le m e n t (m m ) load pressure (kpa) soil only-lab soil only-fem 60% pu-lab 60% pu-fem 60%pu new eq 60% pu ex eq -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 0 50 100 150 200 250 300 350 400 450 s e tt le m e n t (m m ) load pressure (kpa) soil only-lab soil only-fem 80% pu-lab 80% pu-fem 80%pu new eq 80% pu ex eq 9 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 thickness. with the increase in pu foam thickness, the overburden pressure decreases as the lightweight pu foam has partially replaced the soft soil and the upward buoyant force increases as well, thus the settlement reduces. fig. 15: load pressure and settlement relationship for untreated and improved soil sample with different thickness of pu foam to initial soft clay depth. 4. conclusion the design of lightweight pu foam as a ground improvement method should take into account the effect of buoyancy in the consolidation process. this is due to the density of pu foam which is lower than water as well as the saturated soil which has the tendency of uplift due to buoyancy. based on the results of rowe cell consolidation laboratory test as well as the finite element model, plaxis, the existing consolidation settlement equation was modified to integrate the buoyancy effect of the pu foam as a ground improvement. the buoyant force that is introduced by pu foam, fb, equivalent to the weight of water displaced by pu foam is in line with archimedes’ principle and acts in the opposite direction of the overburden load pressure. the consolidation settlement value of the improved soil samples was overpredicted by the existing consolidation settlement equation as the buoyancy effect of the pu foam to the consolidation settlement of the ground was not accounted for. therefore, an alternative equation of consolidation settlement integrated buoyancy might be applied for the ground improved with pu foam in order to avoid overprediction of consolidation settlement value; which is more conservative and increases the construction cost. references [1] ibrahim a, huat bb, asadi a, nahazanan h. (2014) foundation and embankment construction in peat: an overview. electronic journals of geotechnical engineering, 19: 10079-10094. [2] zhang j, zhai jf, wang xm. (2014) instrumented full scale test and numerical analysis to investigate performance of bamboo pile-mattress system as soil reinforcement for coastal embankment on soft clay. applied mechanics and materials, 501: 2132-2137. [3] low ks, tioh nh, ng sc. (2013) lightweight concrete infill buoyant platform and the method thereof. world inventor award festival, 2013 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 0 50 100 150 200 250 300 350 400 450 s e tt le m e n t (m m ) load pressure (kpa) soil only-lab soil only-fem 20% pu-lab 20% pu-fem 20%pu new eq 40% pu-lab 40% pu-fem 40%pu new eq 50% pu fem 50% pu lab 50%pu new eq 60% pu-lab 60% pu-fem 60%pu new eq 80% pu-lab 80% pu-fem 80%pu new eq 10 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 [4] howard gt. (2012) polyurethane biodegradation. environmental science and engineering 2012. springer-verlag berlin heidelberg. https://doi.org/10.1007/978-3-642-23789-8_14 [5] bayer o. (1947) polyurethanes. mod plast, 24:149–152. [6] buzzi o, fityus s, sasaki y, sloan s. (2008).. structure and properties of expanding polyurethane foam in the context of foundation remediation in expansive soil. mechanics of materials, 40: 1012-1021. [7] buzzi o, fityus s, sasaki y, sloan s. (2010) use of expanding polyurethane resin to remediate expansive soil foundation. canadian geotechnical journal, 47: 623-634. [8] badri k. (2012). biobased polyurethane from palm kernel oil based polyol. license intech 2012 [9] ionescu m. (2005) chemistry and technology of polyols for polyurethanes, rapra technology limited, shawbury, uk, isbn 1859574912 [10] polyurethane global market size forecast 2021. https://www.statista.com/statistics/ 720449/global-polyurethane-market-size-forecast/ accessed on 25 september 2019 (11] zeltins v, yakushin v, cabulis u, kirpluks m. (2017) crude tall oil as raw material for rigid polyurethane foams with low water absorption. solid state phenom, 267: 17–22. [12] athawale vd, nimbalkar rv. (2011) polyurethane dispersions based on sardine fish oil, soybean oil, and their interesterification products. j. dispers. sci. technol, 32: 1014–1022. [13] pawar ms, kadam as, dawane bs, yemul os. (2016) synthesis and characterization of rigid polyurethane foams from algae oil using biobased chain extenders. polym. bull, 73: 727–741. [14] figovsky ol. (2000) hybrid non-isocyanate polyurethane network polymers and composites formed therefrom. u.s. patent, 6:120,905. [15] guan j, song y, lin y, yin x, zuo m, zhao y, tao x, zheng q. (2011) progress in study of non-isocyanate polyurethane. ind. eng. chem. res, 50: 6517–6527. [16] li z, zhao y, yan s, wang x, kang m, wang j, xiang h. (2008) catalytic synthesis of carbonated soybean oil. catal. lett, 123: 246–251. [17] tamami gwss .(2004). using tetrabutylammonium bromide catalyst. u.s. patent 20040230009 a1. [18] rathod ma, upadhyaya ds, panchal sl. (2014) preventation of hydrostatic uplift pressure underneath of basement floor slab in high water table area. international journal of futuristic trends in engineering and technology, 1(03): 72-75. [19] heath tl. (1897) the worlds of archimedes. edited in modern notation with introductory chapters, cambridge university press, 257 [20] song lh, liu y, mei gx, zai jm. (2008) experimental study on buoyancy effect on deep foundation in clay. hydrogeology & engineering geology, 35(6): 80–84. [21] song l, kang x, and mei g. (2017) buoyancy force on shallow foundations in clayey soil: an experimental investigation based on the half interval search, ocean engineering, 129: 637–641. [22] ni p, kang x, songl, mei g, zhao y. (2019) model tests of buoyant force on underground structures. journal of testing and evaluation, 47(2): 1216–1235. [23] frydelund te, aaboer r. (2002) lightweight filling materials for road construction. eps geofoam 3rd international conference 2002, salt lake city [24] stephen s. (2016) pressure reduction on wide culverts with eps geofoam backfill. dissertations-all. 548. https://surface.syr.edu/etd/548 [25] rowe pw, barden l. (1966) a new consolidation cell. géotechnique, 16(2): 162-170. https://doi.org/10.1680/geot.1966.16.2.162 [26] head kh (1985). manual of soil laboratory testing, 3: effective stress tests pp.1129-1225 [27] premchitt j, ho ks, evans nc. (1995) conventional and crs rowe cell consolidation test on some hong kong clays. [28] bs1377-part 6:1990: consolidation and permeability tests in hydraulic cells and with pore pressure measurement. [29] brinkgreve rbj (2002). plaxis 2d version 8, material models manual 11 iium engineering journal, vol. 23, no. 1, 2022 che lat et al. https://doi.org/10.31436/iiumej.v23i1.1781 [30] saleh s, ahmad k, mohd yunus n. (2020) evaluating the toxicity of polyurethane during marine clay stabilisation. environ sci pollut res, 27: 21252–21259. https://doi.org/10.1007/s11356-020-08549-y [31] al-atroush me, sebaey ta. (2021) stabilization of expansive soil using hydrophobic polyurethane foam: a review. transportation geotechnics, 27:100494. https://doi.org/10.1016/j.trgeo.2020.100494 [32] abdurahman mn, kasbi basri az, kassim a (2021). assessment of physical and mechanical properties of polyurethane as ground improvement material for peat. neutron, 20(2): 149– 156. https://doi.org/10.29138/neutron.v21i1.99 12 https://doi.org/10.1007/s11356-020-08549-y https://doi.org/10.1016/j.trgeo.2020.100494 https://doi.org/10.29138/neutron.v21i1.99 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 comparative assessment of numerical techniques for weibull parameters’ estimation and the performance of wind energy conversion systems in nigeria ignatius k. okakwu1, daniel o. akinyele1, olakunle e. olabode2, titus o. ajewole2, emmanuel s. oluwasogo3 and ajibola o. oyedeji4* 1 department of electrical and electronics engineering, olabisi onabanjo university, ago-iwoye, nigeria 2 department of electrical and electronics engineering, osun state university, osogbo, nigeria 3 school of energy engineering, kyungpook, national university, daegu, south korea. 4 department of computer engineering, olabisi onabanjo university, ago-iwoye, nigeria. *corresponding author: oyedeji.ajibola@oouagoiwoye.edu.ng (received: 24th september 2022; accepted: 14th december 2022; published on-line: 4th january 2023) abstract: the wind speed of a location is a critical parameter for analyzing wind energy conversion systems. background knowledge has revealed that the two-parameter weibull distribution is commonly used for fitting wind speed data because of its simplicity, flexibility and suitability. this research study examines wind speed data from five locations in nigeria (kano, maiduguri, jos, abuja and akure). it employs five numerical techniques, namely the maximum likelihood method, method of moment, power density method, empirical method and the logarithmic moment method, to estimate the weibull parameters based on the locations’ data. the goodness of fit test is used to determine which numerical method best fits the distribution. the paper also considers the techno-economic design of wind electricity of five 25 kw pitch-controlled wind turbines with dissimilar characteristics. the test result presents the method of moment and empirical method as the best methods for calculating the weibull parameters. results also show that wind turbine-3 has the least cost of energy and wind turbine-5 has the highest cost of energy. abstrak: kelajuan angin sesuatu lokasi adalah parameter kritikal bagi menganalisa sistem penukaran tenaga angin. latar belakang berkaitan telah mendedahkan 2-parameter taburan weibull (wbl) lazimnya digunakan bagi memadan data kelajuan angin berdasarkan kesederhanaan, fleksibiliti dan kesesuaian. kajian penyelidikan ini adalah berkaitan ujian data kelajuan angin pada lima lokasi di nigeria (kano, maiduguri, jos, abuja dan akure). ia menggunakan lima teknik berangka iaitu kaedah kemungkinan maksimum, kaedah momen, kaedah ketumpatan kuasa, kaedah empirikal dan kaedah momen logaritma bagi menganggar parameter weibull berdasarkan lokasi data. ujian kesesuaian digunakan bagi memastikan kaedah berangka adalah padanan paling sesuai bagi taburan. kajian ini juga turut menimbang reka bentuk tekno-ekonomi elektrik angin bagi lima turbin angin 25 kw kawalan anggul dengan ciri berbeza. dapatan kajian menunjukkan momen dan kaedah empirikal adalah kaedah terbaik bagi mengira parameter weibull. ini menunjukkan bahawa turbin angin-3 mempunyai kos tenaga paling rendah dan turbin angin-5 mempunyai kos tenaga tertinggi. key words: wind speed, numerical method, weibull distribution, energy cost 138 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 1. introduction the term “energy” is considered one of the most crucial human needs and is also identified as one of the essential indicating factors for measuring a country’s level of development and the human development index (hdi) [1]. although conventional energy sources, i.e., fossil fuels, play a critical role in meeting the world’s energy demand requirements, its utilization has continued to raise environmental concerns [2]. therefore, the quest to reduce the usage of fossil fuels due to its negative environmental effects, depletion, unstable price and the issue of energy consumption growth has driven the need for cleaner alternative energy resources [3]. despite the global cry for the energy transition to green energy, burning of fossil fuel still occupy the larger percentage of nigeria’s electricity generation both at the utility and the energy users’ levels [4]. the present electricity generation capacity of the country is less than 5000 mw for all sources (thermal, gas and hydro) as at march 2022. this is inadequate considering the country’s population of over 200 million. the gap in generation and the citizens’ demand has resulted in energy poverty and low standard of living [5]. in order to address this problem, it is necessary to grow the country’s energy mix by harnessing the available renewable energy (re) sources, one of which is the wind energy resource. wind energy is naturally-occurring and can be deployed for on-grid and off-grid generation applications [6]. however, in order to utilize wind energy, the probability density function (pdf) related to wind speed must be well assessed or evaluated for the supply of reliable electricity at an affordable cost. such parameter provides crucial information in wind energy planning and implementation and also helps to ascertain a location’s wind power potential. various pdfs have been proposed in the literature to describe the distribution of wind speed, but the 2-parameter weibull (wbl) distribution is widely employed because of its simplicity, flexibility and suitability for fitting recorded wind data [7]. in analyzing wind speed data, the distribution that fits the data statistically needs to be firstly determined, and then the estimations of the relevant parameters concerning this distribution can be calculated. some studies have been presented on wind energy generation in nigeria. some of these scholarly works will be presented in this section for the purpose of laying useful background for this present study. oyedepo et al., [8] presented the wind characteristics and the potential for selected locations in nigeria utilizing data that spans 24 to 27 years, measured at the height of 10 m. the central concern of the paper includes the determination of the annual output power and capacity factor (cfw). adaramola et al., [9] presented wind turbines’ performance for electricity production in seven different areas within the niger-delta region of nigeria based on wind data that spans 9 to 37 years, using the 2-parameter wbl distribution functions. observation showed that 35 kw wind turbine discussed in their work has the highest cfw irrespective of the locations. ajayi et al., [10] presented a techno-economic (te) evaluation of wind turbines for electricity supply to 10 locations in nigeria. the 2-parameter method wpd was used to assess the wind potential for the locations. the turbine matching results reveal that the cut-in and rated wind speeds range from 2.0 to 3.0 m/s, and 10 to 12.0 m/s, respectively. sulaiman et al., [11] also discussed the assessment of the wind potential of 4 different locations in nigeria, emphasizing wind power potentials and wind speed characteristics using the 2-parameter wdf technique. the paper used the cfw calculation to determine the most suitable turbine for the specified locations and reported monthly mean wind speed of 4.50, 3.72, 4.77 and 5.34 m/s with corresponding wind power densities of 67.74, 40.87, 79.52 and 107.49 wm-2 for the sites. 139 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 okakwu et al., [12] discussed the te evaluation of wind resources for power generation in nigeria. the study used a 2-parameter wdf for analyzing the wind potential of four different locations based on the average wind speeds/day measured at the anemometer positioned at 10 m over a period of 11 years. it employed the power density and the cfw to classify the sites and select the most suitable turbine for these locations. it also used the present-value cost to the coe by the wecs at various h/hs. mohammadi et al., [13] considered the te analysis of large-scale wind electricity systems in iran. the paper employed the 2-parameter wdf for analyzing the measured wind data between 2008 and 2009 at the height of 40 m height. however, the authors examined the te analysis of four large-scale wind turbine systems at a height of 70 m height. ajayi et al. [14] discussed the wind profile and turbine system performance assessment in kano, nigeria. the authors also presented the wind energy analysis using the 2-parameter wdf method based on the wind data that spans between 1987 and 2007 at 10 m. the study also employed wind rose to describe the direction of the wind energy in different seasons. alkhalidi et al., [15] evaluated wind potential at coastal and offshore locations in kuwait. this work explores ten coastal and offshore locations for the analysis and then considered the potential at different heights of 50, 80, 100, and 120 m. the authors employed a 2-parameter wbl distribution method to analyze the wind resource and calculate wind energy density. in addition, the study calculated the wbl distribution parameters by using the maximum likelihood method. mostafaeipour et al., [16] analyzed the wind potential and the wecss cost for zahedan, iran using 5-year wind resource data. the wind power density and the energy output have also been determined by using the wdf. the study considered the comparative analyses of the 3 different pdf models such as wbl, rayleigh, and lognormal, to analyze the location’s wind profile. soulouknga et al. [18] evaluated the cost of generating wind‐generated electricity in chad. the work used the wbl distribution for assessing the wind resource data obtained at an anemometer height of 10 m. the work also determined the wbl statistical parameters (k and c) at different heights of 10, 30, 50, and 70 m. belabes et al., [19] evaluated the wind potential and the cost of electricity by the wecss for 6 different areas of the north of algeria. the data recorded for over 10 years were used; the authors also obtained the wbl parameters k and c for all months at different heights of 30, 50 and 70 m by extrapolating the 10 m data at the locations. the reviewed studies have contributed substantially to the body of knowledge in the research direction of wind potential and cost analysis for different locations, all of which are based on the 2-parameter wdf at the height of 10 m. it is also found that [15] used the maximum likelihood method, while some others used the empirical method to calculate wbl distribution parameters. the work in [20] compared the wbl, rayleigh, and lognormal models to assess the locations’ wind resources and profiles. the main focus of the aforementioned studies includes the identification of suitable locations and the selection of wts and coe, which are useful background contributions for understanding wind potential analysis and wecs design and planning. however, this present study will first identify the best fit for the probability density function (pdf) of wind speed data and then ascertain suitable sites for wind power generation. it will also calculate the impact of varying the h/hs on the coe to provide useful insights into decision-making for a sound investment model for wind energy production in nigeria. importantly, this study uses five different techniques, namely the maximum likelihood, method of moment, power density, empirical and logarithmic moment methods, to characterize the wind resource data of 5 different locations in nigeria and then determine the respective wbl 140 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 parameters (i.e., k and c). the comparative analysis is employed to understand the performance of different numerical methods mentioned given the locations’ resource data, which also takes this paper a step further than the analysis presented in some previous studies discussed earlier. in addition, the research study examines the te performances of five 25 kw pitchcontrolled wind turbines (wt1 – wt5) from different manufacturers with dissimilar design characteristics at varying h/hs. the results of this paper are expected to demonstrate a detailed te analysis, which may be useful for designing, planning and assessing wecss for local energy and agricultural applications, e.g. water-pumping. the remaining part of this research article is arranged as follows: section 2 is on materials and methods, section 3 focuses on the results and discussion, while section 4 presents the conclusion of the paper. 2. materials and method 2.1 study area this study considered five locations in nigeria, namely kano, maiduguri, jos, abuja and akure, in the northern and southern parts of the country. the wind speed data used in this work was obtained from the nigeria meteorological agency (nimet), lagos state, nigeria. the wind resource was measured by nimet at a h/h of 10 m by an anemometer cup-generator. table 1 presents the case study areas. table 1: the case study areas [24] locations latitude (0n) longitude (0e) data period kano 12.05 8.52 2002-2012 maiduguri 11.85 13.08 2002-2012 jos 9.64 8.88 2002-2012 abuja 9.00 7.27 2002-2012 akure 7.25 5.20 2002-2012 2.2 simulation software the implementation of the proposed approaches in terms of modelling, simulation and analysis was achieved using matlab version (2013a) and microsoft excel software. 2.3 numerical approaches to weibull parameters' estimation background knowledge of wind resources and systems modelling and analysis shows that several methods can be employed for calculating the wbl parameters k and c. however, five different methods are employed in this paper to characterize the wind speed data under review. 2.3.1. maximum likelihood approach using the maximum likelihood method (mlm), k and c parameters are calculated by eqs. (1) and (2) [21-23]: k = [ ∑ 𝑉𝑖 𝑘𝑛 𝑖=1 ln 𝑉𝑖 ∑ 𝑉𝑖 𝑘𝑛 𝑖=1 − ∑ ln(𝑉𝑖) 𝑛 𝑖=1 𝑛 ] −1 (1) c = [ 1 𝑛 ∑ 𝑉𝑖 𝑘𝑛 𝑖=1 ] 1 𝑘 (2) where 𝑉𝑖 and n are the wind speed in time step 𝑖, and the number of ‘non-zero’ wind speed data points. in the mlm, numerical iterations are required to determine the wbl parameters. 141 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 2.3.2. method of moment in the method of moment (mom), the k and c parameters are given by eqs. (3) and (4) [21-23]: k = [ 0.9874 𝜎 𝑉 ] 1.0983 (3) c = 𝑉 γ(1+ 1 𝑘 ) (4) where; 𝜎 and 𝑉 in this case, are the standard deviation and the mean wind speed. 2.3.3. power density method in employing the power density method (pdm) for wind resource analysis, the value of k parameter is calculated by eqs. (5) and (6) [21-23]: k = 1 + 3.69 𝐸𝑝𝑓 2 (5) the scale parameter (c) in the case of pdm is estimated using eq. (4). 𝐸𝑝𝑓 = 𝑉3 (𝑉) 3 = 1 𝑛 ∑ 𝑉𝑖 3𝑛 𝑖=1 ( 1 𝑛 ∑ 𝑉𝑖 𝑛 𝑖=1 ) 3 (6) 2.3.4. empirical method in the empirical method (epm), the k parameter is estimated by eq. (7), while c parameter is calculated by employing eq. (4) [22-24]: k = [ 𝜎 𝑉 ] −1.086 (7) in which case 𝜎 and 𝑉 represent the standard deviation and the mean wind speed, respectively. 2.3.5. logarithmic moment method in the logarithmic moment method (lmm), the values of k and c parameters are estimated by eqs. (8) and (9) [21-23]: k = [ 1.645 𝜎2 ] 1 2 (8) c = 𝑒𝑥𝑝 [ 𝑘𝑉+0.5772 𝑘 ] (9) 2.4 numerical method accuracy assessments in order to test the accuracy of the presented numerical methods for estimating the wbl parameters, two different approaches are employed, which are the root mean square error (rmse) and the coefficient of determination (𝑅2). the value of rmse is given by eq. (10) [21-23]: 𝑅𝑀𝑆𝐸 = [ 1 𝑛 ∑ (𝑦𝑖 − 𝑥𝑖 ) 2𝑛 𝑖=1 ] 1 2 (10) the coefficient of determination is then given by eq. (11) [21-23]: 142 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 𝑅2 = ∑ (𝑓(𝑉𝑖)−𝑓(𝑉)) 2𝑁 𝑖=1 − ∑ (𝑓(𝑉𝑖)−�̂�(𝑉𝑖) ) 2𝑁 𝑖=1 ∑ (𝑓(𝑉𝑖)−𝑓(𝑉)) 2𝑁 𝑖=1 (11) 2.5 wind speed analysis the daily mean wind speed, 𝑉 and the standard deviation, 𝜎 of the wind resource data can be calculated by eqs. (12) and (13), respectively [12]: 𝑉 = 1 𝑛 (∑ 𝑉𝑖 𝑛 𝑖=1 ) (12) 𝜎 = √ 1 𝑛 ∑ (𝑉𝑖 − 𝑉) 𝑛 𝑖=1 (13) where 𝑉𝑖 and n represent the daily wind speed in time step of 𝑖 and the number of wind speed data points. the wpd function (𝑓𝑤 (𝑣)) and the cumulative distribution function (𝑓𝑤 (𝑉)) are given by eqs. (14) and (15) [20]: 𝑓𝑤 (𝑣) = ( 𝑘 𝑐 ) ( 𝑣 𝑐 ) 𝑘−1 𝑒𝑥𝑝 [− 𝑣 𝑐 ] 𝑘 (14) 𝑓𝑤 (𝑉) = 1 − 𝑒𝑥𝑝 [− 𝑣 𝑐 ] 𝑘 (15) where; v, k and c represent the wind speed (m/s), shape parameter (dimensionless) and the scale parameter (m/s), respectively. in addition, the most probable wind speed (𝑉𝑚𝑝𝑠) and the wind speed at the maximum energy (𝑉𝑒𝑚𝑎𝑥) are given by eqs. (16) and (17) [24]: vmps = c ( k−1 k ) 1 k (16) 𝑉𝑒𝑚𝑎𝑥 = 𝑐 ( 𝑘+2 𝑘 ) 1 𝑘 (17) at times, wind speeds are measured at a reference h/h (ℎ0) but needs to be adjusted to the relevant wind turbine h/h (ℎ). the new wind speed (𝑉ℎ ), scale factor (𝑐ℎ ) and shape factor (𝑘ℎ ) are given by eqs. (18) to (20) by using a relevant power law equation, while eq. (21) is employed to estimate the value of n [25]: 𝑉ℎ = 𝑉0 ( ℎ ℎ0 ) ∝ (18) 𝑐ℎ = 𝑐0 ( ℎ ℎ0 ) 𝑛 (19) 𝑘ℎ = 𝑘0 { [1−0.088 ln ℎ0 10 ] [1−0.088 ln ℎ 10 ] } (20) 𝑛 = [0.37−0.088 ln 𝑐0] [1−0.088 ln ℎ 10 ] (21) where ∝ represents the site surface roughness coefficient and assumed in this work to be 0.143 [11]. 143 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 2.6 wind power estimation the wind power density, 𝑃𝑊𝑃𝐷 is a measure of the capacity of the wind resource of a particular location per unit swept area of the blades. eq. (22a) is employed to estimate the wind power density, while the wind power capacity, 𝑃𝑊𝑃𝐶 is estimated by eq. (22b) [10]: 𝑃𝑊𝑃𝐷 = 1 2 𝜌𝑐3γ (1 + 3 𝑘 ) (22a) 𝑃𝑊𝑃𝐶 = 1 2 𝐴𝜌𝑉𝑚𝑠 3 (22b) where 𝜌 and 𝐴 stand for the air density (i.e., 1.225 kg/m3) and the swept area of the rotor blades (m2). the 𝑃𝑊𝑃𝐷 and 𝑃𝑊𝑃𝐶 parameters are measured in (w/m 2) and (w), respectively. to extend the performance of the wecs further, in terms of the available power in the wind, this study considers the contribution made by albert betz (a german physicist). this scientist made bold in 1919 as part of his contributions to knowledge that there is no wind turbine system that can convert above 16 27 (i.e., 0.593) of the wind’s kinetic energy to mechanical energy for turning the wind turbine rotor [26, 27]. in wind power system engineering, this factor 0.593 is referred to as the betz limit. it is translated as the theoretical maximum power efficiency or (the aerodynamic efficiency of the rotor [28] of a wind turbine system design, i.e., 0.59), implying that not more than 59% of energy can be obtained from the wind by the wt system. it is then referred to as the power coefficient, cp(max) and is added to eqs. (22b) leading to eq. (22c) describes the maximum power obtainable from the wt: 𝑃(𝑊𝑃𝐶)𝑚𝑎𝑥 = 1 2 𝐴𝜌𝐶𝑝(𝑚𝑎𝑥)𝑉𝑚𝑠 3 (22c) it is important to state that the value of the power coefficient in real life limit is practically lower than the betz limit [26, 28]. typical values of the betz limit range from 0.35 to 0.45 even for best wind turbine systems; therefore, after making realistic design considerations for the gearbox, bearings, generator, etc., only around 0.1 to 0.3 fraction of the power of in the wind that is in reality converted into usable electrical energy [26]. 2.7 estimation of wecs’ output power and cfw the wind turbine output power is of a significant benefit, as it presents a good economic indicator compared to its rated capacity. the wind turbine output power, i.e., the power curve, is modelled via four parameters: the cut-in wind speed (𝑉𝑐𝑖), the cut-off wind speed (𝑉𝑐𝑜), the rated wind speed (𝑉𝑟) and the rated power capacity of the wt (𝑃𝑟 ). for a pitch-controlled wt, the power curve model can be approximated by a parabolic law, given by eq. (23) [11-12]: 𝑃 = 𝑃𝑟 { 𝑉𝑚𝑠 2 − 𝑉𝑐𝑖 2 𝑉𝑟 2− 𝑉𝑐𝑖 2 1 0 𝑉𝑐𝑖 ≤ 𝑉𝑚𝑠 ≤ 𝑉𝑟 𝑉𝑟 ≤ 𝑉𝑚𝑠 ≤ 𝑉𝑐𝑜 𝑉𝑟 ≤ 𝑉𝑐𝑖 𝑎𝑛𝑑 𝑉𝑚𝑠 ≥ 𝑉𝑐𝑜 (23) the average power output (𝑃𝑎𝑣𝑒 ) of a wt is given by eq. (24) [13-14]: 𝑃𝑎𝑣𝑒 = 𝑃𝑟 [ 𝑒 −[ 𝑉𝑐𝑖 𝑐 ] 𝑘 − 𝑒 −[ 𝑉𝑟 𝑐 ] 𝑘 [ 𝑉𝑟 𝑐 ] 𝑘 − [ 𝑉𝑐𝑖 𝑐 ] 𝑘 − 𝑒 −[ 𝑉𝑐𝑜 𝑐 ] 𝑘 ] (24) technically, 𝐶𝐹𝑤 of a wt is the ratio of 𝑃𝑎𝑣𝑒 to 𝑃𝑟 and is given by eq. (25) [11-12]: 144 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 𝐶𝐹𝑤 = 𝑃𝑎𝑣𝑟 𝑃𝑟 = [ 𝑒 −[ 𝑉𝑐𝑖 𝑐 ] 𝑘 − 𝑒 −[ 𝑉𝑟 𝑐 ] 𝑘 [ 𝑉𝑟 𝑐 ] 𝑘 − [ 𝑉𝑐𝑖 𝑐 ] 𝑘 − 𝑒 −[ 𝑉𝑐𝑜 𝑐 ] 𝑘 ] (25) in addition, the yearly energy produced by the wt is given by eq. (26): 𝐸𝑎𝑒 = 𝐶𝐹𝑤 × 𝑃𝑟 × 𝑡 (26) where t represents the total hours in a year, i.e., 8760 hours. 2.8 economic cost analysis estimating the unit cost of energy, 𝐶𝑂𝐸, is a way of knowing the most viable wind turbine to select for this study. the economic aspect of this work focuses on calculating the cost of the individual components of the system, which include the investment, operation and maintenance (o and m) and the replacement costs. the wecss life-cycle cost can be calculated by eq. (27) [11]: 𝐶𝐿𝐶𝐶 = 𝐶𝑖𝑛𝑣 + 𝐶𝑜𝑝𝑚 ( 1+𝑖𝑟 𝑑−𝑖𝑟 ) (1 − ( 1+𝑖𝑟 1+𝑑 ) 𝑝 ) (27) where; 𝐶𝑜𝑝𝑚, 𝑖𝑟 , 𝑑, r and p in this case represent the operation and maintenance cost, inflation rate, discount rate, interest rate and the project lifetime, respectively, and the corresponding values of these are assumed to be 0.1 % of investment cost 𝐶𝑖𝑛𝑣, 8.4 %, 11%, 15% and 20 years. the annualized life-cycle cost (𝐶𝐴𝐿𝐶𝐶 ) is given by eq. (28): 𝐶𝐴𝐿𝐶𝐶 = 𝐶𝐿𝐶𝐶 × 𝐶𝑅𝐹 (28) where crf is regarded as the capital recovery factor and is given by eq. (29) [10]: 𝐶𝑅𝐹 = 𝑖𝑟 (1+𝑖𝑟) 𝑛 (1+𝑖𝑟) 𝑛−1 (29) the unit cost of energy is then given by eq. (30) [33]: 𝐶𝑂𝐸 = 𝐶𝐴𝐿𝐶𝐶 8760 ×𝑃𝑟 × 𝐶𝐹𝑤 (30) in this study, five different turbines from different manufacturers were considered and are represented by wt1, wt2, wt3, wt4 and wt5, respectively, with their characteristics shown in table 2. table 2: characteristics of the selected wts [16, 34] characteristics wt1 wt2 wt3 wt4 wt5 rated power 𝑃𝑟 (𝑘𝑊) 25 25 25 25 25 rotor diameter (𝑚) 15 15 15 15 15 cut-in wind speed 𝑉𝑐𝑖 (𝑚 𝑠⁄ ) 2.0 2.5 3.0 3.5 4.0 rated wind speed 𝑉𝑟 (𝑚 𝑠⁄ ) 16 18 15 17 19 cut-off wind speed 𝑉𝑐𝑜 (𝑚 𝑠⁄ ) 25 27 23 28 30 investment cost $ 𝑘𝑊⁄ 1300 1300 1300 1300 1300 3. results and discussion 3.1 comparison of wind speed distributions of estimated wbl pdf figures 1 to 5 show the comparison of the wind speed histogram with the calculated wbl pdfs for the five numerical approaches for the specified locations under study. the wbl 145 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 density function gets narrower and becomes peaked as k becomes larger, meaning that wind speeds tend to stay within a narrow range. the peak also moves in the higher wind speed direction as the value of c increases. for instance, in kano, maiduguri, abuja and akure, as shown in figures 1, 2, 4 and 5, respectively, since the calculated value of k from the lmm is greater than those obtained from the other methods, the peaks of the probability density curves were larger compared to the others. however, in jos as shown in figure 3, the calculated k using mom was greater than the value obtained using the other methods; hence, the peak of its probability density curve is observed to be larger. therefore, figures 1 to 5 demonstrates that lower shape parameters correspond to broader probability density curves (i.e., higher scale parameters), which implies that winds vary over a wide range of wind speeds. fig. 1. comparison of the pdfs for kano fig. 2. comparison of the pdfs for maiduguri fig. 3. comparison of the pdfs for jos the wbl parameters in the locations based on minimum 𝑅𝑀𝑆𝐸 and maximum 𝑅2 are presented in tables 3 to 7, respectively. it is obvious from these results that the values of 𝑘 range from 2.90 in akure to 7.01 in abuja, while those of 𝑐 range from 3.86 in akure to 12.82 in jos. in the cases under study, 𝑅𝑀𝑆𝐸 varies from 0.0584 to 0.1474, 𝑅2 varies from 0.9611 to 0.9988. therefore, tables 3 to 7 summarize the fitness errors between the estimated pdfs and 146 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 the histogram of the observed wind speed data at the height of 10 m. results of calculated weibull parameters from all the five nems (mlm, mom, pdm, epm and lmm) and two statistical methods (rmse and 𝑅2) for measuring the efficiency of these nems in all the five locations considered are presented in table 3-7, respectively. for a robust comparison purpose of all nems, the statistical values for measuring efficiency have been listed up to 9 decimal points. from these tables, it is observed that out of the five nems of estimating weibull parameters, mom and epm have estimated the same values for 𝑘 𝑎𝑛𝑑 𝑐 respectively in kano (table 7), hence, have the same efficiency of estimation. each nems have been ranked against its performance on a scale from 1-5 (with 1 being the best efficient and 5 as the worst efficient). from table 3, it is observed that mom is the best and pdm is the worst with respect to rmse and 𝑅2 respectively. from table 4, epm has been found to be the most efficient and pdm the worst efficient with respect to rmse and 𝑅2 respectively. furthermore, in table 5, it is fig. 4. comparison of the pdfs for abuja fig. 5. comparison of the pdfs for akure observed that mom depicts the best performance and pdm still retains its worst efficient performance with respect to rmse and 𝑅2 respectively. in table 6, epm shows the best performance and pdm still shows the worst performance with respect to rmse and 𝑅2 respectively. however, in table 7, mom and epm were found to be the most efficient, while pdm still retains its worst position. the results shown in tables 3-7 demonstrate that the epm and mom are the best fit across all five locations due to their minimum 𝑅𝑀𝑆𝐸 value and maximum 𝑅2 value. the results also reveal that pdm was the worst-performing nem across all five locations. 3.2 wind characteristics of location the wind speed characteristics of the locations are shown in table 8. it can be seen that 𝑉𝑚𝑠 varies from 3.47𝑚 𝑠⁄ in akure site to 11.63𝑚 𝑠⁄ in jos; 𝑘 varies from 2.90 in akure to 147 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 4.08 in jos, while 𝑐 varies from 3.89 𝑚 𝑠⁄ in akure to 12.82 𝑚 𝑠⁄ in jos. also, 𝑉𝑚𝑝𝑠 varies from 3.36 𝑚 𝑠⁄ in akure to 11.97 𝑚 𝑠⁄ in jos; 𝑉𝑒𝑚𝑎𝑥 varies from 4.66 𝑚 𝑠⁄ in akure to 14.14 𝑚 𝑠⁄ in jos; 𝑃𝑊𝑃𝐷 varies from 36 𝑊 𝑚 2⁄ in akure to 1182.12 𝑊 𝑚2⁄ in jos, all at a h/h of 10 m. the results further show that kano and jos study locations are viable sites for grid integration because the wind power density at the h/h of 10 m is > 400 w/m2. in addition, abuja and akure study locations are not viable for wind electricity production because the wind power density in these locations is < 100 w/m2, while maiduguri is only applicable for a stand-alone application because the wind power density is > 100 w/m2 [11]. table 3. wbl parameters and goodness of fit estimation for kano numerical methods wbl parameters statistical criteria rank k c rmse 𝑹𝟐 mlm 4.62 10.12 0.022298950 0.999994120 4 mom 5.37 10.19 0.015769237 0.999997059 1 kano pdm 3.83 10.39 0.035938398 0.999984726 5 epm 5.34 10.19 0.015880219 0.999997018 2 lmm 5.95 10.12 0.015976125 0.999996982 3 table 4. wbl parameters and goodness of fit estimation for maiduguri numerical methods wbl parameters statistical criteria rank k c rmse 𝑹𝟐 mlm 4.12 6.01 0.029812308 0.999968890 3 mom 4.47 6.02 0.029509497 0.999969519 2 maiduguri pdm 3.57 6.10 0.040316395 0.999943106 5 epm 4.46 6.02 0.029456943 0.999969628 1 lmm 5.05 5.97 0.036872000 0.999952412 4 table 5. wbl parameters and goodness of fit estimation for jos numerical methods wbl parameters statistical criteria rank k c rmse 𝑹𝟐 mlm 5.63 12.41 0.029395252 0.999993500 4 mom 6.57 12.47 0.024726277 0.999995401 1 jos pdm 4.08 12.82 0.052023787 0.999979641 5 epm 6.52 12.48 0.025154590 0.999995240 2 lmm 6.42 12.50 0.026047047 0.999994896 3 table 6. wbl parameters and goodness of fit estimation for abuja numerical methods wbl parameters statistical criteria rank k c rmse 𝑹𝟐 mlm 4.76 5.23 0.074049683 0.999751495 3 mom 5.99 5.25 0.071313582 0.999769520 2 abuja pdm 3.94 5.38 0.097370552 0.999570320 5 epm 5.95 5.25 0.071065282 0.999771122 1 lmm 7.01 5.20 0.076836985 0.999732435 4 148 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 table 7. wbl parameters and goodness of fit estimation for akure numerical methods wbl parameters statistical criteria rank k c rmse 𝑹𝟐 mlm 3.01 3.86 0.019045125 0.999966622 3 mom 3.04 3.88 0.017679962 0.999971235 1 akure pdm 2.90 3.89 0.019662755 0.999964422 4 epm 3.04 3.88 0.017679962 0.999971235 1 lmm 3.17 3.87 0.018876644 0.999967210 2 table 8. wind speed characteristics of the locations location 𝑽𝒎𝒔 k c 𝑽𝒎𝒑𝒔 𝑽𝒆𝒎𝒂𝒙 𝑷𝑾𝑷𝑫 (w/m 2) kano 9.39 3.83 10.39 9.60 11.59 636.84 maiduguri 5.49 3.57 6.10 5.56 6.91 131.60 jos 11.63 4.08 12.82 11.97 14.14 1182.12 abuja 4.87 3.94 5.38 4.99 5.97 87.94 akure 3.47 2.90 3.89 3.36 4.66 36.59 3.3 estimation of cfw of wts although designing a wind turbine that will match a particular site’s wind characteristics is the best practice; however, this can be time-consuming and frustrating [23], hence, the need to utilize available wind turbines in the market (w1 – w5). for this study, the cfw method is used for the wt selection. table 2 shows the characteristics of the wt used for this study. wind turbines with a high value of cfw is usually considered suitable for selection. table 9 presents the results of 𝐶𝐹𝑤 of each turbine with respect to the specified locations. wt1, wt2, wt3, wt4 and wt5 have cfw values of 0.0134 to 0.3705, 0.0083 to 0.2456, 0.0126 to 0.4471, 0.0067 to 0.3017, and 0.0034 to 0.1981, respectively. table 9. cfw of the wind turbines in different locations cfw location wt1 wt2 wt3 wt4 wt5 kano 0.1901 0.1214 0.2393 0.1495 0.0968 maiduguri 0.0314 0.0202 0.0373 0.0225 0.0139 jos 0.3705 0.2456 0.4471 0.3017 0.1981 abuja 0.0134 0.0082 0.0160 0.0090 0.0051 akure 0.0144 0.0089 0.0126 0.0067 0.0034 table 9 demonstrates that wt3 has the highest 𝐶𝐹𝑤 followed by wt1, wt4, wt2 and wt5, respectively. for uniformity of comparison, all the turbines considered have the same rated capacity of 25 kw. however, they have different cut-in and rated wind speeds as the machines are from different manufacturers. 3.4 estimation of coe table 10 presents the𝐶𝑂𝐸 for the selected wts at a h/h of 10 m. wt3 has the least cost performance for all the locations considered in this study. the values of coe for wt3 range from $ 0.041/kwh in jos to $ 1.457/kwh in akure. however, wt5 has the highest cost 149 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 performance of all the systems. its coe values range from $ 0.093/kwh in jos to $5.331/kwh in akure. in nigeria, electricity tariff in the country for residential “band a” customers with daily minimum of 20 hours of electricity availability is $ 0.13. this translates to 𝑁 52 at an official exchange rate of $1 to 𝑁 400. hence, generation of electricity using wind turbines, wt1 – wt5 is suitable for jos and wt1 – wt4 is suitable for kano, while other locations are not economically viable for wind power generation compared with the national grid supply. table 10. coe of the wecss coe ($/kwh) location wt1 wt2 wt3 wt4 wt5 kano 0.096 0.151 0.077 0.123 0.189 maiduguri 0.584 0.909 0.491 0.814 1.316 jos 0.049 0.075 0.041 0.061 0.093 abuja 1.370 2.243 1.149 2.046 3.601 akure 1.278 2.050 1.457 2.728 5.331 3.5 sensitivity analysis cases the sensitivity analysis introduced in this study showcases the dependency of the wecss variable on certain defined input variables. in this study, the variable considered is the effect of change in the h/hs on the probability density curve and the values of k, c, pwpd, cfw and coe. the results are shown in figures 6 to 11. the results in figures 6 and 7 show that the wbl parameters are directly proportional to the h/h; this is because the air mass flow appears to be smoother at a higher height. this is as a result of less impact of land topography obstructions to the flow of moving air. as shown in figures 6 and 7, increasing h/h will lead to an increase in k and c. also, an increase in k and c will make the shape of the pdf narrower (i.e., peaked) and broader by the right side of the graph (i.e., higher wind speeds). this peaked shape is not noticeable because of the little increase in the value of 𝑘 as a result of higher h/hs, while an increase in the value of 𝑐 will make the pdf move to the direction of higher wind speeds as can be seen in figure 8. figure 8 presents the effect of increasing h/hs on the probability density curve. the values of 𝑘 for kano, maiduguri, jos, abuja and akure range from 3.83 to 5.09, 3.57 to 4.75, 4.08 to 5.43, 3.94 to 5.24 and 2.90 to 3.86, respectively, for corresponding h/hs of 10 to 50 m. similarly, the values of 𝑐 for these locations range from 10.39 to 14.13, 6.10 to 9.06, 12.82 to 16.84, 3.89 to 8.16 and 3.89 to 6.22, respectively, for the h/hs ranging from 10 to 50 m. fig. 6. sensitivity analysis relating k with h/h 150 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 fig. 7. sensitivity analysis relating c with h/h fig. 9 shows the impact of varying h/h on the wind power density of the locations. increasing h/hs leads to an increase in wind power density. the values of 𝑃𝑊𝑃𝐷 for kano, maiduguri, jos, abuja and akure range from 636.84 to 1541.34 𝑊, 131.06 to 408.81 𝑊, 1182.13 to 2600.36 𝑊, 87.94 to 296.52 𝑊 and 36.59 to 136.41 𝑊, respectively, for corresponding h/hs of 10 𝑡𝑜 50 𝑚. fig. 8. sensitivity analysis relating pdfs with h/hs fig. 9. sensitivity analysis relating wind power density with h/h table 9 presents the results of the cfw for the wts in the specified locations. the results show that the cfw of the wts range from 0.0968 𝑡𝑜 0.2393, 0.0139 𝑡𝑜 0.0373, 0.1981 𝑡𝑜 0.4471, 0.0051 𝑡𝑜 0.0160 and 0.0034 𝑡𝑜 0.0126 for kano, maiduguri, jos, abuja and akure, respectively. it is also obvious from table 9 that the value of 𝐶𝐹𝑤 of 𝑊𝑇3 is the 151 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 highest in all the five locations, and this is selected for utilization for all the locations under consideration as the most suitable turbine. according to [30], wts with a value of 𝐶𝐹𝑤 ≤ 0.25 is not suitable for grid integration applications. however, those with higher 𝐶𝐹𝑤 in excess of 0.25 are considered the best option any given location. the response of 𝐶𝐹𝑤 of the wts with respect to different h/hs of 10 to 50 m is shown in figure 10. the results show that the h/h is directly proportional to 𝐶𝐹𝑤 , hence, the need to operate wind turbines at a reasonable height in order to achieve a value of cfw that is ≥ 0.25. from figure 10, jos is suitable for grid integration at all the h/hs; kano is suitable for grid integration at a h/h of ≥ 20𝑚; while maiduguri, abuja and akure are not suitable for grid integration at these hub-heights. figure 11 shows the relationship between the 𝐶𝑂𝐸 and the turbine h/h. the results clearly demonstrate that 𝐶𝑂𝐸 decreases with increasing h/hs; this is because the wind turbine harness more energy at a higher height due to an increase in wind speed. therefore, the values of 𝐶𝑂𝐸 obtained for kano, maiduguri, jos, abuja and akure were reduced from0.077 𝑡𝑜 0.033, 0.491 𝑡𝑜 0.202,0.041 𝑡𝑜 0.024, 1.149 𝑡𝑜 0.449 and 1.457 𝑡𝑜 0.579, respectively, for the specified heights of 10 to 50 m. fig. 10. sensitivity analysis relating cfw with h/h fig. 11. sensitivity analysis relating coe with h/h 152 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 3.6 environmental analysis wind energy systems are renewable energy-based power generation technology. the environmental performance of the wecss in the specified locations is realized by quantifying the amount of carbon emissions saved by utilizing the wecss in the specified locations kano, maiduguri, jos, abuja and akure, using the emission factor approach. an emission factor of 1.27 x 103 kg co2 per mwh of electricity generated by a diesel generator [30, 31] is used to estimate the amount of co2 avoided by the wind energy generating systems in the five locations. the environmental aspect, as presented in this study, is a function of the technical performance of the wind power system, which is based on wind energy resources of the locations. it is on this basis that the emission factor is multiplied by eq. (26) to obtained the amount of emissions saved suppose that wecss are employed as alternatives to fossil fuel system (i.e., diesel power systems) in the locations. the values of the annual energy generated by the wind power systems, eae, are presented in figure 12 for different heights 10 to 50 m considered. the energy delivered at these heights for kano, maiduguri, jos, abuja and akure range from 52,341 to 119,793 kwh/yr; 8,168.7 to 19,863.3 kwh/yr; 97,893 to 168,630 kwh/yr; 3,504 to 8,935.2 kwh/yr, and 2,759.4 to 6,942.3 kwh/yr, respectively. the results clearly ranks the wecss in jos, kano, maiduguri, abuja and akure as 1st, 2nd, 3rd, 4th and 5th positions, respectively, in terms of the amount of electricity they generate in a year, or simply the wind energy potential. these align with the results presented in figure 13, which demonstrate that the wind speed determines the wind power as presented by eqs. (22b) and (22c). therefore, the wind speed of a location is a critical parameter that determines what the wind power and the energy output will be. fig. 12. the annual energy produced by the wecss in the locations figure 14 presents the amount of carbon dioxide emissions assumed to be avoided when the wind energy systems are used in the location instead of diesel generating systems at hub heights of 10 to 50 m. the co2 emissions at the specified heights for kano, maiduguri, jos, abuja and akure range from 66,473 to 152,137 kg/yr; 10,374 to 25,226 kg/yr; 124,324 to 214,160 kg/yr; 4,450 to 11,348 kg/yr, and 3,504 to 8,817 kg/yr, respectively. again, the results show a similar trend with those presented in figure 12 and figure 13. this is so because the higher the wind speed, the higher the power and the energy produced and the higher the quantity of emissions saved by the wecss. 153 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 fig. 13. power available in the wind at the locations fig. 14. quantity of co2 emissions saved by the wecss 4. conclusions this study has presented a detailed comparative evaluation of numerical methods for estimating wbl parameters. it then discussed the te analysis of wind electricity production in five different locations in nigeria, such as kano. maiduguri, jos, abuja and akure. the study utilized average daily wind speeds for 10 years, which have been obtained from nigerian meteorological agency (nimet). the paper examined five different numerical approaches for assessing the wbl parameters and employed wind turbines of the same rating of 25kw for wecss in those locations. the study reveals the following as useful conclusions to this paper: i. the study reveals mom as suitable for kano and jos, while epm is suitable for maiduguri and abuja. with both nems suitable for akure. ii. the study also shows that pdm was the worst numerical approach for assessing the wbl parameters. 0 50000 100000 150000 200000 250000 kano maiduguri jos abuja akure a m o u n t o f c o 2 (k g /y r ) co2 emissions saved by the wecss 10 m 20 m 30 m 40 m 50 m 154 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 iii. wecss in jos and kano are viable for grid integration of wind energy, with jos being the most viable for wind energy generation applications. iv. wt3 has the highest 𝐶𝐹𝑤 in all the locations, which is a major determinant in selecting turbines. v. wt3 has the least 𝐶𝑂𝐸 in all the selected locations, hence, it was selected among other wind turbines. vi. wt5 has the highest 𝐶𝑂𝐸 in all the locations considered. vii. it is more efficient to utilize wts at a suitable h/h in order to maximize the location’s wind resources. this is demonstrated in the study that 𝐶𝑂𝐸 decreases with increasing turbine hub-heights. viii. the wecss have the potential to avoid significant carbon footprints when implemented as an alternative to fossil fuel systems. references [1] oyedepo so. (2012) energy and sustainable development in nigeria: the way forward. energy. sustainability and society, 2(15):1-17. [2] mohammadi k, mostafaeipour a, dinpashoh y, pouya n. (2014) electricity generation and energy cost estimation of large-scale wind turbines in jarandagh, iran. journal of energy, 1-8. [3] zheng l, peng g, ruihua h, hexu s. (2019) current status and development trend of wind power generation-based hydrogen production technology. journal of energy exploration and exploitation, 37:5-25. [4] norbert e. (2016) on the path to sustainability: key issues on nigeria’s sustainable development. energy report, 2:28-34. [5] njiru cw, letema sc. (2018) energy poverty and its implication on standard of living in kenya. journal of energy, 1-12. [6] cory b, deanna s, heather t, leon m, dana e, willett k. (2013) cost-minimized combinations of wind power, solar power and electrochemical storage, powering the grid up to 99.9% of the time. journal of power sources, 225:60-74. [7] badawi asa, hasbullaha nf, yusoff sh, khan s, hashim a, zyoud a, elamassie m. (2019) weibull probability distribution of wind speed for gaza strip for 10 years. applied mechanics and materials, 892:284-291. [8] oyedepo so, adaramola ms, paul ss. (2012) analysis of wind speed data and wind energy potential in three selected locations in south-east nigeria. international journal of energy and environment engineering, 3:1-11. [9] adaramola ms, oyewola om, ohunakin os, akinnawonu oo. (2014) performance evaluation of wind turbines for energy generation in niger delta, nigeria. sustainable energy technologies and assessments, 6:75-85. [10] ajayi oo, fagbenle ro, katende j, ndambuki jm, omole do, badejo aa. (2014) wind energy study and energy cost of wind electricity generation in nigeria: past and recent results and a case study for south west nigeria. energies, 7(12):8508-8534. [11] sulaiman ma, okakwu ik, alayande as, olabode oe, ibhaze ae. (2020) wind energy evaluation and turbine identification for power generation in some selected areas in nigeria. journal of engineering studies and research, 26:67-76. [12] okakwu ik, olabode oe, alayande as, somefun te, ajewole to. (2021) techno-economic assessment of wind turbines in nigeria. international journal of energy economics and policy, 11:240-246. [13] mohammadi k, mostafaeipour a, dinpashoh y, pouya n. (2014) electricity generation and energy cost estimation of large-scale wind turbines in jarandagh, iran. journal of energy, 613681:1-8. 155 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 [14] ajayi oo, fagbenle ro, katende j, aasa sa, okeniyi jo. (2013) wind profile characteristics and turbine performance analysis in kano, north-western nigeria. international journal of energy and environmental engineering, 4(27). [15] alkhalidi ma, al-dabbous s, neelamani s, aldashti ha. (2019) wind energy potential at coastal and offshore locations in the state of kuwait. renewable energy, 135:529-539. [16] mostafaeipour a, jadidi m, mohammadi k, sedaghat a. (2014) an analysis of wind energy potential and economic evaluation in zahedan, iran. renewable and sustainable energy reviews, 30:641-650. [17] ayodele tr, jimoh aa, munda jl, agee jt. (2013) a statistical analysis of wind distribution and wind power potential in the coastal region of south africa. international journal of green energy, 10:814-834. [18] soulouknga m, oyedepo so, doka sy, kofane tc. (2020) evaluation of the cost of producing wind-generated electricity in chad. international journal of energy and environmental engineering, 11:275-287. [19] belabes b, youcefi a, guerri o, djamai m, kaabeche a. (2015) evaluation of wind energy potential and estimation of cost using wind energy turbines for electricity generation on north of algeria. renewable and sustainable energy reviews, 51:1245-1255. [20] ayodele tr, ogunjuyigbe aso, amusan to. (2016) wind power utilization assessment and economic analysis of wind turbines across fifteen locations in the six geographical zones of nigeria. journal of cleaner production, 1-32. [21] kang d, ko k, huh j. (2018) comparative study of different methods for estimating weibull parameters: a case study on jeju island, south korea. energies, 11:1-19. [22] kaplan ya. (2017) determination of the best weibull methods for wind power assessment in the southern region of turkey. iet renewable power generation, 11:175-182. [23] okakwu ik, oluwasogo es, ibhaze ae, imoize al. (2019) a comparative study of time series analysis for forecasting energy demand in nigeria. nigerian journal of technology, 38:465-469. [24] rehman s, alam amm, meyer jp, al-hadhrami lm. (2012) wind speed characteristics and resource assessment using weibull parameters. international journal of green energy, 9:800814. [25] dalabeeh ask. (2017) techno-economic analysis of wind power generation for selected locations in jordan. renewable energy, 101:1369-1378. [26] wind turbine power calculations. rwe npower renewables, mechanical and electrical engineering, uk. [27] akinyele do, rayudu rk, nair nkc. (2015) grid-independent renewable energy solutions for residential use: the case of an offgrid house in wellington, new zealand. in proceedings of ieee pes asia-pacific power and energy engineering conference (appeec), pp 1-5. [28] freris l, infield d. (2008) renewable energy in power systems. 1st ed., wiley and sons, uk. [29] olatomiwa l, mekhilef s, ohunakin os. (2016) hybrid renewable power supply for rural health clinic (rhc) in six geo-political zones of nigeria. sustainable energy technology and assessment, 13:1-12. [30] alsema e. (2000) environmental life cycle assessment of solar home systems. department of science technology and society, utrecht university, utrecht, the netherlands, report nws-e15:1-89. [31] jakhrani aq, othman ak, rigit arh, samo sr. (2012) estimation of carbon footprints from diesel generator emissions. in conference on green and ubiquitous technology, pp 78-81. 156 iium engineering journal, vol. 24, no. 1, 2023 okakwu et al. https://doi.org/10.31436/iiumej.v24i1.2611 nomenclature table coe: cost of energy epm: empirical method hdi: human development index mlm: maximum likelihood method mom: method of moment, nimet: nigeria meteorological agency pdm: power density method te: techno-economic wbl: weibull wecss: wind energy conversion systems 𝑘 = shape parameter 𝑐 = scale parameter (m/s) 𝑉𝑖 = wind speed in time step 𝑖 𝑛= number of non-zero 𝜎 = standard deviation 𝑉 = mean wind speed 𝐸𝑝𝑓 = energy pattern factor 𝑉 3 = average of wind speed cubes (𝑉) 3 = cube of average wind speed 𝑦𝑖 = actual data frequency; 𝑥𝑖 = frequency of wbl parameter; 𝑁 = number of intervals; 𝑓(𝑉𝑖 ) = observed pdf value at bin 𝑖; 𝑓(𝑉) = observed average pdf value 𝑓(𝑉𝑖 ) = estimated pdf value of the computed wbl method at the same bin. 𝐶𝑜𝑝𝑚= operation and maintenance cost 𝑖𝑟 = inflation rate 𝑑 = 𝑑𝑖𝑠𝑐𝑜𝑢𝑛𝑡 𝑟𝑎𝑡𝑒, r= interest rate p = project lifetime 157 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 129 static pipeline network performance optimisation using dual interleave routing algorithm siva kumar subramaniam1*, shariq mahmood khan2, anhar titik3 and rajagopal nilavalan4 1 advance sensors & embedded controls system (asecs), centre for telecommunication research & innovation (cetri), faculty of electronic & computer engineering, universiti teknikal malaysia melaka, malaysia. 2 department of computer science & information technology, ned university of engineering & technology karachi, pakistan. 3,4 department of electronic & computer engineering, college of engineering, design & physical sciences, brunel university london, united kingdom. * corresponding author: siva@utem.edu.my (received: 1st april 2017; accepted: 7th feb 2018; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.841 abstract: in the recent years, there is an increasing demand on multi-hop wireless sensor networks (wsn) especially for remote condition and integrity monitoring of oil and gas pipelines. the sensing points are connected through wsn points, known as a wireless communication medium, between the remotely measured locations on a pipeline and a centralised monitoring station, located some distance away. generally, wsn deployment on a multi-hop linear topology has critical factors that contribute towards overall degrading of network performance proportional to the number of nodes. this is especially true in highly dense networks. in general, such a drawback contributes towards poor network reliability, low network capacity, high latency, and inequality with snowballing effect, increasing in the direction of the destination node. this paper introduces the dual interleaving linear static routing (di-lsr) for a multi-hop linear network with high reliability and efficiency to significantly enhance the overall network performance of a pipeline network. the di-lsr was tested and analysed according to ieee 802.11 standard in a various simulation environment for future real-time deployment in a pipeline network. abstrak: sejak beberapa tahun kebelakangan ini, terdapat permintaan yang drastik pada rangkaian multi-hop sensor wayarles (wsn) terutamanya bagi pemantauan jarak jauh dan integriti saluran paip minyak dan gas. kesemua unit pengesan antara lokasi disambung melalui satu saluran wsn yang dikenali sebagai medium komunikasi wayarles dan diukur ke stesen pemantauan berpusat. penempatan wsn pada topologi linear multi-hop mempunyai faktor-faktor penyumbang kepada penurunan prestasi keseluruhan rangkaian yang berkadar dengan jumlah bilangan nod dalam rangkaian yang padat. secara umum, kelemahan ini adalah penyumbang kepada kebolehpercayaan rangkaian, kapasiti rangkaian rendah, respon rangkaian tinggi dan faktor pendorong kesan ketidaksamaan terhadap nod destinasi. kajian ini memperkenalkan dual interleaving linear static routing (di-lsr) iaitu algoritma jalinan komunikasi cekap bagi mencapai peningkatan ketara keseluruhan prestasi dalam saluran paip rangkaian. di-lsr telah diuji dan dianalisa dalam pelbagai persekitaran simulasi mengikut piawaian ieee 802.11 bagi mengatur kedudukan pada masa depan saluran paip rangkaian. iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 130 keywords: multi-hop linear topology; static routing; ieee 802.11; pipeline; wsn 1. introduction to wsn on oil and gas pipelines the multi-hop wsn has been vastly used for oil and gas pipeline condition monitoring from a centralized location. the wsn plays a major role as a communication medium in relaying real-time happenings from sensing points placed throughout the pipelines. in general, a network of pipelines is known as the safest shipping and most costeffective medium [1] in the oil and gas industry, which is still at risk of physical damage or hazardous accidents [2-4]. in recent years, numerous studies have indicated a series of failures in pipeline transportation yet, when compared to railroad transportation, the percentage of reported incidents or accidents are still very low [1]. pipeline accidents (unpredictable) that lead to oil leaks would result in irregular temperature readings beneath the pipe, whereas a ruptured gas line causes a temperature decrease above the pipe. hence, continuous monitoring of both temperature and pressure on oil and gas pipelines would prompt the process of detecting leaks or ruptured pipes, which would enable faster response to any new accidents that could be a threat to the surrounding environment [2, 5, 6]. 2. static pipeline network: challenges and limitations the three common key features in a wsn deployment on oil and gas pipelines are: (1) data reliability, (2) network scalability, and (3) long-term robustness in the all-weather environment of the application. the sustainability of a multi-hop linear wsn is often related to the overall performance of a network over long-term usage. due to the linear geographical layout of oil and gas pipelines, major limitations on overall network performance result in unfeasible wsn deployment on a highly dense network [7, 8]. in any wsn context, the limitation factors can be categorized as the (1) transmission and carrier sensing range between nodes, (2) queue length, usually referred at a certain node in the network, (3) network capacity to handle the generated data packets, (4) energy consumed in the network and (5) bandwidth allocation. in a conventional static multi-hop linear network, the source node is not only limited to detecting anomalies on pipelines but also as an intermediate node that is required to transfer bi-directional packets throughout the network. thus, the data and control packet accumulation at a certain node would result in a bottleneck state and further create node starvation in the network. referring to the ieee 802.11 standard, a series of impending factors in terms of performance can be related to the unpopularity of a multi-hop linear topology when associated with other topologies [9-11]. the three most common factors in a static multihop linear network are; (1) limited scalability that (2) contributes towards passive nodes in the network due to the data accumulation factor at a specific node in the network (commonly close to the destination node). apart from that, (3) wastage of network resources due to competitive data transfer in a large network with a high data rate is a waste of the network allocation, especially of energy usage. technically, with the proposed routing algorithm, these factors can be manipulated with a tailored and improved routing algorithm based on the nature of the application such as the pipeline network, particularly in enhancing the overall network performance [12]. iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 131 3. introduction and background works in pipeline network generally, oil and gas pipelines can be categorised as a fixed infrastructure that is commonly stretched over an extensive distance from one point to another. this is the concept of chain communication over a series of intermediate nodes between detection points (sensing nodes) to the centralised monitoring station (receiving node) in order to transfer data as required by the user [13, 14]. the static wsn comprises a sequence of source nodes (sensing points) that operate as hosts when changes are detected on a sensor and also act as routers in a communication path towards a destination node. in general, a data packet generated at the source node requires a navigated wireless communication path to successfully transmit the data packet to a designated receiver node (destination). the route discovery or route identification on a multi-hop linear network among source nodes (multiple nodes) to a destination node (usually one located at the end of the network) is accomplished with a sequence of broadcast packets referred to the used routing protocol characteristic. the four common routing protocols are; (1) reactive routing protocol also known as the on-demand routing protocol, (2) the proactive routing protocol also known as the table-driven protocol, (3) the hybrid routing protocol (a combination of both reactive and proactive protocols), and (4) manual routing protocols [15, 16]. all these routing protocols are different in nature and have a unique process flow with respect to the route discovery and data transfer process, which in turn has significant implication when applied in a wireless network. the ad hoc on-demand distance vector (aodv) is the most common and popular reactive routing protocol [16-18]. the route search or identification is completed based on demand and real-time changes in a network. the newest route to a destination node is identified from a sequence of numbers at the destination. in a scenario with two nodes located in a transmission radius (range in meter), the node has the possibility to bypass the next immediate node based on the circumstances and real-time changes in the network. another on-demand routing protocol that has a similarity to aodv is the dynamic source routing (dsr) [16, 18] where sender and receiver node route navigation is incorporated with transmitted data packets. the route to a designated destination node is generated by referring to the accumulated route information that is temporarily stored in all the nodes. the drawback of dsr is higher overhead that makes it unreliable for long range multi-hop linear communication. the destination-sequence distance-vector routing protocol (dsdv) is a common proactive routing protocol [14, 17, 18]. there is a minimum delay between the route identification and route setup process in dsdv for an accessible path to a receiver node. the major drawback with dsdv is that frequent routing table updates are required throughout the active period of the network, referred to as a dynamic changing environment in the network. hence, this results in a network that consumes higher energy cost as well as bandwidth allocation even in an idle network state. a table-driven routing protocol that has similarities with dsdv routing protocol is optimised link-state routing (olsr) [16], which identifies the routing path to a receiver node from recognized paths prior to data packet transmission. thus, the accessible path to a designated node requires zero duration in the route discovery process. the drawback of olsr is the higher routing overhead. fixed routing path (frp) is a static manual routing algorithm that is efficient with suppressed broadcast related packets for a pre-calculated optimal shortest path [19, 20]. the multi-hop routing algorithm takes into account all possible paths between nodes in a network with the shortest path. the data merging technique prior to transmission to the iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 132 receiver node through a specific cluster head on a multi-tier cluster-based topology is designed to reduce actual data packet transmission in a wireless network [21, 22]. the power-efficient node placement scheme (penps) is based on optimisation of node and distance to diverse route loss parameters on a linear wsn [23]. a hierarchical node arrangement that segregates nodes into three groups with specific tasks assigned at each level in the network. the basic sensor nodes at the lowest level of the network communicate the data packets to the next level, which is the data relay nodes, before sending the data packets to the data dissemination nodes in a linear network [13]. the author in [24] introduces the flat data collection algorithm for wireless nodes that respond to unplanned data packets in a network. the data packet is then forwarded to a node with minimum waiting time in the neighbouring nodes. in any wireless network, routing protocols are associated with network performance, which is a crucial factor that reflects on various wireless measures. the most important measure in any routing protocol is the link stability between nodes, wherein a link failure state contributes to the loss of data packets in the network. a wireless node generates broadcast-related packets in a periodic cycle (time interval) to all its neighbouring nodes that are in its transmission/communication range to ensure their presence. this process also ensures and helps the nodes to retain the existing route or to identify new routes in the network. hence, this process creates an overwhelming rate of broadcast along with control packets in a wireless network. a simple data accumulation factor on a series of nodes is as shown in eqn. (1) where the shared network allocation towards a receiver node located at the end of a certain network. 𝑁𝑇𝑃 = [(𝐷𝑃𝑗 + 𝐶𝑃𝑗 ) + ∑ (𝐷𝑃𝑘 + 𝐶𝑃𝑘 ) 𝑛 𝑘=𝑗+1 ] ≤ 𝐼𝑓𝑄𝑙𝑒𝑛𝑗 (1) where total bi-directional packets are described as ntp for n number of source nodes, dpj is the total data packets and cpj is the total control packets at node j with 1≤j≤n with ifqlenj is the default queue size set at 50 packets in a network. while dpk is the total data packets and cpk is the total control packets at neighboring node k. the multi-hop linear topology is an important communication architecture on an extended range pipeline network. due to the unique geographical terrain and data accumulation factor in a single path, communication contributes to the occurrence of nodes without data transmission opportunity (passive nodes) between the sender and a receiver node [19, 20]. most of the traditional dynamic and hybrid routing protocols have different characteristics from network initialization to a route discovery process [12, 21, 22]. one of the crucial factors in a multi-hop linear communication is queue overwhelming from both data and control packets that lead to a bottleneck point in the network. such factors in routing protocols are often related to frequent communication link instability. link instability will trigger a route maintenance procedure at a certain point in the network and increase the consumption of network resources, which will eventually contribute to underperformance of network characteristics. this would result in an increasing number of passive nodes or node failures (due to limited power), which is a waste of network resources and allocation that subsequently degrades the overall network performance [17]. the issues with higher routing overhead, queue overwhelming, frequent updates on route and passive nodes, drives the research motivation to the development of a static routing algorithm. this can eliminate broadcast related routing overhead, predefine routing path, reduce the effects of queue overwhelming and eventually enhance the overall network performance. iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 133 4. dual interleaving technique in multi-hop linear network the dual interleaving linear static routing (di-lsr) is designed for a multi-hop linear network to enhance overall network performance compared other routing algorithms, as discussed in section 3. the predefined dual routing path (odd and even) concept introduced in di-lsr would improvise the overall network performance, particularly on the network capacity and issues with passive nodes. a simple seven node arrangement, as proposed in di-lsr, with three source nodes on each path to a single destination node in a predefined route is shown in fig. 1. node placement or arrangement in a multi-hop linear topology plays a major role in the establishment of a sustainable communication between a sensing and a receiver point. connectivity is often highlighted with node placement as one of the affecting factors on optimisation issues in any multihop linear network. referring to fig. 1, nodes are arranged in d distance (uniform interval) where 2d distance is the maximum transmission range. the concept of predefined dual routing path ensures that bi-directional flow of both data and control packets are always in a specific path between a sensing point (source nodes) and receiver point (sink node) in a pipeline network. this essentially splits the overwhelming queue factor into two, further improving the data flow rate towards the destination node. fig. 1: di-lsr with source nodes (on/en) and a single destination node (nd). the eliminated broadcast packets in di-lsr reduces the routing table generating time to near-zero, since the network is always in a known state with the available nodes in the network at the first active period. in a conventional multi-hop linear network, a single routing table is generated for all nodes that are partially/fully kept in all nodes. these routing table entries are updated periodically based on the characteristic of the routing protocol used that is time-consuming as well as energy-consuming, to support the broadcast packets. unlike a standard routing protocol, the di-lsr generates two routing tables; (1) forward for odd and even as described in fig. 2 and (2) reverse routing table that retains all source node entries at the destination node with the respective routing path as described in fig. 3. the routing process in di-lsr starts at the initialization state with no broadcast and hello packets where all nodes in the network are presumed to be at a prefixed position in a standby state at all times. the di-lsr is designed for an ideal network environment without expected changes in the network active period, thus, no routing table updates are expected at any time. the routing table in di-lsr is generated based on the odd and even iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 134 fig. 2: forward path routing table in di-lsr. fig. 3: reverse path routing table in di-lsr. sequence of nodes in the network. the di-lsr generates two bi-directional odd and even route between source to a destination node as shown in fig. 4. the flow of packets (data and control packets) in both source and a destination nodes in di-lsr is restricted on a dedicated path without path crossing possibilities. there is a standard queue limitation as in any routing protocol as mentioned in table i. the concept of queue limitation and data accumulation factor on both odd and the even path is as described in eqn. (2) and eqn. (3) respectively. 𝑇𝑃𝑂 = [(𝐷𝑃𝑂𝑗 + 𝐶𝑃𝑂𝑗 ) + ∑ (𝐷𝑃𝑂𝑘 + 𝐶𝑃𝑂𝑘 ) 𝑛𝑛 𝑘=𝑗+1 ] ≤ 𝐼𝑓𝑄𝑙𝑒𝑛𝑂𝑛 (2) where tpo is the total packets for a nn number of nodes (odd), dpoj is the total data packets and cpoj is the total control packets at node j with 1≤j≤nn with ifqlenon as the queue length in the network. while dpok is the total data packets and cpok is the total control packets at neighbouring node k. 𝑇𝑃𝐸 = [(𝐷𝑃𝐸𝑗 + 𝐶𝑃𝐸𝑗 ) + ∑ (𝐷𝑃𝐸𝑘 + 𝐶𝑃𝐸𝑘 ) 𝑛𝑛 𝑘=𝑗+1 ] ≤ 𝐼𝑓𝑄𝑙𝑒𝑛𝐸𝑛 (3) iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 135 fig. 4: process flow of data packets in di-lsr. where tpe is the total packets for a nn number of nodes (even), dpej is the total data packets and cpej is the total control packets at node j with 1≤j≤nn with ifqlenen as the queue length in the network. while dpek is the total data packets and cpek is the total control packets at neighbouring node k. any incoming data packets at an intermediate node where the queue length > ifqlenon/ifqlenen is discarded at this point. with the proposed dual path technique and low routing overhead routing algorithm further reduce the effect of routing overhead hence allocates more bandwidth for data packets. the end source nodes in odd and the even path will be connected to the destination node with the same queue limitation. the data accumulation factor at a destination node is as described in eqn. (4). ntp = tpo + tpe ≤ ifqlen (4) iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 136 where ntp is the network total packets at the destination for n number of nodes which could be odd/even and the value of tpo/tpe is from eqn. (3/4). the proposed routing algorithm designed with a dual interleaving technique would add great performance enhancement when implemented in a pipeline network compared to any conventional routing algorithm. one of the key features of di-lsr is the reduced basic control packets especially broadcast packets as the nodes in the network is permanently fixed. with limited control packets, di-lsr enables a significant increase in data packet transfer rate as desired in any wireless network. 5. simulation setup in all simulation setups using network simulator 2 (ns2) [25], di-lsr was compared with a reactive routing protocol (aodv), a proactive routing protocol (dsdv), and a manual routing algorithm (frp) for performance comparison. the results are from an average value of five runs with different seed number (1-10) over 500 seconds (simulation duration) with all nodes in a fixed location. the data size is set at 512 bytes at a rate of 1 packet/sec with a random start time generated between 0 – 2 seconds. the agent type used in the simulation is transmission control protocol (tcp) and traffic type is constant bit rate (cbr). table 1 indicates the basic predefined simulation settings in ns2. table 1: ns2 simulation parameters parameters value channel type wireless channel radio propagation model two ray ground mac type 802.11 interface queue type droptail/priqueue source nodes 12, 24, 36, 48, 60, 72, 84, 96, 108, 120 destination node 1 max packet in ifqlen 50 (packets) rx thresh/cs thresh 100 meters/125 meters 6. simulation results in all the simulation environment, the di-lsr was tested and evaluated along with aodv, dsdv and frp on the following wireless metrics: 6.1 packet delivery ratio the most fundamental and crucial parameter measured in any wireless network is the packet delivery ratio that indicates the rate of receiving data packets over send data packets [10, 13, 14]. the packet delivery ratio in fig. 5 for all compared routing protocols is in reverse proportion to the increasing number of source nodes. referring to fig. 5, at low network densities with 12 source nodes, the packet delivery ratio is almost at the same rate among all routing protocols due to the small network size. the packet delivery ratio of di-lsr with the technique proposed in section 4 outperforms all the other routing protocol with varying numbers of source nodes in the simulated environment. the implementation of the predefined dual routing path (splits the traffic into two paths) iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 137 enables better data flow towards the destination node than other routing protocols. creating two interleaving individual paths accommodates more data on the queue as well as promotes a better data transfer rate when compared to the traditional routing protocols in the simulation. the packet delivery ratio rate, in percentage (%), gives a brief understanding of the successfulness of packets received rather than the actual number of packets received. thus, further performance factors can be visualized in the following results. fig. 5: graph of packet delivery ratio (%) versus the number of source nodes. 6.2 throughput the average throughput value from all source nodes in the network [10, 22] can be described as the network capacity to handle a specific data size in a given duration. the performance in a wsn is the ability to achieve higher throughput within the available network resource, which is a desirable goal in any network. the throughput results presented in fig. 6 are measured from a small network size of 12 source nodes to a large network size of 120 source nodes. figure 6 shows that di-lsr outperforms all the other compared routing protocols. the curve pattern of throughput is almost the same as dilsr with a significant difference between 24.12 kbps to 43.73 kbps in the varying number of source nodes compared to the other routing protocols. the di-lsr routing algorithm enhances the data rate among source nodes placed in dual interleaving path with more room to accommodate the generated data on the outgoing queue within the available network resources. the amount of data transferred in a specific duration is critical in a pipeline network for the monitoring station personnel to visualize the integrity of pipelines. moreover, with a small difference in the packet delivery ratio as shown in fig. 5, the di-lsr has a significant impact on throughput for the simulated scenario that makes it a more desirable choice for a multi-hop linear wireless network. 6.3 end-to-end delay end-to-end delay is the average value of total time taken to transmit data over all the flows in the network [10, 13]. referring to fig. 7, the end-to-end delay in di-lsr is fairly low when compared to the received data rate at the destination node. generally, the endto-end delay in a multi-hop linear network has a corresponding effect on received data rate and network fairness measured in the fairness index. therefore, the steady increase in endto-end delay with di-lsr is proportional to the varying number of source nodes (distance between the source and destination nodes increases) in the network, higher packet delivery ratio and throughput rate. the higher throughput rate as shown in fig. 6 using di-lsr iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 138 justifies the reasons for the higher end-to-end delay in fig. 7. to reduce the end-to-end delay to a reasonable rate, controlling the number of generated packets in the network will be applicable as a short-term solution in a multi-hop linear topology. fig. 6: graph on throughput (kbps) versus the number of source nodes. fig. 7: graph of end-to-end delay (ms) versus the number of source nodes. 6.4 fairness index fairness or data transfer equality in a multi-hop linear topology is a crucial factor from the perspective of network stability and scalability. the scalar measurement of resources (data packets) allocation discrimination among all source nodes [22] is known as the throughput fairness index. achieving the optimum throughput fairness index is a challenging task for the routing algorithm in multi-hop linear wireless networks, particularly in a large scale implementation. in a small size linear network, fairness is hardly visible as shown in fig. 8. the result of the fairness index indicated that a network with di-lsr has a reasonable rate of equality in the network when compared to aodv, dsdv and frp. the throughput fairness index of di-lsr outperforms all the other routing protocols with a significant difference of 0.2711 to 0.3735 in all simulated environments. a network with di-lsr has a better data flow and transmission opportunity among source nodes in the proposed dual path instead of a single path as in a traditional multi-hop linear network. with a reasonable rate of throughput fairness index and higher throughput capacity ensures a network with di-lsr to achieve a fair network allocation iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 139 with optimum performance. the fairness index can be further improved by controlling the number of generated packets and the tcp delayed acknowledgement method. fig. 8: graph of throughput fairness index versus the number of source nodes. 6.5 consumed energy the energy consumption per-packet is as shown in fig. 9, which indicates di-lsr and other routing protocols have a constant increase of network energy with the increasing network size. the energy consumption per-packet increase factor in di-lsr is due to the data amplification rate and increasing distance between a source and a destination node in all simulated environments that is higher when compared to other routing protocols. based on the number of data packets received and the throughput fairness index, di-lsr has a fair use of energy when compared to all the other routing protocols shown in fig.9. the energy consumption in a network is relatively related to the network capacity and equality among source nodes as shown in fig. 6 and fig. 8, respectively. theoretically, the energy consumption is proportional to the network size in a multi-hop linear topology due to the increasing distance between a source and the destination node. fig. 9: graph of energy per-packet (joules) versus the number of source nodes. 6.6 normalised routing load the effect of varying the number of source nodes increases the routing overhead in the network for all compared routing protocols as shown in fig. 10. the routing overhead iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 140 in a network with the implementation of di-lsr is relatively lower when compared in terms of received data packets among the other routing protocols between a low network density with 12 source nodes to a larger network density with 120 source nodes. with a reduced rate of control packets, particularly with broadcast related packets, help to reduce the control packet traffic in a network especially with an increasing number of source nodes in a network. the lower routing overhead reduces queue overflow and enables better network resources allocation for data packet transmission between a source and a destination node. a routing algorithm with lower routing overhead is a viable solution for a long-range multi-hop linear architecture such as the pipeline network. fig. 10: graph of network routing load versus the number of source nodes. fig. 11: graph of passive nodes (%) versus the number of source nodes. 6.7 passive nodes passive nodes are known as the nodes in a certain network without the opportunity to successfully send data packets to a destination node. the passive nodes are a result of inequality or bias sharing of the network resources that are undesirable in a multi-hop linear topology. a network with di-lsr has no issues with passive nodes in all simulated environments whereas the other routing protocols have an incrementing factor on passive nodes with the increasing number of source nodes as shown in fig. 11. a routing protocol that requires broadcast packets contributes towards a higher number of passive nodes due to overwhelming of the queue and uncontrolled data packet flow as shown in fig. 11. the fluctuation rate of passive nodes is due to the characteristic of a routing protocol that changes in real-time during the simulation based on the data or traffic pattern in the data iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 141 path that can be corrected with a modification of the data packet transmission rate. generally, such a network state contributes to waste of network resources, poor delivery ratio, lower throughput rate and can lead towards communication termination that may lead to a certain point in a network due to a single point failure factor in a multi-hop linear topology. 7. conclusion the outcome of the implementation of the di-lsr in a pipeline network has emphasized optimization towards the overall network performance in a scalable linear network. the proposed di-lsr features a beaconless routing algorithm that reduces the network routing load which is a crucial factor in a multi-hop linear wireless architecture. the predefined odd and even path further enhances the overall network performance with better network allocation to eliminate issues with passive nodes. simulations to remake a pipeline network were executed to evaluate the proposed di-lsr in varying network densities that result in a significant level of enhancements in reliability (packet delivery ratio), latency (end-to-end delay), and responsiveness (passive nodes) that has critical implication to the sustainability of a pipeline network. 8. future work the overall performance enhancement with di-lsr has functional implications mainly in network capacity and fairness at this state of research that is a common limitation in a multi-hop linear topology, especially with a single destination node. this factor can be further analysed to optimise both performance and fairness using di-lsr. hence on the next stage of work, the di-lsr is proposed to be implemented on a clusterbased topology to further improve the network capacity as well as dealing with passive nodes in the long run. whereas the network equality issues can be improvised with a model of tcp delayed acknowledgement that can be incorporated with di-lsr to optimise fairness in a network. the performance and fairness are often related to the energy consumption on a network. thus, an efficient energy model will add benefit for the implementation in a remote location especially with a non-infrastructure setup. acknowledgement this work is part of a research project entitled analysis and implementation of an iot based remote monitoring of oil and gas pipelines, grant no. pjp/2018/fkekk (5b)/s01618 funded by universiti teknikal malaysia melaka. the authors would like to thank ministry of higher education malaysia, universiti teknikal malaysia melaka and brunel universitylondon for their financial support, lab facilities, sincere encouragement and assistance. references [1] kenneth p. green, taylor jackson. (2015) safety in the transportation of oil and gas: pipelines or rail?. fraser research bulletin; pp.1 14. [2] al-ghamdi a j, abdullah a, khan a m, daraiseh a. (2010) improving safety in oil and gas pipelines and offshore project using wireless sensors networks. in proceedings of the pipeline technology conference 2010; pp. 1-8. iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 142 [3] rao y c, rani s, lavanya p. (2012) monitoring and protection of oil and gas condition in industrial using wireless sensor networks. international journal of electronics communication and computer technology, 2:213-218. [4] devold h. (2013) oil and gas production handbook: an introduction to oil and gas production. lulu press. [5] boaz l, kaijage s, sinde r. (2014) wireless sensor node for gas pipeline leak detection and location. international journal of computer applications, 100:29-33. [6] jung j, song b. (2014) the possibility of wireless sensor networks for industrial pipe rack safety monitoring. in proceedings of the 47th hawaii international conference in system sciences (hicss); pp. 5129-5134. [7] arthi k, vijayalakshmi a, ranjan p v. (2013) critical event based multichannel process control monitoring using wsn for industrial applications. procedia engineering, 64:142148. [8] obodoeze f c, ozioko f e, mba c n, okoye f a, asogwa s c. (2013) wireless sensor networks (wsns) in industrial automation: case study of nigeria oil and gas industry. international journal of engineering research and technology, 2 (3):1-7. [9] pedram radmand, alex talevski, stig petersen, simon carlsen. (2010) comparison of industrial wsn standards. in proceedings of the 4th ieee international conference on digital ecosystems and technologies: 13 16 april 2010; pp. 632. [10] jawhar i, mohamed n, agrawal d p. (2011) linear wireless sensor networks: classification and applications. journal of network and computer applications, 34:1671-1682. [11] savazzi s, guardiano s, spagnolini u. (2013) wireless sensor network modeling and deployment challenges in oil and gas refinery plants. international journal of distributed sensor networks, 2013:1-17. [12] zhengjie wang, xiaoguang zhao, xu qian. (2011) the application and issuse of linear wireless sensor networks. in proceedings of the 2011 international conference on system science, engineering design and manufacturing informatization: 22 – 23 october 2011; pp. 9. [13] jawhar i, mohamed n, mohamed m m, aziz j. (2008) a routing protocol and addressing scheme for oil, gas and water pipeline monitoring using wireless sensor networks. in proceedings of the 5th ifip international conference on wireless and optical communications networks; pp. 1-5. [14] subramaniam s k, khan s m, nilavalan r, balachandran w. (2016) network performance optimization using odd and even routing algorithm for pipeline network. in proceedings of the 8th computer science & electronic engineering conference: 28 30 september 2016; pp. 118-123. [15] goyal d, tripathy m r. (2012) routing protocols in wireless sensor networks: a survey. in proceedings of the 2012 second international conference on advanced computing & communication technologies; pp. 474-480. [16] khan s m, nilavalan r, sallama a f. (2015) a novel approach for reliable route discovery in mobile ad-hoc network. wireless personal communications, 83:1519-1529. [17] paul b, bhuiyan k a, fatema k, das p p. (2014) analysis of aomdv, aodv, dsr, and dsdv routing protocols for wireless sensor network. in proceedings of the 2014 international conference on computational intelligence and communication networks (cicn); pp. 364-369. [18] pathak g r, patil s h, rana a, suralkar y. (2014) mathematical model for routing protocol performance in ns2: comparing dsr, aodv and dsdv as example. in proceedings of the 2014 ieee global conference on wireless computing and networking (gcwcn); pp. 184188. [19] wu z, raychaudhuri d. (2004) d-lsma: distributed link scheduling multiple access protocol for qos in ad-hoc networks. in proceedings of the 2004 ieee on global telecommunications conference globecom'04; pp. 1670-1675. [20] boas l b v, massolino p m, possignolo r t, margi c b, silveira r m. (2012) performance evaluation of qos in wireless networks using ieee 802.11 e. in proceedings of the simpósio brasileiro de telecomunicações: 13-16 november 2012; pp. 1-5. iium engineering journal, vol. 19, no. 1, 2018 subramaniam et al. 143 [21] wang z, zha x, qian x. (2011) the application and issuse of linear wireless sensor networks. in proceedings of the 2011 international conference on system science, engineering design and manufacturing informatization (icsem); pp. 9-12. [22] jamatia a, chakma k, kar n, rudrapal d, debbarmai s. (2015) performance analysis of hierarchical and flat network routing protocols in wireless sensor network using ns-2. international journal of modeling and optimization, 5:40-43. [23] cao m, yang l t, chen x, xiong n. (2008) node placement of linear wireless multimedia sensor networks for maximum network lifetime. in advances in grid and pervasive computing, springer; pp. 373-383. [24] yu h, guo m. (2012) an efficient oil and gas pipeline monitoring systems based on wireless sensor networks. in proceedings of the 2012 international conference on information security and intelligence control (isic); pp. 178-181. [25] issariyakul t, hossain e. (2011) introduction to network simulator ns2, springer science & business media. microsoft word 7-harun-iiumej-30=1-27-2-o.k.doc iium engineering journal, vol. 2, no. 1, 2001 s. w. harun et al. 53 continuously tunable erbium-doped fiber ring laser using fiber bragg grating s. w. harun and h. ahmad department of physics, faculty of science, university malaya, 50603 kuala lumpur p. poopalan telekom malaysia photonics research center, university malaya, 50603 kuala lumpur e-mail: wadi72@yahoo.com abstract: an efficient tunable erbium-doped fiber (edf) ring laser utilizing a single fiber bragg grating (fbg) and an optical circulator is investigated. the laser demonstrates a threshold of 3.43 mw and a slope efficiency of 12.5%. tunability of the fiber laser is obtained by thermal tuning of the fbg. simultaneous temperature tuning demonstrates a 0.01 nm/oc variation in laser wavelength. key words: fiber bragg grating, fiber laser, tunable laser, ring laser, thermal tuning 1. introduction continuous-wave wavelength tunable erbium-doped fiber (edf) ring lasers operating in the 1550 nm band have important applications in wavelength-division multiplexing systems and sensor technology. the two main ingredients of a laser are a gain medium that provides amplification and a suitable cavity that provides positive optical feedback [1]. so far various unidirectional ring or loop configurations have been developed. ring-structure edf laser with transmissiontype filters, such as compound-ring resonator [2], fabryperot filter [3], or mach-zehnder interferometer [4] have been demonstrated. edf lasers using fiber bragg grating (fbg) in a short linear fabry-perot cavity with excellent results were also obtained [5], [6]. however, in a traveling wave fiber ring laser cavity, it is easier to achieve single longitudinal mode operation with a high output power [7]. in this paper, a tunable edf ring laser using an fbg, which is incorporated into the fiber ring laser with an optical circulator, is reported. 2. experiment the experimental set up of the tunable edf ring fiber laser is shown in fig. 1. it consists of a section of an edf, a 980/1550-nm wavelength-division multiplexer (wdm) coupler, a four-port optical circulator, a 3-db wide band coupler (wbc) and an fbg. a 980-nm diode laser pump is coupled into the edf via the wdm coupler. the fbg is connected to port 2 of the circulator, and reflection from the fbg is routed to port 3. the light is split to half by the 3-db coupler. one half of the light propagates through the wdm to initiate laser oscillation. output is obtained from the other port of the coupler. the fbg has a reflectivity of 97.4% at the center wavelength of 1553.4 nm and a 3-db bandwidth of 0.32 nm. it has been fabricated in high germania boron co-doped fiber with a 244-nm argon ion laser and a phase mask [8]. tunability of the edf laser is obtained by thermal tuning of the fbg. the tuning operation can be achieved by tuning the bragg wavelength of the fbg [9], given by = 2neff, where neff is the effective refractive index and  is the period of the fbg. an electric oven is used to subject the fbg to temperature variation. wdm wbc osa ld 980 nm edf c c fbg c c : connector thermal tuning 1 2 3 4 fig. 1 setup of a tunable edf ring laser 3. result and discussion the output power against the coupled-in pump power at the lasing wavelength of 1553.3 nm is shown in fig. 2. it has a measured lasing threshold of 3.43 mw and a slope efficiency of 12.5%. a typical output spectrum of the tunable edf ring laser is shown in fig. 3. it has a stable output with an extinction ratio of 85 db with respect to ground and an output spectralwidth of 0.02 nm limited by the optical spectrum analyzer resolution. the laser wavelength against temperature is shown in fig. 4. simultaneous temperature tuning demonstrates a 0.01 nm/c variation in the laser wavelength. a continuous tuning range of 0.9 nm is obtained by varying the fiber temperature from 39 to 126c, as observed from an optical spectrum analyzer (osa). iium engineering journal, vol. 2, no. 1, 2001 s. w. harun et al. 54 the laser threshold is extremely low since it takes very little pump power to almost fully invert the er3+ ions. the fbg slope efficiency can be improved by increasing the edf length, using higher erbium concentration edf and reducing the cavity loss. the laser operates as a three level laser system when excited by a 980 nm pump laser so that a length of unpumped fiber absorbs strongly at the lasing wavelength. for a given fiber length, lasing can occur only if the gain available from the bleached section equals, or exceeds, the loss of the remaining length. the use of high concentration edf will increase the absorption per unit length and it can reduce the edf length requirement. the low cavity loss increases the oscillating laser power in the cavity. wavelength tuning in the fiber laser is achieved by heating the fbg. the laser oscillates at particular wavelength, corresponding to the center wavelength of the fbg. the variation in bragg wavelength with respect to thermal variation is generally dependent on the fiber thermal expansion and thermo-optic effects. it is given by [10], [11] t where  is the thermal expansion coefficient and  is the thermo-optic coefficient. fig. 2 output power as a function of coupled in pump power fig. 3 spectrum of laser output measured by optical spectrum analyzer fig. 4 fiber laser wavelength against applied temperature 4. conclusions tunable edf ring laser using a high reflectivity fbg incorporated into the laser cavity by an optical circulator is investigated. efficient lasing with a laser threshold of 3.43 mw and a slope efficiency of 12.5% is obtained. a tunability of 0.9 nm is obtained by varying the fiber temperature from 39 ~ 126oc. it is expected that an improved tuning range and tuning response would be found using a grating stretcher/compressor. acknowledgement s. w. harun acknowledges the support of a national science fellowship (nsf), moste. references [1] a. e. siegman, “laser,” university science book, mill valley, california, 1986. [2] j. zhang and j. w. y. lit, “erbium doped fiber compound-ring laser with a ring filter,” ieee photon. technol. lett., 6, 588, 1994. [3] j. l. zyskind, j. w. sulhoff, y. sun, j. stone, l. w. stulz, g. t. harvey, d. j. digiovanni, h. m. presby, a. piccirilli, u. koren, and r. m. jopson, “singlemode diode-pumped tunable erbium doped fiber laser with linewidth less than 5.5 khz,” electron. lett., 27, 2148, 1991. [4] y. t. chieng and r. a. minasian, “tunable erbiumdoped fiber laser with a reflection mach-zehnder interferometer;” ieee photon. technol. lett., 6, 153, 1994. [5] g. a. ball, w. w. morey, “continuously tunable singlemode erbium fibre laser,” opt. lett., 17(6), pp. 420-422, 1992. [6] j. t. kringlebotn, j. l. archambault, l. reekie, j. e. townsend, g. g. vienne, and d. n. payne, “highly efficient, low-noise grating-feedback er3+:yb3+ co-doped fibre laser,” electron. lett., 30 (12), pp. 972-973, 1994. [7] j. l. zyskind, v. mizrahi, d. j. digiovanni and j. w. sulhoff, “ short single-frequency erbium-doped fiber laser,” electron. lett., 28 (15), pp. 1385-1387, 1992. 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0 10 20 30 40 50 pump power, mw o ut pu t p o w er , m w slope = 12.5% -80 -60 -40 -20 0 20 1551 1552 1552 1553 1553 1554 1554 1555 1555 wavelength (nm) o ut pu t p ow er (d b m ) 1553.4 1553.6 1553.8 1554.0 1554.2 1554.4 30 50 70 90 110 130 temperature (c) la se r w av el en gt h (n m ) slope=0.01 iium engineering journal, vol. 2, no. 1, 2001 s. w. harun et al. 55 [8] s. w. harun, p. poopalan, and h. ahmad, “fabrication of fiber bragg gratings in high germania boron co-doped optical fiber by the phase mask method,” submitted to jurnal teknologi, utm. [9] s. w. harun, p. poopalan, and h. ahmad, “temperature sensitivity of fiber bragg gratings fabricated in high germania boron co-doped optical fiber,” submitted to journal sains malaysiana, ukm. [10] g. ghosh, “temperature dispersion of refractive indexes in some silicate fiber glasses,” ieee photon. tech. lett., vol.30, pp.359-370, 1979. [11] g. meltz and w. w. morey, “bragg grating formation and germanosilicate fiber photosensitivity,” in. proc. spie photoinduced self-organization effects in optical fiber, f. ouellette, ed., vol.1516, pp.185-199, 1991. biographies sulaiman wadi harun received his b. eng in electrical and electronic system engineering from nagaoka university of technology, japan in 1996. currently he is studying for his m.sc. in department of physics, university of malaya. prabakaran poopalan received his b.sc. and m.sc from university of malaya in 1994 and 1996, respectively. he is a researcher with telekom malaysia r & d and is involved in fiber bragg grating project. harith ahmad is a professor at physic department, faculty of science, university of malaya. he obtained his ph.d from university of swansea (u.k) in laser technology, 1983 and has been involved in laser related research the past 15 years. he has numerous research papers published both local and international journals. microsoft word 188 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering md. rashid 131 nuclear energy: an ethical use of resources nahrul khair alang md. rashid department of mechatronics engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. nahrul@iium.edu.my abstract: energy is the lifeblood of development, but its amount is finite. it can neither be created nor destroyed; but it can be converted from one form to another. the conversion changes the state of the resources and the change generally is not reversible. nuclear energy steadily contributes about 16 percent to global total electricity demand. its application for electricity production is expected to increase due to dwindling natural resources, concern for greenhouse gaseous emission, and the limited capability of renewable energy and biofuels to be major energy resources. nuclear energy, however, is plagued with ever presence public perception issues, some are real some are due to misperceptions. the trio of accidents: three mile island, chernobyl, and most recently, fukushima, however has slightly dampened the prospect. nuclear energy makes use of uranium, an element that has no peaceful applications other than to be used in nuclear power reactors to generate heat or neutrons, produce steam, and drive turbo-generators for electricity production. other resources, such as oil, coal, and gas have multiplicity of uses that cannot be substituted by uranium. on that premise, this paper argues that the use of nuclear energy is an ethical choice. this choice overrides considerations, such as waste, complexity, and safety that are often projected as reasons for avoiding it altogether. those considerations are of scientific and engineering dimensions that mankind has to wrestle and overcome as the khalifah. in so doing, proper education and ethical use of knowledge become imperative. abstrak: tenaga adalah nadi pembangunan, tetapi jumlahnya terbatas. ia tidak boleh dicipta atau dimusnahkan; tetapi ia boleh ditukar dari satu bentuk ke bentuk lain. pertukaran bentuk ini mengubah keadaan sumber tenaga dan perubahan tersebut tidak boleh ditukarbalik. tenaga nuklear menyumbang kira-kira enam belas peratus kepada jumlah permintaan elektrik global. keperluan tenaga elektrik dijangka meningkat kerana pengurangan sumber asli, kebimbangan atas pelepasan gas rumah hijau, dan keupayaan biofuel dan tenaga boleh diperbaharui untuk menjadi sumber tenaga utama. namun begitu, tenaga nuklear sentiasa dibelenggu oleh isu-isu persepsi umum, sebahagiannya benar dan sebahagian lagi disebabkan oleh salah anggap. ketiga-tiga kemalangan nuklear: three mile island, chernobyl, dan baharu-baharu ini, fukushima, bagaimanapun menjejaskan sedikit prospek berkenaan. tenaga nuklear menggunakan uranium, suatu unsur yang tidak mempunyai sebarang kegunaan aman selain daripada digunakan dalam reaktor nuklear untuk menjana neutron atau haba, menghasilkan wap, dan memacu turbo-generator yang mengeluarkan elektrik. sumber-sumber lain seperti minyak, arang batu dan gas mempunyai pelbagai kegunaan yang tidak boleh digantikan oleh uranium. atas hujjah itu, rencana ini mengutarakan bahawa penggunaan tenaga nuklear adalah pilihan yang beretika. pilihan ini mengatasi pertimbangan-pertimbangan seperti sisa, kerumitan teknologi, dan keselamatan yang sering ditonjolkan sebagai alasan untuk mengelakkan sama sekali kegunaan tenaga nuklear. pertimbanganiium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering md. rashid 132 pertimbangan tersebut adalah dalam dimensi saintifik dan kejuruteraan yang manusia, sebagai khalifah, perlu tangani dan atasi. dalam berbuat demikian, pendidikan yang sempurna dan penggunaan pengetahuan yang beretika menjadi penting. keywords: nuclear energy; greenhouse gas; renewable energy; ethical energy use; nuclear fuel; uranium; nuclear reactor 1. introduction energy is the lifeblood of development. when fire was discovered and its uses were mastered and expanded, mankind has been able to progress by the leaps and bound. it is used both as heat as well as light sources. the use of energy, today, has become one of the yardstick for the measurement of the progress of a country. the international energy agency, in its recent report devised a means for linking energy usage and state of development in an index called energy development index, which is based on per capita commercial and residential energy consumptions, share of modern fuel in total energy use in residential sector, and share of population with access to electricity[1]. it is clear that countries that are more developed has higher energy development index than those that are less developed. energy, however, is finite in amount. it can neither be created nor destroyed. it can be converted from one form to another that suits its intended application. the conversion changes the state of the resources and the conversion is generally not reversible in a short period of time. in this paper, we will be limiting the scope of discussion to only energy in the form of electricity. this is because it is the most used and transportable form of energy, and the first product of nuclear energy in this sense is electricity generation. this paper presents the types of energy resources used for electricity generation in section 2. this is followed by a comparison between the sources in section 3 to lay the basis for subsequent discussions on ethical use in section 4 that lead to a conclusion in section 5. 2. energy sources 2.1 fossil fuels up to now we have relied and still are relying largely on fossil fuels: coal, oil, and gas to produce electricity. these resources are used to produce heat that generate steam to drive turbo-generators that generate electricity. these resources are depleting and gradually become more costly to extract and process. coupled to that is the unsettling political situation in most of the resource rich countries that affect supplies, hence driving the energy cost even higher. furthermore, the effect of large scale usage of coal to the environment has raised a lot of concerns. acid rain and greenhouse gaseous emission are closely attributed to the burning of coal for electricity production. in fossil fueled power stations, the fuel must be fed continuously. hence adequate feedstock must be maintained to ensure continuity of supplies for a specific period of time should supply disruption occurs. oil, however, is gradually being phased out from electricity generation purposes. the transportation sector is the major user of oil. with electrification of mass transport and better public transportation services dependency on oil for transportation could be reduced. this can increase the demand for electricity. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering md. rashid 133 2.2 renewable energy usage does not deplete the resources. this is the premise that makes re attractive. hydroelectric is one of the early means for electricity generation in this category. other sources include solar, wind, wave, tidal, ocean thermal energy conversion and geothermal resources. re has some major limitations. these include generation, distribution, and storage. solar energy is available only for a limited time of the day unless a more efficient and economical means for energy storage is available. this limitation makes them unsuitable for bulk power or base load applications. 2.3 replishnable energy biomass and biofuels tend to be lumped in the same category as re. the author, however, is of the view that they belong to a new category that can be called ‘replenishable.’ this is if we take re to mean usage does not diminish supply, and thus external efforts are not necessary to replenish the supply. we merely need to harvest the source. biomass and biofuels, however, need replenishment. plants must be replanted after they have been harvested for use. at issue on biomass and biofuels, such as the use of corn, palm oil, and jathropha for instance, is related to the competing use of resources for the production of plants. with scarce land resources choice must be made between planting for food and planting for fuel. the choice of agriculture for fuel can drive food price up. to have energy security we should not compromise on food security. both, re and replenishable energy have yet to make impact in the total energy equation. 2.4 nuclear energy another form of energy source, generally termed as ‘alternative’ energy, is the use of nuclear fission process. nuclear power reactors are considered as thermal power stations because apart from the use of nuclear reactions to generate heat, the rest of the plant operate in the same manner as other thermal power stations: steam is generated to drive turbogenerators that in turn generate electricity. about 16% of global electricity production is generated using this means. the international atomic energy agency (iaea) reported that as of january 2010, there are 437 nuclear power reactors in operation with total capacity of 370 gwe and fifty-five are under constructions [2]. france, has the highest percentage of nuclear electricity at 80%. the largest number of nuclear reactors, however, is still in the united states of america. other countries in the asian region is fast catching up, commensurate with the rapid pace of growth in that region. china, for instance is on a fast track to introduce about 30% nuclear electricity by 2020. this translates into the connection to grid of one reactor every year until 2020. it however has reviewed this position in view of the fukushima incident. vietnam is reported to also be on the verge of introducing nuclear in her energy mix. south korea began her fast development to acquire national capability in nuclear power technology about three decades ago. today, south korea can be regarded as one of supplier countries, and has won the contract to develop nuclear energy in the uae. 3. comparisons of resources 3.1 means of electriicity generation iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering md. rashid 134 in order to drive the point on resource utilization, the focus will be on the level of abundance of the fuel supplies, their other competing uses, and comparison of other selected factors. since the sources of renewable energy are ever presence, or impossible to be created by men, unlike ‘replenishable’ resources, they are excluded from our discussion. all energy sources are different, and they satisfy different types of loads. as alluded to above, however, nuclear and fossil fuels are similar in the sense that they are thermal power plants. in order to continuously generate electricity, heat must continuously be supplied. 3.2 fuel supplies coal accounts for about 41% of global electricity production. with current rate of consumption, the world coal association estimates that coal reserve will last for about 120 years. it also gives estimate for oil and gas at 46 and 63 years at current consumption and production level [3]. thus, the use of coal for electricity generation is not expected to be abandoned soon. the burning of coal however creates environmental problems such as greenhouse gaseous emissions and acid rain. it is estimated that coal burning for electricity production releases more than 8 billion tonnes of carbon dioxide annually. new technology could make coal cleaner, but it may also make it expensive that other alternatives such as nuclear becoming more attractive. the use of oil for electricity generation is being phased out. the supply of uranium comes from two main sources: secondary and primary supplies. the secondary supplies includes those from the stockpiled used fuel, uranium from decommissioned nuclear arms following the end of the cold war, reprocessed uranium, mixed oxide fuel, highly enriched uranium fuel, reprocessed fuel, and reenrichment of reprocessed fuel. the primary supplies are those newly mined and processed uranium. the international atomic energy agency (iaea) estimated that until the year 2050, the secondary supply will contribute up to 11% of the cumulative demand for uranium [4]. the trend of uranium production follows closely the demand from two of its main uses (fig. 1). the decline after around 1960 and peaks in 1980 and 1988 correspond to the decrease of its military use and increase in demand for nuclear reactors, respectively [5]. at the current rate of consumption, the nuclear energy agency estimated that the global uranium reserves would last for many centuries [6]. it is estimated that 1 tonnes of uranium can produce 40 million kwhr of electricity, which is equivalent to burning 16,000 tonnes coal or 80,000 barrels of oil. fig. 1: world uranium production, 1948-2000. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering md. rashid 135 3.3 other uses of energy resources oil is largely used for transportation (land, air, sea). in addition to transportation it is also used to produce almost 500 items including many everyday products such as detergents, fertilizers, varnishes, paints, thinners, and industrial resins. the distillates are used for making electrical insulators, cosmetics, water repellant coatings, medicinal tablets, and sealants. the only known peaceful uses of uranium is for the production of electricity. in its current means of generating electricity it can never be used to power vehicles, except submarines. on that premise this paper argues that the use of nuclear energy is therefore an ethical choice. we should as far as possible used it so as to minimize other resources that have multiplicity of uses. considerations such as safety and waste, so often projected as the reasons for avoiding it, are scientific and engineering problems that we, as khalifah, have to master. the next level is ethical use of nuclear energy itself. technical as well as administrative procedures need to be in place for it to be used in ethical way. 4. ethical issues of nuclear energy 4.1 nuclear reactor safety in general, it is unethical to adopt any technology that brings more harm than good. nuclear energy is viewed in that light by some quarters. the recent incident at fukushima nuclear power plants seems to strengthened that view. looking in isolation that could be true to a certain extent; but looking from a different perspective, there are almost 50 more nuclear power reactors in operation elsewhere in that country. a nuclear power plant is built according to a design basis accident that provides reference for the reactor design. it is a hypothetical accident that produce chain of events with eventual grave consequences such as core meltdown and release of fission products to the environment. in addition, the concept of multiple barrier is applied to stop fission products from being released to the environment. for fission products to escape it has to overcome several barriers including the fuel cladding, the reactor pressure vessel, and the containment building. despite being over 40 years old, indicating a technology that was designed at least of the same age, the fukushima nuclear power plants responded positively to earthquake. all reactors shut down; pumps were operating to remove the residual heat to cool the reactor. however, this process was stopped when the offsite diesel generator that powers the pumps was taken by the tsunami. that the reactor core remained intact is a testimony to the design. the inability of the offsite power supply to withstand the tsunami, beyond the design level, is a weak link that points out to a need for future designs to accord higher level of safety to the auxiliary and support systems. 4.2 radiation exposure radiation is part of the environment, but they exist at a background level that is so low to be of health concerns. in fact, it could be the mutative agent that causes the generation of new species of plants and insects that were not discvered before. the effect is used in an accelerated scale in laboratories by inducing mutation in plant through exposure to radiation. this process, called radiation induced mutation breeding, produces new plant cultivars with better desired characteristics. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering md. rashid 136 in light of the fukushima-japan incidents in 2011, there are concerns on public exposure to rdaition especially when it is reported that the level is several folds of the background level. this is anotther issue that besieged the industry, but perhaps it is of their own making when the level is set too low. some of the medical procedures that we have to take involving x-rays and other nuclear-related procedures are several times higher than the exposure limit sets for non-radiation workers. table 1 for instance indicates the natural radioactivilty level in human body. table 1: natural radioactivity in the body. nuclide total mass total activity daily intake uranium 90 µg 1.1 bq 1.9 µg thorium 30 µg 0.11 bq 3 µg potassium-40 17 µg 4.4 kbq 0.39 mg radium 31 pg 1.1 bq 2.3 pg carbon-14 95 µg 15 kbq 1.8 µg tritium 0.06 pg 23 bq 0.003 pg polonium 0.2 pg 37 bq ~ 0.6 µg 4.3 proliferation and technology access the question of ethics are being discussed by many authors from many points of views. the concerns of states with nuclear weapons (nws) could be different from the non-nuclear weapon states (nnws). it is hypothesized that with the increasing use of nuclear energy there would be an increase of the possibility of proliferation of nuclaear weapons. doyle [7] writes on the need for researching three main aspects of nuclear ethics: proliferation control, the threats of nuclear weapons, and relation between ethics and domestic political considerations. the close linkage between nuclear energy for peaceful uses and military applications has been at the heart of most of the international safeguards and control regimes. central to the link is uranium enrichment technology. with the exception of the candu reactors that use natural uranium, nuclear power reactors use uranium enriched to between 3-4% in the isotopes of uranium-235. for non-peaceful purposes, the enrichment should be appraching 100%. the abundance of that isotope in natural uranium is only 0.7%. proliferation is one of the ethical issues discussed internationally. the effectiveness of the non-proliferation treaty to curb the spread of nuclear weapons among nnws, access to technology that are useful for peaceful applications but also has ramifications in access to technologies that are excluded become contentious issues. the non-peaceful uses of nuclear energy has been one of the reasons for continuing negative perception of the public on nuclear energy. greater access to beneficial uses and encouragement on the development of uses in this direction could be an approach that could discourage others to do otherwise. 4.4 correct end use responsibe use could be the correct concept to use to separate the irresponsible use of nuclear technology from its beneficial uses. as every technology is a double-edge sword, iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering md. rashid 137 the concept should be the guiding principle on the use of nuclear energy. it would be hard to justify abandoning a technology on the basis that it can be used for other purposes. a technology is not made bad by the bad intention of the user. 5. conclusion the use of nuclear energy is an ethical choice in view of the multiplicity of uses of other resources. however, for it to be used properly it must be developed and utilized in the most responsible manner, complete with all necessary infrastructure to prevent untoward incidents and to mitigate the consequences of any accidents. references [1] iea, world energy outlook 2010. [2] iaea annual report 2009, iaea, vienna, 2010. [3] world coal association website http:// www.worldcoal.org/resources/coal-statistics/ accessed on 14 april 2011. [4] iaea, analysis of uranium supply to 2050, vienna, 2001. [5] w.i. finch, uranium-fuel for nuclear energy 2002, usgs bulletin 2179-a, 2003. [6] r. price and j.r.blaise, nuclear fuel resources: enough to last?, nea news 2002, no.20.2, 2002. [7] t.e.doyle, “reviving nuclear ethics: a renewed research agenda for the twenty-first century,” ethics & international affairs, vol. 24.3, fall 2010. microsoft word 3-rizk-iiu-ej-39-27-2 o.k..doc iium engineering journal, vol. 2, no. 1, 2001 a. a. rizk and a. s. ashour on leave from faculty of engineering, alexandria university, alexandria, egypt. corresponding author 23 free vibration of variable thickness plates using characteristic orthogonal polynomial strip functions subjected to different combinations of boundary conditions a. a. rizk and a. s. ashour department of science in engineering, faculty of engineering, international islamic university malaysia, 53100 kuala lumpur, malaysia email:, ashour@iiu.edu.my abstract: a set of characteristic orthogonal polynomial strip functions was used to study the flexural vibration of variable thickness plates in one direction. the starting function in the set, which is satisfying the geometry and natural conditions, is developed from the solution of a static beam subjected to an arbitrary load that expanded into a taylor series. the gram-schmidt orthogonalization process is used to generate the reminder functions of the set. the natural frequencies of the plat are calculated by using the finite strip method together with the transition matrix. numerical results are obtained for different combination of boundary conditions, tapered ratio and aspect ratio. it is demonstrated that the method as well as the orthogonal strip functions yield good accuracy and fast convergence by comparisons with available results in the literature. this technique can also be used to solve some other complicated problems in the engineering applications. 1. introduction: plates of variables thickness are commonly used as structural elements in many engineering applications such as aerospace, civil, and ocean engineering systems. the natural frequencies and mode shapes of the plate are useful in their operation environments. in the literature, there are many publications concerning the flexural vibration of uniform and non-uniform plates, see for examples lissisa [1-5]. in last decades, many of the researchers are used different admissible functions to obtain the natural frequencies of rectangular and skew plates of variable thickness. ashour [6] used the eigen functions derived from the solution of a classical beam vibration as basis functions. cheung and zhou [7] used a set of admissible functions that are developed from static solution of beam under arbitrary taylor series load in rayleigh-ritz method. zhou [8] used a combination of sine series and polynomials as the basis functions in rayleigh-ritz method. grossi and bhat [9] used boundary characteristic orthogonal polynomials in rayleigh-ritz method and applied rayleigh-schmidt method in their analysis. singh and saxena [10-12] used boundary characteristic orthogonal polynomials in two variables in rayleigh-ritz method. also lewi and lam [13], and bhat [14] used two-dimensional orthogonal polynomials. malhotra [15] used the conventional beam functions as the basis functions. bhat [16] used a set of orthogonal polynomial functions in rayleigh-ritz method. in this paper, a set of orthogonal polynomial shape functions in x-direction is developed to study the free vibration of variable thickness plate in y-direction. the first strip function in the set that satisfies the geometry and natural boundary conditions is the first term in the series solution obtained by cheung and zhou [7] as a new set of admissible functions that are the static solution of the beam under an arbitrary static load expanded into taylor series. the rest of the orthogonal polynomial strip functions are generated through gramschmidt orthogonalization process, which are also satisfy the geometry and natural boundary conditions. it is shown that, this set is the same as developed by bhat [16]. the finite strip method in conjunction with transition matrix [17-18] is used to calculate the natural frequencies of the plate for different boundary conditions, tapered ratio and aspect ratio. good accuracy and fast convergence for all cases presented in this paper are demonstrated when compared with available results in the literature. 2. the characteristic orthogonal polynomial strip functions: one of the admissible functions that are generated by cheung and zhou [7] is adopted in the present work. consider a beam of length equal l and unit width under an arbitrary static load ( )p x . if the width and the depth of the beam are small compared to its length, the classical beam theory is valid. the non-dimensional iium engineering journal, vol. 2, no. 1, 2001 a. a. rizk and a. s. ashour 24 differential equation that is governing the static deflection of the beam may be put in the form 4 4 d ( ) d y p x x = (1) where x l x = , 4 ( ) ( ) l p p l ei x x= and e i is the flexural rigidity of the beam. the arbitrary static load ( )p x can be expanded into taylor series as ' 0 ( ) ii i p px x ¥ = = å (2) where 'ip are the constants that can be determined if ( )p x is a given function. using equation (2) into equation (1), the general solution of the differential equation can be put in the form 2 3 4 0 1 2 3 0 ( ) [ ]i i i i ii i y p b b b bx x x x x ¥ + = = + + + +å (3) the first term in the series solution will be taken as the first strip function in the set of orthogonal polynomial strip functions, i.e. 2 3 4 1 2 3( )o oy a a a ax x x x x= + + + + (4) where ( 0, 1, 2, 3)ia i = are arbitrary constants to be determined from the boundary conditions. for clamped ends (0) (1) (0) (1) 0.0o oo o dy dy y y d dx x = = = = (5) then the strip function (4) becomes 2 3 4( ) 2oy x x x x= + (6) equation (6) is the same as the strip function developed by bhat [16]. the subsequent orthogonal polynomial functions are generated from gram-schmidt process [19]. the first orthogonal function 1( )y x is obtained from 1 1( ) ( ) ( )oy b yx x x= where 1 1 2 2 1 0 0 /o ob y d y dx x x= ò ò . the higher terms in the set can be obtained by the recurrence relation between three successive members of the orthogonal polynomials set, i.e. 1 2( ) ( ) , 2k k k k ky b y c y kx x -= ³ where 1 1 2 2 1 1 0 0 /k k kb y d y dx x x-= ò ò , 1 1 2 1 2 2 0 0 /k k k kc y y d y dx x x-= ò ò . all the orthogonal polynomials that generated are satisfied the geometry and natural boundary conditions of the beam. 3. problem formulation: assume a homogenous, isotropic, and linearly elastic rectangular plate in (x-y) plane as depicted in fig. 1. the plate is of uniform in x-direction and varying thickness h(y) in y-direction. under the assumption of the classical deformation theory, the partial differential equation governing the vibration of such plate is given by 22 2 22 2( ) w w d y x x y ¶ ¶ ¶ n ¶ ¶ ¶ é ùæ ö÷çê ú÷ç ÷+ê úç ÷ç ÷ê úç ÷÷çè øê úë û 22 2 2 2 2 ( ) w w d y y xy ¶ ¶ ¶ n ¶ ¶¶ é ùæ ö÷çê ú÷ç ÷+ +ê úç ÷ç ÷ê úç ÷÷çè øê úë û 2 2 2 2 2 ( ) (1 ) ( ) w w d y h y x y x y t ¶ ¶ ¶ n r ¶ ¶ ¶ ¶ ¶ é ù ê ú+ = -ê ú ê úë û (7) where 3 2 ( ) ( ) 12(1 ) eh y d y n = is the flexure rigidity of the plate,  is the poisson’s ratio, e the young’s modulus, r is the material density, and w is the deflection of the plate. by normalizing the coordinate system with respect to the plate dimensions as follows: x a x = and y b h = and the variable thickness ( )h y with respect to the thickness of the plate oh at 0h = as 0 ( ) ( ) h f h h h = , equation (7) can be written as { }2 4 2 212 2 ( )w w w f w wxxxx xxhh hhhh hhh xxhb b b h b+ + + + + { }2 2 22 3( ) ( ) 0f w w f whh xxb h b n l h+ + = , (8) where 2l = 4 2 0 oh a d r w is the square of the natural frequency of the plate , od is the flexural rigidity of the plate at 0h = , a b b = is the aspect ratio of the plate and 3 1 3 2 3 2 3 2 3 2 ( )1 ( ) ( ) ( )1 ( ) ( ) 1 ( ) ( ) df f f d d f f f d f f h h h h h h h h h h üïï= ïïïïïïïïï= ýïïïïïï= ïïïïþï (9) iium engineering journal, vol. 2, no. 1, 2001 a. a. rizk and a. s. ashour 25 fig. 1 geometry of rectangular plate of variable thickness for a plate striped in the x-direction as shown in fig.1, the shape function ( , )w x h may be assumed in the form 0 ( , ) ( ) ( ) n i i i w x yx h x h = = å (10) where ( )iy h are the unknown functions in h -direction and ( )ix x are the strip functions in x -direction that are developed in the previous section. substituting equation (10), in equation (8), multiplying both sides by ( )jx x , and integrating from 0 to 1, we may obtain { }2 '' 4 2 2 ''' '1 0 2 2 n iv ij i ij i ij i ij i ij i i q y n y m y f m y n yb b b b = + + + +å { }2 2 '' 22 3 0ij i ij i ij if m y n y f m yb b n l+ + = j = 0, 1, 2,.., n (11) where 1 0 ( ) ( )ij i jm x x dx x x= ò , 1 2 2 0 ( ) ( )iij j d x n x d d x x x x = ò , (12) 1 4 4 0 ( ) ( )iij j d x q x d d x x x x = ò from the orthogonality properties, 0ij ijm q= = for i j¹ , this is true for clamped-clamped boundary conditions in the x-direction. therefore, equation (11) becomes 4 4 jd y d h ' 1 22 0 1 2 2 n ij i i i i jj n y f y f y m n b = ì üï ïï ïé ù¢¢+ + +í ýê úë ûï ïï ïî þ å ''' '' 1 22 j jf y f y+ + 2 34 1 0.0jj j jj q f y m l b é ù ê ú+ =ê ú ê úë û j = 0, 1, 2, ..n (13) the above system of fourth order differential equations can be rewritten as 4-n first order differential equations at any strip k as: { }k k k d a d h = y y (14) where the coefficients of the matrix {a}k , in general, are functions of h and the eigenvalue parameter l . the vector ky is given by 1 2 .. ..k i ny y y yé ù= ê úë û y (15) where ' '' ''' i i i i iy y y y yé ù= ë û (16) solving the above system of first order differential equations using the transition matrix technique [20] at any strip k , with boundaries 1k and k yield [ ] 1k kk -=y b y (17) x y z ho hb a b h(y) iium engineering journal, vol. 2, no. 1, 2001 a. a. rizk and a. s. ashour 26 where [ ]kb is called the transition matrix of the strip k and 1,k k -y y are the nodal vectors of the boundaries k , 1k . 4. boundary conditions: in this paper any combination of the classical boundary conditions such as simply supported, clamped, or free boundary conditions at either y = 0 or y = b is considered. after normalizing the boundary conditions and using equation (10) , we may have 2 2 0 jd y d h = , 0 ( 0, 1)jy h h= = = , (18) for simply supported edges, 0 jd y d h = , 0 ( 0, 1)jy h h= = = . (19) for camped edges, and 1 2 2 2 0 3 0 0 0 3 n j jj f ij i i n j i jj f ij i d y m c n y d d y dy m c n d d h h h = = + = + = å å ( 0, 1)h h= = (20) where 1 2f c n b = and 2 2 (2 ) fc n b = for free edges. 5. numerical results and conclusion: to illustrate the validity of the proposed set of orthogonal polynomial strip functions in finite strip method, the natural frequencies for the free vibration plate of variable thickness in y-direction are calculated and compared with the available results obtained by different numerical methods. numerical results are obtained for different combinations of classical boundary conditions, aspect ratio and tapered ratio. a linearly tapered plate is assumed with nondimensional variable thickness function defined by ( ) (1 )f h dh= + (21) where d is the taper ratio given by 0 0 bh h h d = , where bh is the thickness at 1h = . to investigate the accuracy and the convergence of the proposed admissible functions, the first four natural frequencies are calculated for different two cases, cscs with taper ratio 0.5d = , and cccc with taper ratio 0.4d = as shown in table 1. different terms of the series solution in equation (10) ( )n are considered. some of the results that are obtained by using classical beam functions are calculated and presented to compare the convergent between the two admissible functions. also, the results compared with that obtained from grossi and bhat [9] and singh and saxena [11]. for the purpose of brevity, the symbolism cfcs for example, means a plate with varying thickness in the y-direction having clamped, free, clamped and simple supported edges at the boundaries, x= 0, y = b, x =a, and y = 0, respectively (see fig. 1). in all calculations, a poisson's ratio  = 0.3 was used. table 2 demonstrates the natural frequencies for several combinations of boundary conditions, for two taper ratio d (0,0.5), and two aspect ratio b (1,2). a comparison is made with some results obtained from other numerical methods. good accuracy has been seen for all the cases considered in this paper. table 1: convergence of the first four frequencies of square plate of variable thickness and comparison with data from different techniques (cscs and cccc plates) n   1 2 3 classic cscs 1 1 .5 36.0213 68.3958 2 36.0213 68.3958 85.2728 3 35.9716 68.0789 85.2728 4 35.9716 68.0789 85.2411 polynomial cscs 1 35.9672 68.1654 86.2478 3 35.9227 67.8702 86.2478 5 35.9173 67.8270 86.2303 8 35.9165 67.8188 86.2229 singh and saxena [11] 35.9640 68.033 85.2000 polynomial 1 1 .4 42.9255 87.6976 cccc 3 42.8647 87.4200 88.2030 5 42.8547 87.3755 88.1805 singh and saxena [11] 42.9130 87.2900 87.5300 iium engineering journal, vol. 2, no. 1, 2001 a. a. rizk and a. s. ashour 27 table 2: the first four frequencies i (i = 1,2,3,4) of tapered plate in y-direction for different boundary conditions n   1 2 3 4 5 cccs 1 0.0 31.7809 63.1909 71.8811 100.879 5 0.5 39.6479 89.7691 77.9645 5 2 0.0 73.2638 108.272 168.863 210.392 5 0.5 88.0933 134.256 211.415 singh and saxena [11] 88.2750 134.190 206.890 5 cscc 1 0.5 39.2255 78.7977 87.3291 singh and saxena [11] 39.2820 78.9690 86.404 5 2 0.5 93.6774 134.575 206.9541 93.6773 singh and saxena [11] 93.8310 134.520 202.580 5 cfcc 1 0.0 24.2741 40.2840 62.9298 5 0.5 27.6150 49.8425 68.0844 95.9289 5 2 0.0 31.8625 63.3429 103.4920 127.067 5 0.5 39.5637 75.8020 133.582 144.134 5 cfcf 1 0.0 22.3639 26.7401 43.8835 62.9323 5 0.5 26.8121 34.3755 54.7061 68.0833 5 2 0.0 22.3197 36.5568 62.9065 62.9389 5 cfcs 1 0.5 27.1122 44.2948 68.0726 91.3042 5 2 0.0 26.9892 62.9285 80.0701 108.2721 5 0.5 32.0426 74.2904 101.6199 142.2618 5 cscs 1 0.0 28.9125 54.5913 70.1724 94.7093 5 0.5 35.9173 67.8270 86.2303 126.5393 5 2 0.0 54.5901 94.7081 158.9818 170.1827 5 0.5 67.7910 117.7756 196.9454 211.1377 6. conclusion remarks: the finite strip transition matrix method (fstm) by using new set of orthogonal polynomial strip functions presented in this paper is used to investigate the flexure vibration of plate of generally variable thickness with general classical boundary conditions. the method is easily implemented in a computer program and yield a fast convergence and reliable results. the results obtained by the proposed method are compared with known results from different numerical and approximate methods. excellent agreement has been achieved for all plate configurations considered in this paper. the comparison results illustrate the high accuracy and efficiency of the present method. other complexity effects such as orthotropic, edges restrained against translation and rotation, concentrated masses, etc., can be easily implemented in the present method. references: [1] a. w. leissa, vibration of plates (nasa sp 160), washington, d.c., u.s. governments printing office, 1969. [2] a. w. leissa, the free vibration of rectangular plates, journal of sound and vibration 31, pp. 257-293, 1973. [3] a. w. leissa,  recent research in plate vibration. 19731976classical theory, the shock and vibration digest.10., (1977), pp.13-24, 1977. [4] a. w. leissa,,plate vibration research. 1976-1980: classical theory, the shock and vibration digest.13, pp. 11-22, 1981. [5] a. w. leissa,., recent studies in plate vibrations. 1981-1985, part i, classical theory, the shock and vibration digest.19, pp. 11-18, 1987,. [6] a. s. ashour, a semi-analytical solution of the flexural vibration of orthotropic plates of variable thickness, journal of sound and vibration, in press, 2000. [7] y. k. cheung and d. zhou,  the free vibration of tapered rectangular plates using new set of beam functions with the rayleigh-ritz method, journal of sound and vibration223, pp. 703-722, 1999. [8] d. zhou,  natural frequencies of rectangular plates using a set of static beam function in rayleigh-ritz method , journal of sound and vibration 189, pp. 81 87, 1996. [9] r. o. gross and r.b. bhat, natural frequencies of edge restrained tapered rectangular plates , journal of sound and vibration 185, pp. 335-343, 1995. [10] b. singh and v. saxena,  transverse vibration of skew plates with variable thickness, journal of sound and vibration 206, pp. 1-13, 1997. [11] b. singh. and v. saxena,  transverse vibration of rectangular plate with bi-directional thickness variation, journal of sound and vibration 198, pp. 51 65, 1996. [12] b. singh and v. saxena,  flexural vibration of skew plate using boundary characteristic orthogonal polynomials in two variables, journal of sound and vibration 173, pp. 157178, 1994. iium engineering journal, vol. 2, no. 1, 2001 a. a. rizk and a. s. ashour 28 [13] k. m. liew and k. l. lam, application of two dimensional orthogonal plate function to flexural vibration of skew plates, journal of sound and vibration 139, pp. 241-252, 1990. [14] r. b. bhat, flexura vibration of polygonal plates using characteristic orthogonal polynomials in two variables, journal of sound and vibration 114, pp. 6571, 1987. [15] s. k. malhotra, n. ganesan and m.a. veluswami, vibration of orthotropic square plate having variable thickness (parabolic shape), journal of sound and vibration 119, pp. 184-188, 1987. [16] r.b. bhat, natural frequencies of rectangular plates using characteristic orthogonal polynomials in rayleigh-ritz method, journal of sound and vibration 102, pp. 493-499, 1985. [17] a. m. farag, mathematical analysis of free and forced vibration of rectangular plate, ph.d. thesis, faculty of engineering , alexandria university, alexandria, egypt, 1994. [18] a.m. farag and a.s. ashour, free vibration of orthotropic skew plates , journal of vibration and acoustics vol. 122, pp. 313-317, 2000. [19] s.j. leon, linear algebra with applications. new jersey, prentic-hall international, inc. saddle river, 1998. [20] r. zurmuhl, numerical analysis for engineers and physicists. , new york, springer-verlag berlin heidelberg, 1976. biographies dr. abd elfattah a. rizk is currently associate professor at the faculty of engineering, international islamic university malaysia, malaysia, on leave from faculty of engineering, alexandria university, alexandria, egypt. he was born in alexandria 1952. he obtained his b.sc. in mechanical engineering in 1975, faculty of engineering, alexandria university, egypt, and b.sc. in mathematics in 1979, faculty of science, alexandria university, egypt. he received his m.sc. in 1984 and ph.d. in 1988 from faculty of engineering, lehigh university, usa. his area of interest is solid and fracture mechanics. ahmed a. s. ashour was born in alexandria, egypt in 1959. he received his bachelor's degree in 1982 in telecommunications engineering, his msc. in dynamical system model for traffic noise in 1988 from alexandria university. he obtained his msc in engineering mechanics in 1992 and his phd in acoustics in 1994 from the university of texas at austin, which was comprised of a study of the fracture impedance method. his research interests include wave propagation in solids and fluid, structural vibration and noise, and mathematical modeling and simulation. he is an associate professor at alexandria university, egypt. currently, he is associate professor and head, department of science in engineering, international islamic university malaysia. iium engineering journal iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 the effect of layer thickness on repeatability of 3d printed pla parts produced using openware 3d printer normariah che maideen*, mohd ikmal hisham abdul rahim, salina budin, koay mei hyie and hamid yusoff centre for mechanical engineering studies, universiti teknologi mara, cawangan pulau pinang, permatang pauh campus, 13500 pulau pinang, malaysia. * corresponding author: normariah@uitm.edu.my (received: 9th july 2021; accepted: 16th january 2022; published on-line: 4th july 2022) abstract: fused filament fabrication (fff) is categorized as an additive manufacturing process, recognized as the simplest way to accomplish 3d printing. previous studies have proven that fff can be trusted to create custom parts with high complexity. however, some performance issues still exist with this method that must be resolved to improve conventional manufacturing techniques. one of them is its repeatability performance that is debatable when it comes to producing repetitive runs of similar parts. printing parameter is one of the factors that play a significant role on the repeatability performance of parts produced. in this study, the effect of layer thickness on the repeatability of 3d printed pla, produced using an openware 3d printer (espresso f220), was investigated. two product geometries (part a and part b) were produced. layer thickness was chosen as a variable parameter (0.1 mm, 0.2 mm, and 0.3 mm) for each geometry. data to measure repeatability of the printed pla parts were determined based on the measurements of length, width, thickness and surface roughness for each geometry. then, repeatability performance was analyzed through one-way anova analysis. from the results, the layer thickness parameter did influence dimensional quality and repeatability of samples produced. part length and thickness offered better repeatability performance, to both product geometries being compared, in width and surface roughness. the study reveals that variations in sample properties depends on not only one, but also every printing parameter involved. repeatability performance can be improved by identifying the ideal combination of printing parameters to produce good part quality. abstrak: : fabrikasi filamen fius (fff) yang dikategori sebagai proses pembuatan tambahan, diakui sebagai kaedah termudah bagi menghasilkan pencetakan 3d. kajian terdahulu telah membuktikan bahawa fff dapat menghasilkan komponen khas yang kompleks. walau bagaimanapun, beberapa isu peningkatan mutu masih berlaku, iaitu kaedah ini masih perlu diperbetulkan bagi membaiki teknik pembuatan konvensional. salah satu adalah peningkatan keterulangan bagi menghasilkan komponen yang serupa secara berulang. parameter pencetakan adalah salah satu faktor yang berperanan penting bagi peningkatan keterulangan komponen yang dihasilkan. kajian ini mengkaji tentang kesan ketebalan lapisan terhadap kebolehulangan pla bercetak 3d yang dihasilkan melalui pencetak openware 3d (espresso f220). dua geometri produk (bahagian a dan b) dihasilkan. ketebalan lapisan dipilih sebagai parameter pemboleh ubah (0.1mm, 0.2mm dan 0.3mm) bagi setiap geometri. data bagi mengukur keterulangan bahagian pla yang bercetak ditentukan berdasarkan pengukuran panjang, lebar, ketebalan dan kekasaran permukaan bagi setiap 218 iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 geometri. kemudian, peningkatan keterulangan dianalisa melalui analisis anova sehala. dapatan hasil menunjukkan, parameter ketebalan lapisan mempengaruhi kualiti dimensi dan kebolehulangan sampel yang dihasilkan. panjang dan ketebalan bahagian mempunyai peningkatan keterulangan yang lebih baik bagi kedua-dua geometri produk berbanding lebar dan kekasaran permukaan. dapatan menunjukkan bahawa variasi sifat sampel tidak hanya bergantung pada satu, malah pada setiap parameter pencetakan yang terlibat. peningkatan keterulangan dapat diperbaiki dengan mengenal pasti kombinasi parameter pencetakan yang ideal bagi menghasilkan kualiti bahagian terbaik. keywords: 3d printing; fff; pla; repeatability; layer thickness 1. introduction fused filament fabrication (fff) process comes under additive processes, which proves that this process is a filament extrusion-based process integrated with a cad system, materials science, computer numeric control, and extrusion process to create 3d parts directly from a cad model [1]. fff is also known as fused deposition modelling (fdm) which has been invented by stratasys. inc in the usa in 1990 and has become one of the world's best-known 3d printing techniques [1,2]. fff shapes the 3d structure of individual layers of thermoplastic extruded filaments such as polylactic acid (pla), which have sufficiently low melting temperatures for use in existing non-dedicated facilities in melting extrusion [2,3]. to date, fff technology is widely present in different sectors, including engineering, biomedical, food and so forth [4,5]. with multiple printing parameters associated with the process, the substantial and ideal parameters for better structural and physical properties, such as accuracy and repeatability, of parts produced need to be identified, due to the applications of 3d printing in the market [6]. researchers have taken various means to improve both structural and physical properties since fff/fdm were introduced. yet, for a long time, fff work remained restricted to process parameters, such as layer thickness, and to individual materials [7]. mohan n et al. [8] reviewed the optimization of the fff process materials and process variables. fff printers commonly embrace thermoplastic materials such as pla, abs, metal matrix composites, ceramic composites and natural fiber composites. the simple and portable extrusion process is applicable in many different materials making fff an affordable technology for research institutes, industries and domestic consumers with the capability of revolutionizing many different fields by providing the means to implementing innovative concepts [9,10]. despite many applications and services offered by 3dp, this particular technology is still not completely utilized by manufacturers in terms of end-use goods due to numerous obstacles, one of them is the restricted variation in repeatability [11]. as the technology world grows, several series of 3d printing machines have been produced with different machines offering different repeatability performance. other than that, process parameters also play a major role in determining the repeatability of parts produced by fff. since dimensional properties for functional components are crucial, the impacts of system parameters on repeatability are essential to examine as stated by rebecca kurfess [12]. the researcher stated that in order to characterize the relationships among the various parameters and the repeatability of the parts, further tests should be carried out before these 3d printed parts are used in positions where precision is important. additional research is therefore needed to determine parameters of the printer such as the build orientation, layer thickness 219 iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 and feed rate, especially since the literature on the physical characteristics of parts being produced by fff is rather scarce. fff has proven to be able to produce good quality products. however, there are numerous procedural issues, with respect to product repeatability in particular. the machine’s capability and whether it will be affected by type of fff machine used or not, is essential in ensuring that the product’s performance is highly predictable. previous studies revealed that research on 3d printing has focused on aspects of accuracy rather than machine repeatability performance. past studies have proven that some printing parameters influenced the finished product quality. eventually, one of the printing parameters, layer thickness, should also affect this matter. therefore, there is a possibility to determine the repeatability performance of fff machine in producing pla parts with different layer thickness. thus, in this work, repeatability performance of the 3d espresso f220 is investigated. two product geometries are proposed in this work to further investigate the repeatability of this machine. the two product geometries (part a and part b) of pla samples were material printed with variation in layer thickness (0.1 mm, 0.2 mm, and 0.3 mm). surface roughness, width, height, and depth of 30 fabricated parts were measured. the repeatability performance of the machine in producing pla material has been concluded from this study through one-way anova analysis. 2. methodology four steps are conducted in this study to identify the effect of layer thickness on repeatability of 3d printed pla parts. details for each step are explained in the subsections below. 2.1 product geometry in this study, to measure the reliability performance, two product geometries were used (part a and part b). part a refers to astm d638 type i standard dimension. the design and dimension of the products is shown in fig. 1. fig. 1: (a) part a (above: geometry, below: dimension) and (b) part b (above: geometry, below: dimension). a) b) 220 iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 2.2 sample fabrication part a and part b were printed using an openware 3d printer (3d expresso f220). printing parameters for 3d printing of product geometries is shown in table 1. pla feedstock filament was used for all samples. all printing parameters in table 1 were fixed except layer thickness. in this study, layer thickness varies in three levels which were 0.1, 0.2, and 0.3 mm. five replications were produced for each layer for both part a and part b product geometries. therefore, the sampling size was 30. figure 2 shows a 3d expresso f220 machine that was used in this study. table 1: 3d printing parameter printing parameter value feedstock filament polylactic acid (pla) feedstock filament (diameter) 1.75 mm liquefier / extruder temperature 210 °c bed temperature 50 °c infill percentage 90% infill pattern line printing direction 30°/60° layer thickness 0.1 mm, 0.2 mm, 0.3 mm printing orientation x, y, z printing speed 60 mm/s fig. 2: 3d espresso f220 machine. 2.3 sample measurement and data collection the data to measure repeatability of the printed pla parts are determined based on the measurement of length, width, thickness, and surface roughness for each product geometry (part a and part b). a digital vernier caliper was used to measure length, width, and thickness while a mitutoyo surface roughness tester (surftest sj-210) was used to measure surface roughness. table 2 shows the measurement location for each product geometry. for surface roughness, the dial indicator was placed at the midline of the top surface for both geometries. 221 iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 2.4 repeatability performance in this study, one-way anova is used to get repeatability performance. the null hypothesis, ho and alternate hypothesis h1 used described in table 3. table 2: location of measurement for length, width, and thickness measurement location of measurement (part a) location of measurement (part b) length width thickness table 3: repeatability hypothesis hypothesis description null hypothesis ho = different layer thickness does not affect the repeatability of 3d printed pla produced using 3d espresso f220. alternate hypothesis h1 = different layer thickness does affect the repeatability of 3d printed pla produced using 3d espresso f220. data recorded was analyzed using one-way anova where the single factor would be layer thickness. by using this method, data was analyzed and variance was evaluated between and within groups, which were then identified by f-value, critical f-value, and p222 iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 value. calculations involved in identifying these three significant values were presented in equations (1) through (12). mean value, �̅� = ∑ 𝑥 𝑛 (1) where ∑ 𝑥 is the total of samples value of each group, while n is the number of samples. then, all mean values were added up together. next, the sum of squares, ∑(𝑥2) for each group was calculated before being added up. later, the calculation continued with standard deviation, 𝜎, of each layer thickness group before being summed together as eqn. (2). then, from the data measurement table, degree of freedom was calculated through eqns. (3), (4), and (5). standard deviation, 𝜎 = √ ∑ (𝑥𝑖−�̅�) 2𝑛 𝑖=1 (𝑛−1) (2) between groups (bg) = 𝑘 − 1 (3) 𝑊𝑖𝑡ℎ𝑖𝑛 𝑔𝑟𝑜𝑢𝑝𝑠 (𝑊𝐺) = 𝑁 − 𝑘 (4) 𝑇𝑜𝑡𝑎𝑙𝑠 𝑑𝑒𝑔𝑟𝑒𝑒 𝑜𝑓 𝑓𝑟𝑒𝑒𝑑𝑜𝑚 = 𝑁 − 1 (5) where k acts as the number of groups, which are group of layer thickness, while n is the total sample size. from that, calculation moved onto sum square (ss) that involve correction factor (cf) (eqn. (6)) and sum of squares for totals (sst) (eqn. (7)), between (ssb) (eqn. (8)) and within groups (ssw) (eqn. (9)). 𝐶𝐹 = (∑ ∑ 𝑥)2 𝑁 (6) 𝑆𝑆𝑇 = ∑ ∑(𝑥 2) − 𝐶𝐹 (7) 𝑆𝑆𝐵 = {∑ [ (∑ 𝑥)2 𝑛 ]} − 𝐶𝐹 (8) 𝑆𝑆𝑊 = 𝑆𝑆𝑇 − 𝑆𝑆𝐵 (9) this has led to the calculation of mean square (ms) that involves the mean square between (msb) (eqn. (10)) and within groups (msw) (eqn. (11)). subsequently, f-value, fo calculated using the result of msb and msw (eqn. (12)). 𝑀𝑆𝐵 = 𝑆𝑆𝐵 𝐵𝐺 (10) 𝑀𝑆𝑊 = 𝑆𝑆𝑊 𝑊𝐺 (11) 𝐹𝑜 = 𝑀𝑆𝐵 𝑀𝑆𝑊 (12) then, p-value was determined using fo through f distribution table. lastly, alpha level, α (controlled by researcher and related to confidence levels), was determined before being used to find critical f-value, fc through the same f distribution table. after all values were verified, all the data was then tabulated. next, comparison was made between f-value and critical f-value, as well as between p-value and alpha level, α that will bring to conclusion in two conditions, as stated below. (𝐹𝑜 > 𝐹𝑐 ), (𝑃 − 𝑣𝑎𝑙𝑢𝑒 < 𝛼) ∶ 𝑆𝑡𝑎𝑡𝑖𝑠𝑡𝑖𝑐𝑎𝑙𝑙𝑦 𝑠𝑖𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑛𝑡 223 iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 𝐻𝑜 𝑖𝑠 𝑓𝑎𝑙𝑠𝑒 𝑎𝑛𝑑 𝑐𝑎𝑛 𝑏𝑒 𝑟𝑒𝑗𝑒𝑐𝑡𝑒𝑑. whereas, (𝐹𝑜 < 𝐹𝑐 ), (𝑃 − 𝑣𝑎𝑙𝑢𝑒 > 𝛼) ∶ 𝑆𝑡𝑎𝑡𝑖𝑠𝑡𝑖𝑐𝑎𝑙𝑙𝑦 𝑖𝑛𝑠𝑖𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑛𝑡 𝐻𝑜 𝑖𝑠 𝑡𝑟𝑢𝑒 𝑎𝑛𝑑 𝑎𝑐𝑐𝑒𝑝𝑡𝑒𝑑. from the comparison, the result obtained proved whether ho was a false statement for both product geometry samples. thus, this result reflected the repeatability efficiency of 3d printed pla produced whether it was being influenced by layer thickness differences or not. 3. results table 4 shows a summary of result from one-way anova that was conducted for data collection for both product geometries. in this study, 0.05 of confidence level was used. thus, fc= 3.89 is same for all measurements. based on hypothesis stated in the previous section, an influence of layer thickness to the repeatability performance can be made. based on table 5, hypothesis conclusion on each measurement was made. in the process of producing parts for both product geometries, layer thickness did influence the repeatability performance of the printed part. this result showed that, during formation of length dimension and thickness dimension of the parts, the machine was able to produce repetitive length and thickness, regardless of the different product geometry, with a total of 30 samples produced at three different layer settings. the sampling size used was able to give a significant result for this study. table 4: one-way anova results for all measurements for both product geometries table 5: hypothesis conclusion measurement part a part b length layer thickness does effect layer thickness does effect width layer thickness does not effect layer thickness does effect thickness layer thickness does effect layer thickness does effect surface roughness layer thickness does effect layer thickness does not effect on the other hand, for formation of width dimension, layer thickness did not affect the production of part a, but did affect the production of part b. fig. 3 shows a trend of width measurement for part a. the trend showed a decrease in width over the number of samples due to repeatability performance of the machine during producing the samples and of the shrinkage factor of the material after the process. the width value seems to be repeatable for 0.1 mm layer thickness and 0.2 mm layer thickness. however, the variation of the samples dropped at 0.3 mm layer thickness as the width measurements showed obvious differences between each other. it showed that the longer the time taken to complete the process, the width became less varied (0.1 mm layer thickness took longer time compared to 0.3 mm). this can be proven by the standard deviation calculation, which has indicated that the standard deviation of the 0.3 mm layer thickness spread over a wide range of values measurement part a part b fo fc p fo fc p length 9.4957 3.89 0.0034 5.2588 3.89 0.0229 width 2.4852 3.89 0.1250 12.6481 3.89 0.0011 thickness 10.8723 3.89 0.0020 4.7981 3.89 0.0294 surface roughness 52.4052 3.89 0.0000012 0.3243 3.89 0.7291 224 iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 is higher than the other two-layer thicknesses. for this study, the constant printing parameter fit with 0.1 mm layer thickness leads to an optimal shrinkage percentage of pla (0.3%0.5%) and moderate coefficient linear of thermal expansion (clte: 8.5 x 10-5/oc), thus giving a low variation in the sample’s width. therefore, when the layer thickness increased, the shrinkage percentage also increased if the same value for other parameters was used throughout the study. the distance between the sample locations and the nozzle can also be taken into consideration. as the nozzle moved further from its natural position, the solidified rate for each layer in one sample became higher. thus, this will affect the final dimension of the sample. fig. 3: trend of width measurement for part a. fig. 4: trend of surface roughness measurement for part b. based on the results of surface roughness, layer thickness did not influence in the formation of part b, however it did affect in producing part a. for the surface roughness of 3d printed part b, based on fig. 4, roughness value seems to be repeatable for 0.1 mm layer thickness. however, the variation of the samples dropped as the layer thickness increased, as the roughness readings had spread out over a large range of values. by standard deviation calculation, the statement can be proven, which showed that the standard deviation of the 0.3 mm layer thickness was higher (1.5979) than the other two-layer thicknesses (0.2 mm = 225 iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 1.1482, 0.3 mm =1 .5979). thus, it revealed that the constant printing parameter that was suitable for use with 0.1mm layer thickness that produced a low variation of roughness reading of straight cut samples. however, by changing the constant parameter value, the variation can still be improved. the temperature of the bed was one variable that can be used to improve repeatability and surface roughness. according to previous studies, among printing temperatures, the lower printing bed temperature offers an increase in quality of surface between printing temperatures. if the temperature decreased for all the samples in the set of data, the surface roughness of all the samples decreased. therefore, the results became better and had an increase in repeatability performance of the data. however, this will affect the final dimension of the sample, as a drop-in bed temperature will lead to an increase in thermal stress of pla. this will then cause faster solidification process and in this case, warping deformation tended to occur. regardless of the case, the optimal printing parameter combination should be defined to produce the highest possible repeatability of a set of samples. 4. conclusion in this study, two product geometries were proposed and fabricated to study the effect of layer thickness on repeatability of 3d printed pla parts using an openware 3d printer (3d espresso f220). in total, 30 samples were produced that involved repetition of 5 samples for three variations of layer thickness (0.1 mm, 0.2 mm, 0.3 mm). the sampling size was significant to quantitatively measure the repeatability performance of the product geometry produced. part length, width, thickness, and surface roughness for both product geometries was measured to analyze using the one-way anova method. from the analysis, repeatability performance was achievable when length and thickness dimension were produced for both product geometries. for width dimension, layer thickness did not affect the fabrication of part a. for surface roughness, fabrication of part b was not affected by layer thickness. however, the best layer thickness in ensuring repeatability of 3d printed parts in this study is 0.3 mm for part a that ensured repeatable performance in length and surface roughness. while layer thickness recorded at 0.1 mm for part b geometry ensured repeatable performance in thickness and surface roughness. some improvements can be made to enhance the repeatability for measurements that were not achieved such as by using optimal printing parameter combinations, shrinkage factors, and temperature settings. acknowledgement the authors would like to thank universiti teknologi mara, cawangan pulau pinang for offering a good facility for this research to be conducted as well as funding for this project. references [1] zhao y, chen y, zhao y. (2019) novel mechanical models of tensile strength and elastic property of fff am pla materials: experimental and theoretical analyses. mater. des., 181:108089. [2] chacon jm, caminero ma, garcia-plaza e, nunez pj. (2017) additive manufacturing of pla structures using fused deposition modelling: effect of process parameters on mechanical properties and their optimal selection. mater. des., 124: 143-157. 226 iium engineering journal, vol. 23, no. 2, 2022 maideen et al. https://doi.org/10.31436/iiumej.v23i2.2137 [3] tymrak bm, kreiger m, pearce jm. (2014) mechanical properties of components fabricated with open-source 3-d printers under realistic environmental conditions. mater. des., 58: 242246. [4] yao t, deng z, zhang k, li s. (2019) a method to predict the ultimate tensile strength of 3d printing polylactic acid (pla) materials with different printing orientations. compos. part b eng., 163: 393-402. [5] durga prasada rao v, rajiv p, navya geethika v. (2019) effect of fused deposition modelling (fff) process parameters on tensile strength of carbon fibre pla. mater. today proc. [6] padyal p, mulay a, dhanvijay mr. (2019) experimental assessment of repeatability of openware 3d printer. 1352-1357. [7] harris m, potgieter j, archer r, arif km. (2019) effect of material and process specific factors on the strength of printed parts in fused filament fabrication: a review of recent developments. materials, 12(10): 1664. [8] mohan n, senthil p, vinodh s, jayanth n. (2017) a review on composite materials and process parameters optimisation for the fused deposition modelling process. virtual phys. prototyp, 12(1): 47-59. [9] wang l, gramlich w.m, gardner dj. (2017) improving the impact strength of poly(lactic acid) (pla) in fused layer modeling (flm). polymer (guildf), 114: 242-248. [10] harris m, potgieter j, arif k, archer r. (2017) large scale 3d printing: feasibility of novel extrusion-based process and requisite materials. 24th int. conf. mechatronics mach. vis. pract. m2vip 2017, pp 1-6. [11] albaiji nfs. (2018) repeatability case study of the 3d printer in the school of engineering and applied science lab. [12] rebecca k. (2017) a parametric study of the repeatability of 3d printed lego® – like mechanical couplings. bachelor of science in mechanical engineering thesis. massachusetts institute of technology (mit). 227 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 the harmonic composition of current in zero-working wire with non-linear load igor v. yudaev1*, evgeny v. rud2, mikhail a. yundin3, tamara z. ponomarenko2 and aleksandra m. isupova3 1 department of thermal engineering and information management system, azov-black sea engineering institute of don state agrarian university, zernograd, russian federation 2 icpe “energy institute for advanced studies of the pjsc “kubanenergo”, krasnodar, russian federation 3 department of electric power and electrical engineering, azov-black sea engineering institute of don state agrarian university, zernograd, russian federation * corresponding author: yudaev5303@ubogazici.in (received: 4th august 2020; accepted: 14th october 2020; published on-line: 4th january 2021) abstract: the purpose of this study was experimental investigations and a study of the nature of the change in the main harmonic components of the current in the neutral working wire of a three-phase four-wire network with a voltage of 0.38 kv. the study of the amplitude-phase-frequency characteristics of currents flowing in an electric network with a predominant non-linear load is one of the most urgent tasks, the solution of which will increase the efficiency of electric power transmission and eliminate the negative consequences due to the current flow in a zero-working wire in the network at 0.38 kv. to study the effect of load changes on the amplitude-phase-frequency characteristics of currents in the linear and zero working wires at the input of the load node, measurements were carried out by certified electrical measuring instruments namely, the “resourceuf2m” and “hioki 3196”. with these devices, the phase voltages at the input to the load node were measured. the analysis of the results obtained for the load node whose power was formed mainly by a lighting system with fluorescent and led lamps and a system of office electrical receivers (computers, copiers, printers, scanners, etc.) was performed. it can be concluded that a current comparable to the currents of the linear wires of the network flows from the load node with the predominant nonlinear power receivers through the zero-working wire. at the same time, in the zero-working wire of the network, the third harmonic current prevails over the main frequency currents. abstrak: tujuan kajian ini adalah penyelidikan eksperimental dan kajian mengenai sifat perubahan komponen harmonik utama arus dalam wayar kerja neutral rangkaian empat wayar tiga fasa dengan voltan 0.38 kv. kajian mengenai ciri-ciri frekuensiamplitud-fasa arus yang mengalir dalam rangkaian elektrik dengan beban bukan linear yang dominan adalah salah satu tugas yang paling mendesak, penyelesaiannya akan meningkatkan kecekapan penghantaran tenaga elektrik dan menghilangkan akibat negatif yang disebabkan ke arus semasa dalam wayar sifar bekerja di rangkaian pada 0.38 kv. untuk mengkaji kesan perubahan beban pada ciri frekuensi-fasa frekuensi arus dalam wayar linier dan sifar pada input nod beban, pengukuran dilakukan oleh alat pengukur elektrik yang disahkan iaitu, "resource-uf2m" dan "hioki 3196". dengan peranti ini, voltan fasa pada input ke simpul beban diukur. analisis hasil yang diperoleh untuk simpul beban yang kekuatannya dibentuk terutama oleh sistem pencahayaan dengan lampu pendarfluor dan led dan sistem penerima elektrik pejabat (komputer, mesin fotokopi, pencetak, pengimbas, dll.). dapat disimpulkan bahawa arus yang setanding dengan arus 191 iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 wayar linier rangkaian mengalir dari nod beban dengan penerima kuasa bukan linier yang dominan melalui wayar sifar. pada masa yang sama, dalam wayar sifar rangkaian, arus harmonik ketiga berlaku berbanding arus frekuensi utama. keywords: three-phase four-wire network; zero working wire of the network; harmonic currents; non-symmetry; non-linear power receiver 1. introduction the main reasons for current appearance in the zero-working wire of a three-phase fourwire network are the asymmetry of the loads in the phases and presence of nonlinear power receivers. when flowing through a zero-working wire, the components of the currents of higher harmonics and asymmetries cause additional losses of voltage and electricity; reduction in the service life of cable lines; increase the resistance of grounding devices of electrical installations; and interference in low-voltage communication lines [1-6]. the study of the amplitude-phase-frequency characteristics of currents flowing in an electric network with a predominant non-linear load is one of the most urgent tasks, the solution of which will increase the efficiency of electric power transmission and eliminate the negative consequences due to the current flow in a zero-working wire in the network at 0.38 kv [7]. since the spectral composition of currents in real electric networks is influenced by a large number of simultaneously influencing factors (the composition of power receivers in the load node, their connection diagram, switching frequency, etc.), the study of the harmonic composition of currents of the most common typical consumers is of practical interest. the power of the load node under study was formed mainly by a lighting system with fluorescent and led lamps and a system of office electrical receivers (computers, copiers, printers, scanners, etc.) [8]. to study the effect of load changes on the amplitude-phase-frequency characteristics of currents in linear and zero working wires at the input of the load node, measurements were carried out by certified electrical measuring instruments [9]. the “resource-uf2m” and “hioki 3196” devices controlled currents in linear and zero working (“hioki 3196”) wires. at the same time, the same devices measured the phase voltages at the input to the load node. 2. characteristics of the distortion coefficient of the sine curve in accordance with daily changes the change in the total active power at the input of the load node during the day is shown in fig. 1. the range of changes in the total active power is large – from 5 kw at night up to 68 kw during the day. the greatest loads were during daylight hours from 7:30 to 17:00 hours. the minimum value of the total active power, as seen in fig. 1, was recorded in the morning (from 5:00 to 7:00 hours), and the maximum – in the daytime from 12:00 to 13:32 hours. as can be seen from fig. 1, the power consumption of the load node occurred according to a two-stage schedule. 192 iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 fig. 1: schedule of changes in total active power at the input of the load node. moreover, the change in active capacities during the day is very asymmetric in the network phases (fig. 2). the active power p1 of the first phase l1 during the day turned out to be the smallest most of the time. separate bursts of active power p1 of phase l1 were clearly observed in the period from 5:00 to 6:00 hours, when the load was the greatest. most of the day, the greatest load fell on the l3 phase with an active power of p3. only in the period from 14:00 to 16:32 hours the active power of p2 exceeded p3. fig. 2: daily graphs of changes in active powers for the phases of the network 0.38 kv at the input of the load node. due to the asymmetric load of the phases, the voltage asymmetry coefficients in the zero and reverse sequences of the fundamental frequency were significant (fig. 3). so, for example, the voltage asymmetry coefficient in the zero sequence of the fundamental frequency (k0u) did not fall during the day, even with a minimum (below 2%) load. during periods of greatest power consumption (from 8:00 to 17:00 hours), the voltage unbalance coefficient in the zero sequence of the fundamental frequency often exceeded 5%. the voltage asymmetry coefficient in the reverse sequence of the fundamental frequency (k2u) during the day had lower values. moreover, it turned out to be more stable than the coefficient k0u. the range of variation of k2u ranged from 2% to 4%. the results of these studies, as well as an analysis of literature [10-15] indicate that the active use of switching power supplies in electrical appliances leads to an increase in harmonic distortions of voltages and currents in the electrical network. moreover, the distortion coefficients of 193 iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 the sinusoidality of the voltages have lower values than the distortion coefficients of the sinusoidality of the load currents. fig. 3: diagrams of daily changes in the voltage asymmetry coefficients in the zero and reverse sequence at the input of the load node with the prevailing non-linear power receivers. figure 4 shows graphs of daily changes in the distortion coefficients of the sinusoidality of the voltage curves in the phases of the network at the input of the load node 0.38 kv. it should be noted that in none of the phases at the input of the load node, the distortion coefficient of the sinusoidality of the voltage curves did not exceed the minimum allowable value – 8%. fig. 4: diagrams of daily changes in the distortion coefficients of the sinusoidality of the phase voltage curves at the input of the load node with predominant nonlinear power receivers. 194 iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 during periods of maximum load (from 8:00 to 17:00 hours), the distortion coefficient of the sinusoidality of the voltage curve in the first phase ku1 was the largest, more than 6% (see fig. 4). during load shedding, the distortion coefficients of the sinusoidality of the voltage curves in phases became the same (over 2%). the average amplitude-frequency characteristic of the most significant average daily coefficients of the 3rd, 5th, 7th, 9th and 11th voltage harmonics in the phases of the network 0.38 kv at the input to the load node (fig. 5) clearly show that the odd harmonic voltage components prevail over even ones. among the odd higher voltage harmonics, the 3rd, 5th, and 9th harmonics had the largest amplitudes. it should be noted that the largest amplitudes of the 3rd and 5th voltage harmonics were recorded in the first phase, and the 9th voltage harmonic was the largest in the second phase of the network 0.38 kv (fig. 5). the coefficients of the 3rd voltage harmonic by phase at the input to the load node varied from 4.7% to 5.5%, the coefficients of the 5th voltage harmonic, respectively, from 1.4% to 2.5%, and the coefficients of the 9th voltage harmonic, respectively, from 1.0% to 1.4% (fig. 5). fig. 5: frequency response of the most significant daily average coefficients of the n-th harmonic components of the phase voltage at the input of the load node. 3. changes in current parameters at various loads of the power receiver to assess the degree of distortion of currents sinusoidality during the period of the highest loads, the waveforms of the phase currents and in the zero-working wire at the input of the load node were recorded using the “hioki 3196” instrument (fig. 6). the current waveforms correspond to the time interval on the daily graph of the change in the total active power at the highest load (from 11:40 to 12:00 hours according to the schedule of fig. 1). an analysis of the current shape in the zero-working wire i4(t) on the waveform shows (fig. 6) that it is not substantially sinusoidal. the waveforms of currents in the linear wires of the load node i1(t), i2(t) and i3(t) are also significantly distorted by higher harmonics. 195 iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 fig. 6: a fragment of the waveforms of the phase currents and the zero-working wire at the input of the load node with the prevailing non-linear power receivers. using the “hioki 3196” software package, the amplitudes and phases of the currents were determined for seven significant harmonic components not equal to zero (odd harmonics from the 1st to the 13th). for compact recordings, these transformations are presented in the form of fig. 7, which also shows mathematical models (expressions) of instantaneous current values at the input to the load node. in fig. 7, the fourier expansion is performed up to the 50th harmonic of the current. this allows us to justify the selection of the seven most significant harmonic components of the current by comparison. the sinusoidal distortion coefficients of the curves (see fig. 7) are denoted by thd (total harmonic distortions) and are called the “total current harmonic distortion coefficient”. as can be seen from fig. 5, the values of the sinusoidality distortion coefficients of the current curves thdi1, thdi2 and thdi3 significantly exceed the similar voltage coefficients. in the first linear wire l1 at the input of the load node, the total thdi current distortion factor for the considered time was 23.7%, in the second wire l2 – 15.98%, in the third wire l3 – 36.18%, and in the neutral wire – 138.35%, respectively. the analysis of the harmonic composition of the current of the zero-working wire i4(t) is of interest. as can be seen from fig. 1, in the working (mean square) current i4, the proportion of the main harmonic of the current is 6.77 a. the proportion of the third harmonic components of the currents flowing in the linear wires of the network 0.38 kv, in the zero working wire for the considered time point, is 8.9 a, in 5th harmonic current, respectively, 2.33 a, 7th – 0.79 a, 9th – 1.13 a, 11th – 0.51 a and 13th – 0.58 a. in this case, the total current load of the zero-working wire for the considered time was equal to 12.48 a. with this load mode, the current values in the linear wires of the network 0.38 kv were as follows: i1 = 16.63 a; i2 = 13.54 a; i3 = 18.8 a. that is, the current load of the zero working wire is commensurate with the load of the linear wires. obviously, the third and ninth current harmonics make the main contribution to the increase in the current load of the zero-working wire to the values of the currents flowing in the linear wires of the network 0.38 kv. 196 iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 fig. 7: vector diagrams of currents and voltages at a frequency of 150 hz at the input of a load node with predominant nonlinear power consumers: (a) (b) (c) (d) (e) (f) (g) (h) 197 iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 a), b) – 𝑖1(𝑡) = √2 ∙ ( 15,26 𝑠𝑖𝑛(𝜔𝑡 + 2°) + 3,14 𝑠𝑖𝑛(3𝜔𝑡 − 163°) + +1,31 𝑠𝑖𝑛(5𝜔𝑡 + 16°) + 0,19 𝑠𝑖𝑛(7𝜔𝑡 − 44°) + 0,78 𝑠𝑖𝑛(9𝜔𝑡 − 165°) + +0,59 𝑠𝑖𝑛(11𝜔𝑡 + 27°) + 0,30 𝑠𝑖𝑛(13𝜔𝑡 − 153°) )а c), d) – 𝑖2(𝑡) = √2 ∙ ( 13,34 𝑠𝑖𝑛(𝜔𝑡 − 130°) + 1,34 𝑠𝑖𝑛(3𝜔𝑡 − 173°) + +1,22 𝑠𝑖𝑛(5𝜔𝑡 + 88°) + 0,86 𝑠𝑖𝑛(7𝜔𝑡 + 2°) + 0,47 𝑠𝑖𝑛(9𝜔𝑡 − 42°) + +0,09 𝑠𝑖𝑛(11𝜔𝑡 + 116°) + 0,30 𝑠𝑖𝑛(13𝜔𝑡 − 0°) ) а e), f) – 𝑖3(𝑡) = √2 ∙ ( 17,63 𝑠𝑖𝑛(𝜔𝑡 + 115°) + 5,20 𝑠𝑖𝑛(3𝜔𝑡 + 156°) + +3,26 𝑠𝑖𝑛(5𝜔𝑡 − 177°) + 1,08 𝑠𝑖𝑛(7𝜔𝑡 − 137°) + 0,72 𝑠𝑖𝑛(9𝜔𝑡 + 164°) + +0,68 𝑠𝑖𝑛(11𝜔𝑡 + 167°) + 0,69 𝑠𝑖𝑛(13𝜔𝑡 + 162°) )а g), h) – 𝑖4(𝑡) = √2 ∙ ( 6,77 𝑠𝑖𝑛(𝜔𝑡 − 82°) + 8,90 𝑠𝑖𝑛(3𝜔𝑡 − 7°) + +2,33 𝑠𝑖𝑛(5𝜔𝑡 − 37°) + 0,79 𝑠𝑖𝑛(7𝜔𝑡 + 103°) + 1,13 𝑠𝑖𝑛(9𝜔𝑡 + 17°) + +0,51 𝑠𝑖𝑛(11𝜔𝑡 − 73°) + 0,59 𝑠𝑖𝑛(13𝜔𝑡 − 10°) )а fig. 8: vector diagrams of currents and voltages at a frequency of 50 hz at the input of a load node with predominant nonlinear power consumers. figure 8, obtained using the “hioki 3196” instrument software, shows the logical vector diagrams of currents and voltages at the input of the load node with prevailing nonlinear power receivers at time 11:42 (see fig. 1). along with this, the amplitude of the third harmonic of the current i4(t) is greater than the amplitude of the fundamental harmonic. in addition to the current values of voltage and current, the phase shifts of each value are also indicated here. for the first harmonic (frequency 50 hz) the components of the direct (positive), reverse (negative) and zero (zero) sequences of voltages and currents are given. with these components, real three-phase voltage and current systems can be balanced to a symmetrical system. similar characteristics for the considered time and frequency of 150 hz are presented in fig. 9. a distinctive feature of the vector diagrams of voltages and currents of the third harmonic (fig. 9) is the lack of common mode between the vectors of different phases. along with the lack of phase matching of vectors, they are also characterized by inequality in magnitude. so, for example, the effective current of the third harmonic in the first phase is 3.14 a, in the second phase is 1.34 a, and in the third phase is 5.2 a (see fig. 1). this is 198 iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 explained by the nature of the formation of these currents in the load node in case of accidental switching on of various power consumers under different voltages. fig. 9: vector diagrams of currents and voltages at a frequency of 150 hz at the input of a load node with predominant nonlinear power consumers. 4. conclusions the research contribution of this work lies in the fact that an experimental study was carried out, the nature of the change in the fundamental harmonic components of the current in the zero-working wire of a three-phase four-wire network with a voltage of 0.38 kv was studied. the results obtained during the work will increase the efficiency of electric power transmission and eliminate the negative consequences due to the current flow in a zeroworking wire in the network 0.38 kv. the analysis of the research results shows that in the presence of non-linear power receivers, the current in the zero-working wire of a three-phase four-wire network is comparable with the currents in linear wires. so, in the maximum load mode, with the current value of the zero working wire current 12.48 a, the currents of the linear wires were i1 = 16.63 a, i2 = 13.54 a, and i3 = 18.8 a, respectively. based on the obtained results of the study, it can be argued that the currents of the third harmonic component, which dominate in the neutral working wire of the network 0.38 kv, are not in-phase in the linear wires. the results obtained are of great practical importance when designing technical means that provide current unloading of the zero-working wire of the network 0.38 kv and, ultimately, reduce energy losses during transmission. references [1] grigoriev oa, petukhov vs, sokolov va, krasilov ia. (2003) on the impact of electronic equipment on power networks. computer press, 1. retrieved from http://www.compress.ru/article.aspx?id=9553&iid=404. [2] om pm, abdul gsh, neeraj g. (2015) acritical review of detection and classification of power quality events. renewable & sustainable energy reviews, 41: 495-505. [3] daus yv, yudaev iv, taranov ma, voronin sm, gazalov vs. (2019) reducing the costs for consumed electricity through the solar energy utilization. international journal of energy economics and policy, 9(2): 19-23. 199 iium engineering journal, vol. 22, no. 1, 2021 yudaev et al. https://doi.org/10.31436/iiumej.v22i1.1569 [4] ded av. (2017) to the problem of the current state of the levels of indices of asymmetry of voltages and currents in networks of 0.4 kv. omsk scientific herald, 2(152): 63-65. [5] kosoukhov fd, vasiliev nv, kuznetsova es. (2017) new scientific directions in energy saving in three-phase transformers and four-wire lines with asymmetric, non-linear and reactive loads. news of st. petersburg state agrarian university, 2(47): 300-309. [6] belitsky aa, shklyarsky ye. (2018) estimation of additional power losses in networks with non-linear and asymmetric load. bulletin of tula state university. technical science, 7: 8693. [7] wang t, meskin m, su x, grinberg i, wang z. (2019) optimal inverter based distributed generation units control strategy to improve voltage profiles in unbalanced distribution networks. iet generation, transmission and distribution, 13(21): 4910-4921. [8] zeng xj, zhai hf, wang mx, yang m, wang mq. (2019) a system optimization method for mitigating three-phase imbalance in distribution network. international journal of electrical power & energy systems, 113: 618-633. [9] zhang b, wang l, han x, meng r, ren c, wang q. (2018) source current control strategy of active power filters for unbalanced load compensation in three-phase four-wire distribution networks. journal of power electronics, 18(5): 1545-1554. [10] deokar sa, waghmare lm. (2011) analysis of distribution transformer performance un-der non-linear balanced load conditions and it’s remedial. international journal of technology and advanced engineering, 1(2): 152-161. [11] corasaniti vf, barbieri mb, arnera pl, valla mi. (2006) characteristics of the loads in medium voltage networks from the point of view using active filters. in: ieee pes transmission and distribution conference and exposition: latin america (pp. 1-7). 16-19 august, in caracas, venezuela. piscataway: institute of electrical and electronics engineers. [12] barutskov i.b., vdovenko s.a., tsygankov e.v. (2011) harmonic distortion during operation of frequency converters. chief power engineer, 6: 5-13. [13] om pm, abdul gsh. (2016) topological aspects of power quality improvement techniques: a comprehensive overview. renewableand sustainable energy reviews, 58: 1129-1142. [14] bodart m, denejer a, keppens a, rikart ur, rojzin b. (2010) characteristics of compact fluorescent lamps with integrated ballasts and their comparison with incandescent lamps. lighting engineering, 2: 18-24. [15] suslov kv, stepanov vs, solonina nn. (2013) effect of high harmonics on electricity consumers in distribution networks. proceedings of the 2013 international symposium on electromagnetic compatibility (emc europe 2013): 841-845. 200 magnetically plucked piezoelectric azam et al. 1department of mechatronics engineering, 2department of electrical and computer engineering, international islamic university malaysia, p.o. box 10, kuala lumpur 50728, malaysia. *corresponding author: noorhazrin@iium.edu.my (received:14th aug 2018; accepted:10th oct 2018; published on-line: 1st june 2019) abstract: abstrak: azam et al. keywords: piezoelectric; energy harvester;, hybrid kinetic motion; magnetically plucked m v2 m v azam et al. azam et al. m w m azam et al. azam et al. azam et al. azam et al. d d azam et al. f r2 ke q1 q2 azam et al. f azam et al. azam et al. . . . azam et al. . . << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <feff0633062a062e062f0645002006470630064700200627064406250639062f0627062f0627062a002006440625064606340627062100200648062b062706260642002000410064006f006200650020005000440046002006450646062706330628062900200644063906310636002006480637062806270639062900200648062b06270626064200200627064406230639064506270644002e00200020064a06450643064600200641062a062d00200648062b0627062606420020005000440046002006270644062a064a0020062a0645002006250646063406270626064706270020062806270633062a062e062f062706450020004100630072006f00620061007400200648002000410064006f00620065002000520065006100640065007200200036002e00300020064806450627002006280639062f0647002e> /bgr <feff04180437043f043e043b043704320430043904420435002004420435043704380020043d0430044104420440043e0439043a0438002c00200437043000200434043000200441044a0437043404300432043004420435002000410064006f00620065002000500044004600200434043e043a0443043c0435043d04420438002c0020043f043e04340445043e0434044f044904380020043704300020043d04300434043504360434043d043e00200440043004370433043b0435043604340430043d0435002004380020043f04350447043004420430043d04350020043d04300020043104380437043d0435044100200434043e043a0443043c0435043d04420438002e00200421044a04370434043004340435043d043804420435002000500044004600200434043e043a0443043c0435043d044204380020043c043e0433043004420020043404300020044104350020043e0442043204300440044f0442002004410020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e0030002004380020043f043e002d043d043e043204380020043204350440044104380438002e> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 175-1239 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 59 an investigation on soft magnetic and nonmagnetic materials under low frequency atika arshad, sheroz khan, a.h.m. zahirul alam and rumana tasnim electrical and computer engineering department, faculty of engineering, international islamic university malaysia, jalan gombak, sheroz@iium.edu.my abstract: the recent development of magnetic sensors in biomedical sector has called for urgent investigation on the characterization and relative magnetism of magnetic and nonmagnetic materials. this paper proposes a novel technique to categorize the magnetic and non-magnetic materials by obtaining their impedance peaks. the magnetization effect of a magneto-inductive sensor was detected in low frequency range for different magnetic and nonmagnetic core materials. the distinctive impedance peak values have been obtained for each materials used as core which result in showing different magneto-inductive effect. the results have shown a dominant behaviour of magnetic materials over non-magnetic materials due to the variation of permeability and magnetic strength (number of turns). moreover, variations in permeability originated by the applied alternative current field results in changing the depth (insertion depth) and also in the impedance. the influence of the permeability on materials with different frequencies is detailed. also, concentration is paid to the recent studies in the application base. it should be mentioned that high impedance peaks mean high output voltage in the secondary side. the novelty of this technique lies in the simplicity of ordinary circuits which are used in the experimental setup for characterization purpose. as a whole, this paper aims to investigate and characterize magnetic and non-magnetic materials; thus opening up a new branch of research for the application of soft magnetic materials in biomedical field. abstrak: pembangunan penyelidikan terhadap bahan bermagnet dan bukan bermagnet yang mempunyai karakteristik dan kemagnetan relatif telah dijalankan dengan intensif untuk menghasilkan sensor magnet bagi sektor biomedik. kajian ini adalah untuk mencadangkan teknik bagi menketagorikan bahan bermagnet dan bukan bermagnet dengan mendapatkan puncak rintangan bahan tersebut. sensor bahan teraruh magnet mengesan frekuensi yang rendah kemagnetan daripada teras bahan bermagnet dan bukan bermagnet. puncak rintangan yang signifikan terhasil daripada bahan tersebut menunjukkan kedominan bahan bermagnet daripada bahan bukan bermagnet. ini adalah kerana variasi dan kekuatan tarikan kemagnetan (pengaruh bilangan pusingan). variasi kemagnetan terhasil daripada penggunaan alternatif medan bahan yang menyumbang kepada perubahan kekuatan kemagnetan (kedalaman pergerakan bahan) dan kerintangannya. pengaruh kemagnetan bahan dan frekuensi yang dihasilkan dijelaskan dengan lanjut dalam laporan ini. diketahui bahawa peningkatan kerintangan akan mengakibatkan peningkatan voltan keluar dalam bahagian sekunder. kelainan teknik ini terletak pada penggunaan litar yang mudah dipasang dan digunakan dalam pengkonstrukturan experimen bagi mendapatkan karekter kemagnetan bahan. kesimpulannya, kajian ini adalah untuk menyiasat karekteristik bahan bermagnet dan bukan bermagnet untuk digunakan dalam usaha penyelidikan mencari bahan dengan medan magnet yang sesuai dan boleh diaplikasikan dalam bidang biomedik. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 60 keywords: inductive transducer; magneto-inductive; inductive element under test (ieut);, resistive material under test (mut) 1. introduction magnetic materials are of essential importance in many industrial, biomedical and engineering applications. over the past years research and studies have shown significant development for its numerous range of applications, especially in the biomedical sector. today’s dynamic expression of research interest has called for better understanding of the properties of soft magnetic and non-magnetic materials. the reason for the extensive use of magnetic materials in biomedical field is that they can be easily manipulated by an external magnetic field. recently researchers have focused also on new technologies like nanostructured magnetic materials in order to characterize and specify magnetic materials and its properties for suitable applications. magnetic materials are usually used in noncontact inductive sensors in the form of core materials. magnetic materials can also be employed for magnetic resonance imaging (mri), drug and gene delivery, cell separation, invasive surgery, radionuclide therapy, hyperthermia and other applications [1-6] where wiring accessibility may cause infection and it does not sound a sensible possibility in harsh conditions. thus, contactless transmission of data signal and power can offer a solution alternative to wiring connectivity. today non-contact sensor medical experts are able to intelligently monitor medical condition of patients like detecting and monitoring the respiratory system, the contraction of blood vessels, cardiac pressure disorders etc. a sensor such as the heart rate sensor takes an electrocardiogram reading from the heart rate of a patient and the sensor then relays the collected data to a computer, where the patient is monitored concurrently. moreover, wireless power transmission system uses an inductive coupling (non-contact) means to supply energy to the implanted devices within the human body that eliminates the need for surgery for battery replacement, thus making it safer for patients from getting infected. in this type of wireless system, noncontact inductive sensors use different type of magnetic material. the development of various sensors has opened up several possibilities for significant improvements in the advancement of bio-implantable devices or medical equipment. hence many problems regarding magnetic properties of the magnetic materials exist to be examined from the elementary viewpoint. to select the magnetic material and be completely familiar with the characterization of its magnetic properties proper investigation is required. in biomedical implants like aneurysm clip, the relative amount of magnetism should be evaluated. aneurysm clip is an implant used for closing blood vessels located in hardly accessible regions of patients’ body. it generally undergoes magnetic resonance (mr) procedures in mr systems. previous research [7] of this particular implant emphasized on the significance in evaluating the relative amount of magnetism present in the aneurysm clip. it is found that only the patients or individuals with non-ferromagnetic or weakly ferromagnetic clips are allowed into the mr environment. hereby the identification of materials appears to guide in using for suitable applications. extensive studies [8-11] have gained interest on various magnetic materials for its’ wide range of application. especially magneto-inductive effect on soft ferromagnetic materials as well as ferromagnetic materials has been observed by researchers which led to the design of various noncontact sensors over the years. under an ac magnetic field excitation, these sensors resonate at their resonant frequencies. in the magneto-inductive sensor, the alternating current (ac) impedance of a soft ferromagnetic material alters with the longitudinal component of a direct current (dc) magnetic field. the relative amount of the magnetic materials and the iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 61 characteristics of these material properties should be taken into consideration. in this paper, we have emphasized on a technique to characterize the magnetic and nonmagnetic materials and as a part of experimental work four materials were selected. this method can be used in case of various noncontact inductive sensors including above mentioned wireless passive sensors as both the sensing and biasing elements of these sensors are magnetic materials. this work proposes a novel technique for investigation of soft magnetic and non-magnetic materials under low frequency using experimental approach. the proposed work aims at identifying proper magnetic material to be used as core of inductive sensory transducers, ultimately identifying them for sensors fabrication, thus differentiating the materials by gaining distinctive impedance peaks with unique impedance values. design specifications of the proposed model includes the sensing circuit and simulation results. moreover, we have characterized magnetic and nonmagnetic materials for biomedical applications which require low frequency range. 2. theory of wireless energy system where magneto-inductive sensors are used the wireless energy systembasically concentrates on transferring the data and required energy to a small terminal via noncontact means. inductive coupling has been preferred as the most effective means of transferring energy to low power implanted devices. the magnetic energy transferring techniqueis less sensitive to its surroundings which do not interact with the coupled magnetic field. moreover, the magnetic fields do not impact on human physically [12]. the inductive coupling can be divided into two parts; primary and secondary (two air-core coils) to transfer power wirelessly. the concept is simple: to use the resonance phenomena to wirelessly transmit power. the inductive coupling system acts as magneto-inductive sensor where magnetic and non-magnetic materials are inserted in the form of core. magneto-inductive sensor is basically represented by a hollow solenoid, wounded with core made of the material under test as illustrated in fig.1; the solenoid consists of primary coil and secondary coil. when a core material under test is moved in and out continuously at a given frequency, it leads to producing a change in the inductance and hence a change in the corresponding output. the output from the circuit is calibrated directly against the value of the input such that it becomes a representative of the material the core is made of. the inductance to be measured is dependent on the nature of materials (µr). fig. 1: material testing coil. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 62 changes made in the impedance of the test coil are made to be reflected as changes of the inductance of the sensor circuit and magnetically coupled to the test coil. here the distance changes between the readout circuit and the sensing circuit that are related to the leakage flux lines. the inductance to be measured is dependent on the nature of material (µr). 3. circuit analysis fig. 2: schematic representation of the circuit diagram. figure 2 is used for obtaining the theoretical and experimental results in this work. this model circuit is integrated with three inductive circuits: excitation circuit (marked a), test circuit (marked b), and read-out circuit (marked c). this whole setup makes up a noncontact method of characterizing materials, which is based on inductive coupling for energizing the inductive element under test/ resistive material under test with cores made up of the materials being characterized (see fig.3). a set of two experiments were carried out, the first experiment was done with inductor for two set of coils, and the second experiment was done by replacing the inductor with resistor of two different resistive values. a series of graph was plotted, and then analysed based on their unique peak values. vin is set at a frequency of 1.0 khz and the supply voltage is set at 3v. a. excitation circuit provides an external power supply, which is connecting to the test circuit by non-contact means that is through inductive coupling. there exists a mutual inductance 1 m between the loops. the signal source circuit has an impedance of 1 1 1 z r jwl= + b. test circuit is the transducer processing circuit, connected to both the excitation circuit and the read-out circuit through inductive coupling. to enable the measurement without direct electrical contact, two inductive couplings are used ( )1 2,l l andl . 1m is the mutual inductance which exists between the excitation circuit and the test circuit, and 2 m is the mutual inductance existing between the test circuit and the read-out circuit. 1 ||rxp xz c and 2 ||rxs xz c is the parallel iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 63 impedance of the fixed resistor r and the bypass capacitor 1xc and 2xc respectively. 1x c and 2x c serves as the low impedance bypass capacitors for the coupled ac signal. the transducer processing circuit, has a transducer impedance ieutz , self-impedance x r j lω+ , and reflected impedances rxp z and rxs z . c. readout circuit is the signal measuring circuit which measures 2v , the resultant signal voltage produced when a material is inserted in the ieut coil. fig. 3: flowchart of the experimental setup. from fig.2, zieut is derived as a function of change in inductance where zieut is given by eq. (4) ( ) ( ) ( )( ) ( )1 2|| || mxp xt x rxp x rxs x ieut rxp rxs v i j l r z c z c z z zω = + + + + + + (1) ( ) ( )1 2( ) || ||setup rxp rxs x rxp x rxs xz z z j l r z c z cω= + + + + + (2) mxp xt setup ieut v i z z = + (3) hence, mxp ieut setup xt v z z i = − (4) 4. experimental setup the technique was implemented based on the experimental setup. the equipment used for both the experimental setup includes function generator, oscilloscope, volt-meters and cored coils. the function generator provides the external power needed to excite the iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 64 primary coil. in the experiment, 1v was set with an input of 3ppv v= with frequency ranging from 1 khz to 45 khz. to obtain experimental results, one of the coils was excited by a signal at a given frequency, which was received and measured through another coil. measurements were recorded across the resulting coupled signal in the circuit loop from the read-out circuit. the output value 2 v was recorded for every frequency increment of 1 khz. the inductive transducer coil (ieut/mut) is the subject under test. several different materials were used for the test; steel, plastic and air/ paper core (used as a reference). two sets of experiment were carried out under similar experimental procedures with two different sets of coil. the electrical specification of the coils used in these two experiments is given in table 1 and table 2. table 1: specification of primary and secondary coils. number of turns coil set-1 coil set-2 primary coil 1 200 400 primary coil 2 200 400 secondary coil 1000 2000 internal diameter (mm):10 height (mm):40 material of wire: copper thickness of wire (mm): 0.19 table 2: model parameter of the circuit. symbol description value unit rx fixed resistor 2 ω r1 series impedance in the primary coil 50 ω r2 series impedance in the secondary coil 50 ω c1 bypass capacitor 220 nf c2 bypass capacitor 220 nf 5. results and discussion cores of different materials with the same physical dimensions were used in this work; hence the strength of the magnet will vary in accordance with the core being used. the variation in the strength is due to the varying number of flux lines passing through the core. the permeability of the material �r is a measure for the strength of materials. the permeability of non-magnetic materials, such as plastic, aluminium and air is approximately the same as that of free space µ o. materials having permeability greater than µ o are ferromagnetic (soft magnetic), such as steel. the results obtained are discussed in detail; figures 4-7 present the results obtained by conducting the first experiment for ieut. the coil specifications used are as stated in table 1 (coil-1). figure 4 shows the inductive peak plotted for air core when no material is inserted in the solenoid coil. a highest peak in impedance (8 khz, 1.402921605 ω) is achieved because there was no interruption in the electromagnetic field of the coil. figure 5 shows the results for plastic core. it exhibits non-magnetic and non-conductive properties similar to air, causing impedance peaks at a frequency similar to that of air (8 khz, 0.894600647 ω). the lower iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 65 permeability value of plastic compared to that of air contributes to lower inductive reactance amplitude peak. the plot in case of steel is presented in fig. 6 where a decrease in peak value (4 khz, 1.026549297 ω) compared to air-core and a plastic-core plot is observed. generally steel is a good conductor and is also considered as a magnetic material. a core of magnetic material such as steel when placed in a coil or transformer provides a better path than air or plastic for magnetic flux, thereby increasing the inductance of the coil and raising the coupling between windings accordingly. this in turn causes the impedance peaks at a lower value of frequency considering the circuit component value remaining the same. accordingly the lower peak value is attributed to a lower value of permeability, assuming all other inductive reactance causing reliant factors to remain the same. figure 7 illustrates the overall performance for the three materials fig. 6: inductive peak against frequency variation for steelcore coil-1 setup. fig. 4: inductive peak against frequency variation for aircore coil-1 setup. fig. 5: inductive peak against frequency variation for plastic-core coil-1 setup. fig. 7: overall performance for the three materials with coil-1setup. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 66 used. based on the results obtained, the materials tested appeared to exhibit distinctive and unique features of impedance peaks with varying amplitude and frequency, thus characterizing the materials under observation. among the three materials tested so far, steel was found to be more promising that air or plastic when it comes to applications such as transducers. however, space and weight requirement priorities favour the choice of nonmagnetic materials when the sensitivity is not a pivotal issue of concern. however, in an application-specific situation, conductive material proves better than the nonconductive materials when used as a core for magneto sensor application. in line with the second experiment, the second set of coil was used with an increased number of primary and secondary turns, as specified in table 1 (coil-2). figure 8-11 show the effects on the inductive peaks by the increased number of turns in a coil. the three materials under test for the new set of coils are air core, aluminum core, and steel core. fig. 10: inductive peak against frequency variation for steelcore coil-2 setup. fig. 8: inductive peak against frequency variation for aircore coil-2 setup. fig. 9: inductive peak against frequency variation for aluminiumcore coil-2 setup. fig. 11: overall performance for the three materials with coil-2setup. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 67 figure 8 shows the inductive peak plot for air core when no material is inserted in the solenoid coil. again the highest peak in impedance value for air core is achieved at 7 khz, giving a high inductive peak at 1.061385 ω. figure 9 shows the inductive peak obtained for aluminium in coil-2 setup; aluminium was used instead of plastic in order to consider the inductive response for a paramagnetic material (7 khz, 0.982917 ω). moreover not much difference was observed in the inductive peak values, because the permeability of aluminium and plastic are relatively equal. in fig.10 the inductive peak was obtained in the case of steel core. the inductive peak was observed at a frequency of 3 khz with an inductance value of 1.026549297 ω.it is noteworthy that the peak value was obtained at a faster frequency response when compared with the results of coil-1 setup. figure11 illustrates the overall performance of the materials with a higher number of turns in a coil. for air core, the highest peak is achieved once again owing to have no interruption in the electromagnetic field, as stated earlier. however, when an aluminium core was used, a lower peak value was achieved compared to steel core. this means that soft magnetic material produces a stronger magnetism compared to air and aluminium. for coil-2 setup, the number of turns was doubled, hence the magnetic field produced by each turn in the solenoid adds up, giving a stronger resultant magnetic field inside the solenoid coil. with the increased number of turns in the coil, higher voltage is induced in the coils, thus causing the inductive peak response to be faster than coil-1 setup at a lower frequency. with the experimental setup for resistive material under test coil-1 setup had been used with a resistive value of 30 ω and 240 ω. figures 12-15 present the experimental results when conducted with 30 ω load. figure 12 illustrates the resulting plots for paper core. the graph was plotted for impedance, zmut as a function of frequency, which ranges from 10 khz to 350 khz, by an increment of 10 khz. paper core was used as a reference material under test. note that there is constant increase in the graph, till 2 khz, it then shows a continuous decrease in the values with increasing frequency. figure 13 shows the impedance response for the case of aluminum. the nonmagnetic materials, aluminum and paper, showed almost similar output, since their permeability is approximately equal to of air. the graph showed shows a linear increment for a small change in frequency range. moreover there was a constant decrement of the zmut values with increasing frequency. fig. 12: resistive materials under test with a load resistance of 30 ω for paper-core. fig. 13: resistive materials under test with a load resistance of 30 ω for aluminium-core. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 68 figure 14 shows the impedance response obtained in the case of steel core. steel exhibited a relatively different plot compared to paper and aluminum, as steel is a soft magnetic material. however, atthe frequency of 2 khz, highest impedance peak was obtained for steel. figure 15 illustrates the results of the comparison made between the three materials under test using a 30 ω resistor. there is an overlap in the results for paper and aluminum however there is a slight variation in the plot response for steel. the results obtained using 30ω resistor did not show a positive outcome for the purpose of characterizing materials; hence the experiment was repeated with a higher resistance load. figure 16 shows the results for resistive material under test with a load resistance of 240ω. in the case of paper core a similar output response as in the case of 30 ω resistor was obtained. the impedance peak had resulted at a frequency of 2 khz. figure 17 shows the results obtained for aluminum core condition, by using a higher resistance a very small change in the impedance peak is noted, but the frequency at which the peak occurs remains the same. fig. 16: resistive materials under test with a load resistance of 240 ω for paper-core. fig. 14: resistive materials under test with a load resistance of 30 ω for steel-core. fig. 17: resistive materials under test with a load resistance of 240 ω for aluminium-core. fig. 15: overall performance for the three materials with a load resistance of30 ω. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 69 figure 18 shows the impedance response obtained for the case of steel core. steel exhibited a higher impedance peak compared to paper and aluminium. figure 19 illustrates the results for the comparison of the three materials under test with load resistance of 240 ω. note that not much difference was observed between the high load resistor and the low load resistor for the three resistive materials under test. the results almost overlap. this shows that load resistance in the main circuit is not affecting the current induction on the coil for this specific material; therefore resistors are not very applicable to be used in transducers. moreover it can be concluded that in order to characterize materials, inductors are more well-suited than resistors. as a whole, the distinctive impedance peaks are basically representing the core materials. referring to fig.11, impedance peaks are shown for three materials, i.e., steel, air and aluminium. the figure apparently shows that aluminium and air (both nonmagnetic) are very close to each other in their magnetic properties by exhibiting their peaks at almost the same frequency between 5 and 10 khz, whereasbeing magnetic steel shows similar peak at a frequency of about 0.9 khz, showing resonating behaviour at a much lower frequency. the materials are characterised for their magnetic behaviours at low frequency, justifying the characterization technique accordingly. 6. conclusion in this paper, a magneto-inductive sensor model is used in which magnetic and nonmagnetic materials are inserted to characterize the material by measuring the inductance of magnetic and non-magnetic inductance peaks. the characteristic of the material can be differentiated from other materials by obtaining unique distinctive impedance peaks with unique impedance values. the change in permeability of a material determines the inductance of the output coil, which is changed by changing the positioning of movable core made of the material. this paper uses a simple circuit approach by making use of inductive coupling approach. this characterization technique of magnetic and nonmagnetic material is significantly important for the applications in biomedical equipment and implants requiring low frequency. another reason for this identification technique also comes from the particular fact that magnetic materials over the last twenty years have changed dramatically both in terms of their applications and in the magnitude of their use. fig. 18: resistive materials under test with a load resistance of 240ω for steel-core. fig. 19: overall performance for the three materials with a load resistance of 240ω. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics atika et al. 70 references [1] i. safarikandm. safarikova, “magnetic nanoparticles and biosciences”. monatshefte fur chemie. vol. 133, no. 6, 737-759, 2002 [2] c.c. berryanda.s.g. curtis, “functionalisation of magnetic nanoparticles for applications in biomedicine”. journal of physics d: applied physics. vol. 36, r198-r206, 2003 [3] d. bahadurandj.giri, “biomaterials and magnetism”. sadhana. vol. 28, 639-656, 2003 [4] m.shinkai“functional magnetic materials for medical applications”. journal of bioscience bioengineering. vol. 94, 606–613, 2002 [5] q.a.pankhurst, j. connolly, s.k. jones, and j.dobson,“applications of magnetic nanoparticlesin biomedicine”. journal of physics d: applied physics. vol. 36, 167–181, 2003 [6] c. plank, m. anton, c. rudolph, j. rosenecker and f. krotz,“enhancing and targeting nucleic acid delivery by magnetic force”. expert opinion on biological therapy, 2003. [7] a.kangarlu, and f.g. shellock, “aneurysm clips: evaluation of magnetic field interactions with an 8.0 t mr system”. journal of magnetic resonance imaging. vol. 12, 107-111, 2000 [8] k. fujisaki, “high-response inductive electromagnetic sensor”. ieee journal, transactions on magnetics. vol. 39, no. 5, 2190-2193, 2003 [9] l.ferrigno, c.liguori, and a.pietrosanto, “measurement for the characterization of passive components in non-sinusoidal conditions”. ieee transactions on instrumentation and measurement, vol. 51, no. 6, 1252–1258, 2002 [10] weng-yew chang, kye-yak see, and bo hu, “characterization of component under dc biasing condition using an inductive coupling approach”. ieee transactions on instrumentation and measurement, vol. 59, no. 8, 2109-2114, 2010 [11] m.jagiella, s.fericean, r.droxler, and a.dorneich, “new magneto-inductive sensing principle and its implementation in sensors for industrial applications”. ieee proceeding on sensors. vol. 2, no. 9, 1020-1023, 2004 [12] s.j. mazlouman, a. mahanfar, and b. kaminska, “mid-range wireless energy transfer using inductive resonance for wireless sensors” ieee conference on computer design, 517-522, 2009 nomenclature a area of coil m 2 l length of the coil m l-x core displacement left from the left end m l total inductance h l0 inductance of free space h n total number of turns x core displacement fron the right end m greek letters µ o free space permeability hm -1 µ r permeability of a material hm -1 microsoft word 4-hilbert-2-2.doc iium engineering journal, vol. 2, no. 2, 2001 a. hossen 21 a new fast approximate hilbert transform with different applications abdulnasir hossen information engineering department, sultan qaboos university, p.o.box 33 al-khod, 123 sultanate of oman abhossen@squ.edu.om abstract: a new and fast approximate hilbert transform based on subband decomposition is presented. this new algorithm is called the subband (sb)-hilbert transform. the reduction in complexity is obtained for narrow-band signal applications by considering only the band of most energy. different properties of the sb-hilbert transform are discussed with simulation examples. the new algorithm is compared with the full band hilbert transform in terms of complexity and accuracy. the aliasing errors taking place in the algorithm are found by applying the hilbert transform to the inverse fft (time signal) of the aliasing errors of the sb-fft of the input signal. different examples are given to find the analytic signal using sb-hilbert transform with a varying number of subbands. applications of the new algorithm are given in single-sideband amplitude modulation and in demodulating frequency-modulated signals in communication systems. key words: fast algorithms, hilbert transform, analytic signal processing. 1. introduction the subband decomposition idea applied to both fft[1,2] and dct[3,4] is used in this paper for computing the hilbert transform. the discrete hilbert transform is related to the discrete fourier transform, and both of them can be computed using the fast fourier transform fft [5]. the hilbert transform of a signal is equivalent to a ±90° phase shift in all frequency components of the signal. considering a signal x(t) with fourier transform x(f), the hilbert transform of x(t), denoted by ˆ( )x t , is defined [6]: 1 ( )ˆ( ) x x t d t          (1) from this equation, we note that the hilbert transform ˆ( )x t may be interpreted as the convolution of x(t) with the time function h(t) =1/(π t). so for a discrete sequence x(n), eq. (1) can be represented as: 0 ˆ( ) ( ) ( ) i i x n h i x n i     (2) also we know that the convolution of two functions in time domain is transformed into the multiplication of their fourier transforms in the frequency domain [7]. for the time function 1/(πt), we have a fourier transform of -jsgn(f), where sgn(f) is the signum or sign function defined as 1 0, sgn( ) 0 0, 1 0. f f f f       then, the fourier transform ˆ ( )x f of ˆ( )x t is given by ˆ ( ) sgn( ) ( )x f j f x f  (3) the hilbert transform signal ˆ( )x t is obtained by taking the inverse fourier transform of ˆ ( )x f . the analytic signal for a discrete sequence x(n) has a one sidedfourier transform since negative frequencies are zero. it can be determined by calculating the fft of the input sequence, replacing those fft coefficients that correspond to negative frequencies with zeros, and calculating the inverse fft of the result. the analytical signal of a real sequence is a complex sequence with a real part, which is the original data, and an imaginary part that contains the hilbert transform [5]. the following procedure is to be followed to compute the hilbert transform for a discrete signal[8]: 1. calculating the fft x(k) of the input sequence x(n). 2. creating a vector h(k) whose elements have the values: 1 0, 2 ( ) 2 1, 2, , 1 2 0 1, 2, , 1 2 2 n k n h k k n n k n                3. calculating the element-wise product of x and h. 4. calculating the inverse fft (ifft) of the sequence obtained in step 3. 5. taking the imaginary part of the result of the above step. for narrow-band signals, the subband fft [1], [2] can be obtained by decomposing the input sequence into two iium engineering journal, vol. 2, no. 2, 2001 a. hossen 22 bands corresponding to lowand high-pass sequences. the band with the greater energy is transformed while the other band is ignored leading to a fast and approximate fft. in this work the subband decomposition idea is applied to compute the hilbert transform. the organization of the paper is as follows: in the next section, the idea of the subband fft[1], [2] is reviewed. section 3 introduces the basic idea of the fast approximate hilbert transform with its properties. section 4 compares the complexity of the subband hilbert transform with that of the full-band hilbert transform. the aliasing errors in the subband hilbert transform are discussed in section 5. section 6 contains applications of the fast approximate hilbert transform in analytic-signal generation, in ssbmodulation, and in fm demodulation. in section 7, concluding remarks are given. 2. subband-fft in fig. 1, a(n) and b(n) are the low-pass and high-pass filtered versions of x(n), with g(n) and h(n) denoting their factor-2 down-sampled versions, respectively: )].12()2([ 2 1)( )]12()2([ 2 1)(   nxnxnh nxnxng (4) fig. 1: two-band decomposition of the subband dft. the full-band size-n dft x(k) can be obtained by combining the ffts of g(n) and h(n)[1], [2]: ).k( h f) k n w1()k(gf) k n w1()k(x  (5) equation (5) is approximated for calculating only the low-pass band: ( ) (1 ) ( ) , (0, 1, , / 4 1).n kx k w f k k ng» + î -k (6) the decomposition process in fig. 1 can be repeated m times to get m = 2m subbands, out of which only one band is to be computed depending on information known or derived adaptively [9] about the input signal power distribution. two types of approximation errors (linear distortion and aliasing) are resulted from the decomposition and approximation processes [2]. substituting fg(k) in eq. (6) by the dft of g(n), and taking g(n) from eq.(4), we get: / 2 / 2 1 1ˆ ( ) (1 ) ( (2 ) (2 1)) .2 0 k kn n n n x k w x n x n w n = + + + = å (7) equation (7) can be also written as: 2 2 2 2 1 1 0 0 1ˆ ( ) (2 ) (2 1)2 n n n n kn k kn n n n x k x n w w x n w = = ì üï ïï ï= + +í ýï ïï ïî þ å å 2 2 2 2 1 1 0 0 1 (2 ) (2 1)2 n n n n k kn kn n n n w x n w x n w = = ì üï ïï ï+ + +í ýï ïï ïî þ å å (8) the two types of approximation errors in )(ˆ kx can be taken into account in the following equation [2]: 0 1 ˆ ( ) ( ) ( / 2)x k a x k a x k n= + + (9) where a0 and a1 are two coefficients relating to linear distortions in the exact transform x(k) and aliasing error due to x(k+n/2), respectively. noticing the first half of eq. (8) shows that it is the exact transform x(k) multiplied by a factor of 1/2. the value of x(k+n/2) can be found from x(k) by replacing each k in x(k) with k+n/2. now substituting for x(k) and x(k+n/2) into eq. (9) yields: 2 2 2 2 1 1 0 0 0 ˆ ( ) (2 ) (2 1) n n n n kn k kn n n n x k a x n w w x n w = = ì üï ïï ïï ï= + +í ýï ïï ïï ïî þ å å 2 2 2 2 1 1 0 0 (2 ) (2 1) .1 n n n n kn k kn n n n a x n w w x n w = = ì üï ïï ïï ï+ +í ýï ïï ïï ïî þ å å (10) by comparing eqs. 8 and 10 we obtain the following: 0 1 1 (1 ),2 k na a w+ = + (11) 0 1 1 (1 )2 k na a w -= + . (12) solving eqs. 11 and 12 yields: 0 1 (1 cos(2 / )) ,2a k np= + (13) and 1 2sin( ) .2 j ka n p= (14) thus the one-stage approximation in eq. (6) can be expressed as x1 2 2ˆ ( ) [1 cos( )] ( ) sin( ) ( )2 2 2 jk k nx k x k kn n p p= + + (15) where ˆ ( )x k is the approximate, and x(k) is the true signal spectrum. for m = 2m bands of decomposition, there will be m-1 aliasing terms, uniformly distributed on the frequency axis. for the case of retaining only the low-low band + ++ x(n) ½ + a(n) g(n) fg(k) + + + b(n) h(n) fh(k) + 2 fft 2 fft z-1 iium engineering journal, vol. 2, no. 2, 2001 a. hossen 23 out of m=4 subbands in the approximation, eq. (9) can be written [2]: 10 ˆ ( ) ( ) ( )4 nx k a x k a x k= + + (16) 2 3 3( ) ( ),2 4 n na x k a x k+ + + + and the four aliasing coefficients are found to be: 0 1 2 3 1 2 4( ) [1 cos( )][1 cos( ) ],4 1 4 2 2( ) sin( )[1 cos( ) sin( )] ,8 2 4( ) sin ( )[1 cos( )] ,4 (1 ) 4 2 2( ) sin( ) [1 cos( ) sin( )] .8 k ka k n n j k k ka k n n n j k ka k n n j k k ka k n n n p p p p p p p p p p = + + -= + -= + + = + + (17) 3. subband hilbert transform the subband hilbert transform is obtained using the following steps: 1. calculating the sb-fft x of the input sequence, this results in a sequence of length 2 nl = for half-band case, 4 nl = for quarter-band case, or generally nl m= for m sub-bands. 2. creating a vector h with length l having the values: 1 0, 2 ( ) 2 1, 2, , 12 0 1, 2, , 12 2 lk lh k k l lk l ìï =ïïïïïï= = -íïïïï = + + -ïïîï k k 3. calculating the element-wise product of x and h 4. calculating the ifft of length l for the sequence obtained in step 3. 5. taking the imaginary part of the result of step 4. all properties known for the full-band hilbert transform are applicable also to the subband hilbert transform if the signal to be transformed is a narrowband signal. some of these properties are investigated in this section with simulation examples. in all these examples the input signal is plotted with solid-line and the output signal is plotted with dotted-line. 1. the hilbert transform of a constant is zero. fig. 2 shows that both full-band and half-band hilbert transforms of a constant is zero. 2. the hilbert transform of the cosine function cos(2πfcnt) is equal to sin(2πfcnt). where t is the sampling interval. similarly, the function sin(2πfcnt) has a hilbert transform equal to cos(2πfcnt). both the full-band and the sb-hilbert transformation produce this results, as shown in fig. 3 0 5 10 15 20 25 30 35 40 45 50 -2 -1 0 1 2 full-band hilbert transform 0 5 10 15 20 25 30 35 40 45 50 -2 -1 0 1 2 half-band hilbert transform fig. 2: hilbert of a constant. 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 -1.5 -1 -0.5 0 0.5 1 1.5 sb-hilbert transform of a cosine function 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 -1.5 -1 -0.5 0 0.5 1 1.5 sb-hilbert transform of a sine function fig. 3: hilbert of a cosine function. 3. the energy content of a zero-mean signal is equal to the energy content of the hilbert transform. the property is tested by finding the energy of a sinusoidal signal (used in property 2) and the energy of its full-band hilbert transform and subband hilbert transform with m = 2 and m =4 and m = 8. it is found that the energy is almost the same in all cases depending on the approximation quality of the subband realization. 4. the signal x(t) and its hilbert transform are orthogonal. for the same example used to prove the previous two properties, it is proved that, if ˆ( )x t is used as a full-band hilbert transform, then: ˆ( ) ( ) 0x t x t dt ¥ ¥ =ò (18) and the result is almost zero if subband hilbert transforms of m = 2 or m = 4 or m = 8 are used. 5. the hilbert transformation of a hilbert transform produces a phase shift of  to the original signal. in fig. 4, a sinusoidal signal of 50 hz is applied to two stages of hilbert transform. in each stage either a full-band or a half-band hilbert transform is used. iium engineering journal, vol. 2, no. 2, 2001 a. hossen 24 0 0.02 0.04 0.06 -1 -0.5 0 0.5 1 both full-band transforms 0 0.02 0.04 0.06 -1 -0.5 0 0.5 1 half-band and full-band transforms 0 0.02 0.04 0.06 -1 -0.5 0 0.5 1 full-band and half-band transforms 0 0.02 0.04 0.06 -1 -0.5 0 0.5 1 both half-band transforms fig. 4: hilbert of hilbert transform. 6. the hilbert transform is a linear process. an input data sequence x(n) of length 1024 points is used with three impulses as follows: ( ) ( 25) 1.5 ( 50) 2 ( 75)x n n n nd d d= + + (19) knowing that the hilbert transform of (t) is /a tp . both full-band and sb-hilbert transforms results in fig. 5 prove the linearity theorem. 4. complexity the advantage of using subband decomposition transforms is the reduction of the complexity in comparison to full-band[1-4]. reductions in complexity are obtained from all the steps of section 3. by using sequences of length l instead of n. the subband hilbert transform is compared in computational complexity with the full-band hilbert transform. table 1 shows the percentage reduction in complexity (measured as execution time) of the hilbert transform, if sb-hilbert transforms with different m are to be used instead of full-band transform. 0 50 100 150 200 250 -1 -0.5 0 0.5 1 full-band hilbert transform 0 50 100 150 200 250 -1 -0.5 0 0.5 1 half-band hilbert transform fig. 5: linearity property of hilbert transform. table 1: complexity reduction results. 5. accuracy for n = 16 and m = 2 and if only the first band is calculated, table 2 shows the values of the computed fast approximate (with aliasing errors) half-band hilbert transform ˆ( )x n , assuming that the ratio of the frequency-transform points causing aliasing to the true components in the calculated band is fixed to . the values in table 2 can be computed by calculating the aliasing errors of the sb-fft and then finding the hilbert transform of their time signal. the following numerical example describes this interesting result for n = 8 and m = 2: 1. for a case of no aliasing error, a frequency signal of (1,1,0,0,0,0,0,1) is assumed. the half-band hilbert transform of the first two-points (the lowband case) is found to be 0 and 0.5 respectively. table 2: approximate half-band hilbert transform with aliasing errors.  )0(x̂ )1(x̂ )2(x̂ )3(x̂ 0 0 0.5 0 -0.5 0.1 -0.0457 0.525 -0.0043 -0.475 0.2 -0.0914 0.55 -0.0086 -0.45 0.3 -0.1371 0.575 -0.0129 -0.425 2. if an aliasing component α of 0.1 is assumed outside the low-frequency band, the corresponding frequency signal will be: (1,1,0.1,0.1,0.1,0.1,0.1,1). the half-band hilbert transform of the first two-points is found to be 0.0457 and 0.525 respectively. 3. comparing the results of 1 & 2, the aliasing errors in the hilbert transform of these two points are 0.0457 and 0.025 respectively. 4. the result in the last step can be found by finding first the aliasing errors in the subband-fft from eq. (15). these errors are found to be (0, -0.0414j, -0.1j, -0.2414j) for (k = 0,1,2,3) respectively. 5. the hilbert transform of the corresponding time sequence of this error signal is found to be: 0.0457 and 0.025 for the first two points. the values of the aliasing errors found from steps 3 and 5 are the same. the following numerical example describes the analysis of the aliasing errors in quarter-band sbhilbert transform for n = 16 and m = 4: m reduction in complexity number of input points 64 128 256 512 1024 2 23.01% 25.91% 26.43% 28.93% 31.48% 4 48.11% 50.45% 52.81% 54.82% 56.55% 8 63.58% 65.61% 67.42% 69.14% 70.73% 16 75.09% 76.38% 77.68% 79.01% 80.22% iium engineering journal, vol. 2, no. 2, 2001 a. hossen 25 1. for a case of no aliasing error, a frequency signal of (1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,1) is assumed. the quarter-band hilbert transform of the first twopoints (the low-low-band case) is found to be 0 and 0.125 respectively. 2. if an aliasing component of 0.1 is assumed outside the low-low-frequency band, and the frequency signal is represented as (1,1,0.1,0.1, 0.1,0.1,0.1,0.1,0.1,0.1,0.1,0.1,0.1,0.1,0.1,1), the quarter-band hilbert transform of the first twopoints is found to be -0.0165 and 0.1328 respectively. 3. comparing the results of 1 & 2, the aliasing errors in the hilbert transform of these two points are 0.0165 and 0.0078 respectively. 4. the result in the last step can be found by finding first the aliasing errors in the-fft from eq. (17). these errors are found to be: (0, -0.0153j, -0.354j, -0.077j) for (k=0,1,2,3) respectively. 5. the hilbert transform of the corresponding time sequence of this error signal is found to be: 0.0165 and 0.0078 for the first two points, and this result is the same as that found in step 3 of this example. interpolating the resulting length-n/2 half-band sbhilbert transform by a factor of 2, leads to a length-n approximated hilbert transform )(ˆ nx . table 3 shows the values of the full-band hilbert transform with n=16 and half-band (m=2) subband hilbert transform with and without interpolating the results by a factor of 2. the input signal has a frequency transform of: (1,1,1,1,0.1,0.1,0.1,0.1,0.1,0.1,0.1,0.1,0.1,1,1,1). results show how well the subband hilbert transform values approximate those of the full-band hilbert transform. table 3: interpolating the approximated hilbert transform results. index: n full-band half-band half-band inter. 0 0 -0.0223 -0.0223 1 0.2894 0.2289 2 0.2716 0.3122 0.3122 3 0.1591 0.1717 4 0 -0.0011 -0.0011 5 -0.0103 -0.0127 6 0.0466 0.0539 0.0539 7 0.0699 0.0541 8 0 -0.0006 -0.0006 9 -0.0699 -0.0518 10 -0.0466 -0.0497 -0.0497 11 0.0103 0.0109 12 0 -0.0011 -0.0011 13 -0.1591 -0.1602 14 -0.2716 -0.2914 -0.2914 15 -0.2894 -0.2289 6. applications 6.1 analytic signal there are many applications in communication where it is necessary to perform a 90° phase shift to the frequency components comprising a signal. one common application is the generation of the complex-valued analytic signal ( )x n% . letting )(ˆ nx be the hilbert transform of x(n) with all frequency components shifted by 90°, the analytic signal is given by: )(ˆ)()(~ nxjnxnx  (20) so if x(n)=cos(0nt), )(ˆ nx will be sin(0nt) and )(~ nx will be cos(0nt) + j sin(0nt), which corresponds to only the positive-frequency component of x(n). in fig. 6, both x(n) (solid line) and )(ˆ nx (dotted line) are shown for full-band hilbert transform and subband hilbert transform with three different values of m. in all cases the fundamental frequency is 30 hz, and the sampling frequency is 1024 hz. 0 0.05 0.1 0.15 -1 -0.5 0 0.5 1 1.5 fullband hilbert transform 0 0.05 0.1 0.15 -1 -0.5 0 0.5 1 1.5 subband (m=2) hilbert transform 0 0.05 0.1 0.15 -1 -0.5 0 0.5 1 1.5 subband (m=4) hilbert transform 0 0.05 0.1 0.15 -1 -0.5 0 0.5 1 1.5 subband (m=8) hilbert transform fig. 6: analytic signal generation. 6.2 single sideband modulation a ssb-modulated signal is obtained by multiplying the hilbert transform of the information signal x(n) by a sinusoid of frequency fc and adding (or subtracting) the result to (or from) the product of the signal x(n) and a 90° phase shifted sinusoid of frequency fc [11] for upper and lower ssb signals generation, respectively. fig. 7 shows the generation of a ssb-signal with fundamental frequency of 15 hz and with transmitted carrier frequency 250 hz with a sampling frequency of 1024 hz. both full-band and sb-hilbert transforms with different numbers of subbands are used. the frequency spectrum of the four generated ssb-signals of fig. 7 are shown in fig. 8. iium engineering journal, vol. 2, no. 2, 2001 a. hossen 26 0 0.1 0.2 0.3 0.4 -1 -0.5 0 0.5 1 fullband hilbert transform 0 0.1 0.2 0.3 0.4 -1 -0.5 0 0.5 1 half-band hilbert transform 0 0.1 0.2 0.3 0.4 -1 -0.5 0 0.5 1 quarter-band hilbert transform 0 0.1 0.2 0.3 0.4 -1 -0.5 0 0.5 1 subband hilbert transform m=8 fig. 7: single-sideband modulation examples. 0 0.05 0.1 0.15 0.2 0 20 40 60 80 100 120 fullband hilbert transform 0 0.05 0.1 0.15 0.2 0 20 40 60 80 100 120 half-band hilbert transform 0 0.05 0.1 0.15 0.2 0 20 40 60 80 100 120 quarter-band hilbert transform 0 0.05 0.1 0.15 0.2 0 20 40 60 80 100 120 subband hilbert transform m=8 fig. 8: frequency spectrum of ssb examples. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 -0.5 0 0.5 fullband hilbert transform 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 -0.5 0 0.5 halfband hilbert transform fig. 9: demodulated fm signal examples. 6.3 fm demodulation an fm signal may be demodulated by modulating the hilbert transform of the waveform by a complex exponential of frequency -fc, and obtaining the instantaneous frequency of the result[8]. in fig. 9 a demodulated sinusoidal signal with a frequency 50 hz is shown, the carrier frequency being 200 hz, while the sampling frequency is 1000 hz. both full-band hilbert transform and half-band hilbert transform are used. 7. conclusion a new application to the subband-decomposition idea in computing the hilbert transformation is presented. the result is a fast and approximate hilbert transform. a reduction in complexity of about 20% to 30% in half-band and about 45% to 55% in quarter--band hilbert transforms is obtained with respect to the fullband hilbert transform of a discrete sequence of length n=16 to n=1024. properties of the approximate hilbert transform are examined with different examples. a very interesting relation between the aliasing errors of the sb-fft used for computing the approximate hilbert transform and the aliasing errors of the computed hilbert transform is found. different simulation examples of approximate hilbert transforms with different numbers of subbands are given to describe this relation. application examples in communication systems are also included. acknowledgement the author would like to thank prof. ulrich heute, the head of the department of network and system theory at the university of kiel-germany, for his valuable comments. references [1] o. shentov; s. mitra; u. heute,; and a. hossen. "subbnad dft-part i: definition, interpretation and extensions", signal processing, vol. 41, no. 3, pp. 261-277 , feb. 1995. [2] a. hossen, u. heute, o. shentov, and s. mitra, "subband dft-part ii: accuracy, complexity, and applications", signal processing, vol. 41, no.3, pp.279--294. feb. 1995. [3] s. jung, s. mitra, and d. mukherjee, "subband dct: definition, analysis, and applications", ieee trans. on circuits and systems for video technology, vol.6, no.3, june 1996. [4] a. hossen and u heute, "general adaptive sub-band dct", proceedings of ecsap-97, prague, czech republic, june 1997. [5] s. hann," hilbert transforms in signal processing", artech house, 1996. [6] s. haykin, "communication systems", john wiley and sons, 1994. [7] a. v. oppenheim and r. w. schafer, "discrete-time signal processing", prentice hall, 1989. [8] "matlab signal processing toolbox", the mathworks, 1994. iium engineering journal, vol. 2, no. 2, 2001 a. hossen 27 [9] a. hossen and u. heute, "fully adaptive evaluation of subband-dft", proc. of iscas'93, chicago, pp.655-658, may 1993. [10] l. jackson, "digital filters and signal processing", kluwer academic publishers, 1993. [11] j. proakis and m. salehi, "communication systems engineering", prentice hall, 1994. biography abdulnasir hossen received his dr.-ing. degree in digital signal processing from the ruhr university of bochum, germany in 1994. in 1997, he completed his post doc. research at the technical faculty of kielgermany in the same field. then he joined the applied science university in jordan as an assistant professor for two years. in 1999, he joined the information engineering department, at sultan qaboos university in oman as an assistant professor. dr. hossen’s primary research interests are in digital signal processing, fast algorithms, and their applications in speech, image, radar and biomedical signal processing. iium engineering journal, vol. 2, no. 2, 2001 a. hossen 28 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 classification model for breast cancer mammograms suzani mohamad samuri1,3*, try viananda nova2, bahbibi rahmatullah1,3, wang shir li1,3, ziadoon tareq al-qaysi4 1 department of computing, faculty of art, computing and creative industry, sultan idris education university, malaysia 2 department of informatic, universitas ibn kaldun bogor, jawa barat, indonesia 3 data intelligence and knowledge management special interest group, faculty of art, computing and creative industry, sultan idris education university, malaysia 4 computer science department, college of computer sciences and mathematics, tikrit university, iraq *corresponding author: suzani@fskik.upsi.edu.my (received: 16th january 2021; accepted: 13th october 2021; published on-line: 4thjanuary 2022) abstract: machine learning has been the topic of interest in research related to early detection of breast cancer based on mammogram images. in this study, we compare the performance results from three (3) types of machine learning techniques: 1) naïve bayes (nb), 2) neural network (nn) and 3) support vector machine (svm) with 2000 digital mammogram images to choose the best technique that could model the relationship between the features extracted and the state of the breast (‘normal’ or ‘cancer’). grey level co-occurrence matrix (glcm) which represents the two dimensions of the level variation gray in the image is used in the feature extraction process. six (6) attributes consist of contrast, variance, standard deviation, kurtosis, mean and smoothness were computed as feature extracted and used as the inputs for the classification process. the data has been randomized and the experiment has been repeated for ten (10) times to check for the consistencies of the performance of all techniques. 70% of the data were used as the training data and another 30% used as testing data. the result after ten (10) experiments show that, support vector machine (svm) gives the most consistent results in correctly classifying the state of the breast as ‘normal’ or ‘cancer’, with the accuracy of 99.4%, in training and 98.76% in testing. the svm classification model has outperformed nn and nb model in the study, and it shows that svm is a good choice for determining the state of the breast at the early stage. abstrak: pembelajaran mesin telah menjadi topik yang diminati dalam penyelidikan yang berkaitan dengan pengesanan awal kanser payudara berdasarkan imej mamogram. dalam kajian ini, kami membandingkan hasil prestasi dari tiga (3) jenis teknik pembelajaran mesin: 1) naïve bayes (nb), 2) neural network (nn) dan 3) support vector machine (svm) dengan 2000 imej digital mammogram hingga teknik terbaik yang dapat memodelkan hubungan antara ciri yang diekstraksi dan keadaan payudara ('normal' atau 'cancer') dapat diperoleh. grey level co-occurrence matrix (glcm) yang mewakili dua dimensi variasi tahap kelabu pada gambar digunakan dalam proses pengekstrakan ciri. enam (6) atribut terdiri dari kontras, varians, sisihan piawai, kurtosis, min dan kehalusan dihitung sebagai fitur yang diekstrak dan digunakan sebagai input untuk proses klasifikasi. eksperimen telah diulang selama sepuluh (10) kali untuk memeriksa kesesuaian prestasi semua teknik. 70% data digunakan sebagai data latihan dan 30% lagi digunakan sebagai data ujian. hasil setelah sepuluh (10) eksperimen menunjukkan bahawa, support vector machine (svm) memberikan hasil yang paling konsisten dalam mengklasifikasikan keadaan payudara dengan betul sebagai 'normal' atau 'kanser', dengan akurasi 99.4%, 187 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 dalam latihan dan 98.76% dalam ujian. model klasifikasi svm telah mengungguli model nn dan nb dalam kajian ini, dan ia menunjukkan bahawa svm adalah pilihan yang baik untuk menentukan keadaan payudara pada peringkat awal. keywords: machine learning; breast cancer detection; mammogram images; data mining; data-driven modelling 1. introduction breast cancer screening which is commonly made by mammography is a limited series of x-rays taken of the breast. radiologist sees for any anomalous signs or patterns on the mammogram that might be breast cancer. these signs normally show up on the mammogram before any lump may be thought at the breast. if there is anything odd on this mammogram, more tests get to be made. these tests may add another mammogram, imaging, or a biopsy. whether testing mammograms will change the probability of women dying from breast cancer has been argued for decades [1]. it is definitely not an ideal test. some cancers are failed to be detected by the mammogram. this false-positive mammogram effects lead to more experimentation, which is time-consuming and may have unnecessary apprehension. since mammographic x-ray images are 2d projections of a 3d object, localization of features identified within the breast volume is not trivial. furthermore, mammograms represent highly deformed configurations of the breast due to compression, thus the tumor localization process relies on the expertise of the clinicians. breast cancerrelated studies have long been conducted by researchers around the world. in the last few decades, various information production and machine learning techniques have been produced for breast cancer discovery and categorization, which may be separated into three important phases: preprocessing, feature extraction, and classification. to facilitate explanation and analysis, the preprocessing of mammography images helps improve the clarity of peripheral regions and level system, and various methods have been reported to help in the process. several transform-based quality analysis techniques are used to change the image into a new structure using the spatial frequency properties of the component level variations. in fact, there are many studies related to early detection is possible to show whether the state of the breast to be 'normal' or 'abnormal'. among the most common classifier used for classification and early detection of breast cancer is neural network (nn). it is a model made to imitate the function of learning that owned the human brain. as stated by [2], the neural classifier developed able to perform well by successfully classifying cancer and non-cancer (normal) images with an accuracy of 97%. however, this study did not show any comparison between the developed nn classifier and other types of the classifier. with regard to a single technique, [3] mentioned that in his mapping study, found that decision trees (dt), support vector machines (svm) and artificial neural networks (ann) were those most frequently adopted to build ensemble classifiers. therefore, in this paper on cancer detection, the focus will be on the classification part, whereby the use of three classifiers namely naive bayes (nb), neural network (nn) and support vector machines (svm), to accurately classify the mammographic images of the breast as normal or cancer will be presented. the results of this research will be useful for tracking visible tumors between images, as well as to help radiologists in their tasks to detect subtle abnormalities in a mammogram. 188 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 2. methodology this research methodology uses a data mining approach to classify data. in this case, there is an important phase that must be done to get the best research results. there are four phases involved namely sample selection, image enhancement and feature extraction, model development, and evaluation. 2.1 sample selection a total of two thousand (2000) 2d-digital mammogram images were collected from the central pertamina hospital, indonesia (1000 normal breast images and 1000 cancer images) as shown in fig. 1. these 2d-digital mammogram images were then converted to 3d-digital mammogram images for better analysis. fig. 1: some of the mammogram of normal and cancer images. 2.2 image enhancement and feature extraction in preprocessing phase, the possibility distribution algorithm [4] is used for image enhancement using logical approach fuzzy with 5 parameters, namely α, β1, γ, β2 and max as shown in fig. 2. fig. 2: possibility distribution function [4]. 189 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 from the required parameters, α represents the minimum value of the distribution, γ represents the average value of the distribution and max represents the maximum value of the distribution. the fuzzy transformation function used to get the entire value is defined as follows: α = min (1) β1 = (α + γ)/2 (2) γ = mean (3) β2 = (max + γ)/2 (4) max = max (5) the purpose of using the possibility distribution algorithm in improving image quality is to lower the level of pixel grayness that has a grayish value between β1 and β2. the way to do this is to provide a new intensity value in pixels between β1 and γ, γ and β2 with the opposite board value to the mean γ. the fuzzy rule below is used to perform image contrast enhancement based on fig. 2: rule 1: if α ≤ ui ≤ β1 then p = 2((ui − α)/(γ − α)))2 (6) rule 2: if β1 ≤ ui ≤ γ then p = 1 − 2((ui − γ)/(γ − α)))2 (7) rule 3: if γ ≤ ui ≤ β2 then p = 1 − 2((ui − γ)/(max − γ))2 (8) rule 4: if β2 ≤ ui ≤ max then p = 2((ui − γ)/(max − γ))2 (9) where ui = f(x,y) is the intensity of the i-i pixel. regulations that lower the level of pixel grayness that has a grayish value between β1 and β2 are represented by eqs. (7) and (8). the steps of possibility distribution algorithm can be explained as the following: step 1: initialize parameter data matrix set by image to be improved. from the image, the minimum, maximum and average (mean) grayish values were obtained. the value β1 is set with the result of (min + mean)/2. whereas the value of β2 is set with the result of (mean + max)/2. step 2: fuzzification for all pixels. in this step, fuzzy rules were applied (eq. 6, eq. 7, eq. 8 and eq. 9) to get a new grayish value. step-3: modification for all pixels were executed, the fuzzy value of the data obtained from the new grayish value is powered by two. step-4: defuzzification for all pixels. the new contrast data derived from fuzzy data values is calculated and multiplied by the matrix of the initial image data. in this phase, feature extraction also being done to extract the important variables to be used in the next step which is development of classification model. for feature extraction, glcm (grey level co-occurrence matrix) is being used. glcm is the two dimensions represent the level variation gray at the image. glcm is one of the popular statistical methods of extracting textural feature from images. according to [5], by extracting the features of an image by glcm approach, the image compression time can be greatly 190 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 reduced in the process of converting rgb to gray level image when compared to other discrete wavelet transform (dwt) techniques. in this study, measurement of the contrast, variance, standard deviation, kurtosis, mean, and smoothness are computed as features extracted and shall be used in the classification stage. 2.3 development of data-driven classification model in this work, matlab software is used for developing the classification model and analysis. the three (3) machine learning techniques investigated to produce a data-driven classification models, were neural network (nn), support vector machine (svm) and naïve bayes (nb). figure 3 shows an example of the ‘breast image extracted features – breast state’ modelling structure. the inputs identified for the classification model were contrast, variance, standard deviation, kurtosis, mean, and smoothness. these features were extracted using glcm methods explained in the previous section [5]. whereas the output for this classification model is the state of the breast itself, whether it is ‘normal’ or ‘cancer’. fig. 3: model structure for ‘breast image extracted features – breast state’. )(t = error between actual and predicted breast category. 2.3.1 naïve bayes (nb) the naive bayesian classifier is based on bayes theorem assuming independence among predictors. the naive bayesian model is easy to build, without the estimation of complex iterative parameters that make it very useful for very large datasets. despite its simplicity, the naive bayesian classification often works very well and is widely used because it often outperforms more sophisticated classification methods. bayes theorem provides a way of calculating the probability of posterior, p (c | x), of p (c), p (x), and p (x | c). the basis of the naïve bayes theorem used is the bayes formula as follows [6]: 𝑃(𝐶|𝑋) = 𝑃(𝑥|𝑐)𝑃(𝑐) 𝑃(𝑥) (10) 191 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 the bayes naïve classification assumes that the influence of predictor value (x) on a particular class (c) does not depend on the values of other predictors. this assumption is called class conditional independence. 2.3.2 neural network (nn) neural network is a model created to mimic the learning functions of the human brain. in the neural network, neurons are grouped into layers, called neuron layers. usually, each neuron of a layer is connected to all neurons in the back and front layers (except inputs and outputs). information sent in a nn, propagated layers – per – layers ranging from inputs to outputs without or through one or more hidden layers. depending on the algorithm used, information can also be propagated backwards (backpropagation). figure 4 shows the neural network with three neuron layers. fig. 4: algorithm for neural network. 2.3.3 support vector machine (svm) support vector machine (svm) is one of the prediction techniques, both in the case of classification and regression [7]. svm has a basic principle of linear classifier that is a classification case that can be linearly separated, but nowadays svm is also able to solve non-linear problems by adding kernel concepts to high-resolution workspaces. in this space, a hyperplane (hyperplane) will be searched to maximize the distance between data classes. svm can actually work on linearly separated data only. when the data is nonlinear then, the way that can be used is to use the kernel on the data. kernel can be interpreted as a function that remaps data in the original dimension space into more dimensional space as shown in fig. 5. fig. 5: representation for support vector machine (svm). 2.4 experimental procedure as shown in fig. 3, the features extracted from 2000 mammogram breast images were experimented with different classifiers that are neural network (nn), support vector 192 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 machine (svm) and naïve bayes (nb). the data has been randomized and the experiment has been repeated for ten (10) times to check for the consistencies of the performance of all techniques. 70% of the data were used as the training data and another 30% used as testing data. accuracy based on confusion matrix is used as the performance indicator, to show which technique can best model the classification of normal and abnormal state of the breast. 3. findings in this section, findings from three (3) different classification models nb, nn and svm) will be presented. the inputs identified for all models were the contrast, variance, standard deviation, kurtosis, mean, and smoothness based on the glcm approach applied to 2000 3d-digital breast mammogram images reported in the previous section. the outputs for all models were the breast state: ‘normal’ or ‘cancer’, which represented by ‘1’ and ‘2’ in the modelling process respectively. the extracted features with the breast states were then randomized. 70% of the data were used for training and another 30% were used as testing. the objective of this modelling is to mimic the behavior of the expert in identifying the state of the breast whether it is ‘normal’ or ‘cancer’ by training the model with the extracted features (contrast, variance, standard deviation, kurtosis, mean, and smoothness) from the 3d-digital mammogram images and the identified breast state. the following subsections report the findings on all the training and testing work conducted. 3.1 naïve bayes model training and testing results the first classification model built in this study is using the nb. the scatterplots for training and testing of nb model are shown in fig. 6(a) and (b). while the detail results for the accuracy of the model for each experiment in the training and testing are shown in table 1 and table 2. in table 1, it can be seen, that out of 1400 sample data used for training (70% of the total sample data), there are average of 964 correct predictions and average of 436 incorrect predictions for training. thus, the average accuracy for the training is about 68.83%. whereas for the testing, out of 600 sample data used for testing (30% of the total sample data), there are average of 420 correct predictions and average of 180 incorrect predictions for the whole 10 experiments. therefore, the average accuracy for the nb model testing is about 70.07%. (a) (b) fig. 6: scatterplots for (a) training of the nb model, (b) testing of the nb model. (a) (b) 193 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 table 1: nb model training results for 10 experiments. table 2: nb model testing results for 10 experiments. 3.2 neural network (nn) model training and testing results the next classification model built in this study is using the nn. figure 7(a) and (b) show the scatterplots for training and testing of nn model, while table 3 and 4 show the detail results of the nn model accuracy for each experiment in training and testing. as seen in table 3 and 4, there are average of 1237 correct predictions and average of 163 incorrect predictions for training. thus, the average accuracy for the training is about 88.38%. whereas for the testing, out of 600 sample data used for testing (30% of the total sample data), there are average of 530 correct predictions and average of 70 incorrect predictions for the whole 10 experiments. therefore, the average accuracy for the nn model testing is about 88.27%. (a) (b) fig. 7: scatterplots for (a) training of the nn model. (b) testing of the nn model. (a) (b) 194 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 table 3: nn model training results for 10 experiments. table 4: nn model testing results for 10 experiments. 3.3 support vector machine (svm) model training and testing results the final classification model developed in this study is using the svm. the scatterplots result of svm model for training and testing are shown in fig. 8 (a) and (b), while table 5 and 6 show the detail results for the accuracy of the model for each experiment during training and testing. from table 5, it was found that, the majority of the outputs were correctly predicted by the svm model, with average of 1392 correct predictions and average of only 8 incorrect predictions for training. thus, the average accuracy for the training is about 99.40%. interestingly, table 6 also shown that the svm model is able to correctly predict the output of the testing sample data with average of 593 correct predictions as against the incorrect predictions of only 7. this has made the average percentage of the testing accuracy to be 98.76%, slightly lower than its training accuracy. table 5: svm model training results for 10 experiments. 195 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 (a) (b) fig. 8: scatterplots for (a) training of the svm model, (b) testing of the svm model. table 6: svm model testing results for 10 experiments. 4. discussion in this study, the 2d-digital mammography images were first transformed into 3d-digital mammography and glcm approach is applied to these 3d-digital breast images to extract the contrast, variance, standard deviation, kurtosis, mean, and smoothness as features to be input to the models. the supervised learning technique is used to train the models that infer a function from input data with labeled breast state, 'normal' or 'cancer'. 2000 digital mammogram images of the breast have been analyzed. naive bayes, neural network, and deep learning are among the most common machine learning techniques used in cancer detection [2,8-11]. however, in this study, ten (10) experiments have been conducted using the three (3) machine learning techniques namely naïve bayes, neural network and support vector machine and the accuracy of each model in providing correct prediction for each experiment was recorded as shown in section 3. the result after ten (10) experiments show that the support vector machine (svm) gives the most consistent results in predicting or classifying correctly the state of the breast as 'normal' or 'cancer', with an average accuracy of 99.40% in training and 98.76% in testing. the svm classification model has outperformed nn and nb models in the study, and it shows that svm is a good choice for determining the state of the breast at the early stage. (a) (b) 196 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 as compared to the previously developed nn model reported by [2], the currently developed svm model outperformed their nn model. their study also not considering any other machine learning techniques but just focusing on nn model only. however, these single classifier models can be further experiment and improved. for example, as reported by [3], the majority of research have reported positive results concerning the accuracy of ensemble classifiers as compared to the single classifiers. the following research have supported the given statement [12-21]. apart from that, the performance index used can also be varied, not just focusing on the accuracy of the model but to consider other aspect like computational time for the training and testing to be done, as well as precision-recall curve to capture the exact capability of the classifiers investigated [22-25]. transfer learning has also seen as the alternative to the conventional supervised learning for breast cancer detection and classification as reported by [3]. therefore, comparison of model performance developed based on the supervised learning with transfer learning would be interesting to be explored in the near future. besides testing procedure that has been implemented in this study, validation with expert (radiologist) is seen crucial. the expert validation is time consuming, but it is important to be done in order to further validate the reliability of the developed models. 5. conclusion today, the need for machine learning is rising in the field of breast cancer research. it has been used to screen and differentiate normal breast with cancer. the process of diagnosis can be very complicated. that is why for decades, researchers have developed various machine learning algorithms and architectures that can screen and differentiate cancerous images from normal ones by training the algorithms with various features extracted from the image of the breast. in particular, breast cancer diagnosis is more important than ever because the classification results will affect the treatment and safety of the patients. it requires not only a high prediction of accuracy, but also a high reliability and robustness. in this study, ten (10) experiments have been conducted using the three (3) machine learning techniques namely naïve bayes, neural network and support vector machine, using 2000 2d-digital mammogram images that have been converted into 3d-images. the accuracy of each model in providing correct prediction based on the confusion matrix has been reported for each experiment. the svm classification model has outperformed nn and nb models in the study, and it shows that svm is a good choice for determining the state of the breast at the early stage. however, further improvements can be done to the classifier models in producing more accurate and reliable results, for example, by exploring the ensemble classifier by combining different algorithm from the same type of classifier or different type of classifier to leverage the strength of individual classifiers. as part of the future work, these models can also be extended to further classify the stage of the breast cancer (stage 0, 1, 2, 3 and 4) by using the laboratory results of the patients as well as the auto measured diameter of the detected abnormality extracted from the digital mammogram images. acknowledgement this research study is funded by universiti pendidikan sultan idris, malaysia, under the special university research grant (fundamental), 2017-0184-109-01. 197 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 references [1] rubin r. (2017) do screening mammograms cut breast cancer deaths or lead to overtreatment? probably both. forbes. retrieved from https://www.forbes.com/sites/ritarubin/2017/01/10/do-screening-mammograms-cut-breastcancer-deaths-or-lead-to-overtreatment-probably-both/ [2] mohamad samuri, suzani, megariani tv. (2019) intelligent 3d analysis for detection and classification of breast cancer. jitce (journal of information technology and computer engineering), 3(2): 96-103. https://doi.org/https://doi.org/10.25077/jitce.3.02.96-103.2019 [3] hosni m, abnane i, idri a, de gea jmc, alemán jlf. (2019) reviewing ensemble classification methods in breast cancer. computer methods and programs in biomedicine, 177: 89-112. [4] dubois d, prade, h. (2016) practical methods for constructing possibility distributions. int. j. intell. syst., 31: 215-239. https://doi.org/10.1002/int.21782 [5] mohanaiah p, sathyanarayana p, gurukumar l. (2013) image texture feature extraction using glcm approach. international journal of scientific and research publications, 3(5): 1. [6] han j, kamber m, pei j. (2012) data mining concepts and techniques (3rd ed). usa: elsevier inc. [7] brereton r, gavin l. (2010) support vector machines for classification and regression. the analyst. 135: 230-267. 10.1039/b918972f. [8] hamidinekoo a, denton e, rampun a, honnor k, zwiggelaar r. (2018) deep learning in mammography and breast histology, an overview and futuretrends, medical image analysis. doi:10.1016/j.media.2018.03.006. [9] sahiner b, pezeshk a, hadjiiski lm, wang x, drukker k, cha kh, summers rm, giger ml. (2019).deep learning in medical imaging and radiation therapy. med phys. 46(1):e1-e36. doi: 10.1002/mp.13264. epub 2018 nov 20. pmid: 30367497. [10] sechopoulos i, teuwen j, mann r. (2020) artificial intelligence for breast cancer detection in mammography and digital breast tomosynthesis: state of the art. seminars in cancer biology. https://doi.org/10.1016/j.semcancer.2020.06.002. [11] arcadu f, benmansour f, maunz a. willis j, haskova z, prunotto,m. (2019) deep learning algorithm predicts diabetic retinopathy progression in individual patients. npj digital medicine, 2(1): 1-9. [12] wang h, zheng b, yoon sw, ko hs. (2018) a support vector machine-based ensemble algorithm for breast cancer diagnosis, eur. j. oper. res., 267: 687–699. doi: 10.1016/j.ejor.2017.12.001. [13] huang, m-w, chen c-w, lin w-c, ke s-w, tsai c-f. (2017) svm and svm ensembles in breast cancer prediction, plos one 12: e0161501. doi: 10. 1371/journal.pone.0161501 [14] tsirogiannis gl, frossyniotis d, nikita ks, stafylopatis a. (2004) a meta-classifier approach for medical diagnosis, in: methods appl. artif. intell. pp 154–163. doi: 10.1007/978354024674-9_17. [15] tan ac, gilbert d. (2003) ensemble machine learning on gene expression data for cancer classification. appl. bioinform. 2 :1–10. doi: 10.1186/ 1471-2105-9-275. [16] janghel rr, shukla a, sharma s, gnaneswar av. (2014) evolutionary ensemble model for breast cancer classification. doi: 10.1007/978-3-319-11897-0_2. [17] joanna j, piotr j. (2008) gep-induced expression trees as weak classifiers using gene expression programming to induce, in: lect. notes comput. sci., pp. 129–141. [18] schaefer g, nakashima t. (2015) strategies for addressing class imbalance in ensemble classification of thermography breast cancer features, in: 2015 ieee congr. evol. comput. cec 2015 –proc, pp. 2362–2367. doi: 10.1109/cec. 2015.7257177. [19] lederman d, wang xw, zheng b, sumkin jh, tublin m, gur d. (2011) fusion of classifiers for reis-based detection of suspicious breast lesions, in: med. imaging 2011 image perception, obs. performance, technol. assess., pp. 1–9. doi:79661c \ n10.1117/12.877368. 198 iium engineering journal, vol. 23, no. 1, 2022 mohammad samuri et al. https://doi.org/10.31436/iiumej.v23i1.1825 [20] nguyen tt, liew awc, tran mt, pham xc, nguyen mp. (2014) a novel genetic algorithm approach for simultaneous feature and classifier selection in multi classifier system, in: proc. ieee congr. evol. comput. cec 2014, pp. 1698–1705. doi: 10.1109/cec.2014.6900377. [21] ghorai s, mukherjee a, sengupta s, dutta pk. (2011) cancer classification from gene expression data by nppc ensemble, ieee/acm trans. comput. biol. bioinform. 659–671, doi: 10.1109/tcbb.2010.36. [22] ferri c, hernández-orallo j, modroiu r. (2009) an experimental comparison of performance measures for classification, pattern recognit. lett., 30: 27–38. doi: 10.1016/j.patrec.2008.08.010. [23] davis j, goadrich m. (2006) the relationship between precision-recall and roc curves, in: proc. 23rd int. conf. mach. learn. [24] zaidan aa, ahmad nn, abdul karim h, larbani m, zaidan bb, sali a. (2014) on the multiagent learning neural and bayesian methods in skin detector and pornography classifier: an automated anti-pornography system. neurocomputing, 131: 397-418. https://doi.org/10.1016/j.neucom.2013.10.003. [25] alamoodi, a. h.; garfan, salem; zaidan, b. b.; zaidan, a. a.; shuwandy, moceheb lazam; alaa, mussab; alsalem, m. a.; mohammed, ali; aleesa, a. m.; albahri, o. s.; al-hussein, ward ahmed; alobaidi, o. r. (2020). a systematic review into the assessment of medical apps: motivations, challenges, recommendations, and methodological aspect. health and technology, (), doi:10.1007/s12553-020-00451-4 199 https://doi.org/10.1016/j.neucom.2013.10.003 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 modelling a 1-dof finger extensor machine for hand rehabilitation ifrah shahdad, norsinnira zainul abidin* and ahmad jazlan department of mechatronics engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia * corresponding author: sinnira@iium.edu.my (received: 24th november 2020; accepted: 22nd december 2020; published on-line: 4th july 2021) abstract: it is essential to have an accurate representation of a robotic rehabilitation device in the form of a system model in order to design a robust controller for it. this paper presents mathematical modelling and validation through simulation and experimentation of the 1-dof finger extensor rehabilitation machine. the machine’s design is based on an iris mechanism, built specifically for training open and close movements of the hand. the goal of this research is to provide an accurate model for the finger extensor by taking into consideration various factors affecting its dynamics and to present an experimental validation of the devised model. dynamic system modelling of the machine is performed using lagrangian formulation and the involved physical parameters are obtained experimentally. to validate the developed model and demonstrate its effectiveness, hardware-in-the-loop experiments are conducted in the simulink-matlab environment. mean absolute error between the simulated and experimental response is 1.38° and the relative error is 1.13%. the results obtained are found to be within the human motion resolution limits of 5 mm or 5º and exhibit suitability of the model for application in robotic rehabilitation systems. the model accurately replicates the actual behavior of the machine and is suitable for use in controller design. abstrak: gambaran tepat mengenai model sistem peranti rehabilitasi robotik adalah sangat penting bagi pembangunan sesebuah reka bentuk alat kawalan tahan lasak. kajian mengenai model matematik dan pengesahan melalui simulasi dan eksperimentasi mesin pemulihan 1-dof ‘finger extensor’. mesin ini direka bentuk berdasarkan mekanisme iris, dibangunkan khusus bagi melatih gerakan buka dan tutup tangan. tujuan kajian ini adalah bagi menyediakan model finger extensor yang tepat dengan mengambil kira faktor mempengaruhi dinamik dan pengesahan model eksperimen yang dirancang. model sistem dinamik mesin ini diuji menggunakan formula lagrangian dan parameter fizikal yang terlibat diperoleh melalui eksperimen. model ini disahkan dan diuji keberkesanannya menggunakan eksperimen perkakasan-dalam-gelung melalui matlab-simulink. purata ralat mutlak antara dapatan simulasi dan respon eksperimen adalah 1.38° dan ralat relatif 1.13%. dapatan kajian adalah dalam had resolusi gerakan tangan manusia iaitu 5 mm atau 5º dan didapati model ini sesuai bagi aplikasi sistem rehabilitasi robotik. model ini tepat dalam mereplikasi kelakuan sebenar mesin dan sesuai digunakan bagi reka bentuk kawalan. keywords: modelling; simulation; experimental validation; hand rehabilitation; hardware-in-the-loop 384 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 1. introduction every year, up to 15 million people suffer from stroke, making it one of the leading causes of severe disability in the world [1]. after a neurological injury such as stroke, patients suffer from several impairments, of which the most common and impeding is the impairment to the hand sensorimotor function. the finger extensor muscles develop weakness during voluntary movements as a result of activity deficit. this leads to spasticity which is a velocity-dependent increase in muscle tone. spasticity causes intense muscle contractions and stiffness that manifest in the form of a clenched fist, tensed fingers, a curled wrist and other deformities. these impairments lead to a decreased ability to open and close the hand, control individual finger movements and perform force coordination, thereby severely affecting the quality of life of stroke patients [2]. patients undergo intense physical therapy under the guidance of an occupational therapist to regain functionality in the affected limb. activity-based exercises are known to be effective in helping overcome the motor deficits induced by post-stroke spasticity [3]. however, occupational therapy is expensive and as a result, a vast majority of the patients do not have continuous access to it. besides, conventional therapy is monotonous, repetitive and difficult to be sustained for prolonged periods of time, leading to high dropout rates. furthermore, with conventional therapy, it is not possible to measure the exact progress of patients over time and provide them with well-regulated and a wide range of rehabilitative forces. due to these factors, robot-assisted rehabilitation has seen a growing interest in the last few decades. robotic devices, due to their features of high repeatability, interactivity, ability to provide a wide range of accurate forces and automatic measurement of patient progress, are becoming increasingly popular. the interactive nature of robotaided therapy not only increases physical engagement but also encourages cognitive engagement of the patient through immersive and challenging exercises. patient engagement in rehabilitation is vital because encouraging human users to perform selfinitiated movements is an essential requirement to achieve motor learning and neuroplasticity [4]. furthermore, robot-aided rehabilitation is capable of producing assistive as well as resistive forces that can be tailored to the specific impairment of the patient. when patients gain some amount of motor function in the impaired part, they are subjected to activeresistive therapy whereby, forces are applied on the patient in a direction opposite to the one they are tracing. resistive strategies enhance patient performance as they require additional effort from the patient to resist opposite forces. such efforts induce neuroplasticity and help in development of neural pathways from the impaired muscles to the brain which aids in regaining of motor function [5]. however, all these features of robotic rehabilitation devices are possible only when efficient controllers are developed [6]. a variety of control strategies have been proposed for rehabilitation robots over the past few decades. these control schemes are designed around the central idea of modulating assistance/resistance provided to the patient based on various factors such as force exerted by the patient, limb velocity, tracking error, interaction force/torque, eeg/emg activity [7]. in recent literature, approaches such as force/stiffness control [8] assist-as-needed control (aan) [9-11] and performance-based impedance control [7,12,13] have been implemented on rehabilitation robots. aan control aims at providing minimal intervention in patient recovery. performance-based impedance control modulates the assistance provided, based on real-time measurements of the patient's biomechanical characteristics. 385 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 before the implementation of these control strategies, dynamic and kinematic modelling of the rehabilitation machine is necessary. modelling is the mathematical representation of a physical system [14]. a system model is developed from mathematical equations and then represented graphically in software such as matlab, simulink and stateflow, etc. the developed model is then validated through simulations, reducing the cost associated with experimental validation. during the process of model development, trade-offs have to be made between the fidelity and simplicity of the model. fidelity implies the extent to which the system model mimics the behavior of the real system and simplicity ensures that the model remains simple enough for smooth controller development in later stages. thus, there are some deviations between the behavior of the actual system and its model. after balancing simplicity and fidelity, the model is validated using a hardware-in-the-loop (hil) approach. in this approach, one or more real subsystems interact in a closed loop with the virtual subsystems of the model. a comparison between the response of such a closed-loop interaction with the simulation output reveals performance of the developed model [15]. in [16], dynamic and kinematic modelling of the multipurpose rehabilitation robot, the universal haptic pantograph, was performed. validation of the model was carried out through experiments with healthy subjects reflecting its performance. dynamic modelling and experimental validation of a parallel robot for upper limb rehabilitation was presented in [17]. approximately zero steady-state errors points to a high degree of accuracy and suitability of the developed model. dynamic modelling of a haptic finger actuated by a mckibben artificial muscle built for tele-operated rehabilitation was performed in [18]. upon experimental validation, the model demonstrated a satisfactory performance. in this work, mathematical modelling and system simulation of a 1 degree-of-freedom (dof) finger extensor rehabilitation machine was performed. a model-based development (mbd) [15] approach to controller design was taken. such an approach to design enabled verification and validation at each stage. based on simulation results, modifications to the system could be made easily without incurring high costs. as a first step, mathematical modelling was done, followed by simulation of the system behavior. simulation results were then compared to hardware measurements which demonstrated the accuracy of the realized model. hardware-in-the-loop testing of the model carried out in this study ensures minimization of risks and costs associated with experimental validation. the developed model aids in the design and implementation of a control algorithm for the finger extensor machine. 2. the finger extensor machine the finger extensor rehabilitation machine is a 1-dof device with an iris mechanism lying at the heart of its dynamics. the design of the iris or diaphragm is inspired by the constriction and dilation of the iris of the human eye, which varies size of the pupil, adjusting the aperture of the eye. the iris mechanism built into the finger extensor constricts and dilates the poles at the top of its surface, to allow openings of variable sizes. these poles, as shown in fig. 1 and fig. 2 are grasped by the patient during therapy and enable him/her to practice finger flexion and extension [19]. there are six poles in the current finger extensor design and each pole has a blade associated with it. on the upper end, each blade is connected to a slider and at the bottom, each blade goes into a slot in a disc using a bearing, as illustrated in fig. 2. the disc with slots is in turn connected to the motor actuation system through a chain and sprocket mechanism. as the motor turns, the sprocket induces motion into the slotted disc. this 386 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 causes the blades to slide and move the poles in their own respective slots at the top of the machine. fig. 1: 1-dof finger extensor machine. fig. 2: cad drawing of the side view of the iris mechanism. fig. 3: inner view of the machine. figure 3 shows the actuation system of the machine comprising of a brushed planetary geared dc motor (gear ratio32.5:1). rotation of the motor is recorded by a rotary encoder by esb electronics, japan (counts per revolution500) connected to the sprocket using a flexible shaft coupling. a torque sensor, connected close to the chain-sprocket mechanism provides the torque applied by the machine on to the patient. actuation system and sensors are controlled by arduino microcontroller board which is programmed in the simulink environment. 387 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 3. system modelling 3.1 mechanical model newton-euler and the lagrange-euler methods are the most commonly used approaches for deriving dynamic equations of mechanical parts of robots [20]. the former is ideal for on-line control applications due to reduced computational time. however, it falls short in providing an adequate insight into control design due to recursive computation. the lagrange-euler method is simple and systematic, providing dynamic equations in a matrix form and was chosen for deriving the mechanical model for the finger extensor. dynamic equation describing motion of the finger extensor was written as 𝑀(𝜃(𝑡), 𝜉)�̈�(𝑡) + 𝐷(𝜃(𝑡), �̇�(𝑡), 𝜉) + 𝐺(𝜃(𝑡), 𝜉) = 𝑇(𝑡) (1) where, 𝑀(θ(𝑡), ξ) is the n x n inertia matrix. 𝐷(𝜃(𝑡), �̇�(𝑡), 𝜉) is the n x 1 vector of coriolis and centrifugal forces. 𝐺(𝜃(𝑡), 𝜉) is the n x 1 vector of gravitational forces. 𝑇(𝑡) is the n x 1 vector of torques applied by the actuators. 𝜃(𝑡), �̇�(𝑡), �̈�(𝑡) are the n x 1 vectors of joint displacements, velocities and accelerations respectively. 𝜉 is a vector (with appropriate dimension) of parameters of the mechanism such as payload. for the finger extensor, 𝑀(𝜃(𝑡), 𝜉) is a 1x1 matrix, with one element equal to the moment of inertia of a solid cylinder with iris radius of 0.055m. 𝐷(𝜃(𝑡), �̇�(𝑡), 𝜉) and 𝐺(θ(𝑡), ξ) for a 1-dof machine were null matrices. 𝑇(𝑡) for the finger extensor is calculated in the subsequent sections. for developing the mechanical model of the finger extensor, the next step was to derive equations of motion of the moving parts of the mechanism. these were represented by flywheel and spring mechanical elements as shown in fig. 4. 𝐽1, 𝐽2 represent inertia elements of the motor and iris mechanisms respectively, 𝑘1, 𝑏1 represent the spring stiffness effect and viscous and coulomb friction. fig. 4: block diagram representation. forces acting on the motor and iris sprockets are shown in fig. 5, where 𝜃1 is the angle of rotation of the motor sprocket, 𝜃2 is the angle of rotation of the iris mechanism, 𝑇𝑔 is the torque on the driver sprocket, 𝑇𝑒 is the torque exerted by the user, 𝑓𝑐 𝑟1 and 𝑓𝑐 𝑟2 388 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 are the contact force torques. figures 4 and 5, hence represent eq. (1) in terms of sum of forces (inertial, gravitational, frictional) acting on the machine. as per d’alembert’s law, sum of torques on both flywheels was given by the equations 𝑇𝑔 = 𝐽1𝜃1̈ + 𝑘1𝜃1 + 𝑏1(𝜃1̇ − 𝜃2̇) − 𝑓𝑐 𝑟1 (2) −𝑓𝑐 𝑟2 − 𝐽2𝜃2̈ − 𝑏1(𝜃2̇ − 𝜃1̇) − 𝑇𝑒 = 0 (3) from eq. (3), value of 𝑓𝑐 is calculated as 𝑓𝑐 = 1 𝑟2 [−𝐽2𝜃2̈ − 𝑏1(𝜃2̇ − 𝜃1̇) − 𝑇𝑒 ] (4) fig. 5: forces acting on mechanism. substituting value of 𝑓𝑐 in eq. (2) 𝑇𝑔 = 𝑘1𝜃1 + 𝑏1(𝜃1̇ − 𝜃2̇) − 𝑟1 𝑟2 [−𝐽2𝜃2̈ − 𝑏1(𝜃2̇ − 𝜃1̇) − 𝑇𝑒 ] (5) using the inverse gear ratio, 𝑟2 𝑟1 = n and the equality of arc lengths, 𝑟1𝜃1 = 𝑟2𝜃2, it follows that 𝜃1 = 𝑟2 𝑟1 𝜃2 = 𝑁𝜃2. substituting in eq. (5), 𝑇𝑔 = 1 𝑁 𝐽2𝜃2̈ + 1 𝑁 𝑇𝑒 + 𝑁𝑘1𝜃2 + 𝑉𝑐 (𝜃2̇) + 𝐹𝑐 𝑆𝑔𝑛(𝜃2̇) (6) where, 𝑉𝑐 (𝜃2̇) and 𝐹𝑐 𝑆𝑔𝑛(𝜃2̇) are the viscous and coulomb friction terms. therefore, dynamic equation of the 1-dof finger extensor was represented as 𝑇𝑔(𝑡) = 1 𝑁 𝐽2(𝜃2)𝜃2̈(𝑡) + 1 𝑁 𝑇𝑒 (𝑡) + 𝑁𝑘1𝜃2(𝑡) + 𝑉𝑐 (𝜃2̇)(𝑡) + 𝐹𝑐 𝑆𝑔𝑛(𝜃2̇) (7) 3.2 actuator model the finger extensor is powered by a planetary-geared, 24 v brushed dc motor. a schematic of the motor is shown in fig. 6. using kirchhoff's voltage law and newton's law of motion, dynamic equations of the actuator were written as 𝐽𝑚𝜃�̈�(𝑡) = −𝐵𝑣 𝜃�̇�(𝑡) + 𝑘𝑡 𝑖𝑎(𝑡) − 𝑇𝐿 (𝑡) (8) 𝐿𝑖𝑎(𝑡) = −𝑘𝑣 𝜃�̇� (𝑡) − 𝑅𝑖𝑎(𝑡) + 𝑉(𝑡) (9) where, 𝐽𝑚 is the moment of inertia of the motor (kg. m 2) 389 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 𝜃𝑚(𝑡) is the angular displacement of the motor (rad) 𝐵𝑣 is the viscous friction coefficient (nm/rad/s) 𝑘𝑡, 𝑘𝑣 are the torque and back emf constants (nm/a, v/rad/s) l, r are the armature inductance and resistance (h, ω) 𝑖𝑎(𝑡) is the armature current for the motor (a) 𝑇𝐿 (𝑡) is the load torque for the motor (nm) 𝑉(𝑡) is the voltage input (v) fig. 6: motor schematic. utilizing the relationship between loading torque 𝑇(𝑡) (from the motor) and load torque 𝑇𝐿 (𝑡) (on the motor shaft) and the relationship between the motor's angular position and the machine's angular position, we formulated 𝑇𝐿 (𝑡) = 𝑇(𝑡) 𝑁 , 𝑁 ≥ 1 (10) 𝜃𝑚(𝑡) = 𝑁𝜃(𝑡) (11) where n is the inverse gear ratio. substituting eq. (10) and eq. (11) in eq. (8) and eq. (9), the otherwise linear, timeinvariant actuator dynamic was converted into a non-linear time-variant one. the actuator model in the form of a third-order differential equation was represented as: 𝜃2⃛(𝑡) + { 𝐵𝑣𝐿+𝐽𝑚𝑅 𝐽𝑚𝐿 } 𝜃2̈(𝑡) + { 𝑘𝑣𝑘𝑡+𝐵𝑣𝑅 𝐽𝑚𝐿 } 𝜃2̇(𝑡) + { 𝑅 𝑁2𝐽𝑚𝐿 } 𝑇𝑔(𝑡) + { 1 𝑁2𝐽𝑚 } �̇�𝑔 = { 𝑘𝑡 𝑁𝐽𝑚𝐿 } 𝑉(𝑡) (12) to represent the actuator dynamic model in the state variable form, 𝜃, �̇�, �̈� were chosen as state variables and the state vector for the actuator was given by 𝑋𝐵 (𝑡) = [𝜃(𝑡) �̇�(𝑡) �̈�(𝑡)] 𝑇 (13) the state equation was formulated as 𝑋�̇� (𝑡) = 𝐴𝐵 𝑋𝐵 (𝑡) + 𝐵𝐵 𝑈(𝑡) + 𝐹𝐵 𝑇𝑔(𝑡) + 𝑄𝐵 �̇�𝑒 (𝑡) (14) where 𝐴𝐵 (𝑋𝐵 , 𝑡) = [ 0 0 1 0 1 0 0 𝑎32 𝑎33 ] , 𝐵𝐵 (𝑋𝐵 , 𝑡) = [ 0 0 𝑏31 ] , 𝐹𝐵 (𝑋𝐵 , 𝑡) = [ 0 0 𝑓31 ] , 𝑄𝐵 (𝑋𝐵 , 𝑡) = [ 0 0 𝑞31 ] 390 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 here, 𝐴𝐵, 𝐵𝐵, 𝐹𝐵, 𝑄𝐵 are the system, input, load distribution and rate of load distribution respectively. 𝑈(𝑡), 𝑇𝑔(𝑡), 𝑇𝑒 (𝑡) are the input vector, mechanical link torque and toque exerted by the patient. the values of elements 𝑎32 , 𝑎33 , 𝑏31 , 𝑓31 , and 𝑞31 are 𝑎32 = { −𝑘𝑣 𝑘𝑡 + 𝐵𝑣 𝑅 𝐽𝑚𝐿 } ; 𝑎33 = { −𝐵𝑣𝐿 + 𝐽𝑚𝑅 𝐽𝑚𝐿 } ; 𝑏31 = { 𝑘𝑡 𝑁𝐽𝑚 𝐿 } ; 𝑓31 = − { 𝑅 𝑁2𝐽𝑚𝐿 } ; 𝑞 31 = − { 1 𝑁2𝐽𝑚 } 3.3 integrated model for developing the integrated model of the machine, a time derivative of the dynamic equation of the machine was found. differentiating eq. (7) gave �̇�𝑔(𝑡) = { 𝐽2(𝜃2) 𝑁 } 𝜃2⃛(𝑡) + { �̇�𝑒(𝑡) 𝑁 } + 𝑁𝑘𝜃2̇(𝑡) + 𝐹𝑐 {2𝛿(𝜃2̇)𝜃2̈} + 𝑉𝑐 𝜃2̈(𝑡) (15) substituting eq. (15) in eq. (12), 𝜃2⃛(𝑡) { 𝐽𝑚 𝑁 3 + 𝐽2(𝜃2) 𝐽𝑚 𝑁 3 } + 𝜃2̈(𝑡) { 𝑁2(𝐵𝑣 𝐿 + 𝐽𝑚 𝑅) + 2𝐹𝑐 𝐿𝛿(𝜃2̇) + 𝑉𝑐 𝐿 𝐽𝑚 𝑁 2𝐿 } + 𝜃2̇(𝑡) { 𝑁(𝑘𝑣 𝑘𝑡 + 𝐵𝑣 𝑅) + 𝐿𝑘1 𝐽𝑚 𝑁𝐿 } + 𝑇𝑔(𝑡) { 𝑅 𝑁2𝐽𝑚 𝐿 } + �̇�𝑒 (𝑡) { 1 𝑁3𝐽𝑚 } = { 𝑘𝑡 𝑁𝐽𝑚 𝐿 } 𝑉(𝑡) (16) equation (16) was solved for 𝜃 and put in state-space form, the integrated model of the finger extensor was obtained as �̇�𝐵 (𝑡) = 𝐴𝐵 (𝑋𝐵 , 𝑡)𝑋𝐵 (𝑡) + 𝐵𝐵 (𝑋𝐵 , 𝑡)𝑈(𝑡) + 𝐹𝐵 𝑇𝑔(𝑡) + 𝑄𝐵 �̇�𝑒 (𝑡) (17) where 𝑋𝐵 = [𝜃2 𝜃2̇ 𝜃2̈] 𝑇 𝐴𝐵, 𝐵𝐵, 𝐹𝐵, 𝑄𝐵 are the system, input, load distribution and rate of load distribution respectively. 𝑈(𝑡), 𝑇𝑔(𝑡), 𝑇𝑒 (𝑡) are the input vector, mechanical link torque and toque exerted by the patient. 𝐴𝐵 (𝑋𝐵 , 𝑡) = [ 0 0 1 0 1 0 0 𝑎32 𝑎33 ] , 𝐵𝐵 (𝑋𝐵 , 𝑡) = [ 0 0 𝑏31 ] , 𝐹𝐵 (𝑋𝐵 , 𝑡) = [ 0 0 𝑓31 ] , 𝑄𝐵 (𝑋𝐵 , 𝑡) = [ 0 0 𝑞31 ] equation (17) was put in the state-space form and solved for �̇�𝐵. 𝑎32 = − { 𝑁2(𝑁𝑘𝑣 𝑘𝑡 + 𝑁𝐵𝑣 𝑅 + 𝐿𝑘1) 𝐿(𝐽𝑚 𝑁 3 + 𝐽2(𝜃2)) } , 𝑎33 = − { 𝑁(𝑁2𝐵𝑣 𝐿 + 𝑁 2𝐽𝑚 𝑅 + 2𝐹𝑐 𝐿𝛿(𝜃2 ˙ ) + 𝑉𝑐 𝐿 𝐿(𝐽𝑚 𝑁 3 + 𝐽2(𝜃2)) } 𝑏31 = { 𝑘𝑡 𝑁 2 𝐿(𝐽𝑚 𝑁 3 + 𝐽2(𝜃2)) } , 𝑓31 = − { 𝑅𝑁 𝐿(𝐽𝑚 𝑁 3 + 𝐽2(𝜃2)) } , 𝑞31 = − { 1 (𝐽𝑚 𝑁 3 + 𝐽2(𝜃2)) } the state-space model derived in eq. (17) represents the integrated dynamics of the finger extensor and was utilized in the simulation of the developed system. 3.4 mechanical and electrical parameter determination the development of the integrated model for the finger extensor was followed by determination of mechanical and electrical parameters involved. this step aids in enhancing the fidelity of the developed model. mechanical parameters such as radius of 391 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 the iris and moment of inertia of the inner mechanism were adapted from [20]. electrical parameters associated with the actuator model were experimentally found from the motor characteristic curve as shown in fig. 7. torque and back emf constants 𝑘𝑡, 𝑘𝑣 were found from the torque-current and torque-speed curves with similar values of 0.791 and 0.886, respectively. other parameters such as the viscous friction constant 𝐵𝑣, armature resistance r and inductance l were adapted from [20]. fig. 7: motor characteristic curves. 4. model validation using the mbd approach for designing a controller for the finger extensor, dynamic system modelling was followed by graphical representation of the mathematical formulation in the matlab-simulink environment. simulation results were validated through hardware-in-the-loop experimentation. the same input was provided to both the developed model as well as the machine and comparisons were drawn between resultant outputs. 4.1 simulation for carrying out simulation of the mathematical model of the finger extensor, the voltage and torques from the motor and user acted as inputs to the finger extensor plant while the angle of rotation of the iris was the output. a pid controller was used for optimal position control. rotational position output and its derivatives were used to calculate velocity and acceleration. these values helped in calculating the force acting on the patient. a desired angle of 𝜃 = 121° (2.11 radians) was fed into the plant and the simulated position of the iris was plotted as shown in fig. 8. fig. 8: comparison between target and simulated angular position of the iris. 392 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 4.2 hardware-in-the-loop experiments to validate the developed dynamic model and demonstrate its effectiveness, experiments were conducted making the finger extensor a part of the simulation loop. these experiments were conducted with a healthy subject, a female of 29 years of age. a simple open-close movement of the machine was performed. results from the simulations run in matlab were compared with the experimental tests with the finger extensor. the experimental set-up as shown in fig. 9 consisted of the finger extensor connected to an intel core i5 pc by means of an arduino uno microprocessor board. this board received sensory data from the encoder as well as the torque sensor. communication between the arduino and matlab 2018b software, running on the pc was established using a matlab s-function. this function read data from the encoder i.e. the position sensor of the machine and converted the encoder counts to angular displacement of the iris. fig. 9: experimental setup for hardware-in-the-loop simulation. the movement commands to the motor and consequently to the encoder were provided using simulink's support package for arduino which allowed simulink blocks to control hardware connected to the arduino using pwm signals. in this case, hardware controlled was the motor driver connected to the motor. the desired input angle was fed into the hardware and the finger extensor was run for about 30 seconds, performing openclose movements. the comparison between the simulated and the experimental angular displacement of the machine is shown in fig. 10. fig. 10: simulated and experimental responses during open-close movements. 393 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 the figure shows a complete open and close cycle of the finger extensor for 30 seconds. the poles of the extensor open to their maximum rotation angle of 121° followed by closing motion to 7.89°. from the figure, it is clear that the hardware had a slower response than the simulation and took about 11.20 seconds to sync with the simulation results. however, beyond that time, error was negligible and actual behavior of the finger extensor overlapped with the simulated, modeled behavior. from experimental data, it was observed that the mean absolute error was 1.38° and the relative error was 1.13%. however, for rehabilitation applications, movement accuracy is less critical as compared to surgical applications. also, position resolution of human arm movement is 5 mm or 5º [21], which indicates that a mean absolute error of 1.38° is likely to be acceptable for rehabilitation purposes. figure 11 shows the comparison between the simulated result and the hardware-inthe-loop response, when the finger extensor was programmed to open to an angle of 59.58° (1.04 radians). simulation and experimental curves took 0.3 seconds to reach the desired angle. the root mean squared error (rmse) was calculated as 0.9875. there was a slight overshoot of 2.86º (0.05 radians) which caused the poles of the finger extensor to open to an angle 2.86º greater than the target. however, this negligible overshoot did not inflict any discomfort on the subject. also, the response settled down to its desired value within 0.08 seconds. fig. 11: simulated and experimental responses for target angle experiment. 5. conclusion this paper presented a mathematical model for the 1-dof finger extensor rehabilitation machine, taking into consideration the dynamics of the mechanism as well as that of the actuation system. simulation results show that the developed model tracks the desired position efficiently with minimal error. hardware-in-the-loop experiments carried out with the machine demonstrate the validity of the model. system response using the developed model was compared with that obtained through hardware experimentation. the results illustrate the accuracy of the model to the actual behavior of the rehabilitation system and make it suitable for use in the design of a control scheme for it. obtained results with mean absolute error of only 1.38° are within the human motion resolution limits and exhibit suitability of the model for application in robotic rehabilitation systems. future research with the finger extensor and the developed model will be directed towards development of a control scheme for the machine. this will be aimed at modulating assistance/resistance provided to the patient based on his/her performance using various metrics such as limb velocity, applied force, position error etc. considering patient's strength and residual ability, primary goal of the controller would be to increase 394 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 self-initiated movements and patient engagement in training exercises which would lead to an increase in neuroplasticity. as part of future study, clinical testing of the finger extensor will also be carried out with stroke patients. this will include a detailed study of the level of comfort of the device for use with such patients. acknowledgements the authors would like to acknowledge international islamic university malaysia (iium) for supporting this research under the grant number: p-rigs18-019-0019. references [1] khor kx, chin pjh, rahman ha, yeong cf, su elm, narayanan alt. (2014) a novel haptic interface and control algorithm for robotic rehabilitation of stoke patients. in 2014 ieee haptics symposium (haptics), houston, texas-usa; pp. 421-426. [2] plantin j, pennati gv, roca p, baron jc, laurencikas e, weber k, godbolt ak, borg j, lindberg pg. (2019) quantitative assessment of hand spasticity after stroke: imaging correlates and impact on motor recovery. frontiers in neurology, 10:1-11. [3] cramer sc. (2019) intense rehabilitation therapy produces very large gains in chronic stroke. journal of neurology, neurosurgery & psychiatry, 90: 497. [4] lambercy o, ranzani r, gassert r. (2018) robot-assisted rehabilitation of hand function. in rehabilitation robotics. volume 1. 1st edition. academic press; pp 205–225. [5] popovic mb. (2019) biomechatronics. academic press. [6] miao q, zhang m, cao j, xie sq. (2018) reviewing high-level control techniques on robotassisted upper-limb rehabilitation. advanced robotics, 32(24): 1253-1268. [7] marini f, hughes cm, squeri v, doglio l, moretti p, morasso p, masia l. (2017) robotic wrist training after stroke: adaptive modulation of assistance in pediatric rehabilitation. robotics and autonomous systems, 91: 169-178. [8] su yy, yu yl, lin ch, lan cc. (2019) a compact wrist rehabilitation robot with accurate force/stiffness control and misalignment adaptation. international journal of intelligent robotics and applications, 3(1): 45-58. [9] luo l, peng l, wang c, hou zg. (2019) a greedy assist-as-needed controller for upper limb rehabilitation. ieee transactions on neural networks and learning systems, 30(11): 3433-3443 [10] pehlivan au, losey dp, o’malley mk. (2015) minimal assist-as needed controller for upper limb robotic rehabilitation. ieee transactions on robotics; 32(1): 113-124. [11] pehlivan au, losey dp, rose cg, o'malley mk. (2017) maintaining subject engagement during robotic rehabilitation with a minimal assist-as-needed (maan) controller. in 2017 international conference on rehabilitation robotics (icorr): 2017; london; pp. 62–67. [12] fricke ss, bayon c, rocon e, van der kooij h, van asseldonk eh. (2018) pilot study of a performance based adaptive assistance controller for stroke survivors. in international conference on neuro rehabilitation. springer, pp. 302–306. [13] stroppa f, loconsole c, marcheschi s, mastronicola n, frisoli a. (2018) an improved adaptive robotic assistance methodology for upper-limb rehabilitation. in international conference on human haptic sensing and touch enabled computer applications. springer; pp. 513–525. [14] bringmann e, krämer a. (2008). model-based testing of automotive systems. in 1st international conference on software testing, verification, and validation. ieee; pp. 485-493. [15] soltani a, assadian f. (2016) a hardware-in-the-loop facility for integrated vehicle dynamics control system design and validation. ifac-papers online, 49(21): 32-38. [16] mancisidor a, zubizarreta a, cabanes i, bengoa p, brull a, jung jh. (2019) inclusive and seamless control framework for safe robot-mediated therapy for upper limbs rehabilitation. mechatronics, 58: 70-79. [17] guang h, ji l, shi y, misgeld bj. (2018) dynamic modeling and interactive performance 395 iium engineering journal, vol. 22, no. 2, 2021 shahdad et al. https://doi.org/10.31436/iiumej.v22i2.1706 of parm: a parallel upper-limb rehabilitation robot using impedance control for patients after stroke. journal of healthcare engineering, 2018: 1-11. [18] franco w, maffiodo d, de benedictis c, ferraresi c. (2018) dynamic modeling and experimental validation of a haptic finger based on a mckibben muscle. in iftomm symposium on mechanism design for robotics. springer; pp. 251–259. [19] ali maa, azlan nz. (2006) design of iris mechanism for flexion and extension training in hand rehabilitation. arpn journal of engineering and applied sciences; 11: 4115-4122. [20] osman jhs. (1992) integrated model of industrial robot for control applications. jurnal teknologi, 19(1): 27-41. [21] germanotta m, vasco g, petrarca m, rossi s, carniel s, bertini e, cappa p, castelli e. (2015) robotic and clinical evaluation of upper limb motor performance in patients with friedreich’s ataxia: an observational study. journal of neuroengineering and rehabilitation, 12(1): 1-3. . 396 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 color image retrieval based on fuzzy neural networks and swarm intelligence baydaa ibraheem khaleel computer science department, college of computer science & mathematics, university of mosul, mosul, iraq *corresponding author: baydaaibraheem@uomosul.edu.iq (received: 21st january 2021; accepted: 23rd february 2021; published on-line: 4thjanuary 2022) abstract:image retrieval is an important system for retrieving similar images by searching and browsing in a large database. the image retrieval system can be a reliable tool for people to optimize the use of image accumulation, and finding efficient methods to retrieve images is very important. recent decades have marked increased research interest in field image retrieval. to retrieve the images, an important set of features is used. in this work, a combination of methods was used to examine all the images and detect images in a database according to a query image. linear discriminant analysis (lda) was used for feature extraction of the images into the dataset. the images in the database were processed by extracting their important and robust features and storing them in the feature store. likewise, the strong features were extracted for specific query images. by using some meta heuristic algorithms such as cuckoo search (cs), ant colony optimization (aco), and using an artificial neural network such as single-layer perceptron neural network (pnn), similarity was evaluated. it also proposed a new two method by hybridized pnn and cs with fuzzy logic to produce a new method called fuzzy single layer perceptron neural network (fpnn), and fuzzy cuckoo search to examine the similarity between features for query images and features for images in the database. the efficiency of the system methods was evaluated by calculating the precision recall value of the results. the proposed method of fcs outperformed other methods such as pnn, aco, cs, and fpnn in terms of precision and image recall. abstrak: imej dapatan semula adalah sistem penting bagi mendapatkan imej serupa melalui carian imej dan melayari pangkalan besar data. sistem dapatan semula imej ini boleh dijadikan alat boleh percaya untuk orang mengoptimum penggunaan pengumpulan imej, dan kaedah pencarian yang berkesan bagi mendapatkan imej adalah sangat penting. beberapa dekad yang lalu telah menunjukan banyak penyelidikan dalam bidang imej dapatan semula. bagi mendapatkan imej-imej ini, ciri-ciri set penting telah digunakan. kajian ini menggunakan beberapa kaedah bagi memeriksa semua imej dan mengesan imej dalam pangkalan data berdasarkan imej carian. kami menggunakan analisis diskriminan linear (lda) bagi mengekstrak ciri imej ke dalam set data. imej-imej dalam pangkalan data diproses dengan mengekstrak ciri-ciri penting dan berkesan daripadanya dan menyimpannya dalam simpanan ciri. begitu juga, ciri-ciri penting ini diekstrak bagi imej carian tertentu. persamaan dinilai melalui beberapa algoritma meta heuristik seperti carian cuckoo (cs), pengoptimuman koloni semut (aco), dan menggunakan lapisan tunggal rangkaian neural buatan seperti rangkaian neural perseptron (pnn). dua cadangan baru dengan kombinasi hibrid pnn dan cs bersama logik kabur bagi menghasilkan kaedah baru yang disebut lapisan tunggal kabur rangkaian neural perceptron (fpnn), dan carian cuckoo kabur bagi mengkaji persamaan antara ciri carian imej dan imej pangkalan data. nilai kecekapan kaedah sistem dinilai dengan mengira 116 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 ketepatan mengingat pada dapatan hasil. kaedah fcs yang dicadangkan ini mengatasi kaedah lain seperti (pnn), (aco), (cs) dan (fpnn) dari segi ketepatan dan ingatan imej. keywords:image retrieval; linear discriminant analysis (lda); cuckoo search (cs); ant colony optimization (aco); neural network 1. introduction we are witnessing an era of great development in the fields of information techniques, internet, and services for web. people can take pictures anywhere, anytime, using mobile smart phones or digital cameras. this has led to a significant increase in the use of image groups and digital media. to obtain integrated and rapid capabilities of the current technology and to facilitate dealing with large image groups, there must be effective capabilities and rapid mechanisms for user-driven image searching through huge image datasets. therefore, efficient and fast methods of retrieving images must be used. here, some artificial intelligence techniques are used. image retrieval methods are used in important areas such as security, criminal investigation, and medical imaging [1, 2]. feature extraction refers to the study of dimensionality reduction methods that describe the data. its purpose is to reduce computational costs by using fewer features to represent data, without degrading discriminatory ability. feature extraction is the process of using a subset of the original feature areas [3]. artificial neural networks are a branch of artificial intelligence techniques that are computational structures that can be trained on to learn models from examples. optimal solutions can be reached using the training group that tests the relationship between inputs and outputs and the method of learning, and networks that learn through supervision do local improvement [4]. swarm intelligence is also one of the branches of artificial intelligence technology that depends on social behaviour. its behaviour is inspired by nature, and the swarm has a great tolerance, so the failure of one factor does not stop the performance of the whole system. swarm intelligence has enormous applications in many areas such as image processing, robotics, and telecommunications [5]. in this work, the linear discriminant analysis (lda) algorithm was used for dimensionality reduction and to extract important features from the image datasets and query images. meta heuristic algorithms were used, such as algorithms of cs and aco. single layer perceptron neural network was also used and then the fuzzy membership function with single layer perceptron and cs were combined to produce a new method called fuzzy single layer perceptron neural network (fpnn). fuzzy cuckoo search (fcs) found similar images and place them in one class, i.e. to create several classes of the input images group, each class contained similar images, and to find similarities between the query images and the group of images in the image database being used. 2. previous works the use of aco algorithm to retrieve images from 120 images with an accuracy of 91.6% for the image retrieval system has been reported [1]. ramandeep and ashok used the cuckoo search engine for content based image retrieval. they compared cuckoo search to neural networks, which took more iterations [6]. arvind et al.presented a feed-forward neural network to recall and retrieve images and, due to its highly efficient and accurate classification capability, they obtained a retrieval precision equal to 88% and recall rate equal to 78% [4]. pathareand kimmatkar[7]implemented a system that was a mixture of a color-feature based recovery, firefly, and svm for region-based image retrieval (rbir). the accuracy result gained in the retrieval of the rbir images equalled to 95% and tpr 117 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 was equal to 65%. kurchaniya and johari[8] extracted edge and texture information of images using iehd and rlbp respectively, and they used pso to measure similarities between images. all images in the databases used gave a better result in terms of accuracy and recall, where the system was implemented on three types of database. they reached accuracy rates equal to 84.60% for li database, 85.62% for wang, and 85.20% for caltech-101databases. nie proposed a network model based on the particle swarm optimization algorithm and then established a mathematical model based on swarm intelligence for a use content-based image retrieval [9]. 3. linear discriminant analysis (lda) the goal of the linear discriminant analysis technique is to project the original data matrix onto a lower dimensional space. the lda method has been developed in order to transform features into space with fewer dimensions, and this increases the variance between classes and reduces the variance within the class. this helps to obtain the highest separation between classes. consider a group ofn image samples {x1, x2, .….. xn}, where image space takes upn-dimensional. assumecclasses {c1, c2, ……cc} and each image belongs to one of these classes. there are ni samples in a class. then, ( )  = == n i iii x n cic 1 1,,....,3,2,1  (1) is the mean of the samples in class ci, and the between-class scatter matrixsb is defined as ( )( )t i c i iib n n s  −−=  = 1 1 (2) the within-class matrix swis defined as ( )( )t ii c i ii cx xx n s ik  −−=   =  1 1 (3)   jt b t op wsw wsw wmw   ........... arg 4321 == (4) where{wi|i = 1,2,3,……j} denote generalized eigenvector setssb and swthat correspond to (m) largest generalized eigen values {i = 1,2,3,……j} or their mean [3,10]. jiss iiib ,...,3,2,1 , ==   (5) 4. ant colony optimization meta-heuristic algorithms based on the principles of artificial intelligence are most used in image processing, in the fields of engineering and informatics [5,11]. an ant colony's algorithm is a meta-heuristic algorithm that belongs to the intelligence of swarms and is based on the behavior of ants. ants, by their nature, are able to find the shortest path from the source of the food to the nest. to do this, the ant places a chemical on the ground as a guide for others to find food. the path selection for later ants depends on the density of the chemical, and therefore the behaviour of the ants stimulates the emergence of an algorithm consisting of a group of intelligent ants (artificial ants) as a group of simple agents that work with each other to solve problems by exchanging information via chemicals (pheromones) that act as a distributed memory to the linked ants. therefore, this algorithm representing system ants is applied to a number of complex optimization problems. from the ants' foraging behaviour, the idea of the algorithm came about as follows [12]: 118 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 a group of ants begin to leave the cell randomly in multiple directions. this process occurs the first time only, but subsequently the ants choose a specific path after testing each path. • an ant secretes a certain percentage of pheromone as it passes and that pheromone is used to know the path the ant has passed. • when finding the food source, the ant takes a sufficient amount of it, then returns to the cell, and chooses a specific path where it chooses the path that has the largest amount of pheromone. when the ant returns, the same amount of pheromone is released. • when the ant leaves the cell again, it tests the amount of pheromone in all paths and chooses the path with the largest amount of pheromone. • in each determined time period, the pheromone amount is updated, because the pheromone concentration will disappear over time. it has been observed that the shortest path is always the one that contains the largest pheromone amount. therefore, this is the path through which all ants will pass. the ant algorithm is a dynamic algorithm, meaning that if a problem occurs in the shorter path, a new path ant will choose in same way. the steps of the ant colony optimization algorithm are [12,13]: 1.ant searching behavior as follows: when the antk is in celli, it uses the heuristic functionij, and pheromoneij to calculate the probability that it will choose cellj as the next cell according of the following equation: ( )        =   otherwise njif p k i nj ijij k ij ijijk i 0 . .       (6) ni(k)represents the group of elements that do not belong to the partial solution of the ant. k, , represent fixed values that determine the importance of the pheromone substance and the heuristic information respectively, the heuristic function is calculated by the equation ij ij d 1 = (7) and dijrepresents the distance between the edgei and the edgej. 2. track the path and update the pheromone before returning to the parent node (nest),k, an ant places(k) from a pheromone (the aromatic substance) on the edges it visited, so the value of the pheromoneij at the edge (i,j) that the ant has crossed is calculated as follows )( k ijij  += (8) in general, the increase in the amount of pheromone on a specific edge leads to an increase in the probability of being selected by the rest of the ants in the colony. 3. pheromone trail evaporation. the pheromone begins to evaporate from all edges when k ant moves to next node, as shown in following equation ( ) ij p ij   −= 1 (9) 119 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 ( ) aji  , as the p (0,1) represent the coefficient of evaporation, aindicates the edges that an ant traversed on its way from the parent node to the destination, and generally the evaporation of the pheromone contributes to increasing the ability of the algorithm to explore different paths during the search process, and also contributes to reducing the amount of pheromone on the edges. to update the pheromone after ants return to the main node, according to following equation ( )  = +−= n k k ijij ij p 1 1   (10) the goal of updating the pheromone is to increase the pheromone amount associated with promising and good paths. therefore, the pheromones placed at the edge by thek ant are calculated as shown in the equation: k k ij l r = (11) asr represents a fixed value that works to determine the amount of increase in the amount of pheromone in a limited range,l represents the path that the antk crosses and in general the repetition represents a complete cycle that includes the movement of ants and the evaporation of the pheromone. in this paper, the clustering process was adopted using the mahalanobis distance to find the similarity between the query image and the database images by calculating the distance according to the following equation: ( ) ( ) iji t ijij centerdataacenterdatadist −−= (12) where this algorithm gave satisfactory results in the process of retrieving colour images. 5. single layer perceptron neural network single layer perceptron slp consist of input layer and output layer. each layer consists of one or more neurons (nodes), and each node in the input layer receives information from the outside world and is linked by connection weights with all nodes in the output layer. the data flows from the input layer to the output layer, and in the event of an error during learning, weights are changed. perceptron neural network is used for resolving linearly separable data. the steps of basic perceptron algorithm as follows [4]: firstly, initialize weights at randomwkj , and for each training pair / pattern [xi, ti], wherexi=x1 ,x2 , …… xn, then compute outputy, and compute error ( ) iiii netftte x wf k k ik =      =  (13) and finally use the error to update weights as follows ij old ij new ij www += (14) where ii e * e * = ij w (15) 120 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 is the learning rate, and it is a small value that is greater than zero. repeat the step until convergence [4,14]. in this paper, to improve the work of the perceptron network and accelerate the access to the optimal solution, the neural network was hybridized with fuzzy logic by adding a membership function to the equation of adjusting the weights to ensure that the ideal weights are obtained with the least time and effort. here, a new proposed method was obtained that called it fuzzy single layer perceptron neural network (fpnn) as shown in equations below: ii e * e * )( tuw iij = (16) mf iki u )(= (17)  = − −                 = c p f pk f ik ik m m d d 1 1 1 1 1 1 1  (18) whereuidenotes the fuzzy membership function, anddik = d(xk,wi) represents the euclidean distance between the input data and the weights of the output cells that play an important role in computing the value of the membership function. 6. cuckoo search this algorithm is based on behaviour inspired from nature. a cuckoo will lay its eggs in other birds’ nests so that the other birds will raise their cuckoo babies. if the other bird discovers that an egg in its nest is not its own, the unwanted and unfamiliar egg would be pushed and rejected from the nest. the cuckoo algorithm uses this principle to model a new solution as a cuckoo egg where every egg in a nest represents a unique solution. a bad solution can be replaced by a new solution in the nest. there are basic rules used in the cuckoo algorithm: • only one egg is placed by the cuckoo at a time, where the cuckoo randomly selects a nest and places the egg in it • desired nests with lots of eggs will be passed on to the next generation • the nest of the host will be repaired. the host bird detects an egg that the cuckoo bird lays with probability pd. in such a case, this egg will either be thrown out by the host bird or it will build a new nest elsewhere. according to these basic rules, basic cs algorithm steps can be explained at follows: start objective function ( ) ( ) t s yyyyf ,,........., 21 = initialize a random population of n host nest yi while (t <maxgen) get randomly a cuckoo (example i) by lévy flights fitness function evaluation fi choose randomly a nest from n (example j) with fitness fj if (fj fi) replace j with new solution; end 121 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 abandon worse nests or a fraction pd and build new nests in a new position by lévy flights the best solutions – nests – are preserved solutions and best objective (best nest) are arranged end while loop stop new solutions y(i+1)for cuckoos i, when found, implement lévy flight using the following equation ( ) ( ) vyelyy t i t i += +1 (19) where> 0 represent step size, we can take as 1. denotes of the entry wise multiplications. whereas, lévy flights mainly provide random walk, while from the lévy distribution, its random steps are drawn into large steps, as in equation below. ( )31.~ = − tuvyel (20) lévy flight provides random walking and forms random walking with step length distribution. on the current best solution, new solutions are created which help speed up local search [15,16]. in this method, the clustering principle was used in the retrieval process by using the mahalanobis distance to find the distance between the features of the database images and the query image to calculate the similarity value between these images, and retrieve the images related to the query image with high accuracy by employing this distance within the cuckoo algorithm in the calculation of the fitness function to obtain the optimal solution, high accuracy of retrieval, and excellent results, as shown in the tables. when developing this algorithm by adding the fuzzy membership function to the fitness function, a proposed method was obtained, called fuzzy cuckoo search algorithm (fcs), which obtained better results. 7. design of proposed system the system is designed to retrieve images based on some artificial intelligence techniques such as the swarm algorithms, which are represented by the ant colony (aco) algorithm and the cuckoo search (cs) algorithm. additionally, artificial neural networks were used such as the perceptron neural network (pnn) and the proposed methods of fuzzy perceptron neural network (fpnn) and fuzzy cuckoo search (fcs) that were used to retrieve the images, as shown in fig. 1. these methods (pnn, aco, cs, fpnn, and fcs) have been built to retrieve images from the datasets. in the training phase, these five methods are able to retrieve accurate and similar images with high efficiency on their own. the image retrieval system based on these five methods was designed to include two stages: the training phase and the testing phase. initially, we used the linear discriminant analysis (lda) to extract features for all the images in the database as well as the query image. in the training phase, the features extracted from the images are entered to the aco, cs, pnn, fpnn, and fcs in order to learn these methods, and the base knowledge is stored in these five methods through the training process. this knowledge is used in the testing phase for comparison and decision making by these methods (pnn, aco, cs, fpnn, and fcs). the comparison involves comparing features between query images and the trained image set, where the best images with identical and similar features are retrieved. 122 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 fig. 1: system flowchart of the image retrieval. 8. experimental results in this paper, five artificial intelligent methods were used: cuckoo search (cs), ant colony optimization (aco), and then combined fuzzy membership function with slp neural network and cs to produce fuzzy single layer perceptron neural network (fpnn), and fuzzy cuckoo search (fcs). linear discriminant analysis (lda) was also used for feature extraction of the image database and query image. to evaluate the performance of these methods, we used two indicators, recall and precision [17], as shown in eq. (21), eq. (22): 100 collection in the imagerelevant of no. total retrieved imagesrelevant of no. re =call (21) 100 retrieved images of no. total retrieved imagesrelevant of no. pr =ecision (22) in this work we used an image dataset that contained 10 categories, each category contained different numbers of images. the image categories are shown in table 1. the five methods pnn, aco, cs, fpnn, and fcs were applied to this database. in the training phase, these methods obtained 10 cluster centres, according to ten image categories, these methods discovered all the data in the database completely and accurately. in the testing phase, query images for each category were entered on these methods (pnn, aco, cs, fpnn, fcs). the distance between query image features and cluster centres for 10 categories, minus the distance equates to the similarity. these methods find the similarity and matching between the query image and the images in the stored database. table 1: images dataset category type number of images rate% california_gull 61 17.23 mflowers 44 12.43 cflowers 15 4.24 imageda tabase feature extraction (lda) database images features artificial intelligence techniques: swarm methods (aco, cs), pnn, and proposed methods (fpnn, fcs) feature matching &similar images retrieved images feature extraction (lda) query image features query image 123 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 rose_marron 18 5.08 nflower 15 4.24 blue_winged_warble 59 16.67 brown_pelican 56 15.82 cardinal 57 16.10 horse 10 2.82 human 19 5.37 total 354 100% the recall rate and precision rate were calculated for all these methods. different (recall and precision) rates were obtained for (pnn, aco, cs) and fpnn methods (table 2).while the fcs method obtained recall rate and precision rate equal (100%), the fcs is better than (pnn, aco, cs) and fpnn methods. table 3 shows the results for all methods pnn, aco, cs, fpnn and fcs that were used in this work. this table contains query image, category type, relevant retrieved, retrieved number, recall rate, and precision rating for these methods. from these tables, we note that the fcs method was the best as the values of recall and precision were equal to 100%, while the values of recall and precision for fpnn were equal to 97.2 and 87.83 respectively. we notice that the order of preference of the methods was as follows: first the pnn method gave results that are not good, then the aco method had better results, and when using the cs method, the results became better than the previous two methods. then the pnn method was developed by hybridizing it with fuzzy logic, where very satisfactory results were obtained. from monitoring the results of the cs method, the precision values were equal to 100% and that by the fpnn hybrid method and the recall values were high compared to other methods. therefore, the cs method was hybridized with fuzzy logic to improve its performance. the best results were obtained with this proposed method of fuzzy hybridization, where the values of recall and precision were equal to 100%. figure 2 shows the samples of query images for all categories of database. figures 3-7 show the number of relevant retrieved images for all methods used in this work. table 2: recall rate and precision rate for pnn, aco, cs and fpnn methods category type pnn aco cs fpnn recall rate% precision rate% recall rate% precision rate% recall rate% precision rate% recall rate% precision rate% california_gull 81.967 69.4 95.08 90.63 96.72 100 98.36 98.36 mflowers 68.18 53.57 86.36 79.16 95.45 100 97.72 100 cflowers 60 39.13 73.3 78.57 93.3 100 93.33 87.5 rose_marron 72.2 38.24 83.3 93.75 88.8 100 94.44 100 nflower 66.7 55.6 73.3 91.7 86.7 100 93.33 93.33 blue_winged_warble 61.02 56.3 83.1 92.45 91.53 100 96.61 100 brown_pelican 85.71 64.86 91.07 80.95 94.64 100 98.21 98.21 cardinal 82.46 68.12 92.98 89.83 96.49 100 100 100 horse 80 30.77 80 57.14 90 100 100 90.90 human 57.89 30.6 73.68 60.87 94.74 100 100 100 average 71.6127 50.659 83.217 81.505 92.837 100 97.2 87.83 table 3: the results for pnn, aco, cs, fpnn and fcs methods with query images, category type, relevant retrieved, retrieved number, recall rate, and precision rate query image category type relevant retrieved retrieved number recall rate precision rate method 124 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 california_gull 50 72 81.967 69.4 pnn 58 64 95.08 90.63 aco 59 59 96.72 100 cs 60 61 98.36 98.36 fpnn 61 61 100 100 fcs mflowers 30 56 68.18 53.57 pnn 38 48 86.36 79.16 aco 42 42 95.45 100 cs 43 43 97.72 100 fpnn 44 44 100 100 fcs cflowers 9 23 60 39.13 pnn 11 14 73.3 78.57 aco 14 14 93.3 100 cs 14 16 93.33 87.5 fpnn 15 15 100 100 fcs rose_marron 13 34 72.2 38.24 pnn 15 16 83.3 93.75 aco 16 16 88.8 100 cs 17 17 94.44 100 fpnn 18 18 100 100 fcs nflower 10 18 66.7 55.6 pnn 11 12 73.3 91.7 aco 13 13 86.7 100 cs 14 15 93.33 93.33 fpnn 15 15 100 100 fcs blue_winged_ warble 36 64 61.02 56.3 pnn 49 53 83.1 92.45 aco 54 54 91.53 100 cs 57 57 96.61 100 fpnn 59 59 100 100 fcs brown_pelican 48 74 85.71 64.86 pnn 51 63 91.07 80.95 aco 53 53 94.64 100 cs 55 56 98.21 98.21 fpnn 56 56 100 100 fcs cardinal 47 69 82.46 68.12 pnn 53 59 92.98 89.83 aco 55 55 96.49 100 cs 57 57 100 100 fpnn 57 57 100 100 fcs horse 8 26 80 30.77 pnn 8 14 80 57.14 aco 9 9 90 100 cs 10 11 100 90.90 fpnn 10 10 100 100 fcs human 11 36 57.89 30.6 pnn 14 23 73.68 60.87 aco 18 18 94.74 100 cs 19 19 100 100 fpnn 19 19 100 100 fcs 125 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 fig.2:query images for ten categories of image database. query image fig. 3: number of relevant-retrieved images = 9 for pnn method. query image fig. 4: number of relevant-retrieved images = 11 for aco method. 126 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 query image fig. 5: number of relevant-retrieved images = 14 for cs method. query image fig.6: number of relevant-retrieved images =14 for fpnn method. query image fig. 7: number of relevant-retrieved images = 15 for fcs method. 9. conclusion in this paper, we used some of artificial intelligence techniques for image retrieval. initially, we presented linear discriminant analysis (lda) for feature extraction of images in the dataset. then we used some swarm algorithms such as aco and cs optimization algorithms. we also used artificial neural network such as pnn, and combined the fuzzy membership function with single layer perceptron and cuckoo search to produce new 127 iium engineering journal, vol. 23, no. 1, 2022 khaleel https://doi.org/10.31436/iiumej.v23i1.1802 methods called fuzzy perceptron neural network (fpnn) and fuzzy cuckoo search (fcs). these five methods were applied to an image dataset. we used two measures (recall and precision rate) for evaluating these methods. the fcs method got the best performance for image retrieval among the other methods (pnn, aco, cs) and fpnn used in this work. acknowledgment i offer my gratitude and thanks to the university of mosul in iraq, for providing the facilities to carry out this research. references [1] tessy av. (2010) performance enhanced optimization based image retrieval system. ijca special issue on evolutionary computation,1: 31-34. [2] hung ht, bae mc, shin hl. (2014) rotation-invariant texture image retrieval using particle swarm optimization and support vector regression. applied soft computing, 17: 127-139. [3] santhi n, annbuselvi k, sivakumar s. (2018) performance analysis of feature extraction techniques: pca and lda for face recognition. int jengres compsciand eng, 5(3): 289-294. [4] arvind n, manimozhi, jetendranath m. (2014) content-based image retrieval system using feed-forward backpropagation neural network.int j comp sci network security, 14(6): 70-77. [5] shahbaa ik, karam mms. (2012) detection of network anomaly based on hybrid intelligence techniques. al-rafidain j comp sciences and mathematics, 9(2): 81-98. [6] ramandeep k, ashok kb. (2014) enhanced content-based image retrieval using cuckoo search algorithm. int j advanced res comp sci software engineering, 4(9): 233-241. [7] pathare rn, kimmatkar kw. (2016) multi-step approach for speeding-up region based image retrieval using indexing technique. int res j engineering and technology, 3(8): 323327. [8] kurchaniya d, johari pk. (2017) an efficient approach for image retrieval using particle swarm optimization. int j computer sciences and engineering, 5(6): 90-99. [9] nie q. (2018) research on image network retrieval application based on swarm optimization algorithm.advances in intelligent systems research, 147: 524-529. [10] steven f, joseminb. (2013) performance analysis of pca-based and lda based algorithms for face recognition. int j signal processing systems, 1(1): 1-6. [11] shahbaa ik, ragad wk. (2014) selection and prioritization of test cases by using bees colony. al-rafidain jcomputer sciences and mathematics, 11(1): 179-201. [12] hasancebi o, carba s. (2011) ant colony search method in practical structural optimization. int j optimization in civil engineering, 1: 91-105. [13] fangyuc,hongweiw, chaoq, yongx. (2013) an ant colony optimization routing algorithm for two order pickers with congestion consideration. computers & industrial engineering, 66: 77-85. [14] arvind n, manimozhi i. (2013) content-based image retrieval system using feed-forward backpropagation neural network. int j computer science engineering, 2(4): 143-151. [15] vennilal s, venkatesan a. (2017) improved color satellite image segmentation using cuckoo search algorithm.int j innovative res comp and comm eng, 5(4): 8229-8236. [16] priya v. (2018) ant colony and cuckoo search algorithm for document clustering. arpn jeng appl sci, 13(7): 2429-2437. [17] yogapriya j, saravanabhavan c, ilav. (2017) an effective machine learning algorithm for texture based medical image retrieval system. int res j pharmacy, 8(11): 201-218. 128 microsoft word 171 completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology amara and moawad 21 phac synthases and pha depolymerases: the enzymes that produce and degrade plastic amro a. amara 1,2 and hassan moawad 1,3 1 protein research department, genetic engineering and biotechnology research institute, mubarak city for scientific research and technological applications, alexandria, egypt. 2 microbiology division, pharmaceutics department, king saud university, riyadh, kingdom of saudi arabia. 3 national research center, cairo, egypt. amroamara@web.de abstract: phas are a group of intracellular biodegradable polymer produced by (most) bacteria under unbalanced growth conditions. a series of enzymes are involved in different phas synthesis, however phac synthases are responsible for the polymerization step. phas are accumulated in bacterial cells from soluble to insoluble form as storage materials inside the inclusion bodies during unbalanced nutrition or to save organisms from reduces equivalents. phas are converted again to soluble components by another pathways and enzymes for the degradation process. phas depolymerases are the responsible enzymes. this review is designed to give the non-specialists a condense background about phas especially for researcher and students in medicinal and pharmaceutical field. abstrak: phas (polyhydroxyalkanoate) merupakan sekumpulan polimer terbiodegradasikan intrasel yang dihasilkan oleh (kebanyakan) bakteria di bawah keadaan tumbesaran tak seimbang. satu rangkaian enzim terlibat dalam sistesis phas yang berbeza, namun sintesis phac bertanggungjawab dalam peringkat pempolimeran. phas dikumpulkan dalam sel bakteria dari bentuk larut dan tak larut sebagai bahan simpan di dalam jasad terangkum semasa nutrisi tak seimbang atau untuk menyelamatkan organisma daripada pengurangan tak keseimbangan. phas ditukarkan sekali lagi kepada komponen larut dengan cara lain dan enzim lain untuk proses degradasi. phas depolymerases (enzim yang memangkin penguraian makro molekul kepada molekul yang lebih mudah) merupakan enzim yang bertanggunjawab. kajian semula ini direka untuk memberi mereka yang bukan pakar, satu ringkasan tentang phas terutamanya penyelidik dan penuntut dalam bidang peubatan dan farmaseutikal. keywords: polyhydroxyalkanoate; phac synthase; pha depolymerase iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology amara and moawad 22 1. introduction perhaps, beijerinck wrote the first report about lucent granules of phas in bacterial cells in 1888 (reported in chowdhury, 1963) [1, 2]. poly-β -hydroxbutyrate (phb) was firstly described as an important bacterial product by lemoigne (1923). later, lemoigne (1927) characterized phb chemically and observed that it was involved in the sporulation of bacillus spp [3, 4]. lemoigne and co-workers published 27 articles from 1923 to 1951 [5]. he was the first to observe that these storage materials were not ether soluble, as in lipids. later, he reported that phb is the major constituent of these granules. using microscopic investigation, saponification numbers, and autolysis he proposed a polyester structure with the formula (c4h6o2)nand reported that phb could cast into film like cellulose nitrate material [3-7]. the worldwide demand for degradable plastic is estimated to be 1.4 million metric tons per year by the year 2000, with much of this demand driven by legislation and environmental group [8]. a number of polymers are being developed to meet this demand, with the majority of these being petrochemical based and projected cost at $6.6 kg -1 [9, 10]. natural products being developed as biodegradable plastics include starch blends, polylactic acid, and bacterial polyhydroxyalkanoates (phas). phas are described as natural polyesters [11]. copolymers of poly(β-hydroxybutyrate-coβ -hydroxyvalerate) were produced on a large scale by the imperial chemical industries in billingham, united kingdom [12, 13]. this copolymer is a thermoplastic which resembles polypropylene [14] and has been successfully test marketed as shampoo bottles in europe [15]. although this natural product has great promise, but its high cost is a limiting factor [10]. the large-scale production of bacterial pha has a number of interesting problems. major expenses in the production of pha are determined by the cost of the fermentation substrate, and the extraction of the polymer from inside the cell [12]. dunolp and robards (1973) developed the first models for the structure of the inclusion with intriguing observation that this polymer was stretchable even at very low freeze -fracture temperature [16]. phb was in fact a thermoplastic with properties much like polypropylene [14]. it was shown that phb copolymers that contained an amount of β-hydroxyvalerate and designated p(hb-co-hv) could be formed by co-substrate feeding [17]. 3-hydroxyvalerate synthesis is dependent on the presence of both glucose and propionate [18]. for phas nomenclature and abbreviation refer to amara [2]. many years have been lost after the first bulk interest with this polymer shown by lemoigne and his group. however, minor researches have been made. weibull had isolated the granules of bacillus megaterium by dissolution of the cell wall with a lysozyme [21]. doudoroff and stanier and stainer et al. found that phb can be produced by photosynthetic assimilation of organic compounds by phototrophic bacteria [21, 22]. they described that the reaction involved in the metabolic pathway is responsible for the biosynthesis of phb from acetic acid [22, 23]. lusty and doudoroff have shown a study on depolymerases, which were able to hydrolyze phb [24]. schlegal observed that cupriavidus necator (formally wautersia eutropha, ralstonia eutropha and alcaligenes eutrophus), could accumulate very large amount of phb in a media with low nitrogen content [25]. the most challenging work on phas started when schlegal working with c. necator and dawes working with azotobacter berjerinckii succeeded to isolate and characterize the enzymes catalyse the phb monomer synthesis [26, 27]. isolating iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology amara and moawad 23 the phac synthases was the real step to facilitate the cloning of their responsible genes. the pha synthase operon of c. necator were cloned in three labs nearly in a short span of time [28-30]. wallen and rohwedder reported heteropolymers of hb and 3-hydroxyvalerate in chloroform extracts of activated sewage sludge as major constituents with c6 and possibly c7 3-hydroxyacids as minor components [31]. de smet et al. characterized phamcl in pseudomonas oleovorans during growth on octane [32]. huisman et al. proved that phamcl accumulation was the common criteria of fluorescent pseudomonads [33]. phas are also produced by gram positive, negative and phototrophic bacteria as well as archaea [34-39]. fig. 1: phas metabolic different pathways (modified after amara [2, 19]). 2. phas production examination of the enzymes leading to the formation of phb has shown that the regulation of phb synthesis is controlled by acetyl-co-enzymes a (coa) acyltransferase [26, 40, 41]. under balanced growth conditions, acetyl-coa is fed into the tricarboxylic acid cycle and the resultant coa inhibits acety-coa acyltransferase and phb synthesis. under nutrient limitation (e.g., oxygen limitation) and carbon excess, nadh oxidase activity decrease, nadh increase and inhibits citrate synthase and isocitrate dehydrogenase, and acety-coa iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology amara and moawad 24 acyltransferase by coa is overcome. the ensuing condensation reaction forms acetoacetylcoa and initiates phb synthesis [26, 40]. the high nadh/nad ratio caused oxygen limitation rapidly readjusts as phb synthesis starts, and phb assumes the role of an alternative electron acceptor [40]. the polymer is normally accumulated in response to the limitation of an essential nutrient and much of the past work has concerned the control of the synthesis of phb under in-balanced growth condition [26, 41]. phb is the most broadly studied phas. the phb biosynthesis pathway consists of three distinct enzymatic reactions, as depicted in fig. 1. the regulation of phb synthesis is controlled by acetyl-coenzymes a (coa) acyltransferase [40, 42]. the first reaction comprises the condensation of two acetyl coenzyme a (acetyl-coa) molecules into acetoacetyl-coa by β-ketoacyl-coa thiolase (βketothiolase) (encoded by phaa). the second reaction is the reduction of acetoactyl-coa to (r)-3-hydroxybutyryl-coa by an nadph-dependent acetoacetyl-coa dehydrogenase (encoded by phab). finally, the (r)–3-hydroxybutyryl-coa monomers are polymerized to p(3hb) by p(3hb) synthase (encoded by phac). synthesis of phb is believed to be controlled by the first enzyme, 3-ketothiolase that is inhibited by coenzyme a (coash). synthesis of phas other than p(3hb) which are not related to their growth substrates occurs relatively rare in nature [42]. antonio et al. and amara et al. produced 3hb-3hhx from cultivation of recombinant e. coli on fatty acid using phac class i and acrylic acid [44, 45]. 4hydroxybutyrate (4hb) was produced in recombinant e. coli using succinyl-coa from the citric acid cycle, which is converted to 4-hydroxybutyryl-coa, a precursor for pha biosynthesis [46]. sixty years after the discovery of phb, de smet described the accumulation of the phamcl in pseudomonas oleovorans grown on octane as sole carbon source [32]. pha from pseudomonads rrna homology group i were directly related to the structure of the alkane, alkene or fatty acid they used as carbon source [33, 47]. these substrates called ‘related substrates’. when the carbon source consists of fatty acids with 6 to 12 carbon atoms, monomers of the pha are of the same length as the carbon source or are shortened by 2, 4 or 6 carbon atoms. pseudomonads are able to produce phamcl from sugar. these substrates, which do not resemble the monomers of the accumulated polymer, are named “unrelated substrates’’. pseudomonads of the rrna homology group i like psudomonas putida kt2442, accumulate pha that consists primarily of c10 and c8 monomers, when grown on sugars or gluconate [48, 49]. experimental evidence suggests that these monomers are derived from intermediates of fatty acid biosynthesis and that the composition of the phas is most likely a reflection of the pool of fatty acid biosynthetic intermediates. reush describes native low molecular mass phb in yeast and many other eukaryotic cells [50]. expression of the c. necator phb biosynthetic pathway was successfully achieved in the yeast saccharomyces cerevisiae by leaf et al. [51]. he reported that the expression of phb synthase in the yeast cytoplasm is sufficient for phb accumulation and that wild type yeast synthesis d-3hb-coa could raise from intermediates in fatty acid synthesis or through βoxidation [51]. yeast cells can be used as models to gain information about phas synthesis in eukaryotes [52]. it is confirmed that three thiolases exist in s. cerevisiae functioning in mitochdria, cytoplasm and peroxisomes [53, 54]. safake et al. in their study succeeded to iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology amara and moawad 25 isolate phb producing wild type yeast strain from kombucha tea and reported that the amount of phb is less than that from prokaryotic and the phb amount depend upon the type of culture and species [55]. simple strategy for biosynthesis of polyhydroxyalkanotes in wild type yeasts has been described [56]. synthesis of phascl was established in the peroxisome of a wild-type yeast strain by targeting the c. necator scl polymerase to the peroxisome [57]. other strategies for using yeasts other than s. cerevisiae have been reported [58, 59]. plants are able to produce phas directly from co2 and solar energy after being transgenic [50]. steinbüchel and füchtenbusch reported that the costs of the production of phas in transgenic plants could be of the same order of magnitude of their substrate costs (eg. sucrose, lipids and starch), if all the prerequisites are met [60]. phb has been produced in transgenic arabidopsis thaliana [61], brassica napus [62], gossypium hirsutum [63], nicotiana tabacum [64] and zea mays [52]. the copolyester phb-co-phv [65] and phas consisting of 3hamcl [66] have been produced too. recently petrasovits et al. succeeded to produce of polyhydroxybutyrate in sugarcane [67]. 3. classes of pha synthases pha synthases were classified into four classes based on their substrate specificity and subunit composition. the multiple alignment of the primary structures of these pha synthases show an overall identity with few conserved amino acids residues (fig. 2). however, each synthase from the same class is clustered in one group as in fig. 3. general model for each class can be performed as illustrated in fig. 4. only class iv is clustered with class iii while class iii is so close to it. class i pha synthases, with c. necator synthase as prototype, are composed of one single type of polypeptide chain and use mainly (r)-3hydroxybutyryl-coa, (r)-3-hydroxyvaleryl-coa and other short-carbon chain length hydroxyalkanoic acid coa thioesters including 3-mercaptoalkanoic acid coa thioesters as substrates [68, 69]. class iii pha synthases, as represented by the allochromatium vinosum enzyme, are composed of two different subunits each of about 40 kda [70]. the substrate specificity of class iii is similar to that of class i synthases, although some mcl 3hydroxyfatty acids are also incorporated [71]. class ii enzymes as well as class i pha synthases are composed of only one type of subunit. class i and ii were purified, and there in vitro activities have been determined [72-74]. class ii mainly found in pseudomonades such as p. aeruginosa. one major difference between class ii and both of class i and iii, pha synthases is the substrate specificity. class ii pha synthases incorporate preferentially 3-hydroxyfatty acids of mcl (c6c14) into phas, and the resulting product is a latex-like polymer [74-76]. these substrates are mainly derived from intermediates of fatty acid β-oxidation or from fatty acid de novo biosynthesis provided fatty acids or simple non-related carbon sources [78, 80-83]. class ii pha synthases were purified and in vitro activity was determined [83, 84]. a threading model of the a. vinosum pha synthase was generated [85]. accordingly, a threading model of the class ii pha synthase from p. aeruginosa was developed with the aid of the samt98 algorithm and based on the homology to the structure of the lipase from b. cepacia [86]. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology amara and moawad 26 amara and rhem reported that h479 is not the general base catalyst that activates the nucleophilic c296 for covalent catalysis and that h452 plays a major role [87]. in the multiple alignment of pha synthases only one cysteine residue (cys-319) is highly conserved. therefore, scientists have been searching for several years for the second thiol group. the essential role of cys-319 of the c. necator pha synthase (class i) for the reaction mechanism was obtained from site specific mutagenesis [72]. the weakly conserved cys-459 was supposed to be involved in the catalytic cycle, providing the second thiol group. however, site specific mutagenesis [72] clearly indicated that this amino acid residue is not essential for catalytic activity. in position 260 of the pha synthase from c. necator a conserved serine residue was observed. ser-260 was proposed as target for covalent posttranslational modification by 4-phosphopantetheine, which should provide the second thiol group similar to fatty acid synthase. in order to investigate posttranslational modification by 4phosphopantetheine, radiolabeling experiments were conducted, expressing pha synthase gene from c. necator in e. coli sj16 (pand). since e. coli sj16 is β-alanine auxotroph, specific radiolabeling of 4-phosphopantetheinylated proteins occurs, when cells were fed with 2 -14 c-β-alanine. these experiments indicated that the pha synthase was labeled by 4phosphopantetheine [72]. however, detailed analysis revealed that only a small portion of total pha synthase was labeled [88]. functional low level expression of pha synthases from c. necator and p. aeruginosa, respectively, in e. coli sj16 and also in β-alanine auxotrophic mutants of c. necator with subsequent analysis of 4-phosphopantetheinylated proteins gave no evidence for covalent posttranslational modification by 4-phosphopantetheine [89]. exchange of amino acid residue ser-260 against alanine and threonine, respectively, abolished in vivo and in vitro activity of pha synthase from c. necator [89]. the model of active pha synthase involves two subunits forming a homodimer considering class i and ii pha synthases, and forming a heterodimer (phac and phae) in case of class iii pha synthases. accordingly, class i and ii pha synthases possess two thiol groups provided by conserved cys-319, and in class iii pha synthases the second thiol group might be provided by conserved cys-130 of subunit phae from a. vinosum [88]. a novel pha synthase (class v) from bacillus megaterium required phacbm and pharbm for activity in vivo and in vitro was reported [90]. phacbm showed greatest similarity to the phacs of class iii in both size and sequence (figure 3, 4). unlike those in class iii, the 40 kda phae was not required, and furthermore, the 22 kda pharbm had no homology to phae. 4. phas biodegradation lusty and doudoroff reported the presence of depolymerase activities in pseudomonas lemoignei ans was able to degrade phb [24]. while depolymerases have been studied for about 45 years, the first structural gene of a pha depolymerase (alcaliginus faecalis, phazaf) was cloned and sequenced only in 1989 by saito et al [91]. depolymerases are highly specific for the polymers consisting of monomers in the (r) configuration [92]. phas depolymerase are carboxyesterases (ec 3.1.1) and hydrolyze the water insoluble polymer to water-soluble monomers and /or oligomers and lastly to water and carbon dioxide or methane. early phb degrading bacteria were isolated by selection for microorganisms able to utilize phb as the iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology amara and moawad 27 sole source of carbon and energy [1, 2]. phas degrading bacteria differ from each other depending on the type of phas they degrade, however some bacteria revealed a rather broad polyester specificity and are able to utilize a wide range of phas [93, 94]. three intracellular pha depolymerases (phaz1, phaz2 and phaz3) and a 3hb-oligomer hydrolase (previously designated phaz2), which hydrolyse phas and the cleavage products produced by phazs, were cloned and characterized in c. necator [94-97]. molds also could degrade phas and their depolymerases have been characterized [98, 99]. phas depolymerases show a similar characteristic, they are stable at a range of ph, temperature, relatively small mr (< 70 kda), they are inhibited by reducing agent, e.g. dithioerythritol (dtt), which indicates the presence of essential disulfide bonds, and by serine hydrolase disulfide bonds, and serine hydrolase inhibitors such as diisopropyl-fluorylphosphate (dfp) or acylsulfonyl derivatives [99]. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology amara and moawad 280 * 300 * 320 * 340 * 360 * 380 * 400 i-pseudomonas-putida : cinkfyildlqpqsslvahaldaghqvfilswrnadqsiahktwddyvqegvldpieavkaitgreqintlgfciggtilatalsvaaargehp-aasmtlltamldfsd---------tgvldvfvdeahvqmr : 384 i-burkholderia-ambifaria : cinkfyildlqpenslvahalssghqvflvswrnadasvahktwddymnegllaaidavqqvsgreqintlgfcvggtmlatalavlaargehp-aasmtlltamldftd---------tgildvfvdeahvqmr : 376 i-ralstonia-eutropha : cinkfyildlqpegslvryaveqghtvflvswrnpdasmagctwddyienaairaievvrdisgqdkintlgfcvggtiistalavlaargehp-vasltllttlldftd---------tgildvfvdephvqlr : 375 i-acidovorax-delafieldii : cinkfyildlqpensliryaveqghrtfvvswrnpdeslahktwddyvedgamaaidvvqnitgaeqinalgfcvggtilcnalavlaargdep-vasatflttlidftd---------tgildvfideasvkfr : 349 i-alcaligenes-sp : cinkfyildlqpenslipyaveqghrtfevswrnpddslahktwddyvedgamaaidvvqnitgaeqinalgfcmggtilsnalavlaargdep-vasatflttlidfsd---------tgildvfideafvkfr : 349 i-verminephrobacter-eiseniae : cinkfyildlqpgnsfiryaveqghrsfvvswrnpddslahktwddyvadgaitaidlvqritgagqinalgfcvggtilsnalavlaargqep-vasatflttlidfsd---------tgildvfideafvkfr : 349 i-rhodoferax-ferrireducens : cinkfyildlqpdnsliryavaqghrtfvvswrnpdaslahktwddyiddavikaitvtqditgaksinalgfcvggtmlgtalavlaargekp-vasatfltslldfsd---------tgildvfideafvkyr : 358 i-polaromonas-naphthalenivoran : cinkfyildlqpensliryataqghrtfvmswrnpdqsmsaktwddyienapikaievvreitgadtinalgfcvggtilgtalsvlaargekp-vesvtlltslldfsd---------tgildifidetsvkyr : 363 i-methylibium-petroleiphilum1 : cinkfyimdlqpenslvryavsqghrvfmlswvnadeslgdktwddyiehavirairevqaiskqeqintlgfciggtllatalavlaargehp-sasltmltsfldfsd---------tgvldlfvdeqmvsmr : 346 i-alcaligenes-latus : cinkyyildlqpdnsiirytiaqghrvfvvswrnpdastadktwddyvehgvirairaiqqitgqdklnalgfcvggtilstalavlaargeqp-vasltllttlldfsn---------tgvldlfidetgvrlr : 346 i-herminiimonas-arsenicoxydans : cinkyyildlqphnsfvryaveqghtvfliswrnadasiahatwddyvesgvlqaisvaqaisvqekinvlgfcvggtmlanalalacargekp-aasltllttfldfsd---------tgildvyideakiket : 318 i-janthinobacterium-sp : cinkyyildlqahnsfvryaveqghtvfliswrnadasiahatwndyiedgvlqamhvakaitrqekinvlgfcvggtmltnalalacargeep-aasltllttfldfsd---------tgildvyidegkikei : 342 i-nakamurella-multipartita : cinkyyildlqpansfvghavaqghtvflvswrnagpsqekltwddylqqgvfaaieaalkiskadklnalgfciggtllasalsvlaakgehp-aasltllttlldfsd---------tgeigllvtkegvaar : 356 i-lutiella-nitroferrum : cinkyylmdlqpdnsmvrhfvaqgyrvfliswrsatpemkqftwetyiekgviaaaeavkkvtrqpsmnalgfciggvilttalcvmqakgmnw-idsatfmtslldhtd---------pgeikvfidenvvrsr : 364 ii-pseudomonas-fluorescens5 : qinkfyvfdlspekslarfclrngqqtfivswrnptkaqrewglstyiea-lkeavdvvtaitgskdvnmlgacsggitctallghyaalgekk-vnaltllvsvldttl---------dtqvalfvdeqtleaa : 347 ii-comamonas-testosteroni : qinkfyvfdlspdkslarfclrngqqtfivswrnptkaqrewglstyiea-lkeavdvvtaitgsqdinmlgacsggitctallghyaalgekk-vnaltllvsvldttl---------dtqvalfvdeqtleaa : 347 ii-pseudomonas-chlororaphis : qinkfyvfdlspdkslarfclrngvqtfivswrnptkaqrewglstyiea-lkeavdvvtaitgskdvnmlgacsggitctallghyaalgekk-vnaltllvsvldttl---------dtqvalfvdeqtleaa : 347 ii-pseudomonas-sp : qinkfyvfdlspdkslarfclsnnqqtfivswrnptkaqrewglstyida-lkeavdvvsaitgskdinmlgacsggitctallghyaalgekk-vnaltllvsvldttl---------dsqvalfvdektleaa : 347 ii-pseudomonas-corrugata : qinkfyvfdlspdkslarfclrsnvqtfivswrnptkeqrewglstyiea-lkeavdvvtaitgskdvnmlgacsggitctallghyaalgekk-vnaltllvsvldttl---------dtdvalfvdeqtleta : 347 ii-pseudomonas-mediterranea : qinkfyvfdlspdkslarfclrsnvqtfiiswrnptkeqrewglstyiea-lkeavdvvtaitgskdvnmlgacsggitctallghyaalgekk-vnaltllvsvldttl---------dtdvalfvdeqtleaa : 347 ii-pseudomonas-syringae : qinkfyvfdlspekslarfclrsnvqtfiiswrnptkaqrewglstyiea-lkeavdvvlaitgskdlnmlgacsggitctallghyaalgekk-vnamtllvsvldttl---------dtevalfvdeqtleta : 347 ii-pseudomonas-putida : qinkfyvfdlspekslarfclrshqqtfiiswrnptkaqrewglstyida-lkeavdavlaitgskdlnmlgacsggitctalvghyaalgekk-vnaltllvsvldttl---------dtqvalfvdeqtlesa : 347 ii-aeromonas-hydrophila : qinkfyvfdlspekslaryclrsqqqtfiiswrnptkaqrewglstyida-lkeavdavlaitgskdlnmlgacsggitctalvghyaaigenk-vnaltllvsvldttm---------dnqvalfvdeqtleaa : 347 ii-pseudomonas-entomophila : qinkfyvfdlspekslarfclrsqqqtfivswrnptkaqrewglstyida-lkeavdavlaitgskdlnmlgacsggitctalvghyaalgekk-vnaltllvsvldttv---------dtqvalfvdeqtleaa : 347 ii-burkholderia-caryophylli : qinkfyvfdlspekslarfclrsnvqtfivswrnptkaqrewglstyida-lkeavdavlaitgckdlnmlgacsggitctallghyaalgenk-vnaltllvsvldttl---------dnqvalfvdeqtleaa : 347 ii-pseudomonas-mendocina : qinkfyvfdlspdkslarfllrsqvqtfvvswrnptkaqrewglstyiea-lkeaidvicaitgskdvnmlgacsgglttasllghyaalgqpk-vnaltllvsvldtql---------dtqvalfadektleaa : 347 ii-pseudomonas-stutzeri : qinkfyvfdlspdkslarfllrsqvqtfvvswrnptkaqrewglstyiaa-lkeaievicaitgskdvnmlgacsgglttasllghyaalgeqk-vhaltllvsvldtql---------dtqvalfadektleaa : 347 ii-pseudomonas-fluorescens : qinkyyifdlsptnsfvqyalknglqvfmvswrnpdvrhrewglstyvea-aeealnvtraitgsrevnlvgacaggltiaalqghlqakrqlrrvssatymvslldsqm---------dspatlfadektleaa : 348 iii-bacillus-weihenstephanensi : linkpyimdltpgnslveylvdrgfdvymldwgtfgledshlkfddfvfdyiakavkkvmrtaksdeisllgycmggtltsiyaalhpdmpirn----lifmtspfdfs---------etglygplldekyfnld : 199 iii-bacillus-mycoides : linkpyimdltpgnslveylvdrgfdvymldwgtfgledshlkfddfvfdyiakavkkvmrtaksdeisllgycmggtltsiyaalhpdmpirn----lifmtspfdfs---------etglygplldekyfnld : 199 iii-bacillus-thuringiensis : linkpyimdltpgnslveylvdrgfdvymldwgtfgledshlkfddfvfdyiakavkkvmrtaksdeisllgycmggtltsiyaalhphmpirn----lifmtspfdfs---------etglygplldekyfnld : 215 iii-bacillus-megaterium : linkpyildltpgnslveyllnrgfdvylldwgtpgledsnmklddyivdyipkaakkvlrtskspdlsvlgycmggtmtsifaalnedlpikn----lifmtspfdfs---------dtglygaflddryfnld : 200 iv-bacillus-megaterium : linkpyildltpgnslveyllnrgfdvylldwgtpgledsnmklddyivdyipkaakkvlrtskspdlsvlgycmggtmtsifaalnedlpikn----lifmtspfdfs---------dtglygaflddryfnld : 200 iii-rubrobacter-xylanophilus : linrpyvldlipgnsfieylvgegfdvymldwgipgdedaemsfehyvldylpraarkvmrtsgtedytlfgycmggtmsamyaalfp-ermrn----lvlltapiafpk------e-hlglyalftdskyldpg : 196 iii-syntrophomonas-wolfei : linrpyvldltpgsslveylvnegfdvylldwgefewedrdityadlvydyiataarkvarsagskeisiigycmggtmstlyaalfdrpvlkn----lvylaapidfn---------ragtydvwlkapgydpd : 201 iii-roseiflexus-castenholzii : linkpyifdlrpgnsfveymvqqgydvylvdwgapgpedahltfddyaleylpravrrmqmhsgqrdfsmlgwcigatlaaiyaamrpddglrn----lilltapidfsn------kgamgpfpkwlkeeyfnld : 210 iii-subunit-thioalkalivibrio : lvnrpymtdlqenrstvrglleagldvylidwgypdradrflglddyingyidrcvdvirrrhkldainilgicqggtfslcysalhp-ekvkn----lvtmvtpvdfht----pdnmlsrw------vrhvdvd : 194 iii-allochromatium-vinosum : lvnrpymtdiqedrstikgllatgqdvylidwgypdqadraltlddyingyidrcvdylreahgvdkvnllgicqggafslmysalhp-dkvrn----lvtmvtpvdfkt----pdnllsaw------vqnvdid : 195 iii-synechococcus-sp. : lvnrpfmvdlqedrslvanllklgldiylidwgyptradrwltlddyingyinncvdfirkkhdldkinllgicqggtfslcysaiyp-ekvkn----livmvtpvdfqi----sdsllymrggctlgaealdid : 203 iii-cyanothece-sp : lvnrpfmvdlqegrslvanllklgldvylidwgyptradrwltlddyingyinncvdfirkqhnldkinllgicqggtfsvcysaiyp-ekvkn----livmvapidfrm----pgtllnmrggctigaealdvd : 203 iii-microcystis-aeruginosa : lvnrpymvdlqegrslvanllklgldiylidwgyptrsdrwltlddyingyvdncvdfirqshhldkinllgicqggtfslcysslyp-dkikn----lvtmvtpvdfyq----tetllnmrggcslgaealdid : 203 iii-synechocystis-sp. : lvnrpymvdlqegrslvanllklgldvylidwgypsrgdrwltledylsgylnncvdiicqrsqqekitllgvcqggtfslcyaslfp-dkvkn----lvvmvapvdfeq----pgtllnarggctlgaeavdid : 216 iii-xanthomonas-campestris : lvnrpymvdlqadrslvkgllshgqdvyvldwgypdrseryltledyllryidgavdhlraqsgleavdvlgicqggtfslcyaalqr-dkvrn----litmvtpvdfht----pdnmlsnw------armvdvd : 194 iii-rhizobium-leguminosarum : lvgrytiadlqsdrslvrsllaegtdlwlidwgkpgrterwltmddyvddyiheavhricretghdkvtllgiceggvfttcyaalhp-ekvkn----lvltitpidfhadiddpaaiqgllniwmrslapedid : 206 iii-nitrosopumilus-maritimus : linrfhildiqpekswvrnllqqgfdvymldwgtptsmdkyldfddyvngyldayveyiknesstekislqgyctgatiattyaslhp-esvkn----yiatapvidgwr----dttvisnl------akhmdvd : 193 iii-cenarchaeum-symbiosum : linrfhildihprrswvrnllsqgfdvymvdwgtptrmdryldfddyvngyldnciqfakresgapsvslqgyctggtlaavyaalhp-gsvrn----lvatapvidgwk----dttvvsni------akhvdvd : 172 iii-ferroglobus-placidus : linkpyildlhpersvvrkfldagfdvylikwgdatiadq-fglsgyidifmydfieylkdyagvekisilgycmggglsaiytslyp-envkn----llllaatlyfdk--------evgglvtlsdkrffdpe : 202 7 4 d s w g c g fig. 2: part of the multiple amino acids alignment of different phac synthases, shaded lines show different conserved regions. iium engineering journal, vol. x, no. x, 200x amara and moawad 29 fig. 3: phylogenic tree for class i, ii, iii and iv phac synthases. fig. 4: phac synthase class i model (left) and its conserved amino acids (right). depolymerases have three strictly conserved amino acids: serine, aspartate and histidine. the serine is part of the lipase-box pentapeptide gly-xaa1-ser-xaa2-gly [100]. the oxygen atom of the serine side chain is the nucleophile that attacks the ester bond [93]. many strategies were describing using depolymerases in the biotechnological products using efficient microbial strains [19, 101, 102]. ihssen et al. show a study for using extracellular phamcl depolymerase for targeted binding of proteins to artificial poly[(3-hydroxyoctanoate)-co-(3-hydroxyhexanoate)] granules [103]. 5. protein engineering of phac synthase tha phac synthases show a great homology (as in fig. 2) to each other and the conserved amino acids have been highlighted (fig. 2). aiming to change the phac substrate specificity, improve their activities’, determine their active sites’ and discover new futures, different tools of genetic and protein engineering tools have been implemented to the genes encoded different phac synthases [2]. aiming to enhance the phac synthase activity amara et al. establish a protocol for in vivo random mutagenesis of iium engineering journal, vol. x, no. x, 200x amara and moawad 30 the phacap (aeromonac punctata) [44, 45]. four mutants exhibited enhanced in vivo and in vitro pha synthase activity. the in vitro activities of the overproducing mutants ranged from 1.1 to 5-fold of the wild type activity, whereas the amounts of accumulated pha ranged from 107%-126% to that of the wild type [44, 45]. a list of mutants and their site in the phaccn have been described in details by rehm et al. and their related effect on phaccn structure/activity have been discussed [86]. an attractive observation (in the work done by amara et al. was the increase in weight average molecular mass of the pha synthesized by the modified pha synthase, which suggest a higher processivity of the enzymes with less frequently occurring chain transfer reactions [44, 45]. slight preference of c4 over c6 was observed in the mutants as compared to the wild-type which keep the door open for the possibility of changing the substrate specificity [44, 45]. taguchi et al. have been used another strategy based on in vitro mutagenesis for phaccn using pcr [105, 106]. seven site directed mutations have been performed in phacpa where five conserved residues were replaced by site directed mutagenesis in order to identify the function of these amino acids in catalysis. the substitution of w398 by alanine abolished phamcl synthase activity indicating that w398 is essential for enzyme activity [87]. the substitution of h479 by glutamine did not affect the phamcl activity, which indicates that h479 is not the general base catalyst that activates the nucleophilic c296 for covalent catalysis. the substitution of c296 with serine, which is the general base catalyst in lipases, did not abolish phamcl synthase activity while still exhibiting 20% activity in comparison to the wild type. substitution of c296 with alanine abolished phamcl synthase activity which is a strong evidence that serine may be able to replace cysteine as catalytic nucleophile for changing substrate specificity of pha synthase. for further investigation, another site directed mutagenesis has been done in another conserved histidine (h452), which was replaced with glutamine. the h452q mutant was highly impaired in phamcl activity, which indicates that h452 plays a major role as a general base catalyst instead of h479 [87]. hu et al. (2007) reported an improve for fractions by using site directed mutagenesis. the recombinant e. coli harboring plasmid petj1 (l65a), petj2 (l65v) or plasmid petj3 (v130a) synthesized the enhanced 3hhx fractions of phbhhx from dodecanoate, indicating that leu-65 and val-130 of phaj(ah) play an important role in determining the acyl chain length substrate specificity. the mutated phaj (ah) (l65a, l65v, or v130a) provided higher 3hhx precursors for pha synthase, resulting in the enhanced 3hhx fractions of phb-co-hhx [107]. fusion proteins composed of the n terminal part of the pha synthase from p. aeruginosa and the c terminal part of the pha synthase from c. necator indicated that fusion points located in the �/β-hydrolase fold region are not tolerated. furthermore, these fusion points were located in predicted and structurally conserved α-helical regions [104]. matsumoto et al. reported a chimeric enzyme composed of polyhydroxyalkanoate (pha) synthases from c. necator and aeromonas caviae enhances production of phas in recombinant e. coli. [107]. an p. putida mutant was isolated which is able to grow normally on any carbon source tested and which synthesized phamcl from fatty acids but not from gluconate or glucose [78]. biochemical studies on the affected enzyme revealed that this enzyme catalyses the transfer of (r)-3-hydroxydecanoyl moieties from the acyl carrier protein: coenzyme a transferase. the respective gene, which complemented the mutant, was referred to as phag [78]. which has been also identified and cloned from p. aeruginosa [81] and p. oleovorans [82]. the phag protein overproduced in e. coli as a cterminal his6-tagged fusion protein. the his6x-tagged phag was purified to homogeneity by refolding of phag obtained from inclusion bodies, and a new enzyme assay was established. gel filtration chromatography analysis in combination with light scattering iium engineering journal, vol. x, no. x, 200x amara and moawad 31 analysis indicated substrate-induced dimerization of the transacylase. in the presence of the substrate (r)-3-hydroxyacyl-coa the transacylase appeared in apparent molecular weights of 45.4, 83.7 and 102 kda, which indicated substrate-induced conformational changes and oligomerization of the transacylase [108]. a threading model of phag was developed based on the homology to an epoxide hydrolase (1cqz). in addition, the alignment with the α/β-hydrolase fold region indicated that phag belongs to α/β-hydrolase superfamily [108]. accordingly, cd analysis suggested a secondary structure composition of 29% α-helix, 22% β-sheet, 18% β-turn and 31% random coil that support the phag protein model. using hanging drop methods amara, (2003) obtain crystals from the purified phag [20]. phag is responsible for diverting intermediates of fatty acids to phac synthase to produce new polymers of phascl/mcl. acknowledgment the corresponding author would like deeply to acknowledge ms siham zayer for advices during writing this review. references [1] a chowdhury "poly-β-hydroybuttersäure abbauende bakterien und exoenzyme". arch. mikrobiol. vol. 47 pp. 167-200, 1963. [2] aa amara "polyhydroyalkanoates: from basic research and molecular biology to application". iium engineering journal, vol. 9 (1): pp. 37-73, 2008. [3] m lemoigne "production d'acide β -oxybutyrique par certaines bact’eries du groupe du bacillus subtilis". c.r. hebd. seances acad. sci., vol. 176 pp. 1761, 1923. [4] m lemoigne "etudes sur l'autolyse microbienne. origine de l'acide β-oxybutyrique form’e par autolyse". ann. inst. pasteur (paris). vol. 39 pp. 144, 1927. [5] rd de la rivie`re "notice ne´crologique sur m. maurice lemoigne (1883-1967) " c. r. acad. des sci., paris, t. vol. 264, 1967. [6] m lemoigne "etudes sur l’autolyse microbie acidification par formation d’acide βoxybutyrique, ann. inst. pasteur., vol. 39 pp. 144, 1925. [7] m lemoigne "produits de l’hydration et de polymerisation de l’acide β-oxobutyrique". bull. soc. chem. biol. (paris), vol. 8 pp. 770–782, 1926. [8] r leaversueh "industry weighs the need to make polymer degradable". mod. plastics vol. 64(8) pp. 52-55, 1987. [9] kf lindsay, ""truly degradable" resins are now truly commercial". mod. plastics, vol. 69(2) pp. 62-64, 1992. [10] jw moore "degradable plastics. mod. plastics 69(13) pp. 58-63, 1992. [11] aj anderson, gw haywood, and ea dawes "biosynthesis and composition of bacterial poly (hydroxyalkanoates) ". int. j. biol macromol. 12 pp. 102-105, 1990. [12] d byrom "polymer synthesis by microorganisms: technology and economics". trends biotechnol. vol. 5 pp. 246-250. 1987. [13] wd luzier "materials derivedbiomas/biodegradable materials". proc. natl. acad. sci. usa, vol. 89 pp. 839-842, 1992. [14] pp king "biotechnology. an industrial view. j. chem. tech. biotechnol. vol. 32 pp. 2-8, 1982. [15] d. rotman “monsanto takes a chance on zeneca’s biopol technology”. chemical week, vol.158 pp. 21.1996, [16] wf dunlop and aw robards "ultrastructural sudy of poly-β-hydroxybutyrate granules from bacillus cereus". j. bacteriol. vol. 114 pp. 1271-1280, 1973. [17] pa holmes, lf wright and sh collins "eur.pat.appl.0 052 459, 1981. iium engineering journal, vol. x, no. x, 200x amara and moawad 32 [18] sc slater "production of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) in a recombinant escherichia coli strain". j. applied and environmental microbiology, vol. 58 pp. 1089-1094, 1992. [19] aa amara "from gene to plastic: from phac synthase to polyhydroxyalkanoates". ed amara aa. schüling verlag germany, 2010. [20] aa amara “biochemical and molecular characterization of pha synthases from pseudomonas aeruginosa, ralstonia eutropha, aeromonas punctata as well as of the (r)-3hydroxyacyl-acp:coa transacylase from pseudomonas putida”. ph. d. thesis: isbn: 3930962039-germany, 2003. [21] c weibull "characterization of the protoplasmic constituents of bacillus megaterium". j. bacteriol, vol. 66(6) pp. 696–702, 1953. [22] m doudoroff and ry stanier "role of poly-β-hydroxybutyric acid in the assimilation of organic carbon by bacteria". nature. vol. 183 pp. 1440, 1959. [23] ry stanier, m doudoroff, r kunisawa and r contopoulou "the role of organic substrates in bacterial photosynthesis". proc. natl. acad. sci. u s a, aug; vol. 45(8) pp. 1246–1260, 1959. [24] cj lusty and m doudoroff "poly-β-hydroxybutyrate depolymerases of pseudomonas lemoignei". biochemistry, vol. 56 pp. 960-965, 1966. [25] hg schlegel, h kaltwasser and g gottschalk "[a submersion method for culture of hydrogen-oxidizing bacteria: growth physiological studies.] ". [article in german] arch. mikrobiol., vol. 38 pp. 209-222, 1961. [26] v oeding and hg schegel "β-ketothiolase from hydrogenomonas eutropha h16 and its significance in the regulation of poly-β-hydroxybutyrate metabolism". biochem. j,. vol. 134 pp. 239-248, 1973. [27] pj senior and ea dawes "the regulation of the poly-β-hydroxybutyrate metabolism in azotobacter beijerinckii". biochem. j., vol. 134 pp. 225–238, 1973. [28] a schubert, a steinbuchel. and hg schlegel. "cloning of the alcaligenes eutrophus genes for synthesis of poly-beta-hydroxybutyric acid (phb) and synthesis of phb in escherichia coli". j. bacteriol., vol. 170(12) pp. 5837-5847, 1988. [29] sc slater wh voige and de dennis "cloning and expression in escherichia coli of the alcaligenes eutrophus h16 poly-β-hydroxybutyrate biosynthetic pathway". j. bacteriol., vol. 170 pp. 4431-4436, 1988. [30] op peoples and aj sinskey "poly-β-hydroxybutyrate (phb) biosynthesis in alcaligenes eutrophus h16. identification and characterization of the phb polymerase gene (phbc) ". j. biol. chem., vol. 264 pp. 15298-15303, 1989. [31] ll wallen and wk rohwedder. "poly-β-hydroxy-alkanoate from activated sludge". environ. sci. technol , vol. 8 pp. 576579, 1974. [32] mj de smet, g eggink, bb withold, j kingma and h wynberg "characterization of intracellular inclusions formed by pseudomonas oleovorans during growth on octane". j. biotechnol. vol. 154 pp. 870-878, 1983. [33] gw huisman, o de leeuw, g eggink and b witholt "synthesis of poly-hydroxyalkanoates is a common feature of fluoresent pseudomonads". appl. environ. microbiol., vol. 55 pp. 1949-1954, 1989. [34] r fernandez-castillo, f rodrigues-valera, j gonzalez-ramos and f ruiz-berraquero "accumulation of poly(β-hydoxybutyrate) by halobacteria". appl. environ. microbiol. vol. 51 pp. 214-216, 1986. [35] aj anderson and ea dawes "occurrence, metabolism, metabolic role, and industrial uses of bacterial polyhydroxyalkanoates". microbiol. rev. vol. 54 pp. 450-472, 1990. [36] a steinbüchel "polyhydroxyalkanoic acids. in: byrom d (ed) biomaterials: novel materials from biological sources". stockton, new york, 124-213, 1991. [37] steinbüchel a, b füchtenbusch, v gorenflo, s hein, r jossek, s langenbach and bha rehm "biosynthesis of polyesters in bacteria and recombinant organisms". polym. degrad. stab. vol. 59 pp. 177-182, 1997. iium engineering journal, vol. x, no. x, 200x amara and moawad 33 [38] a steinbüchel and s hein "biochemical and molecular basis of polyhydroxyalkanoic acids in microorganism", in biopolyester, a. steinbuchel, babel, w., (eds), adv. biochem. eng. biotechnol., vol. 71 81-123, 2001. [39] ms shabeb, m younis, aa amara and a shoreit "production of phb-co-phv from compost bioremediation by purple non-sulfur bacteria". egyptian. j. biotechnol. vol. 19 pp. 467-478, 2005. [40] fa jackson, and ea dawes "regulabon of the tricarboxylic acid cycle and poly-bhydoxybutyrate metabolism in azotobacter beijerinckii grown under nitrigen or oxygen limitation". j. gen. microbiol., vol. 97 pp. 303-312, 1976. [41] pj senior and ea dowses "poly-b-hydroxybutytate biosynthesis and the regulation of glucose metabolism in azotobacter beijerinckii". biochem. j. vol. 125 pp. 55-66, 1971. [42] y asada, m miyake, j miyake, r kurane and y tokiwa "photosynthetic accumulation of poly-(hydroxybutyrate) by cyanobacteria-the metabolism and potential for co2 recycling". int. j. biol. macromol. vol. 25(1-3) pp. 37-42, 1999. [43] rv antonio, a steinbüchel and bha rehm "analysis of in vivo substrate specificity of the pha synthase from c. necator: formation of novel copolyester in recombinant escherichia coli". fems microbiol. lett. 182 pp. 111-117, 2000. [44] aa amara, bha rehm and a steinbüchel "biopolymer overproduction by new mutants using simple methods for selection". in daad-bioforum-berlin ‘’grenzenlos forschen’’, daad, biotechnologische methoden. vol. 231-239, 2001. [45] aa amara, a steinbüchel and bha rehm "in vivo evolution of the aeromonas punctata polyhydroxyalkanoate (pha) synthase pp. isolation and characterization of modified pha synthases with enhanced activity". appl. microbiol. biotechnol. 59 pp. 477-482, 2002. [46] he valentin, and d dennis "production of poly (3-hydroxybutyrate-co-4-hydroxybutyrate) in recombinant escherichia coli grown on glucose". j. biotechnol. vol. 58 pp. 33-38, 1997. [47] h brandl, ra gross, rw lenz and rc fuller "pseudomonas oleovorans as a source of poly(β-hydroxyalkanoates) for potential applications as biodegradable polyesters". appl. environ. microbiol. vol. 54 pp. 1977-1982, 1988. [48] a timm and a steinbüchel "cloning and molecular analysis of the poly(3-hydroxyalkanoic acid) gene locus of pseudomonas aeruginosa pao1". eur. j. biochem., vol. 209 pp. 15-30, 1992. [49] gnm huijberts, g eggink, p de waard, gw huisman and b witholt "pseudomonas putida kt2442 cultivated on glucose accumulates poly(3-hydroxyalkanoates) consisting of saturated and unsaturated monomers". appl. environ. microbiol., vol. 58 pp. 536-544, 1992. [50] rn reush "poly-β-hydroxybuyrate/calcium polyhydroxyphosphate, a biodegradable thermoplastic produced in transgenic plants". science, vol. 256 pp. 520-523, 1989. [51] ta leaf, peterson ms, stoup sk, somers d and srienc f "saccharomyces cerevisiae expressing bacterial polyhydroxybutyrate synthase produces poly-3-hydroxybutyrate". microbiology vol. 142 pp. 1169-1180, 1996. [52] jj hahn, ac eschenlauer, mh narrol, da somers and f srienc "growth kinetics, nutrient uptake, and expression of the alcaligenes eutrophus poly(β-hydroxybutyrate) synthesis pathway in transgenic maize cell suspension cultures". biotechnol. prog., vol. 13 pp. 347– 354, 1997. [53] ja kornblatt, and h rundney "two forms of acetoacetyl coenzyme a thiolase in yeast ii. intracellular location and relationship to growth". j. biol. chem., vol. 246 pp. 4424-4430, 1971. [54] jc igual, c gonzalez-bosch, and je perez-ortin "the potl* gene for yeast peroxisomal thiolase is subject to there different mechanisms of regulation". mol. microbiol., vol. 6 pp. 1867-1875, 1992. [55] s safak, n mercan, b aslim and y beyatli "a study on the production of poly-betahydroxybutyrate by some eukyryotic microorganisms". turkish electronic journal of biotechnology, pp. 11-17, 2002. iium engineering journal, vol. x, no. x, 200x amara and moawad 34 [56] dam abd-el-haleem, sa zaki, at abuelhamd, aa amara, , abuelreesh g."biosynthesis of polyhydroxyalkanotes in wild type yeasts". j. appl. sci. environ. manage. vol. 11(3): pp. 5 – 10, 2007. [57] b zhang, r carlson and f srienc "engineering the monomer composition of polyhydroxyalkanoates synthesized in saccharomyces cerevisiae". appl. environ. microbiol., vol. 72(1) pp. 536-543, 2006. [58] t a abuelhamd dam abd-el-haleem, sa zaki, aa amara, gms aboelreesh "genetic engineering of schizosaccharomyces pombe to produce bacterial polyhydroxyalkanotes". j. appl. sci. environ. manage. vol. 11 pp. 1119-8362, 2007. [59] dam abd-el-haleem, aa amara, s zaki, abuelhamd a, abuelreesh g "biosynthesis of biodegradable polyhydroxyalkanotes biopolymers in genetically modified yeasts". int. j. environ. sci. tech. vol. 4 (4): pp. 513-520, 2007. [60] a steinbüchel and b füchtenbusch "bacterial and other biological systems for polyester production". trends biotechnol. vol. 16 pp. 419-427, 1998. [61] y poirier, c somerville, la schechtman, mm satkowski and i noda "synthesis of highmolecular-weight poly((r)-(β)-3-hydroxybutyrate) in transgenic arabidopsis thaliana plant cells". int. j. biol. macromol. vol. 17 pp. 7-12, 1995. [62] he valentin, dj rodriguez, da stone, sr padgette, g kishore and kj gruys "metabolic engineering of arabidopsis and brassica for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer production". nat. biotechnol. vol. 17 pp. 1011-1016, 1999. [63] me john and g keller "metabolic pathway engineering in cotton: biosynthesis of polyhydroxybutyrate in fiber cells". proc. natl. acad. sci. usa 93 pp. 12768-12773, 1996. [64] nakashita h, arai y, yoshioka k, fukui t, doi y, usami r, horikoshi k and yamaguchi i "production of biodegradable polyester by a transgenic tobacco". biosci. biotechnol. biochem. vol. 63 pp. 870-874, 1999. [65] s slater, ta mitsky, kl houmiel, m hao, se reiser, nb taylor, m tran, he valentin, dj rodriguez, da stone, sr padgette, g kishore and kj gruys "metabolic engineering of arabidopsis and brassica for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer production". nat. biotechnol. vol. 17 pp. 1011-1016, 1999. [66] vv mittendorf, ej robertson, rm leech, n kruger, a steinbüchel and y poirier "synthesis of medium-chain-length polyhydroxyalkanoates in arabidopsis thaliana using intermediates of peroxisomal fatty acid oxidation". proc. natl. acad. sci., vol. 95 pp. 13397-13402, 1998. [67] la petrasovits, mp purnell, lk nielsen and sm brumbley "production of polyhydroxybutyrate in sugarcane". plant biotechnol j. vol. 5(1) pp. 162-72, 2007. [68] t. lutke-eversloh, j. kawada, r. h. marchessault and a. steinbuchel, “characterization of microbial polythioesters: physical properties of novel copolymers synthesized by ralstonia eutropha”, biomacromolecules, vol. 3(1), pp. 159-166, 2002. [69] t lütke-eversloh, k bergander, h luftmann and a steinbüchel "identification of a new class of biopolymer: bacterial synthesis of a sulfur-containing polymer with thioester linkages". microbiology, vol. 147 pp. 11-19, 2001. [70] m liebergesell and a steinbüchel "cloning and nucleotide sequences of genes relevant for biosynthesis of poly(3-hydroxybutyric acid) in chromatium vinosum strain d". eur. j. biochem., vol. 209 pp. 135-150, 1992. [71] m liebergesell, s rahalkar. and a steinbüchel "analysis of the thiocapsa pfennigii polyhydroxyalkanoate synthase: subcloning, molecular characterization and generation of hybrid synthases with the corresponding chromatium vinosum enzyme". appl. microbiol. biotechnol., vol. 54 pp. 186-194, 2000. [72] tu gerngross, kd snell, op peoples, aj sinskey, e csuhai, s masamune and j stubbe "overexpression and purification of the soluble polyhydroxyalkanoate synthase from alcaligenes eutrophus: evidence for it required posttranslational modification for catalytic activity". biochemistry vol. 33 pp. 9311-9320, 1994. [73] m liebergesell, k sonomoto, m madkour, f mayer and a steinbüchel "purification and characterization of the poly(hydroxyalkanoic acid) synthase from chromatium vinosum and iium engineering journal, vol. x, no. x, 200x amara and moawad 35 localization of the enzyme at the surface of poly(hydroxyalkanoic acid) granules". eur. j. biochem. vol. 226 pp. 71-80, 1994. [74] r jossek, r reichelt and a steinbüchel "in vitro biosynthesis of poly(3-hydroxybutyric acid) by using purified poly(hydroxyalkanoic acid) synthase of chromatium vinosum". appl. microbiol. biotechnol. vol. 49 pp. 258-266, 1998. [75] a timm and a steinbüchel "formation of polyesters consisting of medium chain length 3hydroxyalkanoic acids from gluconate by pseudomonas aeruginosa and other fluorescent pseudomonads". appl. environ. microbiol., vol. 56 pp. 3360-3367, 1990. [76] q qi, bha rehm and a steinbüchel "synthesis of poly(3-hydroxyalkanoates) in escherichia coli expressing the pha synthase gene phac2 from pseudomonas aeruginosa": comparison of phac1 and phac2. fems microbiol. lett. vol. 157 pp. 155162, 1997. [77] q qi, a steinbüchel and bha rehm "metabolic routing towards polyhydroxyalkanoic acid synthesis in recombinant escherichia coli (fadr): inhibition of fatty acid β-oxidation by acrylic acid". fems microbiol. lett. vol. 167 pp. 89-94, 1998. [78] bha rehm, n krüger and a steinbüchel "a new metabolic link between fatty acid de novo synthesis and polyhydroxyalkanoic acid synthesis". j. biol. chem. vol. 273 pp. 24044-24051, 1998. [79] bha rehm and a steinbüchel "pha synthases-the key enzymes of pha synthesis. in ‘’biopolymers’’, a steinbüchel,. and y doi,. (eds.), wiley-vch, heidelberg, germany, pp. 173-215, 2001. [80] s fiedler, a steinbüchel and bha rehm "phag-mediated synthesis of poly(3hydroxyalkanoates) consisting of medium-chain-length constituents from nonrelated carbon sources in recombinant pseudomonas fragi". appl. environ. microbiol. vol. 66 pp. 21172124, 2000. [81] n hoffmann, a steinbüchel and bha rehm "the pseudomonas aeruginosa phag gene product is involved in the synthesis of polyhydroxyalkanoic acid consisting of mediumchain-length constituents from non-related carbon sources". fems microbiol. lett., vol. 184 pp. 253-259, 2000a. [82] n hoffmann, a steinbüchel and bha rehm "homologous functional expression of cryptic phag from pseudomonas oleovorans establishes the transacylase-mediated polyhydroxyalkanoate biosynthetic pathway". appl. microbiol. biotechnol., vol. 54 pp. 665-670, 2000. [83] bha rehm, q qi, brb beermann, hj hinz and a steinbüchel "matrix-assisted in vivo refolding of pseudomonas aeruginosa class ii polyhydroxyalkanoate synthase from inclusion bodies produced in recombinant escherichia coli". biochem. j. vol. 358 pp. 263268, 2001b. [84] q qi, , a steinbüchel and bha rehm "in vitro synthesis of poly(3-hydroxydecanoate): purification and enzymatic characterization of type ii polyhydroxyalkanoate synthases phac1 and phac2 from pseudomonas aeruginosa". appl. microbiol. biotechnol. vol. 54 pp. 37-43, 2000. [85] y jia, tj kappock, t frick, aj sinskey and j stubbe "lipases provide a new mechanistic model for polyhydroxybutyrate (phb) synthases: characterization of the functional residues in chromatium vinosum phb synthase". biochemistry, vol. 39 pp. 3927-3936, 2000. [86] bha rehm, rv antonio, p spiekermann, aa amara and a steinbüchel "molecular characterization of the poly(3-hydroxybutyrate) (phb) synthase from ralstonia eutropha: in vitro evolution, site-specific mutagenesis and development of a phb synthase protein model". biochim. biophys. acta vol. 1594 pp. 178-190, 2002. [87] aa amara and bha rehm "replacement of the catalytic nucleophile cysteine-296 by serine in class ii polyhydroxyalkanoate synthase from pseudomonas aeruginosa-mediated synthesis of a new polyester: identification of catalytic residues". biochem. j. vol. 1; 374(pt 2): pp. 413-21, 2003. [88] u müh, k snell, e troyano, j wodzinska, aj sinskey and j stubbe "in: ‘’biochemical principles and mechanism of biosynthesis and biodegradation of polymers’’, an international symposium, abstract book, lecture 6, münster, germany. 1998. iium engineering journal, vol. x, no. x, 200x amara and moawad 36 [89] a hoppensack, bha rehm and a steinbüchel "analysis of 4-phosphopantetheinylation of polyhydroxybutyrate synthase from ralstonia eutropha: generation of β-alanine auxotrophic tn5 mutants and cloning of the pand gene region". j. bacteriol. vol. 181 pp. 1429-1435, 1999. [90] gj mccool and mc cannon "phac and phar are required for polyhydroxyalkanoic acid synthase activity in bacillus megaterium". j. bacteriol. vol. 183 pp. 4235-4243, 2001. [91] t saito, k suzuki, j yamamoto, t fukui, k miwa, k tomita, s nakauishi, s odani, ji suzuki and k ishikawa "cloning, nucleotide sequence, and expression in escherichia coli of the gene for poly(3-hydroxybutyrate) depolymerase from alcaligenes faecalis". j. bacteriol. vol. 171 pp. 184-189, 1989. [92] b klingbei, rm kroppenstedt, and d jendrossek, "taxonomic identification of streptomyces exfoliates k10 and characterization of its poly(3-hydroxybutyrate) depolymerase gene". fems microbiol. lett., vol. 142(2-3) pp. 215-221, 1996. [93] a schirmer, matz c and jendrossek d "substrate specificities of pha-degrading bactria and active site studies on the extracellular poly(3-hydroxyactonoic acid) p(3ho)] depolymerise of pseudomonas fluorescens gk13 biovar v". appl. environ. microbiol., vol. 59 pp. 1220-1227, 1995. [94] h saegusa, m shiraki, c kanai and t saito "cloning of an intracellular poly[d(-)-3hydroxybutyrate] depolymerase gene from ralstonia eutropha h16 and characterization of the gene product". j. bacteriol., vol. 183 pp. 94-100, 2001. [95] h saegusa, m shiraki and t saito "cloning of an intracellular d(-)-3-hydroxybutyrateoligomer hydrolase gene from ralstonia eutropha h16 and identification of the active site serine residue by site-directed mutagenesis". j. biosci. bioeng., vol. 94 pp. 106-112, 2002. [96] t kobayashi, m shiraki, t abe, a sugiyama and t saito "purification and properties of an intracellular 3-hydroxybutyrate-oligomer hydrolase (phaz2) in ralstonia eutropha h16 and its identification as a novel intracellular poly(3-hydroxybutyrate) depolymerase". j. bacteriol., vol. 185 pp. 3485-3490, 2003. [97] gm york, j stubbe and aj sinskey "the ralstonia eutropha phar protein couples synthesis of the phap phasin to the presence of polyhydroxybutyrate in cells and promotes polyhydroxybutyrate production". j. bacteriol. vol. 184 pp. 59–66, 2002. [98] tm scherer, fuller, s goodwin and rw lenz "enzymatic hydrolysis of oligomeric models of polyrc 3-hydroxybutyrate". biomacromolecules , vol. 1 pp. 577-583, 2000. [99] p gruchulski, f bouthillier, rj kazlauskas, an serreqi, jd schrag, e ziomek and m cygler "analogs of reaction intermediates identify a unique substrate binding site in candida rugosa lipase". biochemistry, vol. 33 pp. 3494-3500, 1994. [100] ke jaeger a steinbuchel and d jendrossek "substrate specificities of bacterial polyhydroxyalkanoate depolymerases and lipases: bacterial lipases hydrolyze poly(omegahydroxyalkanoates) ". appl. environ. microbiol., vol. 61(8) pp. 3113-3118, 1995. [101] sr salem, hma soliman. and aa. amara "polymer-strips a method for characterization of phb depolymerase activity in alcaligenes xylosoxidans subsp. denitrificans and citrobacter sp". new j. of egyptian microbiology. vol. 16 pp. 191-200, 2007. [102] aa amara and rs salem "characterization of pha depolymerase in phenol degrading bacteria". international j. of biotechnol. biochemi. vol. 3: pp. 69-81, 2007 [103] j ihssen, d magnani, l tho�ny-meyer, q ren "use of extracellular medium chain length polyhydroxyalkanoate depolymerase for targeted binding of proteins to artificial poly[(3-hydroxyoctanoate)-co-(3-hydroxyhexanoate)] granules". biomacromolecules. vol.10, issue: 7, pp. 1854-1864, 2009. [104] s taguchi, a maehara, k takase, m nakahara, h nakamura and y doi "analysis of mutational effects of a polyhydroxybutyrate (phb) polymerase on bacterial phb accumulation using an in vivo assay system". fems microbiol. lett., vol. 198 pp. 65-71, 2001. [105] s taguchi, h nakamura, t hiraishi, i yamato and y doi "in vitro evolution of a polyhydroxybutyrate synthase by intragenic suppression-type mutagenesis". j. biochem., (tokyo), vol. 131(6) pp. 801-806, 2002. iium engineering journal, vol. x, no. x, 200x amara and moawad 37 [106] f hu, y cao, f xiao, j zhang, h li "site-directed mutagenesis of aeromonas hydrophila enoyl coenzyme a hydratase enhancing 3-hydroxyhexanoate fractions of poly(3hydroxybutyrate-co-3-hydroxyhexanoate) ". curr microbiol. vol. 55(1) pp. 20-24, 2007. [107] k matsumoto, k takase, y yamamoto, y doi and s taguchi "chimeric enzyme composed of polyhydroxyalkanoate (pha) synthases from c. necator and aeromonas caviae enhances production of phas in recombinant escherichia coli". biomacromolecules. vol. 10(4) pp. 682-5, 2009. [108] n hoffmann, aa amara, brb beermann, q qi, hj hinz and bha rehm "biochemical characterization of the pseudomonas putida 3-hydroxyacyl acp:coa transacylase which diverts intermediates of fatty acid de novo biosynthesis". j. biol. chem. vol. 277 pp. 4292642936, 2002. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 investigation of multi-zone models for spark ignition engine fueled with ethanol olatunde bilikis olanrewaju1*, dare adebukola ademola2, ismail olawale saheed2, shote adeola suhud1, alamu oguntola jelili3 and sulaiman adedoyin musediq1 1 department of mechanical engineering, olabisi onabanjo university ago iwoye, nigeria 2 department of mechanical engineering, university of ibadan, nigeria 3 department of mechanical engineering, osun state university, nigeria * corresponding author: olatunde.bilikis@oouagoiwoye.edu.ng (received: 12th june 2020; accepted: 19th january 2021; published on-line: 4th july 2021) abstract: this research is aimed at investigating the effect of using ethanol (e100) in multi-zone model analysis consisting of multi-combustion chamber zoning cases. the first case considered is a three-zone model that has an unburned zone, burned zone, and transitory zone. the second case model is also three-zone, consisting of an unburned zone and two partitioned burned zones. the burned zone was imagined partitioned into burned zone-1 and burned zone-2 under uneven fuel distribution having different equivalent ratios. the third case is a four-zone model including two regions of burned zone, an unburned zone and a transitory zone, which is unburned burned zone containing a mixture of unburned and burned gases. arbitrary constants for each of the unburned (cc1) and burned (cc2) zone leakages in the unburned burned zone are 0.00025, 0.0005, 0.001, 0.002, 0.005, 0.1 and 0.5. the mass fraction burned (mfb) for zone-1, x1 and burned zone-2, x2 are computed using partitioned burnt zones ratios (pbzr) of 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 and 8:2. two equivalent ratios, one for each fuel mfb (ф1, ф2), (0.8, 0.6) and (0.6, 0.8) are analyzed using fuel blends of varying percentage. a comparison of values of the three zoning cases is done using peak values from the threezone models to evaluate the four-zone model. the model was compared with a spark ignition engine (sie) operating with a premium motor spirit (pms) serving as baseline. the engine operating conditions were set at an engine speed of 2000 rpm, -35btdc ignition time, and burn duration at 60 oc. the indicated mean effective pressure (imep), thermal efficiency (η), cylinder pressure and emission fraction from the developed models and those of two-zone analysis obtained agreed with literature values. the result showed it is undesirable to have a high volume of burned charge as infiltrate. the threezone segmented model predicted the highest engine thermal efficiency and peak pressure at mass burn ratio of 7:3. a general reduction in n2 emission was observed for the threezone transitional and four-zone models. abstrak: kajian ini menilai kesan etanol (e100) dalam analisis model zon-berbilang yang terdapat pada masalah pengezonan kebuk pembakaran-berbilang. kes pertama yang diambil kira adalah model tiga-zon yang mempunyai zon tidak terbakar, zon terbakar dan zon peralihan. model kedua merupakan juga tiga-zon yang terdiri daripada zon tidak-terbakar dan dua zon bahagian yang terbakar. zon yang terbakar dibahagikan kepada zon-1 terbakar dan zon-2 terbakar di bawah kebakaran tidak sekata yang mempunyai nisbah berlainan. kes ketiga adalah model zon-keempat termasuk dua kawasan zon terbakar, zon tidak-terbakar dan zon peralihan iaitu zon terbakar tidakterbakar di mana ia adalah campuran gas terbakar dan tidak-terbakar. tetapan sebarangan bagi setiap zon kebocoran tidak-terbakar (cc1) dan terbakar (cc2) dalam zon terbakar tidak-terbakar adalah 0.00025, 0.0005, 0.001, 0.002, 0.005, 0.1 dan 0.5. 339 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 pecahan jisim terbakar (mfb) bagi zon-1, x1 dan zon-2 terbakar, x2 dikira menggunakan nisbah zon bahagian terbakar (pbzr) sebanyak 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 dan 8:2. nisbah dua persamaan, setiap satu bahan api mfb adalah (ф1, ф2), (0.8, 0.6) dan (0.6, 0.8) dan diuji menggunakan pelbagai peratus bahan api campuran. nilai perbandingan bagi tiga kes zon dibuat menggunakan nilai puncak dari model tiga-zon bagi menilai model empat-zon. model ini dibandingkan dengan enjin cucuhan bunga api (sie) beroperasi dengan motor alkohol premium (pms) sebagai garis asas. keadaan operasi enjin adalah dihadkan pada 2000 rpm kelajuan enjin, masa pencucuhan -35btdc dan tempoh pembakaran pada 60 oc. tekanan berkesan min tertunjuk (imep), kecekapan haba tertunjuk (η), tekanan silinder dan pecahan pengeluaran dari model yang dibangunkan dan analisis dua-zon yang terhasil adalah sama dengan nilai literatur. dapatan kajian menunjukkan cas terbakar pada isipadu yang banyak adalah tidak diingini sebagai penyerap. model tiga bahagian zon menunjukkan kecekapan haba enjin tertinggi dan tekanan puncak pada jisim bakar dengan nisbah 7:3. manakala, pengurangan umum telah diperhatikan pada pengeluaran n2 di peralihan tiga-zon dan model empat zon. keywords: ethanol; multi-zone; indicated mean effective pressure; emission fraction 1. introduction modification and optimization of combustion chamber geometry has been seen as the end game in achieving stringent emission reduction and better engine performance with several researches conducted and some ongoing. researchers have reported the importance of engine combustion chamber modification and its ability to resolve complications arising from adopting some other methods of engine optimization [1-2]. efforts at combustion chamber modification by [3] was aimed at correcting the lean burn effect, the design modification was carried out for two compression ratios 10 and 11 which necessitated variation in piston bowl size from 16mm to 13.6mm. increased compression ratio from 10 to 11 was reported to have resulted in leaner combustion but adversely higher combustion duration and coefficient of variance necessitating development of a new combustion chamber design. the modified combustion bowl by [3] has six leaves placed eccentrically to create the desired swirl breakup with a cutout for the inlet and exhaust valve seats. the difference in diameter between the inner and outer bowl was reduced to improve flame propagation and strengthen squish effect. more researches on modification of the combustion chamber for the purpose of promoting faster burning of charge in a lean burn engine by using the swirl and squish principles was carried out by [2] and [4]. a chamber modification similar to the one described by [3] is the nebula chamber, employed to retard the swirl motion close to tdc. the nebula combustion chamber used by [5] is such that the bowl shape forces the swirl to develop into colliding air flows thereby creating the desired great turbulence and fast burn effect. [6] went a step further by implementing the squish, nebula, and another named tokyo gas, tg with similar purpose as the nebula but different in that the tg was described as having “a cylindrical dent with semi-circular slants oppositely shaped”. the resulting effect of the tg is large turbulence at the cylinder wall and weak turbulence in the center of the cylinder to stabilize flame ignition. the nebula, tg and squish were reported to have achieved nox reduction, increased thermal efficiency and stable combustion. [7-8], adopted ten different combustion chamber geometries in studying the effect of chamber geometry on flow, combustion, and emissions. of all the geometries studied by [7-8], the cylindrical and square bowl gave the expected turbulence. however, the cylindrical bowl has desired outcome of its peak turbulence close to tdc. the 340 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 experiment further confirmed that combustion chamber shape has an effect on flow field, heat release rates, and emission rate. use of simulation model has been proven to be a cost effective and efficient way of optimizing engine performance and emissions. in [9], three different approaches for combustion modeling in si engines were identified, while the multi-zone approach to engine modeling seemed the cheapest, fastest and yet efficient modeling method [10]. in their study, [10] concluded the use of additional zone lead to increased heat release prediction. furthermore, [11] observed increased engine performance using a three-zone model for predicting the effect of ethanol with diesel fuel. several researches have been carried out on the use of a modeling approach for optimization of combustion processes. additionally, there are still continuous environmental challenges that need to be addressed. this desire has necessitated the need for further study. the attention received by ethanol as an alternative fuel is said to be due to its role in reducing problems such as climate change, depleting fossil oil and high oil prices in the international market. alcohols like ethanol can be produced by fermentation of different biological feedstocks as reported by [12-13]. the most positive properties of ethanol include its ability to be produced from renewable energy sources, its high-octane number, and its high laminar flame speed [14]. the negative aspects include its low heating value due to higher oxygen content compared to gasoline, and it causes corrosion in the metal and rubber parts of an engine [15]. the engine power improves with ethanol as it has better anti-knock characteristics qualities [16]. the engine power also improves with an increase in compression ratio [17]. ethanol has a high latent heat of vaporization, the latent heat cools the intake air and hence, increases the density and volumetric efficiency [18]. the lower heating value of ethanol enables it to have a higher compression ratio as compared to gasoline [19]. it is desirable for si engine to have high octane and low cetane numbers. this implies higher resistance to self-ignition and lower auto-ignition possibility. ethanol can be used as a fuel in spark ignition engines either in pure form (e100) or blended with premium motor spirit (pms). the use of pure ethanol implies some problems during cold start due to lower vaporization compared to gasoline, which in some cases should require an electrical preheating of the engine block. the use of ethanol in conventional spark ignition engines comes with the problem of corrosion [20]. one of the problems is tackled by the invention of flexible fuel vehicles (ffvs) which implies that the fuel system is made using stainless steel, with some rubber parts replaced by nylon, fluorinated plastics, and high-density polyethylene [21,22]. the lower heating value (lhv) of ethanol requires an alteration of the injection control to increase the fuel flow [23]. therefore, only a limited percentage of ethanol, up to 10-25%, is recommended for use in conventional gasoline engines [24]. however, ffvs designed to operate with any gasoline-ethanol mixtures are increasing. the advantage of ffv systems consists of the possibility offered by the control system of the engine to detect the concentration of ethanol in the tank and automatically optimize both injection and ignition [14,25]. according to [21], car manufacturers are capable of making vehicles compatible with hydrated ethanol, e100, at no additional cost. however, some investigation has pointed to the presence of ethanol in higher concentration as the cause of volatile organic matter (voc) emission in the form of benzene [26]. the point line remains that there is more to be discovered for proper evaluation and optimization of ethanol and ethanol-blended fuel usage. numerous researches [18,27-29], have been carried out concerning the use of ethanol blends in si engines, but very few uses of 85-100% ethanol have been documented [21]. [30] investigated the effect of varying ethanol-gasoline blends up to 85% and compared the combustion of gasoline and gasoline-ethanol blends through pressure 341 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 analysis. an increase in engine efficiency was observed, coupled with co2 emission reduction when ethanol blends were used. this study is aimed at investigating the effect of 100% ethanol, e100 on engine performance using a thermodynamic multi-zone model approach. 2. general methodology to investigate the combustion process, three multi-zone models were developed, each with peculiar characteristics to study effects of additional zone(s) on spark ignition engine combustion characteristics using ethanol as fuel. the model geometry developed by the authors and adopted in this work was the same used by [31,32], where a zero-dimensional, multi-zone model was investigated. the developed models are validated making use of the model developed by [33], primarily for the two-zone model si engine using gasoline. in the analysis for the first multi-zone model, which is a three-zone model consisting of the primary burned and unburned zones in addition to a mixed zone described as the transitory zone, the mass infiltration from either of the primary zones, directly into the transitory zone is given in terms of constants of infiltration as shown in eq. 1. mub= cc1* mu and mbu= cc2* mb (1) where cc1 and cc2 are the arbitrary constants of infiltration from burned and unburned zones respectively. the second multi-zone case has its burned zone partitioned in two, the mass of the burned zone is imagined partitioned into burned zone-1 and burned zone-2 as the proportion of the mixture is uneven in the chamber and therefore, has different mass burning rates (x1, x2). the coefficients of heat transfer are predetermined to be (h400, h450, h500), the mass fraction burned, is represented analytically as shown in eq. 2 [34]. 𝑥 = 0.5 ∗ (1 − cos⁡(𝑝𝑖 ∗ (𝜃−𝜃𝑠) 𝜃𝑏 )), (2) where, x is mass fraction burned, θ, 𝜃s, 𝜃b are the crank angle, the start of energy release and duration of energy release respectively. peak results of the two analyses of mass fraction and mass infiltration burned are employed for analysis in the third multi-zone case as a four-zone model. the indices of performance, thermal efficiency (η), indicated mean effective pressure (imep) and emission fractions obtained using the developed models are compared with the standard two-zone model. the engine geometry for the model adopted for validating the developed model codes is shown in table 1 and all are compared with the experimental data; cfd results obtained by [35] for the first multi-zone case and a fourstroke sie (ef7) running on cng [36] for the second multi-zone case. 2.1 development of mathematical models the first law of thermodynamics is applied to all the zones to develop the model equations. in an open system, the rate of change of mass is equal to the net flux of mass across the boundaries of the system. this is expressed by eq. 3. 𝑚 = ∑ 𝑚𝑘⁡⁡̇𝑘 (3) the mass flux of the control volume can be expressed as the addition of all unit zones as shown in eqs. 4-6. 𝑚 = 𝑚𝑢 + 𝑚𝑏 + 𝑚𝑢𝑛 (for first case) (4) 𝑚 = 𝑚𝑢 + 𝑚𝑏1 + 𝑚𝑏2 (for the second case) (5) 342 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 𝑚 = 𝑚𝑢 + 𝑚𝑏1 + 𝑚𝑏2 + 𝑚𝑢𝑛 (for the third case) (6) from the first law of thermodynamics, the energy equation of an open system is expressed as eq. 7. �̇� = ∑�̇�ℎ − ẇ̇ + �̇� (7) equation 7 is therefore applied to expansion, compression, and combustion phases of the internal combustion (ice) cycle. the model equations analysed in a computation environment are as shown in eqs. 8 10 for the three modeled cases considered. detailed mathematical derivation of these equations can be found in [31,32]. sub-models including, air and fuel data, engine geometry inherent in the two-zone model [33] are also employed to analyze the present models. table 1: engine specifications for validating modeled cases 2.1.1 model equation for the first case studied 𝑑𝑃 𝑑𝜃 = { 𝑉𝑢 𝑇𝑢 𝑑𝑇𝑢 𝑑𝜃 + 𝑉𝑏 𝑇𝑏 𝑑𝑇𝑏 𝑑𝜃 + 𝑉𝑢𝑛 𝑇𝑢𝑛 𝑑𝑇𝑢𝑛 𝑑𝜃 + (𝑣𝑏 − 𝑣𝑢) 𝑑𝑚𝑥1 𝑑𝜃 + (𝑣𝑢𝑛 − 𝑣𝑢) 𝑑𝑚𝑢𝑏 𝑑𝜃 + (𝑣𝑢𝑛 − 𝑣𝑏) 𝑑𝑚𝑏𝑢 𝑑𝜃 − 𝑣𝑢 𝑑𝑚𝑙𝑢 𝑑𝜃 − 𝑣𝑏 𝑑𝑚𝑙𝑏 𝑑𝜃 − 𝑣𝑢𝑛 𝑑𝑚𝑙𝑢𝑛 𝑑𝜃 − 𝑑𝑉 𝑑𝜃 }/ 𝑉 𝑃 (8) 2.1.2 model equation for second case studied 𝑑𝑃 𝑑𝜃 = { 𝑉𝑢 𝑇𝑢 𝑑𝑇𝑢 𝑑𝜃 + 𝑉𝑏 𝑇𝑏 𝑑𝑇𝑏 𝑑𝜃 + 𝑉𝑏2 𝑇𝑏2 𝑑𝑇𝑏2 𝑑𝜃 + (𝑣𝑏 − 𝑣𝑢) 𝑑𝑚𝑥1 𝑑𝜃 + (𝑣𝑏2 − 𝑣𝑢) 𝑑𝑚𝑥2 𝑑𝜃 − 𝑣𝑢 𝑑𝑚𝑙𝑢 𝑑𝜃 − 𝑣𝑏 𝑑𝑚𝑙𝑏 𝑑𝜃 − 𝑣𝑏2 𝑑𝑚𝑙𝑏2 𝑑𝜃 − 𝑑𝑉 𝑑𝜃 }/ 𝑉 𝑃 (9) 2.1.3 model equation for third case studied 𝑑𝑃 𝑑𝜃 = { 𝑉𝑢 𝑇𝑢 𝑑𝑇𝑢 𝑑𝜃 + 𝑉𝑏 𝑇𝑏 𝑑𝑇𝑏 𝑑𝜃 + 𝑉𝑏2 𝑇𝑏2 𝑑𝑇𝑏2 𝑑𝜃 + 𝑉𝑢𝑛 𝑇𝑢𝑛 𝑑𝑇𝑢𝑛 𝑑𝜃 + (𝑣𝑏 − 𝑣𝑢) 𝑑𝑚𝑥1 𝑑𝜃 + (𝑣𝑏2 − 𝑣𝑢) 𝑑𝑚𝑥2 𝑑𝜃 + (𝑣𝑢𝑛 − 𝑣𝑢) 𝑑𝑚𝑢𝑏 𝑑𝜃 + (𝑣𝑢𝑛 − 𝑣𝑏) 𝑑𝑚𝑏𝑢 𝑑𝜃 ⁡+ (𝑣𝑢𝑛 − 𝑣𝑏2) 𝑑𝑚𝑏2 𝑑𝜃 − 𝑣𝑢 𝑑𝑚𝑙𝑢 𝑑𝜃 − 𝑣𝑏 𝑑𝑚𝑙𝑏 𝑑𝜃 − 𝑣𝑏2 𝑑𝑚𝑙𝑏2 𝑑𝜃 − 𝑣𝑢𝑛 𝑑𝑚𝑙𝑢𝑛 𝑑𝜃 − 𝑑𝑉 𝑑𝜃 }/ 𝑉 𝑃 ⁡⁡⁡⁡⁡⁡⁡ (10) parameter first case model evaluation [35] 2-zone model [33] second case model evaluation [36] number of cylinder 4 4 4 bore (m) 0.079 0.1 0.085 stroke (m) 0.086 0.08 0.078 compression ratio 16 10 11 displacement (m) 1.7 1.018 inlet valve close 136btdc exhaust valve open 122atdc equivalence ratio 0.8 burn duration angle 60 start of combustion -35 21 end of combustion 30 engine speed (rpm) 1500 1500 2000 343 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 3. model implementation 3.1 transitional model relevant sub-programs such as the air and fuel were implemented for the two-zone model. integration of the governing equations developed using ode45 in matlab code is used to obtain the temperature and pressure distribution for various phases in si engine operation using ethanol for the computation. implementation of the transitional three-zone model is done using selected values of infiltration in the developed code following the steps below; • implementing input parameters (available in engine.m) • cylinder volume and mass are evaluated • determination of relevant thermophysical properties such as u, h, cp, etc. • mass fraction burned is evaluated • heat transfer coefficient is selected using either constant estimated values or woschni equation • inputing selected constants for cc1 and cc2 using additional program • computing the required governing equations. the model employs the parameters of an ice with combustion and operating parameters details as stated in table 1. 3.2 segmented model the mass burned zone is imagined partitioned into burned zone-1 and burned zone-2 since there is a proportion that is unevenly mixed in the chamber and therefore they have different mass burning rates (x1, x2) and heat transfer coefficients, (h400, h450, h500). mass fraction burned, denoted by x, while, θ, 𝜃s, 𝜃b are the crank angle, start of energy release and duration of energy release respectively. these parameters are represented analytically and the equation solved is also presented in eq. 2. 3.3 transitional-segmented model in this model, special consideration is given to mass infiltration into the transitory zone and mass fraction ratio such that predetermined optimal results are analyzed for the third case (four-zone model). 4. results and discussion 4.1 transitional model (first case model) figure 1 shows the thermal efficiency (ƞ), temperature, pressure, and indicated mean effective pressure (mpa) at varying cc1 while the value of cc2 (unburnt) is kept constant at 0.001 and at varying cc2 while the value of cc1 (burnt) is kept constant at 0.001 are shown in fig. 1. highest ƞ, pressure and imep are observed at the least infiltration constant of 0.00025, values of all properties decreased as the infiltration constant increased, an evidenced in the sharp decrease observed from infiltration constant 0.005 to 0.1 for pressure, imep and ƞ. it can be deduced that for the varying cc1, the least infiltration constant from burnt region to the mixed region of unburnt burned is favorable for all performance parameters and that a greater infiltration has adverse effect on the engine efficiency. generally, infiltration from the burned zone has greater effect on the 344 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 engine performance compared to infiltration from the unburned zone as steeper slopes of fig. 1 suggest for cc1 as compared to cc2. it is observed that the difference in variation witnessed for varying cc2 is not as steep as it was for varying cc1 as shown in fig.1 due to the positive implication of unburnt infiltration into the mixed region until optimum values of engine performance are observed and then a decrease in performance beyond this point is evident. it is also evident that slight backflow of burned charge will have noticeable adverse effect on engine performance while these effects are less noticeable and require a lot more unburned charge to infiltrate into the mixed zone to reduce engine performance. practically, infiltration in the combustion chamber could be inform of crevice flow and blowby, it is essential to have a limited amount of burned gas as backflow to avoid reduction in power and efficiency as mentioned by [37]. the observed peak pressure (in table 2) using e100 is 15.7% closer to the experimental data. however, when compared to the 2-zone model it is 16.4% closer to the experimental value. high imep and η are also observed for the e100 3-zone model. in fig. 2, concerning three-zone and two-zone models, there is no significant difference in the general emission patterns of co2, no, and o2. a reduction in values of n2 is observed for the three-zone model which could be attributed to higher oxygen content present in ethanol to react with the n2. fig. 1: 3-zone model for the fractional burnt and unburnt regions, (a) efficiency, (b) temperature, (c) pressure and (d) indicated mean effective pressure. table 2: comparison of 2-zone model, 3-zone model and experimental results 2-zone model experimental values 3-zone model with c1= 0.00025 and c2= 0.001 3-zone model at 0.005 3-zone model at optimal value of c1 = 0.00025 and c2 = 0.005 pressure (mpa) 4.4358e+06 5.30e+06 4.4680e+06 4.4668e+06 4.4651e+06 imep 9.1635e+05 9.5427e+05 9.5382e+05 9.5344e+05 η 0.3741 0.3917 0.3915 0.3914 0 0.1 0.2 0.3 0.4 0.5 0 0.1 0.2 0.3 0.4 0.5 ƞ leakage fraction cc1 (burnt) cc2 (unburnt) (a) 0.00e+00 1.50e+06 3.00e+06 4.50e+06 0 0.1 0.2 0.3 0.4 0.5 p re ss u re ( m p a ) leakage fraction cc1 (burnt) cc2 (unburnt) (c) 0.00e+00 3.00e+05 6.00e+05 9.00e+05 1.20e+06 0 0.1 0.2 0.3 0.4 0.5 im e p (m p a ) leakage fraction cc1 (burnt) cc2 (unburnt) (d) 1.75e+03 2.00e+03 2.25e+03 2.50e+03 0 0.1 0.2 0.3 0.4 0.5 t e m p ( k ) leakage fraction cc1 (burnt) cc2 (unburnt) (b) 345 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 fig. 2: emissions for the 2-zone and case-1 models using ethanol. 4.2 segmented model the η, temperature and imep history for varying segmented burned zones for e100 investigated are as shown in fig. 3 using varying heat transfer coefficient as seen in fig. 3 (a, b, c and d) for heat transfer coefficients, h = 400, 450, and 500, respectively. (a) (b) (c) (d) fig. 3: three-zone model values for the burned zone-1 and burned zone-2 using heat transfer coefficients 500 and 450 (a) efficiency, (b) temperature, (c) imep and (d) pressure. the maximum peak pressures in fig. 3(d) for h400, h450, h500 are 4.57 mpa, 4.55 mpa, 4.54 mpa, respectively are observed using 4:6, although the highest thermal efficiency and imep are observed at a mixture ratio of >7:3, h400 in fig. 3(a and c). expectedly, the engine temperature history increased as mass flow rate increased in fig. 3(b), however, the 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 e m is si o n ( p p m ) 3-zone 2-zone co2 n2 o2 no emissions 0.36 0.37 0.38 0.39 0.4 0.41 ƞ mixture ratio h-500 h-450 h-400 2:8 4:6 6:4 8:2 2.10e+03 2.18e+03 2.25e+03 2.33e+03 2.40e+03 te m p ( k ) mixture ratio h-500 h-450 h-400 2:8 4:6 6:4 8:2 8.75e+05 9.00e+05 9.25e+05 9.50e+05 9.75e+05 1.00e+06 im e p (m p a ) mixture ratio h-500 h-450 h-400 2:8 4:6 6:4 8:2 4.40e+06 4.45e+06 4.50e+06 4.55e+06 4.60e+06 p re ss u re (m p a ) mixture ratio h-500 h-450 h-400 2:8 4:6 6:4 8:2 346 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 peak temperature was observed towards the end of the burn flow. evidently, a partition in the burned mixture had an effect on the engine performance as an increase in engine performance is observed as the mixture ratio increased. it can be argued that a proper and sequential fair variation in mixture ratio to an optimal ratio can increase the engine performance while a decrease in engine performance is observed beyond the optimal value. it is also worthy of note that the sequence of the segment is important, as a ratio of 8:2 is greater compared to a ratio of 2:8. therefore, the flow and turbulence in the engine chamber requires uniformity to a certain degree and later a little variation or reduction in flow towards the end of the combustion process to stabilize flame ignition as described by [6]. 4.3 transitional-segmented model the readings from both analyses of mass fraction and mass infiltration burned from cases-1 and 2 respectively are used for the third case. this work has reported findings from combining the optimal results. table 3 presents the four-zone model results for pressure, imep, η and emission fractions analyzed from the optimal mass infiltration and mass fraction burned values. it was observed that there was a reduction in co2 and increased n2 emission fraction for the 4-zone model as compared to the other 3-zone models. experimental values, 2-zone, 3-zone, and 4-zone models are shown in table 4. from the table, higher pressure values observed for the 4-zone model is 3.9% closer to experimental results while that of the 2-zone model is 4.4% closer to the experimental results. table 3: 4-zone (third case) modelled using ethanol cc1 cc2 pe (mpa) temp (k) imep η co2 h2o n2 o2 no 0.00025 0.005 4.4651e+06 2.3134e+03 9.5344e+05 0.3914 0.1007 0.1511 0.7104 0.0377 0.0001 x1 x2 0.7 0.3 4.4893e+06 2.341e+03 9.7492e_05 0.4002 0.1007 0.1511 0.7104 0.0377 0.0001 case-3 values 4.4565e+06 2.3344e+03 9.4735e+05 0.3867 0.0983 0.1194 0.7428 0.0395 0.0001 table 4: showing comparison of results from 2 -zone model, three cases modeled and experimental results 2-zone model experimental values 3-zone model using x1 = 0.7 and x2 = 0.3 3-zone model using cc1 = 0.00025 and cc2 = 0.005 4-zone model using x1 = 0.7 and x2 = 0.3 (h400), cc1 = 0.00025 and cc2 = 0.005 pe 4.4358e+06 4.640e+06 4.4893e+06 4.4651e+06 4.4565e+06 tbe 2305k 2800k 2.3410e+03 2.3134e+03 2.3344e+03 imep 9.1635e+05 9.7492e+05 9.5344e+05 9.4735e+05 η 0.3741 0.4002 0.3914 0.3867 table 5 shows comparative analysis using ethanol e100 of the three-zone model involving mass infiltration at optimal values of cc1= 0.00025 and cc2 = 0.005, threezone model involving mass burn rate of x1 = 0.7 and x2 = 0.3 and a four-zone model labeled as case 3. emission history for the four-zone model, like the two-zone model, remains the lowest for all emission types. the highest peak pressure, imep, and η are observed at the three-zone case 2 model, and this is clearly shown in fig. 4. it could be concluded that the segmented three-zone model (3zc2) is better for peak in-cylinder pressure and engine efficiency analysis using ethanol, e100. in fig. 4(a-d), the three-zone 347 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 segmented model (3zc2) produces the best results in terms of efficiency, pressure, temperature and imep. table 5: comparison of 2-zone, 3-zones (case-1 and case-2) and 4-zone models (case-3) using ethanol, e100 pressure (mpa) temp (k) imep η emission characteristics co2 h2o n2 o2 no 2-zone model, 2z 4.4358e+06 2305k 9.1635e+05 0.3741 0.0983 0.1194 0.7428 0.0395 0.0001 first case, 3zc1 using cc1 = 0.00025 and cc2 = 0.005 4.4651e+06 2.3134e+03 9.5344e+05 0.3914 0.1007 0.1511 0.7104 0.0377 0.0001 second case, 3zc2 0.7 0.3 4.4893e+06 2.3410e+03 9.7492e+05 0.4002 0.1007 0.1511 0.7104 0.0377 0.0001 third case, 4z 4.4565+06 2.3344e+03 9.4735e+05 0.3867 0.0983 0.1194 0.7428 0.0395 0.0001 2z-2zone model, 3zc1-3zone case 1 model, 3zc23zone case 2 model, 4z4zone model fig. 4: temperature, indicated mean effective pressure (imep) and thermal efficiency (ȵ) for 2-zone model (2z), 3-zone transitory model (3zc1), 3-zone segmented model (3zc2) and 4-zone model (4z) using 100% ethanol fuel. 5. conclusions multi-zone models have been developed for analysis of combustion in spark ignition engines using ethanol as fuel. it is evident that inclusion of additional zones into the combustion chamber analysis and use of ethanol has increased the engine performance in terms of indicated mean effective pressure, thermal efficiency and emission rate. from the developed models and analysis, the following conclusions can be drawn: 4.41e+06 4.44e+06 4.47e+06 4.50e+06 p re ss u re ( p a ) 2z 3zc1 3zc2 4z (a) model 2.30e+03 2.31e+03 2.33e+03 2.34e+03 2.36e+03 te m p e ra tu re ( o c ) 2z 3zc1 3zc2 4z (b) model 9.00e+05 9.30e+05 9.60e+05 9.90e+05 im e p 2z 3zc1 3zc2 4z (c) model 3.50e-01 3.75e-01 4.00e-01 4.25e-01 ƞ 2z 3zc1 3zcz2 4z (d) model 348 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 1. the infiltration of charges in the combustion chamber should be limited for burned gases as found in the range of infiltration (0.0025, 0.005) that gave optimum values of engine performance for burned and unburned gases respectively. 2. homogenous flow; creating uniformity of charge flow of ratio 7:3 is encouraged for burned gases. 3. the three-zone segmented model was observed to give a better result of engine performance. 4. generally, engine zoning has significant effect on engine performance and every zone modelled is user-specific. further investigation is still required to properly mark out the effect of modification on specific engine parameters. 5. the use of ethanol in the internal combustion engine has given better results of engine performance with promising encouraging effect on emission fraction as compared to that of the gasoline standard. references [1] yan b, wang h, zheng z, qin y, yao m. (2018) the effect of combustion chamber geometry on in-cylinder flow and combustion process in a stoichiometric operation natural gas engine with egr. applied thermal engineering, 129: 199-211. [2] evans rl. (1992) combustion chamber design for a lean-burn si engine. sae transactions, 1611-1616. [3] wohlgemuth s, roesler s, wachtmeister g. (2014) piston design optimization for a twocylinder lean-burn natural gas engine-3d-cfd-simulation and test bed measurements (no. 2014-01-1326). sae technical paper. [4] evans rl, tippett ec. (1990) the effects of squish motion on the burn-rate and performance of a spark-ignition engine (no. 901533). sae technical paper. [5] jones mk, heaton dm. (1989) nebula combustion system for lean burn spark ignited gas engines (no. 890211). sae technical paper. [6] sakurai t, iko m, okamoto k, shoji f. (1993) basic research on combustion chambers for lean burn gas engines. sae transactions, 2240-2250. [7] johansson b, olsson k. (1995) combustion chambers for natural gas si engines part i: fluid flow and combustion. sae transactions, 374-385. [8] olsson k, johansson b. (1995) combustion chambers for natural gas si engines part 2: combustion and emissions. sae transactions, 499-511. [9] masoudi r, azad nl, mcphee j. (2014) parameter identification of a quasi-dimensional spark-ignition engine combustion model (no. 2014-01-0385). sae technical paper. [10] kaprielian l, demoulin m, cinnella p, daru v. (2013) multi-zone quasi-dimensional combustion models for spark-ignition engines (no. 2013-24-0025). sae technical paper. [11] juntarakod p, soontornchainacksaeng t. (2014) a quasi-dimensional three-zone combustion model of the diesel engine to calculate performances and emission using the diesel-ethanol dual fuel. eng. sci, 7(1): 19-37. [12] sánche ój, cardona ca. (2012) conceptual design of cost-effective and environmentallyfriendly configurations for fuel ethanol production from sugarcane by knowledge-based process synthesis. bioresource technology, 104: 305-314. [13] alamu oj, waheed ma, jekayinfa so. (2007) biodiesel production from nigerian palm kernel oil: effect of koh concentration on yield. energy for sustainable development, 11(3): 77-82. [14] gnansounou e, dauriat a. (2005) ethanol fuel from biomass: a review. csir, 64 (11): 809-821. http://hdl.handle.net/123456789/5372 349 http://hdl.handle.net/123456789/5372 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 [15] yücesu hs, sozen a, topgül t, arcaklioğlu e. (2007) comparative study of mathematical and experimental analysis of spark ignition engine performance used ethanol–gasoline blend fuel. applied thermal engineering, 27(2-3): 358-368. [16] ceviz ma, yüksel f. (2005) effects of ethanol–unleaded gasoline blends on cyclic variability and emissions in an si engine. applied thermal engineering, 25(5-6): 917-925. [17] verma ap, choube a. (2012) ethanol as alternative fuel for si engine a review. 4(14): 90-95. [18] srinivasan ca, saravanan cg. (2010) study of combustion characteristics of an si engine fuelled with ethanol and oxygenated fuel additives. journal of sustainable energy & environment, 1: 85-91. [19] taraba jl, turner gm, razor r. (1981) energy in agriculture: the use of ethanol as an unmixed fuel for lnternal combustion engines. aees, 14(8): 1-20 [20] park ij, yoo yh, kim jg, kwak dh, ji, ws. (2011) corrosion characteristics of aluminum alloy in bio-ethanol blended gasoline fuel: part 2. the effects of dissolved oxygen in the fuel. fuel, 90(2): 633-639. [21] larsen u, johansen t, schramm j. (2009) ethanol as a future fuel for road transportation: main research report. dtu mekanik, [22] yoo yh, park ij, kim jg, kwak dh, ji ws. (2011) corrosion characteristics of aluminum alloy in bio-ethanol blended gasoline fuel: part 1. the corrosion properties of aluminum alloy in high temperature fuels. fuel, 90(3): 1208-1214. [23] strong, rm. (1911). gasoline and alcohol tests on internal-combustion engines (no. bmbull-32). bureau of mines, washington, dc (usa). [24] bhetalu ad, patil ss, ingole nw. an overview ethanol as a motor fuel. journal of engineering research and studies, 3(2): 50-53. [25] bokhary ayf, alhazmy m, ahmad n, albahkali a. (2014) investigations on the utilization of ethanol-unleaded gasoline blends on si engine performance and exhaust gas emission. international journal of engineering & technology, 14(2): 88-96. [26] karavalakis g, durbin td, shrivastava m, zheng z, villela m, jung h. (2012) impacts of ethanol fuel level on emissions of regulated and unregulated pollutants from a fleet of gasoline light-duty vehicles. fuel, 93: 549-558. [27] yusaf t, buttsworth d, najafi g. (2009) theoretical and experimental investigation of si engine performance and exhaust emissions using ethanol-gasoline blended fuels. in 2009 3rd international conference on energy and environment (icee) (pp. 195-201). ieee. [28] kumar, j, trivedi, d, mahara, p, butola, r. (2013). performance study of ethanol blended gasoline fuel in spark ignition engine. journal of mechanical and civil engineering, 7(3): 71-78. [29] pai s, tasneem ha, rao a, shivaraju n, sreeprakash b. (2013) study of impact of ethanol blends on si engine performance and emission. national conference on challenges in research & technology in the coming decades cp648, pp 1-7. [30] de simio l, gambino m, iannaccone s. (2012) effect of ethanol content on thermal efficiency of a spark-ignition light-duty engine. international scholarly research network renewable energy, 2012(219703): 1-8. [31] dare aa, ismail os, olatunde ob. (2017) development of three-zone transitional model for reciprocating internal combustion engine analysis using gasoline. current journal of applied science and technology, 25(6): 1-11. [32] dare aa, olatunde ob. (2018) development of four-zone segmented transitional model for reciprocating internal combustion engine analysis using gasoline. american journal of science, engineering and technology, 3(2): 46-52. [33] buttsworth dr. (2002) spark ignition internal combustion engine modelling using matlab. faculty of engineering & surveying technical reports tr-2002-02: 1-41. [34] ferguson cr, kirkpatrick at. (2016) internal combustion engine. applied thermosciences. third edition. john wiley & sons, ltd. [35] kodavasal j, keum s, babajimopoulos a. (2011) an extended multi-zone combustion model for pci simulation. combustion theory and modelling, 15(6): 893-910. 350 iium engineering journal, vol. 22, no. 2, 2021 olatunde et al. https://doi.org/10.31436/iiumej.v22i2.1550 [36] asgari o, hannani sk, ebrahimi r. (2012) improvement and experimental validation of a multi-zone model for combustion and no emissions in cng fueled spark ignition engine. journal of mechanical science and technology, 26(4): 1205-1212. [37] heywood jb. (1988) internal combustion engine fundamentals. mcgraw hill, inc. new york series (11) pp.1 351 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 a fuzzy system for evaluating trustworthiness of users in a social network mohammad mahdi shafiei1, hossein shirgahi2*, homayun motameni1and behnam barzegar3 1 department of computer engineering, sari branch, islamic azad university, sari, iran 2 department of computer engineering, jouybar branch, islamic azad university, jouybar, iran 3 department of computer engineering, babol branch, islamic azad university, babol, iran * corresponding author: h.shirgahi@jouybariau.ac.ir (received: 16th november 2020; accepted: 18th february 2022; published on-line: 4th july 2022) abstract: in recent years, the emergence of various web-based social networks has led to the growth of social network users. these networks have become popular as a medium for disseminating information and communication. governments and organizations also use social networks as a platform for better services. however, acting in such networks depends on the level of trust that members have with each other. the combination of personality attributes of a person can create a mental impression of the amount of trust that a person has. this amount of trust can affect the person's future interactions. therefore, trust is an essential and important matter in these networks, especially when someone interacts with someone else on a web-based social network. we discuss this issue in this paper and provide a method for evaluating it. measuring the accuracy is not easy for the users who are interacting with the social network. here, the interactions are virtual. in this paper, we have used fuzzy logic to apply ambiguous data and to evaluate trustworthiness by taking into account the various personality attributes of users such as reliability, availability, interest, patience, and adaptability. as we used these attributes as input to the fuzzy system and based on the relevant fuzzy rules, we evaluated the trustworthiness of users in social networks. the proposed fuzzy system is extendable, because in this system, trust can be defined as a set of one or more personality attributes. epinions social network dataset is also used to simulate and validate the proposed approach. in the proposed method, the mae value is less than 0.015 and fscore value more than 0.86. based on the results, the presented fuzzy system shows an acceptable accuracy for evaluating the trustworthiness of users. abstrak: sejak beberapa tahun kebelakangan ini, kemunculan pelbagai rangkaian web sosial telah menyebabkan pertumbuhan pengguna rangkaian sosial. rangkaian ini telah menjadi popular sebagai medium penularan informasi dan komunikasi. kerajaan dan organisasi juga menggunakan rangkaian sosial sebagai platfom bagi menyediakan servis perkhidmatan terbaik. namun, pemakaian rangkaian ini bergantung kepada kepercayaan pengguna antara sesama pengguna. gabungan ciri-ciri personaliti terhadap seseorang menyebabkan terciptanya persepsi secara mental pada kepercayaan ke atas seseorang. jumlah kepercayaan ini akan memberi kesan terhadap interaksi yang akan berlaku pada masa depan ke atas individu tersebut. oleh itu, kepercayaan sangat penting dalam rangkaian ini, terutama apabila seseorang berinteraksi dengan mereka di jaringan sosial web. isu ini dibincangkan dalam kajian ini dan kaedah evaluasi turut dihuraikan. mengukur ketepatan pengguna dalam jaringan sosial tidak mudah. di sini, interaksi berlaku secara maya. kajian ini menggunakan logik kabur pada data tidak jelas dan bagi mengukur tahap kepercayaan, pelbagai ciri personaliti individu diukur, seperti kebolehpercayaan, kebolehdapatan, minat, kesabaran dan kebolehsesuian. ciri-ciri tersebut digunakan sebagai input kepada sistem rawak dan berdasarkan peraturan rawak, tahap kebolehpercayaan pengguna diukur dalam rangkaian 154 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 sosial. sistem rawak yang dicadangkan ini boleh dilanjutkan, kerana dalam sistem ini kepercayaan boleh dimaksudkan sebagai satu set atau lebih ciri-ciri personaliti. anggapan pada set data rangkaian sosial turut digunakan bagi simulasi dan pengesahan kaedah yang dicadangkan. bagi kaedah yang dicadangkan ini, nilai mae adalah kurang daripada 0.015 dan nilai skor-f lebih daripada 0.86. berdasarkan dapatan kajian ini, sistem rawak yang dikaji ini menunjukkan ketepatan yang boleh diterima bagi mengukur tahap kebolehpercayaan pengguna. keywords: social network; web-based social network; fuzzy logic; trust 1. introduction trust is a multifaceted concept that can be defined differently according to its application, so it is difficult to determine trust and it is possible to make a mistake. different domains have brought about different definitions concerning the concept of trust some of which are referred to below. in [1] and [2] psychologists, in their studies, concluded that trust focuses on the mindset of an individual when he trusts or distrust someone. in [3], trust in computer science generally divides into two parts: 1user, 2system. in [4], with respect to a transaction, trust was considered as a relationship between trustor (someone who trusts) and trustee (one who has been trusted). an analysis of [5] for trust in web-based social networks can be found on the basis of the belief that a person has some actions that will bring good results in the future. based on the definitions given above, this inference stems from different interpretations that may take place with respect to the place and application of the trust. in social networks, one of the topics where trust plays a vital role is the creation and maintenance of relationships, so that one can say that the basis of any relationship is trust. in web-based social networks, the amount of individual's trust comes from his virtual personality due to his interactions on the web and it can’t be compared with daily life as that is face to face. the virtual personality of a person depends on personality attributes that they have viewed virtually. some of the personality attributes that lead to the trustworthiness of users can be reliability, availability, interest, patience, and adaptability. the point that matters is that these attributes are internal and can be interpreted in a variety of ways, based on a definition that we provide about trust. in this research, we have proposed a method in which the trustworthiness of users can be evaluated depending on one or more personality characteristics. the rest of the paper is organized as follows. in section 2, social networks and related properties are expressed. section 3 discusses related works about trust in social networks. section 4 explains the fuzzy system proposed for evaluating trustworthiness. section 5 describes the evaluation of the proposed the fuzzy system and section 6 discusses the conclusion and future works. 2. social networks and trust management social networks can be specified as a set of nodes and edges that are systematic, so that the nodes describe users, groups, and communities and the edges describe communications. web-based social networks provide another way to communicate with others, affecting social relationships in the real world. it can be said that many of the relationships created in these networks, despite being virtual, are stronger than real-world relationships [6]. several definitions of a social network have been proposed in various domains. for example, [7] proposed a graph-based framework with the structure of a decentralized system. 155 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 2.1 social network properties in [8], properties of social networks have been discussed, including the phenomenon of homophily and the small world. homophily means the readiness of users to cooperate, to establish relationships and to make pledges with others. in [9], homophily is discussed in two types. the first type is status homophily, where users tend to associate with those who have similar social attributes with them, such as race, age, occupation, etc. the second type is value homophily, which is based on values, attitudes, and beliefs. this means that users tend to associate with the users who have similar thinking without considering their situation. the phenomenon of the small world visualizes the world as a “small world”, where all users are linked by a small chain. for example, users with similar interests are associated together with web-based social networks. 2.2 the importance of trust in social networks the growth of web-based social networks in online communities has become a major source of communication and can be seen from the popularity of social network sites such as facebook, youtube, instagram, and so on [6]. this popularity has been the impetus for the production and growth of many web-based social networks in specific communities. lots of social networks currently is use are designed to connect and interact with different users in different places [8]. in social networks, the concept of foaf (friend of a friend) has many uses. this concept suggests that someone can interact with a friend of friends and engage in friendship. given the fact that the trust is the basis of each friendship, trustworthiness may not be true for a friend of friends. for this reason, one of the risks is the security of private data on social networks, according to the concept of foaf. such risks have been experienced on social networking sites and are reported in [8, 20]. 2.3 trust management in social network in [11], trust management systems are classified into three categories: 1) credential and policy-based, 2) reputation based, and 3) social networks based. the main purpose of the first category, which is credential and policy-based, is validating the entity to enable access control. the second category, which is reputation based, builds trustworthy and secure communications by evaluating the reputation and popularity of the entity in the environment. the third category in trust management systems, which is based-on social networks in addition to considering the reputation, use social relationships among peers to establish the trusted relationships. 3. related works in [1], trust in social networks has been investigated. in [4], an approach was proposed to determine the quantitative content of the shared contents in terms of its trustworthiness. authors focused on determining trustworthiness of shared content in the health domain as the negative impact of acting on untrustworthy information is high in this domain. in [12], authors provided algorithms for inferring trust among individuals who are not familiar with or interact with each other. also, a way to extract information and integrate it into applications was investigated. the algorithms proposed for inferring trust depend on the reputation information. in [13], an algorithm called tidaltrust was proposed to infer trust. the algorithm described in [13] cannot be properly executed to determine the trustworthiness of the users based on the attributes provided. in [14], a system called powertrust was used to calculate peer-to-peer trust. the scalable system had a useful performance but could not be used to build trust in a social network. 156 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 in [15], a model for trust evaluation based on gravity was discussed. the proposed method was a two-step process. in the first stage, friendships and strengths were calculated, and in the second stage, the social neighbour was applied to calculate the trust. this model could not evaluate the trustworthiness of the users depending on their personality attributes. algorithms for calculating behavioural trust were proposed in [16]. the purpose of this paper was to quantify dual trust based on the observed communication pattern. these actions are statistically defined and do not use any semantic information contained in the messages. in [17], social trust was discussed. two algorithms were presented that access to implicit and explicit social trust. the proposed approach was more robust against manipulation attacks and had its applicability in fields like secure dtn routing. the approach was not directly applicable for evaluating trustworthiness of users in a social network. in [18], a model called strust was designed to create trusted societies in which members could share their information without worry. the model relied on social capital to derive trust value. in [19], trust management was discussed as it relates to internet applications. a notation for specifying trust and recommendation concepts was presented along with a set of tools for specifying, analyzing and monitoring trust relations. in [20], shirgahi et al. used parameters of social network authority, the value of pages’ links authority and semantic authority to assess the trust. in [21], the importance of the trust model was discussed based on user beliefs and credibility. the model is not applicable in the present form to evaluate trustworthiness of users in a web-based social network. the purpose pursued in [22] was the design of a fuzzy system. this trust model was used in distributed systems, but it could not predict the trust of users in social network. in [23], a genetic algorithm-based approach to inferring trust was introduced. the approach used heterogeneous relations for inferring trust. the algorithm achieved higher accuracy for trust values and was scalable and extensible, but it did not evaluate trustworthiness of users in a social network. the focus of [24] was on graphical representation for modelling trust relationships in multiagent e-commerce environments. the work was not applicable for evaluating trustworthiness of users in a web-based social network. in [25], a subjective logic to express distrust and to evaluate the trust probability distribution was suggested, but this method could only be used for the binary trust model. in [26], danesh and shirgahi provided a way to predict trust in a social network with structural similarities through the neural network. in this method, the web of trust data set was first converted to a structural similarity data set based on the similarity of the trustors and trustees. then, on the created data set, 70% of the data set was considered as the training data and it was trained based on the multilayer perceptron neural network. finally, the trained neural network was tested based on the test data. none of the above-mentioned models could evaluate users' trustworthiness based-on a set of personality attributes. in this research, an approach is adopted in which trustworthiness of users can be evaluated based-on a set of personality attributes. this approach supports an unlimited number of personality attributes that can be defined. in the next section, we will explain the proposed approach. 4. the proposed approach for evaluating trustworthiness a web-based social network can be implemented as a directed graph g (v, e) so that v is a set of nodes that denotes users and e is the set of edges that describe the interactions between these users. the number assigned to each edge from vi to vj (user i to user j), indicates the number of times the user i interacts with the user j. as an example, fig. 1 illustrates a simple example of this network. this figure consists of a directed graph and the nodes’ interactions with each other. the values on each edge represent the total number of interactions performed 157 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 by the user with the other users. it should be noted that in this figure, for example i1 is the same as individual1. fig. 1: web-based social network. interactions are different in nature and are based on the rate. the rate of the users interacting corresponds to various attributes. the rating depends on the experience and the feelings received by the users. rating values are processed using fuzzy logic to evaluate trustworthiness. the two most important criteria of graph that are used to evaluate trustworthiness of users are called in-degree and out-degree. the in-degree of a node points to the number of the other users interacting with the selected user, and out-degree of a node points to the number of the users that the selected user interacts with [6]. in other words, it can be said that in-degree node states that the selected user receives information about the other users, and out-degree node points to the fact that the selected user disseminates information on his personality attributes on the social network to the other users. low in-degree and out-degree nodes denote less interactivity, in other words receiving or disseminating less information; and high in-degree and out-degree nodes denote more interaction, that is receiving or disseminating more information. clearly, it is difficult for a user at low in-degree to directly determine the trustworthiness of others. the proposed approach requires that each participant (for example, a user) receives ratings of each entity’s different attributes with which he is interacting. a rating reflects experiences perceived by each entity about another one based on the attribute selected. each scale can be used to rate the attributes from -s to +s. that means, if s=2, then the scale is from -2 to +2. table 1 shows the rating scale for five personality attributes and their meanings. in this paper, we chose these five personality attributes based on our own mental perceptions and our studies. reliability expresses user ability to do something without failure. availability indicates that users are always available to interact with and support each other. interests include factors that make a user attractive. in fact, the more users’ interests are similar, the more they can trust each other. patience means that a patient user is able to tolerate setbacks, delays, or unexpected challenges without becoming anxious or angry. a patient user has a better mental health. adaptability is the emotional and current stability of social relationships. an adaptable user can quickly adapt to changes in plans. a user that is adaptable is associated with his various traits and characteristics. 158 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 table 1: five characteristics and their concepts it is important to note that the proposed method is general and does not depend on the number of attributes. that is, trustworthiness can be considered as a function of characteristics and this is because trust is a mental concept, and it takes different interpretations depending on the conditions and applications. however, to show the usability of the fuzzy system proposed through simulation, 5 attributes have been selected. trustworthiness is considered as a function of these 5 attributes. also, the proposed approach has no limitations on the scales used to rate the experiences for simulation. in general, each rating scale from -s to + s, where s> 0, can be used. an experiences record, in the form of rating various characteristics during different interactions, is maintained by the user about the other user he interacts with. with these experiences, the experience matrix can be formed. experiences with different parameters in various interactions are stored in the experience matrix. the experience matrix is used as an input to a fuzzy system to analyse the others’ trust. in evaluating the attributes of experience, consider that the user u1 interacts with the user u2 with n interaction. ecatt (u1, u2) as a set of experience consisting of n values that represent the feeling experience of the user u1 about the user u2 in n interactions according to attribute defined as follows. ecatt (u1, u2) = {expatt,1, expatt,2, …., expatt , n } as expatt, n is an experience feeling by the user u1 about the user u2 with respect to the att attribute in the nth interaction. ecatt values are recorded by each user for all the users they interact with. that way we can define whole expertise perceived through by user u1 for user u2 with respect to the att attribute, as ecatt (u1, u2) = mode (ecatt (u1, u2)) in it, ecatt (u1, u2) is the whole experience felt by the user u1 for the user u2 according to the att attribute and the mode (ecatt (u1, u2)) is the mode value of the ecatt (u1, u2) set. this process can be generalized to gain experience of the users about others due to various attributes. figure 2 is pseudo code that represents a procedure for calculating the experience of the users from the other users. low values in and out-degree between u1 and u2 provide less accuracy ecatt (u1, u2), while high values provide greater accuracy ecatt(u1,u2) results, while high values provide greater accuracy ecatt (u1, u2) results. 159 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 4.1 generating of matrix of experience(em) figure 2 shows the pseudo-code for calculating the experience matrix. for example, table 2 shows ratings for first user interaction with another user on the five characteristics. by the pseudo-code written in fig. 2, table 3 is obtained from table 2. from table 3, the matrix of experience is achieved that is shown in fig. 3. after the matrix of experience is obtained, depending on one or more characteristics, trust can be calculated. the user can pick the attributes. in fact, the user chooses the specific attributes according to his needs and understanding of trust. the fuzzy system we provided can be used to evaluate trust depending on one or more characteristics. here, it's important to note that choosing the attributes of trust may vary for each user. this standard of system enables a user to model trust based on his own understanding of what happens in the real world. fig. 2: pseudo-code for calculate expertise of the users. table 2: ranking for first user interaction with another user on the five characteristics users count of interaction attributes reliability availability interest patience adaptability u2 8 -1,-1,0,1,2,1,0,1 -2,-2,0,-1, -2,1,0,2 -1,1,0,-1,2,0,1, -1 -1,-2,-1,-2,1,2, -1,0 -2,-1,-1,0,1,-2, -2,-1 u3 6 2,1,1,2,1,2 1,2,2,1,1,1 1,1,0,2,1,0 -2,-2,1,1,0,-2 2,1,1,0,2,2 u4 5 1,2,0,2,1 0,1,2,2,2 -2,2,-2,1,0 -1,2,-1,0,1 1,1,1,2,1 u5 4 -1,-2,-1,-1 -2,-2,-2,-1 -2,-1,-1,-1 -1,-2,-2,-2 -1,-1,-2,-1 u6 9 1,0,0,1,1,0,1,0,0 0,1,1,1,0,1,0,1,1 1,0,0,1,0,0,1,1,0 1,0,0,-1,-1,0,1,-1,1 1,1,1,1,0,0,1,0,0 160 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 table 3: user 1’s ranking of five characteristics of the other users users attributes reliability availability interest patience adaptability u2 -1 -2 -1 -1 -2 u3 2 1 1 -2 2 u4 1 2 -2 -1 1 u5 -1 -2 -1 -2 -1 u6 0 1 0 -1 1 fig. 3: matrix of experience of user u1. 4.2 fuzzy system for trust evaluation of users fuzzy logic has been used to evaluate the trustworthiness based on a rating of 5 personality attributes that have been considered. we use fuzzy logic because there aren’t any exact boundaries for separating these interdependent attributes. according to the initial definition, a fuzzy system has three parameters which include inputs, fuzzy inference system and output. inputs and outputs are the same as the input and output data we want. the fuzzy inference system uses fuzzy rules to obtain the output. figure 4 illustrates our fuzzy system. fuzzy system inputs have five attributes: reliability, availability, interest, patience, and adaptability and the fuzzy system output is trustworthiness. the final values of the ranking of these attributes are obtained by the fuzzy rules that are defined. fig. 4: overview of fuzzy logic-based trust inference system. all five attributes that are our fuzzy system inputs have been rated in table 1. the histogram of the inputs and output variables is shown in fig. 5. also, in fig. 6, the fuzzy sets related to our input and output variables are also shown. 161 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 the most important part in fuzzy systems is their rules, they connect the conceptual relation of the input parameters to the output parameters. in this paper these rules are written according to the train datasets. figure 7 shows an illustration of the rules defined. in general, the 252 fuzzy rules that were used to simulate 5 attributes to gain trustworthiness are included. it is worth noting that any number of attributes can be considered, but as the number of attributes increases, the number of rules can increase exponentially, and as a result, the inference process of the fuzzy system becomes more complicated and the runtime is increased. fig. 5: histogram diagram of the input and output variables. figure 8 contains the rule viewer of a fuzzy system that executes related rules for specific entries and displays the defuzzification final output value. 5. evaluating the proposed approach to evaluate the proposed approach, we have used the epinions dataset, which is a social network dataset. in this way, we performed our own assessment on a part of the data set, including the first 2000 nodes and 77589 edges. one of the benefits of this dataset is that it is a real dataset and is widely used in research in the field of social networking. to simulate this approach, the matlab tool and mamdani fuzzy inference system are used to assess the trustworthiness of the users. during the simulation of the output of the fuzzy system, according to table 4, the trustworthiness was classified into 5 categories. 162 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 fig. 6: fuzzy sets related to our input and output variables. 163 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 fig. 7: illustration of the defined rules. fig. 8: rule viewer of fuzzy system. table 4: trustworthiness categories of users rating category trustworthiness -2 ever untrusty -1 often untrusty 0 no comment 1 often trusty 2 ever trusty for a more accurate evaluation of the fuzzy system, we have examined various types of fuzzy systems, which are presented in table 5. for the input and output variables, we used the trimf membership function. the overall structure of this function is given in eq. (1). 164 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 0, , ( ; , , ) , 0, x a x a a x b b a f x a b c c x b x c c b c x     −     − =   −    −     (1) as shown in table 5, the bases of fuzzy logic used min, prod methods in which the overall structure of the fuzzy reasoning methods are based on eqs. (2) and (3). a,a (a, b) b,a b b min           = (2) ( , ) *prod a b a b= (3) we used gravity centre (centroid), bisector, mom (mean of maximum) and som (smallest of maximum) methods for defuzzification, which are given in eqs. (4) to (6). centroid x × μ (x) dx i x = μ (x) dx i   (4) bisector bisector x β α μ (x) dx = μ (x) dxi ix  (5) ( ) ( )mom a, b = a+ b / 2 (6) table 5: features of the different fuzzy system defuzzification method aggregation implication method or method and method mf type fis type fis name centroid max min max min trimf mamdani fis 1 centroid max prod max prod trimf mamdani fis 2 centroid probor min probor min trimf mamdani fis 3 centroid probor prod probor prod trimf mamdani fis 4 bisector max min max min trimf mamdani fis 5 bisector max prod max prod trimf mamdani fis 6 bisector probor min probor min trimf mamdani fis 7 bisector probor prod probor prod trimf mamdani fis 8 mom max min max min trimf mamdani fis 9 mom max prod max prod trimf mamdani fis 10 mom probor min probor min trimf mamdani fis 11 mom probor prod probor prod trimf mamdani fis 12 som max min max min trimf mamdani fis 13 som max prod max prod trimf mamdani fis 14 som probor min probor min trimf mamdani fis 15 som probor prod probor prod trimf mamdani fis 16 165 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 5.1 parameters of fuzzy system performance evaluation after simulating the fuzzy system described in evaluating the proposed approach, to evaluate the performance of the different fuzzy systems, we considered 10% of the dataset to use as test data and examined the performance of fuzzy systems. for evaluating the fuzzy system performance from various measures including precision, recall, and f-score, we compared them with each other. how to calculate the precision, recall and f-score is noted in eqs. (7), (8), and (9), respectively. truepositive precision = ×100 (truepositive)+(falsepositive) (7) truepositive recall = ×100 (truepositive)+(falsenegative) (8) 2×recall×precission f-score = recall+precission (9) we also calculated the error obtained from the trustworthiness by different fuzzy systems in comparison with the trustworthiness in test data of the main dataset as mae's (mean absolute error), which is given in eq. (10). according to eq. (10), cti refers to the calculated value of trust, and rti is the real trust value, and n is the total number of test data. n |c -r |ti ti i=1 mae= n  (10) the numbers derived from the calculation of these measures and the error rate obtained on the test dataset in various fuzzy systems are given in table 6. table 6: calculation of these measures and the error rate in fuzzy systems fis name precision recall f-score error fis1 0.8222 0.9547 0.8835 0.0085 fis2 0.8222 0.9547 0.8835 0.0071 fis3 0.8222 0.9547 0.8835 0.0089 fis4 0.8222 0.9547 0.8835 0.0076 fis5 0.7991 0.9654 0.8744 0.0062 fis6 0.7991 0.9654 0.8744 0.0048 fis7 0.8222 0.9547 0.8835 0.0074 fis8 0.8222 0.9547 0.8835 0.0060 fis9 0.7991 0.9654 0.8744 0.0014 fis10 0.7991 0.9654 0.8744 0.0016 fis11 0.7991 0.9654 0.8744 0.0077 fis12 0.7991 0.9654 0.8744 0.0016 fis13 0.7991 0.9654 0.8744 0.0068 fis14 0.7991 0.9654 0.8744 0.0016 fis15 0.7991 0.9654 0.8744 0.0077 fis16 0.7991 0.9654 0.8744 0.0016 166 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 also, the comparison of precision measures for various fuzzy systems is in fig. 9. according to fig. 9 the best result belongs to fis1-4 and fis7-8 with 0.822. the comparison of the recall measures for various fuzzy systems is shown in fig. 10. the results of fig. 10 show that fis5-6 and fis9-16 have achieved the highest recall with 0.9655. the comparison of the f-score measure for various fuzzy systems is presented in fig. 11. according to fig. 11, fis1-4 and fis7-8 have achieved the highest f-score with 0.8835 and the comparison of the obtained error rate for various fuzzy systems is shown in fig. 12 which shows the results in fig. 9 have the lowest error mid with 0.0014. fig. 9: comparison of the precision measure for various fuzzy systems. fig. 10: comparison of the recall measure for various fuzzy systems. 167 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 fig. 11: comparison of the f-score measure for various fuzzy systems. fig. 12: comparison of the obtained error rate for various fuzzy systems. 6. conclusion in this paper, we proposed and discussed a fuzzy system for evaluating trustworthiness of the users based on personality attributes in a social network. in the proposed system, our method includes a ranking of 5 personality characteristics such as reliability, availability, interest, patience and adaptability when the users interact with each other. these ratings were analysed using the fuzzy system to obtain the trustworthiness of the users. a fuzzy trust inference system has been used because fuzzy systems have the ability to deal with imprecise and uncertain information. trust can be considered as a set of one or more personality characteristics. the proposed fuzzy system is extendable because in this system, trust can be defined as a set of one or more personality attributes. the attributes can also be expanded. the information extracted through the application of this proposed fuzzy system can be used in many issues related to social networks. according to the results, all considered fuzzy systems have error mid less than 0.015 and among the fis systems, fis9 has the lowest error mid with 0.0014. also, all considered fuzzy systems have an f-score greater than 0.86 and among fis systems, fis1-4 and fis7-8 have achieved the highest f-score with 0.8835. based on the results, the proposed fuzzy system shows an acceptable accuracy and it can be useful for evaluating the trustworthiness of users. 168 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 in future work, we can focus on developing and improving a set of fuzzy rules to make it more precise and accurate. the proposed approach can also be developed to be able to use more or different personality attributes as inputs of the fuzzy system. references [1] firdhous m, ghazali o, hassan s. (2012) trust management in cloud computing: a critical review. international journal on advances in ict for emerging regions, 4(2): 24-36. [2] mcknight h, chervany n. (2001) conceptualizing trust: a typology and e-commerce customer relationships model. proceedings of the 34th annual hawaii international conference on system sciences. [3] marsh sp. (1994) formalising trust as a computational concept. phd thesis. university of stirling. [4] moturu st, liu h. (2011) quantifying the trustworthiness of social media content. distributed and parallel data-bases, springer, 29(3): 239-260. [5] golbeck j, hendler j. (2006) inferring binary trust relationships in web-based social networks. acm transactions on internet technology, 6(4): 497-529. [6] singh s, sidhu j. (2016) an approach for determining trust-worthiness of individuals in a webbased social network. arabian journal for science and engineering, 41(2): 461-477. [7] zhang q, yu t, irwin k. (2004) a classification scheme for trust functions in reputation-based trust management, iswc'04 proceedings of the 2004 international conference on trust security and reputation on the semantic web, 127, pp 52-61. [8] sherchan w, nepal s, paris c. (2013) a survey of trust in social networks. acm computing surveys, 45(4): 1-33. [9] lazarsfeld p, merton r. (1954) friendship as a social process: a substantive and methodological analysis. in freedom and control in modern society, pp. 18-66. [10] young al, quan-haase a. (2009) information revelation and internet privacy concerns on social network sites: a case study of facebook. proceedings of the fourth international conference on communities and technologies, pp. 265-274. [11] suryanarayana g, taylor rn. (2004) a survey of trust management and resource discovery technologies in peer-to-peer applications. institute for software research university of california, irvine. [12] watts dj. (1999) small worlds: the dynamics of networks between order and randomness. princeton university press. [13] golbeck ja, hendler j. (2005) computing and applying trust in web-based social networks, (phd thesis). university of maryland. [14] zhou r, hwang k. (2007) power trust: a robust and scalable reputation system for trusted peerto-peer computing. ieee transactions on parallel and distributed systems,18(4): 460-473. [15] maheswaran m, tang hc, ghunaim a. (2007) towards a gravity based trust model for social networking systems. 27th international conference on distributed computing systems workshops, 24. [16] adali, s., escriva, r., goldberg, m.k., hayvanovych, m., magdon-ismail, m., szymanski, b.k., wallace, w.a., williams, g.t. (2010) measuring behavioral trust in social networks. 2010 ieee international conference on intelligence and security informatics, 150-152. [17] trifunovic s, legendre f, anastasiades c. (2010) social trust in opportunistic networks. infocom ieee conference on computer communication workshops, pp. 1-6. [18] nepal s, paris c, bista sk, wanita s. (2013) a trust model based analysis of social networks. international journal of trust management in computing and communications, 1(1): 3-22. [19] mohanapriya m, krishnamurthi i. (2014) trust based dsr routing protocol for mitigating cooperative black hole at-tacks in ad hoc networks. arabian journal for science and engineering, 39(3): 1825-1833. [20] shirgahi h, mohsenzadeh m, seyyed javadi hh. (2016) trust estimation of the semantic web using semantic web clustering. journal of experimental &theoretical artificial intelligence, 29(3): 537-556. 169 https://www.inderscienceonline.com/doi/abs/10.1504/ijtmcc.2013.052522 iium engineering journal, vol. 23, no. 2, 2022 shafiei et al. https://doi.org/10.31436/iiumej.v23i2.1697 [21] castelfranchi c, falcone r, pezzulo g. (2003) trust in information sources as a source for trust: a fuzzy approach. proceedings of the second international joint conference on autonomous agents and multiagent systems, pp. 89-96. [22] tajeddine a, kayssi a, chehab a, hassan a. (2006) patrol-fa comprehensive reputationbased trust model with fuzzy subsystems. international conference on autonomic and trusted computing, pp. 205-216. [23] akhoondi m, habibi j, sayyadi m. (2008) towards a model for inferring trust in heterogeneous social networks. in: second asia international conference on modeling and simulation, pp. 52– 58. [24] gan z, he j, ding q, varadharajan v. (2009) trust relationship modelling in e-commerce-based social network. in: international conference on computational intelligence and security, 1: 206210. [25] jøsang a, hayward r, pope s. (2006) trust network analysis with subjective logic. in proc. acsc, hobart, tas, australia. pp. 85-94. [26] danesh ah, shirgahi h. (2020). predicting trust in a social network based on structural similarities using a multi-layerd perceptron neural network. iium engineering journal, 22(1): 103-117. https://doi.org/10.31436/iiumej.v22i1.1622 170 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 surface roughness prediction in turning process by applying computer vision method omer wathiq taha1 and osamah fadhil abdulateef2* 1 al-mustafa university college, baghdad, iraq. 2 department of automated manufacturing engineering, university of baghdad, baghdad, iraq. * corresponding author: drosamah@kecbu.uobaghdad.edu.iq (received: 12th june 2020; accepted: 17th january 2021; published on-line: 4th july 2021) abstract: this paper reports the utilization of computer vision and backlight techniques to determine the surface roughness of a workpiece under a variety of process parameters. a ccd (charge-coupled device) camera was used to capture the image of the edge of the workpiece of the turned components using backlight technology to provide an edge roughness profile. the image was processed using srvision software developed in matlab to extract the profile of the workpiece and calculated the arithmetic average value of roughness (ra) and root mean square roughness (rq). the experiments are carried out with aisi 1045 (medium carbon steel), using various feed rates and cutting speeds, comparison is then made of the surface roughness values achieved through the conventional stylus probe method and the image processing technique. the comparison indicates that the vision method provides precise and consistent results with a correlation up to 0.99 with the traditional stylus method. the mean variations in ra and rq between the two methods were just 1.65 and 1.433 percent, respectively. as the vision method is a non-contact procedure, it can be significant potential for application without damaging the machined surfaces in the inprocess inspection of the components as well as aids monitoring of the components in a shorter period. abstrak: kajian ini menggunakan visual komputer dan teknik cahaya belakang bagi memperoleh kekasaran permukaan sesuatu bahan pada pelbagai proses parameter. kamera jenis ccd (peranti terganding-cas) telah digunakan bagi memperoleh imej tepi bagi komponen yang dipusing menggunakan teknologi cahaya belakang bagi menghasilkan profil imej tepi yang jelas. imej ini diproses menggunakan perisian srvision matlab bagi menghasilkan profil bahan dan purata kiraan kekasaran permukaan (ra) dan punca purata kuasa dua kekasaran permukaan (rq). eksperimen dijalankan menggunakan aisi 1045 (besi karbon pertengahan), menggunakan pelbagai kadar suapan dan kelajuan potongan. perbandingan kemudian dibuat pada nilai kekasaran permukaan yang diperoleh melalui kaedah prob jarum stilus konvensional dan melalui teknik pemprosesan imej. perbandingan menunjukkan kaedah visual memberikan ketepatan dan dapatan konsisten yang munasabah dengan korelasi sehingga 0.99 dengan kaedah prob jarum stilus tradisi. purata variasi pada nilai ra dan rq antara dua kaedah adalah sebanyak 1.65 dan 1.433 peratus, masing-masing. adapun kaedah visual adalah prosedur tanpa-sentuh, ianya sesuai dijalankan tanpa merosakkan permukaan mesin dalam proses penilaian komponen, juga membantu mengawasi komponen dalam waktu singkat. keywords: image process; roughness measurement; stylus method; non-contact method 249 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 1. introduction turning is a common machining process that removes material from a rotating cylindrical component using a single-point cutting tool. the turned component has a certain surface roughness that acts as a significant parameter in the performance of its work, much like friction, wear, lubrication, electrical and thermal resistance, fluid dynamics, vibration, and noise. different parameters such as feed rate, cutting speed, cutting depth, cutting tool configuration, machine tool, and material of the component all affect the performance of the required product feature and surface roughness values at an appropriate cost. roughness may be evaluated using two basic methods: contact and noncontact methods. the contact method utilizes a stylus, which is drawn across the measured surface. the surface waveform is collected through an electronic sensor, commonly a linear differential variable transformer, that calculates parameters of surface roughness, like root mean square roughness rq, average roughness ra, maximum peak-to-valley height rt, etc. the main disadvantages of the stylus device are that: (1) it requires direct physical contact, (2) it limits the measuring speed, (3) it cannot be used as an online measurement because the workpiece needs to be withdrawn from the machine for monitoring, and (4) it has restricted versatility in handling the specific geometric component to be measured [1]. non-contact methods may be divided into many categories based on the lighting system used and image analysis. several investigations were performed utilizing noncontact vision methods for the surface roughness assessment. lee et al. [1] employed computer vision techniques to predict a workpiece's surface roughness under many cutting operations. the workpiece surface image was first acquired with a digital camera, and then the surface image feature was extracted. a polynomial grid was implemented utilizing a self-organizing adaptive modeling method to create relations between the surface image characteristics and real roughness of the surface through various turning operations. gadelmawla [2] implemented a vision system to capture images for surfaces to be characterized and software was designed to investigate the captured images based on the “gray level co-occurrence matrix (glcm)”. 3d plots of the glcms for different captured images were implemented, compared, and discussed. also, several statistical parameters were calculated from the glcms and compared with the arithmetic average roughness, ra. al-kindi et al. [3] developed a technique for using computer vision data to achieve accurate measurement of surface roughness parameters. stylus-based measurements were obtained utilizing standard and non-standard roughness parameters and compared to vision-based measurements. two light reflection models were adopted and implemented, namely the “intensity-topography compatible (itc) model” and the “light-diffuse model”, to explain the obtained vision data and to allow appropriate roughness parameter calculation. results revealed that the “itc model” performed better than the “lightdiffuse model”, with notable similar values to those obtained by conventional stylusbased data of roughness parameters. zhongxiang et al. [4] employed a method for determining the three-dimensional roughness of the surface using profile information. they suggested a three-dimensional measuring technique that was used to investigate surface roughness components on the basis of the digital image processing technology, and set up a three-dimensional surface roughness assessment system containing hardware and software architecture. fadare et al. [5] developed a computer vision system appropriate for on-line surface roughness measurement of machined components utilizing an “artificial neural network (ann)” depending on a digital image processing of the machined surface, consisting of a ccd camera, computer, microsoft windows video 250 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 maker, digital image processing software, and two light sources. the machined surface images were captured; analyzed and optical roughness characteristics were assessed using the “2-d fast fourier transform (fft) algorithm”. they concluded that the optical roughness values predicted by ann were considered to be in good agreement with the measured values (r2-value = 0.9529). shahabi et al. [6] proposed a different method for measuring roughness using a 2-d contour extracted from an edge image of the workpiece surface. a comparison with a stylus type device indicated a maximum variation of 10% in the measurement of average roughness ra utilizing the visual method. sridhar et al. [7] used a machine vision method to determine surface roughness through image processing and backlight technique on the turned components. the comparison was then made of the surface roughness values achieved through the image processing technique and the conventional stylus method, which showed that the suggested method provided close and dependable results similar to the traditional stylus method. balasundaram et al. [8] calculated the amplitude and spacing, in addition to functional surface roughness parameters through the dry cutting of aisi 1035 carbon steel utilizing machine vision. a “dslr camera” with high shutter speed was employed to capture a blur-free image of the workpiece surface profile perpendicular to the cutting tool. the edge of the surface profile was identified to subpixel precision using the grey level constant moment and the roughness parameters were calculated using the profile. srivani et al. [9] presented a methodology to characterize the nature of the surface using a computer vision system. for further investigations, a computerized optical microscope was used to collect surface images, and those images were fed into matlab software. qingqun et al. [10] suggested a different method of on-line turned surface inspection by observing the characteristics of the grey value of the surface digital image. the uniformity of the surface image was evaluated and analyzed by fractal analysis, wavelet transform, and discreteness analysis of the wavelength of the texture profile. the normal texture image was extracted from the average wave profile, which indicated the state of the process and turned surface conditions. the results indicated that the turned surface condition could be effectively checked on-line. naresh et al. [11] used the technique of machine vision to observe the surface roughness when turning composite mmcs. the machining surfaces were identified during machining operation utilizing machine vision technology and the stylus probe instrument was used to measure the surface finish of the machined surfaces. patel et al. [12] introduced a computer vision system that captured the surface texture contours of the machined surfaces and extracted images. using the graylevel co-occurrence matrix, the texture function parameters were extracted and compared to various surface roughness parameters reported from a surface profilometer of a contact form. the image analysis was carried out for the extraction of texture characteristics at various levels of roughness. the variation between the characteristics of each texture and the parameter of surface roughness was examined. multiple regression models were expanded to estimate individual surface roughness parameter (ra) estimation and good recognition of surface roughness degree. the linear detection model was found to have better output features compared with a nonlinear recognition model. the findings showed that surface roughness estimation utilizing a linear regression model was a robust method for non-contact measurement. patel et al. [13] presented a surface roughness prediction approach utilizing “computer vision”, “image processing”, and “machine learning”. two machine learning algorithms, “stochastic gradient boosting” and “bagging tree” were compared and assessed on the basis of statistical parameters. it was found that “stochastic gradient boosting” effectively estimated surface roughness for training as 251 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 well as ten-fold cross-validation. the methods may be utilized for online monitoring of machined components and good evaluation. in this paper, a computer vision system for tracking and predicting the surface roughness of the turned components with different cutting conditions (cutting speed, feed rate, and cutting depth) utilizing image processing and backlight technique is presented. the surface roughness values that will obtained by the image processing technique and the conventional stylus method will then be compared. 2. methodology and experimentation the average surface roughness (ra) and root mean square roughness (rq) are commonly used as index of measurements to assess a machined surface finish. estimation of roughness parameters has a significant role in distinguishing difficulties in industrial sectors like contact deformation, friction, and tightness of joint contact precision. 2.1 stylus method description the machining process was performed on a wilton lathe (model no. 52tl1440-3) by 18 medium carbon steel aisi 1045 workpieces having a 30 mm diameter and a 300 mm length. the chemical composition and mechanical properties of aisi 1045 material were measured as shown in tables 1 and 2 respectively. table 1: chemical composition of aisi 1045 material component c si mn p s cr fe wt % 0.324 0.236 0.578 0.002 0.028 0.103 residual table 2: mechanical properties of aisi 1045 material elastic modulus (gpa) tensile strength (mpa) hardness (hb) yield strength (mpa) 216 671 170 353 the experiments were conducted using the taguchi method by changing working parameters like feed rate, cutting speed, and a fixed cutting depth. the direction of the workpiece rotation was fixed in a counterclockwise direction. no cooling was concerned throughout the turning process. table 3 indicates the amount of the parameters during the turning cutting process. a stylus device was used as a contact method for measuring the surface roughness of machined components. it contained a diamond stylus probe that was moved perpendicularly to the direction of roughness, and a characteristic of surface roughness was recorded at the other end. because of its advantages, it is the most widely used technique and generates an object's profile in a clear direction. surface roughness measurements of 18 turned components were performed on the stylus roughness tester type (srt-6210). 2.2 computer vision system description the fundamental components of the vision system designed to capture images of the surfaces to be inspected consist of two parts: hardware and software systems. the hardware system consists of four main items: (1) a sony dsc-wx100 ccd digital camera with a resolution of 18.2 megapixels, (2) an led illumination source, (3) a black tube of cardboard to prevent the effect of environmental light, and (4) a personal computer 252 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 (pc) with matlab program for image processing as software. the camera was fixed using a special frame designed to move horizontally and vertically to ensure that the view of the camera was always perpendicular to the surface of the workpiece and could scan any area that needed to be measured. a software system named "srvision" was developed using matlab software. it was developed to work on any windows environment. the image of the surface that needed to be measured was opened by the software, and then the variation of the surface profile was plotted and the surface parameters were calculated. the actual and schematic configuration of the on-machine measurement system of roughness is shown in figs. 1 and 2, respectively. table 3: cutting condition values utilized in the experimental work [10] workpiece material cutting speed (v) [rpm] feed rate (f) [mm/sec] cutting depth (d) [mm] aisi 1045 140 0.2, 0.29, 0.39,0.77 0.25 250 0.18, 0.36, 0.74 650 0.18, 0.26, 0.36, 0.72 950 0.16, 0.22, 0.34, 0.54 1350 0.15, 0.23, 0.34 fig. 1: the actual setup of the on-machine roughness measurement system. 2.3. system calibration the horizontal and vertical scaling factors were obtained using a standard block with a length of 2 mm to transform the image dimensions from pixels to real dimensions in microns; the block was located at the same level as the shaft. the block width (in pixels) was calculated using the camera calibration toolbox in matlab software and the calibration factors were calculated using the following equation [2]: 𝑓 = 𝑛𝑜. 𝑜𝑓 𝑡ℎ𝑒 𝑝𝑖𝑥𝑒𝑙𝑠 𝑓𝑜𝑟 𝑔𝑎𝑢𝑔𝑒 𝑏𝑙𝑜𝑐𝑘 𝑤𝑖𝑑𝑡ℎ (𝑙𝑒𝑛𝑔𝑡ℎ) 𝑎𝑐𝑡𝑢𝑎𝑙 (𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑) 𝑤𝑖𝑑𝑡ℎ (𝑙𝑒𝑛𝑔𝑡ℎ) 𝑜𝑓 𝑡ℎ𝑒 𝑏𝑙𝑜𝑐𝑘 (1) 253 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 fig. 2: schematic diagram of the on-machine roughness measurement system [14]. 2.4 measuring procedure a procedure for the assessment of surface roughness using the image processing method is described below: 1preparation of specimen: 18 medium carbon steel aisi 1045 components were turned by adjusting the cutting speed and feed rate. the surface roughness values were measured by a stylus type roughness tester. 2components were put under the “ccd camera” and modified for appropriate illumination of the led; the “ccd camera” was focused to get an obvious contour image of the specimen edge. an image of the contour edge of the component being turned was captured and stored in the computer using a usb cable. 3the captured image was converted to a grayscale version to reduce the operating time of the algorithm. 4the area to be measured was cropped from the original image, and unnecessary areas around the shaft edge were deleted. 5the image stored in the computer was recovered and treated using a median filter (mask size 3x3) to remove the noise present in the image. 6the developed srvision software, calculated the image gradient in the y direction to find the change in the intensity from white to black and found the edge of the workpiece. 7converted the grayscale amount of the image into black and white with a binarization technique, the limits were applied on the image so that the component area was black and the rest was white. 8an algorithm was written for scanning the first row to find the first white pixel in the profile, then scanning the second row to find the second white pixel. this method was repeated to find the whole white pixels lying in the image, these pixels reflected the profile of the workpiece's surface profile. 9the best fit line was drawn to the contour image to get a mean line of the contour by least-square fitting. 254 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 10assessment of average surface roughness (ra) and root mean square roughness (rq) by image processing technique from the image contour was performed by subtracting each pixel of the counter profile from the calculated mean line and using the following relationships: 𝑅𝑎 = ƒ 𝑛 ∑ ℎ𝑖 𝑛 𝑖=1 (2) 𝑅𝑞 = ƒ√ ∑ ℎ𝑖𝑛𝑖=1 𝑛 (3) where: n is the number of data points, hi is the absolute distance of the ith point on the profiling measure from the mean line, and ƒ is a scaling factor. figure 3 indicates the different steps of roughness measurement in the srvision. after loading the image into the software, where the software gives the option to choose the area to measure. fig. 3: the main interface of software developed (srvision). 3. results and discussion the results of the stylus and vision methods for measured surface roughness are presented in this section. additionally, their demand results were compared and discussed. 3.1 measuring surface roughness using stylus method a stylus instrument was utilized to compare with the values of measured roughness by the vision system. every surface was measured 5 times at different positions of the workpiece utilizing a cutoff of 0.8 mm. the minimum and maximum values of surface roughness achieved by the stylus method are indicated in table 4. the variation δra between the minimum and maximum ra values changed between 0.24 μm and 0.844 μm for the 18 specimens. the maximum variation as a percentage of the minimum ra value was 13.22% for each workpiece. the difference δrq between a minimum and maximum rq values ranged from 0.13 μm to 1.94 μm. the maximum variation as a percentage of the 255 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 minimum rq value was 15.36 % for each workpiece. the different values of surface roughness at the same workpiece were a result of instability in the machining process performed by the traditional turning machine. table 4: minimum and maximum roughness achieved by stylus device no. v [rpm] f [mm/rev] ra(max) [µm] ra(min) [µm] δ ra [µm] δ ra [%] rq(max) [µm] rq(min) [µm] δ rq [µm] δ rq [%] 1 140 0.206 6.474 6.026 0.448 7.43 8.291 7.4 0.891 10.75 2 0.2886 7.887 7.563 0.324 4.28 8.928 8.736 0.192 2.15 3 0.396 9.9 9.362 0.538 5.75 13.34 11.4 1.94 14.54 4 0.77 13.1 12.86 0.24 1.87 15.45 15.04 0.41 2.65 5 250 0.182 6.512 6.107 0.405 6.63 7.766 6.957 0.809 10.42 6 0.364 9.909 9.302 0.607 6.53 12.813 12.193 0.62 4.84 7 0.742 10.67 10.152 0.518 5.10 12.75 11.24 1.51 11.84 8 650 0.179 6.426 5.946 0.48 8.07 8.353 7.365 0.988 11.83 9 0.256 6.821 6.526 0.295 4.52 7.723 7.154 0.569 7.37 10 0.361 8.696 8.129 0.567 6.98 10.03 9.626 0.404 4.03 11 0.732 15.85 15.22 0.63 4.14 18.351 17.95 0.401 2.19 12 950 0.161 4.53 4.125 0.405 9.82 5.594 4.735 0.859 15.36 13 0.22 8.09 7.321 0.769 10.50 10.11 9.1 1.01 9.99 14 0.335 9.334 8.811 0.523 5.94 11.16 10.27 0.89 7.97 15 0.541 10.43 9.586 0.844 8.80 12.42 11.76 0.66 5.31 16 1350 0.147 4.326 3.821 0.505 13.22 5.246 5.116 0.13 2.48 17 0.228 6.633 6.35 0.283 4.46 8.534 7.321 1.213 14.21 18 0.34 10.212 9.659 0.553 5.73 11.752 11.196 0.556 4.73 3.2 measuring the surface roughness using the vision method every image of the workpiece was measured 4 times at different positions. table 5 indicates the minimum and maximum surface roughness values achieved by the machine vision system. the difference δra between the minimum and maximum ra values ranged from 0.256 μm to 1.184 μm. the maximum variation for each workpiece as a percentage of the minimum ra value was 12.7%. the difference δrq between a minimum and maximum rq values ranged from 0.377 μm to 0.973 μm. the maximum variation for each workpiece as a percentage of the minimum rq value was 10.76 %. 3.3 comparison of roughness values achieved by stylus and vision methods the results of measurements of average surface roughness (ra) and root mean square surface roughness (rq) using the suggested method of a vision system and comparison with the stylus method are shown in table 6. the results show that the maximum ra and rq differences between the two methods were 3,744% and 3,727% respectively. the mean and the standard deviation between the two ra measurements were 1.65% and 1.0% respectively. also, the mean and the standard deviation of the difference for rq were 1.433% and 1.0%, respectively. figures 4 and 5 show a plot of average roughness and root mean square roughness respectively found by the suggested vision method (ra (v)) versus the average roughness found by the stylus measurement (ra(s)). the data were fitted with a linear trend line, and the correlation value was determined in microsoft excel using linear regression. a correlation value would specify a perfectly linear relationship between the two data groups. the high correlation of 0.99 indicates that the visual method is 256 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 capable of giving dependable roughness values for the measurements obtained in this study. table 5: minimum and maximum roughness achieved by vision method no. v [rpm] f [mm/rev] ra(max) [µm] ra(min) [µm] δ ra [µm] δ ra [%] rq(max) [µm] rq(min) [µm] δ rq [µm] δ rq [%] 1 140 0.206 6.326 6.0129 0.3131 5.21 8.368 7.756 0.612 7.31 2 0.2886 7.869 7.613 0.256 3.36 9.146 8.659 0.487 5.32 3 0.396 9.961 9.581 0.38 3.97 12.834 11.861 0.973 7.58 4 0.77 12.956 12.698 0.258 2.03 15.542 14.731 0.811 5.22 5 250 0.182 6.621 6.265 0.356 5.68 7.856 7.17 0.686 8.73 6 0.364 10.09 9.781 0.309 3.16 12.672 11.981 0.691 5.45 7 0.742 10.679 10.293 0.386 3.75 12.896 12.224 0.672 5.21 8 650 0.179 6.816 6.483 0.333 5.14 7.963 7.214 0.749 9.41 9 0.256 6.608 6.174 0.434 7.03 8.125 7.643 0.482 5.93 10 0.361 8.924 8.361 0.563 6.73 10.22 9.654 0.566 5.54 11 0.732 15.624 14.865 0.759 5.11 18.236 17.658 0.578 3.17 12 950 0.161 4.621 4.209 0.412 9.79 5.49 5.113 0.377 6.87 13 0.22 7.953 7.521 0.432 5.74 9.981 9.218 0.763 7.64 14 0.335 9.496 8.432 1.064 12.62 10.861 10.159 0.702 6.46 15 0.541 10.51 9.326 1.184 12.70 12.224 11.476 0.748 6.12 16 1350 0.147 4.286 3.843 0.443 11.53 5.012 4.542 0.47 9.38 17 0.228 6.716 6.283 0.433 6.89 7.962 7.105 0.857 10.76 18 0.34 10.246 9.514 0.732 7.69 11.742 10.954 0.788 6.71 table 6: comparison between roughness’s achieved by stylus and vision methods no. v [rpm] f [mm/rev] ra(v) [µm] ra(s) [µm] δ ra [µm] δ ra [%] rq(v) [µm] rq(s) [µm] δ rq [µm] δ rq [%] 1 140 0.206 6.1277 6.282 0.1543 2.456 8.0184 7.8465 0.1719 2.191 2 0.2886 7.7274 7.684 0.0434 0.565 8.954 8.817 0.137 1.554 3 0.396 9.7024 9.67 0.0324 0.335 12.253 12.183 0.0698 0.573 4 0.77 12.727 13.02 0.293 2.250 15.024 15.245 0.2209 1.449 5 250 0.182 6.3845 6.31 0.0745 1.181 7.4028 7.3705 0.0323 0.438 6 0.364 9.9862 9.7 0.2862 2.951 12.278 12.45 0.1713 1.376 7 0.742 10.506 10.351 0.155 1.497 12.651 12.23 0.4214 3.446 8 650 0.179 6.397 6.337 0.06 0.947 7.475 7.549 0.074 0.980 9 0.256 6.6552 6.795 0.1398 2.057 7.957 7.875 0.082 1.041 10 0.361 8.6246 8.45 0.1746 2.066 9.9618 9.882 0.0798 0.808 11 0.732 15.157 15.343 0.186 1.212 18.08 18.12 0.04 0.221 12 950 0.161 4.487 4.3375 0.1495 3.447 5.2212 5.177 0.0442 0.854 13 0.22 7.7202 7.8 0.0798 1.023 9.5548 9.68 0.1252 1.293 14 0.335 8.74 9.08 0.34 3.744 10.623 10.715 0.0921 0.860 15 0.541 10.1 10.055 0.045 0.448 11.983 11.89 0.0928 0.780 16 1350 0.147 3.9539 4.004 0.0501 1.251 4.8807 5.026 0.1453 2.891 17 0.228 6.4611 6.4 0.0611 0.955 7.4762 7.7656 0.2894 3.727 18 0.34 9.8284 9.964 0.1356 1.361 11.25 11.4 0.15 1.316 257 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 fig. 4: comparison between ra values achieved by stylus and vision methods. fig. 5: comparison between rq values achieved by stylus and vision methods. also, the comparison plot of estimated average surface roughness values (ra) and root mean square surface roughness values (rq) using the stylus approach and vision approach are shown in figs. 6 and 7. it's quite obvious that the estimated values of roughness by the two approaches are accurate with an r-squared of 0.997. fig. 6: the analogy of stylus and vision values for average surface roughness (ra). r² = 0.9968 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 r a (s ) (µ m ) ra(v) (µm) r² = 0.9974 0 5 10 15 20 0 5 10 15 20 r q (s ) (µ m ) rq(v) (µm) 0 2 4 6 8 10 12 14 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 s u rf a ce r o u g h n e ss ( r a ) µ m experimental no. ra (vision) ra (stylus) 258 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 fig. 7: the analogy of stylus and vision values for root mean square surface roughness (rq). 4. conclusion a computer vision system and backlight method for assessing the surface roughness of turned medium carbon steel aisi 1045 specimens under different machining conditions were proposed in this study. the computer vision system captured and stored the enlarged contour edge images of the specimens as they were being turned. srvision software was developed for calculating the surface roughness immediately from the specimen's contour image. the advantage of using a backlighting device is that it is not influenced by industrial environment lighting conditions. the precision of the vision method was compared with the stylus method for many experiments. comparison graphs drawn between the vision and stylus methods demonstrated the percentage error obtained a maximum variation of 3.75 % and the coefficient of correlation (r2) values were close to one. hence the vision method is reliable and appropriate for on-line, non-contact surface roughness measurement of machined components. references [1] lee by, tarng ys. (2001) surface roughness inspection by computer vision in turning operations. international journal of machine tools and manufacture, 41(9): 1251-1263. https://www.sciencedirect.com/science/article/abs/pii/s0890695501000232 [2] gadelmawla es. (2004) a vision system for surface roughness characterization using the gray level co-occurrence matrix. ndt & e international, 37(7): 577-588. https://doi.org/10.1016/j.ndteint.2004.03.004 [3] ghassan a.al-kindi, bijan shirinzadeh. (2007) an evaluation of surface roughness parameters measurement using vision-based data. international journal of machine tools and manufacture, 47(3-4): 697-708. https://doi.org/10.1016/j.ijmachtools.2006.04.013 [4] hu zhongxiang, zhu lei, teng jiaxu, ma xuehong, shi xiaojun. (2009) evaluation of three-dimensional surface roughness parameters based on digital image processing. international journal of advanced manufacturing technology, 40(3): 342-348. https://link.springer.com/article/10.1007/s00170-007-1357-5 [5] fadare da, oni ao. (2009) development and application of a machine vision system for measurement of surface roughness. arpn journal of engineering and applied sciences, 4(5): 30-37. [6] shahabi hh, ratnam mm. (2010) noncontact roughness measurement of turned parts using machine vision. the international journal of advanced manufacturing technology, 46: 275-284. https://link.springer.co/artmicle/10.1007/s00170-009-2101-0 0 5 10 15 20 1 2 3 4 5 6 7 8 9 101112131415161718 s u rf a ce r o u g h n e ss ( r q ) µ m experimental no. rq (vision) rq (stylus) 259 https://doi.org/10.1016/j.ijmachtools.2006.04.013 iium engineering journal, vol. 22, no. 2, 2021 taha and abdulateef https://doi.org/10.31436/iiumej.v22i2.1507 [7] sridhar vg, adithan m. (2012) an in-process approach for monitoring and evaluating the surface roughness of turned components. european journal of scientific research, 68(4): 534-543. [8] mohan kumar balasundaram, mani maran ratnam. (2014) in-process measurement of surface roughness using machine vision with sub-pixel edge detection in finish turning. international journal of precision engineering and manufacturing, 15(11): 2239-2249. https://link.springer.com/article/10.1007/s12541-014-0587-3 [9] srivani a, anthony xavior m. (2014) investigation of surface texture using image processing techniques. 12th global congress on manufacturing and management, gcmm 2014, procedia engineering, 97 (2014): 1943-1947. https://doi.org/10.1016/j.proeng.2014.12.348 [10] qingqun mai, yanming quan, peijie liu, guo ding. (2016) a new method of on-line turned surface monitoring by digital image processing. matec web of conferences, mmme 2016, 63. https://doi.org/10.1051/matecconf/20166304030 [11] naresh p, syed altaf hussain, durga prasad b. (2019) surface roughness measurement of machined surfaces by machine vision technique. international journal of recent technology and engineering (ijrte), 7(icetesm): 129-134. https://www.ijrte.org/wp-content/uploads/papers/v7iicetesm18/ [12] dhiren r patel, mysore bk, vinay vakharia. (2020) modeling and prediction of surface roughness using multiple regressions: a noncontact approach. wiley, engineering reports. 2(e12119): 1-15. https://doi.org/10.1002/eng2.12119 [13] dhiren r patel, harshit thakker, kiran mb, vinay vakharia. (2020) surface roughness prediction of machined components using gray level co-occurrence matrix and bagging tree. fme transactions, 48(2): 468-475. [14] kumar bm, ratnam mm. (2015) machine vision method for non-contact measurement of surface roughness of a rotating workpiece. sensor review, 35(1): 10-19. https://doi.org/10.1108/sr-01-2014-609 260 https://doi.org/10.1016/j.proeng.2014.12.348 https://doi.org/10.1051/matecconf/20166304030 https://doi.org/10.1108/sr-01-2014-609 microsoft word 261 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 209 ethical and religious analysis on euthanasia abdi o. shuriye department of science in engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. shuriye@iium.edu.my abstract: this paper is an analysis on euthanasia from ethical and religious perspectives. historically, the classical greek thinkers including aristotle had categorically accepted euthanasia with the main reason of minimizing pain. however, as science develops ethical and religious isuues related to the subject have increasingly created fervent debates on euthanesia. abstrak: kertas ini mengkaji euthanasia dari perspektif agama dan etika. sejarah telah melihat para pemikir greek termasuk aristotle secara kategorinya menerima euthanasia dengan sebab utama untuk mengurangkan kesakitan. bagaimanapun, apabila sains berkembang, perbahasan mengenai isu-isu agama dan etika tentang euthanasia telah meningkat dengan nyata. keywords: mercy killing; religion; ethics; morality; euthanasia 1. introduction euthanasia is the idea of intentional killing by act or omission of a dependent human being for his or her alleged benefit. it could be voluntary when the person who‘s life is terminated has requested so; and it could be unpremeditated when the person involved provided no consent. it could also be by action if action is performed to the life of the person; or it could be based on omission when necessary care is not provided. the objective of this paper is to study the religious and ethical implications of euthanasia. it explores the qur’anic views and relates to the history and practices. the methodology employed in this study is collection of academic references including books and journals, as well as other reliable references. 2. understanding euthanasia the etymology of euthanasia reflects “good death or mercy killing” though no one has thus far understood the meaning of good death or killing with mercy. nonetheless, what is understood is the fact that the term implies gentle and easy process of death. authorities in the subject talk of “decision of shortening life” as the main definition of euthanasia [1]. authorities also agrees that euthanasia involves decision which have the effect of shortening life. euthanasia is also limited to the medical context. it involves patients’ lives being shortened by doctors [1]. keown argues that the method used could be active as well as intentional, according to him in most cases euthanasia refers to the active or the intentional termination of a patient’s life by a doctor who thinks that death is the ultimate benefit for the concerned iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 210 patient [2]. the doctor is shortening the patient’s life, in the process, without a purpose or intention the doctor would have no business in the issue. keown refers to a report on euthanasia and related matters by the uk house of lords select committee on medical ethics. the report defines euthanasia as “deliberate intervention undertaken with expressed intention of ending a life to relieve intractable suffering” [2]. two types of euthanasia are relevant; active and passive. active euthanasia would mean the use of particular methods which cause death to the patient. it is this aspect or type of euthanasia that we usually refer to as “mercy killing”. the method used in passive euthanasia is quite diverse from active methods, discontinuation of treatment is one method used in this type of euthanasia. in other words, doctor or whoever performs the act withdraws or withhold certain treatment that could keep the patient alive. if the physician provide the drug which could be used for the same purpose with the patient without actively or passively involved directly by himself, this type of euthanasia is termed as “physician assisted euthanasia” [1]. there are also, so to speak, voluntary and non-voluntary euthanasia. the idea of voluntary or otherwise reflects the patient’s involvement in the decision making. it would be considered voluntary if the order is given to the physician by the patient, without the will of the patient however it becomes involuntary [1]. 3. ethical and religious analysis on euthanasia the moral characterization of bringing about someone’s death is incompatible with the values of his or her life. allowing to be killed or cooperating in the process or even been indifferent about it could be morally interpreted as suicide. when one brings about one’s own death, we, most of the time attempt to justify in one form or the other, shahid or martyr who had killed himself could be interpreted as suicide? the martyr been a muslim, christian or jew acts on the assumption of been on the other side of moral grounds and consider himself or herself a hero. on the same grounds from amoral point of view voluntary euthanasia is not different from other cases of suicide. the motive of committing suicide is mainly to get rid of a particular problem. stressed individuals in economically advanced societies commonly commit this agreeably unethical act [1]. religion plays a role, the more a society is highly committed and conscious about its faith in god the less the rate of suicide cases. western authors for instance have recognized that fact that muslims have the lowest rate of suicide cases, but they hardly attribute this to the faith in islam. western scholars have agreed that “suicide rates are generally low in muslim countries, where there has traditionally been strong condemnation on suicide in any circumstances” [1]. generally religion provides, to a certain level, some sort of broad conceptual guidelines that control the bio-behaviour and internal inconsistency which may result from external factors. other roles of religion include to infuse some values to life that may, otherwise, individuals become destroyed from its comprehensive aim, and in fact some individuals have complexity in comprehending the specific objectives of life. the spiritual harmony provided by religion is imperative to balance the level of disorder. it is for these reasons that all religions consider suicide unethical, invalid and improper, as it sinfully violates the teachings of all holy scriptures including the qur’an and the bible [1]. muslim’s for instance, punctually attend the congregational prayers to beat stress, to gunner stronger security and wider network, to increase the degree of integration and discard threat. like euthanasia, suicide is unreligious, with no moral grounds, despite this iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 211 fact however, suicide take place in various ways, a clear indication that religious tenets, though important, are becoming non-essential to the committers [1]. christianity is one major world religion; it does not sanction suicide, and on the contrary recognizes that through religious rites the complex problems could become lighter. christians in general are of the opinion that killing be it mercy killing, or self inflicted killing is an atheistic act against the dominant tenets of christianity. like other faiths, christianity provides ease to the problem. but religion and ethical rules alone will not be adequate to deter mercy killing or suicide instead counseling and comprehending how to control the situation may be employed as effective measures to counter the causes of this immoral and unethical acts [1]. on a related aspect of the issue, it is worthwhile to note that the code of ethics of the american medical association recognizes the distinction and officially encodes that passive euthanasia is morally acceptable. the code however, does not recognize active euthanasia. moral theorists also have disagreed with the distinction between ordinary and extraordinary means of sustaining life. some subscribe to the opinion that it is morally justifiable to withhold extraordinary means of life support but ordinary treatment should go on. the apparent unjustifiable double standards among western philosophers are due to the inconsistency of their religious outlook [1]. the injunction that “do not harm” in the hippocrates oath which clearly specifies that a physician “will neither give a deadly drug to anybody…. nor make a suggestion to this effect” mounts direct opposition to the permissibility bestowed by the western philosophers upon the passive euthanasia, though we all know that the removal of the life support system from the patient constitutes an act of killing the person on immoral and illegal grounds, even the patients with dead brain will fall under this categorization [1]. 4. conclusion to sum up this analysis, i must downrightly state that the argument of this paper revolved on the premises that good death is ethically and religiously debatable. in comparing the two core arguments, paper observed that western ethicists see the right to die purely from human dignity perspective, whilst muslims look at life as trust from god. as such muslim ethicists categorically contend that trust should be preserved and protected, as the qur’an orders man not to cast themselves into perdition by their own hands. unlike abortion all forms of mercy killing, passive or active, suicide, or assisted, are prohibited by islam. although, it must be noted, some muslim jurists have permitted the removal of the machine from the brain dead patients. nonetheless, the mainstream muslim jurists are in agreement on the notion that in islam death means total separation of the soul from the body, as such the death of the brain stem should not be considered as death or reason for killing. the protection is for the soul in the body, with brain-death the soul could be weak but at the same time it may come back, if one believes that things are in the hands of god, therefore the weak and unconscious souls have equal rights to life. references [1] al-qur’an al-karim [2] abdi o. shuriye, islamic ethical values on bioengineering practices: issues in genetic engineering. research management centre, iium, pp. xivxvi, 2006. [3] john keown, euthanasia: ethics and public policy and argument against legislation, cambridge, cambridge university press, 2002, p.11 microsoft word 193 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 151 engineering ethics in islam: an evaluative and comparative study between code of ethics of institution of engineers, bangladesh (ieb) and code of professional conduct of board of engineers malaysia (bem) muhammad amanullah department of fiqh and usul al-fiqh, kulliyyah of islamic revealed knowledge and human sciences international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. amanulllah@iium.edu.my abstract: during the past two centuries or so a number of buildings and bridges had been structurally failed and collapsed all over the world. some of these incidents caused a sizeable number of human casualties. for instance, collapse of tay bridge in 1879 killed at least sixty persons. beside the problems related to their design and construction, probably the failure to follow engineering ethics properly was partially responsible for these incidents. growing engineering professionalism during the nineteenth century gave rise to the development of a number of famous engineering societies, such as american institute of electrical engineers (aiee ( (1884), american institute of mining engineers (aime) (1871), etc. on the other hand, responding to series of significant structural failures mentioned above, some engineering societies developed formal codes of ethics. following these societies, engineers of bangladesh (previous east pakistan) established institution of engineers, bangladesh (ieb). likewise, malaysian engineers established board of engineers malaysia (bem). both of these societies have their codes of ethics. islam also has offered a number of ethics to be followed by the engineers. analyzing the related verses of the qur’an and ahadith of the prophet (pbuh), this paper intends to highlight these islamic ethics and in light of them, tries to evaluate the codes of ethics of these two societies and compare between them. the paper may conclude that although the codes of ethics of ieb and bem are supported by islamic ethics they require further modification. abstrak: sejak lebih kurang dua abad kebelakangan ini, banyak binaan yang gagal dari segi strukturnya dan juga jambatan yang runtuh di merata dunia. sesetengah tragedi yang berlaku juga mengakibatkan kehilangan nyawa manusia. contohnya, robohnya jambatan tay pada 1879 telah meragut nyawa lebih kurang enam puluh orang. selain daripada masalah yang berkaitan dengan reka bentuk dan pembinaanya, mungkin juga kegagalan untuk mematuhi etika kejuruteraan merupakan ssebahagian daripada penyebab tragedi-tragedi ini. pertumbuhan keprofesionalan kejuruteraan dalam kurun kesembilan belas memberikan pertumbuhan pesat terhadap perkembangan beberapa pertubuhan kejuruteraan yang terkenal, seperti institut jurutera elektrikal amerika (american institute of electrical engineers (aiee)-1884), institut jurutera perlombongan amerika (american institute of mining engineers (aime) -1871) dan sebagainya. sebaliknya, dalam memberi respons terhadap kegagalan struktur yang signifikan di atas, beberapa persatuan kejuruteraan telah membangunkan beberapa kod etika formal. berdasarkan kepada pertubuhan-pertubuhan ini, jurutera bangladesh (yang sebelum ini dikenali sebagai pakistan timur) menubuhkan institut jurutera bangladesh iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 152 (institution of engineers bangladesh (ieb)). jurutera malaysia pula menubuhkan lembaga jurutera malaysia (board of engineers malaysia (bem)). kedua-dua pertubuhan ini mempunyai kod etika masing-masing. agama islam juga menyenaraikan beberapa etika yang perlu diikuti. dengan mendalami ayat-ayat al-quran dan hadis rasullullah yang berkaitan, kertas ini bertujuan menekankan etika-etika islam dan juga mengkaji kod etika kedua-dua pertubuhan ini dan membuat perbandingan. kertas ini mungkin merumuskan bahawa walaupun kod etika ieb dan bem disokong oleh etika islam, namun beberapa pendekatan harus diubah. keywords: engineering ethics; islamic ethics; ieb; bem; evaluation 1. introduction different scholars give different definitions of engineering ethics. the researcher does not want to discuss these definitions [1]. rather, he intends to define it according to islamic legal system. he maintains that in islam engineering ethics are a set of rules and principles that an engineer should follow in his professional life [2]. a partial reason of the collapse of a number of buildings and bridges in the past in different parts of the world was probably the failure to follow engineering ethics properly. being faced by these incidents, a number of engineering societies in the west developed ethics for engineering profession by using their intellectual capabilities without looking into what the divine religions might have to say about them. although a number of these man-made ethics are in conformity with what islam or any other divine religion might have regarding them, the intention of these societies was neither to follow any religion nor to take the life hereafter into their consideration. following these societies, engineers of other countries including muslim countries also developed their code of ethics regardless of considering whether they are originated from islam or not. during recent years an attempt has been made to develop islamic ethics for engineering. one of such attempt is the book written by abdi omar shuriye and ahmad faris ismail [3]. it is a good introductory book. but by and large, this book discusses some qur’anic values for the study of a number of engineering disciplines, and seldom touches on ethics that should be followed by engineers in their professional life. this research paper intends to deduce professional ethics for engineering from islamic sources, i.e. the texts of the qur’an and ahadith of the prophet (pbuh), so that these ethics would be called islamic ethics and they would be concerned with the life hereafter besides taking this worldly life into consideration. following the discussion of these islamic ethics, the researcher also quotes the codes of ethics of two engineering societies, i.e. institution of engineers, bangladesh (ieb) and board of engineers malaysia (bem). finally, he attempts to evaluate these two codes of ethics in light of islamic ethics of engineering, make a comparison between two of them and strives to propose some suggestions to improve these codes in future. 2. islamic ethics of engineering 2.1 obedience and compliance a. like any other worker, employee or officer, an engineer should be obedient to his employer and other officers under whom he performs his duty. allah said: “o you who believe, obey allah and obey the messenger and those charged with authority among you”[4] according to this verse, an employer or a head of an office or company is charged with a kind of authority. the one who works under him, whether he is an ordinary worker or an engineer is obliged to obey him. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 153 b. an engineer should follow the prescribed code of ethics of his own organization in which he is a member. likewise, he should follow the rules and regulations of the office or company where he is posted. based on the verse quoted above, following these rules becomes an obligation for an engineer because a part of the obedience to the authority is related to follow the rules adapted by it. 2.2 public interest and welfare a. an engineer should give priority and utmost importance to the public health and safety during doing any work related to his profession. this is because this type of priority is closely related to one of the famous higher objectives of the shari`ah, i.e, protection of life (hifz al-nafs). he must take all different types of precaution before commencing any work so that the public health and safety will be secured and ho harm will be inflicted to them.. allah said: “if anyone saved a life, it would be as if he saved the life of whole people.”[5] the prophet (pbuh) said: “harm neither should be inflicted [to any one] nor should be reciprocated.”[6] b. an engineer should not involve himself in any development project that may be beneficial for contemporary generation but it will be harmful for long term or for the future generations. c. an engineer should not be involved in a project that is harmful for the environment. d. in order to maintain safety of the public and safety of the workers and employees who work under an engineer for developing a project, he should offer them proper safety guidelines regularly. e. an established islamic principle is that if any contradiction occurs between personal/individual interest and public interest, personal interest should be sacrificed for the sake of public interest. an engineer should follow this principle in giving his opinion in favor or against commencement of a new project or in erecting of a new business complex. all these sub-points are supported by the hadith that said that no harm should be inflicted to anyone. 2.3 being trustworthy and responsible, and being free from cheating a. in performing his duty, an engineer should be reliable and trustworthy. b. he should try to fulfill his duty accurately. c. he should be careful about his responsibility on his subordinate employees and workers. allah said: “surely allah orders you to fulfill your trustworthiness to the one who deserves it.”[7] the prophet said: “the one who does not have trustworthiness does not have perfect faith.”[8] d. an engineer must not cheat his employer, client or any other party. allah said: “o people fulfill measure (mikyal) and weight (mizan) justly and do not reduce things for people.”[9] although this verse forbids cheating in measuring and weighing, this forbiddance is applicable for any type of cheating including cheating in engineering profession. cheating also causes one to be out of muslim community. the prophet said: “the one who cheats is not one of us.”[10] 2.4 avoidance of bribery a. in order to receive any project for his company or employer from the government or any other authority or a larger company, an engineer should not offer bribe to any party involved in it. b. he also should not pay bribe to any party for his own promotion or any other personal benefits. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 154 c. likewise, in order to provide any work or any benefit to any party, he himself should not receive bribe from that party. the prophet (pbuh) said: “allah curses the one who offers bribe [to others], or receives it [from others].”[11] according to this hadith, since allah curses people who are involved in giving or taking bribe, all types of bribes including what is practiced by some engineers are forbidden in islam. 2.5 supervision, checking and writing reports a. if an engineer is given the responsibility to supervise other engineers or employees or workers, he should do this job by himself accurately without depending on others. likewise, he should maintain a continuous record of his supervision, so that it will be easier and accurate to keep track of gradual progress of a work. b. if he is given the charge to investigate a project or some works related to it, he should do it by himself and do not depend on others in doing this task. the prophet said: “take account of yourself before you are accounted for.”[12] keeping progress report of a work and doing it personally are considered parts of taking account of oneself, which is applicable for every muslim including an engineer. the prophet also said: “every one of you is considered to be a caretaker, as well as responsible for those who are under his care.”[13] the phrase “every one of you” in this hadith is a general expression that addresses all muslims including an engineer. therefore, an engineer is considered caretaker and responsible for those employees who work under him. he should guide them properly, check their performance and supervise their daily activities. c. likewise, he should not depend on speculation or rumor in doing his investigation. rather, he should base his opinion on practical findings. allah said: “o you who believe, avoid much of speculation because some speculation is sin.”[14] according to this verse, some speculation that leads to tell a lie is not acceptable. therefore, speculation should not be the basis for an engineer to do the job of investigation. allah also said: “o you who believe, if an impious person brings a message, you should critically examine it.”[15] according to this verse, rumors that come from any quarter should not be believed without examining it. an engineer, therefore, should not depend on rumors without examining them practically. d. during his supervision and checking, if an engineer finds that an employee has committed a mistake or showed negligence in doing his duty, the supervising engineer should not fire this employee without giving him chance to correct him by showing him his mistake and warning him. islam encourages forgiving each other unless it is related to the right of an individual. allah said: “hold to forgiveness.”[16] e. if an engineer is given the charge to write a report on a complaint against an employee, office, company, supplier, or contractor, he should be neutral and just in his writing. in order to be just, he should not try to mention only negative or only positive points of the complained party. rather, he should explain both negative and positive points. allah said: “surely allah orders you to do justice.”[17] writing only negative or only positive points is considered to be injustice and hence it goes against this command of allah. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 155 f. if an engineer is requested to write a report, he should not delay to complete this task. rather, he should maintain the deadline. likewise, if he receives any complaint, he should respond to it promptly. g. an engineer should be meticulous in his checking works of others, or in his writing a report, or issuing a certificate of completion of a work. both f and g are supported by a hadith in which the prophet indicated that allah loves those who try to perfect their works as much as they can. 2.6 truthfulness, sincerity, transparency and upholding integrity and dignity a. an engineer should be truthful in his public statement about his ability, area of specialization and capacity to do the works. allah said: “o you who believe, fear allah and stay with truthful people.”[18] according to this verse, muslims including engineers are not allowed to lie in their public statement. they are also not allowed to claim to know what they do not know. allah said: “and pursue not that of which you have no knowledge; for every act of hearing, or of seeing, or of (feeling) in the heart will be enquired into (on the day of reckoning).”[19] in a hadith the prophet said: “the one who cheats us is not one of us.”[20] in another hadith the prophet said: “a truthful and trustworthy businessman will stay with the prophets, truthful people and martyrs [on the day of judgment].”[21] likewise, telling a lie about own quality and capacity is considered to be a sign of hypocrisy. the prophet said: “signs of a hypocrite are three: if he talks, tells a lie; if he promises, he violates; and if he is entrusted, he betrays.”[22] b. according the texts, mentioned above, an engineer should be transparent in dealing with financial aspects of a project. c. according to the same texts, an engineer should uphold the integrity and dignity of his profession. telling a lie or giving incorrect information about own capacity or specialization is against this integrity and dignity. 2.7 helping the poor a. an engineer should have the intention to help poor people. if a person, because of his poverty, is unable to pay the high fees for a design for his house, the concerned engineer or his employer should receive the reduced charge for it. the messenger of allah (pbuh) said: “the one who helps his brother for his need allah will help him [this helper] for his need….”[23] the prophet also said: “the one who releases a believer from an anxiety of this world allah will release him from an anxiety of the day of resurrection. and the one who helps a poor by making his life easy allah will help him by making his life easy in this world and life hereafter….”[24] 2.8 avoidance of building places for committing vices a. a muslim engineer should not participate in building any business complex that is known from the beginning that it will be used for committing vices and obscene deeds which are forbidden in islam. b. a muslim engineer should not make the design for business complexes that are known to be utilized for committing obscene deeds. allah said: “and he [allah] forbids obscene deeds.”[25] he also said: “those who love (to see) that obscene deeds are spread among the believers, will have a painful punishment in this life and in the hereafter.”[26] in a third verse, he said: “you should not approach the obscene deeds.”[27] making design of a business complex or building it knowingly that it will be used for vices and obscene activities is considered a type iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 156 of participation in spreading these vices. therefore, according to these verses, an engineer or any other muslim should not involve himself in doing so. likewise, allah said: “o you who believe, eat from good (lawful) foods that i gave you as sustenance.”[28] the verse indicates that we are not allowed to earn our sustenance from forbidden sources. the prophet said: “seeking lawful sustenance is obligatory for every muslim.”[29] a muslim engineer, therefore, is not allowed to involve himself in any project that is forbidden in islam because it will cause his sustenance to be forbidden. 2.9 avoidance of developing harmful soft wires a. a muslim engineer should not develop any soft wires that are harmful for others, such as developing of viruses that can destroy the contents of the computers of other people. this point is supported by a hadith where the prophet forbade inflicting harms to others. b. a muslim engineer is not allowed to develop any soft wire on obscene entertainments. this point is supported by the verses of the qur’an discussed under b) of sub-section 8. 2.10 no conflict of interest a. if an engineer is an employee under any government office or any company, he should uphold the interest of this office or company. if any conflict of interest occurs, he should not do anything that goes against the interest of this office or company. b. if he receives any fees for consultancy out of his regular duty to this office or company, he is supposed to let his office know this. both of these points are related to inflicting harm to the employer or the office or company. according to a hadith of the prophet, inflicting harm to others is not allowed. 2.11 work for sustainable development islam encourages development works. an important type of sustainable development is to develop a piece of unowned land by making it suitable to cultivate or dwell on it, or to do business on it. the prophet said: “whoever develops a piece of land that does not belong to anyone deserves it most.”[30] he also stated: “people are servants of allah and lands belong to him. therefore, whoever develops any piece of wasteland; it belongs to that individual…”[31] an engineer should try his utmost to participate in sustainable development. he should abide himself by islamic conditions of doing this type of development. an important condition to make a development work as sustainable development is that it should be beneficial for both present and future generations. 2.12 avoidance of unfair competition a. islam encourages striving for good deeds individually as well as collectively. allah said: “then strive together (as a race) towards all that is good….”[32] islam also encourages mutual collaboration for doing good deeds that include beneficial engineering works and projects. allah said: “help each other in righteousness and piety, but do not help each other in sin and rancor.”[33] thus it may be said that fair competition is allowed for muslims including engineers. b. however, an engineer should avoid unfair competition with his colleagues and also with engineers from other companies. likewise, he should not be envious towards his colleagues because of their better performance. islam forbade iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 157 muslims including engineers to envy each other. the prophet (pbuh) said: “you should not compete each other [unfairly] and should not envy each other.”[34] allah taught muslims to seek refuge from the harm of an envious person with him when he practices envy. he said: “say: ‘i seek refuge with the lord of the dawn from the mischief of created things…and from the mischief of the envious one when he practices envy.”[35] c. out of envy or unfair competition, an engineer should not try to oust another engineer or colleague from his post or job. d. however, he is supposed to develop his carrier within the guidelines of his own office or company, which fall under fair and lawful competition. 2.13 continuous struggle towards perfectness a. an engineer is supposed to do his work as perfect as possible. the prophet (pbuh) said: “surely allah loves one from among you who, when he accomplishes any work, accomplishes it perfectly.”[36] since the word “any work” (`amal) in this hadith is a general expression, it includes both worship and other mundane deeds that a human being does in his daily life. likewise, the phrase “one from you” is a general expression that includes all different types of doers and workers, one of whom is an engineer. b. perfectness of works of an engineer requires knowledge of these works. therefore, he should try to have up-to-date knowledge of the development in his field of specialization. allah said through the mouth of the prophet yusuf: “appoint me the supervisor of treasuries of the earth, for i am a very knowledgeable guard/supervisor.”[37] since yusuf had perfect knowledge of supervising the treasuries, he was appointed by pharaoh to perform this duty. accordingly, an engineer should have perfect up-to-date knowledge of his field; otherwise he will be not able to do his work perfectly. however, if any training is required to have up-to-date knowledge of his field, his employer should arrange training program for him. c. struggle for perfectness in his works should be a continuous effort for him as long as he is in his profession. since an engineer, as a muslim continuously tries to perfect his worship for allah, he is also supposed to try continuously to perfect his worldly affairs including employment and other works for getting sustenance. allah loves to see his servant tired because of struggling for sustenance. the prophet said: “surely allah loves to see his servant tired because of seeking lawful sustenance.”[38] d. an engineer should not be a lazy person. islam does not like laziness. the prophet taught all muslims including an engineer to seek refuge with allah from laziness by saying: “o allah, surely i take refuge with you from anxiety, sorrow, inability and laziness…”[39] e. an engineer should be ready to accept constructive criticism of his works by other colleagues because this is a way to improve and become free from mistakes. f. an engineer who is in charge of a project should not delay to complete it without any valid reason because it would cause financial loss to the owner of the project and would damage the reputation of himself and his company. this goes against a hadith in which muslims including an engineer are encouraged to struggle for perfection of their works. delaying a project against this perfection. 3. code of ethics of two engineering societies iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 158 3.1 code of ethics of institution of engineering, bangladesh (ieb) 1. “i solemnly promise that as a member of the institution of engineers, bangladesh i shall uphold and advance the integrity, honor and dignity of the engineering profession using my knowledge and skill and shall hold paramount the safety, health and welfare of the public and shall try to comply with the principles of sustainable development i in the performance of my professional duties. 2. i shall be honest and impartial and serve with complete fidelity the public, employer and clients. i shall not accept remuneration for services rendered other than that from my employer or with my employer’s permission. 3. i shall perform services only in areas of my competence. 4. i shall build my professional reputation of the merit of my services and shall not compete unfairly with others. 5. i shall act in professional matters for my employer or client as faithful agent or trustee and shall avoid conflict of interest and avoid deceptive acts. 6. i shall issue public statements only in an objective and truthful manner, and shall not in a self-laudatory language or in any manner derogatory to the dignity or the profession, or professional bodies, neither advise or write articles for publication, nor shall authorize such advertisements to be written or published by any other person. 7. i, without disclosing the fact to my employer in writing shall not be director of or have a substantial financial interest in, nor be an agent for any company, firm or person carrying on any contracting, consulting or manufacturing business which is or may be involved in the work to which my employment relates, nor shall i receive directly or indirectly any royalty, gratuity or commission or any article or process used in or for the purpose of the work in respect of which i am employed unless or until such royalty, gratuity or commission has been authorized in writing by the employer. 8. i shall support the professional and technical societies of my discipline. 9. i, in connection with work in country other than my own shall order my conduct according to these rules, as far as they are applicable; but where the country has recognized standards of professional conduct, i shall adhere to them. 10. i shall not offer, guide, solicit or receive, either directly or indirectly any political contribution in an amount intended to influence the award of a contract by the public authority. 11. i solemnly promise i shall avoid bribery and extortion in any form. if i encounter such acts done by any member, i shall be ethically bound to report it to the ethical review board (erb) of ieb (erb is to be formed). 12. i shall continue my professional development throughout my career, and shall provide opportunities and support for the professional development of the engineers under my supervision. 13. a member who shall be convicted by a competent tribunal of a criminal offence, which in the opinion of the disciplinary body renders him unfit to be a member, shall deemed to have been guilty of improper conduct. signature________________ name___________________ membership no f/m/am_______(to be filled up by office)”[40] 3.2 boar of engineers, malaysia (bem) code of professional conduct iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 159 a number of codes of ethics have been prescribed by bem. this paper touches on only the code of ethics prescribed for the matured professional engineers of malaysia. following is the full text of this code: a. definition of employer 1. unless it is otherwise expressly provided, the expression ‘employer’ shall for the purposes of this part, include client. b. conduct of registered engineer 2. a registered engineer shall order his conduct so as to uphold the dignity, standing and reputation of the profession. c. responsibility to employer and profession 3. a registered engineer in his responsibility to his employer and the profession shall have full regard to the public interest. d. discharge of duties 4. a registered engineer shall discharge his duties to his employer with complete fidelity. he shall not accept remuneration for services rendered other than from his employer or with his employer’s permission. e. reputation etc. of a registered engineer not to be injured 5. a registered engineer shall not maliciously injure or attempt to injure whether directly or indirectly, the professional reputation, prospects or business of another registered engineer. f. canvassing and advertising prohibited 6. a registered engineer shall not improperly canvass or solicit professional employment nor offer to make by commission or otherwise payment for the introduction of such employment. he shall not advertise except for the purpose of obtaining salaried appointment as permitted by the board. g. a professional engineer in private practice not to practice with any person whose registration has been cancelled 7. a professional engineer in private practice shall not practise engineering with any person whose registration has been cancelled unless he has been reinstated under section 17(1) of the act. h. a salaried registered engineer not to compete with professional engineers in private practice 8. a registered engineer shall not use the advantage of a salaried position to compete with professional engineers in private practice. i. restriction on submission of plans and drawings 9. (1) no registered engineer other than a professional engineer in private practice may submit plans or drawings to any person or authority in the federation unless such plans or drawings are in connection with equipment, plant or specialized products manufactured or sold by his employer or firm, or in connection with his own or his employer’s engineering works and buildings. (2) for the purpose of this rule, "employer" shall not include client. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 160 j. restriction on making payments or placing contracts 10. a professional engineer in private practice shall not be medium of payment made on his client’s behalf unless he is so requested by his client nor shall he, in connection with work on which he is employed, place contracts or orders except with the authority of and on behalf of his client. k. restriction on entering professional partnership 11. a professional engineer in private practice shall not without the occurrence of the board enter into professional partnership with any person other than a professional engineer in private practice, a registered architect, a registered surveyor or a licensed land surveyor. l. a professional engineer in private practice not to intervene or to take over the work of another 12. a professional engineer in private practice shall not, directly or indirectly attempt to supplant another professional engineer in private practice nor shall he intervene or attempt to intervene in or in connection with engineering work of any kind which to his knowledge has already been entrusted to another professional engineer in private practice nor shall he review or take over the work of that other engineer acting for the same employer, until he has either obtained the consent of that engineer or has been formally notified by the employer that the engagement of that engineer with work has been properly terminated. m. a professional engineer in private practice shall not be a contractor 13. (1) a professional engineer in private practice shall not be a contractor at the same time. (2) a professional engineer in private practice shall not act in a professional capacity for an employer and a contractor on the same project unless on the specific instructions of the employer.“[41] 4. evaluation, comparison and suggestions 4.1 evaluation the code of ethics of ieb is considered to be one of the best codes of ethics prescribed by many engineering associations all over the world. it is good that at the beginning of this code the phrase “solemnly promise” has been mentioned. this phrase makes this code binding for the members of ieb. all the ethics mentioned in this code are considered to be good and justified. but nowhere it mentions name of allah, the prophet (pbuh), islam, shari`ah, the qur’an, sunnah or muslims. by reading this code there is no way to figure it out that it has been prepared by muslims. same types of ethics have been prescribed by other engineering associations in america and europe by non-muslims. since majority of the engineers of bangladesh are muslims, it should indicate that through this code they try to follow the rulings of the shari`ah prescribed by allah. although the ethics mentioned in this code islamically supported, it is not appropriate to consider them as islamic code of ethics because in order to make a code islamic there should be an intention and declaration openly that this code will not violate the shari`ah and if any contradiction occurs between these ethics and between what is prescribed by the qur’an and sunnah, the latter will dominate the former. in any case, the researcher does not consider this code as a comprehensive code of ethics for muslim engineers. in order to iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 161 improve this code and make it as a comprehensive code of ethics for muslim engineers, the researcher will later provide some suggestions. likewise, the code of professional conduct of bem is also considered good because all the ethics mentioned in this code are justified. there is no mention of promise to abide by these ethics. however the phrases like “shall order,” “shall have,” “shall not,” etc. used in this code make it binding to the members of bem but with lesser degree of obligation. it is understood that since there are many non-muslim engineers in malaysia, it is not appropriate to mention name of allah, the messenger, shari`ah, islam, the qur’an, sunnah, or muslims in it. although the ethics mentioned in this code are islamically supported, the researcher does not consider it as a comprehensive code of ethics for malaysian muslim engineers. likewise, the researcher finds that this code of ethics is less comprehensive than the code of ethics prescribed by bem for its young engineers. in order to make it comprehensive code for malaysian muslim engineers, the researcher will later provide some suggestions. 4.2 comparison in this sub-section the researcher strives to make comparison between the code of ieb and the code of bem by discussing their similarities and differences as follows: a. similarities 1. both of them are good because ethics mentioned in them are islamically justified. 2. both of them do not say clearly that it is an islamic code of ethics for engineers. 3. both of them avoid making an oath in the name of allah or god at the beginning. 4. it is a coincidence that both of them have the similar numbers of ethics, i.e., 13. 5. both of them do not quote any source for the code. 6. both of them have varying degree of obligatory or binding nature. 7. both of them are not binding for engineers who are not members of them. 8. both of them have some similar ethics. b. differences 1. the code of ieb is considered to be more binding for its members than the code of bem. this is because ieb uses the phrase “solemnly promise,” whereas bem uses phrase like “shall order,” “shall have,” “shall not,” etc. additionally, ieb uses first person like “i,’” “my’” etc. which carry more seriousness and strength than the third person like “he,” “professional engineer,” “registered engineer,” etc. used by the code of bem. moreover, at the end of the code of ieb there is a place for signature of the member who should sign his name on this code; while the code of bem does not have a place for signing it by its member. 2. all 13 points mentioned in the code of ieb are considered ethics, while the point number one of the code of bem is not considered to be an ethic because it provides the definition of employer. 3. some points mentioned by the code of ieb, such as to comply with the principles of sustainable development, and to adhere to the standards of professional conduct of another country in the case of presence of its member in that country, etc., are not mentioned by the code of bem. 4. some points mentioned by bem, such as to be ready to accept peer review, to be transparent, not to try to oust other engineers from their post or job, to be meticulous in certification of a work, etc. are not mentioned by ieb. 5. bem provides a sub-title for each of its ethics, while ieb does not follow this method. rather, depends on the numbers only. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 162 4.3 suggestions 1. both bangladesh and malaysia have engineers from different religious groups. therefore, the researcher suggests that each country should consider its present code of ethics for non-muslims. both countries should prepare a separate code of ethics for muslim engineers by keeping all present points of ethics and adding several new points to them to make it as a comprehensive islamic code of ethics for muslim engineers. 2. at the beginning of the code, taking oath in the name of allah should be mentioned by both codes. 3. the code of bem should use the phrase “solemnly promise” to make it more serious. 4. both codes should clearly mention that they will follow the rulings of shari`ah prescribed by allah. 5. both should strongly state that their members will not involve themselves with any forbidden project. rather, they will strive continuously to earn, invest and work in lawful projects. 6. both should have a plan to help needy and poor people of the society. 7. both should declare not to do any project that goes against the environment. 8. bem should focus on sustainable development. 9. both should clearly say that they will not develop any project or business complex that is known to be used for obscene deeds. 10. both should state that if any contradiction happens between the rulings of shari`ah and between these ethics the former will be prevalent. 11. both should have policy that if any contradiction occurs between personal interest and public interest the latter should be prevalent. 12. both should have policy for their members to increase their knowledge and to have up-to-date information in their specializations. 13. both should declare to follow the rules of supervision, checking and report writing. 14. both should declare that all member engineers should obey their superiors and employers. 15. both should promise not to develop any computer program or soft wires that are harmful in terms of losing the character and also in terms of monitory loss, such as damage of the computer itself by making viruses. 16. engineering ethics should be imposed by the government on all engineers whether they are members of any society or not. 5. conclusion the most important findings of this research are as follows: 1. an engineer should give utmost importance and priority to the public health and safety. 2. an engineer should be trustworthy and responsible. 3. an engineer should not offer or receive bribe. 4. an engineer should be truthful and sincere in all of his activities related to his professional life. 5. an engineer should try to help poor people who need their expertise but cannot afford the cost. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 163 6. an engineer should work for lawful and beneficial projects. he should avoid building projects or soft wires that are islamically illegal and harmful for the public. 7. an engineer should struggle for sustainable development. 8. an engineer should avoid unfair competition with other engineers and employees. 9. an engineer should continuously try for perfectness and excellence in his profession. 10. although ethics mentioned in the codes of both ieb and bem are good and justified, they are not considered islamic ethics of engineering because no where they declare that they follow these ethics for the sake of abiding them by the rulings of the shari`ah. 11. there are a number of similarities as well as differences between the code of ethics of ieb and bem. however, the code of ieb seems to have more binding and obligatory nature than the code of bem. 12. none of the codes of ethics of ieb and bem are considered to be islamically comprehensive. in order to make them islamically comprehensive, a number of ethical points must be added to them. the most important of these added ethics is that they should declare in their codes that they will follow the rulings and guidelines of the shari`ah and whenever there will be any contradiction between their codes and between the rulings of the shari`ah the latter will be prevalent. 13. the researcher proposes that the present codes of ieb and bem more or less suitable for non-muslims. they are not completely suitable for muslim engineers. therefore, a separate code for muslim engineers should be developed by incorporating suggestions provided by the researcher in this research paper. references [1] abdi omar shuriye and ahmad faris ismail, qur’anic values and engineering studies (petaling jaya: pearson malaysia sdn. bhd., 2011), pp. 1-5. [2] the researcher has arrived to this definition according to his understanding of the texts of the qur’an and ahadith of the prophet (pbuh) related to the profession of engineering. [3] shuriye, et al., qur’anic values and engineering studies (petaling jaya: pearson malaysia sdn. bhd., 2011). [4] qur’an surah al-nisa’, 4: 59 [5] qur’an surah al-ma’idah, 5: 32 [6] muhammad bin yazid abu `abd allah bin majah, sunan ibn majah, ed. muhammad fu’ad `abd al-baqi (beirut: dar al-fikr, n. d.), vol. 2, p. 784. [7] qur’an surah al-nisa’, 4:58. [8] musnad al-imam ahmad. see qutub mustafa sano, al-istithmar ahkamuhu wa dawabituhu fi al-fiqh al-islami (jordan: dar al-nafa’is, 2000), p. 155. [9] qur’an surah hud, 11: 85. [10] muslim. see abu zakariyya yahya bin sharaf al-nawawi al-dimashqi, riyad al-salihin, ed. shu`ayb al-arnabut (beirut: ma’assasat al-risalah, 1991), p. 599. [11] sunan ibn majah. see muhammad sabri harun, ahkam al-aswaq al-maliyyah (jordon: dar al-nafa’is, 1999), p. 162. [12] [13] ahmad bin `ali bin hajar al-`asqalani, fath al-bari sharh sahih al-bukhari, 4 th ed. (beirut: dar al-kutub lil-tiba`ah wa al-nashr, 1984), vol. 5, p. 474. [14] qur’an surah al-hujurat, 49: 12. [15] qur’an surah al-hujurat, 49: 6. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering amanullah 164 [16] qur’an surah al-a’raf, 7: 199. [17] qur’an surah al-nahl, 16: 90. [18] qur’an surah al-tawbah, 9: 119. [19] qur’an surah al-isra’, 17: 36. [20] tabrani. see ibrahim isma`il, al-i`lam al-islami wa wasa’il al-ittisal al-hadithah (makkah al-mukarramah: rabitat al-`alam al-islami, 1994), p. 32; muslim. see al-dimashqi, riyad al-salihin, p. 599. [21] bukhari and muslim. see al-dimashqi, riyad al-salihin, p. 321. [22] al-tirmidhi, al-darami, al-darqutni. see al-shaykh wali al-din muhammad bin `abd allah al-khatib al-tabrizi, mishkat al-masbih (lahore: maktaba’i mustafa’i, n. d.), p. 243. [23] bukhari and muslim. see al-dimashqi, riyad al-salihin, p. 148. [24] muslim. see al-dimashqi, riyad al-salihin, p. 149. [25] qur’an surah al-nahl, 16: 90. [26] qur’an surah al-nur, 24: 19. [27] qur’an surah al-an`am, 6: 151. [28] qur’an surah al-baqarah, 2: 172. [29] al-imam al-mundhiri. see amirah `abd al-latif mashhur, al-istithmar fi al-iqtisad alislami (cairo: maktabat madbuli, 1991), p. 255. [30] al-`asqalani, fath al-bari sharh sahih al-bukhari, vol. 5, p. 22. [31] `izz al-din al-khatib al-tamimi, al`amal fi al-islam: akhlaquh, mafahimuh, qiyamuh, ahkamuh (amman: dar `ammar, n.d.), p. 40. [32] qur’an surah al-baqarah, 2: 148. [33] qur’an surah al-ma’idah, 5: 2. [34] muslim. see al-dimashqi, riyad al-salihin, p. 595. [35] qur’an surah al-falaq, 113: 1-5. [36] `izz al-din baliq, minhaj al-salihin min ahadith wa sunnat khatim al-anbiya ‘ wa almursalin, 3 rd ed. (beirut: dar al-fath lil-tiba`ah wa al-nashr, 1984), p. 384. [37] qur’an surah yusuf, 12: 55. [38] qur’an surah yusuf, 12: 210. [39] al-`asqalani, fath al-bari sharh sahih al-bukhari, vol. 11, p. 207. [40] the institution of engineers, bangladesh, constitution of the institution of engineers, bangladesh (dhaka: the institution of engineers, bangladesh, 2005), appendix-a. [41] board of engineers malaysia (bem), (melaka: faculty of engineering and technology, multimedia university, 2010). http://fet.mmu.edu.my/v4/career/bem.html iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 feature extraction and supervised learning for volatile organic compounds gas recognition nor syahira mohd tombel1, hasan firdaus mohd zaki2,3* and hanna farihin binti mohd fadglullah3 1 dept. of science (computational and theoretical), kulliyyah of science, international islamic university of malaysia, kuantan, pahang 2 centre for unmanned technologies (cute), kulliyyah of engineering, international islamic university of malaysia, gombak, kuala lumpur 3 dept. of mechatronic, kulliyyah of engineering, international islamic university of malaysia, gombak, kuala lumpur *corresponding author: hasanzaki@iium.edu.my (received: 11 april 2023; accepted: 13 june 2023; published on-line: 4 july 2023) abstract: the emergence of advanced technologies, particularly in the field of artificial intelligence (ai), has sparked significant interest in exploring their potential benefits for various industries, including healthcare. in the medical sector, the utilization of sensing systems has proven valuable for diagnosing pulmonary diseases by detecting volatile organic compounds (vocs) in exhaled breath. however, the identification of the most informative and discriminating features from voc sensor arrays remains an unresolved challenge, essential for achieving robust voc class recognition. this research project aims to investigate effective feature extraction techniques that can be employed as discriminative features for machine learning algorithms. a preliminary dataset was used to predict voc classification through the application of five supervised machine learning algorithms: k-nearest neighbors (knn), random forest (rf), support vector machines (svm), logistic regression (lr), and artificial neural networks (ann). ten feature extraction methods were proposed based on changes in sensor response as inputs to classify three types of gases in the dataset. the performance of each model was evaluated and compared using k-fold cross-validation (k=10) and metrics derived from the confusion matrix. the results demonstrate that the rf model achieved the highest mean accuracy and standard deviation, with values of 0.813 ± 0.035, followed closely by knn with 0.803 ± 0.033. conversely, lr, svm (kernel=polynomial), and ann exhibited poor performances when applied to the voc dataset, with accuracies of 0.447 ± 0.035, 0.403 ± 0.041, and 0.419 ± 0.035, respectively. therefore, this paper provides evidence that classifying voc gases based on sensor responses is feasible and emphasizes the need for further research to explore sensor array analysis to enhance feature extraction techniques. abstrak: perkembangan teknologi canggih, khususnya dalam bidang kecerdasan buatan (ai), telah mencetuskan minat yang ketara dalam menerokai manfaatnya untuk pelbagai industri, termasuk bidang kesihatan. dalam sektor perubatan, penggunaan sistem penderiaan telah terbukti bernilai untuk mendiagnosis penyakit paru-paru dengan mengesan sebatian organik meruap (voc) dalam nafas yang dihembus manusia. walau bagaimanapun, pengenalpastian ciri yang paling bermaklumat dan mendiskriminasi daripada penderia voc kekal sebagai cabaran yang tidak dapat diselesaikan, penting untuk mencapai pengiktirafan kelas voc yang kukuh. projek penyelidikan ini bertujuan untuk menyiasat teknik pengekstrakan ciri yang berkesan yang boleh digunakan sebagai ciri diskriminatif untuk 407 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 algoritma pembelajaran mesin. set data awal digunakan untuk meramalkan klasifikasi voc melalui aplikasi lima algoritma pembelajaran mesin yang diselia: k-nearest neighbors (knn), random forest (rf), support vector machines (svm), logistic regression (lr), dan artificial neural networks (ann). sepuluh kaedah pengekstrakan ciri telah dicadangkan berdasarkan perubahan dalam tindak balas penderia sebagai input untuk mengklasifikasikan tiga jenis gas dalam set data. prestasi setiap model telah dinilai dan dibandingkan menggunakan pengesahan silang k-fold (k=10) dan metrik yang diperoleh daripada confusion matriks . keputusan menunjukkan bahawa model rf mencapai ketepatan minima tertinggi dan sisihan piawai, dengan nilai 0.813 ± 0.035, diikuti oleh knn dengan 0.803 ± 0.033. sebaliknya, lr, svm (kernel=polinomial), dan ann mempamerkan prestasi yang lemah apabila digunakan pada dataset voc, dengan ketepatan masing-masing 0.447 ± 0.035, 0.403 ± 0.041 dan 0.419 ± 0.035. oleh itu, kertas kerja ini memberikan bukti bahawa mengklasifikasikan gas voc berdasarkan tindak balas penderia adalah boleh dilaksanakan dan menekankan keperluan untuk penyelidikan lanjut untuk meneroka analisis tatasusunan penderia untuk meningkatkan teknik pengekstrakan ciri. keywords: supervised machine learning; volatile organic compound; voc sensor; gas classification; feature extraction 1. introduction volatile organic compounds (voc) have been used as preclinical biomarkers in breath analysis to monitor health and diagnose various pulmonary diseases such as asthma and lung cancer [1] [2] [3][4]. an array of sensors, or electronic nose (e-nose) is known as the alternative for a non-invasive method of detecting volatile organic compounds (voc). e-nose is a device inspired by the olfactory system of humans or mammals (sense of smell), composed of a collection of an array of gas sensors with a pattern recognition system designed to detect and differentiate a wide variety of gas compounds [5]. the advancement of nanosensor arrays with pattern recognition involving pre-processing, feature extraction and machine learning algorithms makes it a powerful tool for the detection and recognition of gas samples with concentration estimation. feature extraction is an essential technique used to extract significant information from the sensor response signal [6] [7] to optimize the performance of pattern recognition algorithms for gas classification [6] [8]. however, the detection of voc using nanosensor technologies still has some constraints in its detection system. the voc sensor as a sensing unit faced a few limitations such as lack of sensitivity and selectivity [9] [10]. besides, it is still not clear which type of features from voc sensor arrays are the most descriptive and discriminative leading to a robust recognition of the voc classes. data collection from a gas sensor array can also be cumbersome and timeconsuming which poses a nuisance in employing data-hungry machine learning algorithms. therefore, this paper proposes employing supervised machine learning algorithms to classify the preliminary data of the individual sensors for voc recognition. the voc detection was performed on a chemiresistive sensor from various functionalised reduced graphene oxide (rgo) as a sensing layer. the targeted voc gases used are acetone, toluene and isoprene which have been suggested as pulmonary disease-related biomarkers [11] with concentration levels ranging from 1 to 6 ppm. concretely, we explore 10 feature sets that were extracted from the sensor’s original response curve. then, we analyse the effect of these features towards voc classification with five benchmark machine learning algorithms including k-nearest neighbours (knn), random 408 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 forest (rf), logistic regression (lr), support vector machine (svm) and artificial neural network (ann). the recognition models were then put into comparison to determine the one which provides the best evaluation and high accuracy in performing the classification of the targeted voc gases using k-fold cross validation (k=10) and confusion matrix. 2. gas sensing mechanism sensing mechanism of the sensor is first studied, to understand the voc detection on the sensor. the thin film is comprised of rgo which is one of the most promising materials for detecting low voc concentrations at room temperature [12]. graphene is a two-dimensional building block made up of a one-atom-thick sheet of a carbon atom. graphene can work well at room temperature because it has enormously high mobility [13]. researchers are interested in modifying graphene into reduced graphene oxide as a sensing element because of its excellent electrical, high thermal conductivity, and mechanical properties [14] [15]. the functionalisation of rgo with nanoparticles and plasma treatment can improve sensor functionality and selectivity in distinguishing different vapours [11]. different functionalisation of sensing elements is a good technique to improve the gas sensor's sensitivity and characteristics. in this research, the sensing layer was deposited on ti/pt interdigitated electrode (ide). the electrode was used to supply current flow from the power source to the device, which improved the sensing material's catalytic properties towards a specific gas [16]. furthermore, the voc sensor employed is a resistive type, which produces a signal based on a change in resistance in response to gas exposure. in general, voc gas detection on a sensor is caused by the adsorption and desorption processes that occur between analytes and the sensor surface [17]. oxygen ion species were absorbed on the sensor surface in the presence of air (humidity) and lowered the electron from the conduction band [18]. the electron density is falling off and forming an electron depletion layer and barrier potential on the surface. electron removal causes an increase in the depletion layer. the related equation for chemisorbed oxygen at temperatures less than 100°c [19] is as follows: o2 (gas)→o2 (adsorption) (1) o2 (gas)+ e (surface)↔ o2 (adsorption) (<100℃) (2) when voc gas was introduced into the chamber, the gas molecules started to react with the absorbed oxygen ions and released electrons back into the conduction band. the predominant carrier in the sensors was modified by the reaction of the voc gas (oxidizing or reducing agent) with the molecules in the sensing layer, resulting in an increasing or decreasing in the resistance measurement as the output [19]. reduced graphene oxide has been reported to exhibit p-type behaviour [20]. however, the functionalised sensor was shown to be an n-type semiconductor in this voc test, and the voc analytes acted as reducing gases [18]. the sensor experienced an electron carrier majority, causing a decrease in depletion width and potential barrier. as a result, the sensor resistance decreased in the presence of voc gas [21]. 409 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 3. related works 3.1. feature extraction feature extraction is a technique that is used to extract significant information from the sensor response graph [6] to ensure better performance of machine learning algorithms in pattern recognition [8]. the information is deemed relevant when the derived value extracted from the measured data is non-redundant, not correlated with other features and projects the decisive features [22]. other than that, feature selection is also related to the dimensionality reduction process of transforming high dimensional data into a low dimensional feature [8]. detection of vocs using gas sensors commonly used real-time analysis and discrimination of “breath prints” to perform the gas classification process [2]. in 2012, vergara and his team applied 8 feature extraction from the time-series sensor, which are the change of the maximal resistance change (δr), the normalized resistance change (||δr||), minimum and maximum exponential moving average(ema) with a value of 𝛼 = 0.001,0.01,0.1 each [10]. on the other hand, many features can be extracted from raw signals and applied in electronic nose applications. commonly extracted features from gas original response curves such as maximum response, the response of special time, time of special response, area, integral, derivative, difference and second derivative [6]. table 1 shows a few lists of feature extraction from electronic nose sensor data for wound detection [23]. table 1: list of feature extraction for wound detection based electronic nose [23] feature description normalization preprocessing the sensor data for features from the steady-state response, eliminate the effect of a concentration difference on recognition. integral and derivative methods integrals may represent the accumulative total of the reaction degree change and derivatives may represent the rate at which the sensor reacts to the odour. the root mean square error (rmse) of curve fitting depends on the type of model and the number of parameters in the model. fourier transform and wavelet transform fourier transform decomposes the original response curve into a superposition of the dc component and different harmonic components. 3.2. supervised machine learning there were few studies which implemented the detection of different gases by supervised learning models such as k-nearest neighbour (knn), support vector machine (svm), artificial neural network (ann), random forest (rf) and logistic regression. the findings were summarised in table 2. there are two gaseous flows in the system: for carrier gas and voc gas. clean dry air (cda) was used as carrier gas, while isoprene, toluene, and acetone as the targeted voc gas. the temperature of the gas and temperature chuck in the sensor chamber were controlled using a cellkraft humidifier p-10 and a nextron temperature controller module (nextron microprobe station, with platier heater and 4 probe needles). agilent smu 34410a was used to drive the voltage and input current. a data acquisition (daq) system that is used to convert the output/measured signal from the sensor system into the computer is via a user interface software that is programmed using the labview program, provided by mimos. 410 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 table 2: summary of implementation of supervised learning algorithms on different types of gas detection. model description references k-nearest neighbour (knn) knn is widely used in the classification of mixed gas and for gas discrimination systems. the knn model is advantageous because it is comprehensible, insensitive to noise, low cost for retaining and good combination with other algorithms. however, this model is sensitive to sample distribution, it has a slow speed for recognition, high spatial complexity, heavy calculation burden and poor interpretability. [24] support vector machines (svm) svm of classifiers can cope well with gas sensor drift and perform better than the baseline competing methods on the extensive dataset. however, the svm model requires a long learning time and poor application for larger data. choice of kernel function is important as it is the key for feature space in svm. [10],[24] artificial neural network (ann) ann is the frequently used method in predicting and analysing complex gas (hashoul & haick, 2019). it has good learning ability, good parallel processing capability and detecting compatibility error. however, this model has poor interpretability for output, long time learning and is easy to overfit. therefore, weight, activation function and the number of hidden layers are important to develop an ann algorithm in performing the classification of targeted output. [24],[25] random forest (rf) rf model is used in a lot of feature datasets as it can prevent overfitting from a decision tree algorithm. in the random forest algorithm, the number of trees affected the accuracy of the model, as each tree has a classification result and the final result is based on the majority decision trees vote [26], [36] logistic regression lr is a classification algorithm that calculates linear output and statistical function through the regression output. logistic regression can perform multiclass classification problems by using one-vs-rest or one-vs-one wrapper models. the algorithm can be applied to a non-linear classification problem with a proper feature selection. lr model can produce high accuracy as it is a good signal to noise ratio. [27] 4. experimental setup as illustrated in fig 1, the gas sensing system for this study comprises a gas supply system, a sensor chamber, a temperature and humidity controller module, and data collection system [28]. fig 2 showed the daq board of the labview that contain all the controller variables for the test measurement such as flow of the cda, flow of the voc gas, input current, input voltage, temperature inside the chamber, temperature of the sensor's heater, relative humidity, and system ramp rate. then, the sensor was tested individually with the targeted voc gas and the sensor’s responses were recorded to study performance of the individual sensor. 411 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 fig. 1. schematic diagram of the experimental setup for gas detection system. fig. 2. manual control of labview gas system. 4.1. voc sensor the gas sensor used in this study is called a voc sensor, which is prepared, fabricated and functionalised by the engineering team at mimos bhd. reduced graphene oxide (rgo) as a sensing membrane was deposited on the platinum-titanium interdigitated electrode (pt/ti ide) on a silicon and silicon dioxide (si/sio2) substrate. the rgo was functionalised with nanoparticles such as; gold (au), silver (ag) and platinum (pt) and plasma treatment such as; hydrogen (h2) and octafluorocyclobutane (c4f8). the sensor was fabricated using a standard semiconductor process using chemical vapor deposition (cvd) by a standard lithography process for the functionalisation with different recipes. the rgo was functionalised with nanoparticles at a different duration of sputtering and relative frequency (rf) power, while functionalisation with plasma treatment at a variety of plasma power and temperature. therefore, there are 21 individual voc gas sensors used in this study and the details are according to table 3. next, the pre-processed signal proceeded with a feature extraction method to extract pertinent information to be input for supervised machine learning at classifying the gas components into targeted gas output. the features were 412 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 decided to extract from the original gas response involving measured resistance in the absence and presence of the voc gas. table 3: list of functionalisation and recipe of voc sensors sample no. nanoparticles power [wrf] time [sec] remarks 1 reference rgo film bare rgo 2 au 30 15 rgo/au (30w 15s) 3 au 30 75 rgo/au (30w 75s) 4 au 70 15 rgo/au (70w 15s) 5 au 70 75 rgo/au (70w 75s) 6 pt 30 15 rgo/pt (30w 15s) 7 pt 30 75 rgo/pt (30w 75s) 8 pt 70 15 rgo/pt (70w 15s) 9 pt 70 75 rgo/pt (70w 75s) 10 ag 30 15 rgo/ag (30w 15s) 11 ag 30 75 rgo/ag (30w 75s) 12 ag 70 15 rgo/ag (70w 15s) 13 ag 70 75 rgo/ag (70w 75s) sample no. plasma treatment power (wrf) temperature (℃) remarks 14 h2 rt rgo/h2 rt ℃ 15 h2 200 rgo/h2 200 ℃ 16 h2 400 rgo/h2 400 ℃ 17 h2 700 rgo/h2 700 ℃ 18 c4f8 150 rgo/c4f8 150 ℃ 19 c4f8 200 rgo/c4f8 200 ℃ 20 c4f8 250 rgo/c4f8 250 ℃ 21 c4f8 300 rgo/c4f8 300 ℃ 4.2. data collection the sensors were tested individually with each of the selected voc gas. the sensor was placed in a chamber with 30℃ of temperature and presence of 40% relative humidity (rh). the voltage and current input were set at 1v and 1.2a respectively. cda was maintained at 1 l/min for 5 minutes to stabilize the baseline reading. then, the voc gas was purged into the chamber with a gradual increase of concentrations, from 1 to 6 ppm in 12 minutes (2 minutes for each concentration). the sensor responses were analysed from the resistance changes of individual sensors that undergo the voc test. 5. data pre-processing and feature extraction in this phase, the analytes of the voc gas were reacting with the sensing element, thus leading to a change in resistance. the sensor response was determined by analysing the measured resistance as a signal output from each sensor. however, the parameter setup was not in optimal condition and the output signal contained unexpected noise from the smu system. a typical sensor response could not be seen clearly from the graph of resistance versus time. as a result, the signal was pre-processed by applying filter and smoothing methods to denoising the signal and reduce the influence of random variation caused by instrumental conditions and atmospheric effects [29]. the data was filtered using a moving average (ma 413 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 length = 3) and smoothed with minitab software using a single exponential method with a constant = 0.02 value. the sensor response was determined by using the formula [30][31]: ∆𝑅 = 𝑅𝑔 − 𝑅𝑎 (3) 𝑆 = ∆𝑅 𝑅𝑎 = 𝑅𝑔− 𝑅𝑎 𝑅𝑎 × 100(%) (4) where, 𝑅𝑎 = resistance in clean dry air, without voc gas 𝑅𝑔 = resistance with the exposure of voc gas next, the pre-processed signal proceeded with a feature extraction method to extract pertinent information as input for supervised machine learning at classifying the gas components into targeted gas output. the features were decided to extract from the original gas response involving measured resistance in the absence and presence of the voc gas. the 10 selected features as listed in table 4. table 4: list of features and formula for the 10 selected features no. feature formula 1 rgas resistance at steady-state phase 2 r0 baseline resistance 3 sensor response, s ∆𝑅 = 𝑅𝑔𝑎𝑠 − 𝑅𝑎𝑖𝑟 𝑅𝑎𝑖𝑟 4 difference, ∆𝑅 ∆𝑅 = 𝑅𝑔𝑎𝑠 − 𝑅𝑎𝑖𝑟 5 relative difference 𝑅𝑔𝑎𝑠 𝑅𝑎𝑖𝑟 6 log relative resistance value 𝑙𝑜𝑔( 𝑅𝑔𝑎𝑠 𝑅𝑎𝑖𝑟 ) 7 normalisation | 𝑅𝑔𝑎𝑠 − 𝑅𝑎𝑖𝑟 𝑅𝑎𝑖𝑟 | 8 g rgas 1 𝑅𝑔𝑎𝑠 9 g r0 1 𝑅𝑎𝑖𝑟 10 conductance difference 𝐺𝑔𝑎𝑠 𝐺𝑎𝑖𝑟 the voc dataset comprises ten feature extraction values and is organised into three categories. in summary, there are 918 total samples, with 252, 324, and 342 each for acetone, toluene, and isoprene gas, respectively. 6. supervised learning for voc gas classification five supervised learning models including k-nearest neighbour (knn), random forest (rf), logistic regression (lr), support vector machines (svm) and artificial neural networks (ann) were benchmarked for the voc gas classification. the model was implemented using the python and scikit-learn library. each model's parameter settings are described in table 5. to avoid bias in the analysis, the dataset was first standardised in the range 0 to 1 to uniform the values with different scales by using the min-max normalisation technique [32]. 414 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 following that, the dataset was divided into 70% for the training set and 30% for the testing set. the performances of each model are then evaluated from confusion matrix-based measures in terms of accuracy, precision and using k-fold cross-validation technique, where k =10. kfold cross validation is a cross validation technique used to evaluate the performance of a machine learning model by the resampling procedure. the training of the models proceeds using the k-1 parts and validation or testing errors from the remaining part [33]. table 5: parameter setting of the approached supervised machine learning model parameter k-nearest neighbour the k-value is decided as one, (k=1) and distance between two points is calculated by applying the distance metric formula (2), (mentioned in chapter 2), with p = 2, to manipulate the generalised distance to euclidean distance. random forest grid search for the setting parameter, with n-estimator:100. artificial neural network a shallow neural network was implemented, with a standard three-layer feed-forward network. for the hidden layer, the size was set up to 50 and used the relu activation function. while softmax activation function for output layer with learning rate 0.001 and 50 epochs. support vector machine (rbf kernel) radial basis function (rbf) was selected as a kernel function for this svm model, as defined in equation (6) (in chapter 2) the kernel function, σ and regularisation, c used gridsearchcv from scikitlearn library to perform grid search for parameter setting. logistic regression the model used ‘l2’ for regularisation (penalty) and solver ‘lbfgs’. 7. result figures 3 a) to e) showed the results of the confusion matrices for each proposed supervised learning method. meanwhile, table 6 below showed the accuracies from the 10fold cross validation from each model. the diagonal values in the confusion matrix denoted the accuracy values of the gas classification to the targeted output [34]. figure 3 shows that the knn and rf models performed well in classifying each of the targeted vocs. the knn model correctly predicted all three gases with greater than 80% accuracy, while the random forest model predicted them with greater than 70% accuracy. on the other hand, logistic regression, support vector machine (kernel = rbf) and artificial neural network performed poor classification on the 3 vocs gases. the svm and ann models misclassified the gas more to isoprene gas while lr model misclassified the toluene and isoprene gas. it is noticeable in table 6, the rf model showed the highest mean accuracy with 0.813 ±0.035, followed by the knn model with 0.803 ±0.033. rf model are known to have advantages in the process of random sampling which can ensure randomness and avoid overfitting. besides, this model is also robust to noise [5] and it is good at handling missing data and imbalance classes [4]. whereas, the knn model has limitations in understanding the relationship between the features and the class (output) thus easily producing the wrong classification for a multiclass problem [4]. therefore, the highest accuracy achieved by knn in this study showed that the features were related well to the output class. 415 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 a) b) c) d) e) fig. 3. comparison of normalised confusion matrix of a) knn, b) rf, c) lr, d) svm (kernel= rbf) and e) ann. however, the ann, lr and svm (polynomial kernel) models had poor performance compared with the rf and knn model with accuracies of 0.447 ± 0.035, 0.403 ± 0.041 and 0.419 ± 0.035 respectively. meanwhile, the svm model with grid search parameters showed 416 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 high accuracy by using a polynomial kernel at degree = 3, compared with other kernels such as linear and rbf. table 6: model performance based on 10-fold cross-validation technique. model 10-fold cross-validation (mean accuracy ± standard deviation) random forest 0.813 ± 0.035 k-nearest neighbors 0.803 ± 0.033 logistic regression 0.403 ± 0.041 support vector machine (kernel = polynomial) 0.419 ± 0.035 support vector machine (kernel = linear) 0.401 ± 0.039 support vector machine (kernel = rbf) 0. 408 ± 0.055 artificial neural network 0.447 ± 0.035 the poor performance from the ann, lr and svm (polynomial kernel) models might be due to their weakness, in which they are very prone to overfitting training data [33] and they required testing with various kernels and model parameters [4]. the ann model also is a learning-based algorithm and is more complex in architecture. thus, it has more hyperparameters required to be tuned [33] and it needs enough samples for training. other than that, the roc curve and auc value are another way of visualising the output performances from the computed confusion matrix. evaluation of the receiver operating characteristics (roc) and area under curve (auc) was done to analyse the performance of the classifiers. the highest value of the auc showed good value prediction of the model to assign a larger probability to a random positive example than a random negative example [35]. the auc value should be between 0.5 and 1.0. the roc curves for each classifier are illustrated in figure 4. as the minimum is 0.541, it can be said that the svm classifier does not predict our dataset very well and could not differentiate the classes, while the highest value of auc goes to the knn classifier which is equal to 0.886 and 0.885 for the rf model. as a result, in this research, the knn and rf are two models that can deal with the selected features in the voc dataset as they obtained the highest accuracy for the gas classification. fig. 4. roc curve of the 5 supervised learning model 417 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 8. conclusion the gas sensor data was collected at a preliminary stage and has been used for the machine learning part, which involved pre-processing, feature extraction and classification algorithm. each sensor was performing well at low operating temperatures and in the presence of humidity. the sensors response on different targeted voc gas from 1 to 6 ppm were collected. then, feature extracted were performed on the resistance-based data. then, feature extracted were performed on the resistance-based data. ten featured were proposed as inputs to five supervised learning algorithms to accurately recognise and classify the selected voc gas based on the labelled output. the confusion matrix and 10-fold cross validation were used to evaluate each model's performance. as a result, the rf and knn models have higher accuracy with 0.813 ± 0.035and 0.803 ± 0.033, compared with lr, svm and ann with the accuracy of 0.447 ± 0.035, 0.403 ± 0.041 and 0.419 ± 0.035 respectively. the two highest accuracies achieved by rf and knn models demonstrated that they distinguished the gas well from the voc dataset. despite the gas sensor's shortcomings, such as low sensitivity, selectivity, and noise in the sensor signal output, the findings of this study can be utilised as a guide for selecting the optimum algorithm for dealing with a gas sensor array. the performance of the knn and rf models is the proof of concept that the algorithm can perform gas classification tasks from the simplest feature selected from the steady-state phase. the feature extraction approach, on the other hand, can be discovered more from the raw signal to build a dataset with more significant features and relevant information to improve the algorithm's performance. acknowledgement this project is a collaboration between the international islamic university malaysia (iium) with the centre of unmanned technologies, kulliyyah of engineering and department of r&d, mimos bhd. this research was partially sponsored by the fundamental research grant scheme (frgs19159-0768) and mimos berhad (spg21-015-0015). great thanks to research team at department of research & development, mimos berhad; dr. ismahadi syono, firzalaila syarina md yakin and siti aishah mohamad badaruddin for their guidance and supervision during data collection and for device preparation. references [1] krisher s, riley a, mehta k. (2014) designing breathalyser technology for the developing world: how a single breath can fight the double disease burden. journal of medical engineering and technology, 38(3), 156–163. doi:10.3109/03091902.2014.890678. [2] dragonieri s, pennazza g, carratu p, and resta o. (2017) electronic nose technology in respiratory diseases. lung, 195 (2):157–165. doi:10.1007/s00408-017-9987-3. [3] thriumani r, zakaria a, hashim yzh, jeffree ai, helmy km, kamarudin lm, omar mi, shakaff aym, adom ah, persaud kc. (2018) a study on volatile organic compounds emitted by in-vitro lung cancer cultured cells using gas sensor array and spme-gcms. bmc cancer, 18:362 doi:10.1186/s12885-018-4235-7. [4] chen c, lin w, yang h. (2020) diagnosis of ventilator-associated pneumonia using electronic nose sensor array signals: solutions to improve the application of machine learning in respiratory research. respiratory research, 21:45. doi:10.1186/s12931-020-1285-6. [5] hu w, wan l, jian y, ren c, jin k, su x, bai x, haick h, yao m, wu w. (2018) electronic noses: from advanced materials to sensors aided with data processing. advanced materials technologies, 4(2),1-38. doi: 10.1002/admt.201800488. 418 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 [6] yan j, guo x, duan s, jia p, wang l, peng c, zhang s. (2015) electronic nose feature extraction methods: a review. sensors, 15, 27804-27831. doi:10.3390/s151127804 27804–27831. [7] zulkhairi ma, mustafah ym, abidin zz, zaki hfm, rahman ha. (2019) car detection using cascade classifier on embedded platform. 7th international conference on mechatronics engineering (icom), putrajaya, malaysia, pp. 1-3, doi: 10.1109/icom47790.2019.8952064. [8] ansari aq, khusro a, ansari mr. (2016) performance evaluation of classifier techniques to discriminate odors with an e-nose. 12th ieee international conference electronics, energy, environment, communication, computer, control: (e3-c3), indicon, 2325-9418. doi:10.1109/indicon.2015.7443838. [9] yi z, li c. (2019) anti-drift in electronic nose via dimensionality reduction: a discriminative subspace projection projection approach. ieee access, 7, 170087–170095. doi:10.1109/access.2019.2955712. [10] vergara a, vembu s, ayhan t, ryan ma, homer ml, huerta r. (2012) chemical gas sensor drift compensation using classifier ensembles. sensors and actuators, b: chemical, 166–167, 320–329. doi: 10.1016/j.snb.2012.01.074. [11] liu b, huang y, kam kw, cheung wf, zhao n, zheng b. (2019) functionalized graphene-based chemiresistive electronic nose for discrimination of disease-related volatile organic compounds. biosensors and bioelectronics: x, 1, 100016. doi: 10.1016/j.biosx.2019.100016. [12] gargiulo v, alfano b, capua rd, alfè m, vorokhta m, polichetti t, massera e, miglietta ml, schiattarella c, francia gd. (2018) graphene-like layers as promising chemiresistive sensing material for detection of alcohols at low concentration. journal of applied physics, 123, 024503. doi:10.1063/1.5000914. [13] lu g, ocola le, chen j. (2009) reduced graphene oxide for room-temperature gas sensors. nanotechnology, 20, 445502, 1-9. doi:10.1088/0957-4484/20/44/445502. [14] lee k, yoo yk, chae ms, hwang ks, lee j, kim h, hur d, jeong hl. (2019) highly selective reduced graphene oxide (rgo) sensor based on a peptide aptamer receptor for detecting explosives. sci rep, 9, 10297. scientific reports, 9. doi:10.1038/s41598-019-45936-z. [15] tian w, liu x, yu w. (2018) research progress of gas sensor based on graphene and its derivatives: a review. applied sciences (switzerland), 8(7). doi:10.3390/app8071118. [16] lee sp. (2017) electrodes for semiconductor gas sensors. sensors, 17, 683; doi:10.3390/s17040683. [17] wang c, yin l, zhang l, xiang d, gao r. (2010) metal oxide gas sensors: sensitivity and influencing factors. sensors, 10, 2088-2106. doi:10.3390/s100302088. [18] baharuddin aa, ang bc, hoong y, haseeb asma, wong yc. (2019) materials science in semiconductor processing advances in chemiresistive sensors for acetone gas detection. materials science in semiconductor processing, 103, 104616. doi: 10.1016/j.mssp.2019.104616. [19] amiri v, roshan h, mirzaei a, neri g, ayesh ai. (2020) nanostructured metal oxide-based acetone gas sensors: a review. sensors, 20, 3096. doi:10.3390/s20113096. [20] norizan mn, zulaikha s, demon n, halim na. (2021) the frontiers of functionalized graphenebased nanocomposites as chemical sensors. nanotechnology reviews, 10: 330-369. doi:10.1515/ntrev-2021-0030. [21] james f, fiorido t, bendahan m, aguir k. (2017) comparison between mox sensors for low vocs concentrations with interfering gases allsensors, pp.39-40. [22] phillips co, syed y, parthaláin nm, zwiggelaar r, claypole tc, lewis ke. (2012) machine learning methods on exhaled volatile organic compounds for distinguishing copd patients from healthy controls. journal of breath research, 6(3). doi: 10.1088/1752-7155/6/3/036003. [23] yan j, tian f, he q, shen, y. (2012) feature extraction from sensor data for detection of found pathogen based on electronic nose. sensors and materials, 24(2), 57–73. [24] feng s, farha f, li q, wan y, xu y, zhang t, ning h. (2019) review on smart gas sensing technology. sensors (switzerland), 19(17), 1–22. doi:10.3390/s19173760. [25] hashoul d, haick h. (2019) sensors for detecting pulmonary diseases from exhaled breath. european respiratory review, 28(152). doi:10.1183/16000617.0011-2019. 419 iium engineering journal, vol. 24, no. 2, 2023 mohd tombel et al. https://doi.org/10.31436/iiumej.v24i2.2832 [26] xu y, zhao x, chen y, yang z. (2019) research on a mixed gas classification algorithm based on extreme random trees. applied sciences (switzerland), 9(9). doi:10.3390/app9091728. [27] thorson j, collier-oxandale a, hannigan m. (2019) using a low-cost sensor array and machine mixtures and identify likely sources. sensors, 19, 3723. doi:10.3390/s19173723. [28] tombel nsm, badaruddin sam, yakin fsm, zaki hfm, syono mi (2021) detection of low ppm of volatile organic compounds using nanomaterial functionalized reduced graphene oxide sensor. aip conference proceedings, 2368 vol. 020004. doi.org/10.1063/5.0057775. [29] smolinska a. (2014) current breathomics a review on data pre-processing techniques and machine learning in metabolomics breath analysis. journal of breath research, 8, 027105: 22. doi:10.1088/1752-7155/8/2/027105. [30] das s, jayaraman v. (2014) progress in materials science sno2: a comprehensive review in structures and gas sensors. progress in materials science, 66, pp. 112-255. doi: 10.1016/j.pmatsci.2014.06.003. [31] maity a, raychaudhuri ak, ghosh b. (2019) high sensitivity nh3 gas sensor with electrical readout made on paper with prevoskite halide as sensor material. scientific report, 9, 7777. doi: 10.1038/s41598-019-43961-6. [32] webb ar (2002) statistical pattern recognition statistical pattern recognition second edition. john wiley & sons,ltd, vol. 9. [33] bastuck m. (2019) improving the performance of gas sensor systems with advanced data evaluation, operation and calibration methods. linköping university electronic press, 298. [34] kong c, zhao s, weng x, liu c, guan r, chang z. (2019) weighted summation: feature extraction of farm pigsty data for electronic nose. ieee access, vol. 7, pp. 96732-96742. doi:10.1109/access.2019.2929526. [35] allwright s. (2022) how to interpret auc score. retrieved from https://stephenallwright.com/interpret-auc-score/. [36] nyssa ssc, xuevz, justin tn, v. r. saran kc, raia cf, michael jl, thomas lw, mike f, gregory js, philippe b, christopher jh, steven jk. (2022) machine learning-based rapid detection of volatile organic compounds in a graphene electronic nose. acs nano 2022 16 (11), 19567-19583. doi: 10.1021/acsnano.2c10240. 420 https://doi.org/10.1016/j.pmatsci.2014.06.003 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 improved constraint handling approach for predictive functional control using an implied closed-loop prediction muhammad abdullah1, john anthony rossiter2, and alia farhana abdul ghaffar1* 1 department of mechanical engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia 2 department of automatic control and systems engineering, the university of sheffield, s1 3jd, uk * corresponding author: aliafarhana@iium.edu.my (received: 6th july 2020; accepted: 24th september 2020; published on-line: 4th january 2021) abstract: predictive functional control is a simple alternative to the traditional pid controller which has the capability to handle process constraints more systematically. nevertheless, the most basic form of pfc has suffered from ill-posed prediction due to its simplicity in formulation and assumption of constant future input dynamics. although some constraints can be satisfied, nevertheless the performance may be very conservative due to this issue. the main objective of this paper is to improve the constrained performance of a pfc controller with a minimum modification of the existing formulation. specifically, a novel constraint handling approach for pfc is proposed based on an implied closed-loop prediction. instead of assuming a constant input as deployed in the conventional open-loop prediction, the implied closed-loop input dynamics are utilised to detect future constraint violations. in addition, a future perturbation is introduced into the prediction structure as an extra degree of freedom for satisfying the constraints. two simulation results confirm that the proposed approach gives far less conservative constraint handling and thus better control performance compared to the nominal pfc. furthermore, this novel implementation also alleviates the well-known tuning difficulties and prediction inconsistency issues that are associated with conventional pfc when handling constraints. abstrak: kawalan kefungsian ramalan adalah alternatif mudah kepada kawalan tradisional pid yang mempunyai kekangan keupayaan bagi mengawal proses secara lebih tersusun. namun, keadaan paling asas pada kesan pfc adalah daripada ramalan tak terajurapi yang disebabkan oleh formula ringkas dan anggapan dinamik input yang sama bagi masa depan. walau kekangan ini dapat diatasi, namun prestasi akan berubah secara konservatif disebabkan oleh isu ini. objektif utama kajian ini adalah bagi membaiki kekangan prestasi kawalan pfc dengan modifikasi minimum formula yang ada. secara spesifik, pendekatan nobel kawalan pfc dicadangkan berdasarkan ramalan lingkarantertutup. selain anggapan input tetap seperti yang dilakukan pada ramalan lingkaranterbuka yang konservatif, dinamik input yang dibuat pada lingkaran-tertutup telah digunakan bagi mengesan kekangan masa depan yang bertentangan. tambahan, gangguan yang bakal berlaku pada masa depan telah diperkenalkan ke dalam struktur ramalan sebagai tambahan darjah pada kebebasan bagi mengatasi kekangan. dua dapatan simulasi kajian menyetujui pendekatan yang dicadangkan dan menyebabkan sangat kurang kekangan pengendalian pada sistem konservatif, oleh itu kawalan yang lebih bagus pada prestasi berbanding pada pfc nominal. selain itu, pendekatan nobel ini juga 323 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 menghilangkan kesukaran pelarasan yang dikenali ramai dan ramalan isu tidak konsisten yang terdapat pada pfc konvensional apabila mengendali kekangan. keywords: predictive functional control (pfc); constraints handling; implied closed-loop prediction; constrained predictive controller 1. introduction advances in the industrial revolution triggered the need for advanced control methods that can work within a constrained environment. generally, constraints can be classified into two categories: i) a hard constraint refers to a physical limitation of process hardware which typically is in terms of input and output rates and ii) a soft constraint refers to a state or output limit which may be violated to some extent when required or perhaps when unavoidable. satisfying all of these constraints can provide several benefits such as lower maintenance costs, maximisation of profits, and a safer control environment [1]. nevertheless, dealing with constrained systems poses several challenges. for example, one often needs to deploy a classical controller such as proportional integral derivative (pid) and ensuring this control loop does not violate the limits may not be straightforward or systematic in general. the more systematic, but far more expensive alternative, is to implement model predictive control (mpc); this approach utilises predictions explicitly and optimises the expected behaviour by minimising a quadratic cost function subjected to predictions satisfying process constraints [2, 3]. however, conventional mpc solutions [4] are expensive and computationally demanding and hence may not be viable for applications where the costs and complexity need to be similar to those of pid. an alternative prediction-based method which is computationally simple and relatively inexpensive is predictive functional control (pfc) [5-7]. whereas a conventional mpc algorithm uses optimisation of a quadratic cost function and the entire prediction trajectory, the most basic pfc utilises the prediction at just one point in the future, which is far simpler to compute, and avoids optimisation by forcing its future prediction to match the desired target trajectory (often first order dynamics) at a specific coincidence horizon. again, for simplicity, a well-known assumption is that the predicted future input dynamics are taken to be constant, as this simplifies the control law definition into the solution of a single degree of freedom (d.o.f) equality expression. thus, programming the algorithm will be simple and it can be used on a low cost processor including a programmable logic controller (plc) [5,8]. of course, as a consequence, pfc performance is suboptimal in general (e.g. measured against typical mpc objective functions), but because it provides straightforward tuning, implementation, and constraint handling, it can be effective for a number of single input single output (siso) processes when compared to both pid and mpc considering its low computation demand and simple coding requirement [6,9]. indeed, these features explain the widespread acceptance and successful implementation of pfc in many real industrial applications ranging from aerospace, automotive, and chemical processes [5,10]. the current implementation of pfc in handling input and rate constraints is by simply applying a clipping or saturation method. if the current manipulated input is violating the limits, then a maximum or minimum value will be sent to the plant. this simple framework can alleviate issues such as integral wind-up, due to its use of predictions, although it may still be suboptimal [5]. as for state and output constraints, the traditional pfc approach uses multiple controllers in parallel whereby the primary regulator is tuned to track the target trajectory while the other one is tuned to satisfy the limits [11], as shown in fig. 1. a realtime prediction is made based on the primary input by a supervisor and if it violates the limits, then the input will be switched. although this simple concept often works and 324 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 provides a fast control solution, it can nevertheless be considered obsolete with modern computing facilities and moreover lacks sufficient rigour. besides, it is easy to formulate scenarios where this approach fails or leads to significant performance degradation [12] and thus improvements are needed. fig. 1: schematics of traditional pfc when handling output constraint. a core aspect of efficient and accurate constraint handling is to ensure that the optimised predictions and the expected closed-loop behaviour are consistent [1,3, 12-13]. when there is inconsistency, ensuring that the model predictions meet constraints may be a poor reflection of whether the resulting closed-loop responses satisfy constraints, leading to either unpredicted constraint violations or the controlled response becomes very conservative in satisfying the constraints. in fact, the core weakness of the traditional pfc is its conventional assumption of its future input predictions being constant; in reality, this assumption is often inconsistent with the resulting closed-loop input to a significant degree [12]. hence, even though pfc can check the expected constraint violations over a long prediction horizon, yet due to the prediction mismatch, the control law will produce a very conservative solution. in previous work [12], an alternative parameterisation of the d.o.f. had been introduced within the pfc framework in order to improve the predictions and closed-loop behaviour’s consistency, thus resulting in more accurate constraint handling and systematic tuning. specifically, a laguerre based parameterisation of the predicted future input replaced the conventional constant input assumption of pfc. this modification showed improvements in the prediction consistency with low order models and thus enabled less conservative constraint handling [14]. however, the use of a simple first order laguerre function is still somewhat limited, and for higher-order systems, significant prediction inconsistency may still exist. while it is possible to increase the order of the laguerre polynomial [15], this is not straightforward in general [16] and not in line with the simplicity concept which is an essential facet of pfc. in summary, the specific objective of this new work is to propose a novel constraint handling concept for pfc, which can be applied to higher order systems and which minimises the prediction inconsistency, thus ensuring that the inequalities used for constraint handling are as accurate as possible and reducing conservatism and risk. in real applications, this is very beneficial as the system can be pushed to work nearer to its high profit boundary region without causing unexpected violations and thus fatigue damage. a core research gap in pfc is that there are no attempts in deploying the well-known concept from dual-mode mpc [3] whereby the predictions are made up by assuming a known feedback control law is in place for the asymptotic part of the predictions. in the case of pfc, a nominal control law is available for the constraint-free case and thus a simple proposal is to exploit this control law within the prediction formulation used for constraint handling. nevertheless, the nominal pfc control law also needs to be modified further by 325 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 | · · · introducing a new slack variable or degree of freedom (d.o.f.) in the formulation to be utilised for handling the constraints. thus, this paper will make two main contributions: (i) first, it will demonstrate how an effective d.o.f. can be incorporated alongside a suitable dual-mode formulation and (ii) second, it will show how the constraint handling can be implemented. 2. background on predictive functional control a brief review of the key assumptions, notations, and principles of conventional predictive functional control laws together with a constraint handling method as proposed in [12] is described in this section. 2.1 target trajectory and control law definition a core principle of pfc is, at sample 𝑘, a desired target trajectory 𝑟(𝑘 +𝑖|𝑘) is defined, where 𝑖 = 1,2,… for future samples 𝑘 +𝑖 based on a desired steady-state target 𝑅. the target trajectory is defined as a first-order-response from the current process output 𝑦𝑝(𝑘) to 𝑅, hence: 𝑟(𝑘 +𝑖|𝑘) = (1−𝜆𝑖)𝑅 +𝜆𝑛𝑦𝑝(𝑘), 𝑖 = 1,2,… (1) where, 𝜆 is the implied desirable pole position. for industrial users, one can use a desired settling time, ts and determine 𝜆 from the relationship [5]: 𝜆 = 𝑒 −3𝑇 𝑇𝑠 (2) with the sampling period, t. the second core principle in pfc is to force the system prediction, that is 𝑦𝑝(𝑘 +𝑛|𝑘), to match the target n samples into the future, where n is representing the coincidence horizon (second tuning parameter) [5]. hence, the control law can be summarised as: 𝑟(𝑘 +𝑛|𝑘) = (1−𝜆𝑛)𝑅 +𝜆𝑛𝑦𝑝(𝑘) = 𝑦𝑝(𝑘 +𝑛|𝑘) (3) this is shown in fig. 2 for clarity. the two tuning parameters or user choices are the desired closed-loop pole, λ, and the coincidence horizon, n. fig. 2: pfc control law definition. remark 2.1: for clarity of formulation, this work will not discuss the pfc framework that is related to a delay control problem and non-constant targets because these issues require more complex algebra and moreover have no effect on the core concepts proposed in this paper. details are available in the references [2,5]. 326 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 2.2 prediction structure and degrees of freedom for solving the control law in eq. (3), it is necessary to define the output prediction 𝑦𝑝(𝑘 +𝑛|𝑘) and its dependence on the control signal 𝑢(𝑘|𝑘). prediction is standard in the literature [1] so just a brief illustration is given here. it is noted that this formulation ensures unbiased prediction in the steady-state and therefore offset free tracking. without loss of generality, the formulation in this paper utilises a state space model as it is easier to demonstrate the proposed control law in the next section. the one-step ahead output prediction for a state-space model with states, inputs and output 𝑥(𝑘),𝑢(𝑘),𝑦𝑚(𝑘) can be formed as: 𝑥(𝑘 +1) = 𝐴𝑥(𝑘)+𝐵𝑢(𝑘) ; 𝑦𝑚(𝑘 +1) = 𝐶𝑥(𝑘 +1) (4) note the use of subscript m to denote model. typically, the real process output 𝑦𝑝 differs from the model 𝑦 𝑚 , so process predictions are estimated using the measured signal 𝑑(𝑘) given in the structure illustrated in fig. 3. hence: 𝑑(𝑘) = 𝑦𝑝(𝑘)−𝑦𝑚(𝑘) → 𝑦𝑝(𝑘 +𝑖|𝑘) = 𝑦𝑚(𝑘 +𝑖|𝑘)+𝑑(𝑘) (5) consequently, the predicted plant output with the assumed predicted constant future input (𝑢(𝑘) = 𝑢(𝑘 +1|𝑘) = 𝑢(𝑘 +2|𝑘),…) can be written as: 𝑦𝑝(𝑘 +𝑖|𝑘) = 𝐶𝐴 𝑖𝑥𝑘 +[𝐶𝐵,𝐶𝐴𝐵, . .𝐶𝐴 𝑖−1𝐵][ 1 ⋮ 1 ] ⏟ 𝐿 𝑢(𝑘)+𝑑(𝑘) (6) remark 2.2: for constraint handling it is convenient to stack the output predictions into matrix form over some prediction horizon and hence one can define: 𝑦 𝑝 → (𝑘+𝑛|𝑘) = 𝐹𝑥(𝑘) + 𝐻𝑢(𝑘) + 𝐿𝑑(𝑘) (7) 𝑦𝑝 → (𝑘 +𝑛|𝑘) = [ 𝑦𝑝(𝑘 +1|𝑘) 𝑦𝑝(𝑘 +2|𝑘) ⋮ 𝑦𝑝(𝑘 +𝑛|𝑘)] ; 𝐹 = [ 𝐶𝐴 𝐶𝐴2 ⋮ 𝐶𝐴𝑛 ] ; 𝐻 = [ 𝐶𝐵 0 0 ⋯ 𝐶𝐴𝐵 𝐶𝐵 0 ⋯ ⋮ ⋮ ⋮ ⋱ 𝐶𝐴𝑛−1𝐵 𝐶𝐴𝑛−2𝐵 𝐶𝐴𝑛−3𝐵 … ] fig. 3: structure of an independent model (im). 2.3 the pfc control law the conventional pfc control law is defined by substituting the predictions in eq. (6) into the control law definition eq. (3). it is understood that one must first choose the desired closed-loop pole, λ (0 < λ< 1), and the coincidence horizon, 𝑛. in fact, the choice of 𝑛 is less simple in general [13], but that discussion is outside the focus of this paper. defining the nth row of matrices 𝐹, 𝐻 to be 𝐹𝑛, 𝐻𝑛 respectively, the control law eq. (3) is defined by solving the following for 𝑢𝑘 (this form would be used in real implementation): 327 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 hnlu(k)+fnx(k)+d(k) = (1−λ n)r+λnyp(k) (8) equation (8) can be solved to determine 𝑢𝑘 but, in order to facilitate some loop analysis (nominal case), this can also be expressed by substituting 𝑦𝑝(𝑘) = 𝑦𝑚(𝑘)+𝑑(𝑘) = 𝐶𝑥(𝑘)+ 𝑑(𝑘). hence, the control law eq. (3) is presented as: (1−𝜆𝑛)(𝑅 −𝑑(𝑘)) = 𝐻𝑛𝐿𝑢(𝑘)+𝐹𝑛𝑥(𝑘)−𝜆 𝑛𝐶𝑥(𝑘) (9) thus, the required control input can be represented as an augmented state feedback: 𝑢(𝑘) = [ −(𝐹𝑛−𝐶𝜆 𝑛) 𝐻𝑛𝐿 (1−𝜆𝑛) 𝐻𝑛𝐿 ] ⏟ 𝑘 [ 𝑥(𝑘) (𝑅 −𝑑(𝑘)) ] ⏟ �̅�(𝑘) (10) where k is the state feedback gain and �̅�𝑘 is the augmented state. remark 2.3: the main reason why pfc is attractive is due to its simplicity in computing the control law of eq. (10). since 𝐻𝑛𝐿 and 𝐹𝑛 are only needed for a single horizon, 𝑛, the required computation is relatively straightforward and indeed can be calculated off-line [2, 5]. 2.4 conventional constraint handling with open-loop predictions a good constraint handling approach for pfc should be systematic and also simple enough to avoid the usage of common optimisers deployed in more expensive mpc algorithms and reference governor strategies [11, 17]. let the rate, input and output constraints at every sample be defined respectively as: δ𝑢 ≤ δ𝑢(𝑘) ≤ δ𝑢 ; 𝑢 ≤ 𝑢(𝑘) ≤ 𝑢 ; 𝑦𝑝 ≤ 𝑦𝑝(𝑘) ≤ 𝑦𝑝̅̅̅ (11) as discussed before, the classical pfc algorithm deploys a saturation method to deal with input and rate constraints [1,5], but that can be severely suboptimal in practice due to the difference between the input prediction and the implied closed-loop evolution. this inaccuracy is even more notable when output/state constraints are introduced in the optimised open-loop predictions, [14], as detailed next. the constraint handling procedure of pfc, as proposed by [12], is outlined as: (1) given a suitably long validation horizon, 𝑛𝑖 (horizon used to check a future limit violation), the whole set of future predictions as formulated in eq. (7) is computed. (2) group all the constraints (input, rate, and output) and the system predictions into a single set of linear inequalities as: 𝑀𝑢(𝑘) ≤ 𝒇(𝐾) (12) 𝑀 = [ 1 −1 1 −1 𝐻𝐿 −𝐻𝐿] ; 𝒇(𝑘) = [ 𝑢 −𝑢 δ𝑢 −δ𝑢 𝐿𝑦𝑝 −𝐿𝑦𝑃] − [ 0 0 𝑢(𝑘 −1) −𝑢(𝑘 −1) 𝐹𝑥(𝑘)+𝐿𝑑(𝑘) −𝐹𝑥(𝑘)−𝐿𝑑(𝑘)] where 𝒇(𝑘) depends on the states and the limits. it is advisable that the output predictions horizon, 𝑦 𝑝 → (𝑘+𝑛), and the row dimension of h, need to be long enough in order to capture all the important dynamics [17]. 328 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 (3) it is noted that the predictions will satisfy constraints if the selected input u(k) satisfies eq. (12), that is, inequalities 𝑀𝑢(𝑘) ≤ 𝒇(𝑘) can be used explicitly to determine this condition. next, a modern pfc constraint handling algorithm is given. this concept utilises a simple “for” loop to choose the 𝑢(𝑘), that is nearest to the unconstrained solution shown in eq. (10) but does not violate the limits in eq. (12). algorithm 2.1. at each time step or sample: (1) compute the unconstrained input 𝑢(𝑘) as defined in eq. (9). (2) define the vector 𝒇(𝑘), from eq. (13) where vector m is fixed. (3) a simple for loop is utilised to inspect each row of m, here: (a) the ith constraint; represented by the ith row of 𝑀𝑢(𝑘) ≤ 𝒇(𝑘), is checked using 𝑎𝑖 = 𝑀𝑖𝑢(𝑘)−𝒇𝑖(𝑘). (b) if 𝑎𝑖 > 0, then 𝑢(𝑘) = 𝒇𝑖(𝑘)/𝑀𝑖; else the original value of 𝑢(𝑘) is retained. it has been proven in [14] that for the nominal case where 𝑑(𝑘) is assumed constant and also for stable open-loop systems, a recursive feasibility property for algorithm 2.1 is guaranteed where 𝑢(𝑘) converges to a feasible value nearest to the unconstrained choice. remark 2.4: since algorithm 2.1 utilises a straightforward for-loop, the programming, coding, and computation becomes far simpler and faster compared to more demanding mpc approaches based on optimisation of a quadratic program. in addition, the algorithm is more systematic and faster than most of the conventional pid methods. however, it should be noted that the usage of pfc is often limited to a single-input-single-output (siso) process and is rarely used for multi-input, multi-output (mimo) systems [5]. 2.5 limitations of conventional pfc constraint handling the main reason behind the popularity of pfc in industrial processes is due to its transparent tuning parameters. here, one only needs to select the desired closed loop time constant, which is equivalent to 𝜆. then, the different choices of coincidence horizon, 𝑛, can be quickly explored using a computer while displaying the associated responses. thus, a user can then select a suitable coincidence horizon, 𝑛, for their system. nevertheless, there are two major trade-offs that need to be considered [8, 13, 15]: (1) smaller values of coincidence horizon, 𝑛, drive the output response closer to the target trajectory where the effect of tuning parameter, 𝜆, becomes more significant. however, smaller, 𝑛, typically leads to poorer consistency between the predicted and actual responses, and thus inaccurate constraint handling and potentially less desirable behaviour. (2) conversely, larger, 𝑛, improves the prediction consistency, yet the closed-loop behaviour then approaches open-loop dynamics which decreases the significance and efficacy of 𝜆 as a tuning parameter. prediction mismatch is potentially catastrophic for reliable constraint handling as predictions satisfying constraints need not imply that the resulting closed-loop responses will satisfy constraints, and vice versa. consequently, the constraint handling algorithm may be either highly conservative [12, 14] and/or overly aggressive. 329 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 remark 2.5: it is well noted that one of the weaknesses of conventional pfc algorithm is its prediction mismatch [1] between its optimised predictions and the closed-loop behaviour that results. this inconsistency arises mainly due to the assumed constant future input prediction. consistency between predictions and actual behaviour is needed to ensure good behaviour, especially for cases dealing with higher order systems. 3. pfc constraint handling based on an implied closed-loop prediction the main weakness of conventional pfc, as indeed with many conventional mpc algorithms, is its assumption of a constant future input. this assumption is typically inconsistent with the actual closed-loop behaviour, and thus incorrect constraint handling decisions are made [12]. to some extent, dual-mode approaches [18] can overcome this issue by ensuring the predictions are as close as possible to the actual closed-loop behaviour, but of course these are computationally demanding. the main contribution here is to exploit a similar concept, that is, to use implied closed-loop predictions for constraint handling, but in a simplified manner to maintain the core selling benefits of pfc. the proposal is novel in that dual-mode approaches still use open-loop predictions in transients, but with a longterm input trajectory that emulates the implied closed-loop after transients. conversely, we will predict the expected closed loop behaviour explicitly for the entire horizon. in summary, the expected benefits of this proposal are: • more accurate predictions when checking output/state constraints implies less conservative decision making. • a smaller coincidence horizon (n) can be selected without worrying about the prediction inconsistency which will retain more tuning capability. • the proposed approach only requires a simple modification in the offline computations required for constraint handling. 3.1 closed-loop prediction pfc (cl-pfc) with constant input perturbation in order to use closed-loop predictions for constraint handling, an extra d.o.f. is required in the predictions. the proposal here is to add a constant perturbation to the implied closedloop input [1] as this structure has been found to be effective elsewhere. hence, based on the control law of eq. (10), the closed-loop prediction model combines the open-loop model and control law, with a constant input perturbation, 𝑐(𝑘), as the new d.o.f. thus: {𝑥(𝑘 +1|𝑘) = 𝐴𝑥(𝑘)+𝐵𝑢(𝑘);𝑢(𝑘) = 𝐾𝑥(𝑘)+𝑐(𝑘);𝑐(𝑘 +𝑖|𝑘) = 𝑐(𝑘), 𝑖 > 0} (13) 𝐴,𝐵 are the augmented model with respect to �̅�𝑘.the implied closed-loop predictions take the following form (for clarity of presentation, we define ϕ = [𝐴+𝐵𝐾] ): [ 𝑦𝑝(𝑘 +1|𝑘) 𝑦𝑝(𝑘 +2|𝑘) ⋮ 𝑦𝑝(𝑘 +𝑛|𝑘)] = [ 𝐶ϕ 𝐶ϕ2 ⋮ 𝐶ϕ𝑛 ] ⏟ 𝑃𝑐 𝑥(𝑘)+ [ 𝐶𝐵 0 0 ⋯ 𝐶ϕ�̅� 𝐶𝐵 0 ⋯ ⋮ ⋮ ⋮ ⋱ 𝐶ϕ𝑛−1𝐵 𝐶ϕ𝑛−2𝐵 𝐶ϕ𝑛−3𝐵 …] ⏟ 𝐻𝑐 𝐿𝑐(𝑘) (14) [ 𝑢(𝑘|𝑘) 𝑢(𝑘 +1|𝑘) ⋮ 𝑢(𝑘 +𝑛|𝑘) ] = [ −𝐾 −𝐾𝜙 ⋮ −𝐾𝜙𝑛−1 ] ⏟ 𝑃𝑐𝑢 𝑥(𝑘)+[ 𝐼 0 0 ⋯ −𝐾�̅� 𝐶�̅� 0 ⋯ ⋮ ⋮ ⋮ ⋱ −𝐾ϕ𝑛−2�̅� 𝐶ϕ𝑛−3�̅� 𝐶ϕ𝑛−4�̅� … ] ⏟ 𝐻𝑐𝑢 𝐿𝑐(𝑘) (15) 330 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 [ δ𝑢(𝑘|𝑘) δ 𝑢(𝑘 +1|𝑘) ⋮ δ𝑢(𝑘 +𝑛|𝑘) ] = 𝑃𝑐𝐷𝑢𝑥(𝑘)+𝐻𝑐𝐷𝑢𝑐(𝑘)+𝑄𝑐𝐷𝑢𝑢(𝑘) (16 remark 3.1: for the unconstrained case, the value of perturbation as in eq. (13) will be 𝑐(𝑘) = 0 since the term 𝑢(𝑘) = 𝐾�̅�𝑘 is derived from the original control law. thus, a nonzero 𝑐(𝑘) is required solely for constraint handling and the underlying loop tuning is based on the original pfc law. 3.2 constraint handling for constraint handling, a similar procedure as discussed in section 2.4, will be employed. the prime conceptual improvement here is the d.o.f., which is now expressed in terms of perturbation 𝑐(𝑘) instead of the input 𝑢(𝑘) and one needs to consider the entire input prediction and not just the first value. thus: 𝑀𝑐𝑘 ≤ 𝒇𝑘, (17) 𝑀 = [ 𝐻𝑐𝑢𝐿 −𝐻𝑐𝑢𝐿 𝐻𝑐𝐷𝑢𝐿 −𝐻𝑐𝐷𝑢𝐿 𝐻𝑐𝐿 −𝐻𝑐𝐿 ] ; 𝒇(𝑘) = [ 𝐿𝑢 −𝐿𝑢 𝐿δ𝑢 −𝐿δ𝑢 𝐿(𝑦𝑝 −𝑑(𝑘)) −𝐿(𝑦𝑃 −𝑑(𝑘))] − [ 𝑃𝑐𝑢𝑥𝑘 −𝑃𝑐𝑢𝑥𝑘 𝑃𝑐𝑢𝑥𝑘 +𝑄𝑐𝐷𝑢𝑢(𝑘 −1) −𝑃𝑐𝑢𝑥𝑘 +𝑄𝑐𝐷𝑢𝑢(𝑘 −1) 𝑃𝑐𝑥𝑘 −𝑃𝑐𝑥𝑘 ] in a similar manner to algorithm 2.1, the goal is to select the d.o.f. c(k) that is closest to its unconstrained value while satisfying the constraints in eq. (11) (equivalently inequalities (17)). algorithm 3.1. at each sample: (1) set 𝑐(𝑘) = 0. (2) define vector �̅�𝑘 as in eq. (17) with the assumption that �̅� does not change. (3) a simple loop is utilised to inspect each row of �̅�, where: (a) the ith constraint represented by the ith row of �̅�𝑐(𝑘) ≤ �̅�(𝒌) is checked with 𝑎𝑖 = �̅�𝑖𝑐(𝑘)− �̅�𝑖(𝑘). (b) if 𝑎𝑖 > 0, then 𝑐(𝑘) = �̅�𝑖(𝑘)/�̅�𝑖, else use the existing 𝑐(𝑘). (4) define the input from 𝑢(𝑘) = −𝐾�̅�𝑘 + 𝑐(𝑘). one can argue that better prediction consistency and more accurate constraint handling is obvious (and will be demonstrated in the examples section). nevertheless, it is also important to establish that the proposed algorithm does indeed retain feasibility, that is the recursive feasibility property in the nominal case and moreover subject to changes in the target r. theorem 3.1: when there is no change in 𝑑(𝑘) and also in the nominal case, algorithm 3.1 can guarantee recursive feasibility with any desired target, r. proof: assume at sample k−1, the solution is feasible, then with no change in r, the choice 𝑐(𝑘) = 𝑐(𝑘 −1) must retain feasibility as the implied predictions at the previous and current 331 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 sample would then be identical. hence, it remains only to show that 𝑐(𝑘) can be chosen to retain feasibility, irrespective of any changes in r. consider then the nominal control law given in eq. (10) and augment this with the proposed perturbation term 𝑐(𝑘) as in eq. (13), hence: 𝑢(𝑘) = [ −(𝐹𝑛−𝐶𝜆 𝑛) 𝐻𝑛𝐿 (1−𝜆𝑛) 𝐻𝑛𝐿 1][ 𝑥(𝑘) 𝑅 −𝑑(𝑘) 𝑐(𝑘) ] (18) it is clear that the terms 𝑅 and 𝑐(𝑘) both act as scaled additive terms to 𝑢(𝑘), and thus any change in r can be countered by a suitable scaled change in 𝑐(𝑘) so that the predictions at sample 𝑘 match those from sample k − 1. in other words, recursive feasibility is guaranteed! corollary 3.2: in practice, algorithm 2.1 uses the smallest perturbation 𝑐(𝑘) possible so that performance is as close as possible to that desired. this also means that, if it is feasible, then 𝑐(𝑘) is driven to zero and offset free tracking will be ensured. the reader will note that we have not attempted to guarantee recursive feasibility subject to parameter uncertainty and disturbance changes as the literature on that area is far more complicated than would fit with the pfc philosophy: that is, simple coding and implementation. of course, in practice, all mpc algorithms have some inherent degree of robustness and thus this lack of a guarantee is rarely a problem except for exceptional and challenging cases where one is unlikely to use pfc anyway. 4. methodology for result analysis in this paper, the developed formulation will be used to set up the control algorithm for an arbitrary siso system with constraints. instead of quantitative analysis, this paper adopts a qualitative analysis since the main objective is to show the improvement between the proposed pfc with a conventional pfc. the control performance can be evaluated by observing its convergence speed to the desired setpoint within the constrained environment. besides, for clarity of presentation, the obtained simulation results will not be compared with other types of controllers as that is not the main contribution of this paper and moreover, those comparisons are already well known in the existing literature. indeed pfc performance cannot be contrasted with more comprehensive mpc alternatives as those deploy more complicated algorithms and are far more costly to implement and maintain. interested readers can refer to these references on the comparison between mpc, pid and pfc [19, 20]. 5. numerical examples this section provides two numerical examples with the characteristics of typical industrial processes to highlight the effectiveness of the proposed algorithm 3.1 compared to the traditional pfc algorithm such as algorithm 2.1. for clarity, the following comparisons are made: (1) investigation of the prediction behaviour of the two algorithms and their associated consistency with the resulting closed-loop dynamics. (2) comparison of the closed-loop controller performance when dealing with output constraints. (3) demonstration of the ability of the proposed controller to handle multiple constraints and uncertainties. 332 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 in order to emphasise a variety of characteristics, the examples use two second order dynamics systems as follows: (1) a second order over-damped system model (pole at 0.4 and another pole at 0.8), with constraints of 𝑢 = 0.12, ∆𝑢 = 0.05, and 𝑦 = 1.5: 𝐺1 = 𝑧−1 +0.3𝑧−2 1−1.2𝑧−1 +0.32𝑧−2 ; 𝑛 = 2 ;λ = 0.7 (19) and to include the model uncertainty in the analysis, the real process representation is given by: 𝐺1,𝑝 = 𝑧−1 +0.28𝑧−2 1−1.21𝑧−1 +0.3𝑧−2 (20) (2) a second order non-minimum phase model (zero at 1.6 and poles at 0.6 and 0.85, respectively), with constraints of 𝑢 = −3, ∆𝑢 = −1, and 𝑦 = 1.5: 𝐺2 = 0.1𝑧−1 −0.16𝑧−2 1−1.45𝑧−1 +0.51𝑧−2 ; 𝑛 = 5 ;λ = 0.7 (21) and its real process representation is given by: 𝐺2,𝑝 = 0.11𝑧−1 −0.15𝑧−2 1−1.44𝑧−1 +0.5𝑧−2 (22) the reader is reminded that λ is selected based on the user preference, which is associated to the desired closed-loop time response (cltr). the selection range is between 0 < λ < 1. in principle, a smaller λ gives faster convergence and vice versa. normally, the coincidence horizon, n, is taken to be at the low end of the values which gives good performance as this ensures that λ is also an effective tuning parameter. 5.1 effect of prediction consistency when identifying future constraint violations in this subsection, only the output constraint will be considered to highlight the performance improvement where the output limit for both examples is set to 𝑦 = 0.8. in addition, the plant transfer function is set to be equal as the model 𝐺𝑝 = 𝐺. notably, and as expected, the unconstrained control law for both pfc and cl-pfc for examples 1 and 2 are the same as shown in figs. 3 and 4, respectively. since pfc is a discrete controller, the results are plotted in terms of sampling instant instead of time. however, in the presence of output constraints, their performances may differ since the adjustment is linked to different inequalities shown in eq. (12) and eq. (17), respectively. the first example is based on open-loop predictions, while the second example is based on implied closed-loop predictions. in this section, we present the optimised predictions for each algorithm, with and without constraint handling, and demonstrate the differences in the resulting decision making. the core observations are as follows: • the unconstrained predictions at the first sample (same for both approaches) violate output constraints for large prediction horizons (refer to figs. 5 and 6). • based on fig. 7 and fig. 8, algorithm 2.1 (pfc, red dotted line) reduces the choice of constant 𝑢(𝑘) substantially to ensure that the maximum value of 𝑦𝑝(𝑘 +𝑖|𝑘) satisfies the constraints, but the consequence is a small initial value of 𝑢(𝑘) and a much slower responding output prediction for both examples 1 and 2 respectively. 333 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 • conversely, algorithm 3.1 (cl-pfc, blue dashed line) recognises that future inputs will change, thus the predictions used for constraint handling can retain the fast transients while not exceeding the constraints. fig. 3: unconstrained closed-loop input and output of pfc and cp-pfc for example g1. fig. 4: unconstrained closed-loop input and output of pfc and cp-pfc for example g2. fig. 5: input and output predictions at the first sample of pfc and cp-pfc for example g1. 334 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 fig. 6: input and output predictions at the first sample of pfc and cp-pfc for example g2. fig. 7: constrained input and output behaviour of pfc and cl-pfc for example g1. fig. 8: constrained input and output behaviour of pfc and cl-pfc for example g2. in summary, due to significant prediction mismatch in the open-loop predictions and the corresponding closed-loop behaviour in algorithm 2.1, the constraint handling is highly conservative/suboptimal. conversely, the proposed algorithm 3.1 removes this mismatch thus ensuring effective and accurate constraint handling, therefore, no more loss of performance than necessary. 5.2 handling multiple constraints and uncertainties in this section, the cl-pfc algorithm is tested with multiple constraints that include input, input rate, and output constraints to demonstrate that algorithm 3.1 deals effectively 335 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 with all of these simultaneously. moreover, some parameter uncertainties are introduced to demonstrate inherent robustness as discussed before in the introduction part of section 4. in addition, to demonstrate the recursive feasibility properties more strongly, the examples include a switch from a feasible to an infeasible r. figures 9 and 10 show the constrained closed-loop performance of cl-pfc for both example 1 and 2, respectively. it is noted that all the constraints are satisfied without a conflict and good performance is retained even in the presence of uncertainty while the system converges to the closest feasible output. fig. 9: constrained and unconstrained performance for example g1. fig. 10: constrained and unconstrained performance for example g2. 5.3 possible application and practical significance as discussed in section 1, pfc is a simple and practical controller that can be implemented in any processor with a few lines of coding. the main attraction of pfc is that it can provide a satisfactory control performance when handling constraints with minimum computation and transparent tuning parameter of the desired closed-loop time constant. it should be noted that this work does not claim that pfc is better than mpc and in fact, it can never be, due to the simplification of the algorithm. for low order processes and siso systems, pfc can work well whereas the implementation of mpc will be very expensive for a simple application. with the proposed framework, the user can get a less conservative control performance compared to a traditional pfc. for example, if this controller is implemented in a car, the car will slow down at the right time before cornering. conversely, with a traditional pfc, the car will slow down long before the corner which will make it unnecessarily conservative/slow. given the nominal performance is the same as conventional pfc, the authors expect that application of cl-pfc to real systems will demonstrate similar benefits [3, 17] in the constrained case; this constitutes future work. 336 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 6. conclusions this work presents a novel constraint handling approach for pfc that employs some of the recent ideas from a more conventional mpc. specifically, by utilising the concept of an implied closed-loop prediction one can make the constraint handling decisions more accurate. with this modification, the constraint handling performance becomes more consistent and reliable when compared with the nominal pfc, as demonstrated in the numerical example simulations. with this finding, a simple system can work nearer to its constraints limits, but without constraint violation or sacrificing the desired dynamic performance. it is also worth highlighting that the required modifications for deploying this method are simple, thus in-line with the key requirements for pfc. in a real application, this benefit may be translated in terms of more production profit and a safer working environment as well as simple coding and maintenance. nevertheless, it should be noted that the constrained control performance is not claimed to be optimal. the underlying algorithm is still based on a simplified and far cheaper version of conventional mpc so the performance is not expected to be comparable. a few aspects which can be addressed next may include the rigorous extension of this approach to handle more challenging open-loop dynamics such as unstable, marginally stable, and oscillating systems. in addition, a more systematic and robust tuning procedure in selecting a suitable coincidence horizon in the presence of parameter uncertainty, noise and disturbances also needs to be investigated. a systematic sensitivity analysis that describes the relationship between the pfc tuning parameter and those uncertainties may provide useful information to a user before deploying this controller. acknowledgements the author would like to acknowledge the international islamic university malaysia research acculturation grant scheme 2018 (irags18-013-0014) and ministry of higher education malaysia for funding this work. references [1] rossiter, j. a. (2018). a first course in predictive control. crc press. [2] haber, r., bars, r., & schmitz, u. (2012). predictive control in process engineering: from the basics to the applications. john wiley & sons. [3] mayne, d. q., rawlings, j. b., rao, c. v., & scokaert, p. o. (2000). constrained model predictive control: stability and optimality. automatica, 36(6), pp 789-814. [4] clarke, d. w., & mohtadi, c. (1989). properties of generalized predictive control. automatica, 25(6), pp 859-875. [5] richalet, j., & o'donovan, d. (2009). predictive functional control: principles and industrial applications. springer science & business media. [6] richalet, j., & o'donovan, d. (2011). elementary predictive functional control: a tutorial. in 2011 international symposium on advanced control of industrial processes (adconip): may 2011; pp 306-313. [7] richalet, j., rault, a., testud, j. l., & papon, j. (1978). model predictive heuristic control. automatica (journal of ifac), 14(5), pp 413-428. [8] khadir, m., & ringwood, j. (2008). extension of first order predictive functional controllers to handle higher order internal models. international journal of applied mathematics and computer science, 18(2), pp 229-239. 337 iium engineering journal, vol. 22, no. 1, 2021 abdullah et al. https://doi.org/10.31436/iiumej.v22i1.1538 [9] haber, r., rossiter, j. a., & zabet, k. (2016). an alternative for pid control: predictive functional control-a tutorial. in 2016 american control conference (acc): july 2016; pp. 6935-6940 [10] richalet, j., lavielle, g., mallet, j., & dreyfus, g. (2005). la commande prédictive. eyrolles. [11] fiani, p., & richalet, j. (1991). handling input and state constraints in predictive functional control. in proceedings of the 30th ieee conference on decision and control: december 1991; pp. 985-990. [12] abdullah, m., & rossiter, j. a. (2019). using laguerre functions to improve the tuning and performance of predictive functional control. international journal of control, pp 1-13. [13] rossiter, j. a., & haber, r. (2015). the effect of coincidence horizon on predictive functional control. processes, 3(1), pp 25-45. [14] abdullah, m., rossiter, j. a., & haber, r. (2017). development of constrained predictive functional control using laguerre function based prediction. ifac-papersonline, 50(1), pp 10705-10710. [15] khan, b., & rossiter, j. a. (2013). alternative parameterisation within predictive control: a systematic selection. international journal of control, 86(8), pp 1397-1409. [16] muehlebach, m., & d'andrea, r. (2017). basis functions design for the approximation of constrained linear quadratic regulator problems encountered in model predictive control. in 2017 ieee 56th annual conference on decision and control (cdc): december 2017; pp. 6189-6196. [17] gilbert, e. g., & tan, k. t. (1991). linear systems with state and control constraints: the theory and application of maximal output admissible sets. ieee transactions on automatic control, 36(9), pp 1008-1020. [18] scokaert, p. o., & rawlings, j. b. (1998). constrained linear quadratic regulation. ieee transactions on automatic control, 43(8), pp 1163-1169. [19] valencia-palomo, g., & rossiter, j. a. (2012). comparison between an auto-tuned pi controller, a predictive controller and a predictive functional controller in elementary dynamic systems. online publication, research gate. [20] haber, r., rossiter, j. a., & zabet, k. (2016). an alternative for pid control: predictive functional control-a tutorial. in 2016 american control conference (acc): july 2016; pp. 6935-6940. 338 microsoft word 8-paper print5bassam.doc iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 31 numerical investigation of parameters affecting the thermal and hydrodynamic characteristics of impinging jets in cross flow b. m. suloiman department of mechanical engineering, university of jordan, amman-jordan b. a. jubran department of mechanical and industrial engineering, sultan qaboos university, al-khod-sultanate of oman abstract: in this investigation the hydrodynamic and the thermal fields due to a single impinging jet in crossflow have been investigated numerically, using a 2-d axisymmetric model in order to predict the ground vortex characteristics. the parameters investigated include the effective velocity ratio, the nozzle height, the nozzle pressure ratio, the intake location, the intake mass flow rate and the jet temperature ratio. it is interesting to note that even with the 2-d modeling limitations it was possible to capture most of the thermal and fluid field characteristics of the ground vortex. it was found that the temperature distribution in the flow field is greatly affected by the effective velocity, and the maximum penetration point of the ground vortex is equal to the hot gas penetration. the ground vortex strength increases slightly with increasing the intake mass flow rate but has a minor effect on the ground vortex geometry and on the penetration of the hot gases. the intake location has a significant effect on the ground vortex strength when it is located upstream of the ground vortex core. key words: numerical investigation, turbulence models, impinging jets, cross-flow. 1. introduction jets in cross flow are encountered in many engineering applications, such as cooling of gas turbine blades and combustion chambers, plume dispersion, reaction control for missiles, flow of waste water into rivers, and vertical and/or short takeoff/landing (v/stol) aircrafts. an extensive bibliography of numerous experimental and numerical investigations on jets in cross flow has been presented by margason [1]. modeling of impinging jets in cross flow with particular application to v/stol aircraft seems to be centered around the hydrodynamic characteristics of the flow with a limited number of investigations on the thermal characteristics associated with such a flow. one could classify these investigations into basically three groups; the first group deals with the validation of various turbulence models, the second group tests the potential of various solution procedures and the third group investigates the effects of various parameters on the flow field of such a problem. jones and mcguirk [2], and childs and nixon [3] modeled turbulent round jets in cross flow using three-dimensional grids and the standard k- model with little success. van dalsem et al [4] investigated the ground vortex associated with a single jet in cross flow using the baldwin-lomax algebraic turbulence model and the predicted results agreed reasonably well with the experimental results. catalano et al [5] modeled a turbulent jet in a confined cross-flow using a power law scheme to account for the combined effects of convection and diffusion between the adjacent grid points. a staggered grid was used with the pressure and the other dependent variables stored in the main grid points while the velocities were stored in the staggered locations. the predicted and the experimental results show good agreement except in the vicinity of the jet where the prediction was relativel y poor due to the anisotropic nature of the flow in this region. barata et al [6] used the quick scheme with a standard k- model to predict the flow field of jet in cross flow and found that such a model was not able to correctly predict the shear stress distribution in the impinging zone. hwang and liu [7] solved the reynolds-averaged compressible navior-stokes equations together with the standard k- turbulence model to predict the impinging jet flow fields associated with flow fields associated with v/stol aircrafts. implicit finite difference schemes were used with implicit boundary treatment to predict the effects of the height of the nozzle on the flow field of a jet in cross flow. agarwal and bower [8] solved the navier stokes and energy equations in a stream function/vorticity form in conjunction with the k- model together with an augmented central difference scheme to preserve the diagonal dominance character of the difference equations at high reynolds numbers. the resulting difference equations were solved by successive point relaxation. the main conclusion of this investigation is that k- model has shortcomings in predicting the thermal as well as the hydrodynamic field of impinging jets relevant to v/stol aircrafts. hwang et al [9] investigated numerically the airfoiljet-ground interaction flow field and planar jet issuing from fuselage under surface in ground effect. implicitfactored scheme with central difference and explicit iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 32 boundary were used to solve the averaged compressible navier-stokes equations for two-dimensional flow that is related to v/stol aircraft. the cross-flow reynolds numbers used were 5,000 and 20,000 while temperature ratio between the jet and the cross flow were 1 and 1.5. it was found that when the temperature of the jet was increased, the jet strength was reduced due to the decrease in the density at the plane of the entering jet. bray and knowles [10] conducted a parametric study for some of the parameters affecting the flow field of impinging jet in cross flow using a standard k- model. their predicted results indicate that the vortex core and the maximum penetration points are coincident with the ground plane minimum and maximum penetration positions. one of their main conclusions is that the effects attributed to the jet height are due to inaccuracies in the modeling of the free jet turbulence. smith et al [11] investigated the jet flow fields that could be generated by v/stol aircraft in ground effect using two commercial packages called flosys and phoenics. both packages predicted the experimental result rather well and found the k- model turbulence model tends to increase the mixing of the jet. the nozzles temperature effects were also investigated and it was found that the predicted temperature in the intake was increased by approximately 180c at h/d=4. the hot gas environment around a v/stol aircraft operating in ground proximity was numerically modeled by van overbeke and james [12] and tafti and vanka [13] using the same configuration of multiple impinging jets with temperature fields close to the engine inlet. the predicted results indicate that the mean inlet temperature rise increased with decreasing the head wind and decreasing distance from the ground. furthermore, the hot gas ingestion (hgi) from the fountain flow was more severe than the hgi due to the recirculating flow. it appears from the aforementioned investigations that most attention has been paid to the flow field characteristics rather than the thermal field. it is hoped that this paper will provide an extended parametric investigation, which will include both hydrodynamic as well as thermal parameters of the flow with some emphasis on the parameters that affect the hgi. 2. mathematical formulation a schematic diagram showing the flow field that would result from the impingement of a jet normal to the surface in the presence of a cross flow is shown in figure 1. the general governing equation for a singlephase, two-dimensional, steady state flow is given by [14]: this equation may be written for plane or axisymmetric geometry as  s)grad(div)v(div   (1) and    sjr y jr yx jr x vjr y ujr x                                 (2) where the co-ordinates are defined in terms of x and y directions with y=r for the axi-symmetric geometry; u and v are the local velocities in the x and y directions, respectively. as was pointed out by bray and knowles [10] that although the problem is inherently unsteady 3-d flow field, yet 2-d modelling is capable of providing an economical parametric investigation. threedimensional modeling can then be used to further investigate some selected conditions. the turbulent exchange coefficient and source terms for the general variable  are  and ,s respectively. the superscript j=1 for the axi-symmetric case and j=0 for the plane case. the expression for the turbulent exchange coefficient and source terms are given for the various solved equations in table 1. the compressibility effect was introduced into the code by using the perfect gas equation (ρ=p/rt), where p, t, and r are the pressure, temperature, and the gas constant of the fluid, respectively. table 1: summary of the coefficients and sources of the variable  equations   s continuity 1 0 0 -momentum u eff 2 21 1 r vj y v r yry u xy x v r yrx u xx eff eff j jeff eff j jeff                                                      y-momentum v eff turbulence energy k keff  / g dissipation   /eff   21 cgck  energy t teff  / 0 iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 33 the standard k-ε model is used in the present investigation where reynolds stress is computed using the boussineseq eddy viscosity concept, which is given by ijijjitji kuuuu  3 2 )( ,,  (3) the eddy viscosity t is found from   / 2kcc dt  where k, and  are the turbulent kinetic energy and its rate of dissipation, respectively. the two transport equations used for the solutions of k and  are given by )p(]kku[)k( ki,i k t it,     (4) )(][)( 21,,        cpc k u kii t it  (5) where pk is the volumetric production rate of the kinetic energy and is given by pk = -uiujui,j, and the standard values of the unmodified empirical constant are; cµcd=0.09, c1ε=1.44, and c2ε=1.92, σk=1.0, and σε=1.314. adjacent to the wall, the model of turbulence must account for the viscous effects and, to do that, the wall function is used. the wall function may be written as follows: where u+=u/uτ, uτ=(τw/ρ) 0.5, y+= uτ y/νℓ, k=0.435, e=0.9 and νℓ is the laminar kinematic viscosity. the flow equations were solved using the embodied simple procedure. additional information on the mathematical procedures used may be found into the team manual [14]. fig. 1 flow field of turbulent impinging jet in cross-flow 3. boundary conditions and computational details the elliptic nature of the problem in question required the specifications of the boundary conditions along all domain boundaries for all dependent variables. the boundary conditions used in this problem may be divided into five types; fluid entry plane where all flow properties must be known and prescribed (  constant), axis of symmetry where the gradients of all properties normal to this axis are zero, fluid exit plane where zero streamwise gradient of all properties are used with a uniform pressure along the exit plane, walls where the velocity components and the turbulent quantities are zero with the use of the wall function, and the entrainment boundary where the pressure is uniform and the tangential velocity component is set to zero. preliminary numerical tests were conducted to explore the grid dependence and the number of iterations. it was found that an independent solution is obtained with a grid of 52x34 for the case without the intake effects and 58x34 for the case with the intake. the grids were generated in such a way that very close to the walls the density of the grid points is high. the grid used in modelling is shown in figure 2. fig. 2a boundary conditions for modeling impinging jet in cross-flow (6) )eyln( k u   1 (7) )cc(uk /dw 212   (8) ky u w 3   iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 34 fig. 2b typical grid used for modeling impinging jet in crossflow a convergence criteria of the residual of 1% was typical for most of the studied cases. however, the two most difficult variables to converge were the kinetic energy k and the dissipation rate  and for these two variables to converge within the 1%, the residuals for the other quantities were usually below around 0.01%. the present predictions were carried out on a vax 8700 computer at the university of jordan. a typical number of iterations for a case without intake is around 5000 iterations, while for the intake case is around 9000 iterations. 4. results and discussion the predicted results will be compared with the experimental and the numerical results of bray [15]. the main parameters which have been investigated include the effective velocity ve the nozzle height to diameter ratio h/d, the pressure ratio pr, the jet temperature to freestream temperature, tj/t∞ ratio, the intake mass flow rate to the jet mass flow rate mi/mj and the location of the intake d/ on the flow field of interest. a summary of the values of parameters investigated is shown in table 2. table 2. summary of parameters used in the numerical modeling parameter values ve 14.4, 17.9, 25.1 and 26.1 pr 1.05, 1.2, 1.5, and 1.6 h/d 2.0, 2.5, 4.0, 5.0, 6.0,7.5, 8.0 and 10 tj/t∞ 0.89, 2.4 and 3.2 mi/mj 0 (no intake), 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 4.0 ℓ/d 10.5, 13.5, 16.5 and 22.5 figure 3 shows the velocity vector plots when h/d=5.0, pr=1.5, tj/t∞=3.2, and ve=25.1. the pressure coefficient distributions at different effective velocities are shown in figure 4(a). it can be seen from these figures that the minimum cp position at x/d=13.5 coincides with the vortex core position while the maximum cp position coincides with the maximum penetration position. these figures also show that when the jet impinges on the ground plane, it stagnates and deflects forward, forming a wall jet that meets the freestream where a stagnation point is formed and the wall jet is deflected backwards. part of this back-flowing fluid is entrained again into the wall jet forming a ground vortex region, figure 3. the predicted results of the horizontal distances of the vortex penetration xp and the ground vortex core xv reveal the existence of a fixed relation which can be determined from the static pressure distributions for all the cases investigated. the predicted relation is given by xp/xv=1.58 compared with the experimental relation of bray [15], which is xp/xv=1.592. it is interesting to note that although both of xp and xv are overpredicted when compared with the experimental ones, the deviation of the experimental and predicted relations is about 0.75%. this numerical correlation is independent of the flow parameters and indicates that the ground vortex can be described by its characteristic locations. another correlation which is useful is the relation between the vertical and horizontal locations of the penetration of the vortex and is found to be given by yv/xv=0.184. one of the important parameters that affect the ground vortex geometry is the effective velocity ratio ve. this is due to the fact that the maximum penetration distance increases with increasing the effective velocity as can be seen from figure 4(a) where it can be seen that the position of cpmax is increased with increasing ve. the rate of increase of xp/d with ve is nearly independent of the nozzle height as it is indicated in figure 4(b). for all cases studied the predicted correlation is given by xp/d=0.86ve. the ground vortex size, which is indicated by, yv/d shows similar trends to xv and the relation between the vortex core height and ve is given by yv/d=0.1ve. this correlation is independent of the nozzle height for the range investigated, h/d=2.0-10.0. the trend of increasing xp/d with ve was found in all previous numerical and experimental studies, such as [15-17]. nevertheless, there is a significant disagreement among investigators regarding the rate of increase of xp/d. this could be partially attributed to the different freestream boundary layer thickness used in the various investigations. a comparison between the present predictions with the experimental and numerical results of bray [15] is shown in figure 5. the rate of increase of xp/d with ve is well predicted, but the absolute values of xp/d are overpredicted. the present predictions are much closer to the experimental results. the present prediction overpredicts the vortex penetration by about 25% whilst bray’s prediction overpredicts the vortex penetration by about 40%. this deviation between the two numerical predictions may be attributed to the different numerical schemes used to interpolate the values of the scalar variables at the control volume faces. while bray used the plds scheme for all variables, the present authors used the quick scheme for the velocity components and the plds scheme for all other scalar variables. it is well known that the quick scheme tends to cause less numerical diffusion than the plds scheme. however, the difference between the experimental and the predicted vortex penetrations may be due to the deficiency of the k turbulence model as well as the two-dimensional modeling of the problem. the effect of height h/d on the vortex penetration is seen to be insignificant from the predicted results of the pressure distributions, figure 6. a comparison between the present predicted results and bray’s experimental and predicted results is shown in figure 7 which shows that the predicted results are not consistent with the experimental results which indicate that there is a slight increase in the vortex penetration with the increase in the height until a critical height is reached, after which there is a slight decrease in vortex penetration. one argument reported by bray[15], which attributed the effects of height, obtained experimentally to the rig interference. similar trends to the present work regarding the effects of height on the vortex penetration were reported by tafti and vanka[13]. iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 35 fig. 3 velocity vector plot of the ground vortex region fig. 4a effect of ev on pc distribution at 5d h fig. 4b effect of ev on d x p at different values of at d h fig. 5 comparison between the experimental and predicted results of d x p at 5d h fig. 6 effect of d h on pc at distribution of at 1.25ev fig. 7 comparison between the experimental and predicted results of d x p at various d h and ev values iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 36 it seems that very little work has been done regarding the effects of the jet temperature on the flow field of jets in cross-flow relevant to v/stol aircraft. in order to shed some light on this, a number of runs at different temperature ratios were obtained. figures 8(a-b) show the effects of the temperature ratio on both the pressure coefficient distributions as well as on the vortex penetration. it is very clear that the effect of the jet temperature is rather minor at all effective velocity ratios. it is worth noting that increasing the jet temperature decreases the jet density and consequently decreases the jet dynamic pressure leading to a decrease in ve. if the freestream velocity was decreased in such a way that ve stays constant, then there will be no effect of the temperature since the temperature effect is included in ve. this makes ve the proper non-dimensional parameter that must be used to model the flow field since it combines both, the effect of the jet to cross-flow velocity ratio together with the effect of compressibility that arises from using different jet and/or cross flow temperatures. this argument was first observed experimentally by abbot [17] who investigated the effect of different jet temperatures and found that the vortex penetration is independent of temperature for the same ve. these findings were also supported by corsiglia et al. [18] who found that the effect of jet temperature on the pressure data was small. the effect of engine inlet conditions on the vortex location and geometry also did not receive enough attention in previous numerical investigations. the effect of inlet was mainly studied experimentally. maclean et al.[19] conducted an experimental investigation on a typical model configuration. the test rig consisted of two inlet configurations with four jets impinging on a flat plate. it was found that the inlet suction appeared to increase the ground vortex location only at low height and low freestream to jet velocity ratios, v∞/vj in order to study the effect of the engine inlet conditions numericall y on the ground vortex, one has to study the two parameters that are related to the inlet conditions, namely; the ratio of the engine inlet mass flow rate to the jet mass flow rate mi/mj, and the horizontal distance between the engine inlet and the nozzle jet location d/ . the two-dimensional modeling used in the present investigation necessitated that the inlet condition was modeled as a horizontal mass sink on the top of the free surface at a height of 10 d above the ground plane. the mass flow rate of the engine inlet was prescribed in such away to satisfy the ratio of mi/mj. brady and ludwig [20] found that the ground board static pressure distribution is independent of mass flow rate. the predicted results shown in figures 9(a-b) support such findings where it can be seen that the effect of mi/mj on the cp distribution in terms of the positions of cpmin and cpmax is negligible. this small effect can be seen from the increase in cpmin as mi/mj is increased which consequently increases the vortex strength except for the case of mi/mj =0 (no intake). however, the size of the ground vortex does not change with increasing mi/mj as long as ve and ℓ/d are the same. figure 10 shows that xp/d decreases only slightly with increasing mi/mj. in the present investigation, the intake location ℓ/d was varied from 10.5 to 22.5 for a fixed value of mi/mj =1. figure 11(a) shows that when ℓ/d = 10.5 and 13.5, the cp plots are nearly the same in terms of the positions and the values of cpmin and cpmax which means that the ground vortex location and strength are the same for these two cases. figure 11(b) indicates that the location of the inlet of the engine has a minor effect on xp/d where it is increased rather slightly as d/ is increased. when higher values of ℓ/d such as 16.5 and 22.5 are used as can be seen from figure 12(a), the cp plots are different in terms of cpmin and cpmax. for both cases, cpmin is low compared with the cases of ℓ/d = 10.5 and 13.5 which means that the ground vortex is weak. when ℓ/d=22.5, cpmax is lower than that of the case ℓ/d =16.5. the velocity vectors shown in figure 12(b) reveal that for ℓ/d=22.5, there is a clear ground vortex and the self-similarity laws are applicable. however, the ground vortex is weak and the stagnation pressure is low, as indicated from the cp plots, figure 12(a). this may be explained by the fact that for ℓ/d=22.5, the cross flow is strongly deflected upwards towards the upper free surface due to the existence of the suction of the inlet, figure 12(b). this strong deflection leads to a reduction in the horizontal component of the cross-flow momentum and consequently leads to a reduction in collision losses with the wall jet and hence the stagnation pressure will be reduced and the ground vortex strength will be also reduced. from the above argument one could conclude that when the intake is positioned ahead of the ground vortex core, the suction effect of the intake will tend to modify the flow structure and hence leads to weaker vortices and/or lower cpmax. however, it must be noted here that it is possible that the 2-d modeling contributed to this flow behavior, since the flow cannot be deflected sideways and it is forced to deflect upwards. the next set of predicted results is the normalized temperature tθ=(t-t∞)/(tjt∞) and is presented as temperature contours in order to investigate the temperature distribution of the hot gases in the flow field. figure 13(a) shows the temperature contours when tj/ t∞= 3.2, ve=14.4, mi/mj=1, and h/d =5. it can be clearly seen that at the centerline of the free jet region, the temperature decreases steadily with the vertical distance from the nozzle. at the jet exit, tθ =1.0, while at the ground plane tθ = 0.6, which means that the jet temperature is reduced by 40%. similarly, for the wall jet, tθ decreases steadily with the distance from the impingement point where it eventually reaches a zero value. the effective velocity ratio ve has a significant effect on the temperature contours, where the penetration of the hot gases increases with increasing ve. it can be seen from figure 13(b) when ve =17.9 that the hot gases in the wall jet penetrates to a greater distance than those shown in figure 13(a) for ve =14.4. iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 37 fig. 8a effect of t t j on pc distribution fig. 8b effect of t t j on d x p at different values of ev fig. 9a effect of low values of j i m m on pc distribution fig. 9b effect of high values of j i m m on pc distribution fig. 10 effect of j i m m on d x p fig. 11a effect of low values of d l on pc distribution iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 38 fig. 11b effect of d l on d x p distribution fig. 12a effect of high values of d l on pc distribution fig. 12b velocity vector plot at 5.22d l fig. 13a temperature contours at 2.3 t t j and 4.14ev fig. 13b temperature contours at 2.3 t t j and 9.17ev iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 39 5. conclusion several points have emerged from the numerical modeling of impinging jet in cross-flow with particular reference to v/stol aircraft. these can be summarized as follows: 1. the effective velocity ratio is the most predominant parameter that affects the ground vortex geometry and the ground vortex strength increases with ve. 2. the ground vortex similarity relation is predicted with high accuracy. the predicted relation is xp/xv=1.58 compared with 1.59 as obtained from experiment. 3. the nozzle height has little effect on the ground vortex, location and strength but it has a significant effect on the temperature at the impinging point where the temperature significantly decreases with increasing the height due to the entrainment action. however, the penetration of the hot gases does not change significantly with increasing the height. 4. the jet temperature has a negligible effect on the ground vortex at constant ve and this effect is included in the effective velocity. furthermore, the jet temperature has a negligible effect on the temperature distribution of the flow field. 5. the intake mass flow rate has a small effect on the ground vortex geometry and location. however, the ground vortex strength increases as the intake mass flow rate increases. 6. the intake location has a negligible effect on the ground vortex if it is positioned above or downstream of the ground vortex core. if it is positioned upstream of the ground vortex core, the strength of the ground vortex decreases. if the intake is positioned upstream of the maximum penetration point, the stagnation pressure is highly reduced. however, the hgi is increased as ℓ/d is decreased. the location of the intake has a negligible effect on the temperature distribution in the flow field. references [1] r. j. margason, “fifty years of jet in cross flow research, “agard conference proceedings, computational and experimental assessment of jets in cross flow, symposium held in winchester, united kingdom, 19-22 april, 1993. [2] w. p. jones, and j. j. mcguirk, “computation of a round turbulent jet discharging into a confined cross-flow,” turbulent shear flows 2, springer-verlag, berlin, pp. 233245, 1980. [3] r. e. childs, d. nixon, “turbulent and fluid/acoustic interaction in impinging jets,” int. powered lift conf., p203, pp. 447-458, paper no. 872345, santa clara, calif., feb. 1988. [4] w. r. van dalsem, a. g. panaras, and j. l. steger, “ numerical investigation of a jet in ground effect with a cross-flow,” int. powered lift conf., p-203, pp. 447-458, paper n0. 872344, santa clara, calif., feb. 1988. [5] g. d. catalano, k. chang, and j. a. mathis, “calculation and measurement of turbulent jet impingement in a crossflow, part 1., “6th international conference on numerical methods in laminar and turbulent flow, vol. 6, pt.2, pp.1895-1906, pineridge press, 1989. [6] j. m. barata, d. f. durao, and j. j. mcgurik, numerical study of a single impinging jets through a cross-flow”, int. j. aircraft, vol. 26, no. 11, 1989. [7] c. j. hwang, and j. l. liu, “numerical study of two dimensional impinging jet flow field,” aiaa journal, vol. 27, no. 7, 1989. [8] r. k. agarwal and w. w. bower, “navier stokes computations of compressible two dimensional impinging jet flow fields,” aiaa journal, vol. 20, no. 5, pp. 577584, 1982. [9] c. hwang, s. yang and j. liu, “numerical investigation of airfoil-jet fuselage undersurface flow field in ground effect,” 28th aerospace science meeting, aiaa 90-0597, reno, nevada, january 9-11, 1990 [10] d. bray, and k. knowles, “numerical modeling of impinging jet in cross-flow,” aiaa/asme/asee 26th joint propulsion conference, aiaa, 90-2246, ornaldo, july 16-18, 1990. [11] a. g. smith, d. n. ing, and p. j. baily, “the experimental and computational study of jet impingement flow fields with reference to vstol aircraft to vstol aircraft performance,” international powered lift conference, 2931 august, 1990. [12] t. j. vanoverbeke, and d. james, “ a numerical study of the hot gas environment around a stovl aircrafts in ground proximity,” aiaa/asme/sae/asee 24th joint propulsion conference, aiaa-88-2882, boston, massachusetts, july 11-13, 1988. [13] d. tafti and s. p. vanka, “hot gas environment around stovl aircraft in ground proximity, part 2: numerical study,” ,” aiaa/asme/sae/asee 26th joint propulsion conference, aiaa-90-2270, orlando, fi., and july 16-18, 1990. [14] p. g. huang and m. a. leschziner, “an introduction and guide to the computer code team,” university of manchester, 1992. [15] d. bray, “jets in cross-flow and ground effect”, ph.d. thesis, cranfield institute of technology, rmcs, england, 1991. [16] j. m. cimbala, d. r. stingebring, a. l. treaster, m. l. billet and m. m. walters,” experimental investigation of a jet impinging on a ground plane in the presence of a crossflow,” international powered lift conference, december 7-10, 1987. [17] w. a. abbott, studies of flow fields created by vertical and inclined jets when stationary or moving over a horizontal surface,” aero. research council, rept. no. cp-911, october 1964. [18] v. r. corsiglia, d. a. wardwell and r. e. kuhn, “smallscale experiments in stovl ground effects,” international powered lift conference, 29-31 august 1990. [19] r. maclean, j. sullivan and s. n. murthy, “hot gas environment around stovl aircraft in ground proximity, part 1: experimental study,” aiaa/asme/asee 26th joint propulsion conference, aiaa 90-2269, ornaldo, fi., july 16-18, 1990. [20] w. g. brady and g. ludwig, “theoretical and experimental studies of impinging jets,” ias 31st annual meeting, ias paper no. 63-29, newyork, jan. 21-23, 1963. iium engineering journal, vol. 1, no. 1, january 2000 b. m. suloiman and b. a. jubran 40 nomenclature pc pressure coefficient, 25.0/)(  vpp  maxpc maximum pc on the ground plane minpc minimum pc on the ground plane 21 , cc standard turbulence coefficient cc d , turbulence model constants  ,, 21 cc turbulence model constants d diameter of the nozzle g turbulence generation h perpendicular height of nozzle exit above ground k turbulent kinetic energy  horizontal distance between the nozzle and the intake m mass flow rate p pressure pr nozzle pressure ratio ppo / re reynolds number s source of  per unit volume t time t temperature u local velocity u turbulent fluctuation velocity u friction velocity u dimensionless near wall velocity v  velocity in vector form ev effective velocity ratio, )5.0/()5.0( 22  vv jj  jv jet exit velocity v freestream (cross-flow) velocity x distance measured against the crossflow y vertical distance measured along the free jet flow y dimensionless wall distance  rate of dissipation of turbulent kinetic energy  general variable ( tkvu or ,,,,,1   )  turbulent exchange coefficient k , standard turbulent constant t prandtl number  laminar dynamic viscosity t turbulent (eddy) viscosity  kinematic viscosity  density subscripts i intake conditions j jet exit conditions p ground vortex maximum penetration point ph hot gases penetration s ground vortex separation point v ground vortex core point  ambient (cross-flow) biography b. a. jubran, professor and head of the department of mechanical and industrial engineering at sultan qaboos university (1999-present). professor, mechanical engineering department at the university of jordan (1994-1997). associate professor (1989-1994). assistant professor (1984-1989). head of mechanical engineering department (1989-1991). he has taken position at the international islamic university malaysia (1997-1999) where he has served as a deputy dean (academic affairs) at the faculty of engineering and university senate member (1997-1998). he has been a visiting professor at the university of karlsruhe, germany, research leave (summer 1994). a visiting professor at the royal military college of science (cranfield university), britain (1991-1992). he has also served as director of the arab council for training students of arab universities, actsau and national secretary of the international association for the exchange of students for technical experience (iaeste), iaestejordan (1994-1997). he has worked as a project engineer at abu-dhabi national oil company, uae (1980-1981). application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 magnetically modified sugarcane bagasse disordered carbon as a cadmium removal agent in water izzaty syahirah baharudin1, noraini mohamed noor2*, ezzat chan abdullah1, raihan othman2 and mubarak nasibab mujawar3 1 malaysia japan international institute of technology, universiti teknologi malaysia, jalan semarak, 54100 kuala lumpur, malaysia 2 science in engineering department, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia 3 department of chemical engineering, curtin university, sarawak campus cdt 250, 98009 miri, sarawak, malaysia * corresponding author: norainimnoor@iium.edu.my (received: 2nd february 2021; accepted: 27th march 2021; published on-line: 4thjanuary 2022) abstract: heavy metals are hazardous to health at certain levels. currently, heavy metals are removed by physicochemical treatments, such as adsorption, flotation, and electrochemical deposition, and also biological treatments, such as algal biofilm reactor and anaerobic ammonium oxidation. in this study, magnetic biochar was produced to enhance the effectiveness and performance of the adsorbent for heavy metal removal. this study aimed to synthesise high-performance magnetic biochar, to determine the optimum parameters and conditions for high yield of magnetic biochar and high removal of cadmium (cd2+) from aqueous solution, and to determine the adsorption kinetics and isotherms for cd2+ removal. nickel oxide (nio)-impregnated sugarcane bagasse was subjected to slow pyrolysis to produce magnetic biochar. the impregnated metal, pyrolysis temperature, and pyrolysis time were varied to determine the optimum parameters and conditions to produce high-performance magnetic biochar. the removal of cd2+ from aqueous solution and batch adsorption study were conducted. the synthesised magnetic biochar was characterised using field-emission scanning electron microscopy (fesem), energy dispersive x-ray (edx), x-ray diffraction (xrd), brunauer-emmett-teller (bet) surface area, fourier transform infrared (ftir), and vibrating sample magnetometer (vsm). the adsorption data agreed well with the pseudo-second-order model and followed the langmuir isotherm model. this study achieved 88.47% removal efficiency of cd2+ from aqueous solution. thus, the removal of this heavy metal as a human carcinogen reduces the hazardous effects on human health and reduces the toxicity in the environment. abstrak: logam berat adalah berbahaya bagi kesihatan di peringkat tertentu. pada masa ini, logam berat disingkirkan melalui rawatan fizikokimia, seperti penyerapan, pengapungan, dan deposit elektrokimia, dan rawatan biologikal, seperti reaktor biofilem alga dan oksidasi ammonium anerobik. kajian ini menghasilkan biochar magnetik bagi meningkatkan keberkesanan dan prestasi penyerapan penyingkiran logam berat. kajian ini bertujuan bagi mengsintesis biochar magnetik pada prestasi tinggi, bagi menghasilkan parameter optimum dan keadaan pengeluaran tinggi biochar magnetik dan penyingkiran tinggi kadmium (cd2+) daripada larutan akues, dan bagi mendapatkan penyerapan kinetik dan isoterma penyingkiran cd2+. nikel oksida (nio)-impregnat hampas tebu adalah 294 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 berdasarkan pirolisis perlahan bagi menghasilkan biochar magnetik. logam yang terimpregnat, suhu pirolisis dan tempoh pirolisis dipelbagaikan bagi mendapatkan parameter optimum dan keadaan bagi menghasilkan biochar magnetik berprestasi-tinggi. penyingkiran cd2+ daripada larutan akues dan kajian penyerapan berkumpulan telah dibuat. biochar magnetik yang disentisis diklasifikasikan menggunakan mikroskopi elektron imbasan medan-pancaran (fesem), tenaga sebaran x-ray (edx), pembelauan x-ray (xrd), kawasan permukaan brunauer-emmett-teller (bet), penjelmaan fourier inframerah (ftir), dan sampel getaran magnetometer (vsm). data penyerapan menunjukkan persetujuan dengan model aturan-kedua-pseudo dan mengikuti model isoterma langmuir. kajian ini mencapai 88.47% keberkesanan penyingkiran cd2+ daripada larutan akues. oleh itu, penyingkiran logam berat ini sebagai karsinogen manusia mengurangkan kesan teruk pada kesihatan manusia dan pengurangan toksik pada alam sekitar. keywords: biomass; heavy metal removal; magnetic biochar 1. introduction heavy metals are hazardous to health at certain concentrations in water. in order to meet the discharge requirements, lead, mercury, silver, chromium, cadmium, zinc, nickel, and tin are heavy metals that need to be removed from wastewater until specific allowable concentrations are achieved. these heavy metals cause serious health risks and affect the environment negatively [1,2]. the treatment of water containing heavy metals is important to reduce health risks [2]. wastewater with high concentrations of heavy metals is hazardous to humans and the environment. wastewater treatment is vital in providing a sustainable and safe environment. various treatment methods have been studied in the past decade. adsorbents from different biomass types, such as magnetic biochar, can be used for heavy metal removal from wastewater. studies on magnetic biochar have attracted attention as the adsorbent possesses high adsorption capability to remove heavy metals from wastewater. moreover, the removal performance of magnetic biochar is relatively higher than biochar. magnetic biochar can be produced from biomass sources, such as pine sawdust, palm kernel shell, cottonwood, and pineapples [1,3-5,6]. several methods are available to synthesise magnetic biochar, but the most used method is pyrolysis, which is the burning of a sample in the absence of oxygen. cadmium is a human carcinogen, which can cause cancer and lead to death [7]. the main cause of death in 2012 was cancer, which is mainly due to genomic instability [8,9]. other than that, the inhalation of high levels of cadmium can severely affect lungs [7]. furthermore, consuming high levels of cadmium can cause stomach pain, resulting in diarrhoea and vomiting [7]. prolonged exposure to cadmium, even at lower concentrations, can also lead to lung damage, fragile bones, and kidney disease [7]. many studies have focused on wastewater treatment, including physicochemical treatment, and there is a growing interest in biological treatment. several physicochemical treatment methods have been studied and are currently used, such as electrooxidation, chemical precipitation, adsorption, flotation, electrochemical deposition, and shales from coal mines [10-12]. meanwhile, biological treatment methods include anaerobic ammonium oxidation, sequencing batch biofilter reactor, algal biofilm reactor, natural biofiltration, and photo-anaerobic membrane bioreactor have been studied [13-17]. activated carbon is preferred for heavy metal removal, which becomes one of the most popular adsorbents in the wastewater industry [18]. however, high-quality activated 295 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 carbon is more expensive and cost-inefficient [18]. low-cost adsorbents have been introduced as alternatives to the expensive activated carbon [18]. these include adsorbents from natural materials and waste products, such as industrial by-products and modified agricultural and biological wastes [12]. among examples of low-cost adsorbents are natural materials (e.g., chitosan, zeolites, and clay), waste products (e.g., coal, fly ash, and oxides), and biosorption products (e.g., hazelnut shells, rice husk, and pecan shells) [12,18]. these adsorbents are inexpensive and cost-efficient due to their availability in large quantities. therefore, in this study, magnetic biochar produced from modified agriculture and biological waste was used to remove cadmium in wastewater. the study of magnetic biochar for heavy metal removal from wastewater is new in malaysia. sugarcane bagasse was selected as the biomass source in this study because this waste material is usually discarded in malaysia. hence, sugarcane bagasse is easy to obtain and cost-effective. the waste also has favourable physicochemical characteristics that can assist in wastewater treatment. chemical modification and impregnation with metals on sugarcane bagasse through slow pyrolysis can enhance the effectiveness and performance of the adsorbent. besides food, sugarcane is also a major source of bioethanol production that is widely used to replace gasoline in several countries, including brazil. however, there is an issue of using food as a biomass source due to the competition between energy and food [19]. sugar is produced from either sugar beet or sugarcane [19]. various by-products are produced during the process, such as molasses, bagasse, pressmud, lime sludge, and beet pulp, and these by-products are renewable raw materials [19]. therefore, these byproducts are preferred as biomass sources to avoid fuel and food competition. in mexico, a study was conducted to simulate the potential of sugarcane and blue agave bagasse in bioethanol production by replacing food with biomass sources [20]. several studies involving magnetic biochar as an effective heavy metal adsorbent have been conducted. until now, several modifications have been made in various studies to improve the properties of biochar, primarily to enhance its adsorption properties for better performance. moreover, the number of studies on sugarcane bagasse adsorbent and magnetic adsorbent has been growing since 2007. however, the studies were more favourable towards magnetic absorbent, except in 2015, where the studies on sugarcane bagasse as absorbent were higher than magnetic absorbent. 2. materials and methods 2.1 materials sugarcane bagasse was obtained directly from the juice stall, where the bagasse is the solid waste from the mechanical extraction of sugarcane. first, the raw sugarcane bagasse was air-dried and crushed to obtain smaller-sized biomass. the crushed bagasse was washed thrice using tap water. then, this sample was oven-dried for 24 h at 70 °c and left in room temperature drying rack for 1 week. this study used a synthetic wastewater sample prepared with a similar concentration of pure cd2+ instead of industrial wastewater to evaluate the removal efficiency of cd2+ using magnetic biochar. this synthetic wastewater sample can help simulate the real industrial wastewater behaviour. in this work, sugarcane bagasse was impregnated with three types of nickel metals {nickel oxide (nio), nickel chloride (nicl2), and nickel sulfate (niso4)}. the impregnation produced sugarcane bagasse magnetic biochar, which was later used for cd2+ adsorption in aqueous solution. 296 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 2.2 synthesis of magnetic biochar the dried sugarcane bagasse was magnetised by the impregnation of metal salts on the biomass surface. the metal salt solutions of nio, nicl2, and niso4 were prepared and biomass was immersed in the solutions with the metal salt-to-biomass ratio of 0.45:1, where the ratio was kept constant throughout the experiment. next, the immersed biomass was placed in a shaker for 1 h at 170 rpm. after completion, the sample was filtered and oven-dried at 70 °c for 24 h prior to slow pyrolysis. the ratio of metal salt per biomass was maintained and the holding time was 10 and 20 min. approximately 5 and 10 g of the impregnated sugarcane bagasse were weighed for the experiments with pyrolysis time of 10 and 20 min, respectively. magnetic biochar was synthesised in oxygen-free conditions through slow pyrolysis in a wisetherm muffle furnace. a vacuum pump was used for degassing prior to pyrolysis to achieve oxygen-free conditions. various temperatures ranging from 400 to 700 °c (400, 450, 500, 550, 600, 650, and 700 °c) were used for the determination of optimum temperature to produce magnetic biochar with high adsorption capacity at 25 °c/min heating rate. this temperature range was selected because the pyrolysis working temperature is between 400 and 700 °c. sugarcane bagasse cannot be magnetised when the temperature is lower than 400 °c, where carbonisation occurs at this temperature range. similarly, gasification occurs when the temperature exceeds 700 °c. after pyrolysis, the magnetic biochar was cooled to room temperature before it was crushed to smaller size. next, the crushed magnetic biochar was rinsed with distilled water several times until it reached the neutral state. finally, the magnetic biochar was ovendried and stored in an airtight plastic container prior to characterisation. 2.3 characterisation of magnetic biochar prior to adsorption, magnetic biochar was characterised using brunauer-emmettteller (bet) surface area, field-emission scanning electron microscopy (fesem), x-ray diffraction (xrd), fourier transform infrared (ftir), and vibrating sample magnetometer (vsm). after cd2+ removal from wastewater, only fesem, xrd, and ftir were conducted to characterise the samples. bet analysis was performed to calculate the surface area of magnetic biochar. the optimum condition to produce magnetic biochar was analysed using ftir to determine the surface functional groups before and after the adsorption of cd2+. fesem was used to observe the porosity and structure of the sample's surface after synthesising magnetic biochar. this characterisation is also required to observe the condition of magnetic biochar after cd2+ adsorption from synthetic wastewater. the phase identification and structure of magnetic biochar before and after adsorption were studied using xrd. meanwhile, vsm was applied to measure and determine the magnetic properties of the synthesised magnetic biochar. 2.4 cadmium adsorption about 0.3 g of each sample was weighed and synthetic wastewater solution with 20 ppm of cadmium concentration was prepared. the samples were added into capillary tubes filled with 10 ml of cadmium solution. the samples in the capillary tubes were agitated at 200 rpm for 1 h using an incubator shaker (ika ks 3000 i control). after completion, the samples were filtered and 10 ml of the solution was collected in smaller capillary tubes. atomic absorption spectroscopy (aas) was utilised to analyse the samples. the optimum time and temperature were selected for the sample with the highest cadmium removal. 297 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 2.5 batch adsorption study after obtaining the aas results, the sample with the optimum time and temperature was selected to conduct a batch adsorption study. cadmium solutions of 20, 40, 60, 80, and 100 ppm were prepared and each solution was filled in a conical flask. then, 0.6 g of the selected sample was added into each conical flask containing 200 ml solution. 3. results and discussion 3.1 magnetic biochar yield and cd2+ removal percentage of magnetic biochar the yield of magnetic biochar was determined by weighing the magnetic biochar before and after pyrolysis (eq. 1). meanwhile, the cd2+ removal percentage was determined by measuring the concentration of cd2+ after adsorption using aas (eq. 2). % 𝑚𝑎𝑔𝑛𝑒𝑡𝑖𝑐 𝑏𝑖𝑜𝑐ℎ𝑎𝑟 𝑦𝑖𝑒𝑙𝑑 = (𝑊𝑒𝑖𝑔ℎ𝑡𝑎𝑓𝑡𝑒𝑟 − 𝑊𝑒𝑖𝑔ℎ𝑡𝑏𝑒𝑓𝑜𝑟𝑒 ) 𝑊𝑒𝑖𝑔ℎ𝑡𝑏𝑒𝑓𝑜𝑟𝑒 × 100 % (1) % 𝑟𝑒𝑚𝑜𝑣𝑎𝑙 = (𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛𝐶𝑑2+,𝑎𝑓𝑡𝑒𝑟 − 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛𝐶𝑑2+,𝑏𝑒𝑓𝑜𝑟𝑒 ) 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛𝐶𝑑2+,𝑏𝑒𝑓𝑜𝑟𝑒 × 100 % (2) figure 1a illustrates the yields of magnetic biochar over pyrolysis temperature using different types of sugarcane bagasse impregnated for 10 min. nio-impregnated sugarcane bagasse showed the highest yield (46.5%) compared to other metals at 400 °c, followed by nio-impregnated sugarcane bagasse at 500 °c with 42.53% yield. the finding clearly shows that a higher pyrolysis temperature will result in a lower yield of magnetic biochar. the percentage of yield decreased with pyrolysis temperature. at elevated temperatures from 400 to 600 °c, biomass decomposed and produced lower magnetic biochar yields, nearly 50% reduction from the initial yield. this result suggests that most of the volatile matter in sugarcane bagasse decomposed at higher temperatures, leaving a small amount of magnetic biochar with high carbon content. on the other hand, slow heating exposed sugarcane bagasse to heat for a longer time, allowing more volatile matter to decompose and form more surface pores [21]. according to fig. 1b, niso4-impregnated sugarcane bagasse achieved the highest yield of 36.03% at 400 °c. from the figure, different anions of metal salts affected the percentage of yield produced, indicating the changes in the primary degradation of the biomass. figure 2a presents the graph of cd2+ removal percentage versus temperature at 10 min of pyrolysis time. nio-impregnated magnetic biochar demonstrated the highest cd2+ removal efficiency of 88.57% at 500 °c, followed by niso4-impregnated magnetic biochar (88.55%) at 400 °c and nicl2-impregnated magnetic biochar (87.69%) at 500 °c. the removal efficiency decreased as the impregnated magnetic biochars were heated from 400 to 500 °c, except nio-impregnated magnetic biochar. in contrast to the impregnated magnetic biochars produced at 20 min of pyrolysis time (fig. 2b), the removal percentage started to increase after 450 °c and decrease beyond 600 °c. the reason for such behaviour is that the development of the pore structure and active sites are insufficient at high pyrolysis temperatures [22]. the best metal to be impregnated with magnetic biochar and the optimum parameters and conditions were determined from the metal-impregnated magnetic biochar producing the best yield and cd2+ removal percentage. therefore, nio-impregnated magnetic biochar 298 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 was chosen due to its high yield of 40.24% and high cd2+ removal efficiency of 88.57% at 500 °c. fig. 1: yield of magnetic biochar at (a) 10 min and (b) 20 min of pyrolysis time. fig. 2: cd2+ removal percentage of magnetic biochar at (a) 10 min and (b) 20 min of pyrolysis time. 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 400 450 500 550 600 650 700 y ie ld ( % ) temperature (ºc) niso4 0.00% 10.00% 20.00% 30.00% 40.00% 400 450 500 550 600 650 700 y ie ld ( % ) temperature (ºc) niso4 86 86.5 87 87.5 88 88.5 89 400 450 500 550 600 650 700 r e m o v a l y ie ld ( % ) temperature (ºc) nicl niso4 86 87 88 89 90 400 450 500 550 600 650 700 r e m o v a l y ie ld ( % ) temperature (ºc) nicl niso4 (a) (a) (b) (b) 299 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 3.2 characterisation of magnetic biochar 3.2.1 field-emission scanning electron microscopy and energy dispersive x-ray spectroscopy analysis the surface structure of raw sugarcane bagasse and magnetic biochar was studied using fesem. figure 3(a-d) depict the morphology of raw sugarcane bagasse, sugarcane bagasse biochar, magnetic biochar before adsorption, and magnetic biochar after adsorption, respectively. raw sugarcane bagasse has a more blocked and smooth surface [23], but the structure is more porous and agglomeration could be observed (fig. 3d) after impregnation and pyrolysis of sugarcane bagasse. this finding suggests that the metals are impregnated on raw sugarcane bagasse after the synthesis process. the widening of pores could be seen from the figures, indicating the extraction of some materials, such as the dissolution of lignin and other components from the bagasse during impregnation. the loss of volatile compounds from within the particles increased gradually when the final temperature increased during heating. fig. 3: morphology of (a) raw sugarcane bagasse, (b) sugarcane bagasse biochar, (c) magnetic biochar before adsorption, and (d) magnetic biochar after adsorption. figure 4 presents the edx analysis of magnetic biochar after cd2+ adsorption, which shows the presence of cadmium element in the magnetic biochar. this analysis agrees that magnetic biochar can remove heavy metals from aqueous solution. fig. 4: edx analysis of magnetic biochar after cd2+ adsorption. (d) 300 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 3.2.2 vibrating sample magnetometer analysis in this study, vsm analysis was conducted to measure the magnetisation of magnetic biochar. figure 5 depicts the magnetic hysteresis cycles of magnetic biochar. the magnetic biochar recorded the coercive field of 163.96 g, saturation magnetisation (ms) of 0.24093 emu/g, and retentivity (mr) of 0.07377 emu/g. meanwhile, raw sugarcane bagasse did not give any magnetisation value. fig. 5: magnetic hysteresis cycles of magnetic biochar. the magnetic hysteresis cycles prove that raw sugarcane bagasse does not have ferromagnetic properties, whereas magnetic biochar shows ferromagnetic properties. therefore, magnetic biochar can be recovered using magnets. a magnet bar was placed outside of glass bottles containing magnetic biochar to test its magnetic separation ability (fig. 6). this phenomenon can be considered a combination of superparamagnetic, ferromagnetic, and paramagnetic behaviours [24]. fig. 6: magnetic separation ability of magnetic biochar before and after putting the magnetic bar. 301 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 3.2.3 fourier transform infrared spectroscopy analysis ftir analysis was carried out to determine the functional groups available in raw sugarcane bagasse and magnetic biochar before and after cd2+ adsorption. figure 7(a) presents the ftir spectra of raw sugarcane bagasse and fig. 7(b) illustrates the ftir spectra of magnetic biochar before and after cd2+ adsorption. the spectra are different in the raw sugarcane bagasse compared to the synthesised magnetic biochar. therefore, the internal structure of magnetic biochar and their functional groups changed during synthesis. fig. 7: ftir spectra for (a) raw sugarcane bagasse and (b) magnetic biochar before and after cd2+ adsorption. table 1 shows the possible functional groups present before cd2+ adsorption. for the ftir spectra before cd2+ adsorption, there is a peak present around 2,921 cm−1, suggesting the presence of ch stretch. meanwhile, the peak at 1,653 cm−1 indicates c=c stretch, which is present due to pyrolysis. other than that, the c–n stretch is present at 1,041 cm−1, showing that organic compounds are present in the magnetic biochar. it is observed that these functional groups are absent after cd2+ adsorption in aqueous solution. this finding indicates that the adsorption of heavy metals breaks the bonds of the functional groups. table 1: possible functional groups of the identified peaks peak position (cm−1) possible functional group 2,921 ch stretch 1,653 c=c stretch 1041 c–n stretch 3.2.4 brunauer-emmett-teller surface area analysis bet surface area analysis was conducted to calculate the surface area of raw sugarcane bagasse and magnetic biochar. table 2 lists the surface area and porosity of raw sugarcane bagasse and magnetic biochar. the results showed higher surface area, total pore volume, and average pore diameter of magnetic biochar than raw sugarcane bagasse. this finding indicates that the pyrolysis of sugarcane bagasse to magnetic biochar increased the surface area and porosity, resulting in higher adsorption capacities. the significant improvement in the surface area and pore volume in magnetic biochar may be due to the significant increase in volatile released [25]. in addition, the nio impregnated 302 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 on the surface of magnetic biochar increased the surface area due to the combustion of the organic molecules trapped in the particles and recrystallization of nio [26]. therefore, magnetic biochar has higher adsorption capacity than conventional biochar or raw sugarcane bagasse. table 2: main textural characteristics of raw sugarcane bagasse and magnetic biochar properties raw sugarcane bagasse magnetic biochar specific surface area (m2/g) 1.8058 10.6364 total pore volume (cm3/g) 0.0011 0.03437 average pore diameter (nm) 2.3330 11.5499 3.2.5 x-ray diffraction analysis xrd analysis was carried out to identify phase characteristics. figure 8 illustrates the xrd patterns of magnetic biochar. the figure suggests that crystalline nio formed in magnetic biochar with the highest intensity of 2θ = 43.3302° at (200) plane. other than that, the nio peaks are observed at 2θ = 37.2722°, 62.8562°, 75.4142°, and 79.3662° at (111), (220), (311), and (222) planes, respectively. the formation of ni is also shown at the peaks around 2θ = 44.5262° and 51.9102° at (111) and (200) planes, respectively. fig. 8: xrd patterns of magnetic biochar. at 400–500 °c, nio is reduced to metallic ni as magnetic biochar most probably acts as a reducing agent [27]. the analysis shows the formation of magnetic biochar, as confirmed by the existence of nio and metallic ni in magnetic biochar. 3.2 batch adsorption study adsorption kinetics and isotherms were examined in the batch adsorption study. according to fig. 9, cd2+ adsorption reached equilibrium at 120 min. the figure also shows that the higher the concentration, the higher the amount of cd2+ absorbed by magnetic biochar due to the increases in adsorption capacity. the increase in the mass transfer driving force where the movement of cd2+ ion into the magnetic biochar surfaces, leading to high adsorption rates [28]. -5000 0 5000 10000 15000 20000 25000 30000 35000 40000 30 40 50 60 70 80 in te n si ty 2θ (°) nio ni (111) (220) (111) (222) (200) (311) (200) 303 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 fig. 9: effect of time on cadmium adsorption capabilities. 3.3 adsorption kinetics the effect of cadmium adsorption kinetics on the magnetic biochar was simulated using two mathematical models: pseudo-first-order (eq. 3) and pseudo-second-order (eq. 4) models. figure 10 (a,b) presents the adsorption kinetics for the pseudo-first-order and pseudo-second-order models, respectively, for cd2+ adsorption on magnetic biochar. ln ( 𝑞𝑒 𝑞𝑒 − 𝑞𝑡 ) = 𝑘1𝑡 (3) 1 (𝑞𝑒 𝑞𝑡 ) = 1 𝑞𝑒 + 𝑘2𝑡 (4) where: qe = amount of cd 2+ adsorbed at time t; qt = amount of cd 2+ adsorbed at equilibrium; k1 = pseudo-first-order rate constant; and k2 = pseudo-second-order rate constant. tables 3 and 4 tabulate the kinetic parameters of cd2+ adsorption for pseudo-firstorder and pseudo-second-order models, respectively. the correlation coefficient (r2) values for both kinetic models clearly show that the experimental data follow the pseudosecond-order model with r2 ≈ 1. therefore, the pseudo-first-order model could not describe the adsorption kinetics of this study. it is assumed that the amount of cd2+ on the surface of magnetic biochar affects the adsorption, and the pseudo-second-order model suggests that the adsorption process is chemisorption as visualised in ftir analysis previously, where cd2+ adsorption in this study is due to the chemical bonds formed [1]. 0 5 10 15 20 25 30 0 50 100 150 200 q t (m g /g ) t (min) 20 ppm 40ppm 60ppm 80ppm 100ppm 304 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 fig. 10: (a) pseudo-first-order and (b) pseudo-second-order models of cd2+ adsorption. table 3: kinetic parameters of cd2+ adsorption for the pseudo-first-order model co (mg/l) qe (mg/g) k1 qe r2 20 60.2683 -2.2364 0.9581 0.5798 40 12.4177 0.0451 0.9922 0.0917 60 18.2750 -2.1395 0.9583 0.7415 80 22.6550 0.1145 0.9915 0.0828 100 28.3737 -1.1692 0.9863 0.4615 table 4: kinetic parameters of cd2+ adsorption for the pseudo-second-order model co (mg/l) qe (mg/g) k2 qe r2 20 60.2683 0.0206 6.6313 0.9986 40 12.4177 0.0210 12.7551 0.9998 60 18.2750 0.0173 18.6220 0.9999 80 22.6550 0.0212 22.9358 0.9999 100 28.3737 0.0091 28.9855 0.9998 the kinetic parameters for the adsorption of heavy metals are insignificant because the experimental data did not fit well with the pseudo-first-order model. -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 0 50 100 150 200 lo g ( q e -q t) t (min) 20ppm 40ppm 60ppm 80ppm 100ppm 0 5 10 15 20 25 30 35 0 50 100 150 200 t/ q t t (min) 20ppm 40ppm 60ppm 80ppm 100ppm (b) (a) 305 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 3.4 adsorption isotherms the isotherm models studied were the freundlich (eq. 5) and langmuir isotherm models (eq. 6). 𝑞𝑒 = 𝑄𝑚𝐾𝐿𝐶𝑒 1+𝐾𝐿𝐶𝑒 (5) 𝑞𝑒 = ln 𝐾𝐹 + 1 𝑛 ln 𝐶𝑒 (6) where: ce = concentration of solution at equilibrium; qe = adsorption of cd 2+ at equilibrium; kl = langmuir model's constant; and kf = freundlich affinity coefficient. both isotherm models assume different adsorption mechanics. the freundlich isotherm model assumes the chemisorption of cd2+ on the heterogeneous surface of magnetic biochar, while the langmuir isotherm model describes the homogeneous surface of magnetic biochar by monolayer adsorption for cd2+ removal. figure 11(a,b) illustrate the freundlich and langmuir isotherm models for cd2+ adsorption of this study, respectively. fig. 11: (a) freundlich and (b) langmuir isotherm models for cd2+ adsorption. table 5 presents the isotherm constants and correlation coefficients of cd2+ adsorption for the freundlich and langmuir isotherm models. the r2 values of the langmuir and freundlich isotherm models for cd2+ adsorption are excellent, explaining that the experimental data are best described by both isotherm models. therefore, the adsorption 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 in q e in ce 0 0.1 0.2 0.3 0.4 0.5 0.6 0 2 4 6 8 10 12 14 16 c e /q e ce (a) (b) 306 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 mechanism of this study agrees with both chemisorption and monolayer adsorption on the surface of magnetic biochar. table 5: freundlich and langmuir isotherm constants and correlation coefficients for cd2+ adsorption freundlich 1/n kf r2 0.5555 6.3859 0.9593 langmuir qmax kl r2 36.6300 0.1777 0.9647 4. conclusion high yield of magnetic biochar was synthesised from nio-impregnated sugarcane bagasse via slow pyrolysis for heavy metal removal in aqueous solution. the optimum temperature and time to synthesise high-performance magnetic biochar were 500 °c at 10 min. high cadmium removal up to 88.47% was obtained using magnetic biochar. the batch adsorption study was conducted for cd2+ removal in aqueous solution using magnetic biochar. the experimental data followed the pseudo-second-order model (r2 ≈ 1) and both freundlich and langmuir isotherm models achieved the best fitting of r2 ≈ 1. for future work, a study on the synthesised nio-impregnated magnetic biochar can be done on industrial wastewater instead of simulated aqueous solution to determine the removal efficiency of the process. furthermore, a study considering various biomass sources can be conducted to determine the biomass with high yield of magnetic biochar and high heavy metal removal efficiency because malaysia has abundant biomass resources, especially agricultural waste. acknowledgement the authors would like to thank the international islamic university malaysia for funding this research under iium research acculturation grant scheme (irags), irags18-0210022. references [1] li t, su x, yu x, song h, zhu y, zhang y. (2018) la (oh) 3-modified magnetic pineapple biochar as novel adsorbents for efficient phosphate removal. bioresource technology, 263: 207-213. [2] rai pk, lee ss, zhang m, tsang yf, kim kh. (2019) heavy metals in food crops: health risks, fate, mechanisms, and management. environment international, 125: 365-385. [3] reguyal f, sarmah ak, gao w. (2017) synthesis of magnetic biochar from pine sawdust via oxidative hydrolysis of fecl2 for the removal sulfamethoxazole from aqueous solution. journal of hazardous materials, 321: 868-878. [4] hao z, wang c, yan z, jiang h, xu h. (2018) magnetic particles modification of coconut shell-derived activated carbon and biochar for effective removal of phenol from water. chemosphere, 211: 962-969. [5] wang s, gao b, li y, creamer ae, he f. (2017) adsorptive removal of arsenate from aqueous solutions by biochar supported zero-valent iron nanocomposite: batch and continuous flow tests. journal of hazardous materials, 322: 172-181. [6] wang b, jiang ys, li fy, yang dy. (2017) preparation of biochar by simultaneous carbonization, magnetization and activation for norfloxacin removal in water. bioresource technology, 233: 159-165. 307 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 [7] engwa ga, ferdinand pu, nwalo fn, unachukwu mn. (2019) mechanism and health effects of heavy metal toxicity in humans. poisoning in the modern world-new tricks for an old dog, 10. [8] ferlay j, colombet m, soerjomataram i, mathers c, parkin dm, piñeros m., ... & bray, f. (2019) estimating the global cancer incidence and mortality in 2018: globocan sources and methods. international journal of cancer, 144(8): 1941-1953. [9] franken c, koppen g, lambrechts n, govarts e, bruckers l, hond ed, loots i, nelen v, sioen i, nawrot ts, baeyans w, larebeke nv, boonen f, ooms d, wevers m, jacobs g, covaci a, schettgen t, schoeters g. (2017) environmental exposure to human carcinogens in teenagers and the association with dna damage. environmental research, 152: 165-174. [10] kazeminezhad i, mosivand s. (2017) elimination of copper and nickel from wastewater by electrooxidation method. journal of magnetism and magnetic materials, 422: 84-92. [11] suto r, ishimoto c, chikyu m, aihara y, matsumoto t, uenishi h, yasuda t, fukumoto y, waki m. (2017) anammox biofilm in activated sludge swine wastewater treatment plants. chemosphere, 167: 300-307. [12] naeem m, mujahid m, umer a, ahmad s, ahmad g, ali j, ... & khalid i. (2019) new trends in removing toxic metals from drinking and wastewater by biomass materials and advanced membrane technologies. j. bio. env. sci, 15(3): 10-17. [13] suto r, ishimoto c, chikyu m, aihara y, matsumoto t, uenishi h, yasuda t, fukumoto y, waki m. (2017) anammox biofilm in activated sludge swine wastewater treatment plants. chemosphere, 167: 300-307. [14] bani-melhem k, al-shannag m, alrousan d, al-kofahi s, al-qodah z, al-kilani mr. (2017) impact of soluble cod on grey water treatment by electrocoagulation technique. desalination and water treatment, 89: 101-110. [15] hom-diaz a, jaén-gil a, bello-laserna i, rodríguez-mozaz s, vicent t, barceló d, blánquez p. (2017) performance of a microalgal photobioreactor treating toilet wastewater: pharmaceutically active compound removal and biomass harvesting. science of the total environment, 592: 1-11. [16] hülsen t, barry em, lu y, puyol d, keller j, batstone dj. (2016) domestic wastewater treatment with purple phototrophic bacteria using a novel continuous photo anaerobic membrane bioreactor. water research, 100: 486-495. [17] domingues a, rosa ic, da costa jp, rocha-santos ta, gonçalves fj, pereira r, pereira jl. (2020) potential of the bivalve corbicula fluminea for the remediation of olive oil wastewaters. journal of cleaner production, 252: 119773. [18] joseph l, jun bm, flora jr, park cm, yoon y. (2019) removal of heavy metals from water sources in the developing world using low-cost materials: a review. chemosphere, 229: 142-159. [19] kamzon ma, abderafi s, bounahmidi t. (2016) promising bioethanol processes for developing a biorefinery in the moroccan sugar industry. international journal of hydrogen energy, 41: 20880-20896. [20] barrera i, amezcua-allieri ma, estupiñan l, martínez t, aburto j. (2016) technical and economical evaluation of bioethanol production from lignocellulosic residues in mexico: case of sugarcan and blue agave bagasses. chemical engineering research and design. 107: 91-101. [21] zhang y, song x, xu y, shen h, kong x, xu h. (2019) utilization of wheat bran for producing activated carbon with high specific surface area via naoh activation using industrial furnace. journal of cleaner production, 210: 366-375. [22] deng ch, gong jl, zeng gm, niu cg, niu qy, zhang w, liu hy. (2014) inactivation performance and mechanism of escherichia coli in aqueous system exposed to iron oxide loaded graphene nanocomposites. journal of hazardous materials, 276: 66-76 [23] jiang w, xing y, zhang l, guo x, lu y, yang m, ... & wei g. (2021) polyethylenimine‐ modified sugarcane bagasse cellulose as an effective adsorbent for removing cu (ii) from aqueous solution. journal of applied polymer science, 138(7): 49830. [24] reitz jr, milford fj, christy rw. (2008) foundations of electromagnetic theory, 4th edn. addison-wesley publishing company. 308 iium engineering journal, vol. 23, no. 1, 2022 baharudin et al. https://doi.org/10.31436/iiumej.v23i1.1816 [25] foo ky, hameed bh. (2012) mesoporous activated carbon from wood sawdust by k2co3 activation using microwave heating. bioresource technology, 111: 425-432. doi:10.1016/j.biortech.2012.01.141 [26] zhu t, chen js, lou xw. (2012) highly efficient removal of organic dyes from waste water using hierarchical nio spheres with high surface area. the journal of physical chemistry c, 116(12): 6873-6878. doi:10.1021/jp300224s [27] collard fx, bensakhria a, drobek m, volle g, blin j. (2015) influence of impregnated iron and nickel on the pyrolysis of cellulose. biomass and bioenergy, 52-62. [28] chen b, zhou d, zhu l. (2008) transitional adsorption and partition of nonpolar and polar aromatic contaminants by biochars of pine needles with different pyrolytic temperatures. environ. sci. technol., 42: 5137-5143 309 308 iium engineering journal, vol. 13, no. 2, 2012 ahmed and muhamad 153 finite element simulation of blanking process afzal ahmed 1 and hasmira muhamad 2 1 comsats institute of information technology, sahiwal, pakistan. 2 school of mechanical engineering, universiti saians malaysia, penang, malaysia. ahmed_462001@yahoo.com abstract: the blanking process can be simulated by abaqus v 6.4 to select punch, die and press and ascertain punch wear and bur height. the experimental and the simulation results agree well with rising punch force up to the point of creation of crack. for a 2mm mild steel sheet, the simulation shows that for the punch force of 240 kn, the crack starts at 30% punch penetration depth and punch force suddenly drops to a value of 70 kn and remains steady till the blanking is complete. comparing simulation and experimental results for a 3mm mild steel sheet, results agree well in the elastic range with the punch force rising up to point of crack creation. however, a discrepancy appears in punch force which increases with punch penetration. at 32% depth of penetration, the discrepancy is 12 % which increases to 60 % at punch penetration of 42%. punch force for experimental and simulation results remains about 90kn beyond punch penetration of 62%. also, increase of the thickness of sheet results in reduced crack height and improved quality of blank. abstrak: proses pengosongan boleh disimulasikan oleh abaqus versi 6.4 untuk memilih tebuk, alat dan tekan; dan menentukan haus tebuk dan ketinggian duri. keputusan ujikaji dan simulasi adalah serupa dengan kenaikan daya tebuk hingga titik retakan diperolehi. bagi kepingan keluli ringan 2mm simulasi menunjukkan bahawa untuk tenaga tebukan sebanyak 240 kn, retak bermula pada 30% kedalaman penembusan 30% tebukan dan daya tebuk tiba-tiba jatuh kepada 70 kn dan jumplah ini kekal sehingga proses pengosongan selesai. apabila hasil simulasi dan eksperimen dibandingkan, keputusan experimen untuk keluli lembut 3mm, bersetuju dengan baik dalam julat anjal dan daya tebukan meningkat sehingga titik penciptaan retak diperolehi. walau bagaimanapun percanggahan muncul apabila daya tebukan meningkat dengan daya penembusan. pada kedalaman penembusan 32% percanggahan adalah 12% dan nilai ini meningkat kepada 60% apabila daya penembusan sebanyak 42%. daya tebukan yang diukur melalui eksperimen dan simulasi kekal pada kira-kira 90kn melepasi penembusan punch sebanyak 62%. apabila ketebalan keputusan kunci ditambah, ketinggian retak dikurangkan dan ini meningkatkan kualiti pengosongan. keywords: simulation; finite element simulation; blanking; computer aided manufacturing 1. introduction in a blanking process, metal is cut by using a punch and die on mechanical or hydraulic press. the quality of sheared edge depends not only on the material but also the process parameters such as the clearance between the punch and the die, the blank holding force, and the sharpness of the edge of punch and die. klingenberg and singh [1] describe the blanking process in five stages; stage i: as punch pushes into the sheet held by the blank holder, the sheet is elastically deformed. stage ii: as the punch continues to push, first outer fibers of sheet then all inner fibers of sheet between punch and die are subjected to iium engineering journal, vol. 13, no. 2, 2012 ahmed and muhamad 154 yield strength. stage iii: the fibers of sheet between punch and die become thin and undergo plastic deformation and a crack starts developing. stage iv: a full crack develops and the force which pushes the punch is reduced. stage v: finally the punch pushes the slug through the die hole. with the advent of computer, the blanking process can be simulated and this can reduce time and cost in engineering decision making and equipment selection. in computer propagation of crack is simulated by mechanical fracture models. three methods are used to realize a fracture in fe-mesh, that is, element splitting, element separation and element deletion. a number of damage models (mclintock [2] cockroft/latham, [3]; rice and tracey, [4]; gurson [5]; lemaitre, [6]; husson et al. [7], tvergaard [8] have been developed to try to simulate the development and propagation of ductile fracture. the aim of paper is to apply fem along with crack damage model to simulate the blanking process and compare with experimental results. the computer program to simulate the blanking process is abaqus/cae v 6.4 [9]. this is finite element program designed to model the behavior of solids and structures under externally applied loading. the simulations were considered for blanks of mild steel sheets of different thicknesses. the results of simulated blanking process are compared with experimental results. 2. simulation of blanking process in this paper lemaitre model is used for crack initiation and propagation[6]. in lemaitre model the isotropic damage variable is the ratio between the total area of the micro cracks and cavities and cross sectional area of the material. 2.1 model geometry fig. 1: geometry of punch, die, blank holder, sheet and clearance. figure 1 shows the schematic diagram of the blanking process components which are punch, die, blank and the blank holder. the punch diameter is 30 mm. the punch-die clearance is 1 % of the blank thickness. the blanks are of mild steel sheet of 2 mm, 3 mm and 4 mm thickness. the tool wear is simulated by rounding off the cutting edge of the punch and die. the punch had edge radii of 0.01 mm, 0.06 mm, 0.12 mm, 0.2 mm, whereas die and blank holder edge radii were of 0.01 mm. following assumptions are made in the analysis: d r holder punch holder die die clearance blank iium engineering journal, vol. 13, no. 2, 2012 1. the process is simplified to a two conditions. 2. the process is considered quasi neglected. 3. the sheet material is considered as elastoplastic while the punch and die are defined as rigid. 4. the friction between sheet and tool follows coulomb’s law. 2.2 input data for modeling the blanking of mild steel s simulated with punches with different edge radii r 0.2 mm; the blank holder and the die with edge radius r blank. the tools are modeled as hard surfaces with rockwell hardness of c60 of elasticity of 210 gpa. because they are stiffer than the blank a two strain model is used. only half of the blanking is modeled bec symmetric about a plane along the center of the blank. the blank is of mild steel having modulus of elasticity, e= 207.0 × 10 undergoes considerable work hardening as it deforms pla 2.3 part definition for abaqus/cae part module four named the blank and other three are rigid parts named punch, holder and the die. the edge radius of the punch, rp is created with required values. a rigid body reference point need to be created. the point at the centre of the arc in view port is selected as the rigid body reference point. in the property module, a material named homogeneous solid section named blanksection is also created that refers to material steel. 2.4 mesh creation in the mesh module , the blank is meshed using cpe4r elements element with thickness in plane strain . it is two dimensional consi along the horizontal edges of the blank and sixteen elements along each region on the vertical edges of the blank are specified. the total numbers of nodes elements1006. figure 2 shows the mesh in shear zone. fig. 2 g journal, vol. 13, no. 2, 2012 ahmed 155 the process is simplified to a two-dimensional situation, under plane process is considered quasi-static, and hence the effects of strain rate are the sheet material is considered as elastoplastic while the punch and die are the friction between sheet and tool follows coulomb’s law. a for modeling the blanking of mild steel sheets as blank of thickness of 2 mm, 3 mm and 4 mm was simulated with punches with different edge radii rp = 0.01 mm, 0.06 mm, 0.12 mm and 0.2 mm; the blank holder and the die with edge radius rd=0.01 mm.that the tools are modeled as hard surfaces with rockwell hardness of c60-62 and modulus of elasticity of 210 gpa. because they are stiffer than the blank a two-dimensional plain strain model is used. only half of the blanking is modeled because the blanking process is symmetric about a plane along the center of the blank. the blank is of mild steel having modulus of elasticity, e= 207.0 × 10 9 pa, and poisson’s ratio = 0.29. the material undergoes considerable work hardening as it deforms plastically. s/cae part module four parts are created. they are: one deformable part named the blank and other three are rigid parts named punch, holder and the die. the edge is created with required values. a rigid body reference point need to be created. the point at the centre of the arc in view port is selected as the rigid body reference point. in the property module, a material named mild steel 2 mm is created. a neous solid section named blanksection is also created that refers to material in the mesh module , the blank is meshed using cpe4r elements, that is, four node element with thickness in plane strain . it is two dimensional consideration. forty elements along the horizontal edges of the blank and sixteen elements along each region on the vertical edges of the blank are specified. the total numbers of nodes were 1143 and figure 2 shows the mesh in shear zone. fig. 2: mesh in the shearing zone. and muhamad dimensional situation, under plane-strain static, and hence the effects of strain rate are the sheet material is considered as elastoplastic while the punch and die are 2 mm, 3 mm and 4 mm was = 0.01 mm, 0.06 mm, 0.12 mm and =0.01 mm.that contacts the 62 and modulus dimensional plain ause the blanking process is symmetric about a plane along the center of the blank. the blank is of mild steel having pa, and poisson’s ratio = 0.29. the material parts are created. they are: one deformable part named the blank and other three are rigid parts named punch, holder and the die. the edge is created with required values. a rigid body reference point need to be created. the point at the centre of the arc in view port is selected as the rigid body mm is created. a neous solid section named blanksection is also created that refers to material , that is, four node forty elements along the horizontal edges of the blank and sixteen elements along each region on the were 1143 and iium engineering journal, vol. 13, no. 2, 2012 ahmed and muhamad 156 the blanking process is carried out as per the procedure described by abacus /cae. figures 3 and 4 show the shape of 2 mm ms sheet before and after the application of punch force. fig. 3: contour of undeformed shape in blanking process of mild steel 2 mm. fig. 4: contour of shape after blanking process of mild steel 2 mm. 3. results and discussion figure 5 shows the simulation of punch force vs punch penetration for a 2 mm thick mild steel. the force rises initially up to about 240 kn with elastic and plastic yielding. a crack develops and force drops to 70 kn. the crack propagates now at a constant force. fig. 5: punch force vs punch penetration of blanking process (2 mm ms sheet). punch force vs punch penetration for mild steel 2mm 0 50 100 150 200 250 0 5 10 18 26 34 42 52 60 68 76 85 94 punch penetration (%) p u n c h f o rc e ( k n ) mild steel 2mm iium engineering journal, vol. 13, no. 2, 2012 ahmed and muhamad 157 fig. 6: punch force vs punch penetration of blanking process (4 mm ms sheet). figure 6 shows the simulation of force vs punch penetration for mild steel sheet of 4 mm thickness. the curve is slightly different from that of 2 mm mild steel sheet because of the effect of increased thickness of sheet. there seems to be a resistance in the initiation of crack as the crack starts at about 70% punch penetration. further the peak force lowers from 270 kn to about 140 kn with penetration up to 80%. unlike 2 mm sheet the crack does not propagate at a nearly constant force but propagates with the reduction of force. further the fracture height is less, that is, fracture height reduces as the sheet thickens. hernandaz et al. [10] studied the effect of clearance between die and punch ranging from 5% to 8% and found that the depth of start of crack increased with smaller clearance, however, decreased when clearance is increased. in the present study for a very small clearance of 1%, high values of punch penetration till the completion of blanking conforms to results of hernandaz et al. [10]. since rd/rp< 0.7, the crack will initiate from the die corner according to farzin et al. [11]. figure 7 shows the comparison of simulation results with that of the experiment. the experimental results are taken from the research paper by hambli and potiron [12]. the experimental and simulation results are for 3 mm mild steel sheet with punch edge radius of 0.01 mm. the figure shows good agreement in experimental and simulation results in elastic and plastic range but the development of crack starts at varying depth of punch penetration. in simulation the crack starts at about 30% penetration wheras in actual crack starts at about 34% penetration. however, the final force in simulation required for separation of blank from sheet tallies with that of experiments. figure 8 shows the experimental results by hambli and potiron [12] for punch force vs punch penetration for 3 mm thick mild sheet for different punch edge radii. the increase in punch edge radius exhibits the wear of the punch. figure 9 shows the simulation results for the similar experimental data of fig. 8. the punch force in elastic plastic region are in close agreement with those from experiment that is all reach 250 kn and also have same start of crack at punch penetration of 30% depth. however, the final force requirement for separation of blank from sheet is different in case of experimental resultsa lower force of 50 kn for the worn punch of edge radius of 0.2 mm. this seems to be because of different worn radius of the punch. in case of simulation the force of separation of blank from sheet is nearly same for tool and worn tool again because of the limitation of damage model. however, by simulation one can estimate the punch force requirement to determine the capacity of press needed. also the punch force vs punch penetration for mild steel 4mm 0 50 100 150 200 250 300 0 10 20 30 40 50 60 70 80 90 96 98 punch penetration (%) p u n c h f o rc e ( k n ) mild steel 4mm iium engineering journal, vol. 13, no. 2, 2012 ahmed and muhamad 158 effect of punch wear on fracture height and bur height can be determined which in turn signify the quality of the blank. fig. 7: simulation compared with experimental results of hambli and potiron [12]. fig. 8: experimental results for punch force vs punch penetration of 3 mm ms sheet for various punch edge radii reported by hambli and potiron [12]. fig. 9: simulation of punch force against punch penetration for various punch edge radius for blanking of 3 mm ms sheet. punch force vs punch penetration for mild steel 3mm 0 50 100 150 200 250 300 0 4 7 12 18 24 30 36 42 50 56 62 68 74 80 88 94 100 punch penetration (%) p u n c h f o rc e ( k n ) experiment simulation punch force vs punch penetration 0 50 100 150 200 250 300 0 3 5 7 10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 70 74 78 punch penetration (%) p u n c h f o rc e ( k n ) rp = 0.06 mm rp = 0.12 mm rp = 0.2 mm punch force vs punch penetration for mild steel 3mm 0 50 100 150 200 250 300 0 3 5 7 10 14 18 22 26 30 34 38 42 46 50 54 58 62 punch penetration (%) p u n c h f o rc e ( k n ) rp = 0.06 mm rp = 0.12 mm rp = 0.2 mm rp = 0.01 mm iium engineering journal, vol. 13, no. 2, 2012 ahmed and muhamad 159 4. conclusion the abaqus v 6.4 satisfactorily simulates the blanking process. the elastic plastic range simulation is well in agreement with experimental results. after plastic deformation a crack develops and the fem model incorporating lemaitre damage model [6] approximates well the crack propagation. as the crack develops the punch force is reduced considerably and punch penetrates depending on the punch edge radius. with increased thickness of sheet the crack height is reduced and the blank quality is improved. the changing punch wear( edge radii) does not change the force markedly in elastic region. however, in the plastic/fracture zone the different punch wears complete the blanking at different forces as observed in experiments by hambli and potiron [12]. this marked difference is not much obvious in simulation because of the use of damage model which does not take into account the punch wear. acknowledgement the research was undertaken at the computer laboratory of school of mechanical engineering, universiti sains malaysia. the authors are grateful to mr. jamari for providing all assistance in carrying this project. references [1] klingenberg, w and singh, u.p. “comparison of two analytical methods of blanking and proposal of a new model.” international journal machine tools and manufacturing 45(2005): 519-27. [2] mcclintock, f.a. “a criterion for ductile fracture by the growth of holes subjects to multiaxi al stress-states.” transactions asme j. appl. mechanics 35(1968): 363-71. [3] cockroft, m.g., latham, d.j. “ductility and workabitity of metals.” journal institute met. 96(no date): 33. rice j.r., tracey, d.m.1969. “on the ductile enlargement of voids in triaxial stress fields.” journal mechanical. physic solids, 7(1968): 201 -217 . [4] gurson, a.l., “continum theory of ductile rupture by void nucleation and growth. part i. yield criteria and flow ru'les for porous ductile media.” journal engineering mater. technology 99(1977): 2-15. [5] lemaitre, i. “a continuous damage mechanics model for ductile fracture.” .i.of engineering materials and technology-transactions asme 107(1985): p83-89 . [6] husson, c., correia j.p.m., daridon,l., ahzi, s. “finite elements simulations of thin copper sheets blanking: study of blanking parameters on sheared edge.” mater. prutcess. tech, 2007. [7] tvergaard, viggo. “material failure by void growth to coalescence.” advances in applied mechanics 27.1 (1990): 83-151. [8] hemandez, j. j.,franco,p.,estrems,m.,faura,f. “modelling and experimental analysis of the effects of tool wear on form errors in stainless steel blanking.” journal of materials processing technology 180(2006): 143-150. [9] farzin, m., javani, h.r.,mashayekhi, m., hambli,r. “analysis of blanking proc€ss using vari ous damage criteria.” i. material process technology 17.7(2006): 287 -290 . [10] hambli, r and potiron, a. “finite element modeling of sheet metal blanking operations with experimental verification.” journal of mater. prutcess. technology 102.1-3(2000): 251 65. microsoft word sddiqie24-final.doc iium engineering journal, vol. 1, no. 2, 2000 h. abdullah et al. 1 the effects of weathering on mechanical properties of glass fiber reinforced plastics (grp) materials. h. abdullah department of mechanical engineering, university of guelph, school of engineering, guelph, ontario, canada n1g 2w1. habdulla@uoguelph.ca s. al araimi and r. a. siddiqui department of mechanical and industrial engineering, sultan qaboos university, p.o.box33, al-khod, muscat-123, sultanate of oman alaraimi@squ.edu.om , siddiqui@squ.edu.om abstract: glass fiber reinforced plastics composite is extensively used as a structural material for pools, oil pipes and tanks because it has good corrosion resistance properties. the effects of weathering on the mechanical properties of glass fiber reinforced plastics (grp) in the sultanate of oman have been studied. the tensile and three point bend specimens were exposed to outdoor conditions (open atmosphere) in sunlight and tested for various intervals of time. it was observed that as the exposure time to sunlight, ultraviolet radiation and dust increases the mechanical properties of grp materials decrease. the effects of relative humidity (%rh) on the mechanical properties were also studied. it was found that as the relative humidity increased in the atmosphere during the exposure time, the tensile strength, flexural strength and modulus of elasticity are lowered. this work has revealed that the decrease in the mechanical properties of grp under weathering conditions is subjected to atmospheric conditions such as humidity, temperature, ultraviolet radiation and pollutant. key words: weathering, glass-fiber reinforced plastics, degradation 1. introduction grp is an industrial term that denotes one of the composite materials, which is called glass fibre reinforced plastics. the grp is used to control corrosion problems in oil fields, marine applications, chemicals and industrial plants. the successful performances of fibre glass reinforced thermo setting plastics have led to its wide use in corrosive services compared to other metallic materials. also, due to its improved properties such as high specific strength and stiffness to weight ratio, glass fibre reinforced polymers composites are utilised successfully as structural material. the mechanical properties of fibreglass reinforced composite material depend on its composition, namely the fibre and the matrix plus the quality of the fibre matrix interface. the percentage of glass fibre (by volume) in reinforced plastics usually ranges between 30% to 60% [1]. the first use of grp material by total took place in 1975 at one of the offshore oil fields in the middle east [1]. the objective was to control the corrosion of firewater and cooling water systems by replacing the existing galvanised carbon steel pipes material with grp. most of the literature available on the degradation is related to the polymers, while studies related to the effects of weathering or environmental resistance on grp itself are scarce. the environmental effects on the material integrity of fibre reinforced polymer matrix composites (pmcs) was investigated by dispennette et al. [2]. the composite materials were composed of carbon fibre reinforced with epoxy matrix. they were exposed to selected environments i.e. moisture, gamma radiation and atomic oxygen (ao) to induce varying degree of degradation. the studied properties were specifically glass transition temperature (tg), weight loss and modulus. from this investigation, it was determined that the erosion behaviour of these materials was significantly effected by the environmental exposures. however, the properties like modulus, were slightly affected. ontsuka [3] reported that the polymer degradation took different forms, such as fracturing, cracking, and chalking, depending on the nature of polymers. he showed that the degradation of polymers depends not only on the environment in which they are practically used, but also on their fabrication processes. the prediction of the polymeric material service life when exposed to outdoor conditions was investigated by tomiita [4]. the weather abilities of this material used outdoors have not been analysed in details. therefore, it was essential to establish a service life prediction system of polymeric materials. the degradation factors include solar ultraviolet irradiation, heat and moisture attack on polymers exposed outdoors. the authors expressed the degradation phenomena by mathematical models as a function of degradation factors and elapsed time. they developed a computer model to determine degradation material constants and predict property changes over time by simulating degradation. iium engineering journal, vol. 1, no. 2, 2000 h. abdullah et al 2 al-bastaki and al-madani [5] exposed the grp specimens directly to solar radiation and natural atmospheric conditions in bahrain. generally, the weather in bahrain has high temperature and humidity during the summer and very little rain during the winter. the flexural strength of the specimens exposed to outdoor conditions showed a little variation. the tensile specimens had a reduction in failure strain and an increase in the modulus of elasticity. the environmental effects on polyesters laminates reinforced with chopped strand glass fibre mat were also investigated by abraham [6] in marine environment. the experimental results have shown a slow decrease in mechanical properties of grp with an increase in the ageing time. bonnian and bunsell [7] work on epoxy resin have revealed that degradation usually occurs in environments with concentration of water. schutte [8] studied the environmental attacks by moisture on the durability of glass fiber polymer composites. it has been found that moisture could degrade the strength of the glass fiber, plasticizer and swell or micro-crack the resin. also, the fiber matrix interface could be weakened by either chemical or mechanical attack. the relative rates of these degradation processes were function of the chemistry of the resin, temperature, length of time of exposure, degree of stress (whether cyclic or static), chemistry and morphology of coating of coupling agent on the glass fiber, and type of glass fibre. bunsell [9] studied the influence of water absorption and heat on the behaviour of epoxy resins and glass fibre. the study revealed that the degradation usually occurred in environment with concentration of water greater than 70 to 80% r.h. the degradation effects were accelerated particularly above 70 oc. degradation occurred by hydrolysis, by resin swelling and by cracking. meanwhile, glass fibres resisted quite well to the attack of neutral water, but were damaged when contacted with acid or alkaline environments. the effects of saline treated fibre on impact and tensile properties of hydrothermal aged glass fabric/epoxy laminates were examined by morii et al [10]. the specimens were immersed in hot distilled water. the static tensile,the impact flexural and change in weight were measured. the weight loss occurred for methacryl treated laminate as a result of debonding of fibre/matrix at the interface and the water penetrates into this interface. this degradation of interface affected the tensile and impact properties and it induced the greater modulus and strength reduction. castaing and lemoine [11] evaluated the mechanical characteristics versus time to investigate the effects of water absorption and osmotic degradation on long-term behavior of glass fiber reinforced plastics. it was shown that the main effects of water on the composite mechanical properties are the plasticization of the matrix and the osmotic delaminating of plies, causing a decrease in mechanical properties. on the other hand, gelcoat blistering had no influence on the durability of plastics. davies et al [12] investigated the influence of water absorption on tensile properties and shear fracture toughness of glass/polypropylene. the immersion time was up to 5months at 50 degree oc. it was observed that the absorption of distilled water was more than seawater. a very small change in the transverse tensile modulus was observed after immersion in the water, but fracture toughness decreases significantly. the reduction in fracture toughness is attributed to the degradation of the matrix due to water absorption as observed by the scanning electron microscope. a study on photodegradation and photo stabilisation of polymer was conducted in 1940s, when it was observed that degradation in air also involved simultaneous oxidation. the basic mechanism of photooxidation degradation was established by bolland and gee [13]. an investigation of accelerated weathering and photo degradation in polymer was conducted by kampf et al. [14]. the work summarised knowledge of the primary processes of photodegradation, emphasising on the significance of incoming light wavelength. the paper highlighted the significance of the wavelength of incoming light. the work also discussed various methods of photodegradation. the effects of the low earth orbital (leo) atomic oxygen and ultraviolet radiation on the degradation of polymers were presented by dever [15]. the ultraviolet radiation and the environmental atomic oxygen can alter the chemistry of polymers resulting in degradation. the author introduced a survey of the interaction and possible damage mechanisms for environmental atomic oxygen and ultraviolet radiation exposure of polymers commonly used in leo. from the literature survey presented above, it is obvious that most of previously published work was conducted on polymers or epoxy resin instead of fibre reinforced polymers. this paper is intended to investigate the effect of atmospheric conditions on the mechanical properties of grp conducted under the most severe weather conditions in the sultanate of oman. the experimental work was carried out in muscat, which is one of the hottest cities in the world. the rainfall is generally light and irregular but the average relative humidity during summer varies between 7585% (rh%) and the temperature can exceed 50 oc. 2. experimental procedure the glass fibre reinforced plastic (grp) sheets were manufactured by amiantit oman company (muscat, sultanate of oman) by hand lay up process and consist of:  resin to bs3532/ crystic 491 e isopthalic, from scott bader, uk  e-glass mat to bs 3496  resin to glass ratio 2.5:1 the tensile specimens are machined according to astm no. d 3039 and three point bend specimens are prepared according to astm d 790-91 standards. the length, width, thickness and weight of each specimen were measured and recorded. all the specimens were hanged on rack and were subjected to natural weathering, consist of changing in temperature, iium engineering journal, vol. 1, no. 2, 2000 h. abdullah et al 3 humidity, solar radiation as well as other factors (such as pollutants present in the environment). weather conditions were recorded daily during the experimental period at sultan qaboos university metrology centre. the exposure time was little more than one year (389 days) in the city of muscat, sultanate of oman. the general atmospheric conditions were high temperature, high humidity in summer and very little rain during winter. the samples were removed periodically during this exposure period (every 10 days on the average) and tested for tensile strength, three-point bend test and moisture content. the tensile test was conducted by lloyd machine with a strain rate of 0.5 mm/min. the three point bend tests were carried out with lloyd instrument with a speed of 2 mm/min. the flexural strength, the load and displacement data, modulus of elasticity and moisture content were calculated from graphs obtained from the testing machines. 3. results and discussion plastics, rubber fibres, paints and lacquers are all degraded in sunlight by basically the same free radical mechanism. similarly, prolonged exposure of grp under natural weathering which includes moisture, temperature ultraviolet radiation etc. will result in degradation of the material. the mechanical properties of a composite depend on the properties of their components namely the fibres and matrix plus the quality of fibre matrix interface. it was difficult to have uniform composition of glass fiber and resin through out the material, especially, by hand lay up process. therefor, the experimental results in fig. 1 to 6 show scattering due to the non-uniform composition of grp produced by hand lay up process. the standard grp specimens were tested after they were exposed to outdoor weathering. the effect on the grp’s tensile strength (mpa =145 psi), after exposing in the natural environment for the period between 7 to 389 days, is presented in fig. 1. minimum of three specimens was tested at each interval and the average results were plotted as shown in fig. 1. it is interesting to note that as the exposure time increases an over all slow decrease in tensile strength of grp was observed. fig. 1 effect of exposure time on the tensile strength of grp fig. 2 effect of exposure time on the weight of grp the change in the weight of the grp (due to humidity) when exposed to the open atmosphere is shown in fig. 2. it is obvious from the experimental results that for a prolonged exposure to humidity, the matrix of the composite material will absorb water, or free diffusion of water will take place in the resin without interaction with the material, fig. 2. also, it shows inconsistency in the results of weight gain by the specimen. this can be expressed as a loss in weight, which is due to evaporation of moisture from the specimens because of high temperature and low humidity during summer periods. the negative value on the graph represents a loss in weight (original weight) and the positive values means a gain in weight by the specimen exposed for a period of 389 days. the effect of average relative humidity on the tensile strength of grp is plotted in fig. 3 respectively. it is found that as the relative humidity in the atmosphere exceeds beyond 40%, the degradation increases. a decrease in tensile strength in most of the grp specimens was observed with ageing time. the decrease in tensile strength could be due to swelling and shrinkage, which is caused by the entry of water via diffusion through the resin. this may break the bond between fibers and matrix leading to a fall in tensile strength of grp. fig. 3 effect of average relative humidity on the tensile strength of grp iium engineering journal, vol. 1, no. 2, 2000 h. abdullah et al 4 figure 4 shows the effect of exposure time in days on flexural strength of grp. it is observed that as the exposure time increases, the flexural strength of the material decreases. this is because of the effect of ultraviolet radiation, moisture content and heat as shown in figs. 1-4. fig. 4 effect of exposure time on the flexural strength of grp the effect of average relative humidity (%rh) on the flexural strength of grp under the outdoor conditions (ultraviolet radiation, moisture and sunlight) is plotted in fig. 5. the results show that as the exposure time and the percentage relative humidity (% rh) increases in the atmosphere, the flexural strength of grp decreases. the variation of modulus of elasticity (e) of grp composite materials as a function of exposure time is shown in fig. 6. a decrease in e is evident from the graphs when the material was exposed to sunlight radiation, humidity and temperature. fig. 5 effect of average relative humidity on flexural strength of grp however, the following observations were recorded during the experimental work. the first one is the effect of a pollutant. it was observed that a thin layer of sand covers the specimens during its exposure in the atmosphere. this thin layer of sand absorbs significant amount of solar radiation and ultraviolet radiation and thus, affects the temperature of the specimens. the second observation was yellowing of the specimens when exposed to the outdoor conditions. yellowing of matrix under the influence of the short wavelength of solar radiation is also a usual cause of degradation. the yellowing effect depends on the composition of the resin as well as on the type and addition of the ultraviolet stabiliser present in the resin. the yellowing is an important factor, which causes the degradation of the resin and an increase in the brittleness of the material. hence, affecting the mechanical properties of the material. fig. 6 effect of exposure time on the modulus of elasticity (e) of grp. there are numbers of mechanisms that contributed to the degradation processes of the tested specimens such as mismatch in the coefficients of thermal expansion between fibre and the matrix, swelling and shrinkage of resin during moisture absorption, hydrolysis and photooxidation, thermal decomposition and surface erosion. in addition, the absorption of water by resin causes a fall in glass transition temperature (tg). the decrease in mechanical properties such as tensile strength, flexural strength and modulus of elasticity of grp on prolong exposure to humidity can be justified on the following basis: in most environments, organic matrix composite will absorb water, and the presence of water may cause changes in the constituents. the simplest model of water up take is based on the free diffusion of water into the resin without interaction with the material [11]. the absorption of moisture gives rise to a reduction of tg and may break the bonds between fibres and matrix, leading to reduction in load transfer and a fall in mechanical properties. the degradation by hydrolysis is caused by differential swelling between the fibres and the resin, which produces serious cracks in the composite material and consequently affect the mechanical properties. bolland and gee established [13] established the basic mechanism of photooxidation degradation. the mechanism involves an initiation reaction of free radical formation by chain scission or some other bond cleavage, which is in the case of outdoor exposure of grp materials, is caused by the ultraviolet radiation of sunlight. this scission causes accelerated degradation of the polymer chain, therefore the mechanical properties iium engineering journal, vol. 1, no. 2, 2000 h. abdullah et al 5 of the tested grp specimens decreases with the increase in the exposure time. accentuation is another sign of deterioration for both polymers and epoxy/glass. as weathering proceeds, the thin resin film above the fibre strand bulges until it eventually burst, the exposed fibre come to the surface and promote dirt pick up. since the fiber are exposed directly to the atmosphere and there is difference between the thermal expansion of fiber and the matrix, the breaking of the bond between fiber and matrix will take place. as a result, the mechanical properties of the composite material will be decreased. 4. conclusion the following conclusions can be drawn from the results of the present investigation: the decrease in the mechanical properties, under weathering conditions is subjected to atmosphere conditions such as humidity, temperature, ultraviolet radiation, and pollutant. in most environments, organic matrix composite absorbs water/moisture by diffusion and the presence of water/moisture causes changes in the constituents. also, it affects the resin by swelling and shrinking, which can break the bonds between fibre and matrix, leading to a reduction in load transfer and fall in the mechanical properties of grp. a similar effect between fiber and matrix is possible due to the difference in the thermal expansion of the materials. sunlight causes some degradation in the organic matrix of the grp, it also involves simultaneous oxidation. this is due to the initiation reaction of forming free radical followed by chain scission cleavage. scission accelerates degradation of the polymer chain hence the mechanical properties are effected. although, sunlight generally causes some degree of surface deterioration in the organic matrix of a composite. it has become clear from various investigations that the combined effect of temperature and humidity is the most aggressive environmental factor affecting grp in outdoor exposure. references [1] c. f. p. aubert, “use of grp materials in piping systems. the experience of total,” materials engineering proceedings of international conference on off-shore mechanics and arctic engineering ome v3, pt a, 1993 published by asme, new york, ny, usa, pp. 279-283, 1993. [2] j. m. dispennette, l. seng, b. z. jang, and r. c. linton, “environmental effects on the material integrity of fiber reinforced polymer matrix composite,” 50 years of progress in materials and science technology international sampe technical conference, vol. 26, sampe, covina, ca, usa, pp. 119-127, 1994. [3] h. ontsuka “degradation of polymers-causes and methods for estimation,” zairyo to kankyo/corrosion engineering, vol. 43, no. 6, pp. 340-346, june 1994. [4] t. tomiita, “service life prediction system of polymeric materials exposed outdoors,” construction and building materials, vol. 8, no. 4, pp. 223-226, december 1994. [5] n. m. s. al-bastaki, and h. m. n. al-madani, “effect of six months exposure to atmospheric conditions on the mechanical properties of grp,” modelling, measurement and control, c: energetics, chemistry earth, environmental & bio-medical problem, vol. 49, no. 1-3, pp. 22-28, 1995. [6] t. abraham, “environmental effect on polyester laminates reinforced with chopped strand glass fibre mats,” kautschuk und gummi kunststoffe, vol. 49, no. 5, 350-353, may 1996. [7] p. bonnian and a. r. bunsell “ a comparative study of water absorption theories applied to glass epoxy composites,“ journal of composite materials vol. 15, pp. 272-278, 1981. [8] c. l. schutte, “environmental durability of glass fiber composites,” materials science and engineering: r: reports vol. 13, no. 7, pp. 265-324, november 1994. [9] a. r. bunsell, “hydrothermal ageing of composite materials,” revue de 1’ institut francais du petrole, vol. 50, no. 1, pp. 61-67, jan.-feb. 1995. [10] t. morii, h. hamada n. ikuta, m. desaeger, and i. verpoest, “effect of saline treated fiber on impact properties of hydrothermal aged glass fabric/epoxy laminates,” sampe technical conference, vol. 27, pp. 1048-1058, 1995. [11] p. castaing, and l. lemoine, “effect of water absorption and osmotic degradation on long-term behaviour of glass fiber reinforced polyester,” polymer composites, vol. 16, no. 5, pp. 349-356, october 1995. [12] p. davies, f. pomies, and l. a. carlsson, “influence of water absorption on transverse tensile properties and shear fracture toughness of glass/polypropylene,” journal of composite materials, vol. 30, no. 9, pp. 1006-1019, 1996. [13] j. l bolland and g. gee, transactions faraday society, vol. 42, pp. 236-244, 1946. [14] g. kampf, k. sommer, and e. zirngiebl, “studies in accelerated weathering part idetermination of the activation spectrum of photodegradation in polymers,” progress in organic coatings, vol. 19, no. 1, pp. 69-77, april 1991. [15] j. a. dever, “low earth orbital atomic oxygen and ultraviolet radiation effects on polymers,” flightvehicle materials, structures and dynamicsassessment and future directions, vol. 2, pp. 422-433, 1994. biography hussein a abdullah received his ph.d degree from the university of glasgow in 1992. he has been a researcher at the department of mechanical engineering, university of glasgow. he joined incorporated technology (itl) as consultant in 1991. in 1995 he joined the sultan qaboos university as assistant professor, in the department of mechanical & industrial engineering. at present he is working as associate professor at the school of engineering, university of guelph canada. his major research interests are manufacturing systems, cad /cam materials processing, robotics, and mechatronic systems. iium engineering journal, vol. 1, no. 2, 2000 h. abdullah et al 6 saeed ali al-araimi received his phd degree from the university of missouri-rolla in 1993. prior to joining squ, he worked as deputy director general of industry in the ministry of commerce & industry in sultanate of oman. he received his b.sc. (cum laude) in industrial engineering from university of haven and mem from northwestern university. his current research interest includes multi-criteria decision-making, total quality management, project management, industrial management and engineering education. rafiq ahmad siddiqui completed his b.sc (hons) and m.sc degree in chemical engineering from the university of punjab. later in 1966 he received his diplom in metallurgy from w. germany & phd in metallurgy from university of strathclyde u.k in 1974. he has worked in various universities of pakistan, canada, saudi arabia, & sultanate of oman as assistant professor, & associate professor. he joined the sultan qaboos university, department of mechanical engineering in 1988. he has been involved in teaching different courses in materials science as well as in manufacturing processing. his major interest is in the field of metallography & microstructure, failure analysis & preventions, fractro-graphy corrosion & composites materials. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 maximizing output voltage of a piezoelectric energy harvester via beam deflection method for low-frequency inputs mohamad safiddin mohd tahir, noor hazrin hany mohamad hanif* and azni nabela wahid department of mechatronics engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia *corresponding author: noorhazrin@iium.edu.my (received: 14th july 2021; accepted: 30th august 2021; published on-line: 4thjanuary 2022) abstract: in micro-scale energy harvesting, piezoelectric (pzt) energy harvesters can adequately convert kinetic energy from ambient vibration to electrical energy. however, due to the random motion and frequency of human motion, the piezoelectric beam cannot efficiently harvest energy from ambient sources. this research highlights the ability of piezoelectric energy harvester constructed using a pzt-5h cantilever beam to generate voltage at any input frequency from human motion. an eccentric mass is used to convert the linear motion of human movement to angular motion. then, using a magnetic plucking technique, the piezoelectric beam is deflected to its maximum possible deflection each time the eccentric mass oscillates past the beam, ensuring the highest stress is induced and hence the highest current is generated. for testing works, the frequency of oscillation of the eccentric mass is controlled using an arduino uno microcontroller. in this work, it is found that when given any input frequencies, the energy harvester produced a consistent ac voltage peak around 5.8 vac. on the other hand, the dc voltage produced varies with respect to the input frequency due to the number of times the peak ac signal is generated. the highest dc voltage produced in this work is 3.7 vdc, at 5 hz, which is within the frequency range of human motion. this research demonstrated that energy can still be effectively harvested at any given low-frequency input, in the condition that the piezoelectric beam is being deflected at its maximum. abstrak: piezoelektrik dapat mengubah tenaga kinetik daripada getaran persekitaran kepada tenaga elektrik melalui penjanaan tenaga berskala mikro. namun, pzt tidak dapat menjana tenaga dengan berkesan dari sumber persekitaran kerana pergerakan dan kekerapan pergerakan manusia adalah rawak. kajian ini adalah mengenai keupayaan penuai tenaga piezoelektrik menggunakan bilah kantilever pzt-5h bagi menjana voltan pada sebarang frekuensi menerusi gerakan manusia. jisim eksentrik digunakan bagi menukar gerakan linear manusia kepada gerakan putaran. kemudian, teknik penjanaan piezoelektrik secara magnetik digunakan bagi memesongkan bilah piezoelektrik ke tahap maksimum. bagi memastikan tenaga tertinggi dihasilkan, jisim eksentrik perlu berayun melepasi bilah pzt. ayunan frekuensi jisim eksentrik ini dikawal melalui kawalan mikro arduino uno. dapatan kajian menunjukkan bagi setiap frekuensi input, pzt ini dapat menghasilkan voltan ac yang konsisten, iaitu sekitar 5.8 vac. namun, voltan dc maksimum yang terhasil adalah berbeza-beza bagi setiap frekuensi input, iaitu berdasarkan bilangan kekerapan maksimum isyarat ac yang terhasil. voltan dc tertinggi ialah 3.7 vdc, pada 5 hz, iaitu pada kadar frekuensi gerakan manusia. ini menunjukkan bahawa tenaga masih dapat dihasilkan secara berkesan pada frekuensi rendah, dengan syarat bilah piezoelektrik terpesong pada tahap maksimum. 434 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 keywords: energy harvesting; piezoelectric; magnetic plucking; random frequency 1. introduction the miniaturization of electronics components such as sensors has been rapidly developed for wearable and portable devices. these sensors have a variety of uses on the human body, including heart monitoring sensors, glucose level sensors, blood pressure and oxygenation sensors, and medication administration systems [1]. the sensors’ diminutive size enables them to be comfortably fastened to a human body part. additionally, the size reduction resulted in a reduction in power usage. by and large, most electronic gadgets use a conventional battery that has a finite life and requires replacement. this increases the attractiveness of alternatives to batteries as a power source. batteries are the single largest source of electronic waste on a global scale. these conventional batteries contain hazardous elements that can be lethal to human health and the environment if not disposed of correctly [2]. one viable solution is to build self-powered gadgets capable of generating their own electricity, a process commonly known as energy harvesting. energy harvesting can be used to harvest energy from a variety of sources, such as vibration, wind, sound, and human motion [3-5]. numerous studies have been conducted on energy harvesting from human motion, which is the conversion of kinetic (vibration) energy to electrical energy. motion from human limbs can be exploited as an input to the energy harvester, which will be used as a power supply to the wearable device. human motion typically has a vibration frequency of between 0.1 to 25 hz [6], which is quite low in comparison to the resonance frequency of the numerous varieties of piezoelectric materials. piezoelectric energy harvesters can have high output voltage from vibration as compared to other conversion mechanisms such as electromagnetic and electrostatic energy harvesters [7]. additionally, it has been demonstrated that pzt-5h can generate a greater voltage than polyvinylidene difluoride (pvdf), aluminum nitride (ain), and barium sodium niobate (ba2nanb5o15) [2]. traditionally, the piezoelectric energy harvester is designed as a linear resonator and only works effectively within a narrow bandwidth of frequency. the range of frequency bandwidth was around 5 hz. for example, a pzt-5h beam has an optimum frequency range between 48 hz and 53 hz, while a pvdf beam has an effective frequency range between 250 hz to 255 hz [8-10]. outside of a specified frequency range, the effectiveness of energy harvesting decreases tremendously. numerous solutions have been proposed to address the issue. one of the approaches is the plucking technique. regardless of the frequency of the input, the energy harvester will always operate at its most efficient state. this technique is capable of matching the low frequency of human motion, such as an arm swinging forwards and backwards in a walking motion, which occurs at approximately 0.9 hz [11], or running motion which occurs at 1.9 hz [12]. this plucking technique can be categorized into two types: contact or non-contact. contact methods, also known as impact types, have been demonstrated by gu and livermore [13]. the piezoelectric was struck by plucking it with another beam with a low resonance frequency. on the other hand, non-contact types use a magnet to pluck the piezoelectric beam, such as in a knee joint harvester [14]. this energy harvester is worn on the knee. by using the motion of the knee while walking or running, the piezoelectric cantilever beams are plucked by the magnets and generate up to 3.3 v of electricity. other research using the same mechanical plucking include impulse excited energy harvester for human body excitation 435 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 [6] and design and simulation of bistable piezoceramic cantilever for energy harvesting from slow swinging movement [15]. although the piezoelectric energy harvester can convert kinetic energy to electrical energy, it could not properly harvest energy from ambient sources due to the unpredictable motion and periodicity of human movements. thus, this paper will highlight the capability of the proposed beam deflection method in addressing the limitation. in this method, by utilizing magnetic force, the piezoelectric beam in the energy harvester device can be bent to its maximum deflection regardless of the input frequencies. the relationship between maximum deflection and applied voltage will be demonstrated by simulation. the findings will be further validated with a prototype to investigate the amount of energy harvested at various frequencies of motion. 2. research method 2.1 system design the principle of using a piezoelectric bimorph beam for energy harvesting based on magnetic plucking motion is demonstrated in this paper. figure 1 shows an assembly of an eccentric mass that was used to convert linear motion into rotational motion. this configuration made it suitable for the piezoelectric beam to be magnetically plucked due to excitation by low frequency or random human motion. the piezoelectric beam used for this research is the pzt-5h piezoelectric bimorph beam with a dimension of 40 mm x 10 mm x 0.5 mm. the magnet used is a neodymium magnet with a diameter of 12 mm and height of 3 mm. this piezoelectric beam consists of a layer of copper sandwiched between two layers of lead zirconate titanate (pzt). the pzt-5h beam was chosen because it has demonstrated a higher capability for voltage generation than other piezoelectric materials such as polyvinylidene difluoride (pvdf), aluminum nitride (ain), and barium sodium niobate (ba2nanb5o15) [16-19]. additionally, according to table 1, pzt-5h has the greatest piezoelectric strain coefficient, d33 value, indicating that it can generate a comparatively greater charge under normal stress applied due to transverse vibration. the parameters of the piezoelectric energy harvester assembly are listed in table 2. table 1: comparison of strain coefficients, d33 for different types of piezoelectric materials material d33 (m/v) pzt-5h 600× 10-12 pvdf 30× 10-12 ain 5.1 × 10-12 barium sodium niobate 319 × 10-12 table 2: parameters of the piezoelectric energy harvester assembly material length/mass diameter eccentric mass 80 mm circular magnet at the tip of the beam (proof mass) 12 mm (diameter), 3 mm (height) mass of the magnet at the tip of the beam (proof mass) 4.64 g rectangular magnet to bend the beam 10 mm x 10 mm x 3 mm piezoelectric beam 40 mm x 10 mm x 0.5 mm 436 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 (a) (b) fig. 1: (a) the design of the piezoelectric energy harvester utilizing beam deflection method, (b) exploded view of the design. referring to fig. 1, the design consists of an 80-mm diameter fabricated eccentric mass (green) with 65-mm length body (red), a pzt-5h piezoelectric bimorph beam, 6-mm diameter of neodymium (ndfeb) magnets, 10-mm length of rectangular ndfeb magnets and a miniature aluminum ball bearing with 8 mm outer diameter and 3 mm inner diameter. the circular neodymium magnet is mounted at the tips of the piezoelectric beam and the rectangular neodymium magnet is placed at the end of the eccentric mass, as shown in fig. 1. due to the identical polarity of the magnets at the piezoelectric beam tip and eccentric mass, the piezoelectric beam will bend when the eccentric mass rotates, causing the magnets to push against one another. as the magnets move away from each other, stress is induced in the piezoelectric beam and output voltage is generated. the distance between the two magnets can be adjusted to ensure that the pzt-5h piezoelectric beam always bends at its 2 mm deflection. according to the product datasheet [20], the maximum deflection of the pzt-5h was 2 mm. 𝑌𝑚𝑎𝑥 = − 𝐹𝑙3 3𝐸𝐼 (1) the cantilever beam formula, eq. (1), was used to calculate the magnetic forces required to deflect the beam at 2mm. the term ymax is maximum deflection, f is force, l is length of the beam, e refers to modulus elasticity of the beam and i refers to moment of inertia. from the calculation, the required force was 0.0344 n. before each experiment began, the deflection was also measured using a vernier scale. this is referred to as the mechanical plucking technique. it is well suited to human motion, which is predominantly random and low in frequency. it is capable of converting low-frequency movements into higher-frequency vibrations. 3d printed shaft. miniature aluminium ball bearing eccentric mass ndfeb magnets pzt-5h body 65 mm 437 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 2.2 simulation study using matlab software when a piezoelectric material experiences mechanical strain, some amount of voltage is generated at its terminal (known as sensor mode), and if a voltage is applied to the piezoelectric material, this will cause it to deform (actuator mode). here, a simulation study was carried out to investigate the relationship between the deflection produced by the piezoelectric cantilever beam with the amount of voltage applied to the beam. the amount of voltage applied to the pzt beam in this study is made equal to the voltage generated when it vibrates at its resonance in sensor mode. matlab software was used to conduct the simulation. the equations used in this paper have been discussed [21]. the typical constitutive equations for piezoelectric material are: {𝑆} = [𝑠𝐸]{𝑇} + [𝑑]𝑇{𝐸} (2) {𝐷} = [𝑑]{𝑇} + [𝜀𝑇]{𝐸} (3) in eq. (2) and (3), constant {s} refers to the deformation vector, {d} is the electric displacement vector, {e} is the electric field vector, [ɛ] is the dielectric constant matrix, [s] and [d] are the elasticity and piezoelectric constant matrices whereas {t} refers to the stress vector. based on the constitutive equations above, the state space equations are derived. { 𝑆11 𝑆22 𝑆33 𝑆23 𝑆13 𝑆12} = [ 𝑠11 𝑠12 𝑠13 0 0 0 𝑠12 𝑠22 𝑠23 0 0 0 𝑠13 0 0 0 𝑠23 0 0 0 𝑠33 0 0 0 0 𝑠44 0 0 0 0 𝑠55 0 0 0 0 𝑠66] { 𝑇11 𝑇22 𝑇33 𝑇23 𝑇13 𝑇12} + [ 0 0 𝑑31 0 0 𝑑32 0 0 𝑑15 0 0 𝑑24 0 0 𝑑33 0 0 0 ] { 𝐸1 𝐸2 𝐸3 } (4) piezoelectric coupling matrices have a few non-zero elements due to the crystal symmetries as shown in eq. (4), and the design of the sensing and actuation device is dictated by the available coupling modes. there are two state-space formulas which are for actuation and sensing mode. however, the actuation mode state-space formula is only used because only the actuation mode will be simulated. the piezoelectric material that will be used is pzt-5h. therefore, pzt coupling matrices are shown below. [𝑑]𝑃𝑍𝑇 = [ 000 000 00 00 𝑑15 0 000 000 00 𝑑15 00 0 𝑑31 𝑑31 𝑑33 00 00 0 ] (5) in this simulation, the electric field will be applied perpendicularly to the poling direction, resulting in transverse displacement, as shown in fig. 5. in order to obtain the bending action, thin pzt materials are bonded on the structure. the geometrical arrangement causes d31 to dominate the design, and the useful direction of expansion is normal to that of the electric field. by solving eq. (3) and (4), a deflection for the bimorph pzt can be found based on eq. (6) [21]. 𝐷𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛 = − 3 2 𝑑33∅ ℎ2 𝐿2 (6) coupling permitivity 438 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 in eq. (6), d33 refers to the piezoelectric strain coefficient at the z-axis direction, ∅ denotes the electrical potential, h and l are the height and length of the piezoelectric beam, respectively. the design of the piezoelectric beam is illustrated in fig. 2. here, the beam material used is pzt-5h in bimorph configuration. fig. 2: piezoelectric beam with a dimension of 40 mm x 10 mm x 0.5 mm. based on fig. 2, e1, e2, and e5 are the length of the pzt-5h beam, which is 40 mm, e7, e6, e4, and e3 are the height of the beam, which is 5 mm. the pzt-5h is a bimorph beam, therefore, the total height is 10 mm. table 3 shows the parameters that are set in the matlab software based on the selected pzt-5h beam according to the datasheet [20]. table 3: parameters of pzt-5h piezoelectric beam parameter value elastic modulus 7.2 x 1010 n/m2 poisson ratio 0.31 shear modulus 4.6 x 1010 n/m2 piezoelectric constant, d31 -270 x 10 -12 m/v piezoelectric constant, d33 600 x 10 -12 m/v maximum deflection 2 mm the amount of voltage that needs to be applied to the beam (actuator mode) in this study is determined via experiment by investigating the maximum voltage produced when the pzt beam vibrates at its resonant frequency (in sensor mode). in accordance with prior work [22], a digital signal analyzer (dsa hp-35670a) was used to provide base excitation to the same piezo cantilever beam over a frequency sweep from 0 hz until 100 hz. the result of this study is shown in fig. 3. at its resonant frequency of 18.33 hz, the pzt beam produced 4.55 v with a proof mass of 2.3 g and 4.01 v without proof mass. although the resonant frequency was within the range of frequency of human motion (1 hz 25 hz)[23], it is observed that the frequency bandwidth was quite narrow. this means that the pzt beam can only efficiently harvest energy at 18.33 hz but will tremendously degrade when there is a slight change in the frequency of vibration. from this study, the voltage 4.55 v will be 439 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 taken as input to the simulation study, as shown in fig. 2. the result will be discussed in a later section. frequency (hz) with proof mass without proof mass fig. 3: frequency sweep of pzt-5h piezoelectric beam. the peaks show the resonant frequencies of the beam with and without proof mass [22]. 2.3 measurement of output voltage from beam deflection an experimental setup for the whole assembly of the fabricated energy harvester in measuring the output voltage is shown in fig. 4. the apparatus for the experiment includes an arduino uno microcontroller to control the servo motor, a servo motor to oscillate the eccentric mass and imitate the average frequency of a human hand swinging forward and backward while walking and running, and a data acquisition board (national instruments cdaq-9171) to acquire the output signals from the piezoelectric beam to send to a computer with labview software. the fabricated prototype was held using a tripod stand. fig. 4: experimental setup. the arduino uno was programmed to oscillate the servo motor at specific frequencies (0.9 hz (walking) [11] and 2 hz (running) [12]) to show that the peak ac voltage will arduinouno microcontroller data acquisition device (ni cdaq-9171) monitor (labview) servo motor vrms (v) eccentric mass pzt-5h beam neodyminium magnets 440 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 always be the same, regardless of the input frequencies. additionally, four more frequencies (1.5 hz, 2.5 hz, 3.0 hz, and 5 hz) were also tested to observe the capability of the proposed design at other frequencies, as shown in table 4. the frequency of oscillation for the eccentric mass was measured using a tachometer during the experiment. table 4: frequency of the human limb motion when walking, running, and randomly pick frequencies test frequency of arm swing forward and backward (hz) walk 0.9 run 2.0 test 1 1.5 test 2 2.5 test 3 3.0 test 4 5 3. results and analysis 3.1 matlab software simulation results the simulation research results stated in section 2.2 will be discussed in this section. at the resonant frequency, the beam vibrates vigorously, resulting in greater deflection than at other frequencies, allowing for more voltage generation. to verify this, identical voltage is applied to the pzt beam and its resulting deflection is recorded. according to fig. 3 (shown in the preceding section), the voltage generated when it vibrates at its initial resonance frequency is 4.55 v. figures 5(a) and 5(b) illustrate the initial condition of the beam before any voltage is applied, during which no deflection occurs. when 4.55 v is supplied, the tip of the beam deflects 1.56 mm in the y-direction as seen in fig. 5(c) and 5(d). according to this investigation, the tip deflection of the beam generated by applying 4.55 v to its terminal is 1.56 mm, but the maximum deflection specified in the datasheet is 2 mm (table 3), a difference of almost 22%. the following section will show experiments conducted to demonstrate that by ensuring the piezo beam deflects maximally via the plucking approach, the same maximum output voltage, vac, can be generated regardless of the frequency. 3.2 voltage output from beam deflection figure 6(a) illustrates the ac output voltage measured by the data acquisition device as the energy harvester device is swung back and forth at a 0.9 hz input frequency. this motion is meant to mimic the frequency of hand gestures made by an average healthy human when walking. magnetic repulsion occurs when the magnets on the beam have the same polarity as the eccentric mass, deflecting or bending the beam. the piezoelectric beam is pushed and operated to its maximum deflection of 2 mm before the magnet is pulled away from the tip mass and the repulsion force is released. within a brief period of time, the beam will vibrate and dampen, bringing the magnets closer together once more. a similar experiment was repeated at a frequency of 2 hz, which is the average frequency of healthy human motion while running. similarly, the peak voltage was produced when the piezoelectric beam was actuated, as shown in fig. 6(b). as shown in the graph, the highest output voltage produced was nearly identical, at 5.9 vac. however, the frequency of the peak voltage produced in fig. 6(b) was greater than in fig. 6(a). this is because the eccentric mass oscillates at a higher frequency. 441 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 (a) (b) (c) (d) fig. 5: (a) initial shape of pzt-5h beam, (b) deflection of pzt-5h beam in the z-direction during initial condition, (c) shape of pzt-5h beam after a deflection in response to voltage, (d) deflection of pzt-5h beam in the z-direction in response to voltage. as illustrated in fig. 6, when the plucking approach is used in the experiment, the peak output voltage does not significantly alter at the different excitation frequencies. this is because the piezoelectric beam always bends at its maximum deflection at the same amount of force every time the eccentric mass's magnet passes beneath it, resulting in the highest peak output ac voltage. however, the frequency of peak voltage is varied because the eccentric mass's frequency varies with the tested frequencies of motion. figure 7 demonstrates that even when the frequency is altered up to 5 hz, the output ac voltage remains constant. it can be observed from fig. 7 that the peak voltages for all four different frequencies vary between 5.76 vpeak (at 3 hz) to 5.88 vpeak at 2.5 hz i.e. 2% difference. the distance between the two magnets is adjusted continuously to maintain the deflection of the piezo beam such that it will be at its maximum value i.e. 2 mm. pzt-5h l = 40 mm h=0.5 mm tip deflection was 1.5552e-03 tip deflection in response to voltage x z x z 442 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 (a) (b) fig. 6: output voltage (a) during 0.9 hz frequency excitation, (b) during 2 hz frequency excitation. fig. 7: result for different tests for frequency (a) 1.5 hz (b) 2.5 hz (c) 3 hz (d) 5 hz. 3.3 signal rectification the ac signals of the generated voltage for all frequencies were converted to dc signals using the same full bridge rectifier circuit in the previous works [22], shown in fig. 8. the rectified signals from the full bridge rectifier circuit were then stored inside a 100 µf capacitor. for each frequency, the experiment was conducted for 5 minutes to allow the dc voltage to stabilize and reach steady state. during the initial stages, the dc voltage will continue to rise [24]. figure 9 shows that the voltage is the highest, 3.7 vdc, when the energy harvester is excited by a 5 hz frequency of motion. this is because its alternating current voltage has a higher peak value than others. as the frequency of the signal rises, the dc voltage stored inside the capacitor increases proportionately. although the walking frequency of 0.9 hz is the lowest due to the lower peak voltage in the ac voltage, it can still generate an average of 1.5 vdc over a 5-minute period, which is sufficient to drive lowpowered electronic equipment. 5.84 vac 5.88 vac 5.76 vac 5.53 vac 443 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 fig. 8: full-bridge rectifier circuit for the assembly [22]. fig. 9: rectified voltage of the energy harvester at different frequencies. the generated voltage is summarized in table 5 for various frequency settings both before and after rectification. as can be seen, the average ac output voltage across all frequencies is 5.77 v. however, the rectified signals changed in response to the amount of frequency excited by the harvester. a higher dc voltage is generated when the excitation frequency is increased, and vice versa. this is proven in another work; a 5 v output was produced by a pzt-5h piezoelectric beam under 50 microstrain loading, which is the ultimate strain limit, over 50 mω load resistance [25]. table 5: summary of the generated voltage frequency (hz) voltage peak of ac voltage (v) dc voltage (v) 0.9 (walking) 5.70 1.6 2.0 (running) 5.90 2.5 1.5 5.84 2.0 2.5 5.88 2.3 3.0 5.76 3.3 5 5.53 3.7 4. conclusion when subjected to input frequencies ranging from 0.9 hz to 5 hz, the fabricated energy harvester device consistently produced peak ac output voltages of 5.5 – 5.8 vac. this implies that the pzt beam always deflects in the same direction when the magnet on the eccentric mass passes below the pzt beam's tip. the results of the studies demonstrate the 444 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 benefits of the suggested energy harvester for wearable devices using a magnetic plucking approach. as the eccentric mass in the proposed design can convert any directions of motion, it is less reliant on one-directional motion thus making it ideal for human applications with varying and random motion. in the future, the efficiency of ac to dc conversion can be improved by employing alternative rectifiers such as voltage doubler rectifiers and synchronized switch harvesting on inductor rectifiers [26]. apart from that, the size can be enhanced by making it more compact, allowing the gadget to be worn comfortably. acknowledgement this work is supported by the fundamental research grant scheme by the ministry of higher education malaysia (frgs/1/2018/tk10/uiam /02/2). references [1] pillatsch p, yeatman em, holmes as. (2013) a wearable piezoelectric rotational energy harvester. in proceedings of ieee internatinal conference body sensor networks: 6-9 may 2013; cambridge, pp 1-6. [2] huda a, noor hazrin hany mh, aliza aini mr. (2019) magnetically plucked piezoelectric energy harvester via hybrid kinetic motion. iium engineering journal, 20(1): 245-257. doi: 10.31436/iiumej.v20i1.981. [3] fan pmy, wong oy, chung mj, su ty, zhang x, chen ph. (2015) energy harvesting techniques: energy sources, power management and conversion. in proceedings of european conference on circuit theory and design: 24-26 august 2015; trondeim, pp 1-6. [4] nguyen s, amirtharajah r. (2018) a hybrid rf and vibration energy harvester for wearable devices. in proceedings of ieee applied power electronics conference and exposition: 4-8 march 2018; san antonio, pp. 1060–1064. [5] sang y, huang x, liu h, jin p. (2012) a vibration-based hybrid energy harvester for wireless sensor systems. ieee tranactions on magnetics, 48(11): 4495-4498. doi: 10.1109/tmag.2012.2201452. [6] pillatsch p, yeatman em, holmes as. (2012) a scalable piezoelectric impulse excited energy harvester for human body excitation. smart materials and structures, 21(11): 1-9. doi: 10.1088/0964-1726/21/11/115018. [7] mohd fauzi ar, kok sl, noraini ma, r. affendi, khairul azha aa. (2013) hybrid vibration energy harvester based on piezoelectric and electromagnetic transduction mechanism. in proceedings of the ieee conference clean energy technology: 18-20 november 2013; langkawi, pp 1–5. [8] fan k, tan q, liu h, zhu y, wang w, zhang d. (2018) hybrid piezoelectric-electromagnetic energy harvester for scavenging energy from low-frequency excitations. smart materials and structures, 27(8): 1-28. doi: 10.1088/1361-665x/aaae92. [9] anton sr, sodano ha. (2007) a review of power harvesting using piezoelectric materials (2003-2006). smart materials and structures, 16(3): r1-r21. doi: 10.1088/0964-1726/16/3/r01. [10] haitao l, weiyang q, chunbo l, wangzheng d, zhiyong z. (2015) dynamics and coherence resonance of tri-stable energy harvesting system. smart materials and structures, 25(1):1-10. doi: 10.1088/0964-1726/25/1/015001. [11] quantification of arm swing during walking in healthy adults and parkinson ’ s disease patients : and validation [https://www.ncbi.nlm.nih.gov/pmc/articles/pmc5685089/]. [12] is the relationship between stride length, frequency and velocity influenced by running on a treadmill or overground ? [https://www.ncbi.nlm.nih.gov/pmc/articles/pmc5685089/]. [13] gu l, livermore c. (2011) impact-driven, frequency up-converting coupled vibration energy harvesting device for low frequency operation. smart materials and structures, 20(4):1-10. doi: 445 iium engineering journal, vol. 23, no. 1, 2022 mohd tahir et al. https://doi.org/10.31436/iiumej.v23i1.2156 10.1088/0964-1726/20/4/045004. [14] pozzi m. (2016) magnetic plucking of piezoelectric bimorphs for a wearable energy harvester. smart materials and structures, 25(4):1-12. doi: 10.1088/0964-1726/25/4/045008. [15] rubes o, hadas z. (2018) design and simulation of bistable piezoceramic cantilever for energy harvesting from slow swinging movement. in proceedings of ieee 18th international conference power electronics and motion control: 26-30 august 2018; budapest, pp 1-6. [16] noor hazrin hany mh, ahmad jazlan m, huda a, mas ehsan r. (2018) rotational piezoelectric energy harvester for wearable devices. cogent engineering, 5(1): 1-11. doi: 10.1080/23311916.2018.1430497. [17] cheng x, wu j, lou x, wang x. (2014) achieving both giant d33 and high tc in patassiumsodium niobate ternary system. acs applied materials and interfaces, 6(2): 1-7. doi: 10.1021/am404793e [18] tian w, ling z, yu w, shi j. (2018) a review of mems scale piezoelectric energy harvester. applied sciences, 8(4): 1-20. doi: 10.3390/app8040645. [19] gao s, ao h, jiang h. (2019) properties and performance of general piezoelectric materials on a novel cantilevered energy harvester. in proceedings of 7th annual international conference on materials science and engineering: 19-20 april 2019; hubei, pp 1-8. [20] steminc steriner & martins inc [https://www.steminc.com/pzt/en/piezo-ceramic-bimorph40x10x05mm-2-khz]. [21] v. piefort (2001) finite element modelling of piezoelectric active structures. phd thesis. universit´e libre de bruxelles, faculty of applied sciences. [22] mohamad safiddin mt, noor hazrin hany mh, muhammad hafizuddin ck. (2021) performance measurement of piezoelectric energy harvester with permanent magnet assembly for wearable devices. in proceedings of ieee international instrumentation and measurement technology conference: 17-20 may 2021; glasgow, pp 1–5. [23] von büren t, mitcheson pd, green tc, yeatman em, holmes as, tröster g. (2006) optimization of inertial micropower generators for human walking motion. ieee sensors journal, 6(1): 28-38. doi: 10.1109/jsen.2005.853595. [24] muhammad aiman za, noor hazrin hany mh, and mohamad safiddin mt. (2021) energy storage system for dual energy harvester for wearable or portable devices. in proceedings of 8th international conference computer and communication engineering: 22-23 june 2021; kuala lumpur, pp 135-139. [25] m. rhimi. (2013) power management and damage assessment techniques for self-powered sensing based on piezoelectric. phd dissertation. university of michigan, civil engineering department. [26] vishnu sidharthan p, bhasker mu, korla s, chandrasekhar ms. (2018) energy harvesting of synchronized switch harvesting on inductor. in proceedings of international conference recent innovations in electrical electronics and communication engineering: 27-28 july 2018; bhubaneswar, pp 2282-2887. 446 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 72 a distributed energy efficient clustering algorithm for data aggregation in wireless sensor networks seyed mohammad bagher musavi shirazi, maryam sabet*, and mohammad reza pajoohan department of computer and electrical engineering, yazd university, yazd, iran. * corresponding author: maryam.sabet@stu.yazd.ac.ir (received: 1st march 2017; accepted: 17th oct 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.825 abstract: wireless sensor networks (wsns) are a new generation of networks typically consisting of a large number of inexpensive nodes with wireless communications. the main purpose of these networks is to collect information from the environment for further processing. nodes in the network have been equipped with limited battery lifetime, so energy saving is one of the major issues in wsns. if we balance the load among cluster heads and prevent having an extra load on just a few nodes in the network, we can reach longer network lifetime. one solution to control energy consumption and balance the load among nodes is to use clustering techniques. in this paper, we propose a new distributed energy-efficient clustering algorithm for data aggregation in wireless sensor networks, called distributed clustering for data aggregation (dcda). in our new approach, an optimal transmission tree is constructed among sensor nodes with a new greedy method. base station (bs) is the root, cluster heads (chs) and relay nodes are intermediate nodes, and other nodes (cluster member nodes) are the leaves of this transmission tree. dcda balances load among chs in intracluster and inter-cluster data communications using different cluster sizes. for efficient inter-cluster communications, some relay nodes will transfer data between chs. energy consumption, distance to the base station, and cluster heads’ centric metric are three main adjustment parameters for the cluster heads election. simulation results show that the proposed protocol leads to the reduction of individual sensor nodes’ energy consumption and prolongs network lifetime, in comparison with other known methods. abstrak: rangkaian sensor wayarles (wsn) adalah rangkaian generasi baru yang terdiri daripada nod-nod murah komunikasi wayarles. tujuan rangkaian-rangkaian ini adalah bagi mengumpul maklumat sekeliling untuk proses seterusnya. nod dalam rangkaian ini dilengkapi bateri kurang jangka hayat, jadi simpanan tenaga adalah satu isu besar dalam wsn. jika beban diimbang antara induk kelompok dan lebihan beban dihalang pada setiap rangkaian iaitu hanya sebilangan kecil nod pada tiap-tiap kelompok, jangka hayat dapat dipanjangkan pada sesebuah rangkaian. satu penyelesaian adalah dengan mengawal penggunaan tenaga dan mengimbangi beban antara nod menggunakan teknik berkelompok. kajian ini mencadangkan kaedah baru pembahagian tenaga berkesan secara algoritma berkelompok bagi pembahagian data dalam wsn, dikenali sebagai pembahagian kelompok kumpulan data (dcda). melalui pendekatan baru ini, pokok transmisi optimum dibina antara nod sensor melalui kaedah baru. stesen utama (bs) ialah akar, induk kelompok-kelompok (chs) dan nod penyiar ialah nod perantara, dan nod-nod lain (nod-nod ahli kelompok) ialah daun bagi pokok trasmisi. dcda mengimbangi beban chs antara-kelompok dan dalam-kelompok komunikasi data daripada kelompok berbeza saiz. bagi komunikasi berkesan dalam-kelompok, iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 73 sebahagian nod penyampai akan memindahkan data antara chs. penggunaan tenaga, jarak ke stesen utama dan induk kelompok metrik sentrik adalah tiga parameter pelaras bagi pemilihan induk kelompok. keputusan simulasi protokol yang dicadang menunjukkan pengurangan penggunaan tenaga pada nod-nod sensor individu dan memanjangkan jangka hayat rangkaian, berbanding kaedah-kaedah lain yang diketahui. keywords: wireless sensor networks; clustering; data aggregatio; multi-hop communication; optimal transmission tree 1. introduction a wireless sensor network consists of a number of sensor nodes deployed over a geographical area to monitor physical environmental conditions such as temperature, humidity, vibrations, seismic events, and so on. normally, a sensor node is a tiny device composed of three basic subsystems: a sensor to gather data from the physical surrounding environment, a local data processing unit and storage, and a wireless communication device for data transmission. a power source is also available to supply the energy for processing and sensing subsystems. this power source is often a limited energy budget battery. moreover, as the nodes may be deployed in a hostile or impractical environment, recharging the battery may not be possible or convenient. thus, the wireless sensor network should have enough lifetime to fulfill the application requirements [1-2]. there are two variations of wireless sensor network (wsn) deployment: structured and unstructured. while in structured wsn, the sensor nodes may be deployed in a preplanned manner, the deployment of all or some nodes in unstructured wsn is random. an unstructured wsn consists of a dense collection of sensor nodes. once deployed, the network is left unattended to perform monitoring and reporting functions. in an unstructured wsn, network maintenance, such as managing connectivity and detecting failures, is difficult since there are so many nodes developed in the network. the advantage of a structured network is that fewer nodes can be deployed with lower network maintenance and management cost. fewer nodes can be deployed if nodes are placed at specific locations to provide coverage whereas ad hoc deployment may leave regions uncovered [3]. wsns are also different from other networks in other aspects: they tend to be densely deployed, nodes are susceptible to failure, and rely on broadcast communications. network topology is dynamic, in which links are established between nodes and may break due to various reasons, such as deliberate changes to the transmission power of the nodes, node failure, or mobility. thereupon, maintaining a fully connected topology for such networks is a challenge that requires careful application of topology control [4]. with clustering algorithms, network performance could be enhanced, particularly for large scale of wsns. clustering algorithms are commonly used for such networks. using the clustering approach, the network is prolonged and the control overhead of routing is limited. network scalability is also increased, and the total network performance is advanced [5, 6]. in this paper, we propose an energy efficient clustering algorithm for data aggregation in wireless sensor networks in a fully distributed manner. it consists of two phases, cluster setup phase and data transmission phase. cluster setup phase has four stages. these are cluster head (ch) selection, relay node candidate specification, cluster formation, and routing tree construction stages. in cluster setup phase chs are selected based on multiple criteria, such as each node’s residual energy, its distance to the base station (bs) and node iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 74 centric metric. qualified nodes are selected as candidate relay nodes that could undertake transmission of data between clusters. in cluster formation stage, each usual node joins to the proper ch, considering the three assumptions related to the number of received chmessages and distance to the chs. a lot of energy is wasted in inter-cluster data communications, the key issue of our protocol scheme is that in the routing tree construction stage, we construct a routing tree with a wiser approach; chs form routing tree edges, bs at root and member nodes and leaves of this tree. for effective inter-cluster communications, in relay node selection, each ch selects an eligible relay node based on residual energy and distance to that ch, which directs ch data closer to the bs. according to the energy that will be consumed, each ch communicates with its parent cluster head or relay node and then finally, in the data transmission phase, data reaches the bs through a constructed routing tree. effective ch selection and routing tree construction leads to power savings in more sensor nodes. the remainder of this paper is organized as follows. section 2 provides a brief survey of some closely related works. section 3 describes the network and energy model in our algorithm. section 4 presents the clustering protocol in detail. section 5 analyzes several properties of the protocol. section 6 evaluates the performance of the algorithm and analyzes the results obtained from simulations. finally, section 7 gives the concluding remarks. 2. literature survey much research has been done to cope with the energy consumption constraint problem in wireless networks. clustering techniques have mostly been the focus, since data is aggregated and fused in each ch and energy would be conserved in every sensor node. this would lead to longer lifetime of the overall wireless sensor network. however, these algorithms face some problems. one of these limitations is that the energy metric is not directly considered while selecting chs. also, more relevant parameters, such as distance, density of nodes, and number of hops to reach the bs, are available that are not considered in the selection of the basic nodes. considering equal cluster sizes causes the early death of chs near the bs and those in the denser areas. besides, constructing an optimal routing tree based on an accurate method is a key to saving energy. therefore, defining a protocol to overcome these shortages is needed. some proposed algorithms are listed herein. low energy adaptive clustering hierarchy (leach) [7] is a well-known distributed clustering protocol in which most nodes transmit to cluster heads, and the cluster heads aggregate and compress the data and broadcast their decisions to the base station. the remaining nodes join the closest cluster head in terms of the communication energy cost. then the role of the cluster head is periodically rotated among the nodes to balance energy consumption, since cluster heads have the extra burden caused by a longrange transmission to a distant bs. nodes that have been cluster heads cannot become cluster heads again. thus, leach counteracts the non-uniform energy dispensation problem by rotating the ch role. however, in leach, node energy is drained quickly as in ch selection the energy parameter is not involved. a hybrid, energy-efficient, distributed clustering algorithm (heed) [8] is also an energy-efficient protocol designed for sensor networks. it introduces a variable known as the cluster radius which defines the transmission power used for intra-cluster broadcast. the initial probability for each node to become a cluster head depends on its residual energy and other parameters like adjustment degree and intra-cluster communication cost. heed relies on the assumption that cluster heads can communicate with each other and form a connected graph. in article [9], a cluster-based routing protocol for wireless sensor networks with a non-uniform node iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 75 distribution which includes an energy-aware clustering algorithm and a cluster-based routing algorithm, is proposed. a cluster-based routing protocol (eadc) constructs clusters of equal sizes using competition range to balance the energy consumption of the cluster nodes. the criteria used to select cluster heads are the residual energy of each sensor node and some relevant parameters. simultaneously, the routing algorithm increases forwarding tasks of the nodes in scarcely covered areas by forcing the cluster heads to choose the next hop with more remaining energy, less cluster members and not further away from the bs than the relay node. to balance the energy consumption among cluster heads a cluster-based inter-cluster routing algorithm that adjusts intra-cluster and inter-cluster energy consumption among sensor nodes is proposed. this protocol may prolong the network lifetime significantly. article [10] presents an energy constrained minimum dominating set based efficient clustering called (ecds) to model the problem of optimally choosing cluster heads with energy constraints. a randomized distributed algorithm for the constrained dominating set runs in few rounds with high probability. multiple extensions to the distributed algorithm for the energy constrained dominating set are also proposed. these extensions perform relatively well in terms of energy usage, node lifetime, and clustering time and, thus, are very suitable for wireless sensor networks. in article [11], the energy and coverage-aware distributed clustering protocol, which is an integrated protocol involving both energy and coverage in the clustering stage, is proposed. for different application coverage problems, corresponding coverage importance cost metrics are introduced. only nodes with higher energy and smaller coverage importance are reliable to be selected as cluster heads and routers. the idea behind this approach is that nodes deployed in sparse areas, or those that can cover fewer interest points alone, are less selected as routing nodes such that they can collect data for a longer period of time. in article [12], an energy efficient clustering algorithm for data aggregation is proposed. the cluster head is selected considering the node's residual energy as well as the distance between the node and its neighbors. furthermore, a type of data aggregation tree is constructed with the help of the clusters to reduce the amount of data transmission, which effectively extends the network's lifetime. in order to solve the problem of minimum energy, data aggregation enhanced converge cost operations in wireless sensor networks paper [13] presents two algorithms: one based on minimum spanning tree and the other on single source shortest path spanning tree. these algorithms are shown to be energy efficient for different extreme values of data growth factor. besides, the data latency was reduced by re-structuring the energy-efficient tree. the goal of the method proposed in article [14] is to lay the foundations to develop algorithms and techniques that simultaneously minimize the data gathering latency and balance the energy consumption among the nodes, thus maximizing the network lifetime. following an incremental-complexity approach, several mathematical programming problems focused on different network performance metrics are proposed. in article [15], an energy-efficient distributed clustering protocol for wireless sensor networks is introduced. the proposed gesc protocol is based on a localized metric for measuring the value of a node in covering the neighborhood when rebroadcasting. the protocol achieves small and linear communication and computation complexity, respectively. in article [16], a structure-free and energy-balanced data aggregation protocol, sfeb, is proposed. sfeb features both efficient data gathering and balanced energy consumption resulting from its two-phase aggregation process and the dynamic aggregator selection mechanism. in article [17], a cluster head weight selection method that takes service parameters for enhancing performance of the overall network has been discussed. in a clustering-based approach, one of the main concerns is the selection of appropriate cluster iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 76 heads in the network and the formation of balanced clusters. cluster heads are selected first in a weight metric based network; then a cluster formation is executed. this approach aims to conserve the energy of the sensors and balances load in the network. in paper [18], a distributed clustering and routing algorithm, jointly referred to as dfcr, is proposed. the dfcr uses a distributed runtime recovery of the sensor nodes due to sudden failure of the cluster heads. it takes care of the sensor nodes that have no ch within their communication range. the algorithm is shown to be energy efficient and fault tolerant. in paper [19], energy-efficient clustering and power management schemes for virtual mimo operation in a multi-hop wsn are suggested. schemes are integrated into a comprehensive protocol, which involves clustering the wsn into several clusters. this protocol achieves energy efficiency by properly selecting the master chs and slave chs, adapting the antenna elements and powers in the inter-cluster communications phase, and using a cross layer mimo-aware route selection algorithm for multi-hop operation. the conditions on the transmission powers of chs and non-chs that ensure the connectivity of the inter-cluster topology are established. paper [20] focuses on designing a predictionbased approach. it exploits both spatial and temporal correlations to form highly stable clusters of nodes sensing similar values. the sink node uses only the local prediction models of cluster heads to forecast all readings in the network without direct communication. in paper [21], clustering problem in lossy wsns with a mobile collector is studied, where a large number of links are unreliable and retransmission is required over such links to provide successful data delivery. these retransmissions cause energy wasting in intracluster communications. the objective is to construct clusters in the network such that packets from cluster members can be transmitted to cluster heads over reliable links, and the mobile collector can collect data from cluster heads directly. two distributed algorithms to construct one hop and k-hop clusters, are also introduced. 3. network and energy model in this section, we explain our assumed energy as well as network model. the network model comprises a bs and some sensor nodes that are distributed in a target area. we make a few assumptions as follows: 1. the network is shaped by n sensor nodes deployed in an m×m (m2) square field. 2. the base station is located outside the sensing field and it doesn’t have any energy constraint so that it can increase its power to send data all around the network. 3. nodes are deployed randomly and they are stationary after deployment. our method determines a fix inter-cluster and intra-cluster data transmission range, since this works well on static networks. 4. sensor nodes can be heterogeneous, which means that they can have different transmission power (which we set properly), but are equipped with an unchangeable battery. our goal is to save energy in unchangeable sensors. 5. the nodes are equipped with power control capabilities to change their transmission power. 6. all sensor nodes are location-unaware. therefore, no gps is needed. 7. each node has a unique id to identify one to others. the expended radio energy for transmitting 𝑙 -bit data 𝐸𝑡, is based on eqn. (1) [7]. (1) 𝐸𝑡 = 𝑙 × 𝐸𝑒𝑙𝑒𝑐 + 𝑙 × 𝑓𝑠 × 𝑑 2 𝑑 < 𝑑0 𝑙 × 𝐸𝑒𝑙𝑒𝑐 + 𝑙 × 𝑚𝑝𝑓 × 𝑑 4 𝑑 ≥ 𝑑0 iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 77 where 𝑑 is the transmission distance, 𝐸𝑒𝑙𝑒𝑐 is the energy being dissipated to operate the transmitter or receiver circuitry per bit, 𝑓𝑠 and 𝑚𝑝𝑓 are the amplifier energy factors for free space and multi-path fading channel models, respectively. d0 is the threshold distance that depends on the environment and the amplifier energy factors. in our work, we consider both the free space (𝑑2 power loss) and multi-path fading (𝑑4 power loss) channel models depending on the distance 𝑑 between the transmitter and receiver. the radio also expends energy to receive 𝑙-bit data given by eqn. (2). 𝐸𝑟 = 𝑙 × 𝐸𝑒𝑙𝑒𝑐 (2) because of short distance between sensors in a cluster (𝑑 < 𝑑0) free space model and long distance between chs and the bs multi-path fading model is intended. according to fig. 1, energy consumption for receiving data from cluster members, data aggregation, and transmission of aggregated data to the next cluster head is as eq. (3). 𝐸𝐶𝐻 = 𝑁 × 𝑙 × 𝐸𝑒𝑙𝑒𝑐 + (𝑁 + 1) × 𝑙 × 𝐸𝐷𝐴 + 𝑙 × (𝐸𝑒𝑙𝑒𝑐 + 𝑚𝑝𝑑𝑐 4) (3) where 𝑁 is the number of member nodes in a cluster, 𝐸𝐷𝐴 is data aggregation energy consumed by ch and 𝑑𝑐 is distance to the next ch. besides, energy consumption of chs for transmitting data to the intermediate relay nodes follows eq. (4). 𝐸𝐶𝐻 = 𝑁 × 𝑙 × 𝐸𝑒𝑙𝑒𝑐 + (𝑁 + 1) × 𝑙 × 𝐸𝐷𝐴 + 𝑙 × (𝐸𝑒𝑙𝑒𝑐 + 𝑓𝑠𝑑𝑟 2) (4) where 𝑁 is the number of non-ch nodes in cluster k, 𝐸𝐷𝐴 is the data aggregation energy and 𝑑𝑟 is distance to the next relay node. therefore, the energy consumption model of chs either follows eqn. (3), or follows eqn. (4), according to the method of determining the next hop node. fig. 1: inter-cluster communication path. 4. clustering protocol distributed clustering for data aggregation (dcda) contains two different stages. in first stage, to have an effective cluster head selection, chs would be selected based on domestic and local information. cluster member nodes choose a deserving cluster head for data aggregation objectives and relay nodes characterized concurrently. since the maximum amount of energy dissipation occurs in inter-network communications, thereupon with constructing an optimal spanning tree among sensor nodes, chs would preserve energy in inter-network and intra-network data communications. in the data transmission stage, each ch navigates its data directly or via other chs to the bs with member-node cluster-head data transmission way dx dc iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 78 multi-hop communications. according to the distance between chs, each data could traverse through a routing tree with the help of relay nodes. by this approach, energy conserves in sensor nodes and hence leads to a longer lifetime of the sensor network. descriptions of control messages, which are used in the proposed scheme, are illustrated in table 1. table 1: description of control messages message description init-msg tuple(token) intro-msg tuple(node-id,node-energy,node-distobs) ch-msg tuple(node-id,node-energy,node-distobs,node-ndeg) routing-msg tuple(node-id,node-energy,node-distobs,nodendeg,node-hopcount) relay-msg tuple(node-id,node-energy,node-distoch) join-msg tuple(node-id, ch-id) schedule-msg tuple(scheduleorder) 4.1 the protocol details in the cluster setup phase of dcda, chs and relay nodes are specified and the routing tree is constructed among sensor nodes. in the data transmission phase, each member node sends its data to the corresponding ch. afterward, each ch sends data directly or via an intermediate relay node to the bs. to increase the network lifetime and reduce the overhead of the algorithm, the data transfer phase is much longer than the cluster setup phase. in each round, the cluster heads are changed and a new path is created. 4.1.1 min-max normalization min-max scaling or normalization means that one function linearly transforms real data values such that the minimum and the maximum of the transformed data take certain values frequently by 0 and 1. this depends on the context. for example the eqn. (5) maps a value 𝑑 of 𝑆 to 𝑑′ in the range [𝑛𝑒𝑤_𝑚𝑖𝑛𝑆, 𝑛𝑒𝑤_𝑚𝑎𝑥𝑆].[22]: 𝑑′ = [𝑑−𝑚𝑖𝑛𝑆] [𝑚𝑎𝑥𝑆−𝑚𝑖𝑛𝑆] × [𝑛𝑒𝑤_𝑚𝑎𝑥𝑆 − 𝑛𝑒𝑤_𝑚𝑖𝑛𝑆] + 𝑛𝑒𝑤_𝑚𝑖𝑛𝑆 (5) where 𝑚𝑖𝑛𝑆 is the minimum value of the attributes and 𝑚𝑎𝑥𝑆 is the maximum value of the attributes. for normalization purposes, we want to map a value 𝑑 of 𝑆 to 𝑑′ in the range [0,1], therefore we consider the value of 𝑛𝑒𝑤_𝑚𝑎𝑥𝑆 equal to one (𝑛𝑒𝑤_𝑚𝑎𝑥𝑆 = 1) and the value of 𝑛𝑒𝑤_𝑚𝑖𝑛𝑆 equal to zero (𝑛𝑒𝑤_𝑚𝑖𝑛𝑆 = 0) in the above eqn. (5). so the formula is converted to the simple min-max normalization as eqn. (6). 𝑑′ = [𝑑−𝑚𝑖𝑛𝑆] [𝑚𝑎𝑥𝑆−𝑚𝑖𝑛𝑆] (6) later on, to evaluate our results in an identical condition and eliminating the effects of different units, the data is scaled to a fixed range (0 – 1). so min-max normalization based on eqn. (6) is used in all equations. 4.1.2 cluster setup phase a) ch selection stage iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 79 at the beginning, bs broadcasts an init-msg message. all nodes set their state as usual node. each node that receives a message from bs and its residual energy is higher than threshold value (𝐸𝑟𝑖 > 𝐸𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑), takes part in the ch selection competition. chs candidate compute distance to the bs based on received signal power strength and broadcast intro-msg in rc based on eqn. (7). competition radius (rc) is a fraction of the transmission range (rr). this equation shows how rc is determined for each sensor node. the intro-msg contains information that is required for a ch selection procedure, such as residual energy and distance to the bs. 𝑅𝑐 = 1/2 × (𝑎 × 𝑑𝑡𝑜𝐵𝑆𝑖 + 𝑏 × 𝐸𝑟𝑖 ) × 𝑅𝑟 (7) where 𝑑𝑡𝑜𝐵𝑆 is each node’s distance (euclidean distance) to the bs and 𝐸𝑟 is the residual energy of that node. 𝑎 and 𝑏 are real values uniformly distributed in [0,1] such that their summation is equal to one. chs near the bs have to collect and aggregate data from member nodes. besides, they are located in the path of the entire network traffic directed to the bs. for load balancing between inter-cluster and intra-cluster communications, clusters closer to the bs should have a shorter radius. moreover, when energy decreases, cluster radius has to be decreased and a smaller number of member nodes would be covered. each ch candidate that receives an intro-msg from others, computes the average energy of neighbor nodes as in eqn. (9), a node-centric metric with eqn. (10) and 𝑓𝑢𝑛𝐶𝐻𝑖 value with eqn. (8) and compares these values. if this new node has a maximum value, then it becomes a ch and promulgates a ch-msg message in rc. 𝑓𝑢𝑛𝐶𝐻𝑖 = 𝑎 × 𝐸𝑟𝑖 𝐸𝑟𝑎𝑣 + 𝑏 × 1 𝑑𝑡𝑜𝐵𝑆𝑖 + 𝑐 × 1 𝑐𝑒𝑛𝑡𝑖 (8) 𝐸𝑟𝑎𝑣 = 1 𝑚 × ∑ 𝐸𝑛𝑒𝑖 (9) 𝑐𝑒𝑛𝑡𝑖 = 1 𝑚 × ∑ 𝑑𝑡𝑜𝑠𝑖 (10) where 𝐸𝑟𝑖 denotes the residual energy of node 𝑆𝑖, and 𝐸𝑛𝑒𝑖 is the residual energy of neighbor node. 𝑑𝑡𝑜𝐵𝑆𝑖 is used to measure node’s distance to the bs. 𝑚 is the number of adjacent nodes. 𝑑𝑡𝑜𝑠𝑖 is each adjacent node’s distance to nearby node. 𝑎, 𝑏 and 𝑐 are real values uniformly distributed in [0,1] such that their sum is equal to one. a node with more energy, less distance to the bs, and fewer member nodes’ average distance to the ch would be a better choice to undertake the ch task. by selecting chs closer to the cluster members, less intra-cluster transmission energy would be consumed. in the proposed scheme, just chs take the responsibility of data aggregation in the network. b) relay node candidate each node that receives a ch-msg from at least two ch and its residual energy is more than the threshold value (𝐸𝑟𝑖 > 𝐸𝑟𝑡ℎ) changes its state to relay node candidate and determines its distance to each ch based on received signal strength. after distance estimation, relay node candidates compute 𝑑 with eqn. (11) and send this value to chs in relay-msg message. 𝑑 = 𝑑𝑥 + 𝑑𝑦 (11) where 𝑑𝑥 and 𝑑𝑦 are the distance of the relay node candidate to each of two chs used in relay node selection decision. iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 80 chs that received a relay-msg in routing tree construction stage decide whether to send data directly or via relay nodes to the upper ch to finally reach the bs. 𝑑𝑥 and 𝑑𝑦 are illustrated in fig. 2. the pseudo-code segment 1 gives the details of the ch selection stage. fig. 2: three inter-cluster communication paths. begin (ch selection algorithm) if 𝐸𝑟𝑖 > 𝐸𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑 then 𝑠𝑡𝑎𝑡𝑒 ← 𝑐𝑎𝑛𝑑𝑖𝑑𝑎𝑡𝑒 𝐶𝐻 calculate rc and broadcast intro-msg in rc end if 𝑠𝑡𝑎𝑡𝑒 = 𝑐𝑎𝑛𝑑𝑖𝑑𝑎𝑡𝑒 𝐶𝐻 then calculate 𝑓𝑢𝑛𝐶𝐻 and compare with neighbors if 𝑀𝑎𝑥 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑓𝑢𝑛𝐶𝐻 𝑛𝑒𝑖𝑔ℎ < 𝑓𝑢𝑛𝐶𝐻 𝑖 do 𝑠𝑡𝑎𝑡𝑒 ← 𝐶𝐻 broadcast ch-msg in rc end end if receive ch-msg from at least two chs && 𝐸𝑟𝑖 > 𝐸𝑟𝑡ℎthen 𝑠𝑡𝑎𝑡𝑒 ← 𝑐𝑎𝑛𝑑𝑖𝑑𝑎𝑡𝑒 𝑟𝑒𝑙𝑎𝑦 𝑛𝑜𝑑𝑒 calculate 𝑑 and send relay-msg to chs end end the pseudo-code segment 1 c) cluster formation stage according to ch-msg information each member node has to choose a proper ch from the eligible ch set to join it. to do this, some assumptions are considered as follow. 1. if a member node receives a ch-msg from just one ch, it joins that cluster by broadcasting a join-msg and sets its next hop to be that specific ch. 2. if a member node receives ch-msg from two or more chs with equal distance, it joins the ch with more residual energy and less distance to the bs in a low density area. eqn. (12) indicates the level of competence for each ch. 𝑓𝑢𝑛𝐽𝑖 = 𝑎 × 𝐸𝑟𝐶𝐻𝑖 + 𝑏 × 1/ 𝐶𝐻𝑑𝑡𝑜𝐵𝑆𝑖 + 𝑐 × 1/ 𝑑𝑒𝑛𝑖 (12) relay-node-candidate candidatecluster-head data transmission path dx dy ds iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 81 where 𝐸𝑟𝐶𝐻𝑖 is the residual energy of ch, 𝐶𝐻𝑑𝑡𝑜𝐵𝑆𝑖 is distance of ch to the bs and 𝑑𝑒𝑛𝑖 is density of cluster or number of ch’s neighbors. 𝑎, 𝑏 and 𝑐 are real values uniformly distributed in [0,1] such that their summation is equal to one. 3. if a member node receives a ch-msg from chs with different distances, it computes 𝑓𝑢𝑛𝐽𝑁𝑖 with eqn. (13) and joins a cluster with higher 𝑓𝑢𝑛𝐽𝑁𝑖 value. this means a ch with less distance from a nearby member node and closer to the bs is more qualified to become a next hop node. also, residual energy and proximity degree are other ch selection criteria. 𝑓𝑢𝑛𝐽𝑁𝑖 = 𝑎 × 𝐸𝑟𝐶𝐻𝑖 + 𝑏 × 1 𝐶𝐻𝑑𝑡𝑜𝐵𝑆𝑖 + 𝑐 × 1 𝑑𝑡𝑜𝐶𝐻𝑖 + 𝑑 × 1 𝑑𝑒𝑛𝑖 (13) where 𝐸𝑟𝐶𝐻𝑖 is the residual energy of the ch, 𝐶𝐻𝑑𝑡𝑜𝐵𝑆𝑖 is a distance of ch to the bs, 𝑑𝑡𝑜𝐶𝐻𝑖 is distance of member node to the ch and 𝑑𝑒𝑛𝑖 is the density of the cluster. 𝑎, 𝑏, 𝑐 and 𝑑 are real values uniformly distributed in [0,1] such that their sum is equal to one. the pseudo-code segment 2 gives the details of this stage. begin (cluster formation algorithm) if 𝑠𝑡𝑎𝑡𝑒! = 𝐶𝐻 && has not sent join-msg then if receive ch-msg from one ch 𝑛𝑒𝑥𝑡 ℎ𝑜𝑝 ← 𝑠𝑒𝑙𝑒𝑐𝑡𝑒𝑑 𝐶𝐻 send join-msg to selected ch end if receive ch-msg from at least two chs if chs have equal distances calculate 𝑓𝑢𝑛𝐽𝑖 and find the maximum 𝑛𝑒𝑥𝑡 ℎ𝑜𝑝 ← 𝐶𝐻 𝑤𝑖𝑡ℎ 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑓𝑢𝑛𝐽 send join-msg to selected ch end if chs have unequal distances calculate 𝑓𝑢𝑛𝐽𝑁𝑖 and find the maximum 𝑛𝑒𝑥𝑡 ℎ𝑜𝑝 ← 𝐶𝐻 𝑤𝑖𝑡ℎ 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑓𝑢𝑛𝐽𝑁𝑖 send join-msg to selected ch end end end end the pseudo-code segment 2 d) routing tree construction stage in transmission of data through the routing tree in the network, because of the long distance between chs, the maximum amount of energy is wasted in inter-cluster data communications. upper level nodes near the bs whose distance to the bs is less than rr ( 𝐶𝐻𝑑𝑡𝑜𝐵𝑆𝑖 < 𝑅𝑟) and hence, could communicate with the bs without any interface, set their next hop to be the bs and others have to specify proper relay nodes. finally, the routing tree is constructed among sensor nodes. e) routing details at the beginning, upper level nodes broadcast a routing-msg in rr and set a hop-count parameter equal to 1. single hop nodes receive this message and perform a routing tree construction procedure. each ch that receives messages selects its next ch candidate based on eq. (14) and increases hop-count value by one (ℎ𝑜𝑝𝑐𝑜𝑢𝑛𝑡 = ℎ𝑜𝑝𝑐𝑜𝑢𝑛𝑡 + 1), iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 82 then broadcasts a routing-msg for lower level chs and 𝑓𝑢𝑛𝑁𝐶𝐻 is computed in the same way. this will be continued until all chs in the network have been reached. 𝑓𝑢𝑛𝑁𝐶𝐻𝑖 = 𝑎 × 𝐸𝑟𝐶𝐻𝑖 + 𝑏 × 1 𝐶𝐻𝑑𝑡𝑜𝐵𝑆𝑖 + 𝑐 × 1 ℎ𝑜𝑝𝑐𝑜𝑢𝑛𝑡𝑖 + 𝑑 × 1 𝑑𝑒𝑛𝑖 (14) where 𝐸𝑟𝐶𝐻𝑖 is the residual energy of ch, 𝐶𝐻𝑑𝑡𝑜𝐵𝑆𝑖 is a distance of ch to the bs, ℎ𝑜𝑝𝑐𝑜𝑢𝑛𝑡 is the number of hops to the bs and 𝑑𝑒𝑛𝑖 is density of the cluster. 𝑎, 𝑏, 𝑐 and 𝑑 are real values uniformly distributed in [0,1] such that their sum is equal to one. according to 𝑓𝑢𝑛𝑁𝐶𝐻, each ch selects next ch candidate, which has higher residual energy, less distance to the bs and lower number of nodes in the path to the bs (less data transmission) in a low density area. fig. 3 shows some hypothetical inter-cluster paths. fig. 3: some assumptive paths between chs. f) relay node selection after determining the next chs candidate, each ch decides to choose a relay node as intermediate or next ch candidate to be the final next hop node. for next hop selection, chs use eq. (15). at first, each ch specifies the most appropriate node as a relay and then compares energy expended for transmitting 𝑙-bit data to the next hop. 𝑓𝑢𝑛𝑅𝑖 = 𝑎 × 𝐸𝑟𝑟 𝐸𝑚𝑎𝑥 + 𝑏 × 1 𝑑 (15) where 𝐸𝑟𝑟 is the residual energy of relay node candidate and 𝐸𝑚𝑎𝑥 is the maximum initial energy of nodes in the network. also 𝑑 is defined in eq. (11) which is the summation of distances to the chs. so a node with more residual energy with less 𝑑 value is more competent for undertaking the relay node task. after the relay nodes competition, chs specify the next hop by comparing the result of 𝐸𝑐𝑜𝑟 and 𝐸𝑐𝑜𝐶𝐻 values defined in eqn. (16) and eqn. (17), respectively. 𝐸𝑐𝑜𝑟 = 𝑙 × (𝐸𝑒𝑙𝑒𝑐 + 𝑓𝑠𝑑𝑥 2) + 𝑙 × 𝐸𝑒𝑙𝑒𝑐 + 𝑙 × (𝐸𝑒𝑙𝑒𝑐 + 𝑓𝑠𝑑𝑦 2 ) + 𝑙 × 𝐸𝑒𝑙𝑒𝑐 (16) = 4 × 𝑙 × 𝐸𝑒𝑙𝑒𝑐 + 𝑙 × 𝑓𝑠 × (𝑑𝑥 2 + 𝑑𝑦 2 ) 𝐸𝑐𝑜𝐶𝐻 = 𝑙 × (𝐸𝑒𝑙𝑒𝑐 + 𝑚𝑝𝑑𝑠 4) + 𝑙 × 𝐸𝑒𝑙𝑒𝑐 (17) inter-cluster radio radius cluster-head member-node data transmission path rr iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 83 = 2 × 𝑙 × 𝐸𝑒𝑙𝑒𝑐 + 𝑙 × 𝑚𝑝 × 𝑑𝑠 4 in fig. 2, 𝑑𝑥, 𝑑𝑦 and 𝑑𝑠 are illustrated. after data transmission, according to results obtained from eqn. (16) and eqn. (17), the one leading to lower energy consumption would be selected as a next hop. the pseudo-code segment 3 gives the details of this stage. 4.1.3 data transmission phase a) intra-cluster communication to avoid collision in inter-network transmissions, adjacent clusters use different transmission channels. each ch based on join-msg messages received from member nodes determines a corresponding transmission time slot with the tdma aid and declares it with schedule-msg to all cluster members. hence, each member node transfers its data to the ch during the determined time slot. this method allows sensor nodes to sleep during other time slots and save more energy. b) inter-cluster communication chs aggregate received data from cluster members and then forward it to the bs along the constructed routing tree. in addition, they may undertake a forwarding task of other chs data and conduct them through the path to the bs. this leads to reduction of data packets. as a result, network lifetime increases and more energy is saved in each sensor node. fig. 4 illustrates one data transmission route among elected chs and relay nodes through the routing tree. fig. 4: a data transmission path through a routing tree. 4.1.4 protocol analysis theorem 1: there is at most one cluster head in every cluster radius rc. proof: as previously mentioned with eqn. (8), each ch candidate’s result value is compared to the value calculated for its neighbors. if there is any adjacent node with more value in the cluster radio radius (rc) it would desist the competition and set its state to be a cluster member node. otherwise, it broadcasts the ch-msg within cluster radius (rc). as soon as each node receives ch-msg from neighbors, it gives up the competition and changes its state to a member node. so in every cluster radius, just an exclusive node with relay node cluster head inter-cluster transmission path cluster radius base station rc iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 84 maximum value will undertake a ch task and other nodes would join clusters as member nodes. therefore, there is no more than one cluster head within each cluster radius rc. theorem 2: the cluster head set generated by dcda can cover all nodes. proof: in dcda each node would be a ch, a cluster member node or a relay. according to ch selection function a node with the most competent would be specified as a ch and broadcast ch-msg in cluster radius. each node that receives this message becomes a member node and would be covered with a ch. relay nodes are those that receive a ch-msg from at least two chs so they would belong to a cluster. any node that has not received the ch-msg, forms a cluster alone and becomes a single ch. thus, the ch set generated by dcda can cover all nodes in the network and avoid the generation of isolated points [23]. theorem 3: the overhead complexity of control messages in the network is o(n). proof: at the beginning of each round, all nodes broadcast intro-msg. thus, at most, n intro-msg messages are exchanged in the whole network. in each round, each ch broadcasts a ch-msg, routing-msg, and a schedule-msg. besides, any relay node candidate would broadcast a relay-msg in the network. each member node joins a ch with a join-msg announcement. for example, if the number of clusters is 𝑐, the total number of join-msg is equal to 𝑁 − 𝑐, the maximum number of relay-msg is equal to 𝑁 − 𝑐 and the number of each other message is 𝑐. thus, the maximum number of control messages exchanged in the whole network follows eqn. (18) and the minimum eqn. (19). 𝑁 + (𝑁 − 𝑐) + (𝑁 − 𝑐) + 𝑐 + 𝑐 + 𝑐 = 3𝑁 + 𝑐 (18) 𝑁 + (𝑁 − 𝑐) + 𝑐 + 𝑐 + 𝑐 = 2𝑁 + 2𝑐 (19) therefore, the overhead complexity of control messages in the network is o(n). theorem 4: dcda can setup the clustering topology in o(1) time. proof: dcda performs a distributed clustering strategy. thus, the time complexity of the entire network is equal to that of a single node o(1). therefore, the time complexity is constant and not related to the network size. 5. simulations in this section, we analyze the performance of a dcda algorithm via simulations using ns2.we assume that the bs is fixed and out of the monitoring region. 100 nodes are randomly disseminated in a (200×200) m2 network field with uniform distribution. the simulation parameters are summarized in table 2. we performed 100 simulations independently and the statistics are averaged over these 100 runs. fig. 5 shows the network topology of the scenarios. we compare our algorithm with heed (a hybrid energy-efficient distributed clustering algorithm) and leach (low energy adaptive clustering hierarchy), two known clustering algorithms. these are two main protocols proposed for clustering techniques in wsns they perform clustering in a distributed manner in which each node independently selects its state as we proposed. however, our algorithm overcame the shortage of these methods. it considers much more relevant parameters and different aspects when developing a routing tree to enhance energy efficiency in data transmission. iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 85 fig. 5: network topology. as previously mentioned, leach [7] forms clusters using a distributed algorithm. it contains several rounds and each round is divided into two phases that are the establishment of cluster and data communication. in the setup stage, chs are specified randomly and clusters are formed. in steady state phase, cluster members transmit sensed data to ch. after data aggregation each ch sends data directly to bs. due to data fusion and communication with bs, cluster heads consume more energy. besides, heed [8] is also a distributed clustering protocol for ad-hoc sensors, and it uses a hybrid criterion for cluster head selection that considers the residual energy of the node and a secondary parameter, such as the node’s proximity to its neighbors or the node’s neighbor degree. nodes join clusters such that communication cost is minimized. it assumes quasistationary networks where nodes are location-unaware and have equal significance. it exploits the availability of multiple transmission power levels at sensor nodes. table 2:parameters of simulations parameter value number of nodes 100 sensor field 200 m × 200 m bs location (250,100) data packet size 500 bytes eelec 50 𝑛𝐽/𝑏𝑖𝑡 𝑓𝑠 10 𝑝𝐽/(𝑏𝑖𝑡 𝑚2) 𝑚𝑝 0.0013 pj/(bit m4) initial energy of nodes 1–4 j esen 0.2 j/bit ecom 5 nj/(bit signal) 5.1 cluster head distribution to evaluate our algorithm in different cases, first we set 𝑅𝑟 = 160. additionally, we consider equal weight for each part used in the equations. for example, in eqn. (7) 𝑎 = 𝑏 = 0.5. fig. 6 shows the number of cluster heads in 30 randomly selected rounds for leach, heed and dcda. the number of chs varies wildly in leach since in leach, cluster heads are determined by a probability with random number generation. 0 20 40 60 80 100 120 140 160 180 200 0 20 40 60 80 100 120 140 160 180 200 iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 86 therefore, the number of cluster heads in leach varies and is not controlled. in heed and dcda, their competition radius ensures that there is only one cluster head within any cluster radius and good distribution of chs over the network is ensured in most rounds. compared with heed and leach, dcda can obtain a better distribution of chs in the network because it considers residual energy, distance to the bs, and each member node distance to the ch when selecting chs. furthermore, the mentioned parameter density and hop-count are also utilized when constructing the inter-cluster routing tree. fig. 6: distribution of the number of cluster heads in three protocols. 5.2 energy consumption fig. 7 illustrates the energy consumption of nodes in leach, heed and dcda. it shows that in leach nodes, the residual energy decreases at a higher rate because, in leach, a node with very low energy may be selected as a ch in several rounds which may drain its energy more quickly. in addition, chs would be selected randomly with a certain probability in a cyclic way through which the energy load of the entire network may not be distributed efficiently among nodes. each ch sends data directly to the bs so it may lead to earlier death of the chs far from the bs. in heed due to considering a hybrid of the node’s residual energy and a secondary parameter, such as node proximity to its neighbors or node degree, more energy is saved in each sensor node. however, heed doesn’t take into account network structure, which causes an imbalance in energy consumption among the clusters. dcda could greatly prolong the network lifetime and reduce energy consumption of nodes within the clusters by considering proximity to the chs when the chs are selected. moreover, as the great amount of energy is consumed in inter-cluster communication, an energy efficient routing tree is established using effective parameters like energy, adjacent degree, distance to the bs and number of hops to the bs. one more solution considered for energy dispensation among sensor nodes is to determine a set of eligible relay nodes that forward ch data to the chs closer to the bs. 0 5 10 15 20 25 1 2 3 4 5 6 7 8 9 ro u n d s number of clusted heads leach heed dcda iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 87 fig. 7: residual energy of nodes in different rounds. 5.3 network lifetime according to the definitions given in [24], network lifetime could be defined in different metrics, the time from the deployment of the network to the death of the first node (fnd), the time when a certain percent of nodes remain alive (pna), and the time when all the nodes are dead in the network (lnd). here we define the network lifetime as the time from the deployment of the network to the death of its first node (first node dies, fnd). we ran leach, heed and the proposed method several times. the main aim of dcda is to prolong network lifetime with effective ch selection and an optimal routing tree construction among sensor nodes. thus, residual energy, distance to the bs, and ch centric metrics are used to choose a set of qualified chs. next hop nodes through the routing tree are selected with regard to various peripheral and internal features of each node. as shown in fig. 8, dcda improves the lifetime of nodes compared with other algorithms. the improvements are approximately 61% and 18% compared to leach and heed, respectively. fig. 9 illustrates the number of alive nodes in some rounds, which is a downward trend. heed improves leach as it uses a variable known as the cluster radius that defines the transmission power to be used for intra-cluster broadcast. also, in the ch selection stage, tentative chs would be determined with regard to the residual energy and final cluster heads are selected according to the intra-cluster communication cost. in heed, clusters do not overlap with each other, so the number of alive nodes is greater in higher rounds. dcda could effectively balance the energy consumption among cluster heads, since relay nodes aid chs in data transmission between clusters and hence balance energy consumption among sensors in the routing tree construction stage. dcda forms clusters of different sizes to balance energy consumption among chs. since nodes closer to the bs take more responsibility for the forwarding task from all around the network to the bs, the cluster size should be decreased compared with those far from the bs. it could help to balance load among chs in intra-cluster and inter-cluster data communications. so 0 50 100 150 200 250 300 350 0 40 80 120 160 200 240 280 320 360 400 440 480 520 re si d u a l e n e rg y (j ) rounds dcda heed leach iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 88 compared to heed, dcda saves more energy in sensor nodes and hence the number of alive nodes is greater in higher rounds. fig. 8: network lifetime. fig. 9: number of alive nodes in each round for three protocols. 6. conclusion remarks in this paper we proposed a distributed energy efficient clustering algorithm for data aggregation in wireless sensor networks (dcda). the main objective is to save energy and balance load among sensor nodes. cdca consists of two stages: clustering and data transmission. in the clustering stage, we form clusters with unequal sizes in a way that chs closer to the bs have a smaller cluster range. this could prevent premature death of chs close to the bs, due to forwarding a large amount of data from all around the network. eligible chs are specified based on some effective parameters, such as distance to the bs, remaining energy of sensors and nodes centric metric. besides, some relay 0 50 100 150 200 250 300 350 400 450 500 n e tw o rk l if e ti m e ( f n d ) ( ro u n d ) leach heed dcda 0 20 40 60 80 100 120 100 130 160 190 220 250 280 310 340 370 400 430 460 490 520 550 580 610 640 n u m b e r o f a li v e n o d e s rounds leach heed dcda iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 89 nodes are selected to transfer data between clusters when direct connection between chs is more costly. common nodes are associated with high energy chs, in a low density area and less total distance to the bs. in next hop and relay nodes selection, dcda utilizes more criteria such as number of hops to the bs and total cost for transmitting data to the next ch. finally, in the data transmission stage, data is transmitted through an optimal routing tree where the bs is located at the root, a ch at each edge, and cluster member nodes in leaves. the simulation results show the proposed dcda algorithm provides more energy efficiency and hence longer network lifetime when compared to the other discussed algorithms. references [1] akyildiz if, su w, sankarasubramaniam y, cayirci e. (2002) wireless sensor networks: a survey. computer networks, 38:393-422. [2] anastasi g, conti m, di francesco m, passarella a. (2009) energy conservation in wireless sensor networks: a survey. ad hoc networks, 7:537-568. [3] yick j, mukherjee b, ghosal d. (2008) wireless sensor network survey. computer networks, 52:2292-2330. [4] aziz aa, sekercioglu y. a, fitzpatrick p, ivanovich m. (2013) a survey on distributed topology control techniques for extending the lifetime of battery powered wireless sensor networks. ieee communications surveys & tutorials, 15:121-144. [5] zhou w. (2011) energy efficient clustering algorithm based on neighbors for wireless sensor networks. journal of shanghai university (english edition), 15:150-153. [6] liu y, xiong n, zhao y, vasilakos a. v, gao j, jia y. (2010) multi-layer clustering routing algorithm for wireless vehicular sensor networks. iet communications, 4:810-816. [7] heinzelman w. r, chandrakasan a, balakrishnan h, (2000) energy-efficient communication protocol for wireless microsensor networks. proceedings of the 33rd annual hawaii international conference on system sciences. [8] younis o, fahmy s. (2004) heed: a hybrid, energy-efficient, distributed clustering approach for ad hoc sensor networks. ieee transactions on mobile computing, 3:366-379. [9] yu j, qi y, wang g, gu x. (2012) a cluster-based routing protocol for wireless sensor networks with nonuniform node distribution. aeu-international journal of electronics and communications, 66:54-61. [10] albath j, thakur m, madria s. (2013) energy constraint clustering algorithms for wireless sensor networks. ad hoc networks, 11:2512-2525. [11] gu x, yu j, yu d, wang g, lv y. (2014) ecdc: an energy and coverage-aware distributed clustering protocol for wireless sensor networks. computers & electrical engineering, 40:384-398. [12] sha c, wang r, huang h, sun l. (2010) energy efficient clustering algorithm for data aggregation in wireless sensor networks. the journal of china universities of posts and telecommunications, 17:104-122. [13] upadhyayula s, gupta s. k. (2007) spanning tree based algorithms for low latency and energy efficient data aggregation enhanced convergecast (dac) in wireless sensor networks. ad hoc networks, 5:626-648. [14] monaco u, cuomo f, melodia t, ricciato f, borghini m. (2006) understanding optimal data gathering in the energy and latency domains of a wireless sensor network. computer networks, 50:3564-3584. [15] dimokas n, katsaros d, manolopoulos y. (2010) energy-efficient distributed clustering in wireless sensor networks. journal of parallel and distributed computing, 70:371-383. [16] chao c. m, hsiao t. y. (2009) design of structure-free and energy-balanced data aggregation in wireless sensor networks. 11th ieee international conference on high performance computing and communications hpcc'09. [17] mahajan s, malhotra j, sharma s. (2014) an energy balanced qos based cluster head selection strategy for wsn. egyptian informatics journal, 15:189-199. iium engineering journal, vol. 19, no. 1, 2018 musavi et al. 90 [18] azharuddin m, kuila p, jana p. k. (2015) energy efficient fault tolerant clustering and routing algorithms for wireless sensor networks. computers & electrical engineering, 41:177-190. [19] krunz m, siam m. z, nguyen d. n. (2013) clustering and power management for virtual mimo communications in wireless sensor networks. ad hoc networks, 11:1571-1587. [20] ashouri m, yousefi h, basiri j, hemmatyar a. m. a, movaghar a. (2015) pdc: predictionbased data-aware clustering in wireless sensor networks. journal of parallel and distributed computing, 81:24-35. [21] gong d, yang y, pan z. (2013) energy-efficient clustering in lossy wireless sensor networks. journal of parallel and distributed computing, 73:1323-1336. [22] jain y. k, bhandare s. k. (2011) min max normalization based data perturbation method for privacy protection. international journal of computer and communication technology, 2:45-50. [23] xinlian z, min w, jianbo x. (2009) bpec: an energy-aware distributed clustering algorithm in wsns. j. comput. res. dev, 46:723-730. [24] katiyar v, chand n, soni s. (2010) clustering algorithms for heterogeneous wireless sensor network: a survey. international journal of applied engineering research dindigul, 1:273274. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 influence of ipns (vinylester / epoxy / polyurethane) on the mechanical properties of glass / carbon hybrid composites karjala santhosh priya1, kuttynadar rajammal vijaya kumar1, *gopi suresh2, rajesh ravi3, chockalingam devanathan4, chinathambi muthukaruppan meenakshi5 1 department of mechanical engineering, dr. m.g.r. educational and research institute, chennai, india. 2 department of mechanical engineering, rajalakshmi institute of technology, chennai, india. 3 school of aerospace and automotive engineering, universite international de-rabat (uir), rabat – 11100, morocco. 4 department of mechanical engineering, rajalakshmi engineering college, thandalam, india. 5 department of mechanical engineering, bharath institute of higher education and research, chennai, india. *corresponding author: saisuresh1979@gmail.com (received: 14th march 2021; accepted: 2nd may 2021; published on-line: 4thjanuary 2022) abstract: the main objective of this study is to compare the interpenetrating polymer networks’ (ipns) physical strengths with different variants of fibers. in this study, e-glass, carbon, and a combination of e-glass and carbon fiber (hybrid) have been taken as the reinforcement. similarly, three combinations of the ipns were chosen as the matrix material, namely epoxy / polyurethane (ep), vinyl ester / polyurethane (vp) and epoxy/vinyl ester (ev) as ipn blends. in order to thoroughly understand the physical characteristics of the combination of blends and fibers, nine variants (laminates) were fabricated: combinations of epoxy / polyurethane / e-glass (epg), epoxy / polyurethane / carbon (epc), epoxy / vinyl ester / glass / carbon (epgc-hybrid), vinyl ester / polyurethane / glass (vpg), vinyl ester / polyurethane / carbon (vpc), vinyl ester / polyurethane / glass / carbon (vpgc), epoxy / vinyl ester / glass (evg), epoxy / vinyl ester / carbon (evc), and epoxy / vinyl ester / glass / carbon (evgc-hybrid), all with help of a hand-layup technique. furthermore, mechanical tests such as tensile, flexural, impact, and hdt (heat distortion temperature) were performed on all the variants as per the astm standards. results shows that carbon fiber reinforcement with all ipn combinations has shown extraordinary performance (double fold) over the e-glass fiber reinforcement, whereas the hybrid (combination of e-glass/carbon) laminates have shown excellent characteristics over e-glass fiber reinforcement, irrespective of ipn matrix material. all the results were compared with each other and their corresponding variations were plotted as bar charts. abstrak: objektif utama kajian ini adalah bagi membandingkan kekuatan fizikal rangkaian polimer saling menusuk (ipn) dengan pelbagai jenis gentian berbeza. kajian ini mengguna pakai gentian kaca-e, karbon dan gabungan kaca-e dan gentian karbon (hibrid) sebagai penguat. begitu juga, tiga kombinasi ipn dipilih sebagai bahan matrik, iaitu epoksi / poliuretan (ep), ester vinil / poliuretan (vp) dan epoksi / ester vinil (ev) sebagai campuran ipn. bagi tujuan memahami secara mendalam ciri-ciri fizikal gabungan campuran dan gentian, sembilan varian (lamina) dihasilkan, malaui kombinasi seperti epoksi / poliuretan / kaca-e (epg), epoksi / poliuretan / karbon (epc), epoksi / ester vinil 339 iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 / kaca / karbon (epgc-hibrid), ester vinil / poliuretan / kaca (vpg), ester vinil / poliuretan / karbon (vpc), ester vinil / poliuretan / kaca / karbon (vpgc), epoksi / ester vinil / kaca (evg), epoksi / ester vinil / karbon (evc), epoksi / ester vinil / kaca / karbon (evgchibrid) dengan teknik susun atur lapisan menggunakan tangan. selain itu, ujian mekanikal seperti tegangan, lenturan, hentaman dan hdt (suhu kelenturan panas) dilakukan pada semua varian mengikut piawaian astm. dapatan kajian menunjukkan bahawa, penguat gentian karbon dengan semua kombinasi ipn telah menunjukkan prestasi luar biasa (dua kali ganda) daripada penguat gentian kaca-e, manakala lamina hibrid (campuran kaca-e / karbon) telah menunjukkan ciri-ciri sangat baik berbanding penguat gentian kaca-e tanpa mengira bahan matrik ipn. semua hasil dapatan dibandingkan antara satu sama lain dan padanan variasi diplot sebagai carta bar. keywords: interpenetrating polymer networks; epoxy; vinyl ester; polyurethane; e-glass/carbon 1. introduction considerable research activity has been initiated in the area of materials, with the goal of finding new materials that can deliver high performance in the way that high performance engineering materials have, for example, composites. meanwhile, the application of these composite materials is among the most important developments in the engineering field in recent years. these materials have become essential to different engineering applications, for example automobile part manufacturing and marine & aerospace applications. since the composite materials explicitly have very high strength to weight ratio, are lightweight, and resistant to high temperatures, they are indeed considered to be pioneer materials in all applications. when compared with traditional metallic materials, composite materials present a wide spectrum of advantages over metallic materials, because metallic materials are prone corrosion when employed in corrosive environments [1-3]. in recent decades, thermoset polymer composites have become recognized and perhaps the most notably desirable materials in all sectors. the inherent properties like modulus to weight ratio, corrosion resistance, and fatigue resistance have further bolstered its wide acceptance in all sectors of engineering applications. on the other hand, thermoset frps (fiberglass reinforced plastics) have lower toughness when compared with traditional metallic materials and alloys. this adverse effect of strength gain is mainly due to interfacial bonding and linkages between the fiber and matrix materials. this is purely based on the property of the modifications on the matrix. meanwhile, researchers have kept trying various synthesis methodologies in the area of matrix modifications as well as adopting the newer techniques such as blending and concept of interpenetrating polymer networks [4-6]. generally, composites are explained as being a mixture of two or more materials that are combined to yield better characteristics than the individual materials in the mix. in contrast to traditional metallic alloys, each mixed material separately keeps its physical, chemical, and mechanical properties. aside from the phase mixing of both materials, reinforcement agents are added that are usually much stronger, stiffer, and harder than the matrix material. normally the reinforcement will be a fiber or a particulate. in the fabrication of particulate composites, the particulates uniformly occupy all areas of the composite material, whereas the strength of fiber-reinforced composites is completely based on the reinforcement direction, size, and shape. different types of fiber and matrix materials are available on the market, where the traditional fibers like glass and carbon fibers are most common in the area of frp fabrication. similarly, in the area of matrix selection, common synthetic resins like epoxy, polyurethane and vinyl ester are often the only resin components considered for a fabricator. each resin has its own unique nature of application in the 340 iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 fabrication of versatile components. epoxy resin is considered to be the highest performance resin due to its inherent properties and resistance to environmental degradation. generally, epoxy consists of a cross-linking reaction group, originally derived from the epoxy group [7-9]. mostly, epoxy is used in the coating and fabrication industries because it shows good adhesion with fiber reinforcement. epoxy also boasts very good chemical resistance, mechanical strength and electrical insulation property. likewise, vinyl ester resin is considerably used in most polymeric industries. basically, vinyl ester is produced by esterification process, where epoxy resin has been chosen as the prime ester substituent. engineers widely consider vinyl ester to be an acceptable substitute material for epoxy resin since it has a comparatively lower cost than the epoxy resin. it is also commonly used in marine industries due to its corrosion resistance and reduced water uptake characteristics, and is extensively used in frp tank vessel manufacturing and their allied components. other classic resins in this series are polyurethane resins (pur), from the family of thermoset and thermoplastic resins. pur is predominately accepted as a versatile material throughout the world due to its inherent properties like toughness, durability, and tear resistance. it is important to remember that all resins have their own positive and negative impact on component fabrication. in order to tap the benefits of two resins, the concept of interpenetrating polymer networks has been suggested and research activity has been successfully initiated in that field. while undergoing the polymerization, each resin would undergo separate curing and have mutual entanglement with the mutual resin [10-12]. in this present work, instead of choosing an individual polymer as the matrix material, the combination or blending of two resins has been implemented in order to fabricate the laminate. three sets of combinations have been taken for physical examination in this study. initially, epoxy with polyurethane was kept as the constant blend for glass, carbon, and glass / carbon fiber reinforcement. then, a vinyl ester and polyurethane blend was taken as the blend for glass, carbon, and glass/carbon fiber reinforcement. finally, epoxy and vinyl ester with a specific proportion was kept as the blend for the reinforcement of glass, carbon, and glass / carbon fiber. all the combinations underwent physical examination in order to have a detailed comparison of all the reinforcements with all blends. tests like tensile, flexural, impact, and moisture exhibit the relative coherence of all the reinforcements [13]. 2. materials and methods 2.1 materials the epoxy resin used in the experimental process as well as diglycidyl ether bisphenol a, vinyl ester resin with corresponding hardener, promotor, and catalyst, and polyurethane and e-glass / carbon fiber with aerial density of 350 gsm were purchased from sakthi fibers, chennai. all fibers and resins used for fabrication were received from the supplier as shown in fig. 1. 2.2 sample preparation initially, the epoxy with hardener was mixed with a ratio of 10:6 wt%. similarly, the vinyl ester and its corresponding hardener (methyl ethyl ketone peroxide), promotor, and accelerator were mixed with a ratio of 100:2:2. finally, the polyurethane prepolymer was mixed with its respective hardener mocca. all the mixtures with their corresponding hardeners were kept for blending as mentioned in the table 1. 341 iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 fig. 1: raw materials used to fabricate the ipn laminate. table 1: ipn – blend with reinforcement combinations notations ipn – blending combination fiber reinforcement epg epoxy + polyurethane glass epc epoxy + polyurethane carbon epgc epoxy + polyurethane glass/carbon vpg vinyl ester + polyurethane glass vpc vinyl ester + polyurethane carbon vpgc vinyl ester + polyurethane glass/carbon evg epoxy + vinyl ester glass evc epoxy + vinyl ester carbon evgc epoxy + vinyl ester glass/carbon 2.3 fabrication technique nine different types of composites, as mentioned in table 1, were made by the handlayup technique. six plies of biaxial woven mat of the fibers were cut. to fabricate the laminate, the woven mat was initially placed on the flattened aluminum plate then completely covered with a polypropylene sheet. following this, the blend was applied over the polypropylene sheet and the respective fiber mat was placed over the wet surface of the combination of ipn laminate. the mats were placed one over another until a 3 mm thickness was obtained. after every combination set was made, the specimens were kept at atmospheric temperature to ensure the complete polymerization. also, laminates were kept in the hot air oven for a period of 2 hours to further enhance the complete polymeric condensation. all the specimens were cut to the sizes mentioned in table 2 in order to subject the specimens to physical examinations. the specimens were cut with help of a diamond saw cutter with utmost care and accuracy [14]. table 2: astm standards with size of the specimens astm standards size of the specimen (length x breadth x thickness) in “mm” astm d 3039 tensile 250 x 25 x 3.2 astm d 790flexural 127 x 12.7 x 3.2 astm d 256 – impact 63 x 12.8 x 3.2 astm d 648 – hdt 125 x 12.7 x 3.2 342 iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 2.4 experimental analysis the tensile and flexural tests were done according to astm d3039 for all set of specimens by a universal testing machine, as mentioned in table 2. in each test, five samples were tested and averages were noted down as the final value. the sample specimens of all the hybrid composites are shown in fig. 2. fig. 2: hybrid test specimens of ipn composite. 3. results and analysis table 3 illustrates test results of the various ipn blends with e-glass and carbon fiber reinforcements. all physical property tests were conducted at ambient temperature. table 3: ipn – blend (e-glass/carbon – reinforced) physical properties ipn – blending combination mechanical properties tensile (mpa) flexural (mpa) impact (kj/m2) hdt (°c) epoxy + polyurethane + glass (epg) 625 415 16 74 epoxy + polyurethane + carbon (epc) 1025 752 19 89 epoxy + polyurethane + glass/carbon (epgc) 834 554 17 81 vinyl ester + polyurethane + glass (vpg) 452 376 12 68 vinyl ester + polyurethane + carbon (vpc) 854 725 19 79 vinyl ester + polyurethane + glass/carbon (vpgc) 667 501 16 72 epoxy + vinyl ester + glass (evg) 554 386 15 76 epoxy + vinyl ester + carbon (evc) 954 786 20 88 epoxy + vinyl ester + glass/carbon (evgc) 776 512 17 81 343 iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 3.1 tensile strength analysis of ipn laminate the results of the tensile strength of the e, e/sf, e/bf, e/cf, and e/sbcf fiberreinforced composites are shown in fig. 3. it was observed that the tensile strength of the pure epg composite had a value of 625 mpa. however, during this test, it was observed that the fracture on the specimen occurred at the gauge length of the specimen. though epoxy is known for its good strength and stiffness, due to the loading of the polyurethane on the epoxy, the strength of the specimen showed a little dip when its tensile strength is considered. past studies have shown that the pure epoxy with glass reinforcement show a predominant tensile strength value against all other sets of thermoset resins. similarly, the fracture purely relied on the phenomenon of crack initiation on the matrix, with subsequent loss of the interfacial strength between the fiber and matrix. also, it was common to notice that the fibers were broken as pull out fractures on the gauge length. the epc specimen showed a tensile strength value of 1025 mpa; this value was nearly 64% higher than the epg specimens. this high tensile strength shows that carbon fiber reinforcement has caused the rise in the tensile strength value. normally, carbon fibers are known for their higher strength, lower weight, and stiffness ratio. the characteristics of the carbon fiber showed the overwhelming response, when present, in its hike in tensile strength. the same failure mechanism seen in the epg was observed in epc. the epgc specimen showed a mixed response, where half of its strength seems due to the glass fiber and half due to the carbon fiber. the specimen showed a 45% increase over previous epc specimens. however, the values obtained on the vinyl ester matrix material showed a different trend, unlike the epoxy-based composites. proof of this is seen in the vpg tensile strength value of 452 mpa. this value was nearly 88% lower than the value obtained from the epgc. although the vinyl ester resin was proven to have a good toughness and impact resistant matrix, it showed a dip in tensile strength value even when loaded with polyurethane matrix. for a second time, it was interesting to note that the vpc had a tensile strength value of 854 mpa, which was nearly 22% higher than the value obtained from vpg. fig. 3: tensile strength analysis of e-glass / carbon fiber reinforced ipn (ep/vp/ev) laminate. from the results, it is proven that the carbon fiber reinforcement maintained a high value when reinforced, irrespective of the matrix material. on the contrary, the vpgc showed an increase in the tensile strength value against the vpc. the obtained value was 667 mpa; this was nearly 17% lower than the carbon fiber reinforcement. from all the results, it was observed that, irrespective of matrix, carbon fiber often offers a very high and good strength bearing capability. in line of the above, the evg shows a tensile strength value as 554 mpa. the obtained value was not higher than epg, but not lower than vpg, from the obtained value, it was proven that the epoxy holds a greater load bearing capability 344 iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 than the other two matrices, namely, the polyurethane and the vinyl ester. the evc exhibits the tensile strength value of 954 mpa, and this was higher than the corresponding epc and vpc. at last, the evgc shows a tensile strength value of 776 mpa, this value is nearly 19% lower than the value of evc. all the results clearly show that the carbon fiber holds the higher load bearing capacity irrespective of ipn matrix materials, similarly the hybridization on the composites increases the laminate strength to many folds greater than the glass fiber and many folds lower than the carbon reinforced ipn laminate [15]. 3.2 flexural strength analysis of ipn laminate the obtained results of the flexural strength of the e, e/sf, e/bf, e/cf and e/sbcf fiber-reinforced composites are shown in fig. 4. the specimen was held between the two rollers in a horizontal direction and the load was applied in the vertical direction. similar trends were seen in the flexural analysis as were seen in the previous tensile strength analysis. the epg showed the flexural strength value of 415 mpa, this was mainly due to the epoxy matrix. epoxy would usually have good interfacial strength; thus, the interlaminar strength was further increased in all combinations. the carbon fiber reinforced ipn laminate exhibited a higher value than the glass fiber reinforcement. this increased percentage (81%) in the epc was due to the carbon fiber reinforcement’s stiffness characteristics. the carbon fiber played a major role in increasing the strength of the laminates to higher levels. fig. 4: flexural strength analysis of e-glass / carbon fiber reinforced ipn (ep/vp/ev) laminate. the hybrid ipn laminate, with a combination of glass and carbon fiber reinforcement showed a lower value than the neat carbon fiber reinforcement. the obtained value shows that the load bearing capacity of the hybridization was based on the tailoring property of the glass and carbon fiber. nevertheless, the vpg, vpc, vpgc showed the flexural strength values of 376 mpa, 725 mpa, and 501 mpa, respectively. the obtained value for vp (vinyl ester and polyurethane) showed again that the matrix influences the load bearing strength of the laminate as discussed in the tensile strength analysis. however, the ev (epoxy and vinyl ester) showed that, for every epoxy-based ipn, the strength of the lpn laminate largely increased the load bearing capacity to a massive level [16]. 3.3 impact strength analysis of ipn laminate figure 5 shows the result of impact strength analysis of different variations of ipn blends with e-glass / carbon fiber reinforced laminates. 345 iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 fig. 5: impact strength analysis of e-glass/carbon fiber reinforced ipn (ep/vp/ev) laminate. the epg specimen showed an impact strength value of 16 kj/m2. this obtained value was comparatively high with respect to all sets of ipn specimens. similarly, the epc showed a value of 19 kj/m2. this value was much higher than the glass fiber reinforcement. again, this study proves that the carbon fiber reinforcement has better entanglement and adhesion property with all sets of ipn matrixes. epgc showed a comparatively lower value than that of epg and epc. similarly, the vpg, vpc, vpgc showed an impact strength value of 12 kj/m2, 19 kj/m2, 16 kj/m2, respectively. though vinyl ester is universally accepted as being a good impact resistant material, when it is mixed with the epoxy, the showed values of 15 kj/m2, 20 kj/m2, and 17 kj/m2, respectively. from all the tests, it was clearly observed that the ipns with hybridization significantly provided higher impact strength than the individual fiber reinforcement [17]. 3.4 heat deflection test of the ipn laminate the heat deflection temperature (hdt) was measured in order to find out the distortion temperature of the respective composites under elevated temperature (0.25 mm deflection), while the specimen was subjected to a standard load. results are shown in the fig. 6. while doing the test on the epg specimen, it exhibited an hdt value of 74 °c. though the neat epoxy reinforced composite exhibited higher hdt value in previous literature, in this study, it showed a lower value than the original neat epoxy-based composites. the main reason behind the lesser distortion was the loading of the polyurethane into the hybrid composite. variation in hdt value was far less than variation in the strength tests. since polyurethane is an elastic material, it loosens its entanglement with the epoxy very quickly as the temperature increases into the system. fig. 6: flexural strength analysis of e-glass / carbon fiber reinforced ipn (ep/vp/ev) laminate. the epc hybrid composite showed an hdt value of 89 °c, this value was nearly 9% higher than the epg. although the epc laminate contains polyurethane, its hdt value was 346 iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 higher than the epg. this was due to the carbon reinforcement into the laminate. however, the carbon reinforcement sustained maximum transverse load when the laminate was subjected to the transverse load. the epgc showed a mixed response much like the value obtained from tensile and flexural tests. the combination shows the mixed strengthened value of e-glass and carbon fiber. this value was 16% lower than the epc. correspondingly, the vpg exhibited an hdt value of 68 °c and the vpc showed an hdt value of 79 °c. though it exhibited a 16% higher value than the earlier reinforcements, the increase in the hdt value clearly showed that the carbon fiber reinforcement takes the maximum load. it also showed the better adhesion characteristics over the matrix material. in the same way, the epgc also showed a reduction in their hdt value as comparted with the vpc. as with the epgc, the glass fiber took less load and the carbon fiber took the maximum load. this is the reason why the specimen showed a mixed response of glass fiber and carbon fiber. the evg showed an hdt value of 76 °c whereas its corresponding carbon fiber reinforcement exhibited a value of 88 °c. from all the tests, it was clearly shown that the polyurethane resin-loaded hybrid composite showed a predominantly lower hdt value as compared with the neat laminates. by the same token, the carbon fiber reinforced ipns showed a higher value, irrespective of the type of ipn used. equally, the hybrid laminates showed mixed responses from glass and carbon fiber reinforcement. 4. conclusion the three sets of ipns (epoxy / polyurethane, vinyl ester / polyurethane, epoxy / vinyl ester) were prepared with a ratio of 70:30 with the variant reinforcements of e-glass, carbon, e-glass / carbon fiber reinforcement. all the variants were subjected to physical tests and their corresponding results are drafted below: 1. during tensile test, ep (epoxy/polyurethane) and ev (epoxy/vinyl ester) specimens showed better tensile strength values as compared to vp (vinyl ester/polyurethane) specimens. this is because of the matrix contributions to the ipn blends. 2. similarly, in flexural stress analysis, the ep (epoxy/polyurethane) specimens exhibited excellent flexural strength values over the remaining set of ipn blends. 3. on the contrary, during the impact strength analysis, the ev (epoxy/vinyl ester) showed better impact resistance value as compared with the remaining set of two variants. this was mainly because of the toughness characteristics of the vinyl ester. 4. while doing the hdt test, it was observed that polyurethane significantly played a role in terms of negative dip in the hdt value. however, carbon fiber reinforcement into the epoxy-based composite cumulatively increased the hdt value. 5. overall, important findings were that carbon fiber reinforcement into the ipn blend significantly increased the physical strengths of the laminates to double fold that of the e-glass fiber reinforcement. this shows that the carbon fiber had considerably better adhesion property with all sets of ipns. references [1] mat serudin a, othuman mydin ma, abdul ghani an. (2021) influence of fiberglass mesh on physical properties of lightweight foamcret. iium engineering journal, 22(1): 23-34. [2] zarinkolah z, bagheri h, hosseinkhani s. (2021) investigation on the mechanical, thermal, bio-degradation, and bio-compatibility properties of poly (lactic acid)/poly (ethylene glycol) blend. iium engineering journal, 22(1): 223-233. 347 iium engineering journal, vol. 23, no. 1, 2022 priya et al. https://doi.org/10.31436/iiumej.v23i1.2031 [3] tiwari a, wiener j, arbeiter f, pinter g, kolednik o. (2020) application of the material inhomogeneity effect for the improvement of fracture toughness of a brittle polymer. eng. fract. mech., 224: 106776. https://doi.org/10.1016/j.engfracmech.2019.106776 [4] bnvs ganesh gupta, hiremath mm, prusty rk, ray bc. (2020) development of advanced fiber-reinforced polymer composites by polymer hybridization technique: emphasis on cure kinetics, mechanical, and thermomechanical performance. j. appl. polym. sci., 137(43): 1–11. https://doi.org/10.1002/app.49318. [5] ke h, zhao l, zhang x, qiao y, wang g, wang x. (2020) performance of high-temperature thermosetting polyimide composites modified with thermoplastic polyimide, polym. test., 90: 106746. https://doi.org/10.1016/j.polymertesting.2020.106746. [6] liu y, wu q, wang c, zhou d, liang r, kang y. (2018) curing behaviors’ characterization of strong and weak crosslinking systems by thermal and dynamic mechanical methods, polym. test., 70: 1-7. https://doi.org/10.1016/j.polymertesting.2018.06.022. [7] shukla mj, kumar ds, rathore dk, prusty rk, ray bc. (2016) an assessment of flexural performance of liquid nitrogen conditioned glass/epoxy composites with multiwalled carbon nanotube, j. compos. mater., 50: 3077-3088. https:// doi.org/10.1177/0021998315615648 [8] suresh g, jayakumari ls. (2015) evaluating the mechanical properties of e-glass fiber/ carbon fiber reinforced interpenetrating polymer networks. polimeros, 25: 49-57. https://doi.org/10.1590/0104-1428.1650. [9] suresh g. (2016) analyzing the mechanical behavior of e-glass fibre-reinforced interpenetrating polymer network composite pipe. j. of composite materials, 50: 3053-3061. [10] ramesh m. (2017) mechanical and water intake properties of banana-carbon hybrid fiber reinforced polymer composites. materials research, 20: 365-376. [11] sumesh kr, kanthavel k, vivek s. (2019) mechanical/thermal/vibrational properties of sisal, banana and coir hybrid natural composites by the addition of bio synthesized aluminium oxide nano powder. mater res exp., 6(4): 045318. https://doi.org/10.1088/2053-1591/aaff1a. [12] vivek s, kanthavel k. (2018) effect of bagasse ash filled epoxy composites reinforced with hybrid plant fibres for mechanical and thermal properties. compos b, 160: 170-176. [13] suresh g, vivek s, ganesh babu l. (2019) evaluation of mechanical behaviour of carbon fiber reinforced nanoclay filled ipn matrix composite. materials res exp, 6(12): 125311. https://doi.org/10.1088/2053-1591/ab54ec [14] shayan asenjan m, sabet sar, nekoomanesh m. (2020) mechanical and high velocity impact performance of a hybrid long carbon/glass fiber/polypropylene thermoplastic composite. iran polym j., 29: 301-307. [15] alikhani a, hakim s, nekoomanesh m. (2017) modified preparation of hdpe/clay nanocomposite by in situ polymerization using a metallocene catalyst. iran polym j., 26: 721731. [16] ramakrishna hv, padma priya s, rai sk. (2006) effect of fly ash content on impact, compression, and water absorption properties of epoxy toughened with epoxy phenol cashew nut shell liquid–fly ash composites. j reinf plast compos., 25(5): 455-462. [17] srinivasan t, suresh g. (2020) experimental analysis of mechanical properties of banana fibre/epoxy (particulate) reinforced composite. materials today proceedings, https://doi.org/10.1016/j.matpr.2020.05.103. 348 https://doi.org/10.1016/j.matpr.2020.05.103 microsoft word 102-459-4-press.doc iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 19 improving nonlinear process modeling using multiple neural network combination through bayesian model averaging (bma) z. ahmad, tang pick ha, rabiatul ‘adawiah mat noor school of chemical engineering, universiti sains malaysia, engineering campus, seri ampangan, 14300 nibong tebal, seberang perai selatan, pulau pinang, malaysia e-mail: chzahmad@eng.usm.my abstract: improving model generalization of aggregated multiple neural networks for nonlinear dynamic process modeling using bayesian model averaging (bma) is proposed in this paper. using bma method, the posterior probability of a particular network being the true model is used as the combination weight for aggregating the network despite of using fixed combination weight as the model. the posterior probabilities are calculated using the sum square error (sse) from the training data on each of the sample time, and tested to the testing data. the selections for the final weight are based on the least sse calculated when each of the posterior probability is applied to the testing data. the likelihood method is employed for calculating the network error for each input data. then, it is used to calculate the combination weight for the networks. two non-linear dynamic system-modeling case studies are selected for this proposed method, which are water tank level prediction and ph neutralization process. application result demonstrates that the combination using bma technique can significantly improve model generalization compared to other linear combination approaches. key words: multiple neural networks, process control, mathematical modeling, bayesian model averaging, nonlinear process, nonlinear dynamics 1. introduction as we know, many processes are complex and require a lot of time and effort to develop and validate the detailed theoretical dynamic models which often end up with a multivariable complicated mathematical model. as an alternative, a simpler empirical nonlinear model is often developed using experimental data. neural networks or artificial neural networks (ann) are attractive whenever it is necessary to model a complex or complicated processes with large input-output data sets as well as to replace models that are too complicated to solve in real time. hence, neural networks have been used extensively in the recent years to model a wide range of physical and chemical phenomena and to model other non-engineering situations [1]. as mentioned by willis et al. [2] more accurate representations of the processes are required to ensure good process control performance especially in advanced process control. therefore, neural network models must be robust, stable and reliable when they are applied to a new (unseen) data. zhang [3] stated that even though neural networks have a iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 20 significant capability in representing nonlinear functions, inconsistency of accuracy still seems to be a problem where neural network models may not perform well when applied to unseen data. even though neural network models are very powerful non-linear modeling tools, noises in the input data sometimes cause the model over-fitting [4]. it can lead to a situation where poor generalization of a neural network model. such circumstance is undesirable since it obviously strays from the goal of using neural network model. another example is phenomena over fitting and under fitting in neural network training where a lot of researchers tried to solve it. over-fitting and under-fitting are two of the problems that should be alleviated in utilizing neural networks. in over-fitting, the error on the training data set is driven to a very small value, but when applied to unseen data, the network error is large and the generalization capability of the neural network is poor. while under fitting is due to that the neural network itself cannot cope with or fails to capture the relationship within the complex data [5]. in order to improve the robustness of neural networks and overcome the over and under fitting phenomena, a number of techniques have been developed lately like regularization (e.g [6]) and the early stopping method (e.g. [7]). ohbayashi [8] implemented the universal learning rule and second order derivatives to increase the robustness in neural network models. robustness is enhanced by minimizing the change in the values of criterion function caused by the small changes around nominal values of system parameters. lack of robustness in individual neural networks is basically due to the over fitting of the models (e.g. [9]). therefore, many researchers concentrate on how over fitting can be eliminated by improving the learning algorithm or by combining multiple imperfect neural networks. the method combining multiple neural networks seems to show some encouraging results in terms of improving the robustness of neural networks [10]. there are several methods of combining multiple neural networks such as stacked neural network and bootstrap aggregated networks where multiple networks are created on bootstrap resample of the original training data. using this method, several networks are combined (aggregated) and the aggregated predictor is used as the final representation as shown in fig. 1. they can be both the same or different structure of neural network from different data sets and the training algorithm. the overall output of the stacked neural network is a weighted combination of the individual network outputs. the main objective of this approach is to improve the generalization capability of the neural network models in such away that it will guard against the failure of individual component networks. combining a set of imperfect models (networks) can be thought of as a way of managing the recognized limitation of the individual models, each is known to have errors but they are combined in so the effect of these errors are minimized. proper determination of the stacking weights is essential for good modeling performance [10 12]. this is because each network output is weighted prior to summation of all the neural networks in the model, which will give the prediction value. iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 21 fig. 1: combining multiple neural networks. re-sampling of x to get final output of y in this paper, it is proposed that bma technique is used to combine multiple neural networks and to compare this method with linear combination techniques which are simple averaging and multiple linear regressions (mlr) techniques. other methods of combining multiple neural networks are nonlinear combination of neural networks such as demspter-shafers which uses rank-based information, voting, order statistic and also turner and ghosh methods. in bma approach, a proper model is selected at each sample of the model input in training data using the probabilities analysis. the probability of an individual network being the true model is calculated using the sum of squared errors (sse) on the training data. each set of weight from each sample time resulting from the training data is then applied to the testing data. for each prediction in the testing data, sse is calculated and the set of weight that produced least sse is selected for the final prediction output and employed to the unseen data as the final model. the paper is organized as follows. section 2 presents the combination using optimum selection of bayesian model averaging (bma). the applications of the proposed technique to two case studies are explained in section 3. section 4 covers the results and discussion and finally, the last section concludes this paper. 2. bayesian model averaging (bma) method for combining multiple neural networks bootstrap re-sampling technique is proposed in this paper to randomly re-sample twenty different set of training, testing and validation data. instead of choosing one ‘best’ neural network model, a set of imperfect estimators (net), which has different prediction performance are combined using bma method to improve the generalization capability of the model. the bayesian approach allows the predictive performance and better accounting of uncertainty. this can be seen as this approach tries to minimize the effect of the errors of the model through its method of using the least sse. it also takes into account every sample and set in the calculation. in some cases, for instance the heart attack data in raftery [13], more than one model may have high posterior probability and these models will give different predictions. by using predictions from only a single model will grossly underestimate the variability of the estimates since it ignores the fact that another model iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 22 with significant posterior probability gives a different prediction. despite of that, one should calculate predictions by using a weighted average over all models in the search space, where the weights are the posterior probabilities of the models [14, 15]. the bma based combination of multiple neural networks can be represented as followed: y* = p1 y 1 + p2 y 2 + p3 y 3 +…+ pkyk (1) where y* is the aggregated network model prediction and pk is the weight for combining the k-th network with yk prediction. for a dynamic process modeling, each of the individual networks model can be represented as eq. (1). suppose that neural network models are to be developed from the data set {x, y}, where x∈r pn× is the input data, y∈r qn× is the output data, n is the number of samples, p is the number of input variables and q is the number of output variables. to develop an aggregated neural network model containing n individual networks, the original data set can be re-sampled using bootstrap re-sampling with replacement to form replications of the original data set [16]. the n replications can be denoted as {x(1), y(1)}, {x(2), y(2)},…, {x(n), y(n)}, where x(i)∈r pn× ,y(i) ∈r qn× , i=1, 2,…, n . a neural network model can be developed on each of these replications, which can be partitioned into a training data set and a testing data set if cross-validation is used in network training and network structure selection and the predictions of these n network on the original data set are denoted as 1 ŷ , 2 ŷ , …. for the start, one should determine the aggregating weight for k-th networks as the posterior probability that k-th network is a true model with the posterior probabilities of the entire n network sum to 1. this aggregating weight is calculated from the training data, ( ) ( )[ ] ( ) ( )[ ]∑ = −−− −− −= 20 1 1 1 2 2 21 21 k yyk t yyk tk t k tt k tt ep ep p σ σ πσ πσ (2) where σ is the variance of the errors of the actual process output, yt for t-th training data, k is the number of variables and t is the sampling data [12, 17]. however, there is a problem when applying eq. (2) to practical applications. the error of each network at time t is required which is unknown as the true value of the process output at time t is unknown and is to be predicted. thus, eq. (2) needs to be modified in order to suit the practical applications. likelihood method is then used to obtain the estimates of the likely errors at time t. this method works in such way that a given model input data point is compared to the model input data in the training and testing data sets. data point in the training and testing data set that are likely is then obtained. bma method is used to select the final value of the prediction output as that of the network with give least sse value of the posterior probability at any given time when apply to the testing data. since earlier, model input data that are likely are employed. therefore, the network prediction error for this data point seems to be closed to its “likely” error in the training and testing data. as the result, the “likely” error in the training and testing data sets are used as an estimate of the error of the network for the given input data point. from the obtained error, aggregated weight is then calculated based on eq. (2). iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 23 the process of developing a model proceeds to the implementing step for the aggregated weight. they are employed to the testing data. the same equation as eq. (1) is used to calculate the value of sse for the testing data with y* is the aggregated network model prediction and pk is the weight for combining k-th network with yk prediction taken from the least sse on the testing data. the value of sse of each sample time is then plotted. the global optimum of sse is selected from all the plotted sse of the testing data. then, the selected weight based on the least or optimum sse value is applied to the validation data to obtain the final prediction output. the steps of obtaining optimum weight can be summarized as follows: step 1: generate n neural networks using bootstrap re-samples of the original training and testing data. step 2: calculate the sse for all networks on the original training data set for each sample time. step 3: set the prior distribution of the 20 neural networks as equal. the neural networks are assumed to have the same prior probability with the sum of the probability of all the networks is 1. hence, each network has a prior of 0.05. step 4: calculate likelihood or conditional probability that k-th network is the true model in the reduced universe of the 20 neural networks prediction for the training data using the sse in step 2. the likelihood is calculated as follows: ( ) ( )[ ]221 σπσ ktt yyk e −−=l (3) in this case, the probability distribution is assumed as a normal distribution where k is the number of variables and t is the sampling data. step 5: find the posterior probability for each network by dividing the joint probability with the marginal probability of the first data set. ste p 6: in training data set, use the posterior probability of the first data set as the prior for the second data set. in the same way, the second data set posterior is set as the prior for the third data set. the iteration continues with new posterior probability calculated using the posterior after the previous data set as the prior for the next data set. step 7: apply each posterior probability in every samples time calculated in step 5 to the testing data. compute sse for each iteration. the selection of the final weight (or posterior probability) will be based on the least sse produced in the testing data. then, the weight is chosen as the final weight to obtain the aggregated neural network prediction. 3. applications to two nonlinear process modeling case studies two case studies are used in this paper for evaluation and analysis of the proposed combination method for multiple neural networks. in each of the case study, 20 networks with fixed identical structure and 20 networks with various structures were developed from bootstrap re-samples of the original training and testing data. the meaning of various structures in this study is the number of neuron in the hidden layer is different in each individual network which randomly select in a certain range. the rational to choose 20 networks for all combination is based on the reference by zhang [16, 18] where 30 neural network models through bootstrap re-sampling method and applied the simple averaging combination method. after combining the aggregated networks, a constant sse was iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 24 observed after about 15 combinations. therefore, combining 20 neural networks is reasonably fine. if the number of networks is too small, one might not get the optimum reduction of the sse in the combination of the network. as a result, the “best” model to represent the system cannot be achieved. in re-sampling the training and testing data using bootstrap re-sampling techniques, the training and testing data were already in discrete time function; therefore by re-sampling the discrete time function, it does not affect the sequence of input-output mapping of the prediction. then, the individual networks were trained by the levenberg-marquardt optimization algorithm with regularization and “early stopping”. all weights and biases were randomly initialized in the range from –0.1 to 0.1. the individual networks are single hidden layer feed forward neural networks. hidden neurons use the logarithmic sigmoid activation function whereas output layer neurons use the linear activation function. to cope with the different magnitudes in the input and output data, all the data were scaled to zero mean and unit standard deviation. the data for neural network model building need to be divided into: (1) training data (for network training); (2) testing data (for cross-validation based network structure selection and early stopping); and (3) unseen validation data (for evaluation of the final selected model). the neural network models for both cases are developed using matlab (the mathworks inc.). in networks with fixed structure, the network structures, i.e. the number of hidden neurons, were determined through cross validation. single hidden layer neural networks with different numbers of hidden neurons were trained on the training data and tested on the testing data. the network with the lowest sum of squared errors (sse) on the testing data was considered as having the best network topology. in assessing the developed models, sse on the unseen validation data is used as the performance criterion. for dynamic system modeling, multi-step-ahead or long range predictions should be taken into consideration. in many advanced process control applications, such as optimal control of batch processes, accurate long range predictions are required. fig. 2: long-range predictions with feedback before the combination of individual networks for one-step-ahead predictions, the process output at time (t-1), y (t-1), is used as a model input to predict the process output at time t, ( )tŷ , as follows: iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 25 ( ) )](),...,2(),1(),(),...,2(),1([ˆ mtututuntytytyfty −−−−−−= (4) where u(t-1) is the process input at time (t-1), y(t) is the predicted process output at time t, m and n are the time lags in the process input and output respectively. in long range predictions or multi-step-ahead predictions, the current and past model predictions are used to predict the future values of the model outputs: ( ) )](),...,2(),1(),(ˆ),...,2(ˆ),1(ˆ[ˆ mtututuntytytyfty −−−−−−= (5) where the model prediction, ( )1ˆ −ty to ( )nty −ˆ , are used in place of the process outputs, y(t-1) to y(t-n), to predict ( )tŷ . here, one should bear in mind that for one-step-ahead predictions, the predicted process output, ( )tŷ is calculated based on previous process output whereas for multi-step-ahead predictions, the predicted process output is determined based on previous and current process predictions. in other words, for onestep-ahead predictions, they request for previous real process output in order to predict future process output while multi-step-ahead predictions, they use previous and current predicted process output to predict future process output. accurate long range predictions are much more difficult to achieve than accurate one-stepahead predictions due to the accumulation of the errors in the recursive predictions [19]. to obtain long range predictions from an aggregated network, two types of network output feedback schemes can be used as indicated in fig. 2 and 3. in fig. 2, the output of each individual network is fed back to its own input and the outputs of the individual networks are combined. this is equivalent to the step of combining the long range predictions of individual networks. in the scheme shown in fig. 3, outputs of the individual networks are combined and the combined output is fed back to the inputs of all individual networks. in this paper, the first feedback scheme shown in fig. 2 was adopted. fig. 3: long-range predictions with feedback after the combination of individual networks. to test the performance of the proposed technique, the following networks/combination schemes are investigated: (a) mean sse with fixed structure; (b) mean sse with various structure; (c) simple average of networks with fixed structures; (d) simple average of networks with various structures; (e) mlr combination of networks with fixed structures, iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 26 (f) mlr combination of networks with various structures; (g) bma combination for fixed structures; (h) bma combination for various structures 3.1 case study 1: water tank level prediction fig. 4: a conic water tank figure 4 shows the schematic diagram of a conic water tank. there is an inlet stream to the tank and an outlet stream from the tank. manipulating the inlet water flow rate will regulate the water tank level [3]. let v, qi and qo be the volume of water in the tank and the inlet and outlet water flows rates respectively, then the material balance in the water tank can be written as: oi qq dt dv −= (6) the outlet water flow rate, qo, is related to the tank level, h, by the following equation: hkq o = (7) where k is constant for a fixed valve opening. the volume of water in the tank is related to the tank level by the following equation: ( )      ++= 2 2 2 tan3tan θθ π hhr rhv (8) where r is the tank bottom radius and is the angle between the tank boundary and the horizontal plane. combining eq. (6) to eq. (8), the following dynamics model for the tank level can be obtained: ( )      ++ − = 2 2 2 tantan 2 θθ π hrh r hkq dt dh i (9) based on the above model, a simulation program is developed to simulate the process. the parameters used in the simulation are r = 10 cm, k = 34.77 cm 2.5 /s and θ = 60°. the sampling time is 10 seconds. the above equation indicates that the relationship between the inlet water flow rate and the water level in the tank is quite non linear. the outlet valve characteristic determines that the static gain increases with tank level. because the tank is of a conical shape, the time constant of the processes increases with the tank level. thus, iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 27 both the static and dynamic characteristics of the process vary with the operating condition. all the network building data were generated from the simulation programme and normally distributed noise with zero mean and a standard deviation of 0.7 cm were added to the simulated tank level. for one-step-ahead predictions, the dynamic model for tank level prediction is of the form: ( ) ( ) ( )[ ]1,1ˆ −−= tutyfty (10) this is based on the one-step-ahead predictions equation as stated earlier in equation 4, where ( )tŷ represents the tank level prediction, y represents tank level, u represents the in let flow rate, f is a nonlinear function represented by the neural networks and t is the discrete time. meanwhile, for long range predictions, it can be calculated as follows: ( ) ( ) ( )[ ]1,1ˆˆ −−= tutyfty (11) where ( )tŷ represents the tank level prediction which is included in the input of the next prediction, f is a nonlinear function represented by the neural networks and u represents the inlet flow rate. in the networks with fixed structure, the number of hidden neurons was determined based on cross validation technique. it was found that using 4 hidden neurons gives the least sse on the testing data. 3.2 case study 2: ph neutralization process fig. 5: cstr for ph neutralization process the neutralization process takes place in a cstr and the re are two input streams to the cstr. one is acetic acid of concentration c1 at flow rate f1 and the other is sodium hydroxide of concentration c2 at flow rate f2 [20]. the apparatus of the cstr are shown in fig. 5 and the mathematical equations of the cstr can be described as follows by assuming that the tank level is perfectly controlled: ( )ζζ 2111 ffcf dt d v +−= (12) ( )ςζ 2122 ffcf dt d v +−= (13) iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 28 [ ] ( )[ ] ( )[ ][ ] awwaa kkhkkhkh −−+++ +++ ζςς 2 (14) [ ]+= hph 10 log (15) where [ ] [ ]−+= achacζ (16) [ ]+= naς (17) the meanings and nominal values of the variables in the above equations are given in table 1. these equations show that the dynamic relation ship between the titration flow and ph in the cstr is very nonlinear. to generate training, testing and validation data, multi-level random perturbations were added to the flow rate of acetic acid while other inputs to the reactor were kept constant. the ph measurements were corrupted with normally distributed random noise with zero mean and a standard deviation of 0.2. for one-step-ahead predictions, the dynamic model representing the neutralization process is of the form: ( ) ( ) ( ) ( ) ( )[ ]2,1,2,1ˆ −−−−= tututytyfty (18) the above equation is reduced from eq. (4) in the previous section, where ( )tŷ is the ph in the reactor at time t, f is a nonlinear function represented by neural networks and u(t) is the acid flow rates at time t. long range predictions are calculated as follows: ( ) ( ) ( ) ( ) ( )[ ]2,1,2ˆ,1ˆˆ −−−−= tututytyfty (19) where the model predictions, ( )1ˆ −ty to ( )2ˆ −ty ,are used in place of the process outputs, y(t-1) to y(t-2), to predict y(t). it was found that using 5 hidden neurons gives the least sse on the testing data in cross validation techniques. 4. results and discussion 4.1 case study 1: water tank level prediction in this case study, 20 single networks with fixed number of hidden neurons (4) and 20 networks with varying number of hidden neurons (between 1 to 10) were developed. figure 6 shows the sse on the unseen validation data of the individual networks for onestep-ahead predictions. for this case study, 79, 99 and 199 data were used for the purposes of training, testing and validation respectively. it can be seen that their performance varies quite significantly. this demonstrates the different generalization capabilities of the individual networks. these phenomena were also observed in long-range prediction. once these individual networks were developed, they were combined using the different combination schemes proposed in section 2 and 3. it is shown in fig. 6 that the lowest sse on the unseen validation data for the single neural networks with fixed number of hidden neurons is 3.3032 (the 17 th network) and the majority of these networks have sse over 3.5. the mean sse for fixed and various structures are 3.8122 and 4.0325 respectively. figure 7 shows the pattern of the sse on the testing data when the bma combination is applied. it is clearly shown that there is a couple of local minima in this combination and iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 29 the final weight for the combination are based on the iteration number 49 and 33 for fixed and various structures respectively which show the least sse. global minima were obtained after certain period of iteration where sometimes it can be assumed as the local minima and this will affect the final prediction. in long-range prediction, the final weight were obtained after 7 and 33 iteration for fixed and various structures respectively as shown in fig. 8. for long-range predictions, sse in the testing data is quite consistent where the local minima are less compare to onestep-ahead predictions. it might be due to the individual neural networks predictions where the sse is high due to the recursive error occurred in the predictions. the overall result for this case study is shown in table 2 for both one-step and long-range predictions. for one-step-ahead predictions, bma shows quite a superior result compare to mlr and gives sse of 3.45 and 3.83 for fixed and various structures, respectively. however, simple averaging performance is slightly better than bma with sse of 3.43 and 3.39 for fixed and various structures. for long-range prediction, bma combination method is superior compare to mean, simple averaging and mlr. the sse for bma is 11.68 and 10.32 for fixed and various structures respectively compare to mlr with an sse of 142.04 and 99.31. mlr is gave the worst performance in this case study and it might be due to the co-linearity of the individual neural networks that deteriorated the performance of mlr. fig. 6: validation sse in single networks with fixed and varying structures for case study 1 iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 30 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 1.55 1.6 1.65 1.7 1.75 1.8 fixed structures s s e ( t e s ti n g d a ta ) various structures 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 1.55 1.6 1.65 1.7 1.75 number of iteration based on testing data s s e ( t e s ti n g d a ta ) number of iteration based on testing data fig. 7: sse in testing data for fixed and varying structures using weight from the training data for case study 1: one-step-ahead prediction 4.2 case study 2: ph neutralization process it is well known that the dynamics of ph is highly nonlinear. in this case study, 20 networks with fixed number of hidden neurons (5) and 20 networks with various numbers of hidden neurons (between 1 and 10) were developed. for this case study, 300 data were used for each training, testing and validation steps. figure 9 shows the sse of long-range predictions on the unseen validation data from the individual networks. it can be seen from fig.10 that single networks give various performance. this demonstrates the variation in individual network performance and the non-robust nature of single networks. figure 9 also indicates that the lowest sse achieved by single networks with fixed and various structures are 49.3 and 39.77, respectively. the worst performance for single networks with fixed structure is from network 9 with an sse of 2966 on the unseen validation data. the worst performance for single networks with various structures is from network 20 with an sse of 293 on the unseen validation data. the mean sse for fixed and various structures are 328.4 and 106.6. the proposed combination scheme was then applied with the results given in fig. 10, fig. 11 and the overall result are shown in table 3. figure 10 shows the variation of sse when applying the weight from the training data to the testing data for fixed and various structures. it is clearly shown that, it is not easy to iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 31 obtain the global minima in this case study. the least sse obtained on iteration number 260 for fixed structures and iteration number 136 for various structures. table 1: nominal values for case study 2 in long-range predictions, the global minima are easy to obtain where the variation of sse is quite consistent as shown in fig. 11. the global minima was achieved after 135 and 84 iteration for fixed and various structures respectively. then, the final weight corresponding to the least sse in the testing data is chosen as the final model for prediction output. the combined networks with fixed and various structures based on the bma give sse of 8.06 and 6.59 respectively on the validation data for one-step-ahead predictions. it is shown in table 4 that the bma combination scheme gives smaller sse on the unseen validation data than mean and simple averaging method for all networks except in mlr with sse of 7.25 and 7.84 respectively. however, this does not leave much effect compare to the bma combination approach. the ‘best’ combination is coming from scheme h which is a bma combination with various structures with sse of 6.59. table 2 overall results for case study 1: one-step-ahead predictions and long-range predictions sse (validation) combination schemes one-step-ahead predictions long-range predictions a 3.80 92.34 b 4.03 52.79 c 3.44 20.62 d 3.99 12.12 e 5.94 142.04 f 7.27 99.31 g 3.45 11.68 h 3.83 10.32 variables meanings nominal values v volume of the tank 1 l f1 flow rate of acid 0.081 l/min f2 flow rate of base 0.512 l/min c1 concentration of acids in f1 0.32 mol/l c2 concentration of acids in f2 0.05 mol/l ka acid equilibrium constant 1.8 x 10 -5 kw water equilibrium constant 1.0 x 10 -14 iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 32 table 3: overall results for case study 2: one-step-ahead predictions and long-range predictions in long-range predictions, combination using bma approach outperforms the other combinations with sse for validation data as 53.04 and 37.21 for fixed and various structures respectively. mlr shows quite poor performance in this case with sse of 124.21 and 270.63 for fixed and various structures. the ‘best’ combination in this case is coming from combination scheme h which is a bma combination with various structures with sse of 37.21. 5 10 15 20 25 30 35 40 1.5 2 2.5 3 3.5 4 4.5 fixed structures number of iteration based on testing data s s e ( t e s ti n g d a ta ) various structures 20 25 30 35 40 45 50 55 60 65 70 0 2 4 6 8 10 12 number of iteration based on testing data s s e ( t e s ti n g d a ta ) fig. 8: sse in testing data for fixed and varying structures using weight from the training data for case study 1: long-range predictions sse (validation) combination schemes one-step-ahead predictions long-range predictions a 10.44 328.00 b 10.12 106.55 c 8.78 57.31 d 7.84 43.84 e 7.25 124.21 f 6.39 270.63 g 8.06 53.04 h 6.59 37.21 iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 33 fig. 9: sse of long-range predictions on the validation data from single networks with fixed and various structures in case study 2 50 100 150 200 250 300 13 14 15 16 17 18 19 fixed structures s s e ( t e s ti n g d a ta ) various structures s s e ( t e s ti n g d a ta ) 50 100 150 200 250 300 12 14 16 18 20 number of iteration based on testing data number of iteration based on testing data fig. 10: sse in testing data for fixed and varying structures using weight from the training data for case study 2: one-step-ahead predictions iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 34 50 100 150 200 250 300 0 100 200 300 400 fixed structures s s e ( t e s ti n g d a ta ) various structures s s e ( t e s ti n g d a ta ) 50 100 150 200 250 300 50 100 150 200 number of iteration based on testing data number of iteration based on testing data fig. 11: sse in testing data for fixed and varying structures using weight from the training data for case study 2: long-range predictions 5. conclusion in multiple neural networks, the generalization capability of each network is somehow different. thus, it is not possible to find the ‘best’ network to model the process by looking at the sse of the training and testing data. combining these networks have proved to be promising in improving the robustness of the model by sharing and averaging out the errors. therefore, in this paper, combination using bma approach is introduced by selectively choose the optimum weight by looking at the weight that have the least sse in training data. as a comparison, linear combination of simple averaging and mlr were implemented. the simple averaging and mlr combinations have not been able to perform well compare to bma proved by the larger prediction errors and unsatisfactory resulting model by using these approaches. even though they are relatively easy to understand, the simple averaging and mlr combinations do not perform adequately well for this application. bma shows a superior result in this study where in both nonlinear case studies, clearly, bma have the advantages. the prediction error is much smaller or decreased compare to other linear combinations and at the same time, bma improves the model selection (weight selection). acknowledgements this work was supported by university science malaysia (usm) through short term grant 6035182 and 6035253. iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 35 references [1] d. e. seborg, t. f. edgar and d. a. mellichamp, “process dynamics and control”, john wiley & sons, us, 2004. [2] m. j. willis, c. di massimo, g. a. montaque, m. t. tham and a. j. morris, “artificial neural networks in process estimation and control”, automatica, vol. 28, no. 6, 11811187, 1992. [3] j. zhang, “developing robust neural network models by using both dynamic and static process operating data”, ind. eng. chem. res., vol. 40, 234-241, 2001. [4] s. mc loone and g. irwin, “improving neural networks training solution using regularization”, neurocomputing,vol. 37, 71-90, 2001. [5] [x. guyon and j. yao, “on the under-fitting and over-fitting sets of model chosen by order selection criteria”, journal of multivariate analysis, vol. 70, 221-249, 1999. [6] f. girosi, m. jones and t. poggio, “regularization theory and neural networks architecture”, neural computation, vol. 7, 219-269, 1995. [7] n. morgan and h. bourlard, “generalization and parameter estimation in feedforward nets: some experiments”, in: touretzkey, d.s. (eds.), advances in neural information processing system 2, san mateo, ca, 630-637, 1990. [8] m. ohbayashi, k. hirasawa, k. toshimitsu, j. murata and j. hu, “robust control for nonlinear system by universal learning networks considering fuzzy criterion and second order derivatives”, proceedings of ieee world congress on computational intelligence, 968-973, 1998. [9] r. caruana, s. lawrence and c. lee giles, “over-fitting in neural networks: back propagation, conjugate gradient and early stopping”, neural information processing system, 13, 402-408, 2000. [10] z. ahmad and j. zhang, “bayesian selective combination of multiple neural networks for improving long-range predictions in nonlinear process modelling”, neural computing and applications, 14, 78-87, 2005. [11] j. zhang and a. j. morris, “recurrent neuro-fuzzy networks for nonlinear process modeling”, ieee transaction of neural networks, vol. 10, no. 2, 313-326, 1999. [12] z. ahmad and j. zhang, “combination of multiple neural networks using data fusion techniques for enhanced nonlinear process modeling”, computers and chemical engineering, vol. 30, 295–308, 2005. [13] a. raftery, “approximate bayes factors and accounting for model uncertainty in generalized linear models”, biometrika, vol. 83, 251-266, 1996. [14] e. e. leamer, “specification searches: ad hoc inference with non-experimental data”, wiley, new york, 1978. [15] r. e. kass and a. e. raftery, “bayes factors”, journal of the american statistical association, vol. 90, no. 430, 773-795, 1995. [16] j. zhang, “developing robust non-linear models through bootstrap aggregated neural networks”, neurocomputing, vol. 25, 93-113, 1999. [17] s. kiartzis, a. kehagias, a. bakirtzis and a. petridis, “short term load forecasting using a bayesian combination method”, electrical power and energy system, vol. 19, no. 3, 171177, 1997. iium engineering journal, vol. 9, no. 1, 2008 z. ahmad 36 [18] j. zhang, “inferential estimation of polymer quality using bootstrap aggregated neural networks”, neural networks, vol. 12, 927-938, 1999. [19] j. zhang, a. j. morris and e. b. martin, “long-term prediction models based on mixed order locally recurrent neural networks”, computers and chemical engineering, vol. 22, no. 7-8, 1051-1063, 1998. [20] t. j. mcavoy, e. hsu and s. lowenthal, “dynamics of ph in controlled stirred tank reactor”, ind. chem. process des. dev., vol.11, 68-70, 1972. nomenclature c1 acetic acid inlet concentration, mol/l c2 sodium hydroxide inlet concentration, mol/l f1 acetic acid input flow rate, l/min f2 sodium hydroxide input flow rate, l/min ka acid equilibrium constant kw water equilibrium constant n number of samples p loading matrix qi inlet water flow rate, cm 3 /s qo outlet water flow rate, cm 3 /s v volume of water in the tank, cm 3 x input data vector y output data vector h water level in the tank, cm k constant for a fixed valve opening, cm 2.5 /s r radius of the tank, cm t sampling time for case study 1, s sampling time for case study 2, min iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 163 retina fundus image mask generation using pseudo parametric modeling technique a.m. aibinu, m.j.e. salami and. a.a. shafie department of mechatronics engineering, faculty of engineering, international islamic university malaysia p. o. box 10, 50728, malaysia. e-mail: maibinu@iium.edu.my abstract : this paper discusses a new pseudo modeling technique for the generation of retina fundus image (rfi) mask. the model coefficients necessary for the generation of the mask has been estimated from the synaptic weights of real-valued neural network. performance analysis of the newly proposed three step technique has been evaluated using drive databases and other rfi obtained from other sources. he accuracy obtained by the application of the proposed technique on rfi contained in the drive database varies between 99.62% and 99.97% . keywords: diabetes, parametric modeling technique, real-valued neural network (rvnn), retina fundus image 1. introduction in recent times, there have been a tremendous increase in age and society related diseases such as diabetes. in sweden, 4% of the country population have been diagnosed of diabetes [1] while approximately 2% of the working class in united kingdom are diabetic patient [2]. similar study in malaysia shows a steady rise in the population of diabetic patient from 0.65% in 1960 to 2% in 1980 [3] and according to america diabetes association, 6.3% of the total population of americans have been diagnosed of this disease [4]. also, it have been estimated that over 13% of the egyptian with age above 20 years will have diabetes by the year 2025 [5, 6] and about 5.5% of the world population have been diagnosed of the disease [6, 7]. diabetes can be described as a disorder in body metabolism. digested food enters the body stream with the aid of a hormone called insulin which is produced by the pancreas to automatically produce the correct amount of insulin needed for allowing glucose absorption from the blood into the cells. for individuals with diabetes, the pancreas either produces too little or no insulin or the cells do not react properly to the insulin that is produced by the body. the build up of glucose in the blood, overflows into the urine and then passes out of the body. therefore, the body loses its main source of fuel even though the blood contains large amounts of glucose [8]. iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 164 the effect of diabetes on the eye is known as diabetic retinopathy (dr) and this can be loosely classified into : background diabetic retinopathy (bdr), proliferate diabetic retinopathy (pdr) and severe diabetic retinopathy (sdr) [9, 10, 11, 12]. if dr is left untreated, the disease can degenerate and lead to blindness. according to world health organization (who) report released in 2002, 8.7% of the population of blindness have been linked to dr and taking a micro look at united state alone, about 8% of the blindness for the age bracket 20 to 74 have been due to dr [4, 13]. early detection, diagnosis and treatment have been identified as one of the ways to achieve reduction in the percentage of visual impairment caused by diabetes [1, 9]. different approaches have been suggested for early detection and monitoring of the dr such as the use of computer aided automatic diagnosis of dr from retina fundus image (caadrfi). caadfri and its variants (as suggested by others researchers) have the ability to reduce the number of blindness due to dr by almost 50% and they provide considerable time saving for patient and ophthalmologists, reduce wears and tears on equipments [6, 11-12]. however, most of the acquired rfi usually have severe limitation such as quality, acquisition and problems. in ensuring that screeners and ophthalmologists have good view of the whole retina fundus image (rfi), more than the needed number of images are sometimes acquired. the existence of good image processing algorithm that can improve and consistently guarantee good image quality will lead to a drastic reduction in the rfi acquisition and storage space requirements since only a sufficient number of images will be saved [5, 9-10]. various algorithms have been developed by various researchers for the caadrfi system, the effectiveness of which greatly depends on the quality of the acquired rfi [221]. most of these techniques can be regarded as a three-stage technique, namely rfi preprocessing stage so as to solve the problems of rfi mask generation, object motion, poor lighting and illumination problems; image segmentation stage and diseases classification for the anatomy detection and classification. a typical rfi used for caadfri is shown in fig. 1a, the whole regions contained in this rfi can be grouped into two main classes, namely the white semi-circular region of interest (roi) and the black background [6]. figure 1b is subsequently referred to in this paper as rfi mask . the process of generating the rfi mask involves labeling pixel belonging to the roi as one group and those belonging to the surrounding areas of the roi as background. incorrect delineation of background from roi greatly affects the results of the caadfri system hence the need for accurate delamination of roi from the background in rfi for a caadfri system. a typical rfi mask is shown in fig. 1b. different methods of generating rfi mask have been suggested in the literature however in this paper, a new method of generating rfi mask using pseudo parametric modeling approach is presented. review of related work is discussed in section 2 while the newly proposed technique is presented in section 3. performance analysis of the proposed technique and conclusion are contained in section 4 and section 5 respectively. iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 165 fig. 1: (a)retina fundus image (rfi) (b) retina fundus image (rfi) mask. 2. literature review a comparative performance measure applicable to the three major rfi preprocessing steps namely: mask generation, illumination equalization and color normalization has been reported in [6]. three methods of automatic mask generation was evaluated in the work, and it was observed that using morphological operators on the thresholded red band result in superior performance over either the simple thresholding of the green band proposed by goatman et al. [2] or thresholding on the the three rgb channels proposed in [19]. in a related work by gagnon et al. [19], several methods of detecting anatomical structures in rfi were presented. the algorithm proceed through five main steps which involve: automatic mask generation using pixels value statistics and color threshold; visual image quality assessment using histogram matching and canny edge distribution modeling; optic disk localization using pyramidal decomposition, hausdorff-based template matching and confidence assignment; macula localization using pyramidal decomposition and vessel network tracking using recursive dual edge tracking and connectivity recovering. results obtained in rfi mask generation stage show that the proposed technique is robust against low visual quality of the images and is independently of the position of the macular optic disk-centered when detecting the optic disk. success rates of 100% is reached for the optic disk detection and 95% for the macula detection. early detection of dr from rfi has been proposed in [20]. rfi model was developed based on probability distribution function of macular pigment, haemoglobin and melanin to represent macular region, retinal vasculature and background, respectively. independent component analysis based on the spectral absorbance of the model was then applied to determine retinal pigments from rfi. the proposed technique outperforms other noninvasive enhancement methods, such as contrast stretching, histogram equalization and contrast limited adaptive histogram equalization techniques, however little or no mention was made of methods of rfi mask generation in this work. in another related work, an expert system for early diagnosis of signs of dr was presented [21]. the process starts with an extraction of sub-image containing the optic iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 166 disk (od) followed by od boundary extraction in parallel from both the red and green channels of this sub-image by means of morphological and lastly the edge detection techniques was then applied. both od boundaries are approximated by a circumference using the circular hough transform. the location procedure succeeded in 99% cases, taking an average computational time of 1.67 s. with a standard deviation of 0.14 s while the segmentation algorithm rendered an average common area overlapping between automated segmentations and true od regions of 86% with an average computational time of 5.69 s having 0.54 s standard deviation. in [14], a computer-aided diagnosis (cad) system that facilitates the interpretation of rfi was developed. in this technique, rfi was converted into a feature vector that was created using histograms obtained from multiple images with different resolutions. an accuracy of about 96.34% was obtained with this technique. similarly, kee et. al developed a computer based approach for automatic segmentation of blood vessels in screening large numbers of vessel abnormalities contained in rfi [14]. although the results in this proposed method were compared to a manually segmented image but no empirical interpenetration of the accuracy was given. a three-stage framework for detection of vascular intersection namely bifurcationpoint (bp) and cross-point in rfi using a hybrid combined cross-point number (ccn) approach was proposed in [11, 12]. using a receiver operator curve (roc) based analysis on the proposed hybrid algorithm, a very high precision and true positive rate with a very small false error rate were obtained, indicating an improved performance when compared to the individual performance of modified cross-point number (mcn) and simple cross point number proposed in [12, 16]. another version to the use of 5 x 5 windowed based ccn was suggested in [11, 12] and also proposed in [16]. the hybrid technique was recently modified by using a 7x7 window in detecting vascular intersection in rfi [16]. the newly modified technique was tested on 100 rfi as opposed to the test performed in [11] on two publicly available rfi images databases. detection of abnormalities related to the inner structures of rfi using image enhancement, max-tree image representation and filtering procedure was proposed in [18]. this method produced an accuracy of 93.95% and 94.21% in detecting associated abnormalities on 40 and 20 rfi respectively. detection of the macula in the processing of rfi was proposed in [13]. regions of dark spots were detected by finding the coordinates with the lowest pixel intensity and determining the average pixel neighborhood intensities and these were ranked to obtain the region containing the macula. in evaluating the performance of this technique, a total of 162 images (81 rfi of left eye and 81 rfi of right eye) were used and 98.8% accuracy was obtained when the algorithm was applied on high quality rfi. however, this proposed technique was unable to accurately detect the macula in a low quality rfi. edge sharpening technique is employed in highlighting the boundary of rfi in the development of automatic detection of lesions in rfi [3]. also, automatic detection and extraction of exudates and optic disk in rfi was proposed in [1]. the rfi was preprocessed in order to improve the contrast and the overall color saturation in the image, then the optic disk was eliminated and the exudates were segmented using spatially iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 167 weighted fuzzy c-means clustering. the proposed algorithm for optic disk detection produced 92.53% accuracy. the sensitivity and the specificity of the proposed algorithm for exudates detection were 86% and 98% respectively. development of an automatic measurement and analysis of vessel tortuosity in color rfi was proposed in [35]. two sets of rfi for normal and diabetic persons were considered in this work and the proposed approach will be suitable for predicting or earlier diagnosis of diabetes or cardiovascular diseases. it was observed that higher vessel tortuosity appears in diabetic persons but this requires confirmation in studies with detailed clinical information and adequate sample size. villalobos and riveron in [36] presented a fast automatic retinal vessel segmentation and vascular landmarks extraction method for biometric applications using a three stage approach namely preprocessing, main processing and postprocessing steps. application of this technique on images in drive database, shows that this proposed method can a accurately detect and extract information from a rfi. 3. development of pseudo intelligent technique for rfi parametric modeling technique involves representation of data in an efficient and parsimonious form using minimum adjustable parameters [22-27]. the steps involved are model selection, model parameters determination and model validation. model selection is basically about choosing an appropriate parametric form for the signal or data to be modeled and some of the known models include autoregressive (ar) model, moving average (ma) model, autoregressive moving average (arma) model and their variants (such as autoregressive with external input (arx) model, vector autoregressive (var), autoregressive moving average with external inputs (armax) model, autoregressive integrated moving average (arima) model, autoregressive integrated moving average model etc) [22-26]. similarly, model parameters determination is concerned with the use of computationally efficient algorithm to determine model parameters while model validation involves the evaluation of how well the selected model captures the key features of the modeled data using the estimated model parameters [22-27]. in this work, new method of generating rfi mask using rvnn is proposed. detailed knowledge about rvnn can be obtained from [28, 29] and differences between a rvnn and its counterpart, the complex valued neural network can be obtained from [30-34]. the required model coefficients are obtained from the synaptic weights and the adaptive coefficients of the activation functions in a trained rvnn. consider the rfi acquired in red-green-blue (rgb) mode shown in figure 1a, with the mask shown in figure 1b, the image consist of three components, namely red (r), green (g) and blue (b) channels. these components fuse to give the final image shown in fig. 1a using the rgb scheme depicted in fig. 2. iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 168 fig. 2: rgb color scheme generation as applicable to rfi. since the final image ),( yxf can be represented by its components color as ),(),(),(=),( yxfayxfayxfayxf bbggrr ++ (1) where gr aa , and b a are the coefficients required to generate the rfi mask (fig. 1b). similarly, consider the ar model shown in fig. 3, which is driven by a white noise sequence )(nx to produce an output sequence )(ny according to )()(=)( 0 1= nxbknyany k p k +−−∑ )()](...2)(1)([= 021 nxbpnyanyanya p +−++−+−− (2) where pka k ≤≤,1 and p are the ar model coefficients and model order respectively. by comparing (1) and (2), the problem of generating the required rfi mask reduces to that of estimating the required coefficients in (1), thus the problem reduces to a pseudo parametric modeling approach. hence, a new three stage pseudo parametric modeling approach for the determination of the model coefficients gr aa , and b a from the synaptic weights and adaptive activation function coefficients of a rvnn is shown in fig. 4. iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 169 fig. 3: ar model representation. fig. 4: rvnn-based pseudo ar model rfi mask generation. iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 170 by considering the rvnn-based rfi mask generation shown in figure 5, the output )(ny is expressed as ))))((((=)( 010 1= 1 1= hgnyvwny lkkl p k ll m l ++∑∑ ôô βα (3) where m is the number of neurons in the hidden layer, 1l w is the weight connecting node l in the hidden layer to output layer, 10 h is the bias term of output neuron, l ϑ is the thl output of the hidden node l , α is the adaptive coefficient of the linear output activation function, kl v is the weight connecting input node k to hidden node l , lg is the bias of the hidden node l , l β is the adaptive coefficient of hidden node linear activation function and p is the number of input nodes. for an rgb-based rfi, 3=p . fig. 5: rvnn-based rfi mask neural network diagram. using linear transfer activation functions in both the hidden and output layer (i.e ()ô is the activation function), the required rfi mask generation coefficients are given as 31 ,= 1 1= ≤≤∑ kvwa lkll m l k βα (4) iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 171 thus, 21 , aa and 3 a are the model coefficients for the r, g and b components of the rgb-based rfi respectively and the coefficients obtained in (4) are equivalent to the required coefficients gr aa , and b a given in (1). 4. performance analysis the evaluation of the proposed technique is presented in this section. performance evaluation of this technique has been carried out using the digital retinal images for vessel extraction popularly known as the drive database. the images in the database were acquired using a canon cr5 non-mydriatic 3ccd camera with a 45 degree field of view (fov). the dataset contains 40 rfi of 584 x 565 pixels and the images have been divided into a training set consisting of 20 rfi and a test set of 20 rfi [37]. in this proposed technique only one single image is enough for training of the proposed rvnn based pseudo modeling technique and the remaining 39 images can be used for testing. in evaluating the performance of this technique some of the mathematical definitions and acronyms used include: np tntp accaccuracy + + =)( fptp tp prprecision + =)( p fp frratepositivefalse =)( positivestotal tp tprratepositivetrue =)( where tp, tn , fp and fn represent respectively true positive, true negative, false positive and false negative[38]. in the training phase, a single rfi is used to generate the training data, sample of the roi and the background serve as the input to the rvnn. the roi is assigned a target value of 1 while the background is assigned a target value of 0 . the input and the target data are concatenated and normalized separately and these are then fed to the rvnn. once the rvnn converged, the synaptic weights and adaptive coefficients are extracted and the required coefficients could be computed. in the testing mode, the obtained pseudo modeling coefficients are applied on the input image, the output is then clustered into two distinct classes, the roi and the background. in this paper, two types of clustering techniques have been evaluated, namely, the simple thresholding and k-means algorithm. one rfi image in the drive database have iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 172 been used for the extraction of the mask coefficients, from which the value of the required coefficients obtained are 2.7677− , 0.5609 , 0.5417− for gr aa , and b a respectively. results obtained from the application of these coefficients on rfi contained in drive database are discussed herein. each experiment has been repeated 30 times and the average accuracy value was then computed, the rfi mask obtained from the use of this technique was compared with the mask given in the drive database and performance measurement criteria discussed earlier were then computed. table 1 shows the results obtained by the application of the obtained coefficients and simple thresholding technique on one of the rfi from the database while table 2 depicts the results obtained by the use of k-means algorithm. as observed from the table, the use of simple thresholding of the rvnn output performs far better than that of k-means algorithm, though the performance of the simple thresholding technique reduces at very low or high threshold values. table 1: rfi mask generation using simple thresholding clustering technique. threshold accuracy precision tpr fpr 0.0500 0.7074 0.7023 1.0000 0.9443 0.1000 0.9433 0.9240 1.0000 0.1831 0.1500 0.9954 0.9933 1.0000 0.0149 0.2000 0.9996 0.9995 1.0000 0.0012 0.2500 0.9995 1.0000 0.9993 0.0000 0.3000 0.9990 1.0000 0.9986 0.0000 0.3500 0.9985 1.0000 0.9978 0.0000 0.4000 0.9981 1.0000 0.9972 0.0000 0.4500 0.9976 1.0000 0.9966 0.0000 0.5000 0.9971 1.0000 0.9958 0.0000 table 2: rfi mask generation using k-means clustering technique. accuracy precision tpr fpr 0.9916 1.0000 0.9878 0.0000 0.9916 1.0000 0.9878 0.0000 0.9916 1.0000 0.9878 0.0000 0.9916 1.0000 0.9878 0.0000 0.9916 1.0000 0.9878 0.0000 0.9916 1.0000 0.9878 0.0000 0.9916 1.0000 0.9878 0.0000 iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 173 0.9916 1.0000 0.9878 0.0000 0.9916 1.0000 0.9878 0.0000 0.9916 1.0000 0.9878 0.0000 table 3 shows the results obtained by the application of the obtained coefficients on all the rfi contained in drive training database. the accuracy of the k-means clustering technique is compared with that of simple thresholding technique over all the rfi contained in the training subset. from the results shown in this table, the use of simple thresholding technique outperforms that of k-means algorithm. table 3: comparing k-means clustering with simple thresholding (with 0.20 threshold value) for rfi mask generation. k-means simple threshold image number accuracy precision tpr accuracy precision tpr 21 0.9990 1.0000 0.9985 0.9934 0.9904 1.0000 22 0.9914 1.0000 0.9876 0.9997 0.9996 1.0000 23 0.9915 1.0000 0.9878 0.9996 0.9994 1.0000 24 0.9916 1.0000 0.9878 0.9996 0.9995 1.0000 25 0.9907 1.0000 0.9864 0.9996 0.9995 1.0000 26 0.9992 1.0000 0.9988 0.9934 0.9905 1.0000 27 0.9921 1.0000 0.9886 0.9997 0.9995 1.0000 28 0.9924 1.0000 0.9889 0.9997 0.9995 1.0000 29 0.9875 1.0000 0.9819 0.9996 0.9994 1.0000 30 0.9931 1.0000 0.9900 0.9996 0.9994 1.0000 31 0.9919 1.0000 0.9883 0.9996 0.9994 1.0000 32 0.9992 1.0000 0.9989 0.9916 0.9879 1.0000 33 0.9923 1.0000 0.9888 0.9997 0.9995 1.0000 34 0.9701 1.0000 0.9565 0.9972 0.9959 1.0000 35 0.9913 1.0000 0.9874 0.9997 0.9995 1.0000 36 0.9928 1.0000 0.9895 0.9996 0.9995 1.0000 37 0.9924 1.0000 0.9890 0.9997 0.9995 1.0000 38 0.9963 1.0000 0.9946 0.9961 0.9943 1.0000 39 0.9930 1.0000 0.9898 0.9997 0.9995 1.0000 40 0.9922 1.0000 0.9887 0.9995 0.9993 1.0000 furthermore, in another experiment using rfi acquired from another hospital in sweden [9-10], the coefficients obtained previously from drive database was applied on the rfi from [9-10], result obtained is shown in figure 6. the unavailability of the ground truth mask leads to only subjective evaluation of the obtained mask. iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 174 (a) (b) (c) fig. 6: (a) original rfi, (b) rfi mask using k-means clustering technique, (c) rfi mask using simple thresholding technique. lastly, the performance of the proposed pseudo modeling algorithm was evaluated on rfi acquired from another fundus camera in malaysia, result obtained is shown in figure 7. the unavailability of the ground truth mask leads to only subjective evaluation of the obtained mask. the superior performance of the simple thresholding technique is depicted in the resulting images 7b and 7c. (a) (b) (c) fig. 7: (a) original rfi, (b) rfi mask using k-means clustering technique, (c) rfi mask using simple thresholding technique. 5. conclusion a new method of extracting rfi using pseudo modeling technique has been presented in this paper and several existing works on caadrfi have been discussed herein. the accuracy obtained by the application of the proposed technique on rfi contained in the drive database varies between 99.62% and 99.97% . it has also been shown that using a simple thresholding to classify the output of the rvnn technique leads to an improved performance as compared to the use of k-means clustering technique. furthermore, the proposed technique has also been used to generate rfi mask from low visual quality rfi using the same extracted pseudo model coefficients. iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 175 acknowledgment this work is partially supported by malaysian e-science grant 0083080101 sf−−− . references [1] conference report: screening for diabetic retinopathy in europe 15 years after the st. vincent declaration the liverpool declaration 2005. retrieved march 18, 2010, from website: http://reseauophdiat.aphp.fr/document/doc/confliverpool.pdf#search='www.drsceening 2005.org.uk' [2] k. a. goatman, a. d. whitwam, a. manivannan, j. a. olson, and p. f. sharp, colour normalisation of retinal images, proc. med. imag. understanding and analysis, 2003. [3] h. yazid, h. arof and n. mokhtar, edge sharpening for diabetic retinopathy detection, ieee conference on cybernetics and intelligent systems, pp 41-44, 2010. [4] p. kahai, k. r. namuduri and h. thompson, a decision support framework for automated screeing of diabetic retinopathy, int. journal of biomedical imaging, pp 1-8, volume 2006, article id 45806. [5] w. h. herman, r. e. aubert, m. a. ali, e. s. sous, and a. badran, diabetes mellitus in egypt: risk factors, prevalence and future burden, eastern mediterranean health j., (3), 144-148, 1997. [6] a. a. a. youssif, a. z. ghalwash, and a. s. ghoneim, a comparative evaluation of preprocessing methods for automatic detection of retinal anatomy, proceedings of the fifth international conference on informatics and systems (infos 07), pp 24 -30, march 24-26, 2007. [7] j. staal, m. d. abràmoff, m. niemeijer, m. a. viergever and b. van-ginneken, ridge-based vessel segmentation in color images of the retina, ieee trans. med. imag.,(23), 501-509, april 2004. [8] abate diabetes: diabetes. accessed march 21, 2006, from website: http://www.abatediabetes.com/diabetes.html [9] a. m. aibinu, m. i. iqbal, m. nilsson and m. j. e. salami, automatic diagnosis of diabetic retinopathy from fundus images using digital signal and image processing techniques, international conference on robotics, vision, information, and signal processing, penang, malaysia, pp. 510 515, nov. 2007. [10] a. m. aibinu, m. i. iqbal, m. nilsson and m. j. e. salami, a new method of correcting uneven illumination problem in fundus images, international conference on robotics, vision, information, and signal processing, penang, malaysia, pp. 445 449, nov.2007. [11] a.m. aibinu, m.i. iqbal, a.a. shafie, m.j.e. salami, m. nilson, vascular intersection detection in retina fundus images using a new hybrid approach, computers in biology and medicine, (40), 81-89, january, 2010. [12] m. i. iqbal, a. m. aibinu, m. nilsson, i. b. tijani, and m. j. e. salami, detection of vascular intersection in retina fundus image using modified cross point number and neural network technique, proceedings of the international conference on computer and communication engineering, pp, 241-246, 2008. iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 176 [13] n. m. tan, d.w.k. wong, j. liu, w.j. ng, z. zhang, j.h. lim, z. tan, y. tang, h. li, s. lu and t.y. wong, automatic detection of the macula in the retinal fundus image by detecting regions with low pixel intensity, international conference on biomedical and pharmaceutical engineering, icbpe '09, pp 1-5, 2-4 dec. 2009, singapore. [14] s. lu, j. liu, j. h. lim, z. zhang, t. n. meng, w. k. wong, h. li, and t. y. wong, automatic fundus image classification for computer-aided diagonsis, 31st annual international conference of the ieee embs minneapolis, pp 1453-1456, 2009. [15] y.p. kee, i. lila iznita, m.h. ahmad fadzil, a.n. hanung, n. hermawan and s.a. vijanth, conference on innovative technologies in intelligent systems and industrial applications (citisia 2009), 2009. [16] v. bevilacqua, s. camb`o, l. cariello,and g. mastronardi, a combined method to detect retinal fundus features, european conference on emergent aspects in clinical data analysis, pisa, italy, sept. 2005. [17] p. aravindhan and p.n. jebarani sargunar, automatic exudates detection in diabetic retinopathy images using digital image processing algorithms, proceedings of the int. conf. on information science and applications icisa 2010, pp 26-30, february, 2010. [18] i.k.e. purnama, k.y.e. aryanto. branches filtering approach to extract retinal blood vessels in fundus image, [19] l. gagnon, m. lalonde, m. beaulieu, and m. c. boucher, procedure to detect anatomical structures in optical fundus images, proc. conf. med. imag. 2001, image processing (spie 4322), san diego, pp.1218-1225, 2001. [20] a. f. m. hani and h. a. nugroho, model-based retinal vasculature enhancement in digital fundus image using independent component analysis, ieee symposium on industrial electronics and applications (isiea 2009), pp 160-164, 2009. [21] a. aquino, m. e. gegúndez-arias and d. marín, detecting the optic disc boundary in digital fundus images using morphological, edge detection, and feature extraction techniques, ieee transactions on medical imaging, (29), 1860-1869, nov. 2010. [22] e. n. bruce, biomedical signal processing and signal modeling, willey press, 2000. [23] s. l. marple, digital spectral analysis with applications, prentice hall, inc., 1987. [24] m. h. hayes, statistical digital signal processing and modeling, john wiley and sons, new york, 1996 [25] j. g. proakis and d.g. manolakis, digital signal processing: principles, algorithms and applications, 4th ed., pearson prentice hall, 2007. [26] d.g. manolakis, v. k. ingle and s. m. kogon, statistical and adaptive signal processing, mc. graw hill, 2000. [27] m. aibinu, m. nilsson, m. j. e. salami and a. a. shafie , voice activity detection using modeling approach submitted for publication in computers in medicine and biology, 2010. [28] y. h. hu and j hwang, introduction to neural networks for signal processing, crc press llc, 2002. [29] s. haykin, neural networks: a comprehensive foundation, 2nd ed., eaglewood, cliffs, nj: prentice hall. iium engineering journal, vol. 11, no. 2, 2010 a.m. aibinu et al. 177 [30] a. m. aibinu, m. j. e. salami, and a. a. shafie, determination of complex-valued parametric model coefficients using artificial neural network technique, aans, volume 2010 (2010), article id 984381 [31] a. hirose, complex-valued neural networks, series on studies in computational intelligence, pp. 176, isbn-10: 3-540-33456-4, isbn-13: 978-3-540-33456-9, new york, nyspringer-verlag, 2006. [32] a. hirose (editor), complex-valued neural networks, theories and applications, series on innovative intelligence, pp. 363, isbn-981-238-464-2, 2003. [33] a. hirose. complex-valued neural networks for more fertile electronics, journal of the the ieice, 87(6):447–449, june 2004. [34] a. hirose, complex-valued neural networks: the merits and origin, proceedings of int. joint. conf. on neural networks pp257–264, june, 2009. [35] a. bhuiyan, b. nath, k. ramamohanarao, r. kawasaki and t. yinwongth, automated analysis of retinal vascular tortuosity on color retinal images, science+business media, llc 2010, 25 may 2010. [36] f. villalobos and e. riveron, fast automatic retinal vessel segmentation and vascular landmarks extraction method for biometric applications', international conference on biometrics, identity and security (bids), 2009, pp 1-10, 22-23 sept. 2009 [37] the drive database, image sciences institute, university medical center utrecht, the netherlands /http://www.isi.uu.nl/research/databases/drive/s, last accessed on 30th april, 2009. [38] t. fawcett, roc graphs: notes and practical considerations for researchers, technical report ms 1143 – extended version of hpl-2003-4, hp laboratories; 2004. openurl. microsoft word 1-bannikoff-f.doc iium engineering journal, vol. 2, no. 2, 2001 m. g. bannikov et al. 1 application of ion beam processing technology in production of catalysts mykola g. bannikov1, javed a. chattha1 vladimir n. zlobin2, igor p. vasilev2, jury a. cherkasov2 and piotr n. gawrilenko2 1fac. of mech. eng., gik institute of eng. sc. and techn., topi 23460, district swabi, pakistan 2east-ukrainian national university, molodejny 20a, luhansk 9104, ukraine abstract: in this paper, the applicability of ion beam processing technology for making catalysts has been investigated. ceramic substrates of different shapes and metal fibre tablets were implanted by platinum ions and tested in nitrogen oxides (nox) and carbon monoxide (co) conversion reactions. effectiveness of the implanted catalysts was compared to that of the commercially produced platinum catalysts made by impregnation. platinum-implanted catalyst having fifteen times less platinum content showed the same co conversion efficiency as the commercially produced catalyst. it was revealed that the effectiveness of the platinum-implanted catalyst has complex dependence on the process parameters and the optimum can be achieved by varying the ions energy and the duration of implantation. investigation of the pore structure showed that ion implantation did not decrease the specific surface area of the catalyst. key words: catalyst, ion implantation, noble metals. 1. introduction growing concern of the world society over clean environment impels manufacturers to look for new, environmentally-friendly technologies. catalysts are widely used to clean industrial and automobile exhausts from oxides of nitrogen (nox), carbon monoxide (co) and unburned hydrocarbons (hc). catalysts are produced by the well-established impregnation technology[1]. with this technology a ceramic substrate is impregnated by a solution of nitrates of catalytic metals. this step is followed by drying and calcination. the whole cycle is carried out in several steps and takes around 50 hours. high water consumption and emission of nox to the atmosphere accompany this process. other drawbacks of this method have to be accounted for. the properties of the carrier are said to be changed, and in some cases the specific area of a catalyst is reduced[2]. unequal distribution of catalytic materials on the carrier surface and their agglomeration has been also observed. the growing of the catalytic material crystals with time leads to the blockage of pores during catalyst exploitation[3]. high expense of catalytic materials is inherent to impregnation technology and this is of very importance when noble metals are used as catalysts. in this connection new technologies of catalyst coating have to be sought and investigated. ion beam processing technology (ibpt) has been already recognised as a competitive method of surface modification. ion implantation has been used to enhance materials engineering performance in areas such as hardness, friction and wear, and corrosion[4-6]. direct metal ion implantation as a part of ibpt has some features that make it applicable for making catalysts. the ion implantation allows virtually any chemical element to be implanted into the surface of any solid. apart from ceramic pellets other carriers such as metallic type or metallic wire may be used as a substrate of a catalyst[7]. it was also found that when a catalyst on a substrate is in the form of atoms its catalytic activity increases[8]. this is additional evidence in favour of an ion implantation. 2. ion implantation installation the ion implanter used for catalyst fabrication includes a vacuum chamber, source of metal ions, a vacuum pumping-out system and power supplies. the 1 m3 vacuum chamber has a hatch for loading the substrate to be coated, a branch pipe for connection with a vacuum pump, an observation port, an air inlet valve for gas and a flange on which a metal ion source is located. the ion source on the basis of a discharge in crossed exh fields with the cathode sputtering of metals has allowed an ion beam to be obtained along with diameter 200 mm, current density 130 a/cm2 and nonuniformity of 5% along the cross section. the vacuum chamber can accommodate several ion sources. the ease of changing the target in the ion source enables different materials to be implanted. the energy of ions can be controlled from 0 to 40 kev. with an ion implantation technique, catalysts are fabricated in a single cycle. the vacuum chamber is loaded with the substrates and a vacuum of up to 0.013 pa is created. coating then starts. this process, in turn, comprises two steps: surface degassing and coating. the first step is fulfilled at the voltage of 10 kv for about 10 minutes. the voltage of the second step determines the depth of ion penetration into the carrier and deiium engineering journal, vol. 2, no. 2, 2001 m. g. bannikov et al. 2 pends on materials processed. in our case it was around 20 kv. the duration of the second step depends on the catalytic material loading required. ion implantation dose ( d ) is proportional to the current density ( i ), surface area processed ( s ) and duration of implantation ( t ): 191.6 10 i t d s      . (1) the mass of the substance implanted ( m ): 271.66 10am d m     (2) where am is the average atomic mass of the chemical element implanted. catalyst loading in wt% is determined as a ratio of mass of catalytic material to mass of substrate. 3. experimental procedure carbon monoxide conversion efficiency of catalyst was measured in the test bed, which comprised the twin cylinder naturally aspirated diesel engine with a bore of 85 mm and a stroke of 110 mm, laboratory catalytic reactor, and gas analysers. design of the laboratory catalytic reactor is described by zlobin et al.[9]. exhaust temperature at the reactor inlet could be changed from 100ºc to 500ºc by an electric heater. giam-14 gas analyser was used for measuring co concentration in the exhaust at the reactor’s inlet and outlet. all engine performance parameters, except exhaust temperature, were maintained as follows: engine speed 1000 rpm, engine brake power 1 kw, air mass flow rate around 37 kg/hr, relative ratio of  = 4.2. exhaust flow could bypassed the reactor to maintain constant volume flow rate through the reactor. the space velocity was 38,000 hr-1. some industrial processes are accompanied by emission of harmful nox. reduction of nox can be achieved using a suitable catalyst in presence of ammonia (nh3) as shown in the following equation: 3 2 26no 4nh 5n 6h o   (3) in this investigation, nox conversion efficiency of catalysts was measured by model gas activity tester. model gas was composed of oxygen (o2), nitrogen (n2) and nitric oxide (no). mass flow rate of nh3 was 0.2% that of the model gas, and volume of the catalytic reactor was 40 cm3, space velocity was 15,000 hr-1. nitric oxide content in the outlet gas was measured by chemiluminescent gas analyser (344-cl-01). the conversion efficiency of a catalyst was calculated as a ratio of mass of contaminant in gas outflow to that in gas inflow. the pore structure of catalysts was investigated by mercury porosimetry and nitrogen physisorption (bet) methods. 4. results and discussion several samples of catalyst on various substrates with different platinum loading were prepared. the first set of experiments was a preliminary investigation on the applicability of an ion implantation technique as a means of manufacturing catalysts. alumina (-al2o3) extrudate (ø4-6 mm, l5-7 mm), alumina rounded granules (ø3-7 mm) and tablets (ø70 mm, l5 mm) made from metal fibre (ø0.1 mm) were implanted with platinum. this resulted in catalysts c1 (pt = 0.110%), c2 (pt = 0.110%), and c3 (pt = 0.114%) respectively. the implantation dose was chosen in a such way as to obtain a platinum loading of catalysts two times less than that of commercially produced platinum catalyst, c5 (pt = 0.2%). the commercial catalyst c5 was manufactured by impregnation method. catalysts obtained were tested in reaction of nox with nh3 at temperature of 280ºc, and results are shown in fig. 1. all catalysts showed satisfactory conversion efficiency but platinum content was still too high to make an ion implantation technique the competitive one. 50 55 60 65 70 75 80 c1 c2 c3 n o c on ve rs io n ef fic ie nc y, % fig. 1: nox conversion efficiency of catalysts. the natural question arises: what regime parameters of an implantation process are to be chosen to obtain maximum efficiency of the catalyst at the minimum expense of a catalytic material? preliminary work carried out to change the process parameters and the catalyst with low platinum content has been obtained. figure 2 shows that the new catalyst c4 (pt = 0.0135%) has the same co conversion efficiency at 340ºc as that of catalyst c5 (pt = 0.2%), even though it contained fifteen times less platinum. also shown in fig. 2 is the conversion efficiency of the commercially produced cuprum-chromium catalyst c6 (cuo : cr2o3 = 5% : 5%). it is only half as effective as platinum catalysts. effectiveness of any catalyst, other things being equal, depends on the catalytic material loading, specific surface area and temperature of reaction. first two properties, in turn, depend on the method of coating. coating obtained by impregnation has a finite thickness and only catalyst on the exterior surface is exposed to reagents whereas the rest does not contribute to reaction. obviously with this technology the maximum catalytic loading must exist over which catalyst effectiveness does not increase. while selecting ion implantation process parameters the following factors are to be taken into account. energy of ions determines the depth of their penetration into the surface of a substrate. if ions are implanted at depth more than 1 m, they probabl y will not be accessible to reagents. loading of catalytic iium engineering journal, vol. 2, no. 2, 2001 m. g. bannikov et al. 3 material is directly proportional to the duration of implantation and current density. in turn both duration of ion bombardment and current density can affect the specific area significantly. for instance nickel ion bombardment with the dose of 5x1016 ions/cm2 increased the specific area by factor of four compared to that of an unprocessed sample[4]. thus, duration of implantation affects both platinum loading and surface properties of the carrier. 0 10 20 30 40 50 60 70 80 90 100 c4 c5 c6 c o c on ve rs io n ef fic ie nc y % fig. 2: co conversion efficiency of catalysts. to estimate the influence of duration of implantation on efficiency of the platinum catalyst the following experiment was carried out. several catalysts were implanted with platinum at different duration of implantation and the same current density. catalysts were tested in co conversion reaction at different temperatures. figure 3 shows that the relative conversion efficiency of catalysts is a non-linear function of the implantation dose. temperature of reaction at which maximum efficiency of each catalyst was observed is a function of duration of implantation as well. moreover, the maximum conversion efficiency in this experiment was obtained at lower temperatures. 370 380 390 400 410 420 430 440 450 0 5.70e+16 1.14e+17 2.50e+17 3.90e+17 implantation dose, ions/cm² t em pe ra tu re , º c 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 r el at iv e ef fi ci en cy temperature relative efficiency fig. 3: effect of implantation dose on the relative efficiency. this experiment could not be used to predict the optimum parameters of an ion implantation process but showed that properties of catalysts produced by an ion implantation could not be explained just by catalytic material loading. possible surface modification caused by an ion bombardment must be taken into account and investigated. as a first step in this direction, the pore structure of carrier and catalysts was investigated by the mercury porosimetry technique. figure 4 shows that curves of pore volume distribution versus pore radius have nearly the same shape for all samples tested. pore structure of samples is characterised by two kinds of pores: macropores with radius from 200 to 1000 nm, and mesopores with radius from 3.7 to 8 nm. a) b) c) fig. 4: pore volume distribution: (a) carrier (-al2o3 pellets), (b) catalyst c4, (c) catalyst c6. with mercury porosimetry method only pores with radius of more than 3.7 nm are accessible. thus if sample contains pores with radius less than 3.7 nm its surface area can be underestimated. therefore surface area of samples was also measured by the bet method with which pores with radius up to 0.32 nm are accessible. as shown in fig. 5, specific surface areas of catalysts measured by mercury porosimetry and bet methods differ significantly. this difference indicates the presence of tiny pores with radius from 0.32 to 3.7 nm in the catalyst samples. this is also confirmed by the iniium engineering journal, vol. 2, no. 2, 2001 m. g. bannikov et al. 4 complete shape of the integral curves in fig. 4. figure 5 shows that specific surface areas of carrier and catlysts c4 and c6 are not much different from each other. when assessing these data the accuracy of measurement must be taken into account. p. fauchais and j. c. labbe suggest that measurement error of methods used can reach 20%[10]. thus, the surface area difference observed is comparable with measurement error. to investigate the effect of an ion bombardment on the surface area additional tests will have to be carried out. nevertheless, the firm conclusion can be made that ion implantation does not decrease the surface area of catalyst. 0 20 40 60 80 100 120 140 mercury porosimetry bet su rf ac e ar ea , m 2 / g carrier c4 c6 fig. 5: surface area of catalysts. 5. conclusion based on the results of the work reported in this paper the following conclusions are drawn: 1. the ion implanter for coating of catalysts has been developed. the installation allows implanting any catalytic materials on various substrates. 2. several samples of catalysts on various substrates have been prepared and tested. platinum-implanted catalyst having fifteen times less platinum content showed the same co conversion efficiency as the commercially produced catalyst. 3. effectiveness of implanted catalysts and temperature at which maximum efficiencies have been achieved had non-linear dependence on the implantation dose. 4. investigation of the pore structure showed that ion implantation did not decrease the specific surface area of the catalyst. modification of surfaces treated with an ion beam demands further investigation. 5. ion beam processing technology may be considered as the potential method of production of noblemetal-based catalysts and research in this direction shall be continued. acknowledgments this research has been done in collaboration between ghulam ishaq khan institute of engineering sciences and technology and east-ukrainian national university. the authors would like to thank both universities for the provision of laboratory facilities and encouragement. list of symbols and abbreviations 1.610-19, c: elementary charge 1.6610-27, kg: atomic mass unit d , ion/cm2: ion implantation dose i , a/cm2: ion beam current density (ibpt): ion beam processing technology m , kg: mass of the substance implanted ma: atomic mass s , cm2: surface area processed t , s: duration of implantation : relative ratio references [1] p. mychlenov, “catalysts technology”, leningrad, chemistry, 1979. [2] o. i. jegalin, n. a. kitrossky, v. i. panchishny, n. n. patrahalcev and a. i. frenkel, “automotive catalytic converters”, moscow: mashinostroenie, 1979. [3] s. laubenstein, “katalytishe abgasreinigung für stationär-motoren”. info-broshüre, h.u.t. heuwieser umwelttechnik gmbh, 1998. [4] j. k. hirvonen, “ion implantation”, new york, academic press, 1980. [5] v. n. zlobin, m. g. bannikov, p. h. draper, a. v. zotov and i. p. vasilev, “hardening of cutting tool inserts by ion implantation”, proceedings of 7th international symposium on advanced materials, islamabad, 17-21 september 2001. [6] r. r. manory, c. l. li, c. fountzoulas, j. d. demaree, j. k. hirvonen and r. nowak, “effect of nitrogen ionimplantation on the tribological properties and hardness of tin films”, materials science & engineering, vol. a253, pp. 319-327, 1998. [7] b. i. musienko, v. d. parhomenko, b. v. farmakovsky and a. p. hinsky, “competitive cleaner of exhaust of gasoline engine”, ecotechnology and effective use of energy resources, no. 2, pp. 20-22, 1994. [8] s. b. grinenko, a. a. denisov, a. g. ohapkin and a. i. pyatnichko, “exhaust catalytic conversion of gasoline engines”, ecotechnology and effective use of energy resources, no. 5, pp. 46-51, 1995. [9] v. n. zlobin, m. g. bannikov, i. p. vasilev, j. a. cherkasov and p. n. gawrilenko, “potential of use of ion implantation as a means of catalyst manufacturing”, proc. instn mech. engrs, part d, journal of automobile engineering, 2002, vol. 216. no. d5, pp. 385-391, may 2002. [10] p. fauchais and j. c. labbe, workshop on thermal plasma applications in surface coating and engineering, islamabad, pakistan, 19th july 2001. iium engineering journal, vol. 2, no. 2, 2001 m. g. bannikov et al. 5 biographies of authors dr. mykola g. bannikov received his master’s degree in mechanical engineering from lugansk engineering institute, ukraine in 1980. he obtained his ph.d degree from kharkov railway transport institute, ukraine in 1989. he is a professor at the faculty of mechanical engineering, ghulam ishaq khan (gik) institute of engineering sciences and technology, pakistan. his area of specialisation is thermo-fluid sciences and particularly their application to modelling of flow and combustion processes of internal combustion engines (ice). currently he is concerned with ice pollutant formation and control. dr. javed ahmad chattha received his bachelor’s degree in mechanical engineering from university of engineering and technology lahore, pakistan in 1978. he obtained his master’s degree in energy technology from the asian institute of technology, bangkok, thailand in1984 and then he did his ph.d from the university of birmingham, uk in 1990. presently he is dean of faculty of mechanical engineering at gik institute of engineering sciences and technology, pakistan. his area of interest is thermo-fluids. dr. vladimir n. zlobin received his master’s degree in physics from omsk state university, russia in 1962 and ph.d degree from the same university in 1973. he is currently a senior lecturer at volgograd polytechnic college, russia. he is the author of the ion implantation installation used in this research. dr. igor p. vasilev obtained his master’s degree in mechanical engineering from lugansk engineering institute, ukraine in 1973 and then graduated with a ph.d degree from east-ukrainian national university (eunu), ukraine in 1992. hi is an associate professor at eunu. his research works focus on the development of new technologies of catalyst coating. mr. jury a. cherkasov received his master’s degree in mechanical engineering from east-ukrainian national university in 1999. currently he is doing his ph.d at eunu. dr. piotr n. gawrilenko received a degree in mechanical engineering from lugansk engineering institute, ukraine in 1973. he graduated with a ph.d degree from volgograd polytechnic institute, russia in 1988. his research interests are working process and emission control of ice. iium engineering journal, vol. 2, no. 2, 2001 6 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 effect of chitin source and content on properties of chitin nanowhiskers filled polylactic acid composites syazeven effatin azma mohd asri1, zainoha zakaria1, azman hassan2* and mohamad haafiz mohamad kassim3 1department of chemistry, faculty of science, universiti teknologi malaysia, skudai, malaysia 2department of bioprocess and polymer engineering, school of chemical and energy engineering, faculty of engineering, universiti teknologi malaysia, skudai, malaysia 3school of industrial technology, universiti sains malaysia, penang, malaysia *corresponding author: azmanh@cheme.utm.my (received: 4th may 2020; accepted: 14th june 2020; published on-line: 4th july 2020) abstract:this study investigates the use of chitin nanowhiskers (chw) from different chitin sources to develop chw reinforced polylactic acid (pla) nanocomposite. chitin sources used in this study were commercial chitin (cc), fermented chitin (fc) and treated fermented chitin (tfc) whereby fc and tfc were obtained from fermentation of prawn waste. the chitin was then undergoes acid hydrolysis to produce commercial chitin nanowhiskers (cchw), fermented chitin nanowhiskers (fchw) and treated fermented chitin nanowhiskers (tfchw). pla was chosen due to several advantages such as biodegradability, good mechanical strength and in line with global pressure to improve environmental pollution aspects. tensile strength for pla/fchw, pla/tfchw and pla/cchw increased with increasing filler content until it reached optimum value at 1 phr, 2 phr and 3 phr, respectively. young’s modulus for the nanocomposites increased with increasing filler content but elongation at break decreased significantly with increasing filler content for all types of nanocomposites. tga results indicated that pla/chw nanocomposites displayed better thermal stability as compared to pure pla. the biodegradability and water absorption of nanocomposites increased with increasing filler content. the overall results confirm that pla nanocomposites from fc are not inferior than pla nanocomposites from cc and therefore has similar potential to be used in packaging applications. abstrak:kajian ini menyelidik penggunaan nanowisker kitin (chw) dari sumber kitin yang berbeza untuk membangunkan komposit poli(asid laktik) (pla) bertetulang chw. sumber-sumber kitin yang digunakan dalam kajian ini terdiri daripada kitin komersial (cc), kitin ditapai (fc) dan kitin ditapai yang dirawat (tfc) di mana fc dan tfc diperoleh daripada penapaian sisa udang. kitin kemudiannya menjalani proses hidrolisis asid untuk menghasilkan nanowisker kitin komersial (cchw), nanowisker kitin ditapai (fchw) dan nanowisker kitin ditapai yang dirawat (tfchw). pla dipilih kerana kelebihannya misalnya kebolehan pereputan-bio, kekuatan mekanikal yang baik dan sesuai dengan tekanan global untuk memperbaiki aspek pencemaran alam sekitar. kekuatan regangan untuk pla/fchw, pla/tfchw dan pla/cchw meningkat dengan peningkatan kandungan pengisi sehingga mencapai nilai optimum masingmasing pada 1 phr, 2 phr dan 3 phr. modulus young bagi komposit nano meningkat dengan peningkatan kandungan pengisi tetapi ciri pemanjangan takat putus menurun dengan ketara dengan peningkatan kandungan pengisi bagi semua jenis komposit nano. 239 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 keputusan tga menunjukkan bahawa komposit nano pla/chw memaparkan kestabilan terma yang lebih baik berbanding dengan pla tulen. kadar pereputan-bio dan penyerapan air komposit nano meningkat dengan peningkatan kandungan pengisi. hasil keseluruhan mengesahkan bahawa komposit nano pla daripada fc tidak lebih rendah daripada komposit nano pla dari cc dan berpotensi serupa untuk digunakan dalam aplikasi pembungkusan. keywords:chitin; nanowhiskers; prawn waste; polylactic acid; nanocomposites 1. introduction chitin is one of the most abundant natural polysaccharides that exist in nature and is found in the outer skeleton of crustaceans such as shrimp, lobster and crab. it is known to possess many desirable properties such as biocompatible, antibacterial [1] and is found to have desirable mechanical properties due to their natural stacks of chitin nanowhiskers (chw) [2]. research and development on chw sparked new interest following the successful use of nanocrystalline fractions from cellulose as fillers in nanocomposites [37] since both cellulose and chitin shared similar backbone structure. natural polymers such as chitin, starch and cellulose consist of both crystalline and amorphous region. various methods have been employed in production of chw. one of the methods that are widely used is through acid hydrolysis [8]. the crystalline region in nanoscale size once isolated can be used as reinforcing nanofillers in polymer nanocomposites [9-10]. synthetic polymers have become an essential part of our lives; having wide applications in various fields including in agriculture, packaging and in medical applications [11]. although synthetic polymers have many advantages, the lack of biodegradability is one of the setbacks and has caused serious polluting effects on the environment. therefore interests on biopolymers which are biodegradable and are synthesized from renewable resources [12] have increased among the academicians and researchers globally as indicated by the expanding literatures [13-15]. polylactic acid (pla) is the most promising bio-based and biodegradable thermoplastic, and is considered as a ‘green’ eco-friendly material. it is an aliphatic polyester and fulfils many requirements as a packaging thermoplastic and is suggested as a material for general packaging applications [16]. to enhance the competitiveness of pla, many properties such as mechanical and thermalcan be further improved. in addition, the reinforcement of pla using natural nano-fillers is interesting to be considered as it is expected to improve biodegradability besides enhancing the mechanical and thermal properties due to their nanosize crystals. previous report mentioned that addition of chitin nanofibrils (cns) as reinfocing fillers do not alter the other properties of pla based materials; hence proposing that this addictive can be used in bioplastic items mainly expoliting its intrinsic anti-microbial and skin regenerating properties [17]. several studies have reported on the use of chw as reinforcing filler in pla [18-19]. the earliest work was on the fabrication and characterization of melt-blended pla/chitin composites in which the chw was produced by an acid hydrolysis. interestingly, the study showed that the stiffness of the composites increased with increasing chitin content while the strength decreased. in a later study, the effect of surface acetylated chw on structure and mechanical properties of pla was determined [20]. in the study, the miscibility between chw and pla was improved by surface acetylation of chw. the acetylated chw was incorporated into a pla matrix by solution blending, and resulted in an increase of tensile strength and young's modulus and they reached to the maximum value as 45 and 37% higher than neat pla film, respectively, with the loading level of 240 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 acetylated chw reaching to 4 wt %. the enhancement could be attributed to that acetylation improved dispersion of acetylated chw in the pla matrix and interfacial adhesion between acetylated chw and pla. recently, the effect of chw on crystallization of triethyl-citrate-plasticized pla has also been reported [21]. the addition of a small amount (1 wt %) of chw to plasticized pla significantly affected its nucleation, crystal size, and crystallization speed. in the previous study, chw were chosen to surface modify pla film to better utilize and combine the advantages of pla matrix and chw [22]. the resulting film prepared via the vertical coating method through shearing force action has significantly better strength and modulus compared to conventional solution blending. on the other study, electrospun composite nanofibers membrane of pla and the surface grafted chitin whiskers resulted in superior tensile strength and modulus as compared to pure pla. this is mainly due to the hydrophilicity of pla was improved by the introduction of chw [23]. in a recent study, it was reported that pla based films containing cns resulted in biocompatibility and able to stimulate the production of cell defensins, acting as an indirect anti-microbial agent [24]. in recent years, a biotechnological approach using lactic acid fermentation to purify chitin from prawn waste [25-26] provides an environmentally friendly approach as opposed to the conventional chemical method. the biological approach produces two industrially important products namely a protein-rich liquid fraction and a chitin solid fraction. besides reducing the usage of hazardous chemicals by the conventional methods, the biological approach is able to conveniently recover the protein-rich fraction via a suitable bioreactor [25] and has been shown to be a suitable source of protein for aquaculture feed [26]. meanwhile, finding good use to the chitin by-product fraction will give added advantage to the fermentation process. in the present work, chw from the chitin fraction of fermented prawn waste is investigated as nanoscale fillers to reinforce pla. prawn waste is widely produced from prawn processing industries and its disposal is becoming an issue due to its high perishability. thus, its proper disposal and putting it to good use is becoming more urgent. to date, no study has been done on using chw obtained from fermented chitin as fillers in pla. in this study, chw from chitin through fermentation of prawn waste is being produced as potential material for polymer reinforcement in an attempt to replace commercial chitin produced through harsh chemical treatment. the objective of this study is to compare the effects of chw from fermented chitin with the chitin obtained through chemical method on mechanical, physical and thermal properties of chw reinforced pla composites. 2. experimental 2.1 materials pla was obtained from natureworktm (pla 300id). the density of pla is 1.25 g/cm3, melting temperature of 145-155°c, glass transition temperature of 55-58°c, cystallinity of up to 37% and it has an average molecular weight of mw: 220 kda and mn: 101 kda. chitin sources are i) fermented chitin (fc) produced by fermentation treatment of tiger prawn waste,ii) treated fermented chitin (tfc) which is basically an fc that undergoes an extra mild acid and alkaline treatment and iii) chitin from prawn shells purchased from sigma aldrich designated as commercial chitin (cc) for comparison. all types of chitin sources underwent hydrolysis and dialysis through treatment with hydrochloric acid to produce chw. the solvent used to dissolve the pla is chloroform, purchased from merck malaysia. 241 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 2.2 production of chitin via fermentation of prawn waste tiger prawn (penaeus monodon) waste obtained from a local prawn processing industry in johor consisted of head, exoskeleton, and tail portion were minced through a 4.5 mm die plate using an industrial mincer (rheninghaus meat mincer, model eve/all 22, italy) and were fermented using effective microorganism (em) which has been activated with palm sugar for a week prior to use [26]. fermentation of minced prawn waste was carried with addition of 10% (w/w) of carbohydrate sources (glucose or brown palm sugar) and 10% (v/w) activated em in a loosely covered bottle and incubated at 37oc for 72 hours. the mixture was occasionally stirred especially during the first 24 hours and ph was monitored using bench top ph meter (hanna instruments, italy). the fermented product is separated into solid chitin; fermented chitin (fc) and liquid proteinaceous fraction. for the production of treated fermented chitin (tfc), fc was hydrolysed in 1m hcl at room temperature for 1 hour followed by another hour in 1m naoh solution. both fc and tfc were washed, dried and kept at room temperature for further use. 2.3 preparation of chitin nanowhiskers (chw) chw was prepared through acid hydrolysis method [8]. fermented chitin (1.0 g) was hydrolyzed in boiling 3n hcl for 1 hour. after hydrolysis, chitin was diluted with distilled water (40 ml) and centrifuged at 3200 rpm for 15 minutes and this process were repeated thrice. the chitin extract was dialyzed in cellulose dialysis tubing against continuous water flow for 2 hours. the dialysis process was continued by immersing the dialysis tubing in a beaker of distilled water until it reaches ph 4. the chitinextractdesignatedas fermented chitin nanowhiskers (fchw) was sealedandstored at 4°c. similar steps were repeated using treated fermented chitin (tfc) and commercial chitin (cc) producing treated fermented chitin nanowhiskers (tfchw) and commercial chitin nanowhiskers (cchw) respectively. all samples of nanowhiskers were characterized using ftir and tem. 2.4 preparation of pla and pla/chw nanocomposites an amount of 10 g of pla pellets were fully dissolved in chloroform through constant stirring in a water bath at 60oc for approximately 60 minutes [7]. the solution was evenly spread on a glass plate using a fabricated spreader and the film was left to dry by evaporation at ambient temperature for 48 hours. dried film was kept in adessicator until further use. the thickness of the cast film was approximately 100 ± 0.125 μm and designated as pla. the pla/chw nanocomposites were prepared by mixing pla with different types of chw (fchw, tfchw and cchw) at different chw contents (1, 2, 3 and 4 phr) following the same method in production of pla film. nanocomposites of pla/fchw, pla/cchw and pla/tfchw were analysed for mechanical, thermal, water absorption properties and biodegradability. 2.5 characterizations 2.5.1 fourier transform infrared spectroscopy ftir spectroscopy was performed using perkin elmer 1600 infrared spectrometer (usa). all types of chw were characterized using liquid method through suspension casting. all samples were recorded at 32 scans with a resolution of 4cm-1 and within the wavenumber range from 370 to 4000 cm-1. 2.5.2 transmission electron microscopy the study of surface morphology of cnw from various sources of chitin (fchw, tfchw and cchw) were evaluated using hitachi hd-2000 scanning transmission electron microcopy (tem). samples were prepared by placing 5 μl diluted suspension of 242 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 fchw, tfchw and cchw on the carbon-coated grid and was allowed to dry at room temperature. the samples were negatively stained by allowing the grids to float in a 1% uranyl diacetate solution for 3 minutes. the samples were examined at an accelerating voltage of 120kv. the tem images were obtained by using soft imagine system software. 2.5.3 tensile testing tensile test was performed according to astm d882 using l1oyd lrx (usa) machine under ambient condition. rectangular specimens were cut from the obtained cast film with dimension 60 x 12.6 x 0.1 mm3. the crosshead speed of 12.5 mm/min with 30 mm gauge length was used. tensile strength, elongation at break and young’s modulus were determined. seven specimens for each formulation were tested and mean value was recorded. 2.5.4 thermogravimetric analysis thermogravimetric analyses (tga) and derivative thermogravimetric (dtg) were used to determine thermal stability of the pla nanocomposites by tracking weight change during a ramp to 600°c at 20°c/min with nitrogen purge. 2.5.5 water absorption water absorption test was carried out according to astm d570-81. the sample (20 x 20 x 0.1 mm3) was dried to a constant weight (wo) in vacuum oven prior to the test and was then immersed in distilled water at ambient temperature for 2 hours and 24 hours. wet weight after immersion (wi) were taken and percentage weight gain was taken as the water absorption values using equation (1), water absorption (%) = [ (wi – wo) / wo] x 100 (1) 2.5.6 soil burial test soil burial test was conducted with the purpose of studying biodegradation of composites in natural conditions using garden soil [25]. the garden soil used contained a balance of three soil materials namely silt, sand and clay with humus. it has a ph of 6-6.5 and high calcium levels because of its previous organic matter content. rectangular samples (20 x 20 x 0.1 mm3 dimension) were kept in a desiccator until a constant weight (w1) was achieved. the samples were buried in garden soil at a depth of 170-220 mm from the soil surface for durations of 1-8 weeks. the soils were sprayed with water every 24 hours to maintain its moisture. after selected durations, samples were washed with water to remove the soil from the surface of samples and dried at 55ºc in vacuum oven and was weighed to a constant weight (w2). the percent weight loss (wl) was calculated according to equation (2). wl (%)= [(w1 –w2) / w1] x 100 (2) 3. results and discussion 3.1 fourier transform infrared spectroscopy ftir spectroscopy is an indispensable technique and relatively simple method to obtain information on any possible changes in the chemical structure of the chitin after undergoing chemical acid hydrolysis to produce chw. ftir spectra of various types of chw (fchw, cchw and tfchw) are shown in fig. 1 and their vibrational assignments are summarized in table 1. 243 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 fig.1: ftirspectra of fchw, cchw and tfchw. table 1:ftir spectra peak assignments for chitin whiskers (fchw, cchw and tfchw). peak assignment peak frequency (cm-1) fchw cchw tfchw o-h groups 3419 3388 3428 n-h stretching 3106 3104 3110 c-h stretching 2923 2883 2869 c=o (amide i) 1630 1637 1641 c=o (amide ii) 1557 1548 1545 c-h bending 1473 1380 1372 c-n groups 1384 1308 1317 c–o stretching 1112 1074 1024 n-h bending 722 762 713 based on the ftir spectra, all samples showed similar absorption bands at two main absorbance regions around 1600 cm-1 and 2800-3500 cm-1 indicating that all samples have similar chemical compositions. the characteristic carbonyl (c=o) stretching around 1640 cm-1 is attributed to the carbonyl vibrations of amide functional group. some of the carbonyl groups (amide i) are bonded through hydrogen bonds to the amino group inside the same chain (c=o---h-n) that is responsible for the vibration mode at around 1640 cm1 while the rest creates similar bond with –ch2oh from the side chain. this additional bond created the slightly lower peak of amide ii at around 1560 cm-1. the existence of these interchain bonds is responsible for the high chemical stability of the α-chitin structure [1,28,29]. the presence of amide group was further strengthened by appearance of c-n absorption band at around 1370 cm-1 and n-h bending around 720-770 cm-1. in the corresponding region of the oh and nh (3600–3000 cm-1) groups, all samples exhibit similar vibrational stretching peaks. this is attributed to the different packing 244 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 arrangements of the macromolecules. the shoulder that appears in the spectrum at 3426 cm-1 is attributed to the intramolecular hydrogen bond involving the oh on carbon 6 and carbonyl oxygen (oh (6)---o=c). the band appears at 3315 cm-1 corresponds to the intramolecular hydrogen bond (oh (3)---o(5) from the ring). the bands at 3100-3270 cm1 are assigned to the vibrational assignments of the nh of the amide (intermolecular hydrogen bond c=o—h-n and the nh groups intramolecularly bonded by h). similar observations have been reported in the study of chitin from shrimp, prawn, king crab, squid and lobster [30]. the ftir spectra of all samples displayed similar absorption bands denoting that there is no significant difference between thechw from various sources of chitin and that the hydrolysis process was successful in producing chw and did not alter the chemical structures. the hydrolysis done in a controlled condition as shown in this study was able to protect the chemical groups of chitin. on another note, it is envisaged that the milder fermentation treatment during production of fermented chitin (fc) could protect the polymeric structure of chitin which in turn will produce a higher aspect ratio chitin nanowhiskers (fchw). 3.2 transmission electron microscopy transmission electron microscopy (tem) was performed to confirm the separation of individual crystallites into nanowhiskers. tem is considered a powerful technique in characterization of nanomaterials. the analysis of the suspension of fchw, cchw and tfchw shown in fig. 2 (a)-(c) revealed some changes in the morphological features of the chitin after the acid hydrolysis treatment. as anticipated, tem images showed the typical rod-like nanoparticles for fchw, cchw and tfchw confirming that the treatment used was successful in producing the individual rod-like chitin nanowhiskers. interesting observations can be seen on the size differences of various chw. fig.2: tem of a) fchw, b) cchw and c) tfchw. the average sizeof fchw was found to be more than 500 nm in length and 10 nm in width as compared to cchw which recorded about 300 nm in length and 10 nm in width. 245 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 meanwhile when the fermented chitin was chemically treated prior to hydrolysis to form whiskers, the width of tfchw was found to be shorter than fchw which is about 300 nm length and 20 nm widths in average. the extra chemical pretreatment of fermented chitin had probably shortened the polymeric chitin chain, hence producing a shorter cchw. based on the usual trend of the positive effect of using higher aspect ratio chw, the slightly higher aspect ratio of fchw is expected to give comparable if not a betterr einforcing performance as fillers in pla compared to using chw from commercial chitin source (cchw). it is also interesting to note that fchw displayed many individual whiskers as compared to aggregated and stacked whiskers in cchw and tfchw. this characteristic may produce a better reinforcement to the pla matrix. 3.3 tensile properties of pla nanocomposites the effects of fchw, cchw and tfchw content on the tensile strength, elongation at break and young’s modulus of pla/fchw, pla/cchw and pla/tfchw composites are shown in fig. 3, 4 and 5, respectively. figure 3 shows that incorporation of all types of chw showed an increase in tensile strength of the nanocomposites as compared to pure pla (11.95 mpa). for all nanocomposite samples, the tensile strength increased until a maximum value before it started to decrease. the maximum values differ for each nanocomposite. the maximum values are 1, 2 and 3 phr for pla/fchw (17 mpa), pla/tfchw (12 mpa) and pla/cchw (21 mpa) respectively. the highest value is pla/cchw nanocomposite, which increased by 91% at 3 phr compared to pure pla. this is followed by pla/fchw by 54% at 1 phr and 36% increment for pla/tfchw at 2 phr content. however, the trend between pla/fchw and pla/cchw were different after 2 phr, whereby the tensile strength of pla/cchw continued to increase until it reached the maximum value at 3 phr. the tensile strength of pla/fchw on the other hand decreased after 2 phr. fig. 3: effect of fchw, cchw and tfchw content on tensile strength of pla/fchw, pla/cchw and pla/tfchw. fig. 4: effect of fchw, tfchw and cchw content on elongation at break of pla/fchw, pla/tfchw and pla/cchw. the general improvement in the tensile strength of nanocomposites indicates that there is a good interfacial adhesion between the fillers (fchw, cchw and tfchw) with pla matrix leading to good stress transfer between the matrix and fillers. this is likely due to the good dispersion of fillers, stiffness of the fillers and existence of hydrogen bonding between n-h group on chw and the lone pair of electrons on c=o of pla matrix. in addition hydrogen bonds may also formed between terminal hydroxyl group of pla and c=o of chw (fig. 6). 246 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 fig.5: effect of fchw, tfchw and cchw content on young’s modulus of pla/fchw, pla/tfchw and pla/cchw. fig. 6: possible intermolecular interactions between pla and chw. the formation of hydrogen bonding was also reported when cellulose nanowhiskers (cnw) were used as fillers in pla nanocomposites due to the presence of polar o-h groups on cnw backbone chain [31]. cellulose and chitin have the same molecular structure except for replacement of oh on carbon-2 with an acetyl amino (amide) group. hence, a slightly lower intermolecular attraction between chw with pla is expected with chw due to fewer amounts of oh groups on chw. as mentioned earlier, after the optimum filler content, the tensile strength for all nanocomposites decreased. the most likely reason is due to agglomeration among the whiskers of fchw, cchw and tfchw in pla when their content increases since hydrogen bonding between chw-chw molecules is more likely to form with increasing filler content. these filler-filler interactions reduce the level of filler-matrix interactions in the system. the aggregation of the filler could act as stress-centralized point and reduced surface area of interaction between filler and matrix leading in an inefficient transfer of stress from matrix to fillers resulting in low tensile strength values of pla nanocomposites. similar observation of reduction in strength after a certain filler content has been reported in many previous studies on pla nanocomposites [7,32]. in terms of comparison between types of chw from different sources, it can be concluded that cchw had the highest increase compared to fchw and tfchw. cchw is a pure chitin whereas fchw had slight impurities of protein and minerals due to the incomplete purification of chitin during fermentation method. as for the tfchw, it was too purified such that the polymeric chitin may have been shorthened and may have affected the resulting tensile strength of the nanocomposites. besides its poorer performance, usage of tfchw is also not cost effective as it needed to undergo an extra 247 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 chemical treatment prior to production of chw. fchw is a promising material for reinforcement of pla as it does increase the tensile strength of pla and also relatively lower cost to produce fchw compared to cchw since fermented chitin is a by-product of fermentation of prawn waste for the production of protein. in fig. 4, results of elongation at break for pla/fchw, pla/tfchw and pla/cchw show that the elongation at break of the nanocomposites decreased upon the addition of fchw, tfchw and cchw fillers into the pla matrix which indicates an enhancement in brittleness of the nanocomposites. it was observed that the decrease is more dramatic for pla/fchw and pla/tfchw nanocomposites at 1 phr. at 2 phr, the elongation of break values is almost similar. overall, it can be said that pla/fchw nanocomposites is the most brittle with 4 % elongation at break for 4 phr fillers content. the decrease in ductility upon addition of fillers were reported previously in many studies on pla nanocomposites [7,25]. the reason for the decrease is that stiff reinforcements of chitin nanowhiskers had probably caused substantial local stress concentrations and failure at reduced strain. the local stress concentration can be affected by volume fraction of the added reinforcement, dispersion of the reinforcement in the matrix, and interaction between the reinforcement and the matrix [33]. the other possible reason is due to the stiffening action of chitin nanowhiskers restricting the segmental chain movement of pla. the young’s modulus of pla/fchw, pla/tfchw and pla/cchw increased with increasing of fchw, tfchw and cchw content respectively (fig. 5). the increase in the modulus with increasing chw content can be explained by increased in hydrogen bond interaction, stiffening effect and high crystallinity index of the chw filler which are the typical characteristics of polymer/filler composites. similar findings have been reported in the physicochemical and mechanical properties study of pla/cellulose nanowhiskers nanocomposites [34-36]. it is noted that the modulus continue to increase with increasing filler content while the tensile strength increase to a maximum value, after which it decreased due to filler agglomeration. the continued increase in modulus can be explained by the fact that modulus is measured at low strain and weak van der waals forces are sufficient to bond the fillers and matrix. therefore modulus is not affected by filler agglomeration which happens at higher filler content. these weak bonds can transfer the stress between fillers and polymer; therefore showing a higher modulus at small strains[37]. the mechanical properties of nanocomposites is dependent on several factors including: i) adhesion between the pla matrix and reinforcements, ii) stress transfer efficiency of the interface; iii) volume fraction of the fibers; iv) aspect ratio of the reinforcements; v) fiber orientation; and vi) the degree of crystallinity of the matrix [38]. the higher tensile strength of the nanocomposites compared to pure pla can be explained based on the aspect ratio of the three chw. all three types of the chw possess rod-like structures or whiskers which has high aspect ratios. the high aspect ratio would increase the effectiveness of stress transfer efficiency at the interface between the matrix and the reinforcement. it is possible in cases where the adhesion is relatively poor, effective stress transfer can still occur due to high aspect ratio of the reinforcement. 3.4 thermogravimetric analysis the addition of fillers into pla could help to increase the temperature region where pla can be used. the tga and dtg curves reveal the weight loss of material as it is heated. figure7(a)-(c) shows the tga and dtg (derivative thermograms) of pure pla and its nanocomposites with various fchw, cchw and tfchw content. the tga and 248 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 (a) dtg curves of neat pla and all pla nanocomposites show a similar decomposition pattern of one-step degradation process represented by a single peak in dtg curve. it can be observed that all samples showed initial weight loss at approximately 100°c. the weight loss was a result of evaporation of moisture and was previously reported in the study of pla-cellulose whiskers composites [5,36]. table 2 summarized the thermal stability pla and nanocomposites based on t20 and tmax values. t20 is the temperature at which 20% of the nanocomposites has decomposed while tmax is the temperature at which the rate of decomposition is highest. both t20 and tmax can be used to determine the thermal stability of the nanocomposites. interestingly based on t20 and tmax, thermal stability of pla nanocomposites for all types of chw were seen to be significantly higher than pure pla. based on t20 values, all the three nanocomposites have almost similar values with pla/tfchw at 3phr being the highest at 355°c, which is 15 degrees higher than pla. this can be considered a significant improvement due to the incorporation of chw and is effective in enhancing the thermal stability. pla/fchw and pla/cchw havesimilarhighest values at 353°c, which is slightly lower than pla/tfchw. meanwhile for tmax, the highest was obtained at 371oc by pla/fchw4, 13 degrees higher than pure pla which is also quite significant. for the cchw, the maximum values are slightly lower at 367oc and tmax reaching maximum values at 3 phr chw content. however, the maximum values for pla/tfchw occurred at 1phr chw content. fig.7: tga and dtg curve of a) pla/fchw, b) pla/cchw and c) pla/tfchw. (c) (b) 249 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 from the tga of pla and the pla/chw nanocomposites, it can be concluded that all the three chw types are effective in enhancing thermal stability of pla nanocomposites. this improvement can be due to the good physical interaction between the pla and chw. beside that, the improvement in thermal stability could also be attributed to the uniform dispersion of the chw in pla matrices resulting in an increase in tortuous path for the [39-40] transfer-outmigration of degraded volatiles to the surface, thus retarding the decomposition rate [41]. previous studies on cellulose/mmt nanocomposites also reported similar results [41-43]. from the overall results, it is difficult to conclude which type of chw is the most effective in enhancing the thermal stability of pla/chw nanocomposites. it can however be said that the chw from the fermented chitin are not inferior compared to the chw from commercial chitin. table 2:effectof chw on thermal stability of pla nanocomposites 3.5 biodegradability and water absorption properties an increase in biodegradability and mechanical strength at lower cost are advantage for the application of pla/chw as packaging materials. the effects of chw source and content on biodegradability and water absorption properties of pla/chw nanocomposites are discussed together in this section since both properties are interrelated.the biodegradability of pla, pla/fchw, pla/cchw and platfchw were conducted using soil burial test. the weight loss of pla, pla/fchw, pla/cchw and pla/tfchw were collected for duration ranging from 14 to 56 days and are shown in table 3. it can be seen that the biodegradability as indicated by the weight loss of all nanocomposites samples were higher than pure pla at all durations. this is attributed to the presence of chitin materials on the surface of the samples which attract the microorganisms such as fungi to consume this material as nutrient source. it was also noted that prolonging the burial time lead to higher weight loss, which is as expected. pure pla hardly showed any weight loss after 14 days unlike the nanocomposites which had started to show some weight loss, especially pla/cchw and pla/tfchw. it was reported that the degradation of pure pla in soil is slow and it takes a long time for degradation to start, probably because of the low temperature and water content and the formulation degradation temperature (°c) t20 tmax pla 340 358 pla/fchw1 342 363 pla/fchw2 345 362 pla/fchw3 342 362 pla/fchw4 353 371 pla/cchw1 348 363 pla/cchw2 347 359 pla/cchw3 353 367 pla/cchw4 328 360 pla/tfchw1 353 367 pla/tfchw2 315 363 pla/tfchw3 355 365 pla/tfchw4 341 366 250 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 relative scarcity of pla degrading organisms [44]. however, in a composting environment, the pure pla is able to be hydrolyzed into smaller molecules after 45-60 days at 50-60°c. it was also observed that biodegradability increased with increasing in the filler content for all types of nanocomposites. the highest weight loss was recorded at 4 phr chw content for all types of nanocomposites with pla/cchw4 having the highest at 3.29% and pla/fchw4 the lowest at 2.28%. the increasing chw content will increase chances for chitinolytic microorganismsto consume the chw as well as increasingthe interaction of chw with water, thus increasing the biodegradation process. therefore the ability of water to diffuse into the polymer matrix has a strong influence on the rate of degradation of pla [45]. the degradation occurs by firstly water being diffused into the material followed by hydrolysis of c-o ester bonds and lowering of molecular weight. rates of hydrolysis increase with water content and temperature and are catalyzed by free carboxyl groups of the hydrolyzed pla ends. hydrolysis occurred faster in the interior of a thick sample since carboxylic acid concentration is higher than the exterior due to leaching of the acidic pla oligomers into the surrounding aqueous medium [46]. table 3:water absorption of pla nanocomposites (%) formulation water absorption (%) 2 hours 24 hours pla 0.00 ± 0.09 0.30 ± 0.09 pla/fchw1 1.90 ± 0.10 3.03 ± 0.09 pla/fchw2 3.40 ± 0.10 3.59 ± 0.03 pla/fchw3 3.60 ± 0.10 3.74 ± 0.07 pla/fchw4 4.70 ± 0.64 5.86 ± 0.18 pl/cchw1 2.00 ± 0.10 2.97 ± 0.05 pla/cchw2 3.17 ± 0.15 3.20 ± 0.12 pla/cchw3 4.04 ± 0.25 4.84 ± 0.27 pla/cchw4 7.07 ± 0.52 9.35 ± 0.37 pla/tfchw1 1.38 ± 0.06 1.94 ± 0.07 pla/tfchw2 2.27 ± 0.10 2.68 ± 0.02 pla/tfchw3 2.51 ± 0.03 2.73 ± 0.03 pla/tfchw4 2.77 ± 0.11 5.15 ± 0.24 in a study by rosdi and zakaria [48] on the effect of chitin particles on degradation of pla by soil burial test for duration of 10 weeks showed weight losses of 7.5% at 56 days which is higher compared to using chw from the present study. however the study showed that addition of chitin particles did not improve the mechanical properties of pla [47] as compared to the increase of strength with the incorporation chw in the present study. from the soil burial test, it can be concluded cchw is more effective than fchw in promoting the degradation of pla but not significantly higher. the plausible reason is the purity of cchw as compared to fchw which was derived from fermented chitin. in the previous study on pla and pla/cellulose nanowhiskers from oil palm empty fruit bunch, it was also found that the incorporation cnw promotes the biodegradability of pla [36]. for 5 phr of cnw, the weight loss after 56 days of soil burial is 2.1% which is less than pla/cchw4 reported in this study which is 3.3%. overall it can be concluded that chw has the potential to degrade pla faster compared to cellulose nanowhiskers. 251 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 the water absorption of pla, pla/fchw, pla/cchw and pla/tfchw after 2h and 24h immersion in distilled water at ambient temperature are shown in table 4. as expected, amount of water absorption increased with time for pla and all pla/chw nanocomposites. it was also observed that the amount of water absorption increased with increasing filler content for all types of chw. similar to the biodegradability results, pla/cchw again showed the highest water absorption at 9.35% after 24h which is around 80% higher than pla/fchw and pla/tfchw. materials with higher water absorptivity displayed better biodegradability mainly due to the fact that hydrophilic material will allow micro-organism to penetrate into the material, further accelerate the breakdown of polymer matrix and increased the degradation process [27]. higher water absorption will also enable micro-organisms such as fungi and bacteria to use the chw as their nutrient source. from both studies, it can be seen the higher the water absorption the faster the biodegradation of the composites. comparing the pla/cchw and pla/fchw provides new knowledge on their potential as biodegradable packaging materials. table 4: weight loss of pla nanocomposites (%) formulation weight loss (%) 14 days 28 days 42 days 56 days pla 0.02 ± 0.01 0.267 ± 0.01 0.34 ± 0.01 0.88 ± 0.02 pla/fchw1 0.05 ± 0.03 0.337 ± 0.03 0.838 ± 0.03 1.47 ± 0.02 pla/fchw2 0.36 ± 0.01 0.783 ± 0.01 1.375 ± 0.06 1.67 ± 0.03 pla/fchw3 0.42 ± 0.06 0.955 ± 0.06 1.61 ± 0.05 1.98 ± 0.03 pla/fchw4 0.44 ± 0.01 1.32 ± 0.02 1.87 ± 0.03 2.28 ± 0.03 pla/cchw1 0.87 ± 0.02 1.10 ± 0.02 1.44 ± 0.02 1.77 ± 0.03 pla/cchw2 1.15 ± 0.02 1.33 ± 0.02 2.13 ± 0.03 2.57 ± 0.10 pla/cchw3 1.48 ± 0.01 1.67 ± 0.03 2.34 ± 0.01 2.85 ± 0.02 pla/cchw4 1.83 ± 0.02 2.09 ± 0.09 2.77 ± 0.03 3.29 ± 0.01 pla/tfchw1 0.88 ± 0.02 1.17 ± 0.01 1.54 ± 0.02 1.85 ± 0.03 pla/tfchw2 1.33 ± 0.02 1.33 ± 0.01 1.75 ± 0.02 2.07 ± 0.07 pla/tfchw3 1.48 ± 0.02 1.88 ± 0.02 2.02 ± 0.01 2.30 ± 0.05 pla/tfchw4 1.77 ± 0.03 2.36 ± 0.06 2.75 ± 0.05 2.89 ±0.01 4. conclusion the objective of this study is tocompare the properties pla/chw nanocomposites in which the source of chw are different, which are commercial chitin and fermented chitin. tensile strength for all nanocomposites increased with increasing filler content until it reached a certain maximum value while young’s modulus increased with increasing filler content. however, elongation at break decreased with increasing filler content for all types of nanocomposites. tga results indicated that the all nanocomposites displayed better thermal stability as compared to pure pla. the addition of fchw, cchw and tfchw into pla improved the biodegradability of pla. the water absorption of all nanocomposites also increased with increasing filler content.the overall results confirm that pla nanocomposites from fc are not inferior than pla nanocomposites from cc and therefore has similar potential to be developed into eco-friendly packaging materials. the future areas of investigation are to further improve the mechanical properties. the ductility can be improved by using plasticisers and hybridization with other nanofillers such as graphene will help to enhance the modulus and strength. 252 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 acknowledgement the authors would like to thank universiti teknologi malaysia (utm) for the research facilities and ministry of higher education malaysia for financial support through frgs grant 4f377. references [1] rinaudo, m. (2006). chitin and chitosan: properties and applications. progress in polymer science, 31(7):603–632. https://doi.org/10.1016/j.progpolymsci.2006.06.001 [2] mincea m, negrulescu a, ostafe v. (2012). preparation, modification, and applications of chitin nanowhiskers: a review. reviews on advanced materials science, 30:225–242. [3] azizi samir mas, alloin f, dufresne a. (2005). review of recent research into cellulosic whiskers, their properties and their application in nanocomposite field. biomacromolecules, 6:612-626. [4] oksman k, mathew ap, bondeson d, kvien i. (2006). manufacturing process of cellulose whiskers/polylactic acid nanocomposites. composites science and technology, 66(15):2776–2784. https://doi.org/10.1016/j.compscitech.2006.03.002 [5] petersson l, kvien i, oksman k. (2007). structure and thermal properties of poly(lactic acid)/cellulose whiskers nanocomposite materials. composites science and technology, 67(11–12):2535–2544. https://doi.org/10.1016/j.compscitech.2006.12.012 [6] eichhorn sj, dufresne a, aranguren m, marcovich ne, capadona jr, rowan sj, weder c, thielemans w, roman m, renneckar s, gindl w, veigel s, keckes j, yano h, abe k, nogi m, nakagaito an, mangalam a, simonsen j, benight as, bismarck a, berglund la, peijs t. (2010). review: current international research into cellulose nanofibres and nanocomposites. journal of material science, 45:1-33. https://doi.org/10.1007/s10853-0093874-0 [7] haafiz mkm, hassan a, zakaria z, inuwa i, islam ms, jawaid m. (2013). properties of polylactic acid composites reinforced with oil palm biomass microcrystalline cellulose. carbohydrate polymers, 98(1):139–145. https://doi.org/10.1016/j.carbpol.2013.05.069 [8] nair kg, dufresne a. (2003). crab shell chitin whisker reinforced natural rubber nanocomposites. 1. processing and swelling behavior. biomacromolecules, 4(3):657–665. [9] nishino t, matsui r, nakamae k. (1999). elastic modulus of the crystalline regions of chitin and chitosan. journal of polymer science part b: polymer physics, 37(11):1191– 1196.https://doi.org/10.1002/(sici)1099-0488(19990601)37:11<1191::aidpolb13>3.0.co;2-h [10] vincent jfv, wegst ugk. (2004). design and mechanical properties of insect cuticle. arthropod structure and development, 33:187–199. https://doi.org/10.1016/j.asd.2004.05.006 [11] luckachan ge, pillai cks. (2011). biodegradable polymersa review on recent trends and emerging perspectives. journal of polymers and the environment, 19(3):637–676. https://doi.org/10.1007/s10924-011-0317-1 [12] singh ak, sharma l, mallick n, mala j. (2017). progress and challenges in producing polyhydroxyalkanoate biopolymers from cyanobacteria. journal of applied phycology, 29(3):1213–1232. https://doi.org/10.1007/s10811-016-1006-1 [13] yates mr, barlow cy. (2013). life cycle assessments of biodegradable, commercial biopolymers—a critical review. resources, conservation and recycling, 78:54–66. https://doi.org/10.1016/j.resconrec.2013.06.010 [14] gandini a, lacerda tm. (2015). from monomers to polymers from renewable resources: recent advances. progress in polymer science, 48:1-39. https://doi.org/10.1016/j.progpolymsci.2014.11.002 [15] pretula j, slomkowski s, penczek s. (2016). polylactides-methods of synthesis and characterization. advanced drug deliveries reviews, 107:3-16. https://doi.org/10.1016/j.addr.2016.05.002 253 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 [16] madhavan nampoothiri k, nair nr, john rp. (2010). an overview of the recent developments in polylactide (pla) research. bioresource technology, 101(22):8493–8501. https://doi.org/10.1016/j.biortech.2010.05.092 [17] coltelli m, cinelli p, gigante v, aliotta l, morganti p, panariello l, lazzeri a. (2019). chitin nanofibrils in poly(lactic acid) (pla) nanocomposites: dispersion and thermomechanical properties. international journal of molecular sciences, 20(3):504-523. https://doi.org/10.3390/ijms20030504 [18] rizvi r, cochrane b, naguib h, lee, p.c. (2011). fabrication and characterization of meltblended polylactide-chitin composites and their foams. journal of cellular plastics, 47:283. https://doi.org/10.1177/0021955x11402549 [19] zeng, j.b., he, y.s., li, s.l. and wang, y.z., (2012). chitin whiskers: an overview. biomacromolecules, 13(1):1–11. https://doi.org/10.1021/bm201564a [20] zhang, q., wei, s., huang, j., feng, j., & chang, p. r. (2014). effect of surface acetylatedchitin nanocrystals on structure and mechanical properties of poly (lactic acid). journal of applied polymer science, 131(2):2-9.https://doi.org/10.1002/app.39809 [21] singh s, maspoch ml, oksman k. (2019). crystallization of triethyl-citrate-plasticized poly (lactic acid) induced by chitin nanocrystals. journal of applied polymer science, 136(36): 47936. https://doi.org/10.1002/app.47936 [22] liu, w., zhu, l., ma, y., ai, l., wen, w., zhou, c. and luo, b. (2019). well-ordered chitin whiskers layer with high stability on the surface of poly (d,l-lactide) film for enhancing mechanical and osteogenic properties. carbohydrate polymers, 212:277-288. https://doi.org/10.1016/j.carbpol.2019.02.060 [23] liu, h., liu, w., luo, b., wen, w., liu, m., wang, x. and zhou, c. (2016). electrospun composite nanofiber membrane of poly(l-lactide) and surface grafted chitin whiskers: fabrication, mechanical propertiesand cytocompatibility, carbohydrate polymers, 147:216225. https://doi.org/10.1016/j.carbpol.2016.03.096 [24] coltelli, m., aliotta, l., vannozzi, a., morganti, p., panariello, l., danti, s., neri, s., fernandez-avila, c., fusco, a., donnarumma g, lazzeri a. (2020). properties and skin compatibility of films based on poly(lactic acid) (pla) bionanocomposites incorporating chitin nanofibrils (cns), journal of functional biomaterials,11(2):21-43. https://doi.org/10.3390/jfb11020021 [25] zakaria z, hall gm, and shama g. (1998). lactic acid fermentation of scampi waste in a rotating horizontal bioreactor for chitin recovery, process biochemistry, 33:1-6. https://doi.org/10.1016/s0032-9592(97)00069-1 [26] zulkeple nm, zakaria z, hamdan s, abdul manaf ms. (2011). fermentation of prawn waste by using effective microorganism (em) for protein production. journal of fundamental sciences, 7(2):108-112. [27] chuayjuljit s, su-uthai s, tunwattanaseree c, charuchinda s. (2009). preparation of microcrystalline cellulose from waste-cotton fabric for biodegradability enhancement of natural rubber sheets. journal of reinforced plastics and composites, 28:1245–1254. https://doi.org/doi 10.1177/0731684408089129 [28] lavall rl, assis obg, campana-filho sp. (2007). beta-chitin from the pens of loligo sp.: extraction and characterization. bioresource technology, 98(13):2465–2572. https://doi.org/10.1016/j.biortech.2006.09.002 [29] pereira agb, muniz ec, hsieh yl. (2014). chitosan-sheath and chitin-core nanowhiskers. carbohydrate polymers, 107:158–166.https://doi.org/10.1016/j.carbpol.2014.02.046 [30] cárdenas g, cabrera g, taboada e, miranda sp (2004). chitin characterization by sem, ftir, xrd and 13c cross polarization/mass angle spinning nmr. journal of applied polymer science, 93(4):1876–1885. https://doi.org/10.1002/app.20647 [31] wang y, cao x, zhang l. (2006). effects of cellulose whiskers on properties of soy protein thermoplastics. macromolecular bioscience, 6(7):524–531. https://doi.org/10.1002/mabi.200600034 [32] arjmandi r, hassan a, haafiz mkm, zakaria z. (2015). effect of microcrystalline cellulose on biodegradability, tensile and morphological properties of montmorillonite 254 iium engineering journal, vol. 21, no. 2, 2020 mohd asri et al. https://doi.org/10.31436/iiumej.v21i2.1469 reinforced polylactic acid nanocomposites. fibers and polymers, 16 (10):2284–2293. https://doi.org/10.1007/s12221-015-5507-3 [33] pei a, zhou q, berglund la. (2010). functionalized cellulose nanocrystals as biobased nucleation agents in poly (l-lactide)(plla)–crystallization and mechanical property effects. composites science and technology, 70(5):815-821. https://doi.org/10.1016/j.compscitech.2010.01.018 [34] zakir km, ifty h, andrew a,rudd cd. (2012). physico-chemical and mechanical properties of nanocomposites prepared using cellulose nanowhiskers and poly (lactic acid). journal of materials science, 47(6):2675–2686.https://doi.org/10.1007/s10853-011-6093-4 [35] hong j,kim ds. (2013). preparation and physical properties of polylactide/cellulose nanowhisker/nanoclay composites. polymer composites, 34(2):293–298. https://doi.org/10.1002/pc.22413 [36] haafiz mkm, hassan a, khalil h, fazita m, islam ms, inuwa i, marliana m, hussin m. (2016). exploring the effect of cellulose nanowhiskers isolated from oil palm biomass on polylactic acid properties. international journal of biological macromolecules, 85:370–378. https://doi.org/10.1016/j.ijbiomac.2016.01.004 [37] bikiaris d. (2010). microstructure and properties of polypropylene/carbon nanotube nanocomposites. materials, 3(4):2884-2946. [38] dufresne a, dupeyre d, paillet m. (2002). lignocellulosic flour-reinforced poly(hydroxybutyrate-co-valerate) composites. journal of applied polymer science, 87:1302–1315. https://doi.org/10.1002/app.11546 [39] lim jw, hassan a, rahmat ar, wahit mu. (2006). morphology, thermal and mechanical behavior of polypropylene nanocomposites toughened with poly (ethylene-co-octene). polymer international, 55(2):204-215. https://doi.org/10.1002/pi.1942 [40] majeed k, hassan a, bakar aa, jawaid m. (2016). effect of montmorillonite (mmt) content on the mechanical, oxygen barrier, and thermal properties of rice husk/mmt hybrid filler-filled low-density polyethylene nanocomposite blown films. journal of thermoplastic composite materials, 29(7):1003-1019. [41] ray ss, okamoto m. (2003). biodegradable polylactide and its nanocomposites: opening a new dimension for plastics and composites. macromolecular rapid communications, 24(14):815-840. [42] cerruti p, ambrogi v, postiglione a, rychlý j, matisová-rychlá l, carfagna c. (2008). morphological and thermal properties of cellulose−montmorillonite nanocomposites. biomacromolecules, 9(11):3004-3013. https://doi.org/10.1021/bm8002946 [43] delhom cd, white-ghoorahoo la, pang ss. (2010). development and characterization of cellulose/clay nanocomposites. composites part b: engineering, 41(6):475-481. [44] karamanlioglu m, preziosi r, robson gd. (2017). abiotic and biotic environmental degradation of the bioplastic polymer poly (lactic acid): a review. polymer degradation and stability, 137:122-130. [45] elsawy ma, kim kh, park jw, deep a. (2017). hydrolytic degradation of polylactic acid (pla) and its composites. renewable and sustainable energy reviews. 79:1346-1352. https://doi.org/10.1016/j.rser.2017.05.143 [46] shogren r, doane w, garlotta d, lawton j, willett j. (2003). biodegradation of starch/polylactic acid/poly (hydroxyester-ether) composite bars in soil. polymer degradation and stability, 79:405–411. [47] rosdi n, zakaria z. (2016). biodegradability properties on chitin/polylactic acid composite films. eproceedings chemistry. universiti teknologi malaysia. 1:48-52. 255 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <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> /suo <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> /sve <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> /tur <feff0130015f006c006500200069006c00670069006c0069002000620065006c00670065006c006500720069006e0020006700fc00760065006e0069006c0069007200200062006900e70069006d006400650020006700f6007200fc006e007400fc006c0065006e006d006500730069006e0065002000760065002000790061007a0064013100720131006c006d006100730131006e006100200075007900670075006e002000410064006f006200650020005000440046002000620065006c00670065006c0065007200690020006f006c0075015f007400750072006d0061006b0020006900e70069006e00200062007500200061007900610072006c0061007201310020006b0075006c006c0061006e0131006e002e0020004f006c0075015f0074007500720075006c0061006e002000500044004600200064006f007300790061006c0061007201310020004100630072006f006200610074002000760065002000410064006f00620065002000520065006100640065007200200036002e003000200076006500200073006f006e00720061006b00690020007300fc007200fc006d006c0065007200690079006c00650020006100e70131006c006100620069006c00690072002e> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 156-871-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abdualkader et al. 1 some biological activities of malaysian leech saliva extract abdualrahman m.abdualkader* 1 , ahmed merzouk*, abbas mohammed ghawi** and mohammed alaama* * pharmaceutical chemistry department, **basic medical science department, kulliyyah of pharmacy, international islamic university malaysia , jalan istana 25200, kuantan, pahang, malaysia. 1 armak1983@gmail.com abstract: leeches were fed on the phagostimulatory solution through parafilm membrane. the satiated leeches were forced to regurgitate the solution by soaking them in an ice-container. the anticoagulant activity was ascertained using thrombin time assay (tt). the result revealed that the saliva concentration which increases tt by 100% (ic100) is 43.205 µg/ml plasma. the antimicrobial activity of the saliva was tested against several bacterial spp. (e. coli, p. aeruginosa, b. cereus, sal. typhi and s. aureus) and fungi spp. (c.albicans and c.neoformans). it was found that saliva has an inhibition activity against sal. typhi (minimal inhibitory concentration mic 78.253 µg/ml), s.aureus (mic 78.253 µ g/ml) and e .coli (mic 121.256 µ g/ml). abstrak: pacat-pacat diberi makan larutan phagostimulatory menerusi membran parafilem. pacat-pacat yang kekenyangan itu dipaksa memuntahkan larutan tersebut dengan direndam di dalam bekas berisi ais. aktiviti antigumpal ditentukan menggunakan cerakin masa trombin (tt). keputusan menunjukkan kepekatan air liur pacat menyebabkan pertambahan tt sebanyak 100% (ic100) iaitu 43.205 µ g/ml plasma. aktiviti antimikrob air liur telah diuji dengan pelbagai jenis bakteria (e. coli, p. aeruginosa, b. cereus, sal. typhi dan s.aureus) dan pelbagai jenis kulat (c. albicans dan c. neoformans). didapati air liur menghasilkan aktiviti perencatan terhadap sal.typhi (kepekatan perencat minima (minimal inhibitory concentration – mic) 78.253 µg/ml), s. aureus (mic 78.253 µ g/ml) dan e. coli (mic 121.256 µ g/ml). keywords: leech; anticoagulant; thrombin time; antibacterial activity 1. introduction over the years, the extremely hazardous blood and infectious diseases have been of a big concern of many researchers looking for new efficacious remedies and treatments. besides, leeches have been reputed to have important therapeutic applications in clinical medicine since the beginning of civilization. clinical usage of leech was outlined in pharoahs paintings, roman manuscripts and arabic islamic writings [1]. more recently, in the 18 th and 19 th centuries, leeches have been used for phelobotomy, inflammation remedy, rheumatism, plastic surgery and tissue transplantation [1, 2]. extensive researches had been undertaken during the 20 th century to isolate and characterize the active contents from leech saliva , especially peptides and proteins. in addition to the most potent antithrombin agent, hirudin which was previously discovered by haycraft in 1884 [3], many blood affecting peptides with different mechanisms of action have been identified. for example, calin [4], a platelet adhesion inhibitor, and iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abdualkader et al. 2 saratin [5], an inhibitor of von willebrand factor, were both isolated from the european hirudo medicinalis leech saliva extract. furthermore, other leech species have been fully investigated and many blood-affecting peptides and proteins have been identified. for instance, potent inhibitors of factor xa (fxa) lefaxin and antistasin were isolated from haementaria depressa and haementeria officinalis, respectively [6, 7]. fig. 1: feeding leeches on the phagostimulatory solution through parafilm membrane. on the other hand, two novel antibacterial peptides, theromacin and theromyzin, had been isolated from the coelomic liquid of the leech theromyzon tessulatum [8]. in malaysia, leeches have been widely used in traditional therapy for various diseases treatment, but scanty scientific researches were undertaken about medicinal malaysian leeches [9]. with this concept in mind, the anticoagulant and antimicrobial activity of malaysian leech saliva have been the subject of this investigation. 2. materials and methods 2.1 leeches sampling and saliva collection 2.1.1 leech sampling leeches were collected by a local supplier from fresh stream water in kuantan, pahang, then maintained in well-aerated plastic containers filled with non-chlorated tap water and kept in a separated room at room temperature. water was regularly changed every two days. 2.1.2 leech feeding starved leech was fed on the phagostimulatory solution of 0.001 m arginine in 0.15 m sodium chloride warmed at the desired temperature (37°c) [10]. then, a glass funnel was wrapped with parafilm sheets and filled with the phagostimulatory solution (fig. 1) [11]. thence, leech was brought nearby the parafilm and let to attach itself to it until the leech drops spontaneously. 2.1.3 extraction after the leech became fully satiated and detached itself from the parafilm, it was kept in a well-closed plastic test tube immersed in an ice container. after an incubation iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abdualkader et al. 3 period of 15-20 min in ice, the leech became completely paralyzed and regurgitated all the solution it had already sucked. then, leech was squeezed from the posterior end forwards in order to get out the remaining sucked solution. last, the used leeches regained their activity by immersing them in warm water (37°c) for 15-30 min. only the colorless fluids were pooled, filtered through 0.45 µm sartorius ® filter paper and then centrifuged at 4°c for 10 min at 3000 rpm. the resulted fluids were named the crude saliva extract, and only the fresh crude was used during the experiments, unless stated otherwise. 2.2 microbial strains reference strains of human pathogens were used including gram-positive bacterial spp. (bacillus cerues atcc25923 and staphylococcus aureus atcc25923), gramnegative bacterial strains (pseudomonas aeruginosa atcc27853, escherichia coli atcc35218 and salmonella typhi from institute for medical research (imr), ministry of health, malaysia) and two fungal strains (candida albicans atcc10231 and cryptococcus neoformans atcc90112). 2.3 chemicals and reagents parafilm was the product of american can company. bovine serum albumin (bsa) and arginine were purchased from sigma aldrich. merck was the producer of sodium chloride. in addition, bradford reagent kit was obtained from amresco inc. thromboclotin ® (thrombin reagent) and control n ® (control plasma) were purchased from siemens healthcare diagnostic. finally, mueller-hinton agar (mha) and mueller-hinton broth (mhb) were purchased from oxoid ltd., whereas potato dextrose agar (pda) and potato dextrose broth (pdb) were purchased from liofilchem. distilled water was used to prepare all solvents and solutions during all experiments. 2.4 total protein estimation the total protein concentration of the crude saliva extract was estimated using bradford assay procedures with bovine serum albumin (bsa) as a standard [12]. all procedures were performed according to amresco bradford reagent method, with a small modification including the usage of the phagostimulatory solution as a blank instead of 0.15 m sodium chloride. a series of standard solutions of bsa and three dilutions of the unknown crude saliva extract were prepared. and their a595 were measured in the presence of bradford reagent using infinite m200, nanoquant tecan multi detection microplate reader. 2.5 antithrombin activity in vitro the antithrombin activity was determined by thrombin time (tt) assay in vitro according to [13] and thromboclotin ® (thrombin reagent) manual using sysmex ca-50 coagulation analyzer. 2.5.1 citrated plasma preparation fresh human blood (4.5 ml) taken by venepuncture was mixed with sodium citrate in a citrate tube containing 0.5 ml of 0.11 mol/l sodium citrate (9 parts of blood : 1 part of sodium citrate) and then centrifuged at 3000 rpm and at room temperature for 10 min. the supernatant citrated plasma was taken and kept at 15-25°c to be used within four hours. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abdualkader et al. 4 2.5.2 thrombin reagent preparation one vial of thrombin reagent (thromboclotin ® ) was reconstituted with 10 ml distilled water. the resulted solution contains 2.5 nihu thrombin/ml and is stable for one week at 2-8°c (according to thromboclotin ® manual). 2.5.3 control plasma preparation one vial control plasma (control n ® ) was dissolved in 1.0 ml distilled water, shaken gently and let to stand for 15 min at 15-25°c. the reconstituted plasma is stable for 4 weeks at -20°c (according control n ® manual). 2.5.4 thrombin time assay an aliquot 100 µ l of citrated plasma was pipetted into a pre-warmed coagulation tube provided with the coagulometer and subsequently incubated at 37°c in the coagulation analyzer well for 3min. then, 10 µ l of the reconstituted thrombin reagent was added and the time until the coagulation starts was measured by the coagulometer. different dilutions of the crude saliva extract were mixed with the citrated plasma to yield a final volume of 100 µl and tt of the mixtures were measured as mentioned above. a control plasma test was always run before each experiment to evaluate the precision and accuracy of the reagents and the coagulation analyzer. 2.6 antimicrobial activity 2.6.1 disc diffusion test disc diffusion test was employed for the determination the anticipated antimicrobial activity of the crude saliva extract as previously stated in [14] with some modifications with the incubation period. 2.6.2 microdilution method microdilution method was performed as described in [14] with some modifications with the incubation period to detrmine the minimal inhibitory concentration (mic) which is the lowest concentration of the crude saliva extract that can inhibit the growth of a test organism. to fulfill the experiment, serial double-fold dilutions from the crude saliva extract were carried out in a sterile 96-well plate. briefy, 100 µ l of sterile meuller-hinton broth was pipetted into the first four columns wells of the plate. then, 100 µ l of the crude saliva extract was mixed with the broth in the first four wells of the first row of the plate. then, dilutions were made by transferring 100-µl aliquots of the mixture from the first four wells into the next four ones vertically, and so forth. subsquently, 10 µ l of the test organism (10 7 cfu/ml) was pipetted into each well of the first three columns and the plate was covered and incubated for 24 hours at 37°c [14]. 3. results 3.1 saliva collection the crude saliva extract collected from many leeches were presented in table 1. 3.2 total protein assay the total protein concentration of the crude saliva extract was estimated by plotting the a595 values of the bsa standard solutions as a function of their concentrations using microsoft excel 2007. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abdualkader et al. 5 table 1: the crude saliva extract collected from the starved leeches. no. starvation period (weeks) collected volume (ml) ph group 1 14 17 6.45 group 2 20 13 6.37 group 3 23 6.5 6.39 group 4 25 15 6.44 the total protein concentration of the crude saliva extract collected from the group 2 was 79.962±3.213 µg/ml . whereas, group 3 saliva had a total protein concentration of 62.602±2.517 µg/ml. all measurments were repeated in triplicates and the mean±standard deviation were considered. 3.3 antithrombin activity in vitro the crude saliva extract collected from group 2 was the subject of the antithrombin activity assay. results revealed that the antithrombin activity (tt prolongation) of the crude saliva extract was a linear function with the volume of the crude mixed with the citrated plasma. accordingly, the concentration of saliva in µ g/ml which increases the tt by 100% (ic100) can be calculated from the curve drawn from plotting saliva volumes (µl) versus thrombin time (sec). see fig. 2 and table 2. consequently, it was found that 54.033 µ l of the crude saliva extract can increase tt by two-folds, corresponding to an ic100 of 43.205 µg/ml plasma. 3.4 antimicrobial activity the antibacterial and antifungal activities of the fresh crude saliva extract and the lyophilized saliva collected from leech group 1,3 and 4 are presented in table 3. notably, the results showed that the fresh crude saliva extract collected after a starvation period of 14 weeks has a remarkable inhibitory activity against at least one of the test organisms (table 3). whereas, neither the fresh crude saliva extract collected from leeches starved for 23 weeks nor the ten-folds concentration of the lyophilized saliva extract collected after 25 weeks of starvation exhibited antimicrobial activity. mic of the lyophilized concentrated saliva extract which showed antibacterial activity against s. aureus and sal. typhi was 78.253 µ g/ml. whereas, mic of the saliva which possessed inhibition activity against e. coli was 121.256 µg/ml. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abdualkader et al. 6 table 2: the anticoagulant (antithrombin) activity of the crude saliva extract. sample volume thrombin time control n ® 100 17.10±1.97 a citrated plasma 100 16.57±0.90 blank (arg+nacl) 70 17.30±1.20 distilled water 70 17.97±0.99 crude saliva extract (group 2) 30 22.43±1.92 50 30.57±2.73 60 35.17±0.90 70 41.43±1.36 a results are expressed as the mean of triplicates ± standard deviation sd. fig. 2. a: the anticoagulant activity of crude saliva extract. the volume which duplicates tt was 54.033 µ l. so, ic100=43.205µg/ml plasma. all values are the mean of triplicates±sd. r 2 =0.989, y= 2.123x-16.31, where y=thrombin time (sec) and x=volume (µ l). b: thrombin time of the crude saliva extract and citrated plasma mixture in triplicates. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abdualkader et al. 7 table 3: the antimicrobial activity of the fresh and the lyophilized concentrated crude saliva extract. sample starvation period bacterial spp. fungal spp. s. aureus p. auroginosa sal. typhi e. coli b. cereus c. albicans c. neoformans zone of inhibition (mm) fresh saliva 14 0 22 25 0 23 0 0 0 0 0 25 0 0 0 0 0 lyophilized saliva 23 a 11 0 10 0 0 0 0 25 b 0 0 0 0 0 0 0 arginin+nacl c 0 0 0 0 0 0 ciprofolxacin (5µ g) d 24 35 26 28 nystatin (100units) e 10 9 a five folds concentrated, b ten folds concentrated, c the phagostimulatory solution as negative control, d,e reference antibiotics 0: no inhibition, -: not determined iium engineering journal, vol. x, no. x, 200x abdualkader et al. 8 4. discussion the wide biodiversity of leech species all over the world has led to set up many researches focusing on the anticoagulant and antimicrobial activity of their salivary gland secretion. of the leech salivary gland secretion, the european hirudo medicinalis saliva was known to contain the most potent natural thrombin inhibitor, hirudin [15, 16]. additionally, other hirudin-like inhibitors were isolated from other leech species, such as bufrudin and hirullin from hirudinaria manillensis and haemadin from the indian leech haemadipsa sylvestris [16]. results revealed that the malaysian leeches exhibited an antithrombin activity since it prolonged tt in a linear dose dependent manner with an apparent inhibition constant (k) of about 2.123. remarkably, the ic100 (43.205 µ g/ml) represented about 50% of the total protein content (79.962 µ g/ml), indicating that the antithrombin components are a major component of the malaysian leech crude saliva extract. in addition of having an anticoagulant activity, the malaysian leech saliva extract revealed a broad spectrum antibacterial activity against both gram-positive (s.aureus) and gram-negative (sal. typhi and e. coli) bacterial strains, whereas no inhibition was observed against any of the test fungi. in contrast, theromacin and theromyzin isolated from the leech theromyzon tessulatum showed inhibitory activity directly against grampositive rather than gram-negative spp. [8], leading to deduce that the active peptides of malaysian leech saliva extract are maybe of a different nature. importantly, the inactive fresh crude saliva extract examined against the active lyophilized concentrated crude saliva leads to conclude that the antibacterial ingredients are minor components of the crude saliva extract. furthermore, starvation period seems likely to be an important factor affecting the antibacterial activity of leech saliva extract, and six months of starvation will totally exhaust leeches. 5. conclusion the results reported here suggest that the malaysian leech saliva extract possesses a similar antithrombin activity to that of the european specie, raising the question of the actual structure of the active peptide, whether it has similarity with the other known antithrombin agents or not. as well, malaysian leech saliva extract seems to contain broad spectrum antibacterial peptides which are supposed to have a novel structure that needs to be investigated. acknowledgement this research was supported gratefully by the grant (edw b 10-0393) from researchmanagement center, international islamic university malaysia, iium. references [1] i.s. whitaker, j. rao, d. izadi and p.e. butler, “historical article: hirudo medicinalis: ancient origins of, and trends in the use of medicinal leeches throughout history,” british journal of oral and maxillofacial surgery. vol. 42, pp. 133-137, 2004. iium engineering journal, vol. x, no. x, 200x abdualkader et al. 9 [2] p. ascenzi, g. amiconi, b. wolfram, w. bode, m. bolognesi, m. coletta and e. menegatti, “proteinase inhibitor from the european medicinal leech hirudo medicinalis structure functional and biomedical aspects”. molecular aspects of medicine. vol. 16, pp. 215-313, 1995. [3] j. haycraft, “on the action of secretion obtained from the medicinal leech on coagulation of the blood”. proceedings of the royal society of london. vol. 36, pp. 478-487, 1884. [4] h. deckmyn, j.m. stassen, i. vreys, e. van houte, r.t. sawyer and j. vermylen, “calin from hirudo medicinalis, an inhibitor of platelet adhesion to collagen, prevents platelet-rich thrombosis in hamsters,” blood. vol. 85, pp. 712-713, 1995. [5] w. gronwald, j. bomke, t. maurer, b. domogalla, f. huber, f. schumann, w. kremer, f. fink, t. rysiok, m. frech and h. kalbitzer, “structure of the leech protein saratin and characterization of its binding to collagen”. j. mol. biol. vol. 381, pp. 913-927, 2008. [6] g.p. tuszynski, t.b. gasic and g.j. gasic, “isolation and characterization of antistasin. an inhibitor of metastasis and coagulation,” j. biol. chem. vol. 262, no. 20, pp. 9718-23, 1987. [7] f. faria, e. kelen, c. sampaio, c. bon, n. duval and a. chudzinski-tavassi, “a new factor xa inhibitor (lefaxin) from the haementeria depressa leech,” thromb haemost. vol. 82, pp. 1469-1473, 1999. [8] a. tasiemski, f. vandenbulcke, g. mitta, j. lemoine, c. lefebvre, p. sautière and m. salzet, “molecular characterization of two novel antibacterial peptides inducible upon bacterial challenge in an annelid the leech theromyzon tessulatum,” the journal of biological chemistry. vol. 279, no. 30, pp. 30973-30982, 2004. [9] c. yule and y. sen, freshwater invertebrates of th malaysian region, malaysia: akademi sains malaysia. [10] m. rigbi, h. levy, f. iraqi, m. teitelbaum, m. orevi, a. alajoutsijärvi, a. horovitz and r. galun, “the saliva of the medicinal leech hirudo medicinalis-i. biochemical characterization of the high molecular weight fraction”. comp. biochem. physiol. vol. 87b, no. 3, pp. 567573, 1987. [11] m. dickinson and c. lent, “feeding behavior of the medicinal leech hirudo medicinalis l”. j. copm physiol a. vol. 154, pp. 449-455, 1984. [12] m.m. bradford, “a rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding”. analytical biochemistry. vol. 72, pp. 248-254, 1976. [13] b. schmied, h. hoeffken, w. hornberger and h. bernard, “peptides with anticoagulant activity”. united states patents. patent number 5,393,873, 1995. [14] m.b. coyle, manual of antimicrobial susceptibility testing, american society for microbiology. [15] f. markwardt, “the development of hirudin as an antithrombin drug,” thromb. res. vol. 74, pp. 1-23, 1994. [16] c. koh and m. kini, “molecular diversity of anticoagulants from haematophagous animals”. thromb. haemost. vol. 102, pp. 437-453, 2009. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 48 production and stability of mycoflocculants from lentinus squarrosulus rwf5 and simplicillium obclavatum rwf6 for reduction of water turbidity nessa jebun, md. zahangir alam*, abdullah al-mamun and raha ahmad raus bioenvironmental engineering research centre (berc), department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. * corresponding author: zahangir@iium.edu.my (received: 8th may 2018; accepted: 21st nov 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.843 abstract: the production and stability of two novel myco-flocculants produced by river water fungus (rwf) were investigated. screening tests were conducted to find suitable nutrients, ph, nutrient concentration, inoculum dose, and stability for two mycoflocculants l. squarrosulus (rwf5) and s. obclavatum (rwf6). the strains showed good flocculating activity in reducing turbidity of kaolin suspension while malt extract was used as nutrient source. supernatants of rwf5 and rwf6 were able to reduce turbidity from 900±10 ntu to 46 ntu (95%) and 195 ntu (78%), respectively. in order to enhance the production, optimization of cultivation conditions were studied using a one-factor-at-atime (ofat) method. l. squarrosulus (rwf5) reduced 96% of turbidity at optimum conditions, comprising of 0.1% (w/v) malt extract, 3% (v/v) inoculum dose, and initial ph 7.0 for 6 days. the results of the compatible mixed culture showed good flocculation activity at 88% compared to a single culture of s. obclavatum at 78%. on the other hand, l. squarrosulus showed better turbidity reduction in the single culture rather than the mixed culture. the stability of l. squarrosulus and s. obclavatum supernatants showed excellent turbidity reduction over a wide ph range of 4-8 with the maximal flocculation rate of 96% and 90%, respectively, at ph 7.0. they also exhibited high turbidity removal ability in a temperature range of 4 oc – 55 oc for 24h with a maximum turbidity removal rate of 96% (rw5) and 87% (rw6) at 25 oc. time stability of the l. squarrosulus supernatant showed good turbidity removal potential at above 90% at room temperature (28± 2 oc) and 85% at low temperature (4 oc) for 12 days. the high flocculating rate of the myco-flocculants and their good stability under wide range of temperature indicated their potentiality as biodegradable flocculants for water and wastewater treatment industry. abstrak: keberhasilan dan kestabilan dua myco-gumpalan baharu oleh kulat air sungai (rwf) telah dikaji. ujian penapisan telah dijalankan untuk mencari nutrien sesuai, ph, kepekatan nutrien, dos inokulum dan kestabilan dua myco-gumpalan l. squarrosulus (rwf5) dan s. obclavatum (rwf6). rantaian menunjukkan aktiviti gumpalan yang baik dalam mengurangkan kekeruhan air sungai dengan penggantungan koalin di mana ekstrak malt telah digunakan sebagai sumber nutrien. larutan supernatan rwf5 dan rwf6, masing-masing mampu mengurangkan kekeruhan dari 900±10 ntu kepada 46 ntu (95%) dan 195 ntu (78%). bagi meningkatkan pengeluaran, keadaan optimum bagi menggalakkan hasil telah diselidiki menggunakan kaedah satu faktor pada tiap masa (ofat). pada takat optimum, l. squarrosulus (rwf5) mengurangkan 96% kekeruhan, iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 49 ianya terdiri daripada ekstrak malt 0.1% (w/v), dos inokulum 3% (v/v) dan ph awal 7.0 selama 6 hari. keputusan kultur campuran yang sesuai menunjukkan aktiviti penggumpalan yang baik pada 88% berbanding kultur sendirian s. obclavatum pada 78%. pada waktu sama, l. squarrosulus menunjukkan pengurangan kekeruhan yang lebih baik dalam kultur sendirian berbanding kultur campuran. kestabilan larutan supernatan l. squarrosulus dan s. obclavatum menunjukkan pengurangan kekeruhan yang sangat baik pada ph yang luas iaitu 4-8 dengan kadar maksimum kekeruhan pada 96% dan 90%, pada ph 7.0 masing-masing. keduanya menunjukkan kebolehan penyingkiran kekeruhan yang tinggi pada skala suhu 4 oc – 55 oc selama 24 jam dengan kadar nyah kekeruhan maksimum pada 96% (rw5) dan 87% (rw6) pada suhu 25 oc. kestabilan masa larutan supernatan l. squarrosulus menunjukkan potensi penyingkiran kekeruhan terbaik atas 90% pada suhu bilik (28± 2 oc) dan 85% pada suhu rendah (4 oc) selama 12 hari. kadar gumpalan yang tinggi oleh myro-gumpalan dan kestabilan yang baik pada julat suhu yang luas menunjukkan potensinya sebagai agen biodegradasi gumpalan kepada air dan industri rawatan loji air. keywords: flocculation; jar test; lentinus squarrosulu; mixed culture; simplicillium obclavatu; stability; turbidity 1. introduction chemical flocculants are widely used in wastewater and drinking water treatment, food and fermentation industries, as well as in downstream processing due to their high flocculating efficiency and cost-effectiveness. [1, 2] generally, flocculating agents that have the most usage in water treatment are the synthetic ones such as aluminium sulphate, ferric chloride, lime, and synthetic polymers. [3, 4] aluminium salts are the most widely used coagulant in water and wastewater treatment because of their proven performance and cost effectiveness. however, chemical coagulants cannot be easily degraded in nature and may result in various health and environmental problems. [5] compared with chemical flocculants, bioflocculants have more advantages, such as being environmentally friendly due to their biodegradability, largely nontoxic with no secondary pollution, and harmless to both humans and animals. [6] therefore, bioflocculants have recently gained global attention in research because they hold immense potential in replacing chemical flocculants. for example, li et al. [7] reported that b. licheniformis produced zs-7 bioflocculant is expected to be a potential replacement for conventional synthetic flocculants such as pac (polyaluminum chloride) and pam (polyacrylamide) for the treatment of low temperature and room temperature (25 oc) drinking water. similarly, gong et al. [8] reported serratia ficaria produced bioflocculant sf-1 showed 91.8 – 93.7% turbidity removal from wastewater, which is better than that of pac and pam. aspergillus flavus produced ih-7 bioflocculant showed better flocculation performance than pac and ih-7 was significantly used to flocculate different types of suspended solids such as activated carbons, kaolin clays, soil solids, and yeast cells [9]. moreover, bioflocculants are widely used for the recovery of suspended solids (ss) from wastewater treatment [10-12]. bioflocculants are secondary metabolites produced during the growth of microorganisms such as bacteria, yeast and fungi that are composed of polysaccharides, proteins, lipids, glycoproteins, and glycolipids [13-15]. the composition and properties of coagulants depend on the type of flocculant-producing microorganisms (bpms), composition of the media, and many conditions. the differences in the composition and properties of polysaccharides and proteins lead to differences in the charge of coagulant [16]. culture conditions screening is a powerful approach to increase the production of extra polymeric substances from microorganism cultivation [17]. although most flocculants can iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 50 be used to flocculate kaolin suspension, they show different flocculating ability for other particles or colloids in aqueous solutions. jebun et al. [18, 19] reported some filamentous fungi isolated from river water samples showed good entrapment potentiality to reduce turbidity from river water. deng et al. [20] reported aspergillus parasiticus produced a coagulant with high flocculating activity for kaolin suspension and water-soluble dyes. pu et al. [21] reported that the compound coagulant produced by two strains of rhizopus sp. was successfully used to reduce turbidity from potato starch wastewater. the same observation was made by luvuyo et al. [22] for turbidity removal from kaolin clay by bioflocculant produced by a mixed culture of methylobacterium sp. and actinobacterium sp. in the present study, we examine the suitable culture conditions for the production of myco-flocculants by two novel l. squarrosulus rwf5 and s. obclavatum rwf6 for reducing turbidity from synthetic turbid water. the screening tests were conducted to find suitable nutrients, ph, nutrients concentration and inoculum size of these two potential fungi to enhance flocculation performance. in addition, stability of the single and compatible mixed culture supernatants (myco-flocculants) was investigated for chemical and environmental conditions to reduce turbidity by jar test. 2. materials and methods 2.1 microorganisms and growth conditions l. squarrosulus rwf5 and s. obclavatum rwf6 were isolated from river water samples collected from the river pusu on the iium campus for coagulant production. l. squarrosulus rwf5 and s. obclavatum rwf6 cultures were maintained on potato dextrose agar (pda) (oxoid, uk) and initial ph was adjusted to 5.8±0.2. distilled water was used to prepare medium solutions and sterilized at 121 oc for 20 minutes. the culture plates were incubated at 32±2 oc for 10 days. subculture was conducted twice in a month and sub culture plates were stored at 25 oc in an incubator for further use. 2.2 myco-coagulants production 2.2.1 screening of nutrients the screening medium consisted of 5 g/l starch, sucrose, yeast extract, and malt extract and each of the medium was mixed with 1 liter of distilled water. the medium was then sterilized by autoclaving it at 121 °c for 15 minutes and then inoculated with 2% (v/v) fungal mycelial inoculum (340 mg/l). the liquid culture was then incubated in a rotary shaker with agitation at 150 rpm at 30± 2oc for 8 days. initial ph of the broth was adjusted at 7.0 ± 0.1 using 1 m naoh or 2 m hcl. supernatants were taken at different time intervals to determine the flocculation activity. the effect of cultivation time for myco-flocculants production was investigated for 8 days. 2.2.2 factors affecting the flocculating rate to study the effect of malt extract concentration of 0-1% (g/l), initial ph values of 5, 6, 7, and 8, and inoculum doses of 1-4% on the flocculating rate were investigated. in this experiment, ofat analysis was followed for three factors such as media concentration, ph, and inoculum dose. 2.2.3 single and mixed culture the production medium consisting of 5 g/l malt extract was autoclaved at 121 °c for 15 minutes. the sterilized medium was inoculated with 2% (v/v) fungal inoculum for single iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 51 and mixed culture (mycelium concentration of 340 mg/l). ten day old culture plates were used to prepare fungal inoculum and the culture was incubated in a rotary shaker with 150 rpm at 30± 2 oc for 6 days. initial ph of the culture was adjusted at 7.0±0.1 using 1 m naoh or 2 m hcl. the cultures were harvested after 6 days of treatment and centrifuged to separate the biomass from supernatant (103 rpm for 10 mins at 25 oc). the supernatants were used as myco-flocculants and stored at room temperature at 28±2 oc for further use. 2.3 myco-flocculant stability 2.3.1 ph stability of supernatants the ph of myco-flocculants from single and mixed cultures was adjusted to 4, 5, 6, 7, and 8 with 1 m naoh and 2 m hcl. a jar test was conducted to observe flocculation activity in different ph. initial turbidity and ph of kaolin suspension were recorded at 900±10 ntu and 7.0±0.1, respectively and the mixture was stirred at 120 rpm for 40 minutes and allowed to settle for 30 minutes. 2.3.2 temperature stability myco-flocculants were treated at different temperatures of 4, 25, 35, 45 and 55 oc for 24 hours. both supernatants were applied in kaolin suspension to reduce turbidity with the same conditions as referred to section 2.3.1. 2.3.3 time stability of l. squarrosulus produced myco-flocculant the myco-flocculant produced by l. squarrosulus rwf5 was tested for flocculation activity capability. the myco-flocculant was kept in room temperature (28±2 oc) and low temperature (4 oc) for 20 days. jar tests were conducted to observe flocculation activity in terms of reducing turbidity from kaolin suspension. 2.3.3 flocculation activity kaolin suspension was prepared using 0.7 g kaolin clay in 1 liter of tap water (turbidity 900±10 ntu). each jar contained 500 ml kaolin suspension was added with 1% supernatant (v/v). the jar apparatus was then operated at a speed of 120 rpm with 40 minutes mixing time and allowed to settle for 30 minutes [19]. next, the top layer of water in each jar was collected with a micro pipette and turbidity was measured with a portable turbidimeter 2100q hach, usa to measure residual turbidity. in the control experiment, 1% (v/v) of supernatant was replaced with 1% (v/v) of nutrient broth. the flocculating activity was calculated according to the following equation [23]. flocculating activity (%) = [ 𝐴−𝐵 𝐴 ] × 100% (1) where, a is the initial turbidity value and b is the residual turbidity after flocculation. 3. results and discussion 3.1 myco-flocculant production 3.1.1 screening of potential nutrient figure 1 (a) shows the flocculating activity of two coagulants for 6 days in media containing starch, sucrose, yeast extract, and malt extract. starch, sucrose, and yeast extract were not favourable for l. squarrosulus and s. obclavatum growth, while the production of coagulants was relatively low when carbon and nitrogen sources were used separately. iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 52 fig. 1: the effects of nutrient and cultivation time on myco-flocculant production. a) screening of potential nutrient, b) culture time with malt extract. the highest myco-flocculant production from l. squarrosulus and s. obclavatum were obtained in malt extract media. malt extract was used as co-substrate to enhance the separation and filtration process of treated sludge by fungal growth formation [24]. aljuboori et al. [25], reported that the highest coagulant production by aspergillus niger was observed when the c/n ratio increased up to 20/1 with a flocculating rate of 79% respectively, but that further increase in the c/n ratio slightly decreased the production. figure 1 (b) shows the cultivation time with flocculation activity in terms of turbidity removal rate of myco-coagulants. the culture during the early stationary phase showed the highest (95% and 82% at 6 days) flocculating rate of l. squarrosulus and s. obclavatum, respectively. results showed the flocculating rate decreased slowly after 6 days, suggesting these strains may be secreting deflocculation enzymes. a similar result was reported in the cultivation of a. parasiticus [20] and b. licheniformis [26]. consequently, a period of 6 days was chosen as the culture time for the subsequent experiments. 3.1.2 effect of media concentration, initial ph, and inoculum size figure 2 shows the effect of malt extract concentration on the flocculating rate of two myco-coagulants. l. squarrosulus and s. obclavatum increased myco-flocculants at 0.1% (w/v) and 0.25% concentration, respectively. the flocculating activity of two fungal strains was poor without malt extract concentration in the culture (0%). small growth was found from the two fungal strains without nutrients (malt extract), suggesting that the strains may not able to secrete any metabolites due to lack of growth. 20 40 60 80 100 starch yeast extract sucrose malt extract t u rb id it y r e m o v a l (% ) nutrients l. squrrosulus s. obclavatum 30 40 50 60 70 80 90 100 2 4 6 7 8 t u rb id it y r e m o v a l (% ) cultivation time (day) l. squarrosulus s. obclavatum control (a) (b) iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 53 fig. 2: effect of media concentration of the flocculation activity on myco-flocculants. figure 3 shows the effect of the initial ph of the culture medium on bio-coagulant production. the flocculating activity increased when ph was varied from 5 to 7 with the maximum flocculating activity of 95%. the removal rate (77%) decreased at an alkaline ph (8) for both of the cultures. salehizadeh et al. [1] investigated that the initial ph of the production medium influences the electric charge of the cell and oxidation-reduction potential, which in turn affects the nutrient absorption and enzymatic reaction. fig. 3: effect of the initial ph of the culture medium on the flocculating activity of myco-flocculants. the flocculating rates obtained from the culture inoculated with 1 to 4% (v/v) inoculum size of two fungal strains are shown in fig. 4. the use of 2 to 3% of l. squarrosulus inoculum dose in production medium recorded the highest flocculating rate of 96%. s. obclavatum was gradually decreased when inoculum dose was increased due to excessive overlapping of cells, resulting in inhibition of coagulant production. aljuboori et al. [13] reported an optimal coagulant production by aspergillus flavus at 2% (v/v) inoculum size, whereas a higher inoculum size of 10% (v/v) was most suitable for coagulant production by rhizopus sp. [21] 30 40 50 60 70 80 90 100 0 1 2.5 5 7.5 10 t u rb id it y r e m o v a l (% ) media concentration (g/l) l. squarrosulus s. obclavatum 50 60 70 80 90 100 5 6 7 8 t u rb id it y r e m o va l (% ) ph l. squarrosulus s. obclavatum iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 54 fig. 4: effect of inoculum dose of culture medium on myco-flocculants production. 3.1.3 compatible mixed culture figure 5(a) shows ten day old single and mixed culture plates of l. squarrosulus and s. obclavatum. figure 5(b) shows the turbidity removal (%) of single and mixed cultures. the flocculation rate was higher at 88% of mixed culture compared to the single culture of s. obclavatum (78%). the mixed culture showed significant growth of l. squarrosulus in the pda plate, which indicated that the compatible mixed culture of l/s may have produced more substances to enhance flocculation to reduce turbidity compared to single s. obclavatum culture. alam et al. [12] reported the fungal mixed culture of aspergillus niger and penicillium corylophilum was enhanced the separation process of wastewater sludge. two strains of rhizopus sp. produced a compound coagulant that was used to reduce turbidity of 91.1% from potato starch wastewater [21]. fig. 5: compatible mixed culture (a) l. squarrosulus (a-a), s. obclavatum (a-b), l. squarrosulus and s. obclavatum (l/s) front side of plate (a-c), l/s reverse side of plate (b) turbidity removal by single and compatible mixed culture. 40 50 60 70 80 90 100 1 2 3 4 t u rb id it y r e m o v a l (% ) inoculum dosage %(v/v) l. squarrosulus s. obclavatum 40 50 60 70 80 90 100 l. squarrosulus s. obclavatum mixed culture control t u rb id it y r e m o v a l (% ) ls ls l s a b c d (a) (b) iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 55 3.1.4 myco-coagulants stability by jar test figure 6(a) shows that l. squarrosulus was stable at a wide range, from ph 4.0 to 8.0 and more than 90% flocculation was achieved within this range. at ph 7.0, the turbidity removal rate was higher for both myco-coagulants and the flocculation rate decreased slowly as the ph increased further. the mixed culture also showed good stability at ph 7.0. thus, these myco-coagulants are suitable to be applied at acidic and neutral conditions. this may be due to the fact that myco-flocculants show different electric charges at different ph levels and affect the flocculation ability of the bio-flocculant for kaolin particles [27]. fig. 6: myco-flocculant stability: a) the ph stability of l. squarrosulus, s. obclavatum and mixed culture; b) temperature stability of l. squarrosulus, s. obclavatum and mixed culture; c) time stability of myco-flocculant (l. squarrosulus). 70 75 80 85 90 95 100 4 5 6 7 8 t u rb id it y r e m o va l (% ) ph l. squarrosulus s. obclavatum mixed culture a 75 80 85 90 95 100 4 25 35 45 55 t u rb id it y r e m o va l (% ) temperature (oc) l. squarrosulus s. obclavatum mixed culture b 50 60 70 80 90 100 0 2 4 6 8 10 12 14 16 18 20 22 t u rb id it y r e m o va l (% ) time (day) 28±2 c 4 c c iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 56 the effect of temperature on the flocculating activity of myco-flocculants was investigated (fig. 6-b). the results showed that both myco-flocculants are fairly temperature-tolerant and had good flocculation activity at a wide range of temperatures. the flocculation ratio varied from 92% to 96% (l. squarrosulus) and 84% to 90% (s. obclavatum) in the temperature range of 4 oc to 55 oc, and only begins to decrease slightly with further temperature increase from 45 oc to 55 oc. the mixed myco-flocculant showed good stability at 4oc, then gradually decreased in temperature range to 45 oc -55 oc. the highest turbidity removal rate of 96% was observed at 25 oc and 35 oc for the l. squarrosulus myco-coagulant. these mycoflocculants were more stable at moderate temperatures (range 25 oc and 35 oc). similar findings were observed by aljuboori et al. [9], on the bioflocculant produced by aspergillus flavus with a residual flocculating activity of about 93% at temperature range from 5 to 45 °c, thus indicating a thermostable bioflocculant. the result was similar to reported for the bioflocculant produced by aspergillus parasiticus and it had moderate heat-stability [20]. figure 6(c) shows the effect of time stability on turbidity removal rate of l. squarrosulus produced myco-flocculant. the highest turbidity removal % was recorded at room temperature (28±2 oc) till 12 days then it showed decreased flocculation activity of the myco-flocculant. this may be due to the fact that the metabolites of the myco-coagulant are deactivated gradually after two weeks of storage. however, turbidity removal rate was 85% at low temperature (4 oc) stored coagulant with 12 days. after two weeks, the flocculation activity was decreased gradually and it reached at about 50% at 20 days. this may have occurred due to the deactivation of metabolites. 4. conclusions this study shows that l. squarrosulus and s. obclavatum produced myco-flocculants that were effective in the removal of turbidity of a kaolin suspension. the optimal conditions of l. squarrosulus myco-flocculant production were malt extract concentration 0.1% (g/l), initial ph 7.0 and inoculum dose 3% (v/v) for 6 day cultivation time which the flocculating activity reached above 95%. the two myco-flocculants’ stability indicates that they can work at different ph ranges between 4-8 and can be stored at room temperature (25 oc). finally, both novel myco-coagulants are expected to be potential replacements of chemical coagulants and widely applied in water treatment and other industries. acknowledgment the authors would like to express their thanks to ministry of higher education (mohe) for granting a fundamental research grant scheme (frgs), project no. frgs-14-109-0350 for the financial support. thanks also to research management centre (rmc), international islamic university malaysia for financial management and monitoring the progress of the project. references [1] salehizadeh h, shojaosadati sa. (2001) extracellular biopolymeric coagulants: recent trends and biotechnological importance. biotechnology advances, 19(5):371-385. [2] you y, ren n, wang a, ma f, gao l, peng y, lee d. (2008) use of waste fermenting liquor to produce bioflocculants with isolated strains. international journal of hydrogen energy, 33(13):3295-3301. iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 57 [3] prakash n b, sockan v, jayakaran p. (2014) waste water treatment by coagulation and flocculation. international j. of engineering science and innovative technology, 3(2):479484. [4] yan c, le l, yan-hong g, zi-wen x. (2013) characteristics analysis of different coagulants in the removal of organic matters of raw yellow river water. information technology journal, 12(20):5746-5750. [5] ruden c. (2004) acrylamide and cancer riskexpert risk assessments and the public debate. food and chemical toxicology, 42(3):335-349. [6] yang yn, ren n, xue jm, yang j, rong bl. (2007) mutation effect of mev protons on bioflocculant bacteria bacillus cereus. nuclear instruments and methods in physics research section b, 262:220–224. [7] li z, zhong s, lei hy, chen rw, yu q, li hl. (2009) production of a novel bioflocculant by bacillus licheniformis x14 and its application to low temperature drinking water treatment. bioresource technology,100(14):3650-3656. [8] gong wx, wang sg, sun xf, liu xw, yue qy, gao by. (2008) bioflocculant production by culture of serratia ficaria and its application in wastewater treatment. bioresource technology, 99(11):4668-4674. [9] aljuboori ah, idris a, al-joubory hh, uemura y, abubakar bi. (2015) flocculation behavior and mechanism of bioflocculant produced by aspergillus flavus. journal of environmental management. 150:466-71. [10] gao q, zhu xh, mu j, zhang y, dong xw. (2009) using ruditapes philippinarum conglutination mud to produce bioflocculant and its applications in wastewater treatment. bioresource technology, 100(21):4996-5001. [11] subramanian sb, yan s, tyagi rd, surampalli ry. (2008) a new, pellet-forming fungal strain: its isolation, molecular identification, and performance for simultaneous sludge-solids reduction, flocculation, and dewatering. water environment research, 80(9):840-852. [12] alam mz, fakhru’l-razi a. (2003) enhanced settleability and dewaterability of fungal treated domestic wastewater sludge by liquid state bioconversion process. water research, 37(5):1118-1124. [13] aljuboori ah, idris a, abdullah n, mohamad r. (2013) production and characterization of a bioflocculant produced by aspergillus flavus. bioresource technology,12:489-493. [14] more tt, yadav js, yan s, tyagi rd, surampalli ry. (2014) extracellular polymeric substances of bacteria and their potential environmental applications. journal of environmental management, 144:1-25. [15] okaiyeto k, nwodo uu, mabinya lv, okoh ai. (2015) bacillus toyonensis strain aemreg6, a bacterium isolated from south african marine environment sediment samples produces a glycoprotein bioflocculant. molecules, 20(3):5239-5259. [16] subramanian sb, yan s, tyagi rd, surampalli ry. (2010) extracellular polymeric substances (eps) producing bacterial strains of municipal wastewater sludge: isolation, molecular identification, eps characterization and performance for sludge settling and dewatering. water research, 44(7):2253-2266. [17] nwodo uu, okoh ai. (2013) characterization and flocculation properties of biopolymeric flocculant (glycosaminoglycan) produced by cellulomonas sp. okoh. journal of applied microbiology, 114(5):1325-37. [18] jebun n, al-mamun a, alam mz, karim mi, raus ra. (2015) evaluation of entrapment potentiality and turbidity removal efficiency of filamentous fungi. jurnal teknologi, 77(24):23-28. [19] jebun n, al-mamun a, alam mz, raus ra. (2016) fungal flocculants to reduce turbidity of river water. arpn journal of engineering and applied sciences, 11(6):4094-4099. [20] deng s, yu g, ting y. (2005) production of a bioflocculant by aspergillus parasiticus and its application in dye removal. colloids and surfaces b: biointerfaces, 44(4):179-186. [21] pu sy, qin ll, che jp, zhang br, xu m. (2014) preparation and application of a novel bioflocculant by two strains of rhizopus sp. using potato starch wastewater as nutrilite. bioresource technology, 162:184-91. iium engineering journal, vol. 19, no. 1, 2018 jebun et al. 58 [22] luvuyo n, nwodo uu, mabinya lv, okoh ai. (2013) studies on bioflocculant production by a mixed culture of methylobacterium sp. obi and actinobacterium sp. mayor. bmc biotechnology, 13(62):1-7. [23] kurane r, hatamochi k, kakuno t, kiyohara m, hirano m, taniguchi y. (1994) production of a bioflocculant by rhodococcus erythropolis s-1 grown on alcohols. bioscience, biotechnology, and biochemistry, 58(2):428-429. [24] alam m, fakhru'l-razi a, molla ah. (2004) evaluation of fungal potentiality for bioconversion of domestic wastewater sludge. journal of environmental sciences, 16(1):132137. [25] aljuboori ah, uemura y, osman nb, yusup s. (2014) production of a bioflocculant from aspergillus niger using palm oil mill effluent as carbon source. bioresource technology, 171:66-70. [26] shih i, van y, yeh l, lin h, chang y. (2001) production of a biopolymer flocculant from bacillus licheniformis and its flocculation properties. bioresource technology, 78(3):267272. [27] pan y, shi b, zhang y. (2009) research on flocculation property of bioflocculant pg.a21 ca. modern applied science, 3(6):106 112. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 in-idris: modification of idris stemming algorithm for indonesian text febiarty wulan suci, nur hayatin* and yuda munarko department of informatics, engineering faculty, university of muhammadiyah malang, malang, indonesia * corresponding author: noorhayatin@umm.ac.id (received: 11th january 2021; accepted: 18th march 2021; published on-line: 4th january 2022) abstract: stemming has an important role in text processing. stemming of each language is different and strongly affected by the type of text language. besides that, each language has different rules in the use of words with an affix. a large number of the words used in the indonesian language are formed by combining root words with affixes and other combining forms. one of the problems in indonesian stemming is having different types of affixes, and also having some prefixes that changes according to the first letters of the root words. implementing idris stemmer for indonesian text is of interest because indonesia and malaysia have the same language root. however, the results do not always produce the actual word, because the idris algorithm first removes the prefix according to rule 2. this elimination directly affected the idris stemmer result when implemented to indonesian text. in this study, we focus on a modified idris stemmer (from malay) to in-indris with indonesia context. in order to test the proposed modification to the original algorithm, indonesian online novels excerpts are used to measure the performance of in-idris. a test was conducted to compare the proposed algorithm with other stemmers. from the experiment result, in-idris had an accuracy of approximately 82.81%. there was an increased accuracy up to 5.25% when compared to idris accuracy. moreover, the proposed stemmer is also running faster than idris with a gap of speed of around 0.25 seconds. abstrak: stemming mempunyai peranan penting dalam pemprosesan teks. stem setiap bahasa adalah berbeza dan sangat dipengaruhi oleh jenis bahasa teks. selain itu, setiap bahasa mempunyai peraturan yang berbeza dalam penggunaan kata dengan awalan. sebilangan besar kata-kata yang digunakan dalam bahasa indonesia dibentuk dengan menggabungkan kata akar dengan afiks dan bentuk gabungan lain. salah satu masalah dalam bahasa indonesia adalah mempunyai pelbagai jenis awalan, dan juga mempunyai beberapa awalan yang berubah sesuai dengan huruf pertama kata dasar. menerapkan stemder idris untuk teks indonesia adalah minat kerana indonesia dan malaysia mempunyai akar bahasa yang sama. namun, hasilnya tidak selalu menghasilkan kata yang sebenarnya, kerana algoritma idris pertama kali menghapus awalan menurut peraturan 2. penghapusan ini secara langsung mempengaruhi hasil batang idris ketika diterapkan ke teks indonesia. dalam kajian ini, kami memfokuskan pada stemmer idris yang diubahsuai (dari bahasa melayu) ke in-indris dengan konteks indonesia. untuk menguji cadangan pengubahsuaian pada algoritma asli, petikan novel dalam talian indonesia digunakan untuk mengukur prestasi in-idris. ujian dilakukan untuk membandingkan algoritma yang dicadangkan dengan stemmer lain. dari hasil eksperimen, in-idris mempunyai ketepatan sekitar 82,81%, ada peningkatan ketepatan hingga 5,25% dibandingkan dengan ketepatan idris. selain itu, stemmer yang dicadangkan juga berjalan lebih cepat daripada idris dengan jurang kelajuan sekitar 0.25 saat. 82 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 keywords: idris stemming; in-idris; nlp; text pre-processing 1. introduction finding the root words of derivative words is still a challenge, especially for text processing. stemming is a process to transform derivative words into root words. stemming methods are widely applied in natural language processing (nlp) and also text mining especially when involved in extracting information that is used to find new information from various written sources [1], such as sentiment analysis [2]. stemmer, an algorithm for stemming, has an important role in text processing because the results of stemming are used to extract features in the text. for the text mining area, stemmer is important in the initial stage, which has a function to convert unstructured text into structured representative formats that can then be processed by machines [3]. implementing stemmer for text processing has proven to improve the performance of text pre-processing [4]. it also has an impact on instance classification results using indonesian quran translation [5], and reduces the different forms of a word into a root word [6]. stemming of each language is different, and it is strongly influenced by the type of text language. moreover, each language has different rules in the use of words with affixes [7]. however, for some languages stemming can be achieved by applying the appropriate morphological rules [8]. indonesian used bahasa indonesia as a formal language. in the indonesian text, words are formed from morphological rules [9]. a large number of the words used in the indonesian language are formed by combining root words with affixes and other combining forms [10]. indonesian has stemming problems that are specific to the language. one of the problems is having different types of affix, another is having some prefixes that change according to the first letters of the root words. for example, the prefix “me-” becomes “mem-” when attached to a root word starting with the letter “b-” as in “mem-buat” (to make, in english), but it becomes “meny-” when attached to a root word starting with the letter “s-” as in “meny-[s]impan” (to store, in english) [11]. in indonesian text processing, some researchers used a stemming algorithm such as nazief and adriani (n&a) [12], confix stripping algorithm (cs) [13], and enhanced confix stripping (ecs) [14], which are developed for indonesian text. however, several researchers also implemented stemmers from other languages such as idris stemmer (for malay language) [15], and potter stemmer (for english) [16]. in this study, we focus on idris stemmer. this is interesting because indonesian and malay have the same language root. malay has similarities with the indonesian language, so the idris algorithm can also be used to process indonesian texts [17]. earlier research compared the processing time and accuracy of the nazief and adriani (n&a) stemmer with the idris stemmer [8]. the research applied to indonesian text to know which algorithm was better. for the evaluation, the researcher used five story texts to compare the stemming result. the result presented that the n&a stemmer obtained a 97% accuracy with a processing time of approximately 0.03 seconds per word, while the idris stemmer reached an accuracy of 91% but needed around 0.02 seconds per word for processing. another research focused on analysing stemmer strength in indonesian text documents based on the parameters of the icf and wc values, and also analysed the level of accuracy and speed based on word results. as a result, idris stemmer was accurate and succeeded in producing root words from indonesian text, but it still had shortcomings namely, increasing the possibility of overstemming. the results of stemming are not appropriate because the idris algorithm first removes the prefix according to rule 2. elimination directly refers to the rule 2 effect on the results of stemming, where the 83 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 algorithm does not always result in the actual word. moreover, other experiments [8] have proven that the idris algorithm has an advantage in the speed of the stemming process but the level of accuracy is still low. to obtain a better level of accuracy and faster process for the stemming, this study proposed to modify the idris algorithm with indonesian text. we measured the accuracy and the speed of the stemming process as a result of the modification of the idris algorithm. the modified algorithm is called in-idris. 2. related work 2.1 indonesian stemmers algorithm the nazief and adriani (n&a) stemmer [12] is based on morphological rules that are interlinked and grouped, then encapsulate the allowed part of the word and do not include affixes such as prefixes, suffixes, and confixes to get the root of a word. the performance of this algorithm is based on three parts, they are grouping affixes, usage rules and the establishment of limits, and use of the dictionary. the dictionary becomes an important part because it is used to check whether a word has met its stem or not. before the affix removal process, several things must be considered in the uses of this algorithm, such as inflexion suffixes, derivation suffixes, derivation prefixes, and prefix disallowed suffixes [18]. the performance of the n&a approach is the most complex approach. confix stripping (cs) algorithm is an indonesian stemmer [6] that was developed based on improvement from the nazief & adriani algorithm. cs stemmer added an additional stemming step called looppengembalianakhiran (final return loop). this algorithm was done by adding some prefix rules and modifying prefix rules, particularly adding rule precedence. from comparing performance results, it is shown that the cs algorithm has better performance than the n&a stemmer [13]. the development of the cs stemmer is the enhanced confix stripping (ecs) [14]. from the experiment, the result showed that the ecs stemmer succeeded in increasing the accuracy from the modification of the ecs stemmer using a non-deterministic method that was able to identify the possibilities of root words that can be formed in a single word through the candidate list [19]. an indonesian stemmer based on the dictionary is the vega stemmer. this algorithm used rule sets to determine whether an affix can be removed from a word. the rules are accessed in the order they are presented in the code. when one rule fails, the algorithm proceeds to the next. a major shortcoming of the vega approach is the absence of a lookup stage where words are only compared to a dictionary of known root words. stemming continues as long as the word contains affix letters, often leading to overstemming. moreover, the algorithm does not cater to cases where recoding is required. finally, the reliance on strict rules necessitates that the rules be correct and complete, and prevents ad hoc restoration of affix combinations [20]. 2.2 idris stemmer algorithm the idris stemmer is developed by idris et al. that is designed for the malay language. the malay language has similarities with the indonesian language [16], so this algorithm is also applicable to indonesian texts. this algorithm has two dictionaries (general and local dictionaries) in determining stemming results [17]; where the local dictionary contained a list of root words in the malay history vocabularies. this algorithm implements only two patterns of the rules which are prefix and suffix rules. by using only two patterns of affixes that are prefix and suffix, it can reduce the numbers of the rule sets. 84 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 idris algorithm first checks the words against prefix rules then checks the words against the suffix rules. if not, many errors such as overstemming can occur [15]. idris algorithm adopts arifin and setiono's assumption that each indonesian word has two prefixes and three suffixes [21]. idris algorithm applied a different recoding scheme and progressive stemming. the algorithm checks the dictionary after each step, stopping and returning the stemmed word if it is found. the scheme works as follows: first, after checking for the word in the dictionary, the algorithm tests if the prefix of the word matches a prefix that may require recoding; second, if recoding is required, it is performed and the resultant word is searched for in the dictionary, while if recoding is not required, the prefix is removed as usual and the word is checked in the dictionary; third, having removed a prefix, suffix removal is attempted and, if it succeeds, the word is checked in the dictionary; and, last, the algorithm returns to the second step with the partially stemmed word. there are two variants of this algorithm: the first changes prefix and then performs recoding, while the second does the reverse [22]. the idris algorithm description is referred to in table 1. table 1: the description of idris algorithm algorithm 1: idris algorithm 1. check the word in the dictionary. if the word is found, then the word is considered as the root word and exit. otherwise, proceed to the next step. 2. check the word in the prefix rules. if the word matches the prefix rules, check the prefix pattern and the first letter of the stem word. otherwise, go to step 7. 3. if the prefix pattern matches the pattern in rule 2, then apply rule 2 to the word. otherwise, remove the prefix and go to step 6. 4. check the prefix of the word, adjust the pattern in rule 2. if it matches the fourth rule, then check the stem word in the dictionary and proceed to the next step. otherwise, remove the prefix and go to step 6. 5. if the word is not in the dictionary, then return to step 4, otherwise, remove the prefix and proceed to the next step. 6. check the word in the dictionary. if the word found, then the word is considered as the root word and exit. otherwise, proceed to the next step. 7. check the words in the suffix rules. if it matches with the suffix rules, then remove prefixes usually give rise to spelling variations and exceptions in the root word. errors may occur during the stemming process where the stemmed word is not complete. the idris algorithm has another rule called rule 2 where it can be applied to the prefix removal only [15]. the rule is if the word stemming is not complete, checking the first letter of the word and if the word starts with a vowel, then: 1. add t after removing menor pen 2. add k after removing mengor peng 3. add s after removing the menyor peny 4. add f or p after removing memor pem 3. modification of idris algorithm in this section, we explain the proposed modification of the idris algorithm, called inidris. from the results of experiments and analysis of the idris stemmer, there are some 85 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 examples of words that are not appropriate. for example, the word "memasukkan" (to enter, in english) found the root word "pasuk". the word is in the dictionary and the algorithm will consider it as the root word, but the word "pasuk" is not meant, and the actual root word is "masuk” (enter, in english). the results of stemming are not appropriate because the idris algorithm first removes the prefix according to rule 2. in the example, after removing the prefix "mem-" the word "asuk" is obtained, so the fourth rule in rule 2 after removing the prefix "mem-" then add the letter p, then it becomes the word "pasuk". elimination directly refers to the rule 2 effect on the results of stemming, where the algorithm does not always result in the actual word. the process occurs because at the 2nd stage, the algorithm only checks whether or not the words are in accordance with the prefix rules and rule 2 patterns without prefix removal and if at the 3rd stage if the checked words are in accordance with rule 2, the algorithm immediately applied the rule to the word. after analysing the results of stemming, the next step is to make improvements by changing the process from stages 2 and 3. the proposed improvements are as follows: 1. in step 2 the algorithm will first check the word in the prefix rule, if appropriate then the prefix will immediately be removed. 2. in step 3 if checking the prefix rule is not appropriate, the algorithm will check the prefix pattern in rule 2 and the first letter of the input word. if it is in accordance with rule 2, the algorithm will apply the rule to the word. the modification of the idris algorithm is described in table 2 below: table 2: the description of in-idris algorithm algorithm 2: in-idris algorithm 1. check the word in the dictionary. if the word is in the dictionary, then the word is considered as the root word and exit. otherwise, proceed to the next step. 2. check the word in the prefix rule. if the word matches the prefix rules, then remove the prefix and go to step 6. otherwise, proceed to the next step. 3. check the prefix pattern and the first letter of the word to be stemmed. if the prefix pattern matches rule 2, then apply rule 2 to the word. otherwise, remove the prefix and go to step 6. 4. check the prefix of the word, adjust the pattern in rule 2. if it matches the fourth rule, then check the stem word in the dictionary and proceed to the next step. otherwise, remove the prefix and go to step 6. 5. if the word is not found in the dictionary, then return to step 4, otherwise, remove the prefix and proceed to the next step. 6. check the word in the dictionary. if the word found, then the word is considered as the root word and exit. otherwise, proceed to the next step. 7. check the words in the suffix rules. if it matches with the suffix rules, then remove the suffix and go to step 1. otherwise, just go to step 1. from fig.1 we can see the step-by-step of the proposed algorithm depicted through the flowchart. the processes with grey colour use the modified rule from idris stemmer. 86 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 start word check the dictionary if word appears in the dictionary? if word matches with prefix rules? check the word againts the prefix rules if matches with the rule 2? remove prefix apply the rule 2 to the word no no no yes yes if word appears in the dictionary? if word matches with suffix rules? root word yes yesno endremove sufix no yes fig. 1: the flowchart of modified idris algorithm (in-idris). 4. experiment and evaluation 4.1 dataset for the experiment process, this study used a dataset retrieved from indonesian online novel excerpts to measure the performance of the proposed algorithm. the novel data were sourced from research by permatasi [6] which have a total of 6 novels, and there were 4 novels from our collection so that there is a total of 10 novels to be used. novel excerpt data represented as a document so that a total of the document is 10 documents for the evaluation process. novel excerpt data used was the only content without using the title of the novel. the dataset needs to go through the preprocessing stage so that it can be processed to the next stage. meanwhile, the dictionary of root words is used based on kamus besar bahasa indonesia (the big indonesian dictionary, in english). kamus besar bahasa indonesia (kbbi) is the most complete indonesian dictionary which is popularly used as a reference in indonesian text processing. 4.2 evaluation scenarios the research evaluation was done by comparing the stemming results of the modification of the idris algorithm (in-idris) and other stemming algorithms (original idris, n&a, ecs). in this experiment, we analysed the accuracy and the speed of every stemmer. testing scenarios that were carried out tested 10 indonesian novels excerpts. generated output was in the form of stemming root words, followed by counting the number of true and false stemming results from each algorithm. several steps were used, 87 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 including case folding, tokenization, eliminating stopwords, and stemming. case folding is the process of changing all letters to lowercase and removing punctuation, numbers, and certain symbols [9]. after that, the tokenization process is breaking a stream of text up into phrases, word, symbols, or other elements [23]. then, the words taken from tokenizing results will be processed to eliminate the unimportant words that are included in the stopwords list. furthermore, each document content will be stemmed. the stemming process is then carried out to process the affix words into root words. the results will be assessed to produce the number of both true words and wrong words; so that the accuracy value of both stemmers can be calculated. this evaluation also measured the speed of processing time during changing the root word from the stem word of the document. eq. (1) [8] is used to calculate the accuracy value of stemming result from each document di where i =1 to 10. furthermore, t represented the total of true words from di while w is the total of the wrong words from di and the word total is represented by n. 𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = ( 𝑡−𝑤 𝑛 )𝑥100% (1) 4.3 experiment results and discussion the first experiment compared the stemming result of the idris and the in-idris stemmer. the testing results are shown in table 3, which describes the experimental results for every document tested. the table also presents the number of words contained in each document, the number of true and wrong words, and also the speed and accuracy value of both stemmers. for both idris and in-idris stemmers, the maximum accuracy resulted from document 2, which changed from 83.13% to 87.95%. on the other hand, the minimum accuracy was produced in document 7 stemming results with around 69.49% for the in-idris and 67.01% for the idris stemmer. table 3: comparison accuracy and speed of both idris and in-idris stemmer doc number of words idris in-idris true word wrong word speed (s) accuracy (%) true word wrong word speed (s) accuracy (%) 1 239 97 27 3.40 78.23 106 17 3.32 86.18 2 261 120 28 3.62 81.08 127 21 3.02 85.81 3 323 138 28 3.79 83.13 146 20 3.80 87.95 4 511 188 46 5.28 80.34 192 42 5.96 82.05 5 608 233 79 7.96 74.68 257 55 8.81 82.37 6 2224 912 230 42.16 79.86 967 173 47.17 84.82 7 1361 522 257 25.56 67.01 539 237 18.52 69.46 8 1210 415 137 14.71 75.18 443 109 13.59 80.25 9 794 361 91 12.95 79.87 384 65 12.90 85.52 10 997 366 114 18.61 76.25 400 78 18.40 83.68 average 13.80 77.56 13.55 82.81 on the other hand, in terms of speed, stemming based on in-idris needed around 13.55 seconds. however, this is faster than processing root words with the idris stemmer which has an average time of around 13.80 seconds. in general, based on the researcher’s experiment (shown in table 3), it could be concluded that documents that have under 600 words just need under 9 seconds for stemming. meanwhile, if the number of the words is 88 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 under 1300, it will take under 25 seconds to process. furthermore, for the documents that have over 2000 words, over 47 seconds are required. figures 2 and 3 show the accuracy and speed comparison from both stemmers represented in a graph. based on fig. 2, in general, it showed that the accuracy value produced by in-idris was higher than the idris stemmer result. the average value of accuracy from the in-idris stemmer was approximately 82.81% while stemming using the idris algorithm showed an accuracy of just 77.56%. in-idris performance dominated for whole documents tested and reached an accuracy of over eight in ten. generally, in-idris presented a faster speed than idris in stem word processing (shown in figure 3). however, idris showed good speed when processing documents 4, 5, and 6. in terms of accuracy, in-idris was better than idris when processing those documents. the average speed of the proposed algorithm reached approximately 13.55 seconds while idris needed 13.80 seconds on average for stemming. as a result, the speed gap between the in-idris and the idris stemmers is around 0.25 seconds. fig. 2: the graph visualization of accuracy comparison between idris and in-idris stemming. fig. 3: the graph visualization of speed between idris and in-idris stemming. 5 15 25 35 45 55 65 75 85 95 1 2 3 4 5 6 7 8 9 10 a c c u r a c y (% ) document idris in-idris 0 5 10 15 20 25 30 35 40 45 50 1 2 3 4 5 6 7 8 9 10 s p e e d ( s ) document idris in-idris 89 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 table 4 shows the sample text of the stemming result from the idris and the in-idris stemmers. the table contained: stem words (the original word taken from the novel collections), the root word for ground truth (the word which is used as a reference for evaluation), and the stemming result from both stemmers. the stemming result columns present which stem words were successfully changed to their root word and also show which were unsuccessful. there are some cases where in-idris was more powerful than idris, as proven from cases no. 1, 2, 4, 5, 6, 7, 9, and 10. however, for case no. 3 both algorithms could not work properly. some cases have shown that the idris stemmer affected character’s reduction, such as root word “pendek” changed to be “dek”, and the root word “tetes” changed to be “tes”. table 4: sample text from stemming result case no. stem word root word ground truth in english stemming result idris in-idris 1 memusnahkan musnah destroyed memusnahkan musnah 2 percayai percaya believe percayai percaya 3 kelahiranmu lahir born kelahiranmu kelahiranmu 4 menyeramkan seram scary menyeramkan seram 5 menyakitkan sakit sick menyakitkan sakit 6 mengerikan ngeri horrified gerik ngeri 7 pendekku pendek short dek pendek 8 terulur ulur stretch out ulut ulut 9 tetesan tetes drops tes tetes 10 menuruni turun down urun turun in a further experiment, we compared the result of the in-idris stemmer with two other algorithms (n&a and ecs) in addition to the previous idris result. table 3 presented the accuracy and speed of those four stemmer results when tested using 10 documents selected. from the table, the accuracy of ecs stemmer in both upper and lower accuracy is around 90.37% and 80.36% respectively. on the other hand, the result of n&a stemmer has a maximum accuracy of 89.86%, and the minimum accuracy is just 73.78%. meanwhile, the accuracy of both idris and in-idris have been described and presented in the previous table. overall, the accuracy results showed significant performance over eight in ten. in terms of speed, table 5 described that the fastest time needed by the ecs stemmer is approximately 2.41 seconds while the longest time is around 30.50 second. this result is not much different from the n&a result that has a speed in maximum and minimum around 36.68 seconds and 2.51 seconds, respectively. meanwhile, idris has around 42.16 seconds as its lowest speed and around 3.40 seconds as its fastest speed. on the other hand, in-idris has the fastest and longest speeds, approximately 3.02 seconds and 47.17 seconds, respectively. in fig. 4, the graph presented a comparison of the accuracy of the four stemming algorithms. overall, the accuracy results showed significant performance over eight in ten. whereas idris produced lower accuracy, which just reached 77.56% inaccuracy, and the ecs stemmer has the highest accuracy of 85.92%. meanwhile, the proposed stemmer, inidris, signified accuracy in 82.81%, which is lower than both the ecs and n&a stemmers, but the accuracy gap was small with just around 3%. 90 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 table 5: comparison accuracy and speed result between idris and in-idris stemmer doc n&a ecs idris in-idris speed (s) accuracy (%) speed (s) accuracy (%) speed (s) accuracy (%) speed (s) accuracy (%) 1 2.51 89.43 2.73 90.37 3.40 78.23 3.32 86.18 2 3.19 89.86 3.14 87.73 3.62 81.08 3.02 85.81 3 4.37 88.55 3.55 85.75 3.79 83.13 3.80 87.95 4 5.87 86.32 2.41 82.58 5.28 80.34 5.96 82.05 5 7.35 84.94 6.71 87.66 7.96 74.68 8.81 82.37 6 36.68 86.93 30.50 88.46 42.16 79.86 47.17 84.82 7 21.66 73.78 13.73 87.00 25.56 67.01 18.52 69.46 8 19.45 86.59 9.59 85.49 14.71 75.18 13.59 80.25 9 12.65 86.49 12.98 85.61 12.95 79.87 12.90 85.52 10 11.97 87.45 16.62 80.36 18.61 76.25 18.40 83.68 average 12.57 85.61 10.20 85.92 13.80 77.56 13.55 82.81 fig. 4: the graph visualization of accurate comparison results for both stemmers. fig. 5. the graph visualization of accurate comparison results for both stemmers. 0 15 30 45 60 75 90 1 2 3 4 5 6 7 8 9 10 a cc u ra cy (% ) document n&a ecs idris in-idris 0 10 20 30 40 50 1 2 3 4 5 6 7 8 9 10 s p e e d ( s) document nazief & adriani ecs idris in-idris 91 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 figure 5 depicts a comparison of the stemming speed of the four algorithms. stemming processed by ecs was the fastest, with just 10.20 seconds, and the longest stemming needed approximately 13.80 seconds when it was processed through the idris stemmer. on the other hand, the proposed method in-idris has a duration time of around 13.55 seconds to transform words into their root. this result is proof that in-idris needs extra time than n&a and ecs in stemming. however, there is one instance when in-idris finished stemming faster than the others, it is shown for document 2, where just needed 3.02 seconds. based on the experiment, the accuracy value is affected by the true word total produced for each document of stemming results. the higher the number of true words, the higher accuracy produced. however, the smaller the number of true words, the smaller the resulting accuracy. furthermore, the result of the stemming accuracy for each document is different for each stemmer. it can be caused by the different rules implemented in each algorithm, which can be called a stemmer characteristic. on the other hand, in terms of speed, the ecs stemmer is faster than the idris algorithm. that result is a refutation for the previous research [6] which was conducted to test the accuracy of the idris and ecs stemmers implemented in indonesian text documents. that research has claimed that idris has an excellent performance in speed. we concluded that the speed processing in stemming related to the number of words contained in each document, where the time needed to do the stemming process is relatively based on the tool or programming language used [24]. it was found that the idris algorithm had a low accuracy value caused by an affix cutting error in the stemming process that affected the results. the error was related to the application of the prefix removal first rule on the idris stemming. this caused root words that had the same letters as a prefix to be discarded, and it caused un-matching and errors in the final result. this error could be corrected by in-idris that obtained good stemming results with an increased accuracy until 5.25% from the idris stemmer. however, in the modification of the idris algorithm, in-idris still had a deficiency that caused words to fail in stemming. there is a shortcoming that in-idris could not handle, such as the affix "seku" on the word "sebelahku" (next to me, in english) whereas with the idris algorithm, the word "sebelahku" was changed to "belah". the challenge to develop a good stemming algorithm for future work is how a stemmer can be able to handle some problems including deletion error particularly occurring due to typing errors and mistakes in place names, people's names, and also foreign languages. the most powerful stemmer is the ecs algorithm, and some of its rules can be adopted to improve in-idris performance. however, the ecs stemmer applied the suffix deletion rule first and checked the dictionary every time it removed the affix. this can lead to word overstemming because the affix removal process was carried out as much as possible according to the applied rules, thus affecting the accuracy results. besides that, there is need for further development that can modify a combination of prefix and suffix rules to produce a better-stemming performance. 5. conclusion and future work in-idris is a new stemmer for indonesian text that was inspired from and improved upon the idris malay stemmer. based on the experiment, the researchers found that the idris algorithm has a low accuracy value caused by affix cutting errors on the stemming process which affected the results. this error could be corrected by in-idris so that it can 92 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 obtain good stemming results with an increased accuracy until 5.25% from idris stemmer. in-idris performance dominated for all documents tested, and overall the accuracy results showed significant performance of over eight in ten. in terms of speed, in-idris presented a faster speed than idris in stem word processing. finally, we conclude that the accuracy value is affected by the total of true words produced for each stemming result document. the higher the true words, the higher accuracy produced. however, the smaller the true words, the smaller the accuracy that resulted. references [1] vijayarani ds, ilamathi, mj., nithya m. (2015) preprocessing techniques for text mining an overview. j. computer science & communication networks, 5(1): 7-16. [2] buntoro g, arifin r, syaifuddiin g, selamat a, krejcar o, hamido f. (2021) the implementation of the machine learning algorithm for the sentiment analysis of indonesia’s 2019 presidential election. iium engineering journal, 22(1): 78-92. [3] nassirtoussia ak, aghabozorgia s, wah ty, david cln. (2014) text mining for market prediction: a systematic review. expert systems with applications, 7653-7670. [4] rizki as, tjahyanto a, trialih r. (2019) comparison of stemming algorithms on indonesian text processing. telkomnika, 17(1): 95-102. [5] utomo fs, suryana n, sanusi azmi, m. (2020) stemming impact analysis on indonesia quran translation and their tafsir classification for ontology instances. iium engineering journal, 21(1): 33-50. [6] permatasari n. (2016) analisis perbandingan algoritma idris dan algoritma enhanced confix stripping (ecs) stemmer pada dokumen teks bahasa indonesia. universitas komputer indonesia. https://repository.unikom.ac.id/130/ [7] titin w, kerami j, arief s. (2017) determining term on text document clustering using algorithm of enhanced confix stripping stemming. international journal of computer applications, 157(9): 8-13. [8] prasidhatama a, suryaningrum km. (2018) perbandingan algoritma nazief & adriani dengan algoritma idris untuk pencarian kata dasar. jurnal teknologi & manajemen informatika, 4(1): 1-4. [9] prihatini pm, putra id, giriantari iad, & sudarma m. (2017) stemming algorithm for indonesian digital news text processing. international journal of engineering and emerging technology, 2(2): 1-7. [10] mena vv, saputri k. (2018) contrastive analysis between english and indonesian prefixes and suffixes in the descriptive texts of student’s textbooks. english community journal, 2(1): 175-182. [11] jelita a. (2007) effective techniques for indonesian text retrieval. melbourne: rmit university. [12] adriani m, asian j, nazief b, tahaghoghi smm, & williiams he. (2007) stemming indonesian: a confix-stripping approach. acm transactions on asian language information processing (talip), 6(4): 1-33. [13] widayanto h & huda af. (2017) comparison nazief adriani and cs stemmer algorithm for stemm real data. in e-proceeding of engineering, 4(3): 5215. bandung, indonesia. [14] arifin az, mahendra ipak, & ciptaningtyas ht. (2009) enhanced confix stripping stemmer and ants algorithm for classifying news document in indonesian language. in international conference on information & communication technology and systems. in the international conference on information & communication technology and systems, 5:149-158. surabaya, indonesia. [15] idris n, mustapha ss. (2001) stemming for term conflation in malay texts. [16] porter, m. f. (1980). an algorithm for suffix stripping. program1, 14(3): 130-137. [17] paramitha es. (2012) analisis dan implementasi stemming menggunakan algoritma idris pada dokumen teks berbahasa indonesia. telkom university, indonesia. 93 iium engineering journal, vol. 23, no. 1, 2022 suci et al. https://doi.org/10.31436/iiumej.v23i1.1783 [18] mardiana t, adji tb, hidayah i. (2016) stemming influence on similarity detection of abstract written in indonesia. telkomnika, 14(1): 219-227. [19] rifai w, winarko e. (2019) modification of stemming algorithm using a non deterministic approach to indonesian text. indonesian journal of computing and cybernetics systems, 13(4): 379-388. [20] vega vb. (2001) information retrieval for the indonesian language. master’s thesis, national university of singapore. [21] arifin az & setiono an. (2002) klasifikasi dokumen berita kejadian berbahasa indonesia dengan algoritma single pass clustering. in prosiding seminar on intelligent technology and its applications (sitia). teknik elektro, institut teknologi sepuluh nopember surabaya. [22] asian j, williams he, & tahaghoghi smm. (2005) stemming indonesian. in proceedings of the twenty-eighth australasian conference on computer science, 38: 307-314. australia. [23] winarti t, kerami j, arief s. (2014) tokenization and filtering process in rapidminer. international journal of applied information systems, 7(2): 16-18. [24] zaman b. (2014) modifikasi algoritma porter untuk stemming pada kata bahasa indonesia. in seminar nasional teknologi informasi dan komunikasi (sentika 2014), 543-550. surabaya, indonesia. 94 microsoft word 189 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 219 availability of literature on engineering ethics in the internet yusof ismail and suhaimi mhd sarif department of business administration, kulliyyah of economics and management sciences, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. yusof_iiu@yahoo.com; albanjari@yahoo.com abstract: internet is becoming a popular tool among career oriented people. among professionals, some of the engineers use the internet in their work to search for information. the study is carried out to ascertain comparative availability of the materials on ethics and engineers in four top internet search engines (ise’s). three ise’s were accessed on 2 february 2011, from 2.21 p.m. to 4.21 p.m. [gombak time] using a combination of selected search terms: education, engineer, engineering, ethics, islam, professional, research, and training. the search results or hits produced by the selected ise’s were analyzed using a specially created instrument/format. the study computes relative ratios of the coverage of selected terms in relation to the number of hits for selected terms within each ise. the ratios are obtained by dividing the hits for a search term or combination into the total hits within each ise. the results of the analysis reveal the ise’s that contain the highest frequency of materials on engineers and ethics. the findings suggest to engineering students and practitioners of varying capabilities among the ise’s used in the study to learn about engineering ethics. limitations of the study and suggestions for further research are included in the study. abstrak: internet menjadi alat yang popular di kalangan staf yang berorientasikan kerjaya. di kalangan profesional, para jurutera menggunakan internet untuk mencari maklumat dalam kerja-kerja mereka. kajian ini dijalankan untuk menentukan ketersediaan perbandingan bahan-bahan mengenai etika dan jurutera dalam empat enjin carian internet (ise) teratas. beberapa ise dicapai pada 2 februari 2011, di antara 2.21 petang sehingga 4.21 petang [waktu gombak] menggunakan gabungan terma carian yang dipilih: pendidikan, jurutera, kejuruteraan, etika, islam, profesional, penyelidikan, dan latihan. keputusan carian atau ‘hits’ yang dihasilkan oleh ise terpilih telah dianalisis dengan menggunakan instrumen/format yang direka khas. kajian itu mengira nisbah relatif liputan terma-terma terpilih tersebut dengan jumlah ‘hits’ bagi kesemua terma bagi setiap ise. nisbah diperolehi dengan membahagikan ‘hits’ bagi istilah carian atau gabungan istilah dengan jumlah ‘hits’ dalam setiap ise. keputusan analisis menunjukkan ise yang mengandungi kekerapan tertinggi bahan-bahan berkaitan dengan jurutera dan etika. hasil kajian menyarankan kepada pelajar-pelajar dan pengamal kejuruteraan bahawa wujud keupayaan yang berbeza-beza di kalangan ise berhubung dengan potensi bahan-bahan berkaitan etika kejuruteraan. batasan kajian dan cadangan untuk penyelidikan selanjutnya dimasukkan dalam kajian ini. keywords: internet search engines; engineer; engineering ethics; training and development iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 220 1. introduction educating engineers with ethics and behavioral science is essential to ensure the sustainability of the development of engineering knowledge [1]. the inclusion of values in engineering requires acceptance from all stakeholders [1]. engineers must maintain their professionalism at all stages of the profession and aspects of life, including how to solve ethical problems professionally [2]. in today’s competitive and globalised world, talent and innovation with ethical dimension is highly valuable [3]. engineers must be concerned with and learn about ethics in their decision making process so that they can remain ethical and competitively better than their rivals [3]. ethics is a study on right (acceptable) and wrong (rejected) conduct or manner in the society or organizations [29-30]. a study on ethics is appropriate for any discipline or profession. this paper examines relative availability of materials related to engineering ethics in order to develop hands-on, professional, ethical and valuable engineers [2][3], which is promoted by the malaysian government in its innovative economic, social, political and technology transformation programs [4]. related terms are also searched for comparative purposes, i.e. based on the premise that rich databases of literature could imply that the concept is progressing rapidly [5]. the main objective of the study is to examine the relative frequency of engineering ethics and related concepts that are available in the internet search engines. it does not investigate the quality of the contents of the web-based materials available in the ise’s. one of the results of the study will be able to answer this question: how many hits are produced when the term “engineering” is used in comparison with “ethics,” “islam,” “professional,” “research,” and “training”? 2. literature review the literature review section discusses two important points: types of internet search engines and extent of usefulness of different internet search engines. 2.1 types of internet search engines there are many internet search engines (ises) that have been used widely in searching for information for the quantity as well as quality [6-7]. for example, mettrop and nieuwenhuysen evaluated thirteen internet search engines, namely altavista, euroferret, excite, hotbot, infoseek, lycos, msn, northernlight, snap, webcrawler, ilse, search.nl, and vindex [8]. fluctuations or complications are characteristics of the performance of the internet search engines [9-10]. the fluctuations in the search results do affect the efficiency of internet search as a publication/communication medium [9, 11-12]. 2.2 extent of usefulness of different internet search engines dreilinger and howe found that large data obtained from the ise’s may pose difficulties in the selection process [13]. it is also time consuming to filter them, which eventually may not render the results useful [12-13]. prior to the preceding study, tomaiuolo and packer found that similar results in one ise also appeared in the other ises [14]. the repetition can be used as checker against the accuracy of the information within and among the ise’s [12-13]. leighton and srivastana argue that these rich results give more confidence in terms of information accuracy but not so much of effectiveness of information retrieval [15]. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 221 wang, xie and goh contend that search engines are widely used as tools to find useful information from the internet [16]. however, most search engines were developed on the basis of technical requirements and without much consideration of the customer's perspective. ideally, ise’s should be very helpful not only to the designers, but also to the users. sullivan identified fourteen internet search engines (ise’s) which he classified as top choices (google, yahoo, and bing), strongly considered (alltheweb, aol, hotbot, and teoma), and other choices (altavista, gigablast, looksmart, lycos, msn, netscape, and open directory) [17]. 3. methodology this section has two parts: objective of the study and method of data collection. while the objective of the study explains the purpose of the study, the method of data collection describes the approaches for collection data for the study. 3.1 objective of the study the objective of study is to ascertain the number of hits of the terms related to engineering ethics that were produced by the selected internet search engines (ise’s). major search terms used include education, engineer, engineering, ethics, islam, professional, research, and training. related terms are included in the search in order to generate comparative data. the study is carried out to ascertain comparative availability of the materials on ethics and engineers in three top internet search engines (ise’s): google, yahoo and bing, from sullivan’s top choices only [17]. sullivan’s complete list comprised: top choices (google, yahoo, and bing), strongly considered (alltheweb, aol, hotbot, and teoma), and other choices (altavista, gigablast, looksmart, lycos, msn, netscape, and open directory) [17]. 3.2 method the internet was accessed on 2 february 2011, from 2.21 p.m. to 4.21 p.m. [gombak time] using a combination of selected search terms: education, engineer, engineering, ethics, islam, professional, research, and training. a tabular format is created to capture the data of interest for each search engine. the ratio of hits for each term within each ise is computed by dividing the hits into the total hits for the search engine. the use of ratios to compute hits produced by the internet search engines provides a means to assess impacts [18]. moreover, it is more appropriate to make inference from the use of ratios [19], although such approach can be less reliable statistically [20]. given time constraints, it is still economical to use ratio approach [19]. there are five stages involved in the process of computing the ratios, namely, (1) identify search engines, (2) record number of hits for specified search terms, (3) compute the ratios, (4) consolidate all the ratios, and (5) perform the analysis. 4. findings the findings section presents the results in terms of the number of hits of the terms related to engineering ethics that were produced by the internet search engines (ise’s). the iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 222 terms searched include education, engineer, engineering, ethics, islam, professional, research, and training. the results of the study are presented according to the five steps enumerated earlier. firstly, identify the internet search engines. the study adopted the list of ise’s identified by sullivan (2004). however, the study limits itself to three “top choices” of internet search engines, namely, google (www.google.com), yahoo (www.yahoo.com), and bing (www.bing.com). secondly, record the number of hits. the researchers recorded the hits shown for all the search terms, i.e., education, engineer, engineering, ethics, islam, professional, research, and training. table 1 shows the hits produced by four ise’s: google, yahoo, alltheweb and aol search. the ises show the highest total hits for the terms “engineer” and its combination with “ethics,” “ethics education,” “ethics islam,” “ethics professional,” “ethics research,” “ethics training,” and “ethics education professional training.” google produced the highest hits (211,000,000) for “engineer,” while yahoo and alltheweb produced the highest hits for “engineer ethics (23,800,000),” “engineer ethics islam (2,020,000),” “engineer ethics training (8,610,000),” and “engineer ethics education professional training (32,500,000).” based on these figures, ethics for engineers is available in the area of education for professional training. in assessing the capability of internet search engines (ises), google scores the highest by capturing 44% of the total hits as opposed to yahoo and alltheweb with 24% each respectively. aol search shows the lowest score, 8%. table 1: hits for search terms “engineer” and others. search terms internet search engines google yahoo alltheweb aol search engineer 211,000,000 59,600,000 59,600,000 34,200,000 engineer ethics 7,780,000 23,800,000 23,800,000 264,000 engineer ethics education 16,500,000 10,900,000 10,900,000 7,370,000 engineer ethics islam 1,340,000 2,020,000 2,020,000 264,000 engineer ethics professional 11,500,000 8,100,000 8,100,000 1,680,000 engineer ethics research 21,100,000 8,720,000 8,720,000 7,540,000 engineer ethics training 784,000 8,610,000 8,610,000 725,000 engineer ethics education professional training 6,840,000 32,500,000 32,500,000 415,000 total 276,844,000 154,250,000 154,250,000 52,458,000 percentage (%) 44 24 24 8 note: 2 february 2011, 2.21 p.m. – 4.21 p.m. malaysian time in gombak, kuala lumpur, malaysia table 2 shows the hits produced by the four ise’s: google, yahoo, alltheweb and aol search. yahoo and alltheweb produced higher hits compared to other ises. the highest total hits are observed for the term “engineering (446,000,000 with google),” but when “engineering” is combined with other terms, yahoo and alltheweb produced the highest. for example, “ethics (41,100,000),” “ethics education (10,600,000),” “ethics islam (2,260,000),” “ethics professional (8,500,000),” “ethics research (8,500,000),” “ethics training (16,000,000),” and “ethics education professional training (33,100,000)”. in terms of internet search engines (ises) capability, google scores the iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 223 highest when it captured 41% of the total hits as opposed to yahoo and alltheweb with 24% each respectively. the lowest score 11% is associated with aol search. when compared with table 2, google’s capability was reduced from 44% to 41% whereas aol search increased from 8% to 11% when the key search terms were changed from “engineer” to “engineering.” table 2: hits for search terms “engineering” and others. search terms internet search engines google yahoo alltheweb aol search engineering 446,000,000 178,000,000 183,000,000 104,000,000 engineering ethics 4,050,000 20,200,000 19,600,000 3,900,000 engineering ethics education 7,160,000 10,600,000 10,600,000 7,100,000 engineering ethics islam 269,000 2,260,000 2,260,000 264,000 engineering ethics professional 643,000 8,470,000 8,470,000 606,000 engineering ethics research 7,370,000 8,500,000 8,500,000 7,350,000 engineering ethics training 492,000 16,000,000 16,000,000 475,000 engineering ethics education professional training 333,000 33,100,000 33,100,000 303,000 ethics 79,300,000 41,100,000 41,100,000 26,100,000 total 545,617,000 318,230,000 322,630,000 150,098,000 percentage (%) 41 24 24 11 note: 2 february 2011, 2.21 p.m. – 4.21 p.m. malaysian time in gombak, kuala lumpur, malaysia. table 3 shows the top 10 total hits for “engineering” and “engineer” combined with several key terms generated by four ise’s: google, yahoo, alltheweb and aol search. the highest rank is “engineering” (46%), followed by “engineer” (18%), “ethics” (9%), and “engineer ethics education” (4%). the remaining is not significant as the score is below 4%. table 3: top 10 of total hits for search terms “engineer,” “engineering” and other terms. search terms total hits rank engineering 911,000,000 (46%) 1 engineer 364,400,000 (18%) 2 ethics 187,600,000 (9%) 3 engineer ethics education professional training 72,255,000 (4%) 4 engineering ethics education professional training 66,836,000 (3.4%) 5 engineer ethics 55,644,000 (2.8%) 6 engineering ethics 47,750,000 (2.4%) 7 engineer ethics research 46,080,000 (2.34%) 8 engineer ethics education 45,670,000 (2.3%) 9 engineering ethics education 35,460,000 (1.8%) 10 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 224 thirdly, compute the ratios. the ratio for specific term in each search engine is computed by dividing the hits of each search term by total hits for the search engine. the higher the ratio the higher the relative coverage of the search terms in the search engine concerned. table 4 produces comparative hits and ratios across the ise’s. the highest ratios were shown for the single term “engineer” with 0.762 (google), 0.386 (yahoo and alltheweb/atw), and 0.652 (aol search). when “engineer” was combined other terms, the ratios reduced significantly, the lowest ratios registered 0.005 for “engineer ethics islam.” likewise, lower ratios were shown for “engineer ethics,” “engineer ethics education,” and the rest. table 5 shows comparative hits and ratios across the ise’s. the highest ratios were possessed by the single term “engineering” with 0.817 (google), 0.559 (yahoo and alltheweb/atw), and 0.693 (aol search). when “engineering” was combined with other terms, the ratios reduced significantly, the lowest ratio was 0.000 for “engineering ethics islam.” likewise, other ratios also showed numbers, for example “engineering ethics,” “engineering ethics education,” and the rest. table 4: ratios for search terms “engineer” and other terms. ises google yahoo atw aol search terms hits ratio hits ratio hits ratio engineer 211,000,000 0.762 59,600,000 0.386 34,200,000 0.652 engineer ethics 7,780,000 0.028 23,800,000 0.154 264,000 0.005 engineer ethics education 16,500,000 0.06 10,900,000 0.071 7,370,000 0.141 engineer ethics islam 1,340,000 0.005 2,020,000 0.013 264,000 0.005 engineer ethics professional 11,500,000 0.042 8,100,000 0.053 1,680,000 0.032 engineer ethics research 21,100,000 0.076 8,720,000 0.057 7,540,000 0.144 engineer ethics training 784,000 0.003 8,610,000 0.056 725,000 0.014 engineer ethics education professional training 6,840,000 0.025 32,500,000 0.211 415,000 0.008 table 5: ratios for search terms “engineering” and other terms. ises google yahoo atw aol search terms hits ratio hits ratio hits ratio engineering 446,000,000 0.817 178,000,000 0.559 104,000,000 0.693 engineering ethics 4,050,000 0.007 20,200,000 0.063 3,900,000 0.026 engineering ethics education 7,160,000 0.013 10,600,000 0.033 7,100,000 0.047 engineering ethics islam 269,000 0.000 2,260,000 0.007 264,000 0.002 engineering ethics professional 643,000 0.001 8,470,000 0.027 606,000 0.004 engineering ethics research 7,370,000 0.014 8,500,000 0.027 7,350,000 0.049 engineering ethics training 492,000 0.001 16,000,000 0.050 475,000 0.003 engineering ethics education professional training 333,000 0.001 33,100,000 0.104 303,000 0.002 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 225 ethics 79,300,000 0.145 41,100,000 0.129 26,100,000 0.174 fourthly, consolidate all the ratios. all of the ratios are aggregated into table 6 to facilitate comparison. the comparative analysis of single search terms “engineering” and “engineer” shows that “engineering” scores the lowest 0.559, whereas “engineer” 0.386 at yahoo and alltheweb (atw). when “engineering” was combined other terms, the lowest ratios produced were 0.000 (“engineering ethics islam” at google) and 0.001 (“engineering ethics professional,” “engineering ethics training,” and “engineering ethics education professional training” at google). table 6: consolidated ratios for search terms “engineering,” “engineer,” and other terms. search terms google yahoo & atw aol search engineering 0.817 0.559 0.693 engineering ethics 0.007 0.063 0.026 engineering ethics education 0.013 0.033 0.047 engineering ethics islam 0.000 0.007 0.002 engineering ethics professional 0.001 0.027 0.004 engineering ethics research 0.014 0.027 0.049 engineering ethics training 0.001 0.050 0.003 engineering ethics education professional training 0.001 0.104 0.002 ethics 0.145 0.129 0.174 engineer 0.762 0.386 0.652 engineer ethics 0.028 0.154 0.005 engineer ethics education 0.060 0.071 0.141 engineer ethics islam 0.005 0.013 0.005 engineer ethics professional 0.042 0.053 0.032 engineer ethics research 0.076 0.057 0.144 engineer ethics training 0.003 0.056 0.014 engineer ethics education professional training 0.025 0.211 0.008 finally, perform the analysis. the last stage of the analysis identified the highest ratios for single search terms generated by each of the search engines. table 7 shows that all the four ise’s could capture the specified search terms despite their producing varying ratios. the most eminent term was “engineering”, which appeared as among the highest hits across all four ises. predictably, search terms under google produced more ratios as opposed to the other ises. clearly, google is able to produce higher ratios (or hits) compared to other ises. total hits and ratios will not be that meaningful if one desires to know the productivity of each ise for specific search terms. reviewing the ratios from various tables and consolidating them in tab. vi gives us the notion of efficiency of each search engine for single and combined search terms. tab. vii shows that google produced the highest hits (0.817) for generic “engineering.” however, if a person wishes to identify the association between “engineering” or “engineer” and “ethics islam”, yahoo and alltheweb are the iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 226 more efficient ises. yahoo is rated with 0.013, whereas google, 0.001 and aol search, 0.002. google stands out among the four ise’s for both single and combined search terms. for single search terms, google’s hits produced the highest among eighteen search terms used in this study. google’s hits for single and combined search terms portray a close association with its ratios. this suggests that it is highly probable that google’s materials for combined hits, which are more specific, are included in the generic and single search terms hits. table 7: consolidated ratios for search terms “engineering,” “engineer,” and other terms under google, under yahoo & atw, and under aol search. under google ratios under yahoo & atw ratios under aol search ratios engineering 0.817 engineering 0.559 engineering 0.693 engineer 0.762 engineer 0.386 engineer 0.652 ethics 0.145 engineer ethics education professional training 0.211 ethics 0.174 ethics 0.145 engineer ethics 0.154 ethics 0.174 engineer ethics research 0.076 ethics 0.129 engineer ethics research 0.144 engineer ethics education 0.060 ethics 0.129 engineer ethics education 0.141 engineer ethics professional 0.042 engineering ethics education professional training 0.104 engineering ethics research 0.049 engineer ethics 0.028 engineer ethics education 0.071 engineering ethics education 0.047 engineer ethics education professional training 0.025 engineering ethics 0.063 engineer ethics professional 0.032 engineering ethics research 0.014 engineer ethics research 0.057 engineering ethics 0.026 engineering ethics education 0.013 engineer ethics training 0.056 engineer ethics training 0.014 engineering ethics 0.007 engineer ethics professional 0.053 engineer ethics education professional training 0.008 engineer ethics islam 0.005 engineering ethics training 0.050 engineer ethics 0.005 engineer ethics training 0.003 engineering ethics education 0.033 engineer ethics islam 0.005 engineering ethics professional 0.001 engineering ethics research 0.027 engineering ethics professional 0.004 engineering ethics training 0.001 engineering ethics professional 0.027 engineering ethics training 0.003 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 227 engineering ethics education professional training 0.001 engineer ethics islam 0.013 engineering ethics education professional training 0.002 engineering ethics islam 0.000 engineering ethics islam 0.007 engineering ethics islam 0.002 5. discussion google stands out among the four ise’s for both single and combined search terms. the search terms used include education, engineer, engineering, ethics, islam, professional, research, and training. for the 18 search terms, google’s hits produced the highest. google’s hits for single and combined search terms reflected its highest ratios. this suggests that it is highly probable that google’s materials for combined hits, which are more specific, are also included in the generic and single search terms hits. some key literature of engineering ethics emphasizes on the obligations of employers, society and industry and potential challenges to implement ethics in engineering or to train engineers to be ethical. the scarcity of materials on engineering ethics may hinder employers, society, industry and engineers from reading and researching into engineering ethics. according to frantz, employers have an obligation to give training on ethics for engineers [21]. when such materials are not readily available in the internet, the employers might take the matter lightly. brenkert contends that, for any industries that need innovation, such as engineering and science, some rules and ethics are essential as precautionary measures [22]. otherwise, such ventures will be less useful for the industry and the users. johnson upholds similar argument that ethics plays an essential role in science and engineering [23]. for any society, ethics is catalyst for any right and effective accomplishment [24]. engineering students need to study ethics because with this knowledge they can identify and evaluate their engineering decisions to be professionally right and ethical [24-25]. bowden argues that teaching ethics to engineers strengthens their profession for the sake of the society and the industry [26]. according to coeckelberg, engineering can learn from ethics, and vice versa [27]. yearley calls for reviews of the societal and ethical aspects of synthetic biology [28]. 5.1 limitations of the study the study attempted to assess the availability of materials on education, engineer, engineering, ethics, islam, professional, research, and training. the relative ratios were comparable among the search engines to afford analysis. ratios are expected to reflect more statistically meaningful indices. despite this, cross comparisons among ise do not accommodate adjustments to size (or frequency of hits). another limitation of the study is its use of cross-sectional data (hits) at a point in time. stretching the study over time, for example quarterly, over a few years should be able to provide a meaningful pattern of coverage of the search terms across search engines. next, a pilot study with four ise’s, i.e. google, yahoo, alltheweb and aol search, may not be considered adequate compared to the availability of many other search engines. future study should include the other ise’s as well. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 228 5.2 significance of the study the study is very significant for theoretical development of engineering ethics, public and business policy for engineering ethics, and the general public. the internet search engine provides instant information on engineering ethics that can be pursued further. for the public and business policy, engineering ethics contributes to the progress of human beings and economic prosperity. the availability of hits promotes visibility of engineering and its professionalism. 6. conclusion based on the results of the specific search terms generated from the four ise’s, we can say that the amount of materials on engineering ethics is scarce. researchers will have to resort to other sources of information to learn about engineering ethics. despite this limitation, one can still opt to use google to gather materials on “engineering” and “engineer” but if he desires to learn only “engineering” or “engineer” who emphasizes “ethics” then yahoo is an appropriate search engine. internet users need to be cautioned that the hits only suggest apparent availability of the materials with the ise’s; they in no way suggest the adequacy and quality of the contents of the materials. references [1] k. mulder, j. segalas-coral, d. ferrer-balas, “educating engineers for/in sustainable development? what we knew, what we learned, and what we should learn.” thermal science, vol. 14, pp.625-639, sept ember 2010. [2] p. bowden, “teaching ethics to engineers – a research-based perspective.” euro. j. eng. edu, vol. 35, pp. 563-572, october 2010. [3] t.guo and j. liu, “multi-disciplinary education for product design and development.” adv. mat. research, vol. 156-157, pp. 681-684, october 2010. [4] g. malaysia. tenth malaysia plan (2011-2015). kuala lumpur: malaysia printing, january 2011. [5] g. jim, j. gao and y. wang, “ a multi-agent based knowledge search framework to support the product development process.” int j. comp. interg. mfg, vol. 23, pp. 237-247, october 2010. [6] m. chau, c.h. wong, y. zhou, and h. chen, “evaluating the use of search engine development tools in it education,” j. ame. soc. info. sci. tech., vol. 61, pp. 288-299, 2010. [7] z. xiang and u. gretzel, “ role of social media in online travel information search,” tourism mgt., vol. 31, pp. 179-188, 2010. [8] w. mettrop and p. nieuwenhuysen, “internet search engines – fluctuations in document accessibility,” j. doc., vol. 57, pp. 623-651, 2001. [9] m. thelwall, “quantitative comparisons of search engin results,” j. ame. soc. info. sci. tech., vol. 59, pp. 1702-1710, 2008. [10] a. uyar, “investigation of the accuracy of search engine hit couts,” j. info. sci., vol. 35, pp. 469-480, 2009. [11] a. pirkola, “the effectiveness of web search engines to index new sites from different countries,” info. res., vol. 14, pp.1-11, 2009. [12] r. prabowo and m. thelwall, “ sentiment analysis: a combined approach,” j. infometric, vol. 3, pp. 143-157, 2009. [13] d. dreilinger and a. howe, “experiences with selecting search engines using metasearch,” acm transac. info. sys., vol. 15, pp. 195-222, 1997. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering ismail and mhd sarif 229 [14] n. tomaiuolo and j. parker, “ an analysis of internet search engines: assessment of over 200 search queries,” comp.lib., vol. 16, pp. 58-62, 1996. [15] h. leighton and j. srivastava, “ precision among www search services (search engines): alta vista, excite, hotbot, infoseek and lycos,” retrieved from http://www.winona.edu/library/webind2.htm, 21 october 2010. [16] h. wang, m. xie and t. goh, “ service quality of internet search engines,” j. info. sci., vol. 25, pp.499-507, 1999. [17] d. sullivan, “ major search engines and directories,” retrieved from http://searchenginewatch.com/author/index.php/dannysullivan, 21 october 2010. [18] k. bharat and a. broder, “a technique for measuring the relative size and overlap of public web search engines,” 7 th intl. world wide web conf., april 1998. [19] s. lawrence and c. giles, “searching the world wide web,” science, pp. 98-100, april 1998. [20] h. chu and m. rosenthal, “ search engines for the world wide web: a comparative study and evaluation methodology,” asis, retrieved from http://www.asis.org/annual96/electronic-proceedings/chu.htm, retrieved 21 october 2010. [21] l. frantz, “engineering ethics: the responsibility of the manager,” eng. mgt. intl., vol. 4, pp. 267-272, january 1988. [22] g. brenkert, “ innovation, rule breaking and the ethics of entrepreneurship,” j.bus.vent., vol. 24, pp. 448-464, september 2009. [23] d.johnson, “the role of ethics in science and engineering,” trends biotech., vol. 28, pp. 589-590, december 2010. [24] w.wulf, “engineering ethics and society,” technology in soc., vol. 26, pp.385-390, aprilaugust 2004. [25] v.weil, “the rise of engineering ethics,” tech. in soc., vol. 6, 341-345, april 1984. [26] p. bowden, “teaching ethics to engineers a research-based perspective,” euro. j. eng. edu., vol. 35, pp. 563-572, october 2010. [27] m. coeckelbergh, “engineering good: how engineering metaphors help us to understand the moral life and change society,” sci. and eng. ethics, vol. 16, pp. 371-385, april 2010. [28] s. yearley, “the ethical landscape: identifying the right way to think about the ethical and societal aspects of synthetic biology research and products,” j. royal soc. interface, vol. 6, pp. s559-s564, may 2009. [29] a. ghillyer. business ethics: a real world approach (2nd ed.). new york: mcgraw-hill, 2010. [30] l. hartman and j. desjardins, j. (2011) (2nd edition). business ethics: decision-making for personal integrity & social responsibility. new york: mcgraw-hill/irwin, 2011 microsoft word 4-nuriium-ej38-27-2-o.k.doc iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. * corresponding author 29 influence of chatter of vmc arising during end milling operation and cutting conditions on quality of machined surface a.k.m.n. amin*, m.a. rizal, and m. razman department of mechanical engineering, faculty o f engineering, iium, gombak, 43100 kuala lumpur, malaysia, e-mail: akamin@iiu.edu.my abstract: machine tool chatter is a dynamic instability of the cutting process. chatter results in poor part surface finish, damaged cutting tool, and an irritating and unacceptable noise. extensive research has been undertaken to study the mechanisms of chatter formation. efforts have been also made to prevent the occurrence of chatter vibration. even though some progress have been made, fundamental studies on the mechanics of metal cutting are necessary to achieve chatter free operation of cnc machine tools to maintain their smooth operating cycle. the same is also true for vertical machining centres (vmc), which operate at high cutting speeds and are capable of offering high metal removal rates. the present work deals with the effect of work materials, cutting conditions and diameter of end mill cutters on the frequency-amplitude characteristics of chatter and on machined surface roughness. vibration data were recorded using an experimental rig consisting of kistler 3-component dynamometer model 9257b, amplifier, scope meters and a pc. three different types of vibrations were observed. the first type was a low frequency vibration, associated with the interrupted nature of end mill operation. the second type of vibration was associated with the instability of the chip formation process and the third type was due to chatter. the frequency of the last type remained practically unchanged over a wide range of cutting speed. it was further observed that chip-tool contact processes had considerable effect on the roughness of the machined surface. key words: chatter, cutting conditions, stable cutting, surface roughness. 1. introduction chatter is a type of self-excited vibration, which appears during the metal cutting process. it is undesirable but some times difficult to avoid during machining. chatter leads to continuous variations of the cutter and the work piece, which leads to low accuracy and surface finish of the machined part. chatter is also harmful from the point of view of machine and tool life and noise hazards. research in this area has been focused mainly on the suppression techniques of chatter. emphasis has been given to chatter monitoring systems with a view to avoiding chatter either by selection of appropriate cutting parameters or through addition of dampers or introduction of forced vibrations of appropriate frequency, amplitude and phase characteristics. there has been also some attempts by a few researchers to determine the primary causes of chatter [2, 3]. though there are controversies on the primary causes of chatter formation, it appears more logical to think of chatter as resonant phenomenon, caused due to mutual interaction between the vibrations of machine components, tool, work piece and the fixture system, by their natural frequencies on one hand and the vibrations caused by the instability of the chip formation process, when the frequencies of the two interacting vibrations are either equal or close to each other [2, 3]. since the primary cause of chatter is believed to be the instability of the chip formation and that in the development of chatter the natural frequencies of the system components play vital role, the current research is intended to investigate the influence of work material properties, cutting variables, as well as the tool dimensions on generation and the frequency-amplitude characteristics of chatter. the work also aims at determining the pattern of surface roughness produced as a function of both chatter and cutting conditions. the other parameter investigated, is the fluctuation of the chip thickness as a result of chatter. 2. experimental setup the experiments were performed on vertical machining center model mcfv 1060 with vickers acramatic controller model a2100 cnc mc. multi component kistler dynamometer type 9257b was used to measure the variation in cutting force. the signals from the dynamometer were amplified by a charge amplifier and recorded by flurke scope meter in waveform. the recorded data in the waveforms were further analyzed by using flurke view software. a schematic view of the experimental setup is shown in fig. 1. a sample of the recorded vibration indicating the low and the higher frequencies is shown in fig. 2. the chips produced under various cutting conditions were investigated to compare the frequencies of fluctuations of chip thickness with the recorded frequency during the cutting. average surface roughness of the work piece at the face and the radial surfaces was measured using the iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. 30 mitutoyo surface roughness measuring instrument model: sv 500. the cutting conditions are listed in table 1. three types of work materials: aluminum alloy aan6061, mild steel aisi1020 and stainless steel aisi446 were machined. the hardness of the work materials was measured on digital hardness testing machine model ark-600. the hardness values are given in table 2. end mill cutters of diameters 20mm and 25mm were used for machining. the machined surface was examined under the scanning electron microscope (sem). the photograph of the middle section of the chip was taken after etching using an optical microscope with normal camera. fig. 1: experimental setup (a) (b) fig. 2: vibration output in wave form at low magnification (a), showing peaks of low frequency chatter and at high magnification (b), showing peaks of high frequency chatter. table 1: values/ranges of cutting parameters cutting parameters workpiece materials al alloy mild steel stainless steel cutting speed, m/min 100-550 25-300 20-140 feed, mm/tooth 0.05, 0.10 and 0.20 depth of cut, mm 1.5, 2.0 and 5.0 cutting tool work material dynamometer amplifier scopemeter pitch of low frequency chatter pitch of high frequency chatter iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. 31 table 2: work material hardness material hardness stainless steel 87.1 hrb mild steel 67.5 hrb aluminum 55.7 hrb 3. results and discussion three main types of vibrations were observed during machining of all the three work materials: one with a very low frequency, equal to spindle rpm times the number of cutter tooth, the other one with a medium frequency, mainly responsible for chatter, and the last type was associated with the serration frequency of the chip. since the highest amplitudes of vibration i.e. chatter phenomenon was associated with the intermediate frequencies, more attention was paid to this type of vibration. the of this frequency range are given in the following sections. 3.1 stainless steel curves of chatter/vibration frequencies and amplitude vs. cutting speed and amplitude and average surface roughness vs. cutting speed were plotted for different combinations of feed and depth of cut. sample relationships among the above parameters are shown in fig. 3 and fig. 4. the feed and depth of cut values used in these cases were respectively 0.10 mm/tooth and 2 mm. it is observed from fig. 3 that the variation in the frequency of vibration is in the range of 395 hz to 560 hz, which is not very high (varies only by 41%) and may be considered to be practically constant. the amplitude of vibration on the other hand varies from 10.42 n to 37.77 n (by 262%), which is quite high. this high fluctuation of vibration amplitude may be explained by the appearance of chatter or resonant vibration. amplitude of chatter varies sharply in the cutting speed range from 35 to 65 m/min and then remains almost constant (varies by only 19%). as it may be observed from fig 4 that the average surface roughness of the work piece varies from 0.13 m m to 0.26 m m for these cutting conditions. the surface roughness values are low in the beginning but increased up to a speed of 95 m/min and then dropped. the rise in surface roughness values with cutting speed is related to the increase in amplitude of chatter in the case of stainless steel the chip shows a serrated nature above 50 m/min. this phenomenon may be observed from the microphotograph of the middle section of the chip as shown in fig. 5. due to intensive tool wear and frequent tool breakages the cutting speed was limited to 140 m/min. the values of amplitude and surface roughness for two tool holder diameters and other cutting conditions are listed in the tables 3 and 4.. 560556543539 446433430397394 24.16 31.04 32.48 33.6 34.6 38.24 37.44 12.9610.42 0 200 400 600 20 35 50 65 80 95 110 125 140 v, m/min fr eq , h z 0 10 20 30 40 50 a m pl itu de , n freq, hz amplit (n) fig. 3: variation of frequency and amplitude of chatter with cutting speed. work material: stainless steel, feed: 0.10 mm/tooth, depth: 2mm 10.42 12.96 24.16 31.04 32.48 33.6 34.6 37.44 38.240.22 0.17 0.26 0.25 0.23 0.25 0.23 0.2 0.13 0 10 20 30 40 50 20 35 50 65 80 95 110 125 140 v, m/min a m pl itu de , n 0 0.1 0.2 0.3  m amplit (n) surf.r.(ra) fig. 4: dependence of surface roughness on amplitude of chatter and cutting speed. work material: stainless steel, feed: 0.10 mm/tooth, depth: 2mm iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. 32 fig. 5: photograph of the chip section. material: stainless steel. a) v=45 m/min; b) v= 105 m/min 3.2 mild steel curves of chatter/vibration frequencies and amplitude vs. cutting speed and amplitude and average surface roughness vs. cutting speed were plotted for different combinations of feed and depth of cut. sample relationships among the above parameters are shown in fig. 6 and fig. 7. the feed and depth of cut values used in these cases were 0.10 mm/tooth and 2 mm, respectively. it may be observed from fig. 6 that the variation in the frequency of vibration was in the range 375 hz to 506 hz up to a speed of 275 m/min, which is not very high (varies only by 35%) and may be considered to be practically constant. the amplitude of vibration varieds from 10.8 n to 52.8 n (by 389%), which is very high. this high fluctuation of vibration amplitude may be explained by the appearance of chatter or resonant vibration. amplitude of chatter changed more sharply in the speed range from 75 to 175 and from 225 to 275 m/min and then started decreasing. as it may be observed from fig 4 and fig. 7, the average surface roughness values in the case of this material was much higher than that of stainless steel at the initial cutting speed values but the pattern of the curve is a bit different from that of stainless steel. the roughness values continuously fell with cutting in a wide rage of cutting speed. roughness values in the cutting speed range 175 to 300 m/min are quite comparable to those of stainless steel in the range 50 to 140 m/min. the average surface roughness of the work piece varied from 0.71 m to 0.10 m for these cutting conditions. the continuous fall in the surface roughness values with cutting speed, may be related to the serration of chips in the case of mild steel, as may be observed from fig. 8, although some marks of vibration may be noticed in the chip section. due to intensive tool wear and frequent tool breakages the cutting speed was limited to 300 m/min. the values of amplitude and surface roughness for two tool holder diameters and other cutting conditions are listed in the tables 3 and 4. 375 388.89 400 436.89 403.07 476.19 601.27 506.33 15.6 18 29.2 36.8 38.8 52.8 48.8 10.8 0 100 200 300 400 500 600 700 25 50 75 125 175 225 275 300 v, m/min f re q, h z 0 10 20 30 40 50 60 a m p lit ud e, n frequency amplitude (n) fig. 6: variation of frequency and amplitude of chatter with cutting speed. work material: mild steel, feed: 0.10 mm/tooth, depth: 2mm iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. 33 10.8 15.6 18 29.2 52.8 48.8 38.836.8 0.71 0.58 0.59 0.38 0.25 0.1 0.260.26 0 20 40 60 25 50 75 125 175 225 275 300 v, m/min a m pl itu d. n 0 0.2 0.4 0.6 0.8  m amplitude (n) surf.roughness(ra) fig. 7: dependence of surface roughness on amplitude of chatter and cutting speed. work material: mild steel, feed: 0.10 mm/tooth, depth: 2mm table 3a: recommended cutting condition to satisfy surface roughness quality criteria and force amplitude of vibration end mill cutter  material feed 0.05 0.1 0.2 depth of cut 1.5 2 1.5 2 s ta in le ss s te el speed 0.96 1.91 10 24.64 6.4 15 1.66 27.2 20 0.76 36.8 25 1.02 17.28 30 0.64 21.92 35 0.5 38.24 40 0.43 12.32 45 0.76 38.24 50 1.12 23.36 55 0.69 36.48 60 0.98 28.48 65 0.60 28.64 70 0.73 31.84 75 0.64 37.28 table 3b: recommended cutting condition to satisfy surface roughness quality criteria and force amplitude of vibration end mill cutter  material feed 0.05 0.1 0.2 depth of cut 1.5 2 1.5 2 m ild s te el speed 1.37 1.02 0.32 0.34 50 9.2 12.4 16.96 17.44 75 0.92 0.89 0.34 0.3 13.6 14.2 53.6 37.08 100 1.07 0.93 0.3 0.32 16.4 26.8 35.2 17.6 125 0.91 0.86 0.29 0.32 14.8 16.4 34.8 38.24 150 1.07 0.95 0.3 0.31 24.8 32 30.8 25.44 175 0.83 0.81 0.29 0.29 19.2 20 65.2 38.24 200 0.9 0.82 0.28 0.29 28.4 36.8 32.4 31.36 225 0.76 0.67 0.29 0.3 22.4 26.8 62.8 38.24 250 0.72 0.63 0.3 33.2 42.8 28.32 275 0.32 0.27 0.29 30 35.6 38.24 iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. 34 table 3c: recommended cutting condition to satisfy surface roughness quality criteria and force amplitude of vibration end mill cutter  material feed 0.05 0.1 0.2 depth of cut 1.5 2 1.5 2 a lu m in um speed 0.91 12.96 0.42 12.48 0.79 11.2 0.8 12.96 50 0.57 0.61 0.58 75 14.24 26 25.28 0.64 0.45 0.32 0.45 100 18.08 19.36 29.2 36.4 0.56 0.19 0.43 125 20.64 52.8 32 0.55 0.43 0.2 0.42 150 22.08 22.08 72.8 36 0.45 175 18.24 0.54 0.48 200 18.4 35.04 0.53 225 25.6 0.5 0.58 250 21.28 34.72 0.7 275 26.16 0.54 0.31 0.28 300 36.32 70.4 38 0.48 0.56 0.48 350 33.76 82.4 40 0.48 0.37 0.32 400 36.64 94 74.8 0.51 0.22 0.32 450 33.28 75.6 92 bold faced figures: acceptable values that meeting grinding surface criteria 0.1 1.60 m force amplitude limited up to 40n upper values in each cell represent surface roughness ra (m) lower values in each cell represent force amplitude (n) table 4a: recommended cutting condition to satisfy surface roughness quality criteria and force amplitude of vibration end mill cutter  material feed 0.05 0.1 0.2 depth of cut 1.5 2 1.5 2 s ta in le ss s te el speed 1.8 10 12.02 20 0.28 0.16 0.22 11.84 7.68 10.42 30 0.23 15.86 35 0.26 0.17 11.36 12.96 40 0.17 17.28 50 0.22 0.25 0.26 21.76 13.6 24.16 60 0.18 26.56 65 0.26 0.25 15.68 31.04 70 0.35 28.4 80 0.44 0.23 20.96 32.48 95 0.27 0.25 23.84 33.6 110 0.26 0.23 34.72 34.6 125 0.29 0.2 38.24 38.24 140 0.2 0.13 38.24 37.44 iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. 35 table 4b: recommended cutting condition to satisfy surface roughness quality criteria and force amplitude of vibration end mill cutter  material feed 0.05 0.1 0.2 depth of cut 1.5 2 1.5 2 m ild s te el speed 25 1.17 0.71 0.83 8.8 10.8 14.8 50 0.98 0.58 0.61 10.4 15.6 13.6 75 0.69 0.59 13.2 18 100 0.4 28.4 125 0.36 0.38 12.4 29.2 150 0.25 31.6 175 0.31 0.26 27.2 36.8 200 0.19 53.2 225 0.16 0.26 18.4 38.8 250 0.18 37.2 275 0.18 0.25 0.16 34 52.8 45.6 300 0.12 0.1 0.16 29.6 48.8 52.8 table 4c: recommended cutting condition to satisfy surface roughness quality criteria and force amplitude of vibration end mill cutter  material feed 0.05 0.1 0.2 depth of cut 1.5 2 1.5 2 a lu m in um speed 100 0.12 0.11 15.2 18 200 0.12 0.11 24.8 28.4 300 0.1 0.11 38.8 51.6 350 0.11 0.11 39.6 39.2 400 0.08 0.09 47.2 62 450 0.08 0.08 78 38.4 500 0.09 0.11 62.4 79.6 550 0.12 0.11 44.4 50.8 bold faced figures: acceptable values that meeting grinding surface criteria 0.1 1.60 m force amplitude limited up to 40n upper values in each cell represent surface roughness ra (m) lower values in each cell represent force amplitude (n) iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. 36 3.3 aluminum alloy curves of chatter/vibration frequencies and amplitude vs. cutting speed and amplitude and average surface roughness vs. cutting speed were plotted for different combinations of feed and depth of cut. sample relation ships among the above parameters are shown in fig. 9 and fig. 10. the feed and depth of cut values used in these cases are 0.20 mm/tooth and 1.5 mm respectively. it may be observed from fig. 9 that the variation in the frequency of vibration is in the range of 221 hz to 305 hz up to a speed of 500 m/min, which is not very high (varies only by 38%) and may be considered to be practically constant. the amplitude of vibration on the other hand varies from 15.2 n to 78 n (by 413%), which is very high. this high fluctuation of vibration amplitude again may be explained by the appearance of chatter or resonant vibration. amplitude of chatter changes more sharply in the speed range from 100 to 300 and from 400 to 450 m/min and then it decreased quite sharply. figures 4, 7 and 10 show that the average surface roughness values in the case of this material was much lower than that of stainless steel and mild steel. at the initial cutting speed values (100-200 m/min) the roughness values are of the order of 0.12 m. roughness gradually fell up to a speed of 450 (up to 0.08 m) but then started rising to the initial value of 0.12 m. this may me due to the high amplitude of chatter. the chip in this case did not show any sign of serration though marks of vibration were observed in the chip at higher cutting speeds. due to intensive tool wear and high vibrations, the cutting speed was limited to 550 m/min. the values of amplitude and surface roughness for two tool holder diameters and other cutting conditions are listed in the tables 3 and table 4 along with the other two work materials. fig. 8: photograph of the chip section. material: carbon steel: a) v=50 m/min; b) v=250 m/min. 221.52 254.85 253.62 270.52 279.13 298.91 305.85 335.65 24.8 38.8 39.6 47.2 78 62.4 44.415.2 0 100 200 300 400 100 200 300 350 400 450 500 550 v, m/min fr eq , h z 0 20 40 60 80 100 a m p lit ud n frequency amplitude (n) fig. 9: variation of frequency and amplitude of chatter with cutting speed. work material: aluminum alloy, feed: 0.20 mm/tooth, depth: 1.5 mm 24.8 38.8 39.6 47.2 62.4 44.415.2 78 0.12 0.12 0.1 0.11 0.08 0.09 0.12 0.08 0 20 40 60 80 100 100 200 300 350 400 450 500 550 v, m/min a m pl itu d , n 0 0.05 0.1 0.15  m amplitude (n) surf.roughness(ra) fig. 10: dependence of surface roughness on amplitude of chatter and cutting speed. work material: aluminum alloy, feed: 0.20 mm/tooth, depth: 1.5 mm. iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. 37 3.4 influence of feed and depth of cut on frequency of vibration the vibration frequencies for different conditions were plotted to study their influence on the formation of chatter. it was observed that the frequency of vibration increased with the cutting speed. however, it appears from curves in fig. 11 that for lower value of depth of cut the higher frequencies. this due to reduction of shear zone where the chip elements can be easily formed or lower energy is required for the formation of the chip elements. the sam characteristics can be seen in the case of feed variation where lower feed rate will lead to higher frequency as can be observed in figure 12. the same relationship holds for the given parameters for different work materials and tool holder diameters. 0 200 400 600 800 0 50 100 150 200 250 300 350 v, m/min f re q, h z feed 0.1 feed 0.2 fig. 11: influence of cutting speed and depth of cut on frequency of chatter. material: mild steel feed: 0.2 mm/tooth, tool diameter: 20mm 0 200 400 600 800 0 50 100 150 200 250 300 350 v, m/min f re q, h z feed 0.1 feed 0.2 fig. 12: influence of cutting speed and feed rate on frequency of chatter. material: mild steel feed 0.2 mm/tooth, tool diameter: 20mm 3.5 influence of tool diameter on frequency the effect of different tool holder diameters on amplitude of chatter and surface roughness may be given in tables 3 and table 4. it may be observed from the tables that lower values of tool holder diameter correspond to higher amplitudes of vibration. lowering of the tool diameter to extremely low values, like 12 mm, leads to drastic reduction of the applicable cutting speed, feed and depth of cut values as supported by the present and previous experimental results. 3.6 amplitude and surface roughness values and recommended cutting conditions table 3 and table 4 lists all the amplitude values expressed in n and placed at the lower portion of each cell, and the average surface roughness values are listed at the upper portions of the cell. cutting conditions have been considered acceptable if the amplitude of vibration is below 40 n and the surface roughness value below 1.6 m m, required for grinding finish (roughness value in the range of 0.4-1.6 m m is required in grinding and 0.1-0.4 m m is required in polishing). 3.7 analysis of surface finish the machined surface was observed and analyzed using the sem in order to explain the causes of gradual improvement of surface finish with the increase of cutting speed. two samples micrographs are shown in fig. 13, for mild steel at depth of cut of 2 mm, feed rate 0.1 mm/tooth at two different cutting speed values. it may be observed from the figure that built-up-edge (bue) present at relatively lower cutting speeds vanishes at higher speeds. the disappearance of bue facilitates the reduction of the average surface roughness value at higher cutting speeds. iium engineering journal, vol. 2, no. 1, 2001 a.k.m.n. amin et al. 38 fig. 13a: machined surface at speed = 100 m/min viewed under sem fig. 13b: machined surface at speed = 175 m/min viewed under sem 4. conclusion the following conclusions were drawn: 1) three different types of vibration, associated with the entering of the milling insert in cutting operation during each rotation of the tool, resonant vibration of the tool/fixture elements, and instability/serrated nature of chip formation, were observed. 2) the intermediate frequency vibrations were caused as a result of the interaction of the instability of chip formation process and the natural frequency of the tool/fixture or the work piece. the frequency of this vibration remains practically unchanged over a wide range of cutting speed. 3) higher frequencies of vibrations were more prominent in the case of stainless steel, which is more prone to serrated chip formation. 4) the surface roughness of machined part is reduced with the increase in cutting speed due to the disappearance of built-up-edge at higher speeds. 5) increase in the amplitude of chatter leads to higher surface roughness value at higher cutting speed ranges, where machining is accompanied with intensive chatter. 6) feed and depth of cut have a significant effect on the frequency and amplitude of chatter. lower feed and depth of cut result in higher frequency of chatter because of the reduction of shear zone, since the chip elements can be easily formed. acknowlegement this research is funded by the research center, international islamic university malaysia. references [1] a.k.m.n. amin and n.v. talantov,, “investigation of chatter on tool wear” mechanical engineering res. bulletin, 10, pp. 11-18, 1987. [2] a.k.m.n. amin and m.k. khalil, investigation of chatter arising in machine-tool–fixtures-work (mtfw) system during turning”, proceeding of international conference on advanced manufacturing technology, johor baru, malaysia, 29 30 august, 1994. [3] a.k.m.n. amin, investigation of the mechanism of chatter formation during metal cutting process”, mechanical engineering res. bulletin, 6, pp. 12-18, 1983. [4] m.a. rizal and m. razman, investigation of chatter arising during metal cutting on vertical machining center, final year project report, faculty of engineering, iium, kuala lumpur, 2000. [5] k. jemialniak,, and a. windota,, “supression of selfexcited vibration by spindle speed variation method”, int. j. mach. tool des. res. 24, pp. 207-214, 1984. [6] e. m. trent, metal cutting, butterworth-heinemann ltd, 5th edition, 2000. biography of the authors dr. a.k.m. nurul amin is currently working as an associate professor and head of the department of mechanical engineering, faculty of engineering, international islamic university malaysia. he was previously serving as head of department of industrial and production engineering, bangladesh university of engineering and technology. he was born in bangladesh in 1954. he obtained his m.sc. degree in production engineering from volgograd polytechnic institute in 1979 and ph.d. from georgian polytechnic institute in 1982. his areas of interest are machinability, machine tool chatter and optimization of metal cutting processes. mohd rizal alkahari and razman mustafa are born in malaysia. they graduated from department of mechanical engineering. faculty of engineering, international islamic university malaysia in the year 2000. they are currently employed as practicing engineers in manufacturing sector of malaysia. microsoft word azram -f.doc iium engineering journal, vol. 2, no. 2, 2001 m. azram 29 anti-plane surface disturbance m. azram department of science in engineering, kulliyyah of engineering international islamic university malaysia, jalan gombak, 53100 kuala lumpur abstract: solution to a problem of half-space subjected to anti-plane surface disturbance via cagniard-de hoop method has been investigated. the solution is very much dependent on the choice of branch cuts, branches, and their behavior along the appropriate selected contour. investigations show that the contour, which simplifies the inversion integral, may or may not exist in some quadrants of -plane and is very much dependent on the position of the point . consequently, the solution is the hankel function of first kind ( )(1)02 i h k r . keywords: cagniard-de hoop method. inversion integral. hankel function. anti-plane shear. waves propagation. fourier transform. 1. introduction surface disturbances give rise to waves. waves are a ubiquitous and important feature of the physical world, and throughout the history it has been a major challenge to understand them. they can propagate on surfaces of solids and of fluids. chemical waves control the heartbeat. in recent years, elastic waves transmitted through the human body have been used for medical diagnoses and therapy. waves propagation as one of basic phenomena in solids is of both theoretical and practical importance. waves propagation in elastic solids is a very broad and attractive research field. the study of waves propagation in elastic solids has a long and distinguished history [1]. cauchy and poisson have studied the propagation of a disturbance in an elastic aether as early as middle of the 19th century. their contribution and work is now, generally known as the “theory of elasticity”. early investigations on the propagation of waves in elastic solids have been carried out by cauchy, clebsch, christoffel, green, lame, ostrogradsky, poisson, and stokes. this work has been briefly discussed in the book “the mathematical theory of elasticity” written by love [2]. another classical book is by timoshenko [3]. lamb, love, and rayleigh contributions in this area are of significant importance. many professionals in engineering, physics, geology, mathematics, and life science encounter problems requiring an understanding of elastic waves. the study of wave propagation in elastic solids have stimulating and wide-ranging engineering applications, such as earthquake phenomena, nuclear explosion, seismology [4-6], structure under high rate of loading, high-speed machinery, ultrasonics and piezoelectric, material science, applied mechanics, in-situ safety and reliability control of complex structural components by acoustic emission, quantitative non-destructive material testing by ultrasonics, dynamic fracture mechanics, fluid mechanics, aerodynamics, anistrophy, geophysics, and elastodynamics[7], etc. for other significant contributions in the field of engineering, reader is encouraged to consult references [1,8-13]. parallel to the study of waves in elastic solids, the propagation of waves has also been investigated within the context of applied mathematics, electromagnetic theory and acoustics[11, 14-19]. exposure to mathematical formulation of governing equations of wave motion is essential to understand the basic principles of wave motion in solids. a wide range of problems in this area has been studied based on mathematical, physical, experimental and numerical approaches. consequently, large numbers of methods have been developed in this domain. currently, the most commonly used methods are finite differences, finite elements[20, 21] , spectral methods and boundary elements, soap-film method, photo elastic method, integral transform, discrete fourier transform, maliuzhinets’ method, numerical modeling, wienerhopf technique, and cagniard-de hoop method. numerical modeling of elastic waves is important in many applications, such as geophysics, non-destructive testing, and fluid-structure interaction. the wienerhopf technique[22] has, since its invention in 1931, proved to be an elegant method in engineering and mathematical physics. advantage of this method is that it provides an exact solution of integral equations. geophysics, elastic and electromagnetic waves, diffraction of acoustic, fracture mechanics etc. are in the domain of its applications. parallel to wiener-hopf technique, an immensely important method is the cagniard-de hoop method. it is within the context of the application of laplace transform but a considerable amount of complex analysis is required. this method was firstly established by[6] and then modified by de hoop[23]. 2. background achenbach [1], has used the cagniard-de hoop method to solve a problem of half-space subjected to anti-plane surface disturbance i.e., he considered the half-space y  0 subjected to the surface disturbance of the form (at y = 0 ) ( ) i t yz t x e w t m= (1) iium engineering journal, vol. 2, no. 2, 2001 m azram 30 where yzt is the shear stress,  is elastic constant, t(x) is the strain,  is the circular velocity, and t is the time. the anti-plane shear disturbance generates a deformation which is governed by 2 2 2 2 2 2 2 1 t w w w x y c t ¶ ¶ ¶ + = ¶ ¶ ¶ (2) where w(x,y,t) is the displacement in z-direction and ct is the transverse velocity. if the surface disturbance has been operating for a long time, it is reasonable to assume that a steady state has been reached, and we may consider the displacement in the form ( , , ) ( , ) i tw x y t w x y e w= (3) the governing equation for w(x,y) follows from (2) as a boundary value problem ( ) 2 2 2 2 2 0 0t y w w k w x y w t x y = ¶ ¶ + + = ¶ ¶ ¶ = ¶ (4) where t t k c w = is the wave number, exponential fourier transform along with inverse transform are defined as; *( ) ( ) i x f e f x dx x x ¥ ¥ = ò (5) *1( ) ( ) 2 i xf x e f dx x x p ¥ ¥ = ò (6) exponential fourier transform (5) applied to (4) yields; ( ) 2 2* * 2 2 ( ) , t k y t t w y e k xx x x = (7) where *( )t x is the fourier transform of t(x). since the solution w(x,y) is required to be bounded as y, hence, w*(,y) in (7) is made bounded as y by making the multiple-valued function 2 2tkx as single-valued by introducing the branch cuts emanating from the branch points  =  kt. branches are chosen such that 2 2re( )tkx is non-negative on the real axis. in addition, we choose 2 2tkx positive for re() > kt, im() = 0. the exact evaluation is carried out by a specific choice of t(x) = (x), where (x) is the dirac delta function, which yields t*() = 1. consequently, the inverse fourier transform of (7) yields the inversion integral 2 2 2 2 1 1 ( , ) 2 ti x k y c t w x y e d k x x x p x = -ò (8) where c is parallel but above and below to the negative and positive real axis respectively, as shown in fig. 1. fig. 1: path in the x -plane. with the introduction of x = r cos  and y = r sin , the integral equation (8) reduces as { }2 2cos sin 2 2 1 1 ( , ) 2 ti r i k c t w x y e d k x q x q x p x -= -ò (9) this inversion integral is equivalent to the most often used inversion integral in elastodynamics given by { }2 2cos sin( , ) ( , , ) t i r i k c w x y f r e d x q x q q x x = ò where the contour c is in the complex  plane. application of the cagniard-de hoop method was the standard approach to find the solution, in which focus was to search a contour c1 such that whenever  is on c1, 2 2cos sints i kx q x q= . this equation can be solved for x as: 2 2cos sints i s kx q q= ± , which yields the hyperbola ( ) ( ) 2 2 re im 1 cos sint tk k x x q q é ù é ù ê ú ê ú=ê ú ê úë û ë û provided 2 2 0ts k³ with s to be real. the required contour was branch of this hyperbola that lies in the righthalf of the  plane as shown in fig. 2. consequently, the multiple valued function 2 2tkx was made single-valued function by introducing branch cuts emanating from the branch points tk± and going to the left and right along the real axis. the branch was chosen which has positive real part for  on c1. the ultimate solution was the hankel function of second kind (2)0( , ) ( )2 t i w x y h k r= . noble[22] considered the same inversion integral with the assumption that tk is complex and  = tk cos( + i t), where - < t < . iium engineering journal, vol. 2, no. 2, 2001 m azram 31 fig. 2: change of contour in the -plane. consequently, the solution was (1) 0 ( )2 t i h k r if tk has small positive imaginary part and (2) 0 ( )2 t i h k r if tk has small negative imaginary part. both achenbach[1] as well as noble [22] searched the solution(s) by simplifying the inversion integral. solution was very much dependent on the choice of branch cuts, branches, and their behaviors along the appropriate selected contour. different modes of solution obtained for the same problem required further investigations of the inversion integral and the corresponding solution. 3. investigation and discussion consider the multiple valued function 2 2( ) tf kx x= with two of its branches 1( )f x and 2 ( )f x defined by 1 2)( 2 1 1 2( ) i f r r e q q x + = (10) where 1 2 1 1 2 2 0, 0, arg( ); 0 2 , arg( ); . t t t t r k r k k k x x q x q p q x p q p = > = + > = < < = + < < 1 2 )( 2 2 1 2( ) i f r r e q q x + = (11) where 1 2 1 1 2 2 0, 0, arg( ); 2 4 , arg( ); . t t t t r k r k k k x x q x p q p q x p q p = > = + > = < < = + < < now, let us investigate the mapping properties of f1 (): if  lies in the first quadrant then; 1 2max( )q q p+ = and 1 2min( ) 0q q+ = , which yields that ( )1 20 2 2q q p< + < , concluding that 1 st quadrant maps into 1 st quadrant. if  lies in the second quarter then; 1 2max( ) 2q q p+ = and 1 2min( )q q p+ = which yields ( )1 22 2p q q p< + < , concluding that 2nd quadrant maps into 2nd quadrant. if  lies in the third quarter then; 1 2max( )q q p+ = and 1 2min ( ) 0q q+ = , which yields that ( )1 20 2 2pq q< + < , concluding that 3 rd quadrant maps into 1st quadrant. similarly; if  lies in the fourth quarter then; 1 2max( ) 2q q p+ = and 1 2min( )q q p+ = , which yields ( )1 2 22p q q p< + < , concluding that 4 th quadrant maps into 2nd quadrant. line segment -k < re()  0 and 0  re () < k maps into 0 < im()  k (twice) i.e., -k < re() < k maps into 0 < im()  k. the positive and negative imaginary axes map into the ray im() > k. it is interesting to observe that 1 2( ) ( )f fx x= ; hence, we may also conclude that 2( )f x maps; 1 st quadrant into 3rd quadrant, 2nd quadrant into 4th quadrant, 3rd quadrant into 3rd quadrant, and 4th quadrant into 4th quadrant. line segment -k < re()  0 and 0  re () < k maps into -k  im() < 0 (twice) i.e., -k < re() < k maps into -k  im() < 0 the positive and negative imaginary axes map into the ray im() > -k. to evaluate 2 2 2 2 1 1 ( , ) 2 ti x k y c t w x y d k e x x x p x -= -ò , (12) we need a branch of multiple-valued function 2 2( ) tf kx x= , which has positive real part along the contour of integration. the only possible contour for the first branch 1( )f x with the condition that ( )2 2re 0tkx > is the contour as shown in figure 3. fig. 3: contour of 1( )f x in the  -plane. the only contour for the second branch 2 ( )f x with the condition that ( )2 2re 0tkx > is the contour as shown in fig. 4. iium engineering journal, vol. 2, no. 2, 2001 m azram 32 fig. 4: contour of 2 ( )f x in the x -plane. hence, we conclude that ( )1 2 2 2 1 2( ) i f r r e q q x + = is an appropriate choice. considering x = r cos  , y = r sin  with 0 <  <  , the integral (eq. 12) reduces as 2 2 1 1 ( , ) 2 i rs c t w x y d k e x p x -= -ò (13) where 2 2cos sints i kx q x q= . to apply cagniard-de hoop method, we need a contour c1 in -plane such that whenever  is on c1, s must be real. let us consider 0 2q p< < , 2 ( )f x maps the first quadrant into the third quadrant and if 1 2ix x x= + , where 1x > 0, 2x > 0, then 2 2 3 4tk ix x x= for some real 3x > 0, 4x > 0, and 2 2cos sints i kx q x q= (14) 1 4 2 3( cos sin ) ( cos sin )s ix q x q x q x q= + + , (15) wherein the imaginary part on right hand side can not be equal to zero. hence, we deduce that no part of c1 can be in the 1st quadrant. similarly, it can also be shown that no part of c1 can be in the 4 th quadrant. hence, we conclude that if c1 exists, it exists only in the left-half plane. similarly, if 1 0tk k> > and 1x x= in the 2nd quadrant then 2 2 1 1 1cos sintk i k kx q q= + , (16) which can be rewritten as 2 2 2 2 1 1 1cos sint tk k k ikx q q= (17) thus, 2 2 1 1 1cos sinti k kx q x q= . (18) hence c1 exist in the 2 nd quadrant and s is negative along this contour. similarly, taking  = 2 in the 3rd quadrant, it can be seen that c1 exist in the 3 rd quadrant and s is again negative along this contour. hence, we deduce that for 0 2 p q< < , c1 is the branch of the hyperbola ( ) ( ) 2 2 re im 1 cos sint tk k x x q q é ù é ù ê ú ê ú=ê ú ê úë û ë û , which lies in the left-half plane as shown in figure 5. fig. 5: change of contour as c1 in the  -plane. by considering appropriate arcs with large radii, contour c can be deformed as c1. as radii , the integration vanishes and consequently, 11 12 2 11 1 1 ( , ) 2 t i r k k t w x y dk kk ex p x ¥ ¶ = + ¶-ò 12 12 2 12 1 1 2 tk i r k t dk kk ex p x¥ ¶ ¶-ò . considering 2 2 2 21 1 1cos sint tk k k ikx q q= and 2 2 2 2 2 1 1cos sint tk k k ikx q q= , the above integral reduces the solution as hankel function of first kind (1)0( , ) ( )2 t i w x y h k r= . similarly, if 2 p q p< < then c1 will be that branch of the hyperbola 2 2 re im 1 cos sint tk k x x q q é ù é ù ê ú ê ú=ê ú ê úë û ë û , which lies in the righthalf plane and the end solution is hankel function of first kind (1)0( , ) ( )2 t i w x y h k r= . 4. comparison and conclusion even earlier than 1973, achenbach had investigated this problem of half-space subjected to anti-plane surface disturbance. he obtained a solution (2) 0( , ) ( )2 t i w x y h k r= . this solution was obtained by assuming the pivotal parameter 2 2cos sints i kx q x q= to be real and positive. this parameter played significant role in applying the cagniard-de hoop method. iium engineering journal, vol. 2, no. 2, 2001 m azram 33 in our analysis, investigations were carried out in detail about the choice of branch cuts, branches and their behavior in different quadrants of the  plane. investigations show that the contour which simplifies the inversion integral, may or may not exist in some part of the  plane and is very much dependent on the position of the point. to apply cagniard-de hoop method, the choice for the required contour c1 to simplify the inversion integral depends particularly on . in the half-plane, if 2 p q p< < , c1 must be selected as that branch of hyperbola which lies in left-half of  plane. while for 2 p q p< < , the contour c1 must be selected as that branch of hyperbola which lies in righthalf of -plane. corresponding to the contour in figure 1, the contour c1 is as shown in figure 5 rather than as shown in figure 2. the parameter s is real but negative for all value of 0 q p< < . the ultimate solution is (1) 0( , ) ( )2 t i w x y h k r= . in this paper, we have discussed an immensely important problem from applications prospective but unique in nature because it has an exact solution. our investigations reflect that a good understanding of mathematical formulation and a considerable knowledge in applied mathematics are the essential ingredients to deal and understand the challenging phenomena of wave propagation. references [1] j. d. achenbach, “wave propagation in elastic solids”, north-holland. 1984. [2] a. b. h. love, “the mathematical theory of elasticity”, n.y, dover publications, inc, 1944. [3] s. p. timoshenko and j. n. goodier, “theory of elasticity”, mcgraw-hill co., 1987. [4] k. b. bullen, “an introduction to the theory of seismology”, cambridge, university press, 1963. [5] w. m. ewing, w. s. jardetzky, and f. press, “elastic waves in layered media”, ny, mcgraw-hill co., 1957. [6] l. cagniard, “reflexion et re fraction des ondes seismimique progressives”, gauthiers-villars, 1939. [7] a. schoch, “schallreflexion, schallbrechung und schallbeugung”, ergebnisse der exakten naturwissenschaften, vol. 23, springer-verlag, 1950. [8] d. gross, and ch. zhang, “on wave propagation in elastic solids with cracks (advance in fracture mechanics series)”, wit press, 1997. [9] j. miklowitz, “elastic waves propagation, applied mechanics surveys”, spartan books, 1966 [10] b. a. auld, “acoustic fields and waves in solids”, vol. i, krieger, 1990. [11] j. billingham and a. c. king, “wave motion”, cambridge university press, 2001. [12] a. bedford and d. s. drumheller, “introduction to elastic wave propagation”, john wiley and sons, 1994. [13] h. kolsky, “stress waves in solids”, ny, dover publications,inc., 1963. [14] l. rayleigh, “the theory of sound”, vol.(i & ii), n.y, dover publications, inc., 1945. [15] l.m. brekhovskikh, “waves in layer media”, ny, academic press, 1960. [16] r. b. lindsay, “mechanical radiation”, ny. mcgrawhill co., 1960 [17] p.m. morse and k.u. ingard, “theoretical acoustics”, ny, mcgraw-hill co, 1968. [18] i. tolstoy and c. s. clay, “ocean acoustics”, ny, mcgraw-hill co., 1966. [19] j. l. davis, “mathematics of wave propagation”, princeton university press, 2000. [20] f. moser, c. valle, l. j. jacobs, and j. qu, “application of finite element methods to study transient wave propagation in elastic wave guides”, “review of progress in quantitative nde, vol.16 a, 1998. [21] f. moser, l. j. jacobs, and j. qu, “application of finite element methods to study wave propagation in wave guides”, “ndt & e int., vol. 32, 1999. [22] b. noble, “wiener-hopf technique”, chelsea pub.co., 1988. [23] a. t. de hoop, “a modification of cagniard’s method for solving seismic pulse problems”, applied science research, b 8, 349-356, 1960. biography dr. mohammad azram received his bachelor degree in mathematics from university of peshawar, pakistan in 1974. he obtained his master degree in mathematics with a position from university of peshawar, pakistan in 1976. he obtained his second master degree in mathematics from university of idaho, usa in 1985 and then graduated with a ph.d. from the same university in 1989. he started his career as a lecturer, department of mathematics, university of peshawar, pakistan in january 1977. he is now a professor in the department of mathematics, university of peshawar, pakistan. he has served the university of peshawar in the capacity of chairman, member academic council, member board of studies, member affiliation committee, member peshawar university teacher's association, and director of postgraduate programmes, department of mathematics, university of peshawar, pakistan. currently, he is a professor at faculty of engineering, iium, malaysia. in addition, he is also deputy dean (academic affairs), centre for postgraduate studies, iium, malaysia. microsoft word 182-1006-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alaama et al. 51 isolation and analytical characterization of local malaysian leech saliva extracts mohamed alaama 1 , manar alnajjar 3 , abdualrahman m. abdualkader 1 , abbas mohammad 2 and ahmed merzouk 1 1 department of pharmaceutical chemistry, 2 department of basic medical science kulliyyah of pharmacy, international islamic university malaysia. kuantan, malaysia. 3 kulliyyah of pharmacy, aleppo university, aleppo, syria. hass83pharm@yahoo.com abstract: leech saliva contains biologically active compounds that are mainly proteins and peptides. in this study a modified and smooth extraction method of saliva was used without leeches’ scarification. uv and bradford assay protein methods showed that the saliva extract contains high concentrations of proteins. rp-hplc chromatogram revealed that more than 30 different peaks were observed in leech saliva extract. gel electrophoresis revealed the existence of proteins and peptides with different molecular weights. the gel showed up to 25 different bands. comparison of gel electrophoresis data with protein database revealed the closeness of four molecular weights to known proteins from hirudinaria leech family. other proteins detected by gel electrophoresis may be related to completely new biologically active proteins and peptides in the saliva extract or to a modification (isoforms) of the existing ones or finally to a mixture of both. abstrak: air liur pacat secara biologinya mengandungi sebahagian besar campuran aktif protein dan peptida. dalam kajian ini, kaedah pengestrakan air liur pacat yang telah diubah suai digunakan tanpa perlu membunuh pacat. kaedah protein cerakin uv dan bradford menunjukkan air liur pacat yang diekstrak mengandungi konsentrasi protein yang tinggi. kromatogram rp-hplc memperlihatkan lebih daripada 30 puncak berbeza diperolehi semasa air liur pacat diekstrak. gel elektroforesis memperlihatkan kewujudan protein dan peptida dengan berat molekul yang berbeza. gel menunjukkan hingga 25 jalur yang berbeza. perbandingan data menggunakan gel elektroforesis seiring dengan pangkalan data protein memperlihatkan persamaan empat berat molekul, dengan protein yang yang dikenali daripada keluarga pacat hirudinaria. jenis protein lain yang dikesan dengan menggunakan gel elektrofosis mungkin juga berkait secara biologinya dengan protein dan peptida aktif yang baru, dalam ekstrak air liur atau pengubahsuaian (beberapa jenis yang berbeza daripada protein yang sama) daripada yang sedia ada ataupun gabungan kedua-duanya. keywords: leech saliva; rp-hplc; gel electrophoresis 1. introduction leech saliva extracts have received much attention because the extensive uses in many medical fields [1]. leech saliva contains active compounds which act as strong anticoagulants [1]. those anticoagulants almost are proteins and peptides secreted by leeches salivary glands while sucking the blood to prevent it from coagulation [2], and furthermore to keep blood in the liquid statue during the period of storage to achieve easier digestion [3], which may last up to six months [4]. hirudin is the most known iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alaama et al. 52 anticoagulant compound isolated from leech hirudo medicinalis [5]. while other species of leeches have been studied and number of proteins and peptides have been found in their saliva extract [6-8]. in malaysia there are many species of leeches belonging to the tropical leech hirudinaria manillensis family [9]. a little work has been undertaken to isolate, characterize and subsequently test for active compounds in their saliva extract. the aim of this study is to throw a light and open the door for wider studies on what malaysian leeches saliva extracts have to offer in term of active peptides and proteins in a much needed medical fields like: oncology, diabetes and infectious diseases. to satisfy this goal, state-of-the art tools of biomedical and analytical methods were used. proteomic techniques tools and proteins database searching are applied in this study to have a better understanding of compounds with high molecular weight proteins contained in the leech saliva extract. 2. materials and methods leeches were collected from local suppliers around pahang area, bradford protein assay reagents (amresco), all gel electrophoresis reagents were purchased from bio rad, peptide marker was purchased from sigma aldrich, hplc grade acetonitrile was purchased from fisher scientific, hplc grade water was from merck. 2.1 leech saliva extraction leeches were kept in plastic containers containing water at 23°c for the period of experiment. water was changed every three days. leeches were starved for three weeks. saliva was obtained by a small variation of a method described in the literature [10]. briefly, parafilm membrane (laboratory film chicago il 60631) instead of baudruche membrane was stretched across a funnel containing 0.001 m arginine in 0.15 m saline solution. the solution was maintained at 37°c and leeches were allowed to suck the solution through the membrane. the weight of leeches before and after sucking was reported. leeches were allowed to suck until satiation. directly after leeches drop down from the membrane, they were immobilized by putting them in plastic container surrounded by ice for 5-10 min. this technique forces the leeches to vomit whatever they have sucked. to complete the saliva collection, leeches were squeezed smoothly from the posterior toward anterior (mouth) sucker. all fluids that have been vomited were collected (bloody fluids were discarded) in clean test tubes and centrifuged at 4°c for 10 minutes at 9000 rpm, and the supernatant fluid was named leech crude saliva extract. the following feeding solutions were tested: 0.001 m arginine, in 0.15 m saline; 0.001 m arginine, 5% sucrose, in 0.15 m saline; 0.001 m arginine, 5% mannitol in 0.15 m saline; 0.001 m arginine, 5% sucrose in distilled water; 0.001 m arginine, 5% mannitol in distilled water. most of the mentioned solutions were rejected except 0.001 m arginine in 0.15 m saline which is used for the whole experiment. 2.2 estimation of protein concentration in leech saliva extract concentration of proteins and peptides in the saliva extract was estimated by using uv absorption and bradford proteins assay methods. the uv method was performed to estimate proteins concentration at a280 maximum absorption [11]. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alaama et al. 53 on the other hand, protein concentration was also estimated by using bradford protein assay method [12] in which bovine-serum albumin (bsa) is taken as a standard in the calibration curve on greiner 96 flat bottom transparent polystyrol [gre96ft.pdfx] at 595 nm wavelength. 2.3 gel electrophoresis of saliva extract one dimensional (1d) electrophoresis was carried out according to what have been described by laemmli [13] using 15% gel to detect proteins and peptides with molecular weight ranging between 10-90 kda. to detect small molecular weight of less than 40 kda the following methods were used: a none urea sds-page [14]; using 19% gel, and 16% gel with tricine sds–page [15] . saliva extract proteins (about 15 µg) and a mixture of peptides marker of 1.02–26 kd (sigma) were applied using mini protein tetra cell instrument (bio rad) and power supplier. gels (1mm thick) of 6×10 cm were used for all tests. coomassie blue staining was carried out according to standard protocol [16]. gels were scanned using a bio rad gel documentation system. 2.4 rp-hplc of saliva extract fresh and lyophilized saliva extract were dissolved in hplc water to an estimated concentration of 100 µ g/ml for fresh saliva and 1000 µ g /ml for lyophilized saliva from which 100 µl was taken and injected through an automatic injector connected to an agilent reversed phase c18 column (4.5×150 mm×5 µm ). buffer a (0.1% tfa in water) and buffer b (0.1 % tfa in acetonitrile) were used as mobile phases. a linear gradient of 5-90% buffer b over 40 min is used for the elution. the absorbance detection was fixed at 214 nm. 3. results 3.1 leeches feeding and saliva collection after three weeks starvation leeches started sucking the phagostimulatory solution. the solution was highly tolerated by leeches. leeches saliva extract was collected by putting them first in an ice container for 7 min. leeches were brought close to parafilm membrane (fig. 1). to complete the extraction, leeches were squeezed smoothly from the posterior toward the anterior (mouth) sucker. the saliva was collected from 140 leeches. the body weight of these leeches ranges between 0.2 –7 grams. the volume of the sucked solution by leeches ranges between 0.9-17 ml. . fig. 1: leech while sucking the solution through the membrane. it was observed that some leeches give a bloody saliva extract. the reason was probably due to the blood that still not completely digested in their gut (recently fed). this bloody saliva extract was somehow related the leech body weight. heavy body mass leeches were more prone to give bloody saliva extracts than the lighter ones. it is iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alaama et al. 54 interesting to observe that the period of starvation did not play an important role in the amount of fluid sucked. table 1: solutions used for leech feeding and their “compatibility”. solution no. of leeches acceptance saline 0.15 m + arg 0 .001 m 5 100% saline 0.15 m + arg 0.001 m + sucrose 5 % 5 80 % saline 0.15 m + arg 0.001 m + mannitol 5 % 5 0 mannitol 5% + arg 0.001 m 5 0 sucrose 5% + arg 0.001 m 5 0 the best solution to feed leeches was saline 0.15 m + arg 0.001 m, leeches still suck the solution after adding sucrose but no more after adding mannitol which seems as inhibitor. 3.2 concentration of saliva proteins the uv absorbance at a280 that has been measured for different leech saliva extracts ranges from 0.159 to 0.521 with a mean of 0.311 and sd= 0.118 (table 2). the protein concentration measured by bradford method ranges from 39 to 105 µg/ml with a mean of 67.9182 µg/ml and sd=29.14 µg/ml (table 3). table 2: a280 for crude saliva extract. no number of leeches volume taken from every leech (ml) period of starvation absorbance at 280nm 1 1 3 3 weeks 0.218 2 45 4 4 weeks 0.241 3 2 2.5 12 weeks 0.521 4 5 2.5 14 weeks 0.448 5 5 5 16 weeks 0.335 6 5 17.5 18 weeks 0.159 table 3: saliva protein concentration using bradford method. no number of leeches volume taken from every leech (ml) period of starvation concentration µg/ml 1 19 8.2 6 weeks 39.97 2 17 1.9 9 weeks 59.2 3 2 2.5 12 weeks 105.35 4 5 2.5 14 weeks 91.41 5 5 17.5 18 weeks 43.661 it has been observed that the proteins and peptides concentration in the saliva extract varies according to the following: iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alaama et al. 55 a) the concentration of proteins and peptides increases by increasing leech starvation. the twelfth week is considered to be the maxima after that the concentration began to decrease. the decrease in the concentration is believed to be related to the leech’s exhaustion. b) the amount of solution sucked by leeches affect the concentration, more solution sucked results in less concentration (dilution factor). 3.3 gel electrophoresis of saliva extract figures 2a and 2b show typical 1d-electrophoregrams of separation of high molecular weight proteins and peptides isolated from saliva of local malaysian leeches. one-dimensional electrophoresis revealed the presence of more than 25 proteins and peptides ranging from 3.7-80 kda. these results are obtained side by side with a proteins and peptides standard reference. the diagram shows some coincidence of known proteins and peptides in related species (table 4) and new bands (new compounds) which are not studied before in hirudinaria leech family (table 5). a b fig. 2a: separation of protein components of the medicinal leech saliva by tricine-sds-page 16%; lane 1= molecular mass markers (in kda); lanes 23= diluted sample. fig. 2b : separation of protein components of the medicinal leech saliva by sds-page 15%: lane 2,3 = lyophilized saliva, lane 1= peptide markers (in kda). table 4: isolated proteins from hirudinaria manillensis. proteins isolated from hirudinaria manillensis observed molecular weight (da) calculated molecular weight (da) gelin [17] 8024-8200 8252 bufrudine [18] 7000 7122 hrulline p18 [19] 6600-6800 6616 manillase [20] 58000 57173 comparison of molecular masses of high molecular weight components of the malaysian leech salivary gland secretion revealed by gel electrophoresis with literature data of calculated and experimentally detected molecular weights of proteins produced by the hirudinaria manillensis leech. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alaama et al. 56 table 5: isolated proteins from other species of leech. proteins isolated from other species of leeches observed molecular weight (da) calculated molecular weight (da) hmw bdellins group b3[21] 20000 20717 calin [22] 65000 64950 lefaxin [8] 30000 30216 hyaluronidase [23] 28500 28713 destabilase lysozyme [24] 12000 12694 3.4 rp-hplc of saliva extract the analytical chromatogram of the crude saliva extract showed the presence of more than 30 peaks with good resolution. this result was the same for fresh and lyophilized saliva extract (fig. 3) and consistently reproducible with different batches taken at different time interval. fig. 3: sample analysis using rp-hplc. column: agilent c18, buffer a is 0.1 % tfa in water , buffer b is 0.1% tfa in acetonitrile, flow rate of 1 ml /min, gradient: 5% b over 5 min , 5-90% b over 40 min, wavelength 215nm. a= fresh saliva, b= lyophilized saliva. 4. discussion in order to have a leech saliva extract with high proteins and peptides concentration one need to starve leeches for a period of time [25]. the optimum period was found to be between 3 weeks [25], and 16 weeks [26]. in our case three weeks starvation was the initial time for leeches to start sucking the phagostimulatory solution, but with a low proteins and peptides concentration as measured by uv and bradford methods. a maximum concentration was obtained after 12 weeks starvation period. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alaama et al. 57 many methods to study saliva content of different leeches family have been described. the majority of these methods are very invasive and consist of scarifying leeches by grounding and mixing their heads [2, 18] or grounding and mixing the whole body [25], or taking out salivary glands by surgery [27]. other method that still need to scarify the animal, consists of immersing a starved leech in 8% ethanol which will cause the animal to regurgitate its saliva [28]. one of the very soft method that spares leeches life and in the same time allows the collection of the desired saliva amount from leeches was described [10]. after several attempts, we found that it is much easier to collect the saliva by putting the leeches in ice bath inside a plastic test tube, the freezing temperature causes the animal to regurgitate (vomit) the desired sucked solution and causes the immobilization of its movement which in turn facilitate the squeezing in order to optimize the amount of saliva obtained. last and not least, the ice does not kill the animal and it is enough to put him again in a warm water to regain all its activity and continue to leave normally for undefined period of times. several phagostimulatory solutions were tested, for instance the best result is obtained with 0.001 m arginine in 0.15 m sodium chloride solution. other solutions were also tested, we found that 5% of sucrose still gives a good result, but when mannitol is used instead of sucrose, the solution is not accepted by leeches. the gel electrophoresis reveals the existence more than 25 proteins and peptides in the leech saliva extract. some of these proteins were also isolated from hirudinaria manillensis family as reported in literature. these include manillase [20], bufiridine [18], gelin [17], and hirullin p18 [19]. other proteins were found to be similar in molecular weight to proteins isolated from other leech species but were not studied in hirudinaria manillensis family. these include calin [22], lefaxine [8], hyaluronidase [23], hmw bdilline group b-3[21], destabilase lysozyme [24]. the other proteins found in this study may be related to unknown biologically active proteins or modification of known proteins or mixture of both. however the malaysian leech saliva extracts need more investigation to know its composition and its biological activities. 5. conclusion leech saliva extract was described using reversed phase hplc and 1d gel electrophoresis, and the full characterization of all active compounds is underway. acknowledgement this research was supported gratefully by the grant (edw b 10-0393) from researchmanagement centre, international islamic university malaysia, iium. references [1] sawyer, r.t., ed. leech biology and behaviour: volume ii: feeding biology, ecology, and systematics. 1986. oxford university press, usa1986. [2] markwardt, f., die isolierung und chemische charakterisierung des hirudins. hoppeseyler´s zeitschrift für physiologische chemie, 1957. 308(jahresband): p. 147-156. [3] wallis, r.b., hirudins: from leeches to man. seminars in thrombosis and hemostasis, 1996. 22(2): p. 185-196. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alaama et al. 58 [4] mann, k.h., leeches (hirudinea) their structure, physiology, ecology and embryology. vol. 11. 1962: pergamon press (oxford and new york) 201. [5] hycraft, j.b., the action of a secretion obtained from the medicinal leech on a coagulation of blood. proc. r. soc. london 1884. 36: p. 478-487. [6] salzet, m., et al., theromin, a novel leech thrombin inhibitor. j biol chem, 2000. 275(40): p. 30774-80. [7] nutt, e., et al., the amino acid sequence of antistasin. a potent inhibitor of factor xa reveals a repeated internal structure. the journal of biological chemistry, 1988. 263(21): p. 10162-7. [8] faria, f., et al., a new factor xa inhibitor (lefaxin) from the haementeria depressa leech. thrombosis and haemostasis, 1999. 82(5): p. 1469-73. [9] fredric r. govedich, w.e.m.a.r.w.d., euhirudinea (leeches). in: freshwater fauna of malaysia and borneo, in fresh water invertebrate of the malaysian region c.y. and .y.h. sen, editor 2004, academy of sciences malaysia publishing. p. 175-190. [10] rigbi, m., et al., the saliva of the medicinal leech hirudo medicinalis--i. biochemical characterization of the high molecular weight fraction. comparative biochemistry and physiology. b, comparative biochemistry, 1987. 87(3): p. 567-73. [11] aitken, a. and m. learmonth, protein determination by uv absorption, in the protein protocols handbook, j.m. walker, editor 1996, humana press. p. 3-6. [12] bradford, m.m., a rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. analytical biochemistry, 1976. 72: p. 248-54. [13] laemmli, u.k., cleavage of structural proteins during the assembly of the head of bacteriophage t4. nature, 1970. 227(5259): p. 680-5. [14] okajima, t., t. tanabe, and t. yasuda, nonurea sodium dodecyl sulfate-polyacrylamide gel electrophoresis with high-molarity buffers for the separation of proteins and peptides. anal biochem, 1993. 211(2): p. 293-300. [15] schägger, h. and g. von jagow, tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis for the separation of proteins in the range from 1 to 100 kda. analytical biochemistry, 1987. 166(2): p. 368-379. [16] ahmed, h., principles and reactions of protein extraction , purification , and characterization, 2005. [17] electricwala, a., et al., biochemical characterisation of a pancreatic elastase inhibitor from the leech hirudinaria manillensis. journal of enzyme inhibition, 1992. 6(4): p. 293-302. [18] electricwala, a., et al., isolation of thrombin inhibitor from the leech hirudinaria manillensis. blood coagul fibrinolysis, 1991. 2(1): p. 83-9. [19] steiner, v., et al., primary structure and function of novel o-glycosylated hirudins from the leech hirudinaria manillensis. biochemistry, 1992. 31(8): p. 2294-8. [20] kordowicz, m.g., detlef; hofmann, uwe; pacuszka, tadeusz; gardas, andrzej; , hyaluronidase from the hirudinaria manillensis, isolation, purification and recombinant method of production 2000. [21] fink, e., et al., the primary structure of bdellin b-3 from the leech hirudo medicinalis. bdellin b-3 is a compact proteinase inhibitor of a "non-classical" kazal type. it is present in the leech in a high molecular mass form. biological chemistry hoppe-seyler, 1986. 367(12): p. 1235-42. [22] munro, r., c.p. jones, and r.t. sawyer, calin--a platelet adhesion inhibitor from the saliva of the medicinal leech. blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis, 1991. 2(1): p. 179-84. [23] yuki, h. and w.h. fishman, purification and characterization of leech hyaluronic acidendo-beta-glucuronidase. the journal of biological chemistry, 1963. 238: p. 1877-9. [24] baskova, i.p., et al., separation of monomerizing and lysozyme activities of destabilase from medicinal leech salivary gland secretion. biochemistry. biokhimiia, 2001. 66(12): p. 1368-73. [25] bagdy, d., et al., [54] hirudin, in methods in enzymology, l. laszlo, editor 1976, academic press. p. 669-678. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alaama et al. 59 [26] baskova, i., et al., proteins and peptides of the salivary gland secretion of medicinal leeches ;hirudo verbana, h. medicinalis&lt; and h. orientalis. biochemistry (moscow), 2008. 73(3): p. 315-320. [27] tuszynski, g.p., t.b. gasic, and g.j. gasic, isolation and characterization of antistasin. an inhibitor of metastasis and coagulation. the journal of biological chemistry, 1987. 262(20): p. 9718-23. [28] munro, r., c.p. jones, and r.t. sawyer, calin-a platelet adhesion inhibitor from the saliva of the medicinal leech. blood coagulation & fibrinolysis, 1991. 2(1): p. 179-184. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 system identification (si) modelling, controller design and hardware testing for vertical trajectory of underwater remotely operated vehicle (rov) fauzal naim zohedi1*, mohd shahrieel mohd aras1, hyreil anuar kasdirin1, mohd bazli bahar1 and lokman abdullah3 1 faculty of electrical engineering, universiti teknikal malaysia melaka, 2 center for robotics and industrial automation (ceria), 3 faculty of manufacturing engineering, universiti teknikal malaysia melaka, 76100 durian tunggal, melaka, malaysia * corresponding author: fauzal@utem.edu.my (received: 20 february 2023; accepted: 20 may 2023; published on-line: 4 july 2023) abstract: underwater remotely operated vehicles (rov) are important in marine industries to accomplish underwater exploration and surveying. the underwater environment makes it hard for rov operators to control the manipulator while holding position simultaneously. this led to modelling and controller design for the vertical trajectory of rov. in this paper, the system identification (si) modeling technique was used to model the vertical trajectory of the rov. then, the proportional, integral, and derivative (pid) controller was implemented to control the trajectory. the si modelling technique was used as it estimates the model based on the input and output relationship. matlab si toolbox was used as the analytical software. step and multiple step inputs were given to the system and the responses were recorded. the model with the best fit of 84.7% was selected and verified by comparing with actual output. the model response was then analyzed and the pid controller was implemented. the actual model had high percent overshoot (%os) and steady state error (sse). the pid implementation successfully reduced the %os and eliminated the sse. abstrak: kenderaan bawah air kendalian jauh (rov) adalah penting dalam industri marin bagi melaksanakan penerokaan dan pemerhatian bawah air. persekitaran dalam air menyukarkan pengendali rov bagi memanipulasi manipulator sambil memastikan kedudukan rov secara serentak. ini membawa kepada pemodelan dan mereka bentuk kawalan pergerakan menegak bagi rov. kajian ini menggunakan teknik pemodelan sistem pengenalan (si) bagi memodelkan pergerakan menegak rov. kemudian, kawalan seimbang, menyeluruh dan terbitan (pid) dilaksanakan bagi mengawal trajektori. teknik pemodelan si digunakan kerana ia menganggarkan model berdasarkan kemasukan dan keluaran. aplikasi matlab si digunakan sebagai perisian analisis. masukan satu langkah dan berbilang kali masukan telah dijalankan dan respons sistem direkodkan. model yang paling sesuai mencapai 84.7% dipilih dan disahkan dengan perbandingan nilai keluaran sebenar. respons model kemudiannya dianalisis dan kawalan pid dilaksanakan. model sebenar mempunyai peratusan tinggi melampaui (%os) dan ralat keadaan stabil (sse). pelaksanaan pid telah berjaya mengurangkan %os dan menghapuskan sse. keywords: system identification (si) modelling; remotely operated vehicle (rov); depth control; pid controller 131 iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 1. introduction underwater remotely operated vehicles (rov) are robots that substitute humans for underwater investigation and exploration. underwater surveillance is important for sustainability of resources and underwater research [1]. underwater exploration and surveillance, oil and gas pipeline monitoring, ship hull cleaning and other [2] complicated tasks require a highly skilled rov operator to operate the rov. the ability to manipulate the manipulator and maneuver the rov at the same time is a must [3,4] for the operator. to ease the operator, automatic trajectory and position holding is necessary to ensure accurate control of the manipulator is achieved [4]. other than that, there are also disturbances made by currents and waves [5,6] in the underwater environment. it increases difficulties for rov operators to maintain the rov at a certain depth. (a) (b) fig 1: (a) rov used in the research project; (b) rov tested in controlled environment. underwater remotely operated vehicles (rov) have six (6) degrees of freedom (dof) which are surge (forward-reverse), sway, heave (vertical), roll, yaw (left and right) and pitch [7,8]. all these six degrees of freedom are coupled together. this coupling makes it difficult to model the rov using mathematical modelling as many assumptions need to be made. another alternative for modelling the rov is using the system identification (si) technique. the si technique is based on experimental data of the actual system. input data is given to the system and the output response is recorded. these data are then run through the si matlab toolbox to estimate the model based on the input-output relationship. in this paper, a small rov prototype was used. it was driven by 4 thrusters where 2 thrusters for vertical trajectory while another 2 thrusters were for forward-reverse and left-right turns. the vertical thrusters were put at the center of the rov and placed side-by-side to provide stability to the rov. the forward and reverse thrusters were placed at both sides of the rov with 45 degrees angle that eased the turning process of the rov. the rov did not need to move fast as its solely used for investigation. the rov had slightly positive buoyancy to ensure its ability to float if anything happened to the system. this position was measured as its initial position. the small rov prototype used in the research project is shown in fig. 1. the rov was tethered using a local area network cable (lan). this cable provided 12v direct current (dc) to all 4 thrusters. the tethered cable also supplied 5v direct current (dc) for the sensor and was also used for data transfer between sensor and controller. the depth of the rov was sensed using an mpc4250 pressure sensor. this sensor produced an output of 1.825 v at 1 atmosphere (atm) and 1.8624 v at 22 cm in the water. the 22 cm is the location of sensor at the initial rov condition floating in the water. this paper focuses on si modelling 132 iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 and the proportional, integral, and derivative (pid) controller was designed for the vertical trajectory of a newly developed small rov. pid was selected as the controller due to its simple and easy implementation. there are several basic controllers that have been implemented to perform rov depth control. the controllers are the pid, a fuzzy logic controller (flc), a neural network controller (ann), and a sliding mode control (smc) [4,9-13]. the easiest controller to implement is the pid controller as it can be tuned using auto-tuning in matlab simulink[14]. the pid is good at controlling linear systems. the flc controller is good at adapting with disturbance [15,16] but difficult to tune. ann tunes its system by using historical data or online data [17,18]. due to this, the ann controller has a slow reaction time. the smc controller works based on limitations set for the system to follow a slide path [19]. its disadvantage is energy waste as it bounces through the path. table 1 shows a summary of advantages and disadvantages of the basic controllers discussed [20]. table 1: comparison of the controller design type of controller advantages disadvantages pid easy to execute and maintain only for linear systems flc no mathematical modelling required and precise order complicated in the tuning process ann convergence to a precise model slower response smc non-linear system energy waste occurs 2. system identification modelling the system identification (si) modelling approach starts with data gathering of the inputs and outputs of the system by experimentation [21-24]. in this project, step input and multiple stairs input were given to the system. the step input was used to model the system while the multiple stairs input was used to verify the model with the actual system. si will estimate the relationship between the input and the output and generate a model with percentage best fit value. the best fit value will indicate how close the model is to the actual system. the si approach consists of five (5) steps [20], [25] which are observation and data gathering, model structure selection, model estimation, model validation, and application. fig. 2 shows the flow chart of the si approach. from fig. 2, the first step is observation and data gathering. in this process, the system is observed, and input-output data are gathered. the next 3 flows, model structure selection, model estimation, and model validation are selected automatically by the matlab si toolbox. model structure selection is where the estimation method is selected. model estimation is where the system will create a model, and model validation is where the generated model is validated. the last step is model application where the generated model is applied with any controller to control the system. the generated model must at least obtain an 80% best fit value to be considered as an acceptable model. the generated model can be in transfer function or state space before implementing to any system, the model must also be checked for controllability. the state space of the model is substituted into eq. 1. if the mc rank is equal to matrix a in the state space, the system is controllable. 𝑀𝐶 = [𝐵 𝐴𝐵 𝐴 2𝐵 𝐴𝑛−1𝐵] (1) 133 iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 fig. 2: flow chart of si approach. 2.1 experimental setup in the experimental setup, there are 5 components as shown in fig. 3. the components are a computer for user interface, a microcontroller arduino mega 2560 as interface between computer and rov, a motor driver l298n to drive the thruster motor, a pressure sensor mpx425 to measure water pressure for depth, and the rov. fig. 3: experimental setup. the vertical trajectory of the rov was observed by giving a step input and multiple stairs input to the system. the setups are listed below: input step signal = 57 cm depth (limitation of tank) repetitive stairs input = 57 cm and 40 cm sampling time = 0.001 s initial depth = 22 cm initial volt = 1.825 v triggered = 0.5 s for step and 0 s multiple input experimental time = 10 s (step input) and 50 s (multiple input) as the step given was 57 cm, the rov submerged until 57 cm and maintained that position for 3 s. for multiple stairs input, the rov submerged between 57 cm and 40 cm. from the sampling time, the step input produced 30000 data points while the multiple stairs input produced 40000 data points. the simulink block diagram for data gathering is shown fig. 4. the highlighted block in fig. 4 shows the conversion block from volt to depth. the measurement from the sensor was divided with 1023 and multiplied with 5 v. this is due to the analog to digital conversion (adc) of the arduino that has a 10-bit configuration. the measured voltage was then converted to depth in centimeters. 134 iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 fig. 4: simulink block diagram for data gathering. 3. controller design for this research project, the pid controller was implemented by simulation and experimentation. it was first developed by elmer sperry in 1911. proportional (p) is used to reduce the time rise (tr) but affects the percentage of overshoot (%os). derivative (d) is used to decrease the %os and increase the stability, while integral (i) is used to eliminate the steady state error (sse) but may affect the performance of the system [26]. equation 2 shows the equation of the pid controller where kp is the gain of p, kd is the gain of d, and ki is the gain for i. 𝒐𝒖𝒕𝒑𝒖𝒕 𝒖(𝒕) 𝒆𝒓𝒓 (𝒆) = 𝑲𝒑 + 𝑲𝒊 𝒔 + 𝑲𝒅𝒔 (2) figure 5 shows the basic block diagram used in this research project for pid controller implementation. the p, i, and d were connected in parallel with each other as highlighted in fig. 5. table 2 shows the effect of varying kp, ki, and kd (fig. 5) to the transient parameters; [26] time rise (tr), percentage overshoot (%os), settling time (ts), and steady state error (sse). for this research project, the pid was tuned manually to get the result. a step input of 57 cm depth was given to the system and the result was discussed and analyzed. fig. 5: basic pid block diagram. table 2: the effect of varying kp, ki, and kd (fig.5) to the transient parameters 135 iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 parameters time rise (tr) overshoot (%) settling time (ts) steady state error (sse) kp decrease increase small change decrease ki decrease increase increase eliminate kd small change decrease decrease small change 4. results and discussion this section displays results and discussion for si modelling and controller implementation. 4.1 si modelling the experimental data for si modelling is shown fig. 6(a) and fig. 6(b). the dash in the figure shows input given while the line given is the output response. the curves and spikes in the result occur because of the vibrations of the thruster motor and tolerance of the sensor. the si approach was implemented using the step data in matlab si toolbox. the result shows 84.7% best fit and is considered acceptable. the nonlinear squares method was automatically selected by the si system. the transfer function generated is shown in equation 3 below. 𝐇(𝐬) = 𝟎.𝟑𝟖𝟎𝟖𝒔𝟐 +𝟎.𝟓𝟖𝟗𝟖𝒔+𝟏.𝟖𝟕 𝒔𝟐+𝟏.𝟓𝟓𝟒𝒔+𝟐.𝟑𝟐 (3) (a) (a) fig. 6: step input (a) and multiple stairs input (b) result. the transfer function was then converted to state space and checked for controllability using eq. 1. the result showed that the transfer function is controllable as the ranks of mc and matrix a are similar. the transfer function was then verified by comparing it with the actual step output and multiple stairs output shown in fig. 7 and fig. 8. the dashes in the figures were the model output while the wavy and spiked lines were the actual output. from the comparison in fig. 7 and fig 8, the model output was almost identical to the actual output. a bit overshoot and steady state error can be seen clearly in the model output and the actual output. the overshoot is 8.18%, the steady state error is about 11.4cm, and the settling time is 5.23 s. the overshoot and the error need were reduced by using the designed controllers. 136 iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 fig. 7: step model output vs actual step output. fig. 8: multiple stairs model output vs actual multiple stairs output. 4.2 controller implementation the controller applied to the rov model was pid. figure 9 shows the result of the controller implementation. fig. 9: pid controller implementation result. the graph result in fig. 9 was analyzed in terms of percentage overshoot (%os), settling time (ts), time rise (tr) and steady state error (sse). the result was tabulated in table 3. table 3: original system versus pid controller result original system pid os (%) 8.18 0.8 ts (s) 5.23 4.37 tr (s) 1.09 2.32 sse (cm) 11.4 0 from the table, the pid shows remarkable reduction in the percentage overshoot (%os) and steady state error (sse). %os went from 8.18% to 0.8% while sse went from 11.4 to 0c 137 iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 m. the settling time (ts) decreased about 0.86 s from 5.23 s to 4.37 s. the drawback of the pid was the time rise (tr) became slower by about 1s from 1.09 to 2.32s. from this simulation result, the pid controller was then implemented experimentally to the rov vertical trajectory. the result is shown in fig. 10. from this figure, the experimentation for the pid controller looked almost identical to the simulation result. it shows that the pid controller can be implemented to the real rov trajectory system. fig. 10: actual output result with pid controller implementation. 5. conclusion the modelling of vertical trajectory of an rov is important to design a depth controller for the rov. for the depth controller to maintain the rov at certain position may offer more flexibility to rov operators to manipulate the rov manipulator or focus on any surveillance task. modelling using the si approach has proven to be successful as it manages to replicate the trajectory movement of the rov at 84.7% best fit. the comparison between actual output and model output also shows near-identical results. in the controller design for the vertical trajectory, pid shows acceptable results in simulation and experimentally. identical simulation and experimental results indicate that the pid controller can definitely be implemented in real life rov trajectory control. the promising result shown by pid in all performance parameters used improve the original system. this paper is hopefully beneficial to engineers or controller designers to implement the si model approach and design a pid controller for any real-life system. acknowledgment we wish to express our gratitude and appreciation the support granted by universiti teknikal malaysia melaka in pursuing this research specially to underwater technology research group, faculty of electrical engineering, centre of research, and innovation management for supporting this research. 138 iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 references [1] li g, wu j, tang t, chen z, chen j, liu h. (2019) underwater acoustic time delay estimation based on envelope differences of correlation functions. sensors, 19(5): 1-11. doi: 10.3390/s19051259. [2] binugroho eh, wafiqqurochman, mas’udi mi, setyawan b, dewanto rs, and d. pramadihanto d. (2019) erov: depth and balance control for rov motion using fuzzy pid method. ies 2019 int. electron. symp. role techno-intelligence creat. an open energy syst. towar. energy democr. proc., pp. 637-643. doi: 10.1109/elecsym.2019.8901673. [3] goheen kr, jefferys er. (1990) multivariable self-tuning autopilots for autonomous and remotely operated underwater vehicles. ieee j. ocean. eng., 15(3): 144-151. doi: 10.1109/48.107142. [4] aras msm, abdullah ss. (2015) adaptive simplified fuzzy logic controller for depth control of underwater remotely operated vehicle. indian j. geo-marine sci., 44(12): 1995-2007. [5] b. huang and q. yang, “double-loop sliding mode controller with a novel switching term for the trajectory tracking of work-class rovs,” ocean eng., vol. 178, no. march, pp. 80–94, 2019, doi: 10.1016/j.oceaneng.2019.02.043. [6] n. kumar and m. rani, “an efficient hybrid approach for trajectory tracking control of autonomous underwater vehicles,” appl. ocean res., vol. 95, no. october 2019, p. 102053, 2020, doi: 10.1016/j.apor.2020.102053. [7] g. antonelli, s. chiaverini, n. sarkar, and m. west, “adaptive control of an autonomous underwater vehicle: experimental results on odin,” ieee trans. control syst. technol., vol. 9, no. 5, pp. 756–765, 2001, doi: 10.1109/87.944470. [8] m. c. nielsen, m. blanke, and i. schjølberg, “efficient modelling methodology for reconfigurable underwater robots,” ifac-papersonline, vol. 49, no. 23, pp. 74–80, 2016, doi: 10.1016/j.ifacol.2016.10.324. [9] m. s. m. aras, s. n. b. s. salim, e. c. s. hoo, i. a. b. w. a. razak, and m. h. bin hairi, “comparison of fuzzy control rules using matlab toolbox and simulink for dc induction motorspeed control,” socpar 2009 soft comput. pattern recognitpp. 711–715, 2009, doi: 10.1109/socpar.2009.143. [10] z. tang, luojun, and q. he, “a fuzzy-pid depth control method with ., overshoot suppression for underwater vehicle,” lect. notes comput. sci. (including subser. lect. notes artif. intell. lect. notes bioinformatics), vol. 6329 lncs, no. part 2, pp. 218–224, 2010, doi: 10.1007/978-3-64215597-0_24. [11] m. s. bin mohd aras, s. m. s. b. syed abdul hamid, f. b. a. azis, f. a. b. ali, and s. shah b abdullah, “study of the effect in the output membership function when tuning a fuzzy logic controller,” proc. 2011 ieee int. conf. control syst. comput. eng. iccsce 2011, pp. 1–6, 2011, doi: 10.1109/iccsce.2011.6190485. [12] m. l. corradini and g. orlando, “brief papers,” brain cogn., vol. 32, no. 2, pp. 273–344, 1996, doi: 10.1006/brcg.1996.0066. [13] m. . aras, m.s.m., abdullah, s.s. , baharin, k.a. nor, a.s.b.m. ,mohd zambri, “model identification of an underwater remotely operated vehicle using system identification approach based on nnpc,” int. rev. autom. control, vol. 8, no. 2, pp. 149–154, 2015. [14] j. ko, n. takata, k. thu, and t. miyazaki, “dynamic modeling and validation of a carbon dioxide heat pump system,” evergreen, vol. 7, no. 2, pp. 172–194, 2020, doi: 10.5109/4055215. [15] k. ishaque, s. s. abdullah, s. m. ayob, and z. salam, “single input fuzzy logic controller for unmanned underwater vehicle,” j. intell. robot. syst. theory appl., vol. 59, no. 1, pp. 87–100, 2010, doi: 10.1007/s10846-010-9395-x. [16] m. w. n. azmi et al., “comparison of controllers design performance for underwater remotely operated vehicle (rov) depth control,” int. j. eng. technol., vol. 7, no. 3.14 special issue 14, pp. 419–423, 2018. [17] n. weake, m. pant, a. sheoran, a. haleem, and h. kumar, “optimising parameters of fused filament fabrication process to achieve optimum tensile strength using artificial neural network,” evergreen, vol. 7, no. 3, pp. 373–381, 2020. 139 iium engineering journal, vol. 24, no. 2, 2023 zohedi et al. https://doi.org/10.31436/iiumej.v24i2.2759 [18] h. han, m. hatta, and h. rahman, “smart ventilation for energy conservation in buildings,” evergreen, vol. 6, no. 1, pp. 44–51, 2019, doi: 10.5109/2321005. [19] h. yu, c. guo, and z. yan, “globally finite-time stable three-dimensional trajectory-tracking control of underactuated uuvs,” ocean eng., vol. 189, no. march, p. 106329, 2019, doi: 10.1016/j.oceaneng.2019.106329. [20] f. n. zohedi, m. s. mohd aras, h. a. kasdirin, and m. b. bahar, “a new tuning approach of single input fuzzy logic controller (siflc) for remotely operated vehicle (rov) depth control,” evergreen, vol. 8, no. 3, pp. 651–657, 2021, doi: 10.5109/4491657. [21] t. n. dief and s. yoshida, “system identification for quad-rotor parameters using neural network,” evergreen, vol. 3, no. 1, pp. 6–11, 2016, doi: 10.5109/1657380. [22] t. n. dief and s. yoshida, “system identification and adaptive control of mass-varying quadrotor,” evergreen, vol. 4, no. 1, pp. 58–66, 2017, doi: 10.5109/1808454. [23] m. sanap, s. chaudhari, c. vartak, and p. chimurkar, “hydrobot: an underwater surveillance swimming robot,” proc. 2018 int. conf. commun. inf. comput. technol. iccict 2018, vol. 2018-janua, pp. 1–7, 2018, doi: 10.1109/iccict.2018.8325872. [24] m. s. m. aras, s. s. abdullah, m. z. a. rashid, a. a. rahman, and m. a. a. aziz, “development and modeling of unmanned underwater remotely operated vehicle using system identification for depth control,” j. theor. appl. inf. technol., vol. 56, no. 1, pp. 136–145, 2013. [25] m. h. f. taib, m. n., adnan, r. and rahiman, practical system identification. penerbit uitm, 2007. [26] m. a. salim, a. noordin, and a. n. jahari, “a robust of fuzzy logic and proportional derivative control system for monitoring underwater vehicles,” 2nd int. conf. comput. res. dev. iccrd 2010, pp. 849–853, 2010, doi: 10.1109/iccrd.2010.187. 140 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 mohamad et al. https://doi.org/10.31436/iiumej.v23i1.1744 design and analysis of a microstrip patch antenna at 7.5 ghz for x-band vsat application sarah yasmin mohamad1*, noralya fatin muzamil1, norun farihah abdul malek1, s.m.a. motakabber1, rafidah abd malik2 and nurain izzati shuhaimi3 1 department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2 department of instrumentation & electronics technology, the science & technology research institute for defence (stride) malaysia. 3 faculty of electrical engineering, universiti teknologi mara, 40450 shah alam, selangor darul ehsan, malaysia. *corresponding author: smohamad@iium.edu.my (received: 12th december 2020; accepted: 16th april 2021; published on-line: 4thjanuary 2022) abstract: in this paper, a microstrip patch antenna is designed to be used for x-band vsat application at 7.5 ghz. the antenna is proposed to replace the massive and commonly used parabolic reflector antennas (46.0 inch × 29.3 inch × 13.5 inch (116.84 cm × 74.42 cm × 34.29 cm) with weight of 66.2 kg) in terms of portability due to its compact and lightweight features, with overall dimensions of 19.00 mm × 30.55 mm. the 7.5 ghz frequency is chosen based on the x-band frequency used in malaysia, as reported by stride. the microstrip patch antenna is first designed and simulated using cst microwave studio (cst mws) and exhibits a good return loss (s11) of -42.09 db, a bandwidth of 399 mhz, directivity of 7.63 db and gain of 7.18 db. the antenna is then fabricated using rt/duroid ® high frequency 5880 substrate with a dielectric constant of εr = 2.2, loss tangent of δ = 0.0009 and thickness of t = 1.574 mm. next, the return loss and radiation pattern measurements are carried out to confirm the simulated results. the measurement of the antenna prototype provides a return loss s11 of -30.53 db, bandwidth of 455 mhz, directivity of 5.51 db and gain of 3.88 db. abstrak: di dalam kajian ini, antena jalurmikro dicadangkan untuk tujuan aplikasi jalur-x vsat pada 7.5 ghz. antena jalurmikro ini dicadangkan untuk menggantikan antena reflektor parabola yang besar dan biasa digunakan (46.0 inci × 29.3 inci × 13.5 inci (116.84cm × 74.42cm × 34.29cm) dengan berat 66.2kg), kerana cirinya yang mudah alih dengan fizikalnya yang kecil dan ringan, dan dimensi keseluruhan 19.00 mm × 30.55 mm. frekuensi 7.5 ghz dipilih berdasarkan frekuensi jalur-x yang digunakan di malaysia, seperti yang dilaporkan oleh stride. antena jalurmikro ini direka dan disimulasi menggunakan perisian cst studio gelombang mikro (cst mws) dan menghasilkan kehilangan pulangan yang baik s11 -42.09 db, lebar jalur 399 mhz, keterarahan 7.63 db dan gandaan 7.18 db. antena jalurmikro ini kemudiannya direalisasikan dengan menggunakan substrat rt / duroid ® frekuensi tinggi 5880 dengan pemalar dielektrik εr = 2.2, tangen kehilangan δ = 0.0009 dan ketebalan t = 1.574 mm. seterusnya, pengukuran kehilangan pulangan dan corak radiasi dilakukan untuk mengesahkan keputusan simulasi. pengukuran prototaip antena jalurmikro menunjukkan kehilangan pulangan s11 -30.53 db, lebar jalur 455 mhz, keterarahan 5.51 db dan gandaan 3.88 db. keywords: microstrip patch antenna; vsat application; x-band communication 60 iium engineering journal, vol. 23, no. 1, 2022 mohamad et al. https://doi.org/10.31436/iiumej.v23i1.1744 1. introduction as technology evolves at a very fast pace, antennas have become extremely important in the world of communication technology. antennas play a major role in transmitting and/or receiving electromagnetic waves with respect to their specific direction and properties for the intended application [1]. there are various forms of antennas available in the market for instances wires, apertures, arrays, parabolic reflectors, lenses, and microstrip patches. the microstrip patch antenna is one of the most used antennas nowadays due to its excellent properties such as having a low profile and lightweight structure, having low cost, ease of fabrication and ease of integration with circuits [1]. a compact and lightweight antenna is always opted for vsat, very small aperture terminal [2,3], satellite applications so that it can be easily carried around or accommodated on moving stations, especially for military communication services [4,5]. generally, the frequency of military communication lies in the x-band range of 8-12 ghz [6-10]. however, according to the science & technology research institute for defence (stride), the range of x-band frequency used in malaysia started at 7 ghz [11]. the common antennas used for this specific application are array and parabolic reflectors. the common dimensions of the parabolic reflectors that were used for x-band operation can reach up to 116.84 cm × 74.42 cm × 34.29 cm, with a load of 66.2 kg [11]. also, this already omits the positioned case that can reach an additional load of 40 kg, which is compulsory to be used together with the parabolic reflectors. the evolution of military technologies nowadays requires an antenna that is not hefty, portable, and easy to carry around or accommodate on moving stations [4,5]. hence, a microstrip patch antenna is proposed in this paper to fulfil this requirement where it can provide the advantages of having a lightweight, low profile and compact structure compared to the parabolic reflectors which are more massive, bulkier, and difficult to use on a moving vehicle. the microstrip patch antenna is designed to be working at 7.5 ghz which lies in the frequency range of xband services in malaysia [11]. 2. design of the microstrip patch antenna the theoretical dimensions of the microstrip patch antenna proposed in this paper are determined using equations (1) to (5); 𝑃𝑎𝑡𝑐ℎ 𝑊𝑖𝑑𝑡ℎ = 𝑣𝑜 2𝑓𝑟 √ 2 𝜀𝑟+1 (1) 𝑃𝑎𝑡𝑐ℎ 𝐿𝑒𝑛𝑔𝑡ℎ = 𝐿𝑒𝑓𝑓 − 2∆𝐿 (2) 𝐿𝑒𝑓𝑓 = 𝑐 2𝑓𝑟√𝜀𝑒𝑓𝑓 (3) ∆𝐿 = (𝜀𝑒𝑓𝑓+0.3)( 𝑤 ℎ +0.264) (𝜀𝑒𝑓𝑓−0.258)( 𝑤 ℎ +0.8) (4) 𝜀𝑒𝑓𝑓 = 𝜀𝑟+1 2 + 𝜀𝑟−1 2 ( 1 √1+ 12ℎ 𝑤 ) (5) by using equations (1) to (5), the length, l and the width, w of the 7.5 ghz rectangular microstrip antenna is calculated to be l = 12.5 mm and w = 15.8 mm. nevertheless, these equations are just the basic step to determine the initial dimension of the antenna for use at 7.5 ghz, and the performance results may slightly differ from the target research’s demand. thus, a huge number of recent studies and designs are referred in order to support the finding 61 iium engineering journal, vol. 23, no. 1, 2022 mohamad et al. https://doi.org/10.31436/iiumej.v23i1.1744 of the optimum dimensions. moreover, the antenna is designed using rt/duroid ® high frequency 5880 substrate with a dielectric constant of εr = 2.2, loss tangent of δ = 0.0009 and thickness of t = 1.574 mm. the substrate is chosen due to its exceptional dielectric constant uniformity over a wide frequency range [12]. fig. 1(a) and table 1 depict the final dimensions of the proposed antenna. the antenna is then manually fabricated. first, the cst file is converted into a gerber file as the layout for the board, followed by printing out the layout with the exact dimensions. the board (substrate rt/duroid ® high frequency 5880) is cut according to the exact dimension before the copper for the interior layers was printed on top of the board. finally, the etching process is carried out to completely remove the unwanted copper. the performance of the fabricated antenna is measured to confirm the simulated results. the fabricated antenna can be seen in fig. 1(b). fig. 1: (a) the front view of the microstrip patch antenna with dimensions, and (b) the front view of the fabricated antenna. table 1: the parameters and values of the microstrip patch antenna. parameters values patch width 13.81 mm patch length 12.54 mm transformer width 1.20 mm transformer length 5.03 mm feeding width 5.04 mm feeding length 4.99 mm patch thickness 0.035 mm dielectric and ground plane width 19.00 mm dielectric and ground plane length 30.55 mm dielectric thickness 1.575 mm ground plane thickness 0.35 mm 3. simulated and measured results the simulated and measured results of the antenna performances are presented and discussed in this section. figure 2 shows the simulated and measured return loss of the proposed antenna. in fig. 2(a), it can be observed that the microstrip patch antenna is resonating at the targeted frequency of 7.5 ghz with return loss, s11 = -42.09 db, which proved that the designed antenna is well-matched to the 50 ohm reference impedance. figure 62 iium engineering journal, vol. 23, no. 1, 2022 mohamad et al. https://doi.org/10.31436/iiumej.v23i1.1744 2(b) shows the measurement result of the return loss of the antenna prototype using the vector network analyzer, as shown in fig. 3(a). the measurement result depicts a return loss of s11 = -30.53 db which differs slightly from the simulated result, but still shows a very good transmission from the antenna. (a) (b) fig. 2: the (a) simulated and (b) measured return loss s11 of the microstrip patch antenna. from these results, the bandwidth of the antenna can also be observed. the simulated result in fig. 2(a) depicts a bandwidth of bw = 399 mhz, while the measured result in fig. 2(b) depicts a bandwidth of bw = 455 mhz. these bandwidth results are calculated based on equation (6); 𝐵𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ = 𝐹𝐻 − 𝐹𝐿 (6) where: fh = higher frequency at s11 at -10 db fl = lower frequency at s11 at -10 db (a) (b) fig. 3: the measurement of the microstrip patch antenna prototype with (a) vector network analyzer and in (b) anechoic chamber. 63 iium engineering journal, vol. 23, no. 1, 2022 mohamad et al. https://doi.org/10.31436/iiumej.v23i1.1744 figure 4 and 5 show the simulated and measured 3d far field radiation pattern of the microstrip patch antenna. moreover, fig. 6 and fig. 7 show the simulated and measured polar far field radiation pattern (in e-plane and h-plane) of the microstrip patch antenna. the antenna’s radiation pattern is measured in an anechoic chamber, as shown in fig. 3(b). it can be seen from fig. 4 to fig. 7 that the antenna exhibits a directive pattern in the 2d and 3d view. from the simulation, it is observed that the directivity and gain of the antenna at the intended frequency of 7.5 ghz are 7.63 db and 7.18 db, respectively. however, the directivity and gain for the measured antenna prototype are 5.51 db and 3.88 db, respectively. it is believed that the gain between the simulation results and measurement results varies due to the mismatch of impedance matching and also due the losses that occur during the measurement. fig. 4: the simulated 3d far field radiation pattern in (a) isometric, (b) y-axis and (c) x-axis view of the microstrip patch antenna at 7.5 ghz. fig. 5: the measured 3d farfield radiation pattern from (a) below, (b) front and (c) top view of the microstrip patch antenna at 7.5 ghz. finally, table 2 summarizes the overall performances (simulated and measured) of the microstrip patch antenna in terms of return loss, bandwidth, directivity, gain, and main lobe direction. 64 iium engineering journal, vol. 23, no. 1, 2022 mohamad et al. https://doi.org/10.31436/iiumej.v23i1.1744 (a) (b) fig. 6: the (a) simulated and (b) measured polar far field radiation pattern for e-plane of the microstrip patch antenna at 7.5 ghz. (a) (b) fig. 7: the (a) simulated and (b) measured polar far field radiation pattern for h-plane of the microstrip patch antenna at 7.5 ghz. 65 iium engineering journal, vol. 23, no. 1, 2022 mohamad et al. https://doi.org/10.31436/iiumej.v23i1.1744 table 2: the overall performance (simulated and measured) of the microstrip patch antenna at 7.5 ghz, in terms of return loss, bandwidth, directivity, gain and main lobe direction antenna performances simulation measurement return loss (db) -42.09 -30.53 bandwidth (mhz) 399 455 directivity (db) 7.18 3.88 gain (db) 7.63 5.51 main lobe direction (degree) 11.0 15.0 4. conclusion a microstrip patch antenna for x-band vsat application at 7.5 ghz has been designed, simulated, and tested. the antenna has a compact and lightweight structure with an overall dimension of 19.00 mm × 30.55 mm. the antenna depicted a good simulated performance with a return loss of -42.09 db, bandwidth of 399 mhz, directivity of 7.18 db. and gain of 7.63 db. the prototype of the antenna is then tested where the return loss s11 measurement is performed using a vector network analyzer, while the radiation pattern measurement is carried out in an anechoic chamber. the antenna prototype exhibits a measured return loss s11 of -30.53 db, bandwidth of 455 mhz, directivity of 3.88 db, and gain of 5.51 db. the proposed antenna can be a good replacement and a solution for the massive and bulkier parabolic reflector antenna for x-band vsat application at 7.5 ghz and will also be suitable for use on a moving vehicle or station. references [1] balanis ca. (2016) antenna theory analysis and design. hoboken, john wiley & sons, inc. [2] madiawati h, suryana j. (2016) design and implementation of mobile antenna vsat with microstrip array based at ku band frequency. in proceedings of the 10th international conference on telecommunication systems services and applications (tssa), pp. 1-5. [3] asci y, curuk e, yegin k, ozdemir c. (2016) improved splash-plate feed parabolic reflector antenna for ka-band vsat applications. in proceedings of the 46th european microwave conference (eumc), pp. 1283-1286. [4] ruslan aa, mohamad sy, badron k, ismail af, abdul malek nf, mohd isa fn. (2020) study of microstrip patch array antenna for side lobe suppression in the x-band region using uniform, binomial and tschebyscheff excitation methods. iium engineering journal, 21(1): 61-72. [5] mohamed n, mohamad sy, abdul malek nf, mohd isa fn. (2019) a compact and lightweight microstrip antenna array with wilkinson power divider for x-band application at 9.5 ghz. in proceedings of the ieee asia-pacific conference on applied electromagnetics (apace); pp. 1-5. [6] esa-satellite frequency bands. available: https://www.esa.int/applications/ telecommunications _integrated_applications/satellite_frequency_bands. [7] ishtaique-ul huque mt, hosain mk, islam s, chowdhury a. (2011) design and performance analysis of microstrip array antennas with optimum parameters for x-band applications. international journal of advanced computer science and applications, 2(4): 81-87. [8] samsuzzaman m, islam mt. (2014) inverted s-shaped compact antenna for x-band applications. scientific world journal: 11. [9] singh v, mishra b, singh r. (2015) a compact and wide band microstrip patch antenna for xband applications. in proceedings of the 2nd international conference on advances in computing and communication engineering, pp. 296-300. 66 iium engineering journal, vol. 23, no. 1, 2022 mohamad et al. https://doi.org/10.31436/iiumej.v23i1.1744 [10] ahmad mustafa am, mohamad sy, abdul malek nf, mohd isa fn and rafiqul im. (2018) a wideband circularly-polarized spiral antenna for cubesat application. journal of telecommunication, electronic and computer engineering, 10(1-8): 17-20. [11] model 1098 fly away integrated terminal system (2017) operations and maintenance manual, avl technologies, 900-085-001-d. [12] rt/duroid 5870 and 5880 data sheet – rogers corporation. available: https://rogerscorp.com/-/media/project/rogerscorp/documents/advanced-connectivitysolutions/english/data-sheets/rt-duroid-5870---5880-data-sheet.pdf 67 copyright notice consent to publish: the author(s) agree to publish their articles with iium press. declaration: the author(s) declare that the article has not been published before in any form and that it is not concurrently submitted to another publication, and also that it does not infringe on anyone's copyright. the author(s) holds the iium press and editors of the journal harmless against all copyright claims. transfer of copyright: the author(s) hereby agree to transfer the copyright of the article to iium press, which shall have the non-exclusive and unlimited right to publish the article in any form, including in electronic media. for the article with more than one author, the corresponding author confirms that he/she is authorized by his/her co-author(s) to grant this transfer of copyright. the iium engineering journal follows the open access policy. all articles published open access will be immediately and permanently free for everyone to read, download, copy and distribute for noncommercial purposes. iium engineering journal at https://journals.iium.edu.my/ejournal is licensed under a creative commons attribution-noncommercial 4.0 international license. iiium engineering journal iium engineering journal editors chief editor ahmad faris ismail, iium, malaysia technical editor sany izan ihsan, iium, malaysia executive editor ahm zahirul alam, iium, malaysia associate editor nor farahidah za’bah, iium, malaysia language editor lynn mason, malaysia copy editor hamzah mohd. salleh, iium, malaysia malay translator nurul arfah che mustapha, iium, malaysia editorial board members abdullah al-mamun, iium, malaysia abdumalik rakhimov, iium, malaysia aishah najiah bt. dahnel, iium, malaysia alya naili binti rozhan, iium, malaysia norsinnira bt. zainul azlan, iium, malaysia hanafy omar, saudi arabia hazleen anuar, iium, malaysia konstantin khanin, university of toronto, canada ma'an al-khatib, iium, malaysia meftah hrairi, iium, malaysia mohamed b. trabia, united states mohammad s. alam, texas a&m university-kingsville, united states mustafizur rahman, national university singapore, singapore ossama abdulkhalik, michigan technological university, united states mohamed hadi habaebi, iium, malaysia mohd. sultan ibrahim bin shaik dawood, iium, malaysia muhammad ibn ibrahimy, iium, malaysia nor fadhillah mohamed azmin, iium, malaysia waqar asrar, iium, malaysia aims & scope of iiumengineering journal the iium engineering journal, published biannually (january and july), is a carefully refereed international publication of international islamic university malaysia (iium). contributions of high technical merit within the span of engineering disciplines; covering the main areas of engineering: electrical and computer engineering; mechanical and manufacturing engineering; automation and mechatronics engineering; material and chemical engineering; environmental and civil engineering; biotechnology and bioengineering; engineering mathematics and physics; and computer science and information technology are considered for publication in this journal. contributions from other areas of engineering and applied science are also welcomed. the iium engineering journal publishes contributions under regular papers and invited review papers. it also welcomes contributions that address solutions to the specific challenges of the developing world, and address science and technology issues from an islamic and multidisciplinary perspective. referees’ network all papers submitted to iium engineering journal will be subjected to a rigorous reviewing process through a worldwide network of specialized and competent referees. each accepted paper should have at least two positive referees’ assessments. submission of a manuscript a manuscript should be submitted online to the iium-engineering journal website at https://journals.iium.edu.my/ejournal. further correspondence on the status of the paper could be done through the journal website. ii international advisory committee a. anwar, united states abdul latif bin ahmad, malaysia farzad ismail, usm, pulau pinang, malaysia hanafy omar, saudi arabia hany ammar, united states idris mohammed bugaje, nigeria k.b. ramachandran, india kunzu abdella, canada luis le moyne, isat, university of burgundy, france m mujtaba, united kingdom mohamed ai-rubei, ireland mohamed b trabia, united states syed kamrul islam, united states tibor czigany, budapest university of technology and economics, hungary yiu-wing mai, the university of sydney, australia. published by: iium press, international islamic university malaysia jalan gombak, 53100 kuala lumpur, malaysia phone (+603) 6421-5014, fax: (+603) 6421-6298 whilst every effort is made by the publisher and editorial board to see that no inaccurate or misleading data, opinion or statement appears in this journal, they wish to make it clear that the data and opinions appearing in the articles and advertisement herein are the responsibility of the contributor or advertiser concerned. accordingly, the publisher and the editorial committee accept no liability whatsoever for the consequence of any such inaccurate or misleading data, opinion or statement. iium engineering journal issn: 1511-788x e-issn: 2289-7860 iii iii iium engineering journal volume 24, issue 2, july 2023 https:/doi.org/10.31436/iiumej.v24i2 table of contents copyright .............................................................................................................................................................. i editorial .............................................................................................................................................................. ii chemical and biotechnology engineering 2590: biodegradation of fats, oil and grease using microorganisms isolated from palm oil mill effluent ......................................................................................................................................... 1 ma'an fahmi rashid al khatib., fadi alqedra and md. zahangir alam 2650: experimental and computational analysis for optimization of seawater biodegradability using photo catalysis ........................................................................................ 11 nayeemuddin mohammed, puganeshwary palaniandy, feroz shaik and hiren mewada 2709: effects of hive sizes and mesh materials on the productivity of propolis and honey produced by tetragonula laeviceps ............................................................................................... 34 muhammad yusuf abduh, annisa shabrina, andreas raden caman, arsy elia pratiwi and muhammad ihsanu 2717: parametric optimization of oil palm mesocarp fiber valorization with hybrid ozonation-ultrasonic pretreatment method ............................................................................ 45 didi dwi anggoro, indahsari kusuma dewi, luqman buchori and aji prasetyaningrum electrical, computer and communications engineering 2698: coronary heart disease classification using improved penguin emperor optimizationbased long short term memory network ..................................................................................... 67 rajeshwari maramgere ramaiah and kavitha kuntaegowdanalli srikantegowda 2700: treble search optimizer: a stochastic optimization to overcome both unimodal and multimodal problems ....................................................................................................................... 86 purba daru kusuma and ashri dinimaharawati 2730: the effectiveness of 6t beamformer algorithm in smart antenna systems for convergence analysis ...................................................................................................................... 100 sadiya thazeen and mallikarjunaswamy srikantaswamy 2752: enhancement of mppt module for partial shading photovoltaic system under uniform irradiance conditions ..................................................................................................................... 117 hameed ali mohammed, rosmiwati mohd-mokhtar and hazem ibrahim ali 2759: system identification (si) modelling, controller design and hardware testing for vertical trajectory of underwater remotely operated vehicle (rov) ................................ 131 fauzal naim zohedi, mohd shahrieel mohd aras, hyreil anuar kasdirin, mohd bazli bahar and lokman abdullah 2814: eye blink identification and removal from single-channel eeg using emd with energy threshold and adaptive filter ....................................................................................................... 141 lutfi aizat mohamed jefri, faridah abd rahman, noreha abdul malik and farah nadia mohd isa engineering mathematics and applied science 2550: modified seird model: a novel system dynamics approach in modelling the spread of covid-19 in malaysia during the pre-vaccination period ......................................................... 159 norsyahidah zulkarnain, nurul farahain mohammad and ibrahim shogar 2736: non-newtonian viscosity behaviour investigation for malaysian waxy crude oils and impact to wax deposition modelling ........................................................................................... 184 astriyana anuar, ismail mohd saaid, petrus tri bhaskoro and rohaizad mohd norpiah iv materials and manufacturing engineering 2442: behaviors of thermoelastic properties in ni-ti-based shape memory alloys, processed by metal forming techniques .............................................................................................................. 209 tarsila tenório luna da silva, fillipe virgolino, niédson silva, carlos oliveira, carlos araújo, oscar olimpio de araujo filho and cezar gonzalez 2778: effect of printing parameters and post-curing on mechanical properties of photopolymer parts fabricated via 3d stereolithography printing .................................... 225 raffle raed diab, abass enzi and omar hashim hassoon 2787: multicriteria decision making on supplier selection using soccer model integrated with analytical hierarchy process .......................................................................................................... 239 muataz al hazza, azura binti dapit, islam faisal bourini, zubaidah muataz and mohammad yeakub ali 2810: enhancing sustainability index parameter using anfis computational intelligence model .................................................................................................................................................... 258 diah septiyana, mohamed abd. rahman, tasnim firdaus mohamed ariff, nor aiman sukindar and erry yulian triblas adesta mechanical and aerospace engineering 2554: use of tio2 as a reinforcement of cassava starch/pva composites on moisture-resistant properties of triboelectric nanogenerators (teng) film ........................................................ 269 aris ansori, sudjito soeparman, denny widhiyanuriyawan and teguh dwi widodo 2695: a comparative finite element analysis of regular and topologically optimised dental implants for mechanical and fatigue responses evaluation ................................................. 286 muhammad ikman ishak, ruslizam daud, bakri bakar and siti noor fazliah mohd noor mechatronics and automation engineering 2296: high accuracy human motion trajectory generation for exoskeleton robot using curve fitting technique .................................................................................................................... 301 muhammad abdul jalil, muhammad fahmi miskon and bazli bin bahar 2766: triple nonlinear hyperbolic pid with static friction compensation for precise positioning of a servo pneumatic actuator ................................................................................ 315 khairun najmi kamaludin1, lokman abdullah, syed najib syed salim, zamberi jamaludin, nur aidawaty rafan, mohd fua'ad rahmat and rprakash ramanathan 2781: application of driving behavior control system using artificial neural network to improve driving comfort by adjusting air-to-fuel ratio .......................................................... 337 aris triwiyatno, suroto munahar, m. munadi and joga dharma setiawan 2799: a robust framework for driver fatigue detection from eeg signals using enhancement of modified z-score and multiple machine learning architectures ....................................... 354 rafiuddin abdubrani, mahfuzah mustafa, and zarith liyana zahari 2803: 3d collision avoidance system for unmanned aerial vehicle (uav) with decentralized approach ............................................................................................................................................... 373 mohamad haniff harun, shahrum shah abdullah, mohd shahrieel mohd aras, mohd bazli bahar and fariz ali@ibrahim 2804: emg based control of wrist exoskeleton ..................................................................................... 391 mohd safirin karis, hyreil anuar kasdirin, norafizah abas, wira hidayat mohd saad and mohd shahrieel mohd aras 2832: feature extraction and supervised learning for volatile organic compounds gas recognition .......................................................................................................................................... 407 nor syahira mohd tombel, hasan firdaus mohd zaki, and hanna farihin binti mohd fadglullah 1-coverpage 2-copyright-jan2023-v24n1 3-editorial_board-jan2023-v24n1 4-toc-volume 24 no.2 2023-july microsoft word 194 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering kabbashi 165 honesty and integrity in the koe, iium nassereldeen ahmed kabbashi department of biotechnology engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. nasreldin@iium.edu.my abstract: the universities and education face great challenges, most of them indirectly or directly related to science. academic honesty and integrity are fundamental values in a community of scholars. the student shares with the faculty the responsibility for maintaining the integrity of scholarship, grades, and professional standards, therefore students at university develop habits that help them to survive. it is necessary for scholars to think and work as a student, and resume the methods developed during undergraduate days. scholars at the kulliyyah of engineering (koe) international islamic university (iium), must satisfactory engage in learning with their students and in various forms of community service and industry liaison, in addition to attend several meetings per semesters. those pressures can attempt people to take short-cut that do not meet koe community standards for honesty and integrity. at the koe incidents of student cheating are very low but the cases start to increase. this paper tries to highlight the reason behind why honesty and integrity among scholars break down and why cases of cheating among students increased as well. abstrak: pihak universiti dan pendidik menghadapi cabaran yang hebat, kebanyakannya secara langsung atau secara tidak langsung berkaitan dengan sains. ketulusan akademik dan kewibawaan merupakan nilai-nilai asas dalam komuniti cendekiawan. para sizwazah berkongsi dengan pihak fakulti tanggungjawab dalam memelihara kewibawaan biayaan, gred, dan standard profesional. dengan ini, siswazah universiti dapat membentuk amalan yang membantu mereka cemerlang. ia adalah penting bagi para cendekiawan untuk memikir dan bekerja sama dengan pelajar, dan meneruskan kaedah yang dikembangkan semasa zaman prasiswazah. para intelektual di koe, iium harus terlibat dalam pengajaran dengan pelajar-pelajar mereka dalam pelbagai bentuk khidmat masyarakat serta kerjasama dengan industri, selain daripada menghadiri mesyuarat setiap semester. tekanan-tekanan sebegini boleh mendorong agar tidak mengambil jalan mudah yang tidak memenuhi standard komuniti di koe dari segi keikhlasan dan kewibawaan. di koe, insiden pelajar menipu adalah rendah tetapi hal ini makin meningkat. kertas ini cuba mengetengahkan sebab kenapa ketulusan dan keutuhan di kalangan siswazah makin runtuh dan kenapa kes-kes penipuan di kalangan pelajar semakin meningkat. keywords: integrity; honesty; iium; koe; allah (swt) 1. introduction the international islamic university malaysia (iium) kulliyyah of engineering (koe), being the newest in malaysia, admitted its first batch of students in june 1994. it has many features common in other malaysian universities: content of the medical curriculum, duration of studies, examinations, and practical training. it in addition has unique characteristics of its own being islamic and international. it has an integrated iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering kabbashi 166 curriculum in which moral and ethical values are taught with the academic and practical aspects. iium does not accept the distinction between ethics as a set of regulations agreed on by consensus in a particular profession and morality as basic inner beliefs. ethics must reflect basic morality otherwise, like any other human rules they can be circumvented by using one loop-hole or another. ethics cannot be learned in a course but can only be internalized so that they become part of the student's personality. the supreme objective is to produce a physician who will act ethically without consciously thinking about rules and regulations. ethical behavior will have become part of behavior as is eating and drinking. the aim is to make sure that ethical behavior is not prompted by fear of punishment or promise for any reward. the only motivation should be from the inner conviction of the physician. being an islamic university, the teaching of ethics is based on the islamic value system. these are the universal human values found in several other faiths and philosophies of life. islam as a religion and way of life has the unique distinction of claiming universality in its basic teachings, practice, cultural, and intellectual values. it is therefore very easy for non-muslim students to follow and understand the ethical input into the curriculum. 2. the integration of islamization curriculum islamic epistemology is based a central principle, allah (swt) is the source of all knowledge. three main sources arise regarding to knowledge. god’s teaching to adam (pbuh), revelation as of qur’an and sunnah principles, and fitrah of human beings. knowledge (’ilm) occupies a dominant position in the islamic world-view. according to franz rosenthal, 1970, ‘in islam, the concept of knowledge enjoyed an importance unparalleled in other civilizations’. it dominated over all aspects of muslim intellectual, spiritual and social life. twentieth century of science began by asking what is the material, why do materials have different properties, what are the ethics of using those materials as weapons in the wars, as genetic modified organisms etc. the holy qur‘an and the sunnah of the prophet (pbuh) should be the primary references in understanding the nature of the learner and knowledge. the major step for the islamization of the curriculum is to ensure that the sources of educational purposes are drawn from the islamic worldview, whether they are about the background of the learner, the character of the knowledge or the subject specialization, or current life itself. 2.1 tawhid all the islamic courses at the kulliyyah of engineering iium mainly concentrate on unity (tawhid) allah (swt) said in the holy qur’an “verify those who say: ‘our lord is allah, and remain firm on that path on them shall be no fear, nor shall they grieve” (qur’an, 46:13)[1]. therefor all ungs courses which explained in the coming section focused on tawhid. 2.2 vision the formulation of a clear philosophy of education based on the islamic worldview is a must in any educational sector. it is crucial to act as the educational guide for the state, school leaders, teachers, parents and students. clear goals and objectives of education must be spelled out as of iium where followed the university's vision, iium endeavour’s: • to undertake the special and greatly needed task of reforming the contemporary muslim mentality and integrating islamic revealed knowledge and human sciences in a positive manner. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering kabbashi 167 • to produce better quality intellectuals, professionals and scholars by integrating the qualities of faith ( iman ), knowledge ( `ilm ), and good character ( akhlaq ) to serve as agents of comprehensive and balanced progress as well as sustainable development in malaysia and in the muslim world. • to foster the islamization of the ethics of muslim academic and administrative staff of iium, and certain aspects of human knowledge particularly in the social sciences and humanities with the view to making them more useful and more relevant to the muslim ummah. • to nurture the quality of holistic excellence which is imbued with islamic moralspiritual values, in the process of learning, teaching, research, consultancy, publication, administration and student life. • to exemplify an international community of dedicated intellectuals, scholars, professionals, officers and workers who are motivated by the islamic world-view and code of ethics as an integral part of their work culture. • to enhance intercultural understanding and foster civilization dialogues in malaysia as well as across communities and nations. • to develop an environment this instils commitment for life-long learning and a deep sense of social responsibility among staff and students. the summary of the mission should read as follows: • integration; • islamization; • internationalization; and • comprehensive excellence 2.3 faith and science the faith and science at the kulliyyah of engineering taught the students all the above courses aiming to reach to the following principles which are: � truthfulness � trust � sincerity � brotherhood � science and knowledge � justice and after students graduated from the kulliyyah, the university level and kulliyyah level monitored those principles with their graduates, and based on the reports about alumni, university level and kulliyyah are optimistic and proud of their graduates and of their doings, which considered as a unique brand of iium. 3. integrity and honesty a book [2] was published to emphasize the importance of professional ethics and to provide a clear understanding of the terms and concepts of engineering ethics. several other books followed [3-4], with the most recent ones [5-7] written as textbooks for some proposed ethics courses. students at koe develop habits that help them to survive. this is most striking to those of us who undertook higher degrees after being in the workforce for a period; it is necessary to think and work as a student, and resume the methods developed during undergraduate days. the habits are mostly centered around maximizing marks, the iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering kabbashi 168 student's single most important objective, and if a course is well crafted this will also optimizing learning. likewise, academic staff members strive to publish their cutting-edge research in leading scholarly journals, since that increasing their seniority, salary and occupancy. they must also satisfactorily engage in learning with their students, and in various forms of community service and industry liaison. 4. integrity and honesty findings based on interviews done with with head of department of electrical and computer engineering (ece), biotechnology engineering (bte) and dean kulliyyah of engineering, and questionnaire with admission and records, koe division on different occasions the out puts were as follows. each staff at the koe suffered from huge number of meetings per month, normal staff at least must attend 2 meetings per week, the dean koe and his two deputies at least they have 3-4 meeting per week, head of department for the 6 programs may have between 3-5 meetings per week and this one varies between department and another based on the experience of the person who headed the department who delegate his tasks to a group and they just summarize him the findings, where as a new head needs time to fully comprehend the system and then (s)he must be involved in many meetings. table 1 shows a typical regiularly scheduled meetings for office bearers and ordinary academic staff. it should be noted that table 1 does not include the emergency meetings, unplanned meetings etc. which puts many academic staff under jobrelated tensions and stress and may affect the staff’s honesty and integrity. table 1: koe management staff meetings. hod = head of department these pressures can attempt people to take short-cuts that do not meet community standards for honesty and integrity. even institutions can cheat, for example under the inspection of external auditors. it is supposed that, in an earlier era, entire libraries and computer labs appeared overnight and then misplaced after the audit visit. # name department number of meetings/week 1 staff member all 2 2 dean koe koe 3-5 3 hod mechatronics 3-4 4 hod biotechnology 4-5 5 hod mechanical 3-5 6 hod electrical and computer 3-5 7 hod science 2-3 8 hod manufacturing and materials 2-3 9 director advanced engineering and innovation centre 2-3 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering kabbashi 169 at koe-iium gombak campus incidents of cheating are not yet to a threaten level, still the students respect the high reputation of the kulliyyah and the university vision and mission, students know that any cheating reduces the value of their degree, cases as paper cheating, some papers in toilets and inside their phones has been caught by the invigilator, this why the rules for students during exams to leave their belongings outside the exam hall, and strict checks for student's matric names, and check the toilets is very important. in education, cheating and not punishing cheating is a failure to uphold community standards. when lecturers and academic managers do not properly deal with serious incidents, they are themselves engaging corrupt conduct as seen in table 2. table 2: cheating cases at koe, semester iii, 2009-2010. source: admission and records, koe fig. 1: cheating cases 2009-2010. no. gender nationality male female malaysian international 1. 1 1 2. 1 1 3. 1 1 4. 1 1 5. 1 1 6. 1 1 7. 1 1 8. 1 1 9. 1 1 total 8 1 6 3 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering kabbashi 170 honesty and integrity are among the most important values that students, academics and institutions can hold dear. these values are impaired when conflict of interest are not adequately managed, as in unfairly gaining higher marks. at iium an ethics statement sets a high tone for the conduct of all staff and students. potential conflicts of interest, which may come up in the normal course events, must be actively avoided, disclosed, and managed. when anyone is considering whether a university is good or not, inquire about honesty and integrity. table 3: cheating cases at koe, semester 1, 2010-2011. source: admission and record koe fig. 2: cheating cases, 2010-2011. 5. future, challenges and opportunities based on all the values and ethics at koe instilled in students by iium authority, perhaps none is as essential as academic integrity. unfortunately, students are not inevitably honest. in fact, a majority of students carry questionable ethical habits into college with them. the problem of dishonesty does not trouble campus classrooms alone, but reaches far into individual persons and even it becomes culture which spread from certain groups into another specially if we know that there are ninety nine different nations and cultures inside iium campus. to have a bright future for the coming generation must learn them that oneday will then become responsible themselves. it is therefore a hope that as everyone establishes a no. gender nationality male female malaysian international 1. 1 1 2. 1 1 3. 1 1 4. 1 1 total 4 2 2 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering kabbashi 171 promise based on trust with his students within his classroom, the model of integrity and personal integration of faith, honest, care and learning will impact their lives and encourage them to do likewise as bright future. acknowledgment the author acknowledges all the kind help in getting the required data from admission and record division koe and in specific brother ahmad hidayat and to iium as well. references [1] holy qur’an, 46:13. [2] mantell, m.i., ethics and professionalism in engineering, the macmillan company, new york, 1964. [3] florman, s.c., the civilized engineer, st. martin's press, new york, 1987. [4] johnson, d.g., ethical issues in engineering, prentice-hall, englewood cliffs, n.j. 1991. [5] davis, m., thinking like an engineer: studies in the ethics of a profession, oxford university press, new york, 1998. [6] whitbeck, c., ethics in engineering practice and research, cambridge university press, 1998. [7] schinzinger, r. and martin, m., introduction to engineering ethics, mcgraw-hill inc, 2000. microsoft word 151-1238 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 33 highly sensitive timer-based resistance deviation to time converter zeeshan s., nadratul a.g., noor amalina r., sumayyah d., rumana t., myo m.o., and sheroz k. electrical and computer engineering department, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. zeesh_87@hotmail.com, sheroz@iium.edu.my abstract: based on an inexpensive popular precision timing chip 555 timer, a resistance to time converter is proposed in this paper it is indeed capable of converting resistive and capacitive changes into pulse widths of proportional durations. this converter exhibits a compatibility of wider conversion range with a reasonable level of sensitivity required for industrial applications. the circuit is expected to have application in oil and water supply schemes. simulated results are shown to be compared with mathematical derivations, both reporting a good level of response matching very closely with the derived results, where a 70% deviation of an elemental value corresponds to a mismatch of 50-70 micro-seconds between derived and simulation results. abstrak: rintangan kepada penukar masa berdasarkan cip pemasaan tepat dan murah yang popular 555, telah dicadangkan dalam kertas kerja ini. ia memang mampu menukarkan perubahan perintang dan pemuat kepada lebar nadi jangka masa berkadar. penukar ini mempamerkan keserasian pelbagai penukaran yang lebih luas dengan tahap sensitiviti yang munasabah untuk aplikasi perindustrian. litar ini dijangka mempunyai applikasi dalam skim bekalan minyak dan air. keputusan simulasi dibandingkan dengan terbitan matematik, kedua-duanya menunjukkan keputusan yang sangat rapat, di mana 70% daripada nilai asas berkaitan dengan tidak sepadan 50-70 mikro-saat antara keputusan simulation dan terbitan matematik. keywords: resistance to pulse converters; linearity; sensitivity; resistance to frequency converters 1. introduction in monitoring, automation and control, small resistive changes can emmulate the physical parameter of our interest such as force, displacement, vibration, and temperature. conversion of resistive changes into corresponding time period or frequency changes has been presented since very long. such conversions have been one of the most reliable and significant measurement steps in resistive transducers applications commonly used in today’s industry. their application is on the rise particularly in cases of automation and control being carried out wirelessly through small distances such as narrow gaps. resistance to time (or frequency) converters of critical importance in small measurements activities. these measurements have been traditionally carried out by transducers normally exhibiting linear precise responses over a limited range. when carried out over a wide range, such transducers usually start showing nonlinear responses, which results in inaccuracies. such inaccuracies were not considered noticeable when iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 34 looked from the traditional transducers’ view point, where even sizeable errors were overlooked. however, in today’s smart applications the overlooked ignorable mismatches are considered unaffordable. therefore, it is crucial to implement a circuit which would be able to produce a linear as well as highly sensitive output. various papers have presented and proposed converter circuit that can be implemented in the transducer to produce a linear as well as highly sensitive output. two main papers of interest are [1-2] which presented the circuit by implementing wheatstone bridge as well as amplifier bridge. in these papers, the effect of offset error and its compensation is being discussed to show that linearity improves with offset compensation scheme. the first paper by mochizuki and watanabe [1] implemented a relaxation oscillator with the combination of the wheatstone bridge resistor. wheatstone is implemented due to its ability to detect small changes in terms of resistance deviations as compared to the early implementation of relaxation oscillator [1]. however, nonlinearity characteristic starts to appear when the period is amplified due to time-delay which is onward solved by using compensation techniques. the second paper by s. kaliyugavaradan [2] proposed a refined version of the circuit which not only rules out the need for using compensation arrangement, but also provided grounded transducer. this paper refines the existing works with by implementing a monostable circuit to produce the same resistance deviation to frequency converter with improved linearity and sensitivity over a wider range. this paper will attempt to prove the reliability of using monostable circuit by presenting the results of the output as compared to the theoretical derivations. 2. state of the art work making use of a bridge, reference [1] suggests a resistance to frequency converter with a resolution of 0.05% and linearity maintained over a given range. the offset error produced by the op amp used is a major obstacle, which is addressed by the feedback of a fraction of the output. the suggested circuit has signal processing applications. a linear resistance-to-time converter with high resolution has been reported [2]. the results obtained had a good level of linearity with the nonlinearity error less than �0.1% over the range of 950 ω 2950 ω and the conversion sensitivity of 50 µs/ω. another highly quoted paper [3], proposes a resistance-to-time converter which is also implemented on a resistive bridge configuration. over a resistance deviation range of 0 –2 ω, the converter exhibits a response with nonlinearity error less than 0.005 %. further, it is reported to have exhibited a conversion sensitivity of 2832.4 µs/ω. all the above converters are suggesting custom built electronic approaches, which on occasions will be making it challenging task, considering the availability of the required components. this converter uses a 555-timer connected in a monostable mode. this circuit produce small resistance variations as pulse-width conversions through the use of a 555-timer, that can be made easily available avoiding the requirement of custom-built electronic conversion circuit. the challenges are to obtain a high level of linearity and better conversion sensitivity over a wider range of resistance deviation. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 35 3. theory and simulation of proposed resistance to time converter the circuit diagram of fig. 1(a) is a basic mono-stable multi-vibrator, also called ‘one-shot’ pulse generation circuit which uses a 555 ic timer circuit. the external resistor and capacitor (rc) network is connected between power supply and ground. an input trigger pulse is applied to trigger input pin (pin4) of the timer which is normally kept at high. the output of the mono-stable multi-vibrator remains at low before it is triggered. as the trigger pin turns low the timer generate a pulse at the output for a period which is equal to the value of its time constant (values of external resistor and capacitor used). the duration of the resulting pulse can be theoretically derived as given in following equation. t= 1.17rc (1) (a) (b) fig. 1: (a) 555-timer based monostable pulse generator (b) output pulse of 555-timer based monostable pulse generator. in another configuration fig. 2 (a), two mono-stable circuits are used and connected in parallel. the same values are used for the external resistor and capacitor, having equal time constants, and as shown in fig. 2(b), no pulse is produced as a result. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 36 (a) (b) fig. 2: (a) two mono-stable circuits connected in parallel, (b) no pulse generated. in another such configuration fig. 3 (a), the two mono-stable circuits are connected in parallel similar to that shown in fig. 2. keeping capacitance the same, the resistance values are kept different for two unequal time constants. so, they do produce a pulse at the output of the exclusive-or gate with width given by t=1.17(r2-r1)c (2) (a) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 37 (b) fig. 3:(a) two mono-stable circuits connected in parallel for resistive deviations (b) generated output pulse of two mono-stable circuits connected in parallel with resistive deviations (3 ω). the final arrangement is presented in fig. 4(a). unlike the circuit of fig. 3, in this circuit each mono-stable circuit has used resistors of equal values while two capacitors of dissimilar values. ultimately this slightly modified arrangement attempts to produce pulse of a width given by t = 1.17 r(c2-c1) (3) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 38 (a) (b) fig. 4: (a). two mono-stable circuits connected in parallel for capacitive deviation (b). generated pulse of two mono-stable circuits connected in parallel for capacitive deviation (49 µ f). 4. simulation results and discussion the proposed circuit has highlighted the conversion of a small resistance changes into narrow pulse widths (microsecond range). the relationship between these changes appears to be linear over a certain range of resistive and capacitive variations. in figure 5(a) pulsewidth versus percentage resistance deviation and while in figure 5(b) pulse-width versus percentage capacitive deviations are shown respectively. these plots are derived from data given in table 1 and 2 respectively (see appendix i). the simulation plots generated using matlab confirm with the mathamatical equations. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 39 fig. 5: (a) pulse width versus percentage resistance deviation (in ω). for resistance changes of up to 10 ω, a pulse width of 200 µs is produced. the maximum width of pulse is about 1400 µs when the resistance deviation is near to about 100%. sensitivity of 20 µs/ω is obtained over this resistive deviation. it is apparent that the converter’s sensitivity is of a poorer value than [8] but has shown a good level of linearity over a much wider range of 0-60 ω (0-100%). further increase of resistive values shows a nonlinear response. fig. 5 (b): pulse width versus percentage capacitive deviation (µf) comparing the response shown fig. 5(b), the conversion of pulse width with percentage increase in capacitive changes shows a direct linear behavior over the ranges 090 µf range. a variation of 100µs pulse width is generated for a cpacitve chnage of 10 µf, giving a sensitivity of 10µs/µf is obtained over the described range of 0-90 µf. 0 10 20 30 40 50 60 70 80 90 100 0 100 200 300 400 500 600 700 percentage capacitance deviation (micro farad) p u ls e w id th ( m ic ro s e c o n d ) mathematical result simulated result 0 10 20 30 40 50 60 70 80 90 100 0 200 400 600 800 1000 1200 1400 percentage resistance deviation (ohm) p u ls e w id th (m ic ro s e c o n d ) simulated result mathematical result iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 40 from the resulting plots given above it is obvious that the size of the pulse width obtained is dependent on resistance and capacitance values respectively. although this conversion of resistive and capacitive changes do not produce subsequent time width of same size, both the suggested circuits behaved in a linear fashion over a time under consideration. the results of this work can be applied in converting small resistive or capacitive changes into their pulses of width equivalent to corresponding changes. the same concepts might be useful for signal extract from embedded transducers as such concepts is the foundation principal of pulse-width-modulation (pwm). further, the resolution and sensitivity of the circuits under consideration could be adjusted to application specific case study requirements. 5. conclusion a new design of resistance deviation to frequency converter utilizing a monostable circuit 555-timer is presented in this paper. from the simulation results, it is evident that the proposed converter circuit produce a good level of linearity of up to 100% ranges with sensitivity of 20 µs/ω and 10 µ s/µ f for resistance and capacitance variations respectively. unlike conventional circuits, this converter avoids using integrator, oscillator and bridge circuits. this simple converter is tolerent to offers better performance in terms of linearity and wider rage of daviations and is suitable for applications in the oil and water treatment industry references [1] kouji mochizuki and kenzo watanabe, “a high-resolution, linear resistance-tofrequency converter,” ieee transactions on instrumentation and measurement, vol. 45, no. 3, june 1996 [2] s. kaliyugavaradan, “a linear resistance-to-time converter with high resolution,” ieee transactions on instrumentation and measurement, vol. 49, no. 1, february 2000 [3] w. schung, m. yan, and s. hson, “a simple resistance-to-time converter for resistive sensors,” icice electronics express, vol. 5, no. 9, 310-315, may 2008 [4] v. ferrari, d. marioli, and a. taroni, “oscillator-based interface for measurand-plustemperature readout from resistive bridge sensors,” ieee trans. instrum. meas., vol. 49, no. 3, pp. 585–590, jun. 2000. [5] zvezditza p. nenova and toshko g. nenov, member, ieee, “linearization circuit of the thermistor connection,” ieee transactions on instrumentation and measurement, vol. 58, no. 2, february 2009 [6] santiago lizón-martínez, bernardo tellini, member, ieee, romano giannetti, senior member, ieee, and guillermo robles, member, ieee, “measurement of asymmetric minor loops in soft ferrites up to medium frequencies,” ieee transactions on instrumentation and measurement, vol. 58, no. 2, february 2009 [7] hoon kim, won-sup chung, hee-jun kim, senior member, ieee, and sang-hee son, “a resistance deviation-to-pulsewidth converter for resistive sensors,” ieee transactions on instrumentation and measurement, vol. 58, no. 2, february 2009 [8] ferran reverter, manel gasulla and ramon pall`as-areny, “analysis of interference effects on period-to-digital conversions,” institute of physics publishing measurement science and technology, meas. sci. technol. 16 (2005) 2261–2264 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 41 appendix i table 1 s.no r1 (ω) r2 (ω) change in r (ω) c (µf) mathematical value 1.17 (r1r2)c (µs) simulated result (µs) percentage resistance variation 1 47 47 0 20 0 0 0 2 47 48 1 20 23.4 22 1.67 3 47 49 2 20 46.8 45 3.33 4 47 50 3 20 70.2 67.5 5.00 5 47 51 4 20 93.6 89 6.67 6 47 52 5 20 117 110 8.33 7 47 53 6 20 140.4 132.5 10.00 8 47 54 7 20 163.8 155 11.67 9 47 55 8 20 187.2 176 13.33 10 47 56 9 20 210.6 197.5 15.00 11 47 57 10 20 234 219.5 16.67 12 47 58 11 20 257.4 241 18.33 13 47 59 12 20 280.8 264 20.00 14 47 60 13 20 304.2 285 21.67 15 47 61 14 20 327.6 308.5 23.33 16 47 62 15 20 351 329.5 25.00 17 47 63 16 20 374.4 353 26.67 18 47 64 17 20 397.8 372.5 28.33 19 47 65 18 20 421.2 395 30.00 20 47 66 19 20 444.6 417.5 31.67 21 47 67 20 20 468 439 33.33 22 47 68 21 20 491.4 462 35.00 23 47 69 22 20 514.8 483 36.67 24 47 70 23 20 538.2 508 38.33 25 47 71 24 20 561.6 527 40.00 26 47 72 25 20 585 545 41.67 27 47 73 26 20 608.4 565 43.33 28 47 74 27 20 631.8 592 45.00 29 47 75 28 20 655.2 614 46.67 30 47 76 29 20 678.6 637 48.33 31 47 77 30 20 702 658 50.00 32 47 78 31 20 725.4 680 51.67 33 47 79 32 20 748.8 702 53.33 34 47 80 33 20 772.2 723 55.00 35 47 81 34 20 795.6 744 56.67 36 47 82 35 20 819 763 58.33 37 47 83 36 20 842.4 790 60.00 38 47 84 37 20 865.8 812 61.67 39 47 85 38 20 889.2 833 63.33 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 42 40 47 86 39 20 912.6 857 65.00 41 47 87 40 20 936 878 66.67 42 47 88 41 20 959.4 898 68.33 43 47 89 42 20 982.8 920 70.00 44 47 90 43 20 1006.2 942 71.67 45 47 91 44 20 1029.6 964 73.33 46 47 92 45 20 1053 988 75.00 47 47 93 46 20 1076.4 1004 76.67 48 47 94 47 20 1099.8 1036 78.33 49 47 95 48 20 1123.2 1052 80.00 50 47 96 49 20 1146.6 1066 81.67 51 47 97 50 20 1170 1100 83.33 52 47 98 51 20 1193.4 1100 85.00 53 47 99 52 20 1216.8 1130 86.67 54 47 100 53 20 1240.2 1160 88.33 table 2. s.no c1 (µf) c2 (µf) change in c (µf) r (ω) mathematical value 1.17 (c2c1)r (µs) simulated result (µs) percentage capacitance variation 1 10 10 0 10 0 0 0.00 2 10 11 1 10 11.7 11.6 1.67 3 10 12 2 10 23.4 22.2 3.33 4 10 13 3 10 35.1 33.5 5.00 5 10 14 4 10 46.8 44 6.67 6 10 15 5 10 58.5 55.5 8.33 7 10 16 6 10 70.2 66.4 10.00 8 10 17 7 10 81.9 77.2 11.67 9 10 18 8 10 93.6 87.4 13.33 10 10 19 9 10 105.3 98.8 15.00 11 10 20 10 10 117 109.6 16.67 12 10 21 11 10 128.7 122 18.33 13 10 22 12 10 140.4 132 20.00 14 10 23 13 10 152.1 144 21.67 15 10 24 14 10 163.8 155 23.33 16 10 25 15 10 175.5 165 25.00 17 10 26 16 10 187.2 175 26.67 18 10 27 17 10 198.9 185 28.33 19 10 28 18 10 210.6 195 30.00 20 10 29 19 10 222.3 209 31.67 21 10 30 20 10 234 219.5 33.33 22 10 31 21 10 245.7 230 35.00 23 10 32 22 10 257.4 240 36.67 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics zeeshan et al. 43 24 10 33 23 10 269.1 251 38.33 25 10 34 24 10 280.8 261 40.00 26 10 35 25 10 292.5 272.5 41.67 27 10 36 26 10 304.2 282.5 43.33 28 10 37 27 10 315.9 297.5 45.00 29 10 38 28 10 327.6 306 46.67 30 10 39 29 10 339.3 320 48.33 31 10 40 30 10 351 330 50.00 32 10 41 31 10 362.7 339.25 51.67 33 10 42 32 10 374.4 350 53.33 34 10 43 33 10 386.1 362 55.00 35 10 44 34 10 397.8 372 56.67 36 10 45 35 10 409.5 383 58.33 37 10 46 36 10 421.2 395 60.00 38 10 47 37 10 432.9 405 61.67 39 10 48 38 10 444.6 418 63.33 40 10 49 39 10 456.3 430 65.00 41 10 50 40 10 468 440 66.67 42 10 51 41 10 479.7 450 68.33 43 10 52 42 10 491.4 460 70.00 44 10 53 43 10 503.1 470 71.67 45 10 54 44 10 514.8 480 73.33 46 10 55 45 10 526.5 495 75.00 47 10 56 46 10 538.2 504 76.67 48 10 57 47 10 549.9 514 78.33 49 10 58 48 10 561.6 524 80.00 50 10 59 49 10 573.3 534 81.67 51 10 60 50 10 585 547.44 83.33 52 10 61 51 10 596.7 547.44 85.00 53 10 62 52 10 608.4 547.44 86.67 54 10 63 53 10 620.1 547.44 88.33 international islamic university malaysia iium (international islamic university malaysia) engineering journal chief editor ahmad faris ismail, iium, malaysia. technical editor md. noor bin salleh, iium, malaysia. executive editor waqar asrar, iium, malaysia. associate editor anis nurashikin nordin, iium, malaysia. language editor israd hakim jaafar, iium, malaysia. copy editor hamzah mohd. salleh, iium, malaysia. editorial board members a.k.m nurul amin, iium, malaysia abdullah al-mamun, iium, malaysia abdumalik rakhimov, iium, malaysia amir akramin shafie, iium, malaysia erwin sulaeman, iium, malaysia hanafy omar, saudi arabia hazleen anuar, iium, malaysia konstantin khanin, university of toronto, canada luis le moyne, university of burgundy, france ma'an al-khatib, iium, malaysia md zahangir alam, iium, malaysia meftah hrairi, iium, malaysia mohammed konneh, iium, malaysia mohammad s. alam, university of south alabama, united states mustafizur rahman, national university singapore, singapore nurul fadzlin hasbullah, iium, malaysia ossama abdulkhalik, michigan technological university, united states rosminazuin ab. rahim, iium, malaysia aims & scope of iium engineering journal the iium engineering journal, published biannually, is a carefully refereed international publication of international islamic university malaysia (iium). contributions of high technical merit within the span of engineering disciplines; covering the main areas of engineering: electrical and computer engineering; mechanical and manufacturing engineering; automation and mechatronics engineering; material and chemical engineering; environmental and civil engineering; biotechnology and bioengineering; engineering mathematics and physics; and computer science and information technology are considered for publication in this journal. contributions from other areas of engineering and applied science are also welcomed. the iium engineering journal publishes contributions under regular papers, invited review papers, short communications, technical notes, and letters to the editor (no page charge). book reviews, reports of and/or call for papers of conferences, symposia and meetings, and advances in research equipment could also be published in iium engineering journal with minimum charges. referees’ network all papers submitted to iium engineering journal will be subjected to a rigorous reviewing process through a worldwide network of specialized and competent referees. each accepted paper should have at least two positive referees’ assessments. submission of a manuscript a manuscript should be submitted online to the iium-engineering journal website: www.eng.iium.edu.my/ejournal. further correspondence on the status of the paper could be done through the journal website and the e-mail addresses of the executive editor: waqar@iium.edu.my faculty of engineering, international islamic university malaysia (iium), p.o. box 10, 50728, kuala lumpur, malaysia. phone: (603) 6196 4482, fax: (603) 6196 4853. http://www.eng.iium.edu.my/ejournal mailto:waqar@iium.edu.my iium (international islamic university malaysia) engineering journal international advisory committee tibor czigany yiuwing mai luis le moyne, isat, university of burgundy, france razi nalim, iupui, indianapolis, indiana, united states farzad ismail, usm, pulau pinang, malaysia ossama abdulkhalik, michigan technological university, united states a anwar, united states abdul latif bin ahmad, malaysia hanafy omar, saudi arabia hany ammar, united states idris mohammed bugaje, nigeria k.b. ramachandran, india kunzu abdella, canada m mujtaba, united kingdom mohamed ai-rubei,, ireland mohamed b trabia, united states mohammad s. alam, university of south alabama, united states m. nazmul karim, united states syed kamrul islam, united states published by: iium press, international islamic university malaysia p.o. box 10, 50728 kuala lumpur, malaysia phone (+603) 6196-5014, fax: (+603) 6196-6298 website: http://iiumpress.iium.edu.my/bookshop printed by: perniagaan normahs no 3, 5 & 7, jalan 12/10, taman koperasi polis fasa 1, 68100 mukim batu, batu caves, kuala lumpur, malaysia. whilst every effort is made by the publisher and editorial board to see that no inaccurate or misleading data, opinion or statement appears in this journal, they wish to make it clear that the data and opinions appearing in the articles and advertisement herein are the responsibility of the contributor or advertiser concerned. accordingly, the publisher and the editorial committee accept no liability whatsoever for the consequence of any such inaccurate or misleading data, opinion or statement. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 flow induced vibration in square cylinder of various angles of attack nur ain shafiza ramzi1, lee kee quen1*, nur amira balqis mohd zainuri1, hooi-siang kang2,3, nor’azizi othman1 and keng yinn wong2 1 mechanical precision engineering, malaysia-japan international institute of technology, universiti teknologi malaysia, kuala lumpur, malaysia 2 school of mechanical engineering, faculty of engineering, universiti teknologi malaysia, malaysia 3 marine technology center, institute for vehicle system and engineering, universiti teknologi malaysia, malaysia *corresponding author: lkquen@utm.my (received: 22nd january 2021; accepted: 24th may 2021; published on-line: 4thjanuary 2022) abstract: an experimental study was carried out to identify the effect of angle of attack on flow-induced vibration (fiv) of square cylinders. the experiment was conducted at the aeronautical and wind engineering laboratory (aerolab), utm kuala lumpur using a wind tunnel that was free from external wind conditions. a supporting structure was designed and fabricated to conduct this experiment. the importance of this support structure was to enable the rigid cylinder to suspend and vibrate freely upon excitation of wind speed. the results were analysed through the response of amplitude and frequency of the rigid cylinder over a velocity range of 0.5m/s to 4.0m/s. the results showed that for a square cylinder of α=0°, vortex-induced vibration (viv) occurred at low reduced velocity (ur) in range of 5 ≤ ur ≤ 10 and galloping occurred at higher reduced velocity which started at ur=15. a tranquil zone was found between viv and galloping in the reduced velocity range of 10 ≤ ur ≤ 15. as for α=22.5° and 45°, only viv response was found at low reduced velocity in range of 4≤ ur ≤ 9. abstrak: satu kajian eksperimentasi telah dilakukan bagi mengenal pasti pengaruh sudut serangan oleh getaran cetusan-aliran (fiv) dalam silinder persegi. eksperimen ini dijalankan di makmal kejuruteraan aeronautika dan angin (aerolab), utm kuala lumpur dengan menggunakan terowong angin yang bebas dari pengaruh angin luar. struktur sokongan telah direka dan difabrikasi bagi tujuan eksperimen ini. ini penting bagi membolehkan silinder pegun tergantung dan bergetar dengan bebas semasa ujian kelajuan angin. dapatan kajian dianalisis melalui tindak balas amplitud dan frekuensi silinder pegun pada kadar halaju 0.5m/s sehingga 4.0m/s. hasil kajian menunjukkan bahawa bagi silinder persegi α = 0 °, getaran pengaruh-vorteks (viv) berlaku pada halaju rendah (ur) dalam julat 5 ≤ ur ≤ 10 dan getaran lebih teruk telah ketara berlaku pada kadar halaju berkurang iaitu bermula pada ur = 15. zon tenang dijumpai antara viv dan getaran teruk pada kadar halaju berkurang 10 ≤ ur ≤ 15. adapun pada α = 22.5° dan 45°, hanya tindak balas viv dijumpai pada halaju rendah dalam kadar 4≤ ur ≤ 9. keywords: flow-induced vibration; square cylinder; galloping; angle of attack; tranquil zone 358 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 1. introduction flow-induced vibration (fiv) of a bluff body has received huge attention in various fields such as the aerospace industry, bridges, tall buildings, smokestacks, power generation, and engineering infrastructure. therefore, fiv has been a hot topic for researchers for the past 20 years and various methods have been undertaken such as experiments and simulations to investigate fiv on cylindrical structures [1-2]. viv and galloping can be categorized under fiv phenomenon, where viv occurs at steady conditions while galloping can be considered as unsteady fiv phenomenon that usually arises in asymmetrical bodies. previous study has reported that galloping usually occurs at high flow speeds [3-10]. failures or problems that may occur from fiv are usually due to improper design. therefore, understanding on the characteristic of flow induced vibration is of utmost importance because of its physical applications and the possibility of causing severe damage if improper design is applied. the collapse of the tacoma narrows bridge in 1940 was a well-known accident that was caused by fiv. due to its catastrophic effects, continuous research on fiv is highly demanded to provide a better understanding of its characteristics in order to avoid such accidents from happening again. in civil engineering, consideration of wind path over buildings and other rectangular structures is particularly vital as it leads to variation in the structure’s angle of attack. angle of attack can be described as the angle between the reference line of the body and the relative oncoming motion flow such as air and water. the angle of attack may result in uneven pressure distributions that can lead to unpredictable loading patterns. based on the previous research, study on the effect of angle of attack is very limited. nemes et al. [11] is one of the few teams that have investigated the interaction between flow-induced vibration mechanisms of a square cylinder with different angles of attack. the experiment was conducted in a free surface recirculating water channel and reported that viv and galloping occurred over a narrow range of angles of incidence. hu et al. [12] conducted an experiment with various angles from 0° to ± 30° and found that as the forward inclination increased, the crosswind responses of the cylinder decreased, while for the backward inclination, the crosswind response did not reduce evenly. on the other hand, kawai, [13] conducted an experiment in a boundary wind tunnel with three types of flow (smooth flow, turbulent boundary layer flow over open terrain, and turbulent boundary layer flow over urban area). from the results, strong viv was noticed at angles of attack of 0° and 15°. when the angle of attack exceeded 15°, viv became weak and could not be detected in the smooth flow. as for turbulent boundary layer flow over urban area, the weak viv was still seen for angles of attack greater than 15°. galloping was also found in this experiment when the angle of attack was 0° with reduced velocity equal to 10. zhao et al. [14] studied fiv on a square cylinder with two angles of incidence of 0° and 45°. the results showed that galloping occurred at 0° while viv occurred at 45°. in the literature review, some conflicts of the outputs are found. for example, obasaju et al. [15] found a tranquil zone between viv and galloping for α =0°, but nemes et al. [11] reported no tranquil zone in their study. other studies did not show relative outputs on this issue [16-20]. hence, this gains our interest for further investigation of the issue. the main purpose of the present study is to identify the characteristic of the fiv around a square cylinder based on various angles of attack, at the same time clarifying whether the galloping occurs right after viv or there is a resting gap without the occurrence of galloping and viv. 359 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 2. methodology 2.1 experimental details the experiments were conducted in the af100 subsonic wind tunnel of the aeronautical and wind engineering lab (aerolab) in the university technology malaysia, kuala lumpur, as shown in fig. 1. the test section size was 33 cm in width, 35 cm in height, and 70 cm in length. the main objective of this experiment was to identify the effect of different angles of attack towards the fiv of a rigid cylinder with one degree of freedom (1dof). by using three different angles of attack, the behavior of fiv could be observed. a clear acrylic was used as the material for the square cylinder. acrylic was chosen because the material is lightweight. the cylinder was attached on the supporting structure using circular acrylic plate with a diameter of 6 cm. fig. 2 shows the schematic diagram of the angle of attack for the rigid square cylinder. to analyse the effect of angle of attack, three angles, namely 0 °, 22.5°, and 45°, were tested in the present study. the reason for using these angles is that they correspond to the conditions where the reactions are dominated by viv and galloping [21]. table 1 shows the specification of the cylinders. in order to attach the coiled spring, holes were made at the end of each circular plate. the function of the coiled spring was to suspend the cylinder on the supporting structure. the coiled springs were attached in parallel for both sides. using laser cutting, 6 holes were made at the circular plate to allow the rigid cylinders to hang in the pre-set angles. the steel supporting structure was made with the dimensions of 29 cm x 29 cm x 29 cm in length, width, and depth, respectively. for the coiled spring, low stiffness was used in the experiment to generate the lock-in condition. the dimensions, the set-up of the rig, and schematic diagram of the experiment are shown in fig. 3(a), 3(b), and 3(c), respectively. fig. 1: the overview of af100 subsonic wind tunnel. fig. 2: the angle of attack of a square rigid cylinder. 360 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 table 1: specification of the cylinder (a) (b) (c) fig. 3: (a) the dimensions of the rig. (b) the set-up of the rig and (c) schematic diagram of the experiment. 2.2 measuring equipment to record all the data obtained from the experiment, it was important to use proper measuring equipment. the equipment used must be sensitive to the vibration test in order to find the dynamic responses of the rigid cylinders. the equipment that was used to gain the results was the ges-28004 anemometer, pitot-static probe, video recorder, and laptop equipped with tracker video analysis and modelling tool software. the uniformity of the wind tunnel was checked using an anemometer and pitot tube as shown in fig. 4 and fig. 5, respectively. anemometer was used to measure the air speed (m/s) in the wind tunnel while overview dimension (cm) weight (g) aspect ratio=1 77.237 width = 3.0 height = 3.0 length = 17.5 coiled spring coiled spring 361 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 the pitot-static probe was used to measure the pressure (pa) of air in the wind tunnel. to record the vibration response of the cylinder, a video recorder was used. the video was converted into the amplitude of the vibration using the tracker video analysis modelling tool software, as shown in fig. 6. in addition, in order to obtain the frequency response of the cylinder, the amplitude data needed to be converted from the time domain into the frequency domain using fast fourier transform (fft). an fft spectrum analyzer implemented fourier’s basic theorem that denotes any waveform in the time domain by weighting the sum of pure sine waves of all frequencies. from the discrete fourier transform, fft is developed with the eq. (1): 𝐴(𝑟) = ∑ 𝑋(𝑠)𝑒 −𝑗2𝜋 𝑁𝑟𝑠 , 𝑟 = 0,2, … , 𝑁𝑁−1𝑘=0 (1) in which, x(𝑠) is the periodic wake that is sampled at nyquist frequency or higher and 𝑠 is the number of samples collected from original signals. fig. 4: anemometer. fig. 5: pitot-static probe. fig. 6: tracker video analysis and modelling tool software. the supporting structure was placed inside the wind tunnel, while the video recorder was used to record the video of the vibration of the cylinder. the recorder was held by the tripod outside the wind tunnel. the experiments were over a range of velocities from 0.5 m/s to 4.0 m/s, corresponding to the reynolds number ranging from 16853~134831. the experiment was conducted with three different angles of attack on the square cylinder. the sampling frequency of the video recorder was 30 hz, which is adequate to collect the motion of the cylinder. the angle was changed in order to observe the dynamic responses at each 362 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 angle of attack. the process of the experimental work can be summarized in the flow chart shown in fig. 7. fig. 7: the process of experimental work. 3. results and discussion 3.1 uniformity of the flow in wind tunnel before conducting the experiments, the uniformity of the wind tunnel needed to be checked to ensure the flow was in a uniform condition. three different velocities were observed, which is 9 m/s, 6 m/s, and 3 m/s. after obtaining the data, the uniformity of each velocity of the experiment was calculated using this eq. (2) [22]: ф = √∑ (𝛽𝑖−𝛽) 2 𝑛 𝑛 𝑖=1 (2) where; 𝛽𝑖 = measured value (velocity) 𝛽 ̅ = average value (average velocity) n = number of samples. from the calculations, the results for non-uniformity (ф) are shown in table 2. based on the calculated results, all of the data shows small values, indicating low non363 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 uniformity of the air flow. hence, the flow uniformity in the wind tunnel was in good condition, and suitable for use to investigate the effect of fiv on the square cylinders. table 2: non-uniformity at different speeds velocity (m/s) ф 3 0.149 6 0.103 9 0.063 3.2 free decay test in this present study, the natural frequency value is important because as the value of the shedding frequency slowly reaches the natural frequency, the vibration of the rigid cylinder will increase to high values. to obtain the natural frequency, a free decay test was conducted by pulling the cylinder downward and allowing it to vibrate freely until it stopped. the natural frequency of the square cylinder was obtained from the power spectrum graph. to verify the experimental value of the natural frequency, the theoretical value of the natural frequency was calculated using eq. (3): 𝑓𝑛 = √ 𝐾𝑇𝑜𝑡𝑎𝑙 𝑚𝑇𝑜𝑡𝑎𝑙 2𝜋 (3) where ktotal is the stiffness of the system while mtotal is the mass of the system. this equation was adopted from previous study of viv with similar experimental settings [23]. the value obtained for spring stiffness of the system was 119.6 n/m as the springs were attached in parallel. table 3 shows the value obtained from experiment and calculation. the percentage error is found to be 9.81%. similar error percentages were also reported in [23] where up to 11.55% of error percentage was achieved using the same equation. since the error percentage was less than 20%, the experimental value should be acceptable [24]. hence, the design of the experimental rig was verified. based on the free decay test, the damping ratio was found to be 0.008185. because the damping ratio was very low, the damping effect was unaccounted in the present study. table 3: the comparison between experimental and theoretical value of the natural frequency natural frequency (hz) percentage of error (%) experimental value theoretical value 6.783 6.177 9.81 3.3 verification of the experiment data strouhal number is a non-dimensional parameter that describes the oscillation of a cylinder. in the present study, the strouhal number considering the viv condition was found at 0.1257, as shown in fig. 8(a) for α=0°. this was in agreement with okajima [25], who suggested that the strouhal number of alternating vortices shed from a square cylinder can be estimated to be about 0.13 in the reynolds-number range between 102 and 3.4 × 105. 364 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 fig. 8: frequency ratio versus reduced velocity with angle of attack α= 0°. maruai et al. [26] conducted a series of experimental measurements of flow-induced vibration using a square cylinder with a downstream flat plate. in their study, they stated that for an isolated square cylinder, only two significant flow-induced vibration behaviours can be observed, namely, viv that occurs at lower branch velocity and galloping that occurs at higher branch velocity. to verify the data of the present study, the existing amplitude ratio of an isolated square cylinder [26] was compared with the square cylinder response of the present study, as shown in fig. 9. the amplitude ratio was defined as a*=y/d where y is the standard deviation of amplitude and d is the cylinder height. a very similar trend was found with small deviation. the patterns of both studies were in good agreement. the occurrence of viv in both studies was at a reduced velocity range of 5 ≤ ur ≤ 11 and galloping at ur > 15. the reduced velocity is defined as ur=u/fnd, where u is free stream velocity, fn is the natural frequency and d is the cylinder height. however, the amplitude of the present study was slightly lower than the previous study because of the different damping ratio value. based on fig. 9, the current experimental work was verified. fig. 9: amplitude ratio versus reduced velocity of the previous study [26] and the present study. 3.4 effect of the angle of attack to investigate the effect of angle of attack on the fiv of the square cylinder, experiments were carried out over a wide range of reduced velocities at angles of attack of α=0°, 22.5°, and 45°. fig. 10 shows the comparison of the amplitude response of various angle of attacks. from the graph, it can be observed that galloping response was only found at α=0° as the vibration amplitude of the cylinder increased with increasing reduced velocity y = 0,1257x 0 0,2 0,4 0,6 0,8 1 1,2 1,4 0 5 10 15 f* ur 365 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 at ur =15. other than that, viv response was also observed at lower branch of reduced velocity in the range of 5 ≤ ur ≤ 10. on other hand, only viv behavior was found for square cylinder of α=22.5° and 45° where galloping is absent. nevertheless, the occurrence of viv for both angle of attacks is at low reduced velocity range 4 ≤ ur ≤ 9, which was slightly earlier than the cylinder of α=0°. it was also observed that the amplitude of the cylinder at α=22.5° was lower compared to the amplitude of cylinder at α=45°. based on this finding, it can be concluded that the cylinder of α=22.5° had less tendency towards the viv response. in fact, cui et al. [27] also has shown the similar results, where in their study, cylinder of α=22.5° had lower viv amplitude compared to the others. next, a region free from viv and galloping was found at reduced velocity in the range of 10 ≤ ur ≤ 15 for α=0°, which is in agreement with maruai et al. [26]. therefore, it can be said that for a square cylinder, a tranquil zone was found between the phenomena of viv and galloping. fig. 10: amplitude ratio of the rigid cylinder of various angles of attack.. fig. 11: frequency ratio of the rigid cylinder of various angles of attack. fig. 11 shows the comparison of the frequency ratio of the different angles of attack where frequency ratio is defined as f*=f/fn, f is the vibrating frequency, and fn is the natural frequency of the cylinder. as shown in fig. 11, the frequency ratio was close to 1 as the ur >5 for α=0°. this indicates that the cylinder underwent lock-in phenomena. supposedly, the frequency ratio would be slightly higher or lower than 1 when galloping occurred at ur >15. the same goes for the frequency ratio for α=22.5° and 45°. the frequency ratio of the cylinder was supposedly higher than 1 when ur>10 and increased monotonically with increasing reduced velocity to indicate that it was outside the lock-in regime and galloping did not occur [27]. however, in the present study, the described condition did not happen. therefore, the power spectrum graph obtained from the fft method were investigated in 366 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 detail to identify the energies that were possessed by the cylinder at different angles of attack. (a) (b) (c) (d) (e) (f) fig. 12: (a) and (b): ur =7 and 17 for α=0°; (c) and (d): ur =7 and 17 for α=22.5°; (e) and (f): ur =7 and 17 for α=45°. fig. 12(a) and (b) show the power spectrum graph of α=0° when ur =7 and ur =17 respectively. for the case of α=0°, both viv and galloping occurred. it was observed that the value of power spectrum density (psd) at ur =7 (where the lock-in condition occurred) was lower than the value of the power spectrum density at ur =17 (where the galloping occurred). this condition can be justified as galloping possesses higher vibration energy than viv. fig. 12(c) and (d) show the power spectrum graph of α=22.5° at ur =7 and 17 respectively, while fig. 12(e) and (f) show the power spectrum density of α=45° at ur =7 and 17 respectively. based on fig. 12(c-f), it can be seen that the value of power spectrum 367 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 density at ur =17 was lower than ur =7. this is because there is no occurrence of galloping at ur =17. in addition, fig. 12(c) and fig. 12(e) show a significant psd peak during lockin condition (ur =7). on the contrary, multiple peaks with relatively small psd values were found at ur =17 (fig. 12(d) and (f)). hence, this justifies that although the frequency ratio remained close to 1 for α=22.5° and 45°, no occurrence of galloping was found and the psd values were small with multiple frequency peaks. acknowledgement this research was financially supported by japan international cooperation agency (jica) research grant (s.k130000.0543.4y191) and universiti teknologi malaysia research grant (q.k130000.3043.03m14). references [1] bearman pw, gartshore is, maull dj, parkinson gv. (1987) experiments on flow-induced vibration of a square-section cylinder. journal of fluids and structures, 1(1):19-34. doi:https://doi.org/10.1016/s0889-9746(87)90158-7 [2] a rahman ma, wan hussin wn, mohd mh, noor harun f, quen lk, paik jk. (2019) modified wake oscillator model for vortex-induced motion prediction of low aspect ratio structures. ships and offshore structures, 14(sup1):1-9. doi:10.1080/17445302.2019.1593308 [3] khalak a, williamson ch. (1999) motions, forces and mode transitions in vortex-induced vibrations at low mass-damping. journal of fluids and structures, 13(7-8):813-851. doi:https://doi.org/10.1006/jfls.1999.0236 [4] bearman pw. (1984) vortex shedding from oscillating bluff bodies. anrfm, 16:195-222. doi:https://doi.org/10.1146/annurev.fl.16.010184.001211 [5] sarpkaya t. (2004) a critical review of the intrinsic nature of vortex-induced vibrations. journalof fluids and structures, 19(4): 389-447. doi:https://doi.org/10.1016/j.jfluidstructs.2004.02.005 [6] carberry j, sheridan j, rockwell d. (2005) controlled oscillations of a cylinder: forces and wake modes. journal of fluid mechanics, 538: 31-69. doi:https://doi.org/10.1017/s0022112005005197 [7] govardhan rn, williamson chk. (2006) defining the 'modified griffin plot' in vortex-induced vibration: revealing the effect of reynolds number using controlled damping. journal of fluid mechanics, 561: 147-180. doi:https://doi.org/10.1017/s0022112006000310 [8] ng yt, luo sc, chew yt. (2005) on using high-order polynomial curve fits in the quasisteady theory for square-cylinder galloping. journal of fluids and structures, 20(1): 141-146. doi:https://doi.org/10.1016/j.jfluidstructs.2004.02.008 [9] klamo jt, leonard a, roshko a. (2006) the effects of damping on the amplitude and frequency response of a freely vibrating cylinder in cross-flow. journal of fluids and structures, 22(6-7): 845-856. doi:https://doi.org/10.1016/j.jfluidstructs.2006.04.009 [10] shirakashi m, chua cp, salim sazs. (2016) design and fabrication of fiv apparatus for classroom lecture demonstration. jurnal teknologi, 78(9): 1-7. doi:https://doi.org/10.11113/jt.v78.4933 [11] nemes a, zhao j, jacono dl, sheridan j. (2012) the interaction between flow-induced vibration mechanisms of a square cylinder with varying angles of attack. doi:https://doi.org/10.1017/jfm.2012.353 [12] hu g, li c, tse kt, kwok kcs. (2018) vortex induced vibration of an inclined finite-length square cylinder. european journal of mechanics-b/fluids, 68:144-152. doi:https://doi.org/10.1016/j.euromechflu.2017.12.004 [13] kawai h. (1995) effects of angle of attack on vortex induced vibration and galloping of tall buildings in smooth and turbulent boundary layer flows. journal of wind engineering and industrial aerodynamics, 54: 125-132. doi:https://doi.org/10.1016/0167-6105(94)00035-c 368 iium engineering journal, vol. 23, no. 1, 2022 ramzi et al. https://doi.org/10.31436/iiumej.v23i1.1804 [14] zhou j, nemes a, jacono dl, sheridan j. (2010) the effect of incidence angle variation of a square cylinder on its dynamic response and wake states. in proceedings of the 17th australasian fluid mechanics conference, pp. 724-727). auckland, new zealand: afmc [15] obasaju ed, ermshaus r, naudascher e. (1990) vortex-induced streamwise oscillations of a square-section cylinder in a uniform stream. journal of fluid mechanics, 213:171-189. doi:http://dx.doi.org/10.11113/jt.v79.9987 [16] du x, chen r, dong h, ma w, xu h, zhao y. (2021) aerodynamic characteristics of two closely spaced square cylinders in different arrangements. journal of wind engineering and industrial aerodynamics, 208: 104462. doi: https://doi.org/10.1016/j.jweia.2020.104462 [17] yanovych v, duda d, uruba v. (2021) structure turbulent flow behind a square cylinder with an angle of incidence. european journal of mechanics-b/fluids, 85: 110-123. doi: https://doi.org/10.1016/j.euromechflu.2020.09.003 [18] cao y, tamura t. (2020) low-frequency unsteadiness in the flow around a square cylinder with critical angle of 14° at the reynolds number of 2.2× 104. journal of fluids and structures, 97:103087. doi : https://doi.org/10.1016/j.jfluidstructs.2020.103087 [19] peng s, wang h, zeng l, he x. (2019) low-frequency dynamics of the flow around a finitelength square cylinder. experimental thermal and fluid science, 109: 109877. doi: https://doi.org/10.1016/j.expthermflusci.2019.109877 [20] zhao j, leontini j, jacono dl, sheridan j. (2019) the effect of mass ratio on the structural response of a freely vibrating square cylinder oriented at different angles of attack. journal of fluids and structures, 86:200-212. doi: https://doi.org/10.1016/j.jfluidstructs.2019.02.008 [21] zhao j, leontini js, jacono dl, sheridan j. (2014) fluid–structure interaction of a square cylinder at different angles of attack. journal of fluid mechanics, 747: 688-721. doi: https://doi.org/10.1017/jfm.2014.167 [22] hassan jm, mohamed ta, mohammed ws, alawee wh. (2014) modeling the uniformity of manifold with various configurations. journal of fluids, 2014. https://doi.org/10.1155/2014/325259 [23] shaharuddin nmr, darus im. (2015) experimental study of vortex-induced vibrations of flexibly mounted cylinder in circulating water tunnel. acta mechanica, 226(11): 3795-3806. doi: https://doi.org/10.1007/s00707-015-1438-8 [24] cecconi m, rhodes a, poloniecki j, della rocca g, grounds rm. (2009) bench-to-bedside review: the importance of the precision of the reference technique in method comparison studies–with specific reference to the measurement of cardiac output. critical care, 13(1):1-6. doi:https://doi.org/10.1186/cc7129 [25] okajima a. (1982) strouhal numbers of rectangular cylinders. journal of fluid mechanics, 123: 379-398. doi: https://doi.org/10.1017/s0022112082003115 [26] maruai nm, mat ali ms, ismail mh, shaikh salim saz. (2017) downstream flat plate as the flow-induced vibration enhancer for energy harvesting. journal of vibration and control, 24(16): 3555-3568. doi:https://doi.org/10.1177/1077546317707877 [27] cui z, zhao m, teng b, cheng l. (2015) two-dimensional numerical study of vortex-induced vibration and galloping of square and rectangular cylinders in steady flow. ocean engineering, 106:189-206. doi:https://doi.org/10.1016/j.oceaneng.2015.07.004 369 https://doi.org/10.1017/jfm.2014.167 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 analytical and numerical thermal analysis on friction stir welding using polygonal tool pin stephen leon joseph leon1*, alfred franklin varghese2, joseph michel2 and gopinath gunasekaran2 1 department of mechanical engineering, saveetha school of engineering, saveetha institute of medical and technical sciences, chennai, tamilnadu, india. 2 engineering department, university of technology and applied sciences-ibri, oman. * corresponding author: stephenleonj@gmail.com (received: 26th november 2020; accepted: 25th january 2021; published on-line: 4th july 2021) abstract: frictional heat generation in the tool/matrix interface followed by the stirring of material along the weld line causes plasticized solid state joining in friction stir welding. in this paper, the existing torque based thermo-mechanical model for the tools with cylindrical pins is remodified for the polygonal tool pin profile by introducing novel multiplication factors with respect to the number of sides in the tool pin geometry. the variation in the effective heat supply with respect to the chosen pin geometry was analyzed. a comparative analysis of the proposed analytical model with the existing model was also carried out to understand the accuracy of the proposed model. furthermore, a transient thermal numerical modelling was carried out in the view of understanding the change in process peak temperature in the stir zone and change in temperature gradient along the heat affected zone with respect to the change in pin geometry for the opted set of process input parameters. an analytically estimated heatinput-based numerical model was adopted in the present study. it was observed that the process peak temperature was directly proportional to the number of sides in the tool pin. abstrak: penjanaan haba geseran antara muka pada alat/matrik diikuti dengan pengacauan material sepanjang garis kimpalan menyebabkan keadaan plastik pepejal melekat bersama geseran kimpalan pengacau. kajian ini berkaitan tork sedia ada berdasarkan model mekanikal-terma bagi alat pin silinder yang terubah suai bagi profil pin alat poligon dengan memperkenalkan faktor gandaan berdasarkan bilangan sisi geometri alat pin. perubahan pada bekalan haba efektif berdasarkan geometri pin pilihan telah dikaji. analisis bandingan pada model analitik yang dicadang bersama model sedia ada, telah dilakukan bagi memahami ketepatan model cadangan. tambahan, model transien numerikal terma telah dibuat bagi memahami proses perubahan suhu puncak ketika zon pengacauan dan perubahan gradien suhu sepanjang zon terkena haba perubahan geometri pin pada set proses parameter input terpilih. kajian ini mengaplikasi model numerik berdasarkan input anggaran haba secara analitik. dapatan kajian menunjukkan suhu puncak proses adalah berkadar langsung dengan bilangan sisi pin alat. keywords: thermal mode; friction stir welding; polygonal tool pin; transient model 352 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 1. introduction the process peak temperature rise in friction stir welding during the welding stage is always maintained lower than the solidus temperature of the material to be joined so that this joining process can be considered as a solid-state metal joining technique. the major heat input for this solid-state welding technique is generated along the tool/matrix contact due to friction and it is assisted by the heat generation through the plastic deformation of material during the joining process under the tool shoulder [1]. the tool rotates and slides over the stationary workpiece, resulting in a relative velocity along the tool/matrix interface that is the root cause of the friction heat. this solid-state joining process is divided into different stages based on the position of the tool (fig.1). temperature gradient developed in the process at various distances from the axis of rotation of the tool is the key factor that decides the post weld mechanical properties of the joint [2]. various software assisted simulations are used to estimate the influence of various internal and external factors of the heat generation. shi et al. [4] studied temperature results through finite element analysis conducted using abaqus. their thermomechanical analysis was validated through experimental results. a two-dimensional finite element model developed by lockwood and reynolds [5] for friction stir welding in aluminum alloy 2024-t351. the obtained temperature distribution from the fe model was validated by the experimental results. (a) (b) (c) fig. 1: stages in fsw: (a) plunging, (b) dwelling, (c) welding. fig. 2: tools with polygonal tool pin. ullessy [2] evaluated the impact of variation in the tool speed on the thermal field by developing a three-dimensional viscoplastic model using computational fluid dynamics. a better simulation was obtained by li et al. [6] using abaqus software for the fully sticking condition of tool-workpiece interface. sanjeev et al. [7] analyzed the influence of the friction coefficient on the simulation output using abaqus and found that the coefficient of friction was equal to 1.0 during a sticking condition. apart from similar material, little research was done to optimize process parameters on the joining of two dissimilar materials [8]. labesh et al. [9] compared the effects of dwell time, tool speed, and plunge depth and found dwell period had higher influence on post weld joint strength over other factors. in this solid-state welding, major amounts of effective heat supply are obtained along the interface of shoulder/matrix and a part of heat generated along the contact surface of the tool pin and material assists to maintain a constant temperature gradient along the stir zone. analysis on the joint efficiency of the various welds developed on the usage of a tool with different non-circular straight pin profiles concluded that the tool with a square pin delivered a superior weld quality [10]. better weld quality [11] was observed on a taper cylindrical pin profile compared to a square pin profile and it was concluded that the 353 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 increase in number of sides of a noncircular pin profile, from square profile to hexagon profile, increased the heat generation rate during welding. an experimental study [12] was carried out to understand the effects of tool pin geometries on the joint strength and it was found that tool pin geometry with square cross-sectional shape delivered a better weld quality than other polygonal shapes. apart from these, various research [13-17] concluded that geometrical change in the tool pin geometry resulted in considerable changes in heat generation that in turn affected the temperature gradient during the joining process. so, tool pin geometry can also be a key factor with other parameters like tool feed rate and tool rotational speed. in this paper, for a given constant working condition, analytical expressions are derived and validated with the published results to analyze the quantity of heat supplied by the different polygonal pin profiles with the number of sides varying from three to six. furthermore, heat generation during dwell, not only plasticizes the metal under the tool but also softens the neighboring material, which reduces the opposing forces to the tool movement [18]. this underlines the importance of analyzing the transient temperature increase during the dwell period. so, the effect of variation in tool pin geometry on the transient temperature gradient during the dwell period in the stir zone were compared through the results obtained from combined analytical and numerical approaches. 2. analytical modelling in the view of simplifying the analytical solution, the following assumptions were made: (i) estimation of total torque developed during the process is the combined effect of friction along the contact surface and plastic deformation under the tool shoulder; (ii) the small quantity of heat developed during the initial stage (plunging) is neglected [19]. fig 3: tool/matrix frictional contact surfaces. total heat-generating surfaces are divided into horizontal and vertical surfaces as shown in fig. 3. frigaard et al. [20] estimated the total heat generation along the horizontal contact surface as, qhorizontal = qshoulder + qpin-tip = 2 3 𝜋𝜎𝑐𝑜𝑛𝑡𝑎𝑐𝑡 𝜔𝑅𝑠 3 in the tool shoulder contact surface, qshoulder = [ 2 3 𝜋𝜎𝑐𝑜𝑛𝑡𝑎𝑐𝑡 𝜔𝑅𝑠 3] qpin-tip qvertical = qpin-side for every tool pin geometry, the geometrical shape of the shoulder does not vary considerably. the uniform shoulder/matrix contact surface indicates that there will not be any change in heat generated by the tool shoulder irrespective of its pin geometrical shape. but there is a considerable change in tool pin contact surface area when the pin geometry varies. 354 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 fig. 4: cross section of pin profiles and segments. polygonal tool pins shown for the current analysis were divided into small triangles as denoted in fig. 4. the total amount of triangular divisions in every polygonal pin geometry was equal to two times the number of sides in the cross-sectional shape of the tool pin. schmidt et al. [21] estimated total torque developed in fsw as, rotating torque = σc ω x 2 dθ dr (1) where σc denotes contact stress, ω represents tool rotational speed, x is the distance of any point form the axis of rotation. considering one segment in fig. 4, 𝑄𝑝𝑖𝑛−𝑡𝑖𝑝 = ∬ 𝜎𝑐 𝜔𝑥 2𝑑𝜃𝑑𝑥 d = f(x,θ) { 0 ≤ 𝜃 ≤ 𝜋 𝑧 0 ≤ 𝑥 ≤ 𝑅𝑝𝑖𝑛𝑐𝑜𝑠𝜃 qpin-tip = σcω∫ 𝑑𝜃 𝜋 𝑧 0 ∫ 𝑓(𝑥)𝑑𝑥 𝑅𝑝𝑖𝑛𝑐𝑜𝑠𝜃 0 torque developed for the entire pin can be obtained by, total torque developed = ∫ ∫ 𝜏𝑐 ω 𝑥 2 dθ dr 𝑅𝑝𝑖𝑛𝑐𝑜𝑠𝜃 0 𝜋/𝑧 0 = σc ω 𝑅𝑝𝑖𝑛 3 ⌈ 1 3 𝑠𝑖𝑛𝜃 − 𝑠𝑖𝑛3𝜃 9 ⌉ 0 𝜋/𝑧 (2) for the tool pin/matrix horizontal contact surface, qpin-tip = z σc ω𝑅𝑝𝑖𝑛 3 [ 2 3 sin ( 𝜋 𝑧 ) − 2𝑠𝑖𝑛3( 𝜋 𝑧 ) 9 ] (3) where z represents the sides in the chosen polygonal pin geometry. fig. 5: vertical surface segments. 355 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 like the horizontal contact surface, the vertical contact surface can also be divided into small segments as denoted in fig. 5. the quantity of rectangular divisions in each shape is equal to two times of the number of sides in the tool pin. for every rectangular vertical surface, 𝑄𝑝𝑖𝑛−𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙 = ∬ 𝜎𝑐 𝜔𝑥 2𝑑𝜃𝑑𝑥 d = f(x,θ) { 0 ≤ 𝜃 ≤ 𝜋 𝑧 0 ≤ 𝑥 ≤ ℎ qpin-tip = σcω∫ 𝑑𝜃 𝜋 𝑧 0 ∫ 𝑓(𝑥)𝑑𝑥 ℎ 0 torque developed = ∫ ∫ 𝜎𝑐 ω𝑅𝑝𝑖𝑛 2 𝑐𝑜𝑠2θdθ dh ( 𝜋 𝑧 ) 0 𝐻𝑝𝑖𝑛 0 = σc ω 𝑅𝑝𝑖𝑛 2 𝐻𝑝𝑖𝑛 [ 𝜋 2𝑛 + 1 4 sin(2𝜋/𝑧)] (4) for the pin vertical/matrix contact surface, qpin-vertical = 𝑧 2 σc ω 𝑅𝑝𝑖𝑛 2 𝐻𝑝𝑖𝑛 [ 2𝜋 𝑧 + sin(2𝜋/𝑧)] (5) where, contact stress 𝜎𝑐 = µ𝑃, µ is the friction coefficient, 𝜔 is the angular velocity of the tool, pin height (hpin) and shoulder radius (rs) represent the dimensions of the pin. p is the vertical force given by the tool. a standard method of prescribing tool pin dimension is through its side length. so the above derived equations have to be rearranged by side length (a). the relationship between pin circumferential radius and pin side length can be represented as, 𝑅𝑝𝑖𝑛 = 𝑎 2𝑆𝑖𝑛( 𝜋 𝑧 ) (6) applying this, equations (3 – 5) can be remodified as, qpin-tip = n σc ω 𝑎3 8𝑆𝑖𝑛3( 𝜋 𝑛 ) [ 2 3 sin ( 𝜋 𝑧 ) − 2𝑠𝑖𝑛3( 𝜋 𝑧 ) 9 ] (7) qpin-tip = 1 12 z σc ω 𝑎3 [ 1 𝑆𝑖𝑛2( 𝜋 𝑧 ) − 1 3 ] (8) qpin-vertical = z σc ω 𝑎2 8𝑆𝑖𝑛2( 𝜋 𝑧 ) 𝐻𝑝𝑖𝑛 [ 2𝜋 𝑧 + sin ( 2𝜋 𝑧 )] (9) qpin-vertical = z σc ω 𝑎2𝐻𝑝𝑖𝑛 [ 𝜋 4𝑆𝑖𝑛2( 𝜋 𝑧 ) − 1 4 cos( 𝜋 𝑧 ) sin( 𝜋 𝑧 ) ] (10) qpin-vertical = z σc ω 𝑎2𝐻𝑝𝑖𝑛 [ 𝜋 4𝑆𝑖𝑛2( 𝜋 𝑧 ) − 1 4tan( 𝜋 𝑧 ) ] (11) these equations can be simplified by introducing multiplication factors as, qpin-tip = xr τc ω 𝑅𝑝𝑖𝑛 3 (12) qpin-vertical = yr τc ω 𝑅𝑝𝑖𝑛 2 𝐻𝑝𝑖𝑛 (13) qpin-tip = xs τc ω 𝑎3 (14) qpin-vertical = ys τc ω 𝑎2𝐻𝑝𝑖𝑛 (15) 356 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 the values of multiplication factors for various number of pin sides are given in table 1. table 1: multiplication factor values pin shape xr value yr value xs value ys value triangular (n=3) 1.33 4.50 0.27 3.40 square (n=4) 1.54 5.01 0.64 7.15 pentagonal (n=5) 1.72 5.44 1.25 12.72 hexagonal (n=6) 1.89 5.82 2.16 20.35 based on the obtained values for the given number of sides, these multiplication factors can be written as a function of number of sides (z), xr = 0.77z 0.5 (16) yr = 3z 0.37 (17) xs = 0.01z 3 (18) ys = 0.2z 2.58 (19) (a) (b) fig. 6: change in multiplication values (xr and yr) (a) when radius of pin is considered, (b) when pin side length is considered. 3. numerical modelling in ansys workbench, transient temperature rises for different pin profiles, triangular(t), square (s), pentagonal (p) and hexagonal (h)) were analyzed using analytically estimated heat input for different pin profiles to analyze variation in dwell period to reach the required peak temperature in order to switch over from dwell period to weld period. applied heat flux does not change in the x and z directions and it varies only with respect to the y direction as the thermal conductivity reduces heat flow towards the depth of the workpiece. so, a two-dimensional cross section geometry model was adopted for the analysis. a aa2024-t3 plate was considered as the base material for the current analysis. other properties considered for the analysis are denoted in tables 2 and 3. table 2: temperature dependent thermal property of base metal [15] temperature (k) 290 373 473 573 673 specific heat capacity (j kg-1 k-1) 864 921 1047 1130 1172 thermal conductivity (w m-1 k-1) 120 134.4 151.2 172.2 176.4 0 5 10 15 20 25 3 4 5 6 7 m u lt ip li ca ti o n f a ct o r v a lu e s number of sides xs value ys value 0 1 2 3 4 5 6 7 3 4 5 6 7 m u lt ip li ca ti o n f a co r v a lu e s number of sides xr value yr value 357 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 table 3: process parameters and tool material properties property/parameter value diameter of tool shoulder (mm) 15 diameter of the pin (mm) 5 height of the tool pin (mm) 5.7 base metal thickness (mm) 6 material density (tool) (kg/m3) 7930 density of base metal (kg/m3) 2780 tool specific heat capacity (j kg-1 k-1) 502 thermal conductivity of tool (w m-1 k-1) 21.4 base metal bottom side heat transfer coefficient at the bottom of the workpiece (w m-2 k-1) 300 base metal top side heat transfer coefficient (w m-2 k-1) 50 base metal other side heat transfer coefficient (w m-2 k-1) except top and bottom surfaces 200 3.1 boundary and initial conditions at tool shoulder/matrix interface k           sholder n t = η(qhorizontal – qpin-tip) | 𝑅𝑝𝑖𝑛 ≤ x ≤ 𝑅𝑠 t > 0 at pin tip/matrix interface k           −tippin n t = η qpin-tip | 0 ≤ x ≤ 𝑅𝑝𝑖𝑛 t > 0 at pin vertical/matrix interface k           −verticalpiin n t = η qpin-vertical | 0 ≤ y ≤ 𝐻𝑝𝑖𝑛 t > 0 convective heat transfer from other surfaces to atmosphere k           −− sidebottomtop n t = hx (tx tamb), where hx represents convective heat transfer coefficient between base metal and atmosphere, tx is surface temperature of the workpiece during the joining process at different points and tamb refers to ambient temperature. for the model simplicity, the bottom surface is also considered to be directly in contact with ambient air. here, η refers to the percentage of heat transferred to the workpiece. for the current analysis it had been considered as 95%, with the remaining 5% transferred through the tool. t(x,y) = tinitial = 22 oc at any point when time t > 0 358 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 (a) thermal distribution when hexagonal shaped pin is used. (b) thermal distribution when pentagonal shaped pin is used. (c) thermal distribution when square shaped pin is used. (d) thermal distribution when triangular shaped pin is used. fig. 7: temperature distribution with different pin shapes used at 12.2 s of dwell period. 4. results and discussion for the current analysis dwell period is considered as the time required to reach a peak temperature of 90% of the melting temperature (775 k) of aa2024-t3. length of the pin side for different pin geometries (c, s, p and h) were selected in such a way that their pin radius remains constant. in the view of validation of the obtained transient model, the estimated amount of effective heat supply during different process conditions is compared with an analytical model developed by gadakh et al. [15], qtotal = 2 3 𝜋𝜏𝑐𝑜𝑛𝑡𝑎𝑐𝑡 𝜔(𝑅𝑠 3 + 𝑋. 𝑅𝑝𝑖𝑛 2 𝐻𝑝𝑖𝑛) (20) where multiplication factor x varies from 0.72 to 3 for different pin profiles. 359 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 comparative analysis of heat generated along the different contact surfaces of the tool with the base metal are denoted in the table.4. table 4: total heat generation at by the different pin profiles pin profile qshoulder (kw) qpin-tip (kw) qpin-vertical (kw) qtotal (kw) qtotal (kw) gadhakh et al. [15] triangular 4335.55 94.2 397.33 4827.09 4699.08 square 4306.51 123.24 458.18 4887.94 4785.11 pentagon 4293.69 136.06 492.19 4921.95 4874.89 hexagon 4288.45 141.3 510.09 4939.84 4964.67 gahakh et al. [15] obtained a heat generation model [eq. 22] based on the assumption that any tool pin shape occupies a circular contact area when it rotates. while obtaining the effective heat supply along the tool horizontal surface (qshoulder + qpin-tip), this assumption was justified as the combined geometry of the horizontal surface of tool shoulder and pin occupies a circular contact shape. but while obtaining the heat generation values separately for shoulder/matrix, tool pin tip/matrix, tool side/matrix interfaces, it did not show any variation in the effective heat supply by the horizontal tool contact surfaces of all pin shapes and variations were absorbed along the vertical contact surface of the tool pin. fig. 8: transient temperature rises for different pin profiles. although the tool pin occupies a circular area irrespective of pin shape while rotating, at any instance of time, contact surface cannot be circular and it varies with 0 100 200 300 400 500 0 5 10 15 t e m p e ra u te ( in d e g re e s) time (in s) triangular shape pin peak temp lowest temp 0 100 200 300 400 500 0 5 10 15 t e m p e ra tu re ( in d e g re s) time (in s) square shape pin peak temp lowest temp 0 100 200 300 400 500 0 5 10 15t e m p e ra tu re ( in d e g re e s) time (in s) hexagonal shape pin peak temp lowest temp 0 100 200 300 400 500 0 5 10 15 t e m p e ra u re ( in d e g re e s) time (in s) pentagonal shape pin peak temp lowest temp 360 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 respect to the number of sides considered. as in the derived equations (eq. 14, 15, 16 & 17) the exact geometry of the tool pin was considered, the accuracy of the obtained result was improved. it can be noticed from table 4. that the estimated heat generation by the horizontal surface varies with the increase in tool pin sides. from fig. 9 it can be observed that the time taken to attain process peak temperature by the hexagonal pin profile is low compared to other shapes and time required increases when the number of sides decreases from pentagonal shape to triangular shape as the heat generated by the contact surface decreases. transient temperature rise in a point where the minimum temperature was absorbed in the stir zone is also denoted in fig. 8. for a constant input rotational speed, maximum and minimum temperatures were observed at different points along the stir zone and shown in fig. 8 to analyze the temperature gradient at an instance of time. rapid peak temperature achievement of the hexagonal pin profiled tool reveals the high intensity of effective heat input by the vertical pin surface which assists in quick plasticization of the nearby layer. isolines obtained from the numerical modelling (fig. 7) explain the relationship between the intensity of heat supplied and the variation of thermal field along the stir zone for an instance of time. the increase in the number of tool pin sides increases the temperature gradient in the material flow zone at the given instance of time. the purpose of the dwell period is to increase the temperature of the material under the tool shoulder until it plasticizes in order to reduce flow stress to obtain a high rate of strain around the tool pin. plasticized material not only has less flow stress but also has lower strength to resist the movement of the tool during the weld, which increases tool life. increase in the heat intensity reduces the ideal dwell period and increases the welding speed [22]. increase in welding speed in turn reduces the heat affected zone. as a result, it is understood that an increase in the tool pin sides results in an increase in energy input which drastically decreases temperature rise in the heat affected zone. failure in fsw joints often occurs in the heat affected zone due to the existence of fewer needle-shaped precipitates. when the effective heat supply intensity is increased, tool feed rate can be increased. when the tool feed rate increased, the heat affected zone is reduced and the temperature gradient in the stir zone also becomes uniform around the tool pin, which in turn reduces the residual stress in the joints. fig. 9: change in peak and low temperatures in the stir zone. obtained results indicate that although the vertical surface has a limited contribution on total heat supply, it has a major influence on the distribution of heat along the stir zone during the joining process in friction stir welding. from the graph (fig. 9) it is evident that 442 444 446 448 450 452 454 3 4 5 6 7t e m p e ra u re ( in d e g e e s) number of sides peak temperaure at 12.2 s 376 378 380 382 384 386 3 4 5 6 7 t e m p e ra tu re ( in d e g re e s) number of sides lowest temperature at 12.2 s 361 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 increase in the number of tool pin sides, increases the percentage contribution of the vertical surface in the total heat generation. 5. conclusions a novel heat generation model was derived and validated with the goal of analyzing the change in the effective heat supply according to the geometrical changes in tool pin. from the analytical and numerical study on the thermal field developed during the joining process, it can be concluded that: • numerical analysis on transient temperature increase during the process suggests that the dwell time is directly proportional to the tool pin sides in the polygonal shape. the increase in tool pin sides has considerable effect on the temperature rise along the heat affected zone. • process peak temperature increases with the increase in tool pin sides. a maximum of 452 oc is absorbed for the hexagonal pin geometry and a minimum of 443.6 oc is observed for the triangular tool pin geometry. • for hexagonal tool pin geometry, the effective heat supply intensity is high, which facilities increase in tool feed rate. when the tool feed rate increased, the heat affected zone is reduced and the temperature gradient in the stir zone is also maintained uniform around the tool pin, which in turn reduces the residual stress in the joints. • from the analytical heat generation estimation, it was understood that the increase in the number of sides in the tool pin increases the percentage contribution of the tool pin on the effective heat supply during the process. for the given process input conditions, usage of the hexagonal tool pin increases the total quantity of heat input up to 330 j/s compared to the heat supply by the tool with the triangular shaped tool pin. references [1] leon js, jayakumar v. (2019) an investigation of analytical modelling of friction stir welding. int. j. mech. prod. eng. res. dev., 9(1): 179-189. doi: 10.24247/ijmperdfeb201918. [2] ulysse p. (2022) three-dimensional modeling of the friction stir welding process. int. j. mach. tools. manuf., 42: 1549–1557. [3] shi q, dickerson t, shercliff hr. (2003) thermo-mechanical fe modelling of friction stir welding of al-2024 including tool loads, 4th international symposium on friction stir welding, park city, utah, usa, 14-16 may 2003. [4] lockwood wd, reynolds ap. (2003) simulation of the global response of a friction stir weld using local constitutive behavior. materials science and engineering, a339: 35-42. [5] li w, shi s, wang f, zhang z, ma t, li j. (2012) numerical simulation of friction welding processes based on abaqus environment. j. eng. sci. tech. rev., 5: 10-19. [6] sanjeev nk, vinayak m, suresh hebbar h. (2014) effect of coefficient of friction in finite element modeling of friction stir welding and its importance in manufacturing process modelling applications. int. j. appl. sci. eng. res., 3: 755-762. [7] palanivel r, mathews pk, murugan n, dinaharan i. (2012) effect of tool rotational speed and pin profile on microstructure and tensile strength of dissimilar friction stir welded aa5083-h111 and aa6351-t6 aluminium alloys. mater. des., 40: 7-16. 362 iium engineering journal, vol. 22, no. 2, 2021 leon et al. https://doi.org/10.31436/iiumej.v22i2.1707 [8] labesh kumar c, jayakumar v, bharathiraja g. (2020) optimization of welding parameters for friction stir spot welding of aa6062with similar and dissimilar thicknesses. materials today: proceedings. https://doi.org/10.1016/j.matpr.2019.07.204. [9] labesh kumar c, jayakumar v, bharathiraja g. (2019) optimisation of friction stir spot welding parameters of aa6062-st1020 lap joint. int. j. mech. prod. eng. res. dev., 3: 10727-10732. [10] suresha cn, rajaprakash bm, upadhya s. (2011) a study of the effect of tool pin profiles on tensile strength of welded joints produced using friction stir welding process. mater. manuf., 26(9): 1111-1116. [11] fujii h, cui l, maeda m, nogi k. (2006) effect of tool shape on mechanical properties and microstructure of friction stir welded aluminium alloys. mater. sci. eng., 419: 25-31. [12] stephen leon j, bharathiraja g, jayakumar v. (2021) experimental analysis on friction stir welding using flat-faced pins in aa2024-t3 plate. fme transactions, 49: 78-86. doi: 10.5937/fme2101078s. [13] vijay sj, murugan n. (2010) influence of tool pin profile on the metallurgical and mechanical properties of friction stir welded al–10 wt.% tib2 metal matrix composite. mater. des., 31: 3585-3589. [14] leon sj, bharathiraja g, jayakumar v. (2020) durability map for the friction stir welding tools with flat faced pins. int j of integrated engineering, 2(8): 83-96 doi: 10.30880/ijie.2020.12.08.008. [15] gadakh vs, kumar a. (2014) friction stir welding window for aa6061-t6 aluminium alloy. proc imeche, part b: j engineering manufacture, 228(9): 1172-1181. [16] stephen leon j, bharathiraja g, jayakumar v. (2020) analytical and experimental investigations of optimum thermomechanical conditions to use tools with non-circular pin in friction stir welding. int. j. adv. manuf. technol., 107: 11-12. doi: 10.1007/s00170-020-05341-7. [17] shi l, wu cs. (2017) transient model of heat transfer and material flow at different stages of friction stir process. j. manuf. proc., 25: 323-339. [18] hamilton c, dymek s, sommers a. (2008) a thermal model of friction stir welding in aluminium alloys. int j mach tools & manuf., 48(10): 1120-1130. [19] schmidt h, hattel j. (2005) modelling heat flow around tool probe in friction stir welding. sci tech weld join, 10: 176-186. [20] frigaard o, grong o, midling ot. (2001) a process model for friction stir welding of age hardening aluminum alloys. metall mater trans, 32(5): 1189-1200. [21] nandan r, debroy t, bhadeshia hkdh. (2008) recent advances in friction-stir welding – process, weldment structure and properties. prog mater sci, 53(6): 980-1023. [22] leon js, jayakumar v. (2020) transient heat input model for friction stir welding using non-circular tool pin. fme transactions, 48(1): 137-142. doi: 10.5937/fmet2001137l. 363 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 optimal piezoelectric shunt damper using enhanced synthetic inductor: simulation and experimental validation muhammad nazri suhaimi, azni nabela wahid*, nor hidayati diyana nordin and khairul affendy md nor smart structure system & control lab (s3crl), mechatronics engineering department, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia *corresponding author: azni@iium.edu.my (received: 4th march 2021; accepted: 17th june 2021; published on-line: 4thjanuary 2022) abstract: piezoelectric material has the ability to convert mechanical energy to electrical energy and vice versa, making it suitable for use as an actuator and sensor. when used as a controller in sensor mode, the piezoelectric transducer is connected to an external electrical circuit where the converted electrical energy will be dissipated through joule heat; also known as piezoelectric shunt damper (psd). in this work, a psd is used to dampen the first resonance of a cantilever beam by connecting its terminal to an rl shunt circuit configured in series. the optimal resistance and inductance values for maximum energy dissipation are determined by matching the parameters to the first resonant frequency of the cantilever beam, where r = 78.28 kω and l = 2.9 kh are found to be the optimal values. to realize the large inductance value, a synthetic inductor is utilized and here, the design is enhanced by introducing a polarized capacitor to avoid impedance mismatch. the mathematical modelling of a cantilever beam attached with a psd is derived and simulated where 70% vibration reduction is seen in comsol. from experimental study, the vibration reduction obtained when using the piezoelectric shunt circuit with enhanced synthetic inductor is found to be 67.4% at 15.2 hz. results from this study can be used to improve psd design for structural vibration control at targeted resonance with obvious peaks. abstrak: material piezoelektrik mempunyai keupayaan mengubah tenaga mekanikal kepada tenaga elektrik dan sebaliknya, di mana ia sesuai digunakan sebagai penggerak dan pengesan. apabila digunakan sebagai alat kawalan dalam mod pengesan, piezoelektrik disambung kepada litar elektrik luaran di mana tenaga elektrik yang ditukarkan akan dibebaskan sebagai haba joule; turut dikenali sebagai peredam alihan piezoelektrik (psd). kajian ini menggunakan psd sebagai peredam resonan pertama pada palang kantilever dengan menyambungkan terminal kepada litar peredam rl bersiri. rintangan optimal dan nilai aruhan bagi tenaga maksimum yang dibebaskan terhasil dengan membuat padanan parameter pada frekuensi resonan pertama palang kantilever, di mana r = 78.28 kω dan l = 2.9 kh adalah nilai optimum. bagi merealisasikan nilai aruhan besar, peraruh buatan telah digunakan dan di sini, rekaan ini ditambah baik dengan memperkenalkan peraruh polaris bagi mengelak ketidakpadanan impedans. model matematik palang kantilever yang bersambung pada psd telah diterbit dan disimulasi, di mana 70% getaran berkurang pada comsol. hasil dapatan eksperimen ini menunjukkan pengurangan getaran yang terhasil menggunakan litar peredam piezoelektrik bersama peraruh buatan menghasilkan 67.4% pada 15.2 hz. hasil dapatan kajian ini dapat digunakan bagi membaiki rekaan psd berstruktur kawalan getaran iaitu pada resonan tumpuan di puncak ketara. 424 iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 keywords: vibration control; piezoelectric shunt damper (psd); synthetic inductance 1. introduction in applications for vibration control, a piezoelectric patch can be perfectly bonded to a vibrating mechanical structure to supply equal and opposite force to its host structure (active control) or dissipate the mechanical energy via joule heat (passive control). in the latter case, whenever the host structure vibrates, an electrical charge will accumulate in the piezoelectric material and this energy can be dissipated as joule heat if the patch terminal is connected to an external shunt circuit matched to the mechanical resonance of its host structure; also known as piezoelectric shunt damping. this results in vibration suppression equivalent to a tuned mass damper in a mechanical system. the concept of electromechanical damping using a piezoelectric shunt damper was introduced by hagood von flotow in 1991 [1] and ever since, there have been various studies conducted due to its potential and versatility in various applications requiring suppression; for example in aircraft [2], marine [3] or railway vehicles [4], and many more. for maximum energy dissipation to occur, the shunt circuit needs to be tuned to the targeted resonant frequency of the host structure, and the simplest form of circuit available uses resistor-inductor (rl) components, equivalent to mass-springs in mechanical systems. the electrical impedance of the shunt circuit matched with the mechanical resonance typically will have a significantly large inductance value. to realize this, a synthetic inductor circuit is introduced using op-amps. although this method has been proven to be successful [5-9], there are areas of improvement that can be made in terms of its efficiency. one of the problems that arise is the large internal resistance developed in the synthetic inductor circuit to generate the huge inductance. as a result, the resistance developed usually exceeds the optimum resistance value required to suppress the matched vibration mode, thereby creating a mismatch in the circuit impedance. to alleviate this, the concept of enhanced shunt circuit will be applied, where an additional capacitor will be added in parallel to the shunt circuit [10,11]. in this work, a resonant-type piezoelectric shunt damper on a cantilever beam will be studied and the optimal shunt circuit will be constructed. in section 2, the mathematical model of a cantilever beam attached with a psd in series configuration is presented. the optimal values of resistance, r and inductance, l for the shunt circuit is also derived and shown. following that, simulation studies are carried out in section 3 to show the performance of the psd in suppressing the first resonant by using comsol multiphysics software. since the value of inductance, l will be large, an enhanced synthetic inductor method will be adopted and shown in section 4 where experimental study is also carried out to validate the findings. 2. mathematical modelling 2.1 modelling of the piezoelectric shunt damper system the piezoelectic constitutive equation can be written as follows [12]: �𝑇𝑇 𝐷𝐷 � = �𝑐𝑐 𝐸𝐸 −𝑒𝑒 𝑒𝑒𝑡𝑡 𝜀𝜀𝑆𝑆 ��𝑆𝑆 𝐸𝐸 � (1) where t is a stress vector, d is an electric displacement vector, s is a strain vector, e is an electric field vector, 𝑐𝑐𝐸𝐸 is an elasticity stiffness matrix evaluated at constant electric field, 𝑒𝑒 is a piezoelectric stress matrix, ɛ𝑆𝑆 is a dielectric matrix evaluated at a constant mechanical 425 iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 strain, 𝑡𝑡 is a matrix transpose. the coupled cantilever beam-piezoelectric equation can be derived after applying hamilton’s principle to obtain the following electromechanical system [13,14]: �𝑀𝑀 0 0 0 ���̈�𝑤 �̈�𝑣 � + �𝐶𝐶 0 0 0 ���̇�𝑤 �̇�𝑣 � + � 𝐾𝐾 𝛩𝛩 𝛩𝛩𝑡𝑡 −𝐶𝐶𝑃𝑃 �� 𝑤𝑤 𝑣𝑣� = � 𝐹𝐹 𝑞𝑞� (2) where [m] is a global mass matrix, [c] is a global damping matrix, [k] is a global stiffness matrix, [cp] is an inherent piezoelectric capacitance matrix, [θ] is an electromechanical coupling matrix of the host structure and piezoelectric material, {𝐹𝐹} is an applied mechanical force vector, {q} is an electric charge vector, {w} is a generalized mechanical coordinate and {v} is a generalized electrical coordinate. the shunt damping voltage can be represented by the current-voltage relationship in the laplace domain when the piezo patch is shunted by an impedance, as illustrated in fig. 1. fig. 1: illustration of a cantilever beam attached with piezoelectric shunt damper (psd). 𝑉𝑉𝑠𝑠ℎ(𝑠𝑠) = 𝑍𝑍𝑠𝑠ℎ(𝑠𝑠). 𝐼𝐼𝑠𝑠ℎ(𝑠𝑠) (3) where vsh (s) is the voltage across the impedance; ish (s) is the current flowing through the shunt circuit; 𝑍𝑍𝑠𝑠ℎ is the shunt impedance and s is a laplace operator. differentiating electric potential, q in eq. (2) and substituting into eq. (3), the following is obtained: 𝑉𝑉𝑠𝑠ℎ(𝑠𝑠) = 𝑍𝑍𝑠𝑠ℎ(𝑠𝑠). �̇�𝑞(𝑠𝑠) = 𝑍𝑍𝑠𝑠ℎ(𝑠𝑠). ( [𝛩𝛩] 𝑡𝑡{𝑤𝑤}𝑠𝑠 − [𝐶𝐶𝑃𝑃]𝑉𝑉𝑠𝑠ℎ(𝑠𝑠)𝑠𝑠) (4) rearranging eq. (4), 𝑉𝑉𝑠𝑠ℎ(𝑠𝑠) = 𝑍𝑍𝑠𝑠ℎ(𝑠𝑠)[𝛩𝛩] 𝑡𝑡{𝑤𝑤}𝑠𝑠 1 + 𝑍𝑍𝑠𝑠ℎ(𝑠𝑠)[𝐶𝐶𝑝𝑝]𝑠𝑠 (5) finally, substituting eq. (5) into eq. (2), the total equation of motion for a cantilever beam attached with a piezoelectric patch connected to a shunt circuit is obtained as follows: [𝑀𝑀]{�̈�𝑤} + (𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡[𝛩𝛩][𝛩𝛩]𝑡𝑡){�̇�𝑤} + [𝐾𝐾]{𝑤𝑤} = {𝐹𝐹} (6) the term 𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 is the total electrical impedance of the shunt circuit where: 𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 = 𝑍𝑍𝑠𝑠ℎ 1 + 𝑍𝑍𝑠𝑠ℎ�𝐶𝐶𝑝𝑝�𝑠𝑠 (7) if the electrical impedance for the shunt circuit is in series configuration, 𝑍𝑍𝑠𝑠ℎ 𝑠𝑠 , it can be written as, 𝑍𝑍𝑠𝑠ℎ 𝑠𝑠 = 𝐿𝐿𝑠𝑠∗𝑠𝑠 + 𝑅𝑅𝑠𝑠∗ (8) piezoelectric patch zsh shunt circuit 426 iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 where 𝐿𝐿𝑠𝑠∗ and 𝑅𝑅𝑠𝑠∗ are the optimal inductance and resistance, respectively. both can be written as follows [7]: 𝐿𝐿𝑠𝑠∗ = 1 𝐶𝐶𝑃𝑃 𝑆𝑆(𝜔𝜔𝑠𝑠𝛿𝛿𝑠𝑠∗ )2 ; 𝑅𝑅𝑠𝑠∗ = 𝑟𝑟𝑠𝑠∗ 𝜔𝜔𝑠𝑠𝐶𝐶𝑃𝑃 𝑆𝑆 (9) where 𝐶𝐶𝑃𝑃 𝑆𝑆 is the piezo capacitance at constant strain, 𝐶𝐶𝑃𝑃 𝑆𝑆 = 𝐶𝐶𝑃𝑃𝑇𝑇(1 − 𝑘𝑘31 2), and 𝐶𝐶𝑃𝑃𝑇𝑇 is the piezo capacitance at constant stress, 𝐶𝐶𝑃𝑃 𝑇𝑇 = 𝐾𝐾3𝑇𝑇 × 𝜀𝜀𝑡𝑡 × 𝐴𝐴𝑃𝑃 𝑡𝑡𝑝𝑝 (10) all the terms in eq. (10) are dependent on the type of piezoelectric patch used where 𝐾𝐾3𝑇𝑇, 𝜀𝜀𝑡𝑡, 𝐴𝐴𝑃𝑃 and 𝑡𝑡𝑝𝑝 are the relative dielectric constant, relative permittivity of free space, area of the patch, and thickness of the patch, respectively. the terms 𝛿𝛿𝑠𝑠∗ and 𝑟𝑟𝑠𝑠∗ in eq. (9) are the optimal tuning ratio and optimal damping ratio for series configuration, which are dependent on the piezo electromechanical coupling coefficient for a transverse mode 31, k31: 𝛿𝛿𝑠𝑠∗ = �1 + 𝑘𝑘31 2 ; 𝑟𝑟𝑠𝑠∗ = √2 𝑘𝑘31 1+𝑘𝑘31 2 (11) the coefficient k31 describes the conversion of energy by the piezo element from electrical to mechanical and vice versa. it can be derived in several ways; one of them is using resonant frequency change with respect to the electric boundary conditions, 𝑘𝑘31 = �(𝜔𝜔𝑡𝑡 2 − 𝜔𝜔𝑠𝑠2)/𝜔𝜔𝑠𝑠2 (12) where 𝜔𝜔𝑡𝑡 and 𝜔𝜔𝑠𝑠 are natural frequencies of the beam when the piezoelectric patch is in open circuit and short circuit condition, respectively. in this work, these values will be obtained experimentally, which will be discussed in section 4. for this work, the electromechanical coupling value for this specific piezoelectic patch is found to be k31 = 0.196. the total electrical impedance in series, 𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝑠𝑠 as shown in eq. (6) can be re-written as, 𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝑠𝑠 = 𝐿𝐿𝑠𝑠∗𝑠𝑠 + 𝑅𝑅𝑠𝑠∗ 𝐿𝐿𝑠𝑠∗𝐶𝐶𝑝𝑝𝑠𝑠2 + 𝑅𝑅𝑠𝑠∗𝐶𝐶𝑝𝑝𝑠𝑠 + 1 (13) the values found for the optimal parameters, as discussed above, are tabulated in table 1. the optimal resistance and inductance in table 1 make up the electrical impedance of the series shunt circuit in order to dissipate the mechanical energy of the host structure at first resonant frequency. these values will be constructed using physical rl components where evidently, the resistance value can be realized by using off-the-shelf resistors, however this is not the case for the inductor. since inductor value typically ranges from 1 μh to 20 h, an enhanced synthetic inductor will be implemented to acquire inductance in the range of kh. table 1: values of optimal tuning and damping ratio and optimal resistance and inductance calculated using eqs. (9) and (11) series shunt circuit optimal tuning ratio, 𝜹𝜹∗ 1.0197 optimal damping ratio, 𝒓𝒓∗ 0.2715 optimal resistor, 𝑹𝑹∗, ω 78.28 × 103 optimal inductor, 𝑳𝑳∗, h 2902.9 427 iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 3. simulation studies for simulation study, a stainless-steel cantilever beam with dimensions of 280 mm x 40 mm x 2 mm is used. a pzt-5a piezoelectric patch with 50 mm x 20 mm x 0.38 mm dimension is attached at the fixed end of the beam. the terminal of the piezoelectric patch is connected to an optimal rl circuit in series configuration as found in table 1. the damping performance of the psd will be investigated where the difference between the displacement of the beam at its first resonant frequency, without damping and with damping is compared. for this, the circuit is made open so there will be no current passing through i.e. the shunt damping circuit is not connected and is hereby considered as a no-damping condition. and when the circuit is made closed, current can pass through the shunt damping circuit and this is when damping condition exists. fig. 2: cantilever beam attached with piezoelectric patch at its fixed end modelled in comsol. fig. 3: comparison of the beam displacement amplitude at first resonance (blue-dashed: open circuit, red-solid: closed-circuit) using comsol. figure 3 shows the response of the beam-psd system simulated via comsol where the terminal of the piezoelectric is set as ‘floating potential’ and ‘terminal’ for open and close circuit condition, respectively. a series rl circuit following the values found in table 1 is connected to the terminal as the optimal shunt circuit. the displacement of the cantilever beam is plotted at a frequency range that covers its first resonant frequency. the responses 15, 16.3 15, 4.9 -2 0 2 4 6 8 10 12 14 16 18 10 12 14 16 18 20 d is pl ac em en t, m m frequency, hz displacement vs. frequency ---open-circuit (without damping) closed-circuit (with damping) 428 iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 when psd is in open circuit (without damping) and closed circuit (with damping) conditions are plotted and compared to see the psd damping performance. from the figure, the difference between the displacement peak i.e. vibration reduction is recorded to be 70% in comsol. 4. optimal shunt circuit construction 4.1 equation of input impedance for synthetic inductor to realize the significantly large value of inductance, a synthetic inductor is constructed utilizing two op-amps, three resistors, and a capacitor with some voltage being supplied to the op-amps. to calculate the input impedance of the synthetic inductor, a few conditions must be stated. first, the op-amp is assumed to be ideal, so that the input impedance of the amplifier is infinitely high. this caused the current at input terminal to be zero. secondly, the voltage gain is infinitely high, therefore the voltage across input terminal is zero while output voltage remained finite [9]. 𝑍𝑍𝑖𝑖𝑖𝑖 = 𝑗𝑗𝜔𝜔 𝑅𝑅1𝑅𝑅3𝑅𝑅5𝐶𝐶4 𝑅𝑅2 (14) from eq. (14), it is shown that the circuit has the same characteristics as an ideal inductor. rearranging eq. (14), 𝐿𝐿 = 𝑅𝑅1𝑅𝑅3𝑅𝑅5𝐶𝐶4 𝑅𝑅2 (15) essentially, the desired inductance can be changed by changing the value of 𝑅𝑅2 accordingly. the optimal inductance, l value for maximum energy dissipation was found earlier to be 2902.9 h. following eq. (14), the resistance values for resistors 𝑅𝑅1, 𝑅𝑅3, and 𝑅𝑅5 are chosen to be 97.4 kω, 101.1 kω and 95 kω, respectively and achieved using potentiometers. for c4, a 1 µf capacitor is used. therefore, the value of r2 needs to be 322, 260 ω to achieve the desired optimal inductance, l. 4.3 enhanced shunt circuit implementation although physically doable, one of the problems that arise is the large internal resistance developed in the synthetic inductor circuit to generate the huge inductance. from this, the developed resistance exceeds the optimum resistance value required to suppress the matched vibration mode, therefore creating a mismatch in the circuit impedance. utilizing the concept of enhanced shunt circuit [10,11], an additional capacitor will be added in parallel to the shunt circuit to increase the capacitance of the piezoelectric patch. in this case, a 4.7 mf capacitor (i.e. polarized capacitor) is connected in parallel to 55 nf piezoelectric, creating an equivalent capacitor of, 𝐶𝐶𝑒𝑒𝑒𝑒 = 𝐶𝐶𝑝𝑝𝑖𝑖𝑒𝑒𝑝𝑝𝑡𝑡 + 𝐶𝐶𝑐𝑐𝑡𝑡𝑝𝑝𝑡𝑡𝑐𝑐𝑖𝑖𝑡𝑡𝑡𝑡𝑐𝑐. the schematic of the shunt circuit to be constructed is shown in fig. 4 using the values obtained in table 1. from fig. 4, the shunt circuit consists of a resistor in series with a synthetic inductor, connected in parallel with a 4.7 mf polarized capacitor and the piezoelectric patch, where the patch can be modelled as a capacitor having an inherent capacitance of 55 nf. figure 5 shows the physical implementation of the shunt circuit. 429 iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 fig. 4: schematic of the piezo patch attached with optimal rl shunt circuit in series utilizing a synthetic inductor. fig. 5: experimental setup of the piezo patch attached with optimal rl shunt circuit in series utilizing a synthetic inductor. 5. experimental studies the complete setup of the experiment is shown in fig. 6. here, a piezoelectric patch is bonded on the surface of cantilever beam using a thin layer of epoxy adhesive. the position of the patch is near the fixed end of the beam as this is where the largest stress and strain is generated when it deflects. in this study, the piezoelectric patch used is quickpack model qp10n made from pzt-5a (3195hd material type). the dimensions of the beam and piezoelectric patch used are shown in table 2. the end of the beam is clamped to an et139 electrodynamic shaker with two accelerometers mounted at the free end and at the clamped end of the beam to measure the output and input to the system, respectively. the piezoelectric terminals are connected to the optimal shunt circuit as constructed in section 3. polarized capacitor piezoelectric patch shunt circuit 430 iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 fig. 6: the complete experimental setup for vibration control using optimal piezoelectric shunt damper. table 2: the dimensions of beam and piezoelectric patch used in experiment length, m width, m thickness, m material beam 0.28 0.04 0.002 stainless steel piezoelectric patch 0.04597 0.02057 0.000381 pzt-5a (3195hd) 5.1 determining short circuit natural frequency, ωs and open circuit natural frequency, ωo the purpose of determining short circuit natural frequency, ωs and open circuit natural frequency, ωo is to determine the electromechanical coupling, k31 of the piezoelectric patch, as stated in eq. (12). here, the open circuit natural frequency is obtained when the beampsd system is excited at its first natural frequency where the terminal is left open; while for short circuit natural frequency, the piezoelectric terminal is put in short circuit condition by connecting a wire through both terminals. figure 7 shows the frequencies obtained for each case. fig. 7: natural frequency in open-circuit (left) and short-circuit (right) condition, ωo = 15.50 hz and ωs = 15.21hz, respectively. from these values, it is determined that electromechanical coupling value for this specific piezoelectic patch to be k31 = 0.196 which will be used throughout the work. 15.5, 49.5916 2 0 20 40 60 0 10 20 30 li ne ar m ag ni tu de frequency, hz open circuit 15.21, 35.15224 0 10 20 30 40 0 10 20 30l in ea r m ag ni tu de frequency, hz short circuit 431 iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 5.2 vibration control of cantilever beam with optimal psd the performance of the piezoelectric shunt damper system is to be validated. the terminal of the piezoelectric patch is now connected to the optimal shunt circuit constructed as discussed in section 4. for implementation of the synthetic inductor, a dc power supply is required to supply voltage to the lm358p op-amps. the experiment is performed by supplying sine-wave input to the beam-psd system through the electromagnetic shaker, capturing the first resonance of the beam. the response of the beam is collected when the piezoelectric terminal is in open-circuit condition (without damping) and when the terminal is connected to the optimal shunt circuit (with damping), respectively. fig. 8: experimental result on the vibration response of the beam-psd with damping (bluesolid) and without damping (red-dashed). figure 8 shows the vibration response of the cantilever beam at its first resonant frequency denoted by the ratio of output and input voltages (vo/vi ) from the accelerometer located at the beam tip (output from the system) and at the beam clamp (input to the system), respectively. two measurements are taken, i.e. in open-circuit and closed-circuit condition, and the data is plotted on the same graph for comparison. reduction of vibration can be seen at the first resonant peak, calculated to be 67.4%. the comparison of the psd performance from simulation and experiment is shown in table 3. it can be concluded that the constructed enhanced optimal shunt circuit manages to dissipate energy from its host structure successfully, and therefore validated the results from simulation studies conducted. table 3: the performance of the vibration reduction using optimum rl values. technique 1st nat. freq. amplitude at 1st nat. freq. vibration reduction percentage, % simulation (comsol) 15 hz 16.3 mm (disp.) – no damping 4.9 mm (disp.) – with damping 70 experiment 15.2hz 52.4 (vo/vi) no damping 17.1 (vo/vi ) with damping 67.4 0 10 20 30 40 50 60 0 5 10 15 20 25 30 v o/ v i frequency, hz vo/vi frequency series shunt circuit without shunt circuit 432 iium engineering journal, vol. 23, no. 1, 2022 suhaimi et al. https://doi.org/10.31436/iiumej.v23i1.1971 6. conclusion in this work, a piezoelectric shunt damper with enhanced synthetic inductor is used to damp the first resonance of a cantilever beam, which is shown both in simulation and via experiment. the optimal resistance and inductance values for the shunt circuit are found to be r = 78.28 kω and l = 2.9 kh, respectively. due to the significantly large value of inductance required, a synthetic inductor is utilized and enhanced by introducing a polarized capacitor attached in parallel to the synthetic inductor to avoid impedance mismatch. finally, the series shunt circuit is tested and it is found that the vibration reduction achieved is 67.4% experimentally which agrees with the simulation study. acknowledgement this research is funded by the ministry of higher education malaysia grant no. irags18020-0021. references [1] hagood nw, von flotow a. (1991) damping of structural vibrations with piezoelectric materials and passive electrical networks. journal of sound and vibration, 146(2): 243-268. [2] chatziathanasiou, g., chrysohoidis, n., kostas, g., & saravanos, d. a. (2021). semi-active vibration control of aircraft structures. in aiaa scitech 2021 forum (p. 1736). [3] pernod, l., lossouarn, b., astolfi, j. a., & deü, j. f. (2021). vibration damping of marine lifting surfaces with resonant piezoelectric shunts. journal of sound and vibration, 496, 115921. [4] yun, y. s., kim, j. c., noh, h. m., & kim, m. s. (2021). reduction in high-frequency wheel noise/vibration of railway vehicles using piezoelectric shunt. international journal of precision engineering and manufacturing green technology, 8(3), 981–995. [5] mohammadi a. (2017) passive vibration control of a cantilever beam using shunted piezoelectric element. 5th rsi int. conf. robot. mechatronics, no. icrom, pp. 389–393. [6] park, c. h. (2003). dynamics modelling of beams with shunted piezoelectric elements. journal of sound and vibration. [7] jeon, j. y. (2009). passive vibration damping enhancement of piezoelectric shunt damping system using optimization approach. journal of mechanical science and technology. [8] lossouarn, b., aucejo, m., deü, j. f., & multon, b. (2017). design of inductors with high inductance values for resonant piezoelectric damping. sensors and actuators a: physical, 259, 68-76. [9] mayer, d., linz, c., & krajenski, v. (2015). synthetic inductor for passive damping of structural vibrations. in 7th eccomas thematic conference on smart structures and materials. smart. [10] park ch, inman dj. (2003), enhanced piezoelectric shunt design. shock vib., 10(2):127–133. [11] fleming, a. j., behrens, s., & moheimani, s. o. r. (2003). reducing the inductance requirements of piezoelectric shunt damping systems. smart materials and structures. [12] american and standard. (1998) ieee standard on piezoelectricity: an american national standard. ansi/ieee std 176-1987 [13] wahid an. muthalif ag, nor ka. (2016) investigating negative capacitance shunt circuit for broadband vibration damping and utilizing aco for optimization. int. j. circuits electron, 1: 168-173. [14] marakakis, k., tairidis, g. k., koutsianitis, p., & stavroulakis, g. e. (2019). shunt piezoelectric systems for noise and vibration control: a review. in frontiers in built environment. 433 1. introduction 2. mathematical modelling 2.1 modelling of the piezoelectric shunt damper system 3. simulation studies 4. optimal shunt circuit construction 4.1 equation of input impedance for synthetic inductor 5. experimental studies 5.1 determining short circuit natural frequency, ωs and open circuit natural frequency, ωo 5.2 vibration control of cantilever beam with optimal psd 6. conclusion acknowledgement this research is funded by the ministry of higher education malaysia grant no. irags18-020-0021. references microsoft word 153-873-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 qasim et al. 93 analyses of impeller type wind turbine a.y. qasim, r. usubamatov and z.m. zain school of manufacturing engineering, university malaysia perlis, ulu pauh, arau, 02600 perlis, malaysia. ayhk66@yahoo.com,ryspek@unimap.edu.my, zuraidah@unimap.edu.my abstract: the new globaldevelopment for wind turbines obliged inventors to create new wind turbine designs that have high efficiency and better than known designs. this paper proposes the impeller wind turbine, which uses more effectively the wind energy and depends only on the acting area of the vanes. the vane wind turbine is designed to increase the drag coefficient and output of a wind turbine that uses kinetic energy of the wind. itcan be used worldwide due to its high efficiency, simple construction, and simple technology and can be made from cheap materials. abstrak: pembangunan global terkini turbin angin menyebabkan pereka harus membina rekaan terbaru turbin angin yang bercekapan tinggi yang lebih baik daripada rekaan-rekaan terdahulu. kertas ini mencadangkan pendesak turbin angin, yang menggunakan kuasa angin secara lebih efektif dan bergantung hanya terhadap permukaan bilah kipas yang terlibat. bilah kipas turbin angin direka sebegini untuk meningkatkan pekali seret dan juga keluaran daripada turbin angin tersebut yang menggunakan tenaga kinetik angin. cara ini boleh digunakan secara meluas di serata dunia kerana ia bercekapan tinggi, mudah dibina, menggunakan teknologi yang ringkas dan diperbuat daripada bahan-bahan yang murah. keywords: wind turbine; vane; design; energy 1. introduction wind power is the conversion of wind kinetic energy into a useful form, such as mechanical or electrical energy that can be harnessed for practical use by using wind turbines. wind turbine technology has steadily improved [1, 2]. various wind turbine mechanisms are proposed and built for capturing and converting the kinetic energy of winds. the wind turbineuse mainly aerodynamic lift force and drag forces acting on the surfaces of blades or vanes. in area of the wind energy there are two main type of wind turbine , the horizontal axial and the vertical axial (darrieus and savonius turbines), and there are many variants of each design as well, as a number of other similar devices under development. the wind screw turbine is most commonly used in large-scale applications constituting nearly all of the turbines in the global market, while the vertical axis turbines are more commonly implemented in medium and small-scale installations. the technical characteristics of wind turbines are to be found elsewhere [3-5]. however, simple analysis of these wind turbine designs shows that these designs are not perfect, the wind force does not use in full-scale due to many technical reasons. a wind screw turbine designed mainly of three blades and use the aerodynamic lift force. the wind passes freely between blades and does not affect on output of turbine. the real iium engineering journal, special issue, mechanical engineering, 2011 qasim et al. 94 output the power of the wind screw turbine is 4-5 times less than theoretical power one. the work of the darrieus-type turbine based also on the aerodynamic lift force, but its power output is small. the work of the savonius-type turbine based on the differences of drag forces, but its power output is small. these two turbines cannot be installed on high altitude due to many engineering limitations. hence, there is necessity to design new type of the wind turbines without mentioned above lacks and with ability of use in wide area of application. designing a wind turbine system that can generate power with high efficiency requires a thorough understanding of the principles of aerodynamics and structural dynamics of the rotor system. first, new design should use the wind kinetic energy by maximum of the betz limit [1]. researchers state that wind turbines of lift force design theoretically have higher power efficiencies than turbines of drag force design. other research states that at conditions of turbulent with rapid changes in wind direction practically more power will be generated by turbines of drag force design, despite its lower efficiency [2]. however, there is the following vital information: the power output of a wind generator is proportional to the acting area of wind turbines and the power output of a wind generator is proportional to the cube of the wind speed. these peculiarities should be considered as main factors of the output power to design new type of wind turbines. hence, capturing and converting the kinetic energy of winds depends on the active area of the blades, vanes or other elements of the wind turbines and on the wind speed, which increases with altitude of the turbine location regarding the earth level. 2.brief description of the design and work of the impeller type wind turbine problems of the wind turbine presented above can be solved by new design of the vertical axis impeller type wind turbine with movable vanes. new turbinehas simple construction, technologically simple in production, anduses the drag force by active area of the working elements. the active area of the vanes can be increased significantly, but should be optimized according to the many limits of design.increase the number of frames increases the vane interframe wind shadow area and increases the weight of turbine. a) b) fig. 1: a) sketch of the vane type wind turbine, b) and general view of wind station. iium engineering journal, special issue, mechanical engineering, 2011 qasim et al. 95 the sketch of the impeller type wind turbine is presented in fig. 1. the turbine can be designed by three, four or more frames that lead to increase the acting area of the vanes and lead to increase of the weight one. frame is designed with movable vanes located on the vertical bars. at a left side of the turbine, under action of the wind force the vanes are rotated and create scoop shape when closed frames, which capture the wind kinetic energy with high value of the drag factor. at a right side of the shaft, the vanes are open and wind force passes through the open frame. the torque created by the wind force rotates frames with the output shaft, which transfers the torque via gearing to the electrical generator.frame elements should be designed in aerodynamic form to reduce a drag force on the wind action for not working elements of a turbine. this turbine typeis similar to savonius design, which works on differences of the drag factors of left and right sides scoops. new turbine uses mainly one side drag factor that can increase dramatically the turbine’s output power. also, new wind turbine enables to use the high wind velocity by lift its construction on high altitude by the metallic frame tower (fig. 1b). 3. analytical approach the theoretical maximum power efficiency of any design of wind turbine operating in open atmosphere is ce = 0.59 the betz limit [1, 2].no more than 59.3% of the available power in the wind can be extracted. no turbine to date has exceeded this limit[11]. in the world the real limit is well below the betz limit with values of 0.35-0.45 in the best designed wind turbines. there are other energy losses in a complete wind turbine system (the generator, bearings, power transmission, etc.) and only 10% -30% of the power of the wind is ever actually converted into usable electricity [10]. the fluid dynamics theory gives a formula with minor variations for calculation of the power for the different wind turbine designs. the fundamental equation that governs the power output of a wind turbine is [7]: p= 0.5*ρ* a* v3* λ, watt(1) where: p power produced by the wind turbine, w; ρ air density, vwind speed approaching the wind turbine, λ = wind turbine efficiency for common case; and a projected area of the turbine perpendicular to the approaching wind. the parameter λ is wind turbine efficiency that consists following factors and calculated by following formula: λ = cp*c* ng* nb where cp coefficient of performance (cp = 0.35 for a good design); c = cl or cd (or resulting of them) are lift and drag factors respectively which are depended on the shape and form of the blades or vanes and on orientation of the wind flow with respect to the object; ng – generator efficiency (80% or possibly more for a permanent magnet generator or gridconnected induction generator); nb gearbox/bearings efficiency (95% for a good design) it is well-known that modern wind turbine is designed with very complex optimality criteria involving more than improving aerodynamic efficiency. the main objective is to iium engineering journal, special issue, mechanical engineering, 2011 qasim et al. 96 maximize the drag factor cd, which is a function of the turbine element geometry, reynolds number, and froude number. determination of cd drag factor is the most difficult part of this procedure. it is highly variable, and many parameters can affect the final cd. shape, altitude, inclination to the wind direction and wind speed, surface roughness, spin, and nose bluntness are just a few that can influence cd. many researches dedicate to study the drag factor and results of investigations can be quite different. the drag factor can vary on cd = 1.2 to 2.1 for simple 2d flat plate [8, 9]. however, among the three methods for calculating cd, which are experimental; theoretical and numerical cfd procedures, the most realistic and straight forward method for the present wind turbine blade shape is using a wind tunnel. this involves solving eq. (1) for cd, then placing a model in a wind tunnel (ρ, a, and v already known). test results are used to measure the force acting on the device that holds the model and calculate cd = f / a. mathematical modeling of the wind turbines power is a very difficult problem and generally should be solved using computational fluid dynamics. finally, results of mathematical modeling should be verified by practical tests in the aerodynamic wind tunnel. for this contribution simple mathematical descriptions of the wind turbine design and its work can give initial information and ability to evaluate the proposed construction. in the present work two models of the scoop-vanes wind turbine are analyzed. plan view of the vane type wind turbine are presented in fig. 2 and 3 the first model of the vane type turbines is four sections of vanes assembled on frames, which are perpendicular to each other and joined with the main output shaft. the second one is three frames the scoop-vanes wind turbine.the model has three sections of scoop-vanes, which forms an angle of 120o to each other and joined with the main output shaft. fig. 2: vane type wind turbine of four frames. power output depends on a wind force and speed and the acting surface area a of vanes that located at one side of the output shaft. relationship between acting physical parameters on the vane can be considered by known approaches. acting forces, location of the vanes, wind shadow, and the wind pressure on the vanes is proportional to some power of the wind speed. the first thing is to calculate the force acting on the vanes due to the momentum iium engineering journal, special issue, mechanical engineering, 2011 qasim et al. 97 change of the air impinging upon them. it is necessary for analytical approach the ultimate simplification of considering the force acting on stationary vanes. fig. 3: vane type wind turbine of three frames. this simplification leads to different results depending on the assumptions made. the important assumptions are as follow: a) the wind turbine vanes are smooth. b)the air hitting the vanes has no viscosity. it is further assumed that air, having struck on the vanes, moves off along the surface without causing a tangential frictional force. c) the drag force acting on the left and right frame components is equal. force component facting on stationary vertical vanes of left side frame is expressed by the following formula [1-3] f = (1/2)cdρa v2sinα = p*a (2) where pis the air pressure. to determine the starting torque t on wind turbine vanes, it is necessary to define the whole vanes area, and distance from centre of output shaft to the centre of wind pressure, then the formula has the following expression t = (1/2)a cd ρv2r sinα (3) where r is distance from the shaft center line to the center of pressure of the vane surface, other parameters specified above. the output power is calculated by the following equation: p = tω = (1/2)acdρv2rsinα*v/r = (1/2)acdρv3sinα (watt) (4) whereω is the angular velocity of turbine rotating, other parameters specified above. next step is to develop the mathematical model of the resultant force acting on moving vanes. this entails determining a) the velocity of oncoming air relative to the front surface of the first frame vanes and iium engineering journal, special issue, mechanical engineering, 2011 qasim et al. 98 b) the affect of the wind on the surface of the second frame vanes. in rotation of the frames with vanes, pressure builds up along the surface of an object. a surface more perpendicular to the stream line of wind tends to have a higher pressure. the resultant force acts in the center of pressure that is found by calculating the pressure distribution across of the variable vanes location, then integrating it. the forces acting on the sides of the frames can be neglected due to face sided small areas. a good vane design will combine the aerodynamics, the mass properties, and the spin of the vane to permit the projectile to be pointy end forward for the entire airstream line. however, the vary location of the frames with vanes contributes to instability of the forces acting on the vanes and instability of the output shaft rotation. the scoop-vane, with its plane normal to the airstream, represents a common situation for wind force loads on the vane. for a scoop-vane its plane normal to the wind flow, the only aerodynamic force will be one parallel to the wind flow, i.e. a wind force. practice shows,that the value of the drag factor cd is variable and depends on many factors like vanes configuration, wind speed, the wind angle of attack with respect to vanes, etc. there is also a tangential component or ‘skin friction’ force [4]. the wind turbine of three frames works variably with one and two frames that located at left side from its vertical shaft. the vanes from right side are mainly open, but some vanes are closed due to angular location and wind force acts on their surfaces (fig. 3). the frames with vanes located 1200 each other due to design of the wind turbine. location of the acting vanes is variable due to rotary motion of the turbine, so the torque created by the wind force also variable. it is very important to know the variation of the torque applied on the shaft to calculate the output power. fig.2, 3 presents the sketch of the calculation the forces acting on the vanes that enables to calculate the torque applied to the wind turbine shaft. the left side of the scoop-vane turbine has acting frames that create the torque due to action of the wind force. the vanes of frames work at different conditions. the second frame vanes acts after rotation of the first frame vanes on 30o. the wind shadow zone is also different. the first frame’s vanes work with wind shadow at some angles of rotation of the second frame vanes. the second frame’s vanes work without wind shadow. thetorque created by the first and second frames with group of vanes can be calculated by the following equations: )]2/()[(1 cbhcpct d  sinα (5) the power generated by the impeller type wind turbine is calculated by the equation:              2 c bhc r v pkcp d  sinα(6) where frame factor k = 1.16 for four frame turbine; k = 0.9 for three frame turbine; other components specified above. 4. a working example iium engineering journal, special issue, mechanical engineering, 2011 qasim et al. 99 the vane type turbine has following dimensions: c = 1.0 m –total vane width, b = 1.0 m, cavity shape with angle (45)° z=0.46 – length of open frame part, h = 2.0 m – height of frame, cd1= 1.6 drag factor accepted conventionally for rotating vanes. cd2 = 1.0 – drag factor accepted conventionally at wind shadow. the pressure acting on the vane: p = 70n – wind force at condition of the wind speed v = 10 m/s. the air density ρ = 1.25kg/m3, coefficient of performancecp = 0.3. the maximum torque created by one frame is nmcbhcpct d 336)]2/1(1[1*2*70*6.1)]2/()[(11  the power generated by the vane wind turbine is calculated by the following equation p = (tavv/r). λ (7) 1. four frames turbine p = (tavv/r). cp.nb.ng = (390*10/1.5)*0.3*0.8*0.95 = 592.8 w, 2. three frames turbine p= (tavv/r) cp.nb.ng = (302.4*10/1.5)*0.3*0.8*0.95 = 459.6 w the power generated by the vane type wind turbine of four frames by known eq. (1) is p= 0.5*ρ*v3*a* λ, watt = 0.5*1.25kg/m3*103 m/s*2.83m2*(0.3*1.6*0.8*0.95) = 645 w, where a = 2*h*c*cos450 = 2.83 m2 – maximum acting area of two acting vanes. there is small difference between results calculated by eq. (7) and eq. (1) that can be explained by approximations accepted for both approaches. 5. results and discussion theoretical calculations of the torque for the vane type turbines conducted by eqs. (1) and (7) shows a small different result even if except low magnitude of power. nevertheless, results shows that new type wind turbines possess better technical properties than other type turbines and can be used for generating a power. the impeller type turbine with scoop-vanes has higher efficiency compares with flat vanes. this is caused the new design wind turbine has a high drag factor, so enables to capture wind energy. this type wind turbine has good technical properties and can be used for generating a power more efficiently for the low speed of the wind. the proposed vane turbine can be designed from cheap material that is highly economical. the work of the vane turbine does not have restrictions. at strong wind conditions, it is possible to design the vane turbine with decreased acting numbers of vanes. the possible flipping of the vanes under action of the wind force can be avoided by simple constructive solutions. 6. conclusion new vane type wind turbine possesses many positives properties and can solve the problem of increase wind energy use. the vane type wind turbine can be high efficiency and enables increase in the vanes acting area and drag factor that can increase the output power. iium engineering journal, special issue, mechanical engineering, 2011 qasim et al. 100 new impeller wind turbine with movable vanes possesses all advantages of vertical and horizontal types of turbines and can be concurrent for known wind turbine designs. the new turbine presents simple construction and uses simple technology, and for manufacturing can be made from cheap materials. for future research, mathematical modeling of the wind turbine work should be conducted on a basis of computational fluid dynamics and proved by practical investigations in the wind tunnel. also, it is necessary to conduct investigations on the optimal design of new turbine (power as a function of the vanes geometry, weight of turbine, aerodynamic shape, wind speed, etc.). tests of the vane type wind turbine in the wind tunnel and correction of the mathematical model can give reliable data in order to design of the vane type wind turbine. references [1]manwell jf, mc gowan jg, rogers al. wind energy explained, theory, design and application. willey& sons 2002;ltd, england. [2] mathew s. wind energy fundaments, resource analysis and economics. 1st ed. springer 2006; vol. 1. [3] ackermann t. wind power in power system, willey & sons 2005: royal institute of technology, stockholm, sweden. [4] burton t, sharpe d, jenkins n, bossanyi e. wind energy handbook. willey & sons 2000; new york. [5] eggleston dm., stoddard fs. wind turbine engineering design. willey & sons 2004. [6] spera dа.wind turbine technology. asme press 1994; new york. [7] munson br, young df.okiishi tн.fundamentals offluids mechanics 4th ed. 2002; john wilеу &sons, inc. [8] mehrdad shademan1, horia hangan. wind loading on solar panels at different inclination angles. 11 americas conference on wind engineering – san juan, puerto rico june 2009 [9] a. fage, f.c. johanson, on the flow of air behind an inclined flat plate of infinite span, proceedings of the royal society of london. 116, no. 773, (1927) 170-197. [10] r. usubamatov, z.m.zain, r. bhuvenesh, f.khammas. new vane type wind turbine of high efficiency, cngrt88. proceedings of world engineering congress 2010 (wec2010), kuching sdaravak, malaysia, p. 418-428. [11] dynamic modeling of ge 1.5 and 3.6 wind turbine-generators. miller, nicholas, william, price and sanchez-gasca, juan. s.l. : ge power systems, 2003. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 wavelet detail coefficient as a novel wavelet-mfcc features in text-dependent speaker recognition system syahroni hidayat1,2*, muhammad tajuddin3, siti agrippina alodia yusuf2, jihadil qudsi4 and nenet natasudian jaya5 1 department of agricultural engineering, university of mataram, mataram city, indonesia 2 research and development, sekawan institute, mataram city, indonesia 3 department of computer science, universitas bumigora, mataram city, indonesia 4 department of medical record, politeknik medica farma husada, mataram city, indonesia 5 depaertment of management, universitas mahasaraswati mataram, mataram city, indonesia * corresponding author: syahronihidayat@unram.ac.id (received: 23rd december 2020; accepted: 12th august 2021; published on-line: 4thjanuary 2022) abstract: speaker recognition is the process of recognizing a speaker from his speech. this can be used in many aspects of life, such as taking access remotely to a personal device, securing access to voice control, and doing a forensic investigation. in speaker recognition, extracting features from the speech is the most critical process. the features are used to represent the speech as unique features to distinguish speech samples from one another. in this research, we proposed the use of a combination of wavelet and mel frequency cepstral coefficient (mfcc), wavelet-mfcc, as feature extraction methods, and hidden markov model (hmm) as classification. the speech signal is first extracted using wavelet into one level of decomposition, then only the sub-band detail coefficient is used as the feature for further extraction using mfcc. the modeled system was applied in 300 speech datasets of 30 speakers uttering “hadir” in the indonesian language. k-fold cross-validation is implemented with five folds. as much as 80% of the data were trained for each fold, while the rest was used as testing data. based on the testing, the system's accuracy using the combination of wavelet-mfcc obtained is 96.67%. abstrak: pengecaman penutur adalah proses mengenali penutur dari ucapannya yang dapat digunakan dalam banyak aspek kehidupan, seperti mengambil akses dari jauh ke peranti peribadi, mendapat kawalan ke atas akses suara, dan melakukan penyelidikan forensik. ciri-ciri khas dari ucapan merupakan proses paling kritikal dalam pengecaman penutur. ciri-ciri ini digunakan bagi mengenali ciri unik yang terdapat pada sesebuah ucapan dalam membezakan satu sama lain. penyelidikan ini mencadangkan penggunaan kombinasi wavelet dan mel frekuensi pekali cepstral (mfcc), wavelet-mfcc, sebagai kaedah ekstrak ciri-ciri penutur, dan model markov tersembunyi (hmm) sebagai pengelasan. isyarat penuturan pada awalnya diekstrak menggunakan wavelet menjadi satu tahap penguraian, kemudian hanya pekali perincian sub-jalur digunakan bagi pengekstrakan ciri-ciri berikutnya menggunakan mfcc. model ini diterapkan kepada 300 kumpulan data ucapan daripada 30 penutur yang mengucapkan kata "hadir" dalam bahasa indonesia. pengesahan silang k-lipat dilaksanakan dengan 5 lipatan. sebanyak 80% data telah dilatih bagi setiap lipatan, sementara selebihnya digunakan sebagai data ujian. berdasarkan ujian ini, ketepatan sistem yang menggunakan kombinasi wavelet-mfcc memperolehi 96.67%. keywords: discrete wavelet transforms; feature extraction; hidden markov models; speaker recognition; wavelet coefficients 68 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 1. introduction speaker recognition is the process of recognizing the speaker from his speech by comparing the sound biometrics of the words he has spoken with his pronunciation model, which has previously been used as a reference and stored in a database [1]. speaker recognition can be used in many aspects; this technology is expected to make daily life easier by accessing personal devices remotely. as a biometric tool, speaker recognition also can be applied in secure access voice control, information structuring, customizing services, and forensic investigation. as a non-invasive biometric, speech can be collected without the knowledge of the speaker [2]. the speaker recognition system first appeared in 1962, in an article published by nature entitled voiceprint identification. the research claimed had developed a method for identifying an individual with high success rates. the research developed a visual representation of speech called a spectrogram. however, the first successful implementation in speaker recognition was a text-dependent system developed in 1977, using euclidean distance as a verification decision. in the last several years, many researchers have been interested in this field and made significant improvements to it [3], especially in feature extraction and classification. in speaker recognition, feature extraction is a necessary process that can affect the performance of the system recognition. these features are used to represent and describe the signal. each speaker has a unique vocal characteristic; this leads to two different features: morphological and behavioral features. morphological features are determined by the length of the vocal tract and the size of vocal folds. at the same time, the behavioral features are determined by education, background, parental influence, personality type, place of birth, and language [1]. there are a few properties of good features, such as the ease of measurement and extraction, robustness, uniqueness, and independence between one feature and another. several feature extraction techniques are commonly used in speaker recognition, such as the mel frequency cepstral coefficient (mfcc), gammatone frequency cepstral coefficient (gfcc), wavelet, and the combination of wavelet-mfcc. each of the methods has its advantages and disadvantages. feature extraction using mfcc is found in [4], the research employed mfcc to extract the features. mfcc is an excellent features extractor; it can form features to mimic human hearing [5]. although it was said that mfcc is the best feature extractor, especially in distant-talking speaker recognition [1], in the matter of robustness towards noise, gfcc is better [6]. ayoub et al. [7] employed gfcc as a features extractor in speaker identification system over voip network. the discrete wavelet transformation (dwt) has also become popular and is employed in a variety of applications. the extension version of dwt, wavelet packet transform (wpt), has superior presentation to dwt; it gives more flexibility in decomposition since wpt decomposes both details and approximations [8]. it is stated that the features extracted using a wavelet give equal accuracy to mfcc. aside from that, many previous kinds of research claim that extracting features using wavelet yielded better results compared to mfcc [9]. wpt was employed to extract features on timit and talung databases [10]. however, it is shown that in the speaker recognition system, mfcc is commonly used as a feature extractor and can be combined with another new method such as dnn [1]. several previous types of research have combined wavelet and mfcc, forming mfcc based on wavelet to overcome the noisy environment. application of both, in combination integrates the merits of both methods. mfcc can represent the speech spectrum in a compact form and is based on the model of human auditory perception, but 69 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 the fft process can cause the loss of information [5,11]. meanwhile, the wavelet can map the signal into the time and frequency domain; thus, no information is lost in this process [9]. mfcc was combined with 3 level decomposition of dwt to extract signal uttering digits 0-9 in the indian language [12]. wpt-mfcc was combined employing all of the sub-band obtained from wpt to find the mfcc [13]. mfcc was combined with wavelet sub-band coefficient (sbc) in an isolated word for speaker recognition [14]. the combination of wavelet-mfcc yielded better results than conventional mfcc and gmm [15]. the modeling and decision making in speaker recognition also vary, starting from the widely used hmm [4,16], vector quantization (vq) [9], svm [14], the classical technique gaussian mixture model (gmm) [10,12,13], and ann [17,18]. however, from the decision-making model, hmm is more suitable for modeling speaker features, especially in text-dependent speaker recognition systems, where there are two types of hmm, ergodic and left-right [19]. much previous research that employed wavelet-mfcc as feature extraction either used approximated sub-band coefficient [9], or a combination of approximated and detailed sub-band of the sub-band [12,17]. there are three aims in this research. first, we determine the best sub-band coefficient as an input for another feature extraction using mfcc. second, we determine the best wavelet family in wavelet-mfcc feature extraction method. we also try to find the influence of gender in the recognition system. then, we compare the proposed method with other feature extractions such as conventional mfcc, mfcc + delta, and mfcc + delta-delta. as for the decision-making, we employed hmm. 2. related works as the algorithm evolves for speaker recognition, one of the best algorithms is mel frequency cepstral coefficient (mfcc) [20]. many previous researchers have used this algorithm to extract features from a sound signal. mfcc was employed as a feature extractor in the ntt database, and the japanese newspaper article sentences (jnas) database and vector quantization (vq) were used as a recognizer [21]. the obtained result shows excellent accuracy, which is 98.75%. it is said that gfcc works better than mfcc to extract features from noisy signals and shows an encouraging result. [7] studied and evaluated the performance of the method in text-independent over voip networks and obtained high identification rates. [10] applied wpt to extract features in two public databases, talung and timit. the research proposed a new method based on a multilayer neural network to reduce the dimension of wavelet packet features. the recognition rate obtained was 94% in the talung database. wpt was also applied in speaker identification for security systems based on the energy of speaker utterance and achieved a 96.6% of recognition rate [11]. the hybrid features were based on wavelet-mfcc [12]. the features were extracted in ten isolated hindi digits using 3 level decomposition of wavelet, then extracted using mfcc on every sub-band. the methods yielded 100% average performance. adam et al. [22] proposed an improved feature extraction method called wavelet cepstral coefficient (wcc) for isolated speech recognition in the english alphabet. the research replaced the dft with dwt in order to obtain the merit of the wavelet transform. the coefficient from dwt is then used as a feature vector to calculate the log power spectrum and dct. 70 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 3. methodology in this research, generally, the proposed method consists of four steps: collecting database, preprocessing, feature extraction, and speech recognition. figure 1 shows the steps of the proposed method. fig. 1: proposed method. 3.1 database the database used in this research was created with the help of 30 volunteers consisting of 20 male and 10 female adults. all of the speakers were native indonesian speakers and asked to utter the word “hadir” in indonesian, which in english means “present,” and repeat the word ten times. the total dataset obtained was 300 datasets. in accordance with collecting the sound database, this research used a smartphone integrated with a microphone and used audacity software. there were two settings done in recording; the first was an environmental setting, and the second was the recording properties setting in audacity software. in the environmental setting, the recording was taken indoors to reduce the noise, and the recorder was placed 0.5 meters from the speaker; the audacity setting was shown in the following table. table 1: recording properties no. variable value 1 recording channel mono 2 frequency sampling 8096 3 bits per sample 16-bit pcm 4 format *.wav 71 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 3.2 preprocessing the aim of preprocessing is to enhance the quality of the signal. there were three steps in the preprocessing stage that consisted of noise reduction, voice activity detection, and signal normalization. in the first step, we applied a pre-emphasis filter to reduce the noise. pre-emphasis is also able to emphasize the high frequency in the signal. generally, the coefficient used in pre-emphasis oscillates between 0.9-0.97. in this research, we used α = 0.97. therefore, the following eq. (1) is used to calculate pre-emphasis, where y[n] is the output, x[n] is the input signal n, and x[n-1] is the previous signal. 𝑦[𝑛] = 𝑥[𝑛] – 𝛼 ∗ 𝑥[𝑛 – 1] (1) the next step was applying the voice activity detection algorithm. by applying this algorithm, the silent sound in the signal was removed [23]. this algorithm was developed by [23], and this algorithm uses the value of energy e as a threshold to distinguish the silent sound in the signal. the energy of the signal can be calculated using eq. (2). 𝐸 = 1 𝑁 ∑ |𝑥(𝑛)|2𝑁𝑛=1 (2) the last step of preprocessing was signal normalization, snorm. signal normalization aims to obtain the same magnitude value. by doing this, the maximum magnitude value is ±1. eq. (3) was used to obtain the normalized signal. snorm is the normalized signal, and max|s| is the maximum value of the signal. 𝑆𝑛𝑜𝑟𝑚 = 𝑠 𝑚𝑎𝑥 |𝑆| (3) 3.3 feature extraction feature extraction is a process to extract features from the signal. the extracted features must be unique and have high variability, among other features. in this step, two different methods were combined, wavelet and mfcc. the goal of this combination was to take advantage of both methods. for wavelet feature extraction, this research applied discrete wavelet transformation (dwt). wavelet transformation is suitable for analyzing stationary and non-stationary signals since it can localize the signal in the time-frequency domain and has multiresolution characteristics [12]. the signal then decomposed into one level decomposition. the decomposition itself was a convolution and decimation process of a signal by a factor of two [24], the result was two sub-bands for each level, sub-band a1, also known as approximation coefficient, obtained from low pass filter (lpf) g[n] and sub-band d, known as detail coefficient, obtained from high pass filter (hpf) h[n]. one level decomposition is shown in fig. 2. raw signal a1 d1 a2 d2 level 1 level 2 fig. 2: dwt with two levels of decomposition. 72 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 the implementation of lpf and hpf shown in eq. (4) and (5) respectively. 𝐴[𝑛] = ∑ 𝑠[𝑘]𝑔[2𝑛 − 𝑘]∞𝑘=−∞ (4) 𝐷[𝑛] = ∑ 𝑠[𝑘]ℎ[2𝑛 − 𝑘]∞𝑘=−∞ (5) then, the signal detail coefficient (d1) was used as a feature vector for further extraction using mfcc. the process of feature extraction using mfcc is shown in fig. 3. signal framing windowing discrete fourier transform (dft) mel frequency warping mel frequency cepstral coefficient (mfcc) fig. 3: mfcc feature extraction. one of the most used and popular algorithms for speaker recognition is mfcc, which is also known for representing the information of the speaker’s vocal tract [25]. extracting features using mfcc consists of several steps: framing, windowing, discrete fourier transform (dft), mel frequency warping, and mel frequency cepstral coefficient. the framing step, also called signal segmentation, is a process to divide the signal into equal sizes of frames; hence, the voice signal was the non-stationary signal. this process assumed the signal as a stationary signal for a short duration. the frame size used in this research was n = 0.025 seconds, with the overlap m = 0.01 second. figure 4 shows how framing works. the framing process caused discontinuity in the framed signal; thus, the windowing function was applied to remove it. we used hamming window function to eliminate the discontinuity. in terms of calculating the hamming window, eq. (6) was used. 𝑤(𝑛) = 0.54 − 0.46 cos( 2𝜋𝑛 𝑁 ) (6) where 0 ≤ n ≤ n and n is frame length. fig. 4: framing step. transforming the signal from the time domain into the frequency domain was the next step. the process was applied using discrete fourier transformation. we used a total of 512 fft points. the algorithm is shown in eq. (7). 𝑋[𝑘] = ∑ 𝑥[𝑛]𝑒−𝑗2𝜋𝑛𝑘/𝑁𝑁−1𝑛=0 (7) where x[k] is the result of dft and x[n] is the n-th discrete signal. 73 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 after transforming the signal using dft, the next step was warping the signal using a triangle filter. this process is called mel frequency warping. this was applied because the signal sound was different from the perception of human hearing, where signal sound did not have frequencies on a linear scale. regarding the mel frequency value, mel(f) and triangle filter hm[k] were used. the following eq. shows how to calculate mel(f) and hm[k], respectively. 𝑚𝑒𝑙(𝑓) = 1125 ln (1 + 𝑓ℎ𝑧 700 ) (8) 𝐻𝑚[𝑘] = { 0 𝑘 < 𝑓[𝑚 − 1] (𝑘−𝑓[𝑚−1]) (𝑓[𝑚]−𝑓[𝑚−1]) 𝑓[𝑚 − 1] ≤ 𝑘 ≤ 𝑓[𝑚] (𝑓[𝑚+1]−𝑘) (𝑓{𝑚+1]−𝑓[𝑚]) 𝑓[𝑚] ≤ 𝑘 ≤ 𝑓[𝑚 + 1] 0 𝑘 > 𝑓[𝑚 + 1 (9) we applied a 26-triangle filter, which means we obtained 26 coefficients, but for features, we used the first 13 coefficients as mfcc. the first aim of this research was to determine the best wavelet coefficient as a feature when combined with mfcc. to achieve this, we decomposed the signal into levels 1 and 2 using haar. the second aim was to determine the best wavelet family when combining with mfcc; hence, we employed all wavelet families, decomposed the signal into one level decomposition, and combined only the detailed coefficient channel with mfcc. figure 5 shows the process of feature extraction using the combination of wavelet-mfcc. raw speech signal approximation coefficients (a1) details coefficients (d1) mfcc mfcc fig. 5: wavelet-mfcc feature extraction process. 3.4 speaker recognition system there are various algorithms for speaker recognition, the most used and proven to have excellent performance is hidden markov model (hmm). hmm works by modeling a stochastic process defined by a set of states and several mixtures per state [26]. hmm can solve two characteristics of problems; the first is state-based characteristics, which include the hidden state and the observation state. in the second, there were two types of data consisting of the observation-state sequence and hidden-state sequence [4]. hmm has two types, ergodic and left-right. the left-right hmm was used to model the speech signal because the speech cannot be repeated to the previous state. moreover, generally, the observation probability distribution of hmm is modeled by gaussian mixture model (gmm) [19]. the following elements model an hmm: 𝜆 = (𝐴,𝐵,𝜋) (10) 74 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 𝐴 is state transition probability defined as eq. (11), 𝜋 is prior probability state distribution defined as eq. (12), and b is observation probability distribution defined as eq. (13). this definition represents the left-right type of hmm. 𝐴 = {𝑎𝑖𝑗} (11) where, 𝑎𝑖𝑗 = 0 for 𝑗 < 𝑖 , and 𝑗 > 𝑖 + 1. 𝑎𝑁𝑁 = 1, 𝑎𝑁𝑗 = 0, for 𝑗 < 𝑁. 𝜋 = {𝜋𝑖} (12) where, 𝜋𝑖 = 1 for 𝐼 = 1, and πi = 0 for i ≠ 0. 𝐵 = 𝑏𝑗(𝑘) (13) generally, the hmm observation probability distribution is defined as gaussian mixture model (gmm). however, in practice, this model gives problems in computation. therefore, the euclidean distance probability approach can be the alternative solution [19]. it is defined as eq. (14) and eq. (15): 𝑑(𝑂𝑡,𝜇𝑗) = √∑ ( 1 1+𝑑(𝑂𝑡,µ𝑗) ) 2 𝑀 𝑘=1 (14) 𝑑(𝑂𝑡,𝜇𝑗) = √∑ (𝑂𝑡𝑘 − 𝜇𝑗𝑘) 2𝑀 𝑘=1 (15) the built model of the recognition system is shown in fig. 6. the signal was first decomposed into one level using wavelet, and then the sub-band detail coefficient was used as a feature for further extraction using mfcc. the probability of the dwt-mfcc features then calculated probability to be used as a model. in this research, the speaker recognition system used is shown in fig. 7. fig. 6: speaker recognition system for the training phase. features extraction calculate probability p(o|λ ) > threshold signal observation sequence (o) λ p(o|λ ) yes no denied accepted fig. 7: speaker recognition system for testing phase. 75 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 the features of the signal were extracted using the proposed method. the extracted features were then called the observation sequence (𝑂), and fed into the viterbi algorithm to measure the probability towards lambda (𝜆). the viterbi algorithm was employed to find the most likely sequence of hidden states, and the result was an observed sequence. lambda is a probability sequence obtained from the training model. the model was then compared to the observation sequence to obtain the classification result. 3.5 evaluation and validation the accuracy of the classification result was evaluated using eq. (16) [2,27]: 𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = 𝑁𝑆𝑅𝐶 𝑇𝑁𝑆 × 100 (15) 𝑁𝑆𝑅𝐶 is the number of speakers recognized correctly and 𝑇𝑁𝑆 is the total number of speakers. the k-fold validation method was applied to keep the variation of accuracy low; this method divided the dataset into k datasets. the first dataset was used as a testing dataset, while the second and third k were used as training datasets. furthermore, the process was repeated, where the second dataset used as testing datasets, the first, third k were used as training datasets. the process was repeated until k times, and the total accuracy is the number of accuracies divided by k. in this research, the number of folds used is 5; thus, in each process, the testing dataset was 20% of the total dataset [28]. 4. results and analysis this research proposed a feature extraction algorithm for speaker recognition based on the combination of wavelet-mfcc. we used 300 sound signals obtained from 30 male and female adult volunteers uttering the word “hadir” in indonesian, and each volunteer repeated the word ten times. each signal was then preprocessed to enhance the quality by applying pre-emphasis and normalization. 4.1 determining the best wavelet coefficient to obtain the result for the first aim, we employed oneand two-level decomposition using the wavelet haar family on both levels of decomposition. the coefficients a1, d1, and a combination of coefficients a1 and d1 were used as features. the next step was extracting those coefficients using mfcc, 13 first coefficients were then used as features. the recognition process was modeled using hmm. we obtained accuracy, as shown in table 2. table 2: accuracy result coefficient accuracy (%) level 1 level 2 a 92 90 d 95 78 a+d 95 85 the highest accuracy was obtained on the one-level decomposition using coefficient d and the combination of a + d, where the accuracy was 95%. nevertheless, increasing the decomposition level reduced the accuracy of the system recognition, where the highest accuracy obtained was 90%. hence, it is not necessary to increase the decomposition level 76 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 as it reduces accuracy. moreover, the use of the sub-band detail coefficient yielded the best accuracy. 4.2 determining best wavelet family once we figured out the best coefficient, we employed all wavelet families and decomposed the signal into one level decomposition. this allowed us to determine the best wavelet family. the one-level decomposition yielded two sub-bands, approximation and detail. the next step was finding the mfcc of the detail coefficient obtained from the previous step. this way, we obtained wavelet-mfcc features. in order to determine the best family wavelet type when combined with mfcc, we employed all family wavelet types. then, in the recognition step, we employed hmm to build the model; we evaluated its accuracy using the k-fold cross-validation method described above. the recognition results are shown in table 3. table 3: recognition result of wavelet-mfcc for each of wavelet family exp (added terms): bior – wavelet biorthogonal, coif – wavelet coiflet, db – wavelet daubechies, sym – wavelet symlet, rbio – wavelet reverse biorthogonal, dmey – wavelet dmeyer 4.3 gender influence in speaker recognition in this research, we also experimented to find out the influence of the speaker’s gender in the recognition system, and there were two focuses on evaluating the influence of gender. first was the influence of gender on each of the wavelet families as a coefficient detail. second was the influence of gender on each of extracting method, such as mfcc, mfcc + delta, and mfcc + delta-delta. in the first condition, as shown in table 4, we obtained better average accuracy for female speakers than the male speakers for each wavelet family. the obtained average accuracy was about 96% for females and about 92% for male speakers. the low accuracy of male speakers was due to the large gap between each wavelet family's highest and lowest accuracy. the obtained gap was up to 8%. while on the female speaker, the gap type acc (%) type acc (%) type acc (%) type acc (%) type acc (%) bior 1.1 96.33 coif7 92.33 db11 94.33 db32 92.00 symlet16 93.33 bior 1.3 94.67 coif8 94.33 db12 93.67 db33 93.00 symlet17 93.67 bior 1.5 94.67 coif9 93.00 db13 93.33 db34 91.33 symlet18 93.00 bior 2.2 94.33 coif10 91.67 db14 93.67 db35 91.00 symlet19 92.67 bior 2.4 93.33 coif11 91.33 db15 92.33 db36 91.00 symlet20 94.33 bior 2.6 93.00 coif12 94.00 db16 93.00 db37 93.00 rbio1.1 96.33 bior 2.8 94.33 coif13 90.33 db17 92.67 db38 93.00 rbio1.3 94.67 bior 3.1 94.00 coif14 92.00 db18 92.33 symlet2 95.33 rbio1.5 92.67 bior 3.3 93.67 coif15 93.00 db19 93.00 symlet3 92.67 rbio2.2 95.33 bior 3.5 93.33 coif16 92.00 db20 91.67 symlet4 93.67 rbio2.4 94.00 bior 3.7 94.00 coif17 91.00 db21 91.67 symlet5 92.67 rbio2.6 92.67 bior 3.9 93.67 db1(haar) 96.67 db22 91.33 symlet6 93.67 rbio2.8 94.00 bior 4.4 93.33 db2 95.33 db23 92.33 symlet7 93.00 rbio3.1 95.33 bior 5.5 93.33 db3 93.67 db24 90.33 symlet8 92.33 rbio3.3 93.33 bior 6.8 94.00 db4 94.33 db25 93.33 symlet9 93.33 rbio3.5 93.00 coif1 95.00 db5 93.67 db26 91.33 symlet10 94.33 rbio3.7 94.67 coif2 93.33 db6 93.67 db27 91.67 symlet11 91.67 rbio3.9 93.00 coif3 92.00 db7 94.67 db28 91.33 symlet12 93.00 rbio4.4 93.67 coif4 92.67 db8 94.00 db29 92.00 symlet13 93.33 rbio5.5 92.67 coif5 95.00 db9 94.33 db30 91.33 symlet14 93.00 rbio6.8 94.00 coif6 93.33 db10 93.33 db31 92.33 symlet15 92.67 dmey 94.33 77 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 between the highest and lowest accuracy was up to 5%, where the highest accuracy was 98.17%, and the lowest was 93.00%. table 4: gender influence the wavelet families wavelet family average accuracy (%) male female max male min male max female min female daubechies 90.89 95.76 95.61 87.44 98.17 93.83 coiflet 91.19 95.11 93.50 88.00 98.17 93.17 symlet 91.49 95.80 93.50 90.22 98.17 93.00 biorthogonal 92.41 96.41 95.06 90.78 98.17 93.83 rbiorhogonal 92.24 96.58 95.11 90.22 98.17 94.83 dmeyer 92.89 96.50 92.89 92.89 96.50 96.50 average 91.85 96.03 94.28 89.93 97.89 94.19 nevertheless, from each wavelet family, it can be said that the best accuracy was obtained using wavelet daubechies. the obtained result is shown in table 3, and table 4 stated that wavelet daubechies is the best wavelet family to combine with the proposed method to create wavelet-mfcc feature extraction. in the second condition, based on the testing result in table 5, we obtained the highest average accuracy using the proposed method in male speaker recognition, where the average accuracy was 95.61%. however, for female speaker recognition, there was no difference between the methods; the average accuracy was varied for each of the methods. the accuracy of male and female speakers was influenced by the acoustical characteristic, fundamental frequency or f0, formant frequency, vocal tract length, and vocal fold. the obtained result was in line with the previous research by [29], [30]. table 5: gender influence accuracy method accuracy (%) male female proposed method (db1mfcc) 95.61 98.17 mfcc 94.00 99.00 mfcc + delta 94.50 99.00 mfcc + delta-delta 93.00 98.00 in the previous research, the recognition of male speakers gives better accuracy than for the female speakers. it was believed that the result was influenced by the f0 of females being higher than males [31]. in males, f0 was around 110 hz in the range of 100-146 hz, while in females, around 200 hz in the range of 188-221 hz. 4.4 comparison of other features extraction method table 6 shows the comparison of the proposed method compared to conventional mfcc, mfcc + delta, and mfcc + delta-delta. table 6: comparison of features extraction method methods accuracy (%) proposed method (db1 mfcc) 96.67 mfcc 95.67 mfcc + delta 96.00 mfcc + delta-delta 94.67 78 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 in this research, we proposed using a detail coefficient as a feature in the combination of wavelet-mfcc feature extraction for speaker recognition. the voice that we heard was obtained from the combination of voice sound, resonance, and articulation. the voice sound was the output of the vocal fold vibration; the voice sound was amplified and modified by the vocal tract resonator. the vocal tract resonator includes the throat, mouth cavity, and nasal passage. this resonator makes the sound that distinguishes individual persons. whereas articulation is the modified process to produce recognizable words. the resonator can distinguish each person because the produced sound has different variability frequencies. in male and female sounds, the variability lies in high frequency. specifically, the speaker’s identity lies in the area where the formant frequency is higher [32]. the higher frequency is generally analogized as noise, but in the case of sound, the noise component plays an essential role in perceiving sound quality. this noise component is usually modeled as white noise, where the spectrum is not flat and portrays the different shapes of spectral [33]. it is affected by the glottal opening, flow rate, and the shape of the vocal tract. the interaction among spectral shape, the relative level of harmonic, and noise energy in the sound source influence the perception of the quality of the sound. hence, it can be concluded that the use of wavelet decomposition separates the voice sound and resonance where the voice sound lies in the approximation coefficient, whereas the resonance, which is the speaker identity, lies in the detail coefficient. 5. conclusion in this research, we employed wavelet-mfcc to extract the features from the sound signal and hmm for recognition. there were several aims in this research. first, determining the best sub-band coefficient. according to the experiment result, the best sub-band was sub-band detail in one level decomposition, where the accuracy was 95%. once we found out the best sub-band, the second aim was to determine the best wavelet family combined with mfcc. from 105 types of wavelet families, we obtained the best wavelet family, daubechies order 1 (haar), where the accuracy was 96.67%. although the gender type of the speaker also influenced the type of wavelet family, we experimented to find the best wavelet family for recognition of each gender. based on the result, we concluded that the wavelet daubechies was the best wavelet family to extract the features on both genders. therefore, it can be said that from the obtained result, wavelet daubechies was the best wavelet coefficient to combine with mfcc. then, we compared the proposed method to other methods such as conventional mfcc, mfcc + delta, and mfcc + delta-delta. from the comparison, we obtained that the best method for feature extraction was the combination of db1 – mfcc. for future research, the proposed method needs to be evaluated using more speaker datasets and in noisy environments so the system's robustness can be seen. in addition, the proposed method needs to be investigated in the speaker-independent recognition system, emotion, gender, and speech recognition. finally, real-time speaker recognition for the proposed method also needs to investigated further. acknowledgement this work was supported by the ministry of research and technology of the republic of indonesia through the applied research scheme. 79 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 references [1] tirumala ss, shahamiri sr, garhwal as, wang r. (2017) speaker identification features extraction methods: a systematic review. expert systems with applications, 90:250-271. doi:10.1016/j.eswa.2017.08.015 [2] alsulaiman m, mahmood a, muhammad g. (2017) speaker recognition based on arabic phonemes. speech communication, 86:42-51. doi:10.1016/j.specom.2016.11.004 [3] shaver, clark d. and acken, john m. (2016) a brief review of speaker recognition technology. electrical and computer engineering faculty publications and presentations. 350. http://pdxscholar.library.pdx.edu/ece_fac/350 [4] wei, y. (2020). adaptive speaker recognition based on hidden markov model parameter optimization. ieee access, 8: 34942-34948. doi:10.1109/access.2020.2972511 [5] huang, xuedong and acero, alex, hon h-w. (2001) spoken language processing: a guide to theory, algorithm, and system development. upper saddle river, nj, united states. [6] zhao x, wang y, wang d. robust. (2014) speaker identification in noisy and reverberant conditions. icassp, ieee int conf acoust speech signal process – proc, 22(4):3997-4001. doi:10.1109/icassp.2014.6854352 [7] ayoub b, jamal k, arsalane z. (2016) gammatone frequency cepstral coefficients for speaker identification over voip networks. 2016 int conf inf technol organ dev it4od. doi:10.1109/it4od.2016.7479293 [8] daqrouq k, al azzawi ky. (2012) average framing linear prediction coding with wavelet transform for text-independent speaker identification system. comput electr eng, 38(6):14671479. doi:10.1016/j.compeleceng.2012.04.014 [9] amelia f, gunawan d. (2019) dwt-mfcc method for speaker recognition system with noise. 7th int conf smart comput commun icscc 2019, pp.1-5. doi:10.1109/icscc.2019.8843660 [10] lung sy. (2007) efficient text independent speaker recognition with wavelet feature selection based multilayered neural network using supervised learning algorithm. pattern recognit, 40(12):3616-3620. doi:10.1016/j.patcog.2007.05.010 [11] wu j da, lin bf. (2009) speaker identification using discrete wavelet packet transform technique with irregular decomposition. expert syst appl, 36(2 part 2):3136-3143. doi:10.1016/j.eswa.2008.01.038 [12] kumar p, chandra m. (2011) hybrid of wavelet and mfcc features for speaker verification. proc 2011 world congr inf commun technol wict 2011, pp. 1150-1154. doi:10.1109/wict.2011.6141410 [13] turner c, joseph aa. (2015) wavelet packet and mel-frequency cepstral coefficientsbased feature extraction method for speaker identification. procedia comput sci, 61:416421. doi:10.1016/j.procs.2015.09.177 [14] kishore kvk, sharrefaunnisa s, venkatramaphanikumar s. (2015). an efficient text dependent speaker recognition using fusion of mfcc and sbc. 1st int conf futur trends comput anal knowl manag ablaze 2015, (ablaze):18-22. doi:10.1109/ablaze.2015.7154960 [15] rathor s, jadon rs. (2017) text indpendent speaker recognition using wavelet cepstral coefficient and butter worth filter. 8th int conf comput commun netw technol icccn, pp.1-5. doi:10.1109/icccnt.2017.8204079 [16] badrit n, tadjt abc, gargourt c, ramachandrant k. (2002) on the use of wavelet and fourier transforms for speaker verification. the 2002 45th midwest symposium on circuits and systems, 2002. mwscas-2002., tulsa, ok, usa, pp. iii-344. doi: 10.1109/mwscas.2002.1187043 [17] adam tb, salam ms, gunawan ts. (2013) wavelet based cepstral coefficients for neural network speech recognition. ieee icsipa 2013 ieee int conf signal image process appl, pp.447-451. doi:10.1109/icsipa.2013.6708048 80 iium engineering journal, vol. 23, no. 1, 2022 hidayat et al. https://doi.org/10.31436/iiumej.v23i1.1760 [18] rozario ms, thomas a, mathew d. (2019) performance comparison of multiple speech features for speaker recognition using artifical neural network. 9th international conference on advances in computing and communication (icacc), kochi, india, pp. 234239. doi: 10.1109/icacc48162.2019.8986182 19. [19] hidayat s. hidayat r. adji tb. (2016) speech recognition of kv-patterned indonesian syllable using mfcc, wavelet and hmm. kursor, 8(2):67. doi:10.28961/kursor.v8i2.63 [20] sharma g, umapathy k, krishnan s. (2020) trends in audio signal feature extraction methods. appl acoust. 158:107020. doi:10.1016/j.apacoust.2019.107020 [21] sunitha c, chandra e. (2015) speaker recognition using mfcc and improved weighted vector quantization algorithm. international journal of engineering and technology, 7(5):1685-1692. [22] adam tb, salam ms, gunawan ts. (2013) wavelet cepstral coefficients for isolated speech recognition. telkomnika, 11(5):2731-2738. doi:10.11591/telkomnika.v11i5.2510 [23] hidayat s, hasanah u, rizal aa. (2016) algoritma penghapus derau / silence dan penentuan endpoint dengan nilai ambang terbobot untuk sinyal suara. in: seminar nasional aptikom (semnastikom), pp.320-323. [24] sekkate s, khalil m, adib a. (2018) fusing wavelet and short-term features for speaker identification in noisy environment. int conf intell syst comput vision, iscv 2018. may:18. doi:10.1109/isacv.2018.8354030 [25] jahangir, r. teh, yw. memon, na. mujtaba, g. zareei, m. ishtiaq, u. akhtar, mz. ali, i. (2020) text-independent speaker identification through feature fusion and deep neural network. ieee access, 8: 32187-32202. doi:10.1109/access.2020.2973541 [26] el-henawy im, khedr wi, elkomy om, abdalla ami. (2014) recognition of phonetic arabic figures via wavelet based mel frequency cepstrum using hmms. hbrc j, 10(1):49-54. doi:10.1016/j.hbrcj.2013.09.003 [27] maurya a, kumar d, agarwal rk. (2018) speaker recognition for hindi speech signal using mfcc-gmm approach. procedia comput sci, 125:880-887. doi:10.1016/j.procs.2017.12.112 [28] picard rr, cook rd. (1984). cross-validation of regression models. j am stat assoc, 79(387):575-583. doi:10.2307/2288403 [29] li l, zheng tf. (2015) gender-dependent feature extraction for speaker recognition. in ieee china summit and international conference on signal and information processing, chinasip 2015 proceedings, pp 509-513. doi:10.1109/chinasip.2015.7230455 [30] kanervisto a, vestman v, sahidullah m, hautamaki v, kinnunen t. (2017) effects of gender information in text-independent and text-dependent speaker verification. icassp, ieee int conf acoust speech signal process proc., pp. 5360-5364. doi:10.1109/icassp.2017.7953180 [31] titze ir. (1989) physiologic and acoustic differences between male and female voices. j acoust soc am, 85:1699-1707. doi:https://doi.org/10.1121/1.397959 [32] lee y, keating p, kreiman j. (2019) acoustic voice variation within and between speakers. j acoust soc am, 146(3):1568-1579. doi:10.1121/1.5125134 [33] zhang z. (2016) mechanics of human voice production and control. j acoust soc am, 140(4):2614-2635. doi:10.1121/1.4964509 81 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 comparative study on degradation of polylactic acid/ syzygium aromaticum composites ageing in outdoor environment and soil burial salina budin*, normariah che maideen, koay mei hyie, hamid yussof and halim ghafar school of mechanical engineering, college of engineering, universiti teknologi mara, cawangan pulau pinang, jalan permatang pauh, 13500 penang, malaysia *corresponding author: salinabudin@uitm.edu.my (received: 28th july 2021; accepted: 24th september 2021; published on-line: 4thjanuary 2022) abstract: major environmental problems resulting from non-degradable components of plastic wastes have awakened great attention to bioplastic as an alternative material. among various bioplastic materials, polylactic acid (pla) is recognised as a promising material especially as a food packaging material. the development of pla composites using various fillers has extensively been in focus in order to preserve the high quality, safety, and extended shelf-life of packed food. among the interesting fillers is syzygium aromaticum (sa). sa, also known as clove, has biological activities such as antibacterial, antifungal, insecticidal, and antioxidant properties. this work investigated the effects of sa filler on the degradations of virgin pla (vpla) and recycled pla (rpla). the vpla/sa composites and rpla/sa composites were prepared using the solvent casting method. the content of sa filler varied in the range of 0 to 20 wt%. the composites were aged in outdoor environment and soil burial. the results revealed that the degradation rate was increased with the increase of sa filler in both ageing environments. after 10 weeks of ageing in the outdoor environment, the weight loss of vpla/sa composites and rpla/sa composites containing 20 wt% of sa were 7.7% and 12.8% respectively. whereas in soil burial, the weight loss of vpla/sa composites and rpla/sa composites with similar sa content were 25.6% and 38.3% respectively. the degradation rate was observed to be more rapid in the soil burial as compared to the outdoor environment. comparably, rpla and rpla/sa composites experienced higher degradation rates than vpla and vpla/sa composites. the degradation rate was consistent with scanning electron microscope (sem) images which observed the formation of holes, cavities, cleavages, and grooves on the surfaces of the samples. thermogravimetric analysis (tga) results on aged samples showed that vpla/sa composites and rpla/sa composites that had aged in soil burial decomposed at lower temperatures. the shortening of degradation time of the vpla/sa composites and rpla/sa composites could increase their potential to be used as food packaging materials. abstrak: masalah utama terhadap alam sekitar yang disebabkan oleh sisa plastik yang sukar terurai, telah menarik perhatian terhadap bioplastik sebagai bahan alternatif. di antara pelbagai jenis bahan bioplastik sedia ada, asid polilaktik(pla) dilihat sebagai bahan yang paling sesuai terutamanya sebagai bahan pembungkusan makanan. perkembangan di dalam penghasilan komposit asid polilaktik yang ditambah dengan pelbagai bahan pengisi telah menjadi fokus terutamanya bagi tujuan meningkatkan kualiti, kesegaran dan jangka hayat makanan. salah satu pengisi yang mendapat perhatian adalah syzygium aromaticum (sa). sa yang juga dikenali sebagai bunga cengkeh mempunyai aktiviti biologi, seperti sifat antibakteria, antijamur, racun serangga dan antioksidan yang tinggi. didalam kajian 396 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 ini, siasatan terhadap kesan penambahan sa terhadap penguraian pla asal (vpla) dan pla kitar semula (vpla). komposit vpla/sa dan komposit rpla/sa disediakan dengan menggunakan kaedah pelarutan pelarut. kandungan pengisi sa adalah didalam julat 0 – 20% mengikut berat. komposit tersebut dibiarkan menua didalam persekitaran luaran dan didalam tanah. keputusan kajian mendapati bahawa kadar penguraian semakin meningkat dengan penambahan peratus berat bahan pengisi sa setelah melalui penuaan didalam kedua-dua persekitaran. setelah penuaan selama10 minggu di dalam persekiran luaran, pengurang berat komposit vpla/sa dan komposit rpla/sa yang mengandungi 20 wt% sa adalah 7.7% dan 12.8%. manakala bagi penuaan didalam tanah, pengurangan berat komposit vpla/sa dan komposit rpla/sa dengan kandungan sa yang sama masing-masing adalah 25.6% dan 38.3%. kadar penguraian diperhatikan lebih cepat bagi penuan didalam tanah dibandingkan dengan penuaan didalam persekitaran luaran. disamping itu, rpla dan komposit rpla/sa mengalami kadar penguraian yang lebih tinggi berbanding vpla dan komposit vpla/sa. kadar penguraian adalah konsisten dengan imej yang dihasilkan oleh imbasan mikroskop elektron (sem) dimana dapat dilihat pembentukan lubang, rongga, pembelahan dan alur di permukaan sampel. hasil analisis termogravimetri (tga) terhadap sampel yang telah dituakan menunjukkan bahawa komposit vpla/sa dan komposit rpla/sa yang melalui penuaan didalam tanah terurai pada suhu yang lebih rendah. tempoh penguraian komposit vpla/sa dan komposit rpla/sa yang lebih pendek ini meningkatkan potensi penggunaannya komposit ini sebagai bahan pembungkusan makanan. keywords: degradation; virgin pla; recycled pla; outdoor environment; soil burial 1. introduction huge employment of plastic materials in various fields is derived from its excellent properties such as its light weight, flexibility, strength, transparency, permeability, and costeffectiveness [1]. approximately 50% of plastics are used for single-use disposable applications, such as packaging, agricultural films, and disposable consumer items [2]. these have led to the continuous generation of bulk plastic wastes that have ended with environmental and marine issues. it has been reported that at least 180 kinds of marine organisms have been detected consuming plastics by mistake ranging from whales to planktons [3]. most commercial plastics are non-biodegradable, highly resistant to microbial attacks, and require a longer time to degrade, which will be approximately around 10 to 1000 years. the issue related to plastic waste management and its disposal is seen to be the main inspiration for the commercialisation of bioplastics. bioplastics are plastics materials produced from renewable biomass sources, such as vegetable fats and oils, corn starch, straw, woodchips, sawdust, and recycled food waste. various bioplastic materials are available such as polyhydroxy-alkanoates (pha) and poly-3-hydroxybutyrate (phb). among these, polylactic acid (pla) is the most popular bioplastic which has higher potential in replacing fossil-based commercial plastic. pla is biobased and easily compostable with a relatively higher production produced by fermentation from renewable substrates such as sugar, starch, sugarcane, corn, beets, rice, and carbohydrates from other crops [4,5]. as a bioplastic material, pla completely decomposes to co2 and h2o as final degradation products without contributing any harmful effects to the environment. moreover, it was reported that pla will take at least 2 years to be fully degraded under normal circumstances [3]. both the chemical and physical properties of pla influence the mechanisms of biodegradation. the surface area, hydrophilic or hydrophobic properties, chemical structure, molecular weight, glass transition temperature, melting temperature, modulus of elasticity, crystallinity, and crystal structure of polymers play important roles in the biodegradation 397 https://en.wikipedia.org/wiki/plastic https://en.wikipedia.org/wiki/biomass https://en.wikipedia.org/wiki/vegetable_oil https://en.wikipedia.org/wiki/corn_starch https://en.wikipedia.org/wiki/corn_starch https://en.wikipedia.org/wiki/straw https://en.wikipedia.org/wiki/woodchips https://en.wikipedia.org/wiki/sawdust https://en.wikipedia.org/wiki/food_waste iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 processes [6]. degradation of pla is primarily due to the hydrolysis of the ester linkages which occurs more or less randomly along the backbone of the polymer. in the presence of water, the hydrolysis takes place via a diffusion reaction mechanism whereby water penetrates the polymer matrix and simultaneously converts the long polymer chain to low molecular weight, water soluble oligomers, and finally the given monomer [7]. it is noteworthy that under uv irradiation and light exposure, the hydrolysis of the pla molecular chain is accomplished through photocleavage, photolysis, and photooxidation [8]. photolysis leads to chain scission especially in the c–o bonds of the pla ester backbone structure through the absorption of a photon while photocleavage takes place at the ester group and ethylidene group next to the ester oxygen in the pla structure leading to chain cleavage and the formation of c=c double bonds and carboxylic acid –oh stretching. photooxidation of pla results in the formation of hydroperoxide derivative and its subsequent degradation into carboxylic acid and diketone end groups [9]. the presence of moisture in the environment would further promote the hydrolysis degradation of pla. pla has been recognised by the united states food and drug administration (fda) as a safe material for food packaging [10]. however, brittleness, low heat distortion temperature, and poor antioxidant, antibacterial, and barrier properties have only limited its application [11]. in order to have high quality, safe packaging and extend the shelf-life of packed food, the packaging material must be able to reduce or retard the growth of microorganisms and inhibit the process of lipid oxidation [12]. the addition of antibacterial and antioxidant agents in pla substrate is one of the rational solutions. moreover, the addition of filler in pla substrate would also accelerate the degradation and decomposition of the pla. a higher degradation rate would assist in accelerating pla waste degradation, especially for single-use products. several efforts have been devoted to the modifications of pla by incorporating various fillers in order to improve those properties. many studies on fillers reacted as antioxidant, antimicrobial, antibacterial, and degradation accelerator agents have been conducted with fillers such as chitosan, cinnamaldehyde, syzygium aromaticum (clove), melissa officinalis l. (lemon balm), salvia officinalis (sage), zinc oxide (zno), titanium oxide (tio), magnesium oxide (mgo) and calcium carbonate [13-17]. besides that, past research has been investigated globally in order to improve the desirable properties for food packaging applications. zhang et al. [18] synthesised pla/cinnamaldehyde (ca) films. the findings proved that the morphology, crystallinity, oxygen resistance, water resistance, and tensile strength properties were improved. the antibacterial activity against escherichia coli and monocytogenes was 100%. similar results were also published by cui et al. [19]. on the other hand, ahmed et al. [11] developed pla/ peg/pcl films loaded with zno and sa/clove essential oil (ceo). the results showed that the reinforcement of zno and ceo were significant in the mechanical properties and structural and barrier properties of the films. meanwhile, chen et al. [12] investigated the effects of polyvinyl alcohol (pva) film with an addition of clove oil (co). it was concluded that the incorporation of co in pva films had demonstrated effective antimicrobial and antioxidant activities. however, the mechanical properties, oxygen barrier properties, and thermal stability of the films were reduced. techawinyutham et al. [20] also reported on the improvement of tensile properties and antibacterial activity with the addition of capsicum oleoresin impregnated porous silica (sico). the authors have remarked that the tensile properties, thermal stability, and rheological properties were reduced when the films underwent ageing in accelerated weathering for 520 hours. however, the aged samples showed good antimicrobial activity against bacteria. in other research done by varsavas and kaynak [21], the mechanical properties of neat pla and pla/glass fibre composite (pla/gf) under outdoor conditions 398 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 were evaluated. the samples were exposed to accelerated weathering conditions of both uv-irradiation and moisture cycles. the authors observed that the decreased in mechanical properties of neat pla was more significant as compared to pla/gf composite. after 400 hours of ageing, the reduction in the tensile strength of the neat pla specimen was as much as 92%, while the reduction for the pla/gf specimen was only 34%. in other works, fathima et al. [22] have developed pla/chitosan films to evaluate the antimicrobial activity of the films against e. coli and listeria monocytogenes. the results revealed that incorporation of chitosan in pla was capable of producing packaging films with good mechanical, barrier, and antimicrobial properties. on the other hand, hadidi et al. [23] reported that pla composites with chitosan nanoparticles encapsulated with clove essential oil exhibited higher antioxidant activity as compared to unencapsulated chitosan nanoparticles. similar results were supported by han et al. [24], which observed that there was a significant improvement in the antibacterial activity of the films against e-coli. the authors also reported on the degradation rate of pla/chitosan films ageing in buffer solutions at 0.01 m, ph 7.4 and 37 °c for 12 weeks. the degradation rate increased as the amount of chitosan increased. the weight loss of pla/cs films was expected to reach up to nearly 45% after 3 months. another research done by vasile et al. [25] examined the soil burial degradation behaviour of pla/tributyl o-acetyl citrate/chitosan (pla/atbc/cs) bio-composites. the results proved that there was a small loss in the samples’ weight after 150 days buried in the soil. however, significant changes were reported on mechanical, thermal, and surface properties. the presence of cs increased the hydrophilicity of biocomposite surfaces and favoured the interaction with moisture, hence promoted an attack by microorganisms. wang et al. [26] developed pla nanocomposite films combined with cnc-zno. the authors reported that the addition of cnc-zno in the pla matrix improved the crystallisation ability, interaction between nanofiller and matrix, uv-shielding performance, and degradation ability. it was reported that after 110 days buried in soil, the weight loss of pure pla and pla/25% cnc-zno were 9% and 28%, respectively. similar trends were reported by rajesh et al. [27]. the authors reported that there was 1.26% of weight loss for neat pla after 90 days buried in soil and 15.2% of weight loss after the pla had been loaded with 25% of sisal fibre. in a separate study, lv et al. [28] looked into the degradation behaviour of pla that was blended with starch and wood flours under soil burial. the outcomes proved that the increase of starch in the pla matrix improved the degradation rate. comparable results were remarked by zuo et al. [29] whereby a significant increment in weight loss was observed after adding starch to the pla matrix. therefore, this research aims to study the effects of sa filler on the degradation of virgin-pla (vpla) and recycled-pla (rpla) ageing in outdoor environment and soil burial. excellent biological properties including antioxidant, antimicrobial, antiseptic, pesticide, analgesic, and anticarcinogenic activities have positioned sa as a potential filler in pla for various applications such as in food, sanitary, biomedical, pharmaceutical, active packaging, and cosmetics industries [23]. although many studies have been reported on the performance of sa as antioxidant and antimicrobial agents, limited outcomes on the degradations of pla/sa composites have been published. thus, it is essential to investigate the degradation behaviours of pla/sa composites under the outdoor environment and soil burial that are the common plastic waste disposal environments. the weight loss, surface morphology, and thermal stability of pla/sa composites after 10 weeks of ageing are examined thoroughly in this study. 399 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 2. methodology 2.1 material vpla pellets were purchased from a local supplier (vistec technology services) in an injection moulding grade, 3251d natureworks ingeo™ (china). the pellets were cylindrical, with an average length and diameter of 3 mm. on the contrary, rpla was retrieved from the 1st cycle of injection moulding wastes. the wastes were mostly collected from runners and crushed using a grinding machine. the recycled ground materials were in angular shape with an average size of less than 4 mm. the sa powder was purchased from a local hypermarket (mydin hypermarket). the size of the powder was in the range of 100 to 200 µm. the size of the powder is measured using energy dispersive x-ray analyzer (edx). 2.2 sample preparation pla/sa composites were prepared through the solvent casting method at various composition contents of pla and sa fillers. five different combinations of blends were prepared for both virgin and recycled pla/sa composites. the list of the composition of the samples that were prepared is summarized in table 1. the amount of sa filler varied in the range of 0 wt% to 20 wt% in 5 wt% increments. the pla resin was pre-conditioned in a drying oven at 70 °c for 12 hours to reduce the moisture content prior to use. pla resin was then dissolved in dichloromethane (dcm). after being completely dissolved, sa filler was added to the solution. in order to obtain a homogenous pla/sa blend, the mixture was continuously stirred using a magnetic stirrer for 30 minutes. the mixture was cast onto a glass plate and dried at room temperature for 24 hours. after drying the pla/sa composites, the substrates were peeled off. the thickness of the pla/sa composites substrates was in the range of 0.5 to 0.9 mm and was cut into 25 x 60 mm sizes. for each composition, six samples were prepared. table 1: sample composition sample composition vpla rpla vpla (wt%) sa (wt%) rpla (wt%) sa (wt%) 1 100 0 100 0 2 95 5 95 5 3 90 10 90 10 4 85 15 85 15 5 80 20 80 20 2.3 ageing condition the degradation of vpla/sa composites and rpla/sa composites was performed in outdoor environment and soil burial. under the outdoor environment ageing, the samples were placed on the roof in order to attain optimum exposure. the geographic parameters of the test site were at the latitude of 5.4˚n, longitude of 100.4˚ e, and altitude of 10 m. the temperature and humidity were monitored weekly within the range of 24 °c to 35 °c and 47% to 84%, respectively. the average normal sun irradiation was 298.9 w/m2 [30]. for soil burial ageing, the samples were buried in organic soil that was placed in a plastic container with a depth of 2 inches from the soil surface. the ph and the humidity of the soil were 6.8 ± 0.5 and 60 ± 10%, respectively. the average soil temperature was 28.5 400 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 ± 1.0 °c. the soil was regularly watered with tap water to ensure the humidity of the soil was consistent. the ageing took place for 10 weeks. the weight of the samples was measured before and after ageing using an analytical balance. after 10 weeks of ageing in the outdoor environment, the samples were subjected to a drying process in a hot oven at a temperature of 70 °c for 3 to 4 hours before the final weight was measured. for samples ageing in soil burial, the samples were dug and rinsed with tap water in order to remove adherent soil. the samples were then dried in a hot oven at a temperature of 70 °c for 24 hours prior to final weight measurement. a longer drying time was required for samples ageing in soil burial due to excessive water content in the samples. the percentage of weight loss for each sample was calculated using eq. (1). % weight loss = (wf -wi)/wi x 100% (1) where wi is the weight of samples before ageing, and wf is the weight of samples after ageing. 2.4 surface morphology the surface morphology of the pla/sa composites after ageing was observed using a hitachi tm3030 scanning electron microscope (sem) at a constant accelerated voltage of 15 kv. the images were captured under a magnification of 100x. 2.5 thermogravimetric analysis the thermal stability of pla/sa composites was analysed using ta instrument, sdtq600 thermogravimetric analysis (tga). the samples were heated from 30° c to 600 °c at a heating rate of 10 °c/min in a nitrogen environment. the flow rate of nitrogen gas was set at 20 ml/min. initial degradation temperature, ti and maximum degradation temperature, tmax (which corresponded to the weight loss) were measured from the thermogram. ti, is the temperature where the weight loss is started to gradually decline, whereas tmax is the temperature where the maximum weight loss occurred. 3. results and discussion 3.1 weight loss the percentage of weight loss after ageing in outdoor environment and soil burial is summarized in table 2. the data shows the percentage of weight loss is increased with the increment of wt% of sa filler. figure 1 represents the plots of weight loss of vpla/sa composites and rpla/sa composites at various contents of sa filler after 10 weeks of ageing in outdoor environment and soil burial. in both ageing environments (outdoor environments and soil burial) it was interesting to observe that the degradation rates of vpla/sa composites were faster than the 100 wt% vpla. a similar trend was noted for rpla/sa composites, which revealed a higher degradation rate compared with the degradation rate of 100 wt% rpla. the weight loss for 100 wt% vpla after ageing in outdoor environment and soil burial were 3% and 13.2% whereas for 100 wt% rpla after ageing in outdoor environment and soil burial were 3.4% and 14.5%. after being incorporated with 20 wt% of sa filler, the weight loss for vpla/sa composites after ageing in outdoor environment and soil burial had increased to 7.7% and 25.6% respectively. 401 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 table 2: weight loss after ageing in outdoor environment and soil burial sample composition weight loss (%) outdoor environment soil burial 1 100 wt% vpla 3.0 13.2 2 95 wt% vpla + 5 wt% sa 3.5 14.5 3 90 wt% vpla + 10 wt% sa 4.5 16.2 4 85 wt% vpla + 15 wt% sa 6.5 21.9 5 80 wt% vpla + 20 wt% sa 7.7 25.6 6 100 wt% rpla 3.4 14.5 5 95 wt% rpla + 5 wt% sa 5.3 16.1 8 90 wt% rpla + 10 wt% sa 6.8 21.6 9 85 wt% rpla + 15 wt% sa 7.7 29.3 10 80 wt% rpla + 20 wt% sa 12.8 38.2 20151050 50 40 30 20 10 0 filler (%) w e ig h t l o s s ( % ) vpla /sa outdoor rpla /sa outdoor vpla /sa soil rpla /sa soil fig 1: plots of sa filler content versus weight loss. while for rpla/sa composites with 20 wt% of sa filler, the weight loss after ageing in outdoor environment and soil burial had increased to 12.8% and 38.2%, respectively. the lowest weight loss exhibited in 100 wt% vpla and 100 wt% rpla was due to its low hygroscopic activity that was attributed to a slower rate of hydrolysis at lower temperatures and to the low degradation capacity of pla microorganisms in composting [31]. when fillers were added to the pla matrix, the interface between filler particles and matrix served as a leading path for the water molecules to penetrate the samples while simultaneously breaking the long polymer chain to low molecular weight. as the content of the filler increased, the interface surface was also increased and consequently accelerated the polymer chain scission and degradation process. the results were noteworthy as they revealed that the degradation rates were more rapid in the soil burial as compared in the outdoor environment. the excessive volume of water in the soil introduced higher water diffusion into the composites, which consequently promoted active hydrolysis degradation of the composites. the presence of microorganisms in the soil would additionally enhance the degradation process of the composites. in contrast, when pla/sa composites were exposed to the outdoor environment, it was known that uv irradiation, heat, and moisture from the atmosphere during ageing process had led to the deterioration in the polymer molecular chain via chain scission reactions through 402 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 photolysis and hydrolysis degradations. the photodegradation and moisture penetration started at the exposed surface followed by propagation through the interior body. it was also noticeable that the weight loss for rpla/sa composites was higher as compared with vpla/sa composites. it was well known that due to shear forces and thermal impact encountered during the processing, rpla exhibited a shorter molecular chain with lower molecular weight [32]. the chain scissions during the processing were reported by chavez-montes et al. [33], in which the authors observed around 30% to 40% of reductions in average molecular weight for virgin pla after undergoing the single stage of injection moulding. the smaller molecular weight would intensively accelerate the degradation process upon ageing in outdoor environment and soil burial. table 3: comparison of weight loss on various pla composites no ageing environment composition weight loss (%) references 1 soil burial 110 days pla 9 [26] pla/15% cnc-zno 28 2 soil burial 90 days pla 1.26 [27] pla/25% sisal fiber 15.2 3 soil burial 105 days pla <1% <1 [28] pla/9% starch/21%wood floor 6 pla/15%starch/15%wood floor 9 pla/21%starch/9%wood floor 12 4 soil burial 120 days pla 0.102 [29] pla/starch 27.11 5 soil burial 18 days pla 18.1 [34] pla/coir fiber 22.6 6 outdoor environment 10 weeks (70 days) 100 wt% vpla 3 present work vpla/20 wt% sa 7.7 100 wt% rpla 3.4 rpla/20 wt%sa 12.8 7 soil burial 10 weeks (70 days) 100 wt% vpla 13.2 present work vpla/20 wt% sa 25.6 100 wt% rpla 14.5 rpla/20 wt%sa 38.2 the comparison between degradation of various pla composites from previous works and present works is listed in table 3. there was not much information related to weight loss in the outdoor environment that was currently available. similarly, the degradation of rpla and rpla composites was also rarely reported. in general, the findings from this work were consistent with the previous findings. the dissimilar percentage in mechanical properties reduction could be explained through the divergent variations in soil conditions such as temperature, humidity, and ph of the soil. the types of microorganisms in the soil also highly affected the degradation rate. the shorter degradation time of the pla/sa composites obtained from this study have increased its potential to be used as food packaging material. 403 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 3.2 surface morphology the surface morphology was examined using sem. before ageing, the surfaces of the vpla/sa composites and rpla/sa composites were smooth. the sa fillers were evenly dispersed in the pla matrix. after 10 weeks of ageing in outdoor weathering and soil burial, the surfaces were observed to be eroded with multiple formations of voids, cavities, cleavages, and grooves. it was also noted that the aged samples were more brittle and easily broken. these might be due to the recrystallisation of pla/sa composites during ageing process. the comparison of the surface morphology of vpla/sa composites after ageing in outdoor environment and soil burial is shown in fig. 2. as demonstrated in fig. 2a and 2b, in both environments, vpla did not show any significant macroscopic alternations on the surfaces as the surfaces were still compact and tight with the presence of minimum voids. this was due to its poor hydrophilic characteristic which had hindered the penetration of water [35]. the number of voids on soil burial samples was more discernible as compared to samples that aged in the outdoor environment. when 5 wt% of sa fillers were added into the vpla matrix, the number of voids increased and the size of the voids was enlarged (as seen in fig. 2c and 2d). as the amount of sa fillers increased to 20 wt%, the surfaces of vpla/sa composites were seriously eroded with multiple formations of cavities, cleavages, and grooves as illustrated in fig. 2g and 2h. the observations on the surface morphologies were consistent with the weight loss findings. a similar pattern was observed on rpla/sa composites. as shown in fig. 3a and 3b, after the ageing processes in outdoor environment and soil burial, numerous voids were present. the presence of sa fillers in the composites had accelerated the formations of voids and cavities. with the increase of sa fillers, the damages on surface morphologies were gradually expanded. as shown in fig. 3c until 3h, the number and size of voids and cavities were increased with increasing of wt% of sa fillers. the presence of voids and cavities indicated that the composites have degraded, and these explained the reductions in weight. similarly, it was seen that the formations of voids and cavities were more significant on the samples that aged through soil burial as compared to the samples that aged under outdoor environment. in the soil burial degradation, the composites were subjected to hydrolysis degradation under the conditions of water and microorganisms while in the outdoor environment, degradation was induced through uv irradiation, photo-thermal factors, and moisture. the degradations from these resources produced ruptures in the molecular chain, reduced the interfacial adhesion between fillers and pla matrix, and finally led to the disintegration and fragmentation of the composites. 3.3 thermogravimetric analysis (tga) thermal stabilities of vpla/sa composites and rpla/sa composites after ageing were evaluated through thermogravimetric analysis (tga). the tga curves for vpla/sa composites and rpla/sa composites are shown in fig. 4. the curves clearly indicate that the composites had undergone a normal single-step thermal degradation process. 404 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 fig. 2: surface morphologies of vpla/sa composites with varying sa filler composition after 10 weeks of ageing in outdoor environment and soil burial (a-b) 0 wt%, (c-d) 5 wt%, (e-f) 10 wt%, (g-h) 15 wt%, (i-j) 20 wt% . 405 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 fig. 3: surface morphologies of rpla/sa composites with varying sa filler composition after 10 weeks of ageing in outdoor environment and soil burial (a-b) 0 wt%, (c-d) 5 wt%, (e-f) 10 wt%, (g-h) 15 wt%, (i-j) 20 wt%. 406 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 fig. 4: thermogravimetric curves of (a) vpla/sa composites and (b) rpla/sa composites. table 4 summarized the initial degradation temperature (ti) and maximum degradation temperature (tmax) for vpla/sa composites and rpla/sa composites with the addition of 10 wt% and 20 wt% sa fillers after ageing in outdoor environment and soil burial. ti and tmax for vpla and rpla before ageing were also included. before ageing, the thermal degradations for vpla and rpla started around 290 °c. a slight decrease in the initial degradation temperature for rpla was seen. the observation was reasonable since rpla experienced molecular weight reduction during reprocessing which naturally affected the onset of degradation temperatures. after ageing in outdoor environment, the initial degradation temperatures for vpla, rpla, and its composites were increased. an increase in ti had become more recognizable with the increment of wt% of sa fillers. an increase in the degradation temperature was probably due to the increased crystallinity during photolysis and photodegradation. as noted by lv et al. [28], during the degradation process, the crystallinity of the pla composites was increased at the initial stages and decreased as degradation progressed. a similar observation was reported by zuo et al. [29]. it was expected that the ti would be decreased with the extension of ageing time and the degradation rate would be rapidly augmented. 407 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 table 4: the initial and maximum degradation temperatures of (a) vpla/sa composites and (b) rpla/sa composites composition ti (°c) tmax (°c) composition ti (°c) tmax (°c) vpla no ageing 291 356 rpla no ageing 286 355 vpla – after ageing (outdoor) 295 359 rpla – after ageing (outdoor) 296 370 vpla – after ageing (soil) 288 347 rpla – after ageing (soil) 291 348 vpla/10sa – after ageing (outdoor) 302 371 rpla/10sa – after ageing (outdoor) 287 372 vpla/10sa-after ageing (soil) 270 335 rpla/10sa – after ageing (soil) 270 335 vpla/20sa – after ageing (outdoor) 313 370 rpla/20sa – after ageing (outdoor) 299 368 vpla/20sa – after ageing (soil) 270 335 rpla/20sa – after ageing (soil) 263 340 in contrast, the ti decreased after ageing through soil burial. the decrease in the ti was more significant with the addition of sa fillers in the pla/sa composites. the results indicated that pla/sa composites started and completely decomposed earlier when buried in soil. elevated diffusion of water molecules accelerated the polymer chain scission. the addition of hydrophilic sa fillers caused a large amount of water molecules to penetrate the composites and provided a boost to the hydrolysis degradation process. additionally, the presence of microorganisms in soil promoted the enzymatic degradation of the composites [36]. the extensive polymer chain scission during the degradation in soil burial consequently decreased the thermal stabilities of the pla/sa composites. 4. conclusions this paper reported on the biodegradations of vpla/sa composites and rpla/sa composites upon ageing in outdoor environment and soil burial. sa was employed and added as a filler in vpla matrix and rpla matrix in the range of 0 to 20 wt%. the results revealed that the degradations of pla in outdoor environment and soil burial increased when sa filler was incorporated in the pla matrix. the weight loss for 100 wt% vpla and 100 wt% rpla after 10 weeks of ageing in the outdoor environment were very low, at approximately 3% and 3.4%, respectively. when sa filler was added to the pla matrix, the weight loss was proportionally increased. the maximum weight loss was observed in pla/sa composites with 20 wt% of sa filler. the weight loss for vpla/sa composites was 7.7% while the weight loss for rpla/sa composites was 12.8%. in comparison, after 10 weeks of ageing in soil burial, the weight loss for 100 wt% vpla and 100 wt% rpla were 13.2% and 14.5% respectively. similarly, when pla was incorporated with sa filler, the degradation rate was found to be rapidly increased. the weight loss for vpla/20 wt% sa was 25.6% whereas the weight loss for rpla/20 wt% sa was 38.2%. in outdoor environment, uv irradiation, light, and heat resources from the sun, the hydrolysis degradation on the molecular chains were accomplished through photocleavage, photolysis, and photooxidation. in contrast, soil burial degradation occurred through the hydrolysis of water molecules on the ester group along the backbone of the polymer chain and enzymatic degradation produced by microorganisms in the soil. the findings proved that the degradation rate of soil burial is higher as compared with photolysis degradation in outdoor environment. 408 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 in conclusion, it can also be concluded that the rpla/sa composites exhibited higher degradation rates than vpla/sa composites. due to the shear forces and thermal impact encountered during the processing, vpla exhibited shorter molecular chain with lower molecular weight which consequently catalysed the degradation process to take place. the shortening of the degradation time of the pla/sa composites may provide a bright potential as an essential alternative for packaging materials. acknowledgement this research is supported by the faculty of mechanical engineering and faculty of chemical engineering, universiti teknologi mara, cawangan pulau pinang. references [1] ingrao c, tricase c, cholewa-wójcik a, kawecka a, rana r, siracusa v. (2017) polylactic acid trays for fresh-food packaging: a carbon footprint assessment. science of the total environment, 537:385–398. [2] hopewell j, dvorak r, kosior e. (2009) plastics recycling: challenges and opportunities. philosophical transactions of the royal society b, 364:2115-26. https://doi.org/10.1098/rstb.2008.0311 [3] wan l, li c, sun c, zhou s, zhang y. (2019) conceiving a feasible degradation model of polylactic acid-based composites through hydrolysis study to polylactic acid/wood flour/polymethyl methacrylate. composite science and technology 181:107675. https://doi.org/10.1016/j.compscitech.2019.06.002 [4] farah s, anderson dg, langer r. (2016) physical and mechanical properties of pla, and their functions in widespread applications — a comprehensive review. advanced drug delivery reviews, 107:367–392. https://doi.org/10.1016/j.addr.2016.06.012 [5] silva d, kaduri m, poley m, adir o, krinsky n, shainsky-roitman j, schroedera a. (2018) biocompatibility, biodegradation and excretion of polylactic acid (pla) in medical implants and theranostic systems. chemical engineering journal, 340:9–14. https://doi.org/10.1016/j.cej.2018.01.010 [6] tokiwa y, calabia cp, ugwu cu, aiba s. (2009) biodegradability of plastics. international journal of molecular sciencee, 10:3722-3742. doi:10.3390/ijms10093722 [7] porfyris a, vasilakos s, zotiadis c, papaspyrides c, moser k, vander schueren l, buyle g, pavlidou s, vouyiouka s. (2018) accelerated ageing and hydrolytic stabilization of poly(lactic acid) (pla) under humidity and temperature conditioning. polymer testing 68:315-332. https://doi.org/10.1016/j.polymertesting.2018.04.018 [8] kaynak c, sarı b. (2016) accelerated weathering performance of polylactide and its montmorillonite nanocomposite. applied clay science 121:86–94. https://doi.org/10.1016/j.clay.2015.12.025 [9] bocchini s, frache a. (2013) comparative study of filler influence on polylactide photooxidation. express polymer letters, 7:431–442. doi: 10.3144/expresspolymlett.2013.40 [10] risyon np, othman sh, kadir basha r, talib ra. (2020) characterization of polylactic acid/halloysite nanotubes bionanocomposite films for food packaging. food packaging and shelf life, 23:100450. [11] ahmed j, mulla m, jacob h, luciano g, bini tb, almusallam a. (2019) polylactide/poly(ɛcaproplactone)/zin oxide/clove essential oil composite antimicrobial films for scrambled egg packaging. food packaging and shelf life, 21:100355. https://doi.org/10.1016/j.fpsl.2019.100355 [12] chen c, xu z, ma y, liu j, zhang q, tang z, fu k, yang f, xie j. (2018) properties, vapourphase antimicrobial and antioxidant activities of active poly(vinyl alcohol) packaging films incorporated with clove oil. food control, 88:105-112. https://doi.org/10.1016/j.foodcont.2017.12.039 409 https://royalsocietypublishing.org/doi/full/10.1098/rstb.2008.0311 https://royalsocietypublishing.org/doi/full/10.1098/rstb.2008.0311 https://royalsocietypublishing.org/doi/full/10.1098/rstb.2008.0311 file:///c:/users/user/desktop/364:2115-26 https://doi.org/10.1098/rstb.2008.0311 https://doi.org/10.1016/j.compscitech.2019.06.002 https://doi.org/10.1016/j.addr.2016.06.012 https://doi.org/10.1016/j.cej.2018.01.010 https://doi.org/10.1016/j.polymertesting.2018.04.018 https://doi.org/10.1016/j.clay.2015.12.025 https://doi.org/10.1016/j.fpsl.2019.100355 https://doi.org/10.1016/j.foodcont.2017.12.039 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 [13] gavril gl, wrona m, bertella a, świeca m, râpă m, salafranca j, nerín c. (2019) influence of medicinal and aromatic plants into risk assessment of a new bioactive packaging based on polylactic acid (pla). food and chemical toxicology, 132:110662. https://doi.org/10.1016/j.fct.2019.110662 [14] sivakanthan s, rajendran s, gamage a, madhujith t, mani s. (2020) antioxidant and antimicrobial applications of biopolymers: a review. food research international, 126:109327. https://doi.org/10.1016/j.foodres.2020.109327 [15] rehman a, jafari sm, aadil rm, assadpour e, randhawa ma, mahmood s. (2020) development of active food packaging via incorporation of biopolymeric nanocarriers containing essential oils. trends in food science & technology, 101:106–121. https://doi.org/10.1016/j.tifs.2020.05.001 [16] hamad k, kaseem m, deri f. (2010) rheological and mechanical properties of poly(lactic acid)/polystyrene polymer blend. polymer bulletin 65:509–519. doi 10.1007/s00289-0100354-2 [17] murariu m, dubois p. (2016) pla composites: from production to properties. advanced drug delivery reviews, 107:17–46. http://dx.doi.org/10.1016/j.addr.2016.04.003 [18] zhang l, huang c, xu y, huang h, zhoa h, wang j, wang s. (2020) synthesis and characterization of antibacterial polylactic acid film incorporated with cinnamaldehyde inclusions for fruit packaging. international journal of biological macromolecules, 164:45474555. http://doi.org/10.1016/j.ijbiomac.2020.09.065 [19] cui r, jiang k, yuan m, cao j, li l, tang z, qin y. (2020) antimicrobial film based on polylactic acid and carbon nanotube for controlled cinnamaldehyde release. journal of materials research and technology, 9(5):10130-10138. https://doi.org/10.1016/j.jmrt.2020.07.016 [20] techawinyutham l, siengchin s, dangtungee r, parameswaranpillai j. (2019) influence of accelerated weathering on the thermo-mechanical, antibacterial, and rheological properties of polylactic acid incorporated with porous silica-containing varying amount of capsicum oleoresin. composites part b, 175:107108. https://doi.org/10.1016/j.compositesb.2019.107108 [21] varsavas sd, kaynak c. (2018) weathering degradation performance of pla and its glass fiber reinforced composite. material today communications, 15:344-353. https://doi.org/10.1016/j.mtcomm.2017.11.008 [22] fathima pe, panda sk, ashraf pm, varghese to, bindu j. (2018) polylactic acid/chitosan films for packaging of indian white prawn (fenneropenaeus indicus). international journal of biological macromolecules, 117:1002-1010. https://doi.org/10.1016/j.ijbiomac.2018.05.214 [23] hadidi m, pouramin s, adinepour f, haghani s, japari sm. (2020) chitosan nanoparticles loaded with clove essential oil: characterization, antioxidant and antibacterial activities. carbohydrate polymers, 236:116075. https://doi.org/10.1016/j.carbpol.2020.116075 [24] han w, ren j, xuan h, ge l. (2018) controllable degradation rates, antibacterial, free-standing and highly transparent films based on polylactic acid and chitosan. colloids and surfaces a 541:128–136. https://doi.org/10.1016/j.colsurfa.2018.01.022 [25] vasile c, pamfil d, râpă m, darie-niţă rn, mitelut ac, popa ee, popescu pa, draghici mc, popa me. (2018) study of the soil burial degradation of some pla/cs biocomposites, composites part b 142:251–262. https://doi.org/10.1016/j.compositesb.2018.01.026 [26] wang yy, yu hy, yang l, abdalkarim syh, chen wl. (2019) enhancing long-term biodegradability and uv-shielding performances of transparent polylactic acid nanocomposite films by adding cellulose nanocrystal-zinc oxide hybrids. international journal of biological macromolecules, 141:893–905. https://doi.org/10.1016/j.ijbiomac.2019.09.062 [27] rajesh g, prasad avr, gupta avssks. (2019) soil degradation characteristics of short sisal/pla composites. materials today: proceedings 18:1–7. https://doi.org/10.1016/j.matpr.2019.06.270 [28] lv s, zhang y, gu j, tan h. (2017) biodegradation behaviour and modelling of soil burial effect on degradation rate of pla blended with starch and wood flour. colloids and surfaces b: biointerfaces, 159:800-808. https://doi.org/10.1016/j.colsurfb.2017.08.056 410 https://doi.org/10.1016/j.fct.2019.110662 https://doi.org/10.1016/j.foodres.2020.109327 https://doi.org/10.1016/j.tifs.2020.05.001 http://dx.doi.org/10.1016/j.addr.2016.04.003 https://doi.org/10.1016/j.jmrt.2020.07.016 https://doi.org/10.1016/j.mtcomm.2017.11.008 https://doi.org/10.1016/j.ijbiomac.2018.05.214 https://doi.org/10.1016/j.carbpol.2020.116075 https://doi.org/10.1016/j.ijbiomac.2019.09.062 https://doi.org/10.1016/j.matpr.2019.06.270 https://doi.org/10.1016/j.colsurfb.2017.08.056 iium engineering journal, vol. 23, no. 1, 2022 budin et al. https://doi.org/10.31436/iiumej.v23i1.2138 [29] zuo yf, gu j, qiao z, tan h, cao j, zhang y. (2015) effects of dry method esterification of starch on the degradation characteristics of starch/polylactic acid composites. international journal of biological macromolecules, 72:391-402. https://doi.org/10.1016/j.ijbiomac.2014.08.038 [30] mohammad st, al-kayiem hh, aurybi ma, khlief ak. (2020) measurement of global and direct normal solar energy radiation in seri iskandar and comparison with other cities of malaysia. case studies in thermal engineering, 18:100591. https://doi.org/10.1016/j.csite.2020.100591 [31] salazar-sánchez mr, campo-erazo sd, villada-castillo hs, solanilla-duque jf. (2019) structural changes of cassava starch and polylactic acid films submitted to biodegradation process. international journal of biological macromolecules, 129:442–447. https://doi.org/10.1016/j.ijbiomac.2019.01.187 [32] zhao p, rao c, gu f, sharmin n, fu j. (2018) close-looped recycling of polylactic acid used in 3d printing: an experimental investigation and life cycle assessment. journal of cleaner production, 197:1046-1055. https://doi.org/10.1016/j.jclepro.2018.06.275 [33] chavez-montes wm, gonzalez-sanchez g, lopez-martinez ei, lira-gomez p, ballinascasarrubias l, flores-gallardo s. (2015) effect of artificial weathering on pla/nanocomposite molecular weight distribution. polymers 7:760-776. https://doi.org/10.3390/polym7040760 [34] dong y, ghataura a, takagi h, haroosh hj, nakagaito an, lau kt. (2014) polylactic acid (pla) biocomposites reinforced with coir fibres: evaluation of mechanical performance and multifunctional properties. composites: part a, 63:76–84. http://dx.doi.org/10.1016/j.compositesa.2014.04.003 [35] qi y, ma hl, du zh, yang b, wu j, wang r, zhang zq. (2019) hydrophilic and antibacterial modification of poly(lactic acid) films by γ‑ray irradiation. acs omega, 4:21439−21445. http://pubs.acs.org/journal/acsodf [36] bahl s, dolma j, singh jj, sehgal s (2021). biodegradation of plastics: a state of the art review. materials today: proceedings 39:31–34. https://doi.org/10.1016/j.matpr.2020.06.096 411 https://doi.org/10.1016/j.ijbiomac.2014.08.038 https://doi.org/10.1016/j.csite.2020.100591 https://doi.org/10.1016/j.ijbiomac.2019.01.187 https://doi.org/10.3390/polym7040760 http://dx.doi.org/10.1016/j.compositesa.2014.04.003 http://pubs.acs.org/journal/acsodf https://doi.org/10.1016/j.matpr.2020.06.096 microsoft word 4-paper print 01 said .doc iium engineering journal, vol. 1, no. 1, january 2000 s. h. ibrahim 1 computer aided design and analysis of a 2-4 ghz broadband balanced microstrip amplifier s. h. ibrahim faculty of computer science and information, el-mansoura university, el-mansoura, egypt abstract: in this paper, a computer-aided design and analysis of a 2-4 ghz broadband balanced microstrip amplifier using a full computer simulation program developed by the author and others is presented. a short and efficient cad procedure for broadband amplifier design is introduced. the first step is to design an initial narrow-band high gain microstrip amplifier at 3-ghz central frequency. the second step is to optimize the initial lengths and widths of the input and output microstrip-matching circuits to get the broadband amplifier over the range 2-4 ghz. the analysis of both narrow and broadband amplifiers is investigated. in addition, with the design and analysis of a low-pass microstrip filter, the paper introduces the design and analysis of a lange coupler. the final ac schematic diagram of the designed amplifier with the lengths and widths of microstrip lines is presented. key words: computer-aided design and analysis, microstrip amplifier, microwave amplifier. 1. introduction presently the design of microwave solid-state amplifiers is performed using microwave bipolar junction transistor (bjt) as an active element. the bjt is usually implanted in a distributed passive network fabricated by microstrip line technology. silicon bjt is widely used in microwave circuit design due to its excellent performance in the microwave range up to 4 ghz. in addition, with the good isolation between input and output, the device has a high gain, high power, and low noise figure when compared with other solid-state devices operating in the same frequency range. the balanced amplifier has many advantages compared to the single device amplifier. these advantages are: 1) improved input and output impedance matching, gain flatness, and phase linearity, 2) possible design for amplifier, simultaneously for minimum noise figure and good input match, 3) gain compression and intermodulation characteristics are good, 4) high stability for short and open circuits, 5) the amplifier gain can be controlled over wide ranges by dc bias with little effect on gain flatness or impedance matching, 7) if one amplifier fails, the balanced amplifier unit will still operate with reduced gain, and 8) easiness to cascade the balanced amplifier to other units. the designed microwave transistor amplifier is a balanced microstrip amplifier using two hxtr 3101 silicon bjts as active elements. the associated passive microwave circuits such as amplifier matching circuits, low-pass filter, and hybrid couplers are designed using microstrip line technology. teflon substrate is used with the following parameters: relative permittivity (r) = 2.2, dielectric thickness (h) = 0.7874 mm, and conductor thickness (t) = 0.005 mm (skin depth–to-conductor thickness ratio  0.1). 2. design and analysis of 2-4 a ghz broadband microstrip amplifier the design of a broadband microstrip amplifier using hxtr 3101 bjt as an active element is performed using a full-scale computer simulation program developed by the author and others [1]. the program can perform complete analytical design of microstrip amplifiers. 2.1 design methodology a short and efficient cad procedure for the design of a broadband microstrip amplifier is performed. the design is based on the scattering-matrix parameters of the active element. the cad procedure is composed mainly of two steps. the first step is to design an initial narrow-band high-gain amplifier operating at central frequency fo = 3 ghz. the developed full-scale simulation program is used for stability consideration and for the design of the input and output matching circuits. the second step is to use an optimization program to adjust the initial designed lengths and widths of the input and output matching circuits to get a broadband over a frequency range 2-4 ghz [2-3]. 2.2 design of a narrow band 3 ghz amplifier in order for the amplifier to deliver maximum power to the load, it must be properly terminated at both input and output ports [4-9], hence the need for an input/output matching circuit arises. the scattering parameters of the hxtr 3101 bjt at 3 ghz and ic=4 ma are: s 11 =0.57 -173o, s 12 =0.043 25o, s 21 =2.2 48o, and s 22 =0.77 -58o. iium engineering journal, vol. 1, no. 1, january 2000 s. h. ibrahim 2 the stability of the transistor is first considered. the corresponding k and || are, respectively, 1.254 and 0.39. the transistor is thus unconditionally stable. for simultaneous conjugate match the source and load reflection coefficients are given by [10-12]: 1 2 1 2 11 2 ||4 c cbb ms   (1) 2 2 2 2 22 2 ||4 c cbb ml   (2) 22 22 2 111 ||||||1  ssb (3) 22 11 2 222 ||||||1  ssb (4) 22111 ssc  (5) 11222 ssc  (6) where ms and ml are the source and load reflection coefficients required for a simultaneous conjugate match fig. 1 |s21|, |s11| and |s22| in db versus frequency in ghz for the 3-ghz amplifier fig. 2 schematic diagram of 3-ghz high-gain amplifier a) input matching circuit using open/balanced stub b) output matching circuit using open/balanced stub 2.3 design of broad band 2-4 ghz amplifier the optimization process adjusts the circuit parameters (lengths and widths of microstrip input and output matching circuits given in table 1) to achieve a flat gain over the range 2-4 ghz. it does this by minimizing an rms error function defined as follows [12]:     q q n n qnn fwnq 1 1 2 )( 1 (14) where fq is the analysis frequency and n is the error in a parameter. for magnitude or other real quantities, goalncalcnn pp ,,  (15) moreover, for phase angles the fractional error is used: 180 ,, goalncalcn n   (16) pn and n are scalar parameters of the circuit at frequency fq. pn is the magnitude of s22 ’, n is a phase angle of s22’, and wn is a weighting coefficient. the optimizer terminates if the error function fails to decrease by a factor of 10-6 between two successive iteration. as a result of the optimization process, the final lengths and widths of the input and output matching circuits for a 2-4 ghz broadband amplifier are given in table 2. table 2 input and output matching circuits for the 24 ghz broadband amplifier length/width of microstrip line input matching circuit output matching circuit length of series line 2.50 mm 9.54 mm length of open/ balanced shunt stub 4.38 mm 2.730 mm width of series line 1.00 mm 1.00 mm width of open/ balanced shunt stub 4.99 mm 4.99 mm figure 3 gives the variations of s 21 , s 11 , and s 22 , all in db, with frequency in ghz for a 2-4 ghz broadband amplifier. fig. 3 |s21|, |s11| and |s22| in db versus frequency in ghz for the 3-ghz amplifier 3. design of a lange coupler the balanced amplifier with coupled-line hybrid as input and output stages has mainly two problems. the first one is that the required even and odd mode characteristic impedances of the coupler are beyond the manufacturing capability, even on high permittivity substrate; this is because the required spacing between the lines is too small. the second problem is that the two outputs emerge on opposite sides of the isolated ports, so a symmetrical circuit layout is difficult to achieve. a lange coupler can be used to overcome these two problems [13]. the developed full-scale computer simulation program is used to design the lange hybrid operated at central frequency fo=3 ghz with four coupled lines and a coupling factor of 3 db. as a result of the developed program, the parameters of the lange hybrid are as follow: strip separation s = 0.142 mm, strip width w = 1.45 mm, even mode impedance zoe = 176.4 , odd mode impedance zoo = 52.5384 , even mode w/h ratio = 1.1689, odd mode w/h ratio = 7.29, and coupled line length l = 17.36 mm. figure 4 shows |s 21 |, |s 31 |, and |s 41 | versus frequency in ghz for a lange coupler operated at 3-ghz central frequency. figure 5 shows the configuration of the lange coupler. iium engineering journal, vol. 1, no. 1, january 2000 s. h. ibrahim 3 4. design of a low-pass filter the low-pass filter is used for passing only the dc bias voltage to the bases and collectors of the two transistors and suppressing the unwanted ac signals. the designed low-pass filter is made by using distributed microstrip lines with teflon substrate. a maximally flat low-pass prototype filter is used to design the low-pass filter. the full simulation program developed by the author and others [1] is used to design the maximally flat low-pass filter taking into consideration the effects of step discontinuities and the equivalent end effect lengths. the program calculates all parameters of the low-pass filter for the given characteristic impedance of the distributed inductance zol = 90 , characteristic impedance of the distributed capacitance zoc = 20 , number of sections n = 1, passband frequency fp = 0.75 ghz, and stop-band fs = 1.5 ghz. as a result of the developed program: the length and width of the inductive microstrip line are 23.52 mm and 0.8312 mm, respectively. the length and width of the capacitive microstrip line are 29.94 mm and 7.82 mm, respectively. the lumped inductance and capacitance of the designed low-pass filter are 0.4579 x 10-12 h, and 0.7132 x 10-11 f, respectively. fig. 4 |s21|, |s31 |and |s41 | versus frequency in ghz for a lange coupler operated at 3 g hz figure 6 shows |s11| and |s21| versus the frequency in ghz for the designed low-pass filter. figure 7 shows the distributed and lumped one-section maximally flat lowpass filter. fig 5 configuration of lange coupler: (1) input port, (2) coupled port, (3) directed port and (4) isolated port fig. 6 |s11| and |s21| versus the frequency in ghz for the designed low-pass filter. fig. 7 schematic of the designed distributed low-pass filter and the corresponding lumped circuit 5. final ac schematic of the designed balanced microstrip amplifier figure 8 shows the schematic of the broadband 2-4 ghz balanced microstrip amplifier, where: fig. 8 ac microstrip schematic of the broadband 24 ghz balanced amplifier a) input lange coupler b) output lange coupler c) input matching circuit of the first amplifier d) input matching circuit of the second amplifier e) output matching circuit of the first amplifier f) output matching circuit of the second amplifier q1) the transistor for the first amplifier q2) the transistor for the second amplifier 1) input port of the balanced amplifier 2) output port of the balanced amplifier 3) isolated port at the output of the balanced amplifier 4) isolated port at the input of the balanced amplifier 5) input of the first amplifier 6) input of the second amplifier 7) output of the first amplifier 8) output of the second amplifier 6. applications the designed broadband microstrip amplifier could have many applications including sensors, pulse doppler communications, airborne radar, traffic control radar, satellite communications, etc. 7. conclusions this paper introduces a computer-aided design and analysis of a broadband 2-4 ghz microstrip amplifier using silicon bjt hxtr 3101 as an active element. the associated microwave circuits comprise matching circuits, 3-db lange couplers, and low-pass filters. a short and efficient cad procedure for the design of broadband amplifier is introduced. an initial narrowband, high gain amplifier is designed. the analytical design procedure approach of the narrow-band high gain amplifier is presented. an optimization program is used to adjust the initial lengths and widths of the input and output matching circuits to get the broadband iium engineering journal, vol. 1, no. 1, january 2000 s. h. ibrahim 4 amplifier over the range 2-4 ghz. a full-scale computer simulation program developed by the author and others is used to get the complete design of input and output matching circuits, lange couplers, and low-pass filters. analyses of the individual parts of the balanced amplifier are performed. the final ac schematic of the designed broadband microstrip amplifier is illustrated. acknowledgment i would like to thank dr. hosny a. el-motaafy, hti, 10th of ramadan city, cairo, egypt, and prof dr. elsayed a. el-badawy, faculty of engineering, international islamic university malaysia (iium), kuala lumpur, malaysia, for their fruitful discussion and comments during the implementation of this work. references [1] h. el-motaafy, h. el-hennawy, el-s. el-badawy, and s. h. ibrahim, “a complete computer program for microstrip circuit design”, european conference on circuit theory and design”, (ecctd-95), aug., 27-31, istanbul, turkey, 1995. [2] s. h. ibrahim, el-s. el-badawy, and h. el-motaafy, “computer-aided design of 2.6 ghz microstrip oscillator”, icn, dec., 14-16, tunisia, 1998. [3] h. el-motaafy, m. .m. el-arabaty, and s. h. ibrahim, “design and realization of microwave oscillators and amplifiers using microstrip technology”, the xiii conference on solid-state science, 20-26 jan., qena, egypt, 1990. [4] e. holzman and ralston, solid-state microwave power oscillator design, artech house, inc., boston, london, 1992. [5] s. y. lio, microwave circuit analysis and amplifier design, prentice-hall, englewood cliffs, nj, 1987. [6] k. kurokawa, introduction to the theory of microwave circuits, academic press, new york, 1969. [7] i. bahl and p. bhartia, microwave solid-state circuit design, john wiley and sons, inc., 1988. [8] d. woods, “reappraisal of unconditional stability criteria for active 2-port network in terms of sparameters”, ieee transaction on circuits and systems, feb., 1976. [9] g. gonzalez, microwave transistor amplifiers, prentice-hall, englewood cliffs, nj, 1984. [10] r. e. collin, foundations for microwave engineering, 2/e, mcgraw-hill, 1992. [11] t. c. edwards, foundation for microstrip circuit design, john wiley and sons, 1981. [12] c/nl2 program, nonlinear consulting, p.o.box.7284, long beach, ca 90807, u.s.a. [13] s. a. maas, microwave mixers, artech house book, norwood, mass, 1992. biography dr. said hassan ibrahim was born in cairo, egypt (aug. 6, 1960). he got both his b.sc. and m.sc. degrees in electrical engineering from military technical college, cairo, egypt, respectively, in july 1983 and jan. 1991 and his ph.d. degree in electrical engineering from faculty of engineering, ain-shams univ., cairo, egypt in oct. 1996. he has worked in education, research, and industry. now he is working as an assistant professor at the faculty of computers and information, mansura univ., mansoura, egypt. he has published more than 30 papers in international and national conferences. 310 iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 161 cluster-based multihop synchronization scheme for femtocell network aisha h. abdalla 1 , rashid a. saeed 2 , mohammad k. hasan 1 , shayla islam 1 and othman o. khalifa 1 1 department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, kuala lumpur, malaysia. 2 department of electronics engineering, faculty of engineering sudan university of science and technology,khartoum, sudan. hasankamrul@msn.com abstract: femtocell technology has been drawing considerable attention as a costeffective means of improving cellular coverage and capacity. it is connected to the core network through an ip backhaul and can only use timing protocols such as ieee1588 or network time protocol (ntp). furthermore, the femtocell is installed indoor, and cannot use a gps antenna for time synchronization. high-precision crystal oscillators can solve the timing problem, but they are often too expensive for consumer grade devices. therefore, femtocell base station (fbs) synchronization is one of the principle technical trends in femtocell deployment. since fbsand macrocell base station (mbs) network operates on the same frequency under a licensed spectrum, fbs network can interfere with the macrocell network. in addition, fbss can also interfere with each other if multiple units are in close proximity. furthermore, in a flat fbs structured network using ieee 1588 synchronization algorithm and fbs-fbs synchronization scheme creates offset and frequency error which results inaccurate synchronization. in order to reduce offset and frequency error (skew), this paper proposed a cluster-based multihop synchronization scheme to achieve precise in fbs neighbor nodes. the proposed scheme is able to reduce the offset and skew significantly. abstrak: teknologi femtocell telah menjadi tumpuan sebagai alat yang kos-efektif dalam memperbaiki liputan mudahalih dan kapasiti. ia menghubungkan jaringan teras melalui ip backhaul dan hanya boleh menggunakan protokol masa seperti ieee1588 atau protokol jaringan masa (ntp). seterusnya, femtocell dipasang di dalam, dan tidak boleh menggunakan antena gps untuk sinkronisasi masa. osilator kristal yang tinggi kejituannya boleh menyelesaikan masalah masa, tetapi ianya mahal bagi gred peranti consumer. oleh itu, sinkronisasi stesen asas femtocell (fbs) adalah salah satu tren teknikal prinsip dalam deployment femtocell. memandangkan fbs dan jaringan stesen asas makrosel (mbs) beroperasi pada frekuensi yang sama di bawah spektrum lesen jaringan fbs boleh mengganggu jaringan makrosel. tambahan pula, fbs juga boleh mengganggu antara satu sama lain jika unit pelbagai adalah close proximity. tambahan lagi, bagi struktur jaringan rata fbs menggunakan algorisma sinkronisasi ieee 1588 dan skema sinkronisasi fbs-fbs mencipta offset dan ralat frekuensi yang menyebabkan ketidaktepatansinkronisasi. bagi mengurangkan offset dan ralat frekuensi (skew), kajian ini mencadangkan multihop berasaskan kluster skema sinkronisasi bagi mencapai kejituan dalam mod kejiranan fbs. skema yang dicadangkan boleh mengurangkan offset dan skew dengan berkesan. keywords: femtocell base station (fbs); synchronization; frequency division multiple access (fdma); inter-cluster, intra-cluster iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 162 1. introduction the femtocell extends network coverage and delivers high-quality mobile services inside residential and business buildings with the better cellular network coverage, and has triggered the design and development of new structured cellular standards such as wimax (802.16e), the third generation partnership project’s (3gpp’s) high speed packet access (hspa) and lte standards, and 3gpp2’s evdo and umb standards. the communication link of the femtocell may be one of wide area network (wan) technologies such as asymmetric digital subscriber line (adsl). since a public network is used to establish the connectivity between the femtocell and core network elements that presents a set of problems for operators. moreover, the femtocell architecture is much more different than existing cellular networks. however, femtocell introduces new challenges to the telecom industries in terms of synchronization issues which is considered corner stone for proper working for femtocell. the main challenging concern in femtocell synchronization is that all the data and control traffics travel through ip broadband network. the ip broadband network is usually owned and managed by third party and not by the mobile operator, which is complicated the synchronization. in addition, the conventional algorithms and schemes has the clock offset and frequency error which degrades the synchronization accuracy and as well as throughput. unsynchronized fbss may cause harm interferences and wrong handover dictions. in this paper the current femtocell synchronization techniques are investigated. possible improvements and recommendation for each method is identified. cluster-based multihop synchronization scheme proposed in order to reduce the clock offsets, skew and increase the synchronization accuracy. the rest of the chapter is organized as follows. section 2 presents femtocell network infrastructure, section 3 analysis of related works, section 4 contribution, in section 5 performance evalution and section 6 summarizes the chapter. 2. femtocell infrastructure a recent development is femtocell, also called home base stations, which are small size short-range low-cost low-power(<10 mw) ip backbone network based on cellular radio systems which are plugged to residential digital subscriber line (dsl), a separate radio frequency (rf) backhaul channel or cable broadband connections to provide improved better indoor signal strength, commonly unattainable by macrocell coverage operating at higher frequencies and increased throughput for mobile data services directly at home. interestingly, with the introduction of the femtocell technology, the cellular systems come closer to wifi through architecture, operating frequency, services offered and data rates. table 1 points the femtocell specifications. table 1: femtocell specifications [2] item femtocell specifications data rates 7.2 – 14.4mbps operation frequency 1.9 – 2.6ghz power 10, 100mw range 20-30m services voice, video, and data iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 163 figure 1 illustrates how femtocell connects to the service provider’s network to establish the connectivity between femtocell and core network elements such as security gateway, femto gateway, clock servers via broadband, typically cable modems and digital subscribers lines (dsls). signals are routed from the home or office from a user’s cell phone over the internet and the provider’s base station. in terms of synchronization, the femtocell will therefore see some synchronization messages being transported over the public network. fig. 1: a femtocell network architecture [2] figure 2 illustrates the fbs operation structure in wireless backhaul network. fig. 2: femtocell base station in wireless backhaul network structure. 3. related works in the conventional system femtocell suffers from network overhead, bandwidth consumption, misalignment message and offset. in this circumstance, network does not perform precise synchronization. to overcome these issues, researchers have put forward their efforts for developing algorithms and schemes, (sungwon. [3], hwang [4], mills[5], [6], peng [7], [8], wada [11] ).the paper [3] enhanced synchronization algorithm in order to estimate the asymmetric ratio of downlink and uplink data rate for the communication link (adsl and vdsl using ieee 1588) with enabling precise evaluation of offset value in the slave clock. the block burst transmission for asymmetric ratio calculation is iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 164 illustrated in fig. 3. due to the enhanced synchronization algorithm, it is possible to lessen offset for the time synchronization in a slave clock according to the scaling factor of the asymmetric ratio (r) and the sync message transmission delay for downlink (1 ms, 10 ms and 100 ms). since, it allows the accurate value calculation of the asymmetric ratio for downlink and uplink efficiently using block burst transmission between the master clock and the slave clock. in paper [4] recommends autonomous group generation and merging scheme of femto bss with a synchronization algorithm within a group as several femto bss are positioned in uncoordinated and unplanned way. within a group femto bss can synchronize to a reference femto bs using multi-hop synchronization path based method, which doesn’t need iterations for full network synchronization. the multi-hop based synchronization overcomes the path loss effect that improve the network synchronization performance compared to the conventional single-hop based scheme that a bs directly synchronizes to a reference bs. this multi-hop based scheme is compared to the conventional single-hop based scheme which allows a bs to synchronize directly to a reference bs. fig. 3: block burst transmission for the asymmetric ratio calculation [3] however, if the distance between the synchronizing femto bs and the reference is short enough, the hop count need not to be increased. in order to reduce interference between different cells, ensuring smooth hands-offs from cell to cell, and achieve seamless operation the overall network needs to be synchronized, a new distributed clock synchronization scheme for heterogeneous networks is proposed in paper [9]. this scheme can significantly reduce the clock drift, message overheads between macrocells and femtocell through employing clock drift information which are available at userequipments (ues) to precise the synchronization between non-interacting femtocells and macrocells. however, it can be found that nodes suffer for accurate timing with faster convergence and more accurate cdr estimation. the investigations are required in order to achieve more resilient and accurate timing synchronization. another method of time synchronization is proposed in paper (xiaoyan [10] ). the proposed method updates the slave clock model in time synchronization that is implemented through exchanging the iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 165 messages. these messages are transmitted in offset calibration, and it does not add any communication cost. with the help of drift compensation, the increase speed of the difference between the time on slave clock and the time on master clock is reduced and it outperforms the conventional synchronization method. in practical application, the communication links are asymmetric. though combining drift compensation and asymmetric communication, the precision of time synchronization is significantly improved. the average bias error of the time on slave clock as a function of the asymmetric ratio. mobile station assisted receiver-receiver synchronization strategy proposed for fbs neighbor nodes in order to get the synchronization accuracy [8]. this scheme followed the reference broadcast synchronization (rbs) to reduce the clocks offset and skews by using the ms and mbs. figure 4 shows the receiver-receiver synchronization scenarios where two fbs nodes considered. fig. 4: the two femtocell synchronization scenarios [8]. fig. 5: average clock offset in different receive delay difference standard deviation, σ [8] this scheme is fully dependent on mobile station and mbs where a reference node is used to synchronize the fbs nodes. in contrast, this strategy is not fully covered in all situations if there has no ms for a long time in any of fbs network. in addition, this iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 166 reference broadcast may flood the message in the fbs network and which results the network overhead. consequently, the clock offset and skews are not minimized in the as the fbs network needs to make it decentralized co-ordination which is demonstrated in fig. 5 and fig. 6. in receiver-receiver synchronization they achieved 2.5 microsecond (µs) for clock offset and frequency accuracy achieved up to 250 parts per billion (ppb). however, the proposed scheme is able to minimize the clock offset and skews better than the mobile station assisted synchronization scheme in order to precise synchronization. moreover the related works are summarized in table 2. fig. 6: average clock skew in different receive delay difference standard deviation, σ [8]. table 2: summary of related works. method advantages drawbacks ieee 1588 precision time protocol (ptp) [3] a. can synchronize with independent clock. b. in ip based cellular network, it is applicable for synchronizing symmetric communication link. c. fast re-synchronization is possible when system changes occur d. synchronization of clocks are done with various precision, resolution and stability e. offers low-cost implementation in multicast messaging networks such as ethernet a. misalignment of the time of the master clock and the slave clock. b. not applicable for synchronizing asymmetric communication link. c. requires hardware assistance as well as upgrading the network devices d. work only for a few subnets (locally) enhanced time synchronization algorithm [4] a. optimize the offset (bias error) for the asymmetric ip based communication links. a. inefficient for asymmetric backhaul link. receiver-reciver synchronization scheme [7] a. clock offsets and skews is minimized. a. for large number of fbs node this scheme will make network overhead by generating the message flooding multihop synchronization scheme [4] a. overcomes the path loss effect that improve the network synchronization performance compared to the conventional single-hop based scheme a. nodes suffer for accurate timing with faster convergence and more accurate cdr estimation ms-assisted receiverreciver synchronization scheme [8] a. followed reference broadcast synchronization and clock offsets and skews minimized. a. this scheme will make network overhead by generating the message flooding for a large number of fbs node frame timing synchronization [11] a. needs to correct the effect of propagation delay time. a. estimation error of the distance may create misalignment of transmission timing. iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 167 4. cluster-based multihop synchronization scheme a cluster-based multihop synchronization scheme is proposed with the purpose of minimizing the network overhead and clock offset as well as bandwidth consumption. figure 7 illustrates the proposed synchronization strategy for fbs nodes. in the beginning, the fbs node initializes the synchronization process in periodically. then fbs node checks out whether the synchronization clock information is received from the macro base station or not. if the node receives synchronized clock from mbs, then the fbs nodes will be synchronized along with its ip address and cell identity. otherwise it will go for the ms assistance checking. in this case, the fbs nodes will synchronize if only they get the ms assistance. however, if the fbs nodes do not get ms assistance, then the nodes will check for broadband connectivity in order to get the most recent clock synchronization. therefore, ieee1588 clock server will synchronize the fbs node. however, in some circumstances, if the bandwidth is limited for updating the clocks, then the synchronization process will be problematic which results in increasing clock offsets and delay time. to overcome these problems, fbs node can use the proposed self-organized synchronization scheme to be synchronized by other synchronized fbss. fig. 7: the proposed synchronization strategy. the proposed scheme mainly separates the fbss through cluster, which involves clustering formulation, inter-cluster time one hop and multihop synchronization. cluster formation is the initial process performed based on time and distance. in this scheme, the two way time exchange techniques are employed to conclude the time synchronization between neighbor nodes and cluster heads through establishing a hierarchical topology or flat structure. for the cluster synchronization intermediate node (in) selection is needed to find the latest sync message to update each of cm inside cluster. in fig. 8 the in selection procedure is shown through flowchart. the total schronization procedure for the inter-cluster is dipicted in fig. 9. figure 9 illustrated that after two in selection clusters start to synchronize each of cm. iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 168 fig. 8: proposed intermediate node (in) selection procedure. fig. 9: proposed inter-cluster synchronization procedure. iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 169 5. performance evaluation in order to achieve better synchronization accuracy, performances of the proposed scheme evaluated. the analytical approach results in satisfactory level of synchronization accuracy for a femtocell network. table 3 outlines the system paremeters. table 3: system parameters. parameters value network size 200 x 200 m 2 transmission range 30 meter cluster radius 30 meter delay difference standard deviation (σ ) 10 µs, 15 µs, 20 µs, 30 µs distance 0-30 meters number of node 10, 25, 50, 100, 200 number of synchronization process (m) 25 fig. 10: cluster head section and cluster formation for 50 nodes. in figure 10, the network size is considered to be 200 x 200 sized areas where 50 nodes are created randomly and this is followed by the selection of 15 ch considering the random clock time and minimum distance. as ch is already created, it starts dominating all the cms and forms the cluster. in some cases, some of the nodes may not join the cluster because of unsatisfactory clock time and distance. from fig. 11, the clock offset can be tabulated in table 4. table 3 suggests that the clock offset can be minimized to 1.32 microseconds which is better for synchronization accuarcy. iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 170 table 4: average clock offset. number of nodes average clock offset m=1 m=10 m=25 σ= 10 µ s σ= 30 µ s σ= 10 µ s σ= 30 µ s σ= 10 µ s σ= 30 µ s 50 34.15µ s 102.89µ s 3.69 µ s 11.66 µ s 1.32µ s 3.61µ s fig. 11: average clock offset on different receive delay difference in standard deviation for 50 nodes. the frequency accuracy performance is evaluated by measuring the average clock skew with a number of synchronization processes for σ = 10 µs, 15 µs, 20 µs, and σ =30 µ s, as shown in figure 12. in a worst case scenario, when σ is 30us and number of synchronization processes are 25, and thenclock skew is significantly reduced from 7 to nearly 0.35 parts per million (ppm). this is how the ultimate aim of obtaining clock skew is achieved with the minimization of frequency error. 0 5 10 15 20 25 0 20 40 60 80 100 120 number of synchronization processes a v e ra g e c lo c k o ff s e t u s σ=10 us σ=15 us σ=20 us σ=30 us iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 171 fig. 12: average clock skew on different receive delay difference in standard deviation for 50 nodes 6. conclusion the proposed synchronization scheme aims to synchronize the fbs neighbor networks. the proposed scheme differs from previously developed ieee 1588, rbs, and even receiver-receiver schemes in the sense of forming clusters among the random number of fbs nodes and applying hybrid (two ways and one way) messaging system to entire synchronization scheme. proposed synchronization scheme is cluster based and can be applied for a large number of femtocell base stations (fbs) nodes in femtocell network. the proposed scheme acheived better synchronization accuracy than the previous ms assisted synchronization strategy. references [1] hasan, m. k. saeed, r. a. aisha-hassan a. h. “femtocell network synchronization.”femtocell communications and technologies: business opportunities and deployment challarges, global publications (usa), 2011. [2] hasan m. k., aisha-hassan a. h., rashid a. saeed, shayta islam, othman o. khalifa an “investigation of femtocell network synchrunixation.” presented at ieee conference on open systems,icos2 2011. doi: l0.l109/icos.20i 15079232. [3] sungwon l. “an enhanced ieee 1588 tirne syrchronization algoithm for asymmetic cammunication link using block burst transmission.” ieee communicalions letters, 2.9 (2008). [4] hwang s. l., jangho y., jaeki l. “muhi-hop based nework sytchronization scheme for femtocell systems.” if,ee 2fth international symposium personal, indoor and mobile radio communications, 2009. [5] mills d. l. “internet time synchronization: the network time protocol.” ieee transaction on communications, 10(1991): 1482-93. 0 5 10 15 20 25 0 1 2 3 4 5 6 7 number of synchronization process a v e ra g e s k e w ( p p m ) σ=10 us σ=15 us σ=20 us σ=30 us iium engineering journal, vol. 13, no. 2, 2012 abdalla et al. 172 [6] mills d., delaware u., martin j., burbank j., & kasch w. “network time protocol version 4: protocol and algorithms specification.” internet engineering task force @td. accessed january 1, 2011 from http:l/tools.ief.org/htmurfc5905. [7] peng j., li z'., mclernon d., & jibo w. . “a novel receiver-receiver time synchronization scheme for femtocells.” ieee wireless communication systems (iswcs), 2010. [8] peng j., li z., m:clemon d . “ms-assisted receiver-receiver time synchronization scheme for femtocell s.” ieee conference on vehicular technology, 2011. [9] hani m., steven d. b., & tommy s. “a new distributed approach for achieving clock synchronization in heterogeneous networks.” globecom 2011next generation networking symposium, 2011. doi: 1 0. 1 1 09/glocom.201 1.6 1 33859. [10] xiaoyan 2., zhijian & houjun w. 201 i . “novel method of time synchronization based on ieee 1588.” jdcta: international journal of digital content technology and its applications, 5.7 : 275 -82 [11] wada t., saitou, n., hara t., & okada m., “frame synchronization among base stations for tdd system.” 4th international symposium on communications, control and signal processing (isccsp), (2010): 14. doi: 1 0. 1 i 09/[sccsp.20r 0.546347 6. microsoft word 203 vetted_final iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 129 surface effect due to incident plane surface horizontal waves jeffry k. department of mathematics, faculty of mathematics and natural science, hasanuddin university, jalan perintis kemerdekaan, 90245 makassar, indonesia. jeffry.kusuma@gmail.com abstract: surface effect due to incident plane surface horizontal waves through anisotropic elastic materials is studied. mathematical formulation over the modeled earth's alluvial valley is transformed into integral equations. these integral equations altogether with the boundary condition and continuity equation are then solved numerically. the solution of these amplification effects over the half circular in homogeneous alluvial valley are shown graphically. abstrak: kajian tentang kesan permukaan yang disebabkan oleh ombak insiden permukaan mengufuk melalui bahan-bahan elastik anisotropik telah di jalankan. penggubalan persamaan pengamiran dibuat berdasarkan model lembah aluvium bumi. persamaan-persamaan ini diselesaikan secara numerikal menggunakan syarat sempadan persamaan selanjar.penyelesaian kepada kesan pembesaran ke atas model separa bulatan lembah aluvium tak homogen telah digambarkan secara grafik. keywords: surface effect; surface horizontal wave; inhomogeneous anisotropic materials. 1. introduction one of the major concerning in engineering seismology is to understand and explain vibration properties of the soil excited by near earthquakes. alluvial deposits, often very irregular geometrically, may affect significantly the amplitudes of incident seismic waves.the ground amplification of seismic wave on alluvial valleys have been studied by numerous authors [1-6]. integral equation formulations have been found to be particularly useful in obtaining numerical solutions to problems of this type. in particular, wong and jennings [4] have used singular integral equations to solve the problem of scattering and diffraction of incident surface horizontaly (sh) waves by canyon so farbitrary cross section. also, bravo [1] extended the method by considering stratified alluvial deposits. clements and larsson [7] extending further these integral formulation techniques by including the case of homogeneous anisotropic materials. in this paper, further extension is being made by including the case of inhomogeneous anisotropic materials. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 130 2. ground motion on an alluvial inhomogeneous anisotropic valley referred to a cartesian frame �������, let’s consider an anisotropic elastic half space occupying the region �� � 0 as illustrated in fig. 1. the half space here is divided into two regions in which the first region contains a homogeneous isotropic material with shear moduli � ��� � ��� and the second region contains an inhomogeneous anisotropic material with the shear moduli � ��� � ����������� � ������� � �������. the materials are assumed to adhere rigidly to each other so that the displacement and stress are continuous across the interface boundary between the first and the second regions and the constants in the shear moduli satisfy the symmetry conditions � �ω� � �ω� for ω 1.2. fig. 1: incident and reflected waves on the alluvial valley and surrounding half-space. let ���� and ���� be the displacement in the �� direction in the half space and the valley respectively. for the propagation of horizontally polarizes sh waves, the displacement satisfies the equations of motion � ��� �������� �� ����� � �������� , �1� for the region 1 and ��� �� ����������� � ������� � ������ � ������� � ������������� � ������� � ������ � ��������� , �2� for region 2. here ���ω� denotes the density, � denotes the time and repeated latin subscripts denote summation from to . iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 131 in view of assuming the form of time dependence as exp �#$��, equation �1� can be reduced to � ��� ��% ����� �� � �����$�% ��� 0, �3� by substituting �������, ��, �� % ������, ��� exp�#$�� . �4� similarly with the equation . by substituting �������, ��, �� % ������, ��� exp�#$�� , �5� we obtain ��� �� ����������� � ������� � ������ � �% ����� � � �����$��������� � ������� � �������% ��� 0. �6� our interest is a plane wave of unit amplitude which propagates toward the surface of the elastic half space %*��� exp #$ +� � ��,� � ��,� , �7� where ,� /���/ sin 4* , ,� /���/ cos 4* , /��� denotes the velocity of the incident waves and 4* denotes the angle of the incident wave. since %*��� in (7) propagates in the first material, it must satisfy equation (3) so that 7/���8� ������sin�4* � 2������sin4* cos 4* � ������cos�4*����� . �8� iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 132 now we consider the case when region 1 and 2 are occupied by the same material. in order to satisfy the traction free condition on �� 0, it is necessary to have a reflected wave of the form %:��� exp #$ +� � ��;� < ��;�. �9� thus, if there are no irregularities, the free field solution of the displacement can be written as %>��� %*��� � %:���. �10� the stresses are given by ? ���� � ��� �% ����� , �11� so that the stress ?����� on �� 0 is ?����� @������,� � ��� ��� ,� a exp b#$ +� � ��,� -c � @��� ��� ;� < ��� ��� ;� a exp b#$ +� � ��;�-c . �12� this stress will be zero for all times t if ;� ,�, �13� 1;� 1,� � 2��� ��� ������,� . �14� these equations serves to provide ;� in terms of the unkwown quantities ,�, ,�, ������ and ������. note that if (9) is substituted into (3) then since it represents a solution to (3) it follows that ������,�� < 2������,�;� � ��� ��� ;�� �����, �15� iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 133 and if (13) is used to substitute for 1/;� in (15) and then into (8) so that (14) ensures (9) is a solution to (3) on the assumption that (7) is also solution to (3). let ;� /d/sin4: and ;� /d/ cos4: where 4: is the angle of the reflection, then tan�4: � ;�;� tan �4* �1 � 2�������/�������tan�4* � , �16� and once 4: has been determined from this equation, the wave speed /dof the reflected wave may be readily determined from equation /d ;� sin�4: �. to include the influence of the inhomogeneous anisotropic alluvial valley in region 2, the solution for the exterior of the deposit is put in the form % ��� %>��� � %g���, �17� in which %g��� is the displacement due to the diffracted waves. in this region 2, the displacement %��� %:��� will be caused by the refracted waves. 3. integral equation proceeding further as in clements and larsson for the region h� with boundary i� and outward pointing normal components j� and j�, the integral equation corresponding to (3) is k%����l, m� n �� ��� �o ����� p j % ��� <qr p� ��� �%����� j o ���� ;s, �18� where k 1 if �l, m� t h� and 0 u k u 1 if �l, m� t i�. the fundamental solution of o ��� is given by o ��� #4 v��� wx�� � v ���y���� � x�� � v ��� r ����z , �19� where, iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 134 y��� [��� < l�� � ������������ ��� < m�� p < p 2������������ ��� < l���� < m�\ r] , �20� r ��� ^��� < l�� � @������������a � ��� < m�� < 2������������ ��� < l���� < m� �p p��� � m�� @������������ < ������ ] ������] a\ r] , �21� v ��� ������������������ < ������] , �22� v ��� w�����$�v���zr], �23� and x� � denotes the hankel function of the second kind of order zero. furthermore, for the regionh� with boundary _� and outward pointing normal components j� and j�, the integral equation corresponding to (6) is v ���%����l, m� n �� ����������� � ������� � ������� �o ����� j %��� <pq] � ����������� � ������� p�������� �% ����� j o ���� ;s, �24� where o ��� à �������� � ������� � ������b�x�� � v ���y����,(25) y��� [��� < l�� � ������������ ��� < m�� p < p 2������������ ��� < l���� < m�\ r] , �26� v ��� [ �����$������������������� < ������] \ r] . �27� iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 135 here, the value of v ��� may be determined by the help of solution of (6) c ��� à �������� � ������� � ������b�x��� v ���s ����, (28) where s��� [��� � ������������ �� � p < p 2������������ ����\ r] . �29� thus, using (28) in (24) in we obtain v ��� 7c ����l, m�8b� n w� ����������� � ������� �p������� �o ����� j c ��� <q] � ����������� � ������� � p������� �c ����� j o ���� ;s, �30� by applying equation (18) and its fundamental solution (19) in the region 1 (outside of the valley) then the only non-zero integral is the integral over the valley's interface boundary (sommerfeld radiation condition). if we denote this interface boundary as curve i� and valley's free boundary as id and specifying the normal components j� and j� pointing outward of the valley's boundary, thus (18) and (24) on the valley's boundary are 12 %����l, m� n �� ��� �o ��� �� p j % ��� <qr p� ��� �% ����� j o ���� ;s, �31� and v ���7% ����l, m�8 n w� ����������� � ������� �p������� �o ����� j %��� <qreqf � ����������� � ������� � p������� �%����� j o ���� ;s. �32� the equation (31) and (32) together with the continuity equations iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 136 %��� % ���, �33� � ��� �% ����� j � ����������� � ������� � ������ � �%����� j , �34� and traction free boundary condition on �� 0 � ����������� � ������� � ������� �% ����� j 0, �35� may be used to solve for displacement and stress over the interface boundary gh and displacement along traction free surface ij k. once this has been done, we can obtain the value of the displacement l�h� and/or l�j� at all points �m, n� in the half space ij � 0 through equation (18) and (24). 4. numerical results suppose we have a semi circular valley (region 2 in fig. 1 which is defined by nondimensional quantities which satisfy equation ��� < 2�� � ��� o 1. furthermore, suppose that the materials properties are non dimensional quantities� �ω�, ���ω�, ���ω�, ���ω�, ���ω�, ω 1,2 and the normalfrequency is defined by p $q/��� , �36� where /��� is given by (8), then the numerical results are ready to be calculated. using the boundary element method by using 80 segments of straight line on the interface boundary and 70 segments on the free valley boundary, we obtain the numerical results as shown in fig. 2 up to fig. 9. these results generated by involving four kinds of alluvial valley’s materials and two angles of the incident waves. the first material of the valley is homogeneous material with ����� 0.00, ����� 0.00, ����� 1.00. the second material is inhomogeneous material with the inhomogeneity varies to �� direction only. this used����� 0.50, ����� 0.00, ����� 0.00. the third material is inhomogeneous material with in-homogeneity varies to �� direction and using ����� 0.00, ����� 0.50, ����� 1.00. the last material is inhomogeneous material with in-homogeneity varies to �� and �� directions by using ����� 0.50, ����� 0.50, ����� 0.00. the results shown in figure 2 up to figure 5 are using these kinds materials respectively with incident waves angle 4* 0° while figure 6 up to figure 9 are generated using the same materials iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 137 as in figure 2 to figure 5 respectively but with incident waves angle 4* 30°. the others materials specification are ������ 0.12, ������ 0.00, ������ 0.12, ����� 3.00, ������ 0.02, ������ 0.00, ������ 2.00, �� ��� 2.00. fig. 2: effect of homogeneous valley with 4* 0° fig. 3: effect of inhomogeneous valley with 4* 0° fig. 4: effect of inhomogeneous valley with 4* 0° iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 138 fig. 5: effect of inhomogeneous valley with 4* 0° fig. 6: effect of homogeneous valley with 4* 30° fig. 7: effect of inhomogeneous valley with 4* 30° iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 139 fig. 8: effect of inhomogeneous valley with 4* 30° fig. 9: effect of inhomogeneous valley with 4* 30° 5. conclusion the results in fig. 2 up to fig. 9 show that amplification effects are significantly influenced by the materials specification and the angle of the incident waves. the flexibility of the boundary integral element methods is an advantage in dealing with irregularities of the alluvial valley. for such kind of alluvial surface, the method described above can be directly used to obtain the amplification effect. the flexibility of the boundary integral element methods is an advantage in dealing with irregularities of the alluvial valley. for such kind of alluvial valley's surfaces can be directly used to obtain the amplification effect. acknowledgement the author wish to thank the ministry of national education of the republic indonesia for financial support in order to publish this paper. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jeffry 140 references [1] m.a. bravo, sánchez-sesma andchávez f. j. garcía, "ground motion on stratified alluvial deposit for incident sh waves," bull. seism. soc. am. 78, (1988)436-450. [2] m.d. trifunac, "surface motion of a semi-cylindrical alluvial valley for incident plane sh waves," bull. seism. soc. am. 61, (1971) 1755-1770. [3] sánchez-sesma, and j. a. esquivel, "ground motion on alluvialvalleys under incident plane sh waves," bull. seism. soc. am. 69,(1979) 1107-1120. [4] h.l. wong and p.c. jennings, "effects of canyon topography on strong ground motion," bull. seism. soc. am. 65, (1975) 1239-1257. [5] h.l. wong and m.d. trifunac, "interaction of a shear wall with the soil for incident plane sh waves : elliptical foundation," bull. seism. soc. am. 64, (1974) 1825-1842. [6] h.l. wong and m.d. trifunac, "surface motion of a semi-elliptical alluvial valley for incident planesh waves," bull. seism. soc. am. 64, (1974) 1389-1408. [7] h.l. wong, m.d. trifunac and b. westermo, "effects of surface and subsurface irregularities on the amplitude of monochromatic waves," bull. seism. soc. am. 67, (1977) 353-368. [8] d.l. clements, and a. larsson, "ground motion on alluvial valleys under incident plane sh waves,"j. austral. math. soc. ser. b 33, (1991), 240-253. [9] f. ursell, "on the exterior problems of acoustic," proc. camb. phil soc 74, (1973), 117-125. microsoft word othman25-final.doc iium engineering journal, vol. 1, no. 2, 2000 m.r. othman and h. mukhtar 1 review on development of ceramic membrane from solgel route: parameters affecting characteristics of the membrane m. r. othman and h. mukhtar school of chemical engineering, universiti sains malaysia, perak branch campus, 31750 tronoh, perak, malaysia. abstract: the importance of laboratory scale ceramic membrane preparation using sol-gel technique with pore sizes in the range of 1-10nm is reviewed. parameters affecting the characteristics of membrane during membrane development are highlighted and discussed in detail. experimental results from literatures have shown that the correct amount of acid, water, pva, appropriate membrane thickness, proper control of drying rate, and appropriate temperature profile selection during sintering process are necessary in order to acquire sufficient strength and reduce the formation of crack in the membrane. the different temperature setting during sintering process also influences the size of pore formed. key words: sol-gel, inorganic membrane, ceramic membrane, gas permeation, sintering, sol properties, membrane morphologies, pore size distribution. 1. introduction ceramic membranes have played an important role in the fields such as particulate filtration, gas separation and analytical application (sensors for gases and chemicals). for alumina membranes in particular, they have made a successful entry into the market as in line gas filters. in microelectronic packaging, food and pharmaceutical industries where clean air is required, removal of fine particles from gas streams can be achieved by means of porous ceramic membranes. the reasons they are selected are due to the following aspects, [1]  they are thermally stable and chemically inert in the application environment.  the rigid ceramic media does not introduce particles into the gas stream by shedding under harsh conditions of flow pulsation and mechanical vibration or shocks.  they do not react with the process gases or generate impurities nor produce hydrogen outgassing problem  their pore size distributions are narrow and can retain an extremely high percentage of particulates  they can be easily regenerated periodically by backflushing when membrane fouling occurs  they can be steam sterilized without changing their microstructure and chemical characteristics. this paper reviews the preparation of ceramic membranes using sol-gel technique to produce membrane having pore sizes between 1 and 10nm. parameters influencing the production of ceramic membranes with desirable characteristics are also highlighted. 2. ceramic membrane preparation laboratory scale ceramic membranes can be prepared by hydrolizing metal-organic compounds or alkoxides such as aluminium secondary butoxide with water to produce sol. peptization of the sol using acid at temperature of about 90c under rigorous stirring condition is ensued to prevent precipitation. the peptized (stable) sol is then cooled down steadily to allow formation of gel. later, the gel is fired (sintered) to obtain the oxide product (refer to fig. 1). this route to obtain ceramic membrane is referred to as sol-gel technique from destabilization of colloidal solutions (dcs). another kind of sol-gel technique based on polymerization of molecular units (pmu) has been described elsewhere [2]. sol-gel method for producing membrane with extremely small pore size has attracted immense interest in the past [3] and it continues to be in the present and future. the sol gel technique is attractive for application on a porous filter support or in other words, composite membrane preparation. in the processes, a sol is first prepared using an organo-metallic oxide as a precursor or starting material. this is followed by addition of viscosity modifier and binders. normally, the sol is stabilized to avoid significant particle aggregation from taking place. this is done by addition of some threshold amount of acid and heat treatment for sufficient period of time. the acid maintains a stable dispersion by producing similar electric charges as the particles that causes the particles to repel each other. later, the thickened sol is deposited or coated as a layer on the support by dip or spin coating, after which it is dried under controlled environment to form a gel. in the final process, the membrane is calcined and sintered before the composite ceramic membrane is obtained. iium engineering journal, vol. 1, no. 2, 2000 m.r. othman and h. mukhtar 2 fig. 1 -alumina membrane preparation using sol gel technique most popular oxide materials that have been made into micro-porous membranes via sol-gel route are alumina, zirconia, titania, silica and porous glass. they are derived from the associated alkoxides. alumina, for example, is derived from aluminum sec-butoxide. more materials have been studied to produce membranes by sol-gel processing. burggraaf et al.,[4] for instance, have successfully obtained ceria membranes with a mean pore diameter of 2 nm. hackley and anderson,[5] have investigated ferric oxide ceramic membranes, which could yield pore diameter of about less than 3.4 nm to 10 nm. combination or addition of inert components such as zirconia [6] and lanthanum during ceramic membrane preparation is also possible. in fact, the application of supported zirconia membrane in aqueous filtration has been made successful [7]. the zirconia membrane was tested in a cross-flow ultrafiltration of soybean oil/hexane solution and the rejection of this solution was found to achieve 37% higher than without zirconia. 3. factors affecting membrane development 3.1. addition of water in the preparation of ceramic membranes, the alkoxide must be hydrolyzed in water heated at about 80-90c for minimum of 18 hours. the correct amount of water is important for the hydrolysis and condensation. water influences the viscosity of the sols and gelation time. excessive use of water increases the drying time of the sol to form gel. for the case of alumina membranes, huang et al., [8] reported that the gelatinized period increased when the molar ratio of h2o to al 3+ was increased. the viscosity however, decreased with increasing amount of water as shown in table 1. table 1 sol’s viscosity at 84c using different h2o/al3+ molar ratio. [8] molar ratio h2 o/al3+ viscosity (x 10-3 pa.s) appearance of sol 50:1 100:1 125:1 150:1 2.370 1.805 1.494 too thick clear sol clear sol clear sol cho et al., [9] claimed that low viscosity sol as a result of excessive use of water would not form gel layer on a porous support. naturally, diluted sol would be absorbed by the support. if the sol concentration is too high, however, thick gel layer could be formed and this would produce crack membranes or membranes with peeling-off layer during drying. 3.2. addition of acid in essence, acid is added for stabilization and peptization of sol during gelation process. the acid added to an uncharged particle system peptizes the larger particles, producing smaller ones, which become positively charged through proton adsorption. table 2 shows the effect of acid addition on sol formation from the work of yoldas [10] in which alkoxide used was al(obu)3 and the acid was hcl. at least 0.03 mole of acid per mole of alkoxide (or hydroxide) had to be added in order to peptize the system to a clear sol. complete peptization could not be attained for molar ratio below 0.03. table 2 effect of acid concentration on the sol formation. [10] sample molar ratio acid/hydroxide sol condition after 4 days heated at 95c 1 2 3 4 5 6 7 8 9 10 0.0154 0.0231 0.0384 0.0467 0.0537 0.0691 0.1075 0.1540 0.2070 0.2460 unpeptized (cloudy sol) unpeptized (cloudy sol) clear sol clear sol clear sol clear sol clear sol clear sol clear sol clear sol not all types of acid can be used for peptization and hence the choice of acid used for peptization is extremely important. there are two general requirements for the selection of acids. in preparing alumina sol for instance, the anion of the acids should be non-complexing or at least very weakly complexing with the aluminum ions. the acid should also be sufficiently strong to produce the necessary charge effect in relatively small quantities with respect to the aluminum concentration [10]. table 3 lists the peptizing effect of various acids on the sol formation. add acid (hno3) to peptize sol add polyvinyl alcohol (pva) to stabilize sol boehmite (-alooh) stable -alooh sol thin -alooh sol layer thin -alooh gel layer thin dry al2o3 layer thin dry  alooh layer (zero gel) thin ceramic alumina (al2o3) layer prepare the sol layer or deposition of coating on filter support (for composite membrane) control drying rate and humidity heat the sol at  90c and stir vigorously calcine at 390 c to decompose boehmite crystal into: -al2o3 + h2o sinter at 400 c (or higher temperature) control drying rate and humidity iium engineering journal, vol. 1, no. 2, 2000 m.r. othman and h. mukhtar 3 table 3 effect of different types of acids on the sol formation. [10] type of acid sol condition after 7 days heat treatment nitric hydrochloric perchloric hydrofluoric iodic sulfuric phosphoric boric acetic trichloroacetic monochloroacetic formic oxalic phthalic citric carbolic (hno3) (hcl) (hclo4) (hf) (hio4) (h2so4) (h3po4) (h3bo4) (ch3cooh) (ccl3cooh) (ch2clcooh) (hcooh) (h2c2o4.2h2o) (c8h4o3) (h3c6h5o7.h2o) (c6h5oh) clear sol clear sol clear sol unpeptized unpeptized unpeptized unpeptized unpeptized clear sol clear sol clear sol to cloudy clear sol to cloudy unpeptized unpeptized unpeptized unpeptized when acid concentration is properly controlled, acid can be used as a mean to adjust the pore size of membranes according to the desired level. leenaars et al., [11] demonstrated that the pore size of the alumina membrane they developed decreased with increasing molar ratio of acid to alkoxide. yoldas [12] found that the pore diameter increased slightly with increasing acid to sol ratio when the ratio was below 0.05-0.06 and it reached a maximum level near the ratio. yoldas [12] also showed that the pore radius of alumina membrane was almost constant for molar ratio of acid/hydroxide between 1:0.03-0.10. for molar acid larger than 0.10, the pore radius was gradually decreased. however, the membrane produced using greater than 0.10 mole of acid formed cracks. in the work of leenars et al.,[11] pore size reduction from 2.8 to 2.5 nm was observed when the acid concentration was increased from 0.05 to 0.11 mol of hclo4 per mol of -alooh, as illustrated in table 4. table 4 pore size against the acid quantity in the sol. [11] molar ratio hclo4/-alooh modal pore size (nm) porosity (%) cylindrical shape slit shape 0.05 4.1 2.8 49 0.07 3.8 2.6 44 0.09 3.7 2.6 42 0.11 3.5 2.5 38 3.3. addition of binders and plasticizers membrane may crack during sol gel process for a number of reasons. membrane layer that is too thick, incorrect molar composition of the alkoxide, water, and acid during sol preparation, are actually few of the reasons for producing crack membrane. commonly, binders are introduced to add strength to the membrane and avoid crack from forming in membrane layer. examples of organic binders used in ceramic processing are polyvinyl alcohol (pva), polyvinyl acetate and cellulose compounds such as methyl cellulose and hydroxyethyl cellulose. the purposes of organic binder are to avoid particle aggregation, permit adjusting of viscosity and increase the mechanical strength of the material by reducing its stiffness and brittleness and maintaining its shape until it is sintered. organic binders are burnt out at a temperature above approximately 300c [1] and they should burn gradually without leaving ashes or tar. pva and cellulose compounds that serve this purpose [2] can be exploited to control the average pore size, pore size distribution and overall porosity in the membrane material. for production of dense structure of an essentially void free sintered product with small grain sizes for instance, low pva content should be used [13]. yang et al.,[14] have shown that the range of pore size distributions increase with increasing pva content. das and maiti [15] reported that higher binder content promotes agglomeration of the ceramic particles, which on firing leads to wider pore size distribution and formation of closed pores. introduction of binder also help in the production of composite membrane. as bae et al., [16] have discovered, an organic binder such as polyvinyl alcohol (pva) was actually necessary for depositing al2o3-tio2 coating on porous supports to enable successful production of composite thin membrane. plastisicer is a liquid oligomer, structurally similar to that of binder. it is normally used with binder to penetrate in the middle of the binder molecules and lubricate them, allowing them to slide against each other and take up the strain to prevent formation of crack in the membrane layer. examples of plasticizers commonly used are water, polyethylene glycol, ethylene glycol, diethylene glycol, tetraethylene glycol, glycerine, dimethyl phthalate, dibuthyl phthalate, octyl phthalate, benzyl butyl phthalate and diethyloxalate [17]. though effective in preventing formation of crack, it should be used with caution because addition of plastisicer such as polyethylene glycol can actually increase the surface area, pore volume and pore diameter of the final ceramic membrane as reported in the work of lambert and gonzalez [18]. 3.4. membrane thickness thick membrane can give rise to peeling and crack layer during drying and calcination. it was discovered that membrane thickness between 1 and 5-7 m prevented the formation of crack layers and pinholes [19]. when membranes surpass this range of thickness, crack tends to form. this phenomenon was observed in the work of leenaars et al.,[11] in which membrane having thickness larger than 20m was used. production of thick layer of film can be avoided if a dilute sol of approximately 0.52 mol al/litre, is used [20]. sol cannot be too diluted however, because it can cause absorption of the sol by support and thus, no gel layer is formed. iium engineering journal, vol. 1, no. 2, 2000 m.r. othman and h. mukhtar 4 for production of desirable coating thickness, the dipping time should be about 3 seconds [21]. greater than the recommended dipping time may result in undesirably thick coating that produces crack, while dipping time that is too short may result in coating that is too thin to hold the support. in another experimental work, huang et al.,[8] have demonstrated that crack free membrane having thickness between 0.1-200 m could be produced successfully if sols were atomized by a high velocity gas and sprayed onto the support. crack free membrane with thickness greater than 200 m could also be produced provided that it was dried at controlled rate. 3.5. drying rate drying, which is described as the elimination of water or solvent from the pores of a solid is a routine procedure to obtain crystallized compounds. the product obtained from ordinary drying is a dry or zerogel in which, it does not decompose or lose matter through sintering. during drying operation, the pore volumes decrease while the density increases as the dimensions of pores become smaller [22]. in practice, there are two stages of drying during membrane development from sol gel technique. in the first stage of drying, water exposed to or near the atmosphere is evaporated. water lies in the pores then migrates to the surface to replace the evaporating water from the outer surface of the gel layer. the removal of water from inner to outer gel continues progressively until the moisture content diminishes. this causes the gel layer to shrink and eventually allow particles in the gel to come in contact with each other. in the second stage of drying, further drying of the gel will remove immobile or residual water. ideally, there should be no reduction of pore volume during the second stage of drying. during drying, warping or deformation of membrane structure may be observed. this is due to the rate of evaporation that is not even. moisture normally evaporates from the top surface first followed by the surface under it. this causes the top surface to shrink faster than the other parts of membrane, and hence result in membrane that may curl upward or sometimes roll to form a shape like a tube. uneven drying is a common cause of crack membrane. in order to prevent uneven drying from taking place, drying of sol should be performed at a slow and steady pace and constantly high humidity. 3.6. sintering temperature the final physical properties including density, porosity distribution, grain size, morphology and microstructures of ceramic membrane are dependent upon the choice of sintering temperature. sintering process is also performed to obtain firm coalescence between particles and particles with the support, and a well-determined membrane structure with good mechanical resistance. depending upon the type of ceramic membrane, the sintering temperature could be as low as 250c to as high as 1700c. the highest temperature in the sintering profile is used to obtain the desired level of porosity. the porosity, which is a result of water driven off from the pores and decomposition of organic materials, may decrease or increase as the temperature is raised depending upon the compositions and minerals that are present in the ceramic [23]. in general, the porosity level increases as the temperature increases but the mechanical strength falls significantly. highly porous membrane as a result of extremely high sintering temperature suffers fragmentation under vibration conditions. this is further exacerbated when membrane material is not free from impurities such as glass and iron. above about 900c, glass in the alumina membrane for instance, becomes fluid and allows deformation and fracture of bridges between alumina grains. while that with iron content degrades its strength at about 1300c [24]. leenars et al., [11] have shown that the pore size of alumina membrane increases with increasing temperature. the increase was more obvious for thick membrane [25]. in another similar work, morell [24]discovered that the porosity and the crystallite size of the membrane exhibit no systematic change during heat treatment in the range of 400-800°c. john [26] emphasizes that under firing of a ceramic can leave the material structurally weak and oversized. on the other hand, over firing can result in excessive grain growth, undesirable pore coalescence, and bloating. larbot et al. [2] claimed that the pore size of alumina membrane could be controlled by varying the sintering temperature. they presented the evolution of pore diameters as a function of sintering temperature in a graphical form (fig. 2) and concluded that the pore diameter increased as temperature increased during thermal treatment. fig. 2 pore diameters plotted against temperature. [2] the relationship between pore and sintering temperature of the 3 respective ceramic membrane materials (titania, alumina, and zirconia) is illustrated in fig. 3 [27]. from the graph, it appears that the pore size of alumina membrane is more stable at higher temperature than the other ceramic membranes and it only increases considerably after sintering temperature reaches beyond 1000c. in another experimental work, the pore size of alumina membrane was found to increase from 3.7 to 78nm when temperature was increased from 200 to 1000 c as shown in table 5. [11] iium engineering journal, vol. 1, no. 2, 2000 m.r. othman and h. mukhtar 5 fig. 3 pore diameters as a function of temperature. [27] table 5 membrane pores as a function of sintering temperature. [11] temperature (c) bet surface area (m2g-1) modal pore size (nm) porosity (%) cylindrical slit 200 315  2 3.7 2.5 41 400 301  7 4.0 2.7 53 500 240  1 4.9 3.2 54 600 209  1 5.5 3.5 55 700 181  1 5.9 3.7 53 800 154  2 7.9 4.8 55 900 99  2 8.9 5.4 48 1000 15  3 78 39 41 the increase of temperature does not only affect or increase the pore size of ceramic membranes but also decrease the bet surface area. the change of membrane phase also takes place at higher temperature as described in the work of leenaars et al., [11]. in this work, the boehmite sol was changed to -alumina and later -alumina as temperature increased from 200 to 1000c illustrated in table 6. table 6 phase change of alumina membrane at different sintering temperature. [11] temperature (c) pore size (nm) (cylindrical) pore size (nm) (slit) phase change 200 3.7 2.5 -alooh 400 4.0 2.7 -al2o3 500 4.9 3.2 -al2o3 600 5.5 3.5 -al2o3 700 5.9 3.7 -al2o3 800 7.9 4.8 -al2o3 900 8.9 5.4 -al2o3 1000 78.0 39.0 -al2o3 4. conclusion in order to obtain ceramic membrane with the desired characteristics and free from defect such as crack layer from the sol-gel method, factors such as the correct amount of acid, water, and binder, appropriate membrane thickness, proper control of drying rate, and appropriate temperature profile described earlier should be taken into account. according to previous works, crack formation can be avoided if sol is not too viscous and membrane layer is as thin as possible. the importance of correct amount of acid in the sol and proper drying condition of sol in preventing the formation of crack layer is also indisputable. a proper amount of acid addition can control the level of membrane pore size. equally importance is the sintering temperature. a proper selection of sintering profile can tailor the size of pore and membrane porosity according to the desired level. acknowledgement the authors acknowledge the research grant provided by university sains malaysia penang that has enabled the production of this article. references [1] h. p hsieh, inorganic membrane for separation and reaction, elsevier, pp. 28-59, 1996. [2] a. larbot, j. p. farbe, c. guizard and l. cot, “inorganic membranes obtained by sol-gel techniques”, j. memb. sci., vol. 39, pp. 203-212, 1988. [3] d. segal, chemistry of solid state materials, chemical syntesis of advance ceramic materials, cambridge university press, new york, usa, 1989. [4] a. j burggraaf, k. keizer and b. a. van hassel, solid state ionic, vol. 32/33, pp. 771, 1989. [5] v. a. hackley and m. a. anderson, j. memb. sci., vol. 70, pp. 41, 1992. [6] c. lijzenga, k. keizer, m. h. b. j. huis in’t veld, a. j. burggraaf and m. a. anderson, “zirconia-coated gamma-alumina membrane toplayers”, key engr. mat., vol. 62& 61 , pp. 383-386, 1991. [7] j. c. s. wu and l. c. cheng, “an improved synthesis of ultrafiltration zirconia membranes via the sol-gel route using alkoxide precursor”, j. memb. sci., vol. 167, pp. 253-261, 2000. [8] x. r huang, g. l. meng, z. t. huang and j. m. geng, “preparation of unsupported alumina membrane by solgel technique”, j. memb. sci., vol. 133, pp. 145-150, 1997. [9] y. k cho, h.k woo and k.h lee, “separation of co2 by modified �-al2o3 membranes a high temperature”, j. memb. sci., vol. 104, pp. 219-230, 1995. [10] b. e. yoldas, “alumina sol preparation from alkoxides”, ceramic bulletin, vol. 54, pp. 289-291, 1975a. [11] a. f. m. leenaars, k. keizer and a. j. burggraaf , “the preparation and characterization of alumina membranes with ultra-fine pores”, j. memb. sci. ̧vol. 19, pp. 10771088, 1984. [12] b. e. yoldas, “alumina gels that form porous transparent al2o3”, j. memb. sci., vol. 10, pp. 18561861, 1975b. iium engineering journal, vol. 1, no. 2, 2000 m.r. othman and h. mukhtar 6 [13] r. mishra and k. j. rao, “thermal and morphological studies of binary and ternary composites of poly (vinyl alcohol) with alumina and zirconia, ceramics intern., vol. 26, pp. 371-378, 2000. [14] w. p. yang, s. s. shyu, e. s. lee and a. c. chao, “effects of poly (vinyl alcohol) content and calcination temperature on the characteristic of unsupported alumina membrane”, j. sep. sc. tech., vol. 31, pp. 1327-1343, 1996. [15] a. c. pierre, “porous sol-gel ceramics”, ceram. intern., vol. 23, pp. 229-238, 1997. [16] d. s. bae, d. s. cheong, k. s. han, s. h. choi, “fabrication and microstructure of al2o2-tio2 composite membranes with ultrfine pores,” ceramic intern., vol. 24 , pp. 25-30, 1998. [17] r. moreno, “the role of slip additives in tape casting technology: part ii – binders and plasticizer”, am. ceram. soc. bul., vol. 71, pp. 147-165, 1992. [18] c. k. lambert and r. d. gonzalez, “effect of binder addition on the properties of unsupported al2o3 membranes,” j. materials. letters, 38, vol. 2, pp. 145149 1999. [19] k. keizer, r. j. r. uhlhorn, r. j. van varen, a. j. burggraaf; “gas separation mechanisms in microporous modified -al2o3 membranes,” j. memb. sci., vol. 39, pp. 285-300, 1988. [20] t. okubo, m. watanabe, k. kusakabe, s. morooka, “preparation of -alumina thin membrane by sol-gel technique and its characterization by gas permeation,” j. memb. sci., vol. 25, pp. 4822-4827, 1990. [21] a. f. m. leenaars and a. j. burggraaf, “the preparation and characterization of alumina membranes with ultrafine pores,” j. col. interf. sc., 105, vol. 1, pp. 27-40, 1985. [22] j. f. le page, applied heterogeneous catalysis, gulf publishing company, texas, 1987. [23] r.w grimshaw, the chemistry and physics of clays and allied ceramics materials, ernest benn ltd., london, vol. 4th ed., pp. 814, 1971. [24] r. morrell, handbook of properties of technical & engineering ceramics, part 2 data reviews, section 1 highalumina ceramics, national physical laboratory, hmso publication center, london, 1987. [25] p. wong, p. huang, n. p. xu, j. shi and y. s. lim, “effects of sintering on properties of alumina microfiltration membranes”, j. memb. sc., vol. 155, pp. 309-314, 1999. [26] a. m john, advance in ceramic: forming of ceramic, am. ceram. soc., vol. 9, pp. 29, 1984. [27] a. c. pierre, “porous sol-gel ceramics”, ceram. intern., vol. 23, pp. 229-238, 1997. biography mohd roslee othman was born on july 4, 1970 in klang, selangor, malaysia. he received his bachelor and master of science degrees from university of missouri-rolla, missouri, usa in 1994 and 1997 respectively. he is currently pursuing his doctoral degree in chemical engineering (membrane separation) at universiti sains malaysia. dr hilmi mukhtar graduated in chemical engineering from university of wales swansea, uk. and obtained msc in chemical engineering from the same university. he obtained his phd in membrane technology in 1995 and a lecturer in usm from 1995 until today. starting from april 2001, he is a lecturer in university of technology petronas. he’s area of research is membrane development for inorganic membrane in particular, membrane modeling for reverse osmosis and nanofiltration membranes and membrane applications especially in wastewater control and downstream processing. other area includes in solvent extraction process in recycling of waste oil. microsoft word 2-a latif f.doc iium engineering journal, vol. 2, no. 2, 2001 s. h. tan et al. 7 separation of aqueous isopropanol through chitosan/poly(vinyl alcohol) blended membranes by pervaporation s. h. tan1, a. l. ahmad1*, m. g. mohd. nawawi2 and h. hassan2 1school of chemical engineering, universiti sains malaysia, engineering campus, 14300 nibong tebal, pulau pinang, malaysia. 2department of chemical engineering, faculty of chemical & natural resources engineering, universiti teknologi malaysia, 81310 utm skudai, johor bahru, malaysia. *chlatif@eng.usm.my abstract: blend membranes consisting of chitosan/poly (vinyl alcohol) (cs/pva) were prepared from a solution casting method and characterized via the pervaporation separation of isopropanol-water mixtures. the solution of pure chitosan was blended with poly(vinyl alcohol) at different compositions. the miscibility of the blended polymers was determined. criteria for miscibility was based on the clarity of the blend and the transparency of the membrane obtained. the effects of feed concentration and chitosan content in membrane on the permeation flux and separation factor were also investigated. for the dehydration of 90 wt.% of isopropanol-water mixtures the performance of the blend ratio of 30:70 (cs:pva) exhibited the highest separation factor. it was shown that under the same operating conditions, the pervaporation separation index (psi) for homogeneous membranes were higher than that of blended membranes for the entire feed concentrations. key words: blend, chitosan, poly (vinyl alcohol), miscibility, pervaporation. 1. introduction pervaporation is a membrane process for separating miscible liquid where a liquid mixture is directly brought into contact with a semipermeable membrane and the permeate is removed as a vapour either by creating a vacuum condition or employing a carrier gas on the permeate side as shown in fig. 1. pervaporation differs from other processes in that the membrane constitutes a barrier between a liquid in the liquid phase and the permeate in the vapour phase [1]. pervaporation can be effectively used in the separation of azeotropic, close-boiling point, and heat sensitive mixtures [2]. according to brüschke [3] pervaporation processes can be utilized for different types of separation such as (i) extraction of water from organic liquids, (ii) extraction of volatile organic substances from aqueous streams and (iii) extraction of organic components from mixtures of organic liquids. among the applications of the pervaporation technique, the dehydration of ethanol was the earliest and best developed practical process [4]. fig. 1: basic schematic diagram of pervaporation (huang et al., 1993). pervaporation is one of the most developed membrane separation technology as it is capable of separating azeotropic mixtures or mixtures that have close boiling points. in 1982-83, gesellschaft für trenntechnik (gft) co., germany, developed the first commercial pervaporation membrane by the use of poly (vinyl alcohol)-polyacrylonitrile composite membrane for the dehydration of alcohol solutions [5]. chitosan membrane is one of the hydrophilic membranes, which exhibited preferential permeation to water. chitosan is a natural product derived from chitin, a polysaccharide found in the exoskeleton of shellfish like shrimp or crabs. chitin is the second most abundant natural biopolymer after cellulose [6]. it was estimated that the worldwide annual recovery of chitin from processing of marine crustacean wastes was 37,300 metric tons [7]. besides chitin, the shrimp shells do contain protein, and others inorganic compounds such as calcium carbonate, pigments and lipids. although various methods have been cited in the literature to remove these impurities, the most common technique involves deproteinization and decalcification by using strong alkaline and acid. chitosan is a polymer of [-(14)-2-amino-2-deoxy-dglucopyranose]. it is more amenable to the chemical, medical and industrial applications[8], because of its solubility in various acidic solvents. in order to improve the pervaporation performances, the modified membranes have been studied. one of the modified membranes is blended membrane. when a mixture comprises of two or more polymers, which is not covalently bonded, it is called a polymer blend. the condensate vacuum or carrier gas retentate liquid vapour feed liquid nitrogen membrane iium engineering journal, vol. 2, no. 2, 2001 s. h. tan et al. 8 common techniques for preparing blends are melt mixing and solution casting [9]. homegeneous membrane is prepared from a single polymer material, while blended membrane is normally prepared from two different types of polymers. polymer blending offers a convenient means to prepare materials with a wide range of properties. through a suitable choice of a pair of polymer, polymer blends can often be tailor-made to have specific and desirable properties [10]. blends of chitosan with poly(vinyl alcohol) [11,12], silk fibroin [13] and hydroxyethylcellulose[14] had been reported. the performance of the membrane used to separate a given binary a-b could be characterized by the experimental data, the total permeation flux, j, the amount of liquid that is transported through the membrane per unit area per unit of time. separation factor  could be calculated by the following equation: a/b = a b a b y y x x (1) where ya and yb are the weight fractions of components a and b in the permeate and xa and xb are the weight fractions of the components a and b in the feed. component a is the more preferentially permeating component in the a/b mixture. from the practical point of view, membranes must have a high permeation flux together with large separation factor. however, in the actual pervaporation process normally there is a trade-off between the separation factor and permeation flux where a high separation factor is accompanied by low flux and vice versa. thus, a new formula called pervaporation separation index (psi) has been used for measuring the separation ability of a membrane. it can be defined as the product of a separation factor  and permeation flux j [15]: psi = j ( 1) (2) when  = 1, no separation occurs; a psi of zero means either zero flux or zero separation. the purpose of this study is to prepare chitosan blend with poly (vinyl alcohol) membranes. the pervaporation separations of the isopropanol-water mixtures through the blended membranes were conducted with isopropanol concentration in feed ranging from 10 to 95%. the performance of membranes in pervaporation was evaluated by the permeation flux (j), and the separation factor (). 2. materials chitosan was prepared from domestic uncooked shrimp shells, which were collected from the hawkers nearby the campus. poly (vinyl alcohol) polymer with the average mw 124,000 – 186,000 was purchased from aldrich chemical company (germany). reagent grade sodium hydroxide was purchased from all chem (sweden), ethanol and isopropanol from j. t. baker (usa). deionized distilled water was used in this study. 3. experimental procedure 3.1 preparation of chitin from shrimp shells the dried shells were cut into pieces with an average size of 2-6 mm. the shells were treated with 2 – 3 molar of aqueous sodium hydroxide (naoh) to remove the protein content. the treatments were carried out at 80º – 90ºc for 2 hours. furthermore, they were treated in 2 m aqueous hydrochloric acid (hcl) at room temperature for 24 hours to remove the calcium from the shells[16]. then the shells were washed with distilled water. 3.2 preparation of chitosan from chitin the chitin were further treated with 50 wt.% of aqueous naoh at temperature of 90º – 110ºc for 3 hours in order to remove the acetyl group (ch3co) from the chitin. the flakes obtained by the alkaline treatment were then washed with distilled water, dried under the sun for three hours and further dried up at room temperature. the products obtained are chitosan which were partly deacetylated. according to robert[17], the solubility of chitosan in dilute aqueous acids is obtained at an extent of deacetylation of ~ 60% or above. 3.3 preparation of homogeneous chitosan membranes a preweighed quantity of chitosan were first dissolved in 10 wt.% aqueous acetic acid solution at room temperature and stirred for 24 hours to produce a casting solution consisting of 2 wt.% chitosan. the chitosan aqueous solution was filtered to remove any impurities and undissolved particles to produce a clear homogeneous casting solution by using a vacuum pump. the solution was allowed to settle down for about 3 – 4 hours and the resulting casting solutions were cast onto a petri dish, allowing the casting solution to evaporate at room temperature for 48 hours. the formed membranes were treated in 3 wt.% naoh solution containing 47 wt. % ethanol, and 50 wt.% of distilled water for 24 hours at room temperature. the membranes were then washed thoroughly with distilled water to remove excess naoh before being peeled off from the plate and dried at room temperature. 3.4 preparation of blended membranes the solution casting method was used in preparation of chitosan/poly (vinyl alcohol) blends, in which both chitosan and poly (vinyl alcohol) homopolymers were separately dissolved in the respective solvent. chitosan solutions were prepared by dissolving preweighed quantities of chitosan in 10 wt.% aqueous acetic acid solution and stirring them at room temperature for 24 hours. poly(vinyl alcohol) solutions were prepared by dissolving preweighed quantities of dry poly (vinyl alcohol) powder in deionized distilled water and heating it at 90ºc for 6 hours. the casting solutions were prepared uniformly by mixing together the two solutions with given ratios. the casting solutions were iium engineering journal, vol. 2, no. 2, 2001 s. h. tan et al. 9 cast onto petri dishes and dried at room temperature for 48 hours. the membranes were treated in 3 wt. % naoh solution containing 50 wt. % ethanol solution for 24 hours at room temperature before being peeled off from the plate. 3.5 experimental test rig the pervaporation test rig is shown in fig. 2. the main component of the pervaporation test rig is the membrane cell. the flat sheet membrane cell is fabricated from 316 stainless steel. the membrane cell consists of two portions namely, top and bottom. the top portion was equipped with two openings which were the inlet and outlet of the feed mixtures. two porous stainless steel plates coated with teflon with the pores size of 30 m, thickness of 1 mm and diameter of 90 mm were used to support the membrane. the two portions of the cell were clamped and tightly sealed using rubber o-ring. the effective area of the membrane cell was 52.81 cm2. the permeate vapour left the cell through the bottom side opening which was kept under vacuum by the vacuum pump to supply the necessary driving force for pervaporation. the feed mixture was stirred using bibby stirrer and circulated from the feed tank to the permeation cell using masterflex pristaltic pumps. a digital temperature controller was used to control the temperature of the feed mixtures. furthermore, swagelok control valve was used to control the downstream pressure. the permeate vapour was condensed in a cold trap by using liquid nitrogen. the condensed permeate was warmed up to ambient temperature and weighed to determine its flux. three samples were taken for measuring of the flux and separation factor at every different feed concentration. the compositions of the permeate were determined by the karl fischer method[18]. fig. 2: schematic diagram of the experimental rig for pervaporation process. 4. results and discussion optical clarity is a good indication of miscibility of polymer blends. the blended solutions of chitosan/pol y (vinyl alcohol) as well as the formed membranes were optically clear and transparent. these results reveal that the blends of chitosan and poly (vinyl alcohol) were compatible. fig. 3 shows the pervaporation characteristics of blended membranes of 90 wt. % of isopropanol in feed solution with different content of chitosan. the results show that the total permeation flux increases with an increase in the chitosan content. however the separation factor increased at an initial stage, it reached a miximum at chitosan content of 30 wt. % and then decreased. the best trade-off between the total permeation flux and its separation factor was achieved at 30 wt. % of chitosan content in the blend ratio. a plasticizing effect by the poly (vinyl alcohol) on the chitosan[11] might have been expected. this resulted in the increase of the segmental mobility of the polymeric membrane as well as its free volume furthermore the diffusivity of permeating components would also be enhanced. chanachai et al.[14] studied the blend of chitosan/hydroxyethylcellulose for the pervaporation of ethanol-water mixtures also found a similar trend. fig. 4 shows the effect of blend ratio on the total and individual permeation fluxes at 90 wt.% of isopropanol in the feed. at chitosan content less than 45 wt. %, high water permeation flux was accompanied by low isopropanol permeation flux. on the other hand, above 45 wt.% of the chitosan content, a reverse trend occurred. based on the above results, it is suggested that the polymer hydrophilicity was well balanced at the blend ratio of 30:70 (cs:pva). thus, the membrane at this particular blend ratio was chosen for further characterisation through pervaporation dehydration of isopropanol/water mixture with the effect of the feed concentrations. 0 20 40 60 80 100 120 140 160 0 20 40 60 80 100 weight percent of chitosan, % t ot al p er m ea tio n fl ux , g /m 2 . hr 0 20 40 60 80 100 120 140 160 180 se pa ra tio n fa ct ortotal permeation flux separation factor fig. 3: flux and separation factor at different % of chitosan. 1 feed tank temperature controller heating tape circulation pump membrane cell pressure gauge cold trap with dewar flaks control valve vacuum pump circulation pump iium engineering journal, vol. 2, no. 2, 2001 s. h. tan et al. 10 fig. 4: flux at different % of chitosan. figure 5 shows the total permeation flux and separation factor versus weight percent of isopropanol in feed solutions. the results showed that there was a trade-off between the total permeation flux and its separation factor for the entire feed solutions. the increase in the isopropanol concentration restricts the degree of swelling of the membranes, thus reducing the diffusivity of the permeating components. furthermore, the molecular size of isopropanol was bigger than that of water, so when the free volume of the membranes decrease at high concentration of isopropanol in feed, the permeation flux for water is higher than that of isopropanol. these could be the reasons why when the total permeation flux decreased, the separation factor increased and vice versa. in order to measure the performance of the homogeneous and blended membranes, both the total permeation flux and separation factor have to be taken into consideration. since there is a trade-off between the permeation flux j and the separation factor , when one factor increases the other decreases. thus the pervaporation separation index (psi), which is defined as the product of j and ( 1) has been widely used to evaluate the overall pervaporation membrane performance. the results are shown in fig. 6. it was found that in terms of psi, the cs/pva membrane was higher than that of homogeneous membrane over the entire range of feed compositions. fig. 5: the total permeation flux and separation factor at different % of isopropanol in feed. fig. 6: psi of the membranes at different % of isopropanol in feed. however, at very high and low isopropanol content in the feed solution, there was no significant difference of psi between the homogeneous and blended membranes. this was due to the high separation factor being compensated by a low permeation flux or vice versa. the above results indicated that the polymer blending technique especially at blend ratio of 30:70 (cs:pva) had the ability to improve the overall pervaporation performances of chitosan membrane for the pervaporation dehydration of isopropanol and water mixtures. 5. conclusion the blend membranes were successfully prepared from chitosan and poly (vinyl alcohol) via a solution casting methods. both the blended solutions and the formed membranes were optically clear and transparent. these revealed that the blends of chitosan and poly(vinyl alcohol) were compatible. among the prepared blend ratios, the membranes with the blend ratio of 30:70 (cs/pva) showed the highest separation factor for pervaporation dehydration of isopropanol/water mixture with 90 wt.% of isopropanol in deed solutions. the blend membranes could improve the overall pervaporation performance, in term of pervaporation separation index (psi), the membranes with the blend ratio of 30:70 (cs:pva) always showed higher psi than that of homogeneous membranes. however, both types of the membranes, homogeneous and blended were capable of dehydration. acknowledgements the financial support provided for this research by the ministry of science, technology and environment of malaysia through irpa project is gratefully acknowledged. 0 20 40 60 80 100 120 140 160 180 0 20 40 60 80 100 weight percent of chitosan, % t ot al p er m ea tio n fl ux , g /m 2 . hr total water isopropanol 0 200 400 600 800 1000 1200 1400 0 20 40 60 80 100 weight percent of isopropanol in feed, % t ot al p er m ea tio n fl ux , g /m 2. hr 0 50 100 150 200 250 300 se pa ra tio n fa ct or total permeation flux separation factor 0 200 400 600 800 1000 1200 1400 0 20 40 60 80 100 weight percent of isopropanol in feed, % t ot al p er m ea tio n fl ux , g /m 2. hr 0 50 100 150 200 250 300 se pa ra tio n fa ct or total permeation flux separation factor iium engineering journal, vol. 2, no. 2, 2001 s. h. tan et al. 11 references [1] r.y.m. huang and w. rhim (1993). “separation characteristics of pervaporation membrane separation process using modified poly(vinyl alcohol) membranes.” polymer international. 30. 123-128. [2] e. ruckenstein and l. liang (1996). “poly(acrylic acid)poly(vinyl alcohol) semiand interpenetrating polymer network pervaporation membranes.” journal of applied polymer science. 62. 973-987. [3] h.e.a. brüschke (1990). “removal of ethanol from aqueous streams by pervaporation.” desalination. 77. 323-329. [4] i. maeda and m. kai (1991). “recent progress in pervaporation membranes for water/ethanol separation.” in huang, r.y.m. “pervaporation membrane separation processes.” the netherlands: elsevier, amsterdam. 111180. [5] r.y.m. huang, fcic and x. feng (1993). “pervaporation separation processes: history, development and separation applications.” canadian chemical news. march. 21-23. [6] a. l. andrady, a. torikai and t. kobatake (1996). “spectral sensitivity of chitosan photodegradation.” journal of applied polymer science. 62. 1465-1471. [7] j. k. yang, i. l. shih, y. m. tzeng, and s. l. wang (2000), “production and purification of protease from a bacillus subtilis that can deproteinize crustacean wastes.” enzyme and microbial technology. 26. 406413. [8] k.d. yao, t. peng, h.b. feng and y.y. he (1994). “swelling kinetic and release characteristic of crosslinked chitosan: polyether polymer network (semi-ipn) hydrogels.” journal of polymer science: part a: polymer chemistry. 32. 1213-1223. [9] d.r. paul, j.w. barlow and h. keskkula (1985). “polymer blends” in mark,bikales, overberger and menges. “encyclopedia of polymer science.” usa: john wiley & sons. 398-461. [10] l. fang and goh, s. h. (2000). “miscible chitosan/tertiary amide polymer blends.” journal of applied polymer science. 76. 1785-1790. [11] h. s. blair, j. guthrie, t. k. law and p. turkington, (1987). “chitosan and modified chitosan membranes i. preparation and characterisation.” journal of applied polymer science. 33. 641-656. [12] l. g. wu, c. l. zhu, and m. liu (1994). “study of a new pervaporation membrane part 1. preparation and characteristics of the new membrane.” journal of membrane science. 90. 199-205. [13] x. chen, w. li, z. shao, w. zhong and t. yu (1999). “separation of alcohol-water mixture by pervaporation through a novel natural polymer blend membranechitosan/silk fibroin blend membrane.” journal of applied polymer science. 73. 975-980. [14] a. chanachai, r. jiraratanano, d. uttapap, g.y. moon, w.a. anderson and r.y.m. huang (2000). “pervaporation with chitosan/hydroxythelcellulose blended membranes.” journal of membrane science. 166. 271-280. [15] p. sampranpiboon, r. jiraratananon, d. uttapap, x. feng and r.y.m. huang (2000). “pervaporation separation of ethyl butyrate and isopropanol with polyether block amide (peba) membranes.” journal of membrane science. 173. 53-59. [16] m.g. mohd. nawawi, s. h. tan, and h. hassan (2001). “pervaporation separation of isopropanol-water mixtures using chitosan based membranes.” 15th symposium of malaysian chemical engineers somche 2001, 115-120, [17] g. a. f. roberts (1992). “chitin chemistry.” 1st ed. london: the macmillan press ltd. 1-53. [18] j. p. brun, c. larchet, g. bulvestre and b. auclair (1985). “sorption and pervaporation of dilute aqueous solutions of organic compounds through polymer membranes.” journal of membrane science. 25. 55-100. nomenclature  separation factor ya weight fraction of component a in permeate yb weight fraction of component b in permeate xa weight fraction of component a in feed xb weight fraction of component b in feed psi pervaporation separation index, (kg/m2.hr) j total permeation flux, (kg/m2.hr) biography of the authors tan soon huat received his b.eng. (chemical engineering) and m.sc. (chemical engineering) from universiti teknologi malaysia (utm) in 1999 and 2002, respectively. his research interest is in developing new types of polymeric membranes for liquid-liquid system and pervaporation process. currently he is an academic staff with the school of chemical engineering, universiti sains malaysia. associate prof. dr. abdul latif ahmad is currently the deputy dean (research and postgraduate study) at the school of chemical engineering, engineering campus, universiti sains malaysia, nibong tebal, penang. he was born in selangor, malaysia in 1967. he received his b.eng. (chemical engineering), m.sc. (chemical engineering) and ph.d (membrane technology), all from the university of wales, united kingdom in 1990, 1991, and 1995 respectively. his area of research interest is membrane separation technology; synthesis and characterisation toward the application of environment monitoring and pollution control including water, wastewater and gas separation. dr. mohd. ghazali mohd. nawawi received his bachelor’s degree in chemical engineering from the new mexico state university, usa in 1987. he obtained his master degree in chemical engineering from university college of swansea, uk in 1990 and then graduated with a ph.d degree from the university of waterloo, canada in 1997. he is currently a senior lecturer at universiti teknologi malaysia. he is the head of separation science and engineering research group (senser). his research works focus on the iium engineering journal, vol. 2, no. 2, 2001 s. h. tan et al. 12 development of natural polymeric membranes for the dehydration of alcohols using pervaporation. hashim hassan graduated from universiti teknologi malaysia (utm) with a b. eng. in chemical engineering in 1988. after graduation, he gained experience in membrane technology as research officer at universiti kebangsaan malaysia (ukm). he received his m. sc. (chemical engineering) in 1994, his thesis was on the production of hollow fiber membrane for gas separation. he joined utm as a tutor in the chemical engineering department in 1994. his research interest is in synthesis and preparation of novel membranes for pervaporation including the development of a mathematical model. 146 iium engineering journal, vol. 13, no. 2, 2012 kini et al. 121 propanoyl(1z)-n-(2,6-dimethylphenyl)-2oxopropanehydrazonoate as inhibitor for corrosion of 6061 al alloy15 % (v) sic(p) composite in hydrochloric acid media u. achutha kini 1 , prkasha shetty 2 , s. divakara shetty 1 , arun isloor 3 and ramadev herle 1 1 department of mechanical and manufacturing engineering, manipal institute of technology, manipal-576104, india. 2 department of printing and media engineering, manipal institute of technology, manipal576104, india. 3 department of chemistry, national institute of technology karnataka, india. achutha_kini@yahoo.co.in abstract: the corrosion inhibition effect of propanoyl(1z)-n-(2,6-dimethylphenyl)2-oxopropanehydrazonoate (pdoh) in the corrosion of 6061 aluminium alloy-15%(v) sic(p) composite in 0.5 and 1m hydrochloric acid medium at four different temperatures (30, 40, 50 and 60 ⁰c) was investigated using potentio-static polarization (tafel extrapolation and linear polarization) and weight loss methods. the results obtained reveal that pdoh is an efficient corrosion inhibitor with around 96% inhibition efficiency within the range of temperature studied. leftward and downward shifts in tafel plots were observed with the addition of the inhibitor, indicating that pdoh inhibits the corrosion process effectively, and that it is a cathodic inhibitor. corrosion rate increases and inhibition efficiency decreases with increase in temperature. results obtained by tafel extrapolation, linear polarization, and weight loss methods are in agreement. the adsorption of the inhibitor onto the surface of the 6061 al alloy 15 % (v) sic(p) composite is found to obey temkins' adsorption isotherm that verifies the assumption of mono-layer adsorption on a uniform homogeneous composite surface with an interaction in the adsorption layer. the inhibition is therefore governed by the physisorption mechanism. abstrak: kesan perencatan kakisan propanoyl(1z)-n-(2,6-dimethylphenyl)-2oxopropanehydrazonoate (pdoh) ke atas kakisan komposit aloi al 6061-15%(v) sic(p) dalam media asid hidroklorik 0.5 dan 1m pada suhu-suhu yang berbeza (30, 40, 50 dan 60⁰c) telah dikaji menggunakan polarisasi statik-upaya (extrapolarisasi tafel dan polarisasi linear) dan kaedah kehilangan berat. keputusan diperolehi menunjukkan pdoh adalah perencat yang efisien dengan 96 % keupayaan perencatan bagi julat suhu yag dikaji. anjakan ke kiri dan ke bawah plot tafel dapat dilihat dengan penambahan perencat, menunjukkan pdoh merencatkan proses kakisan dengan berkesan, dan ia adalah perencat katodik. dengan peningkatan suhu, kadar kakisan meningkat dan keberkesanan perencatan menurun. keputusan dari ekstrapolasi tafel, polarisasi linear dan kehilangan berat.adalah saling bersetuju antara satu sama lain. penjerapan perencat ke atas permukaan komposit aloi 6061 al alloy 15 % (v) sic(p) memenuhi penjerapan temkins’ isoterma yang mengesahkan andaian penjerapan lapisan-mono ke atas permukaan komposit homogenus yang seragam melalui interaksi pada lapisan penjerapan. perencatan dikawal oleh mekanisma fizijerapan. keywords: potentiostatic polarization; aluminium alloy composite; adsorption isotherm; corrosion inhibition; physisorption iium engineering journal, vol. 13, no. 2, 2012 kini et al. 122 1. introduction aluminium and its alloys and composites represent an important category of materials due to their high technological value and wide range of applications, especially in aerospace industry and military applications. the use of these materials in light weight applications because of high strength to weight ratio is widespread and these usages expose them to environments that could be acidic or alkaline [1]. generally, aluminium alloys and composites are highly resistant to corrosion owing to the formation of a protective oxide layer on their surface [2]. corrosion does take place when this protective al2o3-3h2o layer is either unstable or defective. corrosion in al alloys and its composites is either pitting or inter-granular corrosion. pitting takes place in environments where the protective al2o3-3h2o film is partially stable. in these cases, corrosion usually originates adjacent to the flaws in the microstructure of the film [3]. inter-granular corrosion results in selective corrosion at the grain boundaries or any precipitate free zones that might be found adjacent to them, with the remainder of the matrix undergoing very little corrosion. inter-granular corrosion occurs because of the formation of precipitates along the grain boundaries of al and its alloys which are more anodic with respect to the interior of the grains. as a result, preferential dissolution occurs at these sites where these precipitates or precipitate free zones undergo anodic reactions [4]. hydrochloric acid solutions are used for pickling, chemical and electrochemical etching and in various chemical process industries wherein al alloy composites are used. in such cases it becomes very important to use corrosion inhibitors so as to protect the material against excessive corrosion [5]. the effect of any particular organic compound on the corrosion behaviour of metals in acid system depends on the type of metal, environment contamination and its interaction with the surface of the metal. the inhibiting action of organic compounds has been mainly attributed to adsorption of the inhibiting molecule on the surface of the material. this adsorption affects the electrochemical behaviour involved in the corrosion process of metals/alloys/composites [6]. organic compounds are widely used in various industries as corrosion inhibitors in acidic environments. the effective organic inhibitors contain nitrogen, sulphur and oxygen atoms. these heteroatoms are capable of forming coordinate covalent bond with metal owing to their free electron pairs and thus act as inhibitor. compounds with π-bonds also generally exhibit good inhibitive properties due to interaction of π orbital with metal surface. the organic inhibitors function through adsorption on the metal surface blocking the active sites by displacing water molecules and forming a compact barrier film to decrease the corrosion rate. the inhibition effect of 3–methyl–4–amino–5–mercapto–1,2,4–triazole on the corrosion behaviour of 6061 al alloy 15 % (v) sicp composite has been reported [7]. this triazole compound was found to act as an anodic inhibitor with a maximum efficiency of 58 % at 30 °c. allyl thiourea was used as an inhibitor for the corrosion of 6061 al alloy 15 % (v) sicp composite in hcl medium and showed a maximum efficiency of 70% in the temperature range of 30 – 50 °c [8]. in the present work, inhibitive action of propanoyl(1z)-n-(2,6-dimethylphenyl)-2oxopropanehydrazonoate (pdoh) on the corrosion behavior of 6061 al alloy 15 % (v) sic(p) composite in 0.5 and 1 m hydrochloric acid medium at four different temperatures (30 60 °c) has been investigated using tafel extrapolation technique. the results obtained are cross checked by linear polarization and weight loss methods. iium engineering journal, vol. 13, no. 2, 2012 kini et al. 123 2. experimental method 2.1 specimen 6061 al alloy 15 % (v) sic(p) composite having aluminum alloy 6061 as the matrix and 15 vol. % of silicon carbide particles of mean diameter 25 µm are manufactured in the form of cylindrical bars of length 120 mm and diameter 40 mm at vikram sarabhai space centre (vssc), trivandrum by stir casting process. specimen of required length is cut from the extruded bar and machined to the required diameter. the specimen with an exposed bottom surface area of 0.95 cm 2 is polished with emery papers of different grades degreased with acetone and then rinsed with distilled water and finally dried in air. then the specimen surface is covered with teflon tape, to enable the required surface getting exposed to the media. specimen acts as the working electrode in the three electrode cell system and is connected to the potentiostat along with the reference and counter electrodes. this composite material has the chemical composition (% wt): 0.25 cu; 1.0 mg; 0.60 si; 0.20 cr and balance al. 2.2 inhibitor propanoyl(1z)-n-(2,6-dimethylphenyl)-2-oxopropanehydrazonoate (pdoh) is prepared by dissolving 2,6-dimethylaniline (2.26g, 0.01 mol) in dilute hydrochloric acid (22.0 ml i.e 9.0 ml 12 m hcl dissolved in 13.0 ml water) and cooled to 0°c in an ice bath. to this, a cold solution of sodium nitrite (3.2 g, 0.0462 mol in 10.0 ml of water) is added, as the temperature of the reaction mixture maintained below 5 °c. the resulting diazonium salt solution is filtered into a cooled solution of ethylacetoacetate (3.4 ml) and sodium acetate (7.0 g) in ethanol (100 ml). the resulting yellow-orange solid is filtered, washed with ice cold water, dried in air and recrystallized from methanol. [yield 3.65 g, 86.5 %; mol.wt. 278.30]. purity of the compound is checked by its melting point (346 – 348 ⁰c) and elemental analysis [9]. fig. 1: structural formula of pdoh. 2.3 medium analytical reagent grade hcl (merck) and double distilled water are used for preparing test solutions of 0.5 and 1 m hcl. 2.4 tafel extrapolation studies the polarization studies are performed using a wenking potentiostat (lb 95l) and a three electrode cell system. the steady state tafel extrapolation studies are made from 250 mv versus ocp to +250 mv versus ocp in steps of 20 mv from the cathodic side and the corrosion currents are noted. the tafel plots of potential versus logi are drawn and the corrosion current density (icorr) and the corrosion potential (ecorr) are determined. the corrosion rate, the degree of surface coverage (θ) and the percentage inhibition efficiency (% ie) are calculated. the experiments are performed with 1 m hcl at four different temperatures (30-60 °c). temperature is maintained within ±1 °c. nh n ch3 o ch3o och3 ch3 )-n-(2,6-dimethylphenyl)-2-oxopropanehydrazonoate iium engineering journal, vol. 13, no. 2, 2012 kini et al. 124 2.5 linear polarization method linear polarization studies are carried out in the potential (e) range of -20 mv versus ocp to +20 mv vs ocp in steps of 5 mv from the cathodic side and the steady state corrosion currents (i) are noted. the slope of e vs i are used to determine the corrosion current density (icorr) and the corrosion rate (cr). 2.6 weight loss method specimen surface of 1 cm 2 is exposed to 100 ml of hcl solution for 6 hours. prior to exposure, the surface is polished with different grades of emery paper and rinsed with distilled water and acetone, then dried and finally accurately weighed. after exposure, again the specimen is gently polished, rinsed with distilled water and acetone, then dried and accurately weighed. the difference in weight gives the weight loss. experiments are conducted with 0.5 and 1 m hcl in the presence and absence of inhibitor at 30 °c. 3. results and discussion the electrochemical parameters for the inhibiting action of pdoh on the corrosion of 6061 al alloy 15 % (v) sic(p) composite in 0.5 and 1 m hcl solution are studied by potentiostatic polarization technique at four temperatures. the results are presented in table 1 and 2. the corrosion rate, and the percentage inhibitor efficiency (% ie) are calculated by using the following relations [10]. ������� .� �����.�������� � (1) where, icorr is the corrosion current density in µa/cm 2 , eq. wt is the specimen equivalent weight in g, d is the specimen density in g/cc and 0.1288 is the metric and time conversion factor. %�� ��������������� ������ ! � 100 �2� where, icorr and icorr(inh) are the corrosion current densities in µ a/cm 2 in the absence and presence of the inhibitor respectively. the inhibiton efficiency by weight loss method is calculated by using the following expression [11]. %�� �&�&�� & � � 100 �3� where, w and winh are the values of weight loss of the specimen after immersion in test solution without and with inhibitor, respectively. it is observed from the polarization results (tables 1 & 2) and the polarization curve (fig. 2) that there is a large negative shift in the corrosion potential (ecorr) and a drastic reduction in the corrosion current density (icorr) and corrosion rate (cr) values. the shift in corrosion potential in the negative direction indicates that pdoh is an efficient cathodic inhibitor. iium engineering journal, vol. 13, no. 2, 2012 kini et al. 125 fig. 2: tafel extrapolation plot for pdoh in 1 m hcl at 30 °c. table 1: electrochemical parameters for the corrosion inhibition of 6061 al alloy 15 % (v) sic(p) in 0.5 m hcl medium. table 2: electrochemical parameters for the corrosion inhibition of 6061 al alloy 15 % (v) sic(p) in 1 m hcl medium. a comparison of the inhibition efficiency obtained from tafel extrapolation, linear polarization techniques and weight loss method at 30 °c is given in table 3. the results obtained by all the three methods are in agreement. the % ie increases with increase in concentration of pdoh up to 4.5×10 -4 moll -1 (table 1 and 2). the increase in % ie may be due to the blocking effect of the surface by both adsorption and film forming mechanism which decreases the effective area of attack. the results indicate that pdoh is an effective corrosion inhibitor which gives efficiency iium engineering journal, vol. 13, no. 2, 2012 kini et al. 126 values as high as 96 %. the inhibiting effect of pdoh may be due to its parallel adsorption at the 6061 al alloy/sicp composite–acid solution interface. the parallel adsorption takes place owing to the presence of one or more active centers of adsorption. pdoh might have displayed high inhibition efficiency because of the presence of hetero atoms of n in their structure as well as the presence of n rich azo group and o rich ester (carbonyl) multiple functional groups in its structure. table 3: comparison of inhibition efficiencies obtained by tafel extrapolation, linear polarization and weight loss methods for the corrosion inhibition of 6061 al alloy 15 % (v) sic(p) in 0.5 and 1 m hcl media. fig. 3: the scanning electron micrographs of 6061 al alloy 15 % (v) sic(p) composite (a) fresh specimen (b) specimen exposed to 1 m hcl (c) specimen exposed to 1 m hcl containing 4.5×10 -4 moll -1 of pdoh. iium engineering journal, vol. 13, no. 2, 2012 kini et al. 127 the surface analysis of 6061 al alloy 15 % (v) sic(p) composite is carried out using scanning electron microscope (jeol model 8340 la). the scanning electron micrograph of a fresh specimen is shown in fig. 3a. the micrographs for the specimens immersed in 1 m hcl solution at 30° c in the absence and presence of inhibitor are shown in fig. 3b and 3c respectively. the corrosion of 6061 al alloy 15 % (v) sic(p) in hcl medium is presumably due to the anodic dissolution either at the grain boundaries or at the metalmedia interface. it is seen from the fig. 3c that the surface of the composite exposed to solution with inhibitor is smoother than of that exposed to acid solution without inhibitor (fig. 3c). these observations suggest that the inhibitor forms a protective layer on the composite surface, which prevents the attack of acid on the surface. to understand the mechanism of corrosion inhibition, the adsorption behaviour of the inhibitor compound on the composite surface must be known. the surface coverage values for different concentrations of pdoh from the acid solution are calculated. the surface coverage values (θ) are tested graphically by fitting a suitable adsorption isotherm. the plot of θ versus log c (fig. 4) for different concentrations of pdoh shows a straight line indicating that the adsorption of the compound on the composite surface follows temkin’s adsorption isotherm. the applicability of temkin’s adsorption isotherm verifies the assumption of mono-layer adsorption on a uniform homogeneous composite surface with an interaction in the adsorption layer [12, 13]. fig. 4: temkin’s adsorption isotherm for pdoh on 6061 al alloy 15 % (v) sic(p) composite surface in 1 m hcl at different temperatures. table 4: thermodynamic parameters for pdoh corrosion of 6061 al alloy 15 % (v) sic(p) composite in 1 m hcl solution. the thermodynamic parameters for the corrosion of 6061 al alloy 15 % (v) sic(p) in the presence of pdoh are studied (table 4). iium engineering journal, vol. 13, no. 2, 2012 kini et al. 128 the values of activation energy (ea) are calculated using arrhenius equation [14] ln �* *�! + �,-. �/�.0�.1� �4� where, r2 and r1 are the corrosion rates at temperatures t2 and t1 respectively, r is the gas constant, t1 and t2 are the two temperature levels and δt is the difference in temperatures. the equilibrium constant (k) is determined by the relation: 3 45���4� �5� where, θ is the degree of surface coverage on the metal surface and c is the concentration of the inhibitor in moll -1 . the free energy of adsorption (∆gads) is calculated from the following equation [15, 16]. δ89:; +�<=>�55.53� �6� where 55.5 is the concentration of water in solution in moll -1 and t is the temperature in kelvin. the negative values of ∆gads indicate spontaneous adsorption and strong interaction of inhibitor molecules on to the surface of the composite. the ∆gads values for the optimal concentration (4.5×10 -4 moll -1 ) of pdoh are less than -40 kj mol -1 . this indicates that the inhibition is governed by physical adsorption mechanism [17]. 4. concluding remarks a) the corrosion rate decreased drastically in the presence of pdoh in both 0.5 and 1 m hydrochloric acid media over the temperatures studied (30-60 °c). b) pdoh has proved to be an efficient cathodic inhibitor for corrosion of 6061 al alloy 15 % (v) sic(p) composite in 0.5 and 1 m hydrochloric acid media. c) the adsorption of the compound on the surface of 6061 al alloy 15 % (v) sic(p) composite obeys temkin’s isotherm and is governed by physical adsorption mechanism. d) % ie obtained by polarization techniques and weight loss method are in agreement. acknowledgement the authors are thankful to the director and dr. n. y. sharma, former head, department of mechanical engineering, manipal institute of technology for providing the facilities. references [1] g. o. avwiri and f. o. igho, “inhibitive action of veronica amygdalina on the corrosion of aluminium alloys in acid media.” marer. lett. 57(2003):3705. [2] k. a. lucas and h. clarke. “corrosion of aluminium based metal matrix composites.” research studies press ltd., somerset, u.k., 1993. [3] s. wernick, r. pinner and p. g. shasby. the surface treatment and finishing of alumunium and its alloys, 5 th ed., 1.5(1987). iium engineering journal, vol. 13, no. 2, 2012 kini et al. 129 [4] d. w. berkeley, h. e. m. sallam and h. e. m. sallam and h. nayeb-hashemi. “the effect of ph on the mechanism of corrosion and stress corrosion and degradation of mechanical properties of aa 6061 and nextel 440 fibre reinforced aa 6061 composite.” corros sci., 40(1998): 141. [5] b. mernari, h. elattari, m. traisnel, f. bentiss and m. lefrance. “inhibiting effects of 3.5 his (npyridyl)-4-amino-1, 2, 4-triazoles on the corrosion of mild steel in 1 m hci medium.”corros. science 40(1998):391. [6] k. obesegum abiola, n. c. oforka and s. s. angeye, “corrosion behavior of aluminium in hydrochloric acid solution containing mercaptoacentic acid.” materials letters 58(2004): 3461. [7] suma rao, padmalatha, jagannath nayak and a. nithyananda shetty. “3-methyl-4-amino-5 mercapto-1, 2, 4-triazole as inhibitor of corrosion of 6061 al-15 vol. pct. sic(p) composite.” journal of metallurgy and materials sciencej,47.1(2005: 51. [8] suma rao a, padmalatha, jagannath nayak a, nithyananda shetty and k. r. hebbar, “corrosion behavior of al-15 vol. pct sic (p) in hydrochloric acid (a study of inhibitive effect of allysl thiourea).” national conference on corrosion and corrosion control, metcorr -nitk, suraathkal, (2005): 100. [9] arun m isloor, phd thesis. “study on the synthesis and biological activity of some pharmaceutically important heterocyclic compounds.” mangalore university: 104, august 2001. [10] s. divakara sheety and prakash sheety. “inhinition of mild steel corrosion in acid media using n-benzyl-n’-phenyl thiourea.” indian journal of chemical technology 15.3 (2008): 216. [11] m. abdallah. “rodaninc azosulpha drug as corrosion inhibitors of 304-stainless steel in hydrochloric acid solution.” corrosion science 44(2002):717. a. e. stayomova, e. i. sololova and s. n. roichara. “the inhibition of mild steel corrosion in 1 m hci in the presence of linear and cyclic thiocarbamides-effect of concentration and temperature of the corrosion medium on their protective action.” corrosion science 39(1997):1595. [12] pandian, bothi raza and mathur gopalakrishnan sethuraman, “solanum tuberosum as an inhibitor of mild steel corrosion in acid media”, iran journal chemical and chemical engineering 28.1(2009):77. [13] s. s. abd el-rehim, s. a. m. refacy, f. taha, m. b. saleh and r. a. ahmed. “corrosion inhibition of mild steel in acidic medium using 2-amino thiophenol and 2-cyanomethyl benzothiazole.” journal applied electrochemical 31(2001): 429. a. k. putilova, s. a. balezin, y. p. borasanic, metallic corrosion inhibitors, pergomeon press,oxford, 1960. [14] m. a. quaroishi and r. sardar. “the effect of some nitrogen and sulphur based synthetic inhibitors on corrosion inhibition of mild steel in acid solution.” indian journal chemical technology 11(2004):103. [15] b. obot and n. o. obi-egbedi. “inhibition of aluminium corrosion in hydrocholoric acid using nizoral and the effect of iodide addition.” e-journal of chemistry 7.3(2010):837. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 virtual prototype-based kinematic modeling and simulation of a multi-mode amphibious robot mohammed rafeeq1, siti fauziah toha1*, salmiah ahmad2 and mohd asyraf mohd razib1 1 department of mechatronics engineering, 2 department of mechanical engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. * corresponding author: tsfauziah@iium.edu.my (received: 21st july 2021; accepted: 13th october 2021; published on-line: 4th july 2022) abstract: the amphibious robot, which has the capability of multi-mode motion, can maneuver diverse environments with high mobility and adaptability. these are employed in the area of reconnaissance, search and rescue operations, and monitoring. the existing amphibious robots have lower maneuverability over the crawling period on uneven and slope surfaces on the land. in this paper, a kinematic model of the amphibious robot based on virtual prototyping is designed for multi-mode locomotion. adams (automated dynamic analysis of mechanical systems) is a multi-body dynamic solver adopted to build the simulation model for the robot. the novel amphibious robot employs a rockerbogie mechanism equipped with wheel paddles. the locomotion analysis on land involves straight-going and obstacle negotiation, which is simulated using adams. the simulation analysis result demonstrates increased maneuverability, achieving a robot's velocity of 1.6 m/s. normal forces on the front and rear wheels show equal load distribution, contributing more to the robot’s equilibrium over uneven terrain. the simulation result reflects the accurate kinematic characteristics of the amphibious robot and provides a theoretical basis for developing an algorithm for robot motion control and optimization. further, this research will concentrate on the kinematic simulation maneuvering in water mode with the wheel paddle. abstrak: robot amfibia yang memiliki berbilang mod pergerakan, dapat bergerak dalam persekitaran berbeza dengan ketinggian mobiliti dan adaptasi. kebolehan ini dapat digunakan dalam kawasan pengintipan, operasi pencarian dan menyelamat, dan peninjauan. robot amfibia sedia ada mempunyai kurang kebolehgerakan sepanjang tempoh merangkak pada permukaan cerun dan permukaan tidak rata pada tanah. dalam kajian ini, model kinematik robot amfibia berdasarkan prototaip maya dibentuk berdasarkan gerak alih pelbagai mod. sistem mekanikal analisis dinamik automatik (adams) adalah penyelesai dinamik berbilang badan telah diadaptasi bagi membina model simulasi robot. robot amfibia baru dicipta berdasarkan mekanisme rockerbogie beserta padel tayar. analisis gerak alih atas tanah ini termasuk gerakan-lurus dan rundingan halangan, disimulasi menggunakan adams. dapatan simulasi kajian menunjukkan peningkatan kebolehgerakan, mencapai halaju robot sehingga 1.6 m/s. daya tujahan normal pada depan dan belakang tayar menunjukkan keseimbangan agihan beban, menyumbang lebih kepada keseimbangan robot ke atas permukaan yang tidak rata. dapatan kajian dari simulasi menunjukkan ciri-ciri kinematik yang tepat pada robot amfibia dan menyediakan teori asas bagi membangunkan algoritma kawalan pergerakan 246 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 dan pengoptimuman. seterusnya, kajian ini mengfokuskan simulasi gerakan kinematik dalam mod air beserta padel tayar. keywords: amphibious robot; kinematic modeling; virtual prototype; adams 1. introduction nature inspires to develop locomotion systems that exhibit functionality and performance close to the locomotion of animals [1]. amphibians encourage developing locomotion strategies since they have excellent locomotion features in the terrestrial and aquatic environments. they smoothly transit between these mediums by simply alternating body mechanisms to adapt to the environment. the terrestrial and aquatic locomotion environment like near-shore, shallow waters demand high mobility and adaptability because of diverse terrain profiles such as sand, wetlands, rocks, uneven surfaces, and varying obstacles to overcome for complete maneuvering. locomotion metrics like mobility and adaptability in these environments are excellent characteristics of amphibious animals [2]. amphibious robotics has shown advancement in the past two decades; however, the research focuses on developing the propulsive mechanisms of robots to improve mobility performance in the aquatic medium. the research work in the past focused on bio-mimic swimming characteristics to enhance performance in water. however, these amphibious robots’ practical applications demand more capabilities on the land environment, including high terrain adaptability and speed on land, thrust performances, and heading control in the aquatic environment. consequently, maneuvering ability in these robots needs to focus on driving mechanisms and control performance on both land and water. amphibious locomotion of snakes utilizes the undulation of their bodies for propulsion and motion on water and land [3]. the locomotion strategies developed to achieve amphibious locomotion are inspired by legged amphibians like water runners and basilisk lizards [4]. the hybrid mechanism combining leg and wheel is adopted in the whegs robot for terrestrial and underwater locomotion. whegs series use propellers for underwater locomotion and wheel-leg for locomotion on irregular terrain. the amphibious spherical robot by guo. et al. mimics turtles’ legged locomotion on ground and uses waterjet thrusters for generating thrust in underwater environments [5]. the locomotion performance of amphibious robots reported in the literature is suitable for a smooth land environment with lower speed performance in the water. the hybrid mechanisms achieve improved mobility but at the cost of complex control design. an amphibious robot with a single design is proposed with compact control design. the present amphibious robot is suitable for smooth land surfaces, and legged amphibious robots have lower propulsive speed. there is a need for an amphibious robot with higher mobility capable of traversing uneven land. traditionally, researchers utilize experimental methods to validate the mechanical design structure. the experimental work is close to the real environment; however, it involves cost and time. the virtual prototyping validates the kinematic characterization of the model to achieve optimal performance before developing the actual prototype [6]. lin et al. [7] utilizes a virtual prototyping robot to obtain kinematic parameters and validate the model using adams for dynamic analysis of an amphibious spherical robot. zong et al. [8] study the locomotion performance of amphibious robots using a virtual prototype created in adams. the kinematic simulations validate transformable flipper leg performance on complex terrain and underwater environment. zhuang et al. [9] propose a hydraulic-driven quadruped amphibious robot leg movement analysis using adams that facilitates gait 247 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 selection of quadruped amphibious robots to crawl on uneven terrain. virtual prototyping of the model aims to achieve optimal performance before developing the actual prototype and facilitates the iterative process to verify the complete model at early stages, reducing the time and cost of development. dynamic and kinematic analysis of the rocker-bogie based mechanism in adams is performed to study the working principle of an amphibious robot. cao et al. [10] illustrate the modeling process of simple linkage mechanisms like gear and a cam performed in an adams environment. virtual prototyping has become a common tool to analyze the performance of models before they are physically developed. the virtual prototype provides a vital steppingstone for the design optimization of the model. the virtual prototype tool gives the kinematical analysis capability of an amphibious robot, dynamic characteristics, structural parametric study, and static analysis. the robot's complete motion performance analysis is possible by virtual prototyping simulations before physical prototype development. the simulation analysis is also the basis for motor selection and other electronics [11]. to achieve amphibious locomotion in complex environmental conditions, mobility (velocity of robot vehicle on ground and thrust in water) and adaptability in these environments (obstacle negotiating and climbing capability on uneven terrain) are two important performance metrics analyzed in the literature. mobility of some amphibious robots is discussed. for example, acm is a snake-inspired amphibious robot that uses a modular design that can propel itself at 0.4m/s. salamander amphibious robot achieves 0.42 m/s on land 0.28 m/s on water using body undulation and limb design. turtle robot design uses a spherical body and four legs for motion, achieving a crawling velocity of 22.5 cm/s and surge velocity of 16.5 cm/s. amphirobot -iii uses a modular body design with a wheel propeller fin mechanism giving the speed of 0.59 m/s. amphihex-i robot uses a flipper leg design that has higher adaptability with a speed performance of 0.2 m/s. the mobility of present amphibious robots is lower and suitable for smooth land surfaces. kinematic modeling enables development and verification of the model. the implemented kinematic modeling is divided into two methodsone related to the geometric approach [12,13] and the other concerning the transformation approach. a general approach to kinematic modelling of articulated robots traversing uneven terrain was developed by tarokh et al. [14]. in this paper, the kinematics modelling of a six-wheel rocker-bogie mobile robot based on the above literature is deduced. the kinematics model will be helpful and fundamental to subsequent studies on the mobile robot's trajectory tracking and motion control [15]. a novel wheel leg hybrid-based amphibious robot with an integrated rocker-bogie wheel paddle mechanism is introduced in this paper to negotiate obstacles on uneven terrain exploiting the legs of the robot and high-speed mobility using wheels attached to legs. the amphibious robot with a rocker-bogie mechanism can maneuver over uneven terrain on land and achieve efficient propulsive maneuvering on the water with a wheel paddle mechanism. the amphibious robot can locomote a single design of multimodal locomotion on multiple terrains of land and water. the unified mechanical design gives the capability of compact control design. 2. kinematic analysis of model amphibious robots require good propulsive performance on both land and water. in the past literature, amphibious robots were proposed keeping in mind a low demand of terrain 248 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 complexity on the land environment. however, a real environment is uneven, demanding maneuvering on complex terrain profiles. the amphibious robot employs either legged, tracked, wheeled, spherical or hybrid mechanisms for propulsion. a legged robot is suitable and adaptable on complex terrains but at the cost of control and lower speed [16]. wheeled robots are best suited to flat ground surfaces, maneuvering at high speed [17]. however, they are less flexible as compared to legged over uneven terrain. wheeled robots with passive suspension mechanisms increase adaptability on complex terrain and achieve higher obstacle negotiation capability. rocker-bogie mechanisms with a passive suspension mechanism with a wheel paddle fin represent a hybrid mechanism for amphibious operation. the hybrid mechanism on land is a wheel-driven mobile robot with passive suspension. the wheel-driven mechanism increases the motion speed and passive suspension increases the adaptability on uneven terrain, thus increasing overall propulsive performance on land. the general view of the virtual prototype of the amphibious robot is shown in fig. 1. the amphibious robot virtual prototype consists of two major parts, the rocker-bogie mechanism, and the wheel paddle mechanism. the rocker-bogie mechanism has passive suspension [15]. the mechanism has a single rocker attached to the body by a pivot joint. a differential joint appends the rocker and the bogie. the two rockers and bogies are attached on each side of the chassis (main base). the wheel paddle mechanism is a combination wheel design with paddles on the outer surface of the wheel. the wheel's rotation is utilized for locomotion on land, and the same wheel with paddles is used as propulsion in water. 2.1 kinematic modeling the amphibious robot's main body consists of a rocker-bogie mechanism with six wheels driven by individual actuators. the rocker-bogie is a passive suspension mechanism utilized to adapt to uneven terrain and obstacle negotiation. the rocker-bogie mechanism comprises a rocker attached at the front and two bogies attached to a rocker at the rear end. fig. 1: general view of amphibious robot. the wheels are attached to the rocker and bogie with joints. the joints are attached with bearings. solidworks software is utilized to accomplish design indices and carry out the assembly process of the robot body, including the rocker-bogie mechanism and wheels. the adams software accepts geometric position relationships in parasolid format. solidworks exports the model in the required format. however, this process loses model features like material, mass information, and mechanisms due to the constrained relationship. 249 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 (a) (b) fig. 2: (a) tire, (b) wheel paddle. additionally, the robot assembly has a large set of parts; the model is highly complex. the model in adams adopts boolean operation that minimizes the independent parts quantity and retains only the main parts (geometry, mass information) and joints appended to main parts [16]. figure 2 shows the tire used in the kinematic simulation of the amphibious robot. the amphibious locomotion on the water is achieved using a wheel paddle design. table 1 and table 2 detail amphibious robot model specifications. kinematic analysis of an amphibious robot on land is considered for simplicity. according to the kinematic theorem, the velocity relationship of wheel locomotion may be described as follows. eq. (1) and eq. (2) represent the linear velocity of the left and right wheel, respectively. the velocity relationship is related to the radius of the wheel r and angular velocity of the wheel 𝑤𝐿 . the angular velocity of each wheel is related by revolutions of each wheel 𝑛𝐿 or 𝑛𝑅. eq. (3)eq. (5) represents the wheel velocities while turning the wheel, where w is the identical turning angular velocity of the wheel. 𝑉𝐿 = 𝑟. 𝑤𝐿 = 𝑟. 2𝜋𝑛𝐿 360 (1) 𝑉𝑅 = 𝑟. 𝑤𝑅 = 𝑟. 2𝜋𝑛𝑅 360 (2) 𝑉𝐿 = 𝑤. (𝑅 ± 𝑑 2 ) (3) 𝑉𝑅 = 𝑤. (𝑅 ∓ 𝑑 2 ) (4) 𝑛 = 𝑛𝐿 𝑛𝑅 = 𝑅 − 𝑑 2 𝑅 + 𝑑 2 (5) table 1: amphibious robot mechanical structure specification structural part weight (kg) dimensions (mm) main base 1.135 240 x 156 x 60 rocker link 1.410 267 x 96 x 36 bogie 2.634 256 x 87 x 36 rocker top 1.022 255 x 105 x 56 tire/wheel paddle 120 x 60 250 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 the study of kinematics modeling and simulation of amphibious robots is the basis of robot development and optimization. the kinematic analysis verifies the motion model of the moving robot by overcoming the obstacles without tipping or flipping over the terrain profile for the simulation period with the given constraints of the mechanism. the rationality of the kinematics model of the moving robot is verified by analysis of displacement and velocity curves. designers adopted the adams software to build the simulation model of the robot [21]. the robot's kinematics curve was obtained through the kinematics simulation of linear driving and pivot steering performance. this robots' mechanism design verifies the correctness of the kinematic model. 2.2 modeling environment the modeling environment adopted for virtual prototyping is a widely used dynamic modeling and simulation software adams; the environment facilitates the analysis of dynamic systems. the amphibious robot locomotion speed and drive forces on the wheeldriven mechanism can be obtained using the simulation approach based on adams. however, adams has limitations in modeling complex design structures in the spatial domain. therefore, a 3d designing environment like solidworks is employed with parasolid as a base to design solid parts and assemblies. the parasolid design is exported in adams for motion analysis. table 2: robot model specifications vehicle load 8 kg (78.4 n) wheel specification width radius circumference 0.06 m 0.06 m 0.377 m motor torque, mt 0.7848 nm therefore, by combining the powerful three-dimensional solid modeling functionality of solidworks with the accurate movement simulation performance in adams through a common data exchange interface [19], the kinematic simulation environment can be established. then the relationship between structural parameters and propulsive speed can be analyzed, aiming to offer some reference for the optimization design of the propulsive mechanism and motion control. this work acts as a reference for the optimal design of motion control and the propulsive mechanism by analyzing the structural parameters of the rocker and bogie link lengths, pivot and differential joint angles, rocker and bogie height to wheel center, angle of inclination with respect to ground, and maneuvering speed of the amphibious robot. the analysis is possible by exploiting the excellent three-dimensional modeling capability in cad software like solidworks and motion simulation and a common data exchange interface [20-22]. 3. results and discussion of kinematic simulation based on adams 251 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 3.1 straight going path to verify the robot model, it is required to validate the motion stability of the robot. the simulation of the model on land aimed at robot locomotion over the surface along the planned trajectory and tested for stability and heading to reach the target. the rocker-bogie integrated wheel paddle mechanism is designed considering the uneven terrain profile and obstacle negotiation capability. the robot's stability is studied by observing the variation of the center of mass of the robot structure along the horizontal x-axis direction. figure 4 shows the oscillations are smooth on flat terrain profile and encounter sharp changes when the model encounters the obstacle and steady state after the robot passes over the obstacle stabilizing the overall model. figure 4 shows center-of-mass variation is lower than the robot head height, confirming the stability of the model. the robot vehicle is stable when it is in a quasi-static state in which it does not tilt over, as the asymmetric suspension system of the passively articulated vehicle has a significant influence on the vehicle’s effective stability [23]. the computation of the longitudinal stability of the rover makes use of a statical model as it is not symmetric in the longitudinal direction. in a statical model, the mechanical properties of the suspension system are considered. according to [24], the longitudinal stability of the vehicle is given when all wheels have ground contact, and the condition ni > 0 is satisfied, where ni is the normal force at the wheel i. it should be noted that even though this condition is compulsory for the statical model to work, a physical robot vehicle does not necessarily tip if a wheel loses contact with the ground. the velocity of the robot vehicle, as in fig. 4 in the longitudinal direction, achieves 1.6 m/s, which is higher than similar amphibious robots reported in literature like wheg series [5], rhex and asgaurd [25,26], wheel leg propeller [27] and aqua robot [16]. however, it is less than the max speed of the seadog amphibious robot [28] of 2.23 m/s, but mobility on the water of the seadog decreases due to the use of the simple non-holonomic wheels as paddle wheels. the peripheral of the wheel is further encased with adhesive material to reduce the fluctuations affecting other parts and system components. the simulation analysis result demonstrates increased maneuverability, achieving a robot's velocity of 1.6 m/s, verifying the theoretical value obtained from eq. (1) and eq. (6). 𝑉𝐿 = 𝑟. 𝑤𝐿 = 𝑟. 2𝜋𝑛𝐿 360 = 0.06 . 2𝜋 60 255𝑟𝑝𝑚 = 1.6 𝑚/𝑠 (6) fig. 3: terrain profile. 252 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 fig. 4: velocity of robot in the x direction. 3.2 obstacle negotiation of the amphibious robot the terrain profile to test the obstacle negotiation capability of the robot is chosen with different shapes and heights. the obstacle's height should be less than the diameter of the wheel for stability or it will flip over the robot. the obstacle negotiation determines the climbing capacity of the robot. the obstacle shape chosen for simulation is a rigid rectangular block with a height of 20 mm and a width of 50 mm, as shown in figure 5. the load on each wheel for equilibrium studies using wheel terrain contact forces is discussed in section 3.2.1. the other obstacle chosen is hemispherical with a radial height of 20 mm; these obstacle negotiations exhibit the slip conditions of the robot. figures 4 and 6 show the velocity and normal forces of all the wheels successfully negotiating at the obstacles of the chosen terrain profile. fig. 5: obstacle profile. 3.2.1 wheel terrain contact forces the mobile robot locomotion on uneven terrain profiles requires a closer look to critically understand the capability of the robot overcoming obstacles completing the trajectory. the wheel ground contact forces analysis facilitates the study of locomotion on uneven terrain profiles. figure 6 demonstrates the normal forces of the front left tire 1(front wheel), front left tire 2 (middle wheel), and the rear left tire (rear wheel) have equal loading on all wheels up to 1.9 sec because of smooth flat surface. at 1.9 sec, as soon as the left front tire 1(front wheel) touches the hemispherical obstacle, the load is distributed to the middle and rear wheel. the rear wheel is loaded max with a normal force of 29 n at 2.3 sec when both the wheels(bogie) are passed over the hemispherical obstacle. figure 6 shows the middle wheel peak of normal force at 2.75 sec, indicating the middle wheel is entirely at the top of the 50mm rectangular block. at 2.25 sec, the rear wheel crosses the rectangular block followed by equal forces on all the wheels over the flat smooth surface locomotion at the trajectory completion stage. 253 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 fig. 6: normal forces on wheels. 4. conclusion a novel wheel leg hybrid-based amphibious robot with an integrated rocker-bogie wheel paddle mechanism is introduced in this paper to negotiate obstacles on uneven terrain exploiting the legs of the robot and high-speed mobility using wheels. the existing amphibious robots in the literature [2] have minimal suspension suitable only for flat terrain profiles. however, the suspension is achieved through a legged robot with lower speed and mobility performance on both land and water. the analysis proves that the propulsive principle and feature of the wheel paddle mechanism enable efficient locomotion on land and water. the robot is capable of multimodal locomotion on uneven terrain on terrestrial and aquatic mediums. the simulation in the adams environment provides a basis for the kinematic validation of the model. the kinematic simulation in adams of the virtual prototype amphibious robot measures the speed, angular torque, and velocities of the integrated mechanism. in this kinematic simulation, the capabilities on a smooth and uneven surface on land are achieved. the capabilities include straight going on a flat surface, and obstacle negotiations over the obstacles of various heights and shapes that are selected for performance evaluation of the model. in the future, the experiment will be carried out on benchmark terrain profiles considering different height obstacle negotiations for the robot to locomote on land. furthermore, kinematic simulation using the wheel paddle on the water will be tested. the control capability for the amphibious robot can be carried out using the co-simulation capability of adams and matlab/simulink environment. acknowledment the authors would like to acknowledge financial assistance from the ministry of higher education malaysia under the frgs grant frgs17-031-10597. we would like to thank financial support by iium under the koe post graduate tuition fee waiver scheme 2019 (tfw-2019). 254 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 references [1] karakasiliotis k, thandiackal r, melo k, horvat t, mahabadi nk, tsitkov s, ijspeert aj. (2016) from cineradiography to biorobots: an approach for designing robots to emulate and study animal locomotion. journal of the royal society interface, 13(119): 20151089. [2] rafeeq m, toha sf, ahmad s, razib ma. (2021) locomotion strategies for amphibious robots-a review. ieee access, 9: 26323-26342. [3] hopkins jk, spranklin bw, gupta sk. (2009) a survey of snake-inspired robot designs. bioinspiration & biomimetics, 4(2): 021001. [4] park hs, sitti m. (2009) compliant footpad design analysis for a bio-inspired quadruped amphibious robot. in proceedings of ieee/rsj international conference on intelligent robots and systems: october 2009, pp. 645-651. [5] boxerbaum as, werk p, quinn rd, vaidyanathan r. (2005) design of an autonomous amphibious robot for surf zone operation: part i mechanical design for multi-mode mobility. in proceedings of ieee/asme international conference on advanced intelligent mechatronics: july 2005, pp. 1459-1464. [6] ding r, yu j, yang q, tan m. (2009) kinematics modeling and simulation for an amphibious robot: design and implementation. in proceedings of ieee international conference on automation and logistics: july 2009, pp. 35-40. [7] bi l, guo j, guo s. (2015) virtual prototyping technology-based dynamics analysis for an amphibious spherical robot. in proceeding of ieee international conference on information and automation: august 2015, pp. 2563-2568. [8] zhong b, zhou y, li x, xu m, zhang s. (2016) locomotion performance of the amphibious robot on various terrains and underwater with flexible flipper legs. journal of bionic engineering, 13(4): 525-536. [9] zhuang m, yu zw, gong dp, xu ml, dai zd. (2012) gait planning and simulation of quadruped robot with hydraulic drive based on adams. machinery design & manufacture, 7: 100-102. [10] cao x, cleghorn wl. (2010) examples and application of adams software in the mechanics of machines teaching. in 5th international conference on computer science & education: 2010; pp. 1637-1641. doi: 10.1109/iccse.2010.5593596. [11] ding r, yu j, yang q, hu x, tan m. (2009) platform-level design for a biomimetic amphibious robot.in procedding of ieee international conference on robotics and biomimetics: february 2009, pp. 977-982. [12] cox j, wilfong gt. (1990) autonomous robot vehicles. springer-verlag, n.y. [13] iagnemma k, genot f, dubowski s. (1999) rapid physics-based rough terrain rover planning with sensor and control uncertainty. in proceedings of ieee international conference on robotics and automation, detroit, mi; pp. 2286-2291. [14] tarokh m, mcdermott g, hayati s, hung j. (1999) kinematic modelling of a high mobility mars rover. ieee conf. on robotics and automation, detroit, mi. [15] kumar p. (2010) modelling and dynamic analysis of rocker-bogie rover for space exploration. phd thesis, indian institute of technology roorkee, india. [16] dudek g, giguere p, prahacs c, saunderson s, sattar j, torres mla, georgiades c. (2007) aqua: an amphibious autonomous robot. computer, 40(1): 46-53. [17] baines r, fish f, kramer br. (2021) amphibious robotic propulsive mechanisms: current technologies and open challenges. bioinspired sensing, actuation, and control in underwater soft robotic systems, 41-69. [18] tan j, wang z, liu z. (2006) stable programmed manifold solver for virtual prototyping motion simulation, chinese journal of mechanical engineering (english edition), 19(1): 7680. [19] liu xp, zheng jr, zhu zg, gu xl. (2003) study on graphical data exchange between adams/view and solidworks. mechanical engineer, 12. 255 iium engineering journal, vol. 23, no. 2, 2022 rafeeq et al. https://doi.org/10.31436/iiumej.v23i2.2157 [20] yu jc, liao jw, li my, li sh. (2003) design and motion simulation of the autonomous exploration vehicle. in proc. of the 7th international conference on automation technology: september 2003; pp.1-6. [21] malik sm, lin j, goldenberg aa. (2006) virtual prototyping for conceptual design of a tracked mobile robot. in proceedings of canadian conference on electrical and computer engineering: may 2006; pp. 2349-2352. ieee. [22] xing h, guo s, shi l, hou x, liu y, liu h. (2020) design, modeling and experimental evaluation of a legged, multi-vectored water-jet composite driving mechanism for an amphibious spherical robot. microsystem technologies, 26(2): 475-487. [23] ullrich f, goktogan ah, sukkarieh s. (2011) design optimization of a mars rover’s rockerbogie mechanism using genetic algorithms. in proceedings from 10th australian space science conference; pp. 199-210. [24] thuer t. (2009) mobility evaluation of wheeled all-terrain robots metrics and application, phd thesis, swiss federal institute of technology zurich (eth zurich). [25] saranli u, buehler m, koditschek de. (2001) rhex: a simple and highly mobile hexapod robot, int. j. robot. res., 20(7): 616-631. [26] eich m, grimminger f, bosse s, spenneberg d, kirchner f. (2008) asguard: a hybrid-wheel security and sar-robot using bio-inspired locomotion for rough terrain. in proceedings of . robio; pp.774–779. [27] yu j, ding r, yang q, tan m, zhang j. (2013) amphibious pattern design of a robotic fish with wheel-propeller-fin mechanisms: amphibious pattern design of a robotic fish, j. field robotics, 30: 702-716. [28] klein ma, boxerbaum as, quinn rd, harkins r, vaidyanathan r. (2012) seadog: a rugged mobile robot for surf-zone applications. in proceedings of 4th ieee ras embs int. conf. biomed. robot. biomechatronics (biorob): june 2012; pp. 1335–1340. 256 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 influence of light absorption profile on the performance of organic photovoltaics abdul halim ikram mohamed1 and mohd lukman inche ibrahim2* 1 department of electrical and computer engineering, 2 department of science in engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. * corresponding author: lukmanibrahim@iium.edu.my (received:23rd june 2020; accepted: 16th january 2021; published on-line: 4th july 2021) abstract: we investigate how an enhanced light absorption at a specific position inside the active layer affects the performance of organic photovoltaic cells (opvs), namely the short-circuit current density (𝐽𝑠𝑐), the open-circuit voltage (𝑉𝑜𝑐 ), the fill factor (ff), and the power conversion efficiency (pce). the performance is calculated using an updated version of a previously published analytical current-voltage model for opvs, where the updated model allows the light absorption profile to be described by any functions provided that analytical solutions can be produced. we find that the light absorption profile affects the performance through the drift current. when the mobility imbalance is not very high (when the ratio of the mobility of the faster carrier type to the mobility of the slower carrier type is less than about 103), the pce is maximized when the light absorption is concentrated at the center of the active layer. when the mobility imbalance is very high (when the ratio of the mobility of the faster carrier type to the mobility of the slower carrier type is more than approximately 104), the pce is maximized when the light absorption is concentrated near the electrode collecting the slower carrier type. therefore, it is important to ensure that the light absorption profile is properly tuned so that the performance of opvs is maximized. moreover, any efforts that we make to improve the performance should not lead to a light absorption profile that would actually impair the overall performance. abstrak: kajian ini menilai bagaimana penyerapan cahaya yang tinggi pada bahagian tertentu lapisan aktif mempengaruhi prestasi sel fotovoltaik organik (opv), iaitu ketumpatan arus litar pintas (jsc), voltan litar terbuka (voc), faktor pengisian (ff), dan kecekapan penukaran kuasa (pce). prestasi dikira mengguna pakai model terkini yang diperbaharui dari model asal analitikal opv voltan-arus, di mana model ini membenarkan mana-mana profil penyerapan cahaya digunakan asalkan penyelesaian analitikal terhasil. dapatan kajian mendapati profil penyerapan cahaya mempengaruhi prestasi berdasarkan arus hanyut. apabila ketidakseimbangan pergerakan caj tidak begitu tinggi (di mana nisbah pergerakan pembawa caj laju kepada perlahan adalah kurang daripada 103), pce menjadi maksimum jika penyerapan cahaya bertumpu pada tengah lapisan aktif. apabila ketidakseimbangan pergerakan caj sangat tinggi (di mana nisbah pergerakan pembawa caj laju kepada perlahan adalah lebih daripada 104), pce menjadi maksimum jika penyerapan cahaya bertumpu pada elektrod yang mengutip pembawa caj perlahan. oleh itu, kedudukan talaan profil penyerapan cahaya yang tepat adalah sangat penting bagi menentukan prestasi opv dimaksimumkan. tambahan, apa sahaja usaha penambahbaikan prestasi seharusnya tidak menyebabkan pengurangan keseluruhan prestasi profil penyerapan cahaya. 135 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 keywords: carrier mobility; fill factor; open-circuit voltage; power conversion efficiency; short-circuit current 1. introduction organic photovoltaic cells (opvs) have several unique advantages such as lightweight, high mechanical flexibility, good transparency, and low fabrication cost [1]. hence, opvs are viewed as a promising alternative to conventional photovoltaic technologies. for example, opvs have a great potential to be used for powering various devices such as wearable devices [1], next generation self-driven biomedical devices [2], and off-grid devices for the internet of things [3]. the recorded power conversion efficiency (pce) of opvs has been improving steadily from 11% [4] several years ago to 17.3% currently [5]. however, the pce of opvs is still quite low compared with traditional photovoltaics, and even when compared with another emerging photovoltaic technology, namely perovskite solar cells [4]. therefore, improving the performance has been a focus of opv research. there are many factors that influence the performance of opvs such as the carrier mobility [6,7], the work function of the electrodes [8,9], the permittivity of the active layer [7,10] and the thickness of the active layer [11-13]. the light absorption profile inside the active layer has been reported to be another factor that influences the performance [14-16]. the light absorption profile is determined by several factors such as the optical properties of the opv components and the thickness of the active layer [13]. an improvement in the pce by optimizing the light absorption profile can be achieved in practice since the absorption profile can be controlled to a certain extent. for example, optical spacers can be used to alter the absorption profile [14,15]. another method that could be used to control the absorption profile is by employing plasmonic nanoparticles, which can be located outside or embedded inside the active layer [17]. light intensity increases near the plasmonic nanoparticles [17], and hence, the light absorption should be higher near the nanoparticles. therefore, one could control the absorption profile to a certain extent by choosing the embedment positions of the nanoparticles. although understanding the effect of the light absorption profile is clearly important, there is still a gap concerning our understanding on this matter. it has been shown that a high light absorption at a specific position inside the active layer improves the performance [14-16]. in more detail, mescher et al. [14] and islam et al. [16] concluded that a higher light absorption at the center of the active layer gives a better performance but did not conclude on the possible effect of carrier mobility imbalance. on the other hand, tress et al. [15] concluded that the fill factor (ff) improves if more light is absorbed near the contact that collects the slower carrier type even when the mobility imbalance is quite low. hence, there are still uncertainties regarding this matter. for example, from previous studies, we still have no clue on how the optimum light absorption profile evolves as the carrier mobilities evolve from balanced to highly imbalanced. furthermore, there is a disagreement between the results of previous studies. when the mobility imbalance is quite low (when the ratio of the mobility of the faster carrier type to the mobility of the slower carrier type is of one order of magnitude), islam et al. [16] found that the best performance is produced when the light absorption is concentrated at the center of the active layer whereas tress et al. [15] found that the best performance is produced when the light absorption is concentrated near the electrode collecting the slower carrier type. 136 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 in this paper, we will investigate the effect of the light absorption profile on the performance of opvs with the aim of providing insights on how an enhanced light absorption at a specific position inside the active layer affects the opv performance at different levels of mobility imbalance, and enlightening the disagreement between the results of previous studies. 2. methodology 2.1 analytical model the current-voltage model for opvs presented in this section is employed for all calculations in this article. the model is essentially the same as a previously published model [18]. therefore, finer details of the model presented here can be obtained in the published work [18]. the only difference between the model presented here and the previous model is that the charge-transfer (ct) state generation profile here is open to any functions provided that the continuity equations can be solved analytically whereas the ct state generation profile in the previous model has an exponential function. the device structure of the model is illustrated in fig. 1. fig. 1: a schematic showing the energy levels and the device structure. lumod and homod denote the lowest unoccupied molecular orbital (lumo) and the highest occupied molecular orbital (homo) of the donor, respectively. lumoa and homoa denote the lumo and the homo of the acceptor, respectively. eg denotes the effective band gap. efa and efc denote the fermi levels of the anode and the cathode, respectively. 𝐿 is the thickness of the active layer. φpa and φnc denote the hole injection barrier at anode and the electron injection barrier at cathode, respectively. in the operation of opvs, anode is the electrode that collects free holes and cathode is the electrode that collects free electrons. light absorption by the active layer generates excitons. when the excitons reach the donor-acceptor interface, ct states may be produced. free charge carriers are generated from the dissociation of the ct states. when free electrons and free holes recombine bimolecularly, ct states are produced back. therefore, ct states can be generated due to exciton relaxations at the donor-acceptor interface (through photon absorption) and due to bimolecular recombination. since bulk heterojunction design is used to construct the active layer, the photogenerated ct states are produced at approximately the same location where the excitons are photogenerated (or where the photons are absorbed). therefore, the profile of the light absorption can be assumed to have the same equivalent shape as the profile of the ct state photogeneration rate. 137 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 according to the previous model, when the non-geminate recombination is not considered in the electron (hole) continuity equation, the resulting electron (hole) density that arises from the solution of the equation is called the maximum electron (hole) density 𝑛𝑚𝑎𝑥 (𝑝𝑚𝑎𝑥) [18]. the electron and the hole continuity equations at steady state without the non-geminate recombination are given by 𝐷𝑛 𝜕2𝑛𝑚𝑎𝑥 𝜕𝑥2 + 𝜇𝑛𝐹 𝜕𝑛𝑚𝑎𝑥 𝜕𝑥 + 𝑃𝑑 𝐺𝐶𝑇 = 0 (1) 𝐷𝑝 𝜕2𝑝𝑚𝑎𝑥 𝜕𝑥2 − 𝜇𝑝𝐹 𝜕𝑝𝑚𝑎𝑥 𝜕𝑥 + 𝑃𝑑 𝐺𝐶𝑇 = 0 (2) where 𝐷𝑛 (𝐷𝑝) is the electron (hole) diffusion coefficient, 𝜇𝑛 (𝜇𝑝) is the electron (hole) mobility, 𝐹 is the electric field, 𝑃𝑑 is the dissociation probability of ct states, and 𝐺𝐶𝑇 is the ct state photogeneration rate per unit volume. the ct state dissociation probability is defined as 𝑃𝑑 = 𝑘𝑑 𝑘𝑑+𝑘𝑓 (3) where 𝑘𝑑 is the ct state dissociation rate coefficient, and 𝑘𝑓 is the ct state decay rate coefficient. as in the previous model [18], 𝑘𝑑 given by the work of inche ibrahim [19] is used in this article, which is an improvement to the onsager-braun model [20]. solving eq. (1) and eq. (2) are the same as solving non-homogenous second-order linear ordinary differential equations with constant coefficients where 𝐷𝑛 , 𝐷𝑝, 𝜇𝑛, 𝜇𝑝, 𝐹, and 𝑃𝑑 are independent of 𝑥 [18] with 𝑃𝑑 𝐺𝐶𝑇 being the non-homogenous term. any functions can be assigned to the non-homogenous term (i.e. to 𝐺𝐶𝑇 since 𝑃𝑑 is a constant) provided that eq. (1) and eq. (2) can be solved analytically. the boundary conditions as given in the previous model [18] are used and matlab is employed to analytically solve eq. (1) and eq. (2) to obtain 𝑛𝑚𝑎𝑥 and 𝑝𝑚𝑎𝑥. furthermore, according to the previous model [18], when the non-geminate recombination is considered in the electron (hole) continuity equation, the resulting electron (hole) density that arises from the solution of the equation is called the net electron (hole) density 𝑛𝑛𝑒𝑡 (𝑝𝑛𝑒𝑡). the electron and the hole continuity equations at steady state with the non-geminate recombination considered are therefore given by 𝐷𝑛 𝜕2𝑛𝑛𝑒𝑡 𝜕𝑥2 + 𝜇𝑛𝐹 𝜕𝑛𝑛𝑒𝑡 𝜕𝑥 + 𝑃𝑑 𝐺𝐶𝑇 − (1 − 𝑃𝑑 )𝑅𝑏 − 𝑅𝑚𝑛 = 0 (4) 𝐷𝑝 𝜕2𝑝𝑛𝑒𝑡 𝜕𝑥2 − 𝜇𝑝𝐹 𝜕𝑝𝑛𝑒𝑡 𝜕𝑥 + 𝑃𝑑 𝐺𝐶𝑇 − (1 − 𝑃𝑑 )𝑅𝑏 − 𝑅𝑚𝑝 = 0 (5) where 𝑅𝑏 is the non-geminate bimolecular recombination rate per unit volume, and 𝑅𝑚𝑛 (𝑅𝑚𝑝) is the non-geminate monomolecular recombination rate per unit volume for electrons (holes). 𝑅𝑏 is given by 𝑅𝑏 = 𝛾𝑘𝐿 𝑛𝑚𝑎𝑥 𝑝𝑚𝑎𝑥 (6) where 𝛾 is the bimolecular recombination reduction coefficient, and 𝑘𝐿 is the langevin recombination coefficient [18]. 𝑅𝑚𝑛 and 𝑅𝑚𝑝 are given by 𝑅𝑚𝑛 = 𝑘𝑚𝑛 𝑛𝑚𝑎𝑥 (7) 𝑅𝑚𝑝 = 𝑘𝑚𝑝𝑝𝑚𝑎𝑥 (8) where 𝑘𝑚𝑛 (𝑘𝑚𝑝) is the monomolecular recombination coefficient for electrons (holes). it is important to note that 𝑅𝑚𝑛 = 𝑅𝑚𝑝 as explained in the previous model [18]. solving eq. 138 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 (4) and eq. (5) are also the same as solving second-order linear ordinary differential equations with constant coefficients. again, the boundary conditions as given in the previous model [18] are used and matlab is employed to analytically solve eq. (4) and eq. (5) to obtain 𝑛𝑛𝑒𝑡 and 𝑝𝑛𝑒𝑡. the electron current density 𝐽𝑛 and the hole current density 𝐽𝑝 are given by 𝐽𝑛 = 𝑞𝜇𝑛𝐹𝑛𝑛𝑒𝑡 + 𝑞𝐷𝑛 𝜕𝑛𝑛𝑒𝑡 𝜕𝑥 (9) 𝐽𝑝 = 𝑞𝜇𝑝𝐹𝑝𝑛𝑒𝑡 − 𝑞𝐷𝑝 𝜕𝑝𝑛𝑒𝑡 𝜕𝑥 (10) the total current density 𝐽 is the sum of 𝐽𝑛 and 𝐽𝑝. the first terms on the right sides of eq. (9) and eq. (10) are the electron drift current density 𝐽𝑛,𝑑𝑟 and the hole drift current density 𝐽𝑝,𝑑𝑟, respectively, whereas the second terms on the right sides of eq. (9) and eq. (10) are the electron diffusion current density 𝐽𝑛,𝑑𝑖𝑓𝑓 and the hole diffusion current density 𝐽𝑝,𝑑𝑖𝑓𝑓, respectively. 2.2 light absorption profiles and parameter values to achieve the objective of this paper, we need to use the light absorption profile (and hence, the 𝐺𝐶𝑇 profile) that has an enhanced absorption (and hence, an enhanced ct state photogeneration rate) at a specific position inside the active layer. to produce such a profile, we use 𝐺𝐶𝑇 given by 𝐺𝐶𝑇 = 𝐺0 + 𝐺1(𝑥 − 𝐶) 2 (11) where 𝐺0 and 𝐺1 are the ct state photogeneration rate parameters, and 𝐶 is the location of the peak ct state photogeneration rate (or the location of the peak light absorption). the ct state photogeneration rate per unit area of the active layer is 𝐺𝐶𝑇,𝑎𝑟𝑒𝑎 = ∫ 𝐺𝐶𝑇 𝐿 0 𝑑𝑥. hence, 𝐺𝐶𝑇,𝑎𝑟𝑒𝑎 = 𝐺0𝐿 + 1 3 𝐺1[(𝐿 − 𝐶) 3 + 𝐶3] (12) to ensure a fair comparison, each of the studied 𝐺𝐶𝑇 profile must have the same the value of 𝐺𝐶𝑇,𝑎𝑟𝑒𝑎. when 𝐶 ≤ 𝐿 2⁄ , we impose the condition 𝐺𝐶𝑇 (𝑥 = 𝐿) = 0. therefore, when 𝐶 ≤ 𝐿 2⁄ , we have 𝐺1 = 3𝐺𝐶𝑇,𝑎𝑟𝑒𝑎 𝐶 3+(𝐿−𝐶)3−3𝐿(𝐿−𝐶)2 (13) 𝐺0 = −𝐺1(𝐿 − 𝐶) 2 (14) when 𝐶 > 𝐿 2⁄ , we impose the condition 𝐺𝐶𝑇 (𝑥 = 0) = 0. therefore, when 𝐶 > 𝐿 2⁄ , we have 𝐺1 = 3𝐺𝐶𝑇,𝑎𝑟𝑒𝑎 𝐶 3+(𝐿−𝐶)3−3𝐿𝐶 2 (15) 𝐺0 = −𝐺1𝐶 2 (16) in this paper, four different values of 𝜇𝑛 𝜇𝑝⁄ (ratio of the electron mobility to the hole mobility) are considered. table 1 shows the values of 𝜇𝑛 𝜇𝑝⁄ together with the corresponding values of 𝜇𝑛 and 𝜇𝑝 used in this study. the values of the other parameters are shown in table 2. the parameter values in table 2 are typical for opvs [11,18], particularly opvs based on p3ht:pcbm blend [21]. figure 2 illustrates several 𝐺𝐶𝑇 profiles used in this study. 139 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 table 1: values of the electron mobility 𝜇𝑛 and the hole mobility 𝜇𝑝, and the resulting 𝜇𝑛 𝜇𝑝⁄ used in the calculations 𝝁𝒏 (m 2v−1s−1) 𝝁𝒑 (m 2v−1s−1) 𝝁𝒏 𝝁𝒑⁄ 1  10−7 1  10−7 1 9  10−7 9  10−9 102 9  10−6 9  10−10 104 3  10−5 3  10−10 105 table 2: parameter values used in the calculations unless otherwise specified. the symbols in this table are the same as in the previous works [11,18] symbols parameter description value 𝑬𝒈 effective band gap 1.1 ev 𝑵𝒄, 𝑵𝒗 density of states 2  10 26 m−3 𝝁𝒏𝒂 actual electron mobility 200𝝁𝒏 𝝁𝒑𝒂 actual hole mobility 200𝝁𝒑 𝜺 effective permittivity of the active layer 3  10−11 f·m−1 𝝋𝒏𝒂, 𝝋𝒏𝒄 injection barriers 0.05 ev 𝒌𝒇 ct state decay rate coefficient 1  10 8 s−1 𝒂 electron-hole separation of the ct state 1.8  10−9 m 𝑻 temperature 300 k 𝝀 donor-acceptor morphology parameter 0.15 𝑳 active layer thickness 100 nm 𝑮𝑪𝑻,𝒂𝒓𝒆𝒂 ct state photogeneration rate per unit area 1  10 21 m−2s−1 𝜸 bimolecular recombination reduction coefficient 0.002 𝒌𝒎𝒏 monomolecular recombination coefficient for electrons 200 s −1 fig. 2: several profiles of the ct state photogeneration rate per unit volume 𝐺𝐶𝑇 that are used in this study. the expression for 𝐺𝐶𝑇 is given by eq. (11). 𝐺𝐶𝑇 profile with light absorption peaks 𝐶 at 0 nm, 40 nm, 60 nm and 100 nm are also used but are not shown in the figure. 3. results and discussion in this section, we present and discuss the results of our calculations. different values of the carrier mobilities affect the opv performance as shown by previous studies [6,7,18]. therefore, it is imperative that we do not compare between performances of an opv with a given 𝜇𝑛 𝜇𝑝⁄ and an opv with a different 𝜇𝑛 𝜇𝑝⁄ . what we should analyze 140 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 here is how opvs with different values of 𝜇𝑛 𝜇𝑝⁄ respond to different 𝐺𝐶𝑇 profiles. furthermore, for clarity and brevity of this study, we only confine our analysis from the theoretical perspective. we cannot fully control all device parameters when conducting experiments. for example, every time we use a different active layer material in order to change the carrier mobilities, we would also inevitably change a few other device parameters (e.g. the light absorption properties, and thus the value of 𝐺𝐶𝑇,𝑎𝑟𝑒𝑎). therefore, the inclusion of experimental data into our analysis would complicate our explanation and understanding on this matter. 3.1 effect on short-circuit current density figure 3 shows the magnitude of the short-circuit current density (|𝐽𝑠𝑐 |) as a function of 𝐶 for each of the studied 𝜇𝑛 𝜇𝑝⁄ . fig. 3: magnitude of the short-circuit current density |𝐽𝑠𝑐 | as a function of the position of the light absorption peak 𝐶 when (a) 𝜇𝑛 𝜇𝑝⁄ = 1, (b) 𝜇𝑛 𝜇𝑝⁄ = 10 2, (c) 𝜇𝑛 𝜇𝑝⁄ = 10 4, and (d) 𝜇𝑛 𝜇𝑝⁄ = 10 5. if 𝜇𝑛 𝜇𝑝⁄ is increased to a value significantly above 105, |𝐽𝑠𝑐 | produced by the light absorption profile with 𝐶 < 𝐿 2⁄ (e.g. 𝐶 = 20 nm) would even surpass |𝐽𝑠𝑐 | produced by the light absorption profile with 𝐶 = 𝐿 2⁄ . to explain the trend shown in fig. 3, let us explore the role of the drift and the diffusion currents. we define the average electron drift current density 〈𝐽𝑛,𝑑𝑟 〉 and the average electron diffusion current density 〈𝐽𝑛,𝑑𝑖𝑓𝑓 〉 as 〈𝐽𝑛,𝑑𝑟 〉 = 𝑞𝜇𝑛𝐹 ∫ 𝑛𝑛𝑒𝑡 𝐿 𝑑𝑥 𝐿 0 = 𝑞𝜇𝑛𝐹〈𝑛𝑛𝑒𝑡 〉 (17) 〈𝐽𝑛,𝑑𝑖𝑓𝑓 〉 = 𝑞𝐷𝑛 ∫ ( 𝜕𝑛𝑛𝑒𝑡 𝜕𝑥 ) 𝑑𝑥 𝐿 0 𝐿⁄ = 𝑞𝐷𝑛 〈 𝜕𝑛𝑛𝑒𝑡 𝜕𝑥 〉 (18) where 〈𝑛𝑛𝑒𝑡 〉 is the average 𝑛𝑛𝑒𝑡 and 〈𝜕𝑛𝑛𝑒𝑡 𝜕𝑥⁄ 〉 is the average 𝜕𝑛𝑛𝑒𝑡 𝜕𝑥⁄ . table 3 shows 〈𝐽𝑛,𝑑𝑟 〉’s and 〈𝐽𝑛,𝑑𝑖𝑓𝑓〉’s at short-circuit for the balanced mobility case (𝜇𝑛 𝜇𝑝⁄ = 1). as seen in table 3, as the light absorption is concentrated farther from the cathode (i.e. as 𝐶 is lowered), 〈𝐽𝑛,𝑑𝑖𝑓𝑓 〉 remains unchanged because 〈𝜕𝑛𝑛𝑒𝑡 𝜕𝑥⁄ 〉 is 141 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 unchanged, but the magnitude of 〈𝐽𝑛,𝑑𝑟 〉 increases because 〈𝑛𝑛𝑒𝑡 〉 increases. even when we assume there is no non-geminate recombination in our calculations (by using 𝛾 = 0 and 𝑘𝑚𝑛 = 0 s −1), we find that 〈𝑛𝑛𝑒𝑡 〉 still increases if the light absorption is concentrated farther from the cathode. therefore, the non-geminate recombination is not the deciding factor why 〈𝑛𝑛𝑒𝑡 〉 increases as 𝐶 is lowered. table 3: the average electron drift current density 〈𝐽𝑛,𝑑𝑟 〉 and the average electron diffusion current density 〈𝐽𝑛,𝑑𝑖𝑓𝑓〉 at short-circuit for the balanced mobility case (𝜇𝑛 𝜇𝑝⁄ = 1) calculated using 𝐺𝐶𝑇 with different light absorption peak positions c’s. c (nm) 〈𝑱𝒏,𝒅𝒓〉 (a·m −2) 〈𝑱𝒏,𝒅𝒊𝒇𝒇〉 (a·m −2) 20 −1.19848  105 1.19762  105 50 −1.19836  105 1.19762  105 80 −1.19821  105 1.19762  105 to rationalize why 〈𝑛𝑛𝑒𝑡 〉 increases as the light absorption is concentrated farther from the cathode (the electrode collecting free electrons), we consider the following two basic facts. first, the profile of the free electrons per unit volume at steady state (which is 𝑛𝑛𝑒𝑡 profile) is attained after some of the generated electrons are redistributed within the active layer (where some electrons may be (accidentally) extracted from the active layer during the redistribution process) and some of the electrons are involved in the nongeminate recombination. however, we can ignore the effect of recombination since we have shown that it is not the deciding factor. second, the cathode has a higher fermi level than the anode, and thus the resulting boundary conditions [18] mean that the free electrons (holes) must have a significantly higher concentration near the cathode (anode) than near the anode (cathode). now consider the 𝐶 = 20 nm and 𝐶 = 80 nm cases as shown in table 3. in both cases, the electric field magnitudes are the same since both cases are at the same applied voltage 𝑉𝑎 (i.e. at short-circuit). for the 𝐶 = 20 nm case, there should be less free electrons extracted from the active layer in attaining 𝑛𝑛𝑒𝑡 than for the 𝐶 = 80 nm case since majority of the electrons are generated farther from the cathode, and thus are less likely to be extracted during the redistribution process. this means more of the generated electrons are retained inside the active layer, thus causing a higher 𝑛𝑛𝑒𝑡 for the 𝐶 = 20 nm case than for the 𝐶 = 80 nm case. therefore, the 𝐶 = 20 nm case would give a higher magnitude of 〈𝐽𝑛,𝑑𝑟 〉 than the 𝐶 = 80 nm case due to a higher magnitude of 𝑛𝑛𝑒𝑡 (see eq. (17)). from our analysis above, we can conclude that the farther the light absorption is concentrated from the cathode (anode), the more the free electrons (holes) are retained inside the active layer, and this gives a higher |𝐽𝑛,𝑑𝑟 | (|𝐽𝑝,𝑑𝑟 |), but |𝐽𝑛,𝑑𝑖𝑓𝑓 | (|𝐽𝑝,𝑑𝑖𝑓𝑓 |) is effectively unchanged because the gradient of 𝑛𝑛𝑒𝑡 (𝑝𝑛𝑒𝑡) is effectively unchanged. therefore, the farther the light absorption is concentrated from the cathode (anode), the higher the |𝐽𝑛| (|𝐽𝑝|). based on the conclusion above, the results in fig. 3(a) can be rationalized as follows. when 𝐶 = 0 nm (i.e. when 𝐶 is the closest to the anode or the farthest from the cathode), |𝐽𝑛| is at its highest whereas |𝐽𝑝| is at its lowest. as we start increasing 𝐶 from 𝐶 = 0 nm, |𝐽𝑝| increases whereas |𝐽𝑛 | decreases, where the increase in |𝐽𝑝| is stronger than the decrease in |𝐽𝑛|, and hence |𝐽𝑠𝑐 | (i.e. |𝐽| at open-circuit) increases. then, at one point, the 142 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 decrease in |𝐽𝑛| equals to the increase in |𝐽𝑝|, and at this optimum 𝐶, we have the peak |𝐽𝑠𝑐 |. then, as we further increase 𝐶 beyond the optimum 𝐶, |𝐽𝑠𝑐 | decreases since the decrease in |𝐽𝑛| is stronger than the increase in |𝐽𝑝|. for 𝜇𝑛 𝜇𝑝⁄ = 1 case, the contribution from electrons (therefore |𝐽𝑛 |) and holes (therefore |𝐽𝑝|) towards |𝐽𝑠𝑐 | are equal (since electrons and holes have the same mobilities), and therefore |𝐽𝑠𝑐 | as a function of 𝐶 is symmetric about 𝐶 = 𝐿 2⁄ (i.e. the optimum 𝐶). when 𝜇𝑛 𝜇𝑝⁄ = 10 2, the contribution of |𝐽𝑛 | on |𝐽𝑠𝑐 | is stronger than the contribution of |𝐽𝑝| on |𝐽𝑠𝑐 | due to the fact that the electron mobility is higher now, and since |𝐽𝑛| is higher if 𝐶 is closer to the anode, therefore |𝐽𝑠𝑐 | produced by the profile with 𝐶 < 𝐿 2⁄ (i.e. 𝐶 closer to the anode) is higher than |𝐽𝑠𝑐 | produced by the profile with 𝐶 > 𝐿 2⁄ . this explains the results shown in fig. 3(b). as 𝜇𝑛 𝜇𝑝⁄ is increased and becomes more imbalanced, the contribution of |𝐽𝑛 | on |𝐽𝑠𝑐 | becomes even more significant, and this widens the difference between |𝐽𝑠𝑐 | produced by the profile with 𝐶 < 𝐿 2⁄ and |𝐽𝑠𝑐 | produced by the profile with 𝐶 > 𝐿 2⁄ . this explains the trends as we increase 𝜇𝑛 𝜇𝑝⁄ from 1 to 10 5 as shown in fig. 3. due to these trends, we can expect that when 𝜇𝑛 𝜇𝑝⁄ reaches a threshold value (when 𝜇𝑛 𝜇𝑝⁄ ≫ 10 5), |𝐽𝑠𝑐 | produced by the profile with 𝐶 < 𝐿 2⁄ would even surpass |𝐽𝑠𝑐 | produced by the profile with 𝐶 = 𝐿 2⁄ . it is worth noting that the explanation presented in section 3.1 is applicable at any given applied voltage 𝑉𝑎 in general, and not just at the short-circuit. 3.2 effect on open-circuit voltage figure 4 shows the open-circuit voltage 𝑉𝑜𝑐 as a function of 𝐶 for each of the studied 𝜇𝑛 𝜇𝑝⁄ . note that at any given 𝜇𝑛 𝜇𝑝⁄ , the trend of 𝑉𝑜𝑐 as a function of 𝐶 is determined by the trend of |𝐽| (the magnitude of the total current density) as a function of 𝐶 at applied voltage 𝑉𝑎 near but lower than 𝑉𝑜𝑐. this is because, at a given 𝑉𝑎 that is near but lower than 𝑉𝑜𝑐, a higher |𝐽| means a higher 𝑉𝑜𝑐 is expected since a higher extra 𝑉𝑎 is required in order to push and make |𝐽| = 0. for example, for the 𝜇𝑛 𝜇𝑝⁄ = 1 case at 𝑉𝑎 = 0.7 v as shown in fig. 5(a), the profile with 𝐶 = 50 nm has a higher |𝐽| than the |𝐽| for the profile with 𝐶 = 20 nm, and hence the profile with 𝐶 = 50 nm has a higher 𝑉𝑜𝑐 than the 𝑉𝑜𝑐 for the profile with 𝐶 = 20 nm. therefore, the trend of 𝑉𝑜𝑐 shown in fig. 4(a) can be explained by the trend of |𝐽| shown in fig. 5(a), where the results shown in fig. 5(a) can be rationalized in the same way as we rationalize the results shown in fig. 3(a). at high 𝑉𝑎 (near but below 𝑉𝑜𝑐), the electric field magnitude is significantly lower and has significantly less influence in transporting and extracting the carriers than at shortcircuit. hence, at high 𝑉𝑎, the light absorption profile (and thus 𝐶) becomes significantly more important in determining 𝑛𝑛𝑒𝑡 and 𝑝𝑛𝑒𝑡, and thus in determining |𝐽𝑛|, |𝐽𝑝| and |𝐽|, than at short-circuit. consequently, |𝐽| at high 𝑉𝑎 is more sensitive to 𝐶 compared with |𝐽| at short-circuit (i.e. |𝐽𝑠𝑐 |), and therefore the trend of |𝐽| at high 𝑉𝑎 as a function of 𝐶 for a given 𝜇𝑛 𝜇𝑝⁄ (where 𝜇𝑛 𝜇𝑝⁄ > 1) is equivalent to the trend of |𝐽𝑠𝑐 | as a function of 𝐶 but at a significantly higher 𝜇𝑛 𝜇𝑝⁄ . that is why at a high 𝑉𝑎, the |𝐽| produced by the profile with 𝐶 < 𝐿 2⁄ already surpasses the |𝐽| produced by the profile with 𝐶 = 𝐿 2⁄ when 𝜇𝑛 𝜇𝑝⁄ = 104 (see fig. 5(c)) whereas at 𝑉𝑎 = 0 v (i.e. short-circuit), |𝐽𝑠𝑐 | produced by the profile with 𝐶 < 𝐿 2⁄ still does not surpass |𝐽𝑠𝑐 | produced by the profile with 𝐶 = 𝐿 2⁄ when 𝜇𝑛 𝜇𝑝⁄ = 10 4 (see fig. 3(c)). figure 5 shows the trends of |𝐽| at high 𝑉𝑎 as a function of 𝐶 for each of the studied 𝜇𝑛 𝜇𝑝⁄ , and the results shown in fig. 5 give rise to the trends of 𝑉𝑜𝑐 as a function of 𝐶 for each of the studied 𝜇𝑛 𝜇𝑝⁄ which is shown in fig. 4. as mentioned at 143 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 the end of section 3.1, the argument that we use to rationalize the results shown in fig. 3 is applicable at any 𝑉𝑎, and therefore, the same argument can be used to rationalize the results shown in fig. 5. fig. 4: open-circuit voltage 𝑉𝑜𝑐 as a function of the position of the light absorption peak 𝐶 when (a) 𝜇𝑛 𝜇𝑝⁄ = 1, (b) 𝜇𝑛 𝜇𝑝⁄ = 10 2, (c) 𝜇𝑛 𝜇𝑝⁄ = 10 4, and (d) 𝜇𝑛 𝜇𝑝⁄ = 10 5. fig. 5: magnitude of the current density |𝐽| as a function of the position of the light absorption peak 𝐶 for (a) 𝜇𝑛 𝜇𝑝⁄ = 1 at 𝑉𝑎 = 0.7 v, (b) 𝜇𝑛 𝜇𝑝⁄ = 10 2 at 𝑉𝑎 = 0.68 v, (c) 𝜇𝑛 𝜇𝑝⁄ = 10 4 at 𝑉𝑎 = 0.58 v, and (d) 𝜇𝑛 𝜇𝑝⁄ = 10 5 at 𝑉𝑎 = 0.48 v. the applied voltage 𝑉𝑎 used for each 𝜇𝑛 𝜇𝑝⁄ are chosen randomly but is close to the corresponding 𝑉𝑜𝑐 (e.g. for 𝜇𝑛 𝜇𝑝⁄ = 1 case, 𝑉𝑜𝑐 is around 0.73v as shown in fig. 4(a), so we consider 𝑉𝑎 = 0.7 v here). 144 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 3.3 effect on fill factor figure 6 shows the fill factor (ff) as a function of 𝐶 for each of the studied 𝜇𝑛 𝜇𝑝⁄ . to rationalize the trend of the ff as a function of 𝐶, it is important to note that the ff occurs somewhere between the short-circuit and the open-circuit. hence, the trend of the ff as a function of 𝐶 at a given 𝜇𝑛 𝜇𝑝⁄ is simply somewhere between the trend of |𝐽𝑠𝑐 | and the trend of 𝑉𝑜𝑐 as functions of 𝐶 for the same 𝜇𝑛 𝜇𝑝⁄ . for the device considered in this study, the ff occurs at 𝑉𝑎 that is significantly closer to 𝑉𝑜𝑐 than to the short-circuit, and hence the trends of the ff as a function of 𝐶 as shown in fig. 6 is very similar to the trends of 𝑉𝑜𝑐 as a function of 𝐶 as shown in fig. 4. fig. 6: fill factor (ff) as a function of the position of the light absorption peak 𝐶 when (a) 𝜇𝑛 𝜇𝑝⁄ = 1, (b) 𝜇𝑛 𝜇𝑝⁄ = 10 2, (c) 𝜇𝑛 𝜇𝑝⁄ = 10 4, and (d) 𝜇𝑛 𝜇𝑝⁄ = 10 5. mescher et al. [14] concluded that enhanced light absorption at the two edges of the active layer (i.e. near the anode and the cathode) lead to a high unfavorable diffusion current which reduces the ff, whereas an enhanced absorption at the center of the active layer leads to a high ff. these conclusions partially agree with our results here. first, we find the drift current is the one that affects the dependence of |𝐽|, and thus the dependences of |𝐽𝑠𝑐 |, 𝑉𝑜𝑐 and ff on the light absorption profile, whereas the diffusion current basically has no effect (see section 3.1). second, we find that an enhanced light absorption at the center of the active layer leads to the best ff only if the mobility imbalance (i.e. 𝜇𝑛 𝜇𝑝⁄ ) is not very high (see fig. 6). tress et al. [15] concluded that an enhanced absorption near the electrode collecting the slower carrier type would give a higher ff even when the mobility imbalance is very low, whereas islam et al. [16] concluded that when the mobility imbalance is low, an enhanced absorption at the center of the active layer gives the best ff. we find that an enhanced absorption near the electrode collecting the slower carrier type (hole is the slower carrier type in our study here) would give the best ff only when the mobility imbalance is very high (see fig. 6). when the mobility imbalance is not very high, the best ff is produced when the light absorption is concentrated at the center of the active layer. therefore, our results here agree with the results from islam et al. [16], but it is worth 145 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 noting that they did not investigate the role of mobility imbalance on the optimum light absorption profile. 3.4 effect on power conversion efficiency figure 7 shows the power conversion efficiency (pce) as a function of 𝐶 for each of the studied 𝜇𝑛 𝜇𝑝⁄ . the pce is given by 𝑃𝐶𝐸 = 𝐹𝐹 × |𝐽𝑠𝑐 | × 𝑉𝑜𝑐 𝑃𝑖𝑛⁄ (19) where 𝑃𝑖𝑛 is the input power per unit area of the incident light (taken to be under the 1 sun condition which is 1000 w/m2). hence, the trend of the pce as a function of 𝐶 at a given 𝜇𝑛 𝜇𝑝⁄ is simply the combination of the trends of |𝐽𝑠𝑐 |, 𝑉𝑜𝑐 and ff as functions of 𝐶 for the same 𝜇𝑛 𝜇𝑝⁄ . therefore, the trends of the pce shown in fig. 7 can be understood by combining the trends shown in fig. 3, fig. 4, and fig. 6. fig. 7: power conversion efficiency (pce) as a function of the position of the light absorption peak 𝐶 when (a) 𝜇𝑛 𝜇𝑝⁄ = 1, (b) 𝜇𝑛 𝜇𝑝⁄ = 10 2, (c) 𝜇𝑛 𝜇𝑝⁄ = 10 4, and (d) 𝜇𝑛 𝜇𝑝⁄ = 10 5. according to mescher et al. [14] and islam et al. [16], the highest pce is produced when the light absorption is concentrated at the center of the active layer. however, the conclusion is incomplete according to our results. we find that the highest pce is produced by the light absorption that concentrates at the center of the active layer only when the mobility imbalance is not very high (see fig. 7). however, when the mobility imbalance is very high (see fig. 7), the best pce is produced when the light absorption is concentrated near the electrode collecting the slower carrier type. 4. conclusion by using our updated current-voltage model for opvs, we have investigated how the light absorption profile with an enhanced absorption at a certain position inside the active layer affects the performance of opvs. it is found that the light absorption profile affects the opv performance through the drift current. the further the light absorption is 146 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 concentrated from the electrode collecting a given charge carrier type, the higher the drift current and the total current for that carrier type, whereas the diffusion current for that carrier type is unaffected. when the carrier mobilities are balanced, the best |𝐽𝑠𝑐 |, 𝑉𝑜𝑐, ff and pce are produced by the light absorption that concentrates at the center of the active layer. when the mobilities become imbalanced, the |𝐽𝑠𝑐 |, 𝑉𝑜𝑐, ff and pce produced by the light absorption that concentrates nearer to the electrode collecting the slower carrier type improve relative to the ones produced by the light absorption that concentrates at other positions inside the active layer. when the mobility imbalance is high enough (i.e. reach a threshold value), the best |𝐽𝑠𝑐 |, 𝑉𝑜𝑐, ff and pce are produced by the light absorption that concentrates near the electrode collecting the slower carrier type. the mobility imbalance threshold values for |𝐽𝑠𝑐 |, 𝑉𝑜𝑐, ff, and pce are different, where the threshold value for 𝑉𝑜𝑐 is the lowest, whereas the threshold value for |𝐽𝑠𝑐 | is the highest. therefore, if the mobility imbalance is not very high (when the ratio of the mobility of the faster carrier to the mobility of the slower carrier is less than about 103), it is important to ensure that the light absorption is concentrated at the center of the active layer in order to maximize the pce. however, if the mobility imbalance is very high (when the ratio of the mobility of the faster carrier to the mobility of the slower carrier is about 104 or more), the light absorption should be concentrated near the electrode collecting the slower carrier type in order to maximize the pce. acknowledgement this work was supported by the ministry of higher education malaysia under the fundamental research grant scheme (grant no. frgs/1/2017/stg02/uiam/03/2). references [1] scharber mc, sariciftci ns. (2013) efficiency of bulk-heterojunction organic solar cells. progress in polymer science, 38(12): 1929-1940. doi: 10.1016/j/progpolymsci.2013.05.001. [2] park sungjun, heo sw, lee w, inoue d, jiang z, yu k, jinno h, hashizume d, sekino m, yokota t, fukuda k, tajima k, someya t. (2018) self-powered ultraflexible electronics via nano-grating-patterned organic photovoltaics. nature, 561(7724): 516-521. doi: 10.1038/s41586-018-0536-x. [3] teng n, yang s, chen f. (2018) plasmonic enhanced organic photovoltaic devices for low-power light applications. ieee journal of photovoltaic, 8(3): 752-756. doi: 10.1109/jphotov.2018.2797975. [4] green ma, emery k, hishikawa y, warta w, dunlop ed. (2016) solar cell efficiency tables. progress in photovoltaics, 24(7): 905–913. doi: 10.1002/pip.2788. [5] meng l, zhang y, wan x, li c, zhang x, wang y, ke x, xiao z, ding l, xia r, yip h, cao y, chen y. (2018) organic and solution-processed tandem solar cells with 17.3% efficiency. science, 361(6407): 1094-1098. doi: 10.1126/science.aat2612. [6] mandoc mm, koster lja, blom pwm. (2007) optimum charge carrier mobility in organic solar cells. applied physics letter, 90(13): 133504. doi: 10.1063/1.2711534. [7] inche ibrahim ml, ahmad z, sulaiman k, muniandy sv. (2014) combined influence of carrier mobility and dielectric constant on the performance of organic bulk heterojunction solar cells. aip advance, 4(5): 057133. doi: 10.1063/1.4881080. [8] lee jj, lee sh, kim fs, choi hh, kim jh. (2015) simultaneous enhancement of the efficiency and stability of organic solar cells using pedot:pss grafted with a pegme buffer layer. organic electronics, 26: 191-199. doi: 10.1016/j.orgel.2015.07.022. [9] chen a, zhu k, shao q, ji z. (2016) understanding the effects of tco work function on the performance of organic solar cells by numerical simulation. semiconductor science and technology, 31(6): 065025. doi: 10.1088/0268-1242/31/6/065025. 147 iium engineering journal, vol. 22, no. 2, 2021 mohamed and inche ibrahim https://doi.org/10.31436/iiumej.v22i2.1559 [10] koster lja, shaheen se, hummelen jc. (2012) pathways to a new efficiency regime for organic solar cells. advanced energy materials, 2(10): 1246-1253. doi: 10.1002/aen.201200103. [11] inche ibrahim ml, hassan ha. (2019) influence of active layer thickness on the performance of organic photovoltaics with light trapping. ieee transaction electron devices, 66(7): 3124-3128. doi: 10.1109/ted.2019.2917594. [12] lenes m, koster lja., mihailetchi vd, blom pwm. (2006) thickness dependence of the efficiency of polymer:fullerene bulk heterojunction solar cells. applied physics letter, 88(24): 243502. doi: 10.1063/1.2211189. [13] fallahpour ah, gagliardi a, gentilini d, zampetti a, santoni f, auf der maur m, carlo ad. (2014) optoelectronic simulation and thickness optimization of energetically disordered organic solar cells. journal computational electronics, 13(4): 933-942. doi: 10.1007/s10825-014-0611-y. [14] mescher j, christ n, kettlitz s, colsmann a, lemmer u. (2012) influence of the spatial photocarrier generation profile on the performance of organic solar cells. applied physics letters, 101(7): 073301. doi: 10.1063/1.4745510. [15] tress w, merten a, furno m, hein m, leo k, riede m. (2013) correlation of absorption profile and fill factor in organic solar cells: the role of mobility imbalance. advanced energy materials, 3(5): 631-638. doi: 10.1002/aenm.201200835. [16] islam m, wahid s, chowdhury m, hakim f, alam m. (2017) effect of spatial distribution of generation rate on bulk heterojunction organic solar cell performance: a novel semianalytical approach. organic electronics, 46(7): 226-241. doi: 10.1016/j.orgel.2017.04.021. [17] gan q, bartoli fj, kafafi zh. (2013) plasmonic-enhanced organic photovoltaics: breaking the 10% efficiency barrier. advanced materials, 25(17): 2385-2396. doi: 10.1002/adma.201203323. [18] inche ibrahim ml. (2018) an analytical model for organic solar cells incorporating nongeminate monomolecular and bimolecular recombinations. semiconductor science and technology, 33(12): 125005. doi: 10.1088/1361-6641/aadf72. [19] inche ibrahim ml. (2017) dissociation of charge-transfer states at donor–acceptor interfaces of organic heterojunctions. journal of physics d: applied physics, 50(6): 065103. doi: 10.1088/1361-6463/50/6/065103. [20] braun cl. (1984) electric field assisted dissociation of charge transfer states as a mechanism of photocarrier production. the journal chemical physics, 80(9): 4157-4161. doi: 10.1063/1.447243. [21] kniepert j, lange i, van der kaap nj, koster lja, neher d. (2014) a conclusive view on charge generation, recombination, and extraction in as‐prepared and annealed p3ht:pcbm blends: combined experimental and simulation work. advanced energy materials, 4(7): 1301401. doi: 10.1002/aenm.201301401. 148 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 multi-objective mayfly optimization in phase optimization of ofdm abdul azeez*and suraiya tarannum department of electronics and communication engineering, hkbk college of engineering, bangalore, 560045, india * corresponding author: abdulazeez.ec@hkbk.edu.in (received: 10th october 2022; accepted: 8th november 2022; published on-line: 4th january 2023) abstract: communication systems have been used tremendously in recent years which results in the need for high data transmission rates. orthogonal frequency division multiplexing (ofdm) provides robust performance in frequency selective fading due to high bandwidth efficiency and inter-symbol interference. various optimization techniques were applied in existing research to increase the efficiency of ofdm in a communication system. the existing research has a limitation of considering a single objective to improve the efficiency of ofdm and also has a local optima trap. this research proposes a multiobjective mayfly algorithm (momf) to consider multi-objective and provides a proper tradeoff between exploration and exploitation. the partial transmit sequence (pts) is applied in the model to test the performance. the fft sizes and modulation orders are varied to evaluate the performance of the momf technique in phase optimization. the momf technique effectively increases the performance of the model than other existing optimization techniques. the momf technique provides a non-dominated solution to escape from local optima trap. the momf model considers papr, ber, and ser in mimo-ofdm system to increase the efficiency of the system. the exploration-exploitation trade-off helps to improve the convergence and overcome local optima trap. the momf in ofdm phase optimization was evaluated using ber, ser, and peak-to-average power ratio (papr) metrics. the momf method has papr of 3.95 db and pso-gwo method has 4.92 db of papr. abstrak: sistem komunikasi telah digunakan secara meluas sejak beberapa tahun ini dan dapatan kajian menunjukkan keperluan pada kadar transmisi data yang tinggi. pemultipleksan bahagian frekuensi ortogon (ofdm) menyediakan prestasi berkesan dalam pemilihan pemudaran frekuensi berdasarkan keberkesanan lebar jalur tinggi dan gangguan antarasimbol. pelbagai teknik optimum digunakan pada kajian sebelum ini bagi meningkatkan keberkesanan ofdm dalam sistem komunikasi. kajian tersebut mempunyai kekurangan dalam memilih satu objektif bagi membaiki keberkesanan ofdm dan juga mempunyai perangkap optima setempat. kajian ini mencadangkan algoritma mayfly objektif-pelbagai (momf) bagi memilih objektif-pelbagai dan menyediakan keseimbangan yang wajar antara eksplorasi dan eksploitasi. urutan pancar separa (pts) telah digunakan dalam model ini bagi menguji prestasi. saiz fft dan turutan modulasi dipelbagaikan bagi menguji keberkesanan teknik momf pada fasa pengoptimuman. teknik momf dengan berkesan menaikkan prestasi model ini berbanding teknik-teknik sedia ada yang lain. teknik momf menyediakan solusi kepada teknik bukan-dominasi bagi mengelak perangkap optima setempat. model momf ini mengambil kira papr, ber, dan ser dalam sistem mimo-ofdm bagi meningkatkan kecekapan sistem. keseimbangan yang wajar antara eksplorasi-eksploitasi membantu dalam membaiki penumpuan dan mengatasi perangkap optima setempat. momf dalam fasa optimanisasi ofdm telah dinilai menggunakan ber, ser, dan matrik nisbah kuasa puncak-kepada-purata (papr). kaedah momf mempunyai nilai papr sebanyak 3.95 db dan kaedah pso-gwo mempunyai papr 4.92 db. iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 keywords: exploration; multi-objective mayfly algorithm; ofdm phase optimization; partial transmit sequence 1. introduction smart grid systems, digital audio broadcasting (dab), lte, 3gpp, wi-max, wireless lan, and terrestrial digital video broadcasting (dvb-t) of various wireless broadband communication systems are applied with the ofdm technique to improve their efficiency. ofdm systems have superior qualities and have a limitation of high papr for rf signals. ofdm has amplitude variation in the time domain due to its multicarrier nature and also has a large dynamic range or papr [1]. the ofdm signal is clipped when applied to a non-linear high-power amplifier (hpa) if high papr degrades the in-band distortion and out-of-band radiation. a wide dynamic range of expensive linear hpa is required in ofdm transmitters for efficient performance [2]. the many papr reduction methods of ofdm systems include selective mapping (slm), pts, tone reservation and tone injection, non-linear companding, coding, and clipping [3]. the pts and slm are popular distortionless techniques that received substantial attention due to decrease in papr without ber degradation. high computation complexity and side information (si) are major limitations in these techniques. the complexities of the pts and slm papr reduction methods are compared, in which the comparison shows that the pts method has lower complexity and the slm method has high papr reduction [4,5]. less search complexity of several optimization methods has been recently developed to optimize the pts method for cm reduction and papr reduction in ofdm systems. some of the optimization methods are grey wolf optimization (gwo), tabu search (ts), harmony search (hs), adaptive particle swarm optimization (apso), and hybrid genetic algorithm (hga) [6,7]. ofdm of multiple-input multiple-output (mimo) has received wide attention due to its advantages such as channel fading robustness, fading environment diversity, spectral efficiency and high data rate. however, the ofdm-mimo also suffers from disadvantages such as high envelope fluctuations in a transmitted signal called papr that decreases the hpa efficiency, increases complexity of non-linear elements and bit error rate (ber) degradation occurs from out-of-band radiation [8-10]. the contribution of this research is discussed below.  the momf method is proposed to consider papr, ber, and ser in the mimoofdm system to increase the efficiency of the model. the momf method provides a proper exploration-exploitation trade-off that improves the efficiency of the optimization.  the exploration-exploitation trade-off process improves the convergence rate of the method and escapes from local optima trap. the momf method has higher efficiency compared to existing methods in optimization of mimo-ofdm systems. 2. literature review ofdm is a reliable and robust multicarrier modulation method that is sufficient for broadband communication. various methods applied in ofdm for phase optimization are discussed in this section. lavanya et al. [11] applied improved monarch butterfly optimization (imbo) method for papr reduction in the ofdm framework. the imbo method was efficient for optimal character fusion of phase rotation factor for minimizing computation. the imbo method provides efficient search optimization, and using optimum phase factor and phase weighting iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 method with less complexity. the imbo method significantly reduces the papr and computational complexity. sorting was carried out twice with the monarch butterfly optimization method during every generation. the imbo method applies random local perturbation (rlp) and opposition-based learning (obl) to solve the sorting problem. ali and hamza [12] applied teaching learning based optimization (tlbo) for papr reduction in ofdm optimization. the tlbo method has the advantage of less computational effort and no algorithm-specific parameter requirement. the tlbo consists of two-phases, teacher and learner phases, for learning the input data. the interaction between teacher and student is the teaching phase, and the interaction between the learners is the learning phase. the tlbo based method was applied to obtain the phase factor of optimum rotation in the slm method for papr reduction. the tlbo-slm method achieved considerably better performance in papr reduction. sharif and emami [13] proposed the improved flower pollination (ifp) algorithm to reduce the search complexity of partial transmit sequence (pts). the aco-ofdm method was applied with pts technique to reduce high papr in the system. the ifp method was derived from flower pollination behaviors and an asymmetrical clipped optical ofdm system was applied in ifp. the ifp method increased the optimization capability of standard flower pollination using a local pollination operator to increase exploitation ability and the global pollination phase was applied to increase exploration. the ifp method balanced the exploitation and exploration capacity of the optimization method. the ifp method had less computational complexity than the existing method in ofdm optimization. emami and sharif [14] applied a tree growth optimization (tgo) method to reduce the computational complexity for the selection of optimal phase factors in pts. the tgo method was efficient in reducing the high papr of optical ofdm signals. the tgo consists of three operators: seed scattering, root spreading, and competition. the solution population was updated by these operators to find near-optimal solutions for optimization problems. the tgopts method dramatically decreased the papr of the ofdm signal and had higher performance than existing methods in terms of convergence rate and solution quality. emami and sharif [15] applied a chaotic differential search algorithm (cdsa) with an efficient and fast convergence optimizer for ofdm optimization. the cdsa method was an optimization technique to solve non-linear, largescale, and complex problems. the csa method was compared with several optimization methods in terms of mitigation performance and search complexities. the cdsa and pts were combined to solve the search complexity problem in the conventional method and to control a few parameters for exploring phase factors for the optimal set. the cdsa method had considerable performance in phase optimization than existing methods. an improved adaptive simplified optimized iterative clipping and filtering (asoicf) technique has been shown by padarti and nandhanavanam [16] to lower papr in ofdm systems. due to its ease of application in the papr minimization in ofdm, icf, between these papr reduction techniques, drew a lot of interest. the approach uses lagrange multiplier optimization (lmo), which has the benefit of reducing the number of iterations in a specific way. it was discovered that the papr in ofdm signals was greatly reduced by the adaptive technique. the results clearly showed that the suggested approach performed better in terms of computational complexity. the peak of the clipped ofdm affected the noise overhead, therefore, it decreased the ber. iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 a regularization optimization based flexible hybrid companding and clipping technique (rofhcc) employed for papr reduction in ofdm systems was developed by xing et al. [17]. the companding function comprised two components to lessen the complexity of the design. in order to achieve both peak power reduction and small power compensation, it limited the signal samples whose amplitudes exceeded a certain value to a constant value. signals were extended using a linear companding function for samples below a specified amplitude. in order to jointly optimize the companding distortion and the continuity of the companding function, a regularization optimization model was developed. nonetheless, the proposed method could not confirm the average power as constant. 3. research method the input signal is applied to ldpc encoding to encode the signal and apply for its modulation. the pilot insertion of the signal is transformed with ifft and the pilot insertion information is provided as input to the proposed momf optimization to find optimal parameter settings. the optimal parameter settings of the momf optimization method are applied in the stbc encoder as well as in the awgn noise channel. the stbc decoding is carried out and cyclic prefix removal is applied. the fft is applied in the signal and pilot removal is carried out to process the output signal. the block diagram of the momf method in phase optimization of ofdm is shown in fig. 1 and fig. 2. fig. 1: the momf optimization in pilot insertion. fig. 2: the momf optimization in phase factor of ofdm. iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 3.1 papr in mimo-ofdm the subcarriers arrangement of relating subcarriers are adjusted to each signal surrounding the subcarriers m of ofdm data [13], [18], [19]. the mimo-ofd structure of orthogonal m subcarriers is over the period of 0 p g  where the primary data signal period is denoted as g and the near sub-carriers repeat partitioning is denoted as 0 1 /t g . the ofdm movement of complex baseband in m subcarriers is given in eq. (1).   1 2 0 1 , 0o m j nt p nn s p a e p g m      (1) the discrete time adaptation is mentioned as /cg g m and substitutes cp mg which is expressed in eq. (2),   2 1 0 1 , 0,1, , 1 j mn m dm nn s m a e m md m        (2) wherein, the oversampling element is denoted as d . spikes are not found in the inspection of the signal; therefore, it provides optimistic results for papr. fourier change in the ofdm transmits the ordinary power and quick power of papr which is given as (p), as in eq. (3).     2 0 2 p g max a p papr e a p        (3) wherein, the desire expectation is  .e . the consistent time of papr is not unquestionably registered in the nyquist inspecting rate which completely depends on ofdm signal. the ofdm signals of papr in the complementary cumulative distribution function (ccdf) are used to improve papr reduction accurately. the ccdf probability outperforms the edge of papr and is represented in eq. (4).         0qccdf papr a t p papr a t papr  (4) 3.2 partial transmit sequences (pts) the papr diminish technique based on fractional transmit arrangement is pts. this is based on the original ofdm sequence which is divided into sub-grouping experts and each sub-progression weight is varied until the expert is in optimal value [13,20-22]. random space of data information is separated into w sub-pieces of non-covering and has comparable size s of each sub-square. the s/w non-zero segments are present in each sub piece and the real part is zero. the sub-squares are given in eq. (5). 1 ˆ w w ww a c a    (5) here,    0, 2 1, 2, ,wrw wc e w w       . stage pivot of weighting part is denoted as wc and time range of the signal is applied using ifft operation on w a . iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 a proper part mix  1 2, wc c c c  is applied to measure the optimal value for papr reduction, as in eq. (6).   2 1 1 2 , , , , 1 w w ww w min max c arg c a c c c m m            (6) wherein, best estimation is found using the condition of  *arg min and by remembering the ultimate objective of c for papr execution redesign. most of the complication arises on the downside and ifft operations are performed for an extra 1w  times. 3.3 multi-objective mayfly algorithm in mayfly, the nuptial dance and random flight operations help an algorithm escape local optimums and improve the harmony between its exploitation and exploration features. in this way, mayfly efficiently identifies the space of each and every sequence of a given phase factor set. while considering the pso in high-dimensional space, it falls into local optimum and attains a lower convergence rate in the iterative process. therefore, the proposed momf optimization method is applied in the phase factor of ofdm to improve the efficiency of the model, ber, and papr. mayfly group behavior is mimicked to develop the mayfly algorithm with mating behavior [23-30]. female and male mayflies are randomly divided from the population at the initial stage of algorithm. all mayflies are randomly scattered in ddimensional space and  1 2, , , d     expression is considered for the selection of candidate solutions. the position change  1 2, , , d     is represented by the velocity vector. 1) male mayflies’ movement: th i male mayfly with the position of t i  at time t and velocity is denoted as t i  to change ith individual position. male mayflies   1 t  of position 1 t  is expressed in eq. (7). 1 1 , t t t i i i male        (7) the velocity for th j dimension of th i mayfly is denoted in eq. (8).         1 2 , , 1 2 2 exp exp t t t ij male ij male p ij ij t g j ij a pbest a gbets                 (8) the position and velocity of th j dimension of th i mayfly are denoted as t ij  and , t ij male  , respectively. the positive attraction constants are denoted as   1 , 2ia i  that respond based on social components and cognitive rules. the global optimal and local optimal positions are j gbest and ij pbest , respectively. a fixed visibility coefficient is denoted as  , that controls individual visibility to other individuals. cartesian distance is denoted as p  and g  from th i mayfly, respectively for local and global optimal solutions. the global optimal value j gbest and local optimal value ij pbest are calculated using eq. (9 & 10).     1 11, , 1, ,, { } , t t i c i c i i if pbest pbest kept the same otherwise              (9) iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625              1 2 1, , 1, , 1 1, , 2 1, , , , , | , , , n c c c c n gbest pbest pbest pbest cbest dominate pbest pbest pbest             (10) wherein, objective functions are represented as 1,..., : n c r r  . to ensure effective operation of the algorithm, the population of optimal mayflies constantly perform the up and down nuptial dance. the optimal mayflies’ velocities are changed in the following eq. (11). 1 , , t t ij male ij male d       (11) wherein, the position for th j dimension of th i male mayfly is denoted as , t ij male  , a random number of  is in the range of [-1, 1], and the nuptial dance coefficient is denoted as d . 2) movement of female mayflies: for breeding, female individuals move toward males and male mayflies gather in swarms. the corresponding velocity and current position at time t of th i female mayfly are denoted as 1 , t i female   and t i  , respectively. the female mayflies of  1 th t  positions are given in eq. (12). 1 1 , t t t i i i female        (12) a deterministic scheme is used to define the attraction process in the mayfly algorithm optimization process. the fitness function is used by an optimal female and sub-optimal females to provide a tendency toward male individuals and sub-optimal male individuals. the th j dimension of th i female mayfly velocity is used for a minimization problem, as in eq. (13).             1 , 2 , 2 , exp , , t ij female t t t ij female mf ij ij i t ij female i i a if fl if                            (13) wherein, the position and velocity for th j dimension of th i female mayfly are denoted as , t ij female  and t ij  respectively. the cartesian distance of th i male mayfly to th i female mayfly is denoted as mf  . the random walk coefficient is denoted as fl . 3) mating of mayflies: female and male populations are selected as two parents. as per the mating principle, the best male mates with the best female, that creates two offspring as shown in eq. (14) and eq. (15).  1 1offspring male female      (14)  2 1offspring female male      (15) wherein, the random value of male and female individuals in the previous generation is represented as   0, 1   . initial individual velocities in the current generation are 0. 4) multi-objective mayfly algorithm: the momf is a multi-objective variant of the mayfly algorithm based on roulette wheel selection, the strategy of non-dominated sorting, and the archive mechanism. non-dominated pareto optimal solution is applied to generate the present iteration and to archive the upper limit. once a non-dominated iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 solution is achieved, it is compared with the present solution. the least values are eliminated and a better solution is archived. most populated neighborhoods are eliminated using / , 1 i i pro n    and when the archive is full, th i individual number of members is denoted as i n and  is a constant. the roulette wheel method is used to develop solutions that are added to momf. the probability of the roulette wheel is set in eq. (16). / i i pro n (16) a solution is selected from a set of non-dominated solutions using a multiple-criteria selection method. fitness function values are normalized for male and female mayflies in eq. (17).   i j i j i min fitness i j n fitness max min fitness l j n l j n                  (17) the th i fitness function of normalized value is denoted as i jfitness measured from th j female or male mayfly and population size is denoted as n . the th j female or male mayfly is computed using multiple-criteria (mc), as in eq. (18). 1 im jj i mc fitness    (18) the mc values are used to sort male and female mayflies in momf; the lowest mc values of mayfly’s optimal male and female are obtained from individuals and non-dominated solution. 4. results and discussion this research applies the momf algorithm in phase optimization of ofdm to improve its efficiency. the ofdm parameters are given in table 1 and parameter settings of momf are given in table 2. various fft sizes of 64, 128, 256, 512, and 1024 were used to evaluate momf algorithm in ofdm phase optimization. table 1: ofdm parameters fft size 64, 128, 256, 512, 1024 user carriers 52, 104, 156, 208, 260 pilot carriers 12, 24, 48, 60, 72 antenna 2x2, 2x4, 4x2, 4x4 cyclic prefix or guard time 0 to 2e-6s modulation 8 qam, 16 qam, 32 qam, 64 qam, 256 qam oversampling factor 1e6 hz channel type rayleigh channel noise awgn iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 table 2: momf algorithm number of iteration 100 population size (males and females) 25 & 25 npareto (repository size) 30 lowerbound -3 upperbound 6 g (inertia weight) 1 gdamp (inertia weight damping ratio) 1 a1 ( personal learning coefficient) 1.5 a2 & a3 ( global learning coefficient) 1.5 & 1.5 beta (distance sight coefficient) 0.99 dance (mutation coefficient) 0.77 dance_damp ( mutation coefficient damping ratio) 0.77 f1 (random flight) 0.77 f1_damp (random flight damping ratio) 0.99 % mating parameters ncrossover (number of parnets (offsprings)) 4 nmutation (number of mutants) round (0.4*npop) mu (mutation rate) 0.001 the momf optimization method is applied in the phase factor of ofdm to improve the efficiency of the model and ber is shown in fig. 3. the dct and fft techniques have higher efficiency in momf methods. the dwt has lower efficiency in the phase optimization of ofdm. fig. 3: the ber of momf optimization with various techniques. figures 4, 5 and 6 show ber, ser and papr of momf in fft 128 m8 modulation of ofdm phase optimization. the momf has a higher convergence rate and overcomes local optima trap. the existing gwo method has a trap in local optima and pso has lower convergence in optimization. the momf method reduces the papr compared to existing methods in ofdm phase optimization. iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 fig. 4: ber of fft 128 m8 modulation. fig. 5: symbol error rate of fft 128 m8 modulation. fig. 6: momf papr of fft 128 m8 modulation. table 3 shows the difference in papr reduction achieved by various methods including pts, pso, gwo, pso-gwo and proposed momf. table 3 clearly shows that the papr iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 reduction of proposed momf achieved a value of 3.9537 db which is much better when compared to specified methods. table 3: results of papr on fft 64 m16 modulation methods papr (db) mimo-ofdm 7.8345 pts 5.0140 pso 5.0168 gwo 5.1163 pso-gwo 4.9222 proposed momf 3.9537 the momf optimization method is measured with ber and papr in fft 128 m256 modulation, as in fig. 7 and fig. 8. the momf method provides higher efficiency in fft 128 compared to existing methods. the momf method has the advantages of high convergence and overcoming local optima trap. fig. 7: momf ber of fft 128 m256 modulation. fig. 8: momf papr of fft 128 m256 modulation. iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 fig. 9: momf ber of fft 512. fig. 10: momf papr of fft 512. the momf ber and papr in fft 512 in ofdm phase optimization are given in fig. 9 and fig. 10. the momf method has the advantages of higher convergence and overcoming local optima trap. the gwo method is easily trapped into local optima and pso method has lower convergence. the momf method in ofdm phase optimization for m8 and m64 modulation are shown in fig. 11 and fig. 12. the momf method provides a higher efficiency in both modulations than existing methods. the momf ber and papr of fft 1024 in ofdm phase optimization are shown in fig. 13 and fig. 14. the momf method considers various parameters in ofdm to reduce ber, ser and papr. the existing methods consider a single objective and have a limitation of local optima trap. the momf ber of fft 1024 m128 modulation in ofdm phase optimization is given in fig. 15. the momf method has lower ber due to the consideration of multi-objective optimization and has higher convergence. iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 fig. 11: momf ber of fft 512 m8 modulation. fig. 12: momf papr of fft 512 m64. fig. 13: momf ber of fft 1024. iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 fig. 14: momf papr of fft 1024. fig. 15: momf ber of fft 1024 m128. in order to properly balance exploration and exploitation, this research suggests using the multi-objective mayfly algorithm (momf), which takes many objectives into account. the model applies the partial transmit sequence (pts) to test performance. to assess the effectiveness of the momf technique in phase optimization, several fft widths and modulation orders are used. when compared to other optimization strategies, the proposed momf technique significantly improves model performance. from the result analysis, it clearly shows that various fft sizes of 64, 128, 256, 512, and 1024 are used to evaluate momf algorithm in terms of ber and papr. the proposed strategy is a better way to achieve a better trade-off between papr reduction and computing complexity, according to simulation results. 5. conclusion the existing methods in ofdm apply optimization methods to improve the efficiency of the ofdm. the existing methods have limitations of considering a single objective in optimization and also have a local optima trap. this research proposes the momf algorithm to increase the efficiency of ofdm phase optimization by considering multiple objectives. the momf method balances the exploration and exploitation in the search process of optimization. the momf method considers three objectives for ofdm phase optimization: ber, ser, and iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 papr. the momf method is evaluated in various fft and modulations in the ofdm. the momf method provides higher performance in the ofdm phase optimization than existing methods. the gwo method has the limitation of a local optima trap and the pso method has lower convergence. the momf method balances the trade-off between exploration and exploitation that increases the convergence and overcomes the local optima trap. the future work of this research involves applying the enhanced artificial bee colony method to improve the efficiency of the mimo-ofdm system. references [1] singh m, patra sk. (2018) on the pts optimization using the firefly algorithm for papr reduction in ofdm systems. iete tech. rev., 35(5): 441-455. https://doi.org/10.1080/02564602.2018.1505563. [2] aghdam mh, sharifi aa. (2019) papr reduction in ofdm systems: an efficient pts approach based on particle swarm optimization. ict express, 5(3): 178-181. https://doi.org/10.1016/j.icte.2018.10.003. [3] wu w, cao y, wang s, wang y. (2018) joint optimization of papr reduction based on modified tr scheme for mimo-ofdm radar. digital signal process., 80: 27-36. https://doi.org/10.1016/j.dsp.2018.05.008. [4] ahmed ms, boussakta s, al-dweik a, sharif b, tsimenidis cc. (2019) efficient design of selective mapping and partial transmit sequence using t-ofdm. ieee trans. veh. technol., 69(3): 2636-2648. doi: 10.1109/tvt.2019.2928361. [5] hu w, li f, jiang y. (2021) phase rotations of svd-based precoders in mimo-ofdm for improved channel estimation. ieee wireless commun. lett., 10(8): 1805-1809. doi: 10.1109/lwc.2021.3081583. [6] emami h, sharifi aa. (2020) an improved backtracking search optimization algorithm for cubic metric reduction of ofdm signals. ict express, 6(3): 258-261. https://doi.org/10.1016/j.icte.2020.03.001. [7] sarkar m, kumar a, maji b. (2021) papr reduction using twin symbol hybrid optimizationbased pts and multi-chaotic-dft sequence-based encryption in cp-ofdm system. photonic network communications, 41(2): 148-162. https://doi.org/10.1007/s11107-020-00923-7. [8] amhaimar l, ahyoud s, elyaakoubi a, kaabal a, attari k, asselman a. (2018) papr reduction using fireworks search optimization algorithm in mimo-ofdm systems. j. electr. comput. eng., 2018: 3075890. https://doi.org/10.1155/2018/3075890. [9] geetha mn, mahadevaswamy ub. (2020) performance evaluation and analysis of peak to average power reduction in ofdm signal. wireless personal communications, 112(4): 20712089. https://doi.org/10.1007/s11277-020-07140-5. [10] du j, xu w, zhao c, vandendorpe, l. (2019) weighted spectral efficiency optimization for hybrid beamforming in multiuser massive mimo-ofdm systems. ieee trans. veh. technol., 68(10): 9698-9712. doi: 10.1109/tvt.2019.2932128. [11] lavanya p, satyanarayana p, mohatram m. (2022) peak to average power ratio reduction of zt dft-s-ofdm signals using improved monarch butterfly optimization-pts scheme. j. ambient intell. hum. comput. https://doi.org/10.1007/s12652-022-03954-2. [12] ali th, hamza a. (2021) low-complexity papr reduction method based on the tlbo algorithm for an ofdm signal. ann. telecommun., 76(1): 19-26. https://doi.org/10.1007/s12243-020-00777-0. [13] sharifi aa, emami h. (2020) papr reduction of asymmetrically clipped optical ofdm signals: optimizing pts technique using improved flower pollination algorithm. opt. commun., 474: 126057. https://doi.org/10.1016/j.optcom.2020.126057. [14] emami h, sharifi aa. (2020) a novel bio-inspired optimization algorithm for solving peak-toaverage power ratio problem in dc-biased optical systems. opt. fiber technol., 60: 102383. https://doi.org/10.1016/j.yofte.2020.102383. https://doi.org/10.1080/02564602.2018.1505563 https://doi.org/10.1016/j.icte.2018.10.003 https://doi.org/10.1016/j.dsp.2018.05.008 https://doi.org/10.1109/tvt.2019.2928361 https://doi.org/10.1109/lwc.2021.3081583 https://doi.org/10.1016/j.icte.2020.03.001 https://doi.org/10.1155/2018/3075890 https://doi.org/10.1109/tvt.2019.2932128 https://doi.org/10.1016/j.optcom.2020.126057 https://doi.org/10.1016/j.yofte.2020.102383 iium engineering journal, vol. 24, no. 1, 2023 azeez and tarannum https://doi.org/10.31436/iiumej.v24i1.2625 [15] emami h, sharifi aa. (2020) optimizing cubic metric in orthogonal frequency division multiplexing systems using chaotic differential search algorithm. phys. commun., 43: 101231. https://doi.org/10.1016/j.phycom.2020.101231. [16] padarti vk, nandhanavanam vr. (2021) an improved asoicf algorithm for papr reduction in ofdm systems. int. j intell. eng. syst., 14: 352-360. https://doi.org/10.22266/ijies2021.0430.32 [17] xing z, liu k, rajasekaran as, yanikomeroglu h, liu y. (2021) a hybrid companding and clipping scheme for papr reduction in ofdm systems. ieee access, 9: 61565-61576. https://doi.org/10.1109/access.2021.3074009 [18] yuan y, wei s, luo x, xu z, guan x. (2022) adaptive pts scheme based on fuzzy neural network for papr reduction in ofdm system. digital signal process., 126: 103492. https://doi.org/10.1016/j.dsp.2022.103492. [19] carcangiu s, fanni a, montisci a. (2022) a closed form selected mapping algorithm for papr reduction in ofdm multicarrier transmission. energies, 15(5): 1938. https://doi.org/10.3390/en15051938. [20] murad m, tasadduq ia, otero p. (2022) ciphered bch codes for papr reduction in the ofdm in underwater acoustic channels. j. mar. sci. eng., 10(1): 91. https:// doi.org/10.3390/jmse10010091. [21] aghdam mh, sharifi aa. (2021) a novel ant colony optimization algorithm for papr reduction of ofdm signals. int. j. commun. syst., 34(1): e4648. https://doi.org/10.1002/dac.4648. [22] wu y, hu y, wan z, wang t, sun y, zhang q. (2022) joint security enhancement and papr mitigation for ofdm-noma vlc systems. opt. commun., 508: 127719. https://doi.org/10.1016/j.optcom.2021.127719. [23] kumar c, karpurapu a, singh yp. (2022) reduction of papr for fbmc-oqam system using ant colony optimisation technique. soft comput., 26(9): 4295-4302. https://doi.org/10.1007/s00500-021-06503-9. [24] elaziz ma, senthilraja s, zayed me, elsheikh ah, mostafa rr, lu s. (2021) a new random vector functional link integrated with mayfly optimization algorithm for performance prediction of solar photovoltaic thermal collector combined with electrolytic hydrogen production system. appl. therm. eng., 193: 117055. https://doi.org/10.1016/j.applthermaleng.2021.117055. [25] shaheen mam, hasanien hm, el moursi ms, el fergany aa. (2021) precise modeling of pem fuel cell using improved chaotic mayfly optimization algorithm. int. j. energy res., 45(13): 18754-18769. https://doi.org/10.1002/er.6987. [26] liu z, jiang p, wang j, zhang l. (2021) ensemble forecasting system for short-term wind speed forecasting based on optimal sub-model selection and multi-objective version of mayfly optimization algorithm. expert syst. appl., 177: 114974. https://doi.org/10.1016/j.eswa.2021.114974 [27] adnan rm, kisi o, mostafa rr, ahmed an, el-shafie a. (2022) the potential of a novel support vector machine trained with modified mayfly optimization algorithm for streamflow prediction. hydrol. sci. j., 67(2): 161-174. https://doi.org/10.1080/02626667.2021.2012182 [28] wei d, ji j, fang j, yousefi n. (2021) evaluation and optimization of pem fuel cell-based cchp system based on modified mayfly optimization algorithm. energy rep., 7: 7663-7674. https://doi.org/10.1016/j.egyr.2021.10.118 [29] liu y, chai y, liu b, wang y. (2021) bearing fault diagnosis based on energy spectrum statistics and modified mayfly optimization algorithm. sensors, 21(6): 2245. doi: 10.3390/s21062245 [30] tamilmani g, devi vb, sujithra t, shajin fh, rajesh p. (2022) cancer mirna biomarker classification based on improved generative adversarial network optimized with mayfly optimization algorithm. biomed. signal process. control, 75: 103545. https://doi.org/10.1016/j.bspc.2022.103545 https://doi.org/10.1016/j.phycom.2020.101231 https://doi.org/10.1016/j.dsp.2022.103492 https://doi.org/10.1002/dac.4648 https://doi.org/10.1016/j.optcom.2021.127719 https://doi.org/10.1016/j.applthermaleng.2021.117055 https://doi.org/10.1002/er.6987 https://doi.org/10.1016/j.eswa.2021.114974 https://doi.org/10.1080/02626667.2021.2012182 https://doi.org/10.1016/j.egyr.2021.10.118 https://doi.org/10.3390%2fs21062245 https://doi.org/10.1016/j.bspc.2022.103545 international islamic university malaysia iium (international islamic university malaysia) engineering journal chief editor ahmad faris ismail, iium, malaysia. technical editor ir. dr. md. noor bin salleh, iium, malaysia. guest editor m.n.a. hawlader, iium, malaysia. executive editor waqar asrar, iium, malaysia. associate editor hamzah mohd. salleh, iium, malaysia. anis nurashikin nordin, iium, malaysia. israd hakim jaafar, iium, malaysia. language editor israd hakim jaafar, iium, malaysia. copy editor hamzah mohd. salleh, iium, malaysia. editorial board members a.k.m nurul amin, iium, malaysia abdullah al-mamun, iium, malaysia abdumalik rakhimov, iium, malaysia amir akramin shafie, iium, malaysia erwin sulaeman, iium, malaysia hanafy omar, saudi arabia hazleen anuar, iium, malaysia konstantin khanin, university of toronto, canada ma'an al-khatib, iium, malaysia md zahangir alam, iium, malaysia meftah hrairi, iium, malaysia mohamed b trabia, united states mohammed konneh, iium, malaysia mohammad s. alam, university of south alabama, united states mustafizur rahman, national university singapore, singapore ossama abdulkhalik, michigan technological university, united states teddy surya gunawan, iium, malaysia iium (international islamic university malaysia) engineering journal aims & scope of iiumengineering journal the iium engineering journal, published biannually, is a carefully refereed international publication of international islamic university malaysia (iium). contributions of high technical merit within the span of engineering disciplines; covering the main areas of engineering: electrical and computer engineering; mechanical and manufacturing engineering; automation and mechatronics engineering; material and chemical engineering; environmental and civil engineering; biotechnology and bioengineering; engineering mathematics and physics; and computer science and information technology are considered for publication in this journal. contributions from other areas of engineering and applied science are also welcomed. the iium engineering journalpublishes contributions under regular papers, invited review papers, short communications, technical notes, and letters to the editor (no page charge). book reviews, reports of and/or call for papers of conferences, symposia and meetings, and advances in research equipment could also be published in iium engineering journalwith minimum charges. referees’ network all papers submitted to iium engineering journalwill be subjected to a rigorous reviewing process through a worldwide network of specialized and competent referees. each accepted paper should have at least two positive referees’ assessments. submission of a manuscript a manuscript should be submitted online to the iium-engineering journal website: www.eng.iium.edu.my/ejournal. furthercorrespondence on the status of the paper could be done through the journal website and the e-mail addresses of the executive editor: waqar@iium.edu.my faculty of engineering, international islamic university malaysia (iium), p.o. box 10, 50728, kuala lumpur, malaysia. phone: (603) 6196 4482, fax: (603) 6196 4853. http://www.eng.iium.edu.my/ejournal mailto:waqar@iium.edu.my iium (international islamic university malaysia) engineering journal international advisory committee tibor czigany yiuwing mai luis le moyne, isat, university of burgundy, france razi nalim, iupui, indianapolis, indiana, united states farzad ismail, usm, pulau pinang, malaysia ossama abdulkhalik, michigan technological university, united states a anwar, united states abdul latif bin ahmad, malaysia hanafy omar, saudi arabia hany ammar, united states idris mohammed bugaje, nigeria k.b. ramachandran, india kunzu abdella, canada m mujtaba, united kingdom mohamed ai-rubei,, ireland mohamed b trabia, united states mohammad s. alam, university of south alabama, united states m. nazmul karim, united states syed kamrul islam, united states published by: iium press, international islamic university malaysia p.o. box 10, 50728 kuala lumpur, malaysia phone (+603) 6196-5014, fax: (+603) 6196-6298 website: http://iiumpress.iium.edu.my/bookshop printed by: naga global print (m) sdn. bhd. no. 1, jalanindustribatu caves 68100 batu caves, selangor, malaysia whilst every effort is made by the publisher and editorial board to see that no inaccurate or misleading data, opinion or statement appears in this journal, they wish to make it clear that the data and opinions appearing in the articles and advertisement herein are the responsibility of the contributor or advertiser concerned. accordingly, the publisher and the editorial committee accept no liability whatsoever for the consequence of any such inaccurate or misleading data, opinion or statement. microsoft word vol11_no1_final iium engineering journal, vol. 11, no. 1, 2010 amara and salem 89 logical and experimental design for phenol degradation using immobilized acinetobacter sp. culture amro a. amara1,2 and soheir. r. salem3 1pharmaceutics department, faculty of pharmacy, king saud university, riyadh, kingdom of saudi arabia. 2protein research department, genetic engineering and biotechnology research institute, mubarak city for scientific research and technology applications. alexandria, egypt. 3faculty of education, biological and geological science department, alexandria university, alexandria, egypt. email : amroamara@web.de abstract : phenol and phenolic compounds cause severe pollutant to the nature. phenol degradation using microbes has been attracted the attention of many researchers. in this study plackett-burman design has been used to map and optimize the points affect in the degradation process. nine variables include ph (x1), oc (x2), glucose (x3), yeast extract (x4), meat extract (x5), nh4no3 (x6), k-salt (x7), mg-salt (x8) and trace elements (x9) as a media constituents are optimized during the phenol degradation process using immobilized acinetobacter sp. according to plackett-burman design experiments the maximum degradation rate was 31.25 mg/l/h. logical and statistical analysis of the data lead to select ph, temperature and meat extract as the most important three factors affecting on the phenol degradation rate. these three variables have been used in box-behnken experimental design, which result in degradation rate equal to 35.7 mg/l/hr. microsoft excel 2002 solver tool was used to optimize the model created from box-behnken. the calculated degradation rate was 37.30 mg/l/hr while the experimental degradation rate was 38.45 mg/l/hr, which prove the model accuracy. the use of logical analyses of the data covers the limitation of the statistical methods in selecting the correct variables. we recommended using logical and statistical data analysis for optimization the phenol degradation rate and other related processes. keywords: plackett-burman, box-behnken, solver, phenol, degradation, optimization, acinetobacter sp. 1. introduction phenol is a monoaromatic compound produced naturally or chemically [1]. phenolic compounds found in polluted water resources, industrial effluents of many applications like winedistillery, olive oil extraction, green olive debittering, cork preparation, wood debarking, detoxification of coffee husk etc., and land filled run off wastes [2-7]. many strategies have been developed for controlling phenol and preventing it from causing harmful effect on nature [8-10]. microbes are able to utilize phenolic compounds as a carbon source [11]. experimental design is a versatile tool for optimization different parameters and conditions [11, 12]. plackett-burman [11] and box-behnken [13] design iium engineering journal, vol. 11, no. 1, 2010 amara and salem 90 were used in optimization of the environmental and nutritional condition of the phenol degradation process and the results analyzed statistically using different statistical methods. logical interpretation of the statistical analysis as well as the crude data proved useful for selecting the most effective variables. the results of the optimization studies obtained from this study proved to be promising. 2. materials and methods 2.1 microorganism microbial strain used in this study was isolated from soil and characterized using standard criteria and identified as acinetobacter sp. 2.2 immobilization technique two-gram agar and 0.75 g sodium alginate were dissolved in 80 ml water and stirred well before sterilization. after sterilization, 20 ml cell suspension was added to the mixture. the mixture (3 mg dry weight cells/ml gel) was aseptically extruded drop-wise through a needle into a cold solution of 2% cacl2. the beads were transferred to a sterile phosphate buffer solution (1.46% k2hpo4 and 0.22% kh2po4) for 2 h. the beads were then washed and transferred to the mineral medium containing 0.5 g/l phenol. glucose, yeast extract and meat extract were prepared as stock solution and sterilized using bacterial membrane filter (0.22 µm) and added with the quantities as described in table 1, 2 and 6. 2.3 media content (g/l) nh4no3, 1.5; mgso4.7h2o, 0.5; k2 hpo4, 1.0; kh2po4 0.5; nacl, 0.5; caci2, 0.02; (0-4 ml), ph was adjusted as desired. after autoclaving at 12loc for 20 min, trace elements solution was then added [14]. 2.4 trace element solution (g/l) feso4.7h2o, 5 g; h3bo4, 25 mg; cuso4.5h2o, 5 mg; ki, 5 mg; coso4.7h2o, 0.3 g; mnso4.4h2o, 3 g; znso4.7h2o, 5 g; namoo4.7h2o, 12 mg. the solution was filter sterilized with a 0.22 µm membrane filter. 2.5 fermentation procedures phenol degradation was conducted using 250 ml erlenmeyer-flask containing 100 ml media and 20 ml gel (immobilized cells), at a shaking rate of 180 rpm. the media composition, ph, and temperature were changed when running both of plackett-burman and box-behnken design as described in table 2 and 6. 2.6 phenol assay the method described by korenman et al. (1998) was used to determine the phenol degradation rate as mg/l/hr [15]. iium engineering journal, vol. 11, no. 1, 2010 amara and salem 91 2.7 experimental designs a. media constituents effect two experiments with or without the media constituents as described above, in presence of 0.5 g/l phenol, were conducted. one experiment was conducted using all the above described media constituents while the other contain none of them. the phenol degradation rate was determined as mg/l/hr. b. plackett-burman plackett-burman design was used for screening the effect of nine variables include ph (x1), temperature (x2), glucose (x3), yeast extract (x4), meat extract (x5), nh4no3 (x6), k-salt (x7), mg-salt (x8) and trace elements (x9). the experimental design was created following the design described by plackett and burman [12] where sixteen experiments were created to analyze the effect of the different variables on the phenol degradation rate as summarized in table 1. c. multiple regression analysis of the plackett-burman experiments the results of the plackett-burman experiments were analyzed by multiple regression analysis using microsoft excel 2002 as described in details by abdel-fattah and olama [16]. from the statistical analysis of the data as in table 2, which has been tabulated in table 3, the variables whose confidence levels ≥ than 90% were considered to be significant. variables with confidence level between 90% and 70% were considered as being effective [17]. table 1: phenol degradation rate with or without media constituents expt. no. ph oc glucose g/l yeast extract g/l meat extract g/l nh4no3 g/l k salt g/l mg salt g/l trace element ml/100 ml phenol degradation rate mg/l/h r + 1 +1 (8) +1 (40) +1 (15) +1 (4) +1 (4) +1 (1.5) +1 (1.5) +1 (0.5 +1 (4) 0 18 -1 (4) -1 (20) -1 (0) -1 (0) -1 (0) -1 (0) -1 (0) -1 (0) -1 (0) 13.6 iium engineering journal, vol. 11, no. 1, 2010 amara and salem 92 table 2: plackett-burman experiments. expt. no. ph oc glucose g/l yeast extract g/l meat extract g/l nh4no3 g/l k salt g/l mg salt g/l trace element ml/100 ml phenol degradation rate mg/l/hr p la ck et t b u rm an e x pe ri m en ts 1 +1 (8) -1 (20) +1 (15) +1 (4) -1 (0) +1 (1.5) +1 (1.5) +1 (0.5) -1 (0) 0 2 +1 (8) +1 (40) -1 (0) +1 (4) +1 (4) -1 (0) +1 (1.5) +1 (0.5) +1 (4) 31.25 3 -1 (4) +1 (40) +1 (15) -1 (0) +1 (4) +1 (1.5) -1 (0) +1 (0.5) +1 (4) 0 4 -1 (4) -1 (20) +1 (15) +1 (4) -1 (0) +1 (1.5) +1 (1.5) -1 (0) +1 (4) 0 5 -1 (4) -1 (20) -1 (0) +1 (4) +1 (4) -1 (0) +1 (1.5) +1 (0.5) -1 (0) 8.62 6 -1 (4) -1 (20) -1 (0) -1 (0) +1 (4) +1 (1.5) -1 (0) +1 (0.5) +1 (4) 17.86 7 +1 (8) -1 (20) -1 (0) -1 (0) -1 (0) +1 (1.5) +1 (1.5) -1 (0) +1 (4) 15.63 8 -1 (4) +1 (40) -1 (0) -1 (0) -1 (0) -1 (0) +1 (1.5) +1 (0.5) -1 (0) 17.86 9 -1 (4) -1 (20) +1 (15) -1 (0) -1 (0) -1 (0) -1 (0) +1 (0.5) +1 (4) 0 10 +1 (8) -1 (20) -1 (0) +1 (4) -1 (0) -1 (0) -1 (0) -1 (0) +1 (4) 22.73 11 +1 (8) +1 (40) -1 (0) -1 (0) +1 (4) -1 (0) -1 (0) -1 (0) -1 (0) 31.25 12 +1 (8) +1 (40) +1 (15) -1 (0) -1 (0) +1 (1.5) -1 (0) -1 (0) -1 (0) 0 13 -1 (4) +1 (40) +1 (15) +1 (4) -1 (0) -1 (0) +1 (1.5) -1 (0) -1 (0) 0 14 +1 (8) -1 (20) +1 (15) +1 (4) +1 (4) -1 (0) -1 (0) +1 (0.5) -1 (0) 0 15 +1 (8) +1 (40) -1 (0) +1 (4) +1 (4) +1 (1.5) -1 (0) -1 (0) +1 (4) 27.78 16 -1 (4) +1 (40) +1 (15) -1 (0) +1 (4) +1 (1.5) +1 (1.5) -1 (0) -1 (0) 0 iium engineering journal, vol. 11, no. 1, 2010 amara and salem 93 d. generating 1st order model the model created from the analysis of plackett-burman experimental design [12] using multiple regression analysis is based on the 1st order-model: y= ß0 +∑ ßi xi where y is the predicted response, ß0 model constant, ßi variables linear coefficient. e. box-behnken response surface using box-behnken experimental design, modeling and analysis were carried out using the microsoft excel 2000 and essential exp., version 2.205 software. box-behnken experimental design was used to optimize three variables represented at three levels (high, medium and low) which were denoted by +1, 0 and -1 respectively. the variables were ph (x1) 8, 4 and 6, meat extract (x2) 4, 2 and 3 g/l and temperature (x3) 40, 20 and 30oc. fifteen experiments were conducted as in table 6. f. multiple regression analysis of box-behnken experiments the phenol degradation results obtained from the different box-behanken experiments were analyzed by multiple regression analysis using microsoft excel 2000 and essential exp., version 2.205 software. g. 2nd order model the created model was applied using the coefficient result of each variable. for the three variables this equation was used: y = ß0 + ß1x1 + ß2x2 + ß3x3 + ß12x1x2 + ß13x1x3 + ß23x2x3 + ß11x1 2 +ß22x2 2 + ß33x3 2 x1, x2 and x3 represent independent variables, ß1, ß2 , and ß3 are liner coefficients, ß12 , ß13 and ß23 are cross product coefficients and ß11 , ß22 and ß33 are the quadratic coefficients. the various response surface and counter plots for each two variables and their related response (the phenol degradation rate) were performed using microsoft excel 2000 and essential exp., version 2.205 software. h. microsoft excel solver optimization the value of each ph (x1) , meat extract (x2) and temperature (x3) was further optimized to calculate the best y (degradation rate) value using microsoft excel 2002 solver. the experiments for calculated optimum ph (x1), meat extract (x2) and temperature (x3) were then conducted. i. determination of the 2nd order model accuracy to prove the accuracy of the model, the % accuracy was calculated from the following formula: accuracy of the model = [yexperiment / ycalculated] x 100 iium engineering journal, vol. 11, no. 1, 2010 amara and salem 94 3. results 3.1 phenol degradation rate with or without media constituents the preliminary experiments for phenol degradation in the presence or absence of the media constituents indicated that the microbe could degrade phenol in absence of all of the media constituents. the presence of the media constituents appears to hinder the phenol degradation process while the absence of them give degradation rate of 13.6 mg/l/hr. 3.2 statistical analysis of plackett-burman experiments the experimental design using plackett-burman method was produced using +1 and -1 value for each variable as in table 2 where 16 experiments have been conducted and the results are summarized as phenol degradation rate (mg/l/hr) as in table 2. the variations in the results prove the importance of using experimental design in the media optimization. for each variable, the responses mean of the experiments with high value [+1] have been calculated using the following formula (∑+1)/n(+1), while the responses mean of the experiments with the low value [-1] have been calculated using the following formula (∑-1)/ n(-1). the main effect of the responses for each variable has been calculated from the following formula: main effect = ∑(+1)/n(+1)-∑(-1)/n(-1). the different main effect of the different variables were calculated and summarized in fig. 1 and table 3. according to the main effect analysis, ph, temperature, yeast extract, meat extract and trace elements give positive effect on the phenol degradation rate while glucose, nh4no3, k-salt, mg-salt give negative effect. the nine variables were analyzed using linear multiple regression analysis method and the % coefficient level were calculated from the p value and summarized in table 4. the analysis of variance using anova test was generated and summarized in table 5 which gives p = 0.0040. this indicates that there is a statistically significant relationship between the variables at 99% confidence level. fig. 1: effect of environmental and media composition on phenol degradation rate using immobilized acinetobacter sp. culture. iium engineering journal, vol. 11, no. 1, 2010 amara and salem 95 table 3: main effect. code variable values unit main effect ∑(+1)/n(+1)-∑(-1)/n(-1) (∑+1)/ n(+1) (∑-1)/ n(-1) a ph (4/8) 16.08 5.5424 10.5375 b temperature (20/40) 13.5175 8.105 oc 5.4125 c glucose (0/15) 0 21.6225 g/l -21.6225 d yeast extract (0/4) 11.2975 10.325 g/l 0.9725 e meat extract (0/4) 14.595 7.0275 g/l 7.5675 f nh4no3 (0/1.5) 7.65875 13.96375 g/l -6.305 g k-salt (0/0.5) 9.17 12.4525 g/l -3.2825 h mg-salt (0/0.5) 9.44875 12.17 g/l -2.725 i trace element (0/4) 14.4062 7.216 ml/100 ml 7.19 table 4: linear multiple regression analysis of plackett-burman experiments. variables coefficient standard error t statistic p-value confidence level % intercept 10.8112 1.16063 9.31496 0.0001 99.99 temperature 2.98734 1.41294 2.11427 0.0789 92.11 glucose -8.77488 1.54846 -5.66683 0.0013 99.87 k-salt -0.0576222 1.54846 -0.0372125 0.9715 2.85 meat extract 0.969583 1.51081 0.641766 0.5447 45.53 mg-salt -0.563177 1.41294 -0.398585 0.7040 29.6 nh4no3 -1.71674 1.52635 -1.12473 0.3037 69.63 ph 2.89627 1.46897 1.97163 0.0961 90.39 trace element 2.5629 1.46897 1.74468 0.1317 86.83 yeast extract 0.094239 1.52635 0.0617413 0.9528 4.72 table 5: anova test of plackett-burman experiments. analysis of variance source sum of squares df mean square f-ratio p-value model 2198.62 9 244.291 11.33 0.0040 residual 129.319 6 21.5531 total (corr.) 2327.94 15 r-squared = 94.4449 percent r-squared (adjusted for d.f.) = 86.1123 percent standard error of est. = 4.64253 mean absolute error = 2.36908 iium engineering journal, vol. 11, no. 1, 2010 amara and salem 96 the r-squared statistic indicates that the model as fitted explains 94.4449% of the variability in the degradation rate. the adjusted r-squared statistic is 86.1123%. the standard error of the estimate shows the standard deviation of the residuals to be 4.64253. the mean absolute error of 2.36908 is the average value of the residuals. the multiple linear regression model of plackett-burman screening method describes the relationship between the phenol degradation rate and 9 independent variables as indicated in table 3 and 4. the equation of the fitted model is: ydegradation rate = 10.8112 8.77488*glucose 0.0576222*k-salt + 0.969583*meat extract 0.563177*mg-salt 1.71674* nh4no3 + 2.89627*ph + 2.98734*temperature + 2.5629*trace elements+ 0.094239*yeast extract from the statistical analysis, glucose, temperature and ph significantly effect the phenol degradation rate while they have confidence level > 90%. the trace elements are considered as being effective [17], whereas nh4no3 which give 69.63 % confidence level might be affected by the presence of other media constituents containing nitrogen like meat extract. 3.3 statistical analysis of box-behnken experiments based on the t-statistic and p values as well as the % confidence level obtained from plackett-burman experiments (table 3), temperature and ph have positive effect and being statistically significant. they were selected for further optimization. glucose which has a negative effect and statistically being significant in phenol degradation has been omitted from the media where it gives the optimum degradation rate when it equals to 0 mg/l/hr. nh4no3 is omitted too while it has % confidence level less than 70%, even it is so close to 70% (the minimum accepted limit) [17]. trace elements were not used based on its performance in experiment 2 and 11. to get the optimum conditions in box-behnken, variables were used with the same amounts which give maximum phenol degradation rates according to plackett-burman experiment no. 11 (table 2). based on experiment no. 11 the media constituents which have 0 amount were omitted. these constituents represent glucose, yeast extract, nh4no3, k-salt, mg-salt and trace elements (table 2). meat extract, which contains different nutrients could substitute these constituents as shown in experiment no. 11 (table 2). ph (x1) was used in three level 8, 6, 4; meat extract (x2) 4, 2, 0 g/l and temperature (x3) 40, 30, 20 oc. the boxbehnken was created using 15 experiments and the phenol degradation rate was determined and summarized in table 6. iium engineering journal, vol. 11, no. 1, 2010 amara and salem 97 table 6: box-behnken experiments. experiment no. ph x1 meat extract x2 oc x3 phenol degradation rates mg/l/hr 1 6 (0) 0 (-1) 40 (1) 25 2 6 (0) 2 (0) 30 (0) 35.7 3 6 (0) 4 (1) 40 (1) 22.73 4 4 (-1) 0 (-1) 30 (0) 15.63 5 6 (0) 2 (0) 30 (0) 35.7 6 6 (0) 0 (-1) 20 (-1) 25 7 4 (-1) 2 (0) 40 (1) 25 8 4 (-1) 2 (0) 20 (-1) 17.86 9 8 (1) 2 (0) 40 (1) 22.81 10 4 (-1) 4 (1) 30 (0) 17.86 11 8 (1) 4 (1) 30 (0) 27.78 12 8 (1) 2 (0) 20 (-1) 31.25 13 6 (0) 2 (0) 30 (0) 35.7 14 6 (0) 4 (1) 20 (-1) 25 15 8 (1) 0 (-1) 30 (0) 35.7 y = ß0 + ß1x1 + ß2x2 + ß3x3 + ß12x1x2 + ß13x1x3 + ß23x2x3 + ß11x1 2 +ß22x2 2 + ß33x3 2 where x1=ph , x2=meat extract and x3= oc iium engineering journal, vol. 11, no. 1, 2010 amara and salem 98 table 7: linear multiple regression analysis of box-behnken experiments. variables coefficient standard error t statistic p-value confidence level % intercept 35.7 1.74571 20.4501 0.0000 x1 5.14875 1.06903 4.8163 0.0048 99.52 x1x1 -5.83 1.57356 -3.70497 0.0139 98.61 x1x2 -2.5375 1.51183 -1.67843 0.1541 84.60 x1x3 -3.895 1.51183 -2.57635 0.0497 95.03 x2 -0.995 1.06903 -0.930754 0.3947 60.56 x2x2 -5.6275 1.57356 -3.57628 0.0159 98.40 x2x3 -0.5675 1.51183 -0.375373 0.7228 27.71 x3 -0.44625 1.06903 -0.417436 0.6937 30.61 x3x3 -5.64 1.57356 -3.58422 0.0158 98.42 table 8: anova test of box-behnken experiments. analysis of variance source sum of squares df mean square f-ratio p-value model 621.23 9 69.03 7.550 0.01924 residual 45.71 5 9.143 total (corr.) 666.95 14 r-squared = 93.1433 percent r-squared (adjusted for d.f.) = 80.8011 percent standard error of est. = 7.56375 mean absolute error = 3.42139 the analysis of variance used in box-behnken experiment (table 6) was created using anova test as in table 8 which gives p = 0.01924. since the p-value in the anova table is less than 0.05, there is a statistically significant relationship between the variables at the 95% confidence level. the r-squared statistic suggests that the model as fitted explains 93.146% of the variability in the degradation rate. the adjusted r-squared statistic, which is more suitable for comparing models with different numbers of independent variables, is 80.8087%. the standard error of the estimate shows the standard deviation of the residuals to be 3.02366. the mean absolute error of 1.36667 is the average value of the residuals. the multiple linear regression model of the box-behnken analysis experiments describe the relationship between the degradation rate and 3 independent variables as in table 6 and 7. the equation of the fitted model is: iium engineering journal, vol. 11, no. 1, 2010 amara and salem 99 ydegradation rate = 35.7 5.83* ph* ph 2.5375* ph *meat extract 3.895* ph *temperature 5.6275* meat extract* meat extract – 0.5675* meat extract * temperature 5.64* temperature * temperature 0.995*meat extract+ 5.14875*ph 0.44625*temperature from the statistical analysis, it can be concluded that ph is the most significant variable affecting the phenol degradation rate. the best level of the three variable as obtained from the maximum point of polynomial model were estimated using the solver function of microsoft excel 2000 tool and found to be ph =7.12, meat extract = 1.6 g/l, and temperature= 27.77oc, with a prediction calculated degradation rate equal to 37.30 mg/l/hr. the various response surface and counter plots for each two variables and the response (the phenol degradation rate) were drawn using excel 2000 and essential exp. version 2.205 software as shown in fig. 2 to 7. the data obtained from the response surface, counter plots and table 7, show that ph and oc are the most significant variables affecting on the phenol degradation rate. the interaction between ph and oc is significant [16] with confidence level % equal to 95.03, and between ph and meat extract is effective [17] with confidence level % equal to 84.60. on the other hand the interaction between meat extract and temperature is insignificant with confidence level % equal to 27.71. this also clearly proves that ph is the most effective variable.. meat extract has a limit in improving the degradation rate but plays an essential role in stabilizing the media composition. the role of meat extract must be subjected to further investigation concerning its composition. fig. 2 and 3: the response surfaces plot and corresponding contour plot showing the effects of meat extract (above) and ph (below) on phenol degradation rate. iium engineering journal, vol. 11, no. 1, 2010 amara and salem 100 the shape of response surface and counter plots (fig. 2 and 3) show high interaction between ph and meat extract. the results obtained from fig. 4 and 5 concerning the interaction between ph and temperature show high interaction. in case of fig. 6 and 7 the interaction between meat extract and temperature gives only small interaction. the results obtained from fig. 2 to 7 agree with that in table 7. fig. 4 and 5: the response surfaces plot and corresponding contour plot showing the effects of temperature (above) and ph (below) on phenol degradation rate. fig. 6 and 7: the response surfaces plot and corresponding contour plot showing the effects of meat extract (above) and temperature (below) on the phenol degradation rate. iium engineering journal, vol. 11, no. 1, 2010 amara and salem 101 3.4 confirming accuracy of model the y value which has been optimized from the model was calculated using microsoft excel found to be 37.30 at ph=7.12, meat extract=1.6 and temperature=27.77 oc. the in vivo experiment shows that y value of 38.45 mg/l/hr. the calculated model accuracy was 103.08 %. 4. discussion degradation of chemical compounds is an important microbial criterion. phenol, which is a toxic natural or synthetic compound, can be degraded to non-toxic by different microbes [1-11]. phenol can be degraded by aerobic and anaerobic bacteria [18-20]. phenol can be a growth inhibitor to microorganisms at elevated concentration [21]. this criteria lead to a conclusion that each strain, which is able to degrade phenol should be treated, analyzed and optimized as a single case. optimization of the media constituents as well as the other environmental variables like ph, temperature, etc., using well established experimental design can map the conditions affecting on the different processes concerning media optimization [21-25]. while biological system is complex and can be affected by unknown factors, using plackett-burman analysis could detect the weak and the strong points in the process under investigation [12]. microbes have unique criterion and they are usually prefer and utilize simple carbon source such as glucose as opposed to complex carbon sources. in this study the presence of glucose in the media omit any chance that the bacterial strain start to degrade phenol as shown in table 1 and experiments no. 3, 4, 9, 12, 13, 14 and 16 as (table 2). the results from table 1 lead the use of 0 amount as a low level [-1] to investigate which of the media constituents could be removed. the absence of glucose forces the microbe to degrade the phenol as shown in table 2. glucose as an example shows a significant effect on the degradation rate. meanwhile, the main effect analysis as in table 3 and fig. 1 show that this to be a negative effect. using glucose in 0 g/l gave the best result as indicated in table 2. for these reasons, even glucose has the highest % confidence level, it is not considered. the main effect as shown in table 3 and fig. 1 gave clear view about each variable’s mode of action. main effect classified the variables to positive and negative, which support the analysis of variables and highlight in which direction the optimization should be conducted. this study does not follow the usual way of optimization. using the usual way of optimization will lead to select glucose, temperature and ph for further optimization (e.g box-behnken method). temperature and ph are significant variables with % confidence level equal to 92.11 and 90.39, respectively and have been selected for optimizations. based on the results obtained from experiment no. 11 using plackett-burman design beside glucose; yeast extract, nh4no3, k-salt, mg-salt and trace elements have been omitted while they gave the best degradation rate when they were at 0 amount as in table 2. in experiment no. 2 and 11, meat extract was in its high value [+1] (4 g/l). comparing the media constituents in experiment no 2 and 11 lead to a conclusion that meat extract perfectly could substitute the other factors used in 0 amount. however, this fact was not detected by statistical analysis. iium engineering journal, vol. 11, no. 1, 2010 amara and salem 102 box-behnken experimental design was performed using 15 experiments (table 6), and four experiments give phenol degradation rate of 35.7 mg/l/hr, which indicate a possibility for further optimization. using the solver tool in microsoft excel 2002 to optimize the model created from box-behnken the calculated degradation rate was 37.30 mg/l/hr in the optimum calculating condition. to prove the efficiency of using the microsoft excel solver the in vivo experiments were conducted. the degradation rate for the in vivo was 38.45 mg/l/hr. using direct phenol degradation (without media) gives 13.6 mg/l/hr. by using plackett-burman the maximum degradation rate was 31.25 mg/l/hr which represent 2.3 time increase than that at table 1. using box-behnken design the maximum degradation rate was 35.7 which is 2.71 fold increase than that without media and 14.24% more than plackett-burman. using excel solver optimization gives 37.30 mg/l/hr degradation rate mathematically and 38.45 mg/l/hr degradation rate experimentally. the in vivo experiment shows 103.08% model accuracy which indicates the advantage of the experimental design for optimization. applying the conditions which were optimized using excel solver for in vivo experiment result in degradation rate equal 38.45 mg/l/hr which is 2.92 fold increase than that without media and which is 23.04% more than plackett-burman and 7.70% more than box-behnken. different strategies have been developed for controlling phenol and preventing it from causing harmful effect on nature [8-10]. using immobilized technique has also been described [25]. the main problems in different strategies are the phenol degradation optimization. most of the studies describe analysis of one variable at a time, which usually did not give the maximum expected optimization and is time consuming. media optimization using experimental design proved to be more efficient [26]. as what has been done in this study many authors described using different nutrients to improve the growth of microbial strains which will be finally improve phenol degradation rate under some controlling conditions. an example is the glucose has been used to overcome the inhibitory effect of phenol on microbial growth as described by mamma et al. [27]. in this study. glucose completely inhibit the phenol degradation which prove our concept that each microbe should be treated as a special case. experimental design using plackett-burman, box-behnken and excel solver lead to subsequent improvements in phenol degradation rate. logical analysis of the data leads to a better understanding of the roles of variables and investigation as to which one should be used. statistical analysis help a lot in understanding the behavior of each variable but variables which gave the same results should be subjected to logical analysis with the aim to obtain the correct choice. we should highlight that the phenol used in this study did not represent reality while in fact phenol was usually present as a contaminant with other wastes like olive oil. this fact should be taken into consideration in any future studies aimed. while plackett-burman and box-behnken are well-established tools for experimental design, we recommend using our strategy for the best use of both of them. iium engineering journal, vol. 11, no. 1, 2010 amara and salem 103 references [1] k. a. khan, m. t. suidan, and w. h. gross, “anaerobic carbon filter for the treatment of phenol bearing waste water”. j. water pollut. control fed., vol. 53 pp. 1519-1532, 1981. [2] j. a. field, and g. lettinga, “treatment and detoxification of aqueous spruce bark extracts by aspergillus niger”. water science and technology., vol. 24 pp.127-137, 1991. [3] r. borja, a. martin, r. maestro, m. luque, and m. m. duran, “enhancement of the anaerobic digestion of wine distillery wastewater by the removal of phenolic inhibitors”. bioresource technology., vol. 45 pp. 99-104, 1993. [4] d. brand, a. pandey, s. roussos, and c. r. soccol, “biological detoxification of coffee husk by filamentous fungi using a solid state fermentation system”. enzyme and microbial technology., vol. 27 pp. 127-133, 2000. [5] l. lesage-meessen, d. navarro, s. maunier, j-c. sigoillot, j. lorquin, m. delattre, j-l. simon, m asther, and m. labat, “simple phenolic content in olive oil residues as a function of extraction system”. food chemistry., vol. 75 pp. 501-507, 2001. [6] m. minhalma, and m. n. de pinho, “tannic-membrane interactions on ultrafiltration of cork processing wastewater”. separation and purification technology., vol. 22 pp. 479-488, 2001. [7] g. aggelis, c. ehaliotis, f. nerud, i. stoychev, g. lyberatos, and g. i. zervakis, “evaluation of white-rot fungi for detoxification and decololorization of effluents from green olive debittering process”. applied microbiology and biotechnology., vol. 2 pp. 353-360, 2002. [8] g. r. chaudhry, and s. chapalamadugu, “biodegradation of halogenated organic compounds”. microbial. rev., vol. 55(1) pp. 59-79, 1991. [9] s. m. armstrong, and t. r. patel, “microbial degradation of phloroglucinol and other polyphenolic compounds”. j. basic. microbiol., vol. 34(2) pp. 123-135, 1994. [10] j. p. kaiser, y. feng, and j. m. bollag, “microbial metabolism of pyridine, quinoline, acridine, and their derivatives under aerobic and an anaerobic conditions”. microbiol rev., vol. 60(3) pp. 483-498, 1996. [11] i. p. solyanikova, and l. a.golovleva, “bacterial degradation of chlorophenols: pathways, biochemica, and genetic aspects”. j. environ. sci. health b., vol. 39(3) pp. 333-351, 2004. [12] p. plackett, and j. p. burman, “the design of optimum multifactorial experiments biometrika”. vol. 37:305-325, 1946. [13] box, g. e. p. and behnken, d. w. “some new three levels designs for the study of quantitative variables”.. technometrics., vol. 2 pp. 455-457, 1960. [14] h. g. schlegel, h. kaltwasser, and g. gottschalk, „eine submersverfahren zur kulture wasserstoffoxydierender bakterien: wachstums physiologische untersuchungen“. arch. mikrobiol., vol. 38 pp. 209-222, 1961. [15] y. i. korenman, t. a. kuchmenko, and s. a. karavaev, “extractionspectrophotometric determination of phenol using a reaction with 4-amino antipyrine in the two phase poly (ethylene glycol)-ammonium sulphate water system”. j. analyt. chemistry., vol. 53(3) pp. 291-296, 1998. [16] y. r. abdel-fattah and z. a. olama “l-asparaginase production by pseudomonas aeruginosa in solid-state culture: evaluation and optimization of culture conditions using factorial designs”. process biotechnol., vol. 38 pp. 115-122, 2002. iium engineering journal, vol. 11, no. 1, 2010 amara and salem 104 [17] r. a. stowe, and r.p. mayer, “efficient screening of process variables”. ind eng. chem., vol. 58 pp. 36-40, 1966. [18] h. h. p. fang, d. w. liang, t. zhang and y. liu “anaerobic treatment of phenol in wastewater under thermophilic condition”. water res. vol. 40 pp. 427–434, 2006 [19] d. r. lovley and d. j. lonergan “anaerobic oxidation of toluene, phenol, and pcresol by the disssimilatory iron-reducing organism”. gs-15, appl. environ.microb. vol. 56(6) pp. 1858–1864, 1990 [20] m. m. broholm and e. arvin “biodegradation of phenols in a sandstone aquifer under aerobic conditions and mixed nitrate and iron reducing conditions”. j. contam. hydrol. vol. 44 pp. 239–273, 2000 [21] g. a. hill and c. w. robinson “substrate inhibition kinetics: phenol degradation by pseudomonas putida”. biotechnol. bioeng. vol. 17 pp. 1599–1615, 1975 [22] k. w. wang, d. m. tsangaris, b. c and g. a. baltzis “lewandowski, biodegradation of mixed wastes in continuously operated cyclic reactors”. appl biochem biotechnol vol. 57-58 pp. 803-815, 1996 [23] j. shen, z. x. lu, x. m. bie, f. x and x. q. lu “huang, [media optimization for the novel antimicrobial peptide by bacillus sp. fmbj224]”. sheng wu gong cheng xue bao, vol. 21 pp. 609-614, 2005 [24] y. x. wang, z. x. lu and f. x. lu “[media optimization for exopolysaccharide by pholiota squarrosa (pers. ex fr.) quel. as 5.245 on submerged fermentation]”. sheng wu gong cheng xue bao., vol. 20 pp. 414-422, 2004 [25] c. wang, and y. li “incorporation of granular activated carbon in an immobilized membrane bioreactor for the biodegradation of phenol by pseudomonas putida”. biotechnol lett. vol. 9 pp. 1353-1356, 2007 [26] g. annadurai, l.y. ling and j. f. lee “statistical optimization of medium components and growth conditions by response surface methodology to enhance phenol degradation by pseudomonas putida”. j. hazard mater., vol. 151 pp. 171178, 2008 [27] d. mamma, e. kalogeris, n. papadopoulos, d. g. hatzinikolaou, p. christrakopoulos and d. kekos “biodegradation of phenol by acclimatized pseudomonas putida cells using glucose as an added growth substrate’. j. environ. sci. health a. tox. hazard. subst. environ. eng. vol. 39 pp. 2093-2104, 2004 276 iium engineering journal, vol. 13 no. 1, 2012 qasim et al. 59 the parameters affect on power coefficient vertical axis wind turbine a.y. qasim 1 , r. usubamatov 2 , z.m. zain 2 and ghulam abdul quadir 1 1 school of mechatronic engineering, 2 school of manufacturing engineering, university malaysia perlis, pauh putra, perlis, malaysia. ayhk66@yahoo.com, ryspek@unimap.edu.my, zuraidah@unimap.edu.my, gaquadir@unimap.edu.my abstract: this study describes the design of a special type of vertical axis rotor wind turbine with moveable vertically positioned vanes. the novel design increases the torque in the left side of the wind turbine by increasing the drag coefficient. it also reduces the negative torque of the frame which rotates contrary to the wind in the other side. two different types of models, having different vane shapes (flat vane and cavity shaped vane), were fabricated. each type consisted of two models with varying number of frames (three and four frames). the models were tested in a wind tunnel with variable wind speed in order to understand the effect of shape, weight, and number of frames on the power coefficient of the wind turbine. abstrak: di dalam kajian ini, rotor turbin angin berpaksi vertikel sebagai rangka khusus telah direkabentuk dengan lokasi vertikel mudahalih oleh bilah kipas. rekabentuk ini meningkatkan tork di bahagian kiri turbin angin dengan meningkatkan pekali seretan dan mengurangkan tork negatif rangka yang berputar berlawanan dengan angin pada bahagian lain. dua jenis model berbentuk berlainan telah difabrikasi (bilah kipas rata dan bilah kipas berbentuk kaviti), dengan setiap jenis mempunyai dua model dengan bilangan rangka yang berlainan (berangka tiga dan berangka empat). modelmodel telah diuji di dalam terowong angin dengan kelajuan angin yang berbeza bagi mendapatkan kesan rekabentuk, berat dan bilangan rangka ke atas pekali kuasa. keywords: design; wind turbine; drag coefficient; vane 8. introduction wind energy is one of the most cleanly and reliable sources of renewable energy. nowadays, wind energy generates about one percent of total energy used worldwide. the potential of wind energy is huge and study shows if 20 percent of the possible wind resources are utilized. most of the wind resources are harnessed by using propeller type wind turbine, which power output efficiency is quite low about 20 percent only due to shape, design, and other factors. economically, it is quite expensive. world has now come to an era with more inventors creating newer wind turbine with higher efficiency and capability than the current ones. this paper proposes two types of wind turbines, using vane type vertical axis rotation. this type of wind turbine can increase the output of power with less wind kinetic energy required. new design has simple construction, small size, simple technology, and economical material usage. it forms cavity at one side of turbine while letting the other side of turbine open to let go the wind, hence high drag can occur. this ensures higher efficiency and low starting wind velocity. iium engineering journal, vol. 13 no. 1, 2012 qasim et al. 60 there are various types of wind turbines with different efficiencies. the efficiency is defined as the amount of wind kinetic captured by the wind turbines that can be successfully generated into electrical power. our design consists of movable vanes to reduce the negative torque of the frame that rotates contrary to the wind. the wind tunnel is used to measure the power coefficient, torque coefficient and angular velocity as a function of wind velocity. it used different shape, thickness and number of frames (fig. 1). fig. 1 over view vertical axis wind turbine a) scoop-vane frame b) flat-vane wind turbine. 9. theoretical analysis the power of the wind is proportional to air density, drag coefficient (the shape of subject), area of the segment of wind being considered, and the natural wind speed. the relationships between the above variables are provided in eq. 1 below [11]. �� � ½ ��� � . � � ½ �� . �. �. � �. ��� (1) where � is the angular velocity, �� is the drag coefficient, � is swept turbine area and � is density. the two models have the same theoretical analysis. to determine the starting torque t on wind turbine vanes, it is necessary to define the whole vane area, and distance from the centre of the output shaft to the centre of wind pressure, then the formula has the following expression, � ½ �. �� . �. � �. �. ����� (2) where r is the distance from the shaft centre line to the centre of pressure of the vane surface, other parameters are as specified above. the output power (w) is calculated by the following equation � � � � ½ �� .�.��.� �.�. !"#$� � � . �. �� . � . ����� �%&&� (3) where � is the angular velocity of the rotating turbine, � is air density, � is impeller turbine radius. iium engineering journal, vol. 13 no. 1, 2012 qasim et al. 61 the torque created by the frames with group of vanes calculated by the following equation: � �� ' ()* +, . �/0 ���� (4) where �� is drag coefficient, ' is wind pressure, and all the parameters are specified in fig. 2. fig. 2 rotor dimensions open and closed vanes. 10. experimental tests in the wind tunnel 3.1 drag coefficient test cavity shape vane vertical axis wind turbine, has been designed based on obtaining higher values of the drag coefficient. the blade of wind turbine tested used the three model fabricated by metal with same dimensions, [, � 0.07 3, ) � 0.116 3, & � 1 33]. the analyses considered drag force test, and drag force coefficient variation with wind velocity. the typical wind tunnel used stationary turbofan engines that sucked air through a duct equipped with a viewing port and instrumentation where models on the shaft are mounted in order to study. the shaft is connected to a digital scale was used to measure the drag force. the following equation was used to find the drag coefficient: �� � 6� 7.8���� � 6� �∆: (5) results obtained by tests as depicted in fig. 3, show that the frame with cavity shape vane has higher drag coefficients than the flat vane frame. fig. 3 drag coefficient for different vanes angle in frame versus wind speed. iium engineering journal, vol. 13 no. 1, 2012 qasim et al. 62 3.2 various frame tests the object of the wind turbine test is to verif the ability of performance design, to get real data, compare with theoretical results and analysis efficiency of product testing. the wind turbine testing used four models, two model of scoop-vane fabricated by hard plastic with same dimensions presented in fig. 1a, [* � 0.03 3, ) � 0.115 3 and , � 0.07 3, with thickness & � 2 33] and weight is different, [for 3 frame, impeller weight = 172 gram] and [for 4 frame impeller weight = 236 gram]. the two model for flat vane fabricated by metal with dimensions presented in fig. 1b, [for 4 frame * � 0.048 3, ) � 0.06 3 and , � 0.052 3], and [for 3 frame * � 0.044 3, ) � 0.07 3 and , � 0.066 3]. the analyses considered power output test, and number of revolutions per min (rpm) of the rotating shaft. the typical wind tunnel used stationary turbofan engines that sucked air through a duct equipped with a viewing port and instrumentation where models on the ball bearings shaft are mounted in order to study. the testing area of the wind tunnel length is the cube with dimensions 300 @ 300 @ 300 33 . the model of the vane-type wind turbine is located in the middle of the wind tunnel testing area and connected with generator. the range of the wind speed used is between 5 m/s and 18 m/s. the wind speed measure by recorded pressure drop from a pittot tube ∆'� and use bernoulli equation to get wind velocity. the tachometer model compact instrument advent tachopole was used to measure the rotation speed of the wind turbine shaft with the piece of white paper attached, which reflects light. 3.2.1 flat vane test fig. 4 number of revolutions of the wind turbine shaft versus the wind speed. the experiments show that four frames have a higher angular velocity compared to three frames (fig. 4). results obtained in fig. 5 show that the power coefficient for 3 frame and 4 frame wind turbine with wind speed , we can see that maximum power coefficient for 3 frame is (0.18) at wind speed of 9 m/s, and the maximum power coefficient for 4 frame is (0.21) at wind speed of 9 m/s. iium engineering journal, vol. 13 no. 1, 2012 qasim et al. 63 fig. 5 power coefficient various wind velocity for 3 and 4 frames flat vanes wind turbine. 3.2.2 scoop-vane test results obtained by tests show that three frames wind turbine has high angular velocity (rpm) than four frames (fig. 6). fig. 6 rpm of 3 and 4 frames scoop-vane versus wind speed. fig.7 power coefficient for 3 and 4 frames scoop-vane versus wind speed. iium engineering journal, vol. 13 no. 1, 2012 qasim et al. 64 figure 7 shows that three frames turbine model has higher power coefficient than four frames turbine model. 3.3 different thickness test the rotor of wind-turbine model testing used the two models of three frames movable vanes made from the transparent acrylic plates with same dimensions [* � 0.03 3, ) � 0.116 3 and , � 0.07 3] and different thickness of metal [& � 1 33, impeller weight = 114 grams, and & � 2 33, weight = 170 grams]. the analyses considered power output test, and number of revolutions per second of the rotating shaft. fig. 8 rpm of three and four frames impeller versus wind speed. fig. 9 power coefficient for three frames different weight versus wind speed. results obtained in fig. 9 show that the power coefficient wind turbine against wind speed, we can see that maximum power coefficient for low weight impeller is (0.4) at wind speed of 7 m/s, and maximum power coefficient for high weight impeller is (0.31) at wind speed of 6 m/s. iium engineering journal, vol. 13 no. 1, 2012 qasim et al. 65 11. conclusion the impeller type wind turbine with scoop-vanes has higher efficiency compares with flat vanes. this is caused the wind turbine has the high drag factor enables to capture wind energy. this type wind turbine has good technical properties and can be used for generating a power more efficiently for the low speed of the wind. increase drag factor can increase the output power, and the vane type wind turbine can be high efficiency. in a flat vane rotor, increase number of frame can increase angular velocity of the rotor. the power coefficient is measured experimentally to be equals to 0.18 and 0.21 for three and four frames, respectively. figure 3 shows the cavity frame shape increase the drag coefficient to 3, when the drag coefficient for flat vane is 1.3. in cavity shape frame increase the number of frame will decrease angular velocity and give a low-power coefficient. the power coefficient is measured experimentally to be equals to 0.31 and 0.24 for three and four frames, respectively. when we used the different thickness for three frames cavity shape the power coefficient is measured to be equals to 0.4 and 0.31 for thickness 1 mm and 2 mm, respectively. the possible reasons for getting lower results for the four-frame than the three-frame in the experiment are: 1. higher weight (four-frame impeller 236 grams vs. the three-frame impeller at 172 grams) 2. decreasing the distance between two vanes, then the limit has a lower drag force as seen in fig. 8. 3. when the number of blades is increased to four, the air that strikes the second blade is reflected back onto the following blade, so that the following blade rotates in a negative direction compared to the succeeding blade. 4. the vortex consists and still air area behind the vane gives high resistance, in four frames more than three frames. fig. 8 drag force versus wind speed in wind tunnel with different distance between the two vanes. iium engineering journal, vol. 13 no. 1, 2012 qasim et al. 66 weight has significant effect on power coefficient, an increase in the thickness of rotor from 1 mm to 2 mm (weight 114 grams to 172 grams) reduces the power coefficient by around 8% (from 40% to 32%). the new turbine presents a simple construction and can be manufactured from from cheap materials using simple technology. references [1] manwell jf, mc gowan jg, rogers al. “wind energy explained, theory, design and application”. . england:wiley & sons, 2002. [2] sathyajith, mathew,wind energy fundaments, resource analysis and economics. springer 2006;1. [3] eggleston, david m., and forrest stoddard. “wind turbine engineering design”. wiley& sons, 2004. [4] spera david а. “wind turbine technology”. new york. asme press, 1994; [5] r. usubamatov, z.m.zain, r. bhuvenesh, f.khammas. “new vane type wind turbine of high efficiency, cngrt88”.proceedings of world engineering congress, 2010. [6] gasch, robert, and jochen twele, "windkraftanlagen grundlagen." entwurf, planung und betrieb, teubner, wiesbaden (2007). [7] y.a.cendel y.a., “ans j. m. cimbala. fluid mechanics, 2006,” mcgraw hill. [8] usubamatov r., zain z. m., khammas f. a., a. younus. “impeller type wind turbine. published by the australian institute of high energetic materials (abn: 68 126 426 917) 2010.” (2010). [9] robert howell, ning qin, jonathan edwards, naveed durrani. “wind tunnel and numerical study of a small vertical axis wind turbine”. renewable energy 35.2 (2010) 412–22. [10] muller. gerald, mark f. jentsch, euan stoddart. vertical axis resistance type wind turbines for use in buildings. journal renewable energy 34 (2009) 1407–12. [11] johnson, dr. gary l. (november 21, 2001) “wind turbine power – ch 4. wind turbine power, energy and torque.” (2005). microsoft word 191-655 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics ali 73 a philosophical approach to artificial intelligence and islamic values ali a.z. international institute of islamic thought and civilization (istac), international islamic university malaysia, kuala lumpur campus, no. 24 persiaran duta taman duta, 50480 kuala lumpur,malaysia. aaziaee@hotmail.com abstract: artificial intelligence has the potential to empower humans through enhanced learning and performance. but if this potential is to be realized and accepted, the ethical aspects as well as the technical must be addressed. many engineers claim that ai will be smarter than human brains, including scientific creativity, general wisdom and social skills, so we must consider it an important factor for making decisions in our social life and especially in our islamic societies. the most important challenges will be the quality of representing the islamic values like piety, obedience, halal and haram, and etc in the form of semantics. in this paper, i want to emphasize on the role of divine islamic values in the application of ai and discuss it according to philosophy of ai and islamic perspective. abstrak: kecerdasan buatan (ai) mempunyai potensi untuk memberi kuasa kepada manusia melalui proses pembelajaran dan prestasi yang dipertingkatkan. jika potensi ini menjadi kenyataan dan diterima, aspek-aspek etika serta teknikal perlu ditangani. ramai jurutera mendakwa bahawa ai akan menjadi lebih bijak daripada otak manusia, termasuk kreativiti saintifik, kebijaksanaan umum dan kemahiran sosial, jadi kita mesti menganggapnya sebagai satu faktor penting untuk membuat keputusan dalam kehidupan sosial kita dan terutama dalam masyarakat islam. cabaran-cabaran yang paling penting adalah apabila ai digunakan untuk menilai ciri-ciri islam seperti ketakwaan, ketaatan, halal dan haram, dan lain-lain. dalam kertas ini, saya ingin memberi penekanan kepada peranan nilai-nilai islam dalam pengunaan ai yang dibahaskan mengikut falsafah ai dan perspektif islam. keywords: value; expert; community development; artificial intelligence; superintelligence; friendly artificial intelligence 1. introduction artificial intelligence is all around us. intelligent agents are widely used. the physical embodiment of agents, robots, are also becoming more widely used. robots are used to explore the oceans and other worlds, being able to travel in environments inhospitable to humans. it is still not the case, as was once predicted, that robots are widely used by households. expert systems are used by doctors to help with symptoms that are hard to diagnose or to prescribe treatments in cases where even human experts have difficulty. artificial intelligence systems are used in a wide rang of industries, from helping travel agents select suitable holidays to enabling factories to schedule machines. artificial intelligence is particularly useful in situation where traditional methods would be too slow. many computer games have been designed based on artificial intelligence. it is likely that artificial intelligence will become more prevalent in our society. and whether iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics ali 74 or not we eventually create an artificial intelligence that is truly intelligent, we are likely to find computers, machines, and other objects appearing to become more intelligentat least in terms of the way they behave [1]. definitions: what are artificial intelligence, friendly ai, and superintelligence? john mccarthy defines it as making intelligent machines especially intelligent computer programs by the science and engineering. it is related to the similar task of using computers to understand human intelligence, but ai does not have to confine itself to methods that are biologically observable [2]. ai is the area of computer science focusing on creating machines that can engage on behaviors that humans consider intelligent. intelligent agents can plan and adapt plans to respond to changes in circumstances; they can recognize what is significant in a situation; they can learn new concepts from old; they can interact and learn from their environment; they can exercise artistic appreciation [3]. the ability to create intelligent machines has intrigued humans since ancient times and today with the advent of the computer and 50 years of research into ai programming techniques, the dream of smart machines is becoming a reality. researchers are creating systems which can mimic human thought, understand speech, beat the best human chess player, and countless other feats never before possible. find out how the military is applying ai logic to its hi-tech systems, and how in the near future artificial intelligence may impact our lives. ai is a combination of computer science, physiology, and philosophy. ai is a broad topic, consisting of different fields, from machine vision to expert systems. the element that the fields of ai have in common is the creation of machines that can "think". in order to classify machines as "thinking", it is necessary to define intelligence. to what degree does intelligence consist of, for example, solving complex problems, or making generalizations and relationships? and what about perception and comprehension? research into the areas of learning, of language, and of sensory perception have aided scientists in building intelligent machines. one of the most challenging approaches facing experts is building systems that mimic the behavior of the human brain, made up of billions of neurons, and arguably the most complex matter in the universe. 2. values and ai the process of developing active and sustainable communities based on social justice and mutual respect. it is about influencing power structures to remove the barriers that prevent people from participating in the issues that affect their lives. community development expresses values of fairness, equality, accountability, opportunity, choice, participation, mutuality, and continuous learning. in future, we will not face a group of engineers who can program our social life in different fields such as reasoning, problem solving, knowledge representation, planning, learning, natural language processing, motion and manipulation, perception, social intelligence and creativity, but also we will face more complex expert systems such as superintelligence which will surpass all abilities of human being except the intentionality and spirituality as defined in our religious sources. if artificial intelligence claims that it is able to recreate the capabilities of the human mind, by the invention of superintelligence, with which challenges will we confront in the future? should we be worry about our spiritual life, our divine values, emotions, piety, sincerity, belief, and our shari’ah? a few of the most influential answers to these questions are given below. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics ali 75 in this century the information is a main power in society, and the experts who owes this opportunity can influence on the society, and i think in the future instead of human experts we will face expert system in artificial intelligence technology. human values or divine values, secularism or theism, expert system or human expert, it will be our challenge in future and i think we must give a high consideration to this problem for next decades. the new generation of computers will be able to do millions operations at a moment. most ai work today does not require any philosophy, because the system being developed doesn't have to operate independently in the world and have a view of the world. the designer of the program does the philosophy in advance and builds a restricted representation into the program. we have been studying this issue of ai application for quite some time now and know all the terms and facts. but what we all really need to know is what we can represent human values in a formal manner. one conclusion from artificial intelligence research is that solving even apparently simple problems usually requires lots of knowledge. properly understanding a single sentence requires extensive knowledge both of language and of the context. how can we represent the concept of fairness -in the human life as an important base for community developmentin meaningful way for ai [4]. knowledge of development is information about better social life for human and we can describe these terms and conditions by their properties. there are many ways to represent objects. these objects concern to development are complex objects and a complex object may be composed of many other objects. this is a kind of reductionism. the reductionism position is that the complex behavior of the mind may in principle be reduced to similar rules and laws which may be complex but which can be investigated and understood [13] cultural development, economic development, scientific development, and finally community developments depend on many wide areas of human knowledge and values which are accepted with all human beings, but we must know that there is a big gap between secular values and divine values. accepting the values at the level of common sense will result in secularism. secular and liberal values, if we consider them as values, do not serve the interests of muslim communities. how can we represent some concepts such as piety (taqwa), obedience of allah (ta’ah), fear of god (khashiyyah), and etc? engineers in computer science believe that all values will be presented in formal ways to be known by ai or superintelligence and these new creations will influence on our life. as we know ai works with fuzzy logic, approximate concepts, uncertainty and ambiguous data. if ai wants to have freewill it must work with uncertain concepts. with absolute data and information the freewill cannot exist in ai. now we must ask the experts about our beliefs which based on certainty and absolute knowledge, what about divine knowledge which is certain and absolute? is ai can play a positive role in this sensitive field especially in our islamic societies? we should be prepared for a change. our conservative ways stand in the way of progress. the most traditionalists consider the ummah’s traditional thought to be selfsufficient and capable of being presented as it is or with very little alteration. this approach holds that the ummah’s intellectual life can be founded and organized, and that the structure of its civilization can be built on this basis. we should find a way to select our strategies in absorbing new technologies from the traditional thought what is most sound and from modern contemporary thought that one considers and proves to be correct, and weld the two to found an intellectual structure, which will provide a guaranteed basis for achieving what is required [5]. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics ali 76 in response to change, our vision to new technology and our mission of higher islamic education in muslim world needs to be revised. the wake of globalization is multi-dimensional in nature. ai is a new step that is very helpful to the society and its development. machines can do jobs that require detailed instructions followed and mental alertness. ai with its learning capabilities can accomplish those tasks but only if the worlds conservatives are ready to change and allow this to be a possibility. i am not worry about how we can construct this powerful program which will be smarter than the best human brain, but i am worry about how we lead them to human values. i am worry about the worst of ai. there are so many things that can go wrong with a new system so we must be as prepared as we can be for this new technology. ais are like children that need to be taught to be kind, well mannered, and intelligent. if they are to make important decisions, they should be wise. we as citizens need to make sure ai programmers are keeping things on the level. we should be sure they are doing the job correctly, so that no future accidents occur. ai is what nick bostrom calls an existential risk: "one where an adverse outcome would either annihilate earth-originating intelligent life or permanently and drastically curtail its potential." in particular, most forms of unfriendly ai would constitute a "bang"-"earth-originating intelligent life goes extinct in relatively sudden disaster resulting from either an accident or a deliberate act of destruction." within nick bostrom's list of bangs, sorted by probability, "badly programmed superintelligence" is number four out of eleven [6]. artificial intelligence, as an ultratechnology, does not exist in isolation. there are other kinds of advancing technologies; nanotechnology, biotechnology, and nuclear technology, for example. artificial intelligence is unique among the ultratechnologies in that it can be given a conscience, and in that successful development of friendly ai will assist us in handling any future problems. a "friendly ai" is an ai that takes actions that are, on the whole, beneficial to humans and humanity. in a "~human" scenario ("near human", "approximately human-equivalent"), friendly ais would play ~human roles in the existing human economy or society. to the extent that friendly ais have power in the world economy, in human society, or in technological development, they can exert direct influence for good, but mostly in physical world not in spiritual realm such as values and ethics. in the islamic tradition, technology is always tools not goals. human values and ethics should become the guiding principles in utilizing technologies so that the usage of technology is more humane and having beneficial advantages to humanity. for example, a friendly ai working in nanotechnology can enthusiastically work on immunity systems while flatly refusing to develop nanotechnological weaponry. the presence of friendly ais within a society -as an interest group with influencewill tend to influence that society towards altruism. the presence of a friendly ai within a political discussion as a voice advocating a viewpoint will tend to influence that discussion towards lack of bias. this holds especially true insofar if friendly ais have previously gained respect as fair, truthful, unbiased voices. the presence of a friendly ai within a political power structure as a decision-maker will lead to altruistic decisions being made. this holds especially true insofar if decisions which humans keep screwing up due to personal bias tend to get handed off to a friendly ai. the presence of a friendly ai within a technological development process -as a researcherwill tend to accelerat defensive applications and economic applications ahead iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics ali 77 of offensive applications, and largely beneficial technologies ahead of more ambiguous ones. the requirements for fai to be effective, both internally, to protect humanity against unintended consequences of the ai in question and externally to protect against other nonfais arising from whatever source, are: friendliness: that an ai feel sympathetic towards community development in future, and seek for their best interests conservation of friendliness that an ai must desire to pass on its value system to all of its offspring and inculcate its values into others of its kind. intelligence: that an ai be smart enough to see how it might engage in altruistic behavior to the greatest degree of equality, so that it is not kind to some but more cruel to others as a consequence, and to balance interests effectively. self-improvement: that an ai feel a sense of longing and striving for improvement both of itself and of all life as part of the consideration of wealth, while respecting and sympathizing with the informed choices of lesser intellects not to improve themselves. but there are authors who consider the theory of friendly ai is incomplete. they believe that there should be broader political involvement in the design of ai and ai morality and this will has a bad influence on community development. they also believe that initially seed ai could only be created by powerful private sector interests [7]. 3. conclusion educating, enabling and empowering are at the core of community development. i think that community development is conscious social activity that contains the spiritual and material life of the society. we must give the high consideration to the role of human values, spiritual aspect of human being and his cultural and educational inquiries, and to the role of experts and community workers and politic leaders or officers in the community development. it demand the emergence of transformative leadership in leading transformative education for muslim experts especially in managing change and challenges for better developments in our society. a holistic approach in nurturing experts with ethical values and morals is greatly needed in this century, because the rise of globalization with its structural impacts need to be balance up with a more equitable and harmonious approach in teaching and learning. neglecting the importance of compatibility in responding to change, leadership in higher islamic education in its present scope and orientation, and skillful muslim experts with islamic knowledge and better understanding of computer science may lead to the marginalization of the ummah. islamic studies of today demands a new theoretical foundation to address not only the authentic or traditional approach in addressing traditional sources and also turath but also the modern factors in teaching-learning processes which are very contemporary in nature. the chart on the next page illustrates the relationship between these elements if human create supperintelligence in future and i think it will be possible, because in this moment we can produce distributed artificial intelligence which can process faster than human brainour belief to that reality will not change, because we consider supperintelligence as an effect of human mind and creativity and the law of causality proves that the existence of effect depends on the cause, so i believe that superintelligence will not damage our life as we see in hollywood films, but the values of human which organize our better intellectual life must be programmed in the future, and with this iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics ali 78 values transformative leadership experts superintelligence community development approach we can solve the challenge between community development and supperintelligence, we can call it friendly artificial intelligence. references [1] ben coppen, artificial intelligence illuminated, london, jones and bartelett publication, 2004, pp. 23-24. [2] john mccarthy, “what is artificial intelligence?” computer science department, stanford university stanford, ca 94305. [3] janet finaly & alan dix, artificial intelligence, ucl press, 1996, p. 262, [4] nick bostrom, “how long before superintelligence?” in international. journal. of future studies, 1998, vol. 2. [5] based on talks given in a conference on the conceptual aspects of biocommunications, neuropsychiatric institute, university of california, los angeles, october 1962; and in the artificial intelligence sessions of the winter general meetings of the ieee, january 1963. [6] based on the sccd strategic framework, the national occupational standards for cd work, and the latest draft of cdx’s information sheet: what is community development. [7] midgley, j. with hall, a., hardiman, m. and narine, d. (1986), community participation, social development and the state, london: methuen, p. 18. [8] alison cawsey, the essence of artificial intelligence, england, prentice hall, 1998, p. 3. [9] morris w. firebaugh, artificial intelligence, a knowledge – based approach, boston, pws-kent publishing company, 1988, p.14. [10] nick bostrom, “existential risks: analyzing human extinction scenarios and related hazards, in ”journal of evolution and technology, vol. 9, march 2002. first version. [11] ibid. [12] bill hibbard, super-intelligent machines, new york. kluwer academic/plenum publishers. 2002; hibbard, w. super-intelligent machines. computer graphics 35(1), 11-13. 2001. [13] morris w. firebaugh, artificial intelligence, a knowledge – based approach, boston, pws-kent publishing company, 1988, p.14. microsoft word 195 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering muyibi and jami 173 the optimally mobile muslim experts in the service of the ummah s.a. muyibi and m.s. jami department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. suleyman@iium.edu.my abstract : this paper presents a proposal on how the muslim experts made up of academics, professionals and entrepreneurs can be made optimally mobile to utilize their allah endowed resources to serve the ummah and mankind more efficiently and effectively as well as being key players in a world which has become a “global village”. some case studies are presented to illustrate some of the major problems facing the muslim ummah today in not being able to utilize optimally the human as well as material resources endowed to us by allah to enable us fulfill our role as the “best of ummah” created for the benefit of mankind and vicegerent of allah. this proposal includes the setting up of an international organization of optimally mobile muslim experts (ioomme). it is envisaged that ioomme will have a talent bank which will be a database on muslim academics and professionals living and working in both muslim and non-muslim countries with detailed information about the experts, their areas of expertise and products developed etc. furthermore professional resource centers which will be land-based as well as cyberspace or virtual based will be setup made up of published information (journals, technical reports) and specialized research equipment/facilities available in muslim nations where muslim academics and professionals can have access to for their use as well as for developing upcoming muslim academics and professionals. it is envisaged that muslim nations will create the enabling environment through entry visa and professional short visit regulations for muslim academics and professionals to use their sabbaticals, annual vacations, study/research leave, professional short visits etc. academic/ professional staff exchange to go to muslim nations to render their service to the ummah. abstrak: kertas ini membentangkan cadangan bagaimana kumpulan pakar islam yang terdiri daripada kalangan ahli akademik, golongan profesional dan para usahawan dibentuk agar dapat berfungsi secara optimum. kepakaran yang dikurniakan allah wajar digunakan untuk berkhidmat kepada umat manusia secara lebih cekap dan berkesan disamping memainkan peranan penting memandangkan dunia kini telah dikenali sebagai “perkampungan global”. beberapa kajian kes telah dibentangkan untuk menjelaskan beberapa masalah utama umat islam hari ini perlu lalui. apabila kita tidak menggunakan secara optima tenaga serta sumber kekayaan yang diberikan allah, maka kita tidaklah dapat menunaikan peranan sebagai “umat terbilang” dengan sepenuhnya, yang diwujudkan demi manfaat manusia serta khalifah allah. antara cadangannya termasuklah menubuhkan organisasi sedunia pakar islam optima bergerak (international organization of optimally mobile muslim experts (ioomme). ioomme dijangkakan akan mempunyai bank bakat di mana ia akan mempunyai pangkalan data ahli akademik islam dan profesional yang tinggal dan bekerja di negara islam dan negara bukan islam dengan maklumat terperinci mereka, bidang kepakaran masing-masing, produk yang telah dihasilkan dan sebagainya. tambahan pula, pusat sumber profesional yang nyata dan juga di alam siber yang akan ditubuhkan terdiri daripada maklumat iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering muyibi and jami 174 bercetak (seperti jurnal dan laporan teknikal) dan alatan/kemudahan penyelidikan yang khusus. semua kemudahan ini boleh didapati di negara-negara islam di mana ahli akademik dan profesional islam boleh mengakses demi kepentingan mereka dan juga untuk kemajuan para akademik dan profesional islam akan datang. negara-negara islam dijangkakan dapat menyediakan kemudahan menerusi visa masuk dan pas lawatan singkat profesional untuk ahli akademik dan profesional islam dengan menggunakan cuti sabatikal, cuti tahunan, cuti sambil belajar/penyelidikan, lawatan singkat profesional mereka dan sebagainya. dalam tempoh ini mereka dapat pergi ke negara-negara islam lain untuk berkhidmat kepada umat islam di negara-negara tersebut. keywords: muslim academician; professional; talent bank; optimally mobile; service ummah; resource centers 1. introduction the islamic concept of knowledge � ilm � must form the basis of the theoretical and institutional structure of education in islam. in other words, what makes education truly islamic is the fact that it is based on a genuinely islamic notion of knowledge. the concept of ilm, as has been argued forcefully in recent years by numerous muslim scholars, integrates the pursuit of knowledge with values, envelopes factual insight with metaphysical concerns, and promotes an outlook of balance and genuine synthesis. this is the ultimate difference between the western notion of knowledge, which keeps "knowledge" and "values" in two separate compartments, and does not appreciate any form of knowledge that is not gained by sense perception. the integral world-view of islam, on the other hand, furnishes us with a number of concepts which, when operationalized and actualized in all their sophistication at various levels of society and civilization, yield an integrated infrastructure for the distribution of knowledge. in addition to the core concept of tawheed, at least five other islamic concepts — of ilm (knowledge), adl (justice), ibadah (worship) khilafah (trusteeship), istislah (social welfare) — have a direct bearing on education to be pursued in the true islamic spirit. the all-embracing qur’anic concept of ilm shaped the outlook of the muslim people right from the beginning of islam in arabia. islam actually made the pursuit of knowledge a religious obligation: by definition, to be a muslim is to be deeply entrenched in the generation, production and dissemination of knowledge [1]. there is a strong consensus that deficiency in muslim human capital is a major cause of islamic countries remaining poor. to render matters worse, when reasonable quantities of human capital are formed, quite a significant number are lost due to migration leakage. no wonder then that the concern has been to contain the leakage. in the words of a recent world development report: "can something be done to stop the mass departure of trained workers from poorer countries? [2]" are the muslim world today contented to be in the present status quo in which the systems in trade, education, social and culture, communication, finance, development and security and defense, are all intelligently dominated, manipulated, distorted and unfairness dealings by the western powers under globalization [3]? even though our national territories are not shrinking, but our minds and thinking are slowly but surely being exploited, disempowered and technologically colonized by the powerful mass media and communication networks. the western mass media are experts in facts manipulation, unfair reporting, bias information and even worst the misunderstood aspects of islam are being highlighted, and muslims are branded by western medias by many terms which are not accepted in islam. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering muyibi and jami 175 the balance of trade is forever in the red because of near total reliance on importation of goods and services from the developed countries more than what they should do among themselves. even though malaysia exports rm 36.8 billion worth of halal food to oic countries, that amount is like a drop of water in the ocean when you compare it with the amount of western goods and services that are being imported into oic countries [4]. when a highly qualified professional chooses to leave his own country for another, he/she does so for one or several reasons. some of these reasons may be due to legitimate political or economic reasons: peace and security for himself and his family, job satisfaction, better pay and conditions, access to educational opportunities for self and or family, a better quality of life and a challenging environment in which they can thrive and fulfill their potential. furthermore professionals who trained abroad in certain specialized areas will become redundant because they have no place to practice the expertise they have acquired, in their countries of origin, so they have no option but to stay abroad permanently. there are yet others who returned but because of the lack of systems at their homes, they prefer going back abroad. a number of developed countries have also liberalized their immigration policies for the admission of highly skilled professionals. this paper presents a proposal on how the muslim experts made up of academics, professionals and entrepreneurs can be made optimally mobile to utilize their allah endowed resources to serve the ummah and mankind more efficiently and effectively as well as being key players in a world which has become a “global village”. 2. the optimally mobile muslim experts in the service of the ummah globally the optimally mobile expert is that individual or groups of individuals who are committed to put to use their allah endowed resources to render their services and expertise to the ummah in particular, mankind and all allah’s creation on earth whenever the need arise to earn the pleasure of allah only as part of ibadat. such individuals or groups of muslim academicians, professionals, and entrepreneurs shall therefore have the following characteristics or develop these characteristics among others to become optimally mobile. i) be ummatic: this implies that they love the ummah for the sake of allah and express their tawhidic ties with other muslims through networking, sharing of resources etc., ii) be patriotic: this implies they should love their respective countries and contribute to its development. they should maintain a trusted relationship with political leaders in their parent countries. iii) be ethical and principled: this implies the application of islamic values, moral, and ethics in all they do throughout their lives on this earth. they should therefore be always conscious of the fact that as muslims we find out why and how of allah’s endowed resources and use it for the benefit of the ummah in particular and all allah’s creation both animate and inanimate in general. this will enable all humankind to do ibadat efficiently and effectively in ways shown by our beloved rasul muhammad (saw) required by allah to please allah. this will then insha allah make their role as vicegerent of allah to be acceptable to allah. knowledge is the unique faculty of mankind and is an integral part of their personality and their being. it is knowledge that qualifies mankind to be viceroy iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering muyibi and jami 176 of allah our rabb and entitle mankind to command the respect and allegiance even of angels of allah. iv) be strong academically, intellectually, and professionally: this implies that they should be competent, be knowledgeable, and consider the application of their knowledge and expertise as amal which is part of ibadat and therefore compulsory. v) be holistic in approach to solving problems: this implies seeing the world as being interconnected spiritually, economically, politically, technologically, environmentally etc. vi) be cooperative: this implies cooperation with muslims and friendly/sympathetic non-muslim individuals and organizations through networking. positive interpersonal relations should be observed and promoted through implanting principles of brotherhood and compassion among those they come in contact with. 3. strategies for the setting up of international organisation of optimally mobile muslim experts (ioomme) in order to create the enabling environment for the ummah to have optimally mobile muslim academicians, professionals and entrepreneurs, who will provide solutions to the ummatic conundrum in all fields of human endeavor like technology, science, law, commerce, as well as meeting the challenges posed by globalization being imposed on the ummah in particular and mankind in general some strategies are proposed to achieve these objectives. setting up a global organization to be known as international organisation of optimally mobile muslim experts (ioomme). this organization will insha allah be based in malaysia located at the international islamic university malaysia (iium) as the secretariat. it is envisaged that ioomme will have branches in all oic countries as well as non-muslim nations with large concentration of immigrant and revert muslim populations. ioomme will develop a website for the muslim ummah worldwide which will contain some of the following information; a) talent bank which will contain information about muslim academics, professionals, and entrepreneurs, their location, and area of expertise etc. available on line with access based on permission being granted by the website manager or system administrator in consultation with the academician or professional. b) information about facilities e.g. research institutes/centers, specialized institutions like specialist hospitals, technology parks etc in muslim nations which can be made available for use by muslim academicians, professionals, and entrepreneurs in the service of the ummah and mankind. c) through cooperation and networking among muslim nations, there will be the urgent need to create the enabling environment for easy mobility of muslim academicians, professionals and entrepreneurs from one nation to another to render their services to one another for the benefit and development of the iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering muyibi and jami 177 ummah in particular and mankind in general. these objectives can be achieved through some of the following actions: i. introduction of a common k-passport in all muslim nations which will have in built facilities like relaxed work permit, entry visa, and other immigration requirements for muslim academicians. professionals and entrepreneurs . this will encourage brain gain from the present brain drain of muslim academics and professionals from muslim nations to non-muslim nations. ii. relaxed entry visa, work permit etc. for ease of mobility of muslim academics professionals and entrepreneurs from non-muslim nations.encouragement of migration of muslim academics, professionals and entrepreneurs who are citizens of muslim nations as well as those from non-muslim nations with large concentration of immigrant and revert muslim populations to get long term temporary residency as well as permanent residency in muslim nations whose proximity will enable them to render more effective service/ expertise to the ummah. iii. muslim academics and professionals should be encouraged to go for their sabbaticals, study/research leave, professional short visit, annual vacations etc. there should be programs like academic staff/professional exchanges, external examiners, postgraduate training, receiving muslim students in their laboratories etc. iv. there should be access across all muslim nations for the use of their pooled resources like research institutes/centers, specialized institutions like specialist hospitals, technology parks, data banks, library resources etc. v. setting up of waqf funds in muslim nations for research and development, provision of travel grants for visiting scholars and professionals etc. vi. provision of competitive salary and fringe benefits. vii. consultancy and applied research and technology development/transfer in public research institutes. viii. participating in training or research via the network and initiating research and commercialization of products. ix. facilitating business contacts. x. encourage muslim academics and professionals to author books based on islamic principles which will imply a paradigm shift, and publication of scholarly, professional, and application oriented papers in journals. 4. conclusion in conclusion, even though the brain drain is not a recent phenomenon, it has caused serious developmental problems in muslim countries over the last few years. the muslim ummah is losing more skilled people every year. a project like ioomme can be invaluable in recapturing some of the lost skills. however, we realize that the success of ioomme depends on amongst other factors, the willingness and commitment of the expatriates, getting trusted relationships with political leaders etc. it is also important to go beyond just setting up the network, but ensuring that it is self-sustainable and a call from allah (swt) to all muslim academics and professionals that allah (swt) will ask every iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering muyibi and jami 178 one of us what we did with our knowledge and talent for the service of the ummah in particular and mankind in general. “for him( each ) person , there are angels in succession, before and behind him. they guard him by the command of allah. verily allah will not change the ( good) condition of a people as long as they do not change their state ( of goodness) themselves ( by committing sins and by being ungrateful and disobedient to allah). but when allah wills a people’s punishment, there can be no turning back of it, and they will find besides him no protector” [5]. references [1] s. abdul latif (1977) “the basis of islamic culture” i darah –iadabiyat delhi, india. [2] world bank, 1995.world development report 1995. oxford university press, new york.). [3] s. a. muyibi and abu zahrin bin abu bakar “the united muslim ummah (tumu)”. international conference on muslim unity in the 21 st century – opportunities and challenges” organised by international institute for muslim unity, 1 – 2 october 2003 kuala lumpur, malaysia proceedings vol 1. pp 7 34 [4] ""www.arabicnews.com/ansub/daily/ day/010227/2001022720.html"" [5] the holy quran: english translation of the meanings and commentary. king fahd complex for printing of holy quran, madina k. s. a application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 237 a review on rheology of non-newtonian properties of blood esmaeel fatahian1*, naser kordani2and hossein fatahian1 1 department of mechanical engineering, nour branch, islamic azad university, nour, iran. 2 department of mechanical engineering, university of mazandaran, mazandaran, iran. * corresponding author: esmaeelfatahian@gmail.com (received: 5th march 2017; accepted: 22nd may 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.826 abstract: human blood is composed of red cells, white blood cells, and platelets in a fluid called plasma that contains organic and mineral salts and protein. the rheological characteristics of blood are determined by the properties of these combinations and their interaction with each other. the plasma is essentially a newtonian fluid, but the blood as a whole behaves as a non-newtonian fluid showing all signs of non-newtonian rheology including deformation rate dependency, viscoelasticity, yield stress, and thixotropy. the purpose of this study is mainly a review based on past work on blood rheology, determinants of blood viscosity, yield stress, thixotropy, blood viscosity measurement, and heat transfer in blood flow to better understand the non-newtonian effect in the blood circulation system. abstrak: darah manusia terdiri daripada sel-sel merah, sel darah putih dan platlet dalam cecair yang dipanggil plasma, mengandungi garam organik dan mineral dan protein. ciri-ciri sifat reologi darah ditentukan oleh sifat-sifat kombinasi ini dan interaksi antara satu sama lain. plasma adalah pada dasarnya newtonian cecair tetapi secara keseluruhannya darah bersifat sebagai bukan suatu cecair newtonian yang menunjukkan tanda-tanda bukan newtonian reologi, mengandungi pergantungan kadar ubah bentuk, kelikatkenyalan, tegasan alah dan thixotropi. tujuan kajian ini adalah berkenaan ulasan kajian-kajian lepas berkaitan rheology darah, penentu viskositi darah, tegasan alah dan thixotropi, ukuran kelikatan darah dan pemindahan haba dalam aliran darah bagi memahami kesan bukan newtonian dalam sistem peredaran darah. keywords: blood rheology; non-newtonian fluids; shear-thinning behavior; thixotropy 1. introduction a non-newtonian fluid is a fluid with properties that are different in any way from those of newtonian fluids. most commonly, the viscosity (the measure of a fluid's ability to resist gradual deformation by shear or tensile stresses) of non-newtonian fluids is dependent on the shear rate or shear rate history. some non-newtonian fluids with shearindependent viscosity, however, still exhibit normal stress-differences or other nonnewtonian behavior. many salt solutions and molten polymers are non-newtonian fluids, as are many commonly found substances such as ketchup, custard, toothpaste, starch suspensions, (stf)/fabric composites, maizena, paint, blood, and shampoo [1, 2]. blood is a complex fluid with non-newtonian characteristics, it has a shear-thinning behavior [3] and often exhibits a yield stress (viscoplasticity) [4-6] with potential history effects iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 238 (thixotropy) [7]. the rheological complexity of blood is attributed to its constituents. rheologically, blood is primarily characterized as a concentrated suspension of elastic, deformable red blood cells (rbcs). however, it also contains other ingredients such as leukocytes and platelets within plasma. yield stress is an important characteristic of blood rheology and an essential component of its non-newtonian nature. experimental evidence for its association with blood has been provided in many investigations [8, 9] and with different experimental techniques, as described by picard et al. [10]. from a modeling point of view, the role of yield stress is most clearly evaluated under steady-state shear flow conditions. as a shear, thinning fluid, blood is also characterized by a thixotropic behavior, which is confirmed experimentally by a number of studies [11], due to the intimate relation between these two non-newtonian properties [12]. this may also explain a possible controversy about the thixotropic nature of blood [13] as the thixotropic-like behavior may be explained by other non-newtonian characteristics of blood. despite the fact that thixotropy is a transient property, due to the pulsative nature of the blood flow, the thixotropic effects may have long term impact on blood circulation. this equally applies to the time-dependent effects of viscoelasticity. thixotropy is more pronounced at low shear rates with a long-time scale. the effect, however, seems to have a less important role in blood than other non-newtonian effects such as shear thinning [14], and this could partly explain the limited amount of studies dedicated to this property. the thixotropic behavior of blood is very sensitive to blood composition and hence it can demonstrate big variations between different individuals and under different biological conditions [11]. blood is an important fluid in the human body therefore, measuring the viscosity and other properties can be used in the diagnosis of various cardiovascular system diseases. measuring viscosity is an important property of blood requiring the use of the right tools. different tools are used to measure blood viscosity including capillary tube viscometers, cone and plate viscometers, concentric cylinder viscometers, rotating disc viscometers and acoustic wave viscometers. the body’s internal heat transfer is controlled by the blood circulatory system. the blood circulatory system reduces the temperature differences in the body. the most important applications of modeling heat transfer in the body can be noted in surgery (especially open-heart surgery), dialysis devices, and also in the making of artificial blood vessels. the current study, which is basically a brief overview of the rheological properties of blood, is trying to explain the rheological behavior of blood and discuss the four main determinants of whole blood viscosity. we consider the yield stress and thixotropy behaviour that describe the blood rheology and finally investigate heat transfer in blood. 2. rheology of blood blood behaves like a non-newtonian fluid whose viscosity varies with shear rate. the non-newtonian characteristics of blood come from the presence of various cells in the blood (typically making up 45% of the blood’s volume) that make blood a suspension of particles [15,16]. when the blood begins to move, these particles (or cells) interact with plasma and among themselves. hemorheologic parameters of blood include whole blood viscosity, plasma viscosity, red cell aggregation, and red cell deformability (or rigidity). from a biological point of view, blood can be considered as a tissue comprising various types of cells (i.e., rbcs, wbcs, and platelets) and a liquid intercellular material (i.e., plasma). from a rheological point of view, blood can be thought of as a two-phase liquid; it can also be considered as a solid-liquid suspension, with the cellular elements being the solid phase. however, blood can also be considered as a liquid-liquid emulsion based on the liquid-like behavior of rbcs under shear. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 239 3. determinants of blood viscosity much research has been performed to formulate a theory that completely accounts for the viscous properties of blood, and some of the key determinants have been identified [17, 18]. the four main determinants of whole blood viscosity are (1) plasma viscosity, (2) hematocrit, (3) rbc deformability and aggregation, and (4) temperature. the first three factors are parameters of physiological concern because they pertain to changes in whole blood viscosity in the body. the second and third factors, hematocrit and rbc (red blood cells) aggregations, are the main contributors to the non-newtonian characteristics of shear-thinning viscosity and yield stress. 4. yield stress in addition to non-newtonian viscosity, blood also exhibits a yield stress. the source of the yield stress is the presence of cells in the blood, particularly red cells. when such a huge amount (40-45% by volume) of red cells of 8-10 microns in diameter is suspended in plasma, cohesive forces among the cells are not negligible. the forces existing between particles are van der waals-london forces and coulombic forces [19, 20]. hence, in order to initiate a flow from rest, one needs to have a force that is large enough to break up the particle-particle links among the cells. however, blood contains 40-45% red cells and still moves relatively easily. the healthy red cells behave like liquid drops because the membranes of red cells are so elastic and flexible. note that in a fluid with no suspended particles, the fluid starts to move as soon as an infinitesimally small amount of force is applied. such a fluid is called a fluid without yield stress. examples of fluid with no yield stress include water, air, mineral oils, and vegetable oils. examples of fluids having yield stress include blood, ketchup, salad dressings, grease, paint, and cosmetic liquids. the magnitude of the yield stress of human blood appears to be at the order of 0.05 dyne/cm2 (or 5 mpa) [21,22] and is almost independent of temperature in the range of 10-37 ℃ [23]. blood shows a newtonian fluid’s character when it flows through larger diameter arteries at high shear rates, but it exhibits a remarkable non-newtonian behavior when it flows through small diameter arteries at low shear rates [24, 25]. moreover, there is an increase in viscosity of blood at low rates of shear as the red blood cells tend to aggregate into the rouleaux form [26]. rouleaux form behaves as a semi-solid along the center forming a plug flow region. in the plug flow region, we have a flattened parabolic velocity profile rather than the parabolic velocity profile of a newtonian fluid. this behavior can be modeled by the concept of yield stress. the yield stress for blood depends strongly on fibrinogen concentration and is also dependent on the hematocrit. the yield stress values for normal human blood is between 0.01 and 0.06 dyne/cm2 [27]. the casson fluid model is a non-newtonian fluid with yield stress, which is widely used for modeling blood flow in narrow arteries. many researchers have used the casson fluid model for mathematical modeling of blood flow in narrow arteries at low shear rates. it has been demonstrated by blair [28] and copley [29] that the casson fluid model is adequate for the representation of the simple shear behavior of blood in narrow arteries. casson examined the validity of the casson fluid model in his studies pertaining to the flow characteristics of blood and reported that at low shear rates, the yield stress for blood is nonzero [30]. venkatesan et al. investigated the flow of blood through a narrow artery with bell-shaped stenosis, treating blood as casson fluid. results are compared with the results of the herschel bulkley fluid model obtained by misra and shit for the same geometry [31]. resistance to flow and skin friction are normalized in two different ways such that (i) with respect to the same nonnewtonian fluid in a normal artery, it gives the effect of a stenosis and (ii) with respect to the newtonian fluid in the stenosed artery, it spells out the non-newtonian effects of the iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 240 fluid. it is found that the resistance to flow and skin friction increase with the increase of maximum depth of the stenosis, but these flow quantities (when normalized with nonnewtonian fluid in normal artery) decrease with the increase of the yield stress, as obtained by misra and shit [31]. it is also noticed that the resistance to flow and skin friction increase (when normalized with newtonian fluid in stenosed artery) with the increase of the yield stress [32]. yield stress arises from the aggregation of red blood cells at low shear rates to form the three-dimensional micro-structures (rouleaux) that resist the flow [33-35]. studies have indicated that yield stress is positively correlated to the concentration of fibrinogen protein in blood plasma and to the hematocrit level [36, 37]. other factors, such as the concentration of minerals, should also have a contribution. many of the blood rheological characteristics in general, and non-newtonian in particular, are also controlled or influenced by the fibrinogen level [35]. the yield stress characteristic of blood seems to vanish or become negligible when hematocrit level falls below a critical value [36]. yield stress contributes to the blood clotting following injuries and subsequent healing, and may also contribute to the formation of blood clots (thrombosis) and vessel blockage in some pathological cases such as strokes. the magnitude of yield stress and its effect could be aggravated by certain diseased states related to the rheology of blood, like polycythemia vera, or the structure of blood vessels such as stenosis. dependence of yield stress of human blood on hematocrit level on a loglinear plot is shown in fig. 1. other types of correlation have also been obtained in other studies [38, 39]. fig. 1: dependence of yield stress of human blood on hematocrit level on a log-linear plot [38,39]. 5. thixotropy the phenomenon of thixotropy in a liquid result from the microstructure of the liquid system. thixotropy may be explained as a consequence of aggregation of suspended particles. if the suspension is at rest, the particle aggregation can form, whereas if the suspension is sheared, the weak physical bonds among particles are ruptured, and the network among them breaks down into separate aggregates that can disintegrate further into smaller fragments [40]. after some time at a given shear rate, a dynamic equilibrium is established between aggregate destruction and growth, and at higher shear rates, the equilibrium is shifted in the direction of greater dispersion. the relatively long time required for the microstructure to stabilize following a rapid change in the rate of flow makes blood thixotropy readily observable [41]. this effect on viscosity has been studied iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 241 using a steady flow [42]. at high shear rates, structural change occurs more rapidly than at low shear rates. huang et al. [42] investigated the first step for a no-flow condition to a shear rate of 10 s-1. they found that blood viscosity decreased over a period of approximately 20 seconds at the shear rate of 10 s-1 before the final state was attained. next, when the shear rate stepped up from 10 to 100 s-1, almost no time was required to reach the microstructural equilibrium after the change of shear rate. gaspar-rosas and thurston also investigated erythrocyte aggregate rheology by varying the shear rate from 500 s-1 to zero [43]. based on their results, it can be concluded that the recovery of the quiescent structure requires approximately 50 seconds while the high shear rate structure is attained in a few seconds. in other words, in order to minimize the effect of the thixotropic characteristic of blood on the viscosity measurement between the shear rates of 500 and 1 s-1, at least 50 seconds should be allowed during the test to have the fully aggregated quiescent state at a shear rate near 1 s-1. 6. blood viscosity measurement blood viscosity is an important property for the regulation of rheological conditions because it produces resistance to fluid deformations. blood viscosity is mainly determined by the hematocrit and varies with the shear rate as a non-newtonian fluid [44, 45]. blood viscosity is important for understanding physiological blood flow conditions [46, 47]. numerous types of rheometers have been used to measure the viscosity and yield stress of materials [48-50]. typically, shear viscometers can be divided into two groups: drag flows, in which shear is generated between a moving and a stationary solid surface, and pressure-driven flows, in which shear is generated by a pressure difference over a capillary tube [50]. the commonly utilized members of these groups are shown in fig. 2. among the several types of viscometers currently available, rotational viscometers have mainly been used to measure whole blood viscosity because they measure viscosity within a certain shear rate range with a relatively small amount of sample [51]. fig. 2: rheometers [50]. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 242 shin et al. developed a pressure-scanning capillary viscometer that used a pressure transducer to measure the viscosity of non-newtonian fluids including blood [52]. shin et al. also developed a blood hemorheometer, featuring a vacuum suction-type pressure scanning mechanism, that has been successfully employed to detect the mechanical behavior of red blood cell aggregation [53]. lee et al. [54] studied the applicability of two non-newtonian constitutive models (casson and herschel-bulkley models) in the determination of the blood viscosity and yield stress using a pressure-scanning microfluidic hemorheometer. the present results were compared with the measurements through a precision rheometer (ares2). for a newtonian fluid (standard oil), the two constitutive models showed excellent agreement with a reference value and the measurement of ares2. for human blood as a non-newtonian fluid, both the casson and herschel-bulkley models exhibited similar viscosity results over a range of shear rates and showed excellent agreement with the ares2 results. the herschel-bulkley model yielded a slightly higher value than other results at low shear rates (ẏ< 10), which may be due to the relatively high value of the yield stress. the yield stress values for whole blood were 14.4 mpa for the casson model and 32.5 mpa for the herschel-bulkley model, respectively. thus, their study showed that the casson model would be better than the herschel-bulkley model for representing the non-newtonian characteristics of blood viscosity [54]. kang et al. [55] proposed a unique microfluidic device for simultaneously measuring viscosity and flow rate of whole blood circulating in a complex fluidic network. based on the microfluidic device, three sequential flow controls were applied to identify viscosity and flow rate of blood, with label-free and sensor-less detection. to quantify the effect of flow stabilization on flow fluctuations, a formula for the pulsation index (pi) was analytically derived using a discrete fluidic circuit model. using the pi formula, the time constant contributed by the half-circular chamber is estimated to be 8 s. furthermore, flow fluctuations resulting from the peristaltic pumps are completely removed, especially under periodic flow conditions. the result showed that the flow rate and viscosity of blood can be simultaneously measured with satisfactory accuracy. in addition, the proposed method was successfully applied to identify the viscosity of rat blood, which circulates in a complex fluidic network. these observations confirm that the proposed method can be used for simultaneous measurement of viscosity and flow rate of whole blood circulating in the complex fluid network, with sensor-less and label-free detection. furthermore, the proposed method will be used in evaluating variations in the viscosity of human blood during cardiopulmonary bypass procedures or hemodialysis [55]. kang et al. presented the first experimental work on the viscosity measurement of adult zebrafish whole blood using a capillary pressure-driven microfluidic viscometer. after the device calibration with water, the viscosity measurement of human whole blood was performed and in good agreement with published data, demonstrating the reliability of the device. power law and carreau-yasuda rheological models were used to model the non-newtonian behaviors of the human and zebrafish blood [56]. the viscosity measurement of adult zebrafish whole blood is shown in fig. 3. furukawa applied an electromagnetic spinning sphere (ems) viscometer to the measurement of human blood viscosity for the first time. they collected blood samples from 100 healthy outpatient volunteers in order to analyze viscosity dependence on blood cell parameters and on the shear rate. this study demonstrated a strong exponential correlation between the hematocrit and blood viscosity. however, the total count of rbc and platelets correlated more strongly with blood viscosity than the hematocrit. this result indicates that blood viscosity is likely to be more affected by blood cell particle numbers than by blood cell volume. although this comparison has not been addressed in human clinical studies, a previous animal study demonstrated that the blood cell count had a stronger influence on blood viscosity than the hematocrit [57]. this study iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 243 also performed a comparison of hematological and rheological parameters between rats and dogs. although no significant differences were observed in the hematocrit between rats and dogs, blood viscosity and the rbc count were significantly greater in rats than in dogs. finally, this study revealed that its dependence on blood cell parameters varied with the shear rate, while its dependence on the shear rate varied with individual differences, suggesting that actual individual measurements are important for the assessment of blood viscosity. based on this necessity, the ems viscometer has a high degree of usability to measure blood viscosity because of its advantageous measurement characteristics, including less blood contamination, less blood sedimentation and the minimal requirement of a sample volume of only 0.3 ml. therefore, the measurement of blood viscosity with the ems viscometer appears to be promising for understanding the hemodynamic-related pathogenesis of vascular diseases [58]. fig. 3: the viscosity measurement of unadulterated adult zebrafish whole blood at 20 °c. (a) n=0.99814. (b) shear rates range from 184.2 s-1 to 15399.9 s-1 [56]. 7. heat transfer of blood flow internal heat transfer of body is controlled by the blood circulatory system. blood circulatory system reduces the temperature differences in body. the most important applications of modeling heat transfer in the body can be noted in surgery (especially open-heart surgery), dialysis devices, and also making artificial blood vessels. in 1948, pennes investigated the thermal conductivity in human body tissue and the effects of blood flow on the temperature of tissue. according to his model, mass transfer rate between blood and adequate tissue was the difference between the amount of a substance in the tissue and blood multiplied by the intensity of blood flow. so, when the heat transferred from the blood to the tissues’ temperature, differences between the arterial blood into the tissues and venous blood coming out of it were adequate [59]. here, we present a simplified model of the bioheat equation for steady-state, one-dimensional heat transfer. from a one-dimensional energy balance in the x-direction: 𝑑2𝑇 𝑑𝑥2 ⁄ + (𝑞𝑚 + 𝑞𝑝) 𝑘 ⁄ = 0 (1) where qm is the metabolic heat source term and qp is the perfusion heat source term, both per unit volume and the thermal conductivity, k, is a constant. pennes [60] proposed an expression for the perfusion term by assuming that the temperatures of blood entering and exiting capillaries are both constant for any small volume of tissue. we can say that the (a) (b) iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 244 temperatures of the blood at each state are the same as that of the surroundings, namely the arterial temperature and the local tissue temperature. now the perfusion rate, w, must be defined. this is the ratio of the volumetric flow rate of blood per volume of tissue. thus, we have for the perfusion term: 𝑞𝑝 = 𝑊𝜌𝑏𝐶ℎ(𝑇𝑎 − 𝑇) (2) where ρb and cb are the density and specific heat capacity of the blood, respectively. combining these two equations results in: 𝑑2𝑇 𝑑𝑥2 ⁄ + (𝑞𝑚 + 𝑊𝜌𝑏𝐶ℎ)(𝑇𝑎 − 𝑇) 𝑘 ⁄ = 0 (3) which is the pennes bioheat equation for one-dimensional, steady-state, heat transfer. he et al. studied the influence of blood flow rate on body temperature by means of a one-dimensional thermo-fluid model. this model has been recently developed for the circulation system of the upper limb and involves arteries, capillaries, and veins based on the structured-tree arterial model [61]. he concluded that his model can predict the influence of the blood flow rate and the blood pressure, as well as that of the crosssectional area on the blood temperature [62]. craciunescu et al. studied the effect of blood velocity pulsations on bio-heat transfer. a simple model of a straight rigid blood vessel with unsteady periodic flow is considered. a numerical solution that considers the fully coupled navier stokes and energy equations is used for the simulations. the velocity profiles are well documented in different references that include both analytical and numerical approaches for solving for the velocity field [63, 64]. the influence of the pulsation rate on the temperature distribution and energy transport was studied for four typical vessel sizes: aorta, large arteries, terminal arterial branches, and arterioles. the results showed that the pulsating axial velocity produces a pulsating temperature distribution; reversal of flow occurs in the aorta and in large vessels, which produces significant time variation in the temperature profile. there is a small difference between the time-averaged unsteady heat flux due to a pulsating blood velocity and an assumed non-pulsating blood velocity, it is reasonable to assume a non-pulsating blood velocity for the purposes of estimating bio-heat transfer [65]. chakravarty et al. investigated a mathematical model representing the dynamic response of heat and mass transfer to blood streaming through the arteries under stenotic conditions. the blood was treated to be a generalized newtonian fluid and the arterial wall was considered to be rigid having differently shaped stenosis in its lumen arising from various types of abnormal growth or plaque formation. the nonlinear unsteady pulsatile flow phenomenon unaffected by the concentration-field of the macromolecules is governed by the navier–stokes equations together with the equation of continuity while those of the heat and the mass transfers are controlled by the heat conduction and the convection–diffusion equations, respectively. this study records that the patterns of the flow, the heat and the mass transfer, the pressure drop, the wall shear stress and the sherwood number (shd) number were strongly dependent on the shape of the stenosis in addition to the non-newtonian rheology of blood in general, and the irregular shape having closer physiological relevance, in particular. numerical computation of the desired quantities having major physiological significance is primarily based upon the following parameters obtained from [66, 67]: α = 2, re = 300, pr = 0.72, sc = 3, k = 0.1, λ = 40, λ = 50, ro = 0.154 cm, ρ = 1.05 × 10 3 kg.m-3 and l= 43.6 iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 245 while the results of fig. 4 at re =300 represent the qualitative measure of the effect of womersley parameter on the temperature profiles for a moderate irregular stenosis with 48% area reduction, the profiles of fig. 5 for exhibit how they are being influenced significantly by the non-newtonian rheology of the streaming blood. the combined effect of heat and mass transfer on non-newtonian idealization of the streaming blood indicates a gateway to draw linkage to atherosclerosis [68]. fig. 4: profiles of the temperature for irregular stenosis with k = 0.1% and 48% area reduction at re = 300 [68]. fig. 5: profiles of the temperature for irregular stenosis with 48 % area reduction for k = 0.1 and a = 2 at re = 300 [68]. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 246 ahmad et al. investigated the mathematical solution of unsteady, viscous, incompressible, electrically conducting blood flow and heat transfer through a parallel plate channel when the lower plate is stretching. the effects of flow parameters namely grashof number (gr), prandtl number (pr), heat source parameter (n), hartmann number (m) and decay parameter (ƛ) on the velocity and heat functions have been observed. the mathematical analysis and graphical presentations of velocity and temperature distributions are very simple and help to understand physiological fluid dynamics. the results show that temperature field increases with increase in the values of heat source parameter (n), fig. 6 presents the distribution of the temperature for different values of decay parameter (ƛ). the temperature distribution decreases against the decay parameter (ƛ). fig. 7 shows respectively that the effect of grashof number (gr), prandtl number (pr), and heat source parameter (n) on the axial velocity. it is noticed that velocity increases with an increase in the values of these parameters [69]. fig. 6: graph of temperature distribution for different values of decay parameter (ƛ) [69]. fig. 7: graph of axial velocity for different values of heat source parameter (n) [69]. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 247 8. conclusion in this paper, rheological characteristics of blood were studied. as referred to in previous work, blood is a complex fluid with non-newtonian characteristics. it often represents a yield stress (viscoplasticity) and has a shear-thinning behavior and due to the pulsative nature of the blood flow, it shows a thixotropy treatment. blood has four main determinants including plasma viscosity, hematocrit, red blood cell deformability, and temperature. blood shows a newtonian fluid’s character when it flows through larger diameter arteries at high shear rates, but it exhibits a remarkable non-newtonian behavior when it flows through small diameter arteries at low shear rates. despite the fact that thixotropy is a transient property, due to the pulsative nature of the blood flow the thixotropic effects may have long term impact on the blood circulation. it should be remarked that time dependent effects whether thixotropic or viscoelastic in nature, should be expected in blood flow due to the pulsatility of blood flow and the rapid change in the deformation conditions during blood circulation. modeling of heat transfer in the body can be used in surgery, especially open-heart surgery, as well as in making artificial blood vessels. from a simple model of a straight rigid blood vessel with unsteady periodic flow, there is a small difference between the time-averaged unsteady heat flux due to a pulsating blood velocity and an assumed non-pulsating blood velocity, it is reasonable to assume a non-pulsating blood velocity for the purposes of estimating bioheat transfer. the heat and the mass transfer, the wall shear stress and the sherwood number (shd) number are strongly dependent on the shape of the stenosis in addition to the non-newtonian rheology of blood in general. future work • rheological models of blood flow • numerical simulation of the non-newtonian blood flow • effects of temperature on blood viscosity references [1] da silva jl, rao, ma. (2007) rheological behavior of food gels. in rheology of fluid and semisolid foods (pp. 339-401). springer us. [2] kordani, n., & vanini, a. s. (2014) optimizing the ethanol content of shear thickening fluid/fabric composites under impact loading. journal of mechanical science and technology, 28(2):663-667. [3] edward, r. (1969) merrill, rheology of blood. physiological reviews, 49(4):30-43. [4] cokelet gr, merrill ew, gilliland er, shin h, britten a, wells jr re. (1963) the rheology of human blood—measurement near and at zero shear rate. transactions of the society of rheology, 7(1):303-317. [5] merrill ew, gilliland er, lee ts, salzman ew. (1966) blood rheology: effect of fibrinogen deduced by addition. circulation research, 18(4):437-446. [6] merrill ew, cheng cs, pelletier ga. (1969) yield stress of normal human blood as a function of endogenous fibrinogen. journal of applied physiology, 26(1):1-3. [7] dintenfass l. (1962) thixotropy of blood and proneness to thrombus formation. circulation research, 11(2):233-239. [8] merrill ew, pelletier ga. (1967) viscosity of human blood: transition from newtonian to non-newtonian. journal of applied physiology, 23(2):178-182. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 248 [9] chien s, usami s, taylor hm, lundberg jl, gregersen mi. (1966) effects of hematocrit and plasma proteins on human blood rheology at low shear rates. journal of applied physiology, 21(1):81-87. [10] picart c, piau jm, galliard h, carpentier p. (1998) human blood shear yield stress and its hematocrit dependence. journal of rheology, 42(1):1-12. [11] dintenfass l. (1962) thixotropy of blood and proneness to thrombus formation. circulation research, 11(2):233-239. [12] sochi t. (2010) flow of non‐newtonian fluids in porous media. journal of polymer science part b: polymer physics, 48(23):2437-2767. [13] davenport, p., & roath, s. (1981) blood thixotropy. journal of clinical pathology, 34(1):106-117. [14] mandal p k. (2005) an unsteady analysis of non-newtonian blood flow through tapered arteries with a stenosis. international journal of non-linear mechanics, 40(1):151-164. [15] fung yc. (1993) biomechanics–mechanical properties of living tissues, 2nd edn. [16] guyton ac, hall je. (1996) textbook of medical physiology, 9th edition, w.b. sanders company, philadelphia. [17] dinnar u. (1981) cardiovascular fluid dynamics. crc press, boca raton, fl. [18] chien s, dormandy ja, ernst e, matrai, a. (2012) clinical hemorheology: applications in cardiovascular and hematological disease, diabetes, surgery and gynecology (vol. 74). springer science & business media. [19] cheng dc, evans f. (1965) phenomenological characterization of the rheological behaviour of inelastic reversible thixotropic and antithixotropic fluids. british journal of applied physics, 16(11):1599-1614. [20] mewis j, spaull ajb. (1976). rheology of concentrated dispersions. advances in colloid and interface science, 6(3):173-200. [21] nakamura m, sawada t. (1988) numerical study on the flow of a non-newtonian fluid through an axisymmetric stenosis. journal of biomechanical engineering, 110(2):137-143. [22] stoltz jf, singh m, riha p. (1999) hemorheology in practice (vol. 30). ios press. [23] barbee jh. (1973) the effect of temperature on the relative viscosity of human blood. biorheology, 10(1):1-5. [24] cokelet gr. (1972) the rheology of human blood. biomechanics: its foundations and objectives, 72:63-103. [25] rathod vp, tanveer s. (2009) pulsatile flow of couple stress fluid through a porous medium with periodic body acceleration and magnetic field. bulletin of the malaysian mathematical sciences society, 32(2):245-259. [26] boyd w. (1964) a text-book of pathology: structure and function in diseases. lea & febiger: philadelphia. pp. 130-133. [27] chandran kb, rittgers se, yoganathan ap. (2012) biofluid mechanics: the human circulation. crc press. [28] blair gs. (1959) an equation for the flow of blood, plasma and serum through glass capillaries. nature, 183(4661):613-614. [29] copley al. (1960) apparent viscosity and wall adherence of blood systems. flow properties of blood and other biological systems, pergamon press, oxford, uk, p. 97. [30] casson n. (1959) a flow equation for pigment-oil suspensions of the printing ink type. in:mill cc, editor. rheology of disperse systems. new york: pergamon press. pp. 82-104. [31] venkatesan j, sankar ds, hemalatha k, yatim, y. (2013) mathematical analysis of casson fluid model for blood rheology in stenosed narrow arteries. journal of applied mathematics, 2013, pp. 1-11. [32] misra jc, shit gc. (2006) blood flow through arteries in a pathological state: a theoretical study. international journal of engineering science, 44(10):662-671. [33] bodnár t, sequeira a, prosi m. (2011) on the shear-thinning and viscoelastic effects of blood flow under various flow rates. applied mathematics and computation, 217(11):50555067. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 249 [34] fisher c, rossmann j s. (2009) effect of non-newtonian behavior on hemodynamics of cerebral aneurysms. journal of biomechanical engineering, 131(9):091004. [35] replogle rl, meiselman hj, merrill ew. (1967) clinical implications of blood rheology studies. circulation, 36(1):148-160. [36] edward, r. (1969) merrill, rheology of blood. physiological reviews, 49(4):30-43. [37] morris cl, rucknagel dl, shukla r, gruppo ra, smith cm, blackshear p. (1989) evaluation of the yield stress of normal blood as a function of fibrinogen concentration and hematocrit. microvascular research, 37(3):323-338. [38] lee bk, xue s, nam j, lim h, shin s. (2011) determination of the blood viscosity and yield stress with a pressure-scanning capillary hemorheometer using constitutive models. korea-australia rheology journal, 23(1):1-6. [39] fedosov da, pan w, caswell b, gompper g, karniadakis ge. (2011) predicting human blood viscosity in silico. proceedings of the national academy of sciences, 108(29):1177211777. [40] barnes ha. (1997) thixotropy—a review. journal of non-newtonian fluid mechanics, 70(1):1-33. [41] how tv. (ed.). (1996). advances in hemodynamics and hemorheology (vol. 1). elsevier. [42] huang cr, siskovic n, robertson rw, fabisiak w, smitherberg eh, copley al. (1975) quantitative characterization of thixotropy of whole human blood. biorheology, 12(5):279282. [43] gaspar-rosas a, thurston gb. (1988) erythrocyte aggregate rheology by transmitted and reflected light. biorheology, 25(3):471-487. [44] pop gam, duncker dj, gardien m, vranckx p, versluis s, hasan d, slager cj. (2002) the clinical significance of whole blood viscosity in (cardio) vascular medicine. netherlands heart journal, 10(12):512-524. [45] cho yi, cho dj, rosenson rs. (2014) endothelial shear stress and blood viscosity in peripheral arterial disease. current atherosclerosis reports, 16(4):404-419. [46] grotta j, ackerman r correia j, fallick g, chang j. (1982) whole blood viscosity parameters and cerebral blood flow. stroke, 13(3):296-301. [47] brown m, marshall j. (1985) regulation of cerebral blood flow in response to changes in blood viscosity. the lancet, 325(8429):604-609. [48] tanner ri. (1985) engineering rheology, clarendon. oxford, 15, pp. 355-370. [49] ferguson j, kemblowski z. (1991) applied fluid rheology, elsevier, london, pp. 47–115. [50] macosko cw. (1994) rheology: principles, measurements, and applications. vhc publishers inc., new york. [51] rosencranz r, bogen sa. (2006) clinical laboratory measurement of serum, plasma, and blood viscosity. pathology patterns reviews, 125(suppl-1): s78-s86. [52] shin s, keum dy, ku yh. (2002) blood viscosity measurements using a pressure-scanning capillary viscometer. journal of mechanical science and technology, 16(12):1719-1724. [53] shin s, hou jx, suh js, singh m. (2007) validation and application of a microfluidic ektacytometer (rheoscan-d) in measuring erythrocyte deformability. clinical hemorheology and microcirculation, 37(4):319-328. [54] lee bk, xue s, nam j, lim h, shin s. (2011). determination of the blood viscosity and yield stress with a pressure-scanning capillary hemorheometer using constitutive models. korea-australia rheology journal, 23(1):1-6. [55] jun kang y, yeom e, lee sj. (2013) a microfluidic device for simultaneous measurement of viscosity and flow rate of blood in a complex fluidic network. biomicrofluidics, 7(5):054111. [56] kang d, wang w, lee j, tai yc, hsiai tk. (2015, june) measurement of viscosity of adult zebrafish blood using a capillary pressure-driven viscometer. in solid-state sensors, actuators and microsystems (transducers), 2015 transducers-2015 18th international conference on (pp. 1661-1664). ieee. [57] nemeth n, alexy t, furka a, baskurt ok, meiselman hj, furka i, miko i. (2009) interspecies differences in hematocrit to blood viscosity ratio. biorheology, 46(2):155-165. iium engineering journal, vol. 19, no. 1, 2018 fatahian et al. 250 [58] furukawa k, abumiya t, sakai k, hirano m, osanai t, shichinohe h, houkin k. (2016) measurement of human blood viscosity by an electromagnetic spinning sphere viscometer. journal of medical engineering & technology, 40(6):285-292. [59] pennes hh. (1948) analysis of tissue and arterial blood temperatures in the resting human forearm. journal of applied physiology, 1(2):93-122. [60] incropera fp. (2007) introduction to heat transfer, 5th ed. john wiley and sons inc., new york, ny, 581-619. [61] olufsen ms, peskin cs, kim wy, pedersen em, nadim a, larsen j. (2000) numerical simulation and experimental validation of blood flow in arteries with structured-tree outflow conditions. annals of biomedical engineering, 28(11):1281-1299. [62] he y, liu h, himeno r. (2004) a one-dimensional thermo-fluid model of blood circulation in the human upper limb. international journal of heat and mass transfer, 47(12):27352745. [63] atabek hb, chang cc. (1961) oscillatory flow near the entry of a circular tube. zeitschrift für angewandte mathematik und physik (zamp), 12(3):185-201. [64] ling sc, atabek hb. (1972) a nonlinear analysis of pulsatile flow in arteries. journal of fluid mechanics, 55(3):493-511. [65] craciunescu oi, clegg st. (2001) pulsatile blood flow effects on temperature distribution and heat transfer in rigid vessels. transaction-american society of mechanical engineers journal of biomechanical engineering, 123(5):500-505. [66] back lh, cho yi, crawford dw, cuffel rf. (1984) effect of mild atherosclerosis on flow resistance in a coronary artery casting of man. journal of biomechanical engineering, 106(1):48-53. [67] milnor wr. (1992) hemodynamics, baltimore: williams and williams, p. 20. [68] chakravarty s, mandal pk. (2009) effect of heat and mass transfer on non-newtonian flow– links to atherosclerosis. international journal of heat and mass transfer, 52(25):5719-5730. [69] ahmad, f., hussain, s., & ansari, a. (2015) unsteady mhd blood flow with micropolar fluid characteristics and heat source through parallel plate channel. journal of applied environment & biological sciences, 5(4):80-86. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 development of rainfall forecasting model using machine learning with singular spectrum analysis pundru chandra shaker reddy1*, yadala sucharitha2 and goddumarri surya narayana3 1 department of computer science and engineering, cmr college of engineering & technology, hyderabad, india 2 department of computer science and engineering, cmr institute of technology, hyderabad, india 3 department of computer science and engineering, vardhaman college of engineering, hyderabad, india *corresponding author: chandu.pundru@gmail.com (received: 4thfebruary 2021; accepted: 14th april 2021; published on-line: 4thjanuary 2022) abstract:agriculture is the key point for survival for developing nations like india. for farming, rainfall is generally significant. rainfall updates are help for evaluate water assets, farming, ecosystems and hydrology. nowadays rainfall anticipation has become a foremost issue. forecast of rainfall offers attention to individuals and knows in advance about rainfall to avoid potential risk to shield their crop yields from severe rainfall. this study intends to investigate the dependability of integrating a data pre-processing technique called singular-spectrum-analysis (ssa) with supervised learning models called least-squares support vector regression (ls-svr), and random-forest (rf), for rainfall prediction. integrating ssa with ls-svr and rf, the combined framework is designed and contrasted with the customary approaches (ls-svr and rf). the presented frameworks were trained and tested utilizing a monthly climate dataset which is separated into 80:20 ratios for training and testing respectively. performance of the model was assessed using root mean square error (rmse) and nash–sutcliffe efficiency (nse) and the proposed model produces the values as 71.6 %, 90.2 % respectively. experimental outcomes illustrate that the proposed model can productively predict the rainfall. abstrak:pertanian adalah titik utama kelangsungan hidup negara-negara membangun seperti india. untuk pertanian, curah hujan pada amnya ketara. kemas kini hujan adalah bantuan untuk menilai aset air, pertanian, ekosistem dan hidrologi. kini, jangkaan hujan telah menjadi isu utama. ramalan hujan memberikan perhatian kepada individu dan mengetahui terlebih dahulu mengenai hujan untuk menghindari potensi risiko untuk melindungi hasil tanaman mereka dari hujan lebat. kajian ini bertujuan untuk menyelidiki kebolehpercayaan mengintegrasikan teknik pra-pemprosesan data yang disebut analisis-spektrum tunggal (ssa) dengan model pembelajaran yang diawasi yang disebut regresi vektor sokongan paling rendah (ls-svr), dan random-forest (rf), ramalan hujan. menggabungkan ssa dengan ls-svr dan rf, kerangka gabungan dirancang dan dibeza-bezakan dengan pendekatan biasa (ls-svr dan rf). kerangka kerja yang disajikan dilatih dan diuji dengan menggunakan set data iklim bulanan yang masing-masing dipisahkan menjadi nisbah 80:20 untuk latihan dan ujian. prestasi model dinilai menggunakan root mean square error (rmse) dan nash – sutcliffe efficiency (nse) dan model yang dicadangkan menghasilkan nilai masing-masing sebanyak 71.6%, 172 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 90.2%. hasil eksperimen menggambarkan bahawa model yang dicadangkan dapat meramalkan hujan secara produktif. keywords:singular-spectrum-analysis; machine learning;rainfall; svr; rf 1. introduction india's welfare is farming, where most the agribusiness is subject to rainfall as its standard wellspring of water, the time and proportion of rainfall hold high significance and can affect the whole economy of the country. weather plays a major part in our regular day to day life. climate estimating is one of the most testing issues seen by the world, in the latest couple of centuries in the field of science and innovation. as india's economy notably relies upon cultivation, rainfall has a significant impact [1]. variation in the timing of rainfall and its quantity makes estimating rainfall is a challenge for meteorological researchers. predicting is one the greatest difficulties for researchers from an assortment of fields, for example, climate data mining, ecological machine learning, functionalhydrology, and numerical prediction, to make a forecast model for precise rainfall. climate anticipation stands apart for all nations around the world in all the advantages and administrations gave by the meteorological department [2]. rainfall anticipation is significant because severe and sporadic rainfall can have numerous effects like obliteration of yields and farms, harm of property so a superior anticipating model is crucial for an early notice that can limit dangers to life and property and also dealing with the farming a better way. this forecasting predominantly helps ranchers and furthermore, water assets can be used proficiently [3]. rainfall forecast is a difficult task and the outcomes ought to be precise. there are numerous equipment tools for anticipating rainfall by utilizing the climate conditions like temperature, humidity, pressure and so on. these customary strategies can't work in a proficiently so by utilizing ml-based strategies we can design for exact outcomes. we can only do it by having the past data examination of rainfall and can foresee the rainfall for future seasons [4]. taking into account that farming activities and crop yield depend on the rainfall distribution, monthly rainfall estimating is significant for farming planning and flood control. monthly rainfall anticipation with a suitable technique is a fundamental prerequisite to help water management. accordingly, monthly rainfall estimating is broadly appropriate in the field of hydrology. a few procedures for predicting time series have been designed on a worldwide scale [5]. machine learning (ml) or artificial intelligence (ai) and stochastic techniques dependent on information extraction procedures are the mainly utilized time-series modeling for hydrological estimating. nonetheless, ml has been given more consideration in weather anticipating, predominantly because stochastic approaches consider that the time-series are fixed and have a restricted capacity to catch profoundly nonlinear qualities of rainfall series. climatology time-series in tangible utilize are normally non-fixed and non-linear, so foreseeing the greatest values is very complex [6]. the hypothesis of the modular approach and the incorporation of various models have presently increased more enthusiasm for rainfall estimating to address this issue. regression, artificial neural network (ann), decision tree, random forest, fuzzy logic and group cycle of data handling methods are the majority utilized computational strategies utilized for climate forecasting. even though ann or svm in such non-linear issues is generally applied, direct elucidation of the guidelines is complex. then again, classification utilizing decision tree methods is helps display complex associations among attributes with the additional focal points of recognizing the significance of every attribute 173 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 [7]. rf and svr are computationally quick, effectively reasonable and don't need earlier knowledge of the data. because of these reasons, the utilization of rf in the case of prediction is picking up popularity. further, because of its ability to recognize the persuasive part of various features, it's rather beneficial to utilize rf in prediction applications. techniques dependent on data-driven, ml frameworks are broadly and effectively practical in numerous fields. ml has to turn into general inductive practice in rainfall estimation outstanding to its incredibly non-linear, adaptable, and data-driven method training without first receiving catchment and flow methods. notwithstanding the fame of ml techniques for time-series anticipation, they are not an effective device to foresee long-standing rainfall [8]. the most commonly utilized ml-based approaches for rainfall prediction include svm, genetic-programming, ann, and fuzzy-logic. crossbreed methodologies for tending to various climatology issues have been supported by meteorologists. least-square svr has newly got extensive consideration in different forecasting issues. in this research, ls-svr was picked because it is computationally more engaging than the conventional svr. in light of the utilization of quadratic programming by non-linear conditions, the conventional svr has computational challenges to choose the best possible solution. the hybrid reproduction approach dependent on ls-svr as an estimating model conveys incredible results. the singular spectrum analysis (ssa) is a proficient device that can divide the original time-series into a number of discrete segments, together with pattern designs, oscillating segments, and noise. ssa is applied to yearly, monthly, and hourly water temperature time-series to assess its ability and prediction capability to recognize major data from those series. ssa is used to extract the trend and it is a striking trend-extraction procedure, since it needs no approach portrayal of time-series and pattern, mines noisy time-series patterns through unsure motions in time-series, and susceptible to outliers. the noteworthiness of utilizing an appropriate ssa to translate unrefined input data to gracefully superior quality data earlier than being actualized as a design input [9]. existing methods have been led to investigate the benefit of united data pre-processing and ml; evidently, this is the unique that ssa combined among lssvr and rf has been utilized for rainfall estimation. we have seen that the majority of the works claiming higher accuracy have labeled rainfall into three or under three parts or have predicted rainfall utilizing ml methods but have not done rainfall anticipating utilizing ml strategies, very few of them have utilized barely any meteorological parameters for the anticipation of the rainfall [10]. most of the existing works are utilized the regression methods for forecasting rainfall and outcomes are not up to the mark due to selection of correct parameters for modeling. we have proposed a model to foresee the rainfall utilizing a combination ml-based techniques. the expectation of rainfall relies upon different climate attributes. categorizing the rainfall gives us great classification precision but our definitive objective is to anticipate the rainfall utilizing the other climate attributes [11]. in this investigation, objective isn't just to accurately classify rainfall but additionally effectively foresee the rainfall utilizing different climate attributes. there is persuading proof that the hybrid design dependent on ls-svr and rf is solid and that the ssa generates excellent results. subsequently, for enhancing the prediction efficiency of the state-of-art models, the data pre-processing procedure is implemented in the present investigation.the main objectives of the study are: 1. connecting ssa with ml-based methods (i.e., ls-svr and rf) to build hybrid models (ssa-lssvr and ssa-rf) for rainfall prediction. 174 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 2. comparison among the crossbreed models and the conventional models to assess the effectiveness of the data pre-processing strategy. the proposed work is concentrated around understanding the impacts of various meteorological attributes in rainfall estimation alongside an investigation of approaches that were utilized for anticipating rainfall, ml, and their restriction. the proposed model predicts the rainfall for the following season utilizing ml and forecasting approaches. our contribution to this problem is to predict the monthly rainfall using ml-based techniques and compare the performance of the model with state-of-the-art approaches. 2. literature review in this section, the existing works on rainfall forecasting proposed by various researchers are presented. abbot et al. [12] designed a rainfall forecasting model by artificial neural networks which produce more precise results compared to conventional statistical and numerical techniques. fahimi et al. [13] developed a hybrid framework called an adaptive-neuro-fuzzy-inference-system (anfis) for accurate long-term rainfall prediction. the outcome shows that the anfis is fit for catching the rainfall datadynamic behavior and produces agreeable results. kisi et al. [14] presented a framework, which combines anns with wavelet examination (wa) to estimate rainfalls and the model performance was compared with standard anfis. the outcomes exhibit that the proposed model is more productive than the anfis and is reasonable for rainfall anticipating. pandhiani et al. [15] described a rainfall anticipation model by ssa and svr for seasonal rainfall anticipation. the outcomes illustrate a noteworthy growth in model effectiveness contrasted to the standard svr approach. chan et al. [16] presented a monthly rainfall forecasting model by ls-svr. the investigation demonstrates that the svr design is better than the arima approach. the investigation infers that the clarification for svr acceptable execution lies in the non-direct quality of the caught and utilized svr space. karthikeyanet al. [17] described a comparative study of ml-based techniques on rainfall forecasting. they concluded has ann, svr, and rf exhibitions all in all good and rf conveyed the finest output. finally, there is no investigation of rfdependent models with a data pre-processing strategy for rainfall prediction, which timely this recent research to present a crossbreed model pairing rf with a data pre-processing approach. ji et al. [18] designed a rainfall prediction model by a decision tree with cart and c4.5 techniques. the proposed strategy predicts rainfall and it is characterized into three classes in hourly rainfall 0.0 to 0.5 mm as level 1, 0.5 to 2.0 mm as level 2, > 2.0mm as level 3. min minet al. [19] explored and designed an algorithm called quantitative rainfall estimates (qpes) based on random forest (rf), machine learning (ml) techniques for summer-time rainfall forecasting utilizing the himawari study dataset, cloud substantial properties products, and gfs-nwp data. in this study, they used a hybrid forecasting model that incorporates regression techniques with rfs classification for rainfall forecasting. the proposed method works tremendously and is different from the traditional and existing models because it utilizes the rfs ml approach for nowcasting. navidet al.[20]proposed amultiple linear regressions (mlr) technique for forecasting the rainfall in bangladesh. in mlr, first, apply correlation investigation and then regression analysis. mlr is very useful in future rain prediction and the results are very helpful to the agriculture sector for crop management. finally, they concluded has rainfall is influenced by many climate factors and utilized those factors in the forecasting of rainfall to increase accuracy. rodrigueset al. [21] designed the multiple linear regression (mlr) technique 175 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 and time-series arima techniques for monthly rainfall anticipation. the experimental results demonstrate that mlr and arima produce accurate forecast results over the traditional forecasting methods. in the end, the proposed performance of the two models is evaluated in terms of mape and the outcomes and the exactness of predictions made for rainfall by mlr (1.14) is found to be greater over arima (19.61). swainet al. [22] developed a multiple linear regression model (mlrm) to anticipate the yearly rainfall over the cuttack region, odisha, india, utilizing the annual average rainfall data of the previous three years. the proposed model results describe that it is capable to generate precise accuracy matching with the actual data values and the proposed model acquired high r2 (0.974) and adjusted r2 (0.963) when compared to the existing models.razeef mohdet al.[23]presented a rainfall forecast model utilizing nonlinear autoregressive with external input (narx), which was trained by the proposed self adaptive levenberg-marquardt (self adaptive lm) framework and to make it more adaptive, the lm approach was customized with the learning rate to make it more precise for predicting rainfall. the rainfall data were gathered from kashmir and jammu, india. the experiments were conducted and model performance was evaluated with rmse (1.721%) and mse (1.721%) values. faulinaet al. [24] designed a hybrid monthly rainfall prediction framework by using arima and anfis at particular locations in indonesia, namely pujon and wagir. the proposed model was executed and the performance of the model was compared in terms of accuracy against the existing works. the experimental outcomes display that the anfis model is more precise in forecasting the monthly rain-data of pujon, whereas the arima technique outcomes were superior in forecasting the monthly rain-data of wagir. crameret al. [25] describe an intelligent machine learning system for rainfall forecasting where the forecasts of a few target parameters are decisive to a particular purpose. the proposed model was applied and compared with the forecast performance of the base-lines and six other well-liked ml prediction models called m5 model trees, k-nearest neighbours (knn), radial basis neural networks (rbnn), svr, genetic programming, and m5 rules. the investigation results state that the ml prediction models are capable to do better than the conventional models. riveroet al. [26] implemented a short –term rain forecast model using bayesian enhanced modified approach (bema) with relative entropy. the experimental outcomes state the accuracy of the proposed methodology through diverse forecasting models utilizing the smape index for short term rainfall sequence and chosen sequence from standards. mehr et al. [27] presented a new model called hybrid regression for advance month precipitation forecasting in northwest iran. it is designed using svr-ffa and it is trained and tested using monthly rainfall data. johny et al. [28] designed a framework named aeemd-ann for rainfall forecasting and the experimental outcomes show that it is flourishing in predicting swm precipitation of year 2002. samantaray et al. [29] used rnn, anfis and svm combinations for precipitation investigation. they conclude that svm is gives good performance compared to others. zhao et al. [30] developed an enhanced precipitation prediction model using five predictors. the experimental outcomes display that the irfm gives good accuracy with five predictors inside of one predictor. 3. study area and data collection weather data is in extremely enormous amount and it includes forty-seven (47) general parameters such as rainfall, temperature, humidity, sunshine and cloudy hours, wind speed, etc. the major problem of this section is to investigate and process theclimate 176 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 data of the study region, nellore district, andhra pradesh, india. the attributes have to be selected in such a way that it includes the effect of seasonal rainfall. we have to select different input and output variables and find a correlation between those variables using various strategies such as probability distribution method, karl pearson’s coefficient, etc. and preprocess the data using appropriate methods. 3.1 case study region nellore zone of andhra pradesh state in india is the investigation region for the evaluation of rainfall anticipation. nellore station (latitude 14°26' n/longitude 79°92' e) is located in the coastal andhra pradesh region and it is surrounded on the south and north by chittoor and prakasam districts, on the west by veligonda hills neighboring kadapa district and on the east by the bay of bengal as shown in fig. 1. the total area of the nellore region covers 1307600 hectares and 39 % of the region is bound to farming. the major crops around there are rice, sugarcane, cotton, sunflower, groundnut, and tobacco. rainfall got during the southwest monsoon (june-september) is one of the main factors for the groundwater and the average annual rainfall of the nellore is around 835 mm [31]. the study area is one of the most significant agricultural regions in the nation. rapid and independent industrialized development projects have caused environmental changes in the earlier period, consequently raised the need to evaluate elements impacting the present climate anticipation. the daily rainfall information, estimated in millimeters (mm), was acquired from the imd, hyderabad, ts, and india. severe rainfall is seen in many regions during june to september period because of the southwest monsoon (swm). during the swn monthly rainfall at certain regions goes up to 700 mm however during the lean time it stays under 50 mm. the nellore district encounters substantial rainfall and floods each year which causes river-bank erosions and landslides in several parts of the district. farming plays a significant job in the economy of the state. farming which is the principal livelihood of the individuals who establish almost 90% of the all-out populace is additionally influenced by the rainfalls and floods [32]. fig. 1: geographical area of nellore district (source: en.wikepedia.org). 177 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 3.2 dataset description to predict seasonal monthly rainfall, we have to portray various elements which indirectly or directly influence the rainfall. the input variables of rainfall estimation are maximum, minimum and average temperature (oc), vapor pressure (hpa), wind speed (km/h), humidity (%) and cloud cover (%). the dataset details are shown in table 1. table 1:list of input and output parameters sno variable name of the attribute short name type 1 x1 minimum temperature (°c) mintemp input 2 x2 maximum temperature (°c) maxtemp input 3 x3 average temperature (°c) avgtemp input 4 x4 vapor pressure (hpa) vp input 5 x5 wind speed (km/h) ws input 6 x6 relative humidity (%) rh input 7 x7 cloud cover (%) cc input 8 y rainfall (mm) rf output 3.3 primary source of data in this research, the 110 years of climate data (1901-2012) of nellore region, ap, india is taken from the indian meteorological department (imd), hyderabad, ts, india at http://www.imdhyderabad.gov.in, and national climatic data center, asheville, the usa at ncdc.noaa.gov in the form of monthly means. parameters like mintemp, maxtemp, avgtemp, vp, ws, rh and cc are considered as input values and rainfall as output parameter which relies on input attributes. we considered just the relevant, required elements for design the forecasting model. table 3.1 portrays the climate data depiction utilized in the rainfall prediction model. in our proposed model, we considered extended southwest monsoon season sets in by june and lasts till october while the northeast monsoon begins in october and ends in december. to figure out the attributes of the monthly rainfall series in nellore dist., the evocative statistics were utilized for investigating their rainfall properties. 4. proposed methodology the problem examined in this section is that of anticipation of precise monthly rainfall for the accompanying season dependent on the past climate dataset, by using relating prior data. the combined ssa with lssvm and rf framework is applied over this data so as to build up a model to anticipate the monthly rainfall value to the nellore region which is situated on the southeast coast of india, with the water of the bay of bengal. 4.1 least-squares support vector machine in this segment, we quickly discuss the basic hypothesis on ls-svr in time-series anticipation. given a training set as input xi and output yi, the regression equation that interfaces the input vector to the output can be defined as: the ls-svr, a novel kind of svr, involves a series of same supervised strategies that investigate data and recognize trends. it works well in solving convex quadratic issues with more intensity and produces good results for linear equations. further, it has the advantages of shortening the issue and solution finding without losing exactness. in this investigation, the ls-svr is utilized to anticipate monthly rainfall. in the accompanying 178 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 sector, we discuss the essential hypothesis on ls-svr in time-series anticipating. because of a trainingset as input xi and output yi, the regression equation is defined as follows in eq. (1). f(y) = wt ҩ(x) + b (1) where, ҩ(x) is a nonlinear mapping function. converting the regression issue in eq. (1) into a constrained-quadratic optimization issue, by diminishing the cost element, w and b can be determined. in the structural minimization rule, the regression issue can be originated in eqs. (2) and (3): min j (w, e) = 1 2 wt w+ ŕ 2 ∑ 𝑒𝑖 2𝑚 𝑖=1 (2) subject to the following limitations: yi = wt ҩ (xi) + b + ei (i = 1, 2, : : : , m) (3) where ŕ represents the consequence term and ei is the training-error for xi. to crack the optimization problem, the answer for optimizing the ls-svm is to generate a lagrangian equation expressed in eq. (4): l (w, b, e, α) = j(w, e) – ∑ α𝑖 { 𝑚 𝑖=1 w t ҩ (xi) + b + eiyi} (4) where α𝑖 represents the lagrange values. by constructing the kernel function k(x, xi); mercer’s theorem can be fulfilled. next, the ls-svr method is executed in equation (5): f(x) = ∑ α𝑖 𝐾(𝑥, 𝑥𝑖) + 𝑏 𝑚 𝑖=1 (5) 4.2 random forest random-forest is the most remarkable ml technique for analytics, including a collection of basic trees. rf is an improved version of the decision-tree dependent on the strategy for bagging. in bagging, numerous stochastic-error situations are performed by picking training-sets independently and arbitrarily from the training set; totaling the anticipation of every individual trained model is cultivated by taking its average value. rf can likewise evaluate the noteworthiness of disclosing factors to the estimate as per the straightforward guideline, "the more pertinent the illustrative variable, the more significant the impact on the prediction" to utilize the rf model for the selection of factors. in bootstrap-sampling, the annotations are isolated into two parts for every approach: in-bagsubset and out-of-bag subset [33]. the out-of-bag subsets might be utilized to decide the noteworthiness for every testing attribute: (1) randomizing the qualities for one picked logical attribute in the out-of-sack subset; (2) utilizing the randomized out-of-sack-subset and the first example to make new expectations; (3) testing the importance of the picked illustrative attribute by expanding the mse of the new conjecture. 4.2 singular spectrum analysis ssa illustrates a powerful way to deal with time-series investigation in numerous fields of research. it is especially significant when time-series are disintegrated into significant parts like trends, motions, and noise. a significant advantage of the ssa method is that it is non-parametric, which means it tends to be custom fitted to the basic informational index and refuses the requirement for an earlier method [34]. consequently, the ssa is viewed as a model-free technique. as indicated by, two valuable stages are engaged with the ssa strategy: decomposition and reconstruction. the method of decomposition consists of two stages: combining and singular-value-decomposition 179 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 (svd). this disintegration is the fundamental outcome of the ssa technique and it is significant when every restored sub-section can be sorted as either a sample design or as a part of the noise. embedding is the first stage in the ssa technique. this strategy changes the fitted time-series to a multi-dimensional vector series. singular value decomposition (svd) is the trajectory-matrix is the principal module of the decomposition procedure. 4.3 linking ssa with ls-svr and rf the monthly rainfall values were normalized by their particular means and standarddeviations earlier to training the standard approaches (ls-svr and rf). to train these approaches, the normalized rainfall values are utilized. two elements, the penalty-term and the kernel-width should be chosen in the calibration procedure of the ls-svr. the matrix-search strategy is used for improving elements for the period of the calibrating time of the ls-svr. it is fit for delivering optimum element set and can conquer the issues of over-fitting of the approach through the cross-validation system. rf has two elements, the number of factors √𝑀and the number of trees (ntree), which should be estimated. √𝑀 would for the most part produce close ideal outcomes, so the estimation of √𝑀 was chosen by experimentation utilizing the incentive around √𝑀 (estimation of m is 4). the scope of ntree from 0 to 3000 was utilized to look through the best worth. be that as it may, no significant change was accomplished contrasted with the default incentive for ntree of 750. subsequently, the estimation of 750 for ntree was embraced in this research. the monthly rainfall of nellore station was taken from 1925–2000 and the initial 60years of rainfall data were applied for training and the leftover 15 years of rainfall data were utilized for validation. the areal rainfall prediction for the nellore station was executed utilizing the ls-svr and rf. the set of suitable inputs is a significant worry for ls-svr and rf modelling. diverse mix of forerunner values of the rainfall data were considered as inputs (i.e., (1) p(t); (2) p(t), p(t-1); (3) p(t), p(t-1), p(t-2)). the output is rainfall time-series data to be predicted with 1-, 2-, and 3-month lead-time (i.e., p(t+1), p(t+2), and p(t+3)). the crossbreed models were acquired by consolidating two distinct strategies. taking into account the ssa's strength, these approaches are intended to progress determining execution and dependability. the outcomes of the normal and crossbreed models are contrasted to evaluate the accuracy of the model in rainfall anticipation. fig. 2: the famework of the proposed rainfall prediction model. 180 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 the proposed framework has the following steps and is depicted in fig. 2. 1. at first, the time-series of rainfall data was rotten into various principle components (pcs) utilizing ssa. 2. the appropriate pcs are determined based on the pattern or time of every series and new series of each parameter is established by including the essential parts to be characterized. 3. ls-svr and rf approaches are designed for each part of the reconstruction so the design of ls-svr and rf is distinctive for every segment of the restoration. 4. at last, ls-svr and rf approaches are fed with the new series to anticipate the future rainfalls for 1-, 2-, and 3, 4-month lead-time. this is the main thought of pairing ssa with ml strategies. 4.4 forecast verification the proposed model performance is assessed in terms of rmse and nse, for the calibration and testing duration. the formulas are represented in eqs. (6) and (7) respectively. rmse = √ 1 𝑛 ∑ (𝑋 − 𝑌)2𝑛𝑖=1 (6) where, x and yare the fitted and predicted values correspondingly. lesser values of rmse recommend higher precision. nse = 1∑ (𝑋−𝑌)2𝑛𝑖=1 ∑ (𝑋−𝑀)2𝑛𝑖=1 (7) where m is the mean of the fitted values. an nse of 0.75–1.0 relates to“excellent” accuracy, 0.65–0.75 to “good” precision, and 0.5–0.65 to a “sensible precision”, while values below 0.5 imitate unacceptable precision. in spirit, the nearer nse is to 1, the more precise is predicted. 5. results and discussion in this article, we designed the monthly rainfall prediction approaches for 1, 2, 3, 4month lead time for the nellore station. the performance of the standard and hybrid models is compared. the variation is that the customary approaches utilized the direct noisy data as model input, while the crossbreed models utilized the deteriorated input data produced by ssa rather than unrefined data. table 2 displays the prediction performances for 1, 2, and 3, 4month intervals for the customary and hybrid models in terms of rmse and nse. table 2:prediction performances of the proposed models model rmse nse 1-month 2-month 3-month 4-month 1-month 2-month 3-month 4-month lssvr 194.58 193.31 199.56 199.85 0.04 0.06 0.05 0.07 ssa-lssvr 72.29 69.48 71.09 73.54 0.96 0.95 0.86 0.84 rf 197.87 199.24 194.18 200.54 0.04 0.05 0.04 0.03 ssa-rf 111.76 126.77 132.83 142.56 0.73 0.59 0.49 0.65 181 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 in table 3, it is seen that rmse and nse display extremely deprived values for the customary methods utilizing raw data when contrasted with the crossbreed models utilizing data created by ssa. there is additional proof that the customary approaches have been inadequately approved for each interval. the ls-svr outcome is noisesensitive and might not be successful when the degree of clamor is lofty. thusly, the lssvr pairing with the ssa separating the crude rainfall data will diminish the noise impacts and its helpful in enhancing the model performance. figures 3(a,b) and 4(a,b) outline the time-series charts of the fitted and one-month lead-time anticipated rainfall by the customary and hybrid approaches of nellore station. from the figures, we uncover that the predicted values from the crossbreed models are nearer to fitted values than the values estimated by the standard models. the rainfalls anticipated by the crossbreed models were discovered to be firmly restricted to the line of uniformity, though the rainfall determined by the customary models is not near the line of balance. 5.1 comparative analysis the proposed hybrid models are predicted the monthly rainfall reasonably and produced significant results. the proposed model accuracy is assessed by rmse and nse and the results display that the ssa-lssvr and ssa-lsrf are good compare to lssvr and lsrf respectively. in this section, the proposed model performance is compared with existing models in terms of rmse, nse. the results show that the proposed hybrid framework looking good compared to existing techniques in monthly rainfall prediction of nellore station. here we had taken the average values of 1-, 2-, 3-, 4month percentages rmse, and nse values for comparison of the proposed method. these comparison values are displayed in table 3. table 3:the proposed model performance comparison with existing techniques sno model name rmse (%) nse 1 deep esn model (echo state network) [9] (2019) 1.51 0.02 2 multiple linear regression [8] (2020) 26.5 0.837 3 artificial neural network [11] (2018) 68.49 0.69 4 the proposed model (ssa-lssvar, ssa-lsrf) 0.716 0.902 fig. 3a: fitted and predicted values for lssvr model. 0 50 100 150 200 250 300 1 9 6 1 1 9 6 2 1 9 6 3 1 9 6 4 1 9 6 5 1 9 6 6 1 9 6 7 1 9 6 8 1 9 6 9 1 9 7 0 1 9 7 1 1 9 7 2 1 9 7 3 1 9 7 4 1 9 7 5 r a i n f a l l( m m) time ls-svr actual predicted 182 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 fig. 3b: fitted and predicted values for ssa-lssvr model. fig. 4a: fitted and predicted values for lsrf model. fig. 4b: fitted and predicted values for ssa-lsrf model. 0 50 100 150 200 250 300 1 9 6 1 1 9 6 2 1 9 6 3 1 9 6 4 1 9 6 5 1 9 6 6 1 9 6 7 1 9 6 8 1 9 6 9 1 9 7 0 1 9 7 1 1 9 7 2 1 9 7 3 1 9 7 4 1 9 7 5 r a i n f a l l( m m) time ssa-lssvr actual predicted 0 50 100 150 200 250 300 1 9 6 1 1 9 6 2 1 9 6 3 1 9 6 4 1 9 6 5 1 9 6 6 1 9 6 7 1 9 6 8 1 9 6 9 1 9 7 0 1 9 7 1 1 9 7 2 1 9 7 3 1 9 7 4 1 9 7 5 r a i n f a l l( m m) time ls-rf actual predicted 0 50 100 150 200 250 300 1 9 6 1 1 9 6 2 1 9 6 3 1 9 6 4 1 9 6 5 1 9 6 6 1 9 6 7 1 9 6 8 1 9 6 9 1 9 7 0 1 9 7 1 1 9 7 2 1 9 7 3 1 9 7 4 1 9 7 5 r a i n f a l l( m m) time ssa-lsrf actual predicted 183 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 6. conclusion and future work the current research investigated the dependability of integrating a data preprocessing approach (ssa) with ml-based strategies, lssvr and rf, for monthly rainfall estimating in nellore station, india. the study infers that the ssa can acquire and give magnificent forecasts to noteworthy hydrological time series segments with unique uneven practices, for example, rainfall and runoff series. one of the significant discoveries is that the crossbreed approaches (ssa-lssvr and ssa-rf) have superior accuracy over the customary approaches (ls-svr and rf). it tends to be inferred that the crossbreed models are a potential modelling procedure that can be applied to anticipate the monthly rainfall in the current examination area. connecting the rainfall properties of the study area to the estimating design exhibitions is recommended to be additionally examined in future research. further, only one data pre-processing strategy has been accepted; consequently, future work may consider different pre-processing methods and contrast their accuracies with accomplishing added exact prescient results. additionally, just the areal monthly rainfall data from one station was utilized in the present research. more study regions ought to be incorporated for testing the findings. references [1] bojang po, yang tc, pham qb, yu ps. (2020)linking singular spectrum analysis and machine learning for monthly rainfall forecasting. applied sciences, 10(9):1-20. [2] kashiwao t, nakayama k, ando s, ikeda k, lee m, bahadori a. (2017) a neural networkbased local rainfall prediction system using meteorological data on the internet: a case study using data from the japan meteorological agency. applied soft computing, 56(1):317-330. [3] reddy pc, babu as. (2017) survey on weather prediction using big data analystics. insecond international conference on electrical, computer and communication technologies (icecct), ieee: pp 1-6. [4] basha cz, bhavana n, bhavya p, sowmya v. (2020) rainfall prediction using machine learning & deep learning techniques. ininternational conference on electronics and sustainable communication systems (icesc), ieee: pp 92-97. [5] choi c, kim j, kim j, kim d, bae y, kim hs. (2018) development of heavy rain damage prediction model using machine learning based on big data. advances in meteorology, 2018 (2):1-11. [6] reddy pc, babu as. (2020) an enhanced multiple linear regression model for seasonal rainfall prediction, international journal of sensors, wireless communications and control, 10(1):473-483. [7] das s, chakraborty r, maitra a. (2017) a random forest algorithm for nowcasting of intense rainfall events. advances in space research, 60(6):1271-82. [8] moulana m, roshitha k, niharika g, sai ms. (2020) prediction of rainfall using machine learning techniques. international journal of scientific & technology research, 9(3):236240. [9] yen mh, liu dw, hsin yc, lin ce, chen cc. (2019) application of the deep learning for the prediction of rainfall in southern taiwan. scientific reports, 9(1):1-9. [10] reddy pc, sureshbabu a. (2019) an applied time series forecasting model for yield prediction of agricultural crop. ininternational conference on soft computing and signal processing, springer: pp 177-187. [11] shah u, garg s, sisodiya n, dube n, sharma s. (2018) rainfall prediction: accuracy enhancement using machine learning and forecasting techniques. infifth international conference on parallel, distributed and grid computing (pdgc), ieee: pp 776-782. [12] abbot j, marohasy j. (2013) the potential benefits of using artificial intelligence for monthly rainfall forecasting for the bowen basin, queensland, australia. water resources management vii, 171:287. 184 iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 [13] fahimi f, yaseen zm, el-shafie a. (2017) application of soft computing based hybrid models in hydrological variables modeling: a comprehensive review. theoretical and applied climatology, 128(3-4):875-903. [14] kisi o, shiri j. (2011) rainfall forecasting using wavelet-genetic programming and waveletneuro-fuzzy conjunction models. water resources management, 25(13):3135-3152. [15] pandhiani sm, shabri ab. (2013) time series forecasting using wavelet-least squares support vector machines and wavelet regression models for monthly stream flow data. open journal of statistics, 3: 183-194. [16] chan jc, paelinckx d. (2008) evaluation of random forest and adaboost tree-based ensemble classification and spectral band selection for ecotope mapping using airborne hyperspectral imagery. remote sensing of environment, 112(6):2999-3011. [17] karthikeyan l, kumar dn. (2013) predictability of nonstationary time series using wavelet and emd based arma models. journal of hydrology, 502:103-119. [18] ji sy, sharma s, yu b, jeong dh. (2012) designing a rule-based hourly rainfall prediction model. inieee 13th international conference on information reuse & integration (iri), ieee, pp 303-308. [19] min m, bai c, guo j, sun f, liu c, wang f, xu h, et al. (2018) estimating summertime rainfall from himawari-8 and global forecast system based on machine learning. ieee transactions on geoscience and remote sensing, 57(5): 2557-2570. [20] navid mai, niloy nh. (2018) multiple linear regressions for predicting rainfall for bangladesh. communications, 6(1): 1-4. [21] rodrigues j, deshpande a. (2017) prediction of rainfall for all the states of india using autoregressive integrated moving average model and multiple linear regression. in international conference on computing, communication, control and automation (iccubea), ieee: pp 1-4. [22] swain s, patel p, nandi s. (2017) a multiple linear regression model for rainfall forecasting over cuttack district, odisha, india. in 2nd international conference for convergence in technology (i2ct), ieee: pp 355-357. [23] mohdrazeef, butt ma, and baba mz. (2018) salm-narx: self adaptive lm-based narx model for the prediction of rainfall. in 2nd international conference on i-smac (iot in social, mobile, analytics and cloud)(i-smac) i-smac (iot in social, mobile, analytics and cloud)(i-smac), ieee:pp 580-585. [24] ria f, lusia da, otok bw, kuswanto h. (2012) ensemble method based on anfis-arima for rainfall prediction. in international conference on statistics in science, business and engineering (icssbe), ieee: pp 1-4. [25] cramer s, kampouridis m, freitas aa, alexandridis ak. (2017) an extensive evaluation of seven machine learning methods for rainfall prediction in weather derivatives. expert systems with applications, 85(2): 169-181. [26] rivero cr, pucheta ja, baumgartner js, laboret so, sauchelli vh, patiño hd. (2016) short-series prediction with bema approach: application to short rainfall series. ieee latin america transactions,14(8): 3892-3899. [27] mehr ad, nourani v, khosrowshahi vk, ghorbani ma. (2019) a hybrid support vector regression–firefly model for monthly rainfall forecasting. international journal of environmental science and technology, 16(1):335-346. [28] johny k, pai ml, adarsh s. (2020) adaptive eemd-ann hybrid model for indian summer monsoon rainfall forecasting. theoretical and applied climatology, 18(1):1-7. [29] samantaray s, tripathy o, sahoo a, ghose dk. (2020) rainfall forecasting through ann and svm in bolangir watershed, india. insmart intelligent computing and applications, springer: pp 767-774. [30] zhao q, liu y, ma x, yao w, yao y, li x. (2020) an improved rainfall forecasting model based on gnss observations. ieee transactions on geoscience and remote sensing, 58(7):4891-900. [31] https://en.wikipedia.org/wiki/nellore_district. 15.01.2021 [32] https://en.climate-data.org/asia/india/andhra-pradesh/nellore-6270/. 15.01.2021 185 https://en.wikipedia.org/wiki/nellore_district https://en.climate-data.org/asia/india/andhra-pradesh/nellore-6270/ iium engineering journal, vol. 23, no. 1, 2022 reddy et al. https://doi.org/10.31436/iiumej.v23i1.1822 [33] abdel-kader h, abd-el salam m, mohamed m. (2021) hybrid machine learning model for rainfall forecasting. journal of intelligent systems and internet of things, 1(1):5-12. [34] pham qb, yang tc, kuo cm, tseng hw, yu ps. (2021) coupling singular spectrum analysis with least square support vector machine to improve accuracy of spi drought forecasting. water resources management, 35(3):847-868. 186 microsoft word 157-778-1-ed-1 completed.docx iium engineering journal, special issue, mechanical engineering, 2011 arunchala 115 performance deterioration of thermosiphon solar flat plate water heater due to scaling arunchala u.c. department of mechanical and manufacturing engineering, manipal institute of technology, udupi 576104, karnataka, india arunchandavar@yahoo.co.in abstract: the performance of flat plate solar water heater deteriorates within five to twelve years of their installation due to factors related to manufacturing, operating conditions, lack of maintenance etc. especially, problem due to scaling is significant as it is based on quality of water used. the remaining factors are system dependent and could be overcome by quality production. software is developed by incorporating hottel whillier bliss (h-w-b) equation to ascertain the effect of scaling on system efficiency in case of thermosiphon system. in case of clean thermosiphon system, the instantaneous efficiency calculated at 1000 w/m2 radiation is 72 % and it drops to 46 % for 3.7 mm scale thickness. the mass flow rate is reduced by 90 % for 3.7 mm scale thickness. whereas, the average temperature drop of water in the tank is not critical due to considerable heat content in water under severe scaled condition. but practically in case of major scale growth, some of the risers are likely to get blocked completely which leads to negligible temperature rise in the tank. abstrak: prestasi plat rata pemanas air suria merosot selepas lima hingga dua belas tahun pemasangannya disebabkan faktor-faktor yang berkaitan dengan pembuatannya, cara kendaliannya, kurangnya penyelenggaraan dan sebagainya. terutama sekali, masalah disebabkan scaling (tembunan endapan mineral) perlu diambil berat kerana ianya bergantung kepada kualiti air yang digunakan. faktor-faktor selebihya bersandarkan sistem dan ia boleh diatasi dengan mempertingkatkan kualiti pembuatannya. perisian komputer dihasilkan dengan menggunakan persamaan hottel whillier bliss (h-w-b) untuk menentukan kesan scaling terhadap kecekapan sistem dalam termosifon. dalam sistem termosifon bersih, kecekapan seketika dikira pada 1000 w/m2 , pada kadar radiasi 72 % dan ianya jatuh kepada 46 % untuk ketebalan skala 3.7 mm. kadar aliran jisim berkurangan sebanyak 90 % untuk ketebalan skala 3.7 mm. manakala, penurunan suhu purata air di dalam tangki tidaklah kritikal, disebabkan oleh kandungan haba yang tinggi di dalam air di bawah keadaan kerak yang teruk. tetapi dalam kes tumbesaran kerak yang genting, sesetengah penaik akan tersumbat sepenuhnya, mengakibatkan peningkatan suhu di dalam tangki boleh diabaikan. keywords: thermosiphon system; scaling; instantaneous efficiency; h-w-b equation 1. introduction the statistics reflect the reserves of fossil fuels that currently power society and their harmful side effects such as pollution that threatens human health and greenhouse gases iium engineering journal, special issue, mechanical engineering, 2011 arunchala 116 associated with climate change. hence finding sufficient supplies of clean energy for the future is one of society’s most daunting challenge. renewable sources are being thought of as additional resources rather than as substitutes or alternatives because of their inherent nature. the use of non-hydro modern renewable energy technologies (including wind, solar, geothermal, tide and wave energy, and bioenergy) sees the fastest rate of increase in the present energy scenario. now a days both solar electricity and thermal systems are popular. in thermal route particularly low and medium thermal systems have wide publicity due to simple design and low operating and maintenance cost. these are meant for water heating, steam generation, refrigeration etc. solar thermal heating provides an elegant direct route of energy conversion without going through the route of coal thermal plant electrical energy transmission distribution resistance heating. use of sun’s energy to heat water is not a new idea. more than one hundred years ago, black painted water tanks were used as simple solar water heaters (swh) in a number of countries. the flat plate solar water heaters (fswh) is widely used today for the collection of low temperature solar thermal energy. numerous studies have been performed particularly on thermosiphon swh systems since they have the advantage of avoiding a water pump for circulating water in the collector. the thermosiphon fswh had been designed, tested and experimentally validated under no draw off condition by close [1]. here the insolation curve for a clear day is predicted from empirical data, which shows good agreement with experimental result. similar study is carried out by gupta and garg [2] using fortran ii. a test procedure to estimate the daily mean values of the h-w-b constants from the measured variation of the storage tank temperature is investigated by wijeysundera et al. [3].two flat-plate collectors were tested over a period of 11 days each to study the feasibility of the test procedure. the tests were conducted under variable weather conditions and inlet water temperatures. the standard deviations for the daily mean values of h-w-b constants were about 2.8 percent and 4 percent, respectively. the differences between the daily mean values obtained by the proposed method and the steady-state test values for a0 are about 4 percent to 7 percent, while for a1 the differences are 9 percent to 13 percent. the collector efficiency is dependent on the temperature of the plate which in turn is dependent on the nature of flow of fluid inside the tube, solar insolation, ambient temperature, top loss coefficient, the emissivity of the plate and glass cover, slope, etc. theoretical and experimental analysis performed on a fpc by raja sekhar et al. [4] concluded that the emissivity of the absorber plate has a significant impact on the top loss coefficient and consequently on the efficiency of the fpc. based on the literature review on fswh, it is concluded that design method, fabrication procedure and performance tests are well established. in swh i.e. absorber tubes and heat exchanger, scaling can reduce heat transfer due to the additional conductive resistance across the scaled layer, and increase the fluid pressure drop due to narrowing of the flow passage. scaling tendency in case of cross-linked polyethylene (pex), polypropylene random copolymer (pp-r) and copper tubes are studied by sanft et al. [5]. the water with total calcium and carbonate concentration of 3x10−3 m and a ph of approximately 9.1, yielding a supersaturation of 7.8, was pumped through the tubes at a velocity of 0.07 m/ s for 2.5, 5, and 7.5 h. the flow was laminar with reynolds numbers of >1000. the result shows scaling rates iium engineering journal, special issue, mechanical engineering, 2011 arunchala 117 respectively 5.1 x 10-4, 8.3 x 10-4 and 3.0 x 10-4 g/m2s (caco3) when the specimens were exposed to 7.5 h. wu et al.[6] presented an experimental study of scaling of polypropylene and copper tubes exposed to flowing tap water over an eight week period. the chemistry of the tap water is controlled to provide mildly supersaturated conditions at ph equal to 8 and 40°c. the scaling rates for polypropylene and copper tubes are 0.8 x 10-10 and 1.7 x 10-10 (mol ca)/(m2s), respectively. study by baker and vliet [7], compared different indirect swh designs in regard to their susceptibility to problematic scaling using software trnsys. the results predicted the wrap-around design’s performance to be less affected by scale than the external heat exchanger design. literature to date has focused on scaling effect in heat exchangers, flow systems and heat exchanger type swh. however, information related to quantifying the effect of scaling on the performance of direct swh systems is inadequate. 2. solar water heaters broadly speaking, the swh are of three categories viz. heat exchanger type, evacuated tube and flat plate type. they receive both beam and diffuse solar radiation and do not require tracking of the sun. mostly, both heat exchanger and evacuated tube types are installed in places where water hardness is considerable. the removal of scale deposited over the heat transfer surface is quite easy in both the systems. but, these systems are not as simple as fswh. hence fswh is very popular due their work simplicity, robust design and low maintenance cost. either thermosyphon or forced circulation mode is adopted in this case. in case of thermosiphon system as shown in fig.1, the water passing through the riser gets heated up and is delivered to the storage tank due thermosiphon effect. the re-circulation of the same water through absorber panel in the collector raises the temperature to around 80°c on a good sunny day. the bottom of storage tank is atleast a feet higher than the top of the collector to avoid reverse flow during the night. thermosiphon systems still remain as one of the most interesting technologies for exploitation of solar energy. their remarkable efficiencies, combined with simplicity of construction, autonomy in operation, absence of moving parts and thus the minimization of necessary maintenance, make them an interesting alternative to forced circulation systems. fig. 1: thermosiphon system. iium engineering journal, special issue, mechanical engineering, 2011 arunchala 118 3. performance deterioration analysis of fswh impurities present in water used for heating purpose in flat plate collector (fpc), forms deposits in the flow passage. this process of deposition of chemicals on surface is called scaling. it affects both heat transfer and fluid flow. scaling can only occur from water which is supersaturated with respect to a scaling salt, and such kind of water is often described as being hard. calcium carbonate is the most common type of scale produced from domestic water. software called flatscale is developed by incorporating hottel whillier bliss (hw-b) equation to ascertain the effect of scaling on energy efficiency indices like instantaneous efficiency, mass flow rate, overall heat loss coefficient etc. in case of thermosiphon system. the various parameters which deteriorate the performance of thermosiphon fswh due to scaling are discussed here. the instantaneous efficiency is given by = (1) the useful heat gain from the system is = − − (2) the heat loss and gain can thus be calculated, if the average plate temperature is known. however, this temperature is generally not known. it will, therefore, be necessary to consider the flow of heat in the absorber plate and across the fluid tubes to the fluid so that the values of tp can be related to the value of the inlet fluid temperature, which is a known quantity. hence equation (1) is further modified as = − ( ) (3) collector heat removal factor ( ) is the ratio of the actual useful heat gain to the gain which would occurs if the collector absorber plate was at the temperature of water inlet. = ̇ 1 − − ′ ̇ (4) in terms of heat transfer resistances along the heat flow path from the absorber plate to water, collector efficiency factor (f´) can be written for scaled fpc as [8], ′ = [( ) ] / / (5) in eq. (5), the last term in the denominator accounts for the thermal resistance of the scale. figure 2 illustrates various dimensions of a riser with scaling. iium engineering journal, special issue, mechanical engineering, 2011 arunchala 119 since the value of , and are essentially constant, for the given fpc design and its working condition, it is seen from eq. (3) that if is plotted against ( − ) i⁄ a straight line with a negative slope would be obtained. the intercept on the y-axis would give the value of ⁄ , while the slope of the line would give the value of ⁄ . in eq. (1), the value of is based on the collector gross area. it could be based on the absorber plate area also. in that case, the term ⁄ would drop out of eq. (3). the intercept on the yaxis would then be ( ) and the slope of the line would be ( ). hence, = 0 − 1 ( ) (6) equation (6) is widely known as h-w-b equation [9]. here, the value of , and are constant and only values of h-w-b constants ( 0 and 1) are going to change due to scaling. fig. 2: risers with scale formation. fig. 3: thermosiphon head in fpc. 4. pressure drop/pressure gain in the system the hydrodynamic effects of scaling are restriction in flow area inside the collector and associated increased flow resistance. the pressure gain and drop relationship of the collector are determined as functions of mass flow rate and then solved to find the mass flow rate. the iium engineering journal, special issue, mechanical engineering, 2011 arunchala 120 pressure drop in the system comprises of frictional drop in risers and headers, connecting pipes, pipe fittings and storage tank. the larger frictional pressure drop occurs in the risers. the pressure difference required for a thermosiphon flow (pressure gain) is due to the density difference between the collector outlet and inlet water [10]. the pressure gain ‘∆pgain’ responsible for the flow can be considered in two parts (fig. 3), one representing the pressure gain across the collector ‘∆pc’ and the other between the top and bottom of the tank ‘∆ptank’ such that ∆ = ∆ + ∆ (7) let t(x) is the temperature at distance x from the inlet of the collector, the pressure due to buoyancy forces (∆pc and ∆ptank) can be evaluated by the following equations [11]: ∆ = ∫ ( ( ) − ) ∆ = ( − ) (8) then ∆ = ∫ ( ( ) − ) + ( − ) (9) equation (9) can be rewritten as [12] ∆ = ∆ [0.5 + ] (10) the useful heat gain from the riser is = ̇ ∆ (11) the instantaneous efficiency of the riser is the ratio between output and input power of the riser [13]. = (12) incorporating (11) and (12) in (10) to get, δ = ̇ [0.5 + ] 0 − 1 ( ) (13) the total frictional pressure drop ‘∆pdrop’ in the circuit can be separated into the contribution from the collector ‘∆pc’ and that from the piping components outside the collector ‘∆ppc’ as shown in fig. 4. iium engineering journal, special issue, mechanical engineering, 2011 arunchala 121 fig. 4: various pressure losses in fswh. ∆ = ∆ + ∆ (14) the various losses within the collector (∆pc) is the sum of friction loss in the risers ‘∆prf’, friction loss in the header and footer ‘∆phff’ and losses due sudden contraction and expansion ‘∆pec’ in the footer-riser-header assembly. ∆ = ∆ + ∆ + ∆ (15) similarly, different losses encountered in the piping components (∆ ) are the friction loss in connecting pipes ‘∆pcpf’, loss due bends fitted to connecting pipe ‘∆pcpb’ and entry and exit losses at the tank ‘∆ptank’. ∆ = ∆ + ∆ + ∆ (16) by considering laminar flow throughout the collector, eq.(14) is rewritten as ∆ = ∆ 1 + (1 + ) + ( ) + ∆ 1 + ( ) + ( ) (17) equation (17) gives the pressure drop in case of a clean fpc. but for a scaled fpc the pressure drop is given by ∆ = ∆ 1 + (1 + ) + ( ) + ∆ 1 + ( ) + ( ) (18) iium engineering journal, special issue, mechanical engineering, 2011 arunchala 122 for any flow system, if both the thermosiphon/pump pressure gain curve and the pressure drop characteristics of the load are known, the resulting flow rate from the two relationships can be solved [14]. since both the pressure drop and gain equation are the function of mass flow rate, the actual mass flow rate is that which balances the thermosiphon buoyancy force with the frictional resistance in the circuit as shown in fig. 5. by considering the storage tank capacity as 150 l, the average temperature of water in storage tank for any hour is calculated as below: = ( ) ( ) (19) fig. 5: pressure drop/gain versus mass flow rate characteristics. 5. results and discussion the detailed analysis of thermosiphon fswh is done by making use of flatscale. the various energy efficiency parameters like water temperature at collector outlet, water temperature in storage tank, absorber plate mean temperature, overall heat loss coefficient, mass flow rate etc. are brought out for different scale conditions. the assumptions made in the analysis are as follows:  steady state one dimensional heat conduction  thermal conductivity of scale composition is constant  absorber plate temperature is uniform throughout the ???  absorber plate effectiveness is constant  scale formation in risers only; no effect of scaling in header and footer  scale growth is uniform and identical in all risers  temperature of water in the storage tank is uniform  no water drawn off during the sunshine hours  hourly solar radiation level is constant  heat loss from the connecting pipe and storage tank to the surrounding is negligible  effect of wind speed is neglected iium engineering journal, special issue, mechanical engineering, 2011 arunchala 123 in the analytical analysis, a thermosiphon system of size 2 m x 1 m with storage tank of 150 l capacity is considered. the detailed specifications and material properties of fswh are considered. to compare the day long performance with different scale situation, an identical input condition is necessary. hence, the hourly variation of solar radiation and ambient temperature on a typical clean sky day is incorporated in the analysis and is as shown in fig. 6. to check the consistency and accuracy of flatscale, it is tested for the convergence of a0 and a1 values. the experimental validation of various efficiency indicating parameters is done as a separate study [8]. fig. 6: variation of solar radiation and ambient temperature with time. figure 7 shows the variation of mass flow rate with time for different scale conditions. it shows, the mass flow rate is a strong function of solar radiation. the mass flow rate is maximum during 12 noon as solar radiation level is 1000 w/m2. the trend of mass flow rate from morning to evening is similar for different scale conditions. the mass flow rate reduces with scale thickness due to rise in pressure drop. the fig. indicates only 13.8 % drop with 0.7 mm scaling. this variation widens as the scale thickness increases and in case of 3.7 mm scaling, the drop in mass flow rate is 89.5 % compared to scale free fpc. figure 8 indicates the variation of water outlet temperature with time. in case of a clean fpc, water temperature increases constantly throughout the day. further, as the scale thickness increases the maximum outlet temperature of water also rises. in case of 3.7 mm scaling, water attains maximum temperature (close to boiling point) during solar radiation of 1000 w/m2. since the mass flow rate is too low, the outlet water temperature trend follows the absorber plate mean temperature curve. it can be observed from the figure that the influence of scaling on water outlet temperature is nominal till 1.7 mm scale thickness. at the end of the day, the water temperature is fairly same in all cases. figure 9 shows the effect of scaling on absorber plate temperature for the entire day. this temperature is directly related to solar radiation level. if the mass flow rate in the system is considerable, the rise in absorber plate temperature is limited as in the case of 0 mm, 0.7 mm and 1.7 mm. in case of 2.7 mm and 3.7 mm scale thickness, the rise is credible as the mass flow rate is reduced. iium engineering journal, special issue, mechanical engineering, 2011 arunchala 124 figure 10 shows the variation of average temperature of water in the storage tank. the drop in temperature noted is 0.7 k in 0.7 mm scale thickness to 15.3 k in case of 3.7 mm scaling. the analytical result clearly indicates that even though the efficiency of fpc is reduced drastically with scaling, its effect on performance of fswh is not severe. this is due to lower mass flow rate with higher water temperature at collector outlet. the plot presents the upward trend in tank temperature throughout the day. but this rise is highly time based. as indicated, in the 8 – 10 hr and 14 – 17 hr region the rise is not sharp compared to 10 – 14 hr region. this is due to higher solar radiation level and better heat carrying capacity of water. fig. 7: variation of mass flow rate with time. fig. 8: variation of water outlet temperature with time. iium engineering journal, special issue, mechanical engineering, 2011 arunchala 125 fig. 9: variation of absorber plate mean temperature with time. fig. 10 : variation of water temperature in tank with time. iium engineering journal, special issue, mechanical engineering, 2011 arunchala 126 fig. 11 : variation of water energy content with scale thickness. figure 11 shows the storage tank water energy content during the day end by taking ambient temperature as 300 k. as indicated, the loss of energy gain is 6 % for 1.7 mm scaling and in case of 3.7 mm scale thickness, the energy gain drops by 38 %. the analytical result revealed the effect of uniform scaling in risers on water temperature in the storage tank as less significant. but, practically the scale growth pattern is not uniform. from the field study it is understood that, the growth is minimum to maximum from footer to header. for the initial growth of 1-2 mm, the scale coating is more or less concentric with the riser and further scale growth leads to complete blockage of some of the risers and partial opening of the rest. under this situation, the drop in storage tank water temperature is considerable and such result obviously deviates from analytical result. to understand its effect on two different cases are considered. in case of 2.7 mm scale thickness, 3 risers are blocked and for the thickness of 3.7 mm, 6 risers are blocked. these results are compared with 0 mm, 0.7 mm and 1.7 mm cases and shown in fig. 12. it shows that the maximum storage tank water temperature in case of 2.7 mm scale thickness with three risers blocked is 322 k compared to 334 k for 2.7 mm thickness without riser blockage. if the water flow rate through the fpc is stopped, there is no useful heat gain and the efficiency is zero. in this case, the absorber plate attains temperature called stagnation temperature. figure 12 shows the variation of stagnation temperature with time. the maximum temperature observed is 408 k. figure 13 presents the deviation of overall loss coefficient with solar radiation level. since both bottom and side loss coefficients are constant and top loss coefficient is a strong function of absorber plate temperature, the trend in absorber plate variation is repeated here. 0 5 10 15 20 25 30 0 0.5 1 1.5 2 2.5 3 3.5 4 t an k w at er e ne rg y co nt en t (m j) scale thickness, δ (mm) iium engineering journal, special issue, mechanical engineering, 2011 arunchala 127 fig. 12: variation of temperature with time. fig. 13: variation of overall loss coefficient with time. figure 14 shows the variation in a0 value for different scaling with time. this is an important parameter in calculating the instantaneous efficiency of fpc. since ′ ′ is taken as constant, this variation is directly coupled to collector heat removal factor. generally, for the given design and working condition, a0 is relatively constant. but under no scale condition, the sharp decline in a0 value is noted during the end of day. this is due to the absorption of only part of available radiation as water is already carried sufficient heat. plot shows considerable drop in a0 value with 2.7 mm and 3.7 mm thickness of scale. figure 15 indicates the deviation of a1 for different scale condition with time. the trend observed here is similar. since it is a product of fr and ul, under scaled conditions the value of fr reduces and ul increases. but the drop in fr value is significant compare to rise in value of ul, hence a1 decreases with different scaling conditions. iium engineering journal, special issue, mechanical engineering, 2011 arunchala 128 fig. 14: variation of a0 with time. fig. 15: variation of a1 with time. 6. conclusion the application of software to thermosiphon system has given the instantaneous efficiency as 72 % under clean condition for 1000 w/m2 solar radiation and it dropped to 46 % in case of 3.7 mm scale thickness. the mass flow rate was reduced by 90 % for 3.7 mm scale thickness and the highest temperature observed was 371 k. during no flow condition, absorber plate temperature reached was 408 k. under severe scaling, the energy gain drops by 38 %. . this was due to assumed condition of uniform and concentric scale growth in the risers. but in field, under such condition upper portion of most of the risers will be blocked and leads to negligible rise in tank water temperature. iium engineering journal, special issue, mechanical engineering, 2011 arunchala 129 references [1] d.j. close, the performance of solar water heaters with natural circulation, solar energy, no.6, 1962, pp. 33–40 [2] c. l. gupta and h p garg, system design in solar water heaters with natural circulation. solar energy, no.12, 1968, pp. 163–182 [3] n. e. wijeysundera, m. n. a. hawlader and k. y. foong, estimation of collector performance parameters from daily system tests, solar energy(asme), vol.118, february 1996, pp 30-36 [4] y. raja sekhar, k. v. sharma and m. basaveswara rao, evaluation of heat loss coefficients in solar flat plate collectors, arpn journal of engineering and applied sciences, vol. 4, july 2009, pp. 15-19 [5] patricia sanft, lorraine f. francis and jane h. davidson, calcium carbonate formation on crosslinked polyethylene (pex) and polypropylene random copolymer (pp-r), solar energy (asme), vol.128, 2006, pp. 251-254 [6] zhen wu, lorraine f. francis and jane h. davidson, scale formation on polypropylene and copper tubes in mildly supersaturated tap water, solar energy, 2009, pp. 636–645 [7] derek baker and gary vliet, designing solar hot water systems for scaling environments, solar energy (asme), vol. 123, feb. 2001, pp.43-47 [8] u. c. arunachala, m. siddhartha bhatt and l. k. sreepathi, scaling effect of direct solar hot water systems on energy efficiency, solar energy (asme), vol. 132, november 2010 [9] duffie j. a. and beckman w.a., solar engineering of thermal processes, 2nd ed., wiley interscience, new york, 1991 [10] g. l. morrison and b. j. ranatunga, thermosyphon circulation in solar collectors, solar energy, vol. 24, pp 191 -198,1980 [11] a. zerrouki , a. boumedien and k. bouhadef, the natural circulation solar water heater model with linear temperature distribution, renewable energy, 2002, pp. 549–559 [12] u. c. arunachala, siddhartha bhatt m. and sreepathi l. k., performance analysis of solar flat plate collectors in scaling environment, journal of central power research institute, vol. 5, no.1, 2009, pp.109-119 [13] u. c. arunachala, m. siddhartha bhatt and l. k. sreepathi, “prediction, evaluation and prevention of scaling in flat plate solar water heaters”, emerging journal on engineering science and technology, vol. 4, sept. 2009, pp. 37-52 [14] boehm robert f., design analysis of thermal systems, john willey & sons, new york, 1987 nomenclature a0 intercept of the h-w-b equation a1 slope of h-w-b equation w/m2k a area m2 b constant relating density to temperature kg/m3k specific heat of water kj/kgk d diameter m f′ collector efficiency factor fr collector heat removal factor iium engineering journal, special issue, mechanical engineering, 2011 arunchala 130 g acceleration due to gravity m/s2 h convective coefficient of water in riser w/m2k h height m i total flux incident on the top glass cover w/m2 k thermal conductivity of material w/mk l length m n number of risers in fpc δp pressure change n/m2 q rate of heat flow in riser w q rate of heat flow in fpc w t temperature k u collector heat transfer coefficient w/m2k v vol. of water circulated in 1 hr. litres w pitch of risers m m mass flow rate of water in riser kg/s ̇ mass flow rate in fswh kg/s α absorber plate absorptivity β coefficient of cubical expansion k-1 η efficiency θ collector / riser orientation degree ρ mass density of water kg/m3 τ glass cover transmissivity φ absorber plate effectiveness a ambient air c collector cp connecting pipe h header i instantaneous, inner l loss o outer p absorber plate r riser s scale t tank iium engineering journal, special issue, mechanical engineering, 2011 arunchala 131 u useful w water 1 water inlet 2 water outlet application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 islam 59 diminishing seismic effect on buildings using bearing isolation a. b. m. saiful islam department of civil & construction engineering, college of engineering, imam abdulrahman bin faisal university, dammam 31451, kingdom of saudi arabia. * corresponding author: asislam@iau.edu.sa (received: 17th may 2017; accepted: 28th feb 2018; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.844 abstract: adopting suitable seismic protection techniques is presently a foremost concern worldwide and has become a governing principle in the growing construction industry globally. thus, a rapid upsurge in infrastructure development in seismic-prone areas requires proper treatment for building structures. therefore, the aim of the study is to incorporate a rubber bearing isolation device in a building base in order to diminish the seismic effect on the superstructure. the changes of structural parameters and responses of fixed-based buildings for applying high damping rubber bearing (hdrb) are investigated under site-specific ground excitation. twenty representative buildings have been used to examine the responses employing four types of hdrb systems. the study reveals that the hdrb makes the structure more flexible, offering reduced structural responses. the introduction of hdrb may help to decrease floor moment by 31~55%, which can allow the structures to withstand comparatively high seismic tremors safely and efficiently. the base isolated structures experience significant lateral shift between 87.15 and 130.15 mm, and relative floor displacement is below 3% because of additional flexibility. the effective inertia height for the bi buildings remains under twothirds of building elevation showing triangular distribution concentrating to the top story level. the reduction in forces, moments, and relative displacements of the structural members by applying hdrb can ensure economic design and higher structural safety against seismic excitation. abstrak: penerapan teknik yang sesuai bagi pelindungan gelombang seismos menjadi penekanan semasa di seluruh dunia dan telah menjadi prinsip penentu dalam industri pembinaan secara global. oleh itu, kenaikan yang cepat dalam pembangunan infrastuktur dalam kawasan terdedah kepada gelombang seismos memerlukan penyelenggaraan yang betul bagi struktur bangunan. jadi, matlamat kajian ini adalah bagi menggabungkan getah alat pengandar asing dalam teras bangunan bagi mengurangkan kesan seismos pada struktur asas. perubahan pada parameter struktur dan tindak balas tapak-tetap bangunan bagi penggunaan teknik high damping rubber bearing (hdrb) dikaji di bawah setiap kenaikan getaran gelombang sebenar bawah tanah. dua puluh bangunan telah digunakan bagi menilai tindak balas terhadap penggunaan empat jenis sistem hdrb. kajian menunjukkan hdrb membuatkan struktur lebih fleksibel, dan mengurangkan tindak balas terhadap struktur. penggunaan hdrb dalam pembangunan membantu mengurangkan momen lantai sebanyak 31~55%, di mana struktur bangunan lebih tahan terhadap gegaran tinggi secara selamat dan berkesan. struktur asas yang terasing mengalami peralihan sisi yang ketara antara 87.15 dan 130.15 mm, dan anjakan lantai relatif di bawah 3% dengan penambahan sistem fleksibel ini. ketinggian inertia berkesan bagi bangunan bi kekal di antara dua pertiga ketinggian bangunan. ini menunjukkan pengagihan segitiga tertumpu pada aras atas bangunan. pengurangan pada iium engineering journal, vol. 19, no. 1, 2018 islam 60 daya, momen dan perubahan relatif struktur menggunakan hdrb dapat memastikan reka bentuk lebih ekonomi dan selamat pada bangunan tinggi daripada sebarang gelombang seismos. keywords: bearing isolation; high damping rubber bearing; seismic prone building; structural flexibility 1. introduction earthquakes are sudden and overwhelming natural calamities. during earthquakes, extreme ground motion may cause severe damage to structures. the vulnerability of structures to seismic damage has been highlighted by numerous recent earthquakes worldwide. they cause inertia forces on the building structures that are a function of ground accelerations induced by the earthquake and the building mass. when the ground movement accelerates, the strength of the structure must be augmented to prevent the structural damage. however, continuous increase of building strength is not a practical way to solve the issue. it is neither easy nor economic to design seismic-prone buildings for such strength levels. conversely, instead of increasing the strength capacity, seismic base isolation can give a potential solution by reducing the structural responses. though the occurrence of a natural earthquake cannot be controlled, its influence on structures can be diminished by separating superstructures from their foundations. the isolation system provides additional flexibility as well as energy dissipation capability by offering such separation [1]. a new generation device, the high damping rubber bearing (hdrb), has brought an innovative aspect for analyzing and designing base isolated (bi) structures [26]. the hdrb rheology model [7], mechanical models [8] and the stiffening importance of hdrbs [9] are some of the investigations done to predict structural responses of bi buildings. even though the use of isolators is well known, there is a lack of appropriate research on the efficient practical implementation of high damping rubber bearing devices. the actual in-situ earthquake simulations have rarely been done because of lengthy analysis for dynamic response and expensive computation process. due to advancements in computer software and hardware, it has become relatively easier to conduct the numerical investigation [10] precisely. therefore, the present study evaluates the viability of using rubber bearing isolation devices, hdrb, at the base of the buildings and evaluates its effect on superstructure. static and dynamic analyses have been carried out inserting isolators for different configurations of the structures. design parameters of the isolators required for the selected buildings are assessed. moment and displacement behavior of fixed base (fb) and bi buildings have been evaluated. furthermore, the effective height of inertia forces has been appraised. 2. materials and methods 2.1 idealization of building frames reinforced concrete (rc) multi-storied building frames with plan areas and elevations, as shown in fig. 1, are modelled. four moment resisting frame (mrf) buildings of 4 bays @ 7.62m at x and y directions comprising story height @ 3.05m with gradual increase of numbers of stories to 4 (four), 6 (six), 8 (eight) and 10 (ten) have been chosen. for each building, the total seismic weight is disseminated in equal manner over iium engineering journal, vol. 19, no. 1, 2018 islam 61 all the floors. static analyses are carried out initially to get the required loading for the isolation design. for the conventional state, the building natural time periods are 0.50 (4 story), 0.75 (6 story), 0.80 (8 story) and 1.00 (10 story). four types of hdrb system have been used for all the buildings leading to a total number of 16 scenarios. base isolators are designed and evaluated for all the four variations of the studied building. the isolators are attached at the base level confirming all the properties. the building structures without and with hdrb are also analyzed for dynamic responses by using sap2000 [11]. (4@7.62 m bay both ways) fig. 1: plan of the selected multi-storied buildings. 2.2 design of hdrb in this study, the hdrb isolators have been designed according to the procedure mentioned by kelly et al. [12]. a computer code, hdrb-nonlin, has been produced to design hdrb iteratively. the code requires initial input of total seismic weight, dimension of bearing, and number and thickness of bearing layers. the high initial stiffness, post elastic stiffness, effective damping, yield strength, as well as post yield stiffness ratio of the isolation device are computed using this code. the bearings are attached at the bottom of every column defining these parameters in the analysis package. the flow chart in fig. 2 shows the sequential process of designing hdrb. for smaller dimensions, hdrb offers higher shear strain. because of large vertical stiffness, hdrb can withstand substantial structural loads [13]. the characteristics of materials and parameters for designing the hdrb isolators are given in table 1. the hdrbs are demarcated by the circular shape, size of its plan, configurations of rubber layers, as well as steel plates. table 1: salient features of hdrb. elastomer properties unit value modulus of elasticity kpa 1350 shear modulus kpa 400 material constant, k --0.87 ultimate elongation % 650 designed parameter shape --circular no. of bearings --25 diameter of bearing mm 950 thickness of rubber layer mm 10 height of cover plate mm 40 iium engineering journal, vol. 19, no. 1, 2018 islam 62 fig. 2: flow chart of hdrb design. damping has been varied for different bearings. the characteristics of the bearings are given in table 2. the hdrb is assigned to the building columns’ base. the bearings contain alternating layers of high damping rubber in thin layers and steel plates. the low shear modulus of the elastomers controls the bearing’s horizontal stiffness. furthermore, high vertical stiffness is the contribution of steel plates which obviously preclude rubber bulging. lower horizontal stiffness of hdrb devices ensures the natural periods to be higher. high non-linearity of stiffness and energy dissipation is the salient behavior of hdrb, which is shear strain dependent. iium engineering journal, vol. 19, no. 1, 2018 islam 63 table 2: bearing characteristics bearing device period of isolator (sec) damping (%) initial lateral stiffness (kn/mm) post-elastic stiffness (kn/mm) hdrb1 1.5 15 11.085 3.034 hdrb2 2.0 16 10.977 2.452 hdrb3 2.5 17 10.932 2.001 hdrb4 3.0 19 10.921 1.557 2.3 model of hdrb the effective horizontal stiffness of hdrb is contemplated in terms of kr. equivalent viscous damping is employed. the bearing’s force-deformation has been considered in the modelling as equivalent to linear. the shape of force-deformation of hdrb under loading is shown in fig. 3. the post elastic stiffness has been derived as eqn. (1). r r r t ag k   (1) the hysteresis loop area obtained for the respective shear modulus and equivalent viscous damping provides the hysteresis loop area. the parameter shear modulus, gγ is a function of shear strain. the unloading stiffness is named elastic stiffness, ku and is defined by eqn. (2). ru kk  (2) fig. 3: deformation pattern of hdrb (not to scale). the force intercept, q, follows the eqn. (3), which is estimated from effective stiffness, damping eff  , maximum displacement  and yield displacement y  [14].    yeffreff kq  *2/ 2  (3) 2.4 structural analysis simple linear static analyses have been performed with minimum complexity. the lateral loads for ground excitation are obtained using structural parameters such as modification factor response, seismic zone factor, soil profile, etc. in addition to this, the lateral shear force imposed by wind loading has been determined from the related coefficients and code requirements for earthquake and wind analysis that follow the code ubc 1997 [15]. the prototype buildings have been simulated and loaded in the finite element package. the equivalent static analysis considers ri = 8.0 for the traditional fb buildings. on the other hand, a reduced response modification factor of ri = 2.0 has been iium engineering journal, vol. 19, no. 1, 2018 islam 64 considered for the bi buildings with the structural coefficient of 1.0 [15] as per the occupancy. dynamic analysis has been carried out using the response spectrum analysis (rsa). the fb structures are investigated by rsa along with the equivalent static analysis. the structures are then linked to the isolator system and such bi structures are analyzed by rsa to predict the dynamic behavior. the site-specific dhaka earthquake seismic record, generated from the recent nearby earthquake occurrence of 2009, has been chosen for seismic analysis to assess the isolation effect especially at the site condition. the design response spectra [16] of this selected earthquake for fixed and base isolated conditions are shown in fig. 4. fig. 4: response spectra of the selected earthquake. the dynamic equation for the building super structure after the bearing insertion can be designated [2, 10] by means of in eqn. (4). [𝑀]{�̈� + �̈�𝑏} + [𝐶]{�̇�} + [𝐾]{𝑦} = −[𝑀][𝑇𝑔]{�̈�𝑔} (4) where, [c] is damping matrix; [k] is stiffness matrix and [m] is mass matrix of the building superstructure for respective dof at the slabs. [tg] is the coefficient matrix of earthquake effect. in addition, {y} = [yx , yy , yz] t is the displacement vector at the structure’s floor levels associated with the base mass; {yb} = [ybx , yby , ybz] t is the base displacement vector relative to the ground and }{ g y is the ground acceleration vector. this analysis technique uses the design response spectra engendered from seismic excitation of fb buildings. however, for bi buildings, the design response spectrum has been adapted to cope with the damping offered by bearing devices by using a composite spectrum. the b factor has been used to reduce the 5% damped composite spectrum in the isolated modes (fig. 4). 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 0.5 1 1.5 2 2.5 3 3.5 4 s p e c tr a l a c c e le ra ti o n ( g ) time period (sec) response spectrum for fb building response spectrum for bi building iium engineering journal, vol. 19, no. 1, 2018 islam 65 the motion equations have been transferred for the dynamic analysis into a normal coordinate system. modal superposition technique is employed to perform the rsa. the values of modal superposition have been combined according to the complete quadratic combination (cqc) approach. the square root sum of the squares (srss) progression provides the directional combination of the modal values. 2.5 numerical study all sixteen (16) base isolated buildings of varying height comprising the four variations of hdrb isolation systems as well as four fixed based buildings of different elevations have been investigated. each isolation system is incorporated to satisfy the stiffness and strength properties essential for the assessment. the hdrb systems have been designed for 1.5 s, 2.0 s, 2.5 s and 3.0 s effective isolation periods. the properties of hdrb are functions of shear strain applied with around 3 mpa shear modulus for very little strains dropping to 0.75 mpa at 250% strain. yield displacements, δy, is chosen as 0.05~0.10 times the rubber thickness. relying on the individual isolation periods, the damping percentage ranges in between 15%~19%. dynamic analyses of the three-dimensional (3d) buildings are carried out with consideration for the associated nonlinearities. after assigning stiffness values to the isolators, all the isolated structures have been analyzed in sap2000 [11] and the results are critically evaluated. 3. results and discussion due to the additional flexibility of the superstructure, the structural behavior of the base-isolated structure changes. the following sections describe the viability of bearing incorporation as well as improvement of structural responses by applying various hdrb systems. 3.1 viability of hdrb incorporation the fundamental time periods of the selected fb buildings for isolation are ≤1.0 second, which can be considered suitable and within reasonable limits [12]. the horizontal base displacements of the buildings, as per site requirements, are within the allowable limit of 200 mm. furthermore, the lateral shear force imposed by wind is clearly less than 10% of building weight [17], as required. from the static analysis of the fixed base building, it is observed that the maximum wind-induced shear experienced by the 10-story building is around 2.11 % of the building weight. this tendency is closely followed by all other scenarios analyzed. thus, isolators could be inserted at the structural base as an alternative to the conventional fixed base strategy. the isolators’ designed parameters need to meet two conditions: the isolation bearings are capable of securely withstanding the imposed loads and overall performance of the bearings has to be satisfactory. the ability of isolation bearings to carry the loads has been checked using factors of safety (fs). as fs is more than 1.0, the ability of the hdrbs for carrying loads safely can be considered satisfactory. the performance of bi buildings is assessed for both the design basis earthquake (dbe) and maximum credible earthquake (mce) choosing soil profile s3 with the zone factor z = 0.15. the assessments for earthquake levels, dbe and mce have been found to be satisfactory. each and every value of maximum displacements remains within the allowable isolator design static displacement (292.61 mm) under the mce. therefore, the properties of the hdrb devices maintain good agreement and can be reasonably employed. iium engineering journal, vol. 19, no. 1, 2018 islam 66 3.2 moment behavior reduction of seismic damage by inserting a bearing device includes both the structural along with the non-structural systems of buildings. decreasing a building’s nonstructural damage requires reducing the floor moment. as a lateral force, an important response indicator of fb and bi buildings is the moment in superstructure. the distribution of moment force along the height of the superstructure in base-isolated buildings indicates the enhancement of the behavior of the structure. figure 5 shows the improvement of moments for different buildings. it has been seen that moment might be overestimated if hdrb is not incorporated at the structural base. (a) 4 story building (b) 6 story building (c) 8 story building (d) 10 story building fig. 5: moment distribution of fb and bi buildings. crucial reduction of moment of mostly 31~55% at the upper stories (fig. 6) indicates the improvement of structural responses leading to economic design of structure. structural safety against seismic excitation can also be obtained following such force reduction of structural members. especially for the bottom stories, the decrement is very momentous, as clearly shown in table 3. nevertheless, for high-rise buildings, especially for a 10 story case, greater moment values are seen for a few floors and less reduction for some other floors due to the variation in mass participation and nonlinear dynamics of the structural system. this is the gorgeousness of hdrb which attracts the construction industry to keep up with this innovative technique for building construction. 0 50 100 150 f0 f1 f2 f3 f4 moment (kn-m) hdrb1 no bearing 0 50 100 f0 f1 f2 f3 f4 f5 f6 moment (kn-m) hdrb2 no bearing 0 50 100 150 200 f0 f1 f2 f3 f4 f5 f6 f7 f8 moment (kn-m) hdrb3 no bearing 0 100 200 300 f0 f2 f4 f6 f8 f10 moment (kn-m) hdrb4 no bearing iium engineering journal, vol. 19, no. 1, 2018 islam 67 a high damping bearing device can be chosen to reduce the forces, moments, and relative displacement of structural elements that can lead to economic design. (a) 4 story building (b) 6 story building (c) 8 story building (d) 10 story building fig. 6: change of moment after hdrb isolation. table 3: percentage reduction of moment by using hdrb. floor level reduction of moment (%) 4-story 6-story 8-story 10-story f0 79.40 82.64 87.59 92.43 f1 53.29 54.98 9.87 -6.01 f2 36.98 53.06 18.13 15.12 f3 37.64 25.82 99.10 -17.87 f4 31.05 41.94 28.51 22.21 f5 --31.57 3.97 -16.67 f6 --11.60 46.13 11.32 f7 ----33.77 4.23 f8 -----7.60 8.20 f9 ------14.76 f10 -------6.01 3.3 displacement behavior for the fixed base structures, the tendency of inertia is to keep structures in place at the time of ground excitation resulting in large displacements at different stories in 0 50 100 150 f0 f1 f2 f3 f4 change of moment (kn-m) moment reduction(hdrb) no bearing 0 50 100 f0 f1 f2 f3 f4 f5 f6 change of moment (kn-m) moment reduction(hdrb) no bearing -50 0 50 100 150 200 f0 f1 f2 f3 f4 f5 f6 f7 f8 change of moment (kn-m) moment reduction(hdrb) no bearing -50 0 50 100 150 200 f0 f2 f4 f6 f8 f10 change of moment (kn-m) moment reduction(hdrb) no bearing iium engineering journal, vol. 19, no. 1, 2018 islam 68 structures. nonetheless, for base isolated structures, displacement occurs almost uniformly in the whole upper structure and the displacement at the base remains within acceptable limits. as the relative displacement of adjacent stories is minimal, such structures can resist high seismic tremors in a safe and efficient manner against seismic ground excitation. the key points in investigating the dynamic responses of base-isolated buildings are the base displacements and story forces. here, base displacement indicates the superstructure translation in isolation interface. the analyses reveal that the structure is shifted by 87.15 mm ~ 130.15 mm while the bearing is inserted. for bi buildings, the superstructure gets such significant displacement even at base namely, at isolation interface. but in case of fb structures, base displacement is zero and the floor displacements vary nonlinearly commencing from zero to maximum at top story. conversely, the variation of horizontal translation in between floor to floor for bi buildings are not substantial (below 3%), ensuring almost uniform shape of distribution. figure 7 plots the variation of horizontal translation of different number of stories using a unique type of high damping rubber bearing hdrb1. it is logical that with increase of building elevation, the displacements at bearing interface are gradually increased. the 4-story building shows around 33.04% less shift than that of the 10-story building. however, the rate of increment from 8to 10-story structure is 10%, which is less than the rate of increment for lower story buildings of 16~17%. the observation suggests that the pattern of results is comparatively oblivious to the structural period and so representative hdrb1 induced responses are described. the higher the isolator period, the larger the displacement and lesser the equivalent viscous damping. again, to compare the structural response for different bearings, the scaling of the selected ground motions and the choice of the damping reduction factor are of great importance. if both are addressed well, the model developed could be a very useful tool for base isolated buildings, especially in the preliminary stage of structural design. fig. 7: superstructure displacement of bi buildings at bearing interface. 3.4 inertia behavior the shear force of buildings is maximum at base level, which is computed from the concurrent summation of maximum inertia forces at each floor above bearing level. the modal inertia force is a function of structural mass, spectral acceleration, and the participation factor at the respective level. the inertia forces at the respective floor denote the design shears at each level, leading to computation of base shear as well as overturning moment of the building. 0 20 40 60 80 100 120 140 4 story 6 story 8 story 10 story d is p la c e m e n t (m m ) iium engineering journal, vol. 19, no. 1, 2018 islam 69 the distribution of inertia has been computed as the effective inertia height, hc which is the ratio of highest overturning moment by the product of design base shear and building height. this effective height indicated linear inertia distribution when the value is 0.5 and triangular for 0.67 magnitude. the centroids of inertia loads are at half and twothird of the buildings’ height respectively. for hc equaling to 1.0, distribution of inertia forces concentrates at the top story. figure 8 plots these distributions for four building configurations comprising four types of hdrb as well as fixed based buildings in terms of normalized values. it is observed that without bearing the effective height of building inertia is around 0.5 tending to be triangularly distributed. accordingly, it generates a conformist moment for most of the buildings. for the bi buildings, the effective inertia height hc ranges between the two-thirds of building elevation (fig. 8) showing triangular distribution concentrating at top story level except the low-rise building. this trend is followed by all types of hdrb. it is also revealed that in general, the lengthier the isolation period the more flexible the structures are. fig. 8: normalized height of inertia force for different buildings. this behavior is reasonable because of the fundamental mode shape produced by the bearing devices. unfortunately for the 4-story building, the hdrbs provide effective inertia height exceeding building height by a large extent as 1.63~2.67 times. the tendency of effective inertia height exceedance increases with the increase of the isolator period. it indicates the moment distribution has very high shear at the top story. the phenomena of increasing top story shear and moment is also supported by the effective inertial height where the distribution offers a high moment corresponding to the shear. obviously, it confirms the kicking back of building at the base. the consequences of the analyses disclose that the high damping bearing device is expected to diminish the corresponding moments at different floor levels, the superstructure’s relative displacement as well as upsurge to the effective inertia height. the superstructure-foundation contact part acts as a passive control system, through the hdrb device, and can be the main reason behind the stability of the building structures in seismic-prone areas. 0 0.5 1 1.5 2 2.5 3 4 story 6 story 8 story 10 story h e ig h t o f in e rt ia l o a d /h no bearing hdrb1 hdrb2 hdrb3 hdrb4 iium engineering journal, vol. 19, no. 1, 2018 islam 70 4. concluding remarks subsequent findings have been outlined from the analyses conducted in the present study.  anticipated base isolation technique is intended to draw attraction of using the high damping rubber bearing at structural base in seismic-prone areas as a suitable alternative to structural retrofitting.  the moment will be highly overestimated by 31~55% if the bearing is not incorporated in building base. reduction of moments allow the structures to withstand comparatively high seismic tremors in a safe and efficient manner.  for hdrb isolated structures, the superstructures experience significant lateral shift as 87.15 mm ~ 130.15 mm due to structural flexibility. the increase of superstructure shift is 16~17% for low-rise but around 10% between high-rise buildings. the relative floor displacement remains below 3% of adjacent floor.  the lengthier the isolation period, the more flexible the structures are.  the effective inertia height for the bi buildings remains between two-thirds of building elevation showing triangular distribution concentrating to the top story.  the distribution of effective inertia offers high moment corresponding to the shear at top story. obviously, it confirms the kicking back of the building at the base.  the superstructure-substructure contact part acts as a passive control system, through the hdrb device, and might be the main reason behind the stability of these structures in active seismic zones.  high damping bearing device can reduce the forces, moments and relative displacement of structural members which can lead to economic design and structural safety against seismic excitation. acknowledgement the authors gratefully acknowledge the project 2017-212-eng, deanship of scientific research (dsr), imam abdulrahman bin faisal university (iau) for successful completion of the study. references [1] ismail m, rodellar j, ikhouane f. (2010) an innovative isolation device for aseismic design. engineering structures, 32:1168-83. [2] islam abms, hussain rr, jumaat mz, rahman ma. (2013) nonlinear dynamically automated excursions for rubber-steel bearing isolation in multi-storey construction. automation in construction, 30:265-75. [3] islam abms, jameel m, jumaat mz, rahman mm. (2013) optimization in structural altitude for seismic base isolation at medium risk earthquake disaster region. disaster advances, 6:23-34. [4] dicleli m, buddaram s. (2007) comprehensive evaluation of equivalent linear analysis method for seismic-isolated structures represented by sdof systems. engineering structures, 29:1653-63. [5] islam abms, jameel m, uddin ma, jumaat mz. (2012) competent building elevation for incorporating base isolation in aseismic structure. procedia engineering, 50:882-92. [6] tornello me, sarrazin m. (2012) base-isolated building with high-damping spring system subjected to near fault earthquakes. earthquakes and structures, 3:315-40. iium engineering journal, vol. 19, no. 1, 2018 islam 71 [7] bhuiyan ar, okui y, mitamura h, imai t. (2009) a rheology model of high damping rubber bearings for seismic analysis: identification of nonlinear viscosity. international journal of solids and structures, 46:1778-92. [8] markou aa, manolis gd. (2016) mechanical models for shear behavior in high damping rubber bearings. soil dynamics and earthquake engineering, 90:221-6. [9] alhan c, gazi h, kurtuluş h. (2016) significance of stiffening of high damping rubber bearings on the response of base-isolated buildings under near-fault earthquakes. mechanical systems and signal processing, 79:297-313. [10] islam abms, hussain rr, jameel m, jumaat mz. (2012) non-linear time domain analysis of base isolated multi-storey building under site specific bi-directional seismic loading. automation in construction, 22:554-66. [11] csi. (2004) linear and nonlinear static and dynamic analysis of three-dimensional structures computer & structures inc. sap 2000. berkeley (ca). [12] kelly te, robinson wh, skinner ri. (2006) seismic isolation for designers and structural engineers: robinson seismic ltd. [13] islam abms, ahmad si, jumaat mz, hussain rr, rahman ma, darain km. (2014) efficient design in building construction with rubber bearing in medium risk seismicity: case study and assessment. journal of civil engineering and management, 20:621-31. [14] cheng fy, jiang h, lou k. (2008) smart structures: innovative systems for seismic response control: crc press. [15] uniform building code (ubc). (1997) earthquake regulations for seismic isolated structures international conference of building officials. whitter (ca,usa). [16] islam abms, jameel m, ahmad si, salman fa, jumaat mz. (2011) engendering earthquake response spectra for dhaka region usable in dynamic analysis of structures. scientific research and essays, 6:3519-30. [17] deb s. (2004) seismic base isolation-an overview. current science, 87:1426-30. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 mechanical characterization of polyester/ e-glass fiber reinforced/mwcnts nanocomposites naguib g. yakoub faculty of engineering, beni-suef university, beni-suef, egypt * corresponding author: nagibgergeous@eng.bsu.edu.eg (received: 14th february 2021; accepted: 1st may 2021; published on-line: 4thjanuary 2022) abstract: mechanical properties of polyester/glass fiber reinforced by multiwalled carbon nanotubes (mwcnts) were studied. mwcnts nano particles are mixed within resin in various weight fractions of 0.1, 0.2, 0.4 and 0.6 % using sonication. e-glass fiber (chopped strand mat) is used in various weight fractions within the composite like 80/20 wt%, 70/30 wt%, 50/50 wt% to fabricate polyester/csm/mwcnts composites. the effect of the addition of mwcnts nanoparticles on the mechanical characteristics such as hardness and tensile strength were investigated. the effect of various e-glass fiber chopped strand mat (csm) wt.% reinforcement is also investigated. a scanning electron microscope (sem) was used to show the nanocomposites morphological properties such as reinforcement orientation and the bonding between matrix and fiber. it was found that the addition of 0.4 wt% mwcnts improves the mechanical properties of composites, especially the 50 wt% polyester / 50 wt% csm composite. the tensile strength improved by 39.8%, and the hardness improved by 38%. abstrak: ciri-ciri mekanikal bagi poliester / gelas fiber diperkukuh dengan dinding berbilang karbon nanotiub (mwcnts) dikaji. partikel nano mwcnt telah dicampur ke dalam resin pelbagai berat pada pecahan 0.1, 0.2, 0.4 dan 0.6 % menggunakan sonikasi. gentian kaca-e (potongan lembaran) telah digunakan dalam pelbagai pecahan berat dalam komposit 80/20 wt%, 70/30 wt%, 50/50 wt% bagi menghasilkan komposit poliester/csm/mwcnt. kesan penambahan nanopartikel mwcnt pada ciri-ciri mekanikal seperti kekerasan dan kekuatan tensil diuji. kesan pelbagai gentian kaca-e (potongan lembaran) (csm) wt.% bersama agen pengukuh turut dikaji. pengimbas mikroskop elektron (sem) digunakan bagi menilai ciri-ciri morfologi komposit nano seperti orientasi pengukuh dan ikatan antara matrik dan gentian. dapatan kajian menunjukkan dengan penambahan sebanyak 0.4 wt% mwcnt dapat memperbaiki ciriciri mekanikal komposit terutama komposit campuran (50 wt% polyester / 50 wt% csm). ketahanan tensil meningkat sebanyak 39.8%, dan kekerasan telah bertambah sebanyak 38%. keywords: mwcnts; nanoparticles; mechanical properties; polymer nanocomposites; e-glass fiber 1. introduction glass fiber-reinforced composite materials (gfrps) are increasingly used due to their high rigidity, high durability limit, high corrosive resistance, low thermal expansion coefficient and close-net shape, and greater production viability compared to conventional engineering materials [1]. nanocomposites became significant, in the last few decades in particular, to boost mechanical properties for different applications [2]. such 329 iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 nanomaterials are capable of improving mechanical, thermal, and electrical characteristics. recent research has been carried out to investigate the utility of polyester/glass fiber/mwcnts composites in many fields like aerospace and automotive industries because of their light weight and high performance [3-6]. composites based on cnts have been widely studied using a variety of matrix materials like ceramics [4-6], metals [7], and polymers [8-12]. breton [13] improved epoxy resin by adding different kinds of mwcnts and subsequently mechanical characteristics of mwcnts were tested. the results showed that a higher tensile modulus was acquired by the enhancement of mwcnts within epoxy resin of 1, 3, and 6 weight percentage. liu et al. [14] dispersed 2 wt.% of mwcnts in a nylon-6 matrix, they found that the tensile modulus increased about 214% and the yield strength about 162%. allaoui et. al. [15] investigated the mechanical and electrical characteristics of the mwcnts/epoxy composite and concluded that 1 wt.% and 4 wt.% of carbon nano-tubes greatly enhanced the composite’s young’s modulus and yield strength. zhou [16] filled epoxy resin of 0.1 wt%, 0.2 wt%, 0.3 wt%, and 0.4 wt% cnts and studied the loading effects on the mechanical properties of composites. the results show the increased modulus with a higher cnt material content, while the maximum strength was reached by the 0.3 wt% cnt. schadler et. al. [17] investigated the load transition in epoxy composite reinforced by mwcnts and observed that the compression modulus was significantly scattered; its maximum value was 6 mpa which was large compared to the tension modulus of 4.2 mpa. shekar et al. [18] used a sonication technique to distribute mwcnts within polymer matrices efficiently and homogenously. the author also pointed out that the flexural force and flexural modulus of nanocomposites were increased by amino functionalized mwcnt in the epoxy composites. the calendar technique for standardized distribution of mwcnts in epoxy resin was introduced by gojnyet et al. [19] the mechanical properties were improved by the addition of a small wt% of nanotubes compared to the same wt% of carbon black dispersed in the epoxy resin. results indicated that nanotube-filled epoxy resin had improved fracture toughness, tensile strength, and elasticity modulus under ductility retention. shokrieha et al. [20] studied the effect of adding mwnts on properties of mat/polyester composites. they concluded that the flexural strength of the composites was improved by 45% at only 0.05 wt.% of mwnt. furthermore, increasing the amount of mwnts in composites enhanced their tensile, flexural, and compressive moduli. multi-wall carbon nanotubes (mwcnts) were used as a secondary improvement in the current study to strengthen the mechanical properties of the polyester/csm composite. polyester/csm laminate was developed using a hand-layup technique. it was discovered that adding 0.4 wt% mwcnts to composites improved their mechanical properties, especially in 50/50 wt% composites. 2. materials 2.1 fabrication of mwcnts based nanocomposites chopped strand mat (csm) has a fiber length between 20 and 30 mm. fiber mass of 450 g/m2 was used as a first reinforcement and polyester as a matrix. multiwalled carbon nano tubes mwcnts (93%, diameter 10–40 nm and length 5–20 μm) were provided by sigma-aldrich and were used as secondary reinforcement. figure 1 shows the fiber and the mwcnts nanofiller used to fabricate polyester/csm nanocomposites. methyl ethyl ketone peroxide (mekp) was added as a catalyst to the orthophthalic unsaturated 330 iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 polyester as a cure for ambient temperature. both fibers and polyester materials were purchased from al-joumhouria co. cairo, egypt. the polyester/csm/mwcnts nano composites were manufactured using a hand-layup technique [21] these composites were manufactured using a flat wooden mold, as shown in fig. 2, which was horizontally mounted and covered with a thin layer of a release agent of liquid polyvinyl acetate (pva). firstly, mwcnts were added to polyester resin using sonication, then a first layer of mwcnts/polymer resin was rolled across a single roller. next, a layer of csm was laid on top of the first layer of nano-mwcnts/polyester resin. the layer was subsequently mounted on the mold surface. a smooth steel roller was employed to squeeze air out of the layers, which also ensured that the polyester resin layers were evenly distributed across the surfaces. an additional layer of mwcnts / polyester resin was added to the glass fiber sheet. polyester/csm/mwcnts nanocomposites were made up of three layers of csm. glass fibers, were constructed at 4 mm of thickness during the same process. the substance was then treated for 24 hours at room temperature. the composites are produced in various fractions of weight such as: sample code polyester (wt%) csm (wt%) mwcnts (wt%) s1 80 20 0 s2 80 20 0.1 s3 80 20 0.2 s4 80 20 0.4 s5 80 20 0.6 s6 70 30 0 s7 70 30 0.1 s8 70 30 0.2 s9 70 30 0.4 s10 70 30 0.6 s11 50 50 0 s12 50 50 0.1 s13 50 50 0.2 s14 50 50 0.4 s15 50 50 0.6 fig. 1: (a) e-glass fiber chopped strand mat glass fiber, (b) mwcnts nano-powder. a b 331 iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 fig. 2: hand-layup technique. 3. testing 3.1 tensile strength mwcnts nanoparticles in various percentages as 0.1%, 0.2%, 0.4% and 0.6% were introduced to various weight percentages of polyester/glass fiber like 80/20 wt%, 70/30 wt%, and 50/50 wt% then tensile test was conducted using waw-300b (300 kn, zhejiang jingyuan mechanical equipment co., ltd., jinhua, china) tensile testing machine with a constant strain rate of 1 mm/min, according to astm d3039. six samples were tested and an average value was chosen for each nanocomposite. the model tensile specimens are presented in fig. 3 before conducting the tensile test. 3.2 hardness hardness tester (barcol hardness test type 934-1) was used to test specimens according to the astm d638 type iv (fig. 4). about six samples were checked and the average value was chosen for each nanocomposite. the specimen was put under the barcol hardness tester indentor and the specimen was subjected to a uniform pressure up to meeting the optimum dial indicator. the deep penetration was converted to absolute numbers of barcol to obtain hardness in brinell. different weight percent of mwcnts nanoparticles were introduced to investigate different (polyester/csm/mwcnts) composites hardness. fig. 3: the standard tensile specimens. 332 iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 fig. 4: astm d638 type iv standard specimen using barcol tester. 4. results and discussion 4.1 tensile strength of polyester/csm/mwcnts nanocomposites the tensile strength variations versus the weight percent of mwcnts nanoparticles are shown in figs. 5(a-c), various wt.% of polyester/csm/mwcnts specimens were fabricated. fig.5(a) indicates that the tensile strength of (80 wt.% polyester / 20 wt.% csm) without mwcnts has a value of 75.4 mpa. while in case of (80 wt.% polyester / 20 wt.% csm + 0.1 wt.% of mwcnts) the tensile strength value increased from 75.4 mpa to 101 mpa. the maximum tensile strength is then observed to be 104.5 mpa at 0.4 wt.% of mwcnts specimen, that means the tensile strength is improved by 38.5%. by more reinforcement with mwcnts. over 0.4 wt.% the tensile strength was then reduced and it reached a low value of 77.03mpa when mwcnts were added by 0.6 wt.%. it is observed from fig. 5(b) that tensile strength of polyester/fiber (70/30 wt.%) composite has a value of 97.01 mpa. by being reinforced up to 0.1 wt.% with mwcnts nanoparticles, the tensile strength value was increased from 97.01 mpa to 123.11 mpa and reached a maximum value of 140.07 with the addition of mwcnts up to 0.4 wt.% (tensile strength of composite improved by 44%). it was observed that tensile strength decreased by further addition of mwcnts nanoparticles over 0.4 wt.%, and dropped to 94.74 mpa at the 0.6 wt.% of mwcnts. this is close to the pattern of 80/20 wt.% of polyester/csm shown in fig. 5(a). figure 5(c) shows a similar pattern of tensile strength variation of polyester/csm 50/50 weight percentage and the tendency for variation in strength of nanoparticles with various wt.% of the mwcnt. as discussed previously, results were found to be similar. this shows that the percentage value of the material composition changed its tensile strength. also, the addition of mwcnts nanoparticles affects the polyester/csm composite tensile strength values. it is observed that the further increase of mwcnts nanoparticles leads to decrease in tensile strength for all polyester/csm composites. figure 6 indicates a comparison between tensile strength variation vs different wt. percentages of mwcnts nanoparticles reinforces polyester/csm (80/20 wt.%, 70/30 wt.% and 50/50 wt.%). it is concluded that the nanocomposite of 50/50 wt.% of polyester/csm/mwcnts at the same content of 0.4 wt.% of mwcnts has a tensile strength value of 170 mpa compared to 80/20 wt% (about 105 mpa) and 70/30 wt.% composite (about 140 mpa). 333 iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 fig. 5: (a) tensile strength vs % mwcnts of polyester/csm (80/20 wt.%). fig. 5: (b) tensile strength vs % mwcnts of polyester/csm (70/30 wt.%). fig. 5: (c) tensile strength vs % mwcnts of polyester/csm (50/50 wt.%). fig. 6: comparison between tensile strength variation and different wt. percentages of mwcnts reinforces polyester/csm (80/20 wt.%, 70/30 wt.% and 50/50 wt.%). 334 iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 4.2 sem microscopy figure 7(a) shows an sem image of 0.4 wt.% mwcnt-reinforced 50/50 wt.% of polyester/csm. from this figure, a matrix-fiber adhesion is observed. this explains the higher value of tensile strength of this composite. figure 7(b) shows sem image of 0.6 wt.% mwcnt-reinforced 50/50 wt.% of polyester/csm. from fig. 7(b) it is clear that introduction of more mwcnts causes agglomeration of particles and leads to decrease in mechanical properties, explaining the reduced value of tensile strength by further addition of mwcnts. fig. 7: sem image of 50/50 wt.% of polyester/csm reinforced by (a) 0.4 wt.% mwcnts., (b) 0.6 wt.% mwcnts. 4.3 hardness test 4.3.1 hardness of polyester/csm/mwcnts nanocomposites figure 8(a) shows hardness variation of wt.% nano mwcnt-reinforced polyester/csm (80/20 wt.%). it is observed that by the addition of 0.1 wt.% of mwcnts, the hardness value is increased from 32.3 to 40.01 and by adding 0.4 wt.% of mwcnts, the hardness is increased to 41.5%. therefore, the hardness improved by 23.8% and 28.4% by reinforcing with 0.1 wt.% and 0.4 wt.% of mwcnts, respectively. it is obvious that the hardness of 0.1 wt.% and 0.4 wt.% of mwcnts composites is improved. it is also observed that the hardness values are decreased after 0.4 wt.%. figure 8(b) and fig. 8(c) show the hardness variation of mwcnts reinforced (60 wt.% polyester / 40 wt.% csm) and (50 wt.% polyester / 50 wt.% csm), respectively. from the graphs, it is clear that hardness values increase by increasing the weight percent of mwcnts. however, further increase up to 0.6 wt.% of mwcnts leads to a decrease in hardness values for both (60 wt.% polyester / 40 wt.% csm) and (50 wt.% polyester / 50 wt.% csm) composites. comparative plots show that the (50 wt.% polyester / 50 wt.% csm) composite has higher values of hardness about 47 bhn as demonstrated in fig. 9. it is noted from the previous data that, with the increase in mwcnts nanoparticles, tensile strength and hardness first increase and then decrease with more addition of mwcnts nanoparticles. the maximum tensile strength value is seen at 0.4 wt.% of mwcnts nanoparticles and the characteristics are reduced with a higher introduction of mwcnts nanoparticles. the increase in the adhesion of fiber matrix is due to tensile characteristic enhancement by introducing mwcnts. nano particles have an increasing, unique surface and low surface 335 iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 strength. thus, they can react with the macro-molecular chain chemically and physically to improve the connection between the matrix and the fiber. the reduction of the tensile strength for composites reinforced by 0.6 wt% mwcnts could be attributed to nano filler accumulation in the glass fiber polyester matrix. however, with an increase of mwcnts nanoparticle material, the accumulation activity increased, suggesting that nanocomposites of polyester/csm/mwcnts were more incompatible with an excess of mwcnts nanoparticles addition. fig. 8: (a) hardness variation of wt.% nano mwcnts reinforces polyester/csm (80/20 wt.%). fig. 8: (b) hardness variation of wt.% nano mwcnts reinforces polyester/csm (70/30 wt.%). fig. 8: (c) hardness variation of wt.% nano mwcnts reinforces polyester/csm (50/50 wt.%). 336 iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 fig. 9: comparison between hardness variation and different weight percentages of mwcnts reinforces polyester/csm (80/20 wt.%, 70/30 wt.% and 50/50 wt.%). 5. conclusion polyester reinforced by e-glass fiber csm composites were manufactured by means of the hand layup method. different wt.% of mwcnts nanoparticles were used to reinforce composites. tensile and hardness tests were conducted to investigate the effect of mwcnts addition. the experimental data support the following conclusions: 1. the mechanical properties of (polyester/csm/mwcnts) are enhanced due to the presence of mwcnts nanoparticles. adding up to 0.4 wt.% of mwcnts nanoparticles greatly improves the strength and hardness of various composites, especially in the 50 wt.% polyester / 50 wt.% csm composite, where it enhanced both the tensile strength and the hardness by 39.8% and 38%, respectively. however, further addition of mwcnts nanoparticles reduced tensile strength and hardness values. the addition of mwcnts nanoparticles gives strong adhesion between matrix and fiber. it also leads to the improvements of the mechanical properties for different composites. nanoparticle agglomerates cause the decrease in values of both tensile strength and hardness. the presence of further wt.% of mwcnts nanoparticles leads to decrease in mechanical properties as nanoparticles agglomerate and leads the polymer matrix to weaken. in the 50 wt.% polyester / 50 wt.% csm composite, tensile strength decreased by 25.1% by adding 0.6 wt.% of mwcnts over polyester / csm without mwcnts addition. also, hardness value of 50 wt.% polyester / 50 wt.% csm without mwcnts addition was slightly enhanced by 0.8% when 0.6 wt.% of mwcnts was added. 2. for 80/20, 70/30 and 50/50 wt.% of polyester/csm adding mwcnts nanocomposites up to 0.4 wt.%, enhanced hardness and tensile strengths for all composites compared to polyester/csm composites without mwcnts nano particles. 3. 50/50 wt.% of polyester/csm + 0.4 wt.% mwcnts nanocomposite has a hardness of 47 bhn and a tensile strength of 172 mpa and these are the highest values, above all other composites. references [1] palanikumar k. (2010) modeling and analysis of delamination factor and surface roughness in drilling gfrp composites. mater manuf process., 25:1059–1067. 337 iium engineering journal, vol. 23, no. 1, 2022 yakoub https://doi.org/10.31436/iiumej.v23i1.1848 [2] murugan s, rajendran r, fei w. (2016) graphene-zinc oxide (g-mwcnts) nanocomposite for electrochemical supercapacitor applications. j. sci. adv. mater. dev., 1:454-460. [3] sandhya cp, john b, gouri c. (2017) sn/al2o3/c/cnt composite prepared by wet milling as anode material for lithium-ion cells, j. sci. adv. mater. dev., 2:210-214. [4] peigney a, laurent c, flahaut e, rousset a. (2000) carbon nanotubes in novel ceramic matrix nanocomposites. ceramics international., 26(6):677-683. [5] flahaut e, peigney a, laurent c, marliere c, chastel f, rousset a. (2000) carbon nanotubemetaloxide nanocomposites: microstructure, electrical conductivity and mechanical properties. acta materialia., 48(14):3803-3812. [6] peigney a, flahaut e, laurent c, chastel f, rousset a. (2002) aligned carbon nanotubes in ceramic-matrix nanocomposites prepared by high-temperature extrusion. chemical physics letters., 352(1-2):20-25. [7] xu cl, wei bq, ma rz, liang j, ma xk, wu dh. (1999) fabrication of aluminum-carbon nanotube composites and their electrical properties. carbon., 37(5):855-858. [8] cochet m, maser wk, benito am, callejas ma, martínez me, benoit jm, schreiberb j, chauvet o. (2001) synthesis of a new polyaniline/nanotube composite: ‘‘in-situ’’ polymerization and charge transfer through site selective interaction. chem comm., 16:14501451. [9] jin z, sun x, xu g, goh sh, ji w. (2000) nonlinear optical properties of some polymer/multiwalled carbon nanotube-based composites. chem phys lett., 318:505-510. [10] jin z, pramoda kp, xu g, goh sh. (2001) dynamic mechanical behavior of melt-processed multi-walled carbon nanotube/poly (methyl methacry-late) composites. chem phys lett., 337(1-3):43-47. [11] kumar s, doshi h, srinivasarao m, park jo, schiraldi da. (2002) fibers from polypropylene/ nano carbon fiber composites. polymer, 43(5):1701-1733. [12] lourie o, wagner hd. (1999) evidence of stress transfer and formation of fracture clusters in carbon nanotube-based composites. composite science and technology., 59(6):975-977. [13] breton y, esarmot gd, salvetat jp, delpeux s, sinturel c, béguin f, bonnamy s. (2004) mechanical properties of multiwall carbon nanotubes/epoxy composites: influence of network morphology. carbon., 42(5-6):1027-1030. [14] liu t, phang i, shen l, chow s, zhang w. (2004) morphology and mechanical properties of multiwalled carbon nanotubes reinforced nylon-6 composites. macromolecules, 37(19):72147222. [15] allaoui a, bai s, cheng hm, bai jb. (2002) mechanical and electrical properties of a mwnt/epoxy composite. composites science and technology, 62:1993-1998. [16] zhou y, pervin f, lewis l, jeelani s. (2006) experimental study on the thermal and mechanical properties of multi-walled carbon nanotubereinforced epoxy. materials science and engineering., 452-453:657-664. [17] schadler ls, giannaris sc, ajayan pm. (1998) load transfer in carbon nanotube epoxy composites. appl phys lett., 73(26):3842-3844. [18] shekar kc, prasad ba, prasad ne. (2014) effect of amino multiwalled carbon nanotubes reinforcement on the flexural properties of neat epoxy. appl mech mater., 592:912-916. [19] gojny fh, wichmann mhg., fiedler b, schulte k. (2005) influence of different carbon nanotubes on the mechanical properties of epoxy matrix composites – a comparative study. compos sci technol., 65:2300-2313. [20] shokrieh mm, saeedi a, chitsazzadeh m. (2014) evaluating the effects of multi-walled carbon nanotubes on the mechanical properties of chopped strand mat/polyester composites, materials & design, 56:274-279. [21] el-tayeb nsm, yousif bf, yap tc. (2006) tribological studies of polyester reinforced with csm 450-r-glass fiber sliding against smooth stainless steel counterface. wear., 261:443452. 338 microsoft word 198-1250 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics fudhail et al. 97 numerical simulations of flow behavior in driven cavity at high reynolds numbers fudhail a.m. 1 , mohd rody m.z. 1 , nor azwadi c.s. 2 and mohd irwan m.a. 1 1 faculty of mechanical engineering, universiti teknikal malaysia melaka, melaka, malaysia. 2 faculty of mechanical engineering, universiti teknologi malaysia, johor, malaysia. fudhail@utem.edu.my, rody@utem.edu.my, azwadi@fkm.utm.my, adrinata@utem.edu.my abstract: in recent years, due to rapidly increasing computational power, computational methods have become the essential tools to conduct researches in various engineering fields. in parallel to the development of ultra high speed digital computers, computational fluid dynamics (cfd) has become the new third approach apart from theory and experiment in the philosophical study and development of fluid dynamics. lattice boltzmann method (lbm) is an alternative method to conventional cfd. lbm is relatively new approach that uses simple microscopic models to simulate complicated microscopic behavior of transport phenomena. in this paper, fluid flow behaviors of steady incompressible flow inside lid driven square cavity are studied. numerical calculations are conducted for different reynolds numbers by using lattice boltzmann scheme. the objective of the paper is to demonstrate the capability of this lattice boltzmann scheme for engineering applications particularly in fluid transport phenomena. abstrak: sejak kebelakangan ini, perkembangan pesat kuasa pengiraan komputer telah menjadikan kaedah pengiraan sebagai alat penting dalam penyelidikan bidang kejuruteraan. selari dengan perkembangan komputer digital kelajuan tinggi, pengiraan bendalir dinamik bendalir (cfd) merupakan pendekatan baru yang ketiga selain daripada teori dan eksperimen dalam kajian falsafah dan pengiraan dinamik bendalir. kaedah kekisi boltzmann (lbm) adalah satu kaedah alternatif berbanding cfd konvensional. lbm adalah pendekatan baru yang menggunakan model mikroskopik yang mudah untuk mensimulasikan tingkah laku mikroskopik dalam fenomena pengangkutan yang rumit. dalam kertas ini, kelakuan aliran bendalir aliran tidak mampat di dalam rongga penutup empat persegi yang didorong telah dikaji. pengiraan berangka telah dijalankan untuk nombor-nombor reynolds yang berlainan dengan menggunakan kaedah boltzmann kekisi. objektif kertas ini adalah untuk menunjukkan keupayaan kaedah boltzmann kekisi untuk aplikasi kejuruteraan terutamanya dalam fenomena pengangkutan bendalir. keywords: lattice boltzmann method; lid driven cavity; computational fluid dynamics 1. introduction computational fluid dynamics (cfd) has been extensively used for the analysis of system pertaining to engineering field like fluid flows, heat transfer, chemical reaction, evaporation, condensation [1]. over the years, fluid flow behaviors inside lid driven cavities have drawn many interested researchers and scientists. applications of lid driven iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics fudhail et al. 98 cavities are in material processing, dynamics of lakes, metal casting, galvanizing and etc [2]. numerous studies have been carried out on flow patterns inside a cavity. excellent reviews on lid driven square cavity have been reported [3-5]. on the other hand, the numerical simulation of driven cavity flow at high range of reynolds number using high grid numbers had been conducted in [6]. these researchers used the conventional cfd method which is by solving the 2-d navier stokes equation. in recent years, there has been a rapid progress in developing the lattice boltzmann method (lbm) as an efficient alternative way to the conventional cfd methods. the main advantage of lbm is its flexibility in terms of programming and better accuracy in dealing with complicated boundary of geometries [7]. in addition to that, the lbm is also better than the classical cfd in the range of small to moderate reynolds numbers if dealing with flows in complex geometries [8]. 2. lattice boltzmann method the basic idea of boltzmann work is that a gas is composed of interacting particles that can be explained by classical mechanics [9]. the mechanics can be very simple where it contains streaming in space and billiard-like collisions interactions [9]. in addition to that, since there are many particles involves, a statistical treatment is needed and is more suitable. the statistical treatment of a system can be represented in terms of distribution function. this distribution function� ��, �, �� � � is the number of particles which its positions and velocities are dx and dc at time t respectively. each particle would move from x to x + c∆t if there is no collision occurs. each particle velocity would change from c + a∆t in which a is the acceleration due to external forces on a particle at x with a velocity of c. no collision means there is conservation of molecules which can be represented in equations of [10]: �� � �∆�, � � �∆�, � � ∆�� � � �� , �, �� � � 0 (1) however, if there is collision occurs, the equation represent this particular case is as follow: �� � �∆�, � � �∆�, � � ∆�� � � �� , �, �� � � ω ��� � � �2� where f(x, c, t) is the single particle distribution function with discrete velocity of c and ω(f)dxdcdt is the boltzmann collision operator. it is from this equation that bhatnagargross-krook (bgk) collision model was developed and further derived to become bgk lbm equation. in general, the discretised version of bgk lbm equation can be written as follow: �� � � �� ∆�, � � ∆�� � �� � , �� � �∆� ��� � �� �� �� � �3� where �� �� is equilibrium distribution function and �� is the time relaxation. the lattice boltzmann model with bgk collision operator or bgk model in short, is the classical lb fluid model. this model is most often used to solve the incompressible navier-stokes equations. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics fudhail et al. 99 3. results and discussion the simulations of flow of lid driven square cavity were conducted in different range of reynolds (re) numbers. the top wall velocity, u was maintained at 0.1 lattice unit per second (lu/s) while the velocity of other three walls which is right, left and below was set to 0 lu/s. the fluid temperature is maintained to be constant (isothermal). the re numbers were varied from 7500, 8000, 9000 and 12500. the graph of velocity profile at mid height of each x and y axis were plotted for the correspond re numbers as shown in fig.1 to fig. 4 the graph obtained in fig. 1 for re number of 7500 were compared with the numerical results in [3]. good agreements between lbm and in [3] have been found for re number equal to 7500. fig. 1: velocity profile at mid-height (x-velocity,ux and y-velocity,uy) of cavity for re number 7500. line-lbm and symbolghia et al. [3] fig. 2: velocity profile at mid-height (x-velocity, ux and y-velocity,uy) of cavity for re number 8000. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics fudhail et al. 100 fig. 3: velocity profile at mid-height (x-velocity, ux and yvelocity,uy) of cavity for re number 9000. fig. 4: velocity profile at mid-height (x-velocity and y-velocity) of cavity for re number 12500. apart from the numerical results, the streamline patterns were also shown for each re number . these patterns are plotted when steady state solution is achieved. the streamline patterns are shown as in fig. 5 to fig. 8. the figures depict that there is addition in terms of the number of secondary vortex when the re number is increased. as shown in the fig. 8, the number of secondary vortex is increase from 3 to 4 when the reynolds number is increased from 9000 to 12500. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics fudhail et al. 101 fig. 5: streamline patterns for re number of 7500. fig. 6: streamlines patterns for re number of 8000. fig. 7: streamline patterns for re number of 9000. fig. 8: streamline patterns for re number of 12500. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics fudhail et al. 102 on the other hand, the centre of the primary vortex together with results in [3] is shown in table 1. table 1: location of primary vortex for shear driven square cavity. re number 7500 8000 9000 12500 ghia et al. [3] (0.5117, 0.5322) hou et al. [12] (0.5176, 0.5333) lbm (0.5150, 0.5325) (0.5075, 0.5325) (0.5150, 0.5300) (0.5133, 0.5267) the location of the primary vortex obtained by using lbm is then plotted on the graph as shown in fig. 9. from the graph, it is noticed that when the re number is higher, the centre of the primary vortex moves downwards to the left of the cavity. fig. 9: graph of the location of primary vortex for respective re numbers. 4. conclusion the capability of lbm to simulate flow in shear driven square cavity has been demonstrated successfully. numerical results that are obtained for re number of 7500 are in good agreements with the references. apart from that, the number of secondary vortex is affected by the increase of reynolds numbers for shear driven cavity. in addition to that, the location of the centre of the primary vortex in driven cavity flow is also affected by the reynolds numbers. 0.52 0.53 0.54 re 8000 re 12500 re 9000 y re 7500 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics fudhail et al. 103 acknowledgement the authors would like to thank the universiti teknikal malaysia melaka (utem), universiti teknologi malaysia and the government of malaysia for supporting this research activity. references [1] c.s. n. azwadi and a.m. fudhail, “ mesoscale numerical prediction of fluid flow in a shear driven cavity”,unpublished. [2] m.a.r. sharif, “laminar mixed convection in shallow inclined driven cavities with hot moving lid on top and cooled from bottom”, applied thermal engineering., vol. 27, pp. 1036-1042, 2006. [3] u. ghia., k.n. ghia and c.y. shin, “high re solutions for incompressible flow using the navier-stokes equations and a multigrid method”, journal of computational physics., vol. 48, pp. 387-411, 1982 [4] e. erturk., t.c. corke and o. gokcol, “numerical solutions of 2-d steady incompressible driven cavity flow at high reynolds numbers”, international journal for numerical methods in fluids., vol. 48, pp. 747-774, 2005. [5] albensoeder, s. and kuhlmann, h.c., “accurate three dimensional lid-driven cavity flow”, journal of computational physics., vol. 206, pp. 536-558, 2005. [6] c. h. bruneau , and m. saad, “the 2d lid driven cavity problem revisited ”, computers and fluids., vol. 35, pp 326-348, 2006. [7] g. poutrelli, s. ubertin and s. succi, “ the unstructured lattice boltzmann method for nonnewtonian fluid, vol. 06, 2009. [8] o. filippova and d. hanel, “grid refinement for lattice-bgk models”, journal of computational physics., vol. 147, pp. 219-228, 1998. [9] m.c. sukop and d.t. thorne, lattice boltzmann modeling : an introduction for geoscientists and engineers, springer, new york, 2006. [10] c.s. n. azwadi, “ the development of new thermal lattice boltzmann models for the simulation of thermal fluid flow problems. doctor of philosophy, keio university, japan. 2007. [11] c.s. n. azwadi and t. tanahashi, “simplified thermal lattice boltzmann in incompressible limit”, international journal of modern physics, b 20, pp. 2437-2449, 2006.s.q. hou, q. zou, s. chen, g. doolen and a.c. cogley, “simulation of cavity flow by the lattice boltzmann method”, journal of computational physics, vol. 118, pp. 329-347, 1995 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 mechanical properties, water absorption, and failure analyses of kenaf fiber reinforced epoxy matrix composites ikhwan yusuff, norshahida sarifuddin* siti norbahiyah and afifah mohd ali department of manufacturing and materials engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia * corresponding author: norshahida@iium.edu.my (received: 16th december 2020; accepted: 22nd february 2021; published on-line: 4th july 2021) abstract: the potential of natural fibers as one of the candidate materials in the production of fiber-reinforced polymer composites have been widely investigated. in the current study, natural fiber-reinforced polymer composite was fabricated by employing woven kenaf fiber as a reinforcing agent with epoxy resin that acts as a matrix constituent. this composite sample was fabricated using the application of the vacuum infusion method in which the content of kenaf fibers was varied from 30 vol.%, 40 vol.%, and 50 vol.%. the effects of different fiber loadings toward mechanical and physical properties as well as failure properties of kenaf composite were then evaluated. kenaf composites were subjected to mechanical tests including tensile and flexural tests. the result shows that the highest tensile strength and modulus were attained at 76.67 mpa and 2.31 gpa, respectively with kenaf composite fabricated with 40 vol.% fiber content. meanwhile, the highest flexural strength and modulus were recorded at 61.24 mpa and 4.20 gpa, also corresponding to kenaf composite that is loaded with 40 vol.% fibers. fiber pull-out failure was able to be detected in fabricated kenaf composites. meanwhile, fiber breakage resulting from flexural failure could also be observed in the kenaf composite samples. apart from that, it was found that as more kenaf fiber was loaded in the composites, the rate of water absorption tended to increase where the highest rate of water absorption was found at 43.33%, displayed by kenaf composite with 50 vol.% of fiber content. abstrak: potensi gentian semula jadi sebagai salah satu bahan dalam penghasilan komposit polimer bertetulang gentian telah banyak dikaji. dalam kajian terkini, komposit polimer yang diperkuat dengan gentian semula jadi dibuat dengan menggunakan serat kenaf tenunan sebagai agen penguat dan resin epoksi yang bertindak sebagai matriks. sampel komposit ini dibuat menggunakan kaedah infusi vakum di mana kandungan serat kenaf digunakan adalah 30 vol.%, 40 vol.%, dan 50 vol.%. kesan kandungan serat yang berbeza terhadap sifat mekanikal dan fizikal serta sifat kegagalan komposit kenaf kemudiannya dinilai. komposit kenaf diuji dengan ujian tegangan dan lenturan. hasilnya menunjukkan bahawa kekuatan tegangan dan modulus tertinggi dicapai pada 76.67 mpa dan 2.31 gpa, milik komposit kenaf yang dibuat dengan kandungan serat 40 vol.%. sementara itu, kekuatan dan modulus lenturan tertinggi dicatatkan pada 61.24 mpa dan 4.20 gpa juga milik komposit kenaf yang dimuatkan dengan serat 40% vol. kegagalan serat terkeluar dapat dikesan pada komposit kenaf buatan. sementara itu, kerosakan serat akibat kegagalan lenturan juga dapat dilihat pada sampel komposit kenaf. selain itu, didapati bahawa semakin banyak serat kenaf yang dimuatkan dalam komposit, cendurung meningkatkan kadar penyerapan air di mana 316 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 kadar penyerapan air tertinggi didapati pada 43.33% yang ditunjukkan oleh komposit kenaf dengan kandungan serat 50% vol. keywords: natural fiber; kenaf composite; mechanical properties 1. introduction the exploitation of natural fibers such as kenaf, hemp, sisal, and bamboo has been widely adopted in the production of fiber-reinforced composite materials [1,2]. the growth of natural-based composites is due to the properties of natural fibers, especially in terms of cost and biodegradability characteristics [3,4]. moreover, the excellent biodegradability displayed by natural fibers can impart a positive impact on the environment due to the ability to form green bio-composite materials. furthermore, the capability of natural fibers in offering outstanding attributes including non-abrasiveness, low density, as well as exhibiting a comparable specific strength, is another driving force in the utilization of this fiber as a reinforcement in fiber-reinforced composite materials [5,6]. therefore, there are many works available in open literature that have reported on the potential of natural fiber utilization in many engineering applications such as construction, electronic, and automotive industries [7,8]. for example, javadian et al. [9] have investigated the mechanical properties of bamboo fiber to be embedded in composites for construction uses. moreover, gupta [10] has studied the potential of jute composites for electronic applications. the author has found that jute composite shows acceptable dynamic mechanical properties that are suitable for application in making the casing for electronic devices such as mobile phones and laptops. recently, yang et al. [11] have reviewed the future of cellulosic fiber-based (kenaf, bamboo, banana, and pineapple leaf) composites for marine applications. the authors have mentioned that cellulosic fibers (natural fibers) gain great attention in marine applications due to the drawbacks of synthetic fibers, including high cost, poor recyclability, and high embodied energy. moreover, synthetic-based composites are often disposed of in improper ways. incineration after end-of-service may cause serious air pollution and this is another reason that prompted the idea of developing natural fiber-based composites [12]. it is believed that the introduction of natural fibers in composite industries has created a new option, especially for the manufacturers in developing cost-effective green products with comparable mechanical properties. recently, the potential of kenaf fibers to be used as door panels in automotive parts has been discovered [13]. thus, it is necessary to have continuous research that explores the potentials, limitations, and barriers in growing natural fiber composites so that the properties and behaviors of this composite can be properly verified. therefore, the current research is one of the approaches taken to ensure continuity in the development of natural fiber-based composites in order to discover the abilities of these natural resources for future use. 2. materials and experimental designs 2.1 materials plain woven kenaf fiber with an average thickness of 0.8×10-3 m and density of 1220 kg/m3 was utilized as a reinforcing element. meanwhile, epoxy resin grade inf – 114 with corresponding hardener inf – 212 and density of 1140 kg/m3 was applied as a matrix 317 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 constituent to bind the fibers where the ratio of epoxy-to-hardener was fixed at 100:24.7 (g). 2.2 preparation of kenaf reinforced epoxy matrix composites kenaf composites were fabricated based on three different fiber loadings including 30 vol.%, 40 vol.%, and 50 vol.%. woven kenaf fibers were cut into dimensions of 300 mm × 150 mm and 150 mm × 150 mm for tensile test and flexural test, respectively. meanwhile, pristine epoxy was also fabricated as a control sample. the fabrication process involves the application of vacuum infusion method in which epoxy resins were infused within the layer of kenaf fibers using constant pressure at -100 kpa supplied from a vacuum pump. the curing process at room temperature was performed for 24 hours once the epoxy resin completely covered the plies of kenaf fibers in order to solidify the composite panels. fig. 1 illustrates the schematic diagram of experimental set up for fabrication of kenaf composite panels via vacuum infusion method. fig. 1: schematic diagram of the vacuum infusion layout in the fabrication of kenaf composite panel. 2.3 characterization of kenaf composite panels kenaf composites were subjected to three main characterizations including mechanical, physical, and morphological analyses. the mechanical properties were characterized under tensile and flexural tests. for tensile test, samples were cut into dimension of 250 mm × 25 mm in accordance with astm d3039. this testing was performed using a universal testing machine (utm) instron 5582 with a load of 100 kn and crosshead speed of 2 mm/min. meanwhile, for the flexural test, the same machine was used where samples were prepared with a dimension of 127 mm × 13 mm corresponding to astm d970. the same load of 100 kn and crosshead speed 2 mm/min were applied during the bending test. the water absorption (wa) test was carried out based on astm d570 in which the fabricated kenaf composites were dried inside an oven at a temperature of 70 ℃ for 24 hours in order to identify the initial weight. then, samples were immersed inside the distilled water. the weight of composites was measured every day until 30 days and the rate of water absorption was calculated using the following formula: 𝑊𝐴 = 𝑀1 − 𝑀0 𝑀0 × 100 (1) where wa stands for water absorption, m0 denotes the initial mass of the specimen, and m1 represents the dried mass of the sample after removing from the distilled water. 318 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 the tensile fracture surfaces were characterized using a scanning electron microscope (sem) model joel jsm-5600. the specimens were coated with palladium (pd) where the coating process was performed using a quarom sc7620 sputter coater at 10 kv voltage. flexural failure modes were examined using an optical microscope (nikon measuring microscope trinocular head, model mm-trf). 3. results and discussion 3.1 tensile properties of kenaf reinforced epoxy matrix composites figure 2(a,b) shows the tensile properties of fabricated kenaf composites at three different fiber loadings (30 vol.%, 40 vol.%, and 50 vol.%) and also pristine epoxy as a control sample. from the figure, the tensile strength and modulus of pristine epoxy was recorded at 45 mpa and 1.52 gpa, respectively. the incorporation of kenaf fiber has improved the values of tensile strength and the modulus of the fabricated composite panel. moreover, it can be noticed that, when the fiber content was increased from 30 vol.% to 40 vol.%, the tensile strength of the fabricated kenaf composites increased. however, when kenaf fibers were loaded up to 50 vol.% in the composite system, the value of tensile strength was prone to be decrease. specifically, the highest tensile strength attained was 76.67 mpa when 40 vol.% fibers were loaded into the system where the performance of tensile strength decreased by 7.45% (70.96 mpa) when 30 vol.% fiber content was utilized. surprisingly, the value of tensile strength drastically decreased by 34.08% (50.54 mpa) when the level of fibers increased to 50 vol.%. the same trend as tensile strength was observed in the value of the tensile modulus, which increased in the level of fiber content from 30 vol.% (2.09 gpa) to 40 vol.% (2.31 gpa). this improved the behavior of tensile modulus. whereby, the increment of fiber content up to 50 vol.% (1.88 gpa) resulted in a decrement in the performance of the tensile modulus. fig. 2: (a) tensile strength and (b) tensile modulus of fabricated kenaf composites at different fiber contents. it is believed that the behavior of the tensile properties was influenced by the adhesion characteristic between the plies of kenaf fibers with epoxy resin. this is in agreement with cisneros-lópez et al. [14] where outstanding tensile properties were probably due to the formation of a better fiber-matrix interface that resulted from excellent adhesion between fiber and matrix phases. with regards to the current work, the results indicate that the epoxy resin can provide sufficient support in binding the kenaf fibers at 40 vol.% fiber content in which the formation of high lamination quality was achieved at this condition. with regards to the current work, the results indicate that the epoxy resin can provide sufficient support in binding the kenaf fibers at 40 vol.% fiber content in which the 319 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 formation of high lamination quality was achieved at this condition. it is due to its ability to form a strong fiber-matrix interface between the kenaf fibers and the epoxy resin. therefore, 40 vol.% kenaf composite is able to endure more tension load as compared to 30 vol.% and 30 vol.% before experiencing permanent tensile failure. figure 3 shows the stress-strain curve of kenaf composites at different fiber loadings. from the stress-strain curve, a steep slope can be observed in the kenaf composite that was loaded with 40 vol.% fibers. in fact, the steep slope indicates the composite material tends to exhibit higher tensile modulus as compared to the composite that displays the low slope [15]. it is due to the ability to reach a high fracture point before experiencing external tensile failure. it seems that kenaf composites fabricated with 40 vol.% display higher fracture points than 30 vol.% and 50 vol.% kenaf composites. meanwhile, the lowest fracture point was noticed in kenaf composite that produced using 50 vol.% of fibers. these findings have validated the results obtained in tensile properties discussed in the previous point. 0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0 20 40 60 80 s tr e ss ( m p a ) strain (mm/mm) 30 vol.% 40 vol.% 50 vol.% fig. 3: the stress-strain curve of fabricated kenaf composites at different fiber loadings. figure 4(a–f) shows the micrographs for each of the kenaf composites. the appearance of fiber agglomeration due to poor wettability between fibers and matrix can be detected in the fabricated kenaf composites especially in kenaf composites 50 vol.% of fiber content. severe fiber agglomeration in the 50 vol.% kenaf composite signifies this composite panel experienced poor adhesion between fibers and matrix constituent in which fibers can separate easily from the matrix during the application of tension loads. based on fig. 4(b), kenaf composite that was loaded with 40 vol.% fibers was able to display better fiber-matrix lamination than 30 vol.% and 50 vol.% kenaf composites. at high magnification, all fabricated kenaf composites exposed toward fiber pull-out failure as shown in fig. 4(d–f). from fig. 4(f), it can be noticed that the presence of the gap between matrix phase and fiber appeared in kenaf composite with 50 vol.% fiber loading. this reveals that epoxy resin was unable to bind the fibers efficiently and therefore disturbed the process of transferring tension load from matrix to fibers. as a result, kenaf composite with 50 vol.% was prone to show poor tensile strength and modulus. this is in agreement with the findings from the previous discussion. 3.2 flexural properties of kenaf reinforced epoxy matrix composites flexural properties of fabricated pristine epoxy and kenaf composites at three different fiber loadings, namely 30 vol.%, 40 vol.%, and 50 vol.% are shown fig. 5(a,b). based on fig. 5(a), the value of flexural strength and modulus of pristine epoxy stated at 48.52 mpa and 3.26 gpa, respectively. 320 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 fig. 4: tensile fracture micrographs of fabricated kenaf composites – (a) 30 vol.%, (b) 40 vol.%, and (c) 50 vol.% fiber loadings at ×25 magnification and (d) 30 vol.%, (e) 40 vol.%, and (f) 50 vol.% fiber loadings at ×150 magnification. the increment in the trend of flexural strength can be spotted when kenaf fibers were introduced into the composite system. moreover, when kenaf fiber was increased from 30 vol.% to 40 vol.%, the highest flexural strength can be observed at the value recorded at 61.24 mpa. it is believed that this increment is due to the adequacy of epoxy resins to laminate the fiber efficiently [16]. as a result, once the bending load touched the 40 vol.% kenaf composites, the loads were carried by the whole system rather than the individual ply. therefore, greater loads are needed to break the sample before suffering from flexural failure. the introduction of 50 vol.% kenaf fibers result in reducing the performance of the composite material where the value of flexural strength was reduced by 16.88% in comparison to 40 vol.% fiber content. it indicates that, the utilization of kenaf fibers up to 50 vol.% was unable to provide optimum reinforcing effect toward the composite system. moreover, at high level of fiber content, it is difficult for natural-based composite materials to maintain their strong fiber-matrix interface due to poor compatibility with most polymer matrices [17]. therefore, this composite material is incapable of staying longer under bending loads, hence, resulting in poor flexural properties. a similar pattern fiber agglomeration (a) (b) (c) (d) (e) (f) better fiber-matrix lamination severe fiber agglomeration fiber pull-out fiber pull-out fiber pull-out 321 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 of flexural strength was found in the values of flexural modulus in which the highest flexural modulus gained at 4.2 gpa belongs to kenaf composite loaded with 40 vol.% fibers. the values of flexural modulus decreased by 10.23% and 25% with the employment of 30 vol.% and 50 vol.% fiber content, respectively. (a) (b) fig. 5: (a) flexural strength and (b) flexural modulus of kenaf composites fabricated with different fiber contents. fig. 6: flexural failure of kenaf composites at (a) 30 vol.%, (b) 40 vol.%, and (c) 50 vol.% of fiber content. figure 6(a–c) visualizes failure modes of kenaf composites under a flexural condition. the behavior of crack initiation and propagation can be explained based on this figure. the cracks start to initiate at the bottom part of the kenaf composites when the upper part of composite panels are unable to resist the applied bending load due to high stress (a) (b) (c) bottom part bottom part bottom part upper part upper part upper part large propagation of flexural failure crack initiation crack initiation crack propagation crack propagation 322 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 concentration. then, these cracks spread and propagate in the middle layer of kenaf composites until reaching the maximum fracture point and causing permanent bending failure. based on fig. 6(a-c), all the fabricated kenaf composites suffered from fiber breakage failure in which this failure was probably due to the presence of microcracks resulting from the incapability of composite panels to maintain their strong interfacial bonding between fiber-matrix interfaces [18]. severe fiber breakage occurred in the kenaf composite that was fabricated using 50 vol.% fibers where it caused the composite panel to separate. this indicates that cracks can infiltrate easily within the layers of 50 vol.% kenaf composite due to poor interfacial bonding between layers of kenaf fiber and epoxy resins. based on fig. 6(b), less crack propagation can be noticed in the kenaf composite with 40 vol.% fiber content contrasted over 30 vol.% and 50 vol.% composite panels. the formation of a better fiber-matrix interface due to high wettability between kenaf fibers and epoxy resins has slowed down the propagation of cracks within the composite body. as a result, kenaf composite with 40 vol.% compositions of fibers capable of enduring more bending loads and consequently helping this composite to exhibit better flexural properties as compared to the other kenaf composites. 3.3 water absorption behavior of kenaf composite panels figure 7(a) shows the rate of water absorption for kenaf composites fabricated with three different fiber loadings. the rate of water absorption was measured every day up to 30 days. at the beginning of the process, the rate of water absorption for kenaf composites in all-fiber loadings increased linearly, then the trend of water uptake started to slow down until reaching saturation after a prolonged period. this trend was in accordance with the diffusion theory known as the fickian diffusion process [19]. based on the graph, the highest rate of water absorption was displayed by kenaf composite fabricated using 50 vol.% fibers (43.33%), followed by kenaf composite with 40 vol.% fiber content (30.46 %). whereby, the lowest rate of water absorption recorded at 25.49% belongs to kenaf composite that loaded with 30 vol.% fibers. these values indicate that increases in the amount of kenaf fibers in the composite system tend to increase the rate of water absorption of fabricated composite panels. fig. 7: the rate of water absorption of kenaf composites at 30 vol.%, 40 vol.%, and 50 vol.% fiber content for 30 days. this phenomenon occurred due to the nature of natural fibers in which they are very responsive to the watery environment [20]. the presence of cellulose components in kenaf fibers denotes hydroxyl groups that are the principal contributors to moisture absorption 323 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 and increase the attractiveness to the watery condition [21]. the presence of oh groups from cellulose has been confirmed by ftir spectra as shown in fig. 7(b). thus, increasing the level of kenaf fibers will increase the tendency of the composite panel to absorb more water as compared to the composite with fewer kenaf fibers composition. moreover, it also believed that high water absorption, especially in kenaf composite with 50 vol.% fiber contents, is probably due to the ineffectiveness of epoxy resins to play their role as a barrier in protecting the composite from the watery environmental attack. therefore, it may contribute to the fiber swelling phenomena in which this event can promote the appearance of microcracks [21]. thus, the process of water uptakes becomes dominant and active in the microcrack region. as a result, kenaf composite panels with higher fiber content (50 vol.%) are prone to absorb more water in comparison to kenaf composites that are loaded with low fiber content (30 vol.% and 40 vol.%). 4. conclusion the behaviors of kenaf composites in terms of mechanical properties, water absorption, and failure analyses have been studied where the effects of fiber contents toward these properties were carefully evaluated. thus, it can be concluded that: a) the incorporation of kenaf fibers from 30 vol.% to 40 vol.% successfully improved the mechanical properties (tensile and flexural properties) of fabricated composite panels as compared to the pristine epoxy. whereas the utilization of kenaf fibers up to 50 vol.% has reduced the performances of tensile and flexural properties of kenaf composites. b) common tensile failure, which is fiber pull-out able to be detected in all fabricated kenaf composites, and fiber breakage failures appeared in the flexural failure. these failures were severely found in the kenaf composite that was fabricated using 50 vol.% fiber content. c) increasing in the level of kenaf fibers is prone to increase the rate of water absorption of fabricated kenaf composite panels. acknowledgement the authors would like to express their gratitude to the ministry of higher education (mohe) of malaysia for the support through the awarded grant (frgs 17-033-0599), kulliyyah of engineering, international islamic university malaysia (iium), and also to the iium research management centre for facilitating this project. references [1] saadati y, lebrun g, chatelain jf and beauchamp y (2020) experimental investigation of failure mechanisms and evaluation of physical/mechanical properties of unidirectional flax– epoxy composites. j. composite materials, 54(20): 1-21. doi:10.1177/0021998320902243 [2] dhaliwal gs, dueck sm, newaz gm. (2019) experimental and numerical characterization of mechanical properties of hemp fiber reinforced composites using multiscale analysis approach. sn appl. sci., 1: 1361. https://doi.org/10.1007/s42452-019-1383-6 [3] madhu p, sanjay mr, senthamaraikannan p, pradeep s, saravanakumar ss and yogesha b (2018) a review on synthesis and characterization of commercially available natural fibers: part ii. journal of natural fibers, 16: 25-36. doi:10.1080/15440478.2018.1453433 324 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 [4] thyavihalli girijappa yg, mavinkere rangappa s, parameswaranpillai j and siengchin s (2019) natural fibers as sustainable and renewable resource for development of eco-friendly composites: a comprehensive review. frontiers in materials, 6: 1-14. doi:10.3389/fmats.2019.00226 [5] mochane mj, mokhena tc, mokhothu th, mtibe a, sadiku er, ray ss, ibrahim id, daramola oo (2019) recent progress on natural fiber hybrid composites for advanced applications: a review. express polymer letters, 13(2): 159-198. doi:10.3144/expresspolymlett.2019.15 [6] siakeng r, jawaid m, ariffin h, sapuan sm, asim m and saba n (2018) natural fiber reinforced polylactic acid composites: a review. polymer composites, 40: 446-463. doi:10.1002/pc.24747 [7] navaneethakrishnan g, karthikeyan, t, saravanan s, selvam v, parkunam n, sathishkumar g and jayakrishnan s (2019) structural analysis of natural fiber reinforced polymer matrix composite. materials today: proceedings, 21: 7-9. doi:10.1016/j.matpr.2019.05.295 [8] kumar r, ul haq mi, raina a and anand a (2018) industrial applications of natural fibrereinforced polymer composites – challenges and opportunities. international journal of sustainable engineering, 12: 212-220. doi:10.1080/19397038.2018.1538267 [9] javadian a, smith ian fc, nazanin f and hebel de (2019) mechanical properties of bamboo through measurement of culm physical properties for composite fabrication of structural concrete reinforcement. frontiers in materials, 6: 1-15. [10] gupta mk. (2018) effect of variation in frequencies on dynamic mechanical properties of jute fibre reinforced epoxy composites. journal of materials and environmental sciences, 9: 100-106. https://doi.org/10.26872/jmes.2018.9.1.12 [11] yang mfm, hamid h, abdullah am. (2018) potential use of cellulose fibre composites in marine environment a review. in: öchsner a. (eds) engineering applications for new materials and technologies. advanced structured materials, springer, cham, 86: 22-55. [12] kaiser k, schmid m, schlummer m. (2017) recycling of polymer-based multilayer packaging: a review. recycling, 3: 1-26. doi:10.3390/recycling3010001 [13] yuhazri my, amirhafizan mh, abdullah a, husin ma, kamarul am and lau stw (2018) kenaf fibre composites as promising green-composites for automotive car door map pocket application. international journal of mechanical & mechatronics engineering, 8: 15-21. [14] cisneros-lópez eo, gonzález-lópez me, pérez-fonseca aa, gonzález-núñez r, rodrigue d and robledo-ortíz jr (2016) effect of fiber content and surface treatment on the mechanical properties of natural fiber composites produced by rotomolding. composite interfaces, 24: 35-53. doi:10.1080/09276440.2016.1184556 [15] alberto m. (2013) introduction of fibre-reinforced polymers − polymers and composites: concepts, properties and processes. fiber reinforced polymers the technology applied for concrete repair intechopen, pp. 3-40. [16] harsha ap and arjula s. (2010) influence of fibre orientation on three-body abrasive wear behaviour of unidirectional carbon fibre-reinforced polyetherimide composite. journal of materials science, 46: 983-991. doi:10.1007/s10853-010-4856-y [17] adekomaya o, jamiru t, sadiku r and huan z (2017) negative impact from the application of natural fibers. journal of cleaner production, 143: 843-846. doi:10.1016/j.jclepro.2016.12.037 [18] wang w, chouw n, jayaraman k. (2016) effect of thickness on the impact resistance of flax fibre-reinforced polymer. j. reinforced plastics and composites, 35: 1277-1289. doi:10.1177/0731684416648780 [19] peret t, clement a, freour s, jacquemin f. (2019) homogenization of fickian and nonfickian water diffusion in composites reinforced by hydrophobic long fibers: application to the determination of transverse diffusivity. composite structures, 226: 1-9. doi:10.1016/j.compstruct.2019.111191 325 iium engineering journal, vol. 22, no. 2, 2021 yusuff et al. https://doi.org/10.31436/iiumej.v22i2.1747 [20] rozali na, abu bakar mb, masri mn, sulaiman ma, mohamed m, ahmad thirmizir mz (2017) mechanical and water absorption properties of hybrid kenaf/glass fibre mat reinforced unsaturated polyester composites. materials science forum, 888: 228-233. doi:10.4028/www.scientific.net/msf.888.228 [21] maslinda ab, abdul majid ms, ridzuan mjm, and syayuthi ara (2017). water absorption behaviour of hybrid interwoven cellulosic fibre composites. iop conf. series: journal of physics: conf. series, 908: 012015. doi:10.1088/1742-6596/908/1/012015 326 289 iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 131 three dimensional parametric analyses on effect of fibre orientation for stress concentration factor in fibrous composite cantilever plate with central circular hole under transverse loading moon banerjee 1 , n.k. jain 1 and s. sanyal 2 1 department of applied mechanics, national institute of technology, raipur, chattisgarh 492010, india. 2 department of mechanical engineering, national institute of technology, raipur, chattisgarh 492010, india. moonbanerjee@gmail.com; nkjmanit@rediffmail.com; shubhashissanyal@rediffmail.com abstract: a number of analytical and numerical techniques are available for the two dimensional study of stress concentration around the hole(s) in isotropic and composite plates subjected to in-plane or transverse loading conditions. the information on the techniques for three dimensional analyses of stress concentration factor (scf) around the hole in isotropic and composite plates subjected to transverse loading conditions is, however, limited. the present work emphasizes on the effect of fibre orientation (q) on the stress concentration factor in fibrous composite plates with central circular hole under transverse static loading condition. the work is carried out for cantilever fibrous composite plates. the effects of thickness -towidth (t/a) and diameter-to-width (d/a) ratios upon scf at different fibre orientation are studied. plates of four different composite materials were considered for hole analysis in order to determine the sensitivity of scf with elastic constants. deflections in transverse direction were calculated and analysed. all results are presented in graphical form and discussed. the finite element formulation and its analysis were carried out using ansys package. abstrak: terdapat pelbagai teknik analitikal dan numerical untuk kajian tumpuan tegasan dua dimensi di sekeliling lubang-lubang dalam komposit isotropik dan plat pada satah atau keadaan bebanan melintang. bagaimanapun, maklumat mengenai kaedah analisis tiga dimensi untuk faktor ketumpatan tegasan (scf) sekitar lubang dalam komposit isotropik dan plat pada keadaan bebanan melintang adalah terhad. kertas ini menekankan kesan orientasi gentian (θ) pada faktor tumpuan tegasan dalam komposit plat bergentian dengan lubang berpusat di bawah keadaan bebanan melintang. kajian ini dilkukan untuk cantilever plat komposit bergentian. kesan ketebalan terhadap kelebaran plat (t/a) dan diameter terhadap kelebaran komposit (d/a) dengan scf pada orientasi gentian berbeza telah dikaji. plat komposit bagi empat bahan komposit berbeza telah diambilkira bagi kesemua analisis untuk mendapatkan kesensitifan scf dengan konstan elastic. defleksi pada arah melintang telah dikira dan dianalisa. kesemua keputusan telah disembahkan secara grafik dan dibincang. fomulasi unsur finit dan analisis telah dilaksanakan menggunakan pakej ansys. keywords: finite element method; stress concentration factor; composites; transverse loading; deflection; elastic constants iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 132 1. introduction fibrous composite plates with central circular hole are finding a wide range of applications in structural design of aerospace, marine, automobile, mechanical engineering especially for light weight structures that have stringent stiffness and strength requirements. accurate knowledge of deflection, stresses and scf are required for design of such plates with hole. any abrupt change in geometry of plate under loading give rise to stress concentration, as a result stress distribution is not uniform throughout the cross section. composite plates fail due to the failure of individual component (fibre or matrix) or their interface. it is well known that the presence of a notch in a stressed member creates highly localized stresses at the root of the notch. failures such as fatigue crack and plastic deformation frequently occur at the points of stress concentration. various researchers analyzed different cases of stress concentration in plate with circular holes. shastry and raj [1] have analyzed the effect of fibre orientation for a unidirectional composite laminate with finite element method by assuming a plane stress problem under in plane static loading. chaudhuri [2] worked on stress concentration around a part through hole weakening a fibrous plate using finite element method. paul and rao [3-5] evaluated stress and stress concentration in fibre reinforced composite fibrous plate containing central circular hole and two coaxial holes subjected to transverse load by using finite element method using lo christensen wu higher order bending theory. xiwu et al. [6] and [7] studied a finite composite plate weakened by elliptical holes under different inplane loading, treated as an anisotropic multiple connected plates, based on the classical plate theory. using the complex potential method in the plane theory of elasticity of an isotropic body, an analytical solution concerned with stress concentration around an elliptical hole or holes in finite composite fibrous plate was obtained. ting et al. [8-9] presented the alternative method to study the stress distributions of the multiple circular or multiple elliptical holes with the rhombic pattern in the infinite domain. ukadgaonker and rao [10] proposed a general solution for stresses around hole in symmetric laminates under in-plane loading by introducing a general form of mapping function and an arbitrary biaxial loading condition to the boundary conditions, and the basic formulation is extended for multilayered plates. troyani et al. [11] have determined the in-plane theoretical stress concentration factors for short rectangular plates with centered circular holes subjected to uniform tension using finite element method. kotousov and wang [12] have presented analytical solutions for the three dimensional stress distributions around typical stress concentrators in an isotropic plate of arbitrary thickness based on the assumption of a generalized plane strain theory. toubal et al. [13] studied stress concentration in a circular hole in composite plate. ukadgaonker and kakhandki [14] analyzed the stress around an irregular shaped hole for different in-plane loading conditions for an orthotropic fibrous plate. gruber et al. [15] developed analytical solution methods for the analysis of stress concentration in fibre reinforced multilayered composites with pin loaded holes. she and guo [16] have analyzed the variation of three dimensional stress concentration factors along the wall of elliptic holes in finite thickness plates of isotropic materials subjected to remote tensile stress using finite element method. jain and mittal [17] have analyzed the stress concentration and deflection in isotropic, orthotropic and fibrous composite plates with central circular hole subjected to transverse static loading by using two dimensional finite element methods. mittal and jain [18] analyzed the effect of fibre orientation on stress concentration factor in fibrous plate with central circular hole under transverse static loading by using two dimension finite element methods. ghezzo et al. [19] performed a numerical and experimental analysis of the interaction between two notches in carbon iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 133 fibre laminates. the numerical analysis of the stress distribution in-plane stress assumption and within the fibrous plate theory framework has been conducted on two symmetric laminates. ozben et al. [20] compiled fem analysis of laminated composite plate with rectangular hole and various elastic modulus under transverse loads. ozen et al. [21] presented the failure loads of mechanical fastened pinned and bolted composite joints with two serial holes. tsai–wu failure criterion was used to predict first failure loads by finite element analysis for the geometrical parameters. kumar et al. [22] has studied the post buckling strengths of composite laminate with various shaped cut-outs under in plane shear. rao et al. [23] evaluated the stress around square and rectangular cut-outs in symmetric laminates. it has been analyzed that the maximum stress and its location is mainly influenced by the type of loading. in view of the above literature review, it can be concluded that the analysis of more cases of stress concentration in composite plates with hole subjected to transverse loadings needs to be further investigated in detail. the present work aims to study the effect of fibre orientation (θ) on stress concentration factor (scf) in fibrous composite plates with central circular hole subjected to transverse static loading and study of deflection is carried out. the effect of t/a and d/a ratio where t is the plate thickness and a is the plate width and d is the hole diameter on scf for normal stresses in x, y directions (σx, σy), shear stress (τxy), vonmisses (equivalent) stress (σeqv) and deflection in transverse direction (uz) is investigated by using three dimensional finite element analysis in cantilever composite plates with central circular hole. the uz for different materials for cantilever plate under transverse loading is compared with deflection in transverse direction in plate without hole (uz * ). results are obtained for four different materials to find out the sensitivity of scf and deflection on elastic constants also. 2. formulation of the problem the model of fibrous composite plate of dimension 0.2 m x 0.1 m with t thickness with a central circular hole of diameter d under uniformly distributed loading of p (n) in transverse direction (fig. 1.) is taken for analysis. three different t/a ratios of 0.01, 0.05 and 0.1 are varied and for each t/a ratio three different d/a ratios of 0.1, 0.2 and 0.5 are varied respectively. four different composite materials are selected for the analysis. the material properties for the composite materials, selected for analysis are shown in table 1. where e, g, and µ are modulus of elasticity, modulus of rigidity and poisson’s ratio respectively. table 1: material properties of composite materials [24]. material properties e-glass/ epoxy (1) boron/ epoxy (2) wovenglass/epoxy (3) boron/ aluminium (4) ex 39gpa 201gpa 29.7gpa 235gpa ey 8.6gpa 21.7gpa 29.7gpa 137gpa ez 8.6gpa 21.7gpa 29.7gpa 137gpa gxy 3.8gpa 5.4gpa 5.3gpa 47gpa gyz 3.8gpa 5.4gpa 5.3gpa 47gpa gzx 3.8gpa 5.4gpa 5.3gpa 47gpa µxy 0.28 0.17 0.17 0.30 µyz 0.28 0.17 0.17 0.30 µzx 0.28 0.17 0.17 0.30 iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 134 boundary conditions for plate (b) with all edges cantilever ux=uy=uz=0 is selected, fig. 1. fig. 1: cantilever plate with hole under transverse loading. 3. finite element analysis the finite element method was chosen for numerical analysis of the model due to its unique capability to analyze structures of complex material behavior. the model was developed using a 3-d solid element specified as, solid 191 in ansys package. the element is defined by 20 nodes having three degrees of freedom per node; a translation in the nodal x, y and z directions, grouping of 60 nodes per element. it is having high stress stiffening capabilities. typical mesh of the plate using the above element is shown in fig. 2. mapped meshing is used for all models with more elements employed near the hole boundary. number of checks and convergence tests are made for selection of suitable elements from different available elements, following above the element length is decided as 5mm. results were then displayed by using post processor of ansys program. the example of the discretized three dimensional finite element models for d/a =0.2 and t/a=0.05, used in study is shown in fig. 2. fig. 2: element used and generated mesh of the plate. 4. results and discussion model generated are analysed and results thus obtained for various material combinations are presented in graphs. results are discussed case by case further. iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 135 fig. 3: variations of scf for σx versus fibre orientation for different materials. the effect of fibre orientation on scf for σx to different d/a and t/a ratios in cantilever fibrous composite plate made of e-glass/epoxy, boron/epoxy, wovenglass/epoxy and boron/aluminium is shown in fig. 3. following observations can be made. scf for σx for cantilever case is not symmetric about any fibre orientation for all materials considered. the effect of t/a ratios plays a substantial role on scf for σx for all cases considered, while d/a ratios effect is negligible. eglass/epoxy composite for the cantilever case shows a non periodic behaviour. from 0 0 to 30 0 fibre orientation, scf for σx gradually decreases uptill 30 0 orientation and from 75 0 to 120 0 all t/a lines coincide, which shows that effect of t/a and d/a is negligible. boron/epoxy scf for σx decreases from 0 0 to 15 0 orientation and attaining maximum values at 0 0 and 180 0 fibre orientation. the minimum value is obtained for t/a=0.1 ratios and at 60 0 orientation of fibre. wovenglass/epoxy shows very less variation for scf of σx for all orientations with respect to d/a and t/a ratios as compared to simply supported case. boron/aluminium almost neglected the effect of variation of t/a, and shows a very small changes in scf for iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 136 different fibre orientation. maximum scf for σx are 1.77 and 1.03 is obtained for boron/epoxy and wovenglass/epoxy for d/a=0.5 and t/a=0.1 at 0 0 and 180 0 orientation. again for boron/aluminium maximum scf of 1.02 value is obtained for t/a=0.1 and d/a=0.5 at 0 0 and 180 0 orientation and for eglass/epoxy maximum scf value of 1.00 is achieved for t/a=0.01 and d/a=0.1 at again 0 0 and 180 0 fibre orientation. minimum values of scf for σx are 0.48, 0.11, 0.68 and 0.65 is obtained for e-glass/epoxy, boron/epoxy, woven-glass/epoxy and boron/aluminium for t/a=0.1 and d/a=0.1and at 0 0 , 45 0 , 15 0 and 30 0 fibre orientation. fig. 4: variations of scf for σy versus fibre orientation for different materials. the effect of fibre orientation on scf for σy to different d/a and t/a ratios in cantilever fibrous composite plate made of e-glass/epoxy, boron/epoxy, wovenglass/epoxy and boron/aluminium is shown in fig. 4. following observations can be made. s c f s c f iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 137 the effect of t/a and d/a on scf of σy is almost negligible for e-glass/epoxy, and boron/epoxy, whereas slight effect of both the ratios can be observed over wovenglass/epoxy and boron/aluminium. scf for σy continously decreases with increase in orientation from 0 0 to 45 0 and attaining a maximum value at 0 0 and 180 0 fibre orientation for e-glass/epoxy, boron/epoxy and boron/aluminium. woven-glass/epoxy also follows the similar trend, but achieving its maximum value at 0 0 , 90 0 and 180 0 fibre orientation. maximum values of scf for σy are 6.00, 36.59 and 1.60 are obtained for e-glass/epoxy, boron/epoxy and boron/aluminium fibrous composite plate respectively for t/a=0.01 and d/a=0.1, whereas for woven-glass/epoxy maximum 2.98 scf for σy is attained for d/a=0.5 and t/a=0.01 at 0 0 and 180 0 fibre orientation. minimum value of scf for σy are 0.22 and 0.18 is obtained for e-glass/epoxy and boron/epoxy composite plate for t/a=0.01 and d/a=0.1 at 0 0 and 180 0 fibre orientation, whereas for woven-glass/epoxy and boron/alimunium maximum scf value of 0.48 and 0.51 is obtained for t/a=0.1 and d/a=0.2 at 45 0 fibre orientation. fig. 5: variations of scf for τxy versus fibre orientation for different materials. iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 138 the effect of fibre orientation on scf for τxy to different d/a and t/a ratios in cantilever fibrous composite plate made of e-glass/epoxy, boron/epoxy, wovenglass/epoxy and boron/aluminium is shown in fig. 5. following observations can be made. the effect of t/a is prominent for scf of τxy of in e-glass/epoxy and boron/epoxy, whereas d/a ratio has very negligible influence on scf of the materials. significant effect of both the ratios can be encountered for woven-glass/epoxy and boron/aluminium. maximum value of scf for τxy are 11.29, 113.26, 7.02 and 3.66 are obtained for eglass/epoxy, boron/epoxy, woven-glass/epoxy and boron/aluminium fibrous composite plate respectively for t/a=0.01 and d/a=0.5 at 0 0 and 180 0 fibre orientation. minimum value of scf for τxy are 0.17, 0.06 and 0.22 is obtained is obtained for e-glass/epoxy, boron/epoxy and boron/aluminium fibrous composite plate respectively for t/a=0.05 and d/a=0.1 at 0 0 and 180 0 fibre orientation, whereas woven-glass/epoxy achieves its minimum value of scf as 0.25 for t/a=0.1 and d/a=0.1 at 45 0 fibre orientation. fig. 6: variations of scf for σeqv versus fibre orientation for different materials. iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 139 the effect of fibre orientation on scf for σeqv to different d/a and t/a ratios in cantilever fibrous composite plate made of e-glass/epoxy, boron/epoxy, wovenglass/epoxy and boron/aluminium are shown in fig. 6. following observations can be made. d/a ratio effect on all the materials for scf for σeqv is almost negligible, whereas effect of t/a ratios on scf is significant for all composite materials considered. scf for σeqv is seen continously decrease on increasing fibre orientation from 0 0 to 45 0 and then gradually increase from 45 0 to 90 0 orientation attaining maximum at 0 0 and 180 0 orientation for all materials considered. it is to note that maximum scf of σeqv are 1.19 and 1.41 are obtained for e-glass/epoxy and boron/epoxy respectively for t/a=0.01 and d/a=0.5 at 0 0 and 180 0 fibre orientation, whereas for woven-glass/epoxy and boron/aluminium maximum scf are 1.00 and 0.99 for t/a=0.05 and d/a=0.1 at same fibre orientation. minimum value of scf for σeqv are 0.31 and 0.18 is obtained for e-glass/epoxy and boron/epoxy respectively for t/a=0.05 and d/a=0.1 at orientation of 45 0 , whereas for woven-glass/epoxy it is 0.71 for t/a=0.05 and d/a=0.5 and 0.63 scf for boron/aluminium for t/a=0.1 and d/a=0.5 at 45 0 fibre orientation. fig. 7: variations of uz/ uz * versus fibre orientation for different materials. 0.5 1.0 1.5 2.0 2.5 3.0 u z /u z * 0 1 2 3 4 5 6 0 30 60 90 120 150 180 1.1 1.2 1.3 1.4 1.5 u z /u z * 0 30 60 90 120 150 180 0.90 1.05 1.20 1.35 1.50 1.65 t/a=0.01 t/a=0.05 t/a=0.1 t/a=0.01 t/a=0.05 t/a=0.1 t/a=0.01 t/a=0.05 t/a=0.1 t/a=0.01 t/a=0.05 t/a=0.1 e-glass/epoxy boron/epoxy woven-glass/epoxy boron/alumunium iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 140 the effect of fibre orientation on uz/uz * to different d/a and t/a ratios in cantilever fibrous composite plate made of e-glass/epoxy, boron/epoxy, woven-glass/epoxy and boron/aluminium is shown in fig. 7. following observations can be made. the influence of t/a and d/a is significant for uz/uz * for all cases of materials under different fibre orientation. it can be noticed that uz/uz * is continously decrease with increase of orientation of fibre from 0 0 to 90 0 , and gradually increase from 90 0 to 180 0 attaining a maximum value at 0 0 and 180 0 orientation for all materials considered except woven-glass/epoxy following a wavy pattern with continous decrease of uz/uz * from 0 0 to 45 0 and then gradual increment from 45 0 to 90 0 orientation obtaining maximum value at 0 0 , 90 0 and 180 0 fibre orientation. uz/uz * attains its maximum value of 2.63, 5.44 and 1.56 for e-glass/epoxy, boron/epoxy and boron/aluminium for t/a=0.1 and d/a=0.5 at 90 0 fibre orientation. woven-glass/epoxy following a peoridic pattern shows its maximum value as 1.46 again for t/a=0.1 and d/a=0.5 at 0 0 , 90 0 and 180 0 fibre orientation. minimum value of uz/uz * are 0.94, 1.10 and 1.00 for e-glass/epoxy, boron/epoxy and boron/aluminium for t/a=0.01 and d/a=0.1 at 90 0 orientation, whereas for wovenglass/epoxy the minimum value reaches to be 1.12 for again t/a=0.01 and d/a=0.1 but at 15 0 , 75 0 and 165 0 fibre orientation. 5. conclusion a) higher ex/ey & ex/gxy ratios increases the value of scf for σx of e-glass/epoxy & boron /epoxy as they are having highest of these values as compared to wovenglass/epoxy & boron/aluminium. b) scf for σx is maximum near the fixed end of the plate, σy is maximum at the hole boundary towards the longitudnal (x) direction of the plate. σxy is maximum again at fixed end of the plate, but at their extreme corners only. σeqv is showing its maximum value at fixed end of the plate through out its thickness. uz shows its maximum value through out its edge over the fixed end, expanding quarter half of the plate. c) the scf for σx & uz shows its maximum value at 0 0 orientation of fiber. the scf for σy and the materials having higher ex/ey & ex/gxy ratios have almost discarded the effect of both d/a & t/a ratios. again for materials considered with lesser ex/ey & ex/gxy ratios shows significant role in variation of d/a & t/a ratios. d) the effect of d/a ratio is negligible for the scf of σx, σy, σxy and σeqv except for deflection case, only t/a ratios variation can be clearly encountered. e) scf for σy, σxy, σeqv and uz is symmetric for 90 0 fibre orientation except for σx. f) scf values for σx have reached to 1 and less than 1 for d/a=0.5 and all t/a ratios at 30 0 fiber orientation. g) scf values for σx reduces with the increase of t/a and d/a ratios. acknowledgement the authors acknowledge the authorities of n.i.t, raipur for permitting the above work to be carried out. references [1] b.p. shastry and g.v. raj. “effect of fibre orientation on stress concentration in a unidirectional tensile laminate of finite width with a central circular hole.” fibre science technology, 10(1977): 151-4. iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 141 [2] r.a. chaudhuri. “stress concentration around a part through hole weakening laminated plate.” computers and structurcs, 27.5(1987): 601-9. [3] t.k. paul and k.m. rao.” stress analysis in circular holes in frp laminates under transverse load.” computers and structures, 33.4 (1989): 929-35. [4] t.k. paul and k.m. rao. “finite element evaluation of stress concentration factor of thick laminated plates under transverse loading.” computers and structures, 48.2 (1993):3117. [5] t.k. paul and k.m. rao. “finite element stress analysis of laminated composite plates containing two circular holes under transverse loading.” computers and structures, 54(1995): 671-7. [6] x. xiwu, s. liangxin, and f. xuqi. “stress concentration of finite composite laminates with elliptical hole.” computers and structures, 57.1(1995): 29:34. [7] x. xiwu, s. liangxin, and f. xuqi. “stress concentration of finite composite laminates weakened by multiple elliptical holes.” intemational journal of solids structures, 32.20(1995): 3001-14. [8] k. ting, k.t. chen and w.s. yang. “'boundary element alternating method applied to analyze the stress concentration problems of multiple elliptical holes in an infinite domain.” nuclear engineering and design, 187(1999): 303-13. [9] k. ting, k.t. chen and w.s. yang. “stress analysis of the multiple circular holes with the rhombic amay using alternating method.” intemational journal of pressure vessels and piping, 76(1999): 503-14. [10] v.g. ukadgaonker and d.k.n. rao. “a general solution for stresses around holes in symmetric laminates under in plane loading.” composite structure,49(2000): 339-54 [11] n. troyani, c. gomes and g. sterlacci. “theoretical stress concentration factors for short rectangular plates with centered circular holes.” journal of mechanical design, asme, 124(2007): 126-8. [12] kotousov and c.h. wang. “threedimensional stress constraint in an elastic plate with a notch.” lnternational journal of solids and stuctures, 39(2002): 4311-26. [13] toubal, m. karama and b. lorrain. “stress concentration in a circular hole in composite plate.” composite structures, 68(2005): 31-6. [14] v.g. tlkadgaonker and v. kakhandki. “stress analysis for an orthotropic plate with an irregular shaped hole for different in-plane loading conditions-part 1.” composite structures, 70(2005): 255-74. [15] gruber, w. hufenbach, l. kroll, m. lepper and b. zhou. “sress concentration analysis of fibre-reinforced multilayered composites with pin-loaded holes.” composites science and technolog, 67(2007): 1439-50. [16] she and w.guo. “threedimensional stress concentrations at elliptic holes in elastic isotropic plates subjected to tensile stress.” international journal of fatigue, 29(2007): 330-5. [17] n.k. jain and n.d. mittal. “finite element analysis for stress concentration and deflection in isotropic, orthotropic and laminated composite plates with central circular hole under transverse static loading.” materials science and engineering, 498(2008): 115-24. [18] n.k. jain and n.d. mittal. “effect of fibre orientation on stress concentration factor in a laminate with central circular hole under transverse static loading.” indian journal of engineering & material sciences, 15(2008): 452-8. [19] f. ghezzo, g. giannini, f. cesari and g. galigiana. “numerical and experimental analysis of the interaction between two notches in carbon fibre laminates.” composites science and technology, 68(2008): 1057-72. [20] t. ozben and n. arslan. “em analysis of laminated composite plate with rectangular hole and various elastic modulus under transverse loads.” applied mathematical modeling, 34(2010): 1746. [21] m. ozen and o. sayman. “failure loads of mechanical fastened pinned and bolted composite joints with two serial holes.” composites: part b, 2010. [22] kumar and s.b. singh. “post buckling strengths of composite laminate with various shaped cutouts under in-plane shear.” composite structure, 92(2010): 296-7. iium engineering journal, vol. 13, no. 2, 2012 banerjee et al. 142 [23] d.k.n. rao, m.r. babu, k.r.n. reddy and d. sunil. “stress around square and rectangular cutouts in symmetric laminates.” composite structures, 19(2010). [24] i.m. daniel and o. ishai. engineering mechanics of composite materials. new york: oxford university press, 1994. microsoft word 140-476-1-pb vetted-final.doc ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 37 polyhydroyalkanoates: from basic research and molecular biology to application amro abd al fattah amara genetic engineering and biotechnology research institute, mubarak city for scientific research and technological applications. egypt. e-mail: amroamara@web.de abstract: this review describes the polyhydroxyalkanoate (pha), an intracellular biodegradable microbial polymer. phas is formed from different types of three hydroxyalkanoic acids monomers, each unit forms an ester bond with the hydroxyl group of the other one and the hydroxyl substituted carbon has r configuration. the c-3 atom in β position is branched with at least one carbon atom in the form of methyl group (c1) to thirteen carbons in the form of tridecyl (c13). this alkyl side chain is not necessarily saturated. phas are biosynthesized through regulated pathways by specific enzymes. phas are accumulated in bacterial cells from soluble to insoluble form as storage materials inside the inclusion bodies during unbalanced nutrition or to save organisms from reducing equivalents. phas are converted again to soluble components by phas depolymerases and the degraded materials enter various metabolic pathways. until now, four classes of enzymes responsible for phas polymerization are known. phas were well studied regarding their promising applications, physical, chemical and biological properties. phas are biodegradable, biocompatible, have good material properties, renewable and can be used in many applications. the most limiting factor in phas commercialization is their high cost compared to the petroleum plastics. this review highlights the new knowledge and that established by the pioneers in this field as well as the factors, which affect phas commercialization. keywords phac synthase, polyhydroxyalkanoate, polyhydroxybutyrate, plastic, application, commercialization 1. introduction 1.1 polymers polymers are naturally occurring or synthetic compounds, consisting of large molecules, made up of linked series of repeated monomers joined by chemical bonds through chemical reactions (polymerization, polycondensation, polyaddition) to form the polymer. plastic is a generic name of synthetic, semi-synthetic or natural materials that can be moulded or extruded into objects, films, filaments or used to make, for example coatings and adhesives. it is mainly derived from petroleum oil. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 38 1.2 plastic problems the manufacturing of plastic has increased significantly since the 1940s and has successfully replaced wood, mud, metals, glass and other materials [1, 2, 3, 4]. the low cost, stability, durability, good mechanical and thermal properties of plastic make it the best choice for widespread applications [5]. the extensive use of materials made from plastics causes a worldwide problem because they are non-degradable [3, 5, 6, 7]. plastic packages take up about 1/3 of the volume of municipal wastes because of their low density [8, 9, 10]. plastics consistently make up 60 to 80% of the marine debris [11]. barnes (2002) accounts the amount of debris around the coastline of the uk has doubled between 1994 and 1998, in parts of the southern ocean it increased 100-fold [12]. general data show that world production of packages is on the level of about 1500 million tons/year [10]. three hundred and sixty thousand tons of plastic for the production of bottles have been manufactured in europe in 2002 and the world currently needs around 140 million tons of plastic yearly [13]. processing these plastics needed nearly 150 million tons of fossil fuels, which with their high treatment cost and the emission of toxic compounds like dioxin during plastic incineration increase the gravity of the problem [14]. 1.3 biopolymers steinbüshel has classified the biopolymers based on their chemical structure into eight classes: i) nucleic acids, ii) "polyamides" such as a protein poly-(amino acids), iii) polysaccharides, iv) organic polyoxoesters such as poly(hydroxyalkanoic acids), poly(malic acid) and cutin, v) polythioesters, iv) inorganic polyesters with polyphosphate, vii) polyisoprenoides such as natural rubber or gutta-percha and viii) polyphenols such as lignin or humic acids [15]. not all biopolymers have the same properties, few species can be used as plastics and not all of them are biodegradable like polythioesters [16 18]. fig. 1: bacterial cells producing a pha polymer (white granules inside the cell) the most widely known bioplastics, which are produced by microbes, are polyhydroxyalkanoates (phas) and their derivatives [19-21]. phas can solve the solid waste problem by substituting petroleum plastic [4, 22]. phas have proved to be similar in material properties to petroleum plastics, while phas are produced from renewable resources and are biodegradable [22, 23]. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 39 1.4 history of phas phas are widely distributed within different microbial species and are accumulated intracellularly in the form of storage granules. perhaps, the first report about lucent granules of phas in bacterial cells (fig. 1) was made by beijerinck in 1888 (reported in chowdhury, 1963) [24]. the french scientist maurice lemoigne, who worked at the lille branch of the pasteur institute france, had the interest to characterize these inclusion bodies, which were found in bacillus spp. the work done by lemoigne and co-workers were published in 27 publications from 1923 until 1951 [25]. lemoigne was the first to report that the bacterial granules components (lemoigne describes it also as reserved material) were not ether soluble, as in lipids, and later reported that polyhydroxybutanoate (phb) is the major constituent of these granules. using microscopic observations, saponification numbers, and autolysis whose solubility and melting point (tm) variation were correlated with molecular size proposed a polyester structure with formula (c4h6o2)n. lemoigne has also reported that phb could cast into film like cellulose nitrate material [25 29]. during the following years, interest in this unknown material was negligible. in 1953 weibull had isolated the granules of bacillus megaterium by dissolution of the cell wall with a lysozyme [30]. the first report on functions of phb appeared in 1958 by wilkinson and wilkinson who obtained morphologically intact granules from bacillus cereus using alkaline hypochlorite, and macrae and wilkinson in 1958 who described poly-βhyroxybutyrate metabolism in washed suspensions of bacillus cereus and bacillus megaterium [31, 32]. doudoroff and stanier (1959) and stainer et al., (1959) found that phb can be produced by photosynthetic assimilation of organic compounds by phototrophic bacteria and they described that the reaction involved in the metabolic pathway is responsible for the biosynthesis of phb from acetic acid [33, 34]. merrick and doudoroff (1961) isolated and described native phb granules of hemoheterotropic bacteria, rhodospirillum rubrum and b. megaterium [35]. in 1966, lusty and doudoroff have shown a study on depolymerases which were able to hydrolyse phb [36]. lundgren et al., (1965) showed that only the cells that are extracted with chloroform could yield high molecular weight phb [37]. schlegal at the university of göttingen, germany in 1961 observed that cupriavidus necator (formally wautersia eutropha, ralstonia eutropha and alcaligenes eutrophus), could accumulate very large amount of phb in a media with low nitrogen content [38]. merrick and doudoroff (1964) were the first to identify the enzyme responsible for phb polymerization which is the synthase or the polymerase as was known at that time followed by work done by griebel et al., (1968) [39, 40]. schlegal working with c. necator and dawes working with azotobacter berjerinckii (university of hull, england) in 1973 simultaneously were the first to isolate and characterize the enzymes, which catalyse the phb monomer synthesis [41, 42]. wallen gave the first indication that the polymer discovered by lemoigne may contain proportions of 3-hydroxyacids other than 3-hydroxybutyrate and rohwedder, who, in 1974, reported heteropolymers of 3-hydroxybutyrate and 3-hydroxyvalerate in chloroform extracts of activated sewage sludge as major constituents with c6 and possibly c7 3hydroxyacids as minor components [43]. this heteropolymer had a lower melting point than phb and, unlike the homopolymer, was soluble in hot ethanol. findlay and white in ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 40 1983, using gc analysis, detected at least 11 short-chain 3-hydroxyacids, the principal ones being 3hb and 3hv [44]. de smet et al. characterized pha mcl in pseudomonas oleovorans during growth on octane [45]. huisman et al. confirmed that pha mcl accumulation was the common feature of fluorescent pseudomonads [46]. phas are also produced by gram-positive, gramnegative bacteria and phototrophic bacteria as well as archaea [47 52]. phac synthase from an extreme halophilic archaeon has been enzymologically and biochemically characterized [53, 54]. the first halobacterial phas synthase gene sequenced is from haloarcula marismortui [55]. another putative polyester synthase gene was identified in the genome of an uncultivated archaebacterium belonging to crenarchaeota [56]. 2. phas nomenclature there are many ways to abbreviate phas species but two of them are the most dominant; they are based on the number of their carbon atom or classifying them to short, medium or long chain length. phas created from three to five carbon atoms are called short-chain-length, termed scl, while phas with six to fourteen carbon atoms are called medium-chain-length, and termed mcl [48]. in fact, even this abbreviation system is based on the number of c atoms in their monomeric unit’s composition but at the same time it reflects the different physical properties where scl phas are solid or semisolid while mcl phas are latex like, rubber or elastomers. the phas which contain more than fourteen carbon atom are called long-chain-length (lcl). genes coding for proteins involved in the biosynthesis of pha are referred in alphabetical order as phaa (βketothiolase), phab (acetoacetyl-co a reductase), phac (pha synthase), phag (3hydroxyacyl-acyl carrier protein-co a transacylase), etc. [48, 57]. the names of genes involved in phas degradation are referred to opposite alphabetical order such as phaz for pha depolymereses, phay, phax, phaw etc. the genes for phasins and regulator proteins are referred to as phap and phar, respectively. the origin of the gene or protein can be also referred to the first letter of the gene and the species as subscript e.g., phacpa refers to pseudomonas aeruginosa. it is important to sign that using the numbering style to differentiate between the monomer structures is preferable when copolymer is present such as p(3hb-co-4hb). if the polymer is well known it is preferable to use their abbreviation instead of using scl/mcl style. for example, polyhydroxybutyrate usually abbreviate as phb or p3(hb) and polyhydroxybutyrate-co-polyhydroxyvalirate abbreviate as phb-co-phv or p(3hb-co3hv). alternatively, in case of mcl phas and because of the big number of their monomeric composition pha mcl is usually used. finally, phas could be abbreviated using any of the described styles based on the situation. an example for the different abbreviation styles for polyhydroxybutyrate-co-polyhydroxyvalerate are phb-co-phv, p3(hb-co-hv), p(3hb-co-3hv), p(3-βhb-co-3-βhv), p3β(hb-co-hv). few authors are still using β in pha abbreviation. phas will refer to different kinds of polyhydroxyalkanoates including scl, msl and lcl. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 41 fig. 2: chemical structures of phas. 1) general structural of phas. 2) the copolymer poly(3-hydroxybutyrate-co-3hydroxyvalerate) p(3hb-co-3hv) as example of scl. 3) p(hhx-co-ho-co-hdco-hdd-co-…..) as an example for mcl. 3. phas chemical structure like any polymer, phas are chains of monomers repetition either homopolymer or heteropolymer. in general, phas known to be linear, are composed of 3-hydroxy alkanoic acid monomers units, each unit form an ester bond with the hydroxyl group of the other one. the hydroxyl-substituted carbon atom has r configuration in all characterized phas. at the c-3 atom (β position), an alkyl group which length can vary from methyl (c1) to tridecyl (c13) is located as in fig. 2 [48]. this alkyl side chain is not necessarily saturated. unsaturated, aromatic, epoxidized, halogenated, and branched monomers have been reported as well [21, 58 66]. by cross-linking of unsaturated bonds substations in the side chains of phas, for instance, can be added chemically [67]. lütke-eversloh et al was the first report to produce biopolymers with thioester linkages in the polymer backbone using c. necator in media containing 3mercaptopropionate (3mp) or 3-mercaptobutyrate (3mb) in addition to 3-hydroxybutyrate as constituents [16, 17]. many factors affect the phas chemical composition like the microbial strain, the substrate, the cultivation condition, the extraction method, the number of phac, phab genes, the regulator phap (phasin) and the presence of inhibitors. they inhibit different pathways especially those, which supply the synthases with different kinds of monomer or inhibit other pathways, which consume these monomers for their own or degrade it to shorter units like β oxidation pathway. the pha mcl is synthesized with an average molar mass ranging from 5 x 10 4 to 2 x 10 5 g/mol, whereas phb can be produced with an average molar mass of >1 x 10 6 g/mol. in general, the pha composition depends on the pha synthases, the carbon source and the metabolic routes involved [19, 68]. phas’ molecular weights have been established by light scattering, gel permeation chromatograph and sedimentation analysis. their monomer composition has been ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 42 determined by gas chromatography (gc), mass spectroscopy (ms) and nuclear magnetic resonance (nmr) analysis [16, 17, 44]. 4. phas physical properties phas’ crystal structure, polydispersities, melting point, enthalpy of fusion, glass transition temperature and mechanical properties were established by the use of different procedures. phas, ranging from stiff, brittle to rubber-like make them a close substitute for the synthetic plastic. phb, compared with plastic like polypropylene, is considered as having the most common properties [69], and phb was in fact a thermoplastic [70] as presented in table 1. in the case of phb-within the cell it exists in a fluid, amorphous state. however, after extraction from the cell with organic solvents, phb becomes crystalline and rigid but brittle material [71]. the brittleness of phb during mechanical processes makes it unresisting to stress. the major problem of phb is that it decomposes near its melting point. however, if there is another monomer included in the structure of phb such as 3hv it decreases phb crystallinity and increases its elasticity [72]. the rubber or latex-like pha mcl exhibits physical properties significantly different from the pha scl with respect to the melting temperature and the extension at the break point as in table 1. table 1: properties of some phas and polypropylene parameter p(3hb) p(3hbco-3hv) p(3hbco-4hb) p(3ho-co3hh) pp tm (°c) 177 145 150 61 176 tg (°c) 2 -1 -7 -36 -10 crystallinity (%) 70 56 45 30 60 extension at break (%) 5 50 444 300 400 tm, melting temperature; tg, glass transition temperature; p(3hb), poly(3-hydroxybutyrate); p(3hb-co-3hv), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) containing 20% 3hv; p(3hb-co4hb), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) containing 16% 4hb; p(3ho-co-3hh), poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) containing 11% 3hh, and pp is polypropylene (doi, 1990). 5. limitations of phas commercialization the production cost of phas is the main commercialization-limiting factor for these biopolymers. phas’ accumulation requires special growth conditions and it’s usually imbalanced nutrition that causes slow growth. the imperial chemical industries in billingham, united kingdom produced copolymers of phb-co-phv on a large scale [69]. the market penetration is rather scarce, ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 43 and the products are known as “biopol” trademark. in 1990, the german company wella used biopol-made flasks for a new shampoo. bacteria-produced pha is approximately, five to ten times more expensive than its competitors, polypropylene or polyethylene. although this natural product is promising, its price at that time was $17 to $22/kg [73]. the market price of biopol prepared by zeneca bioproducts, a subsidiary company of ici, was about $16/kg. development of better fermentation and purification technologies and the use of genetic engineering lowered the price, which becomes $4/kg, but it is still expensive compared to its competitors. major expenses in the production of pha are determined by the cost of the fermentation substrates, and the extraction of the polymer from the cells [69]. another trill for phas commercialization was started in 1996, when the american company monsanto bought the biopol material from zeneca bioproducts. monsanto tried to produce biopol by using transgenic plants. the genes originating from bacteria were transferred to plants by genetic engineering methods, which produce the polymer. monsanto was optimistic about the phas commercialization researches especially those concerning the transgenic soya and oilseed rape. unfortunately, monsanto has terminated its project in late 1998. developing countries did not have enough experience in the field, but had other positive factors to overcome phas production cost like cheap raw material resources and available work forces [74]. yamane et al. reported that the major cost in pha production is their substrate [75]. it is important to highlight that if microbial cells in their optimum condition are able to accumulate pha it will not exceed certain limit based on their size capacity. unfortunately, usually big microbial cells have lower generation time. the cheapest substrate cost is $0.22/kg of pha while the cost of polypropylene is $0.185/kg [76]. the substrate cost affects the overall cost but the cheapest substrate is not always the ideal choice. when the phb productivity increased from 1.98 to 3.2 g/h, the phb production cost decreased from $5.37/kg to $4.91/kg [77]. in a laboratory fed-batch system using a. latus, the highest reported productivity was 4.94 g/h with cost about $2.6/kg [77]. amara and salem were describing phenol degradation using microbial strains have the pha production system which could be used for phas production during phenol degradation process [78]. 5.1 why are phas still so attractive? scientists and industrialists have been looking for a replacement of petroleum plastic, which causes a lot of environmental, health, biodiversity and economic problems with a more safe type of plastics, which are bio-friendly. phb, and other member of phas family provide the hope as a solution to those problems with petroleum plastic. phas are biodegradable without any toxicity, bio-evaluable and to some extent do not make any stimulation to the human immune system even if the human body can degrade the polymer after a period of time. this will match the request of many medicinal and pharmaceutical applications. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 44 6. phas applications 6.1 industrial applications the first potential application of phas polymers was recognized in the 1960s [79]. phas patents cover a wide range of phas products such as coating and packaging, bottles, cosmetic containers, golf tees, and pens [80 82]. phb alone or with 3hv as a copolymer have been used as diaper back sheets and films [83, 84]. phas have also been processed into fibers, for a nonwoven fabrics material [85]. phb and phb-co-phv have been used as hot-melt adhesives [86]. phas are used as developer compositions and toner or in ion-conducting polymers [87, 88]. phas are used as latex in paper-coating applications, [89], in dairy cream substitutes [90], in food flavour delivery agents [91], or as raw materials for the synthesis of enantiomerically pure chemicals and paints [23, 92 – 96]. phas are also used in packaging materials or agricultural foil [97]. to produce a coating, the pha latex is sprayed onto a substrate such as paper. after the evaporation of water, the pha latex particles readily coalesce into a film [67]. pha might also find marine applications, such as in fishing nets [98, 99]. aiming to widen the range of industrial applications and establishing a method for changing phas compositions as well as phas’ overproduction amara et al., described a new simple strategy for in vivo random mutagenesis and mutants selection using synthase gene from aeromonas punctata employing the mutator strain escherichia coli xl1-red and nile red plates. the mutants mediated synthesis of phas with an increased weight average molar mass. mean while the molar percentage is different which an early indication about the possibility of changing the substrate specificity using random mutagenesis. in vivo random mutagenesis proved to be a versatile tool to isolate mutants exerting improved properties with respect to pha biosynthesis [100, 101]. taguchi et al., used another strategy based on in vitro mutagenesis for phacre using pcr [102, 103]. 6.2 biomedical applications due to the relatively high cost of phas production, it’s wise to apply phas for some cost effective applications like medicinal instruments. phas have been proved biocompatible in tissue engineering, implantations, etc. many prokaryotic and eukaryotic organisms are able to produce low molecular weight phb molecules that are complexed with other biomolecules such as polyphosphates and that are present at low concentrations [104]. over the past years, phas were used to develop many devices and material useful for clinical purposes such as sutures fasteners, meniscus repair devices, rivets, tacks, staples, screws, (including interference screws), bone plates and bone plating systems, surgical mesh, repair patches, orthopedic pins (including bone filling augmentation material), adhesion barriers, stents, guided tissue repair regeneration devices, articular cartilage repair devices, nerve guides, tendon repair devices, pericardial patches, bulking and filling agents, vein valves, bone marrow scaffolds, meniscus regeneration devices, ligament, ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 45 tendon grafts, ocular cell implants, spinal fusion cages, skin substitutes, dural substitutes, bone graft substitutes, bone dowels, wound dressing and hemostats [105 111]. to assess the biocompatibility of phb, the structural organization of cellular molecules involved in adhesion was studied using osteoblastic and epithelial cell lines. on phb, both cell lines revealed a rounded cell shape due to reduced spreading. the filamentous organization of the actin cytoskeleton was impaired. in double immunofluorescence, analyses the co-localization of the fibronectin with the fibril actin was demonstrated [112]. the investigated properties of phb and phb-co-phv films proved to be fundamentally similar [113 117]. phb-co-phv film was chosen as a temporary substrate for growing retinal pigment epithelium cells as an organized monolayer before their subretinal transplantation. the surface of the phb-co-phv film was rendered hydrophilic by oxygen plasma treatment to increase the reattachment of d407 cells on the film surface. the cells were also grown to confluency as an organized monolayer suggesting phb-co-phv film as a potential temporary substrate for subretinal transplantation to replace diseased or damaged retinal pigment epithelium [118]. tesema et al. and malm et al. implanted phb nonwoven patches as transannular patches into the right ventricular outflow tract and pulmonary artery in 13 weanling sheep [119 122]. it is concluded that phb nonwoven patches can be used as a scaffold for tissue regeneration in low-pressure systems. the regenerated vessel had structural and biochemical qualities in common with the native pulmonary artery [122]. phas have been used in tissue engineering, as antibiotic carrier, and many other medicinal applications [123, 124, 125]. chen and wu recently reported that phas possesses the biodegradability, biocompatibility and thermo-processibility for not only implant applications but also controlled drug release uses. phas show a promising future in pharmaceutical application such as drug delivery, which open a new approach. the many possibilities to tailor-made phas for medical implant applications have shown that this class of materials has a bright future as tissue engineering materials [126]. 7. phas detection 7.1 detection using stains sudan black, nile blue and nile red can be easily used for phas detection [74, 127, 128, 129]. nile red is the most common stain used for screening of pha accumulating bacteria [129]. amara et al, described a very simple method using nile red, it depends on the appearance of a clear red color if the colonies on plates are incubated at -4 o c for appropriate time [74] as illustrated in fig. 3 and 4. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 46 fig. 3: agar plate shows fluorescent colonies, which indicate the presence of pha after visualization by uv at 312 nm [74]. fig. 4: nile red plate after incubation at -4 o c. the red colonies shows the +ve pha accumulation while the white colonies show –ve pha accumulation [74]. 7.2 quantitative analysis of pha using gc/ms one simple method has been described by brandl et al. using gc (gas chromatography) to analyze various phas and further described in detail by timm and steinbüchel, [130, 131]. the amount of phas should be calculated based on their different monomeric compositions, eg. if 3hb and 3hhx (3-hydroxy-hexanoate) have the same area the amount of phb monomer will be bigger because it has the lower molecular weight. 8. biochemical aspect about phas biosynthesis 8.1 pha synthases pha synthases are the key enzymes of pha biosynthesis. pha synthases use coenzyme a thioesters of hydroxyalkanoic acids (ha) as substrates and catalyze the polymerization of has into pha with the concomitant release of coa. twenty years ago in three different laboratories, pha synthase operon of c. necator has been cloned [132, 133, 134]. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 47 8.2 pha scl biosynthesis phb is the most extensively investigated phas. the phb biosynthesis pathway consists of three distinct enzymatic reactions. examination of the enzymes leading to the formation of phb has shown that the regulation of phb synthesis is controlled by acetylcoenzymes a (coa) acyltransferase [135, 136]. phb is synthesized from acetyl coenzyme-a (acetyl-coa) by a sequence of three enzymatic reactions. synthesis of phb is believed to be controlled by the first enzyme, 3-ketothiolase that is inhibited by coenzyme a (coash) [137]. (i) β-ketoacyl-coa thiolase (encoded by phaa) the first reaction comprises the condensation of two acetyl coenzyme a molecules into acetoacetyl-coa by β-ketoacyl-coa thiolase (β-ketothiolase). (ii) nadph-dependent acetoacetyl-coa dehydrogenase (encoded by phab) the second reaction is the reduction of acetoacetyl-coa to (r)-3-hydroxybutyryl-coa by an nadph-dependent acetoacetyl-coa dehydrogenase. (iii) phb synthase (encoded by phac) finally, the (r)-3-hydroxybutyryl-coa monomers are polymerized to phb by phb synthase. under balanced growth conditions, acetyl-coa is fed into the tricarboxylic acid cycle and the resultant coa inhibits acetyl-coa acyltransferase and phb synthesis. under nutrient limitation (e.g., oxygen limitation) and carbon excess, nadh oxidase activity decreases, nadh increases and inhibits citrate synthase and isocitrate dehydrogenase, and acetyl-coa acyltransferase by coa is overcome. the ensuing condensation reaction forms acetoacetyl-coa and initiates phb synthesis [135, 136]. the high nadh/nad ratio caused oxygen limitation rapidly readjusts as phb synthesis starts, and phb assumes the role of an alternative electron acceptor [135]. the degradation of phb is initiated by phb depolymerase to form d(-)hydroxybutyric acid. an nad-specific dehydrogenase oxidizes the acid to acetoacetate, which is an intermediate common to the biosynthesis and degradation of phb [99]. 8.3 pha mcl biosynthesis 8.3.1 pha mcl biosynthesis from related substrates in 1983, de smet described the accumulation of pha, the pha mcl , in pseudomonas oleovorans grown on octane as sole carbon source [45]. the compositions of the phas formed by pseudomonads of the rrna homology group i were directly related to the structure of the alkane, alkene or fatty acid used as carbon source [46, 130]. these substrates are referred to as ‘related substrates’. when the carbon source consists of fatty acids with 6 to 12 carbon atoms, monomers of the pha are of the same length as the carbon source or are shortened by 2, 4 or 6 carbon atoms. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 48 thioestrase fatty acid acyl-co a fatty acid ßoxidation (r)-specific enoyl-coa hydratase(r)-3hydroxyacyl-coa transacylase (r)-3-hydroxyacyl-acp fatty acid de novo synthase enoyl-acp acyl-acp acetyl-coa malonylcoa acp+co 2 3-ketoacylacp reductase 3-ketoacylcoa pha mcl synthase polyhydroxyalkanoate triclosan acrylic acid (fadr) fadb (s)-3-hydroxyacylcoa enoyl-coa 3-ketoacylacp malonyl-acp sugre tca cycle acetoacetyl-coa (r)-3hydroxybutyrylcoa phb beta-ketoacylcoa thiolase phaa nadph-dependent acetoacetyl-coa dehydrogenase phb synthase pyrruvatepropionyl-coa 3-ketovalerylcoa phb-co-phvphb-co-4hb phb-co-phhx 3-ketothiolase bktb fig. 5: metabolic pathways leading to the biosynthesis of phas, phb, phb-co-phv, co-4hb, -co-phx, pha mcl . acrylic acid is the inhibitor of fatty acid β-oxidation pathway and triclosane is the inhibitor of fatty acid de novo biosynthesis pathway. aeromonas punctata produces a random copolymer of 3hb and 3hhx, when growing on even-numbered fatty acids or olive oil as sole carbon source. pha production in a. punctata proceeds from the β-oxidation pathway intermediate 3-hydroxyenoyl-coa, which is hydroxylated by the enantiospecific enoyl-coa hydratase (fig. 5). 8.3.2 phamcl biosynthesis from unrelated substrates synthesis of phas other than phb which are not related to their growth substrates occur relatively rarely in nature [22]. these substrates, which do not resemble the monomers of the accumulated polymer, are named ‘’unrelated substrates’’. the phas production under unbalanced conditions is highly naturally engineered. the first indication about the ability of synthases to utilize products from other pathways in their monomeric composition was reported by wallen and rohwedder in 1974 who, reported heteropolymers of hb and 3-hydroxyvalerate in chloroform extracts of activated sewage sludge as major constituents with c6 and possibly c7 3-hydroxyacids as minor components [43]. slater et al., identified that a second β-ketothiolase gene in c. necator is responsible for synthesis of 3-ketovaleryl-coa [138]. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 49 pseudomonads of the rrna homology group i like p. putida kt2442, accumulate phas that consist primarily of c10 and c8 monomers, when grown on sugars or gluconate [131, 139]. these monomers are derived from intermediates of fatty acid biosynthesis and the composition of the phas is a reflection of the pool of fatty acid biosynthetic intermediates. 8.3.3 metabolic engineering of pha mcl 8.3.3.1 linking metabolic pathways different phas could be produced from simple cheap carbon sources; alternatively, the carbon source may be derived from waste materials like whey lactose, coals and methane. steinbuchel in 2001 mentioned that in order to produce phas other than phb from co 2 or renewable resources it will be necessary to link central metabolic pathway with pha synthesis [15]. rehm et al., determined that the gene product of phag, (r)-3-hydroxyacyl-acp:coa transacylase, is responsible for the conversion of (r)-3-hydroxyacyl-acp to (r)-3hydroxyacyl-coa [140]. another example, the citric acid cycle for generating pha precursors in recombinant e. coli; a polymer consisting of 4-hydroxybutyrate (4hb) was produced by drawing succinyl-coa from the citric acid cycle, which is converted to 4hydroxybutyryl-coa, a precursor for pha biosynthesis [141] as illustrated in fig. 5. 8.3.3.2 examples of metabolic engineering wild type p. putida is able to produce pha mcl from related and unrelated substrates [related = eg. fatty acid, unrelated = eg., glucose or gluconate] [46, 130, 131, 139]. an isolated p. putida mutant can grow on any carbon source tested and was able to synthesize pha mcl from fatty acids but not from gluconate or glucose [140]. biochemical studies on the affected enzyme revealed that these enzyme catalyses the transfer of (r)-3hydroxydecanoyl moieties from the acyl carrier protein: coenzyme a transferase. the respective gene, which complemented the mutant, was referred to as phag [140], this one has been also identified and cloned from p. aeruginosa [142] and p. oleovorans [143] (fig. 5). in the presence of the substrate, (r)-3-hydroxyacyl-coa the transacylase appeared in apparent molecular weights of 45.4, 83.7 and 102 kda, which indicated substrate-induced conformational changes and oligomerization of the transacylase [144]. 8.3.3.3 metabolic engineering using e. coli fadb mutants in e. coli fadb mutant ls1298, the dehydrogenase function is defective, whereas the hydratase and also the epimerase function of fadb remain active [145]. when the fadb mutant ls1298 of e. coli harboring phac1 was used for pha biosynthesis, phas were accumulated to a significant level, contributing to 20-25% of the cell dry matter [146]. obviously, (s)-3-hydroxyacyl-coa accumulates in the cytoplasm of the mutant cells to a level that is sufficiently high enough to be effectively converted into the (r)-stereoisomer ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 50 and subsequently incorporated into pha. instead of phac1, phac2 of p. aeruginosa was also used, and very similar results were obtained [147]. the length of the incorporated 3-hydroxyalkanoic acids reflected the length of the carbon chain of the fatty acid provided as carbon source [147]. the fadbapo operon and a class ii pha synthase gene of p. aeruginosa were heterologously co-expressed in e. coli. fadbapo did not mediate phamcl biosynthesis in e. coli wild type strain harboring a pha synthase gene when cultivated on fatty acids as carbon source. however, pha accumulation was strongly impaired in a recombinant e. coli fadb mutant, which harbored a pha synthase gene. these data indicates that pseudomonads fadba does not possess the inherent property, based on a putative epimerase function, to provide the (r)enantiomer of 3-hydroxyacyl-coa efficiently and that other linking enzymes are required to efficiently channel intermediates of β-oxidation towards pha mcl biosynthesis [148]. 8.3.3.4 (r)-specific enoyl coa hydratase in a. punctata, a (r)-specific enoyl-coa hydratase is responsible for the conversion of trans-2-enoyl-coa to (r)-3-hydroxyacyl-coa during the cultivation of this bacterium on e.g. hexanoate [149]. two (r)-specific enoyl-coa hydratase genes were also identified in p. aeruginosa [150]. studies in recombinant strains of e. coli provided evidence that fabg of fatty acid de novo synthesis, which is a 3-ketoacyl-acp reductase, is non-specific and exhibits activity with the corresponding coa-thioesters [151]. on the other hand, it was shown that recombinant strains of e. coli could also use their own β-ketothiolase (fada) in combination with the acetoacetyl-coa reductase (phab) of c. necator for the conversion of fatty acids into pha mcl [152] figure 5. 8.3.3.5 metabolic engineering using inhibitors steinbüchel described six chemicals, which specifically inhibit one or other reactions that affect phas production [15]. whereas acrylic acid [153] inhibits the β-ketothiolase of the β-oxidation pathway, thiolactomycin [154], 3-decenoyl-n-acetylcysteamine [155], triclosan [156] diazaborine [157], and cerulenin [158] inhibit enzymes of the fatty acid de novo synthesis pathway. a different system for the production of pha mcl by e. coli was described using acrylic acid as inhibitor [159]. when recombinant strains of e. coli, expressing either phac1 or phac2 from p. aeruginosa were cultivated on fatty acids such as decanoic acid and in the presence of low concentrations of acrylic acid, phas were found to be accumulated in all investigated strains of e. coli [159]. acrylic acid and cerulenin were applied to investigate the competition of the pathways for phb-co-phv and triacylglycerol (tag) biosynthesis in species of the genus rhodococcus [160]. acrylic acid completely inhibited the accumulation of tags from valerate and caused a two-fold increase in the pha content which consisted exclusively of 3hv [160]. antonio et al., and amara et al., produced 3hb-3hhx from cultivation of recombinant e. coli on fatty acid using phac class i and acrylic acid [101, 161]. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 51 9. in vitro biosynthesis of phas gerngross and martin have first demonstrated in vitro biosynthesis of pha and selfassembly of spherical granules by only using purified polyester synthase and substrate [162]. poly(3hb) was also synthesized by employing the pha synthase of a. vinosum in combination with the auxiliary enzymes propionyl-coa transferase from clostridium propionicum alone or with an acetyl-coa synthase of saccharomyces cerevisiae [163]. in vitro pha biosynthesis was achieved using purified pha synthases alone or together with additional auxiliary enzymes purified from various sources. the auxiliary enzymes over purified ones help to use substrates other than coenzyme a thioesters of hydroxyalkanoic acids and to recycle coenzyme a, which must then be used only in catalytic instead of stoichiometric amounts. phb was synthesized from 3-hydroxybutyryl-coa using the pha synthases from c. necator [162, 164] or a. vinosum [165]. phv was synthesized from 3-hydroxyvalerylcoa using the pha synthase of c. necator [166]. homopolyesters and copolyesters of various scl poly(hascl) such as 3hb, 4hb; and 4-hydroxyvalerate (4hv) were synthesized by employing the pha synthase of a. vinosum plus the butyrate kinase and the phosphotransbutyrylase of clostridium acetobutylicum as auxiliary enzyme [167]. phd was synthesized by using the pha synthase phac1 of p. aeruginosa plus an acylcoa synthase of pseudomonas sp. [168]. 10. pha production in yeast reush, 1989 describes an evidence of phb existing in yeast and many other eukaryotic cells, which contain small amount of low molecular mass phb, which function as complexes with polyphosphate in membrane transport [169]. expression of the c. necator phb biosynthetic pathway was successfully achieved in the yeast saccharomyces cerevisiae by leaf et al.,who reported that the expression of phb synthase in the yeast cytoplasm is sufficient for phb accumulation and that wild type yeast synthesis d-3hb-coa could rise from intermediates in fatty acid synthesis or through β-oxidation [170]. yeast cells can be used as models to gain information about phas synthesis in eukaryotes [171]. it is confirmed that three thiolase exist in s. cerevisiae functioning in mitochondria, cytoplasm [172] and peroxisomes [173]. safake et al, in their study succeeded to isolate phb producing wild type yeast strain from kombucha tea and reported that the amount of phb is less than that from prokaryotic and the phb amount depend upon the type of culture and species [174]. synthesis of phascl was established in the peroxisome of a wild-type yeast strain by targeting the c. necatorscl polymerase to the peroxisome [175]. 11. phas production by transgenic plants plants are interesting targets for production of the biopolyesters. transgenic plants could produce phas directly from co 2 and solar energy [176]. the biosynthesis of phb ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 52 in transgenic arabidopsis thaliana was already reported [3]. later, the c. necator phb biosynthesis genes were also expressed in agricultural crops such as brassica napus [177], gossypium hirsutum [178] and nicotiana tabacum [179]. the copolyester phb-co-phv [180] and phas consisting of 3ha mcl [181] have been produced in plants. 12. organization of pha synthase genes the pha biosynthesis genes and genes for other proteins related to the metabolism of pha remain in cluster in bacterial genomes. in c. necator, the genes for pha synthase (phac), β-ketothiolase (phaa) and the nadp-dependent acetoacetyl-coa dehydrogenase (phab) constitute the phacab operon [132, 134, 138]. approximately 4 kbp downstream of this operon a second β-ketothiolase gene (bktb) was identified [138]. in zoogloea ramigera, methylobacterium extorquens, sinorhizobium meliloti 41, nocardia corallina, r. ruber, paracoccus denitrificans, rhodobacter sphaeroides, rhodospirillum rubrum ha, rhodobacter capsulatus and aeromonas punctata phac seem to be separated from other pha genes. phaa, phab or other genes related to pha metabolism are not directly linked to the phacs genes in these genomes. in contrast, the gene encoding an enoyl-coa hydratase in a. punctata is located downstream of phac. p. oleovorans, pseudomonas sp. 61-3 and p. aeruginosa posses two different phac genes, which are in the genome separated by the structural gene for an intracellular pha, depolymerase. pseudomonas sp. 61-3 contains also these two phac genes in addition to another phac gene, which is co-localized with phab and phaa. in all bacteria, which posses a two-component pha synthase, phac and phae are directly linked in the genomes constituting most probably single operons. in allochromatium vinosum phaa and phab are located on the opposite direction in a gene cluster related to pha metabolism. the organization of the genes is most probably similar if not identical in thiocystis violacea and thiocapsa pfennigii, whereas in synechocystis sp. pcc 6803 further pha genes do not map close to the phaec locus. in r. ruber and a. vinosum the structural genes for phasin proteins (orf3 and orf5, respectively) map close to the respective phac loci [182]. 13. primary structures of pha synthases, classes and substrate specificity pha synthases are classified into four classes based on their substrate specificity and subunits composition. the class i pha synthases, with c. necator synthase as prototype, is composed of one single type of polypeptide chain and use mainly (r)-3-hydroxybutyrylcoa, (r)-3-hydroxyvaleryl-coa and other scl hydroxyalkanoic acid coa thioesters including 3-mercaptoalkanoic acid coa thioesters as substrates [16, 182]. the class iii pha synthases, as represented by the a. vinosum enzyme, is composed of two different subunits each of about 40 kda [183]. the substrate specificity is similar to that of class i synthases, although some medium chain length 3-hydroxyfatty acids are also incorporated [184]. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 53 both classes (i and ii) of pha synthases were purified, and in vitro activity has already been achieved [162, 163, 185, 186]. the class ii enzymes, which are composed of only one type of subunit, are mainly found in pseudomonads such as p. aeruginosa. one major difference between class ii and both, class i and iii pha synthases is the substrate specificity. class ii pha synthases incorporate preferentially 3-hydroxyfatty acids of mcl (c6-c14) into phas, and the resulting product is a latex-like polymer [147, 159]. these substrates are mainly derived from intermediates of fatty acid β-oxidation or from fatty acid de novo biosynthesis [140 143, 188] provided fatty acids or simple non-related carbon sources [141]. class ii pha synthases were purified and in vitro activity was achieved [189, 190]. an amino acid sequence alignment showed that the a. vinosum pha synthase revealed high homology to prokaryotic lipases whose crystal structures are known. the amino acid ser at the active site of the lipase did align with the cys at the active site of the pha synthase. a threading model of the a. vinosum pha synthase was generated [191]. accordingly, a threading model of the class ii pha synthase from p. aeruginosa was developed [192] and based on the homology to the structure of the lipase from b. cepacia. rehm et al. developed threading model for pha synthase from c. necator based on the alignment of the c. necator pha synthase (phacre) with the burkholderia glumae lipase (1tah_a) [193]. in the multiple alignment of pha synthases only one cys residue (cys-319) is highly conserved. therefore, scientists are looking since several years for the second thiol group. the essential role of cys-319 of the c. necator pha synthase for the reaction mechanism was obtained from site-specific mutagenesis [185]. the weakly conserved cys-459 was supposed to be involved in the catalytic cycle, providing the second thiol group. however, site-specific mutagenesis [185] clearly indicated, that this amino acid residue is not essential for catalytic activity. this is fully supported by the alignment of pha synthase sequences. in position 260 of the pha synthase from c. necator a conserved ser residue was observed. this ser-260 was proposed as target for covalent posttranslational modification by 4-phosphopantetheine, which should provide the second thiol group similar to fatty acid synthase. in order to investigate posttranslational modification by 4phosphopantetheine, radiolabeling experiments were conducted, expressing pha synthase gene from c. necator in e. coli sj16 (pand). since e. coli sj16 is β-ala auxotroph, specific radiolabeling of 4-phosphopantetheinylated proteins occurs, when cells were fed with 2-14c-β-ala. these experiments indicated that the pha synthase was labeled by 4phosphopantetheine [185]. however, detailed analysis revealed that only a small portion of total pha synthase was labeled [194]. functional low level expression of pha synthases from c. necator and p. aeruginosa, respectively, in e. coli sj16 and also in β-alanine auxotrophic mutants of c. necator with subsequent analysis of 4-phosphopantetheinylated proteins gave no evidence for covalent posttranslational modification by 4-phosphopantetheine [195]. exchange of amino acid residue ser-260 against alanine and threonine, respectively, abolished in vivo and in vitro activity of pha synthase from c. necator [195]. the current model of active pha synthase involves two subunits forming a homodimer pha synthases have been assigned to four classes based on their substrate specificity and subunit composition. the multiple alignments of the primary structures of these pha synthases showed an overall identity of 9 to 96% with only 8 strictly conserved amino acid residues [193]. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 54 considering class i and ii pha synthases, and forming a heterodimer (phac and phae) in case of class iii pha synthases. accordingly, class i and ii pha synthases possess two thiol groups provided by conserved cys-319, and in class iii pha synthases the second thiol group might be provided by conserved cys-130 of subunit phae from a. vinosum [194]. a novel pha synthase (class iv) from bacillus megaterium required phac bm and pharbm for activity in vivo and in vitro was reported [196]. phacbm showed greatest similarity to the phacs of class iii in both size and sequence. unlike those in class iii, the 40 kda phae was not required, and further more, the 22 kda phar bm had no homology to phae. amara and rehm described seven site directed mutations have been performed in phacpa where 5 conserved residues were replaced in order to identify the role of these amino acids in catalysis. the replacement of w398 by alanine abolished pha mcl synthase activity indicating that w398 is essential for enzyme activity [197]. the replacement of h479 by glutamine did not affect the pha mcl activity, which indicates that h479 is not the general base catalyst that activates the nucleophilic c296 for covalent catalysis. the replacement of c296 with serine which is the the general base catalyst in lipases did not abolish pha mcl synthase activity while still exhibiting 20% activity in comparison to the wild type. replacement of c296 with ala abolished pha mcl synthase activity which is a strong evidence that serine may be able to replace cys as catalytic nucleophile for changing substrate specificity of pha synthase. for further investigation, another site directed mutagenesis has been done in another conserved histidine (h452), which was replaced with glu. the h452q mutant was highly impaired in pha mcl activity, which indicates that h452 plays a major role as a general base catalyst instead of h479 [197]. localized semi-random mutagenesis has been used to alter substrate specificity of the class ii polyester synthase from p. putida [198]. recently, tsuge et al., found that the a510 of the c. necator polyester synthase is involved in substrate specificity [199]. the tertiary structure of pha synthases has not been resolved by x-ray diffraction analysis, yet. secondary structure prediction based on the multiple alignment of pha synthases indicated with an expected accuracy of about 72%, that pha synthases are mainly composed of variable loop (49.7%) and α-helical (39.9%) secondary structures, whereas for only 10.4% a β-sheet structures were predicted [200]. thus, pha synthases belong with respect to their predicted secondary structure content to the mixed class of proteins. purified pha synthase exists in an equilibrium of monomeric and dimeric forms whereas dimerization is significantly induced in the presence of substrate and of trimeric coa analogs (3-hydroxybutyryl)3-coa, respectively. in addition, the enzymatic lag phase is reduced and the specific activity increased in the presence of trimeric analogs [201]. this indicates that the dimeric form is substantially more active than the monomeric form in the absence of the putative primer. since radiolabeled trimeric coa analogs were found to be covalently bound to the pha synthase ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 55 of c. necator, the radiolabel resides only the dimeric form as indicated by size-exclusion chromatography [202]. this homogenous population of particles measuring 11.2-12.8 nm in diameter and data derived from gel filtration chromatography indicate that this pha synthase might be composed of ten subunits [186, 203]. overall, with respect to quaternary structure of pha synthases these data suggest that in vitro the active pha synthase consists of two subunits and that in vivo the pha synthase associated with pha granule surface might be composed of ten subunits in a. vinosum [192]. 14. pha biodegradability biodegradation is a process mediated by special enzymes which able to degrade chemical compounds. without enzymatic degradation, our life will not be imaginable. while depolymerases have been studied for about 40 years, the first structural gene of a pha depolymerase (alcaliginus faecalis, phaz af ) was cloned and sequenced only in 1989 by saito et al. [204]. depolymerases are highly specific for the polymers consisting of monomers in the (r) configuration [205]. phas depolymerase are carboxyesterases (ec 3.1.1) and hydrolyze the water insoluble polymer to water-soluble monomers and/or oligomers and finally to water and carbon dioxide or methane. early phb degrading bacteria were isolated by selection for microorganisms able to utilize phb as the sole source of carbon and energy (fig. 6) [24]. phas degrading bacteria differ from each other depending on the type of phas they degrade, however some bacteria revealed a rather broad polyester specificity and are able to utilize a wide range of phas [206, 207]. three intracellular pha depolymerases (phaz1, phaz2 and phaz3) and a 3hb-oligomer hydrolase (previously designated phaz2), which hydrolyse phas and the cleavage products produced by phazs, were cloned and characterized in c. necator [207 210]. fungi also could degrade phas and their depolymerases have been characterized [211, 212]. phas depolymerases show a similar characteristic, they are stable at a range of ph, temperature, relatively small mr ( < 70 kda), they are inhibited by reducing agent, e.g. dithiothreitol (dtt), which indicates the presence of essential disulfide bonds, and by serine hydrolase disulfide bonds, and serine hydrolase inhibitors such as diisopropyl fluorophosphate (dfp) or acylsulfonyl derivatives [212]. depolymerases have three strictly conserved amino acids: serine, aspartate and histidine. the serine is part of the lipase-box pentapeptide gly-xaa1-ser-xaa2-gly [213]. the oxygen atom of the serine side chain is the nucleophile that attacks the ester bond [206, 214]. 14.1 biotechnological aspect of pha depolymerases the production of enantiomer-pure (r)-hydroxyalkanoic acids by depolymerasecatalysed hydrolysis of pha is possible. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 56 the activities of phas depolymerase may vary depending on the composition and the physical form of the polymer (amorphous or crystalline), the environmental conditions and the dimensions of the sample [215 218]. while pha can be produced by different fermentation processes based on agricultural feedstock’s derived from co 2 and water, their breakdown products by the activity of depolymerase are again co 2 and water. thus, while in some applications the biodegradability is critical, phas are good renewable compounds [219]. fig. 6: scanning electron microscope image for pha surface [2000 x]. the bacterial growth leads to polymer degradation 15. pha granules phas granules are composed of spherical shell-core particles of a phas core enclosed by phospholipids and proteins. in vivo soluble phas synthases are changed into amphipathic enzymes upon the elongation of the water-insoluble phas chains, which remain covalently attached to the enzyme. a self-assembly process suggested to be initiated and leads to the formation of insoluble cytoplasmic inclusions with a phospholipid monolayer and covalently attached phas synthases at the surface. the structural proteins called phasins can be found attached to the granule surface [210, 220, 221]. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 57 dunolp and robards developed the first models for the structure of the inclusion with intriguing observation that this polymer was stretchable even at very low freeze -fracture temperature [222]. it was shown that pha granules consists of a hydrophobic core of amorphous pha that is surrounded by a membrane consisting of pha synthases, the pha depolymerase, amphiphilic phasin proteins and possible additional proteins. according to one model, these proteins are embedded in or associated with a phospholipid monolayer [221]. according to byron, about 8 to 13 granules per cell having diameter range of 0.2 to 0.5 found in c. necator [223]. immunoelectron microscopy studies of granules isolated from a. vinosum, employing gold-labeled anti-phac antibodies clearly indicated the presence of pha synthase complexes at the surface of the pha granule [189, 203]. another model outlines a much more complex membrane structure with two phospholipids membranes [224]. nmr analysis provided evidence that water molecules are present in the core structure of the granules and that these molecules function as plasticizer [225]. thus, the enzyme(s) responsible for pha biosynthesis and consumption operate only on mobile hydrated material and that the solid granules characteristics of dried cells are partially artifactual. pötter et al. described orthologus and paralogous phasins occurring in c. necator. the analysis of the genome sequence of the phas accumulating bacterium ralstonia eutropha (c. necator) strain h16 revealed three homologues (phap2, phap3 and phap4) of the phasin protein phap1. phap1 is known to constitute the major component of the layer at the surface of phb granules. phap2, phap3 and phap4 exhibited 42, 49 and 45% identity or 61, 62 and 63% similarity to phap1, respectively [226]. in addition to pha synthase, pha depolymerases (phaz) are also bound to the pha granule surface. the establishment of in vitro polyester synthesis using purified polyester synthases form various microorganism, such as e.g. from c. necator, a. vinosum, p. aeruginosa (phac1 and phac2) and p. oleovorans (phac1) [163, 167, 168, 201, 227] provided a new tool to study the formation of macroscopic pha granules. in vitro pha synthesis was firstly achieved using recombinantly produced and purified c. necator polyester synthase [162]. the granule formation occurred after only a few minutes when the substrate, (r)-3hydroxybutyryl coenzyme a, was provided to the purified polyester synthase [228]. 16. pha future it is clear from the amounts of research performed on pha indicates that this biopolymer is very promising. what made this kind of polymer has such attraction? it is the pha properties. pha is biodegradable, biocompatible and has good mechanical properties. pha different technological aspects including production, purification, analysis, different applications, changing monomer composition etc., become clear based on the intensive research done concerning phas. every week there is new information about phas. the number of publications exceeds most of the current important research topics. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 58 what makes phas especially important is that the petroleum oil price is increasing tremendously and its stock will be ended approximately in this century! it is important for the global community to have a standby solution for the products derived from petroleum oil. phas at least will be a solution for most of the industries, which depends on material made from plastics. phas are environmentally and human-friendly which will make them more suitable than petroleum-based plastic for many applications. the price of phas’ production decreases significantly, while at the same time the petroleum oil price is constantly increasing. the gap between the petroleum oil and phas prices becomes so close. phas have promising futures in the field of biomaterial. the chemical, physical and biological properties of phas become very clear. the in vivo and in vitro production, controlling their monomer composition and the huge amount of their physical, chemical and biological properties increase the number of their applications. perhaps, it is suitable nowadays to use phas in cost effective products like medical instruments. interesting progress in phas research has been recognized in the last ten years. from the literature, one can see that the developing countries have now an increasing interest in phas’ researches. it might be useful to gain the benefit from collaborating research aiming to decrease the production cost of phas. the developed countries could help a lot for phas commercialization, especially those nations that have natural resources as well as the necessary work forces. finally, the researchers have made a lot of effort to improve this scientific field. highlighting the importance of supporting researches on pha will bring the wealth for all humanity which is one of the aims of this review. phas are safe products and green in all points. acknowledgments i deeply acknowledge the valuable support and encouragement from prof. d. alexander steinbüchel, prof. dr. hassan moawed and prof. dr. bernd rehm especially during my phd study. special thanks to ms siham zayer, for some advices during the writing of this review. i acknowledged the daad for the financial grants, which supported my research in this field. i also acknowledged others from the institute fur molekular mikrobiologie und biotechnologie, universitat munster, germany, and mubarak city for scientific research and technological applications, egypt, who have supported me and sharing their knowledge. references [1] b. lee, iii. al pometto, a. fratzke, t. b. bailey, “biodegradation of degradable plastic polyethylene by phanerochaete and streptomyces species”. appl. environ. microbiol., vol. 57 pp. 678-685, 1991. [2] r. b. cain “microbial degradation of synthetic polymers”. in: frey et al. (eds) “microbial control of pollution”. 48th symposium of the society for general microbiology at university of cardiff, pp. 293-338, 1992. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 59 [3] y. poirier, c. somerville, l. a. schechtman, m. m. satkowski, and i. noda, “synthesis of high-molecular-weight poly([r]-(-)-3-hydroxybutyrate) in transgenic arabidopsis thaliana plant cells”. int. j. biol. macromol., vol. 17 pp. 7-12, 1995. [4] s. y. lee, “bacterial polyhydroxyalkanoates”. biotechnol. bioeng., vol. 49 pp. 1-14. (1996). [5] c. rivard, l. moens, k. roberts, j. brigham and s. kelley, “starch esters as biodegradable plastics: effects of ester group chain length and degree of substitution on anaerobic biodegradation”. enzyme and microbial tech., vol. 17 pp. 848-852, [6] u. witt, r. j. muller, w. d. deckwer, “biodegradation behaviour and material properties of aliphatic/aromatic polyesters of commercial importance”. j. environ. polymer. degrad., vol. l5 pp. 81-89, 1997. [7] r. j. muller, i. kleeberg, w. d. deckwer, “biodegradation of polyesters containing aromatic constituents”. j. biotechnol , vol. 86 pp. 87-95, 2001. [8] w. urbaniak thermal recycling. to burn or not to burn used packages? in: proc. 2nd scientific-instructive conference "packaging and environment protection". ed. arka s.a. konsorcjum poznan , vol. pp. 107-122, 1998 (in polish). [9] w. urbaniak “usage of spent plastics packages”. packaging. 6, 23, 1999 (in polish). [10] a. korzeniowski, h. kubera, “technical and ecological aspects of development in food industry”. food industry, vol. 53 (1), 32 1999. [11] j.g. b. derraik, “the pollution of the marine environment by plastic debris: a review”. marine pollution bulletin., vol. 44, pp. 842-885, 2002. [12] d. k. a. barnes, “invasion by marine life on plastic debris”. nature, vol. 416 (25 april) pp. 808-809, 2002. [13] o. ahlhaus, “new developments and aspects in design and production of polyester bottles for drinks packaging”, in: proc. 11th igwt symposion "commodity science and sustainable development". vienna, pp. 16-18, 1997. [14] p. suriyamongkol, r.weselake, s. narine, m. moloney, s. shah, “biotechnological approaches for the production of polyhydroxyalkanoates in microorganisms and plants a review”. biotechnology advances, vol. 25, pp. 148–175 november, 2007. [15] a. steinbüchel “perspective for biotechnological production and utilization of biopolymer: metabolic engineering of polyhydroxyalkanoate biosynthesis pathways as a successful example”. macromol. biosci., vol. 1 pp. 1-24. 2001. [16] t. lütke-eversloh, k. bergander, h. luftmann and a. steinbuchel, “identification of a new class of biopolymer: bacterial synthesis of a sulfur-containing polymer with thioester linkages”, microbiology, vol. 147(pt 1), pp. 11-19, 2001. [17] t. lütke-eversloh, j. kawada, r. h. marchessault and a. steinbuchel, “characterization of microbial polythioesters: physical properties of novel copolymers synthesized by ralstonia eutropha”, biomacromolecules, vol. 3(1), pp. 159-166, 2002. [18] t. lutke-eversloh, k. bergander, h. luftmann and a. steinbuchel, “biosynthesis of poly(3hydroxybutyrate-co-3-mercaptobutyrate) as a sulfur analogue to poly(3-hydroxybutyrate) (phb) ”, biomacromolecules , vol. 2(3), pp. 1061-1065, 2001. [19] l. l. madison, and g. w. huisman, “metabolic engineering of poly(3-hydroxyalkanoates): from dna to plastic”. microbiol. mol. biol. rev., vol. 63 pp. 21-53, 1999. [20] b witholt, b. kessler, “perspectives of medium-chain-length poly (hydroxyalkanotes), a versatile set of bacterial bioplastics”. curr. opin. biotechnol., vol. 10 pp. 279–285. 2002 ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 60 [21] y. b. kim, r. w. lenz, and r. c. fuller, “preparation and characterization of poly(βhydroxyalkanoates) obtained from pseudomonas oleovorans grown with mixtures of 5phenylvaleric acid and n-alkanoic acids”. macromolecules, vol. 24 pp. 5256–5360, 1991. [22] a. steinbuchel and b. fuchtenbusch, “bacterial and other biological systems for polyester production”. trends biotechnol., vol. 16(10), 419-427, 1998. [23] p. j. hocking, and r. h. marchessault, “biopolyester in chemistry and technology of biodegradable polymers’’. griffin, g. j. l. (ed.), blackie academic, uk, pp.481994. [24] a. chowdhury, “poly-β-hydroybuttersäure abbauende bakterien und exoenzyme”. arch. mikrobiol. vol. 47 pp. 167-200, 1963. [25] r. d. de la rivie`re, “notice ne´crologique sur m. maurice lemoigne (1883-1967) c. r. acad. des sci., paris, t. 12 jun, pp. 264, 1967. [26] m. lemoigne, “production d'acide β -oxybutyrique par certaines bact’eries du groupe du bacillus subtilis”. c.r. hebd. seances acad. sci., vol. 176 pp. 1761, 1923. [27] m. lemoigne, “etudes sur l’autolyse microbie acidification par formation d’acide βoxybutyrique, ann. inst. pasteur. vol. 39. pp.144. 1925 [28] m. lemoigne, “produits de l’hydration et de polymerisation de l’acide β-oxobutyrique”. bull. soc. chem. biol. (paris), vol. 8 pp. 770–782, 1926. [29] m. lemoigne, “etudes sur l'autolyse microbienne. origine de l'acide β -oxybutyrique form’e par autolyse”. ann. inst. pasteur (paris), vol. 39 pp. 144, 1927. [30] c. weibull, “characterization of the protoplasmic constituents of bacillus megaterium”. j. bacteriol. dec; vol. 66(6), pp. 696–702, 1953 [31] d. h. williamson and j. f. wilkinson “the isolation and estimation of the poly-betahydroxybutyrate inclusions of bacillus species”. j. gen. microbiol. aug; vol. 19(1), pp. 198– 209, 1958 [32] r. m. macrae, j. f. wilkinson. “poly-beta-hyroxybutyrate metabolism in washed suspensions of bacillus cereus and bacillus megaterium”. j. gen. microbiol. aug; vol. 19(1), pp. 210– 222, 1958 [33] m. doudoroff and r. y. stanier, “role of poly-β-hydroxybutyric acid in the assimilation of organic carbon by bacteria”. nature, vol. 183, pp. 1440. 1959 [34] r. y. stanier, m. doudoroff, r. kunisawa, r. contopoulou. “the role of organic substrates in bacterial photosynthesis”. proc. natl. acad. sci. u s a, aug; vol. 45(8), pp. 1246–1260, 1959 [35] j. m. merrick, m. doudoroff “enzymatic synthesis of poly-beta-hydroxybutyric acid in bacteria”. nature, mar 18; vol. 189, pp. 890–892, 1961 [36] c. j. lusty and m. doudoroff, “poly-β-hydroxybutyrate depolymerases of pseudomonas lemoignei”. biochemistry, vol. 56, pp. 960-965. 1966. [37] d. g. lundgren, r. alper, c. schnaitman and r.h. marchessault, “characterization of polybeta-hydroxybutyrate extracted from different bacteria”. j. bacteriol, vol. 89, pp. 245-51, 1965. [38] h. g. schlegel , h. kaltwasser , g. gottschalk . “ [a submersion method for culture of hydrogen-oxidizing bacteria: growth physiological studies.] ” [article in german]arch. mikrobiol., vol. 38 pp. 209-222, 1961. [39] j. m. merrick and m. doudoroff, “depolymerization of poly-beta-hydroxybutyrate by intracellular enzyme system”. j. bacteriol., jul; vol. 88, pp. 60-71. 1964 ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 61 [40] griebel r, z. smith and m. merrick, “metabolism of poly-beta-hydroxybutyrate. i. purification, composition, and properties of native poly-beta-hydroxybutyrate granules from bacillus megaterium. biochemistry”. oct; vol. 7(10), pp. 3676-3681, 1968. [41] v. oeding, and h. g. schegel, “β-ketothiolase from hydrogenomonas eutropha h16 and its significance in the regulation of poly-β-hydroxybutyrate metabolism”. biochem , vol. j. 134 pp. 239-248, 1973. [42] p. j. senior and e. a. dawes, the regulation of poly-β-hydroxybutyrate metabolism in azotobacter beijerinckii. biochem. j., vol. 134, pp. 225–238. 1973. [43] l. l. wallen, and w. k. rohwedder. “poly-β-hydroxy-alkanoate from activated sludge”. environ. sci. technol , vol. 8 pp. 576579, 1974. [44] r. h. findlay, and d. c. white, “polymeric betahydroxyalkanoates from environmental samples and bacillus megaterium”. appl. environ. microbiol., vol. 45 pp. 71-78. 1983. [45] de smet, m. j., eggink, g., withold, b. b., kingma, j. and wynberg, h. “characterization of intracellular inclusions formed by pseudomonas oleovorans during growth on octane”. j. biotechnol., vol. 154, pp. 870-878, 1983. [46] g. w. huisman, o. de leeuw, g. eggink, and b. witholt, “synthesis of polyhydroxyalkanoates is a common feature of fluoresent pseudomonads”. appl. environ. microbiol., vol. 55 pp. 1949-1954, 1989. [47] r. fernandez-castillo, f. rodrigues-valera, j. gonzalez-ramos, and f. ruiz-berraquero, “accumulation of poly(β-hydoxybutyrate) by halobacteria”. appl. environ. microbiol., vol. 51 pp. 214-216, 1986. [48] j. anderson and e. a. dawes, “occurrence, metabolism, metabolic role, and industrial uses of bacterial polyhydroxyalkanoates”. microbiol. rev., vol. 54(4), pp. 450-472, 1990. [49] a. steinbüchel, “polyhydroxyalkanoic acids. in: byrom d (ed) “biomaterials: novel materials from biological sources”. stockton, new york, pp. 124-213, (1991). [50] a. steinbüchel, b. füchtenbusch, v. gorenflo, s. hein, r. jossek, s. langenbach, and b. h. rehm, “biosynthesis of polyesters in bacteria and recombinant organisms”. polym. degrad. stab., vol. 59 pp. 177-182, 1997. [51] a. steinbüchel and s. hein, “biochemical and molecular basis of polyhydroxyalkanoic acids in microorganism, in “biopolyester’’ a. steinbuchel, babel, w., (eds), adv. biochem. eng. biotechnol., vol. 71 pp. 81-123, 2001. [52] m. s. shabeb, m. younis, a. a. amara, and a. shoreit. “production of phb-co-phv from compost bioremediation by purple non-sulfur bacteria”. egyptian. j. biotechnol., vol. 19 pp. 467-478, 2005. [53] f. f. hezayen, b. h. rehm, r. eberhardt, and a. steinbüchel, “polymer production by two newly isolated extremely halophilic archaea: application of a novel corrosion-resistant bioreactor”. appl. microbiol. biotechnol. vol. 54, pp. 319–325. 2000. [54] f. f. hezayen, a. steinbüchel, and b. h. rehm, biochemical and enzymological properties of the polyhydroxybutyrate synthase from the extremely halophilic archaeon strain 56. arch. biochem. biophys. vol. 403, pp. 284–291. 2002. [55] baliga, n.s., bonneau, r., facciotti, m.t., pan, m., glusman, g., deutsch, e.w., shannon, p., chiu, y., weng, r.s., gan, r.r., hung, p., date, s.v., marcotte, e., hood, l., and ng, w.v. (2004). genome sequence of haloarcula marismortui: a halophilic archaeon from the dead sea. genome res. vol. 14, pp. 2221–2234. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 62 [56] a. quaiser, t. ochsenreiter, h.p. klenk, , a. kletzin, a.h. treusch, g. meurer, j. eck, c.w. sensen, and c. schleper, “first insight into the genome of an uncultivated crenarchaeote from soil”. environ. microbiol. vol. 4, pp. 603–611. 2002. [57] h. rehm and a. steinbuchel, “heterologous expression of the acyl-acyl carrier protein thioesterase gene from the plant umbellularia californica mediates polyhydroxyalkanoate biosynthesis in recombinant escherichia coli”, appl. microbiol. biotechnol., vol. 55(2), pp. 205-209, 2001. [58] r. g. lageveen, g. w. huisman, h. preusting, p. ketelaar, g. eggink, and a. witholt, “formation of polyesters by pseudomonas oleovorans: effect of substrates on formation and composition of poly(r)-3-hydroxyalkanoates and poly(r)-3-hydroxyalkenoates”. appl. environ. microbiol., vol. 54 pp. 2924–2932, 1988. [59] c. abe, y. taima, y. nakamuraand y. doi, “new bacterial copolyesters of 3hydroxyalkanoates and 3-hydroxy-ù-fluoroalkanoates produced by pseudomonas oleovorans”. polym. commun., vol. 31 pp. 404–406, 1990. [60] y. doi, c. abe, “biosynthesis and characterization of a new bacterial copolyester of 3hydroxyalkanoates and 3-hydroxy-ω-chloroalkanoates”. macromolecules, vol. 23 pp. 37053707, (1990). [61] k. fritzsche, r. w. lenz, and r. c. fuller, “bacterial polyesters containing branched poly(βhydroxyalkanoate) units”. int. j. biol. macromol., vol. 12 pp. 92–101, 1990a. [62] k. fritzsche, r. w. lenz, and r. c. fuller, “production of unsaturated polyesters by pseudomonas oleovorans”. int. j. biol. macromol., vol. 12 pp. 85–91, 1990b. [63] y. b. kim, r. w. lenz, and r. c. fuller, “poly(β-hydroxyalkanoate) copolymers containing brominated repeating units produced by pseudomonas oleovorans.”. macromolecules. vol. 25 pp. 1852–1857, 1992. [64] m. h. choi, and s. c. yoon, “polyester biosynthesis characteristics of pseudomonas citronellolis grown on various carbon sources, including 3-methyl-branched substrates”. appl. environ. microbiol, vol. 60 pp. 3245–3254, 1994. [65] j. m. curley, b. hazer, r. w. lenz, and r. c. fuller, “production of poly(3hydroxyalkanoates) containing aromatic substituents by pseudomonas oleovorans”. macromolecules , vol. 29 pp. 1762–1766, 1996. [66] j. j. song, and s. c. yoon, “biosynthesis of novel aromatic copolyesters from insoluble 11phenoxyundecanoic acid by pseudomonas putida bmo1”. appl. environ. microbiol., vol. 62 pp. 536–544, 1996. [67] g. j. m. de koning, m. kellerhals, c. van mers, and b. witholt, “a process for the recovery of poly(3-hydroxyalkanoate) from pseudomonads”. 2. process development and economic evaluation”. bioprocess. eng, vol. 17 pp. 15-21, 1997. [68] b. h. rehm, a. steinbüchel, “biochemical and genetic analysis of pha synthases and other proteins required for pha synthesis”. int. j. biol. macromol., vol. 25, pp. 3-19. 1999. [69] d. byrom “polymer synthesis by micro-organisms: technology and economics”. trends biotechnol, vol. 5 pp. 246–250, 1987. [70] p. p. king, “biotechnology. an industrial view”. j. chem. tech. biotechnol., vol. 32 pp. 2-8, 1982. [71] y. doi., “microbial synthesis, physical properties, and biodegradability of polyhydroxyalkanoates”. macromol. symp., 98 pp. 585–599, 1995. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 63 [72] r. a. gross, c. demello, r. w. lenz, h. brandl, and r. c. fuller, “biosynthesis and characterization of poly(β-hydroxyalkanoates) produced by pseudomonas oleovorans”. macromolecules, vol. 22 pp. 1106–1115, 1989. [73] j. w. moore, “degradable plastics”. mod. plastics, vol. 69(13) pp. 58-63. 1992. [74] a. a. amara, m. abd ellatif, m. younis and m. shabeb, “strategy for economic production of phas (polyhydroxyalkanoates) by bacterial isolates as a biotechnological model in arabic countries”. egyptian j. of appl. sci., vol. 20 (11b) pp, 455-473, 2005. [75] t. yamane, “yield of poly-d()-3-hydroxybutyrate from various carbon sources: a theoretical study”. biotechnol. bioeng., vol. 41 pp. 165–170, 1993 [76] b. kothuis, f. schelleman, “environmental economic comparison of biotechnology with traditional alternatives”. in: meesters khp, editor. production of poly-(3-hydroxyalkanoates) from waste streams. delft: tudelft. press; p. 4. 1998. [77] s. y. lee, and j. choi, “polymer degrad”. stabil. vol. 387, pp. 59, 1998. [78] a. a. amara and r. s. salem, “characterization of pha depolymerase in phenol degrading bacteria”. international journal of biotechnology and biochemistry, vol. 3 pp. 69-81, 2007. [79] j. n. baptist, “process for preparing poly-β-hydroxybutyric acid”. us patent no.3,036,959. 1962. [80] j. n. baptist january usa. patent 3,072,538. 1963a. [81] j. n. baptist october usa. patent 3,107,172. 1963b. [82] a. webb, february 1990. usa. patent 4,900,299. [83] f. martini, l. perazzo, and p. vietto, may usa. patent 4,826,493. 1989a. [84] f. martini, l. perazzo, and p. vietto, november usa. patent 4,880,592. 1989b. [85] h. son, g. park and s. lee, “growth-associated production of poly-β-hydroxybutyrate from glucose or alcoholic distillery waste water by actinobacillus sp”. el-9. biotechnol. lett. vol. 18, pp. 1229–1234, 1996. [86] t. kauffman, f. x. brady, p. p. puletti, and g. raykovitz, december usa. patent 5,169,889. 1992. [87] r. n. reusch, and w. h. reusch, november usa. patent 5,266,422. 1993. [88] r. n. reusch, and w. h. reusch, may usa. patent re035257. 1996. [89] r. h. marchessault, p. f. lepoutre, and p. e. wrist, september usa. patent 5,451,456. 1995. [90] m. yalpani, july 1993. usa. patent 5, 229, 158. [91] r. rutherford, w. j. hammar, and g. n. babu, march, usa. patent 5,614,576. 1997. [92] h. müller, and d. seebach, “poly(hydroxyalkanoates): a fifth class of physiologically important organic biopolymers? ” angew. chem, vol. 105 pp. 483-509, 1993. [93] k. sudesh, c.y. loo, l. k. goh, t. iwata and m. maeda, “the oil-absorbing property of polyhydroxyalkanoate films and its practical application: a refreshing new outlook for an old degrading material”. macromol. biosci., nov vol. 12;7(11), pp. 1199-1205, 2007. [94] a. steinbüchel, 1996. polyhydroxyalkanoic acids. in: biotechnology vol. 6. rehm, h. j., reed, g., püler, a., stadler, p. (eds), heidelberg, germany:wiley-vch, p. 403. [95] s. f. williams, d. p. martin, d. m. horowitz, and o. p. peoples, “pha applications: addressing the price performance issue i. tissue engineering”. int. j. biol. macromol., vol. 25 pp. 111-121, 1999. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 64 [96] a. m. van der walle, g. j. h busiman, r. a. weusthuis, and g. eggink, “development of environmentally friendly coatings and paints using medium-chain-length poly(3hydroxyalkanoates) as the polymer binder”. int. j. biol. macromol., vol. 25 pp. 123-128, 1999. [97] p. a. holmes, “applications of phb: a microbially produced biodegradable thermoplastic”. phys. technol., vol. 16 pp. 32-36. 1985. [98] y. doi. “microbial polyesters”. vch publishers, inc., yokohama, japan. 1990. [99] y. doi, y. kawaguchi, n. koyama, s. nakamura, m. hiramitsu, y. yoshida, u. kimura “synthesis and degradation of polyhydroxyalkanoates in alcaligenes eutrophus”. fems microbiol. rev., vol. 103 pp. 103-108, (1992). [100] a. a. amara, b. h. rehm and a. steinbuchel, “biopolymer overproduction by new mutants using simple methods for selection”. “in daad-bioforum-berlin-grenzenlos forschen’’, daad, biotechnologische methoden, pp. 231-239, 2001. [101] a. a. amara, a. steinbuchel and b.h. rehm, “in vivo evolution of the aeromonas punctata polyhydroxyalkanoate (pha) synthase: isolation and characterization of modified pha synthases with enhanced activity”. appl. microbiol. biotechnol., vol. 59(4-5), pp. 477482, 2002. [102] s. taguchi, a. maehara, k. takase, m. nakahara, h. nakamura and y. doi, “analysis of mutational effects of a polyhydroxybutyrate (phb) polymerase on bacterial phb accumulation using an in vivo assay system”. fems microbiol. lett., vol. 198(1), pp. 65-71, 2001. [103] s. taguchi, h. nakamura, t. hiraishi, i. yamato and y. doi, “in vitro evolution of a polyhydroxybutyrate synthase by intragenic suppression-type mutagenesis”. j. biochem., (tokyo), vol. 131(6), pp. 801-806, 2002. [104] c. j. addison, s. h. chu and r. n. reusch, polyhydroxybutyrate-enhanced transformation of log-phase escherichia coli, biotechniques vol. 37(3), pp. 376-378, 380, 382, 2004. [105] j. c. knowles, “development of a natural degradable polymer for orthopaedic use”. j. med. eng. technol., vol. 17(4), pp. 129-137, 1993. [106] c. kunze, t. freier, s. kramer and k.p. schmitz, “anti-inflammatory prodrugs as plasticizers for biodegradable implant materials based on poly(3-hydroxybutyrate)”. j. mater. sci. mater. med., vol. 13(11), pp. 1051-1055, 2002. [107] s. cheng, g.q. chen, m. leski, b. zou, y. wang and q. wu, “the effect of d,l-betahydroxybutyric acid on cell death and proliferation in l929 cells”. biomaterials, vol. 27(20), pp. 3758-3765, 2006. [108] s. k. misra, s. p. valappil, i. roy and a. r. boccaccini, “polyhydroxyalkanoate (pha)/inorganic phase composites for tissue engineering applications”. biomacromolecules vol. 7(8), pp. 2249-2258, 2006. [109] s. p. valappil, s.k. misra, a.r. boccaccini and i. roy, “biomedical applications of polyhydroxyalkanoates: an overview of animal testing and in vivo responses”. expert. rev. med. devices, vol. 3(6), pp. 853-868, 2006. [110] g. a. van der walle, g.j. de koning, r.a. weusthuis and g. eggink, “properties, modifications and applications of biopolyesters”. adv biochem eng biotechnol vol. 71, pp. 263-91, 2001. [111] y. w. wang, f. yang, q. wu, y.c. cheng, p.h. yu, j. chen and g.q. chen, “effect of composition of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) on growth of fibroblast and osteoblast”. biomaterials, vol. 26(7), pp. 755-61, 2005. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 65 [112] b. nebe, c. forster, h. pommerenke, g. fulda, d. behrend, u. bernewski, k. p. schmitz, and j. rychly, “structural alterations of adhesion mediating components in cells cultured on poly β-hydroxy butyric acid”. biomaterials , vol. 22 pp. 2425–2434, 2001. [113] i. shishatskaya and t. g. volova, “a comparative investigation of biodegradable polyhydroxyalkanoate films as matrices for in vitro cell cultures”. j. mater. sci. mater. med., vol. 15(8), pp. 915-923, 2004. [114] i. shishatskaya, t. g. volova, a. p. puzyr, o. a. mogilnaya and s. n. efremov, “tissue response to the implantation of biodegradable polyhydroxyalkanoate sutures”. j. mater. sci. mater. med., vol. 15(6), pp. 719-728, 2004. [115] i. shishatskaya, t. g. volova, s. a. gordeev and a. p. puzyr, “degradation of p(3hb) and p(3hb-co-3hv) in biological media”. j. biomater. sci. polym. ed, vol. 16(5), pp. 643657, 2005. [116] i. shishatskaya, i. a. khlusov and t. g. volova, “a hybrid phb-hydroxyapatite composite for biomedical application: production, in vitro and in vivo investigation”. j. biomater. sci. polym. ed, vol. 17(5), pp. 481-498, 2006. [117] i. shishatskaya, o. n. voinova, a. v. goreva, o. a. mogilnaya and t. g. volova, “biocompatibility of polyhydroxybutyrate microspheres: in vitro and in vivo evaluation”, j. mater. sci. mater. med., vol. 19(6), pp. 2493-2502, 2008. [118] a. tezcaner, k. bugra, and v. hasirci, “retinal pigment epithelium cell culture on surface modified poly(hydroxybutyrate-co-hydroxyvalerate) thin films. biomaterials, vol. 24 pp. 4573–4583, 2003. [119] y. tesema, y., raghavan, d. and j. stubbs, “bone cell viability on collagen immobilized poly (3-hydroxybutrate-co-3-hydroxyvalerate) membrane: effect of surface chemistry”. j. appl. polym. sci., vol. 93 pp. 2445–2453, 2004. [120] t. malm, s. bowald, s. karacagil, a. bylock and c. busch, “a new biodegradable patch for closure of atrial septal defect. an experimental study”, scand. j. thorac. cardiovasc. surg., vol. 26(1), pp. 9-14, 1992. [121] t. malm, s. bowald, a. bylock, t. saldeen and c. busch, “regeneration of pericardial tissue on absorbable polymer patches implanted into the pericardial sac. an immunohistochemical, ultrastructural and biochemical study in the sheep”, scand. j. thorac. cardiovasc. surg., vol. 26(1), pp. 15-21, 1992. [122] t. malm, s. bowald, a. bylock, c. busch and t. saldeen, “enlargement of the right ventricular outflow tract and the pulmonary artery with a new biodegradable patch in transannular position”, eur. surg. res., vol. 26(5), pp. 298-308, 1994. [123] z. cai, l. wang, x. hou and g. cheng, “ [application of biodegradable polyhydroxybutyrate in medicine and tissue engineering] ”, sheng wu yi xue gong cheng xue za zhi vol. 19(2), pp. 306-309, 2002. [124] a. c. kassab, k. xu, e. b. denkbas, y. dou, s. zhao and e. piskin, rifampicin carrying polyhydroxybutyrate microspheres as a potential chemoembolization agent, j. biomater, sci. polym. ed. vol. 8(12), pp. 947-961, 1997. [125] s. p. valappil, s. k. misra, a. r. boccaccini and i. roy, “biomedical applications of polyhydroxyalkanoates: an overview of animal testing and in vivo responses”. expert. rev. med. devices. vol. 3(6), pp. 853-868, 2006. [126] g. q. chen and q. wu, “the application of polyhydroxyalkanoates as tissue engineering materials”, biomaterials, vol. 26(33), pp. 6565-6578, 2005. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 66 [127] g. ostle, and j. g. holt, “nile blue a as a fluorescent stain for polyβ -hydroxybutyrate”. appl. environ. microbiol., vol. 44 pp. 238-241, 1982. [128] h. g. schlegel, r. lafferty, and i. krauss, “the isolation of mutants not accumulating poly-β-hydroxybutyric acid”. arch. mikrobiol., vol. 71 pp. 283-294, 1970. [129] p. spiekermann, b. h. rehm, r. kalscheuer, d. baumeister and a. steinbuchel, “a sensitive, viable-colony staining method using nile red for direct screening of bacteria that accumulate polyhydroxyalkanoic acids and other lipid storage compounds”. arch. microbiol., vol. 171(2), pp. 73-80, 1999. [130] h. brandl, r. a. gross, r. w. lenz, and r. c. fuller, “pseudomonas oleovorans as a source of poly(β-hydroxyalkanoates) for potential applications as biodegradable polyesters”. appl. environ. microbiol, vol. 54 pp. 1977-1982, 1988. [131] a. timm and a. steinbuchel, “formation of polyesters consisting of medium-chain-length 3-hydroxyalkanoic acids from gluconate by pseudomonas aeruginosa and other fluorescent pseudomonads”. appl. environ. microbiol., vol. 56(11), pp. 3360-3367, 1990. [132] schubert, a. steinbuchel and h.g. schlegel, “cloning of the alcaligenes eutrophus genes for synthesis of poly-beta-hydroxybutyric acid (phb) and synthesis of phb in escherichia coli”. j. bacteriol., vol. 170(12), pp. 5837-5847, 1988. [133] s. c. slater, w. h. voige, and d. e. dennis, “cloning and expression in escherichia coli of the alcaligenes eutrophus h16 poly-β-hydroxybutyrate biosynthetic pathway”. j. bacteriol., vol. 170 pp. 4431-4436. 1988. [134] o. p. peoples, and a. j. sinskey, “poly-β-hydroxybutyrate (phb) biosynthesis in alcaligenes eutrophus h16. identification and characterization of the phb polymerase gene (phbc)”. j. biol. chem., vol. 264 pp. 15298-15303, 1989. [135] f. a. jackson, and e. a., dawes. “regulabon of the tricarboxylic acid cycle and poly-bhydoxybutyrate metabolism in azotobacter beijerinckii grown under nitrigen or oxygen limitation”. j. gen. microbiol., vol. 97 pp. 303-312, 1976 [136] y. asada, m. miyake, j. miyake, r. kurane and y. tokiwa, “photosynthetic accumulation of poly-(hydroxybutyrate) by cyanobacteria-the metabolism and potential for co2 recycling”. int. j. biol. macromol. vol. 25(1-3), pp. 37-42, 1999. [137] a. mansfield, a. j. anderson and l. a. naylor, “regulation of phb metabolism in alcaligenes eutrophus”. canadian journal of microbiology, vol. 41(suppl. 1), pp. 44–49. 1995 [138] s. slater, k. l. houmiel, m. tran, t. a. mitsky, n. b. taylor, s. r. padgette, and k. j. gruys, “multiple β-ketothiolases mediate poly(β-hydroxyalkanoate) copolymer synthesis in ralstonia eutropha”. j. bacteriol., vol. 180 pp. 1979–1987, 1998. [139] g. n. m. huijberts, g. eggink, p. de waard, g. w. huisman, and b. witholt, ”pseudomonas putida kt2442 cultivated on glucose accumulates poly(3-hydroxyalkanoates) consisting of saturated and unsaturated monomers. ” appl. environ. microbiol., vol. 58 pp. 536-544, 1992. [140] h. rehm, n. kruger and a. steinbuchel, “a new metabolic link between fatty acid de novo synthesis and polyhydroxyalkanoic acid synthesis”. the phag gene from pseudomonas putida kt2440 encodes a 3-hydroxyacyl-acyl carrier protein-coenzyme a transferase”. j. biol. chem., vol. 273(37), pp. 24044-24051, 1998. [141] e. valentin and d. dennis, “production of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) in recombinant escherichia coli grown on glucose”, j. biotechnol., vol. 58(1), pp. 33-38, 1997. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 67 [142] n. hoffmann, a. steinbüchel, and b. h. rehm, “the pseudomonas aeruginosa phag gene product is involved in the synthesis of polyhydroxyalkanoic acid consisting of mediumchain-length constituents from non-related carbon sources ”. fems microbiol. lett. vol. 184, pp. 253-259, 2000 [143] n. hoffmann, a. steinbuchel and b. h. rehm, “homologous functional expression of cryptic phag from pseudomonas oleovorans establishes the transacylase-mediated polyhydroxyalkanoate biosynthetic pathway”. appl. microbiol. biotechnol., vol. 54(5), 665670, 2000. [144] n. hoffmann, a. a. amara, b. b. beermann, q. qi, h. j. hinz and b. h. rehm “biochemical characterization of the pseudomonas putida 3-hydroxyacyl acp:coa transacylase which diverts intermediates of fatty acid de novo biosynthesis”. j. biol. chem., vol. 277 pp. 42926-42936, 2002. [145] c. dirusso, “primary sequence of the escherichia coli fadba operon, encoding the fatty acid-oxidizing multienzyme complex, indicates a high degree of homology to eukaryotic enzymes”. j. bacteriol, vol. 172 pp. 6459-6468, 1990. [146] s. langenbach, b. h. rehm and a. steinbuchel, “functional expression of the pha synthase gene phac1 from pseudomonas aeruginosa in escherichia coli results in poly(3hydroxyalkanoate) synthesis”, fems microbiol. lett., vol. 150(2), pp. 303-309, 1997. [147] q. qi, b. h. rehm and a. steinbuchel, “synthesis of poly(3-hydroxyalkanoates) in escherichia coli expressing the pha synthase gene phac2 from pseudomonas aeruginosa: comparison of phac1 and phac2”. fems microbiol. lett., vol. 157(1), pp. 155-162, 1997. [148] s. fiedler, a. steinbuchel and b. h. rehm, “the role of the fatty acid beta-oxidation multienzyme complex from pseudomonas oleovorans in polyhydroxyalkanoate biosynthesis: molecular characterization of the fadba operon from p. oleovorans and of the enoyl-coa hydratase genes phaj from p. oleovorans and pseudomonas putida”. arch. microbiol., vol. 178(2), pp. 149-160, 2002. [149] t. fukui, and y. doi., “cloning and analysis of the poly(3-hydroxybutyrate-co-3hydroxyhexanoate) biosynthesis genes of aeromonas caviae”. j. bacteriol., vol. 179 pp. 48214830,1997. [150] t. tsuge, t. fukui, h. matsusaki, s. taguchi, g. kobayashi, a. ishizaki and y. doi, “ molecular cloning of two (r)-specific enoyl-coa hydratase genes from pseudomonas aeruginosa and their use for polyhydroxyalkanoate synthesis”. fems microbiol. lett., vol. 184(2), pp. 193-198, 2000. [151] k. taguchi, y. aoyagi, h. matsusaki, t. fukui and y. doi, “co-expression of 3-ketoacylacp reductase and polyhydroxyalkanoate synthase genes induces pha production in escherichia coli hb101 strain”. fems microbiol. lett., vol. 176(1), pp. 183-190, 1999. [152] q. ren, n. sierro, b. witholt, and b. kessler, “fabg, an nadph-dependent 3-ketoacyl reductase of pseudomonas aeruginosa, provides precursors for medium-chain-length poly-3hydroxyalkanoate biosynthesis in escherichia coli”. j. bacteriol., vol. 182 pp. 2978-2981, 2000. [153] j. e. thijsse, “fatty-acid accumulation by acrylate inhibition of β-oxidation in an alkaneoxidizing pseudomonas”. biochim. biophys. acta, vol. 84 pp. 195-197, 1964. [154] s. miyakawa, k. suzuki, t. noto, y. harada, and h. okazaki, “thiolactomycin, a new antibiotic. iv. biological properties and chemotherapeutic activity in mice”. j. antibiot., vol. 35 pp. 411-419, 1982. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 68 [155] g. m. jr. helmkamp, d. j. brock, and k. bloch, “beta-hydroxydecanoyl thioester dehydrase. specificity of substrates and acetylenic inhibitors”. j. biol. chem., vol. 243 pp. 3229-3231, 1968. [156] r. j. heath, y. t. yu, m. a. shapiro, e. olson, and c. rock, “broad spectrum antimicrobial biocides target fabi component of fatty acid synthesis”. j. biol. chem., vol. 273 pp. 30316-30320, 1998. [157] f. turnowsky, k. fuchs, c. jeschek, and g. hogenauer, “envm genes of salmonella typhimurium and escherichia coli”. j. bacteriol., vol. 171 pp. 6555-6565. 1989. [158] g. d'agnolo, i. s. rosenfeld, j. awaya, s. omura, and p. r. vagelos, “inhibition of fatty acid synthesis by the antibiotic cerulenin. specific inactivation of beta-ketoacyl-acyl carrier protein synthetase”. biochim. biophys. acta, vol. 326 pp. 155-156, 1973. [159] q. qi, a. steinbuchel and b. h. rehm, “metabolic routing towards polyhydroxyalkanoic acid synthesis in recombinant escherichia coli (fadr): inhibition of fatty acid beta-oxidation by acrylic acid”. fems microbiol. lett., vol. 167(1), pp. 89-94, 1998. [160] h. m. alvarez, , r. kalscheuer, and a. steinbüchel, “accumulation of storage lipids in species of rhodococcus and nocardia and effect of inhibitors and polyethylene glycol ”. fett/lipid, vol. 99, pp. 239-246, 1997. [161] r. v. antonio, a. steinbüchel and b. h. rehm, “analysis of in vivo substrate specificity of the pha synthase from ralstonia eutropha: formation of novel copolyesters in recombinant escherichia coli”. fems microbiol. lett. vol. 182, pp. 111–117. 2000. [162] t. u. gerngross and d. p. martin, “enzyme-catalyzed synthesis of poly[(r)-(-)-3hydroxybutyrate]: formation of macroscopic granules in vitro”. proc. natl. acad. sci. u s a, vol. 92(14), pp. 6279-6783, 1995. [163] r. jossek and a. steinbuchel, “in vitro synthesis of poly(3-hydroxybutyric acid) by using an enzymatic coenzyme a recycling system”, fems microbiol. lett., vol. 168(2), pp. 319324, 1998. [164] r. w. lenz, c. farcet, p. j. dijkstra, s. goodwin, s. zhang, “extracellular polymerization of 3-hydroxyalkanoate mononers with the polymerase of alcaligenes eutrophus”. int. j. biol. macromol., vol. 25 pp. 55-60, 1999. [165] r. jossek, r. reichelt and a. steinbuchel, “in vitro biosynthesis of poly(3-hydroxybutyric acid) by using purified poly(hydroxyalkanoic acid) synthase of chromatium vinosum”, appl. microbiol. biotechnol., vol. 49(3), pp. 258-266, 1998. [166] l. su, r. w. lenz, y. takagi, s. zhang, s. goodwin, l. zhong, d. p . martin, “enzymatic polymerization of (r)-3-hydroxyalkanoates by a bacterial polymerase, macromolecules, vol. 33, pp. 229-231, 2000. [167] s. j. liu and a. steinbuchel, “exploitation of butyrate kinase and phosphotransbutyrylase from clostridium acetobutylicum for the in vitro biosynthesis of poly(hydroxyalkanoic acid) ”, appl. microbiol. biotechnol., vol. 53(5), pp. 545-552, 2000. [168] q. qi, a. steinbuchel and b. h. rehm, “in vitro synthesis of poly(3-hydroxydecanoate): purification and enzymatic characterization of type ii polyhydroxyalkanoate synthases phac1 and phac2 from pseudomonas aeruginosa”. appl. microbiol. biotechnol., vol. 54(1), pp. 37-43, 2000. [169] r. n. reush, “poly-β-hydroxybuyrate/calcium polyhydroxyphosphate, a biodegradable thermoplastic produced in transgenic plants”. science, vol. 256, pp. 520-523, 1989. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 69 [170] t. a. leaf, m. s. peterson, s. k. stoup, d. somers and f. srienc, “saccharomyces cerevisiae expressing bacterial polyhydroxybutyrate synthase produces poly-3hydroxybutyrate”. microbiology, vol. 142 ( pt 5), pp. 1169-1180, 1996. [171] j. hahn, a. c. eschenlauer, m. h. narrol, d. a. somers, and f. srienc, “growth kinetics, nutrient uptake, and expression of the alcaligenes eutrophus poly(β-hydroxybutyrate) synthesis pathway in transgenic maize cell suspension cultures”. biotechnol. prog., vol. 13 pp. 347–354, 1997. [172] j. a. kornblatt, and h. rundney, “two forms of acetoacetyl coenzyme a thiolase in yeast ii. intracellular location and relationship to growth”. j. biol. chem., vol. 246 pp. 4424-4430, 1971. [173] j. c. igual, c. gonzalez-bosch, and j. e. perez-ortin, “the potl* gene for yeast peroxisomal thiolase is subject to there different mechanisms of regulation”. mol. microbiol., vol. 6 pp. 1867-1875, 1992. [174] s. safak, n. mercan, b. aslim, and y. beyatli, “a study on the production of poly-betahydroxybutyrate by some eukyryotic microorganisms”. turkish electronic journal of biotechnology, pp. 11-17, 2002. [175] b. zhang, r. carlson and f. srienc, “engineering the monomer composition of polyhydroxyalkanoates synthesized in saccharomyces cerevisiae”. appl. environ. microbiol., 72(1), 536-543, 2006. [176] r. n. reush, “poly-β-hydroxybuyrate/calcium polyhydroxyphosphate, a biodegradable thermoplastic produced in transgenic plants”. science. vol. 256, pp. 520-523. 1989. [177] e. valentin, d. l. broyles, l. a. casagrande, s. m. colburn, w. l. creely, p. a. delaquil, h. m. felton, k. a. gonzalez, k .l. houmiel, k. lutke, d. a. mahadeo, t. a. mitsky, s. r. padgette, s. e. reiser, s. slater, d. m. stark, r. t. stock, d. a. stone, n. b. taylor, g. m. thorne, m. tran and k. j. gruys, “pha production, from bacteria to plants”. int. j. biol. macromol., vol. 25(1-3), pp. 303-306, 1999. [178] m. e. john and g. keller, “metabolic pathway engineering in cotton: biosynthesis of polyhydroxybutyrate in fiber cell. proc. natl. acad. sci. u s a, vol. 93(23), pp. 1276812773, 1996. [179] h. nakashita, y. arai, k. yoshioka, t. fukui, y. doi, r. usami, k. horikoshi, and i. yamaguchi, “production of biodegradable polyester by a transgenic tobacco”. biosci. biotechnol. biochem , vol. 63 pp. 870-874, 1999. [180] s. slater, t. a. mitsky, k. l. houmiel, m. hao, s. e. reiser, n. b. taylor, m. tran, h. e. valentin, d. j. rodriguez, d. a. stone, s. r. padgette, g. kishore, and k. j. gruys, “metabolic engineering of arabidopsis and brassica for poly(3-hydroxybutyrate-co-3hydroxyvalerate) copolymer production”. nat. biotechnol., vol. 17 pp. 1011-1016, 1999. [181] v. mittendorf, e. j. robertson, r. m. leech, n. kruger, a. steinbuchel and y. poirier, “synthesis of medium-chain-length polyhydroxyalkanoates in arabidopsis thaliana using intermediates of peroxisomal fatty acid beta-oxidation”, proc. natl. acad. sci. u s a, vol. 95(23), pp. 13397-13402, 1998. [182] h. rehm and a. steinbuchel, “pha synthases-the key enzymes of pha synthesis. in ‘’biopolymers’’. a. steinbuchel and y. doi (eds.), wiley-vch, heidelberg, germany, pp. 173-215, 2001. [183] m. liebergesell and a. steinbuchel, “cloning and nucleotide sequences of genes relevant for biosynthesis of poly(3-hydroxybutyric acid) in chromatium vinosum strain d”, eur. j. biochem., vol. 209(1), pp. 135-150, 1992. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 70 [184] m. liebergesell, s. rahalkar and a. steinbuchel, “analysis of the thiocapsa pfennigii polyhydroxyalkanoate synthase: subcloning, molecular characterization and generation of hybrid synthases with the corresponding chromatium vinosum enzyme”, appl. microbiol. biotechnol., vol. 54(2), pp. 186-194, 2000. [185] t. u. gerngross, k. d. snell, o. p. peoples, a. j. sinskey, e. csuhai, s. masamune and j. stubbe, “overexpression and purification of the soluble polyhydroxyalkanoate synthase from alcaligenes eutrophus: evidence for a required posttranslational modification for catalytic activity”. biochemistry, vol. 33(31), pp. 9311-9320, 1994. [186] m. liebergesell, k. sonomoto, m. madkour, f. mayer and a. steinbuchel, “purification and characterization of the poly(hydroxyalkanoic acid) synthase from chromatium vinosum and localization of the enzyme at the surface of poly(hydroxyalkanoic acid) granules”, eur. j. biochem., vol. 226(1), pp. 71-80, 1994. [187] a. timm and a. steinbuchel, “cloning and molecular analysis of the poly(3hydroxyalkanoic acid) gene locus of pseudomonas aeruginosa pao1”. eur. j. biochem., vol. 209(1), pp. 15-30, 1992. [188] s. fiedler, a. steinbuchel and b. h. rehm, “phag-mediated synthesis of poly(3hydroxyalkanoates) consisting of medium-chain-length constituents from nonrelated carbon sources in recombinant pseudomonas fragi”. appl. environ. microbiol., vol. 66(5), pp. 2117-2124, 2000. [189] q. qi, a. steinbuchel and b. h. rehm, “in vitro synthesis of poly(3-hydroxydecanoate): purification and enzymatic characterization of type ii polyhydroxyalkanoate synthases phac1 and phac2 from pseudomonas aeruginosa”. appl. microbiol. biotechnol., vol. 54(1), pp. 37-43, 2000. [190] h. rehm, q. qi, b .b. beermann, h. j. hinz and a. steinbuchel, “matrix-assisted in vitro refolding of pseudomonas aeruginosa class ii polyhydroxyalkanoate synthase from inclusion bodies produced in recombinant escherichia coli”. j. biochem., vol. 358(pt 1), pp. 263-268, 2001. [191] y. jia, t. j. kappock, t. frick, a. j. sinskey and j. stubbe, “lipases provide a new mechanistic model for polyhydroxybutyrate (phb) synthases: characterization of the functional residues in chromatium vinosum phb synthase”. biochemistry. vol. 39(14), pp. 3927-3936, 2000. [192] k. karplus, c. barrett, and r. hughey, “hidden markov models for detecting remote protein homologies”. bioinformatics, vol. 14 pp. 846-856, 1998. [193] h. rehm, r. v. antonio, p. spiekermann, a. a. amara and a. steinbuchel, “molecular characterization of the poly(3-hydroxybutyrate) (phb) synthase from ralstonia eutropha: in vitro evolution, site-specific mutagenesis and development of a phb synthase protein model”. biochim. biophys. acta., vol. 1594(1), pp. 178-190, 2002. [194] u. müh, k. snell, e. troyano, j. wodzinska, a. j. sinskey, and j. stubbe, “in: “biochemical principles and mechanism of biosynthesis and biodegradation of polymers’’, an international symposium, abstract book, lecture 6, münster, germany. 1998. [195] a. hoppensack, b. h. rehm and a. steinbuchel, “analysis of 4-phosphopantetheinylation of polyhydroxybutyrate synthase from ralstonia eutropha: generation of beta-alanine auxotrophic tn5 mutants and cloning of the pand gene region”. j. bacteriol., vol. 181(5), pp. 1429-1435, 1999. [196] j. mccool, and m. c. cannon, “phac and phar are required for polyhydroxyalkanoic acid synthase activity in bacillus megaterium”. j. bacteriol., vol. 183 pp. 4235-4243, 2001. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 71 [197] a. a. amara and b. h. rehm, “replacement of the catalytic nucleophile cysteine-296 by serine in class ii polyhydroxyalkanoate synthase from pseudomonas aeruginosa-mediated synthesis of a new polyester: identification of catalytic residues”. biochem. j., vol. 374(pt 2), pp. 413-421, 2003. [198] d. s. sheu and c.y. lee, “altering the substrate specificity of polyhydroxyalkanoate synthase 1 derived from pseudomonas putida gpo1 by localized semirandom mutagenesis”. j. bacteriol. vol. 186, pp. 4177– 4184, 2004. [199] t. tsuge, y. saito, m. narike, k. muneta, y. m. normi, y. kikkawa,, t. hiraishi, , and y. doi, “mutation effects of a conserved alanine (ala510) in type i polyhydroxyalkanoate synthase from ralstonia eutropha on polyester biosynthesis ”. macromol. biosci. vol. 4, pp. 963–970, 2004. [200] b. rost and c. sander, “combining evolutionary information and neural networks to predict protein secondary structure”. proteins, vol. 19 pp. 55-72, 1994. [201] u. müh, a. j. sinskey, d. p. kirby, w. s. lane, and j. stubbe, “pha synthase from chromatium vinosum: cysteine 149 is involved in covalent catalysis. biochemistry, vol. 38 pp. 826-837, 1999. [202] j. wodzinska, k. d. snell, a. rhomberg, a. j. sinskey, k. biemann, and j. stubbe, “polyhydroxybutyrate synthase: evidence for covalent catalysis”. j. am. chem. soc., vol. 118 pp. 6319-6320, 1996. [203] f. mayer, m. h. madkour, u. pieper-fürst, r. wieczorek, m. liebergesell. and a. steinbuchel, “electron microscopic observations on the macromolecular organization of the boundary layer of bacterial pha inclusion bodies”. j. gen. appl. microbiol., vol. 42 pp. 445-455, 1996. [204] t. saito, k. suzuki, j. yamamoto, t. fukui, k. miwa, k. tomita, s. nakauishi, s. odani, j. i. suzuki, and k. ishikawa, “cloning, nucleotide sequence, and expression in escherichia coli of the gene for poly(3-hydroxybutyrate) depolymerase from alcaligenes faecalis”. j. bacteriol, vol. 171 pp. 184-189, 1989. [205] b. klingbei, r. m. kroppenstedt, and d. jendrossek, “taxonomic identification of streptomyces exfoliates k10 and characterization of its poly(3-hydroxybutyrate) depolymerase gene”. fems microbiol. lett., vol. 142(2-3) pp. 215-221, 1996. [206] schirmer, c. matz, and d. jendrossek, “substrate specificities of pha-degrading bactria and active site studies on the extracellular poly(3-hydroxyactonoic acid) p(3ho)] depolymerise of pseudomonas fluorescens gk13 biovarv”. appl. environ. microbiol., vol. 59 pp. 1220-1227, 1995. [207] h. saegusa, m. shiraki, c. kanai, and t. saito. “cloning of an intracellular poly[d(-)-3hydroxybutyrate] depolymerase gene from ralstonia eutropha h16 and characterization of the gene product”. j. bacteriol., vol. 183 pp. 94-100, 2001. [208] h. saegusa, m. shiraki, and t. saito, “cloning of an intracellular d(-)-3-hydroxybutyrateoligomer hydrolase gene from ralstonia eutropha h16 and identification of the active site serine residue by site-directed mutagenesis”. j. biosci. bioeng., vol. 94 pp. 106-112, 2002. [209] t. kobayashi, m. shiraki, t. abe, a. sugiyama, and t. saito, “purification and properties of an intracellular 3-hydroxybutyrate-oligomer hydrolase (phaz2) in ralstonia eutropha h16 and its identification as a novel intracellular poly(3-hydroxybutyrate) depolymerase”. j. bacteriol., vol. 185 pp. 3485-3490, 2003. ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 72 [210] g. m. york, j. stubbe, and a.j. sinskey, “the ralstonia eutropha phar protein couples synthesis of the phap phasin to the presence of polyhydroxybutyrate in cells and promotes polyhydroxybutyrate production ”. j. bacteriol. vol.184, pp. 59–66. 2002. [211] t. m. scherer, r. c. fuller, s. goodwin, and r. w. lenz, “enzymatic hydrolysis of oligomeric models of poly-3-hydroxybutyrate”. biomacromolecules , vol. 1 pp. 577-583, 2000. [212] p. gruchulski, f. bouthillier, r. j. kazlauskas, a. n. serreqi, j. d. schrag, e. ziomek, and m. cygler, “analogs of reaction intermediates identify a unique substrate binding site in candida rugosa lipase”. ” biochemistery, vol. 33 pp. 3494-3500, 1994. [213] k. e. jaeger, a. steinbuchel and d. jendrossek, “substrate specificities of bacterial polyhydroxyalkanoate depolymerases and lipases: bacterial lipases hydrolyze poly(omegahydroxyalkanoates) ”. appl. environ. microbiol., vol. 61(8), pp. 3113-3118, 1995. [214] m. nojiri, and t. saito. “structure and function of poly(3-hydroxybutyrate) depolymerase from alcaligenes faecalis t1”. j bacteriol 179 pp. 6965-6970, 1997. [215] d. jendrossek, a. schirmer, and h. g. schlegel, “biodegradation of polyhydroxyalkanoic acids”. appl. microbiol. biotechnol., vol. 46 pp. 451–463, 1996 [216] j. mergaert, a. webb, c. anderson, a. wouters, j. swings, “microbial degradation of poly (3-hydroxybutyrate) and poly(3hydroxybutyrate-co-3-hydroxyvalerate) in soil”. appl. environ. microbiol., vol. 59 pp. 3233-3238, 1993. [217] j. mergaert, c. anderson, a. wouters, and j. swings, “microbial degradation of poly(3hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in compost”. j. environ. polym. degrad. , vol. 2 pp. 177–183, 1994. [218] j. mergaert, a. wouters, c. anderson, and j. swings, “in situ biodegradation of poly(3hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in natural waters”. can. j. microbiol. , vol. 41 pp. 154–159, 1995. [219] s. f. williams, and o. p. peoples, “biodegradable plastics from plants”. chemtech., vol. 26 pp. 38-44. 1996. [220] l. jurasek, and r.h. marchessault, “the role of phasins in the morphogenesis of poly(3hydroxybutyrate) granules”. biomacromolecules vol. 3, pp. 256–261, 2002. [221] a. steinbüchel, k. aerts, w. babel, c. föllner, m. liebergesell, m. h. madkour,., f. mayer, i. pieper-fürst, a. pries, h. e. valentin, and r. wieczorek, “considerations on the structure and biochemistry of bacterial polyhydroxyalkanoic acid inclusions”. can. j. microbiol., vol. 41 pp. 94-105, 1995. [222] w. f. dunlop and a. w. robards “ultrastructural study of polyβ -hydroxybutyrate granules from bacillus cereus”. j. bacteriol. vol. 114 pp. 1271–1280, 1973. [223] d. byrom “polyhydroxyalkanoates”, in: mobley dp (ed), “plastic from microbes: microbial synthesis of polymers and polymer precursors”. hanser munich, pp. 5-33, 1994. [224] b.h. r ehm, “polyester synthases: natural catalysts for plastics”. biochem. j., vol. 376, pp. 15–33, 2003. [225] g. n. barnard, and j. k. sanders, “the poly-beta-hydroxybutyrate granule in vivo. a new insight based on nmr spectroscopy of whole cells ”. j. biol. chem. vol. 264, pp. 3286–3291, 1989. [226] m. potter, h. muller, f. reinecke, r. wieczorek, f. fricke, b. bowien, b. friedrich and a. steinbuchel, “the complex structure of polyhydroxybutyrate (phb) granules: four ium engineering journal, vol. 9, no. 1, 2008 a.a. amara 73 orthologous and paralogous phasins occur in ralstonia eutropha”. microbiology, vol. 150(pt 7), pp. 2301-2311, 2004. [227] h. rehm, q. qi, b. b. beermann, h. j. hinz and a. steinbuchel, “matrix-assisted in vitro refolding of pseudomonas aeruginosa class ii polyhydroxyalkanoate synthase from inclusion bodies produced in recombinant escherichia coli”. biochem. j., vol. 358(pt 1), pp. 263-268, 2001. [228] b. h. rehm, “biogenesis of microbial polyhydroxyalkanoate granules: a platform technology for the production of tailor-made bioparticles”. curr issues mol biol. jan; vol. 9(1), pp. 41-62, 2007 microsoft word musend1yz-3.doc iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 1 knowledge-based trajectory error pattern method applied to an active force control scheme endra pitowarno1, musa mailah, hishamuddin jamaluddin department of applied mechanics, faculty of mechanical engineering universiti teknologi malaysia 81310 skudai, johor darul takzim, tel: 07-5534756, fax: 07-5566159 e-mail: pgep@graduan.fkm.utm.my, musa@fkm.utm.my, hishamj@fkm.utm.my 1 corresponding author abstract: the active force control (afc) method is known as a robust control scheme that dramatically enhances the performance of a robot arm particularly in compensating the disturbance effects. the main task of the afc method is to estimate the inertia matrix in the feedback loop to provide the correct (motor) torque required to cancel out these disturbances. several intelligent control schemes have already been introduced to enhance the estimation methods of acquiring the inertia matrix such as those using neural network, iterative learning and fuzzy logic. in this paper, we propose an alternative scheme called knowledge-based trajectory error pattern method (kbtepm) to suppress the trajectory track error of the afc scheme. the knowledge is developed from the trajectory track error characteristic based on the previous experimental results of the crude approximation method. it produces a unique, new and desirable error pattern when a trajectory command is forced. an experimental study was performed using simulation work on the afc scheme with kbtepm applied to a two-planar manipulator in which a set of rule-based algorithm is derived. a number of previous afc schemes are also reviewed as benchmark. the simulation results show that the afc-kbtepm scheme successfully reduces the trajectory track error significantly even in the presence of the introduced disturbances. key words: active force control, estimated inertia matrix, robot arm, trajectory error pattern, knowledgebased. 1. introduction robot control is a challenging research area in the field of robotic in which a number of problems need to be addressed or solved in order to acquire good coordinated motion and force controlled performance of the robotic system while it is performing specific task. one of the major problems encountered is the inherent non-linear dynamic characteristics of the robotic system that often needs rigorous and complex mathematical model analysis. implementing the model directly into the system controller is often complicated. the most popular and proven method that is widely employed is the classical control method such as the proportionalintegral-derivative (pid) controller. although this method is simple, practical and robust (to a certain degree), it possesses severe limitation when it comes to high-speed operation or in the presence of significant ‘noises’ in the system [1] as the control system losses its effectiveness in the process. these two undesirable conditions normally trigger further non-linearity effects and uncertainties into the system. thus, it is an obvious indication that pure classical control alone is not enough to address and overcome the problem. eventually, many researchers have tried other methods which usually include the classical method alongside their proposed strategies as means to realize an overall robust, efficient and effective controller[2-6]. one of these methods is based on the incorporation of intelligent control mechanism. some researchers in this area claim to have achieved a degree of enhancement (valueadded) in terms of performance when applied to robotic system using features such as neural network [7], fuzzy logics [8], and iterative learning algorithm [9]. most of the proposed intelligent control methods focus on the computation or estimation of the robot inverse dynamics via suitable intelligent algorithm or structure while in some other application, it is used to estimate parameter/s of interest. in this paper, we propose another intelligent method to indirectly control a robot arm using a knowledge-based method. in a number of cases for non-linear system (including robotic), the knowledge-based element is found to be useful in enhancing the decision support system [10]. using the knowledge component of a particular system, a semantic network analysis was successfully implemented [11], [12]. once the knowledge component is clearly defined, the probability of the occurrence of event should also be determined. one of iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 2 the popular method to approximate the probability of an event is bayes rule [13]. the technique is applied to an active force control of a robotic manipulator. we call the system active force control with knowledge-based trajectory-errorpattern method (afc-kbtepm). the first part of the paper highlights the fundamental concepts of afc and kbtepm followed by a brief review of other afc methods including afc based on crude approximation (afcca)[14], the afcann (afc and neural network) [15], and afcafl (afc and fuzzy logic) [16]. simulation study of the afc schemes was then performed. consequently, the analysis and discussion of the obtained results obtained are given followed by conclusion and further works that could be carried out. 2. active force control application of afc to robot arm is first proposed by hewit and burdess [4]. the aim of this control method is to ensure that the system is stable and robust even in the presence of known or unknown disturbances. the main advantage of the method is that it provides a compensating action using mainly the estimated or measured values of certain parameters. this method gives benefits on reducing the mathematical complexity of the robot system that is known to be highly coupled and non-linear[4]. figure 1 shows a schematic diagram of an afc scheme. afc show that the system subjecting to a number of disturbances remains stable and robust via the compensating action of the control strategy. the detailed mathematical analysis of the afc scheme is obtained[4]. from the newton’s second law of motion for a rotating mass, the sum of all torques (t) acting on the body is the product of the mass moment of inertia (i) and the angular acceleration () of the body in the direction of the applied torque, t = i ��� for a robot system with serial configuration, t + q = i()  where, t is the applied torque q is the disturbance torques i() is mass moment of inertia or the robot arm and  is the robot joint angle  is the angular acceleration of the robot arm we can obtain a measurement of q' of q as q' = i' ' t' (3) where the superscript ' denotes a measured or computed (or estimated) quantity. t' can be measured by using a current sensor (with conversion) while ' with accelerometer. i' may be obtained by assuming a perfect model or simply crude approximation. gc(s) i'/m g(s) h(s) 1 / i 1/s 1/s i' xdesired e + + + c t q x q' -+ + + fig. 1: a schematic diagram of an afc scheme for the above open loop system, the estimated variable q' is passed through a function g(s) before subtraction from a command vector c at a summing junction. if there is a suitable choice of g(s), the output x can be iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 3 made invariant with respect to the disturbances q. in this case the selection of proper estimated inertia matrix i' becomes very important. thus, the main computational burden in afc is the multiplication of the estimated inertia matrix with the angular acceleration of the arm before being fed into the afc feed forward loop. apart from that, the output x needs to be computed from the joint angle  via forward kinematics and also the controller gc(s) be determined. 3. mathematical model of the robot arm the general equation of motion (or dynamic model) of a robot arm can be described as follows [14]: tq = h()dd + h(, d) + g() + q (4) where, tq is the vector of actuator torques h() is the n  n dimensional manipulator and actuator inertia matrix h(, d) is the vector of the coriolis and centrifugal torques g() is the vector of the gravitational torques q is the vector of the external disturbance torques for a horizontal two-link rigid planar manipulator as shown in fig. 2, its dynamic model is given by, tq1 = h11dd + h12dd hd 2hdd (5) tq 2 = h22dd + h21dd hd (6) where, h11= m2lc12+i1 + m2(lc12+ lc22+ 2 l1lc2 cos 2 ) + i2 (7) h12 = h21 = m2l1lc2cos 2 + m2lc22 + i2 (8) h22 = m2lc22 + i2 (9) h = m2l1lc2 sin 2 (10) m is the vector of link masses l is the vector of link lengths lc is the vector of link lengths from the joint to the center of gravity of the link 2 1 l1 l2 fig. 2: a representation of a two-link robot arm in this study, the gravitational term in equation (6) has been omitted since the arm is assumed to move only in a horizontal plane. fig. 3 shows the complete schematic diagram of the robot arm including the afc for the robot arm shown in fig. 2. in/k tn k tn 1/ ktn 1/h 1/s 1/s in  ddef + + i c t q q q * + + + coordinate transformatio n k d k p coordinate transformatio n coordinate transformatio n   d  dd i t ia x ddref x ddbar x dbar x bar + + + + + + x d x fig. 3: two-link robot arm with afc iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 4 the notation used in fig. 3 is as follows: ktn is the motor torque constant kp and kd are the controller gains x is a vector of positions in cartesian space is a vector of positions in joint space ic is the current command vector ia is the compensated current vector it is the armature current for the torque motor in is the estimated inertia matrix q* is the estimate of all the disturbance torques tq is the applied control torque the subscript d expresses the velocity vector while dd is for the acceleration vector. the left hand side of fig. 3 represents the x vector (shown by subscript extension bar) of the desired trajectories and the extension ref represents the reference vector. the controller gc(s) chosen here is a resolved-motion-acceleration-control (rmac) using a proportional-derivative (pd) element. the rmac produces the acceleration command vector signal ddref which when multiplied by a decoupling transfer function will give the required command vector to the main afc loop. from fig. 3 we have, g(s)h(s) = 1 (11) where, g(s) = ktn and h(s) = 1/ktn the equation for the estimate disturbance term is, q* = in dd tq (12) where, tq = ktn it. from this expression, torque can be calculated by multiply the it to the motor constant kt n, where it can be measured by using current sensor. 4. the new proposed scheme the real environment of the robot system is often and most likely unpredictable. the system’s input error function may easily change whenever disturbance is introduced while performing a specific task. ideally, this input function should be considered as one of the main parameter to be manipulated so that an accurate and robust control can be achieved by the proposed control strategy. the afc schemes have been excellent in giving a high level of robust performance by minimizing this error function. here, we introduce a simplification and refinement of the input function using knowledge-based method applied to a two-link planar manipulator operated in a horizontal plane. this method is accomplished in view of getting better performance by means of suitably managing the error function. the idea of afc-kbtepm scheme can be seen in fig. 4. a complete schematic diagram of the proposed scheme is shown in fig. 5. the block containing the term kbtepm is developed and modified from the fixed crude’s value of the estimated inertia matrix obtained in the previous study [14]. by giving an input function from the actual task, xbar, the estimated inertia matrix value in depends on the ‘characteristic’ of the actual task as well as the angular acceleration of the arm, dd. the application of the new method is best demonstrated first by reviewing the result of the previous afcca method applied to the robot arm as described in the next section. all the results were based on the simulation works performed using the matlab and simulink software packages fig. 4: the idea of afc-kbtepm scheme actual task desired task 2-link robot arm afc kbtepm iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 5 4.1 knowledge investigation the knowledge that will be used as criterion-based rules in the proposed scheme is explored from the previous experimental results of afcca method [14]. for the purpose of showing the suggested method using knowledge-based, the same simulation of the afcca scheme is reviewed. figure 6 shows the simulink® model diagram of the scheme. a preliminary simulation of the afcca scheme should be first performed to explore the trajectory track error characteristic. for a fair and one-to-one comparison, all the simulation and other important common parameters for all the robot control schemes should be kept exactly the same. the mentioned parameters are as follows: fig. 5: a schematic of the afc-kbtepm pd controller1 trajectory planner1 clock2 afc core disturbance model th1, thd1, th2, thd2 thddref2 thddref1 robot dynamic crude's fig. 6: the simulink® model of the afcca scheme in/k tn k tn 1/k tn 1/h 1/s 1/s kbtepm  ddef + + i c t q q q * + + + coordinate transformation k d k p coordinate transformation coordinate transformation   d  dd i t ia x ddref x ddbar x dbar x bar + + + + + + x d x iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 6 robot parameters: link length: l1 = 0.25 m, l2 = 0.22 m link mass: m1 = 0.3 kg, m2 = 0.25 kg motor mass: mot11 = 1.3 kg ,mot21 = 0.8 kg payload mass: mot22 = 0.1 kg controller parameters of rmac: controller gain: kp = 750 /s, kd = 500 /s2 motor torque constant: ktn = 0.263 nm/a main simulation parameters: integration algorithm: gear simulation time start, tstart: 0.00s simulation time stop, tstop: varies minimum step size: 0.01s maximum step size: 0.10s sampling time: 0.01s trajectory: circular form with centre (0.25, 0.2) in cartesian space and a radius of 0.1m. other parameters: endpoint tangential velocity: vcut = 0.2 m/s disturbances: a spring attached at the end of the second link with stiffness k = [0, 200, 400] n/m. k = 0 n/m denotes no disturbances. figure 7a to 7c show the graphical results of the initial knowledge investigation experiments in afcca scheme considering three disturbance conditions; no disturbance, k = 200 n/m and k = 400 n/m. the track error (te) represents the trajectory track error of the robotic arm. figures 7b and 7c both show a unique form of the curve consisting of the ‘hill and valley’ pattern that is repeated for each cycle of the circular-form trajectory command apart from the first cycle. (a) (b) (c) fig. 7: track error of afcca scheme: (a) k = 0 n/m, (b) k = 200 n/m, and (c) k = 400 n/m. 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 . 0 0 2 0 . 0 0 4 0 . 0 0 6 0 . 0 0 8 0 . 0 1 0 . 0 1 2 0 . 0 1 4 0 . 0 1 6 t i m e ( s e c o n d ) tr ac k e rr or (m ) 0 2 4 6 8 1 0 1 2 1 4 1 6 0 1 2 3 4 5 6 x 1 0 3 t i m e ( s e c o n d ) t ra ck e rr or (m ) 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 . 5 1 1 . 5 2 2 . 5 x 1 0 3 t i m e ( s e c o n d ) t ra ck e rr or (m ) iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 7 figure 8 shows that each loop (cycle) of the circularform trajectory which is generated by the control scheme and at the same time producing a trajectory track error with two ‘hills’ and two ‘valleys’ respectively at 0.5 or 1.5 for the hills and at  or 2 for the valleys. the error is maximum when it is in the form of a hill and becomes minimum when it is a valley. this phenomenon gives us an idea to suppress the error by estimating the probability of the hill and the valley patterns (evidences).by using bayes rule [13], the posterior probability, an expression is derived as follows: ( | ). ( ) ( | ) ( | ). ( ) j i i i j j i i i p e h p h p h e p e h p h   (13) where, hi is a hypothesis (the occurrence of hill or valley) ej is an item of evidence (hill and valley) the posterior probability of each hill or valley is determined by weighting the prior probability occurrence of the hill or valley. by evaluating the trajectory track error of the circular-form trajectory command, we can conclude that the probability of the ‘hill error’ and or ‘the valley error’ is equal to 1 (in the study, a number of trials have been experimented involving loops tried for more than 10 cycles; which give consistent result). this fact (knowledge) of the characteristic can be used to construct an inference mechanism consisting of a set of suitable rules or reasons to be applied in the proposed scheme as expressed in fig. 9. for the rules, the optimum parameter for a ‘crude value’ is set to be equal to 0.95 [14]. the adding/ subtracting values are denoted by (++) or (-) signs and the proposed expression can be obtained as follows: kgain yoxo yo kvkbs 22   (14) where, kvkbs: add/subtract value of the crude value kgain: calibrating gain parameter xo, yo: relative cartesian coordinate axis measured from centre of the circular-form trajectory. the value of kgain would be investigated in this study. in fact, the ‘bad’ setting of the kvkbs will cause an incidental instability for the multiple loops. this will be explained later in the paper. the main knowledge rule: if <the trajectory form> is <circular form> then do <rule1> else <find others knowledge based data’s library> end rule1: if absolute (yo/xo) increase then [crude’s value]new = [crude’s value]old ++ else [crude’s value]new = [crude’s value]old end 0 2 4 6 8 1 0 12 1 4 1 6 0 1 2 3 4 5 6 x 1 0 -3 ti m e (se cond ) tr ac k e rr or (m ) 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 x axis y a xi s x y plot fig. 8: the error generated over one cycle of the circular-form trajectory iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 8 5. simulation 5.1 simulation of the proposed scheme figure 10 shows a simulink model of the proposed afc-kbtepm sch. fig. 11 shows the simulation results when kgain = 0.01. according to the experimental results when kgain value ranging from 0.005 to 0.050 and with a spring force disturbance, an optimum kgain obtained is 0.02. the trajectory track error at k = 0 n/m, k = 200 n/m and k = 400 n/m are shown respectively in fig. 12. 5.2 simulation of the afcann scheme to ensure a fairly comparison the simulation of the afcann[14] with the same parameters is presented. figure 13 shows a simulink® model of the afcann scheme. besides the main common simulation parameters, the following parameters were used in the afcann scheme only: the result of the training process is shown in fig. 14. figure 15 shows the afcann simulation results for the same conditions network type: feed-forward neural network architecture: 2-5-2 training algorithm: error-back propagation learning rate: lr = 2.5 momentum constant: mc = 1.75 error goal: eg = 0.05 5.3 simulation of the afcann scheme to ensure a fairly comparison the simulation of the afcann[14] with the same parameters is presented. figure 13 shows a simulink® model of the afcann scheme. besides the main common simulation parameters, the following parameters were used in the afcann scheme only: the result of the training process is shown in fig. 14. figure 15 shows the afcann simulation results for the same conditions network type: feed-forward neural network architecture: 2-5-2 training algorithm: error-back propagation learning rate: lr = 2.5 momentum constant: mc = 1.75 error goal: eg = 0.05 eme. pd controller clock afc disturbance model th1, thd1, th2, thd2 thddref2 thddref1 robot dynamic kbtepm trajectory planner1 fig. 10: a simulink model of the afc-kbtepm scheme iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 9 (a) (b) 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 . 0 0 2 0 . 0 0 4 0 . 0 0 6 0 . 0 0 8 0 . 0 1 0 . 0 1 2 0 . 0 1 4 0 . 0 1 6 t i m e ( s e c o n d ) tr ac k e rr or (m ) (c) fig. 11: track errors of afc-kbtepm for various loading conditions at kgain = 0.01: (a) k = 0 n/m, (b) k = 200 n/m, and (c) k = 400 n/m 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 . 5 1 1 . 5 2 2 . 5 x 1 0 3 t i m e ( s e c o n d ) tr ac k e rr or (m ) 0 2 4 6 8 1 0 1 2 1 4 1 6 0 1 2 3 4 5 6 x 1 0 3 t i m e ( s e c o n d ) tr ac k e rr or (m ) iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 10 (a) (b) 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 . 0 0 5 0 . 0 1 0 . 0 1 5 t i m e ( s e c o n d ) tr ac k e rr or (m ) (c) fig. 12: track errors of afc-kbtepm at kgain = 0.02: (a) k = 0 n/m, (b) k = 200 n/m, and (c) k = 400 n/m. 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 . 5 1 1 . 5 2 2 . 5 x 1 0 3 t i m e ( s e c o n d ) tr ac k e rr or (m ) 0 2 4 6 8 1 0 1 2 1 4 1 6 0 1 2 3 4 5 6 x 1 0 3 t i m e ( s e c o n d ) tr ac k e rr or (m ) iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 11 fig. 13: the simulink® model of afcann 0 5 0 0 1 0 0 0 1 5 0 0 1 0 -2 1 0 0 1 0 2 1 0 4 e p o c h s um -s qu ar ed e rr or t ra i ni n g fo r 1 5 8 4 e p o c hs 0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 0 1 2 3 e p o c h le ar ni ng r at e fig. 14: training results . disturbance model robot dynamic thddref2 neural network afc core tq1 tq2 pd controller trajectory planner1 clock2 thddref1 iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 12 (a) (b) (c) fig. 15: track errors for the selected afcann schemes: (a) k = 0 n/m, (b) k = 200 n/m, and (c) k = 400 n/m 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 . 0 0 2 0 . 0 0 4 0 . 0 0 6 0 . 0 0 8 0 . 0 1 0 . 0 1 2 0 . 0 1 4 0 . 0 1 6 0 . 0 1 8 t i m e ( s e c o n d ) tr ac k e rr or (m ) 0 2 4 6 8 1 0 1 2 1 4 1 6 0 1 2 3 4 5 6 7 8 9 x 1 0 3 t i m e ( s e c o n d ) tr ac k e rr or (m ) 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 . 7 0 . 8 0 . 9 1 x 1 0 3 t i m e ( s e c o n d ) tr ac k e rr or (m ) iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 13 6. results and discussion by evaluating the results shown in figs. 7, 10, 11, 14 and 15, a number of points can be highlighted for the purpose of comparison. we divided this analysis into three groups according to various types of the applied disturbances, i.e. for no disturbances, disturbance with k = 200 n/m and disturbance with k = 400 n/m. the latter disturbance is deliberately considered to verify the effectiveness of the proposed scheme. 6.1 case 1: no disturbances (k = 0 n/m) figure 16 shows the superimposed track errors of the afcca, afcann and afc-kbtepm schemes when there are no applied disturbances. it is clear that the afcann scheme has the least track error while the afc-kbtepm scheme shows more irregularity in shapes compared to others. however, it is useful to note that the peaks of the error pattern are less than 1 mm (after 2 s). the afcann scheme seems to produce the least error with the initial error registered at approximately 1 mm compared to an amplitude of more than 2 mm for the other two schemes. although afckbtepm has a series of higher peak errors throughout the simulation period, its starting error is slightly lower than those produced by afcca. 6.2 case 2: disturbance with k = 200 n/m figure 17 shows a comparison of the track errors for various afc schemes with the spring stiffness, k = 200 n/m. the trajectory track errors for all the schemes increase significantly when a spring disturbance with k = 200 n/m is applied to the end-effector of the robot arm. the most significant error pattern with high peaks is observed in the afcann scheme as shown in fig. 16. the series of peak reaches more than 3 mm in amplitude. this is an indication of the system’s declining performance in terms of its robustness. this is followed by the afcca scheme. on the other hand, afc-kbtepm produces a very stable performance with the error pattern below the 2 mm margin. 6.3 case 3: disturbance with k = 400 n/m figure 18 shows the track error patterns of the afc schemes under study; this time considering a disturbance with k = 400 n/m. again, it can be seen that the afcann scheme exhibits the worst performance; generating the largest error pattern compared to the other two schemes. evidently, the afc-kbtepm scheme is the best performer with the peak errors reaching only the 2 mm mark while the performance of the afcca scheme lies in between the two schemes. 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 .5 1 1 .5 2 2 .5 x 1 0 -3 t i m e (s e c o nd ) tr ac k e rr or (m ) fig. 16: the track errors of various schemes at no disturbances note: : afcca : afcann : afc-kbtepm iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 14 0 2 4 6 8 1 0 1 2 1 4 1 6 0 1 2 3 4 5 6 7 8 9 x 1 0 -3 t i m e (s e c o n d ) tr ac k e rr or (m ) fig. 17: comparison of the track errors at k = 200 n/m 0 2 4 6 8 1 0 1 2 1 4 1 6 0 0 .0 0 2 0 .0 0 4 0 .0 0 6 0 .0 0 8 0 .0 1 0 .0 1 2 0 .0 1 4 0 .0 1 6 0 .0 1 8 ti m e (s e c o nd ) tr ac k e rr or (m ) fig. 18: comparison of the track errors at k=400n/m 7. conclusions the advantage of using of the feature of trajectory-form of the robot as knowledge for reasoning investigation that will be applied as basis of rule-based algorithm has been proven in the application of the afc within the simulation study. although the afcca itself is basically suitable enough implemented at any condition however it still needs to be more precise in certain job. this investigation has shown that the afc-kbtepm is able to enhance the performance of the afc significantly. the trajectory track error of the afckbtepm scheme has marginally increased in the range of 1 to 2 mm only when the disturbance is applied. this means the proposed control scheme is proven to be very robust in handling the effect of the disturbances. however, the trajectory-form (task) features extraction and the proper adjustment of the parameter kgain of the proposed scheme seem to provide fresh challenges for the researchers to fully explore the potentials of the method. this will be the main subject of further investigation. note: : afcca : afcann : afc-kbtepm note: : afcca : afcann : afc-kbtepm iium engineering journal, vol. 3, no. 1, 2002 e. pitowarno, et al. 15 acknowledgements the authors would like to thank the ministry of science and technology (moste) malaysia and the universiti teknologi malaysia for providing the financial support and facilities. this research was supported using an irpa grant (project no. 09-02-06-0172). references [1] h. asada and j. j. e. slotine, robot analysis and control, john wiley and sons inc., 1986. [2] j.y.s. luh, m.w. walker and r.p.c. paul, resolvedacceleration control of mechanical manipulators, ieee trans. on automatic control, vol. ac-25, no. 3, pp. 468-474, june 1980. [3] m.h. raibert and j.j. craig, hybrid position/force control of manipulators, trans. of the asme, journal of dynamic systems, measurement and control, no. 102, pp. 126-133, june 1981. [4] j. r. hewit and j.s. burdess, fast dynamic decoupled control for robotics using active force control, mechanism and machine theory, vol. 16, no. 5, pp. 535-542, 1981. [5] s. arimoto, s. kawamura and f. miyazaki, bettering operation of robots by learning, robotic systems, pp 123-140, 1984. [6] f. lange and g. hirzinger, learning force control with position controlled robots, proc. of ieee international conference on robotics and automation, minneapolis, april 1996. [7] m. kawato., y. uno, r. isobe and r. suzuki, hiearchical neural network model for voluntary movement with application to robotics, ieee control systems magazine, vol. 8 , pp 8-15, 1988. [8] k. ohnishi, m. shibata and t. murakami, a unified approach to position and force control by fuzzy logic, ieee trans. on industrial electronics, vol. 43, no. 1, pp 81-7, february 1996. [9] p. bondi, g. casalino and gambardella, on the iterative learning control theory for robotic manipulators, ieee journal of robotics and automation, vol. 4, no. 1, pp 14-22, feb.1988. [10] k. hori, an ontology of strategic knowledge: key concepts and applications, knowledge-based systems, vol.13, elsevier, pp.369-374, 2000. [11] j. a. barnden, semantic networks, the handbook of brain theory and neural networks, the mit press, pp. 854-857, 1995. [12] j. g. schmolze, w. snyder, detecting redundancy among production rules using term rewrite semantics, knowledge-based systems vol.12 , elsevier, pp.3-11, 1999. [13] s. growe, t. schroeder, c.–e. liedtke, use of bayesian networks as judgement calculus in a knowledge-based image interpretation system, iaprs journal, vol. xxxiii, pp.101-110, 2000. [14] musa mailah, intelligent active force control of a rigid robot arm using neural network and iterative learning algorithms, ph.d thesis, university of dundee, 1998. [15] musa mailah, ‘a simulation study on the intelligent active force control of a robot arm using neural network’, jurnal teknologi (d), utm, pp 55-78, june 1999. [16] musa mailah and nurul izzah ab rahim, ‘intelligent active force control of a robot arm using fuzzy logic’, ieee international conference on intelligent systems and technologies tencon 2000, vol. ii, pp 291-297, kuala lumpur, september 2000. microsoft word 174 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering mohamed ali 1 on the settling and response times of underdamped second-order systems abdul-fattah mohamed ali environmental engineering department, college of engineering, baghdad university, iraq. tariqjwad@yahoo.com abstract: the normalized settling time (ts /τ) values of oscillatory 2nd-order systems, when subjected to a step-change forcing function (scff), depend on the sensitivity of the measuring instrument employed to indicate the response (± x%). an attempt is made to mathematically relate ts /τ to ± x% utilizing the exact, and a simplified, expression for the lower boundary of the decay envelope (lbde). the two obtained relationships were tested against the actual ts /τ values for a settling band range of ±1% ≤ ±x% ≤ ±6%, covering a damping coefficient range of 0.1 ≤ ζ ≤ 0.65. although the relationships are not exact, their general trend is a marginal overestimation of ts /τ. the relationship based on the simplified lbde was chosen for being simpler and slightly more accurate of the two. this led to a suggested distinction between ts /τ and the normalized response time (tr /τ) with the latter assigned the value 5/ ζ . the ratio ts / tr can thus be readily established for any ± x% value. abstrak: masa enapan ternormal (ts/τ) nilai ayunan system terbit kedua, apabila fungsi memaksa ubah berperingkat (step-change forcing function (scff)) dijalankan ke atasnya, bergantung kepada kepekaan alat pengukur yang digunakan untuk mengukur respons (± x%). satu percubaan dijalankan secara matematik untuk mengaitkan ts/τ to ± x% dengan mempergunakan ekspresi yang tepat dan mudah, pada sempadan bawah sampul reputan (lower boundary of the decay envelope (lbde)). dua hubungan yang diperolehi dikaji terhadap nilai ts/τ sebenar untuk julat jalur enapan ±1% ≤ ±x% ≤ ±6%, melingkungi julat pekali redaman 0.1 ≤ ζ ≤ 0.65. walaupun hubungannya tidak tepat, trend umum merupakan penganggaran marginal ts/τ. hubungan berdasarkan lbde adalah berdasarkan lbde yang telah dipermudahkan, ia dipilih kerana ianya senang dan agak tepat antara keduanya. ini mendorong kepada perbezaan yang disarankan antara ts/τ dan waktu respons ternormal (tr/τ), dengan nilai 5/ ζ yang ditetapkan kemudiannya. keywords: process control; instrumentation; mathematical modelling; transient response; 2nd-order system 1. introduction an underdamped second order system with 0 < ζ ≤ 0.65, when subjected to a scff undergoes a response which is significantly oscillatory. under such condition, the settling time (also called the response or recovery time) is defined as the time required for the normalized response to enter the ±5% band of the step change magnitude. other definitions for ts exist; notably, that related to the ±2% band or as determined by the sensitivity of the measuring instrument [1-5]. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering mohamed ali 2 2. estimation of settling time pollard [2] pointed out that owing to the arbitrary nature of the settling band limits (due to the specific sensitivity of the measuring instrument employed), a mathematical definition for ts is not possible. he concluded that it can be easily measured from the response curve of a recording instrument (i.e. a posteriori). in spite of the aforementioned viewpoint, an estimate of ts value a priori is an advantage in many instances, e.g. in the design and analysis of control loops. the normalized response of an underdamped 2 nd order system to a scff of magnitude a is, y�t� ak 1 � 1 �1 � ζ e ���� sin ��1 � ζ τ t � tan�� �1 � ζ ζ � �1� for a ± x% settling band, its limits would correspond to y(t)/ak values of (1 + 0.01 x) and (1 0.01 x) respectively. this renders the value of the second term of eq. (1) equal to 0.01x in absolute value. therefore, ts/τ is the shortest normalized time which satisfies this condition; provided that the second term will not exceed |0.01 x| for t/τ > ts/τ. the exact expression for the lower boundary of the decay envelope (lbde) related to the normalized response represented by eq.(1) is (1 � ������ e� � ��) (ogata [5]). pollard [2], however, gave it as (1 � e����� ; neglecting � which is justifiable for small values of �. pollard further pointed out that (1 � e����� is the normalized response of a 1 st –order system, whose time constant is τ/ζ, to a scff. these two expressions for the lbde were utilized to obtain the following equations for the estimation of ts/τ as related to a –x% settling band limit. hence, t τ � ln�0.01 x� ζ �2� corresponding to (1 � e����) lbde , and t τ � ln�0.01 x� ζ � 1 2ζ ln �1 � ζ � �3� corresponding to (1 � ������ e� � ��) lbde. eq.’s (2) and (3) were tested against the actual ts/τ values for settling bands ranging from ±1% to ±6% over the range 0.1≤ ζ ≤ 0.65. the results are shown in fig.’s (1) to (6). the two equations generally overestimate ts/τ but give reasonably close values to the actual ones. their respective values of ts/τ were too close to be distinguishable on the same graph; which necessitated the use of separate plots for each ±x% value. the percentage error as defined by; % error �t /τ�+,-+. � �t /τ�,+�.�t /τ�,+�. . 100 �4� iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering mohamed ali 3 ranged from -8.35% to 26.86% with an average of 6.93% for eq.(2) and from 0.00% to 31.62% with an average of 10.00% for eq.(3) over the whole range tested. therefore, it may be concluded that eq.(2) is the better one for being simpler and marginally more accurate. for settling bands of ±2% and ±5%, eq.(2) gives ts/τ = 3.912/� and ts/τ = 2.996/� respectively. these two results correspond to the familiar expressions of ts/τ = 4/ � for ±2% settling band and ts/τ = 3/� for ±5% settling band mentioned in textbooks as approximate relationships (e.g. ogata [5]); further validating the approach presented here. fig. 1: actual and calculated (ts/τ) vs. ζ for ±1% settling band. fig. 2: actual and calculated (ts/τ) vs. ζ for ±2% settling band. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering mohamed ali 4 fig. 3: actual and calculated (ts/τ) vs. ζ for ±3% settling band. fig. 4: actual and calculated (ts/τ) vs. ζ for ±4% settling band. fig. 5: actual and calculated (ts/τ) vs. ζ for ±5% settling band. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering mohamed ali 5 fig. 6: actual and calculated (ts/τ) vs. ζ for ±6% settling band. 3. settling time vs. response time as a consequence of the adoption of eq.(1), the following argument is presented as a basis for suggesting that a distinction should be made between ts and the response time (tr). for a 1 st -order system subjected to a scff, the response time may be defined as that at which the normalized response exceeds 99% of the step change magnitude. hence, a time interval equal to five times the system’s time constant, corresponding to 99.3% of the step change magnitude, would serve this purpose. if this criterion is adopted, then by referring back to pollard’s [2] expression for the lbde, i.e. 01 � e����1, the normalized response time for an underdamped 2nd-order system would accordingly be 5/ζ . in other words, tr/τ would be the normalized settling time for a ± 0.7% settling band according to eq.(2), i.e. t2τ � ln�0.007� ζ 4.962 ζ or 5.0 ζ �5� hence, for a ±x% band limits ts/tr would be, t t2 � ln�0.01 x� 5 �6� table (1) gives rounded-off values of ts/τ, based on eq.(2), and ts/tr, based on eq.(6), for the range 0.7%≤ ±x ≤6% for comparison purposes. 4. conclusion a simple mathematical formula is presented to estimate a priori the normalized settling time values of oscillatory 2 nd -order systems, when subjected to a scff, for any value of the measuring instrument sensitivity. a distinction is made between normalized settling and response times of such systems, with the latter assigned the value of 5/ζ . accordingly, ratios of settling to response times can readily be established. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering mohamed ali 6 table 1 : ts/τ and ts/tr values for 0.7%≤ ±x ≤6% ± x% ζ (ts/ τ) ts/tr 0.7 5.00 1.00 1.0 4.60 0.92 1.5 4.20 0.84 2.0 4.00 0.78 2.5 3.70 0.74 3.0 3.50 0.70 3.5 3.35 0.67 4.0 3.22 0.64 4.5 3.10 0.62 5.0 3.00 0.60 5.5 2.90 0.58 6.0 2.81 0.56 references [1] d.r. coughanowr, and l.b. koppel, "process systems analysis and control", mcgraw-hill kogakusha, tokyo, pp. 85-88, 1965. [2] a. pollard, " process control", 2 nd reprint, heinemann educational books, london, pp. 75-78 , 83, 1981. [3] g. stephanopoulos, "chemical process control", prentice-hall, englewood cliffs, new jersey, pp. 190-191, 1984. [4] d.e. seborg, t.f. edgar, and d.a. mellichamp, "process dynamics and control", john wiley (asia), singapore, pp. 117-118, 2004. [5] k. ogata, “ modern control engineering “ , 5 th edition, pearson, upper saddle river, new jersey, p. 180-183, 2010. notation a scff magnitude k steady state gain tr response time ts settling time ± x% sensitivity of measuring instrument, corresponding to settling band limits y(t) system’s transient response greek ζ damping coefficient τ characteristic time abbreviation act. actual calc. calculated eq. equation lbde lower boundary of the decay envelope scff step change forcing function application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 developing a parallel classifier for mining in big data sets ahad shamseen1, morteza mohammadi zanjireh 1*, mahdi bahaghighat 1, qin xin2 1 computer engineering department, imam khomeini international university, qazvin, iran 2 faculty of science and technology, university of the faroe islands, tórshavn, faroe islands *corresponding author: zanjireh@eng.ikiu.ac.ir (received: 10th july 2020; accepted: 12th november 2020; published on-line: 4th july 2021) abstract: data mining is the extraction of information and its roles from a vast amount of data. this topic is one of the most important topics these days. nowadays, massive amounts of data are generated and stored each day. this data has useful information in different fields that attract programmers’ and engineers’ attention. one of the primary data mining classifying algorithms is the decision tree. decision tree techniques have several advantages but also present drawbacks. one of its main drawbacks is its need to reside its data in the main memory. sprint is one of the decision tree builder classifiers that has proposed a fix for this problem. in this paper, our research developed a new parallel decision tree classifier by working on sprint results. our experimental results show considerable improvements in terms of the runtime and memory requirements compared to the sprint classifier. our proposed classifier algorithm could be implemented in serial and parallel environments and can deal with big data. abstrak: perlombongan data adalah pengekstrakan maklumat dan peranannya dari sejumlah besar data. topik ini adalah salah satu topik yang paling penting pada masa ini. pada masa ini, data yang banyak dihasilkan dan disimpan setiap hari. data ini mempunyai maklumat berguna dalam pelbagai bidang yang menarik perhatian pengaturcara dan jurutera. salah satu algoritma pengkelasan perlombongan data utama adalah pokok keputusan. teknik pokok keputusan mempunyai beberapa kelebihan tetapi kekurangan. salah satu kelemahan utamanya adalah keperluan menyimpan datanya dalam memori utama. sprint adalah salah satu pengelasan pembangun pokok keputusan yang telah mengemukakan untuk masalah ini. dalam makalah ini, penyelidikan kami sedang mengembangkan pengkelasan pokok keputusan selari baru dengan mengusahakan hasil sprint. hasil percubaan kami menunjukkan peningkatan yang besar dari segi jangka masa dan keperluan memori berbanding dengan pengelasan sprint. algoritma pengklasifikasi yang dicadangkan kami dapat dilaksanakan dalam persekitaran bersiri dan selari dan dapat menangani data besar. key words: data mining, big data, decision tree, parallel classifier, sprint 1. introduction recently, too much data is generated and stored on servers per day. this data has great amounts of essential and useful information and therefore, searching through this data can be one of the most essential topics in data science. the process of extracting information from large data sets and discovering patterns is termed data mining and it involves methods from artificial intelligence, machine learning, and database systems. one of the main goals of the data mining process is to build a logical structure from the extracted information and prepare 119 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 this information for further use. the data mining process involves many sub-processes like data collection, database management, data pre-processing, and online updating [1]. in data mining, classification is one of the learning models, and the classifications are used to build a model that classifies the unclassified data in the dataset. these models are rules or patterns that connect the input data with the output target and used to predict the future output of the system that the data was taken from [2] and can be used in several fields such as marketing, advertisement, and medical science [3]. the data mining process steps that were explained by berry and linoff in 2004 [2] are in figure 1. fig. 1. data mining process [2]. to create data mining models, we can use data mining algorithms. first, the algorithm starts by analysing the data set and extracting trends, results, and specific patterns, and these will be used next to determine the priorities and the parameters of the data mining model. finally, these parameters are applied to the data set to find the patterns and statistical needs [4]. selecting the best algorithm for the application depends on the data mining tasks, available data, data kind, and the size of data [5]. the decision tree algorithm is one of the most popular data mining algorithms because it has high accuracy, fast training performance, and is easy to understand. dividing the data into several subsets is the primary purpose of this algorithm. the first step is to evaluate the attributes to determine how to divide the data between the classes. then, this process is applied over all subsets until the decision tree is formed. the decision tree algorithm is a hybrid algorithm because it supports classification and regression tasks. the classification task can be used to predict continuous and categorical variables where the regression task can be used to predict only continuous variables. decision tree algorithms can also be applied for association analysis [4]. the decision tree algorithm has many advantages over all data mining algorithms, which are easy to understand, quick to build the tree, and efficient to a high degree [6]. naive bayes algorithm is another data mining algorithm that achieves the learning phase based on evidence. this algorithm learns the evidence by counting the connection between the critical variables and all other variables [7]. naive bayes can detect the factors in a production line or how the products are related. however, this algorithm cannot classify nonlinearly separable classes correctly [4]. the neural network algorithm is a data mining algorithm that works by creating relationships between the input and output data and then uses these relationships to create 120 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 prediction patterns [4]. the algorithm result is difficult to explain, thus, a data mining process should start with decision trees, and then use the neural network algorithm [8]. the clustering algorithm finds the variable that classifies the data, and it is often used as a step in a big data analysis project. the clustering algorithm uses two methods to assign the clusters. the first method is the k-means method. in this method, the centre is moved to the mean of all assigned objects after the assigned object's phase. the second method is the em method (expectation-maximization method), that uses a probabilistic measure to assign objects to the clusters and uses a bell curve for the dimension from the low centre and a standard deviation [4, 9]. an association algorithm is a rule-based method in data mining. this method is used to discover interesting relations between the attributes in big data sets [10]. this algorithm uses impressive measures to identify the discoverable rules in the data set. the sequence clustering algorithm is a combination of two techniques, the clustering technique and sequence technique [4]. a time-series algorithm is a series of the data collection, which is collected in a timeframe. this algorithm is used to forecast the future based on history. this algorithm can provide many services and the most commonly used specify the seasonality and multiple periods. this algorithm has an excellent advantage, and it can do a great job with minimum information [4]. the data classification process divides the data into classes where each class has a unique symbol. the data in each class have common properties. to classify the data, we have first to determine how many tasks we want, and we have to determine the methods for breaking data into ranges, this method is related to the data that we are classifying and the project that we are working on. data classification has some challenges, such as how to determine the best method to break and split the input data, and the challenge of determining the number of classes and what these classes are. the main goal of classifying data in data mining is to generate a predicted model, by learning from input data. this model can predict and divide the new input data between the classes. predicted models discover relationships between the attributes that would make it possible to predict the outcome [11]. the first step in classification is prepared data in the training set, which is done in three parts [2]: • clean the data: we have to use smoothing techniques to remove the noise from data, and we have to solve the missing data problem by replacing it with the commonly occurring value for that attribute. • irrelevant attribute problem: in some databases, the attributes are not related. therefore, correlation analysis is used to know if there is any connection between attributes. • database normalization: the process of organizing (such as the attributes and tables) for reducing data redundancy and improve data integrity is called normalization. a decision tree is a compact data structure that can be built quickly and provides significant descriptions of the relationships between the input variables and the target attributes. the decision trees can provide accurate predictions if applied to the problems that can be represented with contrapuntal expressions. it can handle continuous and categorical attributes and is very powerful with separate attributes. the decision tree classifier has many advantages over all other classifiers [6]. the first advantage is that the distribution in the decision tree is free, consequently, there is no prior assumption about the previous data distributions. the 121 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 second advantage is that the decision tree does not require as much training as the other classifiers. finally, the most important advantage is that the decision tree is easy to understand. these trees can be a set of rules that describe the connection between the input and target attributes. sometimes the decision tree generates some unwanted and meaningless rules while it is growing deeps. this problem called the overfitting problem. the overfitting problem increases the tree size and data noise in the tree, and reduces the efficiency and accuracy of the data. to solve the overfitting problem, we have to use pruning methods to avoid a large tree size. there are two kinds of pruning methods in the decision tree. post sorting is a kind of pruning that first builds the tree, and then reduces unwanted branches in the decision tree. the second kind of pruning method is pre-sorting. in this kind, the tree keeps on checking in each step of the building phase [12]. each kind of pruning method has many techniques. for post sorting, there are many methods such as reduced error, error complexity, minimum error, and cost-based. for pre-sorting, there are a minimum number of object and chi-square pruning [13]. nowadays, data mining is a critical technology in the world because all the information and data in different fields of work such as business and science are loaded and stored in servers and have much valuable information that needs to be instructed. the classification task in data mining is useful in many fields of life, and classifying data and creating the predictive model allows us an opportunity to have advanced knowledge of events. in the classification process, we are dealing with big data sets. therefore, we have to improve the classification algorithms to be able to handle this size of data and to be more comfortable for implementation. data size is growing very fast every day, faster than the growth in hardware abilities. to analyse and classify this size of data, we have to make classification algorithms more effective in both the time that they take to classify the data and the data structure of the algorithms. the data mining process has many tasks like association, classification, clustering, regression, anomaly detection, and summarization. these tasks can formulate the problem and discover knowledge from data. classification is the most common task in data mining. this technique is used to create a predictive model for future behaviour. decision tree is the most common classification algorithm in data mining and is easy to implement, has a high degree of accuracy, and has easily recognizable patterns. there are many algorithms to build the decision tree; each one of them has advantages and disadvantages. however, in data mining, the size of data is very big, thus in the implementation phase, all of these algorithms struggle with the amount of data that must stay in active memory until the mining process ends. due to the strain on computing assets caused by the massive amounts of data involved, the ideal classifier should take less time to complete the classification process, thus requiring less computer memory. in this research, we propose a new classifier to enhance classification tasks in data mining, and we will compare our proposed classifier with the sprint classifier in parallel computations. the goal of this research is to design and implement a new classifier to build the decision tree for mining in big data sets. the aim is to make the classification process easier and quicker in both parallel and serial implementation and to decrease the data size that should stay in the memory. in this proposed classifier, we solve the problems in the other classifiers such as runtime and memory requirements, and also we fix the incorrect results obtained by some classifiers that are proposed to improve the runtime and memory requirements. 122 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 in our research, we have to implement two decision tree algorithms to test their runtime and the memory requirements. the training data have to be datasets consisting of several attributes. if we download a data set from the internet, we have to make many changes to it to make it more suited to the parallel programs. consequently, we created a dataset with three attributes and use it as a training set for the implementation phase. the rest of this article is as follows. in section 2, we review the literature survey of related researches in the data classification algorithms. the methodology of our proposed classifier method and a comparison with the best previously proposed parallel classifier have been presented in section 3. the simulations and experimental results of the proposed algorithm have been presented in section 4. finally, in section 5, we discuss the conclusion of this research and future work. 2. related work decision trees are one of the most crucial classification algorithms that can be constructed quickly and possess simple and easy-to-use models [6, 14]. the most common decision trees builders are chaid (chi-squared automatic interaction detection), id3 (iterative dichotomies 3), c4.5, cart (classification and regression tree) and mars (multivariate adaptive regression splines). each one of them can be implemented in serial and parallel situations, but sliq (scalable classifier for data mining) and sprint (scalable parallel classifier for data mining) algorithms have a perfect performance in parallel implementation. chaid classifier is a decision tree builder for dependent variables proposed in [15]. this classifier uses chi-squared automatic interaction detection (chaid), which is a technique for analysing a large amount of data by dividing it into separated subsets. the classifier then detects the interactions between categorized variables of a data set that are the dependent variables. the cart algorithm is the classification and regression tree published in [16]. this algorithm is used to build a prediction model from data. the prediction model is created by partitioning the data recursively and fitting a simple prediction model in each partition, then, a decision tree is built to represent and describe the partition graphically. in [17], the authors presented a framework called cls (concept learning system). this system builds a decision tree with the minimum cost of classifying. the cost of classifying consists of two components: the cost of determining the property of an object and the cost of deciding. in [6], ross quinlan presented id3, which is one of the serial algorithms developed from the cls algorithm, which is used to build the decision tree invented. it handles category attributes only, begins with the original set as the root node, and all the attributes in the set belong to the same class. id3 algorithm is suffering from an overfitting problem. to solve the overfitting problem, ross quinlan created a new algorithm in 1993 and named it the c4.5 algorithm. in [18], the mars algorithm, which is a group of techniques implemented together, was presented. this algorithm solves the regression-type problems and has the same purpose as the classification algorithms for predicting the values of the dependent (outcome values) and independent (income values) values. most of the classification algorithms are designed for resident memory data, and this issue limits the ability to mine in large data sets. in [19], the sliq algorithm was proposed to build the decision tree to solve the resident memory data problem by using a new data structure. in [20], the authors designed sprint. this algorithm has the same advantage of sliq, but a 123 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 different data structure. sprint data structure is an attribute list with three rows, the first row is the attribute value, the second row is the class, and the third row is the index of the record. this list is sorted in the first step and only one time. in [21], the scalparc algorithm (scalable parallel classifier algorithm) proposed for enhancing the runtime and the memory required in sprint. scalparc has the same data structure of sprint, and it creates a separate list for each attribute consisting of the attribute, the class, and the index. it then creates another data structure to stay in the memory during execution time that determines to which node each datum belongs to. the difference between the two algorithms is that scalparc distributes the data structure, which stays in memory between the processors to increase the memory request and execute the split by level not by not to increase the communication time [21]. however, in 2000, kevin bowyer has proved that scalparc gives incorrect results in some situations [22]. clouds algorithm is a breadth-first strategy to build the decision tree and uses the gini index for evaluating the split points [23]. it uses either sampling the splitting method or sampling the splitting points with estimation method to determine the splitter at each node of the tree, and it evaluates the split points for categorical attributes as in sprint. in [24], the authors presented a random forest classifier. it consists of numbers of simple trees, each one of these trees is capable of producing a predicted response. for the classification tasks, the response of these trees has a class membership form. this task classifies the independent variables in categories. for the regression task, the response is an estimation of the dependent variable, given the predictors. each tree in the forest has an individual responsibility for the queries. this response depends on the predictor values which have the same distribution for all the trees and are selected independently. the public classifier is developed from sprint and proposed in [25]. it has the same data structure, the same steps, and the phases. the main goal of the public is dealing with data that has much noise and suffers from missing and incorrect values, the kind of problems that can be fixed using the pruning method. 3. methodology the new algorithm has the same data structure for sprint. it creates an attribute list for each attribute. this list consists of three rows: the attribute, the class, and the rids. the sorting process is done in the first phase, and it is done once. our algorithm also uses the hash table to determine the rids in each node and use the gini index to found the best split point in each attribute list. in the first step, the parallel pattern attribute records are distributed equally over all the processors in sprint and the proposed algorithm. thus, in this case, each processor processes the same number of records. figure 2 shows parallel data placement in the proposed algorithm in the first step. in our algorithm, we distribute the hash table between the processors and create a new data structure called the node table. this data structure determines the number of classes in each node because in the calculation phase, each processor calculates (gini) for its rids. in this phase, the processor needs information about the rids in each node and the number of each class in the node; thus, this new data structure determines the number of classes in nodes in each level of the tree. figure 3 shows the new data structure in the proposed algorithm. 124 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 fig. 2. the parallel data placement in the proposed algorithm. fig. 3. the new data structure in the proposed algorithm. the proposed algorithm has many advantages over sprint, and it enhances many weak points in sprint. in sprint, the size of the hash table is equal to the size of the data set, and the hash table is memory resident. each processor has to frequently connect to the hash table to determine the rids in each node of the tree, and the hash table must be updated after each split. the total communication overhead (per processor) in sprint is o(n), where n is the number of records in the dataset, and the total memory requirement (per processor) is o(n), as the size of the hash table is the same order as the size of the training dataset for the upper levels of the decision tree, and it resides on every processor. therefore, sprint is unscalable in runtime and memory requirements. the communication cost in sprint is very high, especially when the data set is vast. in this case, the size of hash table will be a problem because it should stay in memory and the frequent connection with the hash table increases the runtime of the algorithm. figure 4 shows the communication cost in sprint. 125 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 fig. 4. communication cost in sprint. in the proposed algorithm, the hash table is distributed between the processors. in the calculation phase, each processor will connect with part of the hash table to determine the rids in the node and will connect to the node table to determine the number of classes in the node. each processor will update its part of the hash table. in this way, the total communication; over each processor is o(n/p+m/2), p is the number of processors, and m is the size of the node table (m=number of classes* 2), in this case, we decrease the communication cost and the time of the update. figure 5 shows the communication cost in the proposed algorithm. fig. 5. communication cost in the proposed algorithm. in sprint, the records in the attribute list are distributed between the processors equally in the first step after the sorting process, and this distribution continues until the last step. each processor processes the records that were assigned to it in the first step. this approach caused a communication problem when the records that were assigned to one processor are located in more than one node. in this case, the fast processor will wait until the slower processor finishes its work, increasing the runtime of the classification process. the reason for the problem is that the process is done per level. thus, the records in more than one node are evaluated to determine the best split in each node, in this case, waiting time will be considerable because each processor is waiting for another processor to finish its work 126 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 and each processor is evaluating records for more than one node; thus, the creation of a new node will take much more time. figure 6 shows the communication problem in sprint. fig. 6. communication problem is sprint. in our algorithm, distributing the records between the processors is based on two rules. the first rule is that the distribution is done per node, not per level. assigning the record is done in each node, therefore, there is no previous record assignation in the nodes and each processor connect with its part of hash table to determine how many records are in its responsibility in each node and the max number of records that each process handles is (n/p). in this way, the split process in each node is done entirely before going to the next node, and the processors evaluate the split point only for one node, and this will decrease the waiting time in each processor. to determine the best attribute for a split in the node, each processor connects with its part of the hash table and determine the rids that belong to the node. after determining the rids in the node, each processor performs calculation operations on these rids for the records in remaining attributes to select the best attribute for the next split step. figure 7 shows the communication per node in the proposed algorithm. fig. 7. communication per node in the proposed algorithm. the size of the hash table is a critical issue when dealing with a big data set because, in the high level of the tree, the size of the hash table is in the same order as the size of the dataset. in sprint, the entire hash table stays in the memory of each processor, and in each evaluation step, the processor needs to connect to all the elements in the hash table to determine 127 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 the rids in each node. in our proposed algorithm, the hash table is distributed among all the processors; thus, the memory-resident in each processor is (n/p), and the new data structure also stay in memory; thus, the memory-resident of our algorithm is (n/p + m), where m is the size of the node table, and in each evaluate step, the processor connects only with its part of the hash table. figure 8 shows the memory requirements in both sprint and the proposed algorithm. fig. 8. hash table (resident memory) in sprint and the proposed algorithm. in sprint, each processor has to stay in contact with all the hash tables in each step to determine the rids in each node of the tree. therefore, all the hash tables should stay in memory until the build process is completed. however, in the proposed algorithm, there is no need to keep the entire hash table in memory, the hash table is divided between the processors, and each one of them connects with its part of the hash table to determine the rids in the tree node. processors update the hash table in each level of the tree in the proposed algorithm after the split step. because the hash table is distributed between the processors, each processor updates its part of the table. figure 9 shows how hash table parts are updated in each processor. fig. 9. update of the hash table in the proposed algorithm. 128 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 communication cost is one of the most critical issues in the classification process when we are dealing with big data sets. the changes that we have made in the sprint algorithm will decrease this cost and make the algorithm more scalable in runtime and memory size. the new data structure will make the algorithm more efficient for massive data sets, and the connection with the hash table will be at the minimum level. to execute the evaluation step, the split step per node will let the tree be constructed faster, and there will much less waiting time. this approach of work distribution between the processors will make them focus on finishing the tree node by node. the proposed algorithm data structure and the per-node build strategy will enhance the decision tree building process. the communication problem that is happening when the processor evaluates the records in more than one node in one time will be solved. 4. experimental results 4.1. evaluating the execution time we have implemented the sprint algorithm and the proposed algorithm using mpi, and data sets in up to (10^5) and we used six, nine, and twelve processors in a cluster with total processing hardware of 80 cores/10 nodes and ram 16 gb, we got the attribute value from the database and created an attribute list for each attribute, then we sorted the attributes. after the sorting phase, we executed the steps of the algorithm. first, we found the gini for each attribute, then selected the best split and the split point. finally, we executed the split and repeated this circle for the remaining attributes. figure 10 shows the execution time in both sprint and the proposed algorithm. fig. 10. the execution time (in second). 129 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 from figure 2, we can divide the different runtime between two algorithms into three parts, the first part is when data is between (500-3000), the proposed algorithm gives a better result than sprint but the range of execution time is not significant, the second part when data is from (3000-6000), proposed algorithm also gives a better result than sprint and the range in execution time is bigger than the first part. we can see that every time the size of the data gets bigger, the difference range in runtime between the algorithm gets better and the proposed algorithm gives a better result. in sprint, when the data size gets bigger, the hash table does not fit in memory, so we have to do many rounds to update the hash table, these rounds take much time and increase the communication cost because the next step is dependent on the hash table rids to determine the node for each attribute value. in our algorithm, a hash table is distributed between the processors, so even if the data size gets bigger, the hash table in each processor fits in memory, and we need no more rounds. the results of implementation show that the proposed algorithm is faster than sprint in small and big data sets. table 1 shows the results of implementation. table 1: comparing the runtime of sprint and the proposed algorithm (in second). data size (records) sprint 6 sprint 9 sprint 12 my algorithm 6 my algorithm 9 my algorithm 12 500 0.00 0.00 0.00 0.00 0.00 0.00 1500 0.00 0.00 0.00 0.00 0.00 0.00 3000 0.10 0.00 0.00 0.00 0.00 0.00 6000 0.29 0.08 0.00 0.12 0.00 0.00 10000 0.72 0.3 0.12 0.34 0.18 0.00 150000 1.12 0.51 0.22 0.6 0.24 0.12 20000 2.52 0.96 0.3 1.12 0.39 0.22 30000 4.48 1.98 0.72 2.28 0.82 0.31 4.2. evaluating the memory requirement in sprint, the size of the hash table is equal to the order of the size of the training dataset for the upper levels of the decision tree. it is resident in all processors and the number of processors does not have any effect on the size of the hash table. thus, when we are dealing with massive data sets, the hash table size is a series problem. in the proposed algorithm, the hash table is distributed between the processors, therefore, if the data set order is o(n), then the hash table in each processor is o(n/p); by this solution, we solved the memory requirement problem. figure 11 shows memory requirements in each processor for both algorithms. 130 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 fig. 11. the memory requirement in each processor. data size is a severe problem because hardware cannot handle the fast growth of data size, therefore, developing the existing classification algorithms and making them able to handle a huge data size, without the need of potent hardware, is very important. table 2 shows the memory requirement in sprint and our algorithm. table 2: comparing the memory requirement by the record in each processor. data size (records) my algorithm 6 my algorithm 9 my algorithm 12 sprint 500 88 60 46 500 1500 254 171 129 1500 3000 504 338 254 3000 6000 1004 671 504 6000 10000 1671 1116 838 10000 15000 2504 1671 1254 15000 20000 3338 2227 1671 20000 30000 5004 3338 2504 30000 in the previous experiment, the proposed algorithm showed a better result than sprint. it needs a smaller memory size per processor than sprint. in our algorithm, the hash table should stay in memory in all the steps, because it is essential to determine the record rids in each node. in sprint, the hash table in each node has the same size order as the data set, thus, if the dataset is huge, sprint suffers from a memory requirement problem and needs more time to complete the classification process. however, in our algorithm, hash table size is 131 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 distributed equally among the processors. thus, each processor has (n/p) records which stay in memory, and the node table also stays in memory and has size m which is the number of classes, therefore, the memory requirement for our algorithm is (n/p +m). 5. conclusion and future work a decision tree is one of the most popular algorithms in data mining. it has many advantages such as being easy to understand, having a high degree of accuracy, and building the tree very quickly. the decision tree algorithm can handle both categorical and continuous attributes. this algorithm classifies the data set records and builds a predictive model that can be used to predict future outputs. there are many techniques to build the decision tree such as c4.5, id3, cart, and chaid. each one of them has a unique method and has many advantages, which make the building process easier and more efficient. in data mining, the decision tree building algorithms deal with very big data sets; thus, these algorithms must be able to handle this size of data and consider the ability of the computer's hardware. most of the decision tree algorithms are designed for resident memory data, this approach decreases the ability of these algorithms when the data sets are significant. therefore, many studies have been done in this area, and many algorithms have been proposed to solve the limited ability of the existing algorithms to handle big data sets. sprint algorithm is designed to solve the resident memory problem using a new data structure, which decreases the resident memory data size and makes the parallel designing of the decision tree easier. in this paper, we proposed a new parallel builder for the decision tree, which solves the runtime problem and the memory requirement problem in other algorithms. we tested the new algorithm using mpi and compared the results with the best parallel algorithm, sprint. our algorithm showed a better result than sprint with different sizes of data sets. it also showed a better result in runtime because the communication cost of the split step was decreased from o(n) to o(n/p +m/2) after we distributed the hashtable among the processors. distributing the hashtable also solved the memory requirement problem because all the processors share the size of the dataset equally. in this case, the algorithm will not suffer from overfitting problems when the size of the hashtable is too big and there will be no need for many rounds to update the hashtable. also in sprint, the initial distribution of the attribute lists records between the processors was not changed. this approach caused communication problems when the rids for one processor existed in more than one node. however, in the proposed algorithm, we solved this problem by building the tree node by node; thus, in the evaluation step, each processor evaluated its rids in one node, in this case, the process completed the node and went to another node. by evaluating the implementation results for sprint and the proposed algorithm, we can see that the proposed algorithm is better than the sprint in runtime and memory requirements. these advantages make the proposed algorithm more useful when the size of the dataset is significant. selecting the best algorithm to build the decision tree is based on many rules, the size of the dataset is one of the critical issues that should be considered in the selection process. there are many algorithms that are very useful and powerful when the amount of data is not very big such as c4.5 and cart, but, when the size of dataset is big, sprint and the proposed algorithm are better than other algorithms. the new data structure of the proposed algorithm helps to handle this big size, and it is even better than the sprint data structure. 132 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 in parallel computing, load balancing between the processors is essential, and the data load must be divided equally between the processors, otherwise, some processors will work more than others. in the decision tree, some nodes reach a dead end, and this happens when all the records in the node are related to one class. in this case, there is no need to evaluate and process the records in these nodes. our algorithm suffers from an unbalancing problem when some nodes reach a dead end, and some processors are processing more than the others, which increases the runtime of the algorithm. for the future work, we will solve the unbalancing problem when some nodes reach a dead end and divide the work equally between the processors to decrease the runtime. this step will enhance the building process and make the proposed algorithm more powerful and more suitable for massive data sets. nowadays, data scientists are more interested in deploying emerging and strong deep learning (dl) algorithms [26-30]. dl can perform big data analytics efficiently. it can be widely utilized for handling some traditional problems in big data analytics such as data labelling, semantic indexing, probing complex and nonlinear patterns from giant volumes of data, fast and efficient information retrieval, and simplifying discriminative tasks. as a result, it would be a progressive solution to our work in the future. references [1] fayyad, u., g. piatetsky-shapiro, and p. smyth (1996). from data mining to knowledge discovery in databases. ai magazine. 17(3):37-37. https://doi.org/10.1609/aimag.v17i3.1230 [2] berry, m.j. and g.s. linoff (2004). data mining techniques: for marketing, sales, and customer relationship management. john wiley & sons. [3] tan, p.-n., m. steinbach, and v. kumar (2016). introduction to data mining. pearson education india. [4] aggarwal, c.c. (2014). an introduction to data classification. data classification: algorithms and applications. chapman and hall/crc. [5] zaki, m.j. and w. meira (2014). data mining and analysis: fundamental concepts and algorithms. cambridge university press. [6] quinlan, j.r (1986). induction of decision trees. machine learning. 1(1):81-106. https://doi.org/10.1007/bf00116251. [7] rennie, j.d., et al (2003). tackling the poor assumptions of naive bayes text classifiers in proceedings of the twentieth international conference on machine learning: august 21-24, 2003; whasington dc. https://dl.acm.org/doi/10.5555/3041838.3041916. [8] hagan, m., et al (2014). neural network design. 2nd edtion. oklahoma. martin hagan. [9] jain, a.k. and r.c (1988). dubes, algorithms for clustering data. prentice-hall, inc. [10] zhang, c. and s. zhang (2003). association rule mining: models and algorithms. springer. [11] aggarwal, c (2014). data classification: algorithms and applications, ser. frontiers in physics. chapman and hall/crc. [12] esposito, f., et al (1997). a comparative analysis of methods for pruning decision trees. ieee transactions on pattern analysis and machine intelligence. 19(5): 476-491. https://doi.org/10.1109/34.589207. [13] mingers, j (1989). an empirical comparison of pruning methods for decision tree induction. machine learning. 4(2):227-243. https://doi.org/10.1023/a:1022604100933. [14] rokach, l. and o.z. maimon (2008). data mining with decision trees: theory and applications. world scientific. 133 iium engineering journal, vol. 22, no. 2, 2021 shamseen et al. https://doi.org/10.31436/iiumej.v22i2.1541 [15] kass, g.v (1980). an exploratory technique for investigating large quantities of categorical data. journal of the royal statistical society: series c (applied statistics). 29(2):119-127. https://doi.org/10.2307/2986296. [16] breiman, l., et al (1984). classification and regression trees. crc press. [17] hunt, e.b , j. marin, and p.j. stone (1966). experiments in induction. academic press. [18] friedman, j.h (1991). multivariate adaptive regression splines. the annals of statistics, 19(1):167. https://doi.org/10.1214/aos/1176347963 [19] mehta, m., r. agrawal, and j. rissanen (1996). sliq: a fast scalable classifier for data mining. in proceedings of the international conference on extending database technology: 25-29 march 1996; avignon, france; pp 18-32. https://doi.org/10.1007/bfb0014141. [20] shafer, j., r. agrawal, and m. mehta (1996). sprint: a scalable parallel classifier for data mining. in proceedings of the 22nd vldb conference. 3-6 september 1996; mumbai(bombay), india; pp 544-555. [21] joshi, m.v., g. karypis, and v. kumar (1998). scalparc: a new scalable and efficient parallel classification algorithm for mining large datasets. in proceedings of the first merged international parallel processing symposium and symposium on parallel and distributed processing. 30 march-3 april 1998; orlando, fl, usa. https://doi.org/10.1109/ipps.1998.669983. [22] bowyer, k.w., et al. a parallel decision tree builder for mining very large visualization datasets. in proceedings of the ieee international conference on systems, man and cybernetics.'cybernetics evolving to systems, humans, organizations, and their complex interaction. 8-11 oct 2000; nashville, tn, usa. https://doi.org/10.1109/icsmc.2000.886388. [23] ranka, s. and v. singh (1998). clouds: a decision tree classifier for large datasets. in proceedings of the 4th knowledge discovery and data mining conference. 27 – 31 august 1998; new york, usa. https://dl.acm.org/doi/10.5555/3000292.3000294. [24] liaw, a. and m. wiener (2002). classification and regression by random forest. r news. 2(3):18-22. [25] rastogi, r. and k. shim (2000). public: a decision tree classifier that integrates building and pruning. data mining and knowledge discovery. 4(4):315-344. [26] bahaghighat, m., et al (2020). estimation of wind turbine angular velocity remotely found on video mining and convolutional neural network. applied sciences. 10(10):35-44. https://doi.org/10.3390/app10103544. [27] bahaghighat, m., et al (2020). convlstmconv network: a deep learning approach for sentiment analysis in cloud computing. journal of cloud computing: advances, systems and applications. 9(16). https://doi.org/10.1186/s13677-020-00162-1. [28] abedini, f., et al (2019). wind turbine tower detection using feature descriptors and deep learningfacta universitatis, series: electronics and energetics. 33(1):133-153. https://doi.org/10.2298/fuee2001133a. [29] bahaghighat, m., et al (2019). vision inspection of bottle caps in drink factories using convolutional neural networks. in proceedings of the ieee 15th international conference on intelligent computer communication and processing (iccp). 5 7 september 2019; city plaza, cluj-napoca, romania. https://doi.org/10.1109/iccp48234.2019.8959737. [30] bahaghighat, m., et al (2019). a machine learning based approach for counting blister cards within drug packages. ieee access. 7: 83785-83796. https://doi.org/10.1109/access.2019.2924445. 134 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 kathiman et al. https://doi.org/10.31436/iiumej.v23i2.1713 effect of feed flowrates on the physical properties and antioxidant of mahkota dewa (phaleria macrocarpa) encapsulated powder muhammad norzaman kathiman1, siti kholijah abdul mudalip1,2* and jolius gimbun1,2 1 department of chemical engineering, college of engineering, universiti malaysia pahang, 26300 gambang, pahang, malaysia. 2 centre of excellence for advanced research in fluid flow, universiti malaysia pahang, 26300 gambang, pahang, malaysia. * corresponding author: kholijah@ump.edu.my (received: 4th december 2021; accepted: 27th april 2022; published on-line: 4th july 2022) abstract: this paper presents an experimental study on the encapsulation of mahkota dewa extracts by maltodextrin using spray drying. the bioactive compound from dried mahkota dewa was obtained using a subcritical water extraction process prior to a spray drying process. the effect of feed flow rate (485 to 2115 ml/h) was investigated using onefactor-at-a-time (ofat). it was observed that the mean particle size increase varied from 3.55 to 8.38 µm when the feed flow rate increased from 485 to 2115 ml/h. moisture content increased 4.88 to 6.83% as the feed flow rate increased from 485 to 2115 ml/h, whereas the antioxidant activity increased slightly from 90.48 to 91.65%. the findings from this study showed that decrease in feed flow rate reduces antioxidant activity, moisture content, and particle size. abstrak: kertas kerja ini adalah berkenaan kajian eksperimen melalui proses pengkapsulan ekstrak buah mahkota dewa dengan menggunakan maltodekstrin melalui teknik pengeringan semburan. sebatian bioaktif dari buah mahkota dewa kering diperoleh melalui teknik pengekstrakan air subkritikal sebelum proses pengeringan semburan. kesan kadar aliran masuk (485 hingga 2115 ml/jam) dikaji menggunakan konsep satu-faktorpada-satu-masa (ofat). dapatan kajian mendapati bahawa purata saiz zarah meningkat dari 3.55 kepada 8.38 µm ketika kadar aliran masuk meningkat dari 485 sehingga 2115 ml/jam. kandungan kelembapan meningkat dari 4.88 kepada 6.83% dengan kenaikan kadar aliran masuk dari 485 hingga 2115 ml/jam, sedangkan aktiviti antioksida meningkat sedikit dari 90.48 hingga 91.65%. dapatan kajian menunjukkan bahawa penurunan kadar aliran masuk berkurang melalui aktiviti antioksida, kandungan kelembapan dan saiz zarah. keywords: mahkota dewa; spray drying; antioxidant; maltodextrin 1. introduction mahkota dewa (phaleria macrocarpa (scheff.) boerl), which is a member of the thymelaeaceae family, is an important herbal species originating from papua new guinea island (irian jaya), indonesia [1]. the plant is quite popular among south east asian peoples and is traditionally used in local folk medicine as complementary alternative medicine for several diseases such as cancer, hypertension, and diabetes mellitus. the major parts of the plant namely the stem, leaves, egg shell of the seeds, and fruits are mostly enriched in 1 iium engineering journal, vol. 23, no. 2, 2022 kathiman et al. https://doi.org/10.31436/iiumej.v23i2.1713 bioactive compounds such as alkaloids, flavanoids, mangiferin, polyphenols, and saponins [2,3]. in particular, mahkota dewa fruit has been related to antioxidant activity and hence, the use of this fruit can be suggested as a strategy to control hyperglycemia problems in diabetic patients. several studies also have been performed to understand and prove other biological properties related to mahkota dewa fruit, such as its anti-carcinogenic, antihypertensive, anti-tumour, anti-viral, anti-bacterial, anti-fungal, and anti-inflammatory properties [1]. previous researchers reported the extraction of bioactive compounds from mahkota dewa fruits and leaves using conventional and nonconventional extraction techniques such as maceration [4], microwave [5], subcritical water [6,7], and supercritical carbon dioxide [8]. this is because obtaining the targeted bioactive compounds naturally present in plants depends on the extraction techniques employed. other works also reported that the conversion of the liquid extracts to powdered form product is preferred in industry for several reasons. for example, the product in powdered form is easier to handle and has been reported to show better stability, longer shelf-life and more convenience for oral consumption [9]. polyphenols are an example of the bioactive compounds extracted from the plant parts that are very susceptible to an oxidizing environment. spray drying is an established method used to convert the liquid extracts to powdered form product and well known in food industry due to its flexibility, low cost and large scale applicability [10]. however, the operation of spray drying that requires high operating temperature, up to 215 °c, may cause a thermal degradation issue to the extracts and poor quality of the powdered product produced [9]. one such method to overcome the issue is encapsulation of the extracts using a suitable carrier agent or polymer. in this situation, the carrier agent acts as a coating wall and provides a physical barrier between the extracts and the external environment. maltodextrin is frequently employed as a carrier agent in the spray drying of food products. it is a low-cost polysaccharide with a neutral scent and flavour that can diminish powder hygroscopicity if larger doses of the agent are used [11]. according to raja et al. [12], maltodextrin with dextrose equivalent (de) of 10 to 20 is appropriate for use as a carrier agent. previous studies have described the operating conditions and carrier agents used during spray drying for plants such as moringa stenopetala [13] and saffron [14]. a review on the encapsulation technology application in other plants or food products was also reported by ray et al. [15]. to our knowledge, no work reported the conversion of mahkota dewa extracts to powdered form. based on this consideration, this study was performed to investigate the effect of different feed flow rates during the spray drying process on the physical properties and antioxidant activity of mahkota dewa spray-dried extract. the maltodextrin de10 was utilised as a carrier agent. the powdered forms of the products obtained were all assessed in terms of antioxidant activity, moisture content, particle size distribution, and physical appearance. 2. materials and method 2.1 materials and chemicals the commercial dried mahkota dewa fruits were purchased from ethno resources sdn. bhd, selangor, malaysia. the samples were ground to an average size of 520 µm using retsch gmbh dry grinder (germany). the deionized water used for the subcritical extraction process was prepared using milli-q, ultrapure water purification system (massachusetts, usa). the food grade maltodextrin de10, obtained from san soon seng food industries sdn bhd, selangor, malaysia, was used as the carrier agent for the spray drying process. the methanol (99.9 wt% purity) and 1,1-diphenyl-2-picrylhydrazyl 2 iium engineering journal, vol. 23, no. 2, 2022 kathiman et al. https://doi.org/10.31436/iiumej.v23i2.1713 (dpph), purchased from merck sdn. bhd. (selangor, malaysia), were used in the analysis. all compounds were used without any further purification process. 2.2 extraction of mahkota dewa the mahkota dewa was extracted using a subcritical water extraction method described in previous work [7]. about 60 g of ground dried mahkota dewa were weighed and mixed with one liter of deionized water in a beaker. the mixture was stirred and placed in a laboratory pressure reactor system (buchiglasuster kiloclave, switzerland) at 106 °c for 5 h to perform the extraction. after that, the vessel was cooled down to room temperature using cooling water. the cooling water was supplied by a stuart recirculating cooler re300rc (staffordshire, uk). the collected extract was filtered to remove the residual solids using whatman filter paper and kept at -4 °c in a refrigerator until further used in the spray drying process. 2.3 encapsulation using spray drying maltodextrin de10 was dispersed directly into the extract solution and stirred at 1500 rpm using a magnetic stirrer to prepare 20% w/v of spray drying stock solution. the solution was continually stirred and pumped into a laboratory spray-dryer (lab plant sd06a, uk) using a peristaltic pump. the inlet air temperature, dry air velocity, and liquid flow rate were set to 200 °c, 3.9 m/s, and 2115 ml/h, respectively. the spray dried powder was collected in a chamber glass bottle, sealed, and kept in the refrigerator at -4 °c until used for analysis. the same procedures were carried out with liquid flow rates of 485, 900, 1305, and 1665 ml/h. the inlet air temperature and dry air velocity were set at 200 °c and 3.9 m/s, respectively. the experiments were carried out in triplicate. 2.4 characterization methods 2.4.1 moisture content the moisture content of the sample was measured using an a&d ms-70 moisture analyser. the sample was weighed and placed on the moisture analyser pan at a weight of around one gram. once the reading became steady, the moisture content shown in percentage value was recorded. 2.4.2 antioxidant activity the antioxidant activities were determined using tecan infinite m200 pro (switzerland) microplate reader with magellan software at a wavelength of 517 nm. one milligram of spray dried powder was dissolved in 10 ml of deionized water to make a sample solution. methanol was used to make a dpph radical solution at a concentration of one mg/ml. both solutions were combined and incubated in the dark for 20 min before measuring its absorbance. the dpph in methanol and ascorbic acid were used as a standard and blank, respectively. the percentage of inhibition was calculated by using eq. (1): (1) where is the absorbance of the sample and is the absorbance of the control [7]. 2.4.3 particle size distributions a laser diffraction particle size analyser (malvern 2000 mastersizer, malvern instruments co., worcestershire, uk) was used to analyse the particle size distributions. the analyzer was equipped with a sample dispersion unit to ensure that particles were distributed to the measuring region during the analysis. the particle size distribution was 3 iium engineering journal, vol. 23, no. 2, 2022 kathiman et al. https://doi.org/10.31436/iiumej.v23i2.1713 recorded in volume weighted mean. 2.4.4 morphology the morphological images were captured using a field emission scanning electron microscope (tm3030 plus, hitachi high-technologies corporation, japan) at 1e3 kv with a magnification of 1000x. the samples were put on a sample stump made of a double-sided adhesive carbon tape. a sputter coater (quorum technologies q300td, ltd., united kingdom) was used to sputter gold onto the samples. 3. results and discussion 3.1 moisture content moisture content is an important property that determines the flowability, stickiness, and storage stability of microencapsulated powder. it was reported that the powder produced by spray-drying with moisture contents less than 5% is considered safe from microbiological activity and can be stored for long period [16]. the influence of different feed flow rates on moisture content of the spray dried powder is shown in fig. 1. fig. 1: moisture content of spray dried powder at different feed flow rates with 0.224 average standard deviation. as can be seen, the moisture content increased with the increased of feed flow rates pumped into the spray dryer. the lowest moisture content of 4.88 % was achieved at a feed flow rate of 485 ml/h, whereas the highest moisture content of 6.83 % was achieved at a feed flow rate of 2115 ml/h. this result is expected since higher feed flow rates may reduce the contact time between feed samples and drying air. besides that, the droplets with larger surface area, which were produced at higher feed flow rates, reduce the heat and mass transfer efficiency, hence reducing the water removal during the spray drying process [17]. the result obtained shows similar trends with those reported by chegini and ghobadian [18] who studied the effect of feed flow rates on moisture content and bulk density of orange juice powder. hong and choi [19] also reported that the powder moisture content increased with the increased of sample pumping rate and inlet air temperature. braga et al. [20] reported that a feed flow rate of 300 – 900 ml/h used for spray drying of pineapple mint juice showed significant effect on the powder moisture content, where powder with lower 3.0 4.0 5.0 6.0 7.0 8.0 485 900 1305 1665 2115 m o is tu re c o n te n t, % feed flowrate, ml/h 4 iium engineering journal, vol. 23, no. 2, 2022 kathiman et al. https://doi.org/10.31436/iiumej.v23i2.1713 moisture content was obtained when the lower feed flow rate was used. additionally, other work reported that dripping inside the spray drying chamber was observed at high feed flow rates [21]. however, the phenomenon was not observed for the range of feed flow rates used in this work. 3.2 antioxidant activity rezende and co-workers reported that the presence of phenolic compounds contribute to the high antioxidant activities in plant extract [22]. mahkota dewa fruit extract has been reported to provide beneficial bioactivity results such as antioxidant effects due to the present of mangiferin, saponin, alkaloid, and polyphenols [10,12]. figure 2 shows the antioxidant activity in spray dried powder at different feed flow rates. a slight increment of the antioxidant activity was observed when the feed flow rate increased. the highest feed flow rate (2115 ml/h) produced spray dried powder with higher antioxidant activity (91.65%). this is probably caused by an inefficient heat transfer that occurs between the feed solution and hot air inside the spray drying chamber at higher feed flow rate. phisut [23] stated that the inefficient heat transfer inside the main chamber at high feed flow rates may produce powdered product with low yield but high antioxidant activity. fig. 2: antioxidant activity of spray dried powder at different feed flow rates with 0.40 average standard deviation. 3.3 particle size distribution figure 3 illustrates the particle size distribution (psd) of powdered mahkota dewa obtained at different feed flow rates. as can be seen, the psd of the spray dried powder produced are in bimodal shape. the range of psd for feed flow rates of 485 and 900 ml/h is smaller, which is in between 0.2 to 85 μm. whereas, for higher feed flow rates, the range of psd produced is bigger, between 0.9 to 670 μm. the mean diameter and volume weighted mean of spray dried powders produced at different feed flow rates is summarized in table 1. as shown in the table, the mean diameter of the spray dried power produced is larger at higher feed flow rates. this finding could be related to the high moisture content characteristic of the powdered product produced at high feed flow rates. this is because the powdered product with higher moisture content tends to stick together, thus causing larger particles to form, as shown in fig. 3. besides that, bigger droplets obtained at higher feed 80.0 82.0 84.0 86.0 88.0 90.0 92.0 94.0 96.0 98.0 100.0 485 900 1305 1665 2115 a n ti o x id a n t a c ti v it y , % feed flowrate, ml/h 5 iium engineering journal, vol. 23, no. 2, 2022 kathiman et al. https://doi.org/10.31436/iiumej.v23i2.1713 flow rates may contribute to the findings. studies by phisut [23] and chegini and ghobadian [18] also reported that larger psd was produced at higher feed flow rates. fig. 3: particle size distributions of spray dried powder at different feed flow rates. table 1: mean diameter and volume weighted mean of spray dried powders produced at different feed flow rates feed flow rate (ml/h) mean diameter (µm) volume weighted mean d [4,3] (µm) 485 3.549 13.157 900 4.670 14.400 1305 7.169 53.484 1665 7.014 74.706 2115 8.376 60.585 3.4 morphology the micrograph images of mahkota dewa powder were taken using sem and shown in fig. 4. the micrograph images were taken for powdered product obtained with and without maltodextrin de10 as carrier agent. for experiments with carrier agents, micrograph images were taken for powdered samples obtained using feed flow rates of 485 ml/h and 2115 ml/h. as can be seen in fig. 4 (a), the particles obtained without maltodextrin are in spherical and irregular forms. no pores were observed on the external surfaces of the powdered product produced but most of it shows shrinking effect. according to ding et al. [24], the shrinking effect on the particles’ surfaces is probably caused by rapid water evaporation during the drying process. moreover, the shriveled surface, which is a usual characteristic for organic materials produced using spray drying with various sizes, was also observed. as can be seen in fig. 4 (a), a sample’s surface is in the shriveled state and does 0 .0 2 1 0 .0 3 0 0 .0 4 3 0 .0 6 0 0 .0 8 5 0 .1 1 9 0 .1 6 9 0 .2 3 8 0 .3 3 7 0 .4 7 5 0 .6 7 1 0 .9 4 8 1 .3 3 9 1 .8 9 2 2 .6 7 2 3 .7 7 4 5 .3 3 1 7 .5 2 9 1 0 .6 3 6 1 5 .0 2 3 2 1 .2 2 0 2 9 .9 7 5 4 2 .3 4 0 5 9 .8 0 7 8 4 .4 7 9 1 1 9 .3 3 0 1 6 8 .5 5 8 2 3 8 .0 9 5 3 3 6 .3 1 8 4 7 5 .0 6 1 6 7 1 .0 4 2 9 4 7 .8 7 1 1 ,3 3 8 .9 0 4 1 ,8 9 1 .2 5 1 v o lu m e , % particle size, m 485 ml/h 900 ml/h 1305 ml/h 1665 ml/h 2115 ml/h 6 iium engineering journal, vol. 23, no. 2, 2022 kathiman et al. https://doi.org/10.31436/iiumej.v23i2.1713 not attach to other particles. however, the shriveled particles, especially in fig. 4 (b), were attaching to one another. this is probably related to the moisture content in the particles. even though some of the particles were shrunk and had a shriveled surface, other particles had a smooth surface. (a) (b) (c) fig. 4: sem micrographs of powdered samples obtained at (a) without maltodextrin de 10 and feed flow rate of 2115 ml/h, (b) with maltodextrin de 10 and feed flow rate of 2115 ml/h, and (c) with maltodextrin de 10 and feed flow rate of 485 ml/h. the inlet dry air temperature and air flow rate were fixed at 200 °c and 3.5 m/s, respectively. meanwhile in fig. 4 (c), some of the particles had shriveled surfaces, while others had smooth surfaces. the bulk of the particles had shriveled and constricted surfaces when the inlet air temperature was low. the number of particles with smooth surfaces rose as the drying temperatures increased. this is due to the differences in drying rates, or higher temperatures, which resulted in faster water evaporation and the formation of a smooth and hard outer layer. nijdam and langrish [25] demonstrated the formation of more rigid particles when high temperature was used in the spray drying of milk. according to their findings, vacuole shapes form inside a molecule not long after an outer layer appears, and it expands once the molecule temperature exceeds the local ambient boiling point and the vapor pressure inside the vacuole exceeds the local ambient pressure. when the drying temperature is high enough, moisture evaporates quickly and the outer layer becomes dry and hard, preventing the hollow molecule from flattening as it moves towards colder, dryer areas. however, the outer layer remains fluid and supple for longer when the drying temperature is lower, allowing the empty molecule to flatten and wither as it cools [25]. 7 iium engineering journal, vol. 23, no. 2, 2022 kathiman et al. https://doi.org/10.31436/iiumej.v23i2.1713 4. conclusion the effect of different feed flow rates on mahkota dewa extracts encapsulated with maltodextrin using a spray drying technique has been studied. the results show that higher feed flow rates produced powdered product with higher moisture content, antioxidant activity and psd. however, since the powdered product with low moisture content is desirable, the low feed flow rate of 485 ml/h is recommended in this work. besides, the antioxidant activity produced at 485 ml/h is quite high, which is more than 90%. acknowledgement special thanks are dedicated to university malaysia pahang for financial support under internal grant research scheme rdu1803107 and postgraduate research grant scheme (pgrs1903120). references [1] altaf r, asmawi mz, dewa aa, sadikun a, umar mi. (2013) phytochemistry and medicinal properties of phaleria macrocarpa (scheff.) boerl. extracts. pharmacognosy review, 7(13): 73-80. doi: 10.4103/0973-7847.112853 [2] trilaksana n, riwanto i, tjandrawinata rr, winarto r. (2017) inhibition of mahkota dewa (phaleria macrocarpa) bioactive fraction on proliferation of human retinoblastoma tumor cells y-79 through suppression of mrna level of cyclin e. asian pacific journal of tropical biomedicine, 7(4): 280-287. https://doi.org/10.1016/j.apjtb.2017.01.001 [3] ramdani ed, marlupi ud, sinambela j, tjandrawinata rr. (2017) isolation and identification of compounds from phaleria macrocarpa (scheff.) boerl fruit extract. asian pacific journal of tropical biomedicine, 7(4): 300-305. doi : 10.1016/j.apjtb.2016.12.018 [4] fariza n, luqman chuah a, pin ky, dayang radiah ab. (2014) optimisation of extraction of phaleria macrocarpa leaves. medicinal & aromatic plants 3(1): 1000149. doi: 10.4172/2167-0412.1000149 [5] alara or, abdul mudalip sk, abdurahman nh, mahmoud ms, obanijesu eo-o. (2019) data on parametric influence of microwave-assisted extraction on the recovery yield, total phenolic content and antioxidant activity of phaleria macrocarpa fruit peel extract. chemical data collections, 24: 100277. https://doi.org/10.1016/j.cdc.2019.100277 [6] kim w-j, veriansyah b, lee y-w, kim j-h, kim j-d. (2010) extraction of mangiferin from mahkota dewa (phaleria macrocarpa) using subcritical water. journal of industrial and engineering chemistry, 16(3): 425-430. doi:10.1016/j.jiec.2009.08.008 [7] hashim na, abdul mudalip sk, harun n, man rc, sulaiman sz, arshad zim, shaarani sm, azmir j. (2019) mahkota dewa subcritical water extraction process: experimental and molecular dynamics simulation study. chemical engineering & technology, 42(9): 17471756. https://doi.org/10.1002/ceat.201800638 [8] azmir j, zaidul ism, sharif km, uddin ms, jahurul mha, jinap s, hajeb p, mohamed a. (2014) supercritical carbon dioxide extraction of highly unsaturated oil from phaleria macrocarpa seed. food research international, 65: 394-400. https://doi.org/10.1016/j.foodres.2014.06.049 [9] gallo l, ramírez-rigo mv, piña j, bucalá v. (2015) a comparative study of spray-dried medicinal plant aqueous extracts: drying performance and product quality. chemical engineering research and design, 104 681-694. https://doi.org/10.1016/j.cherd.2015.10.009 [10] fang zx, bhandari b. (2011) effect of spray drying and storage on the stability of bayberry polyphenols. food chemistry, 129(3): 1139-1147. https://doi.org/10.1016/j.foodchem.2011.05.093 [11] goula am, adamopoulos kg. (2010) effect of maltodextrin addition during spray drying of tomato pulp in dehumidified air: ii. powder properties. innovative food science & emerging technologies, 11(2): 342-351. https://doi.org/10.1080/07373930802046377. 8 iium engineering journal, vol. 23, no. 2, 2022 kathiman et al. https://doi.org/10.31436/iiumej.v23i2.1713 [12] raja kcm, sankarikutty b, sreekumar m, jayalekshmy a, narayanan cs. (1989) material characterization studies of maltodextrin samples for the use of wall material. starch stärke, 41(8): 298-303. https://doi.org/10.1002/star.19890410805 [13] dadi dw, emire sa, hagos ad, eun j-b. (2020) effects of spray drying process parameters on the physical properties and digestibility of the microencapsulated product from moringa stenopetala leaves extract. cogent food & agriculture, 5(1): 1690316. https://doi.org/10.1080/23311932.2019.1690316 [14] garavand f, rahaee s, vahedikia n, jafari sm. (2019) different techniques for extraction and micro/nanoencapsulation of saffron bioactive ingredients. trends in food science & technology, 89: 26-44. https://doi.org/10.1016/j.tifs.2019.05.005 [15] ray s, raychaudhuri u, chakraborty r. (2016) an overview of encapsulation of active compounds used in food products by drying technology. food bioscience, 13: 76-83. http://dx.doi.org/10.1016/j.fbio.2015.12.009 [16] tontul i, topuz a. (2017) spray-drying of fruit and vegetable juices: effect of drying conditions on the product yield and physical properties. trends in food science & technology, 63: 91-102. https://doi.org/10.1016/j.tifs.2017.03.009 [17] can karaca a, guzel o, ak mm. (2016) effects of processing conditions and formulation on spray drying of sour cherry juice concentrate. journal of the science of food and agriculture, 96(2): 449-455. https://doi.org/10.1002/jsfa.7110 [18] chegini gr, ghobadian b. (2005) effect of spray-drying conditions on physical properties of orange juice powder, drying technology, 23(3): 657-668. doi: 10.1081/drt-200054161 [19] hong j-h, choi y-h. (2007) physico‐chemical properties of protein‐bound polysaccharide from agaricus blazei murill prepared by ultrafiltration and spray drying process. international journal of food science & technology, 42(1): 1-8. https://doi.org/10.1111/j.13652621.2005.01116.x [20] braga v, guidi lr, de santana rc, zotarelli mf. (2020) production and characterization of pineapple-mint juice by spray drying. powder technology, 375: 409-419. https://doi.org/10.1016/j.powtec.2020.08.012 [21] tonon rv, brabet c, hubinger md. (2008) influence of process conditions on the physicochemical properties of açai (euterpe oleraceae mart.) powder produced by spray drying, journal of food engineering, 88(3): 411-418. https://doi.org/10.1016/j.jfoodeng.2008.02.029 [22] rezende yrrs, nogueira jp, narain n. (2018) microencapsulation of extracts of bioactive compounds obtained from acerola (malpighia emarginata dc) pulp and residue by spray and freeze drying: chemical, morphological and chemometric characterization. food chemistry, 254: 281-291. https://doi.org/10.1016/j.foodchem.2018.02.026 [23] phisut n. (2012) spray drying technique of fruit juice powder: some factors influencing the properties of product. international food research journal, 19: 1297-1306. [24] ding j, xu z, qi b, cui s, wang t, jiang l, zhang y, sui x. (2019) fabrication and characterization of soybean oil bodies encapsulated in maltodextrin and chitosan-egcg conjugates: an in vitro digestibility study. food hydrocolloids, 94: 519-527. https://doi.org/10.1016/j.foodhyd.2019.04.001 [25] nijdam jj, langrish tag. (2006) the effect of surface composition on the functional properties of milk powders. journal of food engineering, 77(4): 919-925. https://doi.org/10.1016/j.jfoodeng.2005.08.020 9 microsoft word 265-1134-1-rv completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology raja et al. 197 adaptation of cholesterol requiring ns0 cells to serum free culture conditions junaid muneer raja 1 , nurina anuar 1 and badrulhisham abdul rahman 2 1 department of chemical and process engineering, faculty of engineering and built environment, university kebangsaan malaysia, bangi 43600 selangor, malaysia. 2 innobiologics sdn. bhd.,lot 1, persiaran negeri, 71800 nilai, negeri sembilan, malaysia. junaid.raja@innobiologics.com; drnurina@ukm.my; badrul.abdulrahman@innobiologics.com abstract: colorectal cancer is the third most common form of cancer and the second leading cause of cancer-related death in the western world. the answers to such life threatening diseases and cancers are monoclonal antibodies (mab’s) which are widely used as therapeutic agents. world demand for currently approved mab’s is on the order of a few kilograms per year. however, new therapeutic mab’s are under development and require doses of several hundred milligrams to a gram over the course of therapy. very often to cater for the special requirements for the growth of mammalian cells, serum is added to the cell culture medium. however, removal of serum from the cell culture medium is often carried out, especially if the end product is to be used for human consumption, in order to eliminate various disadvantages such as high physiological variability, high batch to batch variability, risk of contamination and high cost, and challenges posed in the downstream processing of the product. in this paper, the adaptation of cholesterol requiring ns0 cells to commercially available serum free media is presented. abstrak: kanser kolorektum merupakan kanser ketiga paling umum dan kini berada di tempat kedua penyebab kematian berkaitan kanser di negara barat. jawapan kepada penyakit yang mengancam nyawa dan penyakit kanser adalah antibodi monoklon (monoclonal antibodies ((mab’s)) yang digunakan sebagai agen terapeutik. permintaan dunia terhadap mab’s yang diluluskan adalah dalam bilangan beberapa kilogram setahun. namun, terapeutik mab’s yang baru adalah di bawah penyelidikan dan memerlukan beberapa ratus dos milligram hingga satu gram dalam satu peringkat terapi. sering kali untuk memenuhi permintaan terhadap tumbesaran sel mamalia, serum dicampurkan dengan sel kultur perantara. walaupun begitu, pemindahan serum dari sel kultur perantara sering dilakukan, terutamanya jika produk akhir digunakan untuk kegunaan manusia; untuk mengurangkan pelbagai kelemahan seperti kebolehubahan psikologi yang tinggi, kebolehubahan yang tinggi daripada satu kumpulan ke satu kumpulan lain, risiko pencemaran, kos yang tinggi, dan cabaran mendatang dalam pemprosesan produk. dalam perbentangan ini, kolestrol yang diubah memerlukan sel ns0 yang dikomersilkan dengan serum bebas perantara. keywords: ns0; serum-free; monoclonal antibody; growth 1. introduction the usage of monoclonal antibodies (mabs) as therapeutic agents has seen a rapid increase during the past decade or so and thus there are several approved iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology raja et al. 198 antibody based medicinal products in the market today. the prime advantage of mabs as therapeutic agents is their high target specificity, resulting in a low side effect profile. monoclonal antibodies can also be engineered to have additional biological activity beyond binding of the antibody to its antigen. due to the high the therapeutic potential, the process development and production of monoclonal antibodies is being pursued by biopharmaceutical companies globally. monoclonal antibodies are primarily manufactured in genetically engineered mammalian cell lines such as ns0, cho, etc. ns0, a murine myeloma cell line, has been adopted by a number of biotechnology companies for the expression of therapeutic antibodies and has proven to be effective and easily lent itself to process optimization efforts [1-3, 9, 15, 16]. thus, the importance of mammalian cell culture for the production of special biopharmaceuticals and biodiagnostics not only in research but also on clinical diagnostics and therapy has increased exponentially. the products which are produced for direct application to humans must be of extremely high purity and constant quality, and at the same time, the production processes should be economically optimized and efficient [6]. very often to cater for the special requirements for the growth of mammalian cells, serum is added to the cell culture medium. this is because serum contains plethora of proteins, peptides, growth factors, hormones and other components which may be of importance for the cells to be cultivated and may not be present in the serum free media at all [14] . due to these properties, removal of serum from the culture medium is a daunting task. however, removal of serum from the cell culture medium is often carried out in order to eliminate various disadvantages posed by its usage which include high physiological variability, high batch to batch variability, risk of contamination and high cost, and challenges posed in the downstream processing of the product, etc. [5, 6, 8, 10, 13, 14]. it should however be noted that the development of a serum-free culture processes has been particularly challenging for ns0 cells due to their cholesterol autotrophy [10-12]. in order to adapt the cells to serum free media, generally two approaches are common: direct adaptation and indirect (sequential) adaptation. in the former case, cells are directly cultured from a growth medium containing serum to a serum free medium, whereas in the latter case, the concentration of the growth medium containing serum is slowly reduced and replaced with serum free medium [7]. 2. methodolody 2.1 cell culture media and supplements three commercially available serum free media, hyq cdm4ns0 (thermoscientific, product # sh30579.02), excell-ns0(sigma aldrich, product # 14650c ) ex-cell 610-hsf (sigma aldrich, product # 14650c) and combination of dmem and hyqcdm4ns0 in certain ratio were tested for the direct adaptation of the cells to serum free conditions. the supplements that were used included ultra low igg fbs (gibco, product # 16250-078) in a concentration range of 1-5% (v/v) and synthechol (sigmaaldrich, product # ) in a concentration range of 0.2-0.4%(v/v). also, l-glutamine, 2 mm (sigma, product # g8540) was supplemented to the medium. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology raja et al. 199 2.2 cell line and routine culture conditions the ns0 wild type cell line was obtained from innobiologics sdn. bhd., with the courtesy of dr. cristina mateo, center for molecular immunology (cim, havana, cuba). these cells secrete humanized anticea (carcino-embryogenic antigen) and are cholesterol auxotrophs. the cell line was maintained in cryo vials until usage. following vial thaw, cells were routinely grown in static culture using 25 cm 2 t flasks containing 10 ml of dmem medium supplemented with 2 mm l-glutamine and 5% ultra low igg fbs. the cell cultures were sequentially adapted to 1% ultra low igg fbs prior to carrying out any direct adaption to serum free media. the cultures incubated at 37 o c with a 5% co2. every 24-96 hours, when the cells had grown to a density of about 1 x 10 6 cells/ml or more, the culture was passaged by dilution with fresh growth medium to approximately 0.3-0.5 x 10 6 cells/ml. in the presence of serum most of the cells grew loosely attached to the plastic flask and the adherent cells were easily removed by firmly tapping the side of the flask. for both direct and sequential adaptation, cells were seeded form the current growth medium at a seeding density of 0.5 x 10 6 cells/ml. 2.3 analytical methods viable cell density (vcd) and viability were determined by the tryphan blue exclusion method using a haematocytometer. prior to cell counting, samples were diluted 2 to 10-fold with 0.4% trypan blue solution (gibco, prdouct # 15250-061) depending on the cell density. in serum-containing static culture, the cells were first dislodged by tapping the side of the flask. an enzyme-linked immunosorption assay (elisa) was employed to determine the titer of the monoclonal anti-carcinoembruogenic antibody. cells were centrifuged for 5 min at 6000 rpm with a minispin plus microcentrifuge (eppendorf ag, hamburg, germany) prior to the antibody assay. human igg, whole molecule, unconjugated (pierce, product # 31154) was used as a standard. first, 100 µ l capture antibody solution with a dilution of 1:1000 (anti-human igg-fc specific, produced in goat; sigma, product # i2136) was placed in a 96-well microliter plate and incubated at 2-8 o c overnight. next, after rinsing with 1x200 µ l washing buffer (0.05% tween20 in 0.9% nacl), 200 µ l of blocking buffer (0.01% w/v bsa and 0.02% v/v tween20 in 1xpbs) was added and incubated for another 2 hours at 37 o c followed by washing 4x with washing buffer. a 100 µ l sample or standard solution was added to each well and incubated for 2 hours at 37 o c. after rinsing with 4x200 µ l washing buffer, 100 µ l labeled secondary antibody, 1:2500 dilution (anti-human gamma chain specific peroxidase conjugate, produced in goat; sigma, product # a6029) was added and incubated for another 2 hours at 37 o c. the plate was then rinsed with 4x200 µ l washing buffer. then, 100 µ l of enzyme substrate working solution (abts tablets, roche, product # 11 112 442 001, dissolved in abts buffer, roche, product # 11 112 597 001) was added and incubated for 1 hour in the dark. absorbance was measured at a wavelength of 405 nm via a kinetic microplate reader (bio-tek instruments inc., highland park, winooski). samples were diluted 1000 to 10,000fold with blocking buffer prior to assay depending on the antibody concentrations. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology raja et al. 200 3. results and discussion 3.1 direct adaptation out of three media tested for the direct adaption of the ns0 cells, only one of them (excell 610hsf) showed potential in supporting the growth of the cells (fig. 1). only cells in excell 610hsf showed growth after 48 hours of the subculture with a viable cell density of 1.30 x 10 6 cell/ml and a cell viability of 82.96%. in comparison, cells in hyq cdm4ns0 dropped down to a viable cell density of 8.0 x 10 4 cells/ml compared to 5.0 x 10 5 at the beginning of the culture and a cell viability of only 19.23%. also the result with excell ns0 was not much different from hyq cdm4ns0, in the sense that all cells were dead after 48 hours. (a) (b) fig. 1: (a) direct adaptation in t-25 flask, viable cell density (cell/ml) versus time (b) direct adaptation in t-25 flask, cell viabilty (%) versus time (days). 3.2 indirect adaptation for sequential adaptation, the cells were first grown in dmem + hyclone (1:1) + 1% fbs. after three passages, cells were sub-cultured again to dmem + hyclone (1:1) + 0.5% fbs and then to dmem + hyclone (1:3) + 0.025% fbs. as is evident from the batch results in fig. 2 (a and b) the cells don’t grow well and the peak cell density reached is below 1 x 10 6 cells. also, the cell viability just keeps dropping since day one. (a) (b) fig.2: (a) sequential adaptation in t-25 flask, viable cell density (cell/ml) against time (days). (b) sequential adaptation in t-25 flask, cell viabilty (%) against time (days). iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology raja et al. 201 3.3 effect of synthechol on ns0 cell growth and productivity since excell610hsf + 0.4% synthechol supported the serum free growth of ns0 cells, further investigation was carried out for determining the optimal concentration of synthechol supplement for the media. according to the manufacturer’s recommendation (sigma-aldrich) three different concentrations of synthechol were tried and the culture was seeded at 3.0 x 10 5 cells/ml (fig. 3). (a) (b) fig. 3: (a) excell + different synthechol concentration in t-25 flask, viable cell density (cell/ml) versus time (days). (b) excell + different synthechol concentration in t-25 flask, cell viabilty (%) versus time (days). as is evident for the fig. 3 (a and b) above, the maximum cell density was achieved using 0.4% synthechol concentration on day 5. although the cell viability using 0.4% synthechol was not as high in comparison to 0.2% and 0.6% synthechol supplement concentration, but the value was above 90% and remained throughout until the peak cell concentration was observed on day 5. in terms for antibody titer, the culture with 0.2% synthechol concentration produced a cumulative of 31.18 µ g/ml in comparison to 29.10 µ g/ml using 0.4% synthechol and 27.46 µ g/ml using 0.6% synthechol, indicating that synthechol concentration of 0.2% v/v is the best of the three for production secretion (fig. 4). fig. 4: monoclonal anti-cea antibody concentration using different synthechol concentrations. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology raja et al. 202 4. conclusion ns0 wild type cell line was successfully adapted to serum free culture conditions. due to cholesterol auxotrophy, adaptation of ns0 cells to serum free conditions enabled to determine the optimum concentration of cholesterol supplement (synthechol) for monoclonal antibody production. acknowledgement i would like to thank innobiologics sdn. bhd. (negeri sembilan, malaysia) for providing me the ns0 cell line. special thanks to my project supervisors dr. nurina anuar, ukm and dr. badrulhisham abdulrahman, innobiologics sdn. bhd., for their helpful discussions in the course of supervising this work. references [1] bibila t., rancci c., et al. (1994). "investigation of ns0 cell metabolic behaviour in monoclonal antibody producing clones." ann ny acad sci 745: 277-284. [2] dempsy j., ruddock s., et al. (2003). "improved fermentation processes for ns0 cells expressing human antibodies and glutamine synthetase." biotechnol prog 19(1): 175-178. [3] dezengotita vm., miller wm., et al. (2000). "phosphate feeding improves high-cellconcentration ns0 myeloma culture performance for monoclonal antibody production." biotechnol bioeng 69(5): 566-576. [4] erika spens and l. haggstrom (2007). "defined protein and animal component-free ns0 fed-batch culture." wiley interscience 98(6): 1183-1194. [5] freshney, r. i. (2005). culture of animal cells a manual of basic technique wiley-liss. [6] h. buntemeyer, d. lutkemeyer, et al. (1991). "optimization of serum-free fermentation processes for antibody production." cytotechnology 5: 57-67. [7] hewlett, g. (1991). "strategies for optimising serum-free media." cytotechnology 5: 3-14. [8] hochfeld, w. l. (2006). producing biomolecular substances with fermenters, bioreactors, and biomolecular synthesizers, crc press, taylor and francis group. [9] john e. burky., mark c. wesson., et al. (2006). "protein-free fed-batch culture of non-gs ns0 cell lines for production of recombinant antibodies." biotechnol bioeng 96(2): 281-293. [10] keen, m. j. and t. w. steward (1995). "adaptation of cholesterol-requiring nso mouse myeloma cells to high density growth in a fully defined protein-free and cholesterol-free culture medium." cytotechnology 17: 203-211. [11] sato kt, mcclure db, et al. (1984). "cholesterol requirement of ns-1 mouse myeloma cells for growth in serum-free medium." mol biol med 2: 121-134. [12] seth g, mclvovr rs, et al. (2006). "17b-hydroxysteroid dehydrogenase type 7 (hdd17b7) reverts cholesterol auxotrophy in ns0 cells." j biotechnology 121: 241-252. [13] shibuya, k., r. haga, et al. (2008). "a serum substitute for fed-batch culturing of hybridoma cells." cytotechnology 57: 187–197. [14] stoll, t. s., k. miihlethaler, et al. (1996). "systematic improvement of a chemically-defined protein-free medium for hybridoma growth and monoclonal antibody production." journal of biotechnology 45: 111-123. [15] whitford w. (2003). "ns0 serum-free culture and applications." bioprocess int 1(12): 3647. [16] zhou w., chen c., et al. (1997). "fed-batch culture of recombinant ns0 myeloma cells with high monoclonal antibody production." biotechnol bioeng 55: 783-793. iium engineering journal iium engineering journal, vol. 23, no. 2, 2022 ng et al. https://doi.org/10.31436/iiumej.v23i2.2143 characterization and sintering properties of hydroxyapatite bioceramics synthesized from clamshell biowaste chui kim ng1*, kit yee sara lee2, chin hong tan1, singh ramesh3,4, chen hunt ting5, yea dat chuah6, chou yong tan3, and ubenthiran sutharsini7 1 centre for advanced materials, department of materials engineering, faculty of engineering & technology, tunku abdul rahman, university college, 53300 kuala lumpur, malaysia. 2 center of systematic innovation research, department of mechanical engineering, faculty of engineering & technology, tunku abdul rahman, university college, 53300 kuala lumpur, malaysia. 3 centre of advanced manufacturing & material processing (ammp), department of mechanical engineering, faculty of engineering, university of malaya, 50603 kuala lumpur, malaysia. 4 department of mechanical engineering, faculty of engineering, universiti teknologi brunei, tunku highway, gadong be1410, brunei darussalam. 5 department of mechanical and materials & manufacturing engineering, lee kong chian faculty of engineering and science, universiti tunku abdul rahman, jalan sungai long, bandar sungai long, cheras, 43000 kajang, selangor darul ehsan, malaysia. 6 department of mechanical, materials and manufacturing (m3) engineering, university of nottingham malaysia, jalan broga, 43500 semenyih, selangor darul ehsan, malaysia. 7 department of physics, university of jaffna, jaffna ja 40000, sri lanka. * corresponding author: ngck@tarc.edu.my (received: 9th july 2021; accepted: 8th november 2021; published on-line: 4th july 2022) abstract: hydroxyapatite (ha) is a type of calcium phosphate-based bioactive ceramic that resembles the mineral phase of bone and teeth with great potential for bone substitution and biomedical implants. biogenic-derived ha emerges as a cheap and ecosustainable alternative to improve waste utilization. however, hydroxyapatite has limited applications due to its apparent brittleness, thus prompting investigation for enhanced sintering properties. in the present study, the combination of calcination and chemical precipitation technique was used to extract hydroxyapatite (ha) from ark clamshells (anadara granosa). the method successfully produced ha powder with a ca/p ratio of 1.6 and characteristic bands corresponded to pure ha via fourier transform infrared spectroscopy (ftir). the synthesized ha powder was then sintered at temperatures ranging from 1200 °c to 1300 °c, followed by mechanical evaluation of the density, vickers hardness, fracture toughness and grain size. it was revealed that the samples sintered at 1250 °c achieved a relative density of 88%, vickers hardness of 5.01  0.39 gpa, fracture toughness of 0.88  0.07 mpa.m1/2 and average grain size of 3.7 µm. overall, the results suggest that ark clamshell synthesized ha (acs) had the potential to be used as functional bioceramics for biomedical applications. abstrak: hidroksiapatit (ha) adalah sejenis seramik bioaktif berasaskan kalsium fosfat yang menyerupai fasa mineral tulang dan gigi, berpotensi besar mengantikan tulang dalam implan bioperubatan. ha yang berasal dari biogenik muncul sebagai alternatif yang murah dan eko-lestari dalam menambah baik pengurusan sisa. walau bagaimanapun, hidroksiapatit mempunyai aplikasi yang terhad kerana mempunyai kerapuhan yang ketara, menyebabkan penyelidikan diperlukan bagi meningkatkan sifat sintering. gabungan teknik kalsinasi dan pemendakan kimia telah digunakan dalam kajian ini, bagi 228 iium engineering journal, vol. 23, no. 2, 2022 ng et al. https://doi.org/10.31436/iiumej.v23i2.2143 mengekstrak hidroksiapatit (ha) dari kulit kerang (anadara granosa). kaedah ini telah berjaya menghasilkan serbuk ha dengan nisbah 1.6 ca/p dan jalur puncak sepadan dengan ha tulen melalui spektroskopi inframerah transformasi fourier (ftir). serbuk ha ini kemudian disinter pada suhu antara 1200 °c hingga 1300 °c, diikuti penilaian mekanikal pada ketumpatan, kekerasan vickers, kerapuhan dan ukuran bijirin. hasil ujian menunjukkan bahawa sampel yang disinter pada suhu 1250 °c mencapai 88% ketumpatan relatif, kekerasan vickers 5.01  0.39 gpa, kerapuhan pada 0.88  0.07 mpa.m1/2 dan purata ukuran butiran  3.7 µm. secara keseluruhan, dapatan menunjukkan bahawa kulit kerang ha yang disentisis (acs) berpotensi sebagai bioseramik bagi aplikasi bioperubatan. keywords: hydroxyapatite; bioceramics; chemical synthesis; calcination; sintering 1. introduction hydroxyapatite (ha) with a chemical formula of ca10(po4)6(oh)2, is a type of calcium phosphate-based ceramic that comprises the main mineral constituent to human bones and teeth, which is widely used in dental and orthopedic applications. the conventional methods to synthesize ha are solid-state, mechanochemical, chemical precipitation, hydrolysis, solgel, hydrothermal, emulsion, sonochemical, high-temperature processes or a combination of a few techniques [1]. among these methods, wet-chemical precipitation is the most promising and low-cost technique [2,3]. in recent years, biowaste-derived ha has attracted attention as numerous food wastes such as bones, eggshells and seafood shells had piled up in landfill globally. specifically, shell wastes such as oyster, mussel, scallop, clam and cockle are discarded in an abundant amount. million tons of shell wastes have been discarded and piled up in landfills in china, taiwan, spain, south korea, peru, indonesia, nigeria, and malaysia [4-7]. instead, these shell wastes could be utilized to synthesize ha owing to the rich calcium carbonate (caco3) content [8-10]. typically, ha has been successfully synthesized via hydrothermal synthesis method by utilizing various species of clamshell such as strombus gigas, tridacna gigas [11], venerupis [12], corbicula [13,14], mercenaria [15], and anadara granosa [16]. however, the majority of studies did not report the mechanical properties of sintered ha. in the current study, anadara granosa clamshell will be used as the calcium precursor to synthesize natural ha powder, followed by characterization of its properties at various sintering temperatures. 2. materials and methods 2.1 synthesis of powder biogenic sources such as seashells or eggshells are good natural sources of calcium precursor for the synthesis of ha bioceramics. in this study, the anadara granosa clamshells collected from peninsular malaysia were used as the starting materials to synthesize ha. the as-received clamshells were washed thoroughly, rinsed with distilled water, and dried in an oven at 80 °c for one hour. the dried clamshells were then crushed, ground and sieved through a 300 μm test sieve. this was followed by calcination at 1000 °c for four hours in an electrical furnace (carbolite gero, uk), to transform the calcium carbonate (caco3) into calcium oxide (cao). figure 1 depicts the flow chart of the ha synthesis process via wet chemical precipitation technique. first of all, 0.25 m of calcium precursor to 0.15 m of phosphorus precursor was employed to achieve stoichiometric ha with the calcium/phosphorus (ca/p) 229 iium engineering journal, vol. 23, no. 2, 2022 ng et al. https://doi.org/10.31436/iiumej.v23i2.2143 concentration ratio of 1.67. 2.8 g of cao powder was then added in 200 ml of distilled water to formulate the ca(oh)2 solution as the calcium precursor. the solution was subsequently magnetic stirred at 400 rpm for an hour and maintained at ph 12. on the other hand, the 2.05 ml concentrated h3po4 (phosphorus precursor) was diluted into 200 ml of distilled water, stirred and kept at about ph 2. subsequently, the prepared h3po4 solution was then added dropwise into ca(oh)2 solution to begin the titration process, continued with a vigorous stirring at 700 rpm for 30 minutes. the nh4oh solution was then added to adjust the ph to 10. this was followed by magnetic stirring at 500 rpm for an hour after the titration process and aging for 21 hours (to form white precipitate). vacuum filtration was subsequently performed on the precipitates using an electrical aspirator pump (jerio tech, korea). finally, the precipitate was dried in an oven at 100 °c for 16 hours and then crushed and sieved through a 300 μm test sieve to obtain ark clamshell synthesized ha (acs) powder. fig. 1: flow chart of the ha synthesis process via wet chemical precipitation technique. 230 iium engineering journal, vol. 23, no. 2, 2022 ng et al. https://doi.org/10.31436/iiumej.v23i2.2143 2.2 sample preparation the acs synthesized ha powders were compacted into 20 mm disc samples (fig. 2) by a hydraulic press machine (enerpac, usa) at 1000 psi, which was set at a pressure lower than 3000 psi, as recommended by mel et al. [17]. the green samples were then conventionally sintered (carbolite gero, uk) at 1200 °c, 1250 °c and 1300 °c for two hours with a ramp rate of 10 °c/min. the dimension of the green and as-sintered samples was recorded with a digital vernier caliper (mitutoyo, japan) for the shrinkage measurements. prior to characterization, the sintered disc samples were ground with silicon carbide (sic) sandpapers and polished to achieve a 1 μm optical reflective surface. fig. 2: ha green samples. 2.3 characterization and mechanical property evaluation a fourier transform infrared (ftir) spectrum 65 spectrometer (perkin elmer inc., usa) was used to identify the functional groups and composition present in the synthesized powder, at the scan range of 650 to 4000 cm-1. differential scanning calorimetric (dsc)/ thermogravimetric analysis (tga) (ta instruments, usa) was employed to determine the weight loss and phase change of synthesized ha powder, from room temperature to 1400 °c, with a heating rate of 10 °c/min under nitrogen gas environment. bulk density measurement was also performed on the sintered samples using the archimedes’ principle, by taking the theoretical density of ha as 3.156 g/cm3. the microstructure of synthesized and sintered samples was examined via scanning electron microscopy (sem) (sec co. ltd., korea). energy dispersive x-ray (edx) spectroscopy was used to determine the ca/p ratio of the synthesized and sintered samples. the grain size of the sintered samples was measured using the linear intercept method according to astm e112-96. vickers hardness of the sintered samples was evaluated via micro-hardness tester (bowers eseway, uk), with an applied load of 200 gf at a loading time of 10 seconds based on astm e384-99. for each sample, at least five indentations were used to obtain the average hardness and to calculate the standard deviation value. fracture toughness was also obtained via the relationship derived by niihara et al. [18]. 3. results and discussion 3.1 ftir analysis of acs synthesized ha powder the functional groups in the acs synthesized ha powder were identified using ftir and the spectrum is shown in fig. 3. the result confirms that the synthesized powder exhibited the typical spectrum of pure ha powder, with the chemical groups of phosphate group (po4 3-), hydroxyl groups (oh-) and carbonate groups (co3 2-). the distinctive peaks at 1025 cm-1 and 1087 cm-1 are corresponding to the po4 3(v3), while the peak at 962 cm -1 corresponds to the po4 3(v1). on the other hand, weak characteristic peaks observed at 3350 cm-1 and 3570 cm-1 could be related to the ohgroup. the ftir peaks exhibited key characteristics of ha phase. the peaks at 1456, 1420 cm-1 and 874 cm-1 show the presence of co3 2in the samples. similar carbonate bands were also reported in previous studies [1920]. 231 iium engineering journal, vol. 23, no. 2, 2022 ng et al. https://doi.org/10.31436/iiumej.v23i2.2143 fig. 3: ftir spectrum of acs synthesized ha powder. 3.2 edx analysis figure 4 shows that the edx spectrums of acs synthesized and sintered ha samples consist of three main elemental constituents of ha bioceramics, which are calcium (ca), phosphorus (p) and oxygen (o). from the atomic percentage (at %), the calculated ca/p ratio of synthesized biogenic ha powder is 1.60, while the sintered ha bioceramics increased to 1.88 when sintered at 1200 °c and 1250 °c, and reached at 1.97 when sintered at 1300 °c. the obtained ca/p ratio from this work deviated from the theoretical value for pure stoichiometric ha of 1.67. similar observation was reported by ramesh et al. [21] 3570 3350 1644 1456 1420 1087 1025 874 962 element at % ca 12.11 p 7.55 ca/p ratio 1.60 (a) element at % ca 13.59 p 7.27 ca/p ratio 1.87 (b) element at % ca 20.68 p 10.52 ca/p ratio 1.97 (d) element at % ca 25.64 p 13.63 ca/p ratio 1.88 (c) fig. 4: edx spectrum acs (a) synthesized ha powder, sintered ha at (b) 1200 °c, (c) 1250 °c, and (d) 1300 °c. wavenumber (cm-1) transmittance 232 iium engineering journal, vol. 23, no. 2, 2022 ng et al. https://doi.org/10.31436/iiumej.v23i2.2143 3.3 microstructural and grain size analysis figure 5 (a) shows the sem micrograph of the acs synthesized ha powder, which consists of large agglomerates. the microstructural evolution of the acs sintered ha ceramics is presented in fig. 5 (b)-(d). the sem investigation revealed that the average grain size for the sintered ha samples increases with the increase of sintering temperatures. the results show a gradual increase in grain size from 2.14 µm at 1200 °c to 3.70 µm at 1250 °c. as the sintering temperature increased to 1300 °c, the grain size dramatically increased to 6.44 µm. accelerated grain growth in ha samples sintered beyond 1250 °c implied a change in phase stability of ha. 3.4 thermal stability analysis figure 6 shows the differential scanning calorimetric (dsc)/ thermogravimetric analysis (tga) measurement of the acs synthesized ha powder. at 300 °c, a pronounced weight loss of 5.3% was observed from total weight loss of 7.6% of the ha sample. the weight loss could be ascribed to the evaporation of physically adsorbed water molecules. with additional heating upon 500°c, the insignificant weight loss (0.75%) is attributed to the release of interstitial water molecule in the crystal lattice of ha. an endothermic peak at 1000 °c can be postulated as dehydroxylation and decarboxylation of the ha powder. weight loss at higher temperatures may be due to the dissociation of ha to tricalcium phosphate (tcp) and tetracalcium phosphate (ttcp). the decomposition of ha phase is believed to cause the increased in the average grain size and reduced the mechanical properties of the ha. fig. 5: sem images of (a) acs synthesized ha powder and sintered ha at (b) 1200 c, (c) 1250 c, and (d) 1300 c. 5 m 5 m 5 m 5 m a b c d 233 iium engineering journal, vol. 23, no. 2, 2022 ng et al. https://doi.org/10.31436/iiumej.v23i2.2143 fig. 6: dsc/ tga plot of the acs synthesized ha powder. 3.5 mechanical properties the effect of sintering temperature on the relative density, vickers hardness, and fracture toughness of ha ceramics are presented in table 1. the density of acs sintered ha increased from 83.8% at 1200 °c to 88% at 1250 °c. a slight decrease in density (86.7%) was observed when the sintering temperature increased to 1300 °c. the result is in agreement with the grain growth of the sintered ha as shown in the sem images. on the other hand, the vickers hardness of the sintered ha increased from 4.35  0.43 gpa at 1200 °c to a maximum of 5.01  0.39 gpa at 1250 °c. when the sintering temperature reached 1300 °c, the vickers hardness was reduced to 4.03 ± 0.35 gpa, which is corresponding with the reduction in relative density and the grain growth of the sintered ha. this is in agreement with aminzare and co-authors, where the vickers hardness of the sintered biomimetic-synthesized ha decreased from 2.52 gpa to 2.23 gpa when sintered at 1250 °c and 1300 °c, respectively [22]. in the current study, the fracture toughness exhibited similar trends as the hardness, i.e. the fracture toughness increased from 0.67  0.20 mpa.m1/2 to a maximum of 0.88  0.07 mpa.m1/2, when sintered at 1200 °c and 1250 °c, respectively. this was followed by a decrease to 0.71  0.10 mpa.m1/2 when the sintering temperature reached 1300 °c. similarly, the decreased fracture toughness at 1300 °c is related to the decrease of relative density. it is postulated that the reduced density and mechanical properties at 1300 °c was due to the decomposition of ha phase at a high sintering temperature regime (1250 °c) [22-23]. the results also show that calcium-rich ha with the ca/p ratio of 1.88 possessed an overall higher density and mechanical properties as compared to ha with ca/p ratio of 1.97. table 1: the properties of acs sintered ha sintering temp/ holding time grain size (m) relative density (%) vickers hardness (gpa) fracture toughness (mpam1/2) 1200 c/ 2 hrs 2.14 83.8 4.35  0.43 0.67  0.20 1250 c/ 2 hrs 1300 c/ 2 hrs 3.70 6.44 88.0 86.7 5.01  0.39 4.03 ± 0.35 0.88  0.07 0.71  0.10 234 iium engineering journal, vol. 23, no. 2, 2022 ng et al. https://doi.org/10.31436/iiumej.v23i2.2143 4. conclusion the present study revealed that acs synthesized ha samples were successfully synthesized via the calcination and wet chemical precipitation using ark clamshells (anadara granosa) as the calcium precursor. the results also show that acs sintered ha with the ca/p ratio of 1.88 possessed a higher density (88%) and mechanical properties (vickers hardness of 5 gpa and fracture toughness of 0.88 mpa.m1/2) when sintered at 1250 ºc, which shows that the phase stability of ha was retained up to 1250 ºc and the decomposition of ha to tcp and ttcp occurred above 1250 ºc. the finding of this study would promote the recycling and reuse of the animal shells or bones to convert biowaste into value added biomedical products which would help in attaining sustainable development goal targets. future research would encompass further works on two-step or hybrid sintering routes to produce finer microstructure with enhanced mechanical properties. references [1] sadat-shojai m, khorasani mt, dinpanah-khoshdargi e, jamshidi a. (2013) synthesis methods for nanosized hydroxyapatite with diverse structures. acta biomaterialia, 9(8): 75917621. https://doi.org/10.1016/j.actbio.2013.04.012 [2] hongquan z, yuhua y, youfa w, shipu l. (2003) morphology and formation mechanism of hydroxyapatite whiskers from moderately acid solution. materials research, 6: 111-115. retrieved from https://www.scielo.br/pdf/mr/v6n1/v6n1a20.pdf [3] hablee, s, sopyan i, mel, m, salleh, h.m. and rahman, mm. (2018) effect of poly (ethylene glycol) on the injectability, setting behavior and mechanical properties of calcium phosphate bone cement. iium engineering journal, 19(2): 192-202. https://journals.iium.edu.my/ejournal/index.php/iiumej/article/view/913 [4] mo kh, alengaram uj, jumaat mz, lee sc, goh wi, yuen cw. (2018) recycling of seashell waste in concrete: a review. construction and building materials, 162: 751-764. https://doi.org/10.1016/j.conbuildmat.2017.12.009 [5] hembrick-holloman v, samuel t, mohammed z, jeelani s, rangari vk. (2020) ecofriendly production of bioactive tissue engineering scaffolds derived from eggand sea-shells. journal of materials research and technology, 9(6): 13729-13739. https://doi.org/10.1016/j.jmrt.2020.09.093 [6] saharudin sh, shariffuddin jh, nordin ni. (2017) biocomposites from anadara granosa shells waste for bone material applications. iop conference series: materials science and engineering, 257: 012061. retrieved from https://iopscience.iop.org/article/10.1088/1757899x/257/1/012061/pdf [7] musa b, raya i, natsir h. (2016) synthesis and characterizations of hydroxyapatite derived blood clam shells (anadara granosa) and its potency to dental remineralizations. 12(4): 527-38. retreived from https://www.ripublication.com/ijac16/ijacv12n4_04.pdf [8] bee sl, hamid za. (2020) hydroxyapatite derived from food industry bio-wastes: syntheses, properties and its potential multifunctional applications. ceramics international, 46(11, part a): 17149-17175. https://doi.org/10.1016/j.ceramint.2020.04.103 [9] pu'ad nm, koshy p, abdullah hz, idris mi, lee tc. (2019) syntheses of hydroxyapatite from natural sources. heliyon, 5(5): e01588. https://doi.org/10.1016/j.heliyon.2019.e01588 [10] núñez d, elgueta e, varaprasad k, oyarzún p. (2018) hydroxyapatite nanocrystals synthesized from calcium rich bio-wastes. materials letters, 230: 64-68. https://doi.org/10.1016/j.matlet.2018.07.077 [11] vecchio ks, zhang x, massie jb, wang m, kim cw. (2007) conversion of bulk seashells to biocompatible hydroxyapatite for bone implants. acta biomaterialia, 3(6): 910-918. https://doi.org/10.1016/j.actbio.2007.06.003 235 https://doi.org/10.1016/j.actbio.2013.04.012 https://www.scielo.br/pdf/mr/v6n1/v6n1a20.pdf https://doi.org/10.1016/j.conbuildmat.2017.12.009 https://doi.org/10.1016/j.jmrt.2020.09.093 https://doi.org/10.1016/j.ceramint.2020.04.103 https://doi.org/10.1016/j.heliyon.2019.e01588 https://doi.org/10.1016/j.matlet.2018.07.077 iium engineering journal, vol. 23, no. 2, 2022 ng et al. https://doi.org/10.31436/iiumej.v23i2.2143 [12] bramhe s, kim tn, balakrishnan a, chu mc. (2014) conversion from biowaste venerupis clam shells to hydroxyapatite nanowires. materials letters, 135: 195-198. https://doi.org/10.1016/j.matlet.2014.07.137 [13] onoda h, yamazaki s. (2016) homogenous hydrothermal synthesis of calcium phosphate with calcium carbonate and corbicula shells. journal of asian ceramic societies, 4(4): 403406. https://doi.org/10.1016/j.jascer.2016.10.001 [14] alif mf, aprillia w, arief s. (2018) a hydrothermal synthesis of natural hydroxyapatite obtained from corbicula moltkiana freshwater clams shell biowaste. materials letters, 230: 40-43. https://doi.org/10.1016/j.matlet.2018.07.034 [15] pal a, nasker p, paul s, chowdhury ar, sinha a, das m. (2019) strontium doped hydroxyapatite from mercenaria clam shells: synthesis, mechanical and bioactivity study. journal of the mechanical behavior of biomedical materials, 90: 328-336. https://doi.org/10.1016/j.jmbbm.2018.10.027 [16] azis y, jamarun n, arief s, nur h. (2015) facile synthesis of hydroxyapatite particles from cockle shells (anadara granosa) by hydrothermal method. oriental journal of chemistry, 31:1099-1105. [17] mel m, abdeen fr, and sopyan i. (2011). fabrication of ceramic membrane chromatography for biologics purification. iium engineering journal, 12(4): 115-124. [18] niihara k, morena r, hasselman dp. (1982) evaluation of kic of brittle solids by the indentation method with low crack-to-indent ratios. journal of materials science letters, 1(1): 13-16. [19] ramesh s, natasha an, tan cy, bang lt, ching c.y chandran h. (2016) direct conversion of eggshell to hydroxyapatite ceramic by a sintering method. ceramics international, 42(6): 7824-7829. https://doi.org/10.1016/j.ceramint.2016.02.015 [20] kamalanathan p, ramesh s, bang lt, niakan a, tan cy, purbolaksono j, chandran h, teng wd. (2014) synthesis and sintering of hydroxyapatite derived from eggshells as a calcium precursor. ceramics international, 40(10): 16349-16359. https://doi.org/10.1016/j.ceramint.2014.07.074 [21] ramesh s, loo zz, tan cy, chew wk, ching yc, tarlochan f, chandran h, krishnasamy s, bang lt, sarhan aa (2018) characterization of biogenic hydroxyapatite derived from animal bones for biomedical applications. ceramics international, 44(9): 10525-10530. https://doi.org/10.1016/j.ceramint.2018.03.072 [22] aminzare m, eskandari a, baroonian mh, berenov a, hesabi zr, taheri m, sadrnezhaad sk. (2013) hydroxyapatite nanocomposites: synthesis, sintering and mechanical properties. ceramics international. 39(3): 2197-2206. https://doi.org/10.1016/j.ceramint.2012.09.023 [23] ramesh s, tan cy, hamdi m, sopyan i, teng wd. (2007) the influence of ca/p ratio on the properties of hydroxyapatite bioceramics. in international conference on smart materials and nanotechnology in engineering. international society for optics and photonics. 6423: 64233a. 236 https://doi.org/10.1016/j.matlet.2014.07.137 https://doi.org/10.1016/j.matlet.2018.07.034 https://doi.org/10.1016/j.jmbbm.2018.10.027 https://doi.org/10.1016/j.ceramint.2014.07.074 microsoft word 205 completed iium engineering journal, vol. x, no. x, 200x ahmadi 17 remarks on deformation in snow with residual stress and gravitational force by detonation impact siavosh ahmadi department of mathematics, tehran north branch, islamic azad university tehran, iran. s_ahmadi@iau-tnb.ac.ir abstract: estimation of strain (deformation) and strain energy at the time of an explosion has been undertaken in the present investigation. a basic concept of explosive pressure which is required for the estimation of strain and strain energy has been drawn from the underwater explosion with suitable modification to the present studies. one of the most significant aspects of the present investigation is to augment the model by accounting it for gravitational force and residual stresses which are of realistic in nature. studies consist of computational aspect by observing the variation of strain and strain energy with respect to material parameters such as elastic modulus (e), poisons ratio (ν), density (ρ), and flow parameters such as peak pressure (pm), sound velocity (vs), and length of snow slab (l). one of the interesting observation found in the computational aspect is, the deformation is found to decrease as the velocity of sound (vs) in snow increases which appears to be strange but found factual. the model has been compared with the other existing papers in the literature and found that, the present model yields to better results. abstrak: anggaran regangan (canggaan) dan tenaga regangan pada masa letupan diambil kira dalam kajian ini. konsep asas tekanan letupan yang diperlukan untuk anggaran regangan dan tenaga regangan diperolehi daripada letupan bawah air dengan pengubahsuaian yang sesuai dalam kajian terkini. antara aspek penting dalam kajian ini adalah penambahan model dengan mengambil kira daya graviti dan tegasan sisa yang sebenar. kajian terdiri daripada aspek pengiraan, dengan memerhatikan variasi regangan dan tenaga regangan terhadap parameter bahan seperti modulus anjal (e), nisbah poisson’s (ν), ketumpatan (ρ), dan parameter aliran seperti tekanan puncak (pm), halaju bunyi (vs), dan panjang papak salji (l). antara pemerhatian menarik yang ditemui dalam aspek pengiraan ialah, canggaan didapati berkurangan ketika halaju bunyi (vs) salji bertambah. walaupun ini nampak asing, tetapi ianya terbukti benar. model dibandingkan dengan kertas kerja lain dan didapati bahawa, model terkini memberikan keputusan yang lebih tepat. keywords: avalanche dynamics; fracture mechanics; detonation pressure 1. introduction avalanches in snow bound hilly regions are basically due to instability caused in the snow pack lying on the slopes. the causes for such instability are many. it may be due to pressure metamorphism [1] or due to temperature metamorphism [2] or it may be due to wind induced drift phenomenon [3-4]. the studies on avalanches will not only help in forecasting of it (much before the eventuality to occur) but also in taking precaution for the mitigation aspect (preserving either the structure or the lives once the forces iium engineering journal, vol. x, no. x, 200x ahmadi 18 (avalanche) can be estimated beforehand). also, studies help in minimizing the property damage as result of an avalanche. in view of its importance, studies pertaining to avalanches are undertaken in the present investigations. fracture mechanics deals with the propagation of crack as a result of an impact on the material and the relations there on stress and strain with material properties [elastic modulus (e), poison’s ratio (ν), density (ρ), cross sectional area (a), crack length (a), and so forth] [5-6]. since instability in snowpack ultimately results into an avalanche, it is understood that, instability may induce cracks in the snowpack before sliding from the top hill. this crack, it is believed that, has links with fracture mechanics for studying stress and strain aspect of snow as a material. basic concepts of fracture mechanics have been used in analyzing the avalanche related aspects. avalanches are both natural and artificial one. in a natural avalanche, the release of snow mass from the top of the hill is by the natural phenomenon which is described in the earlier paragraphs. whereas in artificial ones, the release of an avalanche, is basically due to an explosion in the snowpack from the remote location. this method of artificial triggering is by and large gaining popularity in snow bound hilly regions in the western countries since much of the habitation is located in the western part of the globe. moreover this method is safe and economical one when compared to the destruction (avalanche) it may cause when released naturally. the studies in the present investigations have been basically focused onto the estimation of important flow parameters [velocity and acceleration] during the explosion in the snowpack. in addition to the focused parts, the studies have been also concentrated onto the estimation of other parameters such as strain and strain energy parameters. as is well-known that strain and strain energy is one of the important parameters in the estimation of avalanche formations as a result of an explosion. it is generally noticed during the artificial triggering that, not all explosive detonation results into an avalanche. though there are various other parameters also required to be estimated ( metamorphic state of snow pack, aging of snow pack, slope aspect and so forth) before going for an avalanche forecasting however, it is generally believed that strain (εy) and strain energy (es) are the most effective parameters to estimate and quantify for it during the explosion aspect. in view of its importance of these parameters, the present paper has been stressed on strain (εy) and strain energy (es) parameters estimations in addition to velocity and acceleration aspects. 2. analysis the model has been aimed at first obtaining important flow parameters [velocity, maximum velocity, and acceleration] before going for the determination of strain (εy) and strain energy (es). 3. estimation of flow parameters the relation between the pressure and velocity at the time of an explosion on the snowpack (lying on slope of hill) is given by [7] 2.p(t) – ρ.vs.v = m dv/dt (1) where p(t) is the pressure, vs is velocity of sound in medium, v is the velocity of projectile, ρ is the density of the water, m is the mass per unit area (water).this relation has been modified to our present requirement of snow as a material. the proposed formula is written as : 2.p(t) – ρ.vs.v + σg – σr = m dv/dt (2) iium engineering journal, vol. x, no. x, 200x ahmadi 19 where σg , σr ρ, and v are gravitational and residual stress, density of snow, and velocity of the snow pack respectively. p(t) is taken to be of the form from ref. [8] as p(t) = pm .exp(-t/t) (3) where pm is the peak pressure, t is the time, and t is the time decay factor. this peak pressure is due to an explosion. schewizer [9] has correlated the term (σg – σr) to snow density (ρ), gravity (g), and to slab depth by (fig. 1) σg / σr =1.5, σ = σg – σr =(1/3) ρ.g.h.sinθ (4) where h is snow slab depth and θ is the slope angle. this relation [eqn.(4)] has been successfully employed in our earlier studies [10]. fig. 1: flow geometry. in order to solve eqn.(2), we need to have one condition (initial or boundary) and this has been taken to be of the from v(0) = 0. using this condition eqn.(2) simplifies to v(t) = [2.pm.t/( ρ.(l vs.t))].{exp(-vs/l) – exp(-t/t)} + [(g.h.sinθ)/3].{1exp(-vs.t/l)} (5) having known velocity, maximum velocity of the snowpack (vmax) soon after the explosion can be estimated by equating its gradient to zero. that is dv/dt = 0. taking differential of (5) with respect to ‘t’ and equating it to zero we get the time to achieve this maximum velocity. tvmax = l.t.ln{[σ.( t.vs l) + 2.pm.vs.t ] / (2.pm.l)}/(vs.t l) (6) substituting this ‘tvmax’ for ‘t’ in equation (5), we get maximum velocity (vmax) as: vmax = [2.pm.t/(ρ.[l-vs.t])].{{[σ.(vs.t-l) + 2pm.vs.t]/(2.pm.l)} v s .t/(l-v s .t) – { [σ.(vs.t-l) + 2pm.vs.t]/(2.pm.l)} l/(l-v s .t) }} + σ/(ρ.vs) [1-{[σ.(vs.t-l) + 2pm.vs.t]/(2.pm.l)} v s .t/(l-v s .t) }] (7) knowing velocity from equation (5), acceleration can be obtained by taking differentiation with respect to “t”. that is a(t) = dv(t)/dt = [2.pm.t/( ρ.(l vs.t))].{(-vs/l)exp(-vst/l)+(1/t) exp(-t/t)} + [(g.h.sinθ)/3].{(vs/l exp(-vs.t/l)} (8) estimation of strain and strain energy from the classical theory of elasticity [5,6], deformation energy (wdef), stress (σyy) in y direction, and strain (εy) are related by iium engineering journal, vol. x, no. x, 200x ahmadi 20 wdef = ∫ σyy dεy (9) where σyy and εy are normal stress and normal strain respectively. σyy and εy are related by [5-6] εx = [σxx ν (σyy + σzz)] / e (10) εy = [σyy ν(σxx + σzz)] / e (11) where e, ν, σxx , σyy, σzz , εx are elastic modulus, poison’s ratio, normal stress in x, y and z directions, and normal strain in the x-direction respectively. assuming σzz and εx both equal to zero, eqn.(10) and (11) simplifies to εy =(1/e) σyy (1-ν 2 ) (12) σyy = e.εy/(1-ν 2 ) (13) we also know that kinetic energy (ke) [wk] is related by ke = wk = ½ m.v 2 max (14) it is assumed that, explosion energy is same as the deformation (strain) energy and is equated to kinetic energy. we get ½ ρ.v2max = {e/[2.(1-ν 2 )].} ε2y (15) substituting for vmax from equation (7) in eqn.(15), we get deformation (normal strain(εy)) as: εy = [ρ.(1-ν 2 )/e] 0.5 . [2.pm.t/(ρ.[l-vs.t])].{{[σ.(vs.t-l) + 2pm.vs.t]/(2.pm.l)} v s .t/(l-v s .t) – {[σ.(c.t-l) + 2.pm.vs.t]/(2.pm.l)} l/(l-v s .t) }} + σ/(ρ.vs) [1-{[σ.(vs.t-l) + pm.vs.t]/(2.pm.l)} v s .t/(l-v s .t) }] (16) substituting εy in equation (13) and using eqn.(9) we get strain energy (es) which is assumed to be same as deformation energy (wdef) as: es = {e/[2.(1-ν 2 )].} ε2y (17) 4. results and discussion flow parameters velocity (v), acceleration (a), maximum velocity (vmax), strain (εy), and strain energy (es) have been computed and their variation have been observed with material parameters such as density, velocity of sound in the medium, elastic modulus (e), and poison’s ratio. the computed values have been shown in fig. 2-6. the present computed values have been compared with the model having no gravitational and residual stress [10]. in order to compute flow parameters we need data on peak pressure pm, ρ, e, t, t, ν, εy, and the same has been taken from ref [11-12]. these data have been shown in table 1. the results indicate, the present computed values are lower (except for density, and velocity of sound vs) in comparison to without gravitation and residual stresses [the solid line in fig. 2-6 indicate for without gravitation and residual stresses]. the reason for such lower values could be attributed due to inclusions of the more realistic parameters in the present investigations which resulted into more accurate values. one of the iium engineering journal, vol. x, no. x, 200x ahmadi 21 interesting observations of velocity computation is, the present variations of v with vs is found to be increasing and realistic whereas without gravitational and residual terms is found decreasing. the reason for this discrepancy could be basically due to subtraction of velocity of sound from peak pressure terms [eqn.(2)]. the time delay factor t did not find much effect on the maximum velocity computations [fig. 3].the results on acceleration [fig. 4] is found to be very distinct when compared with and without gravitational and residual stresses. the justification for this discrepancy could be given in similar conjunction with that of velocity computations. the variation of acceleration with pm [fig. 4] also found not to yield significant variations in comparison to earlier model [10]. the results on strain (εy) with vs, l (slab length) and t indicates that, the addition of gravitation and residual increases the strain component whereas with pm and ρ it decreases [fig. 5]. the variation of strain energy (es) with e, ν, and with εy shows that, strain energy increases with increase in e, ν and εy [fig. 6]. also it is observed that, the present computed values of es with εy are found to be greater than that of without gravitational and residual stress. all the computed results [fig. 2-6] have found to agree with the physics of flows and deformation property. for instance, increase in strain with peak pressure and decrease with elastic modulus adheres to results from classical physics. table 1: data of flow parameters. parameters typical values range peak pressure : pm 300 pa 200-300 distance of blast center: r 90m 90-9000 time decay : t 3 s 2-15 arrival time : t 0.1 s 0-2 density : ρ 200 kg/m3 100-400 slab length : l 4 m 2-8 sound speed in snow : vs 300 m/s 100-300 elastic modulus : e 10 mpa 0.5-10 poison ratio : ν 0.2 0.1-0.3 strain : εy 5.7×10 -5 2×10 -5 – 10 4 iium engineering journal, vol. x, no. x, 200x ahmadi 22 fig. 2: variation of velocity (v) with flow parameters (vs, l). fig. 3: variation of maximum velocity (vmax) with flow parameters (vs,l). fig. 4: variation of acceleration (a) with flow parameters (vs, l). fig. 5: variation of strain (εy) with flow parameters (vs, l). 100 120 140 160 180 200 220 240 260 280 300 0.005 0.01 0.015 0.02 0.025 0.03 100 120 140 160 180 200 220 240 260 280 300 9.2 9.4 9.6 9.8 10 10.2 v vs with gravitational and residual forces(rigth column) without gravitational and residual forces(left column) 2 3 4 5 6 7 8 9.4 9.6 9.8 x 10 -3 2 3 4 5 6 7 8 9.8 10 10.2 v l 100 120 140 160 180 200 220 240 260 280 300 0 0.01 0.02 0.03 100 120 140 160 180 200 220 240 260 280 300 0.01 0.02 0.03 0.04 vmax vs 100 120 140 160 180 200 220 240 260 280 300 0 0.05 0.1 a v s 0 0.005 2 3 4 5 6 7 8 0 0.01 0.02 a l 0.005 0.01 100 120 140 160 180 200 220 240 260 280 300 0 1 2 x 10 -4 100 120 140 160 180 200 220 240 260 280 300 0 1 2 x 10 -4 εγ vs 2 3 4 5 6 7 8 4.2 4.22 4.24 4.26 4.28 4.3 4.32 4.34 4.36 x 10 -5 2 3 4 5 6 7 8 5.64 5.66 5.68 5.7 5.72 5.74 5.76 5.78 5.8 x 10 -5 εγ l iium engineering journal, vol. x, no. x, 200x ahmadi 23 fig. 6: variation of strain energy with strain, elastic modulus. 5. conclusion the present studies deal with the estimation of strain and strain energy at the time of an explosion as these parameters plays significant role in forecasting of an avalanche. the model has been developed with the basic concepts from underwater explosions with suitable modification to the present model. the flow variables (velocity, maximum velocity, and acceleration, strain and strain energy) have been computed for various material parametric effects (density, peak pressure, slab length, elastic modulus, poisons ratio, velocity of sound in medium) and found that the present computed results yield better results when compared with the earlier models. also, the model observed to yield the results which could be quantifiable with the physics of flow and deformation theory from classical theories. the results need to be quantifiable with the avalanche formation which is our continued effort. references [1] palmer,a.g and j.r.rice.the growth of slip surfaces in the progressive failure of overconsolidated clay.proc.r.sac.london.scr.a, 332 (1591),518-527,1973. [2] p.s.negi, r.k aggrawal, d n sethi and uttam chand, “measurment of thermal conductivity of seasonal snow by a pc based transient thermal probe method”, proceedings international symposium on snow monitoring and avalanches(issma-2004), snow and avalanche study establishment(sase), manali, india, 67-70(2004). [3] ronald i, perla m, and martinelli.jr,”avalanche hand book” u.s.dep.agric.,agric.handb.489,254p,1978. [4] paul m.b.fohn,”snow transport over mountain crests”, journal of glaciology,vol 26,469-492,(1980) [5] dowling. n.e. : mechanical behavior of materials (1993).m. young, the technical writer's handbook. mill valley, ca: university science, 1989. [6] kannien, m.f. and popelar, c.h.: advanced fracture mechanics oxford university press (1985). [7] hollyer rs. direct shock-wave damage to merchant ships from non-contact derwater explosion. trans sname 1959;67:773–84. [8] c.f. hunga,*, p.y. hsua, j.j. hwang-fuub: elastic shock response of an air-backed plate to underwater explosion(in detonation file). trans sname 2005:151-158. [9] schweizer j. review of dry snow slab avalanche release. j. cold region science and technology, 30, 43-57 (1999). 3 3.5 4 4.5 5 5.5 6 x 10 -5 0.008 0.01 0.012 0.014 0.016 0.018 3 3.5 4 4.5 5 5.5 6 x 10 -5 2 4 6 8 10 12 x 10 -3 left column rigth column es ε γ 0.1 0.15 0.2 0.25 0.3 0.35 0.0166 0.0168 0.017 0.0172 0.0174 0.0176 0.0178 0.018 0.0182 0.0184 0.1 0.15 0.2 0.25 0.3 0.35 3.75 3.8 3.85 3.9 3.95 4 4.05 4.1 4.15 4.2 x 10 -3 es ν strain = 0.00003 strain = 0.00005 iium engineering journal, vol. x, no. x, 200x ahmadi 24 [10] siavosh ahmadi and r.n. pralhad : modeling propagation of explosive shock waves in snow on hilly top and prediction towards an avalanche release, proceedings34 national society for fluid mechanics and fluid power, bits mesra ranchi, dec. 10-12, 2007. [11] donald albert: reduction of blast noise by a snow cover, primary subject classification: 21.3.4; secondary subject classification: 72.8, 2002. [12] virendra kumar and h. muthurajan : “artificial triggering of avalanches using explosives”, proceedings international symposium on snow monitoring and avalanches(issma-2004): snow and avalanche study establishment(sase), manali, india., 137-144, 2004. microsoft word 59-222-3 press.doc iium engineering journal, vol. 7, no. 2, 2007 h. el zakhem 1 combining moderate pulsed electric fields with temperature and with organic acids to inactivate escherichia coli suspensions h. el zakhem 1* , j. l. lanoiselle 2 , n. i. lebovka 3 , m. nonus 4 , h. allali 4 , and e. voroviev 4 1 department of chemical engineering,university of technology of compiègne, centre de recherche de royallieu; university of balamand, faculty of engineering, pobox: 100 tripoli, lebanon henri.el-zakhem@utc.fr 2 department of chemical engineering,university of technology of compiègne, centre de recherche de royallieu. jean-louis.lanoiselle@utc.fr 3 department of chemical engineering,university of technology of compiègne, centre de recherche de royallieu; institute of biocolloidal chemistry named after f.d. ovcharenko, nas of ukraine 2, blvr. vernadskogo, kyiv 03142, ukraine. nikolai.lebovka@utc.fr 4 department of chemical engineering,university of technology of compiègne, centre de recherche de royallieu. maurice.nonus@utc.fr abstract : the aim of this work was to study the efficiency of inactivation of escherichia coli cells in aqueous suspensions using combined moderate pulsed electric field (pef) and thermal treatments. the inactivation kinetics of e. coli cells in aqueous suspensions (1 wt%) was monitored using conductometric technique. the electric field strength e was within 5-7.5 kv/cm, the effective pef treatment time peft was within 00.75 s, the pulse duration ti was within 0.3-1 ms, the medium temperature was 30-50°c, and the time of thermal treatment tt was within 0-7000 s. the organic acid concentration was within 0-0.5 g/l.the damage of e. coli was accompanied by release of intracellular components. the synergy between the pef and thermal treatments in e. coli inactivation was clearly demonstrated. the damage efficiency was noticeably improved by addition of organic acids, especially lactic acid. key words: escherichia coli, pulsed electric fields, thermal treatment, electrical conductivity, organic acids. 1. introduction pulsed electric field is a new technology recently studied and designated for inactivation of micro-organisms. promising results were obtained using high electric fields within the intensity of 20-80 kv/cm. the pulsed electric field (pef) application to an aqueous suspension of colloidal bio-organisms can result in noticeable changes in the structure of cells and in the state of their aggregation. electric pulses of high intensity and of small duration (typically 1–100 µsec) cause temporary loss of the cell membrane iium engineering journal, vol. x, no. x, 2007 h. el zakhem 2 permeability (electroporation) and ion leakage [1] without significant temperature increase and undesirable effects on cell components. numerous studies have investigated the effect of pef applications for microbial inactivation [2], electrofusion of cells [3], and transport of nanoparticles across the cell wall [4]. electropulsation treatment of some microbial species (e. coli, s. cerevisiae) is expected to be a promising method for recovery of the homogeneous and heterogeneous intracellular proteins having wide biotechnological applications [5,6]. 2. materials and methods 2.1 preparation of e. coli suspensions in this research cells of gram negative bacteria escherichia coli (atcc strain #25255) were used. e. coli was cultured in nutrient broth (biokar diagnostics, beauvais, france). overnight cultures were inoculated in 100 ml of an adapted medium composed from 16 g/l of tryptone, 10 g/l of yeast extract, 5 g/l of lactose, 1.5 g/l of fresh bile, 5 g/l of nacl, 9.4 g/l of k2hpo4, and 2.2 g/l of kh2po4. all chemical products were from fisher scientific (leicestershire, uk). then cultures were grown in a shaker at 200 rpm (infors ag, bottmingen, switzerland) at 37°c for 24 hours. cells were harvested by centrifugation using the sigma 4k10 centrifuge (bioblock scientific, osterode, germany) at 3000 g and at 4°c for 3 min. then cells were washed by saline water, centrifuged again under the same conditions, and the supernatant solution was removed. the saline water used in this study had conductivity of 300 µs/cm at 25°c, and the background electrolyte (nacl) was used for the suspension conductivity adjustment. the above procedure was repeated at least 3 times in order to remove residual substances from the original samples of cells. the suspensions were prepared by one minute vortexing (rotation speed 100 rpm and amplitude 4.5 mm) of centrigugated cells with the saline water (top mix bioblock scientific, germany). the agitation and centrifugation conditions were rather gentle, in order to prevent any additional damage of the cells. the viability of cells at the beginning was 98%. finally, the exact concentrations were calculated on the basis of the dry matter content after drying of suspensions at 105°c for 24 h. in pef thermal treatment experiments, the aqueous e. coli suspensions had dry matter concentration (after heating in the oven at 105ºc for 24h) about 1 wt%, which corresponds to the cellular density of approximately 3.5 x 10 10 cells/ml. in experiments with organic acids additives, the initial cellular density of e. coli cells was approximately 14 x 10 8 cells/ml. 2.2 analysis instruments k-type thermocouple, connected to the data logger thermometer center 305/306 (jdc electronic sa, yverdon-les-bains, switzerland) was used to control the temperature. following pef-thermal exposure, 2 ml of each replicate was centrifuged at 7903 g for 5 min, and the supernatant was used for uv absorption measurements by anthelie advanced spectrophotometer (secomam, domont, france). the wavelength range was within 190 340 nm (with the precision of ±1 nm). the path length of the quartz cell (starna, optiglass ltd, essex, uk) was 5 mm and the scan speed was 1800 nm/min. iium engineering journal, vol. 7, no. 2, 2007 h. el zakhem 3 in experiments with organic acids additives the treated and untreated suspensions were diluted by physiological water and plated (nutrient agar, biokar diagnostics, beauvais, france) in three parallels. the plates were incubated at 37°c for 24 h and cells reduction was expressed by calculating log(no/n). each experiment was repeated, at least, in triplicate to calculate the mean value of the experimental data and the standard deviations. 2.3 pef treatment in pef-thermal treatment experiments, suspensions were treated by pulsed electric field at the field strength e = 5 kv/cm, and simultaneously heated within the temperature range t = 30-50°c, while in organic acid additives experiments the pulsed electric field strength e was 7.5 kv/cm and samples were treated at ambient temperature. the pef generator, 1500 v–20 a (service electronique utc, compiègne, france) provided monopolar pulses of near-rectangular shape. the trains of pulses were used for the pef treatment. an individual train consisted of n pulses with the pulse duration ti and pulse repetition time ∆t. there was a pause ∆tt after each train, and then polarity of the next train was changed to the opposite. suspensions were pumped in the continuous flow treatment chamber (osu-4b, ohio state university, u.s.a.) through six co-field flow, tubular stainless steel electrode gaps, connected in series. the suspension temperature was regulated after each pair of gaps using a water thermostat maintained at the required temperature t. pef-thermal treatment experiments were carried out with the electric field strength e = 5 kv/cm, number of pulses by train n = 1000, pulse duration ti = 10 -3 s, pulse repetition time ∆t = 5 x 10 -2 s, number of trains n = 100-150, and inter-train time ∆tt = 1 s. all the output data (resistance, current, voltage, and temperature) were recorded using a data logger and software developed by service electronique utc, compiègne, france. the pef treatment time during one train was nti. the effective pef treatment time peft was calculated as [7] / pef i g t nt nw w= (1) where wg = ngsh is the treatment volume, s = πr 2 , r = 0.115 cm is the radius of a cylindrical electrode, h = 0.29 cm is the distance between the electrodes, ng = 6 is the number of treatment chambers, w = 50 cm 3 is the total volume of suspension. the effective pef treatment time peft corresponds to the thermal treatment time tt = n(n∆t+∆tt). at such protocol of the pef treatment, n∆t>>∆tt and tt can be approximated as tt ≈ tpef (∆t/ti )(w/wg) ≈ 3.46 x 10 4 tpef (2) the electrical conductivity of suspension σ was measured with a conductivity meter inolab ph/cond level 1 (wtw, weilheim, germany) at the frequency of 50 hz. the electrical conductivity was compared under different modes of pef-thermal treatments. the conductivity disintegration index z was estimated as [8] iium engineering journal, vol. x, no. x, 2007 h. el zakhem 4 )/()( max ooz σσσσ −−= (3) where σo is the initial electrical conductivity of the suspension and σmax is the saturation electrical conductivity of the suspension with maximally disintegrated cells. the value of σmax was estimated by measuring the electrical conductivity of a suspension initially treated by pef at 50°c during tpef = 0.12 s and then heated at 70°c during 1 hour. after such electrical and thermal treatment, the disintegration index was z ≈ 1 and the surviving ratio s ≈ 1-zd, i.e., the ratio of the number of undamaged cells to the total number of cells (values obtained by direct colony counting in the agar plates), was s ≈ 1.1 x 10 5 cfu/ml /3.5 x 10 10 cfu/ml ≈ 3.14 x 10 -6 . in organic acid additive experiment series, batch treatment chamber was used. experiments were carried out with electric field strength e = 7.5 kv/cm, number of pulses by train n = 50, pulse duration ti = 0.3 x 10 -3 s, pulse repetition time ∆t = 10 x 10 -2 s, number of trains n = 50, and inter-train time ∆tt = 40 s. the pulsed electric field effective treatment time tpef = n ti n = 0.75 s. 3. results and discussion the electrical conductivity measurements of e. coli suspensions in the course of treatment time reveal the conductivity disintegration index z kinetics shown in fig. 1. theses results were also confirmed by the direct counts on petri dishes. the conductivity disintegration index z grows with the pef treatment time (tpef), the thermal treatment time (tt) and the temperature t increase. to achieve a high e. coli disintegration degree at only thermal treatment, a long treatment time is required, while, by combining pef with thermal treatment noticeable increase of the conductivity disintegration index z was observed. for example for t = 3600 s, the disintegration index of combined pef thermal treatment was approximately 1, 4 and 1.3 times greater than the disintegration index obtained with sole thermal treatment at t = 30°c, 40°c and 50°c respectively. furthermore, disintegration index z reached approximately 1 after tt = 4000 s with combined pef-thermal treatment. therefore, synergism between the simultaneously applied electric and thermal treatments is evidently present. the absorbance spectra of the supernatant solutions for untreated and pef-thermally treated 1.0 % (wt) aqueous suspensions of e. coli were shown in fig. 2. the effective pef treatment time was peft ≈ 0.116 s, which corresponds to the thermal treatment time tt ≈ 4000 s (eq.(2)). the supernatant solutions were analysed after centrifugation of the bacterial suspensions. the absorbance analysis evidently reveals release of the intracellular components because absorbance values of pef thermally treated suspensions are greater than absorbance values of untreated e. coli suspension. increase of the treatment temperature t leads to the peak intensity increase at the wavelength λmax ≈ 260 nm (a ≈ 0.4, 0.75 and 1.06 for t = 30, 40 and 50ºc respectively). peak at λmax ≈ 260 nm corresponds to the released nucleic acids [9], and the absorbance analysis evidence the leakage of nucleic acids owing to the e. coli cells damage induced by pef-thermal treatments. iium engineering journal, vol. 7, no. 2, 2007 h. el zakhem 5 fig. 1: the electrical conductivity disintegration index z versus effective pef treatment time (tpef) and thermal treatment time (tt) at different temperatures t. error bars are the standard deviations. fig. 2: absorbance spectra of the supernatant solutions for the pef-thermally treated 1.0 % (w/w) aqueous suspensions of e. coli at different temperatures iium engineering journal, vol. x, no. x, 2007 h. el zakhem 6 the effects of addition of the organic acids, such as citric, malic and lactic acids, on the pef treatment efficiency was studied. the advantage of theses acids is that they can be used as food additives, or even occur naturally in some fruit juices. the lactic acid seems to be the most efficient with 8 log cycles of destruction (fig. 3). lactic acid has greater effect than other organic acids because lactic acid, in addition to its antimicrobial property due to the lowering of the ph, also functions as a permeabilizer of the gram-negative bacterial outer membrane [10] and may act as a potentiator of the effects of pulsed electric fields. 0 1 2 3 4 5 6 7 8 9 0 0.25 0.37 5 0.5 acid concentration , g/l l o g ( n 0 /n ) pef + lactic acid pef + malic acid pef + citric acid fig. 3: histogram of the effects of combining organic acids with pef treatments. error bars are the standard deviations. we can suppose certain stagnation of the effect of lactic acid after 0.375 g/l concentration as well as continuous increasing of the efficiency with the increase of citric acid concentration. 4. conclusions we have demonstrated that measurement of electrical conductivity during pef treatment of e. coli suspensions correlated with the petri dishes plating and could be used for monitoring of the extent of cell damage. the synergy between the pef and thermal treatments in e. coli inactivation was clearly shown. the release of nucleic acids increased with temperature increase in the pef-thermal treatments. the damage efficiency was noticeably improved by addition of organic acids in small concentrations (corganic acid ≤ 0.5 g/l) and 8 log cycles reduction was reached by using 0.375 g/l of lactic acid. 5. acknowledgement the authors thank dr. n.s. pivovarova and dr. christo hilan for their help with the manuscript preparation. iium engineering journal, vol. 7, no. 2, 2007 h. el zakhem 7 6. references [1] j. c. weaver and yu.a. chizmadzhev. “theory of electroporation: a review”. bioelectrochemistry and bioenergetics 41, pp. 135 – 160, 1996. [2] g. v. barbosa-canovas, m. m. gongora-nieto, u. r. pothakamury and b. g. swanson. “preservation of foods with pulsed electric fields”. academic press, london, 1998. [3] j. teissié, n. eynard, m.c. vernhes, a. bénichou, v. ganeva, b. galutzov and p.a. cabanes. “recent biotechnological developments of electropulsation. a prospective review”. bioelectrochemistry 55, pp. 107 112, 2002. [4] c. p. jen, y. h. chen, c. s. fan, c. s. yeh, y. c. lin, d. b. shieh, c. l. wu, d. h. chen and c. h. chou. “a nonviral transfection approach in vitro: the design of a gold nanoparticle vector joint with microelectromechanical systems”. langmuir 20, pp. 1369 1374, 2004. [5] t. ohshima, y. hama and m. sato. “releasing profiles of gene products from recombinant escherichia coli in a high-voltage pulsed electric field”. biochemical engineering journal 5 pp 149 155, 2000. [6] v. ganeva, b. galutzov and j. teissié. high yield electroextraction of proteins from yeast by a flow process. “high yield electroextraction of proteins from yeast by a flow process”. analytical biochemistry 315, pp. 77 84, 2003. [7] h. el zakhem, j. l. lanoisellé, n. i. lebovka, m. nonus and e. vorobiev. “behavior of yeast cells in aqueous suspension affected by pulsed electric field”. journal of colloid and interface science 300, pp. 553-563, 2006. [8] e. vorobiev and n. i. lebovka. “extraction of intercellular components by pulsed electric fields”. in pulsed electric field technology for food industry: fundamentals and applications; raso, j., heinz, v., eds.; springer: new york, pp. 153–193, 2006. [9] h. el zakhem, j. l. lanoisellé, n. i. lebovka, m. nonus and e. vorobiev. “the early stages of saccharomyces cerevisiae yeast suspensions damage in moderate pulsed electric fields”. colloids and surfaces b: biointerfaces 47 pp. 189-197, 2006. [10] h.-l. alakomi, e. skyttä, m. saarela, t. mattila-sandholm, k. latva-kala, and i. m. helander. “lactic acid permeabilizes gram-negative bacteria by disrupting the outer membrane”. applied and environmental microbiology 66, pp. 2001-2005, 2000. 7. nomenclature e pulsed electric field strength kv/cm h distance between electrodes cm n number of pulses by train n number of trains ng number of treatment chambers r radius of a cylindrical electrode cm s surviving ratio ti pulse duration s tt thermal treatment time s peft effective pef treatment time s t suspension temperature °c iium engineering journal, vol. x, no. x, 2007 h. el zakhem 8 wg treatment volume cm 3 w total volume of suspension cm 3 z conductivity disintegration greek letters σo initial electrical conductivity of the suspension s/cm σmax suspension saturation electrical conductivity s/cm ∆t pulse repetition time s ∆tt inter-train time pause s application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 24 hydrogen production from ethanol dry reforming over lanthania-promoted co/al2o3 catalyst fahim fayaz1, nguyen thi anh nga2, thong le minh pham3, huong thi danh4, bawadi abdullah5, herma dina setiabudi1 and dai-viet nguyen vo1, 6, * 1 faculty of chemical & natural resources engineering, universiti malaysia pahang, lebuhraya tun razak, 26300 gambang, kuantan, pahang, malaysia. 2 faculty of applied sciences, ton duc thang university, 19 nguyen huu tho, district 7, ho chi minh city, vietnam. 3 institute of research and development, duy tan university, 03 quang trung, danang, vietnam. 4 clean energy and chemical engineering, korea university of science and technology (ust), daejeon, 305-350, korea. 5 chemical engineering department, universiti teknologi petronas, 32610 seri iskandar, perak, malaysia. 6 nguyen tat thanh university, 300a nguyen tat thanh street, ward 13, district 4, ho chi minh city, vietnam * corresponding author: vietvo@ump.edu.my (received: 20th feb 2017; accepted: 12th oct 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.813 abstract: la-promoted and unpromoted 10%co/al2o3 catalysts were synthesized using wet a impregnation method and evaluated in a quartz fixed-bed reactor at different co2:c2h5oh ratios of 2.5:1-1:2.5 and a reaction temperature of 973 k under atmospheric pressure. x-ray diffraction measurements detected the presence of co3o4 and coal2o4 phases on the surface of both promoted and unpromoted catalysts. bet surface area of promoted and unpromoted 10%co/al2o3 catalysts was about 143.09 and 136.04 m 2.g-1, respectively. the la promoter facilitated co3o4 reduction, improved the degree of reduction from 86 to 98% and increased metal dispersion from 9.11% to 16.64%. the lapromoted catalyst appeared to be a better catalyst in terms of catalytic activity and product yield regardless of reactant partial pressure. both c2h5oh and co2 conversions improved significantly with an increase in co2 partial pressure from 20 to 50 kpa for both catalysts whilst a decline in catalytic performance was observed with rising c2h5oh partial pressure. la addition improved c2h5oh and co2 conversions up to about 74.22% and 33.80%, respectively. abstrak: penggalak-la dan bukan penggalak-la mangkin 10%co/al2o3 dihasilkan menggunakan kaedah impregnasi basah dan dinilai dalam reaktor alas-tetap quarza pada pelbagai nisbah co2:c2h5oh sebanyak 2.5:1-1:2.5 dan suhu tindak balas sebanyak 973 k di bawah tekanan atmosfera. hasil daripada ukuran pembelauan x-ray, didapati terdapat kehadiran fasa co3o4 dan coal2o4 pada permukaan kedua-dua mangkin penggalak dan bukan penggalak. permukaan kawasan bet pada penggalak dan bukan penggalak mangkin 10%co/al2o3 adalah masing-masing sebanyak 143.09 dan 136.04 m 2.g-1. penggalak-la membantu dalam pengurangan co3o4, membaiki peratus penurunan daripada 86 kepada 98% dan menambah penyebaran logam daripada 9.11% kepada 16.64%. mangkin penggalak-la dilihat sebagai mangkin terbaik dari segi aktiviti iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 25 pemangkinan dan hasil pengeluaran, biarpun pada tekanan separa reaktan. kedua-dua penukaran c2h5oh dan co2 meningkat dengan ketara dengan kenaikan separa tekanan co2 daripada 20 kepada 50 kpa bagi kedua-dua pemangkin, sementara penurunan dalam aktiviti pemangkinan dilihat dengan kenaikan tekanan separa c2h5oh. penambahan la meningkatkan penukaran c2h5oh dan co2, masing-masing sebanyak 74.22% dan 33.80%. keywords: co-based catalyst; ethanol dry reforming; hydrogen; syngas 1. introduction global warming issues, increasing greenhouse gas emissions, and the diminishing availability of fossil fuels have resulted in growing interest in exploring an ecofriendly and alternative energy for substituting petroleum-based energy. hydrogen, a green energy carrier, has received significant attention from both academia and industry due to its outstanding energy capacity of 120.7 kj.g-1, zero emission during combustion, and employment as a main feedstock for fischer-tropsch synthesis (fts) to produce synfuel [1, 2]. however, currently, industrial hydrogen production uses unsustainable fossil fuels, namely; natural gas and oil-derived naphtha leading to considerable emissions of undesirable co2 greenhouse gas [3]. hence, ethanol dry reforming (edr) has been regarded as an attractive route for h2 synthesis since ethanol is a renewable and co2-neutral feedstock that can be easily derived from lignocellulosic biomass via hydrolysis-fermentation [4]. additionally, edr not only consumes unwanted co2 gas but also converts it to a valueadded syngas, a mixture of h2 and co for the downstream fts. in reforming processes, γ-al2o3 is normally used as support material owing to its mechanical stability, high melting temperature, and low cost [5-7]. in addition, ni-based catalysts are conventionally employed for ethanol reforming reactions because of their low cost and high capability of cleaving c-c and c-o bonds [8-11]. however, carbon deposition via boudouard, methane cracking, and ethylene polymerization reactions, as well as catalyst sintering, are the major issues resulting in the deactivation of ni-based catalysts during the edr reaction [12, 13]. in order to improve the stability of the catalyst and suppress the formation of deposited carbon, ni-based catalysts are normally modified with promoters. la2o3 has been employed as a dopant for reforming catalysts due to its basic properties enhancing co2 adsorption [14] and outstanding oxygen storage capacity hindering carbon formation on the catalyst surface [15]. however, to the best of our knowledge, there is no previous study about promoted co-based catalysts for edr reaction. thus, the objective of this study was to investigate the promotional effect of la dopant on the physicochemical properties and catalytic performance of co/al2o3 catalyst for hydrogen production from edr reaction. 2. experimental 2.1 catalyst preparation both 3%la-10%co/al2o3 and 10%co/al2o3 catalysts were synthesized using a wet impregnation method. alumina support purchased from sasol (puralox scca-150/200) was calcined in air at 1023 k for 5 h with a heating rate of 5 k min-1 to ensure thermal stability. a measured amount of la(no3)3 and co(no3)2 aqueous solutions (sigma-aldrich) were mixed and stirred with pretreated al2o3 support for 3 h followed by drying overnight at 383 k and subsequent air-calcination for 5 h at 823 k with a heating rate of 5 k min-1. the iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 26 resulting solid catalyst was further crushed and sieved to the desired particle size of 125160 µm before being employed for edr evaluation. 2.2 catalyst characterization the catalysts were characterized using brunauer-emmett-teller (bet) surface area, xray diffraction (xrd), and h2 temperature-programmed reduction (h2-tpr) measurements. the multipoint bet surface area was conducted in a micromeritics asap-2010 apparatus using n2 adsorption-desorption isotherms at 77 k. before bet measurement, the sample was degassed in n2 flow at 573 k for 1 h for moisture removal. xrd measurement for identifying crystal structure was studied in a rigaku miniflex ii system using a cu target as a radiation source with a wavelength of λ = 1.5418 å at 30 kv and 15 ma. all specimens were recorded within 2θ range of 3° to 80° with low scan speed of 1° min-1 and step size of 0.02°. h2-tpr experiments were carried out on a micromeritics autochem ii-2920 apparatus for both support and as a catalyst. roughly 0.1 g of sample sandwiched by quartz wool in a quartz u-tube was initially pre-heated at 373 k for 30 min under 50 ml.min-1 of he flow for removal of volatile compounds. the specimen was subsequently heated to 1173 k at 10 k min-1 with flowing 10% h2/ar mixture (50 ml.min -1) and kept isothermally at this temperature for 30 min. 2.3 ethanol dry reforming experiment about 0.1 g of catalyst was mounted by quartz wool in the middle of quartz fixed-bed reactor (l = 17 in. and o.d. = 3/8 in.) placed vertically in a split tubular furnace. ethanol dry reforming reaction was conducted at different co2 to c2h5oh ratios of 1:2.5 to 2.5:1 and reaction temperature of 973 k and atmospheric pressure. high gas hourly space velocity, ghsv of 42 l gcat -1.h-1 was used for all runs to ensure the negligible internal and external transport resistances. a kellymed kl-602 syringe pump was employed for feeding ethanol to the top of the reactor whilst co2 reactant and n2 diluent gas were accurately regulated by alicat mass flow controllers. the composition of gaseous products from the bottom of the reactor was analyzed on an agilent gc 6890 series gas chromatograph equipped with a thermal conductivity detector (tcd). 3. results and discussion 3.1 bet surface area measurements the multipoint bet surface area, pore volume, and pore diameter of the γ-al2o3 support promoted and unpromoted catalysts are shown in table 1. gamma-al2o3 support possesses a bet surface area of 175.29 m2.g-1. the loading of co active metal and la dopant on the support surface resulted in a drop in surface area, pore volume, and pore diameter from 175.29 to 136.04 m2.g-1, 0.46 to 0.34 cm3.g-1, and 10.65 to 10.41 nm, in that order. the reduction in textural properties for unpromoted and promoted catalysts was reasonably due to pore blockage indicating the successful diffusion of both co and la metal oxides on the support surface during the impregnation and calcination processes. 3.2. x-ray diffraction analysis the x-ray diffraction patterns of calcined γ-al2o3 support, la-promoted and unpromoted 10%co/al2o3 catalysts, displayed in fig. 1, are analyzed using the joint committee on powder diffraction standards (jcpds) database [16]. the γ-al2o3 phase on catalysts and support was detected with typical peaks at 2θ = 18.92°, 32.88°, 36.84°, 45.71° and 67.17°. in addition, the characteristic diffraction peaks of co3o4 phase were observed at 2θ value of 31.45° and 36.84°, 55.61° and 56.12° whilst the spinel coal2o4 phase was iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 27 identified at about 59.51° and 65.38° for both promoted and unpromoted catalysts. additionally, as seen in fig. 1(c), la2o3 phase was not observable in xrd pattern of lapromoted catalyst was reasonably due to the high metal dispersion with small la2o3 crystallite size lower than the detection limit table 1: textural properties of γ-al2o3 support, la-promoted and unpromoted 10%co/al2o3 catalysts sample bet surface area [m² g-1] pore volume [cm3 g-1] pore diameter [nm] γ-al2o3 175.29 0.46 10.65 10%co/al2o3 143.09 0.36 10.63 3%la10%co/al2o3 136.04 0.34 10.41 fig. 1: xrd patterns of (a) γ-al2o3 support, (b) 10%co/al2o3 and (c) 3%la10%co/al2o3 catalysts. as seen in table 2, the average crystallite size of catalyst was computed using debyescherrer equation (see eq. (1)) [17]. 0.94 ( ) cos d nm b    (1) where d is the crystallite size, b is the line broadening at half of the maximum intensity (fwhm) and λ is the x-ray wavelength while θ is the bragg angle. based on the relative molar volumes of co3o4 and metallic co 0 phases, cobalt metal particle size, d(co0) may be estimated via eq. (2) [18]. 0 3 4 ( ) 0.75 ( )d co d co o  (2) hence, the dispersion, d (%) of metallic cobalt can be computed from the average cobalt metal particle size (see eq. (3)) assuming spherical and uniform co0 particles with co0 density of 14.6 atoms nm-2 [18, 19]. 0 96 ( ) d d co  (3) 2-theta angle ( o ) 10 20 30 40 50 60 70 in te n si ty ( a. u .) 2 3 3 4 2 4 γ al o co o coal o  (a) (b) (c)      iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 28 as seen in table 2, la addition significantly reduced the average co3o4 crystallite size from 14.05 to 7.70 nm. thus, active metal dispersion was improved from 9.11% to 16.64%. the la2o3 promoter could act as a diluent preventing the agglomeration of co3o4 particles on catalyst surface and hence increasing metal dispersion. table 2: physical properties of la-promoted and unpromoted 10% co/al2o3 catalysts catalyst co3o4 crystallite size, d(co3o4) [nm] co0 crystallite size, d(co0) [nm] metal dispersion, d [%] 10%co/al2o3 14.05 10.53 9.11 3%la-10%co/al2o3 7.70 5.77 16.64 3.3 h2 temperature-programmed reduction the h2-tpr profiles of the catalysts and al2o3 support are shown in fig. 2. there was no peak detected for the al2o3 support during h2-tpr measurement. hence, three discrete peaks (p1, p2, and p3) were observed for 10%co/al2o3 and 3%la-10%co/al2o3 catalysts belonged to the reduction of active metal oxides. the first (p1) and second (p2) peaks were attributed to the reduction of co3o4 to coo phase and the subsequent conversion of the coo intermediate phase to the final metallic co0 form, respectively [20]. the high temperature peak (p3) at about 950 k was also ascribed to the reduction of coal2o4 phase possessing strong metal-support interaction to metallic co0 phase [21]. noticeably, the reduction temperature of peak p1 was shifted towards lower temperature of about 51 k with lapromotion indicating that the transformation of co3o4 to coo phase was more facile with la-addition. fig. 2: temperature-programmed reduction (h2-tpr) profiles of al2o3 support, lapromoted and unpromoted 10%co/al2o3 catalysts. as seen in table 3, both h2 uptake during h2-tpr and degree of reduction increased from 1453 μmol gcat -1 and 85.92% to 1660 μmol gcat -1 and 98.27%, respectively with promoter addition. this observation further confirms that h2 reduction of co3o4 was facilitated with la2o3 modification. the improvement in the degree of reduction with la dopant was rationally due to the increasing electron density on catalyst surface donated by temperature (k) 400 500 600 700 800 900 1000 1100 t c d s ig n al ( a. u .) al2o3 10%co/al2o3 3%la-10%co/al2o3 p1 p2 p3 iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 29 la2o3 promoter. the excessive electron population could alleviate the reduction of co3o4 species [22, 23]. table 3: summary of h2 uptake and degree of reduction for promoted and unpromoted 10%co/al2o3 catalysts catalyst h2 uptake [μmol gcat -1] degree of reduction [%] 10%co/al2o3 1453.18 85.92 3%la-10%co/al2o3 1660.94 98.27 4. ethanol dry reforming evaluation 4.1 effect of co2 partial pressure the effect of co2 partial pressure, pco2, on edr performance was evaluated at a temperature of 973 k with a constant pc2h5oh of 20 kpa and varying co2 partial pressure from 20-50 kpa. as seen in fig. 3, an increase in co2 and c2h5oh conversions with rising pco2 from 20 to 50 kpa was observed for both catalysts reasonably due to the enhancement of co2 gasification of deposited carbon on catalyst surface in co2-rich environment. in addition, jankhah et al. studied the thermodynamics of edr and reported that catalytic performance was favored at high ratio of co2 to c2h5oh [24]. this observation was in agreement with other studies about edr using ni-based catalysts [25]. interestingly, regardless of co2 partial pressure, the la-promoted catalyst exhibited higher c2h5oh and co2 conversions up to about 74.22% and 33.80%, respectively than those of unpromoted catalyst rationally due to the high oxygen storage capacity of la2o3 promoter oxidizing deposited carbon [3, 26] and the enhancement of metal dispersion with la-promotion (table 2). fig. 3: influence of co2 partial pressure on c2h5oh and co2 conversions at pc2h5oh = 20 kpa and t = 973 k. the effect of pco2 on h2 and co yields at pc2h5oh = 20 kpa and t = 973 k are shown in fig. 4. h2 and co yields improved with growing co2 partial pressure from 20 to 50 kpa for both catalysts owing to the enhancement of co2 reforming of ch4 intermediate product formed from ethanol decomposition [24]. interestingly, h2 and co yields for la-promoted catalyst were always superior to those of unpromoted 10%co/al2o3 catalyst for all co2 p co2 (kpa) 15 20 25 30 35 40 45 50 55 c 2 h 5 o h c o n v e rs io n ( % ) 10 20 30 40 50 60 70 c o 2 c o n v e rs io n ( % ) 10 20 30 40 50 60 70 10%co/al2o3 3%la-10%co/al2o3 iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 30 partial pressure. the enhancement of product yield with the la addition could be due to the improved metal dispersion (see table 2) and the basic property of the la2o3 promoter [14] increasing the adsorptive capacity of co2 reactant and hence resulting high catalytic performance. fig. 4: influence of pco2 on h2 and co yields at pc2h5oh = 20 kpa and t = 973 k. 4.2 influence of c2h5oh partial pressure the effect of ethanol partial pressure on edr performance was also studied by varying pc2h5oh from 20 to 50 kpa at pco2 = 20 kpa and t = 973 k. as seen in fig. 5 and fig. 6, both catalysts experienced a considerable drop in reactant conversions and gaseous product yield with increasing c2h5oh partial pressure from 20 to 50 kpa. the reduction in catalytic performance with rising pc2h5oh, exceeding the stoichiometric feed composition was rationally due to the excess presence of ethanol hindering co2 adsorption on catalyst surface and hence lessening the edr reaction. however, irrespective of c2h5oh partial pressure, the catalytic performance of the la-doped catalyst was always greater than that of unpromoted catalyst in terms of reactant conversion and product yield (see fig. 5 and fig. 6). fig. 5: influence of pc2h5oh on c2h5oh and co2 conversions at pco2 = 20 kpa and t = 973 k. p co2 (kpa) 15 20 25 30 35 40 45 50 55 h 2 y ie ld ( % ) 10 15 20 25 30 35 40 45 c o y ie ld ( % ) 10 15 20 25 30 35 40 10%co/al2o3 3%la-10%co/al2o3 p c2h5oh (kpa) c 2 h 5 o h c o n v e rs io n ( % ) 10 20 30 40 50 60 c o 2 c o n v e rs io n ( % ) 10 20 30 40 50 60 10%co/al2o3 3%la-10%co/al2o3 20 30 40 50 5545352515 iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 31 fig. 6: influence of pc2h5oh on h2 and co yields at pco2 = 20 kpa and t = 973 k. 5. conclusions edr reaction runs over both la-promoted and unpromoted 10%co/al2o3 catalysts were evaluated in a quartz fixed-bed reactor at different co2:c2h5oh ratios of 2.5:1 to 1:2.5 with a reaction temperature of 973 k and atmospheric pressure. the co3o4 and coal2o4 phases were formed on both promoted and unpromoted catalysts. however, the la2o3 phase was not detectable, indicating high metal dispersion. the la-addition improved metal dispersion from 9.11 to 16.64% and the degree of reduction from 86% to 98%. the bet surface area, pore volume, and pore diameter were reduced with the introduction of co and la metal oxides indicating the successful penetration of these metal oxides into the porous al2o3 support. additionally, the catalyst was reduced completely at a temperature beyond 1000 k, based on h2-tpr measurements. regardless of co2 and c2h5oh partial pressure, the la-promoted catalyst performed superior catalytic activity and product yield to those of the unpromoted catalyst due to the oxygen storage capacity of the la2o3 promoter resistant to carbon deposition and the improvement of active metal dispersion as well as the basic attribute of la2o3 dopant. regardless of catalysts, reactant conversions improved significantly with increasing co2 partial pressure. however, a considerable decline was observed for both co2 and c2h5oh conversions with rising c2h5oh feed composition. acknowledgements the authors are indebted to the financial support from ump research grant scheme (rdu160323) for conducting this research. fahim fayaz is also thankful for the graduate research scheme award (grs) from universiti malaysia pahang (ump). references [1] haryanto a, fernando s, murali n, adhikari s. (2005) current status of hydrogen production techniques by steam reforming of ethanol: a review. energy and fuels, 19:20982106. [2] vo d.-vn, and adesina aa. (2012) a potassium-promoted mo carbide catalyst system for hydrocarbon synthesis. catal. sci. technol, 2:2066-2076. p c2h5oh (kpa) 15 20 25 30 35 40 45 50 55 c o y ie ld ( % ) 5 10 15 20 25 30 35 40 h 2 y ie ld ( % ) 5 10 15 20 25 30 35 40 10%co/al 2 o 3 3%la-10%co/al 2 o 3 iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 32 [3] li d, zeng l, li x, wang x, ma h, assabumrungrat s, gong j. (2015) ceria-promoted ni/sba-15 catalysts for ethanol steam reforming with enhanced activity and resistance to deactivation. appl. catal. b environ,176-177:532-541. [4] vicente j, montero c, ereña j, azkoiti mj, bilbao j, gayubo ag. (2014) coke deactivation of ni and co catalysts in ethanol steam reforming at mild temperatures in a fluidized bed reactor. int. j. hydrogen energy, 39:12586-12596. [5] cui w, yuan x, wu p, zheng b, zhang w, jia m. (2015) catalytic properties of γ-al2o3 supported pt–feox catalysts for complete oxidation of formaldehyde at ambient temperature r.s.c. adv, 5:104330-104336. [6] chuah gk, jaenicke s, xu th. (2000) the effect of digestion on the surface area and porosity of alumina. microporous mesoporous mater, 37:345-353. [7] zhang z, hicks rw, pauly tr, pinnavaia tj. (2002) mesostructured forms of γ-al2o3. j. am. chem. soc, 124:1592-1593. [8] akiyama m, oki y, nagai m. (2012) steam reforming of ethanol over carburized alkalidoped nickel on zirconia and various supports for hydrogen production. catal. today, 181:413. [9] comas j, marino f, laborde m, amadeo n. (2004) bio-ethanol steam reforming on ni/al2o3 catalyst. chem. eng. j, 98:61-68. [10] yu x.-p, chu w, wang n, ma f. (2011) hydrogen production by ethanol steam reforming on nicumgal catalysts derived from hydrotalcite-like precursors. catal. letters, 141:12281236. [11] zawadzki a, bellido jda, lucrédio af, assaf em. (2014) dry reforming of ethanol over supported ni catalysts prepared by impregnation with methanolic solution. fuel process technol, 128:432-440. [12] torres ja, llorca j, casanovas a, domínguez m, salvadó j, montané d. (2007) steam reforming of ethanol at moderate temperature: multifactorial design analysis of ni/la2o3al2o3, and feand mn-promoted co/zno catalysts. j. power sources, 169:158–166. [13] li m, wang x, li s, wang s, ma x. (2010) hydrogen production from ethanol steam reforming over nickel based catalyst derived from ni/mg/al hydrotalcite-like compounds. int. j. hydrogen energy, 35:6699-6708. [14] mazumder j, de lasa hi. (2014) ni catalysts for steam gasification of biomass: effect of la2o3 loading. catal. today, 237:100-110. [15] al-fatesh as, naeem ma, fakeeha ah, abasaeed ae. (2014) role of la2o3 as promoter and support in ni/γ-al2o3 catalysts for dry reforming of methane. chinese j. chem. eng, 22:28-37. [16] jcpds powder diffraction file. (2000) international centre for diffraction data. swarthmore, pa. [17] patterson al. (1939) the scherrer formula for i-ray particle size determination,” phys. rev, 56:978-982. [18] schanke d, vada s, blekkan ea, hilmen am, hoff a, holmen a. (1995) study of ptpromoted cobalt co hydrogenation catalysts j. catal, 156:85-95. [19] storsæter s, tøtdal b, walmsley jc, tanem bs, holmen a. (2005) characterization of alumina-, silica-, and titania-supported cobalt fischer-tropsch catalysts. j. catal, 236:139152. [20] ewbank jl, kovarik l, kenvin cc, sievers c. (2014) effect of preparation methods on the performance of co/al2o3 catalysts for dry reforming of methane. green chem, 16:885-896. [21] fayaz f, danh ht, nguyen-huy c, vu kb, abdullah b, vo d.-vn. (2016) promotional effect of ce-dopant on al2o3-supported co catalysts for syngas production via co2 reforming of ethanol. procedia eng, 148:646-653. [22] li x, wu m, lai z, he f. studies on nickel-based catalysts for carbon dioxide reforming of methane. appl. catal. a gen, 290:81-86. [23] zhi g, guo x, guo x, wang y, jin g. (2011) effect of la2o3 modification on the catalytic performance of ni/sic for methanation of carbon dioxide. catal. commun, 16:56-59. iium engineering journal, vol. 19, no. 1, 2018 fayaz et al. 33 [24] jankhah s, abatzoglou n, gitzhofer f. (2008) thermal and catalytic dry reforming and cracking of ethanol for hydrogen and carbon nanofilaments’ production. int. j. hydrogen energy, 33:4769-4779. [25] bahari mb, phuc nhh, abdullah b, alenazey f, vo d.-vn. (2016) ethanol dry reforming for syngas production over ce-promoted ni/al2o3 catalyst j. environ. chem. eng, 4:48304838. [26] foo sy, cheng ck, nguyen th, adesina aa. (2011) evaluation of lanthanide-group promoters on co-ni/al2o3 catalysts for ch4 dry reforming. j. mol. catal. a chem, 344:2836. microsoft word 5paper02.doc iium engineering journal, vol. 1, no. 1, january 2000 m. h. ali et al. 7 stress analysis of polarization maintaining optical fibers by the finite element method m. h. aly faculty of engineering, university of alexandria, alexandria 21544, egypt, a. s. farahat, m. s. helmi and m. farhoud faculty of science, university of alexandria, alexandria, egypt abstract: stress-induced birefringence in single mode polarization maintaining optical fibers has been investigated using the finite element method. the modal birefringence caused by external forces in the panda and the side tunnel fibers are calculated. it is found that the modal birefringence is directly proportional to the radial distance from the fiber center. as expected, the modal birefringence vanishes with the variation in the magnitude of the applied external loads. key words: birefringence, polarization, panda fiber, side-pit fiber, finite element method. 1. introduction polarization maintaining (pm) optical fibers are of great importance in optical coherent communications and some optical fiber sensor applications[1]. the fibers that preserve the state of polarization of the guided light can be achieved by destroying the circular symmetry of the refractive index distribution in the core region. however, the birefringence properties of this kind of fiber are much more limited when compared with what can be achieved with stress induced birefringence. recently, a variety of structures has been proposed for the polarization maintaining fibers with stress induced birefringence, most of which are designed to maintain a differential stress in the fiber core region[1]. there are many such successful fiber structure designs, such as panda, bow tie, side tunnel and side pit fibers[1]. shih[2] described a new fiber manufacturing technique called preform deformation. using this technique, a new kind of pm fiber with a circular core, an elliptical stress applying cladding, and an elliptical jacket can be made. this has been studied experimentally by d. marcuse et al.[3]. in our work, full advantage of the finite element method is taken to develop a numerical study of the birefringence due to the effects of external stresses in both side pit and the side tunnel fibers. the birefringence pm fibers manufactured through preform deformation are analyzed. from the calculated stress distribution in the fiber, the refractive index tensor change is obtained. the finite element method is an approximate treatment of physical problems, defined, for example, by differential equations with boundary conditions, or by variation principles. compared to other approximate methods it is successful when the domain of the problem has a complicated shape or when the function involved behaves differently in different parts of the domain. the domain is represented approximately by a collection of finite numbers of connected subdomains of simple shape (e.g., triangles), called finite elements. the finite element method will to be applied in this paper for the determination of the stress distribution and the modal birefringence, due to the effects of external forces acting on the fiber cross section, for the panda and the side tunnel type fibers. the fiber cross section is first divided into “elements”. in this research, a triangular element is used. a linear system of equations can be established according to the principles of the finite element method, and then the stress distribution and, further, the refractive index tensor distribution may be calculated in each element. the details of the use of the finite element method can be found in the literature[4-5]. 2. formulation of the problem by the finite element method 2.1 matrix solution techniques solving the waveguide problem by the finite element method, the key factor affecting storage requirements and computational efforts is the choice of the algorithm to solve the matrix equation. the advantage of higherorder basis functions for the fields is that they give a more accurate solution. but it involves an increased programming effort, particularly when considering anisotropic materials, in the finite element, and penalty functions[6]. another advantage of the higher order polynomials (for given matrix order) is that it increases the density of the matrix. it should be noted the tradeoff optimum choice between low and high order polynomials depends on the matrix algorithm used. 2.2 principle of minimum potential energy the basic principle of the finite element method is that a continuum (the total structure) can be modeled analytically by its subdivision into regions. the principle of minimum potential energy can be used following ref. [1]. among all displacements of admissible form, those that satisfy the equilibrium iium engineering journal, vol. 1, no. 1, january 2000 m. h. ali et al. 8 conditions make the potential energy assume a stationary (minimum) value. the total potential energy of a structure can be expressed as a strain energy, u, plus the potential energy, v, of the applied loads, i.e.,   u v (1) the strain energy u of a complete structure consisting of n elements is simply the sum of the n element strain energies                    e t teeee n 1e e n 1e fuuku 2 1 uu , (2) where the superscript t is the operator to traznspose the vector or the matrix, and {ue}, [ke], and {fte} are the vector of nodal points displacements, the stiffness matrix, and the initial force vector in the eth element, respectively. equation (2) is rearranged to construct the global equation as:         u u k u u ft t t  1 2 , (3) where {u}, [k], and {ft} denote the global nodal point displacement vector, the global stiffness matrix and the global initial force vector, respectively. the potential energy, v, due to external load is expressed by:    v u ft l  , (4) where {fl} is the global load vector acting on each nodal point. inserting expressions for u and v from eq. (3) and eq. (4) into eq. (1), one can get:                1 2 u k u u f u ft t t t l , (5) applying to this the necessary condition for minimum energy, i.e.,            u k u f ft l    0 , (6)       k u f ft l  (7) this equation gives the displacement at all nodal points of the fiber under external forces. once the global nodal point displacement vector, {u}, is determined, stress in each element is given by[1]:           e e e e oed b u   . (8) with e = 1,2,3...n, where [de], [be], and{o} are the material stiffness matrix, the matrix relating nodal displacements to strain field, and the initial strain vector in the eth element, respectively. 3. derivation of strain energy as in the case of optical fibers, when the dimension of the structure in one direction (the z-direction) is very large in comparison with the other two transverse directions (xand y-) and the applied forces act in the xy plane and do not vary in the z-direction, the problem becomes a “plane strain problem”[1]. in the plane strain problem, the longitudinal strain z is zero, as are the shear strains �yz and �zx. introducing the condition on z into the relevant strain-stress equation we get:             21 1 211      tee yxx (9)             21 1 211      tee yxy (10)   xyxy e      12 , (11) where x, y and x, y denote the normal stresses and strains, respectively, and xy, and xy are the shear stress and strain, respectively, e is the elastic modulus,  is poisson’s ratio,  is the thermal expansion coefficient, and t is the temperature change (negative on cooling). these equations are expressed in the form:         od  , (12) where {}and {} denote the stress and strain vectors, respectively, defined as:                 x y xy , (13) and                x y xy , (14)  0 denotes the initial strain, where:               o 1 1 1 0   t , (15) and [d] is the material stiffness matrix given by[1]:            d e                   1 1 2 1 0 1 0 0 0 1 2 2        , , , , , , , , . (16) the strain energy in plain strain is given by[1]:       u dxdy s t o    l 2  , (17) where l is the length of the optical fiber and the integral is carried out over any region s under consideration. in iium engineering journal, vol. 1, no. 1, january 2000 m. h. ali et al. 9 this paper a two-dimensional triangular element is used to determine the variation of stresses in optical fibers. the formulation of this element is well developed and described in many references [6]. the eth element stiffness matrix and initial force vector are:                 ee te bdb s l e k , (18)    eoete db s l  e tf , (19) l is the fiber length and [ke] and {ft e} denote the element stiffness matrix and the element initial force vector, respectively. 4. accuracy of the finite element analysis before conducting the stress analysis of noncircular core fibers, the accuracy of the finite element analysis itself is first investigated. we can estimate the amount of error by comparing the finite element solution with the analytical solutions that show the same behavior. 1. thermal stress: this is the problem of thermal stress developing in long concentric cylinders of different materials, which are joined together at some initial temperature and their temperature is then changed. this has been treated by b.m. azizur et al[7]. stress distributions in the cylinder are given as:          r b a b e       2 2 2 2 1 2 1  t , (0  r  a) (20)     = a 2b t b r 2 2 2 2                 2 1 1 1e , (0  r  b) (21)                  b a b e 2 2 2 2 1 2 1  t , (0  r  a) (22)     = a 2b t b r 2 2 2 2                 2 1 1 1e , (0 r b) (23) where a and b are respectively the inner and outer radii of the concentric cylinder, e, , and t are elastic modules, poisson’s ratio and temperature change in the medium, and 1 and 2 are the thermal expansion coefficients of the mediums 1 and 2, respectively. 2stress by loads: stress distributions on the x-axis induced by the force wo acting on the cylinder along the vertical yaxis direction of the cylinder are expressed as:    x ow b x b x               b 1 4 2 2 2 2 2 , (24)    b y ow b b x                4 1 4 2 2 2 , (25) 3stress fields by finite element analysis: one-quarter of the entire cross section is covered by elements, since the optical fiber under consideration has two symmetry lines, one along the x-axis and the other along the y-axis. typically, we used 140 elements and 93 nodal points in this section. the error in the results obtained by the finite element analysis is less than 4 percent of the analytical results[1]. 5. results and discussion a computer program coded in matlab is used for the analysis of the birefringence properties of optical fibers using the finite element method. the structure of the side tunnel and panda fibers is shown in figs. 1 and 2. the fiber parameters used in this study are shown in table 1. taking into consideration that, in the side tunnel fiber, d is the distance from the nearest edge of saz to the core center and all the refractive indices n1, n2, and n3 have no effect on the strain. fig. 1 side tunnel fiber fig. 2 panda fiber figure 3 shows the stress distribution x and y on the x-axis of the panda type fiber when force is applied along the y-axis. it can be observed from the curve that stresses table i parameters of the panda and the side tunnel fibers y a x n d2 b d1 y n2 n1 a x n3 c n3 b d iium engineering journal, vol. 1, no. 1, january 2000 m. h. ali et al. 10 side tunnel fiber panda fiber 2a (m) 5 ~ 10 10 2b (m) 125 120 1 (o c -1) 2 (o c -1) 3 (o c -1) 7.6  10 -6 5.4  10 -7 3.66  10 -3 2.125  10 -6 5.4  10 -7 1.45  10 -6 d/c a/d 0.15 2.0 ~ 4.0 e (kg /mm2) 7830 7830  0.186 0.186 2c (m) 30 d1 (m) 20 d2 (m) 35 are nearly constant in the core region of the fiber. for the clad region between the core region and the saz region, the first clad region, stresses decrease gradually. reaching the saz, it is observed that the stresses nearly equal zero. the behavior of the stresses in the core and the first clad region can be explained by the resultant stresses because external and internal stresses existing at these regions are not equal and the net stress varies uniformly as we proceed along the fiber cross section. after this region, the stresses are nearly equal resulting in a nearly zero stress. -12 -10 -8 -6 -4 -2 0 2 4 1.14 4.57 8.34 14.29 24 42.29 x( m) s tr es s (k g/ m m2 ) y x fig. 3 stress distribution on the xaxis when force is applied along yaxis in the panda fiber. figure 4 shows the stress distribution on the y-axis when force is applied along the x-axis in the panda fiber. one can observe the same behavior as in fig. 3. as we reach the clad region, one observes that stresses decrease gradually. the decrement of the stresses along the y-axis can be explained by the decrement of the external stresses because the area is affected by the external normal force along the axis that increases when proceeding along the axis. the applied load, wo, in both figs. 3 and 4 is 0.5 kg/cm. based on ref. [8] and stresses shown in fig. 3, the stress-induced modal birefringence in the panda type fiber when force is applied along the x-axis direction is shown in fig. 5. it is observed from the figure that the modal birefringence is directly proportional to the radial distance from the fiber center. this is due to the effect of the stresses at this region. the value of the birefringence also depends on the magnitude of the external applied forces. similarly, the stress-induced modal birefringence when force is applied along the yaxis is shown in fig. 6. the figure shows nearly the same behavior as in fig. 5. it is clear that the birefringence at this applied load equals zero at the core region. changing the applied load, wo, the stress difference, x y, is calculated when the force is applied in xand ydirections, respectively. from this difference, the stress-induced modal birefringence is obtained. -10 -8 -6 -4 -2 0 2 4 1.14 6.97 17.03 42.29 y( m ) s tr es s  ( kg /m m 2 ) fig. 4 stress distribution on the yaxis when force is applied along xaxis in the panda fiber. y x 0 5 10 15 20 25 1. 14 3. 43 5. 83 8. 34 11 .7 17 24 34 .3 49 .1 x (m)m od al b ire fr in ge nc e, b x1 05 fig. 5 modal birefringence in the panda fiber when force is applied along x-axis. iium engineering journal, vol. 1, no. 1, january 2000 m. h. ali et al. 11 -2 0 2 4 6 8 10 12 14 16 18 1.14 5.83 11.66 24 49.14 y(m) fig. 6 modal birefringence in the panda fiber when force is applied along y-axis direction. m od al b ire fr in ge nc e, b x 1 05 the stress difference in the panda fiber when force is applied along x-axis is shown in fig. 7, from which it is noted that the stress difference decreases with the applied loads on the fiber. this means that the stress along the y-axis is greater than the stress along the xaxis. figure 8 shows the modal birefringence in the panda fiber when force is applied along the x-axis. it is clear that the modal birefringence decreases with the applied loads on the fiber. -16 -14 -12 -10 -8 -6 -4 -2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 wo (kg/cm) s tr es s di ffe re nc e   x y (k g/ m m 2 ) fig. 7 stress difference in the panda fiber when force is applied along the x-axis. -6 -5 -4 -3 -2 -1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 wo (kg/cm) m od al b ire fr in ge nc , b (x 1 0 5 ) fig. 8 modal birefringence in the panda fiber when force is applied along x-axis. 0 5 10 15 20 25 30 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 wo (kg/cm) s tr es s di ffe re nc e,  x y (k g/ m m 2 ) fig. 9 stress distribution in the panda fiber when force is applied along y-axis. figure 9 shows the stress distribution in the panda fiber when force is applied along the y-axis. a direct proportionality between the applied loads, wo, and the stress difference is noticed. figure 10 shows the modal birefringence in the panda fiber when force is applied along the y-axis, where an increase is noticed in the modal birefringence with the applied loads. from these results it is expected that we can control the magnitude of the birefringence in the fiber by controlling the external loads acting on the fiber. figures 11 and 12 show the stress distribution for the side tunnel fiber on the x-axis and the y-axis directions. the two figures show nearly the same behavior and the same order of magnitude as the panda fiber. this is expected since the two fibers are different only in the position of the sazs and the parameters this is repeated for the modal birefringence, fig. 13 and 14. as the force is applied along the y-direction in the fiber, one observes that the modal birefringence vanishes nearly at the limit of the fiber. it is also expected that the modal birefringence will vanish as the magnitude of the external applied loads, ow , is varied. similar to the panda fiber, the behavior of the side tunnel fiber is shown in figs. 15 to 18. fig. 10 modal birefringence in the panda fiber when force is applied along y-axis. 0 1 2 3 4 5 6 7 8 9 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 wo (kg/cm) m od al b ire fr in ge nc e, b (x 10 5 ) iium engineering journal, vol. 1, no. 1, january 2000 m. h. ali et al. 12 . -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 1.19 6.07 12.14 25 51.19x(m) s tr es s,  ( kg /m m 2 ) fig.11 stress distribution for the side tunnel fiber on the x-axis when force is applied along y-axis. x y -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 1.19 6.07 12.14 25 51.19 y(m) s tr es s,  (k g/ m m 2 ) fig. 12 stress distribution for the side tunnel fiber on the y-axis when force is applied along x-axis. y x 0 5 10 15 20 25 1.19 6.07 12.14 25 51.19 x(m) m od al b ire fr in ge nc e, b x1 05 fig. 13 modal birefringence in the side tunnel fiber when force is applied along the x-axis. -5 0 5 10 15 20 25 1.19 6.07 12.14 25 51.19 y (m) m od al b ire fr in ge nc e, b x 1 05 fig. 14 modal birefringence in the side tunnel fiber when force is applied along the y-axis. -60 -50 -40 -30 -20 -10 0 0.2 0.4 0.6 0.8 1 1.2 1.4 wo (kg/cm) s tr es s di ffe re nc e,  x y (k g/ m m 2 ) fig. 15 stress difference in the side tunnel fiber when force is applied along x-axis. -2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 w o (kg/cm) m od al b ire fr in ge nc e, b (x 10 5 ) fig. 16 modal birefringence in the side tunnel fiber when force is applied along xaxis. iium engineering journal, vol. 1, no. 1, january 2000 m. h. ali et al. 13 0 5 10 15 20 25 30 35 40 0.2 0.4 0.6 0.8 1 1.2 1.4 wo (kg/cm) s tr es s di ffe re nc e   x y (k g/ m m 2 ) fig. 17 stress difference in the side tunnel fiber when force is applied along y-axis. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0.2 0.4 0.6 0.8 1 1.2 1.4 wo (kg/cm) m od al b ire fr in ge nc e, b (x 10 5 ) fig. 18 modal birefringence in the side tunnel fiber when force is applied along the y-axis. 6. conclusion the finite element method has been applied for both the side tunnel and panda fibers to obtain variation in stresses and modal birefringence. it is found that the modal birefringence is directly proportional to radial distance from the fiber center. it is also found that as the force is applied, the modal birefringence vanishes nearly at the core limits of the fiber. references [1] k. okamoto, t. hosaka and t. edahiro, “stress analysis of optical fibers by a finite element method”, ieee j. quantum electron, vol. qe-17, no. 10, pp. 2123-2129, 1981. [2] s. c. chao, “extended gaussian approximation for single-mode graded index fibers”. ieee j. lightwave technol., vol. lt-12 (3), pp. 392-395, 1994. [3] d. marcuse and c. lin, “low dispersion single-mode fiber transmission”, ieee j. quantum electron, vol. qe-17, no. 6, pp. 869-877,1981. [4] c. x. sho and u r.q. hui, “polarization coupling in single-mode single-polarization fibers”, opt. lett., vol. 13, no. 12, pp. 1120-1122, 1988. [5] p. k. bachmann, dieter leers, hermann wehr and erich r. wehrhahn, “dispersion-flattened single mode fibers prepared with pcvd: performance, limitations, design optimization”, ieee j.lightwave technol., vol. lt-4 (7), pp. 858-863, 1983. [6] k. t. bathe, finite element procedures, prentice hall inc., 1996. [7] b. m. a. rahaman, a. fernandez, and b. davies, “review of finite element methods for microwave and optical waveguides”, ieee j. lightwave technol., vol. lt-13, pp. 1442-1446, 1991. [8] k. hayata and m. koshiba, “stress-induced birefringence of side-tunnel type polarizationmaintaining fiber”, ieee j. lightwave technol., vol. lt-4, 1986. iium engineering journal, vol. 1, no. 1, january 2000 m. h. ali et al. 14 biography prof. dr. moustafa hussein aly is currently professor of engineering physics, faculty of engineering, university of alexandria, alexandria, egypt. he was born in alexandria in 1953. he received his b.sc. in 1976 in communications and electrophysics, his m.sc. in 1983 and his ph.d. in 1987 in engineering physics, all from faculty of engineering, university of alexandria, egypt. he is a member of the optical society of america (osa) and of the egyptian society of solid state (esss). his area of interest is laser and fiber optics where he has about 40 publications. e-mail: mosaly@hotmail.com mr. ashraf m. s. farahat is currently a lecturer, department of physics, faculty of science, university of alexandria, alexandria, egypt. he was born in alexandria in 1972. he received his b.sc. in 1992 and m.sc. in 1999, both in physics, faculty of science, university of alexandria, egypt. dr. maher farhoud is currently associate professor, department of physics, faculty of science, university of alexandria, alexandria, egypt. he was born in alexandria in 30/11/1958. he received his b.sc. in 1980 and m.sc. in 1986, both in physics, faculty of science, university of alexandria, egypt. he received his ph.d. in physics, adam mickiwicz university, poland. his area of interest is laser and nonlinear optics. e-mail: mfarhoud@yahoo.com. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 maintain agent consistency in surakarta chess using dueling deep network with increasing batch rian adam rajagede department of informatics, universitas islam indonesia, sleman, indonesia *corresponding author: rian.adam@uii.ac.id (received: 25th january 2021; accepted: 15th july 2021; published on-line: 4thjanuary 2022) abstract: deep reinforcement learning usage in creating intelligent agents for various tasks has shown outstanding performance, particularly the q-learning algorithm. deep qnetwork (dqn) is a reinforcement learning algorithm that combines the q-learning algorithm and deep neural networks as an approximator function. in the single-agent environment, the dqn model successfully surpasses human ability several times over. still, when there are other agents in the environment, dqn may experience decreased performance. this research evaluated a dqn agent to play in the two-player traditional board game of surakarta chess. one of the drawbacks that we found when using dqn in two-player games is its consistency. the agent will experience performance degradation when facing different opponents. this research shows dueling deep q-network usage with increasing batch size can improve the agent's performance consistency. our agent trained against a rule-based agent that acts based on the surakarta chess positional properties and was then evaluated using different rule-based agents. the best agent used dueling dqn architecture with increasing batch size that produced a 57% average win rate against ten different agents after training for a short period. abstrak: pembelajaran peneguhan mendalam adalah terbaik apabila digunakan bagi mewujudkan ejen pintar dalam menyelesaikan pelbagai tugasan, terutama jika ia melibatkan algoritma pembelajaran-q. algoritma rangkaian-q mendalam (dqn) adalah pembelajaran peneguhan berasaskan gabungan algoritma pembelajaran-q dan rangkaian neural sebagai fungsi penghampiran. melalui persekitaran ejen tunggal, model dqn telah beberapa kali berjaya mengatasi kemampuan manusia. namun, ketika ejen lain berada dalam persekitaran ini, dqn mungkin kurang berjaya. kajian ini melibatkan ejen dqn bermain papan tradisional iaitu catur surakarta dengan dua pemain. salah satu kekurangan yang dijumpai adalah konsistensi. ejen ini akan kurang bagus ketika berhadapan lawan berbeza. kajian menunjukkan dengan penggunaan rangkaian-q dwipertarungan mendalam bersama peningkatan saiz kumpulan dapat meningkatkan konsistensi prestasi ejen. ejen ini telah dilatih untuk melawan ejen lain berasaskan peraturan dan sifat kedudukan catur surakarta. kemudian, ejen ini diuji berpandukan peraturan berbeza. ejen terbaik adalah yang menggunakan rekaan dqn dwipertarungan bersama peningkatan saiz kumpulan. ianya berhasil memenangi permainan dengan purata 57% berbanding sepuluh agen lain melalui latihan jangka masa pendek. keywords: reinforcement learning; dueling deep q-network; increasing batch size; surakarta chess 159 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 1. introduction deep reinforcement learning has been able to produce agents that can solve a variety of complex problems, such as simulated car driving [1], video games [2], or natural language processing [3]. a game is an environment that is often used to evaluate reinforcement learning agents' ability to interact with other agents and make decisions to achieve specific goals. researchers can focus on algorithms with a relatively more straightforward environment before implementing them in more complex environments such as self-driving cars. the deep learning approach successfully captures richer features and improves agent performance when combined in reinforcement learning algorithms. for example, in [2] the produced agent uses deep q-learning, the combination of convolutional neural network [4] and q-learning [5] to play and win atari games. another quite phenomenal one is alpha go [6], an agent that manages to beat the best human players in the world in a reasonably complex game, go, using deep reinforcement learning. in various types of board games, human-level abilities have also been surpassed by intelligent agents, such as in othello [7,8], mancala [9], chess [10,11], go [6,12], or even in a game with incomplete information, such as poker [13]. those agents are trained using reinforcement learning, deep learning, or a combination of both. in [8], the othello game is seen as a classification problem. the agent trained on the game database using a deep convolutional neural network to decide the best action in the given state. in contrast to [7], agents in the othello game trained using neural fitted temporal difference learning, which is a method in reinforcement learning. in chess, the previous studies also use deep learning [11] or deep reinforcement learning [10] to produce a good performance agent. board games have different characteristics compared to atari single-player video games previously researched [2]. in the majority of board games, the agent must interact with one or more players. this environmental behaviour is called a markov game [14]. the presence of other players in the game dramatically affects the agent in making decisions and can make it difficult for us to produce intelligent agents. in [12], agents are trained using convolutional neural network and monte carlo tree search (mcts) by self-playing in the go game without being given explicit information by humans. self-playing means the agent plays games against itself. the method is effective as the agent produced using this method successfully defeats humans in the go game and the agent from the previous research [6] with a shorter training time. another form of the agent training process that can be used is to train the agent against the rule-based player who moves based on the positional values of the board game [15] or uses a database that stores records of previous matches [8]. this research will implement and evaluate the reinforcement learning algorithm, deep q-learning, in the two-player board game of surakarta chess. surakarta chess has unique game characteristics. one of them is that some positions on the board can be very profitable to defeat the opponent. from those properties, we can make rule-based agents train the reinforcement learning agent. the making of intelligent agents in surakarta chess has been studied previously. in those studies, agents were made based on two search methods, αβsearch [16–18] and based on mcts [19,20]. we proposed to use deep q-learning as a different approach to creating an agent in surakarta chess. deep q-learning differs from the other methods mentioned earlier as q-learning is not based on the search method. the use of q-learning on two-player board games has been studied before in several different types of games [9,15,21-24]. in [22], deep q-learning still found it difficult to beat the searching method in the hex game even though it has been trained for two weeks (about 160 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 60,000 episodes). the long training process is also shown in [24]. the model was trained to over 500,000 episodes to achieve about a 50% winning rate against heuristic agents. this research explored deep q-learning architecture variants, including dueling qnetwork [24], and proposed increasing batch size method [25] as a regularization technique in deep q-learning to speed up the training process and improve the agent performance. we trained the agent against a rule-based agent instead of a random agent, as done in [9]. in previous studies, agents were trained and evaluated against the same opponent [9,24]. in this study, to see the agent's consistency in dealing with different opponents, our agent was evaluated against different rule-based agents. agent consistency in facing other agents in achieving a goal is crucial in various tasks, not only in games. 2. research method the process of interaction and training in the reinforcement learning agent (rl agent) is shown in fig.1. agents will be trained to use deep q-learning against a rule-based agent in the surakarta chess environment. at a timestep t, the rl agent will receive a board condition (a state s) and then perform one of the valid actions a based on its policy. in the next turn, the opponent will do the same thing: see the game's condition and then take action. the results of rl agent action on time steps t and opponent actions on time step t+1 make a new game state, s'. the agent will get two types of rewards, r, reward when winning a game, and reward when capturing the opponent's pieces that the system environment already defines. the rl agent learns from a collection of experiences represented by the tuple of (s, a, r, s'). all agents are implemented using pytorch [26] and trained on google colab's gpu. fig. 1: interaction between rl agent, the opponent and the environment. 2.1 surakarta chess surakarta chess is a chess-like game from surakarta, indonesia, contested annually by the international computer game association (icga). surakarta chess is played by two players on a 6x6 board with 8 curves and 12 pieces. the starting position of each player on the board is shown in fig. 2 (a). in each turn, players can move their piece or capture the opponent's piece. the player can move his piece to eight adjacent positions if another piece has not occupied the destination. a player can capture the opponent's piece by moving a piece along a horizontal or vertical line then through at least one curve to reach the opponent's piece without being blocked by another piece. illustrations of piece movement and capture are shown in fig. 2 (b) and fig. 2 (c). 161 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 fig. 2: (a) surakarta chess initial state; (b) available move for a piece in 8 shown as circles with red border; (c) capturing path from 8 to 21 shown as red path. because a piece must be in a particular position to capture, in previous studies, they use position values to measure how good a piece's position is [17,19]. there are three types of positions in surakarta chess based on their relationship to the curve. the three types of positions are shown in fig. 3, distinguished by red, white, black, and yellow. fig. 3: positional value in surakarta chess. surakarta chess consists of three phases [16], namely the opening phase, the middle phase, and the final phase. in the opening phase, the player will focus on placing their pieces in an advantageous position. this is crucial because the player needs to make an unblocked path to capture the opponent's piece. the middle phase occurs after pathways are created. in this phase, players will begin to attack and defend their pieces from their opponent. the final phase is indicated by the small number of pieces on the board. in this phase, the pieces are free to move and capture the opponent's piece because the path to capture is already open. 2.2 surakarta chess environment in this study, we use surakartaenv part of gapoera api [27], a publicly available game environment toolkit. players can access current board information using available functions. one aspect of the information provided to players through surakartaenv is the position of the piece. surakartaenv maps the game board to a matrix with a value of -1, 0, or 1. a value of 0 is given to a position if no pieces are occupying it. a value of 1 or a value of -1 indicates the player's pieces' position depending on the player's perspective. the value 1 indicates the first player's position, while the value of -1 indicates the second player's position. each 162 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 position on the board is numbered from 0 to 35, as shown in fig. 2. from each of these positions, 12 actions can be done, 8 of which are actions to move without capturing in 8 directions and 4 of which are actions to move across the line horizontally or vertically until reaching the curve to capture. therefore, there are a total of 432 available actions. surakartaenv accepts an action a in the form of an integer between 0 to 431. in addition to the position of the pieces, both players can also access other information through surakartaenv. players can get information on which pieces that player can capture, which player pieces that the opponent can capture, and which actions are valid in each turn for both players. the rule-based agent will later use that information to make decisions in every turn. surakartaenv, by default, sets rewards to both players for each action. we use a +10 reward if the player wins the match, and -10 if the player loses, and +0.5 when the player captures the opponent's piece. 2.3 rule-based agent a rule-based agent decides its action based on game information available at the time. in this research, three rule-based agents are made that take action based on a particular priority. when an agent cannot perform any valid moves based on its priority, the agent will make a valid random move. the explanation of each priority for each agent is shown in table 1. the red and black positions refer to fig. 3. a safe place is a place where the player's piece is safe from opponent's attacks. table 1: the priority of each rule-based agent agent name rb1 rb2 rb3 movement priority 1. capture 2. move to black 3. move to a safe place 1. capture 2. move to red 3. move to black 4. move to a safe place 1. capture 2. move to red 3. move to a safe place each agent has an exploration probability parameter ε that gives agents the possibility to make a random move that is not based on their priorities. this random action is intended to create variations both in the training process and in the testing process. in this study, rlagents will be trained against rb1 with ε = 0.1. 2.4 reinforcement learning agent reinforcement learning agents were trained using the deep q-learning method [2]. deep q-learning is the improvement of the q-learning algorithm [5] that uses a deep neural network as an approximator of the action-value function. the neural network architecture used in [2] is convolutional neural network (cnn) [4]. this study will compare cnn architecture with a simple neural network without convolutional layers or commonly called multi-layer perceptron (mlp). both architectures are shown in fig. 4. both architectures are simpler than those proposed in [2], given that the surakarta chessboard size is smaller than the atari game image matrix. in [2], 84x84x4 inputs represent pixels on the screen from the last four frames, while in surakarta, the input is only a 6x6 matrix. it also makes consideration for comparing mlp with cnn in surakarta chess. 163 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 fig. 4: (a) q-network architecture with convolutional layer, (b) q-network architecture using multi-layer perceptron. figure 4 (a) shows the architecture consisting of one convolution layer, one pooling layer, and a fully connected layer. inputs are padded to keep the output size the same after the convolutional process. the convolutional layer uses a 3x3 kernel size and 32 feature maps, while the pooling layer uses a 2x2 size pooling window. the neural network output is a vector with 432 elements, representing all possible actions in surakarta chess. in the mlp architecture, two hidden layers are used with the number of neurons similar to the neurons from the convolutional process on the cnn architecture. we use two techniques proposed in [2], experience replay and the use of two neural networks as policy and target networks in one agent. experience replay uses a replay memory with a capacity c to store the agent's experiences in the form of (s, a, r, s'). in this study, all agents are set to have the same memory replay capacity of 50,000 experiences. during the training process, the agent will take a batch of data from the replay memory as training data. we also explore the effect of increasing batch data size [25] on the model performance. increasing batch size means that samples of experience drawn from replay memory will increase through episodes. in [25], this method can help speed up the model training process. the second technique we use is the use of policy and target networks in one agent that can increase the stability of the model. initially, the target network is a clone of the policy network, but its weight is only updated after the policy network is updated n times. the algorithm used to optimize network policy is adam optimizer [28], with an initial learning rate of 0.0001. the weights and biases of the networks are initialized using the methods proposed in [29, 30]. we also compared another architecture called duelling deep q-network [24]. the duelling network has two separate streams. one will produce a scalar state value v(s), and the other will produce action advantages a(s, a). state values will provide information on whether a state is valuable or not, while action advantages provide information about the advantages of each action. the two values are then combined to get q(s, a) using eq. (1). in previous research [24], a duelling network was proposed using cnn. this research will also compare the model performance when using mlp on the duelling network. the duelling network architecture is shown in fig. 5. 𝑄(𝑠, 𝑎) = 𝑉(𝑠) + (𝐴(𝑠, 𝑎) − 1 |𝐴| ∑ 𝐴(𝑠, 𝑎′ ) 𝑎′ ) (1) during the training process, both agents that use dqn and duelling q-network will use ε-greedy as a policy to decide the action in a state. the value of ε is the agent 's 164 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 probability of taking random actions to explore states. in this study, the value of ε initially used was 13%. this value will be reduced after some episodes, so the agent acts based more on the state action value. each agent was trained for 1250 episodes. in episodes 75, 150, and 250, the value of ε will be reduced by 3.7%. as a result, after 250 episodes, the value of ε is only 1.9%. fig. 5: (a) dueling q-network architecture with convolutional layer, (b) mlp on dueling q-network architecture. 3. results and discussion 3.1 model performance rl agents will be trained and their parameters tuned against rb1 and their performance evaluated against other agents. in the first experiment, we compared the effect of increasing batch size [25]. this experiment used dqn with a convolutional network as a model architecture. three agents were compared. the first was an agent without increasing batch size, the second was an agent with a less frequently increasing batch size, and the third was a model with a more frequent increasing batch size. the result of the agents against rb1 is shown in table 2. table 2: performance comparison of increasing batch size usage increase frequency average score from last episodes last 50 last 100 last 150 last 200 model 1 5.80 5.39 5.39 5.60 model 2 250 5.40 4.82 5.53 5.96 model 3 150 6.80 6.45 6.59 6.38 the agent's score is the number of opponent pieces captured by the agent until the game is finished. model 1 did not use increasing batch size, while models 2 and 3 used it. model 2 used a less frequently increasing batch size that increases the batch size 50% from the current size every 250 episodes, while model 3 used a more frequently increasing batch size that increased the batch size 50% every 150 episodes. this process was conducted until it reached 1000 episodes. all models had an initial batch size of 48. the graph of increasing batch size is shown in fig. 6. table 2 shows that increasing the batch size during training can help the model improve its performance. 165 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 another parameter that affects the agent's performance is the value of n, which is the number of updates made on the policy network before updating the target network. we tested three n values: 10, 210, and 700. the n values used were much smaller than those used in [2] because we used fewer iterations in the training phase. in a single game, we assumed the agent had 70 turns so that when n = 210, the target network was updated around every three games. the score for each model against rb1 for each episode appears in fig. 7. it showed that if we used a too small or too large n, the agent performance became unstable and tended to decrease over episodes. whereas when n = 210, the score obtained by the model was ascending with relatively more stability. the three agents shown in fig. 7 used dqn with a convolutional layer and increasing batch size. fig. 6: batch size throughout episodes. fig. 7: performance comparison of n, using moving average scores for every 150 episodes. this research also compared four agents with different neural network architectures. table 3 shows that the use of the duelling network significantly increased the agent's performance. the scores shown are averages of the last few scores. for example, in the "last 50" column, the value in that column is the average of the rl agent scores for the last 50 episodes, from episodes 1201 to 1250. the use of a duelling network with a convolutional layer outperformed other agents. even the duelling network without a convolutional layer still outperformed the regular dqn with a convolutional layer. scores of each model for every episode are shown in fig. 8. 166 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 table 3: performance comparison of network architecture model type average score from last episodes last 50 last 100 last 150 last 200 dqn-cnn 6.80 6.45 6.59 6.38 dqn-mlp 5.78 5.55 5.49 5.49 dueling-cnn 9.36 8.69 8.25 8.21 dueling-mlp 8.08 7.45 8.25 6.63 fig. 8: performance comparison of q-learning models, using moving average scores for every 150 episodes. 3.2 score against other agents after completing the training process, we evaluated four rl agents with different network architectures using the parameter settings mentioned earlier. these agents competed against five different rule-based agents and one random agent. the random agent was an agent that always took a valid random movement in each turn. each rl agent played 30 games for each rule-based agent. the rl agent played as the first player who makes the first move. in table 4, it shows the number of rl agent wins in 30 games against other agents. we evaluated five agents: • two agents without duelling networks (dqn-cnn and dqn-mlp) • two agents with duelling networks (duelling-cnn and duelling-mlp) • an agent for duelling-cnn that was trained without an increasing batch the last agent we mentioned was used to compare the effect of an increasing batch on agent performance. from the table, we can see that all five agents can defeat the random agent (ra) in all games for a 100% win rate. it also shows that agents trained using the duelling network had the most wins against nine other agents. when an opponent had a greater ε value, meaning that the opponent had a greater chance of moving randomly, agents were expected to exploit this vulnerability to win more. however, as shown in the table, only agents who used the duelling network tended to be able to use it as an opportunity to win the match, whereas, in the dqn-mlp or dqn-cnn model, an increase in the value of ε did not benefit the model 167 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 significantly. the agent that did not use increasing batches had poor performance because of difficulties in the training process, as shown in table 4. duelling network agents can also adapt to agents that have different rules, rb2 and rb3. both rule-based agents had a slight difference in priority for determining their action compared to rb1. this adaptation did not occur in other models that experienced a high number of losses against rule-based agents aside from the training process. the average win rate is calculated by averaging the win rate of an rl agent against the other agents. table 4: performance comparison of models against other rule-based agents. the shaded column is the agent that is countered during the training process model type number of rl agent wins avg. win. rate (%) ra rb1 rb2 rb3 ε=0.1 ε=0.2 ε=0.3 ε=0.1 ε=0.2 ε=0.3 ε=0.1 ε=0.2 ε=0.3 dqn-cnn 30 2 7 5 1 3 2 3 2 1 18.6 dqn-mlp 30 7 4 0 0 0 1 0 0 0 13.9 dueling-cnn 30 13 16 23 12 12 19 9 18 19 57.0 dueling-mlp 30 11 13 13 5 10 11 4 7 13 39.0 dueling-cnn (no inc. batch) 30 0 1 1 0 4 1 0 0 0 12.3 3.3 model consistency to see an agent's consistency in facing other agents, we used the coefficient of variations (cv), as shown in eq. (2), where 𝜎 is the standard deviation, and 𝜇 is the mean of the data. the smaller the cv value, the more consistent the model. we calculated the cv between the three rule-based agents by separating them based on their epsilon value. the results are shown in table 5. 𝐶𝑉 = 𝜎 𝜇 × 100 (2) for example, in table 5, duelling-cnn had a cv of 14.99 in column with ε = 0.1. this was calculated from {13, 12, 9}, the number of duelling-cnn agent wins against rb1 ε = 0.1, rb2 ε = 0.1, and rb3 ε = 0.1, respectively. from table 5, we can see that the duellingcnn model had a relatively small cv value compared to other agents. except when the value ε = 0.3, the duelling-mlp agent had the smallest cv value. the cv value of agent duelling-cnn without increasing batch in column ε=0.1 could not be calculated because the agent had no victory. table 5: coefficient of variations between rule-based agents model type coefficient of variation ε=0.1 ε=0.2 ε=0.3 dqn-cnn 40.82 54.00 63.73 dqn-mlp 141.42 141.42 141.42 duelling-cnn 14.99 16.26 9.27 duelling-mlp 46.36 24.49 7.64 duelling-cnn w/o increasing batch 101.98 70.71 168 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 4. conclusion in this research, a deep reinforcement learning approach was implemented to create agents in surakarta chess. we explored several deep q-learning architectures to find the best agent. the results show that the use of duelling networks and increasing batch size can improve agent performance and consistency in the surakarta chess game. in a short period, agents with duelling network architecture and increasing batch size mechanisms succeeded in obtaining a high average win rate, 57%, against ten different agents. we also found that the best model had better consistency even though it played against agents with different strategies. in the future, duelling networks and increasing batch size can be evaluated in more complex environments. references [1] lillicrap tp, hunt jj, pritzel a, heess n, erez t, tassa y, silver d, wierstra d continuous control with deep reinforcement learning. in 4th international conference on learning representations: 2-4 may 2016; san juan, puerto rico. retrieved from http://arxiv.org/abs/1509.02971. [2] mnih v, kavukcuoglu k, silver d, rusu aa, veness j, bellemare mg, graves a, riedmiller m, fidjeland ak, ostrovski g, petersen s, beattie c, sadik a, antonoglou i, king h, kumaran d, wierstra d, legg s, hassabis d. (2015) human-level control through deep reinforcement learning. nature, 518 (7540): 529–533. doi: 10.1038/nature14236. [3] yogatama d, blunsom p, dyer c, grefenstette e, ling w learning to compose words into sentences with reinforcement learning. in 5th international conference on learning representations: 24-26 april 2017; toulon, france. retrieved from https://openreview.net/forum?id=skvgqgqxe. [4] lecun y, bottou l, bengio y, haffner p. (1998) gradient-based learning applied to document recognition. proceedings of the ieee, 86 (11): 2278–2324. [5] watkins cj, dayan p. (1992) q-learning. machine learning, 8 (3–4): 279–292. [6] silver d, huang a, maddison cj, guez a, sifre l, van den driessche g, schrittwieser j, antonoglou i, panneershelvam v, lanctot m, dieleman s, grewe d, nham j, kalchbrenner n, sutskever i, lillicrap t, leach m, kavukcuoglu k, graepel t, hassabis d. (2016) mastering the game of go with deep neural networks and tree search. nature, 529 (7587): 484–489. doi: 10.1038/nature16961. [7] van den dries s, wiering ma. (2012) neural-fitted td-leaf learning for playing othello with structured neural networks. ieee transactions on neural networks and learning systems, 23 (11): 1701–1713. doi: 10.1109/tnnls.2012.2210559. [8] liskowski p, jaskowski w, krawiec k. (2018) learning to play othello with deep neural networks. ieee transactions on games, 10 (4): 354–364. doi: 10.1109/tg.2018.2799997. [9] kasim mf. (2016) playing the game of congklak with reinforcement learning. in proceedings of 8th international conference on information technology and electrical engineering (icitee). ieee. pp 1–5. doi: 10.1109/iciteed.2016.7863309. [10] lai m. (2015) giraffe: using deep reinforcement learning to play chess. master’s thesis, imperial college london, retrieved from https://arxiv.org/pdf/1509.01549.pdf. [11] david oe, netanyahu ns, wolf l. (2016) deepchess: end-to-end deep neural network for automatic learning in chess. in villa aep, masulli p, pons rivero aj eds artificial neural networks and machine learning – icann 2016. cham, springer international publishing. pp 88–96. doi: 10.1007/978-3-319-44781-0_11.retrieved from http://link.springer.com/10.1007/978-3-319-44781-0_11. [12] silver d, schrittwieser j, simonyan k, antonoglou i, huang a, guez a, hubert t, baker l, lai m, bolton a, chen y, lillicrap t, hui f, sifre l, van den driessche g, graepel t, hassabis d. (2017) mastering the game of go without human knowledge. nature, 550 (7676): 354–359. doi: 10.1038/nature24270. 169 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 [13] moravčík m, schmid m, burch n, lisỳ v, morrill d, bard n, davis t, waugh k, johanson m, bowling m. (2017) deepstack: expert-level artificial intelligence in heads-up no-limit poker. science, 356 (6337): 508. doi: 10.1126/science.aam6960. [14] littman ml. (1994) markov games as a framework for multi-agent reinforcement learning. in machine learning proceedings 1994. elsevier. pp 157–163.retrieved from https://doi.org/10.1016/b978-1-55860-335-6.50027-1. [15] somasundaram ts, panneerselvam k, bhuthapuri t, mahadevan h, jose a. (2018) double q–learning agent for othello board game. in proceedings of 10th international conference on advanced computing (icoac). ieee. pp 216–223. doi: 10.1109/icoac44903.2018.8939117. [16] qiu h, wang y, gao f, quan qiu. (2013) research on search engine techniques of surakarta game. the journal of china universities of posts and telecommunications, 20 117–120. doi: 10.1016/s1005-8885(13)60235-6. [17] liu c, wang j, zhang y. (2014) search strategy research and analysis for surakarta chess game. in proceedings of the 26th chinese control and decision conference (2014 ccdc). ieee. pp 3362–3366. [18] winands mh. (2015) the surakarta bot revealed. in computer games. springer. pp 71–82. [19] zuo g, wu c. (2016) a heuristic monte carlo tree search method for surakarta chess. in proceedings of chinese control and decision conference (ccdc). ieee. pp 5515–5518. doi: 10.1109/ccdc.2016.7531982. [20] li s, qi y, bo j, fu y. (2019) design and implementation of surakarta game system based on reinforcement learning. in proceedings of chinese control and decision conference (ccdc). ieee. pp 6326–6329. doi: 10.1109/ccdc.2019.8832340. [21] draskovic d, brzakovic m, nikolic b. (2019) a comparison of machine leaming methods using a two player board game. in proceedings of ieee eurocon 2019-18th international conference on smart technologies. ieee. pp 1–5. doi: 10.1109/eurocon.2019.8861927. [22] young k, vasan g, hayward r. (2016) neurohex: a deep q-learning hex agent. in computer games. springer. pp 3–18.retrieved from https://doi.org/10.1007/978-3-319-57969-6_1. [23] arvidsson o, wallgren l. (2010) q-learning for a simple board game. phd thesis, bachelor’s thesis, school of computer science and engineering, kth royal institute of technology, retrieved from http://www.csc.kth.se/utbildning/kandidatexjobb/datateknik/2010/rapport/arvidsson_oskar_ och_wallgren_linus_k10047.pdf. [24] wang z, schaul t, hessel m, hasselt h, lanctot m, freitas n. (2016) dueling network architectures for deep reinforcement learning. in proceedings of international conference on machine learning. pmlr. pp 1995–2003.retrieved from http://proceedings.mlr.press/v48/wangf16.html. [25] smith sl, kindermans p-j, ying c, le qv. (2018) don’t decay the learning rate, increase the batch size. in 6th international conference on learning representations: 30 april 3 may 2018; vancouver, bc, canada. retrieved from https://openreview.net/forum?id=b1yy1bxcz. [26] paszke a, gross s, massa f, lerer a, bradbury j, chanan g, killeen t, lin z, gimelshein n, antiga l, desmaison a, kopf a, yang e, devito z, raison m, tejani a, chilamkurthy s, steiner b, fang l, bai j, chintala s. (2019) pytorch: an imperative style, highperformance deep learning library. in wallach h, larochelle h, beygelzimer a, alchébuc f d\textquotesingle, fox e, garnett r eds proceedings of advances in neural information processing systems 32. curran associates, inc. pp 8026–8037.retrieved from http://papers.nips.cc/paper/9015-pytorch-an-imperative-style-high-performance-deeplearning-library.pdf. [27] rajagede ra, mahardhika gp. (2021) gapoera: application programming interface for ai environment of indonesian board game. in arxiv. retrieved from https://arxiv.org/abs/2110.11924. [28] kingma dp. (2015) adam: a method for stochastic optimization. in 3rd international conference on learning representations; san diego, ca, usa. retrieved from http://arxiv.org/abs/1412.6980. 170 iium engineering journal, vol. 23, no. 1, 2022 rajagede https://doi.org/10.31436/iiumej.v23i1.1807 [29] glorot x, bengio y. (2010) understanding the difficulty of training deep feedforward neural networks. in proceedings of the 13th international conference on artificial intelligence and statistics. jmlr workshop and conference proceedings. pp 249–256. [30] he k, zhang x, ren s, sun j. (2015) delving deep into rectifiers: surpassing human-level performance on imagenet classification. in proceedings of the ieee international conference on computer vision. pp 1026–1034. 171 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 potential volumizing effect of the postmorph lime filler in attenuating concrete carbonation muhamad hasif hussin1, mohd haziman wan ibrahim1*, nor hazurina othman2, mohammed yahya mohammed al-fasih3, and mohd fadzil arshad4 1 jamilus research center, faculty of civil engineering and built environment, universiti tun hussein onn malaysia, batu pahat, johor, malaysia 2 departtment of civil engineering, faculty of civil engineering and built environment, universiti tun hussein onn malaysia, batu pahat, johor, malaysia 3 school of civil engineering, faculty of engineering, universiti teknologi malaysia, skudai, johor, malaysia 4 faculty of civil engineering, universiti teknologi mara (uitm), shah alam, selangor, malaysia *corresponding author haziman@uthm.edu.my (received: 16th january 2021; accepted:13th october 2021; published on-line: 4thjanuary 2022) abstract: a study on the crystallography of the lime that comes from mussel shell has been conducted to determine the packing density of the material. the experimental analysis encompasses of concrete samples preparation with lime replacement at 5%, 7.5% and 10% by cement weight. the samples were carbonised naturally over a period of six months and subjected to the phenolphthalein test at 60, 90, 120 and 180 days. it has been found that lime originating from the mussel shell is of both the aragonitic and calcitic crystal types. both crystal polymorphs of aragonite and calcite are denser than the typical normal concrete by 27.8% and 18.3% respectively. this suggest a volumizing effect that is beneficial to reduce carbonation penetration into the capillarity of the concrete. results from the carbonation test indicate that concrete containing mussel shell lime ash showed up to 51% lower carbonation coefficient and significantly lower intensity of capillarity as shown via fesem. abstrak: kajian mengenai kristalografi kapur yang didapati daripada kulit kupang telah dijalankan bagi menentukan kepadatan bahan tersebut. analisis eksperimen merangkumi penyediaan sampel-sampel konkrit yang mengandungi gantian kapur pada 5%, 7.5% dan 10% daripada berat simen. sampel-sampel telah dikarbonatkan secara alami selama enam bulan dan menjalani ujian fenolftalin pada usia 60, 90, 120 dan 180 hari. kajian telah mendapati bahawa kulit kupang terdiri daripada kapur-kapur berjenis aragonit dan kalsit. kedua-dua polimorf kapur aragonit dan kalsit adalah 27.8% dan 18.3% lebih tumpat berbanding konkrit biasa. hal ini berpotensi menjadi bahan penumpat yang bagus untuk mengurangkan serapan pengkarbonatan ke dalam kapilari konkrit. keputusan ujian pengkarbonatan menunjukkan konkrit yang mengandungi abu kapur kulit kupang mempunyai pekali pengkarbonatan sehingga 51% lebih rendah dan mempunyai kerendahan kapilariti yang signifikan seperti yang ditunjukkan melalui fesem. keywords: mussel shell ash; natural carbonation; calcium carbonate crystal 13 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 1. introduction concrete carbonation leads to the precipitation of lime (calcium carbonate) in the pores and this can either be advantageous or problematic, depending on the involved situation. in practice, some civil engineering structures such as mass concrete and girders take advantage of the carbonation process through the densifying property of the lime which can reduce the porosity of concrete. several researchers such as sideris [1], phung et al. [2] and rezvani [3] have indicated the pro-filler attribute of using lime in concretes. carbonation is notoriously known to cause serviceability issue in reinforced concretes. when the embedded steel reinforcement corrodes due to carbonation of concrete, the steel expanded in volume which causes the concrete cover to spall. this can expose the embedded steel and deeper part of the concrete to various other chemical and physical attacks apart from the costly repair. according to ekolu [4], global corrosion related damage cost is at about 3-4% of the global gross domestic product (gdp). these 3-4% out of the gdp figure is accumulative of various industries and not limited to construction alone. however, shibata [5] highlighted that buildings and infrastructures sectors had contributed a staggering 38% out of the global 3-4% figure which summed up to one trillion us dollars. many research and methods were imposed to counter concrete carbonation ever since and this include but not limited to increasing concrete cover (most common) in the range of 25-30 mm as suggested by benitez [6] and nakai [7], using well known substances such as fly ash [8-21], slag [12,13,20,22-24], lime [1,8-10,16,20,25-35] and even using commercial rust inhibitor [36,37]. it has been found that by using cover depth of 25-30 mm, the concrete service life increased significantly. however, there are also several case studies that have been conducted [38,39] which indicated that over-reliance on concrete cover thickness will not suffice. possan [38] study indicated that the mean carbonation depth of the thirty-five years old concrete structure is 33.0 ± 6.6 mm. whereas, oliveira and nogueira [39] study indicated mean carbonation depths for the thirty-one years old concrete structure varied from 54.01-104.83 mm. these are already beyond the limit of the suggested thickness in the previous studies. since the typical and minimum design life of common concrete structures is fifty-years old and can go a maximum of one-hundred years if it is civil engineering structures such as in [38] and [39], the covers indeed underperformed in both cases. thicker concrete cover requires more material, more space allocations and needless to say, bigger budget. none of these are ideal when it comes to modern projects with complex structural twist in the design that may limit available space for extra cover thickness and the typical demand for “minimum cost, maximum output”. fly ash is a very common material used in the industry to carter for special needs in terms of engineering aspect. unfortunately, carbonation studies incorporating fly ash [8, 11,12-14,18-21] at various percentages indicated a trend that is prone to anti-filler effect when it comes to concrete carbonation. about only twenty-two percent of the studies indicated increased in carbonation resistance [10,12,15,16], sixty-seven percent indicated decreased in carbonation resistance [8,11,12-14,18-21] and eleven percent indicated as unresponsive variable [9,17]. the issue with fly ash is that it increases the concrete porosity and this is verified through the extended x-ray (xram) and mercury intrusion porosimetry (mip) methods as discussed in [18]. concrete containing slags showed no better improvement in terms of carbonation resistance either. a study [12] reported that the carbonation resistance of slag concrete is even lower than the fly ash concrete. another study [23] indicated that significant impairment towards carbonation resistance can already be observed at replacement percentage as low as 10%. 14 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 research on concrete containing lime however, showed a more promising outcome with more results that are supportive towards the improvement of carbonation resistance emerged [1,25,27,28,31,33,35]. even so, just as fly ash, there seems little direct correlations between the amounts of replacement with the proor anti-filler effect. this is true since some studies [1,25,31] indicated that high replacements (50% and more) are required to achieve the filling effect, while others [27,28,35] indicated the otherwise. even in the studies that showed anti-filler effect [8,10,16,20,26,29,30,32,34], the replacement percentage has little to do with the outcome. this has led this study to believe that given a proper treatment, lime has a potential to be used as filler even at lower dosage. the aforementioned studies utilized the lime in its final form which is calcium carbonate. calcium carbonate is inert filler and possess little to no hydration property such as the cement. hence, the potential filling effect is limited by the position at which these inert filler particles reside within the concrete. if more of it happened to reside within the capillary chambers, than filler affect may be observed. conversely, if more of these inert particles reside within the gel itself or stuck in the aggregate pores, than the filling effect would have been wasted. hence, the occurrence of the dispersion paradox phenomenon described in [27]. it is the continuous hydration of the cement that makes the concrete increase in strength overtime due to the gel growth and densification that will ultimately filling the void within the binder matrix. this gel growth phenomenon inspired this study to emulate it in other form and this is where this study differs in the method of lime utilization and is explained later in this section. rust inhibitors that depend on cathodic/anodic/cathodic-anodic reactions can protect the steel bar from corrosion but not without sacrifice on cost and additional subject matter expert employment. this is because there are many types of corrosion inhibitors that can be browsed through the market such as organic, inorganic, combination of organic-inorganic, water-based and coating which all have their respective purposes and correct methods of applications. on top of that, research on corrosion inhibitors generally focus on eliminating chloride elements and hydrochloric acid [37]. as to whether or not the inhibition mechanisms work similarly in carbonation rich environment is unknown. the use of rust inhibitor focusses on projects with special requirements such as underground and offshore structures exposed to aggressive chloride environment [37] and certainly not for all-purpose use for just any projects. this is shown in a series of test conducted by [36] which indicated that at given circumstances, calcium nitrate based inhibitors failed to perform its task but alkanolamine based inhibitor did success. hence, rust inhibitor may not be an option for many projects. in light of the highlighted issues along with other out of scope factors, sustainability has become the spotlight for contingency plans throughout the world. in malaysia, ministry of energy, green technology and water, has outlined the 2017 national green-technology policy [40] that encourages people to consume more on the renewable natural resources as an alternative to the non-renewable natural resources apart from emphasizing construction and building sustainability. this is where the wasted mussel shells fit in the research design of this study. the chemistry of concrete carbonation relies on the diffusion of carbon dioxide gas into the hardened binder. to inhibit corrosion due to carbonation, method to isolate the chemical interaction has to be devised and this can be achieved by applying the pro-filler principle of the lime in the aforementioned studies. in this study, a counter-intuitive approach designed to use the carbonation itself to inhibit the carbonation process is proposed. this design is called as the self-suffocation method in which the lime in its designed intermediate form shall hinder the carbon dioxide flux as the carbonation process proceeds. 15 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 lime has a much higher mass unit than the quicklime or slaked lime. in atomic scale, higher mass unit is normally associated with higher atomic radii. this study postulates that the resulting higher atomic radii imposes a volumizing effect. since the carbon dioxide flux proceeds via the capillarity matrix, there is a maximum 80% probability that this volumizing effect happens within [41]. this research named the material of interest as the post-morph lime filler (plf). the idea behind the naming of “post-morph” comes from the expected behavior of the quicklime and slaked lime upon carbonation. the lime crystals will only morphed once the concrete is exposed to carbonation. contrary to many other researchers that incorporate the lime during concrete mixing, this research incorporates the quicklime instead. the term “post-morph” indicates that the actual lime will only be autogenously deposited after the exposure. the amount of deposition strictly dependent of the degree of carbonation. by designing the mechanism of interaction in this way, the natural carbonation process is fully taken advantage of. 2. material preparation and methods the mussel shell sample were obtained from the danga river. the shells were washed using tap water and manually soaked with a brush to remove stubborn impurities. the cleaned shells were then air dried for a few days before being oven dried at 105oc for 24 hours to remove pore humidity. the shells were then isothermally heated at 1000oc for 1 hour to remove carbon dioxide from the calcium carbonate. the calcined shells were left to cool for several hours to the room temperature before being subjected to milling process for 1 hour. the milled calcined shell was sifted to pass the 63 µm aperture and the samples were then considered ready for experimentations. however, some experimentations did used some samples that were not calcined. mix design was prepared using the department of environment method (doe) [42] with a target 28th day mean strength of 35mpa (standard deviation, s of 3.05). concretes were made from tasek (malaysia) brand cem1 opc (grade 42.5), crushed granites with 20 mm maximum size, crushed quarry sand (33.3% passing the 600 µm mesh) and tap water. mixing was done using a rotary mixer with feeding sequence of water, cement+plf mixture, sand and finally granites. mixing time followed recommendation from [43]. table 1 shows the mix design for the control and the plf concretes. table 1: concrete mix design cube size 100 x 100 x 100 mm characteristic strength 30 mpa target mean strength (28th day) 35 mpa margin within 1.64s s = 3.05 mpa w/c 0.6 replacement groups control plf5 plf7.5 plf10 cement (kg/m3) 360 342 333 324 plf (kg/m3) 0 18 27 36 water (kg/m3) 216 sand (kg/m3) 967 granite (kg/m3) 857 conditioning plastic sheathing for 6 and 27 days at room temperature and humidity. 16 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 2.1 methods the beginning part of the study focused more on the fundamental and metallurgic analyses which includes particle dispersion, mineralogy and crystallography. then the focusing shifted to the study of the effect of aforementioned fundamentals in civil engineering aspect which includes carbonation and microstructure analysis. 2.1.1 particle dispersion two groups of materials were given focus for particle size distribution analysis and they were the opc and the plf itself. the test was conducted using cilas1180 laser diffraction machine at room temperature of 25 oc and a mean relative humidity of 65±3%. distilled water was used as dispersing agent and 5-10 grams of samples were prepared for each group. 2.1.2 chemical and mineralogical analyses three materials were tested for either their chemical or mineralogical or both compositions. they are the opc, un-calcined mussel shell, and calcined mussel shell (including plf). all the tested samples were in powdered form and sieved to pass the 63 µm aperture. xrd analysis was carried out using the bruker d8 diffractometer, scanned between 10o – 90o bragg angle with step of 0.02o and x-ray wavelength (λ) of 1.5406 angstrom (å). the chemical and minerals were determined using the evaluation (eva) software and some match analyses were doubly verified using crystallographic open database (cod). the xy coordinates of the obtained diffractograms were used to perform computerized gaussian fitting. this is a specialize technique applied to only the un-calcined mussel shell diffractogram in this study to perform the crystallite size measurement. gaussian fitting was conducted to execute measurements of the full width at half maximum (fwhm) of the selected peaks with the most pronounced intensity. the components of the fwhm were obtained from snyder and jenkins [44]. the obtained components of the fwhm are transferred into a spreadsheet software to perform the necessary crystallite size measurement using the scherer’s equation shown in the eq. (1) below where d is the diameter of the crystallite measured in angstrom (å), k is the correction factor which is typically taken as 1 for spherical shape assumption, λ is the wavelength of the x-ray measured in angstrom (å), b is the fwhm converted in radians and cos(ɵb) is the cosine of the angle of b measured also in radians. 𝑑 = 𝐾  𝐵 cos(𝜃𝐵) (1) the crystallite sizes were used to give a rough estimation of the crystal packing efficiency by comparing the median particle size (d50) obtained via the particle size distribution (psd) analysis, and the amount of crystallite needed to match the longest span (median diameter) of the particle. this was done using eq. (2). 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑐𝑟𝑦𝑠𝑡𝑎𝑙𝑙𝑖𝑡𝑒 = 𝐷50 𝑑𝑚 (2) further justifications were made by using 2-dimensional draws of the involved crystal systems in the un-calcined mussel shell. modelling of any crystal structure was made using the visualization for electronic and structural analysis (vesta) software version 3.4.7. 17 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 2.1.3 carbonation method for testing concrete carbonation was adapted from three standards which are the bs en 14630 (determination of carbonation depth in hardened concrete by the phenolphthalein method) [45], the bs en 13295 (determination of resistance to carbonation) [46] and the bs en 12390 – 10 (determination of the carbonation resistance at atmospheric levels of carbon dioxide) [47]. the exposure was conducted for 6 months at intervals of 60, 90, 120 and 180 days. four groups of concrete were assigned and they were the control group, and concretes containing 5% (plf5), 7.5% (plf7.5) and 10% (plf10) replacements. this test was performed in a natural environment (exposed to ambient air but sheltered from rain). the exposure to the environmental carbon dioxide (co2) at 0.0552% (552 ppm) begun after the 27th day of curing in the plastic wrap. three environmental parameters were recorded on daily basis which are the concentration of the carbon dioxide gas, relative humidity and ambient temperature. in the three aforementioned standards for the carbonation testing, the carbon dioxide gas concentration is to be recorded three times a day, whereas the ambient relative humidity value has to be recorded at least once a day for as long as the carbonating testing proceeds. the carbonation depth of each and every carbonated face were taken in the form of mean average. the test was carried out by pressing the concrete cube in between two metal bars using a hydraulic compression machines and carbonation depth was measured using a digital vernier caliper. the depth of the natural carbonation follows the square root of time function as stated by [47] and was used in this study to obtain the carbonation coefficient. the square root of time function is shown in eq. (3) where d: depth of carbonation in millimeter, k: carbonation coefficient in (mm/√year), and t is time in years. 𝐷 = 𝑘 √𝑡 (3) 2.1.4 fesem and edx the analyses were performed using the jeol jsm 7600f. all samples were coated with aurum (au)/gold to enhance conductivity. the 2-dimensional sem image of the interest topography was subjected to a specialized contouring technique that caused it to become 3dimensional. this is done to give the actual in-depth view of the topography through a more sophisticated approach. any other 3-dimensional objects such as the representation of particle grains were also made possible through graphical enhancement. the capillarity network of the concretes were compared to observe the volumizing effect of the plf at high level magnifications. elemental mapping was also made possible through the complementary edx. 3. results and discussion this subtopic contains the outcomes of the conducted analyses. note that the diffractogram from mineralogical analyses of the tested materials are compiled in a single diffractogram for easier comparison. 3.1 particle dispersion laser diffraction indicated that the prepared mussel shell ash particle dispersion resembles to that of the opc’s (fig. 1). the median particle diameter (d50) of the plf is 19.69 µm which is approximately 23% larger than the opc’s. the typical median average 18 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 (d50) size of the opc can be as low as 10-15 µm [48] and may go as high as 10-20 µm [49]. the tested opc and plf average sizes are tally with the statements in [48] and [49]. however, it is important to also note that in order to achieve a good plf particle dispersion amongst the opc’s, median size (d50) may not be as important as concentration. ideally, the incorporation of plf into the cement through replacement, will naturally increases and decreases certain range of available particle sizes. since it is impossible to know which exact particle size were omitted and which were included, it has become an uncertainty. hence, analysis should focus more on the entire sets of size through the dispersion curve rather than a single number like the d50. the tested particle dispersion of cement containing 5%, 7.5% and 10% plf exhibited overlapping curves with each other within the upper limit (opc) and lower limit (plf) curves. hence, they are not included due to repetition of considerably identical patterns but suffice to say that the incorporation of the plf into the cement at 10% maximum did not alter the original opc particle dispersion significantly. this suggest that within 10% dosage, the plf particle can be in homogeny (disperse properly) with the opc particle. hence, maximizing the filler effect across the binder region of the concrete. fig. 1: particle distribution curve of opc and plf. 3.2 ordinary portland cement mineralogy estimations that have been made through the matching of these signatures in eva and cod give out the percentage of bogue compositions as 59% for tricalcium silicate, 25.9% for dicalcium silicate, 1.6% tricalcium aluminate, 9.7% calcium aluminoferrite and 3.8% gypsum. the estimated amount of triand dicalcium silicates and calcium aluminoferrite are in a good agreement with the values reported by santhakumar [50] which stated that the amount of the tricalcium silicate in opc should varies in the range of 30-50%. whereas, dicalcium silicate varies in the range of 20-45%. calcium aluminoferrite should varies in the range of 6-10%. however, the calcium aluminate content in the tested opc was found to be below average with the typically reported range of 8-12%. the gypsum amount is within the tolerated zone of 2-4%. 3.3 mussel shell (un-calcined form) mineralogy diffraction pattern (refer fig. 8 at later page) of the un-calcined mussel shell powder indicates that it contains largely calcium carbonate with orthorhombic crystal system. orthorhombic profile in calcium carbonate compound is characteristic to aragonite polymorph which is highly anticipated in the shell of carbonate secreting organisms such as 0 20 40 60 80 100 120 0.01 0.1 1 10 100 c u m u la ti v e p a ss in g ( % ) particle size (µm) opc plf 19 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 the mollusk [51]. there are some traces of rhombohedral system which is characteristic to calcium carbonate of the calcite polymorph. according to boggs [51], calcite is the most stable form of calcium carbonate which may take some amount of time to transform from the original aragonite arrangement. the diffractogram peaks (fig. 8) indicate that the tested sample are highly crystalline in regards to the very slim full-width at half maximum (fwhm) intensity [52]. slim fwhm is also an indication of large crystallites [52]. even with very slim fwhm, it is still considered a polymeric (crystal-amorphous) system nonetheless since perfect crystal would be impossible to obtain from the nature, but with a stressed minimum degree of amorphousness. as such, crystallite size measurement through the scherer equation is made possible and shown in table 2 whereas fig. 2 shows the schematic diagram of the crystallites in a single particle grain of the micron size (drawn not to scale). based on fig. 2(a), one particle grain of mussel shell powder has a median diameter (d50) of 19.69 µm as determined through the cilas 1180 particle size analyzer (psa). a single particle grain contains hundreds if not, thousands of crystallites that are nano in size as shown in fig. 2(b). this study believes that the amount of these nano crystallites present in a known grain diameter, can be taken advantage of for an indirect and qualitative density measurement. fig. 2: schematic diagram (a) particle grain (b) crystallites. based on table 2, the mean sizes of the aragonitic and calcitic crystallites are 44.56 nm and 37.54 nm respectively. some minor amount of peaks cannot be analyzed due to poor gaussian fitting and skipped. nevertheless, the data indicated that the present aragonitic crystallite in the tested sample is 18.7% smaller than the calcitic crystallite. by using this information, and considering two mussel shell particle grains, one is composed of pure aragonite, while the other is composed of pure calcite, a qualitative estimation of the crystal packing efficiency can be made. using equation (2), the amount of crystallite that exist along the longest path of the particle can be predicted. figure 3 shows the calculation of the diameter and crystallite packing. based on fig. 3(a), if one mussel shell particle of 19.69 µm in diameter is made up of entirely aragonite crystal, there would be approximately 525 unit of aragonitic crystallite along the red line shown in fig. 3(a). likewise, if the same particle is made up of entirely calcite crystal instead, there would be approximately 442 unit of calcitic crystallite along the red line shown in fig. 3(b). this indicates that for a fixed 2-dimension, aragonitic crystallite can be packed much more than the calcitic crystallite. in simple words, aragonite crystal can be denser than the calcite crystal. this is tally with the reported density values 1 unit crystallite = 10th nm 1 mussel shell particle grain d50 = 19.69 µm magnified to nano scale (a) (b) 20 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 of both crystals which happened to be at 2.94 g/cm3 for aragonite [53] and 2.72 g/cm3 for calcite [52]. table 2: components of the scherer equation for crystallite size measurement of the mussel shell sample peak polymorph fwhm 2-theta theta fwhm(rad) theta (rad) d (å) d (nm) d (µm) 1 ara 0.14886 26.21726 13.10863 0.002598097 0.22878875 547.9539 54.7954 0.0548 2 ara 0.15146 27.23282 13.61641 0.002643476 0.23765119 539.6825 53.9683 0.0540 3 cal 0.13587 31.10151 15.55076 0.002371379 0.27141188 606.9149 60.6915 0.0607 4 ara 0.16921 33.11591 16.55796 0.002953272 0.28899083 489.8041 48.9804 0.0490 5 ara 0.21286 36.09764 18.04882 0.003715108 0.31501134 392.532 39.2532 0.0393 6 cal 0.19361 37.87276 18.93638 0.003379132 0.33050218 433.8019 43.3802 0.0434 7 ara 0.31042 38.56152 19.28076 0.005417851 0.33651274 271.1277 27.1128 0.0271 10 cal 0.19877 42.91974 21.45987 0.003469191 0.37454539 429.4441 42.9444 0.0429 11 ara 0.2348 45.86098 22.93049 0.004098033 0.40021255 367.3733 36.7373 0.0367 12 cal 0.27871 48.39646 24.19823 0.004864407 0.42233879 312.496 31.2496 0.0312 13 ara 0.25499 50.23365 25.11683 0.004450415 0.43837129 344.0885 34.4089 0.0344 14 ara 0.25583 52.42184 26.21092 0.004465076 0.45746685 346.1201 34.6120 0.0346 15 ara 0.27972 52.9827 26.49135 0.004882035 0.46236128 317.3275 31.7327 0.0317 16 ara 0.32815 66.02007 33.01004 0.005727298 0.5761338 288.6959 28.8696 0.0289 17 ara 0.42884 69.00089 34.50045 0.00748467 0.60214636 224.7855 22.4786 0.0225 mean calcite crystallite size (dm) 44.56 0.04456 mean aragonite crystallite size (dm) 37.54 0.03754 fig. 3: mussel shell crystallites unit measurements (a) only an aragonite particle composition, (b) only a calcite particle composition. comparing the density of these crystals with the density of a hardened normal concrete which typically stood at 2.3 g/cm3 (converted from 2300 kg/m3), it can be said that the packing of both crystals is higher than the concrete (27.8% and 18.3% higher respectively). this finding suggests that both type of these calcium carbonate polymorphs (aragonite and calcite) potentially possess densifying attribute when used in concrete. in the view of this study, in regards to the packing efficiency of the said crystal systems, the densely packed aragonitic crystallite is due to the basis arrangement itself which revealed to be orthorhombic system through the xrd analysis. according to wahab [54], orthorhombic system has a higher degree of freedom along the lattice axes such that a ≠ b ≠ 21 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 c. considering crystal habit phenomenon during the formation of the aragonite itself, the crystallite can arrange themselves in every axes with multiple combinations of number a, b and c while maintaining the orthorhombic profile since a, b and c do not strictly need to be the same. hence, the crystal can easily pack themselves. contrary to the rhombohedral (hexagonal) arrangement of the calcite in which a = b ≠ c. two axes have to have equal dimension which result to a limited (rigid) possible crystal arrangement during the formation of the calcite. this is shown in the software-generated and -modified crystals of aragonite and calcite based on the models of antao and hassan [55] and graf [56] respectively. the crystals with polyhedral views are plotted over their own respective 3x2 lattices in fig. 4. within the same lattice size, it can be seen that the arrangement of the calcite (fig. 4(b)) is more geometric and rigidly spaced compared to the aragonite structure (fig. 4(a)). on the contrary, the packing of aragonite crystals can be seen denser than the calcite crystals. this further validates previous discussions by this study. fig. 4: crystal structural arrangements (a) aragonite and (b) calcite. according to moore [57] and haldar [58], calcite polymorph arrangement is thermodynamically stable at atmospheric level of pressure and temperature compared to aragonite. this means that it stays on being calcitic as long as not being subjected to geological event that leads to immense pressurization, water movement and temperature rise. it is due to this stability as well that cause calcite to become practically insoluble in water compared to aragonite. in the view of this study, by taking advantage of this calcite attribute, combined with proper adjustment to the degree of densification through dosage control, outward migration of the lime from concrete capillarity due to fluid movement can be hindered. fluid movement, especially rain penetration can potentially migrate or wash off filler material at surface level. thus, reducing its efficacy. this however, requires further studies and development. figure 5 shows the image of the shell magnified through the electron microscope at x5.0k zoom. the 2-dimensional image (fig. 5(a)) has been processed into 3-dimensional figure (fig. 5(b)) using a specialized technique to have a real and in-depth view of the topographic profile of the un-calcined shell. local chemical constituents that are present have also been determined through the complementary energy-dispersive equipment. based on fig. 5(a), the topographic profile of the un-calcined mussel shell is revealed to be plates of flaky shape. the plates are more pronounced in the rendered 3-dimensional image (fig. 5(b)). the plates are multi-layered which suggest the multi-stages of shell development throughout the life-span of the mussel. the platy profile is tally with the previous discussion aragonite (orthorhombic) calcite (rhombohedral) tight arrangement less-tight arrangement (a) (b) 22 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 that indicates the presence of orthorhombic crystal system that is characteristic to the aragonite polymorph of the calcium carbonate. fig. 5: topographic profiles of the un-calcined mussel shell (a) 2-dimensional topography (b) 3dimensional topography. the platy profile of the un-calcined shell can also be observed in the findings from the previous studies [51,54,59,60]. the redundant proves in several studies signal the agreement of the presence of orthorhombic crystal system mentioned in this article that is characteristic to the aragonite polymorph of the calcium carbonate [61]. orthorhombic system is basically an overextended version of a cubic system over two sides which resulted to a rectangular shape and if sufficiently thin, may assume platy appearance. despite the known petrological knowledge that the existence of aragonite polymorph in normal environment is rare [57], these studies indicated that it is indeed possible via bio-mineralization process by these carbonate secreting organisms such as mussels and oysters. whatever differences in the outcome of research that focus on the utilization of the un-calcined versus calcined shell husk in concrete may owed to this crystallographic variety. hence, the significance of this piece of information. since studies on concrete filler through crystallography point of view is largely insufficient, this particular finding may spark more attention. 3.4 mussel shell (calcined form) mineralogy diffraction pattern of the calcined mussel shell sample indicated 90.61% match as calcium oxide profile and 76.1% match as calcium hydroxide profile as determined from the crystallography open database (cod). analysis has estimated the proportions of the compound as 93.6% cao and 6.4% ca(oh)2. this study suspect that the minuscule presence of the calcium hydroxide is due to the hydration of the calcined mussel shell ash when it is exposed to the environmental humidity during the experimentation. no traces of calcium carbonate can be seen and this signify the effectiveness of the calcining method practiced in this study. in regards to the exposure time during the experimentation, logically the calcium oxide should react with the environmental carbon dioxide to produce calcium carbonate as mentioned by santhakumar [50]. still, no traces of calcium carbonate due to this phenomenon has been detected either. this finding suggest that the rate of hydration is faster than the rate of carbonation. it has been further theorized by this study that the level of carbon dioxide concentration (0.0552%) versus the level of relative humidity concentration (>60%) may have a direct influence in the speed of reaction between the two. 2-dimensional topography 3-dimensional topography platy appearance (a) (b) 23 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 the calcined mussel shell which is technically calcium oxide, is the first intermediate product formed during the high temperature treatment. this is followed by the second intermediate product which is the calcium hydroxide formed during the concrete mixing activity when the intermixed cement-calcined mussel shell ash reacts with the added water. this is verified through the live-image during hydration that was captured using a digital camera that was attached to an optical microscope which showed the characteristic hexagonal morphology of the calcium hydroxide (fig. 6(a) and (b)). this is also observed under sem microscopy (fig. 7) and has been also crossed verified with other study [62]. fig. 6: micrograph of the calcium hydroxide crystal exposed to visible spectrum wavelength (a) at 1000x (b) enlarged (zoom-in). fig. 7: sem image of calcium hydroxide crystal exposed to x-ray spectrum wavelength. figure 8 summarized the diffractograms of the mussel shell at different stages. based on fig. 8, the last stage (post-morphing) was tested at 180 days and it was found that a large portion of the calcium hydrate (ch) remained un-carbonated. there are two hypothetical statements that may be associated with this phenomenon. first, based on the evidence from the microstructure analysis, calcium carbonate appears to engulf the surrounding area where it has grown. this may create a layer of canopy or a blanket that shielded the underneath (1000x optical magnification) (a) (b) (enlarged) 24 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 and deeper ch from reacting with the carbon dioxide gas at surface level. more evidence linking to the blanket appearance of lime is portrayed in several other literatures [63,64]. second, the degree of carbonation may simply has not reach a substantial level to convert a major amount of ch. it is also interesting to note that lime that was originally of the aragonitic system turned out to be calcitic after calcination and re-carbonation for 180 days. this is tally with the statement by boggs [51]. however, this study is yet to fully understand the cause of this event but suffice to say, that the polymorph of these two crystals may change under certain circumstances even though they were once come from the same material. hence, the importance of conducting more future studies on this particular subject. fig. 8: summary of mussel shell chemical and mineralogical analyses at different stages. 3.5 carbonation the obtained (actual) data are paired against theoretical (calculated) data using the model described in [65]. they are found to correlate positively and are in high agreement (r2 approaching 0.9 and above). however, replacement percentage of plf is inversely proportional to the correlation agreement value. this outcome suggests that, at a sufficiently high amount of replacement, the commonly used carbonation estimation model may no longer be valid. as for the scope of this study, it can be seen that 10% replacement exhibit a signal of downtrend in the r2 where the value is marginally reaching 0.9 (fig. 9(d)). this signify the limit of replacement where the model described in neville [65] may stay true. it was found that the average carbonation depths of concrete containing the plf are lower than the control concrete. although, control concrete group in itself performed well below the typical carbonation coefficient range of 3-4 mm/√year. the carbonation coefficient of the control concrete is at 2.92 mm/√year and this indicates a performance of better than average. the presence of the plf improved the performance even more with a descending carbonation coefficient pattern across all experimental concrete samples. the carbonation coefficients of the plf5, plf7.5 and plf10 are 1.83, 1.79 and 1.43 mm/√year respectively. based on the coefficients, plf10 concrete indicated the highest improvement which is up to a maximum of 51% lower carbonation coefficient compared to the control concrete. figure 9 shows the correlational measurements of the actual and calculated data. 25 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 fig. 9: correlative measurement of the actual and theoretical data (a) control sample (b) at 5% of plf (c) at 7.5% of plf and (d) at 10% of plf. incorporation of cementitious material greater than 5% interrupts the original requirement of cem1 opc which does not allow for such matter. higher replacement than 5% will results to the reclassification into different cement class. even so, if this limitation is to be considered, 5% incorporation of plf already improves the carbonation coefficient by as much as 37% which is rather significant. within the scope of this study, it seems possible to push replacement level beyond 5% limitation. palm [66] showed that it is possible to incorporate high lime material (up to 50% replacement) while still keeping the carbonation performance on par with the control concrete. however, palm [66] method required a proper water to cementitious ratio adjustment to achieve that. this is probably due to the different water demand for proper hydration when the cement is replaced at such a higher percentage. in the point of academicals arguments, it is indeed possible. however, practical engineering knowledge may not allow for such a high replacement due to the need of balancing for other admixtures such as plasticizer, accelerator and water proofing. hence, the method practiced in this study (lower replacement but better performance) has better advantage in terms of allocating rooms for other cementitious materials that are synonym in most civil engineering projects. 3.6 fesem and edx concrete samples containing plf which were exposed to natural carbonation for 180 days with a mean co2 level of 552 ppm (global co2 baseline is 400 ppm) at a humidity of 60-75% and daily temperature of 28-34 oc, indicate lesser porosity compared to the control specimen. figure 10 shows the fesem image of the control and plf5 concretes at a similar magnification of 2000x. the red lines are the capillarity of the concrete. the more of these line present, the more intense the capillary networks which are responsible for the overall porosity of the binder matrix. only locations with deep fall were marked. shallow falls were not considered as discontinuity since they may have just been variations in surface elevation. concrete containing 5% (fig. 10(b)) showed significantly lower discontinuity compared to r² = 0.9675 0 0.5 1 1.5 0 0.5 1 1.5 2 2.5 a c tu a l d e p th , m m theoretical depth, mm plf5 r² = 0.938 0 0.5 1 1.5 0 0.5 1 1.5 2 2.5 a c tu a l d e p th , m m theoretical depth, mm plf7.5 r² = 0.8995 0 0.2 0.4 0.6 0.8 1 1.2 0 0.5 1 1.5 2 2.5 a c tu a l d e p th , m m theoretical depth, mm plf10 r² = 0.9865 0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5 a c tu a l d e p th , m m theoretical depth, mm control(a) (b) (c) (d) 26 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 the control concrete (fig. 10(a)) which may explain the lower carbonation depth in the phenolphthalein test, hence lower carbonation coefficient. this study is confident that this phenomenon is contributed by the post-morphing of the plf during exposure. point-by-point surface elemental analysis of the specimen containing 5% plf indicated the presence of all elements that make up the calcium carbonate which are calcium (fig. 10(c)), carbon (fig. 10(d)) and oxygen (fig. 10(e)). no other unknown elements nor elements that are not indigenous to the original composition of a hardened concrete were detected except for aurum (au) which is technically the gold coating, hence excluded. fig. 10: intensity of capillarity (a) control sample (b) sample with 5% plf and surface elemental mapping (c) calcium (d) carbon (e) oxygen. in fig. 11(a), it can be seen that at 8000x magnification, discontinuity, pores and typical hardened concrete products (csh, ettringite, etc.) can clearly be seen. however, this is not the case for the plf concretes especially for the plf7.5 (fig. 11(b)) and plf10 (fig. 11(c)) in which the typical products were not seen at the same level of magnification of 8000x. they are all concealed by the post-morphing of the lime. this is again verified by the edx and the morphological images of the lime are identical across several other literatures such as those depicted by chang [67] and hamester [63]. note that the flakes of lime in for plf7.5 (fig. 11(b)) is thinner than plf10 (fig. 11(c)). this is probably due to the lower concentration of the plf. at lower concentration, the amount of carbonate minerals may not be sufficient to form the 3-dimensional structure vividly. if a sufficiently high concentration of carbonate mineral is present, the geometric arrangement of a = b ≠ c stated (c) (d) (e) scanned area for edx (detected elements) (a) (b) 27 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 in [51] becomes more pronounced such as in plf10 (fig. 11(c)) and hence, emanating cuboidal and “boxy” features across the surface. fig. 11: plf’s filler effect that enclosed (blanket) the concrete surface (a) control sample (b) sample with 7.5% plf and (c) sample with 10%plf. 4. conclusions based on the conducted experiments, several conclusions can be deduced; • mussel shells are composed of aragonitic calcium carbonate in which the crystal system may change to calcitic under certain condition. csh gel flakes of lime (thin) flakes of lime (thick) 28 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 • both aragonitic and calcitic calcium carbonate are denser (27.8% and 18.3% respectively) than concrete, hence their high potential as filler materials. • aragonite is denser than calcite due to its close-pack crystal arrangement. • concrete containing up to 10% plf showed significantly lowered carbonation coefficient (up to 51%) and lower intensity of capillarity. • fesem analysis provided an incontrovertible evidence that the mussel shell ash (plf) has clogged up the experimental concrete pores which was not found within the control sample. acknowledgement the authors acknowledge funding from the research grant vot no. h353, received from the research management centre (rmc) for the universiti tun hussein onn malaysia (uthm) for the success of this research works. references [1] sideris kk, anagnostopoulos ns. (2013) durability of normal strength selfcompacting concretes and their impact on service life of reinforced concrete structures. construction and building materials, 41: 491–497. https://doi.org/10.1016/j.conbuildmat.2012.12.042 [2] phung qt, maes n, jacques d, bruneel e, van driessche i, ye g, de schutter g. (2015) effect of limestone fillers on microstructure and permeability due to carbonation of cement pastes under controlled co2 pressure conditions. construction and building materials, 82: 376–390. https://doi.org/10.1016/j.conbuildmat.2015.02.093 [3] rezvani m, proske t. (2017) influence of chemical-mineralogical properties of limestone on the shrinkage behaviour of cement paste and concrete made of limestonerich cements. construction and building materials, 157: 818–828. https://doi.org/10.1016/j.conbuildmat.2017.09.101 [4] ekolu so. (2016) a review on effects of curing, sheltering, and co2 concentration upon natural carbonation of concrete. construction and building materials, 127: 306– 320. https://doi.org/10.1016/j.conbuildmat.2016.09.056 [5] shibata t. (2002) cost of corrosion in japan. corrosion science & technology, 31(2): 97-102. [6] benítez p, rodrigues f, talukdar s, gavilán s, varum h, spacone e. (2019) analysis of correlation between real degradation data and a carbonation model for concrete structures. cement and concrete composites, 95: 247–259. https://doi.org/10.1016/j.cemconcomp.2018.09.019 [7] nakai a, imamoto k, kiyohara c, sato s, tanaka a, niwano k, amemiya s. (2013) influence of finishing materials on carbonation suprression of concrete in existing structure. rilem international workshop on performance-based specification and control of conrete durability, 377-384. [8] lollini f, redaelli e, bertolini l. (2016) a study on the applicability of the efficiency factor of supplementary cementitious materials to durability properties. construction and building materials, 120: 284–292. https://doi.org/10.1016/j.conbuildmat.2016.05.031 [9] bogas ja, real s, ferrer b. (2016) biphasic carbonation behaviour of structural lightweight aggregate concrete produced with different types of binder. cement and concrete composites, 71: 110–121. https://doi.org/10.1016/j.cemconcomp.2016.05.006 29 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 [10] mohammed mk, dawson ar, thom nh. (2014) carbonation of filler typed selfcompacting concrete and its impact on the microstructure by utilization of 100% co2 accelerating techniques. construction and building materials, 50: 508–516. https://doi.org/10.1016/j.conbuildmat.2013.09.052 [11] singh n, singh sp. (2016) carbonation resistance and microstructural analysis of low and high volume fly ash self compacting concrete containing recycled concrete aggregates. construction and building materials, 127: 828–842. https://doi.org/10.1016/j.conbuildmat.2016.10.067 [12] shah v, bishnoi s. (2018) carbonation resistance of cements containing supplementary cementitious materials and its relation to various parameters of concrete. construction and building materials, 178: 219–232. https://doi.org/10.1016/j.conbuildmat.2018.05.162 [13] li z, li s. (2018) carbonation resistance of fly ash and blast furnace slag based geopolymer concrete. construction and building materials, 163: 668–680. https://doi.org/10.1016/j.conbuildmat.2017.12.127 [14] marques pf, chastre c, nunes â. (2013) carbonation service life modelling of rc structures for concrete with portland and blended cements. cement and concrete composites, 37(1): 171–184. https://doi.org/10.1016/j.cemconcomp.2012.10.007 [15] tekin i, yasin durgun m, gencel o, bilir t, brostow w, hagg lobland he. (2017) concretes with synthetic aggregates for sustainability. construction and building materials, 133: 425–432. https://doi.org/10.1016/j.conbuildmat.2016.12.110 [16] proske t, hainer s, rezvani m, graubner ca. (2014) eco-friendly concretes with reduced water and cement content mix design principles and application in practice. construction and building materials, 67(part c): 413–421. https://doi.org/10.1016/j.conbuildmat.2013.12.066 [17] harilal m, rathish vr, anandkumar b, george rp, mohammed mshs, philip j, amarendra g. (2019) high performance green concrete (hpgc) with improved strength and chloride ion penetration resistance by synergistic action of fly ash, nanoparticles and corrosion inhibitor. construction and building materials, 198: 299– 312. https://doi.org/10.1016/j.conbuildmat.2018.11.266 [18] cui d, banthia n, wang q, sun w. (2019) investigation on porosity of partly carbonated paste specimens blended with fly ash through dual ct scans. construction and building materials, 196, 692–702. https://doi.org/10.1016/j.conbuildmat.2018.11.156 [19] esquinas ar, ledesma ef, otero r, jiménez jr, fernández jm. (2018) mechanical behaviour of self-compacting concrete made with non-conforming fly ash from coalfired power plants. construction and building materials, 182: 385–398. https://doi.org/10.1016/j.conbuildmat.2018.06.094 [20] bucher r, diederich p, escadeillas g, cyr m. (2017) service life of metakaolin-based concrete exposed to carbonation: comparison with blended cement containing fly ash, blast furnace slag and limestone filler. cement and concrete research, 99: 18–29. https://doi.org/10.1016/j.cemconres.2017.04.013 [21] carević v, ignjatović i, dragaš j. (2019) model for practical carbonation depth prediction for high volume fly ash concrete and recycled aggregate concrete. construction and building materials, 213: 194–208. https://doi.org/10.1016/j.conbuildmat.2019.03.267 [22] younsi a, turcry p, aït-mokhtar a, staquet s. (2013) accelerated carbonation of concrete with high content of mineral additions: effect of interactions between hydration and drying. cement and concrete research, 43(1): 25–33. https://doi.org/10.1016/j.cemconres.2012.10.008 [23] yagüe a, valls s, vázquez e, albareda f. (2005) durability of concrete with addition of dry sludge from waste water treatment plants. cement and concrete research, 35(6): 1064–1073. https://doi.org/10.1016/j.cemconres.2004.07.043 30 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 [24] sideris kk, tassos c, chatzopoulos a, manita p. (2018) mechanical characteristics and durability of self compacting concretes produced with ladle furnace slag. construction and building materials, 170: 660–667. https://doi.org/10.1016/j.conbuildmat.2018.03.091 [25] palm s, proske t, rezvani m, hainer s, müller c, graubner ca. (2016) cements with a high limestone content mechanical properties, durability and ecological characteristics of the concrete. construction and building materials, 119: 308–318. https://doi.org/10.1016/j.conbuildmat.2016.05.009 [26] el-hassan h, shao y. (2015) early carbonation curing of concrete masonry units with portland limestone cement. cement and concrete composites, 62: 168–177. https://doi.org/10.1016/j.cemconcomp.2015.07.004 [27] hussin mh, othman nh, wan ibrahim mh. (2019) carbonation of concrete containing mussel (perna viridis) shell ash. journal of engineering, design and technology, 17(5): 904–928. https://doi.org/10.1108/jedt-12-2018-0228 [28] phung qt, maes n, jacques d, bruneel e, van driessche i, ye g, de schutter g. (2015) effect of limestone fillers on microstructure and permeability due to carbonation of cement pastes under controlled co2 pressure conditions. construction and building materials, 82: 376–390. https://doi.org/10.1016/j.conbuildmat.2015.02.093 [29] lollini f, redaelli e, bertolini l. (2014) effects of portland cement replacement with limestone on the properties of hardened concrete. cement and concrete composites, 46: 32–40. https://doi.org/10.1016/j.cemconcomp.2013.10.016 [30] río o, nguyen vd, nguyen k. (2015) exploring the potential of the functionally graded sccc for developing sustainable concrete solutions. journal of advanced concrete technology, 13(3): 193–204. https://doi.org/10.3151/jact.13.193 [31] rezvani m, proske t. (2017) influence of chemical-mineralogical properties of limestone on the shrinkage behaviour of cement paste and concrete made of limestonerich cements. construction and building materials, 157: 818–828. https://doi.org/10.1016/j.conbuildmat.2017.09.101 [32] courard l, michel f. (2014). limestone fillers cement based composites: effects of blast furnace slags on fresh and hardened properties. construction and building materials, 51: 439–445. https://doi.org/10.1016/j.conbuildmat.2013.10.076 [33] valcuende, m., & parra, c. (2010). natural carbonation of self-compacting concretes. construction and building materials, 24(5), 848–853. https://doi.org/10.1016/j.conbuildmat.2009.10.021 [34] meddah ms, lmbachiya mc, dhir rk. (2014) potential use of binary and composite limestone cements in concrete production. construction and building materials, 58: 193–205. https://doi.org/10.1016/j.conbuildmat.2013.12.012 [35] tsivilis s, batis g, chaniotakis e, grigoriadis g, theodossis d. (2000) properties and behavior of limestone cement concrete and mortar. cement and concrete research, 30(10): 1679–1683. https://doi.org/10.1016/s0008-8846(00)00372-0 [36] dhouibi l, triki e, raharinaivo a. (2002) the application of electrochemical impedance spectroscopy to determine the long-term effectiveness of corrosion inhibitors for steel in concrete. cement and concrete composites, 24(1): 35–43. https://doi.org/10.1016/s0958-9465(01)00062-2 [37] dariva cg, galio af. (2014) corrosion inhibitors–principles, mechanisms and applications. developments in corrosion protection, 16: 365-378. http://dx.doi.org/10.5772/57255 [38] possan e, thomaz wa, aleandri ga, felix ef, dos santos acp. (2017) co2 uptake potential due to concrete carbonation: a case study. case studies in construction materials, 6: 147–161. [39] oliveira tv, nogueira aa. (2016) analysis of development of carbonation and surface wear of the concrete: a case study in ship lock 1 of the transposition system of tucuruí dam. journal of building pathology and rehabilitation, 1(1): 1–8. https://doi.org/10.1007/s41024-016-0019-0 31 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 [40] ministry of energy, green technology and water (2017), green technology masterplan malaysia 2017-2030. malaysia. https://doi.org/isbn no. 978-967-5893-09-4 [41] hussin mh. (2018) keupayaan kadar pengkarbonatan konkrit campuran abu kulit kupang sebagai bahan gantian separa simen. master thesis, universiti tun hussein onn malaysia, department of civil engineering. [42] teychenné dc, franklin re, erntroy hc. (1997).design of normal concrete mixes. building research establishment ltd, 331(1): 46. [43] shalon r, reinitz rc. (1958) mixing time of concrete: technological and economic aspects. building research station. [44] jenkins r, snyder rl. (1996) introduction to x-ray powder diffractometry. in introduction to x-ray powder diffractometry. john wiley. https://doi.org/10.1002/9781118520994. [45] british standards institution. determination of carbonation depth in hardened concrete by the phenolphthalein method. london, bs en 14630. 2006 [46] british standards institution. determination of resistance to carbonation. london, bs en 13295. 2004 [47] british standards institution. determination of the carbonation resistance at atmospheric levels of carbon dioxide. london, bs en 12390 – 10. 2017 [48] mehta pk, monteiro pjm. (2006) third edition prenticehall, inc., englewood cliffs, nj. in concrete: microstructure, properties, and materials. [49] khankhaje e, hussin mw, mirza j, rafieizonooz m, salim mr, siong hc, warid mnm. (2016) on blended cement and geopolymer concretes containing palm oil fuel ash. materials and design, 89: 385–398. https://doi.org/10.1016/j.matdes.2015.09.140 [50] santhakumar ar. (2007) concrete technology. oxford university press. [51] boggs s. (2009) petrology of sedimentary rocks, second edition. in petrology of sedimentary rocks, second edition (2nd ed., vol. 9780521897167). cambridge university press. https://doi.org/10.1017/cbo9780511626487. [52] waseda y, muramatsu a. (2004) morphology control of materials and nanoparticles: advanced materials processing and characterization. berlin. springer-verlag. [53] klein and dutrov (2008). the 23rd edition of the manual of mineral science (23rd ed.). hoboken, nj. wiley j. [54] wahab ma. (2009) essentials of crystallography. oxford. alpha science international. [55] antao sm, hassan i. (2010) temperature dependence of the structural parameters in the transformation of aragonite to calcite, as determined from in situ synchrotron powder x-ray-diffraction data. canadian mineralogist, 48(5): 1225–1236. https://doi.org/10.3749/canmin.48.5.1225 [56] graf dl. (1961) crystallographic tables for the rhombohedral carbonates. american mineralogist, 46: 1283–1316. [57] haldar sk. (2020) introduction to mineralogy and petrology (2nd ed.). elsevier. https://doi.org/10.1016/c2012-0-03337-6 [58] moore ch. (2001) developments in sedimentology. elsevier. [59] buasri a, chaiyut n, loryuenyong v, worawanitchaphong p, trongyong s. (2013) calcium oxide derived from waste shells of mussel, cockle, and scallop as the heterogeneous catalyst for biodiesel production. the scientific world journal, 2013. https://doi.org/10.1155/2013/460923 [60] hossain a, bhattacharyya sr, aditya g. (2015) biosorption of cadmium by waste shell dust of fresh water mussel lamellidens marginalis: implications for metal bioremediation. acs sustainable chemistry and engineering. https://doi.org/10.1021/sc500635e [61] monneron-gyurits m, joussein e, soubrand m, fondanèche p, rossignol s. (2018) valorization of mussel and oyster shells toward metakaolin-based alkaline activated material. applied clay science, 162: 15–26. https://doi.org/10.1016/j.clay.2018.05.027 32 iium engineering journal, vol. 23, no. 1, 2022 hussin et al. https://doi.org/10.31436/iiumej.v23i1.1788 [62] rochelle ca, czernichowski-lauriol i, milodowski ae. (2004) the impact of chemical reactions on co2 storage in geological formations: a brief review. geological society, london, special publications, 233(1): 87-106. [63] hamester mrr, balzer ps, becker d. (2012) characterization of calcium carbonate obtained from oyster and mussel shells and incorporation in polypropylene. materials research, 15(2): 204–208. https://doi.org/10.1590/s1516-14392012005000014 [64] hossain mz. (2013) waste shell husks concrete: durability, permeability and mechanical properties. journal of building construction and planning research, 01(03): 61–66. https://doi.org/10.4236/jbcpr.2013.13009 [65] neville am. (2011) properties of concrete (5th ed.). england. longman. [66] palm s, proske t, rezvani m, hainer s, müller c, graubner ca. (2016) cements with a high limestone content mechanical properties, durability and ecological characteristics of the concrete. construction and building materials, 119: 308–318. https://doi.org/10.1016/j.conbuildmat.2016.05.009 [67] chang jj, yeih w, huang r, chi jm. (2003) mechanical properties of carbonated concrete. journal of the chinese institute of engineers, transactions of the chinese institute of engineers,series a/chung-kuo kung ch’eng hsuch k’an, 26(4): 513– 522. https://doi.org/10.1080/02533839.2003.9670804 33 microsoft word 155-755-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 101 application of subsystems change ranking methodology in aircraft redesign process fairuz i. romli, chew junxian and cheang kian hou department of aerospace engineering, faculty of engineering, universiti putra malaysia, 43400 serdang, selangor, malaysia. firomli@eng.upm.edu.my abstract: redesigning an aircraft is hardly a straightforward task. due to its high susceptibility to change effects propagation, it becomes very important to select the right initiating change components to minimize redesign development risks. with realization that there are often several different ways to redesign an existing aircraft for satisfying similar requirements, designers might require assistance in selecting suitable initiating change components in their redesign plan. a methodology that systematically ranks the subsystems of the chosen baseline design according to their estimated redesign risk is proposed here. it is strongly believed that making this information available to designers during the early redesign stages will help them to make a better redesign plan. abstrak: reka semula sesebuah pesawat udara bukanlah satu tugas yang jelas dan mudah. memandangkan ia mudah rentan terhadap perubahan rambatan, amatlah penting untuk memilih penukaran komponen yang sesuai pada peringkat awal untuk mengurangkan masalah pembangunan reka semula. menyedari bahawa terdapat beberapa cara untuk mereka semula pesawat udara yang sedia ada, demi memperolehi keputusan keperluan yang serupa dan memberansangkan, pereka wajar mendapatkan bantuan dari segi penukaran komponen yang sesuai pada peringkat awal pembangunan reka semula yang menepati rangka pelan reka bentuk mereka. metodologi yang sistematik meletakkan subsistem dasar reka bentuk yang dipilih, berdasarkan anggaran risiko reka bentuk semula dicadangkan di dalam kertas kerja ini. menolong pereka merangka pelan reka cipta yang lebih baik. keywords: subsystems ranking; aircraft redesign; redesign plan 1. introduction today, the main challenge for aircraft manufacturers is to develop their technologically sophisticated aircraft with affordable cost and in shorter timeframe [1]. high competition in commercial aircraft industry also introduces big pressure to reduce the development risk [2]. in conjunction to this, aircraft redesign is preferred than building new, original design from scratch. in addition to being cheaper and faster to be developed, derivative aircraft feature improved performance at lower risks and their commonalities to the predecessor designs help to avoid considerable increase in airlines’ maintenance and operational costs [3]. another attractive aspect of derivative aircraft is their design certification. unlike an original aircraft design that is subject to many rigorous safety requirements, it is possible for the derivative aircraft design to benefit from past certification of its predecessor and avoid the stringent certification process. observation on the current commercial aircraft market reflects the iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 102 dominance of derivative configuration and this situation is expected to remain in the near future [4]. since redesign practice is common in aircraft industry, its utmost benefits are typically gained by the fastest manufacturers to design and develop their range of market options without making costly mistakes. in this environment of design adaptation and variation, the handling of design changes becomes a key issue. the manufacturers’ ability to address change requests from their customer airlines as early as during their negotiation process is essential to their market competitiveness [5]. a conducted study in westland helicopters company highlights that 10% to 15% of their helicopter redesign costs occurred before the sales contract is signed [6]. it can be implied that the amount is spent on planning for the required change implementation and evaluating its possible side effects. many engineering changes in aircraft development occur before the design gets to production floor [5]. late design change, as suggested by the general “rule of ten” [7] in product development, will cost as much as 10 times higher than those made in the early stages. in redesign, existing baseline design is readily well-defined and lack of early design information is not an issue. designers can use this information to fully capture the consequences from their redesign proposal and eliminate arising needs for late changes due to overlooked impact. with high constraints on time and resources, any mistakes in redesign planning could be detrimental to its success. to be able to compete with the relatively higher market interest for original designs, derivative aircraft design and development needs to be accomplished with lower costs and in a shorter timeframe. this means that the early redesign decisions have to be correctly made in order to avoid late changes and to minimize the overall redesign risks. at the beginning of aircraft redesign process, designers have to decide on initial changes to be implemented into the baseline design that could improve its capability to satisfy the driving requirements. in general, this is hardly straightforward task because there are often a plethora of ways to modify the aircraft for the same requirements. for instance, if the total aircraft weight is to be reduced, designers have the options to minimize the weight of many onboard subsystems. the key question now becomes: which of these subsystems has minimum level of redesign risk when subjected to the intended changes? each subsystem often has different levels of cost and design complexity; hence the change effects would also be different. additionally, it can be observed that aircraft subsystems are highly and intricately interrelated. this makes its redesign process susceptible to change propagation phenomenon, which refers to the situation where an initial modification necessitates other major changes in the baseline design during its implementation. hence improper choice of change initiating subsystem may produce additional side effects that can negatively affect the development efforts. among others, these include an increased development cost and a prolonged development time. with its high design complexity and total number of parts that amounted to more than a million, the change decisions during aircraft redesign are not easy to make. driven by this realization, the subsystems change ranking methodology (scram) is proposed as a decision-making aid for aircraft designers. in principle, scram is a generic method that can be applied to any product redesign process. nevertheless, in this paper, its application is highlighted for aircraft redesign process. its application is expected to assist designers to identify the subsystems that could be changed with low potential risk for the redesign task at hand. besides facilitating designers in selecting the initial changes, this iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 103 method is also anticipated to improve the overall competitiveness of the aircraft redesign process by minimizing the development risk. 2. selection of initial changes in aircraft redesign the challenges to redesign an aircraft system are mainly due to its multi-disciplinary nature, as characterized by the influence that its design disciplines have on each other. for instance, the aerodynamic lift and yaw moments drive the size of horizontal stabilizer and rudder, which in turn affects the design of flight controls system [2]. this condition also raises the possibility for change effects propagation, which is directly proportional to the connectivity level between parts comprising the design. the interrelationships between aircraft subsystems complicate its redesign with many potentially complex propagation paths that interact with each other. as depicted by error! not a valid bookmark self-reference.: propagation of engineering change effects. , change effects can be directly or indirectly propagated throughout the aircraft design architecture. because of this, it is very easy for the redesign process to become mismanaged and consequently trigger unexpected changes due to any overlooked side effects from the initial change implementation. some examples of drawbacks in the automotive and aeronautics industries due to mismanaged change process have been discussed in [8], which commonly sum up to cost increment and prolonged schedule. error! not a valid bookmark self-reference.: propagation of engineering change effects. 2.1 change initiating subsystem ideally, the redesign planning process could be generalized as in error! reference source not found.. the first step is to identify and establish the customer or market requirements that are driving the needs to redesign the baseline aircraft. to satisfy these iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 104 requirements, suitable redesign changes are planned. the proposed changes will then be assessed and the outcome from the evaluation process determines whether they are approved or disapproved for actual implementation. if approved, the proposal goes through a formal change management process before being applied into the derivative development. no iteration would be required if the proposal is good and the resultant derivative design is able to match all its driving requirements. one of the first decisions to be made during planning of aircraft redesign is to identify the subsystems to be modified in order to satisfy the driving requirements. since the cost and the process complexity to change the design of one subsystem is not similar to each other, different choice of initial change subsystem typically corresponds to dissimilar level of change effects and redesign risks. moreover, the extent of potential change propagation between aircraft subsystems depends on this decision. choosing a highly interconnected subsystem increases the possibility to affect many other subsystems. overall, the selection of initial change subsystems has a big influence to the redesign development process. all efforts and resources spent could be wasted if an improper choice is made. error! reference source not found.: generalized redesign process. to highlight the importance of selecting the right initiating component, consider the notional product architecture shown in fig. 1. each of its components has been arbitrarily assigned with a qualitative label that reflects on their difficulty to be changed. assuming parts b, d and f can be equally chosen to undergo initial modification to satisfy the same driving requirement, it can be seen that each option will lead to different levels of redesign efforts. this is due to their degree of interconnections with each other. while part b has a low difficulty level to be changed, it can iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 105 propagate the change effects to both parts a and c that are of high difficulty. on the other hand, parts d and f are both assigned with high change difficulty ratings. by changing part d, part e that is also of a high difficulty may be affected. part f, despite having a high difficulty rating, is not connected to other parts and therefore contains the change effects to itself. fig. 1: notional example product architecture. it is evident in the above simple example case that the best choice of change initiating component is not straightforward, which is even harder to make in complex redesign tasks. the difficulty to modify the initial subsystem does not reflect on the full extent of redesign efforts that it will cause to the whole aircraft architecture. in short, this highlights the fact that selection of change initiating subsystem requires more considerations than just how difficult it is to change a particular subsystem. 2.1 estimating redesign risk in general, the required amount of redesign costs and efforts will translate into risks if the resultant redesigned product fails to meet all requirements even after the modification has been made. based on a widely-used scheme within the product risk management field, redesign risk associated with changes on a particular component can be estimated by the product of its likelihood to be changed and the measure of subsequent impacts from those changes [9, 10]. in parallel to the interest of this study, derivation of change likelihood and impact parameters must reflect on the focus of initiating change decision. during decisionmaking process to choose initiating change subsystems in early redesign phase, the whole redesign plan is largely unknown. hence the risk of selecting a particular initiating change subsystem has to be estimated without knowing for certain the other subsystems that are affected by its change effects propagation. knowing that propagation of change effects is only possible between two subsystems through their physical or functional links, the number of links can be taken as a descriptive measure for possibility of requiring changes. for instance, if subsystem a is not linked to subsystem b, then choosing subsystem a as the initiating change subsystem will not affect the latter. in the meantime, if a has interconnections to both subsystems c and d, the possibility of c and d to also require changes due to the propagated change effects from a is theoretically proportional to their interrelationship strength. this means, if subsystem a has more links to c than d, then change likelihood for c due to modification made in a should be higher than that for d. in addition, to capture the indirect change propagation effects in the iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 106 estimation of redesign risk, change likelihood of subsystems throughout the possible propagation paths should also be taken into account. as the propagated effects are highly dependent on the change likelihood of previous subsystem in the propagation tree, the probability will cascade from the initiating change subsystem to those at the end of the propagation paths [11]. based on the above arguments, change likelihood for subsystem i that is directly linked to initiating change subsystem j can be estimated using eq. (1). s for ier of linktotal numb i to jlinks fromnumber of ijp  (1) meanwhile, the estimated change likelihood for subsystem k that is indirectly linked to the initiating change subsystem j through component i is given by eq. (2).        s for ker of linktotal numb k to ilinks fromnumber of ijpkjp (2) for most engineering projects, the focus of risk analysis is often placed on the feasibility and the viability of the product design and its development process [12]. this can also be implied for aircraft redesign process. following this argument, change impact measure can be based on the anticipated cost and the process difficulty to execute the modification. to support this, it has been proposed that the competitive measures for an engineering change process be reflected by the number of changes, the duration of its handling time and the required amount of cost or effort [13]. naturally, a difficult design alteration also means higher costs and longer development time. however, recall that at this stage, information on the specific change type and level to be made is not yet available. thus the assignment of change impact measure, designated here as i, can only be based on the assessment of available technologies and resources at the designer’s disposal to execute the prescribed changes. a simple qualitative rating scale is employed here as in table 1. according to this, the highly preferred rating is 1 while a rating of 9 is the least preferred. table 1: change impact rating scale. rating description 1 change impact is expected to be very low and the subsystem is highly preferred to be changed in relative to others. 2 change impact is expected to be low and the subsystem is preferred to be changed in relative to others. 3 change impact is expected to be manageable and there is no preference in changing this subsystem relative to others. 5 change impact is expected to be high and the subsystem is preferred not to be changed in relative to others. 9 change impact is expected to be very high and the subsystem is iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 107 rating description highly preferred not to be changed in relative to others. overall, the estimated total redesign risk, r associated with the selection of subsystem j as the initiating change subsystem, and its modification directly affects subsystem i and indirectly affects subsystem k through subsystem i, can be evaluated using eq. (3).      kikipijpiiijpjijr  1 (3) 3. proposed methodology the overall framework for the method is depicted in error! reference source not found.. in short, it starts with the aircraft change modeling process. using the resultant model, the risk associated with the selection of each subsystem as the redesign change initiator is evaluated in a case-by-case basis. finally, the results are used to rank the subsystems to identify the least risky one. the detailed description for each step of the method is presented in the following sections, which is supported with a notional sample case study. step 1: aircraft change modeling the objective of this step is to create a well-balanced aircraft model for predicting the change effects propagation and analyzing the associated change impacts to help support the decision-making process. firstly, design structure matrix (dsm) representation has been chosen for the change model. at the moment, dsm is the best representation for use in the product engineering change study [14]. secondly, the aircraft needs to be physically broken down in order for interrelationship links between its components to be identified. the model needs to at least capture the major components of its subsystems. moreover, to be aligned with the real industrial practices, the aircraft system physical decomposition is tailored to the standard ata 100 classification [15]. error! reference source not found.: proposed methodology flowchart. the summarized dsm representation of aircraft model to be applied in the subsequent sample case study is shown in error! reference source not found., which involves only nine subsystems instead of the total aircraft subsystems. this is purposely done here to enable a better demonstration of the proposed method. in addition, note that modeling actual existing iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 108 aircraft system is hard due to limited availability of descriptions in public domain regarding their full subsystems build-up. the next best thing is to create a notional aircraft system, which is modeled here using the generalized subsystem information of a few existing aircraft. in error! reference source not found., each “x” mark indicates that the subsystems of respective row and column are interrelated such that change effects can be propagated between them. on contrary, empty boxes indicate no interrelationship between the corresponding subsystems. it is good to note that all indirect change relationships are not visible in this representation. error! reference source not found.: dsm model of aircraft subsystems. ata 22 24 27 28 29 34 36 57 71 22 x x x x 24 x x x x x x x 27 x x x x x 28 x x 29 x x x x x 34 x x x 36 x x 57 x x 71 x x ata 22: automatic flight subsystem, ata 24: electrical power subsystem, ata 27: flight controls subsystem, ata 28: fuel subsystem, ata 29: hydraulics subsystem, ata 34: navigation subsystem, ata 36: pneumatic subsystem, ata 57: wings, ata 71: propulsion step 2: redesign risk estimation once the aircraft model has been successfully constructed, the next following step is to estimate each subsystem’s change likelihood when one of them is subjected to changes. referring to error! reference source not found., each “x” mark is replaced by their corresponding change likelihood as estimated using eq. (1). for the notional aircraft model used in this sample case, the calculated values are indicated in error! reference source not found.. before redesign risk can be estimated, change impact rating for each subsystem has to be assigned based on the rating scale in table 1. once this is done, overall redesign risk associated with the selection of each subsystem as the change initiator can be evaluated using eq. (3). error! reference source not found.: subsystem change likelihood. ata 22 24 27 28 29 34 36 57 71 22 0.04 0.12 0.00 0.01 0.82 0.00 0.00 0.00 24 0.04 0.04 0.04 0.03 0.04 0.03 0.00 0.02 27 0.12 0.04 0.00 0.28 0.02 0.00 0.07 0.00 28 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.05 29 0.01 0.03 0.03 0.00 0.00 0.01 0.09 0.00 34 0.08 0.04 0.02 0.00 0.00 0.00 0.00 0.00 36 0.00 0.03 0.00 0.00 0.01 0.00 0.00 0.00 57 0.00 0.00 0.07 0.00 0.09 0.00 0.00 0.00 iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 109 71 0.00 0.03 0.00 0.05 0.00 0.00 0.00 0.00 ata 22: automatic flight subsystem, ata 24: electrical power subsystem, ata 27: flight controls subsystem, ata 28: fuel subsystem, ata 29: hydraulics subsystem, ata 34: navigation subsystem, ata 36: pneumatic subsystem, ata 57: wings, ata 71: propulsion in general, the assignment of change impact rating will depend on the redesign goals. two scenarios are formulated for the example case study to observe the sensitivity of the proposed method in capturing different preferences and objectives of the redesign process. the first scenario assumes that all subsystems have equal level of expected change impact and there is no obvious change preference between them. this condition is captured by assigning the change impact rating for all subsystems as 1. on the other hand, the second redesign scenario is linked to the cost factor. subsystems with high development cost are taken to be more expensive to be changed and thus they are preferred not to be affected in the aircraft redesign planning. the assignment for this second scenario is made based on cost breakdown in error! reference source not found., which is the fractional manufacturing cost of the boeing b777-200 aircraft. all in all, error! reference source not found. summarizes the assignment of change impact rating for the two scenarios. error! reference source not found.: manufacturing cost breakdown of b777-200 aircraft [16]. error! reference source not found.: assignment of change impact rating. ata change impact rating scenario 1 scenario 2 22 1 2 24 1 2 27 1 2 28 1 1 29 1 1 34 1 2 iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 110 ata change impact rating scenario 1 scenario 2 36 1 1 57 1 9 71 1 3 the redesign risk is then calculated using the likelihood and impact rating values. for this study, a matlab program is developed to calculate redesign risk based on the userdefined model and impact rating inputs. the results for the first scenario are presented in error! reference source not found., which is plotted in relative measure against the highest calculated risk value. in similar fashion, results for the second scenario are shown in . based on this, ranking of the subsystems in terms of their estimated redesign risk can be established. error! reference source not found.: relative redesign risk for scenario 1. iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 111 : relative redesign risk for scenario 2. step 3: subsystems ranking in error! reference source not found., the automatic flight (22) and flight controls (27) subsystems have the highest redesign risk, as both correspond to the relative risk score of 1. on the other hand, the lowest ranked subsystem with respect of being risky to be redesigned is the pneumatic (36) subsystem. to interpret this result, recall back the settings for the first scenario in which all subsystems are assigned with the same impact rating of 1. for this particular condition, the estimated redesign risk heavily depends on the likelihood that the choice of one subsystem as the change initiator will subsequently affect other subsystems. in other words, the resultant ranking reflects on the risk of having to change other subsystems as a result of choosing a particular one as the initiating subsystem. based on the constructed notional aircraft model, both auto flight and flight control subsystems comparatively have among the highest number of interrelationships with the other subsystems. in contrast, pneumatic has the least amount of interconnections. this is also reflected by error! reference source not found., which means that the results are in line with the expectation for this particular scenario. for scenario 1, based on the resultant ranking, choosing auto flight and flight control as the change initiating subsystem corresponds to the highest redesign risk among the nine considered subsystems. on the other hand, pneumatic has the lowest risk if chosen as the change initiator. hence given a redesign task where either one of the nine subsystems can be chosen to be initially changed (such as to reduce aircraft empty weight), then pneumatic appears to be the best choice since any changes made to it will not affect most of the other subsystems. iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 112 on the other hand, scenario 2 mimics the sole consideration of risk due to anticipated development costs. referring back to error! reference source not found., it can be observed that the results are in good agreement with the cost breakdown. wing (57) is decidedly the costliest subsystem to be modified and therefore scores the highest redesign risk as shown in . this is despite the fact that changing the wing will not affect as many subsystems as the other eight. on the other hand, observing the risk scores for automatic flight (22), electrical power (24), flight controls (27) and navigation (34); their differences can be contributed to the risk of their propagated change effects. though they all are assigned with similar change impact rating (they are perceived to be of similar level of change cost), their interrelationships to other subsystems are affecting their risks valuation. comparing the electrical power and flight controls, for instance, the former gets a lower risk score despite having more links to other subsystems than the latter. it could be argued that this condition happens because, though selecting electrical power also means requiring more subsystems to be redesigned than that imposed from the selection of flight controls, most of its directly and indirectly affected subsystems are of low impact ratings. hence its overall redesign risk is lower than that of flight controls. on the whole, given a redesign task where cost is the main factor for manufacturer and any one of these nine subsystems can be selected for modification, wing is not the best choice as it incurs the highest redesign cost. alternatively, pneumatic or fuel is the best choice with the cheapest estimated costs. 4. conclusion and future works this paper proposes a simple yet powerful methodology to assist aircraft designers in deciding on the proper initiating change subsystems during the early redesign stages. the resultant ranking from this method allows designers to gain an insight on how risky it is to choose the subsystem for initial redesign task. definition of risk here can vary depending on the designer’s redesign goal, as demonstrated by the sample case study. the formulated scenarios represent two different redesign process concerns, which correspond to different results. this adds to the flexibility of application for this proposed method. on the whole, the resultant ranking can be used by designer to support their decision-making process as to which subsystem is the best choice to be initially changed such that the incurred risk is low. the results for the sample case study are in line with expectations. nonetheless, having only nine aircraft subsystems instead of the total 34 makes the results too predictable and is not truly representative of the difficulty level of such redesign decision-making process. in addition, these subsystems also have interrelationships to the other subsystems that are not being considered in the sample case study, making the resultant ranking less reflective of the one for the whole aircraft because some propagated change effects (on subsystems that are not considered) are clearly ignored. while the sample case study is believed to be adequate to demonstrate the applicability of the proposed method, the natural next step is to apply it to the full extent of the aircraft subsystems build-up. it is realized that the precision of results from this proposed method highly depends on the inputs for the change impact rating. while the example case study utilizes a simple qualitative rating scale to facilitate the assignment of this impact rating, more standard and iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 113 structured scheme is needed to ensure the precision and the consistency of the results. this is among the areas to be further improved in the future for this proposed method. acknowledgement this research work is financially supported by university putra malaysia through the research university grant scheme (rugs) – 05-04-10-1004ru. references [1] g. e. bock, “dassault aviation: using a collaborative workspace to design and develop the falcon 7x business jet”. 2004, patricia seybold group. [2] j. a. reed, g. j. follen and a. a. afjeh, “improving the aircraft design process using webbased modeling and simulation”. acm transactions on modeling and computer simulation, 2000. 10(1): p. 58-83. [3] p. condom, “derivative strategy shows its limits”, interavia business and technology, 1997. [4] e. m. murman, m. walton, and e. rebentisch, “challenges in the better, faster, cheaper era of aeronautical design, engineering and manufacturing”. the lean aerospace initiative report series. 2000, massachusetts institute of technology: cambridge, ma. [5] a. riviere, f. feru, and m. tollenaere, “controlling product related engineering changes in the aircraft industry”, international conference on engineering design. 2003. stockholm, sweden. [6] p. j. clarkson, c. simons, and c. eckert, “predicting change propagation in complex design”. journal of mechanical design, 2004. 126(5). [7] d. e. carter, and b. s. baker, “concurrent engineering: the product development environment for the 1990s”. 1992: addison-wesley publishing company. [8] a. riviere, c. dacunha, and m. tollenaere, “performances in engineering changes management”. 4th international conference on integrated design and manufacturing in mechanical engineering (idmme). 2002: clermont-ferrand, france. [9] p. j. clarkson, c. simons, and c. eckert, “predicting change propagation in complex design”. asme design engineering technical conferences and computers and information in engineering conference. 2001. pittsburgh, usa. [10] “defense standard 00-56 (part 1): safety management requirements for defense systems”. 1996, uk ministry of defense: glasgow, uk. [11] c. j. ho, and j. li, “progressive engineering changes in multi-level product structures”. international journal of management science, 1997. 25(5): p. 585-594. [12] r. crossland, j. sims williams, and c. mcmahon, “the practical application of design risk assessment models”. journal of engineering manufacture, 2003. 217(2): p. 227-234. [13] g. q. huang, and k.l. mak, “internet applications in product design and manufacturing”. 2003, berlin, germany: springer. [14] d. m. sharman, and a. a. yassine, “characterizing complex product architectures”. systems engineering, 2004. 7(1): p. 35-60. [15] ata official website. [cited september 2005]; available from: http://www.airlines.org. [16] j. markish, “valuation techniques for commercial aircraft program design”. 2002, massachusetts institute of technology. iium engineering journal, special issue, mechanical engineering, 2011 romli et al. 114 nomenclature pij change likelihood for subsystem i due to initiating change subsystem j i change impact rating rj estimated total redesign risk associated with the selection of subsystem j as the initiating change subsystem application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 investigation on the mechanical, thermal, bio-degradation, and bio-compatibility properties of poly (lactic acid) / poly (ethylene glycol) blend zohreh zarinkolah1, hamed bagheri*1, saman hosseinkhani2, and maryam nikkhah2 1 faculty of interdisciplinary science and technology, 2 faculty of biological sciences, tarbiat modares university, tehran, iran * corresponding author: hbagheri@modares.ac.ir (received: 19th may 2020; accepted: 29th july 2020; published on-line: 4th january 2021) abstract: absorbable sutures are widely used in surgery. in addition to acceptable mechanical properties, the surgical sutures should exhibit favorable degradability properties. in this research, the mechanical and thermal properties, hydrophilicity, biodegradability, ph changes, and drug release profile of polylactic acid (pla) and polyethylene glycol (peg) alloy were examined to fabricate absorbable sutures. the test results for the mechanical properties showed that the strength of the pla/peg alloy decreased with increasing peg content, leading to an increase in elongation. the differential thermal analysis indicated that the resulting material was above its glass transition temperature (tg) at ambient temperature and was thus flexible enough. according to the degradation test results, the alloys were degraded similar to the commercial sample. furthermore, the ph measurements revealed that the degradation of the alloy had no significant effect on the ph of the environment. bupivacaine hydrochloride was incorporated into a certain amount of pla and peg, and the drug release rate was then measured. the sample provided a suitable substrate for burst release. moreover, the cytotoxicity test was carried out to evaluate the biocompatibility properties of the pla/peg alloy and it was found that this alloy is biocompatible and the biocompatibility of the material decreases with increasing drug loading. abstrak: sutur boleh serap telah digunakan dalam pembedahan secara meluas. tambahan kepada sifat-sifat mekanikal ini, sutur pembedahan perlu memiliki ciri-ciri kebolehurain yang dikehendaki. dalam kajian ini, sifat-sifat mekanikal dan terma, kehidrofilikan, kebolehuraian, perubahan ph, dan profil penguraian ubat asid polilaktik (pla) dan aloi polietilena glikol (peg) telah dikaji bagi mencipta sutur boleh serap. hasil kajian mendapati sifat-sifat mekanikal menunjukkan kekuatan pla/peg aloi berkurangan dengan penambahan level peg, menyebabkan bertambahnya pemanjangan. analisis pembezaan terma menunjukkan hasil bahan adalah melepasi suhu perubahan gelas (tg) pada suhu sekitar dan oleh itu sangat lentur. berdasarkan hasil kajian degradasi, aloi ini telah digradasi seperti sampel komersial. tambahan lagi, ukuran ph menunjukkan degradasi aloi ini tidak menunjukkan kesan langsung pada ph persekitaran. bupivacaine hidroklorida dimasukkan ke dalam pla dan peg, dan kadar ubat dibebaskan kemudiannya diukur. sampel substrat yang bersesuian disediakan bagi pelepas letus. tambahan, ujian kesitotoksikan telah dijalankan bagi menilai ciri-ciri keserasian-bio aloi pla/peg dan didapati aloi ini serasi-bio dan keserasian-bio bahan berkurangan dengan penambahan beban ubat. 223 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 keywords: surgical suture; drug release; pla / peg; bupivacaine hydrochloride; blend 1. introduction surgical sutures are one of the most common types of biomaterials. natural or synthetic sutures are used to ligate blood vessels or to hold tissues together [1][2]; hence, they can potentially be suitable for the delivery of a pain reliever in the surgical site to reduce the patient’s drug dose and potential side effects. a wide range of biopolymers have been used in various medical applications, including drug delivery. currently, most studies in this field focus on modern controlled drug delivery systems [3]. sutures have been used as a platforms for the release of antimicrobial drugs such as triclosan-coated sutures [4], which, due to drug resistance, were replaced with silver nanoparticles such as silver solution-soaked multifilament absorbable plga sutures [5][6]. to release analgesics such as ibuprofen, the drug was loaded on plga sheets and was physically connected to commercially available vicryl sutures [7]. natural compounds such as plant extracts, which are rich in phenolic compounds, have received much attention in wound healing applications [5]. a new material with desirable properties can be produced by blending various polymers. a wide range of properties can be obtained using this method to reach a specific goal in a relatively short period at a lower cost, compared to polymerization processes [8][9]. the properties of such systems can be improved using appropriate chemical and physical compatibility techniques as well as methods reducing tensile space in the molten state and increasing phase dispersion and adhesion [10]. in this study, drug-loaded sutures were prepared by mechanical blending of polylactic acid (pla) and polyethylene glycol (peg) with bupivacaine hcl as a strong local anesthetic drug having a long-lasting effect [11]. given that mechanical blending is a simple, cost-effective, and large-scale production method, and pla is much cheaper than polymers used in the surgical suture industry, the desired properties can be achieved by combining pla with other polymers. this composition has not yet been used for surgical sutures. the drug loaded on the resulting material is another novelty of the present study. 2. materials and methods 2.1 materials polylactic acid (pla) was purchased from hisun pla---revode190 (l130); polyethylene glycol (peg) with mw (6000) was purchased from merck company; bupivacaine hydrochloride was also purchased from aburaihan pharmaceutical co ltd. synthetic absorbable sutures (monocryl®) were kindly donated from eticon. 2.2 preparation of blends four samples were prepared by blending a mixture of two polymers pla / peg with 5, 10, 15, 20 wt.% peg and 60 g weight {12-14]. the material was dried in an oven at 35 °c for 10 hours. each sample was homogeneous as a result of mixing in an internal mixer manufactured by brabender germany model w50 at 180 °c and 80 rpm for a 15-minute duration. for mechanical and biological tests, the samples were prepared in sheets with 1mm diameter by hot press machine made by toyo seiki model wch (2002) at 190 °c and pressure of 50 kpa for 5 minutes. the sample was then pressurized to 27 kpa for 5 minutes by cold press. 224 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 2.3 preparation of drug-containing samples solvent casting sampling was performed on the pla/peg sample with 15 wt% peg and bupivacaine hydrochloride with 5, 10, and 15 wt% of the drug. the polymer mixture was dissolved in dichloromethane at 10 wt.%. then the weight concentrations of the drug were added to 10 wt% pla/peg polymer mixture [15]. the homogeneous solution was poured into a mold. after 72 hours, the solvent evaporation and the sample containing the drug were prepared. 2.4 mechanical testing prototyping was performed according to astm d882 with length, width, and thickness of 110, 20, and 1 mm, respectively. the test was performed by gt7010-d2e, manufactured by gotech taiwan, at a speed of 5 mm/min, with a 50 mm interval between the jaws. the test was performed on 4 samples with 5, 10, 15, and 20 wt% peg and 3 specimens were taken to determine data point. 2.5 thermal analysis to carry out this test in accordance with iso 11357, the dsc 200 f3, manufactured by netzsch, was set up at a temperature of 25 °c to 220 °c and a rate of 5 °c/min. 2.6 biodegradability test to perform this test in accordance with iso 13781, the samples were prepared in strips of approximately 10 × 20 × 5 mm and placed in 50 ml of pbs buffer with a ph of about 7.4 at 37 °c. the weight loss of the sample was examined over seven months at two-week intervals. at the specified time intervals, the samples were extracted from the buffer solution, washed twice with distilled water, and incubated at a temperature of 45 °c for 5 hours. they were then dried and weighed by scales. 2.7 measuring ph changes the samples were prepared as 10 × 20 × 5 mm strips and placed in 50 ml of phosphate buffer saline (pbs) at ph 7.4 and 37 °c. the ph changes in the solution containing the samples were performed at a time interval of 7 months and two-week intervals. at the end of the experiment, the ph value was measured by ph meter device (made by sana model sana sl-901), and then, was replaced with freshly-made pbs solution every time. 2.8 contact angle test the contact angle was measured with a drop of water (4 μl) using a system equipped with a drop-shot ccd camera and a drop-angle contact angle measurement software at the desired level. 2.9 in-vitro release study to measure the release rate, 10 mg of pla/peg polymeric sample containing 15 wt% peg and bupivacaine hydrochloride with 5, 10, and 15 wt% were prepared and dissolved in 50 ml of phosphate buffered saline (pbs) with a ph of approximately 7.4 at 37 °c by incubator shakers liebherr models manufactured by tintometer germany at 180 rpm. after 0, 0.5, 1, 4, 8, and 24 hours for 14 days, 2 ml of the extract was daily replaced with 2 ml of pbs buffer. the extract absorption rate was measured by using uv spectroscopy manufactured by biochrom u.k. model wpa to determine the concentration of the drug. 225 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 2.10 cytotoxicity test the mtt cytotoxicity test method examined the samples containing drug to measure cell viability in the presence of various concentrations of the drug. the test was performed on the mef (cf-1) and hek-293 cell lines (donated by tarbiat modarres university). 3. results and discussion 3.1 tensile test as shown in fig. 1, the stress is reduced in the samples containing 5, 10, 15, and 20 wt% peg. a comparison between the pla/peg and pure pla strain rates in fig. 2 shows that the strain is significantly influenced by increased peg level due to a decrease in pla level. this finding is reasonable since the pla/peg melt is expected to have interstitial properties. fig. 1: tensile strength properties as a function of increasing (%) peg. fig. 2: elongation properties as a function of increasing (%) peg. the stress and strain rates in pla/peg20% were not similar to the ones observed for the other samples such that the strain rate decreased with an increase in the peg level. 226 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 according to pillin et al. two substances are miscible to a certain extent under blending conditions. therefore, the observed behavior can be caused by the immiscibility of pla and peg in this composition [16]. in this study, blending process aimed at obtaining a composition with desirable properties to fabricate absorbable sutures; therefore, the final blend should have a proper strain to better control and handle the resulting sutures. on the other hand, strength is a significant factor in the preparation of sutures with desirable properties [1,17]. the main point was to find a composition with the maximum elongation against the lowest strength reduction. according to the results of the tensile test and considering the abovementioned criterion, the pla/peg sample with 15 wt% peg had the lowest strength reduction with maximum elongation. 3.2 differential thermal analysis figure 3 shows the differential thermal analysis curve for five samples. as it can be observed, the peaks in the diagram represent the phase changes of the material. fig. 3: dsc curves of pla / peg samples. according to table 1, the amount of the absorbed heat decreased with an increase in the peg level. given that the glass transition temperature (tg) of peg is 63 °c [18], the less heat absorbed for the phase change was due to an increase in the peg level. on the other hand, pla and peg are miscible, and the glass transition temperature of the polymeric alloy is expected to be decreased with the increase in the peg level. considering the low glass transition temperature of peg, the reduction in tg of the alloy is reasonable and indicates the plasticizing effect of peg as a plasticizer. the decrease in the tg peak reveals that the resulting material is softened at ambient temperature. the plasticizing effect of peg is also proven in the tensile test. on the other hand, the peak tm has also decreased due to the decrease in the pla level, and also by calculating the area under the curve of this peak (table1), it proves that the volume of heat received in the whole material has decreased. table 1: thermal properties of pla-peg blends derived from dsc curve pla/peg 20% pla/peg 15% pla/peg 10% pla/peg 5% pure pla sample 4.121 5.435 5.796 6.306 7.936 h (j/g)∆ 227 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 3.3 degradation test figure 4 presents the rate of weight loss for all the samples. all samples experienced a weight loss, compared to pure pla so that the weight loss increased with an increase in the peg level. a comparison of the graphs revealed that the degradability properties of pla were improved as a result of it being mixed with peg. the degradability rate of the commercially available monocryl poliglecaprone 25 sutures was also measured for further comparison. in this regard, pure pla revealed no weight loss within 36 weeks, and this might be due to the crystalline structure of pla [19]. the pla/peg sample containing 15 wt% peg showed a weight loss close to that of the commercial sutures. however, the weight loss of the commercial sutures was measured during a 4-week period, although there was no possibility to measure the weight because of the appearance of the sample. given the semi-crystalline structure of pla, the penetration of buffer or any other liquid into pla mass is difficult [19]. fig. 4: loss of mass of the of pla / peg specimens as a function of (%) peg. with the increase in the amount of peg added to pla, the buffer penetration into the polymeric mass improved due to the nature of peg. this led to the failure of the polymeric backbone, and the weak points in the material then caused cracking. given that wound healing requires a reduction in the strength of sutures and the gradual removal of sutures, the failure at the surface would reduce strength and eventually facilitate the removal of sutures. the micrographs of the degradation test are shown in fig. 5. 3.4 ph changes figure 6 presents ph changes during the degradation of the pla/peg samples. accordingly, the ph measured to the initial ph increased maximum 3 to 4%. given that the ph of the body is about 7.4, and the maximum change was 0.2 units, the prepared samples did not change the ph in the body. 3.5 contact angle test table 2 lists the contact angle of a water droplet on the surface of pure pla and pla/peg blends containing 5, 10, 15 and 20 wt% peg. a smaller contact angle indicates a more hydrophilic nature of the material. in this study, the contact angle decreased with increasing peg in the resulting blend, implying the effect of hydrophilic properties of peg. 228 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 fig. 5: micrograph of samples after 34th week of degradation test. fig. 6: variations in ph of the degradation media as a function of (%) peg. table 2: water contact angle measurement on surface of pla / peg samples pla/peg 20% pla/peg 15% pla/peg 10% pla/peg 5% pure pla sample 21 30 46 57 62 contact angle (degree) this in turn affected the properties of the blend so that the resulting material became more hydrophilic. since the absorbable sutures should be hydrophilic to be effectively degraded, the resulting blend was thus suitable for the desired application. as a result, pla properties were modified in this way. the effect of peg hydrophilic nature was also observed in the degradation test. the micrograph of the contact angle of the samples is shown in fig. 7. 229 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 fig. 7: water contact angle image of pla/peg samples, (a) pla/peg 5%, (b) pla/peg 10%, (c) pla/peg 15%, (d) pla/peg 20%, (e) pla. 3.6 drug release profile figure 8 shows the drug release profiles for 312 hours (13 days). the highest drug release rate occurred during 1-4 h and then a declining trend was observed. in other words, the sample provides a suitable substrate for rapid drug release in the wound site. since this study aimed at achieving sutures with desired properties for rapid drug release in the first hours of injury at the closure site of a trauma or a scar, all the three samples can be used for this purpose. the concentration of the released drug was increased with an increase in drug loading. this means that the prepared material would be a suitable substrate for the controlled drug release at a required rate. fig. 8: modeled in vivo release profiles of bupivacaine hydrochloride of pla/peg samples. 3.7 cytotoxicity test figure 9 shows the viability of mef (cf-1) cell line in the control sample and in the extract containing bupivacaine hydrochloride. as it can be observed, the viability decreased with an increase in the drug percentage [20,21]. figure 10 shows the viability of hek-293 cell line in the bupivacaine hydrochloride extract. in this test, the viability of cells decreased with an increase in the drug concentration, as compared to the control sample [20,21]. 230 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 fig. 9: percentage of cell viability on the series of the diluted extracted solution of (mef (cf-1)) in 24 hours in the vicinity of the samples containing drug. fig. 10: percentage of cell viability on the series of the diluted extracted solution of (hek-293 in 24 hours in the vicinity of the samples containing drug. according to the results of this study as well as statistical calculations, the difference in cell viability percentage is significant and in the vicinity of the cell with the material extract, has led to cell death. as can be seen in fig. 9 and fig. 10, the rate of cell death increased with increasing percentage of drug loaded in the polymer alloy. in the two types of cell lines used, the survival rate of cells is different, which is due to the difference in tolerance of different cell lines. thus, the hek-293 cell line had a lower drug tolerance compared to the cell line (mef (cf-1)). 4. conclusion polylactic acid (pla) and polyethylene glycol (peg) were mechanically blended to obtain interstitial properties. polylactic acid is a rigid brittle polymer with a high mechanical strength. pla is rigid at ambient temperature and is almost hydrophobic. polyethylene glycol is a hydrophilic polymer with a low melting point and high degradation rate. these two polymeric materials are miscible, whose blending results in interstitial properties. the resulting polymeric material is flexible and more hydrophilic than the polylactic acid and exhibits a higher strength than polyethylene glycol. according to the tensile test results, increasing the peg level caused a decrease in strength but an increase in elongation. in this study, blending aimed at obtaining a composition with desirable properties to produce absorbable sutures. accordingly, the final blend should have a proper strain for better control and mobility of the resulting sutures. on the other hand, strength is a critical factor in the preparation of sutures with desirable properties. the main point is to find a 231 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 composition with the maximum elongation against the lowest strength reduction. according to the results of the tensile test and considering the abovementioned criterion, pla/peg sample with 15 wt% peg had the lowest strength reduction with maximum elongation. the results of the degradation test indicated that increasing the peg level led to greater penetration of fluids in the polymeric mass, resulting in an increase in the degradation rate. in this study, a pla/peg sample containing 15 wt% peg showed a weight loss close to that of commercial sutures. it is worth mentioning that the difference in the weights of samples was not significant during the study period, and the material was degraded with no significant weight loss. according to the contact angle test results, the hydrophilic properties of the resulting polymeric material increased with an increase in the peg level. due to the fact that absorbable sutures should be hydrophilic to be effectively degraded, the resulting material would be suitable for the desired application. as a result, pla properties were modified in this way. the drug release profiles revealed that the maximum drug release occurred during 1-4 h, and then a declining trend was observed. with an increase in drug loading, the drug concentration also increased, suggesting that the polymeric material would be a suitable substrate for controlled drug release at a required rate. according to the results of cytotoxicity test on the drug-containing samples, the cell death rate increased with an increase in the amount of drug loaded in the polymeric blend. the cell viability was different in two types of cell lines due to the differences in the tolerance of the cell lines. references [1] pillai cks, sharma cp. (2010) absorbable polymeric surgical sutures: chemistry, production, properties, biodegradability, and performance. journal of biomaterials applications. 25(4): 291-366. http://jba.sagepub.com/content/25/4/291 [2] tajirian al, goldberg dj. (2010) a review of sutures and other skin closure materials. journal of cosmetic laser therapy, 12(6): 296-302. https://doi.org/10.3109/14764172.2010.538413 [3] ratner bd, hoffman as, schoen fj, lemons je. (1997) biomaterials science, an introduction to materials in medicine book (3rd edition) 2013. edited by ratner bd, hoffman as, schoen fj, lemons je. [4] joseph b, george a, gopi s, kalarikkal n, thomas s. (2017) polymer sutures for simultaneous wound healing and drug delivery – a review,” international journal of pharmaceutics, 524(1): 454-466, https://doi.org/10.1016/j.ijpharm.2017.03.041 [5] gallo al, paladini f, romano a, verri t, quattrini a, sannino a, pollini m. (2016) efficacy of silver coated surgical sutures on bacterial contamination, cellular response and wound healing. materials science and engineering, c69: 884-893. https://doi.org/10.1016/j.msec.2016.07.074 [6] hu w, huang zm, liu xy. (2010) development of braided drug-loaded nanofiber sutures. nanotechnology, 21(31): 315104 (11pp) [7] lee je, park s, park m, kim mh, park cg, lee s.h, choi sy, kim bh, park hj, park jh, heo cy, choy yb. (2013) surgical suture assembled with polymeric drug-delivery sheet for sustained, local pain relief. acta biomaterialia, 9(9): 8318-8327. https://doi.org/10.1016/j.actbio.2013.06.003 [8] yu l, dean k, li l. (2006) polymer blends and composites from renewable resources. progress polymer science, 31: 576-602. https://doi.org/10.1016/j.progpolymsci.2006.03.002 [9] lai w, liau w, lin t. (2004) the effect of end groups of peg on the crystallization behaviors of binary crystalline polymer blends peg / plla. polymer, 45: 3073–3080. 232 iium engineering journal, vol. 22, no. 1, 2021 zarinkolah et al. https://doi.org/10.31436/iiumej.v22i1.1478 [10] pracella m. (2017) blends and alloys. modification of properties, elsevier inc. 155-184 [11] terry d. (1990) analytical profiles of drug substances wilson sterling research & group rensselaer, 19: 59-94 [12] mohapatra ak, mohanty s, nayak sk. (2013) effect of peg on pla / peg blend and its nanocomposites: a study of thermo-mechanical and morphological characterization. https://doi.org/10.1002/pc.22660 [13] ozdemir e, hacaloglu j. (2017) characterizations of pla-peg blends involving organically modified montmorillonite. journal of analytical and applied pyrolysis 127: 343-349. [14] bramfeldt h, sarazin p, vermette p. (2008) blends as a strategy towards tailored hydrolytic degradation of poly (ε-caprolactone-co-d,l-lactide)-poly(ethylene glycol)-poly(εcaprolactone-co-d,l-lactide) co-polymers. polymer degradation and stability, 93(4): 877882. [15] weldon cb, tsui jh, shankarappa sa, nguyen vt, ma m, anderson dg, kohane ds. (2012) electrospun drug-eluting sutures for local anesthesia. journal of controlled release, 161(3): 903-909, https://doi.org/10.1016/j.jconrel.2012.05.021 [16] pillin i, montrelay n, grohens y. (2006) thermo-mechanical characterization of plasticized pla: is the miscibility the only significant factor? polymer, 47: 4676-4682. [17] patel ka, thomas weg. (2008) sutures, ligatures and staples. surgery 26(2): 48-53. [18] wang x, michael a, van den mooter g. (2004) study of the phase behavior of polyethylene glycol 6000 – itraconazole solid dispersions using dsc. international journal of pharmaceutics (272): 181-187. [19] davachi sm, kaffashi b, torabinejad b, zamanian a. (2016) in-vitro investigation and hydrolytic degradation of antibacterial nanocomposites based on plla / triclosan / nanohydroxyapatite. polymer, 83:101-110. https://doi.org/10.1016/j.polymer.2015.12.015 [20] wang d, vo nv, sowa ga, hartman ra, ngo k, choe sr, witt wt, dong q, lee jy, niedernhofer lj, kang jd. (2011) bupivacaine decreases cell viability and matrix protein synthesis in an intervertebral disc organ model system. the spine journal, 11(2): 139-146, https://doi.org/10.1016/j.spinee.2010.11.017 [21] quero l, klawitter m, nerlich ag, leonardi m, boos n, wuertz k. (2011) bupivacaine-the deadly friend of intervertebral disc cells? the spine journal, 11(1): 46-53. https://doi.org/10.1016/j.spinee.2010.11.001 233 https://doi.org/10.1002/pc.22660 microsoft word 184-786-2-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology aimi izyana and zairossani 61 effect of spray drying on protein content of natural rubber serum (nrs) i. aimi izyana and m.n. zairossani processing and pollution research unit, technology and engineering division, stesen penyelidikan rrim, malaysian rubber board, 47000, sungai buloh, selangor darul ehsan, malaysia. izyana@lgm.gov.my, zairossani@lgm.gov.my abstract: natural rubber latex comprises approximately 70% natural rubber serum (nrs) which is the aqueous part of the latex. the nrs is made up of mainly water and non-rubber components; sugar, protein and other lipids. the protein component of the nrs is separated using membrane separation and spray dried whereby the amino acid and protein content was monitored during the process. the optimum drying temperatures were first determined to obtain the maximum recovery of the protein powder, whereby the amino acid content was approximately 40 times that of the feed. the production of protein powder from nrs increases the rubber industry’s competitiveness through value addition to the previously discarded nrs but also to the processing industry. nrs protein powder has a great opportunity to be developed as an alternative protein source. abstrak: susu getah asli mengandungi lebih kurang 70% serum getah asli (natural rubber serum (nrs)) iaitu bahagian susu getah yang berair. nrs sebahagian besarnya merupakan air dan komponen bukan getah; gula, protein dan lipid-lipid lain. komponen protein nrs dipisahkan dengan menggunakan membran pemisah dan kaedah kering semburan dimana asid amino dan kandungan protein dipantau semasa proses tersebut. pada mulanya, suhu pengeringan optimum ditentukan untuk mendapatkan hasil maksima serbuk protein, dimana kandungan asid amino adalah lebih kurang 40 kali suapan. penghasilan serbuk protein daripada nrs meningkatkan daya saing industri getah dan industri pemprosesan menerusi pertambahan nilai terhadap nrs yang sebelum ini hanya dibuang. serbuk protein nrs mempunyai peluang besar untuk dimajukan sebagai sumber protein alternatif. key words: proten; spray dry; natural rubber serum 1. introduction natural rubber latex from the hevea brasiliensis tree is made up of an emulsion of rubber particles suspended in aqueous phase. the aqueous phase, called serum, contains several non-rubber matters such as carbohydrates, proteins, lipids, minerals, microorganisms and water. natural rubber serum (nrs) constitutes 60-70% of natural rubber latex, which normally contains 1 to 5% (w/w) of non-rubbers. some of these non-rubbers are physically or chemically attached to the natural rubber component while others are dissolved in the serum. some of the non-rubber substances such as lipids, carotenoid pigments, sterols, triglycerides, glycolipids and phospholipids can influence the final properties of rubber, such as compounded vulcanization characteristics and classical mechanical properties. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology aimi izyana and zairossani 62 although some non-rubbers are useful for the properties of the product rubber, the majority serves no purpose and often constitutes a pollution problem when they end up in the effluent that results from the processing of latex and needs to be treated before discharged to the public waterways. in an effort to overcome this problem, a process was developed to recover and extract valuable biochemical from the nrs [1]. table 1 shows the composition of non-rubber substances in nrs. table 1: composition of non-rubbers in nrs [2]. component amount (% w/w of serum) inositols 2.38 proteins 1.10 sugars 0.40 free amino acid 0.13 ascorbic acid 0.03 nitrogeneous bases 0.06 glutathione 0.02 protein is present in fresh hevea brasiliensis latex to the extent of approximately 11.5% by weight, by which about half is associated with the rubber. it is generally recognized that the presence of protein in fresh latex is an important factor in controlling its colloidal stability. the proteins in the serum are separated and dried to produce the protein powder which has a potential to become animal feed or even nutrient media for cultivating microorganisms due to the presence of various amino acids [3] and phosphatides [4]. utilization of non-rubber components in the nrs not only value adds to the rubber processing technology; but when integrated with membrane separation technology [5] can lead to a “zero discharge” scenario in the industry. serum processing technologies are therefore imperative to be explored extensively in order to greatly benefit the industry and also the nation. 2. materials and methods 2.1 sample preparation latex was first coagulated by adding 10% acetic acid until the ph of the latex reaches 4.2 and left overnight to ensure complete coagulation. the serum was obtained by creping the coagulum, where the serum was then filtered using a 0.2 µ m filter and subjected to membrane separation to separate the protein and sugar fractions of the serum. 70% of the serum was collected as permeate which is the sugar fraction. the rest 30%; the retentate is the protein fraction. all the samples collected were stored at 4°c to retain the integrity of the protein. 2.2 spray drying the spray dryer used in this experiment is the pilot-scale anhydro ms400 (denmark). the protein fraction was first conditioned to room temperature before added into the spray dryer’s feed tank. the drying temperatures were determined based on visual assessment of the product (free-flow and colour) where the inlet and outlet temperatures were varied. once the best parameters were obtained, test runs were conducted to verify iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology aimi izyana and zairossani 63 the validity of the previous assessment where the inlet and outlet temperatures, pressures, heater surface temperature and atomizer speed were monitored and recorded every 30 minutes. 2.3 analysis the protein powder produced was analyzed using waters accqtag to determine the amino acid content. the protein content was determined with the ni™ (noninterfering™) protein assay by gbiosciences (usa). 3. results and discussion previous research [6] for the lab scale production of the powder showed that the process developed is capable of producing stable protein powder with white appearance and has been successfully reproduced in the pilot-scale runs. the quality and characteristics of protein powder were dependent on several variables during processing particularly during the membrane separation and spray drying stages. the protein content was monitored during the sample preparation, especially in the membrane separation to ensure proper concentration of the protein fraction to be subjected to spray drying. during the first trial of the pilot-scale spray dryer, the optimum inlet temperature was determined to be at 175ºc while the outlet temperature at 95ºc by varying the two temperatures while keeping the atomizer speed and pressure difference in the spray dryer constant. the powder produced was assessed visually for their freeflowing properties to determine the best temperatures (table 2). all subsequent spray drying runs therefore are with the determined optimum temperatures. the initial sample needs to be pre-conditioned before being subjected to spray drying in order to produce the best quality powder. purification of the initial sample is important to have a successful spray dry run. initial samples with low ph were found to produce sticky product (table 3). cleaning and proper maintenance of the spray dryer unit are vital to make sure future runs will yield the same result as previous runs. table 2: determination of optimum spray drying parameters. no tin tout powder 1 170 90 fine 2 180 90 not free-flowing 3 190 90 sticky 4 180 95 fine 5 170 95 fine and free-flowing table 3: different ph in initial sample affects quality of powder. run ph % brix powder 1 3.9 1 fine 2 4.7 1 fine and free-flowing 3 4.0 1.5 fine 4 3.5 1.1 not free-flowing 5 3.5 2.5 sticky iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology aimi izyana and zairossani 64 the protein content of the initial sample was determined using the non-interfering assay and also enable the calculation of minimum powder recovery after spray drying (table 4). recovery of the powder depends on its free-flowing properties as high moisture content causes the product to stick to the surface of the bucket and render it difficult to collect the final product. latex composition varies with each sample preparation, resulting in different protein concentration in different feed for the spray drying run. from table 5, the amino acid content in the powder was shown to be more than 40 times that of the acid in the initial sample. the dominant amino acid in both samples is asp with more than 15% of the total content. asp and glu makes up for more than 25% of the amino acid content in both the initial sample and the powder. there is a theoretical loss of ala and val after spray drying. the pilot-scale spray drying runs have therefore showed great promise in producing quality protein powder from nrs. however, future runs may be conducted with different feed i.e. samples from latex processing line in order to truly assess the feasibility of the process to be integrated with current rubber processing facilities. table 4: protein content of the initial sample and powder recovered. run volume of initial sample (l) protein concentration in initial sample (g/l) powder recovered (g) 1 19.1 6.77 290.93 2 19.8 5.08 195.21 3 22.5 3.33 257.50 4 12.7 6.46 84.99 5 20.75 2.69 67.14 table 5: amino acid content before and after spray drying. no amino acid protein fraction protein powder 1 histidine 0.012 0.765 2 serine 0.044 2.229 3 arginine 0.033 1.401 4 glycine 0.058 2.459 5 aspartic acid 0.106 4.066 6 glutamic acid 0.100 3.396 7 threonine 0.035 1.190 8 alanine 0.078 1.126 9 proline 0.032 1.718 10 cysteine 0.034 2.012 11 lysine 0.038 1.727 12 tyrosine 0.017 1.668 13 valine 0.056 0.899 14 isoleucine 0.019 0.711 15 leucine 0.055 2.031 16 phenylalanine 0.014 0.763 iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology aimi izyana and zairossani 65 4. conclusion utilization of by-products of rubber processing particularly non-rubber components of the natural rubber latex for production of value-added biochemicals should be fully exploited to achieve “zero discharge” and to maximize revenue of the industry. potential applications of the nrs protein powder are intended as industrial proteins and enzymes, culture growth media, feed additives and animal feed supplement. nrs protein powder has a great opportunity to be developed as an alternative protein source. furthermore the utilization of nrs directly benefits the rubber industry as it: • increase consumption of nr and provide new applications for latex. • improve competitiveness by reducing waste and generating value-added products. • enhances raw rubber factories through integration of nrs and latex processing (green industry). • minimizes environmental impact and cost of effluent treatment by utilizing nrs. acknowledgement the authors would like to thank the processing & pollution research unit and the malaysian rubber board for the work conducted. assistance rendered by the ppru staff, especially mohd. mustakiem, fatin syahirah, mohd. ikhwan and hishamuddin are gratefully acknowledged. references [1] lau, c.m., tajima, y & machida, m “natural rubber serum concentrate and method for making the same.” malaysian patent appln. pi 8901670, 1998 [2] zairossani m.n., devaraj v., mohd. zin a.k. & zaid i “modern approaches towards effective effluent treatment” proceedings of rubber planters’ conference 2005, kuala lumpur, 15-17 november 2005 [3] whitby, g.s. & greenberg, h. (1941) “the isolation of amino acids from rubber latex”, 1941 [4] smith, r.h. “the phosphatides of the latex of hevea brasiliensis”, 1953 [5] devaraj v. & zairossani m.n “zero discharge and value-added products from nr skim latex processing” malaysian rubber technology development vol 6 p18-21, 2006 [6] zairossani, m.n “production of protein powder from natural rubber serum as a source of industrial biochemicals”, technical brochure distributed at the 34rd international exhibition of inventions, new techniques and products, april 2006, geneva, switzerland, 2006 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 effect of bonded composite patch on the stress intensity factor for a centercracked plate abdul aabid1, meftah hrairi1*, jaffar syed mohamed ali1, ahmed abuzaid2 1department of mechanical engineering, kulliyyah of engineering, international islamic university malaysia, kuala lumpur, malaysia. 2department of aeronautical engineering, sudan university of science and technology, khartoum, sudan. *corresponding author: meftah@iium.edu.my (received: 10th march 2018; accepted: 13th may 2019; published on-line:2nd december 2019) abstract: crack propagation until fracture is an important criterion to predict a structure‘s service life. in order to increase the latter, the cracked component needs to be repaired or replaced. in the present study, a finite element analysis has been carried out to investigate the effects of adhesive thickness, patch thickness and crack length on the passive repair performance of a center-cracked rectangular aluminum plate under mode-i loading condition using finite element ansys package. a comprehensive parametric study shows that the stress intensity factor is influenced by the patch thickness, patch size, adhesive material, and adhesive thickness. abstrak: penyebaran retak sehingga patah adalah kriteria penting bagi menjangka hayat struktur. bagi memanjangkan jangka hayat struktur, komponen keretakan perlu dibaik pulih atau diganti. kajian ini telah menjalankan analisis elemen tak terhingga bagi mengetahui kesan ketebalan pelekat, ketebalan tampalan dan panjang retak pada bahagian keretakan tengah plat petak aluminium yang dibaiki secara pasif, menggunakan pakej ansys di bawah beban mod-i. kajian parametrik yang menyeluruh menunjukkan faktor tekanan intensif dipengaruhi oleh ketebalan tampalan, saiz tampalan, bahan pelekat dan ketebalan pelekat. keywords: stress intensity factor; center crack; composite patch; adhesive; finite element 1. introduction a structure can be damaged by low energy effects and initiated cracks in its inner layer which may propagate and cause failure of the structure. damages such as delamination, notches, and cracks are inevitable in various fields of engineering, especially in the aerospace field, and these damages are mostly due to fatigue, corrosion, and accidents. for the repair of such damaged structures, composite patches have been widely used and proven effective. numerous studies have been reported in this type of passive structural repair in the past four decades. much of the earlier numerical work, reported in the literature, was based on franc2d/l finite element (fe) code. a circular notch in an aluminum 2024-t3 plate repaired with a graphite/epoxy composite patch was investigated using that code [1] where the developed geometry of the plate and patch were not carried out using a 3d element formulation that can be close to experimental work. using the same fe code, 211 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 another study investigated the effect of adhesive layers to repair the cracked plate with bonded composite patch in which distinct types of adhesives were used and the best one was selected to reduce the stress intensity factor (sif) and strain energy release rate (serr) [2]. later, an algorithm was added to that fe code to simulate the temperature effect to determine reduction of sif [3]. using the same code, an investigation of composite patch use to repair a cracked plate was carried out. the effect of the thickness of the patch and adhesive were considered and the patch was designed with circular shape and implemented on an edge-cracked rectangular plate [4]. in recent years, simulation of cracked plate with composite patches has been done using abaqus and ansys software for 2d and 3d analysis. mhamdia et al. [5] repaired the crack with bonded composite patch under thermo-mechanical load to reduce sif. the effect of thermal residual stresses resulting from adhesive curing on the performance of bonded composite repair in aircraft structures was analysed with abaqus software [5]. another study reported experimental results of applying thermal and mechanical load to check the effectiveness of a composite patch over the cracked structure. patch material, patch size, patch shape, and adhesive material were considered effective in sif reduction. a center crack emanating from a circular notch was employed to study the reduction in sif [6]. a composite patch bonded to a cracked plate made of aluminum 2024-t3 under mixed-mode loading was investigated [7]. in this study, 20 noded solid186 element types were used to model the plate, patch, and adhesive bond and the geometry was developed according to the angular changes from 0% to 100% to move mode i to mixed mode. aabid et al. [8-10] numerically analysed the results of stress concentration factor (scf) for a center-holed rectangular aluminum plate with and without composite patch repair and sif when a crack is emanating from the hole. it can be found from the above literature survey that much of the work has been done on edge-cracked rectangular plates. therefore, the aim of this research is to simulate the results for center-cracked rectangular plates. in the present work, numerical simulation under linear-elastic fracture mechanics (lefm) was carried out to establish the effect of composite patch and adhesive characteristics on a center-cracked rectangular plate subjected to a uniform tension load leading to a mode i type of failure. 2. problem definition 2.1 specimen the center-cracked rectangular plate under tensile load with integrated composite material patch is considered for this study, as depicted in fig.1. the material of the cracked rectangular plate is considered to be aluminum 2024-t3 and the adhesive material is considered to be araldite 2014. in the present study, a crack length of mm was used with an integrated composite patch on the crack length under an applied tensile load of 1 mpa. the dimension and mechanical properties of the centercracked rectangular plate, adhesive layer, and composite material are as shown in table 1 and table 2. the composite patch is applied to the damaged area to cover the crack length. the dimensions of the patch are such that it completely covers the damaged area. in the present study boron/epoxy is selected as the composite patch material based on its high strength-to-weight ratio. 212 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 2.2 patch shape a patch with a skewed shape had been shown to be the most optimum patch design. however, one should be careful when designing such patch shapes to ensure the stress level in the plate remains within the design limits [11]. the rectangular shape of the patch was found to be the second best choice. considering mechanical performances and manufacturing aspects, this rectangular shape represents a better compromise. therefore, the patch size was chosen as the minimum patch size that completely covers the crack length and improves the mechanical behavior of the cracked plate under the mode i loading [2]. fig. 1: rectangular plate with a center crack and integrated composite patch. table 1: dimensions of the host plate, boron/epoxy and adhesive dimensions aluminum plate (mm) boron/epoxy (mm) adhesive (mm) height h=200 hp=40 ha=40 width 2w=80 2wp=60 2wa=60 thickness t=1 tp=0.5 ta=0.03 table 2: materials properties of the host plate, boron/epoxy and adhesive parameter aluminum plate boron/epoxy adhesive (araldite 2015) density 2715 kg/m3 1160 kg/m3 poisson’s ratio ʋ12 0.33 0.3 0.345 poisson’s ratio ʋ13 0.28 poisson’s ratio ʋ23 0.28 young’s modulus (e1) 68.95 gpa 200 gpa 5.1 gpa young’s modulus (e2) 19.6 gpa young’s modulus (e3) 19.6 gpa shear modulus (g12) 7.5 gpa shear modulus (g13) 5.5 gpa shear modulus (g23) 5.5 gpa 213 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 3. finite element modelling the finite element modelling (fem) is performed using ansys mechanical apdl software for simulation purposes [12]. the gradient of the stress and strain fields around the crack front is very high, and to describe such behavior, the displacement extrapolation method uses the nodal displacements around the crack tip. to obtain a good representation of the crack tip displacement, singular elements are used as shown in fig. 2(a). the nodes used for the crack tip displacements required for the equation are illustrated in fig. 2(b). fig. 2: (a) the singular element near the crack tip and (b) nodes used for the approximate crack tip displacements. in this work, the sif is calculated using ansys finite element analysis (fea) software with reasonable accuracy. the displacement near the crack tip is obtained from finite element (fe) analysis, and then the sif is calculated according to equation (1). 3.1 mesh sensitivity analysis to study the mesh effect on the computational results, three mesh sizes were considered as illustrated in table 3. the processor, which used to run the different cases of the simulation, was an intel(r) core i7-3770 cpu @ 3.40 ghz, 16.0 gb ram, and a windows-10 64-bit operating system. the parameters selected to run the simulations are: crack length of 10 mm, width of the adhesive bond and the composite patch of 30 mm, height of the adhesive bond and the composite patch of 20 mm, thickness of the adhesive bond of 0.03, mm and thickness of the composite patch of 0.5 mm. the grid structured mesh was used to mesh the adhesive bond and composite patch by applying the size of elements based on mesh type. for the damaged plate, the elements were divided by picking each line, and the generated mesh is of an unstructured type. as shown in table 3, it was found that the refinement of the mesh, from intermediate to fine, slightly improved the solution accuracy of the sif value, leading to a maximum relative difference of 4 %. this comparison indicates that the intermediate mesh provides sufficient resolution and accuracy with around half the computational time, and hence, this mesh size was used for the rest of the simulations. table 3: mesh independence test mesh type no. of elements cpu runtime (seconds) sif (mpa) coarse 6,832 300 0.0691 intermediate 33,180 660 0.0667 fine 68,920 1322 0.0640 214 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 3.1 modelling of the integrated structure in this case, a boron/epoxy composite patch was used, and a solid186 element type was used to model the damaged plate, adhesive layer, and composite patch. solid186 contains a 20-noded higher order element with 5 degrees of freedom. a typical fe model for the center-cracked plate integrated with a composite patch is shown in fig. 3. due to symmetry, only a quarter of the plate was modeled. a total of 10 singular elements were employed to model the crack front. the adopted fe mesh consisted of 7910 coupled-field elements used to model the composite patch, while 21,580 and 3690 high-order reduced integration solid elements were used to model the damaged plate and adhesive bond, respectively. fig. 3: finite element mesh and the location of the singular element. 3.2 validation of finite element model most of the previous work has been done for the edge cracked plate as it can be easily verified through experimental work. therefore, an edge-cracked plate was selected to validate the present finite element model. the meshes that are used to model the center and edge cracked plates are almost identical except for their boundary conditions. to verify the simulation results of passive repair, the case study reported in [13] was simulated using the fe model developed in the present work. the edgecracked rectangular plate integrated composite patch is shown in fig. 4. fig. 4: rectangular plate through an edge-crack integrated composite patch. 215 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 the dimensions and mechanical properties of the cracked plate, adhesive layer and composite material are mentioned in tables 4 and 5. applied tensile stress is 58.33 mpa, and the crack length is 30 mm. the results obtained from the current numerical simulation were compared with that reported in [13] and there was a very good agreement as shown in table 5. table 4: dimensions of the host plate, boron/epoxy patch and adhesive (fm-73) dimensions host plate (mm) boron/epoxy (mm) adhesive (mm) height h=254 hp=75 ha=75 width w=254 2wp=130 2wa=130 thickness t=4.76 tp=2.28 ta=0.15 table 5: material properties of the host plate, boron/epoxy patch and adhesive (fm-73) parameter aluminum plate boron/epoxy adhesive (fm-73) plate strength 350 mpa poisson’s ratio ʋ12 0.33 0.3 0.32 poisson’s ratio ʋ13 0.28 poisson’s ratio ʋ23 0.28 young’s modulus (e1) 72 gpa 200 gpa 2.55 gpa young’s modulus (e2) 19.6 gpa young’s modulus (e3) 19.6 gpa shear modulus (g12) 7.2 gpa shear modulus (g13) 5.5 gpa shear modulus (g23) 5.5 gpa prior to repair validation, the fe model of the unrepaired plate (cracked plate without a patch) was also validated using a fracture mechanics analytical solution [14]. comparing the results gained by tada’s analytical solution [14] according to equation (2) and the present finite element results, there is a good agreement, as shown in table 6. (2) where a is the crack length, and b is the width of the damaged plate. table 6: validation of numerical simulation results condition ref. [9] ref. [10] present results relative error without repair 20.049 20.432 1.874% passive repair 9.789 9.623 1.695% 3.3 boundary conditions for center and edge cracked plate figure 5 shows the applied boundary conditions for the edge and center cracked plate. due to symmetry, the model used for the center-cracked plate is a quarter of the plate and for the edge-cracked plate is half the plate. the dimensions of the adhesive bond and composite patch are illustrated in table 1 for the center cracked plate, and table 4 for edge cracked plate. 216 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 (a) (b) (c) fig. 5: applied boundary conditions (a) center-cracked (b) edge-cracked (a) side view of plate. 4. results and discussion in this section, finite element analysis was carried out to study the effect of a composite patch placed on the damaged area of a rectangular plate under uniform uniaxial tension load for the problem shown in fig. 1. 4.1 comparison between unpatched and patched crack the variation of mode i stress intensity factor is plotted in fig. 6 for five different values of crack length in the unpatched and repaired cracked plates. it can be seen that sif strongly decreased when employing the patch repair and more so for bigger crack lengths since the patch carried the load as the crack grew. this is because the stress singularity around the crack tip is reduced due to the composite patch induced shear force on the crack area. indeed, the sif reduction reached a maximum value of 68% compared to a 60% reduction for the glass/epoxy patch as obtained in [6]. therefore, boron/epoxy patches are more effective for reduction of sif. furthermore, fig. 6 shows that for the repaired plate and as the crack length increases, the sif exhibits an asymptotic behavior. fig. 6: crack length variation with and without patch. 217 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 4.2 effect of patch thickness patch thickness represents one of the best means for improving patch repair performance. thus, many researchers investigated the patch thickness effect on the repair performance in damaged structures [4,5,15]. mhamdia et al. [16] achieved almost 50% decrease in the crack tip sif by increasing the patch thickness to repair a cracked plate under mechanical loading. figure 7 displays this effect on the normalized sif variation. it is clearly illustrated that the normalized sif at the crack tip is reduced proportionally as the patch thickness increases. indeed, the size of the patch is important to transfer shear load at the damaged area. an increase of 45-50% of the patch thickness reduces the normalized sif by the same order. hence to increase the repair performance, the size of the patch should be thicker. moreover, for repairing cracks, it is preferable to use multi-layered composite patches to improve the distribution of stresses. fig. 7: effect of patch thickness for passive repair. fig. 8: effect of adhesive layer thickness for passive repair. 4.3 effect of adhesive thickness figure 8 shows the variation of the normalized sif as a function of the adhesive thickness. it can be seen that a very small increment in the adhesive thickness increases the normalized sif. therefore, when repairing cracked structures, it is desirable to use 218 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 smaller adhesive thickness. this finding correlates well with the results highlighting this effect in [15]. thus, the adhesive thickness should be chosen carefully as on the one hand, a bigger value of thickness will reinforce adhesion but dissipate the transfer of the loads towards the patch, which decreases the favorable effects of the patch. on the other hand, smaller thickness will transfer the load towards the patch but increases the risk of adhesive failure. 4.4 effect of adhesive materials the mechanical stresses between the composite patch and the host cracked plate increase significantly with the increase of the shear modulus of the adhesive. however, it is not recommended to increase the adhesive shear modulus indefinitely as this will reduce the adhesive strength, which can increase the risk of the adhesion failure. thus, the adhesive choice should compromise between allowing stress transmission to the patch while preventing the failure of the adhesion. the variation of the sif as a function of four different adhesive materials, shown in fig. 9, confirms the above statement. the mechanical properties of adhesive materials are illustrated in table 7. it can be seen in fig. 9, that when a crack length increases, the normalized sif will decrease. this means that when the crack length increases, there is a chance that the material will fail drastically if not repaired. therefore, to control this, the composite patch has been used and the adhesive material properties create effective shear loads that depend on shear modulus, as was highlighted in ref. [5]. the araldite 2014 outperforms the other adhesives as it better transfers the load towards the patch, as highlighted by the higher reduction in normalized sif. table 7: mechanical properties of adhesive materials material type e (gpa) ʋ g (gpa) ρ kg/m3 araldite 2014 5.1 0.345 1.89 1160 epon422j 3.49 0.29 1.10 fm-47 2.106 0.3 0.81 fm-73 1.83 0.33 0.688 875 fig. 9: effect of adhesive materials for passive repair. 219 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 4.5 effect of crack length figure 10 displays the normalized sif variation as a function of crack length. it can be seen that the reduction of normalized sif is higher for larger crack lengths. indeed, the normalized stress intensity factor is maximum for smaller cracks, and then it decreases and stabilizes towards an asymptotic value for larger cracks. this behaviour leads us to state that the patch stress absorption is less significant for short cracks. fig. 10: effect of crack length for passive repair. 5. conclusion this work describes the numerical simulation of the composite patch for a damaged rectangular plate under structural load by a finite element analysis ansys package. a substantial reduction in sif is observed with an integrated composite patch. based on present simulations, the following conclusions are drawn; about 68% sif reduction is observed for single side patch repairs for boron/epoxy patches and a crack length of 15 mm. increases of patch thickness reduce the sif at the crack front. increase in adhesive thickness results in a decrease of sif reduction at the crack front. it has been proven that araldite 2014 adhesive material has a good mechanical property to reduce maximum sif at the crack front. the effect of the composite patch on the reduction of sif on a center-cracked rectangular plate subjected to uniaxial load is simulated, and the results demonstrated that the sif decreases linearly with the effect of the composite patch. acknowledgement the authors would like to thank the ministry of higher education, malaysia for supporting this work through research grant frgs 16-066-0565. 220 iium engineering journal, vol. 20, no. 2, 2019 aabid et al. https://doi.org/10.31436/iiumej.v20i2.912 references [1] madani, k, touzain s, feaugas x, benguediab m, and ratwani m. (2009) stress distribution in a 2024-t3 aluminum plate with a circular notch, repaired by a graphite/epoxy composite patch. int. j. adhes. adhes., 29: 225–33. [2] ricci f, franco f, monrefusco n. (2011) bonded composite patch repairs on cracked aluminum plates: theory, modeling and experiments. in advances in composite materials ecodesign and analysis, 445-464. [3] ergun e, suleyman t, muzaffer t. (2012) stress intensity factor estimation of repaired aluminum plate with bonded composite patch by combined genetic algorithms and fem under temperature effects. indian j. eng. mater. sci., 19 (1): 17-23. [4] ouinas d, belkacem a, belabbes b. (2013) the optimization thickness of single/double composite patch on the stress intensity factor reduction. j. reinf. plast. compos., 32 (9): 654-463. [5] mhamdia r, bachir bouadjra b, serier b, ouddad w, feaugas x, touzain s. (2011) stress intensity factor for repaired crack with bonded composite patch under thermomechanical loading. j. reinf. plast. compos., 30 (5): 416-424. [6] vishnuvardhan, nadimpalli l, himanshu p, akhilendra s. (2016) composite patch repair modelling by fem. proceedings of first structural integrity conference and exhibition (sice-2016): 4-6 july 2016. [7] maleki h n, chakherlou tn. (2017) investigation of the effect of bonded composite patch on the mixed-mode fracture strength and stress intensity factors for an edge crack in aluminum alloy 2024-t3 plates. j. reinf. plast. compos., 36 (15): 1074-1091. [8] aabid a, meftah h, jaffar syed mohammed a, ahmed a. (2018) stress concentration analysis of a composite patch on a hole in an isotropic plate. int. j. mech. prod. eng. res. dev., 6 (special issue): 249-255. [9] aabid a, meftah h, jaffar syed mohammed a, ahmed a. (2018) numerical analysis of cracks emanating from hole in plate repaired by composite patch. int. j. mech. prod. eng. res. dev., 6 (special issue): 238-243. [10] aabid a, meftah h, shaik dawood msi. (2019) modeling different repair configurations of an aluminum plate with a hole. int. j. recent technol. eng., 7 (6s): 235-240. [11] mahadesh kumar a, hakeem sa. (2000) optimum design of symmetric composite patch repair to centre cracked metallic sheet. compos. struct., 49 (3): 285-292. [12] ansys inc. (2017) ansys fluent 18.0: theory guidance. canonsburg pa. [13] ouddad w, bouadjra bb, belhouari m, ziadi a. (2015) stress intensity factor for repaired crack with bonded composite patch repair under mechanical loading in aircraft structures. in 12th congress in mechanical, 416-424. casablanca (maroc). [14] tada h, paris pc, irwin gr. (2000) the stress analysis of cracks handbook, third edition. [15] albedah a, bachir bouiadjra b, mhamdia r, benyahia f, es-saheb m. (2011) comparison between double and single sided bonded composite repair with circular shape. mater. des., 32 (2): 996-1000. [16] mhamdia r, serier b, albedah a, bachir bouiadjra b, kaddouri k. (2017) numerical analysis of the influences of thermal stresses on the efficiency of bonded composite repair of cracked metallic panels. j. compos. mater., 51 (26): 3701-3709. 221 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <feff005500740069006c0069006300650020006500730074006100200063006f006e0066006900670075007200610063006900f3006e0020007000610072006100200063007200650061007200200064006f00630075006d0065006e0074006f0073002000640065002000410064006f00620065002000500044004600200061006400650063007500610064006f007300200070006100720061002000760069007300750061006c0069007a00610063006900f3006e0020006500200069006d0070007200650073006900f3006e00200064006500200063006f006e006600690061006e007a006100200064006500200064006f00630075006d0065006e0074006f007300200063006f006d00650072006300690061006c00650073002e002000530065002000700075006500640065006e00200061006200720069007200200064006f00630075006d0065006e0074006f00730020005000440046002000630072006500610064006f007300200063006f006e0020004100630072006f006200610074002c002000410064006f00620065002000520065006100640065007200200036002e003000200079002000760065007200730069006f006e0065007300200070006f00730074006500720069006f007200650073002e> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <feff04180441043f043e043b044c043704430439044204350020044d044204380020043f043004400430043c043504420440044b0020043f0440043800200441043e043704340430043d0438043800200434043e043a0443043c0435043d0442043e0432002000410064006f006200650020005000440046002c0020043f043e04340445043e0434044f04490438044500200434043b044f0020043d0430043404350436043d043e0433043e0020043f0440043e0441043c043e044204400430002004380020043f043504470430044204380020043104380437043d04350441002d0434043e043a0443043c0435043d0442043e0432002e00200421043e043704340430043d043d044b043500200434043e043a0443043c0435043d0442044b00200050004400460020043c043e0436043d043e0020043e0442043a0440044b0442044c002c002004380441043f043e043b044c04370443044f0020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e00300020043b04380431043e00200438044500200431043e043b043504350020043f043e04370434043d043804350020043204350440044104380438002e> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <feff04120438043a043e0440043804410442043e043204430439044204350020044604560020043f043004400430043c043504420440043800200434043b044f0020044104420432043e04400435043d043d044f00200434043e043a0443043c0435043d044204560432002000410064006f006200650020005000440046002c0020043f044004380437043d043004470435043d0438044500200434043b044f0020043d0430043404560439043d043e0433043e0020043f0435044004350433043b044f04340443002004560020043404400443043a0443002004340456043b043e04320438044500200434043e043a0443043c0435043d044204560432002e0020042104420432043e04400435043d04560020005000440046002d0434043e043a0443043c0435043d044204380020043c043e0436043d04300020043204560434043a04400438043204300442043800200437043000200434043e043f043e043c043e0433043e044e0020043f0440043e043304400430043c04380020004100630072006f00620061007400200456002000410064006f00620065002000520065006100640065007200200036002e00300020044204300020043f04560437043d04560448043804450020043204350440044104560439002e> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 1-naim-iiumej-37-1-27-2-o.k..doc iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 1 design and implementation of dsp-based intelligent controller for automobile braking system s.n. sidek and m.j.e. salami mechatronics department, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. snaim@iiu.edu.my, momoh@iiu.edu.my abstract: an intelligent braking system has great potential applications especially, in developed countries where research on smart vehicle and intelligent highways are receiving ample attention. the system when integrated with other subsystems like automatic traction control, intelligent throttle, and auto cruise systems, etc will result in smart vehicle maneuver. the driver at the end of the day will become the passenger, safety accorded the highest priority and the journey optimized in term of time duration, cost, efficiency and comfortability. the impact of such design and development will cater for the need of contemporary society that aspires to a quality drive as well as to accommodate the advancement of technology especially in the area of smart sensors and actuators. the emergence of digital signal processor enhances the capacity and features of universal microcontroller. this paper introduces the use of ti dsp, tms320lf2407 as an engine of the system. the overall system is designed so that the value of inter-vehicle distance from infrared laser sensor and speed of follower car from speedometer are fed into the dsp for processing, resulting in the dsp issuing commands to the actuator to function appropriately. key words: smart vehicle, digital signal processor, fuzzy controller, and infra red laser sensor 1. introduction intelligent braking system has found a lot of potential applications in countries like the united states, japan, germany, france etc. research work on smart vehicle dates back to early 1970's. despite this, it was not until early 1990’s, that some of the research products become common place on the roadways after the research on smart vehicles received tremendous support from governments and private firms. a comprehensive, longterm project called intelligent vehicle highway system (ivhs), also known as intelligent transportation system (its) was later formed and aimed to achieve certain research targets. the intelligent braking system when integrated with other subsystems like automatic traction control, intelligent throttle, auto cruise systems, etc will eventually result in a smart vehicle. the driver at the end of the day will become the passenger, safety is accorded the highest priority and the journey will be optimized in term of time duration, cost, efficiency and comfortability. yet, the need for the driver to have control over certain functions may become indispensable. this comes from the fact that the fullintegrated system does not still completely converge to a stable system and also to alleviate certain problems of liability to a certain extent whenever accident occurs. it seems more natural to allow the driver to gradually transfer control of one function at a time to the automated system until the complete system deployment totally unfolds. in the design of intelligent braking system, the driver is allowed to overtake the handling of the brake pedal from the controller during certain circumstances. for example, when an animal is about to cross the road in front of the moving vehicle. this is due to the lack of capability of machines to classify and predict certain actions. machines, on the other hand, have great information processing power and its ability to withstand the aging has always put it ahead of human. with the advancement of microcontroller technology, the emergence of the digital signal processor has paved the way to many successful achievements specifically in industrial control. this paper discusses the hardware implementation for the intelligent braking system using digital signal processor (dsp) as the heart of the system as well as the communication link between sensor, actuator and other peripheral devices. to achieve this, infrared laser sensor will input the value of inter-vehicle distance into the dsp for signal processing, which later commands the actuator with appropriate signaling. 2. sensor the choice of sensors to measure the inter-vehicle distance has been discussed thoroughly in [1]. besides the capability of infrared laser sensor to measure the long distance range (at least 100 meter), the response time, cost efficiency and size have been put into consideration for this application. there are several ways to configure and position the sensor so as to have the best measurement [1,2]. for the implementation of the system in this research, the vehicle will be equipped with four-beam infrared laser sensor as illustrated in fig. 1. iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 2 fig. 1: sensor positioning and characteristic this configuration will enable the detection of preceding vehicle on bends. the tightest relevant radius on the highway (especially in the highway exit) is assumed to be 500 meters. in this case, the horizontal aperture angle must be at least 80 for an inter-vehicle distance of 75 meters. the vertical aperture is fixed to be 10 and is positioned in such a way to avoid false reading due to the road conditions. to obtain this configuration, the four-beam infrared laser sensor is arranged next to each other in one lateral plane. the outputs of this sensor are then connected to an integrator before being fed into the embedded dsp through p2 (expansion analog connector). each beam of the sensors delivers a signal every 100 ms. thus, at every clock at least four sets of readings are received. for this research work, only part of highways, which are straight in nature have been studied. for that reason only the reading from the two beams in the middle were focused on. the other two readings can be utilized, when they are to detect the inter-vehicle distance while negotiating a corner. as such, another sensor is needed to monitor the steering angle so as to determine the degree of the road curvature and decide which laser sensor readings are to be used. in general, these basic distance readings suffer from serious degradation to a certain extent, that is, there could be great differences in the measured values as compared to the ideal value used in the simulation study. in practice, the signals received may be reflected from traffic signs, guideposts, or crash barriers. for this reason, a special corrective measure can be introduced to preprocess this signal before being sent to the dsp. on the other hand, using data extrapolation from look-up table or knowledge-based system can be another approach to solve this problem. alternatively, each vehicle can be equipped with a special tag that can reflect unique signal to be sensed by the detector of the sensor. 3. actuator the actuator of the system is part of a module called auxiliary hydraulic module (ahm). as shown in fig. 2, ahm consists of hydraulic pump, valves and actuator. the function of the module is to provide input force to the vacuum booster through an actuator and brake pedal. output signal from the dsp controller is in the form of pulse width modulation (pwm) and is amplified using a power amplifier. ahm later processes this signal and generates the necessary pressure against the brake pedal. pwm is a square wave signal of fixed frequency but varied duty cycle. it is possible to control the output force and the brake pedal by varying the duty cycle. if the hydraulic pump draws off a constant amount of fluid through the valves while the valves are opened, no pressure is developed but once it closes completely, an abrupt rise of pressure is attained. by switching the valves at high frequency (typically 100 hz), coupled with varying duty cycle, the pressure inside the cylinder of the actuator can be controlled. eventually, this pressure pushes the piston of the actuator and applies appropriate force to the brake pedal. at the maximum value of duty cycle, which implies the valve is opened for most of the time, no force is applied to the brake. the mapping from the duty cycle to the brake line pressure has been discussed by reza, et al.[4]. the result suggests that the brake model can be approximated by the first order system. fig. 2: block diagram of auxiliary hydraulic module 4. controller successful longitudinal control of vehicles in its applications is highly dependent on adequate control of vehicle subsystems. in particularly, brake system is highly nonlinear and possesses wide range of uncertainties. the observed nonlinearities and uncertainties in the brake system are a combination of friction, dead zones and hysteresis [4,9]. in designing the brake control strategy, the main objective is to cancel the nonlinearities of the system so as to make the dsp hydraulic pump control valves actuator booster vacuum pump master cylinder actuating element manual iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 3 brake system behaves as uniformly as possible throughout the operating range of the system. several control strategies have been developed to deal with the brake dynamics, which first need to be modeled. threestate model strategy has been proposed [10] whilst a nonlinear first order model for the brake dynamics was developed [11,12]. in the former paper, the author employs sliding control technique, which is a kind of robust design technique usually used to compensate for the nonlinearities. the later uses a controller that employs feedback linearization to cancel the nonlinearities and a modified proportional integral (pi) compensator to achieve the desired control action. both approaches involve rigorous mathematical formulation and impose many constraints. due to the severe constraints inherent in vehicles dynamics, sometimes the global results are not very much relevant to the real applications. in this paper, the brake control strategy is in the form of fuzzy inference system (fis) with the model employed being based on the condition that as the front vehicle decelerates rapidly and the engine torque alone may not achieve the vehicle following condition unless with the use of brake. with that assumption made, the dynamic of the vehicles in this situation can be formalized as,  221 1 ffobf f ll vcvcfct m v vx vx       (1) where tb is the braking torque, m is vehicle mass, fo, c1vf, c2vf 2 represent the static friction force, rolling friction force and air resistance force respectively. the control objective is to have the following vehicle speed to track the front vehicle speed as, lf vv  (2) the best set of the fis is then loaded into dsp to perform the input-output data mapping so as to study and evaluate the performance of this control strategy. the technology of dsp features the cross-link between microprocessor and microcontroller technology. in most of the specific driven applications, real time operation, compact and small-scale circuitry coupled with high processing speed are always required. by having harvard type architecture, the dsp is able to have a parallel processing by maintaining two separate bus structures namely program and data buses, and the special instruction set which allows the processor to go for full speed execution [5,6]. the tms320lf2407 is a fixed-point processor optimized for control applications. in this research work, this processor has been chosen to be the processor for the braking system. while some of its features are not comparable to the features found in other type of processors, they are adequate enough to run the application excellently for this research work. for instant, a typical universal microprocessor has faster clock speed compared to dsp. however, when it comes to the signal processing tasks, the dsp supersedes the universal microprocessor in the two to three order of speed [13]. even though a very fast speed universal microprocessor with certain signal processing functions programmed on it can be easily found in the market nowadays, the price is impractical for the braking application. in fact with the usd$11.75 [14] tms320lf2407 30 mhz processor, the problem can be handled relatively better as compared to usd$94.70 [15] intel celeron 566 mhz processor. a dedicated fuzzy chip on the other hand is limited in its usage in the sense that the chip is tailored for fuzzy algorithm without having necessary circuitry for signal processing. among features that tms320lf2407 possesses are integrated on chip adc module, pwm module, memory expansion capability, relatively high speed (30 mhz) and several logging port options [7,8], which are needed for system under study. the system employs tsk fuzzy inference system as a kernel to the controller. it takes two inputs from the sensors namely the inter-vehicle distance and following vehicle speed, whereas the pwm output signal is generated from already fine-tuned thirty set of rules to operate the actuator. the tuning process is done using matlab software through the adaptive neuro fuzzy approach with back propagation algorithm. the matlab generated inference system forms the basis of the file, which would be downloaded into the dsp. this allows the off-line batch updating for the inference system if the input output data pairs are available. fig. 3 shows a brief system architecture where one of the dual event managers is utilized. the general-purpose timer triggers the fetching of data from analog expansion port (p2) and activates the interrupt service routine every 100 ms. the on-chip pwm module outputs the scaled signal and sent this to the power amplifier to finally drive the actuator. the cost of additional circuit such as the integrator is worth it so as to secure the accuracy of sensor reading. the 10 bits adc can have a resolution of up to 0.146 meter compare to the use of on chip counter, which is capable of having a resolution of 5 meters [1]. fig. 3: a brief system architecture 5. hardware setup and results fig. 4 shows a layout of tms320lf2407 dsp used in the research study and the complete module is depicted from sensor p2 dsp integrator circuit fis code timer module pwm module adc power amplifier to ahm (actuator) iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 4 in fig. 5. jtag-compliant scan base emulation set is used as an interfacing between the host computer and the processor and allows the processor to be debugged in real time mode. fig. 6 shows the complete set of devices used for the implementation of this system. the integrated development environment (ide) called code composer for the dsp, as seen in the screen of the computer in the figure, is a useful tool to develop the code for the processor. the program code of fuzzy algorithm is developed in c and the complete program flowchart is shown in fig. 7. the code complies the ansi c specification and can easily be altered based on the fuzzy inference system developed in matlab software. the maximum time marked for 400 samples of set data to be read from the host computer and processed in the processor is 27 sec. this corresponds to about 67.5 msecs for each data to be inferred. it is important that this process consumes less time than the scanning time of the sensor reading, which is 100 msecs for each reading. this further confirms the feasibility of the fuzzy code to be run on the dsp fig. 4: tms320lf2407 evm layout fig. 5: the evm board and jtag-compliant scan base emulation set fig. 6: the dsp setup fig. 7: software implementation of brake controller a series of plots (fig.9-11) are generated for some of the simulation cases using matlab. they are used as a benchmark to measure the reliability of the dsp. this is done through comparing them with the plots generated using the hardware (dsp) shown in fig. 12-15 in the appendix. for each case of hardware tests, the plots start initialization: dsp core, pll, event manager, timers and etc. fuzzy inference system subroutine fetch data from buffer, do the inferencing and calculate the output force low pwm ticnt register timer2 == 100 ms ticmp register timer1 == 10 ms are these values the same? end yes no no yes no yes iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 5 generated are the two inputs to the dsp, namely the distance error and the distance error rate of change. meanwhile the last plot in each case shows the brake command, which is actually the output from the dsp. the observed result shows that the dsp can accurately track the simulation result, which is done using matlab software. table 1 depicts the entire initial values used to distinguish all the cases under study. table 1: initial values for different simulation cases initial value case 1 case 2 case 3 case 4 velocity of following vehicle 30 m/s 30 m/s 30 m/s 30 m/s velocity of front vehicle 25 m/s 25 m/s 25 m/s 20 m/s initial inter-vehicle distance 90 m 50 m 120 m 90 m offset 36 m 36 m 36 m 36 m free time 1.8 s 1.8 s 1.8 s 1.8 s 5.1 comments on case 1 following the well-known 3-second method, the safe distance of the following vehicle from the front vehicle is set based on their velocities. case 1 in table 1 shows the parameters that are used to initialize the simulation of the system. the offset is a constant that needs to be added to have the optimum safe distance value. with the front vehicle moving at 25m/s and then suddenly stops at 0 m/s, it is shown in fig. 8(a) and 8(b), that the following vehicle is capable of stopping safely before collision. figure 8(c) illustrates the brake force applied whenever the braking action of the vehicle takes place. it can be seen that at the very beginning of the simulation, a relatively low force is applied. this is to adjust the safe distance value formulated in supervisory controller. the force later reduces to zero and it is not until the collision has occurred that the braking force is activated again to make sure the following vehicle stops safely 5.2 comments on case 2 for case 2, the initial condition for inter-vehicle distance is set to be close to the value of 50 m. for this set of simulations, it is clear that this distance is crucial in terms of the velocities that both vehicles display. the brake is applied from the first second of the simulation and finally reduced to zero as shown in fig. 9(c). at the tenth second of the simulation, when the current distance is about 53 m, the applied brake force is high to ensure the following vehicle can avoid the collision. even though the brake force manages to stop the vehicle, its application is quite sudden and this can jerk the passengers of that vehicle. however, under real circumstances, this will hardly happen, as the vehicle will be always maintained at an appropriate distance right from the beginning. 0 2 4 6 8 10 12 14 16 18 20 -1000 0 1000 2000 3000 4000 5000 6000 7000 time/s b ra k e fo rc e / n 0 2 4 6 8 10 12 14 16 18 20 10 20 30 40 50 60 70 80 90 time/s c ur re nt d is ta n ce / m e te r 0 2 4 6 8 10 12 14 16 18 20 -1000 0 1000 2000 3000 4000 5000 6000 7000 time/s b ra ke f or ce / n fig. 8: plots for case 1: (a) velocity profiles ( solid – front car). (dash – following car), (b) the inter-vehicle distance and (c) brake force iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 6 0 2 4 6 8 10 12 14 16 18 0 5 10 15 20 25 30 tim e/s v e lo c it y p ro fil e m /s 0 2 4 6 8 10 12 14 16 18 0 5 10 15 20 25 30 tim e/s v e lo c ity p ro fil e m /s 0 2 4 6 8 10 12 14 16 18 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 tim e/s b ra ke f o rc e / n fig. 9: plots for case 2: (a) velocity profiles ( solid – front car). (dash – following car), (b) the inter-vehicle distance and (c) brake force 5.3 comments on case 3 the offset value is set to be 36 m and is automatically added to the safe distance expression. this value was found to be the best constant value so as to increase the reliability of the safe distance formulation. for case 3, whose initial values are shown in table 1, the intervehicle distance is set to be 120 m. the following vehicle applies no brake force until the front vehicle stops abruptly. it stops at the distance of 17 m from the front vehicle in a very smooth action. this is shown in fig. 10(b). 0 2 4 6 8 10 12 14 16 18 20 0 5 10 15 20 25 30 tim e/s v e lo c it y p ro fil e m /s 0 2 4 6 8 10 12 14 16 18 20 0 5 10 15 20 25 30 tim e/s v e lo c it y p ro fil e m /s 0 2 4 6 8 10 12 14 16 18 20 0 20 40 60 80 100 120 tim e/s c ur re nt d is ta n c e / m et e r fig. 10: plots for case 3: (a) velocity profiles ( solid – front car). (dash – following car), (b) the inter-vehicle distance and (c) brake force 5.4 comments on case 4 the different between initial values for case 4 in table 1 and those in case 1 is the slower velocity of the front vehicle, which is now 20 m/s. as expected and shown in fig. 11(c), the brake force is applied from the beginning until the tenth second of the simulation. due to the closer inter-vehicle distance at that time, faster response of brake system can be noted so as to avoid the collision. iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 7 0 2 4 6 8 10 12 14 16 18 0 5 10 15 20 25 30 time/s v e lo ci ty p ro fil e m /s 0 2 4 6 8 10 12 14 16 18 20 30 40 50 60 70 80 90 time/s c ur re n t d is ta n ce / m et e r 0 2 4 6 8 10 12 14 16 18 -1000 0 1000 2000 3000 4000 5000 6000 tim e/s b ra k e fo rc e /n fig. 11: plots for case 4: (a) velocity profiles ( solid – front car). (dash – following car), (b) the inter-vehicle distance and (c) brake force 6. conclusion the use of fuzzy logic algorithm in dsp is a fairly new development in automotive application. tms320lf2407 is a type of processor, which can provide high computation power in signal processing tasks especially when the process heavily involves multiplication and summation operations. when this processor is programmed using fuzzy algorithm, the issue of memory space cannot be avoided. however, with the 192 kwords of total zero wait state external memory interface, the problem is alleviated. in the field of braking system, the notation brake-by-wire implies electronically controlled braking system. the technique of using laser sensor for effective measurement of intervehicle distance via integration procedure has been suggested for optimal performance of the braking system. for the actuator of the system, a module called auxiliary hydraulic module is fixed before the brake pedal so as to apply controllable force upon the pedal. the results of the simulation studies have shown the effectiveness of off line neuro-fuzzy control to achieve a near-human behavior in controlling the braking system. the downloaded fuzzy algorithm in the processor memory bank works efficiently and only consumes less than half of the program memory space. it is also recorded that the speed of the fuzzy inference process is within the time of scanning the input signal obtained from the host computer. this demonstrates the feasibility and practicability of the code to be used in the real time controller. references [1] m.j.e. salami and s.n. sidek, "design of intelligent braking system", vol. ii, kuala lumpur, proc. tencon 2000. [2] g. nocker, and r. muller, "intelligetn cruise control with fuzzy logic", daimler-benz ag, forchung und technik. imeche 1992. [3] j. maretzke, and u. jacob, "distance warning and control as a means of increasing road safety and ease of ooperation", volkswagen ag, germany, 389/359 imeche 1992. [4] h. reza, z. xu, and b. yang, p. a. ioannou, "modeling and control design for a computer-controlled brake system", ieee trans. on control systems technology, vol. 5, no. 3, may 1997. [5] d. popovic, and l. vlacic, mechatronics in engineering design and product development, marcel dekker, inc. 1999. [6] a. l. lilein, "digital signal processors vs. universal microprocessors", esiee paris, spra344, sept. 1996 [7] tms320lf2407 evaluation module technical reference, spectrum digital, august 2000 [8] tms320lf2407, tms320lf2406, tms320lf2402 dsp controllers, sprs094e, august 2000 [9] h.-g. weil, g. probst,, and f. graf.. fuzzy expert system for automatic transmission control. siemens ag zfe st sn 42 at22j412. germany, 1992. [10] j. k. hedrick, j.c. gerdes, d.b. maciuca, and d. swaroop. brake system modeling, control and integrated brake/throttle switching: phase 1. ucb. ucb-its-prr-97-21, 1997. [11] xu, and b. yang., “brake system analysis, reliability, testing and control using bench experiment. ucla. ucb-its-prr-97-10, 1997. [12] l. moklegaard, and a.g. stefanopoulou. advanced braking method for longitudinal control of commercial heavy vehicle. ucb. ucb-its-prr-2000-8., 2000. [13] spra344. digital signal processors vs. universal microprocessors. texas instrument incorporated, 1996 [14] http://www.ti.com [15] http://www.startec.com.my iium engineering journal, vol. 2, no. 1, 2001 s. a. hameed and a. a. abbasi 8 appendix 0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20 time/s d is ta nc e e rr o r/ m e te r (a) 0 2 4 6 8 10 12 14 16 18 20 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 time/s d is ta nc e e rr or r a te m /s (b) 0 2 4 6 8 10 12 14 16 18 20 0 0.05 0.1 0.15 0.2 0.25 time/s n o rm a liz e d b ra k e (c) fig.. 12: (a): plot of distance error vs. time for case 1 (b): plot of distance error rate of change vs. time for case 1 (c): plot of normalized brake output vs. time for case1 iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 9 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 time/s d is ta nc e e rr o r/ m e te r (a) 0 2 4 6 8 10 12 14 16 18 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 time/ s d is ta nc e e rr o r r at e m /s (b) 0 2 4 6 8 10 12 14 16 18 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 t im e/s n o rm a liz e d b ra k e (c) fig. 13(a): plot of distance error vs. time for case 2 (b): plot of distance error rate of change vs. time for case 2 (c): plot of normalized brake output vs. time for case 2 iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 10 0 2 4 6 8 10 12 14 16 18 20 0 5 10 15 20 25 time/s d is ta n c e e rr o r/ m e te r (a) 0 2 4 6 8 10 12 14 16 18 20 -0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 time/s d is ta nc e e rr or r a te m /s (b) 0 2 4 6 8 10 12 14 16 18 20 0 0.05 0.1 0.15 0.2 0.25 time/s n o rm al iz e d b ra k e (c) fig. 14(a): plot of distance error vs. time for case 3 (b): plot of distance error rate of change vs. time for case 3 (c): plot of normalized brake output vs. time for case 3 iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 11 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 time/s d is ta n c e e rr o r/ m e te r (a) 0 2 4 6 8 10 12 14 16 18 -0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 time/s d is ta nc e e rr or r a te m /s (b) 0 2 4 6 8 10 12 14 16 18 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 time/s n o rm al iz e d b ra k e (c) fig. 15(a): plot of distance error vs. time for case 4 (b): plot of distance error rate of change vs. time for case 4(c): plot of normalized brake output vs. time for case 4 iium engineering journal, vol. 2, no. 1, 2001 s.n. sidek and m.j.e. salami 12 biographies momoh jimoh e. salami received his b.sc. degree from university of ife, nigeria in june 1977, postgraduate diploma from philips international institute for technological studies, eindhoven, netherland in dec. 1979 and phd from university of calgary, canada in june 1985. he has wide teaching experience in many high academic institutions in various countries. he joined iium in sept. 1996 and is currently the head of department of mechatronics engineering. he has authored or co-authored more than 50 publications including textbook, journals and conference papers. his research interests include intelligent system design and digital signal and image processing. dr. momoh is a senior member of ieee. shahrul na’im sidek received his b.eng. degree from vanderbilt university in may 1998 and m.sc. degree from international islamic university malaysia in sept. 2001. in 1998, he joined iium and is currently a lecturer in mechatronics department, iium. his research interests include digital signal processing and soft computing in control application. iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 model development of ride splitting service with resource sharing scheme on ride sourcing (online taxi) services in jakarta helen burhan1*, sutanto soehodho2, nahry1 1 department of mathematics, universitas indonesia, depok, indonesia 2 department of civil engineering, universitas indonesia, depok, indonesia *corresponding author: helen.burhan@sci.ui.ac.id (received: 21st june 2020; accepted: 24th october 2020; published on-line: 4th january 2021) abstract: this study aims to solve the increasing number of vehicles for ride-sourcing or online taxi service on the road and the operational issues in those services by developing an optimization model of ride-splitting services in the online taxi with a resource sharing (sharing platform) scheme. ride-splitting service is a ride-sourcing service where one vehicle can serve two or more request customers at a similar time. meanwhile, the resource-sharing scheme interlinks drivers from different platforms in providing services to the customers. that is, a driver from platform x can serve customers from platform y and vice versa, with a predetermined profit sharing. we formulate the optimization problem as a new modified weighted bipartite matching and solve the problem using a greedy heuristic method. based on the simulation, the proposed model can generate higher overall profit for all vehicles serving passengers, use fewer vehicles, and lower passengers’waiting time. abstrak: kajian ini bertujuan menyelesaikan jumlah penambahan kenderaan angkutanberpusat atau servis teksi dalam talian di atas jalan raya dan isu operasi dalam perkhidmatan dengan membangunkan model pengoptimuman pada servis angkutan-pecahan bagi teksi dalam talian dengan skim perkongsian sumber (platform bersama). servis angkutan-pecahan adalah servis angkutan-berpusat di mana satu kenderaan menyediakan perkhidmatan kepada dua atau lebih permintaan pengguna pada satu-satu masa. manakala, perkongsian sumber menghubungkan pemandu dengan platform berlainan dalam menyediakan servis untuk penumpang. iaitu, pemandu platform x boleh mengangkut penumpang platform y dan sebaliknya, dengan menentukan terlebih dahulu keuntungan bersama. kajian ini diformulasi dengan pengoptimuman masalah sebagai perubahan terbaru dalam menilai kesesuian keduadua pihak dan menyelesaikan masalah menggunakan kaedah heuristik rakus. berdasarkan simulasi ini, model yang dicadangkan dapat menghasilkan keuntungan keseluruhan lebih tinggi bagi semua kenderaan perkhidmatan, dengan mengurangkan jumlah kenderaan dan masa menunggu penumpang. keywords: ride sourcing (online taxi) services, ride splitting service, resource sharing scheme, modified weighted bipartite matching, greedy heuristic method. 1. introduction in line with the increasing usage of ride-sourcing service, which is more commonly known as online taxi, new problems stemming from the increasing usage of the service are also arising. one of those problems is the increased number of private vehicles on the road. this is due to the attractive idea of online taxi as a new business potential, so that idle private vehicles are now utilized as the online taxi fleet, some business owners even buy new cars purposely to be 175 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 rented for online taxi services [1]. the increased usage of private vehicles for the online taxi services is not in accordance with the initial purpose of ride-sourcing service, which was initially a ride-sharing concept that was designed to minimize the usage of private vehicles in order to reduce traffic [2, 3]. on the other hand, one of the many services offered by the online taxi provider is ride-splitting, a service that is unfortunately still underused. ride-splitting service is a ride-sourcing service that is in line with the actual concept of ride sharing, where one vehicle (single driver) can serve two or more riders (multi-riders) at a similar time [4]. currently, there are two big companies providing online taxi services in jakarta whose operational services are not yet optimized. this can be concluded from the long waiting time for customers to be picked up, which is sometimes a lot longer that the estimate time shown on the app; and also from the surge pricing system, where the fare will be higher than the standard fare when the demand for services is high and the vehicle availability is low, the surge pricing system is deemed as non-transparent so that it can disadvantage consumers [5]. in the previous research, burhan et.al [6] developed an optimized model of pure ride-sourcing service (single driver single rider) with a resource sharing scheme to tackle the operational problems. therefore, this study aims to solve the increasing number of vehicles for online taxi on the road and the operational issues in online taxi services, by developing an optimization model of ridesplitting services in online taxi with a resource sharing (sharing platform) scheme. to optimize the ride-splitting service with resource sharing scheme, an optimized route is sought to pick up and drop off two or more customer requests (in this research is limited to only two requests) from the nearby or adjacent area at the similar travel time. the resource sharing scheme here is the same one as defined by burhan et.al [6], which is interlinking drivers from different operators (platforms) in providing services to the customers, where a driver from platform x can serve customers from platform y and vice versa, with a predetermined profit sharing. the mathematical model in optimizing issues in this study will be using a new modified weighted bipartite matching problem, while the solving method will be using greedy heuristic method. the rest of the paper is organized as follows. section 2 presents a literature review, while section 3 describes the problem formulation, and section 4 describes the solution method, section 5 present the computational experiment, and finally, section 6 concludes and illustrates future research directions. 2. literature review ride-sourcing service, which is more commonly known as online taxi, is a public transportation service using private owned vehicles as fleet to serve customers as taxi service using technology of smartphones, gps and gis [2,3]. based on the type of service offered, the service can be grouped into two types [4], pure ride-sourcing (single driver, single rider) and ride splitting (single driver, multi riders). in pure ride sourcing, a driver of personal vehicle is connected to one request customer, and in the ride-splitting service, a driver is connected to two or more request customers in which customers can choose to split (share) a ride and fare. based on that classification, ridesplitting is the appropriate form of ride-sourcing based on the ride-sharing concept for single driver multi rider, so that the problem of optimizing the ride-splitting service is the optimization problem in finding the vehicle route to pick up and drop off passengers [7]. the optimization problem in finding the vehicle route to pick up and and drop off passengers on ride-splitting service is similar to dynamic pick up and delivery problem with time windows [8]. generally, the pick up and delivery problems with time windows is one 176 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 variant of vehicle routing problem which aims to find the optimal vehicle route to deliver and pick up a number of customers in an interval of time (time windows), taking into account a number of constraints such as vehicle capacity and some other precedent constraints, with minimum costs [9]. the dynamic term here refers to the requests which gradually revealed throughout the day, so that vehicle routes are constructed in real-time [10]. several previous studies that discussed the problem of optimizing ride-sharing services for the case of a single driver-multi rider, some of which are, hosni et al. [11] use mixed integer programming to model the problem of maximize profit for shared taxi problem and present a lagrangian decomposition approach as well as two heuristics to solve the problem, wang et.al [12] use binary integer programming to model the problem of minimize cost and travel time for a pickup and delivery problem with the use of hov lanes and use tabu search heuristic to solve the problem, santos and xavier [13] use mixed integer programming to model the problem of maximize the number of served requests and minimize the cost for the ride-sharing problem and solved the problem by a greedy randomized adaptive search procedure, mahmoudi and zhou [14] propose a new time discretized multi-commodity network flow model for ride-sharing problem within state space-time network to minimize cost and using a forward dynamic programming solution algorithm and lagrangian approach to solve the problem. while bei and zhang [15] use a three-dimensional matching problem to minimize cost for the ride-sharing problem and use a two-phase greedy approach to solve the problem. to the best of our knowledge, the previous studies have never been including maximizing profit and minimizing waiting time in the objective function simultaneously and explicitly. therefore, in this study, we will use a new modified weighted bipartite graph problem to formulate the optimization problem of ride splitting service to maximize the driver’s profit while minimizing passenger’s waiting time. in the meantime, researches relating to the operational problems in ride-sourcing services are discussing more of the surge pricing problems; because surge pricing is considered as lack transparency and is harmful to the consumer [16-18]. however, since the price for ride service cannot be unlimited, there is usually a reasonable or legitimate range of prices in practice. such a constrained surge pricing strategy fails to balance demand and supply in certain cases, e.g., even adopting the maximum allowed price cannot reduce the demand to an affordable level during peak hours [19]. therefore, this study is developing a resource sharing scheme based on research conducted by burhan, h, et.al [6] to solve the surge pricing problems in ridesourcing services. 3. problem formulation in ride-splitting service with resource sharing scheme, customer from platform x can be served by vehicle from platform y, and the other way around, with a profit sharing between platforms that is predetermined beforehand. with the predetermined scheme, characteristics of the ride-splitting service with the resource sharing scheme in this paper, are as follows: customer will get less waiting time driver will get more profit due to less operational cost by picking up customer from the different platform, whose pick-up location is closer to the driver’s position, rather than picking up customer from the same platform but whose pick-up location is quite far from the driver's position. matching rate between driver and passenger/customer is also increasing, because the probability is bigger for the customer whose pick-up time and location is similar to the driver, as opposed to when compared to the possibility from only the same platform. 177 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 assume, there are two different operators (platforms) providing ride-splitting services, where it can be enlarged to n platforms and a homogenous fleet of vehicles with the same capacities. the request from a customer in this study arrives dynamically, thus the customer’s requests and available vehicles will be grouped first, based on a period of time, and then the optimization process to assign vehicle and passengers is done statically per period. the period length is based on an acceptable time limit of a customer to wait for a decision to be picked up and time for the optimization process. the first period starts at the time, at which the first request from a customer arrived. in the optimization process, initially, we must pair potential vehicles which feasible to serve a request customer by generating the first weighted bipartite graph. then, we will get a set of feasible vehicle and the first customer pairs. in this study, the ride splitting service is limited to serving only two request customers in one trip. thus, next stage is to generate a second weighted bipartite graph to pair a vehicle and the first customer with a potential second request customer. the objective of the optimization problem is to maximize the total profit earned by drivers (vehicles) while minimizing the total passenger's waiting time. then, we model the problem using a new modified weighted bipartite matching. the final stage, use a greedy heuristic method to solve the problem. next, we present the process of generating first weighted bipartite graph as the first stage for the optimization process. 3.1. first weighted bipartite graph let k and r be the number indexes for platform which requested by customer, where 𝒌,𝒓 = 𝟏,𝟐 and 𝝉 be the period for optimization process. let 𝑷𝒌𝒍 𝝉 be the 𝒍 − 𝒕𝒉 passenger of platform 𝒌 in period 𝝉 and 𝑽𝒓𝒔 𝝉 be the s−𝒕𝒉 available vehicle of platform 𝒓 in period 𝝉. then: 𝑃𝑘 𝜏 be a set of customers who request vehicle from platform 𝑘 in period 𝜏, where: 𝑃𝑘 𝜏 = {𝑃𝑘𝑙 𝜏 |the 𝑙 − 𝑡ℎ passenger of platform 𝑘 in period 𝜏; 𝑙 = 1,2,…,𝑛𝑘}, for 𝑘 = 1,2 and 𝑃𝜏 be the set of customers who request vehicle in period 𝜏. 𝑉𝑟 𝜏 be a set of available vehicles from platform 𝑟 in period 𝜏, where: 𝑉𝑟 𝜏 = {𝑉𝑟𝑠 𝜏|the 𝑠 − th vehicle of platform 𝑟 in period 𝜏; 𝑠 = 1,2,…,𝑚𝑟} , for 𝑟 = 1,2 and 𝑉𝜏 be the set of available vehicles in period 𝜏. note that 𝑃𝜏𝑖 consists of all new customer requests in period 𝜏𝑖 and all assigned passengers in the previous period 𝜏𝑖−1, but still not get a passenger pair to share a ride, for 𝑖 = 2,3,…. likewise, 𝑉𝜏𝑖 consists of all newly available vehicles in period 𝜏𝑖 and all available vehicles which still eligible to serve a customer from the previous period 𝜏𝑖−1, for 𝑖 = 2,3,…. each passenger 𝑃𝑘𝑙 𝜏 is associated with time at which customer request a vehicle 𝑡𝑟𝑒𝑞𝑢𝑒𝑠𝑡_𝑃𝑘𝑙 𝜏 , origin or pick up location 𝑜𝑃𝑘𝑙 𝜏 , destination or drop off location 𝑑𝑃𝑘𝑙 𝜏 , an earliest departure time 𝑒𝑑𝑒𝑝𝑡 𝑃𝑘𝑙 𝜏 , a latest departure time 𝑙𝑑𝑒𝑝𝑡 𝑃𝑘𝑙 𝜏 , and the number of passenger 𝑞𝑃𝑘𝑙 𝜏 . also, passenger 𝑃𝑘𝑙 𝜏 must arrive at destination at least on 𝑒𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 , and not after 𝑙𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 , and cannot ride a vehicle more than 𝑡𝑚𝑎𝑥𝑟𝑖𝑑𝑒 _𝑃𝑘𝑙 𝜏 . while, each available vehicle 𝑉𝑟𝑠 𝜏 is associated with origin or current location 𝑖𝑉𝑟𝑠𝜏 , time to leave from or arrive at location on 𝑡𝑖𝑚𝑒𝑖𝑉𝑟𝑠𝜏 𝑉𝑟𝑠 𝜏 , maximum capacity 𝑄𝑉𝑟𝑠𝜏 , and vehicle’s occupation 𝑉𝑟𝑠 𝜏_𝑜𝑐𝑐. let 𝐺1 𝜏 = (𝑁1 𝜏,𝐸1 𝜏) be the first weighted bipartite graph for optimization process, where 𝑁1 𝜏 be the set of nodes of 𝐺1 𝜏 and 𝐸1 𝜏 be the set of edges of 𝐺1 𝜏. defined 𝑁1 𝜏 = 𝑉𝜏 ∪ 𝑃𝜏 be a bipartite node set of all request customers and available vehicles in period 𝜏. for each passenger 𝑃𝑘𝑙 𝜏 in 𝑃𝜏, the distance 𝐷𝑖 𝑉𝑟𝑠 𝜏 𝑂𝑃𝑘𝑙 𝜏 and the travel time 𝑇𝑇𝑖𝑉𝑟𝑠𝜏 𝑂𝑃𝑘𝑙 𝜏 be 178 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 a distance and a travel time of shortest path from origin 𝑜𝑃𝑘𝑙 𝜏 to destination 𝑑𝑃𝑘𝑙 𝜏 . for each vehicle 𝑉𝑟𝑠 𝜏 in 𝑉𝜏, the distance 𝐷𝑖 𝑉𝑟𝑠 𝜏 𝑂𝑃𝑘𝑙 𝜏 and the travel time 𝑇𝑇𝑖𝑉𝑟𝑠𝜏 𝑂𝑃𝑘𝑙 𝜏 be a distance and a travel time of shortest path from vehicle’s origin (current) location 𝑖𝑉𝑟𝑠𝜏 to passenger’s origin 𝑜𝑃𝑘𝑙 𝜏 . for each passenger 𝑃𝑘𝑙 𝜏 , earliest and latest departure time, earliest and latest arrival time, and maximum ride time are determined with the following formula: 𝑒𝑑𝑒𝑝𝑡 𝑃𝑘𝑙 𝜏 := 𝑡𝑟𝑒𝑞𝑢𝑒𝑠𝑡_𝑃𝑘𝑙 𝜏 + 𝜆𝑒𝑎𝑟𝑙𝑦 (1) 𝑙𝑑𝑒𝑝𝑡 𝑃𝑘𝑙 𝜏 := 𝑒𝑑𝑒𝑝𝑡 𝑃𝑘𝑙 𝜏 + 𝜆𝑙𝑎𝑡𝑒 (2) 𝑒𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 ≔ 𝑡𝑖𝑚𝑒𝑖 𝑉𝑟𝑠 𝜏 𝑉𝑟𝑠 𝜏 +((1 + 𝜀) 𝑇𝑇𝑖 𝑉𝑟𝑠 𝜏 𝑂𝑃𝑘𝑙 𝜏 )+ 𝑡𝑠𝑒𝑟𝑣𝑖𝑐𝑒_ 𝑃𝑘𝑙 𝜏 𝑉𝑟𝑠 𝜏 +𝑇𝑇𝑜𝑑 𝑃𝑘𝑙 𝜏 (3) 𝑙𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 ≔ 𝑒𝑎𝑟𝑟 𝑃𝑘𝑙 𝜏 + 𝜆𝑙𝑎𝑡𝑒 (4) 𝑡𝑚𝑎𝑥𝑟𝑖𝑑𝑒 _𝑃𝑘𝑙 𝜏 ≔ ((1 + 𝜇)𝑇𝑇𝑜𝑑 𝑃𝑘𝑙 𝜏 ) (5) where 𝜆𝑒𝑎𝑟𝑙𝑦 be a level of service for early departure time; 𝜆𝑙𝑎𝑡𝑒 be a level of service for early departure or arrival time; 𝑡𝑠𝑒𝑟𝑣𝑖𝑐𝑒_ 𝑃𝑘𝑙 𝜏 𝑉𝑟𝑠 𝜏 be time for passenger to get into (get off from) a vehicle; (1 + 𝜀) and (1 + 𝜇) be multiplier factor for tolerance time deviation, with 0 < 𝜀,𝜇 < 1. vehicle 𝑉𝑟𝑠 𝜏 is feasible to serve a passenger 𝑃𝑘𝑙 𝜏 , if the following criteria are met. 1) time constraints: a) vehicle must arrive at passenger’s origin on departure time windows: 𝑒𝑑𝑒𝑝𝑡 𝑃𝑘𝑙 𝜏 ≤ 𝑡𝑖𝑚𝑒𝑖 𝑉𝑟𝑠 𝜏 𝑉𝑟𝑠 𝜏 +((1 + 𝜀) 𝑇𝑇𝑖 𝑉𝑟𝑠 𝜏 𝑂𝑃𝑘𝑙 𝜏 ) ≤ 𝑙𝑑𝑒𝑝𝑡 𝑃𝑘𝑙 𝜏 (6) b) vehicle must arrive at passenger’s destination on arrival time windows: 𝑒𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 ≤ 𝑡𝑖𝑚𝑒𝑖 𝑉𝑟𝑠 𝜏 𝑉𝑟𝑠 𝜏 +((1 + 𝜀) 𝑇𝑇𝑖 𝑉𝑟𝑠 𝜏 𝑂𝑃𝑘𝑙 𝜏 )+ 𝑡𝑠𝑒𝑟𝑣𝑖𝑐𝑒_ 𝑃𝑘𝑙 𝜏 𝑉𝑟𝑠 𝜏 +𝑇𝑇𝑜𝑑 𝑃𝑘𝑙 𝜏 ≤ 𝑙𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 (7) 2) capacity constraint: the number of passengers in each request must be less than or equal to available vehicle’s capacity: 𝑞𝑃𝑘𝑙 𝜏 ≤ 𝑄𝑉𝑟𝑠𝜏 (8) let 𝑃𝑘𝑙 𝜏 in 𝑃𝜏 and 𝑉𝑟𝑠 𝜏 in 𝑉𝜏. defined an edge in 𝐸1 𝜏 be a pair of (𝑉𝑟𝑠 𝜏 ,𝑃𝑘𝑙 𝜏 ), where vehicle 𝑉𝑟𝑠 𝜏 is met the feasible criterion in (6) – (8) to serve passenger 𝑃𝑘𝑙 𝜏 . then, 𝐸1 𝜏 = {(𝑉𝑟𝑠 𝜏 ,𝑃𝑘𝑙 𝜏 )|𝑃𝑘𝑙 𝜏 and 𝑉𝑟𝑠 𝜏 are feasible match; 𝑉𝑟𝑠 𝜏 ∈ 𝑉𝜏, 𝑃𝑘𝑙 𝜏 ∈ 𝑃𝜏}. the weight of each edge (𝑉𝑟𝑠 𝜏 ,𝑃𝑘𝑙 𝜏 ) in 𝐸1 𝜏 is defined as the fare that has to be paid by passenger 𝑃𝑘𝑙 𝜏 served by vehicle 𝑉𝑟𝑠 𝜏 , where the fare is calculated by using the following formula: 𝐹𝑃𝑘𝑙 𝜏 = 𝑇𝑎𝑟𝑖𝑓𝑓𝑘 × 𝐷𝑜𝑑_𝑃𝑘𝑙 𝜏 (9) where 𝑇𝑎𝑟𝑖𝑓𝑓𝑘 is tariff of platform k for ride splitting service per 1 distance unit. next, mathematical model for the optimization problem of ride splitting service with resource sharing scheme will be presented. before that, we generate a second weighted bipartite graph. 3.2. new modified weighted bipartite matching problem 179 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 let 𝐺2 𝜏 = (𝑁2 𝜏,𝐸2 𝜏) be the second weighted bipartite graph for optimization process, where 𝑁2 𝜏 be the set of nodes of 𝐺2 𝜏 and 𝐸2 𝜏 be the set of edges of 𝐺2 𝜏. let 𝑁2 𝜏 = 𝑉𝜏𝑃𝜏 ∪ 𝐷𝑉𝜏𝑃𝜏, be a bipartite set of nodes of graph 𝐺2 𝜏. for 𝑉𝑟𝑠 𝜏 ∈ 𝑉𝜏 and 𝑃𝑘𝑙 𝜏 ∈ 𝑃𝜏, defined 𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 be a node in 𝑉𝜏𝑃𝜏 if only if (𝑉𝑟𝑠 𝜏 ,𝑃𝑘𝑙 𝜏 ) is an edge in 𝐸1 𝜏. thus, 𝑉𝜏𝑃𝜏 = {𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 |(𝑉𝑟𝑠 𝜏 ,𝑃𝑘𝑙 𝜏 ) is an edge in 𝐸1 𝜏;𝑉𝑟𝑠 𝜏 ∈ 𝑉𝜏,𝑃𝑘𝑙 𝜏 ∈ 𝑃𝜏} and 𝐷𝑉𝜏𝑃𝜏 is a duplication set of 𝑉𝜏𝑃𝜏 where 𝐷𝑉𝜏𝑃𝜏 = {𝑉𝑟′𝑠′ 𝜏 𝑃𝑘′𝑙′ 𝜏 |if 𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 ∈ 𝑉𝜏𝑃𝜏}. let 𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 be a node in 𝑉𝜏𝑃𝜏 and 𝑉𝑟′𝑠′ 𝜏 𝑃𝑘′𝑙′ 𝜏 be a node in 𝐷𝑉𝜏𝑃𝜏, defined, an edge in 𝐸2 𝜏 be a pair of (𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 ,𝑉𝑟′𝑠′ 𝜏 𝑃𝑘′𝑙′ 𝜏 ), where 𝑟 = 𝑟′,𝑠 = 𝑠′ and 𝑉𝑟𝑠 𝜏 is feasible to serve customers 𝑃𝑘𝑙 𝜏 and 𝑃𝑘′𝑙′ 𝜏 . note that, in the edge (𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 ,𝑉𝑟′𝑠′ 𝜏 𝑃𝑘′𝑙′ 𝜏 ), 𝑉𝑟𝑠 𝜏 and 𝑉𝑟′𝑠′ 𝜏 have to be the same vehicles. thus,𝐸2 𝜏 = {(𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 ,𝑉𝑟′𝑠′ 𝜏 𝑃𝑘′𝑙′ 𝜏 )| 𝑟 = 𝑟′,𝑠 = 𝑠′ and 𝑉𝑟𝑠 𝜏 is feasible match with 𝑃𝑘𝑙 𝜏 and 𝑃𝑘′𝑙′ 𝜏 ; 𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 ∈ 𝑉𝜏𝑃𝜏,𝑉𝑟′𝑠′ 𝜏 𝑃𝑘′𝑙′ 𝜏 ∈ 𝐷𝑉𝜏𝑃𝜏}. route of vehicle 𝑉𝑟𝑠 𝜏 to pick up and drop off customers 𝑃𝑘𝑙 𝜏 and 𝑃𝑘′𝑙′ 𝜏 , 𝑅𝑜𝑢𝑡𝑒𝑉𝑟𝑠𝜏 _𝑃𝑘𝑙 𝜏 _𝑃𝑘′𝑙′ 𝜏 is defined as the shortest path from vehicle’s current location 𝑖𝑉𝑟𝑠𝜏 to the first passenger’s origin 𝑜𝑃𝑘𝑙 𝜏 , then to the second passenger’s origin 𝑜𝑃 𝑘′𝑙′ 𝜏 and next to passenger’s destination 𝑑𝑃𝑘𝑙 𝜏 or 𝑑𝑃𝑘′𝑙′ 𝜏 for which one is the closest. then, 𝑅𝑜𝑢𝑡𝑒𝑉𝑟𝑠𝜏 _𝑃𝑘𝑙 𝜏 _𝑃𝑘′𝑙′ 𝜏 is the shortest path between route 𝑖𝑉𝑟𝑠𝜏 − 𝑜𝑃𝑘𝑙 𝜏 − 𝑜𝑃 𝑘′𝑙′ 𝜏 − 𝑑𝑃𝑘𝑙 𝜏 − 𝑑𝑃𝑘′𝑙′ 𝜏 and route 𝑖𝑉𝑟𝑠𝜏 − 𝑜𝑃𝑘𝑙 𝜏 − 𝑜𝑃 𝑘′𝑙′ 𝜏 − 𝑑𝑃 𝑘′𝑙′ 𝜏 − 𝑑𝑃𝑘𝑙 𝜏 . 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑉𝑟𝑠𝜏 _𝑃𝑘𝑙 𝜏 _𝑃𝑘′𝑙′ 𝜏 and 𝑇𝑇𝑉𝑟𝑠𝜏 _𝑃𝑘𝑙 𝜏 _𝑃𝑘′𝑙′ 𝜏 are defined as the distance and the travel time of 𝑅𝑜𝑢𝑡𝑒𝑉𝑟𝑠𝜏 _𝑃𝑘𝑙 𝜏 _𝑃𝑘′𝑙′ 𝜏 . vehicle 𝑉𝑟𝑠 𝜏 is feasible to serve customers 𝑃𝑘𝑙 𝜏 and 𝑃𝑘′𝑙′ 𝜏 , if the following criteria are met: 1) time feasibility: a) vehicle must arrive at passenger’s origin on passenger’s departure time windows: for first passenger, 𝑃𝑘𝑙 𝜏 : 𝑒𝑑𝑒𝑝𝑡 𝑃𝑘𝑙 𝜏 ≤ 𝑊𝑇𝑉𝑟𝑠𝜏 𝑃𝑘𝑙 𝜏 ≤ 𝑙𝑑𝑒𝑝𝑡 𝑃𝑘𝑙 𝜏 (10) where 𝑊𝑇 𝑉𝑟𝑠 𝜏 𝑃𝑘𝑙 𝜏 is passenger 𝑃𝑘𝑙 𝜏 ’s waiting time to be picked up by vehicle 𝑉𝑟𝑠 𝜏 , with 𝑊𝑇 𝑉𝑟𝑠 𝜏 𝑃𝑘𝑙 𝜏 = 𝑡𝑖𝑚𝑒𝑖 𝑉𝑟𝑠 𝜏 𝑉𝑟𝑠 𝜏 +((1 + 𝜀) 𝑇𝑇𝑖 𝑉𝑟𝑠 𝜏 𝑂𝑃𝑘𝑙 𝜏 ) (11) for second passenger, 𝑃𝑘′𝑙′ 𝜏 : 𝑒𝑑𝑒𝑝𝑡 𝑃𝑘′𝑙′ 𝜏 ≤ 𝑊𝑇𝑉𝑟𝑠𝜏 𝑃𝑘′𝑙′ 𝜏 ≤ 𝑙𝑑𝑒𝑝𝑡 𝑃𝑘′𝑙′ 𝜏 (12) where 𝑊𝑇 𝑉𝑟𝑠 𝜏 𝑃𝑘′𝑙′ 𝜏 is passenger 𝑃𝑘′𝑙′ 𝜏 ’s waiting time to be picked up by vehicle 𝑉𝑟𝑠 𝜏 , with 𝑊𝑇 𝑉𝑟𝑠 𝜏 𝑃𝑘′𝑙′ 𝜏 =𝑊𝑇 𝑉𝑟𝑠 𝜏 𝑃𝑘𝑙 𝜏 + 𝑡𝑠𝑒𝑟𝑣𝑖𝑐𝑒 𝑃𝑘𝑙 𝜏 𝑉𝑟𝑠 𝜏 + 𝑇𝑇𝑂 𝑃𝑘𝑙 𝜏 𝑂 𝑃𝑘′𝑙′ 𝜏 (13) b) vehicle must arrive at passenger’s destination on passenger’s arrival time windows: if 𝑅𝑜𝑢𝑡𝑒𝑉𝑟𝑠𝜏 _𝑃𝑘𝑙 𝜏 _𝑃𝑘′𝑙′ 𝜏 is 𝑖𝑉𝑟𝑠𝜏 − 𝑜𝑃𝑘𝑙 𝜏 − 𝑜𝑃 𝑘′𝑙′ 𝜏 − 𝑑𝑃𝑘𝑙 𝜏 − 𝑑𝑃𝑘′𝑙′ 𝜏 , then: for first passenger, 𝑃𝑘𝑙 𝜏 : 𝑒𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 ≤ 𝑊𝑇 𝑉𝑟𝑠 𝜏 𝑃𝑘′𝑙′ 𝜏 + 𝑡𝑠𝑒𝑟𝑣𝑖𝑐𝑒 𝑃𝑘′𝑙′ 𝜏 𝑉𝑟𝑠 𝜏 + 𝑇𝑇𝑜 𝑃𝑘′𝑙′ 𝜏 𝑑 𝑃𝑘𝑙 𝜏 ≤ 𝑙𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 (14) for second passenger, 𝑃𝑘′𝑙′ 𝜏 : 𝑒𝑎𝑟𝑟_𝑃𝑘′𝑙′ 𝜏 ≤ 𝑡𝑠𝑒𝑟𝑣𝑖𝑐𝑒_𝑃𝑘𝑙 𝜏 𝑉𝑟𝑠 𝜏 + 𝑇𝑇𝐼 ≤ 𝑙𝑎𝑟𝑟_𝑃𝑘′𝑙′ 𝜏 (15) where 𝑇𝑇𝐼 = 𝑇𝑇𝑖 𝑉𝑟𝑠 𝜏 − 𝑜𝑃𝑘𝑙 𝜏 −𝑜 𝑃 𝑘′𝑙′ 𝜏 − 𝑑 𝑃𝑘𝑙 𝜏 −𝑑 𝑃𝑘′𝑙′ 𝜏 (16) else if 𝑅𝑜𝑢𝑡𝑒𝑉𝑟𝑠𝜏 _𝑃𝑘𝑙 𝜏 _𝑃𝑘′𝑙′ 𝜏 is 𝑖𝑉𝑟𝑠𝜏 − 𝑜𝑃𝑘𝑙 𝜏 − 𝑜𝑃 𝑘′𝑙′ 𝜏 − 𝑑𝑃 𝑘′𝑙′ 𝜏 − 𝑑𝑃𝑘𝑙 𝜏 , then: 180 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 for first passenger, 𝑃𝑘𝑙 𝜏 : 𝑒𝑎𝑟𝑟_𝑃𝑘′𝑙′ 𝜏 ≤ 𝑊𝑇 𝑉𝑟𝑠 𝜏 𝑃𝑘′𝑙′ 𝜏 + 𝑡𝑠𝑒𝑟𝑣𝑖𝑐𝑒_ 𝑃𝑘′𝑙′ 𝜏 𝑉𝑟𝑠 𝜏 + 𝑇𝑇𝑜 𝑃𝑘′𝑙′ 𝜏 𝑑 𝑃𝑘′𝑙′ 𝜏 ≤ 𝑙𝑎𝑟𝑟_𝑃𝑘′𝑙′ 𝜏 (17) for second passenger, 𝑃𝑘′𝑙′ 𝜏 : 𝑒𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 ≤ 𝑡𝑠𝑒𝑟𝑣𝑖𝑐𝑒_𝑃𝑘𝑙 𝜏 𝑉𝑟𝑠 𝜏 + 𝑇𝑇𝐼𝐼 ≤ 𝑙𝑎𝑟𝑟_𝑃𝑘𝑙 𝜏 (18) where 𝑇𝑇𝐼𝐼 = 𝑇𝑇𝑖 𝑉𝑟𝑠 𝜏 − 𝑜𝑃𝑘𝑙 𝜏 −𝑜 𝑃 𝑘′𝑙′ 𝜏 − 𝑑 𝑃 𝑘′𝑙′ 𝜏 −𝑑 𝑃𝑘𝑙 𝜏 (19) c) the time spent by a customer in a vehicle cannot exceed a given value (maximum ride time) : if 𝑹𝒐𝒖𝒕𝒆𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 = 𝒊𝑽𝒓𝒔𝝉 − 𝒐𝑷𝒌𝒍 𝝉 − 𝒐𝑷 𝒌′𝒍′ 𝝉 − 𝒅𝑷𝒌𝒍 𝝉 − 𝒅𝑷𝒌′𝒍′ 𝝉 then: for passenger 𝑷𝒌𝒍 𝝉 : 𝑻𝑻𝒐 𝑷𝒌𝒍 𝝉 𝒐𝑷𝒌′𝒍′ 𝝉 + 𝒕𝒔𝒆𝒓𝒗𝒊𝒄𝒆_ 𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 + 𝑻𝑻𝒐 𝑷𝒌′𝒍′ 𝝉 𝒅𝑷𝒌𝒍 𝝉 ≤ 𝒕𝒎𝒂𝒙𝒓𝒊𝒅𝒆 𝑷𝒌𝒍 𝝉 (20) for passenger 𝑷𝒌′𝒍′ 𝝉 : 𝑻𝑻𝒐 𝑷𝒌′𝒍′ 𝝉 𝒅𝑷𝒌𝒍 𝝉 +𝒕𝒔𝒆𝒓𝒗𝒊𝒄𝒆_𝑷𝒌𝒍 𝝉 𝑽𝒓𝒔 𝝉 + 𝑻𝑻𝒅 𝑷𝒌𝒍 𝝉 𝒅𝑷𝒌′𝒍′ 𝝉 ≤ 𝒕𝒎𝒂𝒙𝒓𝒊𝒅𝒆 𝑷𝒌′𝒍′ 𝝉 (21) else if 𝑹𝒐𝒖𝒕𝒆𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 is 𝒊𝑽𝒓𝒔𝝉 − 𝒐𝑷𝒌𝒍 𝝉 − 𝒐𝑷 𝒌′𝒍′ 𝝉 − 𝒅𝑷 𝒌′𝒍′ 𝝉 − 𝒅𝑷𝒌𝒍 𝝉 , then: for passenger 𝑷𝒌𝒍 𝝉 : 𝑻𝑻𝒐 𝑷𝒌𝒍 𝝉 𝒐𝑷𝒌′𝒍′ 𝝉 + (𝟐 × 𝒕𝒔𝒆𝒓𝒗𝒊𝒄𝒆_ 𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 ) + 𝑻𝑻𝒐 𝑷𝒌′𝒍′ 𝝉 𝒅𝑷𝒌′𝒍′ 𝝉 + 𝑻𝑻𝒅𝑷𝒌′𝒍′ 𝝉 𝒅𝑷𝒌𝒍 𝝉 ≤ 𝒕𝒎𝒂𝒙𝒓𝒊𝒅𝒆 𝑷𝒌𝒍 𝝉 (22) for passenger 𝑷𝒌′𝒍′ 𝝉 : 𝑻𝑻𝒐 𝑷𝒌′𝒍′ 𝝉 −𝒅𝑷𝒌′𝒍′ 𝝉 ≤ 𝒕𝒎𝒂𝒙𝒓𝒊𝒅𝒆 _𝑷𝒌′𝒍′ 𝝉 (23) 2) capacity feasibility: the number of passengers in each request must be less than or equal to available vehicle’s capacity: 𝒒𝑷𝒌𝒍 𝝉 + 𝒒𝑷𝒌′𝒍′ 𝝉 ≤ 𝑸𝑽𝒓𝒔𝝉 (24) next, we define model of the optimization problem of ride splitting service with resource sharing scheme on graph 𝑮𝟐 𝝉 = (𝑵𝟐 𝝉,𝑬𝟐 𝝉), and we use the following decision variables: 𝒙 𝑷𝒌𝒍 𝝉 ,𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 = { 𝟏 , 𝐢𝐟 𝐩𝐚𝐬𝐬𝐞𝐧𝐠𝐞𝐫𝐬 𝑷𝒌𝒍 𝝉 𝐚𝐧𝐝 𝑷𝒌′𝒍′ 𝝉 𝐬𝐞𝐫𝐯𝐞𝐝 𝐛𝐲 𝐯𝐞𝐡𝐢𝐜𝐥𝐞 𝑽𝒓𝒔 𝝉 𝟎,𝐨𝐭𝐡𝐞𝐫𝐰𝐢𝐬𝐞 𝑧 𝑉𝑟𝑠 𝜏 𝑃𝑘𝑙 𝜏 = { 1 , if vehicle 𝑉𝑟𝑠 𝜏 serves passenger 𝑃𝑘𝑙 𝜏 0, otherwise 𝒘 𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 = { 𝟏, 𝐢𝐟 𝐩𝐥𝐚𝐭𝐟𝐨𝐫𝐦 𝐢𝐧𝐝𝐞𝐱 𝒌 = 𝒓 𝜶, 𝐨𝐭𝐡𝐞𝐫𝐰𝐢𝐬𝐞 𝜶 is profit sharing multiplier, where 𝟎 < 𝜶 < 𝟏 𝑉𝑟𝑠 𝜏_𝑜𝑐𝑐 = { 2,if 𝑥𝑃𝑘𝑙 𝜏 _𝑃𝑘′𝑙′ 𝜏 𝑉𝑟𝑠 𝜏 = 1 and 𝑃𝑘𝑙 𝜏 ≠ 𝑃𝑘′𝑙′ 𝜏 1, if 𝑥 𝑃𝑘𝑙 𝜏 _𝑃𝑘′𝑙′ 𝜏 𝑉𝑟𝑠 𝜏 = 1 and 𝑃𝑘𝑙 𝜏 = 𝑃𝑘′𝑙′ 𝜏 0,else 𝑄𝑉𝑟𝑠𝜏 = { 4, if 𝑉𝑟𝑠 𝜏 𝑜𝑐𝑐 = 0 4 − 𝑞𝑃𝑘𝑙 𝜏 , if 𝑉𝑟𝑠 𝜏 𝑜𝑐𝑐 = 1 0,else 181 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 for each feasible match (𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 ,𝑽𝒓′𝒔′ 𝝉 𝑷𝒌′𝒍′ 𝝉 ) 𝐢𝐧 𝑬𝟐 𝝉, calculate: 1) the operational cost of 𝑹𝒐𝒖𝒕𝒆𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 : 𝒐𝒑.𝒄𝒐𝒔𝒕 𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 = 𝒄𝑽𝒓𝒔𝝉 × 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 (25) where 𝒄𝑽𝒓𝒔𝝉 is vehicle 𝑽𝒓𝒔 𝝉 ’s operational cost per one distance unit 2) the profit of 𝑹𝒐𝒖𝒕𝒆𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 : 𝒑𝒓𝒐𝒇𝒊𝒕 𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 = (𝒘 𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 𝒛 𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 𝑭𝑷𝒌𝒍 𝝉 ) + (𝒘 𝑽𝒓𝒔 𝝉 𝑷𝒌′𝒍′ 𝝉 𝒛 𝑽𝒓𝒔 𝝉 𝑷𝒌′𝒍′ 𝝉 𝑭 𝑷𝒌′𝒍′ 𝝉 ) − 𝒐𝒑.𝒄𝒐𝒔𝒕 𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 (26) 3) the total waiting time of passenger for a ride on 𝑹𝒐𝒖𝒕𝒆𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 : 𝑾𝑻 𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 = 𝑾𝑻 𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 + 𝑾𝑻 𝑽𝒓𝒔 𝝉 𝑷𝒌′𝒍′ 𝝉 (27) 4) the money value of total passenger’s waiting time: 𝑾𝑻̅̅̅̅̅ 𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 = 𝒘𝒕̿̿̿̿ 𝒎𝒐𝒏𝒆𝒚 × 𝑾𝑻𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 (28) where 𝒘𝒕̿̿̿̿ 𝒎𝒐𝒏𝒆𝒚 is money value of passenger’s waiting time per one time unit 5) the weight of edge (𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 ,𝑽𝒓′𝒔′ 𝝉 𝑷𝒌′𝒍′ 𝝉 ): 𝑾𝒈 𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 = 𝒑𝒓𝒐𝒇𝒊𝒕 𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 𝑾𝑻̅̅̅̅̅ 𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 (29) the weight 𝑾𝒈 𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 is defined as a ratio between the profit gained by a vehicle and the money value of total passenger’s waiting time. the mathematical model for the problem is: 𝑴𝒂𝒙 ∑ 𝑾𝒈̅̅ ̅̅̅ 𝑷𝒌𝒍 𝝉 ,𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 ((𝑽𝒓𝒔 𝝉 ,𝑷𝒌𝒍 𝝉 ),(𝑽𝒓𝒔 𝝉 ,𝑷𝒌′𝒍′ 𝝉 ))∈𝑬𝟐 𝝉 𝒙 𝑷𝒌𝒍 𝝉 ,𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 (30) subject to: ∑ 𝒙 𝑷𝒌𝒍 𝝉 ,𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 𝑽𝒓𝒔 𝝉 ∈𝑽𝝉,𝑷𝒌′𝒍′ 𝝉 ∈𝑷𝝉:((𝑽𝒓𝒔 𝝉 ,𝑷𝒌𝒍 𝝉 ),(𝑽𝒓𝒔 𝝉 ,𝑷𝒌′𝒍′ 𝝉 ))∈𝑬𝟐 𝝉 + ∑ 𝒙 𝑷𝒂𝒃 𝝉 𝑷𝒂′𝒃′ 𝝉 𝑽𝒓𝒔 𝝉 𝑽𝒓𝒔 𝝉 ∈𝑽𝝉,𝑷𝒂𝒃 𝝉 ∈𝑷𝝉:((𝑽𝒓𝒔 𝝉 ,𝑷𝒂𝒃 𝝉 ),(𝑽𝒓𝒔 𝝉 ,𝑷𝒂′𝒃′ 𝝉 ))∈𝑬𝟐 𝝉 ≤ 𝟏, ∀ 𝑷𝒌𝒍 𝝉 ,𝑷 𝒌𝒍′ 𝝉 ,𝑷𝒂𝒃 𝝉 ,𝑷 𝒂′𝒃′ 𝝉 ∈ 𝑷𝝉, 𝐟𝐨𝐫 𝒌 = 𝒂′, 𝒍 = 𝒃′ (31) ∑ 𝒙 𝑷𝒌𝒍 𝝉 ,𝑷𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 ,𝑷𝒌′𝒍′ 𝝉 ∈𝑷𝝉:((𝑽𝒓𝒔 𝝉 ,𝑷𝒌𝒍 𝝉 ),(𝑽𝒓𝒔 𝝉 ,𝑷𝒌′𝒍′ 𝝉 ))∈𝑬𝟐 𝝉 ≤ 𝟏 , ∀ 𝑽𝒓𝒔 𝝉 ∈ 𝑽𝝉 (32) 𝒙 𝑷𝒌𝒍 𝝉 ,𝑷 𝒌′𝒍′ 𝝉 𝑽𝒓𝒔 𝝉 ∈ {𝟎,𝟏}, ∀ 𝑷𝒌𝒍 𝝉 ,𝑷𝒌′𝒍′ 𝝉 ∈ 𝑷𝝉;∀ 𝑽𝒓𝒔 𝝉 ∈ 𝑽𝝉 (33) the objective function (30) maximizes the total weight. constraints (31) ensures each passenger at most in one feasible match, and (32) ensures each vehicle at most in one feasible match. finally, constraints (33) enforce the binary condition. in the next section, we will present the solution algorithm to solve the optimization problem in each period. 4. solution methodology the optimization problem will be solved in three stages. at first, algorithm 1 is performed to obtain a set of feasible pair of a vehicle and the first customer by generating the first weighted 182 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 bipartite graph. algorithm 2 in the second stage is performed to obtain the set of feasible pair of a vehicle and two request customers by generating second modified weighted bipartite graph. finally, algorithm 3 is performed to obtain the optimal assignment of vehicle and passenger pair. procedure to generate first weighted bipartite graph is presented in the following algorithm. algorithm 1. generating first weighted bipartite graph step 1: node construction. initially, there is no node in graph 𝑮𝟏 𝝉 .let 𝒕 be time at which the first request from a customer arrived. set period 𝝉 = 𝝉𝟏, where the first period 𝝉𝟏 = [𝒕,𝒕 + 𝜹 − 𝑶𝒑𝒕_𝑻), 𝜹 be an acceptable time limit for a customer waiting for a decision to be picked up; and 𝑶𝒑𝒕𝑻 be time to do assignment optimization. for the next period, set 𝝉𝒊 = [𝒕 + (𝒊 − 𝟏)𝜹 − 𝑶𝒑𝒕𝑻, 𝒕 + 𝒊 ∗ 𝜹 − 𝑶𝒑𝒕𝑻), for 𝒊 = 𝟐,𝟑,… . in this study we set 𝜹 = 60” and 𝑶𝒑𝒕𝑻 = 𝟏𝟎”. create a set 𝑷 𝝉consisting of all request customers with request time 𝒕𝒓𝒆𝒒𝒖𝒆𝒔𝒕_𝑷𝒌𝒍 𝝉 in period 𝝉𝒊 and all assigned customers in the previous period 𝝉𝒊−𝟏 who still not get a customer pair to share a ride in ride splitting service. create a set 𝑽𝝉consisting of all available vehicle in period 𝝉𝒊 including all vehicle which still only assigned to one request customer in the previous period 𝝉𝒊−𝟏. then set 𝑵𝟏 𝝉 = 𝑽𝝉 ∪ 𝑷𝝉, be the set of nodes of graph 𝑮𝟏 𝝉. step 2: shortest path, distance and travel time determination. for each customer in 𝑷𝝉 and each vehicle in 𝑽𝝉, determine shortest path passenger’s origin-destination to get 𝒓𝒐𝒖𝒕𝒆𝒐𝒅 𝑷𝒌𝒍 𝝉 and from vehicle’s current location to passenger’s origin to get 𝒓𝒐𝒖𝒕𝒆𝒊𝑽𝒓𝒔𝝉 𝒐𝑷𝒌𝒍 𝝉 . then, calculate the distance 𝑫𝒐𝒅 𝑷𝒌𝒍 𝝉 and 𝑫𝒊𝑽𝒓𝒔𝝉 𝑶𝑷𝒌𝒍 𝝉 , travel time 𝑻𝑻𝒐𝒅𝑷𝒌𝒍 𝝉 and 𝑻𝑻𝒊𝑽𝒓𝒔𝝉 𝑶𝑷𝒌𝒍 𝝉 . step 3: departure time windows, arrival time windows, and max ride time calculation. for each customer in 𝑷𝝉, calculate earliest and latest departure time, earliest and latest arrival time and maximum ride time using equation (1)-(5). in this study we set 𝜺,𝝁 = 𝟎.𝟐, 𝝀𝒆𝒂𝒓𝒍𝒚 = 𝟓′, 𝝀𝒍𝒂𝒕𝒆 = 𝟏𝟓′ and 𝒕𝒔𝒆𝒓𝒗𝒊𝒄𝒆_ 𝑷𝒌𝒍 𝝉 𝑽𝒓𝒔 𝝉 = 𝟏′. step 4: feasible match determination and edge construction. for each vehicle in 𝑽𝝉 and for each customer in 𝑷𝝉, determine whether a vehicle is feasible to serve a customer by using feasible criterion (6)-(8). then node 𝑽𝒓𝒔 𝝉 in 𝑽𝝉 is adjacent to node 𝑷𝒌𝒍 𝝉 in 𝑷𝝉, or (𝑽𝒓𝒔 𝝉 ,𝑷𝒌𝒍 𝝉 ) is an edge in 𝑬𝟏 𝝉 if and only if vehicle 𝑽𝒓𝒔 𝝉 is met the feasible criterion in (6) – (8) to serve customer 𝑷𝒌𝒍 𝝉 . then 𝑬𝟏 𝝉 = {(𝑽𝒓𝒔 𝝉 ,𝑷𝒌𝒍 𝝉 )|𝑷𝒌𝒍 𝝉 𝐚𝐧𝐝 𝑽𝒓𝒔 𝝉 𝐚𝐫𝐞 𝐟𝐞𝐚𝐬𝐢𝐛𝐥𝐞 match; 𝑽𝒓𝒔 𝝉 ∈ 𝑽𝝉, 𝑷𝒌𝒍 𝝉 ∈ 𝑷𝝉}. step 5: weight calculation. for each edge in 𝑬𝟏 𝝉 calculate its weight, where the weight is the fare that has to be paid by passenger 𝑷𝒌𝒍 𝝉 if served by vehicle 𝑽𝒓𝒔 𝝉 , using equation (9). step 6: output. from step 1 to step 5, set graph 𝑮𝟏 𝝉 = (𝑵𝟏 𝝉,𝑬𝟏 𝝉). the next stage is to perfomed algorithm 2 with the following procedure. algorithm 2. generating the second weighted bipartite graph step 1: node construction. initially, there is no node in graph 𝑮𝟐 𝝉. let 𝑵𝟏 𝝉 and 𝑬𝟏 𝝉 be the set of nodes and the set of edges of 𝑮𝟏 𝝉 from algorithm 1 for 𝑽𝒓𝒔 𝝉 ∈ 𝑽𝝉 and 𝑷𝒌𝒍 𝝉 ∈ 𝑷𝝉, create a set 𝑽𝝉𝑷𝝉 consisting all pairs of 𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 , where (𝑽𝒓𝒔 𝝉 ,𝑷𝒌𝒍 𝝉 ) is an edge in 𝑬𝟏 𝝉. create a set 𝑫𝑽𝝉𝑷𝝉, a duplication set of 𝑽𝝉𝑷𝝉. that is 𝑫𝑽𝝉𝑷𝝉 = {𝑽𝒓′𝒔′ 𝝉 𝑷𝒌′𝒍′ 𝝉 |𝐢𝐟 𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 ∈ 𝑽𝝉𝑷𝝉}. then set 𝑵𝟐 𝝉 = 𝑽𝝉𝑷𝝉 ∪ 𝑫𝑽𝝉𝑷𝝉 be a bipartite set of nodes of graph 𝑮𝟐 𝝉. 183 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 step 2: vehicle route, distance and travel time determination. for each pair of nodes 𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 in 𝑽𝝉𝑷𝝉 and 𝑽𝒓′𝒔′ 𝝉 𝑷𝒌′𝒍′ 𝝉 in 𝑫𝑽𝝉𝑷𝝉, with 𝒓 = 𝒓′ 𝐚𝐧𝐝 𝒔 = 𝒔′, determine shortest path from vehicle’s current location to the first passenger’s origin, then to the second passenger’s origin and next to the closest passenger’s destination to get 𝑹𝒐𝒖𝒕𝒆𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 . then, 𝑹𝒐𝒖𝒕𝒆𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 is the shortest path between route 𝒊𝑽𝒓𝒔𝝉 − 𝒐𝑷𝒌𝒍 𝝉 − 𝒐𝑷 𝒌′𝒍′ 𝝉 − 𝒅𝑷𝒌𝒍 𝝉 − 𝒅𝑷𝒌′𝒍′ 𝝉 and route 𝒊𝑽𝒓𝒔𝝉 − 𝒐𝑷𝒌𝒍 𝝉 − 𝒐𝑷 𝒌′𝒍′ 𝝉 − 𝒅𝑷 𝒌′𝒍′ 𝝉 − 𝒅𝑷𝒌𝒍 𝝉 . next, calculate the distance: 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 and travel time: 𝑻𝑻𝑽𝒓𝒔𝝉 _𝑷𝒌𝒍 𝝉 _𝑷𝒌′𝒍′ 𝝉 . step 3: feasible match determination and edge construction. for nodes 𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 in 𝑉𝜏𝑃𝜏 and 𝑉𝑟′𝑠′ 𝜏 𝑃𝑘′𝑙′ 𝜏 in 𝐷𝑉𝜏𝑃𝜏, with 𝑟 = 𝑟′ and 𝑠 = 𝑠′, check if the vehicle 𝑉𝑟𝑠 𝜏 is feasible to serve customers 𝑃𝑘𝑙 𝜏 and 𝑃𝑘′𝑙′ 𝜏 by using feasible criterion in (10)-(24), then node 𝑉𝑟𝑠 𝜏𝑃𝑘𝑙 𝜏 is adjacent to node 𝑽𝒓′𝒔′ 𝝉 𝑷𝒌′𝒍′ 𝝉 , or (𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 ,𝑽𝒓′𝒔′ 𝝉 𝑷𝒌′𝒍′ 𝝉 ) is an edge in 𝑬𝟐 𝝉. step 4: weight calculation. for each edge in 𝑬𝟐 𝝉, calculate vehicle’s operational cost and profit gained, passenger’s total waiting time and its money value, and the edge weight using formula (25)-(29). step 5: output. from step 1-step 4, set graph 𝑮𝟐 𝝉 = (𝑵𝟐 𝝉,𝑬𝟐 𝝉). finally, performed the greedy heuristic algorithm based on [20] to solve the mathematical model (30)-(33) for the optimization problem. algorithm 3. the greedy heuristic algorithm step 1: select the edge in graph 𝑮𝟐 𝝉 with the largest weight and add it to the matching. let the edge with the largest weight in 𝑬𝟐 𝝉 is (𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 ,𝑽𝒓′𝒔′ 𝝉 𝑷𝒌′𝒍′ 𝝉 ), then set the vehicle 𝑽𝒓𝒔 𝝉 serves customers 𝑷𝒌𝒍 𝝉 and 𝑷𝒌′𝒍′ 𝝉 . update the vehicle 𝑽𝒓𝒔 𝝉 ’ s occupation: 𝑽𝒓𝒔 𝝉 _𝒐𝒄𝒄 and capacity: 𝑸𝑽𝒓𝒔𝝉 . step 2: delete the endpoints of the edge selected in step 1, all nodes related to vehicles 𝑽𝒓𝒔 𝝉 and 𝑽𝒓′𝒔′ 𝝉 , customers 𝑷𝒌𝒍 𝝉 and 𝑷𝒌′𝒍′ 𝝉 , and all edges incident to these nodes. if the graph contains at least two nodes, return to step 1; otherwise stop. 5. computational experiments to test the model and its solution methodology, in this paper we use two periods of time, which consists of six request customers and six available vehicles and three values for parameter 𝜶 (profit sharing multiplier factor) as comparation, those are 85%,90% and 95%. the consideration to use three 𝜶 values is based on the willingness of the driver (and the operator) to share profit with the initial operator requested by the customer and to keep being profitable for the serving driver (operator). all experiments in this study is coded with python 3.7. in the meantime, the number of operators (platforms) providing online taxi services used is two platforms, while the tariff for the ride-splitting service charged to each passenger from each platform is using three cases as a comparison. those cases are the equal tariff, 5% and 10% difference in tariff. table 1 describes the fare charged by platform 1 and 2 for all cases. in the first case, the fare charged by platform 1 and 2 is 2$/ distance unit. at the second case, the difference in tariff between platform 1 and 2 is 5%, whereas the fare charged by platform 1 to the customer in ride-splitting service is 2$ /distance unit, while in platform 2, it is 2.1$ /distance unit. while in the last case, the difference in tariff between platform 1 and 2 is 10%, whereas the fare charged by platform 1 to the customer in ride-splitting service is 2$ /distance unit while in platform 2, it is 2.2$ /distance unit. with the three fare difference cases, it will be seen that the resource sharing scheme used with a certain limit value of profit share, can still be profitable for the driver (and operator) even though there is a difference for the 184 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 cheaper fare paid by the customer. next, the optimization of the ride-splitting service with the resource sharing scheme compared to the optimization without using the scheme, by taking the value of 𝒘 𝑽𝒓𝒔 𝝉 𝑷𝒌𝒍 𝝉 = 𝟏 table 1. fare charged by platform 1 and 2 case fare of platform 1 per distance unit fare of platform 2 per distance unit for equal tariff 2$ 2$ for 5% difference 2$ 2.1$ for 10% difference 2$ 2.2$ gradually, there come four request customers in the first period and two request customers in the second period, where there are four available vehicles in the first period and two new available vehicles in the second period. let figure 1 ilustrates example of a road transportation network where the passenger’s origin and vehicle location are located in the first period. assume that one distance unit can be traveled in one time unit. the weight of each link describes the distance between two different nodes, for example the distance between node 1 and 4 is 16 distance unit. fig.1 ilustration of road transportation network in the first period let the first period start at 700 and end at 701, and the list of customer requests given in the table 2. from table 2, in the first period, there are four customers: 𝑃11,𝑃21,𝑃12 and 𝑃22 which request ride splitting services. let 𝑃11 be the first customer which request a service (vehicle) from platform 1, 𝑃21 be the first customer which request a service from platform 2. the origin (pick up) location of 𝑃11 is at node 2, meanwhile the origin of 𝑃21 is at node 14. the destination (drop off) location of 𝑃11 is at node 8 and 𝑃21 is at node 6. the number of passengers per request of customer 𝑃11 is 1 passenger, which has to be picked up between 7 01 716, meanwhile a request of customer 𝑃21 consists of 2 passengers, which has to be picked up between 7 01 716. table 2. list of customer requests in the first period 185 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 customer 𝒕𝒓𝒆𝒒𝒖𝒆𝒔𝒕_𝑷𝒌𝒍 𝒐𝑷𝒌𝒍 𝒅𝑷𝒌𝒍 𝒆𝒅𝒆𝒑𝒕_𝑷𝒌𝒍 𝒍𝒅𝒆𝒑𝒕_𝑷𝒌𝒍 𝒒𝑷𝒌𝒍 𝑷𝟏𝟏 7 00 2 8 701 716 1 𝑷𝟏𝟐 7 00 5 15 701 716 2 𝑷𝟐𝟏 7 00 14 6 701 716 2 𝑷𝟐𝟐 7 00 13 7 701 716 1 there are four available vehicles in the first period, which are vehicle 𝑉11 and 𝑉12 from platform 1, and vehicle 𝑉21 and 𝑉22 from platform 2. data of available vehicle’s locations and capacities between 700-701 is given by table 3. table 3. data of available vehicles in the first period vehicle 𝒊𝑽𝒓𝒔 𝒕𝒊𝑽𝒓𝒔 𝑽𝒓𝒔 𝑸𝑽𝒓𝒔 𝑽𝟏𝟏 4 7 00 4 𝑽𝟐𝟏 1 7 00 4 𝑽𝟏𝟐 15 7 00 4 𝑽𝟐𝟐 12 7 00 4 let 𝑐𝑉𝑟𝑠𝜏 , the vehicle cost per distance unit, is 1$ and 𝑤𝑡 ̿̿̿̿ 𝑚𝑜𝑛𝑒𝑦, the money value of passenger’s waiting time, is 1$ per minute. using the solution method in section 4 with three fare difference cases, the optimum assignment result in the first period is described on table 4 and the profit gained by driver is described in figure 2. table 4. the optimum assignment result in period 1 ride splitting with resource sharing scheme, for 𝜶 = 𝟖𝟓%, 90% and 95% ride splitting without resource sharing scheme assignment result in period 1 𝑉21 is serving 𝑃11and 𝑃21 𝑉22 is serving 𝑃22 𝑉11 is serving 𝑃12 𝑉12 is not yet serving any customer 𝑉22 is serving 𝑃21 and 𝑃22 𝑉12 is serving 𝑃11 𝑉11 is serving 𝑃12 . 𝑉21 is not yet serving any customer total vehicle used 3 3 total passenger’s waiting time 17 minutes 31 minutes it can be seen from table 4, total passenger’s waiting time to be picked up by a vehicle for the ride splitting service with sharing platform scheme in the first period is 17 minutes, while in the ride splitting service without sharing platform scheme is 31 time unit. 186 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 fig.2 profit gained comparison in the first period based on figure 2, the profit gained by ride splitting service without sharing platform scheme (a) for equal tariff case is 116$, while ride splitting service with sharing platform scheme for 𝛼 =85% (b), 𝛼 =90% (c) and 𝛼 =95% (d) are 113,7$, 116,8$ and 119,9$ respectively. it can be seen that profit gained by ride splitting service with sharing platform scheme using 𝛼 =90% (c) and 95% (d) for all fare difference cases are higher than ride splitting service without sharing platform scheme (a). while, ride splitting service with sharing platform scheme using 𝛼 =85% (b) for all fare difference cases is gaining profit lower than ride splitting service without sharing platform scheme (a). based on the simulation, the parameter value for profit sharing platform scheme will result in higher profit than without sharing platform scheme when the value is greater than or equal to 0.9 ( 𝛼 =90%). in the second period, there are two new customer requests, summarized in the following table 5. table 5. list of customer requests in second period customer 𝒕𝒓𝒆𝒒𝒖𝒆𝒔𝒕_𝑷𝒌𝒍 𝒐𝑷𝒌𝒍 𝒅𝑷𝒌𝒍 𝒆𝒅𝒆𝒑𝒕_𝑷𝒌𝒍 𝒍𝒅𝒆𝒑𝒕_𝑷𝒌𝒍 𝒒𝑷𝒌𝒍 𝑷𝟏𝟑 7 01 16 7 702 717 1 𝑷𝟐𝟑 7 01 11 15 702 717 2 meanwhile, available vehicles in the second period is summarized in table 6, where there are three vehicles originating from the first period and two new vehicles from the second period. based on the assignment result in the first period, vehicle 𝑉11 is serving passenger 𝑃12, so that available seat left is only 2, while vehicle 𝑉22 is serving passenger 𝑃22, so that vehicle capacity left is only 3 seats. table 6. data of available vehicles in the second period vehicle 𝒊𝑽𝒓𝒔 𝒕𝒊𝑽𝒓𝒔 𝑽𝒓𝒔 𝑸𝑽𝒓𝒔 𝑽𝟏𝟏 4 7 00 2 𝑽𝟏𝟐 15 7 00 4 𝑽𝟐𝟐 12 7 00 3 𝑽𝟏𝟑 3 7 01 4 𝑽𝟐𝟑 10 7 01 4 using the solution method in section 4, the optimum assignment results in the first and second period is described on table 7 and profit gained comparison for three fare difference cases is described in figure 3. 187 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 table 7.the optimum assignment results in two periods ride splitting with resource sharing scheme, for 𝜶 = 𝟖𝟓%, 90% or 95% ride splitting without resource sharing scheme assignment result in period 1 and 2 𝑉21 is serving 𝑃11 and 𝑃21 𝑉22 is serving 𝑃22 𝑉11 is serving 𝑃12 and 𝑃23 𝑉23 is serving 𝑃13 𝑉12 and 𝑉13 are not yet serving any customer 𝑉22 is serving 𝑃21 and 𝑃22 𝑉12 is serving 𝑃11 𝑉11 is serving 𝑃12 . 𝑉13 is serving 𝑃13 𝑉23 is serving 𝑃23 𝑉21 is not yet serving any customer total vehicle used 4 (or 66,7% of vehicle availability) 5 (or 83,3% of vehicle availability) total passenger’s waiting time 33 minutes 50 minutes from table 7, it can be seen that total passenger’s waiting time for ride splitting service with sharing platform scheme case is only 33 minutes, lower than without sharing platform scheme case, which is 50 minutes, and so is the total vehicle used, the ride splitting service with the scheme only use 66,7% of available vehicles, while the ride splitting service without the scheme use 83,3% of available vehicles. fig.3 total profit gained comparison for total two periods based on figure 3, total profit gained by ride splitting service without sharing platform scheme (a) for equal tariff case is 144$, while ride splitting service with sharing platform scheme for 𝛼 =85% (b), 𝛼 =90% (c) and 𝛼 =95% (d) are 158,9$, 166,6$ and 174,3$ respectively. it can be seen that profit gained by ride splitting service with sharing platform scheme using 𝛼 =85% (b), 90%(c) and 95% (d) for all fare difference cases are higher than ride splitting service without sharing platform scheme (a). 6. conclusions based on the experiment, it can be concluded that the optimization of ride-splitting service with resource-sharing scheme can reduce the vehicle used for online taxi services. moreover, it can generate higher overall profit for all vehicles serving passenger, and the parameter value a b c d equal tariff 144 158.9 166.60 174.30 5% tariff difference 152.3 166.915 174.71 182.51 10% tariff difference 160.6 174.93 182.82 190.71 0 50 100 150 200 250 p r o f it p e r i o d 1 2 a b c d equal tariff 144 158.9 166.60 174.30 5% tariff difference 152.3 166.915 174.71 182.51 10% tariff difference 160.6 174.93 182.82 190.71 0 50 100 150 200 250 p r o f it p e r i o d 1 2 188 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 for profit sharing platform scheme is better greater than or equal to 0,9 (𝛼 = 90%). meanwhile, total passenger’s waiting time to be picked up by a vehicle for ride splitting service with sharing platform scheme case is lower than without sharing platform scheme case. this study is still using small instance as an experiment to prove that the optimization of ride-splitting service with resource-sharing scheme is possible to be utilized, so that for the next research, bigger data usage is required acknowledgement the authors would like to thank to kemenristek dikti and lpdp for scholarship in order the completion of doctoral studies at universitas indonesia. references [1] burhan, h., soehodho, s., and nahry. (2017). review on the development of ride sharing system using online transportation service in jakarta. proceeding of 6th ieee international conference on advanced logistics and transport, pp.173-178. [2] anderson, d. n.,(2014). “not just a taxi’? for-profit ridesharing, driver strategies, and vmt. transportation 41, pp.1099–1117. http://dx.doi.org/10.1007/ s11116-014-9531-8. [3] rayle, l., dai, d., chan, n., cervero,r., and shaheen, s. (2015). just a better taxi? a surveybased comparison of taxis, transit, and ridesourcing services in san francisco. transp. policy, pp.168–178. [4] shaheen, s., cohen, a., and zohdy, i. (2016). shared mobility: current practices and guiding principles. u.s. department of transportation, federal highway administration. report no. fhwa-hop-16-022. [5] chen, l., mislove, a., and wilson, c. (2015). peeking beneath the hood of uber. in proc. of the acm conference on internet measurement conference, acm. [6] burhan, h., soehodho, s., and nahry. (2019). a resource sharing (sharing platform) scheme on online taxi services. matec web of conferences,vol. 270, art.no.03010. [7] agatz, n.a.h., erera, a.l., savelsbergh, m.w.p., and wang, x. (2012). optimization for dynamic ride-sharing: a review. european journal of operational research, vol.223 (2), pp.295–303. [8] lu, q., and dessouky, m. (2006). a new insertion-based construction heuristic for solving the pickup and delivery problem with hard time windows. european journal of operational research, vol.175 (2), pp.672–687. [9] dumas, y., desrosiers, j., and soumis, f. (1991). the pickup and delivery problem with time windows. european journal of operations research, vol.54, pp.7–22. [10] toth,p. and vigo, d. (2002). the vehicle routing problem. siam, philadelphia http://dx.doi.org/10.1137/1.9780898718515. [11] hosni, h., naoum-sawaya, j., and artail, h. (2014). the shared-taxi problem: formulation and solution methods. transp. res. part b: methodol. 70, pp. 303–318. [12] wang, x., dessouky, m., and ordonez, f. (2015). a pickup and delivery problem for ridesharing considering congestion. transp. lett.: int. j. transp. res.,1942787515y 000000002. [13] santos, d.o., and xavier, e.c. (2015). taxi and ride sharing: a dynamic dial-a-ride problem with money as an incentive. expert systems with applications, vol. 42, pp.6728–6737. [14] mahmoudi, m., and zhou, x. (2017). finding optimal solutions for vehicle routing problem with pickup and delivery services with time windows: a dynamic programming approach based on state-space-time network representations. transport. res. part b: methodol. vol.89, pp.19– 42. [15] bei, x., and zhang, s. (2018). algorithms for trip-vehicle assignment in ride-sharing. in: proceedings of the 32nd aaai conference on artificial intelligence, pp. 3–9. 189 iium engineering journal, vol. 22, no. 1, 2021 hamim et al. https://doi.org/10.31436/iiumej.v22i1.1520 [16] banerjee, s., johari, r., and riquelme, c. (2015). pricing in ride-share platforms: a queueingtheoretic approach. working paper. available at ssrn: https://ssrn.com/abstract=2568258 or http://dx.doi.org/10.2139/ssrn.2568258. [17] chen, y., and hu, m. (2017). pricing and matching with forward-looking buyers and sellers. working paper. available at ssrn: https://ssrn.com/abstract=2859864 or http://dx.doi.org/10.2139/ssrn.2859864. [18] zha, l., yin, y., and xu, z. (2018). geometric matching and spatial pricing in ride-sourcing markets. transportation research part c: emerging technologies, vol.92, pp.58-75. [19] yang, h., shao, c., wang, h., and ye, j. (2018). integrated reward scheme and surge pricing in a ride sourcing market. report, june 18, 2018. available at ssrn: https://ssrn.com/abstract=3198081 or http://dx.doi.org/10.2139/ssrn.3198081. [20] evans, j.r., and minieka, e. (1992). optimization algorithms for networks and graphs, 2nd edition revised. new york. 190 https://ssrn.com/abstract=3198081 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 sophian et al. https://doi.org/10.31436/iiumej.v22i2.1692 machine-learning-based evaluation of corrosion under insulation in ferromagnetic structures ali sophian1*, faris nafiah2,3, teddy surya gunawan4, nur amalina mohd yusof1 and ali al-kelabi1 1 smart structures, systems and control lab, department of mechatronics engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur malaysia 2 school of engineering, london south bank university, london, united kingdom 3 nsirc, twi ltd., cambridge, united kingdom 4 department of electrical and computer engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur malaysia * corresponding author: ali_sophian@iium.edu.my (received: 10th november 2020; accepted: 4th april 2021; published on-line: 4th july 2021) abstract: corrosion under insulation (cui) is one of the challenging problems in pipelines used in the gas and oil industry as it is hidden and difficult to detect but can cause catastrophic accidents. pulsed eddy current (pec) techniques have been identified to be an effective non-destructive testing (ndt) method for both detecting and quantifying cui. the pec signal’s decay properties are generally used in the detection and quantification of cui. unfortunately, the well-known inhomogeneity of the pipe material’s properties and the presence of both cladding and insulation lead to signal variation that reduces the effectiveness of the measurement. current pec techniques typically use signal averaging in order to improve the signal-to-noise ratio (snr), with the drawback of significantly-increasing inspection time. in this study, the use of gaussian process regression (gpr) for predicting the thickness of mild carbon steel plates has been proposed and investigated with no signal averaging used. with mean absolute errors (mae) of 0.21 mm, results show that the use of gpr provides more accurate predictions compared to the use of the decay coefficient, whose averaged mae is 0.36 mm. this result suggests that the gpr-based method can potentially be used in pec ndt applications that require fast scanning. abstrak: hakisan di bawah penebat cui adalah salah satu masalah yang mencabar dalam saluran paip yang digunakan dalam industri gas dan minyak kerana tersembunyi dan sukar dikesan tetapi boleh menyebabkan bencana. teknik pulsed eddy current (pec) telah dikenal pasti sebagai kaedah ujian bukan pemusnah yang berkesan (ndt) untuk mengesan dan mengukur cui. sifat kerosakan isyarat pec umumnya digunakan dalam pengesanan dan pengukuran cui. malangnya, sifat tidak tepat yang terkenal dari sifat bahan paip dan kehadiran pelapisan dan penebat menyebabkan variasi isyarat yang mengurangkan keberkesanan pengukuran. teknik pec semasa biasanya menggunakan rata-rata isyarat untuk meningkatkan nisbah isyarat-ke-kebisingan (snr), dengan kelemahan peningkatan masa pemeriksaan dengan ketara. dalam kajian ini, penggunaan regresi proses gauss (gpr) untuk meramalkan ketebalan plat keluli karbon ringan telah diusulkan dan diselidiki dan tidak ada rata-rata isyarat yang digunakan. dengan ralat mutlak (mae) 0,21 mm, hasil menunjukkan bahawa penggunaan gpr memberikan ramalan yang lebih tepat dibandingkan dengan penggunaan pekali peluruhan, yang rata226 iium engineering journal, vol. 22, no. 2, 2021 sophian et al. https://doi.org/10.31436/iiumej.v22i2.1692 rata mae adalah 0,36 mm. hasil ini menunjukkan bahawa kaedah berasaskan gpr berpotensi digunakan dalam aplikasi pec ndt yang memerlukan pengimbasan pantas. keywords: corrosion under insulation; pulsed eddy current; non-destructive testing; machine learning; fast scanning 1. introduction industrial oil and gas infrastructures, including the transmission pipelines that are used in transportation and distribution, require regular inspection as stipulated by governmental safety regulations all around the world to prevent catastrophic accidents. many of these structures are made of carbon steel materials and covered by insulation for their protection or maintaining the high temperature of the oil or gas flowing inside them. a thin cladding is usually placed outside the insulation to hold the insulation in place and to stop water from seeping into the insulation that may cause or accelerate the growth of corrosion on the outer surface of the pipe. such structures, whose illustration can be seen in fig. 1, will benefit from non-destructive inspection techniques that are able to penetrate through the insulation and cladding, and therefore, detect any presence of the corrosion under insulation (cui). cui is considered a crucial problem with these pipes [1,2]. the ability to detect and assess cui in the pipes without the removal of the insulation is very beneficial [3]. removal of the insulation takes time, which, in turn, would lengthen the downtime of the plant and would require new costly replacements of the insulation or coating. fig. 1: typical setting of insulated pipes with a probe sitting on its cladding. pulsed eddy current (pec) non-destructive testing (ndt) has been identified as one of the solutions with the most potential for non-contact evaluation of corrosion in carbon steel structures [4], which are either coated or otherwise. the low frequency components of the excitation field allow deep penetration into the ferromagnetic structure. for such structures, magnetic saturation has been proposed, although many have proposed the use of pec without magnetically saturating the sample. there have been several different pec signal features proposed by researchers [3]. the signal features also depend on the type of the sensing device, whether it is an inductive coil or a magnetic field sensor. mostly, the features are related to the decay properties of the signals, especially the gradient of the later stage of the decay, thanks to its high correlation to the thickness of the tested structure and its insensitivity to the variation in the distance between the probe and the sample, which is known as the standoff or lift-off. there have been promising results reported, although most of these have been applied on signals obtained by using inductive coils. a technique based on the signal’s inverse time derivative |∇|−1 is shown to allow in-situ calibration and improved estimation compared to the τ0 feature, which is the time at which the induced current’s 227 iium engineering journal, vol. 22, no. 2, 2021 sophian et al. https://doi.org/10.31436/iiumej.v22i2.1692 diffusion phase ceases [1]. an accuracy of 0.67 mm has been achieved with averaging of 16 signals. time to peak as a feature was proposed and its performance was shown to be good on simulation data, while no experimental data were reported [4]. other time domain features have also been discussed in other reports, such as [5-7]. the use of a magnetic sensor, instead of an inductive coil, offers benefit in terms of the spatial resolution. however, relatively less studies have been reported where a magnetic sensor was used. cheng et al. used anisotropic magnet resistance (amr) sensors and the feature used was the decay coefficient, which is the reciprocal of the decay rate of the magnetic field density in the logarithmic scale [8]. pec signals are known to be noisy. some noise reduction techniques have been presented [9,10], and the testing gets even more challenging due to inhomogeneity in ferromagnetic materials [11]. the use of signal averaging is effective to some extent, however it increases the measurement time significantly, depending on the number of signals used. this will prevent fast scanning applications using the pec. in this paper, machine learning is used to predict the thickness of the insulated ferromagnetic sample without applying signal averaging. machine learning, including its latest development known as deep learning, has embraced countless applications in various sectors of industry. non-destructive testing (ndt) is not an exception to this current trend, and eddy ndt current techniques have also seen the applications of machine learning, such as the works reported in [12,13]. in this study, the use of machine learning in processing pec signals obtained without signal averaging is presented. 2. modelling of pec and cui an axisymmetric 2d model, as shown in fig. 2, was built using comsol multiphysics which consists of a few layers, namely the carbon steel sample, the insulation, and the cladding. the inner and outer radii of the excitation coil were 100 mm and 110 mm respectively, while the height of coil was 6 mm. in this work, the model is used to verify the trends in the magnetic field density that will be sensed by the sensor when the lift-off and sample thickness are varied. it is not intended to find the actual magnitudes of the field. fig. 2: 2d-axisymmetric finite element model of the pec system on an insulated sample with a cladding. the model was developed on comsol software. the conductivity and relative permeability of the sample were set to 5 x 106 s/m and 100, respectively. the thickness was varied from 9 mm to 12 mm with an increment of 1 coil cladding air/insulation carbon steel sample axis of symmetry 228 iium engineering journal, vol. 22, no. 2, 2021 sophian et al. https://doi.org/10.31436/iiumej.v22i2.1692 mm. for the cladding, its thickness was 0.5 mm and two different sets of permeability and conductivity values were used to simulate stainless steel and aluminium materials. the model was run for both different sample thicknesses and different insulation thicknesses. the results were plotted in the graphs shown in fig. 3 and they verify that the slope of the signals is affected by the sample thickness but not by the lift-off, as has been reported by other researchers. (a) (b) fig. 3: typical signals obtained by using the developed pec models, (a) for different thicknesses and (b) for different lift-offs. 3. methodology in this study, the thickness approximation techniques using the gradient coefficient and machine-learning-based regression techniques will be compared on pec signals that have been obtained without any signal averaging. 3.1 experimental setup a pec system was built, consisting of a probe, a data acquisition, and a laptop running labview. the probe consisted of an excitation coil and a hall-effect device. a ferrite core was used for concentrating the magnetic flux and strengthening the hall device’s output signal. through the labview code, the signal sampling was set at 100 ks/s and the pulse width was 25 ms. the labview code saved the acquired data to be 229 iium engineering journal, vol. 22, no. 2, 2021 sophian et al. https://doi.org/10.31436/iiumej.v22i2.1692 analysed. the inner and outer diameters of the coil were 100 mm and 110 mm, respectively. its height was 6 mm and it had 200 turns. a mosfet was used to switch the high excitation currents on and off with a pulse width of 25 ms driven to the excitation coil. fig. 4 shows the block diagram of the pec setup used in this work. fig. 4: the block diagram of our pec system. corrosion or wall loss was simulated by thicknesses that were less than the thickness of the sound structure. square plate samples with surface dimensions of 300 mm × 300 mm were used and they had different thicknesses, which were 9.12, 10.02, 11.06, and 12.08 mm. the stand-off was also varied at 3, 5, 8, 10, and 13 mm. fifty signals were obtained for each combination of thickness and stand-off. two different materials were used for the cladding, which were aluminium and stainless steel. the thickness of the cladding was 0.5 mm. 3.2 signal processing (data pre-processing) the falling edge of the hall effect signal and its decay properties were used to predict the thickness. in order to improve the signal-to-noise ratio (snr), a median filter was applied to reduce the high-frequency noise. the logarithmic values of the signal were used to find the decay coefficient. normalization to unity was employed to reduce the effects of the variation in the magnitude of the magnetic field that was induced by the excitation coil, which may be caused by the sample’s inhomogeneity and the change in the excitation coil’s temperature, among others. fig. 5 shows typical signals that have been averaged in order to increase the clarity of the shape of the signals. for the purpose of determination of the decay coefficient, part of the signal that has been used is 10 ms ≤ t ≤ 35 ms. fig. 5: typical averaged signals for different sample thicknesses. 230 iium engineering journal, vol. 22, no. 2, 2021 sophian et al. https://doi.org/10.31436/iiumej.v22i2.1692 3.3 machine-learning-based regression based on preliminary observation, the gaussian process regression (gpr) model consistently provided the best result among other regressions. gpr is a non-parametric and non-linear kernel-based model, and it uses a bayesian approach to model the uncertainty of the prediction. it has been widely used in various applications, thanks to its simplicity and its good performance when small datasets are available, among others. the kernel function that models the similarity between similar predictors was chosen to be the exponential kernel, which is defined by [14], (1) where σ l is the characteristic length scale and r is the euclidean distance between predictors xi and xj, and θ is the vector containing the parameters for the kernel. the decay of the magnetic field that is sensed by the hall device is set as the predictor variables for the regression model. 3.4 model validation and testing validation was performed on machine leaning models in order to test their performance after training, including the generalization of the model. due to the limited quantity of data and to avoid overfitting the model, a cross validation technique known as k-fold was employed in this work. in this technique, the data were split into k groups and the model was trained and validated k times. in every iteration, one different group was excluded from the training and used only in the validation, therefore each and every group of data was used for validation. in this work, 5-fold was used meaning that the data was split into commonly used 5 groups. seventy percent of the overall data that were chosen randomly were used for this training and validation exercise. the remaining 30% of the dataset were used to test and compare the model against the performance of the approach that uses the 1/gradient feature. the performances of both methods, namely decay coefficient and gpr, were evaluated and compared using the following metrics: root mean squared error (rmse), rsquared, mean squared error (mse), and mean absolute error (mae). all these metrics are already well known and widely used for evaluating performances of both measurement systems and machine learning models. 4. results and discussion fig. 6 exhibits the plots of the predicted thickness generated using both methods with the experimental data obtained from all different lift-offs, sample thicknesses, and cladding materials. the error bars in the plots represent the standard deviation. the performance metrics are shown in table 1. table 1: performance metrics of both methods method cladding rmse (mm) r-squared mse (mm) mae (mm) decay coefficient stainless steel 0.4611 0.825 0.213 0.373 aluminium 0.420 0.856 0.177 0.346 gpr exponential stainless steel 0.298 0.928 0.089 0.215 aluminium 0.266 0.942 0.071 0.198 231 iium engineering journal, vol. 22, no. 2, 2021 sophian et al. https://doi.org/10.31436/iiumej.v22i2.1692 (a) (b) fig. 6: the averaged predicted thickness with error-bars representing the standard deviation of the measurement error, (a) aluminum cladding, (b) stainless steel cladding. both the plots and the table demonstrate that the gpr exponential model outperformed the approach using the decay coefficient in terms of both the nominal error and the spread of errors. the averaged rmse, r-squared, mse and mae of the gpr model are better by 36.0%, 11.2%, 59.0% and 42.6% respectively than those of predicted thicknesses using the decay coefficient. 5. conclusion in recent years, machine learning a subset of artificial intelligence has developed very rapidly and seen applications in various sectors, with deep learning being the latest development. insulated industrial pipes develop corrosion or wall thinning that is hidden and challenging to be detected. this work proposed the use of machine learning for processing pec signals, especially when the snr was relatively high (as no signal averaging was used in order to improve the scanning speed), and therefore reducing the inspection time. the experimental data analysis shows that the gpr exponential model generated better results with both lower nominal errors and lower error variances, represented in the improvements in the rmse, r-squared, mse and mae, by 36.0%, 11.2%, 59.0%, and 42.6%, respectively. this suggests that the machine learning method can potentially be used in the applications where fast scanning is required. references [1] nafiah f, tokhi mo, majidnia s, rudlin j, zhao z, duan f. (2020) pulsed eddy current: feature extraction enabling in-situ calibration and improved estimation for ferromagnetic application. j. nondestruct. eval., 39(52). doi: https://doi.org/10.1007/s10921-020-00699w. [2] nicola s, carreto v, mentzer ra, mannan ms. (2013) corrosion under insulation detection technique. in proceedings of corrosion 2013: 17-21 march 2013; orlando, florida [3] sophian a, tian g, fan m. (2017) pulsed eddy current non-destructive testing and evaluation: a review. chinese j. mech. eng. (english ed.), 30:500-514 [4] xu z, wu x, li j, kang y. (2012) assessment of wall thinning in insulated ferromagnetic pipes using the time-to-peak of differential pulsed eddy-current testing signals. ndt e int., 51:24-29. doi: https://dx.doi.org/10.1016/j.ndteint.2012.07.004. [5] ulapane n, nguyen l. (2019) review of pulsed-eddy-current signal feature-extraction methods for conductive ferromagnetic material-thickness quantification. electron., 8(5):470. doi: https://doi.org/10.3390/electronics8050470. 232 iium engineering journal, vol. 22, no. 2, 2021 sophian et al. https://doi.org/10.31436/iiumej.v22i2.1692 [6] ulapane n, alempijevic a, calleja tv, miro jv. (2017) pulsed eddy current sensing for critical pipe condition assessment. sensors, 17(10):2208. doi: https://doi.org/10.3390/s17102208. [7] buck ja, kramer c, lei j, lepine ba. (2016) field implementation of a transient eddy current system for carbon steel pipe thickness measurements. in proceedings of 6th international candu in-service inspection workshop: 15–17 november 2016; ontario [8] cheng w. (2012) pulsed eddy current testing of carbon steel pipes’ wall-thinning through insulation and cladding. j. nondestruct. eval., 31(3): 215-224. doi: https://doi.org/10.1007/s10921-012-0137-9. [9] huang c, xinjun w, zhiyuan x, kang y. (2010) pulsed eddy current signal processing method for signal denoising in ferromagnetic plate testing. ndt e int., 43(7): 648-653. doi: https://doi.org/10.1016/j.ndteint.2010.06.010. [10] huang c, wu x. (2015) an improved ferromagnetic material pulsed eddy current testing signal processing method based on numerical cumulative integration. ndt e int., 69: 35-39. [11] sophian a, tian gy, taylor d, rudlin j. (2003) flaw detection and quantification for ferromagnetic steels using pulsed eddy current techniques and magnetization. laser metrology and machine performance vi, pp 381-390. [12] daura lu, tian gy, yi q, sophian a. (2020) wireless power transfer-based eddy current non-destructive testing using a flexible printed coil array: wpt based fpc-ect. philos. trans. r. soc. a math. phys. eng. sci., 378:20190579 doi: https://doi.org/10.1098/rsta.2019.0579. [13] nafiah f, sophian a, khan mr, zainal abidin im. (2018) quantitative evaluation of crack depths and angles for pulsed eddy current non-destructive testing, ndt e int., 102:180-188. doi: 10.1016/j.ndteint.2018.11.019. [14] kernel (covariance) function options [https://www.mathworks.com/help/stats/kernelcovariance-function-options.html] 233 266 iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 29 sustainable river water quality management in malaysia abdullah a. mamun and zaki zainudin bioenvironmental engineering research center (berc), department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. mamun@iium.edu.my abstract: ecological status of malaysia is not as bad as many other developing nations in the world. however, despite the enforcement of the environmental quality act (eqa) in 1974, the water quality of malaysian inland water (especially rivers) is following a deteriorating trend. the rivers are mainly polluted due to the point and nonpoint pollution sources. point sources are monitored and controlled by the department of environment (doe), whereas a significant amount of pollutants is contributed by both untreated sullage and storm runoff. nevertheless, it is not too late to take some bold steps for the effective control of non-point source pollution and untreated sullage discharge, which play significant roles on the status of the rivers. this paper reviews the existing procedures and guidelines related to protection of the river water quality in malaysia. there is a good possibility that the sewage and effluent discharge limits in the environmental quality act (eqa) may pose hindrance against achieving good quality water in the rivers as required by the national water quality standards (nwqs). for instance, ammoniacal nitrogen (nh3-n) is identified as one of the main pollutants to render many of the rivers polluted but it was not considered in the eqa as a monitoring parameter until the new regulations published in 2009. surprisingly, the new regulation for sewage and industrial effluent limits set allowable nh3-n concentration quite high (5 mg/l), which may result in low water quality index (wqi) values for the river water. the water environment is a dynamic system. periodical review of the monitoring requirements, detecting emerging pollutants in sewage, effluent and runoff, and proper revision of water quality standards are essential for the management of sustainable water resources, in the country. abstrak: satus ekologi malaysia tidak seburuk kebanyakan negara membangun lain di dunia. walaupun akta kualiti alam sekitar (eqa) dikuatkuasakan pada tahun 1974, kualiti air di pedalaman malaysia (terutama sungai) semakin merosot. kebanyakan sungai tercemar akibat pencemaran di punca sumber air dan pencemaran di bukan punca sumber air. punca sumber air dipantau dan dikawal oleh jabatan alam sekitar (jas), tetapi sejumlah besar pencemaran adalah sisa yang tidak dirawat dan air larian ribut. walau bagaimanapun, ia tidak terlambat untuk mengambil beberapa langkah berani untuk mengawal pencemaran di punca sumber air dan sisa tidak dirawat kerana langkah ini memainkan peranan penting bagi kebersihan sungai. kertas kerja ini mengkaji prosedur dan garis panduan sedia ada berkaitan perlindungan kualiti air sungai di malaysia. ada kemungkinan bahawa had kumbahan dan pelepasan efluen dalam akta kualiti alam sekitar (eqa) boleh menimbulkan halangan terhadap mencapai kualiti air yang baik di dalam sungai seperti yang dikehendaki oleh piawaian kualiti kebangsaan air (nwqs). sebagai contoh, ammoniakal nitrogen (nh3-n) dikenal pasti sebagai salah satu bahan pencemar utama yang menyebabkan banyak sungai tercemar tetapi ia tidak dianggap sebagai parameter pemantauan dalam eqa hingga peraturan baru diterbitkan pada tahun 2009. yang menghairankan, peraturan baru menetapkan had iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 30 efluen perindustrian dan kumbahan dibenarkan pada kepekatan nh3-n yang agak tinggi (5 mg / l), dan ini mungkin menyebabkan nilai indeks kualiti air (wqi) sungai rendah. persekitaran air adalah sistem dinamik. menjalankan semakan berkala mengenai syarat pemantauan, mengesan bahan pencemaran di dalam kumbahan, efluen dan aliran, dan semakan piawaian kualiti air yang wajar adalah perlu bagi pengurusan sumber air lestari di negara ini. keywords: environmental quality act (eqa); point source (ps); non-point source (nps); sustainable uses; water quality index (wqi) 1. introduction good quality water is essential for all living beings. even modern technologies could not change our dependency on water. we are more concern about this natural resource when it becomes too little, too much or too dirty. until recently, the quantity of water was not an issue in the country, except in the dry regions of the peninsula. sabah and sarawak did not face any serious shortage of raw water yet. majority of the potable water is tapped from the rivers, which are fed by the rain. on average the peninsular malaysia receives 324 billion m 3 of rainwater annually, where as the current demand is about 11 billion m 3 only [1]. the demand in the year 2050 could be about 18 billion m 3 . as such, it is understood that the availability of raw water in the country, generally, is not an issue. the problem is due to the fact that rainfall is not uniformly distributed over the year temporally and spatially; baseflow is reduced due to urbanisation, supply is less than the demand in the city centres, distribution network is not adequate to transfer water from the low demand to the high demand areas, water get polluted and rendered less suitable for the intakes when passing through the urban centres. variation of annual rainfall is not that significant in malaysia except during the elnino spells. the annual rainfall at one of the well maintained gauging station at did ampang branch is shown in fig. 1. despite ignoring the rainfall during the missing days, the recorded data showed a slightly increasing trend of annual rainfall. thus, water scarcity is not a common phenomenon in malaysia. the recent shortages are due to nonuniformity of rainfall and improper distribution and management of the water resources. however, availability of good quality raw water is reducing. this is reflected in the number of polluted and slightly polluted rivers are increasing, as shown in fig. 2. shortage of water is mainly faced in the city centres where the water demand is high. besides quantity, quality of water resources also concerns the relevant authorities. quality of the surface water is degraded by point and non-point sources pollutants. legislations are available in the form of environmental quality act (eqa) 1974, which deals mainly with point source pollutants from the domestic and industrial sources [2]. other regulatory acts are available at state and federal levels to protect the rivers. besides the point sources (sewage, sullage, industrial effluent, etc.), pollutants from the non-point sources (urban and rural runoff) are also responsible to make river water unsuitable for our uses. management of the pollutants from the point and non-point sources are equally important for sustainable management of water resources. this statement is apparently true as it is observed that despite the implementation of the eqa for more than two decades (which mainly controls point sources) the trend of river water quality is not improving until 2000. it is the year 2001 when significant improvement in the river water quality status was observed which might be linked to the endorsement of the urban stormwater management manual for malaysia (manual saliran mesra alam, msma) by the cabinet in 2000 [3]. iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 31 fig. 1: variation of mean annual rainfall at ampang (stn. no. 3117070). fig. 2: river water quality trend in malaysia (source: doe malaysia). the quality of raw water is crucial for the uninterrupted supply of potable water [4]. there are about 468 water treatment plants (wtps) in the country. many of wtps use conventional treatment technology. therefore, the wtps have their own limitations in treating polluted water for potable use. such limitations can affect the availability of water supply in the country due to the issue of raw water quality despite availability of adequate amount of polluted water in the rivers. elevated level of ammoniacal nitrogen (nh3-n) had resulted in the temporary closing of the cheras wtp thrice in 1997 [4]. more than 30% of the raw water samples taken in the year 2000 by the ministry of health had total bacteria counts above 5,000 cfu/100 ml, the malaysian water association (mwa) and world health organisation (who) standards for raw water. the consequences of polluted raw water include the risk of outbreaking waterborne diseases. the microbial and heavy metal contamination in raw water also can affect the food chain and result in serious health impacts. according to the present practice, the overall river quality is determined based on six (6) parameters, among which nh3-n was not listed either in standard a or standard b of the eqa until the year 2009. it was reported that 43% of the rivers are polluted with ammoniacal nitrogen [5]. suspended solid (ss) is another pollutant, which is contributed from the non-point sources during storm events but not monitored in the doe approved 0 500 1000 1500 2000 2500 3000 3500 4000 m e a n a n n u a l r a in fa ll ( m m ) year trend line of mean annual 0 10 20 30 40 50 60 70 80 90 100 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 n u m b e r o f r iv e rs ( % ) year clean slightly polluted polluted iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 32 programs. interruption and temporary shut down of cheras, bukit jelutong at shah alam, sungai buaya and a few other water treatment plants (wtps) in the country indicates that quality of raw water is also important for sustainable supply. sustainable water use supports the ability of human society to endure and flourish into the indefinite future without undermining the integrity of the hydrological cycle or the ecological systems that depend on it [6]. as such, it is important to consider the quality of water and wastewater for sustainable management of water resources in this country. 2. sources of river water pollution over the past few decades, the situation of good quality water in the country has changed from one of relative abundance to one of relative scarcity [6]. rivers are polluted from point and non-point sources. domestic and industrial wastewater are the main point sources responsible for degraded river water. it is expected that after treatment, the treated wastewater would achieve either standard a or b. not much data is available on the longterm performance of the existing sewage or industrial wastewater treatment plants. without any detailed data, it would be impossible to evaluate the contribution of the wastewater on water pollution. in order to evaluate the contribution of pollutants from the non-point sources, a comprehensive study done in the usa can be referred to [7]. event mean concentration (emc), which represents the flow-weighted pollutant concentration for any storm event, of a few selected pollutants are given in table 1. table 1: typical pollutant concentrations in storm runoff [7] and doe, 2009. source event mean concentration, emc (mg/l) bod cod tss cu zn cd residential runoff (nps) 10.0 80.0 139.0 0.05 0.17 0.002 industrial runoff (nps) 9.5 60.0 87.0 0.05 0.32 0.002 agricultural runoff (nps) 8.5 55.0 52.0 forest runoff (nps) 7.9 50.0 10.0 sewage and industrial effluent (ps) # 20.0 120.0 50.0 0.2 1.0 0.01 # eqa limits in malaysia for standard a [8] in the national urban runoff pollution (nurp) study in the usa revealed that nps pollution plays significant role in degradation of water quality. however, the composition of the pollutants in the runoff in malaysia has not been determined and doe water quality monitoring program does not cover the collection of samples during the rain events when the quality of the river water would be very different from the normal dry periods. based on the overseas experiences, it can be anticipated that annual pollutant load of certain pollutants (e.g. ss, pb, zn, cu, etc.) in the urban centres of malaysia could be as high as 50% of the total pollution load entering the rivers. a study on klang river basin done for the did indicated that the most common pollutants responsible for water pollution e.g. bod and nh3-n are significantly released from the non-point sources, as shown in fig. 3. many of these non-point sources include the sub-urban and squatters areas without proper sanitary system. another source of sediment-laden pollution in the inland water is sand mining in the rivers. the sand mining activities is a significant source of soil particles and iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 33 makes the water treatment operation very costly by increasing the coagulant (alum) and polymer doses. (a) bod loading (kg/d) (b) nh3n loading (kg/d) fig. 3: calculated pollutant load from various sources in klang river basin [9]. it is reported in the national water resources study 2000-2050 [1] that the parameters which have frequently exceeded class iii limits include ammoniacal nitrogen, organic carbons, heavy metals, oil and grease. due to pollution problems a few of the rivers namely sungai. langat at bukit tampoi, sungai klang at shah alam has been classified into class iv. according to table 2, water of class iv and v are not suitable for the water intakes. it is noted that by improving the quality, more water could be sustainably abstracted from the downstream stretches of the river basins. the pollution problems at the downstream reaches compel the water industry to source water from the upstream areas and also from relatively less polluted river basins. industrial 4% (ps) sewage 38% (ps) commercial 10% (nps) residential 48% (nps) industrial 2% (ps) sewage 38% (ps) commercial 38% (nps) residential 22% (nps) iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 34 3. existing standards and related legislations the most frequently referred locals guidelines related to the water quality are the eqa, nwqs and the malaysian water association’s (mwa) raw water quality criteria for the intakes. the standards of related parameters are given in table 2 and table 3 for references. description of the classes, in terms of the utility, is also given in this section. malaysia suffers from existence of many sectoral-based water laws, both at federal and state levels but lacks a comprehensive water law, which should safeguard both quantity and quality of water and wastewater. the water legislations are contained within the laws, which are enforced by the various water related government agencies and many are outdated, redundant or ambiguous [6]. these diversified water legislations are focused on limited aspects of water resources and difficult to enforce effectively. there is a need to enact a comprehensive water law that can deal the water quantity and quality issues effectively. effective regulation of wet-weather pollution management relies on the establishment of a comprehensive legislative framework. current situation calls for revising and repealing outdated laws and introducing additional regulations and procedures in line with usual practices. the water act 1920 provides that "the entire property and control of all rivers in any state is and shall be vested solely in the ruler of such state". if required, federal government shall play its role only for the water bodies shared or bordered by several states. the other legislations to control water pollution are the mining act 1929, the forest enactment 1935, the drainage works ordinance 1954 and the land conservation act 1960. the latest is the environmental quality act 1974 (revised in 1979 and 2009), which provide the regulatory control of point pollution sources. the other guideline mainly focused to reduce flood and nps pollutant is msma [3] table 2: excerpt of national water quality standards (nwqs) for malaysia. parameter unit limits for classes i ii iii iv v ammoniacal nitrogen bod cod dissolved oxygen ph total suspended solids (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) < 0.1 < 1 < 10 > 7 > 7.0 < 2.5 0.1 – 0.3 1 – 3 10 – 25 5 – 7 6.0 – 7.0 25 – 50 0.3 – 0.9 3 – 6 25 – 50 3 – 5 5.0 – 6.0 50 150 0.9 – 2.7 6 – 12 50 – 100 1 3 < 5.0 50 30 > 2.7 > 12 > 100 < 1 < 5.0 > 300 class i: represent water bodies of excellent quality. standards are set for the conservation of natural environment in its undisturbed state. class iia: represent water bodies of good quality. most existing raw water supply sources come under this category. class iia standards are set for the protection of human health and sensitive aquatic species. class iib: the determination of class iib standard is based on criteria for recreational use and protection of sensitive aquatic species. class iii: is defined with the primary objective of protecting common and moderately tolerant aquatic species of economic value. water under this classification may be used for water supply with extensive/advanced treatment. class iv: defines water quality required for major agricultural irrigation activities which may not cover minor applications to sensitive crops. class v: represents other water, which do not meet any of the above uses. iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 35 table 3: wastewater discharge standards and raw water quality criteria for malaysia. parameter (mg/l unless otherwise stated) maximum permitted values ( doe, 2009; doe, 1974) raw water quality [10] standard a standard b temperature (°c) 40 40 ph (units) 6.0 9.0 5.5 9.0 5.5-9.0 bod5 at 20 °c 20 50 6 cod 120 (50) 200 (100) 10 suspended solids 50 100 mercury 0.005 0.05 0.001 cadmium 0.01 0.02 0.005 chromium, hexavalent 0.05 0.05 0.05 (total) arsenic 0.05 0.10 0.05 cyanide 0.05 0.10 0.1 lead 0.10 0.50 0.1 chromium, trivalent 0.20 1.0 copper 0.20 1.0 1.0 manganese 0.20 1.0 0.2 nickel 0.20 1.0 tin 0.20 1.0 zinc 2.0 (1.0) 2.0 (1.0) 1.5 boron 1.0 4.0 iron 1.0 5.0 silver 0.1 (-) 1.0 (-) aluminium 10 (-) 15 (-) selenium 0.02 (-) 0.5 (-) barium 1.0 (-) 2.0 (-) fluoride 2.0 (-) 5.0 (-) formaldehyde 1.0 (-) 2.0 (-) phenol 0.001 1.0 0.002 free chlorine 1 2.0 sulphide 0.50 0.50 ammoniacal nitrogen 10.0 (-) 20.0 (-) colour (admi*) 100 (-) 200 (-) note: data in bracket ( ) is from eqa, 1974. a dash indicates the parameter is not included. 4. procedure to determine water quality index six parameters namely dissolved oxygen (do), biochemical oxygen demand (bod), chemical oxygen demand (cod), suspended solids (ss), ammoniacal nitrogen (nh3-n) and ph are considered for the evaluation of overall status of the river water. the water quality index (wqi) approved by the doe (eqn. 1) is calculated based on the above six parameters. among those, do carries maximum weightage of 22% and ph carries the minimum of 12% in the wqi equation. the wqi equation eventually consists of the subindices, which are calculated according to the best-fit relations given in eqns. 2 to 7. variations of the sub-indices with concentrations of the respective pollutants are shown in fig. 4. high value of the index indicates better quality of water. iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 36 ��� � 0.22 � � � 0.19 ��� � 0.16 ��� � 0.15 ��� � 0.16 ��� � 0.12 ��� (1) where, wqi= water quality index; sido= sub-index of do; sibod= sub-index of bod; sicod= sub-index of cod; sian= sub-index of nh3-n; siss= sub-index of tss; siph= sub-index of ph. all pollutant concentrations are in �� �⁄ except for ph. sub-index for do (in % saturation): � � � � 0 100 �0.395 � 0.030� 2 – 0.00020� 3 " #$% � & 8#$% � ( 92#$% 8 & � & 92 (2) sub-index for bod: ��� � ) 100.4 – 4.23+ � 108, -...//�� – 0.1+ � " #$% + � & 5#$% + � ( 5 (3) sub-index for cod: ��� � 0 �1.331 � � 99.1 � 103, -...2/3�� – 0.041 � " #$% 1 � & 20#$% 1 � ( 20 (4) sub-index for an (an is abbreviation of ammonical nitrogen, nh3-n): ��� � 4 100.5 – 10556 94, -../37�� – 5 856 – 28 0 " #$% 56 & 0.3#$% 0.3 & 56 & 4#$% 56 ( 4 (5) sub-index for ss: ��� � � 97.5, -....:3:�� � 0.05 71,-....2:�� – 0.015 0 " #$% & 100#$% 100 & & 1000#$% ( 1000 (6) sub-index for ph: ��� � ;<= <>17.2 – 17.2?@ � 5.02?@a #$% ?@ & 5.5�242 � 95.5?@ – 6.67?@a #$% 5.5 & ?@ & 7�181 � 82.4?@ – 6.05?@a #$% 7 & ?@ & 8.75 536 – 77.0?@ � 2.76?@a #$% ?@ ( 8.75 " (7) iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 37 iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 38 according to the equation, sub-index of do increases with the increase in concentration while for others it decreases at different rates. in the case of ph, the index follows decreasing trend as it is deviated from the neutral value of 7 (fig. 4f). the equations (2 to 7) indicate smooth variations of indices for do, bod5, cod and ph when their concentrations are changed. in the case of nh3-n and ss, the values decrease sharply until 0.3 and 100 mg/l, respectively (fig. 4d and 4e). according to the equations, maximum values of sub-index for cod, ss and ph could be achieved up to 99.1, 97.5 and 99.4 but not 100 as possible for others. the concentrations of do, bod5, cod, nh3-n and ss that results in zero (0) value of sub-index are 0.5, 54.3, 172.0, 4.0 and 1000, respectively. it was observed that except nh3-n, all these values exceed the limits stated in the effluent standard a and b of the eqa. it is realised that the lower and upper limits of the parameters should be revised with respect to the effluent standards and the requirements for raw water quality criteria set by the mwa. the revision is necessary, especially for the rehabilitation of urban rivers, which does not have much baseflow due to high impervious in the river basin. 5. review of the wqi method it was observed that both the national water quality standard (nwqs) and the raw water quality criteria set by mwa contain many parameters, compared to six in the wqi equations. it is not practical to consider all parameters for evaluation purposes. polluted or clean water is a relative term and expressions to describe the status of water quality mainly depend on the beneficial water use. based on the long-term observation of the doe data, it was realised that ph is not a problem and the weightage of ph in the wqi equation can be reviewed or even taken out of the wqi equation. a comprehensive analysis is required to identify the main and most frequently detected pollutants in the water and revise the wqi equations. it should consist of the most frequently detected and polluting elements, including heavy metals, herbicides, pesticides, coliform, etc. the upper and lower limits of the wqi determining parameters need to be reviewed and set appropriately considering the requirement of the effluent standards, raw water quality criteria and other specific requirements. the wqi may cover more parameters, including the carcinogenic and toxic elements as mentioned above, for wide range applicability of the indices. the doe has taken initiative to rehabilitate 26 polluted rivers to class ii standard [5]. in order to improve the quality from the highest level of class iii to the lowest level of class ii, the minimum improvement required, in terms of numerical wqi value, is 24.6 units (i.e. from 51.9 to 76.5, as given in table 2). the numerical points among the classes are also not uniform. with the increased awareness among the people and decreased assimilative capacities of the rivers due to reduced baseflow caused by urbanisation, it is necessary to review the limits of the wqi values including individual parameters of the nwqs. one major issue should be considered is that the limits of nh3-n was not set in the eqa, 1974 but is considered in the revised regulation in 2009 with high concentration (10 and 20 mg/l for standard a and b, respectively). it was noticed by the practitioners that nh3-n is one of the main pollutants that render wqi value low. although the influence of nh3-n sub-index on the overall equation is 15% only, the sub-index decreases rapidly with the increased concentration of nh3-n (fig. 4d). another inconsistency is that, there is class iia and iib in the nwqs but the wqi does not have such categories (table 2). as such, the class ii in the wqi method may be split into two sub-classes as mentioned in the nwqs. even the chemical oxygen demand (cod) in the new doe regulation [8] for standard a sewage is increased from 50 mg/l to 120 mg/l, which might aggravate the water quality in the rivers. iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 39 6. case study in the eighth malaysia plan (2001-2005) the doe took initiative to control pollution and rehabilitate 26 polluted rivers up to the standard of class ii. this embarkation admits that quality is important for sustainable uses of river water. this section describes case studies of three river basins under the doe scheme of river rehabilitation. one is sungai langat in selangor and the others are sungai tebrau and sungai segget in johor. existing status of the rivers are discussed below and different scenarios were analysed with a target to achieve class ii standards. existing status of the rivers at different stations, including the concentrations of the selected parameters and wqi values, are given in table 4. in general, sg. langat is affected by high cod, ss and nh3-n [12] but sungai tebrau and segget suffers from cod and nh3-n problems [13]. most of the stations in these river basins recorded water inferior to class iii, which indicated that the water are generally not suitable for raw water intakes, especially at the places where the rivers passes through the developed areas, either residential, commercial or industrial. besides the doe data, additional water quality data were collected by individual study [12, 13, 14] to identify the contributing sources of the pollutants, which include both point and non-point sources. in order to achieve class ii in the rivers, the point sources would be identified and the problematic or ineffective sewage treatment plants (stps) would be asked to upgrade. the non-point source pollutants mainly from the storm runoff will be diverted to the water quality treatment trains as proposed in the manual saliran mesra alam msma [3], which includes swale, infiltration facility, bioretention, gross pollutant traps (gpts), sediment ponds, wet ponds, wetlands, etc. possible ways to improve water quality (as wqi) in the rivers are increasing dissolve oxygen (do) by aeration, decreasing bod, cod, nh3-n by appropriate treatment and reducing ss from point and non-point sources. a few options are planned, as given in table 5, to achieve class ii from the existing status of the rivers (especially during dry period). in order to achieve that target, concentration of few pollutants at some locations (stations) need to be reduced by various percentages are given in table 6. the options are set based on the achievable target of pollutant concentration. these case studies show that despite the eqa, status of the rivers is not healthy and significant efforts are necessary to upgrade the rivers up to the level of class ii. table 5: a few feasible options to achieve class ii river in the polluted basins. options pollutant concentration (mg/l) to achieve class ii water in the rivers do bod cod nh3-n tss ph 1 6.0 4.0 20.0 1.5 20.0 6.5 2 6.0 3.0 30.0 1.0 30.0 6.5 3 6.0 5.0 15.0 1.0 45.0 6.5 4 6.5 5.0 15.0 1.3 50.0 6.5 7. upgrading the requirements the nation is heading towards urbanization and industrialization. people are migrating more to the urban areas in search of job and to lead a better life. our rivers, especially at the urban stretches, are being stressed due to reduced base flow (dry weather iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 40 hour) resulting in decreased assimilative capacity and increased pollution loading. during the normal days, most of the urban rivers carry light brown, brown and dark colour of water, which are mainly from the point sources. water quality in the rivers during the storms is yet to be monitored for long term. thus, it was realized that comprehensive studies are required to check back the water quality standards set for various purposes (sewage, industrial effluent, wqi, nwqs, raw water quality, etc.). 8. consideration of other indices good quality of water is more essential for the aquatic flora and fauna. water quality criteria should be more stringent for their survival and ecological balance. for holistic and sustainable use of water other appropriate indices e.g. harkin’s objective index, shanninwiener diversity index (h), sci diversity index, index of biotic integrity (ibi), index of saprobic condition (s), etc. could be considered [11]. this is important because, the normal monitoring program cannot evaluate the river’s ecological status. at least biannual or quarterly sampling of planktons, macrophytes, invertebrates, fish and other aquatic flora and fauna should be done to determine the biological integrity of the rivers in various seasons. 9. concluding remarks malaysia receives adequate rainwater to meet the increasing water demand of the nation. however, despite the eqa, water quality of many rivers is deteriorating in the country. a few of the water treatment plants (wtps) are reported to have problems with raw water quality and had been temporarily shut down several times. the mismatch between availability and demand for water is aggravated by pollution of water sources. water shortage is aggravated by the pollution due to point and non-point sources pollution. during the low flows, the water quality is adversely affected due to inadequate dilution and makes the water unacceptable or costly to treat. the existing legislations, guidelines, standard and procedures to evaluate water quality are discussed. it is recommended to review the wqi equations and procedure, effluent discharge standards in the eqa and limiting values of the nwqs to reduce the inconsistencies and to increase compatibility. the eqa allows discharge of various concentrations of pollutants depending on the source of wastewater. however, the ecosystem does not care whether the pollution load is from sewage, industrial effluent, sullage or storm runoff. therefore, a unified wastewater discharge standard (irrespective of the source) would safeguard the water bodies and aquatic lives in a sustainable manner. case studies in three river basins indicated that most of the urban rivers are stressed and not suitable for water intakes, making the water supply more costly. to make the water resources sustainable for all living beings, other appropriate indices should be adopted and evaluated at reasonable intervals. realising the importance of the quality of water, it is recommended to undertake strict measures on water quality control, monitoring criteria and standards, including control of point and non-point pollutions. iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 41 iium engineering journal, vol. 14, no. 1, 2013 mamun and zainudin 42 acknowledgement the authors gratefully acknowledge the data provided by the doe, asma, did and other sources. references [1] economic planning unit epu. “national water resources study 2000 – 2050”. government of malaysia, department of prime minister’s office 2000. [2] department of environment malaysia doe. “environmental quality act 1974 (act 127) & subsidiary legislations”. government of malaysia, ministry of science, environment and technology. international law book services, 1974. [3] department of irrigation and drainage did. “urban stormwater management manual for malaysia”. government of malaysia, ministry of agriculture, malaysia, 2000. [4] m.s. pillay. “water and health”.. seminar on world day for water. 2001. [5] d. hashim. “water pollution control in malaysia – a regulator’s perspective”. seminar on world day for water. 2001. [6] a.keizrul. “the need for sustainable water use and management”. seminar on world day for water. 2001. [7] united.states. environmental protection agency usepa. “final report of the nationwide urban runoff program”. water planning division, washington dc, 1983. [8] department of environment malaysia doe. “environmental quality act 1974 – environmental quality (sewage) regulations 2009”. government of malaysia, ministry of natural resources and energy. percetakan nasional malaysia berhad, october, 2009. [9] department of irrigation and drainage did. “klang river basin environmental improvement and flood mitigation project”. government of malaysia, ministry of agriculture, malaysia, 2001. [10] malaysian water association “design guidelines for water supply systems”. 1994. kuala lumpur: mwa (1994). [11] department of environment malaysia doe. “classification of malaysian rivers”. final report on development of water quality criteria and standards for malaysia (phase iv – river classification). government of malaysia, ministry of science, technology and the environment, 1994. [12] department of environment malaysia doe. “the study of pollution prevention and water quality improvement of sungai langat”. government of malaysia, ministry of science, technology and the environment, 2003a. [13] department of environment malaysia doe. “the study of pollution prevention and water quality improvement of sungai tebrau and sungai segget”. government of malaysia, ministry of science, technology and the environment, 2003b. [14] department of environment malaysia doe. the study on pollution prevention and water quality improvement of sg. melaka. government of malaysia, ministry of natural resources and environment malaysia, 2004 microsoft word 9-paper print 6 nasse.doc iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 42 high speed submarine optical fiber communication system: pressure and temperature effects a. a. mohammed faculty of electric engineering, menouf, 32951, egypt abstract: in the present paper, the performance of high speed submarine optical fiber cable systems is investigated, taking into account both the pressure and the temperature effects. both the pressure and the temperature are depth-dependent variables, while both the spectral losses and the dispersion effects are temperature as well as wavelength dependent variables. two important cases with real fibers are processed: a case with dispersion cancellation and a case without dispersion cancellation. it is found that the ocean pressure (due to the depth) shifts the dispersion-free wavelength towards the third communication window. in general, as the depth increases the maximum transmitted bit rate increases in the range of interest. the system capacity as well as the spectral losses, and the dispersion effects are parametrically investigated over wide-range ranges of the set of affecting parameters {wavelength, ocean depth (and consequently the ocean pressure and temperature), and the chemical structure}. key words: submarine optical fiber, undersea optical communication, pressure and temperature effects, transoceanic optical communications i. introduction submarine optical fiber cables have been employed in a number of countries to realize long-length high-bitrate optical fiber transmission systems utilizing the second and the third optical windows for one decade. the first generation of undersea systems was installed in 1988 and provided service between north america and europe across the atlantic ocean and between north america and japan across the pacific ocean. the second generation of twice capacity was installed in 1991 and spanned the north atlantic from u.s. and canada to u.k. , france, and spain with multiple landing that was accomplished by undersea branching multiplexers (ubm) capable of exchanging traffic between fiber pairs [1,2]. the first sea trial of submarine optical fiber cable employing dispersion shifted fibers was described in ref. [2], where it included fiber, a structural design for dispersion shifted fiber, cable manufacturing results, fiber splicing, cable laying results, and a high accuracy measurement technique for optical losses and chromatic dispersion. based on these, the feasibility of long-span and high capacity 1.5-m submarine optical fiber cable was demonstrated. two types of fibers can be considered feasible: conventional fiber with 1.3 m zero dispersion wavelength or dispersion shifted fiber with zero dispersion in the 1.5 m wavelength region. based on transmission experiments using fabry-perot laser diode (fp-ld) and distributed feedback laser diode (dfb-ld) optical source, a next generation of optical submarine cable communication systems are designed to operate at 1.55 m [3]. different combinations of fibers and optical sources are investigated to achieve a repeater spacing more than 100 km at 280 mbits/sec. recently, there have been some remarkable reports on coherent optical communication systems which make use of phase, frequency and polarization characteristics of lightwave. polarization fluctuation characteristics of optical fiber submarine cables under 8-km deep sea environmental conditions, optical fiber submarine cable coupling under periodic variable tension, and cable performance during and after installation were analyzed [4]. the history of undersea cable technology has been marked by a few, long periods during which the undersea cable network grew slowly and the technology improved gradually and cautiously. the quiet periods were separated by breakthrough periods during which the technology changed radically, with the previous technology essentially being completely abandoned. the first period-about one hundred years long-was that of single-channel telegraph cables. an extensive cable network was installed during this period, many of which still lie on the sea bottom today (and which have to be removed before new cables can be deployed on the same route). the second period, from about 1950 to 1985, was characterized by the use of coaxial cables carrying analog telephone traffic. the introduction of electronic vacuum tubes, and later on, of semiconductors in the repeaters permitted the transmission of multiplexed 4-khz channels, whose number grew from 36 to 4000 per cable, using high frequency carrier techniques. increasing the capacity mode, it is necessary to increase the diameter of the coaxial cable and to reduce repeater spacing, thus increasing the systems cost. like in the previous period, the cables were essentially used in point-topoint systems and a new transatlantic cable was installed approximately every four years. it was during this period that satellites appeared which competed with undersea cable systems. the first satellite used for intercontinental transmission was launched by intelsat(i) in 1965 with a rather low capacity of 240 channels. however, satellite technology made significant progress as well, and the iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 43 capacity of intelsat (v), launched in 1981, reached 10000 circuits. numerous economic comparisons were made between satellite and undersea cable systems, with ambiguous and often contradictory results. in fact, a complementary relationship developed between satellite and undersea cable systems because of the advantage of mutual restoration in case of failures of either system. the two systems, however, offer different opportunities: undersea cables are well suited for high-capacity, point-to-point transmission whereas satellites provide more flexibility [5]. the advent of optical-fiber cable technology and of optical amplifiers has provided a strong incentive for the development of new undersea cable networks. as a result, significant difficulties have been surmounted, including the problem of the accumulation over very long distances of the effect of imperceptible degradation phenomena. the above problems are currently being solved for 5 gbits/sec undersea cable systems, and solutions are being sought for improving the systems performance and economy. further improvements are still foreseeable, but it is not yet clear when they will be introduced. for instance, ultra-low-loss halide fibers operating at longer wavelengths may permit the achievement of transoceanic distances without any repeaters, the only loss being that of splices. for such fibers, the main foreseeable impairments would come from chromatic-and polarization-mode dispersion [5]. the main trends for the evolution of global undersea cable networks are seen as follows: 1) since several fiber pairs may be present in the same cable, but can be separated inside branching units, network planners no longer need to build point-to point links, but may build more complex undersea networks, so as to connect through one single transoceanic cable several landing stations on each side of an ocean, or to connect numerous stations to an optical undersea backbone parallel to the coast of a continent. 2) the possibility of using undersea branching multiplexers inside the branching unit (using electronic time division multiplexing (tdm) like in the tat 9 technology, and probably all-optical wavelength division multiplexing (wdm) in the future, permits further development of these undersea networks, without increasing the number of fibers per cable. 3) the ever-increasing capacity of optical undersea cables is no longer commensurate with that of satellite transmission systems; therefore, in case of a cable fault, traffic can no longer be restored through satellites. the undersea cable network must, therefore, include its own restoration facilities using, for example, ring architectures. moreover, a new “regional” undersea network, involving tat 12 and tat 13, may include its own network protection system which operates nearly instantaneously. 4) optical undersea cable systems are now being deployed in many parts of the world, and access to undersea cables is becoming available from, virtually, any location. consequently, undersea cables are no longer considered point-to point links, but as elements of a giant global network. undersea cable operators aim at exploiting this situation by optimizing, on a real-time basis, the flow of traffic over these networks, taking into account local time differences and changes in the availability of cables. at present, new undersea cable network development not only relies on technological progress in optical transmission but also on the development of an undersea telecommunication network management system (nms) which should benefit from recent standards work aimed at harmonizing the nms for terrestrial transmission systems based on the synchronous digital hierarchy. the advent of the optical amplifiers has removed the loss limitation of the fiber in the conventional undersea systems using 3r (retiming, reshaping, and regenerating) repeaters, and it has introduced new design criteria for the undersea lightwave systems. the accumulation of the small impairment factors that was negligible in the conventional system becomes significant to determine the transmission performances of the amplified system. the fiber nonlinearity is a distinctive limitation factor that dominates the transmission performance of the amplified system, although it was not a limitation factor in the conventional system. the recent progress of the undersea lightwave cable systems employing optical amplifier repeaters was described in [6]. the limitation factors and polarization-dependent characteristics of the amplified system are described. the system demonstrations with conventional im-dd technology are presented using both recirculating loop and straight fiber transmission line. the system maintenance method is also explained briefly. future technologies adopting the wdm or the optical solitons are also discussed in [6]. the erbium-doped fiber amplifier (edfa), a research curiosity in the late 1980’s, was the backbone of undersea lightwave communications by the mid1990’s. erbium-doped fiber amplifiers have a profound impact on the design, operation, and performance of transoceanic cable transmission systems. the first amplifier systems which was installed in the mid1990’s increased the capacity of undersea systems four-to eight fold over the most advanced digital fiber system in use at that time. later generations of erbiumdoped fiber amplifier systems promise to satisfy the international transmission needs into the 21st century [7]. a new modulation format for optical time domain reflectometry (otdr) to eliminate optical surge and improve otdr performance in optical amplifier submarine transmission systems was proposed where the modulation format, fsk-ask, uses ashore highpower probe pulse and a long dummy pulse, with the slow gain dynamics of erbium-doped fiber amplifiers. both pulses experience an identical gain, equal to the loss of a span, so that the probe pulse maintains its high iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 44 power and does not develop into an optical surge. fault location experiments verify a theoretical prediction that fsk-ask improves the signal-to-noise ratio (snr) of otdr by an amount as large as the power ratio of the probe to the dummy signal. they also confirm the elimination of the optical surge caused by conventional otdr using a solitary probe pulse. an fsk-ask otdr is applied in a commercial submarine amplifier transmission system which has a total transmission length of 890 km and a repeater spacing of 90 km. these field trial results show that subtle fiber anomalies can be located, with a spatial resolution of 1 km, along the entire length of the amplifier transmission system from a terminal end [8]. the fsa submarine optical amplifier system developed for commercial use was designed to transmit 2.5 and 10 gbits/sec signals flexibly. its repeater spacing was 90 km. it contains six line pairs to yield a maximum transmission capacity of 60 gbits/sec. its system configuration, and the characteristics of its fibers and optical amplifiers which realize effective dispersion and optical passband management, are introduced. its performance was discussed with regard to the parameters significant in optically amplified transmission: evolution of zero dispersion wavelength (zdw), polarization mode dispersion (pmd), and fiber-nonlinearity induced impairments. signal-tonoise ratios for 2.5 and 10 gbits/sec signal transmission were measured and the improvements offered by polarization scrambling were also discussed. finally, zdw, pmd, and snr characteristics of the system after installation were reported [9]. optical cables have been installed in bt telecommunications networks for about 10 years. the continued satisfactory operation of these optical networks is dependent on the ability of the cable to withstand the environmental conditions found in service. the most common environmental degradation mechanisms such as fiber bending loss, hydrogen degradation loss and stress corrosion have been described in [10]. the effects of these conditions on cable design have been discussed. designers at present base optical cable structures on theoretical analysis and laboratory results. this leads to a conservative design philosophy but the situation will improve as more field experience is gained. today’s transoceanic systems can span up to 10,000 km, encountering the full range of ocean environments: 6 km ft depths, undersea mountain ranges and eventual landing on different shoreline profiles. traffic at data rates of >2.5 gbit/sec through thousands of kilometers of submarine cable and hundreds of undersea repeaters, were processed. the tremendous need for system reliability, combined with rugged, remote environments in which they are deployed, places a premium on quality. at stc submarine systems, a subsidiary of northern telecom, conformance with iso 9000 standards has played a major role in this quality effort, so necessary to maintaining a presence in submarine telecommunications business [10]. compared to electronic regeneration, direct optical amplification using edfas, possesses many advantages for long-haul repeater and can be quite simply configured regrardless of the line signal bit rate. this feature becomes more significant as the line signal bit rate increases over several gbits/sec at which speed electronic regeneration requires high-speed electronic circuits, thereby resulting in an increase in hardware cost and power consumption. therefore, optical amplifiers are particularly useful in submarine repeaters that have severe space and power constraints. second, optical amplifiers are flexible regarding bitrate and modulation format, and support wavelength division multiplexed signal transmission. these features suggest that installed systems can be upgraded by changing only the terminal equipment. this advantage is inestimable in submarine transmission systems whose undersea components are virtually impossible to alter once they are laid [11]. a knowledge of the refractive index as a function of pressure is necessary in evaluation of chromatic dispersions at different pressures (depths). since it plays a vital role in the ofcs in particular for the undersea submarine optical fiber cables which are used to transmit optical signals from one continent to other. the pressure-dependent sellemeier coefficients are essential to characterize the optical design parameters for the optical fiber communication systems under deep sea environmental conditions. these coefficients are calculated for densified silica glass for the first time to compute the pressure dependence of material dispersion at any wavelength from the ultraviolet to 1.71 m. the zero dispersion wavelength o (1.2725 m at 0.1x106 nm-2) varies linearly with pressure, p, where the rate of variation of o with the pressure (do/dp) is 0.0027 nm/(10 6 nm-2). the calculated value is approximately one-third of the experimental value of 0.0076nm/(106 nm-2) for a germanium-doped dispersion shifted fiber having o=1.5484 m and – 0.0070 nm/(106 nm-2) for a pure silica-core fiber cable having o=1.2860 m. since the refractive indices are increased with pressure, the negative value of shift of the zero-dispersion wavelength is erroneous. the explanations are due to ge-doping in silica glass, a possible temperature fluctuation of 0.16 oc in the pressure-dependent measurement system of the zero dispersion wavelength and different experimental conditions of the silica glass and the optical fibers. this anomaly can also be attributed to the internal strain development at the core-cladding and fiber-jacketing boundaries due to pressure, which shows a larger experimental value. it accounts for the experimental values satisfactorily [12]. edfas have several characteristics that make them an ideal choice for many lightwave applications, including long-haul transmission. edfas can be made with a variety of gains in the low-loss 1550 nm wavelength window of telecommunications fibers, with nearly ideal noise performance, edfas amplify highspeed signals without distortion or crosstalk between wavelengths, even when the amplifier is operated deep in gain compression. edfas are a fiber device, splicing naturally with telecommunication fiber, and are insensitive to polarization effects, and the edfas iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 45 pump laser diodes that are manufactured from the same ingaasp semiconductor family that has proven undersea reliability with millions of device hours on 1.3 m and 1.55 m signal lasers. all other edfa components are passive devices, making amplifier designs simple and ensuring that edfas can be made with high reliability. given these advantages, the next generation of undersea cable transmission systems will use edfas in repeaters to boost signals periodically as they travel across the world’s oceans. edfas will make possible a significant improvement in the capacity of undersea lightwave cable systems installed in the mid 1990’s. the first edfa-based systems will use the nonreturn-to-zero (nrz) modulation format at bit rates up to 5 gbit/sec with dispersion-shifted fiber that is matched to the operating wavelength. at&t, with its partners, installed and operated transoceanic cable systems using edfa repeaters (1995-1996) in the atlantic and pacific [13]. in the present paper, the high speed transmission fiber cable are investigated where both the thermal and pressure effects due to the depth are taken into account. section ii deals with the basic model and analysis where depth-dependent correlations of both the temperature and the pressure are cast, while section iii handles the results and a discussion based on the basic model. finally, section iv summarizes the major conclusion. 2. basic model and analysis: based on reported data of [12], the pressure-dependent sellemeier coefficients and material dispersions for silica fiber glass, will be cast under the form: ),(),(2),,(2  pftnptn  (1) where n is the refractive index,  is the optical wavelength, t is the ambient temperature, p is the pressure. ghosh et al. [12] cast the following: e d c b apn     2 2 2 2 ),(2      (2) with: 2810544763.061086385.929552.1 pxpxa  (3) 281071823.16100899.42809872.0 pxpxb  (4) 21010894313.081056693.021007945.1 pxpxxc  (5) 281013552.16107911.38917151.0 pxpxd  (6) 0.100e (7) p is the pressure in mn/m2 a special software is designed to handle eqs.(1-7) to recast ),(2 pn  under the following form to account for the thermal effects, recalling again eq.(1) as, ),(),(2),,(2  pftnptn  (1) where f(p,) is found to possess the form: ),(1),(  prpf  where: 2),(  pr (8) and:                                        2976 976 953 1 10041.110965.110990.6 10442.310419.710477.2 10252.510293.110424.1 p p xxx xxx xxx    (9) with rms errors of , , and  are 10-11, 10-16, and 10-21 respectively over the following ranges: 300/,0.0 6.1 , 3.1 2   mmnp m (10) the thermal-dependent refractive index n(,t) is cast on the same spirit of [13,14].     3 1 )(22 2)( ),(2 i ti tiatn    (11) based on the data reported by knauss [15], both the pressure, p, and the temperature, t, are correlated to the depth, h, as: 2mn/m ,33101922.021102374.0918.9 hxhxhp  (12) km 10h and 221053838.021062671.02.27 hxhxt  chhhx o ,523156.045994.3321020674.0  (13) km 5.5h and t = constant, h> 5.5 km. equation (1) is the cornerstone in the computation of the dispersion effects and consequently the system capacity; recall that: ),(),( p),f(t),n(p)t,,n( pftn   (14) where ,p)*r(..,p)f  5001(  . based on the models of refs. [16,17], the total chromatic dispersion of a single mode fiber, , depends on n(,t,p) and its first and second derivatives n` and n`` w.r.t.  , respectively, are given by iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 46 ),(),`(),`(),n(p)t,,n`( pftnpft   (15) ),`(),`(2),(),``(),``(),n(p)t,,n``( pftnpftnpft   (16) the thermal-dependent spectral losses, , are processed based on the models of refs. [18-20]. the multi-limitations bit rate (dispersion, losses, and depth) is calculated based on the same spirit of the model of cselet [20], where it is simplified as: )( 8 mf l e rb ublogtfrb    (17) where ft :fiber bandwidth (bw)=0.44/(lf) bu :ultimate bit-rate (limitations-free) lf :repeater spacing m :system marginal loss in the following section, br, will be parametrically processed with special emphasis on the depth of the ocean. 3. results and discussion taking into account the variations of the under surface ocean pressure and temperature due to the ocean depth, a special software is cast to handle the relevant calculations, namely: the ocean depth-pressure variations the ocean depth-temperature variations the spectral losses and the dispersion effects the transmitted bit-rate taking into account the above two limitations. germania-doped fibers are employed with doping percentage (x) to shift the free-dispersion zone toward the zone of minimum optical losses. the reality of the processed calculations is considered via a marginal loss of 0.25 db per repeater spacing, lf which is considered in the present case 60 km due to the amplifier gain. two cases of interest are processed: case 1: without dispersion cancellation: the variation of the set of variables {bit-rate (br), the dispersion (), the fiber bandwidth (bw), the spectral losses ()} against the variations of the optical wavelength at different ocean depths are displayed in figs.1-8 for two types of fibers. i) pure silica x=0.0, and ii) germania doped fiber of x=0.2, with the following set of parameters:  :spectral width=2.5 nm n :refractive index difference=0.0025 lf :repeater spacing=60 km m :system marginal loss=0.25 db bu :maximum available bit-rate without any limitations=6.3 tbit/sec. these figures clarify that: 1) the spectral losses, fig.4, decrease with the ocean depth due to the decrease of the ocean temperature. 2) the dispersion-free zone moves towards the third communication window (1.55 m), fig.3. the fiber bandwidth possesses the features as in fig.2. 3) consequently according to “a” and “b”, the transmitted bit rate possesses the features of fig.1 with movable maxima towards the third communication window (=1.55 m) 4) the same features are found at x=0.2 but at higher optical wavelengths. the maxima of the bit rates, brmax. (dispersion-free) are displayed as functions of the ocean depth as well as the corresponding dispersion-free optical wavelength in figs. 9 and 10 where some sort of saturation (flatness) is shown. based on eq.(17), the dispersion-free bit rate brmax. (=0.0 and consequently bw=) is given by: )( .max mfl ur ebb    (18) which is a losses-limited one. the variations of the set of controlled parameters [ br, wb, , } against the variations of the ocean depth at different optical wavelengths are displayed in figs.11-20. the main features of these figures are: 1) flattened ranges of variations of t, , and  and consequently, in general, flattened variations of br. 2) due to ripples of the variations, br possesses more than one maximum value. 3) whatever the operating optical wavelength, br increases with the depth due to the decrease of t, , , and bw. the complicated variations of this case are due to the opposite effects of variations of both  and  as in figs. 21-24. case 2: with dispersion cancellation in this case, two segments of fibers of numerically equal dispersion bit of opposite sign are spliced in a periodical manner along the cable. each segment is of 2-km length, thus the dispersion is cancelled each 4 km along the path. in such case and from the point of view of dispersion, lf is considered 4 km. the same sort of variations are displayed in figs.25-32, but with the following main features: 1) the dispersion-free wavelength moves towards the third communication window (=1.55 m) 2) the increase of the transmitted bit rates in general is found without sharpening as in fig.1 3) if compared with the first case, the two cases possess the same maxima as in figs. 9 and 10. 4) the increase of x shifts the dispersion-free wavelength to higher values, and consequently the bit rate. 4. conclusion the ocean depth is of a special impact in submarine optical fiber cables due to its effects on pressure and temperature and consequently on the physical parameters of the optical fibers such as the optical losses and the dispersion effects. it is found that as the depth increases, the dispersion-free optical wavelength moves toward the third optical communication window, with a maximum value of the transmitted bit rate. over the range of depth from 1 km up to 5.5 km, iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 47 the maxima of the transmitted bit rates undergo an approximately flattened shape, where the maxima range is from 10 gbit/sec, at x=0.2 up to 45 gbit/sec at x=0.0 (pure silica). in the case of dispersion cancellation, clarified improvement of the transmitted bit-rate is found. iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 48 fig. 1 variations of br against variations of λ at the assumed set of parameters. fig. 2 variations of bw against variations of λ at the assumed set of parameters. fig. 3 variations of τ against variations of λ at the assumed set of parameters. fig. 4 variations of σ against variations of λ at the assumed set of parameters. iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 49 fig. 5 variations of br against variations of λ at the assumed set of parameters. fig. 6 variations of bw against variations of λ at the assumed set of parameters. fig. 7 variations of τ against variations of λ at the assumed set of parameters. fig. 8 variations of σ against variations of λ at the assumed set of parameters. iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 50 fig. 9 variations of λ0 against variations of d at the assumed set of parameters. fig. 10 variations of brmax. against variations of d at the assumed set of parameters. fig. 11 variations of br against variations of d at the assumed set of parameters. fig. 12 variations of bw against variations of d at the assumed set of parameters. iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 51 fig. 13 variations of τ against variations of d at the assumed set of parameters. fig. 14 variations of σ against variations of d at the assumed set of parameters. fig. 15 variations of t against variations of d at the assumed set of parameters. fig. 16 variations of p against variations of d at the assumed set of parameters. iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 52 fig. 17 variations of br against variations of d at the assumed set of parameters. fig. 18 variations of bw against variations of d at the assumed set of parameters. fig. 19 variations of τ against variations of d at the assumed set of parameters. fig. 20 variations of σ against variations of d at the assumed set of parameters. iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 53 fig. 21 variations of τ against variations of t at the assumed set of parameters. fig. 22 variations of σ against variations of at the assumed set of parameters. fig. 23 variations of τ against variations of t at the assumed set of parameters. fig. 24 variations of σ against variations of t at the assumed set of parameters. iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 54 fig. 25 variations of br against variations of λ at the assumed set of parameters. fig. 26 variations of bw against variations of λ at the assumed set of parameters. fig. 27 variations of br against variations of λ at the assumed set of parameters. fig. 28 variations of bw against variations of λ at the assumed set of parameters. iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 55 fig. 29 variations of br against variations of d at the assumed set of parameters. fig. 30 variations of bw against variations of d at the assumed set of parameters. fig. 31 variations of br against variations of d at the assumed set of parameters. fig. 32 variations of bw against variations of d at the assumed set of parameters. iium engineering journal, vol. 1, no. 1, january 2000 a. a. mohammed 56 references [1] p. k. runge, “undersea lightwave systems”, optics & photonics news, vol.1, no.11, pp.9-12, nov. 1991. [2] y. negishi, y. miyajima, o. kawata, and n. yoshizawa, “first sea trial of 1.5 m submarine optical fiber cable”, j. lightwave technol., vol.6, no.2, pp. 281-286, february 1988. [3] s. yamamoto, h. sakaguchi, m. nunokawa, and y. iwamoto, “1.55 m fiber –optic transmission experiments for long-span submarine cable system design”, j. lightwave technol., vol.6, no.3, pp. 380391, march 1988. [4] y. namihira, y. horiuchi, s. ryu, k. mochiruki, and h. wakabayash , “dynamic polarization fluctuations characteristics of optical fiber submarine cable under various environmental conditions”, j. lightwave technol., vol.6, no.5, pp. 728-738, may 1988. [5] j. thiennot, f. pirio, and j. b. thomine, “optical undersea cable system trends”, proc. ieee, vol. 81, no. 11, pp.1610-1622, nov.1993. [6] h. taga, n. edagawa, s. yamamoto, and s. akiba, “recent progress in amplified undersea systems”, j. lightwave technol., vol.13, no.5, pp. 829-840, may 1995. [7] n. s. bergano, “undersea lightwave transmission systems using er-doped fiber amplifiers”, optics & photonics news, pp. 9-14, january 1993. [8] m. sumida, s. furukawa, k. tanaka, and m. aiki, “high-accurate fault location technology using fsk-ask probe backscattering reflectometry in optical amplifier submarine transmission systems”, j. lightwave technol., vol.14, no.10, pp. 2108-2116, october, 1996. [9] m. murakami, t, takashi, m. aoyama, t. imai, m. amemija, m. sumida, and m. aiki, “system performance evaluation of the fsa submarine optical amplifier system”, j. lightwave technol., vol.14, no.12, pp. 2657-2671, december 1996. [10] j. adame and p. estenes, “iso 9000 and undersea fiber cable: meeting the standard makes a difference, “photonics spectra”, pp. 117-122, september, 1992. [11] m. murakami, t. imai, and m. aoyama, “a remote supervisory system based on subcarrier overmodulation for submarine optical amplifier systems”, j. lightwave technol., vol.14, no.5, pp. 617-677, may 1996. [12] g. ghosh, and h. yajima, “pressure-dependent sellmeier coefficients and material dispersions for silica fiber glass”, j. lightwave technol., vol.16, no.11, pp. 2002-2005, november 1998. [13] j. w. fleming , “dispersion in geo2-sio2glasses”, appl. opt., vol. 23, no. 24, pp. 4488-4493, 15 dec., 1984. [14] a. a. aoul-enein, “termal-dependent chromatic dispersion in lightwave system”, proc. 14 the intern. conf. statistics, computer science, social and demographic research, cairo egypt, vol.2, pp.195211, march 1989. [15] j. a. knauss, introduction to physical oceanography, 2/e, prentice hall, inc., u.s.a 1997. [16] l. b. jeunhomme, single-mode optical fiber, marcel dekker, inc., n.y., usa, 1983. [17] m. j. adams, an introduction to optical waveguides; john wiley & sons, n.y, usa 1981, ch.7. [18] s. s. walker, “rapid modelling and estimation of total spectral loss in optical fibers”, j. lightwave technol., vol. 4, no.8, pp.1125-1137, aug. 1996. [19] a. a. aboul enein, f. z. el-halafawy, m. h. a. hassan, a. a. mohammed, “thermal environmental effects”, alex. eng. j., alex. univ., vol.28, pp.169183, 1989. [20] cselet, turino, italy, optical fiber communications, 1/e, mcgraw-hill inc., usa, 1981. biography dr. a. a. mohammed was born in sohag, egypt, 1959. he has obtained his b.sc., m.sc., and ph.d. in electronic engineering, from faculty of electronic engineering, menouf, menoufia university, egypt, in 1986, 1991 and 1994, respectively. his interest is in the area of optical communications: optical sources, optical amplifiers, optical cables, optical networks, different propagation phenomena in different optical channels, etc. other area of interest is the computer-software using different languages and different techniques. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 185 effect of alkaline treatment on properties of rattan waste and fabricated binderless particleboard zuraida ahmad*, maisarah tajuddin, nurul farhana fatin salim and zahurin halim 1 department of manufacturing and materials engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. * corresponding author: zuraidaa@iium.edu.my (received: 18th oct 2017; accepted: 7th dec 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.879 abstract: binderless particleboard (bpb) has become an alternative to avoiding the usage of synthetic resin, possessing excellent properties but having low dimensional stability characteristics. hence, this study aims to investigate the effects of alkaline treatment on properties of rattan furniture waste (rfw) and fabricated bpb. the rfw was fully immersed in a 1% sodium hydroxide (naoh) solution for 10 minutes and dried in an oven at 35°c for two days. then, the treated rfw was used to fabricate the bpb via a hot-pressing process at pressing parameters of 180°c and 5 minutes. the colour of the rfw changed to dark yellowish and chemical analysis showed some reduction in hemicellulose, lignin and ash content after the alkaline treatment, which have been confirmed through peak decline in fourier transform infrared spectroscopy (ftir). only cellulose content increased after treatment due to a disruption of hydrogen bonding on the fibre surface. the treated bpb panels had improved mechanical and dimensional stability compared to untreated bpb panels, and achieved the minimum requirement of board standards. removal of the fibres’ impurities, led to tremendous physical consolidation among fibres. the nature of the panels changed from hydrophilic to hydrophobic as water molecules were released from the fibres during the treatment process. these results were supported by scanning electron microscopy (sem) analysis that displayed cleaner rfw fibres and rougher surfaces on the treated bpb panels. abstrak: papan partikel tanpa pelekat (papan bpb) menjadi salah satu alternatif bagi menggelak penggunaan pelekat sintetik, ianya mempunyai sifat-sifat terbaik walaupun keseimbangan dimensi papan masih berada pada tahap rendah. oleh itu, tujuan kajian ini dijalankan adalah bagi menyelidik kesan rawatan alkali ke atas sifat sisa perabot rotan dan papan bpb yang dihasilkan. sisa perabot rotan direndam penuh ke dalam cecair alkali natrium hidroksida (naoh) berkepekatan 1%, selama 10 minit dan sesudah itu dikeringkan di dalam ketuhar pada suhu 35°c selama dua hari. kemudian, sisa perabot rotan yang telah dirawat ini digunakan bagi menghasilkan papan bpb melalui kaedah tekanan haba pada suhu tekanan 180°c selama 5 minit. warna sisa perabot rotan telah berubah kepada kuning gelap, dan hasil analisa kimia menunjukkan pengurangan pada hemi-selulosa, lignin dan komposisi abu dalam serat rotan selepas rawatan alkali dan terbukti melalui pengurangan nilai puncak pada analisa fourier transform infrared spectroscopy (ftir). hanya kandungan selulosa meningkat selepas rawatan alkali, disebabkan gangguan pada ikatan hidrogen pada permukaan serat. papan bpb yang terhasil menggunakan serat dirawat telah menunjukkan peningkatan pada sifat mekanikal iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 186 dan keseimbangan dimensi papan, serta mencapai piawaian minima papan, berbanding dengan papan bpb yang terhasil menggunakan serat tidak dirawat. hal ini disebabkan pembuangan kotoran serat menghasilkan penyatuan fizikal yang sangat baik antara serat. sifat semulajadi pada papan bpb juga telah bertukar dari hidrofilik kepada hidrofobik, kerana molekul-molekul air dilepaskan dari serat semasa rawatan alkali. keputusan ini disokong melalui analisa mikroskop pengimbas elektron (sem) yang menunjukkan permukaan serat rotan rfw lebih jelas dan permukaan papan bpb yang lebih kasar. keywords: waste; treated; strength; dimensional stability; morphology 1. introduction particleboard is in high demand in many sectors due to cheaper, denser, and more uniform properties compared to conventional wood or plywood [1]. however, the use of synthetic resin inside the particleboard had raised concerns among manufacturers and users, as it is harmful to human health as well as the environment [2]. binderless particleboard (bpb) is pressed via heat treatment to trigger a self-bonding mechanism inside the fibres, by activating the chemical components of the fibres [2-4]. bpb comes as an alternative to current particleboards as it can be produced without using any synthetic resin, which is safer for human health and more environmental friendly. much innovative research on bpb has been conducted to transform waste into wealth, by utilising waste from natural fibres such as kenaf, bagasse, coconut husk, oil palm and many others [3-8]. there is a relatively high level of waste produced during the manufacture of rattan furniture [9, 10]. rattan furniture waste (rfw) has previously been disposed of by on-site incineration through open burning and illegal dumping that contribute to environmental issues, affect local and regional air quality, and eventually lead to global climate change [810]. there is an urgency to promote rfw by converting this waste into bpb, as rfw has good chemical constituents that are expected to produce good quality bpb. the main issue in bpb is the low dimensional stability characteristic, as natural fibres easily absorb moisture from surroundings [2, 4]. the bpb has a high tendency to change its shape, bend, and warp after a certain period of time. at the same time, the bare surface of the bpb, having no added resin, made the bpb fragile and easily degradable although having high strength properties. thus, alkaline treatment applied on the fibres might help to improve the properties of the fabricated bpb [8, 11]. it is hypothesized that the treatment process creates a rough surface on the fibres that enhances the bpb properties. alkaline treatment weakens and softens lignin bonds between the fibres, thereby producing less damaged and more flexible fibres [8, 11-13]. as far as we can conclude from the literature, no research has been conducted on the alkaline treatment of rfw. it is worth studying and analysing the impact of applied alkaline treatment on the rfw and properties of the fabricated bpb, which are believed to have significant effect to the rattan furniture industry in malaysia. therefore, the objective of this study is to investigate the effects of alkaline treatment on rfw including mechanical and dimensional stability properties of fabricated bpb. after undergoing alkaline treatment, the characterisations were conducted on rfw according to their physical, chemical and morphological properties. after that, the fabricated bpb was analysed based on japanese industrial standard (jis) a5908 [14], via bending, dimensional stability, and morphology tests. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 187 2. materials and methods the main material used for this project is rattan furniture waste (rfw) collected from a factory that manufactures rattan furniture as their main product, located in perak, malaysia. the rattan collected from the forest was first cooked using diesel in the factory area, in order to avoid fungi and insect attacks. then, the rattan was dried, separated, and sorted according to size. the rfw from manufactured furniture, which came in the form of chips and powder, were used in this research. the rfw was sieved using a manual sieve to separate all unnecessary materials such as large chips, dust, rubbish, and sand. 2.1 chemical treatment for rattan furniture waste the alkaline treatment was applied to the rfw in the form of chips, and the parameters used for this treatment were taken from a previous study [11]. sodium hydroxide (naoh) in pellet form was crushed using a white porcelain mortar until those pellets turned into fine particles. one gram of the naoh powder was added to 100 ml of distilled water, in order to produce a 1% of naoh solution. the solution was stirred until the naoh powder completely dissolved. the rfw chips were immersed completely in the 1% of naoh solution for 10 minutes. immediately after that, the chips were drained and washed using tap water. after that, the chips were stored in the oven at 35 °c for two days. 2.2 characterization of rattan furniture waste the rfw was characterised after being treated in alkaline treatment for comparison with untreated rfw. the characterisation done on untreated and treated rfw samples were for physical appearance, composition of material using a chemical test and fourier transform infrared spectroscopy (ftir) analysis, as well as a morphology test using sem. 2.2.1 chemical treatment for rattan furniture waste the chemical component test was prepared to discover the contents of lignin, hemicelluloses, cellulose, and ash, according to the methods listed in table 1. table 1: chemical test of rfw component method reference lignin klason lignin method 29 hemicellulose wise method 30 cellulose tappi 203 om-93 29 ash tappi 211 om-02 29 2.2.2 fourier transform infrared spectroscopy a perkin elmer spectrum 2000 spectrometer was used for the ftir analysis to determine the presence of a functional group at mode of 24 scans under resolution range of 550 to 4000 cm-1. the samples, in powder form, were inserted into the crystal spectrometer and the pressure arm was rotated clockwise until the “force gauge” reached 100. 2.2.3 morphology test of rattan furniture waste the morphological analysis was performed using scanning electron microscopy (sem) model jsm-560 at operating voltage of 7 kv. the samples used were non-conductive material, thus these samples were coated with palladium (pd), and were put on the iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 188 aluminium holder using double tape before being placed in the sem machine. observation of the samples’ morphology was then conducted. 2.3 fabrication of binderless particleboard (bpb) panels the untreated and treated rfw in chip form were blended to reduce them to the size of 50 µm that were sieved using an electronic sieve machine with a parameter of 10 mm amplitude for 30 minutes. the sieved powders were dried in an oven for 3 days at 31 °c before being used to fabricate the bpb. after that, the dried powder was put in a mould of 110 mm x 110 mm dimension, and subsequently pressed using a hot-press machine at a pressing temperature of 180 °c for 5 minutes. the fabricated bpb panels were labelled according to their types. 2.4 evaluation of panel properties these panels were prepared for property performance evaluation in terms of mechanical properties (three-point bending and internal bonding tests), dimensional stability properties (water absorption and thickness swelling tests), as well as their morphologies to validate the results from the tests. the panels were cut and labelled according to jis a5908 [14] depending on their type of test 2.4.1 three point bending test this test was performed to determine the strength of bpb panels through the modulus of rupture (mor) in eqn. 1. the measurement of panel width and thickness were taken before being placed in between two parallel supporting pins. the procedures were followed as described in the board standard, where the loading force of 10 mm/min per load was applied to the middle of the sample as in eqn. (1). 𝑀𝑂𝑅 (𝑀𝑃𝑎) = 3𝑃𝐿 2𝑏𝑡2 (1) where, p = maximum load (n), l = length of span (mm), b = panel width (mm), t = panel thickness (mm) 2.4.2 internal bonding test the panels were cut into a dimension of 50 mm x 50 mm, according to the board standard, where the width and thickness of the panels were measured. the device-testing metallic grip was covered with masking tape to prevent an over-gripped clamping onto the panel during testing. the vertical tension loading speed of 2 mm/min was applied, and the internal bonding (ib) was calculated using eqn. (2). 𝐼𝐵 (𝑀𝑃𝑎) = 𝑃′ 2𝑏𝐿 (2) where, p‘ = maximum load (n) at the time of failing force, b = panel width (mm), l = panel length (mm) 2.4.3 dimensional stability test the panels with a dimension of 50 mm x 50 mm were used to perform water absorption (wa) tests according to board standard. each sample was weighed (w1) using an electronic balance and thereupon the panels were fully immersed in the water for 24 hours. after that, the panels were taken out and dried on tissue paper for 10 minutes to remove excess water. the panels were weighed again, w2, and the wa was calculated using eqn. (3). iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 189 𝑊𝐴 (%) = 𝑤2−𝑤1 𝑤1 𝑥 100 (3) where, w1 = weight before immersion (g), w2 = weight after immersion (g) the same panels were used for the thickness swelling (ts) test. the thickness of each panel was measured at 4 different points at using a vernier calliper, and the average thickness was taken as t1. then, the panels were immersed in water, in a transparent beaker container at room temperature for 10 minutes. after 10 minutes, the panels were taken out from the beaker and the average thickness (t2) was measured at the same locations as the previous measurement. the ts was calculated using eqn. (4). 𝑇𝑆 (%) = 𝑡2−𝑡1 𝑡 𝑥 100 (4) where, t1 = thickness (mm) before immersion in water, t2 = thickness (mm) after immersion in water 2.4.4 morphology test the morphology test of the panels was carried out using a sem machine to observe the internal structure of the bpb, using the same procedures applied as above. 2. results and discussion 3.1 characterization of rattan furniture waste for a natural fibre composite, alkaline treatment is one of the most effective techniques to modify the surface of the fibre. previous studies [15-20] described the treatment, applied sodium hydroxide (naoh) at different concentrations, to have diverse effects on the fibre surface. high concentration of alkali caused deterioration to the fibres, which was proven by the occurrence of holes seen in sem micrographs [19, 20]. alkaline treatment eradicates impurities on the fibres such as hemicelluloses, lignin, and pectin, yet it surges the degree of crystallization of cellulose that results in a roughened surface on the fibres [11, 21, 22]. figure 1(a) and 1(b) show the original colour of the rfw taken from the furniture factory and the rfw after alkaline treatment, respectively. the colour changed after the rfw underwent alkaline treatment, from light yellow to dark yellowish, which was proof of a chemical modification occurring during alkaline treatment. this change was in agreement with a previous study [11] that stated that degradation products from hemicelluloses caused darker tonality to the material used. fig. 1: pictures of (a) untreated and (b) treated rfw fibres. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 190 table 2: chemical composition of untreated and treated rfw chemical composition untreated rfw (%) treated rfw (%) lignin 21.0 18.4 hemicellulose 45.6 31.0 cellulose 34.3 38.5 ash 5.4 3.5 table 2 lists the chemical composition of the main components in the untreated and treated rfw. lignin, hemicellulose, and ash content decreased after the alkaline treatment. the hygroscopicity properties of the fibres decreased significantly as the hemicellulose content was removed by almost 32% from the original content, thus affecting properties of the bpb panels and improving its dimensional stability [11,17]. furthermore, mechanical interlocking of fibres improved by removing impurities through the alkaline treatment [22]. although lignin plays an important role in producing bpb panels with good properties, the removal of lignin was replaced by other factors that contributed to binding the fibres together such as physical consolidation or mechanical interlocking after the treatment process [22,23]. this analysis also indicated that cellulose content increased by about 10.9% from the original cellulose content of the untreated rfw. this resulted in an increased degree of crystallization of fibres resulting in fabricated panels that have good strength [23,24]. all these factors significantly contributed to improving properties of the fabricated bpb panels in terms of their mechanical and physical characteristics. fig. 2: comparison of ftir spectra of untreated and treated rfw. table 3: comparison of ftir spectra of untreated and treated rfw wave number (cm-1) ftir band position 3337 o-h stretching, cellulose, hemicellulose, lignin, pectin 1646 c=o stretching, acetyl and carboxyl group of hemicellulose 1329 alcohol group of cellulose oh deformation 1245 hemicellulose, pectin, epidermal waxy tissue 1241-1003 c-o-c symmetric, polysaccharides mainly cellulose 997 c-o stretching, vibration of cellulose and hemicellulose 771 lignin components iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 191 the infrared spectra of the untreated and treated rfw samples were assessed by ftir spectroscopy, as demonstrated in fig. 2, whereas the obtained band positions are explained in table 3. there were significant differences in infrared spectra for the rfw after alkaline treatment. the band at 3337 cm-1 was assigned to o-h stretching vibration of cellulose, hemicellulose, lignin, and pectin structures [11, 17, 20]. alkaline treatment weakened this band’s intensity due to removal of those constituents. meanwhile, the band at 1646 cm-1 decreased due to removal of c=o stretching vibration of acetyl and carbonyl groups of hemicellulose [17, 20, 24]. the finding of decreased intensity at 1329 cm-1 is consistent with alkaline treatment carried out by ramadevi and his team [17]. it is associated with an alcohol group of cellulose oh deformation. the band position of 1245 cm-1 shows a peak decline, indicating the removal of hemicellulose, pectin, and epidermal waxy tissue [11, 17]. the c-o-c symmetry arises at the band position of 1241 cm-1, containing polysaccharides, mainly cellulose [23]. the vanishing band position at 997 cmis explained by the removal of cellulose and hemicellulose due to c-o stretching vibration subjected to the alkaline treatment [11]. at band 771 cm-1, the ch bond is out of plane demonstrating the elimination of lignin during the alkaline treatment. fig. 3: pictures of untreated (left) and treated (right) rfw at 200x magnification. figure 3 displays the micrograph of the untreated and treated rfw for sem analysis under 200x magnification. the untreated rfw in fig. 3(a) shows vascular bundles (vb) and parenchyma cells that were covered with the fibres’ main constituents, consisting of hemicelluloses, cellulose, lignin, pectin, and other impurities. there was a wide metaxylem vessel along with numerous protoxylem vessel elements amongst the vascular bundles [25]. in fig. 3(b), the treated rfw exhibited cleaner fibres and increased cell walls indicating that alkaline treatment had washed away impurities and removed cell wall components that were stuck in vascular bundles [17, 23-26]. these made the vascular bundles become more visible and the fibre surface rougher. the treatment process required the rfw to be immersed in the solution where the fibres absorbed some solution and thus had a higher swelling level that increased the particle sizes with more flexible fibres [11]. the rough surfaces helped mechanical interlocking due to the release of the hydroxyl groups on the fibre surface, thus increasing the fibre-fibre bonding [22]. the treatment also changed the cellulose structure that increased the degree of crystallization with tighter chain packaging so the rfw drastically absorbed less moisture [23, 24]. this resulted in improved mechanical properties with better dimensional stability for the fabricated bpb. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 192 3.2 properties evaluation of bpb panels the fabricated bpb panels were evaluated based on their properties of strength, internal bond, dimensional stabilities, as well as their morphologies. there was an obvious colour change for the treated bpb panel made from treated rfw, which had a darker colour compared to the untreated bpb panel. 3.2.1 effects of alkaline treatment on mechanical properties of panels the strength of the bpb panels is identified using static bending to reflect the bpb behaviour by determining the modulus of rupture (mor) of the panels [23]. figure 4 displays the graph of the untreated and treated bpb panels with mor values of 28.5 mpa and 44.4 mpa, respectively. both bpb panels meet the minimum requirement of the board standard, which is 18.0 mpa [14]. in previous work [2, 3, 7, 11], they found out that bonding mechanisms of boards are attributable to chemical bonding and physical consolidation amongst fibres, along with thermoplastic flow of natural binders inside fibres. as sufficient heat was applied to the fibre during the hot-pressing process, the lignin inside the fibres melted and flowed to the surface of the fibres. lignin acts as a natural binder, distributed amongst fibres hence producing a bpb of good strength [4]. it is important to note that adequate heat applied with sufficient pressing pressure and optimum pressing time are required as vital parameters in fabricating bpb [3, 7]. the mor value of the treated bpb panel increases 35.8% compared to the mor value of untreated bpb, which is in agreement with previous studies [11, 19]. the main components of rfw are cellulose, hemicellulose, and lignin [25]. alkaline treatment removes these constituents from the fibres and cause rougher fibre surfaces [11, 26]. furthermore, this treatment reduces the diameter of the fibres resulting in increased aspect ratios [24, 27]. apparently, these two factors of rougher fibre surface and bigger aspect ratios enhance mechanical interlocking and bonding reaction between the fibres. the amount of crystalline cellulose on the fibres also increased [23], leading to improvement in mechanical properties due to interruption of hydrogen bonding on the fibre surfaces. fig. 4: graph of modulus of rupture (mor) for untreated and treated bpb panels. figure 5 shows the graph of internal bonding (ib) of the untreated and treated bpb panels, where the ib of the untreated and treated bpb is 0.26 mpa and 0.44 mpa, respectively. the ib test was conducted to determine the internal bond of fibres in the fabricated bpb panels. the minimum requirement of ib value according to jis a5908 [14] is 0.30 mpa, where only the treated bpb panel met the requirement. the ib value of the treated bpb panel improved by about 40.9% compared to the untreated bpb panel that also iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 193 contributed to tremendous mechanical properties in the bpb panels. rfw is categorised as a natural fibre that has high hygroscopic properties due to the presence of the hydroxyl group and other polar groups in fibre components [23, 24, 28]. therefore, this resulted in poor wettability and weak interfacial bonding between the fibres. on the other hand, the hydrogen bonding on the fibres’ surfaces were disrupted through the alkaline treatment, where it also increased the cellulose crystallinity of the fibres that contributed to increasing the surface roughness of bpb panels [22, 24, 28]. results additionally suggested that this disruption condition facilitates mechanical interlocking between fibres. fig. 5: graph of internal bonding (ib) for untreated and treated rfw bpb. 3.2.2 effects of alkaline treatment on dimensional stabilities of panels the dimensional stabilities in terms of water absorption (wa) and thickness swelling (ts) of bpb panels are illustrated in fig. 6. the percentage of wa for the untreated and treated bpb panels are 54.5% and 42.9%, while the percentage of ts for the untreated and treated bpb panels are 19.6% and 6.8%, respectively. the standard jis a5908 set the normal type-18 particleboard at no more than 12% ts, which means the treated bpb panel achieved the standard requirement [14]. one of the components that is responsible for the hygroscopic properties of the rfw and natural fibres is hemicellulose. fibre hemicellulose have been removed by chemical modification throughout the alkaline treatment [11, 17, 25], thus decreasing the percentage of wa and ts of the bpb panels. in addition to that, the treatment destroyed the hydroxyl group on the fibre surfaces such that the fibres had less affinity to water [24]. as previously reported by esteve and pereira [23], the chemical modification leads to high cellulose cross-linking where molecules become less elastic, so micro-fibrils have less possibility to expand and absorb water. therefore, the alkaline treatment has improved dimensional stabilities of the treated bpb panels, a fact that was verified in the great strength and excellent ib properties of the bpb panels. the mechanism of the alkaline treatment is demonstrated in fig. 7, where the hydrophilic properties of the fibres were turned into hydrophobic properties as the water molecules were released from the fibres during the treatment process [17, 24, 25, 27]. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 194 fig. 6: graph of dimensional stability of untreated and treated bpb samples. fig. 7: mechanism of alkaline treatment process. 3.2.3 effects of alkaline treatment on morphology of panels the sem analysis was conducted to observe the surface morphology of the fabricated bpb panels made from the untreated and treated rfw, as illustrated in fig. 8. it clearly showed that the fibres were completely compressed when heat and pressure were applied in the hot-pressing process [3, 4, 7]. the untreated bpb panel in fig. 8(a) had a smooth surface attributable to the good fluidity of lignin to fibre surface when the heat was applied to the fibres. lignin acts as a natural binder in the fabrication process of bpb panels [4]. however, the treated bpb panel in fig. 8(b) had rough surface that was obvious to the naked eye, as alkaline treatment removed various constituents inside the fibres [20-26]. fibres attached closely to each other without impurities at the fibre surfaces, increasing interlocking strength between the rfw fibres. this observed figure is evidence of removal of chemical components inside the fibre after the alkaline treatment process, as explained in the previous sub-section. fig. 8: sem micrographs of untreated and treated bpb. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 195 4. conclusion  the alkaline treatment removed impurities consisting of hemicellulose, lignin, ash, and pectin, which was proven through observed change in colour, chemical tests, and ftir analysis.  sem micrographs of the rfw illustrated cleaner and rougher fibres after the alkaline treatment, which helped in improving the mechanical interlocking between the fibres.  the treated bpb panels met the requirements of the board standard especially in terms of thickness swelling.  removal of hemicellulose was responsible for the reduction of hygroscopic properties of the fibres.  the hydrogen molecules were disrupted and released during the alkaline treatment which reduced the moisture absorption by the fibres. acknowledgements the authors wish to thank the ministry of higher education, malaysia for financial support of sponsorship scheme of grant no. frgs15-206-0447, and the lecturers and technicians at the international islamic university malaysia (iium) for the help and facilities provided. references [1] ganiron tuj. (2013) an investigation of moisture performance of sawdust and banana peels ply board as non-veneer panel. international j. of uand eservice, science and technology, 6(3):43-54. [2] hashim r, wan nadhari ws, sato mo, hiziroglu s, kawamura f, sugimoto t, seng tg, tanaka r. (2012) properties of binderless particleboard panels manufactured from oil palm biomass. bioresources, 7(1):1352-1365. [3] quintana g, velasquez j, betancourt s, ganan p. (2009) binderless fiberboard from steam exploded banana bunch. industrial crops and products, 29(1):60-66. [4] okuda n, sato m. (2004) manufacture and mechanical properties of binderless boards from kenaf core. j. of wood science, 50(1):53-61. [5] xu j, widyorini r, yamauchi h. (2006) development of binderless fibreboard from kenaf core. j. of wood science, 52(3):236-243. [6] panyakaew s, fotios s. (2011) new thermal insulation boards made from coconut husk and bagasse. energy and buildings, 43(7):1732-1739. [7] zhou rx, zheng f, li h, lu c. (2010) an environment-friendly thermal insulation material from cotton stalk fibers. energy and buildings, 42(7):1070-1074. [8] luo p, yang c. (2012) production of binderless particleboard using rice straw pre-treated with liquid hot water. applied mechanics and materials, 200:331-334. [9] olorunnisola ao, adefisan oo. (2001) trial production and testing of cement-bonded particleboard from rattan furniture waste. wood and fiber science, 34(1):116-124. [10] olorunnisola ao. (2004) briquetting of rattan furniture waste. j. of bamboo and rattan, 3(2):139-149. [11] geng x, zhang sy, deng j. (2006) alkaline treatment of black spruce bark for the manufacture of binderless fiberboard. j. of wood chemistry and technology, 26:313–324. [12] das s, saha ak, choudhury pk, basak rk, mitra bc, todd t, lang s, rowell rm. (2001) effect of steam pre-treatment of jute fibre on dimensional stability of jute composite. j. of applied polymer science, 76(11):1652-1661. [13] corradini e, morais l, rosa m, mazzetto s, mattoso l, agnelli j. (2006) a preliminary study for the use of natural fibres as reinforcement in starch-glutten-glycerol matrix. macromolecular symposia, 245-246: 558-564. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 196 [14] jis a5908 particleboards (2003) japanese standards association, tokyo, japan, pp 1-24. [15] silverstein ra, chen y, sharma-shivappa rr, boyette md, osborne j. (2007) a comparison of chemical pretreatment methods for improving saccharification of cotton stalks. bioresource technology, 98(16):3000-3011. [16] rokbi m, osmani h, imad a, benseddiq n. (2011) effect of chemical treatment on flexure properties of natural fiber-reinforced polyester composite. procedia engineering, 10:20922097. [17] ramadevi p, sampathkumar d, srinivasa cv, bennehalli b. (2012) effect of alkali treatment on water absorption of single cellulosic abaca fiber. bioresources, 7(3):35153524. [18] pelaez-samaniegoa mr, yadamac v, garcia-pereza m, lowelle e. (2015) abundance and characteristics of lignin liquid intermediates in wood (pinus ponderosa dougl. ex laws.) during hot water extraction. biomass and bioenergy, 81:117-128. [19] machaka m, basha h, chakra dha, elkordi a. (2014) alkali treatment of fan palm natural fibers for use in fiber reinforced concrete. european scientific j., 10(12):186-195. [20] xia z, li xxj. (2010) effect of alkaline treatment of straw fiber on mechanical properties of cement-bonded straw fiber board. in mechanic automation and control engineering (mace), international conference ieee: 26-28 june 2010; wuhan, china; pp. 3006-3008. [21] gonzalez-murillo c, ansell mp. (2009) mechanical properties of henequen fibre/epoxy resin composites. mechanics of composite materials, 45:435-442. [22] yan l, chouw n, yuan x. (2012) improving the mechanical properties of natural fiber fabric reinforced epoxy composites by alkali treatment. j. of reinforced plastic and composites, 31(6):425-437. [23] esteves bm, pereira hm. (2009) wood modification by heat treatment: a review. bioresources, 4(1):370-404. [24] cyras vp, vallo c, kenny jm, vazquez a. (2004) effect of chemical treatment on the mechanical properties of starch-based blends reinforced with sisal fibre. j. of composite materials, 38(16):1387-1399. [25] ebanyenle e, oteng-amoako aa. (2003) anatomy and identification of five indegeneous rattan species of ghana. ghana j. forestry, 11(2):77-90. [26] srinivasa cs, suresh yj, prema kwp. (2012) mechanical behaviour of areca fiber reinforced epoxy composites. advanced polymer technology, 31(4):319-330. [27] channalli m, siddeswarappa db. (2015) effect of alkali treatments on natural filler content performance of polymer composites. international j. of engineering research & technology (ijert), 4(10):11-16. [28] kabir mm, wang h, aravinthan t, cardona f, lau kt. (2011) effects of natural fiber surface on composite properties: a review. in 1st international postgraduate conference on energy, designing and developing the built environment for sustainable wellbeing (eddbe2011) proceedings: 27-29 april 2011; brisbane, australia; pp. 94-99. [29] tappi standards and suggested methods. tappi press, atlanta, ga, usa. [30] wise le, murphy m, d’addieco aa. (1946) chlorite holocellulose, its fractionation and bearing on summative wood analysis and on studies on the hemicellulose. paper trade j., 122(2):35-43. microsoft word amin-2.doc iium engineering journal, vol. 3, no. 1, 2002 n. amin and a. k. sarder 17 influence of work and tool materials on parameters of electrical discharge machining (edm) a.k.m.n. amin* and a.k. sarder** *department of mechanical engineering, international islamic university malaysia **department of industrial and production engineering, bangladesh university of engineering and technology, dhaka-1000, bangladesh, email: akamin@iiu.edu.my abstract influence of the properties of work and tool materials on material removal rate (mrr), tool wear ratio (twr), thickness of the recast layer, surface roughness and accuracy of machining in edm process has been investigated. copper brass, stainless steel, mild steel and grey cast irou have been used in various combinations as work and tool materials. from the experimental results it is found that mrr slows down with machining time. apart from that it has been found that mrr and twr are inversely proportional to the melting points of the work and tool materials respectively. electrical conductivity of the tool material also has appreciable influence on tool wear ratio. wear ratio was found to be minimum in the case of the copper electrode having maximum electrical conductivity. it has been also observed that for all combinations of work and tool materials, a recast layer is formed on the machined surface. it has been observed that the micro cavities formed in the cases of lower melting point electrode materials like copper and brass having higher electrical conductivity are comparatively smaller in size (2-3 m) as compared to the sizes of the micro cavities (8-20 m) formed in the cases of high melting pointer electrodes having also lower electrical conductivity. consequenty the machined surface roughness produced in the latter cases is higher. it has been also observed that the debris concentration increases due to side sparking of the electrode. the tendency of debris concentration is the maximum at the middle of the tooljob interface resulting in high bottom surface inaccuracy, specially when high melting point work materials are machined with electrodes like brass having low melting point and relatively lower electrical conductivity. from the point of view of mrr, brass electrodes have been found to be the most suitable tool, but from the point of view of machining accuracy and surface finish copper electrodes were found to yield the best result for the given set of job materials. so it was concluded that brass electrodes should be recommended for rough machining and copper electrodes for finish machining of the given work materials. 1. introduction with the advancement of science and technology new materials and alloys with high mechanical properties are emerging for applications in various sectors of the industry. the new materials are known for their poor machinability and require special techniques for machining. electrical discharge machining (edm) is one of the earliest non-traditional manufacturing processes successfully employed for machining of most of these materials. the process is mainly applied for final machining of die surfaces. the materials of dies for various applications are stainless steel or various grades of alloy steels. effective application of the edm process for machining of these materials depends on correct choice of the job-electrode materials combination and proper selection of current and voltage parameters. right selection would lead to higher material removal rate, accuracy, surface roughness and surface integrity of the work piece. the main objective of the work was to determine the appropriate tool materials for machining various work materials on the basis of material removal rate, tool wear, machining accuracy, job surface roughness and thickness of the recast layer. 2. experimental procedure experiments were conducted on electrical discharge machine, model no-18401, employing pulse generator and electromechanical type servo motor for spark gap control (figure 1). brass, copper, mild steel, stainless steel and cast iron were used as electrode as well as work piece materials in various combinations during the experiments. machining was performed at right angle to the job surface. kerosene was used as the dielectric fluid. depth of the cavity machined was measured using a dial gauge having micrometer scale readings and tool wear was measured using an instrument microscope after a fixed interval of machining. from these data the material removal rate (mrr) and the wear ratio (w.r) were calculated. calculation of material removal rate was based on the measurement of volume loss of work material per minute of machining time. the thickness of the recast layer (rl) was measured on a metallographic microscope. the wear ratio of the electrode is defined as the percentage of volume of electrode wear per unit volume of material removal in the same machining interval. the average surface roughness of the machined surface was measured on a surface roughness measuring instrument model sulftest ab.5. iium engineering journal, vol. 3, no. 1, 2002 n. amin and a. k. sarder 18 figure 1: electrical discharge machine, model no18401 2.1 condition and assumption of the experiment from the earlier theoretical investigations it was observed that tool wear ratio, material removal rate and job surface roughness depend on electrical conductivity and melting points of the work and tool materials, current polarity, gap between the electrode and the work piece, etc. influence of the magnetic properties on the tool wear was neglected throughout the investigation. influence of dielectric flow on material removal rate was eliminated by employing only immersion type fluid flow. following assumptions were made during the study: (a) temperature and pressure of dielectric fluid were constant. (b) formation of the recast layer on the machining surface occured at steady state condition. (c) current consumption was constant throughout the whole study. (d) particles were eroded uniformly from the electrode. machining conditions feed rate (f): 0-1 mm/min (servo control) gap voltage (v): 23 v. peak current (i) :0.4-0.5 a total machining time (t): 225 mins. 3. experimental results 3.1 material removal rate (mrr) curves of cumulative material removal versus machining time were plotted for various combinations of job and tool materials. from these curves the rate of metal removal were calculated and bar charts are plotted (fig.1). it may be observed from fig. 1 that the mrr for brass, copper and mild steel is the highest for brass tool; whereas in the cases of stainless steel and cast iron, copper and cast iron tools respectively show the highest metal removal rate. the job materials may be placed in the descending order of their average mrr as follows: brass, cast iron, copper, mild steel and stainless steel. it may be observed from figure 1 and table1 that the average mrr for brass having the lowest melting point is the higest. the average mrr for cast iron and copper having relatively lower melting points are also relatively higher. at the same time the average values of mrr for mild steel and stainless steel having higher melting points are relatively lower. this may be associated with lower energy requirement for material removal during edm bombardment in the cases of lower melting point materials. 3.2 tool wear ratio the tool wear ratio is defined as the ratio of the volume of electrode wear to the volume of work material removed. the relationship of tool wear ratio for the given job material and tool material combination is shown in figure 2. minimum wear ratio is observed in the case of copper electrode, while the maximum ratio is obserded in the case of brass electrode for all the combinations of tool and work materials. copper electrodes show lower wear ratio than other electrodes due to their higher electrical conductivity and consequently more efficient table 1: melting points of the job/tool materials. number job/tool material melting point (approximate), 0 c 1 brass 1000 2 copper 1085 3 cast iron 1200 4 stainless steel 1420 5 mild steel 1500 iium engineering journal, vol. 3, no. 1, 2002 n. amin and a. k. sarder 19 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 m at er ia l r em ov al r at e, cu m m /m in a b c d e brass copper s. steel m. steel cast iron fig. 1: material removal rate for different combinations of job materials (a, b, c, d, e) and tool materials 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 t oo l w ea r r at io a b c d e brass copper s. steel m. steel cast iron fig. 2: tool wear ratio for different combinations of job materials (a, b, c, d, e) and tool materials. bombardment on the work material surface by electrons during the edm process. higher wear ratio of brass electrodes is associated with the lower melting point of brass. the electrode particles eroding at a lower temperature require less energy. figure 2 also shows that the ratio is less than one or in other words the mrr is higher than the wear rate of the electrodes. this is associated with the direct polarity used in the process, in which the tool acts as the cathode, causing bombardment of the anode (work piece) by electrons. since the bombardment caused by the electrons has higher energy than the bombardment caused later by job materials: a: brass, b: copper, c: stainless steel, d: mild steel, e: cast iron job materials: a: brass, b: copper, c: stainless steel, d: mild steel, e: cast iron tool materials: tool materials: iium engineering journal, vol. 3, no. 1, 2002 n. amin and a. k. sarder 20 ions and particle from the vaporized anode (job materials), the mrr is higher than that of tool wear. 3.3 recast layer (rcl) metallographic specimens of the middle section of the machined specimens were prepared. a sample of the micro-photographs showing the recast layer is illustrated in figure 3. fig. 3: recast layer. job material: mild steel, tool material: stainless steel. thicknesses of the recast layers on the machied surface for different combinations of the tool and work piece materials are represented in figure 4. this layer is also termed as the white layer due to its appearance since it is unetchable and can be easily identified. the repetitive sparks release energy in the form of local bombardment. as a result local temperature reach an extremely high value at the spot of electrical discharge causing the metal particles to melt and vaporize. these particles are subsequently flushed away by dielectric medium. some droplets of the particles are trapped and then solidified on to the previously eroded surface to form a rcl. this layer is chromatically different from the original surface when observed with polarized light and viewed under the microscope. since the electrode is fed vertically from the top into the work piece it prevents the dielectric from effective flushing of the particles at the bottom of an edm hole. as a result these particles are deposited on to the surface ensuring the reinforcement of the recast layer. figure 4 shows that in all cases, the brass electrodes form a rcl of higher thickness than other electrodes. it may be explaind by the fact that the particles which are eroded from brass electrode having higher density of heat are able to penetrate to higher thickness of job materials. any molten metal which is not expelled during the process is resolidified to form a hard skin on the surface. thermal stress, plastic deformation and shrinkage result in residual tensile stresses. directly beneath the hand skin is a heat affected zone, which is the case with the heat treated materials. this layer is softer than the parent metal due to a loss of hardness of the hardened metal. on the contrary the hardness of the recast layer is higher than the base material hardness, which leads to longer life of the product. this layer has also higher lubricant retaining properties as are desirable for dies [4]. 0 0.5 1 1.5 2 2.5 3 t hi ck ne ss o f r ec as t l ay er , u m a b c d e brass copper s. steel m. steel cast iron fig. 4: recast layer thickness for different combinations of job materials (a, b, c, d, e) and tool materials. tool materials: 2 m job materials: a: brass, b: copper, c: stainless steel, d: mild steel, e: cast iron iium engineering journal, vol. 3, no. 1, 2002 n. amin and a. k. sarder 21 0 5 10 15 20 25 30 35 40 45 a ve ra ge s u rf ac e r ou gh n es s, u m brass copper s.s. m.s. c.i. job materials tool materials brass copper s.s m.s. c.i. fig. 5: machined surface roughness attained for different work-tool material combinations. 3.4 surface finish and micro size cavities the surface roughness produced on the work piece, as shown in figure 5, is higher in the cases of cast iron, mild steel and stainless steel and quite low in the cases of copper and brass. it is associated with the lower micro size cavities (2-3 m), formed on the machined surface by the brass and copper electrodes as compared to the cavities (8-20 m) formed by the other three materals. larger cavity sizes in the cases of electrode materials with high melting point and low electrical conductivity may be related to higher amount of electrical energy that has to be accumulated for the electrical discharge to take place in these cases. on the other hand for electrodes with higher electrical conductivity electrical discharge takes place more frequently with lower accumulation of charge causing lower metal removal during each spark discharge. so the metal removal rate being high in the latter case, the cavity size remains small. 3.5 accuracy of the machined surfaces figure 6 reveals the conical shape of the finished hole. this is due to higher duration of exposure of the side surface of the work piece to the sparking process. the tendency of debris to concentrate at the middle of the tool-work interface results in high bottom surface inaccuracy when the duration of machining is high. a convex shape is imparted to the bottom surface of the cavity specially when higher melting point materials like mild steel are machined with tools like brass having lower melting point (fig. 6a). a): tool: brass iium engineering journal, vol. 3, no. 1, 2002 n. amin and a. k. sarder 22 b): tool: copper fig. 6: the cross sectional view of the machined surface produced on mild steel by brass (a) and copper (b) electrodes. this may be related to the fact that the bottom portion of the tool-work interface does not get effective circulation of the dielectric fluid and gets heated up. at an elevated temperature the low melting point electrode (brass) starts eroding out at a faster rate than the high melting point job material leading to a concave shape of the tool at its bottom surface and a corresponding convex shape to the mating job surface. but when high thermal conductivity material like copper is used as electrode material the out of flatness on the job bottom surface is almost absent because the the tool middle portion and the side surfaces are equally cooled. so in the case of copper electrode the bottom surface is almost flat and side taper is also low, which leads to the more accurate shape of cavity as compared to other electrodes. 4. conclusions from the experimental results and analysis the following conclusions may be drawn: 1. material removal rate offered by brass electrode is the highest in the cases of machining brass, copper and mild steel and also maintains high values in the cases of stainless steel and cast iron. copper electrodes offer higher metal removal rates than brass in the cases of the last two materials. 2. tool wear per unit volume of job material removal (tool wear ratio) is the highest in the case of brass electrode and lowest in the case of copper electrode for all the investigated work piece materials. the remaining thre materials occupy intermediate positions with respect to tool wear ratio. 3. from the point of view of machined surface roughness the tool materials may be ranked in the ascending order as follows: brass, copper, stainless steel, mild steel and cast iron. 4. with regard to debris concentration and accuracy of machining copper is the best tool ad brass is the worst, specially for high melting point job materials. 5. for all the investigated job materials tool materials may be ranked with respect to the thickness of the recast layer formed on the machined surface, in the descending order as follows: copper, brass, stainless steel, mild steel and cast iron. 6. brass electrode offering the highest rate of metal removal may be recommended for rough edm machining of brass, copper and mild steel and copper electrode for rough machining of stainless steel and cast iron and also finish machining of all the investigated materials because of its minimum wear ratio and the highest accuracy of machining. references: [1] s.l. s. mandal,. and s. m. raiskii, "mechanism of electro-erosion of metals", izvestya akademii nauk sssr, moscow (ussr), vol.13, pp.549-565, 1949. [2] v.p aleksandrov, “residual stresses and long term fatigue strength of heat resistant materials after electro-spark machining”, electro spark machining of metals, vol. 3, 1958, consultants’ bureau, newyork, 1958. [3] m.m. barash, "effects of edm on the surface properties of tool & die steels", metals eng. quart, asme, pp.48-51, 1965. [4] k. p. rajurka and s. r. nooka, "surface finish of edm machine components", int. conf. on advanced manufacturing technology, johor, malaysia, 29-30, 1994. [5] p. k madan and r. sagar, "the electrical discharge machining of 6061l/sicp composites", int. conf. on advanced manufacturing technology, johor, malaysia, pp.163-171, 29-30, 1994. 5. nomenclature its intelligent transportation systems gsm global system for mobile communication drgs dynamic route guidance system gps global positioning systems bs base station plmn public land mobile network ta timing advance iium engineering journal, vol. 3, no. 1, 2002 n. amin and a. k. sarder 23 ab access burst glp geographical location parameter rsa relative signal arrival 6. biography 314 iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 173 controller design of unicycle mobile robot m.z. ab rashid and s.n. sidek department of mechatronics engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. iruz_maz@yahoo.com abstract: the ability of unicycle mobile robot to stand and move around using one wheel has attracted a lot of researchers to conduct studies about the system, particularly in the design of the system mechanisms and the control strategies. this paper reports the investigation done on the design of the controller of the unicycle mobile robot system to maintain its stability in both longitudinal and lateral directions. the controller proposed is a linear quadratic controller (lqr) type which is based on the linearized model of the system. thorough simulation studies have been carried out to find out the performance of the lqr controller. the best controller gain, k acquired through the simulation is selected to be implemented and tested in the experimental hardware. finally, the results obtained from the experimental study are compared to the simulation results to study the controller efficacy. the analysis reveals that the proposed controller design is able to stabilize the unicycle mobile robot. abstrak: kemampuan robot satu roda untuk berdiri dan bergerak di sekitar telah menarik minat ramai penyelidik untuk mengkaji sistem robot terutamanya didalam bidang rangka mekanikal dan strategi kawalan robot. kertas kajian ini melaporkan hasil penyelidikan ke atas strategi kawalan robot bagi memastikan sistem robot satu roda dapat distabilkan dari arah sisi dan hadapan. strategi kawalan yang dicadang, menggunakan teknik kawalan kuadratik sejajar (linear quadratic control) yang berdasarkan model robot yang telah dipermudahkan. kajian simulasi secara terperinci telah dijalankan bagi mengkaji prestasi strategi kawalan yang dicadangkan. dari kajian simulasi sistem robot, pemilihan faktor konstan, k yang sesuai di dalam strategi kawalan telah dibuat, agar dapat dilaksanakan ke atas sistem robot yang dibangunkan. keputusan dari kajian simulasi dan tindak balas oleh sistem robot yang dibangunkan akhirnya dibandingkan bagi melihat kesesuaian faktor kostan, k yang dipilih. analisa menunjukkan dengan menggunakan strategi kawalan yang dicadangkan dapat menstabilkan robot satu roda. keywords: unicycle mobile robot; nonholonomic system; lqr 1. introduction unicycle mobile robot is a robot that can move and maneuver around using a single wheel. the advantage of the robot is its mechanism to stand upright without falling down either in the longitudinal or lateral directions within a small space has attracted many researchers to conduct studies on the system. the studies cover from the modeling of the system, designing and prototyping the mechanism, and the controller design. the way a human rides a unicycle has inspired many researchers. the rider of unicycle could stabilize his position by moving his two arms, wrist and body in unison. meanwhile, the pitch angle is stabilized by pedalling the unicycle by using the two legs back and forth, in order to control the speed and the position of the wheel. besides that, the yawing angle iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 174 of the unicycle is stabilized by rotating the left and the right hands synchronously. as a result from this, the researchers have proposed different models of unicycle mobile robot based on their assumptions on the way human rides a unicycle. along with that, they have also proposed a few types of mechanisms and controllers to stabilize unicycle mobile robot. from the exploratory and intensive research conducted by other researchers earlier, different mechanisms of unicycle mobile robot have been proposed. basically, in this paper, the proposed unicycle mobile robot system consists of a wheel, a frame and a rotating disc as mentioned in [1]. the three-dimensional (3d) unicycle robot system can be characterized by the three tilt angles namely the roll, the pitch and the yaw angles. this robot can reach longitudinal stability through appropriate control of the wheel (i.e. the control of pitch angle). it also can reach the lateral stability via applying appropriate torque generated by the rotating disc (i.e. the control of roll angle). the main problem of the research is to control the unicycle mobile robot especially when the posture of the robot needs to be stabilized upright, both whenever the robot is moving or when it is in the still mode. the posture of the robot can be characterized by three tilt angles namely the roll angle that is the lateral tilt angle which is perpendicular to direction of motion, the pitch angle or known as longitudinal tilt angle which is parallel to the direction of motion and lastly the yaw angle. thus, the problem in the research work can be stated as to develop a unicycle mobile robot that can be stabilized by using proper controller based on the operation of the inverted pendulum system autonomously. this is to ensure the unicycle system can stay uprights without falling down longitudinally or laterally. a specific mathematical model of the system developed could lead to multiple ways to construct the robotic platform. on top of that, the system controller is designed and simulated as well as implemented in the real system hardware. in the following, an overview of works done in this field is mentioned in section-2. the dynamic modeling of the unicycle mobile robot is addressed in section-3. section-4 elaborates the controller design. the simulations and the experimental results are reported in section-5. finally a conclusion is drawn in section-6. 2. literature survey 2.1 system classification over the last few decades, many researches and studies have been conducted on inverted pendulum system. inverted pendulum can be defined as a system with a mass attached to a rod which can rotate about a pivot point [2]. according to [3], an inverted pendulum attached to a cart is called a cart-pole system. the pole with mass is pointing upward, while the cart can move back and forth in horizontal plane to make the pole stays upright. another type of system related to inverted pendulum is called inertia wheel pendulum or better known as reaction wheel pendulum mentioned by [4] in their research. reaction wheel pendulum consists of a symmetric disc attached to the end of rod which is freely rotated about an axis, parallel to the axis of rotation of the pendulum. the reaction disc can be actively controlled by coupling torque generated by angular acceleration actuated through a dc motor. in the research done by [5], the author classified the system into two classes; class 1 and class 2. reaction wheel pendulum is considered as class 1 system while cart pole system is a class 2 system. iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 175 from the above mentioned definition, unicycle mobile robot can be composed of class 1 and class 2 systems. the rotating disc and frame (i.e. with fixed wheel) of the robot can be considered as class 1 while combination of robot’s wheel and frame (i.e. fixed rotating disc) can be classified as class 2 system. furthermore, unicycle mobile robot is an under-actuated system because it possesses fewer control inputs compared to degree of freedoms [5]. unicycle mobile robot has two motors to control its position and orientation. besides, unicycle mobile robot is a nonholonomic system because it has dynamic non-holonomic constraint mentioned by [6]. it is considered as non-holonomic since the wheel of unicycle is maintained at a contact point on a planar plane, the wheel is impossible to move transversally and wheel displacement along the plane is equal to the wheel arc [7]. in the next section, the studies done by previous researchers related to the controller to control various unicycle’s mechanism are explored. 2.2 controller design in the research by [8], the author used linear quadratic gaussian (lqg) controller to control the lateral and longitudinal stability of the unicycle mobile robot. the robot developed by this author is in the form of system that mimicked a human riding a unicycle which consists of a wheel, a frame which acted as the rider’s body and rotary turntable as the human arms. during simulation study, the lateral stability could be achieved at nonzero wheel speed by twisting the turntable and the wheel moved forward and backward. the author in [9] had proposed a new modified lqg method to control longitudinal stability of the unicycle robot which previously developed by [8]. however, the control strategy using the same method applied for lateral stability was not mentioned in the paper. the author then used gain scheduled lateral controller to control the lateral stability of the system. the author mentioned that friction effects in forward and yawing direction was contributed by wheel surface friction while drive train friction was considered as pitch and yawing friction. the author had used bang-bang controller to deal with the friction effects on the system. the author in [10] had proposed the unicycle movement based on the design by [8] and assumed that, when the robot moved in longitudinal plane, there is no lateral and yawing effect occurs on it. it was assumed that the linearized model behaved like an inverted spherical pendulum with a base that is free to move in the surface plane. the author proposed linear quadratic regulator (lqr) controller to stabilize the system. the controller however was implemented in the simulation stage only. the author in [11] had proposed to use pd controller to control the lateral stability the unicycle mobile robot which had asymmetric turntable rotor rotated by a geared motor on the top of the system to control the roll angle while the wheel was driven by linkages that were connected to two motors. the linkages were assumed to replace human’s thigh and foot when they were riding the unicycle. from the author point of view, the experimental results conducted depend on initial posture of robot and ground unevenness. in another paper [11], the same author had proposed a new controller by using fuzzy gain schedule pd control technique. experimental results shown that both of the robot’s longitudinal and lateral postures could be successfully stabilized. by comparing the experimental results with pd and d controllers, it was found that the lateral and the pitch controls with two fuzzy gain schedule pd controllers produced better results. iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 176 another controller proposed by [12] and [13] developed a system namely as gyrover which was a single wheel vehicle equipped with an internal gyroscope. this internal gyroscope was aligned with the wheel and spinning in the direction of forward motion. angular momentum from the gyro contributed to the lateral stability when the wheel stopped or moved slowly. a tilt device tilted the gyro’s axis about roll axis with respect to the wheel. because the gyro acts as inertial reference, the effect of tilt action caused the wheel to lean left and right and then caused the wheel to steer. the author in [14] had used lqr optimal control to control the robot whose design is slightly similar as the one in [12] and [13]. the author [14] had considered the motion about roll axis only and neglected the pitch and yaw controls. in the study done by [15], the researchers had used feedback control technique to stabilize the roll and pitch angles of the unicycle system. the system was equipped with two gyros which were used to detect angular velocities around the rolling and the pitching axes. another gyro was applied to detect an angular velocity around yawing axis which was used to find the heading direction. the same control strategy was also applied to control the mechanism discussed in the research done by [12] and [13]. in the paper produced by, [16], a controller had been designed to control the yaw angle of unicycle by applying time phase difference on the roll and pitch angles. however, the study had been conducted only at simulation level. further studied carried out by [17] had proposed a new fuzzy logic controller (flc) to control the unicycle robot in two dimensional system. in the flc design, the author had leveraged the linear quadratic regulator (lqr) and the gain-scheduling technique to obtain the flc parameters. in addition by further comparing the flc with the lqr which was designed around an operating point, the flc coefficients could be easily tuned. however, the controller could only be applied to control the pitch angle of the system dynamics. moreover, in another paper done by [18], the author had used linear controller to stabilize their design. the design done by [18] was based on inverse mouse roller ball. the controller had two loops; the proportional-integration (pi) controller as the inner loop and lqr as the outer loop. the study carried out by [19] had used an adaptive nonlinear control together with radial basis function neural networks (rbfnn) which was based on adaptive back-stepping control technique to stabilize the system design. however, the author only provided the simulated results and no comparison was done between simulated results and experimental results. another method proposed by [20] had used gain scheduling with linear parameter varying technique to control the unicycle robot. the system developed was composed of two gyroscopes acting as actuator for lateral stabilization and a wheel as actuator for longitudinal stabilization. the experimental results for lateral and longitudinal control were very good even though small oscillations still could be observed. research by [21] had used the pole-placement and lqr to control the unicycle robot in longitudinal direction only. the system analysis and estimation of systemcoefficients were completed on the simulated stage. 3. dynamic modeling of the unicycle mobile robot based on [1] and [22], the model of the unicycle mobile robot for this research can be described in the form of non-linear model: iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 177 �� � ���� � ���� (1) where: 1 � � ��� ��� � ��� where α is the roll angle. 2 � ���� ��� � ��� where β is the pitch angle. 3 � ����� ��� � ��� where ω is the wheel angle 4 � ��� ��� � ��� where η is the rotation disc angle 5 � � ��� � �!"�# ( roll angle velocity). 6 � ���� � �!"�# (pitch angle velocity). 7 � ����� � �!"�# (wheel angle velocity) 8 � ��� � �!"�#.(reaction disc velocity) τ1= the torque applied to the reaction disc to control roll angle. τ2= the torque applied to the wheel to control the pitch angle. and ���� � � 5 6 7 8 �1 �2 �3 �4�' ���� � ( ) ) ) ) ) ) * 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 �11 �12 �13 �14 �21 �22 �23 �24 �31 �32 �33 �34 �41 �42 �43 �44, . where: (((( )))) )2(cos2634.0)2cos(00071.01923.0 1)2sin()2cos(651357.0)8665(135.0)2cos(6553.0 1 2 xx axxxxxxxxxxx f ++++−−−− ++++−−−−++++−−−−−−−−−−−− ==== )2(cos2634.0)2cos(00071.01923.0 (x1)2.5692)sinx2)(5.873cos( 1 2 xx a ++++−−−− ++++ ==== )2cos(00456.001195.0 )2sin( 76002023.0)2cos(6004556.0 )1cos(1760.05004067.05002023.0)2cos(50079.0 2 2 22 x x xxxx xxxxx f −−−−         ++++++++ ++++−−−−−−−−−−−− ==== )2(cos004555.001195.0 )2sin( )1cos()2cos(3964.060269.0)2cos(500916.0 )2cos(5004555.0)2(cos501778.0)2cos(764555.0 3 2 2 222 x x xxxxx xxxxxxx f −−−−         −−−−−−−−++++ ++++++++−−−− ==== )2(cos2635.0)2cos(000714.01923.0 1)2(cos652635.0861357.06505729.0)2cos(653919.0 4 2 2 xx bxxxxxxxxxx f ++++−−−− ++++++++−−−−++++−−−− ==== (((( )))) )1sin(5692.2)2cos(8733.51 xxb ++++==== iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 178 )2(cos2635.0)2cos(0007135.01923.0 1 11 2 xx b ++++−−−− ==== )2(cos2635.0)2cos(0007135.01923.0 )2cos( 14 2 xx x b ++++−−−− −−−− ==== 043421312 ================ bbbb 034312421 ================ bbbb )2(cos004555.0012.0 03.0 22 2 x b −−−− ==== )2(cos004555.0012.0 )2cos(06749.0 23 2 x x b −−−− −−−− ==== )2(cos004555.0012.0 )2cos(06749.0 32 2 x x b −−−− −−−− ==== )2(cos2635.0)2cos(0007135.01923.0 1 41 2 xx b ++++−−−− −−−−==== )2(cos2635.0)2cos(0007135.01923.0 )2(cos94.1)2cos(995.0417.1 44 2 2 xx xx b ++++−−−− ++++++++ ==== eqn.(2) as mentioned by [1] and [22] can be linearized so that the linear controller can be used. this equation is linearized with respect to the desired operating point and it can be described as: �� � /� � �0 (2) and the operating point for the system is exx ==== where 0≈≈≈≈ex which is the upright position of the unicycle robot.. in order to linearize eqn. (2), jacobian matrix is developed as shown in eqn. (3); 0,0 ========       ∂∂∂∂ ∂∂∂∂ ==== ux x f a =                     ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ ∂∂∂∂ n nnn n n x f x f x f x f x f x f x f x f x f κ μλμμ λ λ 21 2 2 2 1 2 1 2 1 1 1 , and 0,0 ========∂∂∂∂ ∂∂∂∂ ==== xxu f b (3) by employing eqn. (1) (2), eqn. (3) can be represented as: )2(cos0045555.012.0 3986.0 33 2 x b −−−− ==== iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 179                           ==== 000000018.554164 00000053.63652-0 00000023.819380 000000018.554184 10000000 01000000 00100000 00010000 a                           ==== 9.5669002.19771053.92759.13231-0 09.13231-4.05555570 2.1977-002.19771 0000 0000 0000 0000 b the input to the system, 0 is given as: 0 � 10 0 1 22' (4) 4. controller design in order to control the unicycle mobile robot, a linear controller has been designed. the controller is known as linear quadratic controller (lqr) and designed to control the roll (α) and pitch angles (β) of the unicycle robot system shown in figure 1 for both the simulation and the experimental study at the operating point. the performance of controller is then compared. fig. 1: the generalized coordinate for unicycle mobile robot, roll angle (α), pitch angle (β), disc angle (η) and wheel angle (ω). the advantage of using the lqr controller in this system is, it can regulate the system output, x to zero while stabilizing the closed loop. in other words, it is strictly intended to stabilize the system and to make the time response faster as mentioned in [23]. iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 180 by considering the unicycle mobile robot model in the eqn. (2), a full state feedback regulator for the system is designed based on [24] by using control input vector as in the eqn. (5). 0 � 34���� (5) the target of the designed controller is to obtain the gain k so that u in eqn.(5) can be included into quadratic objective function expressed in eqn. (6). 5 � 6 1�' 7� � 0' 8029:9 ;� (6) where, �� is the final time, and � is the initial time. in this system, we are interested in the steady state behaviour of the unicycle mobile robot system. as such the control period for the system will be infinite. thus, tf in eqn. (6) will be approaching infinity, ∞ and the quadratic objective function then become j∞. j∞ can be considered as the energy function. when j∞ is small, the energy of the closed loop system is also small. since x and u in eqn. (6) governed by j∞, neither x nor u is large. when j∞ is minimized, x becomes zero as tf goes to ∞ and it guarantees that the system is stable. in order to minimize j∞, the matrix q and matrix r need to be selected. matrix q is defined as in eqn. (7) while matrix r can be defined in eqn.(8). 7 � ( ) ) ) * <== 0 0 … 0 0 <?? 0 … 0 0 0 <@@ … 0 a a a b a 0 0 0 … <cc, . (7) 8 � ( ) ) ) * d== 0 0 … 0 0 d?? 0 … 0 0 0 d@@ … 0 a a a b a 0 0 0 … dee, . (8) where, matrix q must be n x n symmetric positive definite matrix, and matrix r should be m x m symmetric positive definite as well. the criteria for selecting matrix q and r is by following the bryson’s rule as the guidelines as mentioned in [25] and these criteria are elucidated in eqn. (9) and eqn. (10) where the diagonal q and r can be: 7ff � = eghfeie gjjkl9gmnk ho p (9) where i=1,2,3,4…n 8ff � = eghfeie gjjkl9gmnk qgnik ir p (10) where j=1,2,3,4…n even though the matrix q and r are bounded by eqn. (9) and eqn. (10), the matrix q and matrix r still need to be found and tested through trial and error to find the optimized performance and the fast response can be obtained if the q11 is quite large compared to q22,q33. iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 181 after selecting matrix q and matrix r, the control input u can be defined as: 0 � 34� � 38s=�'t� (11) from eqn.(11), it is observed that, matrix p is required to solve for the control input u. matrix p is a symmetric and positive semi-definite which can be found by solving an algebraic ricatti equation which is shown in the eqn. (12). t/ � /' t 3 t�8s=�' t � 7 � 0 (12) after obtaining gain value for k, then, the stability of matrix a-bk is tested by finding eigen-values of a-bk. as mentioned previously, if the eigen-values of a-bk are all negatives, then the system is considered as stable system. 5. result and discussion by employing eqn.(5)eqn(11), the values of q and r are shown in the table 1. table 1: list of diagonal q and r. values for q and r for case a: diagonal q 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 diagonal r 1 1 values for q and r for case b: diagonal q 10 10 1 1 1 1 1 1 diagonal r 1 1 values for q and r for case c: diagonal q 5 5 5 5 1 1 1 1 diagonal r 1 1 values for q and r for case d: diagonal q 10 1 10 10 1 1 1 1 diagonal r 1 1 based on table 1 and eqn.(11), the gain k can be acquired. the gain, k obtained can be divided into two segments where k1 is used to control roll angle and k2 is used to control pitch angle. the simulation and the experimental performance of the controller are done on different set of gains. the different sets of gains are listed in the table 2. table 2: list of controller gain. controller gain for case a: k1 -25.3145 0.0000 0.0000 -0.1000 -5.6920 0.0000 0.0000 -0.2097 k2 0.0000 -11.2555 -0.1000 0.0000 0.0000 -2.6621 -0.1728 0.0000 controller gain for case b: k1 -72.8391 -0.0000 -0.0000 -1.0000 -15.6677 -0.0000 -0.0000 -1.5155 k2 -0.0000 -62.6028 -1.0000 -0.0000 -0.0000 -16.0568 -1.5424 -0.0000 controller gain for case c: k1 -88.1863 0.0000 0.0000 -2.2361 -18.8843 0.0000 0.0000 -2.1426 k2 0.0000 -78.2178 -2.2361 0.0000 0.0000 -20.1313 -2.2104 0.0000 controller gain for case d: k1 -99.5209 -0.0000 -0.0000 -3.1623 -21.2502 -0.0000 -0.0000 -2.6076 k2 -0.0000 -89.8938 -3.1623 0.0000 -0.0000 -23.1768 -2.7100 0.0000 iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 182 fig. 2: simulink/matlab block diagram for unicycle mobile robot. iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 183 5.1 simulation results the gain k obtained from all the cases are applied into the simulation block diagram in the simulink/matlab environment as shown in fig. 2. figure 2 shows that the model of the plant is set as state space and the errors of the system are regulated by gain k founded in the previous. the input of the system is set to be zero so that the system can be stabilized at zero position which is the upright position of the system. by using gain k obtained, behavior of the unicycle mobile robot is analyzed. the performance of the controller based on gain k for every case, case a, case b, case c and case d are elucidated in fig. 3 – fig. 12. fig. 3: simulated case 1(a): result for roll angle and disc rotation by using gain k derived from case a. the data of interest for roll and pitch angles versus time are captured. the simulation result for roll angle and disc rotation by using gain k derived from case a is shown in fig. 3 while the simulation result for pitch angle and wheel rotation is depicted in fig. 4. the initial condition set for the unicycle system in roll direction is at [[[[ ]]]]00001.0001.0====x where roll angle, α= 0.1rad or 6 deg and disc angle, η =0.1rad=0.016 rev. for the initial condition in pitch direction, the posture of the robot is set as [[[[ ]]]]000001.01.00====x where pitch angle, β= 0.1rad or 6 deg and wheel angle, ω =0.1rad=0.016 rev. from fig. 3 and fig. 4, it is observed that when the robot is released at positive direction, the reaction disc will rotate in the opposite direction to bring the robot to stabilization point. however, when the robot moves to negative direction, the reaction disc will rotate in the positive direction. from the behavior of the system, it is shown that the force from the reaction disc is imposed in the negative and positive direction in order to compensate the roll angle’s error of unicycle robot. the same behavior also applied to the pitch angle of the robot. when the pitch angle is little bit deviates from the stabilization point, the robot’s wheel will move forward to catch the unicycle robot. the simulation in fig. 3 and fig. 4 shows that the unicycle system reaches the settling time at t = 2s in the roll direction while it’s settling time in pitch direction is in t = 1.5s. 0 1 2 3 4 5 6 7 8 9 10 -20 -10 0 10 20 time (s) r o ll a n g le (a lp h a ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -1 -0.5 0 0.5 1 time (s) d is c r o ta ti o n (e ta ) (r e v ) iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 184 fig. 4: simulated case 1(b): result for pitch angle and wheel rotation by using gain k derived from case a. fig. 5: simulated case 2(a): result for roll angle and disc rotation by using gain k derived from case b. in another case, the roll angle and disc rotation which uses gain value k derived from case b is plotted in fig. 5 while the pitch and wheel rotation from the same case is plotted in the simulated fig. 6. when the robot is released at α = +6 deg, the reaction disc will rotate opposite to the movement of the robot in order to bring the robot to its stabilization point. figure 5 shows that unicycle robot has responded and stabilized faster compared to previous figure (fig. 3).the unicycle robot has swung more and reaches settling time at t = 1.5s in the roll direction. 0 1 2 3 4 5 6 7 8 9 10 -20 -10 0 10 20 time (s) p it c h a n g le (b e ta ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -1 -0.5 0 0.5 1 time (s) w h e e l ro ta ti o n (o m e g a ) (r e v ) 0 1 2 3 4 5 6 7 8 9 10 -20 -10 0 10 20 time (s) r o ll a n g le (a lp h a ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -1 -0.5 0 0.5 1 time (s) d is c r o ta ti o n ( e ta ) (r e v ) iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 185 figure 6: simulated case 2(b): result for pitch angle and wheel rotation by using gain k derived from case b. fig. 7: simulated case 3(a): result for roll angle and disc rotation by using gain k derived from case c. 0 1 2 3 4 5 6 7 8 9 10 -20 -10 0 10 20 time (s) p it c h a n g le (b e ta ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -1 -0.5 0 0.5 1 time (s) w h e e l ro ta ti o n (o m e g a ) (r e v ) 0 1 2 3 4 5 6 7 8 9 10 -20 -10 0 10 20 time (s) r o ll a n g le (a lp h a ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -1 -0.5 0 0.5 1 time (s) d is c r o ta ti o n (e ta ) (r e v ) iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 186 fig. 8: simulated case 3(b): result for pitch angle and wheel rotation by using gain k derived from case c. the simulated case 3(a) and simulated case 3(b) as shown in fig. 7 and fig. 8 are used to simulate the performance of lqr controller on the unicycle robot which uses the gain k value derived from case c previously. figure 7 shows the behavior of the robot when it is released from positive roll direction and the response of the controller can be seen through the response of the reaction disc. the robot has swung more and took longer time to stabilize compared to the previous fig. 3 and fig. 5. the settling time for the robot under this case is at t = 3s. fig. 9: simulated case 4(a): result for roll angle and disc rotation by using gain k derived from case d. 0 1 2 3 4 5 6 7 8 9 10 -20 -10 0 10 20 time (s) p it c h a n g le (b e ta ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -1 -0.5 0 0.5 1 time (s) w h e e l ro ta ti o n (o m e g a ) ( re v ) 0 1 2 3 4 5 6 7 8 9 10 -20 -10 0 10 20 time (s) r o ll a n g le (a lp h a ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -1 -0.5 0 0.5 1 time (s) d is c r o ta ti o n (e ta ) (r e v ) iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 187 fig. 10: simulated case 4(b): result for pitch angle and wheel rotation by using gain k derived from case d. the performance of the controller for the case d can be observed in fig. 9 and fig. 10. by using the same initial condition as the previous cases, the robot requires more time and it swings left and right while the reaction disc rotates in the direction vice versa. the robot achieves the stabilization in roll direction in t = 4 s. the robot’s movement in the pitch direction as shown in figure 10 shows that the robot also requires more time to stabilize. fig. 11: simulated case 5(a): esult for roll angle and disc rotation subjected to disturbance (i.e k derived from case d). the robot’s wheel rotates clockwise and counters clockwise to ensure the robot stabilizes. the robot achieved postural stabilization in pitch direction more than 1.5 s. in order to test the behavior of the robot when it is subjected to the disturbance, two cases have been plotted as shown in fig. 11 and fig. 12. the gain value k from case d is 0 1 2 3 4 5 6 7 8 9 10 -20 -10 0 10 20 time (s) p it c h a n g le (b e ta ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -1 -0.5 0 0.5 1 time (s) w h e e l ro ta ti o n ( o m e g a ) ( re v ) 0 2 4 6 8 10 12 14 -20 -10 0 10 20 time (s) r o ll a n g le (a lp h a ) (d e g s ) 0 2 4 6 8 10 12 14 -1 -0.5 0 0.5 1 time (s) d is c r o ta ti o n (e ta ) (r e v ) iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 188 selected as the case study. the purpose of selecting case d as a case study is to see the behavior of the robot (response and settling time) when it is subjected to disturbance when it is already stabilized. figure 11 illustrates the action of the robot in the roll direction when it deals with the pulse disturbance at time, t = 8s. the robot slants back to the stabilization position after the pulse signal applied to it since it is pushed back by reaction disc. the robot going back to the stabilization position either it is subjected to disturbance in roll or pitch direction as shown in fig. 11 and fig. 12. in fig. 12, wheel response increasing because it is quite not so stable. as a result, fig. 12 (the gain k from case d) is not selected to be implemented in the real hardware system. fig. 12: simulated case 5(b): result for pitch angle and wheel rotation subjected to disturbance (i.e k derived from case d). 5.2 experimental results in order to validate the simulation results, a few numbers of postures of unicycle mobile robot system were inspected experimentally and compared with the results acquired previously. in order to accomplish the experimental study, the posture of the robot in the roll and pitch angle were studied independently. based on the previous simulation results, gain value k obtained through case b was selected to be implemented in the controller to control the system hardware. even though the gain k from case b was used, the value was tuned within the range ±2 in the controller program to improve the performance of the system. the experimental results showed the estimated measurement between gyroscopes and accelerometers from inertial measurement unit (imu) attached to the robot. figure 13 shows the study of the robot’s posture under influence of controller in the roll direction. the robot was released at initial condition, roll angle, α=+6° or 0.1 radian. from the figure, it is observed that when the robot is released, the reaction disc responded in the opposite direction to bring back the unicycle to nearly its stabilization point. this behaviour can be seen clearly from t = 0 s to t = 1 s. the stabilization range for the unicycle mobile robot is between α = -20 ο and +20 ο . the robot swung back and forth between this range and the reaction disc swung in the opposite direction. it was hard to make the unicycle robot to move to α = 0 ο due to the dynamic behaviour of the robot. however, the result is acceptable and matches with the result shown in fig. 5. 0 2 4 6 8 10 12 14 -20 -10 0 10 20 time (s) p it c h a n g le (b e ta ) (d e g s ) 0 2 4 6 8 10 12 14 -1 -0.5 0 0.5 1 time (s) w h e e l ro ta ti o n (o m e g a ) (r e v ) iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 189 in another experiment conducted, the unicycle robot was released in the pitch direction at β = +6deg. when the robot was released at this position, the robot’s wheel tried to catch up the position and made the robot stable. from fig. 14, the stabilization range for the unicycle robot in the pitch direction is between -15 ο to +15 ο . the result from fig. 14 can be said comparable to fig. 6. fig. 13: experimental result for roll angle with initial angle = +6° (i.e. k derived from case b). fig. 14: experimental result for pitch angle with initial angle = +6° (i.e. k derived from case b). in fig. 15 the unicycle robot is released at roll position, α = -6 ο . in the result shown in the figure, when the range of unicycle robot in roll direction is between -10 ο to +10 ο , the reaction disc movement is between -2 rev to +2rev only. in fig. 16, the unicycle robot is released at position β=-6deg. the pitch angle of the robot is still between range -20 ο to +20 ο . the wheel angle rotates from the initial position 0 1 2 3 4 5 6 7 8 9 10 -60 -40 -20 0 20 40 60 time (s) r o ll a n g le (a lp h a ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -5 0 5 time (s) d is c r o ta ti o n ( e ta ) ( re v ) 0 1 2 3 4 5 6 7 8 9 10 -20 -10 0 10 20 time (s) p it c h a n g le (b e ta ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -5 0 5 time (s) w h e e l ro ta ti o n (o m e g a ) ( re v ) iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 190 0 rev and ends at +3rev. the pitch angle measured from the stabilization point, 0 ο and the wheel just rotates forward or backward to ensure the robot achieved postural stabilization in pitch direction. the positive revolution shown by the wheel’s encoder means that the robot moves forward to catch the inclination angle in positive pitch direction. fig. 15: experimental result for roll angle with initial angle = -6° (i.e. k derived from case b). fig. 16: experimental result for pitch angle with initial angle = -6° (i.e. k derived from case b). 6. conclusion this paper discusses the controller design which is based on the system linearized model. the simulation results, the experimental results and the comparison between both are presented and discussed thoroughly. the lqr control scheme is used as the system controller to stabilize the unicycle mobile robot in roll and pitch directions. the simulation studies are carried out to investigate the performance of the controller. the best controller 0 1 2 3 4 5 6 7 8 9 10 -60 -40 -20 0 20 40 60 time (s) r o ll a n g le (a lp h a ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -6 -4 -2 0 2 4 6 time (s) d is c r o ta ti o n (e ta ) ( re v ) 0 1 2 3 4 5 6 7 8 9 10 -60 -40 -20 0 20 40 60 time (s) p it c h a n g le (b e ta ) (d e g /s ) 0 1 2 3 4 5 6 7 8 9 10 -6 -4 -2 0 2 4 6 time (s) w h e e l ro ta ti o n ( o m e g a ) (r e v ) iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 191 parameters are then selected and implemented on the real system controller where the performance is analyzed based on the response recorded. overall, the experimental results show acceptable match with the simulation results. references [1] rashid, mz ab, and s. n. sidek. “dynamic modeling and verification of unicycle mobile robot system.” (icom), 2011 4th international conference on mechatronics ieee, 2011. [2] shen j., sanyal, a. k., and chaturvedi, n. a. “dynamics and control of 3d pendulum.” 43d ieee conference on decision and control, bahamas, 2004. [3] fantoni, i. and lozano, r. “global stabilization of the cart-pendulum system using saturation fnr"tctions.” p.ogesdings of the 42nd iefe conference on decision, 2003. [4] spong, mark w., peter corke, and rogelio lozano. “nonlinear control of the reaction wheel pendulum.” automatica 37.11 (2001): 1845-1851. [5] saber, r.o. “nonlinear control of under actuated mechanical systems with application to robotics and aerospace vehicles.” ph.d. dissertation. massachusetts institute of technology, department of electrical engineering and computer science, cambridge, ma. 2001. [6] anthony m.b, krishnapasad, p.s., jerrold, m., richard, m.m. “nonholarutmic mechanical system with symmetry.” cds technical report: 94-013, california institute of technology, 1995. [7] basilo, b. “nomholomic constaint examples.” politechnico di torino and control, usa: maui,, hawaii, 2009. [8] schoonwinkel, a. “design ntd. test of a computer stabilized unicycle.” ph.d dissertation, stanford university, ca, 1987. [9] vos, d.w. and andreas, h. “dynamics and nonlinear adaptive contol of an autonomous unicycle: theory and experimenrs.” proceedings of the 29'h conference on decision and control, honolulu, hawaii, 1990. [10] naveh, y., yoseph, p., and halevi, y. nonlinear modeling and contrul of a unicycle, in dynamics and control 1.9 (1999): 9-29. [11] sheng, q., yamafuji, k. and ulyanov.s. “study on the stability andmotion control of a unicycle robot.” 3rd report, characteristics of a unicycle robot, the japan society of mechanical engineers, series c, 39.3(1996). [12] benjamin, h.b.jr. and yansheng, xu. “a single wheel gyroscopically stabilized rofutt.”proceedings of the 1996 iff.e, international conference on robotics and automation, minneapolis, minnesota, 1996. [13] yansheng, x., kwok, w.a., nandy, g.c., brown, h.b. “analysis of actuation and waruic balancing for a single wheel robot.” proceedings of &e 1998 ieee/rsj, intl.conference on intel robot and system, canada, 1998. [14] biswas, j. and seth, b. “dynamic stabilization of a reaction wheel actuated robot.” international journal of factory automation, robotics and soft computing, 2008. [15] r. nakajima, t. tsubouchi, s. yuta, and e. koyanagi. a development of a new mechanism of an autonomous unicycle. in proc. ieee/rsj int’l. conf. on intelligent robots and systems, pages 906–12, grenoble, france, september7-11 1997 [16] majima, s., kasai, t. and kadohara, t. a design of a control method for changing yaw direction of an wider actuated unicycle robot, university of tsukuba, 2006. [17] zhaoqin, g., xu, j.x and ke, t.h. “gain-scheduling optimal fuzzy logic contoller design for unicycle.” ieee-asme international conference on advanced intelligent mechatronics suntec convention and exhibition center, singapore, italy 14-17(2009). [18] lauwers, t.b., kantor, g.a. and hollis, r.l “a dynamically stable single-wheeled mobile robot with inverse mouse-ball drive.” proc. ieee internationai conference. on robotics and automation, orlando, fl, may 15-19, 2006. iium engineering journal, vol. 13, no. 2, 2012 ab rashid and sidek 192 [19] chine, c.t., cheng, k.s., sen, c.s., shui, c.l. adaptive nonlinear contol using rbfnn for an electic unicycle, 2008. [20] minh, q.d and lil, k-2' “gain scheduled stabilization control of a unicycle robot.” jsme lnternational journal, series c, 48.4 (2005). [21] chung, n.h. the development of self-balancing contoller for one-weeled vehicles, 2010. rashid, m.z.a, sidek, s.n, abas, n. “dynamic modeling of a unicycle mobile robot and model validation with experimental hardwarz.” australian joumal of basic and applied sciences, 2012. [22] rijanto, e. “robust contol.” theory for application, itb press, 2000. [23] tewari, a. modent control design, john wiley & sons, (2002): 285. [24] hespanha, j .p. linear system theory, princeton university press, (2009). microsoft word 199-1277 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 105 a comparison between single linkage and complete linkage in agglomerative hierarchical cluster analysis for identifying tourists segments noor rashidah r. 1 , sabri a. 1 and safiek m. 2 1 department of mathematics, faculty of science & technology, 2 department of management & marketing, faculty of managment & economics, universiti malaysia terengganu, kuala terengganu, terengganu, malaysia. noor_rashidah84@yahoo.com, sba@umt.edu.my, safiek@umt.edu.my abstract: cluster analysis is a multivariate method in statistics. agglomerative hierarchical cluster analysis is one of approaches in cluster analysis. there are two linkage methods in agglomerative hierarchical cluster analysis which are single linkage and complete linkage. the purpose of this study is to compare between single linkage and complete linkage in agglomerative hierarchical cluster analysis. the comparison of performances between these linkage methods was shown by using kruskal-wallis test. the result of the comparison used for segmenting tourists of kapas island. the statistical software spss has been applied to analyze data of this research. the result from kruskal-wallis test shows complete linkage is more useful in identifying tourists segments. abstrak: analisis gugusan ialah satu kaedah multivariat dalam bidang statistik. analisis gugusan aglomeratif berhierarki ialah satu daripada pendekatan dalam analisis gugusan. ada terdapat dua kaedah rantaian dalam analisis gugusan aglomeratif berhierarki iaitu rantain tunggal dan rantaian lengkap. tujuan kajian ini ialah untuk mencari perbandingan antara rantaian tunggal dengan rantaian lengkap dalam analisis gugusan aglomeratif berhierarki. perbandingan prestasi antara dua rantaian tersebut dibuat menggunakan ujian kruskal-wallis. keputusan perbandingan tersebut digunakan untuk meruas pelancong di pulau kapas. perisian statistic spss telah digunakan bagi menganalisa data kajian. keputusan ujian kruskal-wallis menunjukkan rantaian lengkap adalah lebih berguna untuk mengenalpasti segmen pelancong. keywords: agglomerative hierarchical cluster analysis; single linkage; complete linkage; kruskal-wallis test; tourists 1. introduction in statistics area, there are some methods available to gather observations. some methods have been developed to divide a sample of observations into some smaller groups. one of the methods is cluster analysis. this method involves sorting observations into different groups based on their similarity. cluster analysis also refers as a collection of statistical methods that identifies groups of sample that show similar characteristics. there are many approaches in cluster analysis. one of the approaches is agglomerative hierarchical cluster analysis. the first step need to be considered in this approach is computation of similarity among cases or observation. the similarities among iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 106 cases were considered as distance in agglomerative hierarchical cluster analysis. euclidean distance measure will apply to compute the distance among cases in this study. the cases that have same similarities will be set in the same clusters or groups. the distance among clusters can be compute using single linkage or complete linkage methods. single linkage is a method that focused on minimum distances or nearest neighbor between clusters meanwhile complete linkage concentrates on maximum distance or furthest neighbor between clusters. this research compares the efficiency of single and complete linkage in agglomerative hierarchical cluster analysis. this comparison based on evaluation of the output for both linkage methods. kruskal-wallis is a method that will apply in this research to contrast the performances between single linkage and complete linkage. kruskal-wallis test is a non-parametric test used to make comparison between independent groups of sampled data. the objectives of this research are: a. to compare performances of single linkage and complete linkage in agglomerative hierarchical cluster analysis. b. to assign groups or clusters of tourists those visit kapas island, terengganu. cluster analysis is a multivariate data analysis method that groups similar objects together. agglomerative hierarchical cluster analysis is a method of cluster analysis. the method is initially seeking for the similarities between different points by using euclidean distance measure. the similarities between different clusters are calculated using single linkage and complete linkage methods. therefore, the comparison between these linkage methods by using kruskal-wallis test will be performed in determining the clusters of kapas island tourists. it is difficult to assign groups of these tourists since they come from various backgrounds. this problem is solved using agglomerative hierarchical cluster analysis. cluster analysis is widely used family of multivariate techniques for grouping individuals, objects or behaviors into similar clusters [1]. the flexibility of cluster analysis to accommodate wide range of applications makes it one of the most useful tools for understanding the natural structures among observations [1]. in tourism research, for example, cluster analysis is often used to identify market segments in order to improve the effectiveness of marketing efforts these segments may be based on a variety of variables including demographic characteristics (such as age, income, gender and location) and trip characteristics (such as trip length, purpose, group size and benefits) [1]. reference [2] stated hierarchical cluster analysis is a set of statistical techniques that is particularly useful for separating a set of objects into constituent group or clusters which minimize variation between members of the same groups without making assumptions about the number of groups or the group structure. 2. materials and methods 2.1 research site and instrument the selection site for this research is kapas island. this island is located at marang, terengganu. the sample size preferred for hierarchical cluster analysis is not more than 200 samples [3]. reference [4] mentioned large data sets can be problems with agglomerative hierarchical cluster analysis. an alternative to agglomerative hierarchical cluster analysis for more than 200 data is given by various forms of nonhierarchical cluster analysis [4]. the sample of this research was 200 respondents iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 107 αr + αs + β = 1 αr + αr + β = 1 2 αr + β = 1 2 αr = 1β αr = (1β)/2 included local and international tourists that visit kapas island in july until september 2009. they have been chosen by using snowball sampling technique. it was one of the non-probability sampling techniques. by using this technique, the local and international tourists in this research have been chosen randomly. a questionnaire was distributed to the sample of this research. ten separate visitor surveys were carried out at kapas island. the mode of survey delivery for this research was self-administered questionnaire. the surveys were based on a 7-page questionnaire. there are three sections in this questionnaire. the sections are section a, b and c. in section a, it was included questions about the respondents’ demographic profiles. section b included questions about details of visit. there are 10 questions in this section. the items in this section are frequency of their visit to kapas island, the purpose to visit kapas island and so on. section c is contained items of visitor satisfactions of kapas island. the respondents need to answer 24 questions about their characteristics of visit in kapas island. likert scale has been used in section c. 2.2 agglomerative hierarchical cluster analysis in this method, clustering of each observations or objects begins in separate clusters. next, the clusters of the object or observation that are close together are merged to create one large cluster. the general formula for agglomerative hierarchical cluster analysis as follows [5]: (1) where αr = system parameter corresponds with cluster r αs = system parameter corresponds with cluster s β = system parameter γ = system parameter dk→r = distance between cluster k to cluster r dk→s = distance between cluster k to cluster s dr→s = distance between cluster r to cluster s the value for all parameters as in table 1 will be used for simplification of (1). reference [3] has recommended the following constraints of parameter values to simplify (1). when αr = αs, hence here, αr = (1β)/2. next, a value of β needs to be selected. it is suggested that β =0 since 0<1. if a small value of β has been use such as β = -0.5 or β = 0.5, it becomes or dk→(r,s)=αr dk→r+αs dk→s+ β dr→s+ γ αr + αs + β = 1 ½ + ½ + (-0.5) ≠ 1 αr + αs + β =1; αr = αs; γ = -½ ; β < 1; αr + αs + β = 1 ½ + ½ + (0.5) ≠ 1 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 108 | dk→r dk→s | = dk→s dk→r | dk→r dk→s | = dk→r dk→s table 1: value of parameters. parameter complete linkage single linkage αr ½ ½ αs ½ ½ β 0 0 γ ½ -½ 2.3 complete linkage there are some steps in getting the model or formula of complete linkage by using model of agglomerative hierarchical cluster analysis. by using all the values of parameter for complete linkage as in table i into (1), it becomes (2) if then (3) subsequently, (3) needs to be substituted into (2). therefore, (2) reduces to become as follows: on the other hand, if dk→r < dk→s , then (4) by using all the value of parameters for complete linkage as in table i, (2) reduces as follows: dk→(r,s)= ½ dk→r+ ½ dk→s+ ½ |dk→rdk→r > dk→s dk→(r,s)= ½ dk→r+ ½ dk→s+ ½ |dk→r-dk→s| = ½ dk→r+ ½ dk→s+ ½ dk→r½dk→s = ½ dk→r + ½ dk→r = dk→r dk→(r,s)= ½ dk→r+ ½ dk→s+ ½ |dk→r-dk→s| = ½ dk→r+ ½ dk→s+ ½ dk→s ½ dk→r = ½ dk→s + ½ dk→s = dk→s iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 109 dk→(r,s)= ½ dk→r+ ½ dk→s ½ (dk→r-dk→s) = ½ dk→r+ ½ dk→s ½ dk→r + ½dk→s = ½ dk→s + ½ dk→s = dk→s dk→(r,s)= ½ dk→r+ ½ dk→s ½ (dk→s dk→r) = ½ dk→r+ ½ dk→s ½ dk→s + ½ dk→r = ½ dk→r + ½ dk→r = dk→r since dk→r and dk→s is symmetric, the model of complete linkage approach can be written a follows: 2.4 single linkage there are some steps that need to follow to get the formula or model of single linkage. the first step that needs to follow is substitution the value of parameters for single linkage approach as in table 1 into (2). (5) since the condition of (3) is compulsory for the (5), substitutions of (3) into (5) need to be performed. hence, when the substitution of (4) into (5) is done, the following equation will exist. since dk→r and dk→s is symmetric, the model of single linkage approach can be written a follows: dk→(r,s)= min [(dk→r), (dk→s)] 2.5 kruskal-wallis test kruskal-wallis test is one of statistical tests in nonparametric statistic. comparative studies frequently involve the simultaneous comparison not just of two but of three or more treatments or conditions [7]. kruskal-wallis test used to compare between single linkage and complete linkage in this research. the first procedure in kruskal-wallis test is ranking all the observations in the combined sample. data values are grouped and need to be ranked. next, compute the sum of the ranks for each cluster. the formula of sum of the ranks, ∑ri is given as follows: i iinii i n rrr r +++ =∑ l21 where ni = number of subjects to the ith treatment. ri1 = rank in the 1st treatment group. dk→(r,s)= max [(dk→r), (dk→s)] dk→(r,s)= ½ dk→r+ ½ dk→s + (-½) |dk→r-dk→s| dk→(r,s)= ½ dk→r+ ½ dk→s ½ |dk→r-dk→s| iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 110 h0 : θ1 = θ 2 = … = θ d k = √(n/2) ri2 = rank in the 2 nd treatment group rini = rank in the ni treatment group the kruskal-wallis test is applied after the computation the sum of the ranks. the assumptions for this test are all samples are random samples from their respective population and the measurement scale is at least ordinal. the kruskal-wallis test statistic is given by: ( ) ( )∑ = +− + = k i i i n n r nn kw 1 2 13 1 12 where n = total of respondents n = total of respondents in each cluster r = total of rank the null hypothesis of kruskal-wallis test for a population is they have the same means. this hypothesis can be written in terms of the respective treatment effects as: h1 : at least two θs differ 3. results and discussion ordinal data gathered from research respondents usually not normal distribution, therefore it needs to be analyzed using nonparametric tests [8]. the purpose of normality test is to check whether all the variables that will be applied is not normally distributed since kruskal-wallis test is one of the approaches in nonparametric statistic. 3.1 normality test for ordinal data the assumption is all the variables for ordinal data are qualitative. the hypotheses for this test are as follows: h0 :the sample comes from a normal distribution h1 :the sample does not come from a normal distribution based on table 2, from the kolmogorov-smimov test it can be conclude that since the significant value (p-value) for all variables are 0.000 < 0.05, all the variables are not normally distributed. reference [8] stated for kolmogorov-smirnov and shapiro-wilk tests, data are normal distribution if both of them are not significant, which sig. > 0.05. here, there is enough evidence at the 5% level of significance that significant values (sig.) for all variables are 0.000 which is less than 0.05. hence, it can reject h0 from the above hypotheses. it can be accepted that the sample does not come from normal distribution. 3.2 determination number of clusters the formula of rule of thumb has been used to determine the number of clusters. the formula as follows: where n = number of object iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 111 since the tourists of kapas island be the object that need to build clusters among them, here n=200. hence it shows that the number of clusters that need to be built in this research is ten clusters by using the formula of rule of thumb. table 2: test of normality. kolmogorov-smirnov(a) statistic df sig. weather .247 200 .000 cleanlin .283 200 .000 scenery .296 200 .000 atmosphe .271 200 .000 safety .192 200 .000 friendli .188 200 .000 accomoda .224 200 .000 lotstose .203 200 .000 transp_a .297 200 .000 accomo_a .248 200 .000 accomo_b .251 200 .000 availabi .265 200 .000 entertai .246 200 .000 availibi .206 200 .000 accomo_c .204 200 .000 costofac .229 200 .000 souvenir .191 200 .000 signage .251 200 .000 overallc .178 200 .000 tasteoff .230 200 .000 priceoff .199 200 .000 varietyo .212 200 .000 friendly .243 200 .000 appearan .237 200 .000 3.3 data analysis of agglomerative hierarchical cluster analysis using single linkage when using single linkage in agglomerative hierarchical cluster analysis the members of ten clusters are as presented in table 3. table 3 shows the number of members for each cluster when applied single linkage in agglomerative hierarchical cluster analysis. cluster 1 had the majority members which 191 members while cluster 2, 3, 4, 5, 6, 7, 8, 9 and 10 only had one member in their cluster. table 3: k = √ (200/2)=10 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 112 total of members of ten clusters when applying single linkage in agglomerative hierarchical cluster analysis. cluster total of members percentage 1 191 95.5 2 1 0.5 3 1 0.5 4 1 0.5 5 1 0.5 6 1 0.5 7 1 0.5 8 1 0.5 9 1 0.5 10 1 0.5 total 200 100 3.4 data analysis of agglomerative hierarchical cluster analysis using complete linkage when using complete linkage in agglomerative hierarchical cluster analysis the members of ten clusters are as follows: table 4 shows the number of members for each cluster when applied complete linkage in agglomerative hierarchical cluster analysis. cluster 1 had the majority members which 61 members while cluster 10 only had the minority members which only two members in its cluster. table 4: total of members of ten clusters when applying complete linkage in agglomerative hierarchical cluster analysis cluster total of members percentage 1 61 30.5 2 44 22 3 4 2 4 6 3 5 18 9 6 12 6 7 30 15 8 15 7.5 9 8 4 10 2 1 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 113 total 200 100 table 4 shows the number of members for each cluster when applied complete linkage in agglomerative hierarchical cluster analysis. cluster 1 had the majority members which 61 members while cluster 10 only had the minority members which only two members in its cluster. 3.5 calculation of kruskal wallis test from application of single linkage in agglomerative hierarchical cluster analysis the responds for each respondent on likert scale questions in this research have been total up. the data will be analyzed using kruskal wallis test. hypotheses of research are as follows: h0 : ten clusters of tourists have same satisfaction value about kapas island h1 : ten clusters of tourists have different satisfaction value of kapas island. step 1: arrangement of positions and rank for ordinal scale score the positions of respondents have been arranged in ascending order which start f rom 1 until 200. it is because there were 200 respondents. based on the positions, the ranks of respondents have identified. there were some respondents that have same satisfaction value with other respondents. i.e respondents 16, 139 and 183. so their rank was 09 3 1098 .= ++ step 2: calculation total of ranks for each cluster. total of ranks for each cluster is shown as follows: table 5: total of rank of rank for ten clusters (single linkage). cluster total of rank 1 19714.5 2 19.0 3 25.0 4 25.0 5 39.5 6 47.5 7 45.0 8 52.0 9 16.5 10 72.5 according to table 5, it shows cluster 1 has the highest total of rank (19714.5) meanwhile cluster 9 has the lowest total of rank (16.5). step 3: calculation of estimation kruskal wallis, kw. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 114 by using the formula as follows, the estimation value of kw can be determined. ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) [ ] 792312 603017205264100030 603 2552562527227042025252256 251560270462536101702034877 40200 12 12003 1 572 1 516 1 52 1 45 1 547 1 539 1 52 1 25 1 19 191 519714 1200200 12 13 1 12 22222 22222 1 2 . .. ... .. ... .. = −= −      ++++ +++++ = +−             +++++ +++++ + = +− + = ∑ = kw n n r nn kw k i i i step 4: finding critical value of kw the degree of freedom is df=k-1=10-1=9. by referring table of critical value for chi square on df=9 and significant level, p=0.005, the critical value of kw is 16.92. step 5: making decision for kruskal wallis test the comparison value of estimation kw and critical value of kw shows that the estimation value kw (12.7923) lower than critical value of kw (16.92). therefore it is accepted that hypothesis null, h0 which stated ten clusters of respondents or tourists have same satisfaction value about kapas island. 3.6 calculation of kruskal wallis test from application of complete linkage in agglomerative hierarchical cluster analysis step 1 and step 2 for calculation of kruskal wallis for the data of clusters that exist when applying complete linkage in agglomerative hierarchical cluster analysis is same as analysis for single linkage in agglomerative hierarchical cluster analysis. table 6: total of rank and mean of rank for ten clusters (complete linkage) cluster total of rank mean of rank 1 10037 164.5410 2 3498.5 79.5114 3 184 46.0 4 103 17.1667 5 1661 92.2778 6 131.5 10.9583 7 3400 113.3333 8 693 46.20 9 347.5 43.4375 10 5 2.5 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 115 according to table 6, it shows cluster 1 has the highest total of rank (10037) meanwhile cluster 10 has the lowest total of rank (5). step 3: calculation of estimation value of kruskal wallis, kw by using the formula as follows, the estimation value of kw when applied complete linkage in agglomerative hierarchical cluster analysis can be calculated. ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) [ ] 7401154 6034752252580000030 603 51253131509417630745 3333385333020814413889153273 166717688464505727817085251651497 00030 12003 2 5 8 5347 15 693 30 3400 12 5131 18 1661 6 103 4 184 44 53498 61 10037 201200 12 13 1 12 2222 222 222 1 2 . ... ... ... ... . . . . = −= −           ++ +++ ++++ = +−                     +++ +++ +++ = +− + = ∑ = n n r nn kw k i i i step 4: finding the critical value of kruskal wallis, kw the degree of freedom is similar as in case of single linkage. the critical value of kw can be found by referring the table of critical value for chi square. by referring the table, on df=9 and p=0.05, the critical value of kw is 16.92. step 5: making decision for kruskal wallis test by referring step 3 and step 4 for this case, it shows the estimation value of kw (154.7401) is higher than estimation value of kw (16.92). therefore the null hypothesis was rejected. it can be concluded that ten clusters of respondents that occurred after applying complete linkage in agglomerative hierarchical cluster analysis have the different satisfaction value of kapas island. it shows that cluster 1 have the highest satisfaction value of kapas island compare than other clusters (mean of rank for cluster 1=164.5410, mean of rank for cluster 2=79.5114, mean of rank for cluster 3=46.0 mean of rank for cluster 4=17.1667, mean of rank for cluster 5=92.2778, mean of rank for cluster 6=10.9583, mean of rank for cluster 7=113.3333, mean of rank for cluster 8=46.20, mean of rank for cluster 9=43.4375, mean of rank for cluster 10=2.5). 4. conclusion this study shows that the application of complete linkage approach in agglomerative hierarchical cluster analysis is more useful compare than single linkage approach in segmenting tourists of kapas island. it is because the result from the application of complete linkage in agglomerative hierarchical cluster analysis shows the difference of satisfaction value between ten clusters of tourists. if the clusters had same iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics noor et al. 116 satisfaction value of kapas island, it means the clusters had no difference among them and there is no occurred clusters among tourists. acknowledgements this study was supported by research university grant: ukm-gup-nbt-08-26-095 from, ministry of science, technology and innovation, malaysia. i am also grateful to many people who helped me during my research at kapas island. references [1] d.r. fesenmaier, and j. jeng, cluster analysis. in jafar, j., encyclopedia of tourism,. london and new york: routledge taylor & francis group, 2003, vol.1, p.85. [2] s.c. leung, w.k. fung, and k.h. wong, “the identification of credit card encodes by hierarchical cluster analysis of the jitters if magnetic stirpes,” science & justice journal, vol. 1, pp.85, 2003. [3] m.r. yaacob, spss for business and social science students version 14 for windows, 1st ed. kota bharu, kelantan: pustaka aman press, 2008. [4] p.k. hopke, and l.kaufman, “the use of sampling to cluster large data sets,” chemometrics & intelligent laboratory system, vol. 8, pp 195-204, 1990. [5] k. teknomo. (2009, august 8). hierarchical clustering tutorial.retrieved from http://people.revoledu.com/kardi/tutorial/clustering/index.html [retrieved august 8, 2009] [6] g.n. lance, and w.t. william,”a general theory of classifacatory sorting strategies,” computer journal, vol. 6, pp 373-380, 1967. [7] e.l. lehmann, nonparametric statistical methods based on ranks, new york: springer. [8] c.y. piaw, asas statistik penyelidikan: analisis data skala ordinal dan skala nominal, malaysia: mcgraw hill. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 khan et al. 68 adaptive trimmed mean autoregressive model for reduction of poisson noise in scintigraphic images khan bahadar khan1*, muhammad shahid2, hayat ullah3, eid rehman4 and muhammad mohsin khan3 1 department of telecommunication engineering, university college of engineering &technology (uce &t), the islamia university, bahawalpur, pakistan. 2 the istituto italiano di tecnologia iit, pavis pattern analysis and computer vision lab, italy. 1,3 department of electrical engineering, 4 department of computer science & software engineering, international islamic university, islamabad, pakistan. * corresponding author: kb.khattak@gmail.com (received: 21st march 2017; accepted: 6th march 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.835 abstract: a 2-d adaptive trimmed mean autoregressive (atmar) model has been proposed for denoising of medical images corrupted with poisson noise. unfiltered images are divided into smaller chunks and atmar model is applied on each chunk separately. in this paper, two 5x5 windows with 40% overlap are used to predict the center pixel value of the central row. the ar coefficients are updated by sliding both windows forward with 60% shift. the same process is repeated to scan the entire image for prediction of a new denoised image. the adaptive trimmed mean filter (atmf) eradicates the lowest and highest variations in pixel values of the atmar model denoised image and also average out the remaining neighborhood pixel values. finally, power-law transformation is applied to the resultant image of the atmar model for contrast stretching. image quality is judged in terms of correlation, mean squared error (mse), structural similarity index measure (ssim) and peak signal to noise ratio (psnr) of the image with latest denoising techniques. the proposed technique showed an efficient way to scale down poisson noise in scintigraphic images on a pixel-by-pixel basis. the highest correlation 0.9706, psnr 10.023 and mse 25.902 is achieved by the proposed technique. abstrak: model 2-d auto-pengurangan purata potongan penyesuaian (atmar) telah dicadangkan bagi menghilangkan gelombang bunyi yang dicemari pada imej perubatan dengan bunyi poisson. imej yang tidak ditapis ini telah dibahagikan kepada pecahan kecil dan model atmar telah diadaptasi bagi setiap pecahan. dalam kajian ini, dua 5x5 kotak tetingkap dengan 40% pertindihan telah digunakan bagi mendapatkan nilai tengah piksel pada barisan tengah. pekali ar telah dikemas kini dengan meluncurkan kedua-dua kotak tetingkap ke hadapan dengan 60% perubahan. proses yang sama telah diulang dengan mengimbas imej keseluruhan bagi mendapatkan imej yang telah dinyahbunyi. tapisan purata potongan penyesuaian (atmf) ini menghilangkan perubahan paling bawah dan paling atas dalam nilai piksel imej model atmar yang dinyahbunyi dan menyama-rata saki-baki nilai piksel bersebelahan. akhir sekali, perubahan cara-kuasa telah diadaptasi pada imej akhir model atmar bagi regangan ketara. kualiti imej telah dinilai dari sudut korelasi, kesalahan purata kuasa dua (mse), indeks ukuran persamaan struktur (ssim) dan signal puncak kepada nisbah bunyi (psnr) melalui kaedah terkini nyah-bunyi pada imej. teknik ini menunjukkan cara berkesan bagi menurunkan bunyi poisson pada imej saintigrafik pada asas piksel-kepadaiium engineering journal, vol. 19, no. 2, 2018 khan et al. 69 piksel. korelasi tertinggi adalah 0.9706, psnr 10.023 dan mse 25.902 telah dicapai melalui teknik yang dicadangkan. keywords: denoising; autoregressive model; poisson noise; adaptive trimmed mean 1. introduction scintigraphic or nuclear images allow investigation of the human body by injecting photons from radioactive products and detecting its radiation time. the radioactive product that is associated with a labelled biological molecule is called a tracer that gathers in the organ/tissue of interest after an injection into the blood. the planar gamma camera can be used for capturing radiation emitted by the radioactive product, this imaging technique is called scintigraphy [1]. in nuclear medicine, scintigraphic images are used for investigation of some organs, regardless of their poor resolution. poisson noise is one of the important sources of deterioration in scintigraphic images [2]. numerous techniques have already been used for reduction of poisson noise in scintigraphic and single photon emission computed tomography (spect) images. the degradation in quality of such tomographic images is caused by detection efficiency, attenuation, collimator correction, and scatter of gamma rays. these factors cause the output image to have low contrast, high noise levels, and poor spatial resolution [3]. in tomography, filtering techniques are considered very important for image enhancement. reduction of noise can be achieved before reconstruction, which is called pre-filtering, or during or after reconstruction, which is known as post-filtering [4]. adaptive autoregressive (ar) filters can be used for removal of poisson noise in scintigraphic images [5]. the ar filter is further improved to scale down noise from 3-d reconstructed data of scintigraphic images and also from spect images [6]. it is important to apply the best ar filter for the projection data of scintigraphic images, because a small change in the projection data may cause a large change in the estimated transaxial image [6]. 2. scintigraphic image acquisition the gamma camera invented by anger is used for capturing radiation emitted by the radioactive product [7]. the main components of the gamma-camera for scintigraphic image acquisition are discussed in the following subsections. 2.1 the collimator the collimator puts gamma rays in one direction to reach the crystal; unlike light, gamma rays cannot be concentrated using lenses [8]. incoming gamma rays can be sensed by the collimator and the light generated by the cooperation of the gamma rays and crystal can be converted into an electronic signal by photomultiplier (pm) tubes and preamplifiers [9]. parallel hole, pinhole, converging, and diverging are all different types of collimator. the most popular collimator is the parallel-hole collimator, which retains the dimensions of an image. in the case of non-parallel collimators, the divergence or convergence nature of the collimator and geometrical disposition are the controlling factors of an image dimension and the cause of geometric distortion [7]. holes are detached by the lead “walls” are called septa. resolution/sensitivity depends on the collimator thickness, hole diameter, and septal thickness. generally, the collimator thickness is 0.3-1.4 millimeters and the hole diameter is 1.8-3.4 millimeters [10]. iium engineering journal, vol. 19, no. 2, 2018 khan et al. 70 2.2 the scintillator crystal in the gamma camera, crystals usually consist of thallium-activated sodium iodide (nai (t1)). edges and the front side can be protected from outside moisture and light by coating it with a thin aluminum (al) layer. atomic number (z) and high mass density make the crystal desirable. important properties of the crystal are high energy resolution, high detection efficiency, and low decay constant time [11,12]. crystals generally having a thickness of about 1 cm can detect photons with energies up to a few hundred kev. the energy accumulated in the crystal is proportional to the number of light photons produced by interaction of crystal and gamma rays. the light guide of the glass is optically coupled to the rear side of the crystal, which protects the crystal and directs the light photons to an array of photomultiplier tubes [10]. 2.3 the photomultipliers (pm) tubes the pm tube is responsible for converting photon energy diffused by the crystal to an electrical signal [11]. this is accomplished by the consolidation of several elements placed in a vacuum to permit the flow of electrons. the first element is a photocathode placed in connection with the crystal. light photons extract electrons on metal foil on the photocathode. these electrons are taken captive to the first dynode due to the application of a high voltage between positively charged and the photocathode. the electrons’ expedition sanctions them to extract a much more immensely colossal number of electrons from the dynode. the same phenomenon is repeated on several other cascading dynodes [13]. 3. proposed model the proposed model consists of three major steps: an autoregression (ar) model, adaptive trimmed mean filter (atmf), and a power-law transformation. fig. 1 shows a step-wise block diagram of the proposed technique. the steps of the proposed method are as follows: 1. two 5x5 windows with a 40% overlap are used to predict the center pixel value of each corresponding window. 2. ar coefficients for both windows are calculated using a forward backward prediction (fb) method as shown in equations (2) and (3). 3. using corresponding ar coefficients and neighborhood pixels of each window to predict the central pixel value according to equation (1). 4. using average of ar coefficients of both 5x5 windows to predict the pixel value of the overlapping region. 5. slide both windows forward with a 60% shift and update ar coefficients by following step 2. 6. repeat steps 2 through 5 to scan the complete noisy image and update their predicted values denoted by x_pred. 7. x_err is calculated by using equation (4) to preserve edges and getting predicted image i_pred. 8. now, a 7x7 window of ar denoised image (x_pred) is taken, slid pixel-by-pixel. 9. the mean and variance for each 7x7 individual window is calculated. the overall variance from local variance is computed. 10. the adaptive mean of an image is computed using equation (5) to make boundaries prominent on its true position. 11. the pixel values of the 7x7 window are arranged in ascending/descending order, the ten upper and ten lower outlier pixels are trimmed and the mean of the remaining iium engineering journal, vol. 19, no. 2, 2018 khan et al. 71 pixels is computed using equation (6). ten pixels are trimmed on both sides as it gives good results after performing different experiments with trimming a different number of pixels. 12. the power law transformation is applied using equation (7) for contrast stretching to improve the visual quality of the image. fig. 1: block diagram of the proposed denoising model. 3.1 ar model in the first step, the ar model filter is applied in which each pixel of the image is regressed on its neighborhood pixel values called the prediction region in ar model. the variable of interest in the ar model is predicated using linear combination of the surrounding values of the variables. the ar models are linear prediction models that split an image into two additive components, a predictable image and a prediction error image. in the ar model, no past values of the model input are used [14]. in this research, a new 2dimensional adaptive autoregressive model for filtering of scintigraphic images is introduced. an ar process 𝑋 (𝑛1, 𝑛2) can be expressed as [15]. 𝑋𝑃𝑟𝑒𝑑 (𝑛1, 𝑛2) = − ∑ ∑ 𝑎(𝑘1 𝑘2𝑘1 , 𝑘2)𝑋𝑛𝑜𝑖𝑠𝑦 (𝑛1 − 𝑘1, 𝑛2 − 𝑘2) + 𝑤(𝑛1, 𝑛2) (1) where 𝑎(𝑘1, 𝑘2) are the weighting coefficients, indices 𝑘1 and 𝑘2 define the type of prediction region in a two dimensional array (𝑛1, 𝑛2) matrix, and 𝑤(𝑛1, 𝑛2) represents prediction error, that is, the difference between the original value and the predicted value in this pixel. predicted image 𝑋𝑃𝑟𝑒𝑑 is the image obtained by applying the ar model on the original image 𝑋𝑛𝑜𝑖𝑠𝑦. ar coefficients for both windows are calculated using a forward backward prediction (fb) method. iium engineering journal, vol. 19, no. 2, 2018 khan et al. 72 in scintigraphic images, the same model cannot be applied to the entire image as it consists of large local spatial variations, therefore, the model must be adapted according to the variations. that is why the image is divided into smaller chunks and the ar model is separately applied to each chunk. in this method, two 5 x 5 windows with a 40% overlap are used to predict the pixel value of the central row. if more or less than 40% overlap ratio is selected, the predicted values will come closer to the previous or next pixel values. in order to keep a balanced correlation with the previous and next pixel values, this overlapping ratio is selected experimentally. the ar coefficients on both windows are computed using a forward backward prediction (fb) method as follows. the forward predictor model predicts a sample x(m) from a linear combination of p past samples x(m−1), x(m−2), . . .,x(m−p). 𝑥⏞ (𝑚) = ∑ 𝑎𝑘 𝑥(𝑚 − 𝑘) 𝑃 𝑘=1 (2) where the integer variable m is the discrete time index, 𝑥⏞ (𝑚) is the prediction of x(m), and 𝑎𝑘 are the predictor coefficients. similarly, we can define a backward predictor, that predicts a sample x(m−p) from p future samples x(m−p+1), . . ., x(m) as 𝑥⏞ (𝑚 − 𝑃) = ∑ 𝑐𝑘 𝑥(𝑚 − 𝑘 + 1) 𝑃 𝑘=1 (3) where the integer variable m is the discrete time index, 𝑥⏞ (𝑚 − 𝑃) is the prediction of 𝑥(𝑚 − 𝑃), and 𝑐𝑘 are the predictor coefficients. using corresponding ar coefficients and four closest neighborhood pixels of the window to predict the central pixel value according to equation (1), both windows are slid forward with 60% shift and ar coefficients are updated. the same process is repeated to scan the whole image for prediction of the new denoised image. the ar model changes the nature of poisson distribution somehow, which looks like a gaussian distribution. adaptive trimmed mean filter (atmf) is applied to the resultant image, which gives better results in terms of reduction in poisson noise. 𝑋𝑒𝑟𝑟 is calculated by following equation to preserve edges. 𝑋𝑒𝑟𝑟 = 𝑋𝑛𝑜𝑖𝑠𝑦 − 𝑋𝑝𝑟𝑒𝑑 (4) where 𝑋𝑛𝑜𝑖𝑠𝑦 is the noisy image, 𝑋𝑝𝑟𝑒𝑑 is the predicted image and 𝑋𝑒𝑟𝑟 is the prediction error image. the error image is averaged out by using the averaging filter to sum up with the predicted image for edge enhancement. an example of a two blocks with 40% overlapping is represented in fig 2. iium engineering journal, vol. 19, no. 2, 2018 khan et al. 73 fig. 2: hatched area of 2-dimensional autoregressive model. 3.2 adaptive trimmed mean filter (atmf) atmf is applied to the output denoised image of the ar process. the aim of applying atmf is to remove lowest and highest variations in the pixel values and average out the remaining neighborhood pixel values. the whole image is divided into 7 x 7 smaller blocks and the local mean and variance of each block are computed. atmf for an 𝑚 × 𝑛 image is given by the expression: [16] 𝑔(𝑖, 𝑗) = 𝑓(𝑖, 𝑗) − 𝜎2𝑛 𝜎2 𝐿 [𝑓(𝑖, 𝑗) − 𝑈𝐿𝑇 ] (5) where 𝑔(𝑖, 𝑗) and 𝑓(𝑖, 𝑗) represent the output and input images, respectively. the 𝑈𝐿𝑇 is the local trimmed mean, 𝜎 2𝑛 is the overall noise variance, and 𝜎 2 𝐿 is the local noise variance. if 𝜎2𝑛 is close to zero, it produces an output very close to the input image 𝑓(𝑖, 𝑗). likewise, if 𝜎2 𝐿 ≫ 𝜎 2 𝑛 it also produces an output pixel close to 𝑓(𝑖, 𝑗). otherwise, this filter outputs a pixel close to the local average. 𝑈𝐿𝑇 for an 𝑚 × 𝑛 image is given by expression in: [16] 𝑈𝐿𝑇 = 1 𝑚𝑛−∝ ∑ 𝑓′ (𝑥,𝑦)∈𝑁𝑖𝑗 (𝑥, 𝑦) (6) where ∝ is the total number of maximum brightest and darkest trimmed pixels and 𝑓′(𝑥, 𝑦) is the sum of remaining pixels. atmf removes abnormal pixel variations, preserves boundaries at their true position, and also removes blurriness effects [17]. 3.3 power-law transformation the power-law transformation is applied to the resultant image of the atmf for contrast stretching and to improve visual quality. the power-law transformation can be expressed as follows [17]: 𝑠 = 𝑐𝑟𝛾 (7) where c and γ are positive constants having values 1 and 3 respectively and r is pixel intensity value of the image. 4. simulation and discussion the proposed model is applied on artificial scintigraphic images having different image statistics corrupted with poisson noise. the ar model provides a good result with 40% iium engineering journal, vol. 19, no. 2, 2018 khan et al. 74 overlap but at the cost of some blurring in the image, which is further improved by applying the atmf. power-law transformation is applied for contrast stretching. this technique maintains the high resolution and also preserves the edges along with the noise reduction. the efficiency of the proposed technique is compared with the ar combination of median and wiener filter and advanced filter, i.e. non local mean (nlm) filter [18] in terms of visual quality, correlation, mse, psnr and ssim. the proposed technique produced better results in terms of edge preservation though the ar process & adaptive trimmed mean filter produced a smoothing effect, while the edge loss is observed in the case of the conventional filters such as median filters. the quantitative performance measures such as correlation, mse, psnr and ssim are used to check the performance of poisson noise reduction filtering techniques. experimental results show that the proposed technique performs significantly well than many other conventional & recent filtering techniques like median, wiener and nlm filters, respectively. the aim of scintigraphic image filtering is to restrain statistical noise while sustaining contrast and spatial resolution [19]. the proposed technique simultaneously provides both efficient noise reduction and good spatial resolution for scintigraphic images. a renal scintigraphic image, artificial scintigraphic image, and transaxial slice of the zubal phantom [20], denoised by the proposed model and other comparative methods, are shown in fig. 3, fig. 4 and fig. 5, respectively. the proposed method shows good visual results. fig. 3: renal scintigraphic image (a) noise-free image (b) noisy image (c) denoised image by median filter with combination of ar model (d) wiener filter with combination of ar model (e) nlm filter (f) proposed technique. (a) 20 40 60 80 100120 20 40 60 80 100 120 (b) 20 40 60 80 100120 20 40 60 80 100 120 (c) 20 40 60 80 100120 20 40 60 80 100 120 (d) 20 40 60 80 100120 20 40 60 80 100 120 (e) 20 40 60 80 100120 20 40 60 80 100 120 (f) 20 40 60 80 100120 20 40 60 80 100 120 iium engineering journal, vol. 19, no. 2, 2018 khan et al. 75 fig. 4: artificial scintigraphic image (a) noise-free image (b) noisy image (c) denoised image by median filter with combination of ar model (d) wiener filter with combination of ar model (e) nlm filter (f) proposed technique. fig. 5: transaxial slice of the zubal phantom (a) noise-free image (b) noisy image (c) denoised image by median filter with a combination of ar model (d) wiener filter with a combination of ar model (e) nlm filter (f) proposed technique. the proposed model performed significantly better than other conventional filters in terms of correlation, mse, psnr and ssim shown as coexistent graphical plots with those obtained from median, wiener filter combined with ar and nlm filter in fig. 6, fig. 7, fig. 8 and fig. 9, respectively. the ssim index showing similarity between two images, (a) 100 200 50 100 150 200 (b) 20 40 60 80100120 20 40 60 80 100 120 (c) 20 40 60 80100120 20 40 60 80 100 120 (d) 20 40 60 80100120 20 40 60 80 100 120 (e) 20 40 60 80100120 20 40 60 80 100 120 (f) 20 40 60 80100120 20 40 60 80 100 120 (a) 50 100 150 200 50 100 150 200 (b) 20 40 60 80100120 20 40 60 80 100 120 (c) 20 40 60 80100120 20 40 60 80 100 120 (d) 20 40 60 80100120 20 40 60 80 100 120 (e) 20 40 60 80100120 20 40 60 80 100 120 (f) 20 40 60 80100120 20 40 60 80 100 120 iium engineering journal, vol. 19, no. 2, 2018 khan et al. 76 while considering one image as perfect quality to measure the quality of another. the results from the proposed model show that it is better in suppressing the poisson noise and improving the psnr and mse compared to conventional filters. fig. 6: correlation comparison of noisy image, median + ar, wiener + ar, nlm and the proposed method. figure 6 shows the correlation comparison of the proposed method with median + ar, wiener + ar and nlm filter. the graph clearly shows that the proposed method produced much better results than median + ar, wiener + ar and nlm filter at high noise. nlm shows a good result at low noise but as noise varies from low to high, its results degraded. the graph is computed for different noise variations. fig. 7: mse comparison of noisy image, median + ar, wiener + ar, nlm and the proposed method. iium engineering journal, vol. 19, no. 2, 2018 khan et al. 77 figure 7 is plotted for mse comparison of the original and the denoised image [17]. the mse result of the proposed method is significantly better than median, wiener combined with ar, and nlm filters. mse is represented mathematically as 𝑀𝑆𝐸 = 1 𝑚 × 𝑛 ∑ ∑[𝑓(𝑖, 𝑗) − 𝑔(𝑖, 𝑗)]2 𝑛−1 𝑗=0 𝑚−1 𝑖=0 (8) where 𝑓(𝑖, 𝑗) and 𝑔(𝑖, 𝑗) represent pixel value at coordinate (𝑖, 𝑗) of an image 𝑓 and 𝑔. number of rows and columns are represented by 𝑚 and 𝑛. fig. 8: psnr comparison of noisy image, median + ar, wiener + ar, nlm and the proposed method. figures 8 and 9 show psnr and ssim comparison of the proposed method with other methods on different noise variation. the graph clearly shows that the proposed model is more efficient than other compared methods. the aim of the proposed method is to deal with the noise at high level. at low level noise, the conventional filters, e.g., median and weiner filter perform well but they are failed to eradicate high variation of noise. one can easily eliminate low level noise by simply using these conventional filters. the proposed method is specifically designed to deal with the high variation of noise. that is the reason that the proposed method beats all other methods at a high level of noise. table 1 validated that the proposed method achieved the highest performance in term of mse, psnr, and correlation. table 1. mse, psnr and correlation comparison with different methods metrics noisy image median + ar filter wiener + ar filter nlm filter proposed mse 57.440 66.985 62.277 40.834 25.902 psnr 6.0206 7.3206 7.9217 8.3450 10.023 correlation 0.6976 0.9428 0.9097 0.9536 0.9706 iium engineering journal, vol. 19, no. 2, 2018 khan et al. 78 fig. 9: ssim comparison of noisy image, median + ar, wiener + ar, nlm and the proposed method. 5. conclusion the proposed model shows an efficient way to scale down the poisson noise in scintigraphic images on a pixel-by-pixel basis. edge preservation through calculation of error image 𝑋𝑒𝑟𝑟 after the predicted image through ar model and smoothening through atmf to remove lowest and highest variations in pixel values, are the major contributions of this research work. references [1] hamrouni k, khalifa n. (2006) two methods for analysis of dynamic scintigraphic images of the heart. int. arab j. inf. technol., 3(2):118-125. [2] nawres k, kamel h, noureddine e. (2006) image denoising using wavelets: a powerful tool to overcome some limitations in nuclear imaging. in information and communication technologies (ictta'06), 2nd, vol. 1, 2006:1114-1118. ieee. [3] tsui bm. (1996) the aapm/rsna physics tutorial for residents. physics of spect. radiographics, 16(1):173-183. [4] kangasmaa ts, kuikka jt, vanninen ej, mussalo hm, laitinen tp, sohlberg ao. (2011) half-time myocardial perfusion spect imaging with attenuation and monte carlo-based scatter correction. nuclear medicine communications, 32(11):1040-1045. [5] takalo r, hytti h, ihalainen h. (2011) adaptive autoregressive model for reduction of poisson noise in scintigraphic images. journal of nuclear medicine technology, 39(1):1926. [6] takalo r, hytti h, ihalainen h, sohlberg a. (2015) adaptive autoregressive model for reduction of noise in spect. computational and mathematical methods in medicine. volume 2015. [7] anger ho. (1964) scintillation camera with multichannel collimators. journal of nuclear medicine, 5(7):515-531. [8] kharfi f. (2013) principles and applications of nuclear medical imaging: a survey on recent developments. edited by faycal kharfi, 2013: 1. [9] mihailidis d. (2012) nuclear medicine physics: the basics. medical physics, 39(10):65256525. iium engineering journal, vol. 19, no. 2, 2018 khan et al. 79 [10] de lima jj. (ed) (2010) nuclear medicine physics. taylor & francis. [11] jonasson t. (2003) revival of a gamma camera. master of science thesis, royal institute of technology, stockholm. [12] ritenour, e. russell. (2009) principles and advanced methods in medical imaging and image analysis." medical physics 36, no. 4, 1460-1460. [13] makhlouf f, besbes h, khalifa n, ben amar c, solaiman b. (2013) planar scintigraphic images denoising. open journal of medical imaging. 3, 116-124. [14] marzetta t. (1980) two-dimensional linear prediction: autocorrelation arrays, minimumphase prediction error filters, and reflection coefficient arrays. ieee transactions on acoustics, speech, and signal processing, 28(6):725-733. [15] haykin ss. (2008) adaptive filter theory. pearson education india. [16] oten r, de figueiredo rjp. (2004) adaptive alpha-trimmed mean filters under deviations from assumed noise model. ieee transactions on image processing, 13(5):627-639. [17] gonzales rc, woods er. (2007) digital image processing, 3rd edition. prentice hall. [18] khursheed s, khaliq aa, shah ja, abdullah s, khan s. (2014) third order nlm filter for poisson noise removal from medical images. magnt research reviews, 2(7):482-489. [19] lyra m, ploussi a. (2011) filtering in spect image reconstruction. journal of biomedical imaging, volume 2011, 10. [20] zubal ig, harrell cr, smith eo, rattner z, gindi g, hoffer pb. (1994) computerized three‐dimensional segmented human anatomy. medical physics, 21(2):299-302. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 the durability of hygro-immersion aged cellulose fibre reinforced polymer layered silicate nanocomposites c. s. suhas kowshik1, nanjangud mohan1, nithesh naik1, manjunath shettar1, ritesh bhat1* and shivaksh rohatgi2 1 department of mechanical and manufacturing engineering, manipal institute of technology, manipal academy of higher education, manipal, india 576104 2 department of propulsion aeronautics and space engineering, école centrale de lyon, écully, france 69134 * corresponding author: ritesh.bhat@manipal.edu (received: 19th august 2020; accepted: 21st october 2020; published on-line: 4th january 2021) abstract: this study aims at investigating the effect of water ageing on the durability of cellulose fibre reinforced polymer layered silicate nanocomposite. the material used comprises cellulose fibres from pinewood as reinforcement and high-density polyethene (hdpe) coupled with nanoclay as matrix phase. the prepared material is subjected to tap water ageing for 21 days. the durability is quantified by barcol hardness for the material and measured at an interval period of 7 days. the obtained results indicate a reduction of hardness by 5.24, 13.17, and 16.60% in 7, 14, and 21 days aged nanocomposites. besides, the one-way anova test shows that the immersion time for the composite has a significant effect on the durability of the material with an r2 value of 99.96% tested at 95% confidence interval. the concluding remarks are validated using the results obtained for thickness swelling using the fourier analysis. the work also presents a regression equation with high degree of accuracy, capable of estimating the barcol hardness value for a given immersion time. abstrak: kajian ini bertujuan untuk mengkaji kesan penuaan air terhadap ketahanan nanokomposit silikat berlapis polimer bertetulang serat selulosa. bahan yang digunakan terdiri daripada serat selulosa dari kayu pina sebagai tetulang dan polietena berketumpatan tinggi (hdpe) ditambah dengan nanoclay sebagai fasa matriks. bahan yang disediakan mengalami penuaan air paip selama 21 hari. ketahanan diukur dengan kekerasan bahan barcol dan diukur pada selang waktu 7 hari. hasil yang diperoleh menunjukkan penurunan kekerasan sebanyak 4.74, 8.88 dan 18.90% dalam nanokomposit usia 7, 14 dan 21 hari. selain itu, analisis satu arah ujian varians menunjukkan bahawa masa rendaman komposit mempunyai pengaruh yang signifikan terhadap ketahanan bahan dengan nilai r2 99.96% yang diuji pada selang keyakinan 95%. ucapan penutup disahkan menggunakan hasil yang diperoleh untuk pembengkakan ketebalan menggunakan analisis fourier. karya ini juga menyajikan persamaan regresi dengan tahap ketepatan yang tinggi, yang dapat menganggarkan nilai kekerasan barcol untuk masa rendaman tertentu. keywords: mechanical property; nanocomposites; natural fibres; polymers; anova 1. introduction the usage of modified polymer layered silicate as matrix phase, comprising a base thermoplastic resin and clay as the primary elements have been proven to improve the mechanical and thermal properties of nanocomposites. besides, they are determined to be 259 iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 lighter in weight and have excellent barrier properties compared to simple polymer composites [1]. polyethene, polythene, or polyethylene is a known polymer that accounts for one-third of the world’s total plastic production and is generally compounded with natural minerals to enhance its properties, dimensional stability, and electric insulation properties while being used in composites. the compounding of clay with polythene has been proven by researchers [2] to improve exfoliation. improved exfoliation ought to improve the mechanical performance of the polymer layered silicate matrix nanocomposites. amongst polyethene, high-density polyethene (hdpe) has been considered as a prime base resin for its ease of availability and recyclability compared to other counterparts. furthermore, the addition of clay to the hdpe intends to improve the toughness of prepared nanocomposites [3-4]. addition of nanoclay to hdpe has been proven to reduce gas permeability while increasing mechanical properties, flame retardance, and thermal stability [5]. during the last few years, cellulose fibre reinforced polymer composites have emerged as a significant class of advanced engineering materials and have found a wide range of applications. moreover, the cellulose fibre reinforced polymer layered silicate nanocomposite outperforms natural wood in flexural properties [6]. thus, cellulose fibre reinforced polymer layered silicate nanocomposites with hdpe as base resin coupled with nanoclay, and cellulose fibres as reinforcements, have been a topic of interest for various researchers. for example, delhom et al. [7] investigated the tensile strength, flame retardance, and thermal expansion of cellulose fibre reinforced polyethene layered silicate nanocomposites. authors extracted the cellulose fibres from cotton lint and wood pulp. three variants were studied based on the varying percentages of clay by weight (7, 10, and 15%). the results indicated nanocomposites with 7 wt.% of clay is optimum considering the thermal properties. however, considering the mechanical properties, the nanocomposites comprising 15 wt% of clay proved better as the ultimate tensile strength increased by 80%. sheshmani et al. [8] examined the physical properties of the developed cellulose fibre reinforced polymer layered silicate nanocomposite. the authors used hdpe as base resin coupled with montmorillonite nanoclay to form the matrix with wood fibres as the reinforcement. the result indicated an improvement in the resistance offered to water uptake by the developed nanocomposite over the conventional wood-plastic composites. on a similar account, deka and maji [9] in their extensive experimental work, coupled the montmorillonite nanoclay with several variants and polymers to develop different cellulose fibre reinforced nanocomposites. they investigated the post and pre-effect of the addition. the results indicated that the addition of nanoclay improved thermal stability, flame resistance, hardness, and resistance to water absorption, compared to conventional wood plastic composites. hossen et al. [10] investigated the mechanical and physical properties of cellulose fibre reinforced hdpe layered silicate nanocomposites, wherein the cellulose fibres used were from jute fibres. the result indicated an improvement by 8% in the tensile strength and 15% in modulus when compared to the composites without nanoclay. eshraghi et al. [11] investigated the combined effect of ultraviolet and moisture on the mechanical and physical properties of the cellulose fibre reinforced hdpe layered silicate nanocomposites. the obtained results indicated the nanocomposites having nanoclay particles demonstrated an improvement in the tensile property as well as in the resistance to water uptake under ageing condition compared to the counterpart. besides, the fourier transform infrared spectroscopy indicated the lowest carboxy index in the case of cellulose fibre reinforced hdpe layered silicate nanocomposites. hossen et al. [12] investigated the thermal behaviour of cellulose fibre reinforced hdpe layered silicate nanocomposites, wherein the cellulose fibres used 260 iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 were from the jute fibres. the result indicated a decrease in thermal degradation in the developed nanocomposites when compared to the composites without nanoclay. el-fattah and el-kader [13] demonstrated in their work the influence of nanoclay addition on the mechanical and water absorption properties of cellulose fibre reinforced hdpe layered silicate nanocomposites. with just 2% addition of clay, the tensile strength improved by 9.7% and resistance to water uptake enhanced by 27.5%. the research is neverexhausting and several researchers, even to this date, are working on cellulose fibre reinforced hdpe layered silicate nanocomposites. for example, wang et al. [14] in their research work proved that the tensile properties of cellulose fibre reinforced polymer composites enhances with the addition of the nanoclay in it. hossen et al. [15] assessed the thermal and mechanical behaviour of chemically treated cellulose fibre reinforced hdpe composites with and without nanoclay addition. the results indicated the improvement in thermomechanical properties with the addition of nanoclay. from the literature reviewed, it is evident that the cellulose fibre reinforced hdpe layered silicate nanocomposite is a hot topic of research. though a good amount of research has been conducted on the thermal, mechanical, physical, and microstructural characterisation of the said material, there is a requirement of checking the durability concerning the hardness change due to water immersion effect on the same. besides, the cellulose fibres from pinewood have rarely been used and investigated concerning the cellulose fibre reinforced hdpe layered silicate nanocomposites. thus, adding to the existing literature, the present work focuses on investigating the effect of water immersion on the durability concerning the hardness and of cellulose fibre reinforced hdpe layered silicate nanocomposites, wherein pine wood fibres are used. the results are validated by observing the thickness swelling in nanocomposites. the prepared nanocomposites are immersed in tap water for 21 days, and required responses are measured periodically at an interval of seven days. the one-way analysis of variance (anova) is then used to validate the results statistically. 2. materials and methods 2.1 materials and aging process the cellulose fibre reinforced polymer layered silicate is used in the presented study. high density polyethene (hdpe) having a melt flow of 0.7 g/min at 190 °c and density of 0.962 g/cc was employed as the base resin. finely powdered pine wood (40 mesh size) was used as the reinforcement phase. the montmorillonite nanoclay is also added to make the complete nanocomposite. the cellulose-based nanocomposite comprised 65 wt% of reinforcing pine wood powder, 20 wt.% of hdpe and 14 wt% of montmorillonite nanoclay and looked just like natural wood. the density was measured for five samples using the astm d2395-17 standard, and the average value was determined to be 695 kg/m3. the average maximum tensile strength of five specimens as per astm d638-14 standard is determined to be 18 mpa. nine samples measuring 100 x 65 x 16 mm were prepared for ageing studies. the materials were then submerged in a tub comprising tap water and allowed to age for the required number of days (7, 14 and 21). the marking was made on the tub to prevent any confusion. fig. 1 represents the cross-sectional view of the prepared specimen and fig. 2 represents the arrangement of submerged material in the tub with days and batch marked on it. 261 iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 fig. 1. the cross-sectional view of the prepared specimen. fig. 2. cellulose fibre reinforced hdpe layered silicate nanocomposites immersed in water for ageing. 2.2 experimental procedures hardness is defined as the resistance of any material to the local deformation caused due to the indentation of the predetermined geometry under known loading conditions [16]. hardness is a function of ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and the viscosity [17]. it is an important property to be studied as it acts as the base for discussing the tribological characteristics of materials [18]. thus, the study is focused on evaluating the effect of ageing on the hardness of the material. for this purpose, the barcol hardness test on the specimens is carried out as per the astm d2583-95 standard test method of testing the indentation hardness of the rigid polymer composite material using the portable barcol impressor model 945 (meant for softer materials). the hardness of the material corresponds to the depth of penetration of the indentor. since the specimens are heterogeneous, a minimum of 25 readings was taken on each of the specimens, and the average value was recorded as the final value. besides, all the readings were taken at 3 mm away from the edges. the apparatus was well-calibrated initially as per the standard operating procedure, before all the testing. besides hardness, yet another important property of interest, particularly in cellulosebased composites, is the thickness swelling in composite due to water absorption. the thickness swelling in composites represents the stability performance of the composite materials [19], [20]. thus, to determine the effect of ageing on thickness swelling behaviour of the nanocomposites, the thickness of the specimen was measured daily (gap of 24 h) using digital vernier calliper 1112-150 by insize to get the precise reading up to two decimal values. the materials were removed and wiped with a clean, dry cloth before measuring. since both sides of the specimen were not coated and were completely immersed in water, the ageing can be considered as accelerated and the worst-case scenario. the thickness swelling was measured for five zones for each specimen, and the average value was considered as the final value of swollen thickness for the particular specimen. a large number of readings were taken to eliminate the effect of the variances caused by the inhomogeneous nature of the material. anova is a widely used technique for univariate data. it is a basic tool in many fields of research as it determines and quantifies the effect of experimental factors on the observed outcome of an experiment [21]. one-way anova is the fundamental model that specifies the common mean value for the observations in a group [22]. thus, once all the values were recorded, the one-way anova test was conducted to determine the significance of immersion time on the hardness and thickness swelling of the developed cellulose fibre reinforced hdpe silicate layered nanocomposites. eq. (1) was used to determine the final value of barcol hardness (hbf) and eq. (2) was used to calculate the final value of swollen thickness (tf) for each specimen, where i = 1, 2, 3…,25 and j = 1, 2,..,5. 262 iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 the thickness swelling is determined using eq. (3), wherein t0 represents the initial thickness, and tm represents the thickness after ageing. the number of the ageing period is represented by k = 7, 14, and 21 in eq. (3). 𝐻𝐵𝑓 = ∑ 𝐻𝐵𝑖 25 𝑖=1 (1) 𝑡𝑓 = ∑ 𝑡𝑗 5 𝑗=1 (2) 𝑡𝑗 = 𝑡𝑚𝑘−𝑡0 𝑡0 (3) 3. results and discussion the recorded values of barcol hardness for unaged and aged specimen are given by table 1, table 2, and table 3. the average barcol value for each specimen recorded in the table refers to the average of 25 readings measured on each one of them. fig. 3. represents the comparison bar chart for the average values of barcol hardness concerning unaged and aged specimens. table 1: barcol hardness measurement for 7 days aged samples. sample no. average barcol hardness for unaged material (hb0) average barcol hardness for 7 days aged material (hb7) percentage change in barcol hardness average percentage change in barcol hardness for 7 days aged material 1 39.75 37.58 5.41% 5.24% 2 39.81 37.64 5.28% 3 39.75 37.75 5.03% table 2: barcol hardness measurement for 14 days aged samples. sample no. average barcol hardness for unaged material (hb0) average barcol hardness for 14 days aged material (hb14) percentage change in barcol hardness average percentage change in barcol hardness for 14 days aged material 1 39.75 34.50 13.21% 13.17% 2 39.85 34.45 13.33% 3 39.75 34.60 12.96% table 3: barcol hardness measurement for 21 days aged samples. sample no. average barcol hardness for unaged material (hb0) average barcol hardness for 21 days aged material (hb21) percentage change in barcol hardness average percentage change in barcol hardness for 21 days aged material 1 39.75 33.20 16.48% 16.60% 2 39.85 33.15 16.60% 3 39.75 33.10 16.73% from the results obtained, it is evident that the durability concerning the barcol hardness of the developed cellulose fibre reinforced hdpe layered silicate nanocomposite has decreased with the increase in the immersion time. the overall barcol hardness reduction is determined to be 5.24, 13.17, and 16.60% for 7, 14, and 21 days aged samples. while observing critically, the maximum damage is caused during the 14 days, wherein the change of hardness between 7 to 14 days is recorded approximately 8%. the hardness 263 iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 reduction between the 14th and 21st day is only 3.43%. the same is evident from the bar graph shown in fig. 3. the average barcol hardness value of 7 days aged specimen is 37.67 hb which was reduced to 34.52 hb on the 14th day. however, the average hardness number of 21 days aged material is recorded as 33.150, which is very near to the 14th day specimen. thus, it is a clear indication that the maximum degradation has taken place during the initial period and gradually the rate of degradation is reducing. the phenomenon that took place could be divided into two phases. initially, the water was absorbed by the hygroscopic pine wood material to the maximum possible extent. following the absorption, the interfacial degradation was caused and increased water absorption further. the results could be validated by sem and edx analysis. nevertheless, the present work focuses on just investigating the statistically significant effect of ageing on the hardness and thickness swelling of the developed nanocomposite and not the microstructural analysis. thus the latter portion can be dealt with in detail by researchers in the future. however, the remarks made are validated through the observations made about the thickness swelling due to the ageing effect on the developed nanocomposite. fig. 3: comparison of overall hardness values of barcol hardness for aged and unaged nanocomposites. the thickness swelling phenomenon in the developed and aged nanocomposites, measured using the digital vernier calliper, was recorded and analysed using the curve fitting tool of matlab r2019b. the fourier equation represented by eq. (4) is used to fit the curve and predict the thickness for a given period. the goodness of fit is determined to be extremely good with an r2 value of 98.93 % and r2(adj) value of 98.62 % at a 95% confidence interval. 𝑓(𝑥) = 𝑦 = 𝑎0 + 𝑎1 cos(𝑥𝑤) + 𝑏1𝑆𝑖𝑛(𝑥𝑤) (3) the values of a0, a1, b1 and w are calculated by the analysis as 16.06, 0.006158, 0.05883 and 1.022 respectively. fig. 4. is the fourier curve depicting the change in thickness concerning the increase in immersion time. there is a continuous increase in thickness, and then it retains constancy, which can be said as a fickian behaviour of water absorption. 264 iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 fig. 4: fourier curve representing the effect of ageing on the nanocomposite thickness. the obtained results show that ageing affects the hardness of the developed nanocomposite. now to check whether the effect is significant, an one-way analysis of variance (anova) test is conducted. tab. 4 gives the result of anova concerning the hardness of nanocomposite conducted at a 95% confidence interval. table 4: anova results for the hardness of nanocomposite. source df seq ss contribution adj ss adj ms f-value p-value days 3 80.9441 99.96% 80.9441 26.9814 6361.03 0.000 error 8 0.0339 0.04% 0.0339 0.0042 total 11 80.9781 100.00% the p-value of 0.00 indicates that the effect of ageing is highly significant on the change in hardness. the error is just 0.04%. in other words, the immersion time contributes 99.6% towards the variance in the hardness of the developed composites. thus, for the nanocomposite developed, the durability concerning the hardness can be termed as the function of immersion time and said to have a significant effect of ageing. furthermore, the regression analysis is done with a cubic model to obtain the prediction equation relating the immersion time with the hardness value. the obtained equation is represented by eq. (5), wherein hb represents the barcol hardness, and the term d represents the immersion time in days. the r2 and the (adj)r2 values are 99.94 and 99.92%, which represent an extreme degree of fitness and accuracy for the obtained equation. 𝐻𝐵 = 39.77 − 0.09700𝐷 − 0.3866𝐷2 + 0.001341𝐷3 (3) the cubic regression model curve representing the behaviour of hardness concerning the immersion time is represented by fig. 5, which indicates a drop in the hardness value with the increase in the immersion time as explained with reasons earlier in the article. 265 iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 fig. 5: cubic regression model curve representing the effect of ageing on the hardness of nanocomposites. 4. conclusion the presented work focused on developing a cellulose fibre reinforced polymer layered silicate nanocomposite and testing the effect of ageing on its durability. the pinewood material contributed towards the required cellulose component, and high-density polyethene (hdpe) was used as the base polymer. the montmorillonite nanoclay was also added to make the complete nanocomposite. hardness is a property of interest for most researchers, as it is believed to be a function of a tribological characteristic of the material, and is considered as the measure of durability in the presented work. the material is studied for the ageing condition, wherein it is immersed in tap water condition for 21 days. the hardness is quantified using barcol hardness number. the study indicates that there is a significant effect of immersion time, in other words, ageing on the hardness (durability) of the developed nanocomposites. the one-way anova results conducted at a 95% confidence interval indicates that the immersion time contributes 99.6% towards the variance in the hardness of the developed composites. the phenomenon that took place is due to (i) initially, the water absorption by the hygroscopic pinewood material, followed by (ii) the interfacial degradation, causing a further increase in water absorption. the thickness swelling phenomenon observed and analysed using fourier equation validates the conclusive remarks. acknowledgement we would like to thank ms jaya letchumi for helping us translate the abstract from english to bahasa melayu as per the requirement from the journal. references [1] bafna a, beaucage g, mirabella f, mehta s. (2003) 3d hierarchical orientation in polymerclay nanocomposite films. polymer, 44(4): 1103-1115. doi: 10.1016/s0032-3861(02)008339. [2] osman ma, rupp jep, suter uw. (2005) tensile properties of polyethylene-layered 266 iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 silicate nanocomposites. polymer, 46(5): 1653-1660. doi: 10.1016/j.polymer.2004.11.112. [3] tanniru m, yuan q, misra rdk. (2006) on significant retention of impact strength in clayreinforced high-density polyethylene (hdpe) nanocomposites. polymer, 47(6): 2133-2146. doi: 10.1016/j.polymer.2006.01.063. [4] jamal na. (2010) a linear relationship between the mechanical, thermal and gas barrier properties of mape modified rubber toughened nanocomposites. iium engineering journal, 11(2): 225-239. doi: 10.31436/iiumej.v11i2.114. [5] chrissafis k, paraskevopoulos km, tsiaoussis i, bikiaris d. (2009) comparative study of the effect of different nanoparticles on the mechanical properties, permeability, and thermal degradation mechanism of hdpe. journal of applied polymer science, 14(3): 1606-1618. doi: 10.1002/app.30750. [6] faruk o, matuana lm. (2008) nanoclay reinforced hdpe as a matrix for wood-plastic composites. composites science and technology, 68(9): 2073-2077. doi: 10.1016/j.compscitech.2008.03.004. [7] delhom cd, white-ghoorahoo la, pang ss. (2010) development and characterisation of cellulose/clay nanocomposites. composites part b: engineering, 41(6): 475-481. doi: 10.1016/j.compositesb.2009.10.007. [8] sheshmani s, ashori a, hamzeh y. (2010) physical properties of polyethylene-wood fibreclay nanocomposites. journal of applied polymer science, 118(6): 3255-3259. doi: 10.1002/app.32623. [9] deka bk, maji tk. (2011) study on the properties of nanocomposite based on high density polyethylene, polypropylene, polyvinyl chloride and wood. composites part a: applied science and manufacturing, 42(6): 6860693. doi: 10.1016/j.compositesa.2011.02.009. [10] hossen mf, hamdan s, rahman mr, rahman mm, liew fk, lai jc. (2015) effect of fibre treatment and nanoclay on the tensile properties of jute fibre reinforced polyethylene/clay nanocomposites. fibers and polymers, 16(2): 479-485. doi: 10.1007/s12221-015-0479-x. [11] eshraghi a, khademieslam h, ghasemi i. (2016) effect of weathering on physical and mechanical properties of hybrid nanocomposite based on polyethylene, woodflour and nanoclay. maderas: ciencia y tecnologia, 18(4): 617-626. doi: 10.4067/s0718221x2016005000054. [12] hossen mf, hamdan s, rahman mr, islam ms, liew fk, lai jc, rahman mm. (2017) improved thermal properties of jute fibre-reinforced polyethylene nanocomposites. polymer composites, 38(7): 1266-1272. doi: 10.1002/pc.23691. [13] abd el-fattah a, abd elkader e. (2018) influence of different clays on the mechanical, thermal, and water absorption properties of recycled high-density polyethylene/wood flour hybrid composites. journal of composite materials, 52(9): 1215-1226. doi: 10.1177/0021998317723180. [14] zhu b, wang x, zeng q, wang p, wang y, liu c, shen, c. (2019) enhanced mechanical properties of biodegradable poly(ε-caprolactone)/cellulose acetate butyrate nanocomposites filled with organoclay. composites communications, 13: 70-74. doi: 10.1016/j.coco.2019.03.002. [15] hossen mf, asraf ma, e-zahan mk, haque mm, zamir r, zakaria rm. (2020) optimisation of nanoclay loading on the thermo-mechanical behavior of chemically treated jute polyethylene nanocomposites. journal of materials science research and reviews, 5(3): 1-12. [16] faraji g, kim hs, kashi ht. (2018) mechanical properties of ultrafine-grained and nanostructured metals. severe plastic deformation. elsevier; pp. 223–257. [17] di gianfrancesco a. (2017) technologies for chemical analyses, microstructural and inspection investigations. materials for ultra-supercritical and advanced ultra-supercritical power plants. elsevier; pp. 197–245. [18] stachowiak gw, batchelor aw, stachowiak gb. (2004) simulation of wear and friction. tribology series, 44: 13-23. [19] adhikary kb, pang s, staiger mp. (2008) long-term moisture absorption and thickness swelling behaviour of recycled thermoplastics reinforced with pinus radiata sawdust. chemical engineering journal, 142(2): 190-198. doi: 10.1016/j.cej.2007.11.024. 267 iium engineering journal, vol. 22, no. 1, 2021 kowshik et al. https://doi.org/10.31436/iiumej.v22i1.1587 [20] atiqah a, jawaid m, ishak mr, sapuan sm. (2017) moisture absorption and thickness swelling behaviour of sugar palm fibre reinforced thermoplastic polyurethane. procedia engineering, 184: 581-586, 2017, doi: 10.1016/j.proeng.2017.04.142. [21] hoefsloot hcj, vis dj, westerhuis ja, smilde ak, jansen jj. (2009) multiset data analysis: anova simultaneous component analysis and related methods. comprehensive chemometrics. volume 2. elsevier; pp. 453–472. [22] christensen r. (2001) analysis of variance and generalised linear models. international encyclopedia of the social & behavioral sciences. elsevier; pp. 473–480. 268 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 secure slicing and allocation of resources of 5g networks in softwaredefined networking / network functions virtualization ali j. ramadhan department of computer techniques engineering, college of technical engineering, university of alkafeel, najaf 31001, iraq corresponding author: ali.j.r@alkafeel.edu.iq; ali.j.r@ieee.org (received: 2nd january 2021; accepted: 30th october 2021; published on-line: 4th july 2022) abstract: in 5g communications, higher data rates and lower latency are needed due to the high traffic rate. though resource wastage is avoided by secure slicing, sliced networks are exploited by ddos attackers. thus, in the present paper, traffic-aware setting up is presented for resource allocation and secure slicing over the virtualization of 5g networks enabled by software-defined network/network functions. in the proposed method (called t-s3ra), to authenticate user devices, boolean logic is used with key derivation based on passwords. moreover, the traffic arrangement is based on the 5g access points. to implement secure resource allocation and network slicing, deep learning models are used. renyi entropy computation is employed to predict the ddos attackers. through the experimental results, the effectiveness of the presented approach is proved. abstrak: melalui komunikasi 5g, kadar data yang tinggi dan latensi yang rendah amat diperlukan kerana kadar trafik yang tinggi. walaupun pembaziran sumber dapat dielakkan melalui pemotongan selamat, rangkaian yang dipotong sering dieksploitasi oleh penyerang ddos. oleh itu, kajian ini menyediakan persekitaran sedar-trafik bagi peruntukan sumber dan pemotongan selamat ke atas rangkaian 5g secara maya melalui fungsi rangkaian takrif-perisian. melaui pendekatan yang dicadangkan (iaitu t-s3ra), peranti pengguna disahkan terlebih dahulu menggunakan logik boolean dengan perolehan kunci berdasarkan kata laluan. di samping itu, susunan trafik adalah berdasarkan titik akses 5g. bagi melaksanakan peruntukan sumber yang selamat dan pemotongan rangkaian, model pembelajaran mendalam telah digunakan. pengiraan entropi renyi dibuat bagi meramal penyerang ddos. dapatan eksperimen mengesahkan keberkesanan pendekatan yang dicadangkan. keywords: dynamic offloading; deep learning; resource allocation; network slicing; traffic scheduling 1. introduction network slicing is a critical issue for 5g networks beneath a single physical infrastructure. generally, network slicing is defined as selection of slices and appropriate allocation of resources for each user [1-4]. presently, higher service-satisfaction rates are required by network equipment. for instance, for a 4k ultra hd video streaming application, it is essential to meet more stringent service requirements like high throughput, high reliability, low latency, and higher storage space. larger throughput and limited delay are 85 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 required by this application, thus needing the implementation of resource allocation and network slicing. resource allocation and joint network slicing were presented as the main solution for meeting the requirements of users’ quality of service (qos). using the service type is among the greatest methods to create a slice. data traffic includes the type of service used for configuring the network slicing. moreover, a quick and dynamic response should be offered to satisfy the constraints of service level agreement (sla). mainly, the present solutions for resource allocation and network slicing are expensive computationally while not supporting the mixed slice requests [5,6]. appropriate support is provided by a software-defined network (sdn) for resource allocation and network slicing since it includes the functionality of processing the slice requests and performing data traffic arrangement [7]. sdns have various benefits based on network slicing. moreover, they currently are extensively researched for numerous applications. these advantages include reliable communication, long-distance, urgent solutions, and communication for optimizing problems [8-10]. for similar cases, a heuristic algorithm is utilized. computations require a huge deal of time in these algorithms, due to their complexity. poor results are obtained by the present resource-allocation and network-slicing methods owing to the massive arrival rate of resource requests, numerous network slice requests, and high data traffic within a network slice [11]. moreover, concentrated sdn controllers are also influenced since they behave as a single-point failure, unable to control most urgent service requests (ultralow latency). through a multi-controller sdn environment, these issues are solved. the final decision is made by the controller in the sdn/network function virtualization (nfv)-based slicing to appropriately direct the slices [12-15]. the present study aims to handle the massive heterogeneous services from diverse tools with 5g networks connections [16-22]. currently, three key services are evolved in 5g namely, ultra-reliable low-latency communication (urllc), massive machine-type communication (mmtc), and enhanced mobile broadband (embb) (table i). the qos and security requirements of networks were increased by integrating sdn/nfv and 5g. resource allocation and network slicing in a 5g network enabled by sdn/nfv are challenging since the optimum set of resources and proper slice must be defined. resource allocation and network slicing are implemented in most studies for a few heterogeneous services while considering very restricted metrics. furthermore, fast resource allocation and network slicing are required owing to various throughputs, mobilities, data rates, and delays in different services. the qos can be improved by a universal system. for proper resource allocation and slice selection, a concentrated sdn controller is not practicable since slice privacy and security are not considered and there is higher participation of ddos attackers. thus, massive quantities of traffic are sent to a particular slice by these attackers. nevertheless, the qos requirement for ue cannot be satisfied by the secure network slicing alone since it is essential to serve the high-priority traffic first, in terms of the type of service. the slice network is performed by the global controller while allocating optimal resources to achieve diverse service needs from users. the present study mainly includes the following points. 86 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 the 5g ap audits each authority in a vap to insert, eliminate, and adjust the operations. using a password-based key derivation function 2 (pbkdf2) in terms of boolean logic is considered along with three input parameters including a physically unclonable function (puf), secret key, and timestamp. an asymmetric queue model was used to perform traffic scheduling oriented by bernoulli’s theorem. packet delay, data rate, and packet length were used to schedule the traffic flow. two highand low-priority queues were fixed within the 5g ap. each queue includes asymmetric service rates based on the arrival rate. the international mobile subscriber identity, traffic type, fair sla, device mobility, and slice capacity are considered in network slicing. the present work primarily focused on sla constraints between the service provider and user leading to the fair sla while slicing the network. first, it tried to calculate the service availability ratio (sar), throughput ratio (tr), response time ratio (rtr), and service reliability ratio (srr) accompanied by the fairness or weight for each service. to perform resource allocation, hopfieldnet is used as a quick neural network to find resources for each slice. through the proposed dynamic-flow offloading outline at the local control plane, overloading at network slices is handled. using a fast-weighted bipartite graph (fωbg) was considered in terms of transmission rate, switch service capacity, and loss rate to map multiple flows to the optimal switches enhancing the network reputation. packet classification through renyi entropy was run along with the device authentication. the bandwidth usage is estimated here, for the switches. ultimately, the ns3.26 simulator was used for the experiments to assess the proposed scheme exhibiting highly satisfactory performance compared to the formerly presented schemes based on several metrics like throughput, response time, latency, packet loss ratio, packet transmission ratio, bandwidth consumption, slice acceptance ratio, and slice capacity. the rest of this paper is organized as follows. earlier studies on resource allocation and network slicing are provided in section 2 to recognize the research gap. the main problems explored from the present studies are highlighted in section 3. the presented traffic-aware scheduling is detailed in section 4 for resource allocation and secure slicing (t-s3ra) architecture along with its essential algorithms. the proposed architecture is compared in section 5 with former methods in terms of the experimental results. finally, our contributions are summarized in section 6 while outlining future improvements. 2. related work 2.1 secure network slicing multiple users are allowed to reach a single network followed by authentication through secure slicing. moreover, users’ performances on the slice are assessed by verification of attributes like the strength of passwords and the existence of malware [23]. in the study of wang et al. [24], mitigation of dos attacks in an sdn was focused on through switch bandwidth congestion prediction. specifically, a complete judgment score was determined for each switch representing attack severity. through trust values, multiple buffer queues the priority can be managed by the manager considering various users’ priorities. a weighted round-robin algorithm was used to schedule flow requests from users. the compromises by dos attackers are estimated. through authentication of the users, attack prevention is achieved. thus, attackers are easily eliminated before overloading the controller. the vikor multicriteria decision-making approach was proposed by porambage et al. [25] for network slicing within a 5g environment to find node significance (topology and 87 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 resource attributes) and thus rank the nodes. a candidate physical path is defined among the slice nodes, for maximizing the slice acceptance ratio. however, there is a major drawback in vikor namely, the marginal slice acceptance ratio, which should be higher for the highpriority traffic. accessing the slice by third-party application services, secure keying is made [26], which ensures consent from the monitored devices as well as security features for the keying outline. hence, the security feature is demonstrated by establishing 5g services. the key distribution server initially creates the cryptographic keys. the elgamal cryptosystem was proposed for a key generation where two sets of keys are generated including private and public keys. the resources are made here for key generation. 2.2 resource allocation and network slicing the optimal workload allocation was proposed by ma et al. [27] for distributed 5gbased sdn/nfv networks. an end-to-end network slicing architecture was designed in this method for supporting several services like urllc and embb. moreover, through slicing the requests from clients in the integrated environment (edge computing, nfv, and sdn), the network operating cost is decreased. network slicing was performed by dawaliby et al. [28] in a large-scale internet of things (iot) environment (long-range extensive area network). in this work, three slices of the network were segregated including the reliability and urgency-aware slice, best-effort slice, and reliability-aware slice. first, one-to-many matching (defined by the number of iot devices allocated to the virtual slices) was used to implement cooperative slicing. then, a one-to-one matching game was used to allocate the resources for each slice (inter-slice resource allocation). the higher processing time is used by the coalitional multigame theory resulting in higher computational complexity. packet-based data traffic scheduling was suggested to enhance resource assignment and sharing in 5g slice networks [29]. two operations modes are utilized including dynamic sharing resource (dsr) and static sharing resource (ssr). the allocated capacity weight is determined to assign the resource for each slice and thus the allocated one. the fairness for resource distribution per slice is calculated in the final analysis. a global network controller is needed for operating massive types of slices like popular, sensitive, and heavy slices. the radio resource management (rrm) was investigated by koutlia et al. [30] for multiple slice management. using the rrm function here, the radio resources are divided and allocated. slicing and allocation provisioning were proved by an interaction between the sd-ran and enb controller. the qos requirements for real-time traffic are not met by a single controller while not suiting the complex application setups (drone control and ar/vr). a slice management scheme was proposed by an et al. [31] to assign resources in terms of priority. in this scheme, forwarding high-priority slice requests is performed while transmitting the lower-priority slices and shortest paths to other paths. they used 200 nodes to perform the experiments. through a grid network topology, the nodes were deployed. the average throughput for slices was more than 6%, 13%, and 7% in the final analysis while minimizing the delays of the slices by 11%–14%. the shortest path is used by the flow (high-priority) forwarding within the data plane although it is not available for all cases. thus, it is essential to install the corresponding flow in the controller when there is no consistency between flow and a flow table. hence, a bandwidth scarcity problem is a resultant for users under static resource assignment. a network slice embedding model was presented by tang et al. [7] in terms of reliability. the number of slice requests is increased by the model while reducing the failure rate of the network slices simultaneously. a lyapunov optimization model was used in this 88 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 model to allocate resources and ensure queue stability. the network stability and reliability were guaranteed while effectively improving the network throughput. however, obtaining an abundance of network slices is difficult with lower interoperability between the sdn/nfv and 5g network. service function chaining is utilized for network slicing [32], in which a set of service function chains is included in each slice to deal with any traffic per slice. then, the tradeoffs between slicing and execution runtime are examined by designing a greedy-based heuristic algorithm. ultimately, the required bandwidth and delay are obtained through an optimization model. the mobility of network slices is not taken into account, which reduces the qos and qoe. a scheme was developed by alfoudi et al. for network slicing resource management (nsrm) [33] for the allocation of resources for each slice within a network. an lte network was considered in this work for various slice allocations and fair distribution of bandwidth among slices. deploying the controller, all the slices are handled by the lte slice controller for each slice. the radio network resources are assigned through the lte slice controller by a virtual enodeb. it is very difficult to dynamically provision the slice requests. for instance, large slice request handling is required by the industry 4.0 application. narmanlioglu et al. conducted service-aware multi-resource allocation for cellular networks defined by software [34]. in this work, joint network allocation was demonstrated along with scheduling the available network resources for determining the network slices. based on the sla priorities and constraints, network resources are specifically provided. for each priority, the analytic hierarchy process (ahp) is utilized to calculate the resources (latency, throughput, reliability, and storage). through experiments, they evaluated the method for vertical subscribers and industries cost-efficiently. the network slice capacity is the main factor to determine the needed resources. though, ahp is not able to concurrently support multiple traffic flow resource allocation. the vehicular ad hoc network environment was examined by a dynamic end-to-end slicing method supporting 5g communications [35]. two kinds of slice services were examined including video and web. resources were assigned for network slices in a single physical network infrastructure. in both the control and data planes, the handling of different services from numerous users is supported through virtualized network functionality customization. however, high throughput is not provided by this end-to-end method for limited latency service types. two embb and v2x services were examined by albonda and pérez-romero [36]. they used two approaches of heuristic algorithm and reinforcement learning for resource allocation and network slicing for various slices. according to the simulation results, the latency is reduced by 0.18 s (by 0.26 s for a fixed slicing ratio). however, multiple traffic classes are not supported by this approach in each slice. furthermore, latency can be further reduced by a global controller for each service type. an optimal and quick response method is presented for resource slicing within heterogeneous cellular networks [37]. the real-time advent of slice requests is captured first by this technique through a semi-markov decision procedure (deep double dueling) to predict the service resources and time. through several experiments, the performance of the presented deep dueling method was demonstrated for resource slicing. several challenges are caused by large and dynamic network slices in the control and data plane. such challenges are addressed by presenting load balancing amongst multiple network service 89 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 chains. hence, a novel concept was used (point of existence) to solve the scalability problem while accepting only limited slice users [38-40]. 3. problem definition resource allocation and network slicing are run in sdn/nfv-based 5g networks based on the service requests of user devices [41-43]. massive service requests from the user can be handled through a multiclass queuing and traffic analysis model. low-complexity traffic predictors are employed utilizing a soft gated recurrent unit (gru) to allocate the resources through deep neural networks (dnns). moreover, a multistage analysis is conducted for three various slices (urllc, mmtc, and embb) to carry out m/m/n/k-based queuing. these studies have the following limitations: first, they are oriented by the load, thus, non-real-time traffic for scheduling before real-time traffic is caused by the high response time for processing high-priority class packets. second, based on a first-come-first-serve (fcfs) protocol, particular slices are scheduled thus further increasing the response time leading to poor qos for received requests. third, a single point of failure occurs in an sdn, when it is not possible to handle the requests from various users through a single controller. fourth, the response time is incremented by running both dnn and gru for more realistic and qos-constrained traffic. furthermore, a huge deal of energy and time is used by the dnn. fifth, a random seek pattern is run by the fcfs since requests are not reordered by the slice for minimizing service delay. besides, fair level sla constraints are not used by the queuing theory. since the service must be provided with an availability of 99.99%, ensuring service timeouts of less than 0.01% and completing the 99.99% of the services are essential within the resources. additionally, resources are not distributed properly when utilizing fcfs for scheduling. for embedded services, a dynamic flow migration was proposed under sdn/nfvaided 5g networks to decrease the dynamic traffic load per slice [44]. to address this issue, a heuristic algorithm was used. this approach has the following drawbacks: (1) adaptive flow migration is needed owing to the limited performance of the poisson traffic model. (2) an optimal solution was required by the routing path for flow migration and in former approaches, delay-sensitive traffic cannot be run. (3) the heuristic algorithm is not able to present an optimal solution when arriving at an unexpected flow at the controller. in the present work, the above-mentioned problems are resolved through network slicing, dynamic offloading, resource allocation, security, as well as packet classification. 4. system model to design the presented t-s3ra within an sdn/nfv-permitted 5g network, the mobile device authentication processing abilities were used along with network slicing, traffic scheduling, as well as dynamic offloading, and resource allocation. 4.1 network overview designing the t-s3ra model for resource allocation and secure network slicing included a global control plane, local control plane, user plane, and data plane. some entities are contained in the suggested t-s3ra model such as tools (d1 … dn), vap (va1 … van), 5g aps (ap1 … apn), controllers (gc), switches (ps1 … psn and vs1 … vsn) and some lcs (lc1 … lcn). the secure credentials are submitted in the devices to the 5g ap. generally, there are limited components at the data and control planes based on the resources. moreover, it is essential to use these resources for sending and receiving responses from 90 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 users as well as for action processing. the va is removed when not needed. hence, using the multi controllers resolves the single-controller-failure problem as a result of using both virtual and physical switches. hence, the overload problem is solved. in network slicing, more packet losses and delays are induced by massive traffic. thus, slicing is performed while scheduling the traffic and allocating the resources through deep learning methods. through dynamic offloading actions, imbalance issues are avoided. via various credentials, these actions are kept in the data plane while considering the resource wastage problem. hence, through entropy calculations, ddos attackers are detected arriving at the switches. 5g ap lp queue hp queue network slice 1 network slice n virtual authority p ool authorization message traffic scheduling by asymmetric queuing model gc (nsse) lc1 lc2 lcn physical infrastructure redirected flow switches 1...n authentication self-driving videosm art home sm art city ddos attackers pnf vnf pnf pnfvnf pnf vnf pnf pnfvnf pnf vnf pnf pnfvnf logical flow physical flow sliceneti/ps slice 1 slice n …... logical flow physical flow hopf ield net i/ps se1 sen …... network slice selection resource allocation lc’s management resource allocation gc control plane lc control plane data plane user plane fwbgflows slice 1 slice n …... dynamic flow migration load monitor flow table manager decision maker network slice 1 (embb) network slice 2 (urllc) network slice 3 (mmtc) …… ……… …... 1. data rate 2. packet delay 3. packet length 1. secret key 2. puf 3. timestamp 1 2 1 2 3 4 5 1. traffic type 2. fair sla 3. imsi 4. slice capacity 5. device mobility 1. sinr 2. throughput 3. fair sla 4. slice capacity 5. arrival rate 6. slice value 4 3 1. switch service capacity 2.transmission rate 3. loss rate 5 1 2 3 4 5 1 2 3 4 5 workflow criterions -- fig. 1: the system architecture [1]. figure 1 shows the proposed t-s3ra architecture. the main network entities include: (1) all iot tools with access to the network through the 5g communications network are known as the tools. such devices are dynamic in movement and heterogeneous in nature. higher coverage is required to connect them to the 5g ap. all tools are not approved, and unauthorized user participation is also possible. (2) 5g ap armed with higher communication coverage with a higher data rate, lower latency, and higher throughput. (3) 91 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 vap is a pool comprising some virtual authorities but not a single entity. it is often denoted as a specific entity balancing the authentication process. the 5g ap handles the va creation and deletion process. (4) switches that are commonly used in the data plane and function by matching the incoming flow with the flow table thus performing the actions. (5) controllers that are distributed and deployed within the control plane for resource allocation and network slicing. multiple controllers are utilized in this work to prevent the problem of a single point of failure. 4.2 device authentication the 5g ap audits each authority with a charge for inserting, deleting, and modifying the operations, in the vap. the pbkdf2 is utilized for authentication using three input parameters including puf 𝐼? 𝑢𝑓, secret key , and timestamp —. the request is accepted for the three valid parameters if not, it is not recognized and ended. the operations are conducted in the boolean logic function. pbkdf2 is a function based on the key made by rsa labs overwhelming the brute force attacks resultant from weak user passwords. the following parameters are used to derive a pbkdf2: an iteration count, ; a pseudorandom function, ; a password, ; a salt, ; an output-derived secret key, , and a selected output key length, . a of arbitrary length is driven by pbkdf2. in particular, by the pbkdf2, several possible blocks are generated, required for covering the output secret key length. for 𝑃𝑅𝐹 iteration, each block, is calculated through the count, . any number of iterations can be added for a large secret key length. the inputs are the user password in pbkdf2, l salt values, ; iteration count, ; ; timestamp, , and selected output key length, . a secret key, yields the output. (1) where denotes all security credentials’ concatenation. here, two processes of enrollment and verification handle the puf-based authentication. in the enrollment, all response and challenge pairs of the device are stored by the va, which is verified when entering a device into the network. the device id is received by the verifier to determine the random . the equivalent response is calculated for the issued challenge. the verifier examines the validity of the response in the database and the made response, is made for the valid cases. here, the boolean logic operator is represented as and stated as (2) 4.3 traffic scheduling through traffic scheduling in the 5g ap, congestion was avoided at the sdn controller. here, the devices' traffic flows are categorized and arranged through an asymmetric queue model operating in terms of bernoulli’s theorem [45,46]. using three parameters, traffic flow was scheduled including packet delay 𝐼?𝑑 , data rate , and packet length . thus, the total queuing service rate is: 𝐼_1 + 𝐼_2 = 1 (3) 92 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 a zero-packet loss rate is obtained by focusing on the adaptive queue within the two queues. therefore, hp’s service rate of  = 0.75 was reached and exceeded, while the queue was still in process. a discrete-time system was considered in this study to schedule services dynamically arriving for slicing requests. regarding the type of slots and service, all arriving requests were diverse. a random variable ɣ(t) was defined to represent the queue current state as: ɣ(t)= { 0 𝑄𝑢𝑒𝑢𝑒 𝑖𝑠 𝑖𝑑𝑙𝑒 𝑖 𝑄𝑢𝑒𝑢𝑒 𝑖𝑠 𝑏𝑢𝑠𝑦 𝑤𝑖𝑡ℎ 𝑛 𝑠𝑒𝑟𝑣𝑖𝑐𝑒𝑠 𝑙 + 1 𝑄𝑢𝑒𝑢𝑒 𝑖𝑠 𝑣𝑎𝑐𝑎𝑛𝑡 (4) 4.4 resource allocation and network slicing the network slice selection entities (nss s) were fed in the gc to slice the network via slicenet, which is a light and faster cnn outperforming wavenet, traditional cnns, and bytenet. service type 𝔰𝑡, fair sla 𝔣𝑆𝐿𝐴, slice capacity 𝕊𝒸 𝐼𝑀𝑆𝐼, and device mobility 𝑑𝔐 were all taken into account for slicing the network. this work primarily focused on sla constraints between the service provider and user leading to while slicing the network. followed by the fairness (weight) for each service, rtr, sar, tr, and srr were calculated. forwarding a service request to the controller is performed through the 5g ap over network slicing for a tool. the presented slicenet is sated as a mapping from the input layer to the output layer as: 𝑦 = 𝑓(𝔰𝑡 , 𝔣𝑆𝐿𝐴, 𝐼𝑀𝑆𝐼, 𝕊𝒸 , 𝑑𝔐 ∀(𝑑𝑖 )), (5) in which di represents the tool i. the aforementioned parameters are inserted as inputs into the presented slicenet where the input encoder, decoder, and i/o mixer, are the key components. the input is obtained from the devices by a convolutional module in three stages of separable conv, relu activation, and the layer normalization. the hidden units are normalized and calculated layer-wise in the normalization. generally, the conv_module is written as: 𝐶𝑜𝑛𝑣𝑆𝑡𝑒𝑝 (𝑤, 𝑥) = 𝐿𝑁(𝑆𝑒𝑝𝐶𝑜𝑛𝑣, (𝑤, 𝑅𝑒𝐿𝑈(𝑋)), (6) thus, the conv_module is achieved by stacking 4 convolutional phases: , (7) , (8) , (9) , (10) 𝐶𝑜𝑛𝑣𝑀𝑜𝑑𝑢𝑙𝑒 (𝑋) = { 𝐷𝑟𝑜𝑝𝑜𝑢𝑡 (ℎ4(𝑋), 0.5) 𝑇𝑟𝑎𝑖𝑛𝑖𝑛𝑔 ℎ4(𝑋) 𝑂𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 (11) where h (1…n) (x) represents the number of hidden units, and 0.5 is the learning rate. 93 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 the service requirements and input feature vector similarities are calculated based on the service type. two convolution steps are conducted by the 𝑆𝑜𝑓𝑡𝑚𝑎𝑥 function in this module: , (12) (13) ultimately, the three components’ structure was detailed including i/o mixer, input encoder, and decoder. the concatenation of all the aforementioned components makes the output embedding as: 𝑀𝑖𝑥𝑖=𝐼/𝑂 (𝑚)[𝐼𝑒 (𝑖), 𝑂𝑒 (𝑜)], (14) 𝑂𝑢𝑡𝑝𝑢𝑡𝑠 = 𝐷𝑒𝑐𝑜𝑑𝑒𝑟 (𝑚𝑖𝑥) (15) ultimately, is obtained in the output layer, which is determined as the slice selection indicator. thus, denotes three kinds of services including embb, mmtc, and urllc with different resource configurations. hence, each service type is represented accompanied by the specified network slice. to run resource allocation, hopfieldnet is used as a quick neural network to find the resource for each slice. considering 𝑆𝐼𝑁𝑅, 𝑇ℎ𝑟𝑜𝑢𝑔ℎ𝑝𝑢𝑡, 𝔣𝑆𝐿𝐴, 𝕊𝒸 , arrival rate 𝐴𝑟 , and slice value 𝑠𝑣, the resources were determined for each slice request. here, the resources are assigned for three various processes including computation, communication, and caching as cj, ci and ck respectively. hopfieldnet is an artificial neural network (ann) comprising nodes on a single layer. the input nodes in hopfieldnet are synchronously updated in terms of clock time variations. here, there are the contributing nodes with the connectivity in terms of the defined weight values. the outcomes from network slices are used by hopfieldnet as input to compute the resources for the three groups of slices as urllc, mmtc, and embb. the performance of input loops intended in this network is based on the capability of enriching knowledge, which is operative to resolve complicated computational problems. designing hopfieldnet with a single layer of input nodes linked to other nodes as feedback connections, redirection of the output to the input is assisted. here, there is an equal number of inputs, nodes, and outputs, in this t-s3ra system, and totally r1, r2, r3……,rn nodes are made by resources. the received input weight value is strong-minded from the separate slice service necessities stated in terms of the weight values in the connection as well as the node’s state. the weighted summation of the nodes u is: 𝑈𝑖 = ∑ 𝑤𝑒𝑖𝑗 𝑠𝑡𝑗 𝑁 𝑗=1 , (16) where denotes the connectivity weight between i and j, and stj 10ft he state 10ft he node j. to control the training in hopfieldnet, the storkey learning rule is used for minimizing the errors well. the storkey learning rule is mathematically formulated as: 𝑤𝑒𝑖𝑗 0 = 0 ∀ 𝑖, 𝑗, (17) 𝑤𝑒𝑖𝑗 𝑘 = 𝑤𝑒𝑖𝑗 𝑘−1 + 1 𝑁 𝐼_𝑖 𝑘 𝐼_𝑗 𝑘 − 1 𝑁 𝐼_𝑖 𝑘 ℎ𝑗𝑖 𝑘 − 1 𝑁 ℎ𝑖𝑗 𝑘 𝐼_𝑗 𝑘 (18) 94 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 the weight estimated between 𝑖 and 𝑗 is represented by 𝑤𝑖𝑗 𝑒𝑘 in (17) and (18) only after learning the pattern, while represents the new knowledge pattern. the local field is: 𝐻𝑖𝑗 𝑘 = ∑ 𝑤𝑒𝑖𝑛 𝑘−1𝐼_𝑛 𝑘𝑁 𝑛=1,𝑛≠𝑖,𝑗 , (19) premeditating the hopfieldnet, the resources are categorized in terms of the slice service requirements. as seen in fig. 5, for categorizing the available resource blocks from the slices, the hopfieldnet with a single layer is {x1, x2, …xi…xn} and the equivalent outputs are {y1, y2, y3,…yi…yn}. the inputs are received from all ns defined as {r1, r2, r3……,rn}. for each separate ns, the output in hopfieldnet is attained. the advantage of hopfieldnet is its process for associative memory to store part of the information and allocate the rest of the pattern. recalling the former patterns, using prior information of the resource amount is enabled for each ns. the resource is classified into 3 states. in the suggested t-s3ra, the states of the nodes are estimated as: (20) for each node, the states st are formulated in a trained matrix, where the three groups, ci, cj and ck are the possible states for the resource. the node 𝑠𝑡𝑖 state is defined as: 𝑠𝑡𝑖 = 𝑠𝑖𝑔𝑛(𝑈𝑖 − 𝑇𝐻𝑅𝐸𝑆𝑁 ), (21) in which represents the threshold, , and . no node is related to itself as in this network and all nodes need to follow . thus, the node connectivity weights are stated as: (22) for each node, the threshold thresi is presented based on its service requirements. the threshold for the nodes is presented in matrix format as: (23) where represent the separate threshold values for each node. the threshold can be varied considering the existence of the slice requests in each ns. the threshold is updated when a new slice request is included in the device or user. using the class of the resources at the ns is recognized followed by finding the resources for the ns. then, the individual ns payment status is confirmed to exactly predict the use of the load by the ns. 4.5 dynamic flow offloading a higher traffic volume of slices is resultant from an inadequate bandwidth for switches. comprised fωbg is used in terms of the transmission rate, switch service capacity, and loss rate. by fωbg , multiple flows are mapped to the optimal switches increasing the network reputation. furthermore, fωbg helps to prevent slice capacity problems. 95 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 5. results and discussion 5.1 simulation setup to evaluate the proposed t-s3ra model, the network simulator tool v.ns3.26 was used, which can incorporate the technologies and network modules needed to simulate a network properly. the network simulator was mounted on a system with a 32-bit dual-core processor, the ubuntu 14.04 lts os, and 2 gb of ram. table 1 presents the simulation parameters for designing the testbed. figure 2 represents the suggested t-s3ra architecture model simulation results. the proposed system with various planes is explained based on the simulation steps, as shown above. fig. 2: the simulation results for key generation, network slicing, and node deployment. 5.2 comparative analysis in this comparative analysis section, the efficiencies of the proposed t-s3ra are evaluated based on the methods assessed previously. to compare with the proposed system, some significant metrics are taken into account. to illustrate the performance of former resource allocation and network slicing schemes, the present approaches concentrate on dynamic flow migration (load balancing), resource allocation, or network slicing during network slicing. thus, the present work focusing on all three procedures accompanied by security helps to avoid resource wastage in the control planes and data. a comparison was made on the performances of t-s3ra for three slices, urllc, mmtc, and embb represented as s1, s2, and s3 respectively. 96 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 5.2.1 effect on throughput the throughput performance is demonstrated in fig. 3 based on the number of slice requests. as seen, the network’s throughput possesses greater values in the presented ts3ra than the gru-dnn [42]. fig. 3: the throughput against the number of slice requests. 5.2.2 effect on latency figure 4 shows the comparison of latency performance. a lower latency was obtained by the presented t-s3ra since it utilizes fast algorithms as well as effective resource allocation and network slicing. more time is required to calculate the hyperparameters and tuning required for the dnn. fig. 4: the latency against the number of slice requests. 5.2.3 effects on response time according to fig. 5, the response time performance is improved, by minimizing the latency. the results of the response time comparison are presented in fig. 5. a considerably small response time was obtained since t-s3ra is effective and end-to-end secure. an effective algorithm was not used in the present work. 97 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 fig. 5: the response time and the number of slice requests. 5.2.4 effects on transmission ratio utilizing the asymmetric queue model, the traffic is arranged at the 5g ap increasing the packet transmission ratio. moreover, for all slice requests, resources are optimally allocated resulting in a higher packet transmission ratio. the highest packet transmission ratio was obtained for s2 since highly reliable responses are required by these services. 5.2.5 effects on packet loss ratio to assess the packet loss performance, the number of devices is considered. according to fig.11, the packet loss is lower in the considered t-s3ra than in the gru-dnn. fig. 6: the packet loss ratio versus the number of devices. 5.2.6 effects on slice capacity the comparison of the slice capacity vs. the number of devices is presented in fig. 7. based on the analysis of slice capacity, high performance is obtained by the proposed ts3ra. 0 2 4 6 8 10 12 r e sp o n se t im e ( s) no of slice requests t-s3ra (s1) t-s3ra (s2) t-s3ra (s3) gru-dnn (s1) gru dnn (s2) gru-dnn (s3) 98 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 fig. 7: the slice capacity against the number of devices. 5.2.7 effects on bandwidth consumption the bandwidth consumptions of the estimated and present outlines are presented in fig. 8. traffic offloading along with a multi-controller environment is used by the presented scheme, hence, the lower bandwidth is consumed. however, the higher bandwidth is used for gru-dnn since there are no single controller problems and massive traffic handling. fig. 8: the bandwidth consumption versus the number of slices. 5.2.8 effect on slice acceptance ratio the acceptance ratios of the slice of t-s3ra and gru-dnn are compared in fig. 9. using deep learning-based resource allocation and network slicing can result in a considerably higher slice acceptance ratio. in the former study, the best solution was not obtained using deep learning methods. therefore, there were poor slice acceptance ratios. particularly, limited parameters were considered by the problem for slice selection. therefore, better efficiency is obtained by the presented t-s3ra compared to the grudnn for all network slices. moreover, security is ensured by the presented t-s3ra while performing resource allocation and slicing the network. 99 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 fig. 9: the slice acceptance ratio against the number of slice requests. 5. conclusion in the present work, the qos was enhanced in an sdn/nfv-permitted 5g network in terms of the presented architecture including t-s3ra incorporating the service and sla necessities for requests arriving from a user or device. there are four planes in the presented architecture including device, local controller, data, and global controller. the users or devices are authenticated through the va via 5g ap utilizing pbkdf2. for secure communication, the va is made and authenticated to the 5g ap reducing the communication overhead. then, the traffic from the 5g ap is categorized into two hp and lp queues. it is held by the asymmetric queue model utilizing bernoulli’s theorem. then, the hp request is forwarded to the lc for resource allocation and network slicing. slicenet was proposed in this work for slicing, and resources were assigned utilizing hopfieldnet. furthermore, to run dynamic flow offloading, fωbg was used. to prevent packet dropping and enrich the qos, the flows were matched with underloaded switches. furthermore, ddos attackers were eliminated from the network through packet arrangement utilizing renyi entropy. ultimately, the system’s performance was assessed in terms of qos metrics like throughput, latency, response time, packet loss ratio, packet transmission ratio, bandwidth consumption, slice capacity, as well as slice acceptance ratio. references [1] ramadhan aj. (2021) t-s3ra: traffic-aware scheduling for secure slicing and resource allocation in sdn/nfv enabled 5g networks. int j of eng trend and tech, 69: 215-232. https://doi.org/10.14445/22315381/ijett-v69i7p229 [2] barakabitze aa, ahmad a, mijumbi r, hines a. (2020) 5g network slicing using sdn and nfv: a survey of taxonomy, architectures and future challenges. comput netw, 167: 106984. https://doi.org/10.1016/j.comnet.2019.106984 [3] barmpounakis s, maroulis n, papadakis m, tsiatsios g, soukaras d, alonistioti n. (2020) network slicing-enabled ran management for 5g: cross layer control based on sdn and sdr. comput netw, 166: 106987. https://doi.org/10.1016/j.comnet.2019.106987 [4] ramadhan aj. (2020) smart glasshouse system supported by global system for mobile communications and internet of things: case study: tomato plant. j of eng sci and tech. 15: 3067–3081. 100 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 [5] borylo p, tornatore m, jaglarz p, shahriar n, chołda p, boutaba r (2020) latency and energy-aware provisioning of network slices in cloud networks. comput commun, 157: 1-19. https://doi.org/10.1016/j.comcom.2020.03.050 [6] boutigny f, betgé-brezetz s, blanc g, lavignotte a, debar h, jmila h (2020) solving security constraints for 5g slice embedding: a proof-of-concept. comput sec, 89: 101662. https://doi.org/10.1016/j.cose.2019.101662 [7] tang l, zhao g, wang c, zhao p, chen q (2018) queue-aware reliable embedding algorithm for 5g network slicing. comput netw, 146:138-150. https://doi.org/10.1016/j.comnet.2018.09.014 [8] kim y, kim s, lim h (2019) reinforcement learning based resource management for network slicing. appl sci, 9:2361. https://doi.org/10.3390/app9112361 [9] raza mr, natalino c, öhlen p, wosinska l, monti p. (2019) reinforcement learning for slicing in a 5g flexible ran. j lightwave technol, 37: 5161-5169. https://doi.org/10.1109/jlt.2019.2924345 [10] sun g, xiong k, boateng go, liu g, jiang w. (2020) resource slicing and customization in ran with dueling deep q-network. j network comput appl, 157: 102573. https://doi.org/10.1016/j.jnca.2020.102573 [11] ma t, zhang y, wang f, wang d, guo d. (2020) slicing resource allocation for embb and urllc in 5g ran. wirel commun mob comput, 2020: 1-11. https://doi.org/10.1155/2020/6290375 [12] coronado e, khan sn, riggio r. (2019) 5g-empower: a software-defined networking platform for 5g radio access networks. ieee trans netw serv manage, ieee 16: 715-728. https://doi.org/10.1109/tnsm.2019.2908675 [13] sathi vn, srinivasan m, thiruvasagam pk, murthy sr (january 2020) novel protocols to mitigate network slice topology learning attacks and protect privacy of users’ service access behavior in softwarized 5g networks. ieee trans depend sec comput, 1. https://doi.org/10.1109/tdsc.2020.2968885 [14] thantharate a, paropkari r, walunj v, beard c, kankariya p. (2020) secure5g: a deep learning framework towards a secure network slicing in 5g and beyond. proceedings of the 10th annual computing and communication workshop and conference (ccwc), 72020:0852 [15] ni j, lin x, shen xs. (2018) efficient and secure service-oriented authentication supporting network slicing for 5g-enabled iot. ieee j select areas commun, 36: 644-657. https://doi.org/10.1109/jsac.2018.2815418 [16] afolabi i, taleb t, samdanis k, ksentini a, flinck h. (2018) network slicing and softwarization: a survey on principles, enabling technologies, and solutions. ieee commun surv tutorials, 20: 2429-2453. https://doi.org/10.1109/comst.2018.2815638 [17] khan s, khattak ha, almogren a, shah ma, ud din i, alkhalifa i, guizani m. (2020) 5g vehicular network resource management for improving radio access through machine learning. ieee access, 8: 6792-6800. https://doi.org/10.1109/access.2020.2964697 [18] ye q, zhuang w, zhang s, jin al, shen x, li x. (2018) dynamic radio resource slicing for a two-tier heterogeneous wireless network. ieee trans veh technol, 67: 9896-9910. https://doi.org/10.1109/tvt.2018.2859740 [19] le lv, lin bsp, tung lp, sinh d. (2018) sdn/nfv, machine learning, and big data driven network slicing for 5g. proc ieee. world forum (5gwf) 5g: 20-25. [20] costanzo s, fajjari i, aitsaadi n, langar r. (2018) dynamic network slicing for 5g iot and embb services: a new design with prototype and implementation results. proceedings of the 3rd cloudification of the internet of things (ciot), 2018: 1-7. [21] kammoun a, tabbane n, diaz g, dandoush a, achir n. (2018) end-to-end efficient heuristic algorithm for 5g network slicing. proceedings of the 2018 ieee 32nd international conference on advanced information networking and applications (aina), pp 386-392 [22] trivisonno r, condoluci m, an x, mahmoodi t. (2018) miot slice for 5g systems: design and performance evaluation. sensors (basel), 18: 635. https://doi.org/10.3390/s18020635 101 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 [23] šeremet i, čaušević s. (2019) benefits of using 5g network slicing to implement vehicle-toeverything (v2x) technology. proceedings of the 2019 ieee 18th international symposium infoteh-jahorina (infoteh), pp 1-6 [24] wang t, guo z, chen h, liu w. (2018) bwmanager: mitigating denial of service attacks in software-defined networks through bandwidth prediction. ieee trans netw serv manage, 15: 1235-1248. https://doi.org/10.1109/tnsm.2018.2873639 [25] porambage p, miche y, kalliola a, liyanage m, ylianttila m. (2019) secure keying scheme for network slicing in 5g architecture. proceedings of the 2019 ieee conference on standards for communications and networking (cscn), pp. 1-6 [26] li x, guo c, gupta l, jain r. (2019) efficient and secure 5g core network slice provisioning based on vikor approach. ieee access 7: 150517-150529. https://doi.org/10.1109/access.2019.2947454 [27] ma l, wen x, wang l, lu z, knopp r. (2018) an sdn/nfv based framework for management and deployment of service based 5g core network. china commun, 15: 86-98. https://doi.org/10.1109/cc.2018.8485472 [28] dawaliby s, bradai a, pousset y. (2019) distributed network slicing in large scale iot based on coalitional multi-game theory. ieee trans netw serv manage, 16: 1567-1580. https://doi.org/10.1109/tnsm.2019.2945254 [29] alqahtani sa. (2020) an efficient resource allocation to improve qos of 5g slicing networks using general processor sharing-based scheduling algorithm. int j commun syst, 33:e4250. https://doi.org/10.1002/dac.4250 [30] koutlia k, ferrús r, coronado e, riggio r, casadevall f, umbert a, pérez-romero j. (2019) design and experimental validation of a software-defined radio access network testbed with slicing support. wirel commun mob comput 2019:1-17. https://doi.org/10.1155/2019/2361352 [31] an n, kim y, park j, kwon dh, lim h. (2019) slice management for quality of service differentiation in wireless network slicing. sensors, 19: 2745. https://doi.org/10.3390/s19122745 [32] addad ra, bagaa m, taleb t, dutra dlc, flinck h. (2019) optimization model for crossdomain network slices in 5g networks. ieee trans on mobile comput, 19: 1156-1169. https://doi.org/10.1109/tmc.2019.2905599 [33] alfoudi asd, newaz shs, otebolaku a, lee gm, pereira r. (2019) an efficient resource management mechanism for network slicing in a lte network. ieee access, 7:89441-89457. https://doi.org/10.1109/access.2019.2926446 [34] narmanlioglu o, zeydan e, arslan ss. (2018) service-aware multi-resource allocation in software-defined next generation cellular networks. ieee access, 6: 20348–20363. https://doi.org/10.1109/access.2018.2818751 [35] afaq m, iqbal j, ahmed t, ul islam i, khan m, khan ms. (2020) towards 5g network slicing for vehicular ad-hoc networks: an end-to-end approach. comput commun, 149: 252-258. https://doi.org/10.1016/j.comcom.2019.10.018 [36] albonda hdr, pérez-romero j (2019) an efficient ran slicing strategy for a heterogeneous network with embb and v2x services. ieee access, 7: 44771-44782. https://doi.org/10.1109/access.2019.2908306 [37] van huynh n, hoang dt, nguyen dn, dutkiewicz e. (2019) optimal and fast real-time resource slicing with deep dueling neural networks. ieee j sel areas commun, 37: 14551470. [38] aicardi m, bruschi r, davoli f, lago p, pajo jf. (2018) decentralized scalable dynamic load balancing among virtual network slice instantiations. proceedings of ieee globecom workshops (gc wkshps):1-7. [39] zubov d, kose u, ramadhan a.j, kupin a. (2018) mesh network of ehealth intelligent agents in smart city: a case study on assistive devices for visually impaired people. ceur w proce 2255: 65–81. 102 iium engineering journal, vol. 23, no. 2, 2022 ramadhan https://doi.org/10.31436/iiumej.v23i2.1763 [40] chahlaoui f, el-fenni mr, dahmouni h. (2019) performance analysis of load balancing mechanisms in sdn networks. proceedings of the 2nd international conference on networking. inf syst sec:1–8. [41] kamath s, singh s, kumar ms. (2019) multiclass queueing network modeling and traffic flow analysis for sdn-enabled mobile core networks with network slicing. ieee access, 8: 417-430. https://doi.org/10.1109/access.2019.2959351 [42] chergui h, verikoukis c. (2019) offline sla-constrained deep learning for 5g networks reliable and dynamic end-to-end slicing. ieee j select areas commun, 38: 350-360. https://doi.org/10.1109/jsac.2019.2959186 [43] alqahtani sa, alhomiqani wa. (2020) a multi-stage analysis of network slicing architecture for 5g mobile networks. telecommun syst, 73: 205–221. https://doi.org/10.1007/s11235019-00607-2 [44] qu k, zhuang w, ye q, shen x, li x, rao j. (2020) dynamic flow migration for embedded services in sdn/nfv-enabled 5g core networks. ieee trans commun, 68: 2394-2408. https://doi.org/10.1109/tcomm.2020.2968907 [45] park k, li j, feng sc. (2018) scheduling policies in flexible bernoulli lines with dedicated finite buffers. j manuf syst, 48: 33-48. https://doi.org/10.1016/j.jmsy.2018.05.013 [46] md. zaki fammd, chin ts. (2019) fwfs: selecting robust features towards reliable and stable traffic classifier in sdn. ieee access, 7: 166011-166020. https://doi.org/10.1109/access.2019.2953565 103 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 221 combination of fused deposition modelling with abrasive milling for attaining higher dimensional accuracy and better surface finish abu naser mohammad amanullah tomal1, tanveer saleh2* and md raisuddin khan2 1 department of electrical and electronic engineering, daffodil international university, savar, dhaka, bangladesh 2 department of mechatronics engineering, kulliyyah of engineering, international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia. * corresponding author: tanveers@iium.edu.my (received:22nd june 2018; accepted: 15th aug 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.960 abstract: currently, two manufacturing methods, namely cnc (computer numerical control) machining and rapid prototyping (rp), are widely used to produce final products and prototypes. both the processes have their own advantages. cnc machining such as milling and grinding (subtractive method) can fabricate parts with higher precision and accuracy. on the other hand, rp (additive method), can manufacture parts with complicated 3-d (three dimensional) features, which ensures effective material usage. however, rp produced parts lack accuracy and smooth surface finish. in this research, we are aiming to achieve on-machine mechanical post-processing of 3-d printed (using fused deposition modelling, a kind of rp process) parts to achieve higher dimensional accuracy and better surface roughness. to achieve the goal, we developed a new hybrid system to assimilate both of these processes. there are, however, two vital considerations needed to be taken into account for integrating the two processes. the first concern is the integration of dissimilar control systems for two processes and the second aspect is maintaining the tools’ (milling spindle and the heat extruder) setup accuracy during the changeover step. the developed hybrid machine has been tested with experimentations and the result showed that the dimensional accuracy was improved by 71% to 99% when the fdm part was compared with the final part after abrasive milling operation. at the same time, average surface roughness (ra) was improved up to 91.3%. further, we found that low layer thickness improves the product quality. the proposed system could push the conventional fdm system to the next level to attain better quality of final products. abstrak: dua kaedah terkini proses pembuatan, dinamakan mesin kawalan komputer bernombor (cnc) dan prototaip langsung (rp) telah digunakan secara meluas bagi menghasilkan produk dan prototaip. kedua-dua proses mempunyai keistimewaan tersendiri. mesin cnc seperti mesin penghasil permukaan dan mesin penebuk lubang (melalui kaedah pengurangan) dapat menghasilkan sesuatu bahagian dengan ketepatan tinggi. pada sudut lain, rp (melalui kaedah penambahan), dapat menghasilkan bahagian dengan kaedah 3d (tiga dimensi) yang rumit tetapi berkesan dalam memaksimakan penggunaan material. walau bagaimanapun, penghasilan bahagian melalui kaedah rp mempunyai kekurangan pada ketepatan dan kekurangan pada kekemasan permukaan akhir. kajian ini bertujuan meraih ketepatan dimensi yang lebih tinggi dan kekemasan permukaan yang lebih bagus pada proses terakhir pada bahagian cetakan mesin mekanikal iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 222 3d (menggunakan model deposit fuse iaitu salah satu proses rp). bagi mencapai tujuan ini, kami menghasilkan sistem hibrid terbaru untuk mengasimulasi kedua-dua proses. walau bagaimanapun, terdapat dua perkara penting perlu diambil kira untuk diintegrasi bersama kedua-dua proses. penilaian pertama adalah pada sistem kawalan tidak serupa, dan kedua pada aspek pengekalan alat (gelendung pemutar dan kepanasan pembentuk) ketepatan penyediaan semasa peringkat perubahan. mesin hibrid yang dicipta telah diuji melalui eksperimentasi dan keputusan menunjukkan ketepatan dimensi telah bertambah daripada 71% kepada 99% semasa bahagian fdm dibandingkan dengan bahagian akhir selepas operasi putaran kasar. pada masa sama, purata permukaan kasar (ra) telah bertambah kepada 91.3%. kami juga mendapati ketebalan lapisan bawah telah menambah baik kualiti produk. sistem yang dicadangkan dapat mengubah sistem fdm konvensional kepada peringkat lebih tinggi bagi memperolehi kualiti terbaik pada produk akhir. keywords: fused deposition modelling; abrasive milling; hybrid system; fdm; rapid prototyping 1. introduction in the 1980s, rapid prototyping (rp) technologies were introduced and were used to quickly create prototypes in an automated manner. rp is also known as ‘layered manufacturing’ (lm) and ‘additive manufacturing’ (am). the additive mechanism that involves building the part by combining layers of material (solid sheet, powder or liquid) until the whole product is produced as stated by wohler [1]. this technology has drawn significant interest due to its capability to overcome many drawbacks of traditional manufacturing techniques. its ability to form almost any geometric feature or shape is a great advantage of am as mentioned by gebhardt [2]. this group of technologies was introduced to assist the development of new products, especially for evaluation processes and analysis. at early stages of product development, rp allows design changes and confirms products’ validity before entering full-scale production. as time progresses, rp technologies have advanced, and their scope has been extended to create finished parts. several techniques have been developed to establish rp technology as one of the most reliable manufacturing methods. more developments in rp have invented some advanced techniques that can process metallic materials as well produce polymeric products. various am processes have been introduced to the commercial market by industrial companies as discussed by goldsberry [3] including the arcam in sweden, electro-optical systems (eos) in germany, z corporation and optomec in the united states, stratasys in the uk, and mcp tooling technologies, among others. am processes are divided into the following three broad categories as noted by kruth et al. [4] and kruth [5]: (1) solid based, (2) powder based, and (3) liquid-based, as described. fused deposition modelling also popularly known as 3-d printing is a typical example of solid based rapid prototyping (rp process). in the fdm process, a plastic material such as acrylonitrile butadiene styrene (abs), polylactic acid (pla), investment casting wax, or elastomers is used by extruding it through a nozzle and depositing it layer-by-layer to build a part. mostly, in the fdm method the material is supplied in the form of a filament. a resistive heater alongside the extruder is used to maintain the temperature of the filament just above its phase transitional point. this helps the raw filament to easily flow through the nozzle and deposit as a layer. as the deposited layer is exposed to the ambient it hardens instantly and bonds to the previous layer. this procedure of deposition of the layer continues until the final shape is obtained. the significant advantage of the fdm process is its ability to yield parts with complex features. however, due to the thermal shrinkages that occur during the rp process, the iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 223 attainable surface quality and dimensional accuracy of the produced product are quite limited. the surface quality of the parts produced by pure fdm method is significantly low because of the staircase effect pointed out by pandey et al. [6]. anitha et al. [7] showed that the layer thickness of the fdm process plays the most vital role on the surface roughness of the finished product. in order to improve the surface quality of the fdm parts, there are several post-processing techniques (mechanical) available such as manual sanding, abrasive flow machining, abrasive milling, hot cutter machining, ball burnishing, etc. described by chohan et al. [8]. galantucci et al. [9] proposed abrasive milling using bulk lamellar abrasive paper to achieve 90% improvement in surface finish with reasonable dimensional accuracy. pandey et al. [6] proposed a staircase machining approach for improving the surface roughness of the fdm parts. other post-processing techniques for the products fabricated by rapid prototyping include abrasive flow machining [10], vibratory bowl finishing [11] and barrel finishing [12]. ferreira et al. [13] retrofitted a large-format fdm printer to incorporate open source hardware and software, so that the printer can be used in a versatile way for the future research. liu et al. [14] also developed a large-scale double screw 3-d printer to print large plastic product at a low cost. boschetto et al. [15] proposed a process plan to carry out a finishing operation on the fdm parts using the cnc milling machine. lee et al. [16] developed a machine where the fdm extruder and milling spindle were mounted on the same frame and could be positioned on the workpiece as necessary. this approach of the design made the overall structure of the machine bulky. in order to maintain the product accuracy by avoiding any setup error, it is necessary to carry out the post-processing of the fdm parts on the machine. therefore, the main focus of this paper is to propose a modular design of a hybrid system combining fused deposition modelling and cnc abrasive milling. the post-processing of the fdm parts was carried out by abrasive milling on-machine thus any error due to workpiece transfer was eliminated. 2. materials and methods to carry out the finishing operation on the fdm parts, a hybrid system was developed that integrates both the fdm and the finishing operation. in this project, abrasive milling was chosen as the finishing operation (commercially available abrasive dremel {aluminum oxide} stone was chosen for this purpose). the material that was used to fabricate fdm parts was pla (polylactic acid). as mentioned earlier it is preferred to unify the primary process (fdm in this case) and finishing process (abrasive milling in this case) into a single platform so that any form of setup error is avoided due to the transfer of the workpiece from one workstation to another. to achieve this unification, we chose a modular approach in our design. fig. 1 (a) shows the cad (computer aided design) model of the developed system. the system consists of three translation axes (x, y, and z) and one rotary stage. the rotary stage was mounted on the z axis that holds the milling spindle or the fdm heat extruder as needed. the heat extruder and the milling spindle were bought off the shelf as a standard product. however, the attachment was designed in such a way that these two components can be mounted on the rotary stage as necessary to ensure the modularity in the design. furthermore, as shown in the fig. 1, two infra-red sensors (ir) were placed on the vertical z axis. the signal from these ir sensors ensures the parallelism of the heat extruder and the milling spindle with the z axis. figure 2 shows typical signal output from the two ir sensors received by the developed graphical user interface (gui) for the hybrid system. iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 224 fig. 1: cad model of the developed hybrid system combining fused deposition modelling and abrasive milling; (a) shows mounting of the heat extruder and (b) shows the mounting of the milling spindle. fig. 2: ir sensor feedback to align the fdm extruder and the milling spindle: (a) aligned condition (b) non-aligned condition. (a) (b) iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 225 it can be understood from fig. 2, that when both the ir sensors generate the same voltage level (i.e., the difference is zero as shown in fig. 2 (a)) the heat extruder or the spindle mounted on the rotary stage can be assumed to be parallel to the z axis. however, if the voltage output of the two sensors is not zero, as shown in (fig. 2 (b)), then the rotary axis is rotated accordingly to achieve the desired level of alignment of the heat extruder/ milling spindle. a graphical user interface (gui) was developed using the labview integrated development environment (ide) to integrate the operation of the two processes. the operational sequence of the whole process can be explained by fig. 3. initially, the cad model of the desired object was created and saved in the .stl format using solidworks [17]. next, slic3r [18] software was used to slice the cad model into layers according to the given layer thickness. after that, the g code of the cad model was also generated from the same software to be used for the rapid prototyping purpose. before starting the rapid prototyping operation, the heat bed needs to be levelled with the base of the machine so that the layer of the raw material is deposited properly on it. to level the heat bed a digital calliper was used. several measurements were taken from the base to the upper surface of the heat bed in its four corners. next, the rp process was carried out. several products were produced with layer thickness ranges from 0.1 mm to 0.2 mm. finally, to do the final finishing of the produced fdm parts, the heat extruder was replaced with a cnc spindle and the abrasive milling operation was carried out. fig. 3: flow chart of the whole working process. 3. results and discussion to evaluate the performance of the fdm-abrasive milling-based hybrid system, a test specimen was printed and machined with the following targeted dimension 15 mm x 15 mm x 10 mm. fdm operation was conducted with three layer thicknesses (0.1 mm, 0.15 mm, iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 226 and 0.2 mm). several studies were carried out for both the fdm parts and fdm followed by abrasive milling parts. the scope of the study is limited to evaluate the performance in regards to dimension accuracy and the surface roughness of the final product as they are the two most important aspects in manufacturing. 3.1 study of the dimensional accuracy in order to compare the dimensional accuracy, a cuboid was printed using the fdm process with the programmed dimension of 15 mm x 15 mm x 10 mm. for comparison, fdm parts were further machined (finishing) using a commercially available grinding stone. during the finishing operation, the heat extruder was removed from the machine, and the milling spindle was mounted with proper alignment. the dimensions were measured using a digital calliper with a resolution of 0.01 mm. the findings of our study are plotted in the fig. 4. the measurements were taken for all the three dimensions (length, width, and height). both types of samples (fdm and fdm-milled) were compared with the programmed dimensions. dimensional accuracy was measured as the deviation of the actual dimension from the programmed dimension. it can be seen from fig. 4 that as the layer thickness increases, the dimension deviates positively from the targeted one for the pure fdm samples (without abrasive milling). the reason for this deviation could be explained as follows. the layer thickness of the fdm process is controlled by the vertical step movement (upward) of the z axis, the coarser the upward movement of the extruder the larger the layer thickness. larger layer thickness caused non-uniform overlapped deposition of the melted pla material on the previous layer hence, caused dimensional inaccuracy. fig. 4: shows comparative study of the dimensional accuracy between fdm parts and fdm parts with post finishing process (abrasive milling). as for 0.2 mm of the layer thickness the measured dimension of the fdm part (in length) was 16.05 mm. therefore, the deviation from the programmed dimension was obtained as 16.05-15 = 1.05 mm. however, as the part was milled with the abrasive stone the deviation was reduced to 0.01mm. hence, we can conclude that the abrasive milling process improved the product accuracy (for this particular case) by (1.05-0.01)* 100/1.05 = 99%. the measured dimensions of the fdm parts and fdm parts that underwent abrasive milling are shown in table 1. iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 227 table 1: measured dimensions of fdm parts and fdm parts that underwent abrasive milling layer thickness programmed dimension (mm) fdm parts (mm) deviation (mm) fdm parts with abrasive milling (mm) deviation (mm) improvement (%) 0.1 mm length 15 15.2 0.2 14.96 -0.04 80 width 15 15.25 0.25 14.98 -0.02 92 height 10 10.07 0.07 9.98 -0.02 71 0.15 mm length 15 15.55 0.55 15.05 0.05 91 width 15 15.62 0.62 15.03 0.03 95 height 10 10.2 0.2 10.03 0.03 85 0.2 mm length 15 16.05 1.05 15.01 0.01 99 width 15 16.13 1.13 15.03 0.03 97 height 10 10.35 0.35 10.04 0.04 89 the minimum deviation was attained for the lowest layer thickness of 0.1 mm which is 0.2 mm, 0.25 mm and 0.07 mm for the length (l), the width (w) and the height (h) respectively as shown in table 1 (fdm part). as for the samples with abrasive milling, the inaccuracy was reduced to 0.04 mm, 0.02 mm and 0.02 mm for the length (l), the width (w) and the height (h) respectively as shown in table 1. the standard deviation of the dimensions of the samples (length, width, and height) for different layer thicknesses was in a range of 10’s of micrometres in the case of samples that underwent abrasive milling operation. for the samples without the finishing operation, the value easily rose to 100’s of micrometres. therefore, it can be further concluded that similar levels of dimensional accuracy can be achieved irrespective of the layer thickness (during the fdm operation) if abrasive milling operation is carried out on the samples. 3.2 study of the average surface roughness and morphology average surface roughness and morphology are two important aspects of studying for the fabricated prototypes. the surface roughness of the produced parts was measured with mitutoyo sv-c4500 surface roughness/contour measuring system. the measurement length was kept to be 5 mm to ensure that the stylus does not overshoot and touch the edge of the produced structure. multiple measurements were taken to ensure the integrity of the results. figure 5 shows the surface profile of fdm parts with the abrasive milling operation and without the abrasive milling operation for different layer thicknesses. it can be easily inferred from fig. 5 that the post machining process (abrasive milling in this case) significantly improves the surface profile by reducing the staircase effect of the fdm part. moreover, it can be further concluded that layer thickness plays a significant role in the surface roughness on the fdm parts and the best profile was achieved at 0.1 mm layer thickness for this research. the reason for achieving better surface roughness at lower layer thickness is due to the uniform deposition of the melted pla on the preceding layer. figure 6 shows the plot of average surface roughness (ra) and the total height of the profile (rt). in both cases, it was observed that post finishing process helps to improve the surface roughness parameters. iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 228 fig. 5: raw surface profile of parts produced by fdm and fdm parts that underwent abrasive milling finishing operation, with parts produced (a) at 0.1 mm layer thickness (b) at 0.15 mm layer thickness and (c) at 0.2 mm layer thickness. fig. 6: shows the comparison of ra (a) and rt (b) between pure fdm parts and fdm parts with post finishing operation for different layer thickness. iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 229 the best ra value was achieved at 0.1 mm layer thickness with an abrasive milling finishing process, which was 1.16 µm. the improvement was almost 91.3% as compared with the fdm part without the finishing operation. for the same sample, the rt value was improved by 87.2% from the fdm part without the post-processing. the morphological study by scanning electron microscopy (sem) was conducted after coating the sample with a thin layer of gold because of its’ nonconductive characteristics. figure 7 shows the sem images of the samples which further validate the study of dimensional accuracy and surface roughness. the sem images of fdm parts without post-finishing operation shows typical staircase effects (fig. 7 (a), (b) and (c)). however, for the parts with the finishing operation, sem images (fig. 7 (d), (e) and (f)) confirm that the staircase effect was reduced by a significant margin and the surface becomes smoother. the phenomenon was the same for all layer thicknesses, i.e. 0.1 mm, 0.15 mm and 0.2 mm. furthermore, fig.7 confirms that fdm parts have voids between their layers due to non-uniform overlapping of the layers, as shown in fig. 7 (b) and (c) (white circles). the void remains in the produced parts even after the abrasive milling operation, as shown in the fig. 7(e) and (f) (white circles). the voids created between the layers are the main reason for worsening dimensional accuracy and surface roughness of the fdm parts with greater layer thickness. fig. 7: sem images of the produced samples with different layer thickness. (a), (b) and (c) are fdm parts without the finishing operation; (d), (e) and (f) are fdm parts with the abrasive milling operation. the circle marks shows voids due to nonuniform overlap of the layers for thicker layers. iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 230 4. conclusion this paper proposes a modular design to integrate fdm and post-finishing (abrasive milling) processes into a single platform. conventionally, the finishing operation of the fdm process is carried out off the machine, which increases the chances of product damage due to mishandling and product inaccuracy because of the changeover process from one machine to another. the proposed hybrid system eliminates such possibilities. a rotary axis was integrated with the vertical axis (z axis) to hold the fdm heat extruder or the milling spindle. to maintain the parallelism of the fdm heat extruder or the milling spindle with the z-axis, the rotary axis was adjusted from sensor feedback. experimental studies were conducted to evaluate the performance of the newly built fdm-abrasive milling-based hybrid system. the dimensional accuracy was enhanced substantially for fdm parts after abrasive milling, as compared to pure fdm parts ( improved by a margin of ~5 x (l), ~13 x (w) and ~35 x (h)). similarly, surface roughness was also lowered considerably for fdm parts after the finishing operation (ra reduced by ~11.5 x). moreover, the new system is also capable of carrying out the pure milling operation separately, which helps to achieve the user’s dual manufacturing processes in a single system. in future, the software of the developed system would be further improved so that the system can be fully autonomous. acknowledgement the project was supported by mohe grants (frgs14-112-0353 and prgs16-008-0039). the authors’ are grateful to the international islamic university malaysia for providing resources to conduct the research. references [1] wohlers t. (1998) rapid prototyping & tooling state of the industry: 1998 worldwide progress report. materials technology, 13(4):174-176. [2] gebhardt a. (2003) rapid prototyping. hanser publishers. [3] rapid change in additive-manufacturing landscape plasticstoday [https://www.plasticstoday.com/content/rapid-change-additive-manufacturinglandscape/34506896813194] [4] kruth jp, leu mc, nakagawa t. (1998) progress in additive manufacturing and rapid prototyping. cirp annals, 47(2):525-540. [5] kruth jp. (1991) material incress manufacturing by rapid prototyping techniques. cirp annals-manufacturing technology, 40(2):603-614. [6] pandey pm, reddy nv, dhande sg. (2003) improvement of surface finish by staircase machining in fused deposition modeling. j. materials processing technology, 132(1-3):323331. [7] anitha r, arunachalam s, radhakrishnan p. (2001) critical parameters influencing the quality of prototypes in fused deposition modelling. j. materials processing technology, 118(1-3):385-388. [8] chohan js, singh r. (2017) pre and post processing techniques to improve surface characteristics of fdm parts: a state of art review and future applications. rapid prototyping journal, 23(3):495-513. [9] galantucci lm, dassisti m, lavecchia f & percoco g. (2014) improvement of fused deposition modelled surfaces through milling and physical vapor deposition. [www.poliba.it/didattica/docs/scorepoliba2014_submission_187.pdf.] [10] williams re,walczyk df, dang ht. (2007) using abrasive flow machining to seal and finish conformal channels in laminated tooling. rapid prototyping journal, 13(2):64-75. [11] schmid m, simon c, levy gn. (2009) finishing of sls-parts for rapid manufacturing (rm)–a comprehensive approach. proceedings sff:1-10. iium engineering journal, vol. 19, no. 2, 2018 tomal et al. 231 [12] singh r, trivedi a, singh s. (2017) experimental investigation on shore hardness of barrelfinished fdm patterns. sādhanā, 42(9):1579-1584. [13] ferreira a, arif k. m, dirven s, potgieter j. (2017) retrofitment, open-sourcing, and characterisation of a legacy fused deposition modelling system. the international journal of advanced manufacturing technology, 90(9-12):3357-3367. [14] liu x, chi b, jiao z, tan j, liu f, & yang w. (2017) a large-scale-double-stage-screw 3 d printer for fused deposition of plastic pellets. j. applied polymer science, 134(31):45147. [15] boschetto a, bottini l, veniali f. (2016) finishing of fused deposition modeling parts by cnc machining. robotics and computer-integrated manufacturing, 41:92-101. [16] lee wc, wei cc, chung sc. (2014) development of a hybrid rapid prototyping system using low-cost fused deposition modeling and five-axis machining. j. mater. process. technol., 214(11):2366-2374. [17] 3d cad design software [https://www.solidworks.com/] [18] slic3r g-code generator for 3d printers [http://slic3r.org/] iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 240 on performance analysis of ambr protocol in mobile ad hoc networks tanay dey, m.m.a. hashem and subroto kumar mondal department of computer science and engineering, khulna university of engineering and technology (kuet), khulna 9203, bangladesh. e-mails: dtanay2004@yahoo.com, mma_hashem@hotmail.com, subrota_002@yahoo.com abstract: due to mobility of nodes in ad hoc networks, the most challenging issue is to design and to make sound analysis of a routing protocol that determines its robustness to deliver packets in low routing packet overhead. in this paper, we thoroughly analyzed the adaptive monitor based routing (ambr) protocol by varying different parameters that affect a routing protocol to measure its performance. analysis shows that it requires less routing control overhead comparing with other prevalent routing protocols. an improved analytical model is also presented in this paper. all these analyses firmly prove that ambr is a sound and robust protocol in terms of flooding, routing overhead and hence, enhances reliability. keywords: ad hoc networks, monitor, dynamically route broken, analytical model, affected parameters. 1. introduction an ad hoc network is a class of wireless systems that consists of independent mobile nodes communicating with each other over wireless links, without any static infrastructure such as base stations [1]. a communication session is achieved either through a single-hop radio transmission if the communicating parties are close enough, or through relaying by intermediate nodes otherwise [2]. since the nodes move randomly, the topology of the network changes with time. dynamically changing topology and lack of centralized control make the design of an adaptive distributed routing protocol challenging [1]. due to the limited spectrum, user’s mobility and power constraints, routing remains a challenge, particularly in wireless communication systems such as ad hoc networks. several other challenges complicate routing, including scalability, routing efficiency, adaptation to wireless networks of various densities, and distribution [3]. in this paper, a thorough analysis is performed on the adaptive monitor based routing (ambr) [10] protocol to show its robustness by varying different parameters that affect most of the routing protocols. ambr discovers and maintains routes in hierarchical and distributed fashion and locally repairs the broken link. the main motivation behind the proposed ambr is to drastically cut down flooding, to substantially tame the routing overhead, to repair broken link locally in order to minimize the routing overhead, and to iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 241 increase efficiency in packet movement in the ad hoc networks. in all analyzing cases, it is found that ambr is a bandwidth efficient routing protocol as the routing overhead was drastically cut down. in section 2, we describe the related work and the details of ambr routing protocol and its algorithm is described in section 3 and in section 4, we describe an improved analytical model. simulation results are shown in section 5. finally, section 6 concludes the paper. 2. related work in cbrp [4], problem with having explicit cluster heads is that routing through cluster heads creates traffic bottlenecks. in landmark, lanmar [5] and l+ [6], this is partially solved by allowing nearby nodes to route packets instead of the cluster head, if they know the route to the destination. all of the above schemes have explicit cluster heads, and all addresses are therefore relative to these and are likely to have to change if a cluster head moves away [7]. in janitor based routing [12], janitor works as the cluster head in a cluster but the janitor selection algorithm is complex and the solution for dynamically route broken is not apt. geographical forwarding techniques are used for routing in nogeo [13]. it embeds the network graphs in a virtual two-dimensional co-ordinate space. the main pitfalls of this scheme are that it will only work on certain types of graphs and it has never been evaluate for more than low mobility speed. gem [14], is another coordinate based routing which embeds a sensor network graph in a polar coordinate system. it confronts a heavy concentration of traffic around the root node as it does treebased routing. actually it was designed for sensor networks. in zone routing protocol (zrp) and fisheye state routing (fsr), nodes are treated differently depending on their distance from destination and it incurs less overhead at the cost of decreased precision [7]. dsdv [8], due to its periodic updates and flat routing tables, experiences very high overhead growth as the networks beyond 100 nodes, but nevertheless performs well in comparison with other protocols in the size ranges studied. aodv [9], due to its reactive nature, suffers from high overhead growth both as the size of the network, and the number of flows, grows. while aodv performs very well in small networks, the trend suggests that it is not recommendable for larger networks [7]. 3. ambr routing protocol our proposed protocol ambr uses nodes which are called monitors, whose first hop connectivity (total no of neighbors) acquire a predefined number over the whole network. if a node gets alive, it broadcasts a message named “hello”. this “hello” message is not periodic, rather it is event driven. any node, getting this message from another node should give back a reply to that node only (not a broadcast). monitor detection is completely individual responsibility and it is done in every node after gathering the information of the whole network. if a node has calculated that it’s total number of neighbors or first hop connectivity is equal to a predefined number then it will broadcast a “new monitor” packet and all its covered nodes will accept it and the “hello” propagation iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 242 immediately ends as it is no longer an ordinary node, hence it will now act as a monitor. in the case of rapid network change, number of neighbors of a monitor changes consequently but in our technique the monitor does not need to broadcast extra packet to inform its neighbors about this change. in the network, monitor available messages can be piggy backed with any data or acknowledge packet that has gone to monitor from that node and vice versa. any node that has not sent any data to monitor and has not got any data from monitor over a predefined time, then to avoid complicacy, every node must inform its monitor that it is in its zone by a periodic control packet named “monitor alive request”. this message does not continue in the “hello” session, in fact, when a “hello” session starts it stops and starts when the “hello” session stops with the information given by the “hello” session. the monitor will reply this request with the “monitor alive request repeat” packet only to the node from where it received the request. if the monitor does not receive piggy backed information within a predefined amount of time and no active data delivery is in that session or no monitor alive request packet from a neighbor node in that session then it remove that node from the neighbor node list and if the total number of neighbors is less than the predefined number then it starts a new “hello” session. in this approach, for the data transfer there are a couple of cases to be considered. 1. if the destination (d) is directly connected with the source (s) (fig. 1) then the data is simply sent to destination fig. 1: source is directly connected to destination. 2. if the destination is not directly connected then the following cases may appear: (a) if the source (s) finds that the destination is not directly connected to it and the route of the destination is not in the cache then it sends the data to its monitor (m) and its monitor on behalf of it finds the desired destination. if the destination is directly connected to the monitor then it sends the data on behalf of the source (fig. 2). s d s m d iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 243 fig. 2: source is not directly connected to destination but monitor does. (b) now, if the monitor that is requested by a source node to send data on behalf of that node, finds that the destination is not directly connected to it then it searches the cache to find that route and once found data is send by that route. here, the monitor getting a request from source node finds that it is not directly connected to the destination. so it searches the cache and getting the route it delivers data towards that way (fig. 3). fig. 3: monitor has the destination in its cache. (c) if the source node finds that the route to the destination is in its cache then it follows the route (fig. 4) but if the route gets broken dynamically, the monitor currently has the packet, propagates queries to all the directly connected monitors of it about the destination (fig. 5). this process continues upwards. if any of them has it, then they may follow the reverse path to reply the query made by the monitor. if multiple paths are found then the monitor takes the path from which the reply came first, it keeps that path in its cache. in this way protocol recover the dynamically broken link. fig. 4: source has the destination in its cache. (d) if the route wanted by the source does not evolve in the route cache of the monitor, it propagates queries to all the directly connected monitors of it about the destination node. this process continues upwards. if any of them has it, then they may follow the reverse path to reply(r) the query made by the monitor. if multiple paths are found then the monitor takes the path from which the reply(r) came first. it keeps the path in its cache. here as the source request the monitor and the monitor finds that there is no such route in d m m m m m s m m d m s iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 244 its cache, it then passes the packets to all neighboring monitors and via one of it finds the desired route (fig. 6). fig. 5: dynamically route broken and route discovery. fig. 6: route query made by monitor. (e) if the monitor is querying for destination by asking all the neighboring monitors (m), but the monitor mk finds that it is in certain range from the source that exceeds the certain limit so that monitor mk sends a “destination unreachable” (u) message to the source (fig. 7). fig. 7: monitor forwards “destination unreachable” message. existing routing protocols for ad hoc networks can be classified as � static vs. adaptive [16] m m m u m u u s m m m d u m m m m s m d r m m r r m m d m m m m s m m m iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 245 � proactive vs. reactive [15] � hybrid [15] in static algorithms, the route used by source-destination pairs is fixed regardless of traffic conditions. it can only change in response to a node or link failure. this type of algorithm can’t achieve high throughput under abroad variety of traffic input patterns. most major packet networks uses some form of adaptive routing where the routes used to route between source-destination pairs may change in response to congestion or any other cases where link or path is not found or the link or path is dynamically broken [10]. proactive or table driven protocols continuously evaluate the routes within the network, so that when a packet needs to be routed is already known and can be immediately used. a node propagates routing information among its neighbors whenever there is a change in its link. this information causes other nodes to re-compute their routing tables. it has routes from a node to every other node in the system. hypothetically, the topology is a click in the graph theory. so, it is expensive as route construction takes place even though a node does not need it. proactive protocols are cursed as they waste limited wireless bandwidth of the ad hoc networks. examples of proactive routing protocols are dsdv, tbrpb, wrp, etc. reactive or on-demand protocols invoke a route determination procedure on an ondemand basis by flooding the network with the route query. when a node wants to communicate with another node, it first tries to discover a good route to the destination on which data packets are forwarded. sending node utilizes a route if it is not damaged or broken. problem occurs when poor radio signal exists. whenever a node finds that its link to the next hop is broken, it will send a route error packet back to the source node. this causes waste of available wireless bandwidth as well as a routing delay which results in the increase in latency. the examples of reactive routing protocols for ad hoc networks are aodv, dsr, tora, etc. every reactive protocol has the three basic steps: � flooding � data forwarding and � route maintenance. the on-demand discovery of routes can result on much less traffic than the pro-active schemes, especially when innovative route maintenance schemes are employed. however, the reliance on flooding of the reactive schemes may still lead to a considerable volume of control traffic in the highly versatile ad hoc networking environment. moreover, because this traffic is concentrated during the periods of route discovery, the route acquisition delay can be significant. hybrid protocol refers to the combination of the strengths of several protocols. in most basic hybrid network, one of the protocols would be selected based on its suitability for the specific network’s characteristics. although not an elegant solution, such a framework has the potential to perform as well as the best suited protocol for any scenario, and may outperform either protocol over the entire ad hoc network [12]. iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 246 from the overview of ambr protocol, we have found that the ambr supports suitable features of adaptive and hybrid protocols, so, we can call it adaptive and hybrid and i think that in every cases we will find the best result. ambr protocol uses the following symbols: s=source, m=monitor, d=destination maxdl =maximum depth level ba → = a sends data/message to b )(un =neighbor set of node u )(uc =set of routes in the cache of node u sourcem = monitor connected to the source node )( imnm =set of neighbor monitors of monitor mi ),( mmid k =depth between the monitor(m)and monitor(mk) overall routing technique of the ambr protocol is described in ambr algorithm: ambr algorithm: if )( snd ∈ then ds → //directly connected end if else if )(snd ∉ and )( scd ∉ then ms → // send data to monitor if )( mnd ∈ then dm → //route through monitor end if else if )( mnd ∉ then if )(mcd ∈ then dm → // send data through cache // route of monitor end if else if )( mcd ∉ then call routefinder(m,m,s) end else if end else if end else if else if )( snd ∉ and )( scd ∈ then while(!routebrokendynamically) ds → //route in the cache of source end while if routebrokendynamically then call routefinder(m,m,s) end if end else if function routefinder(msource,m,source) iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 247 [this user defined function finds route between the sourcem and the monitor connected to the destination node] )( mnmm → for every element )( mnmm i ∈ do if max),( dlmmid sourcei > then `)(slemessagenunreachabdestinatiom i → return(1) //destination is unreachable end if else if )( imnd ∈ then query reply to the sourcem and store that path in the cache of the sourcem return(1) //control back to the main algorithm end else if else call routefinder(msource,,mi,source) end else end for 4. analytical model we assume that there are n nodes in the system, and all the nodes have the same distribution of moving speed and direction and the same transmission range r . we assume that: 1. the average route length between the source and destination is le 2. the duration of the packet arrival is exponentially distributed with mean λ/1 . 3. the time between location changes for each node is exponentially distributed with mean µ/1 . 4. all n mobile hosts in the network have the same transmission range r . then, the probability of a route is broken [1], )( λµ µ + =bp (1) and the probability that a route is not broken is )1( bp− . 4.1 packet routing probabilities theorem 1. the probability np that at least one of the ne monitors is able to route from source to destination is, ne bn pp ))1(1(1 3−−−= (2) proof. let the packet is sent from node a to c , where c is not directly connected with a . so, an on demand diagnosis approach invokes a monitor m . the probability of m to iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 248 find the desired route is 3)1( bp−=ρ . if ne be the number of monitors in the network, then k be the number of nodes that want a route by monitor m is given by, kek k e nn ckp −−= )1()()( ρρ (3) thus, the probability that at least one of the ne monitors is able to route from source to destination is given by the above. 4.2 ambr probabilities theorem 2. the probability rp that a route discovery succeeds in ambr protocol is, nkek r ppp )1()1(1 00 −−−= (4) proof. if k hops are counted in the case of a failure of route discovery without asking the monitors, then the probability that self diagnosis fails is, k f pp )1( 00 −= (5) here, p0 is the probability that next desired node is found. again, the probability that total number of ne monitors also fails to discover the route is, nke f pp )1( 01 −= (6) then, the probability that the route recovery succeeds is, nkek ffr ppppp )1()1(11 0010 −−−=−= theorem 3. the probability that a packet is successfully routed by our protocol is, ])1()1(1[)1( )1)( ˆ( )1)(()1( 00 )ˆ( )ˆ(/1 )ˆ(/1/1 1 10 ppp pke pkepp n l l n l n l kek ke b k ke f ke l ke f ke l e f k s −−−−+ −−+ −−+−= − − − (7) proof. a packet arrives in one attempt if it passes along all links without being resent by the original host again. that means that an error does not occur along the whole route and an error occurs in one link and the recovery mechanisms are launched and give the result. therefore, we have ])1()1(1[)1( )1)( ˆ( )1)(()1( 00 )ˆ( )ˆ(/1 )ˆ(/1/1 1 10 ppp pke pkepp n l l n l n l kek ke b k ke f ke l ke f ke l e f k s −−−−+ −−+ −−+−= − − − (8) iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 249 5. simulations 5.1 simulation environment in order to analyze the performance of the proposed ambr protocol, we run the simulation under the ns-2 testbed with a carnegie mellon university (cmu) wireless extension. the simulator parameters are listed in table 1. table 1: simulation parameters. the network area is confined within 1300 m × 1300 m. each node in the network has a constant transmission range of 250 m. constant-bit-rate (cbr) traffic sources are used. the source-destination pairs are spread randomly over the network. only 512 byte data packets are used. the movement pattern of each node follows the random way-point model. each node moves to a randomly selected destination with a constant speed between 0 and maximum speed vmax. when it reaches the destination, it stays there for a random period and starts moving to a new destination. through out the simulation we calculate the total routing overhead per node. 5.2 affected parameters [11] we consider the following parameters that affect the performance of a routing protocol: 5.2.1 network size (n). the number of nodes in a network determines the density of the network. a dense network will cause more collision and contention. 5.2.2 mobility of the node (vmax). the mobility of the node affects the performance of the routing operation. the faster the node moves, the higher is the possibility of the node to lose the information of the neighbors and the information of the monitor. parameter value simulator ns-2(version 2.29) network area 1300 m × 1300 m transmission range 250 m bandwidth 5 kbps data packet size 512 bytes mac layer ieee 802.11 iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 250 5.2.3 pause time (p). at the start of the simulation each node waits for a pause time. it then randomly selects its destination and moves towards this destination with a speed randomly lying between 1 to vmax, where vmax is the maximum speed of a node. once the destination is reached, another random destination is targeted after a pause. 5.3 results and analysis 5.3.1 sensitivity to network size. figure 8 is the corresponding graph to the routing overhead versus network size where vmax is 10 meters per second, (m/s), pause time is 10 second, total simulation time is 200 seconds and the data traffic load constant-packet-rate (cpr) is 10 packets per second (pkt/s). fig. 8: routing packet overhead versus size of the network. we compare the routing overhead against ambr, dsdv [8] and aodv [9] by varying the network size 80, 90, 100, 150, 200. from the graph it can be easily understood that the routing packet overhead of aodv, dsdv and ambr increases as network size increases but increasing rate in the case of aodv and dsdv is much higher than the ambr. even in denser network (network size 200 nodes) the graph shows that the routing packet overhead of ambr is much less comparing with the other two protocols. we know that the main aspects of a reactive protocol are flooding, data forwarding and route maintenance. as a result, its (e.g. aodv) routing packet overhead is more. and though proactive protocols continuously evaluate the routes within the network, its (e.g. dsdv) routing packet overhead is as much as aodv. our protocol is hybrid and adaptive and it has suitable features (mentioned above) compared to others – reactive or proactive. so, its routing packet overhead will be less and here we have found less overhead compared to aodv and dsdv. iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 251 5.3.2 sensitivity to mobility of the node. figure 9 represents the graph showing the effect of the node’s mobility on the performance of routing operation. in this case, n=100, p=10s, total simulation time=200s and cpr=10 packets per second (pkt/s). this graph shows the routing control packet overhead for different mobility of nodes. here, we vary the maximum speed of the nodes from 10 m/s to 50 m/s with an interval of 10 m/s. fig. 9: routing packet overhead versus mobility of the node. from fig. 9, we see that routing packet overhead is affected by the mobility of the node. when mobility of the node increases, routing control packet overhead is also increase but increasing rate in the case of ambr is much less than the other two protocols. from this simulation, we conclude that ambr performs well even when the mobility of the node changes. in case of aodv and dsdv, as the size of the network was increasing, the routing packet overhead was also increasing. and here we have considered mobility of the nodes to observe the performance of ambr comparing with others such as aodv and dsdv. it is well-known that the mobility of the node affects the performance of the routing operation. the faster the node moves, the higher is the possibility of the node to lose the information of the neighbors and the information of the monitor. in proactive protocol a node propagates routing information among its neighbors whenever there is a change in its link. this information causes other nodes to re-compute their routing tables. it is expensive as route construction takes place even though a node does not need it. proactive protocols waste limited wireless bandwidth. reactive protocol also causes waste of available wireless bandwidth as well as a routing delay which results in the increase in latency. so, similar fashion will occur in case of aodv and dsdv. the ambr protocol improves such features as mentioned in the protocol portrayal section. and that is why ambr has less overhead than aodv and dsdv. 5.3.3 sensitivity to pause time. in order to investigate the effect of the pause time on the performance of the ambr protocol, we set the pause time at 50 s, 100 s, 150 s, 200 s, 250 s, 300 s and 350 s. in this case we set, total simulation time=7500s, and cpr=5 packets per second (pkts/s). in iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 252 comparing the ambr with dsr-lrr [1], dsr [1] and dsdv we set, n=50. in fig.3 we compare routing control packet overhead for different pause time. in this case we found that ambr generates lower routing control packet overhead than the other three protocols in different pause time. 0 20 40 60 80 100 120 140 0 50 100 150 200 250 300 350 400 pause time (seconds) r o u tin g c o n tr o l t ra ff ic ( p a c k e ts x 1 0 0 0 ) ambr dsr-lrr dsr dsdv fig. 10: routing packet overhead versus pause time. in the previous two cases we have found that the performance of aodv and dsdv is poor. and now pause time is considered to compare the performance of ambr protocol with others. when the links in the network break dynamically then ambr protocol discovers route dynamically from the immediate node linked with the broken link instead of seeking destination node from the source again. consequently, it will incur less routing overhead in different pause time and its performance will be high. from the figure we have found that as the pause time increases, the performance of other protocols (e.g. dsdv, dsr, dsr-lrr) is degraded compare to ambr. 6. conclusion in this paper, we performed a through analysis of ambr protocol. from the analysis we found that ambr is an efficient technique to route data from source to destination with a low routing cost. firstly, we proposed an improved analytical model which illustrates the packet routing probabilities and ambr probabilities. secondly, using ns-2 simulator and varying different affecting parameters we measured the routing overhead for ambr including dsr-lrr, dsr, dsdv and aodv, and compared with each other. these thorough analyses show the inherent strength of the ambr protocol and firmly determine that ambr protocol is the most feasible protocol for the ad hoc networks. for the selection of monitor, a node should have at least some constant predefined minimum number of neighbors. future work may introduce a technique from which an optimal number can be found dynamically for different network conditions. to alleviate the network from extravagant periodic routing control traffic, our target was to introduce event driven packets as much as possible but still some messages are partially periodic like ‘monitor alive request’ packets as they depends on some events. so as a future work a iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 253 technique can be introduced that can turn these partially periodic packets into fully event driven packets. references [1] r. duggirala, r. gupta, quing-an zeng, and d.p. agrawal. performance enhancement of ad hoc networks with localized route repair. ieee transaction on computers, (52), 854 861, july 2003. [2] khaled m. alzoubi, peng-jun wan, and ophir frieder. new distributed algorithm for connected dominating set in wireless ad hoc networks. proc. 35th hawaii international conference on system sciences (9), 297, 2002. [3] yao zhao, yan chen, bo li, and qian zhang. hop id: a virtual coordinate-based routing for sparse mobile ad hoc networks. ieee transactions on mobile computing, (6), 10751089, september 2007. [4] m. jiang et al.,”cluster based routing protocol (cbrp) functional specification (internetdraft), http://www.ietf.org/internetdrafts/draft-ietf-manet-cbrp-spec-00.txt, aug.1998. [5] g. pei, m. gerla, and z. hong, ”lanmar: landmark routing for large scale wireless ad hoc networks with group mobility,” in proc. ieee/acm mobihoc, pp. 11-18, aug. 2000. [6] b. chen and r. morris. l+: scalable landmark routing and address lookup for multi-hop wireless networks. technical report mitlcs-tr-837, laboratory for computer science, massechusetts institute for technology, march 2002. [7] jokob erikson, michalis faloutsos, and srikanth v. krishnamurthy. dart: dynamic routing for scalable ad hoc and mesh networks. ieee/acm transactions on networking, (15), 119-132, february 2007. [8] c. perkins and p. bhagwat. highly dynamic destination-sequenced distance-vector routing (dsdv) for mobile computers. proc. acm sigcomm, october 1994 [9] c. perkins and e. royer. ad hoc on-demand distance vector routing. proc. of ieee workshop mobile computing systems and applications, (3), 90-100, 1999. [10] tanay dey, subrota kumar mondal and m.m.a hashem. performance enhancement of ad hoc networks with adaptive monitor based routing. proc. 2008 ieee radio and wireless symposium (rws 2008), pp.263-266, orlando, florida, usa, january 22-24, 2008. [11] wei lou, and jie wu. toward broadcast reliability in mobile ad hoc networks with double coverage. ieee transaction on mobile computing, (6), 148-163, february.2007. [12] isnain siddique, rushdi shams, and m.m.a. hashem. performance enhancement of ad hoc networks with janitor based routing. proc. ieee international conference on computer & communication engineering (iccce’06), vol. i, pp. 368-373, kuala lumpur, malaysia, may 9-11, 2006. [13] a. rao, s. ratnasamy, c. papadimitriou, s. shenker. and i. stoica. geographic routing without location information. proc. acm mobicom, pp. 96-108, 2003. [14] j. newsome and d. song. gem: graph embedding for routing and data-centric storage in sensor networks without geographic information. proc. 1st int. conf. embedded networked sensor systems (sensuy’03), new york, ny, pp. 76-88, 2003. [15] m.s. corson, and a.ephremides. a distributed routing algorithm for mobile wireless networks. acm j. wireless networks, pp. 61-81, 1995. iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 254 [16] tony larsson and nicklas hedman. routing protocols in wireless adhoc networks a simulation study. m.s. thesis, lulea university of technology, 1998. microsoft word 196-1241 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 79 unsteady heat transfer in an annular pipe, part ii: swirling laminar flow kelvin h.c.s. 1 , yousif a.a. 1 and andrew c. 2 1 department of mechanical, materials and manufacturing engineering, 2 department of civil engineering, faculty of engineering, the university of nottingham, semenyih, malaysia choon-seng.ho@nottingham.edu.my, yousif.abakr@nottingham.edu.my, andy.chan@nottingham.edu.my abstract: the heat transfer problem in magnetocaloric regenerators during magnetization has been described and investigated for convective heat transfer by means of axial flow in part i of this series. this work will focus on enhancing the unsteady heat transfer using swirling laminar flow generated using axial vanes. the governing parameters for this study are, the d* ratio (inner diameter/outer diameter) and the swirl number, s. the study is conducted using dimensional analysis and commercial cfd codes provided by ansys cfx. the hydrodynamics and the heat transfer of the model are compared with data from similar cases found in literature and is found to be in the vicinity of good agreement. abstrak: abstrak: masalah pemindahan haba semasa pemagnetan dalam penjana semula magnetocaloric telah dikaji untuk pemindahan haba berolak melalui aliran paksi dalam bahagian i siri ini. kerja ini akan memberi tumpuan kepada peningkatan pemindahan haba tak mantap menggunakan aliran lamina pusaran yang dijana menggunakan ram paksi. parameter bagi kajian ini, nisbah d * (diameter inner / diameter luar) dan nombor pusar, s. kajian ini dijalankan menggunakan analisis dimensi dan komersial cfd kod yang disediakan oleh ansys cfx. sifat-sifat hidrodinamik dan pemindahan haba di dalam model telah dibandingkan dengan data daripada kes-kes kajian sebelumnya. kajian ini menemui hasil-hasil yang serupa seperti kajian-kajian yang sebelumnya. keywords: annular ducts; unsteady heat transfer; magnetic refrigeration/cooling; swirling laminar flow; dimensional analysis 1. introduction undoubtedly, the field of heat transfer has been celebrated by its diversity, applications and distinguished peers. max jakob is among the very few whom has not only dedicated his life towards heat transfer research ,but, at the same time inspired and touched the hearts of many [1]. heat transfer enhancement techniques has been extensively researched into throughout the years, but, as new discoveries enhancements in both science and technology takes place, this will undoubtedly bring heat transfer research into new frontiers (e.g. convective heat transfer enhancement through the use of nanosized fluid particles [2]). although a wide range of geometries and configurations exist, but, the heat transfer enhancement techniques used are in general common, namely: active, passive and compound enhancement techniques. active and passive techniques are differentiated by the needs for external power. the former requires an external power iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 80 source to maintain its heat transfer enhancement capability while the latter doesn’t. as mentioned earlier, active techniques require an active power or energy source to sustain its capability (e.g. mechanical or electrical aids, surface of fluid vibration, injection or suction forces etc). passive techniques aim to enhance the heat transfer through either modifying or treating the heat transfer surface (e.g. roughened, treated, extended surfaces etc) or by modifying the flow (e.g. axial, radial vanes etc). finally, the use of one or more combination of techniques from active and/or passive techniques yield compound techniques (e.g. a roughened surface with swirlers). this work will focus on the utilization of swirling flow in a concentric annular duct with the aim of enhancing the heat transfer between fluids and solid (in other words, the heat transfer coefficient of the inner wall). swirling flows in concentric annular ducts can be produced by both active and passive techniques. the distinction between both techniques lies on whether external power is required to generate the swirl phenomenon. in general, swirling flows can be categorized into three distinct groups: curved, rotating and vortex/decaying flows [3]. curved flows are created by coil inserts, twisted tapes, helical vanes etc, the idea of this technique is to modify the path of flow on either the inner tube, outer tube or additional inserts to guide the flow along a distinct path. as a result or the modified path along the flow region, curved flows tend to be continuous swirling flows. rotating flows however are among one of the active techniques and this type of swirling flow is created by either rotating the inner or the outer section of the annular duct. lastly, vortex flows or swirling decaying flows are usually created by means of tangential inlet, radial or axial canes, twisted tape inserts etc. the idea of this type of configuration is to modify the flow pattern at the inlet of the annular duct and once the flow is swirled, it will then decay out of the system (this means that the tangential velocity decreases along the length of the annulus). the rate of decay depends on the physical properties, hydrodynamic properties, swirl creating method etc. the use of swirling flow as a means of heat transfer enhancement can be traced back to the work done by joule [4] on the heat transfer in an annulus using swirling flow(curved flow) created by wire inserts. work on swirling laminar flow in concentric annular ducts can be found in the work done by farias neto et al. [5] after a perusal of the overwhelming literature, heat transfer in concentric annular ducts is still far from being understood especially under unsteady heat flux conditions. part i of this series of papers has briefly described the problem and investigated for axial flows. in this paper, dimensional analysis will be incorporated as a means of preliminary analysis before numerical analysis is done for swirling flows in the laminar region. 2. model description this section will unveil the details of the numerical model. this information includes a description of the model, boundary conditions and transient parameters, a description of relevant materials and general governing equations, numerical methods used and lastly a description on the verification and validation of the model. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 81 3. numerical model description after defining the problem in the previous section, the problem is then investigated numerically using commercial cfd codes. figure 1 shows the 3d schematic of a concentric annular duct with a solid core. (a) (b) fig.1: physical model of problem: (a) cylindrical coordinate system; (b) concentric annular duct. 3.1 numerical model figure 1(a) shows the definition of the coordinate system used by the model and fig. 1(b) shows the 3d schematic of a concentric annular duct with a solid core. the model consists of two parts, core and fluid domain. both domains are assumed to compose of isotropic and homogenous material. the core domain is made of gadolinium metal while the fluid domain is made of water. the length of the model is set to 70 mm and the inner diameter and outer diameter is govern by the d* ratio that varies between 1/8, 1/4, 1/2 and 3/4 with the outer diameter remained at 40 mm. figures 2(a)-(e) show the mesh used to discretize the model. figures 2(a)-(d) show the top view of the model for all d* ratios and fig. 2(e) shows the side view of the model. the total nodes used for each case is approximately (500,000 ± 50,000). in order to improve boundary layer approximations, especially the fluid-solid interface, the boundary has been inflated with layers of nodes and this is depicted in fig. 3(a)-(b). the layers of inflation vary between 10-15 for the outer wall and inner wall. it should be noted that the boundary at the inner wall is divided in both fluid and solid near wall layers. i d l o d ∞t,v,u gd t adiabatic wall adiabatic wall s b s b 0"q = 0"q = iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 82 fig. 2: semi-structured meshes: (a) d*=1/8; (b) d*=1/4; (c) d*=1/2; (d) d*=3/4; (e) side view of mesh. iium engineering journal, vol. 12, no. 6, 201 (a) fig. 3: inflation layers at boundary: since the main aim of this study is to obtain an understanding on the unsteady heat transfer in an annular duct for dis be used as a preliminary tool to heat transfer coefficient is a function of the following parameters; h if the primary measuring units is chosen to be mass, length, time and temperature ( l, t and θ), then, according to the buckingham independent dimensionless relations. the dimensionless quantities are se nusselt number: reynolds number: prandtl number: diameter ratio: aspect ratio: a swirl ratio: =s hence, (re, )( dd k h io f ψ − = the swirl ratio defined here is similar to that of zhang et al. simpler version is opted. g journal, vol. 12, no. 6, 2011: special issue in science and ethics 83 (b) : inflation layers at boundary: (a) fluid-solid interface; (b) outer wall of fluid domain. since the main aim of this study is to obtain an understanding on the unsteady heat transfer in an annular duct for disturbed swirling laminar flows. dimensional analysis will nary tool to identify governing parameters. assuming that the wall heat transfer coefficient is a function of the following parameters; )v,u,c,k,,,l,d,d(h ffffio ∞∞µρ if the primary measuring units is chosen to be mass, length, time and temperature ( , then, according to the buckingham π-theorem[6] we will have (10 independent dimensionless relations. the dimensionless quantities are selected a follows: nusselt number: f k hl nu = reynolds number: f f l lu µ ρ ∞ =re prandtl number: f ff k cµ =pr diameter ratio: o i d d d =* l dd a io −=* ∞ ∞= u v )*,*,pr,(re, sad (1) the swirl ratio defined here is similar to that of zhang et al. [7], but for simplicity the ethics kelvin et al. solid interface; (b) outer wall of fluid since the main aim of this study is to obtain an understanding on the unsteady heat dimensional analysis will assuming that the wall if the primary measuring units is chosen to be mass, length, time and temperature (m, we will have (10-4=6) 6 , but for simplicity the iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 84 it is assumed that the effect of d* and s would be exceedingly significant compared to that of a* and we know that the wall heat transfer coefficient is a function of the reynolds number and the prandtl number, thus, the governing parameters of this study are: (1) d* ratio and (2) s number. the variation in the d* ratio will provide us with a thorough investigation from very thin concentric annular duct to near cylindrical duct configuration. next, dimensional analysis will be used to identify the governing parameters for the wall heat flux. assuming that the wall heat flux is a function of the following parameters; )t,t,h,k,,l,d("q ssi ∆α if we were to choose the same primary units as before, we will have (8-4=4) 4 independent dimensionless relations. the dimensionless quantities are selected a follows: biot number: s i k hd =bi fourier number: 2 α i s d t =fo aspect ratio: l di dimensionless form of fourier law: tk d"q s i ∆ hence, ) l d ,fo,bi( d tk ="q i i s ψ ∆ (2) 3.2 material properties and governing equations the incompressible newtonian fluid used as heat exchanging fluid is water with constant physical properties (table 2). the properties of gadolinium are summarized in table 2 and are assumed to be at a constant value throughout the numerical study. the non-linear partial equations that govern the conservation of mass, momentum, energy and turbulent energy are shown in equations (3-8). mass conservation (r,θ,z): 0 ∂ ∂ ∂ ∂1 ∂ ∂ =+++ z vv rr v r v zrr θ θ (3) momentum conservation (r,θ,z):         ++++ =         +++ 2 2 22 2 222 2 2 ∂ ∂ ∂ ∂2 ∂ ∂1 ∂ ∂1 ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ z vv r v rr v r v rr v r p z v v r vv r v r v v t v rrrrr r z rr r r θθ µ θ ρ θ θθ (4) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 85         +++++ =      +++ 2 2 22 2 222 2 ∂ ∂ ∂ ∂2 ∂ ∂1 ∂ ∂1 ∂ ∂ ∂ ∂1 ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ z vv r v rr v r v rr vp r z v v r vvv r v r v v t v r z r r θθθθθ θθθθθθ θθ µ θ θ ρ (5)         ++++ =      +++ 2 2 2 2 22 2 ∂ ∂ ∂ ∂1 ∂ ∂1 ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ z vv rr v rr v z p z v v v r v r v v t v zzzz z z zz r z θ µ θ ρ θ (6) energy conservation (r,θ,z):         ++      =      +++ 2 2 2 2 2 , ∂ ∂ ∂ ∂1 ∂ ∂ ∂ ∂1 ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ z tt rr t r rr k z t v t r v r t v t t c f zrfpf θ θ ρ θ (7)         ∂ ∂ + ∂ ∂ +      ∂ ∂ ∂ ∂ =      ∂ ∂ 2 2 2 2 2, 11 z tt rr t r rr k t t c ssps θ ρ (8) 3.3 boundary conditions and transient parameters the governing equations in the previous section are subjected to the following boundary conditions. at both walls, the flow is prohibited from slipping and at the same time impermeable (u=v=0). the outer wall is assumed adiabatic while the temperature of the inner wall will vary according to the hydrodynamic parameters of the duct over time. at free stream, both axial and tangential velocity is assumed to approach u∞ and v∞. the flow in the annular duct is assumed steady and uniform throughout the length of the duct. the swirl phenomenon is created as a result of disturbed axial flow by using a set of axial vanes, thus, the flow after the vanes will be two-dimensional (vortex flow or swirling decaying flow). 3.4 numerical computation the numerical study is conducted using cfd codes provided by ansys cfx and the simulated cases are summarized in table 1. the test cases are divided into two groups, the first group will be simulated under constant s ratio for different d* ratios and different axial velocities. the second group is simulated under fixed axial velocity for different s ratios and d* ratios. as per the pre-analysis done using dimensional analysis, we have determined the governing parameters of this study, thus, the above test cases have been structured and selected for this purpose, whereby, the first group of thes cases would study the effect of the d* ratio and reynolds number while the second test group will be used to study the effect of different s ratios. the barth and jesperson (high resolution scheme) and a series of structured mesh are used to discretized the equations (3-8). the transient term is discretized using the second order backward euler scheme. a grid independent test and a time step independent test are conducted on the model [8]. the gird independent test is conducted by comparing between two different node counts (5 x 10 5 and 10 x 10 5 ). the time step independent test is conducted by comparing between two different time steps (300 and 3000). iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 86 3.5 verification and validation tests conducted on the model confirm that the model is indeed grid and time step independent (discrepancies below 0.1%). as a result, x10 5 nodes and 3000 time steps were used throughout the numerical study. finally, the accuracy of computed numerical results over each node satisfies the rms convergence criteria of 10 -12 . 4. numerical results and discussion this section presents the numerical results, in the form of plots and is facilitated with a series of discussion. the first section will discuss on the hydrodynamics and heat transfer characteristics. subsequent sections will focus on the effect of different governing parameters (e.g. s, d* and re). 4.1 on the hydrodynamic and heat transfer characteristics since it is the nature of vortex flows to exhibit signs of decay along the flow path due to friction, thus, for an annular duct with sufficient hydrodynamic length we would expect to witness a significant decay in the tangential velocity component due to the lack of a continuous force to sustain the tangential flow. figure 4 depicts the axial and tangential velocity component for one of the cases (d*=0.125, s=1 and u=0.01 m/s) at different axial distances along the duct. since the flow is still developing, the near wall velocity will tend to decrease as it proceeds further downstream as a result of an increase in the velocity boundary layer until the flow reaches its fully developed state. the hydraulic diameter of this study is defined as the difference between the outer and inner diameter (d0-di) and this is applied consistently throughout the study. a detail discussion on the friction factor, pressure drops and the velocity boundary layer will not be given as it is not within the scope of this paper. furthermore, the hydrodynamics for both steady and unsteady heat fluxes should be the same assuming that the flow characteristics are independent of temperature. (a) (b) fig. 4: axial and tangential velocity plots for d*=0.125, s=1, u=0.01 m/s. 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 a x ia l v e lo c it y , u ( m / s ) (r-ri)/(ro-ri) inner wall outer wall 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 t a n g e n t ia l v e lo c it y , v ( m / s ) (r-ri)/(ro-ri) inner wall outer wall iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 87 for laminar flows, heat transfer through molecular diffusion (molecular conduction) is dominant. since the flow and solid is assumed to be homogenous and isotropic, longitudinal temperature variation of the solid core will be negligible compared to the radial temperature variation. for heat transfer in circular or annular ducts, experience tells us that the wall heat transfer coefficient will always be proportional but not limited to the reynolds number (re) and the prandtl number (pr) (e.g. apenu∝ ), whereby, pe is peclet number which has a power of a. in particular, it is of great interest to understand how the cooling time t is affected by the governing parameters (e.g. nu and q”), at the same time, it is also crucial to investigate how the wall heat flux behaves with respect to different flow and geometrical arrangements over a limited period of time. the prandtl number of water for this study is chose to be 6.3 which is greater that 1, thus, according to boundary layer theory the thermal entrance length will be greater than the hydrodynamic entrance length (δt >>δv). in addition, for a problem of unsteady heat transfer, we would expect the thermal boundary layer to undergo the developing process and subsequently disappears when the solid reaches the same temperature as its surrounding fluid. from the previous section, the use of dimensional analysis has yield fruitful relations. we know that the wall heat transfer coefficient is defined by equation (1). the effect of a* towards h is small compared to the other parameters, thus, a* is removed from the relation, giving; )s*,dpr,(re, )dd( k h io f ψ= (9) the application of further in depth knowledge on dimensional analysis, hydrodynamics and heat transfer will provide further insights on the problem, but, for the meantime the definition of h in equation 9 will suffice. next, a relation for the wall heat flux was also deduced using dimensional analysis (equation (2)). under steady-heat flux conditions, the wall heat flux would often be a function of the biot number, geometrical properties and the temperature gradient, but, under unsteady conditions the dimensionless time defined by the fourier number would be vital. similar to a*, the aspect ratio in the definition of q” may be neglected as well, hence, the simplified definition; )fo,bi( d tk "q i s ψ ∆ = (10) 4.2 on the effect of inlet velocity the inlet velocity is a characteristic of the hydrodynamics of the problem and its effect towards the wall heat transfer coefficient is direct. in this study, the two dimensional flow is assumed created by forcing fluid through a set of vanes which are positioned at a fixed angle on a buff object (e.g. 30˚, 45˚ and 60˚). for discussion purposes, two different reynolds number will be used. the first is rel with was defined during dimensional analysis, and the other reeff which is based on the hydraulic diameter such that ( f iof eff )dd(u re µ ρ = ∞ ). rel is used as a momentum-viscous ratio that is independent of the diameter and it is used to represent the effect of different inlet velocities without the effect of the hydraulic diameter. subsequently, reeff takes into account both inlet velocity and the hydraulic diameter and is used for discussion purposes. since the heat transfer coefficient is known to be proportional to the reynolds number or the fluid velocity, thus, an increase in inlet velocity will lead to an increase in the wall iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 88 heat transfer coefficient. this is shown in fig. 5, whereby the wall heat transfer coefficient is plotted against different reynolds number within the laminar regime. each of the line represents a different d* ratio. from the plot, we can conclude that the wall heat transfer coefficient is linearly proportional to the inlet velocity in the laminar regime. furthermore, an increase in hydraulic diameter also increases the wall heat transfer coefficient and this increase is more significant at higher reynolds numbers. as a result, we have the following relations; fig. 5: variation of wall heat transfer coefficient for different reynolds number for constant d* ratio. uh∝ , h"q ∝ , ∞ ∝ u t 1 . from the axial and tangential velocity plots for s=1 in fig. 6. the velocity plots are taken at three distinct axial locations along the flow path (z/l=0.1, 0.5 and 0.9). it is observed that the momentum flux tend is biased towards the outer wall, but, diminishes as the d* ratio increases. in this case, the use of reeff as a comparison medium would be more fruitful since in involves the d* ratio. as the d* ratio increases, the hydraulic diameter, dh decreases hence the effective reynolds number, reeff. so, for very low reeff the velocity profile will be uniformly distributed, hence, the uniformity of wall heat transfer coefficient on both inner and outer wall. this phenomenon is tends to happen at higher reeff and was also observed by zhang et al. [9]. as a result the wall heat transfer coefficient on the outer wall will be higher compared to the inner wall. although the inlet velocity does not explicitly falls into the relation for wall heat flux, but, a careful inspection eventually reveals its implicit relation to the wall heat flux through the wall heat transfer coefficient, whence, the fourier’s equation for heat transfer coefficient (q″=h(t0-t∞)) and can be traced to the times newton. both are independent parameters which are linked up by ∆t. recalling equation (1), our definition of the wall heat transfer coefficient is a monomial relation with the parameters re, d* and s. the wall heat transfer coefficient will play its role in reducing the temperature gradient between fluid and solid so long as ∆t is not nil. 0 100 200 300 400 500 600 700 800 0 1000 2000 3000 4000 5000 6000 h ( w m 2 k 1 ) re d*=0.125, 0.25, 0.5, 0.75 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 89 (a) (b) (c) (d) fig. 5: axial and tangential velocity plots at z/l=0.1, 0.5 and 0.9 for (a)-(b) d*=0.25,s=1 and u=0.07 m/s and (c)-(d) d*=0.75,s=1 and u=0.07 m/s. 4.3 on the effect of geometric ratio from dimensional analysis we have defined two independent ratios that represents the geometrical configuration of the problem and among them, one is negligible and the other a crucial governing parameter. as per our previous discussions, the effect of d* is said to be dominant to that of a* assuming that the radial temperature gradients are dominant, furthermore, since both do and l are fixed, thus, o i d d *d = and l dd *a io = will present itself under a common purpose under different denominators. as a result, discussion from here on will be made with reference to d* only. 0.060 0.062 0.064 0.066 0.068 0.070 0.072 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 a x ia l v e lo c it y , u ( m / s ) (r-ri)/(ro-ri) inner wall outer wall 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 (r-ri)/(ro-ri) inner wall outer wall t a n g e n t ia l v e lo c it y , v ( m / s ) 0.067 0.068 0.068 0.069 0.069 0.070 0.070 0.071 0.071 0.072 0.0 0.2 0.4 0.6 0.8 1.0 0.065 0.066 0.067 0.068 0.069 0.070 0.071 0.072 0.0 0.2 0.4 0.6 0.8 1.0 0.065 0.066 0.067 0.068 0.069 0.070 0.071 0.072 0.073 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 a x ia l v e lo c it y , u ( m / s ) (r-ri)/(ro-ri) inner wall outer wall 0.060 0.062 0.064 0.066 0.068 0.070 0.072 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 (r-ri)/(ro-ri) inner wall outer wallt a n g e n t ia l v e lo c it y , v ( m / s ) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 90 as mentioned earlier, d* affects dh, hence, reeff. with the application of simple logic and some knowledge in heat transfer and hydrodynamics we can deduce a simple relation between these variables within the limits of the laminar regime for s=1; *d h 1 ∝ these results are shown in fig. 7 for variations of h with reference to different d* ratios under constant rel. observations shows that the nonlinearity between h and d* increases as the inlet velocity increases (e.g. the number of vortices increases as the flow regime transits from laminar to the transition regime). fig. 6: variation of wall heat transfer coefficient for different d* ratios for constant reynolds number. within these limits the wall heat transfer coefficient is inversely proportional to the d* ratio and since the wall heat flux is also proportional to the wall heat transfer coefficient; h"q ∝ we can then deduce a crude approximation between time of cooling and the d* ratio; *dt∝ from the velocity profiles shown in fig. 6 and 8, it is observed that as d* increases from 0.125 to 0.75 the uniformity of the axial velocity profiles tend to increase with the disappearance of the bias towards the outer wall, however, this is different for the tangential velocity profile whereby a variation in d* has little effect towards it. although the tangential component is not sensitive towards d*, but, an increase in the inlet velocity is found to increase the uniformity of the tangential profile. this can be seen by comparing fig. 6 (b) and (d) with fig. 8 (b) and (f). 4.4 on the effect of flow ratio the flow ratio that is defined in this study is the swirl ratio, s which is measure based on the ratio between the tangential and axial velocity component. the swirl ratio is varied from 0.1 up to 1.5 to investigate its effect on heat transfer. when s is less than 1 (s<1), the axial velocity component is dominant, whereas, when s is greater than 1 (s>1) the tangential velocity component is dominant. 0 100 200 300 400 500 600 700 800 0 0.25 0.5 0.75 h ( w m 2 k 1 ) d* re=784, 3921, 5489 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 91 fig. 7:. axial and tangential velocity plots at z/l=0.1, 0.5 and 0.9 for u=0.01 m/s and s=1 (a)-(b) d*=0.25, (c)-(d) d*=0.50 and (e)-(f) d*=0.75. from fig. 8 (a),(b) and 10 (a)-(f), we can observe how different s ratios affect the laminar velocity profiles. it is observed that, when s<0.5 the axial velocity profile is biased towards the inner wall and as s increases, this bias tend to shift towards the outer wall. a change in the s ratio would affect the magnitude of the tangential velocity profile since s varies because of different tangential velocities. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 92 from fig. 9, we know that an increase in s would increase the wall heat transfer proportionally. in addition to that, the wall heat transfer coefficient becomes increasingly sensitive towards a change in d* sensitive when s is above 0.5. since an increase in s yields a corresponding increase in h, as a result, the time needed for cooling will also be reduced. thus, the relations; sh∝ , s t 1 ∝ fig. 8: variation of wall heat transfer coefficient for different s ratios for constant d* ratio and u=0.01 m/s. (a) (b) 0 20 40 60 80 100 120 140 160 180 200 0 0.5 1 1.5 2 h ( w m 2 k 1 ) s d*=0.125, 0.25, 0.5, 0.75 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.0 0.2 0.4 0.6 0.8 1.0 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.0 0.2 0.4 0.6 0.8 1.0 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 a x ia l v e lo c it y , u ( m / s ) (r-ri)/(ro-ri) inner wall outer wall 0.000 0.000 0.000 0.001 0.001 0.001 0.001 0.001 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.000 0.000 0.001 0.001 0.001 0.001 0.001 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.000 0.000 0.001 0.001 0.001 0.001 0.001 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 (r-ri)/(ro-ri) inner wall outer wall t a n g e n t ia l v e lo c it y , v ( m / s ) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 93 (c) (d) (e) (f) fig. 9: axial and tangential velocity plots at z/l=0.1, 0.5 and 0.9 for u=0.01 m/s and d*=0.25 (a)-(b) s=0.10, (c)-(d) s=0.50 and (e)-(f) s=1.50. 5. conclusions the unsteady heat transfer in a concentric annular duct has been investigated using dimensional analysis and commercial cfd codes and the following conclusions can be deduced from the results; 0.010 0.010 0.010 0.010 0.010 0.010 0.0 0.2 0.4 0.6 0.8 1.0 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.0 0.2 0.4 0.6 0.8 1.0 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 a x ia l v e lo c it y , u ( m / s ) (r-ri)/(ro-ri) 0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 (r-ri)/(ro-ri) t a n g e n t ia l v e lo c it y , v ( m / s ) 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 a x ia l v e lo c it y , u ( m / s ) (r-ri)/(ro-ri) inner wall outer wall 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.0 0.2 0.4 0.6 0.8 1.0 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.0 0.2 0.4 0.6 0.8 1.0 z/l=0.9 z/l=0.5 z/l=0.1 (r-ri)/(ro-ri) inner wall outer wall t a n g e n t ia l v e lo c it y , v ( m / s ) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 94 it can be concluded that; a. the heat transfer coefficient for unsteady heat fluxes such as the on above can be briefly represented by the relation; )s, *d (re,h 1 ∝ b. the wall heat flux for such cases can be represented by the relation; h"q ∝ c. the cooling time for such cases can be represented by the relation; ) s *,d, re (t 11 ∝ acknowledgement the authors wish to acknowledge the university of nottingham, malaysia for the financial support to this research work. references [1] a. e. bergles, heat transfer enhancement-the encouragement and accommodation of high heat fluxes, j. heat transfer(trans asme), vol. 119, pp. 8-19, 1997. [2] s. kakaç and a. pramuanjaroenkij, review of convective heat transfer enhancement with nanofluids, int. j. heat mass transfer, vol. 52(13-14), pp. 3187-3196, 2009. [3] r. razgaitis and j. p. holman, a survey of heat transfer in confined swirl flows, heat mass transfer processes, vol. 2, pp. 831-866, 1976. [4] j. p. joule, on the surface-condensation of steam, phil. trans. r. soc. lond., vol. 151, pp. 133-160, 1861. [5] s. r. de farias neto, p. legentilhomme and j. legrand, finite element simulation of mass transfer in laminar swirling decaying flow induced by means of a tangential inlet in an annulus, compu. method appl. m eng., vol. 190(35-36), pp. 4713-4731, 2001. [6] e. buckingham, on physically similar systems; illustrations of the use of dimensional equations, physical review, vol. 4(4), p. 345, 1914. [7] j. zhang, h. lu, l. zhou and s. nieh, simulation of annular swirling turbulent flows with a new algebraic reynolds stress model, numer. heat transfer b, vol. 31(2), pp. 235 249, 1997. [8] m. j. minkowycz, e. m. sparrow and j. y. murthy, handnook of numerical heat transfer. wiley, 2006, new jersey. [9] j. zhang, l. dong, l. zhou and s. nieh, simulation of swirling turbulent flows and heat transfer in an annular duct, numer. heat transfer a, vol. 44(6), pp. 591 609, 2003. nomenclature latin alphabets a area, m 2 bs surface magnetic flux density, t c heat capacity, j kg -1 k -1 d diameter, m d* ratio of inner diameter to outer diameter h heat transfer coefficient, w m -2 k -1 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kelvin et al. 95 id inner diameter, mm k thermal conductivity, w m -1 k-1 l length, mm m mass, kg nu nusselt number od outer diameter, mm p pressure, pa pr prantl number q" heat flux, w m -2 re reynolds number, s swirl number t temperature, k t time, s u,v velocity components, m s -1 greek alphabets α thermal diffusivity of solid, m 2 s -1 µ dynamic viscosity, pa s ρ density, kg m -3 subscript eff effective f fluid h hydraulic i inner diameter ini initial o outer diameter p constant pressure s solid application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 gashti 144 a modified model based on flower pollination algorithm and k-nearest neighbor for diagnosing diseases mehdi zekriyapanah gashti department of computer engineering, payame noor university, tehran, iran corresponding author: gashti@pnu.ac.ir (received: 17th july 2017; accepted28th feb 2018; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.854 abstract: exponential growth of medical data and recorded resources from patients with different diseases can be exploited to establish an optimal association between disease symptoms and diagnosis. the main issue in diagnosis is the variability of the features that can be attributed for particular diseases, since some of these features are not essential for the diagnosis and may even lead to a delay in diagnosis. for instance, diabetes, hepatitis, breast cancer, and heart disease, that express multitudes of clinical manifestations as symptoms, are among the diseases with higher morbidity rate. timely diagnosis of such diseases can play a critical role in decreasing their effect on patients’ quality of life and on the costs of their treatment. thanks to the large data set available, computer aided diagnosis can be an advanced option for early diagnosis of the diseases. in this paper, using a flower pollination algorithm (fpa) and k-nearest neighbor (knn), a new method is suggested for diagnosis. the modified model can diagnose diseases more accurately by reducing the number of features. the main purpose of the modified model is that the feature selection (fs) should be done by fpa and data classification should be performed using knn. the results showed higher efficiency of the modified model on diagnosis of diabetes, hepatitis, breast cancer, and heart diseases compared to the knn models. abstrak: pertumbuhan eksponen dalam data perubatan dan sumber direkodkan daripada pesakit dengan penyakit berbeza boleh disalah guna bagi membentuk kebersamaan optimum antara simptom penyakit dan mengenal pasti gejala penyakit (diagnosis). isu utama dalam diagnosis adalah kepelbagaian ciri yang dimiliki pada penyakit tertentu, sementara ciri-ciri ini tidak penting untuk didiagnosis dan boleh mengarah kepada penangguhan dalam diagnosis. sebagai contoh, penyakit kencing manis, radang hati, barah payudara dan penyakit jantung, menunjukkan banyak klinikal simptom jelas dan merupakan penyakit tertinggi berlaku dalam masyarakat. diagnosis tepat pada penyakit tersebut boleh memainkan peranan penting dalam mengurangkan kesan kualiti hidup dan kos rawatan pesakit. terima kasih kepada set data yang banyak, diagnosis dengan bantuan komputer boleh menjadi pilihan maju menuju ke arah diagnosis awal kepada penyakit. kertas ini menggunakan algoritma flower pollination (fpa) dan k-nearest neighbor (knn), iaitu kaedah baru dicadangkan bagi diagnosis. model yang diubah suai boleh mendiagnosis penyakit lebih tepat dengan mengurangkan bilangan ciri-ciri. tujuan utama model yang diubah suai ini adalah bagi pemilihan ciri (fs) perlu dilakukan menggunakan fpa and pengkhususan data perlu dijalankan menggunakan knn. keputusan menunjukkan model yang diubah suai lebih cekap dalam mendiagnosis penyakit kencing manis, radang hati, barah payudara dan penyakit jantung berbanding model knn. keywords: flower pollination algorithm; k-nearest neighbor; data classification; iium engineering journal, vol. 19, no. 1, 2018 gashti 145 feature selection; diagnosis diseases 1. introduction chronic diseases such as diabetes, hepatitis, breast cancer and heart disease are the main cause of death in many countries [1, 2]. early diagnosis and treatment of these diseases can provide a tremendous effect on improving patients’ quality of life and reducing the costs of their treatment. an effective treatment can be performed either based on the direct and subjective diagnosis by a clinical care team and their advice or based on prediction-based diagnosis. in the prediction-based method, retrospectively collected data from patients and healthy subjects are exploited to determine the probability of particular disease incidence in each person based on his/her medical data. appropriate computerbased methods can handle huge medical data sets in a short time period in order to predict disease incidence based on collected data. different symptoms of the particular disorder can be considered based on their importance and occurrence. for instance, diabetes, a metabolic disease due to the lack of insulin production or to resistivity to insulin, is characterized by high blood glucose levels [2]. hepatitis, on the other hand, is known by inflammation of the liver parenchyma and can be resulted from several etiologies; some of them are contagious and others are not. among the factors creating hepatitis are excess in alcohol consumption, the effects of some medications, and infection with bacteria or viruses [3]. heart disease is mainly manifested by partial or complete arterial occlusion. arterial disorders consequently affect the availability of the blood supply and therefore nutrients and oxygen to different organs including the heart itself [4]. one of the most effective strategies to cope with cardiovascular disorders is to identify the risk factors that play a critical role in the development of such diseases. breast cancer is also one of the most common diseases in modern societies, and a combination of the genetic and environmental factors can affect its incidence [5]. its early diagnosis, by targeting the risk factors involved, plays a critical role on efficiency of the treatment. as the number of features for a particular disease increases, the disease’s diagnosis and prognosis become increasingly challenging, even for a well-qualified medical professionals. to cope with this issue, in recent decades, computer-based diagnosis tools have been developed to assist physicians. computer-based tools offer several advantages including higher speed, precision, and lack of fatigue or condition-dependent decisions [6]. analysis and modeling tools such as artificial intelligence algorithms possess great potential to deal with huge data sets collected from patients, a feature that can significantly improve medical decisions including diagnosis and treatment selection. the purpose of this paper is to offer a new way of diagnosis for diseases such as diabetes, hepatitis, breast cancer, and cardiovascular disorders. in the modified model, fpa [7] helps feature extraction and knn [8] is used for data classification. the basic fs problem is an optimization problem with a performance measure for each subset of features to measure its ability to classify the samples. the aim of modified model is to reduce the dimensions and characteristics of the sample space, and ultimately, improve the accuracy of diagnosis and classification of patients. final results showed that the modified model has more diagnosis accuracy compared with knn [8]. classification, belonging to supervised learning, is one of the most popular data mining techniques [9]. in supervised learning, each instance in the training data is labeled with a class. the task of classification can be divided into two parts: training and testing. testing uses a classifier that is trained to assign a class label to a new unlabeled instance. iium engineering journal, vol. 19, no. 1, 2018 gashti 146 the overall structure of this paper is organized as follows: in section 2, we explain the related models that have been developed for diagnosis of diabetes, hepatitis, breast cancer, and heart disease. in section 3, the modified model is explained. the results of the modified model are presented in section 4. finally, our results are compared with previous models in section 5. 2. related work previous methods that have been tried on disease diagnosis include probabilistic neural networks (pnn) and fuzzy classification systems based on ant colony optimization (fcs-antminer). pnn is a model of artificial neural networks (anns) that has been used on 768 samples and 8 features for diabetes diagnosis using [10] a pima dataset. pnn often learns more quickly than many ann models, such as back propagation networks, and has been exploited for different applications. different neurons are used for testing and training in matlab. the results showed that a pnn model with 82.37% accuracy has better prediction power compared to other models. fuzzy classification system based on an ant colony optimization (fcs-antminer) [11] is a hybrid of the ant colony optimization (aco) and fuzzy is implemented and tested on a pima dataset for the diagnosis of diabetes. an aco-based classification system extracts a set of fuzzy rules for diagnosis of diabetes, named fcs-antminer. the aco model is used for rules and the fuzzy for data classification. the results showed that the accuracy of the fcs-antminer model is 84.32%. a case-based reasoning (cbr) [12] model is a fuzzy-ontology hybrid that was implanted and tested on 2,640 diabetic patients. the system was implemented in six modules: case source preparation, case-based ontology engineering, terminology server, fuzzy case-based ontology population, case retrieval engine, and case query parser. the ontology model was used for communication between the diseases and attributes. fuzzy classification was used to establish rules and diagnosis. the results showed that the accuracy of the fuzzy-ontology model was 97.67%. the linear discriminant analysis and adaptive network based fuzzy inference system (lda-anfis) [13] model is a hybrid of neural networks and fuzzy that was implemented and tested on 768 subjects for diabetes diagnosis. in lda-anfis mode, fuzzy rules have been used to derive and obtain a precise amount. results showed that the recognition accuracy in lda-anfis model was 84.61%. the hybrid k-means-genetic algorithm-support vector machine (k-means-gasvm) [14] model was implemented and tested to detect and predict diabetes on 768 people. the k-means model was used for data clustering and preparing data for svm classification. the basic concept of svm is finding an optimal separating hyper-plane to classify the separable data by maximizing the margin between points from each class. the points lying on the boundaries are called support vectors. as well, ga has been used for selecting the appropriate features. the results showed that the accuracy of k-means-gasvm model was 98.82%. the modified artificial bee colony (mabc) [15] model is a hybrid of the artificial bee colony (abc) and fuzzy that was suggested for classification of diabetic patient data. abc was used for fs and fuzzy for the formation of healthy/unhealthy laws. results of more than 768 data have shown that the mabc model was more accurate when compared with abc and was equal to 82.68%. a j48 decision trees [16] model is a data mining algorithm implemented and tested on the 768 samples to detect diabetes. the j48 algorithm was based on a decision tree, which is a predictive machine-learning model that decides the target value (dependent variable) of a new sample based on various attribute values of the available data [17]. rules have been used iium engineering journal, vol. 19, no. 1, 2018 gashti 147 to recognize healthy/unhealthy property classes. the results showed that the accuracy of j48 diagnosis was 83.83%. a principal component analysis (pca)-cross entropy optimization (ceo)-svm [18] model, based on svm and entropy, was performed and tested on 155 hepatitis patients. svm was used for classification of samples and the pca-ce for selecting the features and entropy of effective and important features. the results showed that pca-cesvm model’s accuracy was 97.2%. a multi-layer perceptron (mlp) [19] model was a model of anns that was performed and tested on 155 samples to detect hepatitis. the mlp model is a three-layer model and its testing and training stages are done by a middle layer. the results showed that the mlp detection accuracy was 91.87%. the incremental back propagation learning network (ibpln) [20] method is a model based on ann’s propagation that has been proposed for the diagnosis of hepatitis of 155 patient samples. the results show that the ibpln model had a higher detection accuracy compared with knn, naive bayes (nb), svm and particle swarm optimization models and its value was 93.34%. table 1: comparison of models for the diagnosis of diseases type model dataset instances accuracy [%] computational complexity ref diabetes pnn pima 768 82.37 high [10] fcs-antminer pima 768 84.32 high [11] cbr data types 2640 97.67 medium [12] lda-anfis pima 768 84.61 high [13] k-means-ga-svm pima 768 98.82 medium [14] mabc pima 768 82.68 low [15] j48 pima 768 83.83 low [16] hepatitis pca-ce-svm hepatitis 155 97.2 medium [17] mlp hepatitis 155 91.87 medium [18] ibpln hepatitis 155 93.34 high [19] breast cancer fuzzy-knn wbcd 699 99.71 high [20] gonn wbcd 699 98.24 high [21] cnn data types 3158 82.43 medium [22] svm wbcd 699 97.13 low [23] knn wbcd 699 95.27 low [23] c4.5 wbcd 699 95.13 low [23] nb wbcd 699 95.99 medium [23] heart fuzzy-ga cleveland 303 high [24] svm data types 214 85.05 low [25] mlp data types 214 84.11 medium [25] rbf data types 214 82.71 medium [25] bn data types 214 80.37 low [25] j48 data types 214 76.65 low [25] c4.5 cleveland 303 86.3 medium [26] ann cleveland 303 86.6 medium [26] iium engineering journal, vol. 19, no. 1, 2018 gashti 148 the fuzzy-knn [21] model was used on the wisconsin breast cancer dataset (wbcd) that contains 699 samples tested and implemented to detect breast cancer. the data set was collected from the patients of university of wisconsin-madison hospitals. when the attributes with missing values were removed, a data set with 239 malignant and 444 benign instances was obtained. the fuzzy model was used to infer the rules and knn was used for data classification. results showed that the recognition accuracy of fuzzyknn model was 99.71%. the genetically optimized neural network (gonn) [22] model, an ann models, has been proposed for breast cancer detection on 699 samples. genetic programming (gp) is used for testing and training of the gonn model. gp is a type of evolutionary algorithm, a subset of machine learning. it initially generates random solutions to solve a problem, and then evolves them based on a fitness function (ff). new and improved individuals are produced by applying reproduction, crossover and mutation operators on individuals of the previous generation. reproduction is an asexual method wherein a selected individual copies itself into the new population. it is effectively the same as one individual surviving into the next generation. crossover is applied in a gp by simply exchanging sub-trees between two trees, thus forming two new offspring from two parents. mutation changes a node within a tree or changes its information, thus, affecting only the individual and creating a new solution. due to crossover and mutation operators, gp techniques do a better job in exploring the search space than other machine learning algorithms. crossover and mutation operations in gp improve the gonn model. the evaluation was done on the wbcd dataset and results have shown that the detection accuracy of gonn was 98.24%. the convolutional neural network (cnn) [23] model is inspired from ann and was implemented and tested over 3,158 data samples. the cnn model is composed of neurons with substantial weight and bias can be learned. each neuron receives a number of inputs and then it calculates by multiplying the weight of inputs. finally, using a nonlinear transfer function, it shows the results. the results showed that the diagnostic accuracy was 82.43%. a semi-supervised deep convolutional neural network [23] was developed for breast cancer diagnosis, which used large amount of unlabeled data to improve the accuracy. svm, knn, c4.5 and nb models have been implemented and tested on 699 samples for breast cancer detection [24]. the models’ assessment was conducted in a weka environment. the svm model had a higher accuracy compared to other models. the fuzzy-ga [25] hybrid model was implemented and tested on the cleveland dataset with 303 patients and 75 features for diagnosing heart disease. the ga model was used for fs and the fuzzy model for deriving laws. in ga for fs, the gene amounts in the chromosomes were selected as 0 and 1. the results showed that the fuzzy-ga model had high accuracy in making laws. svm, mlp, rbf, bn and j48 models were conducted and tested on 214 samples of patients with 19 features for the heart disease diagnosis [26]. the results showed that the svm model had a higher accuracy compared to other models such as the rbf mlp model. the decision support system model [27] based on fuzzy logic was proposed to detect heart disease in 303 samples. the decision support system is a hybrid of c4.5 and ann. the results show that the diagnosis accuracy in the training phase in both models were 86.3% and 86.6%, respectively. table 1 summarizes the comparison of the proposed models for the detection of diseases. iium engineering journal, vol. 19, no. 1, 2018 gashti 149 3. the modified model a disease can be diagnosed by examining the patient’s and other obtained samples. however, for large numbers of patients with multiple tests per patient, an automated decision making system is a valuable tool in clinical practice. this can be achieved by feature selection (fs) methods. fs is the process of extracting the relevant and most informative data from the feature space, so that the feature set is more appropriate for classification. some features are improper and have no ability to increase the discriminative power of the classifier. some features are relevant and highly correlated to a specific classification. the evaluation has been done on the pima diabetes [28] dataset including 8 characters and 768 samples, the hepatitis [29] dataset containing 19 characters and 155 samples, the breast cancer [30] dataset containing 9 features and 286 samples, and the heart [31] dataset including 13 features and 180 samples. each dataset consisted of a set of numeric or categorical attributes (h(1),h(2),h(3),…,h(m),h(m+1)), where m shows predictive attributes and h(m+1) is a class of disease, namely healthy or sick. in fig. 1, the flowchart of the modified model is shown. fig. 1: flowchart of the modified model. in the modified model, after importing the raw dataset of disease, was normalized to remove outliers and repetitive data, and then pre-processing operations were done. the initial population was formed as either 0 or 1. the index of the vectors with a value of 1 reflects the selection of the desired feature. finally, using global pollination operators iium engineering journal, vol. 19, no. 1, 2018 gashti 150 based on eqn. (1) and local pollination based on eqn. (2) operations, updating and the position changing operations were done on the values [7]. (1) )( *1 t k t i t i xglxx    (2) )( 1 t k t j t i t i xxxx    in eqn. (1), xi t it is the ith pollen or solution vector xi at iteration t, and xi t+1 is a candidate solution for iteration t + 1. g is the current best solution, where g∗ = g1, g2, … , gd . the variable l is the strength of pollination, basically a d-dimensional step size, where l = l1, l2, … , ld , and γ is the scaling factor to control the step size. local pollination will cause the diversity of weight ranges and poor neighbors run for the classification process. these operators make the weight ranges have closely adjacent properties for knn classification and they increase the classification accuracy. since the fs problem is meant to select a specific feature or not, the solution is represented as a binary vector, where 1 indicates a feature will be selected to compose the new dataset and 0 otherwise. a sigmoid function is used to build this binary vector by the eqn. (3). (3) )( 1 1 ))(( tx j i j ie txs    firstly, for each element xi of the solution vector xi, a probability 𝑆(𝑥𝑖 𝑗 (𝑡)) is calculated using the sigmoid function defined by eqn. (3). then, using the probability vector 𝑆(𝑥𝑖 𝑗 (𝑡)), each element in the solution vector 𝑥𝑖 𝑗 (𝑡) will either have the value 1 or 0 by applying the condition represented by eqn. (4). thus, eqns. (1) and (3) will be replaced by eqn. (4). (4)         otherwise txsif tx j ij i 0 ))((1 )(  in which 𝑥𝑖 𝑗 (𝑡) represents the new pollen (solution) i with the jth feature vector, where 𝑖 = 1,2, … , 𝑚 and 𝑗 = 1,2, … , 𝑑 at the iteration t and σ ∼ u (0, 1). in the modified model, the ff vectors are calculated based on the amount of features that are 1. the vector with higher value of ff is selected, and the vectors that are not optimized undergo local pollination operations to create a new generation of population. selected features are imported into the knn model. training and testing processes are performed in the knn model. the evaluation is done based on the accuracy of the testing process. the final recognition accuracy is displayed in the output model. in the knn model, a non-classified sample may easily be found by comparing it with the most similar samples in the training set. thus, it is necessary to specify criteria for determining the distance between the samples. if we have a feature vector of  )(),...,(),( 21 xaxaxa n , to obtain the distance between two features of xi and xj according to eqn. (5) we will use the euclidean distance [8]. (5)    n r jrirji xaxaxxd 1 2 ))()((),( knn is a model for classifying test samples based on k closest training examples in feature space. the test sample is assigned to the class occurring most often amongst its k iium engineering journal, vol. 19, no. 1, 2018 gashti 151 nearest neighbors. usually, the euclidean distance is used to measure the closeness of the samples. the knn model is also a supervised learning-based classification algorithm. in classification, the knn model is a type of instance-based learning. it classifies objects based on the closest training examples in the feature space. the classification function is only approximated locally and all computation is deferred until classification. the knn model is amongst the simplest of all machine learning algorithms. the object is classified by a majority vote of its neighbors with the object being assigned to the class most common among its k nearest neighbor (k is positive integer). in fpa, each feature subset can be seen as a position of pollen. each subset may contain n features, where n is the number of features in the original set. the fewer the number of features in the solution and the higher the classification accuracy, the better is the solution. each solution is evaluated according to the modified ff, which depends on two objectives: the solution’s accuracy obtained by the knn classifier and the number of selected features in the solution. the ff used in the modified method is designed to have a balance between the number of selected features in each solution and the classification accuracy obtained by using these selected features, eqn. (6) represents the ff to evaluate solutions. (6) n s accff   . in eqn. (6), 𝑎𝑐𝑐 expresses the classification error rate of a given classifier knn is used here. |s| is the cardinality of the selected subset and |n| is the total number of features in the dataset, 𝜇 and 𝜌 are two parameters corresponding to the importance of classification quality and subset length. in eqn. (6), 𝜇 𝜖 [0,1] and 𝜌 = (1 − 𝜇). the modified model’s results should be analyzed in order to determine its value at the evaluation stage, and its methodology identified in its wake. these criteria can be calculated for educational data collection in the learning stage and also for the collection of trial records in evaluation stage. there are various criteria such as precision, recall, fmeasure and accuracy for the evaluation and we use accuracy criteria in order to examine the modified model [32, 33]. precision = tp tp + fp (7) recall = tp tp + fn (8) )re(pr re*pr*2 callecision callecision measuref   (9) 2/                     fptn tn fntp tp auc (10) )( )( fnfptntp tntp accuracy    (11) accuracy fnfptntp fnfp errorrate     1 )( )( (12) iium engineering journal, vol. 19, no. 1, 2018 gashti 152 where the tn parameter indicates the number of records with a negative category and that the classification algorithm correctly detected it as a negative one. tp represents the number of records that their category is positive and classification algorithm correctly detected it as a positive one. fp represents the number of records that their actual category is negative and that the classification algorithm mistakenly detected them as positive. fn represents the number of records that their actual category is positive and that the classification algorithm mistakenly detected them as negative. 4. evaluation and results in this section, the evaluation and results of the modified model is done on diabetes, hepatitis, breast-cancer, and heart disease in the matlab 2016 environment. the experiments are tested on an intel machine core i7 cpu 2.60 ghz and 6 gb ram and the values of initial population parameters and the number of iterations are considered as 50 and 100. the values of this parameter are effective in the diagnosis and accuracy of data. to study the impact of the standard parameters of the fpa, a set of extensive experiments has been performed using different values of the main parameters in the algorithm, (i.e., number of initial population and the number of iterations). in figure (2), an overview of program implementation is shown. fig. 2: overview of implemented program in matlab 2016a environment. in table (2), the results of the models on different datasets are shown. as shown in table (2), each criterion has a different value based on the data within the dataset. the modified model was much more accurate and had a lower error rate than knn models. the accuracy of the modified model for diabetes, hepatitis, breast-cancer, and heart disease datasets was 86.34%, 85.13%, 82.39%, and 83.04%, respectively. in figure (3), a comparison chart of the models based on the error rate criteria is shown. in figure (3), it is clear that the modified model has less error than the knn model. iium engineering journal, vol. 19, no. 1, 2018 gashti 153 table 2: results of models on different datasets datasets models precision recall f-measure auc accuracy error rate diabetes knn 65.31 69.41 67.30 72.34 81.62 18.38 modified model 71.34 75.49 73.36 79.24 86.34 13.66 hepatitis knn 66.38 67.48 66.93 71.89 79.20 20.80 modified model 73.61 78.01 75.75 80.64 85.13 14.87 breastcancer knn 66.21 68.40 69.27 70.05 73.48 26.52 modified model 69.15 74.68 71.81 79.60 82.39 17.61 heart knn 70.14 71.45 70.79 72.85 76.46 23.54 modified model 73.16 76.11 74.61 79.50 83.04 16.96 fig. 3: comparison chart of models based on the error rate. in table 3, the results of the modified model are shown based on different iterations on the datasets. by increasing iterations, the accuracy value has been increased and the error value has been decreased. the accuracy of the modified model with 500 iterations for diabetes, hepatitis, breast-cancer, and heart disease datasets was 95.76%, 94.79%, 89.90%, and 90.03%, respectively. in table 4, the comparison of models based on fs with 500 iterations is shown. in table 4, a comparison of models is shown, based on the fs. as shown in table 4, when the number of features is low, then the accuracy is better because fewer features need to be evaluated, but the features that have a greater impact on diagnosis and fewer errors are selected. iium engineering journal, vol. 19, no. 1, 2018 gashti 154 table 3: the results of the modified model based on iterations on different datasets datasets iterations precision recall f-measure accuracy error rate diabetes 100 71.34 75.49 73.36 86.34 13.66 150 72.38 76.48 74.34 89.82 10.18 200 74.65 76.98 75.80 92.37 7.63 300 75.63 77.15 76.38 93.47 6.53 500 50.25 81.49 80.87 95.79 4.21 hepatitis 100 73.61 78.01 75.75 85.13 14.87 150 75.38 77.52 76.44 88.34 11.66 200 78.95 79.14 79.04 90.80 9.20 300 80.32 82.31 81.30 91.46 8.54 500 83.79 85.19 84.48 94.79 5.21 breastcancer 100 69.15 74.68 71.81 82.39 17.61 150 70.16 71.62 70.88 86.56 13.44 200 71.49 73.18 72.33 88.17 11.83 300 71.49 72.08 72.01 89.21 10.79 500 72.50 74.10 73.29 89.90 10.10 heart 100 73.16 76.11 74.61 83.04 16.96 150 74.53 75.20 74.86 85.16 14.84 200 82.47 85.14 83.78 88.94 11.06 300 85.95 87.46 86.70 89.63 10.37 500 86.41 85.21 85.81 90.03 9.97 table 4: evaluation and results of the modified model on different datasets based on the fs datasets fs precision recall f-measure auc accuracy error rate diabetes 5 73.94 75.81 74.86 85.16 96.35 3.47 6 73.00 74.81 73.89 83.20 93.18 6.82 7 72.14 73.22 72.68 82.07 92.16 7.84 8 71.34 75.49 73.36 79.24 89.34 10.66 hepatitis 10 77.00 79.01 77.99 86.00 94.05 5.95 12 75.13 76.31 75.72 84.07 91.02 8.98 16 74.82 75.89 75.35 72.16 90.64 9.36 19 73.61 78.01 75.75 80.64 90.13 9.87 breastcancer 5 74.20 76.21 75.19 83.09 91.16 8.84 6 72.61 73.91 73.25 81.44 89.10 10.90 8 70.50 72.46 71.47 80.17 86.88 13.12 9 69.15 74.68 71.81 79.60 86.39 13.61 heart 9 78.35 79.05 78.70 86.12 94.34 5.66 11 75.14 77.68 76.39 83.17 92.19 7.81 12 74.91 75.41 75.16 80.16 89.10 10.90 13 73.16 76.11 74.61 79.50 87.04 12.96 iium engineering journal, vol. 19, no. 1, 2018 gashti 155 in table (4), the accuracy for diabetes with fs=5 and without fs is 96.35% and 89.34%, respectively. the accuracy for hepatitis with fs=10 and without fs is 94.05% and 90.13%, respectively. the accuracy for breast cancer with fs=5 and without fs is 91.16% and 86.39%, respectively. as well, in table (4), the accuracy for heart with fs=9 and without fs is 94.34% and 87.04%, respectively. in figure (4), a comparison chart of the modified model based on fs is shown. in figure (4) it is clear that if the number of features is low, then the error rate will also be lower, because fs is directly related to the error rate and it is effective in determining accuracy error. fig. 4: comparison chart of the modified model based on fs. 5. conclusion and future work some diseases are diagnosed early and appropriate treatment for them would be considered. unfortunately, in the world 70 to 90 percent of diseases are not diagnosed in time and patients are sick (advanced illness) before visiting the doctor, when there would no longer be an appropriate treatment for them. in this paper, by improving the knn and using fpa, a model for predicting diseases was developed. in the modified model, the fs method was used to increase the efficiency and accuracy of the diagnosis system. fs can identify the important features that can help doctors to diagnose the disease in the earliest instance. results on the datasets of diabetes, hepatitis, breast cancer and heart disease showed that the modified model has better recognition accuracy than a knn model. if the number of features is less, the processing will be better and also the key features will be extracted. as future work, we intend to construct a computational model in which, instead of combining feature subsets, we will combine the mathematical formulas that define the feature selection metrics with the goal to achieve a more impartial formula. references [1] begum s, ahmed mu, funk p, xiong n, folke m. (2011) case-based reasoning systems in the health sciences: a survey of recent trends and developments. ieee transactions on systems, man, and cybernetics, part c (applications and reviews), 41(4):421-434. iium engineering journal, vol. 19, no. 1, 2018 gashti 156 [2] srikanth p, deverapalli d. (2016) a critical study of classification algorithms using diabetes diagnosis. in 2016 ieee 6th international conference on advanced computing (iacc). [3] neshat m, sargolzaei m, nadjaran toosi a, masoumi a. (2012) hepatitis disease diagnosis using hybrid case based reasoning and particle swarm optimization. isrn artificial intelligence. 2012:6. [4] bhatia s, prakash p, pillai gn. (2009) svm based decision support system for heart disease classification with integer-coded genetic algorithm to select critical features. [5] arya c, tiwari r. (2016) expert system for breast cancer diagnosis: a survey. in 2016 international conference on computer communication and informatics (iccci). [6] bazazeh d, shubair r. (2016) comparative study of machine learning algorithms for breast cancer detection and diagnosis. in 2016 5th international conference on electronic devices, systems and applications (icedsa). [7] yang x-s. (2012) flower pollination algorithm for global optimization. in unconventional computation and natural computation. berlin, heidelberg: springer berlin heidelberg. [8] martin b. (1995) instance-based learning: nearest neighbour with generalisation, in computer science working papers. university of waikato, department of computer science. [9] duda ro hp, stork dg. (2007) pattern classification. vol. 24. john wiley & sons. [10] temurtas h, yumusak n, temurtas f. (2009) a comparative study on diabetes disease diagnosis using neural networks. expert systems with applications, 36(4):8610-8615. [11] ganji mf, abadeh ms. (2011) a fuzzy classification system based on ant colony optimization for diabetes disease diagnosis. expert systems with applications, 38(12):14650-14659. [12] el-sappagh s, elmogy m, riad am. (2015) a fuzzy-ontology-oriented case-based reasoning framework for semantic diabetes diagnosis. artificial intelligence in medicine, 65(3):179-208. [13] dogantekin e, dogantekin a, avci d, avci l. (2010) an intelligent diagnosis system for diabetes on linear discriminant analysis and adaptive network based fuzzy inference system: lda-anfis. digital signal processing, 20(4):1248-1255. [14] santhanam t, padmavathi ms. (2015) application of k-means and genetic algorithms for dimension reduction by integrating svm for diabetes diagnosis. procedia computer science, 47:76-83. [15] beloufa f, chikh ma. (2013) design of fuzzy classifier for diabetes disease using modified artificial bee colony algorithm. computer methods and programs in biomedicine, 112(1):92-103. [16] hayashi y, yukita s. (2016) rule extraction using recursive-rule extraction algorithm with j48graft combined with sampling selection techniques for the diagnosis of type 2 diabetes mellitus in the pima indian dataset. informatics in medicine unlocked, 2:92-104. [17] gashti mz. (2017) a novel hybrid support vector machine with decision tree for data classification. international journal of advanced and applied sciences, 4(9):138-143. [18] elaboudi n, benhlima l. (2016) a new approach based on pca and ce-svm for hepatitis diagnosis. in proceedings of the mediterranean conference on information & communication technologies 2015. cham: springer international publishing. [19] bascil ms, temurtas f. (2011) a study on hepatitis disease diagnosis using multilayer neural network with levenberg marquardt training algorithm. j med syst, 35(3):433-436. [20] mitra m, samanta rk. (2015) hepatitis disease diagnosis using multiple imputation and neural network with rough set feature reduction. in proceedings of the 3rd international conference on frontiers of intelligent computing: theory and applications (ficta) 2014. cham: springer international publishing. [21] onan a. (2015) a fuzzy-rough nearest neighbor classifier combined with consistency-based subset evaluation and instance selection for automated diagnosis of breast cancer. expert systems with applications, 42(20):6844-6852. [22] bhardwaj a, tiwari a. (2015) breast cancer diagnosis using genetically optimized neural network model. expert systems with applications, 42(10):4611-4620. iium engineering journal, vol. 19, no. 1, 2018 gashti 157 [23] sun w, tseng tb, zhang j, and qian w. (2017) enhancing deep convolutional neural network scheme for breast cancer diagnosis with unlabeled data. comput med imaging graph, 57:4-9. [24] asri h, mousannif h, moatassime ha, noel t. (2016) using machine learning algorithms for breast cancer risk prediction and diagnosis. procedia computer science, 83:1064-1069. [25] ephzibah ep, sundarapandian v. (2012) a fuzzy rule based expert system for effective heart disease diagnosis. in advances in computer science and information technology. computer science and engineering. berlin, heidelberg: springer berlin heidelberg. [26] ghumbre su, ghatol aa. (2012) heart disease diagnosis using machine learning algorithm. in proceedings of the international conference on information systems design and intelligent applications 2012 (india 2012) held in visakhapatnam, india, january 2012. berlin, heidelberg: springer berlin heidelberg. [27] lahsasna a, ainon rn, zainuddin r, bulgiba am. (2012) a transparent fuzzy rule-based clinical decision support system for heart disease diagnosis. in knowledge technology. berlin, heidelberg: springer berlin heidelberg. [28] pima indians diabetes dataset.[https://archive.ics.uci.edu/ml/datasets/pima+indians+diabetes] [29] hepatitis dataset.[https://archive.ics.uci.edu/ml/datasets/hepatitis] [30] breast cancer dataset.[http://www.sgi.com/tech/mlc/db/breast-cancer.all ] [31] heart diseases dataset.[http://www.sgi.com/tech/mlc/db/heart.data] [32] farjamnia g, gashti mz, barangi h, and gasimov ys. (2017) the study of support vector machine to classify the medical data. ijcsns international journal of computer science and network security, 17(12):145-150. [33] ryszard sm, ivan b, avan b. (1998) machine learning and data mining; methods and applications. john wiley \&amp; sons, inc. 456. https://archive.ics.uci.edu/ml/datasets/pima+indians+diabetes https://archive.ics.uci.edu/ml/datasets/hepatitis http://www.sgi.com/tech/mlc/db/breast-cancer.all http://www.sgi.com/tech/mlc/db/heart.data iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 preparation of cao-based pellet using rice husk ash via granulation method for potential co2 capture farah diana mohd daud1*, muhammad mirza mohamad azir1, mudrikah sofia mahmud1, norshahida sarifuddin, hafizah hanim mohd zaki 1 deptartment of manufacturing and materials engineering, kulliyyah of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia *corresponding author: farah_diana@iium.edu.my (received: 11th july 2020; accepted: 18th november 2020; published on-line: 4th january 2021) abstract: co2 capturing has become very significant option to reduce the emission of co2 in the atmosphere and hence, minimizing environmental issues.among solid co2 sorbent, calcium oxide (cao) is an attractive regenerable sorbent for co2 capturing because of their reactivity and high co2 absorption capacity. cao alone suffers from rapid decay of co2 adsorption during multiple carbonation/calcination reaction cycles. the stability of cao sorbents during cyclic runs can be achieved via the incorporation of additive support materials. the silica (sio2) from natural sources such as rice husk is the best candidate to be used as an additive in the sorbents. however, the cao-based sorbent in finely generated powders are prone to severe attrition problems. therefore, this research focuses on preparation of cao-based pellets by using rice husk ash (rha) via granulation method. the result of the raw materials confirmed that ca(oh)2 have crystalline structure with finely distributed grains and rha exhibit amorphous structure with randomly oriented size grains. based on the xrd, it is confirmed that the insertion of rha does not alter the phase structure of the pellets. each ratio yield different intensity value and has formation of new peaks after sintering. meanwhile, the microstructures of the pellets show that the pores reduced as the calcination temperature increased while the incorporation of rha caused the pores size increased with randomly oriented shape. these findings indicate that the optimum value for the pellets is with the ca(oh)2:rha ratio of 80:20 and calcination temperature of 750 °c. abstrak: penangkapan co2 telah menjadi pilihan yang sangat penting untuk mengurangkan pelepasan co2 di atmosfer serta kesan alam sekitar. antara penjerap co2 pepejal, kalsium oksida (cao) adalah penyerapan yang menarik untuk co2 yang ditangkap kerana kereaktifan dan kapasiti penyerapan co2 yang tinggi. cao sahaja menderita daripada pelepasan cepat penjerapan co2 semasa kitaran tindakbalas karbonasi / kalsinasi. kestabilan cao penjerap semasa berlaku kitaran boleh dicapai melalui penggabungan bahan sokongan tambahan. silika (sio2) dari sumber semula jadi seperti sekam padi (rha) adalah calon terbaik untuk digunakan sebagai aditif dalam penjerap. walau bagaimanapun, penjerap berasaskan cao dalam bentuk serbuk halus yang dihasilkan adalah terdedah kepada masalah pergeseran yang teruk. oleh itu, kajian ini memberi tumpuan kepada penyediaan pelet berasaskan cao dengan menggunakan abu sekam beras melalui kaedah granulasi. hasil bahan mentah mengesahkan bahawa ca(oh)2 mempunyai struktur kristalografi dengan bijirin halus dan rha yang mempamerkan struktur bukan kristal dengan butiran saiz berorientasikan secara rawak. berdasarkan xrd, ia disahkan bahawa penyisipan rha tidak mengubah struktur kristalografi pelet. setiap nisbah menghasilkan nilai intensiti yang berbeza dan mempunyai pembentukan puncak baru selepas pensinteran. sementara itu, mikrostruktur pelet menunjukkan bahawa pori-pori berkurangan apabila suhu kalsinasi meningkat sementara pembentukan rha menyebabkan saiz pori meningkat dengan bentuk berorientasikan rawak. penemuan ini menunjukkan bahawa nilai optimum bagi pelet adalah dengan nisbah ca(oh)2:rha 80:20 dan suhu kalsinasi 750 °c. keywords: co2 capture; cao-based pellets; rha; granulation method. 234 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 1. introduction in malaysia, the main contribution of co2 emission is from the energy sectors such as fossil fuels, natural gas, and coal power plants. the energy sectors in malaysia contributed at about approximately 36% of the total global co2 emissions in 2004 and among all of the greenhouse gases, co2 gases responsible for 60% of greenhouse effect that cause the global warming [1]. moreover, malaysia plans to reduce the amount of co2 release by 25% reduction from all sectors and this is according to green technology master plan 2017-2030 proposed by malaysia government [2]. thus, planning and solution must be done in order to control and resolve the problems of co2 emissions and greenhouse gases effect. one of the solutions to reduce the co2 gases emitted to the atmosphere is by introducing the carbon capture and storage (ccs) technology. this technology captures up to 90% of co2 which led to significant reduction of co2 level in atmosphere [3]. among the co2 capture methods, co2 capture by adsorption into a sorbent is the most common technique used in the industry due to its better thermal properties and high amount of co2 adsorption [4]. the adsorbent materials are usually made from ceramic materials such as cao, mgo, and zro2. it is well known that ceramic materials possess better thermal properties, and these materials will be acceptable to be used in the elevated temperature condition. however, the limitation of the recent co2 adsorbent materials is that it has low stability and reduction in reactivity in cyclic operation. recent studies show that other additives such as sio2, mgo, and al2o3 reinforced into the sorbents can improve the cycle loop of the co2 adsorption [4]. improvement of the co2 adsorption is done by designing the co2 capture technologies in the form of pellets rather than sorbents itself and the introduction of biomass resources with the pellets is one of the advantages upon using waste and eco green materials [5]. thus, this paper aims to study the effect of cycling loops with the pellets design when introducing other additives into the sorbents. plus, the utilization of waste materials such as rice husk ash introduced into the pellets will be a huge impact on the economic and environmental factor. there are many methods and techniques have been done on previous study to produce cao-based sorbents with the addition of sio2 including, sol-gel, wet impregnation, biotemplate via infiltration, mixing and extrusion-spheronization methods. among all the methods mentioned above, three of the methods utilizing biomass materials, mainly from the rice husks to act as the additives inside the cao-based sorbents while the other two methods (sol-gel and wet impregnation) used silica sources from synthetic means. rice husk ash used as the precursor in the cao-sio2 sorbent due to the high content of silica. plus, the sources of rice husk are abundant and easy to obtain as it is being produced as the by-product in paddy field makes it the best candidate to be used in the cao-based sorbent. different parameters used in the preparation of the cao-sio2 sorbent play a crucial role in determining the performance of the pellet. there are several parameters needed for the investigation and different parameters usually will give different effects on the pellet whether it will improve the performance or becoming unfavourable. one of them is amount of silica sources incorporated with the cao-based sorbents or the ratio amount between those two materials. previous studies showed that different ratio or amount of silica added exhibits different cyclic adsorption performance. in one study, ratio of 3:7 rha/cao shown better stability over 50 cycles compared to 1:9 rha/cao even though 1:9 rha/cao has better carbonation conversion in early cycles [6]. meanwhile, in the other study, 10%, 20%, 30%, 40% and 50% of rha added into the cao-based sorbent. initially, the ratio of 20% rha express the highest co2 adsorption compare to other ratios but it reduces significantly started 235 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 at the first cycle. then, it is observed that 40% and 50% rha into the cao sorbent maintained the highest co2 capture over the nine cycles [7]. the main objective of this paper is to prepare cao-based pellet with addition of rha as the sacrificial bio-template through granulation method. the pellets were prepared according to two different ratios and undergo calcination process at 750°c. the effect of rha addition and calcination at 750°c on the properties of cao-based pellets were examined through the phase structure and morphological characteristics. 2. experimental 2.1. materials calcium hydroxide from r&m chemical sdn. bhd. was selected as the calcium precursor. the rice husk ash (rha) as the biotemplate material was obtained from mardi perlis. 2.2. preparation of the rha initially, rha is oven-dried at 70°c overnight to eliminate moisture. then, the fine powder of rha is obtained by ball milling process at 200 rpm for 1 hour. finally, the ball milled rha was sieved at the size range of 50 µm to 90 µm. 2.3. preparation of the sorbent pellets next, ca(oh)2 and rha powders were weighed according to two different ratios as shown in table 1. at first, the weighed materials were vigorously mixed in a granulator machine at 73 rpm speed for 10 minutes. then, the mixture undergoes granulation process at the speed of 1700 rpm and simultaneously wetted by spraying 300 ml of deionized water. after the granulation process, the ca(oh)2-rha pellet was obtained in spherical shape and randomly in size. lastly, the cao-sio2 pellets were obtained after calcination process in furnace at 750°c. table 1: two different ratios of ca(oh)2 and rha with different weight of each ratio ratio of ca(oh)2 and rha weight of ca(oh)2 (g) weight of rha (g) 80:20 800 200 70:30 700 300 2.4 characterization 2.4.1 x-ray diffraction (xrd) the phase structure of ca(oh)2, rha and the prepared cao-sio2 pellets, before and after calcination at 750°c was examined by x-ray diffractometer (xrd) model bruker d2 phaser. 2.4.2 scanning electron microscopy (sem) the morphological characteristic of raw materials (ca(oh)2 and rha) and the prepared cao-sio2 pellets at different ratio, before and after calcination process was investigated by jsm-it100 scanning electron microscopy (sem) machine manufactured by jeol. 236 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 3. results and discussion 3.1. analysis on the raw materials fig. 1(a) and 1(b) show the xrd pattern of ca(oh)2 and rha at different scale of intensity. based on the fig. 1(a), sharp peaks at 2θ = 18.1°, 29.45°, 34.15°, 47.25° and 50.85° proved the crystalline structure of ca(oh)2. whereas fig. 1(b) indicated broad peak, centered at about 2θ = 23° which confirms the amorphous structure of rha. it is common that silica contain in rha has amorphous structure, and its transformation to crytalline structure will occur when temperature is increased beyond 700°c [9] . fig. 2 and 3 displayed the sem micrographs of ca(oh)2 and rha. it has been observed for ca(oh)2 that it consist of finely dispersed, small size particles. under x5000 magnification (fig. 2(c)), the morphology of ca(oh)2 revealed that the microstructure is in granular and agglomerated shape. while for rha, the sem images reveals the siliceous nature and with some porosity of the ashes. it was observed that rha has agglomerated particles in various sizes and irregular structures. fig.1. xrd pattern of a) ca(oh)2 and b) rha. (a) (b) 237 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 3.2. characterization of the sorbent pellets 3.2.1 average size of the pellets fig. 4 (a) and (b) show the different ratio of cao-sio2 pellets obtained from the granulation process. as shown in fig. 4 (a) and (b), the average size of particles for 80:20 and 70:30 pellets are 3.0 mm and 4.5 mm respectively. the utilization of high speed of granulator and optimum amount of deionized water added during the granulation process resulted in small size of pellets. a small size of pellets was desired as the smaller the pellets, the higher the surface area of the pellets to covered for potential co2 adsorption application. however, the significant difference in the average particles size among the two ratios is presumed to occur due to the different amount of rha, as the sio2 source added in cao-sio2 pellets. the smaller size of pellets is obtained when lower amount of rha added. table 2 summarized the details of granulation process and the resulted average particles size for each ratio before undergo calcination process at 750°c. fig 3: sem micrographs of rha at magnification of a) 500x and b) x1000x. fig. 2. sem micrographs of ca(oh)2 at magnification of a) 500x, b) 1000x and c) 5000x. 238 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 table 2: summary of the pellets obtained from two different ratios. fig. 5 shows that cao-sio2 pellets after the calcination process at 750°c. as can be observed in fig. 5, all pellets have significant reduction in the size of pellet which is much smaller compared to the one before the calcination. this is probably due to the elimination of moisture from the pellets and significant reduction/shrinkage in pellets size after the calcination indicates huge amount of moisture content in each pellets. 3.2.2 different ratio of cao-sio2 pellets before calcination the phase structure of cao-sio2 pellets for each ratio before the calcination process was characterized by xrd analysis, as displayed in fig. 6 (a) and (b). the peak characteristics of ca(oh)2 and sio2 are detected in xrd pattern of all cao-sio2 pellets. according to fig. 6, it is evident that the main crystalline peaks of ca(oh)2 were detected at about 2θ = 28.76°, ratio of ca(oh)2 and rha impeller and chopper speed (rpm) amount of deionized water (ml) average size (mm) 80:20 73, 1700-1800 300 3.0 70:30 73, 1700-1800 300 4.5 fig. 4 .the obtained pellets from the granulation process of (a) ratio 80:20 and (b) ratio 70:30. fig. 5. pellets after calcination of different ratio ;(a) 80:20 and (b) 70:30. 239 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 34.17°, 47.21° and 62.78°. however, the intensity for each peak was decreased with increasing amount of rha added. besides, the characteristics peak of silica also could be observed from the xrd pattern, however, the intensity of the peaks was very low due to its amorphous nature. the silica peak centered about 2θ = 23° was observed in both xrd spectras of pellets prepared. fig. 6. xrd spectra for different ratio of cao-sio2 before calcination, (a) 80: 20 and (b) 70:30 different ratio of rha addition in the cao-sio2 pellets as the biomass sacrificial template did not disrupted the crystalline structure of the calcium precursor. this is proved by the almost similar xrd pattern obtained from the cao-sio2 pellets with the xrd pattern of the raw ca(oh)2. besides, the detection of similar major diffraction peaks from xrd pattern of all pellets evidenced the incorporation of sacrificial biomass template materials did not modify the crystallinity of the pellets produced [8]. the sem micrograph of the prepared cao-sio2 pellets at different ratios were shown in fig. 7 and 8. all the micrographs illustrated that addition of rha had significantly altered the morphology of cao-sio2 pellets prepared, according to the ratio. based on fig. 8, 80:20 pellet shows large and irregular grains size with random distribution. meanwhile, 70:30 pellet exhibits randomly distributed, irregular, and smaller shape of microstructures. some small needle-like or flake structure could be observed which indicates the presence of ash or biomass material inside the pellets that have been prepared. according to the micrographs obtained, increasing amount of rha added caused the grains size to decrease significantly which lead to the development of irregular microstructures. 240 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 fig.7. sem micrographs of cao-sio2 pellets ratio 70:30 before calcination at different magnification a) 500x and b) 1000x fig.8. sem micrographs of cao-sio2 pellets ratio 80:20 before calcination at two different spots by magnification of 500x 3.2.3 effect of different ratio after 750 °c calcination the effect of calcination at 750°c on the phase structure of cao-sio2 pellets prepared is shown in fig. 9. sharp peaks were detected from all of the xrd pattern obtained which confirmed the existance of crystalline phase. this is due to the formation of cao after sintering at 750°c. the cao peaks can be observed at 2θ = 29.76°, 33.02°, 39.49°, 47.56°, 51.91° and 54.58°. however, there is significant difference in intensity of peak at 2θ = 29.76°. the highest peak intensity was observed in 70:30 pellet followed by 80:20 pellet. supposedly, if the amount of cao is higher compared to the silicate, the significant increment in peak intensity of cao should be obtained whereas the silicate peaks should remain unchanged [10]. but from the xrd pattern obtained, pellet with low amount of cao (70:30 pellet specifically) possessed the highest peak of cao. this is presumed to occur due to the calcination process at 750°c might have altered the phase structure of silica in rha and thus modified the xrd pattern of all pellets. 241 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 fig.9. xrd spectra for different ratio of cao-sio2 pellet calcined at 750°c morphology of the calcined cao-sio2 pellets for each ratio are shown in fig. 10 and 11. after calcination at 750°c, the formation of pores was observed in micrographs acquired. for 80:20 pellet, grains with random sized have been developed after sintering at 750°c with the presence of needle-like structure. the presence of needle-like structure suggests formation of a new compund resulted from the calcination of cao-rha which mainly composed of ca, si and o elements [11]. as for 70:30 pellet, the morphology consists of randomly scattered grains which is small in size as shown in fig. 11. 70:30 pellet has irregular pores structure but not as large as compared to the pore stucture in 80:20 pellet. however, 80:20 pellet shows better porosity as the pores size were larger which caused an increased in porosity. higher amount of well-structured pores were more preferred for co2 capture application; in which it would contribute to an excellent performance of co2 adsorption. fig.10. sem micrographs of cao-sio2 pellets ratio 80:20 after calcination at 750°c with different magnification a) 100x and b) 500x. 242 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 4. conclusion this study presented the cao-based pellets with addition of rha as the sacrificial biotemplate had been successfully prepared via granulation method. the calcium precursor, ca(oh)2 has agglomerates and granular microstructures and rha has an irregular and in definitive shape of microstructures. based on the xrd analysis, the ca(oh)2 has crystalline structure, while rha has amorphous structure. xrd analysis proved that the inclusion of rha in the ca(oh)2 did not disrupted the crystalline structure of the samples and intensity of the peaks were reduced with increasing amount of rha added. however, the calcination at 750°c has significantly modified the xrd pattern of all cao-sio2 pellets. the sharp peaks indicated the development of crystalline cao and different ratio has different peak intensity. the pellets with low amount of rha has finer grain structure observed as for increased the amount of rha caused the pores became agglomerate, increase in size and randomly distributed. to conclude, based from the characterization result it indicates that ratio 80:20 and calcination temperature of 750 °c were the optimum parameters to be used for the pellets production. references [1] rawshan ab, kazi s, sharifah mastura sa, mokhtar j. (2015) co2 emissions, energy consumption, economic and population growth in malaysia. renew.sust. energ. rev., 41:594–601. [2] alifah z. (2017). malaysia to slash another 25% of co2 emission by 2030. retrieved from: https://themalaysianreserve.com/2017/06/21/malaysia-slash-another-25co2-emission-2030/ [3] naeem ma, armutlulu a, kierzkowska a & müller cr. (2017) development of highperformance cao-based co2 sorbents stabilized with al2o3 or mgo. energy procedia, 114: 158– 166. [4] zhang z, tohid ngb, muftah hen. (2018) carbon capture. chapter 4.5, exergetic, energetic environ. dimensions, 997-1016. [5] wang j, huang l, yang r, zhang z, wu j, gao y, wang q, o'hare d, zhong z. (2014) recent advances in solid sorbents for co2 capture and new development trends. energy. environ. sci., 7:3478–3518. fig.11. sem micrographs of cao-sio2 pellets ratio 70:30 after calcination at 750 °c with different magnification a) 100x and b) 500x. 243 iium engineering journal, vol. 22, no. 1, 2021 mohd daud et al. https://doi.org/10.31436/iiumej.v22i1.1544 [6] monica bg, jose, mv, antonio p, pedro esj, luis apm. (2018) low-cost ca-based composites synthesized by biotemplate method for thermochemical energy storage of concentrated solar power. appl.energy, 210:108–116. [7] mustakimah m, suzana y, armando tq, tetsuya k. (2018) utilization of rice husk to enhance calcium oxide-based sorbent prepared from waste cockle shells for cyclic co2 capture in hightemperature condition. environ. sci. pollut. res., 26:33882-33896. [8] liu, w., an. h., qin, c., yin, j., wang, g., feng, b., xu, m. (2012) performance enhancement of calcium oxide sorbents for cyclic co2 capture: a review. energ. fuels, 26:275-2767. [9] maría e, vasilije m, edward ja. (2016) calcium looping sorbents for co2 capture. appl. energy, 180:722–742. [10] sanchez-jimenez pe, perez-maqueda la, & valverde jm. (2014) nanosilica supported cao: a regenerable and mechanically hard co2 sorbent at ca-looping conditions. appl. energy, 118:9299. [11] li y, zhao c, ren q, duan l, chen h, chen x. (2009) effect of rice husk ash addition on co2 capture behavior of calcium-based sorbent during calcium looping cycle. full processing technology, 90: 825-834. 244 19-1544-article text-10559-1-10-20201126.pdf pages from 1544-article text-10834-1-18-20201216.pdf 19-1544-article text-10559-1-10-20201126 microsoft word 144-569-2-pra iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 27 a new method for the determination of toxic dye using ftir spectroscopy mohamed e. s. mirghani 1 *, nassereldeen a. kabbashi 1 , isam y. qudsieh 1 and faiz a. elfaki 2 1 bioenvironmental engineering research unit (beru), department of biotechnology engineering, 2 department of science in engineering, kulliyyah of engineering, international islamic university malaysia (iium), p. o. box 10, 50728 kuala lumpur, malaysia *e-mail: elwathig@iiu.edu.my abstract: a new method was developed to determine toxic dyes content in textile and other products using fourier transform infrared (ftir) spectroscopy with attenuated total reflectance (atr) element and kbr transmission cell. the wavelengths used were selected using pure dyes and dye mixtures. transmittance values from the wavelengths regions 3500 – 2650 and 1675 – 1500 cm -1 and partial least square (pls) regression method were used to derive ftir spectroscopic calibration model for dyes containing –n=n– in their structure. the coefficient of determinations (r 2 ) for the models were computed by comparing the results obtained from ftir spectroscopy against the actual values of the dyes concentrations. r 2 were 0.9321 and 0.9819 for two samples of toxic dyes respectively. the standard errors (se) of calibrations were 1.84 and 1.36 respectively. the calibration model was cross validated within the same set of samples and the standard deviation (sd) of the difference for repeatability and accuracy of the ftir method were determined. with its speed and ease of data manipulation, ftir spectroscopy is a useful alternative method to wet chemical methods for rapid and routine detection of azo dyes as toxic dyes in such products for quality control. keywords: ftir spectroscopy, pls, toxic dye. 1. introduction dyeing is an ancient art which predates written records. it was practiced during the bronze age in europe [1]. primitive dyeing techniques include sticking plants to fabric or rubbing crushed pigments into cloth. nowadays, most of the colors used commercially for dyeing are synthetic, which mostly derived from non-renewable coal tar and petroleum. they are synthesized by various means, from by-products of fossil fuels, e.g., aniline and other aromatic derivatives [2]. because clothing comes into prolonged contact with skin, toxic chemicals are absorbed through the skin, especially when human body is warm and skin pores have opened to permit perspiration. once absorbed by humans, heavy metals tend to accumulate in the liver, kidney, bones, heart and brain. the effects on health can be significant when high levels of accumulation are reached. the effect is particularly serious in children because toxic dye and/or heavy metals accumulation may negatively affect their growth and may be their life as well. iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 28 it is often the dye fixative which is used to bond the dye color to the fabric that causes the most problems. unfortunately, heavy metals have often been used in dye fixatives and also in dyes. toxic chemicals sometimes found in the dyeing process include: • dioxin – a carcinogen and possible hormone disrupter. • toxic heavy metals such as chrome, copper, and zinc – known carcinogens. • formaldehyde – a suspected carcinogen. • azo dyes group – which give off carcinogenic amines. in general, azo dyes can occur in two tautomeric forms; azo (–n=n–) or hydrazone (=n–nh–). the latter is said to be more prone to the oxidative fading, which is the most common photodegradation mechanism in the presence of light, moisture, and oxygen. in oxidation of an azo dye, singlet oxygen attacks on the hydrazone tautomer to form unstable peroxide, which then undergoes decomposition. under anaerobic conditions, azo dye can be reduced to its corresponding amines by abstracting a hydrogen atom from a hydrogen donor [3]. amendments and regulations in some countries stated that azo-dyestuffs, which can release carcinogenic amines, should no longer be used in dyeing consumer goods. 13 c and 15 n-nmr studies of the azo-hydrazone tautomerism of some azo dyes were carried out by antonin and valdimir [4]. many acid and direct dyes which liberate harmful amines such as benzidine, o-tolidine and o-dianisidine after reduction are, however, still used [5]. toxic chemicals from dyes also create widespread environmental havoc. large amounts of water are used to flush conventional synthetic dyes from garments and then this waste water must be treated to remove the heavy metals and other toxic chemicals before it can be returned to water systems, sewers and rivers. most garments are produced in developing countries where pollution controls are often lax or nonexistent. discharges from huge numbers of the textile producers go straight into rivers where the river water might be bright green one day and yellow the next. developing countries are also lacking in standards and enforcement concerning the use of toxic chemicals in dyes and garment finishes. figures 1 and 2 showed the chemical structure of some of the first commercial cellulosic fiber-reaction dyes used in fabric industries that make use of the mono-chlorotriazinyl group. figure 3 shows an orange dye that is covalently bonded with the cotton fiber. low-impact, fiber-reactive dyes have become the dye of choice for many organic clothing manufacturers who want a diverse palette of vibrant colors. depending upon the nature and degree of their chemical sensitivities, people with mild chemical sensitivities can often wear organic clothing with fiber-reactive dyes. un-dyed, natural color or colorgrown fabrics are the best choice for people who react to fiber-reactive dyes or who want only pure fabrics on their skin. as the awareness of the need to preserve our natural resources and environmental factors increases, interest is growing in finding renewable resources, which can be used as alternatives. natural dyes are seen as more eco-friendly as, unlike their synthetic iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 29 counterparts, they are all derived from nature. production of natural indigo from plant material (polygonum tinctorium ait) applying low-technology methods was done successfully by bechtold et al. [6]. a better quality indigo dyestuff was extracted from the indigo plant (indigofera tinctoria l.) [7]. earlier all colors were derived from natural sources, including plants. looking for better quality colors for industry, researcher went to the synthesis of dyes from byproducts of the petrochemical. recent research is looking for the possibility to use plants as commercially viable source of dyes [8]. this means that in order to satisfy the demand for high quality and choice, the plants in question must be studied more closely to allow breeding of useful lines and improved economic returns. in this study, an ftir spectroscopy was used to develop qualitative and quantitative analytical environmentally friendly technique for different types of dyestuffs or dyed substrates. nh n h n nn a 1 a 2 o o so 2 na cl cl fig. 1: anthroquinonoid reactive dye (procion blue). n h n nn cl nh sona n sona n sona oh fig. 2: procion brilliant red. iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 30 n n n nh nh o dye cotton celullose fig. 3: reactive orange dye covalently bonded with the cotton fiber. 2. materials and methods 2.1 samples and chemicals all chemicals were of analytical grade. different types of dyes samples were purchased from local market. fabric and hair dyes samples were used in this study. solid samples were used to make stock solution followed by preparing dilutions of known concentrations ranged from 0 to 80 mg/ml (w/v) to be used as standard solutions. the samples were tightly covered and shaken vigorously to homogeneity on an autovortex sa1 mixer (stuart scientific, redhill, uk). 2.2 chemical analysis hair dyes and some fabric dye samples were determined by photometry using alkaline solutions of fe (ii) triethanolamine as reducing agent following the methods suggested and used by bechtold et al. [9] and merritt et al. [10] respectively, after some modifications on handling samples. 2.3 instrumental analysis the infrared spectra were recorded at room temperature with a perkin-elmer fourier transform infrared spectrometer, model spectra 100 series (perkin-elmer corporation, norwalk, ct, usa), equipped with a deuterated triglycine sulfate (dtgs) detector and controlled by a perkin-elmer pc. the software used for the ftir data collection was the infrared data management (irdm) system. the instruments were maintained in constant humidity to minimize water vapor interference. drops from each standard were placed on atr element and scanned. after each scan, the atr diamond were rinsed three times with acetone and dried with soft tissue before adding the next sample. calibration spectra were obtained from 64 scans at a resolution of iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 31 2 cm -1 with strong apodization through 4000 400 cm -1 frequency region. the spectra were ratioed against the background air spectrum. all the scans were done in triplicate with the spectra recorded as absorbance and stored on a disk for subsequent chemometric analysis. 2.4 statistical analysis all the experiments and measurements were done in triplicate. the relationships between each of the ftir spectrum parameter and the original data from the standard solutions were determined using the software nicolet turbo quant ir-calibration and prediction package, version 1.1 (nicolet instrument co., madison, wi, usa). pls regression was used to derive the dye contents in the standard solutions. the actual and spectral data were correlated and the correlation coefficients (r) taken as estimates of the factor scores, which were then used as regressors to model both the spectral and actual data. selected factors were used in a multiple linear regression (mlr) to predict the spectral values. the optimum number of factors employed in the calibrated models was indicated by the predicted residual error sum of squares (press) values. an example of the press plot is shown in fig. 11, which also shows the f-test significance result for the method (<0.05) and number of factors included in the calibration at the lowest value. the f statistic for each press value was calculated with all the factors prior to the number with the smallest press value. the optimum number of factors was empirically chosen as that which gave the smallest press value such that the f ratio probability drops below 1.0 or below 0.75. microsoft excel spreadsheet software was used to organize the correlation of the ftir predicted and actual or chemical data. the good correlation obtained for the 30 calibration samples indicated the adequacy of the ftir calibration. accuracy was assessed based on the smallest standard error (se) and the highest coefficient of determination (r 2 ) [11]. 2.5 validation the ‘leave-one-out’ cross-validation technique was used to verify the calibration model. the press was computed from the error in prediction from the standards and plotted as a function of the number of factors employed in the calibration. the accuracy was assessed by the standard error of cross validation (secv) and r 2 . further verification was by the mean difference (md) and standard deviation of difference (sdd) for repeatability and closeness of fit (accuracy) between the chemical data and ftir predicted values. 3. results and discussion 3.1 chemical and ftir predicted results table 1 shows the ftir predicted values by the pls statistical method as means and standard deviations (sd) of the actual manually prepared data (standard solutions) for dye contents in the samples. the means and sds for fabric dye were 46.53, 4.05 and 44.17, iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 32 3.75 mg/kg for calibration and cross-validation, respectively. for hair dye, they were 45.20, 3.69 and 45.82, 3.85 mg/kg, respectively. table 1: calibration and cross-validation for dye content in fabric and hair dye samples by ftir methods in comparison with actual values of dye concentration. a fabric dye hair dye data set mean sd mean sd calibration 46.53 4.05 45.20 3.69 validation 44.17 3.75 45.82 3.85 a ftir, fourier transform infrared spectroscopy; sd, standard deviation; all dataset obtained from three replications. figures 4, 5 and 6 illustrate the spectra for dying stuff samples of hair dye, green dye, and henna, respectively. the spectra are in the frequency range 4000 – 400 cm -1 . each spectrum showed the characteristic absorption bands of dyeing stuff according to its chemical structure [12, 13]. figure 4 shows bands at 2020, 1480 and 1419 cm –1 which indicates the presence of alkyl groups. the band at 1510 cm –1 could be assigned for the aromatic compound possibly nitrile type compound alkyne ( c c, c n, and –n=n–) or isocyanate (–n=c=o). the band at 1033 cm –1 could be assigned for carboxylic acid ester (r–co–o–c–) or (r–co–n–). the bands at 856 and 691 cm –1 could be assigned for aromatic ring and –c=s=c–, respectively. the spectrum of green dye (fig. 5) shows bands at 3308 cm –1 and 2970 cm –1 which could be assigned for overlaps of the c–h stretching region and methyl c–h asymmetric stretch, respectively. the band at 1738 cm –1 indicated the presence of carbonyl group (–c=o), 1635 cm –1 may be assigned for quinine or conjugated ketone, 1365 cm –1 absorption band could be assigned for the presence of nitro compounds no2 stretch. the bands at 1229 and 1217 cm –1 may suggest the presence of aromatic ring. the weak band at 1092 cm –1 could be assigned for c–o stretch, most likely for secondary alcohol [14]. for the spectrum of dry henna in fig. 6, the band at 3281 cm –1 indicates the presence of oh stretch or h– bonded oh stretch. the bands at 2919 and 2851 cm –1 could be assigned for methylene c–h asym./sym. stretch. the band at 1630 cm –1 is for alkenyl c=c stretch and may be arylsubstituted c=c. the band at 1365 cm –1 -(which is weak band compared to that one at same wavenumber on fig. 5)could be assigned for the presence of trimethyl or “tert-butyl” (multiplet). a big band at 1027 cm –1 could be assigned for –oh group and/or –nh2 group or both in the same structure. iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 33 fig. 4: spectrum of black hair dye sample (powder). fig. 5: spectrum of green dye (liquid sample). iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 34 fig. 6: spectrum of dry henna (powder). 3.2 selecting the optimal frequency region for prediction the software spectrum quant plus was used to obtain the optimal frequency region for prediction, which is calculated by multiplying the difference between each standard spectrum and the mean spectrum at each wavelength by the difference between the corresponding property concentration and the mean property concentration, and summing over all the standards. peaks that do not correlate with the change in concentration are summed to zero, producing a spectrum that highlights the peaks that change with change in concentration, i.e. the peaks that relate to dye content. thus, the correlation spectrum was used to choose the 3500 – 2650 cm -1 and 1400 – 800 cm -1 regions use for calculating dye contents of the samples as described by fuller et al. [15]. high variances were seen in the same regions (3000 – 2700 cm -1 and 1600 – 1000 cm -1 ) for c-h, -oh, -nh2, –n=n and c=o [16]. hence, the correlation and variance spectra were used to select the best region for prediction using the pls statistical technique to develop calibration from the ftir spectra and chemical data. r 2 and sec from the pls calibration were used to choose the best region for determining dye content in dyestuff samples, 3500 – 2650 and 1675 – 1500 cm -1 region was found to be the best for determination of these types of dyestuffs. 3.3 statistical analysis figure 7 plots the data of actual values against the pls ftir-predicted values for dye content in the fabric dye samples. the best correlation obtained at the highest r 2 (0.9321) and lowest sec (1.84). figure 8 plots the cross-validation for the determination of dye content in fabric dye samples (r 2 = 0.9618 and secv = 1.45). figure 9 plots the actually prepared dye samples against the pls ftir spectroscopy predicted dye contents in hair iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 35 dye samples (r 2 = 0.9819 and sec = 1.36) and fig. 10 the cross-validation plot for dye content in hair dye samples (r 2 = 0.9711 and secv = 1.64). fig. 7: calibration of the actual precisely prepared values of fabric dye from 35 samples versus the pls ftir predicted values. r 2 = 0.9618 -5 5 15 25 35 45 55 65 75 85 0 20 40 60 80 actual value fabric dye content (mg/kg) f t ir -p re d ic te d v a lu e fa b ri c d y e c o n te n t (m g /k g ) fig. 8: validation plot of pls ftir predicted values versus actual values of fabric dye content in 35 samples. iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 36 y = 0.9466x 0.1677 r 2 = 0.9819 -5 5 15 25 35 45 55 65 75 0 20 40 60 80 chemical value hair dye content (mg/kg) f t ir -p re d ic te v a lu e h a ir d y e c o n te n t (m g /k g ) fig. 9: calibration plot of pls ftir predicted values versus chemically determined hair dye content in 35 samples. r 2 = 0.9711 -5 5 15 25 35 45 55 65 75 85 0 10 20 30 40 50 60 70 80 chemical value hair dye content (mg/kg) f t ir -p re d ic te d v a lu e h a ir d y e c o n te n t (m g /k g ) fig. 10: validation plot of pls ftir predicted values versus chemically determined hair dye content in the 35 samples. the optimum number of factors employed in the calibrated models was indicated by the predicted residual error sum of squares (press) values and were 6 and 8 for the fabric and hair dyes samples, respectively. press plot is shown in fig. 11, which also shows the f-test significance result for the method (<0.05) and number of factors included in the calibration of fabric dye samples was 6. the f statistic for each press value was calculated with all the factors prior to the number with the smallest press value. the iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 37 optimum number of factors was empirically chosen as that which gave the smallest press value such that the f ratio probability drops below 0.75. fig. 11: press plot obtained from cross-validation of pls calibration for determination of fabric dye sample. 4. conclusion ftir spectroscopy gives very accurate frequencies in the spectrum this enables processing techniques such as spectral subtraction as well as it has a much shorter sampling time compared to wet chemical methods and even shorter than conventional spectroscopic techniques. ftir spectroscopy is a useful environmental friendly method for rapid and routine detection of azo dyes as toxic dyes in such products for quality control because no chemicals are used in the detection. the full possibilities of ftir spectroscopy are still far from being exploited. references [1] p. j. w. stone, a. l. rhoden, l. s. miller, d. j. walton, a. m. mcroberts and j. heptinstall, polysiloxanes for langmuir-blodgett applications, thin solid films, vol. 244, no. (1-2) 1012-1017, 1994. [2] hélène rudyk, michael h. knaggs, snezana vasiljevic, james hope, chris birkett and ian h. gilbert. synthesis and evaluation of analogues of congo red as potential compounds against transmissible spongiform encephalopathies, european journal of medicinal chemistry, vol. 38, no. 6, 567-579, 2003. [3] katri vikman, studies on fastness properties of ink jet prints using vibrational spectroscopic methods, thesis for the degree of licentiate of science in technology submitted for inspection, espoo, november 18 th , 2002. iium engineering journal, vol. 9, no. 2, 2008 mirghani et al. 38 [4] l. antonin, and m. valdimir, 13 c and 15 n-nmr studies of the azo-hydrazone tautomerism of some azo dyes. dyes and pigments, vol. 7, no.3, 171-185, 1986. [5] s. w. oh, m. n. kang, c. w. cho and m. w. lee. detection of carcinogenic amines from dyestuffs or dyed substrates, dyes and pigments, vol. 33, no. 2, 119 – 135, 1997. [6] t. bechtold, a. turcanu, s. geissler, and e. ganglberger. process balance and product in the production of natural indigo from polygonum tinctorium ait, appling low-technology methods, bioresource technology, vol. 81, 171-177, 2002. [7] h. schmidt, indigo – 100 jahre industrielle synthese, chem. unserer zeit, vol. 31, 121-128, 1997. [8] g. stoker kerry, and t. cooke david. dyes from plants: past usage, present understanding and potential, plant growth regulation, vol. 34, 57-69, 2001. [9] t. bechtold, e. burtscher, and o. bobleter. konzentrationsbestimmung von indigo in ansatzund prozessnadern, text.-prax. int., vol. 47, 44 – 49, 1992. [10] j. t. merritt iii, k. r. bock, c. b. smith, p. j. hauser, and w. j. jasper, determination of indigo in dye baths by flow injection analysis and redox titrations, aatcc rev. ¼: 41 – 45, 2001. [11] j. dubois, f. r. van de voort, j. sedman, a. a. ismail and h. r. rawaswamy, quantitative fourier transform infrared analysis for anisidine value and aldehyde in thermally stressed oils, j. am. oil chem. soc., vol. 73, 787 – 794, 1996. [12] k. nakanishi, and p. h. solomon. infrared absorption spectroscopy, 2 nd edn. holden-day, boca raton, fl, pp. 100 – 235, 1977. [13] n. p. g. roeges, a guide to the complete interpretation of infrared spectra of organic structures, john wiley & sons ltd, baffins lane, chichester, england, p. 339, 1994. [14] j. coates, interpretation of infrared spectra, a practical approach, in encyclopedia of analytical chemistry, r. a. meyers (ed.). john wiley & sons ltd, chichester. pp. 10815 – 10837, 2000. [15] m. p. fuller, g. l. ritter, and c. s. draper, partial least-square quantitative analysis of infrared spectroscopic data, part i: algorithm implementation, applied spectroscopy, vol. 42, no 2, 217-227, 1988. [16] m. p. fuller, g. l. ritter, and c. s. draper, partial least-square quantitative analysis of infrared spectroscopic data, part ii application to detergent analysis, applied spectroscopy, vol. 42, no. 2, 228-235, 1988. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 105 a study on low-complexity transmit antenna selection for generalized spatial modulation adewale alafia*, simeon ajose and agbotiname imoize department of electrical and electronics engineering, faculty of engineering, university of lagos, akoka lagos, nigeria. * corresponding author: adealafia@yahoo.com (received: 19th feb 2018; accepted: 20th july 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.899 abstract: generalized spatial modulation (gsm) maps its information to the index of the transmit antenna combination, making simultaneous transmission of multiple symbol possible. however, sm outperform gsm scheme in terms of error performance of the same data rate, due to average power effect. transmit and receive diversity or the combination of both allow huge improvement in mimo systems in terms of error performance. in this paper, we investigate a near optimal low-complexity euclidean distance antenna selection (lc-edas) technique in gsm system, to further improve the performance of the conventional gsm system. the lc-edas technique independently search across signal and spatial dimension to eliminate the worse channel prior to transmission. secondly, we investigate a sub-optimal low-complexity transmit antenna selection (lctas) in the gsm system to further reduce the computational complexity (cc) imposed by lc-edas. the monte carlo simulation results obtained reveals a tradeoff between the gsm scheme with lc-edas and gsm scheme with sub-optimal transmit antenna selection in terms of error performance and cc. abstrak: modulasi spatial keseluruhan (gsm) menghubung informasi kepada indeks kombinasi antena yang dipancarkan, membuatkan pemancaran keseluruhan simbol dapat dilakukan. walau bagaimanapun, sm lebih bagus daripada skim gsm pada prestasi kesilapan pada kadar data yang sama, kerana kesan purata kuasa. kepelbagaian penghantaran dan penerimaan ataupun kombinasi keduanya memberi pembaharuan yang lebih besar dalam sistem mimo pada prestasi kesalahan. penyelidikan ini akan mengkaji optima terdekat euclidean kurang rumit, melalui teknik (lc-edas) pilihan jarak antenna dalam sistem gsm, bagi menambah prestasi sistem gsm sedia ada. teknik lc-edas secara sendiri mencari signal dan dimensi separa bagi mengurangkan saluran lebih teruk semasa penghantaran. kedua, kami mengkaji sub-optima proses pemilihan kurang rumit penyebaran antena (lctas) dalam sistem gsm bagi mengurangkan kerumitan pengiraan (cc) yang dikenakan oleh lc-edas. keputusan simulasi monte carlo yang diperoleh menunjukkan timbangan antara skim gsm dan lc-edas dan skim gsm bersama suboptima proses pemilihan penyebaran antena berdasarkan kesilapan prestasi dan cc. keywords: multi-input multiple-output; computational complexity; spatial modulation; euclidean distance antenna selection; transmit antenna selection 1. introduction in the past decade, the wireless communication sector has been categorized as the fastest growing sector in the communication industry. this is due to the need for iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 106 improvement in next generation wireless devices in terms of speed, reliability, and throughput [1]. this led to multiple-input multiple-output (mimo) systems [2]. mimo systems exhibits great potential with respect to high throughput and improved reliability in wireless communication [2]. the benefit of employing a mimo system lies on the fact that an improved error performance and high throughput coupled with improved diversity gain can be achieved. however, in mimo systems, the simultaneous transmission of data requires the need for inter-antenna synchronization (ias) and the channel will experience an inter-channel interference (ici) at the receiver [1,2]. hence, it is clear that the dominant consideration in wireless technology is to employ a system that is able to mitigate these impairments. lately, the use of multiple antennas has been investigated in numerous papers as the future of wireless communication [2]. this led to the development of an improved mimo system called spatial modulation (sm) [3], which employs its spatial dimension to convey additional information improving the major drawback of conventional mimo systems. however, the sm system also has a drawback of high complexity, due to the number of required transmit antennas to transmit high data streams [3]. this brought about the generalized spatial modulation system (gsm) [4]. the gsm system [4-6], is an sm-based scheme that maps its information bits to the index of the transmit antenna combination, thus reducing the required number of transmit antennas for high data streams. however, sm outperforms the gsm system in terms of error performance. the attractive features of sm and gsm include avoidance of ici and ias, which formed the major limitation of conventional mimo systems. gsm exhibits significant improvement when compared to a conventional sm in terms of cc [3,5]. the constraint of a large number of transmit antennas required in sm was improved on in gsm [4, 5]. the complexity of the gsm system is still not practically implementable. in literature [7,8], incorporating a transmit antenna selection (tas) into a mimo system can further enhance the performance of the system. this is evident in [9,12], where sm was introduced as an improved mimo scheme. however, practical realization was still a problem due to high cc imposed by the system. in [9], a maximum ratio combining (mrc), was introduced to an sm system, to initially estimate the index of the transmit antenna, which was later employed to detect the transmitted symbol. the result obtained exhibited an improved error performance and the imposed cc was greatly reduced. similarly, in [10], tas was employed in sm to improve the performance of the system, employing a channel amplitude technique to eliminate the worst channel at every transmission instant. transmit and receive diversity or a combination of both in spatial multiplexing allow huge improvement in terms of error performance [7]. employing tas in selecting subset of antennas combination has proven to be extremely beneficial for link initialisation and maintenance [10,11]. likewise, employing tas has shown to increase the achieved diversity gain [12]. the selection criterion proposed in [13] was based on the shannon capacity, and as such, yielded optimal capacity gain. in addition, in [14], a selection criterion that minimised the probability of symbol error rate (ser) for spatial multiplexing systems is investigated. in [12], the availability of additional antennas is revealed as an inexpensive way of exploiting diversity advantage. this was corroborated in [15], whilst further proving that the diversity of space shift keying (ssk) can be improved by increasing the number of surplus transmit antennas. furthermore, tas, which maximised the minimum euclidean distance (ed) of a received constellation to yield an optimal performance, considers ed as file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_1 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_2 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_2 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_1 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_2 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_2 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_3 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_3 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_4 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_4 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_3 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_5 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_4 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_5 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_7 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_8 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_9 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_10 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_7 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_10 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_11 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_12 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_13 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_14 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_12 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_15 iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 107 a function of both the received constellation and the channel. as a result, the ed criterion selects an optimal antenna subset in terms of the minimum error rate [16]. this is evident in [17], where an optimal performance was achieved in the sm system by employing a decision metric that maximized the minimum ed among the transmit vectors. this scheme also increased the diversity order of sm system but at a cost of high complexity. in this study, a low-complexity euclidean distance antenna selection (lc-edas) is introduced to the gsm system to further improve the performance of the system by splitting the exhaustive search of edas into signal, spatial, and joint evaluation. this allowed an independent search across signal, spatial, and joint (signal and channel) to reduce the cc imposed on the system similar to [18]. secondly, we investigate a sub-optimal transmit antenna selection in the gsm system. employing channel amplitude and antenna correlation to further reduce the high cc imposed by lc-edas. the monte carlo simulation result obtained reveals a trade-off in terms of performance and cc between the gsm scheme with lc-edas and gsm scheme with sub-optimal transmit antenna selection. the structure of the remainder of the paper is as follows: in section 2, the system model for the proposed scheme is presented. in section 3, the numerical analysis of the system is presented. in section 4, the cc of the system is presented. in section 5, a summary of findings of the proposed scheme is presented while conclusions are drawn in section 6. 2. system model of the proposed scheme in the gsm system, information bits are mapped into the transmit antenna combination, making the transmission of two symbols possible at the same time. thus, reducing the required number of transmit antennas to transmit a high data rate. 2.1 transmission model of gsm system gsm mapper spatial bits spatial bits g s m t ra n s m itte r r e c e iv e r h 1 2 1 2 input bits output bits. . . . . . tn gsm detector rn fig. 1: system model for a conventional gsm system [4]. figure 1 reveals a conventional gsm system, which is equipped with 𝑁𝑇 transmit antennas and 𝑁𝑅 receive antennas, respectively. the spectral efficiency of the gsm system is 𝑚 = log2(𝑀) + ⌊log2 ( 𝑁𝑇 2 )⌋ b/s/hz. for example, consider a gsm system with a configuration setting of 4 × 4, 4-qam. the spectral efficiency yielded will be 4 b/s/hz, in which the first two bits are used to select the active antenna combination and the last two bits are used to select the constellation symbol 𝑥𝑞 to be transmitted via a rayleigh fading channel 𝑯 of dimension 𝑁𝑅 × 𝑁𝑇, where 𝑁𝑅 and 𝑁𝑇 is the number of transmit and receive antennas, respectively. in the presence of an additive white gaussian noise (awgn) 𝒏. in file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_16 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_17 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_18 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_4 iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 108 this paper, we considered same symbol to be transmitted at both transmit antenna combination at the same time. the received signal vector 𝒚 becomes: 𝒚 = √ 𝜌 𝜇⁄ 𝑯𝑥𝑞 + 𝒏 (1) 𝜌 𝜇⁄ is the average signal-to-noise ratio (snr) and 𝑥𝑞 = [𝑥1 𝑥2]. the transmitted signal can be detected optimally, employing maximum likelihood (ml) such that all possibilities are estimated across all the signal space similar to sm. this can be expressed as [4]: [𝑗, 𝑥𝑞] = argmin ℓ1,ℓ2,𝑥1 𝑞 ,𝑥2 𝑞 (‖𝒚 − √ 𝜌 𝜇⁄ (𝑯𝑥𝑞)‖ 𝐹 2 ) (2) 2.2 transmit antenna selection for gsm system figure 2 reveals a conventional gsm system, equipped with 𝑁𝑇 transmit antennas and 𝑁𝑅 receive antennas, respectively, together with an antenna selection module and a feedback link. fig. 2: system model for the proposed lc-gsm system. in literature [15,17], it has been stated that tas can improve the error performance of a spatial multiplexing system. in [19], edas was employed to select the transmit antenna combination in gsm system. the error performance achieved in the scheme is superior but the cc imposed on the system is high. however, in [18], lc-edas was investigated in sm, imposing a much lower cc and exhibiting a performance near to that of the edas sm scheme of [16]. the gsm system exhibits less error performance compared to sm due to the average power effect, but required less transmit antenna to achieve a high data rate. this motivates us to investigate lc-edas in the gsm system to further improve the performance of the system. secondly, a low-complexity tas (lctas), employing the combination of channel amplitude and antenna correlation to eliminate the worse channel at every transmission gsm transmitter gsm receiver h antenna selection channel state information perfect feedback link 1 1 2 2 . . . . . . tn rn file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_4 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_15 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_17 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_19 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_18 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_16 iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 109 instant in order to maximize transmit diversity of the gsm system to attain a performance similar to sm system is investigated in the gsm system. the cc imposed by this scheme is lower than lc-edas approach but the performance achieved is also lower than that of the lc-edas system. the monte carlo simulation results reveal the trade-off between cc and error performance with lc-edas and lctas. 2.2.1 lc-edas for gsm system in [18], the instantaneous ser for each candidate subsets was computed into signal, spatial, and joint minimum squared euclidean distance denoted as 𝐸𝐷𝑠𝑖𝑔𝑛𝑎𝑙 2(ℓ) (𝑯), 𝐸𝐷𝑠𝑝𝑎𝑡𝑖𝑎𝑙 2(ℓ) (𝑯) and 𝐸𝐷𝐽𝑜𝑖𝑛𝑡 2(ℓ) (𝑯), respectively. the receiver employs the channel estimates to select a subset ℓ ∈ 1: 𝑁𝑠, 𝑁𝑠 = ( 𝑁𝑇𝑜𝑡𝑎𝑙 2 ) and 𝑁𝑇𝑜𝑡𝑎𝑙 > 𝑁𝑇. we employ a similar approach to [18], to compute the three minimum squared euclidean distance for signal, spatial and joint, respectively for the gsm system, maximizing the minimum euclidean distance employing singular value decomposition for the joint evaluation. the close form of expression of the formulated 𝐸𝐷𝐺𝑆𝑀−𝑠𝑖𝑔𝑛𝑎𝑙 2(ℓ) (𝑯), 𝐸𝐷𝐺𝑆𝑀−𝑠𝑝𝑎𝑡𝑖𝑎𝑙 2(ℓ) (𝑯) and 𝐸𝐷𝐺𝑆𝑀−𝐽𝑜𝑖𝑛𝑡 2(ℓ) (𝑯) proceeds as: 𝐸𝐷𝐺𝑆𝑀−𝑠𝑖𝑔𝑛𝑎𝑙 2(ℓ) (𝑯) = 𝜌 2 min 𝑘∈1:𝑁𝑇𝑜𝑡𝑎𝑙 ‖𝒉𝑘1 ℓ + 𝒉𝑘2 ℓ − �̂�𝑘1 ℓ − �̂�𝑘2 ℓ ‖ 𝐹 2 min 𝑥1 𝑞 ,𝑥2 𝑞 ≠�̂�1 𝑞 ,�̂�2 𝑞 𝑥1 𝑞 ,𝑥2 𝑞 ∈𝝌 |𝑥1 𝑞 + 𝑥2 𝑞 − �̂�1 𝑞 − �̂�2 𝑞 | 2 (3) 𝐸𝐷𝐺𝑆𝑀−𝑠𝑝𝑎𝑡𝑖𝑎𝑙 2(ℓ) (𝑯) = 𝜌 2 min 𝑘∈1:𝑁𝑇𝑜𝑡𝑎𝑙 ‖𝒉𝑘1 ℓ + 𝒉𝑘2 ℓ − �̂�𝑘1 ℓ − �̂�𝑘2 ℓ ‖ 𝐹 2 min 𝑥𝑞∈𝝌 |𝑥1 + 𝑥2| 2 (4) 𝐸𝐷𝐺𝑆𝑀−𝐽𝑜𝑖𝑛𝑡 2(ℓ) (𝑯) = 𝜌 2 min 𝑘∈1:𝑁𝑇𝑜𝑡𝑎𝑙 𝑥1 𝑞 ,𝑥2 𝑞 ≠�̂�1 𝑞 ,�̂�2 𝑞 𝑥1 𝑞 ,𝑥2 𝑞 ∈𝝌 ‖𝒉𝑘1 ℓ 𝑥1 𝑞 + 𝒉𝑘2 ℓ 𝑥2 𝑞 − �̂�𝑘1 ℓ �̂�1 𝑞 − �̂�𝑘2 ℓ �̂�2 𝑞 ‖ 𝐹 2 ≥ 𝜌 2 min 𝑘∈1:𝑁𝑇𝑜𝑡𝑎𝑙 𝜎 𝑘,�̂� 2 min 𝑥1 𝑞 ,𝑥2 𝑞 ≠�̂�1 𝑞 ,�̂�2 𝑞 𝑥1 𝑞 ,𝑥2 𝑞 ∈𝝌 ‖ ‖ [ 𝑥1 𝑞 𝑥2 𝑞 �̂�1 𝑞 �̂�2 𝑞 ] ‖ ‖ 𝐹 2 (5) where min 𝑘∈1:𝑁𝑇𝑜𝑡𝑎𝑙 𝜎 𝑘,�̂� 2 is the minimum squared singular value decomposition of the channel matrix [𝒉𝑘1 ℓ + 𝒉𝑘2 ℓ − �̂�𝑘1 ℓ + �̂�𝑘2 ℓ ] and ℓ ∈ [1: 𝑁𝑇]. the channel matrix 𝑯 has entries, which is modelled as an independent and identically distributed (iid) complex gaussian random variables with 𝐶𝑁(0,1). the next sub-section presents the algorithm for a lc-edas for gsm system. algorithm 1 step 1: construct an 𝑁𝑅 × 𝑁𝑇𝑜𝑡𝑎𝑙 dimension channel matrix, where 𝑁𝑇𝑜𝑡𝑎𝑙 > 𝑁𝑇. file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_18 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_18 iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 110 step 2: compute the minimum squared euclidean distance for 𝐸𝐷𝐺𝑆𝑀−𝑠𝑖𝑔𝑛𝑎𝑙 2(ℓ) (𝑯), 𝐸𝐷𝐺𝑆𝑀−𝑠𝑝𝑎𝑡𝑖𝑎𝑙 2(ℓ) (𝑯) and 𝐸𝐷𝐺𝑆𝑀−𝐽𝑜𝑖𝑛𝑡 2(ℓ) (𝑯), respectively. employing eq. (3-5), considering all possible combination of 𝑁𝑠 = ( 𝑁𝑇𝑜𝑡𝑎𝑙 2 ). step 3: choose the minimum instantaneous minimum square euclidean distance for each condition, i.e. 𝐸𝐷𝐺𝑆𝑀 2(ℓ) (𝑯) = min{𝐸𝐷𝐺𝑆𝑀−𝑠𝑖𝑔𝑛𝑎𝑙 2(ℓ) (𝑯), 𝐸𝐷𝐺𝑆𝑀−𝑠𝑝𝑎𝑡𝑖𝑎𝑙 2(ℓ) (𝑯), 𝐸𝐷𝐺𝑆𝑀−𝐽𝑜𝑖𝑛𝑡 2(ℓ) (𝑯)} (6) step 4: select the antenna subset that has the largest instantaneous minimum squared euclidean distance among the candidates in step 3, using: ℓ𝑠𝑒𝑙𝑒𝑐𝑡𝑒𝑑 = max ℓ=1∈𝑁𝑠 {𝐸𝐷𝐺𝑆𝑀 2(ℓ) (𝑯)} (7) where 𝑁𝑠 is the possible antenna pairs in the corresponding vectors in the channel matrix 𝑯. thus, the selected transmit antenna will be employed for transmission at the next transmission instant. 2.2.2 tas based on channel amplitude and antenna correlation for the gsm system employing the concept of channel amplitude with a decision of “the larger the amplitude of the channel, the better it is” as investigated in [8], and an antenna correlation, a concept was investigated in [20], transmit antennas were discarded based on high correlation. employing both channel amplitude and antenna correlation, which are suboptimal techniques will impose a very low cc [15]. this motivates the application of this technique to the gsm system. algorithm 2 presents the step/procedure for the implementation of the channel amplitude and antenna correlation technique. algorithm 2 step 1: construct an 𝑁𝑅 × 𝑁𝑇𝑜𝑡𝑎𝑙 dimension channel matrix, where 𝑁𝑇𝑜𝑡𝑎𝑙 is the total number of transmit antennas available, which is greater than 𝑁𝑇. 𝑯 = [𝒉1 𝒉2 𝒉3 … 𝒉𝑁𝑇𝑜𝑡𝑎𝑙] (8) step 2: compute the channel amplitude using ‖𝑯‖𝐹 for the above channel constructed in step 1 and sort in descending order. step 3: choose 𝑁𝑇 + 1 such that the dimension matrix becomes 𝑁𝑅 × (𝑁𝑇 + 1), i.e. 𝑯 = [𝒉1 𝒉2 … 𝒉𝑁𝑇+1] (9) step 4: calculate the angle of correlation of the channel combination similar to [21] and [22] using: 𝜃 = arccos ( |𝒉𝑎 𝐻 𝒉𝑏| ‖𝒉𝑎‖𝐹‖𝒉𝑏‖𝐹 ) (10) step 5: arrange the angle of correlation in vectors and eliminate the smallest angle (highest correlation) from the channel 𝑁𝑇 + 1 computed in step 4. file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_8 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_20 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_15 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_21 file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_22 iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 111 the number of transmit antennas left will be employed for the next transmission instant in the gsm system, maximizing transmit diversity in the gsm system. 2.2.3 tas for edas gsm tas based on edas, selects the subset of transmit antennas, which maximises the minimum ed between all transmit antenna vectors, achieving an optimal performance. edas for gsm (edas-qsm) is based on the nearest neighbour approximation, the pep of gsm for a given channel 𝑯 is: 𝑃𝑒 ≅ 𝜆 ∙ 𝑄 (√ 1 2 min 𝑥1≠𝑥2∈𝝌 ‖𝑯′(𝑥1 − 𝑥2)‖𝐹 2 ) = 𝜆 ⋅ 𝑄 (√ 1 2 𝑑𝑚𝑖𝑛 2 (𝑯′)) (11) where 𝜆 is the number of neighbor points and 𝑑𝑚𝑖𝑛 2 (𝑯′) = min 𝑥𝑞1≠𝑥𝑞2∈𝝌 ‖𝑯′(𝑥1 − 𝑥2)‖𝐹 2 is the squared minimum euclidean distance between the pair of neighbor symbols. in maximizing the minimum euclidean distance, the selected antennas can be chosen using: 𝑑𝑚𝑖𝑛 2 (𝑯′) = min 𝑥1≠𝑥2∈𝝌 ℓ∈[1:𝑁𝑠] 𝑥1≠𝑥2 𝑞∈1:𝑀 ‖𝒉ℓ1𝑥1 + 𝒉ℓ2𝑥2 − 𝒉ℓ̂1𝑥1̂ − 𝒉ℓ̂2𝑥2̂‖𝐹 2 (12) 3. numerical analysis the monte carlo simulation results obtained from this research work are presented in this section. the notation 𝑁𝑅 × 𝑁𝑇 is used to denote the number of receive antennas and transmit antennas, respectively. this algorithm was adopted from the literature [9,11,20]. the proposed system was compared to the conventional gsm system to validate the relationship between open loop and close loop systems. in fig. 3, the system is equipped with four transmit antennas 𝑁𝑇 and four receive antennas 𝑁𝑅, employing 4-qam modulation orders, i.e. 4 × 4 4-qam. it was observed that the lc-edas-gsm system achieves an snr gain of approximately 4.5 db over the conventional gsm system in terms of error performance at a ber of 10−5. this is due to the exhaustive search employed by the lc-edas-gsm. in addition, in fig. 3, the lctas-gsm system exhibits an error performance gain of approximately 1 db over a conventional gsm system. likewise, the lc-edas-gsm system reveals a gain of approximately 3.5 db when compared to the lctas-gsm system. but at a cost of higher cc due to the exhaustive search approach that was adopted by the lc-edas-gsm technique. the total number of transmit antenna 𝑁𝑇𝑜𝑡𝑎𝑙 available is 6, in which 4 were chosen for transmission i.e. 𝑁𝑇 = 4. iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 112 fig. 3: ber performance comparison of gsm, lctas-gsm and lc-edas-gsm of 4 b/s/hz. figure 4, depicts a similar configuration to fig. 3, a gain of approximately 6 db was achieved with respect to the lc-edas-gsm system when compared to the conventional gsm system. this is due to the higher modulation order that was employed coupled with the high number of available transmit antennas, as gsm systems are said to exhibit a better performance with a high number of transmit antennas at high snr region. likewise, considering the lctas-gsm system, which achieves an snr gain of 2 db over the conventional system, with a lower cc when compared to lc-edas-gsm system. the various variations achieved under different configurations are tabulated in table 1. table 1: snr gain achieved with respect to lc-edas-gsm system scheme 4 b/s/hz 6 b/s/hz 7 b/s/hz gsm 4.5 db 6 db 5 db lctas-gsm 3.5 db 3 db 4 db edas-gsm 1 db 1.2 db 1 db 0 2 4 6 8 10 12 14 16 18 20 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 es/no, (db) b e r 4 b/s/hz gsm (4x4 4qam) lctas-gsm (4x4 4qam ntotal=6) edas-gsm (4x4 4qam ntotal=6) lc-edas-gsm (4x4 4qam ntotal=6) iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 113 fig. 4: ber performance comparison of gsm, lctas-gsm, lc-edas-gsm of 6 b/s/hz. in fig. 5, a gain of approximately 5 db was achieved with respect to the lc-edasgsm system when compared to the conventional gsm system. likewise, considering the lctas-gsm system, which achieves an snr gain of 1 db over the conventional system, with a lower cc when compared to the lc-edas-gsm system. the total number of transmit antennas 𝑁𝑇𝑜𝑡𝑎𝑙 available is 8, in which 5 was employed for transmission i.e. 𝑁𝑇 = 5. the snr gain achieved is tabulated in table 1 with respect to the lc-edas-gsm system. 5. computational complexity a trade-off exists between the lc-edas-gsm and lctas-gsm in terms of cc and error performance. the cc for each tas algorithm employed is formulated based on the floating points of operation (flops) approach similar to [10]. the cc imposed by the lcedas is: i. signal: evaluating the forbenius norm in (3) requires (2𝑁𝑅 − 1) flops, across ( 𝑁𝑇𝑜𝑡𝑎𝑙 2 ) in 𝑁𝑠 times. 0 5 10 15 20 25 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 es/no, (db) b e r 6 b/s/hz gsm (4x4 16qam) lctas-gsm (4x4 16qam ntotal=6) edas-gsm (4x4 16qam ntotal=6) lc-edas-gsm (4x4 16qam ntotal=6) file:///c:/users/prof.dr.hamzah/desktop/iium-ej%20nov%202018/899-article%20text-4844-1-6-20181011-le.docx%23_enref_10 iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 114 fig. 5: ber performance comparison of gsm, lctas-gsm, lc-edas-gsm of 7 b/s/hz. ii. spatial: the cc imposed by the spatial evaluation in eq. (4) requires (2𝑁𝑅 − 1) flops to compute the square forbenius norm, across ( 𝑁𝑇𝑜𝑡𝑎𝑙 2 ) in 𝑁𝑠 times. iii. joint: the joint evaluation requires (2𝑁𝑅 − 1) flops in eq. (5) and there are 4 multiplications, 1 addition, and 2 subtractions that took place within the forbenius norm, across ( 𝑁𝑇𝑜𝑡𝑎𝑙 2 ) in 𝑁𝑠 times. the number of flops required is (9𝑁𝑅 − 1) ( 𝑁𝑇𝑜𝑡𝑎𝑙 2 ) 𝑁𝑠. the overall cc imposed on the system by lc-edas-gsm is: 𝛿𝐿𝐶−𝐸𝐷𝐴𝑆−𝐺𝑆𝑀 = (13𝑁𝑅 − 4) ( 𝑁𝑇𝑜𝑡𝑎𝑙 2 ) 𝑁𝑠 (13) similarly, algorithm 2 of the lctas-gsm approach requires (2𝑁𝑅 − 1) flops across 𝑁𝑇𝑜𝑡𝑎𝑙 in step 2. likewise, step 4 requires 2𝑁𝑅 + 2 flops for ( 𝑁𝑇 + 1 2 ) combinations. therefore, the overall cc imposed by the lctas-gsm is: 0 5 10 15 20 25 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 es/no, (db) b e r 7 b/s/hz gsm (5x4 16qam) lctas-gsm (5x4 16qam ntotal=6) edas-gsm (5x4 16qam ntotal=8) lc-edas-gsm (5x4 16qam ntotal=8) iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 115 𝛿𝐿𝐶𝑇𝐴𝑆−𝐺𝑆𝑀 = 𝑁𝑇𝑜𝑡𝑎𝑙(2𝑁𝑅 − 1) + (2𝑁𝑅 + 2 ) ( 𝑁𝑇 + 1 2 ) (14) the exhaustive search requires ed to be evaluated for all symbol combinations and 4𝑀(4𝑀 − 1) flops is required for the edas-gsm technique across ( 𝑁𝑇𝑜𝑡𝑎𝑙 2 ) 𝑁𝑠, imposing an overall cc of 4𝑀(4𝑀 − 1)𝑁𝑇(2𝑁𝑅 − 1) + 64 ( 𝑁𝑇𝑜𝑡𝑎𝑙 2 ) 𝑁𝑠 flops similar to [10]. the numerical comparison in terms of complexity between both systems is computed in table 2. table 2: numerical comparison of computational complexity of lc-edas-gsm and lctas-gsm configuration lc-edas-gsm lctas-gsm edas-gsm 𝑴 = 𝟒 𝑁𝑇𝑜𝑡𝑎𝑙 = 6 𝑁𝑇 = 4 𝑁𝑅 = 4 10,800 142 21,120 𝑴 = 𝟏𝟔 𝑁𝑇𝑜𝑡𝑎𝑙 = 6 𝑁𝑇 = 4 𝑵𝑹 = 𝟒 10,800 142 127,296 𝑴 = 𝟒 𝑁𝑇𝑜𝑡𝑎𝑙 = 6 (lctas) 𝑁𝑇𝑜𝑡𝑎𝑙 = 8 (lcedas) 𝑁𝑇 = 5 𝑵𝑹 = 𝟒 75,264 192 108,752 5. summary of findings in this research, it is once more validated that tas can further improve the error performance of a spatial multiplexing system. the results in this paper conform to the theory stated in the literature that tas, a closed loop system, can maximize transmit diversity. in table 1, lc-edas-gsm achieves up to approximately 5 db and 4 db snr gain at a bit error rate (ber) of 10−𝟓 of 4 b/s/hz configuration setting when compared to lctas-gsm and the conventional gsm system, respectively. in addition, edas-gsm outperforms other tas techniques employed, due to the exhaustive search. however, the system gain is thus reduced as the spectral efficiency increases, due to the high modulation order employed, as seen in fig. 3 and fig. 4, respectively. likewise, table 2 presents the numerical comparison of both tas techniques, in which lctas-gsm imposed a lower cc with the same configuration settings in lc-edas and edas-gsm imposed a high cc when compared to other techniques employed. this is because the edas cc is a function of the modulation order 𝑴, 𝑵𝑻𝒐𝒕𝒂𝒍, and 𝑵𝑹 while lctas and lc-edas are functions of just 𝑵𝑻 and 𝑵𝑹 6. conclusion this research demonstrated the applicability of transmit antenna selection in improving the reliability/error performance of a mimo based scheme. it was evident from the monte iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 116 carlo simulation results that were obtained that the gsm system equipped with tas can achieve a significant enhancement over the conventional gsm system. to attain a similar result with less cc than the conventional edas algorithm, which employs an exhaustive search across all channel combinations to achieve an optimal performance, an lc-edas tas algorithm, which splits the process into spatial, signal, and joint evaluation was employed. references [1] simon m. k. (2010) digital communication over fading channels. hoboken, wileyinterscience publication. [2] goldsmith a. (2005) wireless communications. cambridge, cambridge university press. [3] mesleh r. y, haas h, sinanovic s, chang wook a, and sangboh y. (2008) spatial modulation. ieee transactions on vehicular technology, vol. (57): pp. 2228-2241. [4] younis a, serafimovski n, mesleh r, and haas h. (2010) generalised spatial modulation. in proceedings of conference record of the forty fourth asilomar conference on signals, systems and computers, november 7-10, 2010; pacific grove, california. edited by michael b. matthews, atk mission research; pp. 1498-1502. [5] mesleh r, ikki s. s, and aggoune h.m. (2014) quadrature spatial modulation. ieee transactions on vehicular technology, vol (64): pp. 2738-2742. [6] mesleh r, and ikki s. s (2014) a high spectral efficiency spatial modulation technique. in proceedings of ieee 80th vehicular technology conference, 14–17 september 2014; vancouver. [7] jintao w, shuyun j and jian s. (2012) generalised spatial modulation system with multiple active transmit antennas and low complexity detection scheme. ieee transactions on wireless communications, vol (11):pp. 1605-1615. [8] rajashekar r, hari k. v. s and hanzo l. (2013) antenna selection in spatial modulation systems. ieee communications letters, vol. (17):pp. 521-524. [9] xu h, naidoo n.r, and quazi t. (2010) spatial modulation: optimal detector asymptotic performance and multiple-stage detection. iet proceedings communications, vol. (10):pp. 1368 – 1376. [10] xu h, pillay n. (2014) low complexity detection and transmit antenna selection for spatial modulation. saiee africa research journal, vol(105):pp. 4-12. [11] yang p, guan y. l, xiao y, di renzo m, li s, and hanzo. l (2015) transmit pre-coded spatial modulation: maximizing the minimum euclidean distance versus minimizing the bit error ratio. ieee transactions on wireless communications, vol. (32):pp. 1-15. [12] yang p, guan y. l, xiao y, li s, and hanzo. l (2016) transmit antenna selection for multiple-input multiple-output spatial modulation systems. ieee transactions on communications, vol. (64): pp. 2035-2048. [13] di renzo m, and haas h. (2010) improving the performance of space shift keying (ssk) modulation via opportunistic power allocation. ieee communications letters, vol.(14): pp. 500-502. [14] yang p, xiao y, di renzo m, li s, and hanzo. l (2015) design guidelines for spatial modulation. ieee communication surveys and tutorials, vol.(17):pp. 6-26. [15] xu h, pillay n. (2015) low-complexity transmit antenna selection schemes for spatial modulation. iet communications, vol.(9):pp. 239-248. [16] nan w, wenlong l, hongzhi m, minglu j, and hongjun x. (2014) further complexity reduction using rotational symmetry for edas in spatial modulation. ieee communications letters, vol. (18): pp. 1835-1838. [17] ping y, yue x, lei l, qian t, yi y, and shaoqian l. (2012) link adaptation for spatial modulation with limited feedback. ieee transactions on vehicular technology, vol.(61): pp. 3808-3813. iium engineering journal, vol. 19, no. 2, 2018 alafia et al. 117 [18] ntontin k, di renzo m, perez-neira a. i, and verikoukis c. (2013) a low-complexity method for antenna selection in spatial modulation systems. ieee communications letters, vol. (17): pp. 2312-2315. [19] xu h, pillay n. (2016) improved generalized spatial modulation via antenna selection. international journal of communication systems, vol. (30). [20] zhou z, ge n, and lin x. (2014) reduced-complexity antenna selection schemes in spatial modulation. ieee communications letters, vol. (18): pp. 14-17. [21] jianping z. (2012) signal vector based list detection for spatial modulation. ieee wireless communications letters, vol. (1): pp. 265-267. [22] xu h, pillay n. (2013) comments on signal vector based detection scheme for spatial modulation. ieee communications letters, vol. (17): pp. 2-3. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 model analyzing for reusing gold wire capillary in the gold wire bonding process chatpon phimpha*and sombat sindhuchao department of industrial engineering, faculty of engineering, ubon ratchathani university, ubon ratchathani 34190, thailand * corresponding author: perpetually09@gmail.com. (received: 3rd december 2020; accepted: 4th february 2021; published on-line: 4th july 2021) abstract: manufacturing process improvement is necessary for manufacturers to gain business advantages. re-using or increasing the useful lives of machine parts is considered to be a process of performance improvement. to re-use parts, the manufacturers must know the effects of the factors related to workpieces' qualities to prevent defects. this research study aims at presenting the results of analysing the effects of the factors and mathematical models for bond shear strength when reusing gold wire bonding capillary in the gold wire bonding process of integrated circuit (ic) products using design experiment. the operation factors in the reference experiment, including bond force, bond time, usg current, efo current and efo gap, are investigated. the fractional factorial design was used to determine five factors that affect the bond shear strength. the analysis of the results show that the bond force is a significant factor where increasing bond force factors leads to increasing bond shear strength. in the end, a regression model of bond shear strength is obtained to show the result between the bond shear strength and effect of factors. abstrak: proses pembaharuan pengilangan adalah penting untuk para pengilang bagi memperoleh keuntungan bisnes. guna-semula atau menambah jangka hayat pada bahagian-bahagian tertentu pada mesin adalah dianggar sebahagian proses penambahbaikan prestasi mesin. bagi mengguna semula bahagian-bahagian ini, pengilang mesti mengetahui akibat sesuatu faktor berkaitan kualiti bahan bagi mengelak kecacatan. kajian ini bertujuan menyampaikan dapatan kajian melalui kesan faktor dan model matematik pada kekuatan ricihan ikatan apabila mengguna semula wayar emas melalui proses kapilari ikatan wayar emas pada produk litar bersepadu melalui rekaan eksperimen. faktor operasi melalui rujukan eksperimen dari daya ikatan, masa ikatan, arus usg, arus efo dan jarak efo dikaji. rekaan faktorial pecahan digunakan bagi mendapatkan lima faktor yang mempengaruhi kekuatan ricihan ikatan. dapatan kajian menunjukkan daya ikatan merupakan faktor penting di mana, pertambahan faktor daya ikatan menguatkan ricihan ikatan. akhirnya, model regression kekuatan ricihan ikatan diperoleh bagi menjelaskan dapatan kajian antara kekuatan ricihan ikatan dan kesan faktor. keywords: reusing capillary; gold wire bonding; bond shear; design of experiment 1. introduction improving the production process to increase efficiency in the working process is an essential part of business. factories are required to understand and develop their production processes to produce products or services that can meet customer needs and enhance business competitiveness with other factories producing the same product [1,2]. 306 iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 machine parts that are expired from the manufacturing process are used. the parts are studied, and the effects of the factors are identified in order to re-use the parts or to increase the parts’ useful lives. this is considered a strategy for reducing manufacturing costs and improving processes for business competitiveness. to re-use expired parts, the parts must be carefully considered, and the effects of the process factors must be identified in order to prevent defects [3]. most studies focus on the factors of the best practices for new parts. however, this study aims at studying the effects of the process factors for expired parts. in order to make the manufacturers understand the effects of each factor of the qualities of the work pieces to efficiently use the parts without affecting the work pieces. the gold wire bonding process is a process of integrated circuit (ic) products, which are the main parts in electronic devices such as mobile phones, televisions, etc., the ic packaging product consists of two main processes, namely, front of line (fol) production, which consists of five sub processes, and end of line (eol) [4], which consists of four sub processes. the most important process of ic packaging production is the gold wire bonding process in the fol because it connects the main circuit of ic packaging using small gold wire [5,6]. in this process, high-precision machining and a large number of adjustment factors are required to process [7,8]. a machine part that is called a gold wire bonding capillary is an important part of the gold wire bonding process because this part presses on work pieces being wired. the gold wire bonding capillary is a small tube for bonding gold wires through the mentioned tube. by checking the manufacturing process, it was found that the gold wire bonding capillary can manufacture 150,000 work pieces. then, the gold wire bonding capillary must be changed. accordingly, this study emphasizes studying the effects of the quality factors of work pieces if the parts are expired in order to provide data for manufacturers who want to improve the efficiency of their processes by re-using parts and to help them know the data and relationships of the factors for manufacturing work pieces according to requirements [3]. statistical methods are used to find the effect of factors to adjust the parameters of the gold wire bonding process to maximize bond shear strength. an experimental approach that defines parameters in a process is the design of experiment method [9]. each of the researched studies demonstrated the application of experimental methods, showing various factors that affected the gold wire bonding process, including showing results of different research. the research work showed that an increase in bonding temperature affected the shear strength of gold bonding. the one-factor experiments were not suitable for the study of most factors in the same experiment [10]. the study also found research related to the use of analysis of variance (anova) to analyse factors that affect the strength of wire bonding. anova is an experiment that can be studied using multiple factors. however, the large number of factors are limitations to the number of the experiments [11]. according to relevant research reviews, the suitable method for determining the optimum conditions of the gold wire bonding process was factorial design (fd) [12]. a full factorial consists of all possible combinations of levels for all factors. the total number of experiments for studying are included in [13]. consider the factors in which five factors were researched with two levels of factors by factorial, the design of a full factorial experiment should involve a total of 32 experiments. the fractional factorial design (ffd) is one type of factorial experiment. it is an experiment that uses half the number of experiments from the design of a full number of factorial experiments. the objective of this research was to use fractional factorial experiment to determine the effect of 307 iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 parameters and show the regression model that is used for bond shear strength in the gold wire bonding process of ic packaging process. 2. materials and methodology the process of bonding gold wire is summarized as follows: gold wire bonding starts with an electric current through a device called an efo wand, which is responsible for distributing electricity to heat the gold wire in the capillary to form a spherical shape. the molten gold wire is then pressed onto the circuit pad, where the first connection is a spherical shape called the first bond, as shown in figure 1(a). the machine then raises the gold wire and drags the gold wire to connect it to the second connection at the lead frame. the lead frame is the point used to connect the circuit of the ic packaging with the integrated circuits of various devices. at the second point of circuit connection, the gold wire is touched onto the lead frame and pressed to break the gold wire, producing a flat shape. this point connection is called the second bond, as shown in fig. 1(b). the quality of the gold wire bonding is checked by bond shear strength. the bond shear test uses a machine to push the first bond area with a constant straight force. this process continues until the connected gold wire is damaged and the maximum strength obtained from the test is recorded. figure 2(a) shows the picture of the product before the bond shear test. figure 2(b) shows the picture of the product after the bond shear test, where the bonded gold wire was broken by the bond shear test as denoted by the red circle. (a) (b) fig. 1: (a) appearance of the first bond, (b) appearance of the second bond. (a) (b) fig. 2: (a)the first bond before the bond shear test, (b) the first bond after the bond shear test. 308 iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 2.1 machine and materials in the experiments, the gold wire bonding capillary that is expired after manufacturing 150,000 work pieces is studied in order to investigate the effects of the factors of the shear forces in the gold wires. the reused capillary is shown in fig. 3. the machines and materials used in this research include the gold wire bonding machine model kns iconn plus as shown in fig. 4(a) and a gold wire size of 1.3 mils to connect the circuit. the 4000 series multipurpose bond tester machine was used for the quality control by recording the maximum shear strength, as shown in fig. 4(b). in the experiments, the gold wire bonding capillary that is expired after manufacturing 150,000 work pieces is studied in order to investigate the effects of the factors of the shear forces in the gold wires. (a) (b) fig. 3: (a) front view of reused capillary, (b) side view of reused capillary. (a) (b) fig. 4: (a) wire bonding machine, (b) the shear testing machine. 2.2 factors and level of factors in experiments by referring to the relevant studies, the factors of the experiments are identified. there are five factors of the strengths of the gold wire bonding, that use five factors to determine the effect of factors to create a regression model of the process. the factors include the gold bonding pressure (bond force), the gold bonding time (bond time), the ultrasonic energy used (usg current), the current released through the efo to melt the gold wire (efo current) and the distance between the efo and the gold wire (efo gap). the level of factors in the research was based on operation processes and machine 309 iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 manuals to determine the appropriate level of each factor used in the experiment so as not to affect the quality of the product, as shown in table 1. table 1: factors and levels of the experiment factors level of factors unit (-1) 0 (+1) (a) bond force 70 80 90 grams (b) bond time 1 2 3 ms (c) usg current 20 35 50 ma (d) efo current 40 45 50 ma (e) efo gap 25 30 35 mils 2.3 methodology in this research, the design of the fractional factorial experiment (ffd) was chosen because it is an experimental design that uses half the number of experiments from the design of a full number of factorial experiments [14,15]. in the case of a study using five factors, the fd experiment used a total of 32 experiments, ffd are used to halve the number of experiments, using only 16, while still maintaining efficient results analysis. there is a good method to create a regression model between the test variable and the response, resulting in a clearer understanding of the main effect and interaction effects between each factor and response. the fractional factorial design was used to determine five factors that affect the bond shear strength. the experiment was repeated twice with 3 centre point experiments per replication to check the curvature of the regression model using a statistical significance level 0.05 = in the experiments. the experiment total is for 38 experiments. the experiments were applied to control other factors that may affect the research response of the three items [16]. the first principle was replication, with two repeated experiments performed; the error of the experiment was calculated and randomized to avoid factors not chosen for analysis [17]. the second was randomization, where the minitab was used to randomize the trial order to prevent errors. the third was blocking, where all other factors were controlled factors so as not to affect the response of the experiment. the controlled factors included experimenter control, tension, and test experimenter control, which were the same for every experiment; the same machine was used throughout and the gold wire bonding material came from the same lot of material throughout the experimental process. based on the fractional factorial analysis, results can obtain the regression model to predict bond shear strength over the experimental region. this regression model of the bond shear strength is eq. 1. (1) where 1 2 3 4 , , ,x x x x , and 5x are the factors of the experiment that represent (a), (b), (c), (d), and (e). ' s coefficients can be obtained from the effect estimates. 0  is the average effect of all responses in the 38 experiments. residual analysis of the fractional factorial test results for the bond shear strength was a preliminary examination, with the results obtained from the actual experiment shown to be consistent. three parts were considered: the requirements that the residues must have a normal distribution and, in considering the normal distribution of the residuals, the normal 0 1 1 2 2 3 3 4 4 5 51 y x x x x x     = + + + + + 310 iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 probability plot and the histogram were further considered. the final test of the residuals of the trial versus the prediction value (versus fits) was considered to be the residual from the trial order (versus order) [18,19]. 3. results the results obtained from a fractional factorial experiment with 38 trials are shown in table 2 as the ball shear strengths are recorded. table 2: the fractional factorial result of bond shear strength experiment parameter ball shear strength std order run order center pt blocks ball force ball time usg current efo current efo gap 18 1 1 1 90 1 20 40 25 55.23 5 2 1 1 70 1 50 40 25 51.55 9 3 1 1 70 1 20 50 25 52.09 7 4 1 1 70 3 50 40 35 51.51 19 5 1 1 70 3 20 40 25 52.31 10 6 1 1 90 1 20 50 35 54.04 13 7 1 1 70 1 50 50 35 52.27 8 8 1 1 90 3 50 40 25 53.94 31 9 1 1 70 3 50 50 25 51.08 30 10 1 1 90 1 50 50 25 55.35 15 11 1 1 70 3 50 50 25 51.78 37 12 0 1 80 2 35 45 30 54.02 38 13 0 1 80 2 35 45 30 51.64 6 14 1 1 90 1 50 40 35 54.79 35 15 0 1 80 2 35 45 30 52.17 33 16 0 1 80 2 35 45 30 52.95 23 17 1 1 70 3 50 40 35 53.58 2 18 1 1 90 1 20 40 25 55.25 21 19 1 1 70 1 50 40 25 52.80 22 20 1 1 90 1 50 40 35 54.50 29 21 1 1 70 1 50 50 35 51.28 12 22 1 1 90 3 20 50 25 53.69 32 23 1 1 90 3 50 50 35 52.80 16 24 1 1 90 3 50 50 35 54.99 20 25 1 1 90 3 20 40 35 54.69 1 26 1 1 70 1 20 40 35 51.88 14 27 1 1 90 1 50 50 25 53.84 3 28 1 1 70 3 20 40 25 51.80 17 29 1 1 70 1 20 40 35 52.79 28 30 1 1 90 3 20 50 25 54.77 4 31 1 1 90 3 20 40 35 53.49 34 32 0 1 80 2 35 45 30 52.51 27 33 1 1 70 3 20 50 35 51.59 36 34 0 1 80 2 35 45 30 53.39 11 35 1 1 70 3 20 50 35 50.85 26 36 1 1 90 1 20 50 35 53.28 24 37 1 1 90 3 50 40 25 53.02 25 38 1 1 70 1 20 50 25 52.05 3.1 analysis effect of factors analysis of the results from the design of the fractional factorial experiments was performed using the minitab program. the results were found to be a significant factor by a p-value of less than 0.05 = , which is statistically significant [20]. the factor affected 311 iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 the bond shear strength to a statistically significant degree. the bond force is shown in table 3, which presents the results of the sum of the square of the factors calculated from the fractional factorial test. figure 5 shows the factors affecting the bond shear strength in the gold wire bonding process via a normal probability plot of the fractional factorial. the results were used to examine the curvature of the regression model, with the bond shear response evaluated by analysis of variance. the p-value was found to be greater than the level of statistical significance according to the linear regression model. table 3:. analysis of variance (anova) of bond shear strength source df seq ss adj ss adj ms f value p value significant main effects 5 45.039 45.039 9.008 13.740 0.000 significant bond force 1 41.598 41.598 41.598 63.430 0.000 significant bond time 1 1.578 1.578 1.578 2.410 0.136 usg current 1 0.014 0.014 0.014 0.020 0.884 efo current 1 1.697 1.697 1.697 2.590 0.123 efo gap 1 0.152 0.152 0.152 0.230 0.635 two-way interactions 10 4.066 4.066 0.407 0.620 0.780 bond force*bond time 1 0.228 0.228 0.228 0.350 0.562 bond force*usg current 1 0.093 0.093 0.093 0.140 0.711 bond force*efo current 1 0.299 0.299 0.299 0.460 0.507 bond force*efo gap 1 0.243 0.243 0.243 0.370 0.550 bond time*usg current 1 0.002 0.002 0.002 0.000 0.956 bond time*efo current 1 0.101 0.101 0.101 0.150 0.699 bond time*efo gap 1 0.611 0.611 0.611 0.930 0.345 usg current*efo current 1 0.241 0.241 0.241 0.370 0.551 usg current*efo gap 1 1.507 1.507 1.507 2.300 0.144 efo current*efo gap 1 0.742 0.742 0.742 1.130 0.300 curvature 1 0.483 0.483 0.483 0.740 0.400 residual error 21 13.771 13.771 0.656 pure error 21 13.771 13.771 0.656 total 37 63.360 86420-2 99 95 90 80 70 60 50 40 30 20 10 5 1 standardized effect p e r c e n t a bond f orce b bond time c u s g c urrent d e f o c urrent e e f o g ap f actor n ame not significant significant effect ty pe a normal plot of the standardized effects (response is bond shear strength, alpha = 0.05) fig. 5: normal probability plot of factor that affect to the bond shear strength. 312 iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 3.2 residual analysis the results of the analysis of the graphs (normal probability plot) and histogram of the experiment showed that the residues of the bond shear strength were normal distribution, with no trend found. for versus fits, there was a random distribution, with no distribution as a trend or pattern occurring. for versus order, the nature of the residual distribution with the trial sequence was random, indicating that the error in the trial sequence was independent, as shown in fig. 6. the bond shear strength therefore showed no abnormalities or residual tend, showing that the results of the experiment were consistent with the prerequisites of the experiment. therefore, these experimental results were able to be used. 10-1 99 90 50 10 1 residual p e r c e n t 5554535251 1.0 0.5 0.0 -0.5 -1.0 fitted value r e s id u a l 1.20.60.0-0.6-1.2 8 6 4 2 0 residual f r e q u e n c y 35302520151051 1.0 0.5 0.0 -0.5 -1.0 observation order r e s id u a l normal probability plot versus fits histogram versus order residual plots for bond shear strength fig. 6: residual plot for the fractional factorial test. 3.3 regression model the regression model showed that increasing the bond force factor in the gold wire bonding process would increase the bond shear force strength. for other factors, it will have the opposite effect. the production process should be carefully considered when adjustments are made in order to take advantage of the regression model to maximize performance. the regression model was concluded and is described in eq. 2. 1 2 3 4 51 46.64 0.11 0.86 0.11 0.08 0.24y x x x x x= + − − − + (2) where, 1 y is the bond shear strength, 1x is the bond force, 2x is the bond time, 3x is the usg current, 4x is the efo current, and 5x is the efo gap. 4. conclusion the statistical method of fractional factorial experiment is a suitable method to determine the effect of large factors in the gold wire bonding process. the experiment was used to determine the effect of five factors by two replications and 3 center point experiments per replication to check the curvature of the regression model. the statistical significance level of the experiments is 0.05 = , a total of 38 trial experiments were performed. the experiment factors of bond force, bond time, usg current, efo current, and efo gap were investigated. the factor found to affect the bond shear strength in the process is the bond force factor of the gold wire bonding process. the regression model 313 iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 demonstrated the correlation between coherence that would influence mutual bonding and thereby increase the bond shear strength of the gold wire and increase the strength of the bond force. in these experiments, the expired gold wire bonding capillary is studied. the factors of the shear forces of the welds are different from that of the relevant studies with many factors of the strengths of the welds. for reusing the parts, the bond force is the only factor that significantly affects the increase in the shear force. therefore, if the manufacturers consider to re-use the expired gold wire bonding capillaries or to increase the useful lives, they can just adjust the bond force of welding to obtain the appropriate shear force. references [1] krajcsák z. (2019) implementing open innovation using quality management systems: the role of organizational commitment and customer loyalty. j. of open innovation: technology, market, and complexity, 5(4): 90. https://doi.org/10.3390/joitmc5040090 [2] prabowo r, singgih ml, karningsih pd, widodo e. (2020) new product development from inactive problem perspective in indonesian smes to open innovation. journal of open innovation: technology, market, and complexity., 6(1): 20. https://doi.org/10.3390/joitmc6010020 [3] phimpha c, sindhuchao s. (2020) the process of reusing machine part in gold wire bonding process of ic packaging product. the international academic conference on engineering, technology and innovations. bali. indonesia, pp.13-14. [4] hung yh. (2007) optimal process parameters design for a wire bonding of ultra‐thin csp package based on hybrid methods of artificial intelligence. microelectronics international, 24(3): 3-10. [5] wang, sun r. (2009) the quality test of wire bonding. modern applied science, 3(12): 50-56. [6] bonding w. (2008) the great debate: copper vs. gold ball bonding. advanced packaging, 17(7): 20. [7] kim bc, ha sj, yang jk, lee ic, kang ds, han bs, han yj. (2017) process capability optimization of ball bonding using response surface analysis in light emitting diode (led) wire bonding. journal of the korea academia-industrial cooperation society, 18(4): 175-182. [8] zhong zw. (2009) fine and ultra‐fine pitch wire bonding: challenges and solutions. microelectronics international, 22(2): 10-18. [9] sciammarella fm, salehi najafabadi b. (2018) processing parameter doe for 316l using directed energy deposition. j. of manufacturing and materials processing, 2(3): 61. [10] wu yx, long zl, lei han, zhong j. (2006) temperature effect in thermosonic wire bonding. transactions of nonferrous metals society of china, 16(30): 618-622. [11] satianrangsarith w, tirakanogsathit m. (2012) design of experiments approach for improving wire bonding quality. international journal of innovation, management and technology, 3(4): 327-331. [12] lu d, wong cp. (2018) materials for advanced packaging. springer international publishing, switzerland. [13] antony j. (2014) design of experiments for engineers and scientists. elsevier. [14] montgomory dc, runger gc. (2011) applied statistics and probability for engineering. john wiley & son inc, u.s.a. [15] gong y, song j, lin s, yang j, he y, tan g. (2020) design optimization of rubber-basalt fiber-modified concrete mix ratios based on a response surface method. applied sciences, 10(19): 6753. [16] mayer rm, montgomery dc. (2011) response surface methodology: process and product optimization using design experiment. john wiley & sons inc, u.s.a. 314 https://doi.org/10.3390/joitmc5040090 https://doi.org/10.3390/joitmc6010020 iium engineering journal, vol. 22, no. 2, 2021 phimpha and sindhuchao https://doi.org/10.31436/iiumej.v22i2.1715 [17] sabry i, el-kassas am, mourad ahi, thekkuden dt, abu qudeiri j. (2019) friction stir welding of t-joints: experimental and statistical analysis. j. of manufacturing and materials processing, 3(2): 38. [18] martin j, de adana ddr, asuero ag. (2017) fitting models to data: residual analysis, a primer. chapter 7. [19] mongomery dc. (2009) design and analysis of experiment. john wiley & sons ltd u.s.a. [20] mongomery dc. (2009) statistical quality control a modern introduction. john wiley & sons ltd u.s.a. 315 compiled journal vol 12 no 2.pdf application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 botnet detection using independent component analysis wan nur hidayah ibrahim1,2, mohd syahid anuar5, ali selamat1,3,4* and ondrej krejcar4 1 school of computing, faculty of engineering, universiti teknologi malaysia, media and game innovation centre of excellence (magicx), universiti teknologi malaysia, 81310 johor baharu, johor, malaysia 2 jabatan teknologi maklumat dan komunikasi (jtmk), politeknik sultan idris shah, 45200 sg lang, selangor, malaysia 3 malaysia japan international institute of technology (mjiit), universiti teknologi malaysia, jalan sultan yahya petra, 54100 kuala lumpur, malaysia 4 center for basic and applied research, faculty of informatics and management, university of hradec kralove, rokitanskeho 62, 500 03 hradec kralove, czech republic 5 razak faculty of technology and informatics, universiti teknologi malaysia, jalan sultan yahya petra, 54100 kuala lumpur, malaysia *corresponding author: aselamat@utm.my (received: 23rd january 2021; accepted: 9th august 2021; published on-line: 4thjanuary 2022) abstract: botnet is a significant cyber threat that continues to evolve. botmasters continue to improve the security framework strategy for botnets to go undetected. newer botnet source code runs attack detection every second, and each attack demonstrates the difficulty and robustness of monitoring the botnet. in the conventional network botnet detection model that uses signature-analysis, the patterns of a botnet concealment strategy such as encryption & polymorphic and the shift in structure from centralized to decentralized peer-to-peer structure, generate challenges. behavior analysis seems to be a promising approach for solving these problems because it does not rely on analyzing the network traffic payload. other than that, to predict novel types of botnet, a detection model should be developed. this study focuses on using flow-based behavior analysis to detect novel botnets, necessary due to the difficulties of detecting existing patterns in a botnet that continues to modify the signature in concealment strategy. this study also recommends introducing independent component analysis (ica) and data pre-processing standardization to increase data quality before classification. with and without ica implementation, we compared the percentage of significant features. through the experiment, we found that the results produced from ica show significant improvements. the highest f-score was 83% for neris bot. the average f-score for a novel botnet sample was 74%. through the feature importance test, the feature importance increased from 22% to 27%, and the training model false positive rate also decreased from 1.8% to 1.7%. abstrak: botnet merupakan ancaman siber yang sentiasa berevolusi. pemilik bot sentiasa memperbaharui strategi keselamatan bagi botnet agar tidak dapat dikesan. setiap saat, kodkod sumber baru botnet telah dikesan dan setiap serangan dilihat menunjukkan tahap kesukaran dan ketahanan dalam mengesan bot. model pengesanan rangkaian botnet konvensional telah menggunakan analisis berdasarkan tanda pengenalan bagi mengatasi halangan besar dalam mengesan corak botnet tersembunyi seperti teknik penyulitan dan teknik polimorfik. masalah ini lebih bertumpu pada perubahan struktur berpusat kepada struktur bukan berpusat seperti rangkaian rakan ke rakan (p2p). analisis tingkah laku ini 95 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 seperti sesuai bagi menyelesaikan masalah-masalah tersebut kerana ianya tidak bergantung kepada analisis rangkaian beban muatan trafik. selain itu, bagi menjangka botnet baru, model pengesanan harus dibangunkan. kajian ini bertumpu kepada penggunaan analisa tingkah-laku berdasarkan aliran bagi mengesan botnet baru yang sukar dikesan pada corak pengenalan botnet sedia-ada yang sentiasa berubah dan menggunakan strategi tersembunyi. kajian ini juga mencadangkan penggunakan analisis komponen bebas (ica) dan pra-pemprosesan data yang standard bagi meningkatkan kualiti data sebelum pengelasan. peratusan ciri-ciri penting telah dibandingkan dengan dan tanpa menggunakan ica. dapatan kajian melalui eksperimen menunjukkan dengan penggunaan ica, keputusan adalah jauh lebih baik. skor f tertinggi ialah 83% bagi bot neris. purata skor f bagi sampel botnet baru adalah 74%. melalui ujian kepentingan ciri, kepentingan ciri meningkat dari 22% kepada 27%, dan kadar positif model latihan palsu juga berkurangan dari 1.8% kepada 1.7%. keywords: botnet detection; flow-based; machine learning; independent component analysis; traffic analysis 1. introduction a botnet is a collection of computers infected by malicious software (malware) that a botmaster manages. all internet-of-things (iots) devices, such as closed-circuit television cameras (cctv), web cameras, computers, and mobile devices, can be infected devices. the vulnerabilities and the computing resources of these infected devices are exploited where they operate remotely as servants following the instructions given by their botmaster. the main aim of assigning a botnet is to launch an assault on the victim. however, the number of bots depends on the frequency of the attacks. therefore, the most significant factor contributing to the frequency of the attacks is the number of bots in botnet environments [1], [2]. they can execute major attacks on victims, such as ddos or email spam, because of the large number of bots, rendering victims unable to function for hours or days. for example, in the mirai incident of 2016, the vast and unlimited number of bots produced a massive impact assault [3]. in the mirai incident of 2016, the attacks were identified from 600,000 internet-ofthings (iot) devices [4]. at that moment, mirai attacks were noteworthy since the bots used internet-of-things (iot) devices, not just computers or laptops. consider the result if 600,000 devices concurrently sent a ping to a specific website, leading to that website being overwhelmed, inaccessible, and its services slowed down. the botnet detection model has become a hot topic among researchers due to the history of botnet attacks and their impact on the industry. the arms race never ends between the botmasters and the researchers trying to beat each one. every group continues to develop its abilities, and this can be seen through the botnet revolution. botnet evolves or mutates every day after the source code has been released to the public [5]. it can be seen in the mirai botnet and the mirai version. two months after the release of the mirai source code to the public, the bots multiplied with variant complexity, from 213,000 to 493,000, twice. they show the statistics of various botnet attacks on securelist websites, and 39.35 percent of new botnet found in 2018 is based on the kaspersky lab botnet monitoring project compared to 2017 botnet attacks [6]. subsection 1.1 briefly clarifies why the botnet relies heavily on the rallying stage or c&c stage command & control server. the importance of preventing the server from being identified by the security system also explains the botnet structure's revolution. the botnet framework revolution switches from centralized to a decentralized. centralized botnet, such as irc and http, via the primary server, call the command & control server. decentralized botnet, such as peer-to-peer (p2p), are more advanced since the bots themselves can act as servers. p2p is designed to hide the c&c server, as stated in [7], [8]. 96 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 the botnet's strength lies in its capacity to elude security systems and carry out large-scale attacks thanks to various tactics such as packet data concealment and encrypted packet data [9]. a botnet can hide from the protection system and imitate the regular traffic flow where normal traffic is usually more random [10], it then waits for stage and imbalanced class distribution. the p2p technique is also a part of the concealment strategy to mask the c&c server [7], [8]. the botnet is now becoming a profitable business, according to [8], where the botmaster provides the service for any cyber-attacks. however, the current capability leading the business of these services must monitor the bots, advise of subsequent attacks, lengthen the duration of the attacks, and avoid monitoring its identity. 1.1 botnet life-cycle and structure it is necessary to understand the life cycle of the botnet when designing a behavior-based analysis of the botnet detection model since the choice of related features of this model depends on it. other than that, identification must also be carried out before the attacks occur and it is too late [11]. as below, the botnet life-cycle can be divided into four main stages: • phase i: injection (i) • phase ii: command & control (c&c) • phase iii: attack • phase iv: release the first stage is injection or replication. this stage can be achieved in several ways on the network, such as exchanging folders, visiting malicious websites, or adding emails. the bot herder increases the number of bots at this level. the command & control stage or 'rallying' stage is the second stage. the infected devices already behave like bots in this process. the bots keep updating the devices' status, and if necessary, the bot herder submits a new source code [12]. the revised source code and the vulnerability report are designed to ensure the bots are undetected and robust [13]. the third stage is the attack phase, where all bots are targeted at attacking specific victims. the botmaster gives an attack launch order, and the bots simultaneously launch the attack based on the command. the release period is the last stage. the release stage is where the botmaster removes fingerprints, substitutes new systems for identified bots, and does not leave a digital footprint behind. often the botmaster distributes the source code to hinder government investigations. during this process, learning from the previous attack, the functionality of the bot system is also enhanced [14]. we concentrate on botnet activity in the process of command & control or rallying for our study. the infected system continues to attempt to connect to the c&c server to send reports of the infected devices. the system also receives updated source code to keep hiding from protection [8]. based on a kaspersky lab study [15], monitoring ddos attacks is the correct time to detect botnet to intercept the command from the command & control. 1.2 motivation and contribution our inspiration is the potential and consequences of a botnet (a botnet attack), to discover its method before the attack is launched. however, our critical general incentive to build a model that can predict a novel botnet is due to the continuous evolution of the botnet. the technological motivation for using behavior-based patterns and flow-based functionality is due to the shortcomings in detecting the new forms of botnets in the signature-based detection model. other than that, we were motivated by the research from [16] that combined principal component analysis (pca) for clustering with k-means. 97 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 fig. 1: the botnet structure and botnet component. in statistics, principal component analysis is a technique used to describe a data set in terms of new uncorrelated variables ("components"). the components are ordered by the amount of original variance they describe, so the technology helps reduce the dimensionality of a data set. in comparison, independent component analysis (ica) is a machine learning technique used to distinguish independent sources from a mixed input. unlike principal component analysis, which focuses on maximizing data point variance, independent component analysis emphasizes independence or independent components. since we are using aggregation for pre-processing data, the vital information might be lost, resulting in decreased performance, so we agreed to use ica. the explanation about ica is in subsection 0. the significant contributions to this analysis are: • this method can detect network packets even in concealment strategies such as obfuscation, code encryption, oligomorphic strategy, polymorphic strategy, and metamorphic. • this method used the ctu-13 botnet benchmark dataset that consists of centralized and decentralized structures. it proves that our framework can detect both structures. • the evaluation of this framework used the different types of botnets, proving that our framework can detect novel botnets. • our result shows the average 74% f-score that tests on five types of novel botnets. • the performance of the framework is compared with other researchers that used the same source of data. 2. related works the latest developments in the concealment technique of packet data in network traffic make the signature-based or content-based inefficient in detecting new forms of botnets. for example, singh et al. [17] suggested that the signature time-to-time was revamped by the botnet and significantly modified. these changes in behavior caused signature-based analysis output to drop on the new release botnet because signature-based analysis relied heavily on the bot's 98 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 signature. in addition, many concealing tactics are used to mask packet data content in network traffic, including obfuscation, code encryption, oligomorphic approach, polymorphic strategy, and metamorphic strategy [18]. patsakis et al. [8] raised many concerns about dns queries that have been used to conceal the botnet on the encrypted channel. although assadhan et al. [17], claimed that packet data contents should be shielded to safeguard the identity of the private information of the individual or user, where only the header of the packets can be released to the public. this author also concentrated on analyzing traffic, exchanging packets, and providing a framework for lightweight security. but their work is considered dns and is only for the dga botnet. a model was also developed by this author using the actions of the botnet when interacting with others, but the time interval used for this study is 31-49 minutes. two common approaches, 1) payload-based and 2) traffic-based can be classified into machine learning models to detect network operations. the payload-based approach trains models based on characteristics derived from the payload/data portion of the packets transmitted over the network, as the name implies. the disadvantages of such models are the resource-intensive challenge (where features for each packet need to be evaluated), privacy problems, and encrypted information where features cannot be extracted [18,19]. by analyzing the communication packet headers or netflow information, the traffic-based approach aims to mitigate some of the model's drawbacks. while privacy remains an issue with such an approach (such as individual ip addresses in features), this can be mitigated by aggregating time window records. 2.1 behavior-based and flow-based features what is behavior-based? what are the differences between behavior-based and signaturebased? behavior-based and signature-based are in contrast to each other. in computing, all objects have attributes that can be used to develop a custom signature. signature-based analysis refers to detecting attacks by searching for specific patterns, like byte sequences in network traffic or known malicious instruction sequences used by malware [22]. this terminology is derived from anti-virus software, which refers to these detected patterns as signatures. although behavior-based analysis is an analysis that does not directly analyze the data like signature-based, there are some advantages of behavior-based analysis compared to signaturebased analysis. for example, it is more secure or effective in detecting new and novel forms of malware threat. in addition, it can detect a single instance of malware that targets a person or organization. it can also identify what the malware does when files are opened in a specific environment and obtains comprehensive malware information. however, according to resende and drummond [21], most research defines behavior-based analysis with anomaly-based detection, but anomaly detection can also be done using signature-based analysis. so, it means that anomaly-based cannot be defined as behavior-based analysis in malware detection. the definition of behavior-based resende and drummond [21] is the most accurate to our definition. resende and drummond [21] define behavior-based analysis in network intrusion detection systems as detection techniques that are not evaluated or referred directly to the source, destination, and payload of packets. it is an analysis that assesses the behavior of an object. behavior-based detection can be performed by using api call logs [24], network flow (netflow) [10], and is also a hybrid between api call and netflow [25]. a flow is a collection of packets that come from the same source and destination. flow-based botnet detection techniques employ statistics of all packet headers in a flow (flow record). because the flow99 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 based approach only catches packet header information, it can reduce the computational complexity [24-26] and be processed very quickly. flow-based features are the characteristics chosen to illustrate the network flow pattern or connection to distinguish either the usual network or a botnet network. flow-based characteristics also relate to packet data information, such as total packets per second, bytes per packet, total packet bytes, and the number of packets [29]. the description of flow-based functionality is shown in table 1 and consists of the features, the time window, and the data tools derived from published work. thus, when designing our characteristics and the time window, table 1 became our crucial guide. the feature selection process was interpreted in the same concept as used in aggregation. as mentioned in gezer et al. [40], one of the challenges in machine learning is feature selection because feature selection needs a good understanding of the domain knowledge. not all features in the data are relevant to building the model (resende and drummond [21]). on the other hand, aggregation is a process of transforming the data based on a specific theory, and it enables the extraction of sufficient data for analysis. based on [30], aggregation is a part of the data mining technique in machine learning for efficient knowledge discovery about network flows. 2.2 independent component analysis independent component analysis (ica) is a source separation technique in signal processing. according to [31], in their survey, ica and pca are among the popular methods used to select essential network features. pca extracts and reduces the dimension of features, while ica separates the noise to enhance and maximize each feature's data pattern [32]. the authors in [33] claim that principal component analysis (pca) is a technique for reducing features by identifying the relevant feature set. the implementations of ica and pca clustering algorithm in feature selection has been reported [16]. it is a semi-supervised model where the author combined unsupervised and supervised techniques. in ica, the mutual connection between features is minimized by maximizing the nongaussianity. research from palmieri et al. [34] is the most similar to our approach. the author used ica in network anomaly detection from the university of naples, italy’s network traffic. on the other hand, we try to find the implementation of ica in detecting botnet, and we only found an article from mao et al. [35] where this author used ica in detecting spamming botnet. we can summaries that behavior-based analysis that used the flow-based features can solve the issues of concealment botnet, but it produces high false alarm (false positive rate). high false alarm in machine learning occurs due to the unclear separation between classes that also come from the unclear pattern produce by the data. although some attempts have been made to address this issue, it still puts limitations on ica implementation. 3. proposed framework and pre-evaluation result in order to reach the objective, this study proposed a new framework as shown in fig. . the proposed framework starts with selecting the network traffic dataset and pre-processing the dataset. this study highlighted the pre-processing phases where the data is provided to produce a high-performance during classification. 100 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 table 1: summary of behavior-based analysis in previous works author features time window (seconds) data resources ehsan and hamid [36] group duration time, number of receive packets, number of send packets, distance from the previous group group duration time kelihos, cvut malware capture facility project stevanovic and pedersen [37] * basic conversation features: port number, layer 7 protocol, duration (last pkt first pkts), the total number of packets, total number of bytes, mean of the number of bytes per packet & std of the number of bytes per packet * time-based-based features: number of packets & bytes per second, mean & std of packets inter-arrival time * bidirectional features: a ratio of number of packets & bytes in and out, a ratio of inter-arrival times in and out * tcp specific features: such as percentage tcp syn packets, percentages of tcp syn-ack packets, percentages of tcp ack & percentages of tcp ack push packets 300 s combination of the dataset: • iscx, isot • contagio • honeyjar • malware capture facility project (mcfp) fernandez maimo et al. [38] * number of flows, number of incoming flows, number of outgoing flows; * % of incoming and outgoing flows over the total * % of symmetric and asymmetric incoming over the total * sum, maximum, minimum, mean, and variance of ip, packets per incoming outgoing, and totals flows 20 30 s ctu-13 debashi and vickers [39] array 1:(src addr), dst port, packet count algorithm 2: dst addr, dst port, packet count. array 2: dst addr, src addr list, src addr count, dst port list, dst port count 60 s isot gezer et al. [40] * total forward & backward volume * max forward & backward packet length * min, max, mean before idle and before active. * max backward inter-arrival time 600 s capture own network data garg et al. [41] send syn, recv ack, recv rst, send pkts, recv pkts, icmp unr, send len, recv len 120 s combination of p2p botnet 101 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 3.1 input: data source and data distribution for this study, the following vital data are extracted from the botnet benchmark dataset ctu-13 [42] from the website of the stratosphere research laboratory. this dataset consists of 13 files with several types of botnets in different protocols and different structures. since this framework aims to detect novel botnet, this dataset is divided into two sets, training and testing, for building the model and evaluating the dataset, as shown in table 2. the model is evaluated with data from the evaluating dataset separated from data for building the model. the separation of this data ensures that the model is derived and tested using a different set of data, as explained in step 2: dividing dataset in section 3.2. table 2: the distribution of bot in training and evaluating dataset data file no duration (hrs) bot name no of bots training dataset evaluating dataset 1 6.15 neris 1 √ 2 4.12 1 √ 3 66.85 rbot virut 1 √ 4 4.12 1 √ 5 11.63 1 √ 6 2.18 menti 1 √ 7 0.38 sogou 1 √ 8 19.5 murlo 1 √ 9 5.18 neris 10 √ 10 4.75 rbot 10 √ 11 0.26 3 √ 12 1.21 nsis.ay 3 √ 13 16.36 virut 1 √ table 2 summarizes the distribution of data based on the data file no. in the third column are the names of bots in the dataset. the explanation of the bot name, bot category, and structure are given in table 3. it is essential to have both structures (centralized and decentralized) in this research. as a result, our data source selection appears reasonable in terms of independent structure and bot reliability. columns 5 and 6 in table 2 show the separation of training and evaluating data for the novel bot. table 3: the description of the bot based on the name bot name bot category structure 1 neris irc centralized 2 rbot irc 3 virut http 4 menti irc 5 soguo http 6 murlo irc 7 nsis.ay p2p decentralized 3.2 data pre-processing pre-processing data is the phase in which the data is prepared before being incorporated into the algorithm to construct the prediction model. since we used behavior-based analysis, the information needed to go through several steps. a behavior-based analysis is not a straightforward extraction process but rather a tool for analyzing the raw data. there are several vital components or measures that we have grouped into the pre-processing data 102 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 module, such as labeling, cleaning, dividing dataset, feature selection, aggregation, and data quality process implementation. fig. 2: the proposed framework for pre-processing flow-based features. 3.2.1 step 1: labeling and cleaning the first step was re-labeling the dataset. although the ctu-13 dataset is supervised, the dataset contains labels but those labels are in string/text, not in numbers. there are 74 types of descriptive labels in ctu13, as we have shown in appendix a, but basically, the label is based on 3 types of labels: ‘normal’, ‘botnet’, and ‘background’. due to that, we re-labeled the ctu-13 as stated in (1) below. once the labeling was completed, we removed the uncertain data in label = 2 for the cleaning process. 𝐿𝑎𝑏𝑒𝑙 = { 0 𝑖𝑓 𝑡ℎ𝑒 𝑙𝑎𝑏𝑒𝑙 𝑠𝑡𝑎𝑡𝑒 𝑖𝑠 "𝑁𝑜𝑟𝑚𝑎𝑙" 1 𝑖𝑓 𝑡ℎ𝑒 𝑙𝑎𝑏𝑒𝑙 𝑠𝑡𝑎𝑡𝑒 𝑖𝑠 "botnet" 2 𝑖𝑓 𝑡ℎ𝑒 𝑙𝑎𝑏𝑒𝑙 𝑠𝑡𝑎𝑡𝑒 𝑖𝑠 "𝑏𝑎𝑐𝑘𝑔𝑟𝑜𝑢𝑛𝑑" (1) 103 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 3.2.2 step 2: dividing dataset after the cleaning process, the data was split into two main data sets: creating model data and analysing data. this separation aimed to ensure that the construction model evaluation is performed on a novel botnet. the model was based on constructing model data, divided into 70-30 ratios of training and testing data. fig. 1: process of dividing dataset for novel botnet. 3.2.3 step 3: features selection and aggregation once the dataset division was completed, the dataset was ready for the following process: selecting the features and aggregating them in a specific time interval. we aimed to build the fastest detection, so for this research we chose a short time interval (1 sec) for aggregation. feature selection is a process of selecting specific variables/features/attributes in the data. the purpose of this process was to reduce the complexity and processing time. we chose the features based on the theory of communication. this theory is between botmaster and its bots during the c&c stage in the botnet life-cycle for this research. as mentioned in the bot life-cycle in subsection 1.1: botnet life-cycle & structure, during the c&c phase, bots and botmaster keep communicating. this communication pattern is different from the regular communication pattern, where a typical communication pattern is usually more random. in contrast, a bot’s communication pattern is more uniform with the same amount of transferring data to multiple destinations. the features that we used for this research are shown in table 4. table 4: data type for features in the dataset no feature data types calculation 1 destination address categorical data n(x) 2 destination port categorical data n(x) 3 packet data continuous data min, max, median, std deviation, n(x) 4 time categorical data ∆t the data are aggregated or grouped in two parameters: time interval (t) and source address (sip), as shown in eq. (2). we used the aggregation technique to calculate the occurrence number of the communication within the time interval that represented the bot’s behavior in a particular given time. 104 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 ⌈𝑆𝑖𝑝, 𝑡⌉ = {𝑋0 , 𝑋1 , … … . , 𝑋𝑛} (2) since the data in the netflow is in continuous type and categorical data type, the aggregation of these two types of data is different, as shown in eq. (3). if the data was continuous, we implemented the statistical technique such as minimum, maximum, median, standard deviation, and specific number, n(x). but if the data type was categorical data, we implemented only the total distinct number, n(x), where the total distinct number (n(x)) that define as the frequency of unique elements in the set can be described as shown in eq. (4). 𝑓 (𝑥) = { 𝑀𝑖𝑛, 𝑀𝑎𝑥, 𝑀𝑒𝑑𝑖𝑎𝑛, 𝑠𝑡𝑑 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛, 𝑛(𝑥) 𝑖𝑓 𝑑𝑎𝑡𝑎 𝑖𝑠 𝑐𝑜𝑛𝑡𝑖𝑛𝑢𝑜𝑢𝑠 𝑛𝑢𝑚𝑏𝑒𝑟 𝑇𝑜𝑡𝑎𝑙 𝐷𝑖𝑠𝑡𝑖𝑛𝑡 𝑁𝑢𝑚𝑏𝑒𝑟, 𝑛(𝑥) 𝑖𝑓 𝑑𝑎𝑡𝑎 𝑖𝑠 𝑐𝑎𝑡𝑒𝑔𝑜𝑟𝑖𝑐𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 (3) 𝑛(𝑥) = {𝑋𝑖 , 𝑋𝑗 , … … , 𝑋𝑛|𝑋𝑖 ≠ 𝑋𝑗 , 𝑖 ≠ 𝑗, 𝑖 ≥ 0, 𝑗 = 1, … … , 𝑛 } (4) while for time, this data is used, whereas the aggregation or rounding process is shown in eq. (1). time is also used in calculating the different time (∆t) between the last time, tn and the start time, t1 in 1 second (time interval) duration. the equation for different time (∆t) is shown in eqs. (5) and (6). 𝑓(𝑡) = {𝑡1, 𝑡2, … … … , 𝑡𝑛} (5) ∆𝑡 = 𝑡𝑛 − 𝑡1 (6) 3.2.4 step 4: data quality process this process is the point where the most interesting things occur. this process improves the quality of the data and features, improving the performance of detecting novel botnets. therefore, we label it as data quality process to be represented as the objective of this combination process. this process utilized a two-step approach of standardization and independent component analysis (ica). specifically, we used this theory because the classifier we chose was related to a distance-based classifier. a) standardization standardization is a re-scaling process for the distribution of the dataset to obtain the mean of the data equal to 0, and the standard deviation equal to 1. in other words, standardization is a process of centering the data. standardizing a data set for a wide range of machine learning estimators is a common need. however, it could be harmful if the individual features do not look more or less like standard normally distributed data (e.g., gaussian with 0 mean and unit variance). therefore, test x is calculated as the standard value of: 𝑧 = (𝑥 − 𝜇) 𝑠⁄ (7) where µ is the mean of the training samples or zero if, with mean= false, s is the standard deviation of the training samples or with std= false, respectively. centering and scaling occurred on each feature independently by computing the relevant statistics on the samples in the training set. mean and standard deviation were then stored in a transform to be used on later data. b) independent component analysis for this research, we used fastica from sklearn. decomposition package in python, as shown in algorithm 1 below. as the name fastica implies, it is the short version of ica. fastica rotates the data until the data looks non-gaussian in every axis. by making the 105 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 mean equal to zero and normalization the variance in all directions, the algorithm can rotate the data in any direction. the process of normalizing the variance is called the whitening process. as shown in algorithm 1, the python code to implement ica is through the whitening process. the whitening process is the decorrelation to ensure that all features are treated equally before the algorithm of ica run. after the centering process (mean equal to zero) and the whitening process (normalization of variance), the data ran the ica algorithm. the main goal of ica is to find the unmixing vector of w, where w is the inverse of a, x is the input data, and a is the mixing signal. the equation is shown in eqs. (8) to (10): 𝑋 = 𝐴 𝑆 (8) 𝑆 = 𝐴−1𝑋 (9) 𝑆 = 𝑊 𝑋 (10) c) features importance ranking we evaluated our feature selection through features importance ranking calculated using extra tree classifier, as shown in algorithm 2. extra trees classifier for features importance in scikit.learn module is based on impurity-based importance where it calculated the importance of training data without reflecting the prediction ability. from the feature’s importance ranking in fig. 2, we can see the percentage of the highest contribute features. for example, the 1st feature increased from 22.75% to 27.74% and the lowest contributing feature, the 9th feature, increased from 1.8% to 4.31%. since no feature had a 0% contribution, the removal process was not executed. fig. 2: the comparison of features ranking with and without ica. b) feature ranking with ica a) original features 106 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 fig. 3: percentage differences in the highest and lowest ranking features. 3.3 building model using classification once the data completed pre-processing, we moved to the classification process. the classifier that we chose is k-nearest neighbor (k-nn). k nearest neighbor (knn) is one of the most straightforward classification machines that stores all available cases and classifies new cases based on a similarity measure [2,41]. the idea behind knn is that if a sample belongs to a specific class in the space of several similar samples (k), the sample is also in the category. thus, techniques based on nearest-neighbor classify samples based on the similarity of the population. knn falls into the algorithm family of supervised learning. informally, this means that a labeled data set consisting of training observations (x, y) is provided, and the relationship between x and y wants to be captured. more formally, our objective was to learn a function h:x→y to predict the corresponding y output confidently with an unseen observation x. first, we needed to determine the k-value of the number of groups (cluster) to use k-nn. for this research, we used elbow method to determine the k value. 3.3.1 determine k-value (elbow method) elbow method ran the k-nn algorithm several times and calculated the wss error for different values of k. to find the optimal value of k, we used the elbow method that derives from the within-cluster sum of squared (wss). the elbow method is a heuristic approach in determining the number of clusters for k-means or k-nn. the equation of wss is described by eq. (11): 𝑊𝑆𝑆 = ∑ ∑ (𝑋𝑖 − 𝜇𝑘 ) 2 𝑋𝑖∈ 𝐶𝑘 𝑘 𝑘=1 (11) where; ck = cluster of k µk = the mean value of the data that point to the cluster xi = an observation to the ck the optimal value of k is at the elbow curve, or the distortion point that starts decreasing linearly, as described in fig. 6. although the value of k = 2 looks like there is a curve/ distortion from k= 2 until the k = 4, the decrease is still significant and not linear. due to that, for this research, the k-value was k = 4. 107 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 fig. 4: the elbow method. 3.3.2 building the model once we have determined the k-value for k-nn, we started training and building the machine learning model. the building model data was divided into training data and testing data with a 70:30 ratio, as explained in section 3.2. during the building model process, once the model was built, the prediction of the evaluation data was ready to start. we tested it file-by-file to evaluate how well the model could predict a particular bot. 4. evaluation we evaluated the performance of our techniques based on the confusion matrix in terms of accuracy, precision, recall, f-score, false-negative rate (fnr), and false-positive rate (fpr). a confusion matrix is the most widely used method to evaluate a machinelearning model's performance. the distribution of the results can be seen clearly by creating a confusion matrix from the model. the confusion matrix consisted of a two-dimensional table with the class "actual" and "cluster/projection" in a single-dimension structure and evaluated only two (2) classes. the other dimension was rated as "botnet" positive and "human" negative. thus, the cases were classified into four fractions: false positive (fp), false negative (fn), true positive (tp), and true negative (tn), as shown in table 5. table 5: the confusion matrix for this article prediction (cluster) normal botnet actual (label) normal tn fp botnet fn tp when the data is in the state “true”, either tp or tn, it shows that the classifier predicted it in the correct class. in the “false” state, there was an incorrect prediction class. for example, when the data was in a false negative state, it means that the classifier falsely predicted as negative (normal) where the data was positive (botnet), while the positive and negative indicate botnet or normal class. 108 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 table 6: the explanation of confusion matrix's fraction used in this article fraction module 2 true positive (tp) tp is counted when the model correctly predicted the botnet traffic/ip true negative (tn) tn is counted when the model correctly predicted the normal (negative) traffic/ip false positive (fp) fp is counted when the model incorrectly predicted the normal (negative) traffic as the botnet (positive) traffic/ip false negative (fn) fn is counted when the model incorrectly predicted the botnet (positive) as the normal (negative) traffic/ip the confusion matrix can generate several performance evaluation parameters, but for this research, we focused on accuracy, precision, recall, f-score, false-negative rate (fnr), and false-positive rate (fpr). these parameters were chosen to make a comparison with other researcher’s results that used the same dataset. the overall performance was from the accuracy, but we preferred to compare the overall performance using the f-score. 4.1 performance parameter 4.1.1 accuracy accuracy is often used to measure the overall performance of the machine learning classifier because it is a parameter that measures how often the algorithm correctly classifies a data point. accuracy is the number of correctly predicted data points from all data points where it can be described in the eq. (12) below: 𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = ∑ 𝑡𝑜𝑡𝑎𝑙 𝑐𝑜𝑟𝑟𝑒𝑐𝑡 𝑝𝑟𝑒𝑑𝑖𝑐𝑡𝑖𝑜𝑛 ∑ 𝑑𝑎𝑡𝑎 = 𝑇𝑃+𝑇𝑁 𝑇𝑃+𝑇𝑁+𝐹𝑁+𝐹𝑃 (12) 4.1.2 precision the ‘precision’ parameter is the count of data classified as a botnet (positive) that are genuinely botnet. precision also can be described as in equation (13): 𝑃𝑟𝑒𝑐𝑖𝑠𝑖𝑜𝑛 = 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒 𝑝𝑟𝑒𝑑𝑖𝑐𝑡𝑖𝑜𝑛 𝑡ℎ𝑎𝑡 𝑡𝑟𝑢𝑙𝑦 𝑝𝑜𝑠𝑖𝑡𝑖𝑣𝑒 ∑ 𝑇𝑜𝑡𝑎𝑙 𝑝𝑜𝑠𝑖𝑡𝑖𝑣𝑒 𝑝𝑟𝑒𝑑𝑖𝑐𝑡𝑖𝑜𝑛 = 𝑇𝑃 𝑇𝑃+𝐹𝑃 (13) 4.1.3 recall a recall is also known as sensitivity, where it is the fraction of actual positives that are identified correctly. recall also can be described as the ability of a model to find the relevant cases. 𝑅𝑒𝑐𝑎𝑙𝑙 (𝑇𝑃𝑅) = 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒 𝑝𝑟𝑒𝑑𝑖𝑐𝑡𝑖𝑜𝑛 𝑡ℎ𝑎𝑡 𝑡𝑟𝑢𝑙𝑦 𝑝𝑜𝑠𝑖𝑡𝑖𝑣𝑒 𝐴𝑙𝑙 𝑏𝑜𝑡𝑛𝑒𝑡 𝑑𝑎𝑡𝑎 = 𝑇𝑃 𝑇𝑃+𝐹𝑁 (14) 4.1.4 f-score f1 score is the harmonic combination of recall and precision. f1 score is the equal weight. 𝐹𝑠𝑐𝑜𝑟𝑒 = 2 ∗ 𝑃𝑟𝑒𝑐𝑖𝑠𝑖𝑜𝑛∗𝑅𝑒𝑐𝑎𝑙𝑙 𝑃𝑟𝑒𝑐𝑖𝑠𝑖𝑜𝑛+𝑅𝑒𝑐𝑎𝑙𝑙 (15) 109 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 5. results and discussion the evaluation for the framework was conducted in 2 parts; one was when building the model and the other one was the prediction of novel data using the evaluating data. 5.1 building model this section summarizes the findings during the model building. the performance of the flow-based features and k-nn framework was compared to the performance of the same framework but with additional ica during pre-processing. both performance evaluations are shown in table 7. table 7: the performance comparison of the training model with and without ica accuracy precision recall f1-score fnr fpr without ica 0.9689 0.9831 0.958 0.9704 0.0419 0.01875 with ica 0.969 0.9846 0.9568 0.9705 0.0431 0.0169 this result was evaluated on the testing data split from the building model data illustrated in fig. 3. table 7 lists the parameters used in the evaluation. from the results in table 7, if we compare the accuracy and f-score, there are tiny increments, but the false positive rate (fpr) decreased from 1.88% to 1.69%. 5.2 prediction novel bots ctu-13, the benchmark botnet dataset, is also used by several researchers to evaluate their prediction model’s performance. so, we compared the result from another article that used the same data source and the same evaluation parameter. there were 5 files in evaluating data that were separated before the building model process. the data is described in table 8. table 8: the data number and the botnet type in evaluating data data number bot name data 1 neris data 2 data 6 menti data 8 murlo data 9 neris table 9: performance differences between models with and without ica against novel botnet k-nn model data number accuracy f1-score fpr without ica data 1 0.6708 0.6895 0.2187 data 2 0.7583 0.784 0.0679 data 6 0.7032 0.6041 0.1826 data 8 0.7658 0.2871 0.1547 data 9 0.5067 0.6436 0.1891 with ica data 1 0.7912 0.8298 0.278 data 2 0.6734 0.6958 0.1262 data 6 0.7767 0.7673 0.2995 data 8 0.8005 0.5859 0.2244 data 9 0.7134 0.8222 0.3309 110 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 based on table 9, the model with ica showed a better f score than the model without ica. but, the model without ica showed the lowest fpr compared to the other model. thus, the yellow box in table 9 indicates the best value, either the highest f score or the lowest fpr. since we were focused on the f-score for comparison, we extracted it to table 10. table 10: the f score for both models (with and without ica) data 1 data 2 data 6 data 8 data 9 without ica 0.6895 0.784 0.6041 0.2871 0.6436 with ica 0.8298 0.6958 0.7673 0.5859 0.8222 table 10 shows that 4 files from 5 novel botnet files had the highest f-score using the k-nn model with ica. only one file, file no 2, showed the opposite result. due to that, we agree that the k-nn model with ica performed better than the k-nn model without ica. the result for the k-nn model with ica was compared to other researcher’s results. the results were directly compared with previously reported findings on a novel botnet prediction model that used the same data sources. table 11 summarizes the comparison result and lists the parameters used in every previous article. table 11: performance model comparison between previous researchers parameter data no/ researcher garcia, s., zunino, a., & campo, m. (2014)[42] garcia, s. (2015). [44] kozik, r. (2018) [45] wang, j. & paschalidis, i.c. (2017)[46] fernandez maimo et al. [38] wnh ibrahim et al. recall 1 0.4 1 0.077 0.91 0.91 0.8357 2 0.3 0.88 0.046 0.55 0.95 0.5687 6 0 0 0.12 0.95 1 0.8836 8 0.1 0 0.044 0.76 0.26 0.9424 9 0.1 0.38 0.08 0.38 0.99 0.7171 precision 1 0.5 0.87 0.86 0.73 0.68 0.824 2 0.6 0.96 0.8 0.65 0.88 0.8961 6 0.4 -1 0.69 0.7 0.92 0.6781 8 0.2 0 0.6 0.4 0.47 0.4251 9 0.4 0.72 0.73 0.95 0.89 0.9635 f1 score 1 0.48 0.93 0.14 0.81 0.77 0.8298 2 0.41 0.92 0.088 0.59 0.92 0.6958 6 0.04 0 0.21 0.8 0.96 0.7673 8 0.14 -1 0.082 0.53 0.33 0.5859 9 0.25 0.5 0.14 0.54 0.94 0.8222 based on table 11, in the f-score parameter, our technique defeated other results for data number 8 (red font). however, three out of five novel botnet files hade the highest fscore from fernandez maimo et al. [31]. to measure the overall performance, we calculated the average for each parameter. the average of each data (data from file 1,2,6,8,9) and parameter (precision, recall, and f score) from table 11 are illustrated in fig. 7. these plots show that our method proposed here outperformed the other approaches except fernandez maimo et al. [31]. 111 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 since the fernandez maimo et al. [31] techniques outperformed the overall evaluation, we compared the different approaches they used. for example, fernandez maimo et al. [31] also used flow-based features, but they considered the features from dual-direction, incoming, and outgoing traffic. their approach resembled our technique in that both methods focused on concealment network traffic and used statistical analysis to aggregate the data. fig. 5: the performance comparison among other researchers on botnet classification. 6. conclusion this paper proposes the framework for novel botnet detection that implements data standardization and independent component analysis (ica) during flow-based features pre-processing data. the strength of our framework is that we used flow-based features that have the benefits of detecting traffic from the concealment network. other than that, the complexity and processing time can also be minimized by flow-based features compared to content-based ones. also, for aggregation, for the quick detection method, we used the shortest time interval. our approach can be applied to botnet concealment and new/novel forms of a botnet. the use of data standardization and independent component analysis (ica) improves key rating attributes and classification outcomes. however, the overall result is still not the best relative to other previous approaches. nevertheless, it generated an improved result using data standardization and independent component analysis (ica). we can also assume that behavior analysis caused some noise to the pattern. future directions are connected to enhancing the collection of functionalities. further developments are expected to lead to a deeper understanding of the nature of the selection of functions. acknowledgement the authors wish to thank universiti teknologi malaysia (utm) for its support under research university grant vot-20h04, malaysia research university network (mrun) vot 4l876, and the fundamental research grant scheme (frgs) vot (frgs/1/2018/ict04/utm/01/1) supported by the ministry of higher education malaysia. the work is partially supported by the spev project (id: 2102-2021), faculty of informatics and management, university of hradec kralove. we are also grateful for the 112 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 support of ph.d. students michal dobrovolny and sebastien mambou in consultations regarding application aspects from hradec kralove university, czech republic. the apc was funded by the spev project 2102/2021, faculty of informatics and management, university of hradec kralove. references [1] ibrahim, w.n.h., selamat, a., anuar, s., & krejcar, o. (2019). clustering botnet behavior using k-means with uncertain data, frontiers in artificial intelligence and applications vol. 318. pp.244–257. [2] liang, x. & znati, t. (2019). on the performance of intelligent techniques for intensive and stealthy ddos detection, computer networks vol. 164. p.106906. [3] gross, g. (2016). detecting and destroying botnets, network security vol. 2016, no. 3. pp.7– 10. [4] white ops. (2018). retrieved june 1, 2020, https://www.whiteops.com/blog/9-of-the-mostnotable-botnets. [5] kolias, c., kambourakis, g., stavrou, a., & voas, j. (2017). ddos in the iot: mirai and other botnets, computer vol. 50, no. 7. pp.80–84. [6] eremin, a. (2019). retrieved june 1, 2020, https://securelist.com/bots-and-botnets-in2018/90091/. [7] khan, r.u., zhang, x., kumar, r., sharif, a., golilarz, n.a., & alazab, m. (2019). an adaptive multi-layer botnet detection technique using machine learning classifiers, applied sciences (switzerland) vol. 9, no. 11. p.2375. [8] patsakis, c., casino, f., & katos, v. (2020). encrypted and covert dns queries for botnets: challenges and countermeasures, computers & security vol. 88. p.101614. [9] bezerra, v.h., da costa, v.g.t., barbon junior, s., miani, r.s., & zarpelão, b.b. (2019). iotds: a one-class classification approach to detect botnets in internet of things devices, sensors (switzerland) vol. 19, no. 14. p.3188. [10] wang, y.-h., li, z.-n., xu, j.-w., yu, p., chen, t., & ma, x.-x. (2020). predicted robustness as {qos} for deep neural network models, journal of computer science and technology vol. 35, no. 5. pp.999–1015. [11] prasad, k.m., reddy, a.r.m., & rao, k.v. (2020). bartd: bio-inspired anomaly based real time detection of under rated app-ddos attack on web, journal of king saud university computer and information sciences vol. 32, no. 1. pp.73–87. [12] su, s.c., chen, y.r., tsai, s.c., & lin, y.b. (2018). detecting p2p botnet in software defined networks, security and communication networks vol. 2018. pp.1–13. [13] mahmoud, m., nir, m., & matrawy, a. (2015). a survey on botnet architectures, detection and defences, international journal of network security vol. 17, no. 3. pp.272–289. [14] mathur, l., raheja, m., & ahlawat, p. (2018). botnet detection via mining of network traffic flow, procedia computer science vol. 132. pp.1668–1677. [15] kupreev, o., badovskaya, e., & gutnikov, a. (2019). retrieved june 1, 2020, https://securelist.com/ddos-report-q3-2019/94958/. [16] aamir, m. & zaidi, s.m.a. (2019). clustering based semi-supervised machine learning for ddos attack classification, journal of king saud university computer and information sciences. [17] singh, m., singh, m., & kaur, s. (2019a). detecting bot-infected machines using dns fingerprinting, digital investigation vol. 28. pp.14–33. [18] bazrafshan, z., hashemi, h., fard, s.m.h., & hamzeh, a. (2013). a survey on heuristic malware detection techniques, ikt 2013 2013 5th conference on information and knowledge technology no. may. pp.113–120. [19] assadhan, b., bashaiwth, a., al-muhtadi, j., & alshebeili, s. (2018). analysis of p2p, irc and http traffic for botnets detection, peer-to-peer networking and applications vol. 11, no. 5. pp.848–861. 113 https://www.whiteops.com/blog/9-of-the-most-notable-botnets https://www.whiteops.com/blog/9-of-the-most-notable-botnets https://securelist.com/bots-and-botnets-in-2018/90091/ https://securelist.com/bots-and-botnets-in-2018/90091/ https://securelist.com/ddos-report-q3-2019/94958/ iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 [20] alauthaman, m., aslam, n., zhang, l., alasem, r., & hossain, m.a. (2018). a p2p botnet detection scheme based on decision tree and adaptive multilayer neural networks, neural computing and applications vol. 29, no. 11. pp.991–1004. [21] santana, d., suthaharan, s., & mohanty, s. (2018). what we learn from learning understanding capabilities and limitations of machine learning in botnet attacks. [22] rauf, m.a.a.a., asraf, s.m.h., & idrus, s.z.s. (2020). malware behaviour analysis and classification via windows dll and system call, journal of physics: conference series vol. 1529, no. 2. [23] resende, p.a.a. & drummond, a.c. (2018). a survey of random forest based methods for intrusion detection systems, acm computing surveys vol. 51, no. 3. pp.1–36. [24] tobiyama, s., yamaguchi, y., shimada, h., ikuse, t., & yagi, t. (2016). malware detection with deep neural network using process behavior, proceedings international computer software and applications conference vol. 2. pp.577–582. [25] muhtadi, a.f. & almaarif, a. (2020). analysis of malware impact on network traffic using behavior-based detection technique, international journal of advances in data and information systems vol. 1, no. 1. pp.17–25. [26] apruzzese, g. & colajanni, m. (november 2018). evading botnet detectors based on flows and random forest with adversarial samples. paper presented at nca 2018 2018 ieee 17th international symposium on network computing and applications. [27] beigi, e.b., jazi, h.h., stakhanova, n., & ghorbani, a.a. (2014). towards effective feature selection in machine learning-based botnet detection approaches, 2014 ieee conference on communications and network security, cns 2014 pp.247–255. [28] cabeza, l.f., solé, c., castell, a., oró, e., & gil, a. (2016). unsupervised network intrusion detection systems for zero-day fastspreading attacks and botnets payam, international journal of digital content technology and its applications(jdcta) vol. 10, no. 2. [29] singh, m., singh, m., & kaur, s. (2019b). detecting bot-infected machines using dns fingerprinting, digital investigation vol. 28. pp.14–33. [30] malik, r. & alankar, b. (2019). botnet and botnet detection techniques, international journal of computer applications vol. 178, no. 17. pp.8–11. [31] koroniotis, n., moustafa, n., sitnikova, e., & turnbull, b. (2019). towards the development of realistic botnet dataset in the internet of things for network forensic analytics: bot-iot dataset, future generation computer systems vol. 100. pp.779–796. [32] huda, s., abawajy, j., al-rubaie, b., pan, l., & hassan, m.m. (2019). automatic extraction and integration of behavioural indicators of malware for protection of cyber–physical networks, future generation computer systems vol. 101. pp.1247–1258. [33] bou-harb, e., debbabi, m., & assi, c. (2014). on fingerprinting probing activities, computers and security vol. 43, no. january 2012. pp.35–48. [34] palmieri, f., fiore, u., & castiglione, a. (2014). a distributed approach to network anomaly detection based on independent component analysis, concurrency and computation: practice and experience vol. 26, no. 5. pp.1113–1129. [35] mao, c.-h., lin, c.-c., pan, j.-y. (tim), chang, k.-c., faloutsos, c., & lee, h.-m. ( 2012). eigenbot: foiling spamming botnets with matrix algebra. paper presented at proceedings of the acm sigkdd workshop on intelligence and security informatics isi-kdd ’12, new york, new york, usa. [36] ehsan, k. & hamid, reza shahriari. (2018). botrevealer: behavioral detection of botnets based on botnet life-cycle, international journal of information security vol. 10, no. 1. pp.55– 61. [37] stevanovic, m. & pedersen, j.m. (2015). on the use of machine learning for identifying botnet network traffic, journal of cyber security and mobility vol. 4, nos. 2–3. pp.1–32. [38] fernandez maimo, l., perales gomez, a.l., garcia clemente, f.j., gil perez, m., & martinez perez, g. (2018). a self-adaptive deep learning-based system for anomaly detection in 5g networks, ieee access vol. 6. pp.7700–7712. [39] debashi, m. & vickers, p. (2018). sonification of network traffic for detecting and learning about botnet behavior, ieee access vol. 6. pp.33826–33839. 114 iium engineering journal, vol. 23, no. 1, 2022 ibrahim et al. https://doi.org/10.31436/iiumej.v23i1.1789 [40] gezer, a., warner, g., wilson, c., & shrestha, p. (2019). a flow-based approach for trickbot banking trojan detection, computers and security vol. 84. pp.179–192. [41] garg, s., peddoju, s.k., & sarje, a.k. (2016). scalable p2p bot detection system based on network data stream, peer-to-peer networking and applications vol. 9, no. 6. pp.1209–1225. [42] garcia, s., zunino, a., & campo, m. (2014). "identifying, modeling and detecting botnet behaviors in the network". [43] han, w., xue, j., wang, y., liu, z., & kong, z. (2019). malinsight: a systematic profiling based malware detection framework, journal of network and computer applications vol. 125, no. october 2018. pp.236–250. [44] garcia, s. (2015). modelling the network behaviour of malware to block malicious patterns . the stratosphere project : a behavioural ips, virus bulletin no. september. pp.1–8. [45] kozik, r. (2018). distributing extreme learning machines with apache spark for netflowbased malware activity detection, pattern recognition letters vol. 101. pp.14–20. [46] wang, j. & paschalidis, i.c. (2017). botnet detection based on anomaly and community detection, ieee transactions on control of network systems vol. 4, no. 2. pp.392–404. 115 iium engineering journal volume 24 no 1 issue january 2023 copyright notice consent to publish: the author(s) agree to publish their articles with iium press. declaration: the author(s) declare that the article has not been published before in any form and that it is not concurrently submitted to another publication, and also that it does not infringe on anyone's copyright. the author(s) holds the iium press and editors of the journal harmless against all copyright claims. transfer of copyright: the author(s) hereby agree to transfer the copyright of the article to iium press, which shall have the non-exclusive and unlimited right to publish the article in any form, including in electronic media. for the article with more than one author, the corresponding author confirms that he/she is authorized by his/her co-author(s) to grant this transfer of copyright. the iium engineering journal follows the open access policy. all articles published open access will be immediately and permanently free for everyone to read, download, copy and distribute for noncommercial purposes. iium engineering journal at https://journals.iium.edu.my/ejournal is licensed under a creative commons attribution-noncommercial 4.0 international license. i iium engineering journal volume 24, issue 1, january 2023 https:/doi.org/10.31436/iiumej.v24i1 iium engineering journal editors chief editor ahmad faris ismail, iium, malaysia technical editor sany izan ihsan, iium, malaysia executive editor ahm zahirul alam, iium, malaysia associate editor nor farahidah za’bah, iium, malaysia language editor lynn mason, malaysia copy editor hamzah mohd. salleh, iium, malaysia malay translator nurul arfah che mustapha, iium, malaysia editorial board members abdullah al-mamun, iium, malaysia abdumalik rakhimov, iium, malaysia aishah najiah bt. dahnel, iium, malaysia alya naili binti rozhan, iium, malaysia norsinnira bt. zainul azlan, iium, malaysia hanafy omar, saudi arabia hazleen anuar, iium, malaysia konstantin khanin, university of toronto, canada ma'an al-khatib, iium, malaysia meftah hrairi, iium, malaysia mohamed b. trabia, united states mohammad s. alam, texas a&m university-kingsville, united states mustafizur rahman, national university singapore, singapore ossama abdulkhalik, michigan technological university, united states mohamed hadi habaebi, iium, malaysia mohd. sultan ibrahim bin shaik dawood, iium, malaysia muhammad ibn ibrahimy, iium, malaysia nor fadhillah mohamed azmin, iium, malaysia waqar asrar, iium, malaysia aims & scope of iiumengineering journal the iium engineering journal, published biannually (january and july), is a carefully refereed international publication of international islamic university malaysia (iium). contributions of high technical merit within the span of engineering disciplines; covering the main areas of engineering: electrical and computer engineering; mechanical and manufacturing engineering; automation and mechatronics engineering; material and chemical engineering; environmental and civil engineering; biotechnology and bioengineering; engineering mathematics and physics; and computer science and information technology are considered for publication in this journal. contributions from other areas of engineering and applied science are also welcomed. the iium engineering journal publishes contributions under regular papers and invited review papers. it also welcomes contributions that address solutions to the specific challenges of the developing world, and address science and technology issues from an islamic and multidisciplinary perspective. referees’ network all papers submitted to iium engineering journal will be subjected to a rigorous reviewing process through a worldwide network of specialized and competent referees. each accepted paper should have at least two positive referees’ assessments. submission of a manuscript a manuscript should be submitted online to the iium-engineering journal website at https://journals.iium.edu.my/ejournal. further correspondence on the status of the paper could be done through the journal website. ii international advisory committee a. anwar, united states abdul latif bin ahmad, malaysia farzad ismail, usm, pulau pinang, malaysia hanafy omar, saudi arabia hany ammar, united states idris mohammed bugaje, nigeria k.b. ramachandran, india kunzu abdella, canada luis le moyne, isat, university of burgundy, france m mujtaba, united kingdom mohamed ai-rubei, ireland mohamed b trabia, united states syed kamrul islam, united states tibor czigany, budapest university of technology and economics, hungary yiu-wing mai, the university of sydney, australia. published by: iium press, international islamic university malaysia jalan gombak, 53100 kuala lumpur, malaysia phone (+603) 6421-5014, fax: (+603) 6421-6298 whilst every effort is made by the publisher and editorial board to see that no inaccurate or misleading data, opinion or statement appears in this journal, they wish to make it clear that the data and opinions appearing in the articles and advertisement herein are the responsibility of the contributor or advertiser concerned. accordingly, the publisher and the editorial committee accept no liability whatsoever for the consequence of any such inaccurate or misleading data, opinion or statement. iium engineering journal issn: 1511-788x e-issn: 2289-7860 iii iium engineering journal iv volume 24, issue 1, january 2023 https:/doi.org/10.31436/iiumej.v24i1 table of contents chemical and biotechnology engineering solid state fermentation of turmeric rhizomes with aspergillus sp. to improve yield and composition of extracted turmeric oil muhammad yusuf abduh, asri ifani ramawati, tinta komariyah and yohanes theda 1 12 effect of the lignocellulolytic substrates and fermentation process parameters on myco-coagulant production for water treatment maroua fellah, md zahangir alam, abdullah al-mamun, nasserldeen ahmed khabbashi, nurul sakinah engliman and sonia hadj arab 13 26 the optimization of growth condition of the bacteria producing cold-active proteolytic enzyme from the antarctic region muhammad asyraf abd latip, noor faizul hadry nordin, siti aisyah alias, jerzy smykla, faridah yusof and mohd azrul naim mohamad 27 39 rhodopseudomonas palustris collagen-like recombinant protein purification using an aqueous two-phase system nursyahidatul azwa awang, azura amid and zatul iffah arshad 40 56 electrical, computer and communications engineering battery energy storage system (bess) modeling for microgrid zahir zulkifly, siti hajar yusoff, nor liza tumeran and nur syazana izzati razali 57 74 analytical model of subthreshold swing for junctionless double gate mosfet using ferroelectric negative capacitance effect hakkee jung 75 87 robust and imperceptible watermarking on medical images using coefficient pair modification ledya novamizanti, andriyan bayu suksmono, donny danudirdjo and gelar budiman 88 105 multi-objective mayfly optimization in phase optimization of ofdm abdul azeez and suraiya tarannum 106 121 design of miniaturized antenna for iot applications using metamaterial ahmad zamani jusoh, nur fatihah husain, norun farihah abdul malek, farah nadia mohd isa and sarah yasmin mohamad 122 – 137 comparative assessment of numerical techniques for weibull parameters’ estimation and the performance of wind energy conversion systems in nigeria ignatius k. okakwu, daniel o. akinyele, olakunle e. olabode, titus o. ajewole, emmanuel s. oluwasogo and ajibola o. oyedeji 138 157 engineering mathematics and applied science higher derivative block method with generalised steplength for solving first-order fuzzy initial value problems kashif hussain, oluwaseun adeyeye and nazihah ahmad 158 169 iium engineering journal iv volume 24, issue 1, january 2023 https:/doi.org/10.31436/iiumej.v24i1 table of contents contd. materials and manufacturing engineering a quick and facile solution-processed method for pedot:pss transparent conductive thin film mei bao lee, chiew tin lee, william woei fong chong and suhaila mohd sanip 170 182 a hybrid of kansei engineering (ke) and analytical hierarchy process (ahp) to develop conceptual designs of portable oil spill skimmer rprakash ramanathan, lokman bin abdullah, muhammad hafidz fazli bin md fauadi, muhammad syafiq bin syed mohamed and khairun najmi bin kamaludin 183 198 mechanical and aerospace engineering terminal control area complexity measurement using simulation model rully medianto, naflah mutiara adinda, yazdi ibrahim jenie, hisar manongam pasaribu and hari muhammad 199 212 performance comparison between predictive functional control and pid algorithms for an automobile cruise control system mohamed al-sideque zainuddin, muhammad abdullah, salmiah ahmad, mohd suhaimi uzir and zaid mujaiyid putra ahmad baidowi 213 225 the ricochet of spinning spheres off water riyah najim kiter, mazin yaseen abbood and omar hassoon 226 243 mechatronics and automation engineering plc-based pid controller for real-time ph neutralization process using palm oil mill effluent azavitra zainal, norhaliza abdul wahab and mohd ismail yusof 244 255 solar thermal process parameters forecasting for evacuated tubes collector (etc) based on rnnlstm muhammad ali akbar, ahmad jazlan, muhammad mahbubur rashid, hasan firdaus mohd zaki, muhammad naveed akhter and abd halim embong 256 268 an integrated rrt*smart-a* algorithm for solving the global path planning problem in a static environment heru suwoyo, andi adriansyah, julpri andika, abu ubaidillah and mohamad fauzi zakaria 269 284 control strategy for power assist upper limb rehabilitation robot with the therapist’s motion intention prediction zulikha ayomikun adeola-bello, norsinnira zainul azlan and salmah anim abu hassan 285 300 non-verbal human-robot interaction using neural network for the application of service robot zubair adil soomro, abu ubaidah shamsudin, ruzairi abdul rahim, andi adrianshah and mohd hazeli 301 – 318 repurposing a sampling-based planner for a six-degree-of-freedom manipulator to avoid unpredictable obstacles hafiz iman and raisuddin khan 319 332 0-jan2023-v24n1.pdf 0-vol24n1_january-2023.pdf 0-1-vol24-no-1.pdf coverp.pdf front_matters-22.pdf toc-iium engineering journal-v3.pdf toc-iium engineering journal-v3.pdf compiled journal vol 12 no 2.pdf application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 numerical modelling of bird strike on a rotating engine blades based on variations of porosity density sharis-shazzali shahimi1, nur azam abdullah1*, meftah hrairi1, ameen topa2,3 and ahmad faris ismail1 1 structural mechanics and dynamics research group, department of mechanical engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia 2 insitute of transportation infrastructure, universiti teknologi petronas, seri iskandar, 32610, malaysia 3 faculty of ocean engineering technology and informatics, universiti malaysia terengganu, kuala terengganu, 21300, malaysia *corresponding author: azam@iium.edu.my (received: 14th july 2021; accepted: 21st september 2021; published on-line: 4thjanuary 2022) abstract: a numerical investigation is conducted on a rotating engine blade subjected to a bird strike impact. the bird strike is numerically modelled as a cylindrical gelatine with hemispherical ends to simulate impact on a rotating engine blade. numerical modelling of a rotating engine blade has shown that bird strikes can severely damage an engine blade, especially as the engine blade rotates, as the rotation causes initial stresses on the root of the engine blade. this paper presents a numerical modelling of the engine blades subjected to bird strike with porosity implemented on the engine blades to investigate further damage assessment due to this porosity effect. as porosity influences the decibel levels on a propeller blade or engine blade, the damage due to bird strikes can investigate the compromise this effect has on the structural integrity of the engine blades. this paper utilizes a bird strike simulation through an ls-dyna pre-post software. the numerical constitutive relations are keyed into the keyword manager where the bird’s sph density, a 10 ms simulation time, and bird velocity of 100 m/s are all set. the blade rotates counter-clockwise at 200 rad/s with a tetrahedron mesh. the porous regions or voids along the blade are featured as 5 mm diameter voids, each spaced 5 mm apart. the bird is modelled as an elastic-plastic-hydrodynamic material model to analyze the bird’s fluid behavior through a polynomial equation of state. to simulate the fluid structure interaction, the blade is modelled with johnson-cook material model parameters of aluminium where the damage of the impact can be observed. the observations presented are compared to previous study of a bird strike impact on non-porous engine blades. abstrak: penyelidikan berangka telah dijalankan ke atas bilah enjin berputar tertakluk kepada impak pelanggaran burung. pelanggaran burung tersebut telah dimodelkan secara berangka sebagai silinder gelatin dengan hujungnya berbentuk hemisfera demi mensimulasikan impaknya ke atas bilah enjin yang berputar. pemodelan berangka bilahbilah enjin yang berputar tersebut menunjukkan bahawa pelanggaran burung mampu menyebabkan kerosakan teruk terhadap bilah enjin terutamanya apabila bilah enjin sedang berputar oleh sebab putaran menghasilkan tekanan asal di pangkal bilah enjin. kajian ini mengetengahkan pemodelan berangka ke atas bilah-bilah enjin tertakluk kepada pelanggaran burung terhadap bilah-bilah enjin yg mempunyai keliangan demi menyelidik dan menilai kerosakan kesan daripada keliangan tersebut. keliangan juga mempengaruhi tahap-tahap desibel ke atas bilah kipas ataupun bilah enjin, kerosakan hasil serangan 412 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 burung boleh menterjemah tahap ketahanan struktur integriti bagi bilah-bilah enjin tersebut. penyelidikan ini mengguna pakai perisian “ls-dyna pre-post” untuk simulasi pelanggaran burung. hubungan konstitutif berangka telah dimasukkan sebagai kata kunci di mana ketumpatan sph burung, masa simulasi 10ms, dan halaju burung ditetapkan kepada 100 m/s. bilah tersebut berputar pada 200 rad/s arah lawan jam dengan jejaring tetrahedron. kawasan berliang atau kosong di sepanjang bilah ditetapkan diameternya kepada 5 mm, dan dijarakkan 5 mm di antara satu sama lain. burung pula dimodelkan sebagai material “elastic-plastic-hydrodynamic” untuk mengkaji sifat bendalir burung melalui persamaan polinomial. demi mensimulasi interaksi struktur bendalir, bilah tersebut dimodelkan sebagai parameter aluminium material “johnson cook” di mana kerosakan daripada impak tersebut dapat diteliti. penelitian-penelitian tersebut dibandingkan dengan kajian terdahulu ke atas serangan burung terhadap bilah-bilah enjin tidak berliang. keywords: bird strike; rotating engine blades; porosity; sph; structural damage 1. introduction bird strikes are one of the most dangerous phenomena threatening aircraft in aviation today. as bird strikes can cause severe damage to an aircraft, especially during take-off and landing, numerous attempts must be made to ensure aircraft are structurally robust, strong, and able to withstand high speed impacts. these birds can strike at any part of the aircraft such as the wings, parts of the fuselage, the windscreen, and the engine. research and experimentations are important to predict and analyze these bird strike impacts as bird strikes have become more frequent in recent times [1]. many aircraft, civilian and military, have been destroyed or damaged by bird strikes; increasing aircraft expenses and lives lost due to these dangerous strikes, calling for a need to make aircraft parts more robust. although birds can strike at any part of the aircraft, the engine is the most dangerous part the bird can impact. if the engines are damaged, this can cause the pilot to lose control of the aircraft, prompting the pilot to attempt an emergency landing. as such, the aircraft must have sufficient power to land safely in the event of bird impact. in the specific event of bird impact to the engine, bird strikes will most probably damage the engine, causing the aircraft to crash land and destroy the aircraft, losing many lives. it is essential to predict and assess these bird strikes on the engine turbine blades during flight. bird strikes were already tested through experimentation during the early 80s. the earliest experimental tests were conducted by wilbeck [2]. the basis of the experimental procedures was conducted through liu et al. [3] on flat plates and guan et al. [4] with fan rotor blades. in these experiments, the bird was modelled as a fluid structure and the design of the bird changed over the years from a spherical model, to cylindrical model, and into the hemispherical-ended cylinder that is the most frequent model in use today. the bird’s mass density is modelled as a gelatin structured bird that can be fired onto the aircraft part, thus analyzing the damage of the aircraft part. numerical simulations have since been more in favor as compared to experimentation. throughout the years, experimentation has become expensive by damaging aircraft parts during testing, and repeated use of gelatin synthetic birds is unsanitary. however, wilbeck’s experiment basis has since been discussed, referred, and verified by other researchers today. the discussions of these impacts to engine blades state that the bird transfers its momentum to the engine blades due to the oscillations of the blade’s rotation [2]. wilbeck analyzed these oscillations and blade response to accurately predict the impact loads of the synthetic 413 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 birds. with these impact loads, comparisons can be made with several different types of aircraft parts impacted by bird strikes. 2. bird strike engine blade structural integrity many numerical simulations have been conducted and expanded pertaining to the structural integrity and materials of aircraft structures [5]. these works discuss the damage and cracking of several aircraft wing boxes. bird strikes must be considered in these research analyses as part of the impact loads that can cause these damage threats to the aircraft structural integrity, especially to the aircraft engine’s blades, as mentioned. there is a gap in the research pertaining to the structural damage on engine blades where the engine blade’s rotational oscillations are involved. most of the research on bird strikes have shown the blade as static where there is in fact blade rotation. there is currently a gap in analysis and numerical modelling in which bird strike impacts the blades as dynamic rotations. a numerical analysis conducted by shahimi et al. [8] and vignjevic et al. [9] has shown that centrifugal forces due to rotation contribute to the loads and stresses experienced by the engine blades as they rotate. both these analyses assess the damage of a numerically modelled engine blade subjected to bird strike impact. even after impact, the stresses persist and affect the structural integrity of the blade. research on aviation has also expanded to include porosity in the wings and blade structure [10], pertaining the need to further expand the scope of bird strike impact on these types of configurations. porosity on aircraft wings and blades have an adverse effect on these aircraft parts in that it can weaken the structural integrity of those mentioned parts due to the holes punctured on the surface of the wing or blade. the trade-off here would be to analyze the damage if such a configuration were to be established on the aircraft parts versus the advantages that porosity offers. the aerodynamics of a porous wing were presented as variations in lift coefficient, drag coefficient, and lift versus drag as a function of porosity. these aerodynamic factors had the adverse effect that porosity on the wing structure shows close agreement with the behavior of the lift coefficient slope and a similar trend in the performance of the lift slope [10]. however, these aerodynamic changes due to porosity, while good, must be analyzed with the structural compromise that might happen in a bird strike event. similarly, methods of reducing noise on aircraft propeller blades were presented where an experimental investigation on the effect of a ‘butterfly acoustical skin’ on the acoustic performance of two-bladed propellers with a rotational speed [11]. the paper discusses different micro and nanostructures of porous scales, applying it fully to the skin surface of a two-bladed propeller. the experiment’s measurements of noise frequency on the porous surface skin are significant, where even a small diameter hole of around 0.5mm to 1.25mm can reduce the wave drag and large side forces and redistribute the pressure on the outer surface by establishing communication between highand low-pressure regions in the holes on the surface of the blade. the studies show that noise reduction of as much as 4 db for a rotating propeller with a ‘butterfly acoustical skin’ with a porous region compared to a hollow region with 2 db [11]. this is a good step into more silent propellers in aviation but as with the mentioned aerodynamics of a wing, this has an adverse effect on the structural integrity of the blade structure in the event of a bird strike. based on all these analyses and observations, this paper assesses the damage of a porous engine blade subjected to a bird strike impact. the numerical simulation was conducted with an ls-dyna prepost software to visualize a rotational porous engine blade impacted by an sph bird model with mass and density parameters [12]. this numerical analysis method 414 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 was validated through a study of parametric engine blades by vignjevic et al. [9]. the engine blade structure was modelled with 5 mm diameter holes punctured on the leading edge of the blades and a johnson-cook failure model constant was implemented through the lsdyna keyword manager. 3. bird model 3.1 bird geometry and sph in bird strike analysis, establishing the method, geometry and bird model is an essential part of the numerical analysis. the smoothed particle hydrodynamics (sph) method is the most common and widely used in numerical simulations for any bird strike cases. various approaches and other methods were presented and compared to be referred in a single study to differentiate the approaches to bird strike modelling [13]. the lagrangian method and the rigid bird model are presented. the method presents the bird model as a geometry mesh with distinctive shapes, whether spherical, cylindrical, or cylindrical with hemispherical ends. however, a cylinder with hemispherical ends does more closely resemble an artificial bird. this model can establish a better bird pressure history in real time with more accuracy during testing. the lagrangian and bird rigid body method, however, shows that during the impact of the bird, the meshes move together and are not treated as individual particles. as the bird impacts the aircraft, large indentations on the aircraft part would show damage at the point of splatter impact with the bird, concentrating the splatter to a single point, rather than to a more diverse splatter that a real bird would produce. this is the advantage that the sph method can present, where each individual particle of the mesh distortions carries the mass, velocity and material law assigned to each particle. as the splatter occurs, a more diverse spread is shown beyond the point of impact, where each particle would then impact other parts of the aircraft, damaging the parts and accurately predicting the analysis. figure 1 presents the sph model of the bird used in this numerical analysis. fig. 1: bird model sph. length to radius ratio equal to two. 3.2 bird parameters and material model the bird parameters are first established as density and diameter of the hemisphere as a function of the bird’s mass. the equations are revised by banerjee et al. [14] as the johnson cook failure constants are also established together further in the paper. the equations of density and diameter of the bird model are presented below: 𝜌 = −0.063(𝑙𝑜𝑔10 𝑚) + 1.148 (1) based on these two relationships, with a density 𝜌 = 950 𝑘𝑔/𝑚3 is obtained to determine the mass, 𝑚 to be 1.145 kg. the volume of the bird model is then determined as: 415 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 𝑉 = 𝑚 𝜌 = 1.205.10−3 𝑚3 (2) 𝑉 = 5𝜋𝐷3 12 → 𝐷 = 0.097 𝑚 (3) referring to eq. (2), the volume is then used to calculate the diameter and length of the bird model as 0.097m and 0.194m, respectively, as the length to radius ratio is equal to two. establishing the material of the bird would often depend on the internal organs of the bird, as would depend on different bird sizes or species. in numerical modelling, the bird’s flesh, blood, and bones must be modelled as close to a real bird’s innards as possible, where gelatin has been established as one of the materials used in simulating bird strikes. real birds were launched from pressure nozzles to strike aircraft parts during early experimentations but this practice has since died down due to it being unsanitary as well as inhumane. having to reuse or replace each bird during testing was not practical. in wilbeck’s experiments, observations show that an important factor in bird strikes are the fact that birds can be considered as a fluid during high velocity impacts. hence the use of sph model would align with this factor as the splatter would spread the organs further. as such, dar et al. [12] proposed the use of elastic-plastic-hydrodynamic (eph) material model to analyze the bird behavior through a polynomial equation of state. this is implemented through the ls-dyna keyword manager in this paper. the pressure-density relationship equation of state for the bird is expressed as an isotropic and non-viscous model, allowing the model to be used as a large strain during deformation and be defined with the yield stress and tangent modulus of the engine blade material. the pressure p is shown below: 𝑃 = 𝐶0 + 𝐶1𝜇 + 𝐶2𝜇 2 + 𝐶3𝜇 3 + (𝐶4 + 𝐶5𝜇 + 𝐶6𝜇 2)𝐸 (4) the internal energy, e and the seven polynomial coefficients, 𝐶𝑖 are the basis of the polynomial equation of state and can be determined to model birds accurately. the relative density, 𝜇 is expressed as the ratio of the instantaneous density 𝜌 to initial density 𝜌0 in eq. (5): 𝜇 = ( 𝜌 𝜌0 ) − 1 (5) as the bird is considered a fluid, banerjee et al. states the coefficients 𝐶4, 𝐶5, 𝐶6 are set to zero to match the behaviour of water. the equilibrium conditions would also mean that 𝐶0 is set to zero. therefore, the physical properties of the bird are presented below in table 1. table 1: bird physical properties [12] density [kg/m3] shear modulus [gpa] yield stress [mpa] c1 c2 c3 950 2 0.02 2.1x109 6.2 10.1 4. porous engine blade 4.1 blade material model a johnson-cook material model is implemented in this paper as the material model of the engine blades. the damage assessed in this paper with a porous engine blade can be compared to the numerical computational bird strike by shahimi et al. [8], it can be observed how a porous blade would compromise the structural integrity of the engine blade during 416 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 bird strikes. high impact velocity would cause high elastic and inelastic strains, where there would be an impact load interaction between the bird and the engine blade. the johnsoncook material is expressed with this high elastic and inelastic strain, thereby accurately simulating the bird strike computationally. the relation is expressed as follows: 𝜎𝑒𝑞 = [𝐴 + 𝐵𝜀𝑝 𝑛 ][1 + 𝑐𝑙𝑛(𝜀̇∗)][1 − 𝑇∗𝑚] (6) the equivalent stress, 𝜎𝑒𝑞 is expressed as a function of plastic strain 𝜀, strain rate 𝜀̇ and temperature, 𝑇. the function’s constants are expressed in table 2 by determining the constants of yield stress a, strain hardening parameter b, strain hardening exponent n, strain rate sensitivity parameter c, and temperature exponent 𝑚 for the material properties of aluminium. the material properties are implemented together with the equation of state as discussed previously in the bird model. table 2: johnson-cook failure model constants for aluminium [14] yield stress [mpa] strain hardening parameter [mpa] strain hardening exponent temperature exponent d1 d2 d3 d4 d5 167 590 0.551 0.859 0.0261 0.263 -0.349 0.247 16.8 4.2 porous blade mesh and assembly porosity is defined as the ratio of void volume to the total volume or can also be the ratio of void area to the total area. the term porosity is defined as a section where there are tiny ‘voids’ that are littered on the surface area, that can be either regional or distributed. a regional porosity is more concentrated such as the leading edge of a wing airfoil section whereas distributed porosity would cover the whole cross-sectional area. as such, the relationship is defined as: 𝑃𝑜𝑟𝑜𝑠𝑖𝑡𝑦 (𝑃) = 𝑣𝑜𝑖𝑑 𝑣𝑜𝑙𝑢𝑚𝑒 𝑡𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 (7) this porosity value can be increased depending on how many voids are covered throughout the whole cross-sectional area. the blade model is meshed as a hexahedron element to accurately observe the computational bird strike and is shown in fig. 2(a). figure 2(b) shows the area of 620209.73 mm2 with an arc length of 1099.71 mm at the leading edge where the porous holes are located along the arc. the porosity of the blade is featured as 5 mm diameter voids each spaced 5 mm apart. with around 103 holes distributed at the leading edge along the curvature, the porosity is determined with eq. (7) to be p = 0.32% of the whole blade. the blade assembly consists of 18 blades: equally spaced 20° around the hub. computationally, the bird interacts with the leading edge, slicing the bird slightly before striking the whole of its weight onto the blade leading edge that causes high deformation. 5. computational results 5.1 computational simulation ls-dyna prepost software was used to computationally mesh and simulate the bird strike impact onto a porous engine blade. the initial velocity of the bird is set to v = 120 m/s from the basis of wilbeck’s experiment. the engine blades were set to ω = 200 rad/s angular rotation to simulate a take-off and landing scenario set by vingjevic et al. [9]. much 417 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 of the computational framework has been established through the keyword manager, where each of the bird model coefficients and blade material johnson-cook failure constants were implemented. the numerical framework established by vingjevic et al. [9] provided much of the initial bird velocity, initial rotation of the engine blades and the implementation of a damage model. (a) (b) fig. 2: (a) blade mesh assembly, (b) blade geometry. this paper studies closely the methodology and numerical framework established by vingjevic. vinjevic's failure model was analyzed as a grüneisen parameter, this paper utilizes the keyword manager of ls-dyna in conjunction with the numerical methods done by vingjevic et al. [9]. it is shown that initial stresses appear at the blade's root due to the engine's rotation creating centrifugal forces. the stresses caused by these centrifugal forces can contribute to the load deformation once impact occurs. the termination time was set to 10 ms to allow observation of the bird impact into the subsequent blade after the initial impact. the simulation results are presented in fig. 5 (a), (b), (c), (d), (e), and (f) where the impact loads are shown at 2 ms, 3 ms, 4 ms, 5 ms, 6 ms, and 7 ms respectively. the numerical analysis is presented as impact loads of von-mises effective stress. it is observed in fig. 5 that as the bird impacts the blade, high stress occurs and bends the leading edge of the engine blade, thus causing deformation. 5.2 computational approach validation the computational method presented for this work is validated through a parametric study of bird strikes on engine blades done by vingjevic et al. [9]. the research performed by vingjevic et al. [9] utilised a grüneisen parameter done through ls-dyna keyword manager and the polynomial equations of state of the bird model. the studies show that there are fringe levels and initial stresses (v-m) due to centrifugal forces. figure 4 shows the resultant displacement (mm) or deformations caused by the bird strike impact along the leading edge and located at the porous regions. the trend here indicates that the bending forces and centrifugal force are consistent at the leading edge despite different modelling 418 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 parameters. the displacement shown at the leading edge has proven that the method used here can be utilized to the same effect. fig. 3: initial stresses occur at the root due to centrifugal forces. fig. 4: numerical validation through resultant displacement of present work with the computational result by vingjenic et al. [9] based at the leading-edge. 5.3 computational results the blade mesh geometry does flow well with the impact of the bird during computation. despite the porous regions being more exposed to heavy impact, this allows the structure to be more visualized in many other aspects of the study. effective stress here would be consistent with the validated procedures and show the behavior of the fluid flow structure interaction between the bird and the blade. the effective mean stress thus relates to the equivalent stress from the johnson-cook relationship that was defined. it is now 419 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 observed that a bird strike event can be computationally composed through the implemented method. (a) (b) (c) (d) (e) (f) fig. 5: v-m stresses (kpa) at time intervals (a) 2 ms, (b) 3 ms, (c) 4 ms, (d) 5 ms, (e) 6 ms, and (f) 7 ms. when the bird interacts with the blade structure, the bird behaves as a fluid body, the sph particles move individually, impacting and spreading the splatter throughout the whole surface of the blade. it is observed here that the impact point at the leading edge shows significant damage at the root and the leading edge where the voids are located. the impact at 2 ms in fig. 5(a) is the initial condition just before impact where the bird travels at 120 m/s at the blade rotating at 200 rad/s. at 3 ms in fig. 5(b), the bird smashes into the leading 420 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 edge, causing high deformation, and damaging the blade completely, bending the root at 339 mpa. part of the bird splatter then moves on to the subsequent blade and also damages part of that blade with the stresses increasing for each subsequent time frame as shown in fig. 5 (c), (d), (e), and (f). 5.4 effect of porosity this paper investigates the effect of porosity implemented on the leading edge of a rotating engine blade. the effect of porosity compromises the structural integrity of the engine blade, causing higher deformation. referring to fig. 6(a) shows the porous blade while fig. 6(b) shows a normal engine blade. the deformation of both the engine blades are slight while focusing on the blue region where the deformation of the model with small holes has slightly more deflection in z direction (0.1349 meters) while the model with no hole’s deflection is only 0.1127 meters. due to the holes disturbing the flow of the bird particles, the sph particles become lodged into porous regions, interrupting the flow of impact as compared to the normal engine blade as shown in fig. 5 (c), (d), (e), and (f). (a) (b) fig. 6: z-displacement of jet engine blade after bird strike. this comparison can be further analyzed by the energy absorbed by the jet engine blades. referring to fig. 7, the energy absorbed by both blade types see a slight drop after the initial impact as all the weight of the bird is concentrated at a that one point of impact. at 2 ms, when the bird has impacted the blade, the energy absorbed by both blades; porous and non-porous appear to be similar, since the bird has only impacted the smooth part of both blades, however, as soon as the sph particles spread, it is more prevalent on the porous blade, the particles are lodged in the porous region and the voids absorb the energy of the impact, thus creating a higher change in absorbed energy for the porous blade at 4 ms. at 6 ms, the sph particles have mainly swept off for the non-porous blade, as the flow of particles are much smoother, but for the porous blade, the jump in energy shows that the lodged particles observe a high increase in energy. after, 8 ms, most of the particles have spread around each blade, stabilizing the energy absorbed for the non-porous but increasing much more for the porous region. 421 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 fig. 7: internal energy (j) vs time (s) for porous and non-porous blade. 6. conclusion this paper analyses the damage of a numerically modelled porous engine blade subjected to bird strike. the bird is modelled as a hemispherical sph particle model to accurately splatter the rotating engine blades at 120 m/s. the computational result for the porous blade observes a high impact damage at the porous region where the sph particles spread and lodge within the voids of the porous, creating a high energy absorption compared to a non-porous engine blade for as much as 38.6 kj or 39.63% increase at 4ms. even the non-porous blade has stabilized by the end of 10ms, whereby the porous blade sees an increase in the energy absorbed, damage is prevalent enough for as much as 65 kj or 34.03%. bird strikes are indeed shown to be dangerous even for a normal engine blade used today. the compromise to the structural integrity of the engine blade is significant if a porous engine blade were to be implemented. as the energy absorbed is higher, the impact reaction toward the engine turbine can cause a very dangerous scenario in the event of a bird strike accident. in terms of energy absorbed, since even though the voids contain no mass, the sph particles are still lodged within the voids by the impact energy transferred by the bird momentum from the initial velocity onto the engine blades. the entire strength of the structure however has been reduced, the porosity on the leading edge is minuscule in that it would not really reduce the strength of the structure but since the bird struck directly at that area, the damage is still significant and the energy absorbed is still increased. where there are voids located in the structure, the vibrational energy is still considered even though there is no mass to absorb the energy [11]. acknowledgement the authors would like to express their gratitude and thanks to the ministry of higher education malaysia and the international islamic university malaysia for funding this research under the fundamental research grant scheme for research acculturation of early careers (racer/1/2019/tk09/uiam//1). references [1] thorpe j. (2012) 100 years of fatalities and destroyed civil aircraft due to bird strikes. 30th meeting of the international bird strike committee, 1-36. 422 iium engineering journal, vol. 23, no. 1, 2022 shahimi et al. https://doi.org/10.31436/iiumej.v23i1.2146 [2] wilbeck js, rand jl. (1981) the development of a substitute bird model. j. engineering for gas turbines and power, 103(4):725-730. [3] liu j, li y, gao x. (2014) bird strike on a flat plate: experiments and numerical simulations. int. j. impact engineering, 70:21-37. [4] guan y, zhao z, chen w, gao d. (2008) foreign objecct damage to fan rotor blades of aeroengine part ii: numerical simulation of bird impact. chinese j. aeronautics, 21(4):328334. [5] abdullah na, akbar m, wirawan n, curiel-sosa jl. (2019) structural integrity assessment on cracked composites interaction with aeroelastic constraint by means of xfem. composite structures, 229. [6] wirawan n, abdullah na, akbar, curiel-sosa jl. (2018) analysis on cracked commuter aircraft wing under dynamic cruise load by means of xfem. j. physics: conference series, 1106(1). [7] ahmad mim, curiel-sosa jl, akbar m, abdullah na. (2018) numerical inspection based on quasi-static analysis using rousselier damage model for aluminium wingbox aircraft structure. j. physics: conference series, 1106(1). [8] shahimi ss, abdullah na, hrairi m, ahmad mim. (2021) numerical investigation on the damage of whirling engine blades subjected to bird strike impact. j aeronautics, astronautics and aviation, 53(2):193-200. [9] vignjevic r, orlowski m, de vuyst t, campbell jc. (2013) a parametric study of bird strike on engine blades. int. j. impact engineering, 60:44-57. [10] aldheeb m, asrar w, sulaeman e, omar aa. (2018) aerodynamics of porous airfoils and wings. acta mechanica, 229(9):3915-3933. [11] kovalev is. (2019) buttefly acoustical skin – new method of reducing aero acoustical noise for a quiet propeller. j. engineering mechanics and machinery, 4(1):1-28. [12] dar ua, awais m, mian hh, sheikh mz. (2019) the effect of representative bird model and its impact direction on crashworthiness of aircraft windshield and canopy structure. proceedings of the institution of mechanical engineers, part g: j. aerospace engineering, 233(14):5150-5163. [13] riccio a, cristiano r, saputo s. (2016) a brief introduction to the bird strike numerical simulation. american j. engineering and applied sciences, 9(4):946-950. [14] banerjee a, dhar s, acharyya s, datta d, nayak n. (2015) determination of johnson cook material and failure model constants and numerical modelling of charpy impact test of armour steel. materials science and engineering, 640:200-209. 423 microsoft word 225 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering srikul and sukawat 37 singular vector for a shallow water model chularat srikul and dussadee sukawat department of mathematics, faculty of science, king mongkut's university of technology thonburi, bangkok 10140, thailand. chularat.s@hotmail.com; dusadee.suk@kmutt.ac.th abstract: the atmosphere is a chaotic dynamical system, small errors in the initial condition of an atmospheric model can lead to growing errors in the forecast. in order to reduce uncertainty in the forecast which occur from using only one initial condition from many possible initial conditions, more initial conditions are required. in practice, however, there is only single observation available for the initial condition. in this paper the singular vector has been applied to a single level shallow water model of the atmosphere to generate more initial conditions from one observation. abstrak: atmosfera ialah satu sistem dinamik yang huru-hara. kesilapan kecil dalam kondisi awal model atmosfera boleh membawa kepada kesilapan yang semakin meningkat di dalam ramalan. dalam usaha untuk mengurangkan ketidakpastian dalam ramalan yang berlaku dari menggunakan hanya satu kondisi awal, lebih banyak kondisi awal diperlukan. secara praktikalnya, walau bagaimanapun, hanya terdapat satu pemerhatian yang sedia ada untuk kondisi awal. kajian ini menerangkan vektor tunggal telah digunakan untuk model air cetek tahap atmosfera untuk menghasilkan lebih banyak kondisi awal dari satu pemerhatian. keywords: shallow water model; tangent linear model; adjoint linear model; singular vector 1. introduction the results from numerical models of the atmosphere can sometimes contain large errors. a reason for this lies in the nature of the atmosphere in which very small errors in the initial conditions can lead to large errors in the forecast. implying a perfect forecast system cannot be created because every detail of the initial state of the atmosphere cannot be observed. to cope with this uncertainty, ensemble forecasting which is a collection of difference forecasts and all valid at the same forecast time is applied. kalney [1] discussed a simple model by using the singular vector technique to create ensemble forecasting. wei and frederiksen [2] used lyapunov vectors and singular vectors to examine errors growth and predictability in atmospheric models. khade and hansen [3] found that the singular error growth in the most parts of the attractor is rapid, in that errors can grow almost by a factor of 3 over one step. in this paper the singular vector method is applied to a linearized shallow water model of the atmosphere to generate more initial conditions from the initial data. 2. methodology 2.1 the shallow water model iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering srikul and sukawat 38 the shallow water model is a simplified version of the equations of motion. the momentum, hydrostatic and continuity equations are given below [4]. (1) (2) (3) (4) where r is the density of the atmosphere, p is the pressure, f is the coriolis parameter which is given by 2 sin= ω θf ( ω is the angular velocity of the earth, θ is the latitude), g is the acceleration due to gravity and ,u v and w are the speed of fluid in the ,x y and z directions, respectively. the shallow water model consists of a set of three equations with three dependent variables ( ), , φu v . (5) (6) (7) where φ is the geopotential height. the vertical velocity does not appear explicitly. the total time derivative is given by (8) 2.2 the singular vector method singular vector (sv) method is explained here according to kalney [1]. the initial conditions for the ensemble prediction system (eps) are created to represent the uncertainties in the operational analysis. they are made by adding to the operation analysis perturbations which produce the fastest growth during the first stage of the forecast period, defined using the singular vector technique. the purpose is to find those perturbations to a given initial state which grow most rapidly [5]. the calculation of the singular vectors is the tangent linear version of the full (non -linear) operational forecast 1 0 ∂ − + = ρ ∂ du p fv dt x 1 0 ∂ + + = ρ ∂ dv p fu dt y 0 ∂ + ρ = ∂ p g z 0 ∂ ∂ ∂ + + = ∂ ∂ ∂ u v w x y z 0 ∂φ − + = ∂ du fv g dt x 0 ∂φ + + = ∂ dv fu g dt y 0 φ + φ∇ ⋅ = h d v dt . d u v dt t x y ∂ ∂ ∂ = + + ∂ ∂ ∂ iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering srikul and sukawat 39 model. a second model, the adjoint of the tangent linear model is also needed in the singular vector calculation. a) the tangent linear model method (tlm) consider a non linear model (9) where 0 ( )x t is the state at the initial time and ( )x t is the state at time t and m is the time integration of the numerical scheme from the initial condition to time t . the tangent linear model (tlm) is defined such that (10) where l is the tangent linear model of m . so the tlm evolves a perturbation in time; (11) where 0 ( )y t is the perturbation state at the initial time 0=t and ( )y t is the perturbation state at time t [3]. b) the adjoint of the tangent linear model the adjoint tangent linear model is the transpose of the tangent linear model. c) the singular vector singular value decomposition theory indicates that for any matrix l there exist two orthogonal matrices ,u v such that (12) where 1 2 0 0 0 0 0 0 σ    σ  =     σ  k k m m m k n s and =tuu i , =tvv i s is a diagonal matrix whose elements are the singular values of l and i is the identity matrix. so that (13) the vector 1 ( , , )k n v v are the right singular vectors of l . consequently (14) 0 ( ) [ ( )]=x t m x t ∂ = ∂ m l x 0 0 ( ) ( , ) ( )=y t l t t y t = t u lv s .= σ i i i lv u = σ t i i i l u v iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering srikul and sukawat 40 the vector 1 ( , , )k n u u are the left singular vectors of l . therefore, the initial singular vectors can be obtained as the eigenvectors of tl l , the final singular vectors can be obtained as the eigenvectors of tll and eigenvalues are the squares of the singular values. consider a basic trajectory (15) (16) applying the tangent linear model l in (11) and (15) and rearrange in the form (17) applying the adjoint of the tangent linear model tl in (11) and (16) (18) applying tl l by running tangent linear model forward in time, and then the adjoint backward in time. (19) 2.3 the numerical method of the shallow water model the forward in time center in space finite difference method is used to solve the shallow water equations on arakawa a grid. a) discretized the shallow water model (20) where 2 ∆ α = ∆ t x , 2 ∆ β = ∆ t y b) initial condition for this research the initial conditions are (21) (22) 0 0 1 ( ) ( ), = = < >∑ n i i i y t y t v v 1 1 1 ( ) ( ), . n i i i y t y t u u = = < >∑ 1 0 ( ), ( ), i i i y t u y t vσ< >=< > 0 1 ( ), ( ),< σ >=< > i i i y t v y t u 2 1 0 ( ), ( ),< σ >= σ < > i i i i y t u y t v ( ) ( ) ( )1 1 1 1 1 1 1 + + − + − + − = − α − − β − + ∆ − α φ − φ j j j j j j j j j j j i i i i i i i i i i i u u u u u v u u tfv g ( ) ( ) ( )1 1 1 1 1 1 1 + + − + − + − = − α − − β − − ∆ − β φ − φ j j j j j j j j j j j i i i i i i i i i i i v v u v v v v v tfu g ( ) ( ) ( ) ( )j 1 j j j j j j j j j j j j ji i i i 1 i 1 i i 1 i 1 i i 1 i 1 i i 1 i 1u v u u v v + + − + − + − + −φ = φ − α φ − φ −β φ − φ − αφ − −βφ − 0 φ = − d u g f dy 0 φ = d v g f dx iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering srikul and sukawat 41 (23) where 2 ( ) * ( 0 * ( 0) 0.5* * ( 0) )= − −φ + − ubar bar f y y beta y y g 5500 φ =ref is the constant reference geopotential height, = 500φamp is the constant amplitude geopotential height. 1=mx and 1=my are wave numbers in x and y directions, respectively. lx and ly are channel lengths in x and y directions, respectively. c) boundary condition the boundary condition in the east-west direction is a cyclic boundary and the north-south direction is an updated boundary. d) experiment the domain of the model is 632 10× meters in x-direction and 68 10× meters in y-direction, grid size in x-direction is 58 10× meters and grid size in y-direction is 58 10× meters, time step is 600 seconds. the output interval from the forecast model is 6 hours. 2.4 step of calculation the singular vector step1: the tangent linear model from (10) for the shallow water model is calculated as (24) the discretized form of (24) is then used to calculate the tangent linear model at each of grid point. step2: the adjoint linear tangent model is the transpose of the linear tangent model. step3: calculating the singular vector and singular value from (13) and (14) have to be repeated many times to generate several perturbations. the maximum norm of perturbations and minimum norm of perturbations are then added to the initial condition to generate the new initial conditions. in this paper the norm of vector is defined as (25) for example, at a point where the initial pertubations 0 0.1871 ( ) 0.4344 277.2987 −    =      y t a single cycle of l and t l transformations result in 1 -10 1.7712 ( ) 0.0629 3.8762e     =       y t . 0 = + +φ φ φ φwave bar ref * sin(2 * * * / ) * cos( * * ( 0) / )φ = φ −wave amp pi mx x lx my pi y y ly 2 2 2 2 2 2 2 2 2 2 2 2 2  ∂ ∂ ∂ ∂ ∂ ∂ ∂ + + + ⋅ −  ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂   ∂ ∂ ∂ ∂ ∂ ∂ ∂ = = + + + +  ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂   ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ + + + + + +  ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂   i u u u u u v z u v f g u t u x x u y y y z x m v v v v v z l f u v g u x v t v x v y y z y z u z v z z z u v z z u v x u x y v y z t z x z y x y 2 2 2 = + + φ i y u v iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering srikul and sukawat 42 3. results and discussion 3.1 result of the shallow water model figure 1 shows the velocity and geopotential field following (21) and (22). figure 2 shows the result of forecast at 6 hours. fig. 1: the initial state of the velocity field (vectors) and geopotential heights (contour lines). fig. 2: the forecast state of the velocity field (vectors) and geopotential heights (contour lines) at 6 hours. table 1: examples of singular vectors and singular values of perturbation at grid point (2,3). state singular vector perturbation v1 v2 v3 i 5 0.859 0.511 6.907e −     −   −  5 0.512 0.859 4.979e −           5 5 3.386e 7.813e 0.999 −     −      0.187 0.434 277.298 −         n 1 1 1 277.2992 f 5 0.221 0.131 1.778e −     −   −  1.598 2.683 0.0001          2.422 7 5.589 7 7.154 7 e e e +    − +   +  10 1.771 0.063 3.877e −           n 0.2574 3.12273 7.154e+11 1.77234 u 0 0.5 1 1.5 2 2.5 3 x 10 7 0 1 2 3 4 5 6 7 8 x 10 6 5100 5200 5300 5400 5500 5600 5700 5800 5900 6000 49.55 m/s u 0 0.5 1 1.5 2 2.5 3 x 10 7 0 1 2 3 4 5 6 7 8 x 10 6 5100 5200 5300 5400 5500 5600 5700 5800 5900 49.55 m/s iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering srikul and sukawat 43 in table 1, i denotes the initial state of singular vector, f is the final state of singular vector and n is the norm of singular vector. the singular vector at the grid point in table 1 can be represented as vectors as shown in fig. 3–5. fig. 3: i v are the initial time singular vectors; x, y and z axes represent u, v, and φ , respectively. fig. 4: i u are the final time singular vectors with 1 0.2574σ = , 2 3.1227σ = and 3 7.1537e11σ = ; x, y and z axes represent u, v, and φ , respectively. the tangent linear model stretches (or shrinks) and rotates each of the perturbation vectors. at each step the initial state can be transformed to the final state as shown in fig. 3. figure 4 shows the adjoint tangent linear model stretches (or shrinks) and rotats for each of the perturbation vectors. fig. 5: i v are the final time singular vectors with 2 1 0.066σ = , 2 2 9.7512σ = and 2 3 5.1175e 23σ = + ; x, y and z axes represent u, v, and φ , respectively. 0 0.2 0.4 0.6 0.8 1 -0.5 0 0.5 1 -0.5 0 0.5 x y z v 3 v 1 v 2 -1 -0.5 0 0.5 -0.5 0 0.5 1 0 0.2 0.4 0.6 0.8 1 xy z u2 u 1 u 3 0 5 10 15 20 -40 -20 0 20 -20 0 20 40 60 xy z v 3 1 v 3 3 v 3 2 iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering srikul and sukawat 44 4. conclusion in this paper a singular vector is applied at a grid point in linearized shallow water wave model. a single vector transformation results in a significant the change in the norm of the initial perturbation. the method can be used to generate initial states to an ensemble shallow water model for ensemble forecasts. acknowledgements the first author would like to thank rajamangala university of technology tawan-ok (rmutto) and mathematics department of king mongkut's university of technology thonburi (kmutt) for the financial support. references [1] kalnay e., 2003, atmospheric modeling data assimilation and predictability, cambridge university press, uk., vol. 341, pp.1-2. [2] mozheng wei and jorgen s. frederiksen., 2000, “iterative methods for lyapunov vectors and singular vectors and atmospheric predictability,” anziam j., vol. 42, pp. 1501-1519. [3] v. m. khade and j. a. hansen., 2004, “state dependent predictability: impact of uncertainty dynamics, uncertainty structure and model inadequacies,” nonlinear processes in geophysics, vol. 11, pp. 351-362. [4] holton j. r., 2004, introduction to dynamic meteorology, 4 th ed., elsevier inc., uk., pp. 188-219 [5] l. magnusson, e. kallen, and j. nycander, 2008, “initial state perturbations in ensemble forecasting,” nonlinear processes in geophysics, vol. 15, pp. 751-759. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 sudhamani https://doi.org/10.31436/iiumej.v22i2.1597 double threshold spectrum sensing with optimization of samples in cognitive radio networks chilakala sudhamani departmentof electronics and communication engineering, cmr technical campus, hyderabad, india corresponding author: sudhamani.ece@cmrtc.ac.in (received: 26thaugust 2020; accepted: 12th november 2020; published on-line: 5thjuly 2021) abstract:in cognitive radio networks spectrum sensing playsa vital role to identify the presence or absence of the primary user.in conventional spectrum sensing one secondary user will makea final decision regarding the availability of licensed spectrum.but secondary user fail to make a correct detection about thepresence of the primary user if he is in fading environmentand it causes interference to the licensed users. therefore toavoid interference to the licensed users and to make correct detection, number of samples is increased, which increases theprobability of detection. in this paper the optimization of samplesis proposed to reduce the system overhead and also to increase thepropagation time. simulation results show the optimized valueof samples for a given probability of false alarm and also thevariation of probability of detection with optimized samples andfalse alarm is shown in the results. abstrak:dalam rangkaian radio kognitif, penginderaan spektrum memainkan peranan penting untuk mengenal pasti kehadiran atau ketiadaan pengguna utama. dalam penginderaan spektrum konvensional, seorang pengguna sekunder akan membuat keputusan akhir mengenai ketersediaan spektrum berlesen. tetapi pengguna sekunder gagal membuat pengesanan yang betul mengenai kehadiran pengguna utama jika dia berada dalam persekitaran yang pudar dan menyebabkan gangguan kepada pengguna yang berlesen. oleh itu untuk mengelakkan gangguan kepada pengguna berlesen dan membuat pengesanan yang betul, jumlah sampel meningkat, yang meningkatkan kemungkinan pengesanan. dalam makalah ini pengoptimuman sampel dicadangkan untuk mengurangi overhead sistem dan juga untuk meningkatkan waktu penyebaran. hasil simulasi menunjukkan nilai sampel yang dioptimumkan untuk kebarangkalian penggera palsu dan juga variasi kebarangkalian pengesanan dengan sampel yang dioptimumkan dan penggera palsu ditunjukkan dalam hasil. keywords: cognitive radio; spectrum sensing; detection threshold; optimization 1. introduction due to the increased use of 3g and 4g mobile servicesand accelerated use of wireless internet services, there is asoaring demand for radio frequency available for wirelesscommunication. for utilizing particular frequency bandlicenses are required. in every country these licenses areauctioned by the governing agencies like department of telecommunication (dot) in india, federal communicationscommission (fcc) in usa, etc. and assigns to licensed usersor primary users (pus). however, research conducted by fcc concluded that the actual dispute is not limited bandwidth but improper usage of available spectrum, and also a largeamount of band is underused [1] by the licensed users. 161 iium engineering journal, vol. 22, no. 2, 2021 sudhamani https://doi.org/10.31436/iiumej.v22i2.1597 when the spectrum is not occupied by the pu then it is termed as spectrum holes. this problem can be solved with the help of cognitive radio (cr) concept [2]. the main focus of cognitive radio is to select wireless spectrum dynamically without disturbing primary user and in accordance to that its transmission and reception parameters changes. this selection of spectrum which is available for communication is done by spotting the presence of pus and enables secondary users (sus) without disturbing pu communication. this process of selection is known as spectrum sensing [3]. spectrum sensing techniques are divided into three major categories: matched filter method, energy detection method and future detection. these three methods have its own pros and cons [46]. energy detection method is having more advantages compared to remaining methods because of its simple architecture but the only problem is at low signal to noise ratio (snr). double threshold method has been proposed to overcome low snr [7-10]. in conventional spectrum sensing, the single cognitive radio is used to detect the presence of primary users which may cause problems like fading, shadowing, and uncertainty [11-13]. in cooperative spectrum sensing, the sensing is done with the cooperation data given by multiple sus.these individual decisions are combined and come to a single conclusion about the presence or absence of primary users at the fusion center with the help of fusion rules. but in css, the energy consumption increases with the increased number of sus. the accuracy of detection can be analyzed by two probabilities: the probability of detection and the probability of false alarm. probability of detection represents that the cr is deciding that the primary user is present when he is actually present i.e. spectrum is busy. where as cr is represented with the probability of false alarm when the report given by cr is that pu is present when pu is absent. probability of false alarm will affect system efficiency because the user will not use the free band [14-15]. in [16], the authors used multitaper spectrum estimation to give a closed-form expression for the probability of detection and false alarm. by comparing multitaper spectrum estimation with an energy detector, authors concluded that energy detector requires more number of samples to attain the same detection and false alarm probabilities. the performance analysis is given by the author in [17] for accurate detection of different hard and soft fusion rules in a real scenario. authors explained about the randomness of signal to noise ratio in the real environment.the author in [18], derived the probability of miss detection in eigen ratio spectrum sensing using a random matrix theory approach. the mathematical expression derived as a function number of cr, samples, and signal to noise ratio of pu. in [19], the authors proposed a two stage spectrum sensing technique compared with existing models for varying snr. in this paper we proposed optimization of samples to reduce the system overhead and to increase the overall detection probability. 2. system model in cognitive radio networks, spectrum sensing plays an important role and in this paper we considered energy detection method as suitable one for increasing the detection performance because of its advantages. block diagram of energy detection method is shown in fig. 1. fig. 1: block diagram of conventional energy detection method 162 iium engineering journal, vol. 22, no. 2, 2021 sudhamani https://doi.org/10.31436/iiumej.v22i2.1597 incoming signal is passed through band pass filter to reduce the noise and then it is squared and integrated to get total signal energy. the received energy is compared with the predefined threshold value to identify the presence or absence of the pu.this is done through hypothesis testing, if pu is present then it is represented by h1 else it is represented by h0. 𝑥(𝑛) = 𝑝(𝑛) + 𝑤(𝑛) ∶ 𝐻1 (1) 𝑥(𝑛) = 𝑤(𝑛) ∶ 𝐻0 (2) where p(n) is a pu signal, w(n) is a gaussian noise and x(n) is a received signal respectively. energy of a signal is estimated through number of samples and is given by [8,18]. 𝑌(𝑛) = ∑|𝑥(𝑛)|2 𝑁 𝑛=1 (3) where n represents the number of samples used to estimate the total energy of a signal. decision statistics of spectrum sensing are probability of detection (pd) and probability offalse alarm (pf), which are given by [18] 𝑝𝑑 = 𝑃𝑟𝑜𝑏(𝑌 > 𝑇|𝐻1) = 𝑄 ( 𝑇 − 𝑁(𝜎𝑝 2 + 𝜎𝑤 2 ) √2𝑁(𝜎𝑝 2 + 𝜎𝑤 2 )2 ) (4) 𝑝𝑓 = 𝑃𝑟𝑜𝑏(𝑌 > 𝑇|𝐻0) = 𝑄 ( 𝑇 − 𝑁(𝜎𝑤 2 ) √2𝑁(𝜎𝑤 2 )2 ) (5) where t is detection threshold with which the received energy of su is compared with to make a final decision about the presence or absence of the pu. for a fixed false alarm probability, detection threshold is calculated from equation (5) as 𝑌(𝑛) = ∑|𝑥(𝑛)|2 𝑁 𝑛=1 (6) in eq.(3), the number of samples used to estimate the energy of a given signal determines the system performance. for large number of samples the performance is good compared to the less number of samples which is shown in the fig. 2. as the number of samples increases detection probability increases because more number of samples gives more accurate values, same can be observed from this figure. fig. 2: probability of detection with probability of false alarm. 163 iium engineering journal, vol. 22, no. 2, 2021 sudhamani https://doi.org/10.31436/iiumej.v22i2.1597 detection threshold, probability of detection and probability of false alarm depends on the number of samples. if the number of samples is go on increasing to increase the performance of a system then the processing time increases which leads to more overhead on this system. the time taken to estimate the detection threshold, probability of detection and false alarm increases, which may cause spectrumun-utilization. if the spectrum is actually free and same is identified by the su after long processing time then it causes spectrum wastage i.e. no one is going to utilize it and also with in the estimation time of su, if primary user want to use then su may cause interference to the pu by accessing the spectrum. therefore, to overcome this problem, number of samples used to estimate the detection probability is optimized in this paper. these optimized numbers of samples are estimated by maximizing the detection threshold. differentiating eq.(6) and equating to zero gives the optimal number of samples,which is given as 𝑑𝑇 𝑑𝑁 = 𝑑 𝑑𝑁 (𝜎𝑤 2 (𝑁 + √2𝑁 (𝑄−1(𝑝𝑓 ))) = 0 (7) after differentiation it gives the optimal number of samplesas 𝑁𝑜𝑝𝑡 = 1 𝜎𝑤 4 (𝑄−1(𝑝𝑓 )) 2 (8) optimized number of samples increases the processing time and reduces the system over head. this increases the system performance and also spectrum utilization. now the proposed threshold is given as 𝑇𝑜𝑝𝑡 = 𝜎𝑤 2 (𝑁𝑜𝑝𝑡 + √2𝑁𝑜𝑝𝑡(𝑄 −1(𝑝𝑓 )) (9) in eq. (9) new detection threshold is estimated toincrease the detection probability. to further improve thedetection probability, double threshold method has been proposed. figures 3 and 4 show the conventional and proposed double threshold spectrum sensing methods. fig. 3: conventional spectrum sensing. fig. 4: double threshold spectrum sensing. in the double threshold spectrum sensing new thresholds are given as (t0) and (t1). if the received signal is less than the detection threshold (t0) then the pu is declared as absent. if the received is greater than the detection threshold (t1) then pu is present. if the received signal lies between (t0) and (t1) then su will re-sense the spectrum. this method reduces themiss detection and false alarm probabilities. new detection thresholds are given as 𝑇1 = 𝑇𝑜𝑝𝑡 + 𝐾𝑇𝑜𝑝𝑡 (10) 𝑇0 = 𝑇𝑜𝑝𝑡 − 𝐾𝑇𝑜𝑝𝑡 (11) where k represents the improvement factor of detection threshold. 164 iium engineering journal, vol. 22, no. 2, 2021 sudhamani https://doi.org/10.31436/iiumej.v22i2.1597 3. simulation results in this paper we considered optimization of number of samples and double threshold method. figure 5 shows the relation between optimal number of samples and probability of false alarm. from this figure it is observed that the optimal n value decreases as the pf increases from 0 to 0.5 and thenit increases as pf increases from 0:5 to 1. this also showsthat the optimal false alarm is 0.5. at this point we need less number of samples to increase the detection probability. figure 6 shows the variation of pd with respective to pf for variable improvement factor k. the factor k is varied from 5% to 50%. from this figure it is observed that the detection probability is high for small values of k because the upper threshold is small for small values of k and it is easy to identify the pu presence or absence. as k increases, upper threshold increases which reduces the detection probability.therefore we can use small improvement factor for increasing the detection probability. from this figure also it is observed that the optimal pf is 0.5. fig. 5: optimized samples with probability of false alarm. fig. 6: probability of detection with probability of false alarm using k. fig. 7: detection threshold with probability of false alarm. figure 7 shows the variation of threshold with false alarm.threshold is high at low pf, because the spectrum sensing depends on detection threshold. at low detection threshold 165 iium engineering journal, vol. 22, no. 2, 2021 sudhamani https://doi.org/10.31436/iiumej.v22i2.1597 probability of false alarm is high which is also shown inthe figure. so, we need high detection thresholds to improve the system performance. with the improvement factor thethreshold value decreases for a given pf. from the three figures it is observed that the optimal falsealarm is 0:5. which is used to increase the overall system performance and the optimal number of samples required isalso less at this pf. this reduces the overhead on the system and time taken to conclude the presence or absence of the pu. 4. conclusion in this paper, we estimated the probability of detection with variable number of samples and false alarm. from the results it is observed that the detection probability is high for large number of samples. but it increases the sensing and decision making time. so to reduce this optimization of samples has been proposed in this paper. the optimal samples and optimal false alarm are estimated from the results, which improves the detection performance and also reduces the processing time and system overhead. this increases the overall spectrum usage than compared to the conventional method. acknowledgement this work is supported by grant no.sr/fst/college 017/2017 under dst fist program2017, received by the department of electronics &communication engineering, cmr technical campus, hyderabad. references [1] federal communications commission. (2002) spectrum policy task force. et docket no. 02-35. [2] sharma v, joshi s. (2018) a literature review on spectrum sensing in cognitive radio applications. second international conference on intelligent computing and control systems: july 2018. [3] mitola j, maguire mg. (1999) cognitive radio: making software radios more personal. ieee personal communications, 6:13-18. [4] cabric d, mishra sm, brodersen rw. (2004) implementation issues in spectrum sensing for cognitive radios. proceedings of asilomar conference on signals, systems, and computers, 1:772-776. [5] yucek t, arslan d. (2009) a survey of spectrum sensing algorithms for cognitive radio applications. ieee communications surveys and tutorials, 11:116-130. [6] ali ss, liu c, jin m. (2014) minimum eigenvalue detection for spectrum sensing. international journal of electrical and computer engineering (ijece), 4:623-630. [7] liu sq, hu bj, wang xy. (2012) hierarchical cooperative spectrum sensing based on double thresholds energy detection. ieee communications letters, 16:1096-1099. [8] xie j, chen j. (2012) an adaptive double threshold spectrum sensing algorithm under noise uncertainty. computer and information technology, 1:824-827. [9] ribas adop, dias us. (2015) on the double threshold energy detection-based spectrum sensing over fading channel. radio and wireless symposium: 2015, san diego, ca. [10] steve arul u, salai chandira rajan s. (2016) spectrum management techniques using cognitive radios. cognitive radio technology: international journal of data mining techniques and applications, 5: 79-82. [11] ganesan g, li yg. (2007) cooperative spectrum sensing in cognitive radio–part i: two user networks. ieee transaction on wireless communications, 6: 2204–2213 166 iium engineering journal, vol. 22, no. 2, 2021 sudhamani https://doi.org/10.31436/iiumej.v22i2.1597 [12] christian i, sangman m, chung i, lee j. (2012) spectrum mobility in cognitive radio networks. ieee communications magazine, 50(6): 114-121. [13] xuping z, jianguo p. (2007) energy-detection based spectrum sensing for cognitive radio. iet conference on wireless, mobile and sensor networks: 944-947. [14] lee sh, oh dc, lee yh. (2009) hard decision combining based cooperative spectrum sensing in cognitive radio systems. international conference on wireless communications and mobile computing: 2009, leipzig, germany. 906-910. [15] hou f, chen x, huang h, jing x. (2016) throughput performance improvement in cognitive radio networks based on spectru prediction. 16th international symposium on communications and information technologies: qingdao, china. [16] wu j, luo t, li j, yue g. (2009) a cooperative double threshold energy detection algorithm in cognitive radio systems. ieee international conference on wireless communication, networking & mobile computing., 1-4. doi10.1109/wicom.2009.5303377 [17] owayed a, mohammed za, mosa aa. (2010) probabilities of detection and false alarm in multitaper based spectrum sensing for cognitive radio systems in awgn. ieee international conference on communication systems: 2010 singapore. 579-584. [18] verma p, singh b. (2015) simulation study of double threshold energy detection method for cognitive radios. 2nd international conference on signal processing and integrated networks: noida. 232236. [19] sengupta a, chattopadhyay s, ghatak sr, biswas v. (2019) two-stage spectrum sensing model for varying snr conditions in cognitive radio network. international conference on electrical, electronics and computer engineering: aligarh, india. 167 https://doi.org/10.1109/wicom.2009.5303377 1. introduction [1] federal communications commission. (2002) spectrum policy task force. et docket no. 02-35. [2] sharma v, joshi s. (2018) a literature review on spectrum sensing in cognitive radio applications. second international conference on intelligent computing and control systems: july 2018. [3] mitola j, maguire mg. (1999) cognitive radio: making software radios more personal. ieee personal communications, 6:13-18. [4] cabric d, mishra sm, brodersen rw. (2004) implementation issues in spectrum sensing for cognitive radios. proceedings of asilomar conference on signals, systems, and computers, 1:772-776. [5] yucek t, arslan d. (2009) a survey of spectrum sensing algorithms for cognitive radio applications. ieee communications surveys and tutorials, 11:116-130. [6] ali ss, liu c, jin m. (2014) minimum eigenvalue detection for spectrum sensing. international journal of electrical and computer engineering (ijece), 4:623-630. [7] liu sq, hu bj, wang xy. (2012) hierarchical cooperative spectrum sensing based on double thresholds energy detection. ieee communications letters, 16:1096-1099. [8] xie j, chen j. (2012) an adaptive double threshold spectrum sensing algorithm under noise uncertainty. computer and information technology, 1:824-827. [9] ribas adop, dias us. (2015) on the double threshold energy detection-based spectrum sensing over fading channel. radio and wireless symposium: 2015, san diego, ca. [10] steve arul u, salai chandira rajan s. (2016) spectrum management techniques using cognitive radios. cognitive radio technology: international journal of data mining techniques and applications, 5: 79-82. [11] ganesan g, li yg. (2007) cooperative spectrum sensing in cognitive radio–part i: two user [12] christian i, sangman m, chung i, lee j. (2012) spectrum mobility in cognitive radio networks. ieee communications magazine, 50(6): 114-121. [13] xuping z, jianguo p. (2007) energy-detection based spectrum sensing for cognitive radio. iet conference on wireless, mobile and sensor networks: 944-947. [14] lee sh, oh dc, lee yh. (2009) hard decision combining based cooperative spectrum sensing in cognitive radio systems. international conference on wireless communications and mobile computing: 2009, leipzig, germany. 906-910. [15] hou f, chen x, huang h, jing x. (2016) throughput performance improvement in cognitive radio networks based on spectru prediction. 16th international symposium on communications and information technologies: qingdao, china. [16] wu j, luo t, li j, yue g. (2009) a cooperative double threshold energy detection algorithm in cognitive radio systems. ieee international conference on wireless communication, networking & mobile computing., 1-4. doi10.1109/wicom.2009.5303377 [17] owayed a, mohammed za, mosa aa. (2010) probabilities of detection and false alarm in multitaper based spectrum sensing for cognitive radio systems in awgn. ieee international conference on communication systems: 2010 singapore. 579-584. [18] verma p, singh b. (2015) simulation study of double threshold energy detection method for cognitive radios. 2nd international conference on signal processing and integrated networks: noida. 232236. [19] sengupta a, chattopadhyay s, ghatak sr, biswas v. (2019) two-stage spectrum sensing model for varying snr conditions in cognitive radio network. international conference on electrical, electronics and computer engineering: aligarh, india. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. towards an efficient traffic congestion prediction method based on neural networks and big gps data wiam elleuch*, ali wali and adel m. alimi research groups in intelligent machines lab (regim-lab), university of sfax, national engineering school of sfax (enis), bp 1173, sfax, 3038, tunisia. *corresponding author: elleuchwiam@gmail.com (received:22nd sept 2018; accepted:30th march 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.997 abstract: the prediction of accurate traffic information such as speed, travel time, and congestion state is a very important task in many intelligent transportations systems (its) applications. however, the dynamic changes in traffic conditions make this task harder. in fact, the type of road, such as the freeways and the highways in urban regions, can influence the driving speeds and the congestion state of the corresponding road. in this paper, we present a nns-based model to predict the congestion state in roads. our model handles new inputs and distinguishes the dynamic traffic patterns in two different types of roads: highways and freeways. the model has been tested using a big gps database gathered from vehicles circulating in tunisia. the nns-based model has shown their capabilities of detecting the nonlinearity of dynamic changes and different patterns of roads compared to other nonparametric techniques from the literature. abstrak: ramalan maklumat trafik yang tepat seperti kelajuan, masa perjalanan dan keadaan kesesakan adalah tugas yang sangat penting dalam banyak aplikasi sistem pengangkutan pintar (its). walau bagaimanapun, perubahan keadaan lalu lintas yang dinamik menjadikan tugas ini menjadi lebih sukar. malah, jenis jalan raya, seperti jalan raya dan lebuh raya di kawasan bandar, boleh mempengaruhi kelajuan memandu dan keadaan kesesakan jalan yang sama. dalam makalah ini, kami membentangkan model berasaskan nn untuk meramalkan keadaan kesesakan di jalan raya. model kami mengendalikan input baru dan membezakan corak trafik dinamik dalam dua jenis jalan raya yang lebuh raya dan jalan raya. model ini telah diuji menggunakan pangkalan data gps yang besar yang dikumpulkan dari kenderaan yang beredar di tunisia. model berasaskan nns telah menunjukkan keupayaan mereka untuk mengesan ketiadaan perubahan dinamik dan pola jalan yang berbeza berbanding dengan teknik nonparametrik yang lain dari kesusasteraan. keywords: neural network; traffic congestion prediction; big gps traces 1. introduction an intelligent transportation system (its) application can be efficient only if the quality and the accuracy of the provided traffic information are guaranteed. this is particularly true for advanced traffic management systems (atms) and advanced traveler information systems (atis) because travelers, traffic managers, and transportation agencies need reliable information about the state of road congestion, travel time, and travel speed. 108 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. considering the nonlinear characteristic of congestion and traffic conditions on the roads, the task becomes harder. however, the increased deployment of sensors in this century provides available data that helps researchers to achieve their purposes. in the literature, many techniques to predict traffic congestion states have been explored to fit all sorts of collected data [1]. most of studies are based on fixed sensors such as the inductive loop detectors [2-4] to infer the travel time in some road links. other works in the computer vision field based their studies on video detectors [5] or web camera sensors [6] to forecast traffic information. while this alternative can give more information about the number of cars in a place, they require high costs of installation and maintenance. moreover, they should be installed everywhere in the city to give more accurate results. therefore, other researchers preferred using data gathered from vehicles and smart-phones equipped with gps systems to predict traffic speed [7] and congestion state [8]. several techniques have been applied in the traffic forecasting field. some statistical parametric approaches, such as the historical smoothing algorithm [9] and smoothing techniques [10], have been developed to predict traffic flow. different variants of autoregressive moving average (arma) models have been widely applied to forecast future values of a traffic parameter based on the previous data such as autoregressive integrated moving average (arima) [11] and seasonal arima (sarima) [12]. since the appearance of arm models, the traffic prediction performance was improved whereas, the computation cost becomes very high even for small databases [13]. non-parametric techniques have been also developed to solve the traffic forecasting problem including knearest neighbor (k-nn), support vector machine (svm) and neural network (nn). knn is the simplest algorithm. it was used to predict traffic flow on a shanghai expressway using historical traffic variables [14]. another work [15] applied this algorithm to forecast traffic flow based on the upstream and downstream road information. yao et al. [16] introduced a traffic speed forecasting model in an urban corridor based on the svm technique. fan et al. [17] introduced the parallel random forests in order to forecast travel time in a highway in taiwan. some other works performed hybridizations between some machine learning algorithms to forecast traffic variables such as the hybridization of the genetic algorithm and cross entropy in [18] to predict inferred congestion on a freeway in california the ann and the decision tree provided by elleuch et al. [8] was used to infer the congestion state based on anomalous events. concerning the nns, they are able to infer complex relationships between nonlinear variables in the inputs and outputs. therefore, they have been used in forecasting traffic variables [19,20]. sharma et al. [19] have proposed a traffic flow forecasting model based on a single back-propagation ann in an undivided two-lane highway. ciskowski et al. [20] have tested the performance of ann in forecasting traffic flow variables on some highways in india. the inputs of this model contain vehicle categories. based on the ability of nns in learning complex and nonlinear relationships, nns have proven interesting performance in forecasting traffic variables [21]. however, we notice that the road type has not been studied in previous research. only a single type has been considered, i.e. highway or an urban region. in addition, the researches provided in [22] proved that the time and the day of the week affect the traffic congestion duration. therefore, we present in this paper a new nns-based model to handle this variation and forecast traffic congestion levels. in this paper, we carried out some statistics to investigate the speed changes in urban regions and on highways. we notice that it is crucial to create a model that is able to take into account the traffic changes. the proposed methodology in this paper is different from previous technologies used in other research. we present an overview of the major aspects 109 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. developed to implement our system. we solve the problem using a nns-based model to learn various traffic situations on highways and in urban regions at different times of day, capture different patterns over several weeks, as well as to forecast traffic congestion states of roads in future time periods. based on our knowledge, there has not been any work in the literature that has studied dynamic traffic variation and the different traffic patterns on highways and in urban regions where the speed interval is totally different. researchers focused on a single type of road. they did not investigate the different traffic conditions in urban regions and on highways. our system helps drivers to detect the eventual congestion state in order to find another way to overcome this problem. furthermore, it provides information about the congestion for transportation managers to locate the frequently congested locations to solve this issue. the remaining parts of this paper are organized as follows. section 2 provides an overview of the gps traces collection step with some analysis. section 3 presents the proposed system and highlights the process of the model development. the experimentation and results were introduced and explained in section 4. finally, we conclude our paper in section 5 and present some perspectives. 2. big gps traces collection to develop an accurate system, it is essential to use an accurate and real database for test and validation of this system. with the lack of public gps databases, we developed a gps tracking system to gather gps traces. this system is mainly composed of gps satellites and gps receivers mounted in cars. the gps satellites send signals to the earth in order to calculate orbit positions. to get more precise positions, it is crucial to use more than three satellites. however, the gps receivers provide the car's position and send the gps traces to the database through gprs network connection. in this section, we present an overview of the collected gps traces. moreover, the pre-processing and map-matching steps are provided to filter the noisy data and guarantee the high quality of gps traces. 2.1 overview of the collected gps traces due to the developed gps tracking system, we gathered big gps traces from cars on the roads of tunisia. the volume of data reached more than 100 gb of raw gps traces. the gps traces are based on the gprmc sentence type [24]. this type of sentence is used because it indicates the speed of the car, which is an important feature in our case. we provide an example of gprmc sentence to explain the role of each feature. the transmission of the data is performed about every minute. the following sample of a gprmc sentence is provided to give an idea about the collected data. $gprmc, 160533.00, a, 3445.5029, n, 01046.8838, e, 037.8,255° c, 071214, 00.0, w, 000ca .each feature in the gprmc sentence is presented in table 1. in the feature extraction step, the main extracted features from the gprmc sentences are the id of the car, the timestamp information, the position coordinates and the speed of the car. we gathered the gps traces from about ten thousands cars and trucks. this number allows us to collect a big gps database. we provide more details on the gps database in [25]. in the transmission process, some problems can be encountered such as the lack of four satellites, which can easily cause the deformation of the gps trace. a filtration step is developed to overcome this problem and remove the noisy data and outliers [26]. an outlier is detected if the validity value in the gprmc sentence is set to v. then, a map-matching step is carried out to verify the accuracy of the collected gps 110 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. traces. figure 1 presents the results of map-matching step of an example of gps traces of car id 43712 to a digital map. table 1: features provided by the transmitted gprmc sentence feature information $gprmc type of the transmitted sentence 160533.00 time (hhmmss.msms) a the validity of the transmitted sentence (if v=invalid) 3445.5029 latitude coordinate in the format ddmm.mmmm s north/south orientation 01046.8838 longitude coordinate in the format ddmm.mmmm e east/west orientation 037.8 instantaneous speed (mile/hour) 255° travel direction 071214 date in the format ddmmyy 00.0 magnetic variation in degree w magnetic variation orientation (e/w) 000ca checksum to verify the transmitted frame accuracy fig. 1: map-matching of gps traces sample. figure 1 shows the gps traces of a car that traveled from sfax city to sousse city through the freeway linking these two cities. we performed a zoom in sfax city to compare the precision of our traces to the digital map. as it is shown in sub-figure (b), the red line and the yellow line of the digital map are completely superimposed which proves the accuracy of our gps traces. 111 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. 2.2 preliminary analysis predicting the traffic state of a road is a very delicate task because traffic congestion is a dynamic event. traffic conditions depend on several components such as the time of day, the day of the week, and the road location. therefore, in the development of a reliable system able to forecast the congestion state, we should take into account the different traffic changes. to achieve our purposes, we analyzed some statistics using our data. we computed the average speed of the cars in different places and in different periods of the day to discover the relationship between speeds, time periods, and places including highways and freeways. we provide fig. 2 and fig. 3 to explain the traffic speed changes along a journey in two different chosen study areas. fig. 2: comparison between the average vehicles' speed measurements on the first week of march on the same freeway in (a) 2014 and (b) 2015. fig. 3: comparison between the average vehicles' speed measurements on the first week of march on the same highway in (a) 2014 and (b) 2015. the preliminary analysis presented in fig. 2 and fig. 3 were performed on a freeway linking sfax and sousse cities and for one of the most congested highways in sfax city 112 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. called taniour highway, respectively, on the first week of march for two different years (2014 and 2015). figure 2 shows that the average speed on the freeway in 2014 is between 70 km/h and 93 km/h which is very low compared to the permitted maximum speed (110 km/h). furthermore, in 2015 the speed is lower and reaches very low levels. this can be explained by the increase in the number of vehicles and some road works on this freeway that directly affected the traffic congestion. concerning fig. 3, the average speed on the highway doesn't exceed 35 km/h in the two years along the week and it becomes more serious in the rush hours (between 7 a.m -9 a.m and 4 p.m-7 p.m). as we said, this road is very congested. it contains many primary schools and child care centers. we conclude that it is necessary to handle the different patterns and traffic speeds along the highways and freeways to elaborate a robust and reliable approach able to overcome real-world conditions. 3. neural networks approach for congestion prediction after the preliminary analysis, we present in this section a combined neural network approach for congestion prediction based on the gathered gps traces able to forecast the traffic congestion in roads. the combination of two neural networks is provided to respond to the need to differentiate between traffic conditions and range of allowed speed along highways and freeways. we present in fig. 4 an overview of the proposed system composed of two main phases. an offline phase is carried out to collect and preprocess the gprmc sentences gathered from cars equipped with gps systems and to develop the neural networks-based model. concerning the online phase, it is composed of a decision module and it is mainly based on the trained neural networks. fig. 4: the proposed system architecture. 3.1 neural network based module this module is an important step to build our system. we applied the neural networks because it is one of the most performing tools in machine learning. the choice of the neural networks among the other techniques can be explained by their ability to deal with predictors with complex relationships. moreover, we highlight the robust capabilities of 113 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. neural networks in forecasting the future state when they know the previous states. furthermore, the results are mostly improved and can reach high accuracy if a large quantity of data is fed into the nn system. these criteria, such as the need for big gps trace data, the complexity of the relationship between the input variables and the desired congested state, are provided in our case which encourage the authors to apply and test the performance of the nns to predict the future congestion state of a road. the common structure of all nns is inspired by biological neural networks. they consist of many calculating units called neurons. their principal components are layers. the first layer is the input layer composed of the predictors. we present in fig. 5 the composition of our nn architecture. fig. 5: architecture of the nn based design. in our system, as it is presented in fig. 5, five inputs extracted from gps traces which are the position coordinates, the speed of the car, and the timestamp information (the number of minutes and the week day). the second layer is composed of the hidden neurons. finally, the output layer is composed of the desired output which, in our case, is the predicted congestion state. the choice of the number of hidden neurons is defined after performing some experiments that will be discussed later. the role of this architecture is to compute the future state of the desired road using the inputs by means of a transfer function called the activation function. the module structure relies primarily on the preliminary analysis made in section 2. in fact, the difference between traffic changes on highways and freeways has an impact on the structure of our neural network-based system. we solved this challenging problem using an architecture composed of a combined neural network. it is composed of two neural networks. each neural network is trained with the gps traces gathered from the correspondent type of road (freeway/highway). the output of the offline phase is the trained combined neural network that will be used in the online phase. 3.2 decision module the online phase is composed of the decision module that is based on the trained combined neural network. it is performed when a driver needs to discover the traffic condition state in a specific place and time. we provide the driver with a mobile application where he can insert the details of the place and the time. we get the required 114 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. information from this application and the current traffic condition from the floating cars in this location. our decision is taken after distinguishing if the required place is a highway or freeway. when we get this information, our system activates the corresponding neural network. finally, the congestion state is predicted and sent to the driver. 4. experimental results and discussions we propose in this paper a combined nns system to forecast congestion state based on two nns in order to take into consideration the traffic changes depending on several variables like the road type road and weekday, as discussed above. we present in this section some experiments and comparisons with other approaches to evaluate our proposed system. to guarantee the high performance of our system, it is crucial to get the best configuration of neural networks. in order to realize the experiments, we used the provided data in table 2, which contains the data repartition used in the training and test steps. table 2: data repartition training data samples test data samples 3 909 756 1 366 830 we notice from table 2 the vast amount of data used in these steps. regarding the experiments, the input variables were fixed and the number of hidden neurons were changed. also, in the training step, we varied the training function. table 3 provides the root mean square error (rmse) given by eq. (1) of all the proposed architectures. (1) where is the real traffic congestion state, is the predicted one and n is the number of gps traces fed in the evaluation process. table 3: rmse of different proposed ann architectures configuration number of hidden neurons training function rmse_ train rmse_ test c1 3 levenberg-marquart 0.0651 0.0655 c2 5 levenberg-marquart 0.0935 0.0947 c3 8 levenberg-marquart 0.0663 0.0765 c4 13 levenberg-marquart 0.0659 0.0715 c5 17 levenberg-marquart 0.0603 0.0692 c6 3 bayesian-regularisation 0.0806 0.0822 c7 5 bayesian-regularisation 0.0637 0.0721 c8 8 bayesian-regularisation 0.0624 0.0636 c9 13 bayesian-regularisation 0.0606 0.0510 c10 17 bayesian-regularisation 0.0566 0.0571 c11 3 scaled conjugate gradient 0.1370 0.1425 c12 5 scaled conjugate gradient 0.1034 0.1073 c13 8 scaled conjugate gradient 0.0931 0.0948 c14 13 scaled conjugate gradient 0.1757 0.1839 c15 17 scaled conjugate gradient 0.1006 0.1027 115 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. table 3 presents the different configurations of the proposed nns to deduce the best network. in our experiment, we performed the variation of the number of hidden neurons from 3 to 17 and the training function. in fact, we tested the most popular training functions: levenberg-marquardt back-propagation, bayesian regularization backpropagation and scaled conjugate gradient back-propagation techniques. among the nns architectures trained with levenberg-marquardt back-propagation function, the best results were given by configuration c1, which has the nn architecture with 3 neurons. for those trained with bayesian-regularisation algorithm, we reached 94% with 17 hidden nodes. finally, using the scaled conjugate gradient, the best result is about 89% with only 8 neurons. we conclude that the best configuration is given by the bayesianregularisation algorithm with 17 neurons. we applied this configuration to the combined neural networks for highways and freeways. the second experiment sets were performed to compare the nn techniques to other nonparametric techniques such as svm and k-nn. figure 6 presents the results given by these three algorithms. fig. 6: rmse of congestion prediction system in highways and freeways. as shown in fig. 6, the best performance was given by our proposed system, which is based on nns on the two types of road. the k-nn gives the worst results even if we change the value of k. the svm provided acceptable results, especially in freeways because of its similar composition to nn. we notice that our system, which is composed of a combined nns, is reliable and provides very interesting results on freeways and in urban regions. these experimentations demonstrate the efficiency of our proposed system which validated our model. 5. conclusion we presented in this paper a nns-based model to predict the congestion state of roads. our model helps drivers to preplan their trips to avoid congested roads. also, it can be efficient for transportation managers to find solutions for congested roads. our model takes into account several traffic changes, spatial patterns in particular. we provided some statistics to analyze the impact of the road type on traffic conditions. we infer that driving speeds are very low on highways in urban regions but very high on 116 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. freeways. based on this analysis, the structure of our model was built using a combination of two nns, one to process highways and another for freeways. thanks to the nns structure, our proposed model has proven its capabilities to deal with several variables and successfully detect the nonlinear relationship between them. it was tested using a big gps database gathered from a huge number of vehicles circulating in metropolitan tunisia. furthermore, our model has shown very high performance in forecasting congestion state compared to other nonparametric techniques. in future studies, we would like to analyze the effect of other parameters such as holidays and workdays on driving speed in a dynamic environment to gather other eventual inputs to our model in order to improve the results. we would like to explore more techniques such as deep learning techniques and perform more experiments based on these huge datasets to obtain a more reliable traffic congestion prediction system. acknowledgement the research leading to these results has received funding from the ministry of higher education and scientific research of tunisia under the grant agreement number lr11es48. the research and innovation are performed in the framework of a thesis mobidoc financed by the eu under the program pasri. references [1] vlahogianni ei, karlaftis mg, golias jc. (2014) short-term traffic forecasting: where we are and where we’re going. transportation research part c, 43: 3-19. [2] robinson s, polak j. (2005) modeling urban link travel time with inductive loop detector data by using the k-nn method. transportation research record: journal of the transportation research board, (1935): 47-56. [3] el faouzi ne, klein la, de mouzon o. (2009) improving travel time estimates from inductive loop and toll collection data with dempster–shafer data fusion. transportation research record, 2129(1): 73-80. [4] lu ccj. (2012) an adaptive system for predicting freeway travel times, international journal of information technology & decision making, 11(4): 727-747. [5] bernaś m, płaczek b, porwik p, pamuła t. (2014) segmentation of vehicle detector data for improved k-nearest neighbours-based traffic flow prediction. iet intelligent transport systems, 9(3): 264-274. [6] zhang s, wu g, costeira jp, moura jm. (2017). understanding traffic density from largescale web camera data. in : proceedings of the ieee conference on computer vision and pattern recognition. 2017. 5898-5907. [7] yao b, chen c, cao q, jin l, zhang m, zhu h, yu b. (2017) short term traffic speed prediction for an urban corridor. computer aided civil and infrastructure engineering, 32(2): 154-169. [8] elleuch w, wali a, alimi am. (2016) intelligent traffic congestion prediction system based on ann and decision tree using big gps traces. in : international conference on intelligent systems design and applications. springer, cham, 2016. pp. 478-487. [9] smith bl, demetsky mj. (1997) traffic flow forecasting: comparison of modeling approaches. journal of transportation engineering, 123(4): 261-266. [10] williams b, durvasula p, brown d. (1998). urban freeway traffic flow prediction: application of seasonal autoregressive integrated moving average and exponential smoothing models. transportation research record: journal of the transportation research board, (1644): 132-141. 117 iium engineering journal, vol. 20, no. 1, 2019 elleuch et al. [11] lam wh, tang yf, chan ks, tam ml. (2006) short-term hourly traffic forecasts using hong kong annual traffic census. transportation, 33(3): 291-310. [12] lee s, fambro d. (1999) application of subset autoregressive integrated moving average model for short-term freeway traffic volume forecasting. transportation research record: journal of the transportation research board, (1678): 179-188. [13] park j, murphey yl, mcgee r, kristinsson jg, kuang ml, phillips am. (2014). intelligent trip modeling for the prediction of an origin–destination traveling speed profile. ieee transactions on intelligent transportation systems, 15(3): 1039-1053. [14] zhang l, liu q, yang w, wei n, dong d. (2013) an improved k-nearest neighbor model for short-term traffic flow prediction. procedia-social and behavioral sciences, 96: 653-662. [15] wu y, tan h, peter j, shen b, ran b. (2015). short-term traffic flow prediction based on multilinear analysis and k-nearest neighbor regression. in : 15th cota international conference of transportation professionalschinese overseas transportation association (cota) beijing jiaotong universitytransportation research boardinstitute of transportation engineers (ite) american society of civil engineers: 556-569. [16] yao b, chen c, cao q, jin l, zhang m, zhu h, yu b. (2017). short term traffic speed prediction for an urban corridor. computer aided civil and infrastructure engineering, 32(2): 154-169. [17] fan sks, su cj, nien ht, tsai pf, cheng cy. (2018). using machine learning and big data approaches to predict travel time based on historical and real-time data from taiwan electronic toll collection. soft computing, 22(17): 5707-5718. [18] lopez-garcia p, onieva e, osaba e, masegosa ad, perallos aa. (2016). hybrid method for short-term traffic congestion forecasting using genetic algorithms and cross entropy. ieee trans. intelligent transportation systems, 17(2): 557-569. [19] sharma b, kumar s, tiwari p, yadav p, nezhurina mi. (2018). ann based short-term traffic flow forecasting in undivided two lane highway. journal of big data, 5(1), 48. ciskowski p, janik a, bazan m, halawa k, janiczek t, rusiecki a. (2016). estimation of travel time in the city based on intelligent transportation system traffic data with the use of neural networksin : international conference on dependability and complex systems. springer, cham, 2016. p. 85-95. [20] kumar k, parida m, katiyar vk. (2013). short term traffic flow prediction for a non urban highway using artificial neural network. procedia-social and behavioral sciences, 104: 755764. [21] laflamme em, ossenbruggen pj. (2017). effect of time-of-day and day-of-the-week on congestion duration and breakdown: a case study at a bottleneck in salem, nh. journal of traffic and transportation engineering (english edition), 4(1): 31-40. [22] park j, murphey yl, mcgee r, kristinsson jg, kuang ml, phillips am. (2014). intelligent trip modeling for the prediction of an origin–destination traveling speed profile. ieee transactions on intelligent transportation systems, 15(3): 1039-1053. [23] elleuch w, wali a, alimi am. (2015). an investigation of parallel road map inference from big gps traces data. procedia computer science, 53: 131-140. [24] elleuch w, wali a, alimi am. (2014). mining road map from big database of gps data. 2014 14th international conference on hybrid intelligent systems (his), 193-198. ieee. [25] elleuch w, wali a, alimi am. (2015). collection and exploration of gps based vehicle traces database. in 2015 4th international conference on advanced logistics and transport (icalt) 275-280. ieee. 118 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <feff04180437043f043e043b043704320430043904420435002004420435043704380020043d0430044104420440043e0439043a0438002c00200437043000200434043000200441044a0437043404300432043004420435002000410064006f00620065002000500044004600200434043e043a0443043c0435043d04420438002c0020043f043e04340445043e0434044f044904380020043704300020043d04300434043504360434043d043e00200440043004370433043b0435043604340430043d0435002004380020043f04350447043004420430043d04350020043d04300020043104380437043d0435044100200434043e043a0443043c0435043d04420438002e00200421044a04370434043004340435043d043804420435002000500044004600200434043e043a0443043c0435043d044204380020043c043e0433043004420020043404300020044104350020043e0442043204300440044f0442002004410020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e0030002004380020043f043e002d043d043e043204380020043204350440044104380438002e> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <feff004f0076006500200070006f0073007400610076006b00650020006b006f00720069007300740069007400650020006b0061006b006f0020006200690073007400650020007300740076006f00720069006c0069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400650020006b006f006a00690020007300750020007000720069006b006c00610064006e00690020007a006100200070006f0075007a00640061006e00200070007200650067006c006500640020006900200069007300700069007300200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e006100740061002e0020005300740076006f00720065006e0069002000500044004600200064006f006b0075006d0065006e007400690020006d006f006700750020007300650020006f00740076006f007200690074006900200075002000700072006f006700720061006d0069006d00610020004100630072006f00620061007400200069002000410064006f00620065002000520065006100640065007200200036002e0030002000690020006e006f00760069006a0069006d0020007600650072007a0069006a0061006d0061002e> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <feff004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <feff04120438043a043e0440043804410442043e043204430439044204350020044604560020043f043004400430043c043504420440043800200434043b044f0020044104420432043e04400435043d043d044f00200434043e043a0443043c0435043d044204560432002000410064006f006200650020005000440046002c0020043f044004380437043d043004470435043d0438044500200434043b044f0020043d0430043404560439043d043e0433043e0020043f0435044004350433043b044f04340443002004560020043404400443043a0443002004340456043b043e04320438044500200434043e043a0443043c0435043d044204560432002e0020042104420432043e04400435043d04560020005000440046002d0434043e043a0443043c0435043d044204380020043c043e0436043d04300020043204560434043a04400438043204300442043800200437043000200434043e043f043e043c043e0433043e044e0020043f0440043e043304400430043c04380020004100630072006f00620061007400200456002000410064006f00620065002000520065006100640065007200200036002e00300020044204300020043f04560437043d04560448043804450020043204350440044104560439002e> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 an investigation of the sensitivity of polymer-coated surface acoustic wavebased gas sensors in the detection of volatile organic compounds aliza aini md ralib* and amirah syahirah syamsil omar department of electrical and computer engineering, kulliyyah of engineering, international islamic university of malaysia, jalan gombak, 53100, kuala lumpur, malaysia * corresponding author: alizaaini@iium.edu.my (received: 3rd august 2020; accepted: 23rd january 2021; published on-line: 4th july 2021) abstract: surface acoustic wave sensors (saws) are excellent at detecting volatile organic compounds (vocs) since a sensing layer can be created by spreading a thin film of material across the delay line. this critically enhances performance as it is sensitive to the physical phenomena of interest. this study aims to provide a thorough investigation of the sensitivity of polymer-coated saw-based gas sensors to vocs using simulations via the finite element method (fem). as such, quartz was chosen as the piezoelectric substrate while polymeric materials were chosen as the sensing layers due to their high sensitivity, low energy consumption, short response time, performance at room temperature, and reversibility after exposure to an analyte. the polymeric materials chosen were: (1) polyisobutylene (pib), (2) polydimethylsiloxane (pdms), (3) polyisoprene (pip), (4) polyimide (pi), and (5) phenylmethyldiphenylsilicone (ov25). the vocs chosen for investigation were: (1) dichloromethane (dcm), (2) trichloroethylene (tce), (3) 1,2dichloroethylene (dce), and (4) carbon tetrachloride (ccl4). the performance of each polymer-coated saw sensor was evaluated in terms of frequency shift and sensitivity to each voc in fem simulations. our study found that the pib-coated sensor had the highest sensitivity (4.0571 khz/ppm) to dcm vapor and good sensitivity (45.257 khz/ppm) to tce vapor. however, the performance of each polymer-coated sensor varied depending on the type of voc being tested. as an example, while the ov25-coated sensor was more sensitive (52.57 khz/ppm) than the pib-coated sensor (53.54 khz/ppm) to tce vapor regardless of the concentration, the pib-coated sensor was more sensitive to dcm vapor at both low (4.06 khz/ppm) and high (3.54 khz/ppm) concentrations than the ov25coated sensor. therefore, the results of our fem simulations indicate that polymer-coated saw-based gas sensors are highly capable of self-powered voc detection. abstrak: sensor gelombang akustik permukaan (saw) adalah sangat baik dalam mengesan sebatian organik meruap yang tidak stabil (vocs), kerana lapisan pengesan dapat dihasilkan dengan melapis nipis bahan pada lapisan garis tunda. cara ini dapat menambah baik prestasi kerana ianya sensitif kepada fenomena fizikal yang dituju. kajian ini bertujuan bagi menyediakan kajian menyeluruh terhadap kesensitifan sensor gas berasaskan saw bersalut polimer pada voc menggunakan simulasi melalui kaedah unsur terhingga (fem). oleh itu, kuarza dipilih sebagai substrat piezoelektrik manakala bahan polimer dipilih sebagai lapisan penginderaan berdasarkan kepekaan tinggi, penggunaan tenaga rendah, respon masa singkat, prestasi suhu bilik, dan faktor keboleh-balikan setelah terdedah kepada analit. bahan polimer yang dipilih adalah: (1) polisobutilena (pib), (2) polidimethilsiloxana (pdms), (3) polisoprena (pip), (4) polimida (pi), dan (5) phenilmethildiphenilsilikon (ov25). voc terpilih bagi kajian adalah: (1) diklorometana 168 iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 (dcm), (2) trikloretilena (tce), (3) 1,2-dikloroetilena (dce), dan (4) karbon tetraklorida (ccl4). prestasi setiap sensor saw bersalut polimer dinilai berdasarkan peralihan frekuensi dan kesensitifan pada setiap voc simulasi fem. dapatan kajian menunjukkan sensor bersalut-pib mempunyai kesensitifan paling tinggi (4.0571 khz/ppm) terhadap wap dcm dan kepekaan yang baik (45.257 khz / ppm) terhadap wap tce. walau bagaimanapun, prestasi setiap sensor bersalut polimer adalah berbeza bergantung kepada jenis voc yang sedang diuji. sebagai contoh, sensor bersalut ov25 adalah lebih sensitif (52,57 khz/ppm) daripada sensor bersalut pib (53,54 khz/ppm) pada wap tce tanpa mengira kepekatan. manakala sensor bersalut pib lebih sensitif terhadap wap dcm pada kedua-dua kepekatan rendah (4.06 khz/ppm) dan tinggi (3.54 khz/ppm) daripada sensor bersalut-ov25. oleh itu, hasil simulasi fem menunjukkan bahawa sensor gas berasaskan saw bersalut polimer adalah sangat berpotensi sebagai pengesan voc berkuasa sendiri. keywords: surface acoustic wave; gas sensor; polymer sensing layer; sensitivity; frequency shift 1. introduction breath analysis has recently emerged as a new and improved diagnostic tool in health examinations with technical advantages, such as being non-invasive, painless, costeffective, user-friendly, easily repeatable, and offering real-time testing methods; over existing methods [1]. current diagnostic methods involve complex, costly, and invasive procedures, such as blood and urine tests, endoscopy, biopsies, imaging etc.; to diagnose diseases. moreover, some diagnostic imaging studies, such as mris, x-rays, and ct scans; cannot be repeated in a short period of time due to exposure to high amounts of radiation [2]. breath analysis is a systematic review of the volatile organic compounds (vocs) exhaled in human breath. each exhaled voc is a biomarker containing clinical information for disease diagnosis. several studies have shown that certain exhaled vocs are clinical biomarkers of metabolic disorders and other diseases [3]. alkanes, for instance, are biomarkers of lung cancer while acetone is used to diagnose diabetes [4]. as such, various detection devices, such as piezoelectric sensors and optical sensors, have been created specifically for this purpose. a saw-based gas sensor is a piezoelectric sensor that measures physical changes such as fluctuations in mass [5]. they are also widely used in medicine and research studies to examine human health via breath analysis. therefore, this study chose to investigate saw-based gas sensors as they are not only highly sensitive and offer faster disease detection but are environmentally friendly as well. the ability to introduce a sensing layer further enhances its performance in terms of sensitivity and selectivity as it enables mass loading that results in changes in acoustic wave velocity and resonant frequency [6]. this study aims to thoroughly investigate the performance of polymer-based sensing layers in saw-based gas sensors through simulation via the finite element method (fem). previous studies have explored the usage of saw-based and quartz crystal microbalance gas sensors for electronic nose applications [7]. fem simulation has also been used to measure the sensitivity of bulk acoustic wave sensor for breath analysis application [8]. however, the sensitivity and selectivity of saw-based gas sensors to different types of vocs warrants further investigation. therefore, this study created simulations to test the ability of five different polymers in sensing four different vocs in a saw-based gas sensor. the performance of each polymer-coated sensor was evaluated in terms of frequency shift and sensitivity to each voc. 169 iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 2. design concept: surface acoustic wave and piezoelectricity piezoelectricity is the ability of some solid materials to generate electrical energy when subjected to mechanical stress. a piezoelectric transducer is basically a “crystal” sandwiched between two metal plates and compressed to generate electricity [9]. direct piezoelectricity occurs when a piezoelectric material is compressed and flows through the metal plates to produce mechanical energy. therefore, the crystal reacts to the pressure of the applied stress and converts it into electrical energy. meanwhile, an inverse piezoelectric effect occurs when a crystal is deformed by the electrical energy applied and converts it to mechanical energy [9]. a saw sensor consists of both input and output interdigital transducers (idts) on a piezoelectric substrate. a thin and highly sensitive layer, capable of changing the resonant frequency of the saw sensor, is then placed between both the idts. figure 1 shows the basic structure of a saw sensor. the choice of piezoelectric substrate is not only important but varies according to the primary function of the sensor [10]. popular choices of substrate materials include zinc oxide (zno), quartz, and lithium niobate (linbo3) [10]. a saw-based gas sensor is used to detect minute changes in surface mass caused by gas absorption by the sensing layer [9] that then causes the resonant frequency of the sensor to shift i.e., the higher the shift in resonant frequency, the higher the sensitivity of the sensor. apart from the sensing layer, the type of material used to coat the substrate also affects sensor performance. fig. 1: schematic diagram of a surface acoustic wave (saw) sensor. resonant frequency, fr is defined as the specific frequency of an acoustic wave oscillating at higher amplitudes. it can be calculated using eq. (1) where, λ is the wavelength and v is the velocity of the acoustic wave. based on these two parameters, a wavelength is a traveling wave that follows the dimensions of the idts [11]. 𝑓 = 𝑣 𝜆 (1) the absorption of gasses by the sensing layer changes its elemental properties, such as density, thickness, elastic modulus, and acoustic velocity, which causes a frequency shift in the saw-based gas sensor. the changes in frequency due to the absorption of gases by nonpiezoelectric, non-conducting, isotropic thin polymer sensing layers are given below where, ∆𝑓 is the frequency shift, ℎ is the thickness of the polymer layer, f0 is the operating frequency, 𝜌 is the density of the polymer layer, k1 and k2 are the constants of the substrate, and 𝜆 and 𝜇 are the lamé constants [12]. 170 iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 ∆𝑓 = (𝑘1 + 𝑘2)𝑓0 2ℎ𝜌 − 𝑘2𝑓0 2ℎ [ 4𝜇 𝑣𝑅 2 ( 𝜆 + 𝜇 𝜆 + 2𝜇 )] (2) the sensitivity of a saw sensor is determined by the difference between the input and output measures. it is also can be determined by the amount of shift in resonant frequency and mass sensitivity as shown in eq. (3) where, cm is the mass sensitivity coefficient independent of frequency, h’ is the thickness of the coating containing gas molecules, and ∆𝜌𝑠 is the change in mass density due to absorption [13]. ∆𝑓 = −𝑐𝑚𝑓0 2ℎ′∆𝜌𝑠 (3) 3. saw sensor simulation via finite element method the saw sensors were simulated using the fem. as shown in fig. 1, each saw-based gas sensor consisted of an input idt, a mass loading area, and an output idt. with an acoustic wave velocity of 3159 m/s [10], quartz was our choice of piezoelectric substrate. based on equation (1), the resonant frequency of the saw sensors was 40 mhz. aluminum electrodes, with a /4-width and 800 nm-thickness, were used as the idts. three reflectors, with a width and spacing of /8, were placed on either side of the sensors. figure 2 shows a 2d model of the simulated saw-based gas sensor while its physical parameters are detailed in table 1. fig. 2: 2d model of the simulated saw-based gas sensor. 3.1 polymeric sensing layers polymers are highly sensitive, making them an ideal choice of sensing layer. when exposed to vocs, the sensing layer absorbs and desorbs these vapor analytes resulting in physical changes in mass and dielectrical properties that affect the resonant frequency, which is then converted into an electrical output signal [14]. polymer-based saw sensors for gasses are highly sensitive, have low energy consumption, short response times, and perform well at room temperature. table 1 lists the polymers used in our fem simulations: (1) polyisobutylene (pib), (2) polydimethylsiloxane (pdms), (3) polyisoprene (pip), (4) polyimide (pi), and (5) phenylmethyldiphenylsilicone (ov25) as well as the physical parameters of the simulated saw-based gas sensors. 171 iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 table 1: physical parameters of the simulated saw-based gas sensors. parameter expression substrate material quartz resonant frequency 47 mhz idts material aluminum (al) wavelength 80 µm width 20 µm sensing layer material polyisobutylene (pib) polydimethylsiloxane (pdms) polyisoprene (pip) polyimide (pi) phenylmethyldiphenylsilicone (ov25) thickness 800 nm voc vapor material dichloromethane (dcm) trichloroethylene (tce) dichloroethylene (dce) carbon tetrachloride (ccl4) 3.2 volatile organic compounds (vocs) a sensor’s response depends on the interaction between the voc vapors and the polymeric sensing layer. to better understand these interactions, as well as the transduction mechanism of the device, these responses should be comparable. it is well established that a saw sensor coated with a permeable material will produce responses proportional to the partition coefficient, k [15]. an increase in sensing layer density indicates vapor absorption. in our fem simulations, sensors are exposed to vocs at room temperature and atmospheric pressure. therefore, as a consequence of mass loading, the simulations will experience changes in the mechanical and electrical boundaries. table 2 lists the vocs used in our fem simulations: (1) dichloromethane (dcm), (2) trichloroethylene (tce), (3) 1,2dichloroethylene (dce), and (4) carbon tetrachloride (ccl4) as well as the critical parameters used to evaluate saw-based gas sensor performance; partition coefficient (k) and molar mass (m). table 2: parameters of the simulated vocs used to calculate the density of vapors absorbed by the polymeric sensing layers type of voc partition coefficient, k molar mass, m (g/mol) dichloromethane (dcm) 101.4821 84.93 trichloroethylene (tce) 102.3994 131.4 dichloroethylene (dce) 101.9215 96.95 4. saw sensor simulation via finite element method the frequency shift is calculated by evaluating the eigenfrequency before and after sensing the absorbed vapors at different concentrations. subtracting the output eigenfrequency value, obtained after exposure to a specific vapor concentration, from the input eigenfrequency value, obtained before exposure to a voc, provides the frequency shift. therefore, the frequency shift of a saw sensor can be determined by dielectrically repeating this procedure [15]. in our fem simulations, quartz was used as the piezoelectric substrate. figure 3 shows the resonant frequency of the saw-based gas sensor before exposure to any vocs. this resonance is caused by constructive interference as most of the 172 iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 acoustic wave propagations occur on the surface and their amplitude decreases according to material depth [16]. fig. 3: 2d model of the simulated saw-based gas sensor. 4.1 saw sensor sensitivity according to polymer the five polymer-coated sensors were used to detect dcm vapor. shifts in frequency were then calculated for analysis. the results of our fem simulation for each polymer-voc interaction are shown in fig. 4. as frequency shift is affected by vapor concentration, the dcm vapor was set at concentrations of 500 ppm to 3000 ppm. the pib-coated sensor had the highest sensitivity (4.0571 khz/ppm) followed by the ov25-coated sensor (3.7143 khz/ppm). pib is highly sensitive as it is highly permeable, thereby allowing quicker absorption, desorption, and reversibility post-vapor analyte exposure which is ideal for mass-sensitive sensors such as the saw-based gas sensor [17]. fig. 4: the sensitivity of polymer-coated sensors to dcm vapor. 4.2 saw sensor sensitivity according to vocs as it had the highest sensitivity, the pib-coated sensor was used to detect each voc which is measured by a downward shift in resonant frequency [15]. the frequency shifts, as a result of increased surface density caused by vapor absorption, of the pib-coated sensor after exposure to dcm, tce, dce, and ccl4 vapors were calculated. as shown in figure 5(a), the higher the vapor concentration, the higher the density of vapor absorbed by the pib-sensing layer, the higher the shift in resonant frequency. figure 5(b) shows that the pib-coated sensor had the highest sensitivity to tce vapor (45.257 khz/ppm) and lowest 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 4.1 pib ps pi pdms peut pip ov25 s e n s it iv it y ( h z /p p m ) type of polymer 173 iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 sensitivity to dcm vapor (4.0571 khz/ppm). this indicated that the pib-coated sensor had excellent selectivity towards tce vapor. . (a) (b) fig. 5: pib-coated sensor sensitivity to dcm, tce, dce, and ccl4 vapors. (a) frequency shift according to vapor concentrations (b) pib-coated sensor sensitivity according to type of voc. 4.3 saw sensor sensitivity according to vocs to further demonstrate this approach, the sensitivity of two polymeric sensing materials; pib and ov25; to tce, dce, and dcm vapors was investigated. quartz was maintained as the substrate material in this simulation. the sensor responses in relation to vapor concentrations were performed to determine the sensitivity of each polymer-vapor combination while individual sensor responses to various pairs of vapors would validate their sensitivity. figures 6 and 7 show the responses of piband ov25-coated sensors to tce, dce, and dcm vapors. figure 6 shows the frequency shifts of piband ov25-coated sensors exposed to low concentrations of tce and dce vapors. the ov25-coated sensor had the highest sensitivity to both concentration in the range of 50 ppm to 300 ppm (52.57 khz/ppm) concentrations of tce vapor in comparison to the pib-sensing layer. fig. 6: frequency shift results of the fem simulations of piband ov25-coated sensors exposed to concentrations of tce and dce vapors in the range of 50 ppm to 300 ppm. 500 1000 1500 2000 2500 3000 0 20 40 60 80 100 120 140 f re q u e n c y s h if t (k h z )) concentraation of gas (ppm) dcm tce dce cci4 dcm tce dce cci4 0 10 20 30 40 50 s e n s it iv it y ( k h z /p p m ) type of voc 50 100 150 200 250 300 0 2 4 6 8 10 12 14 16 18 f re q u e n c y s h if t (k h z ) concentration (ppm) pib_tce ov25_tce pib_dce ov25_dce 174 iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 dcm vapor was selected to evaluate the performance of piband ov25-coated sensors as shown in fig. 7. the pib-sensing layer had marginally higher frequency shifts in reaction to both low (4.06 khz/ppm) and high (3.54 khz/ppm) concentrations of dcm vapor in comparison to the ov25-coated sensor. figure 8 summarizes the sensitivity of both sensing layers to low (500 ppm to 3000 ppm) and high (3000 ppm to 5500 ppm) concentrations of tce, dce, and dcm vapors. the fem simulations clearly indicate that frequency shifts and sensitivity vary according to the polymer-coating and type of voc tested. therefore, the choice of polymer-coating depends entirely on the voc to be detected. (a) (b) fig. 7: frequency shift results of the fem simulations of piband ov25-coated sensors exposed to (a) low concentration and (b) high concentrations of dcm vapor. (a) (b) fig. 8: sensitivity results of the fem simulations of piband ov25-coated sensors exposed to (a) low concentration and (b) high concentrations of tce, dce, and dcm vapors. table 3 shows the comparison of simulation results with other previous work. the results show that the sensor is having higher shift in resonance frequency at high concentrations for both previous works and the current work. 500 1000 1500 2000 2500 3000 2 4 6 8 10 12 14 f re q u e n c y s h if t (k h z /p p m ) concentration (ppm) pib_dcm ov25_dcm 3000 3500 4000 4500 5000 5500 10 12 14 16 18 20 p ib _ d c m concentration (ppm) pib_dcm ov25_dcm 44.57 12.57 4.06 52.57 24.57 3.71 tce dce dcm 0 10 20 30 40 50 60 s e n s it iv it y ( k h z /p p m ) type of voc pib ov25 45.26 11.2 3.54 53.54 24.29 3.43 tce dce dcm 0 10 20 30 40 50 60 s e n s it iv it y ( k h z /p p m ) type of voc pib ov25 175 iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 table 3: comparison of simulation results with other previous work parameter lukose (2009) [12] zhao (2009) [15] this work substrate material quartz st-x quartz quartz resonant frequency 303.79 mhz 158 mhz 47 mhz idts material nickel aluminum (al) sensing layer material fluoroalco holpolysiloxane (sxfa) film with varies thickness of h/lambda (0 – 0.22) pib, ov25 pib, pdms, pi voc vapor material with range of concentration dmmp (10110 mg/m3) tce, dce low concentration (1– 160 mg/m3) high concentration (0.2 – 2.0 g/m3) dcm, tce, dce low concentration (500 to 3000 ppm) high concentration (3000 to 5500 ppm) frequency shift (hz) 220 hz low concentration (2 – 35 khz) high concentration (2 – 500 khz) low concentration (2 – 14 khz) high concentration (1 – 20 khz) 5. conclusion the finite element method (fem) simulations conducted by this study were able to successfully demonstrate the resonant frequency shifts and sensitivity of five polymeric materials: (1) polyisobutylene (pib), (2) polydimethylsiloxane (pdms), (3) polyisoprene (pip), (4) polyimide (pi), and (5) phenylmethyldiphenylsilicone (ov25) to both low and high concentrations of four vocs: (1) dichloromethane (dcm), (2) trichloroethylene (tce), (3) 1,2-dichloroethylene (dce), and (4) carbon tetrachloride (ccl4). it is evident that resonant frequency shifts vary according to polymer-coated sensor and voc interactions. the 800 nm thick pib-sensing layer had the highest sensitivity (4.0571 khz/ppm) to dcm vapor as well as good sensitivity (45.257 khz/ppm) to tce vapor. however, the choice of polymer-coating depends entirely on the voc to be detected. the ov25-sensing layer had the highest sensitivity to both low (52.57 khz/ppm) and high (53.54 khz/ppm) concentrations of tce vapor. the pib-sensing layer had the highest sensitivity to both low (4.06 khz/ppm) and high (3.54 khz/ppm) concentrations of dcm vapor. it is evident that voc concentrations also affect the sensitivity of the polymer-coated sensors. therefore, the findings of this study indicate that polymer-coated saw-based gas sensor are highly capable of self-powered voc detection. acknowledgement this work was supported by the ministry of higher education (mohe) malaysia under the fundamental research grant scheme (frgs) (grant no.: frgs 17-032-0598). references [1] kim id, choi sj, kim sj, jang js. (2015) exhaled breath sensors. in: kyung cm. (eds) smart sensors for health and environment monitoring. kaist research series. springer, dordrecht. https://doi.org/10.1007/978-94-017-9981-2_2 [2] lee bc, tward dj, mitra pp, miller mi. (2018) on variational solutions for whole brain serial-section histology using a sobolev prior in the computational anatomy random orbit model. plos comput biol 14(12): e1006610. https://doi.org/10.1371/ journal.pcbi.1006610 176 iium engineering journal, vol. 22, no. 2, 2021 md ralib and syamsil omar https://doi.org/10.31436/iiumej.v22i2.1612 wang c, sahay p. (2009) breath analysis using laser spectroscopic techniques: breathbiomarkers, spectral fingerprints, and detection limits. sensors (basel, switzerland), 9(10): 8230-8262. https://doi.org/10.3390/s91008230 [4] kim kh, jahan sa, kabir e. (2012) a review of breath analysis for diagnosis of human health. trac trends in analytical chemistry, 33: 1-8. [5] afzal a, iqbal n, mujahid a, schirhagl r. (2013) advanced vapor recognition materials for selective and fast responsive surface acoustic wave sensors: a review. analytica chimica acta, 787: 36-49. [6] aslam, m.z.; jeoti, v.; karuppanan, s.; malik, a.f.; iqbal, a. fem analysis of sezawa mode saw sensor for voc based on cmos compatible aln/sio2/si multilayer structure. sensors 2018, 18, 1687. https://doi.org/10.3390/s18061687 [7] ralib aam, nordin an, salleh h. (2010) a comparative study on mems piezoelectric microgenerators. microsystem technologies, 16(10): 1673-1681. [8] arshak, k., moore, e., lyons, g.m., harris, j. and clifford, s. (2004), "a review of gas sensors employed in electronic nose applications", sensor review, vol. 24 no. 2, pp. 181198. https://doi.org/10.1108/02602280410525977 [9] hazadi ahf, ralib aam, saidin n. (2018) design and simulation of electroacoustic sensor for exhaled breath analysis. in 2018 7th international conference on computer and communication engineering (iccce) pp. 388-391. [10] mujahid, a.; dickert, f.l. surface acoustic wave (saw) for chemical sensing applications of recognition layers. sensors 2017, 17, 2716. https://doi.org/10.3390/s17122716 [11] choi, k., kim, h., ali, k. et al. hybrid surface acoustic waveelectrohydrodynamic atomization (saw-ehda) for the development of functional thin films. sci rep 5, 15178 (2015). https://doi.org/10.1038/srep15178 [12] lukose v, nemade hb. (2019) finite element simulation of one-port surface acoustic wave resonator with thick interdigital transducer for gas sensing. microsystem technologies, 25(2): 441-446. [13] haresh m., pandya, (2010) design and modelling of surface acoustic wave (saw) devices and sensors", ph.d. thesis, bharathiar university, coimbatore: 8. [14] liu x, cheng s, liu h, hu s, zhang d, ning h. (2012) a survey on gas sensing technology. sensors, 12(7): 9635-9665. [15] zhao yg, liu,m, li dm, li jj, niu jb. (2009) fem modeling of saw organic vapor sensors. sensors and actuators a: physical, 154(1): 30-34. [16] johnson s, shanmuganantham t. (2014) design and analysis of saw based mems gas sensor for the detection of volatile organic gases. carbon, 119(5): 0-041316. [17] sayago i, fernández mj, fontecha jl, horrillo mc, vera c, obieta i, bustero i. (2012) new sensitive layers for surface acoustic wave gas sensors based on polymer and carbon nanotube composites. sensors and actuators b: chemical, 175: 67-72. 177 [3] application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 automatic facial redness detection on face skin image izzati muhimmah*, nurul fatikah muchlis and arrie kurniawardhani department of informatics, universitas islam indonesia, yogyakarta, indonesia * corresponding author: izzati@uii.ac.id (received: 1st june 2020; accepted: 2nd september 2020; published on-line: 4th january 2021) abstract: one facial skin problem is redness. on site examination currently relies on examination through direct observations conducted by doctors and the patient's medical history. however, some patients are reluctant to consult with a doctor because of shame or prohibitive costs. this study attempts to utilize digital image processing algorithms to analyze the patient's facial skin condition automatically, especially redness detection in the face image. the method used for detecting red objects on face skin for this research is redness method. the output of the redness method will be optimized by feature selection based on area, mean intensity of the rgb color space, and mean intensity of the hue intensity. the dataset used in this research consists of 35 facial images. the sensitivity, specificity, and accuracy are used to measure the detection performance. the performance achieved 54%, 99.1%, and 96.2% for sensitivity, specificity, and accuracy, respectively, according to dermatologists. meanwhile, according to pt. avo personnel, the performance achieved 67.4%, 99.1%, and 97.7%, for sensitivity, specificity, and accuracy, respectively. based on the result, the system is good enough to detect redness in facial images. abstrak: salah satu masalah kulit wajah adalah kemerahan muka. pemeriksaan di lokasi kini bergantung pada pemeriksaan melalui pemerhatian langsung yang dilakukan oleh doktor dan sejarah perubatan pesakit. namun, sebilangan pesakit enggan berunding dengan doktor kerana rasa malu atau kos yang terhad. kajian ini cuba membuat sistem pengesanan kemerahan wajah yang dapat menganalisis keadaan wajah, terutama kemerahan, melalui gambar kulit wajah. kaedah yang digunakan untuk mengesan objek merah pada kulit wajah bagi penyelidikan ini adalah kaedah kemerahan. keluaran kaedah kemerahan akan dioptimumkan dengan pemilihan ciri berdasarkan luas, intensiti min rgb, dan intensiti min hue intensity. set data yang digunakan dalam penyelidikan ini terdiri daripada 35 gambar wajah. nilai pengesahan yang digunakan adalah kepekaan, kekhususan, dan ketepatan. hasil yang diperoleh berdasarkan pakar dermatologi masingmasing adalah 54%, 99.1%, dan 96.2% untuk kepekaan, kekhususan, dan ketepatan. sementara itu, pt. selain itu, menurut kakitangan avo 67.4%, 99.1%, dan 97.7%, bagi kepekaan, kekhususan, dan ketepatan, masing-masing. berdasarkan dapatan kajian ini, sistem ini cukup baik bagi mengesan kemerahan pada gambar wajah. keywords: digital image processing; face skin; redness; redness method 1. introduction most people experience problems with their facial skin, such as redness [1]. redness is one of the topics that are often discussed in either health and beauty articles or online consultation of health sites. to examine skin problems, we usually see the doctor for on-site 68 iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 examination [2]. however, several patients are reluctant to consult with doctors for reasons such as fear and shame. as a result, they decide to treat their skin problem by themselves, commonly known as self-care. however, self-care can sometimes make the redness worse. examining facial skin redness using digital image processing is one solution [3-5]. one of the studies that has been conducted is assessment of rosacea [4-5]. rosacea is a skin redness problem [6]. sainthillier et al. quantified the extent and intensity of the rosacea using image processing and a neural network. the input images used in their study were localized in a specific area, namely the cheekbone area [4]. furthermore, the investigator selected the zones affected by rosacea on the image as well as the zones without signal (nonrosacea artefacts, e.g., white background). those images were taken using a videocapillaroscope with a 50× magnification. ledoux et al. utilized a perceptual color hit-ormiss transform for detecting rosacea in skin image [5]. input images used in their study were of a specific area of skin that contained rosacea. novin and aarabi conducted research for skin redness analysis and pigmented skin lesions analysis [7]. this research analyzed body skin redness and the results were presented in the form of augmented reality on a smartphone. this research uses rgb color space to detect skin. skin detection using this color space will also detect background objects that have a skin-like color and consider them to be skin as well. rgb color space is also used in the equation to find red regions in the skin. pixels that have a red color above the threshold were set as part of the reddish object. in redness estimation a slider was provided to get a user defined threshold value. this study attempts to utilize digital image processing algorithms to analyze the patient's facial skin condition automatically, especially redness detection. a facial redness detection is needed as early detection of skin redness conditions. it can help patients to analyze their facial skin abnormalities. in addition, in the future, the facial redness detection is expected to provide an overview of skincare products that are suitable for facial conditions. 2. methods and data 2.1 data this research used secondary data obtained from the internet randomly and from beauty product companies (pt. avo innovation technology). data collected are human face images that have redness in their facial skin without certain race boundaries. the characteristics of the image used are color image, face position facing forward, and evenly distributed lighting. the dataset on this research is 35 images, two as training data and 32 as test data. the collected images are jpg, jpeg, png formats. 2.2 redness face skin redness on skin can be caused by increase of hemoglobin saturation, increase in the diameter of the actual skin capillaries, or a combination of these factors [8]. redness sometimes makes facial skin feel warm or gives a burning sensation. redness can make a person feel unconfident with their own appearance. redness on skin can occur due to inflammation, skin irritation, allergies, and bacteria [9]. 2.3 redness method redness method is feature extraction algorithm to calculate the redness value of each pixel. eq. (1) is used to determine the redness value of each pixel [7]. 𝑅𝑒𝑑𝑛𝑒𝑠𝑠 = 𝑚𝑎𝑥 {0, 2𝑅−(𝐺+𝐵) 𝑅 } 2 (1) 69 iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 where r = red intensity in corresponding pixel; g = green intensity in corresponding pixel; and b = blue intensity in corresponding pixel. 2.4 k-means clustering clustering is a method for dividing a set of data into groups. the clustering-based segmentation used in this research is k-means. k in k-mean is the total number of clusters, which is randomly determined. k-means clustering will assign a data to a particular cluster according to the distance between the data and the centroid of the k cluster. data will be assigned to a cluster whose centroid has the shortest distance to the data among the other cluster centroids [10]. 2.5 gaussian filtering gaussian filtering is a pre-processing technique in digital image processing. this filter is usually used when an image has a lot of noise. gaussian filtering reduces the noise by smoothing the image using the gaussian principle [11]. images smoothed using gaussian filtering will usually change to a blurry image. a blurry image helps during the segmentation process because the intensity value of a pixel has a more uniform intensity value compared to its neighbors. 2.6 canny method canny method also known as canny edge detection is a method in digital image processing to detect the edges of objects. canny edge detection uses two thresholds so that it is possible to detect strong and weak edges [12]. edges in digital image processing are found by representing a series of intensities in the image to a graph. if there are curves on the graph, this shows that there is a drastic change in the intensity of an image. this drastic change in intensity is marked as an edge. 2.7 validation the validation applied in this research is a confusion matrix with a single decision threshold method. this validation will compare the detection results performed by the system (predictive value) to the results of the diagnosis by the expert (actual value). according to owens and sox [13], sensitivity is used to measure the percentage of positive data that is correctly identified (both experts and systems detect the same redness object). specificity is used to measure the percentage of negative data that is correctly identified (the system does not detect non-redness objects from candidates as redness objects). accuracy is used to measure the percentage of the system’s precision level in classifying data correctly (data that is predicted correctly by the system is divided by the total number of test data). the confusion matrix table can be seen in table i. table 1: confusion matrices expert true false system true tp fp false fn tn based on the values of true positive (tp), false positive (fp), true negative (tn), and false negative (fn) we can get the values of sensitivity, specificity, and accuracy. 70 iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 following is the calculation for sensitivity, specificity, and accuracy which can be seen in eq. (2), eq. (3), and eq. (4), respectively. 𝑆𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦 = 𝑇𝑃 𝑇𝑃+𝐹𝑁 (2) 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐𝑖𝑡𝑦 = 𝑇𝑁 𝑇𝑁+𝐹𝑃 (3) 𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = 𝑇𝑃+𝑇𝑁 𝑇𝑃+𝑇𝑁+𝐹𝑃+𝐹𝑁 (4) 2.8 methodology the design of this research uses the flowchart seen in fig. 1. the flowchart consists of four main processes. the input of the system is an rgb face image (original image) and the output of the system is a face image with a redness object that has been marked (marked image). the process consists of pre-processing (image resizing), separating face skin from the background (skin segmentation), redness object detection (feature extraction), and redness marking. fig. 1: flowchart of facial redness detection. first, the input image is resized (resized image) when its number of rows or columns exceeds 500 pixels. if the number of rows exceeds 500 pixels and is longer than the columns, the row size will be reduced to 480 pixels and the column size will be adjusted. conversely, if the column size exceeds the row size, then the column size will be reduced to 480 pixels and the row size will adjusted. this process is needed because the dataset used is randomly obtained from the internet so the image size can vary. second, skin segmentation is the process of separating skin and non-skin objects. this skin segmentation assists the redness detection process to prevent the system from detecting any redness objects that are not in the skin area. this segmentation process separates skin and non-skin objects by clustering using k-means in the hsv color space. the resized image from the resize image process is converted to the hsv color space (hsv image). after being converted, hsv image is segmented according to a threshold value (segmented hsv image). the threshold values are less than and equal to 25 for the hue layer and between 0.15 to 0.9 for the saturation layer. next, the segmented hsv image is clustered using k-means clustering. the number of k for k-means clustering is 3, representing skin, non-skin, and background. skin objects that will be taken from the results of k-means clustering are the cluster that has the highest number of members (skin image). this is done by assuming that the skin object has the broadest area in the face image. third, the redness objects in the skin image are sought by identifying their characteristics. the redness method [7] is utilized to calculate the redness value of each pixel in the skin image. the redness method works on rgb images. first, the rgb value of each pixel in skin image is obtained. the redness value of each pixel is computed using 71 iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 eq. (1). furthermore, the median of those redness values of all pixels in an image is determined as the threshold. each pixel that has a value lower than the median will be omitted and each pixel that has a value greater than the median will be retained as a redness object candidate. an image with a redness object candidate is obtained (redness candidate image), but there is noise in that image. a gaussian filter with standard deviation value is 0.5 is applied in that redness candidate image to get a smoother image and to reduce the noise (gauss image). a gaussian image still has non-redness objects, so the object elimination process is needed. first, non-redness objects are eliminated according to pixel value in the gaussian image and redness image. if the pixel value in the gaussian image is equal to 76 (indicating the redness object in a grayscale image), the pixel value in the redness image is retained. otherwise, the pixel value in the redness image is changed to 0 (gaussian redness 1 image). second, the pixel values in the gaussian redness 1 image that are lower than 1 are retained. otherwise, the pixel value in the gaussian redness 1 image is changed to 0 (gaussian redness 2 image). third, objects in the gaussian redness 2 image that have an area wider than 90 are retained. otherwise, the object is eliminated (area image). fourth, non-redness objects are eliminated by a threshold value according to the rgb color value in the original image. the lower threshold value for red intensity is mean intensity value in the red layer subtracted by the multiplication of the standard deviation of the intensity value in the red layer by 1.32. whereas the upper threshold value for red intensity is mean intensity value in the red layer added to the multiplication of the standard deviation of the intensity value in the red layer by 1.32. the same thing is done to find the lower and upper thresholds in the blue and green layers. if the redness object candidate in area image has an average intensity of rgb color in those range thresholds, the redness object candidate will be retained. otherwise, it will be eliminated (rgb eliminated image). fifth. nonredness objects are eliminated by a threshold value according to hue color value in the original image. the lower threshold value for hue intensity is mean intensity value in the hue layer subtracted by the multiplication of the standard deviation of the intensity value in the hue layer by 1.16. whereas the upper threshold value for hue intensity is the mean intensity value in the hue layer added to the multiplication of the standard deviation of the intensity value in the hue layer by 0.5. if the redness object candidate in the rgb eliminated image has an average intensity of hue color in those range thresholds, the redness object candidate will be retained. otherwise, the object is eliminated (hue eliminated image). the last process is redness object marking using the canny method. this process marks the redness objects obtained from the hue eliminated image. first, the edge pixels of each redness object in hue eliminated image are detected using the canny method. in the original image, the intensity value of those edge pixels will be changed to red. 3. results and discussion all processes that have been designed in fig. 1 were implemented into program code using matlab software. the first process is image resizing. the output of this process is the image that looks similar to the original image, but the size of the image is different. the maximum size, 500x500 pixels, is determined based on the training process that gives the best performance for this study. in addition, image size that exceeds 500x500 pixels will take a longer time for computation. the hsv color space is used in the skin segmentation process because it can distinguish between brown, red, or other tones in the skin image. in addition, hsv is purest form of color based on wavelength that can truly describe the human colors. images with non-black 72 iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 and non-white skin color use hue values and saturation for the segmentation processes [14]. this research only uses the hue and saturation layers according to the data set used in this study. the parameter values of hsv are according to [15]. k-means clustering is a process to group the results of the hsv segmentation into three clusters. in the skin segmentation process, there are still background objects in the image that are categorized as skin, so this process is needed. this clustering separates skin, nonskin, and background objects. the system will use the intensity value as a reference to group each pixel. the result of k-means clustering can be seen in fig. 2(a)-(c). the cluster that has the highest number of members, fig. 2(a), is chosen. the cluster that has the highest number of members is chosen because face skin is the largest area in the image. unfortunately, fig. 2(a) has many holes. to close those holes, a region filling algorithm is applied. the result of skin segmentation can be seen in fig. 2(d). the face skin can be segmented except the eyebrow. in the redness detection, this is not an issue because this study looks for the redness object that has red color characteristics. (a) (b) (c) (d) fig. 2: k-means clustering segmentation. (a) (b) (c) fig. 3: redness object detection (a) redness method (b) redness pixel (c) gaussian filtering. next, the result of redness object detection with the redness method can be seen in fig. 3(a) and 3(b). this method identifies the redness pixel using dynamic parameters according to the rgb value of each pixel. it is different from using manual color segmentation which requires the researcher to search the redness range of each image. gaussian filtering is needed to eliminate scattered noise by smoothing the images. this filter can eliminate noise with results that look similar to the original image. noise is eliminated without removing redness objects. the result of image improvement with gaussian filtering is shown in fig. 3(c). however, in fig. 3(c) non-redness pixels are still marked, as in the eyes, nose, and lips. so, to eliminate non-redness pixels, another extraction is conducted. non-redness objects eliminated based on pixel value in gauss image and redness image. area, mean intensity 73 iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 rgb, and hue mean intensity of each object are calculated. the results of those processes are shown in fig. 4(a)-4(d), respectively. the result of the previous elimination process is able to eliminate several non-redness objects in the lips. a threshold of 90 for area is selected according to the smallest area of redness objects in the training data. the non-redness objects that are eliminated are quite numerous, with only the large objects left in the nose and neck. when using rgb intensity, the system can eliminate non-redness object in the neck. while using hue intensity can eliminate the non-redness objects in the nose. (a) (b) (c) (d) fig. 4: feature extraction (a) by index (b) by area (a) by rgb color space (b) by hue intensity. fig. 5: redness object marking. the marking process aims to make it easier for users to find the redness object location in face image. the result of marking process can be seen in fig. 5. the system interface for this study is shown in fig. 6. the interface of this system consists of three panels. the first panel has an “insert image” button and the third panel has a “see result” button to see the detection results. the algorithm is validated using a confusion matrix that evaluates 33 test images. the validation process compares the results given by system to the expert’s diagnostic. the experts are a dermatologist from the faculty of medicine in universitas islam indonesia and personnel of pt.avo innovation technology. the validation results that compare to the dermatologist get low sensitivity value namely 54% but the specificity and accuracy values can achieve 99.1% and 96.2%. the validation results that compare to pt.avo skin innovation technology personnel reach similar results. the sensitivity, specificity, and accuracy values are 67.4%, 99.1%, and 97.7%, respectively. 74 iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 fig. 6: interface for redness object detection. sensitivity that can only reach around 60% indicates that the detection of the redness object has not yet been optimal. to find the cause of detection failure, the researcher compared the results of the redness marking by the system and the assessment of the expert. in this study there are three causes of failure, namely poor image quality, uneven lighting, and overly wide range of redness color objects. the resolution of the image in fig. 7(a) is only 250x250 pixels and the lighting is unevenly distributed. in the segmentation process, several parts of skin pixels are categorized into cluster backgrounds. it makes the redness objects unable to be detected in the following step. in fig. 7(a) the redness objects are diagnosed by experts while in fig. 7(b) the redness objects are detected by the system. in fig. 7(d) there are several redness objects that are not detected by the system, whereas they are diagnosed by experts in fig. 7(c). on the other side, there are also some non-redness objects that were detected as redness objects by the system. those redness objects cannot be selected by the system because of the range of mean intensity. hue colors on the redness object are between 0.01 to 0.17. meanwhile the range of mean intensity of the hue colors of non-redness objects are between 0.02 to 0.05. so, there are non-redness objects detected as objects, namely eyebrows, lips, and neck. in addition, there are also undetectable redness objects, such as in the left cheekbone because it has a value of 0.4. however, if the hue color range is increased, it can make the system detect non-redness parts as an object. (a) (b) (c) (d) fig. 7. redness object detection; (a) by expert (b) by system (c) by expert (d) by system. 4. conclusion this paper tries to make a facial redness detection system that can analyze facial conditions, especially redness, through facial skin images. the system is expected to help patients for early detection of skin redness conditions to make it easier to select appropriate 75 iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 facial care products and health care. the redness detection process begins by detecting facial skin in facial images. furthermore, the redness area will be identified on the facial skin object obtained in the previous process. the method used for detecting red objects on face skin for this research is the redness method. the output of the redness method will be optimized by feature selection based on area, mean intensity of rgb, and mean intensity of hue intensity. the validation value used is sensitivity, specificity, and accuracy based on experts, namely a dermatologist and pt.avo innovation technology personnel. the results obtained based on the dermatologist is 54%, 99.1%, and 96.2% for sensitivity, specificity, accuracy, respectively. meanwhile, the results from pt.avo personnel are 67.4%, 99.1%, and 97.7%, for sensitivity, specificity, accuracy, respectively. the cause of the sensitivity only reaching around 60% are poor image quality, uneven lighting, and an overly-wide range of colors for each object. acknowledgement the authors are grateful to the informatics department, universitas islam indonesia for the financial support granted to cover the publication fee of this research article and to pt.avo innovation technology personnel for image dataset support. references [1] weller h, mann m, hunter h. (2015) cosmetic dermatology: weller h, mann m, hunter h. clinical dermatology. 5th edition. chichester, wiley-blackwell; pp. 323-333. [2] fernando e. (2015) prototype content based image retrieval untuk deteksi penyakit kulit dengan metode edge detection (studi kasus : klinik penyakit kulit rsu. mataher jambiindonesia) (content based image retrieval prototype for detection of skin diseases by edge detection method (case study: skin disease clinic, general hospital, mataher jambiindonesia)). jurnal ipteks harapan, 2: 214-223. [3] herbin m, venot a, devaux j, piette c. (1990). colour quantitation through image processing in dermatology. ieee transactions on medical imaging, 9(3):262-269. [4] sainthillier jm, mac s, humbert p. (2007) assessment of rosacea by image processing and neural network. expert review of dermatology, 2(3): 277-282. https://doi.org/10.1586/17469872.2.3.277 [5] ledoux a, richard n, capelle-laizé as, fernandez-maloigne c. (2015) perceptual color hit-or-miss transform: application to dermatological image processing. signal, image and video processing, 9(5): 1081-1091. [6] gessert ce, bamford jt. (2003) measuring the severity of rosacea: a review. international journal of dermatology, 42(6): 444-448. https://doi.org/10.1046/j.1365-4362.2003.01780.x [7] novin ia, aarabi p. (2014, october) skin lens: skin assessment video filters. in 2014 ieee international conference on systems, man, and cybernetics (smc); pp. 1033-1038. https://doi.org/10.1109/smc.2014.6974049 [8] franks ag. (1993) cutaneous manifestations of disorders of the cardiovascular and pulmonary systems: dermatology in general medicine. 4th edition. new york, mcgraw-hill; pp. 2063-104. [9] fadhilah an, fatimah dds, damiri dj. (2012) perancangan aplikasi sistem pakar penyakit kulit pada anak dengan metode expert system development life cycle (designing expert system application for skin diseases in children with expert system development life cycle method). jurnal algoritma, 9(1): 112-118. [10] zaitoun nm, aqel m. (2015) survey on image segmentation techniques. procedia computer science, 65: 797-806. [11] al-najdawi n, biltawi m, tedmori s. (2015) mammogram image visual enhancement, mass segmentation and classification. applied soft computing, 35: 175-185. 76 iium engineering journal, vol. 22, no. 1, 2021 muhimmah et al. https://doi.org/10.31436/iiumej.v22i1.1495 [12] chavan a, bendale d, shimpi r, vikhar p. (2016) object detection and recognition in images. international journal of computing and technology, 3(3):148-151. [13] owens dk, sox hc. (2014) biomedical decision making probabilistic clinical reasoning. in biomedical informatics, springer, london; pp. 67-107. [14] shaik kb, ganesan p, kalist v, sathish bs, jenitha jmm. (2015) comparative study of skin color detection and segmentation in hsv and ycbcr color space. procedia computer science, 57: 41-48. [15] mujahidi, s. (2012) aplikasi perhitungan jumlah orang dalam satu foto (application for calculating the number of people in one photo). thesis. universitas islam indonesia, department of informatics. 77 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 study of effective omni-directional vertical axis wind turbine for low speed regions alisher bekmurdovich safarov1 and rasul akif-ogli mamedov2* 1department of energy audit, 2department of energy, bukhara engineering technological institute, bukhara, uzbekistan. *corresponding author: rasul_91-92@mail.ru (received:4th august 2020; accepted: 16th january 2021; published on-line: 4th july 2021) abstract: this article presents theoretical and experimental studies of an improved vertical axis wind power device that generates electricity in areas with an average wind speed of 3.5-4.5 m/s. an algorithm has been developed for determining the geometrically optimal dimensions of the outer guiding surfaces to improve the efficiency of the device at low wind speeds. the device uses an afpmg generator with opposite rotation of the stator and rotor. matlab/simulink and solidworks were used to develop a mathematical and physical model of the wind power device. according to the results of the study, it was found that the developed wind power device can reach a rated power of 700 w at a wind speed of 8 m/s. the use of the device in areas with low wind speed is based on the possibility of increasing the efficiency of work by 5-10% at an average wind speed lower than that of other types of wind power devices. abstrak: artikel ini memaparkan kajian teori dan eksperimen berkenaan alat kuasa angin paksi menegak yang diperbaharui dan menghasilkan tenaga elektrik di kawasan kelajuan angin berpurata 3.5-4.5 m/s. algoritma telah dibangunkan bagi menentukan dimensi optimum geometri permukaan berpandu luar dalam meningkatkan kecekapan peranti pada kelajuan angin yang kurang. peranti ini menggunakan penjana afpmg dengan putaran stator dan rotor yang berlawanan. matlab/simulink dan solidworks digunakan bagi menghasilkan model matematik dan fizikal peranti tenaga angin. berdasarkan dapatan kajian, didapati bahawa alat tenaga angin yang dibangunkan ini dapat mencapai daya kuasa sebanyak 700 w pada kecepatan angin 8 m/s. penggunaan alat ini di kawasan kurang kelajuan angin berkemungkinan meningkatkan efisiensi purata kerja sebanyak 5-10% pada kelajuan angin rendah, iaitu lebih rendah daripada segala jenis peranti tenaga angin lain. keywords: wind energy; low speed generator; external reference surface; vertical axis wind turbine; afpmg generator 1. introduction the increase in greenhouse gas emissions into the atmosphere, due to the burning of natural fuel sources, leads to such negative consequences as climate change. this, in turn, makes it important to increase the share of humankind that uses clean energy sources. the use of renewable energy sources such as sun, wind, biomass, geothermal energy, and hydropower is rapidly developing [1-5]. due to the low cost of electricity generated from renewable energy sources, and the fact that it is practically harmless to the environment, such projects are increasingly being implemented, large investments are made in them, and promising developments and research are supported. 149 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 currently, among renewable energy sources, the use of wind energy is one of the most promising projects. today, more than 100 countries use wind energy to provide people and industries with a reliable and clean energy source. china, india, and brazil are leading the way in the design and implementation of vertical-axis wind farms. by 2024, the world plans to increase the use of vertical wind power plants by 24% [6]. 65-70% of the territory of the republic of uzbekistan is steppes and deserts, and 45% of the population lives in remote areas. continuity and reliability of power supply remains the main problem in these areas. to meet the energy needs of the region, the possibility of using renewable energy sources is currently being evaluated. in our region there are opportunities for using solar energy, but in the desert areas, the efficiency of using solar energy is lower. the main reason for this is the high temperature and dustiness of the region. when assessing the possibility of using the potential of wind energy, it was found that the average wind speed in this area is 3.5–4.5 m/s at a height of 10 m [7,8,9]. we can develop social and economic sectors by providing reliable and uninterrupted power supply to autonomous electricity consumers in remote areas of the region. by developing a new design of a wind turbine that works effectively with variable and weak wind flows, it is possible to provide autonomous consumers with reliable and uninterrupted electricity, thereby developing social and economic sectors in the region. 2. literature review solomin v. [10] in his candidate’s dissertation on “methodological foundations for the development and creation of vertical-axial wind turbines for the agro-industrial complex of russia” in 2013 studied a new type of vertical axis wind turbine and performance methodology on the full or partial supply of electricity to small settlements, residential buildings, farms, and small workshops in order to develop infrastructure in remote areas with unstable power supply. xiongfei p. [11] in a patent he received in 2011 for a two-rotor wind turbine, proposed a vertical-axis wind turbine with an opposite rotating top and bottom wind wheel to make efficient use of low-flow wind speeds. zha g. et al. [12] in their patent on a “vertical axis wind power plant” created a wind power plant with single-rotor outer guide surfaces and inner rotating blades to supply power to urban and remote area power consumers. pezaris d. [13] in his patent (invention) for a vertical axis wind turbine with external guide surfaces in 2011 achieved high efficiency in obtaining energy at low speed wind currents by applying a new design of external guide surfaces and internal rotating wind wheels in a vertical axis wind turbine. yadav k. [14] in his research paper “model and experimental test of a generator applied to a savonius type wind turbine” simulated in matlab/simulink environment a mathematical model of a generator (permanent magnet synchronous generator, (pmsg)) applied to a savonius type wind turbine. a wind power unit with a capacity of 1 kw was combined with a pmsg generator to study the dynamic performance of the wind turbine system. kaliyev v. [15] in his dissertation on “machine without a core with permanent magnet of the current” in 2015 theoretically and practically studied a small-speed electric generator consisting of vertical axis of coreless permanent magnets. the feasibility of using this generator for low-power wind turbines has been evaluated. efficiency has been achieved by improving the optimal size of the generator. taran n. [16] in his research analyzed the possibilities of using axial generators of various designs consisting of permanent magnets with low rotational speeds for wind power and small micro-hydro-electric power station 150 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 equipment operating in low-speed wind currents. in his doctoral dissertation written in 2019, the scientist presented and evaluated the methods of mathematical modeling of three types of axial generators. ansys fluent and matlab/simulink were used to analyze the optimal dimensions and energy performance of these generators for efficient operation. lim c. et al. [17] conducted research on the possibility of applying the vertical axis of external reference surfaces to wind turbines to increase the efficiency of wind power equipment. in this study, optimal performance indicators for the use of external guide surfaces were obtained and analyzed. based on the analysis of the above studies, an optimal design of a wind turbine with a vertical axis, using an afpmg generator, the stator, and rotor which rotate in opposite directions, operating under variable and weak wind flows is developed. 3. methodology 3.1 mathematical model of a wind power plant for the theoretical substantiation of the operation of a wind power plant with a vertical axis, operating in variable and weak wind flows, we will construct mathematical models for the structure and the processes occurring in it. the rate of rotation of wind turbine blades depends on the wind speed, the radius of the wind turbine wheel, and the steering angle. this ratio is determined by the following expression [18]: λ = ωтr v = 2πnтr 60v (1) where: ωт is the rotation speed of the wind turbine wheel, r is the radius of the wind wheel, v is the wind speed, nт is the rotational speed of the turbine rotor. the torque coefficient of a wind turbine is determined by the following expression [19]: cт = cp λ (2) the total mechanical moment created in the blades of a wind power device is determined by the following expression [20]: mt = ∑ fd r (3) where: 𝐹𝑑 is the drag force created by the wind blades; 𝑅 is the drag force created by the wind blades. the expression for determining the drag force created by the wind blades in a stationary position is as follows [21]: fd = 1 2 cdρs(vcos(α)) 2 (4) where: ρ − air density; s − frontal area of the blade; v − wind speed; α − the angle between the wind speed direction and the normal direction of the blade surface; cd −drag coefficient. when the wind power device rotates about the central axis, the blades are in two positions. they consist of front and back shapes. the drag coefficient value depends on the shape of the blades. forward torque is generated by the forward blade shape facing the wind direction, while the opposite torque is generated by the rear blade shape facing the wind direction. 151 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 the expression for determining the total mechanical moment created by the vanes in a stationary position is as follows [22]: mст = 1 2 ρsr [∑ cd1(vcos(αi)) 2 − ∑ cd2 (vcos(αj)) 2 i=n 1 i=m 1 ] (5) where: cd1and cd2are the drag coefficients of the front and back surfaces of the blades. m and n the number of blades facing forward and backward in relation to the direction of the wind. r.d. blevins gave in his scientific work the drag coefficients of the blades of wind turbines with a vertical axis. it follows from the study that the drag coefficients of the front and rear surfaces are equal to cd1 = 2,3 and cd2= 1,1[23]. the total mechanical moment created on the blades when they rotate with a certain angular velocity 𝜔т relative to the central axis is determined as follows [24]: mt = 1 2 ρsr [∑ cd1(vcos(αi) − 𝜔тr) 2 − ∑ cd2(vcos(αj) + 𝜔тr) 2i=n 1 i=m 1 ] (6) when using external guide surfaces in a wind turbine, the total mechanical torque generated by the blades is determined as follows: мt = 1 2 ρsr[∑ cd1(vcos(αi) − ωr) 2i=m 1 ] (7) the mechanical force generated in a vertical axis wind turbine is determined by the following relationship: pt = мt𝜔т = 1 2 ρsr𝜔т[∑ cd1(vcos(αi) − 𝜔тr) 2i=m 1 ] (8) to describe the rotational motion of a wind power device, we use the following differential equation [25]: j dωт dt = мт − мg − kωт (9) here: мт is the mechanical torque on the shaft of the wind turbine, мg is the electromagnetic moment of the generator, k is the friction coefficient, j is the total moment of inertia of the wind turbine, 𝜔т is the rotation speed of the wind wheel. if the blades of the windmill are turned in two directions, the total mechanical speed will be equal to their sum: 𝜔𝑇 = 𝜔1 + 𝜔2 the total moment of inertia of the rotating parts of the device is equal to the sum of the moments of inertia of the wind turbine rotor and the generator. this relationship is defined by the following expression: j = jр + jг (10) here: jр is the moment of inertia of the wind turbine rotor, j𝑔 is the moment of inertia of the generator. the moment of inertia of a wind turbine rotor is determined by the following expression [26]: jр = n ∙ j0 = n ∙ m1∙ m2 2 m1+ m2 2 l2 (11) 152 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 here: n is the number of wind turbine blades, m1 is the mass of the turbine blades, m2 is the mass of the profile connecting the turbine blades and the rotor shaft, l is the distance between the centers of the turbine blades and the rotor shaft. 3.2 mathematical model of external guiding surfaces as a result of the use of external guiding surfaces, the wind speed is evenly distributed in the inner rotating part, that is, on the blades of the wind power plant, thereby ensuring the stable operation of the structure. the variable movement of the wind flow is explained on the basis of the law of continuity. the expression for the dependence of the speed of the wind flow entering and leaving the channel of the outer guide surface on the dimensions of the surface channels is as follows: [27]: 𝑉1 𝑉2 = 𝑊2∙𝐻2 𝑊1∙𝐻1 = [ 𝐷2−𝐷1 2𝑡𝑔𝜃 +𝑚]∙𝐻2 [ 𝐷2−𝐷1 2𝑡𝑔𝛽 +𝑚]∙𝐻1 = ( 𝑘+𝑡𝑔𝜃 𝑘+𝑡𝑔𝛽 ) ∙ ( 𝑡𝑔𝛽 𝑡𝑔𝜃 ) ∙ ( 𝐻2 𝐻1 ) (12) here: d1, d2outer and inner diameters of the channel of the guiding surfaces, to which the wind flow is directed; θ, β angles between the guiding surfaces, to which the wind flow is directed; m is the minimum distance between the guides to which the wind flow is directed; k is the construction factor; l is the distance between the outer and inner peripheral part of the guides, to which the wind flow is directed. fig. 1: designation of the geometric dimensions of the outer guiding surfaces. figure 1 shows the determination of the geometric dimensions of the outer guiding surfaces (a, b). having determined the optimal values of the angles β and θ, it is possible to increase the wind speed, thereby reducing the force that adversely affects the rotating blades of the wind power plant. figure 2 shows an algorithm developed to determine the optimal parameters of the outer guiding surfaces, which ensures the stable operation of the device due to the uniform transmission of the wind flow through the channels to the inner part of the wind turbine, that is, on its blades. 3.3 mathematical model of the counter rotating generator to eliminate the disadvantages associated with the use of gearboxes, low-speed generators are used in many low-power wind turbines. the use of low-speed generators in wind power plants intended for use in areas with low wind speeds increases the efficiency and reliability of the devices [28]. 153 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 fig. 2: algorithm for determining the optimal parameters of external guiding surfaces. in the developed wind power plant, a stator and rotor generator were used that rotate in opposite directions (afpmg). for a synchronous machine with noticeable poles without a rotor winding, the voltage equations for the stator circuit [29]: 𝑈𝑑 = 𝑅𝑠𝑖𝑑 + 𝐿𝑑 𝑑𝑖𝑑 𝑑𝑡 − 𝜔𝑒 𝐿𝑞 𝑖𝑞 (13) 𝑈𝑞 = 𝑅𝑠𝑖𝑞 + 𝐿𝑞 𝑑𝑖𝑞 𝑑𝑡 + 𝜔𝑒 𝐿𝑑 𝑖𝑑 + 𝜔𝑒 𝜓𝑃𝑀 (14) 154 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 the electromagnetic power of a three-phase generator consisting of permanent magnets is determined by the following expression [30]: 𝑃𝑒 = 3 2 𝜔𝑒 [𝜓𝑃𝑀 + (𝐿𝑑 − 𝐿𝑞 )𝑖𝑑]𝑖𝑞 (15) the electromagnetic moment of the generator with the number of pole pairs p is determined by the following expression [31]: 𝑇𝑒 = 3 2 𝑝[𝜓𝑃𝑀 + (𝐿𝑑 − 𝐿𝑞 )𝑖𝑑]𝑖𝑞 (16) where: 𝜓𝑝𝑚 is the maximum flow per phase coupling for the excitation system 𝜓𝑃𝑀 = √2𝐸𝑓 𝜔 (17) by applying this low speed generator to a wind turbine, its efficiency can be greatly improved. 4. results and discussion figure 3 shows the appearance of an efficient wind turbine. this wind power plant can be used by electricity consumers located far from the power supply system. fig. 3: external view of the wind power plant. fig. 4: graph of the dependence of the angles of the channel surfaces 𝜃 and 𝛽 coefficient of variability of speed (v2/v1) from the coefficient of construction k. 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 0 10 20 30 40 50 60 70 80 90 v 2 /v 1 β θ=55 θ=65 θ=75 θ=85 155 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 figure 4 shows a graph of the dependence of the angles of the channel surfaces 𝜃 and 𝛽 of the velocity variability coefficient (v2/v1) on the design coefficient k. several values of the angles are taken and analyzed in this graph. in this case, the value of the velocity coefficient will be large for small values of the angle 𝛽 and large values of the angle 𝜃. figure 5 shows the results of the generated physical model of the wind power device in the solidworks application. accordingly, according to bernoulli's law, when a wind flow of 4 m/s is applied to the outer guides, it can be seen that the wind flow speed increases by 3050%. fig. 5: a physical model of the wind power plant in the solidworks application. fig. 6: dynamic (in time) results of the electromagnetic force of a wind power plant, obtained in the matlab/simulink program, for a state in which the stator is stationary and the rotor rotates (w). fig. 7: dynamic (in time) results of the electromagnetic force of a wind power plant, obtained in the matlab/simulink program, for a state in which the stator and rotors rotate in opposite directions (w). figures 6 and 7 show graphs of the electromagnetic power (w) determined from the dynamic (in time) expression 15, built in the matlab/simulink program of the wind turbine. when plotting the graphs, the nominal wind speed was assumed to be 8 m/s. figure 8 shows the stator voltage (a) and stator current (b) at the generator output of a wind turbine rotating at rated speed. the winding of a three-phase generator is starconnected. to ensure the stable operation of the wind power plant, a low-speed generator was developed, the stator and rotors of which rotate in opposite directions (see fig. 9). 156 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 (a) (b) fig. 8: results obtained in the matlab/simulink program. (a) voltage of the stator winding, (b) current of the stator winding. (a) (b) fig. 9: external view of the developed generator in section (a), the process of experimental tests (b). table 1: main parameters of an electric generator intended for a wind farm rated power (w) 700 magnetic flux, (wb) 0.00036 stator winding inductance, (h) 0.000125 moment of inertia (kg) 0.18 rated electromagnetic moment, (nm) 14 stator thickness (mm) 18 rated speed of rotation, (rpm) 300 air gap distance between stator and magnets (mm) 1.5 number of pole pairs 16 electromagnetic induction, (t) 0.6 inductive resistance of the stator winding, (ohm) 0.7 emf generated in the stator winding, (v) 150 active resistance of the stator winding, (ohm) 12 current generated in the stator winding, (a) 4.8 number of windings 12 number of turns in one winding 350 number of phases 3 efficiency, (%) 90 157 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 table 1 shows the main parameters of an electric generator intended for a wind farm. these types of generators are mainly used in small wind turbines and micro hydropower plants. figure 10 shows a comparison of the wind power device developed by us with a prototype that does not have external guide surfaces and also has a fixed stator. fig. 10: graph of the dependence of the wind speed on the rated power of the developed wind power plant from the prototype. fig. 11: graph of the dependence of wind speed on the rated power of the developed wind power plant, as well as wind turbines produced in the republic of uzbekistan and a foreign prototype. figure 11 shows graphs comparing the wind power plant developed by us, as well as wind turbines produced in the republic of uzbekistan by the intellect-dialogue company and a prototype made in china. the research showed that the wind power device we developed works more efficiently in areas with weak wind flow in relation to prototypes with a vertical axis of rotation. -100 0 100 200 300 400 500 600 700 800 0 2 4 6 8 10 12 14 16 18 r a te d p o w e r, w average wind speed, m/s created wind turbine wind turbine prototype -100 0 100 200 300 400 500 600 700 800 0 2 4 6 8 10 12 14 16 18 r a te d p o w e r, w average wind speed, m/s created wind turbine produced by the intellect-dialogue company mbwp-600 (china) wind turbine 158 iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 5. conclusion the optimal parameters of the outer guide surfaces applied to the wind turbine are 𝐷1 = 1.5 m, 𝐷2 = 1 m, h1 = h2, 𝛽 = 25 0, 𝜃 = 500, which significantly reduces the force that negatively affects the rotation of the blades and creates the opportunity to increase the flow wind up to 30-50%. using a counter rotating afpmg generator, it was found that the power rating of the device increased from about 500 to 700 w at a wind speed of 8 m/s. it was found that the developed wind power device is 5-10% higher in performance compared to low-power wind power devices with horizontal and vertical axis, currently used at low wind speeds (3-8 m/s). due to the use of this wind power device, it is possible to provide autonomous consumers of low-power electricity located far from the central power system, which will lead to the development of social and economic spheres. references [1] sadullaev nn, safarov ab, nematov shn, mamedov ra. (2019) research on facilities of power supply of small power capability consumers of bukhara region by using wind and solar energy. international journal of innovative technology and exploring engineering, 8(9s2): 229-235. [2] norhafana m, ismail af, majid zaa. (2015) performance evaluation of solar collectors using a solar simulator. iium engineering journal, 16(2): 79-90. https://doi.org/10.31436/iiumej.v16i2.606 [3] karim ma, amin zm. (2015) mathematical modelling and performance analysis of different solar air collectors. iium engineering journal, 16(2): 43-55. https://doi.org/10.31436/iiumej.v16i2.603 [4] izanlo a, gholamian a, kazemi mv. (2017) direct power control of a dfig based wind turbins under unbalanced grid voltage without rotor position sensor. iium engineering journal, 18(1): 57-71. https://doi.org/10.31436/iiumej.v18i1.676 [5] jami ms, mel m, mohd ariff ar, abdulazeez qm. (2018) investigation of bioflocculant as renewable dewatering aid in sludge treatment. iium engineering journal, 19(1): 15-23. https://doi.org/10.31436/iiumej.v19i1.735 [6] wind turbine market growth statistics [https://www.gminsights.com/industry-analysis/windturbine-market] [7] sadullaev nn, safarov ab, nematov shn, mamedov ra. (2019) statistical analysis of wind energy potential in uzbekistan’s bukhara region using weibull distribution. applied solar energy, 55(2): 126-132. [8] sadullayev nn, safarov ab, nematov shn, mamedov ra, abdujabarov ab. (2020) opportunities and prospects for the using renewable energy sources in bukhara region. applied solar energy, 56(4): 291-301. [9] sadullaev nn, safarov ab, mamedov ra, kodirov d. (2020) assessment of wind and hydropower potential of bukhara region. iop conference series: earth and environmental science: 14-16 october 2020 [10] solomin ev. (2013) methodological foundations for the development and creation of verticalaxialwind turbines for the agro-industrial complex of russia. phd thesis. south ural state university, electrical engineering and renewable energy department. [11] xiongfei p. (2011) dual power wind turbine. china. cn102287334a. [12] zha g, dano b. (2013) vertical axis wind turbine. usa. us20130115069a1. [13] pezaris cd. (2011) omnidirectional vertical-axis wind turbine. usa. us20110033288a1. [14] yadav yk, (2016) a savonius wind turbine with electric generator: model and test. phd thesis. clemson university, mechanical engineering department. [15] kaliyev v. (2015) axial flux permanent magnet coreless machine. phd thesis. university of southern queensland, engineering sciences department. [16] taran n. (2019) optimum design of axial flux pm machines based on electromagnetic 3d fea. phd thesis. university of kentucky, electrical and computer engineering. 159 https://www.scopus.com/authid/detail.uri?origin=resultslist&authorid=57211272325&zone= https://www.scopus.com/authid/detail.uri?origin=resultslist&authorid=57211268259&zone= https://www.scopus.com/authid/detail.uri?origin=resultslist&authorid=57211264082&zone= https://www.scopus.com/authid/detail.uri?origin=resultslist&authorid=57209311049&zone= https://www.scopus.com/record/display.uri?eid=2-s2.0-85098536515&origin=resultslist&sort=plf-f&src=s&st1=mamedov&st2=r.a.&nlo=1&nlr=20&nls=count-f&sid=6fc2f8bf2f9c3e13cdd46eb1f930f9af&sot=anl&sdt=aut&sl=35&s=au-id%28%22mamedov%2c+r.+a.%22+57211264082%29&relpos=0&citecnt=0&searchterm= https://www.scopus.com/record/display.uri?eid=2-s2.0-85098536515&origin=resultslist&sort=plf-f&src=s&st1=mamedov&st2=r.a.&nlo=1&nlr=20&nls=count-f&sid=6fc2f8bf2f9c3e13cdd46eb1f930f9af&sot=anl&sdt=aut&sl=35&s=au-id%28%22mamedov%2c+r.+a.%22+57211264082%29&relpos=0&citecnt=0&searchterm= https://www.scopus.com/sourceid/19900195068?origin=resultslist https://www.scopus.com/sourceid/19900195068?origin=resultslist iium engineering journal, vol. 22, no. 2, 2021 safarov and mamedov https://doi.org/10.31436/iiumej.v22i2.1565 [17] lim yc, chong wt, hsiao fb. (2013) performance investigation and optimization of a vertical axis wind turbine with the omni-direction-guide-vane. procedia engineering, 67: 5969 [18] bezrukikh pp. (2010) wind power. (reference and methodological manual). moscow, "energia", 320 p. [19] lin sy, lin yy, bai cj, wang wc. (2016) performance analysis of vertical-axis-windturbine blade with modified trailing edge through computational fluid dynamics. renewable energy, 99: 654-662. [20] ackermann t, söder l. (2000) wind energy technology and current status: a review. renewable and sustainable energy reviews, 4(4): 315-374. [21] bronstein mg. (2011) harnessing rivers of wind: a technology and policy assessment of high altitude wind power in the u.s. technological forecasting and social change, 78: 736-746. [22] juangsa fb, budiman ba, aziz m, soelaiman ta. (2017) design of an airborne vertical axis wind turbine for low electrical power demands. international journal of energy and environmental engineering, 8:293-301. [23] blevins rd. (2003) applied fluid dynamic handbook. florida, krieger, 558 р [24] ahrens u, diehl m, schmehl r. (eds.) (2013) airborne wind energy. berlin. springer, 611 p [25] obukhov sg, sarsikeev ezh. (2012) low power wind turbine mathematical model in matlab simulink. international scientific journal for alternative energy and ecology, 2: 42-48 [26] komass t, sniders a. (2014) design and verification of vertical axis wind turbine simulation model. 13th international scientific conference engineering for rural development proceedings; 29-30 may 2014; engineering for rural development. edited by l. malinovska, v. osadcuks pp. 335-340 [27] chong wt, fazlizana a, poh sc, pan kc, hew wp, hsiao fb. (2013) the design, simulation and testing of an urban vertical axis wind turbine with the omni-direction-guide-vane. applied energy, 112: 601-609. [28] nikbakhsh a, izadfar h, alinejad beromi,y. (2017) design and optimization of permanent magnet synchronous generator for use in hydrodynamic renewable energy by applying aco and fea. iium engineering journal, 18(2): 158-176. https://doi.org/10.31436/iiumej.v18i2.705 [29] wang w, wang w, mi h, mao l, zhang g, liu h, wen y. (2018) study and optimal design of a direct-driven stator coreless axial flux permanent magnet synchronous generator with improved dynamic performance. energies. suppl 11:1-22. [30] gieras jf, wang r-j, kamper mj. (2004) axial flux permanent magnet brushless machines. kluwer academic publishers, dordrecht [31] minaz mr, çelebi m. (2017) design and analysis of a new axial flux coreless pmsg with three rotors and double stators. results in physics, 7: 183-188. 160 https://www.sciencedirect.com/science/article/pii/s0960148116306656#! https://www.sciencedirect.com/science/article/pii/s0960148116306656#! https://www.sciencedirect.com/science/article/pii/s0960148116306656#! https://www.sciencedirect.com/science/article/pii/s0960148116306656#! https://www.sciencedirect.com/science/journal/09601481/99/supp/c https://www.sciencedirect.com/science/article/pii/s2211379716302819#! https://www.sciencedirect.com/science/article/pii/s2211379716302819#! https://www.sciencedirect.com/science/journal/22113797 https://www.sciencedirect.com/science/journal/22113797/7/supp/c microsoft word 144-864-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 shubhashis 85 structural identification of distinct inversions of planar kinematic chains sanyal shubhashis mechanical engineering department, national institute of technology, raipur (c.g.), india, 492010. shubhashissanyal@rediffmail.com abstract: inversions are various structural possibilities of a kinematic chain. the number of inversions depends on the number of links of a kinematic chain. at the stage of structural synthesis, identification of distinct structural inversions of a particular type of kinematic chain is necessary. various researchers have proposed methods for identification of distinct inversions. present method based on link joint connectivity is proposed to identify the distinct inversions of a planar kinematic chain. method is tested successfully on single degree and multiple degree of freedom planar kinematic chains. abstrak: penyonsangan merupakan kebarangkalian pelbagai struktur suatu rangkaian kinematik. jumlah songsangan bergantung kepada jumlah hubungan suatu rangkaian kinematik. pada peringkat sintesis struktur, pengenalan songsangan struktur yang berbeza untuk suatu jenis rangkaian kinematik adalah perlu. ramai penyelidik telah mencadangkan pelbagai kaedah pengenalan songsangan yang berbeza. kaedah terkini berdasarkan hubungan kesambungan bersama telah dicadangkan untuk mengenalpasti songsangan yang berbeza dalam suatu satah rangkaian kinematik. keywords: kinematic chains; links; joints; link joint connectivity; distinct inversions 1. introduction to generate the constrained relative motion, kinematic chains made up of links and joints are used. to get the above objective one of the links of the kinematic chain is fixed and thus the kinematic chain with a fixed link is known as a mechanism / linkage. the fixed link is also known as a frame link. identification of a frame link is necessary because the input motion is provided at any of the joints attached with the frame link; vice versa the output motion is received from any of the joints attached with the frame link. inversion of a mechanism does not change the motions of its links relative to each other but does change their absolute motions. in case of a four link kinematic chain, four inversions are possible. however, all the inversions in case of four bar kinematic chains are structurally similar since all of them are binary. the case will be different for higher link chains, such as six link, eight link, and nine link chains and so on. in these cases the chains are made up of different type of links, binary, ternary, quaternary etc. the inversions in these cases will be structurally different, since the type of frame link will be different. for example, in case of six link watt’s chain, fig.1, through visual inspection only it is possible to identify that there are two distinct structural inversions, one by fixing any of the four binary link and one by fixing any one of the ternary link. in case of stephenson’s six link chain the number of distinct iium engineering journal, special issue, mechanical engineering, 2011 shubhashis 86 inversions are three. identification of these distinct structural inversions is important at the stage of structural synthesis, since the motion characteristics will be different for different inversions and vice versa. various researchers have proposed methods for identification of distinct inversions. manolescu [1] reported for the first time a total of 219 distinct mechanisms derived from nine link two degrees of freedom kinematic chains. mruthyunjay [2] corrected the above and reported 71, 254 and 1834 distinct mechanisms for eight link single degree of freedom, nine link two degrees of freedom and ten link single degree of freedom kinematic chains. mrythunjaya and raghavan [3] used a modified characteristic polynomial for detecting distinct inversions. ambekar and agrawal [4] extended the min code approach to identify the inversions corresponding to the original kinematic chain. patel and rao [5] presented a method based on velocity graphs and motion transfer matrix. the hamming number technique of rao and raju [6] has the potential to disclose the distinct inversions. chu jin kui and cao wei qing [7] extended the link’s adjacent chain table for detection of inversions. yadav et. al. [8] used a new invariant called arranged sequence of modifiedtotal distance ranks of all the links (asmtdrl) encorporating the degrees of links, degrees of freedom and types of joint of the kinematic chain to identify the distinct inversions. sanyal et. al. [9] proposed a link link probability matrix based method. fuzzy logic and loop based methods are also presented by rao and his coworkers [10, 11, 12]. srinath and rao[13] presented a method based on corelation concept for detection of isomorphism among kinematic chains and their inversions. r. simoni et. al. [14] presented a method based on group theory for enumeration of mechanisms. the symmetry of graphs is identified by a group of autoisomorphism and the set of vertices in the same equivalence class is used to identify the symmetrical links – since every kinematic chain can be presented by its graph. ashok dargar et. al. [15] used link adjacency values – first and second to identify the distinct inversions. the method has the potential of identifying the isomorphic kinematic chains also. bedi and sanyal [17,18] has presented joint connectivity approach for detection of isomorphism and distinct inversions of planar kinematic chains. the method [18] proposed by them also identifies unique joints in a kinematic chain. many of the method proposed by earlier researchers, either does not incorporate direct determination of distinct inversions or are computationally complex and time taking. based on the above literature a computationally simple but reliable method based on link joint connectivity table is proposed to identify the structurally distinct inversions of a kinematic chain. method based on connectivity of links at different level through different type of joints is proposed. care has been taken to incorporate the structural details of the kinematic chain up to the last level of connectivity so as to identify the not only the isomorphism but also the distinct inversions of the kinematic chain. the method is applied successfully to single and multiple degrees of freedom kinematic chains. the results are validated through the earlier reported results for validation. 2. method different type of links is attached with each other through different type of joints. depending upon the difference in these connectivity’s the kinematic chains differ from each iium engineering journal, special issue, mechanical engineering, 2011 shubhashis 87 other. in view of the above literature and in view of the fact that a method based on the accommodating the topological characteristics ofkinematic chain up-to the last level, the present work is proposed for identification of distinct inversions of a planar kinematic chain with revolute joints. a unique link joint connectivity table representing the kinematic chain is proposed by author [16]. the elements of the table represent the number of connecting links and the type of joint through which the connectivity is established. the elements are tabulated up-to the last level so as to incorporate all the topological characteristics of the kinematic chain. the link – joint connectivity table (ljct) and the scheme generated thereof, is proposed for detection of distinct inversions of a kinematic chain. the method is introduced through its application to watt’s and stephenson’s six link planar kinematic chains (fig. 1). fig. 1: watt’s and stephenson’s six link kinematic chain. 2.1 link – joint connectivity table (ljct) link joint connectivity are prepared (tables 1 and 2) for watt’s and stephenson’s six link chains. the element 2, 4, 6 in table 1, for the first link shows the direct connectivity of link1 with three links namely link 2, 4 and 6 (fig. 1). this also states that link1 is a ternary link. further the element in the second row for the first link shows that the connectivity of link 1 with link 2, 4 and 6 is through joint type bt (a binary ternary joint), tt (a ternary – ternary joint) and a bt (a binary ternary joint). the connectivity of further level i.e. level 2 and 3 is also tabulated for link1. a code is generated which represent the type of the parent link and its number of connections up to the last level. for example, code t(3,2) for link1 represent that the link is a ternary link and it is connected to 3 links at first level and 2 links at second level. in this way theconnectivity of all links with other links at all possible levels and its codes are tabulated in the ljct for watt’s and stephenson’s six link chain, table 1 and table 2. 2.2 link joint connectivity schemes (ljcs) for ease of representation a scheme generated from the ljct is proposed. the scheme arranges the codes of the respective links in order. the schemes generated for the watt’s and stephenson’s six link chains are shown below. [4b1(2,2,1), 2t1(3,2)] (1) [2b1(2,3), 2b2(2,3), 2t1(3,2)] (2) iium engineering journal, special issue, mechanical engineering, 2011 shubhashis 88 table 1: link – joint connectivity table table 2: link – joint connectivity table for watt’s six link chain. for stephenson’s six link chain 2.3 isomorphic chains “two kinematic chains will be non – isomorphic if their schemes generated from their link joint connectivity tables are different”. 2.4 distinct inversions: “links having dissimilar codes for a kinematic chain in the link joint connectivity table will be structurally different and will be identified as structurally distinct inversions”. from the two schemes generated following can be concluded: 1. it is obvious that though both the chains are having four binary and two ternary links, they are different due to their topological connectivity’s with different links at different levels, i.e. they are non –isomorphic chains. 2. watt’s chain (fig. 1), has two structurally distinct inversions, watt’s inversion 1, one binary link any of the four binary link with similar code and similar type of joints at the two levels, and watt’s inversion ii, one ternary any of the two ternary with similar topological characteristics at all levels. 3. stephenson’s chain, has three structurally distinct inversions, one binary (either of the links 2 or 4), second binary (either of the links 5 or 6) and one ternary (either of the links 1 or 3), respectively stephenson’s i, ii and iii (fig. 2). iium engineering journal, special issue, mechanical engineering, 2011 shubhashis 89 fig. 2: inversion’s of watt’s and stephenson’s kinematic chain. fig. 3: eight link single degree of freedom non-isomorphic planar kinematic chains. eight link non-isomorphic kinematic chains iium engineering journal, special issue, mechanical engineering, 2011 shubhashis 90 2.5 applications the method is applied to single degree and multiple degrees of freedom kinematic chains successfully. 2.5.1 single degree of freedom kinematic chains the method is applied to six links (fig. 1) and eight link single degree of freedom planar kinematic chains (fig. 3). seventy one distinct inversions are determined for eight link chains (table 3). the results obtained are verified with earlier results reported. table 3: schemes for eight link single degree of freedom kinematic chains. s.no. schemes inversions distinct links 1 [4b1(2,2,2,1), 4t1(3,3,1)] 2 1 binary, 1 ternary 2 [4b1(2,3,2), 4t1(3,4)] 2 1 binary, 1 ternary 3 [b1(2,3,2), b2(2,3,2), b3(2,3,2), b4(2,4,1), t1(3,4), t2(3,4), t3(3,3,1), t4(3,4)] 8 4 binary, 4 ternary 4 [2b1(2,3,2), 2b2(2,3,2), 2t1(3,3,1), 2t2(3,3,1)] 4 2 binary, 2 ternary 5 [2b1(2,3,2), 2b2(2,2,3), 2t1(3,3,1), 2t2(3,4)] 4 2 binary, 2 ternary 6 [2b1(2,3,2),2b2(2,3,2), 2t1(3,3,1), t2(3,2,2), t3(3,4)] 5 2 binary, 3 ternary 7 [b1(2,3,2), 2b2(2,4,1), b3(2,4,1), 2t1,2(3,3,1), t3(3,3,1), t4(3,4)] 6 3 binary, 3 ternary 8 [4b1(2,3,2), 4t1(3,3,1)] 2 1 binary, 1 ternary 9 [4b1(2,4,1), 4t1(3,4)] 2 1 binary, 1 ternary 10 [4b1(2,4,1), b2(2,4,1), 2t1(3,2,2), q1(4,2,1)] 4 2 binary, 1 ternary, 1 quaternary 11 [b1(2,3,2), b2(2,4,1), 2b3(2,4,1), b4(2,5), t1(3,4), t2(3,3,1), q1(4,3)] 7 4 binary, 2 ternary, 1 quaternary 12 [b1(2,2,3), b2(2,3,2), 2b3(2,4,1), b4(2,4,1) t1(3,2,2), t2(3,4), q1(4,3)] 7 4 binary, 2 ternary, 1 quaternary 13 [b1(2,2,3), b2(2,3,2), b3(2,3,2), b4(2,4,1), b5(2,4,1), t1(3,3,1), t2(3,4), q1(4,3)] 8 5 binary, 2 ternary, 1 quaternary 14 [2b1(2,2,2,1), 2b2(2,3,2), b3(2,3,2), 2t1(3,3,1), q1(4,3)] 5 3 binary, 1 ternary, 1 quaternary 15 [6b1(2,3,2), 2q1(4,3)] 2 1 binary, 1 quaternary 16 [4b1(2,4,1), 2b2(2,5), 2q1(4,3)] 3 2 binary, 1 quaternary total number of inversions 71 iium engineering journal, special issue, mechanical engineering, 2011 shubhashis 91 2.5.2 multiple degrees of freedom kinematic chains the method is also applied to nine link two degrees of freedom kinematic chains. it is found that of forty distinct nine link two degrees of freedom kinematic chains, a total of 254 structurally distinct inversions are available. 3. conclusions the method proposed is simple and exhaustive in nature since it includes the structural details of the kinematic chain up to the last level. the method has the potential of testing isomorphism and distinct inversions of kinematic chain. the method is applied successfully to single and multiple degree of freedom kinematic chains. the results obtained for distinct inversions matches with the earlier findings. acknowledgement author is thankful to the institute for allowing the present work to be carried out. references [1] manolescu, n.i, 1973 “ a method based on baranov trusses and using graph theory to find the set of planar jointed kinematic chains and mechanisms”, mechanism and machine theory, vol. 8, pp 3 – 22. [2] t.s. mruthyunjaya, 1984, a computerized methodology for structural synthesis of kinematic chains – part i, ii and iii, mechanism and machine theory, vol. 14, pp. 487 – 530. [3] t.s. mruthyunjaya and m.r. raghavan, 1984, computer aided analysis of the structure of kinematic chain, vol.19, no.3, pp 357 – 368. [4] a.g. ambekar and v.p. agrawal, 1987, canonical numbering of kinematic chains and isomorphism problem: min code, mechanism and machine theory, vol. 22, no. 5, pp. 453 – 461. [5] l. k. patel and a.c. rao, 1988,“ a method for detection of distinct mechanisms of a planar kinematic chain”, transactions of csme,vol.12, no.1, pp 15 20. [6] a.c. rao and d. varada raju, 1991, application of hamming number technique to detect isomorphism among kinematic chains and inversions, mechanism and machine theory, vol. 26, no. 1, pp. 55 – 75. [7] chu jin kui and cao wei qing, 1994, “identification of isomorphism among kinematic chains and inversions using link’s adjacent chain table”, vol. 29, no.1, pp 53 – 58. [8] j.n.yadav, c.r.pratap and v.p.agrawal, 1996, computer aided detection of isomorphism among kinematic chains and mechanisms using the concept of modified distance, pp 439 444. [9] s. sanyal, m. choubey and a.c. rao, 1997, pseudo probabilistic approach to determine distinct inversions of kinematic chains, trans. csme, vol. 21, no. 2. [10] a.c.rao, 1998, topology based rating of kinematic chains and inversions using information theory, mechanism and machine theory, vol. 33, issue 7, pp. 1055-1062. [11] a.c. rao, 2000, application of fuzzy logic for the study of isomorphism, inversions, symmetry, parallelism and mobility in kinematic chains, mechanism and machine theory, vol. 35, pp 1104. [12] a.c. rao and v.v.n.r prasad raju pathapati, 2000, loop based detection of isomorphism among kinematic chains, inversions and type of freedom in multi degree of freedom chain, asme journal of mechanical design, vol. 122, pp. 31 – 42. iium engineering journal, special issue, mechanical engineering, 2011 shubhashis 92 [13] srinath and rao, 2006, correlation to detect isomorphism, parallelism and type of freedom, mechanism and machine theory, 41(6), 646-655. [14] r. simoni, a.p.carboni and d. martins, 2009, enumeration of kinematic chains and mechanisms, proc. i meche., vol. 223, part c: j mechanical engineering science. [15] ashok dargar, ali hasan and r.a.khan, 2009, identification of isomorphism among kinematic chains and inversions using link adjacency values, ijmme, vol.4, no.3, pp 309 – 315. [16] sanyal shubhashis, 2009, detection of isomorphism amongst planar kinematic chains using link joint connectivity table, international conference on applied mechanics and machines, waset09, bangkok. [17] bedi, g.s and sanyal s., 2010, joint connectivity: a new approach for detection of isomorphism and inversions of planar kinematic chains, j. institution of engineers(india), jan. 2010, vol.90, pp 23 – 26. [18] g.s.bedi and s.sanyal, 2011, modified joint connectivity approach for identification of topological characteristics of planar kinematic chains, proc. imeche vol.225, part c: j. mechanical engineering science, pp 2700 – 2717. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 the development of water pollution detector using conductivity and turbidity principles nurulhasanah amir hamzah maju1, hasmah mansor1*, teddy surya gunawan1 and robiah ahmad2 1 department of electrical and computer engineering, international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia. 2 razak faculty of technology and informatic, universiti teknologi malaysia, jalan sultan yahya petra, 54100 kuala lumpur, malaysia. * corresponding author: hasmahm@iium.edu.my (received: 2nd august 2021; accepted: 13th october 2021; published on-line: 4th july 2022) abstract: water pollution has caused negative impacts on human health as humans depend solely on water for drinking, cooking, and cleaning. even more worrying is that the number of polluted rivers seems to increase as time progresses. due to no real-time monitoring device being implemented, the authorities are unaware of any given river's real-time conditions. therefore, this research aims to control the water pollution issue by designing and developing a low-cost device that can detect water pollutants and notifies the authorities if abnormalities occur. in this work, various water pollution sources in malaysia have been identified: biochemical oxygen demand, ammoniacal nitrogen, and suspended solids. the general performance of the proposed device is also evaluated and analyzed. water quality data is collected by the sensors and is sent to an iot platform called thingspeak through a wi-fi module to be visualized and displayed. when the pollution is detected, the website will alert local authorities for their prompt actions. from the experiment conducted, the developed conductivity sensor managed to give readings with 6.84% and 6.35% error compared to the sensor in a benchmark paper and the readymade sensor, respectively. besides, the turbidity sensor also managed to give accurate readings according to various types of solution. the success of this research would help to reduce river pollution and provide positive outcomes to the environment. abstrak: pencemaran air telah menyebabkan kesan negatif terhadap kesihatan manusia kerana kebergantungan mereka terhadap air untuk minum, memasak dan mencuci. lebih membimbangkan adalah, jumlah sungai tercemar yang semakin meningkat seiring tahuntahun yang berlalu. oleh kerana tiada alat pemantauan masa nyata yang dilaksanakan, pihak berkuasa tidak menyedari keadaan semasa air sungai. oleh itu, projek ini bertujuan bagi mengawal masalah pencemaran air dengan merancang dan menghasilkan alat kos rendah yang dapat mengesan pencemaran air dan memberitahu pihak berkuasa sekiranya berlaku bacaan yang tidak normal. melalui kajian ini, pelbagai sumber pencemaran air di malaysia telah dikenal pasti: permintaan oksigen biokimia, nitrogen amonia dan pepejal terampai. prestasi umum alat ini juga dinilai dan dianalisis. kualiti data air dikumpulkan oleh pengimbas dan maklumat dihantar ke platform iot yang disebut thingspeak melalui modul wi-fi bagi tujuan tinjauan dan paparan. apabila pencemaran dikesan, laman web tersebut akan memberi amaran kepada pihak berkuasa tempatan untuk tindakan segera. melalui eksperimen yang dijalankan, pengimbas kekonduksian yang dihasilkan berjaya memberikan bacaan dengan ralat 6.84% dan 6.35% berbanding pengimbas yang terdapat di kertas penanda aras dan pengimbas siap pakai. selain itu, pengimbas kekeruhan yang digunakan mampu memberikan bacaan yang tepat mengikut pelbagai jenis larutan. projek 104 mailto:hasmahm@iium.edu.my iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 ini diharap dapat membantu mengurangkan pencemaran sungai dan memberikan impak positif kepada alam sekitar. keywords: water pollution detector; conductivity; turbidity; thingspeak 1. introduction due to rapid development and lack of awareness, water quality is compromised as water pollution increases day by day. this research is designed to detect water contaminants in real-time so as to notify the authorities once the pollution occurs. the sensors used to detect the contaminants are a conductivity sensor and a turbidity sensor. this is because these sensors can be used as substitutions to detect suspended solids (ss), ammoniacal nitrogen (nh3n) and biochemical oxygen demand (bod). these chemicals impact water bodies as highlighted by the department of environment in the pollution sources inventory report [1]. water pollution can cause serious health issues to human beings such as typhoid fever and even deadly diseases like cholera [2]. the reason is that the contaminants or toxicants can enter the human’s food chain as they eat the fish or animals infected by pollution. on the other hand, in conjunction with the river pollution issue, the department of environment (doe) conducted a river monitoring program. according to the environment quality report 2017 [3], the percentage of clean rivers in malaysia had slightly decreased from 47% to 46% in 2017. unfortunately, the percentage of polluted rivers had somewhat increased from 10% to 11%. in march 2019, the country had been stunted by the news of toxic dumping in sungai kim kim (kim kim river), pasir gudang, johor, malaysia. the impact of toxic dumping caused breathing difficulties among students in a school near the river [4]. it is believed that early detection of toxins could reduce the aftermath of a dumping incident. this incident has proven the need to have a real-time river pollution detection that can alert the authorities immediately so that prompt actions can be taken to curb the spread of toxicants. 2. methodology this system consists of a self-developed conductivity sensor, sen0189 turbidity sensor, arduino uno, esp8266 wi-fi module and an iot platform called thingspeak. by switching on the switch, the led will be turned on and all of the system components will be activated. the block diagram of the overall system is shown in fig. 1. conductivity sensor arduino uno sen0189 turbidity sensor authority (doe) esp8266 wifi module lipo battery thingspeak led fig. 1: the system's block diagram. 105 iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 first, the system started with water quality data collection. the data collected by the conductivity and turbidity sensors are sent to thingspeak through the esp8266 wi-fi module for further data aggregation. the arduino uno circuit board has been used as the interface between the esp8266 wi-fi module and the sensors. a coding containing a unique api key is programmed into the microcontroller to send data to the iot platform. in thingspeak, the conductivity and turbidity data are processed, analyzed and visualized. all the necessary calculations and equations regarding the conductivity and turbidity are programmed into the arduino uno. users can simply monitor the water quality through the website as the data are displayed in graphs and a numeric display. in the case of water pollution occurring, an email alert will be automatically sent to the user, which in this case is the department of environment (doe). considering the outdoor factors, the components are stored in a weatherproofed pvc box to avoid direct contact with the river water. the prototype is shown in fig. 2. the schematic circuit diagram of this device can be seen in fig. 3, and the actual system’s circuit connection can be seen in fig. 4. fig. 2: the system’s prototype. fig. 3: the system’s schematic circuit diagram. turbidity sensor conductivity sensor switch led weatherproofed pvc box 106 iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 fig. 4: the actual circuit’s connection. 2.1 the design of the conductivity sensor water conductivity is the measure of the amount of electrical current that water can carry in the presence of dissolved solids such as chloride, magnesium, and calcium [5]. conductivity can be used to detect the presence of the chemicals in the water. however, it is important to note that conductivity cannot identify the type of chemicals, only their presence. the amount of electrical conductivity allowed by doe according to the national water quality standards (nwqs) is below 6000μ𝑆/𝑐𝑚. rivers with only 1000μ𝑆/𝑐𝑚 of conductivity readings are considered as clean rivers. water conductivity is commonly expressed in μ𝑆/𝑐𝑚, which is derived from ohm’s law where the voltage is equal to the product of current and resistance. 𝑉 = 𝐼𝑅 (1) v = voltage (v) i = current (a) r = resistance (ω) conductance is the reciprocal of resistance which can be seen in eq. (2) the conductance can be measured in mho (℧) which is the backward spelling for resistance’s si unit, ohm (ω). another unit for conductance is siemens (s). both mho and siemens can be used interchangeably. in this work, siemens is used. 𝐺 = 1 𝑅 (2) g = conductance (s) by substituting the conductance into the ohm’s law equation, the relationship between voltage and conductance is as follows: 𝑉 = 𝐼 𝐺 (3) 𝐺 = 𝐼 𝑉 (4) turbidity sensor conductivity sensor wi-fi module battery arduino uno led switch 107 iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 next, to acquire the water conductivity value, a cell constant needs to be considered. this is because conductivity is influenced by the distance between the two electrodes and their surface area. the cell constant is defined as the ratio of the distance between the electrodes to their surface area. this is shown in eq. (5) below. 𝐾 = 𝐷 𝐴 (𝑐𝑚−1) (5) k = cell constant d = distance between the electrodes a = surface area of the electrodes finally, by multiplying the conductance with the cell constant, water conductivity can be obtained, as shown in eq. (6) κ=𝐺•𝐾 (𝑆𝑖𝑒𝑚𝑒𝑛𝑠/𝑐𝑚) (6) κ=water conductivity in this research, the conductivity sensor will collect the water conductivity data and later, the data will be sent to thingspeak. generally, there are three types of conductivity sensors: two-electrode conductivity sensors, four-electrode conductivity sensors, and inductive conductivity sensors. in this work, a two-electrode method is used to design a conductivity sensor. the developed sensor is shown in fig. 5. fig. 4: the developed conductivity sensor. the sensor is designed using the calibration method by adjusting the distance between the electrodes. the calibration is done so that the results acquired satisfy the standard conductivity reading of tap water which is around 500−800 μ𝑆/𝑐𝑚 [6]. the sensor is injected with pulse-width modulation (pwm) to mimic an alternating current (ac). this is to avoid the polarization effect. the electrodes used in this sensor are non-insulated copper plate electrodes. the plates are rectangular and have two pill-like shaped holes. the calculated surface area of the copper plates is 12.44 cm2. then, the distance between the copper plate is adjusted to 2 cm, 3 cm, 4 cm and 5 cm. using the total surface area, the cell constant for each distance can be acquired using eq. (5). the cell constants correspond to each distance as provided in section 3.1. 2.2 the concept of turbidity sensor turbidity is the measure of haziness and cloudiness of water caused by suspended solid (ss) and measured in nephelometric turbidity units (ntu). high turbidity can cause an increase in water temperature as the suspended particles absorb heat from the sunlight. the growth of aquatic plants rate is also obstructed as sunlight cannot penetrate through turbid water and this will eventually disturb the photosynthesis process. following the nqws, the turbidity level for clean rivers set by the doe is around 50 ntu and below. according to the environment quality report (eqr), turbidity can be used to indicate the ss [3]. 108 iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 the turbidity sensor in this research employs the orthogonal scattered light detection principle by measuring the light transmitted and scattered rate influenced by total suspended solid (tss). in this project, the reading obtained from the sensor is processed by the microcontroller, then sent to the cloud for further aggregation process. the sen0189 turbidity sensor used is provided in fig. 6. fig. 5: sen0189 turbidity sensor. this sensor operates at 5 v and a maximum current of 40 ma. by using analog input mode, the turbidity reading gained ranges from 0 to 1023. the arduino uno has a 10-bit analog-to-digital converter (adc) which means it has resolution ranging from 0 to 1023 (210 = 1024). then, this read value is converted to a voltage using eq. 7. the value of turbidity in ntu can be obtained from the voltage and turbidity relationship graph provided by dfrobot in fig. 7. this was done using eq. 8 obtained from the graph to convert it from voltage to ntu. the graph in fig. 7 shows that the smaller the output voltage, the higher the turbidity reading. 𝑉 = 𝑟𝑒𝑎𝑑 𝑣𝑎𝑙𝑢𝑒 × ( 5.0 1024.0 ) (7) 𝑁𝑇𝑈 = −1120.4𝑉2 + 5742.3𝑉 − 4352.9 (8) fig. 6: turbidity and voltage relationship graph. 2.3 the component cost one of the aims of this research is to develop a water pollution detection system with affordable and minimal costs. table 1 shows the cost for each item used in this research for the prototype. the total cost for the hardware is rm213.06, which is considered minimal. other systems on the market could cost up to thousands of ringgits for similar functionality. 109 iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 table 1: itemised prototype (hardware) cost no. item quantity per unit cost (rm) total cost per item (rm) 1 arduino uno atmega328p 1 97.60 97.60 2 sen0189 turbidity sensor 1 59.00 59.00 3 esp8266 wi-fi module 1 14.90 14.90 4 lipo battery (7.4 v 900 mah) 1 20.00 20.00 5 breadboard 1 2.70 2.70 6 copper plates 2 2.50 5.00 7 switch 1 1.50 1.50 8 led 1 0.05 0.05 9 pvc box 1 12.31 12.31 total cost 213.06 3. results and discussion 3.1 conductivity sensor the design of this sensor was done using the calibration method. the distance between the two plates was adjusted accordingly to obtain a conductivity value that satisfies the standard tap water conductivity reading. the standardized conductivity value for tap water is 500 − 800 µs/cm [6]. the calculated cell constant, readings of current and voltage were recorded in table 2. table 2: calibration result distance [cm] current [ma] voltage [mv] cell constant, k [cm-1] conductivity [µs/cm] 2 0.60 280 0.16 344.12 3 0.57 260 0.24 528.57 4 0.53 240 0.32 709.97 5 0.43 186 0.40 928.79 from the result, the 4 cm distance between the electrodes shows a conductivity reading within the range of 500 − 800 µs/cm. even though the conductivity reading for a 3 cm distance also falls within the same range, it is safer to choose the 4 cm distance. it can be observed that as the distance increased, the conductivity also increased. however, both voltage and current showed a decrease. this is because the farther the electrodes are from each other, the harder it is for the ions in the solution to travel because of the higher resistance. this results in a lower current flow. next, by employing [7] as the benchmark paper, the sensor was tested by dipping it in a 500 ml of water mixed with 2 g of salt. nine readings were taken, and the results are recorded in table 3. 110 iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 table 3: conductivity result no. of readings developed sensor [v] developed sensor in [7] [v] ready-made sensor [v] 1 1.74 1.81 1.90 2 1.75 1.94 1.90 3 1.77 1.87 1.91 4 1.76 1.85 1.91 5 1.80 1.90 1.85 6 1.76 1.90 1.85 7 1.77 1.93 1.89 8 1.77 1.94 1.89 9 1.78 1.94 1.89 average 1.77 1.90 1.89 from the result obtained, it can be seen that the sensor developed in this research has an almost constant reading, in the range of 1.74 v to 1.80 v. the average voltage difference between the developed sensor in this research and the benchmark paper in only 6.84%. while the average voltage difference between the developed sensor and the ready-made sensor is 6.35%. 3.2 turbidity sensor the turbidity readings were taken by inserting the probe into five different types of solutions: tap, salt, soap, river, and coffee. these solutions were chosen as all of them have different clarity. the river water was collected from the pusu river near the female sports centre (fsc), international islamic university malaysia (iium), gombak campus. the readings were taken three times for each solution to ensure accurate measurements. table 4 below shows the turbidity result for each solution. table 4: turbidity result solution reading 1 reading 2 reading 3 average voltage [v] turbidity [ntu] voltage [v] turbidity [ntu] voltage [v] turbidity [ntu] voltage [v] turbidity [ntu] tap 4.22 -68.28 4.22 -68.28 4.21 -50.19 4.22 -62.25 salt 4.29 -346.10 4.30 -365.05 4.29 -346.10 4.29 -352.42 soap 4.04 565.10 4.03 581.72 4.03 581.72 4.03 576.18 river 2.47 2995.28 2.48 2997.18 2.46 2992.02 2.47 2994.83 coffee 3.98 755.48 3.99 724.34 3.97 770.96 3.98 750.27 the table shows that tap water has the lowest average turbidity of -62.25 ntu, while river water has the highest average turbidity of 2994.83 ntu. even though coffee is the darkest solution, it only has an average turbidity of 750.27. according to the world health organization (who), tap water is considered safe because the water should have turbidity below 5 ntu to be drinkable [8]. on the contrary, the pusu river water shows the highest turbidity measurement, and it also exceeds the minimum safe level of turbidity in malaysia [9], caused by high amount of silt. the high concentration of silt affects the light that penetrates through the liquid. this is because the turbidity sensor works by measuring the amount of light absorbed and scattered by the 111 iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 suspended solids in the solution. the higher the number of total suspended solids (tss), the higher the sensor's liquid turbidity. it can also be observed from table 4 that the higher the voltage, the lower the turbidity readings. high voltage means that the solution is less hazy because more light penetrates through the solution, resulting in higher voltage. 3.3 thingspeak as the iot platform thingspeak is an open-source internet of things (iot) platform that allows a user to perform data collection, data aggregation, and receive an email alert. figure 8 shows the data visualizations of the collected sensors’ data. the sampling time set at the coding is 1 second, however, for the reporting purposes, the thingspeak platform is 5 minutes. the sampling time and display can be set according to the specifications required by the authority. fig. 8: water quality measurement data visualization in terms of turbidity (ntu) and conductivity (µs/cm). 4. conclusion indeed, water is very valuable to human beings and other living things. however, preserving good water quality has become a big challenge in this modern world. water pollution cases have increased due to lack of awareness and moral values. thus, the development of this research aims to help reduce water pollution. in this research, the major contaminants that contribute the most to river water pollution have been identified and studied, namely the bod, nh3n, and ss. moreover, the water pollution detection system has been developed and designed with affordable and minimal costs. therefore, a low-cost water pollution detection system has been achieved. next, the water pollution detector device that focuses on detecting major contaminants in malaysia has been designed. the general performance of the work was evaluated and analyzed. the self-developed 112 iium engineering journal, vol. 23, no. 2, 2022 maju et al. https://doi.org/10.31436/iiumej.v23i2.2168 conductivity sensor was able to give readings that have a difference of 6.84% and 6.35% compared to the previous paper and ready-made sensor, respectively. the turbidity sensor was also able to give the correct reading according to a different type of solution. to conclude, the research objectives have been achieved and established. acknowledgement the authors would like to express highest appreciation to the international islamic university malaysia and universiti teknologi malaysia for providing facilities for this research to be conducted. references [1] department of environment (doe). (2017) pollution sources inventory, in enviroment quality report 2017, pp. 100-105. [2] afroz r, rahman a. (2017) health impact of river water pollution in malaysia. int. j. adv. appl. sci., 4(5): 78-85. [3] department of environment (doe). (2017) river water quality, in environment quality report 2017, pp. 24-60. [4] 8 critical after inhaling methane in suspected illegal chemical dumping. [online]. available: https://www.nst.com.my/news/nation/2019/03/466921/8-critical-after-inhaling-methanesuspected-illegal-chemical-dumping. [accessed: 26-jul-2020]. [5] assad aig. (2015) quality of tap drinking water in kuwait: physicochemical characteristics. international conference on sustainable mobility applications, renewables and technology, smart 2015, pp. 1-4. [6] heyda m. (2008) conductivity measurement and theory. [online]. available: http://www.mbhes.com/conductivity_measurement.htm. [accessed: 14-dec-2020]. [7] indu k, choondal jj. (2016) modeling, development & analysis of low cost device for water quality testing. 2016 ieee annual india conference, indicon 2016, pp. 1-6. [8] world health organization (who). (2017) water quality and health review of turbidity: information for regulators and water suppliers. who/fwc/wsh/17.01, p. 10. [9] wepa, “national water quality standards for malaysia,” wepa, 2017. [online]. available: http://wepa-db.net/en/topic/waterstandard/malaysia_1_surface.pdf. [accessed: 13-mar-2020]. 113 microsoft word bhattacharya et al.doc iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 1 tracking and monitoring of tagged objects employing particle swarm optimization algorithm in a departmental store indrajit bhattacharya1, kausik das sharma1 and uttam kumar roy2 1kalyani government engineering college, kalyani, nadia, india 2department of information technology, jadavpur university, india e-mails: indra51276@gmail.com, kaushikdassharma@yahoo.com, u_roy@it.jusl.ac.in abstract : the present paper proposes a departmental store automation system based on radio frequency identification (rfid) technology and particle swarm optimization (pso) algorithm. the items in the departmental store spanned over different sections and in multiple floors, are tagged with passive rfid tags. the floor is divided into number of zones depending on different types of items that are placed in their respective racks. each of the zones is placed with one rfid reader, which constantly monitors the items in their zone and periodically sends that information to the application. the problem of systematic periodic monitoring of the store is addressed in this application so that the locations, distributions and demands of every item in the store can be invigilated with intelligence. the proposed application is successfully demonstrated on a simulated case study. key words: radio frequency identification (rfid), particle swarm optimization (pso), departmental store automation system. 1. introduction a departmental store has different types of items enter onto the store and placed in its proper rack. the items are tagged using passive rfid tags and each of them receives a unique identity number. the readers are placed in the strategic positions in the store to automate the identification process and send the information of the items in its communication range. here we have used the passive tags for minimizing the cost of the system. the radio range of the reader is 50 meters. hence a number of readers are required to monitor the items spanned over entire departmental store. the readers gather information of the items in their zones and send that information periodically to the application for taking appropriate decisions. this paper presents the design, development and implementation of a rfid based departmental store to periodically monitor the items and to identify the most and least demanded item list using pso algorithm that in turn would be useful for theft detection and stock updates for that store. iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 2 the rfid technology provides accurate information on the number of items, their locations in the store and their distributions, while the proposed algorithm manages the information, better services and information related to demand of items in the store. swarm intelligence (si) is an artificial intelligence (ai) technique involving the study of cooperative behavior in decentralized systems. such systems are made up by a population of individuals interacting locally with one another and with their environment. there is no centralized control dictating the behavior of the individuals, local interactions among the individuals often cause a global pattern to emerge. si refers to the problem solving behavior that emerges from the interactions between the individuals and the computational swarm intelligence refers to algorithmic models of such behaviors. these algorithmic models have shown to be able to adjust well in changing environments and are greatly flexible and robust. the last decade has shown a rapid growing research interests in si, particularly on the most popular si paradigm namely particle swarm intelligence (pso). pso is a stochastic, population-based optimization algorithm introduced in 1995 by james kennedy and russell c. eberhart [1, 2]. many variants of pso have been developed since, including constrained, multi objective, and discrete or combinatorial versions and applications have been developed using pso in many fields. 2. related work the first practical application of pso was in the field of neural network training and was reported together with the algorithm itself [3, 4, 5, 6]. many more areas of application have been explored ever since, including telecommunications, control, data mining, design, combinatorial optimization, power systems, signal processing, and many others. to date, there are hundreds of publications reporting applications of particle swarm optimization algorithms [4]. in [7] the pso algorithm was applied effectively for locating an intruder in a wireless zigbee based network. although pso has been used mainly to solve unconstrained, single-objective optimization problems, pso algorithms have been developed to solve constrained problems, multi-objective optimization problems, problems with dynamically changing landscapes, and to find multiple solutions [8, 9,10]. in [11] the pso algorithm was effectively implemented to design a fuzzy controller to control the robot movement. in [12] the pso algorithm was successfully implemented to optimally place rfid readers in a rfid network. 3. system description the whole premise of the departmental store is divided into four zones (fig.1), where each zone is equipped with a passive rfid reader with a built-in zigbee transceiver. in that premise there is an entry point and an exit point equipped with rfid reader. in each zone there are several racks, which are used to store the items of the same types. iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 3 fig. 1: layout of the system. while entering to the store each item will be attached with a passive rfid tag and each tag will contain information regarding their identity, which can be described in terms of a record of 5-tuples (type of the product, sub typeof the product, product-id, position, date). the tagging has been done in the following way: tag = [typeofproduct | subtype | product-id | position | date] (1) each tagged item should have five fields. they are: a) type of products: such as garment, utensils, food, electronics goods, etc. here domain of this field is alphabets of english language. for example, all garments products should be tagged by character ‘g’ and so on. b) subtype of products: for each product type there may be sub product types such as electronics good may be of tv, vcd, etc. the domain of this field is alphabets of english language. c) product-id: this field denotes a unique number, which is tagged to each product used for identity of the product. the domain of this field is string of 0’s and 1’s of 16bits long. iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 4 d) position: the domain of position field is simply positive integer. position field once again sub-categorized into two fields, which are xcoordinate and y-coordinate. according to the type and subtype of the item, all items will be stored to their corresponding position (basically in rack kept in each zone). e) date: this field is of the pattern dd-mm-yyyy. whenever an item enters to the store, it is tagged with current date. after the items are tagged, they are placed to their corresponding position in the rack sequentially according as their type and subtype. reader of each zone is capable of monitoring their respective items. so the reader is capable of detecting the presence of all items within its vicinity at that particular zone. the presence or disappearance of a tagged item from a particular zone is automatically reported to a server located in the command room. this server is where the database is kept and it is also where the application software is run. the total database of the items with others is stored in the server. communication between the rfid readers and the server is through the built-in zigbee transceiver and the self-configuring network topology. there are four counters one for each zone. the customers first take their selected items to be purchased to the respective counters. that is, they should carry the garments items to the garment-counter and electronic goods to the electronic goods-counter and so on. from each counter the selected items are sent to the exit point where the billing is done. it should be taken care of the fact that the interference among the items in different zones should be minimized. from the automation application point of view, we add another attribute which is called valid_time of products or items. valid_time is actually threshold time for each product. which signifies that products can be kept in the store for a predefined period of time and after that product should be replaced or renewed. the system is capable of tracking the records of each product and will give a signal if the valid_time of any product is expired. this valid_time can be set by the shop-owner. 4. automation system goals the system can help a departmental store-owner to meet his various needs. for instance, the system will provide the information to the owner after fixed time of interval which products were sold most and which is not. the owner need not take this review manually from the store. 1) the owner may be interested about which products are of high demands to the customers. for this query, owner needs not to approach to the customers because the system can generate this information whenever it is requested. 2) since the automation system is tracking all the objects every time so theft can be prevented using this system. iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 5 the system can also be used to manage stock in an efficient way by virtue of knowing the demands of the items in the store periodically. 5. particle swarm optimization – a brief description in 1995 particle swarm optimization (pso), a population based swarm algorithm was developed by kennedy and eberhart [1][2]. in the pso computational algorithm, population dynamics simulates bio-inspired behavior i.e. a “bird flock’s” or “school of fish” behavior which involves sharing of information and allows particles to take profit from the discoveries and previous experience of all other particles during the search of food. each particle in pso has a randomized velocity vector ( v ) associated to it, which moves through the search space. each particle in pso keeps track of its coordinates in the solution space, which are associated with the best solution (fitness) it has achieved so far. this value is called p (personal best position vector). another best value that is tracked by the global version of the particle swarm optimizer is the overall best value (fitness). its location, called g (global best position vector), is obtained among all the particles in the population. the past best position of the particle itself and the best overall position in the entire swarm are employed to obtain new position vector ( s ) for the particle in quest to minimize (or maximize) the fitness. at each time step t the velocity of the particle is updated and the particle is moved to a new position. this new position is calculated as the sum of the previous position and the new velocity: 11   ttt vss (2) the update of the velocity from the previous velocity to the new velocity is determined as: )(.)(.. 22111 tttttt sgcrspcrvv   (3) the pso concept consists, in each time step, of changing the velocity of each particle flying towards its personal best and global best location with an inertia weight , which controls the magnitude of the old velocity in the calculation of new velocity as: end endstart t witer wwtiter w    max max )()( (4) where itermax is the maximum number of iterations of pso. normally wt is reduced linearly from wstart to wend throughout the pso generation. a typical combination is wstart = 0.9 and wend = 0.4. the velocity is weighted by random terms, with separate random numbers (r1 and r2) being generated for velocities towards personal best and global best locations respectively. iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 6 c1 and c2 are the social parameters used for the learning purpose in the optimization technique. some research approaches investigated the application of constriction coefficients and inertia weights. there are numerous techniques for preventing premature convergence. many variations on the social network topology, parameter-free, fully adaptive swarms, and some highly simplified models have been created. the algorithm has been analyzed as a dynamical system, and has been used in hundreds of engineering applications; it is used to compose music, to model markets and organizations, and in art installations. 6. implementation of pso based rfid tracking system the main focus of our work is to implement an automatic object monitoring system using pso algorithm and rfid technology [13, 7]. here rfid system is being used for tagging and automatic tracking the items of a departmental store and pso is used to modify the movements of items with in the whole premise of departmental store. the main objectives of our system are: 1) develop an automated object monitoring system. 2) provide security of objects belonging to the system. 3) to minimize the zonal interference among the objects moving in the system. 4) to sort objects according to their movements. more precisely, to find which objects are much demanded and which are less demanded. 5) to provide a quick review of current stock. 6) make the authority alert if there is any mismatch of distribution of objects (misplacing of items with respect to their arrangement). 7) identifying those objects which are achieved goal mostly make the authority aware about the demands of customers. the functional description of the system is depicted in the following flowchart: iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 7 fig. 2: flowchart showing the functionality of the system. with analogy of pso the exit point is where the food is located. all members of the group will converge to these points after a period of time. therefore the goal our algorithm is to identify the less demanded and most demanded items from a group of items are based on pso. at the entry point we group the items depending on the product type and subtype and are monitored periodically with in the store. the readers will report the positions of the items periodically. based on the location information the system can work out and record their movements as well as their stay in the zones of the store. these data are used for comparison with each member; those members with the highest discrepancy are identified using an appropriate fitness function from those data can be classified as less-demanded items. those items of the store are either need to be replaced or renewed. in the pso implementation [14, 15, 16, 17] we have considered a problem space, which is divided into four zones. there is one entry point and one exit point. the particles are entered to the store through the particular entry point and then the actual tagging is done. in the tagging procedure we have considered the five attributes for each item. they are the product type, subtype, product-id, (initial x-coordinate, initial y-coordinate), and the date of entry. the unique attribute of an item is the product-id. the items are mapped into a 2d space and will obtain its position (x,y) depending upon it’s type and subtype and that is going to considered as the initial position of the particles in pso. in each zone there is a local counter. the particle after being sold is first moved to the local counter and then from the local counter those are moved towards the exit section where actually the billing is done. for the moving of the particle from the local counter to the exit point, we have considered that the zonal interference should be minimized. in each zone there is a reader, which is monitoring the location and movement of the particle of the specified zone. the reader’s have the monitoring power for a specified radius. there are also two rfid iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 8 readers who are placed in the entry point and the exit point. so the system can get the locations of the items periodically from the readers. each particle has the particular lifetime. the user can easily change the lifetime limit for the particle. the particles are considered to be volume less. the function location is used to search and place the new item in the proper position in the rack of the store. the function also fixes the position of the item in a 2d space depending on the product type and subtype and then they are treated as particles. in this way all the items are get placed in the proper rack of the store in the specified zones. a 2d array is used to check the availability of the position in the rack. initially all positions are initialized with the value zero. when a particle is placed in the shelf its corresponding location is updated with the value one. the function location first checks the array whether the corresponding location is one or zero. if it is zero then it places the particle on the location, otherwise it checks for the availability at the next position. as it is known in case of pso algorithm, the particle best position is determined by the fitness function in each iteration. the fitness function has been calculated by function w. in our work the fitness function is used to keep track of those particles, which are less demanded and does not converge to the solution after a predetermined number of iterations. the user has to fix one specific lifetime for each product. when the particle’s date difference (i.e. difference of entry date from the current date) exceeds the specified threshold value then it is identified as less demanded particle. in our implementation the inertia weight was varied from 0.9 to 0.4 and c1, c2 are the two positive constants set to 0.1. applying pso algorithm the position and velocity of the particles are updated for a specified number of iterations and the particles move towards the destination. 7. simulation results in pso implementation we have considered a problem space, which is the area covered by the departmental store. we have carried out our simulation in a 500x300 pixel area. the whole area is divided into four equal sized zones. each zone is placed with artificial racks. we have assumed that items can be placed at pixels within the racks only. the transmission range of the readers is set to 20 meters and readers are placed in the appropriate position of each zone to periodic monitor each of the items in that zone. we have carried out experiments over five items and performed number of iterations on pso algorithm varying the inertia weights of the particles from 0.9 to 0.4 in each iteration and applied fitness function at each step. the result in figure 3 shows that two particles (denoted as item1 and item5) has been reached to the destination within 100 iterations, and rest of three does not converge to the solution after 200 iterations. this signifies that the items 2,3 and 4 (denoted by the particles in pso implementation) are less demanded items and can be added to the list of less demanded item list which need to be replaced in the store. similarly the item1 and item5 can be identified as two most demanded items in the shop. iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 9 fig. 3: iterations and inertia weight(w) assigned. from fig. 4 we can determine the demands of the items in the departmental store. here we have considered product type as electronics(e), garments(g), foods(f) and others(o). this information can be used by the shop owner for order placing and stock updates. fig. 4: chart showing demands of items according as their types. from fig. 5 it can be concluded that before the iteration number 193, no particles are converged but after that with the increase of iterations particles started to converge and as number of iteration increases the convergence rate also increases. it is obvious that convergence rate will never be 100% from our experimental graph as not all the particles would be eventually converge. our aim here is to identify those particles and hence the items (that information can be found from the database) which do not reach to the iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 10 destination can be considered as less demanded items. here convergence rate has been calculated using following formula: convergence rate = (no. of particles reaches the destination / total no. of particles) * 100 fig. 5: iterations and convergence rate. 8. conclusions in this paper the problem of systematic periodic monitoring of the store is addressed so that the locations, distributions and demands of every item in the store can be invigilated with intelligence. applying pso algorithm in the application it has been possible to identify the less demanded items in the store which need to be replaced. the backbone rfid network monitors the store periodically and sends the item information to the application on which the pso algorithm works. the demand analysis of the items of the store can be done by the system in an efficient manner which may be useful for stock management of the store. references [1] r. c. eberhart and j. kennedy, “a new optimizer using particle swarm theory,” proc. 6th int. symp. micromachine human sci., nagoya, japan, pp 39-43, 1995. [2] j. kennedy and r. c. eberhart, “particle swarm optimization,” proc. ieee int. conf. neural networks, vol. 4, pp. 1942-1948, 1995. [3] j.kennedy “the particle swarm: social adaptation of knowledge” proc. ieee int. conf. on evolutionary computation (indianapolis, indiana), ieee service center, piscataway, nj, pp. 303-308, 1997. [4] r.c. eberhart, y.h. shi “comparison between genetic algorithms and particle swarm optimization” annual conf. on evolutionary programming, san diego, 1998. [5] qiang guan, yu liu, yiping yang, wesshueg yu “genetic approach for network planning in rfid systems” proceedings of the sixth int. conf. on intelligent systems –isda, 2006. iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 11 [6] r. poli “analysis of the publications on the applications of particle swarm optimization” journal of artificial evolution and applications, article id 685175, 10 pages, 2008. [7] m.s. rodrigo, carlos l.s.s. sobrinho, s.araujo, farias rubem “particle swarm optimization applied for locating an intruder by an ultra-wideband radar network” federal university of para, brazil. [8] y.h.shi, r.c. eberhart “a modified particle swarm optimizer. ieee int. conf. on evolutionary computation” anchorage, alaska, may 4-9, 1998. [9] p. j. angeline “evolutionary optimization versus particle swarm optimization: philosophy and performance difference” annual conf. on evolutionary programming, san diego, 1998. [10] a.p.engelbrecht “fundamentals of computational swarm intelligence” willey, 2005. [11] k. das sharma, a. chatterjee and a. rakshit “a hybrid approach for design of stable adaptive fuzzy controllers employing lyapunov theory and particle swarm optimization” ieee transactions on fuzzy systems, vol-17, no.-2, pp-329-342, april, 2009. [12] i. bhattacharya, u.k.roy “optimal placement of readers in an rfid network using particle swarm algorithm”, ijcnc, vol-2, no-6, pp-225-234, november 2010. [13] y.m. siu, w.s.chan, k.k. soo, c.w.leung, s.m. law “exhibition security and safety system using rfid technology and a modified particle swarm optimization algorithm” asia-pacific microwave conf. apmc, 2008. [14] p.j.angeline “using selection to improve particle swarm optimization” ieee int. conf. on evolutionary computation, anchorage, alaska, may 4-9, 1998. [15] y.h.shi, r.c. eberhart “parameter selection in particle swarm optimization” annual conf. on evolutionary programming, san diego, march 1998. [16] wail gueaieb and md. suruz miah “mobile robot navigation using pso and noisy rfid communication” ieee int. conf. on computational intelligence for measurement systems and applications, 14-16 july, 2008. [17] hui zhu, syahrulanuar ngah, ying xu, yuji tanabe, takaaki baba “a random time-varying pso for local positioning systems”. ijcsns, vol 8. no. 6, june, 2008. iium engineering journal, vol. 12, no. 1, 2011 bhattacharya et al. 12 colony composition and biomass of macrotermes gilvus hagen (blattodea: termitidae) in indonesia iium engineering journal, vol. 20, no. 1, 2019 subekti et al. colony composition and biomass of macrotermes gilvus hagen (blattodea: termitidae) in indonesia niken subekti1*, priyantini widiyaningrum2, dodi nandika3 and dedy duryadi solikhin3 1,2biology department, semarang state university, semarang, indonesia. 3forestry department, bogor agricultural university, bogor, indonesia. 4biology department, bogor agricultural university, bogor, indonesia. *corresponding author: nikensubekti@mail.unnes.ac.id (received: 4th dec 2018; accepted: 4th april 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.1032 abstract: there is no study conducted to investigate the composition and biomass of macrotermes gilvus hagen in natural forest ecosystem. this study aimed to analyze the colony composition and biomass of m. gilvus hagen colony in natural forest and to evaluate the need of food of the species as well as factors affecting it. research was conducted in yanlappa sanctuary, bogor, west java. termites were surveyed by collecting individual m. gilvus hagen from different colony at different size of mound, small (0 – 0.99 m), medium (11.99 m), large (≥ 2 m) and then were measured the number of individuals, wet and dry body mass, ratio of dry or wet body mass, and the average of biomass. results indicated that the small mount was dominated by workers, whereas the medium and the large nest was dominated by nymph. mean of the termite biomass was 936 kg/ha2. average of termite biomass collected from large mount was 949.8 kg/km2, medium mount was 605.2 kg/ha2 and small mount was about 537.5 kg/ha2. factor affecting the biomass of subterranean termite m. gilvus hagen are food source, energy efficiency, predators, and environment. the presence of termite mounds influences natural ecosystem, but that the type of mound plays a crucial role in determining the nature of the effects. abstrak: kajian tentang komposisi koloni dan biomas anai-anai tanah m. gilvus hagen di ekosistem hutan semulajadi belum pernah dilakukan. kajian ini bertujuan bagi menganalisa komposisi koloni dan biomas koloni anai-anai tanah m. gilvus hagen di hutan semulajadi dan menganalisa keperluan makanan spesis ini serta faktor-faktor yang mempengaruhi pemakanannya. kajian ini dijalankan di cagar alam yanlappa, bogor, jawa barat. anai-anai ini dikaji dengan mengumpul setiap m. gilvus hagen dari koloni berbeza berdasarkan pada ketinggian sarang, iaitu sarang kecil (0 – 0.99 m), sarang sederhana (11.99 m), dan sarang besar (≥ 2 m). kemudian, setiap koloni ini diukur berat basah, berat kering serta nisbah berat basah atau berat kering, dan purata biomas. hasil kajian menunjukkan bahawa sarang kecil di dominasi oleh koloni pekerja, sementara sarang sederhana dan sarang besar di dominasi oleh koloni nympha. purata biomas anai-anai dari sarang besar adalah 949.8 kg/ha2, sarang sederhana 605.2 kg/ha2, dan sarang kecil 537.5 kg/ha2. faktor-faktor yang mempengaruhi biomas anai-anai tanah m. gilvus hagen adalah sumber pemakanan, tenaga, pemangsa dan faktor sekeliling. kehadiran koloni anai-anai mempengaruhi ekosistem semulajadi, tetapi jenis koloni memainkan peranan penting dalam menentukan sifat kesannya. keywords: biomass; colony; macrotermes gilvus hagen 24 iium engineering journal, vol. 20, no. 1, 2019 subekti et al. 1. introduction macrotermes gilvus hagen has an important role in natural ecosystem, particularly in nutrient cycling as an active decomposer. moreover, this species of termitidae is a crucial component of biogeochemical cycles [1], especially carbon and nitrogen cycle [2]. m. gilvus hagen is widely spread in southeast asia, especially in indonesia. it is one of the subterranean termites consuming much litter and other cellulosic material within the forest. however, there is no more information concerning to its biological study in indonesian natural forest. one parameter associated to those biological roles in certain ecosystem is biomass, a quantitative measurement of total mass of termite from a part or all member of a population in a certain place and time. biomass of this species can change over time, and this certainly depends on colony composition within the colony. biomass is possible to be used as an appropriate indicator to measure the number of food consumed by this species, hence it can be predicted the effects of the species in an ecosystem [3]. no studies have been conducted to investigate the biomass of m. gilvus hagen in indonesian natural forest ecosystem. therefore, research on biomass and colony composition is crucial and needed especially in the field of biology of m. gilvus hagen in the current natural ecosystem. the objective of this research was to study the m. gilvus hagen biomass in natural forest and to evaluate the need of food of the species along with the factors affecting it. biomass is the amount of living matter present at any given time, expressed as mass per unit area or volume of habitat. given the ubiquitous and wide spread distribution of termites throughout savannahs and biomasses estimated to equal that of large herbivores, this nutrient enrichment through mound erosion may contribute significantly to vegetation heterogeneity in savannahs [4]. this present study focused to observe various variables including wet and dry body mass, ratio of dry body mass/wet body mass, and average of biomass based on the mound size of m. gilvus hagen. 2. materials and methods this research was performed in yanlappa sanctuary, bogor, west java (located between 6o40’ s and 106o45’ e. the selection of the area was based on the high density of termite m. gilvus hagen mound after a census. subterranean termites m. gilvus hagen samplings were conducted by using colony classification [3] at different size of mound: small mound height (0 – 0.99 m), medium mound height (1 – 2.99 m) and large mound height (≥ 3 m) [2]. height mound means size mound from land surface to on top of mound. furthermore, the procedure was continued by calculated the colony termites composition in the mound. it was obtained by digging and dismantling the mound vertically and horizontally at as much 3 of each nest type. termite specimens of each sample mound were then collected using vacuum cleaner (3.5 kva). after dismantled, the mound were then closed using dark plastic for 3 hours to give the remaining time for termite foragers back to the nest. all specimens were subsequently dried in 100 oc oven for 24 hours. dried specimens were then measured for each colony to obtain the dry body mass value. all materials were cooled and stored in desiccator and balanced. all measurements were replicated 10 times. 3. results and discussion results showed that large mound had ten times higher colony size than small mound, whereas medium mound had four times higher than small mound. the comparison between colonies in small and large mound was consistent, while in the medium mound, the number of major soldier was strongly high. the small mound was dominated by 25 iium engineering journal, vol. 20, no. 1, 2019 subekti et al. workers, whereas the medium and the large mound was dominated by nymph (table 1). avona and correlation test presented that there was a significant correlation between the number of individuals and the mound size. table 1: the number of individuals in termite colony at three different types of mounds, yanlappa sanctuary, bogor colony nest type major soldier minor soldier worker nymph total small 1,297 ± 179 261 ± 91 10,196 ± 1,455 8,468 ± 210 20,223 ± 1,919 medium 4,021 ± 289 906 ± 573 3,167 ± 706 38,173 ± 645 46,267 ± 2,073 large 2,964 ± 158 360 ± 423 29,277 ± 183 151,233 ± 8,24 183,825 ± 7,742 table 2: wet and dry body mass of macrotermes gilvus hagen in natural forest, yanlappa sanctuary, bogor (n=300) colony / sub colony wet body mass (g) dry body mass (g) ratio dry body mass/ wet body mass (%) worker 6.08 ± 18.06 3.63 ± 7.17 59,70 ± 10.27 major soldier 33.30 ± 39.31 14.37 ± 16.89 43,15 ± 31.20 minor soldier 8.43 ± 20.69 6.60 ± 13.76 78,29 ± 14.24 nymph 8.67 ± 14.84 6.23 ± 7.16 71,85 ± 9.52 queen 1,082.30 ± 66.70 444.10 ± 14.01 41.03 ± 17.78 king 1,038.80 ± 10.75 654.20 ± 67.54 63.00 61.99 in the study area, there were 43 points of termite colonies consisted of 15 spots of large mound, 23 spots of medium mound, and 5 spots of small mound. termite biomass m. gilvus hagen found in the study area was approximately 936 kg/ha2 with biomass average for small mound was 537.5 kg/ha2, medium mound was 605.2 kg/ha2, and large mound was 949.8 kg/ha2 (table 3). this variation is due to the size and age of the individuals of mound. the traps which were installed near the colony were found to have adult workers, soldiers as well as nymphs and therefore a large number of individuals were recorded in 1 mound sample [5]. table 3: mean of biomass for each colony based on the size mound of macrotermes gilvus hagen in natural forest colony/sub colony biomass for each mounds (kg/ha) small medium large worker 2.458 ± 2.788 2.524 ± 3.104 5.517 ± 8.666 major soldier 9.058 ± 10.375 10.135 ± 11.261 11.414 ± 13.164 minor soldier 2.575 ± 3.153 3.175 ± 3.431 3.681 ± 4.033 nymph 0.764 ± 1.361 1.192 ± 1.614 5.517 ± 8.666 total 5.375 6.052 9.498 537.5 kg/ ha2 605.2 kg/ ha2 949.8 kg/ha2 the highest biomass of m. gilvus hagen was recorded in major soldiers, and then followed by minor soldier, worker, and nymph. the highest number of biomass of major soldier may be related to its contribution to the colony that is smaller compared with minor soldier and worker colony. in the present study, number of workers was found to be higher 26 iium engineering journal, vol. 20, no. 1, 2019 subekti et al. compared with other colonies with its portion was about 80% of the total colony. the colony composition in social insects can be influenced by environmental factors such as temperature. furthermore, colony composition in termite colony or foraging groups of termites are known to vary with time of day, season, species, and colony size or age [6]. meanwhile, individual shifting was faster in worker colony compared with soldier. the soldier was reported to live longer than the others [3]. in a colony, worker is responsible for various kinds of tasks including food foraging and feeding other colonies, repairing the nest, and also building new nests. it also helps to control air circulation especially for ch4 and co2, to maintain fungus plantation, as well as controlling mound humidity [4]. the smallest biomass was recorded for nymph, which may be related to phenology of termite since nymph is immature phase that is still growing to become mature termite with certain function for the colony. foods consumed by termites are not only used for growth and energy but they are also stored inside termite’s gut. feces and water secreted from the body are also converted into energy, tissue, organ, and another use [5]. the worker’s gut fungus-growing subterranean termites (macrotermes) secreted enzymes used for final oligosaccharides digestion [7]. gut of subterranean termites m. gilvus hagen worker was in alkaline condition (ph 8.83 ± 0.31) and strongly supported the lignocellulose digestion [8]. these workers also transported enzymes from mature fungi to the inoculated plant substrate [9]. environmental factor has a strong relationship with termite biomass. higher number of m. gilvus hagen biomass might be related to their habitats in the tropic with abundant food around it and high level of decomposition, which result in low level of energy utilization. fewer predators around the colony will result in more efficient of energy utilization compared with lots of predator living around it [10]. 4. conclusion this study concludes that the small mound was dominated by workers, whereas the medium and the large mound was dominated by nymph. the mean of m. gilvus hagen biomass reached 936 kg/ha2. mean of termite biomass m. gilvus hagen for large mound was 949.8 kg/ha2, medium mound was 605.2 kg/ha2 and small mound was 537.5 kg/ha2. the variation in percent workers colony suggests that environmental factors such temperature; relative humidity and rainfall affect the ratio of the workers to soldiers. acknowledgement this work was financially supported by the ministry of research, technology and higher education of the republic of indonesia through universitas negeri semarang, semarang, indonesia. references [1] brune a. (2014). symbiotic digestion of lignocellulose in termite guts. nat. rev. microbiol., 12(3): 168-180. [2] meyer vw, crewe rm, braack leo, groeneveld ht, linde mj. (2001). biomass of macrotermes natalensis in the northern kruger national park, south africa-the effects of land characteristics. j. sociobiol., 38(3): 431-448. [3] turner js. (2006). termites as mediators of the water economy of arid savanna ecosystems. in dryland ecohydrology (pp. 303-313). springer, dordrecht. 27 iium engineering journal, vol. 20, no. 1, 2019 subekti et al. [4] cleo mg, joris pgm, cromsigt, mpanza n, olff h. (2012). effects of erosion from mounds of different termite genera on distinct functional grassland types in an african savannah. ecosystems, 15: 128-139. [5] strassmann je, queller dc. (2007). insect societies as divided organisms: the complexities of purpose and cross-purpose. department of ecology and evolutionary biology, rice university, houston usa [6] sattar a, naeem m, ul haq e. (2013). impact of environmental factors on the population dynamics, density and foraging activities of odontotermes lokanandi and microtermes obesi in islamabad. springerplus, 2: 349 [7] poulsen m, hu h, li c, chen z, xu l, otani s, nygaard s, nobre t, klaubauf s, schindler p m, hauser f. (2014). complementary symbiont contributions to plant decomposition in a fungus-farming termite. pnas, 111(40): 14500-14505. [8] subekti n, fibriana f, widyaningrum p, adfa m. (2017). determination of the major compounds in the extract of the subterranean termite macrotermes gilvus hagen digestive tract by gc-ms method. ukrainian biochem. j., 89(4): 77-82. [9] da costa rr, hu h, pilgaard b, vreeburg sm, schückel j, pedersen ks, kračun sk, busk pk, harholt j, sapountzis p, lange l. (2018). enzyme activities at different stages of plant biomass decomposition in three species of fungus-growing termites. appl. environ. microbiol., 84(5): e01815-17. [10] meyer vw, braack leo, biggs hc, eberson c. (1999). distribution and density of termite mounds in the northern kruger national park, with specific reference to those constructed by macrotermes holmgren (isopteran: termitidae). african entomol., 7: 123-130. 28 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 192 effect of poly (ethylene glycol) on the injectability, setting behavior, and mechanical properties of calcium phosphate bone cement sufiamie hablee1, iis sopyan1*, maizirwan mel2, hamzah mohd. salleh3 and md. mujibur rahman4 1 department of manufacturing and materials engineering, kulliyyah of engineering, 2 department of biotechnology engineering, kulliyyah of engineering, 3 international institute for halal research and training (inhart), international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia 4 department of mechanical engineering, college of engineering, universiti tenaga nasional (uniten), selangor, malaysia. * corresponding author: sopyan@iium.edu.my (received: 13th march 2018; accepted: 17th july 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.913 abstract: the present paper reports on the effect of poly(ethylene glycol) (peg) addition on injectability, setting behaviour, and mechanical properties of calcium phosphate cement (cpc) for injectable bone filling applications. calcium hydroxide, ca(oh)2, and diammonium hydrogen phosphate, (nh4)2hpo4, have been used as precursors in wet chemical precipitation synthesis of hydroxyapatite powder. cement paste was prepared with different powder-to-liquid ratios, varied at 1.0, 1.3, 1.5 and 2.0. the incorporation of peg was also varied at 1, 2, 3, 4 and 5 wt% at the powder-to-liquid ratio of 1.3. the cpc produced was then evaluated in terms of injectability, setting time and mechanical strength. the results indicated that peg addition significantly improved setting time, injectability, as well as compressive strength of cpc. without peg, the initial setting time ranged between 3 and 122 min, while the final setting time ranged between 5 and 277 min. the addition of peg has significantly improved setting time where the initial setting time ranged from 47 to 88 min and the final setting time ranged from 182 to 228 min. the extrusion load decreased when peg was added, which revealed an improvement in injectability; 82.5% without peg addition and 95.5% when 5% peg was added. the compressive strength of cpc is in the range of 0.59 to 1.344 mpa and its porosity is in the range of 39.2% to 47.1%. with the incorporation of peg, the compressive strength greatly increased to the range of 1.167 and 1.786 mpa.. abstrak: penyelidikan ini melaporkan tentang kesan menambah polietilina glikol (peg) terhadap sifat-sifat simen kalsium fosfat seperti keupayaan suntikan, masa pengerasan dan kekuatan mekanikal. kalsium hidroksida dan diammonium hidrogen fosfat digunakan sebagai reagen dalam kaedah pemendakan kimia basah bagi menghasilkan serbuk hidroksiapatit. pes simen disediakan dengan nisbah serbuk kepada cecair yang berbeza, dengan nisbah 1.0, 1.3, 1.5 dan 2.0. kemudian, peg ditambah ke dalam simen kalsium fosfat dengan kepekatan yang berbeza, bernilai 1, 2, 3, 4 dan 5 wt% bagi 1.3 nisbah serbuk kepada cecair. simen yang terhasil diuji bagi menilai keupayaan suntikan, masa pengerasan dan kekuatan mekanikal. keputusan ujian-ujian tersebut menunjukkan bahawa penambahan peg ke dalam simen telah meningkatkan kebolehan simen untuk disuntik, mengurangkan masa pengerasan simen dan meningkatkan kekuatan iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 193 mekanikal simen. simen tanpa peg mempunyai masa pengerasan awal daripada 3 min kepada 122 min dan masa pengerasan akhir daripada 5 min kepada 277 min. apabila peg ditambah, masa pengerasan simen menjadi lebih baik dengan masa pengerasan awal daripada 47 min kepada 88 min dan masa pengerasan akhir daripada 182 min kepada 228 min. peningkatan dalam keupayaan simen untuk disuntik telah dibuktikan dengan pengurangan beban penyempitan apabila peg ditambah ke dalam simen. simen tanpa peg mempunyai 82.5% keupayaan suntikan dan meningkat kepada 95.5% apabila 5% peg ditambah. kekuatan mampatan simen bernilai antara 0.59 dan 1.334 mpa dan keliangan simen bernilai antara 39.2% dan 47.1%. kekuatan mampatan simen meningkat dengan ketara apabila peg ditambah, bernilai antara 1.167 dan 1.786 mpa. keywords: calcium phosphate cement; injectability; polymeric additives; wet chemical precipitation method 1. introduction autograft and allograft are standard procedures in bone grafting to repair bone defects. however, bone grafting has a number of limitations including inadequate bone supply and requiring additional operations for autograft, while there is high risk of immunological reactions and disease transmission in allograft [1,2]. development of synthetic biomaterials has been an alternative to overcome the limitations of bone grafting; bone cement has been attracting considerable attention as human hard tissue filler and joint anchorage materials since the second half of the last century. clinically available bone cement materials are polymethylmethacrylate (pmma), calcium phosphate cement (cpc) and calcium sulfate cement (csc). pmma-based cement offers biocompatibility, high mechanical strength, and excellent setting and injectability. the disadvantages of pmma-based cement are its lack of bioactivity and resorbability, high stiffness, exothermic setting reaction, as well as monomer toxicity and leakage [3]. meanwhile, csc has higher mechanical strength than cpc, but it degrades much faster, which causes different rates of bone regeneration and cement degradation [3]. cpc is significant and clinically accepted as injectable bone filling material. this recognition is due to its remarkable biological response, injectability, and potential to set in vivo [4-6]. cpc can be injected and molded to fill and take the shape of defect sites. injectable cpc is obtained by mixing calcium phosphate powder of various phases and water at certain ratios and sets at body temperature via dissolution-precipitation mechanism [5]. apatite cements of hydroxyapatite (ha) are formed upon mixing phases such as tetracalcium phosphate (ttcp) and α–tricalcium phosphate (α-tcp) with water [7]. various methods have been employed to synthesize cpc, which can be classified into dry and wet methods. dry methods include solid-state synthesis and the mechanochemical process. meanwhile, wet methods include chemical precipitation, hydrolysis, hydrothermal, sol-gel, emulsion, and sonochemical methods [8,9]. wet-chemical precipitation method has been widely used to synthesize cpc because it offers a simple route, low reaction temperature, highly pure end products, and inexpensive resources [10]. clinical application of cpc is limited by poor injectability and low mechanical strength. addition of polymeric additives is one of the approaches to enhance performance and improve properties of cpc such as injectability, setting time, cohesiveness, mechanical strength and biological response [11,12]. several studies have addressed the use of polymeric additives including chitosan, alginate, poly(lactic-co-glycolic acid) (plga), poly(ethylene glycol) (peg) and poly(vinyl alcohol) (pva) [11]. iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 194 peg is a polyether composed of glycerol monomers. it has been used in biomedical fields because of its non-toxicity, good water solubility, flexibility, and anti-coagulant activity [13]. peg acts as a thickening agent and keeps the cement paste stable, which has been applied to prepared premixed cpcs [11,13]. with the addition of peg, cpc is expected to have shorter setting time, better anti-washout performance, but lower injectability [11]. the present work investigates the effect of powder-to-liquid (p/l) ratio and peg content on the injectability, setting behavior, and mechanical properties of cpc synthesized from a wet chemical precipitation method. 2. experimental 2.1 synthesis of powder a wet chemical precipitation method was employed to synthesize cpc based on the procedure reported elsewhere [14]. in this case, the ha powder was prepared using calcium hydroxide, ca(oh)2, and diammonium hydrogen phosphate, (nh4)2hpo4, as the calcium and phosphorus precursors respectively, and the solvent used was distilled water. calciumto-phosphate (ca/p) ratio was fixed at 1.67. each precursor was dissolved in distilled water to produce a calcium and phosphorus solution. then, it was followed by drop-wise addition of a phosphorus solution into the calcium solution. 25% ammonia solution was added until ph 11 was achieved. the mixture was then refluxed at 90 ºc, followed by aging overnight at room temperature, washing with distilled water, and filtration. afterwards, the precipitate was dried overnight in an oven at 85 ºc and, finally, crushed. 2.2 cement preparation preparation of cpc was done by mixing the as-synthesized ha powder and liquid phase at certain ratios. the p/l ratio was varied at 1.0, 1.3, 1.5 and 2.0. the p/l ratio of 1.3 was selected to prepare the cpc incorporated with peg (mw300, sigma) based on its optimized properties. peg addition into the liquid phase was varied at 1, 2, 3, 4 and 5 wt%. 2.3 powder characterization the wet chemical precipitation-derived powder underwent morphology and phase characterization. phase analysis was done using x-ray diffraction (xrd). an empyrean, panalytical xrd system was employed under cukα radiation (λ = 1.5406 å) with 2° per minute scan speed and 0.02° step size over the 2θ range of 20-60°. a fourier transmission infrared (ftir) spectrometer was employed for identification of functional groups of the sample. a perkin elmer spectrum 100 ftir spectrometer was operated over the 4000-500 cm-1 scanning range at 4 cm-1 resolution. morphology evaluation was done by using transmission electron microscopy (tem) jeol jem-2100f. 2.4 injectability test the extrusion method has been employed for the injectability test of cpc, in which a non-needle 5 ml polyethylene syringe was used. the extrusion of the cement paste has been done under compression mode of a lloyd lr 10 k+ universal testing machine ran at 50 mm/min crosshead speed and 300 n maximum load. figure 1 presents the schematic diagram of the experimental setting of the injectability test. the result was plotted in graph form of extrusion force (n) against the extrusion time (s). the percentage of injectability was calculated based on equation (1). % 𝑖𝑛𝑗𝑒𝑐𝑡𝑎𝑏𝑖𝑙𝑖𝑡𝑦 = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑥𝑡𝑟𝑢𝑑𝑒𝑑 𝑝𝑎𝑠𝑡𝑒 𝑓𝑟𝑜𝑚 𝑠𝑦𝑟𝑖𝑛𝑔𝑒 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑝𝑎𝑠𝑡𝑒 𝑏𝑒𝑓𝑜𝑟𝑒 𝑖𝑛𝑗𝑒𝑐𝑡𝑖𝑜𝑛 × 100% (1) iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 195 the effect of p/l ratio (1.0, 1.3, 1.5 and 2.0) and peg addition (1, 2, 3, 4 and 5 wt%) on the injectability of cpc have been evaluated. fig. 1: schematic diagram of the injectability test. 2.5 setting time the initial and final setting times of cpc were determined using a gillmore needle method. powder and liquid phases were mixed for 2 min, and then the cement paste was put into a plastic mold. the effect of p/l ratio (1.0, 1.3, 1.5 and 2.0) and peg addition (1, 2, 3, 4 and 5 wt%) on the setting time of cpc have been determined. the determination of initial and final setting times was done by vertically indenting the thick and thin needle on the cement surface. the initial setting time is the time when no visible indentation is observed as the thick needle with a fixed low load is applied, while the final setting time is the time when no visible indentation is observed as the thin needle with a fixed high load is applied [2]. 2.6 mechanical strength compression strength test has been done by using a lloyd lr 10 k+ universal testing machine operated at a crosshead rate of 1 mm/s. the cement pastes were left for 48 hours to set after molded in a teflon mold. the sample dimension was 10 mm diameter x 15 mm length. 2.7 porosity measurement the measurement of density was done using a densitometer. the resultant apparent density was then used to calculate the porosity of cpc using equation (2) and (3): % 𝑝𝑜𝑟𝑜𝑠𝑖𝑡𝑦 = 100% − 𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 (2) 𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 𝜌𝑎𝑝𝑝 𝜌𝑡ℎ × 100% (3) where, ρapp is the apparent density measured by densitometer and ρth is the theoretical density of ha, taken as 3.156 g/cm3. iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 196 3. results 3.1 powder characterization the xrd pattern of the wet chemical precipitation-derived powder is shown in fig. 2. from the xrd pattern in fig. 2, ha is the main phase as the peaks present are attributed to hydroxyapatite according to the standard data of the card no. 09-432. the phase purity and crystallinity degree of the synthesized powder have been confirmed by the presence of sharp and clear peaks. the tem image in fig. 3 shows the nanorod shape of ha particles, with the sizes of 150-300 nm length and 10-30 nm width. fig. 2: xrd pattern of the wet chemical precipitation-derived powder. fig. 3: tem micrograph of the wet chemical precipitation-derived ha powder. the existing functional groups in the as-synthesized powder were measured using ftir and the spectrum shown in fig. 4. the bands at 1455 cm-1 and 874 cm-1 suggest the presence of co3in ha powder [15,16]. this might happen due to the adsorption of atmospheric carbon dioxide during the synthesis process [15,17]. po4derived bands appear at 1025 cm1, 602 cm-1 and 560 cm-1 [15-18]. the ftir and xrd measurements have proven the assynthesized powders to be pure ha. position [°2theta] (copper (cu)) 30 40 50 counts 0 2500 10000 22500 uia_r9296-p2 : ha iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 197 fig. 4. ftir spectrum of the wet chemical precipitation derived ha powder. 3.2 calcium phosphate cement characterization 3.2.1 setting time cpc was prepared by varying its p/l ratios, from 1.0, 1.3, 1.5 and 2.0. figure 5 presents that the setting time of cpc shortens with the increase in p/l ratio. faster hardening time is attributed to the higher content of powder in the cement paste. the initial setting time ranged from 3 to 122 min, whereas the final setting time ranged from 5 to 277 min. the optimum workable setting times of cpc is achieved at the p/l ratio of 1.3, with the initial and final setting times of 88 min and 228 min, respectively. fig. 5: setting times of cpc with various p/l ratios. cpc incorporated with peg was then prepared using the p/l ratio of 1.3, and the peg content was varied at 1, 2, 3, 4, and 5 wt%. the initial setting time is between 47 min and 88 min, whereas the final setting time is between 228 min to 182 min. figure 6 shows the incorporation of peg into cpc has improved setting time of cpc by shortening the hardening time of cpc. the dissolution of peg in water formed a network structure leading to the entanglement with three dimensional apatite structures during the hydration process, and finally resulted in the acceleration of setting time [13,19]. this is true only for the addition of peg content below 5%. the increase in both initial and final setting times were observed with the addition of 5% peg. this result indicates that a proper amount of peg is required to improve the setting time of cpc. 4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 510.0 3.0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105.0 cm-1 %t co3 po4 po4 po4 po4 co3 iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 198 fig. 6: effect of peg addition on setting times of cpc prepared with the p/l ratio of 1.3. 3.2.2 injectability the injectability result of cpc shown in fig. 7 indicate that an increase in p/l ratio reduces injectability. this is due to the higher powder content which escalates the extrusion load, and hence injectability is reduced. cpc with the p/l ratio of 2.0 shows no injectability since no paste can be extruded out of the syringe. this is in good agreement with the percentage of injectability of cpc, such that it varied from 96%, 82.5%, 75.4% and 0% for p/l ratio 1.0, 1.3, 1.5 and 2.0 respectively. fig. 7: injectability of cpc with various p/l ratios. in fig. 8, an increase in peg content improves injectability of cpc as the extrusion load decreased. this is supported by the results of percentage injectability, such that the injectability varied from 82.5%, 88.1%, 89.3%, 92.4%, 93.7% and 95.5% for 0, 1, 2, 3, 4 and 5% peg content respectively. this result is in agreement with the study by hesaraki et al. [20] that revealed significant improvement of cement paste after peg addition as compared with paste using water only because peg lowered the friction between cpc particles. on the other hand, chen et al. [13] reported that injectability decreased when peg concentration increased due to the increase in viscosity of cement paste. hydration reaction between the peg solution and cpc powder formed a spatial net structure via the formation of colloidal particles that join together through van der waals force, and hence strengthen iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 199 the network of cement paste [13]. wang et al. [19] also demonstrated that the addition of 0.5 wt% peg 200 decreased injectability of cpc as compared with using only water because the viscosity of the paste was higher. fig. 8: effect of peg addition on injectability of cpc prepared with the p/l ratio of 1.3. 3.2.3 mechanical strength a compressive strength test of the cpc has been done to investigate the effect of p/l ratio on the mechanical strength of cpc. figure 9 shows the result for the compression test of cpc with different p/l ratios. the average strength of cpc without addition of peg ranged from 0.590 mpa to 1.344 mpa. the highest strength is 1.344 mpa, achieved by cpc with the p/l ratio of 1.3. the increase in p/l ratio enhances compressive strength of cpc. however, the strength starts to decrease to 1.106 mpa and 0.621 mpa when the p/l ratios of 1.5 and 2.0 were used, respectively. this is because of insufficient water content, thus hampering the formation of apatite via dissolution-precipitation mechanisms. fig. 9: compressive strength of cpc with various p/l ratios. when peg is added into cpc, the strength is in the range of 1.167 mpa to 1.786 mpa. this shows the incorporation of peg has improved the compressive strength of cpc. figure iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 200 10 presents that cpc with 2% peg gives the highest strength with 1.786 mpa. this result indicates that an optimal amount of peg is required to produce cpc with better mechanical properties. fig. 10: effect of peg addition on the compressive strength of cpc prepared with the p/l ratio of 1.3. 3.2.4 porosity the average porosity of cpc ranged from 39.2% to 47.1%. their apparent density ranged between 1.67 to 1.92 g/cm3. from fig. 11, the porosity of cpc decreases with the increase in p/l ratio. this is attributed to the decrease in water component in the cement paste. this result is in disagreement with the compressive strength of cpc. generally, the strength improved with a decrease in porosity as the density increased. however, water content plays an important role in cpc to induce the formation of apatite crystals through the dissolution-precipitation mechanisms. hence, the lack of water content in the cement paste might have negatively affected the strength of the cement by reducing the strength, as demonstrated by the cpc with the p/l ratios of 1.5 and 2.0 in fig. 9. fig. 11: porosity of cpc with various p/l ratios. the porosity of cpc is in the range of 39.6% to 51.4% when peg is added and the apparent density is between 1.53 to 1.90 g/cm3. the result shows that incorporation of peg into cpc increases porosity of cpc as presented in fig. 12. the higher the peg content, the lower its porosity. this is true only for 1% to 4% peg content. the porosity started to iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 201 increase again when 5% peg was added. this indicates that an appropriate amount of peg is needed to reduce porosity of cpc, and hence improves its mechanical properties. fig. 12: effect of peg addition on the porosity of cpc prepared with the p/l ratio of 1.3. 4. conclusion the pure nano scale ha has been successfully synthesized through wet-chemical precipitation method using calcium hydroxide and diammonium hydrogen phosphate. the injectability, setting behavior, and mechancial strength have been detemined to explain the effect of p/l ratio and addition of peg on the properties of cpc. the present work reveals that high p/l ratio shortens setting time and improves mechanical strength, but reduces injectability. the optimized condition of cpc is achieved at the p/l ratio of 1.3: 88 min initial setting time, 228 min final setting time, 82.5% injectability and 1.344 mpa compressive strength. this study has proven that addition of peg is able to shorten the setting time, as well as enhance injectability, and mechanical strength. incorporation of 2% peg into cpc provides an optimum condition which revealed significant improvement in setting time, injectability, and compressive strength: 60 min initial setting time, 209 min final setting time, 89.3% injectability and 1.781 mpa compressive strength. therefore, the incorporation of peg into cpc could become a promising injectable bone filling material in the future. acknowledgement this work was financially funded through fundamental research grant scheme (frgs) by ministry of higher education (mohe), malaysia with the project id of frgs15-246-0487. references [1] bohner m. (2010) resorbable biomaterials as bone graft substitutes. materials today, 13(12):24-30. [2] zhang j, liu w, schnitzler v, tancret f, bouler j. (2014) calcium phosphate cement for bone substitution: chemistry, handling and mechanical properties. acta biomaterialia, 10: 1035-1049. [3] no yj, roohani-esfahani si, zreiqat h. (2014) nanomaterials: the next step in injectable bone cements. nanomedicine, 9(11):1745-1764. iium engineering journal, vol. 19, no. 2, 2018 hablee et al. 202 [4] barinov sm, komlev vs. (2011) calcium phosphate bone cements. inorganic materials, 47(13):1470-1485. [5] dorozhkin sv. (2011) self-setting orthophosphate formulations: cements, concretes, pastes and putties. intl. j. materials and chemistry, 1(1):1-48. [6] sugawara a, asaoka k, ding sj. (2013) calcium phosphate-based cements: clinical needs and recent progress. j. materials chemistry b, 1:1081-1089. [7] alqap asf, sopyan i, husni m, athirah n. (2012) the effects of calcium excess, water amount and mixing time on the injectability of calcium phosphate filling material. applied mechanics and materials, 110-116:8-12. [8] sadat-shojai m, khorasani mt, dinpanah-khoshdargi e, jamshidi a. (2013) synthesis methods for nanosized hydroxyapatite with diverse structure. acta biomaterialia, 9:75917621. [9] okada m, matsumoto t. (2015) synthesis and modification of apatite nanoparticles for use in dental and medical applications. japanese dental science review, 51:85-95. [10] monmaturapoj n. (2008) nano-size hydroxyapatite powders preparation by wet-chemical precipitation route. j. metals, materials and minerals, 18(1):15-20. [11] perez ra, kim h, ginebra m. (2012) polymeric additives to enhance the functional properties of calcium phosphate cements. j. tissue engineering, 3(1):1-20. [12] engstrand j, persson c, engqvist h. (2013) influence of polymer addition on the mechanical properties of a premixed calcium phosphate cement. biomatter, 3(4):e27249. [13] chen f, liu c, wei j, chen x, zhao z, gao y. (2011) preparation and characterization of injectable calcium phosphate cement paste modified by polyethylene glycol-6000. materials chemistry and physics, 125:81800-824. [14] hablee s, sopyan i, mel m, salleh hm, rahman mm, singh r. (2017) novel injectable calcium phosphate bone cement from wet chemical precipitation method. iop conf. series: materials science and engineering, 205:012012. [15] wang p, li c, gong h, jiang x, wang h, li k. (2010) effects of synthesis conditions on the morphology of hydroxyapatite nanoparticles produces by wet chemical process. powder technology, 203:315-321. [16] ungureanu dn, angelescu n, ion rm, stoian ev, rizescu cz. (2011) synthesis and characterization of hydroxyapatite nanopowders by chemical precipitation. recent researches in communications, automation, signal processing, nanotechnology, astronomy and nuclear physics, 296-301. [17] eslami h, solati-hashjin m, tahriri m, bakhshi f. (2010) synthesis and characterization of nanocrystalline hydroxyapatite obtained by the wet chemical technique. materials sciencepoland, 28(1):5-13. [18] azzaoui k, lamhamdi a, mejdoubi e, berrabah m, elidrisi a, hammouti b, zaoui s, yahyaoui r. (2013) synthesis of nanostructured hydroxyapatite in presence of polyethylene glycol 1000. j. chemical and pharmaceutical research, 5(12):1209-1216. [19] wang x, ye j, wang h. (2006) effects of additives on the rheological properties and injectability of calcium phosphate bone substitute material. j. biomedical materials research part b: applied biomaterials, 78(2):259-264. [20] hesaraki s, borhan s, zamanian a, hafezi-ardakani m. (2013) rheological properties and injectability of β–tricalcium phosphate-hyaluronic acid/polyethylene glycol composites used for the treatment of vesicouretheral reflux. advances in biomedical engineering research (aber), 1(3):40-44. microsoft word islam and hassan 13-30.doc iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 13 variability analysis of 6t and 7t sram cell in sub-45nm technology aminul islam 1 and mohd. hassan2 1department of electronics and communication engineering. birla institute of technology (deemed university) mesra, ranchi, jharkhand, india 2department of electronics engineering zakir husain college of engineering and technology aligarh muslim university, aligarh, u.p., india e-mail: aminulislam@bitmesra.ac.in abstract : this paper analyses standard 6t and 7t sram (static random access memory) cell in light of process, voltage and temperature (pvt) variations to verify their functionality and robustness. the 7t sram cell consumes higher hold power due to its extra cell area required for its functionality constraint. it shows 60% improvement in static noise margin (snm), 71.4% improvement in read static noise margin (rsnm) and 50% improvement in write static noise margin (wsnm). the 6t cell outperforms 7t cell in terms of read access time (tra) by 13.1%. the write access time (twa) of 7t cell for writing “1” is 16.6 × longer than that of 6t cell. the 6t cell proves it robustness against pvt variations by exhibiting narrower spread in tra (by 1.2  ) and twa (b y 3.4×). the 7t cell offers 65.6% saving in read power (rpwr) and 89% saving in write power (wpwr). the rpwr variability indicates that 6t cell is more robust against process variation by 3.9×. the 7t cell shows 1.3× wider write power (wpwr) variability indicating 6t cell’s robustness against pvt variations. all the results are based on hspice simulation using 32 nm cmos berkeley predictive technology model (bptm). key words: cell ratio, pull-up ratio, static noise margin (snm), read access time, write access time, static random access memory (sram), drain-induced barrier lowering (dibl) introduction due to aggressive scaling of device dimensions, random variations in process, supply voltage and temperature (pvt) poses major challenges to the future high performance circuits and system design [1-3]. the microscopic variations in number and location of dopant atoms in the channel region of the device induce deviations in device characteristics [4-6]. these fluctuations are more pronounced in minimum-geometry devices commonly used in area-constraint circuits such as sram cells [7]. the intrinsic fluctuations are independent of transistor location on a chip. the threshold voltage (vt) mismatch between neighbouring cell transistors due to intrinsic fluctuations typically iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 14 contributes to larger reductions in static noise margin (snm) [7]. the snm model in [8] assumes identical device threshold voltages across all cell transistors, making it unsuitable for predicting the effects of threshold voltage mismatch between adjacent transistors within a cell. therefore, designers will require reevaluation and analysis of static noise margin in scaled technologies to ensure stability of sram cell. the pvt variations affect the device threshold voltage (vt), which in turn modulates the drain to source current (ids). the variation is normally (as it is called gaussian or normal distribution) distributed and its ±3σ variation is about 30 mv at 32 nm technology node. the spread in read access time (tra), write access time (twa), read power (rpwr) and write power (wpwr) is due to variation in ids. pvt variations can be mitigated by various design techniques. adaptive body biasing is one such technique [9]. circuit design technique such as body biasing will help, but their effect diminishes with technology scaling [10]. sram is a highly used circuit in modern chips — it is used in caches, register files, fifos, etc. consequently, sram constitutes more than half of chip area and more than half of the number of devices in modern designs [11]. hence, the analysis and evaluation of sram cell in terms of its design criteria is not only important but also its robustness against pvt variations is essential in nanometer regime. this work analyses 6t and 7t sram cells and compares various sram design metrics. in standby mode sram cells are inactive and consume power for data retention due to various leakage components. this paper investigates leakage power consumption and the impact of pvt variations on sram’s design metrics at 32 nm technology node. it presents analysis of snm, tra, twa, rpwr, wpwr and their variations due to the impact of process parameters, voltage and temperature variations. the analysis shows that the standard 6t sram cell outperforms 7t sram cell in terms of robustness against pvt variations with respect to most of its design metrics. the remainder of this paper is organized as follows. section 2 briefly discusses impact of drain-induced barrier lowering (dibl) on nmos transistor at 32 nm technology. various stability metrics, failure mechanisms and operations of sram are briefly reviewed in section 3. section 4 presents a brief discussion on 7t sram cell, and its device/technology parameters. section 5 explores the impact of pvt variation on sram’s various design metrics. simulation measurements and comparisons between 6t and 7t sram cell are detailed in section 6. finally, the conclusion of the paper appears in section 7. 2. impact of drain-induced barrier lowering on scaled devices reevaluation and computation of voltage ripple (vqb) developed at storage node qb in fig. 2(a) at scaled technology is a necessity as threshold voltage (vt) of a small-sized transistor depends not only on substrate doping concentration (na) and other process parameters but also on dibl effect. analytical expression of vt is given by: iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 15  ||2-||2vv t0t fsbf v  (1) where vt0 is the threshold voltage at vsb = 0 v and is mostly a function of the manufacturing process, difference in work-function between gate and substrate material, oxide thickness, fermi voltage, charge of impurities trapped at the surface, dosage of implanted ions, etc; vsb is the source-bulk voltage; f = vtln(na/ni) is the bulk fermi potential (where vt = kt/q = 26 mv at 300 k is the thermal voltage, na is the acceptor doping concentration, ni is the intrinsic carrier concentration in pure silicon);  = (2qnasi)/cox is the body-effect coefficient (where si is the relative permittivity of silicon, cox is the gate oxide capacitance). equation (1) is not suitable for predicting vt at scaled technology where impact dibl is pronounced. the impact of dibl on vt is modeled as: dsdibltt vvv  0 (2) where vt0 is the threshold voltage at vds = 0 v, and ηdibl is the dibl coefficient. for nmos at 32 nm technology node, the dibl effect on vt is plotted in fig. 1(a), which shows the dependency of vt on vds. it particularly, shows that the vt is 0.6292 v at vds = 0 v and the vt drops to 0.4381 v at vds=1 v. as is well known, drain to source saturation voltage (vdsat) depends on both gate to source voltage (vgs) and vds. the vdsat of nmos at vgs=1 v versus vds is plotted in fig. 1(b). it shows the dependency of vdsat on vds. it particularly shows that vdsat is 0.2711 v at vds = 0.2 v. it is also evident from fig. 1(b) that the vdsat increases to 0.3338 v at vds=1 v. fig. 1: (a) threshold voltage (vt) versus drain to source voltage (vds) of nmos transistor. it shows vt variation due to dibl. (b) drain to source saturation voltage (vdsat) versus drain to source voltage (vds) of nmos transistor at 32 nm technology node. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 16 3. sram cell design metrics, failure mechanisms and operations 3.1 sram design metrics design of sram requires the smallest transistors, which are particularly sensitive to process variations. balancing the trade-offs between small areas, low powers, fast reads/writes are an essential part of any sram design. that is, sram design requires balancing among various design criteria such as minimizing cell area using smaller transistor, maintaining read/write stability, minimizing power consumption by reducing power supply, minimizing read/write access time, minimizing leakage current, reducing bitline swing to reduce power consumption, improving soft error immunity, etc. some of the design criteria are conflicting in nature. for example, higher cell ratio (cr) defined in [12] prevents read failure, but results in larger area and increased leakage. 3.2 sram failure mechanisms the designer of sram should take care of the above design criteria along with various sram cell parametric failures which may occur mainly due to [13, 14] read, write access and hold failures. read failure – this failure occurs while reading the content of an sram cell. assume that node qb in fig. 2(a) is storing a “0” and blb is discharging through mn3 and mn1. if the resistance of pull-down transistor mn1 is higher than that of pass transistor mn3, a voltage ripple vqb is developed due to resistive divider formed by mn1 and mn3. if vqb exceeds the switching threshold of the inverter formed by mp2 and mn2, the cell state flips while reading. the read failure can be reduced by increasing the difference between the voltage rise at the node storing “0” and the trip-point of the inverter associated with the node storing “1”. write failure – it is an unsuccessful write to the sram cell. write failure occurs if the node storing “1” cannot be discharged through the access transistors during the wordline turn on time. the write failure can be reduced by increasing the wordline turn on time with write access time increased, which unfortunately makes sram slower. access failure – access failure occurs if the voltage difference between the two-bitlines at the time of sense amplifier firing remains below the offset voltage of the sense amplifier [12, 15]. access failure occurs due to the reduction of the bit-line discharging current through the pass transistor and pull-down transistor. clearly, a faster bitline discharge can be achieved by reducing the resistance in the discharge path by making the pull-down transistor stronger. however, such improvements come at the price of larger cell area which is not recommended for high density srams. hold failure the hold failure occurs due to high-leakage of the pull-down nmos transistors connected to the node storing “1”. in scaled technology, at lower supply voltage (vdd), due to high leakage of the pull-down transistor, the node storing “1” reduces from vdd. if that voltage becomes lower than the trip-point of the inverter storing “0” the cell flips in the hold mode. this failure can be avoided by reducing leakage in standby mode using high-vt pull-down transistors. this improvement comes at the price of read delay. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 17 fig. 2(a): standard 6t sram cell [12]. (b): sense amplifier [12]. 3.3 sram’s mode of operations an sram cell offers the following basic modes of operation: data retention or standby mode: an sram cell is able to retain the data indefinitely as long as it is powered. read mode: an sram cell is able to communicate its stored data. this operation does not affect the data i.e., read operation is non-destructive as compared to dram’s read operation. write mode: the data of an sram cell can be set to any binary value regardless of its original stored value. read operation – during correct read operation, the stored data in q (say, storing “1”) and qb (storing “0”) are transferred to the bitline (bl) and bitline bar (blb) leaving bl at its precharged value and by discharging blb through mn3 and mn1 (fig. 2(a)). a careful sizing of mn1 and mn3 is needed to avoid accidental read upset due to building up of vqb at qb. minimum-sized transistors are necessary to design small-sized bitcell, which will result in longer tra (read access time) because of slow discharging of large bitline capacitance through small-sized transistor (offering higher resistance). as the difference between bl and blb builds up, the sense amplifier shown in fig. 2(b) [12] is activated by asserting sense enable (se) high to accelerate the reading process. boundary condition on mn1 and mn3 sizing to avoid read upset is achieved by equating discharging currents through mn3 and mn1 as given below:                       2 , 2 , 2 1 2 3 qb qbtnddmnn dsatn dsatntnqbddmnn v vvv v vvvv (3) which simplifies to       cr vvcrcrv vvcrv v tndddsatn tndddsatn qb             222 1 (4) where cr is called cell ratio (cr) or  ratio defined as 3 1 )/( )/( mn mn lw lw cr  (5) iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 18 with the assumption that voltage ripple (vqb) developed at qb will lie near zero and hence vds is arbitrarily taken to be 0.2v with the corresponding vdsat = 0.2711v and vtn = 0.59v. the value of vqb as a function of cr using 32 nm cmos bptm is computed on the basis of these assumption using (4) and (5). fig. 3(a) plots the value of vqb versus cr. in section v, we have analyzed standard 6t sram cell and estimated static noise margin (snm) to be 150 mv and read static noise margin (rsnm) to be 140 mv. at this technology node, where vtn ranges from 0.4381 v to 0.6292 v for vds ranging from 1 v to 0 v (fig. 1(a)), read upset may not occur due to voltage rise while reading, but as is evident from the fig. 3(a), cell failure may occur due to static noise if cr is not kept greater than 0.7, because vqb=147 mv at cr=0.7. static noise is dc disturbance such as offsets and mismatches due to processing and variations in operating conditions. an sram cell should be designed such that under all conditions some snm is reserved to cope with dynamic disturbances caused by α particles, crosstalk, voltage supply ripple, and thermal noise. write operation – a reliable write operation is possible if node storing “1” (say, q) is pulled low enough – below the threshold voltage of mn1, so that writing a “1” is possible on to the other storage node (say, qb) by flipping the cell state. sizing of the transistors mp2 and mn4 should be such that this occurs causing flipping of state, failing which will cause write failure. sizing constraint on mp2 and mn4 to avoid write failure is obtained by equating currents passing through pm2 and mn4 as given below:                       22 2 2, 2 4, dsatp dsatptpddmpn q qtnddmnn v vvv v vvv (6) which simplifies to                 2 2 2 2 dsatp dsatptpdd n p tnddtnddq v vvvprvvvvv (7) where pr is called pull-up ratio (pr) or  ratio defined as 4 2 )/( )/( mn mp lw lw pr  (8) figure 3(b) plots voltage rise vq versus pr. to avoid write failure, pr must be chosen such that vq falls below threshold voltage of mn1. according to 32 nm cmos berkeley predictive technology model (low power), vtn ≈ 0.438 v @ vds ═ 1 v. as can be seen from fig. 3(b), vq ═ 0.392 v at pr ═ 2.1, which implies that pr can be raised up to 2.1 without write failure. but write static noise margin (wsnm) of 6t sram cell found later in section v is 160 mv. therefore, pr should be judiciously set below 2.1 so that some snm is reserved to cope with dynamic disturbances caused by α particles, crosstalk, voltage supply ripple, and thermal noise. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 19 fig. 3(a): voltage ripple (vqb) versus cell ratio while reading 6t sram cell. (b): voltage ripple (vq) versus pull-up ratio while writing to 6t sram cell at 32 nm technology node. 4. 7t sram cell and device/technology parameters this paper analyzes design concepts addressing the realistic design challenges and issues such as hold power (hpwr), static noise margin (snm), read static noise margin (rsnm), write static noise margin (wsnm), read access time (tra), tra variability, read power (rpwr), write access time (twa), and twa variability, write power (wpwr) and wpwr variability in nanoscale regime. 4.1 7t sram cell authors in [16] proposed a 7t sram cell shown in fig. 4 and reduced the activity factor αbl for reduction of dynamic power while writing to a cell given by pwrite = αbl×cbl×v2fwrite. but static power consumption in a sram cell is more critical than dynamic power consumption (during read and write operation due to bitline charging and discharging), since whole part of the cache remains idle most of the time except the row being read from or written to. moreover, the 7t sram cell in [16] needs dual-vt transistors requiring advanced technology and additional masking cost. in addition to that, its transistor sizing constraint for meeting its functionality poses additional area penalty. read/write operation: both bl and blb are precharged high before and after each read/write operation. the write operation in 7t cell starts by turning off mn5. complement of data to be written to node q is applied to blb and mn3 is turned on by asserting wl high, leaving mn4 off. bl and mn4 do not take part in write operation. during standby mode mn3 and mn4 are kept off applying wl and r low, mn5 is kept on asserting w high. read operation of 7t cell is similar to that of 6t cell. blb discharges through the critical read path consists of mn3, mn5 and mn1 during read operation with qb storing “0”. bl discharges through the read path mn4 and mn2 during read operation with qb storing “1”. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 20 fig. 4: 7t sram cell. 4.2 device/technology parameters important device and technology parameters for the 6t and 7t sram cell are tabulated in table 1. as mn1 ≥3 and mn2 ≥2 ensure stable read operation, the transistors in 7t sram cell are sized as shown in the table 1. mn1 of 6t sram cell is upsized to make a fair comparison between 6t and 7t sram cell with an area penalty (defined as difference in cell area between 6t and 7t) of 11.1% in 7t compared to 6t sram cell. table 2 presents comparison of cell area between 6t and 7t sram cell. it shows that the cell area of 7t is 10240 nm×nm whereas the cell area of 6t is 9216 nm×nm. the 11.1% area penalty is due to the functionality constraint of 7t sram cell. other transistors used for the design are of minimum-sized. the simulation is run on hspice using 32 nm cmos bptm where vtn0 ≈ 0.63 v and vtp0 ≈ − 0.58 v. the next section presents a brief discussion on pvt variation and relates sram’s various design metrics with it. table 1: device/technology parameters. device/parameter 6t 7t 0tnv 0.63 v 0.63 v 0tpv -0.5808 v -0.5808 v mp1 w = 32 nm l = 32 nm w = 32 nm l = 32 nm mp2 w = 32 nm l = 32 nm w = 32 nm l = 32 nm mn1 w = 64 nm l = 64 nm w = 96 nm l = 32 nm mn2 w = 32 nm l = 32 nm w = 64 nm l = 32 nm mn4 w = 32 nm l = 32 nm w = 32 nm l = 32 nm mn5 absent w = 32 nm l = 32 nm iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 21 table 2: cell area comparison. parameter area (nm×nm) % area penalty 6t 9216 __ 7t 10240 11.1 5. impact of process and temperature variation a large portion of the silicon area of many contemporary digital designs is dedicated to the storage of data and program instructions. more than half of the transistors in today’s high-performance microprocessors are devoted to cache memories, and this ratio is expected to further increase. there is a prediction that memory modules typically realized with sram will occupy more than 90% of an soc area in near future. high-performance work-stations and computers today contain several giga bytes of semiconductor memory, a number that is continuously rising. due to device scaling there are several design challenges for nanometer sram design. to reduce the power consumption, supply voltage has been scaled down which has consequently reduced the threshold voltage. reduction of threshold voltage and ultra–thin gate oxide have increased subthreshold leakage and gate leakage current increasing standby power consumption. besides this, read access time (tra) and write access time (twa) also get significantly affected. intrinsic parameter fluctuation like random dopant fluctuation (rdf), line edge roughness (ler) and oxide thickness fluctuation further degrade the stability of sram cell. the intra-die vt variation due to rdf results in failure of sram cell. the vt shifts of the cell transistors due to rdf can be considered as independent gaussian random variables with standard deviation given by [14, 17, 18]: lw wnqt dmsub ox ox vt 3  (9) where, tox is the oxide thickness, wdm is the maximum width of depletion region, and nsub is the substrate doping concentration. in short-channel devices, a variation in channel length also induces a change in threshold voltage due to sce (short-channel effect) [18]. tra and twa are crucial design criteria in high-performance microprocessor where sram cache is embedded. they are also crucial design metrics for designing fpga where sram is embedded as look-up table. the distributions of tra and twa are even more problematic than their absolute values because meeting the design specification with variations in tra and twa is difficult for a designer. the spread in tra and twa are computed based on central limit theorem [19]. as per the central limit theorem, the distribution of a random variable (say, y) which is the summation of a large number of independent random variables (say, 1x , ..., nx ) can be assumed to be normal with mean and the standard deviation given by: iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 22    n 1i 2 xi 2 y 1 and n i xiy (10) if all the variables are identically distributed (i.e. all with equal mean µx and standard deviation σx) we further obtain: x x y y xyxy n n        1 n and (11) from (11), it can be observed that, the spread (standard deviation/mean) of the variable y is less than the spread in the variable x and the spread of y reduces as more number of variables is added together. monte carlo simulation has been carried out to investigate the impact of the random variations of process parameters and temperature on the read access time (tra) and write access time (twa) which are presented in the next section. 6. simulation measurements and comparisons this section presents measurements of various design metrics which are measured during simulation on hspice using 32 nm cmos bptm [20]. monte carlo simulations are performed for the measurements. monte carlo simulation is a method for iteratively evaluating a design. the goal is to determine how random variation on process parameters, voltage and temperature affects the performance and reliability of a design. the arithmetic mean )( is the measure of central tendency that is found to fluctuate less than any other measure of central tendency if many samples are drawn from the same statistical data and standard deviation )( is a measure of dispersion (or variability) that states numerically the extent to which individual observations vary on the average. 6.1 data retention or hold power the leakage current is the major contributor to the power consumption in the sram cell. the total leakage current in an sram cell mainly (excluding minor components) consists of the subthreshold leakage current (isub), the gate leakage current (igate) and the reverse-biased drainand source-substrate junction band-to-band tunneling (btbt) leakage current (ijn) through different transistors as shown in fig. 5 [21]. 214 mpsubmnsubmnsubsub iiii  2143 2 mpjnmnjnmnjnmnjnjn iiiii  111222433 mngdmpgsmpgdmngsmngdmpgdmngdmngsmngdgate iiiiiiiiii  .gatejnsubleak iiii  (12) iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 23 fig. 5: leakage components in standard 6t sram cell. the above currents are dependent on stored value on the storage nodes q and qb. these current equations are valid for vqb = “1” and vq = “0”. if the stored values on the nodes q and qb are interchanged the current equations are required to be changed. the leakage power (hpwr) or the data retention power or hold power consumed due to these leakage currents is measured at nominal voltage of vdd = 1 v and at 0.9 v (−10% of vdd) for both the designs. the measured results are reported in table 3. the normalized values are presented in bracket. as can be observed from the table 3, 7t sram cell consumes 57.3× and 30.7× higher hold power than that of 6t sram cell at vdd = 1 v and at vdd = 0.9 v with qb storing “1” respectively. the table also shows that the 7t cell consumes 2.1× at vdd = 1 v and 1.76× at vdd = 0.9 v higher hold power than that of 6t cell with qb storing “0” respectively. this is attributed to the extra transistor and cell area of 7t sram. the 7t sram cell has one transistor more, i.e. mn5 and its one cell occupies 11.1% extra area as compared to 6t sram cell. it is evident from fig. 5 that the leakage increases due to increase in number of transistor and the area of the transistors involved in the sram cell. table 3: hold power (hpwr). sram hold power while qb storing “1” (pw) hold power while qb storing “0” (pw) vdd (volt) 6t 29.37(1) 29.37(1) 1 7t 1683(57.3) 61.94(2.1) 1 6t 19.73(1) 19.73(1) 0.9 7t 606.4(30.7) 34.66(1.76) 0.9 iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 24 6.2 static noise margin (snm) measurements the static noise margin (snm) of sram cell is defined as the minimum dc noise voltage necessary to flip the state of the cell. snm of an sram is a widely-used design metric that measures the cell stability. fig. 6 shows a conceptual test setup for measuring snm. the measured results when plotted is called "butterfly curve". fig. 7(a) and 7(b) plot “butterfly curve” of 6t and 7t sram cell respectively. the butterfly curve is obtained in the following way with the test circuit: 1) word line (wl) is biased at ground and bit lines (bl, blb) are biased at vdd. 2) voltage of n1 is swept from 0 v to vdd while measuring voltage of qb. 3) voltage of n2 is swept from 0 v to vdd while measuring voltage of q in the same way. 4) measured voltages are plotted to obtain a butterfly curve. the side length of maximum square that can be fitted within the smaller wing of the butterfly curve represents the snm of the cell. as can be seen in the plot, initially node qb remains stable, but as the noise source at node q increases, qb starts falling, eventually flipping the cell. as can be seen in fig. 7(a) and 7(b), the snm of 6t sram cell is 150 mv where as the snm of 7t sram cell is 240 mv, showing 60% improvement in 7t cell. to understand why this happens, consider the case when the value of noise voltage (vn) increases from 0. this causes vtc (voltage transfer characteristic) for inverter 2 formed with mp2 and mn2 to move to the right and vtc-1 (inverse vtc) for inverter 1 formed with mp1 and mn1 in the figure to move downward. once they both move by the snm value, the curves meet at only two points. any further noise flips the cell. it can be noted that, both the inverters of 7t have stronger nmos transistors shifting its vtc to the left and pushing vtc-1 down. fig. 6: test setup for measuring snm. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 25 fig. 7: (a) static noise margin (snm) of 6t and (b) snm of 7t sram cell. 6.3 read static noise margin (rsnm) measurements the sram cell is most vulnerable to noise during read access since the “0” storage node rises to a voltage higher than ground due to a voltage division along the access transistor and inverter pull-down nmos drivers between the precharged bitline and the ground terminal of the cell. the ratio of the widths of the pull-down transistor to the access transistor, commonly referred to as the cell ratio or β ratio, determines how high the “0” storage node rises during a read access. smaller cell ratios translate into a higher voltage drop across the pull-down transistor, requiring a smaller noise voltage at the “0” storing node to trip the cell. read static noise margin (rsnm) is a measure of how much noise voltage required at the node storing “0” to flip the state of an sram cell while reading. therefore, rsnm is more critical design metric of sram cell than snm. rsnm of both the design has been measured during simulation. figure 8(a) and 8(b) plot the rsnm of 6t and 7t sram cell respectively. the plots show that the 7t outperforms 6t in terms of 71.4% improvement in rsnm. these butterfly curves are obtained with test setup shown in fig. 6, and using the same measuring technique as done for snm except biasing wl at vdd. fig. 8: (a) read static noise margin (rsnm) of 6t and (b): rsnm of 7t sram cell. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 26 6.4 write static noise margin (wsnm) measurements the write static noise margin (wsnm) is another sram cell’s design metric, which implies the write ability of sram cell. it is a measure of ability of the cell to pull down the node storing “1” to a voltage less than the switching threshold voltage of the other inverter storing “0” so that flipping of the cell state occurs. wsnm is measured while writing “1”. it is observed from simulation results that there is 50% improvement in wsnm in 7t sram cell. 6.5 read access time and its variability measurements the read access time (tra) measurements are taken with qb storing “0”. the measured average tra are plotted in fig. 9(a) and reported in table 4. as evident from the fig. 9(a) and table 4, the read delay of 7t is increased by 13.1% and 16.7% at vdd = 1 v and 0.9 v respectively compared to 6t sram cell. this is attributed to the fact that the read path of 7t cell consists of mn1, mn5 and mn3 that represents a critical read path with qb storing “0”. this longer read path offers higher resistance and therefore lesser blb discharge current while reading. also to understand this fact, note that the vqb developed during blb discharge makes vbs5 negative, resulting in an increase in the threshold voltage (larger body effect) of mn5 thereby reducing discharge current. the spread of tra of both the sram cells are plotted in fig. 9(b) and tabulated in table 5. the fig. 9(b) and table 5 show that the spread of tra of 7t is 1.2  wider than that of 6t at vdd = 1 v and 1.18  wider than that of 6t at vdd = 0.9 v. it shows that 6t sram is more robust against process variations. this is attributed to the fact that mn1 of 6t is longer than that of 7t. longer device is less sensitive to drain-induced barrier lowering (dibl) and short-channel effect (sce). therefore, 6t cell is less sensitive to pvt variation compared to 7t cell. fig. 9: (a) read access time (tra). (b) read access time variability. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 27 table 4: average read delay. sram average tra (µ) while qb storing “0” (ps) vdd (volt) 6t 27.20 1 33.25 0.9 7t 30.75 1 38.79 0.9 table 5: read delay variability. sram tra variability (σ/μ) while reading with qb storing “0” vdd(volt) 6t 0.009(1) 1 7t 0.011(1.2) 6t 0.011(1) 0.9 7t 0.013(1.18) 6.6 read power measurements power consumption during read operation is also an important parameter of sram cell as it contributes a considerable amount to total power. the read power is measured at supply of 1 v and 0.9 v. the measured values of average (µ) read power (rpwr) and rpwr variability (σ/µ) are tabulated in table 6. the normalized values of variability are reported in bracket. the values show that the 7t cell offers saving in rpwr (65.6% @ vdd = 1 v and 71.4% @ vdd = 0.9 v), while reading with qb storing “1”. the normalized values of the rpwr variability indicate that 6t cell is robust against pvt variation by 3.9× @ 1 v and 3.7× @ 0.9 v. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 28 table 6: read power and its variability measurements. sra m rpwr (σ) while qb storing “1” (nw) rpwr (µ) while qb storing “1” (nw) rpwr variability (σ/μ) vdd (volt) 6t 1.263 95.99 0.013(1) 1 7t 1.445 32.98 0.044(3.9) 6t 0.7898 79.07 0.010(1) 0.9 7t 0.8283 22.64 0.037(3.7) 6.7 write access time measurements the write access time (twa) is measured during simulation and plotted in fig. 10(a), which shows that the 7t cell takes 16.6× @ 1 v and 41.7× @ 0.9 v longer time than 6t cell for writing “1” at qb. fig. 10(b) plots the write delay variability while writing “1” at qb. it is evident from fig. 10(b) that the 7t sram cell is more prone to pvt variation − 3.4× @ 1 v and 3× @ 0.9 v compared to 6t sram cell. fig. 10: (a) write access time (twa). (b) write access time variability. 6.8 write power measurements power consumption during write operation is measured while writing “1” at qb. the measurement results are plotted in fig. 11(a). it is clear from the fig. 11(a) that the 7t cell offers 89% reduction in write power @ vdd = 1 v and 93.6% reduction @ vdd = 0.9 v. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 29 fig. 11(b) plots write power (wpwr) variability while writing 1 @ qb. it is observed from this plot that 6t cell is more robust against pvt variation. in this plot, 7t cell shows 1.3× @ 1 v and 1.4× @ 0.9 v wpwr variability. fig. 11: (a) write power and (b) write power variability. 7. conclusion this paper has analyses the impact of process, voltage and temperature variations on read/write access time and read/write power of 6t and 7t sram cells. all the simulations are performed at the nominal voltage of vdd = 1v with – 10% variations. the process parameters (±10%) as well as temperature (from 24°c to 134°c) are varied normally using gaussian function. simulation measurements are taken for both the designs against 3 variation of process parameters and temperature. the analysis shows that 6t sram cell is more robust against process variation in terms of most of the design parameters compared to 7t sram cell. references [1] k. bowman, et al., “impact of die-to-die and within die parameter fluctuations on the maximum clock frequency distribution for gigascale integration,” ieee j. solid-state circuits, vol. 37, no. 2, pp. 183-190, feb. 2002. [2] s. borkar, et al., “parameter variations and impact on circuits and microarchitecture,” acwieee dac, 2003, pp. 338-342. [3] t. karnik, t. de, and s. borkar, “statistical design for variation tolerance: key to continued moore’s law,” in proc. int. conf. integrated circuit design and technology, 2004. pp. 175-176. iium engineering journal, vol. 12, no. 1, 2011 islam and hassan 30 [4] r. w. keyes, “the effect of randomness in the distribution of impurity atoms on fet thresholds,” app. phys. a: materials science & processing, vol. 8, no. 3, pp. 251–259, jun. 1975. [5] t. mizuno, j. okamura, and a. toriumi, “experimental study of threshold voltage fluctuations using an 8k mosfet array,” in proc. symp. vlsi tech., 1993, pp. 41–42. [6] x. tang, v. de, and j. d. meindl, “intrinsic mosfet parameter fluctuations due to random dopant placement,” ieee trans. very large scale integr. (vlsi) syst., vol. 5, no. 4, pp. 369–376, dec. 1997. [7] d. burnett, k. erington, c. subramanian, and k. baker, “implications of fundamental threshold voltage variations for high-density sram and logic circuits,” in proc. symp. vlsi tech., 1994, pp. 15–16. [8] e. seevinck, f. list, and j. lohstroh, “static-noise margin analysis of mos sram cells,” ieee j. solid-state circuits, vol. sc-22, pp. 748–754, oct. 1987. [9] j. w. tschanz, et al., “adaptive body bias for reducing impacts of die-to-die and within-die parameter variations on microprocessor frequency and leakage,” ieee j. solid-state circuits, vol. 37, no. 11, pp. 1396-1402, nov. 2002. [10] s. borkar, “design challenges of technology scaling,” in proc. ieee micro, vol. 19, no. 4, 1999, pp. 23-29. [11] s. rusu, et al., “a 65-nm dual-core multithreaded xeon processor with 16-mb l3 cache,” ieee j. solid-state circuits, vol. 42, no. 1, pp. 17-25, jan. 2007. [12] j. rabaey, “digital integrated circuits (a design perspective),” englewood cliffs, nj: prentice-hall, 1996. [13] s. mukhopadhyay, et al., “statistical design and optimization of sram coll for yield enhancement,” in proc. int. conf. computer aided design, 2004, pp. 10-13. [14] s. mukhopadhyay, et al., “modeling and estimation of failure probability due to parameter variations in nano-scale srams for yield enhancement,” in proc. symp. vlsi circuits, 2004, pp. 64 – 67. [15] b. wicht, et al., “yield and speed optimization of a latch type voltage sense amplifier,” ieee j. solid-state circuits, vol. 39, no. 7, pp. 1148-1158, jul. 2004. [16] r. aly, m. faisal, and a. bayoumi, “novel 7t sram cell for low power cache design,” in proc. ieee soc conf., 2005, pp. 171–174. [17] bhavnagarwala, et al., “the impact of intrinsic device fluctuations on cmos sram cell stability,” ieee j. solid-state circuits, vol. 36, no. 4, pp. 658-665, april 2001. [18] y. taur and t. h. ning, “fundamentals of modern vlsi devices,” new york: cambridge univ. press, 1998. [19] a. papoulis, s. u., pillai, “probability, random variables and stochastic process,” 4th ed., mcgraw-hill publishing company, 2002. [20] berkeley predictive technology model (bptm), university of california, berkeley device group. [online]. available: http://wwwdevice.eecs.berkeley.edu/~ptm/. [21] k. roy, s. mukhopadhyay, and h. mahmoodi-meimand, “leakage current mechanisms and leakage reduction techniques in deep-submicrometer cmos circuits,” in proc. ieee, vol. 91, no. 2, 2003, pp. 305–327. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 10, no. 2, 2009 ali et al. 81 decoy state quantum key distribution sellami ali1,2*, suhairi saharudin2 and m.r.b. wahiddin1,2 1department of computational and theoretical sciences, faculty of science, international islamic university malaysia p. o. box 141, 25710 kuantan, malaysia. 2information security cluster, mimos berhad, technology park malaysia. *e-mail: sellami2003@hotmail.com abstract: experimental weak + vacuum protocol has been demonstrated using commercial qkd system based on a standard bi-directional ‘plug & play’ set-up. by making simple modifications to a commercial quantum key distribution system, decoy state qkd allows us to achieve much better performance than qkd system without decoy state in terms of key generation rate and distance. we demonstrate an unconditionally secure key rate of 6.2931 x 10-4 per pulse for a 25 km fiber length. keywords : quantum cryptography, quantum key distribution, decoy state protocol, optical communications 1. introduction quantum key distribution (qkd) has drawn many attentions from scientists. different from the classical cryptography, quantum key distribution (qkd) [1-3] can help two remote parties to set up the secure key by non-cloning theorem [4]. further, proofs for the unconditional security over noisy channel have been given [5-8]. unfortunately, in view of implementation, “perfect” devices are always very hard to build. therefore most up-todate qkd systems substitute the desired perfect single photon sources by heavily attenuated coherent laser sources. qkd can be performed with these laser sources over more than 120 km of telecom fibers [9, 10]. however, this substitution raises some severe security concern. the output of coherent laser source obeys poisson distribution. thus the occasional production of multi-photon signals is inevitable no matter how heavily people attenuate the laser. recall that the security of bb84 protocol [3] is guaranteed by quantum non-cloning theorem, the production of multi-photon signals is fatal for the security: the eavesdropper (normally denoted by eve) can simply keep an identical copy of what bob possesses by blocking all single-photon signals and splitting all multi-photon signals. most up-to-date qkd experiments have not taken this photon-number splitting (pns) attack into account, and thus are, in principle, insecure. hwang [11] proposed the decoy state method as an important weapon to combat those sophisticated attack: by preparing and testing the transmission properties of some decoy states, alice and bob are in a much better position to catch an eavesdropper. hwang iium engineering journal, vol. 10, no. 2, 2009 ali et al. 82 specifically proposed to use a decoy state with an average number of photon of order 1. hwang’s idea was highly innovative. decoy pulse qkd theory gives a rigorous bound of the characteristics of the single photon pulses, which are the only source pulses that contribute to the secure bit rate. in [14], combining the idea of security proofs using the entanglement distillation approach in gllp [10] with decoy method; they gave a formula for the key generation rate { }2 1 2 1( ) ( ) [1 ( ) ]r q q f e h e q h eµ µ µ≥ + − (1) where q depends on the protocol, the subscript μ is the average photon number per signal in signal states, qμ is the gain of signal states, eμ is the quantum bit error rate (qber) of signal states, q1 is the gain of the single photon states in signal states, e1 is the error rate of single photon states. f(x) is the bi-directional error correction rate [13], and h2(x) is binary shannon information function: h2(x) = −x log2(x) − (1 − x) log 2 (1 − x). (2) our implementation is based on bb84 [3] protocol. among total n pulses sent in experiment, ns pulses are used as signal states. therefore the factor q is given by q = ½ ns/n . qμ and eμ can be measured directly from experiments. in [12], they have proposed a practical protocol with weak + vacuum states with average photon number 0 and v. such a protocol is relatively simple to implement. the gain of the weak decoy state qv and its error rate eμ could also be required directly from experiments. considering statistical fluctuations, the lower bounds of q1 , and the upper bound of e1 2 2 2 2 1 1 02 2 2 0 l l ueq q q e q e y e µ υ µ υ µ µ υ µ υ µυ υ µ µ −   − ≥ = − −   −    are given by [12]: (3) 1 1 1 u e qe e q υ υ≤ = (4) in which 1l u q q n q α ν ν ν ν   = −     0 0 0 0 1l u y y n y α   = −     0 0 0 0 1u u y y n y α   = +     iium engineering journal, vol. 10, no. 2, 2009 ali et al. 83 in this paper, we will present the experimental implementation of weak decoy + vacuum states qkd using commercial qkd systems are bi-directional. to show conceptually how simple it is to apply the weak decoy + vacuum state idea to a commercial qkd system, we chose id-3000 commercial quantum key distribution system manufactured by id quantique. to implement the one decoy state protocol, we have to add some new optical and electronics components to id quantique and have to attenuate each signal to the intensity of either signal state or weak decoy or vacuum state randomly. in our implementation, the attenuation will be done by placing a voa (variable optical attenuator) in alice’s side. specifically, our qkd system requires the polarizations of the two pulses from the same signal to be orthogonal. therefore the voa must be polarization independent so as to attenuate the two pulses equally. the voa utilized in our experiment to attenuate signals dynamically is acousto-optic modulator (aom). 2. experimental setup existing commercial qkd systems are bi-directional. to show conceptually how simple it is to apply the decoy state idea to a commercial qkd system, we chose id-3000 commercial quantum key distribution system manufactured by id quantique. the prototype of this qkd system is described in section 2 of [8]. here we describe it briefly: a frame of np pulses (in our experiment, np = 624) is generated from bob and sent to alice. within a frame, the time interval between signals is 200 ns. the next frame will not be generated until the whole frame has returned to bob. the long delay line inside jr. alice promises that the incoming signal and returning signal will not overlap in the channel between bob and jr. alice so as to avoid rayleigh scattering. this qkd system is called p&p auto-compensating set-up, where the key is encoded in the phase between two pulses traveling from bob to alice and back (see fig. 1) . a strong laser pulse (@ 1550 nm) emitted at bob is separated at a first 50/50 beam splitter (bs), after having traveled through a short arm and a long arm, including a phase modulator (pmb) and a 50 ns delay line (dl), respectively. all fibers and optical elements at bob are polarization maintaining. the linear polarization is turned by 90 degree in the short arm, therefore the two pulses exit bob’s step-up by the same port of the pbs. the pulses travel down to alice, are reflected on a faraday mirror, attenuated and come back orthogonally polarized. in turn, both pulses now take the other path at bob and arrive at the same time at bs where they interfere. then, they are detected either in d1, or after passing through the circulator (c) in d2. since the two pulses take the same path, inside bob in reversed other, this interferometer is auto-compensated. the implementation of weak + vacuum protocol requires amplitude modulation of three levels: μ, v and 0. note that it would be quite hard for high-speed amplitude modulators to prepare the real ‘vacuum ‘state due to finite distinction ratio. however, if the gain of the ‘vacuum’ state is very close (like within a few standard deviations) to the dark count rate, it would be a good approximation. in our implementation, the attenuation is done by placing a voa (variable optical attenuator) in alice’s side. figure 1 illustrates the schematic of the optical and electric layouts in our system. the commercial qkd system by id quantique consists of bob and “jr. alice”. in our decoy state experiment, the actual iium engineering journal, vol. 10, no. 2, 2009 ali et al. 84 (sender’s) system is called “alice”. it consists of “jr. alice” and four new optical and electronics components added by us. more concretely, for our decoy state protocol, we place the decoy acousto optic modulator aom (denoted by da in fig. 1) right in front of jr. alice. its “idle state” is set to maximum transmittance. when the frame comes from bob, the decoy aom is in the idle state. after the first pulse reaches coupler c2, it will be detected by the classical detector and a synchronization signal will be output to trigger the decoy generator. the decoy generator (dg in fig. 1), being triggered, will hold a delay time td before outputting np modulation voltages driving the decoy aom to attenuate the intensity of each the np signals to be either that of signal state or decoy state dynamically, according to the decoy profile. the compensating aom (ca) is used only for the purpose of shifting the frequency of the signal and, thus maintaining the alignment between alice’s and bob’s interferometers. a compensating generator (cg) is used to drive the compensating aom (cg).] fig.1: experimental setup of weak-vacuum state protocol. 3. results and discussion after the transmission of all the signals, alice broadcasted to bob the distribution of decoy states as well as basis information. bob then announced which signals he had actually received in correct basis. we assume alice and bob announced the measurement outcomes of all decoy states as well as a subset of the signal states. from those experimental data, alice and bob then determined qμ, qv, eμ, and ev , whose values are now listed in table 1. note that our experiment is based on bb84 [10] protocol, thus q = (½)nsμ /n, where nsμ is the number of pulses used as signal state when alice and bob choose the same basis, and n = 105 mbit is the total number of pulses sent by alice in this experiment. we performed numerical simulation to find out the optimal parameters. according to simulation results, we choose the intensities as μ = 0.55, v = 0.152. numbers of pulses used as signal state, weak decoy state and vacuum state are nμ = 0.635 n, nv = 0.203 n, and n0 = 0.162 n, respectively, where n = 105 mbit is the total data size we used. in our analysis of experimental data, we estimated e1 and q1 10uα = very conservatively as within 10 standard deviations (i.e., ), which promises a confidence interval for statistical fluctuations of 1 − 1.5 x 10-23 the experimental results listed in table 1 are the input for eqs (1), (3), (4), whose output is a lower bound of the key generation rate, as shown in table 2. even with our very conservative estimation of e . 1 and q1, we got a lower bound for the key generation iium engineering journal, vol. 10, no. 2, 2009 ali et al. 85 rate rl = 6.2931 x 10-4 para. value per pulse, which means a final key length of about l = nr = 66 kbit. table 1: direct results from our experiment. para. value para. value qµ 0.0094 qν 0.0027 eµ 0.0107 eν 0.0221 q 0.319 f (e) [13] 1.22 table 2: the lower bounds of q1, r and the upper bound of e1 para. value . para. value 1 lq 0.0037 1 ue 0.0271 lr 6.2931x 10-4 the values are calculated from eqs. (1), (3), and (4), taking statistical fluctuation into account. 4. conclusion experimental weak + vacuum decoy qkd system using commercial qkd system has been demonstrated over a 25 km fiber with an unconditionally secure key rate of 6.2931 x 10-4. it is unconditionally secure against all types of attacks, including the pns attack. we conclude that decoy pulses improve the security and performance of weak pulse qkd. however, sources and detectors must be calibrated accurately to avoid any artifacts that may compromise security. references [1] m. a. nielsen and i. l. chuang, quantum computation and quantum information, cambridge university press, uk, 2000. [2] n. gisin, g. ribordy, w. tittel, h. zbinden, rev. mod. phys. 74, 145 (2002), references therein. [3] c.h. bennett and g. brassard, in : proc. ieee int. conf. on computers, systems, and signal processing, bangalore (ieee, new york, 1984) p.175. [4] w.k. wootters and w.h. zurek, nature 299, 802 (1982). [5] p.w. shor and j. preskill, phys. rev. lett. 85, 441 (2000). [6] h.-k. lo and h.f. chau, science 283, 2050 (1999). iium engineering journal, vol. 10, no. 2, 2009 ali et al. 86 [7] d. mayers, j. assoc. comput. mach. 48, 351 (2001). [8] a.k. ekert, phys. rev. lett. 67, 661 (1991), c.h. bennett, d.p. divincenzo, j.a. smolin, and w.k. wootters, phys. rev. a 54, 3824 (1996). [9] c. gobby, z. l. yuan, a. j. shields, appl. phys. lett. 84, 3762 (2004) [10] x. mo, et al. opt. lett. 30, 2632 (2005) [11] w.-y. hwang, phys. rev. lett. 91, 057901 (200). [12] x.ma, b. qi, y. zhao and h.-k. lo, “ practical decoy state for quantum key distribution”. http://www.arxiv.org/abs/quant-ph/0503005(2005) [13] g. brassard and l. salvail, in advances in cryptology eurocrypt’ 93,vol. 765 of lecture notes in computer science, edited by t.helleseth ( springer, berlin, 1994),pp.410-423 http://www.arxiv.org/abs/quant-ph/0503005(2005)� tunable bandpass filter using rf mems switches 2.1 one mems bridge parallel with the resonator 2.2 two mems bridge parallel with the resonator 2.3 one mems bridge perpendicular to the resonator 2.4 mems bridges parallel and covering all the resonators acknowledgement references keywords : quantum cryptography, quantum key distribution, decoy state protocol, optical communications 2. experimental setup influence of polarization mode dispersion on the effect of cross-phase modulation in intensity modulation-direct detection wdm transmission system introduction system model theoretical analysis 3.1 modulation of the probe field results and discussion conclusion acknowledgement references towards a scalable scientific data grid model and services introduction related works the p2p data grid model the simulation study experiments and results conclusion and future work references anomalous electrodeposition of fe-ni alloy coating from simple and complex baths and its magnetic property microsoft word 218-1052-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alade et al. 161 removal of oil and grease as emerging pollutants of concern (epc) in wastewater stream abass o. alade, ahmad t. jameel, suleyman a. muyubi, mohamed i. abdul karim and md. zahangir alam bioenvironmental engineering research unit, biotechnology engineering department, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. abasslad@yahoo.com abstract: wastewater characteristics, which depend on wastewater source, are increasingly becoming more toxic in recent times. the concentrations of oil and grease in wastewater streams have been observed to increase in wastewater stream with increasing adverse effects on the ecology. this results from the increasing use of oil and grease in high-demanded oil-processed foods, establishment and expansion of oil mills and refineries worldwide, as well as indiscriminate discharge of oil and grease into the water drains, domestically and industrially. this study reports the applications, efficiencies and challenges of the wastewater treatment techniques currently employed in the removal of oil and grease from the industrial wastewater and municipal water stream. the results shows that the concentrations of oil and grease injected into the ecosystem are of higher environmental impact and this needs to be given the desired attention. the desired development for effective removal of oil and grease as emerging pollutants of concern (epc) in wastewater stream are thus proposed. abstrak: ciri-ciri air sisa, bergantung kepada punca air sisa tersebut, menjadi semakin toksik akhir-akhir ini. kepekatan minyak dan gris dalam air sisa anak sungai dilihat makin bertambah dalam air sisa anak sungai dengan bertambahnya kesan negatif ke atas ekologi. ini disebabkan oleh peningkatan penggunaan minyak dan gris dalam makanan berproses yang tinggi permintaannya, penubuhan dan perkembangan kilang pertroleum dan loji penapisan di seluruh dunia. minyak dan gris juga dibuang sewenangwenangnya ke dalam parit air, dari kalangan domestik dan industry. kajian ini membentangkan tentang aplikasi, keberkesanan dan teknik cabaran rawatan air buangan yang kini digunakan dalam pembuangan minyak dan gris dari air sisa industry dan air sungai perbandaran. keputusan menunjukkan kepekatan minyak dan gris yang wujud dibuang ke dalam ekosistem mempunyai impak yang lebih tinggi terhadap persekitaran dan hal ini perlu diambil berat. keinginan untuk kemajuan penyingkiran minyak dan gris sebagai keprihatinan terhadap pencemaran (emerging pollutants of concern (epc))ke atas air sisa sungai dicadangkan. keywords: emerging pollutants of concern (epc); oil; grease; wastewater 1. introduction oil contaminated wastewater comes from variety of sources such as crude oil production, oil refinery, petrochemical industry, metal processing, compressor condensates, lubricant and cooling agents, car washing, restaurants [1]. oily wastewater contains toxic substances such as phenols, petroleum hydrocarbons, polyaromatic iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alade et al. 162 hydrocarbons, which are inhibitory to plant and animal growth, equally, mutagenic and carcinogenic to human being. similarly, oily wastewater contains high oil content, chemical oxygen demand (cod) and colour [1]. the increase in global demand for edible oils has in the last few decades has resulted in a tremendous increase in the cultivation of oil seeds, particularly of soybean and oil palm [2]. the oil seeds are usually processed to obtain the oil contents which are subsequently processed for human consumption and industrial applications. thus the vegetable oil industries are, equally, associated with oil extraction, refining, transportation, uses and reuses. however, these industries have been linked with environmental pollutions resulting from oil spill, oily effluent discharge into water bodies and oily sludge discharge into the environment indiscriminately, untreated or in conditions below the standard discharge limits. oil and grease containing wastes generated from vegetable oil origin are generally classified as serious types of hazardous pollutants particularly when injected into the aquatic environments where they pose high toxicity to the aquatic organisms and other ecology damages to the water bodies [3]. oil and grease is defined as a group of related materials rather than a specific chemical compound extractable by certain solvents, such as hexane [4, 5]. they are nonpolar and, as a result, are hydrophobic in nature [5]. generally, oil is not soluble in the water-phase and the nature of the oil-phase in oily wastewater is different from one case to another [6, 7]. under anaerobic conditions, oils and grease hydrolyze to long chain fatty acids (lcfa) and glycerol [8, 9]. the glycerol further degrades to 1, 3-propanediol [10] and subsequently to acetate [11]. oil-water mixture with droplets greater than or equal (≥) to 150 microns is classified as free oil while oil-water mixture with droplets size ranging between 20 and150 microns, are classified as dispersed oil mixture. emulsified oil mixture are oil-water mixture with droplet sizes smaller than 20 microns and oil-water mixture with droplet sizes smaller than 5 microns are classified as soluble oil mixture [12]. this study focuses on wastewater containing oil and grease resulting from the extraction, refining, transportation and utilization of vegetable oil obtained from plant and animal sources except otherwise in a general form to include oil from other sources like petroleum and others. 2. vegetable oil sources the consumption of vegetable oil increased (3.5%) rapidly nearly twice more than the world population increased (1.6%) between 1980 and 2000. predominant oil-bearing crops sourced for the production of vegetable oil include soybean, palm, sunflower, safflower, cottonseed, rapeseed, and peanut. world major exporters of vegetable oils include malaysia, argentina, indonesia, the philippines, and brazil while countries such as the netherlands, germany, the united states, and singapore are both major exporters as well as importers of vegetable oils [13]. countries such as china, pakistan, italy, and the united kingdom are the leading world major importers of vegetable oils. vegetable oils are generally obtained through extraction and refining processes of oils and fats from vegetable and animal sources. the initial crude oil obtained usually contains free fatty acids, phospholipids, sterols, water, odorants, and other impurities. furthermore, refined oils and fats contain small amounts of free fatty acids and water [14]. preliminary preparation of vegetable oil raw materials includes husking, cleaning, crushing, and conditioning after which the oil is extracted through mechanically pressing or using solvents such as hexane. the oil are carefully recovered from the extraction process through is skimming, filtration, and distillation depending on the method of extraction while the refining processes includes degumming, neutralization, bleaching, iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alade et al. 163 deodorization, and advanced refining process for specific demand from industries such as pharmaceutical [15]. 3. sources of oil and grease in wastewater the largest source of wastewater is produced during oil extraction processes in most oil mills and the mill effluents such as palm oil mill effluent pome may be categorized as an oily wastewater due to its high concentrations (4000 to 6000 mg/l) of oil and grease [16]. the concentration of oil and grease in an untreated domestic wastewater is always in the range between 50 to 100 mg/l [17]. kitchen greywater is reported as the highest contributor of oil and grease in domestic greywater, though oil and grease is present in all greywater streams [18]. the presence of oil and grease has been detected in greywater, which are often designated for irrigation purposes [5, 18]. travis et al. [5], showed that soils irrigated with greywater indicate accumulation of oil and grease up to 200 mg kg -l within the first 20-cm of depth and this consequently lead to a significant reduction in the soils ability to transmit water. some food processing industries such as slaughterhouses, dairy and meat packing industries are well known for producing effluents containing oil and grease [19-21]. oil containing wastewater is also sourced from non-vegetable oil manufacturing industries such as the steel, machine, petroleum refining, metal cutting and metal forming, and textile industries [7]. oily wastewater from the metalworking and finishing industries is generated from the application of coolants and lubricants used for cooling the work pieces and machine tools, reducing friction and wear of tools and dies, as well as improving the surface quality of work pieces. industrialized countries such as united kingdom, italy and germany produced large volume of such effluent [22]. the bilge water usually contains fuel oils, lubricating oils, hydraulic oils, and detergents and their concentrations largely depend on the ship type and ship-operating mode [23]. thus, such large of amount oily wastewater has qualified oil and grease as emerging pollutants of concern (epc) in wastewater stream. 4. environmental impact of oil and grease in wastewater world water bodies are increasingly polluted with oily water, its effects can be irreversible for aquatic living organisms, and the consequences of these effects are transferred, indirectly or directly, to humans, as they are also involve in the in the food chain of the ecosystem. the presence of oil and grease in water bodies leads to the formation of oil layer, which causes significant pollution problem such as reduction of light penetration and photosynthesis. it further hinders oxygen transfer from atmosphere to water medium and this leads to decreased amount of dissolved oxygen (do) at the bottom of the water and this adversely affects survival of aquatic life in water [24]. stams and oude [25] reported the effects of oil and grease in wastewater steam to include physical blockages in sewers, pump, screens and filter distributor arms, and these consequently lead to increase maintenance costs. these effects also include accumulation of lighter oils in the wet wells of pumping stations, fouling of electrodes or float systems which leads to pump controls failures. where the nature of oil is highly flammable, it leads to explosion hazard in the treatment works [21]. excessive grease in the wastewater stream causes difficulties in sludge pressing because of ‘blinding effect’ on the filter cloths [26]. furthermore, oil and grease interfere with aerobic biological wastewater treatment processes by reducing oxygen transfer rates. equally, oil and grease reduce the efficacy of anaerobic treatment processes by reducing the transport of soluble substrates to the iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alade et al. 164 bacterial biomass [27, 28]. similarly, in the municipal water treatment plant, oil and grease cause objectionable taste and odors, turbidity and film, and make filtration treatment difficult [29]. 5. test method for extraction of oil and grease in wastewater the test procedures used to measure the concentrations of oil and grease in typical oily wastewater target only conglomerate of oily substances that are extractable by specific solvents. the american public health association (apha)’s methods for the examination of water and wastewater [30] suggested the use of the partition-gravimetric method (503a) which involves the extraction of dissolved and emulsified oil and grease using trichlorotrifluoroethane. other provisions are the partition-infrared method (503b) which uses an extraction process identical to the 503a method together with infrared detection methods and the soxhlet extraction method (503c) which is based on an acidification of the sample, separating the oils from the liquid through filtration and extraction using trichlorotrifluoroethane. the environmental protection agency (epa), similarly favours 503a method under the general pretreatment regulations, 40 cfr 403.12(b) (5) (vi) for wastewater sampling and analyses. a new astm method d7066-04 is currently recommended as quick and easy field analysis method for determining oil and grease concentrations particularly for offshore oil platforms, soil remediation sites and industrial wastewater measurement. this development is due to the montreal protocol in 1995 banned on the use of freon 113, which is widely employed in the astm method (d3921) for analyzing wastewater. the new astm method d 7066–04, standard test method for dimmer/trimmer of chlorotrifluoroethylene (s-316) under recoverable oil and grease and nonpolar material by infrared determination, uses a similar extraction procedure with a more ozone friendly solvent called s-316. a variety of infrared instruments such as the full spectrum fourier transform infrared (ftir) spectrometers as well as portable and relatively inexpensive fixed filter infrared analyzers such as the wilks infracal tog/tph analyzer can be used with astm method d7066-04. with the new astm method, options for onsite analysis of oil and grease have increased and thus lower laboratory costs, avoid out-of compliance fees, and improve remediation efficiency [31]. 6. discharged regulations for oil and grease in wastewater the emerging strict legislation for protection of environment demands for the application of appropriate treatment technology for the wastewater emanating from oil processing industries. the early daily allowable maximum limit for oil and grease in industrial nation such as the united state of america was 35 mg/l and the average per month was less than 17 mg/l [32]. upward review of these regulations shifted the new maximum limit for daily allowable oil to 15 mg/l and the average per month is 12 mg/l. the malaysian department of environment (doe) has limited the standard discharge of oil and grease, particularly in palm oil mill effluents (pome), to 50 mg/l, under the current environmental quality practice for the palm oil mills [33]. 7. treatment processes for oil and grease in wastewater iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alade et al. 165 oil and grease in the wastewater from oil processing industries are removed by various accepted techniques and the selection of the required equipment depends on the condition of the oil-water mixture. some of the common conventional methods of oily wastewater treatment include flotation, gravitational methods, chemical treatment, biological treatment, dissolved air flotation (daf) and use of membranes [34]. however, these methods are not efficient enough to treat the oily wastewater particularly when the oil are finely dispersed droplets and in dilute concentration, as well as inconsistent variations in the composition of the wastewater. oil droplets of about 50 µm have been removed effectively by low cost equipment such as api separators, corrugated plate interceptors (cpi), and parallel plate interceptors (ppi), for primary treatment of oily water [35]. oil droplets less than 50µm size have been removed by packed beds and dissolved air flotation (daf) [36]. de-emulsification which is effective in breaking stable emulsions using chemicals such as sulphuric acid, iron and aluminum sulphate and reducing the amount of oil in the water, has not been widely embraced due to its high cost and relatively low removal efficiency [37-39]. wastewaters containing oil and grease, derived from vegetable oils, with a significant amount of linoleic acid have been reported to be challenging to treat due to the presence and concentration of linoleic, palmitic and myristic acids produced [40]. wastewaters containing fat and oils were traditionally treated physically, which is currently considered insufficient if the fat is in a dispersed form [41]. abid baig et al., [29] studied effectiveness of gravity separation and dissolved air floatation for the removal of oil and grease from industrial and domestic wastewaters and about 85% removal efficiency was achieved in removal as emulsified oil from the wastewaters. microbial degradation of oil wastewater involving the application of variety of microorganisms such as bacteria, molds, and yeasts, which have demonstrated effective degradability of oil-wastewater, has attracted attention in recent time [42-46]. biological treatment of salad oil and grease from food wastewater by yarrowia lipolytica w29 has been studied [47]. similarly, treatment of wastewater containing high concentrations of oil and grease matter with photosynthetic bacteria from food and agricultural wastewater has been reported in the literature [48-50]. adsorption techniques using various adsorbents such as clay minerals have been successful in removing oil-grease from wastewater streams [24, 51, 52]. the application of membrane separation for the treatment of oily wastewater is demanded due to its high efficiency to handle a low concentration of oil. though the use of membranes is generally hindered by membrane fouling, its economical advantage has not been that robust [53-56]. however, studies have investigated improvement and modification to obtain less fouling and higher fluxes. application of membrane processes using pressure as the driving force for the treatment of oily water have been applied at different locations [57-60]. the membrane technology has been integrated in some existing treatment plants to improve the quality of the treated wastewater in order to meet required limits for oil in discharged wastewaters, though it may be operated independently. oil and grease treatment process involving aerobic biological process alone or in combination with physicochemical treatment alternatives involves high capital investments, requires skilled work force in addition to being energy intensive. in comparison, anaerobic treatment system involves low investment, omitting aeration equipment, sludge disposal facility, and recirculation and provides biogas as a fuel substitute and therefore, the system is a more viable alternative as a pretreatment facility. the challenges militating against anaerobic treatment of wastewater containing oil and grease are the adsorption of a thin layer of oil and grease around biomass particles, iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alade et al. 166 which cause biomass flotation and washout. acute toxicity of the resulting lcfa, especially unsaturated lcfa, to both methanogens and acetogens, adversely affect the application of anaerobic treatment to wastewater containing oil and grease [28, 61]. in the last few years the development of upflow anaerobic sludge blanket (uasb) concept has improved the anaerobic wastewater treatment technology and hence it wide application [62-64]. saatci et al., [65] reported about 70% removal efficiency of total lipids (tl) and fatty acids (fa) from wastewaters of a sunflower oil factory in turkey using upflow anaerobic sludge blanket (uasb) reactor. treatment of wastewaters with high oil and grease content using thermophilic treatment facilitates solubility of these contaminants in the water stream; however, it leads to fall in the sludge settleability as the temperature increases and consequently, washout of biomass and low quality effluent [66-69]. many studies have attempted to minimize the disadvantages of this process by coupling thermophilic reactor with membrane [70, 71]. removal efficiency (>90%) of oil and grease was obtained by kurian and nakhla [72] using an aerobic membrane-coupled bioreactor (mbr) operating at mesophilic thermophilic transitional temperatures (40°c). 8. conclusion wastewaters containing high concentration of oil and grease are increasing in volume due to the expansion in the oil processing industries worldwide. the has increased the percentage composition of oil and grease in wastewater stream, which in turn caused avert effects on the ecology and the equipment used in the treatment plants. this invariably has identified oil and grease as emerging pollutants of concern (epc) in wastewater stream and this has opened up research opportunity in the field of wastewater treatment. acknowledgement the invaluable suggestions, contributions and corrections of the reviewers and the editor to the iium engineering journal are humbly appreciated. references [1] w.u. lan, g.e. gang, and w.a.n. jinbao, biodegradation of oil wastewater by free and immobilized yarrowia lipolytica w29, journal of environmental sciences vol. 21, pp. 237– 242, 2009. [2] s. yacob, progress and challenges in utilization of palm biomass, advanced agriecological research sdn. bhd. http:// www.jst.go.jp/asts/asts_j/files/ppt/15_ppt.pdf., december, 2008. [3] s. mendiola, j.j. achutegui, f.j. sanchez, and m.j. san, polluting potential wastewater from fish-meal and oil industries. grasa aceites , vol. 49, pp. 30–33, 1998. [4] usepa, epa. method 1664 revision a: n-hexane extractable material (hem; oil and grease) and silica gel treated n-hexane extractable material (sgt-hem; non-polar material) by extraction and gravimetry. washington dc: united states environmental protection agency, 1999. [5] m.j. travis, n. weisbrod,, and a. gross, accumulation of oil and grease in soils irrigated with greywater and their potential role in soil water repellency. science of the total environment, vol. 394, pp. 68–74, 2008. [6] h. e. tatem, b. a. cox, and j. w. anderson, the toxicity of oils and petroleum hydrocarbons to estuarine crustaceans, estuarine, coastal and shelf science, vol. 6, pp. 365– 373, 1978. [7] h. wake, oil refineries: a review of their ecological impact on the aquatic environment, estuarine, costal and shelf science, vol. 62, pp.131-140, 2005. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alade et al. 167 [8] k. hanaki, t. matsuo, and m. nagase, mechanism of inhibition caused by long-chain fatty acids in anaerobic digestion process. biotechnol. bioeng., vol. 23, pp.1591–1610, 1981. [9] e. salminen, j. rintala, l.ya. lokshina, and v.a. vavilin, anaerobic batch degradation of solid poultry slaughterhouse waste. water sci. technol., vol. 41, no.3, pp. 33–41, 2000. [10] a.-i. qatibi, a. bories, and j.-l. garcia, sulfate reduction and anaerobic glycerol degradation by mixed microbial culture. curr. microbiol., vol. 22, pp. 47–52, 1991. [11] h.c. dubourguier, e. samain, g. prensier, and g. albagnac, characterization of two strains of pelobacter carbinolicus isolated from anaerobic digesters. arch. microbiol., vol. 145, pp. 248–253, 1986. [12] f. s. manning, and h. s. eric, assessment data base for petroleum refining wastewater and residues. washington: u.s. department of commerce, ntis, pp. 94-101, 1983. [13] b.k. bala, studies on biodiesels from transformation of vegetable oils for diesel engines. energy edu. sic technol., vol. 15, pp.1−43, 2005. [14] f. ma, and m.a. hanna, biodiesel production: a review. bioresource technology, vol. 70, pp.1-15, 1999. [15] a. demirbas, and h. kara, new options for conversion of vegetable oils to alternative fuels energy sour part a recov. util. environ effects, vol. 28, pp.619−626, 2006. [16] a. l. ahmad, s. bhatia, n. ibrahim, and s. sumathi, adsorption of residual oil from palm oil mill effluent using rubber powder. brazilian journal of chemical engineering, vol. 22, no.3, pp. 371-379, 2005. [17] g. b. techobanglous, and l. franklin, wastewater engineering, 3rd edition, metcalf and eddy inc., 1995. [18] e. friedler, quality of individual domestic greywater streams and its implication for on-site treatment and reuse possibilities. environ technol., vol. 25, pp.997–1008, 2004. [19] g. vidal, a. carvalho, r. mendez, and j.m. lema, influence of the content in fats and proteins on the anaerobic biodegradability of dairy wastewaters. bioresource technology, vol. 74, pp.231–239, 2000. [20] m.c. cammarota, and g.l.s. annajr, metabolic blocking of exopolysaccharides synthesis effects on microbial adhesion and biofilm accumulation. biotechnology letters, vol. 20, pp.1–4, 1998. [21] e. el-bestawy, m. h. el-masry, and n.e. el-adl, the potentiality of free gram-negative bacteria for removing oil and grease from contaminated industrial effluents. world journal of microbiology & biotechnology, vol. 21, pp.815–822, 2005. [22] g. t. m. busca, doctoral diss., treatment of semi-synthetic metalworking fluids: membrane filtration and bioremediation, university of nottingham, uk. 2004. [23] k. karakulski, w. a. morawski, and j. crzechulska, purification of bilge water by hybrid ultrafiltration and photocatalytic process, separation and purification technology, vol. 14, pp.163-173, 1998. [24] t. mohammadi, and a. esmaelifar, journal of membrane science, vol. 254, pp.129 – 137, 2005. [25] a.g. stams, and e.s.j. oude, understanding and advancing wastewater treatment. current opinion in biotechnology, vol. 8, pp. 328–334, 1997. [26] f.a. el-gohary, s.i. aboelella, and h.i. ali, management of wastewater from soap and food industries: a case study. science of the total environment, vol. 6, pp. 203–212, 1987. [27] a.c. chao, and w. yang, biological treatment of wool scouring wastewater. journal of the water pollution control federation, vol. 53, no.3, pp. 311–317, 1981. [28] a. rinzema, m. boone, k. van knippenberg, and g. lettinga, bactericidal effect of long chain fatty acids in anaerobic digestion. water environ. res., vol. 66, pp. 40–49, 1994. [29] m. abid baig, m. mir, z. i. bhatti, and m a. baig, removal of oil and grease from industrial effluents. ejeafche, vol. 2, no 5, pp.577-585, 2003. [30] apha, standard methods for the examination of water and wastewater, 16th edn. american public health association, new york, 2005. [31] s. rintoul, new astm test method offers quick and easy oil and grease measurement for water and soil samples. wilks enterprise, inc., www.wilksir.com, pp. 1-3, 2010. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alade et al. 168 [32] m. cheryan, and n. rajagopalan, membrane processing of oily streams, wastewater treatment and waste reduction, journal of membrane science, vol. 151, pp.13-28, 1998. [33] laws of malaysia. environmental quality act and regulations. malaysia: mdc publishers sdn bhd., 2003. [34] a.j.k. chowdhury, m.z. alam and s.h. shahlizah, isolation, purification and screening of fungal strain fro effective bioconversion of palm oil mill effluent. proceedings of the 1st international conference on natural resources engineering & technology 2006. putrajaya, malaysia, pp.167–75, 2006. [35] l. k. wang, y. t. hung, h. h. lo, and c. yapijakis, (eds) handbook of industrial and hazardous wastes treatment, second edition, 2004, marcel dekker, new york, 2004. [36] j. rubio, m. l. souza, and r. w. smith, overview of flotation as a wastewater treatment technique, minerals engineering, vol. 15, pp.139–155, 2002. [37] k. karakulski, a. kozhiwski, and a. w. morawski, purification of oily wastewater by ultrafiltration, separation technology, vol. 5, pp.197-205, 1995. [38] y. c. song, i. s. kim, and s. c koh, demulsification of oily wastewater through a synergistic effect of ozone and salt, water science and technology, vol. 38, pp.247–253, 1998. [39] b. meyssami, and a. b. kasaeian, use of coagulants in treatment of olive oil wastewater model solutions by induced air flotation, bioresource technology, vol. 96, pp.303-307, 2005. [40] j.a. lalman, and d.m. bagley, anaerobic degradation and inhibitory effects of linoleic acid. water res., vol. 34, no.17, pp4220–4228, 2000. [41] m.h. el-masry, e. el-bestaway, and n.i. el-adl, bioremediation of vegetable oil and grease from polluted wastewater using a sand biofilm system. world journal of microbiology and biotechnology, vol. 20, pp551–557, 2004. [42] t. h. erguder, e. guven, and g. n. demirer, anaerobic treatment of olive mill wastewaters in batch reactors. process biochemistry, vol. 36, no.3, pp.243–248, 2000. [43] m. kissi, m. mountadar, o. assobhei, e. gargiulo, g. palmieri, and p. giardina, roles of two white-rot basidiomycete fungi in decolorization and detoxification of olive mill wastewater. applied microbiology and biotechnology, vol. 57, no.12, pp. 221–226, 2001. [44] k. ettayebi, f. errachidi, l. jamai, a. m. tahri-jouti, k. sendide, and m. ettayebi, biodegradation of polyphenols with immobilized candida tropicalis under metabolic induction fems microbiology letters, vol. 223, no.2, pp.215–219, 2003. [45] e. ammar, m. nasri, and k. medhioub, isolation of phenol degrading enterobacteria from the wastewater of olive oil extraction process. world journal of microbiology and biotechnology, vol. 21, no.3, pp.253–259, 2005. [46] a. dhouib, m. ellouz, f., aloui, and s., sayadi, effect of bioaugmentation of activated sludge with white rot fungi on olive mill wastewater detoxification. letters in applied microbiology, vol. 42, no.4 pp.405–411, 2006. [47] l. wu, y. p. luo, j. b. wan, and s. g. li, use of yarrowia lipolytica for the treatment of oil/grease wastewater. research of environmental science (china), vol. 19, no.5, pp 122– 125, 2006. [48] k. sasaki, n. noparatnaraporn, and s. nagai, use of photosynthetic bacteria for the production of scp and chemicals from organic wastes, in bioconversion of waste materials to industrial products. ed. a.m. martin. elsevier applied science publishers, new york, london, tokyo, pp. 223–262, 1991. [49] m.a. hassan, y. shirai, n. kusubayashi, m.i.a. karim, k. nakanishi, and k. hashimoto, the production of polyhydroxyalkanoate from anaerobically treated palm oil mill effluent by rhodobacter sphaeroides. journal of bioscience and bioengineering, vol. 83, pp.485–488, 1997. [50] k. takeno, y. yamaoka, and k. sasaki, treatment of oil-containing sewage wastewater using immobilized photosynthetic bacteria. world journal of microbiology & biotechnology, vol. 21, pp.1385–1391, 2005. [51] k. almalah, m.o.j. azzam, and n.i. abu-lail, separation and purification technology, vol. 20, pp. 225 – 234, 2000. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology alade et al. 169 [52] b. tryba, a.w. morawski, r.j. kalenczuk, and m., inagak, spill science of technology bulletin, vol. 8, no.5–6, pp.569 – 571, 2003. [53] u. daiminger, w. nitsch, p. plucinski, and s. hoffmann, novel techniques for oil/water separation, journal of membrane science, vol. 99, pp.197-203, 1995. [54] j. kong, and k. li, oil removal from oil-in-water emulsions using pvdf membranes. sep. purif. technol., vol. 16, pp.83–93, 1999. [55] m., gryta, k. karakulski, and a. w. morawski, purification of oily wastewater by hybrid uf/md, water res., vol. 35, no.17, pp. 3665–3669, 2001. [56] t.-h. bae, s.-s. han and t.-m. tak, membrane sequencing batch reactor system for the treatment of dairy industry wastewater. process biochem. vol. 39, pp. 221–231, 2003. [57] s.b. lee, y. aurelle, and h. roques, concentration polarization, membrane fouling and cleaning in ultrafiltration of soluble oil. j. membrane sci., vol. 19, no1, pp. 23–38, 1984. [58] m. nyström, ultrafiltration of o/w emulsions stabilized by limiting amounts of tall oil, colloids and surfaces, vol. 57, pp. 99-114, 1991. [59] b. tansel, j. regula, and r. shalewitz, treatment of fuel oil and crude oil contaminated waters by ultrafiltration membranes, desalination, vol. 102, pp.301-311, 1995. [60] s. panpanit, and c. visvanathan, the role of bentonite addition in uf flux enhancement mechanisms for oil/water emulsion, journal of membrane science, vol. 184, pp.59-68, 2001. [61] i. angelidaki, and b.k. ahring, effect of free long-chain fatty acids on thermophilic anaerobic digestion. appl. microbiol. biotechnol. vol. 37, pp. 808–812, 1992. [62] l. hulshof pol, h. euler, a. eitner, and d. and grohganz, gtz sectoral project, promotion of anaerobic technology for the treatment of municipal and industrial sewage and waste. in: proc. 8th international conference on anaerobic digestion, sendai, japan, vol. 2. pp.282– 285, 1997. [63] l.h.a. habets, a.j.h.h. engelaar, and n. groeneveld, anaerobic treatment of inuline effluent in an internal circulation reactor. water sci. technol., vol. 35, no10, pp.189–197, 1997. [64] m.m. alves, j.a. mota vieira, r.m. alvares pereira, m.a. pereira, and m. mota, effect of lipids and oleic acid on biomass development in anaerobic fixed-bed reactors. part i: biofilm growth and activity. water res., vol. 35, no.1, pp.255–263, 2001. [65] y. saatci, e.i. arslan, and v. konar, removal of total lipids and fatty acids from sunflower oilfactory effluent by uasb reactor bioresource technology, vol. 87, pp.269–272, 2003. [66] f.d. çetin, and g. sürücü, effects of temperature and ph on the settlability of activated sludge flocs. water sci. technol., vol. 22, no.9, pp. 249-254, 1990. [67] t.a. barr, j.m.taylor, and s.j.b. duff, effect of hrt, srt and temperature on the performance of activated sludge reactors treating bleached kraft mill effluent. water res., vol. 30, no.4, pp. 799-810, 1996. [68] c. s. tripathi, and a. d. grant, comparison of mesophilic and thermophilic aerobic biological treatment in sequencing batch reactors treating bleached kraft pulp mill effluent. water res., vol. 33, no.3, pp.836-846, 1999. [69] t.m. lapara, and j. e. alleman, thermophilic aerobic wastewater treatment. water res., vol.33, no.4, pp. 895908, 1999. [70] j. lopetegui, and l. sancho, aerated thermophilic biological treatment with membrane ultrafilteration: alternative to conventional technologies treating paper mill effluents. water sci. technol.: water supply, vol. 3, no. 5-6, pp245-252, 2003. [71] c. g. klatt, and t. m. lapara, aerobic biological treatment of synthetic municipal wastewater in membrane-coupled bioreactors, biotechnology and bioengineering, vol. 82, no.3, pp. 313-319, 2003. [72] r. kurian, and g. nakhla, performance of aerobic mbr treating high strength oily wastewater at mesophilic –thermophilic transitional temperatures. water environment foundation, ontario canada, 2006 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 34 optimization of red pigment production by monascus purpureus ftc 5356 using response surface methodology nor farhana hamid and farhan mohd said* faculty of chemical and natural resources engineering, universiti malaysia pahang, lebuhraya tun razak, 26300 kuantan, pahang, malaysia. * corresponding author: farhan@ump.edu.my (received: 20th feb 2017; accepted: 23rd feb 2018; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.814 abstract: factors such as environmental conditions and nutrients are significant for successful growth and reproduction of microorganisms. manipulations of the factors are the most effective way to stimulate the growth of the microorganism, which can be used to optimize the yield of a product. in this study, central composite design (ccd) of response surface methodology (rsm) was used to optimize the production of red pigment by monascus purpureus ftc 5356 using the petioles of oil palm fronds (opf) as a substrate in solid state fermentation (ssf). the data was analyzed using design expert software. the optimum combination predicted via rsm was confirmed through experimental work. the interactions between three variables such as initial moisture content (%), initial ph value (ph), and peptone concentration (%) were studied and modelled. the statistical analysis of the results showed that the optimal conditions for red pigment production 47 au/g with the biomass of 425.1 mg/g was at 55% initial moisture content, 3% of peptone, and at ph 3. the rsm results showed that the initial ph value had a significant effect on red pigment production (p-value <0.05). the validation of these results was also conducted by fermentation with predicted conditions and it was found that there was a discrepancy of 0.39% between the values of the experimental result and those of the predicted values. abstrak: keadaan persekitaran dan nutrien merupakan faktor-faktor penting dalam pertumbuhan mikroorganisma. manipulasi faktor-faktor tersebut adalah kaedah terbaik bagi meningkatkan pertumbuhan mikroorganisma dan mengoptimumkan penghasilan produk. kajian ini mengguna pakai rekaan gabungan pusat (ccd) melalui kaedah tindak balas permukaan (rsm) bagi penghasilan pigmen merah optimum oleh monascus purpureus ftc 5356 menggunakan batang pelepah kelapa sawit (opf) sebagai perumah dalam proses penapaian pepejal (ssf). data telah dianalisis menggunakan perisian design expert. gabungan parameter optimum seperti cadangan rsm telah disahkan secara eksperimen. interaksi antara tiga pemboleh ubah seperti kandungan lembapan awal (%), nilai ph awal (ph), dan kepekatan pepton (%) telah dikaji dan dimodelkan. analisis statistik menunjukkan penghasilan optimal pigmen merah adalah pada 47 au/g dengan biomas sebanyak 425.1 mg/g, pada 55% lembapan awal, 3% pepton dan pada ph 3. hasil keputusan rsm menunjukkan ph awal memberikan kesan signifikan kepada penghasilan pigmen merah (nilai p <0.05). pengesahan analisis juga telah dijalankan melalui proses penapaian dan hasil ujikaji mendapati 0.39% lebih tinggi daripada nilai jangkaan. keywords: response surface methodology; red pigment; oil palm frond; monascus pigment iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 35 1. introduction in recent years, colorants have been extensively used in the food industry. however, to overcome the unlimited usage of synthetic pigment, which is found to be hazardous and toxic to human health, the development of alternate sources for the production of natural pigment has been focused on. nowadays, productions of pigment from microbial origin have attracted more attention from the food industry. particular focus has been given to monascus sp., which is a nontoxic fungi that has been widely used as a natural colorant and food additive in east asia. monascus pigment can produce three groups of pigment: orange, red, and yellow. among these pigments, the red pigment is gaining high market demand for its use [1]. it is important to study the effect on the red pigments produced by monascus sp. under different culture conditions, for the safe and successful application in food and pharmaceutical industries [2]. previous study was done on the usage of petioles and leaflets of oil palm frond (opf) as a substrate [3]. the finding revealed that 100% petiole rendered the best results. thus, the goal of this study was to optimize the most significant of the multivariable factors for substrates made solely of petiole, in order to influence red pigment production. factors observed include initial moisture content, peptone concentration, and initial ph value. the traditional ‘one factor at a time’ (ofat) approach used for optimizing a multifactor system is not only effort and time consuming, but also often misses in representing the interaction effect between different factors [4]. however, ofat could be used as a preliminary experiment to set the range of the factor efficiently, making the results more reasonable and credible [5]. therefore, the traditional approach of ofat still can be applied. the range of factors obtained in ofat can be used by adopting a statistical approach, such as response surface methodology (rsm), to solve the complexity involved in red pigment production. recently, many types of statistical experimental design methods have been discovered for optimization [6-8]. among them, rsm is the most suitable technique to reduce the number of experimental trials needed. it is also used to evaluate the most significant single factors and to effectively seek the optimum conditions for the multivariable system [8]. several studies have applied rsm for optimization of red pigment [9-11]. however, to the best of our knowledge, no research has been reported on the application of rsm for optimization the red pigment production using monascus purpureus ftc 5356 on petioles of oil palm fronds (opf). therefore, in order to determine the significant optimization factors in red pigment production, response surface methodology was applied in the present study. 2. materials and methods 2.1 microorganism the strain used in this study was monascus purpureus ftc 5356 obtained from malaysian agricultural research and development institute, serdang, malaysia. the stock culture was maintained on potato dextrose agar (pda) media and incubated at 28-30 oc for 7 days, preserved at 4 oc and sub-cultured once every 4 weeks [12]. 2.2 inoculum preparation monascus purpureus ftc 5356 was grown on pda slants at 30 oc for 7 days. the spores were then scrapped off and suspended in 5 ml sterile distilled under aseptic conditions at room temperature. the suspension was adjusted to 108 spores/ml with sterile distilled iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 36 water. the spore numbers were counted using a neubauer hemacytometer (cole-parmer 79001-00). the adjusted spore suspension (10% v/w) was used for further solid state fermentation [12]. 2.3 substrate preparation fresh oil palm fronds (opf) were obtained from the federal land development authority (felda) bukit goh, kuantan, pahang. the leaflets and petioles were separated from the opf. the petioles were then cut into small pieces approximately 3-4 cm in length, washed, and dried at 60 oc for 3 days. the dried petiole was shredded and ground using a commercial grinder (retsch zm-200, germany) to a particle size smaller than 1 mm by passing through 1 mm sieve screens using a vibrator sieve shaker (retsch, germany). 2.4 solid state fermentation the experimental work was done based on the experimental design being set by design expert (version 7.1.6, 2008, minneapolis mn, usa), (table 1 and table 2). the best range of each factor was selected by applying the one factor at a time (ofat) method as in the preliminary experiment (data not shown). all experiments have been carried out in replicates and the whole flasks were discarded. each substrate was inoculated and incubated in the dark at 30 oc for 8 days. table 1: independent variables, responses and the levels in the experimental design. no designation factors -1 0 +1 1 x1 initial moisture content (%) 40 55 70 2 x2 peptone concentration (%) 2 35 5 3 x3 initial ph value 6 8 10 response 4 y1 red pigment production (au/g) 5 y2 biomass (mg/g) 6 y3 glucose concentration (µg/g) table 2: the central composite design matrix developed for three independent variables run x1 x2 x3 1 0 0 -1 2 -1 -1 -1 3 +1 -1 -1 4 -1 +1 -1 5 +1 +1 -1 6 0 0 0 7 -1 0 0 8 0 0 0 9 0 0 0 10 0 0 0 11 +1 0 0 12 0 +1 0 13 0 -1 0 14 +1 -1 +1 15 +1 +1 +1 16 0 0 +1 17 -1 +1 +1 18 -1 -1 +1 iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 37 2.5 pigment extraction and determination the harvested fermented solid was dried at 60 oc for 24 hours in an oven (memmert ufb-500). the dried fermented solid was extracted with 95% ethanol in a ratio of 1:10 w/v for 1 hour at 200 rpm, in an incubator shaker (infors ag-ch-4103 bottmingen). the extract was then allowed to stand for 15 min, and filtered through whatman no.1 filter paper. ethanol extracts of unfermented substrates were used as blanks. analysis of pigment concentration was done using a uv-vis spectrophotometer (hitachi u-1800). the wavelength used was 500 nm. pigment yield was expressed as absorbance units (au) per gram of dried solids [12-14]. 2.6 reducing sugar determination reducing sugar was measured using a dinitrosalicylic acid (dns) method [12, 15]. the reducing sugar was measured at 575 nm by uv-vis spectrophotometer (hitachi u-1800). 2.7 biomass (cell dry weight) total fungal biomass was determined by measuring the n-acetylglucosamine released by acid hydrolysis of the chitin present in the fungal cell walls. the acid hydrolysis of the sample was carried out by mixing 0.5 g of dry fermented opf powder with 2 ml of 60% (vol/vol) sulfuric acid, h2so4 and the mixture was incubated at 25 oc in a fume hood for 24 h [16]. then the mixture was diluted with distilled water to make a 1 n solution of sulfuric acid that was then autoclaved at 121 oc for 1 h. the mixture was allowed to cool at room temperature and neutralized with 5 n naoh to ph 7 and the final volume was brought up to 60 ml with deionized water. later, the filtered acid hydrolysis sample (1 ml) was mixed with 1 ml of acetyl acetone reagent (2% (vol/vol) of acetyl acetone in 1 n sodium bicarbonate (na2co3) before being placed in a boiling water bath for 20 min [12]. after cooling, 6 ml of ethanol (95%) was added, followed by 1 ml of ehrlich reagent (2.67% (w/v) of p-dimethylaminobenzaldehyde (merck) in 1:1 mixture of ethanol and concentrated hydrochloric acid) [17]. the mixture was incubated in a water bath at 65 oc for 10 min. after cooling, the optical density was read at 530 nm against the reagent blank, nacetylglucosamine (sigma-aldrich) as the external using a uv-visible spectrophotometer [12, 18]. 2.8 experimental design the red pigment production was developed and optimized using response surface methodology (rsm) provided by design expert software (version 7.1.6, 2008, minneapolis mn, usa). a standard rsm design tool known as central composite design (ccd) was applied to study the significant production factor of red pigment. the three identified independent variables were the initial moisture content (40-70%), peptone concentration (2-5%), and initial ph (ph 6-8). the critical ranges of selected factors were determined by preliminary experiment using ofat and screening by factorial design (data not shown). during the screening process of petiole used as a substrate, the initial moisture content (imc), initial ph, interaction of peptone, and ph were found to be significant. thus, three factors were chosen for optimization. screening was done to eliminate the insignificant factor. table 1 lists the ranges and levels of the three independent variables with actual and coded levels of each factor. the lower and upper levels were coded as -1 and +1; the middle level was coded as 0. a total of 18 runs with 4 central points were generated. the center points are usually repeated 4-6 times to determine the experimental error (pure error) and the reproducibility of the result. three responses, red pigment (au/g), biomass (mg/g) and glucose concentration (µg/g), were measured. the experiments were run in triplicate. the iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 38 complete design matrix corresponding to the ccd design in terms of real and coded independent variables is displayed in table 2. 2.9 validation experiment the validation experiment was performed by conducting the experiment with the suggested optimal conditions of higher pigment. 3. results and discussion the statistical significance of the model equation was evaluated by the f-test analysis of variance (anova). the anova statistics for responses y1, y2, and y3 were summarized in table 3, 4, and 5, respectively. multiple regression analyses of the response surface design were developed as in equations 1, 2, and 3. in order to determine the optimal level of each variable for maximum production of red pigment and biomass, a 3d surface plot was designed as a function of two factors at a time, holding all other factors at a fixed level. this design was helpful for understanding both the main and the interaction of the two factors. the response values for the variables can be predicted from these plots. table 3: anova analysis for red pigment production (y1) source sum of squares df mean square f-value prob>f model 4915.48 9 546.16 52.33 <0.0001 significant x1initial moisture content 9 x 103 1 9 x103 8.6 x 104 0.9773 x2peptone concentration 26.9 1 26.9 2.58 0.1471 x3initial ph value 126.74 1 126.74 12.14 0.0083 x1x2 16.24 1 16.24 1.56 0.2475 x1x3 0.18 1 0.18 0.017 0.8988 x2x3 0.13 1 0.13 0.012 0.9156 x1 2 44.47 1 44.47 4.26 0.0729 x2 2 444.04 1 444.04 42.54 0.0002 x3 2 1195.10 1 1195.10 114.51 <0.0001 residual 83.50 8 10.44 lack of fit 76.15 5 15.23 6.22 0.0817 not significant pure error 7.35 3 2.45 r2 0.9833 adeq precision 18.345 iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 39 table 4: anova analysis for biomass response (y2) table 5: anova analysis for glucose concentration response (y3) source sum of squares df mean square f-value prob>f model 1.28 x 105 9 14169.99 7.63 0.0044 significant x1initial moisture content 124.61 1 124.61 0.067 0.8022 x2peptone concentration 108.24 1 108.24 0.058 0.8153 x3initial ph value 2982.53 1 2982.53 1.61 0.2408 x1x2 296.46 1 296.46 0.16 0.7 x1x3 5.95 1 5.95 3.2 x 10 3 0.9563 x2x3 0.66 1 0.66 3.6 x 10 4 0.9854 x1 2 4302 1 4302 2.32 0.1666 x2 2 9802.12 1 9802.12 5.28 0.0507 x3 2 25466.58 1 25466.58 13.71 0.0060 residual 14864.29 8 1858.04 lack of fit 13890.42 5 2778.08 8.56 0.0536 not significant pure error 973.87 3 324.62 r2 0.8956 adeq precision 7.105 source sum of squares df mean square f-value prob>f model 90779.97 9 10086.66 91.77 <0.0001 significant x1initial moisture content 1.51 1 1.51 0.014 0.9095 x2peptone concentration 442.89 1 442.89 4.03 0.0796 x3initial ph value 3997.20 1 3997.20 3637 0.0003 x1x2 1074.62 1 1074.62 9.78 0.0141 x1x3 7.57 1 7.57 0.069 0.7997 x2x3 25.56 1 25.56 0.23 0.6425 x1 2 1516.91 1 1516.91 13.80 0.0059 x2 2 9162.68 1 9162.68 83.37 <0.0001 x3 2 17555.18 1 17555.18 159.73 <0.0001 residual 879.26 8 109.91 lack of fit 235.72 5 47.14 0.22 0.9319 not significant pure error 643.54 3 214.51 r2 0.9904 adeq precision 25.360 iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 40 3.1 optimization of red pigment production the second order polynomial equation model for prediction of the optimal point between the response variable (red pigment production) and the independent variables was expressed in eqn. 1: 𝑌1(red pigment) = 45.66 − 0.03𝑋1 + 1.64𝑋2 + 3.56𝑋3 − 1.42𝑋1𝑋2 + 0.15𝑋1𝑋3 + 0.13𝑋2𝑋3 − 405𝑋1 2 − 12.80𝑋2 2 − 21𝑋3 2 (1) where y1 is the response for red pigment production, x1 is the code for initial moisture content, x2 is for peptone concentration, x3 is for initial ph value. based on the anova table, as presented in table 3, the quadratic model indicated that this model could be accepted to navigate the design space. the model fvalue of the response y1 with the value 52.33 implies that the model was significant at 95% confidence level. the p-value was used as a tool to check the significance of each coefficient, which in turn designates the pattern of interaction between the factors. the smaller the p-value, the larger the significance of the coefficient was. as in table 3, the p-values for the y1 was <0.0001, which was less than 0.05. therefore, it can be concluded that the model terms were statistically significant. in addition, the main model terms indicated that the significant factor was the initial ph (x3), while the significant quadratic terms were peptone concentration (x2 2) and initial ph (x3 2). the lack of fit test with p-value (0.0817), which was not significant (p-value> 0.05 is not significant), supported the hypothesis that the model was satisfactorily fitted to the experiment data. the ‘not significant’ term of lack of fit is most-desired as a significant of lack of fit indicates the presence of the contribution in the regressor-response relationship that is not accounted for by the model [19]. the correlation coefficient (r2) is a tool to identify the ‘goodness of fit’ between the experimental and the predicted values. based on table 3, the r2 for y1 (0.9833) was found to be close to 1, which indicated the presence of a good relation between experimental and predicted values for red pigment (y1). the adequate precision for y1 is 18.345. these large values of adequate precision demonstrated that these quadratic models were significant for the process. the evaluation of residuals was analyzed to validate the adequacy of the model. a normal probability plot of the residuals for y1 is displayed in fig. 1. based on the figure, it clearly shows that the residuals distribution was nearly a straight line. thus, it can be concluded that the errors were distributed evenly. fig. 1: normal plot of residuals for red pigment production (y1). iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 41 figures 2a, 2b, and 2c show the 3d surface plots of the relationship between the main factors x1x2 (initial moisture content and peptone concentration), x1x3 (initial moisture content and initial ph), and x2x3 (peptone concentration and initial ph), respectively. in fig. 2a, the increment of initial moisture content from low level 40% to 55% leads to the increase in red pigment to a maximum level. however, a further increase in the initial moisture content (>55%) did not further increase the pigment. this result clearly shows that the red pigment decreased above and below the 55% initial moisture content. the poor yield of red pigment at high moisture content (>55%) was possibly due to the agglomeration of substrate, consequently reducing oxygen supply for the growth of monascus. while, the decrease in red pigment at low moisture content was because of the insufficient nutrient supply due to the low nutrient salt dissolution [19]. a similar trend of effect on the response was observed for the initial moisture content and the initial ph. an increase of the initial moisture content and initial ph, up to the optimum point, maximized the red pigment production and a further increase of the factors decreased the red pigment, as shown in fig. 2b. this reaction process was in agreement with orozco and kilikian [20] in which changing the ph value of the medium from ph 5.5 to ph 8, caused the drastic excretion of the red pigment. in addition, they also claimed that the best condition for red pigment production was at alkaline medium (ph 8.0 or ph 8.5). between these two ph values, ph 8 had been chosen to be the best condition due to the maximum yield of red pigment production. the interaction effect of the peptone concentration with initial ph as shown in fig. 2c clearly suggested the best combination for production of red pigment. an increase in the peptone concentration with initial ph, optimized the red pigment gradually. however, at higher peptone concentration (> 3.5%) and higher initial ph (> ph 8), the pattern is reversed. the decrease in yield may due to excessive nutrients provided in the medium that became toxic and inhibited the red pigment production. therefore, the optimum conditions for maximum red pigment production were obtained at the initial moisture content of 55%, peptone concentration of 3.5%, and initial ph value of 8. the maximum red pigment achieved was 47.9 au/g. 3.2 optimization of biomass production based on the experimental results and regression analysis, a quadratic polynomial equation was developed to determine the relationship between the biomass of monascus purpureus and the factors. the model of coded units can be stated as in eqn. 2: 𝒀𝟐(𝐛𝐢𝐨𝐦𝐚𝐬𝐬) = 𝟑𝟖𝟐. 𝟕𝟓 + 𝟑. 𝟓𝟑𝑿𝟏 + 𝟑. 𝟐𝟗𝑿𝟐 + 𝟏𝟕. 𝟐𝟕𝑿𝟑 − 𝟔. 𝟎𝟗𝑿𝟏𝑿𝟐 − 𝟎. 𝟖𝟔𝑿𝟏𝑿𝟑 − 𝟎. 𝟐𝟗𝑿𝟐𝑿𝟑 − 𝟑𝟗. 𝟖𝟓𝑿𝟏 𝟐 − 𝟔𝟎. 𝟏𝟓𝑿𝟐 𝟐 − 𝟗𝟔. 𝟗𝟓𝑿𝟑 𝟐 (2) where y2 is the response for biomass production, x1 is the code for initial moisture content, x2 is for peptone concentration, and x3 is for initial ph value. from the analysis of variance (anova) as presented in table 4, the model for biomass was highly significant (p-value, 0.0044) and the r2 (0.8956) was relatively good, as evidenced by the significance of the model. there was no significance of a single factor or interaction between factors that influenced the biomass production, however, the quadratic terms of initial ph value was found to be significant. furthermore, the lack of fit was not significant with p-value of 0.0536 (>0.05), indicating that the experimental data obtained fitted well with the model. iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 42 fig. 2: response surface curve showing combined effect between the main factors: (a) initial moisture content (x1) and peptone concentration (x2), (b) initial moisture content (x1) and initial ph value (x3), (c) peptone concentration (x2)and initial ph value (x3). the residual analysis was carried out for the confirmation of the adequacy of the model. this was done by observing the normal probability plot of the residual in fig. 3 where the residuals were on a straight line, suggesting that the errors were distributed evenly. fig. 3: normal plot of residuals for biomass response (y2). figures 4a, 4b, and 4c show the 3d surface plots of biomass responses after combining the effect of the main factors. the effect of the initial moisture content and peptone concentration on the biomass is shown in fig. 4a. an increase of initial moisture content with peptone concentration up to the optimum point increased the fungal biomass to a maximum level and a further increase in the initial moisture content and peptone c r e d p ig m e n t (a u /g ) b r e d p ig m e n t (a u /g ) a r e d p ig m e n t (a u /g ) iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 43 concentration did not further increase the trend. this finding was supported by krishna [21], who stated that the low initial moisture content could reduce nutrient diffusion consequently affecting the growth of the monascus. however, if the initial moisture content is too high, water will occupy the voids where airflow is required for fungal growth. increased factors of initial moisture content and initial ph up to the optimum point, maximized the biomass production (fig. 4b). from the 3d plot, it was obviously shown that monascus was grown successfully at ph 8 indicating that the biomass achieved the maximum yield. however, the fungal biomass production started to decrease with a further increase of initial ph ( > ph 8) of substrate. the interaction effect of the peptone concentration with initial ph in fig. 4c clearly suggested the best combination for the production of fungal biomass. an increase in the peptone concentration and initial ph optimized the biomass gradually but at higher peptone concentration and initial ph, the pattern is reversed. it was studied that nitrogen is the major element of cell membranes and nucleic acid, therefore supplying nitrogen sources to the medium may facilitate the growth of the fungus. however, if the nitrogen concentration is too high ( > 3.5%), it might inhibit the fungal growth. therefore, the optimum biomass was observed at the initial moisture content of 55%, peptone concentration of 3.5%, and initial ph of substrate of ph 8. the maximum biomass achieved was 430.8 mg cell dry weight/g dry matter. fig. 4: response surface curve showing combined effect between the main factors: (a) initial moisture content (x1) and peptone concentration (x2), (b) initial moisture content (x1) and initial ph value (x3), (c) peptone concentration (x2) and initial ph value (x3). b io m a ss ( m g /g ) a ) b io m a ss ( m g /g ) b ) b io m a ss ( m g /g ) c ) iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 44 3.3 glucose concentration on the glucose consumption, a second order polynomial can be obtained by the design expert. multiple regression equations (in term of coded factors) were represented in eqn. 3: 𝑌1(glucose concentration) = 130.65 − 0.39𝑋1 − 6.66𝑋2 − 19.99𝑋3 + 11.59𝑋1𝑋2 − 0.97𝑋1𝑋3 − 1.79𝑋2𝑋3 + 23.66𝑋1 2 + 58.15𝑋2 2 + 80.49𝑋3 2 (3) where y3 is the response for glucose concentration, x1 is the code for initial moisture content, x2 is for peptone concentration, x3 is for initial ph value. the anova table implies that the model was significant with the f-value of 91.77 (table 5). the p-value (<0.0001) was less than 0.05, which indicated the model terms were highly significant. in addition, the main model terms indicated that the significant factor was initial ph value (x3) and the interaction terms were found to exist between initial moisture content (x1) with peptone concentration (x2). while, the significant quadratic terms were initial moisture content (x1 2), peptone concentration (x2 2), and initial ph value (x3 2). the lack of fit value of 0.22 confirmed that the lack of fit was not significant, relative to the pure error when p-value was 0.9319 and > 0.05. the insignificant lack of fit demonstrates the good predictability of the model. in addition, the value of r2 was 0.9914, indicating that the model was fitted and explains 99.14% of the variability in glucose concentration. the high values of adequate precision with the value of 25.360 demonstrated that these quadratic models were significant for the process. figure 5 displays the normal plot of residuals of response y3 glucose concentration. it was obviously shown that the points cluster around the diagonal line which indicated the good fit of the model. fig. 5: normal plot of residuals for glucose concentration response (y3). figures 6a, 6b, and 6c show the 3d surface plots of glucose concentration response after combining the effect between the main factors. from the figure, it was observed that the glucose was decreased when the initial moisture content, peptone concentration and initial ph value were 55%, 3.5% and ph 8, respectively. the 3d surface plots of glucose concentration were totally different with the previous figures (figures 2a, 2b, 2c, 4a, 4b, and 4c). the glucose concentration decreased when the fungal biomass and red pigment production achieved the maximum yield. this phenomenon suggested that the rapid consumption of glucose by monascus caused the depletion of glucose, consequently iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 45 resulting in an insufficient glucose supply that reached its supply limitation [22]. the lowest final glucose concentration of 114.73 µg/ g was obtained. fig. 6: response surface curve showing combined effect between the main factors: (a) initial moisture content (x1) and peptone concentration (x2), (d) initial moisture content (x1) and initial ph value (x3), (e) peptone concentration (x2)and initial ph value (x3). 3.4 validation in order to confirm the optimization of red pigment production by monascus purpureus ftc 5356, an experiment was performed under the predicted optimal conditions. this experiment was conducted in triplicate. under these suggested conditions, the predicted optimal values of the variables were 56% initial moisture content, 3.5% peptone, and ph 8.2. the prediction of the total red pigment was 45.85 au/g and the actual value obtained through the triplicate experiments was 46.03 au/g, as shown in table 6. the percentage error calculated based on the eqn. 4 was 0.39%. therefore, the experimental results agreed well with the model predicted values. 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑒𝑟𝑟𝑜𝑟 = (experimental value − predicted value) experimental value 𝑥 100% (4) g lu c o se c o n c e n tr a ti o n ( µ g /g ) a ) g lu c o se c o n c e n tr a ti o n ( µ g /g ) b ) g lu c o se c o n c e n tr a ti o n ( µ g /g ) c ) iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 46 table 6: optimum factors of rsm on red pigment factor value predicted (au/g) actual (au/g) percentage error (%) initial moisture content (%) 56 45.85 46.03 0.39 peptone (%) 3.5 ph 8.2 4. conclusion this study shows that response surface methodology is a fast and error-free approach for optimization of media composition to obtain the best performance of red pigment production and biomass. besides, an interaction study among all the components was an additional advantage of employing rsm. results obtained from response surface methodology critically point out the importance of initial ph value of the substrate for red pigment production as well for the fungal biomass. acknowledgement this work was funded by research grant granted by ministry of higher education of malaysia under frgs grant no. rdu 150105. references [1] hakim ma. (2015) food coloring analysis in four selected dishes. american j. biology and life sci., 395: 187-189. [2] miyake t, isato k, nobuyuki n, sammoto h. (2008) analysis of pigment composition in various monascus cultures. food sci. and technol. res., 14: 194-197. [3] hamid nf, said fm. (2016) factorial design screening for the red pigment production by monascus purpureus ftc 5356. jurnal teknologi, 78(11-2): 13-17. [4] poorniammal r, gunasekaran g, murugesan r. (2015) statistical optimization of culture medium for yellow pigment production by thermomyces sp. j. appl. and natural sci., 7(1): 203-210. [5] ren x, he l, cheng j, chang j. (2014) optimization of the solid state fermentation and properties of a polysaccharide from paecilomyces cicadae (miquel) samson and its antioxidant activities in vitro. plos one, 9(2): e87578. [6] ajdari z, ebrahimpour a, manan ma, ajdari d, abbasiliasi s, hamid m, mohamad r, ariff ab. (2012) a statistical modeling study by response surface methodology and artificial neural networks on medium optimization for monascus purpureus ftc 5391 sporulation. minerva biotech., 24: 71-81. [7] dikshit r, tallapragada p. (2016) statistical optimization of lovastatin and confirmation of nonexistence of citrinin under solid state fermentation by monascus sanguineus. j. food and drug analysis, 24: 433-440. [8] sani j, montira n, panit k, taweerat v, anan t. (2013) statistical optimization for monakolin k and yellow pigment production and citrinin reduction by monascus purpureus in solid state fermentation. j. biotechnol. microbiol., 23(3): 364-374. [9] prajapati vs, soni n, trivedi ub, patel kc. (2013) an enhancement of red pigment production by submerged culture of monascus purpureus mtcc 410 employing statistical methodology. biocatalyst and agricultural biotechnol., 3: 140-145. iium engineering journal, vol. 19, no. 1, 2018 hamid and mohd said ________________________________________________________________________________________ 47 [10] dikshit r, tallapragada p. (2014) collective effects of stress on optimization of pigment production by monascus purpureus. chiang mai j. sci., 41(3): 524-530. [11] ahmad m, panda bp. (2014) optimization of red pigment production by monascus purpureus mtcc 369 under solid state fermentation using response surface methodology. songklanakarin j. sci. and technol., 36(4): 439-444. [12] said fbm. (2010) monascus ruber icmp 15220 fermentation for the production of pigment. phd thesis. massey university. new zealand. [13] johns mr, stuart and dm. (1991) production of pigments by monascus purpureus in solid culture. j. industrial microbiol., 8: 23-28. [14] lin tf, demain al. (1992) fermentation of water soluble monascus red pigments by biological and semi synthetic processes. j. industrial microbiol. 9: 173-179. [15] miller gl. (1959) use of dinitrosalicylic acid reagent for determination of reducing sugar. anal. chem., 31: 426-428. [16] roopesh k, ramachandran s, nampoothiri km, szakacs g, pandey a. (2006) comparison of phytase production of wheat bran and oil cakes in solid state fermentation by mucor racemosus. bioresource technol., 97: 506-511. [17] swift mj. (1973) the estimation of mycelial biomass by determination of the hexosamine content of wood tissue decayed by fungi. soil biology biochem., 55: 321-332. [18] babitha s, soccol cr, pandey a. (2006) jackfruit seed—a novel substrate for the production of monascus pigments through solid state fermentation. food technol. biotechnol. 44: 465– 471. [19] noordin my, venkatesh vc, sharif s, elting s, abdullah a. (2004) application of response surface methodology in describing the performance of coated carbide tools when turning aisi 1045 steel. j. material processing technol., 145: 46-58. [20] orozco sfb, kilikian bv. (2008) effect of ph on citrinin and red pigment production by monascus purpureus cct3802. world j. microbiol. and biotechnol., 24: 263-268. [21] krishna c. (2005) solid state fermentation system-an overview. critical review in biotechnol., 25(1-2): 1-30. [22] babitha s, soccol cr, pandey a. (2007) solid state fermentation for the production of monascus pigment from jackfruit seed. bioresource technol., 98: 1554-1560. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 1, 2019 abdulsada et al. intelligent control system of a wheelchair for people with quadriplegia paralysis hayder fadhil abdulsada1*, saif hussam abdulwahed2 and yassen sadoon atiya3 1babylon technical institute, al-furat al-awsat technical university, 51015 babylon, iraq. 2najaf technical institute, al-furat al-awsat technical university, 31001 najaf, iraq. 3al-imam al-kadhim university college for islamic sciences, babylon, iraq. *corresponding author: inj.had1@atu.edu.iq (received: 14th feb 2019; accepted: 29th april 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.909 abstract: our system proposes a wheelchair controlled by head gestures for people with quadriplegia paralysis (qp) or for those suffering from amputation of their hands and legs during the war in iraq. the wheelchair design has an intelligent control that works with the movement of a patient‘s head in order to enable the patient to drive the wheelchair in the desired direction. the system consists of two main parts. the first is the transmitter in which sensing signals are transmitted to the second part and it consists of a 3-axes accelerometer (adxl-345), a 433 mhz rf wireless receiver transmitter module, and arduino uno. the adxl-345 sensor is placed in front of a hat that the patient wears. the system detects the direction of the patient's head movement then sends appropriate instructions to the wheelchair’s control part (receiving part). the receiving part is the wheelchair control system that consists of a 433 mhz rf wireless receiver transmitter module and an arduino uno. the arduino processes the signals coming from the first part and moves the wheelchair accordingly in the desired direction. the research also provides an obstacle avoidance system with a range of 50 cm that prevents the wheelchair from colliding with objects. the head movement angles have been selected to be 40, 35 degree for vertical and horizontal movement respectively so that the qp patient feels comfortable to tilt his head in all directions and control the wheelchair easily. the system provides a very effective performance and accuracy. abstrak: sistem ini bergantung kepada kerusi roda yang dikawal menggunakan isyarat kepala untuk mereka yang lumpuh kuadriplegia (qp) ataupun mereka yang dipotong tangan dan kaki semasa perang di iraq. ia merupakan reka bentuk pintar pada kerusi roda dan pesakit boleh mengawal pergerakan mereka dengan isyarat pada kepala. sistem ini terdiri daripada dua bahagian utama iaitu yang pertama merupakan pemancar yang menghantar isyarat gerakan ke bahagian kedua dan ianya terdiri daripada 3 axis accelerometer (adxl-345), modul penerima isyarat pemancar tanpa wayar 433 mhz rf dan arduino uno. sensor adxl-345 ini diletakkan di bahagian depan topi yang dipakai oleh pesakit. sistem ini mengesan arah gerakan kepala pesakit dan kemudiannya arahan dihantar ke bahagian pengendali kerusi roda (bahagian penerimaan isyarat). bahagian ini merupakan sistem pengendalian kerusi roda yang terdiri daripada modul pemancar penerimaan tanpa wayar 433 mhz rf dan arduino uno. arduino memproses isyarat yang datang dari bahagian pertama bagi menggerakkan kerusi roda ke arah yang dikehendaki. kajian ini turut menyediakan sistem mengelak halangan pada jarak 50 cm bagi menjauhi kerusi roda daripada melanggar objek. sudut gerakan kepala telah dipilih pada 40, 35 darjah bagi gerakan menegak dan mendatar masing-masing, supaya pesakit 194 iium engineering journal, vol. 20, no. 1, 2019 abdulsada et al. qp merasa selesa bagi mengerakkan kepalanya ke semua arah dan mengawal kerusi roda dengan mudah. sistem ini juga sangat cekap dan tepat dalam mengawal arah. keywords: head gesture recognition; quadriplegia paralysis; wheelchair controlling 1. introduction at present, many people suffer from physical disability as a result of wars and diseases; therefore, there is a need for advanced support devices with high safety to help individuals navigate easily. intelligent wheelchairs have been developed to assist disabled and injured people. these wheelchairs are supported by some techniques to enhance performance and efficiency [1,2]. the continuity in research has led to important developments in the design of supporting devices for people who are injured, wounded, or affected by some cases of paralysis. this research includes many techniques to drive wheelchairs such as joysticks, voice recognition, hand gestures, and cameras. [3,4]. the work in this paper presents intelligent control of wheelchairs for people suffering from quadriplegia paralysis (qp) or for people who suffer from amputation of their hands and legs. the subsequent paragraphs are some research regarding the field of wheelchair control techniques. in 2014, warad et al. described a motorized wheelchair for handicapped humans utilizing a speech control technique and flex sensing application. the system permits a disabled person to drive the wheelchair using voice recognition including voice commands for movement (forward, backward, and stop) and for speed control of motors (maximum, medium, and minimum). the flex sensor is used to control the wheelchair direction (left and right) [5]. chitte et al. developed a wheelchair control system for disabled persons with hand gesture sensing. the system is divided into a gesture part and a wheelchair part. depending on the direction of the accelerometer sensor that is fixed on the hand, the arm7 controller gives orders to move the wheelchair to the desired direction. in case of emergency, an sms message alert is sent via gsm to the family of the person [3]. suchitra and brinda implemented a hand gesture system to drive and control a car utilizing a 3-axes accelerometer sensor (mems sensor). the sensor is placed on the user's finger and the car moves in four directions according to the hand movement. the arduino uno microcontroller is used to control and monitor the comprehensive performance of the system [6]. saharia et al. introduced a joystick control wheelchair for disabled people. the wheelchair movement was controlled by a joystick. the command of movement was done by utilizing the joystick and then transmitting the order to the arduino microcontroller that processes the command. after that, the controller transmits a digital signal to the motor driver circuit to control wheelchair movement [7]. sainath et al. considered hand gestures for controlling and driving a wheelchair. the sensing circuit included an accelerometer that translates the hand tilting into pitch and roll. the system is implemented based on a microcontroller that receives the tilting data from the sensor, processes it, and then transforms it into digital signals for the motors that drive the wheelchair [8]. in some cases of disabilities, the above techniques are useless because of their limitations. a wheelchair controlled by a joystick or hand gesture does not fully achieve the requirements of individuals who are suffering from parkinson's paralysis, quadriplegia paralysis, or weakness in their hands because they cannot properly control their wheelchairs [9]. additionally, the wheelchair controlled by voice instructions provides 195 iium engineering journal, vol. 20, no. 1, 2019 abdulsada et al. services for people who cannot use hands and legs to drive the wheelchair, but it is not suitable for people who have speech difficulties [10,11]. the limitations in the previous works can be overcome using the technique used in this work, which is suitable for multiple cases of disabilities such as quadriplegia paralysis, parkinson's paralysis, speech difficulties, amputation in hands and legs. the work includes an intelligent control technique based on head gestures. in addition, it provides an obstacle avoidance system. 2. proposed system design the proposed system is designed to help people with quadriplegia where they can only move their head or people suffering from amputation of their hands and legs. the accelerometer sensor is placed in front of the patient's hat. it is used to detect the movement of the patient's head, then the arduino sends appropriate instruction of digital bits via an rf-transmitter. the transmitting part of the proposed system is shown in fig. 1. fig. 1: transmitter part of the proposed system (hat part). fig. 2: receiving part of the proposed system (wheelchair part). the signal is received at the other end by the rf-receiver and is analyzed by the arduino. the arduino gives an order to the motor driver circuit to control the wheelchair motors and to move the wheelchair in the desired direction according to the direction of movement of the patient's head. figure 2 illustrates the block diagram of the receiving part. the patient wears the hat on his head to drive and control the wheelchair. in case of forward head motion, the wheelchair moves forward, while it moves backward when the head rotates in the back direction as in fig. 3. when the patient moves his head to the right side, the wheelchair moves to the right and vice versa for the left direction as illustrated in fig. 4. an ultrasound-sensor is placed in the back of the wheelchair to detect obstacles behind the wheelchair in the case of rotating the head backward. the sensor detects the obstacles on a range up to 50 cm then the arduino holds the wheelchair back moving to avoid collision with obstacles. figure 5 illustrates a wheelchair model pictures including the ultrasonic-sensor. accelerometer sensor x-axis comparator y-axis comparator arduino rf-transmitter dc driver motor circuit arduino-uno rf receiver ultrasonic sensor motor 1 motor 2 196 iium engineering journal, vol. 20, no. 1, 2019 abdulsada et al. fig. 3: pictures show cases of patient head movement (forward and backward). fig. 4: pictures show cases of patient head movement (left and right). fig. 5: pictures of side and back of the wheelchair. ultrasonic sensor arduinouno rf433 mhz receiver batteries 197 iium engineering journal, vol. 20, no. 1, 2019 abdulsada et al. the programming code is written then uploaded to the arduino uno board to be programmed. figure 6 shows the practical system of the block diagram which is explained in fig. 3. it shows the patient's hat including accelerometer sensors (adxl345), arduino uno, and rf433 mhz transmitter. figure 7 shows the flowchart of the overall system. at first, we make a suitable configuration for the motors, accelerometer, and ultrasonic systems, then we connect them to the arduino pins. the readings of the x and y axes of the accelerometer are monitored to choose proper angles of head movement. then, the wheelchair moves in a direction that is compatible with the desired x and y axes values. fig. 6: picture of practical transmitting system. . fig. 7: flow-chart of proposed system. rf433 mhz transmitter patient's hat adxl345 accelerometer arduino uno start make a suitable configuration for motors, accelerometer, and ultrasonic monitor the x and y axes of the accelerometer reading if -16< x <-15 if 3< x <4 move the wheelchair to right move the wheelchair to left if 8< y <9 move the wheelchair to forward if 0< y <1 stop yes if ultrasonic reading= 0 move the wheelchair to backward no yes no 198 iium engineering journal, vol. 20, no. 1, 2019 abdulsada et al. 3. results and discussion the proposed system is based on the use of two arduino uno boards and an accelerometer for hardware implementation of intelligent wheelchair control by head gestures for people with qp. the software and hardware results show that the system operates very well to help the patients and gives accurate results. the system is set and calibrated so that the qp patient can properly control the wheelchair. the patient wears the hat and moves his head in each direction to choose an appropriate angle of his head movement. the horizontal angles (right and left) have been selected to be 35 degrees, as shown in fig. 8. these angles allow the qp patient to move his head in all directions to some extent, and provides comfortable conditions for the patient without moving the wheelchair. fig. 8: graph of degree of wheelchair direction versus horizontal head tilting degree. the vertical angles (forward and backward) have been selected to be 40 degrees as shown in fig. 9. the vertical and horizontal angles can be modified to be appropriate to many qp patient cases. figure 10 illustrates the x and y axes sensor readings that represent the horizontal and the vertical head tilting respectively, where the shaded areas act the corresponding wheelchair movement. when the patient moves his head to the left or the right, then the reading of x-axis of the accelerometer sensor changed gradually and when he moves his head forward or backward, then the reading of y-axis of the accelerometer sensor changes. it is worth mentioning that when the head is in a straight position, the sensor readings are about -6 for x-axis and 4.5 for y axis. table 1 displays the wheelchair performance accuracy which is calculated after several trials of movement in all directions. for each direction, 50 trials were made to test the wheelchair movement; the successful movements were as described in the table. the performance accuracy was calculated by dividing the successful movements in each -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 -50 -40 -30 -20 -10 0 10 20 30 40 50 degree of head tilting degree of wheel direction right movement left movement 199 iium engineering journal, vol. 20, no. 1, 2019 abdulsada et al. direction on the number of trials for the same direction. after calculating the accuracy for each direction, the average performance accuracy was calculated to be about 97.5%. fig. 9: graph of degree of wheelchair direction versus vertical head tilting degree. fig. 10: head tilting angles and their wheelchair movement response. table 1: system performance accuracy movement trials number successful outcomes accuracy forward 50 50 100% backward 50 47 94% right 50 49 98% left 50 49 98% average accuracy : 97.5% 0 0.2 0.4 0.6 0.8 1 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 degree of head tilting degree of wheel direction 0 1 2 3 4 5 6 7 8 9 -17-16-15-14-13-12-11-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 vertical head tilting forward movement backward movement horizontal head tilting right-backward right-forward backward left-backward right left left-forward forward stop wheelchair movement 200 iium engineering journal, vol. 20, no. 1, 2019 abdulsada et al. 4. conclusion the proposed control system has been successfully designed and implemented to move the wheelchair in four directions or to stay in same position based on a patient's head tilting. this work is useful to support people with qp or disabled people by providing alternative means to control the wheelchair by the movement of the head. the system also provides a safety mechanism to prevent collision on a range of 50 cm in case of backward movement of the wheelchair. the system has a very effective performance and high accuracy, which is about 97.5%. acknowledgments the researchers thank the wounded officer in the iraqi army (ahmed hamza) who drove the wheelchair easily. references [1] eun yk. (2016) wheelchair navigation system for disabled and elderly people. mdpi sensors, 16(11):1-24. [2] saud l, vineet y, anupmani t, archana c, nilesh n, jaymala c. (2017) accelerometer based gesture controlled wheelchair. international journal of computer applications, 161(10):9-12. [3] chitte pp, khemnar sb, kanawade aa, wakale sb. (2016) a hand gesture based wheelchair for physically handicapped person with emergency alert system. international research journal of engineering and technology (irjet), 3(4):277-281. [4] anjaneyulu d, siva k. (2015) hand movements based control of an intelligent wheelchair using accelerometer, obstacle avoidance using ultrasonic and ir sensors. international journal of engineering research and development, 11(7):1-9. [5] shruti w, vijayalaxmi h, preeti d, vishwanath b, bhagavati pb. (2014) speech and flex sensor controlled wheelchair for physically disabled people. proceedings of 10th irf international conference, 60-62. [6] suchitra t, brinda r. (2017) hand gesture recognition based auto navigation system for leg impaired persons. international journal of advanced research in electrical, electronics and instrumentation engineering, 6(2):251-257. [7] trinayan s, jyotika b, chayanika b. (2017) joystick controlled wheelchair. international research journal of engineering and technology, 4(7):235-237. [8] sainath g, bhanu m, ranjith. (2018) hand gestured controlled wheelchair. international journal of electronics, electrical and computational system, 7(3):476-480. [9] yassine r, makrem m, farhat f. (2018) intelligent control wheelchair using a new visual joystick. journal of healthcare engineering, 1-20. [10] jesse l, hung ml. (2017) a comprehensive review of smart wheelchairs: past, present and future. ieee transactions on human-machine systems, 47(4):1-13. [11] khyati m, shubham g, vijay k. (2017) voice controlled wheelchair. international journal of electronics, electrical and computational system, 6(4):23-27. 201 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <feff004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e> /ptb <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> /rum <feff005500740069006c0069007a00610163006900200061006300650073007400650020007300650074010300720069002000700065006e007400720075002000610020006300720065006100200064006f00630075006d0065006e00740065002000410064006f006200650020005000440046002000610064006500630076006100740065002000700065006e007400720075002000760069007a00750061006c0069007a006100720065002000640065002000ee006e00630072006500640065007200650020015f0069002000700065006e00740072007500200069006d007000720069006d006100720065006100200064006f00630075006d0065006e00740065006c006f007200200064006500200061006600610063006500720069002e00200044006f00630075006d0065006e00740065006c00650020005000440046002000630072006500610074006500200070006f00740020006600690020006400650073006300680069007300650020006300750020004100630072006f0062006100740020015f0069002000410064006f00620065002000520065006100640065007200200036002e003000200073006100750020007600650072007300690075006e006900200075006c0074006500720069006f006100720065002e> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 high accuracy human motion trajectory generation for exoskeleton robot using curve fitting technique muhammad abdul jalil1*, muhammad fahmi miskon2, bazli bin bahar2 1 mechanical engineering department, polytechnic port dickson, port dickson, malaysia 2 center of excellence in robotic and industrial automation (ceria), faculty of electrical engineering, universiti teknikal malaysia, melaka, malaysia *corresponding author: muhammadaj@polipd.edu.my (received: 24 january 2022; accepted: 22 may 2023; published on-line: 4 july 2023) abstract: robotic systems often require trajectory planning algorithms that can generate natural human-like movements for tasks such as grasping and manipulation. however, conventional trajectory planning methods may not accurately capture the complex movement patterns observed in humans. in this paper, we present a trajectory planning algorithm based on polynomial curve fitting that aims to address this issue. the algorithm determines the polynomial coefficient values that accurately match the natural human trajectory profile and is evaluated using matlab simulations. we compare the proposed algorithm to the conventional quintic polynomial trajectory method, analysing the accuracy, precision, and via-point continuity. the result shows that the algorithm has the ability to generate a trajectory profile with accuracy of 99.8% and a precision of 0.002°. however, the result for via-point continuity shows an error on every sub-phase transition, with the lowest error of 0.0031 between the transition of sub-phases 1 and 2. the result also shows that the lowest fitting error recorded is 0.00014°. the results demonstrate that our algorithm can generate trajectory profiles with higher accuracy and naturalness, potentially improving the performance and usability of robotic systems. abstrak: sistem robotik sering memerlukan algoritma perancangan trajektori yang dapat menghasilkan gerakan semulajadi seperti manusia bagi tugas seperti memegang dan memanipulasi objek. walau bagaimanapun, kaedah perancangan trajektori konvensional mungkin tidak dapat merekodkan pola gerakan kompleks seperti yang dihasilkan manusia secara tepat. kajian ini adalah berkenaan algoritma perancangan lintasan berdasarkan penyepaduan lengkung polinomial bagi menyelesaikan masalah ini. algoritma ini menentukan nilai pekali polinomial yang sepadan dengan profil gerakan semulajadi manusia dan dinilai menggunakan simulasi matlab. algoritma yang dicadangkan ini telah dibandingkan dengan kaedah perancangan lintasan polinomial kuintik konvensional, dianalisis kejituan, ketepatan, dan keberterusan titik lalu. keputusan menunjukkan bahawa algoritma tersebut mampu menghasilkan profil lintasan dengan kejituan sebanyak 99.8% dan ketepatan sebanyak 0.002°. walau bagaimanapun, dapatan kajian mengenai keberterusan titik lalu menunjukkan ralat pada setiap peralihan fasa-sub dengan ralat terendah sebanyak 0.0031 pada peralihan antara fasa-sub 1 dan fasa-sub 2. dapatan kajian juga menunjukkan bahawa ralat penyepaduan terendah yang direkodkan adalah sebanyak 0.00014°. keputusan ini menunjukkan bahawa algoritma ini mampu menghasilkan profil lintasan dengan ketepatan dan sifat semula jadi yang lebih tinggi, berpotensi meningkatkan prestasi dan kegunaan sistem robotik. keywords: trajectory generation; polynomial; curve fitting; via-point; exoskeleton 301 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 1. introduction trajectory refers to a time history of the position, velocity, and acceleration for each degree of freedom (dof) [1]. in trajectory generation, the desired trajectory for motions is generated based on the prediction of how the system (robot) responds to the input trajectory. generally, trajectory generation deals with the problem of 1) how to specify a trajectory with a simple description, 2) how the trajectory is represented, 3) how to generate the trajectory in real-time [1], and 4) how to find a relationship between two domains: time and space [2]. according to miskon et al. [3], there are three strategies for generating a trajectory for robot applications: off-line, on-line, and combined or hybrid. the off-line strategy is a strategy that uses either a mathematical model such as a polynomial equation [4], fourier transform [5], central pattern generation (cpg) [6], neural oscillator [7], or uses recorded or normalized human motion data [8]. the advantage of this strategy is that it does not require any dynamic relationship between the robot and the environment. however, the main drawback of this strategy is adaptation due to environmental uncertainties. also, some of the off-line methods required very accurate robot modelling before the trajectory was planned. on the other hand, the on-line strategy does not need a predefined trajectory to generate the motion. it has the capability to produce the trajectory according to the working space environment. the implementation of neural network [9] and fuzzy logic [10] attached with an additional sensor [11,12] is used to improve the accuracy of the generating trajectory. however, this strategy must consider issues such as the fastest time adapting for real-time application and accuracy. meanwhile, the hybrid strategy used both advantages of off-line and on-line strategy to generate a trajectory for the robot. the normative human trajectory has been studied to ensure that the robot (in this case, bipedal or exoskeleton) can follow the nature of human motion. two types of trajectory approaches can generate trajectory profiles using the cartesian and joint space approaches. the cartesian space trajectory generation approach will involve inverse kinematics. there will be multiple solution problems in which matching with human motion will be an issue. craig [1] stated that there are three general problems in the cartesian space trajectory scheme: first, unreachable intermediate points; second, high joint rates near a singularity; and lastly, start and goal being reachable in different solutions. meanwhile, in the joint space trajectory approach, the robot's motion design is to be made using joint space values such as joint space position, velocity, etc. the general problem of this approach is the lack of visualization of joint motion and position of the end-effector during the time. various methods of implementation have already been established. within that, the accuracy of the trajectory is an important parameter when designing the trajectory of the robot that operates alongside humans, such as an exoskeleton. the trajectory's accuracy can be viewed as an error between generated (target) trajectory and the reference robot trajectory. the less error shows a higher accuracy of the generating trajectory. the more accurate trajectory generated, the more naturally it follows human motion. many methods have been discussed to improve the accuracy of trajectory in exoskeleton robots. in gomes et al. [13], gait pattern adaptation (gpa) was designed to generate natural human motion for the lokomat rehabilitation robot. the gpa adjusted the generating trajectory to suit the desired trajectory based on torque interaction between humans and robots. this method was also studied in different approaches [14-16]. the nature-gaits is also a technique that is used to generate the trajectory that follows natural 302 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 human motion for rehabilitation studies [17]. these two methods used predefined trajectories generated from mathematical (cubic) or recorded motion data. other methods like complementary limb motion estimation (clme) [18], neural oscillator [7], gait phase switching algorithm (gpsa) [6], radial basis function (rbf) [19], neural network [9], polynomial [20,21], probabilistic foam method (pfm) [22] have also been used to improve accuracy of the generated trajectory profiles to the wearer. however, all the methods discussed so far require redefining constraint parameters (i.e., start time, stop time, start velocity, stop velocity, etc.) before implementing the method in the robot can be done. there are advantages of having many constraints that need to be considered, such as smooth trajectory, accuracy, etc. however, these constraints can increase the trajectory generator's computation cost and computation error [2]. this paper presents the trajectory generation algorithm that generates an accurate human-like trajectory profile to overcome the limitations stated. unlike other methods, this method does not require additional parameters such as velocity or acceleration at the trajectory via-point to design trajectory profile. the only parameter required in this design is the joint displacement of the actuator. the complete cycle of time series data consisting of natural human motion data is mapped using the curve fitting approach; then, the quintic polynomial coefficient is produced. the polynomial trajectory is used because of its high precision and ability to calculate the kinematics, dynamics, and control parameters [23]. this paper's main contribution lies in proposing a trajectory generation algorithm that generates highly accurate and natural human-like trajectory profiles. this algorithm can potentially improve the performance and usability of robotic systems in a range of applications, such as grasping and manipulation tasks. 2. polynomial curve fitting trajectory planning (pcftp) in robotics, trajectory planning is designed by assigning the initial (t0) and final time (tf) and other constraints on position, velocity, acceleration and so on at t0 and tf [2]. for the robot application that works alongside humans, such as an exoskeleton, the performance of the trajectory generator is how close the generated trajectory is to the human reference trajectory. figure 1 shows the application of an exoskeleton robot in the rehabilitation process taken from [24]. in this application, the robot must generate a similar joint trajectory profile to the normal human walking joint to ensure the patient recovers quickly and avoids discomfort. fig. 1: illustration of hip, knee and ankle joint trajectory in exoskeleton robot application taken from [24]. 303 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 the trajectory generation technique requires some parameters to be set up before generation of the required trajectory. table 1 shows the initial trajectory parameters. the trajectory generation technique requires the generation of a reference trajectory. it is shown that the current trajectory technique requires multiple initial setup trajectory parameters. having multiple parameters in the initial setup will improve the accuracy performance of the trajectory generator. however, this will burden the system for processing and require exact mathematical modeling of the robot. table 1: initial parameter setup for trajectory generation technique trajectory generation technique initial trajectory parameters quintic polynomial start boundary parameter: i.e., starting angular position, velocity, acceleration, jerk, tstart stop boundary parameter: i.e., stoping angular position, velocity, acceleration, jerk, tstop neural oscillator neuron parameters: frequency, coupling coefficients, different phase matrix com trajectory parameters: gait phase switching algorithm (gpsa) neuron parameters: frequency, coupling coefficients, different phase matrix gait parameters: i.e., amplitude, regulating signal figure 2 shows the algorithm based on a curve fitting approach to identify the polynomial coefficients. this algorithm can be applied to all strategies discussed in [3] since it requires complete data to represent the motion. these data can be off-line, obtained from biomechanical studies, or come from an on-line time-series sequence received from the actuator encoder. however, in this paper, our algorithm will implement and evaluate only off-line situations. this paper used the human hip motion profile data from a biomechanical study [24] as a reference trajectory. algorithm 1: pcftp 1: determine data size of motion profile, mdata 2: rearrange motion data followed by phases boundary parameter i = phases number 3: determine the size of phases data msi 4: while (i < imax) 5: select polynomial power (n) 6: while (∑msi < mdata) 7: calculate the polynomial coefficient for selected n, mdata, and msi 8: end 9: end fig. 2: pcftp algorithm. step 1: data acquisition the dataset used in this paper was based on a biomechanics study conducted by [25], which employed 40 healthy subjects. the dataset consisted of two different groups, adult and young, with different walking speeds recorded and labeled as normal walking (n), very slow walking (xs), slow walking (s), medium walking (m), fast walking (l), walking on toe (t), walking on heel (h), stair ascending (u) and stair descending (d). in this paper, we used an adult hip normal walking profile. this paper does not cover how joint trajectory is 304 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 generated from 40 healthy subjects and the criteria for selecting their subject. other datasets can also be used and are not rigid from the stated researcher. step 2: divided motion data based on biomechanical gait cycle fig. 3: phases of human walking gait. in human biomechanical studies, gait is defined as any method of locomotion characterized by periods of loading and unloading of the limbs [26]. this definition is not restricted to walking; it includes running, hopping, skipping, swimming, and cycling. since walking is the most frequently used gait in the activities of daily living (adls), most of the research definition of gait refers to walking. the gait cycle in walking is defined as a time interval or sequence of motion occurring from heel strike to heel strike [27]. fig. 3 shows the complete phases of the human walking gait, with seven phases in the human walking motion [28]. in general, human walking data shows that there is smooth and continuous motion between phase transitions (via-point section). this became the most challenging parameter for both methods to design trajectory profiles while accurately ensuring motion continuity and smoothness. table 2 shows the complete walking cycle's human hip motion parameter phase. each phase has its own parameter starting and ending. based on [1], these starting and ending parameters are critical when designing the via-point. table 2: human hip phases joint angle parameters based on [28] and [25] gait phases gait cycle (%) starting angle (deg) ending angle (deg) starting time (s) ending time (s) initial contact 0 – 10 25.20 21.00 0.00 0.10 mid stance 10 – 30 21.00 -1.30 0.10 0.30 terminal stance 30 – 50 -1.30 -16.10 0.30 0.50 pre swing 50 – 60 -16.10 -10.40 0.50 0.60 initial swing 60 – 73 -10.40 15.10 0.60 0.73 mid swing 73 – 87 15.10 25.10 0.73 0.87 terminal swing 87 100 25.10 24.10 0.87 1.00 step 4: polynomial curve fitting trajectory planning the curve fitting technique is the main core of our proposed algorithm. it determines the polynomial coefficient from the normative hip walking profile. the curve fitting method is chosen because of its ability to deal with a series of data. there are two approaches in the curve fitting technique that have the ability to generate a polynomial coefficient. the first is least-squares regression (lsr), or regression in short, and the second is an interpolation. this paper used the least-square regression approach to generate a polynomial coefficient. the polynomial regression curve fitting technique is formulated in eq. (1). where ai is a polynomial coefficient. the core idea of this technique is the regression that is used to 305 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 minimize the sum of the squares of residuals, sr between the desired yi and the forecast y’ as shown in eq. (2), where all summation from i =1 through m (number of data) and n (polynomial order). θ(t)= ∑ ait i n i=0 (1) sr= ∑ ∑ (yi-ajxi j ) 2 n j=0 m i=1 (2) equation (3) shows the partial derivative of the sum of the residuals over the coefficient ( ∂sr ∂aj ) in eq. (2). and also in a matrix form of eq. (3) as shown in eq. (4). ∂sr ∂aj =-2 ∑ ∑ x i j (y i -ajxi j ) n j=0 m i=1 { i=1,2,…..m j=1,2, …..n (3) [ m ∑ xi j … ∑ xm n ∑ x i j … … ∑ xm n+1 ⋮ ∑ xi n … … … … ⋮ ∑ xm 2n ] [ a0 a1 ⋮ an ] = [ ∑ yi ∑ xiyi ⋮ ∑ xi ny i] (4) the standard error sy x⁄ , eq. (5) and the coefficient correlation, eq. (6), is used as a performance evaluation for the pcftp method. sy x⁄ =√ sr m-(n+1) (5) r2= ∑ (y 1 -y̅) ∑ s r ∑ (y 1 -y̅) (6) 3. simulation setup we used matlab to demonstrate the accuracy of the trajectory generated from the pcftp algorithm and the effectiveness of generation using the trajectory algorithm compared to the quintic polynomial method. 3.1 comparison of quintic trajectory generation for generating hip joint trajectory profile the quintic polynomial is a fifth-degree polynomial formulated in eq. (7). besides position, other constraints, such as velocity and acceleration, must be considered when designing the trajectory. a higher-order polynomial gives more constraints (time derivatives) that can be used to adjust the trajectory to suit the application requirement. however, the more constraints are considered, the more complex it is to determine the unknown coefficients. this constraint provided high computation cost and produced a numerical error for a higher value of polynomial degree [2]. the quintic polynomial can provide five constraints instead of three, as mentioned in eqs. (7) to (9). these three constraints are enough to obtain a smooth trajectory profile. the suitable initial and final constraints for the position eq. (7), velocity eq. (8), and acceleration 306 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 eq. (9) [2] are determined first. besides, the number of boundary constraints is usually even, and the degree of the polynomial function is odd. 𝜃(𝑡) = ∑ 𝑎𝑖𝑡 𝑖 𝑛 𝑖=0 (7) �̇�(𝑡) = ∑ 𝑖𝑎𝑖𝑡 𝑖−1 𝑛 𝑖=1 (8) �̈�(𝑡) = ∑ 𝑖(𝑖 − 1)𝑎𝑖𝑡 𝑖−2 𝑛 𝑖=2 (9) therefore, from eq. (7) to (9), there are six boundary constraints (starting position, 𝜃0, ending position, 𝜃𝑓, starting velocity, 𝑣0, ending velocity, 𝑣0, starting acceleration, 𝑠0 and ending acceleration, 𝑠𝑓) of a quintic polynomial as shown in eq. (10), that needs to be determined. 𝜃(𝑡0) = 𝜃0 (10) 𝜃(𝑡𝑓) = 𝜃𝑓 �̇�(𝑡0) = 𝑣0 �̇�(𝑡𝑓) = 𝑐 �̈�(𝑡0) = 𝑠0 �̈�(𝑡𝑓) = 𝑠𝑓 this constraint is then used to determine the quintic coefficient, as shown in eq. (11). the first three coefficients, a0, a1, and a2, are the initial values of the generated trajectory's position, velocity, and acceleration. table 3 shows the polynomial coefficients generated using quintic polynomial trajectory planning for each sub-phase. table 4 shows the polynomial coefficients using curve fitting. all these coefficients are then used again to generate the trajectory. this trajectory is then compared to the recorded trajectory profile to validate the accuracy and effectiveness of the proposed method. 𝑎0 = 𝜃0 (11) 𝑎1 = 𝜃0̇ 𝑎2 = 𝜃0̈ 2 𝑎3 = 20𝜃𝑓 − 20𝜃0 − (8𝜃�̇� + 12𝜃0̇)𝑡𝑓 − (3�̈�𝑓 − �̈�0)𝑡𝑓 2 2𝑡𝑓 3 𝑎4 = 30𝜃𝑓 − 30𝜃0 − (14𝜃�̇� + 16𝜃0̇)𝑡𝑓 − (3�̈�𝑓 − 2�̈�0)𝑡𝑓 2 2𝑡𝑓 4 𝑎5 = 12𝜃𝑓 − 12𝜃0 − (6𝜃�̇� + 6𝜃0̇)𝑡𝑓 − (�̈�𝑓 − �̈�0)𝑡𝑓 2 2𝑡𝑓 5 307 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 4. results this section comprehensively analyses a significant problem known as the via-point disjointed problem. within this context, we explore trajectory accuracy, employing two distinct methods: the quintic polynomial method and the pcftp method. by thoroughly examining and comparing the outcomes generated by these methods, we aim to understand better their respective strengths, limitations, and overall effectiveness in achieving accurate trajectories. error! reference source not found. shows the hip joint motion simulation r esult based on the quintic polynomial trajectory method, and error! reference source not found. shows the hip joint motion simulation result based on the polynomial curve fitting method. fig. 4: hip joint trajectory profile generated using quintic polynomial. 4.1 via-point disjointed analysis via-point is an intermediate position that the system or object needs to pass through during its movement from the initial position to the final destination. the via-point is located at every phase's transition. based on winter [28], the seven phases of human walking require six via points for the complete cycle. as mentioned in the previous section, the ending position for phase 1 is a starting position for phase 2. fig. 5: hip joint trajectory profile generated using pcftp. 308 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 table 3: coefficient of a polynomial using quintic polynomial trajectory method phases coefficient a5 𝒂𝟒 𝒂𝟑 𝒂𝟐 𝒂𝟏 𝒂𝟎 1 -8.102 x105 2.108 x105 17178 0 0 25.2 2 32128 -35861 15985 -3572.4 285.07 15.497 3 -2268.6 4303.8 -2828.9 958.46 -298.374 48.981 4 -8.039 x106 -2.216 x106 2.439 x106 1.339 x106 3.666 x105 -40040 5 1.932 x105 -6.268 x105 8.072 x105 -5.152 x105 1.630 x105 -20480 6 -99297 4.0306 x105 -6.5399 x105 5.2952 x105 -2.136 x105 34301 7 64871 --3.364 x105 6.915 x105 -7.052 x105 3.571 x105 -71816 table 4: coefficient of a polynomial using the pcftp method phases coefficient 𝒂𝟓 𝒂𝟒 𝒂𝟑 𝒂𝟐 𝒂𝟏 𝒂𝟎 1 75178 -82804 14364 -1158.9 6.0584 25.193 2 91252 -88042 32870 -5978.7 424.14 13.481 3 -88293 1.72 x105 -1.32 x105 50020 -9507.7 732.37 4 2.140 x105 -5.62 x105 5.90 x105 -3.09 x105 80235 -8293.4 5 1.61 x105 -5.34 x105 7.02 x105 -4.58 x105 1.48 x105 -19082 6 84648 -3.37 x105 5.33 x105 -4.22 x105 1.67 x105 -26431 7 2.17 x105 -1.06 x106 2.08 x106 -2.02 x106 9.84 x105 -1.91 x105 309 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 table 5 compares generated via-point for each sub-phase between the quintic polynomial and pcftp. it shows that the quintic polynomial method handles via-points without encountering problems during each phase. however, the pcftp method demonstrates a notable concern with disjointed via-points in the phase transitions. this disparity highlights the quintic method's ability to seamlessly incorporate via-points across all phases, while the pcftp method experiences challenges in maintaining continuity and cohesiveness in the trajectory when navigating through different phases. table 5: start and stop position at via-point phases quintic polynomial (deg) pcftp (deg) start stop start stop 1 25.200 21.000 25.193 21.046 2 21.000 -1.300 21.087 -1.265 3 -1.300 -16.100 -1.303 -16.167 4 -16.100 -10.400 -16.143 -10.443 5 -10.400 15.100 -10.453 13.473 6 15.100 25.100 13.480 25.316 7 25.100 24.100 25.310 24.086 the issue with our algorithm is rooted in the fundamental characteristics of the curve fitting technique. this method utilizes a best-fitting strategy to effectively incorporate and precisely depict the data within a designated interval, as outlined in eq. (5) and eq. (6). on the other hand, the quintic method integrates the initial and final values as constraints in eq. (11). the utilization of constraints guarantees that the trajectory's initiation and termination occur at predetermined positions, thereby enabling accurate management of the start and end points. in table 6, the absolute errors associated with each via-point are presented, reflecting the performance of the pcftp method. notably, the most significant error is observed during the transition from phase 4 to phase 5, specifically for the stop position, with an error magnitude of approximately 1.627°. additionally, the transition from phase 5 to phase 6 exhibits an error of approximately 1.620°. it is important to note that these errors directly impact the overall smoothness and continuity of the trajectory, underscoring the need for further analysis and potential improvements in the pcftp method to mitigate such errors and enhance trajectory quality. table 6: absolute error of a via-point in each phases transition for curve fitting phases transition absolute error start position (deg) absolute error stop position (deg) 1 – 2 0.007 0.046 2 – 3 0.087 0.035 3 – 4 0.003 0.067 4 – 5 0.043 1.627 5 – 6 1.620 0.216 6 – 7 0.210 0.014 4.2 overall fitting performance analysis an extensive evaluation was performed to compare the fitting errors of the quintic polynomial method and pcftp methods' fitting errors to obtain significant insights into the precision and efficiency of trajectory generation techniques. fig. 6 compares fitting errors between the quintic method and the curve fitting method. based on fig. 6, the pcftp approach has a lower fitting error than the quintic trajectory generation. 310 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 fig. 6: fitting error comparison between quintic polynomial and pcftp methods. table 7 shows the comparison of mae for each phase for both methods. mae is the mean of fitting error for each phase. table 6 shows that the polynomial curve fitting method gives a high efficiency with the lowest generation error 0.002° phase. however, the lowest generation error for the quintic polynomial approach is 0.086° phase. the overall mae for the quintic polynomial approach is 0.112° phase and 0.011° phase for the polynomial curve fitting approach. the mae represents the difference between the desired trajectory and generated trajectory. table 8 shows the root mean square error (rmse) comparison between the quintic polynomial and pcftp methods. these values indicate the accuracy of the trajectory profile. it shows that the pcftp method exhibits superior precision in trajectory profile compared to the quintic polynomial method. table 7: mean absolute error (mae) comparison between quintic and pcftp methods sub-phase method quintic (deg) curve fitting (deg) 1 0.115 0.009 2 0.101 0.032 3 0.164 0.012 4 0.086 0.002 5 0.101 0.013 6 0.089 0.004 7 0.129 0.006 table 8: rmse comparison between quintic polynomial and pcftp methods sub-phase method quintic (deg) curve fitting (deg) 1 7.030 x 10-2 6.783 x10-15 2 2.900 x10-2 4.289 x10-14 3 1.431 x10-1 4.602 x10-13 4 1.440 x10-2 4.151 x10-11 5 9.210 x10-2 1.221 x10-11 6 3.730 x10-2 6.500 x10-11 7 1.267 x10-1 3.035 x10-10 311 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 considering the rmse values obtained, we can observe that the pcftp method consistently outperforms the quintic polynomial method regarding trajectory accuracy. this outcome underscores the efficacy of the pcftp method in achieving a closer fit to the desired trajectory, resulting in minimized deviations from the intended motion path. these findings highlight the potential advantages of adopting the pcftp method over the quintic polynomial method, particularly in applications with high trajectory accuracy, such as robotics, motion planning, and autonomous navigation systems. 5. conclusion in conclusion, the proposed pcftp algorithm generates natural human motion profiles more accurately than the quintic polynomial trajectory generation method. the algorithm does not require constraint parameters such as angular position, velocity, and acceleration, which is a significant advantage. however, it requires the complete datasets or trajectory profiles to be modelled, which can sometimes be challenging. the proposed algorithm achieved a trajectory profile accuracy of 99.8% and precision of 0.002°, significantly improving over existing methods. moreover, the performance validation is based on human biomechanics walking data from [25]. this walking data is not based on a single person but on the normalization of 40 healthy people. different biomechanics data can be used as well instead of this data. however, the result might vary slightly due to a few factors. first, the curve fitting technique performance is based on data trends in each segment or phase. if the data trend is well segmented, the fitting performance is high. second, the polynomial degrees are used to model the trajectory data. however, an open question for a proposed method is how to improve, especially in disjointed via-point problems on every phase transition. this disjointed issue will affect the overall smoothness of the motion profile. the future work for this research is the new extension of this method that determines the numbers of via-points based on best fitting accuracy (eqs. (5) and (6)) and continuity. also, implementing the proposed algorithm to real-time data will guide us to a new dimension of using the curve fitting approach in trajectory planning since the curve fitting approach works only if all fitting data are complete. acknowledgment the authors would like to thank the ministry of higher education malaysia for funding this project under the rags research grant scheme rags/1/2014/tk03/fke/b00054. this project was conducted at the center of excellence in robot and industrial automation (ceria), universiti teknikal malaysia melaka. references [1] craig jj. (2014) introduction to robotics: mechanics and control, 3rd edition pearson. [2] biagiotti l, melchiorri c. (2009) trajectory planning for automatic machines and robots. berlin, heidelberg, heidelberg: springer berlin heidelberg. doi: 10.1007/978-3-540-85629-0. [3] miskon mf, yusof mbaj. (2014) review of trajectory generation of exoskeleton robots., in 2014 ieee international symposium on robotics and manufacturing automation (roma), ieee, 12-17. doi: 10.1109/roma.2014.7295854. [4] wang h, zhao q, li h, zhao r. (2022) polynomial-based smooth trajectory planning for fruitpicking robot manipulator. information processing in agriculture, 9(1): 112-122. doi: 10.1016/j.inpa.2021.08.001. 312 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 [5] kulak t, silverio j, calinon s. (2020) fourier movement primitives: an approach for learning rhythmic robot skills from demonstrations., in robotics: science and systems xvi, robotics: science and systems foundation. doi: 10.15607/rss.2020.xvi.056. [6] wei s, wu h, liu l, zhang y, chen j, li q. (2022) a cpg-based gait planning and motion performance analysis for quadruped robot. industrial robot: the international journal of robotics research and application, 49(4): 779-797. doi: 10.1108/ir-08-2021-0181. [7] liu c, yang j, bu w, chen q. (2016) a trajectory generation method for biped walking based on neural oscillators., in 2016 ieee 13th international conference on networking, sensing, and control (icnsc), ieee, 1-6. doi: 10.1109/icnsc.2016.7478995. [8] wang q, qian j, zhang y, shen l, zhang z, feng z. (2007) gait trajectory planning and simulation for the powered gait orthosis., in 2007 ieee international conference on robotics and biomimetics (robio), ieee, 1693-1697. doi: 10.1109/robio.2007.4522420. [9] watanabe t, johnson en. (2018) trajectory generation using deep neural network. 2018 aiaa information systems-aiaa infotech @ aerospace, (january): 1-12. doi: 10.2514/6.2018-1893. [10] aly aa, vu mt, el-sousy ffm, alotaibi a, mousa g, le d, mobayen s. (2022) fuzzy-based fixed-time nonsingular tracker of exoskeleton robots for disabilities using sliding mode state observer. mathematics, 10(17): 3147. doi: 10.3390/math10173147. [11] kundu as, mazumder o, chattaraj r, bhaumik s, lenka pk. (2014) trajectory generation for myoelectrically controlled lower limb active knee exoskeleton., in 2014 seventh international conference on contemporary computing (ic3), ieee, 230-235. doi: 10.1109/ic3.2014.6897178. [12] schuy j, mielke t, steinhausen m, beckerle p, rinderknecht s. (2015) design and evaluation of a sensor minimal gait phase and situation detection algorithm of human walking. ieeeras international conference on humanoid robots, 2015-dec: 20-25. doi: 10.1109/humanoids.2015.7363517. [13] gomes ma, silveira glm, siqueira aag. (2011) gait pattern adaptation for an active lowerlimb orthosis based on neural networks. advanced robotics, 25(15): 1903-1925. doi: 10.1163/016918611x588899. [14] siqueira aag, jardim b, vilela prc, winter tf. (2008) analysis of gait-pattern adaptation algorithms applied in an exoskeleton for lower limbs., in 2008 16th mediterranean conference on control and automation, ieee, 920–925. doi: 10.1109/med.2008.4602081. [15] gomes ma, silveira glm, siqueira aag. (2009) gait-pattern adaptation algorithms based on neural network for lower limbs active orthoses., in 2009 ieee/rsj international conference on intelligent robots and systems, iros 2009, ieee, 4475-4480. doi: 10.1109/iros.2009.5354232. [16] silveira glm, gomes ma, siqueira aag. (2010) first experimental results on adaptation algorithms for lower limbs active orthoses., in 18th mediterranean conference on control and automation, med’10, ieee, 1316-1321. doi: 10.1109/med.2010.5547868. [17] wang p, low kh, mcgregor ah. (2011) a subject-based motion generation model with adjustable walking pattern for a gait robotic trainer: nature-gaits., in 2011 ieee/rsj international conference on intelligent robots and systems, ieee, 1743-1748. doi: 10.1109/iros.2011.6048809. [18] vallery h, van asseldonk ehf, buss m, van der kooij h. (2009) reference trajectory generation for rehabilitation robots: complementary limb motion estimation. ieee transactions on neural systems and rehabilitation engineering, 17(1): 23-30. doi: 10.1109/tnsre.2008.2008278. [19] daachi me, madani t, daachi b, djouani k. (2015) a radial basis function neural network adaptive controller to drive a powered lower limb knee joint orthosis. applied soft computing, 34: 324-336. doi: 10.1016/j.asoc.2015.04.034. [20] mohammed mq, miskon mf, ali sa. (2017) the effectiveness of kinematic constraints on the accuracy of trajectory profile of human walking using pspb technique. international journal of mechanical and mechatronics engineering, 17(6): 86-96 313 iium engineering journal, vol. 24, no. 2, 2023 abdul jalil et al. https://doi.org/10.31436/iiumej.v24i2.2296 [21] sapiee mr, marhaban mh, ishak aj, miskon mf. (2020) trajectory generation for hip rehabilitation exoskeleton using trajectory morphing method. international journal of human and technology interaction, 4(1): 45-51 [22] nascimento lbp, barrios-aranibar d, alsina pj, santos vg, fernandes dhs, pereira ds. (2020) a smooth and safe path planning for an active lower limb exoskeleton. journal of intelligent and robotic systems: theory and applications, 99(3-4): 535-553. doi: 10.1007/s10846-019-01134-7. [23] sidobre d, desormeaux k. (2019) smooth cubic polynomial trajectories for human-robot interactions. journal of intelligent & robotic systems, 95(3-4): 851-869. doi: 10.1007/s10846-018-0936-z. [24] low kh. (2011) subject-oriented overground walking pattern generation on a rehabilitation robot based on foot and pelvic trajectories. procedia iutam, 2: 109-127. doi: 10.1016/j.piutam.2011.04.012. [25] bovi g, rabuffetti m, mazzoleni p, ferrarin m. (2011) a multiple-task gait analysis approach: kinematic, kinetic and emg reference data for healthy young and adult subjects. gait & posture, 33(1): 6-13. doi: 10.1016/j.gaitpost.2010.08.009. [26] kirtley c. (2006) introduction., in clinical gait analysis, elsevier, 5-14. doi: 10.1016/b978-0-443-10009-3.50004-7. [27] malanga g., delisa j. (1998) clinical observation. in gait analysis in the science of rehabilitation. edited by delisa j. baltimore, diane publishing; pp 1-10. [28] winter da. (2009) biomechanics and motor control of human movement, 4th ed.: new jersey: john wiley & sons, inc. doi: 10.1002/9780470549148. 314 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 production of carrageenan by different strains of kappaphycus alvarezii cultivated in serang, indonesia anas zakaria1, egi nurul rahman1, ulin noor rahmani1, robert manurung1, noor illi mohamad puad2, muhammad yusuf abduh1* 1 school of life sciences and technology, institut teknologi bandung, jalan ganesha no. 10 bandung 40132 indonesia 2bioprocess and molecular engineering research unit, department of biotechnology engineering, kulliyyah of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia *corresponding author: yusuf@sith.itb.ac.id (received: 22nd january 2019; accepted: 26th june 2019; published on-line:2nd december 2019) abstract: kappaphycus alvarezii is one of the main seaweeds cultivated in indonesia. its use as a raw material for the kappa-carrageenan industry has increased its cultivation activities. however, standard cultivation protocol for kappaphycus alvarezii has yet to be well-documented, particularly on strain selection for kappa-carrageenan production. there are various strains of kappaphycus alvarezii grown in indonesia, specifically in serang, banten such as green, red, and yellowish green strains. in this study, growth rate, carrageenan yield, and gel strength from different strains of kappaphycus alvarezii were investigated. it was observed that the specific growth rate of green type (4.14% /day) differed significantly from the other two types (red; 3.41% /day and yellowish green; 3.47% /day). the red type had the highest yield of carrageenan (45.16%) followed by yellowish green (36.66%) and green strain (33.67%). gel strength was not significantly affected by the strain variations where the observed values for yellowish green, green, and red strain were 344.46, 316.91 and 313.10 g/cm2, respectively. green kappaphycus alvarezii had the highest biomass (0.27 g/cm/d) and carrageenan productivity (0.012 g/cm/d). it can be concluded that the green strain of kappaphycus alvarezii is the most suitable for cultivation in serang, particularly for the kappa-carrageenan industry. abstrak: kappaphycus alvarezii adalah sebahagian daripada rumpai air yang dituai di indonesia. penggunaannya sebagai bahan dasar kepada industri kappa-carrageenan telah menambah kepada aktiviti penuaian. walau bagaimanapun, protokol penuaian biasa bagi kappaphycus alvarezii adalah tertakluk pada dokumentasi penuh terutama dalam pemilihan strain pada penghasilan kappa-carrageenan. terdapat pelbagai jenis strain kappaphycus alvarezii yang tumbuh di indonesia, terutama di serang, banten seperti hijau, merah, dan strain hijau kekuningan. kajian ini, kadar pertumbuhan, hasil karaginan dan kekuatan gel daripada pelbagai strain kappaphycus alvarezii telah dikaji. didapati bahawa kadar pertumbuhan tertentu pada jenis hijau (4.14% /hari) berbeza ketara berbanding dari dua jenis lain (merah; 3.41% /hari dan hijau kekuningan; 3.47% /hari). jenis merah mempunyai hasil karaginan tertinggi (45.16%) diikuti oleh hijau kekuningan (36.66%) dan strain hijau (33.67%). kekuatan gel adalah tidak ketara mempengaruhi kepelbagaian variasi di mana nilai yang dipantau pada strain hijau kekuningan, hijau dan merah adalah 344.46, 316.91 dan 313.10 g/cm2, masing-masing. kappaphycus alvarezii hijau mempunyai biojisim tertinggi (0.27 g/cm/d) dan penghasilan karaginan (0.012 g/cm/d). kesimpulannya strain hijau kappaphycus 12 iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 alvarezii adalah lebih sesuai untuk disemai di serang terutamanya pada industri kappakaraginan. keywords: kappaphycus alvarezii; carrageenan yield; gel strength; productivity; specific growth rate 1. introduction kappaphycus alvarezii belongs to the rhodophyta group and its growing habitat is generally located at the top of the sub-territorial zone beneath the seawater tidal line on the rock or sand with moderate or medium speed ocean waves [1]. k. alvarezii has several strains that are distinguished mainly because of the difference in their color. it is the main source of kappa-carrageenan, a hydrocolloid that has been used extensively as an additive in various industries such as food, cosmetics, and pharmaceutical industries [2,3]. carrageenan is a linear sulfated polysaccharide made up of a repeating disaccharide sequence of α-d-galactopyranose linked 1,3 called the a residue and β-d-galactopyranose residues linked through positions 1,4 (b residues) that can be extracted from k. alvarezii [4]. k. alvarezii was firstly reported to be cultivated in the philippines back in 1970 [5]. then in the year 1985, with the increasing global demand for carrageenan, the cultivation of k. alvarezii made a debut in indonesia [6]. several factors, such as climate and weather conditions, ease, and low costs required for its cultivation have contributed to the vast amount of cultivation activities in indonesia [7]. the three strains commonly cultivated in serang, indonesia are red, green, and yellowish green strains. however, there is still a lack of reports regarding the characteristics of carrageenan produced from these strains. this study aimed to determine the effect of strain variations towards the yield and gel strength of the extracted carrageenan. the results would assist the local community in selecting a strain yielding a good quality of carrageenan to be cultivated in serang, indonesia. 2. materials and methods 2.1 cultivation of k. alvarezii the cultivation of k. alvarezii was carried out at desa lontar, kecamatan tirtayasa, kabupaten serang, banten, indonesia using the off-bottom method. the cultivation period in this study was set similar to the common practice in the field, namely 45 days. the cultivation parameters were: salinity of sea water ranging between 30 ppt 33 ppt; average water temperature of 32 c; sea water ph of 7.9-8.3; depth of sunlight penetration of 13.75 cm and received light intensity ranging between 59,100 – 62,400 lux. the shoots of vegetative growth of green, red, and yellowish green strains were obtained from desa lontar, serang. about 30 g of seaweed fragments were tied on polyethylene (pe) ropes and the spacing between those fragments were 5, 10, and 15 cm, respectively (fig. 1). the rope was then mounted on the pile horizontally. fig. 1: schematic diagram of k. alvarezii strains cultivation (a) green (b) yellowish green and (c) red with different spacing of seaweed fragments (5 cm, 10 cm and 15 cm). 13 iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 the fresh weight of each k. alvarezii strain was recorded every 7 days during the 45 days period of cultivation. the seaweed was then harvested after 45 days and the fresh weight was again measured. the growth rate (eq. (1)) was then calculated according to lignell and pedersen [8]. ℎ (%) = − 1 × 100 (1) where wt = fresh weight after 45 days (g); wi = initial fresh weight (g); n = cultivation period (45 days). 2.2 carrageenan extraction each strain of 45 days old k. alvarezii was sun-dried for 3 days until the water content reached 20-25%. extraction was carried out by adding 3 g of dried k. alvarezii to 4% naoh solution [9]. the process was carried out for 2 hours at 80 c with continuous stirring. the extract was vacuum-filtered and the carrageenan was recovered from the solution by precipitation with 5% kcl solution. the precipitate containing carrageenan was then again immersed in a 5% kcl solution prior to washing with water. the extracted carrageenan was dried in an oven at 105 c until a constant dry weight was achieved. the yield of carrageenan extract was calculated using eq. (2). (%) = ( ) . × 100% (2) 2.3 carrageenan extract analysis the gel strength of extracted carrageenan was determined by dissolving 1.5% on a weight basis (w/w) of carrageenan in an aqueous solution at 90 c. the solution was then poured into a plastic tube (15 mm in diameter) and left at the room temperature for 3 hours [10]. the gel strength was analyzed using a ta-xt plus texture analyzer (stable micro systems, england) by applying a 2 kg maximum force using a 1 cm (diameter) cylindrical probe. the probe pressed the gel at a rate of 2 mm/s. maximal penetration strength was considered as the gel strength, which was registered by the texture expert software (stable micro systems ltd., england). all analyses were conducted in triplicates. 2.4 estimation of carrageenan productivity the productivity of the cultivation process and carrageenan yield were determined based on the data of 10 cm cultivation spacing, 45 days cultivation time, as well as the growth rate and carrageenan yield for each k. alvarezii strain (eq. (3)).= ( − )/ (l x t) (3) where p = biomass productivity (g/cm/d); wt = the final weight of biomass (g), wi = weight of initial biomass (g), l = length of cultivation distance (cm), t is the cultivation time (d). the estimation of carrageenan productivity was calculated using eq. (4).= / (4) where cp = carrageenan productivity (g/cm/d); y = carrageenan yield (%) and md = mass of dried k. alvarezii after extraction with 25% of water (g), t is the cultivation time (d). 14 iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 2.5 statistical analysis all experiments in this study were carried out using a completely randomized design with one main factor: variation of the k. alvarezii strain (green, red, and yellowish green). each treatment was repeated three times (randomly). the data was processed using spss 23 for macbook pro at a 95% confidence level. 3. results and discussion 3.1 the growth of different strains of k. alvarezii the rate of biomass accumulation for k. alvarezii green strain for various cultivation spacing as shown in fig. 2 implies that the spacing did not significantly affect its growth rate (p> 0.05). similar observations were recorded for the red and yellowish green strains. hence, 10 cm spacing was further used and discussed in this study since it is the common distance used by the seaweed farmers in the serang area. the growth rate calculated using eq. (1) was then compared with the strains grown in real conditions at serang (fig. 3). the calculated and observed values were in a good agreement with each other and it indicates that eq. (1) can be used to estimate the rate of biomass accumulation of k. alvarezii. fig. 2: growth profile of k. alvarezii green strain at different cultivation spacing between seaweed fragments. the green strain of k. alvarezii had the highest growth rate (4.14 %/day) compared to red (3.41 %/day) and yellowish green (3.47 %/day) strains (fig. 4). the difference in terms of growth rate between the green strain and the other two strains were significant (p <0.05). this result is similar with what has been reported by munoz et al. [11] that green strain of k. alvarezii demonstrated a higher growth rate compared to the red strain. however, it was also reported that the red strain (3.8 %/day) achieved a slightly higher growth rate when compared to the green strain (3.4 %/day) [12]. meanwhile for the red strain in this study, the growth rate was lower than reported by munoz et al. [12], which ranged from 1.1 %/day to 3.8 %/ day but below the range that has been reported by hayashi et al. [2] (5.2-7.2 %/day). overall, the values of k. alvarezii growth rate indicated that the lontar village area, serang is a suitable place to cultivate k. alvarezii. this is because its growth rate falls within the range of 3-5 %/day which is the standard value to specify a suitable cultivation areas for k. alvarezii [1]. 15 iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 3.2 carrageenan yield and gel strength carrageenan yield is one of the parameters observed in this study. this is because the yield of carrageenan from the k. alvarezii extraction process would directly affect its productivity and economic value. the yield of carrageenan extract for three strains of k. alvarezii is depicted in fig. 5. the highest yield of carrageenan was produced by the red strain (45.16%) whereas the carrageenan yield from green and yellowish green strains were 33.67% and 36.66%, respectively. these values were higher than reported by hayashi et al. [2] which ranged between 20-32% and were comparable with the range (830%) reported by valderrama et al. [13]. the difference in the yield of carrageenan for each strain was obvious, especially between the green and red strains (fig. 5). this is possibly due to their pigment compositions. each pigment has a different absorption rate for the color spectrum, which will eventually affect the main product of photosynthesis which is carrageenan [14]. the results of the anova analysis suggest that strain variations had a significant effect on the carrageenan yield ((p < 0.05). carrageenan properties, such as gel strength, have made carrageenan into an additive in various industries. in this study, the gel strength varied from 313.10 344.46 g/cm2 (fig. 6). the minimum gel strength was found in the carrageenan extracted from the red strain (313.10 g/cm2) while the maximum one was produced by the yellowish green strain (344.46 g/cm2). the results of the anova analysis suggest that strain variations did not have a significant effect on the gel strength ((p > 0.05). the gel strength values were higher compared to the one reported previously which ranged from 3 to 112 g/cm2 [15]. however, carrageenan gel strength in this study was lower compared to the carrageen quality standard set by the food and agriculture organization (fao) which lies in the range of 900 and 1200 g/cm2 [16, 17] as well as from the values reported by basmal et al. [18] which lie in the range of 1029-1243 g/cm2. variations in the reported gel strength values might be due to different carrageenan extraction processes. the yield and quality of carrageenan produced is not only influenced by the strains of seaweed that are being cultivated but also by several biological and environmental parameters such as plant age, light, nutrient, temperature, and salinity of the seawater [2, 19-24]. there could be other factors that contribute to the differences in the results achieved in this study with other reported results from studies conducted in different places. 3.4 comparison of biomass and carrageenan productivity the biomass productivity was estimated based on the difference between the final and initial weight of k. alvarezii during 45 days of cultivation on polyethylene rope with a 10 m spacing between seaweed fragments. the cultivation was carried out for 45 days following the common practice in the field that the final weight of the biomass may have reached up to 400% of its initial weight [25]. it has been reported in a previous study that the highest biomass productivity of k. alvarezii was recorded after 44 days of cultivation, after which it started to decline when the cultivation period was prolonged to 59 days [2]. in another study, it is also reported that k. alvarezii that was cultivated for 45 days had a higher neutrophic activity than k. alvarezii that was harvested sooner (15 days) [26]. in this study, the percentage of biomass increase varies for all the three strains with the green strain having the highest percentage of biomass increase (496%) followed by the yellowish green strain (349%) and the red strain (337%). 16 iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 (a) (b) (c) fig. 3: actual and modelled biomass accumulation rate for various k. alvarezii strain (a) green, (b) red, (c) yellowish green strains. 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 fr es h w ei gh t ( g) time (day) model actual 0 20 40 60 80 100 120 140 160 0 10 20 30 40 50 fr es h w ei gh t ( g) time (day) model actual 0 20 40 60 80 100 120 140 160 0 10 20 30 40 50 fr es h w ei gh t ( g) time (day) model actual 17 iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 fig. 4: growth rate of k. alvarezii for different strain variations. fig. 5: comparison of carrageenan yield for different strains of k. alvarezii. fig. 6. comparison of carrageenan gel strength for different k. alvarezii strains. there is no significant difference for each strain type. 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 green red yellowish green g ro w th r at e (% /d ay ) 0,00 10,00 20,00 30,00 40,00 50,00 green red yellowish green y ie ld o f c ar ag ee na n (% ) 0 50 100 150 200 250 300 350 400 green red yellowish green g el s tr en gt h (g /c m 2 ) 18 iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 in a previous study on the cultivation of k. alvarezii using a longline method in southwest sulawesi, the biomass was cultivated for 40 days and recorded a percentage of biomass increase of 350% [27]. the study also compared a different cultivation technique, namely floating cage, and reported a higher percentage of biomass increase of 676%. several studies have reported the advantages of the floating cage method as compared to the longline method because it provides a protection to the seaweed from various herbivores and has a higher biomass productivity [27,28]. however, a longline method was used in this study due to the low depth of the cultivation area in serang. moreover, the longline method has been widely used by seaweed farmers in the serang area for cultivating k. alvarezii. overall, the productivity of the green strain in terms of biomass and carrageenan was the highest among the strains (table 1). the biomass productivity of the green strain was 0.27 g/cm/d while the red and yellowish green strains were 0.16 g/cm/d and 0.17 g/cm/d. the results resemble the biomass productivity of 0.22 g/cm/d reported in a previous study for the cultivation of k. alvarezii using a longline method in southwest sulawesi [27]. based on the yield of carrageenan obtained in the previous section, the estimated productivity of carrageenan in ascending order for yellowish green, red and green are 0.008, 0.01 and 0.012 g/cm/d, respectively. although several studies have reported the yield of carrageenan extraction process, studies that provide estimation on carrageenan productivity are still very scarce. hence, the estimated carrageenan productivity reported in this study may provide useful information to produce carrageen from k. alvarezii. table 1: productivity of k. alvarezii strains strain productivity (g/cm/d) biomass carrageenan green 0.27 0.012 red 0.16 0.010 yellowish green 0.17 0.008 4. conclusion in brief, variations of cultivation spacing between seaweed fragments did not affect the growth rate of k. alvarezii. on the other hand, different strains of k. alvarezii showed different growth rates and carrageenan yields. the green strain recorded the highest growth rate (4.14% /day) while the highest carrageen yield (45.16%) was produced by the red k. alvarezii strain. green k. alvarezii had the highest biomass productivity (0.27 g/cm/d) as well as carrageenan productivity (0.012 g/cm/d) compared to the other two strains. these observations can be used as a reference in selecting k. alvarezii strain to be cultivated in the area of serang, banten. references [1] mchugh dj. (2003) a guide to the seaweed industry. food and agriculture organization of the united nations. [2] hayashi l, oliveira ec, bleicher-lhonneur g, boulenguer p, pereira rtl, von seckendorff r, shimoda vt, leflamand a, vallée p, critchley at. (2007) the effects of selected cultivation conditions on the carrageenan characteristics of kappaphycus alvarezii (rhodophyta, solieriaceae) in ubatuba bay, são paulo, brazil. journal of applied phycology, 19: 505-511. 19 iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 [3] masarin f, cedeno fr, chavez eg, de oliveira le, gelli vc, monti r. (2016) chemical analysis and biorefinery of red algae kappaphycus alvarezii for efficient production of glucose from residue of carrageenan extraction process. biotechnology for biofuels, 9:122. [4] campo vl, kawano df, silva dbd, carvalho i. (2009) carrageenans: biological properties, chemical modifications and structural analysis – a review. carbohydrate polymers, 77(2): 167-180. [5] azanza-corrales r, sa-a p. (1990) the farmed eucheuma species (gigartinales, rhodophyta) in danajon reef, philippines: carrageenan properties. hydrobiologia, 204(1): 521-525. [6] luxton dm. (1993) aspects of the farming and processing of kappaphycus and eucheuma in indonesia. hydrobiologia, 260(1): 365-371. [7] wwf-indonesia tp. (2014) better management practices (bmp)budidaya rumput laut jenis kotoni (kappaphycus alvarezii), sacol (kappaphycus striatum), dan spinosum (eucheuma denticulatum). indonesia: wwf-indonesia. [8] lignell å, pedersén m. (1989) agar composition as a function of morphology and growth rate. studies on some morphological strains of gracilaria secundata and gracilaria verrucosa (rhodophyta). in: botanica marina; pp 219. [9] minghou j. (1990) processing and extraction of phycocolloids. in: report on the regional workshop on the culture and utilization of seaweeds (vol. ii) bangkok, thiland: naca. [10] thrimawithana tr, young s, dunstan de, alany rg. (2010) texture and rheological characterization of kappa and iota carrageenan in the presence of counter ions. carbohydrate polymers, 82(1): 69-77. [11] munoz j, freile-pelegrin y, robledo d. (2004) mariculture of kappaphycus alvarezii (rhodophyta, solieriaceae) color strains in tropical waters of yucatan, mexico aquaculture, 239: 161-177. [12] hurtado-ponce aq. (1995) carrageenan properties and proximate composition of three morphotypes of kappaphycus alvarezii doty (gigartinales, rhodophyta) grown at two depths. in: botanica marina, pp 215. [13] valderrama d, cai j, hishamunda n, ridler n. (2013) social and economic dimensions of carrageenan seaweed farming. in: rome: food and agricultural organizarion (fao) fisheries and aquaculture technical paper, pp 217. [14] sunarto. (2008) karakteristik biologi dan peranan plankton bagi ekosistem laut. bandung: universitas padjajaran. [15] bono a, anisuzzaman sm, ding ow. (2014) effect of process conditions on the gel viscosity and gel strength of semi-refined carrageenan (src) produced from seaweed (kappaphycus alvarezii). journal of king saud university engineering sciences, 26(1): 39. [16] fao. (2003) a guide to the seaweed industry. rome: fao fisheries technical paper. [17] fao. (2007) carrageenan. fao jecfa monographs 4 2007; prepared at the 68th jecfa. [18] basmal j, ikasari d. (2014) production of semi refine carrageenan (src) from fresh kappaphycus alvarezii using modified technique with minimum use of fuel squalen bulletin of marine & fisheries postharvest & biotechnology, 9(1): 17-24. [19] freile-pelegrín y, robledo d. (2009) carrageenan of eucheuma isiforme (solieriaceae, rhodophyta) from nicaragua. in: nineteenth international seaweed symposium: proceedings of the 19th international seaweed symposium, held in kobe, japan, 26-31 march, 2007. edited by borowitzka ma, critchley at, kraan s et al. dordrecht: springer netherlands, pp 87-91. [20] glenn ep, doty ms. (2001) growth of the seaweeds kappaphycus alvarezii, k. striatum and eucheuma denticulatum as affected by environment in hawaii. aquaculture, 84(3):245-255. [21] hurtado aq, agbayani rf, sanares r, de castro-mallare mtr. (2001) the seasonality and economic feasibility of cultivating kappaphycus alvarezii in panagatan cays, caluya, antique, philippines. aquaculture, 199(3): 295-310. [22] de paula ej, pereira rtl, ohno m. (1999) strain selection in kappaphycus alvarezii var. alvarezii (solieriaceae, rhodophyta) using tetraspore progeny. journal of applied phycology, 11(1): 111-121. 20 iium engineering journal, vol. 20, no. 2, 2019 zakaria et al. https://doi.org/10.31436/iiumej.v20i2.1062 [23] mendoza wilson g, ganzon-fortes edna t, villanueva ronald d, romero jumelita b, montaño marco nemesio e. (2006) tissue age as a factor affecting carrageenan quantity and quality in farmed kappaphycus striatum (schmitz) doty ex silva. in botanica marina, pp 57. [24] mulyani s, tuwo a, syamsudin r, jompa j. (2018) effect of seaweed kappaphycus alvarezii aquaculture on growth and survival of coral acropora muricata. aacl bioflux, 11(6): 1792-1799. [25] kamlasi y. (2008) kajian kajian ekologis dan biologi untuk pengembangan budidaya rumput laut (euchuema cottonii) di kecamatan kupang barat kabupaten kupang nusa tenggara timur (tesis). sekolah pascasarjana institut pertanian bogor. [26] tirtawijaya g, meinita mdn, marhaeni b, hazque mn, moon is, hong yk. (2018) neutrophic activity of the carrageenophyte kapphycus alvarezii cultivated at different growth period in various areas of indonesia. evidence-based complementary and alternative medicine, 1-7. [27] kasim m, mustafa a. (2017) comparison growth of kappaphycus alvarezii (rhodophyta, solieriaceae) cultivation in floating cage and longline in indonesia. aquaculture reports, 6: 49-55. [28] kasim m, mustafa a, munier t. (2016) the growth rate of seaweed (eucheuma denticulatum) cultivated in longline and floating cage. aacl bioflux, 9(2): 291-299. 21 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <feff0054006f0074006f0020006e006100730074006100760065006e00ed00200070006f0075017e0069006a007400650020006b0020007600790074007600e101590065006e00ed00200064006f006b0075006d0065006e0074016f002000410064006f006200650020005000440046002000760068006f0064006e00fd006300680020006b0065002000730070006f006c00650068006c0069007600e9006d0075002000700072006f0068006c00ed017e0065006e00ed002000610020007400690073006b00750020006f006200630068006f0064006e00ed0063006800200064006f006b0075006d0065006e0074016f002e002000200056007900740076006f01590065006e00e900200064006f006b0075006d0065006e0074007900200050004400460020006c007a00650020006f007400650076015900ed007400200076002000610070006c0069006b0061006300ed006300680020004100630072006f006200610074002000610020004100630072006f006200610074002000520065006100640065007200200036002e0030002000610020006e006f0076011b006a016100ed00630068002e> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <feff0130015f006c006500200069006c00670069006c0069002000620065006c00670065006c006500720069006e0020006700fc00760065006e0069006c0069007200200062006900e70069006d006400650020006700f6007200fc006e007400fc006c0065006e006d006500730069006e0065002000760065002000790061007a0064013100720131006c006d006100730131006e006100200075007900670075006e002000410064006f006200650020005000440046002000620065006c00670065006c0065007200690020006f006c0075015f007400750072006d0061006b0020006900e70069006e00200062007500200061007900610072006c0061007201310020006b0075006c006c0061006e0131006e002e0020004f006c0075015f0074007500720075006c0061006e002000500044004600200064006f007300790061006c0061007201310020004100630072006f006200610074002000760065002000410064006f00620065002000520065006100640065007200200036002e003000200076006500200073006f006e00720061006b00690020007300fc007200fc006d006c0065007200690079006c00650020006100e70131006c006100620069006c00690072002e> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 effect of magnetic field on the physical and chemical properties of flowing lubricating cooling liquids used in the manufacturing process erkin odilov1, umidjon mardonov2*, khusniddin abdirakhmonov2, abdugani eshkulov1 and behzod rakhmatov3 1 faculty of mechanic, 2 faculty of machine construction, tashkent state technical university, tashkent, uzbekistan 3 faculty of chemical technology of inorganic substances, tashkent institute of chemical technologies, tashkent, uzbekistan * corresponding author: fff8uma@mail.ru (received: 5th january 2021; accepted: 5th march 2021; published on-line: 4th july 2021) abstract: in this paper, the effect of magnetic field on lubricating cooling liquids, which are used in the cutting process in manufacturing, was studied. we chose three different lubricating cooling liquids that are commonly used in local manufacturing factories to conduct the experiment. three main properties of these lubricoolants, boiling point, kinematic viscosity, and density, were analysed after magnetizing them. the magnetization processes were conducted in two conditions of liquids. at the first stage, the authors magnetized the liquids in stationary conditions; at the second stage, they magnetized the flowing liquids and analysed the difference among all the obtained results. this article shows the results of the comparisons and analyses the magnetic field influence on different types of fluids. moreover, the paper investigates the dependence of magnetic field strength on the influence of magnetic field on liquids. it was found that the examined three parameters of liquids were changed after magnetic field treatment. the finding of this research offered a simple approach to improve the lubricating and cooling process in machining details in manufacturing. abstrak: dalam makalah ini, pengaruh medan magnet pada cecair pendingin pelincir, yang digunakan dalam proses pemotongan dalam pembuatan, telah dikaji. kami memilih tiga cecair penyejuk pelincir berbeza yang biasa digunakan di kilang pembuatan tempatan untuk menjalankan eksperimen. tiga sifat utama pelincir ini seperti takat didih, kelikatan kinematik, dan ketumpatan dianalisis setelah memagnetkannya. proses pembesaran dilakukan dalam dua keadaan cecair. pada peringkat pertama, kami memagnetkan cecair dalam keadaan pegun dan membandingkan hasilnya; pada peringkat kedua, kami memagnetkan cecair semasa mengalir dan menganalisis perbezaan antara hasil yang diperoleh. artikel menunjukkan hasil perbandingan ini dan menganalisis pengaruh medan magnet pada pelbagai jenis cecair. lebih-lebih lagi, makalah ini meneliti pergantungan kekuatan medan magnet terhadap pengaruh medan magnet pada cecair. didapati bahawa tiga parameter cecair yang diperiksa diubah setelah rawatan medan magnet. penemuan penyelidikan ini menawarkan pendekatan mudah untuk meningkatkan proses pelinciran dan penyejukan dalam perincian mesin dalam pembuatan. keywords: boiling point; cutting, liquid; magnetic field; manufacture 327 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 1. introduction there are many scientific works about the effect of magnetic field on the physical and chemical properties of water. when liquids are exposed to magnetic field effects, they become magnetized liquids. nikolskiy et al. analytically and experimentally investigated the influence of magnetic and electric fields with tension gradient in the direction of the movement of the contacting gas-liquid phases [1]. rashid at al. presented an investigation of water evaporation through a magnetic field of 0.5 t, which was located at different locations of tested water height (water-air interface, water mid-height, and bottom) [2]. amiri and dadkhah investigated whether or not a physical water treatment reduces the surface tension of water, as reported in some scientific literature [3]. tritigin et al. studied the influence on the microflora of water-oiled lubricating cooling liquid of a weak electromagnetic pulse field [4]. ageev noted that one of the hypotheses explaining the effect of a weak magnetic field on biological objects is that water properties were changed by magnetic field [5]. hassan and rahmon’s study is a step towards gaining a better understanding of the effect of magnetism on water properties and on the biology of culture organisms, such as the brine shrimp, artemia salina. their study evaluated the effects of magnetic field exposure on water properties, which in turn affected the hatchability of a. salina [6]. baresel et al. have taken the concept of water treatment by functionalized magnetic particles one step forward by integrating the technology into a complete proof of concept, which included the preparation of surface-modified beads, their use as highly selective adsorbents for heavy metals ions (zinc, nickel), and their performance in terms of magnetic separation [7]. mardonov et al. studied the effect of magnetic field on the dynamic viscosity coefficient of flowing water. they found that the dynamic viscosity coefficient of water changed after magnetization. they magnetized flowing water using different magnetic field strengths. after magnetization, they measured the coefficient and found that dynamic viscosity of water was decreased [8]. the effect of magnetic field on liquids is still a controversial issue, and there is a lack of research in this field. almost all of the research about magnetic field effect on liquids were conducted on water and the majority of that research was effectively used in the agriculture field. the authors of this paper suggest that use of magnetic field treatment in the manufacturing process would have a great advantage. although many scientific works about the influence of magnetic field on some parameters of water have been reported from many studies, no scientific works analysed the effect of magnetic field on lubricating cooling liquids, which are used in cutting processes. kinematic viscosity, boiling point, and density are effectively the most important parameters of lubricating cooling liquids used in cutting processes. analysing the influence of magnetic fields on the properties of lubricants would help to increase the efficiency of machining and increase the wear resistance of the cutting tool. the purpose of this research work is to study the effect of magnetic field on these three properties of lubricating cooling liquids such as boiling point (heating from room temperature until the liquids boil), kinematic viscosity, and density. the experiment suggests that some parameters of liquids, such as boiling point, kinematic viscosity, and density were changed by the magnetic field. it is essential to point out that in this research, three different liquids were studied, including water, and the results were applicable for other types of liquids. it has been proven, here, that magnetic field treatment decreases the boiling point of any liquid with respect to the magnetic field strength. in addition, the effect of magnetic field on kinematic viscosity and density of liquids were investigated in this study. moreover, the influence of the magnetic field strength on magnetization effect was studied. 328 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 2. methods and materials 2.1 magnetization the first liquid (liquid-1) was tap water and it was from a local water supply company (“suvsoz”, uzbekistan), the second and the third liquids (liquid-2 and liquid-3) were taken from a local manufacturing factory (meridian-a). these three liquids were used as lubricating cooling liquids in the “meridian-a” manufacturing factory. the second liquid, liquid-2, was a compound of water and k2cr2o7 powder with 0.2% concentration. more accurately, m=50 grams k2cr2o7 powder was dissolved in m0=25 kg of water. lubricating cooling liquid with that concentration is used in cutting details made from mild steel. liquid3 is also a lubricating cooling fluid and it is mainly used for machining details where the material’s hardness is higher (hard alloys) than other details. it is a 5% concentration of special cutting fluid marked bm-76m with water. the magnetizing equipment umd-1 was developed for magnetizing liquids, the equipment consisted of 8 magnets, and the size of each magnet was 120x80x16 (length, width, height) with a minimum strength of 40 mt. the details of umd-1 magnetizing equipment are given in fig. 1. fig. 1: umd-1 magnetizing equipment. 1 – magnets on the top, 2 – magnets below, 3 – wooden part for separation. four magnets (1) were placed on the other four (2) with a gap between them. they were separated by a non-conductor material (3) between them. three types of magnetic field strength (40 mt, 60 mt, 80 mt) were selected to magnetize the liquids and magnetic field strength was controlled by changing the distance between magnets. more clearly, changing the non-magnetic parts with ones of different height, resulted in various magnetic field strengths. a pvc pipe was placed between the magnets, and its diameter was 10 mm. four hundred eighty mm of the polyvinyl chloride (pvc) pipe passed through umd-1 magnetizing equipment and this was the length of the magnetic field. when a liquid flowed through the pvc pipe, it turned into a magnetized liquid. all of the samples circulated at a flowing speed of 0.4 m/s for 30 min in umd-1 magnetizing equipment. the scheme of the magnetizing process is given in fig. 2. fig. 2: 1 – umd-1 magnetizing equipment, 2 – pvc pipe, 3 – container, 4 – pump, 5 – liquid, 6 – tap, 7 – flowing direction of the liquid. 329 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 the magnetic field strength, magnetizing condition, and velocity of liquids were considered as three influential factors that affected the changes caused by the magnetic field [9,10]. therefore, all of the experiments were conducted in the same laboratory conditions and the specification of the laboratory conditions is given in table 1. table 1: example system technical data item value atmospheric pressure 770 mmhg humidity 80% height above sea level 440 meter flowing speed of liquid 0.4 m/s diameter of the pvc 10 mm 2.2 measurement of the kinematic viscosity a capillary glass viscometer vpj-4 (fig. 3) is one of the commonly used devices to measure the viscosity coefficient of liquids and it was designed to determine the kinematic viscosity of liquids in accordance with gost 33-66. its range of measurement is from 0.6 mm2/s to 10000 mm2/s and it was very easy to measure and is also a popular method for measurement in laboratory conditions. capillary viscometer vpj-4 (fig. 3) is a device in the form of a u-shaped tube, the elbow (1) is soldered with the capillary (5). measuring viscosity by a viscometer is based on the determination of the time required for a certain volume of liquid to flow out through the capillary. (a) (b) fig. 3: vpj-4 capillary viscometer. 1, 2 – bend of the viscometer; 3 – discharge pipe; 4 – upper reservoir of the viscometer; 5 – capillary; 6 – lower reservoir of the viscometer; m1 and m2 – labels, limiting the measured volume of the lower reservoir viscometer. to determine the flow time to the discharge pipe (3), a rubber tube connected to a rubber bulb was inserted. then, holding the bend (2), the viscometer was turned over and the bend (1) was immersed in a reservoir with liquid. the liquid was sucked in (with a pear) to the m1 mark, without letting air bubbles form in the liquid. at the moment when the liquid reached the m2 mark, the device was removed from the vessel and immediately turned over to its original position. excess fluid was removed from the bend (1), the rubber tube was removed from the bend (2), and it was put on the bend (1). then, the viscometer was placed in the thermostat so that the expansion (4) was lower than the liquid level in the thermostat. it was kept in a thermostat for more than 30 minutes at a given temperature and then the 330 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 liquid was sucked into the bend to the level of one-third of the expansion (4). the rubber tube was disconnected and the time for the meniscus level to drop from the m1 mark to the m2 mark was measured with a stopwatch. the diameter of the capillary was 3.55 mm. the kinematic viscosity of the liquid was determined using the following eq. (1) [gost 33-66], 𝑉 = 𝑔 9.807 ∙ 𝑇 ∙ 𝐾 (1) where, k – constant of the viscometer (9.224 mm2/s2 according to gost 33-66) v – kinematic viscosity of liquid [mm2/s] t – liquid flow time in seconds g – acceleration of gravity [m/s2] 2.3 measurement of the density density is one of the main physical quantities that characterizes the properties of a substance. when exercising control over technological processes and product quality, measuring the density of substances plays an essential role. it is known that to determine the density of a solid or liquid, it is sufficient to define the ratio of body weight to its volume. on the other hand, the ratio of the densities of a solid and a liquid determines, for example, the condition for the floating of a solid in a liquid, and the values of their density are the magnitude of the pushing forces from the liquid and the weight of the body inside the liquid. this relationship opens the ability to measure density through the interaction of a liquid and a solid immersed in that liquid. in our experiment, we used the densimeter with second class of accuracy according to gost 1300-57 and its measurement range was from 1.000 to 1.800 (fig. 4). (a) (b) fig. 4: 1 – liquid; 2 – densimeter; 3 – density measuring scale of the densimeter; 4 – tanker, 5 – ballast. densimeters and hydrometers are commonly used to measure the density of different types liquids. the densimeter is a glass float of constant mass and volume, the expanded (lower) part of which is filled with ballast – clean and dry metal shot, filled with a layer of resin with a melting point of at least 80 °c. thanks to the ballast (5), the densimeter is in a vertical position during measurements. in the upper thinned part of the float, there is a scale graduated in units of density. the use of a densimeter to determine the relative density of a liquid is based on archimedes' law, therefore, the upper divisions of the scale correspond to 331 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 the lowest density, and the lower divisions correspond to the highest density. the readings are counted along the lower meniscus of the fluid. in the manufacturing and canning industry, sets of standard general-purpose densimeters of at least 2nd class of accuracy are used, calibrated to measure the relative density at a temperature of 20 °c with a measurement range from 0.7000 to 1.840 or from 820 to 1840, respectively. 2.4 measurement of the boiling point the tp300 (fig. 5) digital thermometer (xi′an lonn m&e equipment co., ltd., china) was used to measure the boiling point of magnetized and non-magnetized liquids under different conditions. the boiling point is determined by the nature of the substance and depends on external pressure. it is a characteristic of bodies located only in solid-state and for high molecular weight compounds. to determine the boiling point of fluids, we took a container and filled it with liquid (100 ml), and started to heat. while heating we put a tp300 digital thermometer into the liquid and marked the boiling point of the liquid. fig. 5: tp300 digital thermometer (measurement range is from -50 oc to +300 oc). 3. results and discussion 3.1 effect of magnetic field on the boiling point of lubricating cooling liquids the digital thermometer recorded the boiling point of the three different liquids. as stated above, three different liquids were analysed under the influence of magnetic field with three different magnetic field strengths (40 mt, 60 mt, and 80 mt). to compare the results, at first, the boiling point of liquids without magnetic field effect was measured under laboratory conditions. second, the magnetic field was affected, with a mfs of 80 mt, to liquids in a stationary condition (not flowing) and the results were compared. the boiling point results were consistent with reports in the literature that the boiling point of water increases after magnetic field treatment [11]. figure 6 shows the difference between the obtained results. it is noticeable from fig. 6 that liquids under the effect of magnetic field in peace (still) condition, have lower boiling point than their natural boiling point. every liquid’s natural boiling points differed from each other, but when they were affected by the magnetic field, there was difference between boiling points of magnetized liquids in peace condition and non-magnetized liquids. then the effect of the magnetic field with different mfs on flowing liquids was analysed. after 30 minutes of magnetic treatment under each magnetic field strength in the same laboratory condition, as specified in table 1, the following results, given in fig. 7, were obtained. 332 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 fig. 6: the boiling point of not-magnetized and magnetized (in peace condition) liquids. fig. 7: the boiling point of not-magnetized and magnetized (in the flowing condition) liquids. the boiling point is one of the main physical parameters of fluids and its value might be changed under the effect of the magnetic field. the boiling point of liquids depends on the condition and other parameters of liquids such as atmosphere and properties of fluids. as can be seen in fig. 7, the boiling point of magnetized liquids decreases as magnetic field strength increases. the difference between boiling point of not magnetized and magnetized fluids (in the flowing condition) under the 80 mt of magnetic field strength were 1.9 oc for liquid-1, 3 oc for liquid-2, and 2.2 oc for liquid-3 respectively. in addition, it is interesting to note that the higher the magnetic field strength the lower the boiling point of the liquids. the lowest boiling point was determined in 80 mt magnetic field strength. it was found that, if magnetic field strength was increased the effect of magnetic field on liquids was also increased. 3.2 effect of magnetic field on the kinematic viscosity coefficient of lubricating cooling liquids viscosity coefficient is one of the important properties of lubricating cooling liquids used in the machining process in manufacturing. analysing the effect of magnetic field on that parameter of liquids will help to increase the efficiency of the manufacturing process. 333 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 under laboratory conditions, the vpj-4 measuring device was used to record the results. this device commonly used in uzbekistan. to analyze the effect of the magnetic field on the viscosity coefficient of liquids, the three different lubricating cooling liquids in stationary condition were magnetized for 30 minutes. eight permanent magnets with 80 mt magnetic field strength were used to make the magnetizing condition. then, the viscosity coefficient of unmagnetized and magnetized (in peace condition) liquids (fig. 8) were compared. it is clear from the data given in fig. 8, that under the influence of the magnetic field, the kinematic viscosity coefficient of each liquid decreased noticeably. the difference between kinematic viscosity coefficient of unmagnetized and magnetized liquids were 0.323 mm2/s for liquid-1, 0.057 mm2/s for liquid-2, and 0.156 mm2/s for liquid-3. fig. 8: the kinematic viscosity coefficient of not magnetized and magnetized (in peace condition) liquids. following this experiment, the influence of the magnetic field on flowing liquids was assessed. a umd-1 magnetizing device was used to magnetize the flowing liquids. lubricating cooling liquids passed through the umd-1 magnetizing device at 0.4 m/s. the diameter of the pipe, which was used to pass flowing liquid through the umd-1, was 10 mm. after 30 minutes of the magnetizing process, the kinematic viscosity of liquids was measured and the results are given in fig. 9. fig. 9: viscosity coefficient of not magnetized and magnetized (in flowing condition) liquids in different magnetic field strengths. 334 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 results given in fig. 9 show that a magnetic field can cause a decrease in the viscosity coefficient of flowing liquids. moreover, the viscosity coefficient of flowing liquids depends on the magnetic field strength, because as the strength of the magnetic field increases, the kinematic viscosity of liquids decreases. the lowest viscosity coefficient was determined under the influence of the highest magnetic field strength (80 mt). comparisons show that the value between the unmagnetized and magnetized liquids, under the highest mfs, were 1.246 mm2/s for liquid-1, 0.803 mm2/s for liquid-2, and 0.295 mm2/s for liquid3. it was also found that the effect of magnetic field on flowing and not flowing liquids depends on the properties of the liquids. it is clear from the numbers obtained in figs. 8 and 9 that liquid-1 was affected by the magnetic field more than the other two liquids. liquid-3 had the least change among the three liquids after magnetization. because the concentration of liquid-3 has more components than other liquids and its crystals are differentiated from tap water (liquid-1) more than liquid-2. it is investigated that the greater the percent concentration of liquids, the less the magnetization effect on the liquids. 3.3 effect of magnetic field on the density of lubricating cooling liquids the magnetic field effect on the density of lubricoolants is also important in machining details in the manufacturing process. for the purpose of increasing efficiency in machining details, the effect of magnetic fields on the density of liquids was given greater attention by authors. as above, at first, the difference between the density of unmagnetized and magnetized (in peace condition) liquids was compared. there were also differences among the obtained results (fig. 10). figure 10 shows that after magnetizing liquids, their density increased and the differences were 0.002 g/cm3 for liquid-1, 0.001 g/cm3 for liquid-2 and 0.002 g/cm3 for liquid-3. fig. 10: the density of unmagnetized and magnetized (in peace condition) liquids. when the flowing liquids were magnetized in different magnetic field strengths, the results changed noticeably with respect to the magnetic field strength. the results, which were taken in the same laboratory conditions, are given in fig. 11. despite the fact that the density of the liquids differed from each other in the same conditions, the density of each liquid was increased after 30 minutes of the magnetization process while they were flowing (fig. 11). the density of the first sample was 1.000 g/cm3 before magnetization, but it reached to 1.005 g/cm3 after magnetizing at 40 mt. when the mfs increased to 80 mt, the density reached its highest point in the experiment (1.007). liquid-2 and liquid-3 also increased from 1.002 g/cm3 to 1.006 g/cm3 and from 1.009 g/cm3 335 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 to 1.011 g/cm3 respectively. in fact, the highest density was obtained at 80 mt of magnetic field strength. fig. 11: the density of unmagnetized and magnetized (in flowing condition) liquids in different magnetic field strengths. a decrease in the viscosity coefficient after magnetic field treatment was found. when magnetic field influences liquids, their crystals are regulated in the magnetic field direction by the magnetic field. this regulation of crystals causes a decrease in the viscosity coefficient after magnetic field treatment. moreover, the regulation of crystals causes an increase in the density after magnetic field treatment. also, it has been explored that, the effect of magnetic field on liquids depends on the properties of fluids, or more accurately, in the same laboratory condition and same magnetic field strength, magnetic field influence was different on various liquids. it is worth noting that the influence of a magnetic field on liquid depends on what kind of chemical elements are dissolved in the liquid. moreover, the maximal change in all of the experiments was obtained at 80 mt of magnetic field strength while the lowest change was reached at 40 mt of magnetic field strength. obtained results are very influential to manufacturing processes because the changes in these parameters of liquids have an impact on the wear resistance of the cutting tool used in the machining process. the influence of magnetized lubricating cooling liquids on the wear resistance of cutting tools helps to increase the efficiency in the machining process and saves energy [8,15,16]. however, this issue about magnetic field treatment of liquids remains controversial. complete understanding of the influence of magnetic fields on fluids has a great impact on agriculture, industry, and other fields [12-14]. some scientists are working on the issue of magnetic field treatment of water, but there lack of researches on this issue, especially the magnetic field effect on different liquids. 4. conclusion the results obtained in the laboratory experiment showed that there was an increase in the density of liquids when they were affected by the magnetic field. in spite of the fact that the increase was not always noticeable on the density of fluids, it depended on the magnetic field strength. also, the density of water was more affected by the magnetic field than the other two dissolved liquids which means that the density of dissolved liquids is less likely to be influenced by the magnetic field. however, the influence of the magnetic field on the boiling point of dissolved liquids were about 1.5 times higher than tap water. in addition, 336 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 it was found that kinematic viscosity and boiling point of experimented liquids were decreased after magnetic field treatment. however, after magnetic field treatment of flowing liquid, the kinematic viscosity of liquid-1 decreased by 24% while the kinematic viscosity of liquid-2 and liquid-3 decreased by 8% and 19% respectively. the difference between the effect of magnetic field on stationary and flowing liquids was also examined and it was explored that flowing liquids were influenced more than liquids in stationary conditions. references [1] nikolskiy vy. (2017) primenenie elektromagnitnyx poley dlya intensifikatsii teplomassoobmena v sovmeщennyx gazojidkostnyx protsessax [application of electromagnetic fields to intensify heat and mass transfer in combined gas-liquid processes]. vostochno-yevropeyskiy jurnal peredovyx texnologiy, 3(8): 1729-3774. https://media.neliti.com/media/publications/307213-application-of-electromagnetic-fieldsfo-6a3064eb.pdf [2] rashid fl, hassan nm. (2013) increasing water evaporation rate by magnetic field. international science and investigation journal, 2: 61-68. http://isijournal.info/journals/index.php/isij/article/view/12 [3] amiri mc, dadkhah aa. (2006) on reduction in the surface tension of water due to magnetic treatment. colloids and surfaces a: physicochemical and engineering aspects: 278(1-3): 252-55. https://doi.org/10.1016/j.colsurfa.2005.12.046 [4] tyrtygin vn, sobgayda na, potexa vl, shayxiev ig, makarova ya. (2013) vliyanie elektromagnitnogo impulsnogo polya na mikrofloru smazochno-oxlajdayuщey jidkosti [influence of the electromagnetic pulse field on the microflora of the cutting fluid]. vestnik kazanskogo texnologicheskogo universiteta, 16(3):176-178. https://cyberleninka.ru/article/n/vliyanie-elektromagnitnogo-impulsnogo-polya-namikrofloru-smazochno-ohlazhdayuschey-zhidkosti/viewer [5] ageev im, shishkin gg, yeskin s. (2007) izuchenie vliyaniya nizkochastotnogo magnitnogo polya na vodu [study of the effect of low frequency magnetic field on water]. raditexnika i electronica, 28: 8-16. https://www.elibrary.ru/item.asp?id=10412034 [6] hassan sm, ridzwan ar. (2016) effects of exposure to magnetic field on water properties and hatchability of artemia salina. arpn journal of earth sciences, 11(11): 416-23. [7] christian b. (2019) functionalized magnetic particles for water treatment. heliyon, 5(8): 17. https://doi.org/10.1016/j.heliyon.2019.e02325 [8] umarov eo, mardonov ut, shoazimova uk. (2020) influence of the magnetic field on the viscosity coefficient of lubricoolant that is used in the cutting proces. international journal of mechatronics and applied mechanics, 8(2): 144-149. https://www.doi.org/10.17683/ijomam/issue8.50 [9] liu b, gao b, xu x. (2011) the combined use of magnetic field and iron-based complex in advanced treatment of pulp and paper wastewater. chem eng j, 178(1): 232-238. https://doi.org/10.1016/j.cej.2 011.10.058 [10] manyà jj, jr mja, kinoshita ck, stephen mm. (2011). specific heat capacity of pure water at 4.0 mpa between 298.15 and 465.65 k. ind eng chem res, 50(10): 6470-6484. https://doi.org/10.1021/ie102462g [11] youkai wang, huinan wei, zhuangwen li. (2018) effect of magnetic field on the physical properties of water. results in physics, 8: 262-267. https://doi.org/10.1016/j.rinp.2017.12.022 [12] wang xy, zhang b, gong z, gao k, ou y, zhang j. (2013) the effect of a static magnetic field on the hydrogen bonding in water using frictional experiments. j mol struct, 1052(11): 102-104. https://doi.org/10.1016/j.molstruc.2013.08.021 [13] cai r, yang h, he j, zhu w. (2009) the effects of magnetic fields on water molecular hydrogen bonds. j mol struct, 938(1-3): 9-15. https://doi.org/10.1016/j.molstruc.2009.08.037 [14] toledo ejl, ramalho tc, magriotis zm. (2008) influence of magnetic field on physical– chemical properties of the liquid water: insights from experimental and theoretical models. j mol struct, 888(1-3): 409-415. https://doi.org/10.1016/j.molstruc.2008.01.010 337 https://media.neliti.com/media/publications/307213-application-of-electromagnetic-fields-fo-6a3064eb.pdf https://media.neliti.com/media/publications/307213-application-of-electromagnetic-fields-fo-6a3064eb.pdf http://isijournal.info/journals/index.php/isij/article/view/12 iium engineering journal, vol. 22, no. 2, 2021 odilov et al. https://doi.org/10.31436/iiumej.v22i2.1768 [15] umarov eo, mardonov ut. (2020) analysing the effect of magnetic field on lubricoolant in machining process. international journal of applied research, 6(5): 347-352. https://www.allresearchjournal.com/archives/?year=2020&vol=6&issue=5&part=f&article id=6723 [16] turakhodjaev n, tashbulatov sh, zokirov r, tursunbaev s, baydullaev a. (2020) studying the scientific and technological bases for the processing of dumping copper and aluminum slags. journal of critical reviews, 7(11): 441-444. http://dx.doi.org/10.31838/jcr.07.11.79 338 http://dx.doi.org/10.31838/jcr.07.11.79 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 passively q-switched ytterbium-doped fiber laser employing samarium oxide as saturable absorber khairul nizam rusdi1, afiq arif aminuddin jafry2, nur farhanah zulkipli3, farina saffa mohamad samsamnun3, mohamad badrol hisyam mahyuddin3, sulaiman wadi harun3, mohd shahnan zainal abidin1 and norazlina saidin1 1 department of electrical and computer engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia 2 department of physics, faculty of science, universiti teknologi malaysia, 81310 skudai, johor, malaysia 3 photonics engineering laboratory, department of electrical engineering, faculty of engineering, university of malaya, 50603 kuala lumpur, malaysia * corresponding author: norazlina@iium.edu.my (received: 13th march 2020; accepted: 13th august 2020; published on-line: 4th january 2021) abstract: the rapid developments in transition metal dichalcogenide materials as saturable absorbers (sas) have been reported to be efficient materials for generating q-switched fiber lasers. in this paper, we report on the use of samarium oxide (sm2o3) saturable absorber (sa) for 1-micron q-switched fiber laser generation. the sm2o3 thin film sa was constructed in-house through which the sm2o3 powder was mixed and stirred in polyvinyl alcohol (pva) solution. it was then integrated into the ytterbium-doped fiber laser (ydfl) ring cavity, hence producing a sequence of q-switched pulsed lasers at 1062.49 nm wavelength. the stable pulse train appeared from 69.97 to 111.1 khz between the applied pump power of 57 mw to 96 mw. the signal-to-noise ratio (snr) of 38.56 db was recorded at the 57 mw pump power, whereas the pulse energy raised until 15.21 nj at 96 mw. these results showed that the sm2o3 could be a favourable sa material to iniatiate q-switched ytterbium-doped pulsed fiber laser. abstrak: perkembangan pesat dalam bahan logam peralihan dichalcogenide sebagai bahan penyerap boleh larut (sas) telah dilaporkan sebagai kaedah yang berkesan bagi menjana laser fiber q-switched. kajian ini menggunakan samarium oksida (sm2o3) saturable absorber (sa) bagi menjana laser gentian q-switched 1-micron. filem nipis sm2o3 sa telah dihasilkan melalui campuran serbuk sm2o3 ke dalam cecair polivinil alkohol (pva) dalam persekitaran makmal. kemudian, ia diintegrasi ke dalam rongga gelang laser gentian dop-ytterbium (ydfl), lalu menghasilkan denyut laser q-switched stabil pada jarak gelombang 1062.49 nm. denyutan stabil muncul dari 69.97 kepada 111.1 khz pada kuasa pam yang dikenakan antara 57 mw hingga 96 mw. nisbah isyarat-hinggar (snr) pada 38.56 db telah direkodkan pada pam kuasa 57 mw, sementara denyut tenaga ditingkatkan kepada 15.21 nj pada 96 mw. keputusan menunjukkan sm2o3 merupakan bahan sa penggalak yang memuaskan bagi menjana denyut laser gentian dop-ytterbium q-switched. keywords: q-switched; sm2o3 saturable absorber; samarium oxide; ytterbium-doped fiber pulsed laser 58 iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 1. introduction a q-switched laser operating in the 1 to 2 µm region have gained research attention due to their vast applications in material fabrication, radar transmission, corrective eye surgery, remote sensing and biomedicine [1-5]. generation of q-switched lasers takes place once the losses inside the resonator surpass the gain in active medium, therefore bringing the quality factor to a low level. the losses are often introduced by acoustoor electro-optic active modulation that require externally driven components such as shutters, mirrors, and chopper wheels. these components are necessary as a voltage-controlled modulator to control the intracavity losses [6, 7]. although the frequencies of these active modulation techniques for pulsed laser generation are reliable and adjustable, they however acquired disadvantages; e.g being bulky and costly [8]. on the other hand, the passive method introduces simpler techniques and low fabrication costs. normally, a material-based saturable absorber (sa) is preferred for fabricating a real sa. its simpler implementation is such that the fabricated sa can be placed within the laser cavity for pulse generation. this simpler technique might stimulate the research on new sa materials for generating a pulsed fiber laser. studies on two-dimensional (2d) materials found that they have strong optical saturable absorption as is the case with carbon nanotubes (cnt) and graphene which are used as saturable absorbers (sa) that function as the nanotube film thickness. transition metal dichalcogenides (tmds) for instance; molybdenum diselenide (mose2), tungsten diselenide (wse2), molybdenum disulfide (mos2) and tungsten disulfide (ws2) have shown a good nonlinear absorption ability [9-11]. in view of the fact that layered tmds have a bandgap in the perceptible frequency range, they developed a strong saturable absorption at visible wavelengths. with bandgap modification for laser generation through mechanical exfoliation, the few-layers of tmds are turned into atomically thin layers. this then makes them compatible with pulsed initiation in the near-infrared region [12, 13]. likewise, black phosphorus (bps) was also proposed to initiate q-switching and mode-locked operation [14,15]. an orthorhombic structure of bps exhibits excellent chemical stability with the absence of high heat supply, and wide optical tunability in the near-infrared region [16]. however, according to [17] bps are highly sensitive to their environment, especially water, which can disrupt its stability as an effective sa for all-fiber laser configurations. hisyam et al. [15] reported a stable generation of mode-locked ytterbium-doped fiber lasers (ydfl) using bp layers as a sa, subsequently producing stable mode-locked pulses centered at 1085.58 nm with a repetition rate and pulse energy of 13.5 mhz and 5.93 nj, respectively. besides, luo et al. [18] also reported on generating all-fiber pulsed lasers at visiblewavelengths using 2d materials based on layered tmds (ws2, mos2 and mose2) as a sa. the work successfully generated a visible-wavelength passive q-switching laser at 635 nm with a repetition rate of 232 to 512 khz, and pulse width and pulse energy of ∼200 ns and 28.7 nj, respectively. of all reported 2d material-based sas for pulsed fiber laser generation, very few reported a q-switched laser generation for the 1-micron region that utilize tmd materials. use of ytterbium (yb) ions for 1 µm laser generation is widely known for its wide spectral coverage in short-band wavelengths from 0.98 to 1.2 μm [19, 20]. ytterbium-doped fiber possesses a low quantum defect due to its 2-level energy diagram and is therefore capable of providing high optical efficiencies and producing very low thermal load [21]. apart from that, aluminosilicate glass containing yb ions has broader emission with wavelengths longer than 1070 nm. it will be more susceptible to obtain lasing in the longwave spectral region allowing the glass to achieve a high level of inversion population which is needed to make the ydf transparent [20]. therefore, most reported works for high59 iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 power ydfls operated in 1060 to 1090 nm for the low absorption of yb ions [22-24]. this distinct optical characteristic of ydf and the wide application in the wavelength region has attracted much attention for researchers to focus on ydf. the q-switching generation in the 1-micron region using tmd materials as a q-switcher is not widely reported. apart from exhibiting excellent choice for q-switching generation, most of the tmds present complex fabrication procedures, low damage threshold, low modulation depth, and wavelength-dependent emission ability. thus, the search for a new material as sa in the allfiber laser cavity is ultimately relevant. previously, rare-earth oxide (reo) had also been manipulated as sa in near-infrared pulsed laser generation (1-2 µm) [25, 26]. das et al. [27] demonstrated samarium-doped fiber as sa for ytterbium-doped fiber lasers which successfully generated pulses in the 1 µm range. with a fast response time of 5 ns, samarium oxide (sm2o3) has excellent nonlinear absorption ability of 33% in a 1.5 µm regime [28, 29]. its thin film is reported to have high chemical and thermal stability, making it efficient for pulsed laser generation due to its ability to withstand high power illumination from laser pumps [30]. the excellent performance of sm2o3 thin film suggests its capability to initiate pulses in the near-infrared region as a new sa. in view of this, we demonstrated the sm2o3 thin film as sa in ydfl generating q-switched with a pulse width as short as 4.9 to 2.86 µs corresponding to a repetition rate of 69.97 to 111.1 khz. to the best of our knowledge, this work marks among the earliest demonstrations employing sm2o3 as sa for q-switching operation of ytterbium doped fiber laser. we hope that this work will open up other insights into research on 2d material photonics. 2. fabrication method samarium oxide (sm2o3) pva films were synthesized by mixing the sm2o3 powder into a polyvinyl alcohol (pva) solution [29]. initially, 120 ml of distilled water was used to dissolve 1 g of pva powder. this was done for 30 minutes on a magnetic mixer with speed and temperature of 300 rpm and 100 oc, respectively, until the pva powder completely dissolved and became a solution. next, 50 mg of sm2o3 grain was immersed into 50 ml of the prepared pva solution and stirred by magnetic stirrer at a speed of 300 rpm for 12 hours. finally, the sm2o3-pva solution was sonicated for 1 hour using an ultrasonic bath. upon completion, it was dispensed onto a petri dish and left to dry for 48 hours or more at room temperature, until it completely became a thin film. the synthesized sm2o3 pva film was characterized using the field emission scanning electron microscope (fesem), x-ray diffraction (xrd), linear absorption profile and nonlinear absorption profile. figure 1(a) shows the xrd analysis of sm2o3 film. figure 1(a) shows the diffraction peaks observed at 29.11o, 40.79o, and 50.27o. they can be assigned at (4 0 1), (-5 1 1), and (0 2 0) planes of sm2o3. the high and strong peak patterns of sm2o3 film xrd proves the successful implant of the sm2o3 film onto the pva polymer. figure 1(b) shows a homogenous distribution of sm2o3 particles and pva solution observed by fesem image. figure 1(c) shows the absorption loss of about 6 db near to 1040 nm, indicating the mode-locking process mainly corresponding to sm2o3. the nonlinear absorption profile of the sm2o3 can be seen via the balanced twin-detector measurement as shown in fig. 1(d). the point reference shows flat output transmission, while the sm2o3 thin film sa shows the result of nonlinear transmission which fitted accordingly. the transmissions at various input intensities were recorded. the sm2o3 thin film sa had a modulation depth of 33%, saturable intensity of 25 mw/cm2 and a nonsaturable absorption of 65%. the edx data in fig. 1(e) shows the element of samarium is 64.00% (wt) and 15.51% (at), oxygen (o) and carbon (c) from pva film is 32.68% (wt) and 74.43% (at), 3.31% (wt) and 10.06% (at), respectively. this data can confirm and 60 iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 prove the presence of the samarium element in this pva film. such characteristics of the sa reveals the ability of sm2o3 to act as good saturable absorber. fig. 1: characterization of sm2o3 pva film as sa (a) xrd (b) fesem (c) linear absorption profile (d) nonlinear absorption profile (e) energy dispersive x-ray. 3. experimental demonstration in order to perform a pulsed laser, the homemade sm2o3 sa thin film was integrated in the all-fiber ring cavity laser setup. as shown in fig. 2, the thin film sa that was placed between fiber ferrule was capped together using a fiber connector. each end of the connector was spliced to 90/10 coupler and wavelength division multiplexing (wdm). the 90/10 coupler was used to allow 90% of the power to oscillate back in the resonator. the feedback power hit the sa when the amplified spontaneous emission gain oscillated in the resonator. 61 iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 the 1064 nm wavelength division multiplexor (wdm) was spliced to the other end of the connector to form the resonator for oscillation. the 980/1064 nm wdm was used in the setup to compliment the 980nm laser diode and ~1064 nm wavelength laser that were built up from ytterbium-doped fiber (ydf) as a gain medium (2m), respectively. the isolator was placed after the ydf to prevent any unwanted signal feedback. the whole length of the ydfl cavity was approximately 9.5 m. the feedback process occurs continuously, hence accumulates the energy fed into the gain medium (ydf). when the resonator losses decrease until reaching saturation energy of the gain medium, the fiber laser will start to perform. in this experiment, an optical spectrum analyzer (anritsu ms9710c, 0.6 1.75 µm) and optical power meter (pm100d thorlabs) were used to record the spectrum and power, respectively from the 10% output of the coupler. the photodetector (det01cfc thorlabs ingaas biased detector) was attached to it to record the time and frequency domain of q-switched pulsed using an oscilloscope (gds-3352 350 mhz 5gs/s) and radio frequency (rf) spectrum (anritsu, 9 khz 7.8 ghz). fig. 2: the schematic for the q-switched ytterbium laser setup incorporating sm2o3 based saturable absorber (sa). 4. results and discussion by using homemade sm2o3 sa, the stable q-switching operation was obtained, as shown in figure 3. the generated q-switched pulses exhibit a pulse duration between 4.9 to 2.86 μs. the pulse pattern and its characteristic display the normal features of q-switched fiber lasers. unlike a mode-locked laser, in q-switching pulses, longer or shorter pulse duration is hard to determine with the modulation depth. however, it was suggested that the pulse width can be scaled down by preparing a sa with a higher modulation depth in a mode-locked case or having a short total cavity length. the inset of fig. 3 shows a stable pulse to pulse spectral range of 14.4 µs which translates into a repetition rate of ~69.97 khz, recorded when the pump power is 57 mw (at threshold). the pulse repetition rate shown in fig. 4(a) rises from 69.97 to 111.1 khz, while pulse width declines and becomes narrower, in the range of 4.9-2.86 µs, as opposed to the repetition rate. both outputs were plotted as a function of pump power ranging from 57 to 96 mw. in case of q-switching operation, the increase in pump power would cause the repetition rate to increase. higher pump power will increase the amplifier gain for ydf thereby contributing to the saturation of sa. the pulse energy was calculated given 8.96 nj using an equation of 62 iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 𝑄 [𝐽] = 𝑃0 𝑓𝑟 where 𝑃0 is the average output power and 𝑓𝑟 is the repetition rate. fig. 3: the measured oscilloscope trace for the q-switched laser at 69.97 khz. the inset shows the free spectral range for successive pulses. (a) (b) fig. 4: q-switched performance in terms of (a) pulse width repetition rate, (b) pulse energy and output power, versus pump power. stable passively q-switched operation was successfully obtained when the pump power was tuned in the range of 57–96 mw, resulting in the output power from 0.62 to 1.69 mw, as can be seen in fig. 4(b). the laser efficiency calculated from the output power versus pump power was 5.56% whereas the pulse energy trend was increasing from 8.96-15.21 nj. 63 iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 figure 5 and its inset exhibit the output laser power spectrum with and without the sm2o3 thin film, respectively. the central wavelength was positioned at 1062.49 nm, similar to the one observed in the q-switched laser (with sm2o3) exhibiting fwhm of ∼0.1 nm. the threshold power of the continuous wave (cw) was recorded to be 43 mw and the qswitched laser could be observed via oscilloscope at the pump power of 57 mw after further increment. the pulsed laser was successfully detected for 10 consecutive readings and sustained up to 96 mw. however, the q-switched pulsed laser showed instability and the pulses diminished when the pump power was increased further. in order to check whether our sm2o3 sa was able to withstand higher power, the pump power was increased to the maximum allowable threshold, which is 200 mw. as we tuned back the power to 96 mw, the q-switched pulses were observed as before. therefore, it is confirmed that the high pump power did not cost the perseverance of our homemade sm2o3 thin film sa. the excellent properties from our sm2o3 sa and high bandgap energy of 4.33 ev [30] contribute to the realization of q-switched fiber laser in the 1-micron region. nonetheless, if the nonsaturable losses could be reduced, the fiber laser performance might be improved. figure 6 recorded the relative rf spectrum analyzer when the pump power was 57 mw within 750 khz span measured using a 1 khz resolution bandwidth (rbw) and 300 hz video bandwidth (vbd). the signal-to-noise (snr) ratio of 38.56 db was observed at the fundamental rf peak when the repetition rate was 69.97 khz. this result indicates a stable q-switching operation. the harmonics in the rf spectrum decrease linearly before disappearing at the ninth harmonic. in this work, we also verified the generation of qswitching operation by taking out the connector that contains the sa. when the pump power was turned on up to 200 mw, no pulse was observed, however, when the sa was restored, the q-switched pulses were detected. hence, our q-switched pulse is confirmed due to our homemade sm2o3 sa. fig. 5: spectrum of cw laser (without sa) and q-switched laser (with sa). 64 iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 fig. 6: q-switched ydfl rf spectrum when the pump power is 57 mw. 5. conclusion this work successfully demonstrated a new 2d material, sm2o3 as a sa to generate passive q-switching operation for ydfl. the sm2o3 based sa was embedded with a pva solution to form the sm2o3 thin film. a piece of sm2o3 sa was attached between connectors and placed in the ydfl resonator. the q-switching operation was observed at a 1062.49 nm wavelength and the pulsed fiber laser was initiated at 57 mw. the pulse width and repetition rate were obtained in the range of 4.9-2.86 µs and 69.97-111.1 khz, respectively. the pulse energy was calculated as a change in output power over repetition rate, therefore giving the acceptable pulse energy ranging from 8.96 to 15.21 nj. a stable pulse generation was confirmed by a high snr of 38.56 db. our results suggest that the excellent properties of sm2o3 has led to the pulsed fiber laser generation in the 1-micron region. the outcome of this research may promote other related research and applications in the area of material cutting and manufacturing processes. acknowledgement this work was supported by the ministry of higher education (mohe), malaysia under the fundamental research grant scheme (frgs), grant no. [frgs/1/2018/ tk04/uiam/03/1]. references [1] raimondi mt, eaton sm, nava mm, laganà m, cerullo g, osellame r, (2012). twophoton laser polymerization: from fundamentals to biomedical application in tissue engineering and regenerative medicine. journal of applied biomaterials & functional materials, 10(1): 56-66. [2] shih pt, chen j, lin ct, jiang wj, huang hs, peng pc, chi s, (2009). optical millimeterwave signal generation via frequency 12-tupling. journal of lightwave technology, 28(1): 71-78. [3] hodge c, mcalinden c, lawless m, chan c, sutton g, martin a (2015). intraocular lens power calculation following laser refractive surgery. eye and vision, 2(1): 7. [4] masket s, masket se. (2006). simple regression formula for intraocular lens power adjustment in eyes requiring cataract surgery after excimer laser photoablation. journal of cataract & refractive surgery, 32(3): 430-434. [5] walsh bm, lee hr, barnes np. (2016). mid infrared lasers for remote sensing applications. journal of luminescence, 169: 400-405. 65 iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 [6] al-masoodi ah, ahmed mh, latiff aa, azzuhri sr, arof h, harun sw. (2017). passively mode-locked ytterbium-doped fiber laser operation with few layer mos2 pva saturable absorber. optik, 145: 543-548. [7] kuznetsov ag, podivilov ev, babin sa. (2015). actively q-switched raman fiber laser. laser physics letters, 12(3): 035102. [8] keller u (2003). recent developments in compact ultrafast lasers. nature, 424(6950): 831838. [9] hu p, liu f, huang y, liu y, han k, zhang f, liu x. (2019). passively q-switched ytterbium-doped fiber laser operating at 1120 nm by molybdenum disulfide saturable absorber. optik, 189: 97-102. [10] liu w, liu m, han h, fang s, teng h, lei m, wei z .(2018). nonlinear optical properties of wse 2 and mose 2 films and their applications in passively q-switched erbium doped fiber lasers. photonics research, 6(10): c15-c21. [11] wang qh, kalantar-zadeh k, kis a, coleman jn, strano ms. (2012). electronics and optoelectronics of two-dimensional transition metal dichalcogenides. nature nanotechnology, 7(11): 699. [12] aiub ej, steinberg d, de souza ea, saito la. (2017). 200-fs mode-locked erbium-doped fiber laser by using mechanically exfoliated mos 2 saturable absorber onto d-shaped optical fiber. optics express, 25(9): 10546-10552. [13] khazaeinezhad r, kassani sh, jeong h, yeom di, oh k. (2015). femtosecond soliton pulse generation using evanescent field interaction through tungsten disulfide (ws 2) film. journal of lightwave technology, 33(17): 3550-3557. [14] al-masoodi ah, yasin m, ahmed mh, latiff aa, arof h, harun sw. (2017). modelocked ytterbium-doped fiber laser using mechanically exfoliated black phosphorus as saturable absorber. optik, 147: 52-58. [15] hisyam mb, rusdi mf, latiff aa, harun sw. (2016). generation of mode-locked ytterbium doped fiber ring laser using few-layer black phosphorus as a saturable absorber. ieee journal of selected topics in quantum electronics, 23(1): 39-43. [16] li s, yin y, lewis e, garrell g, wang p. (2019). a twelve-wavelength thulium-doped fibre laser based on a microfibre coil resonator incorporating black phosphorus. optics communications, 437: 342-345. [17] island jo, steele ga, van der zant hs, castellanos-gomez a. (2015). environmental instability of few-layer black phosphorus. 2d materials, 2(1): 011002. [18] luo z, wu d, xu b, xu h, cai z, peng j, weng j, xu s, zhu c, wang f, sun z. (2016). two-dimensional material-based saturable absorbers: towards compact visible-wavelength all-fiber pulsed lasers. nanoscale, 8(2): 1066-1072. [19] pask hm, carman rj, hanna dc, tropper ac, mackechnie cj, barber pr, dawes jm. (1995). ytterbium-doped silica fiber lasers: versatile sources for the 1-1.2/spl mu/m region. ieee journal of selected topics in quantum electronics, 1(1): 2-13. [20] kurkov as. (2006). oscillation spectral range of yb-doped fiber lasers. laser physics letters, 4(2): 93. [21] paschotta r, nilsson j, tropper ac, hanna dc. (1997). ytterbium-doped fiber amplifiers. ieee journal of quantum electronics, 33(7): 1049-1056. [22] yu h, wang x, tao r, zhou p, chen j. (2014). 1.5 kw, near-diffraction-limited, highefficiency, single-end-pumped all-fiber-integrated laser oscillator. applied optics, 53(34): 8055-80599. [23] yan p, yin s, he j, fu c, wang y, gong m. (2011). 1.1-kw ytterbium monolithic fiber laser with assembled end-pump scheme to couple high brightness single emitters. ieee photonics technology letters, 23(11): 697-699. [24] jeong ye, sahu jk, payne dn, nilsson j. (2004). ytterbium-doped large-core fiber laser with 1.36 kw continuous-wave output power. optics express, 12(25):6088-6092. [25] muhammad ar, haris h, arof h, tan sj, ahmad mt, harun sw. (2018). all-fibre qswitching ydfl operation with bismuth-doped fibre as saturable absorber. journal of modern optics, 65(8): 946-950. 66 iium engineering journal, vol. 22, no. 1, 2021 rusdi et al. https://doi.org/10.31436/iiumej.v22i1.1396 [26] zhang h, lu sb, zheng j, du j, wen sc, tang dy, loh kp. (2014). molybdenum disulfide (mos 2) as a broadband saturable absorber for ultra-fast photonics. optics express, 22(6):7249-7260. [27] das g, chaboyer zj, navratil je, drainville ra. (2015). passively q-switched yb-and smdoped fiber laser at 1064 nm. optics communications, 334:258-264. [28] preda ce, ravet g, mégret p. (2012). experimental demonstration of a passive all-fiber qswitched erbium-and samarium-doped laser. optics letters, 37(4):629-631. [29] zulkipli nf, batumalay m, samsamnun fs, mahyuddin mb, hanafi e, izam tf, khudus mi, harun sw. (2019). nanosecond pulses generation with samarium oxide film saturable absorber. chinese physics letters, 36(7):074203. [30] dakhel aa. (2004). dielectric and optical properties of samarium oxide thin films. journal of alloys and compounds, 365(1-2):2 33-239. 67 finite element simulation of mems piezoelectric energy scavenger based on pzt thin film iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. finite element simulation of mems piezoelectric energy scavenger based on pzt thin film aliza aini md ralib1, nur wafa asyiqin zulfakher1, rosminazuin ab rahim, nor farahidah za’bah and noor hazrin hany mohamad hanif2 1department of electrical and computer engineering, 2department of mechatronics engineering, international islamic university malaysia, p.o. box 10, kuala lumpur 50728, malaysia. *corresponding author: alizaaini@iium.edu.my (received:27th aug 2018; accepted:24th jan 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.991 abstract: vibration energy harvesting has been progressively developed in the advancement of technology and widely used by a lot of researchers around the world. there is a very high demand for energy scavenging around the world due to it being cheaper in price, possibly miniaturized within a system, long lasting, and environmentally friendly. the conventional battery is hazardous to the environment and has a shorter operating lifespan. therefore, ambient vibration energy serves as an alternative that can replace the battery because it can be integrated and compatible to micro-electromechanical systems. this paper presents the design and analysis of a mems piezoelectric energy harvester, which is a vibration energy harvesting type. the energy harvester was formed using lead zicronate titanate (pzt-5a) as the piezoelectric thin film, silicon as the substrate layer and structural steel as the electrode layer. the resonance frequency will provide the maximum output power, maximum output voltage and maximum displacement of vibration. the operating mode also plays an important role to generate larger output voltage with less displacement of cantilever. some designs also have been studied by varying height and length of piezoelectric materials. hence, this project will demonstrate the simulation of a mems piezoelectric device for a low power electronic performance. simulation results show pzt-5a piezoelectric energy with a length of 31 mm and height of 0.16 mm generates maximum output voltage of 7.435 v and maximum output power of 2.30 mw at the resonance frequency of 40 hz. abstrak: penuaian tenaga getaran telah berkembang secara pesat dalam kemajuan teknologi dan telah digunakan secara meluas oleh ramai penyelidik di seluruh dunia. terdapat permintaan yang sangat tinggi di seluruh dunia terhadap penuaian tenaga kerana harganya yang lebih murah, bersaiz kecil dalam satu sistem, tahan lama dan mesra alam. manakala, bateri konvensional adalah berbahaya bagi alam sekitar dan mempunyai jangka hayat yang lebih pendek. oleh itu, getaran tenaga dari persekitaran lebih sesuai sebagai alternatif kepada bateri kerana ia mudah diintegrasikan dan serasi dengan sistem mikroelektromekanikal. kertas kerja ini membentangkan reka bentuk dan analisis tenaga piezoelektrik mems iaitu salah satu jenis penuaian tenaga getaran. penuai tenaga ini dibentuk menggunakan lead zicronate titanate (pzt-5a) sebagai lapisan filem tipis piezoelektrik, silikon sebagai lapisan substrat dan keluli struktur sebagai lapisan elektrod. frekuensi resonans akan memberikan hasil tenaga maksima, voltan tenaga maksima dan getaran jarak maksima. mod pengendalian juga memainkan peranan penting bagi 90 iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. menghasilkan tenaga yang lebih besar. reka bentuk yang mempunyai ketinggian dan panjang berlainan juga telah diuji dengan menggunakan bahan piezoelektrik yang sama. oleh itu, projek ini akan menghasilkan simulasi piezoelektrik mems yang sesuai digunakan bagi alat elektronik berkuasa rendah. hasil simulasi menunjukkan dengan panjang 31 mm dan ketinggian 0.16 mm, piezoelektrik pzt ini menghasilkan voltan maksima sebanyak 7.435 v dan tenaga output maksima 2.30 mw pada frekuensi resonans 40 hz. keywords: mems; piezoelectric energy harvester; pzt thin film 1. introduction recently, researchers have shown increasing interest in wireless sensor networks (wsn). wireless sensor networks have gained attention through many applications such as in industrial, medical, and military [1]. wsn has many advantages to the consumer because it is easier, costs less, has faster data transfer, and uses low power to save energy. however, one of the problems encountered while using wsn is that it requires a battery to supply power to sensor nodes, and that this battery presents limited capacity and limited life span. thus, the battery will negatively affect the performance of wsn. the best solution for this problem is to get a continuous supply of energy from the environment or by harvesting energy. energy harvesting is the term used to describe the process of converting ambient energy to electricity to power small electronic devices. energy harvesting can contribute both environmental benefits and new technological opportunities. it produces an environmentally friendly device, it reduces the cost, and it is easy to use. energy harvested from the surrounding environment can be used to run electronic devices directly to replace batteries for future use. there are three potential sources for energy scavenging: solar, wind, and vibration energy harvesting. for vibration energy harvesting, there are three mechanisms to generate power: piezoelectric, electrostatic, and electromagnetic [2]. mechanical vibration energy has a greater advantage in energy harvesting through wsn while solar and wind energy may not be suitable choices because of limited access to energy sources. the technique to harvest energy through electrostatic vibration is by converting kinetic energy to electrical energy by using a capacitor [3] while for electromagnetic vibration energy it can retrieve energy and generate voltage from the movement between a coil and a magnet [4]. most researchers have widely used piezoelectric vibration energy scavenging because of the device’s small volume. it is capable of generating electrical voltage when mechanical stress is applied. in addition, electrostatic and electromagnetic vibration energy scavenging are not the best choices because electrostatic requires a higher frequency than piezoelectric while electromagnetic has a complex design. piezoelectric energy harvesting is one of the effective methods for harvesting available ambient energy. piezoelectric energy harvesting is able to transform the applied strain energy into ambient electric energy or the ability to convert the mechanical vibrations into electric energy. piezoelectric thin films are usually fabricated in the form of a cantilever beam. one of the advantages of piezoelectric thin film is its compatibility with microelectromechanical system (mems) [5]. thus, the design and simulation of piezoelectric mems energy harvesting is proposed in order to reduce the cost, lengthen the operating life, and provide silicon compatibility. the aim of this project is to design and simulate a mems piezoelectric energy harvester. the energy harvester was formed using piezoelectric (pzt-5a) as the piezoelectric material, silicon as the substrate layer, and structural steel as the electrode layer. the rest of the paper is structured as follows. section 2 describes the 91 iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. design concept of mems piezoelectric energy scavenging. the results and analysis of finite element simulation is described in section 3. finally, the conclusion is shown in section 4. 2. theory and design concept piezoelectric energy harvesting is able to transform the applied strain energy into ambient electric energy or the ability to convert the mechanical vibrations into electric energy [10]. piezoelectric components are mechanically deformed in the presence of an electric field and produce an electrical charge if mechanical deformation occurs. a key aspect of piezoelectric is that it has greater power density and can easily be integrated into a system. it also can be in the form of a cantilevered beam with a couple of piezoceramic layers namely, unimorph and bimorph [6]. figure 1 shows the cross section of a mems piezoelectric energy scavenger with proof mass. the design consists of a lead zirconate titanate (pzt-5a), a structural steel electrode, and a silicon substrate. pzt thin film was chosen because it has very high stiffness and a large piezoelectric coefficient compared to zinc oxide (zno) and aluminum nitride (aln) thin piezoelectric thin films [7]. fig. 1: cross section of mems piezoelectric energy scavenger with proof mass. piezoelectricity is a coupling behavior of a material’s mechanical and electrical properties. it is the generation of electric field from applied pressure. the symmetrically charged crystal materializes the piezoelectricity electromechanical coupling. the cathode and anode charges are distributed in a crystal symmetrically. then, random orientation of ferroelectric domains is aligned by poling process. the poling consists of inducing dc voltage across the material. as a result of pressure being applied to the object, a negative charge is produced on the expanded side and a positive charge on the compressed side. after polarization process, the piezoelectric materials will undergo piezoelectric effects where it is divided into two different phenomenon: direct and converse piezoelectric effects. direct piezoelectric effect means the production of electricity when stress is applied. the resonance frequency is the natural frequency of vibration that is shown in equation (1). (1) where: f = resonance frequency of the vibration ϵ = young modulus of piezoelectric h = thickness of the beam 92 iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. l = length of the beam ρ = density of the material there has been a significant increase in research on piezoelectric materials and its properties as it has been proven to be valuable for energy scavenging applications. there are different types of piezoelectric materials for power harvesting. some are natural piezoelectric material (e.g. silk, dna and dentin), single crystals (e.g. zno, quartz and rochelle salt), polymers (e.g. polyvinylidene fluoride) and ceramics (e.g. sodium potassium niobate, lead zirconate titanate and barium titanate) [8-10]. table 1: comparison properties of piezoelectric materials piezoelectric material form d31 m/v quartz single crystal 2.30 pzt polycrystalline 320 pvdf film 23 zinc oxide film 14.3 as can be seen from table 1, pzt in polycrystalline form has the highest strain coefficient [11-12]. table 2 illustrates the material properties of pzt-5a. additionally, pzt also has a very broad range of dielectric constant. thus, it can be concluded that pzt shows an excellent piezoelectric material property and has been chosen as the dominant material for piezoelectric energy harvesting. table 2: material properties of pzt-5a parameter value density (kg/ ) 7750 elastic constants matrix (pa) [ ] 6x6 matrix [1] piezoelectric strain coefficient, d (c/ ) [ ] 3x6 matrix [2] relative dielectric constant, ] 3x3 matrix [3] poisson ratio 0.31 the elastic stiffnesss coefficients, piezoelectric strain coefficient and relative dielectric constant for pzt 5a thin film are shown in equation (2)-(4) (2) (3) 93 iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. (4) 3. finite element simulation the behavior of a piezoelectric mems energy harvester is described using finite element simulation. the objective of the simulation is to investigate the optimum dimension of the design on the output voltage and output power produced. the structure of the boundary condition is fixed at the base. the electric field in the dielectric is computed in this interface. a force is applied at the end of the proof mass. boundary load is used to apply pressure to boundaries. in meshing, the domain can be divided into triangular or quadrilateral subdivisions. a free triangular node has been used in this design to create a uniform triangular mesh in 2d domain. the element size is set to normal. then, the simulation is run using comsol multiphysics to determine the resonance frequency, output voltage and output power. the resonance frequency theory can be calculated using equation (1). table 3 and fig. 2 show the proposed design dimensions. the length and height of the piezoelectric are varied to analyze the effect of output voltage and power to the dimensions of the piezoelectric energy harvester. it should be noted that the chosen dimensions can be fitted into low power electronics devices for the purposes of wsn. table 3: proposed design dimensions design material length (mm) height (mm) substrate si 1 1 piezoelectric pzt 11,16,21,26,31,36,41 0.06, 0.11, 0.16, 0.21, 0.26, 0.31, 0.36, 0.41 electrode steel 20 0.04 fig. 2: 3d view of proposed design of mems piezoelectric energy scavenger with proof mass. 4. results and discussion simulation results of the piezoelectric energy harvester have been analysed in determining the resonance frequency, output voltage, and output power. the objective of 94 iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. this paper is to design a mems piezoelectric energy harvester that is able to produce optimum power at a low frequency vibration. this design is simulated and optimized using comsol software. frequency domain is a study to compute the response of a linear model when subjected into harmonic excitation for one or more frequencies. it solves the resonance frequency and the mode shape. the value of the resonance frequency, displacement and mode of the cantilever will be explained in the next section. the displacement mode of the cantilever beam is in 2d mode shape as shown in fig. 3. (a) (b) fig. 3: displacement of the piezoelectric energy harvester for 21 mm x 0.16 mm design at (a) 79 hz (b) 81 hz. from the simulation results, the design produced an output power of 2.30 mw and output voltage of 7.435 v as displayed in fig. 4. the simulation result shows the displacement of the cantilever with a value of 6.0 x mm and resonance frequency of 80 hz. fig. 4: output voltage and output power of piezoelectric energy harvester versus frequency for 21 mm x 0.16 mm design at 81 hz resonance frequency. 4.1 analysis of the effect of different pzt length on resonance frequency, output voltage, and output power for this analysis, the height of the piezoelectric is fixed while the length of piezoelectric is varied to different dimensions. variation of piezoelectric length will give a big impact on resonance frequency as shown in theory calculation. in this investigation, the length is varied in the range of 5 mm from 11 mm to 41 mm as depicted in table 4. from the simulation results, it can be seen that as the length of piezoelectric increases, the resonance frequency decreases, which agrees well with equation (1). 95 iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. table 4: cantilever performance for different pzt length height (mm) length (mm) resonance frequency (theory) resonance frequency (simulation) output voltage output power 0.16 11 280.30 260 2.625 0.287 0.16 16 132.50 130 3.481 0.505 0.16 21 77 81 5.400 1.220 0.16 26 50.20 60 3.053 0.388 0.16 31 35.30 40 7.435 2.300 0.16 36 26.17 30 5.728 1.367 0.16 41 20.20 30 2.444 0.248 figure 5(a) shows the frequency response for voltage. as the length of the piezoelectric increases, the resonance frequency shifts towards left side of the graph where it illustrates that the resonance frequency decreases. this is due to the fact that when the length of the pzt increases, the stiffness decreases. thus, the resonance frequency shifts to a lower value. varying the length can also affect the output voltage and output power. output power versus resonance frequency is plotted in fig. 5(b) for different lengths of pzt to show that varying the length can also affect the output power. the maximum power is obtained at the length of 31 mm with an output power of 2.3 mw. (a) (b) fig. 5: (a) resonance frequency vs output voltage, and (b) resonance frequency vs output power for different pzt length. in summary, the optimum length of the piezoelectric that is suitable to harvest energy is 31 mm because it produces a high voltage of 7.435 v and high output power of 2.3 mw with moderate resonance frequency value of 40 hz. 96 iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. fig. 6: pzt length vs resonance frequency at different pzt length. 4.2 analysis on effect of different pzt height on resonance frequency, output voltage, and output power a simulation on different heights of piezoelectric has been conducted to investigate the effect of the height of the piezoelectric towards resonance frequency. the length of the piezoelectric is maintained with the optimum value of 31 mm. the height is varied from 0.06 mm to 0.41 mm. table 5 below provides the simulation data on height of piezoelectric, resonance frequency, output voltage, and maximum power. table 5: cantilever performance for different pzt heights height (mm) length (mm) resonance frequency (theory) resonance frequency (simulation) output voltage output power 0.06 31 13.24 10 4.46 0.83 0.11 31 24.27 20 2.33 0.226 0.16 31 35.30 40 7.435 2.30 0.21 31 46.33 60 6.59 1.80 0.31 31 57.35 80 3.32 0.46 0.36 31 68.38 100 3.80 0.60 0.41 31 79.41 120 4.60 0.88 based on the results shown above, the variation of the height of the cantilever produces a higher resonance frequency. the resonance frequency increases from 10 hz to 140 hz. the simulation results were plotted as seen in fig. 7. it can be seen that the graph shifted towards the right side, which indicates that the resonance frequency is increased. these results are in good agreement with the theory calculation based on equation (1). varying the height not only affects the frequency but also affects the output voltage. as shown in the graph, the generated peak-to-peak voltage is obtained when the height of the piezoelectric is at 0.16 mm with resonance frequency of 40 hz. as displayed in figure 7, the maximum output power can be obtained by varying the height of the pzt. from the graph, the maximum power obtained is 2.30 mw and optimum at the height of 0.16 mm with resonance frequency of 40 hz. both simulation and theoretical results verified the fact that as the height of the piezoelectric increased, the resonance frequency also increased. therefore, the height of the pzt is at optimum when the output voltage which is 7.435 v and output power is at 2.30 mw with resonance frequency of 40 hz. the optimum dimension value obtained based on simulation results is shown in table 97 iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. 6. pzt has shown the best performance over zno because it can generate maximum output voltage and high output power even at low frequency. (a) (b) fig. 7: (a) resonance frequency vs output voltage, and (b) resonance frequency vs output power for different pzt height. fig. 8: pzt length vs resonance frequency for different pzt height. table 6: optimum dimension of piezoelectric energy harvester piezoelectric material height ( mm) length (mm) resonance frequency (simulation) resonance frequency (theory) output voltage output power pzt 0.16 31 40 35.30 7.435 2.30 5. conclusion this paper presented the finite element simulation of a mems piezoelectric energy scavenger based on pzt thin film. the energy harvester was formed using lead zicronate titanate (pzt-5a) as the piezoelectric thin film, silicon as the substrate layer, and structural steel as the electrode layer. the expected results have been obtained and analysed. the design consists of pzt-5a, a structural steel electrode, and a silicon substrate where it is simulated to gain a low frequency that can nevertheless generate a high peak-to-peak voltage and high maximum power. an analysis on the effect of the height of the piezoelectric on the 98 iium engineering journal, vol. 20, no. 1, 2019 md ralib et al. resonance frequency has been carried out in this research. based on the results provided above, it shows that the variation of the height of the cantilever will produce a higher resonance frequency (which increased from 10 hz to 140 hz). the optimum height of the piezoelectric, that can have a big impact on the output voltage, is 0.16 mm. therefore, when the height of the pzt is optimal, the output voltage is 7.435 v, output power is 2.30 mw, and the resonance frequency is 40 hz. hence, this work indicates that a mems piezoelectric energy scavenger based on pzt thin film has high potential for the future of wireless communication system. acknowledgement this research was also supported by research initiative grant scheme rigs16-083-0247 from international islamic university malaysia and ministry of higher education malaysia. references [1] zieliński m, mieyeville f, navarro d, bareille o. (2014). a low power wireless sensor node with vibration sensing and energy harvesting capability. in ieee computer science and information systems (fedcsis), federated conference: 7-10 september 2014; warsaw; pp. 1065-1071. [2] wei c, jing x. (2017). a comprehensive review on vibration energy harvesting: modelling and realization. renewable and sustainable energy reviews, 74: 1-18. https://doi.org/10.1016/j.rser.2017.01.073 [3] khan fu, qadir mu. (2016). state-of-the-art in vibration-based electrostatic energy harvesting. journal of micromechanics and microengineering, 26(10): 103001. https://doi.org/10.1088/0960-1317/26/10/103001 [4] li p, gao s, cai h. (2015). modeling and analysis of hybrid piezoelectric and electromagnetic energy harvesting from random vibrations. microsystem technologies, 21(2): 401-414. https://doi.org/10.1007/s00542-013-2030-6 [5] siddique arm, mahmud s, van heyst b. (2015). a comprehensive review on vibration based micro power generators using electromagnetic and piezoelectric transducer mechanisms. energy conversion and management, 106: 728-747. https://doi.org/10.1016/j.enconman.2015.09.071 [6] priya, s., song, h. c., zhou, y., varghese, r., chopra, a., kim, s. g., ... & polcawich, r. g. (2017). a review on piezoelectric energy harvesting: materials, methods, and circuits. energy harvesting and systems, 4(1), 3-39. [7] shung kk, cannata jm, zhou qf. (2007). piezoelectric materials for high frequency medical imaging applications: a review. journal of electroceramics, 19(1): 141-147. https://doi.org/10.1007/s10832-007-9044-3 [8] anton sr, sodano ha. (2007). a review of power harvesting using piezoelectric materials. smart materials and structures, 16(3): r1. https://doi.org/10.1088/0964-1726/16/3/r01 [9] ralib, a. a. m., nordin, a. n., & salleh, h. (2010). a comparative study on mems piezoelectric microgenerators. microsystem technologies, 16(10), 1673-1681. https://doi.org/10.1007/s00542-010-1086-9 [10] ramadan ks, sameoto d, evoy s. (2014). a review of piezoelectric polymers as functional materials for electromechanical transducers. smart materials and structures, 23(3): 033001. [11] kim hu, lee wh, dias hr, priya s. (2009). piezoelectric microgenerators-current status and challenges. ieee transactions on ultrasonics, ferroelectrics, and frequency control, 56(8),1555-1568. https://doi.org/10.1109/tuffc.2009.1220 [12] kim hs, kim jh, kim j. (2011). a review of piezoelectric energy harvesting based on vibration. international journal of precision engineering and manufacturing, 12(6): 11291141. https://doi.org/10.1007/s12541-011-0151-3 99 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <feff04180437043f043e043b043704320430043904420435002004420435043704380020043d0430044104420440043e0439043a0438002c00200437043000200434043000200441044a0437043404300432043004420435002000410064006f00620065002000500044004600200434043e043a0443043c0435043d04420438002c0020043f043e04340445043e0434044f044904380020043704300020043d04300434043504360434043d043e00200440043004370433043b0435043604340430043d0435002004380020043f04350447043004420430043d04350020043d04300020043104380437043d0435044100200434043e043a0443043c0435043d04420438002e00200421044a04370434043004340435043d043804420435002000500044004600200434043e043a0443043c0435043d044204380020043c043e0433043004420020043404300020044104350020043e0442043204300440044f0442002004410020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e0030002004380020043f043e002d043d043e043204380020043204350440044104380438002e> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <feff30d330b830cd30b9658766f8306e8868793a304a3088307353705237306b90693057305f002000410064006f0062006500200050004400460020658766f8306e4f5c6210306b4f7f75283057307e305930023053306e8a2d5b9a30674f5c62103055308c305f0020005000440046002030d530a130a430eb306f3001004100630072006f0062006100740020304a30883073002000410064006f00620065002000520065006100640065007200200036002e003000204ee5964d3067958b304f30533068304c3067304d307e305930023053306e8a2d5b9a3067306f30d530a930f330c8306e57cb30818fbc307f3092884c3044307e30593002> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <feff004c006900650074006f006a00690065007400200161006f00730020006900650073007400610074012b006a0075006d00750073002c0020006c0061006900200069007a0076006500690064006f00740075002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c0020006b006100730020007000690065006d01130072006f00740069002000640072006f01610061006900200075007a01460113006d0075006d006100200064006f006b0075006d0065006e0074007500200073006b00610074012b01610061006e0061006900200075006e0020006400720075006b010101610061006e00610069002e00200049007a0076006500690064006f0074006f0073002000500044004600200064006f006b0075006d0065006e00740075007300200076006100720020006100740076011300720074002c00200069007a006d0061006e0074006f006a006f0074002000700072006f006700720061006d006d00750020004100630072006f00620061007400200075006e002000410064006f00620065002000520065006100640065007200200036002e003000200076006100690020006a00610075006e0101006b0075002000760065007200730069006a0075002e> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <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> /suo <feff004b00e40079007400e40020006e00e40069007400e4002000610073006500740075006b007300690061002c0020006b0075006e0020006c0075006f0074002000410064006f0062006500200050004400460020002d0064006f006b0075006d0065006e007400740065006a0061002c0020006a006f0074006b006100200073006f0070006900760061007400200079007200690074007900730061007300690061006b00690072006a006f006a0065006e0020006c0075006f00740065007400740061007600610061006e0020006e00e400790074007400e4006d0069007300650065006e0020006a0061002000740075006c006f007300740061006d0069007300650065006e002e0020004c0075006f0064007500740020005000440046002d0064006f006b0075006d0065006e00740069007400200076006f0069006400610061006e0020006100760061007400610020004100630072006f0062006100740069006c006c00610020006a0061002000410064006f00620065002000520065006100640065007200200036002e0030003a006c006c00610020006a006100200075007500640065006d006d0069006c006c0061002e> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 90 investigation of the need for specific propagation model for specific environment based on different terrain characteristics jide julius popoola*, akinlolu adediran ponnle, yekeen olajide olasoji and samson adenle oyetunji department of electrical and electronics engineering, school of engineering and engineering technology, federal university of technology, p.m.b. 704, akure, ondo state, nigeria. * corresponding author: jjpopoola@futa.edu.ng (received: 9th dec 2017; accepted:12th july 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.886 abstract: owing to their speed of excution as well as their limited reliance on detailed knowledge of the terrain characteristics of the service environments, empirical propagation models have enjoyed general acceptability in the wireless communication research community. however, recent industrial observations show that no single propagation model can best fit all the radio service environments, which led to the hypothesis of specific models for specific environments. in order to scientifically verify this hypothesis, the study presented in this paper investigated the performance of the free space propagation loss (fspl) model in two different radio environments characterised with different types of obstructions. the investigation was conducted through field strength distribution measurement of two broadcasting radio stations transmitting at 96.5 mhz and 102.3 mhz. the field strength measurement data obtained were analysed. the result of the analysis shows gross disparity between the measured path losses and calculated path losses using fspl model. the disparity thus necessitates the modification of the fspl model in order to develop each propagation model for each of the two radio stations employed and their environment. the developed models were then evaluated to ascertain their performances relative to the fspl model. the performance evaluation results show that the predictions of the developed propagation models vary for each of the two environments. furthermore, the comparative performance evaluation result of the developed models with similar studies in the literature shows that the developed models perform favourably. the overall result from the developed models confirms the hypothesis that each location requires a specific propagation model for proper radio wave design and quality of signal transmission and reception. abstrak: kelebihan yang ada pada kelajuan perlaksanaannya dan juga kurang pergantungannya pada butiran terperinci ciri-ciri khusus bentuk rupa bumi di persekitaran servisnya, model penyebaran empirik telah diterima umum dalam komuniti kajian komunikasi tanpa wayar. walau bagaimanapun, pemerhatian industri terkini menunjukkan tidak ada sebarang model penyebaran yang sesuai bagi semua keadaan servis radio, ini menghala kepada hipotesis keperluan model tertentu pada keadaan servis tertentu. bagi menentusahkan secara saintifik hipotesis ini, kajian yang dibentangkan dalam kertas ini mengkaji tentang prestasi model kehilangan penyebaran pada ruang bebas (fspl) dalam dua persekitaran radio berlainan melalui beberapa jenis halangan berbeza. kajian telah dijalankan ke atas dua stesen radio penyiaran pada frekuensi 96.5 mhz dan 102.3 mhz melalui ukuran sebaran ruang keupayaan. data ukuran ruang keupayaan telah diperoleh iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 91 dan dianalisa. keputusan analisis menunjukkan keputusan tidak seragam yang melampau antara ukuran kehilangan laluan dan pada kiraan model fspl. ketidaksamaan ini memungkinkan keperluan mengubah model fspl bagi membangunkan model penyebaran pada setiap dua radio stesen yang digunakan dan persekitarannya. model yang dibangunkan ini kemudiannya dinilai bagi mengesahkan prestasinya dengan model fspl. keputusan penilaian menunjukkan perbezaan pada jangkaan model penyebaran bagi setiap dua keadaan. tambahan, keputusan perbandingan model yang dibangunkan dalam karya ini adalah serupa seperti kajian lain yang berkaitan. secara keseluruhannya model yang dibangunkan ini mengesahkan hipotesis bahawa setiap lokasi memerlukan model penyebaran bagi rekaan gelombang radio yang sesuai dan juga kualiti signal penyebaran dan penerimaan. keywords: obstructions; propagation mechanisms; path loss; propagation models; inverse square law 1. introduction outdoor natural and man-made obstructions, such as vegetation, rocks, buildings, and cars on radio wave paths do interfere with the radio wave propagation, thus causing radio signal reduction and poor reception. this is because interaction of radio waves with either natural or man-made obstructions reduces its strength. therefore, in radio communication systems where antennas are employed in transmitting information from the transmitter to the receiver, the channel between and/or around the transmitter and the receiver has a key influence on the quality of the transmitted radio signal. this is because radio wave propagation is highly sensitive to both the properties and effects of the communication channel between and/or around both the transmitting and the receiving antennas [1]. therefore, when the incoming radio signal impinges on either a natural or man-made obstruction, some of its energy may be reflected back in the same direction. on the other hand, some of its energy may be refracted while some may either be diffracted or scattered. these phenomena, reflection, refraction, diffraction, and scattering, are the basic propagation mechanisms that impact radio wave propagation between transmitter and receiver and cause fluctuations in the received signal’s phase and amplitude [2]. in radio communication systems, these fluctuations in the received signal’s phase and amplitude are as a result of reduction in or loss of signal strength that propagated from the transmitter to the receiver. the loss that occurred between the transmitter and the receiver in radio communication systems is known as propagation path loss [2-4]. propagation path loss is defined as a measure of the average attenuation a transmitted signal suffered when it arrives at the receiving end after it has traversed a path of several wavelengths [5]. thus, its model is used in estimating the signal-to-interference ratio, received signal level, and carrier-to-interference ratio [6]. basically, as a result of both the complexity and versatility of the radio wave propagation environments, the received signal strength in wireless systems usually changes with time and space. thus, during wireless systems planning, it is necessary to estimate the average signal that would be received by the receiver(s) located in various areas around the transmitter. this makes efficient path loss prediction an important activity for proper design and maintenance of wireless communication systems. different kinds of obstructions influence radio wave propagation in a wireless communication channel. for instance, as reported in [7], vegetation plays a significant role in radio wave signal strength reduction in wireless communications. similarly, within the built up areas, shadowing effects of tall buildings and other natural and man-made obstructions do affect the signal strength of radio iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 92 waves [8]. likewise, in an indoor environment, man-made obstructions like indoor furniture arrangement and the building’s walls do cause radio signal reduction. on the other hand, in an outdoor environment where the tendency of foliage occurring within the vicinity of radio signals, especially in suburban and rural areas, the adverse effect of foliage is inevitable. this is because the presence of the foliage in such areas, where topographic features are much more dominant than buildings, adversely affected radio signal reception [9]. fundamentally, radio signal reduction or path loss is usually being predicted using propagation models. as reported in [10], a number of radio wave propagation models are available to predict path loss over different types of terrains. these radio wave propagation models are broadly classified into three classes: deterministic, empirical, and stochastic. while the deterministic models make use of the laws governing electromagnetic wave propagation to estimate the received signal power at a specified location, the empirical models are based on observations and measurements alone [11]. on the other hand, stochastic models, according to [11], model the environment as a series of random variables. a propagation model is defined in [2] as an empirical mathematical formulation for estimating the signal’s paths of radio transmission and the connected losses in a given environment based on varying parameters such as the distance between the transmitter and receiver, operating frequency band, and obstacles in the transmission path. it is also defined in [12] as an empirical mathematical formulation for characterization of radio wave propagation as a function of frequency, a function of distance between the transmitting and receiving antennas, and a function of other conditions. it is a very significant tool for the design and development of wireless communication systems. it is useful in both network planning and interference preventive studies as the wireless deployment proceeds. its accuracy and reliability prediction helps in optimizing the wireless system coverage area, transmitter power efficiency, and the possibility of eliminating interference problems with other transmitter(s) in the vicinity. there are various propagation models available for predicting the path loss. however, observations have shown that all the existing propagation models available in literature cannot be generalized to different environments [10,13] as suitability of the models differs for different environments. this necessitates the proposal made in [13] that specific models need to be developed for specific environments. therefore, the primary focus in this paper is to technically investigate this proposal made in [13]. the study presented in this paper was also motivated by the encouragement given by the international telecommunications union radiocommunication section (itu-r), which reported in [14] that scientists and engineers should carry out research that would lead to the development of signal propagation models suitable for their respective localities. it was on this premise and the proposal in [13] that the study presented in this paper was conceived to investigate the proposal raised as well as developing suitable propagation models for vhf broadcast systems in lagos state and ondo state, nigeria. in achieving this objective, some existing radio propagation models were briefly reviewed. field measurements were conducted using two broadcasting stations as case studies. the field measurement results obtained were later analyzed. detailed information on the analysis results that necessitate the development of new propagation models for each of the locations used as case studies are presented in this paper. in enhancing logical presentation of the study in this paper, the rest of the paper is organized as follows. in section 2, a brief review on related works on radio wave propagation models was carried out. section 3 explains in detail the method used to carry out the study presented in this paper. iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 93 the results obtained were presented and discussed in section 4 while the paper is concluded in section 5. 2. review of some radiowave propagation models researchers in most countries of the world have developed and published the propagation models for various parts of their countries. selected among these propagation models are okumura, hata, okumura-hata, free space propagation, longley-rice, cost231, egli, international telecommunication union (itu) and cost 231 walfisch-ikegami (w-i). brief reviews of fspl and egli models are presented, upon which the models in this study are based 2.1 egli model this propagation model is an example of a terrain model for radio frequency (rf) propagation. as reported in [15], the model was first introduced by john egli in 1957. the model, as reported in [16] is based originally on the free space propagation model. it is applicable for path loss prediction at frequencies from 40 mhz to 900 mhz with linking distance between the transmitter and receiver less than 60 km. as reported in [17], the model is one of the best known statistical models for estimating radio wave propagation loss in either urban or rural environments. the model was developed from actual data on uhf and vhf television transmissions in several large cities. the model is based on plane earth propagation. authors in [15] observed that there was a tendency for the median signal in a small area to follow an inverse fourth-power law with distance from the transmitter. the mathematical expression for the egli’s propagation path loss prediction model is expressed in [16, 17] as;         10;log209.85 10;log103.76 log20log40log20 10 10 10101050 rr rr t hh hh hdfdbl (1) where  dbl 50 is the 50th percentile or median path loss, f is the operating frequency from 40 mhz to 900 mhz, th is the transmitter antenna height, rh is the receiver antenna height and d is the distance between the transmitter and receiver. 2.2 free space propagtion model this model, according to [17,18], is the primary model being used to predict received radio wave signal strength when there is a clear and unobstructed line-of-sight path between the transmitter and the receiver. in the free space propagation model, the radio wave is neither reflected nor absorbed [19]. thus, the free space propagation model is a typical propagation model to predict the path loss in signal strength of a propagating radio wave that results from a line-of-sight path through free space without obstructions to cause absorption, refraction, reflection, diffraction, or scattering. microwave links and satellite communications are typical examples of wireless communication systems that can be modeled as free space propagation links [19]. for this propagation model, the received signal power, rp , at distance, d , from the transmitter is expressed in [20] as;     22 2 4 d ggp dp rtt r    (2) where t p is the power of the transmitter, t g is the gain of the transmitter, rg is the gain of the receiver,  is the signal wavelength and d is the distance between the transmitter and iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 94 the receiver. all the parameters in equation (2), except the distance, d , are all system constants. the fundamental relationship, known as the free space or friis equation, is derived from equation (2) as;     22 44                df v gg d gg p dp rtrt t r   (3) where v is the velocity of radio waves. equation (3) shows that free space propagation obeys an inverse square law, which is a principle that expresses the manner with which radiant energy propagates through space. the law states that the power intensity per unit area from a point source transmitter varies inversely according to the square of the distance from the source. as a result of the inverse square law, the path loss in free space propagation prediction increases with the square of the transmission frequency. similarly, both the path loss and received power increase and fall, respectively, by 6 db when the operating frequency and range are doubled. thus, high gain antennas can be used to compensate for this loss [21]. fortunately, design for high-gain antennas at frequencies in and above the vhf band is relatively easier. this provides a remedy for point-to-point or fixed wireless links using isotropic antennas, usually used in vhf and uhf links. thus, for two isotropic antennas  1 rt gg with a distance, d , between them, the free space path loss is expressed mathematically in [20, 22, 23] as;   dfdbl p 1010 log20log2044.32  (4) where all the parameters are same as earlier defined. when the transmitting antenna is located in free space, it has a gain, t g , in the direction toward a receiving antenna. thus the power density, w , at a distance, d , in a specified direction is expressed in [21] as;  2 2 4 e d gp w tt  (5) where e is the electric field strength and  is the characteristic wave impedance of free space. since it is convenient to write the expression for the electric field strength at a known distance from the transmitting antenna than the power density or power per unit area [21], equation (5) can be expressed as; 2 2 4120 d gpe tt   (6) this implies that; d gp e tt 30  (7) as a result of the convenience of expressing the electric field strength for free space, the free space propagation model, eq. (7) was employed as the model propagation for this study. the model performances in the two environments where this study was conducted were iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 95 evaluated and compared with results obtained from measured data. the results of the comparative analysis for the two radio wave propagation environments were used to verify the hypothesis investigated in the study presented in this paper. detailed information on the methodology involved in carrying out the study is presented in the next section of this paper. 3. methodology the study presented in this paper was conducted using two radio broadcasting stations. the first broadcasting station is ondo state radiovision corporation (osrc), which is owned by the ondo state government, while the second broadcasting station is radio continental, which is a privately owned broadcasting station situated in lagos state. the two stations in nigeria are both frequency modulation (fm) stations operating in vhf bands. in carrying out this study, the methodology involved is divided into three stages: the data collection and estimation stage; the propagation model development stage; and the evaluation stage. while detailed information on the third stage is presented in section 4, the detailed information on each of the first two stages is presented in the following subsections. 3.1 data collection and estimation stage in this stage, relevant data required for the study were collected. the first class of data collected was the basic operating parameters of the two broadcasting stations, which are presented in table 1. the second class of data required was measured using different instruments and materials. the two instruments used were bc 1173 field strength meter and global positioning system (gps) meter known as germin gpsmap78s shown respectively in fig. 1(a) and fig. 1(b), respectively. similarly, the two main materials used in gathering the second class of data for the study were the maps of the two primary service areas of the two broadcasting stations and radioworks software. four cardinal routes were created for each of the stations, where the signal strength values were measured. the field measurement requires the physical presence of the investigators in the various locations where the experimental signal strength data were measured. the bc 1173 field strength meter was used to measure the electric field strength of the transmitted radio signal at each location along the different routes while the coordinates of each location where the signal strength values were measured were determined with the aid of the global positioning system (gps) meter. the experimental data were recorded in multiples to achieve a high degree of accuracy. the typical characteristics of each of the service areas of osrc and rc broadcasting stations are shown in fig. 2(a) and fig. 2(b), respectively. in addition, both the collected and measured data were used in the brief analysis conducted at this stage. the analysis involved estimation of the path loss encountered in all the four routes for each station. the essence of the estimation was to determine any disparity in the path loss along each route using the free space path loss model and the calculated path loss obtained using the measured value in each route. only one typical analytical result, out of four, for each of the routes employed for osrc and rc respectively is presented in fig. 3 and fig. 4 due to limited space. iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 96 table 1: the radio broadcasting stations’ parameters parameter broadcasting stations osrc fm rc fm site coordinates long. 7.25710n, lat. 5.20580e long. 6.59620n, lat. 3.39180e location akure, ondo state ketu, lagos state operating frequency 96.5 mhz 102.3 mhz bandwidth frequency 200 khz 200 khz transmitter power 35.0 kw 25.0 kw effective radiating power 12.5 kw 17.5 kw antenna gain 85.6 db 86.5 db antenna polarization circular circular antenna type/model yagi-uda yagi-uda antenna maximum height 150 m 150 m maximum elevation 300 m 17 m fig. 1: pictures of (a) field strength and (b) gpsmap78s gps meters used. fig. 2: obstruction characteristic of (a) orsc and (b) rc service environments. (a) (b)(a) (b) (a) (b) iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 97 the obtained results, as shown in fig. 3 and fig. 4, show that there is a disparity between the path losses estimated using the fspl model and the calculated path losses obtained based on the measurement conducted. the losses predicted by the fspl are higher than the actual losses the radio signals from the stations really experience. this indicates that there is need to develop appropriate models for each route and the entire service areas for each of the radio stations. fig. 3: typical disparity in fspl and estimated path loss for osrc. fig. 4: typical disparity in fspl and estimated path loss for rc. 3.2 propagation model development stage having observed that there is wide disparity between the measured and the predicted fspl model losses, it is necessary to develop propagation models for each of the routes considered for each broadcasting station. a least square regression test method was employed to develop the proposed propagation model because the measurements obtained along the four routes reveal a linear relationship between the estimated path loss from the coverage area and corresponding line of sight distance. the overall average value of the least square regression analysis for the four routes finally formed the developed model. the least square test plots for the four routes for osrc are presented in fig. 5 while the corresponding plots for the four routes for rc are presented in fig. 6. from the result, the multiple r shows the correlation between the points and line of best fit which is between the ranges of 0.98-0.94 for all routes considered. also, r square shows the percentage of points that fall on the straight line, which is between 98% and 82%. the coefficient of the x-variable is the slope at the intercept point on the line across the path loss axis. hence, coefficients of the x-variable and the intercept were used to develop the equation for the path loss. from fig. 5, the obtained path loss propagation model for route a is 73.68423 + 0.000108d where d is the distance in kilometers (km). the corresponding obtained path iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 98 fig. 5: regression plots for osrc routes a-d model development. fig. 6: regression plots for rc routes a-d model development. (b)(b) (a)(a) (c)(c) (d)(d) (a)(a) (b)(b) (c)(c) (d)(d) iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 99 loss models for route b, route c, and route d are 68.21458 + 0.000249d, 71.29911 + 0.000162d, and 71.98258 + 0.000162d, respectively. the overall obtained path loss propagation model developed, which is the average value of the four routes, is expressed mathematically as 71.29513 + 0.0003405d. similarly, from fig. 6, the obtained path loss propagation model for route a is 67.55847 + 0.0005d where d is the distance in kilometers (km). the corresponding obtained path loss models for route b, route c, and route d are 66.22881 + 0.000608d, 68.5224 + 0.000376d, and 67.31792 + 0.000446d, respectively. the overall obtained path loss propagation model developed is expressed mathematically as 67.4069 + 0.0004825d. these respective obtained path loss propagation models are used to predict the path loss for the coverage areas of the stations. the least square regression was used for predicting the relationship between the path loss and distance because of its capability to minimize the sum of the squares of errors between the observed values and the fitted values provided by the developed model. the effectiveness of the two overall developed propagation path loss models is finally evaluated by comparing their respective performance with the fspl model. in validating the performance of the developed models, their respective results are equally compared with result of a related study in surveyed literature. the performance evaluation results obtained and further analysis results obtained from the field measurement conducted are presented and discussed in next section. 4. results and discussion this section is devoted to the obtained results presentation and discussion. the section is divided into two subsections. in the first subsection, the results obtained during the conducted field measurements were analyzed. in the second subsection, the comparative performance evaluation test carried out on the developed propagation models for the two broadcasting stations and free space path loss model were presented and discussed. details on each subsection as well as their respective importance are presented and discussed. 4.1 comparative effects of dissimilar obstructions on radio signals in this subsection, the data obtained during the field measurements conducted were analyzed using radioworks software. the analysis provides the typical obstruction levels that the radio signals from the two radio stations undergo or experience in each of their respective service areas. only one typical analytical result, out of four, for each of the routes employed for osrc and rc respectively is presented in fig. 7 and fig. 8 due to limited space. figures 7 and 8 show the line of sight plots between the transmitter and the receiver. the spikes where the elevation line crosses the line of sight in fig. 7 show the effect of obstructions, which are predominantly rock, hill and tree, in osrc service areas. the results thus show that the vegetation and other natural obstructions such as hills and rocks that characterized the service areas of osrc, as shown in fig 7, have profound negative effects on osrc’s radio signal when compared with high rise buildings, which characterized rc service areas, as shown in fig. 8. this degree of disparity between obstructions constituted by vegetation and high rise buildings in the two service areas as reported in [24] is because fixed-size obstacles such as foliage or tree trunks usually cause higher blockage of the fresnel clearance zone. thus, according to [9], knowledge of propagation effects due to foliage is essential in order to establish a reliable near line-of-sight link. the results also buttress observation in [9] that besides terrain and man-made blockages, signal degradation due to vegetation must be considered during the planning of fixed terrestrial communication links for efficient information transmission in fixed communication systems. iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 100 fig. 7: typical obstruction level in osrc service area. fig. 8: typical obstruction level in rc service area. the results, therefore, show clearly that vegetation, which is an inherent component of most outdoor environments in a forested region like nigeria, has adverse effect on radio propagation. thus, as shown in fig. 7, every location where the elevation data plot crosses the line of sight indicates an adverse effect the obstruction constitutes on the radio signal. the crosses are prominent with osrc service areas due to fact that the areas are in a region covered in vegetation. the vegetation causes radio signal attenuation in osrc service areas primarily due to scattering and absorption caused by both leaves and branches of the trees iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 101 dominant in the areas. on the other hand, fig 8, where the elevation data plots do not cross the line of sight, does not indicate that the rc radio signal is attenuation-free but the rc signal in all the routes are on line of sight (los) without obstruction. basically, location division to either los or non-line of sight (nlos) propagation condition is made according to clearance of the first fresnel zone. thus, it means that 60% of the first fresnel zone in rc service areas is clear of any obstructions while at least 60% of the first fresnel zone in osrc service areas is not clear of obstructions. 4.2 comparative performance evaluation of the developed models in this subsection, the two developed propagation models were evaluated by comparing their performance with that of the fspl. the result obtained is presented graphically in fig. 9, which shows that the path loss predictions by the fspl model in the two service locations are relatively higher when compared with the prediction results from the developed models. this indicates that the existing fspl model is not applicable for either of the studied broadcasting stations. the comparative performance result also shows that the prediction results of the developed models differ for the two broadcasting stations. the overall comparative result thus buttress the finding in [25] that there is no single or universal propagation model that exactly fits all terrains, applications, and environments. similarly, the comparative performance evaluation result has clearly shown the finding in [26], that a radio propagation model that gives an acceptable prediction in one scenario might not be suitable in another scenario. furthermore, the performance evaluation result of the two developed path loss propagation models for this study also shows that their predicted path losses are lower than the corresponding predicted values by the fspl existing model. this establishes the correctness of the hypothesis in [10, 13] that there is need to develop specific propagation models for specific locations to enhance efficient information transmission and reception in wireless communication. fig. 9: comparative performance evaluation of the developed models with fspl. to further evaluate and validate the performance of the two developed models, their path losses prediction results were compared with results from recent study in surveyed literature. the choice of the reference study [1] was characterized by: (i) usage of the same existing model in literature; (ii) presence of the same sets of dominant obstructions (buildings and vegetation); and proximity of the study locations. however, there are three differences between the study presented in the paper and reference study. the first is on how the path losses to be compared were determined. while this study used an estimation method through the two developed models, the reference study measured the path losses. the second observed difference is the unit used in measuring the distance. while the distance in the iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 102 study was measured in kilometers (km), it was measured in meters (m) in the reference study. the third observed difference between the study presented in this paper and reference study is the operating frequency employed. while the frequencies of the transmitters employed in this study are 96.5 mhz and 102.3 mhz, the frequency of operation employed in [1] is 2400 mhz. however, since the reference study is also a wireless application, the differences in operating frequency will not constitute any con to the validation result. this is because the essence of the validation test is not to compare the result but to show that the result obtained in the study follows the same pattern with other study in literature. the result of the reference study is reproduced and presented graphically in fig. 10 for easy comparison with the results of this study shown in fig. 9 critical observations of fig. 9 and fig. 10 show that the results of this study follow the same pattern as other studies in the surveyed literature. the comparative analysis result of fig. 9 and fig. 10 also shows that buildings constitute a higher obstruction to radio signal loss or attenuation than vegetation because high buildings are the predominant obstruction in the reference study’s area. in addition, the comparative analysis result further shows that path loss is directly proportional to distance. furthermore, the comparative analysis result establishes the validity of the study presented in this paper as well as confirms that this study’s results compare favorably with similar studies in the literature. fig. 10: predicted path loss for fspl and developed models at different terrains. 5. conclusion over the last two decades, tremendous development in wireless or radio communication has led to the emergence of a series of wireless applications and services as well as techniques for improving information transmission and quality of service of wireless communication systems. one such technique is accurate in its modeling of complex radio environments to enhance optimum design and planning of wireless communication systems. in achieving this objective, this paper technically investigates the hypothesis that there is need to develop specific propagation models for specific radio environments. in achieving the objective, the fspl model was modified to develop two new set of propagation models for the vhf broadcasting band using two fm broadcasting stations as case studies. the developed models were evaluated to determine their performances, which show some level of differences based on the terrain characteristics of the environment in which each of the broadcasting stations employed is located. this confirms the hypothesis for specific model for specific location in order to enhance service planning and quality of service in wireless communication systems. in addition, the path loss prediction results obtained from the two iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 103 developed models show that the two developed models perform favorably well with related studies in literature. references [1] nwawelu un, nzeako n, ahaneku ma. (2012) the limitations of campus wireless networks: a case study of university of nigeria, nsukka [lionet]. int. j. networks and communications, 2(5):112-122. [2] zakaria y, ivanek l. (2016) propagation modeling of path loss models for wireless communication in urban and rural environments at 1800 gsm frequency band. information and communication technologies and services, 14(2):139-144. [3] kumari m, yadav t, yadav p, sharma pk, sharma d. (2011) comparative study of path loss models in different environments. int. j. engineering science and technology, 3(4):2945-2949. [4] adegoke as, siddle d, salami so. (2016) vegetation attenuation and its dependence on foliage density. eur. j. enginering and technology, 4(3):1-7. [5] sarkar tk, ji z, kim k, medouri a, salazar-palma m. (2003) a survey of various propagation models for mobile communication. ieee antennas and propagation magazine, 45(3):51-82. [6] faruk n, ayeni aa, adeniran ya. (2013) characterization of propagation path loss at vhf/uhf bands for ilorin city, nigeria. nigerian journal of technology, 32(2):253-265. [7] song y, lee yh, ng bc. (2009) the effects of tropical weather on radio-wave propgation over foliage channel. ieee transactions on vehicular technology, 58(8):4023-4030. [8] sah n, thakur t. (2005) effects of clustters on path loss proposed by walfisch-ikegami propagation model. proceedings of the 11th national conference on communications, kharagpur, india, 28-30 january, 617-620. [9] ly pl, ly pl, rahman ta, abu mk. (2010) investigation ofg foliage effects via remote data logging at 5.8 ghz. wseas transaction on communications, 9(4):237-247. [10] mawjoud sa. (2013) path loss propagation model prediction for gsm network planning. int. j. computer applications, 84(7):30-33. [11] abbaayawardhana vs, wasell ij, crosby d, sellars mp, brown mg. (2005) comparison of emprical propagation path loss models for fixed wireless access systems. proceedings of the 61st ieee vehicular technology conference, stockholm, sweden, 30 may-1 june, doi:10 1109/vetecs.2005.1543252. [12] sati g, singh s. (2014) a review on outdoor propagation models in radio communication. int. j. computer engineering and science, 4(2):64-68. [13] famoriji jo, olasoji yo. (2013) development of a radiowave propagation model for hillyareas. int. j. electronics communication and computer engineering, 4(2):536-539. [14] akinbolati a, akinsanmi o. ekundayo kr. (2016) signal strength variation and propagation profiles of uhf radio wave channel in ondo state, nigeria. int. j. wireless and mocrowave technologies, 4:12-28 [15] mardeni r, kwan kf. (2010) optimization of hata propagation prediction model in suburban area in malaysia. progress in electromagnetic research c, 13:91-106. [16] nissirat l, ismail m, nisirat ma. (2012) macro-cell path loss prediction, calibration, and optimization by lee’s model for south of amman city, jordan at 900, and 1800 mhz. j. theoretical and applied information technology, 41(2):253-258. [17] bolli s, khan mza. (2015) a novel lmmse based optimized per-vega zamannillo propagation path loss model in uhf/vhf bands for india. progress in electromagnetic research b, 63:17-33 [18] pathania p, kumar p, rana sb. (2014) a modified formulation of path loss models for broadcasting applications. int. j. recent technology and engineering, 3(3):44-54 [19] obot a, simeon o, afolayan j. (2011) comparative analysis of path loss prediction models for urban macrocellular environments. nigerian journal of technology, 30(3):50-59. iium engineering journal, vol. 19, no. 2, 2018 popoola et al. 104 [20] zar pt, hlaing as. (2014) modification of propagation prediction for 2.4 ghz indoor wireless environment. proceedings of the international conference on advances in engineering and technology, singapore, 29-30 march,360-364. [21] parsons jd. (2000) the mobile radio propagation channel, second edition, john wiley and sons ltd, new york, 1-433. online [available]: http://read.pudn.com/downloads114/ebook/480003/mobile-radio-propagation-channel.pdf. retrived on october 5, 2017. [22] shoewu o, edeko fo. (2011) analysis of radio wave propagation in lagos environs. am. j. scientific and industrial research, 2(3):438-455. [23] podder pk, islam f, sarker dk, hasan mg, kundu d. (2012) an analysis study for the performance analysis of propagation models in wimax. int. j. computational engineering research, 2(1):175-181. [24] rodriguez i, abreu r, almeida epl, lauridsen m, loureiro a, mogensen p. (2016) 24 ghz cmwave radio propagation through vegetation: suburban tree clutter attenuation. proceedings of 10th ieee european conference on antennas and propagation, davos, swizerland, 10-15 april, doi:10.1109/eucap.2016.7481471. [25] milanović j, rimac-drlje s, majerski i. (2010) radio wave propagation mechanisms and empirical models for fixed wireless access systems. technical gazette, 17(1):43-52. [26] temaneh-nyah c, nepembe j. (2014) determination of a suitable correction factor to a radio propagation model for cellular wireless network analysis. 5th proceedings of ieee international conference on intelligent systems, modelling and simulation, sheraton langkawi beach resort teluk nibong langkawi, malaysia, 27-29 january,175-182. http://read.pudn.com/downloads114/ebook/480003/mobile-radio-propagation-channel.pdf.%20retrived%20on%20october%205 http://read.pudn.com/downloads114/ebook/480003/mobile-radio-propagation-channel.pdf.%20retrived%20on%20october%205 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 134 recent trends in dengue detection methods using biosensors ahmad anwar zainuddin*, anis nurashikin nordin and rosminazuin ab rahim department of electrical and computer engineering, kulliyyah of engineering, international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia. * corresponding author: mr. anwarzain@gmail.com (received:30th april 2018; accepted: 11th july 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.931 abstract: dengue illness is an infectious tropical disease, transmitted by aedes mosquitos, that poses a serious health threat to the tropical world. this disease causes widespread infection worldwide, with about 50 million cases of dengue occurring per annum out of which 500,000 recorded cases of dengue hemorrhagic fever and 22,000 deaths. currently, there are no effective vaccines available to prevent the spread of the infection. accurate and rapid laboratory diagnostic tests are required for early detection to reduce patient mortality rate. in this paper, common laboratory diagnosis methods for detecting dengue virus infection are discussed. currently, virus isolation, rt-pcr and serology methods provide the most direct and accurate response for detection of dengue. however, these methods require tedious steps, expensive requirements and expert staffs. recent research have proposed the usage of biosensors as an alternative new technology for detection of dengue. in this work, various types of biosensors such as electrochemical, piezoelectric, and optical biosensor have been described and compared to evaluate their effectiveness in dengue detection. it is observed that the optical biosensor offers the best detection due to its high sensitivity as compared to others, although it is popularly known as an expensive method. alternatively, the use of electrochemical and piezoelectric biosensors (qcm) is highly recommended for detection of dengue due to their ease-of-use, low cost, low reagent consumption, disposability, and minimal sample preparation. these approaches have the potential to improve the rate of survival, particularly in resource-limited countries. abstrak: virus denggi adalah penyakit berjangkit tropika bawaan nyamuk aedes yang menimbulkan ancaman serius kepada kesihatan global. penyakit ini menyebabkan jangkitan yang meluas di seluruh dunia, dengan kira-kira 50 juta kes denggi yang berlaku setiap tahun di mana 500,000 kes demam denggi berdarah dan 22,000 kematian direkodkan. buat masa ini, tiada vaksin yang berkesan untuk mencegah penyebaran jangkitan ini. ujian diagnostik makmal yang cepat dan tepat diperlukan untuk pengesanan denggi awal untuk mengurangkan kadar kematian pesakit. dalam artikel ini, kaedah diagnosis makmal yang biasa dilakukan untuk mengesahkan jangkitan virus denggi akan dibincangkan. pada masa kini, kaedah pengasingan virus, rt-pcr dan serologi adalah tindak balas yang paling cepat dan tepat untuk mengesan denggi. walau bagaimanapun, kaedah-kaedah ini memerlukan langkah-langkah yang melecehkan, kos penyelenggaraan yang tinggi dan kakitangan yang terlatih. penyelidikan terkini telah mencadangkan penggunaan biosensor sebagai teknologi baru alternatif untuk mengesan denggi. dalam artikel ini juga pelbagai jenis biosensor seperti iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 135 biosensor elektrokimia, piezoelektrik, dan biosensor optik telah dijelaskan dan dibandingkan untuk menilai keberkesanannya dalam pengesanan denggi. difahamkan bahawa biosensor optik menawarkan pengesanan terbaik kerana kepekaannya yang tinggi berbanding dengan yang lain, walaupun ia dikenali sebagai kaedah berkos tinggi. sebaliknya, biosensor elektrokimia dan piezoelektrik (qcm) sangat disyorkan untuk mengesan denggi kerana ia mudah digunakan, berkos rendah, penggunaan bahan uji yang terhad, boleh dipakai buang, dan mempunyai penyediaan sampel yang minima. pendekatan-pendekatan ini berpotensi untuk meningkatkan kadar kemandirian di kawasan-kawasan sumber terhad. keywords: denv e-protein; ns1; laboratory methods; biosensors 1. introduction dengue is a rapid-spreading, febrile, mosquito-borne viral disease caused by the dengue virus, which is prevalent in most tropical and subtropical regions. in the past century, denguerelated incidents have increased by approximately thirty fold, where an estimated 50 million cases of dengue occur per annum with 500,000 recorded cases of dengue hemorrhagic fever and 22,000 deaths [1]. the disease has been endemic to southeast asia, where epidemic dengue is a major public health problem in indonesia, sri lanka, thailand, and timor leste [2]. the dengue epidemic causes significant health, social, and economic burdens particularly in affected areas [2]. while dengue outbreaks often occur in urban areas such as jakarta and west java where cases number in the hundreds of thousands, focal outbreaks in rural areas have higher fatality rates of 3-5% compared to 1% in urban areas. the average annual number of dengue fever and dengue hemorrhagic fever cases that have been reported to who is shown in fig. 1(a). due to the rapid-spread nature of the disease and its high fatalities, dengue is a threat for health security that can constitute a public health emergency of international concern as it can cause a borderless epidemic across several countries [1]. decreasing the number of outbreaks and if possible eliminating the disease altogether are indeed of the utmost importance. as of recently, there are no specific vaccines to treat dengue except the cyd-tdv (dengvaxia, sanofi pasteur), the first licensed dengue vaccine that is approved by the u.s. food and drug administration (fda). however this vaccine is compromised by several limitations such as being restricted to patients who have experienced previous denv infection [3-4]. the dengue virus belongs to the flavivirus genus of the flaviviridae family. in terms of human infection, dengue fever could lead to a wide spectrum of illnesses, ranging from mild febrile illnesses to fatal hemorrhagic diseases. figure 1(b) shows the course of dengue illness over a period of 10 days. the entire course of the illness can be categorized into three phases such as febrile, critical, and recovery. dengue patients normally have dengue fever or viremia in the early stage. in this stage, the patient has dehydration and low levels of hematocrit. signs and symptoms of dengue fever include high fever (40 °c), headaches, nausea, vomiting, joint pain, fatigue, and rashes. during the critical phase, the patients get worse where the hematocrit level starts to increase and the platelet level starts to decrease. in this phase also, the temperature of the patients will drop and may progress to shock bleeding, which can result in death if not managed properly [5]. during the recovery phase, the platelet level returns back to normal or increases, the hematocrit level reduces and temperature gets back to normal. some of infected patients may experience severe complications such as dengue hemorrhagic fever (dhf) and dengue shock syndrome (dss), which have high risk of death. additional symptoms in iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 136 dhf/dss cases include plasma leakage from blood vessels, fluid accumulation in the chest, blood concentration increase, organ dysfunction, and severe bleeding [1]. furthermore, severe dhf/dss commonly happen when the patients get a second dengue infection thereafter [1]. several warning signs for severe dengue include persistent vomiting, mucosal bleeding, lethargy, abdominal pain or tenderness, clinical fluid accumulation, restlessness, liver enlargement of more than 2 cm, and an increase in the hematocrit count with a rapid decrease in platelet count [1]. patients usually recover if identified early and with proper fluid and electrolyte administration [6-8]. fig. 1: (a) average annual number of dengue fever and dengue haemorrhagic fever cases reported to who and number of countries reporting dengue from 1955-2007 [1]. (b) the course of dengue illness over a period of 10 days [1]. 2. dengue detection methods 2.1 overview the rapid nature of dengue illness, which can progress from mild to severe within a few days, makes it necessary to have a quick diagnostic test for proper treatment. the optimal window for diagnosing a dengue infection is typically from the onset of fever until 10 days post-infection [9]. early diagnosis should be able to distinguish dengue from other diseases such as malaria, leptospirosis, typhoid, typhus, and chikungunya, all of which present similar symptoms [10]. recently, much of work in early detection of dengue via biosensor was reported to play an important role due to their cost effective method, rapid measurements and high efficiency in bio-sensing analyses as compared to common conventional methods [11-12]. among parameters that can be used to evaluate biosensors are specificity, selectivity, limit of detection (lod), and sensitivity. the selectivity and specificity are evaluated to study the reliability tests of the analytical response. these reliability tests also can help to improve the issue of cross reactivity or false-positive tests of specific detection in bio-sensing layers. based on the international union of pure and applied chemistry (iupac) guidelines, all these parameters are defined accordingly in this paper [13-14]. (a) (b) iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 137 specificity is defined when the analyte alone is responsible for the relative signal that is measured with great accuracy. selectivity refers to the quality of response of the method that can be achieved to discriminate a particular analyte without interference from any other component in a mixture via quantitative or qualitative method. in the quantitative method, a complex evaluation is acquired via computational selectivity based on a multivariate statistical method such as chemometric and classification methods. in this regard, the use of the qualitative method has been widely adopted in spectroelectrochemical sensors based on three levels of selectivity that can be determined from an ion-exchange protein on the electrode, potential selection, and wavelength. furthermore, this method directly reflects the considerations among analytical chemists to optimize the selectivity [15]. limit of detection (lod) is the lowest concentration level that can be determined to be statistically different from an analytical blank [16]. sensitivity (m) is the magnitude of the response per unit concentration within the dynamic range of the instrument [16]. in general, lod and sensitivity can be quantitatively calculated via a calibration plot derived from at least triplicate of data measurement (k≥3) in accordance with the confidence level of 99.86%. in fact, these measurements are assumed to follow a normal distribution of the raw analytical signals from blank samples. these measurements, within the context of this study, are the signal responses towards varied concentrations of target analytes. figure 2 shows the lod, which represented as the concentration,cl, is expressed as eq.(1) [16]: m ks c b l  (1) where k=3 is the minimum numerical factor (number of experiments). sb is the standard deviation of number of blanks reading. m is defined as the sensitivity in analytical chemistry, which is evaluated from slope of the calibration curve. fig. 2: analytical calibration curve of response, x vs. concentration of target, c, showing the relationship of ksb to the limit of detection, cl. the unknown signal, xu, is referred to an unknown concentration, cu via the equation x = mc + i, where m is the slope and i is the yintercept [16]. 2.2 conventional methods figure 3 presents an overview of the common laboratory methods for diagnosing dengue. the methods can be categorized into detection of virus, genome, antigen, and serological methods [17]. virus isolation, genome detection, and antigen detection provide higher iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 138 specificity compared to serological methods. however, serology offers better practicality and widespread use due to its lower cost and easier sample handling, assay operations, and operator training. direct virus detection of live virus or virus components (rna or antigens) can be done in serum, plasma, whole blood, and infected tissues can be used for early identification of dengue infections during the acute phase (viremia) of the disease [18-19]. direct virus detection procedures are not routinely performed by laboratories, and few commercial kits that have been independently validated are available to aid in this area of dengue diagnosis. the details of each detection are explained further in the following sections. fig. 3: comparative laboratory methods of direct and indirect diagnosis of dengue infection. illustrations were redrawn, according to [17]. 2.2.1 virus isolation many studies have recorded the virus isolation methods as the best diagnostic method for detecting dengue infection [20-21]. in this method, the infected blood samples are cultured in a variety of cell lines of either mosquito (ap61, tra-284, ap64, c6/36, and cla-1 cells) or mammalian (llcmk2, vero, and bhk-21 cells) origin or in live mosquitoes. this is followed by the immunofluorescent assays via serotype-specific monoclonal antibodies (mabs) for virus serotype identification [17]. the virus isolation detection method relies on the cultivation and identification of virus techniques that are sensitive and time-consuming. although these methods display high specificity in dengue diagnosis, they have greatly tedious steps (long virus isolation time), limited time for culturing virus at the acute phase of infection (2-5 days), and high-cost facilities to protect the cell condition [22]. 2.2.2 genome detection the dengue genome detection methods are generally discovered by reverse transcriptase polymerase chain reaction (rt-pcr) in serum of dengue patients in the acute phase of the disease. these methods offer several advantages including the ability to differentiate dengue serotypes that have higher specificity when combined with real-time technology such as taqman assays [23], and are cheaper than virus isolation methods [22]. however, these methods require specialist operators, expensive reagents and apparatuses, thus restricting their iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 139 use in many developing countries [24-25]. furthermore, they are also easily contaminated by non-template pcrs present in the laboratory environment [26]. 2.2.3 antigen detection in recent years, the use of nonstructural protein 1 (ns1) has gained attention as a diagnostic tool of dengue detection [10]. this dengue diagnosis can be done during early stage of dengue infection by detecting the viral antigen in the bloodstream. a newly developed antigen-capture enzyme-linked immunosorbent assay (elisa) method can be utilized to detect ns1. dengue patients with primary and secondary (up to 9 days) dengue infections have high concentration of this ns1 antigen. high efficiencies of ns1-elisa method have led to the commercial development of ns1 capture elisas and rapid strip tests. ns1 commercial development has recently been known as the new standard for early dengue diagnostics due to low-technology assays that have high sensitivity and specificity [10]. however, the disadvantage of these methods is that they are unable to differentiate among dengue serotypes. this is due to ns1 being conserved among all four dengue serotypes, and expressed or secreted by infected host cells. apart from that, it is produced during the dengue virus replication and circulated in serum at high concentration during acute infection [17]. 2.2.4 serology tests serological test is the best diagnostic method to detect the presence of immunoglobulins (igm, igg and iga) which are produced in response to dengue virus infection after the acute illness phase (2-7 days). different levels of response of these antibodies can be measured where the antibody igg abd igm rise rapidly after viremia phase as shown in fig. 1(b). conventional serological tests include hemagglutination inhibition (hi) [27-28], plaque reduction neutralization test (prnt) [19], [29] and enzyme-linked immunosorbent assay (elisa) [30]. among these tests, igg/igm assays using elisa methods are typically used due to their simplicity of operation, rapid results, and reasonable sensitivity. however, serology tests have reported significant cross-reactivity among flavivirus antibodies, which necessitates multiple serum samples to be derived from the acute and convalescent phases during serological diagnosis, slowing the overall process due to the required incubation period (from a few hours up to two days) thus making the tests less efficient [31]. the automated elisa system requires a high-level of expertise and expensive equipment. elisa systems are not always available in hospital, and consume considerable amounts of reagents [28]. recently, an integrated colorimetric igg-enzyme-linked immunosorbent assay (igg-elisa) has been developed using a lab on compact disc (locd) system for dengue detection [32]. figure 4 shows the detection of igg antibody in sera of patients using this sensor. although they achieved high sensitivity (95%) and specificity (100%) for dengue detection, this work was still at its infancy and needs further improvement in term of its limit of detection and portability. this integrated elisa method (igg-elisa using lab on compact disc) is a cost-effective, rapid, automatic testing method of the purpose of point-of-care testing and has high potential as a dengue diagnostic tool iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 140 fig. 4: (a) prototype of the lab on compact disc (locd) elisa reader; (b) smartphone application displaying igg-elisa test results; (c) operating principle in evaluating absorbance. reprinted with permission [32]. 2.3 recent trends of dengue biosensors to overcome the drawbacks of conventional methods, the employment of biosensors has been planned as another technology for speedy detection of dengue and its antibodies. biosensors are described as analytical devices that involve an integration between a molecular recognition platform with a physicochemical transducer to produce a single detection processing unit [33]. several biosensor techniques are used in biosensing applications such as electrochemical biosensors (measurement of voltage, current, impedance, and capacitance), piezoelectric biosensors (evaluation on mass sensitivity due to change of frequency) and optical biosensors (light properties are detected through any of the light parameters such as intensity, phase, polarization, or wavelength). recently, various types of biosensors have been employed to quantify different targets (analyte probes) for dengue diagnosis. these different targets such as ns1, igm, igg, glycoprotein, deoxyribonucleic acid (dna) and ribonucleic acid (rna) flavivirus are capable of detecting the presence and severity of dengue in patient samples. in this work, electrochemical, piezoelectric, and optical biosensors have been described and compared to evaluate their effectiveness in dengue infection. 2.3.1 electrochemical biosensors generally, electrochemical biosensors detect current or impedance changes in the electrode surface owing to redox reaction or surface reactions. these sensors use an electrochemical cell to facilitate chemical reactions through the introduction of electrical energy. the three-electrode system is the electrode configuration most used for in situ electrochemistry system, which consists of working electrode, reference electrode and counter electrode. figure 5 shows the conventional three-electrode set up and commercial screen printed electrode used in electrochemical measurements. iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 141 electrochemical impedance spectroscopy (eis) is one of the electrochemical measurements that is widely used due to its high sensitivity and non-destructive operation. this method measures the changes in the electrode and solution interface due to the interaction with the captured analyte in a real sample. it utilizes a low amplitude sinusoidal perturbation as a function of frequency evaluation of a non-destructive steady-state technique that is capable of probing the relaxation phenomena of like-affinity reactions [34]. apart from eis, cyclic voltammetry (cv) and differential pulse voltammetry (dpv) are also commonly used in this detection of dengue, which possess the ability to measure both reduction and oxidation potentials. however, an optimal direct current is required to minimize current interference issues. fig. 5: three electrode setup for electrochemical measurements using (a) conventional and (b) commercial screen printed electrodes. illustrations were redrawn, according to [35]. to date, much of work has been done in the development of electrochemical biosensor for dengue detection. figure 6 shows an impedimetric biosensor to test neat serum for ns1 dengue diagnosis [36]. the commercial screen printed gold electrode (spge) biosensors have been utilized via mixed self-assembly monolayer (sam) application. this activated mixed selfassembly monolayer (sam) – with n-hydroxysuccinimide-n, n-(3-dimethylaminopropyl)-n’ethylcarbodiimide (nhs-edc) reagent and bovine serum albumin (bsa) as a blocking agent has been immobilized on the gold electrodes. the impedance response was measured via an aqueous electrolyte of k3[fe(cn)6], k4[fe(cn)6]·3h2o. although their immobilization method was outdated, they obtained a low limit of detection of 3 ngml-1 and 30 ngml-1, in both ns1 protein measurement in phosphate-buffered saline (pbs) and serum samples, respectively. furthermore, they observed a good selectivity test via 2 µgml-1 of fetuin in pbs (blood protein) in order to evaluate possible non-specific interactions with the electrode. consequently, it showed that fetuin showed a response for less than 3% of blank samples. this result was in iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 142 contrast to a response of 46% of blank samples for the specific response to ns1 protein at a clinically relevant level. they also found that new applications into the potential use of this spge biosensor for point-of-care (poc) applications for early dengue diagnosis. fig. 6: step by step process of electrode functionalization with an activated mixed self-assembly monolayer (sam) for ns1 dengue diagnosis. illustrations were redrawn, according to [36]. figure 7 indicates the working electrode surface has been functionalized via sandwich immunocomplex and immunonanobeads (aunps–ab-fc) with nanoparticle-linked detection of dengue ns1 antibodies [37]. the use of spge sensors enables quantification together with the facility of a lateral flow test strip to detect the analyte dengue ns1 protein in the presence of 5 mm ferrocene acetic acid. this work had a lower detection limit of 0.5 ngml-1 as compared to cecchetto’s work previously. for selectivity tests, they immobilized non-specific capture antibody (mouse igg) on the surface of spge. from these results, no significant changes were observed in the cyclic voltammetry and impedimetric responses of current and impedance responses for ns1 concentration ranging from 0.5 ngml-1 to 400 ngml-1. although this work was still at its infancy, it offered on-site poc diagnostics for early dengue detection due to its operational simplicity, biocompatibility, disposability, and low cost. an electrochemical biosensor to evaluate for all four serotypes of dengue virus has been demonstrated [38]. this biosensor was activated via zinc oxide/platinum-palladium (zno/ptpd) nanocomposites on a modified fluorine doped tin oxide (fto) glass plate. it was found that the hybridization between probe dna(pdna) and target hybridized dna (tdna) was detected by reduction in current via an intercalating agent (methylene blue (mb) with free guanine (3′g) of ssdna). they reported high selectivity to dengue detection that was capable of reducing the possibility of false result with the smallest detection and quantification limit, which were 4.3×10−5 m and 9.5×10−5 m, respectively. owing to that, small low cross-reaction due to no significant change in current response was observed upon addition of noniium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 143 complementary dna relative to the pdna. overall, this genosensor was cost-effective in noble metal catalyst due to the combination of smart nano-materials of pd/zno and pt/zno, thus improving the stability of nano-catalyst in chemical reactions [39]. fig. 7: formulated immunonanobeads (aunps–ab-fc) and sandwich immunocomplex formation on spge sensor. illustrations were redrawn, according to [37]. recently, a molecularly imprinted polymer (mip)-graphene based electrochemical sensor for dengue and anti-dengue antibodies detection has been reported [40]. the sensor was reported to detect dengue ranging from 1 to 2000 pfu/ml and between different dengue serotypes and h5n1. it was observed that an mip functioned as a recognition element, which had the advantage of removing antibody transducers. however, this material lacked the specificity and binding affinity of antibodies. 2.3.2 piezoelectric biosensors most piezoelectric biosensor studies have been conducted using constant resonance devices. sauerbrey et al. was the first group of researchers who not only developed but also demonstrated the relationship between mass and resonant frequency and recognized the potential usefulness of quartz crystal microbalance (qcm) technology [41]. these qcm sensors are recognized as the best acoustic wave sensors that function effectively for sensing applications as well as in gaseous form and in contact with liquids without excessive damping. figure 8 shows the conceptual diagram of qcm in liquid bio-sensing. an alternate current (ac) signal is applied to the top and bottom electrodes of at-quartz to generate acoustic wave energy (resonance frequency). due to presence of antigens and antibodies deposited at the top electrode; frequency change will be produced due to addition of mass. apart from qcm sensors, surface acoustic wave (saw) sensors are also developed as piezoelectric biosensors, especially in non-liquid bio-sensing such as insorption gas, vapor sensors, and sound (noise) detection [42]. in the last decades, the use of piezoelectric biosensors has seen great interest among researchers, specifically in tropical countries for detecting early dengue infection. iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 144 fig. 8: application of qcm sensor in liquid bio-sensing. a highly sensitive dna–qcm sensor combined with the method of layer-by-layer aunpprobe amplification for dengue dna serotype-2 detection has been reported [43]. the change of frequency was recorded for the techniques of probe oligonucleotide immobilization (∆f = 45 hz), and dna hybridization of probes and targets (∆f = 80 hz). it is followed by the signal amplification of detection in the dna–qcm system (∆f = 200 hz) by layer-by-layer aunp probes using target sequences (∆f = 130 hz). these techniques were complex due to tedious steps, long incubation time and less selectivity (up to 60%) for dengue detection. nevertheless, they observed that the detection limit of 2 pfuml-1 was relatively comparable to the fluorescent (rt-pcr) methods (1-50 pfuml-1). furthermore, this method was less expensive and was label free as compared to rt-pcr methods. the qcm sensor with a functionalized interface via the monoclonal immunoglobulin g (iggns1) antibodies attachment has been developed [44]. figure 9 shows the sensor has been modified with bacterial cellulose nanocrystal (cn) thin films for ns1 of dengue detection. this sensor provides a few advantages such as short-time analysis, simplicity, real-time monitoring, and label-free detection. however, it was observed that this sensor was not selective to ns1 dengue detection in serum samples due to high frequency interferences. as a result, it showed that the large variation of detection limit for ns1 detection in pbs and serum samples, which was 0.03 µgml-1 and 0.32 µgml-1, respectively. figure 10 indicates a surface acoustic wave (saw) dengue sensor in human habitations based on matlab simulation and real mosquito flight tones has been demonstrated [45]. the dengue detection was analyzed via the wing beat frequency produced by female aedes mosquitoes via the feasibility of a saw sensor (acoustic-based device). based on the aedes mosquitoes’ gender and genus, which corresponded to a frequency of 400−500 hz in females and 700−900 hz in males could be distinguished by this saw sensor. decreased resonant peak amplitude with different wing beat frequencies were observed. consequently, this saw sensor offered a non-invasive method (no serum samples) for dengue detection, and was the first report of an saw dengue sensor in acoustic wave sensing. furthermore, this sensor showed its uniqueness since no surface chemistry modification is performed as compared to other biosensors discussed previously. however, this saw sensor required an expensive fabrication iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 145 process since it was developed in the cleanroom that required masking followed by metal deposition. fig. 9: schematic representation of sequential immunochip assembly. illustrations were redrawn, according to [44]. 2.3.3 optical biosensors basically, two types of optical biosensor formats have been recognized, which are optical sensors (commonly known as surface plasmon resonance (spr sensors)) and optical fibers. spr comprises an optical system, correlated with the refractive index changes at the surface of the biosensor, caused by a concentration change of the binding medium when the antibodies as the target bind to the immobilized antigens acting as probes. meanwhile, optical fibers are dependent on the total internal reflection of light and the characterization of a surface by the difference in the angle of incidence of reflected light upon sensor surface modifications. overall, the use of an electronic system supporting the optoelectronic components is required to allow for data processing for both types of optical biosensors. currently, a lot of research has been done in the exploitation of dengue optical biosensors [46-48]. figure 11 depicts a study on 10-minutes of early detection for all four dengue virus serotypes via surface plasmon resonance (spr) technique [46]. this work has been done to detect the igm antibody, a chip of gold sensor surface was initially activated with a mixture of edc/nhs to produce reactive succinimide esters. it was continued by injecting the diluted ligand (each serotype of dengue antigen) with acetate buffer. to deactivate the remaining active esters, the ethanolamine was passed over the sensor surface and the chip was then placed into the spr device to measure the spr angle variations for each sample. the success of immobilized antigens was verified via sem and afm images of immobilized antigens as shown in fig. 11 (b,c,d). from the result, it showed that two distinctive types of hills that were observed in 3d afm images. the first hill exhibited homogeneous, dense, and low gold hills that were established from amine groups. the second hill showed sporadic hills arising from immobilized antigens. iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 146 fig. 10: the vector network analyzer (vna) was used to measure the resonance frequency saw sensor to capture the mosquito’s wingbeat frequency. illustrations were redrawn, according to [45]. fig. 11: (a) the spr dengue virus diagnosis process. (b) the cross-sectional sem image estimated the gold layer (52 nm thick). the verification of immobilized antigens (c) 2d (d) and 3d afm images. reprinted with permission [46]. to date, this group has been continued their projects on kinetic analysis of igm monoclonal antibodies binding to denv-2 antigens using the spr technique [48]. in these projects, prior to dengue sample injection, a chip of gold sensor surface was initially activated with iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 147 immobilization of carboxymethyl-dextran matrix as a linker layer, n-hydroxysuccinimide (nhs) and n-ethyl-n-(dimethylaminopropyl) carbodiimide (edc). ethanolamine and 10 mm glycine-hcl solutions are utilized as a blocking agent on the gold surface. finally, it was followed by the igm monoclonal antibodies addition to the analyte flow. they observed that the binding of analyte to the immobilized antigens caused a rise in the refractive index of the chip surface as compared to their previous study as described previously. thus, although spr techniques used for both studies (2014 and 2017) recorded good sensitivity (83-93%) and specificity (100%) for all four dengue virus serotypes and detection limit of 2×105 pfuml-1 for denv-2 antigen, the use of a commercial biacore system for spr measurements used in both studies was very expensive [49]. fig. 12: the osa was used to laser-excite into one end of the tapered fiber sensor, and monitor the transmission spectrum from the other end. the denv-2 (e protein) specific binding of antigens-antibodies in the tapered region could be analyzed through phase shift of the spectrum. illustrations were redrawn, according to [47]. a study on 15-minutes of label-free detection of denv 2 via tapered fiber sensor has been proposed [47]. this sensor was fabricated via a standard single-mode fiber with cladding and core diameters of 125 μm and 8 μm. to realize the successful coating of the tapered optical fiber with antibodies of denv 2, a treatment of tapered region via sodium hydroxide was initially done to offer a functionalization of hydroxyl group (-oh) onto the surface. the significance of this treatment was to promote a high selectivity attachment of a silant agent (3aminopropyl) tri-ethoxysilane, aptes is used to activate the non-organic fiber surface layer to bind with the organic compound such as protein. then, the use of glutaraldehyde was done to enhance the homogeneity of the antibody immobilization on the surface of the tapered fiber prior to binding antibodies specific to e proteins of denv-2. finally, variation of concentration of antigens specific to recombinant monoclonal antibodies to denv-2 e proteins was established to observe an immune complex on the tapered region. all these steps were observed via optical spectrum analyzer (osa) to record any changes on the spectrum signal due to molecules bound on the taper surface as shown in fig. 12. consequently, this sensor showed that sensitivity and detection limit values of 5.02 nm/nm and 1 pm for detection of denv-2. for the selectivity test, the use of avidin as a negative control observed a no shift spectrum iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 148 output, thus no additional layer was formed. table 1 and table 2 list recent biosensor methods and development for detection of dengue as described in this work. table 1: comparison of recent biosensors methods for detection of dengue method advantages disadvantages electrochemical sensors [36-38] 1. cost effective 2. ease of operation 3. small analyte volumes 4. label-free detection 1. less sensitive in non-specific binding 2. slow measurement 3. spge cannot be reused piezoelectric: quartz crystal microbalance (qcm) [43-44] 1. cost effective and wellsuit/ functionalized for specific purpose 2. label-free analysis 3. higher sensitivity compared to electrochemical sensing 4. cost effective production when fabricated in array 5. the sensor can be reused. 1. very fragile 2. limit the sensor sensitivity when react in liquid sensing resonances frequency 3. the sensitivity of sensor is dependent on thickness of quartz piezoelectric: surface acoustic wave (saw) [45] 1. non-invasive detection (no liquid/blood) 2. easy miniaturization 3. cost effective production when fabricated in array 4. flexible sensor 5. the sensor can be reused 1. expensive of sensor fabrication process 2. not suitable for liquid sensing optical: surface plasmon resonance (spr) [46],[48] 1. higher sensitive detection as compared to electrochemical and piezoelectric sensing 2. ease of handling 1. extremely expensive instrument iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. ___________________________________________________________________________ 149 table 2: recent development of dengue biosensors activities samples approach methods lod response time ref. denv, ns1-antigen spge activated with a mixed-sam layer cv,eis pbs = 3ngml-1 serum = 30 ngml 30 min [36] denv, ns1-antigen spge lateral flow modified with sandwich immunocomplex and immunonanobeads cv,eis pbs = 0.5 ngml-1 30 min [37] denv-1,2,3,4 (dna) (fto) glass plate modified with nano material (zno/pt-pd) cv,dpv 4.3×10−5 m 120 min [38] denv-2 (dna) qcm modified with layer-by-layer aunp-probe amplification qcm 2 pfuml-1 not mentioned [43] denv, ns1 qcm modified with bacterial cellulose nanocrystals (cn) thin films qcm pbs = 0.03µgml-1 serum = 0.32 µgml-1 not mentioned [44] dengue mosquitos saw sensor in human habitations based on real mosquito flight tones saw not mentioned not mentioned [45] denv-1,2,3,4 (ns1-antigen) gold chip modified amine coupling (nhs/edc) spr sensitivity = 83-93% specificity = 100% 10 min [46] denv-2 antigen gold chip modified with amine coupling (nhs/edc) in pbs/gly using sam layer spr 2×105 pfuml10 min [48] denv-2 antigen tapered fiber modified with aptes optical fiber 1 pm 15 min [47] iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. 150 3. conclusion this work compares the current laboratory diagnosis methods for detection of dengue virus infection. it was observed that virus isolation, rt-pcr, and serology methods are the most direct approach to dengue diagnosis. however, these methods require tedious steps, expensive requirements, and expert staff. in this work, various type of biosensors such as electrochemical biosensors (measurement of voltage, current, impedance, and capacitance), piezoelectric biosensors (evaluation on mass sensitivity due to change of frequency), and optical biosensors (light properties are detected through any of the light parameters such as intensity, phase, polarization or wavelength) have been described and compared to evaluate their effectiveness in dengue detection. among these biosensors, optical sensing offers the best method due to its high sensitivity as compared to others, although it is popularly known as an expensive method. alternatively, the use of electrochemical and piezoelectric biosensors (qcm) is highly recommended for detection of dengue due to ease-to-use, low cost (since it requires less reagent), disposability, and minimal sample preparation. these approaches have the potential to improve chances of survival, particularly in resourcelimited countries. acknowledgement this research is a collaborative research between linkoping university (sweden), xlim research institute of limoges university (france) and international islamic university malaysia. it is funded by the swedish research council (2014-4254) and the malaysian ministry of higher education under frgs15-217-0458. references [1] special programme for research and training in tropical diseases, world health organization (eds.), (2009). dengue: guidelines for diagnosis, treatment, prevention, and control, new ed. ed. tdr : world health organization, geneva.world health organization and the special programme for research and training in tropical diseases (tdr) [2] gubler, d. j. (2002). epidemic dengue/dengue hemorrhagic fever as a public health, social and economic problem in the 21st century. trends in microbiology, 10(2): 100–103. [3] wilder-smith, a., vannice, k. s., hombach, j., farrar, j., & nolan, t. (2016). population perspectives and world health organization recommendations for cyd-tdv dengue vaccine. the journal of infectious diseases, 214(12): 1796–1799. [4] wang, w.k. and gubler, d.j., (2018). potential point-of-care testing for dengue virus in the field. journal of clinical microbiology, 56(5), e00203-18. [5] low, g.k.k., ogston, s.a., yong, m.h., gan, s.c. and chee, h.y., (2018). global dengue death before and after the new world health organization 2009 case classification: a systematic review and meta-regression analysis. acta tropica, 182: 237-245 [6] liu, l., dehning, m., phipps, a., swienton, r., harris, c., & klein, k. (2017). clinical update on dengue, chikungunya, and zika: what we know at the time of article submission. disaster medicine and public health preparedness, 11(3): 290-299. [7] vaughn, d. w., green, s., kalayanarooj, s., innis, b. l., nimmannitya, s., suntayakorn, s.,& nisalak, a. (1997). dengue in the early febrile phase: viremia and antibody responses. journal of infectious diseases, 176(2): 322-330. [8] green, s., vaughn, d. w., kalayanarooj, s., nimmannitya, s., suntayakorn, s., nisalak, a., & ennis, f. a. (1999). early immune activation in acute dengue illness is related to development of plasma leakage and disease severity. the journal of infectious diseases, 179(4): 755-762. iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. 151 [9] zhang, b., salieb-beugelaar, g. b., nigo, m. m., weidmann, m., & hunziker, p. (2015). diagnosing dengue virus infection: rapid tests and the role of micro/nanotechnologies. nanomedicine: nanotechnology, biology and medicine, 11(7): 1745–1761. [10] muller, d. a., depelsenaire, a. c., & young, p. r. (2017) clinical and laboratory diagnosis of dengue virus infection. the journal of infectious diseases, 215.suppl_2: s89–s95. [11] oliveira, m. d., nogueira, m. l., correia, m. t., coelho, l. c., & andrade, c. a. (2011). detection of dengue virus serotypes on the surface of gold electrode based on cratylia mollis lectin affinity. sensors and actuators b: chemical, 155(2): 789–795. [12] rashid, j. i. a., yusof, n. a., abdullah, j., hashim, u., & hajian, r. (2016). surface modifications to boost sensitivities of electrochemical biosensors using gold nanoparticles/silicon nanowires and response surface methodology approach. journal of materials science, 51(2): 1083–1097. [13] den, b. g., & hulanicki, a. (1983). recommendations for the usage of selective, selectivity and related terms in analytical chemistry. pure and applied chemistry, 55(3): 553–556. [14] persson, b.-a., & vessman, j. (2001). the use of selectivity in analytical chemistry–some considerations. trac trends in analytical chemistry, 20(10): 526–532. [15] laidler, k. j. (1996). a glossary of terms used in chemical kinetics, including reaction dynamics (iupac recommendations 1996). pure and applied chemistry, 68(1): 149–192. [16] long, g. l., & winefordner, j. d. (1983). limit of detection. a closer look at the iupac definition. analytical chemistry, 55(7): 712a–724a. [17] peeling, r. w., artsob, h., pelegrino, j. l., buchy, p., cardosa, m. j., devi, s., … yoksan, s. (2010, december 1). evaluation of diagnostic tests: dengue [comments and opinion]. [18] chua, k. b., mustafa, b., wahab, a. a. h., chem, y. k., khairul, a. h., kumarasamy, v., rasid, a. k. (2011). a comparative evaluation of dengue diagnostic tests based on singleacute serum samples for laboratory confirmation of acute dengue. the malaysian journal of pathology, 33(1): 13-20. [19] raengsakulrach, b., nisalak, a., maneekarn, n., yenchitsomanus, p., limsomwong, c., jairungsri, a.,others. (2002). comparison of four reverse transcription-polymerase chain reaction procedures for the detection of dengue virus in clinical specimens. journal of virological methods, 105(2): 219–232. [20] darwish, n. t., alias, y. b., & khor, s. m. (2015). an introduction to dengue-disease diagnostics. trac trends in analytical chemistry, 67: 45–55. [21] darwish, n. t., sekaran, s. d., & khor, s. m. (2017). point-of-care tests: a review of advances in the emerging diagnostic tools for dengue virus infection. sensors and actuators b: chemical, 255(3): 3316-3331. [22] parkash, o., & shueb, r. h. (2015). diagnosis of dengue infection using conventional and biosensor based techniques. viruses, 7(10): 5410–5427. [23] kong, y. y., thay, c. h., tin, t. c., & devi, s. (2006). rapid detection, serotyping and quantitation of dengue viruses by taqman real-time one-step rt-pcr. journal of virological methods, 138(1–2):123–130. [24] cavalcanti, i. t., silva, b. v. m., peres, n. g., moura, p., sotomayor, m. d. p. t., guedes, m. i. f., & dutra, r. f. (2012). a disposable chitosan-modified carbon fiber electrode for dengue virus envelope protein detection. talanta, 91: 41–46. [25] fry, s. r., meyer, m., semple, m. g., simmons, c. p., sekaran, s. d., huang, j. x., … young, p. r. (2011). the diagnostic sensitivity of dengue rapid test assays is significantly enhanced by using a combined antigen and antibody testing approach. plos neglected tropical diseases, 5(6): e1199. [26] watthanaworawit, w., turner, p., turner, c. l., tanganuchitcharnchai, a., jarman, r. g., blacksell, s. d., & nosten, f. h. (2011). a prospective evaluation of diagnostic methodologies for the acute diagnosis of dengue virus infection on the thailand-myanmar border. transactions of the royal society of tropical medicine and hygiene, 105(1): 32– 37. [27] wright, w. f., & pritt, b. s. (2012). update: the diagnosis and management of dengue virus infection in north america. diagnostic microbiology and infectious disease, 73(3):215– 220. iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. 152 [28] chutinimitkul, s., payungporn, s., theamboonlers, a., & poovorawan, y. (2005). dengue typing assay based on real-time pcr using sybr green i. journal of virological methods, 129(1): 8–15. [29] sirivichayakul, c., sabchareon, a., limkittikul, k., & yoksan, s. (2014). plaque reduction neutralization antibody test does not accurately predict protection against dengue infection in ratchaburi cohort, thailand. virology journal, 11(1): 48. [30] balmaseda, a., guzmán, m. g., hammond, s., robleto, g., flores, c., téllez, y., … sandoval, e. (2003). diagnosis of dengue virus infection by detection of specific immunoglobulin m (igm) and iga antibodies in serum and saliva. clinical and diagnostic laboratory immunology, 10(2): 317–322. [31] f. r. r., prazeres, d. m. f., & lima-filho, j. l. (2005). trends in dengue diagnosis. reviews in medical virology, 15(5): 287–302. [32] thiha, a., & ibrahim, f. (2015). a colorimetric enzyme-linked immunosorbent assay (elisa) detection platform for a point-of-care dengue detection system on a lab-oncompact-disc. sensors, 15(5): 11431–11441. [33] miserere, s., & merkoçi, a. (2015). microfluidic electrochemical biosensors: fabrication and applications. in lab-on-a-chip devices and micro-total analysis systems, springer. pp 141–160. [34] zainuddin, a. a., nordin, a. n., rahim, r. a., ralib, a. a. m., khan, s., guines, c., … pothier, a. (2018). verification of quartz crystal microbalance array using vector network analyzer and openqcm. indonesian journal of electrical engineering and computer science, 10(1): 84–93. [35] katz, e., & willner, i. (2003). probing biomolecular interactions at conductive and semiconductive surfaces by impedance spectroscopy: routes to impedimetric immunosensors, dna-sensors, and enzyme biosensors. electroanalysis, 15(11): 913–947. [36] cecchetto, j., carvalho, f. c., santos, a., fernandes, f. c., & bueno, p. r. (2015). an impedimetric biosensor to test neat serum for dengue diagnosis. sensors and actuators b: chemical, 213:150–154. [37] sinawang, p. d., rai, v., ionescu, r. e., & marks, r. s. (2016). electrochemical lateral flow immunosensor for detection and quantification of dengue ns1 protein. biosensors and bioelectronics, 77:400–408. [38] singhal, c., pundir, c. s., & narang, j. (2017). a genosensor for detection of consensus dna sequence of dengue virus using zno/pt-pd nanocomposites. biosensors and bioelectronics, 97:75–82. [39] bao, z., yuan, y., leng, c., li, l., zhao, k., & sun, z. (2017). one-pot synthesis of noble metal/zinc oxide composites with controllable morphology and high catalytic performance. acs applied materials & interfaces, 9(19): 16417–16425. [40] navakul, k., warakulwit, c., yenchitsomanus, p., panya, a., lieberzeit, p. a., & sangma, c. (2017). a novel method for dengue virus detection and antibody screening using a graphene-polymer based electrochemical biosensor. nanomedicine: nanotechnology, biology and medicine, 13(2): 549–557. [41] sauerbrey, g. (1959). the use of quartz oscillators for weighing thin layers and for microweighing. z. fur. phys., 155, 206–222. retrieved from [42] a. arnau (2004), piezoelectric transducers and applications, springer. switzerland. [43] chen, s.-h., chuang, y.-c., lu, y.-c., lin, h.-c., yang, y.-l., & lin, c.-s. (2009). a method of layer-by-layer gold nanoparticle hybridization in a quartz crystal microbalance dna sensing system used to detect dengue virus. nanotechnology, [44] pirich, c. l., de freitas, r. a., torresi, r. m., picheth, g. f., & sierakowski, m. r. (2017). piezoelectric immunochip coated with thin films of bacterial cellulose nanocrystals for dengue detection. biosensors and bioelectronics, 92: 47–53. [45] salim, z. t., hashim, u., arshad, m. k. m., fakhri, m. a., & salim, e. t. (2017). frequency-based detection of female aedes mosquito using surface acoustic wave technology: early prevention of dengue fever. microelectronic engineering, 179: 83–90. iium engineering journal, vol. 19, no. 2, 2018 zainuddin et al. 153 [46] jahanshahi, p., zalnezhad, e., sekaran, s. d., & adikan, f. r. m. (2014). rapid immunoglobulin m-based dengue diagnostic test using surface plasmon resonance biosensor. scientific reports, 4: 3851. [47] kamil, y. m., bakar, m. a., mustapa, m. a., yaacob, m. h., abidin, n. h. z., syahir, a., mahdi, m. a. (2018). label-free dengue e protein detection using a functionalized tapered optical fiber sensor. sensors and actuators b: chemical, 257: 820–828. [48] jahanshahi, p., wei, q., jie, z., ghomeishi, m., sekaran, s. d., & mahamd adikan, f. r. (2017). kinetic analysis of igm monoclonal antibodies for determination of dengue sample concentration using spr technique. bioengineered, 8(3): 239–247. [49] rich, r. l., & myszka, d. g. (2004). why you should be using more spr biosensor technology. drug discovery today: technologies, 1(3): 301–308. microsoft word 119-488 vetted-abd.doc iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kh. s. karimov and m. abid 1 combined uncovered sheet-and-tube pvtcollector system with built-in storage water heater kh. s. karimov 1,2 and muhammad abid 1 1 gik institute of engineering sciences and technology, topi, pakistan. 2 s.u.umarov physical technical institute of academy of sciences, dushanbe, tajikistan. khasan@giki.ed.pk, abid@giki.edu.pk abstract: this work describes the design and investigation of a simple combined uncovered sheet-and-tube photo-voltaic-thermal (pvt) collector system. the pvtcollector system consists of a support, standard pv module (1.22 x 0.305 m, area=0.37m2, fill factor=0.75), sheet-and-tube water collector and storage tank-heater. the collector was fixed under pv module. inclination angle of the pvt-collector to the horizontal plane was 45 degree. the storage tank-heater played double role i.e. for storage of hot water and for water heating. the pvt-collector system could work in the fixed and tracking modes of operation. during investigations of pvt-collector in natural conditions, solar irradiance, voltage and current of pv module, ambient temperature and water temperature in storage tank were measured. average thermal and electrical powers of the pvt-collector system at the tracking mode of operation observed were 39w and 21w, with efficiencies of 15% and 8% respectively at the input power of 260w. the maximum temperature of the water obtained was 42 oc. the system was observed efficient for low-temperature applications. the pvt-collector system may be used as a prototype for design of pvt-collector system for domestic application, teaching aid and for demonstration purposes. abstrak: kerja ini menerangkan reka bentuk dan penyiasatan sebuah sistem pengumpul berbentuk helaian dan tiub foto voltan (pvt) yang mudah. sistem pengumpul pvt terdiri dari alat sokongan, modul pv standard (1,22 x 0,305 m, kawasan = 0.37m2, faktor isi = 0.75), sistem pengumpul dan pemanas air berbentuk helaian dan tiub. sistem pemungut diletakkan di bawah modul pv. sudut kecondongan pengumpul pvt satah mengufuk adalah 45 darjah. tangki penyimpanan memainkan dua peranan, iaitu sebagai tempat menyimpan dan memanaskan air. sistem pvt-pengumpul boleh bekerja dalam mod tetap dan juga mod pengesanan. dalam kajian ini, kelakuan pvt pemungut-dalam keadaan semulajadi, sinaran suria, voltan dan sekarang pv modul, suhu ambien dan suhu air di dalam tangki simpanan telah diukur. purata haba dan kuasa elektrik sistem pvt-pemungut pada mod pengesanan operasi yang diukur adalah 39w dan 21w, dan kecekapan masing-masing adalah 15% dan 8% pada kuasa input 260w. suhu maksima air yang diperolehi ialah 42 oc. sistem ini berkesan pada suhu-suhu rendah. sistem pvt-pengumpul ini sesuai digunakan sebagai prototaip bagi reka bentuk sistem pvt-pemungut untuk aplikasi domestik, alat pengajaran dan untuk tujuan demonstrasi. keywords: combined system; module; collector; storage water-heater iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kh. s. karimov and m. abid 2 1. introduction utilization of solar energy, which is environment-friendly, is very important for the sustainable development. as is known that one of the limiting factors of solar modules and collectors applications in especially urban area is the availability of the required sufficient land [1,2], therefore, during the last years, combined photo-voltaic-thermal collectors’ designs were implemented and investigated in practice [3-12]. the main advantage of the pvt-collector system observed is to produce more electrical and thermal energy in comparison to the conventional pv modules and collectors that partially cover the same area. in addition, in comparison to separate thermal and pv system, the pvt-collectors provides architectural uniformity, reduce installation cost [13]. basically four groups of water type pvt-collectors namely: sheet-and-tube pvt-collectors, channel pvtcollectors, free flow pvt-collectors and two-absorber pvt-collectors were evaluated and optical and thermal efficiencies of the pvt-collectors were calculated [13]. except of the uncovered pvt-collector all discussed designs with additional glass sheet bring more reflection losses and less electrical efficiency of the system. it is also concluded in [13] that the uncovered pvt-collector for low temperature applications is most promising design. table 1 shows transmission-absorption factors for the various design concepts (am 1.5 spectrum) of sheet-and-tube pvt-collectors. τα, ταw and τpv are transmissionabsorption coefficients of pvt-collector, water and pv-module respectively [13]. maximum τpv is observed for the uncovered pvt-collector showing potentially highest output electric energy in comparison to pvt-collectors with one-cover and twocovers. on the other hand uncovered pvt-collector shows lower thermal efficiency compared to the covered by glass sheet pvt-collectors. so it would be reasonable to design the uncovered pvt-collector system where at high electrical efficiency the thermal efficiency would be improved. therefore in this paper we present the design of uncovered pvt-collector system where unlike to [13] the built-in storage water heater is installed. table 1: transmission-absorption factors for the various design concepts (am 1.5 spectrum) of sheet-and-tube pvt-collectors. design concept of pvt-collector τα ταw τpv uncovered sheet-and-tube 0.78 1.00 one-cover sheet-and-tube 0.74 0.92 two-cover sheet-and-tube 0.71 0.84 2. materials and methods figure 1a shows the design of a pvt-collector system consisting of a metallic support (1), standard pv module (2), sheet-and-tube water collector (3), and storage tank-heater (4). the water temperature in the metallic storage tank-heater was measured by thermometer (5). wheels (6 and 7) allowed changing position of the pvt collector manually at the tracking mode of operation. in the front and two sides of the right-angle prism tank (4) the glazing was made (8) with air gap of 1cm and the surface of the tank from outside was blackened for additional heating of water by solar radiation. the bottom, iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kh. s. karimov and m. abid 3 back side and the top of the tank was covered by glass-wool and aluminum foil. the volume of water tank was 20 liters. connecting pvt-collector and the tank pipes were insulated by glass-wool and aluminum foil. the cold water was filled in the system through inlet (9), the tap (10) served to release the hot water. the dimensions of the pv module were 1.22 x 0.305 m with a total area of 0.37 m2. pv module with crystalline silicon cells that was used in the pvt-collector system, inclination arrangement and absorbing plate is shown in fig. 1b-d. the sheet-and-tube water collector’s design mainly was similar to the described in [14]. figure 2 shows the design of the collector. on copper sheet of size of 0.86 x 0.25 m four parallel copper tubes were fixed by welding. the copper was selected due to high thermal conductivity (385 w/moc) as compared to aluminum (211 w/moc) and steel (54 w/moc). the collector was insulated by glass-wool, covered by aluminum foil and plywood and fixed under pv module. interfaces of pv module’s back and collector’s sheet were in good thermal contact as collector was squeezed to the back of the module. table 2 shows geometrical parameters of the collectors: w is distance between of the centers of neighboring tubes, d is external diameter of the tube, δ is thickness of the metallic absorbing plate. internal diameter of the tubes used in the present work was 0.006 m. (a) (b) (c) (d) fig. 1: (a) design of pvt collector system, (b) pv module, (c) inclination setup, (d) absorbing plate. the latitude (φ) of the place where the pvt-collector was investigated was 34 degree. therefore an inclination angle (β) of the pvt-collector to the horizontal plane used was 45 degree (usually β= φ+11degree, φ and φ-11 degree in winter, spring/autumn and summer respectively) as the experiments were conducted from february to april 2009 at gik institute during 7-9 hrs. the storage tank-heater played double role i.e. for storage of hot water and for water heating. the pvt-collector system could work in the fixed and tracking modes of operation. during investigations of pvt-collector in natural conditions, solar irradiance, voltage and current of pv module, ambient temperature and water temperature in storage tank were measured. 1 2 3 4 6 7 9 45o 8 5 10 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kh. s. karimov and m. abid 4 fig. 2: design of pvt collector. table 2: geometrical parameters of the sheet-and-tube water collectors. reference w (m) d (m) δ (m) [1] 0.200 0.020 0.003 [14] 0.125 0.008 0.035 [14] 0.100 0.008 0.045 present work 0.060 0.008 0.003 3. results and discussion figure 3a shows i-v characteristics of the module at average irradiance of 878 w/m2 and inclination angle of 45o. the fill factor (ff) of the modules was 0.75. figure 3b shows the output electric power at the tracking mode of operation measured during one of the cloudy day for one pv module. the output electric power (pel) was calculated as per [2]: pel = isc voc ff (1) where isc and voc are short circuit current and open-circuit voltage respectively. the average efficiency (ηel) of the conversion of solar energy into electric power was calculated as per [13]: ηel =pel / ga (2) where g is irradiance in w/m2, a is area of the module. efficiency (ηel) of 8% was calculated with average solar input power of 260 w. inlet outlet module absorbing plate tubes a a module a-a tubes absorbing plate glass wool aluminum foil plywood welding iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kh. s. karimov and m. abid 5 0.0 0.5 1.0 1.5 2.0 0. 0 6. 8 13 .6 13 .6 13 .6 15 .6 15 .7 15 .9 17 .8 17 .9 18 .0 c ur re nt (a ) voltage (v) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 7. 5 8. 0 8. 5 9. 0 9. 5 10 .0 10 .5 11 .0 11 .5 12 .0 12 .5 13 .0 13 .5 14 .0 14 .5 15 .0 15 .5 16 .0 16 .5 17 .0 o ut pu t p ow er (w ) time of a day (hr) (a) (b) fig. 3: (a) i-v characteristics of the module at irradiance of 878w/m2 and inclination angle of 45o, (b) electric output power vs day time for the pvt-collector system for a variable cloudy day. figure 4 shows the temperature of water (tw) in the tank versus day time (t) relationship at the tracking mode of operation for the variable cloudy day. it is seen that the tw increased from 26 ºc to 42 ºc. average ambient temperature (ta) observed is 26 oc. the collector-tank-pipes loop is considered as a thermosyphon system where the water flow takes place due to the differences of the density of the hot and cold water [1]. at the same time, experimentally water temperature in the tank was measured where in the first approximation it was assumed that the water is in the static condition. therefore thermal output power (pth) for the case of static mass can be calculated as [1]: 20.0 25.0 30.0 35.0 40.0 45.0 8. 0 8. 5 9. 0 9. 5 10 .0 10 .5 11 .0 11 .5 12 .0 12 .5 13 .0 13 .5 14 .0 14 .5 15 .0 15 .5 16 .0 16 .5 17 .0 t em pe re ra tu re ( c ) time of a day(hr) fig. 4: the temperature of water in the tank vs day time for a variable cloudy day. pth = mc (dtw / dt) (3) where m is a mass of water, c is specific heat capacity. by evaluation of the average dtw/dt from fig. 4, pth was calculated and finally the efficiency of solar energy was converted into the thermal power as: ηth = pth / ga (4) ηth of 15% was calculated and may be considered the minimum as the water was not taken from tank during a day i.e. the total mass of water was constant during a day. if the tank’s water is used several times a day, definitely the efficiency will increase. in the case of fixed mode of operation, without tracking, the experiments were conducted in variable cloudy day during 6 hrs, hence; it was observed that at the input power of 290 w the maximum temperature of water was almost 35 oc at the average ambient temperature of 28 oc. the efficiencies of solar energy conversion into electric and thermal powers iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kh. s. karimov and m. abid 6 calculated were 7% and 13% respectively. at the tracking mode of operation the efficiencies of solar energy conversion into electric and thermal powers calculated were 8% and 15% respectively. in this case the experiments were conducted during 9.5 hrs. different duration of daily experiments was due to the variable clouds in february to april, 2009. at the same duration of experimental days and clear sky the efficiency of the tracking system is approximately 30% more than the fixed system [15]. in [13] annual thermal (24%) and electrical (7.6%) efficiencies were calculated for the case of uncovered sheet-and-tube pvt-collector system. the electrical efficiency is approximately the same as obtained in the present study, but the thermal efficiency is higher. the reasons of this is in the intensity of radiations, ambient temperature, construction of collector etc., and mainly maybe due to the approaches that were used for the calculations of the thermal power and accordingly the efficiency. in [13] the thermal power was calculated by: pth = c(t2-t1) dm/dt (5) where dm/dt is mass flow through the collector in a unit of time and t1 and t2 are the temperatures of water in the inlet and outlet of the collector. table 3 shows the efficiencies for the pvt-collectors design concepts: annual average efficiencies for the systems described in [13] and average efficiency for the february-april 2009 for the designed pvt-collectors presented in this study. table 3: average efficiencies for the pvt-collectors design concepts [13]. 4. conclusion the uncovered sheet-and-tube pvt-collector system worked successfully in both the fixed and tracking modes of operation. during investigations of pvt-collector in natural conditions, solar irradiance, voltage and current of pv module, ambient temperature and water temperature in storage tank were measured. average thermal and electrical powers of the pvt-collector system at the tracking mode of operation observed were 39 w and 21 w, with efficiencies of 15% and 8% respectively at the input power of 260 w. the maximum temperature of the water obtained was 42 oc. whereas at at the fixed mode of operation the efficiencies of solar energy conversion into electric and thermal powers calculated were 7% and 13% respectively at the input power of 290 w.the system was system thermal efficiency electrical efficiency pv 7.2% sheet and tube pvtcollector uncovered 24% 7.6% sheet and tube pvtcollector 1 cover 35% 6.6% sheet and tube pvtcollector 2 covers 38% 5.8% present work 15% 8.0% iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics kh. s. karimov and m. abid 7 observed efficient for low-temperature applications. the pvt-collector system may be used as a prototype for design of pvt-collector system for domestic application, teaching aid and for demonstration purposes. the output power of the pvt-collector system can be increased easily by increase of the number of pvt-collector units. acknowledgements the authors acknowledge pakistan science foundation for funding to complete this project and gik institute for support to carry out this research work. the authors are thankful to a. iftikhar and h. safeer for their help in fabrication of the pvt-collector system and experimental work. references [1] twidell ,j.w. and weir, a.d. renewable energy resources. e & f.n. spon, london, 1986. [2] markvart t. , solar electricity .john wiley & sons, new york, 2000. [3] russell t., beall j., lofersky j.j., roessler b., dobbins r., shewchun j., krikorian j., case c., doodlesack g., oates w. proceedings of ieee photovoltaic specialists conference, 1981. [4] hendrie s.d. report mit lincoln laboratory, 1982. [5] bergene t., lovvik o.m. solar energy, 55 (6), (1995), pp.453-462. [6] tripanagnostopoulos y., nousia t., yianoulis p.solar energy, 72 (3), (2002), pp. 217-234. [7] rockendorf g., sillman r., podlowski l., litzenburger b. proceedings of ises 1999 solar world congress, july 4-9, jerusalem, israel. [8] sorensen b. proceedings of 17th european photovoltaic solar energy conference, october 22-26, munich, germany, 2001. [9] sandnes b., rekstad j. solar energy 72 (1), (2002), pp. 63-73. [10] leenders f., schaap a.b., van der ree b.c.g., van helden w.g.j. proceedings of eurosan 2000, copenhagen, denmark. [11] bakker m., zondag h.a., van helden w.g.j. proceedings of pv in europe-from pv technology to energy solutions conference and exhibition, october 7-11, rome, italy, 2002. [12] bazilian m.d., prasad d. proceedings of eurosun 2000, copenhagen, denmark. [13] zondag h.a., de vries d.w., van helden w.g.j., van zolingen r.j.c., van steenhoven a.a. solar energy, 74 (2003) , pp. 253-269. [14] tiwari g.n. solar energy fundamentals, design, modeling and application. narosa publishing house, new delhi, india, 2004. [15] karimov kh.s., saqib m.a., akhter p., ahmed m.m., chattha j.a., yousafzai s.a. solar energy materials & solar cells. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 an enhanced packet scheduling algorithm for the downlink cognitive long term evolution-advanced huda adibah mohd ramli, mohamad ismat hafizi mansor department of electrical and computer engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. *corresponding author: hadibahmr@iium.edu.my (received: 18th june 2019; accepted: 30th july 2019; published on-line: 20th january 2020) abstract: a packet scheduling algorithm known as enhanced maximum-largest weighted delay first (em-lwdf) is proposed in this paper. it aims to maximize the number of real time (rt) and non real time (nrt) users that meet their desired quality of service (qos) in the cognitive long term evolution-advanced (lte-a). this cognitive lte-a allows its component carriers (ccs) to be combined with licensed ccs from another system. this enables the lte-a to further expand the available bandwidth for packet transmission. the em-lwdf algorithm decides the priority of each user on the basis of the desired qos of each packet, the urgency of each packet, channel quality and the average throughput. the potential of this algorithm is validated via computer simulation where it is able to simultaneously maximize more users that meet their desired qos in realistic rt and nrt multimedia of the downlink cognitive lte-a. abstrak: algoritma penjadualan paket yang dikenali sebagai enhanced maximumlargest weighted delay first (em-lwdf) dicadangkan dalam kertas ini. ia bertujuan untuk memaksimumkan bilangan pengguna real time (rt) dan non real time (nrt) yang memenuhi kualiti perkhidmatan yang dikehendaki (qos) dalam system kognitif long term evolution-advanced (lte-a). kognitif lte-a ini membolehkan carrier component (cc) untuk digabungkan dengan cc berlesen dari sistem lain. ini membolehkan lte-a untuk memperluaskan jalur lebar yang tersedia bagi penghantaran paket. algoritma emlwdf menentukan keutamaan setiap pengguna berdasarkan qos yang dikehendaki dari setiap paket, kecemasan setiap paket, kualiti saluran dan purata penghantaran. potensi algoritma ini disahkan melalui simulasi komputer di mana ia dapat memaksimumkan lebih banyak pengguna yang memenuhi qos yang dikehendaki mereka dalam realistik rt dan nrt multimedia dari downlink sistem kognitif lte-a. keywords: maximum-largest weighted delay first (m-lwdf); packet scheduling; long term evolution-advanced; quality of service; real time and non-real time 1. introduction the introduction and evolution of various real time (rt) and non-real time (nrt) multimedia content have drastically increased the number of wireless subscriptions. it should be noted that rt content are sensitive to delay whereas nrt is a loss-sensitive multimedia content. to address this scenario, long term evolution-advanced (lte-a) that promises a significant increase in the data speed whilst maximizing the number of users that meet their desired quality of service (qos) was standardized. such increase in the data speed is 51 iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 achieved via carrier aggregation (ca) method. this method combines a number of component carriers (ccs) of the same or different frequency bands. given the current escalating demand on the multimedia contents, the limited ccs of the lte-a will soon be saturated. to offload some portion of the ccs usage, integrating the ccs of the lte-a with other licensed ccs via cognitive radio (cr) seems a feasible solution. it should be noted that the federal communication commission reported in its study that some portions of licensed ccs are heavily utilized while other portions of the ccs licensed to digital video broadcast (dvb) and tv systems are lightly used [1]. this allows more available ccs to be exploited for use by the lte-a users. cr is a technology that allows unlicensed users (for example, lte-a users) to opportunistically utilize the vacant portions of the licensed ccs and quickly release these portions when licensed users (such as dvb users) become active. transmission of multimedia content takes place via packet-switched technology. therefore, packet scheduling is of significant importance in the lte-a. a large number of packet scheduling algorithms have been developed. for example, the most popular conventional maximum largest weighted delay first (m-lwdf) [2] algorithm was developed to meet the desired qos of the rt multimedia content in the single-user legacy wireless systems that have only one cc. the m-lwdf chooses a downlink user to receive its packets based on eq. (1). )( )( *)(*)( iat icq irtai k k kkk (1) k k k tb a log (2) )1(* 1 *)1()( 1 1)1( icq t iiiat t iat k c kk c k (3) where μk(i) is the priority of user k at time i, ak is the desired qos of user k, δk is the contentdependent packet loss threshold of user k, and tbk is the content-dependent buffer delay threshold of user k. it should be noted that the maximum residence time of rt/nrt content in the buffer at the base station is determined by content-dependent buffer delay threshold. rtk (i) is the residence time of the head-of-line (hol) packet at the base station of user k at time i, cqk(i) is the channel quality of user k at time i, atk(i) is the average throughput of user k at time i, tc is a time constant and ik(i+1) is an indicator of the event where packets of user k were transmitted at time k+1. it can be observed in eq. (1) that the packet scheduler in these single-user legacy wireless systems chooses only one user to receive its packets at each time. moreover, in this system, all of the available bandwidth in a cc is used to transmit the packets to this user. this is contrary to packet scheduling in multi-user wireless systems that allows more than one user to receive its packets at each time. similarly in the multi-user wireless systems, a number of extensions of the well-known m-lwdf versions are available. this includes the algorithms developed in [3-5] that exploited the resource block (rb), the average throughput and the packet residence time to further improve the multi-user wireless performance. it should be noted that an rb is the smallest unit of radio resource in lte-a. it contains twelve subcarriers of 15 khz bandwidth 52 iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 each and is of one ms interval. for example, the modified maximum-largest weighted delay first (mm-lwdf) algorithm discussed in [3] uses eq. (4) when determining the priority of each user on each rb, on each cc and at each time. max 1 , ,, ,, )( )( *)(*)( ccl l lk mlk kkmlk iat icq irtai (4) where μk,l,m(i) is the priority of user k on cc l on vacant rb m at time i, ak is the desired qos of user k as defined in eq. (2), rtk (i) is the residence time of the hol packet at the base station of user k at time i, cqk,l,m(i) is the channel quality of user k on cc l on vacant rb m at time i, atk,l (i) is the average throughput of user k on cc l at time i (as defined in eq. (3)) and ccmax is the total number of licensed ccs. besides the extended versions of the m-lwdf, other studies that investigated the packet scheduling algorithms in the literature include [6-14]. based on our study, it was observed that the majority of these conventional multi-user packet scheduling algorithms offer to meet the desired qos of either for rt packets or nrt packets. those ps algorithms that were developed for simultaneous support of both rt and nrt were computationally expensive, did not consider a realistic rt and nrt traffic, or require further performance investigation if these algorithms were to be implemented in the downlink cognitive lte-a. due to the limitations of the conventional packet scheduling algorithms and motivated by the work in [3], this paper proposed an enhancement of the mm-lwdf known as an enhanced m-lwdf (em-lwdf) with the intention to provide support for more rt and nrt users that meet their desired qos. the em-lwdf algorithm takes the desired qos of each packet (either rt or nrt), the channel quality, the average throughput and the urgency of each packet into consideration when scheduling packets on each rb and on each cc. the remaining parts of this paper are structured as follows: section ii explains in detail the proposed em-lwdf algorithm, thereafter followed by the description of the simulation environment in section iii. results are analytically discussed in section iv whereas section v marks the conclusions of the paper. 2. enhanced maximum-largest weighted delay first (em-lwdf) algorithm the co-existence of the downlink lte-a and dvb system as shown in fig. 1 is considered in this paper. it should be noted that the base station of the lte-a is known as enodeb. it is assumed that the dvb system has a total of two licensed ccs of 3 mhz bandwidth each. the ccs of the lte-a are not taken into account as this paper aims to investigate the impact on cognitive lte-a performance for opportunistic use of the vacant portions of the licensed dvb ccs via cr. the em-lwdf algorithm aims to simultaneously provide satisfactory qos for both rt and nrt multimedia contents for more users. therefore, to achieve its intention, the proposed algorithm selects the packets that maximize eq. (5) at each time, on each licensed cc and on each vacant rb. 53 iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 fig. 1: downlink cognitive lte-a topology [15]. max 1 , ,, ,, )( )( * )( )( *)( ccl l lk mlk kik ki kmlk iat icq irttb itb ai (5) where μk,l,m(i) is the priority of user k on cc l on vacant rb m at time i, ak is the desired qos of user k as defined in eq. (2), and tbk is the content-dependent buffer delay threshold of user k. rtk (i) is the residence time of the hol packet at the enodeb of user k at time i, cqk,l,m(i) is the channel quality of user k on cc l on vacant rb m at time i, atk,l (i) is the average throughput of user k on cc l at time i (as defined in eq. (3)) and ccmax is the total number of licensed ccs. the em-lwdf has the following similarities with the mm-lwdf. it takes into account the desired qos of each user, channel quality on each licensed cc and on each vacant rb as well as the average throughput on each licensed cc when making scheduling decisions. the desired qos allows the em-lwdf as well as the mm-lwdf to give a slightly higher priority for delay-sensitive rt packets whereas the channel quality enables the multiuser diversity to be exploited (i.e. a user with a good channel quality is favoured for packet transmission over the ones located at the cell edge. this allows the user to receive more packets as the channel quality on vacant rb used for packet transmission is good). if only the channel quality is accounted, then it will starve other users of poor channel qualities. therefore, the average throughput on each licensed cc is accounted so as to increase fairness among the users by increasing the chances to users whose packets were not selected in the previous time to be scheduled in the consecutive time. the main difference between the em-lwdf and the mm-lwdf is the exploitation of the residence time of the hol. in this case, the mm-lwdf only considers the packets that have resided the longest at the enodeb (rtk(i)) whereas the em-lwdf considers the outcome of )(irttb tb kk k so as to ensure that the most urgent packets are given a higher priority than the packets that have resided the longest at the enodeb. this is one of the attempts made so as to reduce the number of discarded packets for violation of the content-dependent buffer delay threshold and hence reduce the rt and nrt packet loss 54 iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 3. simulation environment the performance of the proposed em-lwdf algorithm was evaluated on the basis of a packet loss ratio (plr) metric given that it is the most important metric when evaluating the qos of multimedia performance. definition of the plr metric is given as follows: k k t i k k k t i k ipacketarrive ipacketdiscard plr 1 1 1 1 )(_ )(_ (6) where discard_packetk(i) is the size of discarded packets of user k at time i, arrive_packetk(i) is the size of packets that arrived at the enodeb buffer of user k at time i, k is the total number of users, and t is the total simulation time. the performance evaluation was conducted via a computer simulation and the simulation was run for a sufficient length of time to get stable results. the downlink cognitive lte-a was modelled to contain only one enodeb. this enodeb is located at the centre of a cell of 450 m radius. users are assumed to have uniform distribution within the cell and move at 30 km/h speed. a total of two dvb ccs of 3 mhz bandwidth is assumed and these ccs are of 700 mhz and 704 mhz bandwidths. given that this paper aims to investigate the performance improvement due to rt and nrt multimedia scheduling in the cognitive ltea system, the ccs of the lte-a are not taken into account in this performance evaluation. the content-dependent buffer delay threshold for rt and nrt contents are capped at 50 ms and 200 ms respectively. rt and nrt packets are discarded and considered as loss packets if their residence times exceed these thresholds. the plr threshold for rt multimedia content is limited to 10-3 whereas 10-6 is the limiting plr threshold for the nrt content. these thresholds are considered acceptable 3gpp thresholds. moreover, it is assumed that the rt users are streaming video with 256 kbps average data speed whereas the nrt users are browsing the web. it was assumed that the system has a variable number of rt and nrt users (i.e. 50:50, 75:25 and 25:75) to allow for the collection of more accurate simulation results. 4. results and discussion to assess the em-lwdf, its performance was evaluated and compared with the wellknown single-user m-lwdf [2] (also referred to as (single carrier m-lwdf, scmlwdf) and mm-lwdf [3] algorithms. the sc m-lwdf was selected as the benchmark given its popularity and ability to meet the desired multimedia qos in the single-user wireless systems. moreover, to investigate m-lwdf in the multi-carrier wireless system, mm-lwdf was considered for benchmarking the em-lwdf. the results are divided into three subsections for different distribution of rt and nrt cognitive lte-a users. 4.1 50:50 rt and nrt cognitive lte-a users rt plr of the em-lwdf, sc m-lwdf and mm-lwdf algorithms with increasing number of cognitive lte-a users is illustrated in fig. 2. as previously discussed in section 3, the desired rt qos is met if the plr is kept below 10-3 (see threshold line in the figure). the figure depicts that the em-lwdf outperforms the sc m-lwdf and mm-lwdf in maximizing the number of cognitive lte-a users at the required rt plr. table 1 shows that the em-lwdf supports 185% and 9.6% more cognitive lte-a users over the sc m55 iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 lwdf and mm-lwdf algorithms respectively. this improvement can be considered significant as the rt users are streaming video at 256 kbps average data speed. the nrt plr performance with increasing number of cognitive lte-a users of the em-lwdf, sc m-lwdf and mm-lwdf are demonstrated in fig. 3. when compared with the rt, the nrt content is more sensitive to lost packets. it requires its plr to be maintained below 10-6 threshold. the figure demonstrates that with increasing number of cognitive lte-a users, the em-lwdf has a comparable performance with the mm-lwdf whereas the sc m-lwdf is the worst. however, the threshold of 10-6 threshold is exceeded by all three ps algorithms even for a small number of cognitive lte-a users. this can be considered as acceptable because of the vacancy of the rbs in the downlink cognitive lte-a (vacant rbs can only be used by the cognitive lte-a users when licensed dvb users are not active and these cognitive lte-a users have to compete for these scarce vacant rbs among themselves). fig. 2: rt plr vs cognitive lte-a users 50:50. fig. 3: nrt plr vs cognitive lte-a users 50:50. table 1: maximum number of cognitive lte-a users with satisfied qos of rt contents (50:50) ps algorithms maximum number of cognitive lte-a users percentage of improvement over benchmark ps algorithms em-lwdf 57 sc m-lwdf 20 185% mm-lwdf 52 9.6% 4.2 75:25 rt and nrt cognitive lte-a users in fig. 4, the rt plr performance of em-lwdf, sc m-lwdf and mm-lwdf are illustrated where 75% of the system capacity is rt cognitive lte-a users and the remaining 25% is the nrt cognitive lte-a users. the figure implies that em-lwdf and mm-lwdf have a significantly greater number of rt cognitive lte-a users that met the required rt plr compared to sc m-lwdf. based on table 2, the em-lwdf supports 200% and 15.4% more rt cognitive lte-a users compared to sc m-lwdf and mm-lwdf, respectively. in comparison with the data in table 1, the em-lwdf improves 15% and 5.8% more rt users compared to sc m-lwdf and mm-lwdf respectively in maximizing rt cognitive lte-a users at the required rt plr. 56 iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 fig. 4: rt plr vs cognitive lte-a users 75:25. fig. 5: nrt plr vs cognitive lte-a users 75:25. table 2: maximum number of cognitive lte-a users with satisfied qos of rt contents (75:25) ps algorithms maximum number of cognitive lte-a users percentage of improvement over benchmark ps algorithms em-lwdf >60 sc m-lwdf 20 200% mm-lwdf 52 15.4% the nrt plr performance of em-lwdf, sc m-lwdf and mm-lwdf when the distribution of rt and nrt cognitive lte-a users is 75:25 is shown in fig. 5. it is demonstrated in the figure that similar to the results achieved in sub-section 4.1, all algorithms exceed the nrt plr threshold. this is due to the nrt contents being more sensitive to packet loss as compared to the rt. however, the figure shows that the emlwdf has comparable performance as mm-lwdf while the sc m-lwdf significantly lags behind both algorithms. 4.3 25:75 rt and nrt cognitive lte-a users the rt plr performance of em-lwdf, sc m-lwdf and mm-lwdf with 25:75 distributions of rt and nrt cognitive lte-a users are demonstrated in fig. 6. it can be seen in the figure that em-lwdf achieves similar performance compared to mm-lwdf and significantly outperforms the sc m-lwdf algorithm. table 3 shows that em-lwdf supports the same number of rt users as mm-lwdf and 130.8% more rt users compared to sc m-lwdf. the sc-mlwdf supports more users (i.e. 26 in 25:75 rt and nrt cognitive lte-a users distribution as compared to 20 in 75:25 rt and nrt cognitive ltea users distribution) because there are smaller number of rt users as compared to nrt users competing for the scarce vacant rbs. finally, the nrt plr that indicates similar performances as in fig. 3 and fig. 5 are provided in fig. 7. the nrt plr threshold of 10-6 is more sensitive compared to the rt plr threshold of 10-3 thus resulting in all of the three algorithms exceeding the nrt plr threshold. however, em-lwdf still manages to achieve comparable performance compared to mm-lwdf whereas the performance of the sc m-lwdf significantly degraded. though the results indicate a fluctuation trend, this does not affect the overall performance of each algorithm given that the scale is very small. 57 iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 fig. 6: rt plr vs cognitive lte-a users 25:75. fig. 7: nrt plr vs cognitive lte-a users 25:75. table 3: maximum number of cognitive lte-a users with satisfied qos of rt contents (25:75) ps algorithms maximum number of cognitive lte-a users percentage of improvement over benchmark ps algorithms em-lwdf >60 sc m-lwdf 26 131% mm-lwdf >60 0% the substantial improvement (especially in maximizing the number of cognitive lte-a users with the desired rt qos) of the em-lwdf over the sc m-lwdf is because the sc m-lwdf assigns all of the vacant rbs to a selected user at each time and on each licensed cc. at a time, a number of vacant rbs in a licensed cc may not be utilized if the packets of the chosen user in the enodeb buffer have all been transmitted. on the contrary, the emlwdf allows efficient use of the vacant rbs at each time and on each licensed cc, by selecting a cognitive lte-a user for packet transmission on each vacant rb. the rt plr of em-lwdf is slightly better than the mm-lwdf because the algorithm always prioritizes cognitive lte-a users with the most urgent packets (i.e. the residence time of the packets are approaching the content dependent-buffer delay threshold). this is one of the attempts made so as to reduce the rt plr where it avoids rt packets from being discarded due to delay violation in the consecutive scheduling time. even though there is a slight improvement achieved by the em-lwdf as compared to the mm-lwdf, the emlwdf does not introduce any new complexity in its algorithm given that the information of tbk and rtk are available at the enodeb packet scheduler. based on the results obtained in this performance evaluation it can be concluded that when compared with benchmark ps algorithms, the implementation of em-lwdf in the downlink cognitive lte-a system is more suited. 5. conclusion an enhanced packet scheduling algorithm known as em-lwdf is proposed in this paper. the em-lwdf algorithm was developed to prioritize the user with most urgent packet instead of the user with the packet that has waited the longest. in order to validate this improvement, several performance comparisons have been conducted. the results demonstrated that the proposed algorithm outperforms sc m-lwdf in supporting more 58 iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 cognitive lte-a users at the required rt plr where it supports 185%, 200%, and 131% more cognitive lte-a users in 50:50, 75:25, and 25:75 distributions of rt and nrt cognitive lte-a users. the em-lwdf algorithm also slightly outperforms mm-lwdf algorithm where it supports 9.6% and 15.4% more cognitive lte-a users at required rt plr in 50:50 and 75:25 distributions of rt and nrt cognitive lte-a users and provides similar performance in the 25:75 situation. em-lwdf achieves this feat without introducing any new complexity in its algorithm as compared to the mm-lwdf. future works include enhancement of the em-lwdf such that the desired qos of the rt and nrt multimedia content can be simultaneously met. additionally, the performance of the em-lwdf will be compared with other packet scheduling algorithms that were developed for downlink cognitive lte-a that simultaneously support rt and nrt multimedia contents. performance evaluation of the em-lwdf in multiple hexagonal cells taking the mobility and handover into account as well as with larger number of users (not capped at 60) will also be a part of future study. acknowledgement this research is funded by the kementerian pendidikan malaysia under the grant id of frgs/1/2019/tk04/uiam/02/2. references [1] osa v, herranz c, monserrat jf, gelabert x. (2012) implementing opportunistic spectrum access in lte-advanced. eurasip journal on wireless communications and networking, 2012(1): 1-17. [2] andrews m, kumaran k, ramanan k, stolyar a, whiting p, vijayakumar r. (2001) providing quality of service over a shared wireless link. ieee communications magazine, 39(2): 150154. [3] ramli ham. (2014) performance of maximum-largest weighted delay first algorithm in long term evolution-advanced with carrier aggregation. 2014 ieee wireless communications and networking conference (wcnc): 1415-1420. [4] aiyetoro g, takawira f. (2015) a new user scheduling scheme in lte/lte-a networks using cross-layer design approach. milcom 2015 2015 ieee military communications conference: 1-5. [5] aiyetoro g, takawira f. (2014) a cross-layer based packet scheduling scheme for multimedia traffic in satellite lte networks. 2014 6th international conference on new technologies, mobility and security (ntms): 1-6. [6] bahreyni ms, sattari-naeini v. (2014) fairness aware downlink scheduling algorithm for lte networks. journal of mathematics and computer science, 11(2): 53-63. [7] alfayly a, mkwawa ih, sun l, ifeachor e. (2015) qoe-driven lte downlink scheduling for voip application. 2015 12th annual ieee consumer communications and networking conference (ccnc): 603-604. [8] chung yl, jang lj, tsai z. (2011) an efficient downlink packet scheduling algorithm in lte-advanced systems with carrier aggregation. 2011 ieee consumer communications and networking conference (ccnc): 632-636. [9] mnif k, masmoudi a, kamoun l. (2014) adaptive efficient downlink packet scheduling algorithm in lte-advanced system. the 2014 international symposium on networks, computers and communications: 1-5. [10] li j, xu b, xu z, li s, liu y. (2006) adaptive packet scheduling algorithm for cognitive radio system. international conference on communication technology: 1-5. [11] mansor mih, ramli ham, asnawi al, isa fnm, (2017) simulation of packet scheduling in cognitive long term evolution-advanced. indonesian journal of electrical engineering & computer science 8(2): 533-540. 59 iium engineering journal, vol. 21, no. 1, 2020 mohd ramli and mansor https://doi.org/10.31436/iiumej.v21i1.1178 [12] zhang y, zhang y, teng y, song m (2014) an efficient carrier scheduling scheme in cognitive lte-advanced system with carrier aggregation, ieee 25th annual international symposium on personal, indoor, and mobile radio communication (pimrc): 1970-1974. [13] vijayarani r, nithyanandan l, (2017) dynamic slot-based carrier scheduling scheme for downlink multimedia traffic over lte advanced networks with carrier aggregation. turkish journal of electrical engineering & computer sciences, 25(4): 27962808. [14] kaur r, kaur n, (2016) a delay reduced scheduling approach for fast spectrum access in cognitive radio. international journal of engineering development and research, 4(2) 19461955. [15] ramli ham, isa fnm, asnawi al, jusoh az, azman aw, (2019) urgency-aware scheduling algorithm for downlink cognitive long term evolution-advanced. ieee 89th vehicular technology conference (vtc2019-spring): 1-6. 60 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 biodelignification of lemon peels using aspergillus sp. to improve yield and composition of extxracted lemon oil muhammad yusuf abduh*, enjelina nababan, firdanta ginting, jenny juliati and husna nugrahapraja school of life sciences and technology, institut teknologi bandung (itb) jalan ganesha no. 10 bandung 40132 indonesia *corresponding author: yusuf@sith.itb.ac.id (received: 24th december 2019; accepted: 12th april 2020; published on-line: th july 2020) abstract: lemon oil obtained from lemon peels has a high market value. however, the presence of lignocellulose composed of cellulose, hemicellulose, and lignin, can inhibit the extraction process. this study aimed to determine the effect of biodelignification on lemon peels using aspergillus sp. towards lignin content, yield, chemical composition, and productivity of lemon oil. a solid-state fermentation was carried out under controlled relative humidity of 99% and a light intensity of ~0 w/cm2 for 0, 3, 6, and 9 days. the number of spores used was in the range of 0.3-5 x 105 spores/gram substrate with a ratio of spore solution and substrate of 1:1. extraction was performed using a steam distillation method at 97-98°c for 6 hours. the results showed that the lignin content decreased with an increased fermentation time: 8.01%, 6.97-7.28%, 5.83-7.28%, and 4.35-5.44% dry weight for day 0, 3, 6, and 9, respectively. lemon oil yield increased as the period of fermentation increased up to 0.27%, 0.29-0.31%, 0,30-0.46%%, and 0.67-0.79% for day-0, 3, 6, and 9, respectively. a major component of lemon oil is d-limonene. the d-limonene content reached 72,54% for day-0, 73-99% for day-3, 75,09-84.59% for day-6, and 88,0399% for day-9. abstrak: minyak lemon yang terhasil dari kupasan lemon mempunyai nilai tinggi dalam pasaran. walau bagaimanapun, kehadiran lignoselulosa yang terdiri daripada selulosa, hemiselulosa dan lignin, boleh merencatkan proses pengekstrakan. kajian ini bertujuan memperolehi kesan biodelignifikasi pada kulit lemon menggunakan aspergillus sp. terhadap kandungan lignin, hasil, komposisi kimia, dan penghasilan minyak lemon. penapaian keadaan-pepejal dijalankan di bawah 99% kawalan kelembapan relatif dan keamatan cahaya ~0 w/cm2 bagi 0, 3, 6 dan 9 hari. bilangan spora yang digunakan adalah dalam lingkungan substrat 0.3-5 x 105 spora/gram dengan nisbah larutan spora kepada substrat adalah 1:1. pengekstrakan dijalankan menggunakan kaedah penyulingan stim pada suhu 97-98°c selama 6 jam. keputusan menunjukkan kandungan lignin berkurangan dengan pertambahan masa penapaian: 8.01%, 6.97-7.28%, 5.83-7.28%, dan 4.35-5.44% berat kering pada hari 0, 3, 6, dan 9, masing-masing. hasil minyak lemon bertambah dengan pertambahan masa penapaian sehingga 0.27%, 0.290.31%, 0,30-0.46%%, dan 0.67-0.79% pada hari 0, 3, 6, dan 9, masing-masing. komponen major minyak lemon adalah d-limonina. kandungan d-limonina mencapai 72,54% pada hari-0, 73-99% pada hari-3, 75,09-84.59% pada hari-6, dan 88,03-99% pada hari-9. keywords: aspergillus sp.; biodelignification; lemon oil; lemon peels; lignin content 55 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 1. introduction essential oils are volatile aromatic compounds that can be obtained from natural sources, usually plants [1]. essential oils contain the characteristic fragrance of the plant from which it is derived. the market of essential oils was valued at usd 3.4 billion in 2016 and it was projected to expand at a compound annual growth rate (cagr) of 9.7% from 2016 to 2024 [2]. this growth was driven by increasing market demand of fragrance and flavouring. essential oils have high economic potential in indonesia, one of the major sources of raw materials for essential oils including lemon [3]. lemon (citrus limon (l.) osbeck) is an evergreen tree that belongs to the family rutaceae with an annual production of 123 million metric ton [4]. most lemon processing industries used lemon flesh and juice as sellable products, but other parts were thrown away as wastes. the wastes consist of peel, seed, and leftover of lemon juice [5]. the lemon peels can be further valorised as a raw material for producing essential oil, particularly lemon oil. lemon oil is one of the essential oils that have high demand worldwide. in 2007, lemon oil world production reached up to 9,200 metric tons [6] and the market is anticipated to expand at a 5.5% cagr for the period of 2018-2027 [7]. lemon oil is typically produced via steam distillation of the lemon peels and primarily composed of dlimonene which lies in the range of 72.4-94.5% [8,9]. limonene is a relatively stable monoterpene that can find applications as a stress reliever, antibacterial, antifungal, antioxidant, and neuroprotection [10]. one of the key issues in the production of lemon is its relatively lower yield which lies in the range of 0.65-1.3% on a dry weight basis [9] due to the presence of the rigid structure of the cell wall that consists of lignin, cellulose, and hemicellulose. according to janati et al. [11], lemon peel contains approximately 15.2% lignin which will hinder the isolation of lemon oil during the distillation process. the presence of lignin in lemon peel may be degraded by the use biological agents such as fungus to increase the lemon oil yield. aspergillus sp. can degrade complex carbohydrates into monosaccharides and disaccharides. aspergillus sp. is one of the most effective fungi in terms of utilizing simple saccharides as an organic carbon source to help its growth [12]. therefore, aspergillus sp. is expected to degrade lignin and carbohydrates in order to facilitate the isolation of lemon. aspergillus sp. is reported to contain lignin degradation enzymes such as laccase, lignin peroxidase, and manganese peroxidase [13-15]. a previous study on the solid-state fermentation of aspergillus niger with coir waste had been carried out by mrudula and murugammal [16] for optimum production of cellulase. the fermentation was carried out at ph 6, 30°c, and moisture ratio of 1:2 (weight: volume) for 72 hours to optimize the biosynthesis of cellulase with an enzyme activity of 8.89 u per g of dry mycelial bran. botella et al. [17] also has investigated the effect of particle size, initial moisture, and supplementation with carbon sources for the solid-state fermentation of grape pumice with aspergillus awamori to produce high-value hydrolytic enzymes. it has been reported that xylanase activity reached a maximum value of 40.4 ± 15.6 iu/gds after 24 hours of fermentation whereas cellulase reached a maximum value of 9.6 ± 0.76 iu/gds within the first 24 hours of the fermentation period. in another study, aspergillus oryzae, was used in a solid-state fermentation of wheat bran and other substrates for producing glucoamylase. optimum production of glucoamylase 1986 μmoles of glucose produced per minute per gram of dry fermented 56 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 substrate) was obtained when the fermentation was carried out at ph 6, 30ºc with 1% starch and 0.25% urea on a weight basis and 100% (volume: weight) initial moisture for 120 hours. other studies also reported that optimum conditions for the growth of aspergillus sp. are at a light intensity of ~0 w/cm2 and controlled humidity of 99% [18,19]. although previous studies on the solid-state fermentation of aspergillus sp. have been reported, systematic studies that report on the biodelignification of lemon peels using different species of aspergillus sp. are still very scarce. hence, this study aims to investigate effect of solid-state fermentation of lemon peels with three different species of aspergillus sp. namely aspergillus oryzae, aspergillus niger, and aspergillus awamori on the yield and chemical composition of lemon oil. 2. materials and methods 2.1 preparation of lemon peels approximately 13.1 kg fresh lemons were squeezed to remove the lemon juice. lemon peels were then separated from the pulps. lemon peels were cut into square-shapes with a size of 0.5 cm x 0.5 cm. finally, lemon peels were sterilized using an autoclave for 15 minutes at 121°c and 1.5 atm [17]. 2.2 preparation of inoculum for aspergillus sp. aspergillus sp. cultures in 39 g/l potato dextrose agar were mixed with 5 ml of nacl (0.85%). subsequently, an inoculating loop was used to retrieve spores on the medium surface. nacl solution mixed with the spores was moved to beaker glasses and the number of spores was counted using a haemocytometer. the spores solution was finally diluted using distilled water to reach a concentration of 0.3-5 x 105 spores/g substrate [17]. this preparation was carried out under aseptic conditions. 2.3 fermentation of lemon peels with aspergillus sp. sterilized lemon peels were moved into punctured trays. after that, the spore solution was added with a ratio of 0.1 ml for one g of substrate into trays and mixed [20]. trays were then covered using black coloured plastics. rami yarns were used to attach plastics to the trays. subsequently, these substrate-containing trays were moved onto container trays to reduce water loss (figure 1). fungus inoculation on lemon peels were carried out using 2 trays for each fungi species with each tray containing approximately 2.2 kg of lemon peels. the inoculation was carried out under aseptic conditions. the fermentation was conducted for 0, 3, 6, and 9 days and the relative humidity was set constant (99%) [20,21]. excess water collected in the container trays was returned to the substrate tray once a day throughout the fermentation process. 57 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 fig. 1: fermentation of lemon peels with aspergillus sp. using two level trays (light intensity: ~0 w/cm2, relative humidity: 99%) 2.4 measurement of lignin content in lemon peels lignin content in the lemon peels was determined using a klason method [22]. lemon peels were cut and dried in an oven until a moisture content of 4%. dried lemon peels were then mashed up using a blender. after that, dried lemon peel powders were sieved using mesh 35 (a size of 0.5 mm). subsequently, 1 g of sieved powders was added with 15 ml of h2so4 (72%) in a beaker glass at room temperature (25°c) while being stirred for 2-3 minutes. afterwards, the beaker glass was covered using a watch crystal for 2 hours and stirred occasionally. the sample was then removed from the beaker glass and mixed with distilled water and h2so4 to achieve an h2so4 concentration of 3%. after that, the mixture was heated for 4 hours and the volume was kept constant followed by settling at room temperature and filtered with a büchner funnel. the lignin content in the sample was calculated using equation (1). (1) where m is mass in gram (g). 2.5 measurement of moisture content in lemon peels the moisture content of the lemon peels was measured using an oven-drying method. lemon peels were weighed before the oven-drying process. the drying was carried out at a temperature of 105 °c until the weight remained constant [23]. the moisture content in the sample can be calculated using equation (2). (2) where m is mass in gram (g). 2.6 extraction of lemon oil using a steam-distillation method fermented lemon peels were dried using an oven at 50°c until the moisture content lies in the range of 70-80%. approximately 200 g of dried fermented lemon peels were mixed with distilled water (2:5 on a weight to volume basis). the distillation was carried out at 96-98°c for 6 hours [9]. the mixture of lemon oil and hydrosol were separated using a separatory funnel. subsequently, the separated lemon oil phase was weighed, and its volume was measured. lemon oil yield was calculated on dry weight basis using equation (3). the productivity of lemon oil can be calculated using equation (4). (3) where m is mass in gram (g). 58 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 (4) where m is mass in gram (g) with distillation time and fermentation period in day. 2.7 characterization of lemon oil the density of lemon oil was calculated by measuring the weight and volume of the lemon oil. the lemon oil mass was weighed using an analytical balance whereas the volume was measured using a 5 ml graduated cylinder. the density was calculated using equation (4). (5) where m is mass in gram (g) and v is volume in millilitre (ml) 2.8 determination of composition using a gas chromatography-mass spectrometry method the composition of lemon oil was analysed using a gas chromatography-mass spectrometry (gc-ms) method at the forensic laboratory centre of bareskrim polri, jakarta. a shimadzu gcms-qp2010 ultra instrument was used for the analysis with the oven temperature of was set an initial temperature of 80°c and final temperature of 100°c in 25 minutes. the front inlet used a split model condition of 290°c, 19.23 psi, and total flow 202.2 ml/minute. the capillary column has nominal length 60 m and set at constant flow mode with a maximum temperature of 350°c, initial pressure of 19.24 psi and initial flow of 1 ml/minute. the thermal aux was operated at an initial temperature of 290°c. the ms equipment was set under a quad ms of 150°c (maximum 200°c) and a source ms of 250°c (maximum 300°c). 3. results and discussion 3.1 effect of moisture content on lemon oil yield after oven-drying at 50°c for 3-24 hours, the moisture content of the lemon peels lies in the range of 45-81%. figure 2 shows that the lemon yield is highly influenced by the moisture content with an optimum moisture content of 77% producing a lemon oil yield of 0.71% dry weight (% dw). drying of essential oil-bearing plants prior to distillation is important to increase the yield of isolated essential oil [24]. low temperature and short drying time have been reported to increase essential oil yield whereas high temperature (>50°c) and long drying period (>24 hours) will decrease essential oil yield due to diffusion of the oil to the surrounding [25]. in this study, lemon peels were oven-dried at 50°c prior to the distillation to increase the lemon oil yield because the presence of water in the cells impedes the extraction of essential oil [27]. hence, reducing the presence of water by oven-drying at 50°c increased the lemon oil yield. however, prolonged drying may result in a moisture content that too low that will disrupt the oil gland and essential oil losses along with water vapour [28,29]. 59 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 fig. 2: effect of moisture content on lemon oil yield 3.2 effect of fermentation time on lignin content and lemon oil yield the fermentation of lemon peels using aspergillus niger, aspergillus awamori, and aspergillus oryzae was carried out for 3, 6, and 9 days as suggested by ferreira et al. [30] that the activity of lignin degradation enzyme (ligninase) of aspergillus sp. increased along with fermentation time and reached an optimum value on the 7th day of incubation. figure 3 shows that the lignin content in lemon peel decreased with the incubation period whereas fig. 4 highlights that the lemon oil yield increased with the incubation period. fig. 3: effect of fermentation with different species of aspergillus sp. on lignin content in lemon peels. 60 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 fig. 4: effect of fermentation with different species of aspergillus sp. on lemon oil yield. initially, the lemon peels contained approximately 8% ± 1.1% dw lignin. this value resembles a lignin content of 7.6% dw reported in the literature [31]. after 9 days of fermentation with aspergillus sp., the lignin content in the lemon peels decreased to 4.4 – 5.4% dw. this may be due to the presence of various lignin degradation enzymes such as lignin peroxidase, manganese peroxidase, and laccase secreted by the aspergillus sp. that were able to attack the lignin structure and caused an oxygen molecule reduction process to become water [32]. as a result of the biodegradation process, the lemon oil yield increased from 0.3% ± 0.02% dw up to 0.67 – 0.79% dw. the increased in lemon oil yield may also be caused by the presence of other enzymes such as cellulase and pectinase that can facilitate the secretion of essential oil from lemon peels [17,33]. gonzález et al. [33] had previously demonstrated that pre-treatment of lemon peels with cellulase increased the lemon oil yield up to 100% from 0.009 to 0.017% on a weight basis after the 3 hours of pretreatment at 30°c [33]. although the lemon yield reported by gonzález et al. [33] was lower as compared to the lemon oil yield reported in other studies, a significant amount of fermentable sugars such as glucose were also produced for further valorisation. 3.4 characterization of lemon oil the lemon oil has a pale-yellow colour that resembles the results reported by boughendjioua and djeddi [34] and in line with the specification for lemon oil. the lemon oil has a density of 0.856 ± 0.001 g/ml which lies in the range of 0.845-0.870 g/ml as reported in the literature [34]. the composition of lemon oil was also analysed by gas chromatography-mass spectrometry (gc-ms) and the results are shown in table 1. from table 1, it can be seen that the composition of lemon oil produced from the solid-state fermentation of lemon peels with different species of aspergillus vary from one another. the major composition of lemon oil in the non-fermented sample (control) is d-limonene (72.5%) which resembles the composition reported in the literature. solid-state fermentation of lemon peels with aspergillus awamori; aspergillus niger, aspergillus oryzae increased the content of d-limonene to 73.1-99%. according to a previous study by wilkins et al. [35], fermentation of lemon peels increased the percentage of limonene 61 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 secretion up to 38-60% due to its inhibitory effect. the secreted limonene would allow more lemon oil to be isolated during the distillation process. in another study by lota et al. [36], citrus sp. cultivated under different soil conditions and different areas proved to contain different d-limonene compositions which lie in the range of 38.1 to 95.8%. the composition of d-limonene in the lemon oil increased from 73.1% (day-3) to 99% (day-9) when the lemon peels were incubated with aspergillus awamori. in contrast, the composition of d-limonene reached its maximum value on day-3 of fermentation when the lemon peels were incubated with aspergillus niger and aspergillus oryzae before slightly decreasing on day-6 and slightly increasing again on day-9. the data shows that the biosynthesis of d-limonene is highly affected by the presence of aspergillus sp. nevertheless, reported studies that can explain the mechanism that results on different dlimonene compositions when lemon peels were incubated using different aspergillus sp. are still very scarce. hence, further studies are required to explain the possible mechanism of the biosynthesis of d-limonene. 3.5 productivity of lemon oil in a laboratory scale the productivity of lemon oil produced through solid-state fermentation of lemon peel followed by a steam distillation is estimated using equation (4) and the results are shown in table 2. the estimated productivity of lemon in a laboratory scale for the nonfermented sample (control) is of 0.5 g/day which resembles a lemon oil productivity of 0.48 g/day reported by ferhat et al. [37]. from table 1, it can be observed that the productivity of lemon oil decreased with fermentation since a longer time was required to isolate the lemon oil. the highest productivity of lemon oil for the fermented samples is 0.044 g/day, which is around 91% lower when the lemon peel was incubated with aspergillus niger for 3 days with a d-limonene content of 93.7%. the productivity of lemon oil decreased as a result of long fermentation time that was incomparable to the increase of lemon oil as suggested by díaz [38]. although the productivity of lemon oil decreased for the fermented samples, but the composition of d-limonene in the oil increased up to 37.7% as a result of biodegradation of lignocellulosic component by the aspergillus sp. [39]. after the 9th day of fermentation with aspergillus awamori, the productivity of lemon oil is 0.039 g/day with a d-limonene content of approximately 99%. hence, a compromise is required between productivity and quality of the desired lemon oil. table 1: composition of lemon oil for non-fermented and fermented lemon peel with aspergillus sp. no. compounds composition (%) day-0 day-3 day-6 day-9 ref. [8] aa1 an2 ao3 aa1 an2 ao3 aa1 an2 ao3 1 α-thujene 0.12 0.27 2 α-pinene 0.23 0.54 0.98 3 β-pinene 2.32 0.30 0.58 6.60 4 mycrene 1.33 1.04 1.65 1.16 1.33 3.15 2.69 1.73 5 limonene 72.54 73.10 93.66 99.00 81.97 75.09 84.56 99.00 88.03 89.43 72.48 6 (z)-β-ocimene 1.59 6.30 4.42 1.46 0.07 7 linalool 0.13 62 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 8 nonanal 0.84 <0.05 9 citronellal 0.86 0.07 10 decanal 0.50 0.05 11 nerol 6,13 0.28 0.07 12 undecanal 0.29 0.27 <0.05 13 neryl acetate 0.56 0.15 1.21 14 geranyl acetate 2.41 0.59 15 trans-α-bergamotene 1.42 1.66 2.74 4.89 2.09 2.39 2.30 0.41 16 (e)-β-farnesene 0.55 0.38 0.35 0.16 <0.05 17 β-bisabolene 2.12 1.32 4.78 7.29 2.96 3.07 2.82 1,22 18 spathulenol 0.05 19 caryophyllene oxide 0.22 0.22 <0.05 20 1,6-octadien-3-ol, 3,7-dimethyl-, formate 2.18 21 1-nonanol 0.50 22 β-fencyl-alkohol 2.52 0.71 23 2,6-octadienal, 3,7dimethyl-, (z) 7.28 2.26 1.09 24 siklooktana 0.39 9.49 25 2-(5-methyl-5vinyltetrahydro-2furanyl)-2-propanol 11.1 1 26 1,6-octadien-3-ol, 3,7-dimethyl-, propanoate 27 dodecanal 0.44 0.49 0.28 0.28 28 α-bisabolene 0.45 0.77 0.26 0.11 0.26 29 α-bisabolol 0.68 0.97 0.44 0.38 0.44 30 1,5,9-decatriene, 2,3,5,8-tetramethyl 0.43 0.33 31 2,6,10-dodecatrien-1ol, 3,7,11-trimethyl 0.28 32 decanol 1.27 33 1,6-octadien-3-ol, 3,7-dimethyl-, acetate 0.69 0.14 34 santolina epoxide 0.52 35 4-(2,2-dimethyl-6methylenecyclohexyl) butanal 0.68 36 2,3-dehydro-1,8cineole 0.14 37 1,3-cyclohexadiene, 1-methyl-4-(1 methylethyl) 0.12 38 bicyclo[2.2.1]heptane, 2-methyl-3 methylene-2-(4methyl-3-pentenyl) 0.35 39 patchouli alcohol 2.95 0.12 63 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 40 cyclohexanebutanal, 2,2-dimethyl-6methylene 0.27 2.95 41 1-vinyl-1-(4-methyl) pentan-3-enylcycloprane 0.13 42 1,2,4methenoazulene, decahydro-1, 5,5,8atetramethyl 0.09 43 nonadienol 0.42 note: 1aspergillus awamori; 2aspergillus niger, 3aspergillus oryzae table 2: estimated productivity of lemon oil for non-fermented and fermented lemon peel with aspergillus sp. parameter day-0 day-3 day-6 day-9 aa1 an2 ao3 aa1 an2 ao3 aa1 an2 ao3 oil mass (g) 0,125 0,137 0,142 0,134 0,211 0,145 0,137 0,362 0,343 0,308 oil yield (% dry weight) 0,27 0,30 0,31 0,29 0,46 0,32 0,30 0,79 0,75 0,67 oil productivity (g /day) 0,5 0,042 0,044 0,041 0,034 0,023 0,022 0,039 0,037 0,033 note: 1aspergillus awamori; 2aspergillus niger, 3aspergillus oryzae 4. conclusion a solid-state fermentation of lemon peels using aspergillus sp. has been carried out to investigate the effect of biodelignification towards yield and chemical composition of lemon oil isolated from the lemon peels. the results show that the lignin content in lemon peel decreased from 8% to 4.4–5.4% whereas the yield increased from 0.27% to 0.67-0.79% as the fermentation time increased. the results obtained in this study highlights that the fermentation of lemon peels with aspergillus oryzae, aspergillus niger, and aspergillus awamori increased the yield of lemon oil isolated from lemon peels. the major content of lemon oil, particularly d-limonene, also increased from approximately 73% up to 99%, depending on the species of aspergillus used in the fermentation. the largest reduction of lignin content (49%) and increment of yield (193%) were obtained when the lemon peels were subjected to fermentation with aspergillus awamori for 9 days which results to an increase of d-limonene up to 99%. references [1] pratiwi a, utami l. (2018) isolasi dan analisis kandungan minyak atsiri pada kembang leson. bioeksperimen 4 (1): 42-47. https://doi.org/10.23917/bioeksperimen.v4i1.5930 [2] grand view research. (2018) essential oils market size, share & trends analysis report by product (orange, corn, mint, eucalyptus, citronella, pepper mint, lemon, clove leaf, lime, spearmint), by application, and segment forecasts, 2018-2025. https://www.grandviewresearch.com [3] rosiantiningsih d. (2017) minyak atsiri, emas terpendam indonesia. http://marketplus.co.id/2017/03/minyak-atsiri-emas-terpendam-indonesia/. [4] gonzález-molina e, domínguez-perles r, moreno da, garcía-viguera c. (2010) natural bioactive compounds of citrus limon for food and health. j. pharmaceutical and biomedical analysis, 51 (2): 327-345. https://doi.org/10.1016/j.jpba.2009.09.049 [5] nurlaila a. (2001) upaya pemanfaatan limbah jus jeruk lemon (citrus limon (linn) burm. f.) sebagai bahan baku pengolahan jeruk lemon. bogor, institut pertanian bogor. http://repository.ipb.ac.id/handle/123456789/13152 [6] sonneman t. (2012) lemon a global history. london, reaktion books ltd. 64 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 transparency market research. (2019) lemon essential oil market to expand at 5.5% [7] cagr during 2018-2027. https://www.prnewswire.com [8] gök a, kirbaşlar ifgk. (2014) comparison of lemon oil composition after using different extraction method. journal of essential oil research, 27(1): 17-22. https://doi.org/10.1080/10412905.2014.982872 [9] sikdar d, nikila r. (2017) extraction of citrus oil from lemon (citrus limon) peels by steam distillation and its characterizations. international journal of technical research and applications, 5(2): 29-33. https://pdfs.semanticscholar.org [10] dosoky ns, setzer wn. (2018) biological activities and safety of citrus spp. essential oils. international journal of molecular sciences, 19 (7): 1966-1991. https://doi: 10.3390/ijms19071966. [11] janati sssf, beheshti h, feizy j, fahim n. (2012) chemical composition of lemon (citrus limon) and peels its consideration as animals food. gida-journal of food, 37(5): 267-271. https://dergipark.org.tr [12] chen h. (2014) biotechnology of lignocellulose: theory and practice. dordrecht, springer. [13] ahammed s, prema p. (2002) influence of media nutrients on synthesis of lignin peroxidase from aspergillus sp. applied biochemistry and biotechnology, 327-336. https://doi.org/10.1385/abab:102-103:1-6:327 [14] dos santos tc, dos santos rn, silva tp, machado fd, bonomo rc, franco m. (2016) prickly palm cactus husk as a raw material for production of ligninolytic enzymes by aspergillus niger. food science and biotechnology, 25(1): 205-211. https://doi.org/10.1007/s10068-016-0031-9 [15] shah mp, reddy gv, banerjee r, babu pr., kothari il. (2005) microbial degradation of banana waste under solid state bioprocessing using two lignocellulolytic fungi (phylosticta spp. mps-001 and aspergillus spp. mps-002). process biochemistry, 40(1): 445-451. https://doi.org/10.1016/j.procbio.2004.01.020 [16] mrudula s, murugammal r. (2011) production of cellulase by aspergillus niger under submerged and solid state fermentation using coir waste as a substrate. brazilian journal of microbiology, 7:1119-1127. https://doi.org/10.1590/s151783822011000300033 [17] botella c, diaz a, de ory i, webb c, blandino a. (2007) xylanase and pectinase production by aspergillus awamori on grape pomace in solid state fermentation. process biochemistry 42 (1): 98-101. https://doi.org/10.1016/j.procbio.2006.06.025 [18] steviani s. (2011) pengaruh penambahan molase dalam berbagai media pada jamur tiram putih (pleurotus ostreatus). surakarta, universitas sebelas maret. https://digilib.uns.ac.id [19] silva r. (2016) mycology: current and future developments: fungal biotechnology for biofuel production volume 1. sharjah, benthan science publishers. [20] zambare v. (2010) solid state fermentation of aspergillus oryzae for glucoamylase production on agro residues. international journal of life sciences, 16-25. https://doi.org/10.3126/ijls.v4i0.2892 [21] abduh my, zuliansyah w, aprina l, arazella n. (2019) effect of pectin biodegradation with aspergillus niger on total flavonoid content of citrus limon l. j biodjati, 4(2):194-203. https://doi.org/10.15575/biodjati.v4i2.4537 [22] gwalingo e, rahman nsa, al-marzouqi ah, omar mma, khaleel aa. (2018) klason method: an effective method for isolation of lignin fractions from date palm biomass waste. chemical and process engineering research, 57:46-58. https://www.iiste.org/journals/index.php/cper/article/view/41830 [23] carneiro jd, noguera rm, martins ma, valladão dm, pires em. (2018) the ovendrying method for determination of water content in brazil nut. bioscience journal 34 (3), 595-602. https://doi.org/10.14393/bj-v34n3a2018-37726 [24] kandi m, sefidkon f. (2011) the influence of drying methods on essential oil content and composition of laurus nobilis l. journal of essential oil bearing plants, 14 (3), 302-308. https://doi.org/10.1080/0972060x.2011.10643938 65 iium engineering journal, vol. 21, no. 2, 2020 abduh et al. https://doi.org/10.31436/iiumej.v21i2.1320 [25] rahimmalek m, goli sa. (2013) evaluation of six drying treatments with respect to essential oil yield, composition and color characteristics of thymys daenensis subsp. daenensis. celak leaves. industrial crops and products, 42(1): 613-619. https://doi.org/10.1016/j.indcrop.2012.06.012 [26] ambrose dc, annamalai s, naik r. (2013) effect of drying on volatile oil yield of patchoulli. indian journal of science and technology, 6(12): 5559-5562. http://52.172.159.94/index.php/indjst/article/view/43613 [27] hobir y, nuryani e, anggraeni. (2003) peningkatan produktivitas dan mutu minyak nilam melalui perbaikan varietas dan teknik pengolahan. balitro, bogor. [28] hamrouni-sellami i, wannes wa, bettaieb i, berrima s, chahed t, marzouk b, limam f. (2011) drying sage (salvia officinalis l.) plants and its effects on content, chemical composition, and radical scavenging activity of the essential oil. food and bioprocess technology, 5(8): 2978-2989. https://pubag.nal.usda.gov/catalog/448611 [29] hasmita i, adisalamun a, alam pn, satriana s, mahlinda m, supardan, m. d. (2015) effect of drying and hydrodistillation time on the amount of ginger essential oil. international journal on advanced science, engineering, and information technology, 5(5): 300-303. http://dx.doi.org/10.18517/ijaseit.5.5.567 [30] ferreira fl, dall'antonia cb, shiga ea, alvim lj, pessoni ra. (2018) sugarcane bagasse as a source of carbon for enzyme production by filamentous fungi. hoehnea, 45(1): 134-142. https://doi.org/10.1590/2236-8906-44/2017 [31] mamma d, christakopoulos p. (2013) biotransformation of citrus by-products into value added products. waste biomass valorization, 5(4): 529-549. https://doi.org/10.1007/s12649-013-9250-y [32] brijwani k, rigdon a, vadlani pv. (2010) fungal laccases: production, function, and applications in food processing. enzyme research, 1: 110. https://doi.org/10.4061/2010/149748 [33] chávez-gonzález ml, lópez li, rodríguez-herrera r, contreras-esquivel jc, aguilar cn. (2015) enzyme-assisted extraction of citrus essential oil. chemical papers, 70(4): 1-10. https://doi.org/10.1515/chempap-2015-0234 [34] boughendjioua h, djeddi s. (2017) organoleptic and physicochemical properties of algerian lemon essential oil. world journal of applied chemistry, 2(3): 96-100. https://doi.org/10.11648/j.wjac.20170203.14 [35] wilkins mr, grohmann k, widmer ww. (2006) effect of d-limonene on the fermentation of citrus peel waste. american society of agricultural and biological engineers, 1(1): 1-7. https://doi.org/10.1080/15435075.2017.1307753 [36] lota ml, de rocca sd, tomi f, jacquemond c, casanova j. (2002) volatile components of peel and leaf oils of lemon and lime species. journal of agricultural and food chemistry, 50(4): 796–805. https://doi.org/10.1021/jf010924l [37] ferhat ma, meklati by, smadja j, chemat f. (2006) an improved microwave clevenger apparatus for distillation of essential oils from orange peel. journal of chromatography a, 1112 (1): 121-126. https://doi.org/10.1016/j.chroma.2005.12.030 [38] díaz ab, ory id, caro i, blandino a. (2012) enhance hydrolytic enzymes production by aspergillus awamori on supplemented grape pomace. food and bioproducts processing, 90(1): 72-78. https://doi.org/10.1016/j.fbp.2010.12.003 [39] tang pl, hassan o, maskat my, badri k. (2015) production of monomeric aromatic compounds from oil palm empty fruit bunch fiber lignin by chemical and enzymatic methods. biomed research international, 5: 114. https://doi.org/10.1155/2015/891539 66 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <feff0633062a062e062f0645002006470630064700200627064406250639062f0627062f0627062a002006440625064606340627062100200648062b062706260642002000410064006f006200650020005000440046002006450646062706330628062900200644063906310636002006480637062806270639062900200648062b06270626064200200627064406230639064506270644002e00200020064a06450643064600200641062a062d00200648062b0627062606420020005000440046002006270644062a064a0020062a0645002006250646063406270626064706270020062806270633062a062e062f062706450020004100630072006f00620061007400200648002000410064006f00620065002000520065006100640065007200200036002e00300020064806450627002006280639062f0647002e> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <feff005400650020006e006100730074006100760069007400760065002000750070006f0072006100620069007400650020007a00610020007500730074007600610072006a0061006e006a006500200064006f006b0075006d0065006e0074006f0076002000410064006f006200650020005000440046002c0020007000720069006d00650072006e006900680020007a00610020007a0061006e00650073006c006a006900760020006f0067006c0065006400200069006e0020007400690073006b0061006e006a006500200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e0074006f0076002e0020005500730074007600610072006a0065006e006500200064006f006b0075006d0065006e0074006500200050004400460020006a00650020006d006f0067006f010d00650020006f00640070007200650074006900200073002000700072006f006700720061006d006f006d00610020004100630072006f00620061007400200069006e002000410064006f00620065002000520065006100640065007200200036002e003000200074006500720020006e006f00760065006a01610069006d0069002e> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 1, 2019 thuong et al. adsorptive removal of pb (ii) using exfoliated graphite adsorbent: influence of experimental conditions and magnetic cofe2o4 decoration nguyen thi thuong1,2, nguyen thi ngoc thu3, bach long giang2, nguyen duy trinh2, bui thi phuong quynh1 1faculty of chemical technology, ho chi minh city university of food industry, ho chi minh city, vietnam 2ntt hi-technology institute, nguyen tat thanh university, ho chi minh city, vietnam. 3faculty of food, chemical and environmental sciences, nguyen tat thanh university, ho chi minh city, vietnam. *corresponding authors: quynhbtp@hufi.edu.vn; phuongquynh102008@gmail.com (received: 5th july 2018; accepted: 17th april 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.965 abstract: the worm-like exfoliated graphite (eg) based adsorbents prepared from low-cost natural graphite flakes via facile synthesis processes have been found to be efficient adsorbents when it comes to removing pb (ii) from aqueous solution. eg was fabricated by chemical intercalation and microwave assisted exfoliation. furthermore, the magnetic exfoliated graphite (meg) was developed by incorporating cofe2o4 particles into the eg layers using the citric acid based sol-gel technique. adsorption behaviour of pb (ii) on the as-prepared adsorbents was investigated by taking several experimental conditions into consideration such as contact time, initial concentration, adsorbent dosage, and ph value. the results with initial neutral ph indicated that the adsorption isotherms for pb (ii) on the eg and meg were well consistent with the langmuir isotherm model revealing the maximum adsorption capacity of 106 mg/g and 68 mg/g for eg and meg, respectively. the adsorption kinetics of pb (ii) was found to adhere to the pseudo-second-order kinetic model. the chemical interaction between π electrons on graphite sheets and pb (ii) ions was suggested to play an essential role in the adsorption mechanism. the introduction of magnetic cofe2o4 to the eg was found to induce the shift of optimal ph value to a more basic condition. the characterization of the adsorbents was performed using relevant analysis techniques such as scanning electron microscope (sem), x–ray powder diffraction (xrd), vibrating-sample magnetometer (vsm), and fourier-transform infrared (ftir). the results of this work suggest a high possibility for the application of the as-prepared modified graphite to remove hazardous substances in practical wastewater treatment systems. abstrak: 202 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. keywords: adsorption; heavy metal; exfoliated graphite; pb (ii) ions; wastewater treatment 1. introduction in the past decades, environmental contamination due to the presence of heavy metals in wastewater from industrial processes and products has increasingly grown. heavy metal contamination adversely affects human health and organisms due to the high toxicity of metal ions even at low metal concentration. among many kinds of heavy metals, lead (pb) poisoning has caused a major public health risk as it can lead to symptoms like delirium, convulsions, persistent vomiting, coma, and also cause serious damage to hematopoietic, central nervous, and reproductive systems [1]. thus, the efficient decontamination of water containing pb2+ has been considered as one of the most important tasks for environmental scientists. there are various techniques for this, including membrane filtration, solvent extraction, chemical precipitation, and adsorption. among the aforementioned techniques, the adsorption method is still more favoured since it can offer many important benefits such as high removal efficiency, simple operation, wide adaptability, recyclability, and economic feasibility. among a cascade of adsorbents developed for decontamination of heavy metals, a number of products from graphite have been demonstrated to be very efficient [2-7]. the adsorption behaviour of heavy metal ion appeared to depend strongly on the textural, physical, and chemical properties of graphite related adsorbents that are essentially determined by the synthesis approach. in attempts to obtain high adsorption capacity, several preparation protocols and precursors have been employed. for instance, graphene layers fabricated from graphite rods by complete exfoliation to graphene layers containing 30 wt.% pf6 – showed high adsorption capacity for pb2+ (406.6 mg/g) and cd2+ (73.42 mg/g) [2]. additionally, the lead ion uptake of graphene nanosheets was found to be significantly improved under vacuum heat treatment [3]. reportedly, the introduction of fe3o4 particles onto graphene platforms could support high removal efficiencies and fast adsorption rates for cu2+, cd2+ and pb2+ [5]. in another work [4], the graphene surface modified by iron nanoparticles exhibited the maximum adsorption capacity of 4.86, 3.26, and 6.00 mg/g for cr(vi), as(v), and pb (ii) respectively at an initial metal ion concentration of 5.0 ppm. more recently, high removal efficiency of pb (ii) and cd (ii) ions were achieved using the composite of a significant amount of spinel magnetic particles and graphene sheets [6]. the adsorption of heavy metals on graphene-related materials was suggested to occur via chemical interaction of functional groups on the 203 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. adsorbent surface. despite very high adsorption capacity and fast adsorption kinetics, the practical application of graphene/graphene oxide structured materials in the removal of hazardous substances still faces several difficulties including the cost and the complication of their fabrication process. owing to its layered structure, graphite can allow easy addition of various atoms and molecules into these layers to form graphite intercalated compounds (gics). exfoliated graphite (eg) is a modified graphite material that has a certain expansion degree of distance between the carbon layers afforded via thermal exfoliation of the gics. the exfoliation process can be obtained by either using microwave irradiation or thermal shock [8-15]. the eg exhibits fascinating properties such as low density, large surface area, and a worm-like porous structure and thus has found a number of applications such as electromagnetic interference shielding, electrochemical electrodes, vibration damping, and, recently, purification of oil-polluted water [16,17]. however, the utilization of eg can cause some problems due to difficulty in gathering the low-density materials after adsorption. in order to restrict this shortcoming, the magnetic component was added to the eg adsorbent to allow easy recovery of the used adsorbents from wastewater under a magnetic field [18-21]. herein, we developed efficient adsorbents from the low-cost, abundantly available natural graphite flakes for remediation of lead-contaminated water. the exfoliation of graphite flakes was assisted by microwave irradiation, which is advantageous over conventional heating in terms of efficient, uniform heat distribution, and short-time treatment. furthermore, a sufficient amount of magnetic cofe2o4 species was incorporated into the exfoliated graphite layers via the simple citric acid based sol-gel process to afford the feasible collection of used materials from solution under an applied magnetic field. the presence of a small amount of cofe2o4 particles between the graphite sheets can not only provide eg with susceptibility to magnetic field but can also help stabilize the structure of expanded graphite layers. the adsorption of pb (ii) was studied taking into account the effects of various experimental factors including adsorbent dosage, initial pb2+ concentration, contact time, and ph value. the adsorption isotherms and adsorption kinetics were interpreted using the relevant adsorption models. properties of the adsorbents were analyzed using sem, xrd, vsm and ftir techniques. 2. experimental procedure 2.1 chemicals and materials natural flake graphite with granule size > 1.25 mm and carbon content ≥ 85% was collected in yen bai province, vietnam. chemicals including h2so4 (98%) and h2o2 (30%), fe(no3)3.9h2o, co(no3)2.6h2o, nh4.oh, pb(no3)2 were supplied by guang chemical company, china. 2.2 preparation of the exfoliated graphite (eg) and the magnetic decorated exfoliated graphite (meg) the eg was synthesized by intercalation method using h2o2 as an oxidizing agent and h2so4 as an intercalating agent as follows. natural graphite flakes were added into the mixture of h2so4 and h2o2 (20:1.6 v/v). after 50 minutes, the intercalated mixture was continually washed with water until the ph value reached 5-6. then, the resulting black powder was collected by vacuum filtering and dried in an oven. the eg was obtained by exfoliation in a microwave oven at the power of 750 w for 10 s. in the next step, the magnetic cofe2o4 nanoparticles were then introduced to eg surface by sol-gel method as 204 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. the following procedure. a mixture of fe(no3)3.9h2o, co(no3)2.6h2o (with molar ratio of fe3+/co2+= 1:2) were homogeneously dissolved in 0.02 m citric acid solution (with molar ratio of acid/fe3+ = 4:1). in order to keep the sols stable, the solution had the ph regulated to about 7-8. following this, eg was added and the solution was stirred for up to 30 minutes or until the floating eg disappeared on the surface of the solution. the obtained composites were further baked in a furnace at 600 oc for 1 hour. 2.3 adsorption experiments in the batch adsorption experiments, erlenmeyer flasks containing 50 ml of aqueous solution of pb (ii) ions and a predetermined amount of absorbent were shaken at 200 rpm for 2 h. the residual concentrations of heavy metals were confirmed by aas analysis. the removal efficiency and the adsorption capacity (qe) were calculated as follows: (1) where co and cf are the initial and equilibrium pb (ii) concentrations (ppm), respectively. (2) where v (ml) is the volume of the pb (ii) solution, w (g) is the weight of the adsorbent, dadsorbent (g/l) is the dosage of the adsorbent. investigated input factors included shaking time, initial pb (ii) concentration, adsorbent dosage, and ph of solution. the processes are as follows. first, the effect of contact time on lead (ii) adsorption was conducted by shaking the mixture of 3 g/l of adsorbent and 100 ppm of pb (ii) concentration in different time intervals (10-360 min) in a neutral medium. second, the effect of the initial lead concentration was studied by adding 3 g/l of adsorbent to pb (ii) solution of various concentrations (10-600 ppm) in a neutral medium for 120 min. third, for adsorbent dosage, we investigated its effect by varying eg dosage from 1 g/l to 6 g/l, where the initial concentration of pb (ii) ions and contact time were 100 ppm and 120 min, respectively in a neutral medium. lastly, the investigation of the effect of initial ph was conducted by varying ph value from 2 to 12 in initial pb (ii) solution of 100 ppm and adsorbent dosage of 3 g/l for 120 min. 2.4 characterization methods the x–ray powder diffraction (xrd) of ac was recorded on a d8 advance bruker powder diffractometer with a cu–kα excitation source at a scan velocity of 2o (2θ) min-1. the angle range (2θ) was investigated between 0o and 50o. a scanning electron microscope (sem) technique was employed on the s4800, japan instrument to investigate the morphology of adsorbent surface. fourier transform infrared (ft-ir) analysis of samples was determined using a bruker alpha ft-ir spectrophotometer with kbr as a matrix in the range of 4000−400 cm−1. to determine specific surface area and porous structure, the nitrogen adsorption/desorption measurement of adsorbent was performed on nova station b. a gmw 3474-140 magnetometer equipped with a superconducting magnet capable of producing fields up to 16 koe was used to measure static magnetic moment. to detect the amount of pb (ii) ions remaining in solution, atomic absorption spectroscopy (aas) measurement was conducted with aa 6800 shimadzu equipment. 205 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. 3. results and discussion 3.1 adsorptive removal of pb (ii) using the exfoliated graphite (eg) 3.1.1 characterization of the exfoliated graphite morphology of the graphite flake and the eg were characterized by sem as presented in fig. 1. it can be seen that structure of the graphite consists of rigidly stacking multilayers (fig. 1a). after the intercalation followed by microwave exfoliation, the worm-like particles and layered aggregative structure with interconnected open pores are shown in fig. 1b. a closer view in fig. 1c reveals a multi-porous structure. figure 2 reveals n2 adsorption/desorption curves of ng and eg. it can be seen that the type iv isotherm was determined for eg which indicates the existence of a large number of mesopores and very little micropores in graphite-based adsorbents. the obtained results showed that the specific surface area for the eg is 30.0 m2/g while such parameter of raw graphite is 6.5 m2/g, implying the formation of highly porous structure after exfoliation process. fig. 1: sem images of the graphite (a) and eg (b, c). fig. 2: the n2 adsorption/desorption isotherm curves of graphite and expanded graphite. 3.1.2 effects of experimental conditions on adsorption behavior of pb2+ on eg the influence of the contact time on the percentage removal of pb (ii) using eg adsorbent was displayed in fig. 3a. visually, prolonged contact leads to increased lead ion adsorption and equilibrium was attained after shaking for 120 min. initially, the removal of pb (ii) occurred rapidly, reaching approximately 75% within the first 50 min. the adsorption then rises gradually before reaching the saturated level at 81.8 % at 120 min. the high initial adsorption rate of pb2+ on eg can be attributed to easy diffusion of lead ions to its large external surface area and possibly into the wrapping adsorption space between stacking layers and large pores in each particle [6]. after 50 min, the significant occupation of pb2+ ions inside the pores and also on the external surface may become a 206 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. barrier hindering the contact between the active sites and other pb2+ ions thus resulting in a slower adsorption rate. based on this result, further adsorption experiments were all conducted in 2 hours. regarding initial concentration, the graph suggested that this factor induced a downward trend to the adsorption of pb (ii) at a fixed eg dosage (fig. 3b). the efficiency dropped from 81.6% to 26% as the concentration increased from 100 ppm to 600 ppm. at low initial concentration, increased availability of adsorption sites could easily bind the pb (ii) ions [3]. as the concentration of pb2+ ion in the solution was higher than the adsorption capacity of the eg, the removal efficiency started to drop. by contrast, the increment of adsorbent dose from 1 g to 6 g/l increased the percentage removal of pb (ii) from 45.2% to 89% (fig. 3c). the efficiency of lead uptake steadily rose with as the adsorbent dose increased from 1 g/l to 3 g/l but further addition of eg up to 6 g/l just afforded a slight enhancement in percentage removal. it can be explained that increasing the adsorbent dose provided a greater amount of active sites to capture metal ions thus allowing higher treatment efficiency. the relationship between adsorption of pb2+ and the ph value of the solution is presented in fig. 3d. it can be observed that variation of ph value between 2 and 8 did not significantly alter the pb2+ uptake on eg while the adsorption was much more favoured in strongly basic solution, as evidenced by a steady increase (from 74% to 97%) in removal efficiency in relation to increased ph value of 10 and 12. in more basic condition, the decreased competition of h+ led to an increase in the adsorption of lead ions. justification for that could be the protonated surface functional groups and severe competition with the adsorption of lead ions caused by excess h+ at low ph values [22]. at the ph of 12, the removal percentage achieved its highest level of almost 97%, possibly owing to the combined effect of adsorption and precipitation [3]. fig. 3: the effect of adsorbent dosage (a), the initial concentration (b), the contact time (c) and the ph (d) on the removal efficiency of pb (ii) using eg. 207 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. 3.1.3 adsorption kinetics and adsorption isotherms in order to analyse the adsorption kinetics, we fit the experimental data with the linear form of the pseudo-first-order and pseudo-second-order kinetic models described respectively as follows: (3) (4) where qe (mg/g) is the amount of pollutant adsorbed at equilibrium, qt (mg/g) is the amount of pollutant adsorbed at time t, k1 (min-1) is the pseudo-first-order rate constant, and k2 (g/mg.min) is the pseudo-second-order rate constant [23]. estimated parameters of the two models are summarized in table 1. the high correlation coefficient r2 (0.9984) shows good consistency between he pseudo-second order kinetic model and the experimental data. in contrast, the fitting to the pseudo-first-order kinetic model was more deviated as demonstrated by a lower correlation coefficient (r2 = 0.7255). table 1: isotherm and kinetics parameters for the adsorption of pb (ii) on eg pseudo-first-order pseudo-second-order langmuir isotherm freundlich isotherm qe(mg/g) 5.3150 qe(mg/g) 27.7008 qe(mg/g) 106.3830 kf 1.5866 k1 (min-1) 0.0076 k1 (min-1) 0.0058 kl (l/mg) 0.0109 1/n 0.572 r2 0.7255 r2 0.9984 r2 0.9768 r2 0.8158 rl 0.1867 the way in which the adsorbates interact with eg adsorbent is crucial and could be described via adsorption isotherms. such isotherms give some insights into the adsorption process and provide important parameters to disclose the adsorption mechanism. reportedly, langmuir and freundlich isotherms could accurately characterize the adsorption behaviour of heavy metals on various substrates. the langmuir isotherm model is based on the assumption that the adsorption occurs at specific homogeneous sites within the adsorbent and there is no significant interaction among adsorbed species [24]. the following equation presented the langmuir isotherm [23]: (5) where qe (mg/g) is the amount of adsorbates adsorbed at equilibrium, qm (mg/g) is the maximum monolayer adsorption capacity of the adsorbent, ce (mg/l) is the concentration of the adsorbate under equilibrium condition and kl (l/mg) is the langmuir constant. from langmuir’s model, the separation factor rl is calculated as follows: (6) where c0 (mg/l) is the highest metal concentration in solution and kl (l/mg) is the langmuir constant. adsorption is considered (i) unfavourable if rl> 1, (ii) linear if rl= 1, (iii) favourable if 0 < rl< 1 and (iv) irreversible if rl= 0. from table 1, it could be concluded that the adsorption of pb (ii) onto the surface of eg was favourable since the calculated rl value fell within 0 and 1. values of the constants can be deduced from the figure 4c, which plotted linear relationship of (1/qe) versus (1/ce). 208 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. inherent within the freundlich isotherm model, it is assumed that the stronger binding sites are occupied first and the affinity for binding is inversely proportional with number of occupied sites due to the adsorption of adsorbates onto heterogeneous surfaces. the freundlich isotherm is defined as the following equation: (7) where kf [(mg/g).(l/mg)n] is freundlich constant and 1/n is the adsorption intensity. the value of 1/n indicates that adsorption is favourable (n < 1, monolayer adsorption) and a value more than 1 implies cooperative adsorption. fig. 4: adsorption kinetics and isotherms for pb (ii) ions: pseudo-first-order (a) and pseudo-second-order (b) kinetic plot, langmuir (c) and freundlich (d) adsorption isotherm of the eg. langmuir isotherm and freundlich isotherm showed correlation coefficients (r2) of 0.9768 and 0.8158 respectively for pb (ii) ions on graphite layers. these results suggested the close fit of experimental data of adsorption for pb (ii) ion with the langmuir isotherm model (r2=0.98) indicating the formation of pb2+ monolayers over eg surface. the maximum adsorption capacity of pb (ii) ions onto eg was calculated to be 106 mg/g. in addition to this, the adsorption of eg for pb (ii) ions was favourable since the rl value was found to be between 0 and 1. 3.1.4 ftir analysis recorded ftir spectra of before and after pb (ii) adsorption representing the mechanism of adsorption of pb (ii) ions on the eg is presented in figure 5. the spectrum of eg reveals the presence of characteristic peaks as follows: 3445 cm-1 (stretching vibration of oh), 2967 cm-1 (stretching vibration of c-h in ch, ch2 and ch3), 1635 cm-1 (stretching vibration of c=o), 1385 cm-1 (blending and scissor vibration of ch3 and ch2), 1048 cm-1 (stretching vibration of c-o), 790 cm-1 (deformation vibration of the ch2 bond) 209 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. [25,26]. during adsorption process, there were some interactions between the eg and pb (ii) ions in the aqueous phase, consequently resulting in shifts of the characteristic peaks. as observed in fig. 5, the adsorption peak at 3445 cm-1 before shifting towards 3450 cm-1 is possibly caused by the bonding of ohwith pb (ii) ions [27]. moreover, the shifts of 2967, 1635, 1385, 1048 and 790 cm-1 to 2925, 1626, 1390, 1049 and 797 cm-1, respectively, can be easily recognized. these shifts might be ascribed to electrostatic interaction between the π electrons of graphite layers and pb2+ ions [28]. note that both the external surface and internal surface of pores in eg can take part in the adsorption of pb2+ efficiently. moreover, it is worthy to note that the curled structure of eg could possibly behave like a heavy metal trap and wrapped up pb (ii) ions inside the pores as similar with the function of nanotube-structured adsorbent. fig. 5: ftir spectra of eg and pb (ii) adsorbed eg. 3.2 adsorptive removal of pb (ii) using the magnetic decorated meg 3.2.1 characterization of meg to enable collection of eg using a magnetic field, cofe2o4 particles were introduced to the exfoliate d graphite layers by the citric acid based sol-gel process. in attempts to achieve sufficient magnetic susceptiblity with minimized metal oxide loading, the influence of different eg/cofe2o4 ratios was considered. figure 6a illustrated the separation of meg samples under external magnetic field. the nearly complete separation was obtained with the eg:cofe2o4 ratio of 1:1 and 3:1 while the ratio of 5:1 appeared insuffficient. this phenomenon agreed well with results analyzed using vsm measurement at room temperature. figure 6b showed that the magnetization hysteresis loops of meg were the s-like curves; the saturation magnetization values (ms) increased strongly from 5 emu/g to 32 emu/g when reducing the eg/cofe2o4 weight ratio from 5:1 to 3:1 but further decrease of this ratio to 1:1 just slightly enhanced the ms to 42 emu/g. since the eg/cofe2o4 ratio of 3:1 with ms of 32 emu/g was able to allow feasible magnetic separation, this ratio was selected for further investigation. as observed in fig. 6c, besides the peaks characteristic of eg structure, the additional appearance of a small peak at 2θ = 35.5 can be ascribed to the (311) plane of the cofe2o4 [29,30]. furthermore, the disappearance of the peak at 44.4o in the spectrum of modified eg implied that graphite sheets were further expanded during the heat treatment at 600 oc. the successful incorporation of cofe2o4 particles into eg layers were also confirmed by the sem analysis. figure 6d shows the morphology of meg as investigated by sem analysis. the meg surface was found to consist of various wrinkled and folded domains 210 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. evenly decorated with cofe2o4 particles in the nanosize range (about 50-80 nm) without large aggregations (inset of fig. 6d). these analysis results prove the successful incorporation of magnetic property to the eg via addition of nanosized cofe2o4 particles. fig. 6: properties of magnetic cofe2o4-eg samples; (a), inset (1): solution without meg, (2) eg:cof2o4 = 1:1, (3) eg:cof2o4 = 3:1 and (4) eg:cof2o4 = 5:1; (b) the magnetization hysteresis loops of meg: cofe2o4; (c) xrd and (d) sem of meg (eg:cof2o4 = 3:1). 3.2.2 effect of experimental conditions on adsorption behaviour of pb2+ on the meg impacts of various experimental factors on the percentage removal of pb2+ using meg adsorbent were shown in fig. 7. in general, the change tendency is quite similar with eg but meg exhibited lower pb2+ uptake than eg in neutral solution. for instance, at the fixed concentration of 100 ppm, dosage of 3 g/l, in a neutral environment, the time to obtain equilibrium condition was 60 min, which was much shorter than in the case of eg (fig. 7a). this is partly ascribed to the adsorbate-adsorbate steric effects [31]. when the expanded graphite was covered by cofe2o4 species, a number of functional groups responsible for metal binding, on either external surface or internal surface of pore channels, may be blocked by cofe2o4 species thus resulting in decrease in adsorption performance. although the cofe2o4 incorporation was found to reduce the adsorption capacity of eg, it still possessed a significant adsorption capacity for practical application. at the meg dosage of 3 g/l, the removal efficiency dropped from about 70% to 22 % when increasing the initial pb2+ concentration from 10 ppm to 600 ppm (fig. 7b). raising the meg dosage from 1g/l to 6 g/l also induces a 60 point rise in the percentage removal from 22 % to about 82% (fig. 7c). it can be deduced that the deposition of cofe2o4 nanoparticles inside the pores may block the diffusion of metal ions to internal surface of carbon layers, limiting adsorption capacity and deferring equilibrium of eg (as compared to unmodified eg). 211 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. the ph value appeared to have more significant impact on the adsorption process on meg than on eg. as can be seen from fig. 7d, an upsurge in percentage removal (from 22% to nearly 100%) was observed with increasing ph from 2 to 8. accordingly, the optimal ph condition for adsorption on meg can be defined in the range of 8-10. it means that the optimal ph value was shifted to less basic condition after incorporation of cofe2o4. compared to eg, adsorption of pb2+ on meg in the ph range of 8-10 was higher (80% vs 96%), which likely indicate the presence of synergistic effect afforded by cofe2o4, carbon layers and hydroxide species present in the solution. fig. 7: the effects of contact time (a), initial concentration (b), adsorbent dosage (c) and ph (d) on the removal efficiency of pb (ii) using the meg. 3.2.3 adsorption kinetics and adsorption isotherms the studies of adsorption kinetics and isotherms for meg were performed in the similar experimental conditions with eg. the derived model parameters are summarized in table 2. the plots for pseudo-first order and pseudo-second order models are illustrated in fig. 8a and 8b. in a similar manner with eg, the pseudo-second-order kinetic model was found to fit well with adsorption data for the cofe2o4 decorated eg as evidenced by a high correlation coefficient (r2 = 0.9997). the rate constant k1 for meg was found higher than that for eg (0.0071 vs 0.0058). table 1: isotherm and kinetics parameters for the adsorption of pb (ii) on eg pseudo-first-order pseudo-second-order langmuir isotherm freundlich isotherm qe(mg/g) 6.1404 qe(mg/g) 18.5529 qm(mg/g) 68.0272 kf 0.6208 k1 (min-1) 0.0021 k1 (min-1) 0.0071 kl (l/mg) 0.0109 1/n 1.5212 r2 0.8665 r2 0.9997 r2 0.9936 r2 0.9364 rl 0.1323 212 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. the plots of langmuir and freundlich isotherms are presented in fig. 8c and 8d. again, the langmuir model still best described the adsorption behaviour of pb2+ on meg (r2 = 0.9936). the correlation coefficient from freundlich model was lower at 0.9364. the maximum adsorption capacity as calculated from langmuir equation was 68 mg/g. the rl value of 0.1323 indicates favourable adsorption as found between 0 and 1. fig. 8: adsorption kinetics and isotherm for pb (ii) ion: (a) pseudo-first-order (a) and pseudo-second-order kinetic plots (b), langmuir (c) and freundlich isotherms (d) of the meg. 4. conclusion efficient exfoliated graphite-based adsorbents for pb2+ elimination from aqueous solution were developed from the low-cost, abundantly available natural graphite flakes via facile preparation procedures. the magnetic eg was also fabricated by incorporation of cofe2o4 particles into the exfoliated graphite layers. adsorption capacity of eg and meg for pb (ii) ions increased with higher adsorbent dosage, contact time and ph and decreased as initial concentration of pb (ii) increased. the pseudo-second order kinetic model and langmuir model are two models that well described adsorption behaviour of pb (ii) ions onto both as-prepared eg and cofe2o4 decorated eg. the langmuir equation suggested that the maximum adsorption capacity of eg and meg for pb2+ ions were 106 and 68 mg/g, respectively. the presence of cofe2o4 particles in the carbon layers shortened the contact time to equilibrium, reduced the elimination efficiency in neutral solution but increased that in more basic solution (ph = 8-10). it is suggested that the binding pb (ii) ions to eg surface was afforded due to its curled structure and chemical interaction between π electrons of carbon layers and positively charged metal ions. according to the obtained results, the as-prepared eg and meg with advantages of lowcost and abundantly available graphite precursor, non-complicated fabrication process and 213 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. significant adsorption capacity hold reasonable practicality for treating water for heavy metal contamination. acknowledgement this work was supported by the kist institutional program (project no. 2z04820-16090). references [1] flora g, gupta d, tiwari a. (2012). toxicity of lead: a review with recent updates. interdisciplinary toxicology, 5:47-58. [2] deng x, lu l, li h, luo f. (2010). the adsorption properties of pb(ii) and cd(ii) on functionalized graphene prepared by electrolysis method. journal of hazardous materials, 183:923-930. [3] huang zh, zheng x, lv w, wang m, yang qh, kang f. (2011). adsorption of lead(ii) ions from aqueous solution on low-temperature exfoliated graphene nanosheets. langmuir : the acs journal of surfaces and colloids, 27:7558-7562. [4] gollavelli g, chang c-c, ling y-c. (2013). facile synthesis of smart magnetic graphene for safe drinking water: heavy metal removal and disinfection control. acs sustainable chemistry & engineering, 1:462-472. [5] zhang w, shi x, zhang y, gu w, li b, xian y. (2013). synthesis of water-soluble magnetic graphene nanocomposites for recyclable removal of heavy metal ions. journal of materials chemistry a, 1:1745-1753. [6] santhosh c, kollu p, felix s, velmurugan v, jeong sk, grace an. (2015). cofe2o4 and nife2o4@graphene adsorbents for heavy metal ions kinetic and thermodynamic analysis. rsc advances, 5:28965-28972. [7] pourbeyram s. (2016). effective removal of heavy metals from aqueous solutions by graphene oxide–zirconium phosphate (go–zr-p) nanocomposite. industrial & engineering chemistry research, 55:5608-5617. [8] kim j, kim h, kim b, jeon k-j, yoon s-h. (2014). expanding characteristics of graphite in microwaveassisted exfoliation. scientific cooperations international workshops on engineering branches, 273-277. [9] zhu y, murali s, stoller md, velamakanni a, piner rd, ruoff rs. (2010). microwave assisted exfoliation and reduction of graphite oxide for ultracapacitors. carbon, 48:21182122. [10] sykam n, kar kk. (2014). rapid synthesis of exfoliated graphite by microwave irradiation and oil sorption studies. materials letters, 117:150-152. [11] toyoda m, inagaki m. (2000). heavy oil sorption using exfoliated graphite new application of exfoliated graphite to protect heavy oil pollution. carbon, 38:199-210. [12] inagaki m, toyoda m, iwashita n, nishi y and konno h. (2001). exfoliated graphite for spilled heavy oil recovery. carbon science, 2:1-8. [13] tryba b, morawski aw, kaleńczuk rj, inagaki m. (2003). exfoliated graphite as a new sorbent for removal of engine oils from wastewater. spill science & technology bulletin 8:569-571. [14] zheng y-p, wang h-n, kang f-y, wang l-n, inagaki m. (2004). sorption capacity of exfoliated graphite for oils-sorption in and among worm-like particles. carbon, 42:26032607. [15] tryba b, przepiórski j, morawski aw. (2003). influence of chemically prepared h2so4graphite intercalation compound (gic) precursor on parameters of exfoliated graphite (eg) for oil sorption from water. carbon, 41:2013-2016. [16] chung ddl. (2016). a review of exfoliated graphite. journal of materials science 51:554568. 214 iium engineering journal, vol. 20, no. 1, 2019 thuong et al. [17] cai m, thorpe d, adamson dh, schniepp hc. (2012). methods of graphite exfoliation. journal of materials chemistry, 22:24992-25002, [18] ding x, wang r, zhang x, zhang y, deng s, shen f, zhang x, xiao h, wang l. (2014). a new magnetic expanded graphite for removal of oil leakage. marine pollution bulletin, 81:1885-1890. [19] wang g, sun q, zhang y, fan j, ma l. (2010). sorption and regeneration of magnetic exfoliated graphite as a new sorbent for oil pollution. desalination, 263:183-188. [20] lutfullin ma, shornikova on, vasiliev av, pokholok kv, osadchaya va, saidaminov mi, sorokina ne, avdeev vv. (2014). petroleum products and water sorption by expanded graphite enhanced with magnetic iron phases. carbon, 66:417-425. [21] jin c, dong jh, li dx, zhu mc, zhang yc. 2011. characterization and application of expanded graphite coated by fe3o4 nanoparticles. advanced materials research, 356360:554-557. [22] mallampati r, xuanjun l, adin a, valiyaveettil s. (2015). fruit peels as efficient renewable adsorbents for removal of dissolved heavy metals and dyes from water. acs sustainable chemistry & engineering, 3:1117-1124. [23] huang y, li s, chen j, zhang x, chen y. (2014). adsorption of pb(ii) on mesoporous activated carbons fabricated from water hyacinth using h3po4 activation: adsorption capacity, kinetic and isotherm studies. applied surface science, 293:160-168. [24] raad mt, behnejad h, jamal me. (2016). equilibrium and kinetic studies for the adsorption of benzene and toluene by graphene nanosheets: a comparison with carbon nanotubes. surface and interface analysis, 48:117-125. [25] yusuf m, elfghi fm, zaidi sa, abdullah ec, khan ma. (2015). applications of graphene and its derivatives as an adsorbent for heavy metal and dye removal: a systematic and comprehensive overview. rsc advances, 5:50392-50420. [26] yang x, cui x. (2013). adsorption characteristics of pb (ii) on alkali treated tea residue. water resources and industry, 3:1-10. [27] pandey r, ansari ng, prasad rl, murthy rc. (2014). pb(ii) removal from aqueous solution by cucumissativus (cucumber) peel: kinetic, equilibrium & thermodynamic study. american journal of environmental protection, 2:51-58. [28] fan m, li t, hu j, cao r, wu q, wei x, li l, shi x, ruan w. (2016). synthesis and characterization of reduced graphene oxide-supported nanoscale zero-valent iron (nzvi/rgo) composites used for pb(ii) removal. materials, 9:687-708. [29] gandha k, elkins k, poudyal n, ping liu j. (2015) synthesis and characterization of cofe2o4 nanoparticles with high coercivity. journal of applied physics, 117:1-4. [30] shi m, zuo r, xu y, jiang y, yu g, su h, zhong j. (2012). preparation and characterization of cofe2o4 powders and films via the sol–gel method. journal of alloys and compounds, 512:1665-1670. [31] zhou c, zhu h, wang q, wang j, cheng j, guo y, zhou x, bai r. (2017). adsorption of mercury(ii) with an fe3o4 magnetic polypyrrole–graphene oxide nanocomposite. rsc advances, 7:18466-18479. 215 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <feff005500740069006c0069006300650020006500730074006100200063006f006e0066006900670075007200610063006900f3006e0020007000610072006100200063007200650061007200200064006f00630075006d0065006e0074006f0073002000640065002000410064006f00620065002000500044004600200061006400650063007500610064006f007300200070006100720061002000760069007300750061006c0069007a00610063006900f3006e0020006500200069006d0070007200650073006900f3006e00200064006500200063006f006e006600690061006e007a006100200064006500200064006f00630075006d0065006e0074006f007300200063006f006d00650072006300690061006c00650073002e002000530065002000700075006500640065006e00200061006200720069007200200064006f00630075006d0065006e0074006f00730020005000440046002000630072006500610064006f007300200063006f006e0020004100630072006f006200610074002c002000410064006f00620065002000520065006100640065007200200036002e003000200079002000760065007200730069006f006e0065007300200070006f00730074006500720069006f007200650073002e> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <feff0041006e007600e4006e00640020006400650020006800e4007200200069006e0073007400e4006c006c006e0069006e006700610072006e00610020006f006d002000640075002000760069006c006c00200073006b006100700061002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400200073006f006d00200070006100730073006100720020006600f60072002000740069006c006c006600f60072006c00690074006c006900670020007600690073006e0069006e00670020006f006300680020007500740073006b007200690066007400650072002000610076002000610066006600e4007200730064006f006b0075006d0065006e0074002e002000200053006b006100700061006400650020005000440046002d0064006f006b0075006d0065006e00740020006b0061006e002000f600700070006e00610073002000690020004100630072006f0062006100740020006f00630068002000410064006f00620065002000520065006100640065007200200036002e00300020006f00630068002000730065006e006100720065002e> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 influence of palm oil biomass clinker and empty fruit bunch fibers on concrete properties mohd haziman wan ibrahim1*, sajjad ali mangi2, sharifah salwa mohd zuki1, ramadhansyah putra jaya3, dadang supriyatno4 1 jamilus research center, faculty of civil engineering and built environment, universiti tun hussein onn malaysia, 86400, parit raja, johor, malaysia. 2 department of civil engineering, mehran university of engineering and technology, szab campus khairpur mir’s, sindh, pakistan. 3 department of civil engineering, college of engineering, universiti malaysia pahang, 26300, kuantan, pahang, malaysia. 4 faculty of engineering, universitas negeri surabaya, indonesia. * corresponding author: haziman@uthm.edu.my (received: 3 rd november 2019; accepted: 22 nd march 2020; published on-line: 4 th july 2020) abstract: this study aims to evaluate the influence of palm oil empty f r ui t bunch (efb) fibers on flexural strength performance of concrete in the presence of palm oil biomass clinker (pobc). this study considered various proportions of palm oil efb fibers as 0%, 0.2%, 0.4%, and 0.6% in concrete with fixed amount of pobc as 10% . i t was investigated that there is substantial influence of palm oil efb fibers on pr oper t i es of concrete containing 10% pobc as sand replacement. the experimental findings of this study indicated that the workability of fresh mix concrete decreases as palm oil e f b fiber content increased. besides that, hardened properties of concrete were found to be improved as the amount of palm oil efb fibers increased in the concrete. it was not i ced that flexural strength was improved with addition of 0.2% palm oil efb fibers that act as reinforcement and deliver growth in flexural strength for concrete containing 10% of pobc. hence, it was concluded that palm oil efb fiber could be utilized as fiber reinforcement in concrete to improve flexural strength performance of the concrete. abstrak: kajian ini bertujuan mengkaji pengaruh gentian tandan kelapa sawit ( e f b) terhadap kekuatan lentur pada konkrit dengan kehadiran klinker minyak kelapa sawit biomas (pobc). kajian ini mengguna pakai pelbagai peratus serat efb kelapa sawit dalam konkrit iaitu sebanyak 0%, 0.2%, 0.4%, dan 0.6% dengan jumlah tetap pobc sebanyak 10%. didapati bahawa gentian tandan kelapa sawit efb yang mengandungi 10% pobc berpengaruh besar sebagai pengganti pasir dalam bahan konkrit. p enem uan eksperimen menunjukkan bahawa kebolehkerjaan campuran baru konkrit berkurangan apabila kandungan gentian efb minyak sawit meningkat. selain itu, sifat-sifat mengeras pada konkrit didapati bertambah baik apabila jumlah gentian efb minyak sawit meningkat dalam konkrit. di samping itu, kekuatan lenturan meningkat dengan penambahan sebanyak 0.2% serat efb minyak kelapa sawit, berfungsi sebagai penguat dan penambah kekuatan lenturan pada konkrit yang mengandung 10% pobc. ol eh i t u, serat efb minyak kelapa sawit boleh digunakan sebagai penguat gentian dalam konkr i t bagi meningkatkan kekuatan lenturan konkrit. keywords: bunch fiber; biomass clinker; compressive strength; flexural strength 100 mailto:haziman@uthm.edu.my iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 1. introduction the production of palm oil has been increased over the years. according to a re c e n t report by the malaysia palm oil board (mpob), crude palm oil production has incre a se d from 24.91 to 28.64 million tons in a year [1]. this huge quantity of palm oil p ro d uc tio n left behind the waste by-products known as palm oil biomass clinker (pobc) a n d p a lm oil empty fruit bunch (efb). in malaysia, efb is being utilized as a fertilizer for the agricultural field and pobc is being considered in concrete as cement and sand replacement material. pobc is a waste material produced through incineration of oil palm shells and mesocarp fiber as fuel for stream turbines in mills [2]. a mass iv e q u a n tity o f pobc is usually dumped into landfills, which causes environmental problems. h o w ev e r, use of sustainable materials should be given immediate attention and emphasis on the sustainable development through adopting waste by -products into the potential construction material [3]. the pobc has a lower value of specific gravity and higher crushing value, which indicates its potentiality to be considered as an alternative source of fine aggregate. th e re is no pre-treatment or modification required for this material. the ad op tio n o f po bc a s fine aggregate to some extent could save the depletion of natural resources [2]. recent study was conducted by wan ibrahim et al. [4] on pobc as fine aggregate replacement in concrete with hooked-end steel fibers. they considered a 10% proportion of po bc to b e an optimum replacement level of fine aggregates in concrete. however, th is m e th o d c a n reduce the self -weight of concrete, which delivers lightweight and green and s u s ta in ab le concrete. beside that palm oil efb fiber is one of the local natural fibers, which can easily be obtained at low cost and low level of energy either in manpower or technology. henc e, this study aims to investigate the influence of palm oil efb fiber on the fresh and hardened concrete properties with 10% pobc as fine aggregate. 2. previous related research 2.1 effects of pobc on concrete properties concrete containing pobc as fine aggregate is influenced by the physical prope rtie s of poba. however, pobc is a porous material that absorbs more water than normal aggregates, its water absorption was noted in the range of 4.7-26.5%, wh ic h d e liv e r lo w workability concrete [5]. it was also declared by ahmmad, et al. [6] that lightweight concrete can integrate more waste materials like crushed oil palm shell (ops) a s c o a rs e aggregate and palm oil clinker (poc) as a replacement of fine aggregate. they d e c la red that the modulus of elasticity was 23% higher in ops concrete. the lower compressive strength of self -compacting concrete was observed when fully or partially coarse and f in e aggregate were replaced with poc [2]. gunasekaran et al. [7] considered coconut shell concrete (csc). they declare d th a t workability and tensile and flexural strength were improved. overall, csc bond s tre ngth is comparable to that of normal and lightweight aggregate concretes. however, they further declared that coconut shells fulfil the provisions to be used as aggregate for lightweight concrete. abutaha et al. [8] investigated the compressive strength of concrete with palm oil clinker (poc) as coarse and fine aggregate. they declared that the amount of poc in th e mix reduces the compressive strength of the concrete as shown in fig. 1, which shows that the targeted compressive strength of grade 40 concrete was achievable with 1 0 % c o ars e aggregate replacement with poc. the strength declined by 11.73%, 16.79%, 18.94%, 101 iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 19.66%, 21.60% and 30.37% at the replacement levels of 10%, 20%, 40%, 60%, 80% an d 100% respectively. the maximum drop of strength was noticed with full re p la c em e nt o f coarse aggregate. nevertheless, the compressive strength performance of concrete with poc as fine aggregate is far better than coarse aggregate replace ment. it was observed that poc as fine aggregate can enhance the compressive strength as shown in fig. 2. it indicated that at the replacement level of 10%, 20%, 40%, 60% and 100% the compressive strength was noticed as decreased by 4.07%, 4.43%, 0.15%, 0.80%, and 5.17%, respectively. however, compressive strength was found to be 5% improved at 80% replacement. these results show the potentiality of poc to be utilized as re p la c e m e nt o f fine aggregate. therefore, this study also considered the 10% replacement. fig. 1: concrete strength performance with poc as replacement of coarse aggregates [8]. . fig. 2: concrete strength performance with poc as replacement of fine aggregates [8]. furthermore, shahreen et al. [9] examined the flexural strength of concrete comprising poc as fine aggregate replacement. it showed a positive increment in flexura l strength at early ages due to the presence of poc fine particles, which creates a pozzolanic reaction and densification of the concrete mix and enhanced internal bond s among aggregates and cement paste, resulting in the development of strength as seen in the results provided in fig. 3. they declared that fine particles of poc occup y the free space s in th e 102 iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 concrete and fill the voids, which delivers high density and increases the s ta b ility o f th e concrete mix. it was noticed that the flexural strength of concrete wa s in c re a se d a rou nd 28% and 33% with incorporation of 5% and 10% of pobc as fine aggregates , respectively [9]. however, the opposite results were found with more than 10% of pobc [10]. the adverse influence was noticed with the utilization of pobc as coarse and fine aggre ga te s in concrete. fig. 3: flexural strength result of poc concrete and conventio nal concrete [9]. from the literature review it can be concluded that the presence of pobc c a n a f fec t the performance of concrete. therefore, the flexural strength performance would be improved with the addition of fiber along with the 10% proportion of pobc as fine aggregate replacement. 2.2 effects of natural fiber to concrete particularly in tropical states like malaysia and indonesia, palm oil efb are the abundant waste that is left behind after the fruits are stripped from fruit bunches f or the oil extraction process [11]. efb fiber is a type of fiber that is clean and free from pes tic id es . this fiber could be utilized in concrete to improve its performance. it was previously w e ll known that the inclusion of fibers in concrete creates reinforced concrete that delivers better strength than normal concrete. for instance , previous research work has been summarized below on the fiber proportion and performance of concrete. sim et al. [12] investigated the influence of basalt fiber on structural concrete and found that basalt fiber is a good substitute for strengthening concrete structures. in addition, kim et al. [13] considered two type of concretes; normal concrete and high fluidity concrete. whereas, they found that the addition of 1% jute fiber by volume in th e normal strength concrete does not deliver significant increment, but in high-fluidity concrete it gives a substantial rise in compressive strength , around 55%, a s c o m p are d to one without fiber. the compressive strength of 0% jute fiber content for high-fluidity concrete gives 25 mpa and for 0.5% of jute fibe r content deliver about 42 mpa, which indicated that the presence of fibers could positively influence the concrete perform a nc e. hence, it was generally observed that the flexural strength can be increased as the fibe r content increased in concrete. however, presence of fiber can resist tensile load and increase the flexural strength. 103 iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 3. materials and methodology 3.1 materials ordinary portland cement (opc) was used in this study. the coarse aggrega te s w e re collected from muar, johor, malaysia. this study considered a 10 mm average o f c o ars e aggregate. after collection, coarse aggregates were dried under open sun for f e w d a y s to achieve saturated surface dry (ssd) conditions. however, the fine aggregates (sand) w e re transported from a river in kahang, johor, malaysia. the fine aggregates were a ls o d rie d for a few days under open sunlight to achieve saturated surface dry (ssd) cond itions. before mixing, the sand was sieved through a 5 mm sieve. 3.2 palm oil biomass clinker this study considered palm oil biomass clinker (pobc) as shown in fig. 4, which was collected from a biomass steam plant located in tanjung langsat, man age d b y tpm technopark sdn bhd. initially, it was partially replaced by the fine aggregate (sand ). th e optimum replacement percentages of sand with pobc was chosen as 10% based previo us studies [4]. afterward, pobc were passed through a 5 mm sieve size. furthermore, a random sample of pobc was investigated with a scanning electron microscope (sem) for an understanding of its microstructure, as shown in fig. 5. it was observed that po bc has micro voids that could affect the properties of concrete and create weak region s in th e form of free voids. the presence of voids is the significant cause of reduction in s tre n gth of concrete. these voids also provide a gap between particles and result in wea k e r b o nd s in the hardened concrete. some organic compounds were noticed on the surface of the pobc. it can be concluded that pobc contain s voids and organic compounds tha t a f fec t its porosity and low value of specific gravity. fig. 4: palm oil biomass clinker. fig. 5: sem image of pobc. 3.3 palm oil empty fruit fibers palm oil empty fruit bunch (efb) fibers, as shown in fig. 6, were used in th is s tu d y . the length of the palm oil efb fiber was fixed at the range of 30 mm to 50 mm with a diameter of around 0.05 mm. the aspect ratio of the palm oil efb fibers was in the ra n ge of 60 to 100 for better strength development. 104 iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 fig. 6: palm oil empty fruit bunch fibers. 3.4 experimental procedure in this study, normal concrete mix design was prepared for 25 mpa at 28 days w ith a fixed water-to-cement ratio of 0.50. a total of four mixes were prepared; one was the reference mix with 10% pobc but without fibers and the other three c o nta in ed v a ryin g amounts of palm oil efb fiber at 0.2, 0.4 and 0.6% by weight total batch mix. the quantity of fiber was calculated by multiplying the overall weight of ingredients of the concrete mix with the percentage of fiber content. the concrete mix details are provided in table 1. table 1: mix design detail (kg/m3) for concrete containing pobc with palm oil efb fiber sample notation cement sand ca pobc water efb fibers 0% efb 18.24 37.80 28.62 0.00 9.12 0.2% efb 18.24 34.02 28.62 3.78 9.12 0.195 0.4% efb 18.24 34.02 28.62 3.78 9.12 0.390 0.6% efb 18.24 34.02 28.62 3.78 9.12 0.585 overall, 48 specimens were prepared to explore the compressive and flexural strength of the concretes at 7 and 28 days, as mentioned in table 2. concrete cubes of 100 mm size were cast for the purpose of compressive strength. the prisms of 100 mm in cross -sectio n and 500 mm in length were cast for the evaluation of flexural strength. furthermore, curing of concrete was observed under water immersion conditions. table 2: the specimen prepared for strength performances palm oil efb fibers (%) 7 days 28 days compressive flexural compressive flexural 0 3 3 3 3 0.2 3 3 3 3 0.4 3 3 3 3 0.6 3 3 3 3 sub total 12 12 12 12 tota l sa mples 48 105 iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 4. results and discussion 4.1 particle size distribution particle size distribution has been done through sieve analysis. fig. 7 illustrates the cumulative percentages passing for sand and pobc at various sieve size s. h o w e v er, th e sand and pobc particle size distribution curve did not exceed the upper and lower lim it s . both sand and pobc used in the experiment fulfil the particle size behaviour stated in bs 882: 1992, the required percentage by mass passing bs sieve for sand. in this study, aggregates used were air dried to obtain saturated dried surface. to achieve this condition, aggregates were dried at room temperature for 24 hours. coarse aggregates of 10 mm size were used, and less than 5 mm were removed through sieving. the specific gravity for sand and pobc used in this study has the average specific gravity of 2.07 and 2.63, respectively. the specific gra v ity o f po bc is 21% lower than the average specific gravity of sand. fig. 7: particle size distribution of sand and pobc. 4.2 workability of concrete workability is an aspect of concrete, which indicates flow without mechanical shaking. the workability performance of concrete containing 10% pobc along with various proportions of palm oil efb fiber are presented fig. 8. it shows a reduction in workability due to the addition of fiber content. the slump value dropped from 2 0 m m to 18, 12, and 8 mm at fiber contents of 0.2, 0.4, and 0.6%, respectively. the results sh o w ed a substantial decrease in workability due to presence of fibe r. as the fiber content increased, workability was reduced. however, the presence of fiber absorbed mo re w a te r in the concrete mix [14] and resulted in the drop in workability. an adequate performan c e was noticed with 0.2% fiber. it was also previously noticed by ahmad et al. [1 5 ] th a t th e addition of fibers cause the reduction in workability. however, the palm oil efb f ib e r is an organic fiber that could reduce the quantity of free water in a concrete mixture and affect the mobility of concrete. 106 iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 fig. 8: the slump value with various percentage of reinforced palm oil efb fibe r. 4.3 compressive strength compression strength test performances of concrete with 10% pobc as a fine aggregate replacement with the addition of 0.2%, 0.4%, and 0.6% of palm o il efb f ib e r has been presented in fig. 9. the experimental findings indicate that compressive strength was reduced as fiber quantity increased in the concrete. the control sample with o u t f ibe r shows the highest compressive strength of 27.23 mpa at 28 days. compressive strength results with the addition of 0.2%, 0.4% and 0.6% palm oil efb fibe r show a red u ctio n in strength of 12.6%, 17.7%, and 21.7% respectively. comparatively, the strength performances with 0.2% fiber is considered to be satisfactory, due to the lower re d u ctio n in the strength [4,16,17]. this study clarifies that there is a continual decrease in compressive strength as palm oil efb fibers increase in the concrete mix. it shows that concrete becomes more porous and delivers lower strength. this study also validated th a t in the presence of both materials, pobc and palm oil efb fiber, concrete depletes its water content, since more water is absorbed by these two materials. as a result, redu c tion in water content could slow the hydration process of concrete and ultimately cause it to exhibit lower strength, even at 28 days. fig. 9: compressive strength of fiber reinforced concrete at different curing periods 4.4 flexural strength experimental results of flexural strength of concrete incorporating 10% pobc as fine aggregate replacement along with the addition of 0.2%, 0.4% and 0.6% o f p a lm o il efb 20 18 12 8 0 5 10 15 20 25 0% (c ontrol) 0.2% 0.4% 0.6% s lu m p ( m m ) pe rce n tage of pal m o il efb fi be r (%) 25.71 27.23 21.26 23.73 20.94 22.40 20.39 21.30 20 22 24 26 28 30 7 days 28 days c o m p r e s si v e s tr e n g th ( m p a ) c u ri n g age (days) 0% (c ontrol) 0.2% 0.4% 0.6% 107 iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 fiber has been demonstrated in fig. 10. it was observed that flexural strength o f c o nc re te was better in the presence of fibers. it was noticed that flexural strength was increased from 2.18 mpa to 2.43 mpa with the addition of 0.2% fiber, which is almost 11. 47 % ris e in flexural strength at 28 days. however, 0.4% and 0.6% fiber content also delivers around 5.96% and 4.59% improvement in the flexural strength of concrete. hence, it is worth noting here that the increase in palm oil efb fiber content causes a reductio n in f le xu ral strength. it was previously acknowledged that the addition of supplementary materials along with fibers enhances the flexural strength of concrete [4,18,1 9, 2 0, 21 ]. th is s tu d y also experimentally validated that 0.2% proportion of fiber enhances the concrete properties in terms of flexural strength, and it is hereby recommended a s a n a p p ro pria te proportion of fibers in a concrete mix. fig. 10: concrete flexural strength at curing periods of 7 and 28 days. 5. conclusions this experimental study confirmed that pobc has a good potential to be utilized a s a fine aggregate replacement. based on the performance of concrete containing 10% po bc as fine aggregate with addition of palm oil efb fibe r, the following conclusions can be made: • concrete containing 10% pobc as a fine aggregate along with additio n o f p a lm oil efb fiber delivers lower workability performances and around 10% reduc tio n in workability with the addition of 0.2% fiber in concrete. • concrete compressive strength was also reduced with addition of 0.2%, 0.4% a n d 0.6% palm oil efb fiber, which gives around 12.6%, 17.7%, and 21.7% reduction in compressive strength, respectively. however, 0.2% fiber content is declare d a s optimum, due to minimum reduction in the strength. • the flexural strength performances of concrete were found to be in c re as e d f ro m 2.18 mpa to 2.43 mpa with the addition of 0.2% fiber, which is almost an 11.47% rise in flexural strength at 28 days. therefore, based on the experimental outcomes, the appropriate proportion of fiber is recommended to be 0.2%. 2.18 2.18 2.22 2.43 2.20 2.31 2.18 2.28 2 2.1 2.2 2.3 2.4 2.5 7 days 28 days f le x u r a l s tr e n g th ( m p a ) c u ri n g age (days) 0% (c ontrol) 0.2% 0.4% 0.6% 108 iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 acknowledgements this study was supported by universiti tun hussein onn malaysia (uthm) and ministry of education malaysia through fundamental research grant scheme vot no. frgs/1/2018/tk01/uthm/02/3. references [1] kushairi a, loh sk, azman i, hishamuddin e, abdullah mo, mohd noor izuddin zb, razmah g, sundram s, ahmad parveez mk. (2018) oil palm economic performance in malaysia and r&d progress in 2017 – review article. journal of oil palm research 30(2):163-195. doi: https://doi.org/10.21894/jopr.2018.0030 [2] kanadasan j, razak ha. (2015) engineering and sustainability performance of selfcompacting palm oil mill incinerated waste concrete, j. clean. prod., 89:78-86. https://doi.org/10.1016/j.jclepro.2014.11.002 [3] alengaram uj, al muhit ba, jumaat mzb. (2013) utilization of oil palm kernel shell as lightweight aggregate in concrete – a review, constr. build. mater., 38:161–172. https://doi.org/10.1016/j.conbuildmat.2012.08.026 [4] wan ibrahim, mh, mangi sa, ridzuan mb, burhanudin mk, jamaluddin n, li kh., shahidan s, sheikh kf, arshad mf, ramadhansyah pj. (2019) compressive and flexural strength of concrete containing palm oil biomass clinker with hooked-end steel fibers, int. j. integr. eng., vol. 10(9):152–157. https://publisher.uthm.edu.my/ojs/index.php/ijie/article/view/2559 [5] aslam m, shafigh p, jumaat mz. (2016) oil-palm by-products as lightweight aggregate in concrete mixture: a review, journal of cleaner production, 126:56-73. https://doi.org/10.1016/j.jclepro.2016.03.100 [6] ahmmad r, jumaat mz, bahri s, saiful islam abm. (2014) ductility performance of lightweight concrete element containing massive palm shell clinker, constr. build. mater., 63:234-241. https://doi.org/10.1016/j.conbuildmat.2014.04.022 [7] gunasekaran k, kumar ps, lakshmipathy m. (2011) mechanical and bond properties of coconut shell concrete, constr. build. mater., 2:592-98. https://doi:10.1016/j.conbuildmat.2010.06.053 [8] abutaha f, razak ha, kanadasan j. (2016) effect of palm oil clinker (poc) aggregates on fresh and hardened properties of concrete, constr. build. mater., 112:416–423. https://doi.org/10.1016/j.conbuildmat.2016.02.172 [9] shahreen e, wahab a, omar r, che osmi sf, muhamad khairussaleh na, abdullah a. (2012) preliminary study on mechanical properties of concrete added with fine palm oil clinker, in jordan engineers association conferences. http://www.jeaconf.org [10] shafigh p, mahmud hb, jumaat mzb, ahmmad r, bahri s. (2014) structural lightweight aggregate concrete using two types of waste from the palm oil industry as aggregate, j. clean. prod., 80. 187–196. https://doi.org/10.1016/j.jclepro.2014.05.051 [11] gunawan fe, homma h, brodjonegoro ss, hudin abb, zainuddin ab.(2009) mechanical properties of oil palm empty fruit bunch fiber, j. solid mech. mater. eng., 3(7):943–951. https://doi.org/10.1299/jmmp.3.943 [12] sim j, park c, moon dy. (2005) characteristics of basalt fiber as a strengthening material for concrete structures, compos. part b: eng., 36(6–7):504–512. https://doi.org/10.1016/j.compositesb.2005.02.002 [13] kim j, park c, choi y, lee h, song g. (2012) an investigation of mechanical properties of jute fiber-reinforced concrete. in: parra-montesinos g.j., reinhardt h.w., naaman a.e. (eds) high performance fiber reinforced cement composites 6. rilem state of the art reports, vol 2. springer, dordrecht. https://doi.org/10.1007/978-94-007-2436-5_10 [14] shreeshail bh. (2015) effects of coconut fibers on the properties of concrete, int. j. res. eng. technol., 04(01):5–11. 109 https://doi.org/10.1016/j.jclepro.2014.11.002 https://doi.org/10.1016/j.conbuildmat.2012.08.026 https://publisher.uthm.edu.my/ojs/index.php/ijie/article/view/2559 https://doi.org/10.1016/j.jclepro.2016.03.100 https://doi.org/10.1016/j.conbuildmat.2014.04.022 https://doi.org/10.1016/j.conbuildmat.2016.02.172 http://www.jeaconf.org/uploadedfiles/document/f083dc62-9a66-4c91-afb2-c70fb8e6b6d1.pdf https://doi.org/10.1016/j.jclepro.2014.05.051 https://doi.org/10.1299/jmmp.3.943 https://doi.org/10.1016/j.compositesb.2005.02.002 iium engineering journal, vol. 21, no. 2, 2020 wan ibrahim et al. https://doi.org/10.31436/iiumej.v21i2.1285 [15] ahmad z, saman hm, tahir pm. (2010) oil palm trunk fiber as a bio-waste resource for concrete reinforcement, int. j. mech. mater. eng., 5(2):199-207 [16] mangi sa, wan ibrahim mh, jamaluddin n, arshad mf, memon fa, ramadhansyah pj, shahidan s. (2019) a review on potential use of coal bottom ash as a supplementary cementing material in sustainable concrete construction, int. j. integr. eng., 10(9):127– 135. https://publisher.uthm.edu.my/ojs/index.php/ijie/article/view/2496 [17] mangi sa, wan ibrahim mh, jamaluddin n, arshad mf, ramadhansyah pj. (2018) effects of ground coal bottom ash on the properties of concrete, j. eng. sci. technol. 14 (1):338– 350. http://jestec.taylors.edu.my/vol%2014%20issue%201%20february%202019/14_1_24.pdf [18] dullah h, akasah za, nik soh nmz, mangi sa. (2017) compatibility improvement method of empty fruit bunch fibre as a replacement material in cement bonded boards: a review, iop conf. ser. mater. sci. eng., 271: 1–7. https://iopscience.iop.org/article/10.1088/1757-899x/271/1/012076 [19] jamaluddin n, hamzah af, wan ibrahim mh, ramadhansyah pj, arshad mf, zainal abidin ne, dahalan, nh. (2016) fresh properties and flexural strength of self-compacting concrete integrating coal bottom ash, matec web conf., 47:01010. https://doi.org/10.1051/matecconf/20164701010 [20] ramadhansyah pj, abu bakar bh, megat azmi mj, wan ibrahim mh (2011) engineering properties of normal concrete grade 40 containing rice husk ash at different grinding times, int. j. technol., 2(1):10–19. [21] mangi sa, wan ibrahim mh, jamaluddin n, shahidan s, arshad mf, memon sa, ramadhansyah pj, mudjanarko sw, setiawan mi. (2019) influence of ground coal bottom ash on the properties of concrete, int. j. sustain. constr. eng. technol., 9(2):26–34. https://publisher.uthm.edu.my/ojs/index.php/ijscet/article/view/3296 110 https://publisher.uthm.edu.my/ojs/index.php/ijie/article/view/2496 http://jestec.taylors.edu.my/vol%2014%20issue%201%20february%202019/14_1_24.pdf https://iopscience.iop.org/article/10.1088/1757-899x/271/1/012076 https://doi.org/10.1051/matecconf/20164701010 https://publisher.uthm.edu.my/ojs/index.php/ijscet/article/view/3296 application of digital cellular radio for mobile location estimation development of low-cost additive manufacturing system through selective inhibition sintering (sis) process and evaluation of mechanical characteristics of fabricated parts mesfin sisay mengesha*, balasubramanian esakki, arunkumar ponnambalam, silambarasan mathiyazhagan and rajamani devaraj centre for autonomous system research, vel tech rangarajan dr. sagunthala r&d institute of science and technology, chennai 600062, india *corresponding author: mesfins245@gmail.com (received: 4th february 2020; accepted: 19th may 2020; published on-line: 4th july 2020) abstract: additive manufacturing (am) is widely being used in today’s contemporary industry; however, products fabricated by the existing am techniques are costly due to the high machine cost and low production rate. therefore, the focus of this work is to design and fabricate a cost-effective and novel powder based selective inhibition sintering (sis) system. various subsystems of the machine such as the infrared heater assembly, inhibition deposition mechanism, build and feed tank assemblies, powder deposition, and the compaction system have been indigenously designed and fabricated. an electronic control system is also established through integrating sensors, linear and rotary actuators, belt and pulley mechanism, and temperature feedback control unit. the customized sis system is developed by integrating the assembly of all the subsystems, and the electronic modules with an open-source platform to generate the necessary motion characteristics. besides, an open source reprap user interface firmware has been used to control the machine. thermo-structural finite element analysis has been used to study the sintering behaviour of powder material. inhibitor material selection and preparation have been carried out by performing an experimental investigation on the inhibition effects of various materials. the machine has been tested through fabricating parts from hdpe polymer powder. finally, the performance of the produced parts has been evaluated by conducting an experimental investigation. the results of the investigation indicated that the fabricated parts have attained sufficient mechanical strength and, hence, the developed sis system can be utilized to manufacture functional parts. abstrak: industri pembuatan bahan tambahan (am) banyak digunakan dalam industri kontemporari semasa; walau bagaimanapun, produk yang terhasil daripada teknik sedia ada am adalah mahal disebabkan harga mesin yang mahal dan kadar penghasilan yang rendah. oleh itu, tujuan kajian ini adalah bagi mereka cipta serbuk baharu dengan harga berpatutan berdasarkan sistem pensinteran rencatan pilihan (sis). pelbagai mesin subsistem seperti pemasangan pemanas inframerah, mekanisme pemendapan rencatan, binaan dan pemasangan tangki suapan, deposisi serbuk, dan sistem pemadatan telah direka cipta secara alami dan dipasang siap. sistem kawalan elektronik juga diadakan melalui integrasi sensor, lelurus dan penggerak putaran, jaluran dan mekanisme takal dan suhu unit kawalan suap balik. sistem sis yang dibuat mengikut pesanan ini dihasilkan dengan mengintegrasi pemasangan kesemua subsistem, dan modul elektronik melalui platfom sumber terbuka bagi menghasilkan ciri-ciri pergerakan bersesuaian. selain itu, sumber terbuka reprap perisian tegar antara muka telah digunakan bagi mengawal mesin. 212 analisis unsur terhingga struktur-terma digunakan bagi mempelajari perihal pensinteran bahan serbuk. pilihan bahan perencat dan persediaan telah dijalankan dengan menjalankan siasatan eksperimen pada kesan perencat pelbagai bahan. mesin diuji melalui pemasangan bahagian daripada hdpe serbuk polimer. akhirnya, bahagian yang terhasil diuji melalui ujian eksperimen. hasil kajian menunjukkan pemasangan bahagian telah mencapai kekuatan mekanikal mencukupi, dengan itu sistem sis yang dibina boleh digunakan bagi mengilang bahagian berkaitan. keywords: additive manufacturing; selective inhibition sintering; ir heater; tensile strength; flexural strength 1. introduction additive manufacturing (am) is a process that fabricates functional parts directly from three-dimensional (3d) computer-aided design (cad) data through adhesion of materials layer-upon-layer as opposed to the subtractive methodology [1,2]. because am can manufacture any complex geometry in a short span of time, and production volume does not affect the cost of the fabricated part as it would in the case of the subtractive manufacturing method [3], it is widely being considered in today’s contemporary industry. moreover, unlike a traditional fabrication technique, the am process does not require tooling such as jigs, fixtures, and cutters as well as coolants to operate [4]. kurth et al. [5] classified the am process based on the state of the raw materials used as solid, powder, and liquid based processes. amongst these classifications, the selective inhibition sintering (sis) process, first invented by khoshnevis et al. [6], at the university of southern california, is a powder-based process that operates based on the principle of inhibiting a selected region from sintering to make a part [6-9]. sis is a contemporary approach to selective laser sintering (sls) [10]. unlike the sls process, the sis process uses a low cost infrared heat source instead of a high power laser. hence, it is an economical powder based additive fabrication method that fabricates parts on a layer-upon-layer basis. moreover, adaptability to various materials such as polymers, ceramics, and metals is another key advantage of the sls and sis processes. unlike other am manufacturing technologies, sls and sis do not require support material as the unsintered powder acts as support material. the principal idea in the sis system is to inhibit selected regions of powder layer from fusing using precise delivery of inhibitor material. the high melting point inhibitor material is deposited on the selected region of the powder bed to define the part profile and a ceramic heater is used to supply heat energy across the predetermined surface area of a layer. due to the large difference between melting points of inhibitor and polymer powder, the region printed with inhibitor material will absorb heat energy and therefore be inhibited from sintering while the remaining area is sintered. finally, the inhibitor and un-sintered powder can be washed away from the part after the building of the part is complete. as mentioned above, the major difference between the sls and sis processes are the heat sources and the sintering mechanisms. in addition, the sis process has many advantages over the sls processes. as a result of eliminating the high power heat source (the sis system does not use high power lasers and cooling circuitry) the carbon footprint associated with sis is much less compared to other laser enabled am processes. hence, compared to the existing 3d printing techniques, sis will have a significantly less detrimental effect on the environment. it has a higher printing speed due to area sintering instead of point sintering as used in the sls process. moreover, similar to the sls process, its adaptability to various materials such as polymers, ceramics, and metals is an important feature of the sis process. therefore, this fabrication technique can be implemented for processing a wide range of indigenously 213 available polymer materials such as polypropylene, hdpe, ldpe, polycarbonates, and polystyrene [6,9,11]. since the invention of the first sis system, improvements were done to the existing system in terms of adapting to metallic materials. khoshnevis et al. [9] developed an alpha selective inhibition sintering machine and characterized the process parameters of the machine by fabricating bronze parts and studying their quality features. in addition, petros et al. [12] developed a -sis machine that fabricates metallic products. torabi et al. [13] introduced an sis metal machine that uses a commercial piezoelectric inkjet printer-head to deliver the inhibitor material. a bronze part was produced with the machine and the mechanical property of the fabricated part was investigated. some of the drawbacks of the existing sis systems are: compaction related problems during the spreading of the powder layer, material wastage, and the presence of significantly large numbers of process variables that influence the quality characteristics of the fabricated parts [14]. asiabanpour et al. [15] identified more than 30 factors that influence the sis process. the presence of a large number of process parameters has complicated the optimization problem of identifying the best combinations of parameters and their settings. as a result, sis process characterization has become a tedious task. thus, improving the quality of the sis fabricated part has become a cumbersome task and consequently, quality characteristics such as the mechanical properties, dimensional tolerance, and surface roughness of the sis fabricated parts has been inferior [13]. several research works were conducted to enhance the quality of the sis fabricated part. balasubramanian et al. [16] have optimized the settings of the few significant sis process factors to improve the dry sliding wear behaviour of high-density polyethylene (hdpe). baligidad et al. [17] studied and optimized sis factors’ settings that affect the dimensional accuracy of products. yoozbashizadeh et al. [18] explored the effect of the inhibitor materials and the sintering phenomenon on the mechanical strength of sis fabricated metallic parts. rajamani et al. [19] investigated the influence of the sis process variables on shrinkage characteristics of sis parts. optimization problem of sis process was studied by various researchers. the effect of process variables on surface quality characteristics was examined by rajamani et al [20]. as a result, impact of some process variables on part quality has been comprehended, and the result of the investigation showed that the mechanical, dimensional, and surface characteristics of the products are in acceptable ranges. despite the reports of the experimental studies, none of the aforementioned sis systems are being utilized in the fabrication of functional parts. as a result, it is not commercialized and is not available in the additive manufacturing market yet. in addition, a design document for the fabrication of the sis system has not been addressed sufficiently in the literature. however, with innovative design approach, it can be made applicable for fabricating prototypes and functional aircraft parts, uav structures, automobile components, prosthetics, and exoskeleton devices. thus, a new approach needs to be followed to design and develop an sis system that eliminates the issue of the existing system. therefore, this work presents a comprehensive and systematic approach to the design and development of a low cost sis system. the functionality of the developed machine has been tested by fabricating parts from hdpe polymer powder. the polymer material used to fabricate the test specimens and prototypes has been chosen by examining the thermostructural behaviour of various polymers through finite element analysis. in addition, the inhibitor solution was selected by conducting multiple pilot tests on their inhibition and penetration effects. finally, the produced parts were tested for tensile and flexural strength to evaluate their performance. in this paper, the detailed design of sis subsystems such as 214 the heater assembly, inhibition system, build and feed tanks, powder deposition, electronic control unit, and software and hardware integration are presented. testing of developed sis system and component fabrication is discussed. furthermore, evaluation of the mechanical strength of the fabricated part was performed to determine the applicability of the developed system for fabricating useful products. 2. materials and methods 2.1 selection of inhibitor in the sis process, the selected region of the powder layer is wetted through a liquid called an inhibitor which defines the part boundary. inhibitor liquid is a saturated aqueous solution of high melting point salt with high water solubility [7,10]. bhuvaneshwaran et al. [21] investigated a few of the salt materials as inhibition purposes. in order to reduce the surface tension of the aqueous solution, avoid the formation of droplets, and thereby achieve effective penetration into the powder layer, a small amount of isopropyl alcohol was mixed with the solution. as the amount of isopropyl alcohol added to the solution increases, salt gets precipitated [21]. therefore, about 17% to 20 % of alcohol was an optimum amount for 100 ml of water to produce the desired effect. preliminary experiments were performed to evaluate the performance of each inhibitor material by applying heat energy on the polymer powder with an inhibitor at the periphery. it is observed that barium chloride (bacl2) and potassium iodide (ki) produced less uniform penetration than other inhibitors, [21]. however, ki is preferable due to its high solubility to water which is essential for effective inhibition. 2.2 selection of polymer in the present work, various polymer materials were considered as candidate materials for the sis process, and the selection of specific polymers was carried out by evaluating their thermo-structural load carrying capacity using a finite element (fe) analysis. figure 1 indicates the fe model of the powder bed and inhibitor solution. the polymer material and inhibitor material are represented in light grey and dark grey colours respectively. for the thermal analysis, 85% of the melting point of the polymer was used as input heat energy and the rate of heat transfer through the free surface is computed by assuming a free convection heat transfer coefficient, h= 30w/m2k. figure 2(a) and 2(b) show the result of the fe analysis and it indicates the coupled effect of thermal as well as structural loads on a single sintered layer as temperature distribution is applied as an input to the structure assuming a fixed bottom polymer layer. fig. 1: fe model of polymer and inhibitor part. 215 fig. 2: (a) displacement (b) thermal stress of different polymer materials i) pp, ii) pc, iii) ps, iv) hdpe. in comparison to other polymers, hdpe [22] attained minimal displacement and thermal stress as shown in fig. 2(a) and fig. 2(b) respectively, and hence it is considered for part fabrication. 3. design and development of the selective inhibition sintering (sis) system the sis system comprises the following sequence of operations to build functional parts layer by layer: how to use this document? • spread a thin layer of powder over the build tank from the feed tank • wet selected region of powder layer with inhibitor liquid to define the periphery of the part. • expose both the wetted and un-wetted powder layer to a heat source. • move down the build tank and simultaneously move up the feed tank through a small distance which defines layer thickness of the part. • spreading another layer of powder over the previously sintered layer. • repeat the process for each layer until the desired part is completed. in order to attain the aforementioned operations, various subsystems such as build and feed tank assembly, powder deposition and compaction mechanism, inhibitor deposition, and heater assembly are indigenously designed and fabricated. 3.1 feed, build and collector tank the sis system is comprised of a feed and build tank. the feed tank is a reservoir that stores the powder material, and build tank is the platform where parts are constructed. these two platforms move vertically up and down in the opposite direction synchronously. when a build tank moves downward to a certain distance, the feed tank moves upward by the same distance equal to the desired layer thickness. in addition, a collector tank is provided to collect surplus powder during the powder deposition and compaction process. the platforms are made from high-grade aluminium plate machined to the required dimension using a water jet cutting process that provides precision and surface finish to avoid misalignments during assembly. a build tank of 200 x 200 x 200 mm, a feed tank of 250 x 200 x 200 mm and a collector tank of 50 x 200 mm is designed as shown in fig. 3. 1 3 5 7 10 20 30 40 50 60 70 80 90 10 0 11 0 12 0 13 0 14 0 15 0 d is pl ac em en t ( m ) time (ms) pc ps pp hdpe 0 10 20 30 40 50 60 70 80 10 20 30 40 50 60 70 80 90 10 0 11 0 12 0 13 0 14 0 15 0t he rm al s tr es s (m p a) time (ms) pc ps (a) (b) 216 fig. 3: feed and build platforms assembly. the upward and downward movement of the two tanks is achieved through a power screw driven by nema-23 stepper motors. four round steel bars are used to guide the bedplates of both tanks in their upward and downward motions. the movement of the feed and build tank is designed so that the required amount of powder is made available in order to deposit a powder layer thickness with the required layer thickness. the possible swaying of the top plate as it moves vertically up and down is eliminated with the help of linear bearings fitted at the bottom of the tanks as shown in fig. 3. 3.2 powder spreading and compaction system a simple mechanism (fig. 4) that deposits a layer of powder on the build platform and compresses it to the required level of density is designed and fabricated. it is made up of a blade and a round bar. in order to reduce the number of voids and increase density, the powder bed requires compression using a roller. the blade spreads the powder on the build platform and the roller follows the blade to compact the powder bed to the required density. hence, a round bar follows the blade during powder layer preparation. fig. 4: powder feeding and compacting mechanism. the height of the roller from the build platform determines the layer thickness of parts. therefore, depending on the strength required from the final sintered part, the height of the spreader-roller needs to be varied. as a result, the height of the spreader-roller is designed to be adjustable. in addition, the lower edge of the blade (spreader) is positioned slightly above the roller to ensure that a sufficient amount of material is provided for achieving the desired part density. 217 the inhibitor deposition mechanism consists of a syringe, a linear lead screw, and a stepper motor (fig. 5). the stepper motor is used to drive the plunger linearly in a reciprocating manner. the rotational motion of the stepper motor is converted into a reciprocating motion of the plunger (piston) to compress the inhibitor solution through the nozzle. two round steel bars are used to avoid sidewise swaying of the plunger thereby it moves perpendicular to the cross-sectional area of the syringe barrel without the piston head pushing the inner wall of the barrel. this enables the mechanism to deposit inhibitor solution efficiently on the powder layer. the designed inhibitor deposition system has a capacity of 60 ml of inhibitor and a plastic dispensing tip of 0.4 mm nozzle diameter [8] was used. the flow rate of the inhibitor is influenced by the actuator's power (speed and torque). droplet size is controlled through fitting cheap dispensing tips at the tip of the syringe. multiple iterations were carried out to obtain an optimum printer feed rate. this mechanism is a low cost mechanism, yet it is able to dispense inhibitor solution as desired. fig. 5: inhibitor deposition mechanism. 3.4 heater assembly a short-wave infrared heater is used as a heat source for sintering the powder bed. the heat energy is transmitted from the source to the powder layer through electromagnetic radiation. the heating element, shown in fig. 6, is made up of two lamps, each with 1000watt / 240-volt. the lamps are fixed to a casing that is constructed from aluminium sheet metal because aluminium has better reflectivity property of infrared light and strength to weight ratio. during the sintering process, the heat source moves in a single-axis (y-axis) over the build tank at the required speed. in addition, a 150 mm x 150 mm flat mica heater bed heater of 150-watt / 230-volt is fitted beneath the build tank. therefore, part wrapping during sintering is prevented by preheating the build platform with the bed heater to a temperature of approximately 90 ºc 100 ºc during and prior to depositing the powder layer. fig. 6: heating element. 218 3.5 x-y positioning mechanism the x-y positioning system used in this machine is an h-bot that uses a low cost single timing belt to guide and position the cart on which the inhibitor depositor is attached as shown in fig. 7(a). two low-priced nema-17 stepper motors are used to actuate the x-y micro positioning mechanism. the motor mount blocks on which the actuators are fitted and the cart that hold the nozzle are also machined from low cost aluminium. round stainless steel bars are used as a guide for the moving elements of the mechanism. (a) (b) fig. 7: x-y positioning mechanism. all elements of the mechanism except the belt and the stainless-steel rods are made of al6061 and is fabricated using a cnc milling process. in this mechanism, fixed rotary drivers are connected by a single h-bar gt-2 timing belt of width 6mm via gt-2 timing pulley. as indicated in fig.7 (a), (b), the coordinated motion of the drive motors helps the mechanism to achieve the required movement. that is the nozzle of the inhibitor depositor mechanism can be moved along the required direction (x, y, and combination of x and y), by controlling the motion of the drives. as can be seen from the figures, when motor 1 and motor 2 rotates in the counter-clockwise direction by 1q and 2q angles respectively, the angles 1q and 2q are shared by the linear displacement x and y . equation (1) and (2) below show the relationship of 1q and 2q with x and y distance movement of the nozzle. yxq1 and yxq2 (1) )( 2 1 21 qqx and )(2 1 21 qqy (2) therefore, when both drives rotate in the clockwise direction, the nozzle moves along the negative x direction. however, when they rotate counter-clockwise, the nozzle makes a positive x-axis movement. similarly, when one of the motors rotates in clockwise and the other rotates in the opposite direction, the nozzle moves along y-axis. the rotation of a single drive enables the nozzle to move diagonally in the x-y plane. therefore, this mechanism can precisely position the nozzle at any point in x-y plane over the build platform. 3.6 base structure the base structure that supports the entire setup of the sis machine is required to be strong, tough and rigid as the kinematics of the system cannot be compromised. most of the relatively heavy components are made from aluminium 6061 and the top support sheet is drive 1 idler drive drive 2 y x ss rod belt drive 2q 2q 219 made from mild steel. in addition, stainless steel rods are chosen to support and guide the inhibition mechanism, the heating element, and the powder spreader and compactor mechanism. hence, the beam and column of the machine are loaded with the lumped weight of all the components that is approximately 35 kg. the aluminium extrusion profile is chosen for the frame of the support structure as it is a lightweight and good corrosion-resistant material. it is also easy and economical to fabricate a structure from aluminium extrusion profiles than plastics or steel structures. moreover, t-slot aluminium profiles have high specific density than a steel structure. hence, an aluminium extruded profile (30 mm x 30 mm) frame is chosen for the support structure to provide structural rigidity to the machine. 3.7 hardware and software integration customized design of the hardware (fig. 8) showing all the connection of the actuators, sensors and control unit is created using the proteus platform. the circuit shown in the figure is divided into two major categories as direct and alternating current circuits. the direct current circuit is the electronic controller that guides the computer-controlled sis system to achieve desired characteristics. fig. 8: electronic control circuit. a megatronics v3.1 microcontroller is used to control the six stepper drivers (x, y, z, extruder 1, extruder 2 and extruder 3) and the two heaters (bed and ir heater). an input of 12v power is delivered to the controller board via the 30a switch mode power supply. the stepper drivers are designed to control the independent motions of the following components of the developed system: powder deposition-compression mechanism (y), nozzle motions (x and y), feed tank (z), inhibitor deposition mechanism (extruder 1), liner movement of build tank (extruder 2) and motion of ir heater (extruder 3). nema-23 stepper motors are used to drive x, y, z linear motions and extruder 2 as they require relatively high torque motors. on the other hand, extruder 1 and extruder 3 are 220 driven using nema-17 stepper motor. a4988 and tb6600 stepper drivers are used to drive the nema-17 and nema-23 stepper motors respectively. in addition, the x and y axis travel limits are controlled using micromechanical end stops. the control system of the heating elements is a closed-loop, and the output temperature of the infrared heater and bed heater is measured using 100k thermistors and k type thermocouple temperature sensors respectively. the microcontroller controls the temperatures through an ssr-25 solid state relay. software was developed by customizing an open-source marlin firmware program based on the number and types of input and output devices of the developed machine and was uploaded to the megatronics v3.1 microcontroller. part fabrication using the developed system begins with creating the 3d cad model of the required part in stl format. the cad model then sliced into desired layer thickness using slic3r software, and corresponding g – codes are generated. finally, based on the generated g-codes, pronterface software is used to generate a numerical control (nc) machine tool path. 3.8 assembly of sis subsystems and development of sis system the designed subsystems such as build and feed tanks assembly, powder deposition and compaction mechanism, inhibition deposition mechanism and heater assembly are assembled to make the sis system which is shown in fig. 9. preliminary testing on linear and rotary actuators, tanks assemblies, nc tool path generation, inhibitor deposition, heater motion, temperature feedback controller and limit switch sensing is performed. fig. 9: developed sis system. to minimize the cost of the sis system, selection of temperature sensors, linear actuators, and belt drive systems are carried out with due consideration of cost-effectiveness and superior performance. a novel inhibition delivery mechanism is developed for the precise delivery of inhibitor. the composition of inhibitor material preparation was crucial to obtain precise inhibition effect on the polymer powder surface and is successfully achieved. the 221 low-cost sis system is developed by assembling the various components. the preliminary functionality tests demonstrate that the developed sis system is applicable in all aspects and it can be used to produce functional parts. however, one major limitations of the developed sis system is material wastage. in the sis part fabrication process the entire powder bed is heated by the infrared heater which fuses the whole powder layer except the region that is wetted by the inhibitor solution. consequently, the powder that is not in the waste powder is not reusable. in this developed system the powder bed region that make up the part body as well as the region outside the part cross sectional area is sintered which causes powder loss. 3.9 mechanical strength testing of sis fabricated parts to evaluate the performance of the developed system and determine the influence of its process parameters such as heater feed rate, printer feed rate, layer thickness, and heat energy on the tensile and flexural strength of the fabricated part, sample parts were fabricated and their mechanical characteristics have been assessed. specimens were fabricated from high-density polyethylene (hdpe) polymer powder, supplied by jp polymers, india. as per the datasheet of the supplier, the grain size of the selected powder particles was in the range of 35 m to 80 m. the powder used was 100% virgin so that any possible irregularities in the sintered parts were avoided. box-behnken based rsm approach was followed to perform an optimal set of experiments through varying sis process parameters [20,23]. the process parameters were varied with three levels as indicated in table 1. table 1: sis process parameters and levels s. no. parameters units levels low medium high 1 layer thickness mm 1 2 3 2 heat energy j/mm2 25.32 28.48 30.06 3 heater feed rate mm/sec 3 3.25 3.5 4 printer feed rate mm/min 100 110 120 the range of settings for the considered process variables were determined based on the thermal property of the polymer powder by conducting numerous preliminary tests. 222 the tensile strength test was performed according to the astm d638 standard [24] with a test speed of 5 mm/min at room temperature and 40% relative humidity. similarly, the flexural strength test was carried out based on astm: d790 [25] standard with a test speed of 1.2 to 1.8 mm/min. the instron 3369 dual column universal testing system shown in fig. 10 and 11 were employed to carry out both tensile and flexure strength test. 4. results and discussion the result of the experiment and the combinations of corresponding parameters and their settings are given in table 2. table 2: experimental results of tensile and flexural strengths run layer thickness (mm) heat energy (j/mm2) heater feed rate (mm/s) printer feed rate (mm/min) tensile strength (mpa) flexure strength (mpa) 1 3 28.48 3.5 110 23.05 25.46 2 2 30.06 3 110 21.29 26.64 3 1 28.48 3.5 110 22.53 26.34 4 2 28.48 3.25 110 25.55 28.63 5 3 25.32 3.25 100 24.39 26.35 6 1 28.48 3.25 120 24.94 27.18 7 2 30.06 3.5 120 20.53 24.20 8 2 28.48 3 120 20.41 24.11 9 2 30.06 3.5 110 25.92 27.57 10 2 28.48 3.25 110 25.12 28.55 11 2 30.06 3.25 100 24.64 28.13 12 2 25.32 3.5 100 23.97 27.90 13 3 28.48 3 110 20.86 26.18 14 2 25.32 3.25 120 21.29 27.04 15 2 25.32 3.5 110 19.34 25.24 16 3 25.32 3.25 110 23.77 28.57 17 2 28.48 3.25 110 24.29 27.22 18 1 28.48 3 110 25.87 29.60 19 2 28.48 3.5 100 21.62 26.40 20 2 30.06 3.25 110 24.90 28.22 21 2 28.48 3.25 110 24.70 22.10 22 2 25.32 3 100 24.97 28.05 23 2 30.06 3.5 120 25.25 28.19 24 1 30.06 3.25 100 24.85 27.11 25 1 28.48 3.25 110 26.54 32.08 26 1 25.32 3.25 110 23.80 27.01 27 3 30.06 3.25 110 24.97 28.94 28 2 25.32 3 110 24.47 28.71 29 3 28.48 3.25 120 22.90 26.77 from the result of the experiments, it is evident that maximum tensile strength and flexural strength of 26.54 mpa and 32.08 mpa respectively were obtained for process 223 variables settings: layer thickness of 1mm, heat energy of 28.48 j/mm2, printer feed rate of 110 mm/min and heater feed rate of 3.25 mm/sec. the influence of input process parameters such as layer thickness, heat energy, heater feed rate and printer feed rate on tensile and flexure strengths were analysed as depicted in fig. 12 and 13. the effect of each process parameter was distinctly analysed where other parameters were set at their mid-levels. fig. 12: effect of process parameters on tensile strength of sis parts. as can be seen from fig. 12 (a) and 13 (a) an increase in layer thickness leads to a reduction in tensile and flexural strengths. this is because at minimal layer thickness the bonding between successive layers is stronger. on the contrary, at maximum thickness of the powder layer, micro voids are developed which leads to the reduction of tensile strength [26]. heat energy in the range of 27 j/mm2 31 j/mm2, which is about 77 % to 85 % of the energy required to achieve the melting point of hdpe has resulted in a more compact structure due to better fusion of powder particles. strong intermolecular attraction between the polymer particles occurs in the specified range of temperature. as a result, mechanical strength increased with an increase of heat energy as shown in fig. 12 (b) and 13 (b) [27]. therefore, heat energy necessary to bring strong bonding between powder particles helps to achieve high mechanical strength on the fabricated part. 224 furthermore, the effect of the heater feed rate as shown in fig. 12 (c) and 13 (c), and printer feed rate indicated in fig. 12 (d) and 13 (d) on the mechanical strength is nonlinear. as seen from the graphs mechanical strength increases up to the optimal value of the heater feed rate and printer feed rate which then decreases drastically. an increase in heater feed rate causes porosity between layers which diminishes the mechanical strength. the printer feed rate influences the inhibition penetration effect, which affects the dimensional and geometric characteristics of the part. fig. 13: effect of process parameters on flexure strength of sis parts. figure 14 (a–c) shows the sem images of the fractured surface of the tensile test specimens fabricated with a heat energy of 28.48 j/mm2. analysis of the sem images showed some porosity in the fractured surface. these voids act as stress concentrators and cause uneven distribution of the normal stress over the cross-sectional area of the test specimens. therefore, such pores and voids observed need to be eliminated by optimizing the compaction pressure during layer making. figure 15 (a-c) shows the sem micrograph of the flexural fractured surface of the specimens fabricated with heat energy of 28.48 j/mm2. it is evident from fig. 15 (a) that there is interphase de-lamination at the cross-section of the sintered specimen due to the applied flexural load. voids are also observed in fig. 15 (b) due to poor interfacial bonding between sintered particles. however, the formation of voids and uneven sintering of 225 polymer particles are comparatively higher in the case of specimens fabricated below the applied heat energy of 28.48 j/mm2. fig. 14: fractured surfaces of sis fig. 15: fractured surfaces of sis fabricated tensile test specimen. fabricated flexural test specimen. an identical load was constantly applied on the specimens’ surface that created a shear band along the middle section of the specimens resulting in its breakage as seen in fig. 15 (c). in addition, elongated dimples normal to the loading axis are observed in fig. 15 (c). moreover, few voids and bulk cohesion of particles are seen in the fractured surface, these can be attributed to the non-uniform heat distribution during sintering. response surface methodology (rsm) has been used for the optimization of mechanical strength characteristics as it handles the interaction effects of input parameters [28]. in order to validate the results obtained, confirmation experimental tests were conducted as shown in table 3. table 3: validation table a) comparison of predicted tensile strength with experiment result layer thickness (mm) heat energy (j/mm2) heater feed rate (mm/s) printer feed rate (mm/min) predicted value (mpa) experimental value (mpa) error percentage 1 28.48 3.2 110 27.21 27.80 2.12% b) comparison of predicted flexural strength with experiment result layer thickness (mm) heat energy (j/mm2) heater feed rate (mm/s) printer feed rate (mm/min) predicted value (mpa) experimental value (mpa) error percentage 1 28.48 3.2 110 33.60 34.59 2.86% as can be seen from the table, the deviation of the actual tensile strength and flexural strength values from the predicted values are only by 2.12% and 2.86% respectively. hence, it can be concluded that the predicted value is in good agreement with the experimental value. in addition, to evaluate the dimensional accuracy and geometric complexity of the a a b c c b 226 parts fabricated using the developed low cost sis system; sample components shown in (fig. 16) were manufactured. these samples have shown dimensional accuracy of about 1 mm which shows that the developed system has the capability of producing parts with acceptable mechanical strength as well as dimensional accuracy. fig. 16: fabricated sis parts. therefore, parts fabricated by the developed sis system can be utilized as load carrying structural machine elements replacing components fabricated using another fabrication processes such as sls and injection moulding. 5. conclusion the developed sis system is custom-built through the integration of an indigenously designed h-bot x-y precision position mechanism, inhibition depositor, heating element and build and feed tank assemblies. to minimize the cost of the sis system, selection of temperature sensors, linear actuators, and belt drive systems are carried out with due consideration of cost-effectiveness and superior performance. a novel inhibition delivery mechanism that minimizes the controllable process variables has been developed and implemented for the precise delivery of inhibitor. in addition, an innovative low cost powder spreader was used, and thus the cost of the current machine has been brought down significantly so that it is economically affordable. the capability of the machine was tested by fabricating various parts from polymer powder, and the mechanical and geometric characteristics of the fabricated parts were evaluated. the polymer materials used to test the performance of the developed system were selected by evaluating its thermo-structural load carrying capacity using finite element analysis. the fea studies indicated that hdpe attains minimal displacement and thermal stress. besides, ki was identified as the best inhibitor material because of its high solubility to water and high melting point. tensile and flexural specimens have been fabricated from the selected hdpe polymer powder and their mechanical property was evaluated. the result showed that the hdpe parts fabricated by the developed sis system achieved a tensile and flexural strength of 27.8 mpa and 34.59 mpa respectively. furthermore, the fabricated components have been found to have achieved good dimensional accuracy. therefore, from these observations, it can be deduced that the indigenously designed and fabricated sis system can be utilized to manufacture functional prototypes from various polymer powders of melting point up to 300 c for diverse applications. furthermore, in this study the sis process variable settings 227 have been investigated only for hdpe polymer powder. in order to use the system for materials other than hdpe, a parametric study needs to be carried out to achieve optimum part quality. in addition, more optimization research needs to be conducted on the sis process variables in order to enhance the quality of the fabricated parts. the developed sis system has great potential for commercialization in the additive manufacturing sector in the near future. references [1] achillas c, tzetzis d, raimondo mo. (2017). alternative production strategies based on the comparison of additive and traditional manufacturing technologies. international journal of production research, 55(12):3497-3509. https://doi.org/10.1080/00207543.2017.1282645 [2] gardan j. (2016). additive manufacturing technologies: state of the art and trends. international journal of production research, 54(10):3118-3132. https://doi.org/10.1080/00207543.2015.1115909. [3] abdulhameed o, al-ahmari a, ameen w, mian, sh. (2019). additive manufacturing: challenges, trends, and applications. advances in mechanical engineering, 11(2):1-27. https://doi.org/10.1177/1687814018822880. [4] krassimir d. (2009). rapid prototyping and engineering applications: a toolbox for prototype development. assembly automation. https://doi.org/10.1108/aa.2009.03329cae.001. [5] kruth, jp (1991). material incress manufacturing by rapid prototyping techniques. cirp annals manufacturing technology, 40(2):603-614. https://doi.org/10.1016/s00078506(07)61136-6. [6] khoshnevis b, asiabanpour b, mojdeh m, palmer k. (2003). sis–a new sff method based on powder sintering. rapid prototyping journal, 9(1):30-36. [7] asiabanpour b, palmer k, khoshnevis b. (2004). an experimental study of surface quality and dimensional accuracy for selective inhibition of sintering. rapid prototyping journal, 10(3):181-192. [8] asiabanpour b. (2003). an experimental study of factors affecting the selective inhibition of sintering process. [9] khoshnevis b, yoozbashizadeh m, chen y. (2012). metallic part fabrication using selective inhibition sintering (sis). rapid prototyping journal, 18(2):144-153. https://doi.org/10.1108/13552541211212122 [10] asiabanpour b, khoshnevis b, palmer k. (2006). advancements in the selective inhibition sintering process development. virtual and physical prototyping, 1(1):43-52. [11] aravind a, siddiqui tn, arunkumar p, balasubramanian e. (2017). comparative study of high performance polymers in selective inhibition sintering process through finite element analysis. polymers and polymer composites, 25(3):199-202. https://doi.org/10.1177/096739111702500303 [12] petros m, torabi p, khoshnevis b. (2016). the influence of build strategies in selective inhibition sintering (sis). international journal of advanced manufacturing technology, 84(5-8):969-979. https://doi.org/10.1007/s00170-015-7766-y [13] torabi p, petros m, khoshnevis b. (2014). selective inhibition sintering: the process for consumer metal additive manufacturing. 3d printing and additive manufacturing, 1(3):152155. [14] asiabanpour b, khoshnevis b, palmer k, mojdeh m. (2003). advancements in the sis process. 14th international symposium on solid freeform fabrication, austin, tx. [15] palmer k., khoshnevis b. (2003). performance factors in the selective inhibition of sintering process. iie annual conference. proceedings, 1. institute of industrial and systems engineers (iise). [16] balasubramanian e, rajamani d, arunkumar p. (2018). investigation on dry sliding wear behavior of selective inhibition sintered hdpe parts using simulated annealing algorithm. materials today: proceedings, 5(2):6534-6542. https://doi.org/10.1016/j.matpr.2017.11.308 228 [17] baligidad sm, chandrasekhar u, elangovan k, shankar s. (2018). taguchi’s approach: design optimization of process parameters in selective inhibition sintering. materials today: proceedings, 5(2):4778-4786. https://doi.org/10.1016/j.matpr.2017.12.051 [18] yoozbashizadeh m, khoshnevis b (2019). the effects of sintering conditions on selective inhibition sintering process for bronze. 3d printing and additive manufacturing, 6(5):262271. [19] rajamani d, balasubramanian e, arunkumar p, silambarasan m, bhuvaneshwaran g. (2018). experimental investigations and parametric optimization of process parameters on shrinkage characteristics of selective inhibition sintered high density polyethylene parts. experimental techniques, 42(6):631-644. https://doi.org/10.1007/s40799-018-0286-6 [20] rajamani d, ziout a, balasubramanian e, velu r, sachin s, mohamed h. (2018). prediction and analysis of surface roughness in selective inhibition sintered high-density polyethylene parts: a parametric approach using response surface methodology–grey relational analysis. advances in mechanical engineering, 10(12). 168781401882099. https://doi.org/10.1177/1687814018820994 [21] bhuvaneshwaran g, sisay m, manivannan r, arunkumar p, silambarasan m. (2019). development of inhibition system for sis process. lecture notes in mechanical engineering, 383-389. https://doi.org/10.1007/978-981-13-2697-4_42 [22] shaikh h, anis a, poulose am, alam m, a-otaibi mn, alam ma, al-zahrani sm. (2016). studies on high density polyethylene reinforced with phosphate ore particles: thermal, rheological, mechanical and morphological properties. polymer-plastics technology and engineering, 55(17):1831-1841. https://doi.org/10.1080/03602559.2016.1171875 [23] esakki b. (2017). modeling and prediction of optimal process parameters in wear behaviour of selective inhibition sintered high density polyethylene parts. progress in additive manufacturing. https://doi.org/10.1007/s40964-017-0033-z [24] astm d638-14. (2014). standard test method for tensile properties of plastics. astm international, west conshohocken, pa, 82(c):1-15. [25] astm d790–03. (2017). standard test methods for flexural properties of unreinforced and reinforced plastics and electrical insulating materials. astm international, west conshohocken, pa. [26] shubham p, sikidar a, chand t. (2016). the influence of layer thickness on mechanical properties of the 3d printed abs polymer by fused deposition modeling. key engineering materials, 706:63-67. https://doi.org/10.4028/www.scientific.net/kem.706.6 [27] khalil y, kowalski a, hopkinson n. (2016). influence of energy density on flexural properties of laser-sintered uhmwpe. additive manufacturing, 10:67-75. https://doi.org/10.1016/j.addma.2016.03.002 [28] im ek b, ç, yt, im ek eh. (2016). a rsm-based multi-response optimization application for determining optimal mix proportions of standard ready-mixed concrete. arabian journal for science and engineering, 41(4):1435-1450. https://doi.org/10.1007/s13369-015-1987-0 229 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <feff0130015f006c006500200069006c00670069006c0069002000620065006c00670065006c006500720069006e0020006700fc00760065006e0069006c0069007200200062006900e70069006d006400650020006700f6007200fc006e007400fc006c0065006e006d006500730069006e0065002000760065002000790061007a0064013100720131006c006d006100730131006e006100200075007900670075006e002000410064006f006200650020005000440046002000620065006c00670065006c0065007200690020006f006c0075015f007400750072006d0061006b0020006900e70069006e00200062007500200061007900610072006c0061007201310020006b0075006c006c0061006e0131006e002e0020004f006c0075015f0074007500720075006c0061006e002000500044004600200064006f007300790061006c0061007201310020004100630072006f006200610074002000760065002000410064006f00620065002000520065006100640065007200200036002e003000200076006500200073006f006e00720061006b00690020007300fc007200fc006d006c0065007200690079006c00650020006100e70131006c006100620069006c00690072002e> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 graphene oxide microcapsules (goms) with linseed oil core via pickering emulsion method: effect of disperse speed nurul nadiah sahir1, noor azlina hassan1*, norita hassan1 and norhasnidawani johari2 1 department of manufacturing and materials engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia 2 department of mechanical precision engineering, malaysia-japan international institute of technology, utm, 54100 kuala lumpur, malaysia *corresponding author: noorazlina_hassan@iium.edu.my (received: 25th march 2020; accepted: 3rd september 2020; published on-line: 4th january 2021) abstract: graphene oxide microcapsules (goms) have been prepared through pickering emulsion method by varying the disperse speed to study its effect on the gom’s size. the goms were characterized through phase separation observation, polarized optical microscope (pom), and particle size analyser (psa). phase separation observation showed more viscous and cloudy emulsion was produced when the disperse speed was increased. after 24 hours, only 800 rpm emulsion did not show any phase separation. pom characterization depicted that increasing the emulsification energy led to the finer emulsion with the 1200 rpm sample showing the smallest microcapsule size of around 8 μm. however, psa analysis suggested that although the disperse speed controls the goms size, the amount of go in the emulsion plays an important role for the microcapsule to maintain its stability. emulsion produced at 800 rpm possesses satisfactory stability with goms diameter of 11.15 μm. the result also suggested that graphene oxide encapsulated linseed oil may act as a promising candidate for healing microcapsules in a self-healing coating system. abstrak: mikrokapsul graphene oksida (goms) telah dihasilkan melalui kaedah emulsifikasi pickering dengan memvariasikan tenaga pengemulsi untuk mengkaji kesannya terhadap saiz goms. goms dicirikan melalui pemerhatian pemisahan fasa, mikroskop optik polarisasi (pom) dan penganalisis saiz zarah (psa). pemerhatian pemisahan fasa menunjukkan emulsi yang lebih likat dan keruh dihasilkan apabila kelajuan pengemulsi meningkat. selepas 24 jam, hanya emulsi 800 rpm tidak menunjukkan pemisahan fasa. pencirian pom meunjukkan bahawa peningkatan tenaga pengemulsi menghasilkan emulsi yang lebih halus dengan sampel 1200 rpm menunjukkan saiz mikrokapsul terkecil, sekitar 8 μm. walau bagaimanapun, analisis psa mencadangkan bahawa walaupun kelajuan pengemulsi mengawal saiz goms, jumlah go dalam emulsi memainkan peranan penting untuk mengekalkan kestabilan mikrokapsul. emulsi yang dihasilkan pada 800 rpm mempunyai kestabilan yang memuaskan dengan purata saiz goms sekitar 11.15 μm. berdasarkan dapatan kajian, graphene oksida yang terkandung minyak biji rami boleh menjadi salah satu mikrokapsul penyembuh dalam sistem cat auto-sembuh. keywords: graphene oxide; pickering emulsion; linseed oil; microcapsules 213 iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 1. introduction graphene oxide (go), is the most important derivative of graphene. go is a twodimensional material that consists of partially broken sp2-bonded carbon networks. phenol, hydroxyl and epoxide groups occupy the basal planes of the sheet and carboxylic acid groups attached to the edges make the go sheet possess the amphiphilic property and be readily dispersed in water or any solvent [1]. although the thickness of the go sheet is only in nanometers, its excellent impermeability indicates go possesses a superior barrier property [2]. many researchers utilize this advantage by incorporating the go sheets into a protective coating for metals, polymer membranes for gas barrier films, and water treatment applications [3-5]. di et al. found that go incorporated coating exhibits good anti-corrosion properties by delaying the migration of corrosive species to the underlying substrate, while ammar et al. reported that the gas barrier property of go infused polymer increased dramatically [6,7]. go has also been utilized in liquid crystals (lc) for various applications such as supercapacitors, sensors, optical-switching devices, and also graphene oxide-based foam and aerogel for sound absorbers [8-11]. graphene oxide liquid crystals (golcs), a highly anisotropic fluid consist of the long-range crystal-like ordering of go. this latest class of 2d nanomaterials possesses colloidal liquid crystallinity contributed by their intrinsic disclike shape anisotropy [12]. as reported by abedin et al., water is the most reported media for golc due to the extensive hydrogen bonding [13]. the colloidal system containing 2d go sheets can be effectively aligned by external shear force because of their self-alignment ability in nematic phases. jalili et al. suggested that this behaviour makes the golc suitable to synthesize macroscopic objects such as fibers, film, membranes, and foams [14]. this paper reports on the utilization of golcs to encapsulate the healing agent as the potential candidate for a healing agent reservoir in a self-healing coating. the graphene oxide microcapsules (goms) were synthesized through the pickering emulsion method. pickering emulsion is an emulsion of any type, whether oil-in-water (o/w) or water-in-oil (w/o) stabilized by solid particles [15]. the interesting differences between the pickering emulsions compared to the classical emulsion are the absence of surfactant, superior stability, and low toxicity [16]. by employing go as the stabilizer in the pickering emulsion system, it is possible to tailor microscopic capsules due to its surface flexibility and strong van der waals force between individual go sheets [17]. the excellent barrier properties of go sheets also make them suitable candidates to store the healing agent in self-healing coatings where the impermeability to diffusion is needed [18]. the core material for the goms, linseed oil (lo), is the most popular seed extract for corrosion inhibition and was also reported as a hydrophobic agent [19]. it is a type of drying oil that undergoes oxidative polymerization if it is exposed to the atmosphere [20]. linseed oil has been encapsulated within various materials including poly(urea) formaldehyde (puf), ethylcellulose and poly(methyl methacrylate) for self-healing coating application [21-23]. in this research, goms is produced by using only go sheets and linseed oil with the help of high shear stirring. the disperse speed is varied to study their effect on the microcapsule’s size. the optimum shear speed for the fabrication of goms is proposed for their application in water-based self-healing coating for future works. 2. materials and method goms were synthesized through the pickering emulsion method as discussed by li et al. [24]. the disperse speed (rpm) is the parameter that affects the microcapsule’s size. briefly, goms were prepared by adding 0.37g linseed oil (sigma aldrich, 0.93 g/ml) into 214 iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 the 5 ml graphene oxide solution (hummer method, graphene supermarkettm, 3.7 mg/ml) followed by mixing it with an overhead stirrer for 10 minutes. the disperse speed (rpm) was varied (400, 800, 1200, 1600, 2000, and 2400 rpm) while maintaining the same amount of go concentration. the emulsion formed is then transferred to 7 ml polyethylene vials. the resultant emulsions were characterized through phase separation observation and polarized optical microscope (pom) (model: lext ols4100). the emulsions formed were viscous and not suitable for optical microscope characterization. to capture the image clearly, the emulsions were diluted with deionized water with a dilution factor of 3. then, they were dropped onto the surface of a glass slide and characterized immediately. the goms size is recorded based on the pom images. the coefficient of variation, cv of the goms was calculated by using the eq. (1) below: 𝐶𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑉𝑎𝑟𝑖𝑎𝑡𝑖𝑜𝑛 (𝐶𝑣) = 𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛 𝑚𝑒𝑎𝑛 𝑠𝑖𝑧𝑒 𝑜𝑓 𝐺𝑂𝑀𝑠 (1) droplet size distribution for oil-in-water emulsions was analyzed by particle size analyzer (psa) (model: malvern zetasizer nano). the refractive index is set to 1.4795 (linseed oil). 3. results and discussion 3.1 phase separation observation to study the effect of emulsification energy on the properties of the emulsions formed, the disperse speed was varied from 400 to 2400 rpm. figure 1 shows the digital images of the emulsions right after the synthesis. emulsion in fig. 1(b) to 1(f) showed a successful emulsification process based on the cloudy appearance. emulsion tends to appear cloudy because the light is scattered off the phase interphases between the oil and water components [25]. the visible cloudiness is also an indication that the goms produced are in micronranges [26]. as reported by kim et al. go sheets can stabilize the linseed oil in water as they could behave like a colloidal surfactant [27]. by increasing the mixing speed, the emulsion is observed to be more viscous. this is also another indication that the size of the goms is reduced and the amount of the goms is increased, which in turn increases the interfacial area. an early study by thompson et al. found that the increase in the interfacial area led to an increase in interfacial viscosity effects and also an increase in hydrodynamic interactions [28]. gohtani & yoshii also reported the same phenomenon where the emulsion diameter was found to significantly affect the emulsion viscosity, in which the viscosity increased as the emulsion diameter decreased [29]. emulsions as shown in fig. 1(a), stirred with low rpm, showed not all solid particles and oil participate in the emulsification process. this can be proven by the formation of two different phases with the oil phase occupying the upper part of the mixture. the dark brown colour of the lower water phase shows that there is a large amount of go left in the water. the emulsification energy supplied for emulsion (a) is not sufficient enough to fully emulsify the linseed oil. as the disperse speed increased, the colour of the emulsion becomes lighter, as depicted by the colour bar in fig. 1. 215 iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 fig. 1: digital image of the emulsions formed with different rotational shear speed a) 400 rpm, b) 800 rpm, c) 1200 rpm, d) 1600 rpm, e) 2000 rpm, and f) 2400 rpm. based on fig. 2, the emulsion prepared at 800 rpm is the only sample that showed no phase separation layer, while destabilization occurred to the rest of the emulsion. the bottom part was occupied by the continuous phase, while the top region or the creaming part was rich with the goms. it was postulated that the destabilization happened due to an insufficient amount of go sheets to stabilize the goms. fig. 2: digital images of emulsions containing goms prepared with varied disperse speed monitored after 24 hours, a) 800 rpm, b) 1200 rpm, c) 1600 rpm, d) 2000 rpm, and e) 2400 rpm. 3.2 polarized optical microscope (pom) analysis pom characterization was done directly after the emulsification process. the images in fig. 3 showed that goms were present in all samples, based on the existence of bright shining halos around the emulsion droplets. under normal light, the milky emulsion was difficult to observe. therefore polarized light was needed. the presence of shining halos around the oil droplets suggested the go sheets assembled themselves at the liquid-liquid interface. the distinct shining halos observed indicate the emulsion was isotropic except for the bright go shells. the birefringence has a cross-shape that originates from the presence of oil droplets in the anisotropic colloidal structure [30]. note that emulsions formed without go do not behave in this way due to the fact that they are optically isotropic, which means they cannot emit the liquid crystal behaviour [31]. the liquid crystal structure is formed when go align themselves around the oil droplets and these molecularly ordered go sheets are what gave off the birefringence property, which is a typical fingerprint of liquid crystals [32]. therefore, it shows that goms were successfully obtained. go sheets tend to localize between the liquid-liquid interface to minimize the interfacial energy between two immiscible liquids (linseed oil and water). the high surface area of the 216 iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 go sheets enables them to wrap around the linseed oil droplets. the wettability of go also made this possible. the wettability test done by panda et al. showed that go obtained through hummer method possess the contact angle (θw) of less than 90°, which is around 46.5° [33]. the test involves the measuring of the contact angle between the go film and water. this indicates that go is partially hydrophilic and prone to stabilize oil-in-water (o/w) emulsion due to its particle surface resides more in water than in oil. this is in line with our experimental results. goms are readily dispersed in water, implying the formation of an o/w emulsion system with linseed oil droplets as the dispersed phase and go solution making up the continuous phase. figure 3 also showed the images of goms with uneven size distribution and as the shear speed was increased, finer and more even microcapsule sizes were produced. the average size and coefficient of variation (cv) for each emulsion listed in table 1 also supported the finding. as the speed increased, the value of cv decreased, indicating a low variation of droplets diameter [34]. this is in good agreement with chevalier & bolzinger suggesting that in pickering emulsion, a high energy emulsification process can break the oil into small droplets resulting in finer emulsions [35]. fig. 3: image of the emulsion under a polarized optical microscope, a) 400 rpm, b) 800 rpm, c) 1200 rpm, d) 1600 rpm, e) 2000 rpm, f) 2400 rpm, g) single gom under polarized light and h) single gom under optical microscope. table 1: average size and cv value for each emulsion disperse speed [rpm] average size [μm] coefficient of variation [cv] 400 20.36 0.73 800 11.15 0.34 1200 8.57 0.31 1600 8.33 0.26 2000 8.02 0.29 2400 8.11 0.24 to further understand the goms formation, fig. 4 depicts the schematic representation of the preparation process and encapsulation mechanism. an overhead stirrer breaks the oil 217 iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 into small droplets (fig. 4b) followed by the stabilization of the oil droplets by hydrophilic go sheets that assembled themselves at the oil-liquid interface (fig. 4c). figure 4(d) showed the desired final product that was called graphene oxide encapsulated linseed oil, or graphene oxide pickering emulsion or goms. fig. 4: encapsulation process, a) emulsion preparation, b) breaking of linseed oil into small droplets by the propeller, c) go sheets assembled themselves around the linseed oil droplets, d) stabilized pickering emulsion (goms). it needs to be noted that a small microcapsule with an even size distribution is more favourable to be used in self-healing coatings. the incorporation of the bigger container into the coating can disrupt the barrier properties and reduce the coating resistance [36]. although increasing the shear speed does decrease the microcapsule’s size, there is no significant size reduction observed for the goms when the disperse was higher than 1200 rpm. this might be due to the oil droplets reaching their maximum limit to further break down into smaller droplets and a limited amount of go sheets to stabilize them. 3.3 particle size analyzer (psa) analysis figure 5 displays the size distribution for all emulsions. as the size of the goms did not change much when they were prepared at 1200 rpm and above, only four emulsions were characterized. in contrast with pom results, the result obtained from particle size analyzer showed a different trend where the droplet size increased as the disperse speed was increased. the psa result showed goms prepared with the disperse speed of 400 rpm exhibits the smallest size compared to others but its pom result displayed the emulsion is only partially stabilized. it should be noted that the sample taken for psa characterization is from the continuous phase and not from the creaming part. the psa characterization was done after 24 hours which allowed the emulsions to settle down. this phenomenon explains why the increasing trend happened. the oil droplets were able to maintain their size for a while but after a few hours, they started to coalesce due to lack of stabilizing moieties. increasing the shear speed breaks the oil into small droplets, resulting in the increasing amount of droplets present in the continuous phase. this will also cause the surface area of the droplets to increase, thus, requiring more go particles to wrap the linseed oil droplet and form a stable emulsion. this result is also supported by the phase separation observation discussed in section 3.1 previously. it is worth mentioning that other stabilizers or surfactants could be added to hold the goms structure to maintain their sizes 218 iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 prior to the psa characterization. however, pom analysis may give more accurate and reliable results as the goms used in this study only utilized go sheets as a stabilizer. fig. 5: the droplet size distribution of goms, a) 400 rpm, b) 800 rpm, c) 1200 rpm and d) 1600 rpm. this finding implied that the disperse speed and stabilizing moieties go hand in hand and controlling only one parameter is not enough to produce stable goms. studies done by tsabet & fradette also supported the above-mentioned observations. they suggested that by increasing the energy will promote droplet generation and produce a larger interface, and the amount of stabilizing particles also need to be increased to cover and stabilize the interface [37]. figure 6 displays the goms size comparison obtained through pom and psa. there are some discrepancies between pom and psa results as the pom measures the goms diameter which includes the go shell thickness, while psa measures only the linseed oil droplet’s diameter. nevertheless, the increasing size pattern that comes from the psa analysis needs to be taken into account and cannot be ignored. by comparing pom and psa analysis, 800 rpm is the preferable speed for the preparation of goms with satisfied microcapsule size. this was further supported by the phase separation observation discussed in section 3.1, where only goms prepared at 800 rpm maintained its stability. fig. 6: average size distribution based on pom images and psa of the emulsions. 219 iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 4. conclusion goms were successfully produced through the pickering emulsion method. the pom analysis showed the disperse speed affects the size of the produced goms, where insufficient emulsification energy led to a partially stabilized emulsion. however, psa analysis suggests the go-hms size depends on both disperse speed and the amount of stabilizing moieties. controlling only one parameter is not sufficient to produce fine and stable emulsions. although pom images showed that the disperse speed of 1200 rpm produced the smallest diameter of goms (around 8 μm), considering the psa pattern and phase separation observations, 800 rpm is chosen as the ideal processing speed to produce goms with satisfactory size (11.15 μm) and stability. linseed oil is effectively wrappedup by go in the oil-in-water emulsion system based on the presence of shining halos around the oil droplets. this finding also showed go is capable to encapsulate healing agents and may be a suitable candidate for microcapsules to be used in waterborne self-healing coating. acknowledgement this work was funded by rigs17-107-0682 and frgs19-058-0666 research grants. the authors would like to acknowledge the kuliyyah of engineering, international islamic university malaysia (iium), ministry of higher education (mohe), malaysia and every party involved both directly and indirectly in this work. references [1] shao, jj, lv w, yang qh. (2014) self‐assembly of graphene oxide at interfaces. advanced materials, 26(32): 5586-5612. [2] wu j, huang g, li h, wu s, liu y, zheng j. (2013) enhanced mechanical and gas barrier properties of rubber nanocomposites with surface functionalized graphene oxide at low content. polymer, 54(7): 1930-1937. [3] ramezanzadeh b, niroumandrad s, ahmadi a, mahdavian m, moghadam mm. (2016) enhancement of barrier and corrosion protection performance of an epoxy coating through wet transfer of amino functionalized graphene oxide. corrosion science, 103: 283-304. [4] bandyopadhyay p, park wb, layek rk, uddin me, kim nh, kim hg, lee jh. (2016) hexylamine functionalized reduced graphene oxide/polyurethane nanocomposite-coated nylon for enhanced hydrogen gas barrier film. journal of membrane science, 500: 106-114. [5] wang j, zhang p, liang b, liu y, xu t, wang l, cao b, pan k. (2016). graphene oxide as an effective barrier on a porous nanofibrous membrane for water treatment. acs applied materials & interfaces, 8(9): 6211-6218. [6] di h, yu z, ma y, li f, lv l, pan y, lin y, liu y, he y. (2016) graphene oxide decorated with fe3o4 nanoparticles with advanced anticorrosive properties of epoxy coatings. journal of the taiwan institute of chemical engineers, 64: 244-251. [7] ammar a, al-enizi am, almaadeed ma, karim a. (2016) influence of graphene oxide on mechanical, morphological, barrier, and electrical properties of polymer membranes. arabian journal of chemistry, 9(2): 274-286. [8] wang b, liu j, zhao y, li y, xian w, amjadipour m, macleod j, motta n. (2016) role of graphene oxide liquid crystals in hydrothermal reduction and supercapacitor performance. acs applied materials & interfaces, 8(34): 22316-22323. [9] choi sj, yu h, jang js, kim mh, kim sj, jeong hs, kim id. (2018) nitrogen‐doped single graphene fiber with platinum water dissociation catalyst for wearable humidity sensor. small, 14(13): 1703934. [10] shen tz, hong sh, song jk. (2014) electro-optical switching of graphene oxide liquid crystals with an extremely large kerr coefficient. nature materials, 13(4): 394-399. 220 iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 [11] oh jh, kim j, lee h, kang y, oh ik. (2018) directionally antagonistic graphene oxidepolyurethane hybrid aerogel as a sound absorber. acs applied materials & interfaces, 10(26): 22650-22660. [12] narayan r, kim je, kim jy, lee ke, kim so. (2016) graphene oxide liquid crystals: discovery, evolution and applications. advanced materials, 28(16): 3045-3068. [13] abedin mj, gamot, td, martin st, ali m, hassan ki, mirshekarloo ms, majumder m. (2019) graphene oxide liquid crystal domains: quantification and role in tailoring viscoelastic behavior. acs nano, 13(8): 8957-8969. [14] jalili r, aboutalebi sh, esrafilzadeh d, konstantinov k, moulton se, razal jm, wallace gg. (2013) organic solvent-based graphene oxide liquid crystals: a facile route toward the next generation of self-assembled layer-by-layer multifunctional 3d architectures. acs nano, 7(5): 3981-3990. [15] chevalier y, bolzinger ma, briançon s. (2015) pickering emulsions for controlled drug delivery to the skin. in percutaneous penetration enhancers chemical methods in penetration enhancement (pp. 267-281). springer, berlin, heidelberg. [16] wu j, ma gh. (2016) recent studies of pickering emulsions: particles make the difference. small, 12(34): 4633-4648. [17] teo gh, ng yh, zetterlund pb, thickett sc. (2015) factors influencing the preparation of hollow polymer-graphene oxide microcapsules via pickering miniemulsion polymerization. polymer, 63: 1-9. [18] ullah h, azizli, ka, man zb, ismail mbc, khan mi. (2016) the potential of microencapsulated self-healing materials for microcracks recovery in self-healing composite systems: a review. polymer reviews, 56(3): 429-485. [19] montemor mf. (ed.) (2015). smart composite coatings and membranes: transport, structural, environmental and energy applications. elsevier. [20] hughes ae, mol jm, zheludkevich ml, buchheit rg. (2016) active protective coatings. active protective coatings: new-generation coatings for metals, springer series in materials science, vol. 233. isbn 978-94-017-7538-0. springer science+ business media dordrecht. [21] çömlekçi gk, ulutan s. (2019) acquired self-healing ability of an epoxy coating through microcapsules having linseed oil and its alkyd. progress in organic coatings, 129: 292-299. [22] abbaspoor s, ashrafi a, abolfarsi r. (2019) development of self-healing coatings based on ethyl cellulose micro/nano-capsules. surface engineering, 35(3): 273-280. [23] navarchian ah, najafipoor n, ahangaran f. (2019) surface-modified poly (methyl methacrylate) microcapsules containing linseed oil for application in self-healing epoxybased coatings. progress in organic coatings, 132: 288-297. [24] li j, feng q, cui j, yuan q, qiu h, gao s, yang j. (2017) self-assembled graphene oxide microcapsules in pickering emulsions for self-healing waterborne polyurethane coatings. composites science and technology, 151: 282-290. [25] afshar ghotli r, raman aa, ibrahim s, baroutian s. (2013) liquid-liquid mixing in stirred vessels: a review. chemical engineering communications, 200(5): 595-627. [26] yamashita y, miyahara r, sakamoto k. (2017) emulsion and emulsification technology in cosmetic science and technology (1st edition), elsevier, pp 489-506. [27] kim j, cote lj, kim f, yuan w, shull kr, huang j. (2010) graphene oxide sheets at interfaces. journal of the american chemical society, 132(23): 8180-8186. [28] thompson dg, taylor as, graham de. (1985) emulsification and demulsification related to crude oil production. colloids and surfaces, 15: 175-189. [29] gohtani s, yoshii h. (2018) microstructure, composition, and their relationship with emulsion stability. in food microstructure and its relationship with quality and stability (pp. 97-122). woodhead publishing. [30] lapointe cp, mason tg, smalyukh, ii. (2009) shape-controlled colloidal interactions in nematic liquid crystals. science, 326(5956): 1083-1086. [31] wan w, zhao z, hughes tc, qian b, peng s, hao x, qiu j. (2015) graphene oxide liquid crystal pickering emulsions and their assemblies. carbon, 85: 16-23. 221 iium engineering journal, vol. 22, no. 1, 2021 sahir et al. https://doi.org/10.31436/iiumej.v22i1.1426 [32] andrienko,d. (2018) introduction to liquid crystals. journal of molecular liquids, 267: 520541. [33] panda d, nandi a, datta sk, saha h, majumdar s. (2016) selective detection of carbon monoxide (co) gas by reduced graphene oxide (rgo) at room temperature. rsc advances, 6(53): 47337-47348. [34] low le, wong sk, tang sy, chew cl, de silva ha, lee jmv, hoo ch, kenrick k. (2019) production of highly uniform pickering emulsions by novel high-intensity ultrasonic tubular reactor (hutr). ultrasonics sonochemistry, 54: 121-128. [35] chevalier y, bolzinger ma. (2013) emulsions stabilized with solid nanoparticles: pickering emulsions. colloids and surfaces a: physicochemical and engineering aspects, 439: 23-34. [36] borisova d, akçakayıran d, schenderlein m, möhwald h, shchukin dg. (2013) nanocontainer‐based anticorrosive coatings: effect of the container size on the self‐ healing performance. advanced functional materials, 23(30): 3799-3812. [37] tsabet e, fradette l. (2015) effect of processing parameters on the production of pickering emulsions. industrial & engineering chemistry research, 54(7): 2227-2236. 222 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 study of microstrip patch array antenna for side lobe suppression in the x-band region using uniform, binomial and tschebyscheff excitation methods ahmad alhadi ruslan, sarah yasmin mohamad*, khairayu badron, ahmad fadzil ismail, norun farihah abdul malek and farah nadia mohd isa department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia *corresponding author: smohamad@iium.edu.my (received: 20th august 2019; accepted: 30th october 2019; published on-line: 20th january 2020) abstract: in this paper, a microstrip patch array antenna is designed and simulated to operate in the x-band frequency region at 9.5 ghz. for x-band communication transmission, it is necessary to suppress the side lobe radiation pattern of the antenna as much as possible to avoid the transmission being intercepted and/or received by undesirable neighbouring satellites. the geometrical design of the microstrip patch array antenna is simulated and executed using cst microwave studio (cst mws) in order to study the effects of various antenna parameters such as s11, gain, directivity, side lobe level, and angular width. it is shown that the proposed antenna exhibits a low side lobe level of -14.2 db with an acceptable high gain and directivity of 16.5 db and 17.7 db, respectively. the antenna configuration also has a size of only 285 mm × 59.275 mm which is much more compact and lightweight compared to the standard reflector antennas that are used for most x-band communication transmission. abstrak: kajian ini berkaitan antena cantuman barisan jalurmikro yang direka dan disimulasi beroperasi pada 9.5 ghz frekunsi daerah jalur-x. pada transmisi komunikasi jalur-x, corak radiasi sisi-lobus antena perlu ditahan sebanyak mungkin bagi mengelak transmisi dipintas dan/atau diterima oleh satelit tetangga yang tidak di ingini. rekaan geometri antena cantuman barisan jalurmikro disimulasi dan diuji menggunakan perisian cst studio gelombang mikro (cst mws) bagi mengkaji pelbagai kesan parameter antenna seperti s11, gandaan, keterarahan, tahap sisi-lobus dan lebar sudut. didapati bahawa antena yang dicadangkan mempunyai tahap sisi-lobus -14.2 db yang rendah dengan gandaan tinggi yang boleh diterima dan keterarahan sebanyak 16.5 db dan 17.7 db, masing-masing. tatabentuk antena mempunyai saiz 285 mm × 59.275 mm yang kompak dan ringan berbanding antena pemantul piawai, di mana telah digunakan pada kebanyakan jalur-x transmisi komunikasi. keywords: array antenna; microstrip antenna; side lobe suppression; x-band communication 1. introduction microstrip antennas are used for many communication applications and systems due to several advantages. these types of antennas offer benefits in terms of flexibility, 61 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 simplicity, and size [1]. microstrip antennas are usually compact and very lightweight, making them easily portable compared to other types of antennas such as satellite parabolic dishes or reflector antennas, which are more massive and hefty [2]. they also possess a planar structure and provide low fabrication costs [3]. moreover, reflector antennas have high side lobe levels that make it possible for other parties to intercept the transmitted signals. in terms of radiation pattern, most microstrip antennas exhibit a directional pattern, where its radiation intensity is mostly directed in a single direction [4]. these accumulated advantages make it very useful in developing and improving communication systems. nevertheless, despite all these advantages, microstrip antennas also present some drawbacks. while offering a possible compact size structure, the gain and directivity of the antenna is quite low compared to other directional antennas. this, however, can be solved by improvising the microstrip antennas to operate as an array. array antennas are a group of single element antennas that are arranged and connected in a regular structure [5]. one of the benefits of using the array configurations are the increase in directivity and gain that cannot be achieved using a single element antenna [6]. in this paper, the microstrip patch array antenna is proposed for use in the x-band communication frequency range (8-12 ghz) [7], specifically at 9.5 ghz. the antenna is expected to be compact, portable, exhibit fairly high gain/directivity, and able to reduce the side lobe radiation pattern. as explained earlier, currently used antennas such as parabolic dish antennas have high side lobe levels, as illustrated in fig. 1. for an excellent x-band communication, the side lobe radiation must be suppressed as much as possible to avoid the transmission being intercepted and/or received by undesirable neighbouring satellites. it should also be noted that much research has been carried out and is still ongoing in order to develop and improve this type of antenna to give better performance [2, 8-12] (summary of recent work can be seen in table 6). in this project, our proposed microstrip patch array antenna is shown to be able to provide a low side lobe level, with a fairly high gain and directivity, and a compact and lightweight structure. fig. 1: parabolic dish antenna radiation pattern with high side-lobe levels. neighbouring satellite neighbouring satellite side lobes side lobes main satellite main lobe 62 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 2. design of the microstrip patch antenna this paper focused on the design of a microstrip patch array antenna for x-band satellite communication. the antenna is designed to work in the x-band region, specifically at 9.5 ghz. 2.1 design of the single element microstrip patch antenna the microstrip patch antenna is initially designed and simulated as a single element (fig. 2) using a specialized microwave tool, the computer simulation technology (cst) microwave studio. the optimized parameters of the antenna are shown in table 1. the rogers’ rt/duroid 5880 is used as the substrate with a dielectric constant of εr = 2.2, loss tangent of δ = 0.0009 and thickness of t = 1.574 mm. the ground plane is designed to be larger than the substrate in order to ensure that the direction of the main beam is set to 0 deg. and also to reduce the back lobe radiation [3]. fig. 2: the single element microstrip patch antenna. table 1: parameters of the single element microstrip patch antenna. parameters optimized value resonant frequency 9.5 ghz width of patch 12.163 mm length of patch 9.318 mm λ/4 feeding line width 1.344 mm 50ω feeding line width 5.044 mm dielectric material rt/duroid 5880 dielectric constant 2.2 dielectric height 1.574 mm dielectric length 35.275 mm dielectric width 25 mm ground length 59.275 mm ground width 60 mm 2.2 design of the microstrip patch array antenna the microstrip patch antenna is further improved to be an array with ten elements (fig. 3) in order to increase the gain and directivity. the ten elements are selected for the array implementation since the array produced the most optimal results in terms of gain and directivity when the elements are increased. the design parameters for the microstrip patch array antenna are shown in table 2. the spacing between the patch is set at two different spacing, s = 0.5λ and s = 0.75λ, to compare the effect of these parameters to the simulation performances. 63 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 fig. 3: the microstrip patch array antenna with ten elements. table 2: parameters of the microstrip patch array antenna parameters optimized value resonant frequency 9.5 ghz width of patch 12.163 mm length of patch 9.318 mm λ/4 feeding line width 1.344 mm 50ω feeding line width 5.044 mm dielectric material rt/duroid 5880 dielectric constant 2.2 dielectric height 1.574 mm dielectric length 35.275 mm dielectric width 250 mm ground length 59.275 mm ground width 285 mm 3. simulated results 3.1 simulated results of the single element microstrip patch antenna the simulated results of the single element microstrip patch antenna using the cst microwave studio software are presented. from fig. 4, it can be observed that the resonant frequency of the microstrip patch antenna is 9.5 ghz with a 11 parameter of 39.11 db. this proves that the designed antenna radiated well in the intended resonant frequency. next, the side-lobe level is shown to be -12.345 db (fig. 5). it is also observed that the angular width of the microstrip patch antenna is very wide (74.1 deg.). this is inconvenient for the intended satellite communication in the x-band, which requires the beam width to be small enough for the transmission of data. this issue can be solved with an array antenna. moreover, based on fig. 6, it is observed that the microstrip patch antenna radiated in a directional pattern, where the gain and directivity of the antenna are 7.44 db and 8.54 db, respectively at the main lobe direction of 0 deg. the gain and directivity will be further improved by improvising the single element antenna to be working as an array (results in section 3.2). the simulated results of the single element microstrip patch antenna in terms of gain (db), directivity (db), side-lobe level (db) and angular width (deg.) are summarized in table 3. 64 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 fig. 4: return loss for the single element microstrip patch antenna. fig. 5: side-lobe level for the single element microstrip patch antenna. fig. 6: radiation pattern for the single element microstrip patch antenna. table 3: simulated results of the single element microstrip patch antenna in terms of gain (db), directivity (db), side-lobe level (db) and angular width (deg.). parameters optimized value gain (db) 7.44 directivity (db) 8.54 side-lobe level (db) -12.345 angular width (deg.) 74.1 side-lobe level 65 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 3.2 simulated results of the microstrip patch array antenna as mentioned earlier, the single element antenna is then improved to work as an array with ten elements (fig. 3) in order to improve some of its performance characteristics. three types of excitation methods (uniform, binomial, and tschebyscheff) are applied to the microstrip patch array antenna, which radiates in a directional pattern and is suitable to for use in x-band satellite communication. the simulation was run for two different spacings between the patches, i.e. s = 0.5λ and s = 0.75λ, to observe the effect of spacing on the overall performances of the antenna. figures 7 to 9 show the simulated return loss for the array antenna using uniform, binomial, and tschebyscheff excitation signals. all three excitation methods resonated well at the targeted frequency of 9.5 ghz. among the three excitation methods, the tschebyscheff and binomial signals provided the best return loss with s11 = -24.56 db, followed by the uniform signal with s11 = -16.46 db. table 4 shows the simulated results of the microstrip patch array antenna using uniform, binomial, and tschebycheff excitation methods for the two different spacings. the gain (db), directivity (db), side lobe level (db) and angular width (deg.) of the array antenna can be observed for each method. it can be seen that the uniform signal excitation produced the highest gain of 17.3 db (s = 0.75λ) and 15.5 db (s = 0.5λ), followed by tschebycheff with 16.5 db (s = 0.75λ) and 14.6 db (s = 0.5λ). the binomial amplitude excitation produced the lowest gain among the three with 14.5 db (s = 0.75λ) and 12.6 db (s = 0.5λ). furthermore, among the three different types of excitation, the uniform signal excitation produced the highest directivity for both spacings between the patches with 18.5 db (s = 0.75λ) and 16.8 db (s = 0.5λ). this is followed by tschebycheff with 17.7 db (s = 0.75λ) and 16 db (s = 0.5λ), and binomial amplitude excitation with the lowest directivity among the three, with 15.8 db (s = 0.75λ) and 14 db (s = 0.5λ). (a) (b) fig. 7: return loss for uniform excitation signal with (a) s = 0.5λ and (b) s = 0.75λ. 66 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 (a) (b) fig. 8: return loss for binomial excitation signal with (a) s = 0.5λ and (b) s = 0.75λ. (a) (b) fig. 9: return loss for tschebyscheff excitation signal with (a) s = 0.5λ and (b) s = 0.75λ. 67 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 table 4: simulated results of the microstrip patch array antenna in terms of gain (db), directivity (db), side lobe level (db) and angular width (deg.) using uniform, binomial and tschebycheff excitation signals with s = 0.5λ and s = 0.75λ. excitation method uniform binomial tschebyscheff spacing (mm) 0.5λ 0.75λ 0.5λ 0.75λ 0.5λ 0.75λ gain (db) 15.5 17.3 12.6 14.5 14.6 16.5 directivity (db) 16.8 18.5 14 15.8 16 17.7 side lobe level (db) 2.2 4.2 -55.6 -32.1 -17.3 -14.2 angular width (deg.) 10.0 6.7 19.9 13.3 12.8 8.6 in terms of side lobe level, binomial amplitude excitation exhibits the lowest level with -55.6 db (s = 0.5λ) and -32.1 db (s = 0.75λ) as shown in fig. 11. this is followed by tschebycheff with -17.3 db (s = 0.5λ) and -14.2 db (s = 0.75λ) as shown in fig. 12. the uniform excitation signal exhibits the highest level of side lobes (which resulted the poorest performance) with 2.2 db (s = 0.5λ) and 4.2 db (s = 0.75λ) as shown in fig. 10. furthermore, in terms of beam width, binomial amplitude excitation produces the widest angular width with 19.9 deg. (s = 0.5λ) and 13.3 deg. (s = 0.75λ) among the three amplitude excitation methods. it should be noted that the beam width of the main lobe must be as narrow as possible in the x-band satellite communication system. therefore, uniform and tschebycheff methods are more preferable than the binomial method in this case. (a) (b) fig. 10: side lobe level for uniform excitation signal with (a) s = 0.5λ and (b) s = 0.75λ. (a) (b) fig. 11: side lobe level for binomial excitation signal with (a) s = 0.5λ and (b) s = 0.75λ. side lobe level side lobe level side lobe level side lobe level 68 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 (a) (b) fig. 12: side lobe level for tschebycheff excitation signal with (a) s = 0.5λ and (b) s = 0.75λ. table 5 shows the radiation pattern of the microstrip patch array antenna with uniform, binomial, and tschebyscheff excitation methods, at two different spacings of s = 0.5λ and s = 0.75λ. based on these results, the uniform and tschebyscheff amplitude excitation methods produced the narrowest beam width, which is parallel to their high directivity and gain. however, they also produced the highest side lobe levels, which could risk the signal to be intercepted by neighbouring satellites through the side lobes. the binomial excitation method produced the widest beam width among the three, but with better side lobe level suppression, which will reduce the risk for the signal being intercepted. table 5: radiation pattern of the microstrip patch array antenna with uniform, binomial and tschebyscheff excitation signal, at two different spacing of s = 0.5λ and s = 0.75λ. s = 0.5λ side lobe level side lobe level s = 0.75λ 69 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 table 6 concludes the contribution of this work in comparison to previous work done by others [2, 8-12]. by observing the side lobe level of each proposed antenna in the previous work, we can assume that the produced range of side lobe level is in between -10 db to -20 db. through this research, we have proven that the side lobe level can be improved using three different excitation methods. in this work, the side lobe level improved from 4.2 db to -32.1 db using binomial excitation and from 4.2 to -14.2 db using tschebycheff. unfortunately, this is gained at the cost of reduced gain and directivity by changing the excitation method from a uniform method to a non-uniform method (binomial and tschebycheff). table 6: contribution of this work in comparison with previous work [2, 8-12]. authors antenna proposed no. of element freq. band resonant freq. (ghz) size (mm) gain (db) side lobe level (db) chaurasia et al. (2017) microstrip antenna 1 x 11 30 (w) 35 (l) 10.38 n/a mao et al. (2017) dual-band sharedaperture cp array antenna 4 4 x 8.2 110 (w) 110 (l) 17.5 -15 2 2 c 5.3 110 (w) 110 (l) 14.5 -12.5 huang et al. (2017) circularlypolarized (cp) planar patch antenna array 16 6 ku 340 (w) 137 (l) 26.4 n/a suryana and madiawati (2016) antenna microstrip array 2 16 ku 14 20 (w) 5 (l) 17.91 n/a ku 12 20 (w) 5 (l) 18.69 n/a so and chan (2016) circularly polarized patch antenna array 16 16 ku 12 n/a > 30 n/a chen and yan (2016) microstrip phased array antenna 8 12 k 24 n/a 25 -18 this work (tschebycheff) microstrip patch array antenna 1 10 x 9.5 285 (w) 59.275 (l) 16.5 -14.2 this work (binomial) microstrip patch array antenna 1 10 x 9.5 285 (w) 59.275 (l) 14.5 -32.1 this work (uniform) microstrip patch array antenna 1 10 x 9.5 285 (w) 59.275 (l) 17.3 4.2 practically, implementing the non-uniform excitation method would be difficult to achieve and maintain due to its variation in the excitation amplitude, especially for the 70 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 binomial excitation method compared to the tschebycheff excitation method as in table 7. table 7: uniform, tschebyscheff and binomial excitation coefficients. uniform tschebyscheff (with major-tominor lobe ratio of 30 db) binomial port1 1 2.5177 1 port2 1 4.2036 9 port3 1 6.5436 36 port4 1 8.5866 84 port5 1 9.78006 126 port6 1 9.78006 126 port7 1 8.5866 84 port8 1 6.5436 36 port9 1 4.2036 9 port10 1 2.5177 1 4. conclusion in conclusion, a microstrip patch array antenna for side lobe suppression has been developed for use in x-band communication at 9.5 ghz. the antenna performance such as s11, gain, directivity, side lobe level and angular width have been investigated and discussed. the antenna was first designed as a single element and further modified to work as an array in order to increase the gain and directivity, and also to reduce the beam width, which is convenient for transmission of data for specific satellite communication in the xband region. furthermore, the proposed array antenna has been simulated using three different signal excitation methods, which are uniform, binomial, and tschebyscheff, at two different spacing of s = 0.5λ and s = 0.75λ. based on the radiation pattern produced, the tschebycheff amplitude excitation method provides the best antenna performance compared to the other two excitation methods. the proposed antenna configuration has met all the objectives set (i.e. having low side-lobes level of -14.2 db, an acceptable high gain of 16.5 db, a directivity of 17.7 db, an angular width of 8.6 deg., and a compact structure of 285 mm × 59.275 mm), which is convenient for mobility purposes. therefore, it can be summarized that our microstrip patch array antenna can be an alternative choice for a future x-band antenna to replace the currently used reflector antennas that are massive, heavy, and produce very high side lobe levels. acknowledgement this research was supported by international islamic university malaysia and ministry of education malaysia through fundamental research grant scheme for research acculturation of early career researchers frgs-racer (racer19-053-0053) (racer/1/2019/tk04/uiam//1). 71 iium engineering journal, vol. 21, no. 1, 2020 ruslan et al. https://doi.org/10.31436/iiumej.v21i1.1220 references [1] balanis ca. (2016) antenna theory analysis and design. hoboken, john wiley & sons, inc. [2] chaurasia rk, mathur v, saini ak, mukherji r. (2017) design and analysis of microstrip antenna for x-band communication. iup journal of telecommunications, 9(3): 38-43. [3] mohamad s, cahill r. (2017) spiral antenna with reconfigurable his using liquid crystals for monopulse radar application. in proceedings of the ieee conference on antenna measurements and applications (cama); pp 55-58. [4] mohamad s, cahill r, fusco v. (2015) tri-band his backed spiral antenna for wireless lan applications. microwave and optical technology letters, 57(5):1116–1121. [5] balanis ca. (2012) advanced engineering electromagnetics. hoboken, john wiley & sons, inc. [6] rahman da, mohamad s, abdul malek nf, rahman da, zabri sn. (2018) a wideband mm-wave printed dipole antenna for 5g applications. indonesian journal of electrical engineering and computer science, 10(3): 943-950. [7] ahmad mustafa a m, mohamad s, abdul malek nf, mohd isa fn, md. rafiqul islam. (2018) a wideband circularly-polarized spiral antenna for cube sat application. journal of telecommunication, electronic and computer engineering, 10(1-8): 17-20. [8] mao cx, gao s, wang y, chu qx, yang xx. (2017) dual-band circularly polarized shared-aperture array for c-/xband satellite communications. ieee transaction and propagation, 65(10): 5171-5178. [9] huang j, lin w, qiu f, jiang c, lei d, guo yj. (2017) a low profile, ultra-lightweight, high efficient circularly-polarized antenna array for ku band satellite applications. ieee access, 5: 18356-18365. [10] suryana j, madiawati h. (2016) design and implementation of mobile antenna vsat with microstrip array based at ku band frequency. in proceedings of the 10th international conference on telecommunication systems services and applications (tssa). [11] so kk, chan ch. (2016) circularly polarized patch antenna array for satellite communication in ku band. in proceedings of the ieee 10th european conference on antennas and propagation (eucap); pp. 1-4. [12] chenlj, yan mj. (2016) design of 24 ghz microstrip phased array antennas with low sidelobe. in proceedings of the ieee international conference on electronic information and communication technology. 72 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <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> /eti <feff004b00610073007500740061006700650020006e0065006900640020007300e400740074006500690064002c0020006500740020006c0075007500610020005000440046002d0064006f006b0075006d0065006e00740065002c0020006d0069007300200073006f00620069007600610064002000e4007200690064006f006b0075006d0065006e00740069006400650020007500730061006c006400750073007600e400e4007200730065006b0073002000760061006100740061006d006900730065006b00730020006a00610020007000720069006e00740069006d006900730065006b0073002e00200020004c006f006f0064007500640020005000440046002d0064006f006b0075006d0065006e0074006500200073006100610062002000610076006100640061002000760061006900640020004100630072006f0062006100740020006a0061002000410064006f00620065002000520065006100640065007200200036002e00300020006a00610020007500750065006d006100740065002000760065007200730069006f006f006e00690064006500670061002e> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <feff005400650020006e006100730074006100760069007400760065002000750070006f0072006100620069007400650020007a00610020007500730074007600610072006a0061006e006a006500200064006f006b0075006d0065006e0074006f0076002000410064006f006200650020005000440046002c0020007000720069006d00650072006e006900680020007a00610020007a0061006e00650073006c006a006900760020006f0067006c0065006400200069006e0020007400690073006b0061006e006a006500200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e0074006f0076002e0020005500730074007600610072006a0065006e006500200064006f006b0075006d0065006e0074006500200050004400460020006a00650020006d006f0067006f010d00650020006f00640070007200650074006900200073002000700072006f006700720061006d006f006d00610020004100630072006f00620061007400200069006e002000410064006f00620065002000520065006100640065007200200036002e003000200074006500720020006e006f00760065006a01610069006d0069002e> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word w2_inside cover_volume 16, no. 1, 2015.docx iium engineering journal chief editor ahmad faris ismail, iium, malaysia technical editor erry yulian triblas adesta, iium, malaysia executive editor ahm zahirul alam, iium, malaysia associate editor anis nurashikin nordin, iium, malaysia language editor lynn mason, malaysia copy editor hamzah mohd. salleh, iium, malaysia editorial board members abdullah al-mamun, iium, malaysia abdumalik rakhimov, iium, malaysia amir akramin shafie, iium, malaysia erwin sulaeman, iium, malaysia hanafy omar, saudi arabia hazleen anuar, iium, malaysia konstantin khanin, university of toronto, canada ma'an al-khatib, iium, malaysia md zahangir alam, iium, malaysia meftah hrairi, iium, malaysia mohamed b. trabia, united states mohammad s. alam, texas a&m university-kingsville, united states muataz hazza faizi al hazza, iium, malaysia mustafizur rahman, national university singapore, singapore nor farahidah binti za'bah, iium, malaysia ossama abdulkhalik, michigan technological university, united states rosminazuin ab. rahim, iium, malaysia waqar asrar, iium, malaysia aims & scope of iiumengineering journal the iium engineering journal, published biannually, is a carefully refereed international publication of international islamic university malaysia (iium). contributions of high technical merit within the span of engineering disciplines; covering the main areas of engineering: electrical and computer engineering; mechanical and manufacturing engineering; automation and mechatronics engineering; material and chemical engineering; environmental and civil engineering; biotechnology and bioengineering; engineering mathematics and physics; and computer science and information technology are considered for publication in this journal. contributions from other areas of engineering and applied science are also welcomed. the iium engineering journal publishes contributions under regular papers, invited review papers, short communications, technical notes, and letters to the editor (no page charge). book reviews, reports of and/or call for papers of conferences, symposia and meetings, and advances in research equipment could also be published in iium engineering journal with minimum charges. referees’ network all papers submitted to iium engineering journal will be subjected to a rigorous reviewing process through a worldwide network of specialized and competent referees. each accepted paper should have at least two positive referees’ assessments. submission of a manuscript a manuscript should be submitted online to the iium-engineering journal website: http://journals.iium.edu.my/ejournal. further correspondence on the status of the paper could be done through the journal website and the e-mail addresses of the executive editor: zahirulalam@iium.edu.my faculty of engineering, international islamic university malaysia (iium), jan gombak, 53100, kuala lumpur, malaysia. phone: (603) 6196 4529, fax:(603) 6196 4488. ii international advisory committee a. anwar, united states abdul latif bin ahmad, malaysia farzad ismail, usm, pulau pinang, malaysia hanafy omar, saudi arabia hany ammar, united states idris mohammed bugaje, nigeria k.b. ramachandran, india kunzu abdella, canada luis le moyne, isat, university of burgundy, france m mujtaba, united kingdom mohamed ai-rubei, ireland mohamed b trabia, united states mohammad s. alam, texas a&m university-kingsville, united states nazmul karim ossama abdulkhalik, michigan technological university, united states razi nalim, iupui, indianapolis, indiana, united states syed kamrul islam, united states tibor czigany, budapest university of technology and economics, hungary yiu-wing mai, the university of sydney, australia. published by: iium press, international islamic university malaysia jalan gombak, 53100 kuala lumpur, malaysia phone (+603) 6196-5014, fax: (+603) 6196-6298 website: http://iiumpress.iium.edu.my/bookshop whilst every effort is made by the publisher and editorial board to see that no inaccurate or misleading data, opinion or statement appears in this journal, they wish to make it clear that the data and opinions appearing in the articles and advertisement herein are the responsibility of the contributor or advertiser concerned. accordingly, the publisher and the editorial committee accept no liability whatsoever for the consequence of any such inaccurate or misleading data, opinion or statement. iium engineering journal issn: 1511-788x e-issn: 2289-7860 http://iiumpress.iium.edu.my/bookshop iii volume 19, issue 2, december 2018 https://doi.org/10.31436/iiumej.v19i2 table of content editorial ................................................................................................................................................. i chemical and biotechnology engineering chlorella vulgaris logistic growth kinetics model in high concentrations of aqueous ammonia .................................................................................................................................................... 1 azlin suhaida azmi, nurain atikah che aziz, noor illi mohamad puad, amanatuzzakiah abdul halim, faridah yusof, suzana yusup synthetic antimicrobial agent and antimicrobial fabrics: progress and challenges ............10 norashikin binti mat zain, john olabode akindoyo, mohammad dalour hossen beg civil and environmental engineering performance of high strength lightweight concrete using palm wastes .............................. 30 md. nazmul huda, mohd zamin jumaat, abul bashar mohammad saiful islam, walid abubaker al-kutti electrical, computer and communications engineering wide range modulation indexes featured carrier-based pwm stepped waveform for halfbridge modular multilevel converters ............................................................................................ 43 majdee tohtayong, sheroz khan, mashkuri yaacob, siti hajar yusoff, nur shahida midi, musse muhamud ahmed a novel method to estimate economic replacing time of transformer using monte carlo algorithm and ann ............................................................................................................................................................. 54 mehdi zareian jahromi, m. hossein mehrabanjahromi, mohsen tajdinian, mehdi allahbakhshi adaptive trimmed mean autoregressive model for reduction of poisson noise in scintigraphic images .............................................................................................................................. 68 khan bahadar khan, muhammad shahid, hayat ullah, eid rehman, muhammad mohsin khan evaluation of the w-metric routing using rpl protocol in llns ................................................................ 80 rosminazuin ab rahim, abdallah m. awwad, aisha hasan abdalla, aliza aini md ralib investigation on need for specific propagation model for specific environment based on different terrain characteristics ....................................................................................................... 90 jide julius popoola, akinlolu adediran ponnle, yekeen olajide olasoji, samson adenle oyetunji a study on low-complexity transmit antenna selection for generalized spatial modulation ............................................................................................................................................. 105 simeon olumide ajose, adewale akanbi alafia, agbotiname lucky imoize a new spectrum and energy aware routing protocol in cognitive radio sensor network .......................... 118 sara moshtaghi, sayyed majid mazinani recent trends in dengue detection methods using biosensors ....................................................................... 134 ahmad anwar zainuddin, anis nurashikin nordin, rosminazuin ab rahim numerical analysis of tunnel led lighting maintenance factor ................................................................. 154 mehmet sait cengiz, çiğdem cengiz engineering mathematics and applied science about the silicon sensitivity of the deep level with alternating pressure .............................. 164 ikrom gulamovich tursunov, abdurahim abduraxmonovich okhunov, odiljon oxundadaevich mamatkarimov the hydrodynamic coefficients for oscillating 2d rectangular box using weakly compressible smoothed particle hydrodynamics (wcsph) method .................................................................................................... 172 muhammad zahir ramli an analytical technique to obtain higher-order approximate periods for the nonlinear oscillator ................................................................................................................................................ 182 md sazzad hossien chowdhury, md. alal hosen, mohammad yeakub ali, ahmad faris ismail iium engineering journal iv materials and manufacturing engineering effect of poly (ethylene glycol) on the injectability, setting behavior and mechanical properties of calcium phosphate bone cement .............................................................................. 192 sufiamie hablee, iis sopyan, maizirwan mel, hamzah mohd. salleh, md. mujibur rahman mechanical and aerospace engineering study of mesh quality improvement for cfd analysis of an airfoil .......................................... 203 farah aqilah, mazharul islam, franjo juretic, joel guerrero, david wood, farid nasir ani mechatronics and automation engineering color recognition wearable device using machine learning for visualy impaired person ............................... 213 tarek mohamed bolad , nik nur wahidah nik hashim, noor hazrin hany mohamad hanif combination of fused deposition modelling with abrasive milling for attaining higher dimensional accuracy and better surface finish ............................................................................................................... 221 abu naser mohammad amanullah tomal, tanveer saleh, md raisuddin khan application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 a comparative finite element analysis of regular and topologically optimised dental implants for mechanical and fatigue responses evaluation muhammad ikman ishak1*, ruslizam daud1, bakri bakar1 and siti noor fazliah mohd noor2 1 faculty of mechanical engineering & technology, universiti malaysia perlis, kampus alam unimap, pauh putra, 02600 arau, perlis, malaysia 2 advanced medical and dental institute, universiti sains malaysia, bertam, jln. tun hamdan sheikh tahir, 13200 kepala batas, pulau pinang, malaysia * corresponding author: ikman@unimap.edu.my (received: 19 december 2022; accepted: 29 may 2023; published on-line: 4 july 2023) abstract: topology optimisation is a prominent method to improve the performance of any systems by optimising geometrical factors to save materials without compromising the system functionality. currently, there is limited published data discussing the topologically optimised dental implants that makes the matter still unclear. this study aimed to evaluate the mechanical and fatigue behaviours of regular and topologically optimised dental implant designs using 3-d fea. geometrical models were developed in accordance with iso 14801 using solidworks 2020 before being analysed in ansys 18.1. the new implant design was created by topology optimisation analysis. the material properties of all parts were assumed to be isotropic, linearly elastic, and homogenous. nine different compressive load values ranging from 100 to 500 n were applied on the loading structure as separated cases. the vertical and bottom surfaces of the holder were fully constrained. the results showed that the topologically optimised implant recorded about 12.3% lower implant stress than the regular implant. both implant designs revealed a comparable displacement result with a percentage difference of only 2.3%. the optimised design was also found to produce longer fatigue life and approximately 12.3% higher safety factor compared to the regular design. the increase in the compressive load value has increased the stress and deformation, whilst decreased the fatigue life and safety factor in both designs. although it was estimated that the volume of the new implant could be reduced to about 24% of the traditional one, the implant functionality may still be retained or even be improved. abstrak: pengoptimuman topologi adalah kaedah utama bagi meningkatkan prestasi mana-mana sistem dengan mengoptimumkan faktor geometri bagi menjimatkan bahan tanpa menjejaskan fungsi utama sistem. dewasa ini, terdapat kurang data diterbitkan berbincang mengenai implan gigi yang dioptimumkan secara topologi yang menjadikan perkara ini masih tidak jelas. kajian ini bertujuan bagi menilai perlakuan mekanikal dan kelesuan bagi reka bentuk implant gigi biasa dan yang dioptimumkan secara topologi menggunakan 3-d fea. model geometri telah dibangunkan mengikut iso 14801 menggunakan solidworks 2020 sebelum dianalisis dalam ansys 18.1. reka bentuk implan baharu telah dibuat melalui analisis pengoptimuman topologi. sifat pada semua bahagian bahan diandaikan sebagai isotropik, keanjalan linear, dan homogen. sembilan nilai beban mampatan berbeza antara 100 hingga 500 n telah dikenakan pada struktur pembebanan sebagai kes berasingan. permukaan menegak dan bawah pemegang dikekang sepenuhnya. keputusan menunjukkan bahawa implan yang dioptimumkan secara topologi 286 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 merekodkan tegasan implan 12.3% lebih rendah daripada implan biasa. kedua-dua reka bentuk implan menunjukkan hasil anjakan yang setanding dengan perbezaan peratusan hanyalah 2.3%. reka bentuk yang dioptimumkan juga didapati menghasilkan hayat kelesuan yang lebih lama dan kira-kira 12.3% faktor keselamatan yang lebih tinggi berbanding reka bentuk biasa. peningkatan dalam nilai beban mampatan telah meningkatkan tegasan dan perubahan bentuk, sementara mengurangkan hayat kelesuan dan faktor keselamatan dalam kedua-dua reka bentuk. walaupun dianggarkan bahawa isipadu implan baru boleh dikurangkan kira-kira 24% daripada implan tradisional, fungsi implan masih boleh dikekalkan atau dipertingkatkan. keywords: deformation; dental implant; fatigue; finite element analysis; topology optimisation 1. introduction endosseous dental implants are a popular treatment choice for partially or completely edentulous patients to restore dental performance and improve dental aesthetic appearance [1]. this artificial surgical part is always in high demand and reported to possess a satisfactory success and survival rate [2]. titanium is the most common material for dental implants due to its biocompatible properties allowing the implant to remain stable and function successfully. the root form implant is one of the types of the endosseous dental implant that occupies the vertical bone region mimicking the root structure of a natural tooth [3]. among the typical configurations of the root form implant are cylindricaland screwtype where both are available in solid or hollow form. the hollow-cylindrical implant is introduced to increase the total contact surfaces between the implant and the bone compared to the solid-cylindrical implant. the solid-cylindrical design is exposed to destructive shear force and dependent on surface treatment for improving retention to the bone. the solidscrew implants, alternatively, possess macroscopic retaining features along the body for primary bone anchorage. apart from reducing the impact of shear load, the implant retentive elements may also decrease the potential of overloading at the bone-implant interface. the solid-screw implants offer an improved functional contact surface with the adjacent bone and easier surgical placement compared to hollow-cylindrical or hollow-screw designs. biomechanical compatibility of a dental implant is influenced by many factors such as the applied occlusal loading, implant geometry, implant dimensions, implant material stiffness, and bone quality and quantity [4]. the connection of the implant with the attached living tissues is indicated by a physiological phenomenon that is described as osseointegration. in the early stage of implantation, it is normally observed that peri-implant bone resorption occurs due to less mechanical stimulation. as the high stress value and concentration can exist in the vicinity of the implant, particularly at the implant neck region, this could also predict the occurrence of bone loss [5]. it has been suggested that in lowquality bone, the implant with large diameter, long, and straight body wall is highly preferable. besides, the application of a platform switching concept in dental implants, where the diameter of the abutment is much smaller than the implant platform, produces lower tensile and compressive bone stresses than the platform-matched implant [6]. the platform-switched implants could preserve alveolar bone level by shifting the stresses from the area of compact bone to the area of trabecular bone. in terms of the applied load and bone quality, these two factors are challenging to alter for an optimum implant stress response at the bone-implant interface. many attempts have been made to optimise the design of dental implants including by resembling the shape of a natural tooth. the optimised implant design with a tapered and wider neck exhibited considerably lower peak stresses relative to the traditional implant design [7]. 287 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 topology optimisation provides an optimised material allocation in a given design space based on a set of constraints and loadings [1,8,9]. in other words, it is a method for shape optimisation to establish material outline. an ideal design of structure demands an even stress dissipation within the body up to tolerable limit. there is a possibility to remove material at the minimally stressed regions such that the final design could achieve similar function with a reduced mass. for instance, a topologically optimised design of spinal cage managed to reduce the volume of existing design about 36% and increase the space for bone augmentation while maintaining afforded spinal stability [10]. regarding dental implants, apparent high stress concentration is commonly observed at the regions interfacing with the compact bone with minimal stress accumulation at the implant apex. the mathematical algorithm in topology optimisation technique is in reference to objective function, design variables, and constraints [11]. through finite element analysis (fea), the optimisation method iteratively analyses the design performance to remove the redundant materials without affecting the structural stability and function. the fea has been proven as a useful and widely accepted method to solve complex mathematical problems regarding stability and failure analyses in many fields such as structure, biomedicine, electronics, fluid, and heat. the use of fea in implant dentistry began in 1973, and has since been increasingly used to predict responses that are challenging to obtain in experimental and clinical works. to date, limited published data could be found on the topologically optimised solid dental implant that makes this matter still unclear and inconclusive. in a study by chang et al. [8], it was reported that the volume of the original implant design could be decreased about 17.9%. the study analysed the implant embedded in the maxillary first molar region and applied with a static occlusal load. a more recent investigation by gupta et al. [1] demonstrated a volume reduction of 32 – 45% could be achieved with the implant still able to retain its function. the variation in the length and diameter of the implant and bone quality were studied under the application of constant static load. dental implants are highly exposed to fatigue failure due to repetitive occlusal loading. many existing computational studies have only evaluated the performance of traditional implants and analysed the optimum topology of an implant under static loading, without emphasising on fatigue characteristics. critical grasp of fatigue conditions is important to comprehend the force transfer within a dental implant system. the main objective of the present study was to examine and compare the mechanical and fatigue responses between a regular and topologically optimised dental implant designs under different vertical compressive load values using three-dimensional (3-d) fea. four types of result criteria, namely maximum equivalent von mises stress, maximum total deformation, minimum fatigue life, and minimum safety factor were interpreted from the models. the null hypothesis of this study was that the traditional and new implant designs demonstrate insignificant difference in the response data investigated. the novelty of our study was to shed light on the determination of redundant material distribution in a threaded dental implant and generation of clearer quantitative mechanical and fatigue response data for regular and topologically optimised implant designs. this may give valuable insights for clinicians and/or implant manufacturers in the development of new implant macrogeometry design with reduced mass and acceptable strength. it is also expected that this study could provide an improved comprehension of the force transfer in different implant designs under the evaluation of fatigue conditions. 2. materials and methods 2.1 geometrical model 288 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 the geometry of a commercial dental implant system (dual-fit (dfi)) from alpha-bio tec, petach tikva, was used as a reference to build a 3-d model of a solid threaded dental implant. the length and diameter of the implant body are 11.5 and 3.75 mm, respectively. besides, a 3.5-mm high straight abutment, and a 2.2-mm wide and 8.0-mm long abutment screw were also modelled. the abutment screw is used to rigidly attach the abutment to the implant body at the implant platform. in this study, the implant platform was designed with an internal hexagonal connection as stated in the implant manufacturer’s catalogue. apart from the implant components, the 3-d geometrical modelling also includes a holder (40.9 mm (l) x 39.8 mm (h) x 23.0 mm (w)), a hemispherical cap (6.5 mm (l) x 5.1 mm (w)), and a loading structure (12.0 mm (l) x 11.0 mm (w)). as the study covers the fatigue prediction, the 3-d model setup was prepared based on the fatigue testing standard iso 14801 using a computer-aided design (cad) software, solidworks 2020 (solidworks corp., concord, massachusetts, usa). related in-built geometrical shape creation tools provided in the software such as extrude, mirror, revolve, sweep, and/or loft were employed to develop the models. all the models were assembled and placed under the testing condition described in iso 14801. figure 1(a) exhibits the exploded view of the final geometrical analysis model. the implant body was virtually embedded into a 4.5-mm diameter cylindrical hole created on the holder. boolean subtraction option was adopted to place the implant body into the holder. a bone loss of 3.0 mm measured from the implant platform to the holder surface (fig. 1(b)) was simulated, and the abutment and its screw were attached to the implant body. the hemispherical cap was then placed onto the abutment for loading. the central axis of the cap, abutment, abutment screw, and implant body were ensured to be aligned. the central point of the cap was set to be at 11.0 mm from the bone (holder) level to represent a moment arm. the assembled model was then transferred into ansys 18.1 software (ansys inc., houston, tx, usa) to generate the model mesh and pre-processing settings of the fea. fig. 1: (a) exploded view of the model. (b) dimensions for the implant placement. (c) loading and support locations of the model. 289 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 2.2 material properties each component in the model was considered to be isotropic, homogenous, and linearly elastic. the abutment, abutment screw, and implant body were made of titanium alloy (ti6al-4v) with a yield strength of 847 mpa [12]. additionally, the hemispherical cap and loading structure were assigned with steel alloy. according to iso 14801 specifications, the implant body must be fixed in a rigid clamping holder having the elastic modulus of at least 3.0 gpa. therefore, in this study, we have chosen aluminium alloy as the material of the holder. a summary of the material properties for the model setup is shown in table 1. table 1: material properties for the model setup material part young’s modulus, e (gpa) poisson’s ratio, v references ti-6al-4v abutment, abutment screw & implant body 113.8 0.342 yalçın et al. [13] aluminium alloy holder 71 0.33 bayata et al. [14] steel alloy cap & loading structure 200 0.31 yao et al. [15] 2.3 interface conditions all the interfaces were modelled as perfectly bonded using contact and target elements in ansys software. this type of contact modelling was also implemented in many previous related studies [16]. the bonded contact type indicates no penetration or loosening among the interfaces of the implant body-holder, abutment screw-implant body, abutmentabutment screw, abutment-implant body, cap-abutment, and cap-loading structure. 2.4 loading and boundary condition as recommended by iso 14801, to simulate the experimental test condition, a vertical load was applied on the flat surface of the loading structure model. this load configuration basically represents an oblique load at an inclination of 30° with respect to the implant longitudinal axis [17]. the applied compressive load was varied from 100 to 500 n with an increment of 50 n that signify the range of normal bite forces [18]. the location of the loads was at a distance of 11.0 mm from the holder inclined surface. fatigue analysis was performed on the implant complex to predict the mechanical responses and corresponding fatigue behaviours of the titanium alloy components. the analysis was executed by a repetitive simulated masticatory loading sets (as stated earlier) with alternating load value using fatigue algorithm based on goodman fatigue theory in the elasticity mode using ansys software. the fatigue lives and potential failure regions were predicted for infinite fatigue life criteria. for the model boundary condition, all the nodes on the vertical and bottom surfaces of the holder were constrained in all degrees of freedom. this denotes that the nodal displacement is set to zero at the stated surfaces. figure 1(c) depicts the loading and boundary condition used in the analysis. 2.5 topology optimisation in clinical practices, most dental implant designs used have a circular cross-sectional area. this kind of design possesses low resistance towards shear or torsional forces especially when the abutment screw is tightened or even when the implant is free-standing. the inclusion of antirotational features such as vent or hole in the apical part of the implant body is expected to increase inner space for bone ingrowth while not losing too much 290 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 stiffness. topology optimisation tool in ansys software was employed to construct a new dental implant design that targeted to increase internal contact surfaces of the implant body. it is important to note that the strength of the implant body must be retained with the decreasing volume. the main goal of topology optimisation is to reduce the structure compliance energy. reducing the compliance is similar to increasing the global stiffness of the structure. in other words, the standard formulation of the method is minimising the structure compliance and at the same time satisfying a limitation on the structure volume. the topology optimisation problem is described as follows (eq. (1) to eq. (6)): ( ) c uminimisefunctionobjective = (1) ( )ni i ,,3,2,110limitation ==  (2) * 0 vvv − (3) = iivv  (4) ( ) ii ee = (5)      iii e  = (6) where uc = energy of structure compliance; ηi = internal pseudodensities that are assigned to each finite element (i) in the topology problem; v = computed volume; v0 = original volume; v* = amount of material to be removed; vi = volume of element i; ei = elasticity tensor for each element; e is the elasticity tensor; i = stress vector of element i; εi = strain vector of element i. the variables of density η range from 0 to 1 in which a value close to 1 indicates that the material should be kept, while a value close to 0 indicates material should be removed. in the optimisation analysis, the volume of the entire regular implant body (design domain) was set to be decreased by about 50% with 10 iterations as the pre-set response constraints. the convergence accuracy was defined as 0.1%. by applying 100-n vertical static force normal to the implant platform and fixedly constrained the outer surfaces along the implant body, we managed to obtain a reasonable distribution of material for a new implant design as illustrated in fig. 2. it was observed that only the internal portion of the apical implant body volume was removed. a comparison of mechanical and fatigue behaviours between regular and topologically optimised implants were made and evaluated. fig. 2: main stages of topology optimisation analysis. 291 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 2.6 model meshing since the geometrical shapes of the implant parts are irregular, complex, and small in dimensions, ten-node quadratic tetrahedral elements (solid187) were applied in this study to assure the continuity of the force and displacement transfers on the nodes, as considered in some earlier studies [19,20]. prior to final model discretisation, it is worth mentioning that a mesh convergence analysis was performed so that the analysis results are independent of mesh condition. a smaller mesh size provides a better estimate for the exact solution. however, a high number of nodes and elements may increase computing time. thus, an agreement must be achieved between the ideal mesh size and the demand for a reliable solution. in this mesh independence test, the details of material properties, contact modelling, and boundary conditions are as mentioned in the previous sections with the 100n applied load. the maximum equivalent von mises stress within the abutment-implant complex was recorded for variety mesh sizes. a total of nine relative characteristic mesh sizes was considered which are 2.2 mm (tet a: ~34,000 elements), 2.0 mm (tet b: ~43,000 elements), 1.8 mm (tet c: ~67,000 elements), 1.4 (tet d: ~114,000 elements), 1.2 mm (tet e: ~117,000 elements), 1.0 mm (tet f: ~300,000 elements), 0.95 mm (tet g: ~349,000 elements), 0.8 mm (tet h: ~581,000 elements), and 0.7 mm (tet i: ~865,000 elements). upon refining the mesh, the acceptability of the result is determined based on the variation of maximum stress value among the mesh sizes, which should be less than 5% [21, 22]. in general, there was a significant difference found on the stress values generated among the mesh sizes. after four refinements, the result seemed to yield at the mesh size of 1.2 mm (tet-e) with the relative deviation of 1.2%. the total number of nodes and elements are approximately 250,000 and 176,500, respectively. the illustration of mesh sensitivity plot and mesh distribution in the coarse (tet-a) and refined (tet-e) models are shown in fig. 3. fig. 3: (a) mesh sensitivity plot for different element numbers. (b) mesh distribution in the coarse (tet-a) and refined (tet-e) models. 2.7 model verification a comparison was made between our proposed model with those published in earlier studies that considered similar analysis type, modelling design, and analysis software. the pre-processing settings used in the selected previous studies were replicated as closely as possible. it was found that our implant stress result was comparable with that of previous studies as shown in table 2. a little difference was recorded that could possibly be due to different detailed geometrical features of the models and several assumptions made. 292 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 table 2: comparison of implant equivalent von mises stress results between literature and our models past studies literature results proposed model results wang et al. [16] 368.4 mpa 326.19 mpa cheng et al. [23] 625.21 mpa 462.02 mpa bayata et al. [14] 368.68 mpa 392.02 mpa 3. results 3.1 topology optimisation analysis the new implant design was successfully developed from the topology optimisation analysis. as depicted in fig. 2, only the apical third part of the implant body was affected, and the corresponding volume was removed. the reduction of volume was about 24% considering the change from 123.13 mm3 (traditional implant) to 93.63 mm3 (new implant). meanwhile, the finite element model of the new complex implant was reconstructed and consisted of 249,500 nodes and 176,000 elements. 3.2 mechanical behaviour of the regular and topologically optimised implant designs the magnitude of the maximum equivalent von mises stress and maximum total deformation of the implant-abutment complex for all loading values was extracted in the post analyses to predict the risk of implant failure. the colour contour outline of the results was also provided to clearly scrutinise the mechanical stimuli distribution. 3.2.1 maximum equivalent von mises stress results in comparison, the regular or standard implant design exhibited a greater maximum equivalent von mises stress value within the implant-abutment assembly than the topologically optimised one, irrespective of loading levels (fig. 4(a)). the increase in the load value led to the linear increase in the output stress for both designs with the peak values of 794.23 mpa and 707.12 mpa recorded in the regular and optimised designs, respectively, under 500-n load. meanwhile, the lowest stress was generated by 100-n load with the value of 158.85 mpa (regular design) and 141.42 mpa (optimised design). it became evident that the regular design recorded about 12.3% higher implant stress as compared to the new design in all loading values. fig. 4: (a) maximum equivalent von mises stress and (b) total deformation of the implantabutment assembly for both designs under all loading conditions. 293 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 figure 5 depicts the maximum stress concentration was found in the abutment specifically at the interface region of the implant platform. besides, a high stress amplification region was also observed around the upper threads of the implant body and near the junction of the holder regardless of implant design. the distribution of stress within the assembly was comparable between the regular and new designs for all loading values. fig. 5: dissemination of equivalent von mises stress in the implant-abutment complex for (a) regular and (b) topologically optimised designs. 3.2.2 maximum total deformation results the displacement of the implant-abutment assembly for the regular form was relatively lower than that for the topologically optimised design in all loading values (fig. 4(b)). similar to the stress results, it was shown that the total deformation was proportionally increased with the increase in the loading value for both implant configurations. the load of 500 n resulted in the maximum deformation of the implantabutment assembly with the value of 0.1073 and 0.1098 mm for the regular and new implant designs, respectively. the minimum deformations were 0.0215 mm (regular design) and 0.022 mm (optimised design) generated under 100-n load. the displacement of the new model was only increased by about 2.3% compared to that of the regular model regardless of loading values. fig. 6: distribution of total deformation of the implant-abutment complex for (a) regular and (b) topologically optimised designs. 294 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 3.3 fatigue behaviour of the regular and topologically optimised implant designs the minimum value of fatigue lives and safety factor of both implant designs under different loading magnitudes were presented. the outcomes were also interpreted in the form of spectrum colouring scale for a clearer understanding. 3.3.1 minimum fatigue life results figure 7(a) shows a comparison of minimum fatigue life (cycles) between the regular and topologically optimised designs. our results demonstrated that fatigue failure was only predicted for the applied loading values ranging from 350 – 500 n by considering the fatigue life limit of 5 x 106 cycles based on existing experimental fatigue testing. these loads were equivalent to the resulting stresses of 555.96 – 794.23 mpa and 494.99 – 707.12 mpa for the regular and new implant designs, respectively. it was observed that the regular design showed a shorter estimated life with the lowest cycle number of 0 as compared to the optimised design that yielded at 2.69 x 105 cycles under 500-n load. there was no difference in the number of cycles (1 x 107 cycles) at the lower loading values (100 – 300 n) among both designs. fig. 7: (a) minimum fatigue life and (b) safety factor of the implant-abutment assembly for both implant designs under all loading conditions. fig. 8: distribution of safety factor of the implant-abutment complex for (a) regular and (b) topologically optimised designs under all loading conditions. 295 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 3.3.2 minimum safety factor results the safety factor values for fatigue life were computed based on goodman fatigue theory in accordance with infinite fatigue life criteria. the plot of minimum safety factor in the implant-abutment complex versus the applied loads is depicted in fig. 7(b). the safety factors for the new design were greater than those for the regular design irrespective of loading values. the maximum safety factors were 3.45 and 3.87 for the regular and optimised designs, respectively, under the load of 100 n. it is noted that the safety factors were below 1 when the models were subjected to the load from 350 n for the regular design, and from 400 n for the optimised design. this finding was consistent with the fatigue life results where the load lower than 350 n was predicted to be safe against fatigue. it was observed that critical regions that could attribute implant to failure were the abutment-implant connection and the middle threads of the implant body as illustrated in fig. 8. safe regions were more dominant at the apical portion of implant body and top part of the abutment. 4. discussion dental implants are used to transmit the occlusal force to the neighbouring bones. therefore, the main functional design objective can be associated with the distribution of external loads by improving the function of implant-supported prosthesis. the integration of fundamental scientific knowledge related to geometrical features and force with engineering solutions may accomplish the targeted clinical goals. presently, there is a high number of studies investigating the perseverance of bone-implant attachment in order to obtain optimal mechanical stimuli transfer. however, low emphasis is placed, and limited information available, on the structural optimisation design of dental implants, particularly for fatigue prediction. our topology optimisation analysis showed that approximately 24% of the whole implant body volume was redundant material. only the internal volume of the apical part was removed while the other regions were kept intact. the suggested regions to be removed also covered the vicinity underneath the threaded hole for the abutment screw attachment. however, this was not completely removed so as to preserve the appropriate volume in sustaining the screw integrity and to minimise the potential of high stress concentration in that region. one study performed by chang et al. [8] reported that the decreased volume of the traditional implant as a result of topology optimisation was lower compared with the one of our findings where the reduction percentage was only about 17.9%. in contrast, the finding from gupta et al. [1] predicted a far greater volume reduction of 32 – 45% for a topology study that also considered the effect of the implant macrogeometry and bone quality. the differences could possibly be due to the different geometrical shape of the models and pre-processing settings of the analysis employed. nevertheless, the consistency was found for the location of the removed material which is the apical part of the implant body. to examine the mechanical and fatigue behaviours of the regular and topologically optimised implant designs, linear static fea was performed under a variation of occlusal loading values to analyse the stress and displacement of the implant-abutment complex. the level of stress in the newly modified implant was about 12.3% lower than the one in the traditional implant. however, the pattern of stress dissemination over the regions in the assembly seemed to be identical in both designs. our findings disagreed with the results of chang et al. [8] where the optimised design (128.1 mpa) generated 13% higher implant stress value compared to the original one (113.3 mpa) under the 204-n oblique load. in contrast, the findings of gupta et al. [1] were consistent with ours by which a lower implant 296 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 stress was recorded by the modified design (33.21 mpa) than the traditional design (54.26 mpa) at the imposed volume reduction of 50%. a possible explanation of our results is that the reduction of implant material tends to minimise the stress shielding effect. therefore, the mechanical stress transfer from the high stiff implant to the surrounding region having lower stiffness is increased. as a result, the implant-abutment embodiment for the optimised design sustained less stress. in terms of the region of stress distribution, apparent stress amplification occurred at the connecting part of the abutment, and at the implant neck near the junction of the holder. this is parallel with the stress colour contour plots in past studies [1, 8]. one can conclude that the removal of volume from the end of the implant body up to its mid region can be made. a study by shi et al. reported that alternative implant design with a larger and tapered crestal part radius was preferred compared to the commercially available implant due to a lower peak stress generated [7]. besides, the topologically optimised implant design could increase the area for osseointegration ingrowth by providing more spaces in the apical region [24]. to relate our results with more realistic studies that concern biological situations, it is commonly found that high stress intensity is located at the interface with the compact bone or peri-implant bone region. a bone stress higher than the strength of the cortical bone, 170 mpa, means a prediction of failure. in implant dentistry, peri-implant bone loss is one of the main manifestations regarding osseoinsufficiency which could lead to detrimental implications such as patient complaints, aesthetic compromise, soft and hard tissue deformation, and implant removal [25]. a greater decrease in the bone level was noticed in the first year of implantation of about 1.0 mm; however, it was reduced to 0.2 mm on average in the following years. the loosening and fracture of the implant due to the resorption of supporting bone could cause eventual implant failure. as such, the effect of bone loss should be minimised by achieving optimum mechanical stress transfer at the bone-implant interface. in this study, titanium alloy ti-6al4v is the main material used for the implant components in both implant designs. we found that the peak implant stress regardless of implant designs under all loading values (141. 42 – 794.23 mpa) was lower than the yield strength of ti-6al-4v (847 mpa) [12]. this would predict the success of the implants or low tendency of failure. in implant dentistry, rigid fixation of an implant is desired as it is the criterion of successful treatment. rigid fixation is defined as the attainment of implant stability without clinical mobility or the displacement evaluated with horizontal or vertical forces, similar to analysing natural teeth. a healthy natural tooth moves about 56 – 73 μm [26], while a firm implant displaced less than 75 μm [27] with no clinical movement. the implant is exposed to a higher risk of failure than a natural tooth if its motion is higher than 0.5 mm horizontally. our results revealed that a higher displacement occurred in the abutment rather than in the implant body in both designs which could be due to less resistance towards direct loading imposed from the cap. the optimised design showed a slightly greater abutment deformation relative to the regular one that possibly caused by the reduced retention on the apical portion of the implant body. the loss of volume in that region attributed the implant body to instability, thus increasing the tendency of dislocation. concerning the displacement of the implant body itself, it was evident that the peak value of the optimised and regular designs was 22.2 and 20.7 μm, respectively, under the 500-n applied load. compared to the motion of a healthy implant, the values were relatively 70.4% (optimised) and 72.4% (regular) lower than 75 μm. the optimised design still offered acceptable rigid fixation to maintain implant stability although it recorded about 2.3% greater deformation than the regular design. for the fatigue behaviour assessment, one cyclic loading consisted of one 30° oblique loading [17]. the traditional and topologically optimised models survived up to 1 x 107 297 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 cycles under different loading limits which are 300 n and 350 n, respectively. further to that, under the highest loading value of 500 n, a total failure was found for the regular implant, while the new implant yielded at 2.69 x 105 cycles. according to iso 14801, a dental implant can sustain a life of at least 5 x 106 without demonstrating any damage [14]. our results therefore corresponded well with the standard. the optimised implant design was expected to have higher resistance to fatigue failure in their life as compared to the regular design. the safety factor of the implant-abutment assembly was above 1 for the loading magnitudes up to 300 n and 400 n in the regular and optimised models, respectively. it is determined by the relation between mean stress, σm and alternating stress, σa according to the modified goodman theory as, 2 minmax   + = m (7) 2 minmax   − = a (8) fu m e a nss 1 =+  (9) where se = endurance limit, su = ultimate tensile strength of the material, and nf = the safety factor for fatigue life in a loading cycle. the safety factor values were decreased in the regular implant compared to the optimised implant due to the increased stress level in the regular implant. the most critical value of 0.69 was recorded in the regular implant under the applied load of 500 n. thus, considering the safety factor in the mechanical aspect, the topologically optimised implant is more favourable for dental implant application. albeit that robust outcomes of the study were found, the quantitative result data were still predictive and could be relying on several limitations of the analyses. in fact, the implant was placed in the non-living material under static loading, while the real applied one is embedded in the complex living tissues without a definite pattern, and this argument may somewhat affect the results. besides, this study only analysed the single restoration type, thus the findings were attributed to this kind of treatment. several important aspects can be considered in future topology optimisation studies such as assessing different material stiffnesses and dimensions of the implant body, employing more complex geometrical models, considering more realistic dynamic occlusal loading, and simulating implant extraction from the bone socket. although the outcomes of the present study could not directly be inferred to actual clinical situation, they managed to reveal a difference in the mechanical and fatigue behaviours through simulation analysis. in vitro and in vivo studies are needed in order to validate the prognosis of implant perseverance even at low levels. the null hypothesis of the study was rejected as the traditional and topologically optimised implant designs demonstrated a significant difference in the responses obtained. 5. conclusion the new implant designed by topology optimisation analysis has reduced the volume of the traditional implant by about 24%. however, this topologically optimised design was still able to maintain the implant fixation in sustaining the loadings. • it was shown that the newly modified implant generated nearly 12.3% lower implant stress than the regular one. 298 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 • in terms of displacement, insignificant difference was found among both designs where the percentage deviation was merely 2.3%. • the optimised implant design also promoted a longer fatigue life and an improved safety factor by approximately 12.3%. • the manufacturing cost of the new implant might be high using conventional machining processes. however, it could alternatively be manufactured using additive manufacturing methods, which is expected to offer much lower cost. acknowledgment the authors would like to acknowledge the support from fundamental research grant scheme (frgs) under a grant number of frgs/1/2020/tk0/unimap/03/2 from the ministry of higher education malaysia. the authors reported no conflicts of interest related to this study. references [1] gupta y, iyer r, dommeti vk, nutu e, rana m, merdji a, biswas jk, roy s. (2020) design of dental implant using design of experiment and topology optimization: a finite element analysis study. proc inst mech eng h: j eng med., 235(2): 157-166. https://doi.org/10.1177/0954411920967146 [2] agustin-panadero r, leon-martinez r, labaig-rueda c, faus-lopez j, sola-ruiz mf. (2019) influence of implant-prosthetic connection on peri-implant bone loss: a prospective clinical trial with 2-year follow-up. int j oral maxillofac implants., 34(4): 963-968. https://doi.org/10.11607/jomi.7168 [3] samieirad s, mianbandi v, shiezadeh f, hosseini-abrishami m, tohidi e. (2019) tapered versus cylindrical implant: which shape inflicts less pain after dental implant surgery? a clinical trial. j oral maxillofac surg., 77(7): 1381-1388. https://doi.org/10.1016/j.joms.2019.02.027 [4] bidez mw, misch ce. (2015) chapter 5 clinical biomechanics in implant dentistry. in dental implant prosthetics. 2nd edition. st. louis, mosby; pp 95-106. [5] gil j, sandino c, cerrolaza m, pérez r, herrero-climent m, rios-carrasco b, rios-santos jv, brizuela a. (2022) influence of bone-level dental implants placement and of cortical thickness on osseointegration: in silico and in vivo analyses. j clin med., 11(4): 1027 https://doi.org/10.3390/jcm11041027 [6] chang cl, chen cs, hsu ml. (2010) biomechanical effect of platform switching in implant dentistry: a three-dimensional finite element analysis. int j oral maxillofac implants., 25(2): 295-304. [7] shi l, li h, fok as, ucer c, devlin h, horner k. (2007) shape optimization of dental implants. int j oral maxillofac implants., 22(6): 911-20. [8] chang c-l, chen c-s, huang c-h, hsu m-l. (2012) finite element analysis of the dental implant using a topology optimization method. med eng phys., 34(7): 999-1008. https://doi.org/10.1016/j.medengphy.2012.06.004 [9] seitz kf, grabe j, köhne t. (2018) a three-dimensional topology optimization model for tooth-root morphology. comput methods biomech biomed engin., 21(2): 177-185. https://doi.org/10.1080/10255842.2018.1431778 [10] zhong z-c, wei s-h, wang j-p, feng c-k, chen c-s, yu c-h. (2006) finite element analysis of the lumbar spine with a new cage using a topology optimization method. med eng phys., 28(1): 90-98. https://doi.org/10.1016/j.medengphy.2005.03.007 [11] zhang k, cheng g, xu l. (2019) topology optimization considering overhang constraint in additive manufacturing. comput struct., 212: 86-100. https://doi.org/10.1016/j.compstruc.2018.10.011 299 https://doi.org/10.11607/jomi.7168 https://doi.org/10.1016/j.joms.2019.02.027 https://doi.org/10.1016/j.medengphy.2012.06.004 https://doi.org/10.1016/j.medengphy.2005.03.007 https://doi.org/10.1016/j.compstruc.2018.10.011 iium engineering journal, vol. 24, no. 2, 2023 ishak et al. https://doi.org/10.31436/iiumej.v24i2.2695 [12] lee h, jo m, noh g. (2021) biomechanical effects of dental implant diameter, connection type, and bone density on microgap formation and fatigue failure: a finite element analysis. comput methods programs biomed., 200: 105863. https://doi.org/10.1016/j.cmpb.2020.105863 [13] yalçın m, kaya b, laçin n, arı e. (2019) three-dimensional finite element analysis of the effect of endosteal implants with different macro designs on stress distribution in different bone qualities. int j oral maxillofac implants., 34(3): e43–e50. https://doi.org/10.11607/jomi.7058 [14] bayata f, yildiz c. (2020) the effects of design parameters on mechanical failure of ti-6al4v implants using finite element analysis. eng fail anal., 110: 104445. https://doi.org/10.1016/j.engfailanal.2020.104445 [15] yao k-t, chen c-s, cheng c-k, fang h-w, huang c-h, kao h-c, hsu m-l. (2018) optimization of the conical angle design in conical implant–abutment connections: a pilot study based on the finite element method. j oral implantol., 44(1): 26-35. https://doi.org/10.1563/aaid-joi-d-17-00149 [16] wang k, geng j, jones d, xu w. (2016) comparison of the fracture resistance of dental implants with different abutment taper angles. mater sci eng c., 63, 164-171. https://doi.org/10.1016/j.msec.2016.02.015 [17] zhang x, mao j, zhou y, ji f, chen x. (2020) study on statics and fatigue analysis of dental implants in the descending process of alveolar bone level. proc inst mech eng h., 0954411920926080. https://doi.org/10.1177/0954411920926080 [18] levartovsky s, peleg g, matalon s, tsesis i, rosen e. (2022) maximal bite force measured via digital bite force transducer in subjects with or without dental implants a pilot study. appl sci., 12(3): https://doi.org/10.3390/app12031544 [19] amruta g, rajeev s, gaurang m, simran m, mishal ds, kunal m. (2022) comparative evaluation of stress on the peri-implant bone of different densities in mandible restored by various diameter of implants a finite element analysis. j electron sci., 12(11): 161-177. [20] satheesh kumar p, satheesh kk, john j, patil g, patel r. (2013) force transfer and stress distribution in an implant-supported overdenture retained with a hader bar attachment: a finite element analysis. isrn dent., 2013, 369147. https://doi.org/10.1155/2013/369147 [21] niroomand mr, arabbeiki m. (2020) implant stability in different implantation stages: analysis of various interface conditions. inform med unlocked, 19: 100317. https://doi.org/10.1016/j.imu.2020.100317 [22] jeng m-d, lin y-s, lin c-l. (2020) biomechanical evaluation of the effects of implant neck wall thickness and abutment screw size: a 3d nonlinear finite element analysis. appl sci., 10(10), 3471: https://doi.org/10.3390/app10103471 [23] cheng y-c, jiang c-p, lin d-h. (2019) finite element based optimization design for a onepiece zirconia ceramic dental implant under dynamic loading and fatigue life validation. struct multidiscipl optim., 59(3): 835-849. https://doi.org/10.1007/s00158-018-2104-2 [24] lawrence aa, singh n, davis r, sahil ansari m, tewari yv, francis v. (2022) chapter 13 topological design optimisation of dental implant. in optimization of industrial systems. 1st edition. edited by panchal d, tyagi m, sachdeva a, pamucar d. scrivener publishing llc. [25] naveau a, shinmyouzu k, moore c, avivi-arber l, jokerst j, koka s. (2019) etiology and measurement of peri-implant crestal bone loss (cbl). j clin med., 8(2): 166. https://doi.org/10.3390/jcm8020166 [26] rudd kd, o'leary tj, stumpf aj jr. (1964) horizontal tooth mobility in carefully screened subjects. tech doc rep us air force syst command electron syst div, 94: 1-6. [27] sekine h, komiyama y, potta h, yoshida k. (1986) mobility characteristics and tactile sensitivity of osseointegrated fixture-supporting systems. in tissue integration in oral maxillofacial reconstruction. 1st edition. edited by van steeberghe d. amsterdam, excerpta medica; pp. 326–332. 300 https://doi.org/10.1016/j.cmpb.2020.105863 https://doi.org/10.11607/jomi.7058 https://doi.org/10.1016/j.engfailanal.2020.104445 https://doi.org/10.1563/aaid-joi-d-17-00149 https://doi.org/10.1016/j.msec.2016.02.015 https://doi.org/10.1177/0954411920926080 https://doi.org/10.1016/j.imu.2020.100317 https://doi.org/10.3390/app10103471 https://onlinelibrary.wiley.com/authored-by/contribauthorraw/panchal/dilbagh https://onlinelibrary.wiley.com/authored-by/contribauthorraw/tyagi/mohit https://onlinelibrary.wiley.com/authored-by/contribauthorraw/sachdeva/anish https://onlinelibrary.wiley.com/authored-by/contribauthorraw/pamucar/dragan https://doi.org/10.3390/jcm8020166 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 a review of flow conflicts and solutions in software defined networks (sdn) mutaz hamed hussien khairi1,2*, sharifah hafizah syed ariffin1, nurul muaazah. abdul latiff1, kamaludin mohamed yusuf1 and mohamed khalafalla hassan1,2 1 school of electrical engineering, faculty of engineering, university technology malaysia, johor, malaysia 2 faculty of engineering, future university, khartoum, sudan * corresponding author: taza1040@gmail.com (received: 17th september 2020; accepted: 16th february 2021; published on-line: 4th july 2021) abstract: software defined networks (sdn) are a modern networking technology introduced to simplify network management via the separation of the data and control planes. characteristically, flow entries are propagated between the control plane layer and application or data plane layers respectively while following flow table instructions through an openflow protocol. more often than not, conflicts in flows occur as a result of traffic load and priority of instructions in the data plane. several research works have been conducted on flow conflicts in sdn to reduce their adverse effect. solutions to flow conflict in sdn have three main limitations. first, the openflow table may still cause a defect in the security module according to the priority and action matching in the openflow of the control plane. second, flow conflict detection requires more time due to flow tracking and incremental update, whereas in such a case, delay affects the efficiency of sdn. besides, the sdn algorithm and mechanism have substantially high memory requirement for instruction and proper functioning. third, most of the available algorithms and detection methods used to avoid flow conflicts have not fully covered the security model policy. this study reviews these limitations and suggest solutions for future research directions. abstrak: rangkaian perisian tertentu (sdn) adalah teknologi rangkaian moden yang diperkenalkan bagi memudahkan pengurusan rangkaian melalui pecahan data dan kawalan permukaan. seperti biasa, aliran kemasukan disebar luas antara lapisan permukaan kawalan dan aplikasi atau lapisan permukaan data masing-masing, sambil mengikuti arahan meja melebar melalui protokol aliran terbuka. kebiasaannya konflik dalam aliran berlaku disebabkan oleh beban trafik dan keutamaan arahan pada permukaan data. beberapa kajian dibuat terhadap konflik aliran sdn bagi mengurangkan kesan konflik. solusi konflik aliran dalam sdn mempunyai tiga kekurangan besar. pertama, jadual aliran terbuka mungkin masih menyebabkan kekurangan dalam modul keselamatan berdasarkan keutamaan dan tindakan persamaan dalam aliran terbuka permukaan kawalan. kedua, pengesanan aliran konflik memerlukan lebih masa bagi pengesanan aliran dan peningkatan kemaskini, kerana setiap penangguhan memberi kesan terhadap kecekapan sdn. selain itu, algoritma sdn dan mekanisme memerlukan memori yang agak besar bagi memproses arahan dan berfungsi dengan baik. ketiga, kebanyakan algoritma dan kaedah pengesanan yang digunakan bagi mengelak konflik pengaliran tidak sepenuhnya dilindungi polisi model keselamatan. oleh itu, kajian ini meneliti kekurangan dan memberi cadangan penambahbaikan bagi arah tuju kajian masa depan yang terbuka. keywords: software defined networking; open flow table; flow conflicts 178 iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 1. introduction software defined network (sdn) is a modern network architecture that has been proposed to mitigate the shortcomings related to traffic management, security, virtualization and complexity of traditional networks [1]. the main characteristics of sdn include: 1) separation and abstraction of the control and data plane; 2) logical centralization of network intelligence that enables global view of the entire network and swift response changing needs; 3) ability to develop different applications from the underlying network infrastructure; 4) programmable data plane for networking automation and flexibility; 5) much higher innovation speed to accelerate business innovation and possibility of reprograming of the network by the it network operators in real time to meet specific business needs. moreover, through the virtualization process, the network infrastructure can be extracted from individual network services [2]. openflow is a sdn protocol designed to facilitate server communication with network switches; particularly regarding sending and receiving packets. as a flow-based network virtualization architecture, it allows multiple logical networks to share the same physical infrastructure. while the network virtualization layer allows for a set of controllers to manage multiple switches per slice, controllers are responsible for installing flow entries in the assigned domain of switches. in such a design, one physical switch could belong to multiple virtual networks which may be controlled by one or more set of controllers. this design setup leads to flow conflicts [3]. in today’s internet, network traffic is routed based on the destination address prefixes. while this approach allows an efficient implementation of shortest-path (and more complex) routing protocols, it does not provide fine-grained control over network traffic. however, many proposals for future internet architectures require that the network data plane implement routing and forwarding at the level of individual connections or their aggregate e.g., for network virtualization, or for network services [4,5]. 2. problem background and objectives of the research conflict in flow entries manifest in different ways in sdn such as where a physical switch belongs to multiple virtual networks that are often controlled by one or a set of controllers; thus, resulting in the occurrence of flow conflict. flow conflicts may also occur when vague packets match flow entries. based on the priority of the flow entry, flow entry conflicts in an open flow table can cause defects in the security module that runs on top of the sdn. an approach used, is to match flow entry packets based on the priority of flow entries. however, because of the similarities between different flow entries, a single packet can be matched to several flow entries, thereby resulting in flow entry conflict [1]. while representative algorithms and detection methods have been proposed to mitigate flow entry conflicts [1-3], they have been shown to have high memory requirements and require a significant amount of time to apply their instructions in the flow table. specifically, the time taken to add or update flows in case of conflict in the flow entry is high; thus, affecting the performance of the sdn network. in addition, most of these past studies used old versions of flow table in their simulations and experiments. the present study was initiated, i. to study and analyze flow entry conflicts in openflow table. 179 iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 ii. to review the existing detection methods used for flow conflict resolution in openflow table. 3. sdn architectural components the three core components of the sdn architecture are: the sdn controller, also known as control layer; the data plane layer, which is made up of a collection of network devices like routers, switches and openflow switches that act as middle boxes for network communication; and the application layer, where the execution of all network applications take place. figure 1 shows the sdn architecture. it can be clearly observed that it is characterized by the separation of the control and infrastructure layers. this is advantageous in that the application layer can be developed and modified by application developers by using a northbound interface that provides advanced policy applications and services as well as programmable application programming interfaces (api) for this purpose. moreover, the southbound interface also provides the openflow protocol, which is a standard api [4,5]. fig. 1: software defined networking framework [6]. 4. openflow (of) in sdn openflow was one of the first software defined networking (sdn) standards. it was originally a communication and connection protocol in sdn environments that allowed the controller to directly interact with the forwarding plane of network devices for better adaptation to changing business requirements [7]. 4.1 openflow switch and protocol openflow was driven by the characteristic separation of the control and forwarding planes in sdn. the openflow switch architecture is illustrated in fig. 2. the openflow switch, which also contains a number of flow tables, is connected to the controller via an openflow channel. likewise, openflow switches also have an abstraction layer through which they communicate with the controller via the openflow protocol. the flow table checks which packet belongs to which flow in order for the packets to be processed and delivered [1,4]. 180 https://www.sdxcentral.com/wp-content/uploads/2013/08/sdn-framework1.jpg iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 fig. 2: openflow switch [5]. • group table: for packet lookup and forwarding. • openflow channel: responsible for connection between controller and switch. • flow table: flow entry – match field – counter and set instruction. 4.2 openflow ports openflow ports perform the function of transferring packets between open flow switches and other devices in the network such as routers or hosts. all openflow switches in the sdn network are connected through openflow ports. some network interfaces may also be disabled in the openflow switch [8]. 4.3 openflow table and entry the openflow switch is comprised of several flow tables, each of which has flow entries. the processing pipeline of openflow stipulates the interaction between packets and flow tables. depending on the application and network structure, an openflow switch may have one or more flow tables [8]. 4.4 flow table flow tables consist of several flow entries as shown in table 1. table 1: flow entries and their definitions [8]. match fields priority counters instructions timeouts cookie used to match between packets for matching priority of flow entries to update the proper packets to adjust the action set of a flow entry maximum time or inactive time before switch terminates a flow entry for reporting a modified or deleted flow entry to controller 181 iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 5. exisiting solutions to flow conflicts in sdn this section discusses the research that has been conducted on detecting flow conflicts in sdn. the studies are explained based on their method, controller type, switch, conflict type, topology, and target application respectively, as in table 2. table 2: list of existing solution on flows conflict in sdn method or techniques reference research controller model switch model conflict type network topology target application mechanism or algorithm lo et al. [1] flow entries single topology network optimization performance hu et al. [3] floodlight openflow switch flow rule tree topology security fang and lu [7] flow rule single topology network efficiency pisharody et al. [9] open daylight openflow switch flow rule tree topology security lu et al. [10] nox openflow switch policy rule tree topology security wang and youn [11] floodlight open vswitch flow entries single topology network optimization performance cui et al. [12] floodlight openflow switch flow rule tree topology network efficiency hao et al. [13] nox openflow switch flow rule tree topology network optimization performance halder et al. [14] of controller openflow switch flow rule tree topology security batista et al. [15] of controller openflow switch flow entries single topology security hong and wey [16] floodlight open vswitch flow rule tree topology network optimization performance analytical method metter et al. [2] flow rule single topology network optimization performance lin et al. [17] ryu openflow switch flow entries tree topology network optimization performance tran and danciu [18] flow rule tree topology network optimization performance yoshioka et al. [19] flow rule single topology link utilization 5.1 purpose of flow conflict detection techniques flow entry conflict detection methods in sdn applications have been used for different purposes such as security, load balance, and firewall amongst others, as shown in table 2. a number of detection algorithms have attempted to optimize the performance of the 182 iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 controller by checking and arranging its workload. in [16], the controller was used to control elephant and safety-critical flows using interactive routing. in the study, switch layers were designed to move micro flows through multipath wildcard routing without soliciting or using the controller plane. a firewall policy, named flow guard, that is meant to secure the policy contravention in flow table of the openflow switch with controller was proposed in [3]. it tracks flow or path spaces in the network to detect firewall policy contravention within network updates. in a separate work in [20], a method was proposed to check and detect contradiction between the rules installed in a firewall with flow table instructions. the rules applied in the openflow design is to increase the safety and security capabilities for sdn. 5.2 method and algorithm used for flow conflict detection one of the famous approaches used in the detection of conflicts in flow entries within sdn is the reduced bit vector algorithm. this algorithm uses the concept of bit vectors alongside one of the classification methods to classify flow entries in two main groups. in the first group, flows have the same prefix length while the second group contains a decrease in the redundant bits of vectors [1]. one of the solutions introduced and built for optimizing and securing flow entry in sdn research is a security module that minimizes the amount of controller workload by separating the responsibilities of each controller [16]. a simple analytical model is formulated to enable network performance optimization relative to the signaling rate and table occupancy [2]. the research used a flow guard method for building a firewall to conduct checks and detect violation of firewall policy along the network flow path when updating the status of the network [3]. a routing method is used to ensure optimal link utilization as well as in the minimization of flow entry size. to ensure optimal link utilization, the proposed method assigns the same paths to flows that can be grouped together [19]. a security application, named fresco, has been proposed and implemented to address security challenges. the fresco framework consists of an application layer and a security enforcement kernel [21] brew. the proposed policy is used to analyze the controller settings to detect conflicts and create solution modules which avoids conflict in flow rules within a distribution-based sdn system [9]. source routing has also been used in flow route control. in [22], a source routing based link protection method whose link has paths to dedicated backup was used to direct packets to their backup paths by updating the header of the source router in case of link failure. performance evaluation of this method has been shown to significantly update the source routing header. 5.3 experimental environment used in flow conflict detection the experimental environment used for flow entry conflict detection in sdn varies according to the method or algorithm. this section details the experimental environments used in flow conflict detection studies in sdn. [16] developed a simple network with four switches (grid network) connected to one host. using a floodlight controller with openflow switch version 1.3, all tests and observations were simulated and analyzed with mininet software. many studies in sdn use matlab software with mininet and virtual machine software as simulation tools for analyzing and optimizing the traffic and flow entry in sdn. figure 3 shows an example of a similar research, where the design structure depends on how the openflow switch deals with controller under fresco instruction [2]. additionally, fig. 4 shows the brew system model. it uses two virtual switches connected to a controller where all the conflicting flow entries are checked and analyzed in line with the controller plane [9]. 183 iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 fig. 3: high level overview of the fresco architecture [2]. fig. 4: system architecture showing brew solution models [9]. 5.4 sdn controller used in flows conflict detection techniques the sdn controller is called the “network brain” [23]. it ensures that different network tasks are performed through effective management of the application modules of the network. the applications typically leverage an api, as in [24], to enable advanced network functionalities while facilitating communication with core controller modules. we discuss both commercial and open-source controllers that are widely used in load balancing modules of the server. while the software load balancing module in the commercial controllers are standalone systems connected to the controller for api utilization purposes, they function as part of the controller system within the application layer in the open-source version. a popular open-source controller is the high-performance java-based openflow controller called flood light controller, which is based on beacon controller, an experimental openflow controller from stanford university that now has a large community of developers that supports it. the latest version of floodlight has support for openflow version 1.4 [25]. open daylight (odl) sdn controller is another type of controller used to implement brew [9]. 184 iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 5.5 parameter measure in flow conflict detection flow entry in sdn is generally measured by different types of parameters, we focus only on parameters such as time of search, update time, elephant flows, and link bandwidth as measured parameters in the flow entry conflict detection. 6. analysis and discussion we aim, by this research, to define the types of flow rule conflict that occur in sdn. a number of researchers have used a static programming language module by leveraging the of analyzer module named brew; a security policy analysis framework that is developed on an open daylight (odl) based sdn controller [9]. in [10], a method was proposed for accurate detection of universal conflicts. in the proposed mechanism, checks are carried out for policy conflict with machine learning for 500 policies applied in a simulated network. the study also introduced a novel flow management project for mfts for open vswitch in sdn. the memory requirement of the research shows that the ex table requires a large memory space [11]. the authors of [7] used the mtbdd algorithm to conduct and clarify switch conflict rules in sdn. the test of algorithm offers good functionality on incremental updates of two different rule groups from stanford’s internet network. in a separate research, tcdr was used to reject illegal flow rules, thus, avoiding substantial conflicts in flow rules while incurring minimal overhead [12]. the detection mechanism for conflicting flows in the rules of a flow table as presented in [13] takes 1ms of time. however, it should be noted that the effect of the firewall rule is not considered for table update. in [14], a graph based technique is applied to produce a guide graph from obtainable flow rules built-up by several controller applications within sdn to determine flow transgression. a classification method is proposed to classify the flow entries in two main groups; with the first group of the flow having same prefix length, while the second group contains a decrease in the redundant bits of vectors . in using rvb, there is still notable delay in time of search and incremental update (over 2 ms) [1]. in [15], the author used an intelligent technique for conflict in flow entries within sdn. while the proposed method effectively detected most of the conflicts that appeared in the flow table, its high memory requirement remained a major shortcoming. lin et al. [17] used most of the parameters configured in openflow tables to conduct cross-layer testing between two different flow entries. the priority of flow of the entire inflow table was experimentally observed. the proposed method showed impressive accuracy. the research analytically showed that the conflict of applications in sdn can be detected and analyzed without stopping the application [18]. an analytical model has been proposed for sdn signaling traffic and flow table occupancy in [2]. the model was designed to allow network performance optimization relative to signaling rate and table occupancy. the importance of this model could decrease in the near future when switches are upgraded or the size of the flow table is increased. a method of optimizing controller workload with a view to minimizing the amount of controller workload by separating the responsibility of each controller has been demonstrated in [16]. the potential services considered and checked in this research do not include file transfer protocol (ftp). a method, called flow entry aggregation, capable of reducing the maximum number of flow entries while suppressing the maximum link utilization, was proposed in [20]. 185 iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 however, a key drawback of this method is that it cannot by itself prevent any loops from occurring in the network; thus, it is susceptible to flow entry conflicts [19]. 7. conclusion what has been presented in this research is mainly concerned with flow conflict issues in sdn and how they have been mitigated in the flow table. according to the reviewed and discussed articles, flow conflicts can be classified into two major types, flow rules and flow entries. summarily, researchers have used only two methods to detect flow conflict in sdn; majority of them using an algorithmic approach while a few used analytical methods. floodlight, open daylight, pox and ryu controllers were the most commonly used controllers in experimental and test studies while only two types of network topologies, tree and single topology, were used in the pertinent literatures. the target application in most studies is network optimization and performance while only a few studies targeted security issues. from all the reviewed studies, a research involving the use of artificial intelligence such as the machine learning method to detect flow conflicts in the openflow table for network security related issues still remain lacking. thus, this study proposes an anomaly detection algorithm using machine learning to detect and classify flow conflicts in the openflow table as an interesting future research direction. the goals of such an algorithm will be to classify flow rules while concurrently reducing the delay in the update flow table of the controller. references [1] lo c, wu p, kuo y. (2015) flow entry conflict detection scheme for software-defined network. international telecommunication networks and applications conference (itnac), sydney, australia, pp. 220-225. [2] metter c, seufert m, wamser f, zinner t, tran-gia p. (2017) analytical model for sdn signaling traffic and flow table occupancy and its application for various types of traffic. ieee transactions on network and service management, 14(3): 603-615. [3] hu h, han w, ahn gj. zhao z. ( 2014) flowguard: building robust firewalls for software-defined networks. in proceedings of the third workshop on hot topics in software defined networking august 2014. pp 97-102. [4] akyildiz, if, lee a., wang p, luo m, chou w. (2014) a roadmap for traffic engineering in sdn-openflow networks. computer networks, 71: 1-30. [5] bozakov z, sander v. (2013) openflow: a perspective for building versatile networks. in: network-embedded management and applications, clemm a, wolter r. (eds). springer, new york, ny. https://doi.org/10.1007/978-1-4419-6769-5_11 [6] sdx central [https://www.sdxcentral.com/networking/sdn/definitions/what-the-definition-ofsoftware-defined-networking-sdn] [7] fang y, lu y. (2019) checking intra-switch conflicts of rules during preprocessing of network verification in sdn. ieee communications letters, 23(9): 1547-1550. [8] openflow specification [http://networkstatic.net/wp-content/uploads/2013/02/openflowspec-v1.3.0.pdf] [9] pisharody s, natarajan j, chowdhary a, alshalan a, huang d. (2019) brew: a security policy analysis framework for distributed sdn-based cloud environments. ieee transactions on dependable and secure computing, 16(6): 1011-1025. [10] lu y, fu q, xi x, chen z, zou e, fu b. (2019) a policy conflict detection mechanism for multi-controller software-defined networks. international journal of distributed sensor networks 15 no (5),http://doi.org/10.1177/1550147719844710. [11] wang c, youn hy. (2019) entry aggregation and early match using hidden markov model of flow table in sdn. sensors, 19(10), 2341; https://doi.org/10.3390/s19102341. 186 https://doi.org/10.1177%2f1550147719844710 https://doi.org/10.3390/s19102341 iium engineering journal, vol. 22, no. 2, 2021 khairi et al. https://doi.org/10.31436/iiumej.v22i2.1613 [12] cui j, zhou s, zhong h, xu y, sha k. (2018) transaction-based flow rule conflict detection and resolution in sdn. 27th international conference on computer communication and networks (icccn), hangzhou, china, pp. 1-9. [13] hao w, jiang y, j. gao j. (2017) detection mechanisms of rule conflicts in sdn based on a path-tree model. 8th ieee international conference on software engineering and service science (icsess), beijing, china, pp. 336-339. [14] halder b, barik ms, mazumdar c. (2017) a graph based formalism for detecting flow conflicts in software defined network. 2017 ieee international conference on advanced networks and telecommunications systems (ants), bhubaneswar, india, pp. 1-6. [15] lopes alcantara batista b, lima de campos gm, fernandez mp. (2014) flow-based conflict detection in openflow networks using first-order logic. 2014 ieee symposium on computers and communications (iscc), funchal, portugal, pp. 1-6. [16] hong etb, wey cy. (2017) an optimized flow management mechanism in openflow network. 2017 international conference on information networking (icoin), da nang, vietnam, pp. 143-147. [17] lin yd, lai yk, tsou yl, lai yc, liou ec, chiang y. (2019) generic validation criteria and methodologies for sdn applications. ieee systems journal, 13(4): 3909-3920. [18] tran cn, danciu, v. (2020) a general approach to conflict detection in software-defined networks. sn comput. sci, 1(1), 9, https://doi.org/10.1007/s42979-019-0009-9 [19] yoshioka k, hirata k, yamamoto m. (2017) routing method with flow entry aggregation for software-defined networking. 2017 international conference on information networking (icoin), da nang, vietnam, pp. 157-162, [20] pallavi n., anisha a.s., leena v. (2017) detection of incongruent firewall rules and flow rules in sdn. in: dash s., vijayakumar k., panigrahi b., das s. (eds) artificial intelligence and evolutionary computations in engineering systems. advances in intelligent systems and computing, vol 517. springer, singapore. https://doi.org/10.1007/978-981-10-3174-8_2. [21] shin sw, porras p, yegneswara v, fong m, gu g, tyson m. (2013) fresco: modular composable security services for software-defined networks. in february 201320th annual network & distributed system security symposium. http://hdl.handle.net/10203/205914 [22] huang l, shen q, wenjuan s. (2016) a source routing based link protection method for link failure in sdn. 2nd ieee international conference on computer and communications (iccc), chengdu, china, pp. 2588-2594. [23] jarschel m, zinner t, hoßfeld t, tran-gia p, kellerer w. (2014) interfaces, attributes and use cases: a compass for sdn. ieee communications magazine, 52(6): 210-217. [24] zhou, j. (2014) multicatalyst system in asymmetric catalysis. john wiley & sons. [25] openflow switch specification openflow switch specification, o.s., version 1.4. 0, october 14, 2013. [https://opennetworking.org/wp-content/uploads/2014/10/openflow-specv1.4.0.pdf] 187 microsoft word 207 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 213 understanding engineering ethics abdi o. shuriye department of science in engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. shuriye@iium.edu.my abstract: engineering ethics aims to enhance engineer’s ability to confront moral issues raised by engineering activities. it covers engineering as social experimentation, the engineer’s responsibility for safety, and the rights of engineers. what constitutes engineering ethics is the underlining question of this research. hence, the objective of the research is to systematically provide answers to the aforementioned question. the research also studies the scope and the origin of the subject matter. at the same time, the research highlights the significance of the subject from diverse perspectives; including western and islamic perspectives. abstrak: etika kejuruteraan bertujuan meningkatkan keupayaan juruera menghadapi isu-isu moralyang timbul dari aktiviti-aktiviti kejuruteraan. ia merangkumi kejuruteraan sebagai eksperimentasi sosial, tanggungjawab jurutera terhadap keselamatan dan hak-hak jurutera. persoalan utama penyelidikan ini adalah apa yang merangkumi etika kejuruteraan. penyelidikan ini juga mengkaji skop dan asal usul etika kejuruteraan. kajian ini turut membincangkan subjek kajian dari pelbagai perspektif, barat dan islam. keywords: engineering ethics; engineer; akhlaq; values; confidentiality; corruption; conflict of interest; whistle-blowing 1. introduction this research explores the functions of engineering ethics. the researcher employed a library-based evaluative method to arrive at comprehensive findings. the significance of this research is that it contributes to the better understanding of engineering ethics. the data of this research is mainly collected from the available resources. the study on engineering ethics is a timely exercise as engineers increasingly confront with ethical problems in their workplace. these ethical prdicaments and decision-making dilemmas include engineering confidentiality, corruption, conflict of interest, whistle-blowing and other related ethical impasses. 2. roots of ethical studies in islam the etymology and hermeneutics of akhlaq (islamic ethics) are found in the qur’an and in the hadith, whereas in the west ethics is rooted in philosophy. this positioning of ethics and moral studies is imperative here. it indicates that in islam akhlaq is part or at least directly related to godly principles, whereby in the west ethics and religion are two demarcate poles of the same intent. for that reason the term akhlaq hermeneutically speaking should not be directly interpreted as ethics or morals. on balance, ethics in the western sense of understanding is a set of principles of right conduct, it also refers to theories or systems of moral values, but iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 214 it does not refer to spiritual principle or godly rewards in the hereafter, (al-thawab fi alakhirah). whilst, akhlaq in islam has direct relations to spiritual standards of human behavior, attitude and character and its general sense of hermeneutics revolve around character, islamic customs and islamic way of life. the qur’anic constituents are tawhid, shari’ah and akhlaq, the hadith covers the same. prophet muhammad was appointed and selected by allah the almighty as the final prophet for mankind because he had a high level of akhlaq, not because of any other factor or criterion. he was told by allah: “and you are on an exalted standard of character” the prophetic bears this a witness and said: “i have been sent down “only” to perfect good manners” (qur’an, 68:4) a muslim faith without akhlaq is shaky and serves not religious values. the prophet told us in an authentic hadith that: “the most perfect man of the believers (mu’minin) in their faith is that who has the best akhlaq among you” (sahih al-bukhari) from the time of prophet ibrahim to prophet muhammad to the time of this author and his students, from the time of the greek period of scientific development to the period of modern western economic crisis ethics as a tool to measure human action remains relevant. however, as many will agree with me, ethical studies are of diverse. in some aspects they evaluate and characterize the meaning of ethical terms and statements. other part of ethical studies deal with how people actually behave. most ethical studies however, are teleological in nature, promoting the idea that actions are moral, provided that they target moral goal. (abdi o. shuriye, 2006) ethics is related to rationality. socrates (470-399 b.c.) started the pursuit of ethics is from rational perspective. plato’s (428-348 b.c.) approach is similar to that of his teacher, as the theory of reality became the bases for his ethical studies. the theory of forms described morality and ethics as the form or the idea of eternal and static structure. morality, according to plato, therefore, falls under these structures, and it becomes knowledge as moral people are wise, just, rational, courageous, moderate and harmonious with their soul. (abdi o. shuriye, 2006) ethicists refer to aristotle (384-322 b.c.) as one who drew distinction between him and plato as he based morality or human nature. meeting the needs or achieving happiness, the ultimate goal for life, is the purpose of ethics for aristotle. to achieve happiness, however, requires following some structured guidelines through reasoning, as a rational person adheres to some traits to maintain or achieve happiness. epicureanism, an early school of moral philosophy, which was developed after the demise of aristotle, is worth mentioning in this regard. epicurus (341-270 b.c.) the founder of what later to be known as epicureanism, believed that the highest good is to avoid pain and pursue pleasure. another ethicist school of the same period, the stoicism, advocated control of the emotions as the highest level of moral standards. (abdi o. shuriye, 2006). after the emergence of christianity however, the literature on ethics, methods and approaches of study took diverse directions. god became the ultimate reality in the mind of many ethicists and scholars formulated new methods and trends. as the purpose of life in christianity is to rule the earth on moral grounds, and not merely attaining world pleasure, which is a religious message, st. augustine (354-430 a.d) spearheaded the trend of christian moral harmony. other christian theologians include thomas aquinas (12251274 a.d.). aquinas moral theory was based upon natural law. he contended that the ultimate good of humans is spiritual union with god. christians accept that ethical issues iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 215 are part of larger scheme of revelation. unlike the contemporary western knowledge which places ethics under the studies of philosophy. (abdi o. shuriye, 2006) it must be reiterated that the systematic study of values is what ethicists call ethics; it is the study of how to live decent, as such ethicists are concerned with how to determine standards. the two terms “ethics” and “morality” become imperative at this point. these terms are interchangeable in most cases. morality deals with code of conduct. however, authorities of the subject argue that ethics refer to system of values, while, morality connotes righthood or wronghood. that indicates the fact that ethics is concerned with the systematic study of human values including the theories of conduct and focuses on moral dimensions of human life. (abdi o. shuriye, 2006) ethical studies also evaluate moral concepts and identify the significant of their approach. utilitarian ethicists focus on maximizing human well being as a whole. basic approaches of utilitarianism are act-utilitarianism which focuses on actions, not the rule, of the individual. john stuart mill (1806-1873) is considered one of the advocates of act utilitarianism, as we will illustrate it in the related chapters. (abdi o. shuriye, 2006) another approach is what ethicists term it as rule-utilitarianism which holds that moral rules are more imperative as the ethical rules will, in its general outlook, lead to the well being of all. duty ethics is another moral theory; an idea that our duty to behave morally becomes obligatory upon us. right ethics theory which advocates the contention that societies have moral rights and violating it is deemed unethical is another ethical theory related to. both right and duty ethics theories do not take consequences of an action or overall good of the action, into considerations. meanwhile virtue ethics theory outlines the idea of moral distinction, traits and character-fine, emphasizing on the personality. (abdi o. shuriye, 2006) 3. engineering ethics in this section i shall attempt to put engineering ethics into clear perspective. engineering ethics is a purpose of virtues and the ideals to the goal of creation of useful and safe technological products and services. (abdi o. shuriye and ahmad faris ismail, 2011) it is also a shared moral values by engineers, without these common values it would be exceedingly intricate for engineers to agree on any one course of action in the workplace. (abdi o. shuriye and ahmad faris ismail, 2011) it must be said that engineering ethics covers the principles of moral reasoning and relates it to the engineer’s professional life. moreover, engineering ethics is the part of ethics related to the work of engineers, engineering studies, and engineering curriculum. in other words it acts as a moral guidance for engineers, as it enables engineers to critically understand and reflect the moral issues surrounding them. it further helps engineers to conceptualize ethical challenges. however, it must be said that, engineering ethics refers to a set of specific engineering problems. as it also refers to accepted codes and standards in various organized groups of engineering societies. (abdi o. shuriye and ahmad faris ismail, 2011) as far as its functionality is concerned, engineering ethics employs normative inquisitions, and through this normative inquest, moral directives and ethical rules are established. this reminds us that engineering ethics is the ability to implement awakened sense of integrating professional life and personal conviction to maintain moral autonomy and integrity. (abdi o. shuriye and ahmad faris ismail, 2011) iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 216 engineering ethics is about moral rights of the engineers. the term moral rights refer to what is morally and ethically there for engineers. it also reflects the ability of an engineer to claim what is morally hers or his, what is under her or his control, and what action is morally acceptable. (abdi o. shuriye and ahmad faris ismail, 2011) on a related aspect, it must be observed that, engineering ethics is an appliance of descriptive investigation, it means, engineering ethics describes how engineers behave and what sorts of moral standards they claim to follow. if we understand engineering ethics this way we will be able to comprehend the attitude of engineers and what they do or have believed about moral rules. (abdi o. shuriye and ahmad faris ismail, 2011) engineering ethics covers diverse spectrum of issues related to engineering work and engineering professions. these includes but for sure not limited to confidentiality, whistle blowing, conflict of interest and corruption. in engineering practices, confidentiality is the process of ensuring that information is accessible only to those authorized to have access to. confidentiality, therefore, is the scheme of reality, that no facts, data, or information should be revealed without the prior consent of the client. (abdi o. shuriye and ahmad faris ismail, 2011) engineering corruption on the other hand is anything associated with illegitimate personal or organizational gain. engineering bribery is a favour offered or given to an engineer in a position of trust in order to induce him/her to act dishonestly or against his/her profession. one must bear in mind that, engineering corruption is of broader spectrum than engineering bribery, and may encompass fraud and misuse of power. (abdi o. shuriye and ahmad faris ismail, 2011) conflict of interest refers to a set of conditions in which professional judgment concerning a primary interest tends to be unduly influenced by a secondary or personal interest. (krimsky, s. and rothenberg, l.s., 2001) thus, conflict of interest exists when an engineer has influence on official decisions where the outcome of that decision might affect the engineer’s personal interest. (warner, t. d. and gluck, j. p., 2003) there are three types of conflict of interest; namely, actual, potential and appearance of conflict of interest. actual or direct conflict of interest is any act that compromises objective engineering judgment. (conflict of interest handbook, 2009) potential conflict of interest on the other hand is a situation where an engineer befriends with a supplier, client or service provider. although this situation does not necessarily constitute a conflict of interest, there is a potential that the engineer’s judgment might conflict with the needs to maintain the friendship. (conflict of interest handbook, 2009) appearance conflict of interest occurs on commission based jobs. (ackerley, n., eyraud, j. and mazzotta, m., 2007) whistle-blowing is a recent term in the hermeneutics of ethical studies. it connotes an act of engineer in disclosing unethical or illegal behaviour by an employer or supervisor by informing the public or higher management. it occurs when an insider reports alleged organizational misconduct to the public. whistle-blowing consists of four essences; act of disclosure, topic, agent and recipient. as such, engineer is obliged to blow the whistle on acts or project which violates ethical, religious or universal values. engineers also have the professional right to disclose any wrongdoing within their organizations and expect to see appropriate action taken. (abdi o. shuriye and ahmad faris ismail, 2011) in islamic norms, whistle-blowing is associated with negative as well as positive aspects of human action. instance of this is that an act of whistle-blowing by an engineer could be interpreted as backbiting (ghibah), spying on others (tajasus), rumour mongering iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 217 or scandalous statements (fadhihah or fitnah). at the same time it could be seen as an advice (nasiha), enjoin good and forbidding bad (al-amr bi al-ma‘rufi wa an-nahy ‘an almunkar), arbitration (sulh or islah). (abdi o. shuriye and ahmad faris ismail, 2011) so it will depend on how the engineer concern puts it, therefore, the act of blowing a whistle should be in line with the universal norms. engineering professional ethics refers to the moral rules that professionals should adhere to. duties performed by engineers, for instance, are comparatively risky and could annihilate nations if ethical rules ignored. professional duty requires extensive formal education, use of judgment and high level of skills with governing standard principles. (abdi o. shuriye, 2006) professional duty also comes with autonomy, knowledge, recognition and licensing or certification from a recognized bodies and authorities. construction sector, road and rail networks, transportation systems, and environment, are only some areas that unethical professionals could contaminate it. exposing of deadly virus by an immoral physician could cause the death of millions before it could be contained. for this raison d'être, profession requires deontological oath which makes the professional to be duty-based. professional organizations have made the oath mandatory to set a moral stage. nonetheless, poor services and selfish personal interest, unfortunately remains, intact. (abdi o. shuriye, 2006) 4. conclusion finally it must be said that engineering ethics is concerned with professionalism, itqan (perfection), ihsan (goodness in production), taqwa (god consciousness at work) and ‘adalah (justice) not only by muslim engineers but to certain scale in universal stage. engineering ethics is the study of moral issues and decisions confronting the engineer in the workplace. as a matter of fact, amoralists, axiologists, deontologist, sensationalists, metaethicists, synteresists, and utilitarians are all ethical schools of thought and doctrines investigate ethical issues. this itself connotes the imperativeness of engineering ethics. a world without ethics is a world devoid of guiding principles. ethicists have taken diverse positions in their approach but concur on the fact that ethics is an integral part of an engineer’s professional life. engineering ethics is also an imperative tool to measure the attitude, and the work-ethics of an engineer. references [1] al-qua’an al-karim. [2] abdi o. shuriye and a. f. ismail, qur’anic values and engineering studies: approaches and methods in the process of islamizing engineering curriculum. pearson international, kuala lumpur, pp. 2-4, 21-23, 2011 [3] abdi o. shuriye, islamic ethical values on bioengineering practices: issues in genetic engineering. research management centre, iium, pp. xivxvi, 2006. [4] s. krimsky and l.s. rothenberg, “conflict of interest policies in science and medical journals: editorial practices and author disclosures.” science and engineering ethics, vol.7, pp. 205-218, 2001. [5] t. d. warner and j. p. gluck, “what do we really know about conflicts of interest in biomedical research?” psychopharmacology, vol.171, pp.36–46, 2003. [6] n. ackerley, j. eyraud, and m. mazzotta, “measuring conflict of interest and expertise on fda advisory committees (task order no. 14 contract no. 223-03-8500).” eastern research group, inc., p.55, 2007 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering shuriye 218 [7] conflict of interest handbook, the california state university, p. 14, 2009. [8] c.b. fleddermenn, “engineering ethics.” prentice hall, p. 88 1999. [9] mohamed bin ismail al-bukhari, sahih al-bukhari, dar al-qalam, beirut, in al-adab alifrad, 1987. [10] abi da’ud, sulayman ibn ash-‘ashath as-sajastani. sunan abi da’ud, beirut, dar al-kutub al-ilmiyah, in bab al-fadail, 2001. [11] abdul haq ansari, islamic ethics: concept and prospect, in the american journal of social sciences, vol. 6, no. 1, p. 87, 1989. [12] fazlur rahman, law and ethics in islam, in ethics in islam ed by richard g. hovannisian, undena publications, california, p. 7, 1985. [13] majid fakhry, ethical theories in islam, e.j. brill, leiden, 1990. [14] abdullah omar naseef, the role of faith and islamic ethics in the teaching of natural and applied sciences, in the islamic quarterly: a review of islamic culture, vol. 26, no. 3, p. 135, 1982. [15] charles e harris et al, engineering ethics, england, wadsworth publishing company, p.27, 1995. [16] martin, m. w. and schinzinger, r., ethics in engineering, mcgraw-hill, usa, p. 34, 1991. microsoft word 138-557-1-pra-last iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 39 toward software engineering principles based on islamic ethical values shihab a. hameed electrical and computer engineering department, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. e-mail: shihab@iiu.edu.my abstract: software is the core for computer-based applications which became an essential part for critical control systems, health and human life guard systems, financial and banking systems, educational and other systems. it requires qualified software engineers: professionally and ethically. literature review (l.r.) and survey results show that software engineering professionals are facing several ethical-related problems which are costly, harmful and affected high ratio of people. professional organizations like acm, ieee, abet and csac have established codes of ethics to help software engineering professionals to understand and manage their ethical responsibilities. islam considers ethics an essential factor to build individuals, communities and society. islamic ethics are set of moral principles and guidance that recognizes what is right behavior from wrong, which are comprehensive, stable, fair, and historically prove success in building ethically great society. the estimated 1.3 billion of muslims with tens of thousands of software engineers should have an effective role in software development and life, which requires them to understand and implement ethics, specially the islamic ethics in their work. this paper is a frame-work for modeling software engineering principle. it focuses mainly on adopting a new version of software engineering principle based on islamic ethical values. keywords: ethics, software engineering ethics, islamic ethics, computer crime. 1. introduction in this computer and information era, computer-based applications became an essential part of human life. it is the core for critical control systems, health and human life guard systems, financial and banking systems, scientific and educational systems, entertainment and games, and other systems related to different aspects of human life. software is the core for such computer-based systems. software development requires qualified professional and ethical software engineers. computer ethics is one of the essential branches of ethics that is growing and changing rapidly as computer technology grows and develops. in stanford encyclopedia of philosophy [1], computer ethics might be understood narrowly as the efforts of professional philosophers to apply traditional ethical theories or virtue ethics to issues regarding the use of computer technology; or might be understood broadly to include standards of professional practice, codes of conduct, aspects of computer law, public policy, corporate ethics beside certain topics in the sociology and psychology of computing. since information technology has begun to affect community iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 40 life, family life, human relationships, education, freedom, etc; so the computer ethics can be understood as the branch of applied ethics which studies and analyzes such social and ethical impacts of information technology. walter maner [2] in mid 1970s defined the computer ethics as one which examines "ethical problems aggravated, transformed or created by computer technology". deborah johnson [3] thought that computers gave a "new twist" to old ethical issues which were already well known. moor's [4] defined computer ethics as a field concerned with "policy vacuums" and "conceptual muddles" regarding the social and ethical use of information technology. moor's way is very powerful, suggestive, broad enough to be compatible with a wide range of philosophical theories and methodologies, and it is rooted in a perceptive understanding of how technological revolutions proceed. this very broad view of computer ethics employs concepts, theories and methodologies from applied ethics, sociology of computing, technology assessment, computer law, and other relevant disciplines [5]. this way of understanding computer ethics is reflected in recent developments such as brey's "disclosive computer ethics" methodology [6] and the emerging research field of "value-sensitive computer design" [7, 8, 9]. in gotterbarn's view, computer ethics should be viewed as a branch of professional ethics, which is concerned primarily with standards of practice and codes of conduct of computing professionals [10]. gotterbarn has been involved in a number of activities, such as co-authoring the third version of the acm code of ethics and professional conduct and working to establish licensing standards for software engineers [11, 12] based on this view. sommerville [13] in his software engineering book denoted that: computer science is concerned with theory and fundamentals; system engineering is concerned with all aspects of computer-based systems development including hardware, software and process engineering; software engineering is concerned with the practicalities of developing and delivering useful software. software engineers must accept that their job involves wider responsibilities than simply the application of technical skills. they must also behave in an ethical and moral responsible way if they are to be respect as professionals. to understand the computer and software engineering ethics, we have to understand the concept of ethics, ethical problems and its role in human life. one of the recognizable and effective concept of ethics is the islamic concept, which is still not studied broadly by computer and software engineering professionals. 2. ethics and ethical problems the results of joining several conferences, having several discussions with experts and professionals, and reading different articles related to ethics can be concluded as: ethics have several definitions, which reflect the philosophers or authors viewpoints and their culture, but there is a common area between all these viewpoints. so ethics can be defined as “set of principles of right conduct”, “theory or system of moral values”, or “motivation based on ideas of right and wrong”. wikipedia encyclopedia [14] shows that: socrates was one of the first greek philosophers to encourage both scholars and the common citizen to turn their attention from the outside world to the condition of man. aristotle posited an ethical system that may be termed "self-realizationism"; when a person acts in accordance with their nature and realizes their full potential, they will do good and be content. iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 41 people are daily facing ethical issues at their life; but how many of us know how to deal with them? several surveys were done which shows a whole array of issues being faced by employees such as stealing, lying, fraud and deceit [15]. internationally, the ethical values are also deficient. in a survey of 300 companies across the world, over 85% of senior executives indicated that the following issues were among their top ethical concerns: employee conflicts of interest, inappropriate gifts, sexual harassment, and unauthorized payments [16]. a survey of 2,000 major us corporations revealed that the following ethical problems concerned managers: drug and alcohol abuse, employee theft, conflicts of interest, quality control issues, discrimination in hiring and promotion, misuse of proprietary information, abuse of company expense accounts, plant closings and layoffs, misuse of company assets, and environmental pollution [17]. in computer, and software development; there are several problems related to ethical issues. these issues include professional responsibilities, social responsibility, quality as moral issue, software ownership and intellectual property rights, privacy, computer crimes, confidentiality, responsibility and liability, professional competence, impact on society and work place, security and reliability, and safety [18]. ethical related problems in computer and software are very costly, harmful and affected high ratio of people. the federal bureau of investigation (fbi) study shows that in 2006 the estimated computer crimes’ cost was usd 67.2 billion yearly. on the other hand, software engineers participate in developing advanced software as a core for all intelligent and massdestruction weapons systems. the unethical usage of such weapons causes hundreds of thousands of innocent victims as well as the huge destructions for wealth and environment, which means that software engineer participates indirectly in such crimes and destructions. a survey study done on internet’s usage and ethical problems in education; the sample is selected from higher education institutions in malaysia. internets' users (students, academic staffs and non-academic staffs) represent different nations, races, cultures, genders, experiences, ages and qualifications; this makes the selected sample of users more representing the population that we need to study. survey results in table 1 show that: − 73% of total users consider sexual related data is harmful data factor. − 51% of total users consider anti-religious related data is harmful data factor. − 42% of total users consider advertisements and commercial announcement related data is harmful data factor. − 19% of total users consider anti-culture related data is harmful data factor. − 19% of total users consider political related data is harmful data factor. − 14% of total users consider security related data is harmful data factor. it also shows that 75% of the users get such harmful data by e-mails. table 1: harmful data factors percentages. harmful data factors female % male % total % anti religious 0.37 0.58 0.51 anti-culture 0.16 0.2 0.19 sexual 0.76 0.71 0.73 political 0.24 0.16 0.19 security 0.16 0.13 0.14 advertisement 0.5 0.38 0.42 iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 42 3. ethics in islam islam is the last religion revealed by the god (allah): “this day, i have perfected your religion for you, completed my favour upon you, and have chosen for you islam as religion” [qur’an 5:3]. islam is basically based on two sources: the qur’an [19] and the sunnah of prophet muhammad (peace be upon him or, which is mainly defined by muslim scholars as: “all what prophet muhammad says, acts, or agreed on”. sunnah is documented in six authenticated resources (sahih al-bukhari, sahih muslim, sunan abi-daud, jamea altermethi, sunan ibn-maja, and sunan al-nisaae). the general understanding of ethics in islam can be express as a “set of moral principles and guidance that recognizes what is right behavior from what is wrong or what one should do or not”. qur’an and sunnah, show that all the muslims’ life should be guided by islamic ethics [20-23]. allah said “verily this qur’an doth guide to that which is most right (or stable)” [qur’an 17:9]. allah uses the term akhlaq or khuluq in the qur’an to refer to the ethics. the importance of ethics in islam is shown when allah prescribes prophet muhammad that he is with a great ethics: ”prophet of allah had been raised to a great spiritual dignity” [qur’an 68:4]. also, prophet muhammad said, “i was sent to complement the best of ethics”. the qur’an represents the main dimension for the concept of ethics in islam; when aisha, the wife of prophet muhammad, was asked about the ethics of prophet; she replied: “his ethics was the qur’an” [20]. allah orders the muslims to follow and obey prophet muhammad as a model “you have indeed in the messenger of allah an excellent example” [qur’an 33:21]. allah describes people of the best nation as: “you are the best of peoples, evolved for mankind, enjoining what is right (ma‘ruf), forbidding what is wrong (munkar), and believing in allah” [qur’an 3:110]. the qur’an and sunnah use set of ethical terms to describe the concept of goodness such as: sidq (truth), khayr (goodness), birr (righteousness), qist (equity), ‘adl (equilibrium and justice), haqq (truth and right), ma‘ruf (known and approved), amanah (honesty), ikhlas (sincerity), and taqwa (piety). pious actions are described as salihat and impious actions are described as sayyi’at. [24]. some of these terms are repeated in tens of qur’anic verses as well as the sunnah. table 2 shows a survey result for the frequency of some ethical terms used in the qur’an; which show that islam supports and rewards people for all goodness and warns, prohibits or punishes people for badness. historically, many of muslim’s scientists and scholars have great effort in the field of ethics. they wrote many books and articles to explain the concept of ethics in islam. they consider ethics as the best honorable science or the crown of sciences, which leads to bring success, happiness for individuals, communities and society. alfairuzabady [25] and ibn mandhor [26] mention that linguistically ethics means your default behavior “tab’a or sajiyyah”, kindness (moroa’a) or religion, which reflect the mankind natural characteristics that is straightforward consistent besides the acquired characteristics that became as natural characteristics [25-28]. on the other hand ibn miskawah [29] and abo-hamid al-ghazali [23] define ethics as a fixed situation of mankind soul and according to it, the mankind acts or behaves easily and simply without need for thinking or his acts become as default. abd al-karim zaydan [30] view ethics as set of fixed characteristics and meaningful values in mankind soul and iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 43 according to the act consider accepted as good or rejected as bad so that he will perform or reject [28-30]. table 2: frequency of ethical related terms in the qur’an. ethical related terms (good ethics) frequency truth (sidq) >110 fair and right (‘adil, haq) > 300 goodness (khair, maaroof) > 180 love & good dealing (hub, husn) > 180 forgiveness & kindness (afo, ghafoor, raoof) > 350 merciful (raheem) > 250 keep promises & sincere (ahd, ikhlas) > 40 wisdom (hikma) > 160 science & education (elm, taaleem) > 800 ethical related terms (bad ethics) frequency lie (katheb) > 240 unfair (dhulm) >210 hypocrisy (nefaq, fitnah) >55 (fuhsh, fusoq) > 80 plotting (makr, ifteraa) >110 islam considers ethics as an essential factor in developing or rebuilding the society based on understanding of the qur’an and sunnah. this ethical rebuilding of human behavior will bring benefit, peace, and prosperity to mankind [31]. the ethical behavior affected by set of factors, which can be classified according to their level of effect into: global, nation, community, family, and individual. historically, islamic system is the only system that produces encyclopedic scientists such as al-khawarizmi, ibn-rushd, ibnhayyan, ibn-sena, ibn-albetar, and ibn-alhaitham. each one of them was scientists in several fields such as fiqh, hadith, language and art, mathematics, chemistry, physics, medicine, or astronomy. they were models and behave according to the islamic ethics. 4. why islamic ethical principles are needed according to our experience, analysis of the literature and survey results of ethical terms in the qur’an and the sunnah, there is lack of knowledge and misunderstanding about islam and islamic ethics by many of non-muslims. we can summarize the main characteristics for islamic ethical principles as: − historically, islamic ethical principles was tested in real life and shown that it is the suitable solution to convert society to the best. the clear example shown when islam converts the bedouin society in the arab-land into modern society within two decades, then build a great nation, which leads and develop main part of world (with great ethics such as justice, fairness, honest, truth, goodness) as shown in the umayyad, abbasid and andalusia eras. − islamic ethics are comprehensive, which organize the relation between mankind and allah, mankind them self, mankind and other creatures, and mankind and iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 44 environment. allah said to the prophet “we have not send thee but as messenger to all mankind, giving them glad tiding, and warning them against sin” [qur’an 34:28], also “we send thee not, but as mercy for all creatures” [qur’an 21:107]. − islamic ethical principles are stable and standard. it deals with people in justice, fairness and equality regardless of their race, relationship, nation, religion, or color. allah said “verily this qur’an doth guide to that which is most right (or stable)” [qur’an 17:9]. the prophet said “all people are equal; there is no difference between arabic and non-arabic except in taqwa (piety). − islamic ethical principles work toward reactivating the purity (fitra) of people as they created by allah and out of devil’s affect. “so set your face towards the religion of pure islamic monotheism; allah’s fitra with which he has created mankind” [qur’an 30:30]. − islamic ethics rebuild the society through building individuals; starting before or from day of birth and continue through all his life. − islamic methodology of life is guided by islamic ethics. it associated theoretical principles with implementation through set of worshiping and dealing acts. there are more than fifty verses in qur’an mentioned to “those who believe and do deeds of righteousness”. − islamic ethical principles associate mankind acts with his intension, which is known by allah. “except as allah wills; for he knoweth what is manifest and what is hidden” [qur’an 87:7]. the prophet also said “all your acts are associated with your intentions”. − islam considers human life is a challenge between mankind and the devil. allah supports the mankind with forgiveness and mercy using (tawba and isteghfar). also allah duplicating rewards for good deeds and canceling sins when we make istighfar or tawba. “verily the devil (satan) is an enemy to you: so treat him as enemy” [qur’an 35:6]; also “allah who forgiveth sin, accepteth repentance” [qur’an 40:3]. the unethical behavior for some muslims can be consider as one of the essential reasons for their weakness, which also leads to the unfair concept about islam and islamic ethics by some of the non-muslims. several lectures and articles show that muslims’ population is approximately 1.3 billions which represent more than 20% of the world population. they are distributed mainly in more than 60 countries. they are dealing with computer and it related applications directly or indirectly. yearly, many muslims graduated from computer and information technology programs within hundreds of universities in the islamic world and other universities as well as training centers. this offers tens of thousands of muslims as computer and software engineering professionals. this shows that the muslims especially the software engineering professionals should have an effective role in computer and software engineering field and its related code of ethics. conferences, discussions, and literature reviews show that muslims’ researchers have simple effort in computer and software engineering ethics and they still do not adopt standard code of ethics based on islamic values. also, there is a lack of an efficient and effective comprehensive database, e-learning tool, and textbooks related to islamic ethical values in computer and software engineering. iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 45 5. software engineering professionals ethics software engineering professionals have specialized knowledge and often have positions with authority and respect in the community so, they are able to have a significant impact upon the world, including many of the things that people value [32]. computer professionals find themselves in a variety of professional relationships with other people [33, 34] that involve a diversity of interests, and sometimes these interests can come into conflict with each other. professional organizations in the u.s., like acm (association for computing machinery) and ieee (institute of electrical and electronic engineers), have established codes of ethics, curriculum guidelines and accreditation requirements to help computer professionals understand and manage ethical responsibilities. in addition, both the acm and ieee have adopted codes of ethics for their members [13]. abet (accreditation board for engineering technologies) has long required an ethics component in the computer engineering curriculum. in 1991, csac/csab (computer sciences accreditation commission / computer sciences accreditation board) also adopted the requirement that a significant component of computer ethics be included in any computer science degree granting program that is u.s. accredited. ieee and acm are two of the main professional committees in field of computer and engineering. they work toward define standard principles for software engineer in term of professional and code of ethics. they produce early versions and try to upgrade it from time to time. major revisions were made between version 3.0 that was widely distributed and version 5.2, the recently approved version [18]. the preamble was significantly revised to include specific standards that can help professionals make ethical decisions. the short version of the code summarizes aspirations at a high level of abstraction. software engineers shall commit themselves to making the analysis, specification, design, development, testing, and maintenance of software a beneficial and respected profession. in accordance with their commitment to the health, safety, and welfare of the public, software engineers shall adhere to eight principles [35]. we can summarize the results of l.r. and survey for the ethical related problems for software engineering professionals as: although there is big effort done by many international organizations but we still have several problems related to ethics in computer and software engineering. many of the software engineering professionals are still participating in developing software to support many of computer-based system that cause huge destruction for human, health, wealth and environment. there is no standard code of ethics or principles for software engineering professionals based on islamic values. lack of knowledge (especially software engineering professionals, students and lecturers) about real islamic ethical values and capability of implementing it in real life. lack of dedicated database and e-learning tool for islamic ethical values. lack of guidelines to enhance curriculum with islamic ethical values especially for software engineering related courses. there is no ethical evaluation model for software engineering professionals based on the defined islamic code of ethics. iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 46 6. framework for modeling software engineering principles based on islamic ethical values to solve the ethical related problems for software engineering professionals and to help muslims to understand the islamic ethics we propose this framework for modeling software engineering principles based on islamic values as shown in fig. 1. the main objectives for this framework can be summarized as: − offering solutions for some of the problems related to ethics in software engineering. − offering standard code of ethics or principles for software engineering professionals based on islamic ethical values. − offering a suitable advising and warning for software engineering professionals to avoid participation directly or indirectly in harming of innocents or destruction of health, wealth and environment. − offering a valuable knowledge about real islamic ethics to clarify the current cloudy picture about islam or islamic ethics, especially by the non-muslims. − offering a comprehensive database and web-based e-learning tool for ethics, islamic ethics, and software engineering professional ethical principles which offer ethical guidelines for a high ratio of people, especially 1.3 billion muslims with tens of thousands of computer and software engineering professionals to guide them in their work and life based on islamic values. − offering guidelines for curriculum developer to enhance computer and software engineering courses with islamic ethical values. − offering an effective mathematical / statistical evaluation model for software engineering based on islamic ethical values, which is a supportive tool for sw quality management. − offering a path or guidance for people specially the software engineering professionals to reactivate their good ethics and show them how to implement theoretical aspects of good ethics practically. in this research paper we focus on defining a new version of software engineering principles based on islamic values. the other objectives will appear later in other publications. iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 47 fig.1. framework for modeling swe principles based on islamic ethical values. l.r. and survey start extract ethical principles for swe ethics, islamic ethics, swe code of ethics or principles (islamic) swe curriculum identifying ethical principles for swe based on islamic values islamic resources (qur’an & sunnah) enhancing swe curriculum with islamic ethics mathematical & statistical rules developing swe ethical evaluation model extract islamic ethics developing e-learning tool end sw quality metrics iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 48 7. software engineering principles based on islamic ethical values this research paper work toward defining novel version of standard code of ethics or principles for swe professional based on islamic ethical values. it represents the integration between the islamic ethics (according to qur’an and sunnah) and current software engineering professionals' ethical principles. section 3 and 4 in this paper summarize: the concept of ethics in islam, its importance in enhancing individual’s behavior, and its main characteristics. software engineering professionals have to commit themselves to follow these principles in all software development phases: communications, data collection, analysis and requirements, design and specifications, construction, testing and maintenance. these following proposed ethical principles are guidance for software engineering professionals especially the muslims: − work as vicegerent of allah: the main objective of creating all mankind by god is to worship him; by developing and reconstructing the earth for the best (as vicegerent or caliph) through their good acting and deeds. allah said “i have only created jinn and men, that they may serve me” [qur’an 51:56]. “allah said to the angels: i will create a vicegerent on earth” [qur’an 2:30]. − spend your age in performing goodness and collect your wealth in ethically legal ways: the age and wealth for any mankind are predetermined and fixed by allah swt before they born; but they are responsible for their acts and decisions as shown in the following verses of qur’an. ”to every people is a term appointed: when their term is reached, not an hour can they cause delay, nor an hour can they advance” [quran 7:34]. “for them a substance determined” [qur’an 37:41], “there is no moving creature on the earth but its sustenance dependeth on allah” [qur’an 11:6]. ”verily, we showed him the way, weather he be grateful or ungrateful” [qur’an 29:3]. − no secret act and each act with good intention: god knows all what we declared or keep it secretes as well as all our acts are associated with our intentions (niyyah); so we have to be clear in our work. “allah he kneweth what is manifest and what is hidden” [qur’an 87:7]. the prophet said “all your acts are associated with your intention”. − performing duty is a worship: software engineering professionals have to know that, performing their duty is a worship and allah swt will reward them for goodness and punish them for evil/sinful deeds. allah swt said in qur’an “then shall anyone who has done an atom’s weight of good, see it and anyone who has done an atom’s weight of evil, shall see it” [qur’an 99:7-8]. the prophet in his hadith said “work is worship”. − understand and follow the standard ethics, especially islamic ethics: software engineering professionals have to understand the standard islamic ethics (based on quran and sunnah). they have to consider it as the highest standard that they should follow in their life and work. “verily this qur’an doth guide to that which is most right (or stable)” [qur’an 17:9]. “the religion be for allah is islam” [qur’an 3:19]. − work in consistent with goodness of ummah or nation interests: software engineering professionals have to work consistently with the ummah (nation) interest, which are based on islamic ethical values and should not make harm for it. “every muslim is shepherd (leader) and he is responsible for that which he shepherds”. iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 49 − work in consistent with goodness of community or organization interests: software engineering professionals have to work in a manner that is in the best interests to their committee or organization and in consistent with the nation interest based on islamic standards. the prophet said “those who cheat us are not part of us (our ummah)”. − meet the highest professional: software engineering professionals have to ensure that their products and related modifications meet the highest professional standards and not conflict with ethical values. the prophet said in a qudsi’s hadith: “allah loves those who accomplish their job in its best (perfect) manner”. − fair judgment: software engineering professionals have to maintain integrity and independence in their professional judgment and have to be fair according to ethical values. allah swt said in qur’an “when you judge between others you judge with justice”.[ qur’an 4:58] − management with honesty: software engineering professional managers and leaders have to subscribe to and promote an ethical approach to the management of software development and maintenance. they have to show the honesty (amanah) and equity in performing their duty. − work with highest profession: software engineering professionals have to advance the integrity and reputation of the profession consistent with the ummah (nation) interest. they have to do their best using their highest profession. − be cooperative and supportive: software engineering professionals have to be fair to and supportive of their colleagues and avoid the selfish. allah mentions in qur’an: “help you one another in virtue, righteousness and piety (bir and taqwa); but do not help one another in sin and transgression” [qur’an 5:2]. − lifelong learning: software engineering professionals have to participate in lifelong learning regarding the practice of their profession and shall promote an ethical approach to the practice of the profession. the prophet said ”seek knowledge from birth to death”. − protect the confidentiality: software engineering professionals have to protect the confidentiality and security for the client, employer or community and nation (ummah). − remember the judgment day: software engineering professionals have to know that doing goodness and producing useful knowledge will be rewarded by allah in their life and after death to the day of judgment. 8. concluding remarks software is the core for any computer–based system, which affect all aspects of our life. software development is a complex, expensive, and ethical engineering task which requires qualified software engineering professionally and ethically. although ethical and professional principles for software engineering professionals were adopted by professional organizations and committees such as ieee, acm, abet; but l.r., studies and survey results show that software engineering professionals still facing many ethical related problems. islamic sources (qur’an and sunnah) provide a high standard of ethics for individual, communities and ummah (nation) levels. islamic ethics are stable, comprehensive, fair and standard ethics which are suitable for all nations and times; and when followed leads to create a ethically great society. since there is lack of effort in iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 50 considering islamic ethics in developing software engineering principles, we propose a framework for modeling software engineering principles based on islamic ethical values. the paper proposes adopting new software engineering principles based on islamic ethical values. this effort can help in solving many of the current ethical related software development problems. it offers a good opportunity for software engineers specially muslims to understand and implement such standard and comprehensive ethical values in their life as well as having their right role in software development. acknowledgement the malaysian ministry of higher education (mohe) and iium university kindly provided funding for the research through the "iium fundamental research grant system" (ifrgs) project no: 0703-76 references [1] stanford encyclopedia of philosophy, “computer ethics”, 2001. [2] walter maner, “starter kit in computer ethics”, helvetia press (published in cooperation with the national information and resource center for teaching philosophy), 1980. [3] deborah g. johnson, “computer ethics”, prentice-hall, 2nd edition, 1994. [4] james h. moor, "what is computer ethics?" in bynum, terrell ward, computers and ethics, blackwell, 266-75, 1985. [5] in bynum, terrell ward, walter maner and john l. fodor, "computer ethics in the computer science curriculum.", teaching computer ethics, research center on computing & society, 1993. [6] philip brey, "disclosive computer ethics." in r. a. spinello and h. t. tavani, eds., readings in cyberethics, jones and bartlett, 2001. [7] batya friedman, “human values and the design of computer technology”, cambridge university press, 1997. [8] batya friedman, and helen nissenbaum "bias in computer systems", acm transactions on information systems, vol. 14, no. 3, 330-347, 1996. [9] lucas d. introna, "privacy and the computer: why we need privacy in the information society," metaphilosophy, vol. 28, no. 3, 259-275, 1997. [10] donald gotterbarn, "computer ethics: responsibility regained," national forum: the phi beta kappa journal, vol. 71, 26-31, 1991. [11] anderson, ronald, deborah johnson, donald gotterbarn and judith perrolle, "using the new acm code of ethics in decision making," communications of the acm, vol. 36, 98-107, 1993. [12] donald gotterbarn, miller keith, and rogerson simon, "software engineering code of ethics," information society, vol. 40, no. 11, 110-118, 1997. [13] l sommerville, “software engineering”, addison wesley: 8th ed, 2006. [14] wikipedia, “the free encyclopedia”: http://en.wikipedia.org/ iium engineering journal, vol. 9, no. 2, 2008 shihab a. hameed 51 [15] j. o. cherrington, and d. j. cherrington, “a menu of moral issues: one week in the life of the wall street journal.” journal of business ethics, 11, pp. 255-265, 1993. [16] mary baumann “ethics in business.” usa today. she was citing data from the conference board, 1987. [17] america’s most pressing ethical problems. washington, dc: the ethics resource center, p1, 1990. [18] d. gotterbarn, r. riser, “ethics activities in computer science departments:goals and issues”, www.cs.utexas.edu/users/ethics/professionalism/ethics_activities.html [19] the nobel qur’an, english translation of the meaning and commentary, king fahh complex for printing holy qur’an, ksa, 1417 h. [20] abi da'ud sulayman ibn al-ash'ath al-sijistani al-izdi, “sunan abi da'ud”, bayrut : dar ibn hazm, 1997. [21] muhammed bin ismail al bukhari , “sahih al-bukhari”, bayrut : dar al-fikr, 1981 [22] muhammad al-ghazali, “khuluq al-muslim”, damascus : dar al-qalam, 2004. [23] abu hamed al-ghazali , “ihya' 'ulum al-din”, bayrut : dar al-ma’arifa, 1900. [24] majid fakhry, “ethical theories in islam”. leiden: e. j. brill, pp. 12-13, 1991. [25] muhammed bin yaqub alfairozabady, “al-qamus al-muhit”, bayrut : moassasat al-resala, 1987. [26] muhammed bin makram ibn mandhour, “lisan al-'arab” bayrut : dar al-fikr, 1970. [27] al-husain bin muhammed al-ragheb al-asfahani, “al-mufradat fi gharib al-qur'an”, bayrut : dar al-ma'rifah, 1999. [28] muqdad al-jen, “ilm al-akhlaq al-islamiyah”, riyadh: dar alam al-kutub, 1992. [29] ahmed bin muhammed ibn meskawah, “tahdhib al-akhlaq wa-tathir al-a'raq”, bayrut : maktabat al-thaqafah al-diniyah, 2001. [30] abd al-karim zaydan, “usul al-da'wah”, baghdad : maktabat al-quds, 1991. [31] beekun r. issa, “islamic business ethics”, iiit institute, va, 1996. [32] donald gotterbarn, "informatics and professional responsibility", science and engineering ethics, vol. 7, no. 2, (2001). [33] deborah g. johnson, "proprietary rights in computer software: individual and policy issues", 1992. [34] in bynum, terrell ward, walter maner and john l. fodor, “software ownership and intellectual property rights”, research center on computing & society, (1992). [35] j. pressman, “software engineering: practioners approach”, john wiley: 6th ed, 2006. microsoft word 216 completed-corrected iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 141 preliminary investigation of myo-inositol phosphates produced by asuia279phytase on mcf-7 cancer cells n.mohd. yusoff 1 , t. nuge 1 , n.h. zainan 1 , y.z.h-y. hashim 1 , p. jamal 1 , anis shobirin meor hussin 2 , abd-elaziem farouk 3 and h.m. salleh 1 1 bioprocess and molecular engineering research unit, department of biotechnology engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2 department of food technology, faculty of science and food technology, 43400, university putra malaysia, serdang, selangor, malaysia. 3 department of biotechnology, faculty of science, taif university, 21974 taif, al-hawiayah, p. o. box. 888, saudi arabia. hamzah@iium.edu.my; yumi@iium.edu.my abstract:phytate or myo-inositol hexakisphosphates (ip6) is widely distributed in plants like rice bran. the production of myo-inositol phosphate intermediates has received much attention due to the remarkable potential health benefits offered by the compounds. in this study, the cytotoxicity of the partially purified myo-inositol phosphate fractions and commercial ip1 and ip6 were investigated against mcf-7 breast cancer cell lines. the study showed that the commercial standard ip1 and ip6 showed good inhibition towards the mcf-7 cell line. the mcf-7 cells growth was inhibited in minimum concentration of myo-inositol phosphates (<1000 µ g/ml). however, no inhibition observed on the mcf-7 cell line by the myo-inositol phosphates fractions partially purified from rice bran at concentration <1000 µg/ml. the inhibition of mcf-7 was only observed at concentration more than 30 mg/ml with more than 40% cells were inhibited. this indicates that the partially purified rice bran myo-inositol phosphates degraded by asuia279 phytase on mcf-7 breast cancer cells exhibit positive results towards the inhibition of cancer cells growth at relatively high concentration. abstrak: fitat atau myo-inositol hexakisphosphate (ip6) dikenali umum teragih di dalam tumbuhan seperti dedak padi. penghasilan perantaraan fosfat myo-inositol mendapat perhatian memandangkan ia berpotensi tinggi dalam kesihatan. dalam kajian ini, kesitotoksikan sebahagian daripada fosfat myo-inositol separa tulen, ip1 komersil dan ip6 komersil dikaji terhadap produk yang berupa sel kekal (cell lines) kanser payu dara mcf-7. tumbesaran sel mcf-7 direncatkan dalam pekatan minima fosfat myoinositol (<1000 µg/ml). tetapi, tidak ada perencatan dilihat terhadap sel kekal mcf-7 oleh sebahagian fosfat myo-inositol separa tulen daripada dedak padi pada kepekatan <1000 mg/ml. perencatan mcf-7 hanya dilihat pada kepekatan lebih daripada 30 mg/ml dengan lebih daripada 40% sel terencat. ini menunjukkan bahawa fosfat myo-inositol daripada dedak padi separa tulen terdegradasi oleh fitat asuia279 terhadap sel kanser mcf-7 dimana ia menunjukkan keputusan positif terhadap perencatan tumbesaran sel kanser pada kepekatan tinggi. keywords:myo-inositol phosphates; phytase; mcf-7cell line; cancer iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 142 1. introduction phytate or myo-inositol hexakisphosphates (ip6) is widely distributed in plants, particularly in cereals and legumes, such as corn, soybean, wheat bran, rice bran, cotton seeds, rape seeds and soybean with a concentration range between 0.4% to 6.4% (w/w) and also in mammalian cells at concentrations of 10 µm to 1mm [1]. phytase (myoinositol hexakisphosphate phosphohydrolase) is a phosphomonoesterase that acts on phytate in sequential and stepwise manner, releasing inorganic orthophosphate (pi) and yielding partially phosphorylated myo-inositol phosphates which may again become substrates for further hydrolysis (fig. 1) [2]. it catalyzes the degradation of phytic acid into lower myo-inositol phosphates; pentakis(ip5), tetrakis(ip4), tris(ip3), bis(ip2), and mono phosphate/s (ip1); with the release of inorganic orthophosphate (pi) in sequential manner [3]. phytases are found naturally in plants and microorganisms, particularly fungi [4]. fig. 1: dephosphorylation of myo-inositol hexakisphosphate (phytate) by phytase. rice bran, the brown part of rice kernel, is a by-product of rice milling process, composed of seed coat, the major part of the germ, and most of the outer layer of the kernel together with some broken kernels [5]. due to highly nutritious content of fat, protein and vitamins, it has been used as animal feed in most part of the world. the bran constitutes about 8.5% of the whole grain [6]. current research interest is focused in utilizing this rice bran in many areas such as food, environmental, health and industrial purposes. in addition, rice bran also has been used as fermentation substrate for the production of enzymes such as lipase by candida sp. [7], in combination with cassava starch and rice hulls for the production of glucoamylase by aspergillus sp. [8], with wheat bran for the production of alkaline protease by trichoderma koningii [9] and also for the production of protease from rhizopus sp. [10]. the production of myo-inositol phosphate intermediates has received much attention due to the remarkable potential health benefits offered by the compounds [11]. myoinositol phosphates have potential applications in many fields including pharmaceutical research and development. myo-inositol (1,3,4,5,6) pentakisphosphate has an antiangiogenic and antitumour effects which are useful for anticancer therapeutic strategies [12]. some myo-inositol phosphates, including phytate, are present as intracellular molecules [13]. in addition, the second messenger d-myo-inositol (1,4,5) trisphosphate has a range of cellular functions including secretion, contraction, cell division, cell differentiation and cell death cell via mobilizing intracellular ca 2+ [13]. meanwhile, it is believed that d-myo-inositol (1,2,6) trisphosphate can prevent diabetes complications and treat chronic inflammations besides cardiovascular diseases [14]. furthermore, a study showed that a combination of inositol hexakisphosphate (ip6) and iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 143 inositol gave better inhibition in different cancers such as in soft tissue, colon, metastaticlung, and mammary cancers than was either one alone [15]. in this present work, anion-exchange chromatography was used to partially separate myo-inositol phosphates from the reaction mixturecontaining rice bran and asuia279 phytase. the partially purified myo-inositol phosphates were then subjected to a cytotoxicity test on mcf-7 cells. 2. materials and method 2.1 production of asuia279 phytase the cells of asuia279 [16] were grown in rice bran with distilled water under aseptic condition (ph 7, 37°c, 250 rpm, 60 hour incubation time). samples were withdrawn at time intervals, centrifuged at 12,000 rpm for 30 min, 16°c to remove the particulates and the supernatant kept at -20°c for further analysis. twenty milliliters of aliquot were collected and kept at -20°c for storage. 2.2 phytase assay phytase assay was performed according to [17] with minor modifications to measure the enzyme activity of phytase produced. it was measured in a mixture of 25 µl of 0.1 m sodium acetate buffer, ph 4.5 and 10 µl 1.03 mm sodium phytate in 200 µl microcentrifuge tube. enzyme (5 µl) was added to the mixtures to initiate reaction. the mixtures of the enzyme and buffer was incubated for 30 min at 50°c in block heater (sht 100d, stuart scientific). the released phosphate was quantified by ammonium molybdate method [18]. stop solution (150 µl) consists of acetone / 5n sulphuric acid / ammonium molybdate (2:1:1) was added to the assay mixture followed by 10 µl 1.0m citric acid. any cloudiness was removed by centrifugation (minispin®, eppendorf) at room temperature, 10, 000 rpm for 10 min prior to spectrophotometric measurement at 355 nm by micro plate reader, infinite® 200 pro series (tecan group ltd.). the phytase activity was expressed as 1 micromol of phosphate liberated per min (equation 3.1). (ε microplate = 0.3094 µ / m. cm; d depth of microplate for 200 µl solution = 0.59 cm; t = incubation time (min); abs355 = absorbance at 355 nm; vtotal = total volume of assay solution; venzyme = volume of enzyme used). enzyme total vtd vabs activity ××× × = ε 355 (1) 2.3 extraction of myo-inositol phosphates rice bran (donated by bernas tanjung karang, selangor darul ehsan) was used as a fermentation media for the production of bacterial phytase from local isolates, asuia279. the cell culture broth of asuia279 was grown in the presence of 10% w/v rice bran with distilled water under aseptic condition and ph 7, 37°c and 250 rpm. samples withdrawn from 0 hour until 72 hours were then centrifuged at 12,000 rpm for 30 min to remove particulates and the supernatant kept at -20°c for further analysis. 2.4 separation and recovery of myo-inositol phosphates ag1 x-4 (100-200 mesh) (biorad laboratories, usa) anion exchanger resin was packed in a glass column (2.5 x 30 cm) and equilibrated with distilled water. about 15 ml of the supernatant was loaded on to the column. three concentrations of hydrochloric acid (merck, germany) were used to elute the sample in a stepwise gradient; 0.1 m, 0.5 m, 1.0 iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 144 m. all collected samples were kept at 4°c. following thawing, solvent was removed by a rotary evaporator. the dried samples were diluted with a small amount of distilled water and further concentrated by a spin-concentrator. the completely dried residue (partially purified myo-inositol phosphate) was kept in a desiccator to avoid any reintroduction of moisture. the percentage yield of myo-inositol phosphates and myo-inositol phosphate intermediates eluted by three different concentration of hcl from asuia279were determined. ( ) 100 1 12 % × − = w ww yield (2) w1 = weight of centrifuge tube w2 = weight of centrifuge tube and dried sample 2.5 effects of myo-inositol phosphates on mcf-7 breast cancer cell line 2.5.1 preparation of standards and samples for mcf-7 tests six standard samples of myo-inositol phosphates were used as reference during the investigation (table 1). the standards were diluted in 1ml of 10% dmso. table 1: amount of myo-inositol phosphates standards used. standard concentration (stock solution) (g/ml) concentration (dilution) (µµµµg/ml) ip1 0.05 1000 ip2 0.0005 100 ip3 0.0025 500 ip4 5 x 10 -5 10 ip5 2.5 x 10 -4 50 ip6 0.125 1000 a small quantity of partially purified myo-inositol phosphates were dissolved in 1ml of 10% dmso to a maximum concentration (table 2). mcf-7 cells were cultured in dulbecco modified eagle medium (dmem) supplemented with 10% fetal bovine serum and the cell lines were maintained at 37˚c in a 5% co2 incubator and the media were changed twice weekly. 2.5.2 cancer inhibition assay: sulforhodamine b (srb) assay the srb assay was performed to assess growth inhibition based on colorimetric principles. this assay estimates cell number indirectly by staining total cellular protein with srb dye. briefly, 190 µ l/well of cell suspensions (seeding density of 2.0 x 10 4 cells per well) and 10 µ l/well myo-inositol phosphates of different concentrations (31.25 µ g/ml to 1000 µg/ml prepared in dmso, table 2) were seeded in 96-well microtiter plate. the 96-well plate was then incubated for 72 hours at 37ºc and 5% co2, to allow for cell attachment. without removing the cell culture supernatant, the cells were fixed with 100 µl of 10% (w/v) trichloroacetic acid at 4˚c for 1 hour and the supernatant was removed from the 96 well plates. the plate was then washed four times with slow running tap water iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 145 and excess water was removed using a blow dryer or just allowed to stand at room temperature. each well was stained for 30 min with 100 µl of 0.4% (w/v) srb dissolved in 1% acetic acid and washed four times with 1% acetic acid. the protein bound dye was solubilized with 200 µ l of 10 mmol/l tris base, ph 10.5. the absorbance (od) of each well was read on an elisa plate reader at 510 nm. percentage of control cell growth was calculated using the formula: % of cell growth = [mean od sample/mean od negative control]. a dose response curve was then plotted. negative control = 10% dmso. table 2: concentration of myo-inositol phosphates in dmso. sample aliquot (hour) eluent (hcl) concentration (molar, m) weight of myoinositol phosphates (µµµµg) concentration of myoinositol phosphates in 1 ml 10% dmso (µµµµg/ml) before inoculation 0.1 2500 2500 0.5 4000 4000 1.0 2800 2800 0 0.1 6100 6100 0.5 4600 4600 1.0 2600 2600 16 0.1 5800 5800 0.5 40300 40300 1.0 66800 66800 24 0.1 24400 24400 0.5 7700 7700 1.0 3900 3900 40 0.1 13000 13000 0.5 5700 5700 1.0 5500 5500 48 0.1 18300 18300 0.5 5000 5000 1.0 2300 2300 64 0.1 14300 14300 0.5 1500 1500 1.0 4400 4400 72 0.1 5600 5600 0.5 9400 9400 1.0 2500 2500 iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 146 3. results and discussion 3.1 analysis of myo-inositol phosphate obtained three different concentration of eluent: 0.1 m, 0.5 m and 1.0 m hcl (table 3) were used to elute the myo-inositol phosphates from ag1 x-4 resins. further, asuia279 was incubated and monitored for 72 hours. the highest yield of myo-inositol phosphates obtained is at 16 hours incubation time (fig.2) and then it started to decrease by time. it is known that during enzymatic phytate degradation, the hydrolysis rate decreased markedly [19]. this might be due to product inhibition by phosphate or a lower hydrolysis rate of the lower phosphate esters of myo-inositol. another factor is because of the conditions used during the hydrolysis reaction [20]. a very slow degradation also had been observed by van der kaay and van haastert [21] which is during degradation of myo-inositol trisphosphate intermediate and the missing capability to degrade the myo-inositol bisphosphate intermediate. table 3: percentage yield of myo-inositol phosphates and intermediates eluted by three different concentration of hcl from asuia279. sample aliquot (hour) eluent (hcl in m) weight of myo-inositol and its intermediates (µµµµg) yield (%) before inoculation (control) 0.1 0.0811 7.68 0.5 0.0495 4.69 1.0 0.045 4.26 0 0.1 0.1126 10.67 0.5 0.049 4.64 1.0 0.0516 4.89 16 0.1 0.0788 7.47 0.5 0.2009 19.03 1.0 0.02991 28.34 24 0.1 0.0681 6.45 0.5 0.0188 1.78 1.0 0.0111 1.056 40 0.1 0.1046 9.91 0.5 n.a* n.a* 1.0 0.0521 4.94 48 0.1 0.0785 7.44 0.5 0.0441 4.18 1.0 0.0047 0.45 64 0.1 0.1291 12.23 0.5 0.0435 4.12 1.0 0.0414 3.92 72 0.1 0.0546 5.17 0.5 0.149 14.17 1.0 0.0438 4.15 iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 147 0 5 10 15 20 25 30 yield (% ) before inoculation 16 40 64 incubation time (hour) 0.1m hcl 0.5m hcl 1.0m hcl fig. 2: fraction of myo-inositol phosphate intermediates separated by anion exchange chromatography from asuia279 by three different concentrations of hcl. since lower myo-inositol phosphates have less negative charge compared to higher myo-inositol phosphates, the lower myo-inositol phosphates (e.g. ip1, ip2, ip3) will be eluted earlier and easily by low concentration of hcl. meanwhile, higher myo-inositol phosphates (e.g. ip4, ip5, ip6) will be eluted by higher concentration of hcl. moreover, the effective charges of myo-inositol phosphates (e.g. ip5 and ip6) will be decreased if the acidity of eluent is increasing, which proves the existence of ion suppression mechanism in eluent [22]. the higher the effective charge of the analyte, the longer the retention time of the ips, and this is also applicable to the isomers. the fluctuated reading of the yield might be caused by the insufficient elution of the myo-inositol phosphates or weaker binding of the phytate to the anion exchanger resin [23]. 3.2 the effects of myo-inositol phosphates to mcf-7 breast cancer cell line a novel anticancer function of inositol hexaphosphate (ip6) has been shown both in vivo and in vitro [24]. commonly, most research about inhibition of cancer cells growth were focused on ip6 and applied in various cell lines including human leukemia cells [25], human colon cancer cells [26], both estrogen receptor-positive and estrogen receptornegative human breast cancer cells [27], laryngeal carcinoma [28], cervical cancer [29], prostate cancer [30], hepatoma [31], pancreatic [32] and melanoma cell line [33]. due to a limited amount of standards available, different concentration of sample was used. as can be observed from the experiment, multi well plate that contain ip6 and ip1 immediately change to yellow colour after exposure of cell to the solution containing myoinositol phosphates. in consequence, highest concentration of ip1 and ip6 showed good inhibition towards the mcf-7 cell line (fig. 3). this showed that ip6 supported by vucenik and shamsuddin [15] , and ip1 efficiently inhibit the cancer cell growth. based on the observation, minimum concentration of myo-inositol phosphates (<1000 µ g/ml) contributed minimum inhibition against the growth of mcf-7 cell line. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 148 fig. 3: optical density of six standards of myo-inositol phosphates measured at 510 nm. the next step is to study the inhibition of partially purified myo-inositol phosphates extracted from rice bran towards the mcf-7 cell line. table 2 listed the concentration of myo-inositol phosphates used in this study. prior to that, a serial dilution of samples ranges from 62.5 µ g/ml to 1000 µg/ml were applied to mcf-7 cell line. nevertheless, no significant changes had been observed throughout the experiment. once again, lower concentration (<1000 µg/ml) of partially purified myo-inositol phosphates were not capable to inhibit the growth of mcf-7 cell line. since rice bran only has 4% of phytate content [34] compared to pure phytate, it is relevant if 1000 µ g/ml was not efficiently inhibit the growth of mcf-7 cells as the standard of ip1 and ip6. theoretically, in 1ml of sample, about 0.04 fractions were myo-inositol phosphates. the insufficient amount of myo-inositol phosphates used before, leads us to use larger amount of myo-inositol phosphates which diluted in 10% dmso (table 2). the srb assay was then carried out and measured by microplate reader at 510 nm. figure 4 illustrated the percentage of growth for mcf-7 cells after applied by partially purified myo-inositol phosphates. the minimum amount of observed optical density indicated the inhibition of mcf-7 cells growth in the mixture. two samples showed positive results supporting this conclusion. a decrement of growth had been observed for samples at 16 hour incubation time for 0.5m and 1.0m elution of hcl respectively. the highest concentration contained in both samples proved that the growth of mcf-7 cells really can inhibit by partially purified myo-inositol phosphates. according to statement by adachi et al. [34], about 1.612 mg/ml and 2.672 mg/ml of phytates content in both samples, respectively. however, for samples containing less than 30mg/ml of partially purified myo-inositol phosphates showed none or minimum inhibition of mcf-7 cells growth. moreover, throughout the analysis, more than 40% inhibition of mcf-7 cells had been observed by partially purified myo-inositol phosphates extracted from rice bran. about 44.6% and 46.6% of inhibitions had been calculated for both 0.5m and 1.0m elution of hcl at 16 hour incubation time of asuia279. mostly, myo-inositol phosphates consist of ip3, ip4, ip5 and ip6 were in both samples and able to inhibit the mcf-7 cells growth. ip6 inhibited the growth of cancer cell lines in a doseand time-dependent manner, irrespective of whether they were epithelial or mesenchymal in origin [35]. moreover, the anticancer activity of ip6 is a result of its rapid intake by tumor cells was shown when mcf-7 human breast cancer cells were incubated with [ 3 h]-ip6. as early as 1 minute after incubation, 3.1% of ip6-associated radioactivity was taken up by mcf-7 cells iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 149 and 9.5% after 1 hour. anion-exchange chromatography showed that 58% of the absorbed radioactivity was in ip6 form, indicating that externally applied ip6 enters the cells followed by dephosphorylation. however, ip4 appeared to be a predominant metabolite of ip6, which possibly might have important role in its anticancer activity [35]. shamsuddin and vucenik [36] cited that ip6 also was used to enhance the anti-proliferative effects of tamoxifen and adriamycin to mcf-7 cells line. as a whole, ip6 and its metabolites can differentially inhibit the proliferation of cancer cells without affecting the normal cells, inhibit cell proliferation of cancer cells irrespective of their hormonal receptor status and individual ip6 metabolite(s) or combinations could be specifically effective against specific cancers, thereby increasing the chances of successful therapy [34]. fig. 4: percentage of mcf-7 cells growth after treated with partially purified myoinositol phosphates from three different elution concentration of hcl at different incubation time. 4. conclusion as a conclusion, the application of partially purified rice bran myo-inositol phosphates degraded by asuia279 to mcf-7 breast cancer cells exhibit positive results towards the inhibition of cancer cells growth with more than 40%. therefore, through this research findings, a promising value-added product can be obtained from low cost and easily available raw material, rice bran, via hydrolysis reaction by phytase. acknowledgements this research work is funded by sciencefund research project (sf 0106-03), ministry of science, technology and innovation (mosti), malaysia. special thanks to sirim berhad for providing samples as well as to all who had contributed directly or indirectly in this research. references [1] a. m. shamsuddin, “metabolism and cellular functions of ip6: a review”, iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 150 anticancer res, vol. 19, pp. 3733 – 3736, 1999. [2] r. greiner, a. farouk, n.g. carlsson and u. konietzny, “myo-inositol phosphate isomers generated by the action of a phytase from a malaysian waste-water bacterium”, protein j. doi: 10.1007/s10930-007-9100-5, 2007. [3] t. hayakawa, k. suzuki, h. miura, t. ohno and i. igaue, “myo-inositol polyphosphate intermediates in the dephosphorylation of phytic acid by acid phosphatase with phytase activity from rice bran”, agric. biol. chem., vol. 54 (2), pp. 279-286, 1990. [4] m. wyss, r. brugger, a. kronenberger, r. remy, r. fimbel, g. oesterhelt, m. lehmann, and l. apgm. van, “biochemical characterization of fungal phytases (myo-inositol hexakisphosphate phosphohydrolases: catalytic properties”, appl. environ mirobiol, vol. 65, pp. 367-373, 1999. [5] j. r. loeb, n. j. morris and f. g. dollear, “rice bran oil. iv. storage of the bran as it affects hydrolysis of the oil”, the journal of the american oil chemists’ society, pp. 738 – 743, 1949. [6] m. c. kik and r. r. williams, bull. nat.res. council., vol. 112, pp. 30-36, 1945. [7] p. v. rao, k. jayaraman, and c. m. lakshmanan, “production of lipase by candida rugosa in solid-state fermentation. 1: determination of significant process variables”, process biochem., vol. 28, pp. 385-389, 1993a. [8] y. tani, v. vongsuvanlert, and j. kumnuanta, “raw cassava starch-digestive glucoamylase of aspergillus sp. n-2 isolated from cassava chips”, j. ferment. technol., vol. 64, pp. 405410, 1986. [9] h. k. manonmani and r. joseph, “purification and properties of an extracellular proteinase by trichoderma koningii”,enzyme microb. technol., vol. 15, pp. 624-628, 1993. [10] a. sumantha, p. deepa, c. sandhya, g. szakacs, c. r. soccol and a. pandey, “rice bran as a substrate for proteolytic enzyme production”, brazilian archives of biology and technology, vol. 49 (5), pp. 843-851, 2006. [11] r. greiner, a. farouk, m. l. alminger and n.g. carlsson, “the pathway of dephosphorylation of myo-inositol hexakisphosphate by phytate-degrading enzymes of different bacillus spp.”, can. j. microbiol, vol. 48, pp. 986 – 994, 2002. [12] t. maffucci, e. piccolo, a. cumashi, m. iezzi, a. m. riley, a. saiardi, h. y. godage, c. rossi, m. broggini, s. iacobelli, b. v. l. potter, p. innocenti and m. falasca, “inhibition of the phosphatidylinositol 3-kinase/akt pathway by inositol pentakisphosphate results in antangiogenic and anti-tumour effects”, cancer res, vol. 65, pp. 8339 – 8349, 2005. [13] s. b. shears, “the versatility of inositol phosphates as cellular signals”, biochim biophys acta, vol. 1436, pp. 49-67, 1998. [14] a. l. carrington, n. a. calcutt, c. b. ettlinger, t. gustafsson, and d. r. tomlinson, “effects of treatment with myo-inositol or its 1,2,6-trisphosphate (pp56) on nerve conduction in streptozotocin-diabetes”. eur j pharmacol, vol. 237, pp. 257 – 263, 1993. [15] vucenik and a. m. shamsudin, “cancer inhibition by inositol hexaphosphate (ip6) and inositol : from laboratory to clinic”, journal of nutrition, vol. 133, pp. 3778s-3784s, 2003. [16] anis shobirin, m. h., farouk, a., greiner, r., salleh, h. m. and ismail, a. f. “phytatedegrading enzymes production by malaysian soil bacteria”. world journal of microbiology and biotechnology 23, 1653-1660, 2007. [17] r. greiner, u. konietzny and k-d. jany, “purification and characterization of two phytases from escherichia coli”. arch. biochem. biophys., vol. 303, pp. 107-113, 1993. [18] j. k. heinonen and r. j lahti, “a new and convenient colorimetric determination of inorganic orthophosphate and its application to the assay of inorganic pyrophosphatase”, anal biochem, vol. 113, pp. 313-317, 1981. [19] u. konietzny, r. greiner, and k-d. jany, “purification and characterization of a phytases from spelt”, j. food biochem, vol. 18, pp. 165-183, 1995. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd. yusoff et al. 151 [20] r. greiner, k-d. jany, and m. larsson alminger, “identification and properties of myoinositol hexakisphosphate phosphohydrolyses (phytases) from barley (hordeum vulgare)”. j. cereal. sci., vol. 31 (2), pp. 127-139, 2000a. [21] j. van der kaay and j. m. van haastert, “stereospecificity of inositol hexaphosphates dephosphorylation by paramecium phytase”, biochem. j., vol. 312, pp. 907-910, 1995. [22] q. c. chen and b. w. li, “separation of phytic acid and other related inositol phosphates by high performance ion chromatography and its applications”, journal of chromatography a, vol. 1018, pp. 41-52, 2003. [23] m. y. noraini, m. s. hamzah, and j. parveen, “degradation of phytate in rice bran by local bacteria phytase”, proceeding of icce-2009, special issue of research journal of chemistry and environment, pp. 361-365, 2009. [24] a. m. shamsuddin, “inositol phosphates have novel anticancer function”, j. nutr, vol. 125, pp. 725s–732s, 1995. [25] g.l. deliliers, f. servida, and n.s. fracchiolla, “effect of inositol hexaphosphate (ip6) on human normal and leukaemic haematopoietic cells”, br j haematol, v ol. 117, pp. 577587, 2002. [26] l. weglarz, b. parfiniewicz, a. orchel, and z. dzierzewicz, “antiproliferative effects of inositol hexaphosphate and verapamil on human colon cancer caco-2 and ht-29 cells”, acta poloniae pharm, vol. 63, pp. 443-445, 2006. [27] a. m. shamsuddin, i. vucenik, and k. e. cole, “ip6: a novel anticancer agent”, life sc., vol. 61, pp. 343–354, 1997. [28] m. dorsey, h. benghuzzi, m. tucci, and z. cason, “growth and cell viability of estradiol and ip6 treated hep-2 laryngeal carcinoma cells”, biomed sci instrum, vol. 41, pp. 205-210, 2005. [29] s. ferry, m. matsuda, h. yoshida, and m. hirata, “inositol hexakisphosphate blocks tumor cell growth by activating apoptotic machinery as well as by inhibiting the akt/nfkappabmediated cell survival pathway”, carcinogenesis, vol. 23, pp. 2031-2041, 2002. [erratum appears in carcinogenesis. 2003 jan; 24(1): 149]. [30] x. zi, r.p. singh, and r. agarwal, “impairment of erbb1 receptor and fluid-phase endocytosis and associated mitogenic signaling by inositol hexaphosphate in human prostate carcinoma du145 cells”, carcinogenesis, vol. 21, pp. 2225-2235, 2000. [31] i. vucenic, a. passaniti, m. i. vitolo, k. tantivejkul, p. eggleton and a. m. shamsuddin, “anti-angiogenic activity of inositol hexaphosphate (ip6)”, carcinogenesis, vol. 25 (10), pp. 1-9, 2004. [32] b. mcmillan, d.r. riggs, b.j. jackson, c. cunningham, and d.w. mcfadden, “dietary influence on pancreatic cancer growth by catechin and inositol hexaphosphate”, j surg res, vol. 141, pp. 115-119, 2007. [33] i. rizvi, d.r. riggs, b.j. jackson, a. ng, c. cunningham, and d.w. mcfadden, “inositol hexaphosphate (ip6) inhibits cellular proliferation in melanoma”, j surg res, vol. 133, pp. 36, 2006. [34] a. adachi, y. yatani, and t. okano, “utilization of rice bran to prevent bulking in the activated sludge process”. journal of health sciences, vol. 51 (5), pp. 549-556, 2005. [35] a. matejuk and a. shamsuddin, “ip6 in cancer therapy : past, present and future”, current cancer therapy reviews, vol. 6 (1), pp. 1-12, 2010. [36] a.m. shamsuddin and i. vucenik, “ip6 & inositol in cancer prevention and therapy”, current cancer therapy reviews, vol. 1, pp. 259-269, 2005. microsoft word 229-1019-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 185 process simulation and quality evaluation of incremental sheet forming salah b. m. echrif and meftah hrairi mechanical engineering department, international islamic university malaysia p.o. box 10, 50728 kuala lumpur, malaysia. meftah@iium.edu.my abstract: single point incremental forming (spif) is a promising sheet-metalforming process that permits the manufacturing of small to medium-sized batches of complex parts at low cost. it allows metal forming to work in the critical ‘necking-totearing’ zone which results in a strong thinning before failure if the process is well designed. moreover, the process is complex due to the number of variables involved. thus, it is not possible to consider that the process has been well assessed; several remaining aspects need to be clarified. the objective of the present paper is to study some of these aspects, namely, the phenomenon of the wall thickness overstretch along depth and the effect of the tool path on the distribution of the wall thickness using finite element simulations. abstrak: pembentukan tokokan mata tunggal (single point incremental forming (spif)) merupakan satu proses pembentukan kepingan logam yang membolehkan pembuatan dalam jumlah yang kecil hingga sederhana, bahagian-bahagian yang kompleks pada kos yang rendah. jika proses ini direka dengan baik, kaedah ini membolehkan pembentukan logam yang baik terhasil. jika tidak, semasa peringkat zon kritikal ‘perleheran-ke-pengoyakan’ menyebabkan penipisan keterlaluan yang boleh menyebabkan logam tersebut rosak. tambahan pula, proses ini agak kompleks, kerana ia melibatkan beberapa pemboleh ubah. maka, walaupun proses ini telah dinilaikan seeloknya; masih terdapat beberapa aspek lain yang perlu diperjelaskan. objektif kertas ini dibentangkan adalah untuk mengkaji beberapa aspek tertentu, seperti, ketebalan dinding regangan berlebihan di sepanjang kedalaman dan kesan tool path (beberapa siri posisi koordinat untuk menentukan pergerakan alatan memotong ketika operasi memesin) terhadap pengagihan ketebalan dinding menggunakan simulasi unsur terhingga. keywords: incremental sheet forming; finite element method; ls-dyna; alumunium; thickness distribution 1. introduction nowadays, many industrial sections use forming processes like deep drawing and stamping in order to manufacture sheet metal components with high productivity. these processes need large initial investments and long die-preparation times, with specific dies for each part, particularly when the parts have complex shapes or are only needed in small series, as is the case with unique aeronautic and automotive parts. therefore, there is a need for a flexible technology that is also viable for small and medium-sized iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 186 enterprises. incremental sheet forming (isf) is a new process for manufacturing sheet metal parts which is well suited for small batch production or prototyping [1, 2]. in order to use this process on a large scale, some aspects of the process need to be further clarified. therefore, the objective of this paper is to investigate the use of the finite element (fe) method to predict thickness and stress distribution on the sheet during forming in order to improve the knowledge o f the isf process. the remainder of this paper is structured as follows: an overview of the incremental sheet forming process is given in section 2. the limitations of the process are addressed in section 3. section 4 elaborates the process formability analysis in this simulation based investigation and the finite element results are reported in section 5. drawn conclusions are contained in section 6. 2. overview of the isf process incremental sheet forming is relatively a new process capable of producing complex sheet parts by the movement of a single point tool mounted on a standard 3-axis cnc machine without dedicated dies as shown in fig. 1. in order to avoid excessive thinning for parts having almost straight wall angles (wall angles greater than 60°), multistage forming strategies have to be used [3]. compared to traditional sheet forming processes, the single point incremental forming (spif) process enables much higher strains. when spif is applied to single stage formations, it is limited by deformation types that are near the strain plane. fig. 1: incremental sheet metal forming process [4]. existing experimental configurations for incremental forming can be put into two general types: negative and positive incremental forming. negative die-less incremental forming, also known as single point incremental forming (spif) as illustrated in fig. 2, is the first form of incremental forming. iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 187 single point incremental forming was developed in recent years as an innovative numerically controlled sheet metal forming technology [5 , 6 ]. for small batches, as small as a single exemplar, it is a very economical process. fig. 2: single point incremental forming (spif) [7]. many application fields are considering this innovative technology, among them are automotive manufacturing [8], manufacturing of customized medical products [9], and automotive sheet metal forming, specifically the calibration of the void nucleation model [10]. the process is categorized as ‘‘negative and positive incremental forming’’ [11]. localized deformation [12] is a key feature of this technology because it enhances sheet-metal formability. for incremental forming, the forming limit diagram has a limit curve that is a straight, negative slope line within the stretching region [13, 14]. as shown in fig. 3, the blank is firmly clamped to the fixture. the tool used to form can be programmed in the three axes of translation along with spindle rotation. the form-giving tool representing the required shape remains stationary throughout the process. using a suitable tool path strategy, the forming tool moves around the formgiving tool, from top to bottom. it covers the component level by level, in the predefined vertical increments, in contact with the blank and incrementally deforming the blank until the desired shape has been formed. thus, a cnc controlled movement of a universally usable forming tool produces the desired shape. fig. 3: the working principle of spif [15]. iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 188 3. limitations of incremental forming the final thickness of a part formed by spif can be estimated using the sine-law. this law was originally developed for the shear forming process and simply states that:          2 sin01 tt (1) where t0 is the initial thickness, t1 the final thickness, and α the wall-angle measured with respect to the horizontal. this law is illustrated in fig. 4; it describes the thickness distribution well and shows that parts with drawing angles greater than 60-80° in one stage are not achievable. fig. 4: prediction of the thickness in spif using the sine law [16]. the sine law is based on the fact that the material is approximately in a plane strain state in the direction of the tool movement and is only able to move vertically toward its final position when starting from a horizontal flat sheet. as shown in fig. 4, the comparison between the measured thickness and the one predicted by the sine law is very good. a direct consequence of the sine law is that the thickness decreases as the angle increases, as illustrated in fig. 5. in particular, the theoretical thickness of a part wit h vertical walls would be zero. the wall angle is a major limitation of spif [17]. the limitation in the maximum wall angle is only valid for parts formed in one pass, i.e., when the tool follows the shape of the final geometry. other strategies have been developed to overcome this limitation. using a mult i stage strategy is one way to circumvent the limitations imposed by the sine-law. using such a strategy has been attempted before in spif. kitazawa [19] used various two stage strategies in the production of hemi ellipsoidal shapes, while varying the radius and height of the shape in order to determine the fracture limits. here, the intent is to extend deformation across all the material indicated by the curved lines and then to identify the effect of the said extension. the first stage stretches the sheet until the end of the part depth. the next stages gradually shift the middle of this section towards the corner. iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 189 fig. 5: thickness reduction in spif as predicted by the sine law [18]. 4. formability analysis areas requiring more investigation remain within the isf research field. two such areas are material formabilit y and a complete understanding of process mechanics. with respect to process knowledge, many improvements have been introduced in the form of simple laws suited to industrial use. from the literature review [20, 21], primarily, two parameters are used to classify the process formability, namely:  the α max, representing the maximum wall slope angle at which the part can be manufactured without damage;  the fld0 point, corresponding to the intersection of the flc and the major strain axis. sadly, the complexit y of the process creates recognizable drawbacks based on those same two parameters. firstly, both parameter values depend directly on the process parameters that were adopted so that they cannot describe the whole process synthetically. secondly, while α max is an easier parameter to work with industrially, it only provides a partial description of the overall process feasibility. in fact, there have been applications where parts with complex geometries and variable slope walls were successfully manufactured with angles greater than the critical angle, despite the presence of angles greater than critical angle [22]. 5. simulation and results incremental forming processes can be simulated by a series of steps including:  building cad models (support, tool blank, , part with desired shape);  generating tool-paths for controlling the tool movement;  building finite element model, applying boundary conditions, defining material properties, contact parameters etc;  solving model, post processing. iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 190 the second step, tool-path generation, may not be necessary for the simulation of forming processes on metals. however, when simulating incremental forming, tool path generation will create a pre-defined trajectory for the tool. for simple cases, the tool path can be generated using a simple spreadsheet program. for more elaborate forms, as in the current study, a (cad/cam) computer automated manufacturing system (catia) is used. finite element analysis of the metal forming step was performed to avoid the possibility of multiple trials and errors and therefore save costs and time. in this work, the spif process was simulated using ansys/ls-dyna version ls971s. the forming tool and the backing plate are set as rigid. five integration points are used for the thickness simulation of fully integrated shells (type 16 in dyna). adaptive re-meshing is adopted. the simulated tool movement matches real experiments including aspects such as rotation. aluminum aa1050 h111/o is used as sheet metal and it is considered isotropic with a flow stress. the coulomb friction coefficient was assumed to be equal to 0.1. forming tools with a semi-spherical tip have a radius of 6 mm. 5.1 depth overstretch first and second stages have a fixed vertical step size of 0.5 mm. figure 6 shows the geometries used in both stages with h = 82.5 mm and r = 82.5 mm. fig. 6: two-stage strategy for forming a cup. an undesirable phenomenon was observed during simulation. in the second forming stage, a small plateau was formed below the tool as it moved downward. as a result, a residual cone was formed in the bottom of the cup. the defect is created as the depth of the cup was increased during the second stage but the tool path remained at 82.5 mm. the residual cone can be seen in fig. 7, and it was measured to be approximately 20 mm too deep. to avoid the stretch downwards and to get the desired depth a small un-deformed section remains in the first stage with depth of 40 mm whereas the part is fully deformed in the second stage until the depth of 82.5 mm as shown in fig. 8. iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 191 5.2 wall thickness reduction it is found that sheet metal formability is dependent on slope along the bottom (depth) of the fabricated part. if the slope changes along the depth, then the shell thickness is reduced at a faster rate than a case with a fixed slope. forming process has been simulated using five stages as shown in fig. 9. the first three stages have fixed slope. the first stage has forming angle of 20° with depth of 20 mm whereas the second stage has an angle of 30° with depth of 40 mm. fig. 7: residual cone in the center. fig. 8: modified two stage strategy for forming the cup. iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 192 fig. 9: five stage forming process. the depth of the third stage has 60 mm with forming angle of 40°. starting from the fourth stage the forming tool goes down 80 mm with parabolic curve and the last stage with circular curve and 82.5 mm deep. among varying slope parts (formed with a curved line) those that were formed with parabolic trajectories (4th stage) exhibited the best forming limits of the sheet-metal without sharp reduction of the sheet thickness as shown in fig. 10. the parabolic curve parts had consistently higher thinning limits and forming angle limits than those wit h any form of constant forming angles or slopes. as a result, parts with varying slope can be formed without making the wall thickness very thin. on the other hand, part s wit h fixed slopes along the depth cause sharp thinning along wall thickness. moreover, switching from fixed slope to varying slope reduces the thinning of the sheet and the possibility of having crack. figure 11 shows the relation between the thickness and the depth of the formed part. most of the thinning occurs at the center of the part where there is a low drawing angle, which is necessary in order to achieve vertical sides in subsequent stages. iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 193 fig. 10: wall thickness distributions as function of time. fig. 11: thickness as a function of depth. theoretically, the dependence between the sheet metal’s formabilit y and the slope distribution used to create it can be shown. for two parts, one with variable slope as described in fig. 12a and another with a fixed slope as described in fig. 12b, both created by incremental forming. the resultant forming force is denoted by f, and the instantaneous position of the tool is denoted by n. in the case of the variable slope (fig. 12a), the component force fsinθ is acting on a subset of the mn curve, called segment ln. in the case of the fixed slope (fig. 12b), the entire mn curve undergoes the same component force fsinθ. the constant force weakens the mn segment far more than the iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 194 changing forces in the first case. correspondingly, the constant force causes greater thinning within the walls of the part. fig. 12: forming forces required to form: (a) parts with varying slope and (b) parts with fixed slope along depth. [23]. 6. conclusion when incremental forming techniques are applied to sheet metals, formabilit y is dependent on the slope distribution during the formation of a part. a variable slope along the depth of the part has a great effect on the wall thickness, or in other words it depends upon how the forming of the sheet changes during the process from fixed slope to varying slope to minimize the thinning of the sheet. thus, such mechanism can enhance the dimensional accuracy and delay the fracture. consequently, this will give the chance to form the sheet in a high forming angle such as 90°. references [1] e. hagan; j. jeswiet, “a review of conventional and modern single-point sheet metal forming methods”. proceedings of the institution of mechanical engineers, part b: journal of engineering manufacture 2003, 217 (2), 213–225. [2] g. hussain; l. gao; n. hayat,; x. ziran, “a new formability indicator in single point incremental forming”. journal of materials processing technology 2009, 209, 4237–4242. [3] g. hirt, j. ames, m. bambach, r. kopp, “forming strategies and process modelling for cnc incremental sheet forming”. annals of the cirp 52(1):203–206 (2004). [4] jr. duflou, b. lauwers, j. verbert, “study on the achievable accuracy in single point incremental forming”. advanced method in material forming 2007, 252-262. [5] t. maki, “sheet fluid forming and sheet dieless nc forming”. amino corporation, japan. [6] s. matsubara, “incremental backward bulge forming of a sheet metal with a hemispherical head tool”. journal of jstp 1994, 35:1311. iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 195 [7] j. jeswiet, f. micari, g. hirt, a. bramley, a. duflou, j. allwood, “asymmetric single point incremental forming of sheet metal”. cirp annals-manufacturing technology 2005, 54: 88114. [8] h. amino, y. lu, s. ozawa, k. fukuda, t. maki, “dieless nc forming of automotive service panels”. in proceedings of the conference on advanced techniques of plasticity; 2002: 1015– 1020. [9] g. ambrogio, l. de napoli, l. filice, f. gagliardi, m. muzzupappa, “application of incremental forming process for highly customized medical product manufacturing”, journal of materials processing technology 162–163 (2005) 156–162. [10] w.b. livers, a.k. pilkey, d.j. lloyd, “using incremental forming to calibrate a void nucleation model for automotive aluminum sheet alloys”, acta materialia 52 (2004) 3001–3007. [11] j.-j. park, y.-h. kim, “fundamental studies on the incremental sheet metal forming technique”, journal of materials processing technology (2003) 447–453. [12] h. iseki, “an approximate deformation analysis and fem analysis for the incremental bulging of sheet metal using spherical roller”, j. mater. process. technol. 111 (2001) 150. [13] h. iseki, h. kumon, “forming limit of incremental sheet metal stretch forming using spherical rollers”, j. jstp 35 (1994) 1336. [14] m.s. shim, j.-j. park, “the formability of aluminum sheet in incremental forming, j. mater. process”. technol. 113 (2001) 654. [15] j. jeswiet, f. micari, g. hirt, a. bramley, a. duflou, and j. allwood, “asymmetric single point incremental forming of sheet metal”, cirp annals-manufacturing technology 54(2), 2005, pp. 88-114. [16] g. hirt, s. junk, and n. witulski. “incremental sheet forming: quality evaluation and process simulation”. in proc. of the 7th ictp conference, vol. 1, pp. 925_930, 2002. [17] j. r. duflou, j. verbert, b. belkassem, j. gu, h. sol, c. henrard, and a. m. habraken. “process window enhancement for single point incremental forming through multi-step toolpaths”. cirp annals _ manufacturing technology 57 (2008), pp. 253_256. [18] c. henrard, “numerical simulations of the single point incremental forming process”, phd thesis, november 2008, university of liège. [19] k. kitazawa , , m. nakane, “hemi-ellipsoidal stretch-expanding of aluminum sheet by cnc incremental forming process with two path method”, keikinzoku/journal of japan institute of light metals, 47, (1997), 440-445, (in japanese). [20] h. iseki, “an experimental and theoretical study on a forming limit curve in incremental forming of sheet metal using spherical roller”, in: proc. metal forming, (2000), 557-562. [21] l. filice, l. fratini, f. micari, “analysis of material formability in incremental forming”, annals of the cirp, 51/1, (2002) 199-202. [22] g. ambrogio, l. de napoli, l. filice, f. gagliardi, m. muzzupappa, “application of incremental forming process for high customized medical product manufacturing”, journal of materials proc. tech., vol. 162-163, (2005), 156-162. [23] g. hussain, l. gao, “a novel method to test the thinning limits of sheet metals in negative incremental forming”, international journal of machine tools & manufacture 47 (2007) 419– 435. iium engineering journal, special issue, mechanical engineering, 2011 echerif and hrairi 196 nomenclature isf incremental sheet forming spif single point incremental forming cad computer added design cam computer added manufacturing fld forming limit diagram flc forming limit curves cnc computer numerical controller application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 a new hardware architecture for highperformance parallel turbo decoder sujatha elukuru1*, subhas chennapalli2 and giriprasad mahendra nanjappa2 1 department of electronics and communications, sree vidyanikethan engineering college, andhra pradesh, india. 2 department of electronics and communications, jntua college of engineering, andhra pradesh, india. * corresponding author: sujathaece88@gmail.com (received: 1st january 2022; accepted: 26th march 2022; published on-line: 4th july 2022) abstract: recent wireless communications demand maximum achievable data rates without intervention. the channel decoder in the physical layer would support such high data rates with a flexible hardware structure. the turbo channel decoder offers flexible hardware architecture and reliable decoding, but the turbo decoder design is complex, and its hardware architecture consumes more power and area in a communication system. hence, an optimized high-performance turbo decoder architecture with simplified qpp interleaver is needed for supporting various data rates. in this context, this article presented a new hardware architecture with a three-stage pipeline parallel turbo decoding process and each map decoder in the proposed parallel turbo decoder with a three-stage micro pipeline process. the proposed structure optimized the circuit complexity and improved the throughput through parallel pipeline decoding process. also, this article presents a simplified semi-recursive qpp interleaver, which avoids complex ‘mod’ operations for a high-performance turbo decoder. the performance analysis has been done using model sim, xilinx vivado design suite, and estimated performance analysis was observed on various 28 nm cmos technology fpgas and compared with the conventional designs. analysis of the proposed design showed improvement throughput up to 55.6% and a reduction in the power consumption up to 43% as compared to the recently reported architectures. abstrak: komunikasi tanpa wayar terkini menuntut kadar data maksimum yang boleh dicapai tanpa intervensi. penyahkod saluran dalam lapisan fizikal akan menyokong kadar data yang tinggi dengan struktur perkakasan fleksibel. penyahkod saluran turbo menawarkan seni bina perkakasan fleksibel dan penyahkodan yang boleh dipercayai. tetapi, penyahkod turbo merupakan blok yang kompleks, lebih berkuasa dan menggunakan kawasan yang luas dalam sistem komunikasi. oleh itu, seni bina penyahkod turbo optimum berprestasi tinggi dengan antara lembar qpp yang mudah diperlukan bagi menyokong pelbagai kadar data. dalam konteks ini, kajian ini merupakan seni bina perkakas baru dengan proses penyahkod turbo selari bersama salur paip tiga peringkat dan setiap penyahkod map yang dicadangkan dalam penyahkod turbo selari bersama proses saluran paip mikro tiga peringkat dibentangkan. struktur yang dicadangkan dapat mengurangkan kerumitan litar dan meningkatkan daya pemprosesan melalui penyahkodan saluran paip selari. selain itu, kajian ini merupakan antara lembar mudah qpp rekursif, yang dapat mengelakkan operasi 'mod' yang kompleks bagi penyahkod turbo berprestasi tinggi. analisis prestasi telah dilakukan menggunakan sim model, reka bentuk suit xilinx vivado, dan analisis prestasi anggaran telah diperhatikan pada pelbagai teknologi fpga cmos 28 nm dan dibandingkan dengan reka bentuk konvensional. analisis reka bentuk 125 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 yang dicadangkan menunjukkan peningkatan sepanjang 55.6% dan pengurangan penggunaan kuasa sehingga 43% berbanding seni bina laporan terkini. keywords: turbo decoder; map decoder; vlsi; interleaver; fpga 1. introduction channel coding techniques are essential for a wireless communication system to achieve a reliable and high-performance transmission between transmitter and receiver, in a noisy channel. state-of-the-art iterative channel codes such as turbo codes [1], lowdensity parity-check codes (ldpc) [2], and polar codes [3] are often used. turbo codes offer more flexible architecture for their encoder and decoder than ldpc and polar codes. also, turbo codes achieve high diversity, reliable data transmission, and possible large coding gain in fading channels. the efficient-hardware implementation of turbo codes, in order to meet real-time constraints, is an active area of research and there is a need for innovation in the vlsi design of high-performance turbo decoders in terms of throughput, silicon area, and powerefficiency as well. hence, the present study is aimed at developing a high-throughput, low area, and low power turbo decoder by modifying the hardware architecture of the decoder, simplifying mathematical computations involved in the decoding and interleaving process, and applying the optimization techniques. maximum a-posteriori probability (map) algorithm introduced by bahl-cocke-jelinek-raviv (bcjr) [4] for siso decoders and the simplifications of map algorithm called log-map and max-log-map [5] were studied and max-log-map algorithm is adopted in the design and hardware implementation of the proposed turbo decoder due to its lower complexity than the log-map algorithm. to improve the throughput performance of the turbo decoder, the number of map decoders could be increased and all operated in parallel at the cost of degradation in errorcorrecting performance, especially with higher code rates. moreover, employing multiple decoders to increase the throughput does not solve the additional challenge of lower latency requirements. the throughput could also be increased by increasing the block size (from 40 to 6144), but this would result in consequent complexities in computational latency, area requirement, and power consumption. the trade-off among the performance parameters could be best compromised by effective hardware design and suitable optimization techniques [6]. interleaver is an essential part of turbo decoder and is also responsible for ber performance of decoding. the algebraic properties and contention-free property of qpp interleaver [7] guarantee contention-free access to memory and generated addresses. also, one of the problems in the implementation of highly parallel decoders is memory contention during decoding, where all the sub-block of map decoders simultaneously tries to access the same memory bank on reading or writing the extrinsic information from or into it. to solve this problem, an efficient approach of collision-free parallel interleavers in which data is read or written on the intra-sub block as well as inter-sub block of map decoder to achieve low complexity architecture having no additional hardware resources. some benchmarked research works on high throughput turbo decoders were discussed here. a high throughput turbo decoder with 8 and 64 parallel radix-2 map decoder architecture in 90 nm cmos technology was proposed [8]. this paper proposed a new ungrouped backward recursion scheme and a new state metric normalization technique to offer retiming and pipelining in architecture for performance improvement. also, this work adopted a fine-grain clock gating technique to solve the power issue and the throughput achieved is 301 mbps at 272 mw of power. a highly parallel turbo decoder structure in 126 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 2015 was reported [9] to achieve the highest throughput rate of 1.45 gbps implemented in 90 nm cmos technology. this work was aimed at improving the decoding efficiency and this improvement was possible by modifying the parallel window map decoding algorithm. a fully parallel turbo decoding [fptd] algorithm was reported [10] which allows parallel processing to offer higher processing throughput. this novel fptd algorithm reduced computational complexity by 50% and enhanced its suitability for fpga implementations. it was concluded that the fully parallel turbo decoder with radix-2 and 6144 parallel map decoders resulted in 14.8gbps but this design utilized 9618 mw of high power at 100 mhz clock frequency. various vlsi architectures were presented in [11] for the computing blocks of the turbo decoder and made the siso decoder support radix2/4/8 modes. the design resulted in throughput in the range of 80mbps to 270 mbps, reducing power consumption to up to 61% as compared to the other state-of-art designs. a parallel turbo decoder with reverse address generator in interleaver for low latency and high throughput architecture with double buffer technique was proposed in [12] for effective utilization of fpga resources for broadcasting systems. this work resulted in a throughput performance of 2.12 gbps at 250 mhz and a latency of 23.2 µsec with 64 parallel map decoders. a memory-reduced turbo decoder was proposed by a reverse recalculation technique using the log-map algorithm with a focus on power reduction [13]. it was reported that the technique helped to reduce the memory and power consumption as compared to other conventional turbo decoder designs. the vedic multiplier-based implementation presented in [14] could be preferred in-branch metric calculations in max-log-map algorithms for low latency turbo applications, but the implementation consumes more area. an optimized turbo decoder for performance improvement of turbo decoder, where the parallel computation of state metrics, reusing of memory and single siso decoder in the hardware implementation was proposed [15]. a low memory turbo decoder with reverse calculation techniques was reported where the trellis diagram was partitioned and the max* operator was simplified [16]. the findings revealed that the architecture achieved a 65% reduction in state metric cache (smc) capacity with other designs and lower power dissipation. by this motivation, the present study focused on developing a new hardware architecture for parallel turbo decoder to achieve high performance and balanced hardware implementation using optimization techniques. 2. turbo decoder design perspective the general structure of a turbo decoder consists of two siso decoders connected through an interleaver and de-interleaver to perform the iterative process of soft bits to provide a-posteriori llrs after the required number of iterations. the soft-demodulated values of transmitted bits are referred to as a-priori probability values and are fed to constituent siso decoders as input llrs, shown in fig. 1 [17]. each decoder operates on the systematic and parity bits associated with its constituent encoder and produces soft outputs of the original data bits in the form of a-posteriori probabilities. the extrinsic information is computed using a-posteriori probability values from the siso decoder, interleaved/non-interleaved a-priori probability values, and interleaved/de-interleaved extrinsic information from another siso decoder. such extrinsic information values are shuffled between two siso decoders and are iteratively processed along with a-priori probability values to produce error-free a-posteriori probabilities of the transmitted bits. 127 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 fig. 1: block diagram of iterative turbo decoder. in the iterative process, the map algorithm decodes the probabilities for each bit correctly. the complexity of the map algorithm has been reduced by operating the algorithm in the log domain variants such as the log-map algorithm and max-log-map algorithm. in order to realize the high-performance turbo decoder, siso decoders involved in the turbo decoder should provide high-speed data transmission without significant coding loss. major tasks of the siso decoder are computation of branch metrics, state metrics, and llr computation to extract the final extrinsic information. however, two siso decoders do not work simultaneously in each half iteration to compute the state metrics. hence, the present study utilized the turbo decoder with a single siso decoder for one complete iteration as shown in fig. 2. fig. 2: block diagram of turbo decoder with single siso decoder. the main objective of the present study is to design an efficient parallel turbo decoder that can support higher throughputs using streaming techniques. qpp interleaver plays a vital role in turbo encoder/decoder error correction. hardware design of the qpp interleaver involves complex mathematical functions and dependency of previous computations. a semi recursive qpp interleaver is proposed in the present study which simplifies the aforementioned disadvantages of qpp interleaver. 3. qpp interlever qpp interleaver is an integral part of the turbo encoder and decoder and it plays a critical role in turbo codes, especially in turbo decoder, for achieving high-speed decoding. for each of the 188 block lengths, a different set of f1, f2 parameters were pre-defined in 3gpp lte [17]. in the recent 3gpp lte/ lte-a, qpp interleaver is based on algebraic properties and contention-free properties, providing contention-free memory access for any specified code block size between 40 to 6144. the efficient design of a conflict-free reconfigurable qpp interleaver for turbo encoder and turbo decoder is a pre-eminent task in turbo channel coding scheme. the hardware implementation of qpp interleaver/de-interleaver should support parallel interleaving for the high-performance parallel decoder. this research work proposed the design of reconfigurable semi-recursive qpp interleaver for parallel and direct 128 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 computation of address locations of all the bits for turbo decoder by semi recursive computation approach as explained below. 3.1 semi recursive qpp interleaver the mathematical complexity and dependency of the current address location of the previous address location are solved by the semi-recursive computation method. the address locations of interleaved bits/the sequence of numbers of interleaving 𝜋(𝑖) of current symbol 𝑖 in qpp interlever is computed as 𝜋(𝑖) = (𝑓1𝑖 + 𝑓2𝑖 2) 𝑚𝑜𝑑𝐾 (1) in eq. 1 [17], parameters 𝑓1𝑎𝑛𝑑 𝑓2 depend on ′𝐾′and all the possible variants of block size 𝐾 and variables 𝑓1𝑎𝑛𝑑 𝑓2, are defined. in hardware implementation of eq.1, the address computation of current index i, depends on previous computations recursively and this recursive dependency creates high decoding latency and is not preferable for highperformance turbo decoders. the proposed design does not contain mod operation, as mod operator implementation is complex in the hardware design of the qpp interleaver; it is replaced by an add-compare-select (acs) unit. the acs unit is composed of only arithmetic operators like addition and subtraction. replacing the mod operation by the acs unit is called the modulo normalization technique. to simplify the complex interleaver computation and to avoid large storage requirements, the proposed semi recursive computation approach for parallel interleaver supports the independent parallel computation of interleaved addresses. the input sequence (num) is denoted as metric weight (mw) and it is represented as mw (1, k+1) in the first column. the subsequent columns are defined as mentioned below. case 1: if mod (num, 2) ≠0, then num = num+1 and mw (2, k+1) = (num+1)/2; mw (3, k+1) = mw (2, k+1) 1; case 2: if mod (num, 2) =0, then num= num; mw (2, k+1) = num/2; mw (3, k+1) = num mw (2, k+1); then, value (v) is defined as, v = δ(0) x mw (2, k+1) + δ(1) x mw (3, k+1), where, δ(0) = f1 + f2 and δ(1) = δ(0) + 2f2 ; it can be observed from tables 1 and table 2, that computation of address locations of 40 bits was done within 5 clock cycles independently. this approach is proposed to minimize the computational complexity and avoid the storage of interleaver tables. table 1: metric weight table in semi recursive order mw (1, k+1), num mw (2, k+1) mw (3, k+1) value (v) π(i) = mod (v,40) 0 0 0 0 0 1 1 0 13 13 2 1 1 46 6 3 2 1 59 19 4 2 2 92 12 129 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 table 2: proposed parallel computation of sub blocks clock subblock1 sub block2 sub block3 sub block4 sub block5 sub block6 sub block7 sub block8 clock1 0 5 10 15 20 25 30 35 clock2 1 6 11 16 21 26 31 36 clock3 2 7 12 17 22 27 32 37 clock4 3 8 13 18 23 28 33 38 clock5 4 9 14 19 24 29 34 39 from tables 1 and 2, it can be observed that the parallel computation of 40 bits has been done with 8 parallel operations. in the first clock cycle, bits 0, 5, 10, 15, 20, 25, 30 and 35 will be computed simultaneously. similarly in the second, third, fourth, and fifth clock cycles, the parallel computation of the remaining bits is performed in the order shown in table 2. the proposed method is most suitable for highly parallel turbo decoding architectures. the proposed design and fpga implementation of a new hardware architecture for a high-performance turbo decoder using streaming techniques is presented below. 4. parallel turbo decoder the parallel decoding approach of turbo decoder with p parallel map decoders roughly increases the decoding throughput by a factor of ‘p’ compared to non-parallel turbodecoders. modern parallel hardware architectures can have either spatial or functional parallelization to improve the throughput performance. for a high-performance turbo decoder, this article proposed a new hardware architecture, which is an 8-parallel map decoder structure. the proposed architecture is designed in a three-stage pipelined process. in the first stage, the input llrs load into the three buffers namely systematic buffer, parity-1 buffer and parity-2 buffer in parallel. here, the input llrs could be related to any of 188 block sizes varying from 40 to 6144. in the second stage, the data of eight coded words are processed parallel with the eight bcjr decoders as shown in fig. 3. in the second stage, the bcjr decoder is further processed into three micro pipeline stages. two siso decoders, named siso-1 and siso-2, the first decoder processes the systematic input, parity-1 and a-priori data. similarly, the second decoder process interleaved systematic input, parity-2, interleaved a-priori data in the micro-pipeline stage is presented below. fig. 3: block diagram of proposed three-stage pipeline parallel turbo decoder. in the first micro pipeline stage, all the siso decoders are processed in parallel with the given two inputs and then extrinsic information is produced as the output of the siso 130 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 decoder. in the second micro-pipeline stage, the produced output information is processed to interleaved/ de-interleaved block. finally, in the third micro-pipeline stage, the third input of de-interleaved a-priori data to siso decoder blocks to process the extrinsic information. this three-stage micro pipeline process continues for 8 number of iterations. this process is depicted in fig. 4. then the third pipeline stage of the parallel ‘8’ turbo decoder continues until maximum convergence is achieved and the output llrs are processed into the output buffer. fig. 4: block diagram of three stages micro pipeline turbo decoder. 4.1 simplified computation of soft-output the soft output 𝐿 can be computed as shown in eq. 2 [18] from the state metrics and branch metrics to find maximum value as, 𝐿 = max (𝛼0 ′ + 𝛽0 + 𝛾00, 𝛼1 ′ + 𝛽4 + 𝛾00, 𝛼2 ′ + 𝛽5 + 𝛾01, 𝛼3 ′ + 𝛽1 + 𝛾01, 𝛼4 ′ + 𝛽2 + 𝛾01, 𝛼5 ′ + 𝛽6 + 𝛾01, 𝛼6 ′ + 𝛽7 + 𝛾00, 𝛼7 ′ + 𝛽3 + 𝛾00) − max (𝛼0 ′ + 𝛽4 + 𝛾11, 𝛼1 ′ + 𝛽0 + 𝛾11, 𝛼2 ′ + 𝛽1 + 𝛾10, 𝛼3 ′ + 𝛽5 + 𝛾10, 𝛼4 ′ + 𝛽6 + 𝛾10, 𝛼5 ′ + 𝛽2 + 𝛾10, 𝛼6 ′ + 𝛽3 + 𝛾11, 𝛼7 ′ + 𝛽7 + 𝛾11) (2) where, 𝛼0 ′ 𝑡𝑜 𝛼7 ′ denotes the forward state metrics, 𝛽0 to 𝛽7 denotes backward state metrics of 8 states and 𝛾00 𝑡𝑜 𝛾11 denotes branch metrics. equation 2 is further simplified as eq. 3 in our proposed simplification for computing soft output (𝐿) with common 𝛾00 𝑡𝑜 𝛾11 , 𝐿 = max (max(𝑠0, 𝑠1) + 𝛾00, max(𝑠2, 𝑠3) + 𝛾01 − max(𝑡0, 𝑡1) + 𝛾11, max(𝑡2, 𝑡3) + 𝛾10 ) (3) where, 𝑠0= max (𝛼0 ′ + 𝛽0, 𝛼1 ′ + 𝛽4) 𝑠1= max (𝛼6 ′ + 𝛽7, 𝛼7 ′ + 𝛽3) 𝑠2= max (𝛼2 ′ + 𝛽5, 𝛼3 ′ + 𝛽1) 𝑠3= max (𝛼4 ′ + 𝛽2, 𝛼5 ′ + 𝛽6) 𝑡0= max (𝛼0 ′ + 𝛽4, 𝛼1 ′ + 𝛽0) 𝑡1= max (𝛼6 ′ + 𝛽3, 𝛼7 ′ + 𝛽7) 131 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 𝑡2= max (𝛼2 ′ + 𝛽1, 𝛼3 ′ + 𝛽5) 𝑡3= max (𝛼4 ′ + 𝛽6, 𝛼5 ′ + 𝛽2) the extrinsic information/ a-posteriori information λ𝑜𝑢𝑡 (𝑘) can be calculated as in eq. 4 [18], with the aid of l(k), x(k) and y(k) as, λ𝑜𝑢𝑡 (𝑘) = 1 2 𝐿(𝑘) − 𝑥(𝑘) − λ𝑖𝑛 (k) (4) where, 𝐿(𝑘) denote soft-output, x(k) is the received soft systematic information, λ𝑖𝑛 (k) is a-priori information. 4.2 performance analysis the performance analysis of the channel decoder can be done by decoding delay/latency and the throughput obtained. but a hardware digital system/circuit performance will be measured in three parameters called power, area, and throughput. this analysis can be done when the proposed architecture is synthesized by hardware design tool like xilinx ise/vivado. for the proposed design of turbo decoder, the decoding delay is calculated as eq. 5 and 6 [17] for block sizes less than 264 and from 264 to 6144, if k< 264, 𝐷 = (26 + (2𝑓(𝐾, 𝑁) + 14)2𝐼) (5) if k≥ 264, 𝐷 = (26 + (𝑓(𝐾, 𝑁) + 46)2𝐼) (6) where, k denote block size, n denote number of decoders and i denote number of iterations and f (k, n) = { k n if k is divisible by n k 8 if k is not divisible by n decoding latency (𝐿) is calculated as 𝐿 = 𝐷 𝑓𝑚𝑎𝑥 𝑠𝑒𝑐 (7) the throughput (𝑇) is calculated as 𝑇 = [𝐾∗𝑓𝑚𝑎𝑥] 𝐷 𝑏𝑝𝑠 (8) where, 𝑓𝑚𝑎𝑥 denote the maximum operating frequency, which effects both latency and throughput as in eq. 7 and 8 [17]. for instance, if the operating frequency of this hardware is about 250 mhz, then the throughput for the block size of 40 bits is 24.38 mbps and for block size of 6144 bits is 117.7 mbps. 5. results and discussion in order to get a higher throughput and lower latency, the most commonly adopted design methodology is to improve the level of parallelism. a new architecture consisting of 132 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 an 8-parallel decoder structure has been proposed for the high-performance turbo decoder proposed in the present study. the proposed hardware architecture of the turbo decoder is designed into the three-stage pipeline and three-stage micro-pipeline procedures for high performance. the high-level block diagram is shown in fig. 5, the simulation waveform and performance analysis of the proposed design are discussed below. the three-stage pipeline and three-stage micro-pipeline procedure in the proposed parallel turbo decoder is to improve the speed of data processing in the whole structure to improve the throughput and to reduce the latency. the proposed architecture has been designed, simulated in mat lab and modelsim for functionality verification and the simulation waveform is shown in fig. 6. from the simulation diagram, the throughput latency, or the time taken to produce the first output for the given input, is 1.9 ns. fig. 5: high level block diagram of proposed turbo decoder. fig. 6: simulation waveform of proposed parallel turbo decoder. 133 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 then, the rtl schematic shown in fig. 7 is observed for the proposed architecture in detail for hardware components utilized. also, the submodules of the proposed parallel decoder, like branch metrics, parallel state metric computations, and llr computations, are run to find the maximum value of the computed posteriori llrs to finalize whether the decoded bit belongs to either “0” or “1”. fig. 7: rtl schematic of proposed parallel turbo decoder using xilinx vivado. the architecture is implemented over xilinx vivado for 28 nm cmos technology kintex 7, vertex-7, and zynq-7000 zed fpga evaluation boards for its performance analysis. the hardware utilization is summarized in table 3. it can be observed from table 3 that a much smaller number of logic cells and memory cells are occupied by the proposed design with vlsi optimization techniques than the standard design. as acs units have been used for metric computation, instead of many arithmetic/logical units, the hardware resource utilization has been reduced. it is evident from the observation that hardware utilization is less at post-implementation than post-synthesis of the design. table 3: hardware resource utilization of parallel turbo decoder hardware resource utilization (%) utilization (%) available post-synthesis post-implementation utilization (%) ff 809 (0.76%) 809 (0.76%) 106400 lut 1072 (2.02%) 1059 (1.99%) 53200 i/o 38 (19%) 34 (17%) 200 bram 32 (22.86%) 32 (22.86%) 140 bufg 1 (3.12%) 1 (3.12%) 32 power consumption (in watt) 0.157 once the functionality is proven, then the netlist of the design is ready for further processing. synthesized-netlist has been placed, routed, and checked for timing violations. 134 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 the timing report was generated for the proposed design and the critical path delay of 3.04ns and the respective maximum operating clock frequency obtained was 329mhz, as presented in table 4. table 4: throughput, latency, and power utilization of the proposed turbo decoder platform critical path delay ns max.clock frequency fmax mhz block size k latency l µs throughput t mbps kintex-7 28 nm cmos 3.04 329 40 1.34 32 3.04 329 6144 39.67 155 the proposed parallel turbo decoder on xilinx kintex-7 fpga, achieved a throughput of 155 mbps and 32 mbps, and the latency of 39.67 µs and 1.34 µs for the block lengths of 6144 and 40, respectively. furthermore, maximum clock frequency fmax of 329 mhz was observed as listed in table 4. it can be seen from table 4 that this parallel design achieved 155 mbps of throughput at maximum flock frequency of 329 mhz and 39.67 µs of latency for block size 6144 on 28 nm cmos kintex-7 fpga. the proposed parallel architecture with these techniques gives reduction in energy consumption of the proposed architecture compared to the general architecture. the estimated performance analysis of the proposed turbo decoder on various xilinx fpga and the comparison of obtained results with other recent turbo decoder designs are shown in table 5. it is observed that the present work provides a balanced design between performance parameters of speed, area, and power. it is evident from the results that for similar algorithm, block size, and approximately the same number of interactions, the proposed turbo decoder gives a much better throughput. table 5: comparison of the proposed turbo decoders with other reported works parameter z yan 2016 [19] hua. l 2017 [18] vadim b 2017 [20] rahul 2018 [11] farzana 2019 [21] farzana 2019 [21] present work present work target device/ fpga family 130 nm cmos 28 nm vertex-7 virtex-7 28nm 28 nm zynq 28 nm vertex-7 28 nm vertex-7 28 nm vertex7/zynq kintex-7 parallelism/radix 08-apr 64 8/2 8 8 8 algorithm maxlog map maxlog map maxlogmap max-logmap max-logmap max-logmap max-logmap max-logmap block size 6144 6144 6144 6144 6144 6144 6144 6144 number of iterations 5.5 8 5 8 8 8 8 8 maximum clock rate (mhz) 290 250 270.9 276 86.3 86.3 252.5 329 throughput (mbps) 384.3 2120 5 80 86.3 10.7 118 155 6. conclusions the present study highlights the concept of a new architecture with a three-stage pipelined parallel turbo decoder and three-stage micro-pipelined map decoder. these techniques have specifically improved the throughput and operating clock frequency by 135 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 pipelined parallel implementation of the turbo decoder and shortened the critical path delay in the whole design. algorithmic approximation and architectural optimization like pipelining and parallelizing were used to minimize the critical path and attain a higher throughput. however, the hardware complexity advances linearly as the number of subblocks or iterations increases and increased recursions in architecture of the map decoder normally limit the throughput of the turbo decoder. the estimated performance has been observed by implementing the proposed parallel turbo decoder at 28 nm cmos technology xilinx kintex7 fpga and achieved a maximum estimated throughput of 155 mbps with 8 iterations, which is suitable for 3gpp-lte-advanced, as per its specification. the proposed design improved throughput to the tune of 55.6% as compared to other recently reported designs. from the performance analysis of the proposed turbo decoders and comparison with other recent turbo decoder designs, it is evident that the proposed architecture provides a balanced design among performance parameters, speed, and area. it can be concluded that throughput increases for the optimized turbo decoder and parallel turbo decoder architectures as compared to the standard design. however, the area requirement or power consumption increases proportionately with the throughput. acknowledgement the authors would like to thank the editors and anonymous reviewers for their insightful comments and constructive suggestions. this work was supported by the department of science and technology, government of india under women scientist scheme-a (wosa) (sr/wos-a/et-72/2017) and the work was carrying out at sree vidyanikethan engineering college, tirupati, andra pradesh, india. references [1] berrou c, glavieux a, thitimajshima p. (1993) near shannon limit error correcting coding and decoding: turbo-codes. proceedings of ieee international conference on communication: pp 1064-1070. doi: 10.1109/icc.1993.397441 [2] mackay djc, neal rm. (1996) near shannon limit performance of low density parity check codes. electronics letters, 32(18): 1645-1646. doi: 10.1049/el:19961141 [3] arıkan e. (2009) channel polarization: a method for constructing capacity achieving codes for symmetric binary-input memoryless channels. ieee transactions on information theory, 55(7): 3051-3073. doi: 10.1109/tit.2009.2021379 [4] bahl l, cocke j, jelinek f, raviv j. (1974) optimal decoding of linear codes for minimizing symbol error rate (corresp.). ieee transactions on information theory, 20(2): 284-287. doi: 10.1109/tit.1974.1055186 [5] robertson p, villebrun e, hoeher p. (1995) a comparison of optimal and sub-optimal map decoding algorithms operating in the log domain. proceedings of ieee intenational conference on communications: pp 1009-1013. doi: 10.1109/icc.1995.524253 [6] parhi kk. (1999) vlsi digital signal processing systems: design and implementation. hoboken, nj: wiley. [7] nimbalker a, blankenship tk, classon b, fuja te, costello dj. (2008) contention-free interleavers for high throughput turbo decoding. ieee transactions on communications, 56(8): 1258-1267. doi: 10.1109/tcomm.2008.050502 [8] shrestha r, paily r. (2014) high-throughput turbo decoder with parallel architecture for lte wireless communication standards. ieee transactions on circuits and systems—i: regular papers, 61(9): 2699-2710. doi: 10.1109/tcsi.2014.2332266 136 https://doi.org/10.1109/icc.1993.397441 https://doi.org/10.1049/el:19961141 https://doi.org/10.1109/tit.2009.2021379 https://doi.org/10.1109/tit.1974.1055186 https://doi.org/10.1109/icc.1995.524253 https://doi.org/10.1109/tcomm.2008.050502 https://doi.org/10.1109/tcsi.2014.2332266 iium engineering journal, vol. 23, no. 2, 2022 elukuru et al. https://doi.org/10.31436/iiumej.v23i2.2272 [9] jing-shuin l, ming-der s, chung-yen l, der-wei y. (2015) efficient highly parallel turbo decoder for 3gpp lte-advanced. international symposium on vlsi design automation and test (vlsi-dat): pp 1-4. [10] li a, xiang l, chen t, maunder rg, al-hashimi bm, hanzo l. (2016) vlsi implementation of fully parallel lte turbo decoders. ieee access, 4: 323-346. doi: 10.1109/access.2016.2515719 [11] shrestha r, sharma a. (2018) vlsi-architecture of radix-2/4/8 siso decoder for turbo decoding at multiple data-rates. proceedings of ifip/ieee international conference on very large sale integration (vlsi-soc): pp 131-136. doi: 10.1109/vlsi-soc.2018.8644753 [12] luo h, zhang y, li-ke h, cosmas j. (2017) low latency turbo decoder implementation for future broad casting systems. ieee international symposium on broadband multimedia systems and broadcasting: pp 1-4. doi: 10.1109/bmsb.2017.7986227 [13] shi y, zhan m, zeng j. (2018) fpga implementation and power estimation of a memory reduced lte-advanced turbo decoder. proceedings of ieee conference on iot, green computing and communications, cyber, physical and social computing, smart data, block chain, computer and information technology: pp 607-611. doi:10.1109/cybermatics_2018.2018.00124 [14] narayanan a, murugan s, bhakthavatchalu r. (2019) low latency max log map based turbo decoder. proceedings of international conference on communication and signal processing (iccsp): pp 721-724. doi: 10.1109/iccsp.2019.8697955 [15] sujatha e, subhas c, giriprasad mn. (2019) performance improvement of turbo decoder using vlsi optimization techniques. ieee international conference on vision, towards emerging trends in communication and networking (vitecon): pp 84-90. doi: 10.1109/vitecon.2019.8899585 [16] zhan m, pang z, yu k, wen h. (2021) reverse calculation-based low memory turbo decoder for power constrained applications. ieee transactions on circuits and systems i: regular papers, 68(6): 2688-2701. doi: 10.1109/tcsi.2021.3068623 [17] evolved universal terrestrial radio access (e-utra); multiplexing and channel coding. (2008) 3gpp technical specification group radio access network ts 36.212 rev. 8.3.0 release 9. [18] hua l, yue z, li-ke h, john c. (2017) low latency turbo decoder implementation for future broad casting systems. ieee international symposium on broadband multimedia systems and broadcasting, cagliari, italy: pp 1-4. [19] yan z, he g, he w, wang s, mao z. (2016) high performance parallel turbo decoder with configurable interleaving network for lte application: integration. the vlsi journal, 52: 77-90. https://doi.org/10.1016/j.vlsi.2015.05.003 [20] belov v, mosin s. (2017) fpga implementation of lte turbo decoder using max-log map algorithm. sixth mediterranean conference on embedded computing (meco): pp 1-4. doi: 10.1109/meco.2017.7977157 [21] farzana s, butt mfu, agha s, ng sx, maunder rg. (2019) performance analysis of high throughput map decoder for turbo codes and self concatenated convolutional codes. ieee access, 7: 138079-138093. doi: 10.1109/access.2019.2942152 137 https://doi.org/10.1109/access.2016.2515719 https://doi.org/10.1109/vlsi-soc.2018.8644753 https://doi.org/10.1109/bmsb.2017.7986227 http://dx.doi.org/10.1109/cybermatics_2018.2018.00124 https://doi.org/10.1109/iccsp.2019.8697955 https://doi.org/10.1109/vitecon.2019.8899585 https://doi.org/10.1109/tcsi.2021.3068623 https://doi.org/10.1016/j.vlsi.2015.05.003 https://doi.org/10.1109/meco.2017.7977157 https://doi.org/10.1109/access.2019.2942152 microsoft word paper-2-press.doc iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 9 treatment of pome by pilot plant anaerobic fluidised bed reactor a. a. mamun 1* and a. idris 2 1 department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. * e-mail: mamun@iiu.edu.my fax: +603-61964442 2 department of chemical & environmental engineering, faculty of engineering, universiti putra malaysia, 43400 upm serdang, selangor, malaysia. email: azni@eng.upm.edu.my fax: +603-86567120 abstract : a pilot scale anaerobic fluidised bed reactor (anfbr) of 2000 l capacity was studied to determine its ability to treat palm oil mill effluent (pome). the pilot plant was operated at ambient temperature with diluted pome as substrate. it took 17 days for the start-up of the reactor with pre-seeded sand media. the mean influent concentration of bod, cod and tss were 1110, 2194 and 1004, respectively. the anfbr was capable to remove a large portion of organics at relatively shorter retention time. maximum and minimum cod removal efficiency of 85% and 65% were attained at a loading rate of 4.0 and 13.8 kgcod/m 3 .d. bod and tss removal rates varied within the range of 64% 91% and 68% 89%, respectively. the average residual cod, bod and tss concentration was 330, 95 and 110 mg/l, respectively. the anfbr exhibited less sludge production with lower values of sludge volume indices (svi). maximum and minimum effluent indices for the effluent were 35 ml/g and 11 ml/g, respectively. low svi values indicated that, anaerobic fluidised bed reactors generate less sludge with fast settling properties. promising performance at ambient temperature and for detention time shorter than the present practices supported the possibility of anfbr to pretreat pome to meet the new requirement set by the doe malaysia. keywords: anaerobic digestion, palm oil mill effluent, pilot scale bioreactor. 1. introduction palm oil mill effluent (pome) is the single largest source of industrial wastewater pollution in malaysia. the commonly used conventional treatment facilities (e.g. holding ponds, decanter, anaerobic digesters and aerated lagoons) are unable to meet the guidelines [1] set by the department of environment (doe), which sets bod as a controlling parameter with a limit of 100 mg/l. therefore, high rate treatment systems are necessary to treat pome to protect the river system from water pollution. anaerobic treatment of industrial wastewaters is a well-established technology, which has been proven to be the cheapest and versatile method for a wide range of application [2]. new process innovations like high-rate filtration, fluidised bed [3] up-flow sludge blanket [4] and hybrid reactors [5] have already emerged as today's most viable anaerobic treatment technology. among them anaerobic fluidised bed reactor (anfbr) has been used for wastewater treatment since early 1970s. promising features of the anfbrs are the capability of treating high strength wastewaters at both ambient and elevated temperatures [6] for a iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 10 minimum energy, with low sludge production and ability to tolerate shock loads in terms of volumetric loading rates (vlrs), ph and temperature without any substantial long term detrimental effects. as such, anfbr could be a potential system to treat pome to meet the target set by the doe. therefore, the overall performance of a pilot plant anaerobic fluidised bed reactor in treating palm oil mill effluent (pome) is reported in this paper. 2. materials and methods 2.1 substrate characteristics various types of solids, semisolids and liquid wastes are generated from different steps of oil processing units of an oil palm industry. in practice, all these wastes are bulked which gives a yellowish liquor containing both dissolved and fine suspended matter and residual oil with very high bod and cod values. the slightly acidic wastewater consists of about 90-95% water, 5-10% total solids and 0.5-1% residual oil and grease [7]. in this study, the pome was diluted 10 times with distilled water to overcome the problem of collecting huge amount of wastewater required to run the system. general characteristics of undiluted raw pome and diluted substrate for the pilot plant are given in table 1. table 1: typical characteristics of the substrate (pome) parameter ma [7] kam [8] this study (undiluted pome) diluted substrate bod (mg/l) 25,000 34,000 31,240 990 – 2080 cod (mg/l) 50,000 62,000 59,700 2,000 – 5,000 tss (mg/l) 18,000 37,000 30,230 959 – 1,937 vss (mg/l) 34,000 26,000 25,300 735 – 1,596 o&g (mg/l) 6,000 – 8,000 – tn (mg/l) 750 – 1,940 – tp (mg/l) – – 268 – ph (–) 4.2 4.3 4.5 7.0 2.2 reactor properties the reactor was fabricated based on the geometrical up-scaling of the lab-scale reactors studied by hafiz [9] and tiong [10]. mild steel plates, available in the market, was used to build the 3.8 m tall reactor. top portion of the reactor was tapered to increase the diameter and to reduce the upward velocity in order to minimise the unwanted wash out of any biosolids. 2.2.1 dimensions of the anfbr according to the actual scale-up ratio, required volume of the reactor was 5000 l. however, due to various limitations, diameter of the anfbr was limited to 770 mm, which resulted in a total reactor volume of about 2000 l and an aspect ratio (h/d) of 4.94. high aspect ratio was preferred for better mixing and easy fluidisation but not critical for system performance [11]. technical and logistic support was not available to build and install a taller reactor keeping the volume and aspect ratio high. schematic diagram of the reactor is shown in fig. 1. iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 11 2.2.2 media properties natural sands were chosen to be used as media for the reactor due its easy availability, low cost and high stability. random grab samples were taken from the dried sands and analysed to determine particle size distribution. one third of the media had a particle diameter of 0.35 mm to 0.56 mm and only 10% of the materials had a diameter of less than 0.20 mm. uniformity coefficient (cu) and coefficient of gradation (cc) of the media was 1.60 and 1.09 respectively. these media provided an approximate specific surface area of 5237 m 2 /m 3 of media volume. fig. 1: schematic diagram of the anfbr pilot plant (not to scale). 3. results and discussion a few technical problems, such as leaking through improperly welded joints, pump malfunction and breakdown of the piping system delayed the full operation of the pilot plant anaerobic fluidised bed reactor. 3.1 start-up of the reactor in order to overcome the start-up problem experienced by hsu and shieh [12], the sand media were pre-seeded in a tank for three months. the media were fed with raw pome and stirred (manually) twice a day. during the start-up period, the volumetric loading rate was between 1.8 and 2.0 kgcod/m 3 .d at an hrt of 24 hours. about 200 l of active sludge from an anaerobic pond was mixed with the feed. cod removal rate was considered as the controlling parameter to study the start-up performance. however, bod, cod, tss and svi were monitored after the start-up of the reactor. due to presence of solids and biomass in the pre-seeded media, effluent cod on the first day was higher than that of the influent (fig. 2). iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 12 0 500 1000 1500 2000 2500 0 5 10 15 20 time (day) c o d c o n c e n ta rt io n ( m g /l ) influent effluent fig. 2: influent and effluent cod during the start-up of the reactor with average chemical oxygen demand (cod) concentration of 2100 mg/l, oliva et al. [13] obtained a start-up within 14 days for a full-scale brewery wastewater treatment plant. tiong [10] completed start-up period when the cod removal rate was around 86% and hafiz [9] ended start-up when cod removal efficiency varied between 70% and 80%. thus, the start-up in this study was completed when the cod removal rate was around 70%. from fig. 2 it was observed that, the reactor could start at an early period of 17 days, indicating that pre-seeding of media might be an alternative way to get an early start-up of fixed film reactors. on the other hand, denac and dunn [14] obtained start-up of the reactor within 21 days. 3.2 pollutant removal many forms of substrates, including bod, cod and solids were monitored to study the performance of the anfbr for pome treatment. the influence of the applied substrate on the reactor performance is discussed according to the forms of substrates. five steady state conditions were attained and, for the simplicity of the discussion, were termed as run 1, 2, 3, 4 and run 5. values of different parameters at each steady state are given in table 2. influent concentration was doubled for run 4 and 5. 3.2.1 bod removal biochemical oxygen demand (bod) was determined every week and at the steady states. the observation of bod removal rate against operation time revealed that removal rate increased at a higher rate during the 1st run at hrt of 12 hrs and the maximum removal rate was observed to be 91.4% at the loading rate of 2.6 kgbod/m 3 .d (table 2). minimum bod removal rate throughout the whole operation was 64.7% at 4-hour retention time with a vlr of 6.1 kgbod/m 3 .d. from the plot of specific biological loading rate (blr) applied and utilised as kgbod/kgvss.d (fig. 3), it can be noticed that specific substrate utilization rates decreased with the increase in loading rate. fig. 4 indicated that bod removal rate decreased from 91.4% to 64.7% with the increase in volumetric loading rate (vlr) from 1.5 kgbod/m 3 .d to 6.12 kgbod/m 3 .d. iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 13 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 blr applied (kgbod/kgvss.d) b l r u ti lis e d ( k g b o d /k g v s s .d ) observed values 100% efficiency line 0 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 vlr (kgbod/m 3 .d) b o d r e m o v a l r a te ( % ) table 2: anfbr performance at different steady state conditions parameter run 1 run 2 run 3 run 4 run 5 hrt (hr) 12 8 4 24 12 influent bod (mg/l) 1280 1030 1020 1640 1800 effluent bod (mg/l) 110 260 360 300 570 bod load (kg/m 3 .d) 2.6 3.1 6.1 1.6 3.6 bod removal (%) 91.4 74.8 64.7 81.7 68.3 influent cod (mg/l) 2000 2200 2300 4600 5000 effluent cod (mg/l) 300 500 800 1000 1800 cod load (kg/m 3 .d) 4.0 6.6 13.80 4.6 10 cod removal (%) 85.0 77.3 65.22 78.3 70 influent tss (mg/l) 959 967 1081 1772 1937 effluent tss (mg/l) 105 230 302 483 619 tss load (kg/m 3 .d) 1.9 2.9 6.49 1.8 3.9 tss removal (%) 89.1 76.2 72.10 72.7 68 fig. 3: specific bod removal rate as biological loading rate (blr) fig. 4: variation of bod removal rate with volumetric loading rate (vlr) iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 14 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 blr applied (kgcod/kgvss.d) b l r u ti lis e d ( k g c o d /k g v s s .d ) observed values 100% efficiency line 3.2.2 cod removal effluent cod concentration increased with the increased loading rate. effluent cod concentration was the highest at 1800 mg/l in the 5th run when the influent cod was 5000 mg/l. influent cod was doubled in the 4th and 5th run and subsequent fluctuations were observed for the effluent cod. the maximum cod removal rate achieved at steady state was 85% and the minimum was 65.2% (table 2). this was achieved at hrt of 12 and 4 hour under vlr of 4.0 and 13.8 kgcod/m 3 .d, respectively. it was observed that the cod removal rate decreased steadily with increasing loading rate (fig. 5). this observation was in agreement with the trend reported by chen et al. [15]. a similar trend is noticed in fig. 5. however, even during the stabilisation periods during each run, the removal rate of cod never dropped below 45%. at steady states, most of the removal rates were within 5% variation. this indicates that, the anfbr was able to absorb minor changes in influent concentration. the maximum specific cod utilization at steady states was 1.4 kgcod/kgvss.d when the applied load was 1.76 kgcod/kgvss.d (fig. 6). fig. 5: variation of cod removal rate with volumetric loading rate (vlr) fig. 6: specific cod removal rate as biological loading rate (blr) 0 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 vlr (kgcod/m 3 .d) c o d r e m o v a l r a te ( % ) iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 15 3.2.3 tss removal tss removal rate throughout the 1st run was excellent. maximum tss removal rate achieved was 89% at an hrt of 12 hour. this removal rate was achieved at a vlr of 1.92 kgtss/m 3 .d (table 2). specific tss utilization rate was analysed in a fashion similar to those of bod and cod analysis. as expected, the specific tss removal rate deviated from the 100% efficiency line with the increase in loading rates. tss removal efficiency was declining with the increase in vlr but the decrement was less at loading rates greater than 4 kgtss/m 3 .d. 3.2.4 sludge volume index sludge volume index (svi) was measured in all steady states using a conical flux of 1l volume (fig. 7) and using the following relationship: svi = (settled sludge volume in ml in 30 minutes) x 1000 / (1l x tss in mg/l) lower values of svi indicate good settle ability of sludge and vice versa. it was observed that svi improved when there were sufficient solids in the sample. there could be some relation between svi and minimum sludge concentration [16], which affects the floc formation, sludge compaction and svi values as well. maximum and minimum effluent sludge volume indices were 35 ml/g and 11 ml/g respectively. svi values less than 100 proved that, similar to other anaerobic processes, anfbr also produces less sludge which is good for efficient wastewater management. fig. 7: sludge volume index (svi) test. iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 16 4. conclusions an early start-up period of 17 days was experienced with pre-seeded media for the pilot plant anaerobic fluidised bed reactor to treat pome. the anfbr was capable of removing a large portion of organics at relatively shorter hdt from 4 to 24 hr indicating that successful operation of anfbr is possible at ambient temperature of malaysian climate. maximum cod removal efficiency of 85% was attained at an hrt of 12 hr with a loading rate of 4.0 kgcod/m 3 .d. the minimum cod removal rate was 65% at a vlr and hdt of 13.8 kgcod/m 3 .d and 4 hr respectively. bod and tss removal rates varied within the range of 64% 91% and 68% 89% respectively. influent concentration had marked effect on removal efficiency. reactor performance was found to decrease steadily with the increase in loading rate. during the whole operation, the anfbr exhibited low sludge production with lower sludge volume indices (svi). maximum and minimum effluent indices for the effluent were 35 ml/g and 11 ml/g, respectively. low svi values indicated that, anaerobic fluidised bed reactors generate less sludge with fast settling properties. promising performance at ambient temperature and hydraulic retention time shorter than the present practices supported the feasibility of anfbr for full-scale installation in the palm oil producing industries. however, additional polishing would be necessary through aerobic system and settling tank (clarifier) to further reduce the cod, tss and other pollutants in the effluent produced by the anaerobic digester. acknowledgement: this study was financed by ministry of science, technology and environment malaysia; irpa grant no 50384: high-rate waste treatment. 5. references [1] doe. “environmental quality act.” department of environment (doe) malaysia, 1974. [2] a.j.m.l. borghans, w.m.a.van gils, b. huisman, and e. wind. “10 years experience on the full scale anaerobic treatment of sugar industry wastewater in the netherlands with the biomethane process”. in ewpca conference, amsterdam, 15-19 september, 1986. [3] j.j. heijnen, a. mulder, r. wellevrede, j. hols, and h.l.j.m. van leeuwen. “large scale anaerobic-aerobic treatment of complex industrial wastewater treatment of complex industrial wastewater using biofilm reactors”. wat. sci. tech. 23(7-8):1427-1436, 1991. [4] g. lettinga, a.f.m. van velsen, w. de zeeuw, and s.w. hobma. “feasibility of the upflow anaerobic sludge blanket (uasb) process”. in proceedings of international conference on environmental engineering, new york: asce 35, 1979. [5] p.j. reynolds, e. colleran. “comparison of start up and operation of anaerobic fixed bed and hybrid sludge bed/fixed bed reactors treating whey waste water”. in ewpca conference, 15-19 september, amsterdam, 1988. [6] m.a. bull, r.m. steritt and j.n. lester. “an evaluation of four start-up regimes for anaerobic fluidized bed reactors”. biotech. letters 5(5):333-338, 1983. [7] a.n. ma, s.c. cheah and m.c. chow. “current status of palm oil processing wastes management”. in yeoh, b.g., chee, k.s, phang, s.m., isa, z., idris, a. and mohamed, m. (ed.) waste management in malaysia: current status and prospects for bioremediation, kuala lumpur:111-136, 1993. [8] k.h. kam. “scale-up studies on 2-stage biofilter pome treatment system.” b.sc. thesis, universiti pertanian malaysia, selangor, malaysia, 1995. iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 17 [9] m. hafiz. “combined anaerobic-aerobic treatment of industrial effluent utilizing fluidized bed technology”. b.sc. thesis. universiti pertanian malaysia, selangor, malaysia, 1996. [10] t.k. tiong,. “performance evaluation of a high-rate anaerobic fluidized bed reactor using diluted palm oil mill effluent with a steady-state biofilm”. b.sc. thesis, universiti pertanian malaysia, selangor, malaysia, 1994. [11] j. iza, e. colleran, j.m. paris and w.m. wu. “international workshop on anaerobic treatment technology for municipal and industrial wastewaters: summery paper”. wat. sci. tech. 24(8):1-16, 1991. [12] y. hsu, and w.k shieh. “start-up of anaerobic fluidized bed reactors with acetic acid as the substrate”. biotech.bioengg. 41:347-353, 1993. [13] e. oliva, j.c. jacquart and c. crevot. “treatment of wastewater at the el aguila brewery (madrid, spain)”. wat. sci. tech. 22(1-2):483-490, 1990. [14] m. denac and j.j. dunn. “packed and fluidized-bed biofilm reactor performance for anaerobic wastewater treatment”. biotech. bioengg. 32:159-173, 1988. [15] s.j. chen, c.t. li, and w.k. shieh. “performance evaluation of the anaerobic fluidized bed biofilm reactor: methane production from glucose”. in 40th purdue university industrial waste conference, west lafayette.:925-936, 1985. [16] g. tchobanoglous and f.l. burton. “wastewater engineering: treatment, disposal and reuse”. mcgraw hill inc., 1991. iium engineering journal, vol. 9, no. 1, 2008 a. a. mamun 18 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi a combined deep learning model for persian sentiment analysis zahra bokaee nezhad1 and mohammad ali deihimi2 1department of information and computer science, zand university, shiraz, iran. 2department of electrical and electronics engineering, bahonar university, shiraz, iran. *corresponding author: m.a.deihimi@gmail.com (received: 10th dec 2018; accepted: 17th april 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.1036 abstract: with increasing members in social media sites today, people tend to share their views about everything online. it is a convenient way to convey their messages to end users on a specific subject. sentiment analysis is a subfield of natural language processing (nlp) that refers to the identification of users’ opinions toward specific topics. it is used in several fields such as marketing, customer services, etc. however, limited works have been done on persian sentiment analysis. on the other hand, deep learning has recently become popular because of its successful role in several natural language processing tasks. the objective of this paper is to propose a novel hybrid deep learning architecture for persian sentiment analysis. according to the proposed model, local features are extracted by convolutional neural networks (cnn) and long-term dependencies are learned by long short term memory (lstm). therefore, the model can harness both cnn's and lstm's abilities. furthermore, word2vec is used for word representation as an unsupervised learning step. to the best of our knowledge, this is the first attempt where a hybrid deep learning model is used for persian sentiment analysis. we evaluate the model on a persian dataset that is introduced in this study. the experimental results show the effectiveness of the proposed model with an accuracy of 85%. abstrak: hari ini dengan ahli yang semakin meningkat di laman media sosial, orang cenderung untuk berkongsi pandangan mereka tentang segala-galanya dalam talian. ini adalah cara mudah untuk menyampaikan mesej mereka kepada pengguna akhir mengenai subjek tertentu. analisis sentimen adalah subfield pemprosesan bahasa semula jadi yang merujuk kepada pengenalan pendapat pengguna ke arah topik tertentu. ia digunakan dalam beberapa bidang seperti pemasaran, perkhidmatan pelanggan, dan sebagainya. walau bagaimanapun, kerja-kerja terhad telah dilakukan ke atas analisis sentimen parsi. sebaliknya, pembelajaran mendalam baru menjadi popular kerana peranannya yang berjaya dalam beberapa tugas pemprosesan bahasa asli (nlp). objektif makalah ini adalah mencadangkan senibina pembelajaran hibrid yang baru dalam analisis sentimen parsi. menurut model yang dicadangkan, ciri-ciri tempatan ditangkap oleh rangkaian neural convolutional (cnn) dan ketergantungan jangka panjang dipelajari oleh long short term memory (lstm). oleh itu, model boleh memanfaatkan kebolehan cnn dan lstm. selain itu, word2vec digunakan untuk perwakilan perkataan sebagai langkah pembelajaran tanpa pengawasan. untuk pengetahuan yang terbaik, ini adalah percubaan pertama di mana model pembelajaran mendalam hibrid digunakan untuk analisis sentimen persia. kami menilai model pada dataset persia yang memperkenalkan dalam kajian ini. keputusan eksperimen menunjukkan keberkesanan model yang dicadangkan dengan ketepatan 85%. 129 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi keywords: sentiment analysis; natural language processing; deep learning; persian; machine learning 1. introduction in recent years, social media sites have gained a considerable number of members. these sites allow users to express their ideas, so there is a great opportunity for companies and organizations to be informed of users’ ideas as public view [1]. today many companies try to provide acceptable customer services to encourage people to buy their products. there is also a profound need for some organizations to know people’s political views. on the other hand, with such massive opinionated text data, such as comments in social media sites, reviews in different websites, or even blog posts, companies and organizations must rely on tools to analyse this data. sentiment analysis technique has emerged for these purposes [2]. it is one of the most popular applications of nlp. sentiment analysis can be applied at different levels of scope: document level, sentence level, and aspect level. document level sentiment analysis is used to detect the whole document sentiment. sentence level sentiment analysis is used to determine a sentence sentiment while aspect level sentiment analysis is used to recognize every aspect of each entity which is mentioned in a sentence. for example in the sentence: “i really love apple products, but the latest iphone is not that great!” there is a positive sentiment about apple products but a negative opinion about the latest iphone [3] [4]. although extracting features from documents plays an important role in classification tasks, most persian sentiment analysis research uses traditional machine learning methods. these methods need to manually extract features from data. some of the famous techniques are naïve bayes (nb), support vector machine (svm) and logistic regression [5]. on the other hand, text inputs should be fed into neural networks in a proper way. bag of words (bow) is one famous method to represent each sentence to the proper form for machine learning. this method is quite simple and effective, but it ignores word order in the document [6], which can cause a significant problem in sentiment analysis tasks for two sentences with the same set of words and different sentiments. bow also doesn’t consider the semantic similarity between words [7]. there are several methods for representing a word properly to feed to machine learning algorithms such as n-gram and binary features. currently, except scant research in chinese and indian languages, the majority of the research is performed on english text. moreover, persian language faces some challenging complexity such as a wide variety of suffixes, lack of enriched dataset, etc. [5]. deep learning has become the main part of many new applications such as speech recognition, object detection, text mining, etc. in this study, a novel deep learning model for persian sentiment analysis is presented. it combines two types of artificial neural network: convolutional neural network (cnn) and recurrent neural network (rnn). in recent years, cnn and rnn have been used successfully in sentiment analysis tasks. cnn is well suited to extract local features from text [8]. rnn is used for processing sequential data [9]. lstm is a special kind of rnn that is capable of learning long-term dependencies. it can also solve the problem of gradient diffusion and gradient explosion [10]. in this paper, convolution and recurrent neural network are combined for persian sentiment analysis. we take advantage of automatic feature extraction by using cnn. long-distance dependencies are also learned by lstm. on the other hand, instead of representing each word by its index in the vocabulary, we use word2vec as an embedding 130 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi algorithm, which is key to the state-of-the-art results achieved by the proposed neural network architecture. two datasets are introduced in this study. they have about 9000 and 3000 sentences respectively that are labelled as positive, negative and neutral. the contents of this paper are divided into the following sections: section 2 talks about previous works. section 3 consists of the proposed model. we describe our hybrid cnn and rnn model in detail in this section. section 4 describes the dataset and presents experimental results. finally, the paper is concluded in the last section. 2. related work sentiment analysis is a field of nlp that focuses on identification and extraction of people’s opinions. generally, the various challenges present in the persian language have limited the quantity of works done on persian sentiment analysis. however, sentiment analysis is an on-going field of research, and in this section, some studies on sentiment analysis are summarized. pang and lee [11] used a movie reviews dataset and selected different words from their dataset as features. they examined features through different machine learning techniques such as naive bayes, max-entropy and svm. in comparison to studies reported for standard topic-based categorization, they were not able to achieve desirable results. they also couldn't address the co-reference problem in a sentence. wang and manning [12] investigated a simple nb and svm variant for sentiment classification. they showed that using word-bigram features created robust results. furthermore, their study showed that svm and nb were effective for full-length and short reviews respectively. for text classification, bag of words model was used to represent their document. one drawback of this model occurs when the size of the training set is small. bow also ignores the grammatical structure and word order. however, mass et al. [13] introduced a novel model that captured both semantic and sentiment similarities among words. to capture sentiment similarities, they used a supervised learning method. the semantic similarities were also learned by word2vec. although their model was sensitive to seed words and missing key words could lead to poor performance, they achieved acceptable results. socher et al. [14] used a sentiment treebank and proposed a model which is called recursive neural tensor network (rntn). it was too similar to the model that was proposed by socher one year before [15] which is called matrix-vector rnn (mv-rnn). mv-rnn was similar to recursive neural network but to represent words and phrases, it assigned both a vector and a matrix to each node in the parse tree. their model could learn the meaning of each word. it could also learn how a word modifies its neighbours. however, one main problem with mv-rnn was that the number of parameters heavily depended on the size of the vocabulary and became very large. to address this problem, the authors proposed a rntn model that used the same, tensor-based composition function for all nodes. le and mikolov [6] proposed a paragraph vector, an unsupervised algorithm that learned continuous distributed vector representations. they used their model for sentiment analysis task and achieved state-of-the-art results. the novelty of their study was that the model could be applied to variable-length pieces of texts. their model also represented each document by a dense vector. bagheri et al. [16] suggested a model based on a lemmatization approach for persian sentiment analysis. they employed a naive bayes algorithm for classification. their model, such as most of other persian sentiment analysis studies used traditional machine 131 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi learning models (alimardani et al. [17], hajmohammadi et al. [18], basiri et al. [19]). one drawback of these studies was that they relied on manual feature engineering while the proposed model tries to learn high-level features from data in an incremental manner using a deep learning model. hence, the feature extraction step is not done by expertise. the proposed model can also be more accurate and precise. roshanfekr et al. [20] proposed a deep learning model for persian sentiment analysis. their model had two learning phases, using skip-gram model for learning vector representation of words and utilizing two deep neural networks (bidirectional lstm and cnn) separately in a supervised way. in our study, two hybrid neural network architectures are employed to classify persian reviews and comments. concatenated cnn with lstm and cnn with gated recurrent unit (gru) are used to classify sentiments into three classes as positive, negative, and neutral. in the proposed model, local features can be captured by cnn and context can be learned by lstm or gru whereas in just another work with deep learning for persian sentiment analysis, two single networks were used separately [20] and their model couldn't harness both cnn's and lstm's abilities. however, the ordering of layers in our proposed model plays a significant role in how well it performs. to obtain word embedding, word2vec technique is used in the proposed model. word2vec uses a neural network with a single hidden layer to train the model. this technique addresses some of the challenges in persian such as different writing style, existence of inter words space, etc. while most of other word representing models such as term frequency, which was deployed in the previous persian sentiment analysis studies such as bagheri et al. [16] alimardani et al. [17], couldn't solve these difficulties. as mentioned before, there isn’t enough research on persian sentiment analysis with deep learning. based on the author’s knowledge, it is the first study on persian sentiment analysis with a hybrid deep learning architecture. we propose the combination of cnn and rnn (lstm, gru) that gives a better performance than cnn and rnn separately. 3. proposed methodology in this study, a hybrid deep learning model is presented to classify each persian sentence as positive, negative, or neutral sentiment. figure 1 shows the overall framework of the proposed model. according to fig. 1, after creating a persian dataset, for each sentence, the word embedding step is done by word2vec. afterward, cnn extracts local features. multiple kernel sizes are used in this step. a rectified linear unit (relu) is also applied as activation of cnn layer output. kim [21] demonstrated that cnn can improve results in sentence classification tasks. after using a pooling layer to create higher order features, the low-level translation constant features which are learned by cnn passed to lstm as the inputs. lstm can learn the long term dependencies and process sequence inputs. finally, after using a fully connected layer, the model tries to predict the sentiment of each input sentence as positive, negative, or neutral. the content of this section is divided into the following parts: word embedding, convolutional, pooling, dropout, rnn, and fully connected. 132 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi fig. 1: system architecture of the proposed model. 3.1 word embedding to perform sentiment analysis, the first step is choosing a proper representation of the target document. this step plays a significant role in deep learning. in this study, we use unsupervised learning of word-level embedding using a word2vec model [22]. this model consists of both skip-gram and continuous bag of words for computing vector representation. these vectors capture some useful semantic information about words and their relationship to each other. let s be the size of bag of words and le be the length of a word-embedding, so the word embedding for vocabularies is encoded by column vectors in an embedding matrix q r s*le. a sentence can be represented in the way that is shown in eq. (1): (1) the sentence-level representation presents in the eq. (2-3): (2) (3) 3.2 convolution cnn is a specific type of neural network. cnn can work well with spatial data because it only uses the certain connection from the previous layer; it can understand the sentiment of inputs in an acceptable way [8]. the convolution operation goes across the whole input matrix that was mentioned in section 3.1 to extract sentiment features. for each window of given input with the size of w, the same weight matrix is applied to extract local features vector of size l-w+1 by utilizing the matrix over all words of the input. a rectified linear unit (relu) is also applied as activation of a cnn layer output that replaces negative outputs with zero. the output of this layer has the same shape as the input. 3.3 max pooling we apply the max-pooling operation to the output of the convolutional layer, so the feature maps are passed on to this layer to take the maximum feature value. let ci be a feature that was generated in the previous section: max-pooling operation takes the maximum feature value cmax among one map c in the way that shows in eq. (4). 133 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi (4) 3.4 drop out in this section, we use a dropout layer that randomly sets a portion of the input to zero. this layer prevents network overfitting. it also distributes the network so as to not concentrate on particular pieces of input. 3.5 rnn a recurrent neural network (rnn) is a type of artificial neural network. it is used in several nlp studies. they are designed to recognize the characteristics of a sequence of data. [23] as mentioned before, features are captured by cnn. in this step, lstm and gru as two kinds of recurrent neural networks are used to learn context. therefore, the features are taken to long short term memory (lstm) and gated recurrent unit (gru). lstm is an artificial recurrent neural network. it is capable of learning long-term dependencies so it can process the entire sequence of data. a common lstm unit is composed of a cell, an input gate; a forget gate and an output gate. the input gate determines which information should enter the cell state. the forget gate determines which information must be removed from previous cell states to only keep relevant information. the output gate determines how much of the internal state should be exposed to the higher layers. figure 2 shows how lstm computes hidden state with eq. (5-10) [23]. (5) (6) (7) (8) (9) (10) where i, f, o are input, forget, and output gates, respectively. σ denotes the logistic sigmoid function, w is the recurrent connection at the previous and current hidden layer. u is the weight matrix that connects the inputs to the current hidden layer. x is the input vector. ĉt is a candidate hidden state. ct is the internal memory of the unit. fig. 2: lstm unit. gru is a gating mechanism in rnn. it is like lstm but has fewer parameters. it is also easy to train. a gru unit has two gates: an update gate and a reset gate. the update gate 134 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi determines how much of the previous memory should be kept around. the reset gate determines how to combine the new input with the previous memory. figure 3 shows how gru computes the hidden state with eq. (11-14) [23]. (11) (12) (13) (14) where r is a reset gate, and z is an update gate. fig. 3: gru unit. 3.6 fully connected the last layer is a fully connected layer that receives all the features generated before the final output. we utilize cross-entropy as the loss function, which measures the difference between the real and the output sentiment distribution. the output of dense layer is calculated by loss function. adam optimizer is also used in this step. the fundamental architecture of the proposed model for a persian sentence is shown in fig. 4. according to fig. 4, for each input sentence, word embedding step is done by word2vec. afterward, the model tries to predict each sentence sentiment with the combination of two neural networks: cnn and lstm. fig. 4: proposed model diagram. 135 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi 4. experiment and results the experimental setup consists of a window operating system running a python virtual environment on python 3.6. the setup was done on pycharm, which is an open-source application. this section is divided into the following parts: data, convolutional and activation, max-pooling and dropout, rnn and baseline. 4.1 data in persian, one problem of nlp tasks is that there is no standard dataset for sentiment analysis. in this section, we used a crawler to collect our data from www.digikala.com which is a famous persian site for electronic products. we named this dataset “pe” which stands for persian electronic dataset. we also used twitter streaming api for creating our second dataset about the political issue in persian. we named this dataset “pp”, which stands for persian political dataset. “pe” as the basic dataset, has 9066 sentences and “pp” has 2550 sentences. we manually classified each sentence as positive, negative, or neutral using ten different computer scientists and native speakers to decide about each sentiment. table 1 illustrates all details about each dataset. in the table (nu, n+, n-) are the number of neutral, positive, and negative sentences respectively. table 1: dataset dataset n+ nnu total pe 3022 3022 3022 9066 pp 850 850 850 2550 the following sections determine the optimal parameters drawn by the experiment. 4.2 convolutional layer and activation the optimal 1dimensional kernel sizes were 3, 5, and 7. these kernel sizes produced higher accuracy. the optimal number of the filter was 128. the relu activation layer was also used in this section 4.3 maxpooling and dropout regarding our experiment for max-pooling, the optimal kernel size was 2. the dropout layer was set at the rate of 0.5 to reduce overfitting. it conducted the model for understanding the data in a better way and could also be the cause of a higher accuracy. 4.4 rnn lstm and gru have 128 and 256 units respectively. regarding the experiment, increasing or decreasing, the number of units causes overfitting. it can also reduce accuracy. 4.5 results we compared our results with four well-known sentiment analysis studies. table 2 reports the experimental results of each model on our persian dataset. according to the table, model 1 is one of the best traditional approaches called nbsvm [12]. model 2 and 3 are two studies on persian sentiment analysis. they deployed naive bayes and logistic regression respectively [19] [17]. model 4 and 5 are suggested as other deep learning studies in persian [20]. they utilized bidirectional-lstm and cnn separately on their proposed models. the results show the hybrid deep learning model outperforms other models since it can harness both cnn's and lstm's abilities. furthermore, the proposed model tries to learn high-level features from data in an incremental manner. the proposed model also uses word2vec as an unsupervised learning 136 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi step for word representation. word2vec uses semantic information from the corpus. it helps the model to perform better and overcomes most challenges in persian such as the different writing style, etc. as shown in the table, cnn-lstm works almost better in comparison to cnn-gru, so cnn-lstm is chosen as the final proposed architecture. table 2: comparative results of different methods on persian dataset model f-score precision recall modell1:nbsvm 44% 70.7% 31.9% model 2: naïve bayes 62.5% 65.4% 61.7% model 3: logistic regression 67.1% 68.9% 65.4% model 4: bidirectional-lstm 53.8% 54.3% 55% model 5: cnn 67% 66% 67% proposed model: cnn-lstm 85% 86.5% 86% cnn-gru 85.8% 85% 82% gru 74% 77.5% 75.6% figure 5 is the illustration of the roc curve for the proposed model. the roc curve analysis is a fundamental tool for evaluating the performance of different models. it compares true positive with false positive rates for all possible thresholds. figure 5 shows roc evaluation for cnn-lstm model on the first dataset (pe). according to the curve, macro and micro evaluation for three classes (class 0: positive, class 1: negative and class 2: neutral) of this study are 86% and 83% respectively. a macro-average computes the metric independently for each class and then takes the average while a micro-average aggregates the contributions of all classes to compute the average metric. the roc curve also shows the evaluation of each class separately. fig. 5: roc curve. 5. conclusion sentiment analysis is an on-going field of study. however, limited studies have been conducted in persian language. based on the author’s knowledge, this is the first study on 137 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi persian sentiment analysis that uses hybrid deep learning architecture cnn-lstm. the cnn-lstm architecture involves cnn for feature extraction and lstm for learning the long term dependencies. therefore, the model can harness both cnn‘s and lstm’s abilities and gets better results with an accuracy of 85%. additionally, we collected two different persian datasets from twitter and digikala as the most famous digital products site. we labelled these sentences as positive, negative, or neutral. they can be useful datasets for persian language. references [1] rajadesingan, a., r. zafarani and h. liu (2015). sarcasm detection on twitter: a behavioural modeling approach. in proceedings of the eighth acm international conference on web search and data mining, (2015): 97-106. [2] jandail, r. r. s., p. sharma and c. agrawal (2014). a survey on sentiment analysis and opinion mining: a need for an organization and requirement of a customer. in international conference on trends in mechanical, aeronautical, computer, civil, electrical and electronics engineering, india, (2016):17-24. [3] feldman, r. (2013). techniques and applications for sentiment analysis. communications of the acm, 56: 82-89. [4] mir, j. and m. usman (2015). an effective model for aspect based opinion mining for social reviews. in tenth international conference on digital information management (icdim), south korea, (2015): 49-56. [5] bagheri, a., m. saraee and f. d. jong (2013). sentiment classification in persian: introducing a mutual information-based. in 21st iranian conference on electrical engineering (icee), iran, (2013):1-6. [6] le, q. and t. mikolov (2014). distributed representations of sentences and documents. in proceedings of the 31 st international conference on machine learning, china, (2014): 1-9. [7] socher, r., j. pennington, e. h. huang, a. y. ng and c. d. manning (2011). semi-supervised recursive auto encoders for predicting sentiment distributions. in emnlp '11 proceedings of the conference on empirical methods in natural language processing, united kingdom, (2011):151-161. [8] lecun, y., l. bottou, y. bengio and p. haffner (1998). gradient-based learning applied to document recognition. in proceedings of the ieee, 86: 2278 – 2324. [9] mikolov, t., m. karafi´at, l. burget, j. h. cernocky and s. khudanpur (2010). recurrent neural network based language model. in interspeech, japan, (2010): 1045-1048. [10] hochreiter, h. and j. schmidhuber (1997). long short-term memory. neural computation, 9(8): 1735-1780. [11] pang, b., l. lee and s. vaithyanathan (2002). thumbs up? sentiment classification using machine learning techniques. in conference on empirical methods in natural language processing (emnlp), philadelphia, (2002): 79-86. [12] wang, s. and c. d. manning (2012). baselines and bigrams: simple, good sentiment and topic classification. in proceedings of the 50th annual meeting of the association for computational linguistics, republic of korea, (2012): 90-94. [13] maas, a. l., r. e. daly, p. t. pham, d. huang, a. y. ng and c. potts (2011). learning word vectors for sentiment analysis. in proceedings of the 49th annual meeting of the association for computational linguistics: human language technologies, portland, oregon, (2011): 19. [14] socher, r., a. perelygin, j. y. wu, j. chuang, c. d. mannin, a. y. ng and c. potts (2013). recursive deep models for semantic compositionality over a sentiment treebank. in proceeding of the conference on empirical methods in natural language processing (emnlp), (2013): 1631–1642. [15] socher, r., b. huval, c. d. manning and a. y. ng (2013). semantic compositionality through recursive matrix-vector spaces. in proceedings of the 2012 joint conference on empirical 138 iium engineering journal, vol. 20, no. 1, 2019 bokaee nezhad and deihimi methods in natural language processing and computational natural language learning, korea, (2013): 1201–1211. [16] bagheri, a., m. saraee and d. j. franciska (2013). sentiment classification in persian: introducing a mutual information-based method for feature selection. in 21st iranian conference on electrical engineering (icee), mashhad, (2013): 1-6. [17] alimardani, s. and a. aghaei (2015). opinion mining in persian language using supervised algorithms. journal of information systems and telecommunication, 3:135-141. [18] hajmohammadi, m. s. and r. ibrahim (2013). a svm-based method for sentiment analysis in persian language. in international conference on graphic and image processing, singapore. [19] basiri, m. e. and a. kabiri (2017). sentence-level sentiment analysis in persian. in 3rd international conference on pattern recognition and image analysis (ipria 2017), iran, (2017): 84-89. [20] roshanfekr, b., s. khadivi and m. rahmati (2017). sentiment analysis using deep learning on persian texts. in 25th iranian conference on electrical engineering (icee2017), iran, (2017):1503-1508. [21] kim, y. (2014). convolutional neural networks for sentence classification. in proceedings of the 2014 conference on empirical methods in natural language processing (emnlp), qatar, (2014): 1746–1751. [22] mikolov, t., k. chen, g. corrado and j. dean (2013). efficient estimation of word representation in vector space, in arxiv preprint arxiv. [23] chung, j., c. gulcehre, k. cho and y. bengio (2014). empirical evaluation of gated recurrent neural networks on sequence modeling. in arxiv preprint arxiv. 139 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <feff004e006100750064006f006b0069007400650020016100690075006f007300200070006100720061006d006500740072007500730020006e006f0072011700640061006d0069002000730075006b0075007200740069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c002000740069006e006b0061006d0075007300200076006500720073006c006f00200064006f006b0075006d0065006e00740061006d00730020006b006f006b0079006200690161006b006100690020007000650072017e0069016b007201170074006900200069007200200073007000610075007300640069006e00740069002e002000530075006b00750072007400750073002000500044004600200064006f006b0075006d0065006e007400750073002000670061006c0069006d006100200061007400690064006100720079007400690020007300750020004100630072006f006200610074002000690072002000410064006f00620065002000520065006100640065007200200036002e00300020006200650069002000760117006c00650073006e0117006d00690073002000760065007200730069006a006f006d00690073002e> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <feff004200720075006b00200064006900730073006500200069006e006e007300740069006c006c0069006e00670065006e0065002000740069006c002000e50020006f0070007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740065007200200073006f006d002000650072002000650067006e0065007400200066006f00720020007000e5006c006900740065006c006900670020007600690073006e0069006e00670020006f00670020007500740073006b007200690066007400200061007600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020005000440046002d0064006f006b0075006d0065006e00740065006e00650020006b0061006e002000e50070006e00650073002000690020004100630072006f00620061007400200065006c006c00650072002000410064006f00620065002000520065006100640065007200200036002e003000200065006c006c00650072002e> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 huda et al. 30 performance of high strength lightweight concrete using palm wastes md. nazmul huda1, mohd zamin jumaat1, abul bashar mohammad saiful islam2* and walid abubaker al-kutti2 1 department of civil engineering, university of malaya, kuala lumpur 50603, malaysia. 2 department of civil & construction engineering, imam abdulrahman bin faisal university, dammam 31451, saudi arabia. * corresponding author: asislam@iau.edu.sa (received: 4th april 2018; accepted: 5th nov 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19i2.919 abstract: the performance of high strength structural lightweight concrete (lwc) using palm wastes, oil palm shell (ops) as well as palm oil clinker (poc) is of foremost concern. existing literature used either ops or poc individually for production of lwc. in this study, both ops and poc have been put together as coarse aggregate on the way to see the improvement of mechanical properties of waste-based lwc. regular coarse aggregate has been fully replaced by ops and poc in the concrete. this structural-grade, lightweight concrete is called palm shell and clinker concrete (pscc). a series of ops and poc mixtures have been investigated aimed at identifying better performance. the quantity of ops and poc mix has been varied as 30, 40, 50, 60 and 70%. evaluated mechanical properties of pscc include density, workability, compressive strength at different ages, flexural strength, splitting tensile strength as well as modulus of elasticity. it is revealed that the proposed pscc has extensive potential in terms of high compressive strength and good material behavior to perform as a better lwc. the study could offer structural lightweight concrete of compressive strength up to 46.47 mpa that is 30.5% higher than the control mix (p100). the usage of 50% ops to 50% poc coarse aggregate by vol. in the concrete mix is found to be the optimum mix. furthermore, simple correlation equations have been developed that can be used to predict the compressive strength, splitting tensile strength, flexural strength, modulus of elasticity and ultrasonic pulse velocity of the lightweight concrete using poc. abstrak: prestasi struktur konkrit ringan (lwc) berkekuatan tinggi menggunakan sisa sawit, iaitu daripada minyak kulit kelapa sawit (ops) dan juga mendakan (klinker) minyak kelapa sawit (poc) adalah keprihatinan utama. kajian sedia ada telah mengguna pakai sama ada ops atau poc secara berasingan bagi menghasilkan lwc. dalam kajian ini, kedua-dua ops dan poc telah digabungkan sebagai agregat kasar bagi mengkaji pembaikan pada ciri-ciri mekanikal sisa lwc. agregat kasar tetap telah digantikan sepenuhnya dengan menggunakan ops dan poc dalam konkrit. struktur gred konkrit ringan ini telah dinamakan sebagai kulit kelapa sawit dan konkrit mendakan klinker (pscc). satu siri campuran ops dan poc telah dikaji bagi mengenal pasti prestasi terbaik. kuantiti campuran ops dan poc telah diubah kepada 30, 40, 50, 60 dan 70%. ciri-ciri mekanikal yang dikaji pada pscc ini adalah ketumpatan, kebolehkerjaan, kekuatan mampatan pada umur berlainan, kekuatan lenturan, kekuatan tegangan pecahan, serta keanjalan modulus. hasil menunjukkan pscc ini mempunyai potensi luas dari segi kekuatan mampatan yang tinggi dan struktur material yang baik sebagai lwc terbaik. kajian ini menawarkan struktur konkrit ringan berkekuatan mampatan sehingga 46 mpa iaitu sebanyak 31% lebih baik daripada campuran kawalan. penggunaan 50% ops kepada 50% poc agregat kasar secara vol. dalam campuran konkrit adalah campuran optimum. iium engineering journal, vol. 19, no. 2, 2018 huda et al. 31 tambahan pula, korelasi mudah telah dibangunkan bagi menjangkakan dengan mudah kekuatan mampatan, kekuatan tegangan pecahan, kekuatan lenturan, keanjalan modulus dan halaju signal ultrasonik konkrit ringan. keywords: palm waste; oil palm shell; palm shell clinker; structural concrete; lightweight aggregate concrete;high strength 1. introduction the recent trend in the construction industry shows increasing usage of lightweight concrete, which is more advantageous than traditional concrete of the same grade. structural lightweight concrete allows engineers to use smaller structural elements due to the reduction of self-weight. as the lightweight aggregate concrete (lwac) reduces the structural weight and hence the construction cost noticeably, it has a significant advantage over normal weight concrete (nwc) [1,2]. for this reason, production of structural lightweight concrete is becoming more popular every day in the construction industry. on the other hand, it is presently a thoughtful issue to find a suitable way to manage the solid waste produced from the agricultural and manufacturing industries [3]. therefore, researchers expect to use the waste materials from the manufacturing industry to produce lwac [4-6]. yielding more than 50% of the world’s palm oil supply every year has made malaysia into the second largest source of palm oil globally [7,8]. the ops and poc are the residues of the industry during palm oil production. recently these agricultural wastes are being used for landfilling and production of charcoal. this causes soil pollution and affects groundwater supply. therefore, its usage as a building construction material effectively turns waste into resources; a very efficient waste management option as well as a very useful structural design option. obviously, the ideology can control the depletion of natural resources as well as retain ecological balance. the oil palm shells are light, flaky and have an irregular shape, as per the nut breaking pattern [9]. as the ops are hard and from a stable organic source, such materials do not leach or contaminate the concrete mix with toxic constituents [10]. it is revealed in existing works of literature that construction industries have introduced lightweight concrete using ops of around 40 mpa [11-14] and using palm kernel shell aggregate of about 25–30 mpa [10] of 28-day cube compressive strength. besides, poc is obtained from the blast furnace where ops and ops fibers are burned at high temperature in a boiler to generate energy. the lumped clinkers are then crushed and sieved to obtain the preferred particle sizes. the fine aggregate has a particle size of less than 5 mm and coarse aggregate has a particle size in the range of 5 – 12 mm. the compressive strength of poc concrete can range in between 25.54 – 44.89 mpa [3,15] that is clearly larger than the minimum strength requirement of structural lwc of 17 mpa. the limitation of ops lightweight concrete is that it sustains less compressive strength but the failure is rather ductile [16]. steel fiber may improve the flexural toughness and other mechanical properties [17]. besides, poc in concrete largely improves the consistency and compressive strength but in failure mode, becomes considerably brittle [16]. however, all the studies have employed ops or poc separately. it is also clear that both ops concrete and poc concrete have their advantages and disadvantages. in this study, the feasibility of combining ops and poc as coarse aggregate will be explored in depth in the search to produce an improved high strength structural lwac. the workability and density, compressive strength, modulus of elasticity flexural strength, and splitting tensile iium engineering journal, vol. 19, no. 2, 2018 huda et al. 32 strength are evaluated for the present innovative structural grade lightweight aggregate concrete, palm shell and clinker concrete (pscc). 2. materials and methods 2.1 concrete constituents 2.1.1 cement ordinary portland cement was utilized in the lightweight concrete throughout the experiments. the physical properties viz. specific gravity and specific surface area of this malaysian manufactured cement were 3.14 and 3510 cm2/g, respectively. such binder material produced concrete with 34.2 mpa (at 7 days) and 45.9 mpa (at 28 days) compressive strength, respectively. 2.1.2 aggregate as a fine aggregate, malaysian local sand was used in the lightweight concrete mix with 2.68 specific gravity fineness modulus of 2.65 and the maximum nominal grain size was 4.75 mm. fig. 1: local waste (a) ops as coarse aggregate; (b) poc as coarse aggregate. the waste materials from the malaysian palm oil industry, namely ops and poc, were chosen as coarse aggregates in this study (fig. 1). while ops is a direct agriculture waste product form oil palm production, poc is produced through the incineration process of pos. the ops, as shown in fig. 1(a), was washed after collection and then a stone-crushing machine was used to crush them in the laboratory [18]. such crushing decreases the ops flakiness in order to enhance the performance of the coarse aggregates and obtain higher compressive strength. thereafter, the crushed ops were sieved and the aggregates larger than 5 mm size were identified and used in the mixes. the poc aggregate has been illustrated in fig. 1(b). for poc as with the ops, the palm oil clinker was sieved after crushing and aggregates larger than 5 mm were selected, expecting a greater abrasion value. table 1 describes the physical properties and mechanical properties of both lightweight coarse aggregates. iium engineering journal, vol. 19, no. 2, 2018 huda et al. 33 table 1: physical and mechanical properties of ops and poc coarse aggregate [3,19] c o a rs e a g g re g a te a g g re g a te s iz e (m m ) s p e c if ic g ra v it y [s a tu ra te d su rf a c e d ry ] w a te r a b so rp ti o n f o r 2 4 h ( % ) a g g re g a te a b ra si o n v a lu e , l o s a n g e le s (% ) b u lk d e n si ty [c o m p a c te d ] (k g /m 3 ) f in e n e ss m o d u lu s, f m f la k in e ss i n d e x (% ) e lo n g a ti o n in d e x ( % ) a g g re g a te im p a c t v a lu e (% ) ops 5-12.5 1.17 23.3 4.8 590 6.24 65.17 12.36 7.86 poc 5-12.5 1.82 4.35 27.09 781.08 6.75 25.36 2.1.3 admixture the concrete mixes comprise sika viscocrete 2199 as a super plasticizer (sp), which is chloride free. this admixture was produced by sika kimia according to en 934-2. to enhance the workability of lwac, the sp was added as 2.0% of cement weight. 2.1.4 water the lwc mixes used potable water available in the materials laboratory. similar water was used for curing the lwac. 2.2 concrete mixtures composition the lwac was designed by trial mixes [20]. several studies used 480-550 kg/m3 cement maintaining 0.3-0.4 water-cement ratio expecting compressive strength 30-44 mpa [21]. this study exploited 450 kg/m3 cement contents and 0.35 water-cement ratio aimed at getting optimum trial mixes. seven trial mixes were conducted. four of the trial mixes were able to achieve grade 45 concrete offering high workability. another two mixes were taken from the previous study to compare the results. identical water-cement ratio was ensured in each and every mix. the sp was given in all the mixes to get the required workability. the mining sand fills the place of a fine aggregate. the ops and poc were used as coarse aggregate in various proportions. in the mix p70, opc to poc proportion in coarse aggregate was 70-30% by volume. this proportion was gradually varied in the successive mixtures as 60-40%, 50-50%, 40-60%, and 30-70% referred to as p60, p50, p40, and p30, respectively. p100 and c100 were incorporated with only ops and poc, respectively. table 2 shows the proportions of ingredients and specifications of the lwac concrete mixes. table 2: concrete mix proportions in kg/m3 mix id cement water w/c ratio sp sand ops poc p70 450 158 0.35 2% 1013 248 (70%) 141 (30%) p60 450 158 0.35 2% 1025 212 (60%) 187 (40%) p50 450 158 0.35 2% 1158 148 (50%) 195 (50%) p40 450 158 0.35 2% 1048 142 (40%) 281 (60%) p30 450 158 0.35 2% 1060 106 (30%) 328 (70%) p100 450 158 0.35 1% 978 354 (100%) 0 c100 450 158 0.35 2% 1095 0 469 (100%) 2.3 specimen preparation the concrete ingredients, cement, sand, ops, and poc, were blended with a pan mixer for 5 minutes to prepare the lwac mixtures. once thoroughly mixed, the sp mixture was iium engineering journal, vol. 19, no. 2, 2018 huda et al. 34 added with about 80% water. the remaining 80% sp was added after 5 minutes of mixing into the pan mixture while continuing the mixing process for 10 min. afterward, the samples were cast in steel molds and vibration table to compact the specimens. the specimen casting follows the code bs 1881 [22]. the samples were demolded after 24 hours. curing was continued until testing days in water at a temperature of 28 ± 2 °c. to obtain average values, three samples of each category were prepared. 2.4 measurement device and experimental testing at the outset, the slump tests were performed for the lwac mixes. the lwac specimens’ compressive strengths were measured for the 1st, 3rd, 7th and 28th day. flexural tensile strength and splitting tensile strength were tested on the 3rd, 7th and 28th day as well. the modulus of elasticity was measured on the 28th day. all the tests followed bs 1881: part 116 [22] employing a universal compression testing machine of 3000 kn capacity, which maintained a loading controller rate. the results of the tests were then averaged for the three randomly selected samples for every category. figure 2 shows the equipment setup for (a) the flexural strength test and (b) the compressometer for modulus of elasticity (es). fig. 2: equipment setup for (a) the flexural strength test, (b) the compressometer for es. 3. results and discussion 3.1 workability the workability results of pscc are presented in fig. 3. each and every trial mix shows acceptable workability. as the water-cement ratio and the usage of sp were kept quite constant, identical slump values are expected with acceptable workability. p50 shows the lowest slump value of 50 mm. the slump of other trial mixes ranges from 55 mm to 70 mm. in the p50, about 13% more fine aggregate is used than other trial mixes. hence, the total surface area in the p50 has increased. therefore, p50 absorbs more water than others. the slump value of p50 has been found to be lower than other mixes as the w/c ratio and amount of sp are the same. the compaction of this mix is satisfactory among the trial mixes. all the coarse aggregates were taken as saturated surface dry condition (ssd). therefore, in measuring the slump value, no influence of coarse aggregate has been observed. mehta and (a) (b) iium engineering journal, vol. 19, no. 2, 2018 huda et al. 35 monteiro [23] recommended a slump of 50–75 mm for structural lwc to obtain workability similar to 100–125 mm slump for regular concrete. in this experimental program, trial mixes having slump value within the suggested acceptable limits indicate the acceptable performance of the pscc in the real application. fig. 3: slump values for different trial mixes. 3.2 density the presented pscc can be treated as structural lightweight concrete, which should have a density in oven dry condition of below 2000 kg/m3 [24]. the densities of each and every mix are in the structural lwc range (table 3). the 28-day oven dry density of pscc range between 1951 to 2075 kg/m3 and their air-dry densities are from 2190 to 2060 kg/m3. considering the density of nwc to be 2400 kg/m3, the oven dry density and air-dry density of pscc at 28-days are around 16–19% and 10–14% less than the corresponding densities of ordinary concrete. table 3: densities at different condition mix id density (kg/m3) air dry density oven dry density p70 2083 1951 p60 2115 1991 p50 2175 2020 p40 2130 1970 p30 2190 2069 p100 2060 1888 c100 2189 2075 3.3 compressive strength the 28-day compressive strength of pscc reduces with an increase in ops percentage in coarse aggregate content (table 4). the p50 mix, having 50% poc shows a maximum compressive strength of 46.47 mpa and it is 30.5% greater than the p100. the mix with the highest percentage of ops content, p70, exhibits the lowest compressive strength. again, 100% replacement of ops content with poc aggregate increases the compressive strength 65 60 50 70 55 60 65 0 10 20 30 40 50 60 70 80 p70 p60 p50 p40 p30 p100 c100 s lu m p v a lu e ( m m ) mix id iium engineering journal, vol. 19, no. 2, 2018 huda et al. 36 about 15%, whereas its 50% replacement upsurges compressive strength by about 30%. in p70, ops content goes up to 70%, resulting in 18% lower compressive strength than p50. this may be due to the round and plain surface texture of ops that is responsible for poor bondage to concrete if excessively present. the compressive strengthening value is a little bit lower than p50 but higher than for the p40 mix, though it has a high slump of 70 mm. it also shows a good combination. it is noteworthy that the ops is of larger size than poc. the void of such 40% ops is getting more poc to be filled as the mix has 60% poc and such interaction reflects good bonding among coarse aggregate. therefore, the p40 mix shows its potential for contributing 42.35 mpa to the 28-day compressive results and may be the second choice of optimum mix. definitely, the poc aggregate induces strong bonding with cementing paste due to its rough and porous texture. p100 and c100 show the 28-day compressive strength for opsand poc-based concrete, respectively. concrete containing ops only (p100) poses the lowest compressive strength. besides, concrete containing poc only (c100) shows a compressive strength of 41 mpa, 12% lower than p50. because of shortcoming of ops and poc individually, an optimum mix should be designed that may ensure enhanced compressive strength as well as better bonding. the p50 mix refers to the desired optimum mix. table 4: compressive strength of pscc concrete mix id compressive strength (mpa) 1 day 3 day 7 day 28 day p70 22.87 31.39 35.43 38.28 p60 26.62 33.70 36.01 38.57 p50 32.34 39.95 44.64 46.47 p40 30.70 36.23 40.13 42.35 p30 27.88 34.86 38.56 40.64 p100 21.45 26.86 30.55 35.60 c100 30.10 38.47 39.79 41.08 the relationship of the development of compressive strength in 28-d with the concrete age is shown in fig. 4. usually, the logarithmic increment offers high coefficient values with increasing age of the concrete [25]. lo, cui [26] stated a correlation of 82-90% for 28d lwac compressive strength at 7-d age incorporating coarse aggregate, expanded clay that is comparable to this study (85-95%). the equations of correlations of compressive strengths are derived in eq. (1) ~ (7) for the selected mixes. the scenario shows the maximum development of compressive strength in the case of p50. the strength expansion is deliberated sequentially by the gradual equations. 𝑓𝑐28(𝑃50) ′ = 4.2339 ln(𝑑𝑎𝑦) + 34.10 (1) 𝑓𝑐28(𝑃40) ′ = 3.5108 ln(𝑑𝑎𝑦) + 31.76 (2) 𝑓𝑐28(𝐶100) ′ = 3.0926 ln(𝑑𝑎𝑦) + 32.43 (3) 𝑓𝑐28(𝑃30) ′ = 3.7891 ln(𝑑𝑎𝑦) + 29.45 (4) 𝑓𝑐28(𝑃60) ′ = 3.4669 ln(𝑑𝑎𝑦) + 28.20 (5) 𝑓𝑐28(𝑃70) ′ = 4.5484 ln(𝑑𝑎𝑦) + 24.74 (6) 𝑓𝑐28(𝑃100) ′ = 4.2338 ln(𝑑𝑎𝑦) + 21.87 (7) iium engineering journal, vol. 19, no. 2, 2018 huda et al. 37 fig. 4: correlation of compressive strength with concrete age. 3.4 splitting tensile and flexural strength the splitting tensile and flexural strengths of the trial mixes are illustrated in table 5. from the tabular sketch, it is seen that 2.86 mpa is the lowest 28-day splitting tensile strength that fulfills the minimum requirement (2.0 mpa) for lightweight concrete [27]. besides, the minimum 28-day flexural strength has been found to be 3.93 mpa. p50 has the largest value of splitting tensile (3.67 mpa) and flexural strength (6.0 mpa) over the control mixes p100 and c100. about 80-90% of both types of strength are developed during the first 7 days. therefore, the splitting tensile together with the flexural strength of structural member made from this lwac may be exploited at an early age of 7 days. usually, different equations are required for lightweight concrete made from different aggregates. hence, the relationship among the compressive strength (fc), splitting tensile strength (ft) and flexural strengths (fr) at 28 days of pscc have been engendered and presented in fig. 5. accordingly, empirical equations have been suggested to predict splitting tensile (eq. 8) and flexural strength (eq. 9) of the pscc concrete. 𝑓𝑡 = 0.0748𝑓𝑐 1.0126 (8) 𝑓𝑟 = 0.0011𝑓𝑐 2.2401 (9) table 5: flexural and splitting tensile strength of ops and poc concrete mix id splitting tensile strength (mpa) flexural strength (mpa) 3 day 7 day 28 day 3 day 7 day 28 day p70 2.41 2.76 2.90 3.71 3.75 3.93 p60 2.36 2.75 3.02 3.98 3.85 4.33 p50 3.38 3.53 3.67 5.18 5.83 6.00 p40 2.86 3.14 3.37 4.77 5.21 5.47 p30 2.32 2.52 3.11 4.04 4.15 4.27 p100 2.50 2.76 2.86 2.93 3.03 3.34 c100 2.79 3.00 3.25 4.00 4.44 4.69 iium engineering journal, vol. 19, no. 2, 2018 huda et al. 38 from table 5, the influence of ops-poc aggregate combinations in the pscc can be observed. it is perceived that if the percentage of ops aggregate is greater, the splitting tensile and flexural strength is also lower. these strengths increase gradually with the upsurge of poc content. after the ratio of 50% of ops and 50% of poc aggregate mix (p50), both the splitting tensile as well as flexural strength tend to reduce. this happens due to the round surface of ops aggregates possessing a weaker bond in concrete and bonding strength reduction for allowing cementing material entering to the pores of poc aggregate [16]. therefore, p50 is the optimum mix that obtains the maximum splitting tensile and flexural strength. fig. 5: correlation among 28-day compressive, splitting tensile and flexural strength. 3.5 modulus of elasticity for calculating the deflection and the stiffness of any structural element, modulus of elasticity (es) appears to be an important parameter. therefore, it is necessary to find a suitable correlation depending on the compressive strength for predicting this modulus of elasticity that relies on the elastic modulus of its components and their volumetric proportions [28]. for addition of poc aggregate contents in the lwc mix, the modulus of elasticity increases as shown in fig. 6. this increase results from the higher specific gravity of poc content. in this study, the mixture with p50, gives the maximum value of modulus of elasticity. p40 shows 6% lower value of elastic modulus. when the mixes (p60 and p70) contain poc lower than 50% by vol., the modulus of elasticity dips down about 20%. figure 6 shows a correlation of es and cube compressive strength of pscc which have been compared with the previously used equation (eq. 10) for predicting es of lwc in cep/fip manual [29]. figure 6 also compares empirical equations (eq. 11 and eq. 12) suggested by existing research to predict the es for ops concrete, but none of them are universally accepted [16,30]. ft = 0.0748fc 1.0126 r² = 0.9423 fr = 0.0011fc 2.2401 r² = 0.9251 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 34 36 38 40 42 44 46 48 t e n si le s tr e n g th , m p a compressive strength, mpa splitting tensile strength flexural strength iium engineering journal, vol. 19, no. 2, 2018 huda et al. 39 𝐸𝑠(𝑝𝑟𝑒) = [𝜌/2400] 2 𝑥 𝑓𝑐 1/3 𝑥 9.1 (10) 𝐸𝑠(𝑝𝑟𝑒) = [𝜌/2400] 2 𝑥 𝑓𝑐 1/3 𝑥 5.0 (11) 𝐸𝑠(𝑝𝑟𝑒) = 0.0005 𝑥 𝑓𝑐 2.69 (12) where, es(pre) (gpa) is the predicted elastic modulus, fc (mpa) is cube compressive strength and 𝜌 (kg/m3) is the concrete’s air-dry density. figure 6 shows that the ceb/fip manual highly overestimates the es. the equation derived by the alengaram, mahmud [30] also overestimates the es for the pscc that contains lower amounts of poc content. the equation proposed by ahmmad, jumaat [16] also approaches the higher es value for the pscc that contains a higher amount of poc content. from the above experimental findings, a simplified equation (eq. 13) has been suggested for predicting the es as per the experimental compressive strength data. 𝐸𝑠 = 0.0257 𝑥 𝑓𝑐 1.6205 (13) fig. 6: compressive strength vs. modulus of elasticity curve. 3.6 correlation of ultrasonic pulse velocity with compressive strength in the existing literature, a distinctive correlation of concrete compressive strength and its ultrasonic pulse velocity (upv) is rarely found [31]. however, it is obvious that the water/cement ratio affects the hardened mortar and consequently the upv values are influenced. if water fills the voids, the travelling of upv comes quicker compared to that for air filling. this phenomenon indicates that the upv of the concrete is also affected by the moisture. the concrete containing the upv values ranging from 3.66 to 4.58 km/s is labeled as ‘good’ [32]. such concrete doesn’t have large voids or cracks leading to reduced structural integrity. on the other hand, the concrete strength might be evaluated using this upv test outcome. in the experimental investigation, all the mixes execute the upv values es = 0.0257x (fc) 1.6205 r² = 0.8828 5 10 15 20 25 30 35 35 38 41 44 47 m o d u lu a s o f e la st ic it y , e ( g p a ) 28 day compreesive strength, fc (mpa) experiment (presnt study) short and kinniburgh [29] rasel et al. [16] alengaram et al. [30] iium engineering journal, vol. 19, no. 2, 2018 huda et al. 40 higher than 3.66 km/s. in addition, for the variation of coarse aggregate content, the lwac strength also changes. here, an empirical relation of compressive strength and upv of the presented lightweight aggregate concrete, pscc varying the percentages of coarse aggregates has been established (fig. 7). accordingly, succeeding equation (eq. 14) has been derived for prediction of upv. 𝑓𝑐 = 5.0658 𝑥 (𝑈𝑃𝑉) 1.4502 (14) fig. 7: compressive strength vs. ultrasonic pulse velocity. 4. concluding remarks the following findings can be summarized from the study:  this research produces high strength structural lightweight concrete, pscc of 28day compressive strength of 46 mpa that can be used for structural purposes.  the usage of 50% ops to 50% poc coarse aggregate by vol. in the concrete mix is the optimum mix to produce grade 45 concrete. it requires 450 kg/m3 cement, which is lowest among the recent studies for manufacturing grade 45 concrete.  the average oven-dry density of pscc having 28-day compressive strength in between 38–46 mpa is 18.7% lower compared to the case of normal weight concrete.  pscc has structural grade splitting tensile strength and flexural strength. however, poc content helps to gain these strengths up to a certain limit (50% poc content and 50% ops content). after this limit, it tends to yield lower strength values.  the modulus of elasticity increases with the increase of poc content in pscc. however, if the poc content is greater than 50%, the modulus of elasticity is greater than 10 gpa, which conforms to the lightweight concrete requirement.  the developed simplified equation easily determines the modulus of elasticity from compressive strength.  the regression analysis of relating compressive strength of pscc with upv shows good correlation. the value for the r2 is 0.8981. fc = 5.0658(upv) 1.4502 r² = 0.8981 30 35 40 45 50 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 c o m p re ss iv e s tr e n g th , fc ( m p a ) upv (km/s) iium engineering journal, vol. 19, no. 2, 2018 huda et al. 41  in order to enable the universal equation for predicting the splitting tensile strength, flexural strength, and modulus of elasticity, the regression model can be done by incorporating a vast amount of experimental data for future study. acknowledgement the authors gratefully acknowledge university of malaya (um), malaysia as well as the dsr project 2017-212-eng, imam abdulrahman bin faisal university (iau), saudi arabia for successful completion of the work. references [1] mannan m, ganapathy c. (2001) mix design for oil palm shell concrete. cement and concrete research, 31:1323-1325. [2] shafigh p, mahmud hb, jumaat mz, zargar m. (2014) agricultural wastes as aggregate in concrete mixtures – a review. construction and building materials, 53:110-117. [3] mohammed bs, foo w, abdullahi m. (2014) flexural strength of palm oil clinker concrete beams. materials & design, 53:325-331. [4] shafigh p, jumaat mz, mahmud h. (2011) oil palm shell as a lightweight aggregate for production high strength lightweight concrete. construction and building materials, 25:1848-1853. [5] huda mn, jumaat mz, islam abms, soeb mr. (2016) influence of palm oil factory wastes as coarse aggregate species for high performance lightweight concrete. revista de la construcción, 15:133-139. [6] al-kutti w, islam abms, nasir m. (2017) potential use of date palm ash in cement-based materials. journal of king saud university engineering sciences. doi: https://doi.org/10.1016/j.jksues.2017.01.004 [7] teo dcl, mannan ma, kurian vj. (2006) structural concrete using oil palm shell (ops) as lightweight aggregate. turkish journal of engineering and environmental sciences, 30:251257. [8] huda mn, jumat mzb, islam abms, darain kmu, obaydullah m, hosen ma. (2017) palm oil industry’s bi-products as coarse aggregate in structural lightweight concrete. computers and concrete, 19:515-526. [9] alengaram uj, jumaat mz, mahmud h. (2008) ductility behaviour of reinforced palm kernel shell concrete beams. european journal of scientific research, 23:406-420. [10] okafor fo. (1988) palm kernel shell as a lightweight aggregate for concrete. cement and concrete research, 18:901-910. [11] basri h, mannan m, zain m. (1999) concrete using waste oil palm shells as aggregate. cement and concrete research, 29:619-622. [12] alengaram u, jumaat m, mahmud h. (2008) influence of cementitious materials and aggregates content on compressive strength of palm kernel shell concrete. j appl sci, 8:3207-3213. [13] mannan m, ganapathy c. (2001) long-term strengths of concrete with oil palm shell as coarse aggregate. cement and concrete research, 31:1319-1321. [14] mannan m, alexander j, ganapathy c, teo d. (2006) quality improvement of oil palm shell (ops) as coarse aggregate in lightweight concrete. building and environment, 41:12391242. [15] huda mn, jumat mzb, islam abms. (2016) flexural performance of reinforced oil palm shell &amp; palm oil clinker concrete (pscc) beam. construction and building materials, 127:18-25. [16] ahmmad r, jumaat m, bahri s, islam as. (2014) ductility performance of lightweight concrete element containing massive palm shell clinker. construction and building materials, 63:234-241. https://doi.org/10.1016/j.jksues.2017.01.004 iium engineering journal, vol. 19, no. 2, 2018 huda et al. 42 [17] mo kh, yap kkq, alengaram uj, jumaat mz. (2014) the effect of steel fibres on the enhancement of flexural and compressive toughness and fracture characteristics of oil palm shell concrete. construction and building materials, 55:20-28. [18] shafigh p, jumaat mz, mahmud hb, alengaram uj. (2011) a new method of producing high strength oil palm shell lightweight concrete. materials & design, 32:4839-4843. [19] mannan m, ganapathy c. (2004) concrete from an agricultural waste-oil palm shell (ops). building and environment, 39:441-448. [20] shetty m. (2005) concrete technology theory and practice. 1st multicolour illustrative revised ed: s. chand & company, new delhi, india. [21] aci committee 211.2. (1998) standard practice for selecting proportions for structural. lightweight concrete aci journal proceedings, 64. [22] bs, part,116:. (1983) method for determination of compressive strength of concrete cubes. london: british standard institution. [23] mehta pk, monteiro pj. (2006) concrete: microstructure, properties, and materials: mcgraw-hill new york. [24] newman j, choo bs. (2003) advanced concrete technology 3: processes: butterworthheinemann. [25] ahmad s, al-kutti wa, al-amoudi osb, maslehuddin m. (2008) compliance criteria for quality concrete. construction and building materials, 22:1029-1036. [26] lo ty, cui hz, li zg. (2004) influence of aggregate pre-wetting and fly ash on mechanical properties of lightweight concrete. waste management, 24:333-338. [27] kockal nu, ozturan t. (2011) strength and elastic properties of structural lightweight concretes. materials & design, 32:2396-2403. [28] neville am. (1970) hardened concrete: physical and mechanical aspects, american concrete institute, usa. [29] short a, kinniburgh w. (1978) lightweight concrete: applied science publishers london. [30] alengaram uj, mahmud h, jumaat mz. (2011) enhancement and prediction of modulus of elasticity of palm kernel shell concrete. materials & design, 32:2143-2148. [31] neville a. (2008) properties of concrete ctp-vvp. [32] leslie j, cheesman w. (1949) an ultrasonic method of studying deterioration and cracking in concrete structures. journal of the american concrete institute, 21:17-36. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 samat et al. https://doi.org/10.31436/iiumej.v20i2.1066 dynamic mechanical and water absorption properties of microcrystalline cellulose reinforced polypropylene composites: the effect of unconventional irradiation route noorasikin samat*, nurul hakimah mohd lazim, zahurin halim department of manufacturing and materials, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. *corresponding author: noorasikin@iium.edu.my (received: 25th january 2019; accepted: 5th july 2019; published on-line:2nd december 2019) abstract: the unconventional electron beam (eb) irradiation route in preparing microcrystalline cellulose (mcc) fiber reinforced recycled polypropylene (rpp) composites was studied. in this route, the rpp was first subjected to eb irradiation at various doses (10-50kgy) and was then used as a compatibilizer. unirradiated and irradiated rpps were blended at two different ratios (90:10; 50:50) and added with mcc at contents of 5, 20 and 40wt%. dynamic mechanical analysis (dma) and water absorption tests were carried out. the dma spectra exhibited high stiffness and damping behaviour. as the content of mcc increased, the water resistance of composites dropped slightly as compared to the controlled rpp. however, some compositions (50:50/40mcc-10kgy and 50:50/5mcc-50kgy) had shown opposite results. the improvement in the studied properties proved the existence of the compatibility effect that occurred at low irradiation doses, and also depended on the ratio (unirradiated and irradiated rpp) and mcc contents. abstrak: kaedah sinaran gelombang elektron secara bukan konvensional dalam penyediaan komposit polipropilena kitar semula (rpp) bersama serat selulosa mikrohablur (mcc) telah dikaji. dalam kaedah ini, rpp telah didedahkan kepada sinaran gelombang elektron dengan dos yang berbeza (10-50kgy) dan kemudiannya digunakan sebagai penserasi. rpp tidak tersinar dan tersinar telah dicampur dengan nisbah (90:10; 50:50) dan ditambah dengan mcc pada kandungan 5, 20 and 40wt%. analisis dinamik mekanikal (dma) dan ujian penyerapan air telah dijalankan. spektrum dma menunjukkan sifat kekakuan dan pengenduran yang tinggi. apabila kandungan mcc bertambah, kerintangan komposit terhadap air berkurang sedikit berbanding rpp terkawal. bagaimanapun sebahagian komposisi (50:50/40mcc-10kgy and 50:50/5mcc-50kgy) telah menunjukkan keputusan sebaliknya. penambahbaikan sifat bahan dalam kajian ini membuktikan kewujudan kesan keserasian yang berlaku pada dos sinaran rendah, dan juga bergantung kepada nisbah (rpp tidak tersinar dan tersinar) dan kandungan mcc. keywords: polypropylene; cellulose; compatibilizer; electron beam irradiation; mechanical properties 1. introduction the changing of chemical, structural, and other physical properties of polymers through the application of ionizing radiation (ir) is not a new technique. of all the 188 iium engineering journal, vol. 20, no. 2, 2019 samat et al. https://doi.org/10.31436/iiumej.v20i2.1066 existing irradiation methods, the most common modes of ir used are the gamma irradiation and electron beam (eb) processing. there are a few advantages to the use of eb irradiation. it is fast, simple, can be carried out at room temperature, and the technology is completely environmentally friendly. during the irradiation process, the energy is transferred from the irradiating source to the atoms of irradiated materials. this will result in a few chemical reactions taking place, such as chain scission, branching, and crosslinking [1-2] that subsequently alter the mechanical and thermal properties of the materials [2-7]. generally, the formation of crosslinking will lead to improvements of properties. many industries, such as those producing heat shrink tubes, crosslinked wires and cables, packing films, and foams have adopted the eb radiation technique in their product development segment [8-9]. eb processing is also used for sterilization of medical devices, drug delivery systems, preservation of food, and surface curing [10-11]. due to its wide usage, numerous published works have employed eb techniques in the study of polymer composites. in the conventional route for polymer composites, the ir is usually applied after the composites have been fabricated [12-14]. however, a new irradiation route for preparing reinforced polymer composites has been reported by karsli et al. and gomes et al., where the polypropylene (pp) that was exposed to gamma and eb irradiation respectively, was compounded with short carbon and piassava fibers [15-16]. tensile tests were performed in both cases to evaluate the function of irradiated pps as a compatibilizer. this unconventional irradiation route had also been further explored in our previous works [25] in recycled polypropylene (rpp) that was reinforced with microcrystalline cellulose (mcc). here, the possibility of irradiated recycled pp being a compatibilizer was assessed based on the tensile, impact strength and thermal properties. in all of these cases [2-5, 1516], the properties of composites had been better than the controlled polymer, thereby proving the compatibility effect of the virgin pp or recycled pp through the use of ir. apart from using coupling agents to improve the compatibility between natural fiber and polymer [17-19], the use of eb via the unconventional irradiation route would offer an alternative solution in overcoming this drawback. the major advantage of this route is that the modification was carried out on the polymer matrix itself without any chemical modifier or coupling agent. therefore, the present work aims to further investigate the effects of irradiated recycled pp on dynamic mechanical analysis (dma) and water absorption properties from the developed composites. the results derived from this analysis is a supplementary research on an earlier study conducted by lazim et al. [2-3] and samat et al. [4]. 2. materials and method 2.1 materials recycled polypropylene (rpp) from industrial waste was purchased from top flow sdn. bhd., shah alam, selangor. the reinforcement material was microcrystalline cellulose (mcc) in the form of a fine white powder with a density of 0.6 g/cm3, which was obtained from sigma-aldrich co. (m) sdn. bhd. the polymer and the mcc had been dried in an oven at 40-60 °c for at least 7 hours before use. 2.2 preparation of composites the rpp pellets were irradiated using a 3mev electron beam (eb) using the eb model eps-3000 at room temperature under oxygenated conditions. irradiation doses were varied 189 iium engineering journal, vol. 20, no. 2, 2019 samat et al. https://doi.org/10.31436/iiumej.v20i2.1066 at 5, 10, and 50 kgy, respectively. the unirradiated and irradiated rpp pellets were blended at corresponding ratios of 90:10 wt% and 50:50 wt% according to weight before being added with the various mcc loadings (5, 20, and 40 wt%) using a brabender twin screw extruder machine at a screw speed of 70-90 rpm. the compounded materials were pelletized and fed into battenfield hm 600/850 injection moulding to form specimens according to the testing standards (astm: d638). 2.3 dynamic mechanical analysis (dma) dynamic mechanical analysis was conducted over a wide range of temperatures as a means of studying the viscoelasticity behaviour of the materials. dma was conducted using a perkin elmer pyris diamond dmta machine using astm d7028. the testing was carried out in three-point bending mode at a frequency of 1 hz. the temperature range was -50 °c to 150 °c with heating rate at 5 °c/min. the storage modulus (e’) and damping factor (tan δ) of the samples were measured as a function of temperature. 2.4 water absorption all of the samples had been immersed in distilled water for seven days in a closed container at room temperature. the samples were wiped with tissue and weights were recorded for the initial two 6 hours, which was followed by the next 12 hours and subsequently 24 hours with the whole process repeated until day seven. the percentage of increase in water in relative to the initial weight of each sample was reported as the amount of water absorbed. six samples of replicated specimens for each composition were used to obtain the average value. the water absorption percentage after being soaked (mt) was calculated according to eq. (1) (astm d570-98): where wi = initial and wf = final weight, respectively. 2.5 gel content analysis the result of gel content for neat rpp and rpp/mcc composite samples has been reported in our previous work [2]. the gel content of was determined by the extraction of samples in xylene solvent at 130oc for 24 h (astm d2765). these samples were dried and weighed and the gel fraction was calculated as: where w0 = initial and w = final weight , respectively. 3. results and discussion 3.1 dynamic mechanical analysis (dma) figure 1 shows the effect of rpp:i-rpp ratio, mcc content and the irradiation dosage to the storage modulus (e’) of the rpp reinforced with 40 wt% mcc fibers. it was observed that in the glassy region, the e’ of the neat rpp and rpp:i-rpp/mcc composites had remained fairly constant before gradually decreasing across the measured temperature ranges. no rubbery plateau was noticed in these dma curves. upon further analysis, it was observed that there had been a greater increase of the e’ of the rpp:i-rpp/mcc composites as compared to the neat rpp. this implies that the addition of mcc fibers had enhanced the stiffness by restricting the flow of rpp matrix, which is in line with the results obtained from young’s modulus [3-4]. the storage moduli at specific 190 iium engineering journal, vol. 20, no. 2, 2019 samat et al. https://doi.org/10.31436/iiumej.v20i2.1066 temperatures; -50 °c (glassy region), +27 °c (room temperature) and +100 °c (possible use temperature) were selected as a means of comparing the effect of rpp:i-rpp ratio and irradiation dose. the results are presented in table 1. fig. 1: the storage moduli of (a) neat rpp, (b) 90:10/40mcc-10kgy, (c) 50:50/40mcc-10kgy, and (d) 50:50/40mcc-20kgy. table 1: storage moduli and tg values of rpp and rpp: i-rpp/mcc composites at -50 °c, the increase of the storage moduli of composites with 10 kgy i-rpp at 50:50 ratio was larger than that of 90:10. moreover, the difference in the storage moduli values of sample 50:50 at 20 kgy is an indication the benefit derived from i-rpp as a second contributor to the enhancement of stiffness. previously, it was found that at a ratio of 50:50, the increase in the stiffness of composites was dominated by the presence of higher mcc content and that the presence of i-rpp promoted a ‘compatibilizing effect’ [4]. from the ftir [2] and morphological analysis [2-4], this effect is attributed through the formation of crosslinking and better filler-matrix interfacial adhesion, respectively. the existence of crosslinking in the 50:50/40mcc-10kgy sample was evident in its ftir spectra through the absence of the absorption peak assigned to a carbonyl group (c=o) [2]. according to lazim et al., the disappearance of this absorption peak shows the suppression of the oxidation process associated with the presence of crosslinking structure [2]. in contrast, for the 90:10/40mcc-10kgy sample, the absorption peak of the carbonyl group was pronounced. therefore, it is likely, a higher i-rpp content had formed harder domains in the rpp through the formation of greater crosslinking, thereby increasing the samples e’ at -50°c (mpa) e’ at +27°c (mpa) e’ at +100°c (mpa) rpp 3000 1620 294 90:10/40mcc10kgy 4033 2184 585 50:50/40mcc-10kgy 5662 2658 691 50:50/40mcc-20kgy 4310 2986 658 191 iium engineering journal, vol. 20, no. 2, 2019 samat et al. https://doi.org/10.31436/iiumej.v20i2.1066 e’. the influence of greater crosslinking to the increase of storage modulus of composites was also reported by banik et al. and pang et al. [20-21]. it is worth noting that the improvement in the storage modulus had occurred at a low irradiation dose (10 kgy). earlier on, it was discovered that that higher dosage had led to chain scission; which also reduced the level of crosslinking [2]. from table 1, when the temperature was increased from -50 to +100 oc, it was evident that there was a reduction in the values of e’, indicating a shift to the rubbery phase. the changing of phase was due to the loosening of chains between the rpp and mcc fibers that led to the increased flexibility of the composite. it was noticed that the e’ value of rpp had dropped considerably compared to those of the composite samples. fig. 2: the tan d of (a) neat rpp, (b) 90:10/40mcc-10kgy, (c) 50:50/40mcc-10kgy, and (d) 50:50/40mcc-20kgy. results of the damping behaviour of rpp composites along with their glass transition temperature (tg) values are presented in figure 2. as seen from the illustration, the neat rpp has the lowest tg value, which is 5.29 °c. the deviation relative to rpp was evident for the composite samples, where the tg had shifted to higher values. this finding had also validated the existence of crosslinking in the rpp composites. according to wongsuban et al., cross-linked structure inhibits the mobility of the polymer chains [22]. consequently, a higher temperature is required to trigger the change of phases (glassy to rubbery) in the rpp matrix, which was demonstrated by the marked increment in the sample of rpp:irpp/40mcc-10kgy (tg=13.27 °c). in fact, this enhancement had almost doubled as compared to rpp (tg=5.29 °c), suggesting that the sample had the most prominent compatibilizing effect. interestingly, unlike the other natural fiber reinforced polymer system; the intensity of the tan delta peak had declined with the increase of filler content [19, 23-24]. nevertheless, in our case, the peak curve of tan delta of sample rpp:irpp/40mcc-10kgy was observed to be higher than the rpp, which suggests a better damping behaviour. indeed, the similar sample (50:50/40mcc-10kgy) had also demonstrated substantial improvement of the impact strength as reported in our earlier work [2]. 192 iium engineering journal, vol. 20, no. 2, 2019 samat et al. https://doi.org/10.31436/iiumej.v20i2.1066 3.2 water absorption figure 3 depicts the water absorption results for the neat rpp and composite samples. in general, the composites had exhibited a higher water uptake percentage as compared to the neat rpp at all immersion time and composition ranges. this was due to the addition of hydrophilic mcc fibers into the polymer matrices, which had increased the ability of rpp composites to absorb more water. during the initial immersion period (<12hr), the difference in the water absorption percentages for all samples had been negligible. as observed in figure 3, the water uptake of composites had increased steadily after the immersion period was extended beyond 24 hours. this result was expected due to the increased interaction between the hydrogen molecule from water and the -oh molecule from the mcc fibers. nevertheless, the overall water uptake of the composites is considered low since the highest percentage shown was less than 5%. therefore, it is suggested that i-rpp promotes the hydrophobicity of the rpp/mcc composites through the formation of better interfacial adhesion. fig. 3: water absorption percentage of rpp and rpp/mcc composites over a period of seven days. as discussed earlier, the varied irradiation doses along with the mcc content caused different crosslinking densities, which subsequently affected the filler-matrix interfacial adhesion. to gain a better perspective on this circumstance, a comparison between the gel content (table 2) and water uptake results (fig. 3) was made. apparently, the composites that possessed higher gel content value had shown a better water resistance than those with lower gel content values. hence, it is suggested that higher crosslinking densities decrease the diffusion rate of water molecules in the composite, which subsequently leads to lower water uptake. a lower crosslinking density, on the other hand, would only ease the diffusion of water molecules mainly in the amorphous parts [25]. furthermore, the decrease in the water absorption in this work is similar to the case in natural fiber/polymer composites treated with coupling agent [26-27]. this observation indicates that the introduction of i-rpp was beneficial to improve resistance against water absorption. 193 iium engineering journal, vol. 20, no. 2, 2019 samat et al. https://doi.org/10.31436/iiumej.v20i2.1066 table 2: water absorption and gel content percentage of rpp/mcc composites ratio sample 12hr 24hr 96hr 144hr gel content (%) [2] 90:10 5mcc-10kgy 0.523 1.178 1.557 1.662 40mcc-10kgy 0.127 1.184 4.083 4.271 13.16 5mcc-50kgy 0.445 1.138 3.992 4.121 40mcc-50kgy 0.118 1.021 3.036 4.057 20.18 50:50 5mcc-10kgy 0.249 2.578 2.839 3.101 24.41 40mcc-10kgy 0.353 1.531 1.675 1.911 61.43 5mcc-50kgy 0.170 1.138 2.067 2.277 40mcc-50kgy 0.379 1.413 2.996 3.349 4.65 4. conclusion from this investigation, the irregular irradiation route has offered a promising technique on inducing the compatibility behaviour that enhances the recycled pp composites’ properties. the enhancement in stiffness (storage modulus) of composites and the damping property had depended on higher levels of mcc content, rpp:i-rpp ratio and crosslinking value. a greater crosslinking density also slows down the absorption of water into the composites. sample 50:50/40mcc-10kgy exhibits tremendous properties compared to other compositions. acknowledgement the authors would like to thank the international islamic university malaysia (iium) and ministry of higher education (mohe), malaysia (frgs14-163-0404) for the support of this research. references [1] miranda lf, pereira nc, faldini sb, masson tj, silva lga, silveira lh. (2009) effect of ionizing radiation on polypropylene composites reinforced with coconut fibers. in proceedings of the international nuclear atlantic conference:27 september – 2 october 2009; rio de janeiro, brazil; pp 1-9 [2] lazim nh, samat n. (2019) the influence of irradiated recycled polypropylene compatibilizer on the impact fracture behavior of recycled polypropylene/microcrystalline cellulose composites. polymer composites, 40(s1): e24-e34. [3] lazim nh, samat n. (2017) effects of irradiated recycled polypropylene compatibilizer on the mechanical properties of microcrystalline cellulose reinforced recycled polypropylene composites. procedia engineering, 184:538–543. [4] samat n, lazim nh, motsidi snr, azlina hn. (2017) performance properties of irradiated recycled polypropylene as a compatibilizer in recycled polypropylene/microcrystalline cellulose composites. materials science forum, 894:62-65. [5] samat n, motsidi snr, lazim nh. (2018) effects of electron beam radiation dose on the compatibilization behaviour in recycled polypropylene/microcrystalline cellulose composites, iop conference series: mater. sci. eng.,290: 012034. [6] moldovan a, patachia s, vasile c, darie r, manaila e, tierean m. (2013) natural fibres/polyolefins composites (i) uv and electron beam irradiation. j. of biobased materials and bioenergy, 7(1):58-79. [7] rimdusit s, wongsongyot s, jittarom s, suwanmala p, tiptipakorn s. (2011) effects of gamma irradiation with and without compatibilizer on the mechanical properties of polypropylene/wood flour composites. j. of polymer research, 18(4):801-809. 194 iium engineering journal, vol. 20, no. 2, 2019 samat et al. https://doi.org/10.31436/iiumej.v20i2.1066 [8] cleland m, parks l, cheng, s. (2003) applications for radiation processing of materials. nuclear instruments and methods in physics research section b: beam interactions with materials and atoms, 208:66-73. [9] tamada, m. (2018) radiation processing of polymers and its applications. in radiation applications, volume 7. edited by kudo h. singapore, springer; pp 63-80. [10] cai x, blanchet p. (2015) electron-beam curing of acrylate/nanoparticle impregnated wood products. bioresources, 10(3): 3852-3864. [11] porto kmb, napolitano cm, borrely si. (2018) gamma radiation effects in packaging for sterilization of health products and their constituents paper and plastic film. radiation physics and chemistry, 142:23-28. [12] kim sw, park k, lee sh, kang js, kang kh. (2007) dependence of mechanical and thermal properties of thermoplastic composites on electron beam irradiation. int. j. thermophysics, 28:1067-1073. [13] moldovan a, patachia s, vasile c, darie r, manaila e, tierean, m. (2013) natural fibres/polyolefins composites (i) uv and electron beam irradiation. j. of biobased materials and bioenergy, 7(1): 58-79. [14] yan j, kim b, jeong yg. (2015) thermomechanical and electrical properties of pdms/mwcnt composite films crosslinked by electron beam irradiation. j. of materials science, 50(16):5599-5608. [15] karsli gn, aytac a, akbulut m, deniz v, güven o. (2013) effects of irradiated polypropylene compatibilizer on the properties of short carbon fiber reinforced polypropylene composites. radiation physics and chemistry, 84:74-78. [16] gomes mg, ferreira ms, oliveira rr, silva va, teixeira jg, moura ea. (2013) influence of electron beam irradiation on pp/piassava fiber composite prepared by melt extrusion process. in proceedings of the international nuclear atlantic conference: 24-29 novevember 2013; recife, pe, brazil;pp 1-10. [17] awanis j, anis sofia s, samat n. (2012) effect of coupling agent on mechanical properties of composite from microcrystalline cellulose and recycled polypropylene. advanced materials research, 576:390-393. [18] samat n, marini cd, maritho ma, sabaruddin fa. (2013) tensile and impact properties of polypropylene/microcrystalline cellulose treated with different coupling agents. composite interfaces, 20(7): 497-506. [19] zulkifli n, samat n, anuar h, zainuddin n. (2015) mechanical properties and failure modes of recycled polypropylene/microcrystalline cellulose composites. materials & design, 69:114-123. [20] banik i, bhowmick ak. (2000) effect of electron beam irradiation on the properties of crosslinked rubbers. radiation physics and chemistry, 58(3):293-298. [21] pang y, cho d, han so, park wh. (2005) interfacial shear strength and thermal properties of electron beam-treated henequen fibers reinforced unsaturated polyester composites. macromolecular research, 13(5):453-459. [22] wongsuban b, muhammad k, ghazali z, hashim k, ali hassan m. (2003) the effect of electron beam irradiation on preparation of sago starch/polyvinyl alcohol foams. nuclear instruments and methods in physics research section b: beam interactions with materials and atoms, 211(2):244-250. [23] essabir h, achaby me, hilali em, bouhfid r, qaissbou a. (2015) morphological, structural, thermal and tensile properties of high density polyethylene composites reinforced with treated argan nut shell particles. j. of bionic engineering, 12:129-141. [24] md. salleh f, hassan a, yahya r, azzahari ad. (2014) effects of extrusion temperature on the rheological, dynamic mechanical and tensile properties of kenaf fiber/hdpe composites. composites: part b, 58; 259-266. [25] samat n, burford r, whittle a, hoffman m. (2010) the effects of water and frequency on fatigue crack growth rate in modified and unmodified polyvinyl chloride. polymer engineering & science, 50(2):352-364. [26] samat n, mokhtar wna, zulkifli ni. (2014) properties of eco-friendly composite from recycled polypropylene. advances in environmental biology, 8(8):2760-2766. 195 iium engineering journal, vol. 20, no. 2, 2019 samat et al. https://doi.org/10.31436/iiumej.v20i2.1066 [27] pérez fonseca aa, arrelano m, rodrigue d, gonzález núñez r, robledo-ortiz j. (2016) effect of coupling agent content and water absorption on the mechanical properties of coiragava fibers reinforced polyethylene hybrid composites. polymer composites, 37(10): 3015-3024. 196 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <feff0633062a062e062f0645002006470630064700200627064406250639062f0627062f0627062a002006440625064606340627062100200648062b062706260642002000410064006f006200650020005000440046002006450646062706330628062900200644063906310636002006480637062806270639062900200648062b06270626064200200627064406230639064506270644002e00200020064a06450643064600200641062a062d00200648062b0627062606420020005000440046002006270644062a064a0020062a0645002006250646063406270626064706270020062806270633062a062e062f062706450020004100630072006f00620061007400200648002000410064006f00620065002000520065006100640065007200200036002e00300020064806450627002006280639062f0647002e> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 characterization of mortar with pennisetum purpureum ashes as cement replacement material mohd haziman wan ibrahim1*, mohammed yahya al-fasih2, nik nadia amira nik pa1, ramadhansyah putra jaya3, and muhammad ikhsan setiawan4 1 jamilus research center, faculty of civil engineering and built environment, universiti tun hussein onn malaysia, parit raja, johor, malaysia 2 forensic engineering centre (fec), institute of smart infrastructure and innovative construction (isiic), school of civil engineering, faculty of engineering, universiti teknologi malaysia, 81310 johor bahru, johor 3 department of civil engineering, college of engineering, universiti malaysia pahang, 26300 gambang, pahang, malaysia. 4 department of civil engineering, faculty of engineering, narotama university, surabaya, jawa, indonesia * corresponding author: haziman@uthm.edu.my (received: 27th august 2020; accepted: 30th january 2021; published on-line: 4th july 2021) abstract: in this study, the properties of mortar such as standard consistency, setting time, compressive strength, and water absorption rate were investigated. the cement was replaced with pennisetum purpureum ashes (ppa) in different particle sizes and dosages. ppa was produced in greyish-white ash with total reactive oxides ranging from 37% to 41.1%. pennisetum purpureum grass (ppg) was burned with a controlled process at 350 °c for the first 3 hours and 600 °c for another 3 hours at a heating rate of 10 °c/min. then, ppg was ground in three different grinding durations (1, 3, and 6 hours) producing ashes with particle sizes of 10.58 µm, 10.25 µm, and 9.30 µm, respectively. the physical, chemical, and microstructural properties of ppa were evaluated through several tests; particle size analysis, x-ray diffraction analysis, loss on ignition, and chemical composition. results indicated that ppa is more suitable for use as filling material as a substitute for cement than pozzolanic material as its reactive oxides are less than 50%. the 15% 6h-ppa at 28 days was found to be the optimum ppa replacement dosage and grinding time with cement as it achieved the highest strength and lower water absorption rate among all samples at 7 and 28 days. abstrak: kajian ini berkenaan sifat mortar seperti konsistensi standard, masa penyediaan, kekuatan menyeluruh, dan kadar penyerapan air. simen ditukar dengan abu pennisetum purpureum (ppa) dalam saiz partikel dan sukatan berbeza. ppa pula dihasilkan melalui habuk putih-kekelabuan dengan total reaktif oksida dengan julat purata 37% ke 41.1%. rumput pennisetum purpureum (ppg) dibakar dengan proses kawalan pada 350 °c selama 3 jam pertama dan 600 °c pada 3 jam berikutnya pada kadar pemanasan 10 °c/min. kemudian, ppg dikisar dalam tiga tempoh kisaran berbeza (1, 3, dan 6 jam) menghasilkan abu dengan saiz partikel 10.58 µm, 10.25 µm, dan 9.30 µm, masing-masing. fizikal, larutan kimia dan sifat struktur mikro ppa telah dikaji melalui pelbagai ujian; analisis saiz partikel, analisis pembelauan x-ray, kehilangan semasa penyalaan dan kandungan kimia. dapatan kajian menunjukkan ppa adalah lebih sesuai digunakan sebagai material pengisian ganti kepada simen berbanding material pozzolanik kerana reaktif oksida adalah kurang daripada 50%. ppa adalah maksimum pada 15% 6h83 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 ppa selama 28 hari, didapati lebih sesuai sebagai dos pengganti dan masa kisaran bersama simen, kerana kekuatan menyeluruh adalah paling tinggi dan kadar penyerapan air paling kurang antara semua sampel pada 7 dan 28 hari. keywords: pennisetum purpureum ashes; ppa mortar; replacement dosage; grinding time 1. introduction the cement industry is one a strategic industry acting as a contributor to several other industries such as real-estate, construction, and infrastructure, where it plays an important role in the world economy [1]. concrete materials should not only possess good workability, excellent mechanical properties, and durability, but also offer environmental and economic benefits. however, the cement production of the world, which is estimated at around 1.6 billion tons, contributes about 7% of the global carbon dioxide emissions due to the burning of limestone and clay. thus, widespread cement usage in the industry has been considered unsustainable. therefore, an alternative need to be found to help the cement industry, protect the environment, and also to promote sustainable development for the construction industry and the country. the sustainability concept in engineering practice is focused on the development of new materials for construction purposes and environmentally friendly materials. recently, the search for alternative binders, natural admixtures, or cement replacement materials has been the subject of many studies. the waste raw materials have been used as cement replacement materials to reduce the carbon footprint and enhance sustainability. the biomass waste ashes that contain a high amount of silica content such as sugar cane bagasse ashes [2], rice husk ashes [3], palm oil fuel ash [4], and corn cob ash [5] can be used as supplementary cementitious materials (scms). biomass is defined as a sustainable energy source with carbon dioxide (co2) neutralization potential. ghiasvand and ramezanianpour [1] reported that the energy consumption and carbon dioxide (co2) emissions can be reduced through using scms. furthermore, a portion of cement in a concrete system replaced by scms will participate in primary or secondary hydration reactions, increasing the volume fraction of binding phases and decreasing porosity in the microstructure of the concrete. other than traditional cementitious materials such as rice husk ash, silica fume, and fly ash, one of the alternatives is the ashes extracted from elephant grass or napier grass (pennisetum purpureum). the leaves of elephant grass are currently used as a food source for ruminants, but its trunks are dumped in the landfill. the trunks from the grass could be recycled into silica-based products. napier grass can be harvested four times a year and it has the potential to produce about 100 barrels of oil equivalent per hectare [6]. elephant grass is used now in malaysia as a sustainable resource for the electricity supply system due to its advantages of yield capability, wide propagation, and high dry material [7]. however, a large quantity of elephant grass ashes was generated during the direct burning process of these activities. these ashes will finally be deposited in landfills with the consequent environmental, technical, economic, and social problems [8]. the output energy from napier grass is estimated as 25 times higher than the input energy consisting of a high amount of lignocellulosic material. however, elephant grass contains a considerable amount of amorphous silica due to the extraction of ortho-silicic acid from groundwater by the plant and its ashes can be economically attractive to the production of a pozzolan, which is similar to some byproducts used as biomass such as sugar cane bagasse and rice husk [8]. saruchera et al. [9] 84 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 found that elephant grass was suitable for ash production as all results of chemical composition meet the minimum requirement to be classified as a pozzolan. nakanishi et al. [10] found that the pozzolanic behavior of elephant grass paste was similar to silica fume paste where the main hydrated phases in egc/ca(oh)2 consisted of c-s-h gels similar to sf/ca(oh)2 paste. therefore, using napier grass as an alternate binder resource may protect the environment and enable the building industry to grow sustainably. several studies have already reported the potential activity of ppa and its effect on the mechanical properties of concrete or mortar. cordeiro and sales [8] found that the 28-day compressive strength, young’s modulus, and water absorption did not change due to the replacement of 20% of the cement with ega compared to the reference concrete. cordeiro and sales [11] found that the compressive strength increased after 180 days of curing compared to the reference concrete. however, erika et al. [12] reported that the compressive strength decreased by 12% due to 20% cement replacement with ega. in the context of pozzolanic ash, ramadhansyah et al. [13] reported that the use of finer particles of the ash produced better strength and affected the workability, creep, shrinkage, and water-cement ratio properties. as the fineness of the material relies on their grinding times, it was proven that the strength of concrete increased with the increase of the grinding time of the rice husk ash until the optimum value is reached [13]. since the ashes from the pozzolanic material are expected to behave similarly, the grinding time of the ppa might also improve the mechanical properties of the mortar. therefore, the objective of this study is to investigate the effects of grinding times and dosages of ppa as a partial replacement for cement on the mechanical properties of the blended-cement pastes. the compressive strength, standard consistency, setting time, and water absorption rate of the cement blended paste were considered. the pozzolanic character of ppa was determined through the particle size analysis, scanning electron microscope (sem), loss on ignition, and chemical composition. 2. organizing experimental program 2.1 materials the cement used in this study was ordinary portland cement (opc) conforming to en 197-1: 2000 standard [14] and manufactured by tasek corporation berhad (iso 9001, iso 14001 and ohsas 18001 certified company). physically, the portland cement particle size of 63 µm and the fine aggregates that passed 2.36 mm sieve were used for cement mortar. pennisetum purpureum, also known as napier grass of taiwan type, was used. the raw materials of p. purpureum grass were supplied from hole grass farm pagoh, muar, johor, malaysia. 2.2 pennisetum purpureum ash (ppa) production the production of ppa included four steps: first, the p. purpureum grass was cut into small pieces, and washed with tap water to remove undesirable residue. then, the grass was oven-dried at 110 °c for 24 hours to ensure the grass was completely dried. the oven-dried grass then burned using lenton atmospheric control furnace at 350 °c for the first 3 hours and 600 °c for another 3 hours to produce final ash with a heating rate of 10 °c/min. the ash was allowed to cool down inside the furnace. the ppa was sieved and ground in fritsch ball mill for 1, 3, and 6 hours to produce ash with three different particle size ranges. the production process is shown in fig. 1 and fig. 2. 85 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 (a) cut and washed (b) 24 hours’ oven-dried at 110 °c fig. 1: pieces of p. purpureum plant. (a) at lenton atmospheric control furnace (b) after 6 hours of the burning process (c) ground ppa (final ashes) fig. 2: burning process of ppa. 2.3 characterizations and microstructural analysis of ppa the particle size distributions of the ppa and opc were determined using the laser particle size analyzer (fritsch analysette 22) as shown in table 1. it can be observed that ppa particle size decreased or specific surface area increased with the increase in grinding duration. the average particle size (d50) of the ppa was less than the cement particle size (18 µm) so that it can be classified as fillers as stated by abu bakar et al. [15]. also, it can participate actively with the mixes through pozzolanic reaction as stated by venkatanarayanan and rangaraju [12]. table 1: granulometric value for d10, d50, and d90 of materials sample grinding duration (hours) specific surface area (cm2/cm3) *d10 (µm) *d50 (µm) *d90 (µm) 1h-ppa 1 10949 3.41 10.58 20.58 3h-ppa 3 11008 3.11 10.25 21.03 6h-ppa 6 12671 2.55 9.30 21.97 opc 3350 1.2 18 67 *d10: particle size which lies below 10% of the material; d50: particle size which lies below 50% of the material; d90: particle size which lies below 90% of the material. the chemical composition analysis of raw materials was carried out using x-ray fluorescence (xrf). table 2 shows that ppa mostly consists of silica, iron, and alumina with small quantities of sulfate, magnesium, and calcium, etc. despite different grinding durations, there are no significant variations in the chemical composition of the ppa. 86 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 summations of the percentage of sio2, al2o3, and fe2o3 present in ppa were 37.98%, 37.02%, and 41.15% for 1h-ppa, 3h-ppa, and 6h-ppa, respectively. thus, the ppa does not achieve a desirable amount of reactive oxides to be classified as class f or class c pozzolan where the total reactive oxides (sio2, al2o3, and fe2o3) must be above 50% and 70%, respectively. table 2: chemical composition of ppa by weight percent oxide 1h-ppa (*wt.%) 3h-ppa (*wt.%) 6h-ppa (*wt.%) opc (*wt.%) sio2 31.7 30.4 33.8 17.9 al2o3 4.54 4.70 5.45 4.69 fe2o3 1.74 1.92 1.81 2.97 so3 5.52 5.23 4.95 mgo 0.74 0.75 0.78 1.62 cao 20.8 21.0 22.2 k2o 1.62 1.87 1.62 0.51 tio2 0.25 0.23 0.27 *wt% means weight percent the microstructural analysis for ppa was conducted using a jeol scanning electron microscope (sem) for all grinding periods as shown in fig. 3. it was found that the unground ppa (ug-ppa) sample has an irregular shape with many sizes as shown in fig. 3a. the ug-ppa grains have a porous structure that was quite similar to that found by [10,11]. the skeleton of a honeycomb-like particle and vesicular shape in the ug-ppa, whereas the particles are in highly irregular shapes and porous structures as shown in fig. 3b. after being ground as shown in fig. 3 c, d, and e, the particle sizes become smaller, which indicates a significant degradation of the ppa structure due to the grinding process. the particle shape of the ground ppa had better dispersion than ug-ppa which proved that the mechanical grinding improved the particle surface and morphology of ppa. 2.4 mix proportions five different percentages of ppa with cement by weight of 0%, 5%, 10%, 15%, and 20% were prepared. three different particle sizes of ppa from three different grinding times (1, 3, and 6 hours) were considered in this study. the cement to sand ratio was 1:2.75 by weight while the water-cement ratio for all samples was 0.485. the mixed composition of the mortar cube was shown in table 3. a total of 234 sample cubes was prepared in which 9 samples were prepared for each mixing batch. 2.5 testing 2.5.1 loss on ignition test the loss on ignition is defined as the percent mass loss of a constant weight of a sample as ignited at a high temperature. the loss on ignition test was conducted for both the opc and ppa as per astm c114-07 (part16) [16]. an empty platinum crucible was weighed and marked as w1. about 1.5 grams of the sample were weighed in the platinum crucible and marked as w2. then, the platinum crucible was covered and ignited in a muffle furnace at a temperature of 950°c±50°c for 15 minutes. the sample was taken out and cooled for 20 minutes, then weighted and marked as w3. the percentage of loss on ignition was calculated to the nearest 0.1 using eq. 1. loss on ignition (%) = [(w2-w3) / (w2-w1)] × 100% (1) 87 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 (a) ug -ppa contained irregular shapes (b) ug-ppa contained a honeycomb-like structure (c) 1h-ppa (d) 3h-ppa (e) 6h-ppa fig. 3: microstructural analysis of p. purpureum ashes. table 3: the mix composition of mortar cube sample water-to-cement ratio water (ml) cement (g) ppa (g) sand (g) control 0.485 359 740 2035 5% 0.485 359 703 37 2035 10% 0.485 359 666 74 2035 15% 0.485 359 629 111 2035 20% 0.485 359 592 148 2035 2.5.2 standard consistency and setting time tests the standard consistency test was applied to the ordinary portland cement and blended cement paste with 5%, 10%, 15%, and 20% of replacement by ppa as per astm c187 [17]. the vicat apparatus with a plunger of diameter 10 mm was used for the test. the amounts of water for normal consistencies of all samples were calculated using eq. 2. normal consistency (%) = 𝑀𝑊 𝑀𝐶 × 100% (2) where mw is the mass of water (g) and mc is the mass of cement (g). on the other hand, the setting time test was conducted as per astm c191 [18] to determine the value of the vicat initial and final time of setting of opc and blended paste with 5%, 10%, 15%, and 20% cement replacement with ppa. a paste that was proportioned and mixed to normal consistency, as described in the test method astm c187 [17], was molded and placed in a moist cabinet and allowed to start setting. periodic penetration tests were performed on this paste by the vicat apparatus with a needle of diameter 1 mm. 88 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 the vicat initial setting time was the time elapsed between the initial contact of cement and water and the time when the penetration is measured to be 25 mm. the vicat final setting time was the time elapsed between initial contact of cement-water and the time when the needle does not leave a complete circular impression on the paste surface. the vicat setting times were calculated to the nearest 1 minute according to eq. 3. setting time = (( (𝐻−𝐸) (𝐶−𝐷) ) × (𝐶 − 25)) + 𝐸 (3) 2.5.3 compressive testing the samples were cast into cubical molds with a size of 50 mm × 50 mm × 50 mm. the top of the sample was smoothened and leveled off with a straight edge trowel. the samples were placed in a moist place immediately upon completion of molding. after 24 hours, the samples were removed from the molds and immersed in the water storage tanks until the testing day. compressive strength tests were conducted as per astm c109 [19] for each replacement percentage and grinding time at the age of 3, 7, and 28 days curing age. the load rate with a range of 900 to 1800 n/second was applied to the specimen. 2.5.4 water absorption testing procedure mortar cube samples of size 50 mm × 50 mm × 50 mm were cast for water absorption testing. after 24±1 hour of curing, the mortar cube samples were cured in a moisture tight plastic bag at 24±8 °c until it reaches the age of 3, 7, and 28 days. then, the mortar cube samples were dried in a ventilated oven at 110±5 °c for around 24 hours. the successive weights of the samples were checked at an interval of 2 hours until two successive weights showed an increment of loss not greater than 0.2%. the mortar cube samples were then removed from the oven and were cooled until the samples achieved ambient temperature. then after 24 hours, the water absorption test was conducted by following the average absorption standard test method for rate of water absorption of mortars astm c1403 [20]. the water absorption rate at 24 hours ± 15 minutes was calculated following eq. 4, and recorded as “at”. the at (avg.) was calculated for each set of three cube samples. at = (wt – w0) × 10000 / (l1 × l2) (4) where wt (g) is the weight of cube sample at time t, w0 (g) is the initial weight of cube sample, l1 is the average length (mm) of test surface of cube sample, and l2 (mm) is the average width of test surface of cube sample. the percentage of water absorption at (%) also was calculated using eq. 5. at = [(wt – w0) / (w0)] × 100% (5) 3. results and discussion 3.1 loss on ignition the results of loss on ignition (loi) for all ppa samples were shown in table 4. based on the results, the loi of all ppa samples was below 6%, ranging from 5.27% to 5.47%. the lack of significant variations between samples means that the grinding durations do not affect the loi of ppa. meanwhile, the loi for opc was 2.25%, which was lower than ppa. however, cordeiro and sales [9] stated that it is important to emphasize that all ashes presented loi lower than 5%, indicating that the burning procedures were appropriate to produce pozzolan from ppa in the context of carbon content. however, loi lower than 5% could not be achieved in this study, possibly due to untreated ppa with hydrochloric acid 89 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 pretreatment. however, astm c618-3 [21] limits the loi of pozzolanic materials to less than 6%, largely because higher loi levels commonly result in discoloration, poor air entrainment, segregation, and low compressive strength of the mixed components. note that this standard is specified principally for fly ashes. for other calcined natural pozzolans, the astm c618-3 [21] limits the loi at 10%, since these materials are produced at lower burning temperatures (500 °c to 800 °c) and contain higher loi levels. table 4. loss on ignition of ppa sample 1h ppa 3h ppa 6h ppa opc weight of crucible, w1 (g) 24.383 24.385 24.383 24.387 initial weight of crucible + ppa, w2 (g) 25.883 25.885 26.183 25.887 final weight of crucible + ppa, w3 (g) 25.804 25.803 26.087 25.853 loss on ignition (%) 5.27 5.47 5.33 2.25 legend: 1h-ppa: 1-hour ground ppa; 3h-ppa: 3-hour ground ppa; 6h-ppa: 6-hour ground ppa. 3.2 standard consistency of cement paste containing ppa according to astm c191 [18], the standard consistency test is related to the quantity of water that should be able to flow in the fresh mixture. the plasticity of cement capacity to flow will increase if excessive water is added, while the cement will be stiff with a lower quantity of water. fig. 4 shows the standard consistency results of cement paste containing ppa compared to the opc paste. from the results, the standard consistency of opc was 38%. meanwhile, the standard consistency of cement paste containing ppa increased with the increase of replacement level percentage of ppa. the standard consistency of the samples with 5%, 10%, 15%, and 20% 1h-ppa were 39%, 41%, 50%, and 53%, respectively. for the cement paste containing 5%, 10%, 15%, and 20% of 3h-ppa, the standard consistency was 40%, 53%, and 57%, respectively, which does not differ much from the standard consistency of 1h-ppa. the same pattern applies to cement paste containing 5% to 20% of 6h-ppa with normal consistency ranges from 42% to 57%. all of the above results show that the cement pastes containing ppa have higher standard consistency than opc due to the properties of ppa that absorbed the water during the early hydration process of cement and ppa mixtures. the standard consistency of cement paste containing ppa also increased with the increase of ppa sizes. as the specific surface area of ppa increased, the water demand would be increased [22]. however, the standard consistency of cement paste containing 15% and 20% of 3h-ppa was the same as 15% and 20% of 6h-ppa. the increased water demand for the ppa paste to achieve the same level of consistency may be due to the ability of the ppa particles to quickly absorb the mixed water from the paste due to their cellular microstructure. at any constant replacement level and particle size of ppa, the standard consistency of the ppa paste was higher than the control opc paste. this is because the rate of water absorption of the ppa particles is higher than that of the opc particles due to the presence of larger pore sizes and wider pore size distribution of the former. venkatanarayanan and rangaraju [23] proved that the grinding of ppa may not significantly reduce the absorption of water by its grains and hence, affected the workability characteristics of concrete and mortars. the opc paste registered lower standard consistency probably due to the lower specific surface area and non-cellular shape of the opc particles compared to the ground ppa paste. 90 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 fig. 4: standard consistency of cement paste containing ppa at different replacement rate and control paste. 3.3 setting time of cement paste containing ppa the results of the setting time of opc paste and paste containing ppa were shown in fig. 5. the initial setting time (i-st) for the samples containing ppa started from 226 minutes for 5% 1h-ppa to the longest i-st of 298 minutes for 20% 6h-ppa while the ist of the cement paste was 269 minutes. fig. 5: setting time of cement paste containing ppa at different replacement rates and control paste. the final setting time (f-st) started from 261 minutes for 5% 1h-ppa to the longest f-st of 412 minutes for 20% 6h-ppa while the f-st of cement paste was 365 minutes. based on the results, it was found that the mortar containing ppa achieved lower i-st and f-st than the control mortar except for those containing 15% and 20% ppa. however, both i-st and f-st increased with the increase of cement replacement percentage with ppa. also, both i-st and f-st slightly increased with the increase of grinding time in which 3hppa and 6h-ppa have longer initial and final setting times than 1h-ppa pastes. the setting time behavior is a function of the rate of stiffening of the paste influenced by the effective water to cement ratio [23]. the effective water to cement ratio is the remaining water available to react with portland cement after the water was absorbed by the pozzolan grains. at any percentage of replacement of ppa, the lower grinding time of ppa was shown to absorb more water due to greater porosity resulting in lower effective water to cement ratio in pastes. thus, the final setting time would be shorter for the specimens containing larger 91 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 particle sizes of ppa due to the reduction of porosity with continued hydration, hence affecting their stiffening rate of the paste. 3.4 water absorption rate of mortar containing ppa the effects of ppa replacement with cement at different percentages and particle sizes on the water absorption rate of cement mortar mixes are shown in fig. 6. the results show that all samples containing ppa initially exhibited a high-water absorption rate for 3 days. the water absorption rate significantly slowed down for 7 days and 28 days as most of the pores available had become saturated. it is found that the absorption rate of the mortar containing ppa was higher than the control samples at all testing ages and replacement levels. however, 15% 6h-ppa samples at 7 days and 28 days displayed a lower water absorption rate than the control sample. it was observed that the water absorption rate increased as the replacement level of 1h-ppa and 3h-ppa increase, while it remains unchanged for 6h-ppa. fig. 6: percentage of water absorption of 1h-ppa mortar after 24 hours of immersion. based on fig. 6, the finer samples (3h-ppa and 6hh-ppa) exhibited a lower water absorption rate than 1h-ppa samples. this is due to the filler effect, in which the voids between the cement grains are filled with a micro size of silica particles available in pozzolan to enhance its structural properties. a higher packing density resulted in lower water demand of the mixture with the right composition of pozzolans, which also contributed to the strength enhancement due to the reduced capillary porosity [24]. the higher the percentage of ppa replacement, the denser the particle packing in cement mortar, which also applies to the fineness of ppa. also, the incorporation of suitable fine pozzolan refined the pore structure and reduces the porosity of cement-based materials due to filler and nucleation effects [25]. 3.5 compressive strength with activity index of mortar containing ppa the results of the compressive strength of cement mortar containing ppa for all percentages based on grinding durations at the testing age of 3 days, 7 days, and 28 days were illustrated in fig. 7. based on the plot, the strength of mortar increased linearly with the curing ages for all samples. the results also displayed that the compressive strength of the mortar sample increased with the increase of cement replacement of up to 15% with ppa in the mortar mix, but then the strength mostly decreased after 15% of ppa replacement. however, the strength 92 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 obtained was still higher than the control mortar. the filler supplemented the dense-pack structure in cement mortar and the filler dispersed very well. filler effect or particle size effect is defined as the proper arrangement of small particles that fill the voids and contribute to the increment of compressive strength without any chemical reaction [26]. the compressive strength of cement mortar may be increased due to pore refinement from the pozzolanic reaction of ppa with the cement particles. furthermore, finer ppa could react more quickly with ca(oh)2 and increase the compressive strength of mortar due to the pozzolanic reaction. fig. 7: compressive strength of mortar containing ppa at 3 days, 7days, and 28 days. overall, the compressive strength of cement mortar decreases with increased ppa dosage starting from 10% of replacement. it is observed that the optimum compressive strength is approximately 10% of ppa replacement. however, the mortar containing 15% of 6h-ppa at 28 days has the highest strength among all samples in which it achieved a strength of 30 mpa. in the context of grinding time, the 3 hours grinding time achieved the highest compressive strength at 3 days followed by 6 hours, and 1 hour, respectively. however, the compressive strength at 7 days and 28 days increased with the increase of the grinding time of the ppa in which the 6-hours grinding time achieved the highest compressive strength followed by 3 hours and 1 hour, respectively. therefore, the 6-hours grinding was found to be the optimum grinding time for the ppa as a replacement of cement for the mortar. the compressive strength activity indices for all mortars containing ppa are listed in table 5. at each testing time, the strength index is defined as the ratio of the compressive strength of the mortar containing ppa to the strength of the control sample. it is mostly depending on the hydration rate. the minimum requirement of 75% of the strength activity index was achieved by mortar containing ash as specified in astm c618 [21]. based on table 5, all strength activity indices at the ages of 3 days, 7 days, and 28 days were higher than the minimum requirement of 75% as stated in astm c618 [21]. it was found that the strength activity index decreased compared to the control sample due to replacing 10%, 15%, and 20% 1h-ppa at the age of 28 days, as well as 20% 1h-ppa at the ages of 3 days and 7 days. this is due to the mitigation influence and delay of the pozzolanic reaction of ppa/ca(oh)2. altwair et al. [27] found the same result for a 20% replacement of opc with pofa at the age of 3 and 7 days. however, the samples with a high fineness (3h-ppa and 93 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 6h-ppa) achieved strength indices higher than the control samples for all replacement percentages. this is due to the amorphous aluminous and siliceous minerals that still actively react with ca(oh)2, producing c-s-h and hydrated calcium aluminates, improving interfacial bonding between the sand and pastes. the outcome of this study is in agreement with altwair et al. [27] in which the pofa cement mortar recorded a strength activity index of 101.72 %. table 5: strength activity index (%) sample testing age (days) 3 7 28 control 100 100 100 5%1h-ppa 120 119 115 10%1h-ppa 131 138 81 15%1h-ppa 106 100 76 20%1h-ppa 87 84 78 5%3h-ppa 150 132 91 10%3h-ppa 159 149 127 15%3h-ppa 123 127 112 20%3h-ppa 118 124 97 5%6h-ppa 123 133 123 10%6h-ppa 149 160 138 15%6h-ppa 141 169 144 20%6h-ppa 104 108 117 furthermore, the impact of replacing cement with ppa in the mortar was examined using the microstructure images analysis through sem at 28 days as shown in fig. 8. the microstructure of mortar containing 15% of ppa has hydrated products consisting of ettringite and c-s-h particle as shown in fig. 8d. ettringite formed in needle-like or club shape crystal, while c-s-h was in fine layer particle, both found in a mortar containing 15% ppa at 28 days curing period but did not exist in the control mortar. this is illustrated the highest strength for 28 days curing period of 15% of ppa. 4. conclusion based on the results, the following conclusions can be drawn: • the characterization of ppa material based on chemical composition, particle size distribution, and x-ray diffraction showed that the ppa material is adequate to produce pozzolan; however, it did not achieve 50% and 70% of reactive oxides to be classified as class f or class c pozzolan, respectively. therefore, the ppa is more suitable as filling material than the pozzolanic material as a substitute for opc, which helps in reducing the environmental pollution during the disposal of excess elephant grass wastes. although the particle shape of the ground ppa had better dispersion than ug-ppa, the grinding durations do not affect the chemical composition and loi of ppa. 94 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 (a) control (b) 5% ppa (c) 10% ppa (d) 15% ppa (e) 20% ppa fig. 8: scanning electron micrographs of mortar mixtures at 28 days. • the mortar containing ppa achieved a higher standard consistency value than the control sample while it gained a lower setting time except for those containing 15% and 20% ppa. however, the standard consistency and setting time of cement paste containing ppa increased with the increase of ppa grinding time. • the compressive strength of cement mortar increased with the increase of ppa until 10% for all grinding times, then it was decreased with the increase of ppa percentage. • the mortar containing ppa achieved a water absorption rate higher than the control samples at all testing ages and replacement levels. the water absorption rate 95 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 increased as the replacement level of 1h-ppa and 3h-ppa increased, while it remained unchanged for 6h-ppa. • the 6-hours grinding was found to be the optimum grinding time for the ppa as a replacement of cement for the mortar as it achieved the highest compressive strength at 7 and 28 days. • the 15% of 6h-ppa at 28 days was found to be the optimum ppa replacement dosage and grinding time with cement as it achieved the highest strength and lower water absorption rate among all samples at 7 and 28 days. • finally, based on the results of chemical analysis and strength activity index, the characterization displayed the potential pozzolan of ppa, although it is not class f or class c pozzolan. therefore, the ppa can be considered as filler and source of pozzolan production in tropical regions. acknowledgement the research described in this paper was financially supported by research management centre (rmc), universiti tun hussein onn malaysia (uthm), under grant gpps vot no. u45. references [1] ghiasvand e, ramezanianpour a. (2017) effect of grinding method and particle size distribution on long term properties of binary and ternary cements. construction and building materials, 134: 75-82. https://doi.org/10.1016/j.conbuildmat.2016.12.122 [2] cordeiro gc, kurtis ke. (2017) effect of mechanical processing on sugar cane bagasse ash pozzolanicity. cement and concrete research, 97: 41-49. https://doi.org/10.1016/j.cemconres.2017.03.008 [3] ambedkar b, alex j, dhanalakshmi j. (2017) enhancement of mechanical properties and durability of the cement concrete by rha as cement replacement: experiments and modeling. construction and building materials, 148: 167-175. https://doi.org/10.1016/j.conbuildmat.2017.05.022 [4] thomas bs, kumar s, arel hs. (2017) sustainable concrete containing palm oil fuel ash as a supplementary cementitious material–a review. renewable and sustainable energy reviews, 80: 550-561. https://doi.org/10.1016/j.rser.2017.05.128 [5] adesanya da, raheem aa. (2009) development of corn cob ash blended cement. construction and building materials. 23(1): 347-352. https://doi.org/10.1016/j.conbuildmat.2007.11.013 [6] mohammed i, abakr y, kabir f, yusup s. (2015) effect of aqueous pretreatment on pyrolysis characteristics of napier grass. journal of engineering science and technology, 10(11): 14871496. http://jestec.taylors.edu.my/vol%2010%20issue%2011 [7] ghani wwak, salleh mam, adam sn, shafri hm, shaharum sn, lim kl, tapia jf. (2019) sustainable bio-economy that delivers the environment-food-energy-water nexus objectives: the current status in malaysia. food and bioproducts processing, 118: 167-186. https://doi.org/10.1016/j.fbp.2019.09.002 [8] cordeiro gc, sales cp. (2015) pozzolanic activity of elephant grass ash and its influence on the mechanical properties of concrete. cement and concrete composites, 55: 331-336. https://doi.org/10.1016/j.cemconcomp.2014.09.019 [9] saruchera l, mupa m, muchanyereyi-mukuratirwa n, witzleben s. (2018) a study on the pozzolanic properties of pennisetum purpureum ash. journal of interdisciplinary academic research, 1: 1-10. https://doi.org/10.32476/b9691748-2ac0-4d2fab85-6660b03aeac5 96 https://doi.org/10.32476/b9691748-2ac0-4d2fab85-6660b03aeac5 iium engineering journal, vol. 22, no. 2, 2021 wan ibrahim et al. https://doi.org/10.31436/iiumej.v22i2.1599 [10] nakanishi ey, frías m, martínez-ramírez s, santos sf, rodrigues ms, rodríguez o, savastano jr h. (2014) characterization and properties of elephant grass ashes as supplementary cementing material in pozzolan/ca(oh)2 pastes. construction and building materials, 73: 391-398. https://doi.org/10.1016/j.conbuildmat.2014.09.078 [11] cordeiro gc, sales cp. (2016) influence of calcining temperature on the pozzolanic characteristics of elephant grass ash. cement and concrete composites, 73: 98-104. https://doi.org/10.1016/j.cemconcomp.2016.07.008 [12] nakanishi ey, frías m, santos sf, rodrigues ms, de la villa rv, rodriguez o, junior hs. (2016) investigating the possible usage of elephant grass ash to manufacture the eco-friendly binary cements. journal of cleaner production, 116: 236-243. https://doi.org/10.1016/j.jclepro.2015.12.113 [13] ramadhansyah pj, bakar ba, azmi mm, ibrahim mw. (2011) engineering properties of normal concrete grade 40 containing rice husk ash at different grinding times. international journal of technology, 2(1): 10-19. [14] en 197-1 (2000) cement: part 1. compositions and conformity criteria for common cements. [15] abu bakar bh, ramadhansyah pj, megat azmi mj. (2011) effect of rice husk ash fineness on the chemical and physical properties of concrete. magazine of concrete research, 63(5): 313-320. https://doi.org/10.1680/macr.10.00019 [16] astm c114 (2007) standard test methods for chemical analysis of hydraulic cement. astm international. west conshohocken, pa. [17] astm designation c187-04 (2004) standard test method for normal consistency of hydraulic cement. west conshohocken, pa. [18] astm c191-08 (2008) standard test method for time of setting of hydraulic cement by vicat needle, west conshohocken, pa, usa. [19] astm c109-08 (2008) standard test method for compressive strength of hydraulic cement mortars. astm international, west conshohocken, pa. [20] astm c1403-14 (2014) standard test method for rate of water absorption of masonry mortars, astm international, west conshohocken, pa. [21] astm c618 (2008) standard specification for coal fly ash and raw or calcined natural pozzolan for use as a mineral admixture in concrete cement; lime; gypsum, annual book of astm standards, vol. 04.01, american society for testing and materials, philadelphia, pa. [22] sathawane sh, vairagade vs, kene ks. (2013) combine effect of rice husk ash and fly ash on concrete by 30% cement replacement. procedia engineering, 51: 35-44. https://doi.org/10.1016/j.proeng.2013.01.009 [23] venkatanarayanan hk, rangaraju pr. (2015) effect of grinding of low-carbon rice husk ash on the microstructure and performance properties of blended cement concrete. cement and concrete composites, 55: 348-363. https://doi.org/10.1016/j.cemconcomp.2014.09.021 [24] rai s, tiwari s. (2018) nano silica in cement hydration. materials today: proceedings, india, 5(3): 9196-9202. https://doi.org/10.1016/j.matpr.2017.10.044 [25] wang d, shi c, farzadnia n, shi z, jia h, ou z. (2018) a review on use of limestone powder in cement-based materials: mechanism, hydration and microstructures. construction and building materials, 181: 659-672. https://doi.org/10.1016/j.conbuildmat.2018.06.075 [26] jaturapitakkul c, tangpagasit j, songmue s, kiattikomol k. (2011) filler effect and pozzolanic reaction of ground palm oil fuel ash. construction and building materials, 25(11): 4287-4293. https://doi.org/10.1016/j.conbuildmat.2011.04.073 [27] altwair nm, johari mam, hashim sfs. (2011) strength activity index and microstructural characteristics of treated palm oil fuel ash. international journal of civil & environmental engineering, 11: 100-107 97 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 suharsono et al. https://doi.org/10.31436/iiumej.v22i1.1398 solution of the reverse flow reactor model using homotopy analysis method suharsono1, sri wulandari1, aang nuryaman1, mustofa usman1, wamiliana1 and jamal ibrahim daoud2 1 department of mathematics, fmipa universitas lampung, jl. prof. dr. soemantri brojonegoro no. 1, bandarlampung 35145, indonesia 2 department of science in engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia * corresponding author: aang.nuryaman@fmipa.unila.ac.id (received: 13th march 2020; accepted: 21st july 2020; published on-line: 4th january 2021) abstract: methane (ch4) is one of the most dangerous greenhouse gases in the atmosphere. a reverse flow reactor is utilized to convert ch4 to carbon dioxide (co2) as a means of reducing the effect of global warming. the dynamics of its dependent variables can be stated by a set of convective-diffusion equations. in this article, we examined analytical solutions of temperature dynamics and methane conversion for a 1-d pseudo homogeneous model without refrigeration by using the homotopy analysis method. the results show that temperature and conversion of methane will go to constant when time goes to infinity. abstrak: metana (ch4) merupakan salah satu gas rumah hijau paling berbahaya di atmosfera. reaktor aliran balik telah dipakai bagi menukar ch4 kepada co2 bagi mengurangkan kesan pemanasan global. dinamik pemboleh ubah bersandar ini dapat diterangkan melalui satu set persamaan konvektif-difusi. artikel ini akan mengkaji penyelesaian analisis dinamik suhu dan penukaran metana bagi model 1-d pseudohomogen tanpa penyejukan dengan menggunakan kaedah analisis homotopi. hasil kajian menunjukkan bahawa suhu dan penukaran metana akan berterusan dengan masa tak terhingga. keywords: analytical solution; 1-d pseudo homogeneous model; reverse flow reactor; homotopy analysis method 1. introduction there are several mathematical models in differential equation form that are difficult to solve using ordinary analytic partial differential equations. hence, various methods have been developed to solve these equations, such as the laplace transformation method, the perturbation method, the finite difference method, etc. one natural phenomena that gets very intensive attention is global warming caused by greenhouse gas emissions. one of the dangerous and numerous greenhouse gases in the atmosphere is methane (ch4). reducing the global warming effect can be achieved by converting ch4 into carbon dioxide (co2) according to the oxidation (combustion) equation: ch4 + 2o2 → co2 + 2h2o δh298 = −802,7 kj/mol (1) 129 iium engineering journal, vol. 22, no. 1, 2021 suharsono et al. https://doi.org/10.31436/iiumej.v22i1.1398 every one mole of oxidized ch4 gas will release as much heat energy of 802.7 kj. hence, converting ch4 gas to co2 gas will reduce the heating effect by 87%. the presence of fairly small amounts of methane gas in the air (0.1–1% by volume) causes the conversion of methane gas to co2 gas but needs a catalyst so that the reaction can take place. on the other hand, low methane temperature (around 303 k), so far from the reaction temperature, requires preheating of the feed gas. one technology which can be used to anticipate the negative impact and characteristic of methane is the use of a reverse flow reactor (rfr) to oxidize ch4 into co2. further explanation about rfr can be seen in [1,2]. a mathematical model illustrating the dynamics of temperature and concentration on oxidation of ch4 through rfr has been revealed by khinast et al. [3] and van norden [4]. in those articles, a one-dimensional (1d) pseudo homogeneous model was used to describe the dynamic of dependent variables in a cooled-reverse flow reactor. previous studies [5,6] used this model to investigate operating parameter sensitivities of rfr on the behavior of dependent variables for periodic feed gas by using a numerical approach. whereas in [7,8], this model was used to construct singular perturbation problems by considering certain assumptions for steady state conditions and solved them using asymptotic methods. while for the unsteady state case, nuryaman [9] reported an analytical solution for conversion equation that was derived from the 1-d pseudo homogeneous model which assumed that the reaction took place spontaneously at a certain reaction rate. the homotopy perturbation method was used to get its analytical solution. in this article, we consider the 1-d pseudo homogeneous model in [4] and we assume that the reactor is in the condition without cooling such that the equations become as follows: 𝑢𝑡 = 𝑎𝑢𝑥𝑥 − 𝑏𝑢𝑥 + 𝑐𝑔(𝑢)(1 − 𝑣), 𝑥 ∈ [0,1] (2) 𝑣𝑡 = 𝑒𝑣𝑥𝑥 − 𝑓𝑣𝑥 + 𝑙 𝑔(𝑢)(1 − 𝑣), 𝑡 ≥ 0, (3) 𝑔(𝑢) = 1,6656 ×10−5exp ( 25,785(𝑢−1) 𝑢 ) 1,6656 ×10−5+exp (− 25,785 𝑢 ) (4) where 𝑢 = 𝑢(𝑥, 𝑡), 𝑣 = 𝑣(𝑥, 𝑡) are dimensionless variables for temperature and conversion variables. here 𝑎, 𝑏, 𝑐, 𝑒, 𝑓,and 𝑙 are dimensionless parameters which values are given in table 1, and 𝑔(𝑢) is a nonlinear function that corresponds to the rate of reaction in the rfr. table 1: the dimensionless parameter values of rfr [4] no parameter values 1 𝑎 6.9393 x 10−4 2 𝑏 0.1749 3 𝑐 1.5577 x 10−6 4 𝑒 2.4038 x 10−3 5 𝑓 174.06 6 𝑙 0.01 based on equations (2)-(3) and under the certain assumptions, in this article, we investigate an analytical solution by applying the homotopy analysis method (ham). in recent years, ham can be applied for solving various linear and nonlinear systems, and homogeneous and nonhomogeneous equations [10]. the ham is used to solve problems 130 iium engineering journal, vol. 22, no. 1, 2021 suharsono et al. https://doi.org/10.31436/iiumej.v22i1.1398 using the determination of series convergence with respect to an embedded parameter [11]. in fact, the homotopy method is easier to use in solving difficult problems. therefore, the ham method will be applied herein solving the rfr model. 2. methodology the homotopy analysis method (ham) was designed firstly in 1992 by liao [12] and was then modified in 1997 [13]. this is a semi-analytics technique for solving ordinary nonlinear problems or partial differential equations. homotopy can be defined as a link between two different objects in mathematics that have the same characteristics in several aspects [13]. the ham is based on concepts in topology and differential geometry to produce a series convergence of a nonlinear system. the concept of homotopy is then traced back to jules henri poincare, a french mathematician. homotopy explains a kind of deformation variation in mathematics. for example, a circle can be deformed continuously into an ellipse, and the shape of a coffee cup can be deformed continuously into a donut shape. suppose there are zeroth-order differential equations: 𝑁𝑘[𝑧𝑘(𝜔, 𝜏)] = 0, 𝑘 = 1, 2, … , 𝑚 (5) where 𝑁𝑘 are nonlinear operators that represent the whole equations, 𝜔 and 𝜏 denote the independent variables, and 𝑧𝑘(𝜔, 𝜏) are unknown functions. liao constructed the deformation equations as (1 − 𝑞)𝐿[𝜙𝑘(𝜔, 𝜏; 𝑞) − 𝑧𝑘,0(𝜔, 𝜏)] = 𝑞ℏ𝑘𝑁𝑘[𝜙𝑘(𝜔, 𝜏; 𝑞)] (6) where 𝑞 is an embedding parameter, 𝑞 ∈ [0,1], ℏ𝑘are nonzero auxiliary functions, 𝐿 is an auxiliary linear operator, 𝑧𝑘,0(𝜔, 𝜏) are initial guesses of 𝑧𝑘(𝜔, 𝜏), and 𝜙𝑘(𝜔, 𝜏; 𝑞) are unknown functions. one has great freedom to choose auxiliary objects such as ℏ𝑘 and 𝐿. obviously, when 𝑞 = 0 and 𝑞 = 1, 𝜙𝑘 hold: 𝜙𝑘(𝜔, 𝜏; 0) = 𝑧𝑘,0(𝜔, 𝜏)and 𝜙𝑘(𝜔, 𝜏; 1) = 𝑧𝑘(𝜔, 𝜏) (7) thus, if 𝑞 increases from 0 to 1, then the solutions 𝜙𝑘(𝜔, 𝜏; 𝑞) move from 𝑧𝑘,0(𝜔, 𝜏) to 𝑧𝑘(𝜔, 𝜏). 𝜙𝑘(𝜔, 𝜏; 𝑞) are then expanded in taylor series with respect to 𝑞, and then becomes 𝜙𝑘(𝜔, 𝜏; 𝑞) = 𝑧𝑘,0(𝜔, 𝜏) + ∑ 𝑧𝑘,𝑛(𝜔, 𝜏)𝑞 𝑛+∞ 𝑛=1 (8) where 𝑧𝑘,𝑛 = 1 𝑛! 𝜕𝑛𝜙𝑘(𝜔,𝜏;𝑞) 𝜕𝑞𝑛 |𝑞=0. (9) when ℏ𝑘, 𝐿, 𝑧𝑘,0(𝜔, 𝜏), and 𝜙𝑘(𝜔, 𝜏; 𝑞)are properly chosen, then equation (8) converges at 𝑞 = 1 and 𝜙𝑘(𝜔, 𝜏; 1) = 𝑧𝑘,0(𝜔, 𝜏) + ∑ 𝑧𝑘,𝑛(𝜔, 𝜏) +∞ 𝑛=1 (10) which has to be one of the solutions. as ℏ𝑘 = −1, equation (6) becomes (1 − 𝑞)𝐿[𝜙𝑘(𝜔, 𝜏; 𝑞) − 𝑧𝑘,0(𝜔, 𝜏)] + 𝑞𝑁𝑘[𝜙𝑘(𝜔, 𝜏; 𝑞)] = 0 (11) the governing equations can be deduced from the zeroth-order deformation equation (6). define the vectors 𝑧𝑘,𝑚⃗⃗⃗⃗⃗⃗⃗⃗ = {𝑧𝑘,0(𝜔, 𝜏), 𝑧𝑘,1(𝜔, 𝜏), … , 𝑧𝑘,𝑚(𝜔, 𝜏)} (12) 131 iium engineering journal, vol. 22, no. 1, 2021 suharsono et al. https://doi.org/10.31436/iiumej.v22i1.1398 the nth order deformation can be found by differentiating (6) n times with respect to 𝑞 and then putting 𝑞 = 0. after that divide it by 𝑛! such that 𝐿[𝑧𝑘,𝑛(𝜔, 𝜏) − 𝜒𝑛𝑧𝑘,𝑛−1(𝜔, 𝜏)] = ℏ𝑘𝑅𝑘,𝑛(𝑧𝑖,𝑛−1⃗⃗ ⃗⃗ ⃗⃗ ⃗⃗ ⃗⃗ ) (13) where 𝑅𝑘,𝑛(𝑧𝑘,𝑛−1⃗⃗ ⃗⃗ ⃗⃗ ⃗⃗ ⃗⃗ ⃗) = 1 (𝑛−1)! 𝜕𝑛−1𝑁𝑘[𝜙𝑘(𝜔,𝜏;𝑞) 𝜕𝑞𝑛−1 |𝑞=0 (14) and 𝜒𝑛 = { 0, 𝑛 ≤ 1 1, 𝑛 > 1 (15) note that 𝑧𝑘,𝑛(𝜔, 𝜏) (𝑛 ≥ 1) are governed by (13) with boundary conditions coming from the original problem. 3. result and discussion consider the 1-d pseudo homogeneous model in equations (2)-(3). by using a rescaling process and the assumption that the reaction rate takes place at certain temperature such that the nonlinear term approach to one. we obtain a dimensionless equation set that illustrates the dynamics of temperature and conversion of methane gas to methane oxidation using rfr without cooling as follows: 𝑢𝑡 − 𝑎𝑢𝑥𝑥 + 𝑏𝑢𝑥 + 𝑐𝑣 − 𝑐 = 0 (16) 𝑣𝑡 − 𝑒𝑣𝑥𝑥 + 𝑓𝑣𝑥 + 𝑙𝑣 − 𝑙 = 0 (17) where 𝑢 = 𝑢(𝑥, 𝑡), 𝑣 = 𝑣(𝑥, 𝑡) are dimensionless variables for temperature and conversion and 𝑎, 𝑏, 𝑐, 𝑒, 𝑓, and 𝑙 are dimensionless parameters which values given in table 1. in this case, initial conditions are 𝑢(𝑥, 0) = 𝛽, 𝛽 > 1 (18) where 𝛽 is constant and 𝑣(𝑥, 0) = 0 (19) the linear operator 𝐿[𝜑𝑘(𝑥, 𝑡; 𝑞)] = 𝜕𝜑𝑘(𝑥,𝑡;𝑞) 𝜕𝑡 , 𝑘 = 1,2 (20) with 𝐿[𝑝𝑘] = 0, where 𝑝𝑘(𝑘 = 1,2) are integral constants. the nonlinear operator 𝑁1[𝜑1(𝑥, 𝑡; 𝑞)] = 𝜕𝜑1(𝑥,𝑡;𝑞) 𝜕𝑡 − 𝑎 𝜕2𝜑1(𝑥,𝑡;𝑞) 𝜕𝑥2 + 𝑏 𝜕𝜑1(𝑥,𝑡;𝑞) 𝜕𝑥 + 𝑐𝜑2(𝑥, 𝑡; 𝑞) − 𝑐 (21) 𝑁2[𝜑2(𝑥, 𝑡; 𝑞)] = 𝜕𝜑2(𝑥,𝑡;𝑞) 𝜕𝑡 − 𝑒 𝜕2𝜑2(𝑥,𝑡;𝑞) 𝜕𝑥 2 + 𝑓 𝜕𝜑2(𝑥,𝑡;𝑞) 𝜕𝑥 + 𝑙𝜑2(𝑥, 𝑡; 𝑞) − 𝑙 (22) using the above definition, we construct the zeroth-order deformation equations (1 − 𝑞)𝐿[𝜑𝑘(𝑥, 𝑡; 𝑞) − 𝑧𝑘,0(𝑥, 𝑡)] = 𝑞ℎ𝑘𝑁𝑘[𝜑𝑘(𝑥, 𝑡; 𝑞)], 𝑘 = 1, 2 132 iium engineering journal, vol. 22, no. 1, 2021 suharsono et al. https://doi.org/10.31436/iiumej.v22i1.1398 when 𝑞 = 0 and 𝑞 = 1, respectively, yields 𝜑1(𝑥, 𝑡; 0) = 𝑧1,0(𝑥, 𝑡) = 𝑢0(𝑥, 𝑡) 𝜑2(𝑥, 𝑡; 0) = 𝑧2,0(𝑥, 𝑡) = 𝑣0(𝑥, 𝑡) 𝜑1(𝑥, 𝑡; 1) = 𝑢(𝑥, 𝑡) 𝜑2(𝑥, 𝑡; 1) = 𝑣(𝑥, 𝑡) after expanding 𝜑𝑘(𝑥, 𝑡; 𝑞)in taylor series with respect to 𝑞, it yields 𝜑𝑘(𝑥, 𝑡; 𝑞) = 𝑧𝑘,0(𝑥, 𝑡) + ∑ 𝑧𝑘,𝑛(𝑥, 𝑡)𝑞 𝑛 +∞ 𝑛=1 where 𝑧𝑘,𝑛(𝑥, 𝑡) = 1 𝑛! 𝜕𝑛𝜑𝑖(𝑥, 𝑡; 𝑞) 𝜕𝑞𝑛 |𝑞=0 the above series will converge at 𝑞 = 1, so that 𝑢(𝑥, 𝑡) = 𝑧1,0(𝑥, 𝑡) + ∑ 𝑧1,𝑛(𝑥, 𝑡) +∞ 𝑛=1 𝑣(𝑥, 𝑡) = 𝑧2,0(𝑥, 𝑡) + ∑ 𝑧2,𝑛(𝑥, 𝑡) +∞ 𝑛=1 these are the solution of the nonlinear equation systems (16, 17). now, we define the vector 𝑧𝑘,𝑚⃗⃗⃗⃗⃗⃗⃗⃗ = {𝑧𝑘,0(𝑥, 𝑡), 𝑧𝑘,1(𝑥, 𝑡), … , 𝑧𝑘,𝑚(𝑥, 𝑡)} so, the nth-order deformation equations is 𝐿[𝑧𝑘,𝑛(𝑥, 𝑡) − 𝜒𝑛𝑧𝑘,𝑛−1(𝑥, 𝑡)] = ℏ𝑘𝑅𝑘,𝑛(𝑧 𝑘,𝑛−1) where 𝑅1,𝑛(𝑧 𝑘,𝑛−1) = (𝑧1,𝑛−1)𝑡 − 𝑎(𝑧1,𝑛−1)𝑥𝑥 + 𝑏(𝑧1,𝑛−1)𝑥 + 𝑐(𝑧2,𝑛−1) − 𝑐 + 𝑐𝑋𝑛 𝑅2,𝑛(𝑧 𝑘,𝑛−1) = (𝑧2,𝑛−1)𝑡 − 𝑒(𝑧2,𝑛−1)𝑥𝑥 + 𝑓(𝑧2,𝑛−1)𝑥 + 𝑙(𝑧2,𝑛−1) − 𝑙 + 𝑙𝑋𝑛 now, the solution of the nth-order deformation equation for 𝑛 ≥ 1 becomes 𝑧𝑘,𝑛(𝑥, 𝑡) = 𝜒𝑛𝑧𝑘,𝑛−1(𝑥, 𝑡) + ℏ𝑘 ∫ 𝑅𝑘,𝑛( 𝑡 0 𝑧 𝑘,𝑛−1) 𝑑𝜏 + 𝑝𝑘 where the integration constants 𝑝𝑘 = 0. we, now successively have 𝑧1,0(𝑥, 𝑡) = 𝛽 𝑧1,1(𝑥, 𝑡) = −𝑐ℎ𝑡 𝑧1,2(𝑥, 𝑡) = −𝑐ℎ𝑡 − 𝑐ℎ 2𝑡 − 𝑐𝑙ℎ2𝑡2 2 133 iium engineering journal, vol. 22, no. 1, 2021 suharsono et al. https://doi.org/10.31436/iiumej.v22i1.1398 z1,3(x, t) = −𝑐ℎ𝑡 − 2𝑐ℎ 2𝑡 − 𝑐𝑙ℎ2𝑡2 − 𝑐ℎ3𝑡 − 𝑐𝑙ℎ3𝑡2 − 𝑐𝑙2ℎ3𝑡3 6 z1,4(x, t) = −𝑐ℎ𝑡 − 3𝑐ℎ 2𝑡 − 𝑐𝑙ℎ2𝑡2 − 3𝑐ℎ3𝑡 − 3𝑐𝑙ℎ3𝑡2 − 𝑐𝑙2ℎ3𝑡3 2 − 𝑐ℎ4𝑡 − 3𝑐𝑙ℎ4𝑡2 2 − 𝑐𝑙2ℎ4𝑡3 2 − 𝑐𝑙ℎ2𝑡2 2 − 𝑐[3ℎ4𝑡4 24 z1,5(x, t) = −𝑐ℎ𝑡 − 4𝑐ℎ 2𝑡 − 2𝑐𝑙ℎ2𝑡2 − 6𝑐ℎ3𝑡 − 6𝑐𝑙ℎ3𝑡2 − 𝑐𝑙2ℎ3𝑡3 − 4𝑐ℎ4𝑡 − 6𝑐𝑙ℎ4𝑡2 − 2𝑐𝑙2ℎ4𝑡3 − 𝑐𝑙3ℎ4𝑡4 6 − 𝑐ℎ5𝑡 − 2𝑐𝑙ℎ5𝑡2 − 𝑐𝑙2ℎ5𝑡3 − 𝑐𝑙3ℎ5𝑡4 6 − 𝑐𝑙4ℎ5𝑡5 120 z2,0(x, t) = 0 z2,1(x, t) = −𝑙ℎ𝑡 z2,2(x, t) = −𝑙ℎ𝑡 − 𝑙ℎ 2𝑡 − 𝑙2ℎ2𝑡2 2 z2,3(x, t) = −𝑙ℎ𝑡 − 2𝑙ℎ 2𝑡 − 𝑙2ℎ2𝑡2 − 𝑙ℎ3𝑡 − 𝑙2ℎ3𝑡2 − 𝑙3ℎ3𝑡3 6 z2,4(x, t) = −𝑙ℎ𝑡 − 3𝑙ℎ 2𝑡 − 3𝑙ℎ3𝑡 − 3𝑙2ℎ3𝑡2 − 𝑙3ℎ3𝑡3 2 − 𝑙ℎ4𝑡 − 𝑙3ℎ4𝑡3 2 − 3𝑙2ℎ2𝑡2 2 − 3𝑙2ℎ4𝑡2 2 − 𝑙4ℎ4𝑡4 24 z2,5(x, t) = −𝑙ℎ𝑡 − 4𝑙ℎ 2𝑡 − 6𝑙ℎ3𝑡 − 𝑙3ℎ3𝑡3 − 4𝑙ℎ4𝑡 − 2𝑙3ℎ4𝑡3 − 2𝑙2ℎ2𝑡2 − 6𝑙2ℎ4𝑡2 − 𝑙4ℎ4𝑡4 6 − 𝑙ℎ5𝑡 − 𝑙3ℎ5𝑡3 − 6𝑙2ℎ3𝑡2 − 𝑙4ℎ5𝑡4 6 − 2𝑙2ℎ5𝑡2 − 𝑙5ℎ5𝑡5 120 the solutions then have the form 𝑢(𝑥, 𝑡) = 𝑧1,0(𝑥, 𝑡) + 𝑧1,1(𝑥, 𝑡) + 𝑧1,2(𝑥, 𝑡) + 𝑧1,3(𝑥, 𝑡) + 𝑧1,4(𝑥, 𝑡) + 𝑧1,5(𝑥, 𝑡) + ⋯ 𝑣(𝑥, 𝑡) = 𝑧2,0(𝑥, 𝑡) + 𝑧2,1(𝑥, 𝑡) + 𝑧2,2(𝑥, 𝑡) + 𝑧2,3(𝑥, 𝑡) + 𝑧2,4(𝑥, 𝑡) + 𝑧2,5(𝑥, 𝑡) + ⋯ by putting ℎ = −1, yields 𝑢(𝑥, 𝑡) = 𝛽 + 𝑐𝑡 − 𝑐𝑙𝑡2 2 + 𝑐𝑙2𝑡3 6 − 𝑐𝑙3𝑡4 24 + 𝑐𝑙4𝑡5 120 − ⋯ = 𝛽 + 𝑐𝑡 + 𝑐 𝑙 (− 𝑙2𝑡2 2 + 𝑙3𝑡3 6 − 𝑙4𝑡4 24 + 𝑙5𝑡5 120 − ⋯ ) = 𝛽 + 𝑐𝑡 + 𝑐 𝑙 (1 − 𝑙𝑡 − 𝑒−𝑙𝑡) = 𝛽 + 𝑐𝑡 + 𝑐 𝑙 − 𝑐𝑡 − 𝑐𝑒−𝑙𝑡 𝑙 = 𝛽 + 𝑐 𝑙 − 𝑐𝑒−𝑙𝑡 𝑙 = 𝛽𝑙 + 𝑐 − 𝑐𝑒−𝑙𝑡 𝑙 134 iium engineering journal, vol. 22, no. 1, 2021 suharsono et al. https://doi.org/10.31436/iiumej.v22i1.1398 𝑣(𝑥, 𝑡) = 0 + 𝑙𝑡 − 𝑙2𝑡2 2 + 𝑙3𝑡3 6 − 𝑙4𝑡4 24 + 𝑙5𝑡5 120 − ⋯ = 1 − 𝑒−𝑙𝑡 using the physical data available in table 1, the solution graph for 𝑢(𝑥, 𝑡) and 𝑣(𝑥, 𝑡), as shown in fig. 1 and fig. 2. fig. 1: the solution graph for 𝑢(𝑥, 𝑡) at certain position. fig. 2: the solution graph for 𝑣(𝑥, 𝑡) at certain position. in rfr, the heat that is stored in the reactor can be used to preheat the feed. if the reaction temperature has been reached, the reactor system no longer needs a preheater for preheating the feed so that the process has high energy efficiency. this condition is illustrated by the graph 𝑢(𝑥, 𝑡).as shown in figure 1, there is an increase in temperature within a certain time interval, after which the temperature does not increase or decrease but moves constantly. this condition has reached the steady state; thus, no preheater is needed. the 𝑣(𝑥, 𝑡)graph in figure 2 illustrates the amount of concentration that reacts. after the concentration reacts entirely within a certain time, then the graph will move constantly. when this condition is reached, it means that the feed gas has completely reacted. thus no more heat is released so that the temperature of the reactor becomes constant. 4. conclusion in this article, we consider the 1-d pseudo homogeneous model that describes the dynamics of temperature and conversion variabls in rfr without the cooling process. here, we consider only the feed gas flow from left to the right end of rfr. then, we solve this 135 iium engineering journal, vol. 22, no. 1, 2021 suharsono et al. https://doi.org/10.31436/iiumej.v22i1.1398 model using the homotopy analysis method. based on the description above, it can be concluded that the solution of the dimensionless equation system describing the dynamics of temperature and conversion to methane oxidation using rfr without refrigeration is obtained as 𝑢(𝑥, 𝑡) = 𝛽𝑙+𝑐−𝑐𝑒−𝑙𝑡 𝑘 and 𝑣(𝑥, 𝑡) = 1 − 𝑒−𝑙𝑡. the solution graph of 𝑢(𝑥, 𝑡) illustrates an increase in temperature within a certain time interval, after which the temperature does not increase or decrease but it moves constantly. this condition has reached the steady state; thus, no preheater is needed. the solution graph of 𝑣(𝑥, 𝑡) describes the amount of concentration that reacts. after the concentration reacts entirely within a certain time, then the graph will move constantly. future studies can be extended by considering the cooling process term in the 1-d pseudohomogeneous model. in the real problem, the heat energy expended during the methane oxidation should be controlled so that reactor overheating will not occur. acknowledgement the authors would like to thank the reviewers for invaluable suggestions and corrections. also, the authors would like to thank universitas lampung for the facilities, funding through blu research grants no. 2280/un.21/pn/2019, and support during the research. references [1] frank-kamenetskii da. (1955) diffusion and heat transfer in chemical kinetics. princeton univ. press, princeton, nj. [2] matros yu. sh., bunimovich ga. (1999) reverse-flow operation in fixed bed catalytic reactors. catalysis reviews: science & engineering, 38: 1-68. [3] khinast j, jeong yo, luss d. (1999). dependence of cooled reverse-flow reactor dynamics on reactor model. a.i.ch.e. journal, 45: 299-309. [4] van noorden tl, verduyn lunel smv, bliek a. (2003) the efficient computation of periodic states of cyclically operated chemical processes. ima journal of applied mathematics, 68: 149-166. https://doi.org/10.1093/imamat/68.2.149 [5] nuryaman a, riyanto r, saidi s. (2019) dynamics of temperature and concentration on oxidation reactionusing reverse flow reactor with periodic feed gas like square wave function: a numerical approach. j. of phys.: conf. ser., 1338: 012040. https://doi.org/10.1088/1742-6596/1338/1/012037 [6] nuryaman a, zakaria l, suharsono s. (2020) parameter sensitivity analysis onmathematical model of methane oxidation using reverse flow reactor with periodically perturbed feed gas. jp journal of heat and mass transfer, 19(1): 31-42. issn 0973-5763. http://dx.doi.org/10.17654/hm019010031 [7] nuryaman a, gunawan ay, sidarto as, budhi yw. (2012) a singular perturbation problem for steady state conversion of methane oxidation in a reserve flow reactor. itb j. sci., 44(3): 275-284. doi number 10.5614/itbj.sci.2012.44.3.7 [8] nuryaman a, gunawan ay. (2017) a singular perturbation problem in steady state of methane combustion using reverse flow reactor. far east journal of mathematical sciences, 102(9): 2069-2079. http://dx.doi.org/10.17654/ms102092069. [9] nuryaman a. (2018) an analytical solution of 1-d pseudo homogeneous model for oxidation reaction using homotopy perturbation methods. journal of research in mathematics trend and technology, 1: 7-12. https://doi.org/10.32734/jormtt.v1i1.751 [10] sami bataineha, noorani msm, hashim, i. (2008). approximate analytical solutions of systems of pdes by homotopy analysis method. computers and mathematics with applications, 55: 2913-2923. https://doi.org/10.1016/j.camwa.2007.11.022 136 https://doi.org/10.1093/imamat/68.2.149 mhtml:file://d:/paper%20penelitian/jphmt/paper%20no.%20pph%201910054%20hmt%20final.mht!https://doi.org/10.1088/1742-6596/1338/1/012037 http://repository.lppm.unila.ac.id/18210/ http://repository.lppm.unila.ac.id/18210/ http://repository.lppm.unila.ac.id/18210/ http://dx.doi.org/10.17654/hm019010031 http://dx.doi.org/10.17654/ms102092069 https://doi.org/10.32734/jormtt.v1i1.751 https://doi.org/10.1016/j.camwa.2007.11.022 iium engineering journal, vol. 22, no. 1, 2021 suharsono et al. https://doi.org/10.31436/iiumej.v22i1.1398 [11] liao sj. (2012). homotopy analysis method in nonlinear differential equation. highereducation press, beijing. [12] liao sj. (1992). the proposed homotopy analysis techniques for the solution of nonlinear problems, ph.d. dissertation, shanghai jiao tongroblem university, shanghai. (in english). [13] liao sj. (1997). an approximate solution technique which does not depend upon small parameters (part 2): an application in fluid dynamics. internat. j. non-linear mech. 32: 815-822. 137 iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 223 environmental degradation of durian skin nanofibre biocomposite siti nur e’zzati mohd apandi, hazleen anuar* and siti munirah salimah abdul rashid department of manufacturing and materials engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia *corresponding author: hazleen@iium.edu.my (received: 27th feb 2018; accepted: 9th april 2018; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.903 abstract: the effect of ultraviolet radiation on tensile properties, water absorption and optical properties of polypropylene (pp) reinforced with durian skin nanofibre (dsnf) composites was investigated. dsnf was obtained from fermentation of durian skin fibre using rhizopus oryzae. x-ray diffraction (xrd) analysis and sherrer equation were applied to measure the average particle size of dsnf which was determined as 51.2 nm. pp and dsnf were melt-blended in a haake internal mixer before compression moulded into composite specimens. the composites were exposed under ultraviolet (uv) radiation to simulate the effect of sunlight. the significant effect of maleic anhydride polypropylene (mapp) was observed by the improvement recorded in tensile properties and reduction of water absorption in pp/dsnf composite. the colour index of composites increased with uv radiation exposure. transmission electron microscope (tem) images showed dsnf was well-dispersed in pp matrix in the presence of mapp. abstrak: kesan ultraungu (uv) terhadap sifat tegangan, penyerapan air dan sifat optik bagi polypropylene (pp) diperkuatkan dengan nanofiber kulit durian komposit telah disiasat. dsnf telah diperolehi daripada process penapaian fiber kulit durian menggunakan rhizopus oryzae. analisis difraksi sinar-x dan persamaan sherrer telah digunakan untuk mengukur purata saiz zarah untuk dsnfyang telah diperolehi sebanyak 51.2nm. pp dan dsnf telah dicampur dalam pembancuh haake sebelum mampatan dibentuk menjadi spesimen komposit. komposit telah didedahkan di bawah radiasi ultraungu (uv) untuk mensimulasikan kesan cahaya matahari. kesan yang penting terhadap polipropilena maleik (mapp) telah diperhatikan dan setiap peningkatan dalam sifat tegangan dan pengurangan penyerapan air dalam komposit pp / dsnf telah direkod. indeks warna komposit meningkat dengan pendedahan radiasi uv. imej mikroskop elektron penghantaran (tem) menunjukkan dsnf telah disebarkan dengan baik dalam matriks pp dengan kehadiran mapp. key words: durian skin nanofibre, ultraviolet radiation, mapp, color index, water absorption, rhizophus oryzae. 1. introduction natural fibre reinforced composite for external application might experience exposure to harsh environments with high humidity. biodegradable fibres are hydrophilic in nature and tend to attract water although in air (ahmad et al. 2015). celluloses present in the natural fibres are responsible for water uptake. in cellulosic cell wall fibre, the hydroxyl groups iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 224 bond with water and hydrogen exhibit more tendencies to water. the higher volume fraction of fibre, the higher cellulose content, thus increase the moisture absorption. moisture swells the fibres and break apart the fibres. the humidity absorbed by the composite without compromising decreased the mechanical and physical properties of the composite (badia et al., 2014). jana and zhong (2007) reported that during ambient condition, fungal may be developed on surface of flax fibre when expose to hygrothermal condition for only 3 days. therefore, the surface treatment is applied on biocomposite substance to overcome fungal growth. the chemical treatment using maleic anhydride polypropylene (mapp) is one of methods to modify the hydrophilicity of natural fibre apart from strengthening the bonding between matrix and fibre (joseph et al. 2002). food packaging is one of the main growing industry within plastic packaging market. those of product packaging made from conventional plastic. due to their durability and resistance to degradation tends to stay within landfill after been used (yousif and haddad, 2013). recently, new research on food packaging industry essential for the composite materials developed to degrade under the exposure of ultraviolet. the polypropylene, polyethylene and polystyrene matrix are usually sensitive to ultraviolet rays. the plastic products will degrade their polymer chain via scission and destroyed the cross linking between polymeric molecules (lopez et al. 2006). exposure to ultraviolet radiation leading to reduction in mechanical properties of composite. different type of radiations results in different kind of damage in products. jana and zhong (2007) revealed that composite used for outdoor application are exposed to uv radiation from sunlight and degraded the integrity of matrix. the degradation process by uv exposure are significance for food packaging application. degradation of composite leads to significant change in its structure, usually characterized by a loss of its fragmentation properties and also reduction of its molecular weight when placed under uv environmental conditions. several damaging effects on composite are dimensionless, surface erosion, and colour faded. natural fibres however contributed to uv light absorption. alternatively, to increase the lifespan of composite materials, coupling agent such as mapp can be employed to alter the compatibility of composite constituent subsequently increase the durability of composite material. the current work discussed the effect of uv radiation on the tensile properties, water absorption and optical properties of pp/dsnf composites. different exposure times were studied to determine the degradation of composite. the influence of coupling agent in prolong the performances of pp/dsnf composite under ultraviolet radiation was also deliberated. comparison was made with unexposed pp composite in terms of mechanical, physical and optical properties. 2. experimental method polypropylene grade 6331 was bought from titan pro polymers (m) sdn. bhd. maleic anhydride polypropylene was supplied by sigma-aldrich. durian skin waste was collected from pahang, malaysia. preparation of dsnf started with chopped, ground and sieved of durian skin fibre (dsf) into 100-250 μm mesh-size. then, durian skin nanofibre (dsnf) was produced through mechanical pre-treatment of dsf. the treatment process was continued with biological fermentation of rhizopus oryzae. rhizopus oryzae is a type of fungi that is naturally occurred from the expired bread and its strain with reference collection of american type culture collection (atcc). it was sporulated and grown on potato dextrose agar (pda). it was stored at 37 ºc for 3 days. the medium for fermentation was potato dextrose broth (pdb) which was prepared under controlled of ph 6 and sterilized in an iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 225 autoclaved at 121 ºc. the biological treatment started as rhizopus oryzae grown on pda collected by shaving using l-loop and extracting it with 25 ml sterilized distilled water. size of the inoculum was 2-5 × 105 spore’s ml-1. the inoculums were then added into 250 ml erlenmeyer flasks that contained 1 g dsf, 50 ml pdb and 50 ml deionized water. the biological fermentation process was conducted at 25 ºc for 7 days with an agitation speed of 250 rpm (nur aimi et al. 2011). the structure and crystallinity of dsnf was determined using a shimadzu x-ray diffractometer (xrd 6000) machine. the diffracted intensity of cukα (wavelength of 0.1542 nm) was recorded between 10o and 35o (2θ angle range) at 50 kv and 40 ma. the crystallinity index (ci) of the dsnf was calculated according to scherrer equation as in eq. (1). 𝐷 = (0.9 × 0.1541) ÷ (𝛽 × 𝐶𝑜𝑠𝜃) (1) pp and dsnf were mixed in haake internal mixer at temperature 180 ºc and 50 rpm screw rotational speed. 3 % of dsnf were added in compounding. the mixing process was carried out for 12 min. for composite with coupling agent, 2.5 g mapp was added and premixing was conducted before the ingredients were discharged into internal mixer. the composites were then compression moulded into specimens at 180 ºc for 12 min for characterization purposes. the samples of composite material were placed in the xenon arc tester (q-sun xe1) according to astm d2565. the samples were then exposed under uv light radiation by using fluorescent lamp with wavelength of 420 nm (1.1 w/m2) at temperature 65 oc. this uv intensity offers spectrum which is similar to sunlight conditions during sunny day. the sunlight exposure provides different condition at different period of time due to different climate. however, the sunlight exposure limits the intensity with the existence of weather and humidity (lopez 2006). therefore, the uv radiation applied to samples was applicable to acquire accurate correlations with outdoors exposure. in this study, samples were exposed to 500, 1000 and 2000 h uv radiation. after uv radiation, all the composites specimens underwent tensile test, physical and optical analysis. tensile tests were conducted in according to astm d638 using a universal testing machine (lloyd). the load cell was 10 kn and the crosshead speed was 50 mm/min. for water absorption test, pp/dsnf composites were immersed in water as per astm d570. the immersion took place until saturated data was obtained which was two months. the dimension and weight of the samples were recorded every day for the first 14 days and once a week afterwards. the degradation of composite due to ultraviolet exposure was analyzed based on the colour index. the colour index measured by comparing the specimen before and after uv exposure. according to ramos et al. (2014), colour value was evaluated in terms of l* for (0 = black and 100 = white), a* for (-a = red or +a = green) and b* for (-b = yellow or +b = blue) index in cie lab colour test. the colour index analyzed and compared using a varian 50 conc uv–visible spectrophotometer. the overall total colour difference index (e) which states the deviation from the reference stage was used as an indicator of degree of degradation. the colour index (e) is calculated as in eq. (2). ∆e= [(∆l *) 2 + (∆a*) 2 + (∆b*) 2]1/2 (2) where, δl = l – lref, δa = a – aref, δb = b – bref, l, a, b = colour accounted for the samples, lref, aref, bref = color coordinates of the control sample (dsnf/pp and dsnf/pp-mapp before uv exposure). iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 226 morphological observation of tensile fracture specimen was conducted under field emission scanning electron microscope (fesem) jeol jsm-6700f. transmission electron microscope (tem) was used to observe the dispersion of dsnf in pp matrix. the sample were cut using ulra-microtome under glass transition temperature, tg. then, it is mounted using cryogenic tool. the sample were prepared with dimension 0.5mm x 0.5mm by cutting it used glass knife before placed inside the copper grid. in 12 hours, the sample were dip in osmium tetroxide. the cm 12 philips transmission electron microscope (tem) (the netherlands) with different magnification analysis was used to assess nanoto micro-scale dispersion. 3. results and discussion 3.1. crystal structure of dsnf the crystal structure of durian skin nanofibre (dsnf) was analyzed using x-ray diffractometer and x-ray diffractogram of dsnf is demonstrated in fig. 1. the particle dimension was calculated using scherrer equation in eq. (1). fig. 1: x-ray diffractogram of dsnf. according to fig. 1, the maximum peak of diffraction occurred at 22.4o. another significant peak also appeared are at 35.1o and 29.5o. thus, the average diameter according to three maximum peak is 51.2 nm. the end result indicates that the fibres were in nanometer range size. roncero et al. (2005) reported that the intensity of crystalline peak is within 22o and 23o of 2θ angle, whereas for amorphous materials are between 18o and 19o. the particle size of dsnf were calculated and tabulated in table 1. the average diameter based on three maximum peak is 52 nm. table 1 shows the fibre diameter was reduced to nanometer scale. 1 g of dsf produced about 0.5 g of dsnf due to the removal of hemicellulose, lignin and pectin. iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 227 table 1: diameter of durian skin nanofibre. d1 d2 d3 2-theta 38.725 o 29.7362 o 22.36 o diameter 48.6 nm 47.94 nm 60.68 nm 3.2. effect of ultra violet radiation on tensile properties of pp/dsnf composites the tensile strength of pp/dsnf composites with and without mapp under ultra violet (uv) radiation is shown in fig. 2. it should be noted that the amount of dsnf in the pp matrix was 3 wt% based on optimum fibre content. from fig. 2, composites without uv exposure showed the highest tensile strength, 27 mpa (pp/dsnf) and 38 mpa (pp/dsnfmapp), respectively. tensile strength for pp/dsnf-mapp composite however dropped by almost 19% as uv radiation reached 2000 h. the loss of tensile strength of pp/dsnf composites were due to degradation of fibres and matrix. the ultraviolet radiation absorbed by polymers alters the chemical structure, providing molecular chain scission as well as chain crosslinking (azwa et al. 2013). uv radiation will lead to photodegradation due to photo-oxidation. energy of exposure sunlight is adequate to cause the disruption of c-c bonds as a consequence of degradation (yousif and haddad, 2013). the high amorphous region in pp/dsnf composites from table 2 further expedites the photo-oxidation process because of high permeability to oxygen (beg et al. 2008). it is noted in fig. 2 that the tensile strength for both composites reduced with uv radiation. the presence of mapp that function to bridge the pp and dsnf produced higher tensile strength than composite without mapp. the presence of dsnf increased the oxidation rate, however good dispersion of fibre with compatibilizer decreased the oxidation rate (matuana et al. 2011). besides mapp, dsnf in the form of nanofibre also imparted its strength thus enhanced the tensile properties of composite (nur aimi et al. 2014). fig. 2: the effect of dsnf content on tensile strength of pp/dsnf composites under uv radiation. table 2: diffracted intensity and crystallinity of pp/dsnf composites. iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 228 the effect of uv exposure on the tensile modulus of polypropylene composites is shown in fig. 3. in general, tensile modulus for pp composites are lower with uv exposure time. the trend was similar to tensile strength as seen in fig. 2. deterioration of polymer chain bonding in pp molecules downgraded the tensile modulus with time. in fig. 4, the carbonyl groups detected at peaks 1732.38 and 1716.69 cm-1 in ftir spectrum are strongly believed to be one of the reasons that contributed to the absorption of 420 nm uv light and helped initiation of photochemical reactions (matuana et al. 2011). in fig. 4, there is a peak appeared at 2908 cm-1 and 2921 cm-1. this indicates the c-h stretching vibrations or known as carboxylic group. in fig. 5, the carboxylic is seen in the region 2949.59, 2949.76, 2917.65 and 2917.71 cm-1. carboxylic groups were formed throughout the oxidative degradation of uv radiation (munajat et al., 2018). during oxidation process, uv radiation generated carbon-oxygen bond react with oxygen-hydrogen single bond where cause increasing carboxylic functional groups. the reaction rate increased with number of broken polymer chains bonds in the exposure sample. fig. 5 also illustrated the same peak at this region as in fig. 4. as shown in fig. 4 (b), one broad peak appeared in sample exposed under uv which related to o-h functional group located between range 3400 to 3200 cm-1. this peak appeared due to reaction o-h bond with aging of oxidation process (munajat et al., 2008). meanwhile, this peak not invisible in fig. 4(a). according to bajwa et al. (2015), the peak presented in uv exposed specimens are typically related with existence of carboxylic group. this indicates that photodegradation occurred under uv light in pp composites. fig. 3: the effect of dsnf content on tensile modulus of pp/dsnf composites under uv irradiation. aging or degradation of pp/dsnf composites are also attributed to lignin. dsnf composes of about 10% lignin (nur aimi et al. 2015). lignin absorb the uv radiation and diffracted intensity at amorphous region (iam) diffracted intensity at crystalline region (icr) percentage crystallinity (%) pp/dsnf 2.98 1.10 26.9 pp/dsnfmapp 2.38 1.01 29.8 iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 229 photo yellowing mechanism occur in lignin (beg et al. 2008). uv light encourages the production of radicals by oxidation. radicals cause the chains of matrix to breakdown. fig. 4: ftir of pp/dsnf composite before uv radiation. fig. 5: ftir of pp/dsnf composite after uv radiation. observation under fesem in figs. 6-7 revealed the debonding occurred possibly due to uv radiation which evidenced by the decrement both in tensile strength and tensile modulus of composites. in the absence of mapp, fibres are easily pulled-out and debonding from the matrix. fibre breakage is also noticed in fig. 6. void spaces between fibre pull-out iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 230 and matrix is clearly seen in fig. 6. the dsnf particle was weak attached to the pp matrix when load is applied it lead the fillers to be debond from the pp matrix and easily leaving behind evidences of voids. manshor et al. (2014) mentioned in their analysis that the formation of void is appeared due to poor fiber orientation. meanwhile, in fig. 7 where the biocomposites with presence mapp shows the dsnf were embedded in pp matrix. there is less traces of fiber pulled out due to strong interlocking bonding between fiber and matrix. however, the size of fiber tends to increase due to agglomeration and some error during produce dsnf. the nanofiber size already be proved in xrd test (fig 1) and under tem observation (fig. 11). therefore, further experiment required to improve this problem. fig. 6: fesem micrograph of pp/dsnf composite after uv radiation. fig. 7: fesem micrograph of pp/dsnf-mapp composite after uv radiation. 3.3. effect of ultra violet radiation on water absorption of pp/dsnf composites the effect of uv radiation on the water absorption of pp/dsnf composites are presented in fig. 8. the water greatly affects the composite with regards to dsnf content in pp matrix from 0 to 5 wt%. it was noted in fig. 8, the first two weeks of immersion process demonstrated substantial water uptake by all the composites. polypropylene matrix iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 231 was the least absorbed water due to it hydrophobic characteristic. the water absorption test was conducted up to 70 days until saturated trend was obtained. there were seven different compositions presented in fig. 8. sample without mapp absorbed more water than the sample with coupling agent. lack of wettability adhesion in composites resulted in poor interlocking between fibre and matrix (joseph et al. 2002). in addition, water molecules are easily entrapped in gap of interfacial area leading to increasing of water absorption in fibre-matrix interphase. composite with 5 wt% dsnf was dominated in water uptake with more than 5.74% water absorbed through 70 days. the amount of water uptake showed that the amount of fibre content influenced the behavior of composite material. composites with 5 wt% dsnf absorbed the highest amount of water and vice versa. the fibres consist of cellulosic components giving rise to hydrophilic characteristic and thus tend to attract water. according to patpen et al. (2015), natural fibre are exposed to water molecules in moisture condition. therefore, the composite experienced swelling due to water absorption through voids spaces generated between fibre and matrix. fig. 9 showed mechanism in biocomposites in the presence of water. fig. 8: the effect of dsnf content on water absorption of pp/dsnf composite under uv radiation. fig. 9 demonstrated the effectiveness of coupling agent where composite with mapp able to stop the water absorbed into pp/dsnf composite as compared to composite without mapp. similar observation was reported by badia et al. (2014) where the presence of mapp reduced the water uptake into biocomposites. mapp provides increase interfacial adhesion where less water accumulated in the interfacial voids and prevent water from entering dsnf. the effectiveness of mapp decreased amount of water uptake by bamboo reinforced polymer which was reported by thwe and liao (2002). with the improvement as seen in fig. 8, it is believed that mapp induced less hydrophilicity in the pp/dsnf composite and promotes interfacial adhesion. iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 232 fig. 9: the effect of water molecule on biocomposite (faruk 2012). 3.4. effect of ultra violet radiation on optical properties of pp/dsnf composites the effect of uv radiation on optical properties of pp/dsnf composites are shown in fig. 10. the optical properties investigated were compared for samples before and after uv exposure on composites with and without mapp. the optical properties are given as lvalue measured the effect of uv radiation on the physical appearance of pp/dsnf composites. the strength of colour were gained from the elements presence in the composites (ramos et al. 2014) fig. 10 demonstrated the l-value for pp/dsnf composites at 0, 500, 1000 and 2000 hours of uv exposure. sample with 2000 h uv exposure showed the highest l-value as compared to other uv exposure time. the changes in colour lightness was due to photodegradation process via uv exposure time. thermoplastic composites subjected to uv radiation may experience yellowish before photo-bleaching mechanism took place after 250 h exposure (matuana et al. 2011). this showed that longer uv exposure time resulted in increased of colour index (∆e) of pp/dsnf composites. according to lopez et al. (2006), samples exposed longer under sunlight or outdoor would resulted in easy detect in terms of colour changes in the samples. however, the presence of mapp as coupling agent slightly changed the colour of pp/dsnf composite. bajwa et al. (2015) also reported that discolouration of composite occurred due to uv radiation and oxidation of degraded polymer took place owing to chain scission between matrix and reinforcement. the presence of mapp also protected the penetration of uv radiation in pp/dsnf composite. iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 233 fig. 10: the l-values of pp/dsnf composites. 3.5. transmission electron microscopy of pp/dsnf composites the tem images in fig. 11 showed microstructure of pp/dsnf and pp/dsnfmapp composites. fig. 11(a) illustrated the image of a section of pp/dsnf without the presence of coupling agent where the black spots are the dsnf. from fig. 10(a), the aggregations of dsnf are thicker and clearly evident which led to poor dispersion of nanofibre in pp composite. fig. 2 also demonstrated weak tensile strength due to absent of coupling agent in pp composite. similar finding was observed by deng et al. (2010) on polypropylene and carbon nanotube. they reported poor adhesion occurred at the interface of polypropylene and carbon nanotube without the addition of coupling agent. additionally, uv degraded the composite microstructure where there were different structures due to crack behavior occurred on the surface. thus, the pp/dsnf composite as plastic packaging application can be decompose due to weathering condition. fig. 11(b) exhibited the images of pp/dsnf in the presence of mapp coupling agent. fig. 11(b) revealed that dsnf were well-dispersed. this indicated that the addition of mapp improved the interaction between polypropylene and dsnf by reducing the agglomerations between them. selvakumar et al. (2010) also reported that the tensile strength increased with addition of 5 wt% maleic anhydrides grafted polypropylene (mahg-pp) where the reinforcement dispersed in pp/mmt nanocomposites. this finding confirmed the presence of coupling agent in composites led to increment of tensile properties as shown in figs. 2-3. iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 234 fig. 11: transmission electron microscopy (tem) of (a) pp/dsnf and (b) pp/dsnfmapp composite. 4. conclusion remarks as conclusion, durian skin nanofiber was successfully produced via fermentation using rhizopus oryzae. the main targets of this project have been attained which also recommend that the application of durian skin nanofiber (dsnf) in biocomposites as reinforcement with mapp can improves the mechanical properties of specimens. the environmental degradation under uv exposure significantly degraded the tensile and optical properties of pp/dsnf composites. the presence of mapp however delayed the water absorbed by composites owing to good interaction of pp and dsnf. as food packaging application, uv exposure is one alternative ways to speed up the degradation process of materials. however, further experiment required to improve the result outcome. acknowledgement this work was financially supported by fundamental research grant scheme (frgs16-003-0502) from ministry of education malaysia. the authors would like to thank iium for research facilities in making this studies success. (a) (b) iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 235 references [1] ahmad f, choi hs, park mk. (2015) natural fiber composites selection in view of mechanical, light weight and economic properties. a review. macromolecular material engineering, 300: 10–24. [2] azwa, zn, yousif bf, manalo ac, karunasena w. (2013) a review on the degradability of polymeric composites based on natural fibres. material destruction, 47: 424-442. [3] badia jd, kittikorn t, strömberg e, santonja-blasco l, martínez-felipe a, ribes-greus a, ek m, karlsson s. (2014) water absorption and hydrothermal performance of phbv/sisal biocomposites. polymer degradation stability, 108: 166-174. [4] bajwa ds, bajwa sg, greg ah. (2015) impact of biofiber and coupling agents on the weathering characteristics of composites. polymer degradation stability, 120: 212-219. [5] beg mdh, pickering kl. (2008) accelerated weathering of unbleached and bleached kraft wood fibre reinforced polypropylene composites. polymer degradation stability, 93: 19391946. [6] deng h, bilotti e, zhang r, peijs t. (2010) effective reinforcement of carbon nanotubes in polypropylene matrices. journal applied polymer science, 118: 30-41. [7] faruk o, bledzki ak, fink hp, sain m. (2012) biocomposites reinforced with natural fibers: 2000-2010. progress polymer science,37: 1556-1596. [8] jana s, zhong wh. (2007). ftir study of ageing epoxy resin reinforced by reactive graphitic nanofibers. journal applied polymer science, 106: 3555-3563. [9] joseph pv, rabello ms, mattoso lhc, joseph k, thomas s. (2002) environmental effects on the degradation behaviour of sisal fibre reinforced polypropylene composites. composites science technology, 62: 1357-1372. [10] lopez, jl, sain m, cooper p. (2006) performance of natural-fiber–plastic composites under stress for outdoor applications: effect of moisture, temperature, and ultraviolet light exposure. journal applied polymer science, 99: 2570–2577. [11] matuana lm, jin s, stark nm. (2011) ultraviolet weathering of hdpe/wood flour composites coextruded with a clear hdpe cap layer. polymer degradation stability, 96: 97106. [12] munajad a, subroto c, suwarno (2018). fourier transform infrared (ftir) spectroscopy analysis of transformer paper in mineral oil-paper composite insulation under accelerated thermal aging. energies, 11(3), 364-378. [13] nur aimi mn, kamalbahrn mam, mohamed ns, anuar h, mel m, othman r. (2011). effect of rhizopus oryzae fermentation on kenaf-based polylactic acid’s monomer. iium engineering journal, 12: 83-87. [14] nur aimi mn, anuar h, manshor mr, wan nazri wb, sapuan sm. (2014) optimizing the parameters in durian skin fiber reinforced polypropylene composites by response surface methodology. industrial crops product, 54: 291-295. [15] nur aimi mn, anuar h, maizirwan m, sapuan sm, wahit mu, zakaria s. (2015). preparation of durian skin nanofibre (dsnf) and its effect on the properties of polylactic acid (pla) biocomposites. sains malaysiana, 44: 1551–1559. [16] patpen, p, rahman ra, talib ra, abdan k. (2015) mechanical properties and water absorption behaviour of duriam rind cellulose reinforced poly (lactic acid) biocomposites. international journal on advanced science engineering information technology, 5: 343349. iium engineering journal, vol. 19, no. 1, 2018 e’zzati et al. 236 [17] ramos m, jiménez a, peltzer m, garrigós mc. (2014) development of novel nanobiocomposite antioxidant films based on poly (lactic acid) and thymol for active packaging. food chemical, 1-31. [18] roncero alt, colom jf, vidal t. (2005) the effect of xylanase on lignocellulosic components during bleaching of wood pulps. bioresource technology, 96: 21-30. [19] selvakumar v, palanikumar k, palanivelu k. (2010) studies on mechanical characterization of polypropylene/na+-mmt nanocomposites. journal of minerals and materials characterization and engineering, 9: 671-681. [20] thwe mm, liao k. (2002) effects of environmental aging on the mechanical properties of bamboo-glass fiber reinforced polymer matrix hybrid composites. composites: part a, 33: 43-52. [21] yousif e, haddad r. (2013) review: photodegradation and photostabilization of polymers, especially polystyrene. springerplus, 2: 398. microsoft word 142-1039-1-ed completed corrected.docx iium engineering journal, special issue, mechanical engineering, 2011 okubo 65 on-orbit demonstration of a sun sensor on the micro-satellite maido-1 hiroshi okubo department of aerospace engineering, osaka prefecture university, sakai, 5998531, japan. okubo@aero.osakafu-u.ac.jp abstract:a 50-kg-class microsatellite “maido-1 (sohla-1)” was launched, along with six other piggyback subsatellites, by a japanese h-2a rocket on january 23, 2009. the fundamental and detailed designs of the satellite were developed by university students under the technical guidance of the japan aerospace exploration agency (jaxa). a stringtype sun sensor (fudai sun sensor; fss) was also developed by the students with the technical assistance of jaxa and advanced engineering services (aes) co. ltd. the fss was mounted on the satellite as an experimental component. this paper reports the development of maido-1 and fss as well as the satellite operation by the students and the results of on-orbit experiments. abstrak: satu mikrosatelit kelas 50 kg “maido-1 (sohla-1)” telah dilancarkan, bersama enam lagi subsatelit gendong, dengan menggunakan roketh-2a (jepun) pada 23 januari, 2009. rekabentuk satelit yang asas dan terperinci dibangunkan oleh para pelajar universiti di bawah bimbingan teknikal agensi explorasi aeroangkasa jepun (japan aerospace exploration agency (jaxa)). sejenis penderia matahari bertali (fudai sun sensor; fss) juga dibangunkan oleh para penuntut dengan bantuan teknikal dari pihak jaxa dan advanced engineering services (aes) sdn. bhd. fss telah dilekapkan ke satelit sebagai komponen eksperimental. kertas ini membentangkan perkembangan maido-1 dan fss, operasi satelit oleh pelajar-pelajar dan keputusan eksperimen semasa dalam orbit. keywords:microsatellite;sun sensor;satellite operation;on-orbit experiment;attitude control component 1. introduction a 50 kg class micro-satellite “maido-1 (sohla-1)” has been developed by space oriented higashiosaka leading association (sohla), a corporation of middle-sized enterprises in higashi-osaka and kansai district [1]-[3].the configuration and specifications of maido-1 are shown in fig. 1 and table 1. the fundamental design and detailed designs of the bus-systems has been carried out by the students of osaka prefecture university under the technological support of japan aerospace exploration agency (jaxa). the main objectives of the “sohla-1” program is to realize the low-cost and short term development of a micro-satellite on the basis of a technology transfer between “microlabsat” and the micro-satellite design technique of jaxa with the cooperation of a small and medium enterprise group in higashi-osaka and osaka prefecture university. one of the main objectives is to provide the engineers and students training opportunities for developing the iium engineering journal, special issue, mechanical engineering, 2011 okubo 66 micro-satellite and learning systems design technique. the “small satellite design workshop” was conducted by osaka prefecture university, jaxa, and sohla in order to study the design problems of maido-1. the design and development of the maido-1 bus system were carried out by graduate and undergraduate students of osaka prefecture university and ryukoku university under the technical support of jaxa. the vibration test, thermal balance test, etc., were carried out at tsukuba space center and creation core higashi-osaka, where the students participated in the planning, execution, and post-analysis of the tests and obtained valuable experience. the main missions of maido-1 were the engineering demonstration of newly developed on-board instruments such as a monitor camera, gps receiver, and broadband vhf digital interferometer for lightning observation from space. among them, aprototype sun sensor, named fudai sun sensor (fss)was developed by the students of opu with technical support from the jaxa and advanced engineering services (aes) co. ltd., and it was loaded onto maido-1. the fss works on the “one string method,” whereby a string is used to create shade on a linear sensor [4]. the string method has two advantages over the precision slit system, e.g. [5]. first, it is easier to manufacture and has less constraints of the measurement range. second, it is possible for even smaller downsizing for small and micro satellites. moreover, it can also put in perspective for microminiaturization through micro electro mechanical systems (mems) technology. the aim of developing this sensor was to demonstrate a new type of sun sensor based on the string method and to apply the technique for developing satellite components at the university. for this purpose, the breadboard model (bbm), engineering model type 1 (em1), engineering model type 2 (em2), and flight model (fm) of the fss were developed. fig. 1:configuration of maido-1. the “maido-1”was successfully launched, together with other six piggy-back subsatellites, by a japanese h-2a rocket on january 23, 2009. the mission experiments conducted in the regular operation period (about three months) were all successful, which include the on-orbit demonstration of monitor cameras, fss, boom deployment, and lightning observation from space. the operation was continued for about 9 months, and the satellite system was shut down on the 10th of october by a command from the ground.this paper reports the developmentof maido-1 and fssand on-orbit experiment of fss which osaka prefecture university was mainly participated. iium engineering journal, special issue, mechanical engineering, 2011 okubo 67 table 1: specifications of maido-1. size 50 (w) x 50 (d) x 50 (h) cm mass 50 kg orbit leo, sun synchronous communication s-band; amateur band altitude control spin stabilized, 3 rpm (tbd) power control ppt control thermal control passive control operation period > 3 months 2. development of maido-1 the design and development of the maido-1 bus system were carried out by graduate students and the students of osaka prefecture university and ryukoku university. they undertook the development of a subsystem in which each special research field was intensive; moreover, they studied satellite design technology under researchers and specialists from jaxa; furthermore, they also studied manufacturing technology from the engineers of higashiosaka. the “small satellite design workshop” was jointly conducted by osaka prefecture university, jaxa, and sohla in order to study the design problems of sohla-1. the workshop was held more than 30 times during fy 2004–2005. the vibration test, thermal balance test, etc., were performed at the tsukuba space center and creation core higashi osaka, where the students participated in the planning, execution, and post-analysis of the tests and obtained valuable experience. outline of the systems design on the electrical power system, structural system, thermal control system, and attitude control system, in which osaka prefecture university was mainly involved, is presented as follows: in microsatellites, the electric power system (eps) design is a very important factor because the surface area available is limited. several methods of eps analysis were employed in order to confirm the feasibility of the satellite system. an eps simulator has been developed to examine the electrical power control parameters and a new peak power tracking (ppt) algorithm has been proposed. from the vibration tests performed on the structure thermal model, it was found that the damping characteristic of the initial design is very low. several vibration suppression systems have been experimentally examined. among these, the vibration suppression system using polyimide tape was found to be very effective, and the magnitude of vibration response of the revised satellite structure was reduced to 1/3rd of the original. in order to verify the validity of the preparatory design and analysis, the thermal balance test has been performed two times. the experiments have been conducted using a skin heater iium engineering journal, special issue, mechanical engineering, 2011 okubo 68 and an ir cage. a new design method has been developed for the thermal control system of a small satellite using a genetic algorithm. the proposed method is effective in reducing the computational time and is suitable for the thermal control system design of a small satellite. the primary method of attitude control is the spin stabilized control. nutation damping and spin control are achieved by driving magnetic torques based on onboard computing. spin axis estimation is achieved by using solar and magnetic sensors; spin axis control is based on offline computing. a novel improved spin axis control algorithm has been developed for maido-1, and its effectiveness has been examined both by a simulation test and a flight test using microlabsat. 3. development of sun sensor a sun sensor named “fudai sun sensor (fss)” was developed by osaka prefecture university with the technical support of the jaxa and aes. the fss works on the “one string method,” where a string is used to create shade over a linear sensor in order to geometrically measure the angle between the sun direction and the spin axis (total sun angle). the string method has two advantages over a precision slit system. first, it is easier to manufacture and has less constraints on the measurement range. second, it is possible to further downsize it for application to small and microsatellites. moreover, it can also put in perspective for microminiaturization through the micro-electromechanical system (mems) technology. the aim of developing this sensor was to present a novel sun sensor based on the string method and to apply the same technique for developing satellite components at the university. as shown in fig. 2, the breadboard model (bbm), engineering model type 1 (em1), engineering model type 2 (em2), and flight model (fm) of the fss were developed. the fm of the fss was completed in august 2007. fig. 2: development of fudai sun sensor (fss). iium engineering journal, special issue, mechanical engineering, 2011 okubo 69 3.1 summary of fss the fss comprises of a surface component and a light-receiving component. the surface component usually has a slit or a pinhole to limit incident light. in the light-receiving component, the electric current output of solar battery cells or the light-receiving point is detected by a ccd to measure the angle of incidence. in contrast to regular sun sensors, the fss employs a string to create shade. table 2 lists the specifications of the fss. the fss is a uniaxial sun sensor: it measures the angle between the spin axis of the satellite and sunlight. this angle is defined as the total sun angle (tsa). as shown in fig. 3, the intensity of sunlight is reduced by using an nd filter. a string placed between the nd filter and the linear sensor forms the shade over the linear sensor.figure 4 shows a block diagram of the fss. the linear sensor measures the position and brightness of the shade. these data are transformed into the digital format by an a/d converter having a built-in microcomputer, and the tsa is calculated. when the operation mode of the fss changes, the ground station sends a command to the fss through an amateur-band transponder and receiver (htrx). table 2: specifications of fudai sun sensor (fss). mass 0.450 ± 0.050 kg size about 80 x 150 x 39 mm installed satellite sohla-1 maximum consumption power ≤ 1 w feasible temperature -20 oc – 40 oc measurement method one string method detection accuracy 2o ~3o (on board) 1o (off board / aim) detection range 58 ± 29o (on board) 48 ± 25o (off board / aim) life span 3 months table 3: modes of operations of fss. mode function standby mode turn on fss normal mode obtain tsa at 1 hz high-speed mode obtain tsa at 5 hz message mode output character on program area iium engineering journal, special issue, mechanical engineering, 2011 okubo 70 conversely, telemetry from the fss is sent to the ground station through htrx. as shown in table 3, the fss prepares some operation modes for its own control. moreover, the fss has a changing threshold value function in order to vary the threshold value to the strength of sunlight so that the shade can be discerned manually or automatically (valid for normal or high-speed mode). the fss also employs reset functions for hardware and software troubleshooting. fig. 3: structure of fss. fig. 3: bock diagram of fss. 3.2specification definitions the fss is an experimental component that is used in the nominal position. considering some errors and problems, the detection range can therefore be defined at ±30° from the measurement center, which is the normal tsa of maido-1. as shown in fig. 5, the detection range is given as follows: iium engineering journal, special issue, mechanical engineering, 2011 okubo 71 on the fss, l = 9 mm and the measuring center tsa = 67.5. thus, the distance between the light-receiving element and the sensor head when the detection range is 60can be calculated. the relationship between the detection range and the maximum resolution is described as follows: the fss consists of a 64 pixel linear sensor and its detection range is 60[deg]; thus, its maximum resolution is 0.9375. measurement errors and the size of pixels of the linear sensor, however, should be considered. the target accuracy is therefore defined as 1. fig. 4: light-receiving element and sensor head. 3.2detection accuracy in order to reconfirm the validity of the nd filter design for em2 and to confirm the measurement accuracy of the fss, an accuracy test (quasi-sunlight irradiation test) was performed in the solar battery evaluation room of the jaxa tsukuba space center. the accuracy was found to be about 0.5°~1°. figure 6 compares the actual value of the sun angle and the sun angle value obtained from the fss. fig. 6: tsa theoretical value and output of fss. iium engineering journal, special issue, mechanical engineering, 2011 okubo 72 in order to develop a “space” component, resistance to space as well as the launching environment is extremely important. it mainly consists of temperature resistance, vacuum resistance, and vibration resistance. 4. on-orbit oprations and experiments maido-1 was launched on january 23, 2009, as a subsatellite of the greenhouse gases observing satellite (gosat) aboard h-iia launch vehicle no. 15. the satellite was in the initial functional verification operation for about one month after completing its critical operation on january 27, 2009 (jst). then, the normal operation phase was executed smoothly for three months (march–may 2009) and was immediately followed by the extended operation phase (june–october 2009). 4.1 operation/control system satellite operation/control and the acquisition of telemetry data, such as, experimental data and image data, were conducted by the jaxa space technology demonstration research center at tsukuba space center. the ground station network of jaxa, masuda, okinawa, and katsu’ura stations supported the communications with the satellite using sband frequencies. an amateur-band radio transceiver (htrx) was also on-board, and osaka prefecture university also operated its own amateur-band ground station and performed an on-orbit demonstration of the newly developed solar sensor (fudai sun sensor, fss). the data measured by the fss was sent to the ground as amateur-band telemetry. satellites daily revolve around the earth for about 98 min to pass over japan in the afternoon and late night hours; over 25 students were participating in the operation of the satellite operation by changing of the crew members. moreover, sohla was working for the civil service in conjunction with amateur radio and amateur radio clubs, and its daily operations were published on the web. figure 7 shows the system configuration of the operation and control consisting of s-band and amateur radio frequency band ground stations. fig. 7: operation and communication stations. iium engineering journal, special issue, mechanical engineering, 2011 okubo 73 4.2 on-orbit demonstration of fss on-orbit test of the fss was performed using an amateur-band communication system to obtain the experimental measurements as the telemetry data.figure 8 is a graphical depiction of the telemetry obtained from the fss showing the ccd sensor output vs. sensor element number. as compared to the results of ground quasi-sunlight irradiation test, it is observed that the shadow of the string has a clearer boundary. the tsa is geometrically obtained from the sensor numbers corresponding to the boundaries of the shadow. the time sequences of the averaged ccd output are shown in figs. 9and 10 for the normal mode andhigh-speed mode, respectively. the cyclic variation of output level represents the spin of the satellite and the time between the peaks indicates the spin period. fig. 8: ccd sensor output (on-orbit test/ground test). fig. 9: time sequence of ccd output (normal mode). 0 20 40 60 80 100 120 140 0 10 20 30 40 50 60 c c d s en so r o ut pu t sensor number observed exam 0 10 20 30 40 50 0 10 20 30 40 50 60 70 c c d o ut pu t t [sec] iium engineering journal, special issue, mechanical engineering, 2011 okubo 74 fig. 10: time sequence of ccd output (high-speed mode). fig. 11: daily variation in tsa. fig. 12: daily variation in spin rate. figures 11 and 12show the daily variations in of tsa and spin rate of the satellite, respectively. average measurements of fss are plotted for comparison with the sohla-1 bus-sensor (a flax magnetic sensor, fms) estimates. although deviations of -1.0°~-2.5° are 0 5 10 15 20 25 30 35 40 0 10 20 30 40 50 60 c c d o ut pu t t [sec] 0 10 20 30 40 50 60 4/18 4/22 4/26 4/30 t s a [ de g] date tsa (fss) tsa (fms) 0 1 2 3 4 5 6 7 8 4/18 4/22 4/26 4/30 sp in r at e [r pm ] date spin rate (fss) spin rate (fms) iium engineering journal, special issue, mechanical engineering, 2011 okubo 75 observed, the daily variations are congruous. these results demonstrate the usefulness of the sensor. fig. 13: trajectories of maido-1 and solar eclipse. fig. 14: time sequence of sun sensor output (at solar eclipse). a solar eclipse was observed in asia and the pacific on july 22, 2009. we successfully observed the solar eclipse using the fss. figure 13 shows that the on-earth trajectoriesof maido-1(orange line) and the center of the region under the solar eclipse (double red line)crosses each other at jst 12:28. figure 14 shows the average solar sensor ccd photodetector output (representing the intensity of the received sun light). normally, the data is almost steady and the peak value is constant; however, the peak value for the solar eclipse decreases as sohla-1 approaches the centre of the eclipse. the maximum reduction was about 60% of the normal level at 12:28. 4. conclusion the development of the microsatellite miaido-1 and fss has been presented. the details of the operation and a brief summary of the on-orbit demonstration of the fss have also been presented.the detection accuracy of fss was estimated to be 0.5°~1° by on-ground 0 5 10 15 20 25 30 35 40 12:24 12:25 12:26 12:27 12:28 c c d s en so r o u tp u t time iium engineering journal, special issue, mechanical engineering, 2011 okubo 76 experiment and it was confirmed in on-orbit operation. this performance is enough for applying to a sun tracking attitude control system. the developed sensor is only a prototype model, and there are many challenges to finish it as a practically useful space instrument for microsatellites, e.g., the microminiaturizing of the hardware system through mems technology. acknowledgement we appreciate the technical support from japan aerospace exploration agency (jaxa) and advanced engineering services (aes) co. ltd. references [1] h.okubo, h.azuma, and m.chiba, “participation of students for the development of the small satellite sohla-1 and the role of the small satellite research center,” proceedings of the 25th international symposium on space technology and sciences, pp. 1360–1365 (2006). [2] h.okubo, h.azuma, and m. chiba, “development and operation of micro-satellite sohla1(maido-1),” international astronautical congress, iac-09-b4.3.8, 6 pages, 2009. [3] h. okubo, t. isono, k. obata, “development and operation of micro-satellite maido-1 and onorbit demonstration of sun sensor,” ifac international conference on aerospace control, nara, 2010. [4] t. obata, k. itoh, y. kakimi, and h. okubo, “development of fudai sun sensor (fss),” trans. jsass, space technology japan, vol. 7, pp.tf_25–tf_30, 2009. [5] j.h. hales and m. pedersen, “two-axis moems sun sensor for pico satellites,” 16th annual aiaa/usu conference on small satellites, ssc02-vi-6, 2002. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 border surveillance using face recognition, mobile otp and email naresh kumar1 and deepali gupta2 1department of computer science and engineering, msit, janakpuri, new delhi, india. 2chitkara university institute of engineering and technology, chitkara university, punjab, india. *corresponding author: narsumsaini@gmail.com (received: 24th december 2019; accepted: 13th march 2020; published on-line: 4th july 2020) abstract: expanding strains over indian borders with illegal crossings and examining past assaults on the nation, it is clear that in a large portion of the cases, security powers are uninformed of the movement of these interlopers. for this reason, a framework is needed to manage the border issue that would be equipped for working in sloping landscapes where there is no power. this paper manages identification and situating of interlopers crossing the border utilizing pir sensors and cameras. in the event of any undesirable crossing in the area, the sensor quickly detects it and the camera will stream pictures to the base station (bs). relying upon the guidance originating from the bs, the sensor will either activate the camera for further streaming or turn it off. the objective of this paper is to give a framework that will help the border security force (bsf) in controlling all sorts of illicit activities near the outskirt in a superior and precise manner. abstrak: merentas isu sempadan india dengan kegiatan pencerobohan sempadan dan dengan mengambil kira kutukan lepas terhadap bangsa kami, adalah jelas dalam banyakbanyak kes ini pegawai keselamatan tidak diberitahu tentang bahagian yang dicerobohi. dalam keadaan ini, kita memerlukan rangka kerja bagi mengurus masalah sempadan di mana kelengkapan perlu dipasang di tebing landskap yang tidak mempunyai sumber tenaga. kajian ini mengurus identiti pengenalan dan kedudukan kegiatan haram yang berleluasa di sempadan dengan mengguna pakai pengesan pir dan kamera. apabila terdapat perubahan pergerakan yang tidak diingini di sempadan, pir akan mengesan pergerakan dengan cepat dan kamera akan menggaris arus gambar-gambar ke stesen utama (bs) dan bergantung kepada panduan pengkalan di bs, pengesan akan membuat kamera lebih bergaris arus atau berhenti merekod. kajian ini pentng bagi menunjukkan rangka yang membantu penguatkuasaan keselamatan sempadan (bsf) dalam mengawal semua kegiatan haram berhampiran sempadan dengan bermutu dan tepat. keywords: eigenface; face detection; face recognition, training set 1. introduction outskirt security system is a creative plan to verify wildernesses insightfully without the mediation of humans. it gives protection to the nation and simultaneously reduces manpower and asset usage. the outskirt security framework recognizes any interloper and also monitors every one of the activities occurring close to the territory. because the border area is an enormous and perilous region, it is difficult to secure a constant power supply for the system. nonetheless, an effective national shield requires a constant 143 iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 monitoring of the border areas, with the associated labour and equipment costs. for this reason, an automated framework for surveillance is fundamental. the automated system must include specialized issues and use of legitimate calculation with the goal that any interruption identified in the outskirt can easily be transmitted to inform vital responses from authorities. appropriate use of the framework may help border security force (bsf) to control those exercises in a superior and increasingly exact manner. a report of [1] in the us in 2014 showed 1.7% of aggressive offense and robbery cases increased by 1% from total of 311936 cases of 2014. lots of research has been carried out on face recognition border security systems and the information is available in [2-7]. similar home security systems are also mentioned in [8-11]. facial discovery is a pc innovation that decides the area and size of human face in a self-assertive (advanced) picture. the facial highlights are identified and some other items like trees, structures and bodies and so on are overlooked from the computerized picture. it can be seen as classification of instances where one can find the area with size of all the places and its class. face recognition is basic element of face limitation. in face confinement, the errand is to discover the areas and sizes of a known number of appearances (normally one). essentially there are two so rts of ways to deal with the distinguished facial part in the given picture for example highlight base and picture base approach. feature base methodology attempts to remove highlights of the picture and compare it with the information on the face highlights. the method is based on the image to provide the best match between training and the image to be tested. faces are a factor that is exceptionally simple to recall, all things considered. for the most part, people can recall and perceive an individual dependent all over. it is proven that a face is one of a mind boggling set of variations when seen from the point of view of pc vision. human countenances have various highlights and qualities of every individual with the goal that face acknowledgment is generally excellent to be applied in different territories, including excitement, savvy cards, data security, and so forth. the essential idea of pc vision is as valuable data from a solitary picture or a succession of pictures, generally utilizing the technique of programmed extraction, investigation and learning. probably the best technique to perform facial acknowledgment is to utilize the principal component analysis (pca) calculation. pca is likely the most prevalent multivariate measurable procedure and it is utilized by practically all logical orders. it is additionally liable to be the most seasoned multivariate strategy. multivariate investigation can essentially be translated as a strategy related with enormous factors in at least one examination. this strategy can separate the fundamental trademark information from different information that we have. pca is a multivariate procedure that breaks down an information table wherein perceptions are depicted by a few between corresponded quantitative ward factors. the eigen face based approach is used by pca. in this paper, the proposed approach uses a human face with an eigen face approach to provide security at border. 2. related works face acknowledgment has been considered by numerous specialist utilizing different calculation and approach. biometric use is the most noteworthy security framework contrasted with conventional frameworks (utilizing secret word or different identity card for verification) on the security framework. face acknowledgment itself has two fundamental strides as a rule [12], namely face discovery and face acknowledgment. to 144 iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 perform face identification, cascade classifier technique is used. in [13] the feed forward neural networks (ffnw) is used to accomplish face acknowledgment. face recognition was performed in [12] and [13] by principal component analysis (pca). by watching the writing, particularly [12,13], and pca calculation is chosen to play out the face acknowledgment. this exploration is likewise bolstered by another examination like [14]. 3. challenges of border security some of the challenges encountered in border security are as follows: a) infiltration and ex-filtration of armed militants b) narcotics and armed smugglers c) illegal migrations d) export of fundamentalist terrorism 4. objectives of border security based on literature review and challenges identified in section ii and iii, the following are the major objectives of this paper: a) to identify intruders with cameras and sensors like pir and ir sensors. b) to effectively eliminate the intruder using a gun firing mechanism. c) to eliminate the need for being physically present in any location for security of the border. 5. proposed method the architecture of proposed method is shown in fig. 1, which elaborates the complete process of how the work in the proposed approach is accomplished. the architecture shown in fig.1 utilizes red green blue (rgb) images captured by webcam as essential information and can use optional information, such as xml classifier documents, for facial identification and recognition. it comprises info factors of the initial face picture and the prepared face picture. the yield factors of this examination are level of similarity and recognition of a suspect’s face [15]. the module-wise explanation of architecture is: 5.1 object detection the initial step to accomplish for face location is to get to the camera that will be utilized for face identification and acknowledgment. the detection process is shown in fig. 2. this stage will also check whether the webcam is on. on the off chance that the camera is turned off, the procedure cannot be continued. the recognition procedure begins by identifying objects utilizing cascade_find_biggest_object as a course classifier that will only look through the one biggest item. moreover, the underlying information picture of rgb arrangement is converted to grayscale design. the following stage is to contract the camera picture to a sensible size on the grounds that the speed of face discovery depends on the size of the picture. it will be delayed for enormous pictures and will be quick for little pictures. it is likewise still genuinely dependable to identify faces even at low resolution. 145 iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 fig. 1: architecture of the face detection system. fig. 2: face detection process. training images (subset -1) training images (subset -2) convert rgb image to gray scale recognize the faces recognizer image compare the grayscale images for results open camera stop camera take photo 146 iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 to improve the contrast and sharpness, histogram adjustment is applied. from that point onward, we can at last recognize the face from a little improved grayscale picture. the next significant step is to grow the outcomes if the picture was briefly contracted due to a past contracting step. the last advance of distinguishing an object as a face is to restore the face recognized and put it away in "objects". pre-processing is done to limit disappointment in the acknowledgment process. it starts by recognizing the area of the eye from the underlying information picture. it is graphically represented in fig. 3. the captured eye area has been retained. the geometric change process is then completed by turning, scaling, and interpreting the pictures with the goal that the eyes are adjusted, trailed by the expulsion of the foundation from the face picture. to have a better arrangement, the recognized eyes are utilized to adjust the face so that the location of the two eyes line up consummately in the desired positions. the turning stage pivots the face with the goal that the two eyes are even. the scaling stage will make the separation between the two eyes consistent and equivalent. then, the interpreting stage will decipher the face with the goal that the eyes are constant ly focused on a level plane and at an ideal height. a significant number of the cases wherein face acknowledgment failed, were due to the lighting factor, both the absence of lighting, the light just originating from one side, or as unreasonable lighting. in this manner, it is important to do a histogram evening out independently on the left and right parts of the face, to have institutionalized sharpness and complexity on each side of the face. the two histogram balances will be applied bit by bit from the left or right towards the middle and blend it in with an entire face histogram adjustment, so the inside utilizes a fig. 3: face preprocessing. start detect eye from original image convert rgb image to grayscale do geometric transformation on grayscale apply histogram equalization on separate face sides reduce pixel noise using bilateral filter end 147 iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 smooth blend of left or right value and the entire face adjusted value. the last phase of this procedure is to apply the respective channel, which is valuable for smoothing the vast majority of a picture while keeping edges sharp. 5.2 collect and train the faces face information assortment is determined and information is prepared for the model. each face capture takes place at a time interval of one second and should surpass the limit estimation of similarity > 0.3. the edge likeness esteem is helpful for checking whether recently captured and subsequent face pictures have variations, supposing that the information is increasingly changed the better the consequence of face acknowledgment is finished. to provide variation in the facial training data set, a mirror version is also added. then the data is saved in the “data” folder in .pgm format and the process of training is performed which converts the data into a model and then stores it in xml format. at the final average face value, eigenvector and eigen values are calculated using a pca algorithm whose steps are explained in fig. 4. the possibility of an eigenface is a movement of eigenvectors used to see human faces in a pc vision. eigenvectors are obtained from covariance order which has a high probability scattering and vector space estimation to see the likelihood of a face [12]. step 1: start. step 2: the value of average face is compiled using the formula: step 3: value of substract mean is calculated from test image(d): step 4: find covariance matrix(c): step 5: find eigen values and eigenvector. the value of p dimension vector is also calculated. step 6: eigen image (ei)is determined as: ei = (d)(eigenvector) step 7: choose highest eigen vector. step 8: weight matrix (wm) is calculated as: wm = (d) (transpose of largest ei) step 9: stop fig. 4: pca algorithm. 148 iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 5.3 recognition to play out a face acknowledgment process, the initial step to do is to stack the .xml document from the prepared facial picture of the past procedure and the .xml record of the course classifier that will be utilized to recognize faces and eyes. in the event that the .xml document has been effectively stacked, at that point check whether the webcam is available. on the off chance that the webcam isn't available, the procedure will consequently stop and exit, generally the framework will continue the discovery process. the aftereffects of face pre-processing will be contrasted and the preparation model that has been handled into a reproducible face by back-anticipating the eigenvectors and eigenvalues [16]. the edge esteem utilized for examination is 0.5. in the event that the estimation of comparability/estimation of the correlation results is not exactly the edge esteem, then the client's face can be perceived by the framework, otherwise it will be considered as an "obscure" client. 6. experimental setup and results discussion the proposed approach is implemented in python. some other circuitry used includes: arduino uno is a microcontroller dependent on the atmega328p with 14 computerized input pins with 6 information sources, 16 mhz, usb, a power jack, an icsp header and a reset mechanism. the hog highlights are broadly used for object recognition. hoard disintegrates a picture into little squared cells, figures a histogram of arranged angles in every cell, standardizes the outcome utilizing a square shrewd example, and returns a descriptor for every cell. stacking the cells into a squared picture area can be utilized as a picture window descriptor for object identification, for instance by methods for a svm. servo engine is an electric device to push an item with exactness. a cascade classifier is prepared with two or three hundred example perspectives on a specific article (i.e., a face or a vehicle), called positive models, that are scaled to a similar size (say, 20x20), and negative models subjective pictures of a similar size. a short image of complete setup is shown in fig. 5. fig. 5: hardware setup of proposed architecture. 149 iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 the proposed approach is tested by making a data set of 100 different human faces and the results found are extremely good. the whole process of the project is also explained with the help of snapshots. the facial recognition provides accurate results, so the initial step is to detect the face as shown in fig. 6. fig. 7 shows the finest eigenface images available in the database. eigen values can be used to reconstruct the initial input image. the reconstructed image is shown in fig. 8. the face recognition by taking live image is performed on the system and is shown in fig. 9. if the system recognizes the person then the barrier will open and allows the person to go on. if the person is not recognized, it means an unauthorized person as shown in fig. 10, it will then restrict the person and display a message as shown in fig. 11. fig. 6: average face detection. fig. 7: finest eigenface images. fig. 8: reconstructed image. fig. 9: face recognition at barrier. fig. 10: unauthorized person fig.11: dialogue box showing unauthorized access 150 iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 in parallel, it sends a message to higher authorities to warn of unauthorized access. if higher authorities know the person, they will send an otp on user mobile, then the user will enter this otp on the provided interface (as shown in fig. 12) within a specified time limit and the motor will rotate to 90 degrees (as shown in fig. 13) and the person will be allowed to go ahead. if the otp is incorrect or not entered, the system will send an email to higher authorities as shown in fig. 14. fig. 12: otp authentication. fig. 13: servo motor rotating at 90 degree. fig. 14: email for unauthorized access. 7. conclusion and future scope the conclusion of the complete approach for the paper has been explained as below: face recognition utilizing course classifier technique has an awesome and quick capacity to distinguish between faces of human. light & edge feature identification process is compelling in support of the acknowledgment procedure, hence the pre-processing of faces must be complete that comprises of rgb shading varied nearly to grayscale picture and geometric picture change comprising of turning, scaling, and deciphering the picture, and perform histogram balance independently on the two sides of appearances to compose it balance among differentiate and brilliance. the varieties in faces preparing information about the framework has improved after effects of face acknowledgment and that can limit the acknowledgment of vague faces as one of the recognized face in the framework. 151 iium engineering journal, vol. 21, no. 2, 2020 kumar and gupta https://doi.org/10.31436/iiumej.v21i2.1322 acknowledgment procedure determination admirable when the discovery of caught face outcome is obvious and not hidden. person face acknowledgment utilizing an eigenface approach runs quite well and fast. the utilization of eigen values and eigen vectors in produces excellent facial pictures and can be presented as an examination of recently prepared pictures. in the current scenario, governments all over the world are looking the ways to tighten the security of respective borders. for this purpose they are inventing and experimenting different approaches and technologies to lower the occurrence of terrorism. a versatile human identification interface may become very important in the future. face recognition can provide quick and accurate information in identification of any unauthorized access. we are currently working on this idea by incorporating biometric identification and eye retina to make it more successful. references [1] federal bureau of investigation united states department of justice. crime in the united states, 2015. [2] phillip iw, john f. (2006) facial feature detection using haar classifiers. journal of computing sciences in colleges, 21(4):127-133. [3] richard jq, ibrahim ms, kristine em. (1998) a robust real-time face tracking algorithm. in proceedings of image processing, 1998 international conference on, volume 1, 131–135. [4] ha md, craig m, meiqin l, weihua s. (2014) humanrobot collaboration in a mobile visual sensor network. in robotics and automation (icra), 2014 ieee international conference on, pp 2203-2208. [5] weihua s, yongsheng o, duy t, eyosiyas t, meiqin l, gangfeng y. (2013) an integrated manual and autonomous driving framework based on driver drowsiness detection. in intelligent robots and systems (iros), 2013 ieee/rsj international conference on, 4376– 4381. [6] duy t, eyosiyas t, weihua s, yuge s, meiqin l, senlin z. (2016) a driver assistance framework based on driver drowsiness detection. in cyber technology in automation, control, and intelligent systems (cyber), 2016 ieee international conference on,173178. [7] davis ek., dlib-ml. (2009) a machine learning toolkit. journal of machine learning research, 10:1755–1758. [8] adt. security systems, home automation, alarms and surveillance. [visited: 08-12-2019]. [9] vivint smart home security systems. smart home security solutions. 2016. [visited: 08-122019]. [10] protect america. affordable home security systems for everyone., 2016. [visited: 08-122019]. [11] jeffrey sc, darryl i. (1999), facial recognition system for security access and identification, us patent 5,991,429. [12] singh a, kumar s. (2012) face recognition using pca and eigenface approach, thesis: national institute of technology rourkela. [13] kumar d, rajni. (2014) an efficient method of pca based face recognition using simulink, international journal of advanced in computer science and technology, vol. 3, pp. 364-368. [14] abdi h, williams lj. (2010) principal component analysis, john wiley & sons inc, vol. 2, pp. 433-459. [15] urifan i, hidayat r, soesanti i. (2010) pengenalan wajah dengan metode eigenface, jurnal penelitian teknik elektro, 3: 320-323. [16] slavkovic m, jevtic d. (2012) face recognition using eigenface approach. serbian journal of electrical engineering, 9:121-130. 152 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <feff04180437043f043e043b043704320430043904420435002004420435043704380020043d0430044104420440043e0439043a0438002c00200437043000200434043000200441044a0437043404300432043004420435002000410064006f00620065002000500044004600200434043e043a0443043c0435043d04420438002c0020043f043e04340445043e0434044f044904380020043704300020043d04300434043504360434043d043e00200440043004370433043b0435043604340430043d0435002004380020043f04350447043004420430043d04350020043d04300020043104380437043d0435044100200434043e043a0443043c0435043d04420438002e00200421044a04370434043004340435043d043804420435002000500044004600200434043e043a0443043c0435043d044204380020043c043e0433043004420020043404300020044104350020043e0442043204300440044f0442002004410020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e0030002004380020043f043e002d043d043e043204380020043204350440044104380438002e> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <feff004f0076006500200070006f0073007400610076006b00650020006b006f00720069007300740069007400650020006b0061006b006f0020006200690073007400650020007300740076006f00720069006c0069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400650020006b006f006a00690020007300750020007000720069006b006c00610064006e00690020007a006100200070006f0075007a00640061006e00200070007200650067006c006500640020006900200069007300700069007300200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e006100740061002e0020005300740076006f00720065006e0069002000500044004600200064006f006b0075006d0065006e007400690020006d006f006700750020007300650020006f00740076006f007200690074006900200075002000700072006f006700720061006d0069006d00610020004100630072006f00620061007400200069002000410064006f00620065002000520065006100640065007200200036002e0030002000690020006e006f00760069006a0069006d0020007600650072007a0069006a0061006d0061002e> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 optimal distribution network reconfiguration using multi-objective cuckoo search algorithm azrin saedi1, mohd shahrin abu hanifah1*, hilmi hela ladin2 and siti hajar yusoff1 1 department of electrical and computer engineering, 2 departmentt of mechanical engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. * corresponding author: shahrin@iium.edu.my (received: 28th september 2021; accepted: 16th january 2022; published on-line: 4th july 2022) abstract: in power system electricity delivery, the distribution system has the most electricity loss as the system has the highest r/x ratio and has a radial network at one time. optimal reconfiguration of the distribution network is needed in order to reduce power losses. however, as it is also involved with multiple objectives and constraint problems such as switching frequency, voltage, and current limits, it is difficult to find the optimal solution. hence, this paper proposes the multi-objective cuckoo search (mocs) algorithm to find the optimal reconfiguration of distribution networks by considering minimizing power losses and switch operations. based on the simulation results on the ieee-33 bus system, the performance of the mocs-based scheme has been found to be significantly better than the single-objective algorithm thereby reducing approximately 33% of the power losses. abstrak melalui sistem penghantaran jana kuasa elektrik, sistem pengagihan mempunyai pembaziran tenaga elektrik terbesar kerana sistem ini mempunyai nisbah r/x paling tinggi dan mempunyai satu rangkaian radial pada tiap-tiap satu masa. konfigurasi semula rangkaian pengedaran yang optimum diperlukan bagi mengurangkan pembaziran tenaga. walaubagaimanapun, oleh kerana ia melibatkan objektif dan kekangan masalah yang pelbagai seperti kadar peralihan, had voltan serta arus, adalah sukar bagi mendapatkan bacaan yang optimum. oleh itu, kajian ini mencadangkan carian cuckoo pelbagai objektif (mocs) bagi mencari konfigurasi semula yang optimum bagi sistem pengagihan tenaga dengan mengambil kira pengurangan pembaziran tenaga dan kadar peralihan. berdasarkan keputusan simulasi pada sistem bas ieee-33, pretasi mocs telah menunjukkan peningkatan yang ketara berbanding algoritma objektif tunggal dan pengurangan sebanyak 33% tenaga. keywords: distribution network reconfiguration (dnr); multi-objective cuckoo search (mocs) algorithm; power loss reduction; switch operations; pareto optimal 1. introduction an efficient and high-reliability power system is crucial because global electricity demand has increased due to the rising population. since the primary source of power around the world comes from non-renewable energy sources such as fossil fuels, coal, and natural gas, power loss in electricity delivery can be seen a contributor to global warming 114 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 [1]. the distribution system has the most power loss compared with other systems as it has a high r/x ratio. this ratio means the reactance is much higher in the system [2]. system reconfiguration can be manipulated by two methods, power line restructuring and switch opening and closing. the tie switch (normally open) and sectionalizing switch (normally closed) are used to connect and disconnect power to the load entity to reduce the power loss in the distribution network. the procedure of changing the open/closed switch status is called distribution network reconfiguration (dnr). dnr is primarily performed to minimize losses and maximize the load balancing, system reliability, and voltage profile at the network level [3]. to manually change the status of the switches requires much time and cost and consumes energy. in the literature, two approaches have been used in optimizing this problem, which are using (i) a single-objective approach [4-8] and (ii) a multi-objective approach [9-12]. for the single-objective approach, the author in [4] has focused on minimizing the power/energy losses and network loading index using a hybrid heuristic-genetic algorithm. while authors in [5,6] have compared several heuristic algorithms for minimizing power loss and enhancing voltage profile and applied them with to various scales of the distribution networks. at the same time, [5] has considered the integration of distributed generation (dg) in the network. other researchers have investigated the optimal placement and sizing of unified power quality conditioners (upfc) along with dnr for real power loss reduction [7]. however, the common drawback of these approaches is that the values of variables and parameters in each objective function vary depending on the case study and type of the network. besides, it requires a weight factor in the objective function, which needs to be tuned to get the optimal solution. on the other hand, multi-objective optimization is a technique when two or more objectives are considered simultaneously to achieve the most desired outcome. this technique is used in many fields like economics, logistics, management, science, and engineering [13]. unlike single-objective, this approach does not require a weight factor in the objective function. there are trade-offs among the objectives to achieve the outcome as the objectives might conflict with each other [9]. in dnr, research has been conducted using multi-objective approaches such as multi-objective evolutionary algorithm [10] and non-sorting genetic algorithm [11] for service restoration, and bayesian learning-based evolutionary algorithm for absorption rate of wind power and voltage stability improvement [12]. however, less work has been reported on minimizing power losses and switching operations simultaneously using single-objective or multi-objective approaches. hence, this paper proposes a solution for power loss reduction and switching minimization using the multi-objective cuckoo search (mocs) algorithm. mocs is the extended version of the cuckoo search algorithm developed by yang and deb [14]. it has been tested against relevant test functions and then successfully applied to numerous problems [15-18]. this study uses mocs to solve the dnr optimization problem focusing on power loss reduction and switching operations. the optimal model is developed in a matlab environment using the ieee-33 bus test system. then the result is compared to a single objective cuckoo search algorithm. 2. problem formulation in this paper, the dnr problem is formulated as a multi-objective and multi-constrained problem. the various objective functions and constraints considered in this work are explained as follows. 115 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 2.1 objective functions the following equations express the objective functions aimed at minimizing the power loss and number of switch operations. a) minimization of power losses: min 𝑓1 = ∑ 𝑅𝑖 𝑃𝑖 2 + 𝑄𝑖 2 𝑉𝑖 2 𝑁𝑏𝑟 𝑖 (1) where nbr is the total number of branches, ri is the branch resistance i, vi is the voltage at sending end node of ith branch, and pi and qi are the active and reactive power at the sending end node of ith branch. b) minimization of switch operations: min 𝑓2 = ∑|𝑆𝑊𝐵𝑗 − 𝑆𝑊𝐴𝑗 | 𝑁𝑠 𝑗 (2) where ns is the number of operated switches, swaj and swaj are the status of jth operated switch in the network before and after reconfiguration. 2.2 constraints the followings are the constraints that secure an optimal power flow calculation and preserve the network radial condition [6]. a) voltage limit 𝑉𝑖,𝑚𝑖𝑛 ≤ 𝑉𝑖 ≤ 𝑉𝑖,𝑚𝑎𝑥 (3) where 𝑉𝑖,𝑚𝑖𝑛 is 0.9 p.u and 𝑉𝑖,𝑚𝑎𝑥 is 1.1 p.u which is the voltage limit at end node of ith branch. b) current limit 𝐼𝑖 ≤ 𝐼𝑖,𝑚𝑎𝑥 (4) where 𝐼𝑖 is the current at ith branch and 𝐼𝑖,𝑚𝑎𝑥 is the maximum current at ith branch. c) radial topology constraint in any network, the number of main loops can be calculated using the following relation: 𝑁𝑛𝑜𝑑𝑒 − 𝑁𝑏𝑟𝑎𝑛𝑐ℎ = 1 (5) where the configuration is radial, and the system has no isolated node. the number of nodes in the system is notated as 𝑁𝑛𝑜𝑑𝑒 . 3. methodology 3.1 multi-objective cuckoo search (mocs) algorithm the cuckoo search algorithm is based on the aggressive way that cuckoo birds use to sustain the survival of their species. the bird would lay eggs in a host nest, and the survival of the eggs depends on the probability that the host bird discovers the eggs. the host bird would either abandon the nest or throw the eggs if they are discovered. cuckoo birds develop the way to survive by mimicking the appearance of the host bird egg or the egg 116 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 hatched earlier from the host bird egg. the pseudocode and the flowchart of mocs is shown in fig. 1 and fig. 2 respectively. initialize objective functions 𝑓1(𝒙), … , 𝑓𝐾 (𝒙)𝒙 = (𝑥1, … , 𝑥𝑑 ) 𝑇 generate an initial population of 𝑛 host nests 𝒙𝑖 and each with 𝐾 eggs while (𝑡 < maxgeneration) or (stop criterion) get a cuckoo (say 𝑖) randomly by lévy flights evaluate and check if it is pareto optimal choose a nest among 𝑛 (say 𝑗) randomly evaluate 𝐾 solutions of nest 𝑗 if new solutions of nest 𝑗 dominate those of nest 𝑖, replace nest 𝑖 by the new solution set of nest 𝑗 end abandon a fraction (𝑝𝑎 ) of worse nests keep the best solutions (or nest with non-dominated sets) sort and find the current pareto optimal solutions end postprocess results and visualization fig. 1: multi-objective cuckoo search algorithm pseudocode [14]. start initialize objective functions generate initial population of n host nests and k eggs converge? get a cuckoo randomly by levy flights evaluate and check if it is pareto optimal choose a nest among n randomly evaluate solutions new solution dominated? replace chosen nest by new solution rand < pa replace the worst solutions keep best solution sort and find current optimal solutions postprocess results and visualization end no no yes yes no yes fig. 2: multi-objective cuckoo search algorithm flowchart. cuckoo search algorithm has three general rules: 1) each cuckoo bird lays one egg in only one random nest at a time; 2) the best egg would survive for the next generation; 3) the number of available host nests is the same; the probability of laid cuckoo egg to be discovered is between 0 and 1. the host bird would throw away the bird egg or abandon the nest, building a new nest [19]. 117 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 in the multi-objective cuckoo search algorithm, the first and third general rules are changed: 1) each cuckoo bird lays k eggs in only one random nest at a time; k refers to the number of objectives. 2) the best egg would survive for the next generation; 3) the number of available host nests is the same. the probability of laid cuckoo k eggs to be discovered is between 0 and 1. the host bird would build a new nest with k eggs in respect of the egg differences. diversity would happen by random mixing. 3.2 proposed algorithm and pareto optimal the algorithm aims to obtain the pareto optimal with respect to some switch changes and power loss with the highest voltage stability limit. this algorithm is improved for pareto optimal from the mocs algorithm in [18]. the algorithm steps are: 1. data of the bus system (e.g. branch, bus and load number) are obtained. 2. bus voltage and power loss (𝑃𝑙𝑜𝑠𝑠) are calculated by running the load flow program. 3. voltage stability limit is calculated by the formula: 𝑉𝑆 = 1 𝜆 , while λ is the load value. 4. a set of the initially closed switches is defined as 𝑅𝑖 = ( (𝑅𝑖 )1 1 ⋯ (𝑅𝑖 )𝑛𝑒 1 ). 5. parameters for the algorithm are set such as nest dimension (𝑛𝑑 ), nests number (n), switch opened dimension (𝑛𝑒 ), the probability to be discovered, and step size (α), lower limit and upper limit search space, and maximum iteration number (n). 6. search space 𝑛 × 𝑛𝑑 is generated randomly. each row represents a solution, while every element represents power loss for every connection 𝑃𝑐 to the load. 𝑃𝑐 = ( (𝑃𝑐 )1 1 ⋯ (𝑃𝑐 )𝑛𝑑 1 ⋮ ⋱ ⋮ (𝑃𝑐 )1 𝑛 ⋯ (𝑃𝑐 )𝑛𝑑 𝑛 ) 7. search space 𝑛 × 𝑛𝑒 is generated. each row represents a set of switches opened in the distribution network, while every element represents a switch closed for every radial network, 𝑅𝑐 .𝑅𝑐 = ( (𝑅𝑐 )1 1 ⋯ (𝑅𝑐 )𝑛𝑒 1 ⋮ ⋱ ⋮ (𝑅𝑐 )1 𝑛 ⋯ (𝑅𝑐 )𝑛𝑒 𝑛 ) 8. then, reactive power (𝑄𝑙𝑜𝑠𝑠)′ would be added to the bus and each 𝑃𝑐 row, new power loss (𝑃𝑙𝑜𝑠𝑠)′ and bus voltage is calculated. (𝑄𝑙𝑜𝑠𝑠)′ = 𝑄𝑙𝑜𝑎𝑑 − 𝑃𝑐 9. then, power loss reduction is calculated as: ∆𝑃 = 𝑃𝑙𝑜𝑠𝑠 − (𝑃𝑙𝑜𝑠𝑠)′ 10. then, switch change number (𝑗) is calculated as this conditional loop statement: for every element 𝑅𝑖 ≠ 𝑅𝑐 𝑗 is incremented by 2 11. the optimal value for minimum power loss (𝑓1) with the lowest switch change (𝑓2) is obtained. 12. the bus voltage value is accepted if the bus voltage value is within the range of acceptable value. 118 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 13. levy flight is applied to obtain a new solution. 14. then, step 6 to 9 is repeated. 15. an unaccepted solution is abandoned, and a new solution is generated 16. step 12 is repeated. 17. iteration value is increased if it does not reach the maximum number from step 10. 18. then, if the voltage stability limit is not the maximum value, the value of λ is increased, and step 3 is repeated. otherwise, the algorithm is terminated. 19. then, all surviving solutions of the cuckoo search are plotted using the pareto optimal. 3.3 ieee-33 bus test system the effectiveness of the mocs algorithm has been studied on the standard ieee-33 bus model system [12] in a matlab environment using the matpower package [20]. this test model is a power distribution system with 33 busses attached to the load points, and it is connected with 37 switches (sectionalize and tie switches), as shown in fig. 3. each load is identified by the number given, and in one mainline, the load number must be in sequence. any tie switch would connect one point of the load with another point of the load of the different power lines. this tie switch would be closed to accommodate the breakdown of other sectionalizing switches to make sure every load is receiving power. the tie switch and sectionalizing switch can be alternately switched on and off to optimize power loss. this model system can be assumed to have constant base power, sbase = 50 mva, and base voltage, vbase = 33 kv. the real power of the load is 3.715 mw, and the reactive power of the load is 2.3 mvar. minimum and maximum per-unit voltages are 0.95 p.u and 1.05 p.u, respectively. the initial power losses recorded in the model system is 208.46 kw. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 26 27 28 29 30 31 32 33 23 24 25 19 20 21 22 substation load sectionalize switch tie switch s1 s2 s3 s4 s5 s6 s7 s8 s9 s10 s11 s12 s13 s14 s15 s16 s17 s26 s27 s28 s29 s30 s31 s32 s23 s24 s19 s20 s21 s33 s35 s36 s34 s37 fig. 3: the initial state of the ieee-33 bus system [12]. 4. results and discussion in this paper, the mocs algorithm is used to obtain the optimal dnr for minimizing the power losses and switch operation simultaneously. the result is analyzed using the pareto optimal front, and the voltage profile for all solutions are presented. then, it is compared to a single objective approach cuckoo search algorithm. finally, the performance of mocs is analyzed using the convergence rate in terms of generalized distance [14] and validated against the multi-objective genetic algorithm (moga) [21]. 119 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 4.1 pareto optimal front the pareto front generated by four non-dominated solutions after 50 iterations is presented in fig. 4. the graph is aligned with pareto optimal as it shows that the higher number of switch changes, the lower the power loss in the distribution network. the number of operated switches ranges between two and eight, contrary to the broadest possible range between zero and ten. at the same time, the power losses ranged from 138 kw to 156 kw. the detailed result for each pareto point is tabulated in table 1. from the table, all solutions show a significant reduction in power losses after obtaining optimal reconfiguration using mocs. the lowest power loss is obtained by solution 1, which decreased from 208.46 kw to 138.93 kw, bringing approximately 33% reduction. it requires eight switches to be operated, which are number 7, 9, 14, 32, 33, 34, 35, and 36. on the other hand, the lowest number of operated switches is recorded by solution 4, which only changed switches number 7 and 35. however, the power losses decreased to 155.80 kw, equivalent to a 25% reduction, which is slightly lower. fig. 4. pareto optimal multi-objective cuckoo search algorithm. table 1: simulation before and after reconfiguration using mocs before reconfiguration after reconfiguration solution 1 solution 2 solution 3 solution 4 tie switch 33 34 35 36 37 7 9 14 32 37 7 9 14 36 37 7 11 34 36 37 7 33 34 36 37 power loss 208.46 kw 138.93 kw 141.43 kw 143.80 kw 155.80 kw power loss reduction 33.36 % 32.15 % 31.02 % 25.26 % no. of operated switch 8 6 4 2 minimum voltage 0.911 p.u 0.942 p.u 0.938 p.u 0.938 p.u 0.937 p.u 120 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 4.2 voltage profile fig. 5 presents the voltage profile of ieee-33 bus system for each solution obtained by mocs. the graphs show that the voltage profiles are significantly improved after the network is reconfigured across all solutions. besides, the minimum voltages are also increased by approximately 3% compared to before reconfiguration. (i) solution 1 (ii) solution 2 (iii) solution 3 (iv) solution 4 fig. 5: voltage profile of the network before and after reconfiguration for each solution. 4.3 comparison with single-objective algorithm in order to see the effectiveness of the multi-objective technique, the above results are compared with the single-objective approach [22] demonstrated in error! reference source not found.. it is apparent that the power loss obtained by the single-objective is 157.65 kw which is almost 1% lower power loss reduction compared to the solution 4 recorded by mocs in table 1. furthermore, in terms of switch operations, both single-objective and multiobjective approaches were at the same level. overall, mocs shows better effectiveness compared to the single-objective algorithm. besides, it provides multiple solutions to be chosen and does not require a weighting factor as a single-objective method. 121 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 table 2: simulation result of single objective cuckoo search algorithm before reconfiguration after reconfiguration tie switch 33 34 35 36 37 7 34 35 36 37 power loss 208.46 kw 157.65 kw power loss reduction 24.38 % no. of operated switch 2 minimum voltage 0.911 p.u. 0.930 p.u. 4.4 generational distance (gd) measurement furthermore, in order to see the proposed mocs performance, we also tested the same problems using a similar multi-objective technique, which is moga [21]. the performance is measured in terms of generational distance (gd)[14]. gd is designed to measure the sum of adjacent distances of solutions sets obtained by different algorithms, especially multiobjective evolutionary algorithms. the comparison of the convergence rates between proposed mocs and moga is plotted in fig. 6. this figure shows that mocs converged slightly faster than moga even though there were opposite patterns shown at early iterations, which could be neglectable. nevertheless, overall, mocs delivers better performance than moga. fig. 6: convergence comparison between mocs and moga. 5. conclusion power losses are critical in electrical power systems due to their impact on system reliability. thus, distribution network reconfiguration (dnr) is introduced to minimize power losses and switch operations. in this study, a multi-objective cuckoo search (mocs) algorithm for finding the optimal reconfiguration is presented. the simulation result is validated on the standard ieee-33 bus test system in the matlab environment, and matpower package is used for power flow calculation. the results show that mocs obtained approximately 25% to 33% reduction results of power losses where two to eight switches were operated. compared to the single-objective approach, mocs recorded slightly better losses reduction and was on par in terms of switch operations. besides, the convergence comparison with a similar multi-objective technique, moga, indicates the 122 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 superiority of mocs to obtain better optimal reconfiguration. hence, the objectives of this paper to minimize the power losses and switch operations is achieved. furthermore, the obtained pareto optimal front shows the trade-offs between two objectives in solving the dnr problem. in this case, the system operator can benefit from the results of the mocs application to decide the priority between power losses and numbers of switch operations based on actual circumstances. as a way forward, this research may be extended to the large-scale networks such as ieee-69 and ieee-129 bus system models with the integration of renewable energy sources. acknowledgement this work was supported and funded by international islamic university malaysia (iium) under iium-ump-uitm sustainable research collaboration grant 2020 (srcg20-0090009). references [1] surana k, jordaan sm. (2019) the climate mitigation opportunity behind global power transmission and distribution. nature climate change, 9(9): 660-665. https://doi.org/10.1038/s41558-019-0544-3 [2] singh b, chauhan s, reddy cc. (2017) power loss minimization in electrical power distribution networks by use of hybrid reconfiguration method. 3rd international conference on condition assessment techniques in electrical systems (catcon), ieee. pp. 349-354. https://doi.org/10.1109/catcon.2017.8280243 [3] thakar s, vijay as, doolla s. (2019) system reconfiguration in microgrids. sustainable energy, grids and networks, 17100191. https://doi.org/10.1016/j.segan.2019.100191 [4] jakus d, čađenović r, vasilj j, sarajčev p. (2020) optimal reconfiguration of distribution networks using hybrid heuristic-genetic algorithm. energies, 13(7): 1544. https://doi.org/10.3390/en13071544 [5] nguyen hd, valeev im. (2019) improvement methods for solving the distribution network reconfiguration problem. energetika, 64(4): 174-185. https://doi.org/10.6001/energetika.v64i4.3892 [6] landero a, koziel s, abdel-fattah mf. (2019) distribution network reconfiguration using feasibility-preserving evolutionary optimization. journal of modern power systems and clean energy, 7(3): 589-598. https://doi.org/10.1007/s40565-018-0480-7 [7] gholami k, karimi s, dehnavi e. (2019) optimal unified power quality conditioner placement and sizing in distribution systems considering network reconfiguration. international journal of numerical modelling: electronic networks, devices and fields, 32(1): e2467. https://doi.org/10.1002/jnm.2467 [8] samadaei e, khosravi a, sheikholeslami a. (2017) optimal allocation of active power filter on real distribution network for improvement of power quality by use of bbo: a case study. iium engineering journal, 18(1): 85-99. https://doi.org/10.31436/iiumej.v18i1.688 [9] gunantara n. (2018) a review of multi-objective optimization: methods and its applications. ai q, editor. cogent engineering, 5(1): 1502242. https://doi.org/10.1080/23311916.2018.1502242 [10] sanches ds, london junior jba, delbem acb. (2014) multi-objective evolutionary algorithm for single and multiple fault service restoration in large-scale distribution systems. electric power systems research, 110: 144-153. https://doi.org/10.1016/j.epsr.2014.01.017 [11] shahrin m, aoki h. (2016) application of multi-objective optimization for service restoration problem in distribution systems. ieej transactions on power and energy, 136(3): 275-283. https://doi.org/10.1541/ieejpes.136.275 123 iium engineering journal, vol. 23, no. 2, 2022 saedi et al. https://doi.org/10.31436/iiumej.v23i2.2190 [12] zhong t, zhang h-t, li y, liu l, lu r. (2020) bayesian learning-based multi-objective distribution power network reconfiguration. ieee transactions on smart grid, 12(2): 11741184. https://doi.org/10.1109/tsg.2020.3027290 [13] khan mr, badran m, toha sf, zainal abidin z. (2021) multi-objective optimization of snake robot in serpentine locomotion. iium engineering journal, 22(2): 364-383. https://doi.org/10.31436/iiumej.v22i2.1691 [14] yang x-s, deb s. (2013) multiobjective cuckoo search for design optimization. computers & operations research, 40(6): 1616-1624. https://doi.org/10.1016/j.cor.2011.09.026 [15] zainal mi, yasin zm, zakaria z. (2021) optimizing voltage profile and loss minimization using multi objective cuckoo search algorithm. 2021 ieee 11th ieee symposium on computer applications & industrial electronics (iscaie), ieee. pp. 116-122. https://doi.org/10.1109/iscaie51753.2021.9431835 [16] yasin zm, aziz nfa, salim na, wahab na, rahmat na. (2018) optimal economic load dispatch using multiobjective cuckoo search algorithm. indonesian j. electrical engin. comp sci, 12(1): 168. https://doi.org/10.11591/ijeecs.v12.i1.pp168-174 [17] zhou x, liu y, li b, li h. (2017) a multiobjective discrete cuckoo search algorithm for community detection in dynamic networks. soft computing, 21(22): 6641-6652. https://doi.org/10.1007/s00500-016-2213-z [18] rao nt, sankar mm, rao sp, rao bs. (2021) comparative study of pareto optimal multi objective cuckoo search algorithm and multi objective particle swarm optimization for power loss minimization incorporating upfc. journal of ambient intelligence and humanized computing, 12(1): 1069-1080. https://doi.org/10.1007/s12652-020-02142-4 [19] yang x-s, deb s. (2009) cuckoo search via lévy flights. 2009 world congress on nature & biologically inspired computing (nabic), ieee. pp. 210-214. https://doi.org/10.1109/nabic.2009.5393690 [20] zimmerman rd, murillo-sanchez ce, thomas rj. (2011) matpower: steady-state operations, planning, and analysis tools for power systems research and education. ieee trans power sys, 26(1): 12-19. https://doi.org/10.1109/tpwrs.2010.2051168 [21] bevilacqua v, pacelli v, saladino s. (2011) a novel multi objective genetic algorithm for the portfolio optimization. lecture notes in computer science (including subseries lecture notes in artificial intelligence and lecture notes in bioinformatics), pp. 186-193. https://doi.org/10.1007/978-3-642-24728-6_25 [22] fuad naa, azlin aan, zahari mfd, hanifah msa. (2018) power distribution loss reduction using cuckoo search. 2018 7th international conference on computer and communication engineering (iccce), ieee. pp. 333-337. https://doi.org/10.1109/iccce.2018.8539252 124 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 azmi et al. 1 chlorella vulgaris logistic growth kinetics model in high concentrations of aqueous ammonia azlin suhaida azmi1, nurain atikah che aziz1, noor illi mohamad puad1*, amanatuzzakiah abdul halim1, faridah yusof1 and suzana yusup2 1 department of biotechnology engineering, kulliyyah of engineering, international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia. 2 department of chemical engineering, universiti teknologi petronas, seri iskandar, 31750 tronoh, perak, malaysia. * corresponding author: illi@iium.edu.my (received: 14th feb 2018; accepted: 8th aug 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.893 abstract: the ability of microalgae to utilize co2 during photosynthesis and grow rapidly shows their potential in co2 bio-fixation to capture and store the gas. however, co2 capture by this biological approach is very slow compared to chemical reactionbased processes such as absorption using amine or aqueous ammonia. integration between chemical (aqueous ammonia) and biological (microalgae) aspects might enhance the capturing process and at the same time the microalgae can assimilate co2 for beneficial bioproduct formation. thus, it is important to assess the growth of the microalgae in various concentrations of ammonia with co2 supply. hence, the main objective of this study is to investigate chlorella vulgaris growth and its kinetics in aqueous ammonia. to achieve that, c. vulgaris was cultivated in various concentrations of aqueous ammonia between 0 to 1920 mg/l at room temperature (i.e. 27 °c) and supplied with 15% (v/v) of co2 under illumination of 3500 lux of white fluorescent light. result shows that the maximum growth capacity (xmax) of c. vulgaris is deteriorating from 1.820 au to 0.245 au as the concentration of aqueous ammonia increased. however, no significant change in maximum specific growth rate (µmax) was observed. the growth data was then fitted into the logistic growth model. the model coefficient of determination (r 2 ) is decreasing, which suggests modification of the model is required. abstrak: keupayaan alga-mikro untuk menggunakan co2 semasa proses fotosintesis dan pembiakannya yang pesat menunjukkan potensi dalam penggunaan dan penyimpanan gas ketetapan-biologi. walau bagaimanapun, penggunaan co2 melalui cara ini adalah sangat perlahan berbanding proses tindak balas kimia melalui penyerapan amina ataupun cecair ammonia. percampuran antara tindak balas kimia (cecair ammonia) dan tindak balas biologi, memungkinkan penambahan proses percampuran dan pada masa sama alga-mikro akan menyerap co2 bagi kepentingan pembentukan hasil biologi. dengan itu, adalah sangat penting untuk mengawasi pertumbuhan algamikro dalam pelbagai ketumpatan ammonia bersama kandungan co2. oleh itu, objektif utama penyelidikan ini adalah untuk menyiasat pertumbuhan chlorella vulgaris dan proses kinetik dalam cecair ammonia. bagi memperoleh hasil tersebut, c. vulgaris telah dikulturkan pada ketumpatan cecair berbeza antara 0 ke 1920 mg/l pada suhu bilik (iaitu 27 °c) dan dibekalkan dengan 15% (v/v) co2 di bawah cahaya putih flurosen 3500 lux. iium engineering journal, vol. 19, no. 2, 2018 azmi et al. 2 keputusan menunjukkan kapasiti pertumbuhan terbanyak (xmax) c. vulgaris telah berkurang daripada 1.820 au kepada 0.245 au apabila ketumpatan cecair ammonia dikurangkan. walau bagaimanapun, tiada perubahan ketara pada kadar pertumbuhan (µmax) dapat dilihat. data kadar pertumbuhan kemudiannya dikemas kini pada model pertumbuhan logistik. model pekali penentu (r 2 ) telah direndahkan di mana cadangan untuk mengubah model adalah diperlukan. keywords: aqueous ammonia; chlorella vulgaris; growth kinetics; logistic growth model 1. introduction climate change and global warming issues related to excessive emission of co2 have been deliberatively discussed over years. to address this problem, malaysia has participated and pledged to reduce 40% of co2 emission intensity by 2020 and re-pledged for 45% of co2 reduction by year 2030 [1,2]. to achieve the goal, co2 mitigation is part of the crucial areas identified by the paris agreement [1]. microalgae and cyanobacteria have potential in mitigating co2 levels in the atmosphere as well as capturing directly from industrial plant flue gas [3-5]. the growth of photosynthetic microalgae is directly related to the rate of co2 fixation from the atmosphere. their ability to grow rapidly and undergo photosynthesis makes them strong candidates for use in mitigating co2 levels [6]. however, the removal rate is still slower and the fixation capacity is lower compared to the chemical solvent absorption process using amine or aqueous ammonia [7,8]. integrating chemical and biological systems to enhance the removal while simultaneously fixing or sequestrating co2 for its bioproducts, such as biofuel [9, 10], animal feed, or stable isotopes biochemical compound [11] derived from the microalgae, seems appealing. previous studies show that chlorella vulgaris a green microalga, was able to grow in wastewater containing a high level of ammonia [12,13]. the growth varied with the ammonia concentration at the respective process conditions, which is mostly no aeration or supply of co2, and the growth was limited by the toxicity of the free ammonia present in the culture. thus, it is important to assess and understand the growth of c. vulgaris in the presence of aqueous ammonia and model the growth. generally, like any other microorganisms, there are six phases of c. vulgaris growth in a batch culture which are lag, acceleration, growth or exponential, decline, stationary, and death phases (fig. 1). a general growth model is represented by the exponential growth model of eq. (1) [14]. this mathematical model equation, when plotted, will produce a j-shape curve where the exponential growth is represented by µmax, whereas, the typical growth curve shown in fig. 1, has an s-shape (lag phase to stationary phase). the s-shape growth can be better represented by the logistic growth model of eq. (2) which was originally proposed by verhulst in the eighteenth century [15]. the model provides carrying capacity (xmax) as a moderating force in the growth rate [15] which is influenced by substrate depletion as well as toxic compounds in the environment [16]. the integral form of eq. (2) is shown by eq. (3). 𝑑𝑋 𝑑𝑡 = 𝜇𝑚𝑎𝑥 𝑋 (1) 𝑑𝑋 𝑑𝑡 = 𝜇𝑚𝑎𝑥 ( 𝑋𝑚𝑎𝑥 − 𝑋 𝑋𝑚𝑎𝑥 ) 𝑋 (2) iium engineering journal, vol. 19, no. 2, 2018 azmi et al. 3 𝑿(𝒕) = 𝑿𝒎𝒂𝒙 𝟏 + ( 𝑿𝒎𝒂𝒙 𝑿𝒐 + 𝟏) 𝒆−𝝁𝒎𝒂𝒙𝒕 (3) where µmax, t, xmax, xo and x represent the specific growth rate, time, maximum biomass concentration, initial biomass concentration and actual biomass concentration, respectively. the objective of this study is to assess c. vulgaris growth kinetics for its ability to grow in various concentrations of aqueous ammonia with periodically aerated co2 gas during the cultivation and model the growth based on the logistic growth equation. fig. 1: growth curve of microalgae culture in batch with phases; (1) lag, (2) acceleration, (3) growth, (4) deceleration, (5) stationary, and (6) death. 2. materials and methods 2.1 microalgae cultivation stock culture of c. vulgaris was purchased from the institute of ocean and earth sciences, university malaya and was kept aseptically in a bold basal medium (bbm). a 250 ml of culture solution was prepared in triplicates which contained 10% (v/v) of c. vulgaris in bbm medium with the addition of aqueous ammonia at different concentrations. eight experimental runs were conducted at various aqueous ammonia concentrations i.e. 0 mg/l, 30 mg/l, 60 mg/l, 120 mg/l, 240 mg/l, 480 mg/l, 960 mg/l and 1920 mg/l. the culture was grown under illumination of 3500 lux from a white fluorescent lamp for 6 days with continuous (24 h) supply of filtered air at 0.5 lpm. pure co2 mixed with filtered air was supplied at a concentration of 15% (v/v) every day for 30 minutes continuously. the control of this experiment was conducted without aqueous ammonia (0 mg/l) with continuous supply of filtered air without extra co2 (i.e. culture acquired co2 from the air only). all experimental runs were conducted at room temperature (27 oc) in triplicate. each flask was fitted with two silicon tubes (one for gas inlet and the other for gas outlet) and the culture was aerated for 24 hours with filtered air generated by air pump through a silicon tube. the sampling for each flask was carried out on a daily basis to measure c. vulgaris growth and the ph of the medium. 2.2 determination of growth kinetic growth observation was based on the optical density (od). the absorbance of c. vulgaris was determined by measuring the optical density of a 3 ml sample at a wavelength of 660 nm for every 24 hours using a uv-vis spectrophotometer. the data was then fitted nonlinearly using a nonlinear regression software, curveexpert professional software, version 2.4.0. the logistic equation model (eq. 3) was selected to fit the data. eq. (4) was used to calculate µmax and compared it to µmax obtained from the logistic growth model of eq. (3). doubling time was calculated based on eq. (5). 1 2 3 4 5 6 time c e ll c o n c e n tr a ti o n iium engineering journal, vol. 19, no. 2, 2018 azmi et al. 4 𝜇𝑚𝑎𝑥 = ln ( 𝑥𝑛−1 𝑥𝑛 ) ( 𝑡𝑛−1 𝑡𝑛 ) ⁄ (4) 𝑡𝑑 = ln 2 𝜇𝑚𝑎𝑥 (5) 3. results and discussion 3.1 growth of c. vulgaris in bbm with air supply growth of c. vulgaris in bbm with the continuous air supply was studied before introducing aqueous ammonia and co2. this is to observe the typical growth kinetic and the stationary phase of c. vulgaris as illustrated in fig. 1. since the stationary phase of growth was observed as it entered the 4th day of cultivation, a subsequent cultivation run was conducted up to the 6th day after inoculation. figure 2(a) shows growth data in absorbance unit of optical density at 660 nm, while fig. 2(b) is the same growth data in the form of natural-logarithms. generally, the growth curve consists of six phases that have been discussed earlier. the same phases were also observed in c. vulgaris growth except for the death phase. this is due to a longer stationary phase (more than 12 days) of c. vulgaris which some have recorded being up to one month depending on the growth conditions [17,18]. in this study, the growth was monitored only for the duration of up to 12 days, thus the death phase was not perceived. fig. 2: the growth profile of c. vulgaris in bbm medium with (a) fitted model in dash line for circle symbol data and (b) growth curve in logarithms. according to doran [14], lag phase is best observed and confirmed in a logarithmic plotted curve as shown in fig. 2(b). the figure shows that the cells required one day of adaptation (lag phase) to the new environment before entering the exponential (growth) phase. the exponential phase was started from day 2 to day 4 before entering the stationary phase (day 4 onwards). the maximum specific growth rate (µmax) and doubling time (td) of the microalgae were 0.847 day -1 (0.036 h-1) and 0.818 day (0.034 h-1), respectively, as shown in table 1. the µmax obtained in this research is much lower compared to lehana [19] (i.e. 0.24 h-1) in a continuous culture but higher than converti et al. [20] (i.e. 0.14 day-1) grown in batch culture at about the same culture conditions as the current study. however, those studies used larger culture volumes of 3 l with 8% of co2 in air and 2 l with air only supplied to the culture, respectively whereas the current study is in a 250 ml culture medium with filtered air. microalgae culture grown with aeration of (a) (b) iium engineering journal, vol. 19, no. 2, 2018 azmi et al. 5 extra co2 as in lehana [19] in continuous culture, has been shown to improve its growth rate compared to the culture grown with air only [4]. however, the lower maximum specific growth rate by converti et al. [20] is due to the size of the culture, which in our study the air was supplied at flowrate of 2 vvm (0.5 lpm). the growth of the current study was then modelled using the logistic growth equation with a coefficient of determination (r2) of 0.95. however, the model predicted a very low rate of initial growth compared to the experimental data and this affected the values of other parameters shown in table 1. table 1: comparison of parameters obtained from logistic growth model fitting (fig. 2(a)) and experimental data (fig. 2(b)) for growth in bbm only. parameter value predicted by model value from experimental data xo (au) 0.017 0.233 xmax(au) 1.399 1.524 µmax(day -1) 2.190 0.847 td (day) 0.317 0.818 r 2 0.95 1 3.1 growth kinetics of c. vulgaris at different concentrations of ammonia this experiment was conducted to understand how c. vulgaris responded to different concentrations of ammonia with the aeration rate of 0.5 lpm for 15% (v/v) co2 in filtered air for 30 minutes every day under the illumination of 3500 lux. since c. vulgaris growth reached the stationary phase in the beginning of day 5 (fig. 2), subsequent observation of the microalgae growth was only recorded until day six in variation of ammonia concentrations (fig. 3). the control run (0 mg/l ammonia with 15% co2) achieved the highest growth capacity (xmax) of 1.8 au (absorption unit) at od660 (fig. 3(a)). the growth was higher compared to the growth supplied with air only (fig. 2). this shows that, even though 15% (v/v) of co2 was supplied for only 30 minutes every day, it had a positive influence on c. vulgaris growth (note that the initial cell density was maintained at around 0.2 au for all runs). many have reported how co2 influences the growth of photosynthetic microorganisms such as c. vulgaris [4,21,22] under illumination of light. the surrounding air, which contains only 0.03–0.06% co2, had limited c. vulgaris photosynthetic activity and slowed down its cell growth [23]. however, when aqueous ammonia was introduced in the culture at different concentrations, it is apparent that c. vulgaris growth was significantly influenced by the addition of aqueous ammonia. this is reflected by the decrease in the carrying capacity (xmax) values from both the model and the experimental data (table 2). nitrogen is a crucial nutrient for microalgae growth, which is assimilated in the form of nitrate (no3 -) or ammoniacal nitrogen (nh4 +/nh3). however, higher ammonia concentration can be toxic to the microalgae growth. this is especially depicted by fig. 3 (g) and (h) where ammonia concentration of 960 mg/l and above showed that the growth of the microalgae was nearly inhibited. however, this is not the case for µmax. generally, µmax (table 2) obtained from experimental data (calculated based on eq. (4)) are about the same, even though concentration of ammonia increased in a double amount of the previous concentration. the same was also observed by tam and wong [24]. a few papers suggested that µmax is an important parameter in modelling microalgae or microbial population in batch production that is influenced by environmental factors [15,25]. in our iium engineering journal, vol. 19, no. 2, 2018 azmi et al. 6 case, no significant change in µmax was observed at various concentrations of ammonia. however, the xmax should also be considered as it is directly influenced by the environmental factor such as ph, temperature, nutrient, and others, which in this case is the ammonia toxicity. fig. 3: growth of c. vulgaris fitted in modified logistic equation at (a) 0 mg/l, (b) 30 mg/l, (c) 60 mg/l, (d) 120 mg/l, (e) 240 mg/l, (f) 480 mg/l, (g) 960 mg/l and (h) 1920 mg/l. (a) (b) (c) (d) (g) (f) (e) iium engineering journal, vol. 19, no. 2, 2018 azmi et al. 7 c. vulgaris growth is well fitted into the logistic growth kinetic model as depicted in fig. 2 with r2 between 0.88 to 1 (table 2) except for the ammonia at the concentration of 1920 mg/l. the equation perfectly modelled the growth without ammonia with co2 supply. however, as the ammonia concentration increased, the r2 was reduced and overestimated some of the parameters. this suggests that a model modification or application of another growth model that takes ammonia concentration and toxicity into account might be needed. table 2: comparison of parameters obtained from logistic growth model and experimental data for variation of ammonia concentration. nh3 concentration (mg·l-1) parameters predicted by model parameter from experimental data r2 xmax (au) xo (au) µmax (day-1) xmax (au) xo (au) µmax (day-1) 0 1.00 1.8200 0.4300 0.7787 1.8200 0.43 0.7787 30 0.95 1.5135 0.0433 2.1813 1.6660 0.239 1.2909 60 0.94 1.3217 0.0169 2.1137 1.4840 0.201 1.1075 120 0.96 1.6024 0.0704 1.9631 1.7890 0.231 1.2410 240 0.96 0.8128 0.0039 4.2902 0.8870 0.127 1.3481 480 0.92 0.7367 0.0080 2.6265 0.8170 0.115 1.4614 960 0.88 0.4997 0.0000 8.8764 0.5620 0.111 1.6968 1920 0.67 0.0001 0.0728 0.0001 0.2450 0.12 1.1670 the ph of the medium was originally adjusted to 6.8 with 1 n koh before inoculation of the green microalgae. there were no significant changes in ph when ammonia was added in the medium until the ammonia concentration increased to 240 mg/l and above, the ph changed to 9.97 and higher as shown in fig. 4. however when co2 was introduced in the culture medium, the ph reduced before it increased back as cell growth was observed. the increase of ph level as growth increased was also reported by others [26-28]. the growth of c. vulgaris in cultures containing ammonia is usually accompanied with a change in ph as the medium becomes acidic in the lag phase and then changes to alkaline when the cells are in the log or stationary phase. fig. 4: medium ph of c. vulgaris culture at different ammonia concentrations . 0 2 4 6 8 10 12 0 1 2 3 4 5 6 7 0 mg/l 30 mg/l 60 mg/l 120 mg/l 240 mg/l 480 mg/l 960 mg/l 1920 mg/l iium engineering journal, vol. 19, no. 2, 2018 azmi et al. 8 6. conclusion growth of c. vulgaris in bbm with continuous air pumped into the culture was observed for a duration of 12 days to study the growth characteristic of c. vulgaris before introducing co2 and ammonia. the growth profile exhibits all phases (except death phase), with a significant extended stationary phase starting from day 4 onwards. due to that, subsequent experimental runs were conducted for only six days. subsequently, eight runs were conducted at various concentrations of ammonia from 0 mg/l to 1920 mg/l with 15% (v/v) of co2 aerated at the volumetric flow rate of 0.5 lpm under illumination at 3500 lux (12 light:12 dark) at 27oc. the highest growth was observed from the culture with 0 mg/l of aqueous ammonia aerated with co2. c. vulgaris growth capacity however declined with the increase of ammonia concentration. the data were also not well fitted into the logistic growth model as the concentration increased, suggesting modification of the model is required. the ph of the culture medium is influenced by growth of the cell in the presence of ammonia. acknowledgement the authors are grateful to the management of international islamic university malaysia for a research fund (rigs16-089-0253) for this work. references [1] begum ra. (2017) tackling climate change and malaysia’s emission reduction target, in scientific malaysian. [http://magazine.scientificmalaysian.com/issue-13-2017/tacklingclimate-change-malaysias-emission-reduction-target/] [2] lokman t. (2017) pm: malaysia on course to reduce carbon emissions by 40 pct by 2020, in new straits times. [https://www.nst.com.my/news/nation/2017/12/310231/pm-malaysiacourse-reduce-carbon-emissions-40-pct-2020] [3] benemann j, pedroni pm, davison j, beckert h, bergman p. (2003) technology roadmap for biofixation of co2 and greenhouse gas abatement with microalgae, in second national conference on carbon sequestration. [https://www.netl.doe.gov/publications/proceedings/03/carbon-seq/pdfs/017.pdf] [4] azmi as, amid a, puad nim, jamal p. (2017) the effect of co2 concentrations and the injection strategy on synechococcus sp. pcc7002 culture, asia pacific of molecular biology and biotechnology, 25:56-60. [5] fan lh, zhang yt, cheng lh, zhang l, tang ds, chen hl. (2007) optimization of carbon dioxide fixation by chlorella vulgaris cultivated in a membrane‐photobioreactor, chemical engineering & technology, 30:1094-1099. [6] zhang x. (2015) microalgae removal of co2 from flue gas. iea clean coal centre, uk. [7] clément‐larosière b, lopes f, gonçalves a, taidi b, benedetti m, minier m, pareau d. (2014) carbon dioxide biofixation by chlorella vulgaris at different co2 concentrations and light intensities. engineering in life sciences 14:509-519. [8] yeh ac, bai h. (1999) comparison of ammonia and monoethanolamine solvents to reduce co2 greenhouse gas emissions. science of the total environment, 228:121-133. [9] blinová l, bartošová a, gerulová k. (2015) cultivation of microalgae (chlorella vulgaris) for biodiesel production. research papers faculty of materials science and technology slovak university of technology, 23:87-95. [10] ahmad a, yasin nm, derek c, lim j. (2011) microalgae as a sustainable energy source for biodiesel production: a review. renewable and sustainable energy reviews, 15:584-593. [11] spolaore p, joannis-cassan c, duran e, isambert a. (2006) commercial applications of microalgae. j. bioscience and bioengineering ,101:87-96. iium engineering journal, vol. 19, no. 2, 2018 azmi et al. 9 [12] he p, mao b, shen c, shao l, lee d, chang j. (2013) cultivation of chlorella vulgaris on wastewater containing high levels of ammonia for biodiesel production., bioresource technology, 129:177-181. [13] kim j, lingaraju bp, rheaume r, lee j-y, siddiqui kf. (2010) removal of ammonia from aastewater effluent by chlorella vulgaris. tsinghua science & technology, 15:391-396. [14] doran pm. (1995) homogeneous reactions. in bioprocess engineering principles, academic press, london,great britain; pp257-296. [15] peleg m, corradini mg, normand md. (2007) the logistic (verhulst) model for sigmoid microbial growth curves revisited. food research international, 40:808-818. [16] escalante fm, reyna‐angeles ka, villafaña‐rojas j, aguilar‐garnica e. (2017) kinetic model selection to describe the growth curve of arthrospira (spirulina) maxima in autotrophic cultures. j. chemical technology and biotechnology, 92:1406-1414. [17] blair mf, kokabian b, gude vg. (2014) light and growth medium effect on chlorella vulgaris biomass production. j. environmental chemical engineering, 2:665-674. [18] sibi g. (2015) low cost carbon and nitrogen sources for higher microalgal biomass and lipid production using agricultural wastes. j. environmental science and technology, 8(3):113121. [19] lehana m. (1990) kinetic analysis of the growth of chlorella vulgaris. biotechnology and bioengineering, 36:198-206. [20] converti a, casazza aa, ortiz ey, perego p, del borghi m. (2009) effect of temperature and nitrogen concentration on the growth and lipid content of nannochloropsis oculata and chlorella vulgaris for biodiesel production. chemical engineering and processing: process intensification, 48:1146-1151. [21] singh s, singh p. (2014) effect of co2 concentration on algal growth: a review. renewable and sustainable energy reviews, 38:172-179. [22] anjos m, fernandes bd, vicente aa, teixeira ja, dragone, g. (2013) optimization of co2 bio-mitigation by chlorella vulgaris. bioresource technology, 139:149-154. [23] wang b, li y, wu n, lan c. (2008) co2 bio-mitigation using microalgae. applied microbiology and biotechnology, 79:707-718. [24] tam nfy, wong ys. (1996) effect of ammonia concentrations on growth of chlorella vulgaris and nitrogen removal from media. bioresource technology, 57:45-50. [25] dalgaard p, koutsoumanis k. (2001) comparison of maximum specific growth rates and lag times estimated from absorbance and viable count data by different mathematical models. j. microbiological methods, 43:183-196. [26] kim j, lee j-y, keener t. (2009) growth kinetic study of chlorella vulgaris. aiche annual meeting, american institute of chemical engineers, nashville, tn, united states; pp 1-6. [27] przytocka-jusiak m, duszota m, matusiak k, mycielski r. (1984) intensive culture of chlorella vulgaris/aa as the second stage of biological purification of nitrogen industry wastewaters. water research, 18:1-7. [28] santoso a. (2015) increasing lipid accumulation of chlorella vulgaris using spirulina platensis in flat plate reactor for synthesizing biodiesel. energy procedia, 65:58-66. evaluation on the effectiveness of visual learning environment on programming course from students’ perspectives iium engineering journal, vol. 20, no. 1, 2019 dina et al. evaluation on the effectiveness of visual learning environment on programming course from students’ perspectives nasa zata dina1*, eto wuryanto2, rachman sinatriya marjianto3 1,3 faculty of vocational studies, universitas airlangga, surabaya, indonesia 2faculty of science and technology, universitas airlangga, surabaya, indonesia *corresponding author: nasazatadina@vokasi.unair.ac.id (received: 12th september 2018; accepted: 15th may 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.993 abstract: this paper discusses the effectiveness of visual learning environment which is used to help students in university to study programming course. the visual learning environment which is used in this study is greenfoot and alice. the main goal of this article is to obtain the correlation between students‘ satisfaction level and their grades in studying programming course using visual learning environment tools. the participants were conducted on 110 students who took programming course during their first year. a survey was sent to students about their satisfaction level in learning programming course. two-variable correlation analysis, significance test and descriptive analysis were conducted to find out the relationship between students' learning satisfaction level and their grades in programming course. this study discusses the student perspectives that are summarized in ten questions. there is a significant correlation between independent and dependent variables. the β value is 2.09 which proves that the independent variable in the form of student's learning satisfaction level is useful to obtain better assessment of their grades. based on their perspectives, it is found that visual learning environment tools have more significant influence in improving the students‘ grade than traditional learning method. further research is needed to find out other impact factors. abstrak: makalah ini membincangkan keberkesanan persekitaran pembelajaran visual yang digunakan untuk membantu pelajar di universiti untuk mempelajari kursus pengaturcaraan. persekitaran pembelajaran visual yang digunakan dalam kajian ini ialah greenfoot dan alice. matlamat utama artikel ini adalah untuk mendapatkan korelasi antara tahap kepuasan pelajar dan gred mereka dalam mengkaji kursus pengaturcaraan menggunakan alat-alat persekitaran pembelajaran visual. para peserta telah diadakan pada 110 orang pelajar yang mengambil kursus pengaturcaraan pada tahun pertama mereka. satu tinjauan telah dihantar kepada pelajar tentang tahap kepuasan mereka dalam pembelajaran kursus pengaturcaraan. analisis korelasi dua-pembolehubah, ujian penting dan analisis deskriptif telah dijalankan untuk mengetahui hubungan antara tahap kepuasan belajar pelajar dan gred mereka dalam kursus pengaturcaraan. kajian ini membincangkan perspektif pelajar yang diringkaskan dalam sepuluh soalan. terdapat korelasi yang signifikan antara pembolehubah bebas dan bergantung. nilai β ialah 2.09 yang membuktikan bahawa pemboleh ubah bebas dalam bentuk tahap kepuasan pembelajaran pelajar adalah berguna untuk mendapatkan penilaian yang lebih baik dari gred mereka. berdasarkan perspektif mereka, didapati alat persekitaran pembelajaran 100 iium engineering journal, vol. 20, no. 1, 2019 dina et al. visual mempunyai pengaruh yang lebih besar dalam meningkatkan gred pelajar daripada kaedah pembelajaran tradisional. kajian lanjut diperlukan untuk mengetahui faktorfaktor kesan yang lain. key words: learning method, programming course, students’ perspective, visual learning environment 1. introduction programming course is one of the compulsory subjects that must be taken in the first year of diploma and undergraduate students in the information systems study program at universitas airlangga. it is considered the most challenging course. according to mckeescott [1], students perceived that programming courses in the first and second semester are difficult to understand. begosso et al. [2] states that the main concern of lecturers is to find out the effective method or strategies that can help the students understand the course better. the programming course is a basic course in computer science study program in university and it is considered as the most difficult course to be learned by the students. zumaytis and karnalim [3] conducted a research about students who studied programming course and the result stated that some students took longer time to understand the algorithm which is the main topic of the programming course. some students required more detailed information from lecturers than other students. the students were expected to study the algorithm themselves when they were not in the class session. in addition, new students face difficulty in debugging and writing code because they never write code before college. the programming courses are required in the first year because they are the basic courses before taking more advanced courses. there are many courses in information systems study program’s curriculum including programming, object oriented programming, web programming and mobile programming. in the first semester, the programming course was called logic programming then in the following semester there is an object-oriented programming course. the programming courses are divided into theories and practical programming courses. when the students successfully understand the theory and practice of basic programming courses, it is easier for them to understand the rest of the information systems course. this is supported by law et al. [4], they taught that one of the key competencies that supported many disciplines were computer programming skills, especially in engineering and computer science. people who work in that field must have good programming skills. learning programming requires not only intelligence, but also a lot of motivation to learn and practice. chu and hwang [5] agreed that if one of the important goals of learning a programming course is to build cooperation and collaboration between students while developing the information system. although some online forums exist to provide discussion among students, doing learning activities based on case studies is more needed. chu and hwang [5] proposed assistance to lecturers on how to conduct case studies based on online learning activities. the results show that the needs of students and lecturers can be fulfilled by the online learning activities and it is quite helpful to improve the effectiveness of learning. challenges faced by lecturers often occur when dealing with methods used to teach the students. not all students have learned programming course before, and most of them have never developed software application before. ouahbi et al. [6] concluded that there were researchers who had noted some of the problems faced by students in the programming courses. they reveal that some of the problems that arise during the theory and practice of programming learning are codes writing, loop manipulation, and method 101 iium engineering journal, vol. 20, no. 1, 2019 dina et al. structure. in addition, poor teaching methodology, low level students interaction and lack of interest are considered as challenges in learning programming course. law et al. [4] reported a preliminary study on factors that influenced the learning program at university. they found that students’ attitudes and expectations, clear material, rewards and recognition were motivating factors. they suggested e-learning as one of the facilitations that improve learning motivation. after that, evaluation results should be made to the students in the programming course [4], [7], [8], there are many learning methods and software tools such as scratch, greenfoot and alice that have been built to help students to eliminate the difficulties in learning programming. visual learning environment has been built to support student learning such as: scratch, greenfoot, alice. all methods introduce the concept of programming through animation. students are expected to practice programming based on case studies. students build game projects and animation projects using software tools. jose-manuel et al. [9] suggest students to make a simple game using scratch game environments. maloney et al. [10] states that scratch is a visual programming environment that allows young users who are primarily aged 8 to 16 years to learn computer programming. meanwhile, dina et al. [11] conducted a comparative study of two groups of students who were taught by educational software tools (greenfoot and alice) and traditional method teaching without any educational software tools. dina et al. [11] only use grades from two student groups to compare the effectiveness of the educational software tools. the result showed that the students’ grades who utilized educational software tools were higher than group of students who did not use. slightly different with previous study [11], the current study uses not only grades to compare the effectiveness of using visual learning environment, especially greenfoot and alice, but also questionnaire which would be completed by the students to measure the students’ satisfaction level in studying programming course. thus, the research question of this article is what is the correlation between the students‘ satisfaction level and their grades in using visual learning environment in studying programing course? therefore, the purpose of this study is to discover whether the visual learning environment is effective to be used in programming course based on the students’ perspective. the following research hypothesis was expanded from research question: h0: there is no positive correlation between the students’ satisfaction level and their grades in using visual learning environment in studying programming course. h1: there is positive correlation between the students’ satisfaction level and their grades in using visual learning environment in studying programming course. the significance of this study is to promote the use of visual learning environment as an educational software tools in programming course, increase students‘ grade in programming course and motivate students in learning programming course. 2. method a survey was conducted on 110 students from information systems study program at universitas airlangga. questionnaires were designed by two academic lecturers who teach programming course and the questionnaires were distributed to students. the questionnaires used 4-point likert scale as a ranking indicator in the survey form to measure the percentage of respondent's approval from each construction. a likert score of 1 indicates that respondents strongly disagree and a score of 4 indicates that respondents strongly agree. for assessing the content validity and reliability, the questionnaire was 102 iium engineering journal, vol. 20, no. 1, 2019 dina et al. given to 2 academics who were also lecturers in programming course while to ensure clarity of wording, the questionnaire was given to 5 non-participating students. in this study, to measure the correlation between students’ satisfaction level and students’ grades in programming course, three analyses were designed (a) descriptive statistics; (b) correlation analysis and significance testing. there are two variables used: variable x (students’ learning satisfaction), and variable y (students’ grades). pearson correlation is applied to identify the correlation between level of students’ satisfaction and students’ grades in programming course. pearson correlation is applied to measure the correlation between those two variables because the pearson correlation evaluates the linear relationship between two continuous variables. the first step to check the relationship is by scatter diagram for linearity [12]. the scatter diagram from fig. 2 shows the linearity so that pearson correlation is suitable to measure the correlation. 3. result and discussion 3.1. descriptive analysis descriptive analysis were used to describe the data used in this study. the data descriptions included mean, median, and mode, and standard deviation (sd), range, minimum and maximum values. those are shown in table 1. according to fig. 1, most data indicate that the students' satisfaction level are directly proportional to the students’ grades. it proves that there is a linear relationship between the two variables (students’satisfaction level (x) and students‘ grades (y)). table 1: the percentage of descriptive statistic variables mean median mode sd range min. max. n x 69.09 75 75 1.57 75 25 100 110 y 69.94 75 75 2.25 100 0 100 110 fig. 1. frequency distribution of research data 3.2. correlation analysis and significance testing after compiling the data into the frequency distribution and measuring the distribution to describe the main characteristics of the distribution, then the next stage was to test the correlation between variables x and y. the test is used to measure the strength and the weakness of the correlation and whether the direction is directly proportional or inverse proportional. therefore, a correlation analysis was performed. then, to check the 103 iium engineering journal, vol. 20, no. 1, 2019 dina et al. linearity of two variables, the scatter diagram was used. it was also used to provide a visual representation of the correlation of two variables. scatter diagram from data survey can be seen in fig. 2. the level of student's learning satisfaction is an independent variable while the students’ grades is the dependent variable. in table 2, the strength of the correlation between two variables was calculated using pearson correlation coefficient (pearson r). the value of pearson r is 0.197. the pearson r value showed that it is a weak correlation but it is not a zero correlation because the pearson r value is not between 0 and 0.1. the pearson r value corresponds to the scatter diagram where there is much distribution around the line drawn through the middle of the data. table 2: pearson correlation students’ satisfaction students’ grades students’ satisfaction 1 0.197063581 students’ grades 0.197063581 1 fig. 2. scatter diagram showing students’ satisfaction level and students’ grades the next step was to analyze the regression equation by testing the hypothesis. it is used to see the slope of the regression line if it is different from zero value. hypothesis test is done so that the researcher can conclude whether the independent variable is fit or not to the dependent variable. the null hypothesis which is the slope of the regression line in the population is equal to zero (h0: β = 0) whereas the alternative hypothesis which is the slope of the regression line is not equal to zero (h0: β ≠ 0). the statistical calculation uses statistical software named excel’s analysis toolpak whose results can be seen in tables 3 and 4. in table 3, the results show that the value of the relation coefficient or multiple r is 0.197. then, in table 4 which is the table of hypothesis test, the slope of the line’s value (b) is 0.281. the intersection is 50.465 and the standard error coefficient (sb) is 0.134. to test the null hypothesis, t distribution is used with (n-2). according to the formula, t value is (b-0) / sb with degrees of freedom n-2. the results of t distribution is (0.281-0) / 0.134 so that the t value is 2.09. after getting the t value, the next step is to compared with t table with 0.05 significance level and 108 degrees of freedom. the degrees of freedom is obtained from n-2 = 110-2. from t table, the value is 1.984. because t value > t table is 2.09 > 1.984; then null hypothesis (h0) is rejected. the t value exceeds the t table of 104 iium engineering journal, vol. 20, no. 1, 2019 dina et al. 1.984; thus it rejects the null hypothesis (h0) and accepts the alternative hypothesis (h1). also, it is supported by p-value in table 4 which shows that the value is under 0.05; thus, it rejects the null hypothesis (h0) and accepts the alternative hypothesis (h1). therefore, it can be concluded that the slope of the regression line (β) is greater than zero, and the independent variable in the form of student's satisfaction level is useful to obtain a better students’ grades in programming course. table 3: regression statistic regression statistic multiple r 0.197063581 r square 0.038834055 adjusted r square 0.02993437 standard error 23.33998462 observations 110 table 4: regression slope test coefficients standard error t stat p-value intercept 50.46542553 9.586257887 5.264351 0.000000721 students’ satisfaction level 0.281914894 0.134958101 2.088907 0.039066039 table 5: consensus matrix no. questions strongly disagree (%) disagree (%) agree (%) strongly agree (%) no response (%) 1 have you ever heard of greenfoot and alice? 45.83 25 22.92 4.17 2.08 2 do you understand the concept of programming by using greenfoot and alice? 0 27.08 68.75 4.17 0 3 do you understand the concept of programming by self-study? 10.42 35.42 43.75 6.25 4.17 4 do you agree if learning programming does not need visualization like greenfoot and alice? 31.25 50 18.75 0 0 5 do you find it confusing when learning programming using green and alice for the first time? 16.67 52.08 31.25 0 0 6 do you find it helpful learning programming using greenfoot and alice to understand the concept of programming? 0 29.17 62.5 8.33 0 7 do you understand if-else well using alice and greenfoot? 4.17 20.83 68.75 6.25 0 8 do you understand looping well using alice and greenfoot? 6.25 35.42 50 8.33 0 9 do you understand the use of function well using alice and greenfoot? 6.25 22.92 62.5 8.33 0 significant testing is generated to calculate the contribution of students‘ satisfaction level to visual learning given by lecturer through alice and greenfoot and correlate it with students’ grades at end of semester. from the analysis result, the independent variable that 105 iium engineering journal, vol. 20, no. 1, 2019 dina et al. is student satisfaction level (x) has significant contribution to each students’ grade (y) for each student. the results are consistent with williams and williams [13] who mentioned that the four main keys that motivate students were students themselves, faculty, lecture materials, and learning methods. yukselturk et al. [14] argued that the level of students’ learning satisfaction is one factor that affected the success and quality of the learning experience. the level of students’ learning satisfaction is influenced by the ability of lecturers, facilities and infrastructure, the learning environment and the quality of the material taught [15][16]. a factor about the learning method has a fairly high contribution. halawah [17] also agreed that the learning method has an important role in motivating students to obtain higher score because during study, students understand the lecture materials well. interesting learning method makes students be motivated to learn independently [18] and will certainly contribute a big impact with the grades, especially in courses which are avoided by students such as programming courses. in the second part, students were asked to compare learning programming course using visual learning environment (alice and greenfoot) or without it. table 5 shows that students tend to choose study programming course using visual learning environment although 70.38% of them have never learned or even heard about visual learning environment like alice and greenfoot. the main concept in programming such as the concept of looping, if-else and the function is understood very well by students. it is shown by the percentage of an average of 70% of students understand the concepts. as a recommendation, lecturers should change the teaching style according to the needs of the students. this can be identified by evaluating teaching methods at the end of semester by taking the perspective of the students so that the lecturers are able to plan the learning style/methods and obtain good results at the end of the lecture. the assumption of programming course which is considered difficult by students can be overcome by introducing visual learning environment. in short, visual learning environment assists students better in enjoying programming course than traditional method. 4. conclusion remarks this research yields some conclusions among them: (1) students' satisfaction level significantly influences the students competency achievement which is proved by students‘ grades; (2) student perspective is one of the best ways to access the needs of students in teaching and learning activities; (3) visual learning environment, in this case, alice and greenfoot manages to improve students' satisfaction level. this motivates the students to learn independently thus the quality of learning is also getting better. references [1] mckee-scott, j. (2015.) a study of an educational game for learning programming. (thesis). canada: the university of british columbia. [2] begosso, l. c., begosso, l.r., goncalves, e. m., goncalves, j. r. (2012). an approach for teaching algorithms and computer programming using greenfoot and python, in frontiers in education conference. seattle, 3 october 2012. [3] zumaytis, s. and karnalim, o. (2017). introducing an educational tool for learning branch & bound strategy. journal of information systems engineering and business intelligence, 3(1), 8-15. [4] law, k. m. y., lee, v. c. s. and yu, y. t. (2010). learning motivation in e-learning facilitated computer programming courses. computers & education. 55(1), 218–228. 106 iium engineering journal, vol. 20, no. 1, 2019 dina et al. [5] chu, h. and hwang, g.-j. (2010). development of a project-based cooperative learning environment for computer programming courses. international journal innovation and learning, 8(3), 256–266. [6] ouahbi, i., kaddari, f. and elachqar, a. (2015) learning basic programming concepts by creating games with scratch programming environment , procedia social and behavioral sciences. 191(1), 1479–1482. [7] kobsiripat, w. (2015). effects of the media to promote the scratch programming capabilities creativity of elementary school students. procedia social and behavioral sciences. paris, 25 june 2014. [8] ferrer-mico, t., prats-fernandez, m.a., redo-sanchez, a. (2012). impact of scratch programming on students’ understanding of their own learning process. procedia social and behavioral sciences, 46(1), 219–1223. [9] jose-manuel s. l., marcos r. g., esteban v. c. (2016). visual programming languages integrated across the curriculum in elementary school : a two year case study using scratch in five schools. computers & education, 97(1), pp. 129–141. [10] maloney, j., resnick, m., rusk, n., silverman, b., and eastmond, e. (2010). the scratch programming language and environment. acm transactions on computing education, 10(4), 1–15. [11] dina, n.z., imama, w.i. and kartono. (2019). the impact of using visual learning environment on student programming course learning achievement: a case study of universitas airlangga. journal of engineering science and technology. 14(2). 712-725. [12] akoglu, h. (2018). user’s guide to correlation coefficients. turkish journal of emergency medicine. 18. 91-93 [13] williams, k.c. and williams, c.c. (2013). five key ingredients for improving student motivation. research in higher education journal, 12(1), 1-23. [14] yukselturk, e. and yildirim, z. (2008). investigation of interaction, online support, course structure and flexibility as the contributing factors to students’ satisfaction in an online certificate program. educational technology & society, 11(4), 51-65. [15] hasan, n., malik, s.a. and khan, m.m. (2013). measuring relationship between students’ satisfaction and motivation in secondary schools of pakistan. middle-east j. of scientific research, 18(7), 907-915. [16] calvo, r.a., markauskaite, l. and trigwell, k. (2010).factors affecting students’ experiences and satisfaction about teaching quality in engineering. australasian j. of eng. educ., 16(2), 139-148. [17] halawah, i. (2011). factors influencing college students’ motivation to learn from students’ perspective. education, 132 (2), 379-390. [18] demir, i., kiliç, s. and depren, ö. (2009). factors affecting turkish students’ achievement in mathematics. us-china educ. review, 6(6), 47-53. 107 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <feff0054006f0074006f0020006e006100730074006100760065006e00ed00200070006f0075017e0069006a007400650020006b0020007600790074007600e101590065006e00ed00200064006f006b0075006d0065006e0074016f002000410064006f006200650020005000440046002000760068006f0064006e00fd006300680020006b0065002000730070006f006c00650068006c0069007600e9006d0075002000700072006f0068006c00ed017e0065006e00ed002000610020007400690073006b00750020006f006200630068006f0064006e00ed0063006800200064006f006b0075006d0065006e0074016f002e002000200056007900740076006f01590065006e00e900200064006f006b0075006d0065006e0074007900200050004400460020006c007a00650020006f007400650076015900ed007400200076002000610070006c0069006b0061006300ed006300680020004100630072006f006200610074002000610020004100630072006f006200610074002000520065006100640065007200200036002e0030002000610020006e006f0076011b006a016100ed00630068002e> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <feff004f0076006500200070006f0073007400610076006b00650020006b006f00720069007300740069007400650020006b0061006b006f0020006200690073007400650020007300740076006f00720069006c0069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400650020006b006f006a00690020007300750020007000720069006b006c00610064006e00690020007a006100200070006f0075007a00640061006e00200070007200650067006c006500640020006900200069007300700069007300200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e006100740061002e0020005300740076006f00720065006e0069002000500044004600200064006f006b0075006d0065006e007400690020006d006f006700750020007300650020006f00740076006f007200690074006900200075002000700072006f006700720061006d0069006d00610020004100630072006f00620061007400200069002000410064006f00620065002000520065006100640065007200200036002e0030002000690020006e006f00760069006a0069006d0020007600650072007a0069006a0061006d0061002e> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <feff004c006900650074006f006a00690065007400200161006f00730020006900650073007400610074012b006a0075006d00750073002c0020006c0061006900200069007a0076006500690064006f00740075002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c0020006b006100730020007000690065006d01130072006f00740069002000640072006f01610061006900200075007a01460113006d0075006d006100200064006f006b0075006d0065006e0074007500200073006b00610074012b01610061006e0061006900200075006e0020006400720075006b010101610061006e00610069002e00200049007a0076006500690064006f0074006f0073002000500044004600200064006f006b0075006d0065006e00740075007300200076006100720020006100740076011300720074002c00200069007a006d0061006e0074006f006a006f0074002000700072006f006700720061006d006d00750020004100630072006f00620061007400200075006e002000410064006f00620065002000520065006100640065007200200036002e003000200076006100690020006a00610075006e0101006b0075002000760065007200730069006a0075002e> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 terminal control area complexity measurement using simulation model rully medianto1,2*, naflah mutiara adinda1, yazdi ibrahim jenie1, hisar manongam pasaribu1 and hari muhammad1 1 faculty of mechanical and aerospace engineering, bandung insitute of technology, bandung, indonesia 2 faculty of aerospace technology, institut teknologi dirgantara adisutjipto, yogyakarta, indonesia * corresponding author: hmpasaribu@itb.ac.id (received: 9th november 2021; accepted: 18th june 2022; published on-line 4th january 2023) abstract: traffic density in the terminal control area will increase flight safety risks. one effort to reduce the risk is to minimize the controller’s workload when affected by air traffic complexity. this research uses a simulation model to measure air traffic complexity in terminal control areas. the aircraft performance model has been constructed from adsb data and represents the aircraft movement in the terminal control area of soekarno-hatta international airport. the simulation model can detect and resolve conflicts to keep separations between aircraft at a specified minimum separation limit. air traffic complexity measurement uses several indicators, i.e., aircraft density, number of climbing and descending aircraft, aircraft type mixing, conflict control, aircraft speed difference, and controller communication. the weighting factor for each indicator has been obtained from jakarta air traffic service center (jatsc) controller perception using an analytic hierarchy process. the simulation results show that the variation of resolution type affects the complexity level significantly. the results of this study can be used as consideration for improving air traffic control procedures and air space structures. abstrak: kepadatan trafik di kawasan terminal kawalan bakal menyebabkan peningkatan risiko keselamatan penerbangan. salah satu cara bagi mengurangkan risiko adalah dengan meminimumkan beban kerja pengawal yang terlibat dengan kesesakan trafik udara. kajian ini menggunakan model simulasi bagi mengukur kesesakan trafik udara di kawasan terminal kawalan. model pretasi pesawat telah dibina menggunakan data ads-b dan ini mewakili pergerakan pesawat di terminal kawalan lapangan terbang antarabangsa soekarno-hatta. model simulasi ini dapat mengesan konflik dan membuat resolusi bagi mengekalkan penjarakan antara pesawat mengikut had penjarakan minimum yang ditetapkan. beberapa indikator telah digunakan bagi mengukur kerumitan trafik udara, iaitu: ketumpatan pesawat, bilangan pesawat mendaki dan menurun, jenis pesawat, kawalan konflik, perbezaan kelajuan pesawat dan pengawal komunikasi. faktor pemberat bagi setiap indikator telah diperoleh daripada pengawal persepsi pusat servis trafik udara jakarta (jatsc) menggunakan proses analisis hierarki. keputusan simulasi menunjukkan pelbagai jenis resolusi mempengaruhi tahap kerumitan dengan ketara. hasil kajian ini boleh digunakan bagi menambah baik prosedur kawalan trafik udara dan struktur ruang udara. keywords: terminal control; air traffic complexity; simulation model; analytic hierarchy process 199 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 1. introduction the terminal control area (tca) is airspace with the most complex and dense system compared to other airspace sectors. three modes of flight operations run simultaneously: arrival, departure, and cross-flight [1]. tca is highly sensitive to changes in traffic, weather, flight procedures, runway used, and other unusual events. the assessment of the system's performance is important and is affected by the system's complexity [2]. the air traffic complexity rate can be very high due to the traffic intensity and patterns in mutual interactions between different traffic flows and individual aircraft in the tca. the increasing complexity of the tca will increase the complexity of controller tasks and result in increased workload [3]. the management of traffic flow and airspace can be carried out correctly to avoid excessive controller workload if the measurement and prediction of air traffic complexity can be carried out accurately [4]. table 1: air traffic complexity indicators summary air traffic complexity indicators arad [8] grossberg [9] mogford et al. [10] pawlak et al. [11] laudeman et al. [12] majumdar et al. [13] chatterji et al. [14] koros et al. [15] diaconu et al. [4] sector design/geometry √ √ √ aircraft density/volume √ √ √ √ √ √ aircraft speed difference √ √ √ √ √ emergency operations √ altitude change √ √ √ √ √ the horizontal distance between aircraft √ √ √ √ √ the vertical distance between aircraft √ √ √ √ aircraft type mixing √ √ √ √ √ √ frequency of atco's communication √ √ √ flight entering and exiting the sector √ potential conflict control √ √ √ √ number of cruising aircraft √ √ √ number of climbing/descending aircraft √ √ √ √ √ √ √ weather condition √ √ √ aircraft heading change/difference √ √ special flight √ √ √ √ radiofrequency congestion √ √ number of intersecting airways √ restricted airspace √ √ the proximity of sector boundary √ √ atc's procedure √ √ it is necessary to consider the interactions between individual aircraft and their flight characteristics to determine complexity more precisely. the interactions involve possible conflicts and the tendency for aircraft movement to converge at one point. [5]. there are at 200 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 least nine references from mogford et al., diaconu et al. and dervic and rank (2 that mention various indicators of complexity [4,6,7]. table 1 shows the summary of some complexity indicators. air traffic complexity can be measured by experts, who have experience controlling air traffic under various conditions, or by the complexity indicator obtained from air traffic data and the number of interactions between aircraft in a particular sector [16]. another method to determine air traffic complexity is using a dynamic weighted network model. the nodes represent aircraft, waypoints, and airways in the network model. the total weights of all network edges represent air traffic complexity [17]. andrasi et al. used an artificial neural networks model to estimate air traffic complexity. the best configuration of artificial neural networks was determined by a genetic algorithm [18]. this research developed an atm model simulation in the tca using matlab to reflect aircraft movements and the air traffic control process. the simulation model is then used to analyze air traffic complexity in the tca, specifically at soekarno-hatta international airport, jakarta. the simulation model has several advantages in describing the air traffic system and its complexity, i.e. the movement of the aircraft can be visualized to analyze and validate it [19]. the simulation parameters also can be modified easily to obtain various scenarios. 2. modelling 2.1 system description the atm system model represents arrival and departure operations for runway 25r and 25l on soekarno-hatta international airport jakarta (jakarta). the arriving aircraft will enter the tca from the en-route airspace through the transition points. the aircraft then fly towards the runway following a specific trajectory profile defined by some waypoints. the arrival trajectory profile refers to standard terminal arrival routes (star). the departing aircraft enter the tca from the aerodrome control area and fly to the airway following the standard instrument departure trajectory profile (sid). the information about star and sid can be accessed in the aeronautical information regulation and control (airac) as a supplement to the aeronautical information publication (aip) published by the directorate general of civil aviation (dgca) of indonesia [20]. with flight management computer (fmc) support, aircraft can automatically fly along with these profiles. under certain circumstances, the aircraft must follow the instruction from the air traffic controller containing the aircraft's direction (heading), altitude, and speed changes, often referred to as vectoring. arrival operations have more significant conflict potential than departures because aircraft have trajectories that converge, especially when entering a merging point. aircraft speed on arrival will also experience a reduction so that the aircraft in front tends to be overtaken by the aircraft behind it. the departure model has a smaller potential for conflict than the arrival because the trajectory tends to be diverging. potential conflicts with arriving aircraft are also minimal due to differences in altitude and flight path. there are six tca sectors related to runway 25r and 25l are modeled in this study: jakarta lower control north (ln), jakarta lower control center (lc), jakarta lower control east (le), jakarta terminal west (tw), jakarta terminal east (te), and jakarta terminal south (ts). each sector has boundaries described by latitude-longitude, altitude/flight level, and radius from atc head radar. information about the boundaries can 201 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 be accessed in standard operating procedures air traffic services approach control service published by airnav indonesia branch of jakarta air traffic service center (jatsc) [21]. the arrival traffic model has six trajectory profiles, and the departure traffic model has ten. complete trajectory profiles and tca sectors related to the runway 25r and 25l air traffic model are shown in fig . 1. fig. 1: trajectory profiles and tca sectors related to runway 25r and 25l. 2.2 air traffic model the air traffic model was built using matlab software by combining discrete-event and agent-based models. the wind speed model was added as an environmental element influencing the system. the wind speed consists of wind velocity and direction represents the weather condition. each aircraft has a fixed parameter that will not change during simulation: aircraft type and trajectory profile based on sid/star. there are also dynamic parameters that will change during simulation; these parameters are: ▪ position: in the form of local ned (north, east, down) coordinates with a reference point at the nokta waypoint (x, y, z); ▪ airspeed: airspeed in the local ned direction (vx, vy, and vz); ▪ waypoint: present the waypoint to which the aircraft is headed; ▪ heading: heading aircraft relative to local north; ▪ distance to waypoint: the distance of the aircraft to the next waypoint; ▪ right of way: priority of aircraft when heading/being on the same track; ▪ conflict status: free from conflict or not; ▪ resolution: selected conflict resolution mode (vectoring, speed control, or altitude control); ▪ tas and gs: aircraft true airspeed and ground speed; ▪ vertical speed: vertical aircraft speed when climbing (+) or descent (-); and ▪ radar radius: radius from radar. each trajectory has a unique profile based on star and sid published in aeronautical information publication (aip) [20]. each aircraft will move along the trajectory with the 202 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 waypoint as profile guidance. the aircraft distance relative to the waypoint is obtained by the equation [22]: 𝑑𝑥𝑡 = 𝑋𝑤𝑝 − 𝑋𝑡 (1) 𝑑𝑦𝑡 = 𝑌𝑤𝑝 − 𝑌𝑡 (2) 𝑑𝑧𝑡 = 𝑍𝑤𝑝 − 𝑍𝑡 (3) 𝑑𝑠,𝑡 = √(𝑑𝑥𝑡 ) 2 + (𝑑𝑦𝑡 ) 2 + (𝑑𝑧𝑡 ) 2 (4) with, xt, yt, zt: aircraft coordinates on each coordinate axis; xwp, ywp, zwp: waypoint coordinates on each coordinate axis; dxt, dyt, dzt: distance to the waypoint on each coordinate axis; ds,t: aircraft distance relative to the waypoint. after getting the distance relative to the waypoint using the above equation, then the heading angle can be calculated relative to the waypoint (𝜃𝑡 ) apply the equation: 𝜃𝑡 = tan −1 𝑑𝑥𝑡 𝑑𝑦𝑡 (5) the aircraft heading angle relative to the waypoint is used to calculate the relative aircraft speed on each axis (vx, vy, vz) using the equation below: 𝑉𝑥𝑡 = { = 𝑉𝑡 cos 𝜃𝑡 , 𝑑𝑧𝑡 = 0 ≠ (√𝑉𝑡 2 − 𝑉𝑧𝑡 2) cos 𝜃𝑡 𝑑𝑧𝑡 ≠ 0 (6) 𝑉𝑦𝑡 = { = 𝑉𝑡 sin 𝜃𝑡 , 𝑑𝑧𝑡 = 0 ≠ (√𝑉𝑡 2 − 𝑉𝑧𝑡 2) sin 𝜃𝑡 𝑑𝑧𝑡 ≠ 0 (7) 𝑉𝑧𝑡 = { = 0, 𝑑𝑧𝑡 = 0 ≠ 0 𝑑𝑧𝑡 ≠ 0 (8) furthermore, it can be determined the position of the aircraft for each axis at a time (t + 1) through the equation: 𝑋𝑡+1 = (𝑉𝑥𝑡 ∗ 𝛿𝑡) + 𝑋𝑡 (9) 𝑌𝑡+1 = (𝑉𝑦𝑡 ∗ 𝛿𝑡) + 𝑌𝑡 (10) 𝑍𝑡+1 = (𝑉𝑧𝑡 ∗ 𝛿𝑡) + 𝑍𝑡 (11) the separation between aircraft is maintained by using conflict detection and resolution models. it is necessary to calculate horizontal (dhor) and vertical (dver) separations between aircraft (a and b) to check whether the separation between aircraft is still safe (does not exceed the minimum limit) using the following equation: 𝑑ℎ𝑜𝑟 = √(𝑋 𝑎 − 𝑋𝑏 )2 + (𝑌𝑎 − 𝑌𝑏 )2 (12) 𝑑𝑣𝑒𝑟 = √(𝑍 𝑏 − 𝑋𝑎 )2 (13) x, y, and z are the aircraft coordinates a and b on each coordinate axis. after the separation between aircraft is known, whether the separation is still safe or if there has been a potential conflict (smaller than the specified minimum separation buffer) can be checked. conflicts at tca more often occur when the plane is heading to the merging point. if several aircraft experience conflict, it will be determined which aircraft gets the right of way (row) based on the closest distance to the merging point. the aircraft that gets the first row continues to fly following the specific trajectory without resolving conflict. the other aircraft should make specific maneuvers as part of conflict resolution. 203 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 the flowchart of the aircraft's movement in the simulation model is shown in fig. 2. the model has three conflict resolution modes: vectoring, airspeed control, and altitude control. fig. 2: flow chart of aircraft movements in the simulation model. 2.3 flight parameter model flight parameter models were extracted from ads-b data provided by flightradar24. the ads-b data was collected from more than 38800 flights that departed and landed at soekarno-hatta international airport, jakarta [23]. the models included five aircraft flight parameters: airbus a320, boeing b737, airbus a330, boeing b777, and boeing b787. machine learning was used to handle a large quantity of ads-b data to identify the phase of the flight and the time when the aircraft flew across specific waypoints. one advantage of this technique is that ads-b data can be efficiently and cost-effectively gathered over the internet. ads-b data was combined with weather data from aviation meteorological information system in meteorological, climatology, and geophysical agency (bmkg) to develop the flight parameter model [24]. the waypoints used for analysis were the waypoints flown by aircraft using runway 25r and 25l for departing and arriving. the waypoint information was obtained from the soekarno hatta international airport terminal chart published by the indonesia dgca [20]. the k-nearest neighbor algorithms processed flight parameters from ads-b data when the aircraft had the nearest position to specific waypoints within a radius of 1 nm. the altitude and the vertical speed were processed straight from the ads-data. the true airspeed was generated from the ground speed and wind speed data from weather data. three probability distribution functions (normal distribution, beta distribution, and gamma distribution) approached flight parameter models using maximum likelihood estimation. the best distribution was determined using kolmogorov-smirnov test. the flight parameters for this research used the mean value from the models. validation was carried out on previous research by comparing the estimated parameters with flight 204 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 parameters from the eurocontrol aircraft performance database [25] and the reference parameter from the jakarta (wiii) terminal chart issued by the indonesia directorate general of civil aviation [26]. table 2 shows some of the aircraft's flight parameter models when flying by specific waypoints. table 2: flight parameter models for each type of aircraft when flying by waypoints 2.4 air traffic complexity the calculation of air traffic complexity at tca begins by determining the indicators affecting the complexity and relevance of the airspace sector. after that, the weight of each indicator needs to be determined using the analytic hierarchy process (ahp) method. the most mentioned indicators relevant to the tca airspace sector can be selected based on table 1. hence, air traffic complexity measurement in this paper uses seven indicators: air traffic density (nin), number of climbing (nclb) and descending (ndes) aircraft, aircraft type mixing (ttyp), potential conflict control (crossing and overtaking conflict, ttrf), aircraft speed difference (tspd), and frequency of controller's coordination or communication (tcom). the weight of each indicator was obtained using an analytic hierarchy process (ahp) method. waypoint altitude (feet) true airspeed (knot) vertical speed (m/s) a320 b737 a330 b777 b787 a320 b737 a330 b777 b787 a320 b737 a330 b777 b787 abilo 35834 35834 35834 35834 35834 436 436 436 436 436 836 836 836 836 836 ajuna 7758 7339 7131 6492 7208 287 283 279 285 278 2524 2473 2484 2115 2283 alamo 38228 38228 38306 38228 38228 450 450 450 477 477 425 425 425 524 524 arkap 2227 2215 2368 2350 2300 190 180 187 190 183 216 239 263 366 305 bunik 22799 22771 21798 22370 22788 395 373 389 389 391 1838 1630 1619 1543 1562 ca 10107 10929 11161 11161 11161 455 454 454 455 455 777 696 1193 1193 1193 carta 14032 14032 14032 13618 14101 314 336 335 330 326 1558 1789 1465 1396 1407 coril 8482 9483 9483 9483 9483 464 458 458 458 16 890 1096 1096 1096 1096 dapik 1262 1310 1320 1381 1291 217 214 208 212 207 371 560 384 601 397 dendy 24419 24419 24124 23850 24169 378 378 390 392 393 1259 1259 1389 1554 1511 dolta 27591 29814 28087 26436 32599 446 453 443 470 473 1007 1171 1377 1479 1918 esala 3316 3317 3371 3627 3489 288 286 285 286 282 1271 1256 1227 1141 1251 frida 32125 33409 33409 33409 33409 463 456 463 463 463 776 731 776 776 776 gapri 6909 6682 6912 7103 7335 375 365 378 375 362 1699 1538 1494 1105 1119 gaspa 9155 9335 8314 9020 9056 449 384 430 429 431 1180 775 1714 1750 992 hlm 4093 4203 4363 4620 4620 354 361 20 361 374 1987 2263 2093 3375 3375 imu 8813 8765 8964 9254 9254 425 423 424 438 438 1350 1450 1554 1823 1823 kurus 9418 8932 9079 9273 9273 447 432 460 469 469 2046 1715 1961 2338 2338 laras 21015 21015 19140 22357 19524 397 397 402 434 405 1778 1778 1578 1968 1856 lepas 29868 29868 29868 34739 31644 457 457 457 480 483 874 874 874 211 1040 nabil 4425 4217 4121 4298 4298 356 346 350 350 367 2111 2259 1924 2338 2338 nadin 7942 7670 7944 8185 8185 405 394 401 399 399 1731 1554 1591 1362 1362 nokta 11931 12443 12207 12385 13008 290 284 290 295 295 1403 1185 1185 1136 1132 priok 3537 3712 3395 3425 3309 218 216 215 212 211 643 802 582 648 663 pw 7538 7847 9144 9144 9144 433 423 423 437 437 1235 966 1738 1738 1738 ramal 17531 17660 16867 17489 17576 342 329 338 343 345 1636 1426 1543 1535 1559 rambu 6905 6998 6768 7241 7202 255 256 259 262 262 1050 1112 1005 1088 1186 ratih 15998 15998 16475 18685 16634 377 377 373 400 379 2034 2034 1737 2071 1870 sikad 18000 17300 17675 17675 17675 358 362 414 414 414 2100 2300 2800 2800 2800 tegar 2122 2146 2110 2115 2031 247 249 245 247 246 902 1027 813 899 857 wetes 5062 4967 5088 5284 5043 331 327 333 330 320 1596 1511 1604 1453 1335 winar 6157 5757 5409 5016 5271 278 274 264 273 271 2635 2595 2535 2144 2429 205 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 the first step in the ahp method was to collect input data with pairwise comparisons of the indicators. complexity indicators were paired with a rating that determined which indicator was more critical. this data was collected by a survey involving respondents from experts and practitioners. the questionnaire was created to assess the relative importance (weight value) of the target respondents, experts, and air traffic controllers from airnav indonesia, notably the jakarta air traffic services center (jatsc). the questionnaire was filled out by respondents using online media. the second step was to average the input comparison values using the row geometric mean method (rgmm). the average ri value was determined using the following equation. 𝑟𝑖 = 𝑒𝑥𝑝 [ 1 𝑁 ∑ 𝑙𝑛(𝑎𝑖𝑗 ) 𝑁 𝑗=1 ] = (∏ 𝑎𝑖𝑗 𝑁 𝑖=1 ) 1 𝑁 (14) the comparison matrix a = aij with dimensions of n×n, n = 7 (number of indicators). the third step was calculating the first eigenvector of matrix a (eigen 1 in the e1 matrix). the fourth step was calculating the second eigenvector (eigen 2 in the e2 matrix). then proceed to the fifth step, calculating the difference between e1 and e2. the sixth step was to assess the consistency of the respondent's answers in the following way. a. calculate the weighted sum vector (wsv) by multiplying the rows of matrix a by matrix e1. b. divide each element of the wsv matrix by each element of the e1 matrix to obtain the consistency vector (cv). c. calculate the lambda (λ) by averaging cv and calculating the consistency index (ci) using the following equation. 𝐶𝐼 = 𝜆−𝑁 𝑁−1 (15) d. divide ci by the random consistency index to get the consistency ratio (cr) (ri). 𝐶𝑅 = 𝐶𝐼 𝑅𝐼 (16) table 3 shows the ri value for a given n value. table 3: random consistency index [4]. n 1 2 3 4 5 6 7 8 9 10 ri 0 0 0,58 0,9 1,12 1,24 1,32 1,41 1,45 1,49 after knowing the value of each indicator and its weight of importance, the general equation for the function of air traffic complexity at tca can be calculated. 𝐹𝑐 = (𝑊𝑖𝑛 × 𝑁𝑖𝑛 ) + (𝑊𝑐𝑙𝑏 × 𝑁𝑐𝑙𝑏 ) + (𝑊𝑑𝑒𝑠 × 𝑁𝑑𝑒𝑠 ) + (𝑊𝑡𝑦𝑝 × 𝑇𝑡𝑦𝑝) + (𝑊𝑟𝑡𝑓 × 𝑇𝑟𝑡𝑓 ) + (𝑊𝑠𝑝𝑑 × 𝑇𝑠𝑝𝑑 ) + (𝑊𝑐𝑜𝑚 × 𝑇𝑐𝑜𝑚 ) (17) air traffic complexity values were calculated for several scenarios. the scenarios were varied on the inter-arrival time (iat) and the percentage of possible resolution types (speed control, altitude control, and vectoring). 3. results and discussion the simulation animation is used to validate the model by observing the model's behavior while the simulation is running [27]. some entities (aircraft) are observed moving from the time they enter the system to the time they leave the system to determine whether 206 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 the aircraft moves correctly according to the predetermined modeling concept and whether the conflict detection and resolution have been applied. the animation observations show that the entity followed its arrival and departure trajectory according to the predetermined trajectory route. the data validation and operational graphics results also show that the model correctly implemented the applied conflict detection and resolution. no aircraft violated the minimum separation rules when the simulation ran in normal conditions. the waypoint modeling for soekarno-hatta international airport is based on local coordinates of ned with nokta as a reference point. the model is used to simulate the air traffic in the tca, especially at jakarta tca for runway 25r and 25l. the model visualized 2-dimensional forms that moved for each unit of time. flight parameters were estimated from ads-b data for specific waypoints. the movement of the aircraft in the simulation were repreented by a green dot when there was no conflict, a yellow dot when there was a potential conflict, and a red dot when there was a conflict with other aircraft. the simulation had twelve entry points and ran for 7200 units or the equivalent of 7200 seconds. there were three scenarios, each was running for just one resolution mode choice to solve the traffic conflict. air traffic complexity was measured by calculating seven complexity indicators recorded during the simulation. visualization of the simulation model is shown in fig. 3. a total of 119 questionnaire respondents from the jatsc controller provided information to determine which complexity indicator was more critical among the indicators that have been paired. the questionnaire results were then processed by ahp to obtain the weighting value for each indicator, as shown in table 4. fig. 3: visualization of the simulation model with aircraft movement representation. the level of consistency (consistency ratio) of the ahp was 0.72% which means that the answers were consistent (cr < 10%). this cr value indicated that the weighting values that were obtained could be used in the simulation. as shown in the table, the indicator that most influences complexity is the potential conflict control for crossing and overtaking conflict, with a weighting value of 38.87%. the indicator with the smallest weighting value 207 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 is the number of climbing aircraft (8.99%). thus, the general function for air traffic complexity at jakarta tca can be written as follows. 𝐹𝑐 = (0.1218 × 𝑁𝑖𝑛 ) + (0.0899 × 𝑁𝑐𝑙𝑏 ) + (0.1078 × 𝑁𝑑𝑒𝑠) + (0.1015 × 𝑇𝑡𝑦𝑝) + (0.3887 × 𝑇𝑟𝑡𝑓 ) + (0.0924 × 𝑇𝑠𝑝𝑑 ) + (0.0980 × 𝑇𝑐𝑜𝑚 ) (18) table 4: weighting value of each complexity indicator complexity indicators weighting value air traffic density (𝑁𝑖𝑛) 12.18% number of climbing aircraft (𝑁𝑐𝑙𝑏 ) 8.99% number of descending aircraft (𝑁𝑑𝑒𝑠) 10.78% aircraft types mixing (𝑇𝑡𝑦𝑝) 10.15% potential conflict control (𝑇𝑟𝑡𝑓) 38.87% aircraft speed difference (𝑇𝑠𝑝𝑑 ) 9.24% frequency of air traffic controller's coordination or communication (𝑇𝑐𝑜𝑚) 9.80% function (18) shows that the number of descending aircraft is more critical than the number of climbing aircraft in influencing air traffic complexity. it is also shown that the aircraft type mix is more important than the aircraft speed difference. this result is different from diaconu et al. (2014) in which the climbing was more important than the descent, and the aircraft speed difference was more important than the aircraft type mix [4]. the controller's significant preference with the same indicator may vary for different air traffic service units. so it is necessary to analyze the weighting value of the complexity indicator for related air traffic service units before measuring the air traffic complexity in specific airspace sectors. controller task load is represented by controller communication time in the function through the frequency of the controller's coordination or communication (𝑇𝑐𝑜𝑚 ). the complexity rate will increase the more frequently the controller coordinates or communicates with the pilot and another controller. the weighting of communication time in the complexity function is more critical than the number of climbing aircraft (𝑁𝑐𝑙𝑏 ) and aircraft types mixing (𝑇𝑡𝑦𝑝). in addition to task load, other factors such as equipment capability, individual preferences, and cognitive controller strategies are required to obtain a complete picture of the correlation between complexity and workload [28]. the simulation run for ten repetitions with aircraft type mix is a 9:1 ratio for medium type (boeing b737 and airbus a330) and heavy type (airbus a330, boeing b777, and boeing b787). when entering the arrival point, time separation is set to 4 minutes, and departure is about 6 minutes. this gives high traffic density to the model. the minimum separation is 5 nm with a buffer of 15 nm to solve the potential conflict. a graphic of complexity measurement from a simulation (altitude control mode only) for each tca sector is shown in fig. 4. from fig. 4, jakarta lower control north and jakarta terminal west have a high rate of complexity relative to the other sectors. jakarta terminal east has the lowest complexity rate compared with the others on runway 25r and 25l operation. the model can show the complexity rate comparison between sectors. it can be used to assess what sector has a higher rate of complexity for a particular runway operation, and the management should take some action to balance it. 208 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 fig. 4: result of complexity measurement (altitude control mode only). simulation results of air traffic complexity measurement and the number of potential conflicts for specific resolution mode scenarios in each sector are shown in fig. 5 and 6. fig. 5: values of air traffic complexity on sectors for specific resolution mode's scenario. (a) jakarta lower control north (b) jakarta lower control center (c) jakarta lower control east (d) jakarta terminal west (e) jakarta terminal east (f) jakarta terminal south 209 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 fig. 6: number of potential conflicts on sectors for specific resolution mode's scenario. figure 5 shows that the speed control mode assigns a higher complexity rate for all sectors except jakarta lower control north. for lower rate complexity, vectoring mode gives the lowest complexity than the other resolution mode, as seen in jakarta lower control north, jakarta lower control centre, and jakarta terminal south. altitude control mode gives a higher rate of complexity and more potential conflict if applied to the sector with many departure trajectories like jakarta lower control north. fig. 5 and 6 elaborate that speed control to solve the conflict increases complexity and creates more potential conflict for almost all sectors. vectoring mode gives the least potential conflict than the other modes except on jakarta terminal west. the simulation result can compare the complexity between sectors in a tca and its effect on potential conflicts. however, the model cannot yet determine how this complexity affects aviation safety risks. as we know, complexity will affect the controller's workload level [5]. representation of the human factor is needed to measure the controller workload, and its effect on safety risk factors can be observed. future research needs methods to represent the human factor in a simulation model, including adding a controller to the simulation (human in the loop simulation) [16] or developing a controller workload model [29]. 4. conclusion the weighting value of seven air traffic complexity indicators has been calculated using the ahp method in this study. the indicator that most significantly affects the air traffic complexity is the potential conflict control. the consistency of respondents' answers is less than 10%, indicating that these results are consistent. it can determine the air traffic complexity rate in the jakarta tca model. the simulation has been run to measure the air traffic complexity of jakarta tca in a high-density situation. the simulation result explains that the resolution mode selection (g) jakarta lower control north (h) jakarta lower control center (h) jakarta lower control east (i) jakarta terminal west (j) jakarta terminal east (k) jakarta terminal south 210 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 influences the complexity rate and potential conflicts. the simulation model requires further development by representing the human factor in the model so the model can be used to analyze safety risks. acknowledgement the authors would like to acknowledge jakarta air traffic services center (jatsc), airnav indonesia, for providing information and the indonesian endowment fund for education (lpdp scholarship) for the financial support. references [1] bouarfa s. (2015) agent-based modelling and simulation of safety and resilience in air transportation. doctoral dissertation, delft university of technology. https://doi.org/10.4233/uuid:b676db6c-ed86-4b42-9940-9b90b94651f1 [2] netjasov f, janic m, tosic v. (2009) the future air transport system: looking for generic metrics of complexity for terminal airspace. 88th transportation research board (trb) annual meeting, washington dc, usa. [3] netjasov f, janic m, tosic v. (2011) developing a generic metric of terminal airspace traffic complexity. transportmetrica 7(5), 369-394. https://doi.org/10.1080/18128602.2010.505590 [4] diaconu ag, stanciu v, pleter ot. (2014) air traffic complexity metric for en-route and terminal areas. u.p.b. sci. bull., series d, vol. 76, iss. 1. [5] djokic j, lorenz b, fricke h. (2010) air traffic control complexity as workload driver. transportation research part c emerging technologies 18(6):930-936. https://doi.org/10.1016/j.trc.2010.03.005 [6] mogford rh, guttman ja, morrow sl, kopardekar p. (1995) the complexity construct in air traffic control: a review and synthesis of the literature. report n0. dot/faa/cttn95/22. u.s. department of transportation, federal aviation administration, office of aviation research, washington, d.c. [7] dervic a, rank a. (2015) atc complexity measures: formulas measuring workload and complexity at stockholm tma. department of science and technology, linköping university, sweden. [8] arad ba, golden bt, grambart je, mayfield ce, van saun hr. (1963) control load, control capacity, and optimal sector design (report no. rd64-16). federal aviation administration, atlantic city, nj. [9] grossberg m. (1989) relation of sector complexity to operational errors. quarterly report of the faa office of air traffic evaluations and analysis. [10] mogford rh, murphy ed, yastrop g, guttman ja, roske-hofstrand r. (1993) the application of research techniques for documenting cognitive processes in air traffic control (report no. dot/faa/ct-tn93/39). federal aviation administration, atlantic city, nj. [11] pawlak ws, brinton cr, crouch k, lancaster km. (1996) a framework for the evaluation of air traffic control complexity. american institute of aeronautics and astronautics, inc. [12] laudeman i, shelden s, brannstrom r, brasil c. (1998) dynamic density: an air traffic management metric. ames research center. [13] majumdar a, ochieng wy. (2000) the factor affecting air traffic controller workload: a multivariate analysis based upon simulation modelling of controller workload. center for transport studies. [14] chatterji gb, sridhar b. (2001) measures for air traffic controller workload prediction. first aiaa aircraft technology, integration and operations forum. https://doi.org/10.2514/6.2001-5242 211 iium engineering journal, vol. 24, no. 1, 2023 medianto et al. https://doi.org/10.31436/iiumej.v24i1.2223 [15] koros a, della rocco ps, panjwani g, ingurgio v, d'arcy jf. (2003) complexity in air traffic control towers: a field study. part 1: complexity factors. dot/faa/ct-tn03/14. federal aviation agency, atlantic city, nj. [16] radišić t, andraši p, novak d, juričić b, antulov-fantulin b. (2020) risk assessment in air traffic management. edited by p. castán and j. alberto. intechopen, london. pp 56-83. [17] wang h, song z, wen r. (2018) modeling air traffic situation complexity with a dynamic weighted network approach. journal of advanced transportation, vol. 2018 vol. 2018, article id 5254289, 15 pages. https://doi.org/10.1155/2018/5254289 [18] andraši p, radišić t, d. novak, and b. juričić (2019) subjective air traffic complexity estimation using artificial neural networks. traffic & transportation, 31(4): 377-386. https://doi.org/10.7307/ptt.v31i4.3018 [19] medianto r, pasaribu hm, muhammad h. (2019) development of hybrid simulation model of air traffic management in the terminal control area. iop conf. series: materials science and engineering, 645: 012003. https://doi.org/10.1088/1757-899x/645/1/012003 [20] directorate general of civil aviation (2019) nr: the establishment and revision of instrument flight procedures at soekarno hatta international airport – jakarta, airac aip supplement 14/19 25 apr 19. directorate of air navigation, directorate general of civil aviation, republic of indonesia. flightradar24 data/history flights. [21] airnav indonesia (2020) standard operating procedures air traffic services approach control service. airnav indonesia branch of jakarta air traffic service center. [22] horasio k. (2019) air traffic conflict resolution modelling and analysis in controlled airspace. master's thesis. bandung institute of technology, aerospace engineering department. [23] flightradar24 flight database [https://www.flightradar24.com/data/flights] [24] metar/speci & trend forecast, aviation meteorological information system in meteorological, climatology, and geophysical agency (bmkg) [http://aviation.bmkg.go.id/web/metar_speci.php] [25] pasaribu hm, medianto r, jusuf j, oktafianto r, atiqah r (2021) ads-b data processing to develop aircraft kinematics model parameters. aip conference proceedings, 2366: 02001. https://doi.org/10.1063/5.0060611 [26] medianto r, jusuf j, oktafianto r, atiqah r, sembiring j, pasaribu hm, jenie yi, muhammad h. (2021) stochastic modelling of aircraft flight parameters in terminal control area based on automatic dependent surveillance-broadcast (ads-b) data. iop conference series: materials science and engineering, 1173: 012053. https://doi.org/10.1088/1757899x/1173/1/012053 [27] sargent rg. (2005) verification and validation of simulation models, proceedings of the 2005 winter simulation conference, 130-143. https://doi.org/10.1109/wsc.1994.717077 [28] mogford r, guttman j, morrow s, and kopardekar p. (1995) the complexity construct in air traffic control: a review and synthesis of the literature, federal aviation administration. [29] li-na s, li z, lei z. (2015) the sector capacity evaluation considering the controller's workloads. international journal of control and automation, 8: 307-324. https://doi.org/10.14257/ijca.2015.8.7.31 212 https://doi.org/10.1063/5.0060611 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 using modification of prim’s algorithm and gnu octave and to solve the multiperiods installation problem wamiliana1*, mustofa usman1, warsono1, warsito2 and jamal ibrahim daoud3 1department of mathematics, fmipa universitas lampung, bandarlampung, indonesia 2department of physics, fmipa universitas lampung, bandarlampung, indonesia 3department of science in engineering, faulty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. *corresponding author: wamiliana.1963@fmipa.unila.ac.id (received: 19th february 2019; accepted: 28th november 2019; published on-line: 20th january 2020) abstract: the minimum spanning tree (mst) is one of the famous problems that is used mostly as the backbone in many network design problems. given a graph g(v,e), where v is the set of vertices and e is the set of edges connecting vertices in v, and for every edge eij there is an associated weight cij ≥0. the multi period degree constrained minimum spanning tree (mpdcmst) is a problem of finding an mst while also considering the degree constrained on every vertex, and satisfying vertices installation requirement on every period. two algorithms (wwm1 and wwm2) are proposed for solving this problem. gnu octave is used for coding and visualization. gnu is a recursive acronym for "gnu's not unix!", and that name is chosen because it is like unix but differs from unix because it is free and contains no unix code. those algorithms were implemented using 300 randomly generated problems. moreover, we compare wwm1 and wwm2 algorithms using existing data from the literature and the results show that wwm2 is the best. abstrak: minimum spanning tree (mst) merupakan salah satu masalah mahsyur yang banyak digunakan sebagai tulang belakang kepada masalah banyak rekaan jaringan. menerusi graf g(v,e), di mana v adalah himpunan titik dan e adalah himpunan garis yang menghubungkan titik-titik dalam v, dan bagi setiap garis eij terdapat berat berhubung cij ≥0, multi-period degree constrained minimum spanning tree (mpdcmst) merupakan masalah dalam menentukan mst, pada masa sama turut menimbangkan kekangan pada setiap titik vertek, dan memenuhi syarat keperluan pemasangan pada setiap detik. dua algoritma (wwm1 dan wwm2) dicadangkan bagi menyelesaikan masalah ini. gnu octave digunakan bagi pengaturcaraan dan visualisasi. gnu merupakan suatu singkatan kepada “gnu's not unix”, dan nama tersebut dipilih karena ianya seperti unix, tetapi berbeza dari unix kerana ia percuma dan tidak mempunyai kod unix. algoritma tersebut dilaksana dengan menggunakan 300 masalah terhasil secara rawak. tambahan, algoritma wwm1 dan wwm2 dibandingkan dengan kajian terdahulu dan hasil kajian menunjukkan wwm2 adalah terbaik. keywords: multi-period; degree constrained; minimum spanning tree; prims’ algorithms; gnu octave 1. introduction in most network design problems, the minimum spanning tree (mst) is usually used as the backbone. if we add degree restriction on the vertices (can represent cities, 100 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 stations, etc.) of the graph (represents the network), the problem becomes a degree constrained minimum spanning tree (dcmst) problem. moreover, if we restrict and divide the stages or periods of the network’s installation, the problem emerges as a multi period degree constrained minimum spanning tree (mpdcmst) problem. the later constraint usually occurs because of the fund limitation for installing (connecting) the network. this problem arises when we want to design a network that requires that every vertex (node) restricts the number of connections/interfaces whilst also considering a set of vertices that have to be connected/ installed in a certain period due to the fund restriction (weather, etc.) in this paper, we organize the discussion as follows: in section, 2 we give the history of the problem; in section 3, we discuss how to apply the algorithms developed using gnu octave and implement them; in section 4, we discuss the results; followed by a conclusion. 2. the constrained minimum spanning tree problem it because of its specific structure and use in many network design problems, the minimum spanning tree problem has been studied extensively and a variety of fast algorithms have been developed. an efficient and fast minimum spanning tree algorithm that requires computational time nearly linear in the number of edges had been developed [1]. the mst problem is one of the classical problems where the objective is to construct a minimum cost/weight network. this problem usually arises in network design applications that must satisfy other graph parameters such as: degree, distance, diameter, connectivity, flow, etc. for instance, in a transportation network, a distance restriction on the flow commodities could represent the maximum distance allowed for delivery. the degree constrained minimum spanning tree (dcmst) problem is a minimum spanning tree with a degree restriction on every vertex. this problem arises when designing networks where the degree restriction represents the number of allowable links on that vertex, i.e. the handling capacity of each of the vertices imposes a restriction on the number of edges (or wires/roads) that can be connected to a vertex. for example, the application of the dcmst is present in designing the road system, where the set of roads must connect a collection of suburbs/towns, but there is a restriction that no more than a certain number of roads (example: four roads) are allowed to meet at an intersection. there are lots of investigations regarding the dcmst problem. this problem is considered to be an np-complete problem. an np-complete problem is any of a class of computational problems for which no efficient solution algorithm has been found. because of its np-completeness [2], heuristic methods have dominated such as: the greedy algorithm based on prim’s and kruskal’s algorithm by [3], the genetic algorithm by zhou and gen[4], the iterative refinement by deo and kumar [5], the simulated annealing by krishnamoorthy et al [6], the modified penalty by wamiliana [7], and the tabu search by caccetta and wamiliana [8], wamiliana and caccetta [9-10]. in real situations, connecting all components in a network requires a certain time and process in order to be completed. the time of completion can vary depending on the need and priority of the network itself. the multi period degree constrained minimum spanning tree (mpdcmst) problem was introduced in 2002 by kawatra [11] and it proposed the hybrid of branch exchange and lagrangean relaxation method to solve the problem on directed graph with vertex order ranging from 40 to 100. by modifying the problem in using the undirected graph, some algorithms based on kruskal’s and prim’s 101 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 algorithms were developed. wadr1 and wadr2 algorithms were developed by doing some modifications on kruskal’s algorithm [12], while wadr3 and wadr4 are the algorithms developed as varians of wadr1 and wadr2 [13]. motivated by the connectivity property on the process of finding mst by prim’s algorithm, some algorithms were developed by wamiliana et al. [14-16]. wamiliana et al. [17] illustrated why the quality of the solution also depends on the number of vertices in hvti (the set of vertices that must be installed/connected in ith period or before). the comparison of some algorithms developed and implemented on undirected graphs was given in wamiliana et al [18] especially on the process of installation/connection of vertices in hvti. 3. gnu octave, mpdcmst and implementation 3.1 gnu octave gnu octave is a free software that runs on gnu/linux, macos, bsd, and windows. this software originally was intended as a companion to a chemical reactor design course, but the one who first developed it is john w. eaton [19]. since this is free software, users are encouraged to modify and develop this software and are free to distribute it as well. the difference in using gnu octave as opposed to other language programming (such as java), is that gnu octave is more rigid. certain rules must be followed (such as converting to matrix form or others). java is more flexible to development of the program. for example, the data used for implementation represent the edges of the complete graph for certain vertex orders. for vertex order 10, the number of edges is 45, which is obtained from the formula n(e) = , n =10. before putting in gnu octave, we have to modify this equation to be . this is a quadratic equation and to find n, is used. thus, to read the data, the source code for reading the data (vertex order) is as follows ( let n(e) = un): function vertex = check_vertex(matrix) bykedge=length(matrix);%bykedge=un c=2*bykedge; n=(1+sqrt(1+(4*c)))/2; vertex=n; end in gnu octave, the graph was represented using a matrix, therefore a source code was designed so that when a problem is entered as a data problem, then the program would automatically detect the data and arrange it as two matrices, one as the matrix for original vertices (x) and the other for terminal vertices (y). for example, if the data of a complete graph with order ten (consists of 45 edges) is entered, then the program automatically defines x and y as follows: x = 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 4 4 4 4 4 4 5 5 5 5 5 6 6 6 6 7 7 7 8 8 9 y = 2 3 4 5 6 7 8 9 10 3 4 5 6 7 8 9 10 4 102 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 after the x and y are generated, the value of the weight will be put to connect x and y in the form of a symmetrical matrix k, as follows (example for datafile 10.dat): for implementation, the same data used as in [12, 14, 16]. the data are generated randomly with the edge weight varying from 1 to 1000. for every vertex order, 30 problems were generated. 3.2 wwm1 and wwm2 algorithms we developed two algorithms to solve the mpdcmst based on prim’s algorithm and modified them to satisfy the given constraints. the reason for choosing prim’s algorithm was that prim’s maintains the connectivity property during the connection/installation process. in these algorithms, we used the terminologies hvti as the set of vertices that must be installed/connected on ith period or before, and maxvti as the maximum number of vertices that can be connected on the ith period. the reason for using hvti was that in reality, it is possible to add some requirements that some components in the network be connected early due to public needs or other reasons. for example, in designing a fresh water pipe or electricity network, there is a requirement that some buildings (hospitals, police stations, government buildings, etc.) must be installed/connected within a certain period or earlier in the network. 3.2.1 wwm1 algorithm the wwm1 algorithm starts by setting vertex 1 as the root and puts it in set v. v is the set of vertices in the network. initially, v only contains vertex 1 as the central vertex, v ={1}, and no edges in t, t ={}. then, the algorithm checks the nearest vertices in hvti to be connected/installed in v and the corresponding edges to the network (t). the algorithm will continue connecting/installing those vertices in hvti as long as the connection neither violates the degree restriction nor constitutes a cycle. if degree violation occurs, then edge exchange will be performed while also maintaining the connectivity of vertices in hvti. next, the algorithm will check the maxvti, and connect the edges with the smallest edge weight to t, as long as the connection neither violates the degree constraint nor constitutes a cycle. if the number of vertices connected on that period is already the same as maxvti, the algorithm will continue to the next period, and the process is similar to the previous period until all vertices are connected/installed. to illustrate the wwm1 algorithm we used one problem with vertex 5 6 7 8 9 10 5 6 7 8 9 10 6 7 8 9 10 7 8 9 10 8 9 10 9 10 10 103 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 order 10 in the data (datafile.22 dat). the weight of the problem is given in table 1. the data represents a complete graph of order 10, and the graph is illustrated in the fig. 1. moreover, we use the same set of hvti as in [12-17] as given in table 2, and also use maxvti as the floor function of , . table 1: datafile.22.dat (graph with order 10) edge e12 e13 e14 e15 e16 e17 e18 e19 e1,10 e23 e24 e25 e26 e27 e28 weight 740 572 447 835 427 807 362 832 120 221 109 276 741 978 352 edge e29 e2,10 e34 e35 e36 e37 e38 e39 e3,10 e45 e46 e47 e48 e49 e4,10 weight 368 403 505 921 757 884 369 886 545 639 253 750 251 187 857 edge e56 e57 e58 e59 e5,10 e67 e68 e69 e6,10 e78 e79 e7,10 e89 e8,10 e9,10 weight 807 926 781 605 112 559 411 473 743 882 693 851 509 434 828 fig. 1: the graph of datafile.22.dat. table 2: element of hvti for every period n hvt1 hvt2 hvt3 10 2 3 4 20 2 3 4 30 2,3 4,5 6,7 40 2,3,4 5,6,7 8,9,10 50 2,3,4,5 6,7,8,9 10,11,12,13 60 2,3,4,5,6 7,8,9,10,11 12,13,14,15 70 2,3,4,5,6,7 8,9,10,11,12,13 14,15,16,17,18,19 80 2,3,4,5,6,7,8 9,10,11,12,13,14,15 16,17,18,19,20,21,22 90 2,3,4,5,6,7,8 9,10,11,12,13,14,15 16,17,18,19,20,21,22 100 2,3,4,5,6,7,8,9 10,11,12,13,14,15,16,17 18,19,20,21,22,23,24,25 for the first period, the algorithm checks the vertices in hvt1= {2}. vertex 2 is the only vertex in hvt1 then the algorithm connects vertex 2 to t using edge e12 with weight 740. v and t are updated to v= {1,2} and t ={e1-2}. next, the algorithm checks the difference of maxvt1 = = 3 and the number of vertices in hvt1. hvt1 is the number of vertices in hvt1, hvt1 =1. since the difference of maxvt1 and hvt1 is 2, then it is possible to add two more vertices. therefore, the algorithm searches for the next smallest edge with the vertices in the network which is e2-4 with weight 109. adding e2-4 to 104 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 t neither creates a cycle on t nor violates degree restriction on the vertices in v. then, e24 is added to t and vertex 4 to v. v and t are again updated to v= {1,2,4} and t = {e1-2, e2-4}. since vertex 4 was already added to v, then only one more vertex can be added, and e1-10 is the next smallest edge with weight 120. adding e1-10 neither creates a cycle in t nor violates degree restriction on vertices in v. therefore e1-10 was added to t and vertex 10 to v. v and t are updated to v= {1,2,4,10} and t = {e1-2, e2-4, e1-10}. since maxvt1 is achieved, the first period is finished. the following figure shows the network after the first period is finished. fig. 2: the network after the first period of wwm1 algorithm is done. on the second period, hvt2 ={3}, therefore the algorithm connects vertex 3 to the network using the smallest edge of incidence with vertex 3; edge e2-3 is the smallest. adding e2-3 to t neither violates the degree condition nor constitutes a cycle, therefore e2-3 is added to t and vertex 3 to v. v and t are updated to v= {1,2,4,10,3} and t = {e1-2, e24, e1-10, e2-3}. then, the algorithm checks maxvt2 hvt2 which is 2. therefore, in this period, we can add two more edges to t and two more vertices in v. the next smallest edge of incidence with the vertices in v is e5-10 with a weight of 112. adding e510 to t neither violates the degree condition nor constitutes a cycle, therefore e5-10 is added to t and vertex 5 to v. v and t are updated to v= {1,2,4,10,3,5} and t = {e1-2, e2-4, e1-10, e2-3, e5-10}. next, the algorithm searches the smallest edge of incidence with the vertices in v which is e4-9 with a weight of 187. adding e4-9 to t neither violates the degree condition nor constitutes a cycle, therefore e4-9 is added to t and vertex 9 to v. v and t are updated to v= {1,2,4,10,3,5,9} and t = {e1-2, e2-4, e1-10, e2-3, e5-10, e4-9 }. this is the end of the second period, and the network is illustrated in fig. 3. fig. 3: the network after the second period of wwm1 algorithm is done. now, there are seven vertices already in the network, which are vertex 1, 2, 10, 4, 3, 5, and 9; and there are three more vertices that need to be connected. those vertices are vertex 6, 7, and 8. please note here that vertex is 4 already in the network (installed on the 105 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 first period). after the second period was done, vertex 3 (the member of vertices in hvt2) was in the network, as well as vertex 4 (an element in hvt3). therefore, the algorithm is just searching for the smallest edges of incidence to the uninstalled vertices and to connect them to the network. three edges that satisfy that condition and also neither create a cycle nor violate the degree condition (maximum degree is 3 for every vertex) are e4-8, e6-8, e6-7 with weight 251, 411, and 559 respectively. v and t are updated to v= {1,2,4,10,3,5,9,8,6,7} and t = {e1-2, e2-4, e1-10, e2-3, e5-10, e4-9, e4-8, e6-8, e6-7}. all vertices are then in set v, so the algorithm stops. figure 4 represents the network when the third period is finished. fig. 4: the network when the third period is finished. table 3 gives the information about the period when the edges are installed/connected, the weight, and the total weight after the connection are done. table 3: the period when the vertices were connected in wwm1 algorithm period from vertex to vertex weight 1 1 2 740 1 1 10 120 1 2 4 109 2 2 3 221 2 10 5 112 2 4 9 187 3 4 8 251 3 8 6 411 3 6 7 559 total 2710 3.2.2 wwm2 algorithm the wwm2 algorithm is similar with the wwm1 algorithm, except in the wwm2, the process of connecting the vertices in hvti is more flexible. those vertices in hvti 106 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 can be installed in the beginning of the period or at the end, as long as the installation/connection process is still within that period or before. in the first period of the wwm2 algorithm, vertex 2 is not installed first, but the algorithm searches for possible smallest edges among those in the data that connect to vertex 1. this is possible because maxvt1 = 3 and the number of hvt1 = hvt1 =1 (only consist of vertex 2). therefore, it is possible to add two more vertices (but not vertex 2) in the network. therefore vertex (node) 10 was connected first, followed by vertex 5, and finally, because vertex 2 must be installed/connected in the first period, then vertex 2 is installed. figure 5 shows the network after the first period of the wwm2 algorithm is done. fig. 5: the network after the first period of wwm2 algorithm is done. for the second period of the wwm2 algorithm, the vertex in hvt2 is vertex 3. however, the algorithm first checks the difference between maxvt2 and the number of hvt2. since maxvt2 hvt2 = 2, then it is possible to add the other two vertices (besides vertex 3). however, if vertex 3’s incidence with the smallest edge that connected with the vertices already in the network during the first period, then vertex 3 will be installed/connected first on the second period (of course, without violating the degree requirement on the vertices that are already in the network). since the smallest edge on the second period is edge e24 then that edge is connected first on the second period, followed by edge e49. after edge e49 was added in the network, then there are no more choices except adding the smallest edge of incidence with vertex 3, because vertex 3 must be installed/connected on the second period or before. figure 6 shows the network after the second period of the wwm2 algorithm is done. similar with the wwm1 algorithm, on the third period of the wwm2 there are 7 vertices already in the network and there are three more vertices still uninstalled. those vertices are vertex 6, 7, and 8. the difference between wwm1 and wwm2 is that vertex 4 in wwm1 is installed/connected on the first period, while in wwm2, vertex 4 is connected on the second period. the next three smallest are e48, e28, and e210. there are no degree restrictions and cycle occurrences by adding e48, therefore vertex 8 is connected. however, there is a problem with adding e28. the degree of vertex 2 is already 3, then adding e28 will violate the degree restriction, therefore e28 is omitted, and not connected. a different reason is applied to e210. adding e210 will create a cycle, therefore e210 is also omitted. now, the algorithm is just searching for the next two smallest edges of incidence to the uninstalled vertices to connect them to the network (as long as the connection neither violates the degree restriction nor creates a cycle). the next two smallest are e68 and e67. figure 7 shows the network after the third period is finished. 107 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 fig. 6: the network after the second period of wwm2 algorithm is done. fig. 7: the network after the second period of wwm2 algorithm is done. table 4: the period when the vertices were connected in the wwm2 algorithm period from vertex to vertex weight 1 1 10 120 1 10 5 112 1 5 2 276 2 2 4 109 2 4 9 187 2 2 3 221 3 4 8 251 3 8 6 411 3 6 7 559 total 2246 table 4 gives the information about the period when the edges are installed/connected, the weight, and the total weight after the wwm2 algorithm finishes the process. 108 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 4. results and discussion the wwwm1 and wwm2 algorithms were compared against wadr5, wac1 and wac2 algorithms because those three algorithms are developed based on the same algorithm (prim’s algorithm). moreover, those algorithms were implemented using the same data, same set of hvti,, maxvti and the number of periods. the data used for implementation was random problems generated using uniform distribution with weight ranging from 1 to 1000 (integer). for every vertex order, there are 30 problems generated and the vertex order used are 10 to 100 in increments of 10. therefore, there are a total of 300 problems implemented. the solution taken is the average solution from 30 problems for every vertex order. the following table shows the result: table 5: the comparative solutions vertex order mst dcmst wwm1 wwm2 wadr5 wac1 wac2 10 1129.43 1178.8 1498.6 1286.6 1341.93 1495.1 1359.93 20 1196.1 1299 1804.97 1428.57 1557.63 1790.37 1437.5 30 1177.43 1319.53 2039.97 1490.03 1755.40 2018.9 1516.43 40 1151.23 1286.3 2117.1 1440.03 1719.27 2079.73 1455.3 50 1223.43 1356.47 2427.27 1566.6 1844.10 2381 1603.7 60 1175.57 1320.73 2389.87 1573.57 1851.20 2364.4 1639.53 70 1242.1 1410.03 2558.5 1612.27 1963.83 2520.2 1671.9 80 1236.83 1410.23 2579.4 1675.2 1942.40 2547.8 1722.23 90 1248 1404.93 2618.43 1613.23 1941.33 2588.07 1649.33 100 1234.1 1370.8 2564.07 1567.53 1992.40 2535.2 1597.63 average 1201.42 1335.68 2259.82 1525.36 1790.95 2232.08 1565.35 from table 5 we can see the average solutions for mst, dcmst, wwm1, wwm2, wadr5, wac1, and wac2. for the algorithms developed for solving mpdcmst (wwm1, wwm2, wadr5, wac1, and wac2) the best performance is gained by the wwm2 algorithm, which is slightly close to the performance of wac2, while the wwm1 and wac1 are the two worse algorithms compared in this study. wwm1 and wac1 are two algorithms developed based on the modified prim’s algorithm where the priority vertices in the set hvti must be installed/connected as soon as possible, while wwm2 is a modification of wwm1, and wac2 is a modification of wac1. the modification made for those two algorithms is the same: relaxing the process of connecting the priority vertices in hvti whilst also maintaining those vertices to be connected in the ith period or before. wadr5 is an algorithm developed based on modified prim’s algorithm where the algorithm searches two smallest edges for being considered to be connected in the network, except the last one in the period. in this study, we compared the ratio of the algorithms (wwm1, wwm2, wadr5, wac1, and wac2) against their lower bound (dcmst). the ratio is lb lbh , where h is the heuristic (algorithm) and lb is the lower bound (dcmst). table 6 below shows the ratio of lb lbh . 109 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 table 6: the value of ratio lb lbh of the algorithms against the lower bound vertex order mst dcmst wwm1 wwm2 wadr5 wac1 wac2 10 1129.43 1178.8 1498.6 1286.6 1341.93 1495.1 1359.93 27.129% 9.145% 13.839% 26.832% 15.366% 20 1196.1 1299 1804.97 1428.57 1557.63 1790.37 1437.5 38.950% 9.974% 19.910% 37.827% 10.662% 30 1177.43 1319.53 2039.97 1490.03 1755.40 2018.9 1516.43 54.598% 12.921% 33.032% 53.001% 14.922% 40 1151.23 1286.3 2117.1 1440.03 1719.27 2079.73 1455.3 64.588% 11.952% 33.660% 61.683% 13.138% 50 1223.43 1356.47 2427.27 1566.6 1844.10 2381 1603.7 78.940% 15.491% 35.949% 75.530% 18.226% 60 1175.57 1320.73 2389.87 1573.57 1851.20 2364.4 1639.53 80.950% 19.143% 40.165% 79.022% 24.138% 70 1242.1 1410.03 2558.5 1612.27 1963.83 2520.2 1671.9 81.450% 14.342% 39.276% 78.733% 18.572% 80 1236.83 1410.23 2579.4 1675.2 1942.40 2547.8 1722.23 82.906% 18.789% 37.736% 80.665% 22.124% 90 1248 1404.93 2618.43 1613.23 1941.33 2588.07 1649.33 86.374% 14.826% 38.180% 84.213% 17.396% 100 1234.1 1370.8 2564.07 1567.53 1992.40 2535.2 1597.63 87.049% 14.352% 45.346% 84.943% 16.548% average 68.293% 14.094% 33.709% 66.245% 17.109% from table 6 we see that average ratio of the wwm1 and wac1 algorithms against the lower bound are above 50%. these values show that the performance of the algorithm is not good. the performance of wwm2 and wac2 are below 20%, while the ratio of wadr5 is around 34%. the smaller the value of the ratio, the better the performance. the closer the solution of the algorithm to the solution of the dcmst, the better the algorithm. figure 8 shows the performance of the algorithm. fig. 8: performance of wwm1, wwm2, wadr5, wac1, and wac2 algorithms. 5. conclusions from the results and discussion we can see that among wwm1, wwm2, wadr5, wac1, and wac2 algorithms, wwm2 performs the best, followed by wac2 algorithm. these two algorithms have similar approaches: relaxing the time of installation for vertices in hvti or adding flexibility to the algorithm. accepting flexibility in the process of connecting/installing the vertices without violating the rules gives a better solution rather than sticking with the schedule of connecting the vertices in a certain order. 0 500 1000 1500 2000 2500 3000 20 30 40 50 60 70 80 90 100 so lu tio n vertex order performance of some algorithms for the mpdcmst mst dcmst wwm1 wwm2 wadr5 wac1 wac2 110 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 acknowledgement this research work was supported by research grant no: 582/ un26.21/ku/2017. the authors would also like to acknowledge the contributions and financial support from the directorate general of higher education, ministry of research, technology and higher education, republic of indonesia. references [1] gabow h.n and r.e. tarjan.(1984) efficient algorithms for a family of matroid intersection problems. journal of algorithms, 5:80-131. [2] garey, m.r.,and johnson, d.s.(1979) computers and intractibility, a guide to the theory of np-completeness. freemann, san francisco. [3] narula, s.c., and c. a.ho.(1980) degree-constrained minimum spanning tree. computer and operation research, 7:239-249. [4] krishnamoorthy, m.,a.t. ernst and y. m sharaila.(2001) comparison of algorithms for the degree constrained minimum spanning tree. journal of heuristics, 7(6): 587-611. [5] deo n. and n. kumar.(1997) computation of constrained spanning trees: a unified approach. network optimization ( lecture notes in economics and mathematical systems. editor : panos m. pardalos, et al. ,springer-verlag, berlin, germany: 194 – 220. [6] zhou, g. and m gen. (1997) a note on genetics algorithms for degreeconstrained spanning tree problems. networks, vol. 30: 91 – 95. [7] wamiliana. (2004) solving the degree constrained minimum spanning tree using tabu and penalty method. jurnal teknik industri:1-9. [8] caccetta l. and wamiliana.(2001) heuristics algorithms for the degree constrained minimum spanning tree problems.proceeding of the international congress on modelling and simulation (modsim),canberra, editors: f. ghassemi et.al:2161-2166. [9] wamiliana and l. caccetta. (2003)tabu search based heuristics for the degree constrained minimum spanning tree problem.proceeding of south east asia mathematical society:133-140. [10] wamiliana and l. caccetta.(2012) the modified cw1 algorithm for the degree restricted minimum spanning tree problem, proceeding of international conference on engineering and technology development, bandarlampung 20-21 june:36-39. [11] kawatra r. (2002)a multi period degree constrained minimum spanning tree problem, european journal of operational research,143: 53 – 63. [12] [wamiliana, d. sakethi, and r. yuniarti,(2010) computational aspect of wadr1 and wadr2 algorithms for the multi period degree constrained minimum spanning tree problem. proceeding snmap, bandar lampung 8 – 9 december:208 – 214. [13] wamiliana, amanto, and m. usman.(2013) comparative analysis for the multi period degree constrained minimum spanning tree problem. proceeding the international conference on engineering and technology development (icetd):39 – 43. [14] ]wamiliana, f. a.m. elfaki, m. usman, and m. azram. (2015) some greedy based algorithms for multi periods degree constrained minimum spanning tree problem. arpn journal of engineering and applied sciences, 2015: 10 (21): 10147 – 10152. [15] wamiliana, m. usman, d. sakethi, r. yuniarti, and a. cucus.(2015) the hybrid of depth first search technique and kruskal’s algorithm for solving the multiperiod degree constrained minimum spanning tree problem. the 4th international conference on interactive digital media (icidm). ieee explore, dec 2015 [16] wamiliana, asmiati, m. usman, a. hijriani, and w. c. hastono. (2018) comparative analysis of some modified prim’s algorithms to solve the multiperiod degree constrained minimum spanning tree problem. indian journal of science and technology,11(11):1-6. 111 iium engineering journal, vol. 21, no. 1, 2020 wamiliana et al. https://doi.org/10.31436/iiumej.v21i1.1088 [17] wamiliana, warsono, asmiati, a. hijriani, and w. c. hastono.(2018) different time installation effect on the quality of the solution for the multiperiod installation problem using modified prim’s algorithm. far east journal of electronics and communications, 18(2): 291-300. [18] gnu octave. available: https://www.gnu.org/software/octave. 112 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 pavement condition analysis via vehicle mounted accelerometer data ahmad jazlan1*, muhammad fahim rosli1, noor hazrin hany mohamad hanif1, hasan firdaus mohd zaki1, muhammad afif husman1, asan gani abdul muthalif2 and deepak kumar3 1smart structures, system and control research lab s3crl, department of mechatronics engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. 2department of mechanical and industrial engineering, college of engineering, qatar university, p.o. box: 2713 doha, qatar. 3school department of electrical engineering, motilal nehru national institute of technology, allahabad, 211004, india. *corresponding author: ahmadjazlan@iium.edu.my (received: 26th august 2019; accepted: 27th november 2019; published on-line: 20th january 2020) abstract: road anomalies and irregularities such as potholes and uneven surfaces are a common hazard in south east asia and developing countries. such hazards pose a threat to the safety and well-being of both civilians going about their daily routine and tourists who are exploring the city. since bicycles and rickshaws are still a common mode of transport used by both civilians and tourists in many south east asian countries, it is essential to improve the overall quality and smoothness of pavements which are traversed by these vehicles. management of international sporting and recreational events also require satisfactory road and pavement conditions. before pavement conditions can be improved, it is an essential prerequisite to obtain comprehensive information about road irregularities such as the location and also severity of the road irregularity (depth of the potholes and height of bumps). in this paper, we propose a method for obtaining mathematical models that represent the overall condition of the pavements that are part of a commonly traversed cycling route. such mathematical models and coefficients can be stored in the cloud of an internet of things (iot) data analytics systems subsequently leading to identification of regions with severe road irregularities. abstrak: kerosakan pada permukaan jalan raya merupakan salah satu faktor risiko kemalangan yang berlaku secara meluas di negara asia tenggara dan negara membangun yang lain. memandangkan kenderaan seperti beca dan basikal masih diguna pakai secara meluas di negara membangun, adalah mustahak untuk membaik pulih kerosakan jalan raya. pengurusan sukan antarabangsa dan rekreasi juga memerlukan keadaan jalan dan laluan pejalan kaki yang baik. sebelum kerja membaik pulih dapat dilakukan, maklumat lengkap mengenai tahap kerosakan jalan raya dan lokasi kerosakan diperlukan. dalam kajian ini satu kaedah telah diperkenalkan untuk mendapatkan persamaan matematik yang menggambarkan keadaan sebenar permukaan jalan raya, di mana sebahagiannya merupakan laluan berbasikal yang selalu digunakan. model matematik dan pekali ini boleh di simpan dalam sistem analisis data awan internet benda (iot) kemudiannya dapat mengenal pasti kawasan jalan yang rosak dan tidak rata. 73 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 keywords: road quality monitoring; accelerometer; vibrations; envelope detection 1. introduction cycling is increasingly becoming a preferred means of transport in developing countries due to the awareness of the benefits of daily physical activity and also the awareness of the importance of environmental preservation. in kuala lumpur, dedicated cycling lanes have been recently constructed to cater to the increasing number of malaysian cyclists. dedicated cycling lanes are a norm in developed countries such as australia, the uk, and many parts of europe. ensuring the smoothness and quality of the roads and pavements is essential for the ride comfort and safety of cyclists and even pedestrians. uneven surfaces and road irregularities may lead to trips and falls, thus endangering both cyclists and pedestrians alike. before the local city council utilizes materials, resources and manpower to repair uneven and irregular road surfaces, it is essential to obtain an overall representation of the condition of the pavements or roads in order to devise and optimal strategy for repair works that efficiently utilize existing resources and manpower. in this paper, we develop mathematical models that represent the overall condition of a pavement by utilizing vertical z-axis accelerometer data that have been collected by a sensor package mounted onto the handle of a bicycle. the z-axis accelerometer data corresponds to vertical vibration of the bicycle, which directly corresponds to the condition of the road. a sensor package consisting of a combination of an adxl 335 mems accelerometer, an arduino nano microcontroller, and an sd card (for data storage) are mounted onto a bicycle and the subsequent accelerometer data, reflecting the condition of the pavement, are collected and stored in the sd card for further offline data processing and analysis. mathematical models that describe the condition of the pavement can then be obtained. the location of the pavement irregularity can be estimated with a mathematical model that represents the pavement condition and also takes into consideration the sampling rate used for the accelerometer measurements together with the distance traversed and time taken to reach the destination. 2. existing work existing work regarding road quality analysis utilizing accelerometer data have focused primarily on the road quality analysis of larger roads such as highways. therefore, in our study, in order to address the current research gap, we have chosen to analyse the road quality of pavements meant for cyclists and pedestrians that cannot be traversed by larger vehicles such as cars and trucks. nevertheless we describe herewith recent work on road quality analysis to equip the reader with some background knowledge about the current state of the art. chenglong et al. developed a system to calculate the international roughness index (iri) in real time based on road quality information collected from wireless accelerometer data and also vehicle position information collected from gps data [1]. zigbee and 3g based wireless communication was utilized to transfer information collected from the accelerometers and gps to a central computer. field tests conducted in selected locations in zheijang demonstrated the feasibility of the proposed system to deliver real-time road quality information. 74 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 xiao li and goldberg described the usage of citizen sensing or mobile crowd sensing in which the public can utilize their smartphones, which have a variety of sensors, in order to collect data in the form of spatial series of the geo-referenced z-axis accelerations of the road surface [2]. the collected data was then used to compute two novel assessment indexes that represent the road quality. harikrishnan and gopi proposed a method to monitor road surfaces, detect potholes and humps, and predict severity by analysing the vertical vibration signals obtained as the vehicle moved along a particular road [3]. the inbuilt accelerometer inside the smartphone is used to capture the vehicle vibrations in which the z-axis reading corresponds to the vehicle vertical vibrations. a gaussian model-based mining algorithm has been proposed for detecting road abnormalities. the x-z ratio filtering had been applied for event classifying and discriminating potholes and humps. a severity estimation algorithm has been proposed that utilized the relation between vertical acceleration and relative vertical displacement of the vehicle. wickramarathne, garg and bauer had developed a simplified approach towards characterizing road surface conditions from vertical acceleration measurements based on a signal transmission model that captures the complete system dynamics of the vehicle suspension system [4]. mukherjee and majhi had demonstrated the feasibility of using smartphones placed inside the vehicles in characterisation of road bumps. however, they highlighted that the smartphone’s capability of discerning different types of speed bumps while travelling in heterogeneous vehicles is still an open problem [5]. 3. main work the block diagram of the proposed methodology is shown in fig. 1. firstly, vibration signals that reflect the condition of the pavement are collected using a combination of an accelerometer, microcontroller, and sd card that have been mounted onto a bicycle. alternatively, a portable data acquisition device (daq), such as the ni-6008/6009 by national instruments, together with a laptop could also have been used to record vibration signals from the output of the adxl 335 accelerometer with a superior sampling rate. however, at this stage of the study, we desired to have a small, light, portable, and detachable package for measuring the vibration signals that reflect the condition of the pavement. 3.1 data acquisition 3.1.1 accelerometer sensor package for this system, we have developed an accelerometer sensor package that consists of an adxl 335 microelectromechanical systems (mems) accelerometer, an arduino nano microcontroller, a micro sd card that is used together with an spi icsp micro sd card adapter for data storage, and a 9v rechargeable battery for power supply, as shown in fig. 2. the adxl 335 is a tri-axial accelerometer which is capable of measuring vibrations along the x, y, and z axes. this combination of components were selected to ensure that the package is small, light, and can be easily fitted onto the handlebar, frame, or any other suitable position on the bicycle that can effectively capture the vibrations generated as the bicycle travels on both smooth and bumpy pavements. in this experiment, the bicycle speed will be monitored using an app installed on a smartphone. figure 2 shows the accelerometer sensor package together with its components whereas fig. 3 shows the placement of the asp and smartphone on the handlebar of the bicycle. 75 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 although the adxl 335 mems accelerometer is capable of measuring vibrations along the x, y, and z axes, in this study we are primarily concerned with the vibrations generated along the z axis since the vibrations recorded along the z axis correspond to vertical vibrations of the bicycle as the bicycle is traveling along the pavement which corresponds to the degree of smoothness of the pavement. the sampling rate of the arduino nano microcontroller is set at 50 samples per second. this selected sampling rate adheres to the nyquist criteria in order to prevent signal aliasing. 76 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 fig. 1: block diagram of the proposed methodology for pavement condition monitoring. fig. 2: accelerometer sensor package. fig. 3: accelerometer sensor package and smartphone placement on bicycle handlebar. 3.1.2 vibration data collection in this study, pavements located on two separate cycling routes were chosen for the vibration data measurement and analysis. the first cycling route consists of a smooth pavement, as shown in fig. 4 (left), whereas the second cycling route consists of an uneven pavement with irregularities due to branching roots from a nearby tree, as shown in fig. 4 (right). the distance travelled by the bicycle on both routes was set to 50 meters. the width of the road was 1.5 meters. in this study, we are primarily concerned with the acceleration data recorded along the vertical z axis since this data best reflects the pavement condition. accelerometer data 77 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 from the x and y coordinates are discarded in this study. during the bicycle ride in each region, the speed of the bicycle was fixed at 5km/h and the distance travelled was 45 meters. an app installed on the smartphone was used to keep track of the speed of the bicycle and also of the distanced travelled by the cyclist. fig. 5 shows the pavement that has been divided into 10 regions. each region will be traversed by the bicycle and data corresponding to the overall pavement condition in each region has been collected. fig. 4: smooth pavement (left) and uneven pavement with irregularities (right). fig. 5: division of pavement into 10 regions which will be traversed by the bicycle. 3.2 signal processing in order to extract meaningful information regarding the condition of the pavement in each of these 10 regions traversed by the bicycle from the accelerometer data, the raw accelerometer data needs to be processed in order to reveal the presence of significant irregularities on the pavement such as potholes and bumps and also the severity of the irregularity. for example deeper potholes or higher bumps on the pavement will result in higher amplitudes of the accelerometer data collected. this is one of the advantages of analyzing the condition of the pavement with accelerometer data compared to computer vision based methods. computer vision based methods are able to accurately detect the location of a road anomaly whatever the depth or severity but the irregularity cannot be fully captured and analyzed using computer vision based methods alone [6-10]. 78 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 3.2.1 envelope detection the accelerometer data collected from each of the regions (region 1 to region 10) reflects the condition of the pavement, as shown in fig. 6 to fig. 10. all the raw data have been full wave rectified to eliminate all the negative values in the results. in this paper an envelope detection method that consists of a combination of calculating the absolute value of the raw accelerometer data (full wave rectification) combined with low pass filtering with a very low cut off frequency is implemented to obtain an envelope of the raw accelerometer data. the amplitude of the enveloped signal is a representation of the severity of the irregularity. a low pass filter was designed in order to complete the envelope detector design. figure 11 shows the magnitude response for a 51st order fir low pass filter with a cut off frequency of 13 hz that was used for the envelope detection method and was designed using the matlab filter design toolbox. 3.2.2 offset correction before envelope detection is performed, another preprocessing method known as offset correction is required. offset correction is required since the accelerometer is highly sensitive even to minute variations in the evenness of the pavement, which are insignificant to our analysis and do not correspond to significant irregularities of the pavement such as bumps and potholes. therefore, baseline accelerometer measurements are required. baseline measurements are obtained by logging accelerometer measurements while the bicycle is travelling on a smooth pavement with no significant irregularities. the accelerometer data obtained by any other accelerometer measurement will then be subtracted with the average of the baseline measurements resulting in offset correction. offset correction ensures that insignificant accelerometer readings that represent minute variations in the pavement are discarded from the analysis of the pavement condition. from test rides conducted on a smooth road, it was found that the highest signal amplitude is 0.2 m/s2. therefore, all collected data will be subtracted by this value resulting in the offset corrected results shown in fig. 12 to fig. 14. the offset corrected data gives a better indication of which parts of the pavement contain significant irregularities such as potholes and bumps. fig. 6: rectified accelerometer data for regions 1-2. fig. 7: rectified accelerometer data for regions 3-4. 79 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 fig. 8: rectified accelerometer data for regions 5-6. fig. 9: rectified accelerometer data for regions 7-8. fig. 10: rectified accelerometer data for regions 9-10. fig. 11: magnitude response of fir low pass filter used for envelope detection. 80 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 fig. 12: offset corrected accelerometer data for regions 1-2. fig. 13: offset corrected accelerometer data for regions 3-4. fig. 14: offset corrected accelerometer data for regions 5-6. 3.2.3 polynomial curve fitting polynomial curve fitting can be utilized in order to obtain a mathematical polynomial model that represents the condition of the pavement at each of the regions from 1 to 10. polynomial curve fitting has been applied to all of the data presented in fig. 6 to fig. 8 resulting in polynomial functions that reflect the condition of the pavement. the polynomial functions that correspond to each of the regions are represented by y1(s) to y10(s) as shown below. y1(s) = 0.00000015s60 · · · − 0.0003s2 + 0.0033s − 0.357 (1) y2(s) = 0.00000021s60 · · · − 0.001s2 + 0.0103s + 0.0274 (2) y3(s) = 0.00000011s60 · · · − 0.0003s2 + 0.0033s + 0.0357 (3) y4(s) = 0.00000001s60 · · · − 0.001s2 + 0.0155s − 0.0363 (4) y5(s) = 0.00000005s60 · · · − 0.0001s2 − 0.0053s + 0.0907 (5) y6(s) = 0.00000003s60 · · · + 0.0009s2 − 0.0134s + 0.1167 (6) y7(s) = 0.00000009s60 · · · + 0.0011s2 − 0.0185s − 0.1516 (7) y8(s) = 0.00000005s60 · · · + −0.0003s2 + 0.0056s + 0.0189 (8) y9(s) = 0.00000004s60 · · · + 0.0018s2 − 0.0287s + 0.1963 (9) y10(s) = 0.00000008s60 · · · + 0.0004s2 + 0.0036s + 0.0455 (10) 81 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 figure 15 shows the rectified and offset corrected accelerometer data from region 5, together with the graph of the polynomial approximation function of this data. from these graphs it becomes apparent that there are three significant irregularities of the road that could be due to uneven surfaces due to branching roots, potholes, or other road/pavement construction factors such as uneven bricks. upon obtaining the polynomial approximation together with prior knowledge of the speed of the bicycle, the sampling rate used for the accelerometer data collection, and the distance of the road, we can determine the location of the irregularity and subsequently manpower and resources can be effectively utilized for the pavement/road repair works. finally, the processed accelerometer data, either by envelope detection or polynomial approximation, can be extrapolated and combined to form a 3d plot that is an overall representation of the condition of the pavement, as shown in fig. 16 and fig. 17. fig. 15: processed accelerometer data indicating 3 pavement irregularities together with corresponding polynomial approximation. fig. 16: 3d plot of pavement condition extrapolated envelope detection data. 82 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 fig. 17: 3d plot of pavement condition extrapolated polynomial approximation data. 4. conclusion in conclusion, a method for obtaining mathematical models that represent the overall pavement conditions has been proposed using bicycle-mounted accelerometer data. the proposed method based on accelerometer data is advantageous compared to image processing methods since the severity of the irregularity can be effectively captured by accelerometers. for future work, the proposed technique can be further extended by placing accelerometer sensor packages on multiple bicycles or vehicles that are traversing the same route. each accelerometer sensor package can be equipped with an antenna to send the collected data to a gateway resulting in a complete internet of things (iot) application. acknowledgement the authors would like to thank the ministry of education malaysia for funding this research project under the fundamental research grant scheme grant no: frgs19057-0665 and frgs16-053-0552 and also the international islamic university malaysia for funding this research under the research initiative grant scheme grant no: rigs17152-0727. references [1] liu c, wu d, du y, li s. (2016) application of vehicle mounted accelerometers to measure pavement roughness. international journal of distributed sensor networks, 12(6):1-8. [2] li x, goldberg dw. (2018) towards a mobile crowdsensing system for road surface assessment. computers, environment and urban systems, 69: 51-62. [3] harikrishnan pm, gopi vp. (2018) vehicle vibration signal processing for road surface monitoring. ieee sensors journal, 17(16): 5192-5197. [4] wickramarathne t, garg v, bauer p. (2018) on the use of 3-d accelerometers for road quality assessment. proceedings of the 2018 ieee 87th vehicular technology conference (vtc spring), porto, pp. 1-5. [5] mukherjee a, majhi s. (2016) characterisation of road bumps using smartphones. european transport research reviews, 8(13):16-20. [6] ryu s-k, kim t, kim y-r. (2015) image-based pothole detection system for its service and road management system. mathematical problems in engineering, 968361, pp. 1-10. 83 iium engineering journal, vol. 21, no. 1, 2020 jazlan et al. https://doi.org/10.31436/iiumej.v21i1.1223 [7] wang p, hu y, dai y, tian m. (2017) asphalt pavement pothole detection and segmentation based on wavelet energy field. mathematical problems in engineering, 1604130, pp. 1-13 [8] fernandez c, fernandez-llorca d, sotelo ma. (2017) a hybrid vision-map method for urban road detection. journal of advanced transportation, 7090549, pp. 1-21. [9] jo y, ryu s. (2015) pothole detection system using a black-box camera. sensors, 15(1): 29316-29331. [10] fernández c, fernández-llorca d, et al. (2012) free space and speed humps detection using lidar and vision for urban autonomous navigation. proceedings of the 2012 ieee intelligent vehicles symposium, pp. 698-703. 84 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <feff005500740069006c0069006300650020006500730074006100200063006f006e0066006900670075007200610063006900f3006e0020007000610072006100200063007200650061007200200064006f00630075006d0065006e0074006f0073002000640065002000410064006f00620065002000500044004600200061006400650063007500610064006f007300200070006100720061002000760069007300750061006c0069007a00610063006900f3006e0020006500200069006d0070007200650073006900f3006e00200064006500200063006f006e006600690061006e007a006100200064006500200064006f00630075006d0065006e0074006f007300200063006f006d00650072006300690061006c00650073002e002000530065002000700075006500640065006e00200061006200720069007200200064006f00630075006d0065006e0074006f00730020005000440046002000630072006500610064006f007300200063006f006e0020004100630072006f006200610074002c002000410064006f00620065002000520065006100640065007200200036002e003000200079002000760065007200730069006f006e0065007300200070006f00730074006500720069006f007200650073002e> /eti <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> /fra <feff005500740069006c006900730065007a00200063006500730020006f007000740069006f006e00730020006100660069006e00200064006500200063007200e900650072002000640065007300200064006f00630075006d0065006e00740073002000410064006f006200650020005000440046002000700072006f00660065007300730069006f006e006e0065006c007300200066006900610062006c0065007300200070006f007500720020006c0061002000760069007300750061006c00690073006100740069006f006e0020006500740020006c00270069006d007000720065007300730069006f006e002e0020004c0065007300200064006f00630075006d0065006e00740073002000500044004600200063007200e900e90073002000700065007500760065006e0074002000ea0074007200650020006f007500760065007200740073002000640061006e00730020004100630072006f006200610074002c002000610069006e00730069002000710075002700410064006f00620065002000520065006100640065007200200036002e0030002000650074002000760065007200730069006f006e007300200075006c007400e90072006900650075007200650073002e> /gre <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> /heb <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> /hrv <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> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <feff004c006900650074006f006a00690065007400200161006f00730020006900650073007400610074012b006a0075006d00750073002c0020006c0061006900200069007a0076006500690064006f00740075002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c0020006b006100730020007000690065006d01130072006f00740069002000640072006f01610061006900200075007a01460113006d0075006d006100200064006f006b0075006d0065006e0074007500200073006b00610074012b01610061006e0061006900200075006e0020006400720075006b010101610061006e00610069002e00200049007a0076006500690064006f0074006f0073002000500044004600200064006f006b0075006d0065006e00740075007300200076006100720020006100740076011300720074002c00200069007a006d0061006e0074006f006a006f0074002000700072006f006700720061006d006d00750020004100630072006f00620061007400200075006e002000410064006f00620065002000520065006100640065007200200036002e003000200076006100690020006a00610075006e0101006b0075002000760065007200730069006a0075002e> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <feff04120438043a043e0440043804410442043e043204430439044204350020044604560020043f043004400430043c043504420440043800200434043b044f0020044104420432043e04400435043d043d044f00200434043e043a0443043c0435043d044204560432002000410064006f006200650020005000440046002c0020043f044004380437043d043004470435043d0438044500200434043b044f0020043d0430043404560439043d043e0433043e0020043f0435044004350433043b044f04340443002004560020043404400443043a0443002004340456043b043e04320438044500200434043e043a0443043c0435043d044204560432002e0020042104420432043e04400435043d04560020005000440046002d0434043e043a0443043c0435043d044204380020043c043e0436043d04300020043204560434043a04400438043204300442043800200437043000200434043e043f043e043c043e0433043e044e0020043f0440043e043304400430043c04380020004100630072006f00620061007400200456002000410064006f00620065002000520065006100640065007200200036002e00300020044204300020043f04560437043d04560448043804450020043204350440044104560439002e> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 performance analysis of 5g path loss models for rural macrocell environment muhammad akramuddin mohd nordin and huda adibah mohd ramli department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. *corresponding author: hadibahmr@iium.edu.my (received: 27th september 2019; accepted: 27th november 2019; published on-line: 20th january 2020) abstract: 5g networks are expected to use the millimeter wave (mmwave) frequency band and this frequency provides wider bandwidth allowing a better quality of service to be offered to the users. however, the mmwave frequencies may lead to a higher path loss due to several factors including blockages,rain and atmosphere. therefore, to allow optimal positioning of the 5g base stations, the study of path loss model in this 5g mmwave frequencies is crucial. this paper investigates the 5g path loss models as well as their parameters that are most suitable for cross-polarized antennas under rural macrocell environment in malaysia. path loss models namely close in free space reference distance path loss model (ci) model, and alpha beta gamma (abg) or floating intercept (fi) model along with their parameters achieved from the previous studies were evaluated by comparing the parameters and models that are closest to the sampled path loss when using antennas that have different patterns and polarizations in an open-source simulator. results obtained indicate that fi model can be adapted to the majority of the environment where this model showed the lowest root mean square error (rmse). the study of path loss models by using advanced simulator or field measurement, and studies on other rural areas from other states in malaysia will be considered in future works. abstrak: rangkaian 5g dijangka menggunakan jalur frekuensi gelombang milimeter (mmwave) dan frekuensi ini menyedia jalur lebar yang lebih lebar membolehkan kualiti servis yang lebih baik untuk para pengguna. walau bagaimanapun, frekuensi mmwave mungkin menyebabkan kehilangan penyebaran yang tinggi disebabkan beberapa faktor seperti halangan, hujan dan atmosfera. oleh itu, untuk membolehkan stesen pangkalan 5g berada dalam kedudukan optimum, kajian model kehilangan penyebaran dalam frekuensi mmwave untuk rangkaian 5g ini sangat penting. kertas ini menyiasat beberapa model kehilangan penyebaran rangkaian 5g serta parameter yang paling sesuai untuk antenna polarasi-silang dalam persekitaran sel makro luar bandar di malaysia. model-model kehilangan penyebaran iaitu model kehilangan penyebaran berdekatan ruang bebas bersama rujukan jarak (ci), dan model alpha, beta, gamma (abg) atau dipanggil model pintasan apungan (fi) telah dinilai dengan membandingkan beberapa parameter dan model yang paling hampir dengan kehilangan penyebaran yang sudah disampel apabila menggunakan antenna yang mempunyai corak dan polarasi yang berbeza melalui simulator sumber-terbuka. kajian ini mendapati bahawa model fi boleh diadaptasi ke persekitaran majoriti di mana model ini menunjukan prestasi statistik punca min ralat kuasa dua (rmse) yang terendah. kajian model-model kehilangan penyebaran ini akan mempertimbangkan penggunaan simulator yang canggih atau 85 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 pengukuran lapangan, dan juga kawasan luar bandar di negeri-negeri lain di malaysia untuk kerja masa akan datang. keywords: 5g networks; path loss modelling; rural macrocell 1. introduction the fifth generation (5g) network is expected to provide a better quality of multimedia services for significantly larger number of mobile phone users [1,2]. to achieve this expectation, the standardization bodies proposed the millimeter wave (mmwave) frequencies (i.e. the frequency range of 3 ghz to 300 ghz) to be used for the 5g given that the lower range of frequencies are mostly congested [2,3]. however, it was found in a number of studies that the mmwave has implementation issues especially in terms of path loss. for example, the study conducted by [4] shows that path loss in mmwave frequency at shorter distance under non-line of sight (nlos) condition is above 100 db. this indicates that mmwave frequencies is very sensitive to certain factors such as rain, atmosphere and blockages [5]. based on this observation and given the importance of path loss in the network planning for optimal installation of 5g base stations, path loss needs to be accurately modelled. there are a number of well-known path loss models proposed for use in the 5g networks. the basic path loss models include close-in free space with reference distance (ci), and alpha, beta, gamma (abg) or floating intercept (fi) [1,6]. the majority of the other path loss models are derived by modifying the values of the path loss parameters of these basic models. however, it is difficult to obtain the optimal values of path loss parameters due to several factors such as different areas and countries, environment, and type of antennas. this lead to inaccurate optimal values of path loss parameters been established. given this limitation, this paper will focus on finding the optimal values of path loss parameters in malaysia context. besides the limitation previously stated, another limitation include the existing studies did not highlight the type of antenna polarization been used as well as the line of sight (los) or nlos conditions been assumed. for instance, research conducted in [4] focus on different polarizations at los condition but fail to state the antenna polarization type use at nlos condition. another example is the work in [7] that do not mentioned the antenna polarization type been used. given the newly stated limitation, this paper will be investigate on the 5g path loss model for the case of cross-polarized antennas. crosspolarized antennas can be described as a polarization type where the transmitter transmits different polarization to the receiving antenna. according to [8], multiple and reconfigurable polarization of antennas (which includes cross-polarized antennas) will be used for 5g network implementation. therefore, this shows the importance to study on 5g path loss model for cross-polarized antennas. besides the limitations on antenna polarizations, limited studies have been conducted in rural macrocell areas. only research in [9] and [10] focused in this type of area. however, these two researches focused for ci model and its modification only. there could be possibility that fi or abg models could be suitable for this area. therefore, this research will utilizes these path loss models to identify whether these models are suitable for rural macrocell areas in malaysia. rural macrocell can be defined as larger coverage of cell sizes for undeveloped and less populated areas[11]. although most 5g path loss studies were conducted in urban areas, the study for rural areas seems to be important as 5g network will also be implemented in rural areas in near future. hence, by combining 86 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 all the limitations of the existing studies, this paper will investigate the performance of 5g path loss models based on their optimal values of path loss parameters for cross-polarized antennas in malaysia’s rural macrocell environment. it should be noted that identification of the optimal values of the path loss parameters will be based on the values achieved from previous studies [4,6,7,9,10,12-14]. the remaining sections of this paper is described as follows. section 2 explains the wellknown path loss for 5g networks followed by section 3 that highlights on the research methodology. section 4 analyzes the results obtained while conclusion and improvements of this research are discussed in section 5. 2. well-known path loss models for 5g networks the basic path loss models investigated in this paper are close-in free space reference distance path loss model (ci) and floating intercept or alpha-beta-gamma model (fi or abg). each model is described next. 2.1 close-in free space reference distance path loss model (ci) the first basic path loss model for 5g networks is ci path loss model where this model depends on the frequency and it is obtained by applying the ci reference distance upon law made by friis as below [1] 3 , 10 3( , d )[db] ( 1 ) 10 log ( ) ci c d c dpl f fspl f m n d (1) where, n is the path loss exponent (ple) found by measured data error minimization to eq. (1), where d3d is the seperation distance and it is must greater > 1m and fspl(fc, 1m) is the free space path loss equation at 1m given as below 10 c [ ] 32.4 20log (f )fspl db (2) where fc is the carrier frequency. the ci model is simple and accurate as it requires to optimize the ple value only and it offers similar prediction of path loss to the measured path loss [6,13]. as an evidence, results obtained in [10] showed that when modelling the path loss at los settings using ci model, the result were almost identical to the measured path loss and hence indicating ci model is very accurate model under los. however, the weakness of this model is that the transmitter power needs to be standardized so that same ple can be achieved at the same frequency [15]. 2.2 floating intercept or alpha-beta-gamma model (fi or abg) the abg model is determined by finding the best fit values for error minimization between model and the measured data. this is by introducing the α, β, and γ parameters. the equation for this model is as follows [6] 10 10, [ ] 10 log ( ) 10 log ( ) abg abg abg abg c cpl f d db d f (3) where αabg and γabg are coefficients indicating the path loss dependence on distance and frequency, respectively, βabg is an optimized offset path loss value in db, d is separation distance between receiver and transmitter in meters and fc is the carrier frequency in ghz. when γabg is 0, this model becomes floating intercept (fi) as follows: 10, [ ] 10 log ( ) fifi fi cpl f d db d (4) 87 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 where α fi and β fi are the same parameter described as βabg and αabg respectively. sun et al. state that abg or fi offers slightly improved accuracy of measured path loss [14]. whereas [6] shows that abg or fi model able to give good prediction at short range compared to ci model. however, the good prediction at short range only works at specific measurement range. furthermore, abg or fi model is difficult as it requires optimization of two or three parameters compared to ci. 2.3 related works using ci and fi or abg models a number of studies extended the basic path loss models for use in the outdoor 5g networks. for example, third generation partnership project (3gpp) and 5g channel model (5gcm) proposed their own path loss based derived from the ci and abg models [1]. the advantage of their proposed path loss model is that the model can be used in the frequencies ranging from 6 ghz to 100 ghz and without modification on the values of the path loss parameters (i.e. ple). however, this proposed model assumed the usage of omnidirectional antennas. it should be noted that the directional antennas will be considered for implementation in the 5g networks [8]. directional antenna is the antenna pattern that makes an antenna to transmit or receive signal at a specific directions. while omnidirectional antenna is defined as an antenna patterns that make an antenna to transmit and receive signal at all directions. rappaport et al. [1] stated that the predicting of path loss on the basis of omnidirectional antenna as a replacement for directional antennas is not effective unless understanding on the modelling of the directional antenna patterns and true spatial and temporal multipath channel statistics are achieved. zhao et al. [7] argues that similar parameter values of ple, α, and β cannot be achieved under los condition when the ci and fi or abg models are utilized for different antenna patterns. this might be due to the antenna gain of the omnidirectional antenna is independent as compared to the directional antennas and therefore lead to the omnidirectional antenna obtained lower path loss. consequently, the results obtained by zhao et.al support the argument made by rappaport et al. with respect to the ineffectiveness for assuming the omnidirectional antennas as the replacements for directional antennas [1,7]. given that the polarization method was not mention in the zhao et.al, this becomes one of the limitations of their work. to address the limitation faced by zhao et al., [4] investigated the impact of using cross polarized antennas on path loss. this paper compares [4] and [7] given that these two works use similar frequency and identify that cross-polarized antenna requires higher parameter values of ple, α, and β. this is probably due to higher path loss obtained by cross-polarized antennas in [4] compared to the unknown polarization used in [7]. this indicates that different antenna polarization requires different parameters values of ple, α and β. this research [4] however, did not mention the polarization use for nlos condition and investigation of antenna polarization in nlos condition is important given the sensitivity of mmwave to blockages. in regards to path loss study for rural macrocell areas, research in [10] investigated ci path loss model at 73 ghz frequency at rural macrocell area and obtained ple of 2.16 and 3.04 for los and nlos respectively. when the results obtained in [10] are compared with [4], it is observed that the ple obtained in [10] is slightly lower than in [4] although the research in [10] uses higher frequency than the research in [4]. this is probably due to higher transmitter height used in [10] which causes the path loss measured in [10] to be lower than [4]. nevertheless, the researchers in [10] used unknown polarization and focus 88 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 at ci model only. better results can be obtained if known polarization and other models are used. 3. research methodology this chapter describes the methodology used for this research. the methodology of this research begins with the description on how the path loss samples is collected and ends with how the path loss models are benchmarked using root mean square error (rmse) calculation. 3.1 research flow the research begins with the collection of path loss samples by using a simulator called nyusim [15]. this software is very popular given that several researches had used this software for 5g path loss study as discussed in [16] and [17]. this is probably because nyusim is an open-source simulator and provides samples that are similar to field measurements of signal levels as claimed in [15]. thus, these advantages motivates the usage of nyusim for this research. for further information on how nyusim works, it can be referred in [15]. due to the time constraint and given the main aim of this research, this paper only considers path loss (pl) figure (the values obtained from the figure will become the path loss samples) in power delay profile (pdp) output, though a number of output were generated from the software. one of the disadvantages of the nyusim is that only the pl figure of ci model was generated. this does not fulfil the aim of this paper where investigation of other basic path loss models need to be conducted. therefore, additional results of other basic path loss models described in section 2 will be plotted by using matlab software. fig. 1: location for path loss samples collection for rural macrocell area. besides that, another disadvantage of nyusim is that this simulator is not a mapbased channel simulator. this may lead to inaccurate values of path loss sample collection. furthermore, these inaccurate values may contradict to the one of the nyusim’s advantages which is to provide samples that are similar to field measurements. therefore, a thorough geographical studies were conducted to identify the rural macrocell area in malaysia to be as the reference location for collecting path loss samples. based on the 89 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 assistance of google earth, the chosen location is depicted in fig. 1 where it is located in tanjong karang, selangor. the reason for choosing this area is because this area is not similar to other rural areas in malaysia where it is not covered by dense foliage. therefore, input parameter of foliage loss provided by nyusim can be ignored for collecting path loss samples for this location. this is because, when testing the performance of nyusim, it is found out that less number of output samples especially for pdp output can be taken from this simulator when higher rain rate and foliage loss are considered for path loss study. table 1 describes the relevant parameters that will be used for processing path loss samples. this table has been categorized into two categories which are channel parameters, and antenna properties. it should be noted that some of the parameters used were based on weather websites on 6th april 2019, guidelines from ericsson and international telecommunication union (itu), some parameters in [13] and what is provided by nyusim [18-20]. table1: simulation parameters for path loss samples collection [13,18-20] environment rural macrocell location tanjong karang, selangor channel parameters frequency (ghz) 40 scenario rma conditions los and nlos distance (m) 100 to 10000 tx power (dbm) 40 dbm antenna height (m) 35 barometric pressure (mbar) 1011 humidity (%) 88 temperature (°c) 26 rain rate (mm/hr) 90 polarization cross polarized number of rx locations 20 antenna properties array type uniform rectangular array number of tx antenna elements, nt 16 number of rx antenna elements, nr 16 number of tx element per row,wt 8 number of rx antenna elements per row, wr 8 tx antenna azimuth half-power beam width (hpbw),° 7.8 tx antenna elevation hpbw,° 7.8 rx antenna azimuth hpbw,° 7.8 rx antenna elevation hpbw,° 7.8 after the path loss samples using the parameters provided in table 1 have been collected, the path loss samples are then extracted into matlab software for path loss modelling. the modelling of path loss are based from the models described in section 2 alongside with the parameters from the previous studies [4,6,7,10,12-14]. thereafter, the 90 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 optimal parameters (parameters showing the closest plot to the path loss samples) from each path loss models are identified by observing the output plot from matlab. the predicted path loss values with their optimal parameters are compared with the path loss samples on the basis of root mean square error (rmse) calculation. the calculation of rmse are as below: sampled 2 ,n ,predicted 1 (pl pl ) n n nrmse n (5) where plsampled is the path loss samples, plpredicted is the predicted path loss obtained from the path loss models and n is number of samples obtained from the path loss samples. based on equation (5), the path loss model with respect to the identified parameters that has the lowest rmse indicates that this model has the closest path loss prediction. thus, this model is chosen as the suitable model to be used for 5g networks in rural macrocell environment in malaysia. calculation on rmse percentage degradation between identified model and the suitable model is also conducted. the reason of conducting this calculation is to see how much the rmse of other identified models are degraded from the rmse of the suitable model. the percentage degradation is depicted on equation (6) below. rmse degradation (%) = x 100 | |identifiedmodel suitablemodel suitablemodel rmse rmse rmse (6) where rmseidentifiedmodel is the rmse of the other identified models and rmsesuitablemodel is the lowest rmse identified from each models. as a summary for this section, it is described in a form of research flow as shown in fig. 2. fig. 2: research flow for finding the accurate path loss model for 5g networks in rural macrocell environment in malaysia. 4. results and discussion this section contains results obtained via simulation being compared with the path loss samples obtained via measurement. the parameters of path loss models obtained from the previous studies that are closest to the path loss samples are identified and later analyse based on rmse calculation so as to identify path loss model with the most start collection of path loss samples from pdp output in nyusim extract the path loss samples model the well-known 5g path loss model with the parameters obtained in previous literature and also the scatter plot of the path loss sample compare the modelled path loss based on optimal parameters with the path loss samples by using rmse calculation end 91 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 optimal parameter for different scenarios in rural macrocell environment in malaysia. the scenarios studied include los or nlos condition and cross-polarized antennas with respect to directional and omnidirectional patterns. directional and omnidirectional patterns are considered because according to [13], directional antenna is used to cope with the feature of beamforming and beam combining techniques for implementing 5g networks, while omnidirectional antennas is studied because wireless user equipment (ue) uses this antenna pattern as ue needs to receive signal from all directions. thus, showing that these two antenna patterns are required in the implementation of 5g networks. the authors in [13] further defined the conditions where los is a condition where a clear propagation path occurred between transmitter and receiver while nlos is a condition where transmitter and receiver are obstructed by blockage and there is no clear path of propagation between them. thus, from the description of these two conditions, in real time, 5g users will always move from one location to another leading to changing condition of los or nlos based on user’s location. given the popularity of ci and abg or fi models alongside with their parameters from [4,6,7,10-14], these basic path loss models are studied in this paper. 4.1 analysis of path loss model for rural macrocell in malaysia at los condition simulation results of path loss models alongside with the scatter plot of the path loss samples for rural macrocell environment under los condition at 40 ghz is shown in fig. 3. it was observed that there are four parameters that are closest to the path loss samples for cross-polarized antennas with different patterns. for ci model, the ple parameters that are closest to the path loss samples are 3.4 and 4.3. fi model that have α value of 45.2 db with β value 4.6 and α value of 90.4 db with β value of 2.8 are observed to be the closest to the path loss samples. meanwhile, the parameters of abg model that are closest to the path loss samples have values of α, β and γ that equal to 2.9, 2.4 db and 3.8 respectively. for ci and fi models, the values of the parameters were similar to [4] while for abg model, the values obtained were similar to [12]. these two studies were conducted based on field measurement in malaysia and probably have the same environmental condition set in the nyusim for this paper. (a) directional cross-polarized antenna under los condition. (b) omnidirectional cross-polarized antenna under los condition. fig. 3: 40 ghz rural macrocell simulated path loss model alongside scatter plot under los condition. 92 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 thereafter the rmse calculation was performed so as to find the most optimal parameters of path loss model for rural macrocell in malaysia. table 2 showed that different path loss models are suitable for cross-polarized antennas with different antenna patterns. the suitable path loss model for directional pattern is ci model with ple of 4.3 while fi model with α and β parameters of 45.2 db and 4.6 is suitable for omnidirectional pattern. referring to table 2, for directional pattern, ci model with ple of 4.3 has the lowest rmse of 8.60 db compared to other models with respect to different values of parameters. the reason why this model has the lowest rmse probably because the ple of 4.3 gives closer prediction of path loss when the separation distance are at 53.3 m, 1436.2 m and 2034.1 m as observed in fig. 3(a). compared to fi model with α and β parameters of 45.2 db and 4.6 which scores the second lowest of rmse (i.e. 7.33% degradation as compared to the rmse obtained by ci model with ple of 4.3), the β parameter of this model can only give two predicted path loss values that are closest to the path loss samples which is when the location of the receiver are 1109.4 m and 1436.2 m away from the transmitter. thus, showing that ci model with ple of 4.3 is suitable due to the number simulated/predicted path loss that are closer (smaller value of rmse) to the path loss samples. furthermore, ci model with ple of 4.3 which was proposed in [4] also can be adapted for path loss modelling for rural macrocell environment in malaysia under los condition when using cross-polarized directional antenna. referring back to table 2, fi model with α and β parameters of 45.2 db and 4.6 have the lowest rmse among the other models for omnidirectional pattern which is around 8.72 db. based on observation in fig. 3(b), this model obtained the lowest rmse probably because at distance of 1109.4 m, the β parameter of 4.6 obtained from this model provide closer predicted path loss values to the path loss samples where the difference between predicted path loss and path loss samples is around 2.22 db. compared to ci model with ple of 4.3, where at 1109.4 m, larger difference value between the measured and predicted values of path loss was observed in which the difference is 7.85 db. hence, contributing to ci model with ple of 4.3 to have slightly higher rmse than fi model with α and β parameters of 45.2 and 4.6. furthermore, the findings achieved by [4] is suitable to be adapted in cross-polarized antenna for los rural macrocell environment by using ci model with 4.3 ple for directional type and fi model with α and β parameters of 45.2 db and 4.6 for omnidirectional type. table 2: rmse value for rural macrocell environment under los condition polarization antenna pattern rmse [db] ci model fi model abg model ple 3.4 ple 4.3 α[db]= 90.4 and β= 2.8 α[db]= 45.2 and β = 4.6 α = 2.9, β [db]= 2.4 and γ= 3.8 crosspolarized directional 22.80 8.60 17.24 9.23 37.45 rmse degradation (%) 165.28 100.49 7.33 335.65 omnidirectional 21.99 9.83 17.05 8.72 36.47 rmse degradation (%) 152.06 12.71 95.43 318.08 93 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 4.2 analysis of path loss model for rural macrocell in malaysia at nlos condition the results of path loss samples and the simulated path loss models with the best chosen parameters for rural macrocell environment in malaysia under nlos condition is shown in fig. 4. it is observed in the figure that there are four parameters that have the closest prediction to the path loss samples. parameters of ci model that are closest to path loss samples have ple of 5.1 and 4.199 which were achieved in [4] and [7] respectively. parameters α equal to 34.6 db with β equal to 5.5 and parameters α of 38 db with β of 5.3 of fi model are the closest to the path loss samples and the values of these parameters came from the research made in [13]. abg model is excluded because most of parameters from this model of the previous studies give poor prediction of path loss under nlos condition. therefore, the only parameters that give closer prediction to the path loss samples obtained in this paper are the parameters α equal to 34.6 db with β equal to 5.5 and parameters α of 38 db with β of 5.3 of fi model and ple of 5.1 and 4.199 of ci model. however, to simplify the process of finding the suitable path loss model based on the identified optimal parameters for malaysia’s rural macrocell environment under nlos condition, rmse calculations were conducted which are shown in table 3 respectively. fi model with parameters α equal to 34.6 db and β of 5.5 are suitable as it has the lowest rmse around 8.70 and 8.14 for directional and omnidirectional respectively. the reason is because the parameter β of this model provide the smallest average of difference between the measured and predicted path loss for all distances measured (admppl). this average is calculated as below. i sampled i 1 predicted| ( ) ( ) | admppl = [db] pl pl n i n (7) where plpredicted is the predicted path loss in db, plsampled is the sampled path loss, and n is the number of sampled path loss obtained in the nyusim simulator. the reason for utilizing eq.(7) is because each identified path loss model has some predicted values that are close to the sampled path loss at certain distances. for instance and as tabulated in table 5, using cross-polarized omnidirectional antenna, ci model with ple 4.199 gives closer prediction at 567.9 m where the difference between predicted path loss and path loss samples is around 0.71 db, compared to fi model with α equal to 34.6 db and β equal to 5.5 where the difference is around 5.28 db. however, the latter model gives closer prediction of path loss when the receiver is at 1533.9m where the difference between predicted path loss and the sampled path loss is around 2.08 db compared to the former model where difference is 13.69 db. these examples leads to the requirement of using eq.(7) for better justifications on why fi model with α equal to 34.6 db and β equal to 5.5 has the lowest rmse. based on table 6 and referring to omnidirectional type as an example, using equation (7), the average for this suitable model is 6.76 db compared to the second lowest path loss which is fi model with α equal to 38 db and β equal to 5.3 where the average difference around 7.93 db. thus, this lowest admppl gives the former model to have lowest rmse and leads to this model to have the best fit of slope to the path loss samples. further, the results obtained also agree with the statement made by [14] as path loss prediction made by the fi model with parameters α equal to 34.6 db and β of 5.5 give slight accuracy to the sampled path loss. 94 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 (a) directional cross-polarized antenna under nlos condition. (b) omnidirectional cross-polarized antenna under nlos condition. fig. 4: 40 ghz rural macrocell simulated path loss model under nlos condition. table 3: sampled path loss and predicted path loss results for rural macrocell environment under nlos condition polarization antenna distance [m] sampled path loss [db] predicted path loss [db] ci model fi model ple 4.199 ple 5.1 α[db]= 34.6 β = 5.5 α [db] = 38 β = 5.3 crosspolarized directional 567.9 183.5 180.10 204.91 186.08 183.98 1060.2 215.7 191.48 218.74 201.00 198.35 1533.9 211.9 198.21 226.92 209.82 206.85 omnidirectional 567.9 180.8 180.09 204.91 186.08 183.98 1060.2 213.9 191.48 218.74 201.00 198.35 1533.9 211.9 198.21 226.92 209.82 206.85 table 4: rmse value for rural macrocell environment under nlos condition polarization antenna pattern rmse [db] ci model fi model ple 4.199 ple 5.1 α[db]= 34.6 β = 5.5 α [db] = 38 β = 5.3 crosspolarized directional 16.18 15.20 8.70 10.44 rmse degradation (%) 85.96 74.65 19.95 omnidirectional 15.17 16.63 8.14 9.62 rmse degradation (%) 86.40 104.36 18.17 95 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 table 5: difference of sampled path loss and predicted path loss results for rural macrocell environment under nlos condition polarization antenna distance [m] | sampled path loss predicted path loss | [db] ci model fi model ple 4.199 ple 5.1 α[db]= 34.6 β = 5.5 α [db] = 38 β = 5.3 cross-polarized directional 567.9 3.4 21.41 2.58 0.48 1060.2 24.22 3.04 14.7 17.35 1533.9 13.69 15.02 2.08 5.05 omnidirectional 567.9 0.71 24.11 5.28 3.18 1060.2 22.42 4.84 12.9 15.55 1533.9 13.69 15.02 2.08 5.05 table 6: admppl calculation results as to find justification on why fi model with parameters of α equal to 34.6 db and β = 5.5 has the lowest rmse for rural macrocell environment under nlos condition polarization antenna pattern rmse ci model fi model ple 4.199 ple 5.1 α[db]= 34.6 β = 5.5 α [db] = 38 β = 5.3 crosspolarized directional 13.77 13.15 6.46 7.63 omnidirectional 12.27 14.65 6.76 7.93 4.3 analysis of suitable 40 ghz path loss models for rural macrocell in malaysia after finding out the suitable parameters of path loss models for cross-polarized antenna under los and nlos conditions for rural macrocell in malaysia, a summary of these suitable models is tabulated in table 7. the table shows the most effective model that provide good path loss prediction is fi model and only ci model is obtained in crosspolarized directional antenna under los condition. this is probably because the various β parameter values of fi model obtained in the previous studies give the best fit of slope to the scatter plot of the path loss samples for most antenna patterns polarizations. therefore, the results shown in table 7 validates the statement made by [14] that abg or fi model offers slightly improved accuracy of the path loss samples. another finding is that most of the suitable path loss models have the same parameter values for the case of different antenna patterns under nlos condition. this is probably due to the slight difference of path loss samples when directional and omnidirectional patterns are used. thus, these findings are in line with the findings obtained in [7] when using cross-polarized antenna with different patterns under los condition whereas results from nlos condition differ from this study. 96 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 table 7: summary of path loss models suitable for rural macrocell environment in malaysia condition antenna pattern model parameters los directional ci model ple 4.3 omnidirectional fi model α[db]= 45.2 and β = 4.6 nlos directional fi model α[db]= 34.6 and β = 5.5 omnidirectional fi model α[db]=34.6 and β = 5.5 5. conclusion and future works this research aims to study the performance of 5g path loss models based on their optimal parameter values for cross-polarized antennas in malaysia’s rural macrocell environment. results show that when tested in los and nlos conditions with different antenna patterns, the fi model with their respective parameters is the most suitable model to be used for the majority of the scenarios of rural macrocell in malaysia whereas ci model only can be used for cross-polarized directional antenna under los scenario only. this is because the suitable models score the lowest rmse compared to all models. besides that, similar parameter values of fi model can be used for different antenna patterns under nlos condtion only as small difference of sampled path loss values were obtained for both cross-polarized directional and omnidirectional antennas. as a conclusion, the results obtained from this research can be recommended to be standardized for malaysia’s 5g implementation for rural macrocell areas when using cross polarized antennas as the parameter values of the basic path loss models are from the studies made from previous researches. this research can be improved by using map-based simulator or field measurements as the total number of path loss samples taken is less than 10 samples and at inconsistent distance intervals. this due to nyusim placed the receivers at unknown and random locations and at distances that causes the sampled path loss value to exceed the threshold limit set by this simulator. thus, new weakness on using nyusim is found based on this findings. other than that, the results could also be better if more locations of rural macrocell areas in malaysia are tested. this is to ensure that the path loss models that are suitable for other rural macrocell areas are similar to the suitable models obtained in this research. therefore, the results obtained in this research can be more accurate if large number of path loss samples is obtained through known locations and consistent distance intervals and tested in various rural macrocell locations in malaysia. acknowledgements we are very grateful to ministry of education malaysia for supporting this research under the grant id of frgs/1/2019/tk04/uiam/02/2. 97 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 references [1] rappaport ts, xing y, maccartney gr, molisch af, mellios e, zhang j. (2017) overview of millimeter wave communications for fifth-generation (5g) wireless networks-with a focus on propagation models. ieee transactions on antennas and propagation, 65(12): 6213-6230. [2] mitra rn, agrawal dp. (2015) 5g mobile technology: a survey. ict express, 1(3): 132137. https://doi.org/10.1016/j.icte.2016.01.003 [3] prabu rt, benisha m, bai vt, yokesh v. (2016) millimeter wave for 5g mobile communication application. in proceedings of 2016 2nd international conference on advances in electrical, electronics, information, communication and bio-informatics (aeeicb), 27-28 february 2016, chennai, india; pp. 236–240. [4] al-samman am, hindia mn, rahman ta. (2016) path loss model in outdoor environment at 32 ghz for 5g system. in proceedings of 2016 ieee 3rd international symposium on telecommunication technologies (istt), 28-30 november 2016, kuala lumpur, malaysia; pp. 9–13. [5] andrews jg, buzzi s, choi w, hanly s, lozano a, soong ack, zhang jc. (2014) what will 5g be? ieee journal on selected areas in communications, 32(6):1065-1082. [6] sun s, rappaport ts, rangan s, thomas ta, ghosh a, kovacs iz, rodriguez i, koymen o, partyka a, jarvelainen j. (2016) propagation path loss models for 5g urban micro-and macro-cellular scenarios. in proceedings of 2016 ieee 83rd vehicular technology conference (vtc spring), 15-18 may 2016, nanjing,china; pp.1–6. [7] zhao x, li s, wang q, wang m, sun s, hong w. (2017) channel measurements, modeling, simulation and validation at 32 ghz in outdoor microcells for 5g radio systems, ieee access, 5:1062-1072. [8] gupta a, jha rk. (2015),a survey of 5g network: architecture and emerging technologies. ieee access, 3:1206-1232. [9] maccartney gr, rappaport ts. (2017) study on 3gpp rural macrocell path loss models for millimeter wave wireless communications. in proceedings of ieee international conference on communications, 2017, 21-25 may 2017, paris,france; pp. 3–9. [10] maccartney gr, rappaport ts. (2017) rural macrocell path loss models for millimeter wave wireless communications. ieee journal on selected areas in communications, 35(7): 1663-1677, [11] rural area. [https://www.nationalgeographic.org/encyclopedia/rural-area/]. [12] al-samman am, rahman ta, hindia mhdn, daho a, and hanafi e (2018) path loss model for outdoor parking environments at 28 ghz and 38 ghz for 5g wireless networks. symmetry, 10(12):1-15. doi: 10.3390/sym10120672. [13] rappaport ts, maccartney gr, samimi mk, sun s. (2015) wideband millimeter-wave propagation measurements and channel models for future wireless communication system design. ieee transactions on communications, 63(9): 3029-3056. [14] sun s, rappaport ts,thomas ta, ghosh a, nguyen hc, kovacs iz, rodriguez i, koymen o, partyka a. (2016) investigation of prediction accuracy, sensitivity, and parameter stability of large-scale propagation path loss models for 5g wireless communications. ieee transactions on vehicular technology, 65(5): 2843-2860. [15] sun s, maccartney gr, rappaport ts. (2017) a novel millimeter-wave channel simulator and applications for 5g wireless communications. in proceedings of ieee international conference on communications, 21-25 may 2017, paris, france; pp.1-5 . [16] reddy mmp. (2018), the effect of cross polarization and co polarization on channel modeling in 5g communications. international journal for science and advance research in technology, 4(3):53-58. retrieved from http://ijsart.com/content/pdfdocuments/ijsartv4i321194.pdf [17] budalal aa, islam mr, habaebi mh, rahman ta. (2018) millimeter wave channel modeling present development and challenges in tropical areas. in proceedings of the 2018 7th international conference on computer and communication engineering (iccce), 19-20 september 2018, kuala lumpur,malaysia; pp.23–28. 98 iium engineering journal, vol. 21, no. 1, 2020 mohd nordin and mohd ramli https://doi.org/10.31436/iiumej.v21i1.1247 [18] weather forecast. available: https://www.worldweatheronline.com/ [19] characteristics of precipitation for propagation modelling p series radiowave propagation. [https://www.itu.int/dms_pubrec/itu-r/rec/p/r-rec-p.837-6-201202-s!!pdf-e.pdf] [20] advanced antenna systems for 5g networks. [https://www.ericsson.com/4a8a87/assets/local/reports-papers/whitepapers/10201407_wp_advanced_antenna_system_nov18_181115.pdf] 99 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <feff004200720075006700200069006e0064007300740069006c006c0069006e006700650072006e0065002000740069006c0020006100740020006f007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400650072002c0020006400650072002000650067006e006500720020007300690067002000740069006c00200064006500740061006c006a006500720065007400200073006b00e60072006d007600690073006e0069006e00670020006f00670020007500640073006b007200690076006e0069006e006700200061006600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020004400650020006f007000720065007400740065006400650020005000440046002d0064006f006b0075006d0065006e0074006500720020006b0061006e002000e50062006e00650073002000690020004100630072006f00620061007400200065006c006c006500720020004100630072006f006200610074002000520065006100640065007200200036002e00300020006f00670020006e0079006500720065002e> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <feff005500740069006c0069007a00610163006900200061006300650073007400650020007300650074010300720069002000700065006e007400720075002000610020006300720065006100200064006f00630075006d0065006e00740065002000410064006f006200650020005000440046002000610064006500630076006100740065002000700065006e007400720075002000760069007a00750061006c0069007a006100720065002000640065002000ee006e00630072006500640065007200650020015f0069002000700065006e00740072007500200069006d007000720069006d006100720065006100200064006f00630075006d0065006e00740065006c006f007200200064006500200061006600610063006500720069002e00200044006f00630075006d0065006e00740065006c00650020005000440046002000630072006500610074006500200070006f00740020006600690020006400650073006300680069007300650020006300750020004100630072006f0062006100740020015f0069002000410064006f00620065002000520065006100640065007200200036002e003000200073006100750020007600650072007300690075006e006900200075006c0074006500720069006f006100720065002e> /rus <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> /sky <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> /slv <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> /suo <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> /sve <feff0041006e007600e4006e00640020006400650020006800e4007200200069006e0073007400e4006c006c006e0069006e006700610072006e00610020006f006d002000640075002000760069006c006c00200073006b006100700061002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400200073006f006d00200070006100730073006100720020006600f60072002000740069006c006c006600f60072006c00690074006c006900670020007600690073006e0069006e00670020006f006300680020007500740073006b007200690066007400650072002000610076002000610066006600e4007200730064006f006b0075006d0065006e0074002e002000200053006b006100700061006400650020005000440046002d0064006f006b0075006d0065006e00740020006b0061006e002000f600700070006e00610073002000690020004100630072006f0062006100740020006f00630068002000410064006f00620065002000520065006100640065007200200036002e00300020006f00630068002000730065006e006100720065002e> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 crack influence on a pipe with double slope under internal pressure: numerical simulation with xfem salmi houda1*, hachim abdelilah1,2, el bhilat hanan1 and el had khalid1,2 1hassan ii university of casablanca, national higher school of mechanics (ensem), laboratory of control and mechanical characterization of materials and structures, casablanca, morocco 2institute of maritime studies, laboratory of materials and structures casablanca, morocco *corresponding author: houda.salmi111@gmail.com (received: 14th april 2020; accepted: 9th may 2020; published on-line: 4th july 2020) abstract: this work analyses the effect of elliptical cracks on a pipe with double slope thickness transition, using the extended finite element method (xfem), level sets were defined to describe the three-dimensional (3d) cracks. the computation of the stress intensity factors (sifs) of cracks is performed. the values of sifs are compared between straight pipes and pipes with a double (single) slope thickness transition. the results show that the xfem is an effective tool for modelling cracks in pipes. a pressurized pipe with double slope thickness transition is more sensitive to the defect in comparison with another type of pipe. parameters of the transition zone have an effect on stress intensity factors, precisely, the parameters of the first thickness transition are more influential on the gravity of the defect compared to the second thickness transition. abstrak: kajian ini menganalisa kesan retakan elips pada paip dengan peralihan ketebalan cerun berganda, menggunakan kaedah elemen terhingga dipanjangkan (xfem), set tahap ditentukan bagi menentukan keretakan tiga dimensi (3d). pengiraan faktor intensiti tekanan (sif) retakan dilakukan. nilai sif dibandingkan antara paip lurus dan paip peralihan ketebalan cerun berganda (tunggal). hasil kajian menunjukkan bahawa xfem adalah alat yang berkesan bagi memodel keretakan paip. paip bertekanan mengikut peralihan ketebalan cerun berganda, lebih sensitif terhadap kecacatan berbanding paip lain. parameter zon peralihan mempunyai pengaruh terhadap faktor intensiti tegangan, tepatnya, parameter peralihan ketebalan pertama lebih mempengaruhi pada graviti kecacatan berbanding dengan peralihan ketebalan kedua. keywords: extended finite element method (xfem); pipe with double slope thickness transition; stress intensity factors (sifs); three-dimensional cracks 1. introduction presently, pressure equipment is used in various applications, such as energy production and chemical industry [1-4]. in the field of pressure equipment, cylindrical or spherical structures are often found, those shells can be affected by axi-symmetric or semielliptical internal or external cracks, it is then very important to evaluate the influence of these cracks on pressure equipment [5]. 256266 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 the french alternative energies and atomic energy commission (cea) [6] developed the finite element software (castem) for structural and fluid mechanics [7]. cea [6-8] used the finite element method (fem) to investigate straight pipes with circumferential cracks. the field of pressure equipment also deals with the thickness of transition pipes, these pipes are classified into two types: transitions with a single slope and transitions with a double slope [3,4]. those structures correspond to a connection between two cylinders of the same internal radius but with different thicknesses, those structures are subjected to circumferential cracks at the base of the thickness transition, those defects are modelled as cracks located in a pipe of uniform thickness t [1,3,4]. using fem, rahman et al. [1] evaluated the effect of the thickness transition zone on the crack opening displacement (cod), [1] showed that the thickness transition produces a dissymmetric distribution of the cod on the crack lips. hariri [3,4] used 3d finite element method (fem) to study transition with a single slope containing elliptical crack subjected to tensile stress and bending moment, the result showed that for elastic plastic material, the thickness transition zone is the weakest position of the whole pipe. the traditional finite element calculations have a cumbersome cost in the modelling of a crack. the accuracy of the results in the fem depends on the mesh refinement, but a fine mesh implies a large number of nodes, so it requires a long calculation time [8]. hence, xfem is introduced to facilitate the solving of crack problems in complex geometries. in this work, the xfem is used to analyse in 3d the external circumferential elliptical cracks in the thickness transition zone. in this method, the standard finite element approximation is locally enriched to discontinuities modelling [9,10]. for stationary cracks, the xfem gives an accurate result, thanks to enrichment functions even with coarse meshes near the crack tip [9]. the xfem was initiated by belytschko and black [11]. stolarska et al. [12] coupled between the level set method (lsm) and xfem to investigate the problem of cracks. in the field of pressurized equipment, [13] used the xfem to study the fracture behaviour of pipes under internal detonation loads. sharma [14] performed a numerical investigation with xfem to evaluate the stress intensity factor of a semi-elliptical crack in a pipe band. using the xfem to investigate the effect of the crack on a thickness transition with two slopes besides evaluating the influence of transition zone on sif were however not treated in [3], also, taking account of internal pressure was required to complete the work in [3]. the purpose of this work is the application of xfem to evaluate the effect of a 3d external circumferential crack in thickness transition with a double slope in a pipe and investigate the effect of the parameters of the transition zone on sif. 2. xfem methodology 2.1 xfem formulation using enrichment functions, the displacement approximation u is given by eq. (1) [9]: (1) where ni is the standard finite element (fe) function of node i. ui is an unknown of the standard fe part at a node i. n is a set of all nodes in the domain. nd is a nodal subset of the enrichment heaviside function h(x). 257267 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 (2) where ( )x is the normal level set function. ia is an unknown of the enrichment h (x) at a node i , these nodes are surrounded by a square in fig. 1. pn n is a nodal subset of the enrichment , the tip of the crack is described by four enrichment functions [9]. (3) where 2 2( )r and 1tan ( ) with and are respectively normal and tangential level sets. ib is an unknown of the enrichment at a node i , these nodes are surrounded by a circle in fig. 1. fig. 1: the strategy of the enrichment in xfem. 2.2 calculation of sif in xfem the energy release rate g is the energy released for a crack advance, the gtheta is a method that calculates the j -integral in elastic-plastic behaviour [16]. rice [15] showed that the j-integral can be approached by the energy release rate g in the elastic range. let i, a point in crack front c, c a crack surface that is composed with an outer surface c and an inner surface .c we consider v a volume containing the crack front c (red arc in fig. 2a) with 0 1 2c cv . for calculating the sif in xfem, the level sets are used as a local basis at the crack front. 258268 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 fig. 2: (a) the domain v in integral j computation, a (b) example of field in 2 dimensions. sukumar [17] has used the gradient of the level sets, [16] has defined this local basis (fig. 3) by 1 2,e e and 3 1 2e e e . fig. 3: the local basis on the crack front. j is expressed in a local basis (fig. 6) formed of level set functions, j is given by eq. (4) [16]: (4) where i jp is the eshelby tensor [17], it is given by eq. (5): (5) where w is the elastic energy density, and are respectively stress and strain expressed in the basis ( , , )1 2 3e e e (fig.3). is a field of displacement parallel to the plane of the crack and normal to the front (fig. 2. b), it is defined by eq. (6): (6) for elastic behaviour of materials, g is deduced from the j -integral by eq. (7) [9]: (7) 259269 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 the sif is deduced from g by eq. (8) [9]: (8) 2.3 the meshing of the cracked pipe the cracked pipe is symmetrical, so we modelled only a half-pipe with thickness transition and an external elliptical crack (fig. 4b), we used 3150 xfem xc8r elements with 512 gauss points in block crack. we used 18080 standard elements cub8 for the rest of the mesh. the thickness transition with two slopes is generally located at the outlet of reservoirs (valves) [3], therefore in boundary conditions, we fixed the displacement of the end of the thicker part of the pipe, in addition, we blocked the translation and the rotation in yu and zu axes by applying symmetry boundary conditions (fig. 4a). in this study, the crack is represented by level sets, we defined a normal level set from the crack front (red bow fig. 4b) and tangential level function from the crack face. fig. 4: (a) cracked half –pipe with thickness transition with double slope, (b) meshing of the crack. (a) (b) 260270 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 the normal level set (phi) gives the distance of a point x to the surface of the crack and the tangential level set (psi) gives the distance of a point x to the crack tip, these level functions define the crack as follows: for a point x of the solid (fig. 5a): (9) fig. 5: (a) representation of a crack with level sets, (b) normal level set, phi, (c) tangential level set, psi. 3. geometry and loading the study considered the elastic behaviour of the material in p265gh steel with the following properties. the geometries of the studied cracked pipes are defined by dimensionless parameters: a fraction of thickness t on the inner radius of the pipe: ( / ir ). shape parameter defining elongation of the elliptical crack: (a/c). the depth of the defect standardized by the thickness of the tube: ( 1/a t ). in the present work, we model a pipe of average thickness ( / ir =0.1), the parameter (a/c) takes values 1, 1/2, 1/4, and 1/8, ( 1/a t ) takes values 0.1, 0.2, 0.4, 0.6, 0.8. this gives a set of 20 geometries. (a) (b) (c) 261271 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 table 1: properties of p265gh steel young's modulus, e, ( )mpa yield stress, , ( )mpa poisson’s ratio, breaking stress, , ( )u mpa nominal stress, , ( )f mpa 200000 320 0.3 470 148 elliptical cracks are considered to be located at the base of the transition in the thin part of the pipe (figs. 4 and 6). the study considered pipe with thickness transition with a single slope ( , , ) and thickness transition with double slopes ( , , , , ) (fig. 6). pressurized pipe with thickness transition is a connection between pipe of thickness assembled to another pipe of a thickness t2 and t3 (t3 > t2 > t1). fig. 6: geometry of different types of pipes: (a) straight pipe, (b) pipe with thickness transition (single slope), (c) pipe with thickness transition (double slope). is the thickness of the pipe, with j {1, 2, 3}. ( )j is the slope of a thickness transition in a pipe with j {1, 2}. sif, (k) is the stress intensity factor. the purpose of this study is (a) (b) (c) 262272 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 the investigation of the impact of and ( )j on the stress intensity in a pipe with thickness transition. so, we consider and ( )j as variable parameters, and analyse their effect on sif. pipes are subjected to an internal pressure p (fig. 7), for the purpose of comparison with the straight cylinder, the internal pressure is calculated in the thin part (thickness ) of the pipe with thickness transition, p is calculated according to the codap (c2.1.4.2) instructions [18]: (10) where z is the welding coefficient. erm id r is the inner diameter of the pipe. ir and er are respectively inner and outer radius of thin pipe where e 1r it r . so, eq. (10) becomes: (11) the internal pressure is p = 14mpa, this pressure does not cause general plastic behaviour in the pipe of an average thickness ( 1 it r = 0.1). (a) (b) fig. 7: pipe with thickness transition: (a) subjected to internal pressure, (b) von mises stress. 263273 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 4. results and discussion 4.1 verification of the xfem model the castem 2016 software [7] was used for modelling and calculation; it has xfem and g-theta capabilities. the position of a point p on the crack front is defined by the angle ( ) (fig. 8), takes the value of 90° at the deepest point (d point) and 0° at the surface point (s point), those two points characterize the semi-elliptical crack. in general, the evaluation of sif at those two points is enough to judge the severity of the defect. at those points, the average value of k is given by eqs. (12) and (13) [8]: (12) (13) fig. 8: definition of average values on the element [8]. the french alternative energies and atomic energy (cea) [6] studied straight pipes containing external circumferential cracks, cea [8] calculated the influence factor ( 0i ) using the finite element method (fem). (14) where p is the pressure calculated in eq. (10) and k is the sif calculated by the g – theta method in xfem. the verification of the model was made by the comparison of the values 0i calculated by xfem in the present paper and the results of cea [8]. the relative error was calculated according to the eq. (15): (15) 0i is calculated at d and s points and along the crack front (fig. 8) for all fractions (a/ ) and (a/c), a sample of the results is presented in figs. 9-11. the relative error between the xfem results and literature [8] is between 0.09% and 0.7%. this gives confirmation to use numerical simulation based on xfem to investigate the sif at a thickness transition with one and two slopes in pressurized pipe. 264274 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 fig. 9: comparisons of 0i calculated by xfem in the present study with the literature [8], at s point, 1 / it r = 0.1. fig. 10: comparisons of 0i calculated by xfem in the present study with the literature [8], at d point, 1 / it r =0.1. fig. 11: comparisons of 0i calculated by xfem in the present study with the literature [8], along the crack front. 0 0.2 0.4 0.6 0.8 1 1.2 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 i0 (a/c =1 ,t/ri=0,1) i0 cea (a/c =1 ,t/ri=0,1) i0 (a/c =0,5 ,t/ri=0,1) i0 cea(a/c =0,5 ,t/ri=0,1) i0 (a/c =0,25 ,t/ri=0,1) i0 cea (a/c =0,25 ,t/ri=0,1) i0 (a/c =0,125 ,t/ri=0,1) i0 cea(a/c =0,125 ,t/ri=0,1) i0 a/t1 0 0.5 1 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 i0 (a/c =1 ,t/ri=0,1) i0 cea (a/c =1 ,t/ri=0,1) i0 (a/c =0,5 ,t/ri=0,1) i0 cea(a/c =0,5 ,t/ri=0,1) i0 (a/c =0,25 ,t/ri=0,1) i0 cea (a/c =0,25 ,t/ri=0,1) i0 (a/c =0,125 ,t/ri=0,1) i0 cea(a/c =0,125 ,t/ri=0,1) i0 a/t1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.5 1 1.5 2 2.5 3 0 20 40 60 80 100 i0 i0 cea relative error i0 t/ri =1/10,a/c = 1/8 and a/t1=0,8 r elative error 265275 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 4.2 comparison between k of the pipe with uniform thickness and the pipe with thickness transition in a previous paper, we analysed the effect of cracks in the thickness transition zone of pressurized pipes using xfem [19,20]. we have considered the elastic behaviour of the material and thickness transition with a single slope. the calculations of k for different geometries of the pipe subjected to internal pressure showed that cracks in the transition are the most severe. this result is in concordance with [3] which considered tensile stress and a bending moment. the present paper extends the previous work to the case of thickness transition with two slopes. figures 12 and 13 present the evolution of k value according to a/ in deepest and surface points in case of 1 / it r =0.1, for three types of pipes: uniform thickness, thickness transition with one slope, thickness transition with two slopes. fig. 12: evolution of k value according to a/t for pipes: uniform thickness, transition thickness with one slope, transition thickness with one slope, d point, 1 / it r =0.1, internal pressure. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 2 4 6 8 10 12 14 16 k, thickness transition, one slope,deepest,a/c=0,5 k, thickness transition, two slopes, deepest,a/c=0,5 k, thickness transition, two slopes, deepest,a/c=1 k, thickness transition, one slope,deepest,a/c=1 k, uniform thickness, deepest,a/c=1 k, uniform thickness, deepest,a/c=0,5 k, uniform thickness, deepest,a/c=0,125 k, thickness transition, one slope,deepest,a/c=0,125 k, thickness transition, two slopes, deepest,a/c=0,125 k(mpa m) a/t1 266276 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 fig. 13: evolution of k value according to a/ for pipes: uniform thickness, transition thickness with one slope, transition thickness with one slope, s point, 1 / it r =0.1, internal pressure. the results show that for the deepest point we have: k increases when 1/a t increases for all types of pipe that to say k is higher for depth crack ( 1/a t =0.8) for all pipes with different thicknesses and slopes. k is sensitive to the parameter a/c, k increases when a/c decreases for all depths of the crack ( 1/a t ), that's to say k is higher (14 mpa) for longer crack (a/c=0. 125). k is high for pipe with thickness transition, at the same time thickness transition with two slopes have the highest k for all forms of cracks. the results show that for the surface point we have: k depends on the parameter a/t for different pipes k varies slightly when a/c decreases for all depths of the crack ( 1/a t ), for a/c =0. 125 k attain only 5 mpa. as a result, in the case of a pipe with an average thickness ( 1 / it r =0.1), for a fixed angle = 30°and = 45°, we found that the thickness transition with two slopes has the greatest value of k, so it presents the greatest risk compared to the straight pipe and pipe with thickness transition and a single slope. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 1 2 3 4 5 6 k, thickness transition, two slopes, surface, a/c=1 k, uniform thickness, surface,a/c=0,5 k, thickness transition, one slope, surface, a/c=0,5 k, thickness transition, two slopes, surface, a/c=0,5 k, uniform thickness, surface,a/c=1 k, thickness transition, one slope, surface, a/c=1 k, uniform thickness, surface,a/c=0,125 k, thickness transition, one slope, surface, a/c=0,125 k, thickness transition, two slopes, surface, a/c=0,125k(mpa m) 1 / it ra/t1 267277 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 do these values of = 30° and = 45°, lead to a greater value of k? how does the variation of the parameters , and (j {1,2,3}) influence the variations of k for a pipe with average thickness? 4.3 effect of the transition zone on the variation of k based on the triangular relation, the length of the thickness transition is related to the angle of the slope by the following relation: (16) (l) mainly depends on ( ), ( ), . we consider those parameters as variable and analyze their effect on the variation of k. 4.3.1 effect of the slope in thickness transition on the variation of k in this study, we considered a pipe with an average thickness where ( )= ( ) =2.5, the pipe contained an elliptical crack defined by a/c=0.125 and a/ =0.8, the pipe is exposed to internal pressure . figure 14 (a) presents the evolution of k according to for a fixed value of in a deepest and surface points. the result shows that k increases when increases, k attains the maximum ( = 55 ) for =30°. for > 30°, k decreases and tends to stabilize to equal a great value compared with the value of k when < 30°. k in deepest point is higher than k in surface point for 20° < < 50° but for >50° exceeds . the transition reacts as an amplifier of stress, it magnifies the stress close to the surface, so the value of k is higher for the great value of ( > 50° ) of the slope of the first transition ( is fixed). when decreases ( < 50°), the concentration of the stress decreases at s point, because at s point, the thickness transition impact noticeably reduces in comparison with the effect of internal pressure which increases the concentration of stress in the deepest point. therefore, the value of k at d point becomes higher compared to the value of k in the surface point for small values of . fig. 14: variation of k at deepest and surface points: (a) according to 1, (b) according to 2. figure 14 (b) presents the evolution of k according to for a fixed value of in deepest and surface points. the result shows that k increases in a weak way, when 0 10 20 30 40 50 60 0 50 100 k ,deepest , 2 =20° k, surface , 2 =20° 1 0 5 10 15 20 25 30 35 0 50 100 k ,deepest , 1 =15° k, surface , 1 =15° 2 (a) (b) 268278 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 increases and it attains the maximum ( = 29 ) for =45°. for >45°, k keeps a stable value, at the same time, the values of k at the deepest point are close to those of k at the surface point for all values of , that’s to say the angle of the slope does not have a great effect on the variation of k. as a result, the slopes 30° and 45° present a grave case for thickness transition with a double slope, also the angle of the first slope( ) in thickness transition has more impact on the variations of k than the angle of the second slope ( ). 4.3.2 effect of parameters ( , ( )) and ( , ( )) on the variation of k in thickness transition with a double slope in the part (4.3.1), we supposed and as variables and analyzed their effect on the variation of k in thickness transition for fixed values of ( ) and ( ). in this part, firstly ,we consider and ( ) as variables and we fix ( ) and , in this case, the parameter is varied within the range of 5°to 50°and the ratio ( ) is varied from 1.1 to 6, secondly, we vary and ( ) and fix other parameters, the ratio ( ) is varied from 1.1 to 4. figure 15a-b present the variations of k according to the parameters and ( ), for ( ) =1.30 and =30°at deepest and surface points. figure 15a-b, show that for both d and s points, we have: for 1.1 ( ) 1.5, the value of k is high and exceeds the toughness of materials p265gh ( =96mpa ). for all values of , in the case of 1.5 < ( ) , we note that k decreases when( ) increases and stabilizes for ( ) greater than 4.5. for 30°, k takes the greatest value for all ( ). as a result, the great value of the angle of the first slope in a cracked pipe has an important effect on the variation of k, more precisely 30° is a grave case for the construction of the pipe and increasing the ratio of thicknesses ( ), is an effective way to reduce the risk of the defect in a pipe. figure 15c-d present the variations of k according to the parameters and ( ), for ( ) =1.40 and =30°at deepest and surface points. the curves of stress intensity show that for d and s points, we have: in the case of 30°; k exceeds the toughness of materials ( ), k decreases when ( ) increases. in the case of < 30°; k increases when ( ) increases but it but this evolution of k as a function of ratio ( ) is not remarkable. as a result, the parameter ( ) does not have more impact on the variation of k in thickness transition with a double slope for a pressurized pipe. 4.3.3 effect of parameters ( , ( )) and ( , ( )) on the variation of k in thickness transition with a double slope proceeding as before; we analysed the evolution of k in the thickness transition by fixing two parameters of the transition zone and varying the rest. 269279 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 fig. 15: variation of k at deepest and surface points: (a-b), according to ( ), (c-d), according to ( ). figure 16a-b present the variations of k according to the parameters and ( ), for ( ) =1.30 and =20°at deepest and surface points. the parameter is varied within the range of 10°to 50°and the ratio ( ) is varied from 1.1 to 6. the result shows that the stress intensity curves don’t depend on the variation of for s and d points. the variation of k relates mostly on the parameter ( ) of the first thickness transition, the range 3.5 ( ) 4 allows small values of k (k<9mpa). figure 16c-d present the variations of k according to the parameters and( ), for ( ) =1.40 and =20° at deepest and surface points. the ratio ( ) is varied 0 50 100 150 200 250 0 2 4 6 8 k, surface , 1 =50° k, surface , 1 =40° k, surface , 1 =15° k, surface , 1 =20° k, surface , 1 =30° k, surface , 1 =5° t2/t1 0 50 100 150 200 250 300 350 400 450 0 2 4 6 8 k ,deepest , 1 =50° k ,deepest , 1 =40° k ,deepest , 1 =15° k ,deepest , 1 =20° k ,deepest ; 1 =30° k ,deepest , 1 =5° t2/t1 0 50 100 150 200 250 0 1 2 3 4 k, surface , 1 =20 k, surface , 1 =15 k, surface , 1 =5° k, surface , 1 =40 k, surface , 1 =50 k, surface , 1 =30 t3/t2 (c) 0 50 100 150 200 250 300 350 400 450 0 1 2 3 4 k ,deepest , 1 =20° k ,deepest , 1 =15° k ,deepest , 1 =5° k ,deepest , 1 =40° k ,deepest , 1 =50° k ,deepest , 1 =30° t3/t2 (d) (a) (b) 270280 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 from 1.1 to 4.5. the results show again, that does not have enough effect on the variation of k, in addition, k increa,ses when ( ) increases but this variation of k is not very remarkable, the range 1.5 ( ) 2.5 allows small values of k (k < 35 mpa). as a result, the parameters of the thickness transition in a pipe have an influence on the variations of k, precisely the parameters of the first thickness transition ( , ( )) are more influential on the gravity of defect compared to the second thickness transition ( , ( )). fig. 16: variation of k at deepest and surface points: (a-b) according to ( ), (cd) according to ( ). 5. conclusion in this paper, we analysed the effect of an external circumferential elliptical crack located at the thickness transition zone of a pipe with double slopes. the study showed that for the surface and the deepest points, the angle = 30° and 1.1 ( ) 1.5 are grave cases of the first slope of the thickness transition. the angle = 45° and ( )=3.5 lead to an increase in the value of k but in general, the effect of the son slope 0 5 10 15 20 25 0 2 4 6 k, surface , 2=10 k, surface , 2=25 k, surface , 2=35 k, surface, 2=45 k, surface , 2=50 t2/t1 0 5 10 15 20 25 30 35 40 45 0 2 4 6 k ,deepest , 2=10 k ,deepest , 2=25 k ,deepest, 2=35 k ,deepest , 2=45 k ,deepest , 2=50 t2/t1 0 5 10 15 20 25 30 35 40 45 50 0 1 2 3 4 5 k, surface , 2=50 k, surface , 2=45 k, surface , 2=35 k, surface , 2=25 k, surface , 2=10 t3/t2 0 5 10 15 20 25 30 35 40 45 50 0 1 2 3 4 5 k ,deepest , 2=50 k ,deepest , 2=45 k ,deepest , 2=35 k ,deepest , 2=25 k ,deepest , 2=10 t3/t2 (a) (b) (c) (d) 271281 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 isn’t remarkable, that is to say the parameters ( , ( ) ) are more influential than the parameters ( , ( ) ). considering the internal pressure, this work highlighted the investigation of a 3d crack problem in a thickness transition pipe using xfem. in xfem, level sets and enrichment zone were defined. a crack is easily modelled by enrichment functions. the comparison between the stress intensity factors showed that the pipe containing a thickness transition with double slopes is more sensitive to the considered cracks. the decreasing of the angle of slopes and the increase of the ratio of thickness is one effective method of reducing the sif. references [1] rahman s, ghadiali n, wilcowski gm, moberg f, brickstad b. (1998) crack-opening-area analysis for circumferential trough-wall cracks restrain of bending thickness transition and weld residual stresses. int j pres ves pip, 75(6):397-415. [2] hanan el bhilat, khalid el had, houda salmi, abdelilah hachim. (in press). thermomechanical characterization of post-consumer recycled high impact polystyrene from disposable cups: influence of the number of processing cycles. journal of computational & applied research in mechanical engineering (jcarme). doi 10.22061/jcarme.2019.5187.1643 [3] abdelkader saffih, hariri s. (2006) numerical study of elliptical cracks in cylinders with a thickness transition’ international journal of pressure vessels and piping; 83(1):35-41. doi: 10.1016/j.ijpvp.2005.10.002 [4] abdelkader saffih, hariri s. (2006) comparison of semi-elliptical cracks in cylinders with a thickness transition and in a straight cylinder – elastic-plastic behavior, engineering fracture mechanics, 73(4):2685-2697 [5] hariri s, el hakimi a, azari z. (2008) etude numérique et expérimentale de la nocivité des défauts dans des coques cylindriques et sphériques: aide à la détermination des facteurs de contraintes, revue de mécanique appliquée et théorique, 1(10):791-804. http://smsm.fsac.ac.ma/larevue/2008/art9vol1n10.pdf [6] cea; the french alternative energies and atomic energy commission (cea). ‘commissariat à l’energie atomique (france)’ http://www.cea.fr/. [7] castem; [http://www-cast3m.cea.fr/] [8] chapuliot s, lacire mh. (1999) stress intensity factors for external circumferential cracks in tubes over a wide range of radius over thickness ratios. american society of mechanical engineers, pressure vessels and piping division, 50(2):395-106. https://inis.iaea.org/collection/nclcollectionstore/_public/31/058/31058406.pdf [9] moës n, gravouil a. belytschko t. (2002) non-planar 3d crack growth by the extended finite element and level sets; part i: mechanical model. international journal for numerical methods in engineering, 53(11):2549-2568. https://doi.org/10.1002/nme.429 [10] salmi h, el had k, el bhilat h, hachim a. (2020) numerical study of sif for a crack in p265gh steel by xfem. in: dos santos s., maslouhi m., okoudjou k. (eds) recent advances in mathematics and technology. applied and numerical harmonic analysis. birkhäuser, cham. doi.org/10.1007/978-3-030-35202-8_6 [11] belytschko t, black t. (1999). elastic crack growth in finite elements with minimal remeshing, int. j. numer. methods eng, 45(5):601–62. [12] stolarska m, chopp d, moes n, belytschko t. (2001) modelling crack growth by level sets in the extended finite element method, int. j. numer. methods eng, 51(1):943–960. [13] seyed javid zakavi, behzad shiralivand, mohammad nourbakhsh. (2017) evaluation of combined hardening model in ratcheting behavior of pressurized piping elbows subjected to in-plane moments. journal of computational & applied research in mechanical engineering (jcarme); 7(1): 57-71. doi 10.22061/jcarme.2019.5187.1643 272282 iium engineering journal, vol. 21, no. 2, 2020 houda et al. https://doi.org/10.31436/iiumej.v21i2.1454 [14] kamal sharma ivs, mishra bk, bhasin v. (2014) numerical modeling of part-through cracks in pipe and pipe bend using xfem, procedia materials science, 6(2):72-79. [15] rice jr. (1968) a path independent integral and the approximate analysis of strain concentration by notches and cracks, journal of applied mechanics, 35(1):379-386. [16] sukumar n, chopp dl, moran b. (2003), extended finite element method and fast marching method for three-dimensional fatigue crack propagation, engineering fracture mechanics, 70(1): 29-48. [17] eshelby jd. (1956) the continuum theory of lattice defects, solid state physics, 3(2):79144. [18] codap (2005); french construction code. construction des appareils à pression non soumis à l’action de la flamme, ‘the code for construction of unfired pressure vessels, division 1, part c – design and calculation, section c2 – rules for calculating cylindrical, spherical and conical shell subjected to internal pressure. [19] houda salmi, khalid el had, hanan el bhilat, abdelilah hachim. (2019). numerical analysis of the effect of external circumferential elliptical cracks in transition thickness zone of pressurized pipes using xfem. j. appl. comput. mech., 5(5):861-874. doi: 10.22055/jacm.2019.28043.1452. [20] houda salmi ; khalid el had; hanan el bhilat; abdelilah hachim (in press). numerical modeling and comparison study of elliptical cracks effect on the pipes straight and with thickness transition exposed to internal pressure, using xfem in elastic behavior. journal of computational and applied research in mechanical engineering. doi: 10.22061/jcarme.2019.3597.1448. 273283 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <feff005500740069006c0069007a00610163006900200061006300650073007400650020007300650074010300720069002000700065006e007400720075002000610020006300720065006100200064006f00630075006d0065006e00740065002000410064006f006200650020005000440046002000610064006500630076006100740065002000700065006e007400720075002000760069007a00750061006c0069007a006100720065002000640065002000ee006e00630072006500640065007200650020015f0069002000700065006e00740072007500200069006d007000720069006d006100720065006100200064006f00630075006d0065006e00740065006c006f007200200064006500200061006600610063006500720069002e00200044006f00630075006d0065006e00740065006c00650020005000440046002000630072006500610074006500200070006f00740020006600690020006400650073006300680069007300650020006300750020004100630072006f0062006100740020015f0069002000410064006f00620065002000520065006100640065007200200036002e003000200073006100750020007600650072007300690075006e006900200075006c0074006500720069006f006100720065002e> /rus <feff04180441043f043e043b044c043704430439044204350020044d044204380020043f043004400430043c043504420440044b0020043f0440043800200441043e043704340430043d0438043800200434043e043a0443043c0435043d0442043e0432002000410064006f006200650020005000440046002c0020043f043e04340445043e0434044f04490438044500200434043b044f0020043d0430043404350436043d043e0433043e0020043f0440043e0441043c043e044204400430002004380020043f043504470430044204380020043104380437043d04350441002d0434043e043a0443043c0435043d0442043e0432002e00200421043e043704340430043d043d044b043500200434043e043a0443043c0435043d0442044b00200050004400460020043c043e0436043d043e0020043e0442043a0440044b0442044c002c002004380441043f043e043b044c04370443044f0020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e00300020043b04380431043e00200438044500200431043e043b043504350020043f043e04370434043d043804350020043204350440044104380438002e> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 135-492 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 9 development of virtual assembly layout with modeling languages approach and simulation using delmia™ quest ® norhidayah m. 1 , yupiter h.m. 2 , roseleena j. 2 , shaharudin a. 2 , and erry y.a. 3 1 faculty of engineering technology, multimedia university, bukit beruang, 75450 melaka, malaysia. 2 faculty of mechanical engineering uitm shah alam 40450 shah alam, selangor darul ehsan, malaysia. 3 department of manufacturing and materials engineering, international islamic university malaysia, 53100 kuala lumpur, malaysia. nhidayah.mohamad@gmail.com abstract: the paper presented the development of virtual layout model with modeling languages approach. this research also explores the flexibility of the model configurations through the development process of database for storing and representing the virtual model. the concept and mechanisms of database development involves the use of extensible markup language (xml). the objectives of the research are therefore to obtain a basic understanding on how these modeling languages are used to develop virtual model, representing the simulation by using delmia™ quest® and develop a database for share, store and future usage. therefore, the generated simulation presents the feasibility of interchanging models using modeling language approach as an intermediate representation and provides an opportunity to improve simulation quality. abstrak: kertas penyelidikan ini membentangkan pembangunan model tataatur maya dengan menggunakan pendekatan bahasa permodelan. kajian ini juga meninjau kefleksibelan konfigurasi model melalui proses pembangunan pangkalan data untuk menyimpan dan mewakili model maya. konsep dan mekanisme pembangunan pangkalan data melibatkan penggunaan bahasa extensible markup (xml). objektif kajian ini ialah untuk mencapai kefahaman asas tentang bagaimana bahasa permodelan dapat digunakan bagi membangun model maya, mewakili simulasi dengan menggunakan delmia™ quest® dan membangunkan pangkalan data bagi tujuan berkongsi, menyimpan dan penggunaan masa depan. ini bermakna, simulasi yang terjana dapat melahirkan kemungkinan saling tukar model dengan menggunakan pendekatan bahasa permodelan sebagai perwakilan perantaraan dan melahirkan peluang untuk memperbaiki kualiti simulasi. keywords: modeling languages; virtual layout model; database; simulation; delmia™ quest®, xml 1. introduction computer simulation was started by implemented in 3rd generation languages such as fortran or basic. many disciplines related to engineering have been using various sophiscated simulation languages such as general purpose simulation system (gpss), siman which used to define the logical and physical components of a system, simscript, slam and stella [1]. these languages were used by previous iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 10 researchers to reduce the amount needed in constructing a model by including a variety of features pertinent to simulation. the model interchange for specific purpose can also be enabled by defining a superset language of all the systems as mentioned above. a variety of modeling languages exist to support various applications of simulation for certain functionality in term of creation or manipulation of entity attributes. simulation packages that are currently available are no longer to require a strong background in mathematics or computer programming languages in order to perform realworld and interactive simulations [2]. from this new simulation modeling technique, perhaps it will increase efficiency in modeling iterations, creating a form of standard simulation data exchange, and use an innovative method for executing simulation model constructions. bollen [3] has applied the concept of language determination by providing initial model for creating in business area simulation. the natural language modeling (nlm) is used to construct the model by information of communication document and schematic of process flow perspective. although some simulation languages are designed to handle continuous systems exclusively, delmia quest and the languages (scl and bcl) discussed here enable the modeling of both discrete events to occur when necessary, and determine function values for differential stochastic simulation. from this approach, an exploration comes out towards the scl and bcl to establish a model design for industry layout and define the model custom behaviors. balci [4] described how to conduct the programming process in high-level languages in his work. this is the process of experimenting with the simulation model for a specific purpose. some purposes of experimentation are for evaluation of system behavior, forecasting, and determination of functional relations. the process of experimentation then produces the simulation results. the result of experimental model represents the current form of the system. next users may alter it for obtaining another set of results and modifying it for other purpose use. development of database oriented for exchanging data between simulations and other manufacturing applications is needed for efficiently in reusing existing simulation model data [5]. however, developing simulation models are time-consuming work that often must be repeated to undertake different simulation studies. the development of layout data formats for storing simulation models enables the development of reusable models, and hence it could greatly improve the accessibility of simulation technology to industry as identified from the research conducted by mclean et al. [6]. this approach brings the potential in supporting the simulation technology to be more accessible to a wide range of industrial users [7]. the simulation models also result in a more in-depth understanding of manufacturing parameters and clear understanding of the improvements as indicated by farahmand [8]. most of model developers created the discrete event simulations (des) with a wide variety of software packages and programming languages. these simulations execute models of particular systems. reichenthal [9] defines model sharing as the ability for a simulation system to use models developed for another system. the variety of representations of des models complicates their reuse. simulation developers always determine all new solutions that enable simulation model interchange and make simulation development more effective. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 11 2. materials and method the languages were structured for the design and the development of virtual assembly layout (val) prescribed an integrated rule-based approach to simulate and optimize a manufacturing layout model. the research methodology and procedures undertaken in this research are summarized and illustrated in fig.1. fig.1: the research methodology and procedures. the modeling activity involves by determining the element of machines, workstations, and other facilities. the process of designing the layout in order to analyze the virtual layout function of an assembly work area which contributes the flow of processing part, assembling, the quantity of the elements or entities used, and the number iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 12 of labour work-in-process at workstations. the data integration specification is structured onto a file-based in order to execute the process of simulation. 2.1 the modeling languages orientation the conceptual manufacturing layout used the modeling languages, which are simulation control language (scl) and batch control language (bcl). manufacturing design layout is developed by composing the control language and synthesizing the structures: control, data, and operational. the modeling language is based on a set of object classes that simulates the behaviour of a real system component. 2.1.1 the simulation control language (scl) the scl provides modeling rules that govern the action and all aspects of element in order to meet the unique needs of designed model and show determination of the outline structure in a fabrication manufacturing layout. the scl logic tracking functions are compiled and appended into the file-based by associating the modular procedural programs with specific resource entities. the elements in the val model are controlled by a set of rules to control the model behaviour at a very detailed level. the model directly simulates the system behaviours through a distributed logic that is associated with each resource that includes route, buffering policies, storage and retrieval and lastly by requestbased decision-making. the most commonly needed logic is easily selected from a comprehensive logic lists and many driven parameters for even greater flexibility. this high-level, structured language provides distributed processing access to all system variables. the logic that drives the val will possibly changed due to the capability of scl and the library of logic created will gain unlimited control over the simulation. the language assists with the built-in distribution functions which, in conjunction with streams, return random values according to a statistical distribution. write a model program in text editor <notepad.scl> file store file in the right folder within library directory compile scl logic file scl called out function check prone errors and debugging load model test logic and run iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 13 fig. 2: route steps of appending scl program file to val. figure 2 presents the step to upload the scl file to execute the val simulation. when assigning any logic to an element, the file name from the library has choose first, and then list of the procedure is selected within that file. through scl program, the program was compiled within the logics dialog box. files were named appropriately and with the correct format extension. scl will link to the model and the model states can be saved and recalled at any point during the simulation. this convenient feature speeds up trouble-shooting time and reduces the warm-up time required to perform a steady-state simulation experiment. 2.1.2 the batch control language (bcl) contrast to the scl, the bcl is used to create a series of runs with alternative scenarios without interruptions, furthermore it has been developed beyond the interface control stage to edit or modify the parameters of simulation environment when manipulate the model. bcl will create a series of runs with alternative scenarios without interruptions. bcl also comprises of a set of commands and alternative methods for creating and executing the val model. the applications of bcl including: a. creating scripts of bcl commands for running and manipulating the val model without interruption. b. interfacing the built model and run processes with data provided by third party software. c. creating self-optimize models driven by another program. d. changing model parameters from scl by calling bcl commands. the bcl commands were typed in one at a time, which will change an existing model which is part of the quest software. elements in bcl codes of the model are derived from the sub-data file content. there are bcl macros were assigned for the model in the quest modeling environment. this utilizes the bcl macro function to execute bcl codes in quest. upon calling up the bcl macro, the bcl codes executed and generated line by line into the quest interface. the bcl consist of a set of commands and alternative methods for creating and executing the val model. the process of implementing bcl function for model designed, quest software must be loaded first with a file of bcl commands. a text of bcl commands are specified as providing the initial instructions to quest which includes building or reading a model and modifying and running the model. almost all bcl commands can be apply through scl programming. the scl script is written to read a list of element names and locations, and execute bcl calls to create and locate those elements by keying in or typing the bcl (command_text: string): for integer function within an scl script. a string argument (command_text: string): that contains specific bcl command should be provided along with a complete scl script and quest to execute it. if the bcl function returns an integer containing an error code, it indicates either the command executed is proper or vice versa. a list of error code numbers and their corresponding descriptions are located in the bclerr.inc file in the questlib\include folder. 2.2 the virtual assembly layout development iium engineering journal, vol. the val model was built incrementally by dividing the factory layout into smaller areas of assembly process line one at a time. the concept of assembly layout aisle is by implementing the group technology (gt) cell through the identification of parts moving from machine to another. although the flow is not unidirectional, functional machines are located in close proximity. the virtual assembly layout (val) model contains several kinds of information including information about the syste processing logic, routing logic, and stochastic information of the model elements. the process of designing the layout in order is to analyze the function of the isle of the work area prior to layout design process which contributes from the flow and buffer storage, the quantity of the equipment or entities used, and the labour work process at workstations. the elements were gathered with a set of inputs and outputs, groups of machine process, labour, and part flow path a system layout which starts from an input, assembly areas and ends with the output points. 2.3 layout data file in order to accomplish the val model layout configuration task, the assembly line of the manufacturing process sequences was mapped into the layout data file. the microsoft notepad is a free source code editor tool that is used to create the layout data file. it supports several programming languages include scl and bcl. it is used to simplify data entry and population of the internal object structure. additional features and parameter modifications are done by changing the information fig.3 represents the schematic model simulation. fig. 3: schematic val figure 3 is the schematic on how conceptually flow of the layout data file works for the simulation system and interpret the result on the computer screen are depicted. the layout data file above is used to fabricate the layout models c verified using simulation. in the file, the assembly layout model is constructed manually by creating a hierarchy of data representing the designed layout information model. scl&bcl scl & bcl applications g journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 14 the val model was built incrementally by dividing the factory layout into smaller areas of assembly process line one at a time. the concept of assembly layout aisle is by implementing the group technology (gt) cell through the identification of parts moving from machine to another. although the flow is not unidirectional, functional machines are located in close proximity. the virtual assembly layout (val) model contains several kinds of information including information about the syste processing logic, routing logic, and stochastic information of the model elements. the process of designing the layout in order is to analyze the function of the isle of the work area prior to layout design process which contributes from the flow process part, assemble and buffer storage, the quantity of the equipment or entities used, and the labour work process at workstations. the elements were gathered with a set of inputs and outputs, groups of machine process, labour, and part flow path and it is a typical manufacturing system layout which starts from an input, assembly areas and ends with the output points. in order to accomplish the val model layout configuration task, the assembly line of manufacturing process sequences was mapped into the layout data file. the microsoft notepad is a free source code editor tool that is used to create the layout data file. it supports several programming languages include scl and bcl. it is used to data entry and population of the internal object structure. additional features and parameter modifications are done by changing the information in the layout data file. 3 represents the schematic model simulation. fig. 3: schematic val model simulation. 3 is the schematic on how conceptually flow of the layout data file works for the simulation system and interpret the result on the computer screen are depicted. the layout data file above is used to fabricate the layout models configuration and was verified using simulation. in the file, the assembly layout model is constructed manually by creating a hierarchy of data representing the designed layout information model. run the val model the layout data file upload the db save statistics in xml format from the multirun page( eg: xml/virtual_assembly_layout_ stats.xml ) scl & bcl applications towards the database start quest : special issue in science and ethics norhidayah et al. the val model was built incrementally by dividing the factory layout into smaller areas of assembly process line one at a time. the concept of assembly layout aisle is by implementing the group technology (gt) cell through the identification of workflow parts moving from machine to another. although the flow is not unidirectional, functional machines are located in close proximity. the virtual assembly layout (val) model contains several kinds of information including information about the system layout, processing logic, routing logic, and stochastic information of the model elements. the process of designing the layout in order is to analyze the function of the isle of the work process part, assemble and buffer storage, the quantity of the equipment or entities used, and the labour work-inprocess at workstations. the elements were gathered with a set of inputs and outputs, nd it is a typical manufacturing system layout which starts from an input, assembly areas and ends with the output points. in order to accomplish the val model layout configuration task, the assembly line of manufacturing process sequences was mapped into the layout data file. the microsoft notepad is a free source code editor tool that is used to create the layout data file. it supports several programming languages include scl and bcl. it is used to data entry and population of the internal object structure. additional features and in the layout data file. 3 is the schematic on how conceptually flow of the layout data file works for the simulation system and interpret the result on the computer screen are depicted. the onfiguration and was verified using simulation. in the file, the assembly layout model is constructed manually by creating a hierarchy of data representing the designed layout information model. save statistics in xml format from the multirun page( eg: xml/virtual_assembly_layout_ stats.xml ) run the val model iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 15 2.4 manufacturing information (mi) database the development of the mi is continuing to support store the input of data for the entire the val model. the purpose to develop mi database is to provide a mechanism for configuring the assembly layout model and sharing data between simulations. figure 4 displays a portion of the machining data and the rest of several elements’ data are described in the following sections. this xml instance document, which contains parts, sources, machine classes, buffers, sinks, logical connections, operation-definitions, unitsof-measurement, and process distributions, is manually generated to support this virtual assembly line layout model. fig. 4: assembly machining data within mi database. a snapshot of fig. 4 represents a part of the information for machining sequences process. for this assembly station, the distribution of part due to machining sequences is constant and is referred to as a coordinate set command of assignment function. content that is not intended for the xml parser, such as notes about document structure or editing, can be included in a comment. the process element contains process specifications that describe how production includes routing, operation, and logic programs that support work to be performed in the assembly layout. routing are the plans used to define job and task-level work items, respectively, in the work hierarchy. these process plans define the steps, precedence constraints between steps, and resources required to produce parts and perform support activities. the parts data element is created to maintain the broad range of information that is needed about each part that is handled by the assembly line. part data includes an identifying part number, name, description, size, and color. this mi defines the physical locations of resource objects and part instances within the shop. it also defines reference points, area boundaries, and paths. 3. model simulation one factor in the selection of delmia™ quest® is that it allows the creation of a simulation model from scratch using two of its built-in programming languages, scl and bcl. by using a program which translates the information in a layout data file into bcl database iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 16 and scl, the quest® models need to generate a layout model of configuration and simulate the part flow movement within the assembly line. figure 5 which is the flowchart to generate the model. fig. 5: flowchart to generates val model simulation. in an assembly line, part assembly is split into two stations and working simultaneously. figure 6 displays the val model draft before and after simulation. when one station is finished with a part, it passes it on to the sink that considered as output. in this case, the val model system simulation, there are multiple paths through the system and routes for each possible travel. parts leaving the source enter into work cell area then the running parts in the queues at the machines for mode of processes picked by labors move along path following the sequences set up. if the newly animated model simulate, occasionally parts will run over or pass each other. this is due to a combination of the data gathered and the manner in which model was animated. all parts transferred assumed to be one second regardless of the distance traveled. quest sets the speed of a route entity based on the transfer time and the physical length of the route on the animation. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 17 fig. 6: the val model from draft into simulated. during simulation of the assembly line, raw material enters the line at a selected distribution rate for the process of installation with child part or with any other individual parts. the sink element process completes assembly activities by exiting from cell, and delivery to truck store, and collecting statistics data. both of the assembly line process performed the same operation; fasten other child part with module part. assuming no loss of time when moving a part from one station to another, the longest stage on the assembly line determines the throughput (1000 seconds for the child part installation) so a part can be produced with minimum of 50 pieces. 4. results and discussion the development of an assembly layout model with modeling languages approach demonstrated the capability of a simulation method in generating result and optimizing the performance of virtual layout design. the demonstration and testing models only contain a few of supported item referring with the initial plan design. therefore there are no issues of scope arose during experimentations. however, observed problems were associated with issues of syntax data exposure application which implicates with larger the data file created, the more time are require to compile and list all the procedures. if a single error in critical sections of this code are distinguish for example, the code which creates an entity in quest from specific data could propagate throughout the simulation model and lead to serious problems. the techniques used to achieve confidence in modeling the val were detailed code checking and testing, code execution tracing in debug mode, running models under simplified conditions where model output can be predicted and observing animation outputs when running models under different scenarios. even though after completing all iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 18 stage for perception, never assume that the logic always working during launched the model. user may use statements in the code to track which events that occurred for that particular model. then the statement may be verified by running at every segment of the model manually. 4.1 the val model animation an animation was the effective way to find invalid model assumptions and to enhance the credibility of a simulation model. the availability of built-in animation is one of the reasons for the increased use of simulation modeling. the key elements of the system of val animation represented on the screen dynamically can be change the coordinates point, type of distribution and attributes as the simulation model evolves through time via the modification of the layout data file. in an animation, key element of the system are represented on the screen by the icons that dynamically change position, color and shape as the simulation model evolves through time. visualization (animation) of a simulation model greatly assists in model verification and validation [4, 11]. in the concept of the layout data file for val model developed, a generic conceptual model was first created and validated during the design phase of the virtual assembly layout associated database. the verification of the layout data file includes all the usual verification considerations to simulate the val model. this practice is to eliminate any of or even a single error in critical sections of this code that creates an entity in layout model from specific data which will proliferate throughout the simulation model and end up with failure on the model implementation. verification of the model-builder code itself remains an important and potentially a difficult task. but once completed, it does not have to be repeated for each model generated. the features of this model was constrained by the manufacturing layout domain and determined by the functionality designed into the model builder software compliance with the associated database structures. with regards to inputs, outputs, assumptions and simplifications, some limited configuration options provided by the model-builder software will be encountered. fig. 7: flow step of debugging the val model. model modifications test the val model run syntax error determination distinguish the error with entire model iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 19 regarding to the flow process in fig.7, in step 1, the model is tested revealing the existence of errors (bugs). given the detected errors, the cause of each error is determined in step 2. in step 3, the model changes believed to be required for correcting the detected errors are identified. the identified model changes are carried out in step 4. step 1 is reexecuted right after step 4 to ensure successful modification because a change correcting an error may create another one. this iterative process continues until no errors are identified in step 1 after sufficient testing. 4.2 manufacturing information (mi) evaluation the verification of a mi database includes all the usual verification considerations, and the verification of the xml tag code input parameter and logical structure of val are must presented. the mi driven data is not successfully transferred to transform into and execute using the proposed approach as the layout data file do due to the discrepancy or conflict occurred during transformation to view the simulation model. discrepancies exist between the way some of the data is stored in mi, how it is modeled in the val simulation model and there are no translator package developed to transform the model data. in general, discrepancies will be resolved by creating tentative extensions to the mi database specification rather than changing the simulation model. 5. conclusion the selection software of delmia™ quest® with its macro-language, scl and bcl are fulfilling these requirements and brought considerable development benefits on the ability to change important attributes of certain elements in the model, depending on the current contexts that prompt in defining element coordination and characteristic expression. delmia™ quest® simulation tools offer considerable flexibility when are used to represent the val model behavior and observe the impact upon the model’s system performance during simulation. this method undertakes to provide an optimum level of realism and validation for the model. this research also demonstrates the interaction data, layout data file developed which using scl and bcl makes the compliant model (val) can be rapidly creates and modifies the val layout model’s parameter and entities. the manufacturing information data for modeling effort is a computer-interpretable representation that allows for the storing structural information data and the exchange of manufacturing entities or parameters. the implementation of the developed mi driven will support the integration of manufacturing parameters applied in selected area such as in whole factory layout and other specific areas. the proposed methodology will be further tested in the ongoing project and induce for collaborations with other faculty especially computer science or others who are intense to involve in this effort. therefore, it can be concludes that the generated simulation demonstrates the feasibility of interchanging models using modeling language approach as an intermediate representation and provides an opportunity to improve simulation quality. acknowledgement we would like to thank the editor and all the anonymous referees for their helpful comments and suggestions, which led to an improved version of this manuscript. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics norhidayah et al. 20 references [1] zeigler, b. p., praehofer, h., & kim, t. g. “theory of modeling and simulation” (2nd), san diego: academic press, 2000. [2] meyers, matthew p. et.al, manufacturing facilities design and material handling 3 rd edition. pearson prentice hall, 2005. [3] bollen,p. “nlm for business application semantics,” journal of information science and technology, 2005, pp. 18-48. [4] o. balci, “principles and techniques of simulation validation, verification, and testing”, in proceedings of the 27th conference on winter simulation conference, 1995 [5] azadeh and f. ghaderi,” a framework for design of intelligent simulation environment”, department of industrial engineering, research institute of energy management and planning, university of tehran, iran, 2006. [6] charles mclean, al jones, t. lee, frank riddick,” an architecture for a generic datadriven machine shop simulator,” manufacturing systems integration division national institute of standards and technology gaithersburg, proceedings of the winter simulation conference, 2002. [7] lee, and y. t. “information modeling: from design to implementation,” proceedings of the second world manufacturing congress, durham, u.k. 1999. [8] kambiz farahmand, “using simulation to support implementation of flexible manufacturing cell”, university department of mechanical & industrial engineering. proceedings of the winter simulation conference, 2000. [9] reichenthal, s. w. “srml case study: simple self-describing process modeling and simulation”. proceedings of the winter simulation conference. 2004. [10] o. balci, “validation, verification, and testing techniques throughout the life cycle of a simulation study” in proceeding of winter simulation conference, 1994, pp.121-173 121. [11] law, averill m., “simulation modeling and analysis 4 th edition”, mc graw-hill.new york, 2007. [12] y.t. lee and y. luo. “data exchange for machine shop simulation”, manufacturing systems integration division national institute of standards and technology gaithersburg, md 20899-8260, u.s.a. proceedings of the winter simulation conference, 2005. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 design of wlan and wimax band rejection utilizing uwb planar antenna comprising slit in the conductor planes siti fatimah jainal1, norliza mohamed2 and azura hamzah3 1faculty of engineering, lincoln university college (luc), kelana jaya, selangor, malaysia. 1,3malaysia japan international institute of technology, utm kuala lumpur, malaysia. 2razak faculty of technology and informatics, utm kuala lumpur, malaysia. *corresponding author: sitifatimah@lincoln.edu.my (received: 27th february 2019; accepted: 30th july 2019; published on-line:2nd december 2019) abstract: a compact and low profile ultra wideband planar antenna comprises dual notched-band characteristics for wimax and wlan are presented. uwb communication system is allocated between 3.1 and 10.6ghz, which coexisted with the wlan and wimax frequency bandwidths at 3.3 to 3.6ghz, and 5 to 6ghz, repsectively. the coexistence between multiple frequency bandwidths possibly can cause interference into the communication systems such as data loss and signal disruption. thus, it is essential to eliminate the coexisted frequency bandwidhs from uwb spectrum. the uwb planar antenna is costructed with a radiator of an elliptical-shaped, and half-ground element which is subjected to suppress the frequency bandwidth for 3.3 to 3.7 and 5 to 6 ghz. slits are engraved in the elliptical radiator and ground element by etching the conductor elements. slit shapes are designed in simple and optimized to realize the maximum band notch characteristics. slit placements are scrutinized and the band notch characteristics are determined. it is considered that the slit in the ground element and the elliptical radiator have stimulated the band notches frequency bandwidths for 3.3 to 3.7 and 5 to 6 ghz, respectively. the uwb planar antennas are compared with the reference antenna and the results are verified. measured reflection coefficient s11 for band notch peaks at the wlan and wimax frequency bandwidths are about -3.0 and -4.0 db, respectively. radiation pattern co-polarizations in the hand e-plane are in omniand bi-directional, respectively. maximum gain g is located in the –z –axis and –x –axis in hand e-plane in the frequency of interest. surface currents are distributed in the slit areas. slits in the elliptical radiator and the ground element are not substantially affect the uwb planar antenna overall performances. abstrak: antena jalur lebar paling satah yang padat dan bersusuk rendah telah diperkenalkan dan terdiri daripada dua ciri lebar-takik bagi wimax dan wlan. sistem komunikasi uwb berada pada 3.1 dan 10.6ghz, bertindan dengan jalur lebar frekuensi wlan dan wimax yang berada pada 3.3 hingga 3.6ghz, dan 5 hingga 6ghz, masingmasing. sifat bertindan antara beberapa jalur lebar frekuensi mungkin akan menyebabkan gangguan pada sistem komunikasi seperti kehilangan data dan gangguan isyarat. oleh itu, adalah penting bagi membuang jalur lebar frekuensi yang bertindan dengan spektrum uwb. antena satah uwb telah dibina dengan radiator pemancar berbentuk elips, dan unsur separuh-bumi (lapisan asas) dibawah jalur lebar frekuensi pada 3.3 hingga 3.7 dan 5 hingga 6 ghz. jalur celahan telah diukir pada radiator elips dan lapisan asas dengan mengukir unsur konduktor. jalur celahan telah direka mudah dan dioptimumkan bagi mencapai jalur takik maksimum. kedudukan jalur celahan diteliti dan ciri-diri jalur takik diperolehi. jalur celahan pada lapisan asas dan radiator elips diperhatikan menyebabkan frekuensi jalur lebar takik sebanyak 3.3 hingga 3.7 dan 5 hingga 6 ghz, masing-masing. 90 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 antena satah uwb dibandingkan dengan antena rujukan dan dapatan kajian telah disahkan tidak mempengaruhi keputusan antena planar uwb dengan ketara. ukuran pantulan pekali s11 yand diukur pada frekuensi jalur lebar takik wlan and wimax adalah -3.0 dan -4.0 db, masing-masing. corak pancaran radiasi ko-polar pada satah hdan eadalah omnidan bi-arah, masing-masing. kekuatan isyarat maksima g berada di paksi –z dan –x pada satah hdan epada frekuensi yang dipilih. elektrik pada permukaan tersebar dalam kawasan jalur celahan. celah radiator elips dan lapisan asas tidak mempengaruhi prestasi keseluruhan antena satah uwb. key words: ultra wideband, planar antenna, wlan, wimax, and slit 1 introduction ultra wideband (uwb) frequency bandwidth is assigned from 3.1 to 10.6 ghz and has been commonly applied for communications and sensors, position location and tracking [1], wireless monitoring of transplanted organs [2], monitoring human’s activities such as sport and quality of sleep by using wireless body network (wban) [3], sensor to detects positioning and tracking of a target by a quad-copter and target [4], detection of human’s body behind wall [5], and indoor positioning, radar/medical imaging and target sensor data collection [6-7]. ultra wideband communication system benefits such as high data rate transfer, less path loss and better immunity to multipath propagation, availability in lowcost transceivers, and low transmit power and low interference, and the requirements in the means of reducing interference due to the coexistence with other narrowband systems have been discussed in [6]. uwb antenna has been proposed in [8] in the means of improving its performances by using conductive adhesive of carbon composite. uwb frequency bandwidth coexisted with other narrowband system and the uwb communication characteristics has been compared with single co-channel interference for various materials of partitions in real environments such as brick board, cloth office partition, concrete block, dry-wall, plywood, structure wood, and single co-channel, had been investigated in [9] where the study shows that the channel capacity had degraded with interference for mostly on the drywall partition and found lowest for structural wood partition. uwb interference has been studied in [10] and channel loss estimation using the okumura channel and tested within the zigbee circuit with dual-power. possible interference between an indoor uwb system and an outdoor fixed wireless access (fwa) system operating in the 3.5-5.0 ghz has been discussed in [11]. multiband-orthogonal frequency-division multiplexing (mb-ofdm) coexistence with time hopping ultrawideband (th-uwb) networks has been studied analytically in the means of modeling the interference for th-uwb [12]. mutual interference performance has been studied in [13] by performing pulse shaping from uwb to other narrowband system. the wavelet technique and reduction of interference from other narrowband system to uwb system in conjunction with transmitted-reference (tr-uwb) signaling scheme with adaptive receiver is utilized. multiple access interference in the bi-orthogonal modulation for uwb communication systems performances has been investigated in [14]. uwb interference such as uwb activity or uwb density is a critical matter when protecting wibro performance and analytical method based on a system level simulation of a wibro (ofdma) is proposed in [15]. the narrowband interferences which had affected the wideband system has been investigated and characterized in [16-17]. interference from a uwb transmitter into a narrowband receiver has been studied in [18]. 91 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 the impacts of ultra wideband in narrowband interferences have also been investigated in [19-22] and had described the degradation of the system, and although filtering can be used in the system in the means of correcting the narrowband interference, it has failed in at high interference level. the analysis of the effect of narrowband interference on uwb system in the presence of multipath fading had demonstrated narrowband problems at certain condition as stated in [23]. uwb signals had encountered many interference sources primarily from narrowband systems and also had affected many narrowband radios as described in [24]. thus, studies have been indicating that the coexistence between multiple frequency bandwidths could cause interferences to other communication systems. the effects could be in signal degradation, data loss, buzzing sound and communication error. furthermore, more severe effects could have been resulted by the interference such as system failure and malfunction. thus, it is essential to eliminate the coexistence frequency bandwidth from the uwb frequency bandwidth. there are various methods to suppress the mutual narrowband interference (nbi) in uwb communication system. chirp waveforms of two non-linear uwb based on the arctrigonometric and archperbolic variable is proposed in the means of alleviating the narrowband interference (nbi) in [25]. the effect of interference to bit error rate performance which used the time hopping pulse modulation for impulse radio ultrawideband is analyzed in [26]. method of using chirp waveforms of non-linear in the means of suppressing the interference of narrowband in uwb communication system has been explained in [27]. band-stop filter is applied to prevent the narrowband interference (nbi) in a receiver for transmitted-reference ultra-wideband (tr-uwb) systems consists of narrowband interference (nbi) and inter-pulse interference (ipi) mitigation [28]. a null phase-shift polarization (npsp) which combined a linear polarization-vector transformer (pvt), single notch polarization (snp) filter and an amplitude and phase compensator (apc) has been proposed in [29] to suppress narrowband interference (nbi). elimination of narrowband interference (nbi) could use antenna design modification as an option. the method is simple and low profile as it requires the etching of the conductor element of the antenna which has been reported [30-38]. structure for the reference and proposed antenna were discussed in section 2. results were substantiated in section 3 and then concluded in section 4, respectively. 2 structures of uwb planar antennas slit placements in the elliptical radiator and ground element are simulated in the early stage for uwb planar antenna type 2a and 2b. slit is etched in four points known as point a, b, c, and d, consecutively as depicted in figure 1. slit is etched in one-sided of the elliptical element and ground plane as it is in symmetric. thus, the results would be in identical. the elliptical radiator and ground element is divided into two parts (lower and upper). the origin is placed in the middle point of the elliptical radiator and ground element, respectively. slit is positioned in the centre of the lower and upper area of the elliptical radiator and ground plane. the point coordinates for the slit placement a, b, c, and d are tabulated in table 1. slit placements are simulated consecutively and the reflection coefficients s11 are compared. band notch characteristics are studied in the means of achieving the desired band notch frequency bandwidths. slit placements are optimized in order to obtain the optimum band notch characteristics for uwb planar antenna type 2a, and 2b, respectively. the finalized slit configurations are listed in table 2. 92 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 fig. 1. slit placements for uwb planar antenna table 1: slit placements in the elliptical element and ground plane point p(x,y,z) a p(-6, 12, 0.035) b p(-6, 4, 0.035) c p(-11,-6, 0.035) d p(-11,18,0.035) table 2: parameters for slit s1 and s2 antenna type slit type parameter dimension 2a s1 length, l 7.12 mm width, w 1.10 mm slope angle, 7.98 deg s2 length, l 11.0 mm width, w 0.60 mm slope angle, 39.43 deg 2b s1 length, l 8.28 mm width, w 0.13 mm slope angle, 1.38 deg s2 length, l 11.27 mm width, w 0.60 mm slope angle, 41.04 deg the reference, uwb planar antenna type 2a, and 2b structures are illustrated in figure 2 and the dimensions are tabulated in table 3. uwb planar antenna type 2a and 2b substrates used fr-4 with the permittivity r of 4.6 and 4.4, respectively. the dielectric electric tangent delta is given 0.019. size of the reference antenna is compact. the conductor planes are placed one-sided on the substrate and half-ground element is used. thickness of the substrates for uwb planar antenna type 2a and 2b are different due to the value of the substrate permittivity r, thus to achieve impedance matching. 93 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 uwb planar antenna type 2a and 2b used the thickness hs(2a)=1.6 and hs(2b)=0.76 mm, respectively. however, the conductor planes thickness and the size of the antenna are maintained. impedance matching is achieved by determining the eccentricity e of the elliptical radiator as eq. 1. (1) fig. 2. uwb planar antenna (a) reference (b) type 2a (c) type 2b (d) side view table 3: parameters for uwb planar antenna parameter dimension [mm] ls 45 lg 24 l1 16 l2 12.8 wg 21 hc 0.035 hs(2a) 1.6 hs(2b) 0.76 r(2a) 4.6 r(2b) 4.4 slits are engraved in the elliptical radiator and the ground element, respectively. slit is etched in the middle side of the elliptical radiator for uwb planar antenna type 2a and 2b. however, slit in the uwb planar antenna type 2a is etched slanted compare with slit in horizontal for type 2b. slit configurations are determined by the impedance matching and to optimize the reflection coefficient s11. higher value of the reflection coefficient s11 is desired for the band notch characteristics. slit in the ground plane is etched slanted and downwards in about at the centre of the ground plane. slit configurations in the ground plane are quite similar to each other for uwb planar antenna type 2a and 2b. however, slits in the elliptical element have major different in slit width w and slope angle, . theoretically, this is owing to the difference in the substrate permittivity r, and slit s1 and s2 configurations are counted in the means of optimizing the band notch characteristics. generally, surface current distributions are drifted in the elliptical element compared in the ground plane owing to the feed point. therefore, slit placements in the elliptical element have become critically affected the band notch characteristics compared in the ground plane, where the surface current is disseminated inferiorly. 94 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 simulation procedure was depicted in figure 3. first step is to set the simulation setting. simulation parameters such as boundary, background, and frequency bandwidth are encoded. optimization is carried out in the means of achieving the optimum band notch characteristics for uwb planar antenna type 2a and 2b. reference and uwb planar antenna type 2a and 2b are simulated by time domain in computer simulation software (cst) using antenna-planar (microwave/radio frequency/optical) module. simulation frequency is allocated between 3 and 11ghz. the boundary condition and reflection level are given in open-space and 0.0001, respectively. fig. 3. workflow for uwb planar antenna the open boundary is in convolution perfect match layer (cpml) for minimizing the reflection at the boundary during simulation. uwb planar antenna operating frequency is n start setup simulation setting identify slit s1 parameters for antenna type 2a and simulation of the antenna type 2a and 2b reflection coefficient 5~6ghz yes identify slit s2 parameters for antenna type 2a and simulation of the antenna type 2a and reflection coefficient yes report writing end yes validation no fabrication measurement experimental results simulated results analysis 95 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 between 3.1 and 10.6ghz, thus the reflection coefficient s11 must be below -10db between this frequency bandwidth. however, the reflection coefficients s11 for the band notch frequency bandwidths must be above -10db level in the means of eliminating the band notch frequency bandwidths. the higher reflection coefficients s11 level between the band notch frequencies bandwidths the better eliminations of the band notch frequency bandwidths. 3 result and discussion the reference, uwb planar antenna type 2a, and 2b performances are compared after optimization of the band notch characteristics by adjusting the slits parameters. it is desired that the uwb planar antenna type 2a and 2b performances are unchanged when compared with the reference antenna. thus, it is substantiated that the slits existence on the conductor elements not significantly changes the uwb planar antenna type 2a and 2b performances. the uwb planar antennas are compared with [39-40] as their structures are nearly similar to the uwb planar antenna and etching method also been used for the band notching, and the results are comparable. however, the slits structures are more complicated compared to the uwb planar antennas. the reflection coefficients s11 for the band notch peaks are in the same range. the radiation patterns also exhibit in omni-directional and bi-directional for the hand e-plane, respectively similar to the uwb planar antennas. the numbers of lobes are increased for higher frequency regions. the maximum gains g for the uwb planar antenna is comparable with [39-40] as the maximum gain is achieved at 6.9 db. however, the overall gains g for [40] is lower than the uwb planar antennas. it is considered that the slit structures in the radiator could affect the overall gain g of the designed antenna due to slit in [40] is considered larger than the uwb planar antenna. reflection coefficient s11, surface current distribution, radiation patterns, gain, and efficiency are discussed in sub-section 3.1, 3.2, and 3.3, consecutively. 3.1 reflection coefficient reflection coefficient s11 for eccentricity e and slits placement is depicted in figure 4 and 5, consecutively. band notch characteristics for the slit placements are tabulated in table 4. the reflection coefficient, s11 level for operating frequency, f is known below -10 db. the frequency bandwidths for 4.3~4.9 and 7.3~8.7ghz are located above -10db when e=0, where as for 3.3~8.3 and 8.8~11ghz when e=1, for type a. frequency bandwidths were to be found at 8.7~9.3ghz for e=0, and are placed for 3.6~9 and 9.7~11ghz for e=1, for type b respectively. the results substantiate that eccentricity e=0.6 is ideal for type 2a and 2b as it is within the operating frequency level. centre frequencies fc for slit placements at point a for type 2a and 2b is located at 6.7 and 7.3ghz, respectively. point d is located at 4.4 and 4.3ghz for type 2b, respectively. thus, point a and d are adjusted in the means of realizing band notch characteristics for 5~6 and 3.3~3.7ghz, respectively. reference and uwb planar antenna type 2a and 2b were simulated and measured. the comparisons for the reflection coefficient s11 are presented in fig. 6, respectively. 96 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 (a) type 2a (b) type 2b fig. 4. reflection coefficient, s11 due to eccentricity e (a) type a (b) type b fig. 5. reflection coefficient s11 for slit placements 97 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 table 4: band notch characteristics due to slit placements antenna type point centre frequency, fc [ghz] reflection coefficient, s11 [db] a a 6.7 -5.7 b 7.6 -2.5 c 4.5 -5.1 d 4.4 -8.1 b a 7.3 -6.0 b 8.4 -3.6 c 4.4 -6.9 d 4.3 -9.2 (a) type 2a (b) type 2b fig. 6. finalized reflection coefficient, s11 for reference and uwb planar antenna type 2a and 2b bn1 and bn2 are known as the band notch characteristics realized for the frequency bandwidth at 5~6 and 3.3~3.7ghz, correspondingly. the dual notched-band characteristics r ef le ct io n co ef fi ci en t, s 1 1 db frequency ghz r ef le ct io n co ef fi ci en t, s 1 1 db frequency ghz 98 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 for uwb planar antenna type 2a and 2b are tabulated in table 5. it is substantiated that dual band notch are generated due to the slits in the elliptical radiator and ground element. the slit in the elliptical radiator and ground element are considered to generate the notchedband at the frequency bandwidth in 5~6ghz and 3.3~3.7ghz, correspondingly. theoretically, it is considered that the frequency bandwidths for 5~6 and 3.3~3.7ghz are suppressed from the uwb communication system. simulated and measured results are compared and results have shown reasonable agreement between both. table 5: dual band notch characteristics performances for uwb planar antenna type 2a and 2b antenna type band notch characteristic centre frequency, fc [ghz] reflection coefficient, s11 [db] frequency bandwidth, fbw [ghz] 2a simulated bn1 5.5 -3.7 1.0 bn2 3.6 -4.4 0.4 measured bn1 5.4 -3.4 1.0 bn2 3.6 -3.3 0.4 2b simulated bn1 5.6 -3.3 1.0 bn2 3.6 -5.0 0.4 measured bn1 5.4 -3.2 1.0 bn2 3.7 -3.4 0.5 3.2 surface current distributions surface current distributions for the reference and uwb planar antenna type 2a, and 2b for the centre frequency fc, 3.5 and 5.5ghz are exemplified in table 6. surface currents are centralized around the slits area. theoretically, the surface currents surge vertically in the elliptical radiator and ground element. slits are sited horizontally to intercept the vertically-polarized surface current and consequently mismatched the input impedance in the antenna. surface currents are surged in the edges of the ground element in the lower frequency area and mainly in the elliptical radiator in the middle frequency region. surface current is surged in slit in the ground plane and elliptical element for the frequency 3.5 and 5.5ghz, respectively. hence, it is contemplated that slit in the ground plane and elliptical element have generated the band notch characteristics in the uwb planar antenna type 2a and 2b, accordingly. 3.3 radiation patterns radiation patterns rp, gain g and efficiency eff of the reference, uwb planar antenna type 2a, and 2b are exhibited in fig. 7 and 8, consecutively. it is demonstrated that the radiation patterns in the hand e-plane for the uwb planar antenna type 2a and 2b is in omniand bi-directional, respectively. radiation patterns in the h-plane of the uwb planar antenna type 2a and 2b is comparable with the monopole antenna. this is as a result of the vertically positioned of the feeding cable on the ground plane. radiation patterns rp performances are tabulated in table 7. it is corroborated that the higher gain g is pointed in the –z –axis and –x –axis in hand e-plane, correspondingly. however, maximum gain g for the frequencies of interest 7.5 and 9.5ghz for uwb planar antenna type 2b in the eplane is pointed in the +x –axis. 99 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 table 6: surface current distributions for reference antenna and uwb planar antenna type 2a and 2b antenna type surface current distribution / frequency ghz 3.5 5.5 a b 2a 2b it is considered that the slit in the elliptical radiator is placed in the +x –axis, hence has influenced the radiation patterns of the uwb planar antenna type 2b, accordingly. radiation patterns of the reference are equated with uwb planar antenna type 2a and 2b, and the results are passable. it is preferred that the performances for uwb planar antenna type 2a and 2b not significantly amended from the reference antenna. radiation efficiency eff for the frequency 5~6 and 3.3~3.7ghz have substantiated deterioration for the uwb planar antenna type 2a and 2b, correspondingly. it is demonstrated that the band notch are realized in the respective frequency bandwidths, accordingly. (a) type 2a (b) type 2b fig. 7. radiation patterns for uwb planar antenna type 2a and 2b 100 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 (a) gain g (b) efficiency eff fig. 8. gain g and efficiency eff for uwb planar antenna type 2a and 2b table 7: radiation pattern performances for uwb planar antenna type 2a and 2b antenna type frequency ghz main lobe plane efficiency % gain db hesimulate measured simulated measured 2a 4.5 180 162 96.2 94.2 3.6 6.3 7.5 258 196 94.0 100.0 3.6 4.8 9.5 173 136 91.7 83.9 5.3 4.8 2b 4.5 177 164 94.8 81.3 2.9 5.4 7.5 172 347 95.5 100.0 4.0 5.4 9.5 181 42 94.4 87.5 4.7 4.9 101 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 4 conclusion uwb planar antenna comprises dual notched-band characteristics to decline the frequency bandwidth for wimax and wlan are presented. the method employed in the design is simple and low profile. slits in the elliptical radiator and ground element apparently have initiated the band notch characteristics in uwb planar antenna type 2a and 2b. the structure of the reference and uwb planar antenna type 2a and 2b uses halfground plane, and designs are compact. the impedance mismatched is corresponded with the surface currents distributions in the slits area, respectively. the reflection coefficients s11 have decreased promptly at the notched-band frequency bandwidths and have achieved about -3.0 and -4.0db at the center frequency 5.5 and 3.5ghz, respectively. gain g values are plunged at the band notch center frequencies, 5.5 and 3.5ghz to 4.0 and 3.5db, respectively. radiation efficiency erad for the uwb planar antennas have dropped to 70% from the overall performances. thus, it is indicated that the frequency bandwidths for 5 to 6 and 3.3 to 3.7ghz are suppressed from the uwb frequency bandwidth, accordingly. however, the radiation patterns for the uwb planar antennas are compared with the reference antenna and have indicated that it is not significantly affected by the slits in the conductor elements. the uwb planar antenna type 2a and 2b performances are evaluated with the reference antenna and the results are verified. acknowledgement this research work is funded by universiti teknologi malaysia (utm) through razak grant fund vote no. 4j283. antenna measurements were conducted in antenna research center (arg), faculty of engineering (foe), universiti teknologi mara (uitm-shah alam). references [1] applications on uwb technology. available: https://arxiv.org/abs/0911.1681. [2] pongphan leelatien, koichi ito, kazuyuki saito, manmohan sharma, akram alomainy. (2018) channel characteristics and wireless telemetry performance of transplanted organ monitoring system using ultra wideband communication. ieee journal of electromagnetics, rf and microwaves in medicine and biology, 2(2):94-101. [3] timo kumpuniemi, juha pekka makela, matti hamalaine, kamya yekeh yazdandoost, jari iinatti. (2017) dynamic uwb off-body radio channels-human body shadowing effect. available: 10.1109/pimrc.2017.8292584. [4] robust target-relative localization with ultra-wideband ranging and communication. available: https://researchgate.net/publication/324602380. [5] jawad ali, roshayati yahya, noorsaliza abdullah, syarfa zahirah sapuan. (2017) ultrawideband antenna for behind the wall detection. international journal of electrical and computer engineering (ijece), 7(6):2936-2941. [6] ultra wideband antennas-past and present. available: https://www.researchgate.net/ publication/46093503. [7] weihua zhuang, xuemin sheman shen qi bi. (2003) ultra-wideband wireless communications. wireless communications and mobile computing, 3:663-685. [8] erick reyes-vera, mauricio arias-correa, andreas giraldo-munoz, daniel catano-ochoa, juan santa-marin. (2017) development of an improved response ultra-wideband antenna based on conductive adhesive of carbon composite. progress in electromagnetics research c, 79:199-208. [9] chien-ching chiu, chun-liang liu, shu-han liao. (2011) channel characteristics of ultrawideband systems with single co-channel interference. wireless communications and mobile computing, 13:864-873. 102 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 [10] lei gao, qun chen. (2017) channel loss estimation and test of ultra-wideband propagation from 2 to 10 ghz application. indonesian journal of electrical engineering and computer science, 6(3):663-670. [11] romeo giuliano, gianluca guidoni, ibrahim habib, franco mazzenga. (2004) evaluation of interference due to uwb hot spot on fixed wireless access systems. j. wireless communications and mobile computing, 4:947-961. [12] farshad sarabchi, chahe nerguizian. (2015) impact of th-uwb interference on mb-ofdm uwb systems: interference modeling and performance analysis. wireless communications and mobile computing, 16:960-976. [13] bikramaditya das, ch. sasmita das, susmita das. (2010) interference cancellation schemes in uwb systems used in wireless personal area network based on wavelet based pulse spectral shaping and transmitted reference uwb using awgn channel model. international journal of computer applications, 2(2):88-93. [14] simone morosi, romano fantacci, enrico del re, leornardo goratti. (2005) performance of the bi-orthogonal modulation for ultra-wideband communication systems with multiple access interference. wireless communications and mobile computing, 5:5-14. [15] young-keun yoon, heon-jin hong, ik guen choi. (2007) ultra-wideband coexistence with wibro. j. etri, 29(2):234-236. [16] j.r. foerster. (2002) the performance of a direct-sequence ultra wideband system in the presence of multipath, narrowband interference, and multiuser interference. ieee conference on ultra wideband systems and technologies, 21-23 may. baltimore (usa), 87-91. [17] n.g. ferrara, m.z.h. bhuiyan, and s. soderholm. (2018) a new implementation of narrowband interference detection, characterization, and mitigation technique for a softwaredefined multi-gnss receiver. avaible:https//researchgate.net/326784680. [18] k.siwiak. (2001) impact of ultra wide band transmissions on a generic receiver. ieee vts 53rd vehicular technology conference, 6-9 may. rhodes (greece), 1181-1183. [19] a.taha, and k.m.chugg. (2002) a theoretical study on the effects of interference uwb multiple access impulse radio. available:https://ieeexplore.org/abstract/document/1197276. [20] j.bellorado, s.s.ghassemzadeh, l.j.greenstein, t.sveinsson, and v.tarokh. (2003) coexistence of ultra-wideband systems with ieee-802.11a wireless lans. available:https://ieeexplore.ieee.org/abstract/document/1258271. [21] kai shi, yi zhou, burak kellici, timothy wayne fischer, erchin serpedin, and aydin iker karsilayan. (2007) impacts of narrowband interference on ofdm-uwb receivers:analysis and mitigation. ieee transactions on signal processing, 55(3):1118-1128. [22] a.giorgetti, m.chiani, and m.z.win. (2005) the effect of narrowband interference on wideband wireless communication systems. ieee transactions on communications, 53(12):2139-2149. [23] xiaoli chu, and r.d.murch. (2004) the effect of nbi on uwb time-hopping systems. ieee transactions on wireless communications, 3(5):1431-1436. [24] ananthram swami, b.m.sadler and j.turner. (2001) on the coexistence of ultra wideband and narrowband radio systems. available:https//researchgate.net/publication/3937675. [25] zhiquan bai, xiatong li, dongfeng yuan, kyungsup kwak. (2010) non-linear chirp based on uwb waveform design for suppression of nbi. wireless communications and mobile computing, 12:545-552. [26] yamen issa, iyad dayoud, waala hamouda. (2015) performance analysis of multiple-input multiple-output relay networks based impulse radio ultra-wideband. wireless communications and mobile computing, 15:1225-1233. [27] hanbin shen, weihua zhang, kyung sup kwak. (2007) non-linear chirp uwb ranging system with narrowband interference suppression abilities. j. etri, 29(4):521-523. [28] s.cui, k.c.teh, k.h.li, y.l.guan, c.l.law. (2009) performance analysis of transmittedreference uwb systems with narrowband interference suppression. wireless communications and mobile computing, 9:1081-1088. 103 iium engineering journal, vol. 20, no. 2, 2019 jainal et al. https://doi.org/10.31436/iiumej.v20i2.1097 [29] xing peng mao, jon w.mark. (2008) polarization filtering for narrowband interference suppression in ultra-wideband communications. wireless communications and mobile computing, 8:941-952. [30] a compact fractal uwb antenna with open-ended quarter wavelength slot for band notch characteristics.available:https://www.researchgate.net/publication/229566986. [31] a wlan notched wideband monopole antenna for ultra-wideband communication applications. available: https://www.researchgate.net/publication/324463199. [32] circular slotted monopole printed antenna with grounded stub wlan band-notch for uwb applications. available: https://doi.org/10.1080/1448837x.2018.1452331. [33] dual-band shared-aperture uhf/uwb rfid reader antenna of circular polarization. available: https://www.researchgate.net/publication/325327219. [34] dual notch band uwb antenna with improved notch characteristics. available: https://www.researchgate.net/publication/323646136. [35] hemachandra r.gorla, frances j.harackiewicz. (2015) dual trident uwb planar antenna with band notch for wlan. progress in electromagnetics research letters, 54:115-121. [36] novel design of dual band-notched rectangular monopole antenna with bandwidth enhancement for uwb applications. available: https://www.researchgate.net/ publication/325380975. [37] muhibbur rahman, jung-dong park. (2018) the smallest form factor uwb antenna with quintuple rejection bands for iot applications utilizing rsrr and rcsrr. national center for biotechnology information us national library of medicine (ncbi) 18(911):1-16. [38] ammar alhegazi, zahriladha zakaria, noor azwan shairi, sharif ahmed, tole sutikno. (2017) uwb filtenna with electronically reconfigurable band notch using defected misrotrip structure. indonesian journal of electrical engineering and computer science, 8(2):302-307. [39] soufian lakrit, sudipta das, ali el alami, debaprasad barad, sraddhanjali mohapatra. (2019) a compact uwb monopole patch antenna with reconfgurable band nocthed characteristics for wi-max and wlan applications. aeu international journal of electronics and communications. available: https://www.science direct.com/science/article/pii/s1434841119303048. [40] bing gong, chuang ma, fan jing, yaling hou, ruibing shen. (2018) a novel uwb antenna with two ultra narrow and closely space notched bands. journal of physics, 1176(2019), 1-7. 104 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 optimization of the regularization of the solution to plate heat transfer problems fargana akter1, abdumalik rakhimov2*, ahsan ali khan1 and torla hj hassan2 1department of materials and manufacturing engineering, 2department of science in engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. *corresponding author: abdumalik@iium.edu.my (received: 16th april 2019; accepted: 14th october 2019; published on-line: 20th january 2020) abstract: optimization of the regularization of the fourier series in the case of a steady state heat transfer plate and heat transfer insulated plate problems are investigated and the regularization of the series solutions at a fixed point on the plates are studied at initial time and critical index. abstrak: pengoptimuman aturan siri fourier telah dikaji pada keadaan tetap masalah plat pindah haba dan plat penebat pindah haba. penyelesaian bersiri secara aturan pada titik tetap plat telah dikaji pada masa mula dan indeks penting. keywords: optimization; regularization; heat transfer; initial time; critical index 1. introduction heat transfer problems confront researchers in many branches of science and engineering. many researchers use fourier transforms to solve the heat problem in different kinds of engineering applications such as in [1], where the problem of a hydromagnetic hot two-dimensional laminar jet supplying quiescent fluid of a lower temperature is studied using the fourier series method. therefore, it is shown that the process which is based on the fourier series is very efficient and appropriate to solve boundary layer equations applied to plane jet flows with high accuracy. a temperature fourier series solution in a hollow sphere subjected to periodic boundary conditions is studied in [2]. in this case, the material of the sphere is presumed to be homogeneous and isotropic with time-independent thermal properties [2]. the main purpose of [3] is to identify the flow types and exhibit augmented heat transfer in dependence on a magnetic induction gradient using fast fourier transform analysis. fourier transform blackbody spectroscopy to measure the radiation from blackbody sources operated at a series of various temperatures is studied in [4]. in [5], the author used a three-dimensional fourier series solution to discuss the thermal characterization of electronic packages. here, a fourier series solution is used for computing local temperature distributions, heat fluxes and thermal resistances. optimization of the regularized fourier series solution for a fixed point plate vibration problem is studied at initial time and critical index [6]. the solutions of all above mentioned problems are based on the application of the fourier series and transformations. therefore, a regular summation method is required in 113 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 the case of some singularities within the problem’s input data. an example of this is when input data is expressed by singular distributions. in this paper, we will classify the singularity in terms of the sobolev spaces and the reisz method of summation will be considered as regularization of the fourier series solutions to the problems. 2. preliminaries convergence or divergence of the fourier series of an integrable function at a certain point depends only from the behaviour of the function in an arbitrary small neighbourhood of that point (localizations principles). when both expansions (fourier series and integral) converge or diverge at the same time and same term, it is called equiconvergence. in the liouville space )(2 nl tl , for any arbitrary self-adjoint elliptic operators, the sufficient condition for the localization of the reisz means of order s of multiple fourier series and integrals is [7] p p nn sl 1, 1 , 2 1 (1) but for any elliptic operator, a sufficient localization condition is p n sl 1 [7]. moreover, the sufficient localization condition (1) can be weakened if summation of the multiple fourier integrals occurs by the surface level of the elliptic operators from the class ar, p p r p n sl 1,, 2 111 (2) in n-dimension, equiconvergence for both expansions (fourier series and integral) is not valid for the rectangular partial sums. equiconvergence in summation of the fourier expansion of the linear continuous functional that is associated with an elliptic polynomial is discussed in [8]. moreover, the general expanded expansions of the distributions are discussed in [9-19]. let )( nt be the space of an infinitely differentiable function φ: nt → c. the system of semi norm for any compact subset k of nnt ],[ is defined by, )()( sup, xdp kx k (3) where is a multi-index denoted by )......( 21 n and )......,( ,21 n is n dimensional vector with the non-negative integer components j (j = 1, 2 ...., n). for instance, , where . for any functional f (where is the conjugate space of the locally convex topological space ), we can write ,)2( 2/ nzn inx n n eff (4) n ndddd ........21 21 njxi d j j ,.....2,1, 1 )( nt )( nt )( nt 114 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 where nz is the set of all vectors with integer components, nf is the fourier coefficient, which is defined as the value of f on the test function on inxn e2/)2( and . consider the following elliptic polynomial: where m is a positive integer number and r= 0, 1, 2, ……, n-1. polynomial a(n) is a homogeneous of degree 2(m + 1) and an elliptic (a(n) > 0). note that, rana )( but 1)( rana [20]. for any non-negative real number s, the riesz means of order s of the fourier series in equation (1) is defined as, )( 2 ).exp( )( 1)2()( na n sn s inxf na xf (5) now, we extend a distribution f from n dimensional torus nt to the whole space by zero. then the bochner-riesz means of order s of the fourier integral of f is, ,)exp()(ˆ )( 12)( )( 2 dxiyf a xfr s a n s (6) where, )exp()2(,)(ˆ 2/ xifyf n is the fourier transformation of the extended functional f and it acts on , )exp()2( 2/ xin via x. for any real number l, the sobolev space of distributions is (7) theorem 1 we have l l n lt 2)( . the dirac delta function ll2 (where 2/nl ), and l nrmrn s } 2 1 , 22 )2/11)(1( max{ .then for any )(2 nl tlf l ss foxfrxf )1()()( (8) where l . is a norm in )(2 nl tl : 222 )1()2( n zn l n l fnf n [8] (9) in [21,22] mathematical models of thermo control processes in a rectangular plate are studied. in [21] it is considered that the temperature in a plate is controlled by heat exchange through one boundary while the other three are insulated. in these two papers, they study sufficient conditions for achieving the given projection by controlling the parameter on the boundary. mathematical models of thermo control processes when control parameter is a vector function are studied in [23]. in [24] a control of the heat transfer was studied based on time/norm and it found sufficient and necessary conditions ntx n j j m n rj j m r j j nnnna 1 2 2 2 1 1 1 2)( .),........,( 21 n n znnnn nr )(2 nl tl })1(:{)( 2 2 2 n zn lnl fnftl n 115 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 for such a control. equiconvergence of the spectral expansions associated with the operators with singular coefficients was studied in [25] and for the sturm liouville operator in [26]. the definition of the operator a(n) and application of the poisson summation method is explained in [27]. in the next sections, for a steady-state heat transfer problem and insulated heat problems, we will verify this theorem numerically for different plates subjected to different boundary conditions. as mentioned, the regular summation method will be used for excellent accuracy and convergence. 3. description of the problem consider a thin square plate made of some thermally conductive material. suppose the dimensions of the plate are x × y. the plate is heated in some way. for example, in a steady state heat transfer problem or heat transfer insulated (no heat escapes from this surface) plate problems. the plate is homogeneous, that is -its mass per unit volume is a constant. assume that, v(x, y, t) = temperature of the plate at position (x, y) and time t. for a fixed t, v(x, y, t) gives the temperature of the plate at position (x, y). for the thin plate in which the temperature v is a function of time t and position (x, y) satisfy the two-dimensional heat equation cybxvvhv yyxxt 0,0,)( (10) where h is the heat conductivity coefficient and it is constant. the solution of the heat equation (10) is subject to the boundary conditions and initial conditions. the solution of the heat transfer problems in the two dimensional case has a form of a double fourier series by eigenfunctions and these eigenfunctions depend on the boundary conditions. the coefficient of the fourier series is found from the initial conditions. that is why convergence or divergence of the corresponding fourier series depends on the smoothness or singularity of the initial conditions. if the initial conditions are given by very good functions then this series converges. in many engineering phenomena, the initial data may be not represented by good functions. sometimes initial conditions may not even be functions. for example, initial conditions can be expressed as the dirac delta function. in a one dimensional case, the fourier series of the dirac delta function diverges at a regular point. however, the arithmetic means of the fourier series of the dirac delta function converges. thus, for the solutions of the corresponding heat problems some regularizations of the fourier series solutions are required. here, based on the singularity, we consider the reisz method of summation as regularization of the fourier series solutions of the heat problems. when we increase the order of the reisz means, the solutions will converge but the numerical calculations will be increase. so, the regularized fourier series solutions need optimization. optimization of the regularization of the solutions of the plate heat transfer problems is finding the solutions from the regularized fourier series for minimum order of the reisz means. the minimum order is s > (n 1)/2 + l. here, s is the order and n is dimension. 116 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 after optimization, we will calculate the numerical solutions. here, we will find the optimization of the regularization of the series solutions at a fixed point on the plates at the initial time and critical index. finally, we will verify if the solution is convergent or not. 3.1 problem 1: steady-state heat transfer problem fig. 1: a plate of dimensions × in the xy-plane. consider an aluminium plate of dimensions × in the xy-plane as shown on fig. 1. the steady state equation subjected to the boundary conditions is yxuu yyxx 0,0,0 (11) ,0,0 yu (12) ,00,xu (13) ,0, yu (14) , 2 , xxu (15) where is a dirac delta function. solution of the steady state problem is, ,)(, 1 nxsinnyhsinayxu n n (16) where, na is a constant coefficient. after putting the boundary condition in equation (16) we found the value of na , )( 2 nsinh n sin an (17) now, the solution of the steady state problem is, 2/x ,4/ (0, 0) 117 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 ,)( )( 2, 1n nxsinnysinh nsinh n sin yxu (18) the steady state solution at y = is , 2 , 1n nxsin n sinxu (19) therefore, to find the convergence of the series we have to choose a point. we know that in the point 2 , the value of the series is infinity. now, take a point in x = axis except the dirac delta function. here we choose x = 4 and y = . it should not be convergent. here, regularization is required in order to solve this series in a stable manner. the riesz means of order s (s is non-negative real number) of the fourier series in equation (19) is defined as n s s nxsin n sin n xue )( 2 1, (20) 3.1.1 regularization of the steady-state heat transfer plate problem at initial time here, we will test the regularization of the series in equation (20). we set order s = 0, 1 and time t = 0. the series solution in equation (20) for different values of λ and at the point 4 is given below: table 1: solution of the regularized series in equation (20) for different s (s = 0, s = 1) and time t = 0. λ 350 -0.707106781 0.002020305 450 0.707106781 0.001571348 550 -0.707106781 0.001285649 650 0.707106781 0.001087857 750 -0.707106781 0.000942809 850 0.707106781 0.000831891 950 -0.707106781 0.000744323 1050 0.707106781 0.000673435 1150 -0.707106781 0.000614875 1250 0.707106781 0.000565685 1350 -0.707106781 0.000523783 1450 0.707106781 0.000487663 from table 1, it is clear that for s = 0 the fourier series diverges. after regularization, the reisz means of order s = 1 of the fourier series is convergent. the solution of the series of the riesz means of order s = 1 is approximately very near to zero. 3.1.2 regularization of the steady-state heat transfer plate problem at critical index 118 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 from table 1, it is clear that when s = 1, the series converges. we know that the series will converge when l n s 2 1 . so s = 1/2 is the critical point for the regularized series. here, we choose a more complicated point, the critical point s = 0.5. to understand the difference between values below the critical point and values above the critical point, we take two more points: 0.5 – and 0.5 + ( is very small number). here, we choose = 0.1.where all the other parameters are kept the same. table 2: solution of the regularized series in equation (20) for different s (s = 0.4, s = 0.5, s = 0.6). λ 650 0.041758111 0.019793588 0.009259818 700 0.020462554 0.013759143 0.008979066 850 0.037451159 0.017249285 0.007826599 1300 -0.015876433 0.009997791 0.006101631 1450 0.030173547 0.013132134 0.005611037 1900 0.013602391 0.008230995 0.004822541 3700 -0.010381654 0.005860529 0.003197979 4250 0.019565055 0.076112881 0.002889619 9500 0.007096985 0.003635011 0.001795733 from table 2, it is clear that below the critical point, the series diverges and after the critical point, the series is converges. but, at the critical point, the answer of the regularized series is so near to zero but still diverges. 3.2 problem 2: heat transfer problem of the insulated plate (when the lower plate is insulated) fig. 2: an aluminium plate of dimensions 1 × 1 in the xy-plane. consider a square aluminium plate of dimensions 1 × 1 in the xy-plane as shown in fig. 2. the plate is insulated in the x-axis. the heat transfer equation subjected to boundary conditions is 10,10,)( yxuuku yyxxt (21) 4 1 , 4 1 (1, 0) (0, 0) (0, 1) (1/2, 1/2) insulated 119 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 ,0,,0 tyu (22) ,0,0, txu y (23) ,0,,1 tyu (24) ,0,1, txu (25) , 4 1 , 4 1 0,, yxyxu (26) where is a dirac delta function. solution of the steady state problem is, , 2 12 )(,, 1 ) 2 12 ( 0 2 2 2 y m cosxnsineutyxu n t m nk m n m (27) where, mn u is a constant coefficient. after putting the boundary condition in equation (27) we can find , 8 12 4 m cos n sinu mn (28) now, the solution of the heat transfer problem is, y m cosxnsin m cos n sinetyxu n m t m nk 2 12 )( 8 12 4 ,, 1 0 ) 2 12 ( 2 2 2 (29) in this problem, we know that at the point 4 1 4 1 , the value of the series is infinity. now, choose a point in the plate except the dirac delta function. here, we take x = 2 1 and y = 2 1 . in this case, the input data has some singularities. it should not be convergent. here, regularization is required in order to solve this series in a stable manner. the riesz means of order s (s is non-negative real number) of the fourier series in equation (29) is defined as y m cosxnsin m cos n sine mn tyxue mn t m nk s s 2 12 )( 8 12 4 1,, 22 2 2 2 ) 2 12 (22 (30) 3.2.1 regularization of the two dimensional heat transfer problem at initial time here, we will test the regularization of the series in equation (30). therefore, we take order s = 0, 1, 2 and time t = 0. the series solution in equation (30) for different value of λ and at the point 2 1 2 1 is given below: 120 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 table 3: solution of the regularized series in equation (30) for different s (s = 0, s = 1, s = 2) and time t = 0. λ 1700 -4.889995713 0.008050281 0.002943257 2500 -9.416538804 -0.003613664 0.001310513 5500 4.039739941 0.001821067 0.000226622 6500 11.13298168 -0.003669672 0.000153341 8500 -14.55226918 0.003217023 0.000077823 10500 17.22542063 -0.002024961 0.000047231 12500 -27.03824111 0.001093712 0.000040143 12700 30.23102475 -0.003398458 0.000039281 12900 9.304453421 0.001452938 0.000035381 13400 -15.70031947 -0.000344863 0.000030437 from table 3, it is clear that for s = 0 the fourier series diverges. although after regularization the value of the riesz means of order s = 1 of the fourier series is approximately near to zero but the series is diverges. finally, when the reisz means of order s = 2, the series converges. 3.2.2 regularization of the square plate steady-state heat transfer problem at critical index from table 3, it is clear that the series converges for s = 2. we know that the series converges when order l n s 2 1 . so, s = 3/2 is the critical point for the regularized series. here, we choose the critical point s = 1.5. to understand the difference between below the critical point and above the critical point we take two more points 1.5 – and 1.5 + ( is very small number). here, we choose = 0.1.where all the other parameters are kept the same. table 4: solution of the regularized series in equation (30) for different s (s = 1.4, s = 1.5, s = 1.6). λ 500 0.005020001 0.006763001 0.009379112 6500 0.000085401 0.000119112 0.000134201 7500 0.000150021 0.000130211 0.000118011 10500 -0.000038311 0.000006641 0.000066401 10520 0.000114353 0.000069814 0.000050122 10550 -0.000003256 0.000024155 0.000024811 10650 0.000117794 0.000069664 0.000020271 10800 -0.000057245 -0.000002461 0.000011784 18500 0.000004991 0.000007342 0.000009682 33000 -0.000000511 0.000009821 0.000000756 from table 4, we can conclude that below the critical point, the series diverges and after the critical point, the series converges. but, at the critical point, the answer of the regularized series is so near to zero but it diverges. 3.3 problem 3: heat transfer problem of the insulated plate (when the upper plate is insulated) 121 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 fig. 3: a square plate of dimensions 1 × 1 in the xy-plane. consider a square aluminium plate of dimensions 1 × 1 in the xy-plane as shown on fig. 3. the plate is insulated in the x = 1 axis. the heat transfer equation subjected to boundary conditions is 10,10,)( yxuuku yyxxt (31) ,0,,0 tyu (32) ,0,0, txu (33) ,0,,1 tyu (34) ,0,1, txu y (35) , 4 1 , 4 1 0,, yxyxu (36) where, is a dirac delta function. solution of the heat transfer equation of the insulated plate subjected to the boundary condition is, , 2 12 )(,, 1 ) 2 12 ( 0 2 2 2 y m sinxnsinevtyxu n t m nk m n m (37) where, mn v is a constant coefficient. from the dirac delta function and the boundary condition, we found , 8 12 4 m sin n sinv mn (38) finally, the solution of the heat transfer problem is, y m sinxnsin m sin n sinetyxu n m t m nk 2 12 )( 8 12 4 ,, 1 0 ) 2 12 ( 2 2 2 (39) 4 1 , 4 1 (1/2, 1/2) (0, 0) (0,1) (1,0) insulated 122 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 in the point 4 1 4 1 , the temperature of the plate is infinity. here, we choose another point in the plate except the dirac delta function. therefore, we take x = 2 1 and y = 2 1 . in the above series, the input data has some singularities. it should not be convergent. here, regularization is required in order to solve this series in a stable manner. the riesz means of order s (s is non-negative real number) of the fourier series in equation (39) is defined as y m sinxnsin m sin n sine mn tyxue mn t m nk s s 2 12 )( 8 12 4 1,, 22 2 2 2 ) 2 12 (22 (40) 3.3.1 regularization of the two dimensional heat transfer problem at initial time now, we will test the regularization of the heat transfer plate. here, we take order s = 0, 1, 2 and time t = 0. for different values of λ and a fixed point 2 1 2 1 , the series solution (40) is given below: table 5: solution of the regularized series in equation (40) for different s (s = 0, s = 1, s = 2) and time t = 0. λ 500 2.75804036 0.01009106 0.01553744 1500 1.58279358 -0.00267634 0.00178935 1700 -2.56669864 0.00588032 0.00140549 2100 21.1892037 -0.00640545 0.00093207 2300 -12.4315789 0.00600931 0.00078491 2500 3.13509121 -0.00789911 0.00067197 3500 -19.2678209 0.00344795 0.00035346 5500 18.9915902 -0.00108365 0.00015099 8500 -24.9696107 0.00417739 0.00006941 10500 34.1948078 -0.00256344 0.00004952 13500 -13.6204239 0.00238150 0.00003851 from table 5, we can summarize that for s = 0, the fourier series diverges. although, after regularization the value of the riesz means of order s = 1 of the fourier series is approximately near to zero but the series diverges. finally, for s = 2, the series converges. 3.3.2 regularization of the two dimensional heat transfer problem at critical index from table 5, it is clear that the series converges for s = 2. we know that the series converges when order l n s 2 1 . so, s = 3/2 is the critical point for the regularized series. here, we choose the critical point s = 1.5. to understand the difference between below the critical point and above the critical point we take two more points 1.5 – and 1.5 + ( is very small number). here, we choose = 0.1.where all the other parameters are kept the same. 123 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 table 6: solution of the regularized series in equation (40) for different s (s = 1.4, s = 1.5, s = 1.6). λ 4500 0.00020801 0.00017612 0.00017332 6500 -0.00000105 0.00005941 0.00008501 8500 0.00010912 0.00008002 0.00006922 10500 -0.00004652 0.00000438 0.00002671 10550 0.00002892 0.00003761 0.00004122 10750 -0.00002072 0.00001082 0.00002711 10900 0.00005763 0.00004984 0.00004572 11100 -0.00002301 0.00001051 0.00002701 14500 0.00002222 0.00002484 0.00002722 from table 6, it is clear that below the critical point, the series diverges and after critical point, the series converges. but, at the critical point, the answer of the regularized series is so near to zero but it diverges. 4. conclusion in this paper, we studied optimization of the regularization of the fourier series of the plate problems such as the steady state heat transfer problem and insulated heat transfer problems. here, we investigated the regularized fourier series solution at a fixed point on the plate at the initial time and critical index. as it is expected, we achieved the good convergence after the critical point. references [1] rosales-vera m, niño y, valencia a. (2012) on the application of the fourier series solution to the hydromagnetic buoyant two-dimensional laminar vertical jet. mathematical problems in engineering, 2012. [2] atefi g, moghimi m. (2006) a temperature fourier series solution for a hollow sphere. journal of heat transfer, 128(9): 963-968. [3] pyrda l. (2014) application of fast fourier transform in thermo-magnetic convection analysis. in journal of physics: conference series (vol. 530, no. 1, p. 012060). iop publishing. [4] steele ag, rowell nl. (2001) fourier transform blackbody spectroscopy: toward thermodynamic temperature measurement. in thermosense xxiii (vol. 4360, pp. 455-464). international society for optics and photonics. [5] culham jr, yovanovich mm, lemczyk tf. (2000) thermal characterization of electronic packages using a three-dimensional fourier series solution. journal of electronic packaging, 122(3): 233-239. [6] fargana a, rakhimov aa, khan aa, hassan tbh. (2018) optimization of the regularization of the solution of the plate vibration problem. international journal of applied engineering research, 13(8): 6364-6368. [7] alimov sha. (1974) on the localization of spectral decompositions. differ. uravn. 10(4), 744-746. english translation (1975). differ. equations 10, 576-578, zbl. 284.35059. [8] fargana a, rakhimov aa, khan aa, hassan tbh. (2017) equiconvergence in summation associated with elliptic polynomial. in journal of physics: conference series (vol. 949, no. 1, p. 012001). iop publishing. 124 iium engineering journal, vol. 21, no. 1, 2020 akter et al. https://doi.org/10.31436/iiumej.v21i1.1143 [9] rakhimov a, ahmedov a, zainuddin h. (2011) localization principle of the spectral expansions of distributions connected with schodinger operator. australian journal of basic and applied sciences, 5(5): 1-4. [10] rakhimov aa, zakaria k, khan nla. (2010) on the uniformly convergence spectral expansions connected with schrödinger’s operator of continuous functions in a closed domain. nucleus, 47(4): 261-265. [11] rakhimov aa. (2003) localization of the spectral decompositions of distributions, connected with the schrödinger operator. modern problems of math. physics and information technologies, tashkent, 1: 167-172. [12] alimov sha, rakhimov aa. (1996) localization of spectral expansions of distributions. differential equations. 32(6), 798-802. [13] alimov sha, rakhimov aa. (1997) localization of spectral expansions of distributions in a closed domain. difference equations. 33: 80-82. [14] rakhimov aa. (2000) on the localization of multiple trigonometric series of distributions. dokl. math. 62(2): 163-165. [15] rakhimov aa. (1996) localization conditions for spectral decompositions related to elliptic operators from class ar. mathematical notes. 59(3): 298-302. [16] rakhimov a, ahmedov a, zainuddin h. (2012) on the spectral expansions of distributions connected with schrodinger operator. applied mathematics letters. 25: 921-924. [17] rakhimov aa. (1996) spectral decompositions of distributions from negative sobolev classes. difference equations. 32, 1011-1013. https://zbmath.org/?q=an:0890.47031. [18] rakhimov aa. (1987) on uniform convergence of spectral resolutions of a continuous function in a closed domain. izvestiya akademya nauk uzssr, 6: 17-22. [19] rakhimov aa. (2017) on the uniform convergence of fourier series on a closed domain. eurasian mathematical journal 8 (3), 60-69. [20] ashurov rr. (1983). localization conditions of spectral expansions, corresponding to elliptic operators with constant coefficients. mathematical notes, 33(6): 434-439. [21] fayziev ye. (2018). on the control of the heat conduction. iium engineering journal, 19(1): 168-177. [22] fayziev ye, khalilova n. (2016) on a control problem associated with the heat transfer process, j. vestnik nuu, 2:1 49-54. [23] alimov sa. (2010) on a control problem associated with the heat transfer process. eurasian mathematical journal, 1(2): 17-30. [24] fattorini ho. (2003) time and norm optimal controls for linear parabolic equations: necessary and sufficient conditions. in control and estimation of distributed parameter systems (pp. 151-168). birkhäuser, basel. [25] denisov sa. (1998) equiconvergence of a spectral expansion, corresponding to a schrödinger operator with integrable potential, with the fourier integral. differentsial'nye uravneniya, 34(8): 1043-1048. [26] sadovnichaya iv. (2010) equiconvergence of eigenfunction expansions for sturm-liouville operators with a distributional potential. sbornik: mathematics, 201(9): 1307. [27] khavin vp, nikol’skiı nk. (1992) commutative harmonic analysis. iv, encyclopaedia of mathematical; sciences, vol. 42. 125 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <feff005500740069006c006900730065007a00200063006500730020006f007000740069006f006e00730020006100660069006e00200064006500200063007200e900650072002000640065007300200064006f00630075006d0065006e00740073002000410064006f006200650020005000440046002000700072006f00660065007300730069006f006e006e0065006c007300200066006900610062006c0065007300200070006f007500720020006c0061002000760069007300750061006c00690073006100740069006f006e0020006500740020006c00270069006d007000720065007300730069006f006e002e0020004c0065007300200064006f00630075006d0065006e00740073002000500044004600200063007200e900e90073002000700065007500760065006e0074002000ea0074007200650020006f007500760065007200740073002000640061006e00730020004100630072006f006200610074002c002000610069006e00730069002000710075002700410064006f00620065002000520065006100640065007200200036002e0030002000650074002000760065007200730069006f006e007300200075006c007400e90072006900650075007200650073002e> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 effects of ph, dosage and contact time on boron removal from synthetic saline water using moringa oleifera seeds mohammed saedi jami1*, nur syahirah zakaria1, moussa mahamed ahmed1, nik rashida nik abdul ghani1, mohammed ngabura2, and mani malam ahmad3 1department of biotechnology engineering, kulliyyah of engineering, international islamic university. malaysia, jalan gombak, 53100 kuala lumpur, malaysia 2department of chemical and environmental engineering, faculty of engineering, universiti putra malaysia, 43400 upm serdang, selangor, malaysia 3department of biology, faculty of science, kano university of science and technology, wudil, 3244 wudil-gaya road, kano, nigeria *corresponding author: saedi@iium.edu.my (received: 18th july 2019; accepted: 12th may 2020; published on-line: 4th july 2020) abstract: boron is one of the key elements required in flora, fauna, as well as human beings. however, human life and eco-systems could be seriously affected when exposed to excessive levels of boron, especially in seawater and groundwater. in this work moringa oleifera was selected as a precursor adsorbent owing to its eco-friendliness characteristics and favourable removal efficiency of adsorbates. besides, m. oleifera does not significantly affect the conductivity of water and ph value after the treatment. the main aim of this work was to investigate the potentiality of m. oleifera in the treatment of boron from contaminated saline water. the effect of adsorption parameters such as ph (7 9), adsorbent dose of 4000 – 8000 mg/l of solution and contact time of 60 – 180 min was thoroughly investigated. face-centred central composite design (fcccd) was applied to optimize these parameters. consequently, the highest percentage of removal (65%) was achieved at the ph of 8, 120 min of contact time and 6000 mg/l of adsorbent dosage. the adsorption studies stated that the adsorption fitted well with the freundlich isotherm. therefore, the outcome of this work revealed that boron could be significantly treated using a prepared adsorbent from m. oleifera. abstrak: boron merupakan salah satu elemen yang diperlukan oleh flora, fauna, juga manusia. walau bagaimanapun, hidup manusia dan ekosistem pasti terkesan apabila di dedahkan secara berlebihan, terutama pada air di lautan dan daratan. kajian ini menggunakan moringa oleifera sebagai penjerap kerana ia mempunyai ciri-ciri mesra dan berkesan membuang bahan terjerap dengan berkesan. selain itu, m. oleifera tidak langsung memberi kesan kepada konduktiviti air dan nilai ph selepas perawatan. tujuan utama kajian ini adalah mengkaji potensi m. oleifera dalam larutan rawatan air garam boron yang tercemar. kesan parameter penjerapan seperti ph (7-9), dos penjerapan 4000 – 8000 mg/l larutan dan masa interaksi 60 – 180 minit di kaji dengan teliti. kaedah komposisi tumpuan tengah muka (fcccd) digunakan bagi mengoptimumkan parameter-parameter ini. hasilnya, peratus tertinggi penyingkiran adalah sebanyak (65%) pada ph 8, 120 min masa interaksi dan 6000 mg/l dos penjerapan. kesimpulannya, kajian penjerapan ini menyokong kuat teori isoterma freundlich. oleh itu, hasil kajian ini menunjukkan boron dapat dirawat dengan menggunakan larutan penjerapan daripada m. oleifera. 12 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 keywords: optimization; boron; sea water; moringa oleifera seeds 1. introduction boron is a major constituent needed in plants, animals, and humans for metabolic and biosynthesis [1, 2]. it is an essential component for carbohydrate metabolism, sugar translocation, and other hormonal mechanisms in plants. it was reported that it is the basic marker for animal and human immune mechanism specifically in bone metabolism and central nervous systems [3]. its deficiency in plants leads to retarded growth and enzymatic activities that could result in the death of the plants. in human and animals, deficiency may lead to low absorption capability for nutrient components and cause the deformity in embryo development for vertebrates as well as in cardiovascular coronary [4]. however, despite the importance of this chemical to plant and animal life, its redundancy (excess) may be toxic, leading to severe health and environmental damages. the toxicity in humans is manifested by nausea, vomiting, poor appetite, and weight loss [5, 6]. moreover, its excess in soil and irrigation water could endanger plant life [7]. numerous conventional techniques for boron removal from sea water are reported including reverse osmosis (ro), membrane distillation, and ion exchange methods [8-10]. however, these current techniques are identified with certain drawbacks such as high cost and high energy intensity [11]. adsorption technique is an effective and recommended method to remove boron from water even at very low concentration. a wide range of sorbents have been used in the adsorption processes to remove boron such as activated carbon, clays, fly ash, biological materials, natural minerals, nanoparticles, layered double hydroxide, and other complexing membranes [12-14]. on the other hand, adsorption technique using agro-based materials was found to be cost effective, eco-friendly, easily accessible, easy to handle, and highly selective [15]. moringa oleifera trees also known as a drumstick trees have a deciduous shrub characteristic in a rapidly growing small tree. the size of the tree is about 10-13 m tall and 35-45 cm in diameter with an umbrella-shaped open cap [16]. moringa oleifera belongs to the moringaceae family and is the most widely distributed species worldwide [17, 18]. the fruit changes to brown colour when mature and usually contains about 10 to 50 seeds inside it [16]. the moringa oleifera seeds have demonstrated to be persuasive as primary coagulants for water treatment after being tested over the years and can be compared to conventional chemical coagulant (alum). its high efficiency removal rate and its edible properties make the m. oleifera seeds adsorbent a standout potential candidate for boron removal from sea water [19]. in the present study, the optimal values of ph, contact time and adsorbent dosage as the process parameters for effective boron removal were established using face-centred central composite design (fcccd). in addition, the prediction ability of the established model was tested based on the freundlich and langmuir adsorption isotherms. 2. materials and methods 2.1 materials the dry moringa oleifera seeds were purchased from an accredited agent in sabah, malaysia. all reagents were commercial products of analytical grade. 13 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 2.2 experimental procedures 2.2.1 sample preparation the seeds of moringa oleifera were peeled manually and dried in the oven at a temperature of 105 °c for 24 hours to eliminate the moisture content according to the reported standard procedure [20]. afterwards, the seeds were ground in a common processor and then sieved using standard sieve of 212 μm size mesh. stock solution for synthetic sea water was prepared by measuring and suspending 5.719 g of boric acid into 1000 ml distilled water from which a working concentration of 5 mg/l was made through an appropriate dilution. for synthetic seawater preparation, stock solution of boron (1000 μg/ml) was prepared by dissolving 0.5636 g boric acid in water and diluting to 100 ml in a volumetric flask as described by zarei et al. [21]. 2.2.2 spectrophotometric assay for the analysis of boron depletion, samples were systematically withdrawn according to the methods described by zarei et al. and ahmad et al. [21, 22]. standard methylene blue method by zarei et al. [10] was applied and the analysis was done by observing the absorbance on spectrophotometer. one (1) ml of the boron solution was poured into 15 ml centrifuge tube then 0.5% of naf (1 ml) was added followed by 1 ml of 1.5 mm methylene blue and 1 ml of 0.2 m sulfuric acid. then, the contents were mixed well by vortex before diluted with 1 ml distilled water. dichloromethane (100 μl) was prepared in 400 μl of acetonitrile solvent and added into the reaction solution. after a cloudy solution was formed, the solution was centrifuged for 2 minutes at 3800 rpm. the supernatant was discarded and the remaining pellet was dissolved with 400 μl acetonitrile. then, the absorbance was measured at 657 nm. the standard curve (fig. 1) from this assay was utilized to determine the final concentration of boron. 2.2.3 batch adsorption experiments a series of experiments was conducted batch wise in 500 ml erlenmeyer flasks mounted on a hot plate with magnetic stirrer. the flask was covered with aluminium foil paper to prevent splash. the agitation was maintained at 200 rpm, while ambient temperature was adopted throughout the experiment. the removal efficiency of boron (%) was determined using the eq. 1: boron removal (%) = × 100 (1) where co and ct are the initial and final concentrations of lead in the solution (mg/l), respectively. 2.2.4 adsorption isotherm langmuir and freundlich isotherms were investigated to explain the metal ion distribution between solid and liquid phases. the langmuir model demonstrates there is no interaction between adsorbate molecules on adjacent sites and the adsorption occurs on a set of distinct localized adsorption sites within the natural material [23], whereas the freundlich theory states that the uptake of metal ions occurs on a heterogeneous surface by monolayer sites adsorption. the adsorption capacity of the m. oleifera can be obtained from eq. 2 below. = (2) 14 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 where ci is the initial concentration (mg/l) and cf is the final concentration (mg/l). the standard and linearized equations for langmuir isotherm are given in eq. 3 and eq. 4: = (3) = + (4) where, qe is the quantity of adsorbate adsorbed in mg/g, ce is the equilibrium concentration (mg/l), b is the constant of adsorption equilibrium (l/mg) which is related to the energy of adsorption, and qm (mg/g) is the maximum adsorption capacity. the langmuir isotherm experimental data were plotted as ce/qe against ce graph. the model parameters can be obtained from the slope of the straight-line graph, 1/qm and the y-intercept, 1/bqm 1/b [24]. the freundlich isotherm equations can be expressed as given in eq. 5: = (5) linearized form of eq. 5 is given as: = (6) where kf (mol2/kj2) is an indicator of adsorption capacity and 1/n (mg/l) is a measure of intensity of adsorption. in freundlich isotherm, the linearized graph of log(qe) against log (ce) gives a slope of 1/n and an intercept of log 10 (k). 2.3 design of experiment and statistical analysis three process parameters, namely, ph (7-9), contact time (60-180 min) and adsorbent dosage (0.4-0.8 g) were optimized using fcccd with design expert software (stat-ease, inc., version 10.0.5.0 minneapolis, usa) as reported by [24]. a total of 20 experiments with three-coded levels (1, 0 and +1) were conducted. regression analysis was performed using second-order polynomial empirical model to correlate the influence of independent variables on boron removal (eq. 7). jiijijiiiiiiii xxxxy 2 0 (7) where y is the predicted response, βo is the offset term, βi is the ith linear coefficient, βii is the ith quadratic coefficient, and βij is the ijth interaction coefficient. 3. results and discussion 3.1 standard curve of boron the standard curve used in finding the final concentration of boron illustrated in fig. 1. the equation was = 0.0054 + 0.0363, where = 0.9702. the standard curve is accepted as the value of r2 was more than 0.95. the final concentration of boron determined by inserting the measured value of absorbance at 657 nm of solution after the batch experiment was done as y value whereby the x value is the final concentration of boron. 15 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 fig. 1: standard curve of boron. 3.2 effect of time figure 2 shows the effect of contact time for the adsorption of boron using moringa oleifera seeds. the figure shows that the contact time has remarkable influence on the adsorption of boron. the highest boron removal by m. oleifera seeds can be observed at 120 minutes of contact time with 60% of removal. fig. 2: effect of time on boron removal at ph 8 and 6000 mg/l of adsorbent dosage. initially, the percentage removal of boron increased gradually until it reached the peak that is 120 minutes of contact time, afterwards, the rate starts decreasing until equilibrium was achieved. this trend could be due to the saturation on the available adsorption sites present on the m. oleifera seed. initially the adsorption is fast but gradually decreased after it reached equilibrium due to the aggregation of m. oleifera seeds when it is increased. this phenomenon decreased the availability of adsorption surface area and increased the diffusion path length of boron. besides, the unavailability of the surface area of adsorbent, the number of vacant sites and the interaction between the ions in the solution would lower the adsorption process [25,26]. 3.3 effect of ph the percentage of boron removal was observed to be at its highest peak in the condition of 0.6 g adsorbent dosage within 120 minutes of contact time. the agitation speed was fixed at 200 rpm throughout the experiment. the adsorption capacity of the adsorbent with varying ph values was plotted in fig. 3. y = 0.0054x + 0.0363 r² = 0.9702 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 20 40 60 80 100 120 a bs or ba nc e at 6 57 nm concentration (μg/ml) 0 10 20 30 40 50 60 70 0 20 40 60 80 100 120 140 160 180 200 p er ce nt ag e r em ov al b (% ) time (min) 16 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 fig. 3: effect of ph on boron removal at 120 minutes of contact time and adsorbent dosage of 6000 mg/l. the effect of ph on the adsorption of boron onto moringa oleifera seed was studied in the range from ph 2 to ph 10. the result displayed that boron removal was at its highest peak at ph 8 with about 59% removal of boron. initially, the percentage removal of boron increased with an increment of ph until it reached optimal ph value of 8. further ph increment causes a dramatic decline in the adsorption percentage because of the electrostatic force of attraction become weak between the different charges of an adsorbate and adsorbent resulting in the lowering of adsorption. simply at that ph, the protein of m. oleifera seeds have isoelectric point where over 90% of the amino acid molecules are in ionized state [21]. 3.4 effect of adsorbent dosage the effect of adsorbent dosage on boron removal was investigated at varying adsorbent dosage from 2000-10000 mg/l of boron solution with 5 mg/l of boron concentration. the results are presented in fig. 4. fig. 4: effect of adsorbent dosage on boron removal at 120 minutes of contact time with ph 8. from fig. 4 above, the graph displayed that the highest percentage removal of boron using moringa oleifera seeds was at 6000 mg/ l of adsorbent dosage. the removal of boron increases rapidly from 2000 mg/l until it reached maximum peak at 6000 mg/l adsorbent dosage before gradually decreases and approaching equilibrium at 10000 mg/l dosage. continuous increase of dosage does not increase the boron removal percentage because the effective contact surface area of the adsorbent decreased at higher adsorbent dosage which 0 10 20 30 40 50 60 70 0 2 4 6 8 10 12 p er ce nt ag e r em ov al b (% ) ph 0 10 20 30 40 50 60 0 2000 4000 6000 8000 10000 12000 p er ce nt ag e re m ov al b (% ) adsorbent dosage (mg/l) 17 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 results in a decreasing of unit adsorption capacity as too large amount of adsorbent will reduce the adsorption saturation sites besides create particle aggregates which cause a decrease in the total surface area that results in a decrease of adsorption capacity. 3.5 adsorption isotherm the distribution of metal ions between liquid phase and the solid phase can be described by several isotherm models such as langmuir and freundlich [23]. the equilibrium data for freundlich and langmuir isotherm models were presented in table 1 and 2, respectively while the linearized graph of the two freundlich and langmuir models was plotted as shown in fig. 5 and fig. 6, respectively. table 1: equilibrium data for freundlich isotherm model qe (mg/g) ce (mg/l) ln qe (mg/g) ln ce (mg/l) 1.9595 3.8103 0.6727 1.3377 2.1524 4.1595 0.7666 1.4254 2.2087 4.6543 0.7924 1.5378 2.3175 4.9421 0.8405 1.5978 table 2: equilibrium data for langmuir isotherm model qe (mg/g) ce (mg/l) ce/qe (g/mg) 4.6231 21.76 4.7067 4.5584 26.63 5.8421 5.5645 34.50 6.2001 5.4297 39.61 6.9267 5.1818 45.6 8.8011 fig. 5: freundlich isotherm for boron removal using m. oleifera seeds. from the plots, the estimated isotherm parameters were calculated and presented on table 3. from the data, r2 for freundlich adsorption isotherm was 0.9422 whereas that of langmuir isotherm was 0.9115. the results showed that adsorption process evidently fitted well with the freundlich isotherm model with high regression value. this expression predicted that the boron uptake takes place on a heterogeneous surface by monolayer sites adsorption of m. oleifera seeds. 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.3 1.4 1.5 1.6 1.7 1.8 ln q e ln ce 18 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 fig. 6: langmuir isotherm for boron removal using m. oleifera seeds. from the plots, the estimated isotherm parameters were calculated and presented on table 3. from the data, r2 for freundlich adsorption isotherm was 0.9422 whereas that of langmuir isotherm was 0.9115. the results showed that adsorption process evidently fitted well with the freundlich isotherm model with high regression value. this expression predicted that the boron uptake takes place on a heterogeneous surface by monolayer sites adsorption of m. oleifera seeds. table 3 isotherm parameters for adsorption of boron into m. oleifera seeds isotherm model estimated isotherm parameter freundlich 0.7014 1.8231 0.9422 langmuir ( ) ( ) 6.6357 0.1055 0.9115 the standard curve equation, y = 0.0054x +0.0363 was used to find the final concentration of boron with r2 = 0.9702 by measuring absorbance at 657 nm. y-value is indicated by the measured absorbance value at 657 nm of solution after each batch experiment, whereas xvalue is the final concentration of boron. 3.4 modelling by statistical analysis in this study, the model was structured by design expert version 6.0.8 and created by factorial central composite design (fccd) under response surface method. the three parameters which were optimized using fccd are ph, contact time and dosage of adsorbent. other parameters such as agitation speed were fixed at 200 rpm and the experiment was conducted at room temperature. from the 20 experimental runs, the results were analysed using the analyses of variance (anova) (table 4). the highest removal efficiency of 65 % was found at ph 8, adsorbent dosage of 6000 mg/l and contact time of 60 min. table 5 shows the anova for boron adsorption by m. oleifera seeds. 4 5 6 7 8 9 10 20 25 30 35 40 45 50 c e /q e ce (mg/l) 19 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 table 4: results for batch adsorption experiment using m. oleifera seeds run a: ph b: adsorbent dosage (gram) c: contact time (min) percentage boron removal (%) − × 1 8 0.6 120 65 2 9 0.4 180 35 3 7 0.8 180 40 4 7 0.4 60 20 5 8 0.6 120 65 6 9 0.8 60 45 7 8 0.6 120 65 8 7 0.4 180 30 9 9 0.4 60 30 10 7 0.8 60 45 11 9 0.8 180 50 12 8 0.6 120 65 13 8 0.8 120 58 14 8 0.6 60 40 15 8 0.6 120 65 16 8 0.4 120 30 17 9 0.6 120 59 18 8 0.6 120 65 19 8 0.6 180 53 20 7 0.6 120 30 table 5: anova analysis for the adsorption using m. oleifera seeds source sum of square df mean square f value prob > f model 2744.60 9 304.96 4.00 0.0319 significant a 291.60 1 291.60 3.82 0.0863 b 864.90 1 864.90 11.34 0.0098 c 78.40 1 78.40 1.03 0.3404 a2 175.60 1 175.60 2.30 0.1677 b2 197.98 1 197.98 2.59 0.1459 c2 99.49 1 99.49 1.30 0.2865 ab 3.13 1 3.13 0.041 0.8447 ac 3.13 1 3.13 0.041 0.8447 bc 28.13 1 28.13 0.37 0.5606 residual 610.40 8 76.30 lack of fit 534.40 5 106.88 4.22 0.1328 not significant pure error 76.00 3 25.33 cor total 3534.55 19 based on the analysis of the model in table 5 above, the model f-value of 4.00 implies the model is significant. there is only a 3.19% chance that a "model f-value" this large could occur due to noise. values of "prob > f" less than 0.0500 indicate the model are significant. in this case b is a significant model term. values greater than 0.1000 indicate the model terms are not significant. the "lack of fit f-value" of 4.22 implies the lack of fit is not significant relative to the pure error. there is a 13.28% chance that a "lack of fit f-value" this large could occur due to noise. non-significant lack of fit is good as it shows that the model is in a good fit. 20 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 table 6 overall analysis of the model std. dev. 8.73 r-squared 0.8181 mean 46.15 adj r-squared 0.6134 c.v. 18.93 pred r-squared -1.1132 press 7089.85 adeq precision 6.450 a negative "pred r-squared" implies that the overall mean is a better predictor of the response than the current model. "adeq precision" measures the signal to noise ratio. a ratio greater than 4 is desirable. the ratio of 6.450 indicates an adequate signal. this model can be used to navigate the design space. the coefficient of variation % (cv%) which can be used to measure the reliability and precision of the experiment was found to be 18.93 which is quite reliable. the higher the value of cv%, the less reliable is the experiment. the cv value is a measure of residual variation of the data relative to the size of the mean. the value of predicted residual sum of squares (press) is found to be 7089.85. it is a measurement of how fit of each point in the design. the smaller the press value, the better the model fits the data points. according to the model equation generated by design expert 6.0 software, the 3d plots were plotted to investigate the interaction between variables. the 3d plots were generated by plotting the response (boron percentage removal) on the z-axis against any two independent variables (fig. 6). these plots hold a single constant variable at its centre, while the other two variables were varied in the range of experimental values. from the 3d plot indicated that it is possible to increase the percentage removal of boron further when the contact time, ph value and adsorbent dosage increased. previous studies on optimization of boron removal that adsorbed by different adsorbent are compared with the m. oleifera adsorption in terms of ph and adsorption capacity. the optimum ph value for m. oleifera was in agreement with other adsorbents such as rice husk, date seed ash, chitosan and magnesite-bentonite clay where the values were in the range of ph 7 to 10 which was in an alkaline environment [27-30]. meanwhile, m. oleifera presented higher adsorption capacity than chitosan and magnesite-bentonite clay [27,30]. 4. conclusion in conclusion, the results indicated that the highest percentage of boron removal was achieved up to 65% from table 4 at optimum values of ph 8, 120 min of contact time and 6000 mg/l of adsorbent dosage. the decrease in removal rate after the optimum time of 120 min was probably due to continuous aggregation at the adsorption sites. the effect of ph variation with boron removal was associated with weak electrostatic forces between the adsorbate and the adsorbents, which manifested much at ph greater than 8. it was shown that boron removal increases with increase in adsorbent dosage with climax at 6000 mg/l. however, removal plummeted beyond this range due to decrease in the contact surface area available. the adsorption studies showed that the expressions were well fitted to freundlich isotherm compared to langmuir isotherm model. statistical analysis modelling showed that the model was significant and thus confirm the effect of the combination parameters and conditions for the removal of boron from the solution. 21 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 a) b) c) fig. 6: (a) 3d plot for percentage removal of boron as a function of contact time and adsorbent dosage; (b) 3d plot for percentage removal of boron as a function of ph and adsorbent dosage; (c) 3d plot for percentage removal of boron as a function ph and contact time. 22 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 acknowledgement the authors express their thanks to ministry of higher education (mohe) malaysia for granting a fundamental research grant scheme (frgs), project no. frgs-19-194-0803 for the financial support for this work. references [1] princi mp, lupini a, araniti f, longo c, mauceri a, sunseri f, abenavoli mr (2016). boron toxicity and tolerance in plants: recent advances and future perspectives. in plant metal interaction, edited by parvaiz a. elsevier; pp 115–147. [2] zhang j, cai y, liu, k. (2019). extremely effective boron removal from water by stable metal organic framework zif-67. industrial & engineering chemistry research, 58: 4199– 4207. doi.org/10.1021/acs.iecr.8b05656 [3] khaliq h, juming z, ke-mei p (2018). the physiological role of boron on health. biological trace element research, 186: 31-51. doi:10.1007/s12011-018-1284-3 [4] guan z, lv j, bai p, guo x. (2016). boron removal from aqueous solutions by adsorption a review. desalination, 383: 29-37. doi.org/10.1016/j.desal.2015.12.026 [5] guidelines for drinking-water quality, 2nd ed. addendum to vol. 2. health criteria and other supporting information. (1998) world health organization, geneva. [6] kabu m, akosman m s. (2013). biological effects of boron. reviews of environmental contamination and toxicology, edited by whitacre d m. springer; pp 57-75. doi:10.1007/978-1-4614-6470-9_2 [7] tu k l, nghiem l d, chivas a r (2010). boron removal by reverse osmosis membranes in seawater desalination applications. sep. purif. technol, 75: 87-101. doi:10.1016/j.seppur.2010.07.021 [8] kim bc, hung p v x, moon s h (2010). boron removal from seawater by combined system of seawater reverse osmosis membranes and ion exchange process: a pilot-scale study. desalination and water treatment, 15: 178–182. doi:10.5004/dwt.2010.1683 [9] kabay n, bryjak m (2015). boron removal from seawater using reverse osmosis integrated processes. in boron separation processes, elsevier 219–235. doi:10.1016/b9780-444-63454-2.00009-5 [10] biniaz p, torabi ardekani n, makarem m, rahimpour m (2019). water and wastewater treatment systems by novel integrated membrane distillation (md). chemengineering, 3: 1-36. doi:10.3390/chemengineering3010008 [11] tagliabue m, reverberi a p, bagatin r (2014). boron removal from water: needs, challenges and perspectives. journal of cleaner production, 77: 56 64. doi:10.1016/j.jclepro.2013.11.040 [12] ozturk n, kavak d (2005). adsorption of boron from aqueous solutions using fly ash: batch and column studies. journal of hazardous materials, 127: 8188. doi:10.1016/j.jhazmat.2005.06.026 [13] yüksel s, yürüm y (2009). removal of boron from aqueous solutions by adsorption using fly ash, zeolite, and demineralized lignite. separation science and technology, 45: 105-115. doi:10.1080/01496390903256042 [14] montalvo-andia j p, yokoyama l, cesar teixeira l a (2018). study of the equilibrium, kinetics, and thermodynamics of boron removal from waters with commercial magnesium oxide. international journal of chemical engineering, 2018: 110. doi:10.1155/2018/6568548. [15] wibowo e, rokhmat m, abdullah m (2017). reduction of seawater salinity by natural zeolite (clinoptilolite): adsorption isotherms, thermodynamics and kinetics. desalination, 409:146-156. doi.org/10.31436/iiumej.v21i1.1254 [16] anjorin t b, ikokoh p, okolo s (2010). mineral composition of moringa oleifera leaves, pods and seeds from two regions in abuja, nigeria. int. j. agric. biol. 12: 431434. 23 iium engineering journal, vol. 21, no. 2, 2020 jami et al. https://doi.org/10.31436/iiumej.v21i2.1203 [17] kansal s k, kumari a (2014). potential of m. oleifera for the treatment of water and wastewater. chem rev.114: 4993-5010. doi: 10.1021/cr400093w [18] reddy d h k, harinatha y, seshaiaha k, reddy a v r (2010). biosorption of pb(ii) from aqueous solutions using chemically modified moringa oleifera tree leaves. chem. eng. j. 162: 626-634. [19] camacho f p, sousa v s, bergamasco r, teixeira m r (2017). the use of moringa oleifera as a natural coagulant in surface water treatment. chem. eng j., 313: 226-237. [20] reck i m, paixão r m, bergamasco r, vieira m f, vieira a m s (2018). removal of tartrazine from aqueous solutions using adsorbents based on activated carbon and moringa oleifera seeds. j. clean prod., 171: 85-97. [21] zarei a r, nobakht s, zaree m a (2012). a new separation and preconcentration system based on dispersive liquid-liquid microextraction for spectrophotometric determination of trace amounts of boron in water samples, jtafd, 1: 1-13. [22] ahmad m m, azoddein a a m, zahari m a k m, seman m n bin a, saedi m j, olalere o a, alara o r (2019). optimization of process parameters in mixed sulfide oxidation bacterial culture using response surface methodology as a tool. journal of king saud university, 31: 836 843. doi.org/10.1016/j.jksus.2017.11.001 [23] glass b, using s, techniques m b, shimada k, kobayashi m, tominaga g. (2016). adsorption study on moringa oleifera seeds and musa cavendish as natural water purification agents for removal of lead, nickel and cadmium from drinking water. iop conf. series: materials science and engineering 136: 1-10. 012044 doi:10.1088/1757899x/136/1/012044 [24] mahvi a h, ghanbarian m, nasseri s, khairi a (2009). mineralization and discoloration of textile wastewater by tio2 nanoparticles. desalination, 239: 309-316. doi:10.1016/j.desal.2008.04.002 [25] al haddabi m, ahmed m, al jebri z, vuthaluru h, znad h, al kindi m (2016). boron removal from seawater using date palm (phoenix dactylifera) seed ash. desalination and water treatment, 57: 5130–5137. https://doi.org/10.1080/19443994.2014.1000385 [26] mohammed s j, nur syahirah z, moussa m a, mohammed n, mani m a (2018), optimization of process parameters for boron adsorption from sea water using moringa oleifera seeds, 5th international conference on biotechnology engineering icbioe, kuala lumpur, malaysia 19 20. [27] copello g j, villanueva m e, gonzález j a, lópez egües s, diaz l e (2014). teos as an improved alternative for chitosan beads cross-linking: a comparative adsorption study. journal of applied polymer science, 131: 1-8. doi.org/10.1002/app.41005 [28] guan z, lv j, bai p, guo x (2016). boron removal from aqueous solutions by adsorption a review. desalination, 383: 29-37. doi.org/10.1016/j.desal.2015.12.026 [29] al haddabi m, ahmed m, al jebri z, vuthaluru h, znad h, al kindi m (2016). boron removal from seawater using date palm (phoenix dactylifera) seed ash. desalination and water treatment, 57: 5130 -5137. doi.org/10.1080/19443994.2014.1000385 [30] masindi v, gitari m w, tutu h, debeer m (2016). removal of boron from aqueous solution using magnesite and bentonite clay composite. desalination and water treatment, 57: 8754-8764. doi.org/10.1080/19443994.2015.1025849 24 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <feff03a703c103b703c303b903bc03bf03c003bf03b903ae03c303c403b5002003b103c503c403ad03c2002003c403b903c2002003c103c503b803bc03af03c303b503b903c2002003b303b903b1002003bd03b1002003b403b703bc03b903bf03c503c103b303ae03c303b503c403b5002003ad03b303b303c103b103c603b1002000410064006f006200650020005000440046002003ba03b103c403ac03bb03bb03b703bb03b1002003b303b903b1002003b103be03b903cc03c003b903c303c403b7002003c003c103bf03b203bf03bb03ae002003ba03b103b9002003b503ba03c403cd03c003c903c303b7002003b503c003b103b303b303b503bb03bc03b103c403b903ba03ce03bd002003b503b303b303c103ac03c603c903bd002e0020002003a403b1002003ad03b303b303c103b103c603b10020005000440046002003c003bf03c5002003b803b1002003b403b703bc03b903bf03c503c103b303b703b803bf03cd03bd002003b103bd03bf03af03b303bf03c503bd002003bc03b50020004100630072006f006200610074002003ba03b103b9002000410064006f00620065002000520065006100640065007200200036002e0030002003ba03b103b9002003bd03b503cc03c403b503c103b503c2002003b503ba03b403cc03c303b503b903c2002e> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 the characteristics of reed lightweight clay bricks after drying process ghazwan abdulsamad salman ministry of higher education and scientific research, contract department, baghdad, iraq *corresponding author: ghazwan_salman@yahoo.com (received: 16th november 2019; accepted: 11th february 2020; published on-line: th july 2020) abstract:the drying procedure is one of the basic stages in the brick making process, particularly when utilizing the extrusion framing technique. this stage decides the quality and amount of the brick samples. one of the characteristic waste vegetable materials is reed, whish is found in huge amounts in iraq and numerous other nations. five weight proportions of reed crumbs (5,10,15,20 and 25%) were utilized to produce lightweight clay bricks. lab samples were shaped with dimensions of (25×38×76mm) using the vacuum extraction method. brick properties were tested after drying to determine the values of longitudinal drying shrinkage, bulk density, and compression strength. in order to check the property of lightweight clay brick samples, the samples were burned in the furnace at a temperature of 1000°c with a burning rate of 2°c per minute. the significance of this research is to know the optimal proportions of the reed crumbs that prompts exact control of the drying procedure. this fine control brings about samples of lightweight bricks of the required dimensions and without cracks that influence their properties after drying and become more visible after burning. this knowledge will prompt the decrease of waste in raw materials and energy utilized in the manufacturing of a particular amount of lightweight bricks and, along these lines, reduce the expense of production. abstrak: prosedur pengeringan merupakan salah satu peringkat asas dalam proses membuat bata, terutamanya apabila menggunakan teknik pembingkaian penyemperitan. peringkat ini memutuskan kualiti dan jumlah sampel bata. salah satu daripada bahanbahan sayur-sayuran sisa buatan adalah buluh, ia didapati dalam jumlah besar di iraq dan banyak negara yang berbeza. sebanyak 5 buah berat serbuk reed (5,10,15,20 dan 25%) digunakan untuk menghasilkan bata tanah liat yang ringan. model makmal dibentuk dengan dimensi (25 × 38 × 76mm) dengan menggunakan kaedah pengekstrakan vakum. ciri-ciri bata telah diuji selepas pengeringan untuk menentukan nilai-nilai kepekatan pengeringan longitudinal, ketumpatan pukal dan kekuatan mampatan. untuk memeriksa sampel tanah liat ringan tanahpropertyof, model-model tersebut dibakar dalam relau pada suhu 1000 ° c dengan kadar pembakaran 2°c seminit. kepentingan kajian ini adalah untuk mengetahui perkadaran optimum serbuk reed yang menimbulkan kawalan tepat terhadap prosedur pengeringan. kawalan halus ini membawa model-model bata yang ringan dari dimensi yang diperlukan dan tanpa retak yang mempengaruhi sifatnya selepas pengeringan dan menjadi lebih terlihat selepas terbakar. pengetahuan ini akan mendorong penurunan sisa bahan mentah dan tenaga yang digunakan dalam pembuatan sejumlah bata ringan dan di sepanjang garisan ini mengurangkan perbelanjaan pengeluaran. keywords:drying process; optimal proportions; vacuum extraction method; reed; lightweight clay bricks 111 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 1. introduction the drying procedure is a means of preparing thermally-shaped samples for a specific time frame at a temperature of 110°c with the goal that the humidity does not surpass (25%) of the initial moistness. this procedure builds the mechanical strength of the samples, which facilitates the process of transfer and placing into the furnaces. the drying procedure is completed in stages where in the primary stage free water among the particles of the clays is lost, causing a convergence of particles with each other leading to the occurrence of dry shrinkage. the shrinkage in the body is equivalent to the measure of vanished water. in the following stage, the thin water surrounding the clay particles vanishes, causing more combinations of the particles and some additional shrinkage. in the last stage, the water in the pores is lost and the water travels through the pores to the particle surface to replace the vanished water from the surface. this stage is described by no shrinkage and the air in the long run replaces the water in the capillary pores, making the dried mass permeable. the drying stages cannot be set and isolated from one another obviously on the grounds that they are overlapping. numerous scientists considered the effect of adding agricultural waste to soil in order to create lightweight bricks. one of the most well-known agricultural wastes is rice husk. it has been found that, the perfect proportion of the rice husk ranges from 10-20% by weight. adding rice husk to the clay is restricted because it reduces the compression strength of the brick as the rice husk content increases [1,2]. demir [3,4,5] discovered that the compression strength of the dried brick samples containing sawdust, tobacco, and grass remained unequivocally increased in spite of the increased drying shrinkage of the clay body and these results led to a reduced use of the scraps because of handling issues of unburned blocks. similar conclusions were reached by samia et al. [6], they found that the drying shrinkage and the compression strength before firing were also increased after raising the content of two types of organic waste, namely olive stones and hay, at 1-10% replacement-to-clay in order to manufacture clay bricks. this behaviour was due to the binding effect of the agricultural waste in the block's structure before burning and that increase was found useful in reducing cracks while transporting bricks to kilns and in maintaining brick dimensions. ahmad et al. [7] produced clay samples within the limits allowed for most of the recommended standards by including 5-15% by weight of coal and wheat peel additives to the clay, moreover the drying shrinkage was found to be lower than 8% within the limits and decreased with the increase of percentage of additives. in addition, porosity of the sample can be constrained by the proportion of sawdust mixture and for structural purposes where compression strength is significant, the level of sawdust ought not surpass 10 to 15 percent by weight of the insulating fired bricks [8]. the use of reed morsels for manufacturing of lightweight clay bricks has been exploited in iraq by the addition of 5-25% by weight of reed morsels to the clay and the mixes burned at different temperatures of 800,900 and 1000°c, respectively. the results showed the possibility of manufacturing lightweight clay bricks with comparatively good properties such as bulk density and compression strength in the brick samples containing 5% by weight of reed crumbs. on the other hand, the results of the studies indicated a decrease in thermal conductivity and longitudinal shrinkage. moreover, the produced bricks can be made in the same factories that manufacture the ordinary brick clay and in the same step of producing ordinary clay bricks [9,10]. 112 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 the purpose of this research was to determine the effects of the addition of reed crumbs in the brick mixture on the drying technique. the bulk density, drying shrinkage and compression strength properties were examined. 2. materials physical, chemical and metallic tests were conducted to evaluate the raw materials used in the production of this brick. 2.1 soil soil (100 kg) from two unique quarries was fetched from al-nahrawan quarry in the baghdad zone. the soil was moist and contained masses with a maximum diameter of 5 cm. the soil was cleaned by removing foreign and organic materials from it and then dried in large containers outside the laboratory as a result of exposure to sunlight. after that, the masses of soil were transferred to the oven for drying at a temperature of 110 °c for 48 hours and pounded with an iron ball plant to be passed through sifter no. 22 (710) micron. chemical and physical analyses were carried out on the soil sample. the chemical investigation of the clay was done by x-ray fluorescence. table 1 and 2 show the chemical and physical characteristics of the clay utilized in this research. to decide the grain size distribution of soil utilized, wet sieving and hydrometer technique were utilized based on astm d422[13] and astm d2487[14]. table 3demonstrates the grain size distribution of the clay utilized. table 1: chemical compounds of the soil utilized chemical compound content in soil (%) standard requirement [11,12] (%) sio2 40.80 50-60 cao 16.04 5-10 al2o3 10.49 20-30 fe2o3 4.90 5-7 mgo 2.42 1 k2o 1.3 2-2.76 na2o 1.08 0.1 so3 2.0 t.s.s 2.28 l.o.i 18.6 3-4 table 2: physical characteristics of the soil utilized type of test result test specification specification limit moisture content % atterberg astm d 4318 [12] liquid limit 32 not more than 55 plastic limit 21.3 not more than 55 plastic index 11.3 not more than 30 113 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 table 3: the grain size distribution of the soil utilized grain size of soil (%) results (%) typical range (%) [13,14] sand 21 20-45 silt 45 25-45 clay 34 20-35 2.2 reeds the reeds were transported from the banks of a stream in baghdad as shown in fig. 1. the reed was cut with a target length of approximately 4 cm. the principal attributes of the reeds utilized appear in table 4. a manual system was utilized to produce reed crumbs with a little mallet and an electric saw. the reeds were shredded utilizing an electric saw as can be seen in fig. 2, at that point they were dried in a stove at a temperature of 110°c for 48 hours. after the reeds were granulated, the dried reeds were changed over to crumbs using a little mallet and went through strainer 52, size 300 to be prepared for use as an added substance to deliver lightweight blocks, as seen in fig. 3. fig. 1: the reed plants from the banks of the stream. table 4: properties of the reeds [15] characterization shortened form value specific gravity s.g 2.44 silica (%) sio2 65.2 sulfur trioxide (%) so3*** 1.52 calcium (%) cao 6.4 alumina (%) al2o3 12.3 iron (%) fe2o3 2.6 potassium (%) k2o** 2.5 chloride (%) ci n.r sodium (%) na2o n.r phosphorus (%) p2o5 0.03 magnesium (%) mgo n.r titanium (%) tio2 0.19 manganese (%) mno 0.08 moisture content (%) w 0 loss on ignition (%) l.o.i 1.47 *chemical compound values are determined utilizing edx-7000 instrument. **k2o value is determined utilizing xrd-6000 instrument. ***so3 value is determined utilizing mxf-2400 instrument. 114 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 fig. 3: the reed crumbs produced in this study. fig. 2: electrical saw table 5: plasticity coefficients of soil with and without different percentages of reeds crumbs. mix symbol raw materials plasticity index (%) s soil (reference) 31 s1 soil + 5% rc 34 s2 soil + 10% rc 38 s3 soil +15% rc 44 s4 soil + 20% rc 49 s5 soil + 25% rc 52 *where rc=reed crumbs 3. mix proportions and mixing process the production of lightweight clay block mixtures was done by adding (5, 15, and 25%) by weight of the reed crumbs to the clay. the pefferkorn method was used for deciding the measure of water required for changing the plasticity index with the different percentage of the reed additions. table 5 shows the plasticity coefficients for mixes of soil with and without various rates of the additional reeds crumbs. the blending procedure was done in a bigpan and the mixture bowl was cleaned before each blending procedure. to set up the reference blend, the clay was soaked with the fundamental water (as indicated by the plasticity coefficient) and the blending procedure was done in the big pan for 15minutes so as to acquire a homogeneous blend. concerning blends containing reed crumbs, the specified quantities of soil and reed morsels were blended into the skillet for 10 minutes without adding any water in order to get a homogeneous blend. then the water was added to the dry blend and blended for another 15 minutes. after the blending procedure is finished, the blend is set in a closed loop container for 24 hours to guarantee the homogeneity of water and soil in the blend. 115 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 4. sample preparation, drying and firing the soil blocks were produced in the lab by an extruded expulsion of air technique, using a vacuum extruder (fig. 4). specimens of 75 mm length, 38 mm width, and thickness of 25 mm height measurements were made. the drying method was started by leaving the framed soil samples in the lab for 7 days and then drying them in a stove at a temperature of 110±5°c for 48 hours. later the block samples were taken away from the stove and left to cool at a lab temperature of 23±2°c for 48 hours. the dried specimens were transferred to an electric kiln to start the firing procedure where the warming rate and the soaking time were constant. the dried blocks were sorted inside the kiln, (fig. 5) in an effort to guarantee that the warmth reached all surfaces of the samples uniformly. the dried clay blocks were burned at a 1000°c degree of firing by electrical kiln (fig. 6). the dried blocks of every blend were burned independently using a similar firing program and at the time of drenching for two hours until arriving at the planned firing temperature 1000°c. the firing rate was 2°c per minute, to guarantee adequate time for firing of every natural material with the complete arrival of carbon dioxide. after the firing procedure was finished, the kiln was turned off and the block samples were left inside until the temperature decreased to the temperature of the lab. in order to ensure a lightweight block, bulk density and compression strength tests were performed. fig. 4: clay extrusion device. fig. 5:.curing and drying furnace. 116 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 fig. 6:.burning furnace. 5. test procedure 5.1 longitudinal shrinkage test one of the significant properties after the drying process of reed lightweight clay bricks is the shrinkage of the clay mass, which mainly affects the accuracy of the final brick dimensions and the bulk density. the longitudinal shrinkage test was carried out according to specification [16] after drying the brick samples at a temperature of 110°c for 48 hours and then cooling to the laboratory temperature of 23±2°c. the length of the sample was measured before and after drying from two different sides and the average length was recorded. the length of brick blocks was measured after and before the drying process to determine the longitudinal shrinkage proportion. the following equation was used to calculate the longitudinal shrinkage: ( . )% = ( – ) 100 (1) where: (l. s)= longitudinal shrinkage, h =sample length before drying process (mm) andhr=sample length after drying process (mm).an average of 10 specimens was used. 5.2 bulk density test the bulk density of the samples was determined based on the specification [14] and after drying process by weighing them with a high sensitivity electric balance and accuracy up to ±0.01 g. dimension measurements were performed on two sides with a vernier caliper and the rate was recorded. an average of 10 specimens was used. the bulk density of the dried lab samples was estimated using equation (2): . = (2) where: b . d=bulk density (g/cm3), w= weight of samples after drying (g) andv= volume of samples after drying (cm3). the same equation was used to calculate the bulk density after the burning process. the bulk density of the firing block samples was determined as per astm c373 [17]. 5.3 compression strength tests the values of the compression strength tests after drying are influenced by cracks and defects that show up in the sample bricks and are considered to be a primary measure of the final compression strength of these samples after burning. the increase in the compression strength of the dried samples is an indication of the lack of cracks and other 117 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 defects in the brick samples, which helps not to damage them during the loading and transporting process before burning. this test began after the samples were dried at 110°c and cooled to the laboratory temperature. the test was carried out by covering the top and bottom surfaces of the sample with two pieces of 3 mm-thick plywood to ensure uniform distribution of the load on the loading surface as seen in fig. 7 and fig. 8. a load of 15 n/mm2 per minute was applied until failure occurred. compression strength for each sample was calculated from the following relationship: = (3) where: =compression strength (n/mm2), p=the applied loading when the sample fails and a= the area of the sample which exposed to the applied load. an average of 10 specimens was used. the compression strength after firing process was determined according to astm standard astm c373-88[17] using eq. 3. fig. 7: compressive strength test machine. fig. 8: sample under compressive strength test. 118 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 6. results and discussion from these experiments, it was observed that the amount of moisture increased for the formation of brick samples with the addition of reed crumbs. this behaviour was due to the addition of reed crumbs which resulted in more difficult extrusion. this is due to the fibrous nature of the reed crumbs and their internal water channels that lead to increased water absorption which is the main reason for the increasing demand for water. some difficulties occurred during the mixing and extrusion process when the percentage of the reed crumbs reached 20% 25% due to the fibrous nature of the reed. no defects were observed after the drying process of the samples except for the samples with the addition of 20 and 25% of reed crumbs, where small cracks occurred and increased with the percentage of reed crumbs added during the drying process, resulting in failure during firing. splits, swelling, and other perceptible deformities are seen after the burning procedure for the samples with 20 and 25% of reed crumbs. after combustion, an increase in weight loss when ignition is observed in block samples containing high levels of reed crumbs compared to samples with little or no additive ratio. increased demand for energy was also noted during the firing process due to the high amount of water needed to form the brick samples. no black cores were seen in broken samples after the compression strength test. lightweight clay bricks were created by merging no more than 5% (by weight) of reed crumbs into soil which met the compression strength prerequisites of blocks utilized for partitions, as indicated in astm standard c62 [18]. 6.1 longitudinal shrinkage the drying shrinkage property is influenced by the method used to form the bricks. the extrusion method used in the formation of bricks needs a higher water content than the critical water content and an increase in the formation water content leads to increased drying shrinkage causing contraction in the body of the brick [19]. the results of the longitudinal shrinkage after drying process were shown in fig. 9. a high increase in the drying shrinkage values was observed in the samples compared to the control (clay only). the percentage of increase for longitudinal drying shrinkage were 7.3, 17.08, 34.15, 43.90, and 68.29% for s1, s2, s3, s4, and s5 samples respectively compared to reference mix s. this linear increase in longitudinal drying shrinkage is attributed to the increase in the percentage of reed crumbs that led to an increase in the formation water content and plasticity index due to the fibrous nature of reeds that absorb water, which results in higher shrinkage values after drying as plotted in fig. 9. however, despite of increment in the plasticity index, the longitudinal drying shrinkage does not increase to the same degree, as we can see in fig. 10. this condition is because of the hollow and sorbent nature of the reed crumbs which somewhat balances out the drying conduct of the clay body notwithstanding the increment in water demand with the increment of reed crumbs. in general, the longitudinal drying shrinkage values of the clay mixtures containing reed crumbs were higher than the longitudinal drying shrinkage value of the reference mixture samples. this conclusion was reached by a group of researchers who used different types of agricultural waste in a number of lightweight brick industry research [3,4,5,6]. this behaviour continues after burning the brick samples as can be seen of the longitudinal shrinkage results in fig. 10. the percentage of increase in longitudinal shrinkage values of the fired samples was 11.98, 21.87, 32.30, 41.15 and 52.08% for the mixes s1, s2, s3, s4, and s5 respectively compared to the reference mix s. accordingly, there is a direct increment in the drying and complete longitudinal shrinkage as the quantity of reed crumbs in the blend increases. brick samples containing 20-25% of reed crumbs were found to be unsuitable due to high shrinkage after drying which caused large cracks after burning. 119 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 fig. 9: effects of % reed addition on longitudinal shrinkage of dried and fired clay brick samples fig. 10: the relationship between longitudinal shrinkage and the plasticity index of dried and fired brick samples. 6.2 bulk density the results of the bulk density tests after the drying are shown in fig. 11. these results showed that the values of bulk density after drying gradually decreased for mixing samples s1, s2, s3, s4 and s5 compared to the reference mixture samples (s). the percentage of decrease was 8.13, 16.06, 21.83, 27.68, and 30.24%for s1, s2, s3, s4, and s5 respectively compared to reference sample s. this indicates that bulk density after drying of samples containing reed crumbs is lower than that of samples manufactured from brick clay only as shown in fig. 11.a rise in the quantity of reed crumbs brings about more decreases in bulk density values. this reduction in the bulk density of the samples containing reed crumbs is due to the decrease in the proportion of clay in the blend, which was replaced by reed crumbs with less density than the clay. in addition, the increase in the amount of water to maintain the plasticity required for the mixture with an increase in the proportion of reed crumbs, which subsequently evaporates after the end of the drying process, leads to more decrease in the dry density. similar findings were reached in several previous studies that used different types of agricultural waste as clay replacement material in brick. according to [3,4,5,6] the addition of different agricultural waste such as kraft pulp production residues, processed waste tea, sawdust, tobacco, grass, olive stones, and hay to the soil used for the production of clay bricks leads to a reduction in the bulk density of the brick samples. this is due to the partial replacement of high density of soil with a low density additive such as the agricultural waste in addition to the high plasticity coefficients of the mixing samples s1, s2, s3, s4 and s5 with increasing ratios of 0 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 dried samples fired samples amount of reed crumbs (%) lo ng itu di na l s hr in ka ge ( % ) 1 2 3 4 5 6 7 8 25 30 35 40 45 50 55 60 fired samples dried samples lo ng tu di na l sh rin ka ge (% ) plasticity index (%) 120 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 addition, which leads to a decrease in density of the samples. in addition, bulk densities of the samples containing reed crumbs after firing have a lower value compared to the reference samples made from clay only. the bulk density test results of samples containing reed crumbs after firing are plotted in figure11. the level of reduction was 12.73, 23.35, 25.90, 36.77 and 41.93% for s1, s2, s3, s4, and s5 samples individually contrasted with s. further reed crumbs increase in mixes s1-s5 caused just a slight further decrease. the burning of reed crumbs through the sintering time is the main reason behind this behaviour. fig. 11: effects of amount of reed on bulk density of dried and fired clay brick samples. 6.3 compression strength compression strength after drying is influenced by several factors, the most important factors are the type and percentages of additives. agricultural waste additives are characterized by their fibrous nature. the compression strength depends on the strength of these fibers. compression strength increases with the increase of the fiber’s strength and decreases with lower strength [5]. another factor affecting compression strength after drying is formation water content. an increase in formation water content leads to the separation of the clay molecules from each other and the decrease of body strength, in addition to the increase in the proportion of capillary cracks formed due to drying shrinking with the increase of the formation water content which causes the weakening of the body and leads to reduced strength. the results of compression strength tests after drying are shown in fig. 12. as can be seen in fig. 11, mixes s1, s2, and s3, which contain 5, 10 and 15% of reed crumbs, have higher compression strength after drying compared to the reference mixture (s), which is made solely from soil. the level of increment of the blends of s1, s2, and s3 was 29.26,42.89 and 7.95% contrasted with a reference blend s. this behaviour was due to the fibre strengthening effect of the of reed crumbs with low porosity which increase compression strength of samples s1, s2, and s3. this result is similar to the findings of the group of researchers who pointed to the increase in compression strength with 5 – 10% clay replacement with different types of agricultural waste in a number of lightweight clay brick industry research. according to [3-6], the addition of 5 – 10% of different agricultural waste such as kraft pulp production residues, processed waste tea, sawdust, tobacco, grass, olive stones and hay to the soil used for production clay bricks leads to increase in compression strength after drying. as they discovered, this phenomenon is due to the fibre strength of agricultural waste with low porosity that leads to increase the compression strength after drying. this increase in compression strength after drying was discovered to be extremely valuable in avoiding the handling problems of the lightweight clay brick. subsequently, the increase in reed crumbs to 20% of weight and then 25% of weight resulted in reduced compression strength after 500 700 900 1100 1300 1500 1700 1900 2100 0 5 10 15 20 25 30 dried samples fired samples amount of reed crumbs (%) bu lk d en si ty (k g /m 3 ) 121 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 drying of mixtures s4 and s5 respectively compared to the reference mixture s. the level of decrease in compression strength was 28.98 and 48.86% for blends s4 and s5 in comparison with a reference blend s. this decrease in compression strength after drying is due to the increase in porosity of the brick body to a high degree due to the high content of the formation water which overcomes the strength of the fibrous nature of reed crumbs. as shown in fig. 12, the compression strength values after burning was decreased with the increase of the addition of reed crumbs to soil. the level of reduction was 19.1, 36.8, 49, 66.56, and 75.23% for blends s1, s2, s3, s4, and s5 individually comparing with a reference blend s. the reduction in compression strength after burning with the increase in the rate of addition of reeds crumbs was due to the increase in the amount of carbon dioxide gas caused by the combustion of carbon materials as well as the gaps left by the penetrating gas, which increase the porosity of the body and thus reduce the resistance of the brick body. replacing part of the soil with reed crumbs also reduces the clay content in the mass, this clay content is responsible for forming the crystalline minerals which increasing the compression strength of the product [6,9]. fig. 12: effects of % reed addition on compression strength of dried and fired clay brick samples. 7. conclusion lightweight clay brick samples were manufactured by incorporating 5-25% (by weight) of reed crumbs into soil. lightweight clay bricks samples meeting the requirements for blocks used for partitions, as indicated by astm standard c62 [18], were made by adding 5% of reed crumbs into soil. the following conclusions were reached based on the results of laboratory tests on the manufactured brick samples: •the addition of reed crumbs to the mixes of clay bricks caused no difficulties during the blending and extrusion process, but at the same time increased the required water content to keep the plasticity of the reed clay mixture. hence, this leads to an increase of the water content and plasticity coefficient simultaneously. the increase in plasticity coefficient ranged from 9.7 to 22.58% when the reed crumbs were added in percentages ranging from 5 to 25% to the brick mixture. the ability of water channels within cellulose fibres to naturally absorb water is believed to be the main reason for the increased water demand in order to maintain the plasticity. •a higher increase was found in the longitudinal drying shrinkage of reed-containing specimens than that of the brick clay sample only. the level of increment was discovered to range from 7.3 to 68.29% when the addition of reed crumbs ranged from 5 to 25%. this action is due to the increase in the water content needed to maintain the plasticity of the mixture when adding reed crumbs. ratios of addition 0 2 4 6 8 10 12 14 0 5 10 15 20 25 30 dried samples fired samples co m pr es si on st re ng th (n /m m 2 ) amount of reed crumbs(%) 122 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 of 20 and 25% of reed crumbs to brick mixtures was found unsuitable for brick making due to high shrinkage after burning. •the rate of increase in the longitudinal drying shrinkage is less than the rate of increase in plasticity coefficient when the same percentage of reed crumbs are added to the slurry mixture of the brick samples. •the bulk density values for dried samples containing reed crumbs were lower than that of clay samples only. the percentage decrease in bulk density values for brick samples with an added 5, 10, 15, 20 and 25% of reed crumbs was 8.13, 16.06, 21.83 and 27.68% respectively compared to samples made from clay only. this behaviour is due to the replacement of part of the high-density clay with lowdensity reed crumbs which increased plasticity coefficient of these mixtures. •the ratios of adding up to 15% of reed crumbs were discovered to considerably increase the dry compression strength of the clay samples. the ratio of increase in compression strength values was 29.26 ,42.89, and 7.95% when including 5, 10, and 15% of the reed crumbs to the clay blends respectively compared with the reference samples produced from the clay only. this behaviour was due to the fibre strength of reed crumbs which increase the dry compression strength;this increase was found very valuable in avoiding handling problems. •increasing the additives of reed crumbs more than 15% causes a reduction in compression strength after drying. the ratio of reduction in compression strength values was 28.98 and 48.86% when adding 20 and 25% of the reed crumbs to the clay blends respectively compared with the reference samples produced from the clay only. this reduction in compression strength after drying was found due to the increase of water content and plasticity coefficient in order to keep the plasticity of clay mixture which increased porosity and cracks after drying. •generally, the reed crumbs can be used as a type of additive to form pores in the clay body without any detrimental effect on the drying process of lightweight clay bricks. conversely, the addition of these reed crumbs was found very valuable in preventing handling problems of the lightweight clay bricks due to the increases in the compression strength after drying caused by the strength of the reed fibres. •the percentage of the scraps resulting from the handling problems of unfired bricks were found to be low when the reed crumbs were added by no more than 10%. a high percentage of the scraps were seen when the addition of reed crumbs was more than 15%. this knowledge is very important in order to maintain the raw materials from loss when using high percentages of reed crumbs. acknowledgement the researcher would like to express profound thanks and appreciation to prof.dr.shakir ahmed salih for his support and encouragement during the planning of this research. references [1] görhan g, şimşeko.(2013)porous clay bricks manufactured with rice husks. construction and building material,40:390-396. [2] carter gw, cannor am, mansell ds. (1982) properties of bricks incorporating ungrounded rice husks. build environmental, 17(4): 285-291. 123 iium engineering journal, vol. 21, no. 2, 2020 salman https://doi.org/10.31436/iiumej.v21i2.1293 [3] ismail d,serhatb , mehmet o .(2004) utilization of kraft pulp production residues in clay brick production. building and environment, 40: 1533–1537. [4] demir i. (2005) an investigation on the production of construction brick with processed waste tea. building and environment,41:1274-1278. [5] demir i. (2007) effect of organic residues addition on the technological properties of clay bricks. waste management,28:622-627. [6] arezki s, chelouah n, tahakourta.(2015)study of the influence of agricultural waste on the porosity of clay brick,available online: http://fstroj.uniza.sk/journal-mi/pdf/2015/03-.pdf . [7] safeer a, yaseen i, razm.(2017) effects of coal and wheat husk additives on the physical, thermal and mechanical properties of clay bricks, boletín de la sociedad española de cerámica y vidrio, 56:131-138. [8] kumar, a. mohanta, k. kumar, d. and parkash, o. (2012).properties and industrial applications of rice husk. j. engineering technology and advanced engineering, 2:5-10. [9] ghazwans,shakir s. (2019) effect of firing temperatures on physico-mechanical properties of clay bricks containing reeds. international journal on advanced science, engineering and information technology, 9(1):321-238. [10] ghazwans,shakir s. (2018) effect of burning temperature of clay bricks containing reeds on its longitudinal shrinkage, modulus of rapture and thermal conductivity. international journal of civil engineering and technology, 9(9):1388-1402. [11] astm d 4327 (2013)determining chloride and sulfate contents in soils.astm international, west conshohoken, pa, usa., [12] astm d 4318(2006)standard test method for liquid limit, plastic limit, and plasticity index of soils. annual book of astm standards. [13] astm d422 (2006)standard test method for particle size analysis of soils.annual book of astm standards. [14] astm d2487 (2011) standard practice for classification of soils for engineering purposes (unified system)". astm international, west conshohocken , pa, usa. [15] karim hh, samuel zw, ahmed sf.(2015)geotechnical properties of soft clay soil stabilized by reed ashes, 2nd international conference on buildings, construction and environmental engineering. [16] beech, dg(1974). testing methods for brick and tile manufacture, britain ceramic research association.publication(84). [17] astm c 373 (2006)standard test method for water absorption, bulk density, apparent density and apparent specific gravity of fired whitewares products", annual book of astm standards,. [18] astm standard c 62.(2006) standard specification for building brick (solid masonry units made from clay or shale)," annual book of astm standards, 2006. [19] clews fh. (1969) heavy clay technology, 2nd ed., new york, pp 9-16. 124 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <feff005500740069006c0069006300650020006500730074006100200063006f006e0066006900670075007200610063006900f3006e0020007000610072006100200063007200650061007200200064006f00630075006d0065006e0074006f0073002000640065002000410064006f00620065002000500044004600200061006400650063007500610064006f007300200070006100720061002000760069007300750061006c0069007a00610063006900f3006e0020006500200069006d0070007200650073006900f3006e00200064006500200063006f006e006600690061006e007a006100200064006500200064006f00630075006d0065006e0074006f007300200063006f006d00650072006300690061006c00650073002e002000530065002000700075006500640065006e00200061006200720069007200200064006f00630075006d0065006e0074006f00730020005000440046002000630072006500610064006f007300200063006f006e0020004100630072006f006200610074002c002000410064006f00620065002000520065006100640065007200200036002e003000200079002000760065007200730069006f006e0065007300200070006f00730074006500720069006f007200650073002e> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 137-545-2-le iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 53 theoretical evaluation of nonlinear effects on optical wdm networks with various fiber types yasin m. karfaa 1* , m. ismail 1 , f. m. abbou 2 , a. s. shaari 1 1 department of electrical, electronics and systems engineering, universiti kebangsaan malaysia, 43600 ukm, bangi, selangor, malaysia. 2 faculty of engineering, multimedia university, 63100 cyberjaya, selangor, malaysia. *yasin_m_k@yahoo.com abstract: a theoretical study is carried out to evaluate the performance of an optical wavelength division multiplexing (wdm) network transmission system in the presence of crosstalk due to optical fiber nonlinearities. the most significant nonlinear effects in the optical fiber which are cross-phase modulation (xpm), four-wave mixing (fwm), and stimulated raman scattering (srs) are investigated. four types of optical fiber are included in the analysis; these are: single-mode fiber (smf), dispersion compensation fiber (dcf), non-zero dispersion fiber (nzdf), and non-zero dispersion shifted fiber (nzdsf). the results represent the standard deviation of nonlinearity induced crosstalk noise power due to fwm and srs, xpm power penalty for smf, dcf, nzdf, and nzdsf types of fiber, besides the bit error rate (ber) for the three nonlinear effects using standard fiber type (smf). it is concluded that three significant fiber nonlinearities are making huge limitations against increasing the launched power which is desired, otherwise, lower values of launched power limit network expansion including length, distance, covered areas, and number of users accessing the wdm network, unless suitable precautions are taken to neutralize the nonlinear effects. besides, various fiber types are not behaving similarly towards network parameters. keyword: nonlinear effects, nonlinearity standard deviation, ber, power penalty, and wdm. 1. introduction high capacity long reach transmission systems employ a large number of wavelength division multiplexed (wdm) channels with dense channel spacing and high bit rate per channel. in conventional wdm systems, the main transmission impairments are fiber losses, group velocity dispersion (gvd) and nonlinear fiber effects [1]. due to the desired long distance between amplifiers, high channel powers are required in order to achieve sufficiently large signal-to-noise ratios (osnr). the use of erbium doped fiber amplifiers (edfa) allows overcoming the first limitation while the others are usually minimized by optimizing the dispersion compensation with a proper management. all these system requirements give rise to nonlinear impairments. in long distance transmission links above 100 km including analog signals over optical fibers, high transmission powers are involved which give rise to nonlinear effects such as self-phase modulation (spm) in a single channel system, cross phase modulation (xpm), four wave mixing (fwm), iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 54 stimulated raman scattering (srs), and stimulated brillouin scattering (sbs) between channels in a wdm system and can be highly detrimental in the presence of dispersion [2]. these nonlinear effects can limit performance in both digital and analog systems. 2. system theoretical analysis avoid using tab or enter buttons whenever possible. (normal) (what is this??). figure 1 below shows a typical wc channels optical wdm system. it is assumed that the network is experiencing all the three nonlinear effects under study; these are xpm, fwm, and srs. for this network, the analysis of all the nonlinear effects is possible by taking their effects on pulses propagating inside an optical fiber and to be included by using the nonlinear schrödinger equation (nlse), which is used to describe the slowly varying complex envelope of the optical field when expressing any of the nonlinear effects in the form that is given by [3] as in eq. (1) below: 2 3 2 2 21 1 1 1 1 21 31 1 1 2 3 12 3 1 9 2 2 6 a a ai a i a a a a z t t ω α β β γ ψ ∂ ∂ ∂  + + − = +  ∂ ∂ ∂ ( 1 ) since three of the nonlinear effects are considered here, so, eq. (1) contains a last term on the r.h.s ( ωψ ) to account for spm and sbs that are not included in this study; where n α represents the n th channel’s attenuation parameter, n2 β represents the n th channel’s second order dispersion parameter, n3 β represents the n th channel’s third order dispersion parameter, n γ represents the n th channel’s nonlinearity coefficient where ( eff can / 02 ωγ = ), nr t represents the n th channel’s raman shift, mn d represents the walk-off parameter between channels m and n . fig. 1: optical communication system for multiple transmitted channels and various types of fiber (of: optical fiber, can be smf, dcf, nzdf, or nzdsf). 2.1 theoretical analysis of xpm xpm is a fatal nonlinear impairment in wdm systems as a nonlinear phase noise results after the interaction of optical amplified spontaneous emission (ase) and fiber kerr nonlinearities [4]; it is one of the dominant degradation effects for bit rates as much as 10 gbps in wdm systems although it can be of use as in case of the optical signal regeneration for future high-speed optical communication systems; when the interaction iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 55 takes place between continuous optical waves, constant phase changes and constant polarization rotations are induced, but, if the intense wave is pulsed or intensity modulated, the induced nonlinear phase shift becomes time dependent, leading to phase modulation and polarization modulation of the co-propagating waves. thereby, new spectral components are generated on their optical spectra resulting in an xpm-induced spectral broadening. in some researches where the channel spacing is reduced, the degradation due to xpm and fwm increased and the optimum dispersion compensation scheme is significantly affected by these effects. the dispersion is the middle parameter that increasing it minimizes fwm but increases xpm and vice versa. therefore, since fwm can be minimized using a high local dispersive transmission fiber such as a smf and thus the main inter-channel nonlinear effect is xpm. the mathematical expression to calculate xpm induced crosstalk power is derived following literature models [5-7]. the xpm power fluctuation due to one channel interference is [5]: ( ) ( ) ( ) ( ) 2 , , 0 2 sin / 2 , 4 cl j x k j k d p l p p e j k α ω ω γ ω α β ω ω − = + ∆ (2) where 2 / cλ ωλ∆ = ∆ is the wavelength spacing, and 2 2 2 / c d cπ β λ= − is the chromatic dispersion, 2 β is the group velocity dispersion. by taking the magnitude and ignoring 2α being too small: ( ) ( ) ( )2 , , 0 sin / 2 , 8 cl j x k j k c d p l p p e d k α ω ω πγ ω λω − = ∆ (3) considering the contributions from c w number of channels, eq. (2) can be rewritten as: ( ) ( ) ( )2 , , 0 sin / 21 , 8 cl j x k j k c c d p l p p e w d k α ω ω πγ ω λω − = ∆ ∑ (4) the total noise variance due to xpm-induced power fluctuation for an im/dd system xpm p is obtained by applying the integration of eq. (4) for the interval 1 2 ( , )ω ω as follows: ( ) ( ) 2 1 2 2 , , , xpm d j x k p r p l h d ω ω ω ω ω= ∆∫ (5) 2.2 theoretical analysis of fwm fwm occurs when the channels in a wdm system are equally spaced, so that the new waves generated by fwm will fall at channel frequencies and, thus, will give rise to crosstalk; its severity is maximized when dispersion is minimized by some proper techniques, so they are inversely proportional because the fwm products add coherently in each span. fwm may result when three light signals at different wavelengths interact in the fiber to create a fourth light signal at either a different or same wavelength causing a distortion to the desired signal. the new optical waves frequencies are judged by fijk=fi+fjfk, which is θ + ; or it results when two propagating waves at frequencies f1 and f2 mix and generate sidebands at 2f1-f2 and 2f2-f1, which is θ . these sidebands co-propagate with initial waves and grow at their expense, besides creating inband crosstalk that cannot be iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 56 filtered optically or electronically and channels beat against each other to form intermodulation products. the mathematical expression to calculate fwm induced crosstalk power is derived with following the models done by [8-11]: 4 2 2 1/ 2 1/3 2 2 2 2 4 10 ( ) [ ] 9 ( ) ijk ijk a ijk fwm ijk eff c ijk f g l n u p p ca d λ γ ω α β × = ∆ + ∆ ∑ (6) where ijk f is the frequency for channels i , j , k respectively, λ is the operating wavelength of the optical signal, 1 jkl g = for two-tone products, gjkl = 2 for three-tone products, l is the length of fiber line, a n is the number of edfas, ijk u is the degeneracy factor and takes values of 3 or 6, c is the speed of light in free space, eff a is the fiber core effective cross-section area, f∆ is the channel spacing, c d is the chromatic dispersion, β∆ is the phase matching coefficient for fwm to occur. figure 2 below shows the power spectral representation of the fwm, xpm, and srs nonlinear effects as it appears in the output for a regular input to the system when c w frequency channels are transmitted in optical wdm system. fig. 2: nonlinear impairments in an optical wdm network as a limiting power degradation factor. 2.3 theoretical analysis of srs srs causes the optical power from one mode (with a higher frequency) to be transferred in the forward direction to the same or other modes, at a lower frequency. it depends critically upon the optical power density within the fiber and hence only becomes significant above threshold power levels; therefore, the launched power into the system is limited because of these raman effects [12]. beside that, the large-capacity and long haul network transmission essentially use the erbium-doped fiber amplifiers (edfas) to compensate the fiber attenuation without using electrical regenerators. the expansion of the optical network dimensions to thousands of kilometers with the feasibility of the concept of transparent optical networks introduces some problems like accumulated ase noise and aggravation of fiber nonlinearity effects, where srs is one of them. even the mitigation techniques of srs will give some undesired results, for example, the mitigation by having a large core and short fiber which reduces both the optical power density in the iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 57 core and the interaction length of the optical field in the fiber, but this leads to a multimode core, and can consequently lead to a significant degradation of the output beam quality. other techniques have their drawbacks as well. anyhow, there are many attractive features as a frequency converter, beam clean-up, pulse compression, etc. for the above network where the occurrence of srs problem is assumed, the mathematical expression to calculate srs induced crosstalk power is derived with following the models done by [1316]. when channel 0 with the shortest wavelength shortest λ is affected by a longer longest λ denoted by channel i, the probabilities for the channels in on state are: 0 p o (channel 0 is on) = on p (7) i po (channel i is on) = on p (8) assuming both channels are random and independent from each other, the probability that both channels are in on state is: 2 0rbon i on on on p p o po p p p= × = × = (9) srs happens when both channels involved are in on state, of which the probability is shown as above. the average srs power depletion in channel 0 due to interference from channel i, 0d i µ is defined as: 0 0d i p rbon d pµ = × (10) where 0p d is the fractional power lost by channel 0 due to all other channels, and is defined as: 1 6 0 1 0 1.4 10 4 cw c i eff i i p i eff w pol d a ωλ γ πλ − − = ∆ = × ×∑ (11) where c w is the wavelength channels number, i p is the optical power carried in the i th channel, i po is the i p at on state, eff a is the effective core area of the fiber, eff l is the effective fiber length given by (1 exp( )) / eff l lα α= − − , where α is the fiber loss coefficient and l is the fiber length. the raman gain coefficient i γ that is coupling the first and i th channel can be expressed using the triangular raman gain as follows: 13 1.5 10 i p i v γ γ ∆ = × for 13 1.5 10i v∆ < × and 0 i γ = otherwise (12) here, p γ is the peak raman gain coefficient with a value of 126 10−× cm/w2 and v∆ is the channel frequency spacing. the mean and standard deviation of 0p d are related according to the following relation [16]: case i: walk-off length w l is very large. 0 0 2(2 1) 3 ( 1) c d i d i c c w w w σ µ − = − (13) iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 58 case ii: walk-off length w l is very small. 0 0 ( 1) w d i d i c c l w w α σ µ= − (14) the total srs induced crosstalk noise power due to interactions of all channels srs p is given by: 1 3 1/ 4 1 1 0 2.2 10 2 2 cw c i i effi a srs i eff b c w lpo n p k a r d λ γ ω λ π − − = ∆ = × × ×∑ (15) where 1/ 4 1 2(2 1) 3 ( 1) c c c w k w w − = − , 1/ 4 ( 1) w c c l w w α − for large and small walk of respectively. then, the bit error rate for the system due to nonlinearities is given by [3]: 01 _1 _ 0 1 4 ( ) 2 2 dd nl nl ase ase i ii i ber erfc erfc p σ σ     −−  = +       +      (16) where nl p is to account for the calculated nonlinear crosstalk noise power; so it can be xpm p , fwm p , or srs p ; d i is given by [3]: 0 1 1 0 0 1 d i i i σ σ σ σ + = + (17) where 1 i is the transmitted current for bit ‘1’, 0 i is the transmitted current for bit ‘0’, d i is the threshold current level for the decision circuit, 1_ase σ is the amplified spontaneous emission (ase) noise for transmission of bit ‘1’, 0_ase σ is the ase noise for transmission of bit ‘0’. the accumulated ase_ase beat noise for bits ‘1’ and ‘0’ is given by [17]: 2 2 2 _ 0 2 0 4 ( ) (2 ) ch e ase ase d ase accn e b r p b b b σ − = − (18) where d r is the photo detector responsivity, ch ase accn p − is the accumulated ase noise for any channel, 0 b is the optical bandwidth, and e b is the electrical bandwidth. 3. materials and method the first step of the method of evaluating the nonlinear effects is by conducting the theoretical analysis with modeling the optical wdm network under three considered nonlinear effects; these are: xpm, fwm, and srs. then, the second step is to use the findings of other researchers for specifying the best model among those. the third step is to derive the relevant expressions for finding the xpm, fwm, and srs induced crosstalk. the fourth step is to simulate the theoretical expressions of the three nonlinear effects with iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 59 the mathematical calculations using the matlab software. the fifth step is to analyze the results of the simulations. and the last step is to conclude the outcome of the evaluation of nonlinear effects. for all of the three models of nonlinear crosstalk derivations, the same basic equation is used, which represents the pulses propagating inside, that is the nonlinear schrödinger equation (nse), which is commonly used to describe the slowly varying complex envelope of the optical field when expressing the xpm, fwm, and srs in the form [3] (hanging sentence??). with taking nse equation, then some other models are considered or followed to ease the derivations with some approximations. those models are indicated to when used. (poorly written; consider rephrasing) the model of this optical wdm system is shown in fig. 1. this system is suffering from nonlinear effects. since the figure shows a single-line transmission system with multiple channels, so, it is assumed that at each one certain time, there is a certain type of fiber to be used, and replace by other types alternatively. tables 1 and 2 for the values of system parameters that are used in the simulation are shown below. (last two sentences are poorly written; consider rephrasing) table 1: input parameters used in the simulation of all nonlinear crosstalk effects. parameter values number of channels, c w 128 number of nodes, n 20 number of amplifiers, a n 20 optical fiber length, l 200 input power, in p 0 bit rate, b r 10 optical bandwidth, o b 20 electrical bandwidth, e b 10 operating frequency, v 1.9355×10 14 frequency channel spacing, ω∆ 50 to 100 wavelength spacing, λ∆ 0.4 to 0.8 nonlinear refractive index, 2 n 2.6×10 -20 group index, g n 1.46 basic operating light wavelength, λ 1550 receiver’s responsivity, d r 1 load resistence, l r 50 inversion factor, e f 3 amplifier’s gain, g 20 iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 60 raman gain coefficient, r g 6×10 -13 temperature, t 300 table 2: parametric characteristics of many types of optical fibers. fiber type 2( ) eff a mµ ( / / )cd ps km nm ( / )db kmα 1( )w kmγ − smf 80 17 0.2 2.5 dcf 20 –80 0.29 3 nzdf 72 –3 0.23 3.9 nzdsf 50 4.5 0.25 3.84 4. results and discussion a matlab software is used to validate the three analytical expressions for the nonlinear crosstalk noises xpm, fwm, and srs. some of the system parameters used are number of channels, c w = 128 channels, input power = 0-20 dbm, fiber loss coefficient = 0.2-0.25 db/km, channel spacing range 10-100 ghz (0.08-0.8 nm). the xpm power penalty and crosstalk noises due to fwm, and srs are shown in fig. 3, 4 and 5 respectively versus number of channels and input powers respectively. figure 3 is for the network when it is impaired by xpm, and shows the xpm power penalty versus input power, whereas fig. 4 shows the standard deviation of fwm induced crosstalk versus number of channels when the optical wdm network is experiencing fwm nonlinear effect. figure 5 is for the network which is influenced by srs. four types of optical fiber are used in the calculations for the graphic relations: single-mode fiber (smf), dispersion compensation fiber (dcf), non-zero dispersion fiber (nzdf), and non-zero dispersion shifted fiber (nzdsf). these fibers differ from each other in the specifications that are expressed by all the necessary parameters for the computations to satisfy the algorithm of finding the different fiber nonlinearity originated noise phenomenon’s (like xpm, fwm, and srs in this case). the used parameters in the calculations are fiber attenuation, chromatic dispersion, nonlinearity refractive index coefficient, fiber nonlinearity factor, and fiber core cross-sectional area. the differences in the parameters’ values among the various fiber types continue to appear finally in the graphic relations of power penalties versus input powers, and so, they vary in the graphs. using the mathematical meaning for this, it seems that different types of fiber respond differently to the effect of changing the input powers and the relevant changes in the power penalties due to fiber nonlinearities. lastly, figure 6 shows ber versus received power in the presence of all the three nonlinear effects: xpm, fwm, and srs. standard fiber smf is used, while the parameters are fixed at 8 nodes, 100 ghz channels spacing, while the rest of the parameters are as in tables 1 and 2. iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 61 fig. 3: penalty due to xpm versus input power for various fiber types where ase noises are not counted. fig. 4: standard deviation of fwm induced crosstalk versus input power for various fiber types. iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 62 fig. 5: standard deviation of srs induced crosstalk versus input power for various fiber types. fig. 6: ber due to nonlinear effects (xpm-fwm-srs) versus received power using standard smf fiber. 5. conclusion in this paper, a theoretical study is carried out to investigate the transmission of signal for n nodes optical wdm network in the presence of nonlinear crosstalk due to xpm, fwm, and srs. the performance analysis is done by calculating the xpm power penalty, and the standard deviation of the noises due to fwm and srs that the optical signal is experiencing when transmitting through 128-144 channels. the power penalty and standard deviation to evaluate the nonlinear crosstalk noise power in the analysis are chosen because those give an indication of signal transmission in a problem of compensation requirement or an extra budget to pay back for the lost power, since the iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 63 ber of the system must be kept at a level of 9 10 − or below, which is preferable as it means that more packets are transmitted with no errors. when the ber is high, the performance of the network deteriorates as it indicates corrupted and lost data. the results using matlab show that a higher ber and nonlinear crosstalk occurs in a wdm network when the number of nodes is large. this is true for large number of channels; that means small channel spacing (except srs that reduces with increasing number of channels or reducing channel spacing). the dispersion is working proportionally with xpm and oppositely with fwm and srs. the noises due to nonlinear effects are not same for different types of fiber, and that indicate the nature of the limitations due to nonlinearity and due to fiber type. narrowing channel spacing is also not preferable as it increases the ber. in conclusion, to transmit signal in optical wdm networks, physical impairments such as xpm, fwm, and srs should be taken into account as those directly affect the ber. the standard single-mode fiber (smf) is showing better results in the performance evaluation than the other tested three types of fiber (dcf, nzdf, and nzdsf). then, since the dcf fiber is used in the dispersion management and dispersion map as a solution to go close to the trade-offs in the way to keep the negative effects of the fiber nonlinearities to the minimum at the acceptable level that helps to improve the system’s performance, so, this dcf fiber is the best to use in alternative mixing techniques to play this turn. 6. acknowledgement dr. hairul azhar abdul rashid, the senior lecturer in faculty of engineering, multimedia university kindly provided technical support, printing facilities, downloading reference papers, and many useful discussions. references [1] t. alves, n. costa, and a.v. cartaxo, “dependence of xpm degradation on the dispersionmap for 10 gbit/s wdm links over standard-fiber employing duobinary format,” in transparent optical networks, 9 th icton intern. conference. proc. no.1, 79-82. 2007. [2] b. s. marks, c. r. menyuk, a. l. campillo, and f. bucholtz, “analysis of interchannel crosstalk in a dispersion-managed analog transmission link,” journ. of lightwave technol. vol. 24, no. 6, 2305-2310, 2006. [3] g. p. agrawal, “fiber optic communication systems,” john wiley & sons: new york, 2002. [4] x. li, f. zhang, z. chen, and a. xu, “optimum dispersion mapping of 40 gb/s rz-dpsk wdm transmission systems with xpm-induced nonlinear phase noise,” in intern. nanooptoelectronics workshop i-now '07 proc. 156-157, 2007. [5] b. xu, and m. b. pearce, “comparison of fwmand xpm-induced crosstalk using the volterra series transfer function method,” journ. of lightwave technol. vol. 21, no. 1, 40-53, 2003. [6] a. v. t. cartaxo, “cross-phase modulation in intensity modulation direct detection wdm systems with multiple optical amplifiers and dispersion compensators,” journ. of lightwave technol. 17(2): 178-190, 1999. [7] i. b. djordjevic, a. stavdas, c. skoufis, s. sygletos, and c. matrakidis, “analytical modeling of fiber non-linearities in amplified dispersion compensated wdm systems,” intern. journ. of modeling and simulation. vol. 23, no. 4, 226-233, 2003. iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 64 [8] r. ramaswami, and n. s. kumar, “optical networks: a practical perspective,” 2 nd edition: academic press, 2002. [9] m. eiselt, “limits on wdm systems due to four-wave mixing: a statistical approach,” journ. of lightwave technol. vol. 17, no. 11, 2261-2267, 1999. [10] s. song, t. c. allen, k. r. demarest, and r. hui, “intensity-dependent phase-matching effects on four-wave mixing in optical fibers,” journ. of lightwave technol. vol. 17, no. 11, 2285-2290, 1999. [11] a. r. chraplyvy, “limitations on lightwave communications imposed by optical-fiber nonlinearities,” journ. of lightwave technol. vol. 8, no. 10, 1548-1557, 1990. [12] m. k. abdullah, z. a. t. al-qazwini, m. d. a. samad, and m. mokhtar, “optimum transmit power for optical cdma transmission systems considering stimulated raman scattering (srs) effects,” in wireless and optical communications networks wocn’7 ifip intern. conference. proc. 1-4, 2007. [13] a. r. chraplyvy, “optical power limits in multi-channel wavelength-division-multiplexed systems due to stimulated raman scattering,” electronics lett. vol. 20, no. 2, 58-59, 1984. [14] f. forghieri, r. w. tkach, and a. r. chraplyvy,” effect of modulation statistics on raman crosstalk in wdm systems,” ieee photon. technol. lett. vol. 1, no. 1, 101-103, 1995. [15] m. eiselt, “the impact of non-linear fiber effects on fiber choice for ultimate transmission capacity,” in optical fiber communication conference. proc. no. 1, 58-60, 2000. [16] k. p. ho, “statistical properties of stimulated raman crosstalk in wdm systems,” journ. of lightwave technol. vol. 18, no. 7, 915-921, 2000. [17] g. keiser, “optical fiber communications, “ 3 rd edition, mcgraw-hill, 2000. nomenclature in p input power (launched power) w rec p received power w nl p overall nonlinearity lost power w on p power when channel is on state w 0d i µ average power depletion w 0p d fractional power loss w 0d i σ standard deviation of power loss db c w number of wavelength channels n number of nodes a n number of amplifiers g gain of the amplifier db r g raman gain coefficient db β∆ phase-matching coefficient iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 65 r t raman frequency shift thz p γ peak raman gain 2cmw − i γ coupling raman gain coefficient for channels 1, i l optical fiber length m in p input power dbm b r bit rate gbps 0 b optical bandwidth ghz e b electrical bandwidth ghz v operating frequency hz f any frequency of any channel hz ω∆ frequency channel spacing ghz λ∆ wavelength spacing nm λ basic operating light wavelength nm 2 n nonlinear refractive index 2 1 m w − g n group index 2 1 m w − d r responsivity of the receiver 1 aw − l r load resistance ohm e f inversion factor u degeneracy factor t temperature k ο d walk-off parameter w l walk-off length m c speed of light in free space 1 ms − eff a cross-sectional area of fiber core (effective) 2 m eff l effective optical fiber length m ber bit error rate db xpm cross-phase modulation fwm four-wave mixing srs stimulated raman scattering iium engineering journal, vol. 9, no. 2, 2008 karfaa et al. 66 d i decision level of current for logic circuitry a 1 σ standard deviation of lost power for bit σ standard deviation of lost power greek letters α fiber loss coefficient (attenuation) γ nonlinearity coefficient of the fiber ψ to account for unstudied nonlinear effects ω any angular frequency β dispersion of any order σ standard deviation of lost power subscript i channel number j channel number k channel number n index m index accn accumulated ase amplified spontaneous emission o optical e electrical c chromatic eff effective rbon probability of both channels is on nl nonlinear d decision level w walk-off superscript ch any channel application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 experimental verification of three mode controller for home appliance using wireless technology maswoodhur rahman abdul wahidh and muruganandam masilamani 1 engineering department, university of technology and applied sciences, ibri, sultanate of oman *corresponding author: maswood.abdul@ibrict.edu.om (received: 20th september 2020; accepted: 12th november 2020; published on-line: 4th july 2021) abstract: an attempt is made to enhance the automation and sophistication of a home appliance. in this work, electric lamp is considered as a home appliance and it is controlled through three different modes. technology is a never-ending process, the home automation is a well-known field of recent research, which makes the customer to reach the next level of sophistication. one such next level is presented in this article. the proposed paper is about design, experimentation and testing of three-way control for a lamp, using low cost microcontroller, bluetooth module and android mobile application. the three modes of control are manual switch mode, light dependent resistor (ldr) mode and bluetooth based wireless communication mode. the work is initially simulated using proteus 8 professional application and then implemented as a real time working model. also, the working performances were tested using the simulation and developed working model. the control in bluetooth mode is based on an android application. a dedicated android application is developed for testing the developed working model, using mit app inventor. abstrak: percubaan dibuat untuk meningkatkan automasi dan kecanggihan perkakas rumah. dalam karya ini, lampu elektrik dianggap sebagai perkakas rumah dan ia dikendalikan melalui tiga mod yang berbeza. teknologi adalah proses yang tidak pernah berakhir, automasi rumah adalah bidang penyelidikan baru-baru ini, yang menjadikan pelanggan mencapai tahap kecanggihan yang seterusnya. satu tahap seterusnya ditunjukkan dalam artikel ini. makalah yang dicadangkan adalah mengenai reka bentuk, eksperimen dan pengujian kawalan tiga arah untuk lampu, menggunakan mikrokontroler kos rendah, modul bluetooth dan aplikasi mudah alih android. tiga mod kawalan tersebut ialah mod suis manual, mod perintang bergantung cahaya (ldr) dan mod komunikasi tanpa wayar berasaskan bluetooth. karya ini pada mulanya disimulasikan menggunakan proteus 8 professional application dan kemudian dilaksanakan sebagai model kerja masa nyata. juga, prestasi kerja diuji menggunakan simulasi dan model kerja yang dikembangkan. kontrol dalam mod bluetooth didasarkan pada aplikasi android. aplikasi android khusus dikembangkan untuk menguji model kerja yang dikembangkan, menggunakan mit app inventor. keywords: proteus 8 professional; arduino uno; bluetooth module; android phone; mit app inventor 1. introduction in the modern era of automation and sophistication, there are tremendous changes and impacts in the human life style [1,2]. undoubtedly, electricity has a major role in the 188 mailto:maswood.abdul@ibrict.edu.om iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 betterment of human life style. the expectation of sophistication in our day to day life is on the increasing trends. the field of automation, drives the controllability of electrical appliances to an innovative level, for meeting the future requirements. wireless communications are becoming more popular around the world and the consumers appreciate this wireless life style which gives them relief from the congestion of more wires [3,4]. usually the control of electric applications is achieved by using switches i.e., when switched on, the electric supply will be given to the applications and vice versa. if the user wants to control the application, he should be near the switch. in case if he wants to control the application from a faraway place then he should carry a remote always. bluetooth (wireless) technology finds its usage in the field of home automation [5,6]. the day to day advancements in smart phones and its features, make the users to think about replacement of the recent smart phones as the remote for the home appliances [7,8]. using a smart phone as a remote not only decrease the human intervention, also it reduces the time of control. adopting the smart phones as a remote, to control the appliances will make it easy to do switching operation of an electric appliances, by elderly or handicapped persons. so, the mobile phones were introduced into the monitoring and control of home appliance, by avoiding dedicated remote to control the electrical appliances [9, 10]. many researches have been made and exhibited related to the control of a lamp using arduino uno microcontroller. but in all the basic controlling strategy we can control the lamp by only one mode, i.e., the manual switch mode. while going for the sensor based lamp control, an electric lamp can be controlled according to the signal received from the sensor. in this a light dependent resistor (ldr) is used to detect the surrounding light and control (on / off) the lamp accordingly [11-13]. in the recent days, some home automations were also proposed using bluetooth communication. the traditional control of home appliance through wall mounted switches were changed into wireless control of appliances. here home electrical appliances were controlled through bluetooth communication between the bluetooth module (hc-06) and the bluetooth enabled android smart phone. the bluetooth mobile phone will work as a transmitter and the bluetooth module connected with the microcontroller will act as the receiver. [14-16]. to command the bluetooth receiver, the bluetooth enabled android phone, i.e., the bluetooth transmitter, should have the proper application installed in it, to ensure proper control of electrical appliances. the research work related to the development of an android mobile application development, for the purpose of home automation by arduino microcontroller and bluetooth module has been proposed [17, 18]. these papers gain us ideas about android mobile application development using mit app inventor, for lamp control using bluetooth, through three different modes. the previous researches were proposed to control the electric lamp in any one mode (or in very few cases two modes) of operation. this will give the user only a certain level of sophistication. the implemented system is designed to integrate all the three individual control techniques into a single control system, which controls the electric lamp in all the above said 3 different modes, say manual switch mode, ldr mode and bluetooth mode. this will make the user of lamp to reach the next level of sophistication. 2. the proposed method block diagram of the proposed system is illustrated in fig. 1. the control of lamp is based on two types of connectivity. a wired channel controls the lamp in manual mode or 189 iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 ldr mode and another wireless channel controls the lamp in bluetooth mode. for the manual switch mode of operation, a two pin spst switch is used. for the ldr mode, a 10k ldr is used in series with a 10k ohm resistor, as a voltage divider network. the control signal to the microcontroller is taken from the mid-point between the resistor and the ldr. fig. 1: block diagram of the proposed system. the bluetooth communication is achieved by using hc-06 module. this module will establish a wireless connectivity between the controller and the android mobile phone. upon receiving the control signal from the android mobile phone, the micro controller will change the lamp status accordingly. the android mobile will have a dedicated application which is developed for controlling the lamp. the lamp is connected to the microcontroller through relay module. 3. hardware description 3.1 arduino uno arduino is an open-source electronics platform supported with easy to use hardware and software supports. arduino uno is a low-cost microcontroller board, built around atmega328p processor. it has 6 analog pins and 14 digital pins. the board can be powered by usb cable or 12v external power supply. the board can be programmed to control any pins, through arduino software (ide). in recent years the arduino boards finds it application in all of the electronics projects ranging from beginner level to highest level like scientific solutions etc. 3.2 relay module it is an electrically isolated switch, which isolates the power circuit from control circuit. the control signal (5 v) which will be available in one off the digital pin can be connected to the input side of the relay. now the output of this relay can even be connected to any 240 v power supply side, if we desire to control a 240 v load. this switch operates through a relatively small electric current that can turn or off a much larger electric current. 3.3 bluetooth module the bluetooth module used here is hc-06. it is easy to use bluetooth serial port protocol module. this module works on serial communication. hc-06 is a master/slave module. by default, every module will be set to slave. it can be reconfigured to master, through at commands. as it is a slave module, it can only accept connections, whereas master module can initiate a connection to other devices. the operating range of this module 190 iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 is around 2.4 ghz, with a distance of about 10 meters at a speed of 1 mbps. the smart phone will send serial data to the bluetooth module when a button is pressed on the app. 3.4 light dependent resistor (ldr) ldr is a variable resistance whose resistance value will vary according to the intensity of light falling on lit. the ldr will offer less resistance when the light intensity on the ldr is more and the resistance offered will be more when the light intensity on the ldr is less. due to this property, it will be commonly used as day/night sensor in street lighting projects. since on day time, the resistance of ldr will be less and on night time resistance of ldr will be high. 4. software description 4.1 arduino ide the arduino ide (integrated development environment) is an open-source software that allows the user to do coding, editing, compiling of program. the written program will be uploaded into the arduino boards. arduino ide was available for all of the major os. the arduino ide has inbuilt functions and libraries that works on java platform. 4.2 mit app inventor this is also another integrated development environment (ide) used to develop applications for android phone using web browser. this application can be connected to a mobile phone or an emulator. in mit app inventor, there will be two main windows, one is the designer window to design the graphical user interface (gui) and the second window is the block programming window. figures 2 and 3 show the designer window and block programing window respectively. fig. 2: android application developed. in mit app inventor, there will be no coding to develop an android app, rather we will be doing a much easier block programming (pick and place programming). this app inventor is available for all major os and easy to upload the developed app in any android smart phone. the most interesting feature of this paper is the graphical user interface, developed in mit app inventor. this will be installed in the android smart phone. the smart phone used throughout this paper was samsung a5-2017.this user interface is developed in such a way that; it will help the user to pair the smart phone with the arduino bluetooth module. the communication between the bluetooth module and the android smart phone will be using bluetooth protocol. the gui will have a list picker, which will list all the 191 iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 available bluetooth devices, around the android smart phone. also, the gui will have a label, to display the bluetooth device connectivity status. fig. 3: android application developed. in addition, two buttons were provided in the application, one to switch on the lamp and another button to switch off the lamp. to increase the facility for elderly/physically changed people, voice reply is also added in the application to say the status of lamp. 5. simulation of the proposed system proteus is the one of the simulation software to do the all type of electronics project from simple rectifier circuit to advanced level controllers with all the recent sensors, switches, wireless communication devices and controllers. here the proteus 8 professional application is used for the proposed system simulation. figure 4 depicts the complete circuit diagram of the proposed system with proteus simulation software. here the same arduino code and the android mobile application are used for controlling the lamp for both simulation and for hardware implementation. in simulation the arduino sketch is initially compiled and the developed hexadecimal code path is identified and it will be entered into the arduino controller. similarly, for the bluetooth, the input com port number is identified and it will be entered into the bluetooth device for connectivity between mobile and the computer for simulation. figure 5 illustrates the simulation output, in which the lamp is turned on by manual switch. out of three mode of control the first mode is simulated and illustrated here. from fig. 5, it is clear that the ldr torch is near, meaning that more light is fall on the ldr also no signal from bluetooth device, only the manual switch is turned on and the lamp is glowing. 192 iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 fig. 4: proteus simulation – lamp off condition. fig. 5: proteus simulation – lamp on through manual switch. fig. 6: proteus simulation – lamp on through ldr. figure 6 demonstrates the simulation output, in which the lamp is turned on by ldr sensor. out of three mode of control, the second mode is simulated and demonstrated here. from fig. 6, it is clear that the manual switch is turned off also no signal from bluetooth device, but the ldr torch is moved away meaning that the light is not falling on the ldr, hence the lamp is glowing. this mode is automation mode whenever the surrounding light intensity is less or dark, the lamp will be turned on automatically by using the ldr sensor. 193 iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 fig. 7: proteus simulation – lamp on through bluetooth communication. figure 7 shows the simulation output, which the lamp is turned on by bluetooth communication. out of three mode of control the third mode is simulated and displayed here. from fig. 7, it is clear that the manual switch is turned off also the ldr torch is near, meaning that more light falls on the ldr, but the bluetooth device receives signal from the android mobile app which is developed using mit app inventor, hence the lamp is glowing. this mode is sophistication mode whenever the light illumination is needed then the lamp may be turned on using the mobile application which was developed and installed on the user’s android smart phone. 6. implementation and verification of the proposed system the lamp will be controlled in three different ways. one is the manual mode, by using a spst switch. second is the automatic mode. in this mode, the ldr will work as a day/night sensor and get the surrounding light intensity. if the surrounding light is dark, the lamp will be on. if the surrounding light is bright, then the lamp will be made off through the relay. fig. 8(a): experimental setup (lamp on condition). fig. 8(b): experimental setup (lamp off condition). 194 iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 fig. 8(c): comment lines on the serial port monitor of arduino ide. the third mode is through wireless bluetooth communication. the bluetooth module will be connected to the arduino controller. figure 8(a) and (b) shows the lamp status, while fig. 8(c) show the comment lines which were made printed on the serial port monitor in the arduino ide for the corresponding status of the lamp. depending on the data sent from the bluetooth module the arduino controller will make the relay module on or off. the lamp will be turned on or off through the relay driver module. the data sent to bluetooth module will be varied in the android smart phone. the communication between android smart phone and bluetooth module is through serial data communication. all the three modes of operation were represented in fig. 9 as a flowchart. fig. 9: flow chart of the operation. 7. results and discussion the project was tested and the results obtained were represented as in a table format as shown in table 1. the obtained results were found to be accurate. in manual operation mode, when the manual switch is made on then the lamp will be made on through relay. the delay time elapsed by the lamp for switching form off state to on state was measured to be 2 sec. similarly, if the manual switch is made off, then the lamp will be made off. again, the time elapsed by the lamp was measured to be 2 sec. 1 0 dark off on start check manual switch lamp on surrounding light intensity bright bluetooth data lamp off 195 iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 fig. 10: control of lamp in different modes and delay time elapsed in respective mode in ldr mode of operation, if the surrounding light intensity is dark, the lamp will be made on. similarly, if the surrounding light intensity is bright, then the lamp will be made off. this is made automated that no need of human intervention to change the lamp status, in ldr mode of control. the time taken by the lamp to change from on state to off state or vice versa was measured to be 2 sec. in wireless mode, the android smart phone is paired with the bluetooth module correctly, either by media access control (mac) address or by giving a specific name to the bluetooth module. the distance between android smart phone and hc 06 bluetooth module was kept to be 10 meters during the test. the control word (data) will be sent from the android mobile phone through the android app developed. this data will be received by the bluetooth module and the same data will be checked by the microcontroller. if the data received is 1 (by pressing on button in the app), the lamp will be made on. similarly, if the data received is 0 (by pressing off button in the app), the lamp will be made off. in bluetooth mode the delay time for reaching on status in the lamp is measured to be 2 sec, and the same for reaching off status in the lamp is measured to be 4 sec. 8. conclusion the endowment of innovation to human kind is to make life more straight forward. in this paper, a three-way control of electric lamp was outlined, exhibited and executed. the lamp is controlled individually without the requirement of line of sight. the relay activity and thereafter the lamp can be controlled with an automated mode and also in bluetooth control mode. this proposed system not only make it easy to do switching operation of an electric appliances, by elderly or handicapped persons, but also decrease the human intervention into the lamp control cycle and reduce the time delay in manual mode of control. the control over the lamp is secured, to the access from any other intruders, through a pairing password, for the bluetooth control. through this unauthorized bluetooth device entries were avoided, which give more security to the system. this project can be used for any other electrical appliance that requires on/off switching, without internet connections. the full functionality of the lamp was tested in all three modes using manual switch, ldr operation and bluetooth wireless communication, between the android smart phone and the bluetooth module. the results achieved were 100% accurate. 196 iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 in the presented paper, the design, verification and gui were designed and executed for one lamp. the delay time to turn on the lamp is 3 secs and to turn off by bluetooth mode is 4 sec. the work of this paper can be extended to reduce the delay time in the appliances control, implement “internet of things” instead of bluetooth communication, increase the distance coverage of the bluetooth communication to control the lamp, etc. references [1] oditis i, bicevskis j. (2010) the concept of automated process control. scientific papers, university of latvia. computer science and information technologies, 756: 193-203. [2] adetiba e, matthews vo, awelewa aa, samuel ia, badejo ja. (2011) automatic electrical appliances control panel based on infrared and wi-fi. a framework for electrical energy conservation. international journal of scientific and engineering research, 2(7): 1-7. [3] muruganandam m, maswoodhur rahman a. (2019) simulation and implementation of loop based bank locker security system using cost effective microcontroller and gsm module. international journal of advanced research in electrical, electronics and instrumentation engineering, 8(9): 2175-2181. https://doi.rog/10.15662/ijareeie.2019.0809005 [4] cotta a, devidas nt, ekoskar vkn. (2016) wireless communication using hc-05 bluetooth module interfaced with arduino. international journal of science, engineering and technology research, 5(4): 869-872. [5] piyare r, tazil m. (2011) bluetooth based home automation system using cell phone. ieee 15th international symposium on consumer electronics, 837-843. https://doi.rog/10.1109/isce.2011.5973811. [6] harikrishnan d, nikhil s, roy mt, mathew sv. (2017) android based home automation using bluetooth. international journal of advanced research in electrical, electronics and instrumentation engineering, 6(4): 2605-2609, https://doi.rog/10.15662/ijareeie.2017.0604073 [7] yoo w-s, shaik sa. (2016) development of home management system using arduino and app inventor. ieee 40th annual computer software and application conference, 2: 379380. https://doi.rog/10.1109/compsac.2016.96. [8] gaikwad pv, kalshetty yr. (2017) bluetooth based smart automation system using android, international journal of new innovations in engineering and technology, 7(3): 24-29. [9] bhadane ds, wani md, shukla sa, yeole ar. (2015) a review on home control automation using gsm and blue-tooth. international journal of advanced research in computer science and software engineering, 5(2): 419-421. [10] badrul hisham aa, ishak mhi, teik ck, mohamed z, idris nh. (2014) bluetooth-based home automation system using an android phone, jurnal teknologi, 70(3): 57-61. https:// doi.rog/10.11113/jt.v70.3463 [11] vancea ap, orha i. (2018) smart home automation and monitoring system. carpathian journal of electronic and computer engineering, 11(1): 40-43. https://doi.rog/10.1109/10.2478/cjece-2018-0007 [12] david n, chima a, ugochukwu a, obinna e. (2015) design of a home automation system using arduino. international journal of scientific & engineering research, 6(6): 795-801. [13] rath dk. (2016) arduino based: smart light control system. international journal of engineering research and general science, 4(2): 784-790. [14] das s, ganguly s, ghosh s, sarker r, sengupta d. (2016) a bluetooth based sophisticated home automation system using smartphone. ieee international conference on intelligent control power and instrumentation (icicpi). 236-240. https://doi.rog/10.1109/icicpi.2016.7859709 [15] aung t. (2019) arduino based home lighting control by android phone. international journal of trend in scientific research and development, 3(5): 1634-1638 197 iium engineering journal, vol. 22, no. 2, 2021 abdul wahidh and masilamani https://doi.org/10.31436/iiumej.v22i2.1618 [16] preethi m, dharmalingam r. (2017) based on the wireless bluetooth microcontroller controlling home appliances. international journal of advanced research in electronics and communication engineering, 6(5): 440-445. [17] adiono t, anindya sf, fuada s, afifah k, purwanda ig. (2019) efficient android software development using mit app inventor 2 for bluetooth-based smart home. international journal of wireless personal communication, 105: 233-256. https://doi.org/10.1007/s11277-018-6110-x [18] krishnakanth k, kavipriya p. (2013) android application development for environment monitoring using smart phones. international journal of mobile network communications & telematics, 3(3): 41-45. https://doi.org/10.5121/ijmnct.2013.3305 198 https://doi.org/10.5121/ijmnct.2013.3305 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 software, algorithms and methods of data encryption based on national standards rakhmatillo djuraevich aloev1, mirkhon mukhammadovich nurullaev2* 1department of computational mathematics and information systems, national university of uzbekistan named after m. ulugbek, tashkent, uzbekistan 2department of information communication technology, bukhara engineering technological institute, bukhara, uzbekistan *corresponding author: mirxon@mail.ru (received: 13th june 2019; accepted: 30th september 2019; published on-line: 20th january 2020) abstract: the article provides a brief description of the cryptography service provider software developed by the authors of this article, which is designed to create encryption keys, create private and public keys of electronic digital signature, create and confirm authenticity of digital signatures, hashing, encrypting, and simulating data using the algorithms described in the state standards of uzbekistan. it can be used in telecommunications networks, public information systems, and government corporate information systems by embedding into applications that store, process, and transmit information that does not contain information related to state secrets, as well as in the exchange of information, and ensuring the legal significance of electronic documents. the cryptography service provider includes the following functional components: a dynamically loadable library that implements a biophysical random number sensor; a dynamic library that implements cryptographic algorithms in accordance with the state standards of uzbekistan; a module supporting work with external devices; an installation module that provides the installation of a cryptography service provider in the appropriate environment of operation (environment). abstrak: artikel ini memberikan penerangan ringkas tentang perisian penyedia perkhidmatan kriptografi yang dibangunkan oleh pengarang artikel ini, yang direka untuk membuat kunci penyulitan, kunci persendirian dan awam tandatangan digital elektronik, membuat dan mengesahkan kesahihan tandatangan digital, hashing, penyulitan dan simulasi data menggunakan algoritma yang dinyatakan dalam standard negeri uzbekistan. ia boleh digunakan dalam rangkaian telekomunikasi, sistem maklumat awam, sistem maklumat korporat kerajaan dengan memasukkan aplikasi aplikasi yang menyimpan, memproses dan menghantar maklumat yang tidak mengandungi maklumat yang berkaitan dengan rahsia negara, serta pertukaran maklumat dan memastikan undang-undang kepentingan dokumen elektronik. penyedia perkhidmatan kriptografi termasuk komponen berfungsi sebagai berikut: perpustakaan dinamik yang boleh dimuatkan yang melaksanakan sensor nombor rawak biofisika; perpustakaan dinamik yang melaksanakan algoritma kriptografi mengikut standard negeri uzbekistan; modul menyokong kerja dengan peranti luaran; modul pemasangan yang menyediakan pemasangan penyedia perkhidmatan kriptografi dalam persekitaran operasi yang sesuai (persekitaran). key words: tools of cryptographic protection of information, data encryption algorithm, cryptographic provider, hash function, encryption key. 142 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 1. introduction the cryptography service provider (csp) provides the creation of private and public electronic digital signature keys and encryption keys; creation and confirmation of authenticity of electronic digital signature according to the algorithms described in [2, 7]; the formation of derived encryption keys used by data encryption algorithms described in [4, 5]; work with key information stored on external media; hashing of memory areas and other data according to the algorithms described in [3, 6]; and encryption of memory areas and other data in accordance with the data encryption algorithms described in [4, 5]. the cryptography service provider provides support for identifiers of algorithms and parameters for compatibility with third-party crypto-providers in terms of the ability to work with public-key certificates issued by third-party registration centers, provided they use the cryptographic algorithms described in [2, 3, 4, 5, 6, and 7]. the cryptography service provider provides the ability to work with digital certificates of public keys, which are structured in binary asn.1 format, conforming to the itu-t x.509 v.3 standard and ietf rfc 5280 and rfc 3739 recommendations. the cryptography service provider provides work with external key carriers such as usb-flash, and etoken aladdin (etoken pro 72k (java)). as part of cipf1 – csp, modules are provided that provide for calling cryptographic functions through the microsoft cryptoapi 2.0 interface when running under microsoft operating systems. in accordance with the functional purpose of a cryptography service provider, it generates public and private electronic digital signature keys, hash keys, functional keys and encryption keys for use, respectively, in the algorithms described in [2, 3, 4, 5, 6, and 7]. in applications where the cryptography service provider will be integrated, an appropriate key manufacturing and distribution system is provided, which will be based on the key generation functions of the cryptography service provider. the cryptography service provider allows the use of a multi-level key protection model using random and derivative keys of key protection. protection of keys is carried out on the basis of cryptographic transformations in accordance with the pkcs #5 standard [9] using the state standards of uzbekistan [3], [4] or the interstate standard [5]. a cryptography service provider provides storage of key information on a hard magnetic disk drive (hdd) and/or external key storage devices, such as usb-flash or etoken aladdin (etoken pro 72k (java)). a cryptography service provider provides work with key containers of signature keys, encryption keys, and additional information necessary to ensure the cryptographic protection of keys and ensure control of their integrity. to protect key information from substitution and/or distortion during its storage on hdd and external key carriers, as well as during distribution, key information is supplied with a checksum. in order to ensure the safe use of the cryptography service provider installed on a pc, organizational measures are provided, as well as software and hardware methods and means of protecting information are used to ensure the secrecy of secret keys located in the pc's memory during the operation of the cryptography service provider, as well as the service cryptography service provider parameters stored on the hard disk. the cryptography service provider contains a component that allows you to verify the operability of the cryptographic algorithms implemented in it. functioning is carried out on the basis of test examples. to ensure the safe use of an application with a built-in ics-csp, mechanisms are provided to control the integrity of the cryptography service provider libraries. in the cryptography service provider, a biophysical sensor of random numbers is used to generate random binary 1 cipf cryptographic information protection facility 143 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 sequences, which implements the mechanism for generating secret digital signature keys, encryption keys, initialization vectors using various algorithms. the paper briefly describes the software necessary for the operation of the tools of cryptographic protection of information (tcpi) data encryption cryptography service provider which is developed by the authors based on national standards. furthermore, the purpose, capabilities of the tcpi csp software and its main characteristics, and the limitation of the using area of this software are given here. one of the following operating systems is necessary in order to perform the tcpi csp: microsoft windows xp (32 bit) professional sp3; microsoft windows vista (32 bit) ultimate sp2; microsoft windows 7 (32 bit) ultimate; microsoft windows server 2003 (32 bit) enterprise edition r2 sp2; microsoft windows server 2008 (32 bit) enterprise edition sp2. the original programming languages for the tcpi csp are c and c ++. tcpi csp performs the following main functions: generation of encryption keys for the data encryption algorithm o`z dst2 1105: 2009 [1] and the algorithm gost3 28147-89 [6]; encryption of ram4 areas and other data in accordance with the data encryption algorithm o`z dst 1105: 2009 [1] and the algorithm gost 28147-89 [6]; generation of keys for implementing and verifying the electronic digital signature (eds) using algorithms 1 and 2 of o`z dst 1092: 2009 [3] and the algorithm of gost r 34.10-2001 [8]; hashing of memory areas and other data according to algorithm 1 with the parameter p = 256 o`z dst 1106: 2009 [2] and the algorithm gost 34.11-94 [7]; formation and verification of the eds result in accordance with o`z dst 1092: 2009 [3] algorithms 1 and 2 and gost r 34.10-2001 [8]; work with key information stored on external media. tcpi csp can be used as a default crypto-provider for the windows operating system. tcpi csp supports the cryptographic algorithms of the republic of uzbekistan and russia as well as some of the common cryptographic algorithms used in windows os, such as rsa, 3des, sha-1 etc. 2. functions of working with key information tcpi csp product works with key information in a key container storage (key container). since tcpi – csp is built in accordance with microsoft technology, the container contains the following keys: at_keyexchange key used to encrypt and exchange session keys; at_signature keys used to create and verify a digital signature. 2 o`z dst state standard of uzbekistan 3 gost interstate standard 4 ram random access memory 144 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 note: private keys (encryption keys and secret signature keys) contained in the container are protected using a security key, which is derived from the value of the user's pin-code of the token. cryptographic procedures are invoked in tcpi csp using the pkcs #11 interface. the underlying concepts of the pkcs #11 interface are slot and token. the token is a repository of some personal information (various keys, certificates, private data, etc.), and the slot acts as a link between a computer and a token that allows different tokens to be connected at different times. for both at_keyexchange and at_signature, the same and different pkcs #11 slots can be used. tcpi csp supports work with containers located both on the hard disk of the computer and on removable media such as flash memory and smart card. each container has a unique name consisting of a prefix or several prefixes and the name itself. prefixes in the container name are separated from each other by the “\” symbol. the container name can contain from zero to three prefixes: container name = [pref1 \] [pref2 \] [pref3 \] name the location of the media is determined by the first prefix in the container name, depending on the presence of the crypt_machine_keyset flag in the cpacquirecontext function. in the container name, the second prefix is a reference to the slot for at_keyexchange, and the third is for at_signature. if the third prefix is absent, then at_keyexchange and at_signature are stored in the same slot. protection of token's private objects is carried out using the pkcs #5 cryptographic interface. this algorithm solves two problems at once: encrypting private data and protecting it from accidental or intentional distortion. 3. encryption function the encryption function is a cryptographic algorithm, which is a bijective mapping from a finite set of plaintext to a finite set of encrypted texts, in which the mapping function depends on a secret parameter called a key. the encryption function is used to encrypt and decrypt information. the encryption function in accordance with [1] can use cryptographic keys of length 256 or 512 bits for encrypting and decrypting data blocks of length 256 bits. the encryption function is used for cryptographic protection of data storing and transmitting in computer networks, telecommunications, in separate computing systems or in computers of enterprises, organizations, and institutions. in symmetric cryptosystems, data exchange takes place in three stages: 1) the sender of the message sends the encryption key (or/and functional key) to the recipient via a secure channel that is known only to them; 2) the sender, using the encryption key and the function key, converts the original data into encrypted data and sends them to the recipient via the communication channel; 145 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 3) the recipient, having received the encrypted data, decrypts it with the help of an encryption key and a function key. both sides may use these keys several times. in addition to data protection, the encryption function can be used to protect the symmetric keys themselves as they are transmitted over unprotected communication channels. in this case, the transmitted symmetric key is encrypted with some other key, called the security key. the encryption function [1] contains two modes: electronic codebook mode (ecm); block chaining mode (bcm). the electronic codebook mode is an encryption mode in which all plaintext blocks are encrypted independently of one another on the same key, in accordance with the data encryption algorithm. есm mode is usually used when encrypting symmetric keys. the block chaining mode of encryption is a mode in which each encrypted (decrypted) depends on the previous block of an encrypted (decrypted) block. for the first block, the initialization vector is used as the previous block. if the last block of text is not complete, it is supplemented to the required length. this procedure is called padding. bcm mode is usually used when encrypting data. the purpose of these functions and functionality of operation algorithms are presented in the document “o`z dst 1105: 2009. state standard of uzbekistan. information technology. cryptographic protection of information. data encryption algorithm.” 4. hash function the hash function is designed to implement a unidirectional compressing mapping from set to set , the input of which is a message of arbitrary length м, and the output is a string of fixed length . using a hashing transform allows you to reduce the input text redundancy. the hashing function is used in cryptographic methods for processing and protecting information, including for the implementation of electronic digital signature procedures (herein after referred to as eds5) when transferring, processing and storing information in automated systems. the following are the basic requirements for a hash function: the input of the function must be a message of any length; at the output of the function, a message of fixed length is obtained; the hash function is simply calculated for any message; hash function unidirectional function; knowing the message , it is almost impossible to find another message for which . in the tcpi csp hash function, the output sequence and the hash key have fixed lengths of 256 bits. 5 eds electronic digital signature 146 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 the composition and purpose of this function, functionality, and functioning algorithm are presented in the document “o`z dst 1106: 2009. state standard of uzbekistan. information technology. cryptographic protection of information. a hash function”. 5. signature function the electronic digital signature function is used to generate and confirm the authenticity of an electronic digital signature (eds) under a given message (electronic document) transmitted over unprotected public telecommunications channels. upon receipt of the message, the recipient can verify the integrity of the message transmitted by the sender and verify the authenticity of the sender's authorship. eds is an electronic analog of a written signature and therefore an eds can be used by the recipient or a third party to verify that the message was actually signed by the sender. to describe the formation and confirmation of the authenticity of a digital signature, two algorithms are used (algorithm 1, algorithm 2)6. algorithm 1 is considered in two basic modes: without session key7; with a session key. algorithm 2 is used in the classical (without session key) mode. algorithm 1 provides a backup path for detecting a fake digital signature by introducing a session key procedure used in the process of authenticating the authenticity of a digital signature to the eds generation process. the composition and purpose of this function, functionality, and functioning algorithm are presented in the document “o`z dst 1092: 2009. state standard of uzbekistan. information technology. cryptographic protection of information. processes of formation and verification of electronic digital signature”. functional restrictions on the use of tcpi – csp the cryptographic interface tcpi csp is implemented in accordance with the csp standard, which is applicable only in the windows operating system and is not applicable in other operating systems such as linux, mac, unix, etc. since cryptographic algorithms of the republic of uzbekistan are implemented in tcpi csp, which are not recognized by standard windows tools, embedding tcpi in typical windows applications (ms outlook, internet explorer, vpn, etc.) requires changes to the standard os software (advapi32.dll, cryptsp.dll, crypt32.dll, inetcomm.dll, schannel.dll, secur32.dll, mailcomm.dll, etc.). making such changes to windows can be done in various ways. 6. description of the logical structure 6.1. the algorithms and methods used when implementing cryptographic algorithms of the republic of uzbekistan, including the implementation of operations with big numbers, the source texts of programs from the 6 algorithm 1, algorithm 2 a description of these algorithms is given in the document “o`z dst 1092: 2009. state standard of uzbekistan. information technology cryptographic protection of information. processes of formation and verification of electronic digital signature”. 7 a session key is a single-use symmetric key used for encrypting all messages in one communication session. 147 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 openssl8 the software package was used. when implementing cryptographic algorithms of the republic of uzbekistan, all simple numbers that are part of the parameters of the algorithms are checked for simplicity using the standard procedures contained in the openssl package. 6.2. data encryption algorithm data encryption in tcpi csp supports both cryptographic algorithms of the republic of uzbekistan [1] and cryptographic standards of the russian federation (gost 28147-89) [6]. data encryption cryptographic provider tcpi csp supports various algorithms for symmetric data encryption (sde) [10], including the data encryption algorithm of the republic of uzbekistan [1]. according to section 6.4 [1], an sde in tcpi csp is implemented in three different ways: dea9 with key 256-bit; dea with key 512-bit; dea with the function key update. here is the implementation of all three of these methods using the tcpi csp. 6.2.1. dea with key 256-bit to implement a dea with a key of 256 bits, you need to: 1) get the key for the algorithm calg_symm10. this key can be obtained in the following ways, in which algid = calg_symm: cryptgenkey, cryptderivekey, either through cryptimportkey from simpleblob11 or symmetricwrapkeyblob12, created previously via cryptexportkey; 2) call function cryptencrypt or cryptdecrypt depending on the operation performed. 6.2.2. dea with key 512-bit to implement a dea with a key of 512 bits, you need to: 1) get the key of the dea algorithm with the key 256 (in accordance with paragraph 1 of the dea with the key of 256 bits); 2) perform a function cryptsetkeyparam with parameter kp_func_key (#define kp_func_key 200). the value pbdata will be the value of the function key that can be generated, in particular, using the function cryptgenrandom or by other means; 3) perform a function cryptencrypt or cryptdecrypt depending on the operation performed. 8 openssl openssl is a robust, commercial-grade, and full-featured toolkit for the transport layer security (tls) and secure sockets layer (ssl) protocols. it is also a general-purpose cryptography library. 9 dea data encryption algorithm 10 calg_symm the description of this parameter is given in the document [1] 11 simpleblob the description of this parameter is given in the document [1] 12 symmetricwrapkeyblob the description of this parameter is given in the document [1] 148 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 6.2.3. dea with the function key update to implement a dea with a function key update, you need to: 1) get the key of the dea algorithm with the key 256 (in accordance with paragraph 1 of the dea with the key of 256 bits); 2) if necessary, install a function key (see p. 2 of the dea with a key of 512 bits); 3) perform a function cryptsetkeyparam with parameter kp_oid (#define kp_oid 102). as a value for pbdata fed to the input value of the function szoid_symm_b13; 4) call function cryptencrypt or cryptdecrypt depending on the performed operation. in the encryption function, the lengths of the input and output blocks, as well as the length of the elements of the array holat14 are equal 256 bit. the length of the encryption key and the function key are also equal 256 bit. the number of steps for the encryption feature is set to . in both the encryption mode and the decryption mode, the algorithm uses a one-time conversion forming an array of the session key and the next four bytes oriented and one bit oriented conversion at each stage. these transformations include: forming arrays of step keys; mixing data based on the session key array; cyclic shifts of rows and columns of the array holat for various values of displacement; byte-wise replacement of bytes of the holat array based on linear array arrays; addition operation modulo 2 holat arrays and an array of the stage key ; cyclic shifts of a linear array of a session-stage key by the same value of bits at each stage. when encrypting a cryptographic module is initialized, the encryption key and functional key , number of stages аnd also initialization vector for mode m=shbil is first loaded into the cryptographic module. also, when encrypting a cryptographic module into the holat array, the plaintext is loaded; when decrypted, the ciphertext is loaded. at the beginning of the encryption procedure, shaklseanskalitbayt( )15, shaklseanskalit( )16 and shaklbosqichkalit( ) crypto-transformations are initialized. at the outputs of crypto transformations shaklseanskalitbayt( ), shaklseanskalit( ), byte-level arrays of substitutions and a session key consisting of diamatrix parts are formed at the byte level. these arrays are used in the following sessions as long as remain constant. at the output of the crypto-transformation shaklbosqichkalit( ) the initial key and the set of stage keys formed for each stage are formed. 7. cryptographic transformations aralash() – is a function that is a cryptographic transformation and is performed on diamatrix parts during encryption and decryption. 13 szoid_symm_b the description of this parameter is given in the document [1] 14 holat array containing one block of information 15 shaklseanskalitbayt( ) is a function that is used to generate the key for each session and to perform the baytalmash() conversion when encrypting and decrypting. 16 shaklseanskalit( ) is a function that is used to generate the key for each session and to perform the aralash() transformation when encrypting and decrypting. 149 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 when encrypting, the input data are the diamatrix parts of the holat array, the and arrays, the output is the holat array. the aralash (holat, ) transformation involves performing the following operations: if m=sh, then: 1) is accepted ; 2) is calculated ; 3) the result is written to arrays ; 4) copy the result to an array holat; if m=dsh, then: 5) is accepted ; 6) is calculated ; 7) the result is written to arrays ; 8) copy the result to an array holat. the operation of diamatrix multiplication is performed on the basis of the following expressions, here the index used in the expressions takes the values . expressions for : , , , , expressions for : , , , , , , , 150 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 , , , , , this transformation is more efficient compared to the matrix transformation. here, when changing one element in the holat source array, depending on the address of the changed element, 6 or 7 elements change. baytalmash() – a function that is a cryptographic transformation and is used to replace elements of the holat array with elements of the replacement array at the byte level. the input data of this crypto-transform is holat array, linear array of or replacements at the byte level, output data is holat array at the byte level. baytalmash(holat, ) conversion involves performing the following operations: 1) renaming the holat[8,4] array, specified at the byte level, as holatb[8, 4] at the byte level; 2) if m=sh, then accepted ; each element of the holatb[8, 4] is replaced with an element of the array located at an address equal to the value of the holatb[8,4] array element; the resulting holatb[8, 4] array is assigned to the holat[8, 4] array specified by the byte level; 3) if m=dsh, then accepted ; replaces each element of the array holatb[8,4] element of the array located at the address equal to the value of the element of the array holatb[8, 4]; the resulting holatb [8,4] array is assigned to the holat [8,4] array specified by the byte level, here . sur() – a function that is used when encrypting and decrypting to thoroughly mix the elements of the holat array. the input data of this transformation is the holat array, while the output data is encrypted: hol holat array with columns cyclically shifted downwards and rows cyclically shifted to the right; when decrypted, the output is a holat array with columns cyclically shifted upwards and rows cyclically shifted to the left. the sur (holat) conversion is to perform the following operations: if m = sh, then first cyclically shift the j-column of the holat array to bytes down, then shift the i-string of the resulting array to bytes right; if m=dsh, then first cycle the string of the holat array by bytes left, then shift the j-column of the resulting array by bytes up. here, . 151 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 8. key generation shaklseanskalitbayt() – a function that is used to generate a key for each session and to perform the baytalmash() transformation when encrypting and decrypting. in this transformation, the input data is the encryption key and the function key , the output is arrays or byte level. the shaklseanskalitbayt( ) transformation is to perform the following operations: 1) calculation and the remaining 672 bits on the left, here is 192 bits on the right. note. when generating an encryption key, a set of functional keys that are updated using an encryption key, and forming a key based on them, they must be checked based on randomness criteria and 672 bits are allocated from the left side of the resultant kse; 2) selection from the right side of 256+64 bits, from the left 256-bit part of the formation of a linear array of , consisting of byte elements, from the remaining 64-bit part, the formation of a linear array , consisting of elements at the byte level; 3) formation of a pair of arrays from the elements of the linear array and and the formation of the three parameters ( and ( based on the following rules: for , if , is accepted , otherwise ; for , if , is accepted , otherwise ; for , if , is accepted , otherwise ; for , if , is accepted , otherwise ; for , if , is accepted , otherwise ; for , if , is accepted , otherwise ; for , if , is accepted , otherwise , here ; for , if , then is accepted ; for , if , is accepted ; for , if , is accepted ; 4) formation of a pair of arrays ( , ) to perform transformations at the byte level and get the encrypted text; 5) raising to the power with the parameter modulo 257 value , corresponding to each address , the result is given modulo 256 and in each step the current value compared with the value of the previous step and . if the values are equal or if the current value is close to the previous value, then the current value is replaced with ( )) with and on ( ) with . here, . note. in the pseudo-code, in the odd-numbered stages, the is used, and in the even-numbered stages, the is used. the algorithm of calculations includes the following operations: 1) calculation bsa[i] (((i+l) mod 256)+1 )| ds (mod 257)(mod 256) 152 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 for ; 2) condition check and , at every step since . if both conditions are met, then the value is accepted. otherwise, when , swap and the element located at , or when the position and the element located at . then accepted for or for ; 3) formation of a pair of linear arrays ( , ) of the elements . it is necessary to get the cipher text at the byte level, i.e. for use in sh mode; 4) formation of a pair of linear arrays ( , ) for decryption at the byte level, i.e. for use in dsh mode; 5) replacing each element with a value in the linear array with an index equal to its value and positioning the elements of the formed array in increasing order of the address. it is necessary to get the cipher text (dsh) at the byte level. here, . note. in the pseudo-code in the odd-numbered stages, the array is used, in the even-numbered stages, the array is used; shaklseanskalit() – is a function that is used to generate a key for each session and to perform the aralash() conversion when encrypting and decrypting. the input to this transformation is the array at the byte level; the output is a pair of arrays ( , ) or ( , ), consisting of diamatrix of a special structure. the shaklseanskalit ( ) transformation is to perform the following operations: 1) the formation of a linear array , consisting of 20 byte elements from the left of the linear array , consisting of byte elements; if for , to replace on ; if , to replace on ; if , to replace on ; if , to replace on ; if , to replace on ; if , to replace on ; if , to replace on ; if , to replace on ; if , to replace on . 2) formation of two-dimensional arrays and from the elements of the linear array in the following order: 153 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 division of the linear array into two linear arrays and . each of them is uniquely displayed in an ordered set and the formation of the elements of arrays and ; the formation of the remaining elements of the array , based on the following rule: for , if , then the corresponding elements are equal in value ; for , corresponding elements are equal in value ; for , corresponding elements are equal in value ; 3) as a result, for use in encryption mode as a pair of diamatrix of a special structure is formed and ; array array 154 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 4) calculation of the inverse matrix of a special structure for the matrix of the special structure for use in sh mode; 5) calculation of the inverse matrix of the special structure for the matrix of the special structure for use in dsh mode; 6) obtaining an inverse matrix for the diamatrix of a special structure (here ), in which the diadetergent is not zero, consists in calculating the inverse matrix for the matrix obtained as a result of performing a diagonal transformation over it and the result of performing a transform over the obtained inverse matrix; 7) as a result of the inversion of the diamatrices of the special structure and the diamatrices of the special structure and , are formed, having the following form ( and ). array array in sh mode, a pair consisting of ( , ), is fed to the input; in dsh mode, a pair consisting of ( , ) is fed to the input. shaklbosqichkalit() – is a function that is used to form a stage key from a session-stage key and to perform the qo’shbosqichkalit() transformation when encrypting and decrypting. the input data of this transformation is the linear array of the session-stage key , the output data is the two-dimensional array specified by the byte level ; 155 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 the shaklbosqichkalit ( ) transformation (generation of a linear session-stage key) occurs as follows: 1) if bosqich=1 and m=sh, then the array of the linear session-stage key is left unchanged, if bosqich=1 and m=dsh, then the array is shifted by 672-(е х 83) mod 672 bits to the right; 2) the left 256 bit part of the linear session-stage key array is separated and the array is formed from it at the byte level. this conversion is performed for all stages prior to the start of the encryption procedure; 3) if and m=sh, then the array cyclically shifts 83 bits to the left, if and m=dsh, then the array cyclically shifts 83 bits to the right; 4) the left 256 bit part of the linear session-stage key array is separated and an array is formed from it at the byte level . this conversion is performed for all stages prior to the start of the decryption procedure. 9. simple crypto-transformation qo’shbosqichkalit() – is a function that is simple crypto-transform and consists of performing an exclusive “or” (bitwise addition modulo 2) when encrypting and decrypting holat arrays and an array of the step-key . the input data of this transformation are the holat and arrays at the byte level, the output data is the holat array at the byte level. the qo’shbosqichkalit (holat, ) transformation consists of performing an exclusive “or” operation (bitwise modulo-2 addition) on elements of the same name at the byte level of holat and arrays. for : . the result must be copied to the holat array. qo’shholat() – is a function that is a simple crypto-transform and is performed on blocks of encrypted blocks using the xor operation when encrypting and decrypting in all modes except the electronic codebook mode. in the qo’shholat(holatn, holat) transformation, each byte of the holatn array is added bitwise using the xor addition operation (modulo 2 addition operation) the same byte of the holat array. holatn array consists of eight words. when these words are in the range of , the elements of the holat array that are in the columns are added separately as follows: , here: hn array elements holatn, – elements of the resulting array. the result of the conversion is copied to the holat array. 9.1. encryption of symmetric keys using symmetric keys to encrypt symmetric keys using symmetric keys, a dea is used in ecm mode. to produce imitation protection, a hash function from cryptographic standards of uzbekistan in 156 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 256 bit mode is used. the first 4 bytes of the key's hash function is the simulated prefix for the encrypted key. 9.2. encryption of symmetric keys using asymmetric keys when encrypting symmetric keys using asymmetric keys, the following algorithm is used. using the diffie-hellman method, a common key of the form is formed, where , are private keys, the common key size is 256 and 64 bytes for algorithms 1 and 2, respectively. this shared key is used instead of a password to generate a shared symmetric key and initialization vector in accordance with pkcs #5. the original symmetric key is encrypted in bcm mode using a common symmetric key and an initialization vector. the size of the encrypted key is 64 bytes. imitation protection provides padding size of 32 bytes. 9.3. an algorithm of generation and verification of eds processes of formation and verification of electronic digital signatures in tcpi csp supports both cryptographic algorithms of the republic of uzbekistan [3] and the cryptographic standard of the russian federation (gost r 34.10-2001) [8]. the function of eds (formation and verification) is designed to ensure the reliability of the transmitted and received information and confirm its authorship. 9.4. development and verification of eds the following parameters are used for the signature function: ( ) –pair of integers private key of eds; ( ) – pair of integers – public key eds; ( ) – pair of integers – electronic digital signature under the message ; ( ) – pair of integers – fake detection key eds, which is a pair of control and session public key; ( , ) – special private key of the authorized subject. the generally accepted digital signature model spans three processes: generation of eds keys; formation of eds; verification (authentication) eds. 9.4.1. algorithm 1 algorithm 1 uses the following parameters: – is a module, a prime number. the upper limit of this number should be determined by the specific implementation of the electronic digital signature algorithm, depending on the type of cryptographic module: for software, hybrid and hardware types and for special hardware type; is a prime number, which is a factor (simple factor) , where ; – is the parameter a positive integer satisfying the condition ; can be an open, shared private key for a limited group of users or a component of a special private key of an authorized entity; m = h( ) – is a hash function that displays the message in a string of length 256 bits; in software, hybrid and hardware types of a cryptographic module, a hash function without a key is used, and in a special hardware type, a key hash function. 157 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 to implement eds processes (i.e., eds key generation, eds generation, and eds authentication), each user must have a private eds key ( ), where: are private keys, randomly or pseudo-randomly generated integers satisfying the condition , ; the parameter is a private or public parameter representing an integer that is calculated: , the public key of the digital signature ( ). where: ( ) are public keys calculated by the formula and ; if the open parameter (base) is used, then and ; and the eds fake detection key ( ), where: is the control key (open or closed), selected from the range ; if is closed, then must be a joint secret key for the signer and the verifier; – is a session (public) key calculated for each electronic digital signature as a result of exponentiation with the parameter. formation of electronic digital signature and session key to create a digital signature and session key under the message m for algorithm 1, the following actions are performed: 1) the hash function of the message is calculated: . moreover, ; 2) is calculated. if , then is assumed and it is necessary to return to step 2; 3) calculate with the parameter ; 4) calculate . if , then ) is assumed and it is necessary to return to step 3. 5) is calculated. if , then is assumed and it is necessary to return to step 3; 6) compute . if , then , is output and calculations stop; 7) calculate . if , then is assumed and it is necessary to return to step 3; 8) is calculated. if , then is assumed and it is necessary to return to step 3; 9) with the parameter is calculated and output . further, the signed message (message and addition) is transmitted to the receiving side. also, the session key is transmitted to the receiving side if the session key mode is used. digital signature authentication to confirm the authenticity of eds under the received message, , the following actions are performed: 1) hash function is calculated; 2) if then go to the next step, otherwise the “signature is not authentic” is accepted; 3) is calculated with the parameter r; 4) is calculated; 5) is calculated with the parameter r; 6) is calculated; 7) is calculated; 158 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 8) if and , then the output is “signature authentic”; if and , then go to the next step; if , then the “signature is not authentic” is accepted; 9) is calculated; 10) is calculated; 11) is calculated; 12) is calculated; 13) ; 14) is calculated with the parameter ; 15) is calculated with the parameter ; 16) is calculated; 17) if , then “signature is authentic” is accepted, otherwise “signature is not authentic” is accepted. algorithm 1 uses a one-way function in a group with a parameter, calculations for which are carried out easily at the same level of labor intensity as in the exponentiation operations, and inverting (inversion) of a function requires no less computational time and effort than in solving a discrete problem logarithm the main operations of multiplication, exponentiation, and treatment in a group with a parameter are called multiplication, exponentiation, and treatment of the parameter. the one-sided exponentiation function is a special case of this one-way function. 9.4.2. algorithm 2 for algorithm 2, the following parameters are used: elliptic curve e, given by its invariant j(e) or by coefficients ; integer w is the order of a group of points of an elliptic curve e; prime t is the order of a cyclic subgroup of a group of points of an elliptic curve е for which the following conditions are satisfied: point of an elliptic curve , with coordinates ( ), satisfying the equality [t] ; hash function , displaying the message , in a string of length 256 bits. for the listed parameters of eds the following requirements are met: 1) for all integers where satisfies the inequality ; 2) ; 3) the invariant of the curve satisfies the condition or 1728. to implement eds processes (i.e., eds key generation, eds generation and eds authentication), each user must have an eds private key, an integer , satisfying 159 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 and the public eds key is a point of an elliptic curve with coordinates ( ), satisfying the equality [d]n=t . formation of electronic digital signature to obtain a digital signature under the message, , the following actions are performed: 1) calculate the hash function of message: ; 2) calculate . if , then define ; 3) a random (pseudo-random) integer is generated, satisfying the inequality ; 4) the point of the elliptic curve is calculated and , is determined, where is the coordinate of point . if , then it is necessary to return to step 3; 5) compute the value of . if , then you need to return to step 3; 6) issue to the output of and as a digital signature. digital signature authentication to confirm the authenticity of eds under the received message, , the following actions are performed: 1) if , then go to the next step, otherwise the “signature is not authentic” is accepted; 2) calculate the message hash function: ; 3) compute by . if , then define ; 4) calculate the value of ; 5) values are calculated; 6) the point of the elliptic curve is calculated and is defined, where – is the coordinate of point ; 7) if the equality holds, then the “signature is authentic” is accepted, otherwise “the signature is not authentic”. algorithm of generation and verification of eds using the algorithm of the russian federation for the algorithm of the russian federation, the following parameters of the digital signature scheme are used: a prime number is a module of an elliptic curve such that ; the elliptic curve is defined by its invariant or the coefficients , where is a finite field of p elements. is related to the coefficients and as follows , and ; integer is the order of a group of points of an elliptic curve, must be different from ; a prime number , the order of a cyclic subgroup of a group of points of an elliptic curve, that is, ; for some . also lies within ; 160 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 the point of the elliptic curve , which is the generator of a subgroup of order , that is, and for all , where is a neutral element groups of points of an elliptic curve ; hash function (gost r 34.11-94) [7], which displays message in binary vector length of 256 bits. every digital signature user has private keys: encryption key integer number within ; decryption key , calculated as . additional requirements: , any , where ; . digital signature generation to obtain a digital signature under the message m, the following actions are performed: 1) calculation of the hash function from the message ; 2) calculation of , and if , set . where is an integer corresponding to ; 3) generation of a random number such that ; 4) calculation of the point of the elliptic curve , and finding where is the coordinate of the point . if , we return to the previous step; 5) verification of . if , go back to step 3; 6) digital signature generation , where and are vectors corresponding to and . verifying digital signatures. to confirm the authenticity of eds under the received message m, the following actions are performed: 1) calculation by digital signature of numbers r and s, taking into account that , where and are numbers corresponding to vectors and . if at least one of the inequalities and is incorrect, then wrong signature; 2) calculation of the hash function from the message ; 3) calculation of , and if , set . where is an integer corresponding to ; 4) calculation of ; 5) calculation of and ; 6) calculation of the point of the elliptic curve ; 7) definition , where is the coordinate of the curve definition , where is the coordinate of the curve ; 8) in the case of equality the signature is correct, otherwise is incorrect. 161 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 program structure this subsection presents the general structure of the tcpi csp, as well as a description of the functions of each module of the system. 10. general structure tcpi csp is implemented in the form of the following dynamic libraries: csp.dll loading the csp interface using the crypto api; cspfunc.dll loading the csp interface directly; pkcs11.dll loading the pkcs #1117 interface (pkcs #11 interface for tcpi csp, hereinafter pkcs #11); sctoken.dll functions for working with a smart card through the interface pkcs #11; vtoken.dll functions for working with virtual slots and tokens through the interface pkcs #11; cryptosp.dll a library of cryptographic procedures. the above libraries are located in the windows \ system32 folder. also, the following modules are included in the scope of delivery of tcpi csp: gui.dll interface for entering the password to the key, random number generation using the electronic roulette mechanism; csp_integral_test.exe integral test for tcpi csp; pkcs11ini.exe initialization of virtual slots and tokens for the pkcs #11 interface; cryptotest.exe tests of cryptographic algorithms; keymanager.exe test program for obtaining and viewing certificates; km.dll dynamic library for supporting the work of the test program keymanager.exe; cspcon.dll is a dynamic library for supporting the import and export of private keys in the pfx format. note. the keymanager.exe program and two dynamic libraries supporting it are intended only for testing the operation of csp with certificates and private keys. 11. csp interface the tcpi csp interface consists of two dynamic libraries csp.dll, cspfunc.dll, as well as an auxiliary test program csp_integral_test.exe. the cryptographic interface tcpi csp was created in accordance with the requirements of the microsoft cryptography service provider (csp) standard. a description of the csp standard (with a detailed description of all functions) can be found on the microsoft website (http://msdn.microsoft.com/en-us/library/aa380245(v=vs.85).aspx). the tcpi csp 17 pkcs #11 is one of the standards of the public-key cryptography standards (pkcs) family. it defines a platformindependent software interface for accessing cryptographic devices (smartcards, tokens, cryptographic accelerators, key servers and other means of cryptographic information protection). 162 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 interface was developed for the implementation of cryptographic algorithms of the republic of uzbekistan [1], [2], [3], russian encryption algorithms and electronic signatures [6, 7, 8] using pkcs #11 [5] interface. when developing the software implementation of the cryptographic interface of tcpi csp, the source texts of programs from the world famous and freely distributed software package openssl were widely used. using tcpi csp can be done directly, by loading the cspfunc.dll library using the loadlibrary mechanism and obtaining addresses of cryptographic functions using the getprocaddress18 command, or via the cryptoapi19 interface. input and output data the cryptographic interface of tcpi-csp was created in accordance with the requirements of the microsoft cryptography service provider (csp). a description of the csp standard can be found on the microsoft website. a description of the input and output data for the csp standard can also be found on the microsoft website at the links below. csp connection functions: function & description cpacquirecontext – associates a key container with a csp pointer. cpgetprovparam – displays csp parameters. cpreleasecontext – frees pointer received by cpacquirecontext. cpsetprovparam – sets specific csp parameters. key generation and csp key exchange functions: function & description cpderivekey – creates a key from a password. cpdestroykey – removes a key from memory. cpduplicatekey – creates a copy of the key. cpexportkey – export key. cpgenkey – generates a random key. cpgenrandom – generates random numbers. cpgetkeyparam – gets key parameters. cpgetuserkey – gets a user key pointer. 18 getprocaddress the getprocaddress function retrieves the address of the exported function or variable from the specified dynamic link library (dll). 19 cryptoapi cryptoapi is an application programming interface that provides windows developers with a standard set of functions for working with a cryptographic provider. included in the microsoft operating systems. most cryptoapi features are supported starting from windows 2000. cryptoapi supports asymmetric and symmetric keys, that is, allows you to encrypt and decrypt data, as well as work with electronic certificates. the set of supported cryptographic algorithms depends on the specific cryptographic provider. 163 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 cpimportkey – imports key. cpsetkeyparam – sets key parameters. encryption and decryption functions: function & description cpdecrypt – decrypts encrypted text with a key for encryption. cpencrypt – encrypts plaintext with an encryption key. hashing and eds functions: function & description cpcreatehash – creates a hash pointer. cpdestroyhash – deletes a hash pointer. cpduplicatehash – creates a copy of the hash function. cpgethashparam – gets the properties of the hash function. cphashdata – hashes data cphashsessionkey – hashes session key. cpsethashparam – sets hash options. cpsignhash – sets signature hash function. cpverifysignature – sets signature verification hash function. 12. conclusion remarks this work is devoted to a brief description of the csp software, which is designed to create encryption keys, private and public keys of an electronic digital signature, creating and authenticating eds, hashing, encrypting and simulating data using the algorithms described in the state standards of uzbekistan. it can be used in telecommunications networks, public information systems, government corporate information systems by embedding into applications that store, process and transmit information that does not contain information related to state secrets, as well as in the exchange of information and ensuring the legal significance of electronic documents [11]. csp includes the following functional components: a dynamically loadable library that implements a biophysical sensor of random numbers; dynamic library that implements cryptographic algorithms in accordance with the state standards of uzbekistan; module supporting the work with external devices; installation module that provides the installation of csp in the appropriate environment of operation (environment). csp provides the creation of private and public eds keys and encryption keys; creation and confirmation of authenticity of eds according to the algorithms described in [2, 7]; the formation of derived encryption keys used by data encryption algorithms described in [4, 5]; work with key information stored on external media; hashing of memory areas and other data according to the algorithms described in [3, 6]; encryption of memory areas and other data in accordance with the data encryption algorithms described in [4, 5]. csp provides support for identifiers of algorithms and parameters for the implementation of compatibility with third-party cryptographic providers in terms of the ability to work with 164 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 public-key certificates issued by third-party registration centers, provided they use the cryptographic algorithms described in [2, 3, 4, 5, 6, and 7]. the cryptography service provider provides the ability to work with digital certificates of public keys, which are structured binary in asn.1 format, conforming to itu-t x.509 v.3 standard and ietf rfc 5280, rfc 3739 recommendations. csp provides work with external key carriers such as usb-flash, etoken aladdin (etoken pro 72k (java)). as part of csp, modules are provided that provide for calling cryptographic functions through the microsoft cryptoapi 2.0 interface when running under microsoft operating systems. in accordance with the functional purpose, csp provides the generation of public and private eds keys, hashing keys, functional keys and encryption keys for use, respectively, in the algorithms described in [2, 3, 4, 5, 6, and 7]. in the application where the csp will be integrated, an appropriate system for the manufacture and distribution of keys will be provided, which will be based on the functions of generation of csp keys. csp allows the use of a multi-level key protection model using random and derivative keys of key protection. protection of keys is carried out on the basis of cryptographic transformations in accordance with the pkcs #5 standard [9] using the state standards of uzbekistan [3], [4] or the interstate standard [5]. csp provides storage of key information on a hard disk drive (hdd) and/or external key storage devices, such as usb-flash, etoken aladdin (etoken pro 72k (java)). csp provides work with key containers containing: signature keys, encryption keys and additional information necessary to ensure the cryptographic protection of keys and ensure control of their integrity. to protect key information from substitution and/or distortion during its storage on hdd and external key carriers, as well as during distribution, key information is supplied with a checksum. in order to ensure the safe use of the csp installed on the pc, organizational measures are provided, as well as software and hardware methods and means of protecting information are used to ensure that secret keys stored in the pc's memory during operation of the csp are kept secret, as well as the csp service parameters stored on the hard drive. csp contains a component that allows you to verify the operation of cryptographic algorithms implemented in it. functioning is carried out on the basis of test examples. to ensure the safe use of an application with a built-in csp, mechanisms are provided to control the integrity of the csp libraries. in csp, a biophysical random number sensor is used to generate random binary sequences that implement the mechanism for generating secret digital signature keys, encryption keys, initialization vectors using various algorithms. references [1] o`z dst 1105: 2009. state standard of uzbekistan. information technology cryptographic protection of information. data encryption algorithm. [2] o`z dst 1106: 2009. state standard of uzbekistan. information technology cryptographic protection of information. a hash function. [3] o`z dst 1092: 2009. state standard of uzbekistan. information technology cryptographic protection of information. processes of formation and verification of electronic digital signature. [4] pkcs #5 v2.0: password-based cryptography standard. rsa laboratories. march 25, 1999. [electronic resource]. access mode: https://tools.ietf.org/html/rfc2898. [5] expansion of pkcs #11 for the use of russian cryptographic algorithms. moscow, 2008. [6] gost 28147-89 information processing systems. cryptographic protection. an algorithm of cryptographic transformation. [7] gost r 34.11-94 information technology. cryptographic protection of information. a hash function. 165 iium engineering journal, vol. 21, no. 1, 2020 aloev et al. https://doi.org/10.31436/iiumej.v21i1.1179 [8] gost r 34.10-2001 information technology. cryptographic protection of information. processes of formation and verification of electronic digital signature. [9] rfc 4357 additional cryptographic algorithms for use with gost 28147-89, gost r 34.1094, gost r 34.10-2001, and gost r 34.11-94 algorithms. [10] aloev r.d., nurullaev m.m. (2019) cryptography service provider data encryption. in proceedings of the 10 th international multi-conference on complexity, informatics and cybernetics: 12-15 march 2019; orlando, florida, usa. edited by nagib gallaos, hsing-wie chu, jeremy horne, suzanne k. lunsford, belkis sánchez, michael savoie; pp 127-131. [11] aripov m.m., alaev r.h. (2019) research of the application of the new cryptographic algorithms: applying the cipher algorithm o'zdst1105:2009 for ms office document encryption. in proceedings of the 5th international conference on engineering and mis (icemis '19): 06-08 june 2019; astana, kazakhstan. acm, new york, ny, usa. https://doi.org/10.1145/3330431.3330434. 166 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 computationless palm-print verification using wavelet oriented zero-crossing jitendra prabhakar chaudhari1*, hiren kantilal mewada2 amit vinubhai patel1, keyur kamaldasji mahant1, alpesh dudabhai vala1 1 charusat space research and technology centre, department of electronics and communication engineering, cspit, charotar university of science and technology , changa, gujarat, india 2 department of electrical engineering, prince mohammad bin fahd university, kingdom of saudi arabia * corresponding author: jitendrachaudhari.ec@charusat.ac.in (received: 27th may 2021; accepted: 15thjuly 2021; published on-line: 4thjanuary 2022) abstract: palmprints can be characterized by their texture and the patterns of that texture dominate in a vertical direction. therefore, the energy of the coefficients in the transform domain is more concentrated in the vertical sideband. using this idea, this paper proposes the characterization of the texture features of the palmprint using zerocrossing signatures based on the dyadic discrete wavelet transform (dwt) to effectively identify an individual. a zero-crossing signature of 4 x 256 was generated from the lower four resolution levels of dyadic dwt in the enrolment process and stored in the database to identify the person in recognition mode. euclidean distance was determined to find the best fit for query palmprints zero-crossing signature from the dataset. the proposed algorithm was tested on the polyu dataset containing 6000 multi-spectral images. the proposed algorithm achieved 96.27% accuracy with a lower recognition time of 0.76 seconds. abstrak: pengesan tapak tangan boleh dikategorikan berdasarkan ciri-ciri tekstur dan corak pada tekstur yang didominasi pada garis tegak. oleh itu, pekali tenaga di kawasan transformasi adalah lebih penuh pada jalur-sisi menegak. berdasarkan idea ini, cadangan kajian ini adalah berdasarkan ciri-ciri tekstur pada tapak tangan dan tanda pengenalan sifar-silang melalui transformasi gelombang kecil diadik yang diskret (dwt) bagi mengecam individu. pada mod pengecaman, tanda pengenalan sifar-silang 4 x 256 yang terhasil daripada tahap diadik resolusi empat terendah dwt digunakan dalam proses kemasukan dan simpanan di pangkalan data bagi mengenal pasti individu. jarak euklidan yang terhasil turut digunakan bagi memperoleh padanan tapak tangan paling sesuai melalui tanda pengenalan sifar-silang dari set data. algoritma yang dicadangkan ini diuji pada set data polyu yang mengandungi 6000 imej pelbagaispektrum. algoritma yang dicadangkan ini berjaya mencapai ketepatan sebanyak 96.27% dengan durasi pengecaman berkurang sebanyak 0.76 saat. keywords:multi-scale edge detection; palmprint recognition; feature extraction 1. introduction people authentication is now a necessity in the digital world. biometric-based identification is considered to be a most reliable system for protection and reliable authentication. in the current mechanization era, artificial intelligence systems prepare 222 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 data about everything and use it to solve several complex problems. although many organizations have built state of the art security systems, recent terrorist attacks have uncovered significant vulnerabilities in complex security schemes. consequently, various organizations look to the uniqueness of each human body to establish information frameworks, often called biometrics, because they are more “real” or more difficult to counterfeit. automatic personal identity recognition can be accomplished through the use of different biometric identifiers. in many biometric baseline systems, anatomical individuality such as thumbprints, fingerprints, and morphology of the iris, retina, head, nose, or hand or behavioral characteristics such as signature, keystroke mechanics, and gait are used for identification. each biometric innovation has its own particular merits and constraints, and therefore no system exists with better performance for all applications [1].biometric system, which uses the iris, is one of the mainstream biometric frameworks with exceptionally high precision [2]. since the iris acquisition method is costly, it requires very high cooperation from the user and has a high failure rate of enrolment. because of their simplicity, good accuracy, and low cost, face and finger print recognition have gained a large popularity. however, the present covid situation makes these systems fail from occlusion due to masks hiding the facial features and frequent sanitization reducing the fingerprint features [3]. recently, a hand geometry-based identification has been proposed in [4]. however, this system is tedious, sensitive to the acquisition process, and computationally complex. new emerging ear trait recognition is explained in [5]. mewada et al. [5] used cnn for learning and discriminating between ear features. a moving human leg angle-based gait recognition system, explained in [6], uses average statistical features of eight frames. a palmprint-based identification system has many advantages compared to other biometric systems: 1) hand features of the human have high stability and uniqueness. 2) for data, acquisition needs extremely minimal support from clients. 3) non-intrusive data collection. 4) inexpensive devices are sufficient to acquire good data quality. 5) the mechanism provides high accuracy and uses low-resolution images. 6) more features can be extracted from palmprints as it allows for a larger surface area compared to fingerprints. 7) since low-resolution imaging sensors are used for acquiring palmprint images, the computation required for pre-processing and extracting features is minimal. 8) palmprints can be considered a trustworthy human identifier as these patterns are unique in monozygotic twins [7]. therefore, this paper presents a unique approach requiring less computation and complexity in the palmprint recognition process. the proposed system is sustainable with low memory devices and makes it suitable for embedded platform implementation. 2. literature study a recent advancement in machine learning has obtained the greatest attention in classification models. various deep learning based neural networks outperformed the traditional methods of classification, achieving enormous classification accuracy. jia et al. [8] presented a detailed study on various deep learning-based palmprint recognition algorithms. all these algorithms succeeded in achieving classification accuracy ranging from 80% to 100%. from the computation study, it has been observed that gpu based computation efficient architecture requires at least 390m flop operations (i.e. scarletnas architecture) and minimum identification time of 183 ms for nasnet architecture (excluding training time). thus, deep learning provides the highest accuracy at the cost of computation time and hardware complexity. 223 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 another comparative analysis of palmprint recognition was presented in [9]. this study involved all traditional methods used in multispectral recognition including principle component analysis, fisher linear discrimination, fuzzy method, edge map generation, radon transform, etc. bounneche et al. [10] used oriented log-gabor filters to enhance the recognition rate. features obtained from the log-gabor filters were matched using hamming distance for palm identification. the feature extraction required an average time of 894 ms and a matching time of around 5.6 ms. to tackle the problem of misalignment, a local micro-structure tetra pattern (lmtrp) based local feature extraction was proposed in [11]. initially, gabor based features were obtained and later a histogram using lmtrp in local regions was generated for matching purposes. raghavendra et al. [12] proposed discrete wavelet transform based multi-spectral fusion of palm features. they extracted the average coefficients from dwt from each spectrum of the palm and fused these coefficients based on a weighted function. then inverse dwt was calculated to get a fusion of roi from the wavelet domain. for identification purposes, gabor filters were used with distance calculation. they achieved a 5.97 error rate in classification. the overall method was complex, as it requires multiple spectrum’s dwt feature fusion. the moving human leg angle-based gait recognition system is explained in [13] and uses average statistical features of eight frames. a least square regression model named salient and discriminative descriptor learning method described in [14] solved the sparse nonnegative noise interference error problem. kokila et al. used pca to extract the features and an ann model for matching purposes [15]. a simple basic operation (additions and subtractions) based method that forms code for a palmprint is described in [16]. chaudhari et al. [17] used a histogram of radon transform for feature extraction from low resolution images. jaafar et al. [18] touched on a less recognized algorithm, where a mobile camera was used for palm acquisition. they used histogram equalization and thresholding for feature extraction. a fuzzy based nearest centroid neighbor was proposed for palm recognition achieving accuracy of 98.78%. hong et al. [19] de-blurred palm images using a gaussian focused degradation model and a vese–osher decomposition model was used to extract the texture features from roi. the normalized correlation coefficient was calculated to find the similarity between two palms and obtained 0.9210 eer. a sparse based image enhancement, pca based dimensionality reduction and voting based recognition, was proposed in [20]. this algorithm was tested on a polyu dataset and obtained a 99.87% accuracy. tamrakar and khanna [28] used approximation coefficients obtained from the haar wavelet for feature extraction. further, the image was processed with a gaussian derivative to obtain local phase information. later,a block-based histogram was used as a feature vector for recognition. they claimed 100% recognition rate on polyu dataset. their extraction time and recognition time were lower (i.e. 16.942 ms and 188.4471 ms) but the training time requirement was 3502 ms. this paper presents a unique approach where feature extraction and matching require less time and make the system approachable to real-time. the proposed system uses dyadic wavelet transform, which is fast and compatible with hardware as it works in discrete and power of 2. the discriminative features obtained using signature formation makes it robust for intra-variation. further, reduction in matching time is obtained with exclusion of the coarsest level features. 224 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 3. discrete dyadic wavelet transform edges of the palm print are important features in the recognition process. an edge can be thought of as a series of fast transitions in image amplitude. for a given image f(x,y), the image gradient ∣∇f(x,y)∣ takes a local maximum value indicating the edge. however, image texture also obtains a similar transition. therefore, to discriminate the edge from the texture, scale factor needs to be considered in the calculation. the dyadic wavelets that account for the scaling and smoothing function can easily discriminate the edges from the texture regions. the ddwt of image f(x,y) calculated multi-scale edge at point (s,t) can be expressed as 𝑊𝑗 𝑘 (𝑠, 𝑡) =< 𝑓(𝑥, 𝑦)𝜑𝑗 𝑘 (𝑥 − 𝑠, 𝑦 − 𝑡) > (1) where j and k =1, 2 are integers andφ is the wavelet function which can be expressed as 𝜑𝑗 𝑘 (𝑥, 𝑦) = 2 𝑗 2𝜑(2𝑗 (𝑥, 𝑦) − 𝑘) (2) the modulus of ddwt |𝑊𝑗 𝑘 (𝑠, 𝑡)|reaches a maximum value locally in the neighbourhood of point (s,t). similar to the 1d example, the scale dependency of the magnitude of the modulus maxima is applied to the hölder exponent of f(x,y) and hence provides knowledge to differentiate between edges and textures. for a certain decision of wavelets, the ddwt change can be executed inside a fast hierarchical digital filtering scheme using multi-resolution analysis. a mallat pyramid based hierarchical filtering to obtain ddwt is shown in fig.1. fig.1: filter bank realization of a 1-d dyadic dwt at three levels (left) of dwt decomposition and (right) dwt reconstruction, where g(w) is a complex conjugate of h(w). in fig.2, 𝐻(𝜔) is a low pass filter, 𝐺(𝜔)is a high pass filter, and 𝐾(𝜔)is a high pass filter for 𝑟 = 1 and a low pass filter when 𝑟 = 2 and 𝑝 > 0. figure 2 represents the successive partition of the frequency spectrum. the initial frequency spectrum of [0, π] is divided into equivalent subintervals i.e. [0, π/2] and [π/2, π]. the upper spectrum has t/2 ddwt coefficients. these coefficients are the basis for the next level. in the next level of the decomposition from the previous level-1, the lower spectrum is further subdivided into two equal subintervals i.e. [0, π/4] and [π/4, π/2].the subdivision process proceeds, successively separating the lower subintervals until it can no longer go any further. 225 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 let the sampling shifted digital filter be expressed as𝐹𝑠(𝜔) = 𝑒 −𝑗𝜔𝑠𝐹(𝜔). this digital filter can be formulated to divide the spectrum into two intervals. the required condition in the design of these filters is that filters should be asymmetrical and they should have small compact support. the family 𝐺(𝜔), 𝐻(𝜔) 𝑎𝑛𝑑 𝐾(𝜔) that satisfy these conditions is expressed as 𝐻(𝜔) = 𝑒𝑗𝜔/2 (cos ( 𝜔 2 )) 2𝑝+1 𝐺(𝜔) = 4𝐽𝑒𝑗𝜔/2 ( sin ( 𝜔 2 )) 𝑟 𝐾(𝑤) = 1 − |𝐻(𝑤)|2 𝐺(𝑤) in the opposite operation of the decomposition referred as reconstruction, the signals are up-sampled to obtain the signal back. a unique approach of signature formation from these wavelet decompositions and reconstructions has been proposed in next section. fig.2: sample palm print signatures (a) palmprint roi (b) corresponding ps obtained with reference to the horizontal line passed from the center of the extracted roi. 4. palmprint feature extraction using ddwt the basic requirement in palmprint recognition is that obtained features shall be translation and rotation invariant. therefore, the region providing distinguished features (a) (b) (a) (b) (a) (b) 0 50 100 150 200 250 300 0 20 40 60 80 100 120 pixel number p ix e l in te n s it y signature of palmprint signature of palmprint 0 50 100 150 200 250 300 0 10 20 30 40 50 60 70 pixel number p ix e l in te n s it y signature of palmprint signature of palmprint 0 50 100 150 200 250 300 0 10 20 30 40 50 60 70 80 pixel number p ix e l in te n s it y signature of palmprint signature of palmprint 226 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 must be obtained first to extract these features. this region extraction process, consisting of five steps, is well explained in [21]. the main contribution of this paper lies here. the traditional wavelet approach uses multi-resolution edge-oriented features i.e. principle lines of palms, ridges i.e. loop, arch and whorl or cores and delta in the recognition process. this paper proposes the formation of zero-crossing signatures using ddwt. the ddwt is applied to this region providing unique features for recognition. these steps to obtain the zero-crossing signature of each palm are as follow: the palmprint's extracted roi has been used to plot the signature in the preprocessing operation step. to get the signature, a horizontal line is passed through the center of the roi. the pixel intensities are recorded on that line and a corresponding unique signature has been generated for each palmprint. figure 2 demonstrates the unique signatures obtained from three different palmprints. (a) (b) (a) (b) (a) (b) fig.3: the palmprint signatures at various scales (a) extracted roi of palmprint, (b) corresponding ps along with six resolution levels of the ddwt. the signals obtained using a piecewise constant function between sequences of two consecutive zeros are used as unique features to represent the palmprint instead of the zerocrossing of the wavelet transform at various scales. this signal is referred to as a piecewise constant function of palmprint signature (pcps). for ddwt, all scales are restricted 0 50 100 150 200 250 300 0 20 40 60 80 100 120 signature of palmprint lowpass filter 1 lowpass filter 2 lowpass filter 3 lowpass filter 4 lowpass filter 5 lowpass filter 6 0 50 100 150 200 250 300 0 10 20 30 40 50 60 70 signature of palmprint lowpass filter 1 lowpass filter 2 lowpass filter 3 lowpass filter 4 lowpass filter 5 lowpass filter 6 0 50 100 150 200 250 300 0 10 20 30 40 50 60 70 80 signature of palmprint lowpass filter 1 lowpass filter 2 lowpass filter 3 lowpass filter 4 lowpass filter 5 lowpass filter 6 227 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 with power of 2 only. the ps has been calculated with a finite resolution that forces a finer scale while calculating the dyadic wavelet transform instead of computing the wavelet transform on all scales of2𝑗 for j varying from -∞ to +∞. the resolution is restricted by the finite larger scale and a nonzero finer scale. for implementation purposes, the finer scale is equal to 1 and the largest scale is 2𝑗 . further experimentation has been carried out at different resolution/scales of ddwt. figures 3 and 4 present the ps and corresponding pcps obtained using ddwt at various scales. (a) (b) (a) (b) (a) (b) fig.4: piecewise constant function representation of ps (a) extracted roi of palmprint, (b) pcps corresponding to the lowest four resolution levels of the dyadic wavelet transform. 5. results and discussion polyu database [23], available on the internet, has been used for dyadic dwt testing for palmprint images as unimodal biometrics. in the experiment, 4 level dyadic decomposition was used. features based on discrete dyadic wavelets were measured to evaluate the performance accuracy of the proposed algorithm. when testing the algorithm, each image from the database was matched with the same dataset's remaining images. 0 50 100 150 200 250 300 -100 -50 0 50 100 150 zero crossing level 3 zero crossing level 4 zero crossing level 5 zero crossing level 6 0 50 100 150 200 250 300 -60 -40 -20 0 20 40 60 zero crossing level 3 zero crossing level 4 zero crossing level 5 zero crossing level 6 0 50 100 150 200 250 300 -80 -60 -40 -20 0 20 40 60 zero crossing level 3 zero crossing level 4 zero crossing level 5 zero crossing level 6 228 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 if the test image matched another image in the dataset, it was counted as correct matching. otherwise, it will be counted as incorrect matching. in the matching method, the euclidean distance between the feature sets was used. the minimum euclidean distance amongst two palmprints' features was considered the best fit for the test image for stored prototypes. the system's performance was calculated using false acceptance ration (far) and genuine acceptance ration (gar). fig.5: performance of the proposed algorithm of person identification using discrete dyadic wavelet transform in terms of percentage far and gar plotted at various thresholds. far represents that the system has accepted and recognized the imposter, and its values must be as low as possible. gar means true acceptance of the user. the far and gar percentages for palmprints were plotted, taking into account various threshold values. fig.6 shows this performance plot. the maximum recognition accuracy of 96.27% is achieved for palmprint images from the polyu database using dyadic dwt. the testing time of 0.76 seconds indicates the computational efficiency of the algorithm. the table 1 discusses the comparative analysis of the proposed dwt based signature model with other dwt based palmprint recognition models. table 1: palmprint recognition accuracy comparison using dwt approaches authors key points max. accuracy kozik and choraś [24] haar wavelet transform based geometrical feature extraction 94% giełczyk et al. [25] computationless geometric feature extraction 91% l. zhang and d. zhang [26] fusion of signatures of gravity, density, spatial disperse and energy in dwt domain 98% agrawal et al. [27] curvelet transform based energy computation 85% chaudhari et al. (proposed method) zero crossing signature using dyadic dwt 96.27% kozik and choraś [24] developed geometric characteristics from the haar wavelet transform and giełczyk et al. [25] proposed a further reduction in computation. zhang and zhang [26] calculated the statistical signatures across all the dwt scale using the density, energy, gravity, and dispersivity and achieved an accuracy of 98% at the cost of high future sets. in contrast, the proposed method uses the zero-crossing points to establish a 229 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 signature size of 4x 256 and can achieve near-by precision at the lower future level. thus, the strategy proposed is more effective than other methods focused on the dwt. table 2 presents the computational time requirement from the literatures section. as discussed, machine learning approaches can achieve better performance but at the cost of long computation i.e. training time. table 2 suggests that the accuracy of the traditional methods is also better and require less execution time. here, the extraction of the palm region has not been considered and computation has been partitioned into two parts: the feature extraction process and the matching process. gabor-based approaches require a long time for feature extraction since the large number of orientations and scales in gabor forms the large number of features. therefore, their feature extraction time is large. wavelet has only four bands per unit decomposition and therefore, it requires less execution time in comparison with gabor. therefore, the proposed approach requires shorter execution time of 21.04 ms including only feature extraction and matching. table 2: computation time comparison with related techniques reference method feature extraction time (ms) recognition time (ms) accuracy (%) bounneche et al. [10] gabor filter and hamming distance 894 5.6 99.33 li et al. [11] gabor filter + lmtrp histogram + euclidean distance 82.68 95.60 raghavendra et al. [12] fusion of haar dwt features from multiple spectrum 42000 (total) 96.52 tamrakar et al. [28] 16.94 304 99.98 hong et al. [18] debluring + vese– osher decomposition model 30.9 0.059 99.07 jaafar et al. [19] histogram equalization + thresholding + fuzzy k nearest centroid neighbor 255 (total) 98.78 imad et al. [20] sparse representation+ pca+ 2d-lda + voting 600 (total) 99.87 proposed dwt + palmprint signature 20.25 0.76 96.27 6. conclusion and future scope the fusion of features, i.e. multi-modal biometric, improves the accuracy at the cost of complexity and execution time. this paper presented an alternative to these two problems. dyadic dwt has been used in palmprint retrieval and identification. the energy of dyadic dwt is more concentrated in the vertical sideband. therefore, a dwt based multi-resolution analysis is performed to obtained coefficients characterizing the palm. a zero-crossing signature is created to represent the texture features of the palm roi using this sideband. the goal is to cut out recognition time and ensure recognition accuracy. the recognition accuracy has been improved to 96.27% without the fusion of 230 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 multiple features. therefore, we can say that it provides a light-weight palmprint verification framework. this may be aimed for mobile applications in the future. references [1] zhang dd. (2004) palmprint authentication. springer science & business media. [2] kim d, jung y, toh ka, son b, kim j. (2016) an empirical study on iris recognition in a mobile phone. expert systems with applications, 54: 328-339. [3] lunter j. (2021) everyday biometrics: can face replace fingerprint recognition?. biometric technology today, 2021(4): 7-10. [4] shawkat sa, al-badri ksl, turki ai. (2019) the new hand geometry system and automatic identification. periodicals of engineering and natural sciences, 7(3): 996-1008. [5] mewada hk, patel av, chaudhari j, mahantk, vala a. (2020) wavelet features embedded convolutional neural network for multiscale ear recognition. journal of electronic imaging, 29(4): 043029. [6] shaban al-ani m, mohammadi m, alyannezhadi mm. (2020) gait recognition based on measurements of moving human legs angles. international journal of engineering, 33(5): 975-983. [7] kong a, zhang d, lu g. (2006) a study of identical twins’ palmprints for personal authentication. in international conference on biometrics (pp. 668-674). springer, berlin, heidelberg. [8] jia w, xia w, zhao y, min h, chen yx. (2021) 2d and 3d palmprint and palm vein recognition based on neural architecture search. international journal of automation and computing, 18(3): 377-409. [9] aberni y, boubchir l, daachi b. (2019) multispectral palmprint recognition: a survey and comparative study. journal of circuits, systems and computers, 28(07): 1950107. [10] bounneche md, boubchir l, bouridane a, nekhoul b,ali-chérif a. (2016) multi-spectral palmprint recognition based on oriented multiscale log-gabor filters. neurocomputing, 205: 274-286. [11] li g, kim j. (2017) palmprint recognition with local micro-structure tetra pattern. pattern recognition, 61: 29-46. [12] raghavendra r, busch c. (2014) novel image fusion scheme based on dependency measure for robust multispectral palmprint recognition. pattern recognition, 47(6):2205-2221. [13] shaban al-ani m, mohammadi m, alyannezhadi mm. (2020) gait recognition based on measurements of moving human legs angles. international journal of engineering, 33(5): 975-983. [14] zhao s, zhang b. (2020) learning salient and discriminative descriptor for palmprint feature extraction and identification. ieee transactions on neural networks and learning systems, 31(12): 5219-5230. [15] kokila mk. (2020) accurate palm print verification with adaptive histogram equalization and deep learning algorithm. journal of critical reviews, 7(19): 3701-3710. [16] almaghtuf j, khelifi f, bouridane a. (2020) fast and efficient difference of block means code for palmprint recognition. machine vision and applications, 31(6): 1-10. [17] chaudhari j, patil pm, kosta yp. (2012) feature extraction using histogram of radon transform for palmprint matching. international journal of advances in engineering & technology, 5(1): 416. [18] jaafar h, ibrahim s, ramli da. (2015) a robust and fast computation touchless palm print recognition system using lheat and the ifkncn classifier. computational intelligence and neuroscience, 2015. [19] hong d, liu w, wu x, pan z, su j. (2016) robust palmprint recognition based on the fast variation vese–osher model. neurocomputing, 174: 999-1012. [20] rida i, al-maadeed s, mahmood a, bouridanea, bakshi s. (2018) palmprint identification using an ensemble of sparse representations. ieee access, 6: 3241-3248. 231 iium engineering journal, vol. 23, no. 1, 2022 chaudhari et al. https://doi.org/10.31436/iiumej.v23i1.2086 [21] zhang d, kong wk, you j, wong m. (2003) online palmprint identification. ieee transactions on pattern analysis and machine intelligence, 25(9): 1041-1050. [22] černá d, finěk v. (2017) quadratic spline wavelets with short support satisfying homogeneous boundary conditions. arxiv preprint arxiv:1712.03643. [23] the hong kong polytechnic university (polyu) multispectral palmprint database [online](2013). http://www.comp.polyu.edu.hk/~biometrics/multispectralpalmprint/msp.htm, 2013. [24] kozik r, choras m. (2010) combined shape and texture information for palmprint biometrics. ratio, 1(d2), d2. [25] giełczyk a, choraś m, kozik r. (2019) lightweight verification schema for image-based palmprint biometric systems. mobile information systems, 2019. [26] zhang l, zhang d. (2004) characterization of palmprints by wavelet signatures via directional context modeling. ieee transactions on systems, man, and cybernetics, part b (cybernetics), 34(3): 1335-1347. [27] agarwal s, sharma v, verma pk. (2019) palm print recognition using ceda. in 2019 3rd international conference on computing methodologies and communication (iccmc) (pp. 929-932). ieee. [28] tamrakar d, khanna p. (2016) kernel discriminant analysis of block-wise gaussian derivative phase pattern histogram for palmprint recognition. journal of visual communication and image representation, 40: 432-448. 232 227 iium engineering journal, vol. 13 no. 1, 2012 zaman et al. 27 effects of different methods of slaughtering on protein expression in chicken meat rahela zaman 1 , hamzah mohd. nassir 1 , nafiu bidemi abdurrazq 1 , hamzah mohd. salleh 2 and mohammad tariqur rahman 1 1 department of biotechnology science, faculty of science, international islamic university malaysia, jalan istana, bandar indera mahkota, 25200, kuantan, malaysia. 2 department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. tarique@iium.edu.my abstract: this study investigated the variation in total protein profile in chicken skeletal muscle which is thought to be influenced by variations in the method of slaughtering. two types of samples, depending on the method of slaughtering using a sharp knife, were examined. these were: (i) ctneck was cut off completely and body was tied until the animal expired, and (ii) prneck was cut off partially leaving the spinal cord intact and the body was released immediately after slaughtering. proteins, expressed in higher amounts, were mostly found to be distributed in the range of mw 4566 kda -as resolved using sds-page. 2d-page resolution showed differences in protein expression between the samples. protein spotted on the gel near ph 5.0 and mw 116 kda was found in the skeletal muscle from ct samples but were absent in the pr samples. abstrak: variasi profil jumlah protein di dalam otot skeletal telah dikaji dengan jangkaan bahawa ianya dipengaruhi oleh kaedah penyembelihan yang berbeza. berdasarkan kaedah penyembelihan, dua jenis sampel telah diperiksa: (i) ct – leher telah dipotong sepenuhnya dan badan haiwan diikat hingga mati and (ii) pr – leher dipotong separuh meninggalkan kord tulang belakang dalam keadaan sempurna dan badan dilepaskan serta-merta selepas penyembelihan. kandungan protein didapati tinggi dalam taburan mw 45-66 kda sebagai terurai menggunakan sds-page. sementara itu, kandungan protein yang berbeza diperhatikan di dalam penguraian 2d-page. tompok protein kelihatan pada gel sekitar ph 5 dan mw 116 kda telah dijumpai pada ct otot skeletal, tetapi tidak kelihatan pada sampel pr. keywords: 2d-page; slaughtering; protein; slaughtering 1. introduction methods of poultry slaughtering varies depending on the concern over painless sacrifice of the animal applying pre-slaughtering stunning; ease of handling in case of industrial slaughtering by applying physical restriction such as shackling; and consumers’ safety. animals are also sacrificed based on ritual slaughtering laws such as halal (for muslims) and kosher (for jews). recommended codes for halal and kosher slaughtering involve cutting off the carotid arteries, jugular vessels, esophagus and trachea in the throat, without any specific reference to pre-slaughter stunning. in halal slaughtering practice, stunning is allowed with certain restrictions [1]. variation in slaughtering eventually iium engineering journal, vol. 13 no. 1, 2012 zaman et al. 28 determines the time needed to die and it varies enormously, depending on which blood vessels in the neck are cut [2]. in this study, chickens are slaughtered manually by cutting ventrally both of the jugular veins and carotid arteries without pre-slaughtering stunning. possible changes in total protein profile were observed in skeletal muscle due to variation in handling the chicken during slaughtering. i.e., whether or not (i) the chicken will be released immediately after slaughtering and (ii) the neck is completely or partially severed effects the expression of protein. beheading or complete severing of the neck raptures the spinal cord while releasing the animal immediately after slaughtering allows free muscle movements until the death. earlier it was reported that, separation of the jugular vein and carotid arteries leaving the nerves intact to function, shortens the time of death compared to other methods; and separation of whole head disrupts the nervous system (spinal cord damage) by causing asphyxia and suffocation [2]. these differences influence neurophysiologic response mediated muscular movement. on the other hand, existence of external pressure on muscle such as keeping the animals tied up until the animal dies might affect the suffering level. therefore, it has been hypothesized that those variations during slaughtering might affect the neurophysiological parameters of the chicken that could be reflected by the variation in protein expression. 1d and 2d polyacrylamide gel electrophoresis (page) are used to study differential expression of total protein. in this study, possible variations in differentially expressed proteins in chicken skeletal muscle were assessed using 1d and 2d-page. chickens were slaughtered in either way: (i) ctneck was cut off completely and body was tied until the animal died and (ii) prneck was cut off partially leaving the spinal cord intact and body was released immediately after slaughtering. 2. materials and methods 2.1 sample preparation slaughtering method applied in this study was conventional manual slaughtering which is practiced universally. all experiments were conducted at research facilities at kulliyyah of science, international islamic university malaysia. animal handling and management procedures were carried out in accordance with the ethical guidelines of international islamic university malaysia (iium). twenty one (21) days old chickens (weight 750-850 g), purchased from local farm, were slaughtered in either of the following conditions: (i) necks were partially cut-off (by cutting both of the jugular veins, carotid arteries and oesophagus without cutting the spinal cord) and birds were released immediately after slaughtering (pr); (ii) necks were completely cut-off and birds remained restrained immediately after slaughtering (ct). approximately 1 g of muscle sample was homogenized on ice in 10 ml of 0.25 m phosphate buffer (ph 7.5) with 0.1% triton x-100. solution was then centrifuged at 6000×g for 30 min at 4° c and supernatant was collected and preserved in 1ml aliquots at -80° c until further use. protein quantification was then performed with spectrophotometer at 595 nm. 2.2 protein quantification solubilized protein was quantified using the bradford assay. five milliliter of bradford reagent (ge healthcare, uppsala, sweden) was mixed with 100 µl of sample solution. iium engineering journal, vol. 13 no. 1, 2012 zaman et al. 29 prior to that, the sample solution was diluted (1/10 dilution). absorbance value was measured at 595 nm. a standard curve was generated with serial dilutions of bovine serum albumin (bsa) to get the concentrations of the samples. 2.3 sds-page to resolve the variation in total protein profile in terms of their molecular weight equal amount of protein (120 µg) were electrophorsed on 12.5% polyacrylacimde gel in denaturing condition in a 6×8cm 2 dimensional gel (mini-protean 3 cell, biorad, hercules, usa ) with 250 v. to further verify the result two other samples were ran on 12.5% gel of 8×12 cm 2 dimensions in se 600 ruby™ vertical unit (ge healthcare) with 450 v. all the gels were stained with coomassie brilliant blue. 2.4 two-dimensional gel electrophoresis to further resolve the variation in total protein profile, samples were also electrophoresed in 2d gel essentially followed by manufacturer’s instruction (ge healthcare). briefly, sample was mixed by vortexing with rehydration buffer and incubated at room temperature (rt) for 30 min. sample (200 µl) containing 120 µ g of protein was loaded to 11 cm of immobilized ph gradient (ipg) strip, ph 3-10 in immobiline drystrip reswelling tray and left on desk at room temperature overnight ensuring proper rehydration of the strip. isoelectric focusing (ief) was conducted with multiphor ii (ge healthcare). strips were placed on the plastic aligner on top of the glass tray, gel faced up. ief was conducted at 1 ma and 10° c in 3 steps 300 v for 3 h and 30 min, 3500 v for 1 h and 30 min and 3500 v for 1 h and 45 min. the strips were then equilibrated in two steps each for 15 min at room temperature using 10 ml sds equilibration buffer containing 6 m urea, 50 mm tris-hcl (ph 8.8), 30% glycerol, 2% sds and 0.002% bromophenol blue, and either 50 mg dtt (for first step) or 125 mg iodoacetamide (for 2nd step). the strips were then applied to 12.5% sds polyacrylamide gel for electrophoresis using se 600 ruby™ vertical unit (ge healthcare) at 45 v overnight at 16° c. at the end of the run, proteins in gel were visualized by silver staining using plusone silver staining kit (ge healthcare). each sample was run in duplicate to minimize the gel to gel biasness. 2.5 gel analysis gels were analyzed with image master 2d platinum (v 7.0) (ge healthcare). parameters for spot detection were as follows: minimum area 100; smooth factor 4.0; saliency 115. a gel was used as reference gel from each group. comparative analysis was done by comparing the intensity of individual spots within and between groups. differential expression of a spot was considered when all four gels showed the upor down-regulation of the protein. 3. results 3.1 protein quantification muscle proteins were solubilized in pb buffer with 0.1% triton x-100 and then assessed for protein concentration with spectrophotometer. protein concentrations were found between 5.3-11.1 µ g/µ l (table 1). iium engineering journal, vol. 13 no. 1, 2012 zaman et al. 30 table 1: protein concentration in meat solubilized in pb buffer. sample id protein conc.(µ g/µl) pr 12.23 � 4.14 ct 13.22 � 7.79 3.2 total protein profile showed differential protein expression due to difference in slaughtering samples were then run on polyacrylamide gel that separates proteins based on molecular weight (mw) (fig. 1). protein profiles of ct and pr were found different both in terms of presence or absence of bands and on their intensity when resolved in a gel of smaller dimension (6×8 cm 2 ) (arrow marked in fig. 1a). further resolution in gel of higher dimension (8×12 cm 2 ) demonstrated similar variations in protein profile (arrow marked in fig. 1b). notably the variations were identified with the proteins having mw in the range between 45-66 kda. fig. 1 chicken total skeletal muscle protein expression in 12.5% sds-page gel. (a) protein samples were resolved on gel (6×8 cm 2 ) pr (lane 1) and ct (lane 2). difference in band intensity are marked with arrow between 66-45 kda. (b) proteins from each sample were run in duplicates: pr (lane 1 &2); ct (lane 3 & 4) on gel (8×12 cm 2 ). the arrow identifies band intensity difference in similar region between 6645 kda. 3.3 total protein profile showed differential protein expression due to difference in slaughtering for 2d-gel electrophoresis, 1 st dimension was carried out in precast ipg strips, ph range 3.0-10. after first dimension separation based on protein pi value, proteins were transferred to 2 nd dimension, 12.5% polyacrylamide gel which separates protein based on mw. figure 2 shows two representative gels from two different types of sample, pr and iium engineering journal, vol. 13 no. 1, 2012 zaman et al. 31 ct. gels were matched with the help of specialized image analysis software, image master 2d platinum (v 7.0) (ge healthcare). the differentially expressed protein was marked with circle. in ct, it has been expressed near ph 5.0 and mw 116 kda while it is absent in pr (fig. 2). comparison between the differentially expressed proteins with their magnified and cropped image and respective 3d view that were generated (fig. 3) with the software also demonstrated the proteins spotted in the said location from the sample ct. fig. 2 differential protein expression in samples pr (a) and ct (b) in 2d-gel electrophoresis. protein spot identified with differential expression is marked in circle. protein spotted in ct near ph 5.0 and mw 116 kda which is absent in pr. fig. 3 image analysis of the differentially expressed proteins. 3d view using image master 2d platinum (v 7.0) (ge healthcare) of the spots identified from the 2-d gels (fig 2) shows the 3-dementional image manifestation of the area for the protein in sample ct (b) compared to that from sample pr (a). iium engineering journal, vol. 13 no. 1, 2012 zaman et al. 32 4. discussion poultry slaughtering may involve physical restriction of the bird by shackling. difference in poultry slaughtering practices is also observed in terms of cutting the neck, with or without injuring spinal cord during slaughtering. variation in these two parameters i.e., physical restriction and spinal cord damage is expected to affect the neurophysiogcal in/activation hence alter the expression of protein at neuromuscular junction. this study investigated the changes in protein expression, due to the variations in slaughtering techniques, as mentioned above, in muscle samples collected from slaughtered chickens. total proteins were resolved by sds-page in gels with two different dimensions: 6×8 cm 2 (fig. 1a) and 8×12 cm 2 (fig. 1b). protein bands were found to be distributed between higher (116 kda) and lower (14 kda) molecular weights. highly expressed proteins are distributed within mw of 35-66 kda. the protein bands between mw 35-66 kda were previously identified as albumin, pyruvate kinase, beta-enolase and creatine kinase [3]. these proteins are also reported as highly expressed in chicken skeletal muscle. expression pattern and intensity of the proteins were found similar when compared the resolution of the bands between two gels having different dimensions (fig. 1). the differentially expressed proteins were identified when total proteins were resolved in 2d-page based on the pi and mw of the proteins. proteins differentially expressed in different conditions of slaughtering have been marked with circles in reference gels (fig. 2). quantitative and qualitative assessment of the protein expressed in low level by 2dpage has been considered as a common drawback of the technique [4]. however when a large number of proteins are expressed in higher amount it is also hard to identify the variation in expression using 2d-page. despite all the shortcomings, it is considered as one of the best methods to get a glance of soluble proteins which may form a ground for further studies on differentially expressed protein [5]. therefore, variation in protein expression in the current study as observed in sds-page was analyzed by 2-d gel electrophoresis and matched within the set of four gels and then between pair of slaughtering techniques. protein spotted near ph 5.0 and mw 116 kda in ct were absent in pr. one of the possible candidate for this protein to be the 20s catalytic subunit of the enzyme acetylcholine esterase (ache) having mw 110 kda [6], expression of which is expected to be altered at neuromuscular junction (nmj) due to variation in neurophysiological in/activation. notably, the 20s subunit is the heavier, collagen tailed, asymmetric form of ache in birds which was found to be a hybrid molecule with three subunitsache catalytic subunit (apparent mw 110 kda), buche catalytic subunit (72 kd) and a collagenous tail subunit (58 kda) [6]. this preliminary observation of the total protein expression with the differentially expressed proteins as spotted will be further analyzed for identification and characterization. acknowledgement this research was supported by the research grant from the ministry of higher education, malaysia (frgs 01-06-24), basic and applied biomedical research cluster unit and faculty of science, iium. authors are grateful to assoc. prof. dr. azura amid, shahidah abu samah and maliza azrain for their support and advices. iium engineering journal, vol. 13 no. 1, 2012 zaman et al. 33 references [1] m lópez m, carrilho mc, campo mm, lafuente r, halal slaughter and electrical stunning in rabbits: effect on welfare and muscle characteristics." proceedings of the 9th world rabbit congress, verona, italy, 10-13 june 2008. world rabbit science association, 2008. [2] davis karen, in prisoned chickens, poisoned eggs: an inside look at the modern poultry industry. summertown: book publishing company; 2009. [3] rivers j, simpson dm, robertson dh l, gaskell sj, beynon rj, absolute multiplexed quantitative analysis of protein expression during muscle development using qconcat. molecular & cellular proteomics 6.8 (2007): 1416-27. [4] kint g, sonck kaj, schoofs g, de coster d, vanderleyden j, de keersmaecker scj, 2d proteome analysis initiates new insights on the salmonella typhimurium luxs protein. bmc microbiology 9.1 (2009): 198. [5] ohlendieck k. skeletal muscle proteomics, current approaches, technical challenges and emerging techniques. skelet muscle 1.1 (2011): 6-6. [6] t tsim, k. w., william r. randall, and eric a. barnard, synaptic acetylcholinesterase of chicken muscle changes during development from a hybrid to a homogeneous enzyme. the embo journal 7.8 (1988): 2451-56. abbreviations 2d-page: two dimensional polyacrylamide gel electrophoresis ief: isoelectric focusing application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 coronary heart disease classification using improved penguin emperor optimization-based long short term memory network rajeshwari maramgere ramaiah1*and kavitha kuntaegowdanalli srikantegowda2 1 department of computer science & engineering, visvesvaraya technological university, belagavi-590018, karnataka, india 2 department of computer science and engineering, dayananda sagar college of engineering, bengaluru, karnataka 560078, india * corresponding author: rajeshwari_maya1@yahoo.com (received: 24 december 2022; accepted: 26 january 2023; published on-line: 4 july 2023) abstract: ventricular fibrillation (vf) is the most life-threatening and dangerous type of cardiac arrhythmia (ca), with a mortality rate of 10-15% in a year. therefore, early detection of cardiac arrhythmia is important to reduce the mortality rate. many machine learning algorithms have been proposed and have proven their usefulness in the classification and detection of heart problems. in this research manuscript, a novel long short term memory (lstm) classifier with improved penguin optimization (ipeo) is implemented for vf classification. the ipeo is used in finding optimal hyperparameters that overcome the overfitting problem. the presented model is tested, trained, and validated using two standard datasets that are available publicly: massachusetts institute of technology-beth israel hospital (mit-bih) and the china physiological signal challenge (cpsc) 2018 dataset. both of them consist of ecg recordings for five seconds of coronary heart disease (chd) patients. furthermore, fuzzy c-means and enhanced fuzzy rough set method (fcm-etifrst) are used for feature selection to extract informative features and to cluster membership degree, non-membership degree, and hesitancy degree. on the mit-bih dataset, the proposed model achieved accuracy, sensitivity, specificity, precision, and matthews’s correlation coefficient (mcc) of 99.75%, 98.29%, 98.39%, 98.35%, and 97.79% respectively. on the cpsc 2018 dataset, the proposed model achieved accuracy of 99.79%, sensitivity of 99.11%, specificity of 98.20%, precision of 99.43%, and mcc of 98.57%. hence, the results proved that the proposed method provides better results in the classification of vf. abstrak: pemfibrilan ventrikel (vf) adalah ancaman nyawa nombor satu dan jenis aritmia jantung (ca) berbahaya dengan kadar kematian 10-15% setahun. oleh itu, pengesanan awal aritmia jantung sangat penting bagi mengurangkan kadar kematian. terdapat banyak algoritma pembelajaran mesin yang telah dicadangkan dan terbukti berkesan dalam pengelasan dan pengesanan sakit jantung. kajian ini mencadangkan kaedah baru pengelasan memori ingatan jangka panjang pendek (lstm) dengan pengoptimuman penambahbaikan penguin (ipeo) yang dilaksanakan bagi klasifikasi vf. ipeo digunakan bagi mencari hiperparameter yang dapat mengatasi masalah padanan berlebihan. model yang dicadangkan diuji, dilatih dan disahkan menggunakan dua dataset piawai yang dapat diperoleh secara terbuka: institut teknologi hospital massachusettsbeth israel (mit-bih) dan cabaran signal psikologi cina 2018 (cpsc). kedua-dua data ini mempunyai rakaman ecg selama lima saat daripada pesakit penyakit jantung koronari (chd). malah, kajian itu turut menggunakan purata-c kabur dan kaedah set 67 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 kasar kabur dipertingkat (fcm-etifrst) untuk pemilihan bagi mengekstrak ciri-ciri dan mengelaskan kelompok tahap keahlian, bukan ahli dan tahap keraguan. bagi dataset mit-bih, model yang dicadangkan mencapai ketepatan, tahap sensitif, tahap spesifik, kejituan dan pekali kaitan matthews (mcc) sebanyak 99.75%, 98.29%, 98.39%, 98.35%, dan 97.79% masing-masing. bagi dataset cpsc 2018 pula, model yang dicadangkan mencapai ketepatan sebanyak 99.79%, 99.11% tahap sensitif , 98.20% tahap spesifik, 99.43% kejituan dan 98.57% mcc. oleh itu, dapatan kajian membuktikan kaedah yang dicadangkan menunjukkan keputusan lebih baik dalam pengelasan vf. keywords: coronary heart disease; fuzzy c-means and enhanced fuzzy rough set method; improved penguin emperor optimization; long short term memory; ventricular fibrillation 1. introduction as per the world health organization (who), coronary heart disease (chd) is a substantial global epidemic and the most common cause of death worldwide, accounting for one in every three deaths. coronary heart disease (chd) is a substantial global epidemic and the most common cause of death worldwide, accounting for one in every three deaths. in 2002, 16.7 million cardiac disease (cd)-related deaths were reported, and this is expected to rise to 23.3 million by 2030 [1]. age, obesity, smoking, exercise, hypertension, diabetes, and high blood cholesterol are all risk factors for cd. heart disease diagnosis is conducted using a variety of medical tests, a medical history, and an examination of the patient's lifestyle. there are many variables to consider when diagnosing heart diseases, thus a specialist is usually involved [2-3]. the contraction of the ventricles that exceeds 100 bpm causes ventricular tachycardia (vt), and when the ventricles' contraction exceeds 500 bpm, it is referred to as ventricular fibrillation (vf), which is the most abnormal cardiac arrest. vt and vf are the two subsets of ventricular arrhythmias (vas) [4]. nearly all countries face a significant coronary artery disease (cad) burden, due to limited resource availability for providing comprehensive health care of cad patients, and insufficient awareness campaigns on such diseases [5]. various machine learning methods are developed to detect chd at an early stage using different software libraries and platforms to extract huge amounts of information from large datasets. the predictive analysis of chd includes preprocessing the data collected from datasets, preparing the data for implementing suitable algorithms, training, testing, and validating the chosen model, and making final predictions with fine-tuned parameters [6,7]. atrial fibrillation (af) detection has been done in many types of research depending on the activities of the atrial region of the heart, which also includes the detection of p-wave, the entropy of wavelet samples, and the detection of fwaves [8]. to detect p-wave or r-r wave irregularities with manual instructions on longterm ecg recordings, af uses currently available algorithms. any change to p waveform in shape or blunt from lead 2 and 4 results in irregularity, and it directly relates to the condition of atrial activity since it is known as a depolarization wave of the atrial region [910]. in this work, a design of methodology to detect and classify chd is developed by using ecg signals of mih-bit and cpsc 2018 dataset. the major contributions of the paper are described as follows: • to resolve the problem of class imbalance and dimensionality curse, the method of fcm-etifrst has been included in the process of feature selection. • for accurate classification of mit-bih arrhythmia and cpsc 2018 datasets with reduced overfitting issues, an efficient lstm classification has been considered. 68 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 • an improved penguin emperor optimization (ipeo) has been proposed in this research for finding the optimal hyperparameters to operate lstm without overfitting issues. this is done by improving the exploitation and exploration stage of peo by levy flight and gaussian mutation mechanism. 2. literature review li et al. [11] developed a novel feature fusion framework that used phonocardiogram (pcg) signals of 175 subjects to identify cad features. a sum of 110 features from different domains were extracted, reduced, and selected. the obtained images were taken as cnn input for feature learning. the feature selection and the features of deep learning were then combined and led to a multilayer perceptron for classification purposes. this proposed framework outperformed deep learning features and multi-domain features with the highest accuracy, sensitivity, and specificity. too many features inhibit the model learning process and result in poor generalization, which is a limitation of this work. future work can be focused on improving the detection accuracy of cad by using dynamic features and multichannel pcg signals. nguyen et al. [12] developed a stacking method to predict atrial fibrillation (af) from ecg signals and perform statistical segment-based feature recognition, which was done by support vector machine (svm), the segmentation units produced by a convolutional neural network. to validate this method, the ecg dataset from the physionet/computing in cardiology challenge 2017 was used, which contained 8528 ecg recordings. the proposed method applied to the same dataset and metric outperformed state-of-the-art methods with a high f1 score. the limitation of this method was the nature of the dataset that was chosen. the af signal segment was not included with af due to the absence of information about af or the occurrence of other ecg signals. the proposed method was applied to other medical signal-related problems. jahmunah et al. [13] proposed an automated system (as) using automated categorization of ecg signals with cnn, which classified signals into normal, cad, myocardial infarction (mi), and congestive heart failure (chf) classes. the proposed gaborcnn achieved better performance with 98.5% accuracy. the use of gaborcnn resulted in low computational complexity which was an added advantage for this work. furthermore, the system was validated with a large database and was seen to exhibit the highest potential to assist clinicians in screening for cvds using ecg signals. only a few subjects and smaller datasets were used for cad and chf, which was the limitation of this work. to improve the classification accuracy of gaborcnn, more data needs to be trained to the network in the future, so that the onset of cad is detected early and prevented from progressing to mi or chf. tseng et al. [14] developed a method for vf prediction which was a novel deeplearning method. for training and validation of the data, ecgs from mit-bih datasets were used. the estimated results demonstrated that the proposed two-dimensional short-time fourier transform (2d stft)/continuous wavelet transform (cwt) convolutional neural network (cnn) model achieved the highest recall and accuracy. the proposed model was also compared with 1d cnn and 2d time-domain models and again achieved the highest accuracy. the database did not identify concomitant diseases, and the influence of these diseases on ecg signals was unknown, which was one of the limitations of this work. in the future, larger datasets should be used to build a more accurate model. additional data from conventional and portable hospital vital sign monitors, as well as wearable devices should be collected. panigrahy et al. [15] proposed a novel approach to detect the vf rhythm that involved algorithms namely: support vector machine (svm), adaptive boosting (adaboost) and differential evolution (de). these algorithms were implemented with the help of optimal variable combinations. the training and test datasets were taken and 69 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 validated from three databases namely the arrhythmia database, cudb database, and mitbih malignant ventricular arrhythmia databases for this methodology. the proposed approach achieved the highest accuracy, sensitivity, and specificity in detecting vf rhythm. further, the proposed method was suitable for implementation during real time detection of vf rhythm. çınar et al. [16] developed a deep learning architecture with svm for the classification of normal sinus rhythm (nsr) which was based on hybrid alex-net along with ecg signals of abnormal arrhythmia (arr) and congestive heart failure (chf). this approach was implemented on 192 ecg signals, out of which 96 were arrhythmias, 30 were chfs, and 36 were nsrs. svm and knn algorithms were implemented on arr, chr, and nsr signals for classification purposes. later on, these signals were classified using long short-time memory (lstm). chen et al. [17] proposed a cnn model for ca classification from ecg signals of the china physiological signal challenge (cpsc) 2018 dataset. the dataset provided 6,877 recordings with a 12-lead ecg dataset, in which different types of diagnoses for 476 patients were predicted. the proposed technique obtained an overall highest f1-score, and first rank in the classification-and-challenge competition. this approach still needed to be filtered to achieve an equal level of performance on other datasets, which is a limitation of this work. various ca types and wearable ecg devices are possible to be developed for use with this approach in the future. 3. methodology the framework for the proposed work is a combination of feature selection with fcmetirst and lstm classification with improved emperor penguin optimization (iepo) hyperparameter optimization for reducing the problems of dimensionality curse and overfitting in chd analysis and it is illustrated in fig. 1. because of the nature of time-step order in cnn with its several hidden layers, it is used to extract the features from the complex data of ecg signals. the characteristics of time will be taken by the layers of lstm while classification is skipped at the stage of feature extraction. to optimize the computational resources and make more efficient detection of chd, the proposed ipeo algorithm is utilized to optimize hyperparameters of lstm. the steps of the proposed methodology workflow are designed as shown in fig. 1. fig. 1: flowchart of the proposed iepo based lstm model. 3.1 data pre-processing ecg recordings of vf patients are considered from two datasets namely mit-bih and cpsc 2018. the mit-bih dataset consists of 23 publicly available ecg recordings which include four types of rhythms: af, vf, av junction, and normal. however, in this work, only vf signals are classified and sampled at a frequency of 250hz. the proposed algorithm is implemented for detecting vf by pre-processing ecg signals in a window length of 5 70 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 seconds. the cpsc 2018 also consists of ecg signals in which all forms of arrhythmias are available. all signals are segmented into a number of episodes, where each episode is labeled by the clinician and divided into training, test, and validation datasets. two leads are selected for this work from the dataset, and the data is divided into vf and non-vf categories. the ecg signals from the cpsc dataset are sampled at a frequency of 500hz and segmented into 5-second episodes. a lead 1 sample signal from the cpsc dataset is considered, as shown in fig. 2, and is segmented into normal signal and vf signal as shown in fig. 3(a) and fig. 3(b). lead 2 normal signal and vf signal are shown in fig. 4(a) and fig. 4(b) respectively. fig. 2: sample signal from mit-bih dataset. (a) (b) fig. 3. lead 1 sample signal (a) normal, (b) vf. 71 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 (a) (b) fig. 4: lead 2 sample signal (a) normal, (b) vf. 3.2 feature extraction here, the extraction of features is done using cnn layer architecture which is based on the 1-d framework. timing characteristics and sequence of data can be retained with the representation of cnn-related features in the proposed framework. the following features are to be extracted from the proposed chd framework. 3.2.1 1-d approximation and details coefficients by use of low pass and high pass filtering operations on the transform coefficients group, a set of coefficients namely, ‘approximation from low pass’ and ‘detail from high pass’ is obtained. consider the parameters of coefficients for approximation and details to be 𝐶𝐴𝑗 and 𝐶𝐷𝑗 correspondingly, in case of a stationary signal, the transform their properties for the level of 𝑗 as mentioned in eq. (1) and eq. (2). 𝐸(𝐶𝐴𝑗 ) = √2−𝑗 𝑁 ∫ 𝑓(𝑡) (1) 𝐸(𝐶𝐷𝑗 ) = √2 −𝑗 ∫ 𝑓(𝑡)𝐸𝑛[𝜑(2 −𝑗 𝑡 − 𝑛)]𝑑𝑡 (2) where 𝐶𝐴𝑗 and 𝐶𝐷𝑗 are parameters of coefficients at the level of 𝑗, 𝐸𝑛 represents the wavelet transform of the signals at 𝑛-level coefficients, 𝜑(𝑡) and 𝑓(𝑡) represents the wavelet coefficient transformation functions. n represents the total number of wavelets obtained from the signal. 3.2.2 hjorth activity signal power is represented using an activity parameter that is time function variance, as given in eq. (3). this activity denotes the power spectrum surface in the frequency domain. 𝐴𝑐𝑡𝑖𝑣𝑖𝑡𝑦 = 𝑣𝑎𝑟(𝑦(𝑡)) (3) where the signal is denoted using 𝑦(𝑡). 3.2.3 hjorth mobility the mean frequency or power spectrum of standard deviation proportion is represented as a mobility parameter. a first derivative variance of the square root of signal 𝑦(𝑡) divided by signal variance 𝑦(𝑡), which is explained in eq. (4). 72 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 𝑀𝑜𝑏𝑖𝑙𝑖𝑡𝑦 = √ 𝑣𝑎𝑟( 𝑑𝑦(𝑡) 𝑑𝑡 ) 𝑣𝑎𝑟(𝑦(𝑡)) (4) 3.2.4 hjorth complexity the frequency change is denoted using the complexity parameter. the signal’s similarity and a pure sine wave are compared using the parameter, where the value converges to 1 if the signal is similar, as given in eq. (5). 𝐶𝑜𝑚𝑝𝑙𝑒𝑥𝑖𝑡𝑦 = 𝑀𝑜𝑏𝑖𝑙𝑖𝑡𝑦( 𝑑𝑦(𝑡) 𝑑𝑡 ) 𝑀𝑜𝑏𝑖𝑙𝑖𝑡𝑦(𝑦(𝑡)) (5) 3.2.5 mean curve length (mcl) katz fractal dimensions are measured using mcl and this measures eeg signals activity, as given in eq. (6). 𝐶𝐿[𝑛] = 1 𝑁 ∑ |𝑥[𝑚] − 𝑥[𝑚 − 1]|𝑘𝑚=𝑘−𝑁+1 (6) where the epoch last sample is denoted as 𝑘, the window length is denoted as 𝑁, and the eeg time series is denoted as 𝑥[𝑚]. 3.2.6 mean teager energy (mte) eeg research was widely carried out using mte feature, as given in eq. (7). 𝑀𝑇𝐸[𝑘] = 1 𝑁 ∑ (𝑥[𝑚 − 1]2 − 𝑥[𝑚]𝑥[𝑚 − 2])𝑘𝑚=𝑘−𝑁+3 (7) where the last epoch sample is denoted as 𝑘, the window length is denoted as 𝑁, and the eeg time series is denoted as 𝑥[𝑚]. 3.2.7 zero crossing rate the rate of signal changes from negative to zero to positive or positive to zero to negative is denoted as zero-crossing rate (zcr), as in eq. (8). 𝑍𝐶𝑅 = 1 𝑇−1 ∑ 1𝑅<0(𝑆𝑡 𝑆𝑡−1) 𝑇−1 𝑡=1 (8) where the indicator function is denoted as 1𝑅<0 and the length of the signal is denoted as 𝑆. the above-mentioned features are extracted and forwarded to the process of feature selection for further enhancement of dimensionality and to enable better output on the overfitting of classifiers. 3.3 feature selection the fcm – etifrst feature selection method is applied to the extracted features to select relevant features for arrhythmia classification. 3.3.1 fuzzy c means feature selection on the proposed method is done based on the clustering of fuzzy cmeans and enhanced fuzzy rough set method. the fcm method has the advantage of producing better results for overlapped datasets than the k-means method. the data point is an assigned membership to every cluster to form the appropriate cluster [18]. the data point is applied with membership based on the distance between the data point and cluster center 𝑐. if more data is near to 𝑐, then the cluster has more data point membership. 73 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 the estimated membership is increased for every iteration. an enhanced fuzzy c-means algorithm is implemented in the proposed method. the algorithm is given as follows: step 1: clusters number 𝑐 varies from 2 to 𝑐𝑚𝑎𝑥. a certain value 𝑐 is considered and initial class prototypes are selected and use 𝜖 > 0. step 2: image 𝜍 of new linearly weighted sum in terms of 𝜍𝑘 is calculated using eq. (9). 𝜍𝑘 = 1 1+𝛼 (𝑥𝑘 + ( 𝛼 𝑁𝑅 ) ∑ 𝑥𝑗𝑗∈𝑁𝑘 ) (9) where 𝑘𝑡ℎ pixel gray value of 𝜍 are 𝜍𝑘 and 𝑥𝑘 (8-bit resolution is usually encoded for gray value) respectively. the neighbor 𝑥𝑗 and the set of neighbours 𝑁𝑘 is present in a window which is nearby 𝑥𝑘. the mean-filtered pixel value is ∑ 𝑥𝑗𝑗∈𝑁𝑘 where neighbor terms’ effect controls 𝛼 with a value approximately near to 1. step 3: image matrix 𝜍 is updated using eq. (10). 𝑓𝑖𝑙 = (𝜍𝑙−𝑣𝑖) −2 𝑠−1 ∑ (𝜍𝑙−𝑣𝑗) −2 𝑠−1𝑐 𝑗=1 (10) the 𝑖𝑡ℎ cluster prototype is 𝑣𝑖 and 𝑓𝑖𝑙 is gray value 𝑙 of fuzzy membership that is with respect to cluster 𝑖. the 𝑙 value varies from 1 to the number of gray levels denoted as 𝑑 (gray level has a maximum value of 256 levels) of the image and each fuzzy membership of 𝑠 weighted component parameter that estimates the final classification of fuzziness. step 4: prototype 𝑣𝑖 is calculated using eq. (11). 𝑣𝑖 = ∑ 𝑥𝑙𝑓𝑖𝑙 𝑠𝜍𝑙 𝑑 𝑖=1 ∑ 𝑥𝑙𝑓𝑖𝑙 𝑠𝑑 𝑖=1 (11) convergence criteria are measured as |𝑣𝑛𝑒𝑤 − 𝑣𝑜𝑙𝑑 | < 𝜖 by repeating step 3 and 4, cluster prototypes hold vectors 𝑣 that is represented as 𝑣 = [𝑣1, 𝑣2 … … 𝑣𝑐 ]. 3.3.2 enhanced fuzzy rough set feature selection the fcm has a wide range of applications and is significantly applied in numerous fuzzy clustering methods. every sample point of membership degree to the class center is used as objective function optimization [19]. euclidean distance is applied for the objective function of the sample point and clustering center. solving the non-similarity index value function is the minimum value of every clustering center. the generalization is given in eq. (12). 𝐽(𝑈, 𝑐1, 𝑐2, … , 𝑐𝑐 ) = ∑ 𝐽𝑖 𝑐 𝑖=1 = ∑ ∑ 𝑢𝑖𝑗 𝑚𝑑𝑖𝑗 2𝑛 𝑗 𝑐 𝑖=1 (12) where the weighted index number is denoted as 𝑚, the 𝑗𝑡ℎ sample point of 𝑖𝑡ℎ clustering center of euclidean distance is 𝑑𝑖𝑗 = 𝑘𝑐𝑖 − 𝑥𝑗𝑘 , the fuzzy set of clustering center, and 𝑢𝑖𝑗 is between 0 and 1. the constraint formula of the lagrangian multiplier is constructed based on the derivate of input parameters in eq. (13) and eq. (14) to reach the minimum. 𝑐𝑖 = ∑ 𝑢𝑖𝑗 𝑚𝑥𝑗 𝑛 𝑗=1 ∑ 𝑢𝑖𝑗 𝑚𝑛 𝑗=1 (13) 𝜇𝑖𝑗 = 1 ∑ ( 𝑑𝑖𝑗 𝑑𝑘𝑗 ) 2 𝑚−1 𝑐 𝑘=1 (14) 74 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 the fcm outputs are centers 𝑐 and membership matrix 𝑈. every object degree contains 𝑈, which belongs to centers 𝑐. a fuzzy rough set of lower approximations is given in eq. (15). 𝑠𝑖𝑚𝑎(𝑥𝑖 , 𝑥𝑗 ) = 1 − √𝛼 (𝜇𝑎(𝑥𝑖 ) − 𝜇𝑎(𝑥𝑗 )) 2 + 𝛽 (𝑣𝑎(𝑥𝑖 ) − 𝑣𝑎 (𝑥𝑗 ) 2 + 𝛾 (𝜋𝑎 (𝑥𝑖 ) − 𝜋𝑎 (𝑥𝑗 ) 2 )) (15) where object 𝑥𝑖 of hesitancy degree, non-membership, and membership are denoted as 𝜋𝑎(𝑥𝑖 ), 𝜐𝑎(𝑥𝑖 ) and 𝜇𝑎(𝑥𝑖 ), respectively. the weighted factors are 𝛼, 𝛽 and 𝛾. each pixel membership degree is normalized and initialized as in eq. (16). 𝜇𝐷 (𝑥𝑖𝑗 ) = 𝑥𝑖𝑗−(𝑥𝑖𝑗)𝑚𝑖𝑛 (𝑥𝑖𝑗)𝑚𝑎𝑥 −(𝑥𝑖𝑗)𝑚𝑖𝑛 (16) where the image pixel of minimum and maximum intensity is denoted as (𝑥𝑖𝑗 )𝑚𝑎𝑥 and (𝑥𝑖𝑗 )𝑚𝑖𝑛 . complexity is reduced in the normalization process, which calculates in between 0 and 1. non-membership value is present in the new method in uncertain presence. a high grade of certainty is measured based on observations when the membership value is near 0 or 1 and the membership value is near 0.5 for a high grade of uncertainty. non-membership value is measured in eq. (17) 𝑣𝐷 (𝑥𝑖𝑗 ) = (1 − 𝜇𝐷 (𝑥𝑖𝑗 )) (𝑒𝑥𝑝 ( −𝜇𝐷(𝑥𝑖𝑗) 𝑎𝜎 )) 1 𝑎 (17) where (𝜇𝐷 (𝑥𝑖𝑗 )) membership value measures standard deviation , which is in the range of 0.39 – 0.41. the hesitation degree is measured using 𝜋𝐷 (𝑥𝑖𝑗 ) = 1 − 𝜇𝐷 (𝑥𝑖𝑗 ) − 𝑣𝐷 (𝑥𝑖𝑗 ). every feature of fuzzy clustering gets every object membership degree, as given in eq. (18). 𝜇𝑅𝑎(𝑥) = 𝑈𝐹𝐶𝑀(𝑎)[𝑥] (18) model equality is based on equivalence relations; approximate similarity or equality is measured based on fuzzy equivalence. fuzzy equivalence relation 𝑅 is used, as in eq. (19). 𝑅(𝑥, 𝑦) = 𝑎−𝑎|𝑥−𝑦|+𝑏𝑚𝑖𝑛(𝑥,𝑦) 𝑎−(𝑎−1)|𝑥−𝑦|+𝑏𝑚𝑖𝑛(𝑥,𝑦) (19) the size of the opening on one side is denoted as value 𝑏. if 𝑏 is equal to 0, then the function makes sure to balance two objects, otherwise it is not able to balance the two objects. 3.4 improved emperor penguin optimization for hyperparameter optimization in iepo, three strategies are incorporated into epo to maintain a suitable balance between exploration and exploitation to solve the drawback of the standard epo [20]. these strategies are opposition-based learning, levy flight, and gaussian mutation. equation (20) contains the fundamental formula for the epo algorithm, which moves the penguins toward the center to locate the ideal value by measuring their distance from one another in the population. however, it is simple to get caught in the local optimal problem when the epo algorithm optimizes the hyperparameters of lstm. the strategy strengthens the bonds between penguins and improves each penguin's capacity for jumping to address this issue. the hyperparameters taken for lstm have been given in the following table 1. 75 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 the distance between the penguins is represented mathematically, as shown in eq. (20), with the term depth. the proposed method incorporates the gaussian mutation (gm) into eq. (20) because the epo's unpredictability is a vulnerability. table 1: hyperparameters for long short term memory hyperparameters range number of hidden layers 3-10 dropout 0.2 0.5 decay rate 0.2-0.9 learning rate 0.0 0.1 momentum 0.5 0.9 batch size 32,64,128,256 epochs 10-100 the gm has excellent randomization capabilities, which it can use to strengthen the penguin relationships and accomplish the goal of leaving the local optimal. the following formula can be used to represent the updated mathematical model: 𝑃𝑒𝑞 (𝑥 + 1) = 𝑃(𝑥) − 𝐴 × 𝐷𝑒𝑝⨁𝐺(𝛼) (20) the individual penguins are then observed to move slowly while readily guiding the swarm to the regional ideal. the suggested strategy enhances the individual penguin's update position formula by utilizing the levy flight's strong stochastics. the levy flight expands the swarm's search area while simultaneously improving each penguin's capacity to jump. the best penguin can therefore swiftly arrive at the greatest answer. this is how it is formulated: 𝑃 𝑙𝑒𝑣𝑦 𝑒𝑞(𝑥 + 1) = 𝑃(𝑥) × 𝐿𝑒𝑣𝑦 − 𝐴 × 𝐷𝑒𝑝⨁𝐺(𝛼) (21) where, 𝑃 𝑙𝑒𝑣𝑦 𝑒𝑞 represents the updated position of the 𝑖th solution. through the levy flight mechanism, a new candidate solution is generated, which increases the knowledge diffusion across objects and yields a better solution, as levy flight is a random process and the jump size leads to the levy probability distribution function. the best penguin may also leave the search arena due to the addition of levy flight and the strong randomness of gaussian mutation. by doing this, the swarm might avoid falling into the infinite cycle and also the best solution from being updated. the opposition based learning (obl) is added to the epo algorithm to reduce the upgraded algorithm's ability to jump. the obl broadens the search domain's exploration, which in turn diversifies the swarm. it can be created using eq. (22) 𝑃𝑒𝑞 = 𝑃𝑚𝑎𝑥 + 𝑃𝑚𝑖𝑛 − 𝑃𝑏𝑒𝑠𝑡 + 𝑟(𝑃𝑏𝑒𝑠𝑡 − 𝑃𝑒𝑞 ) (22) where 𝑃𝑒𝑞 is the 𝑖𝑡ℎ opposite penguin’s location within the search domain. the 𝑖𝑡ℎ variables lower and upper bounds are 𝑃𝑚𝑎𝑥 and 𝑃𝑚𝑖𝑛 respectively. 𝑃𝑏𝑒𝑠𝑡 is the location of the best penguin, and r is an element-filled random vector within the range[0,1](0,1). p is the 𝑖th penguin in the population's position vector. then, based on the fitness of the opposing sites, the best penguin is modified. to make the penguin change more quickly and discover the best value for the chosen hyperparameters, the new technique delivers greater performance and higher convergence velocity. 76 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 3.5 classification using lstm due to its outstanding performance in the extraction of temporal and spatial variables, the classification network used in the framework is an lstm and its architecture is shown in fig. 5. according to fig. 5, the model is made up of an input layer, a single lstm cell, a hidden layer, a normalization layer, and a classification layer. performance is improved by the idea of integrating the most recent data along with older data to predict the subjects one step ahead. with the benefits of a hidden layer selffeedback mechanism, the lstm model solves the long-term dependence problem [21]. gates of input state, output state, and forget state in the lstm model are known to be three unique gates that are used to update data that are meant to be stored in the memory cell. fig. 5: lstm architecture. the input feature for lstm is denoted and it contains the characteristics obtained via fcm-etirst. the previous instant output of the lstm cell is marked as ℎ𝑡 , a cell of the memory unit is represented, and the output of the lstm cell is indicated for the unit of lstm input data at a time. the following steps illustrate the lstm unit's process. 1) as shown in eq. (1), the cell of memory for the candidate, the matrix of weight and the bias are assessed in (23). 𝑐�̃� = 𝑡𝑎𝑛ℎ (𝑊𝑐 . [ℎ𝑡−1, 𝑥𝑡 ] + 𝑏𝑐 ) (23) 2) the gate of the input state modifies the memory state value depending upon the data input being used at the time; the function activation of sigmoid, matrix of weight, and bias are shown in eq (24). 𝑖𝑡 = 𝜎(𝑊𝑖 . [ℎ𝑡−1, 𝑥𝑡 ] + 𝑏𝑖 ) (24) 3) by using past data, the gate of forget state modifies the memory state value; the bias gate is indicated by the weight matrix which is given in eq (25). 𝑓𝑡 = 𝜎(𝑊𝑖 . [ℎ𝑡−1, 𝑥𝑡 ] + 𝑏𝑓 ) (25) 4) as shown in eq (26), the value of the most recent lstm unit is calculated by measuring the value of the current memory state. 𝑐𝑡 = 𝑓𝑡 ∗ 𝑐𝑡−1 + 𝑖𝑡 ∗ 𝑐�̃� (26) where the dot product is represented by "*". depending upon the state values of the last and candidate cells, the input state and forget state gates regulate the updated memory cell. 5) the matrix of weight in the layer 𝑊0, the bias 𝑏0, and the output value of the gate controls the output of the memory cell value, as shown in eq. (27) 77 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 eq.𝑜𝑡 = 𝜎(𝑊0. [ℎ𝑡−1, 𝑥𝑡 ] + 𝑏0) (27) 6) as shown in eq. (28), the output of the lstm is measured as: ℎ𝑡 = 𝑜𝑡 ∗ 𝑡𝑎𝑛ℎ (𝑐𝑡 ) (28) according to the 3 gates of control and memory state, the lstm continuously stores, reads, resets, and updates the data. because the lstm internal parameter is shared, the weight matrix's dimensions are changed to regulate the size of the output unit. the lstm's input and feedback are separated by a significant amount of time. the internal state of the memory cell's architecture maintains a constant error flow, and the gradient doesn't explode or vanish [22]. the lstm classifier predicts the type of arrhythmia present in the chd and those results are evaluated in the following section. 4. results in this work, the proposed modified model is replicated using enhanced lstm with the system requirements. the performance of the modified model is analyzed by means of sensitivity, specificity, accuracy, f-score, and mcc on the actual educational dataset. the feature length of 506 is obtained after feature selection. specificity is defined as the test to appropriately recognize the areas that are negatively less in learning skills. sensitivity is defined as the test to correctly identify the regions that are positively high in learning skills. further, accuracy is the most important performance measure that is utilized in the lms, where it is the ratio of correctly predicted observations to the total observations. accuracy, sensitivity, specificity, and mcc are mathematically defined in the eqs. (29) to (33), 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐𝑖𝑡𝑦 = 𝑇𝑁 𝐹𝑃+𝑇𝑁 × 100 (29) 𝑆𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦 = 𝑇𝑃 𝐹𝑁+𝑇𝑃 × 100 (30) 𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = 𝑇𝑃+𝑇𝑁 𝑇𝑃+𝑇𝑁+𝐹𝑃+𝐹𝑁 × 100 (31) f-score is determined as the harmonic mean of the model's recall and precision, and its mathematical equation is followed in eq. (32). 𝐹 − 𝑠𝑐𝑜𝑟𝑒 = 2𝑇𝑃 2𝑇𝑃+𝐹𝑃+𝐹𝑁 × 100 (32) 𝑀𝐶𝐶 = 𝑇𝑃×𝑇𝑁−𝐹𝑃×𝐹𝑁 √(𝑇𝑃+𝐹𝑃)(𝑇𝑃+𝐹𝑁)(𝑇𝑁+𝐹𝑃)(𝑇𝑁+𝐹𝑁) × 10 (33) 4.1 quantitative analysis the performance analysis of enhanced lstm without augmentation in accuracy, sensitivity, specificity, f-score, and mcc, with and without feature selection, are shown in tables 2, 3, 4 and 5 respectively. table 2 demonstrates the quantitative analysis of different classifiers with and without feature selection for the mit-bih dataset. table 3 demonstrates the quantitative analysis of different classifiers with and without feature selection for the cpsc 2018 dataset. the performance measure of classifiers on the mit-bih dataset with feature selection is highest compared to those without feature selection. the accuracy, sensitivity, specificity, precision, and mcc of neural network (nn), rnn (recurrent neural network), gan (generative adversarial network), and dnn (deep neural network) are measured and compared with the proposed iepo-based lstm. the obtained results show that the proposed iepo based lstm achieves the highest values with the accuracy of 99.75%, the 78 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 sensitivity of 98.29%, specificity of 98.29%, the precision of 98.35%, and mcc of 97.79% while considering feature selection compared to the other classifiers. the simulation results of the proposed method by varying different classifiers on mit-bih dataset, with and without feature selection are specified in fig. 6 and fig. 7. table 2: simulation results of iepo-based lstm by varying the classifiers for the mit-bih dataset without feature selection results methods accuracy (%) sensitivity (%) specificity (%) precision (%) mcc (%) nn 88.99 87.53 89.44 88.91 86.5 rnn 90.49 88.63 90.84 90.71 89.4 gan 91.99 90.53 93.74 92.81 90.4 dnn 93.39 91.73 95.64 94.81 92.1 iepo based lstm 96.29 95.83 95.74 95.51 94.3 with feature selection results nn 90.69 89.53 92.14 91.31 87.7 rnn 92.32 94.18 95.61 92.71 92.34 gan 92.25 92.28 89.98 91.43 89.91 dnn 90.86 94.53 93.21 93.04 90.56 iepo based lstm 99.75 98.29 98.29 98.35 97.79 fig. 6: performance of mit-bih arrhythmia classification without feature selection. fig. 7: performance for mit-bih arrhythmia classification with feature selection. 79 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 table 3: simulation results of iepo based lstm by varying the classifiers for cpsc 2018 dataset without feature selection results for cpsc 2018 dataset methods accuracy (%) sensitivity (%) specificity (%) precision (%) mcc (%) nn 85.49 86.03 87.04 90.71 88.6 rnn 88.02 88.58 89.61 92.71 90.44 gan 89.15 90.38 90.28 91.03 91.71 dnn 92.16 93.63 92.71 93.94 92.16 iepo based lstm 95.75 94.09 94.19 95.35 94.49 with feature selection results methods accuracy (%) sensitivity (%) specificity (%) precision (%) mcc (%) nn 90.28 90.05 91.13 92.09 88.43 rnn 92.03 94.68 96.56 93.48 91.90 gan 90.40 92.58 89.59 91.55 88.81 dnn 50.28 51.65 52.75 53.23 51.65 iepo based lstm 99.79 99.11 98.20 99.43 98.57 the performance measure of classifiers on cpsc dataset with feature selection is highest when compared with the values of performance metrics without feature selection. the accuracy, sensitivity, specificity, precision, and mcc of neural network (nn), rnn (recurrent neural network), gan (generative adversarial network), and dnn (deep neural network) are measured and compared with the proposed iepo-based lstm. the obtained results show that the proposed iepo based lstm achieves highest values with accuracy of 99.79%, sensitivity of 99.11%, specificity of 98.20%, precision of 99.43% and mcc of 98.57% while considering with feature selection compared to the other classifiers. the simulation results of the proposed method by varying different classifiers on cpsc dataset with and without feature selection are specified in fig. 8 and fig. 9. fig. 8: performance for cpsc arrhythmia without feature selection. the fcm – etifrst method selects the unique features to represent the class that solves the problem of imbalance and overfitting. the modified non-membership function helps to provide exploitation, and the modified membership function performs exploration. the similarity measure helps to maintain the exploration and exploitation of the feature 80 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 selection process. lstm shows higher sensitivity than other classifiers due to its efficiency in handling the features. fig. 9: performance for cpsc arrhythmia without feature selection. table 4 describes the performance of optimizing the hyperparameters of lstm using various multi-objective optimization methods like particle swarm optimization (pso), fruit fly optimization (ffo), anti colony optimization (aco), salt swarm optimization algorithm (ssa) with the selected features obtained from fcm-etirst on mit-bih arrhythmia dataset. in the observation, the results infer that the proposed iepo algorithm has chosen the best set of hyperparameters for lstm to perform at its better stage, when compared to the resultant parameters obtained from other optimization algorithms. it also shows an improvement of around 3% in accuracy compared to the existing optimization algorithm ssa. the performance comparison of different hyperparameter optimization techniques on mit-bih dataset, with and without feature selection is graphically represented in fig. 10 and fig. 11. table 5 represents the performance analysis of k-fold validation in terms of performance metrics like accuracy, sensitivity, specificity, precision, and mcc on the mitbih dataset and its graphical representation is specified in fig. 12. table 4: comparison of hyper parameter optimization method on mit-bih dataset without feature selection hyper parameter optimization method comparison methods accuracy (%) sensitivity (%) specificity (%) precision (%) mcc (%) pso 85.89 84.69 86.14 80.59 86.38 ffo 83.33 84.23 84.06 83.24 86.00 aco 96.17 92.03 94.83 97.08 97.54 ssa 95.31 90.67 96.00 94.04 96.30 iepo based lstm 98.95 99.49 99.49 98.45 97.99 with feature selection hyper parameter optimization method pso 85.89 84.69 86.14 80.59 86.38 ffo 83.33 84.23 84.06 83.24 86.00 aco 96.17 92.03 94.83 97.08 97.54 ssa 95.31 90.67 96.00 94.04 96.30 iepo based lstm 98.95 99.49 99.49 98.45 97.99 81 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 fig. 10: performance of hyper parameter optimization with feature selection. fig. 11: performance of hyper parameter optimization without feature selection. table 5: performance analysis of k-fold validation on mit-bih dataset [13] k-fold values accuracy (%) sensitivity (%) specificity (%) precision (%) mcc (%) 4-fold 97.99 97.08 97.55 97.19 96.65 5-fold 98.95 99.49 99.49 98.45 97.99 7-fold 97.83 96.09 97.19 97.95 96.74 9-fold 97.47 96.28 96.15 96.37 95.45 10-fold 98.67 95.47 96.33 95.93 90.61 82 fig. 12: k-fold validation performance. iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 5. comparative analysis the comparative analysis of the proposed vf classification using ipeo based lstm to the existing boosted svm based de algorithm and hybrid cnn-svm deep neural networks using the lstm model in terms of accuracy, specificity, sensitivity, and precision is shown in table 6. the proposed model is trained, tested, and validated using two publicly available standard datasets namely the massachusetts institute of technology-beth israel hospital (mit-bih) and the china physiological signal challenge cpsc 2018 dataset and both consist of ecg recordings for 5 seconds of coronary heart disease (chd) patients. the accuracy was improved to 99.75%, with a specificity of 98.29%, a sensitivity of 98.39% and the precision held was 98.35%. the proposed ipeo was evaluated for efficient classification using the vf technique by overcoming overfitting problems and dataset classification. table 6: comparative analysis of existing svm classifier to the lstm classifier technique dataset accuracy (%) specificity (%) sensitivity (%) precision (%) boosted svm based de algorithm[15] mit-bih 98.20 98.18 98.25 hybrid cnn-svm deep neural networks using lstm [16] cpsc 98.69 99.99 97.74 iepo based lstm mit-bih 99.75 98.29 98.39 98.35 cpsc 98.11 97.21 97.79 98.29 6. conclusion in this paper, a novel classification method for classifying vf rhythm has been developed on the mit-bih and cpsc datasets consisting of ecg recordings of chd patients. the method uses an lstm classifier to classify vf and fcmetifrst for feature selection and performs clustering of membership, non-membership, and hesitancy degrees. the method uses a window size of 5 seconds that requires less memory and obtained the highest accuracy of 99.75%. the proposed algorithm, on the other hand, combines traditional machine learning algorithms and cnn algorithms. the deep cnn was able to successfully extract useful deep features for ecg classification from raw ecg signals without prior knowledge of ecg signals or cardiac rhythm disorders. the proposed method outperformed the existing classification models on chd by improving the efficiency of arrhythmia classification with suitable hyperparameter optimization in the lstm algorithm. the improved performance of the proposed method on different test datasets suggests that it has the potential for clinical application. future work can be focused on improving classification accuracy for both vf and af by considering a window size of more than 5 seconds and it will be analyzed in real-time events. data availability statement dataset links: mit bih arrhythmia dataset : https://archive.physionet.org/cgi-bin/atm/atm cpsc 2018 dataset: http://2018.icbeb.org/challenge.html 83 https://www.google.com/url?q=https://archive.physionet.org/cgi-bin/atm/atm&sa=d&source=hangouts&ust=1624608195408000&usg=afqjcngjsoxp998cptdavixph-7vull_hq https://www.google.com/url?q=http://2018.icbeb.org/challenge.html&sa=d&source=hangouts&ust=1624608195408000&usg=afqjcnegvgvyymehdztimj9f0yajsei0ja iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 references [1] nilashi m, ahmadi h, manaf aa, rashid ta, samad s, shahmoradi l, aljojo n, akbari e. (2020) coronary heart disease diagnosis through self-organizing map and fuzzy support vector machine with incremental updates. int. j. fuzzy syst., 22(4): 1376-1388. https://doi.org/10.1007/s40815-020-00828-7 [2] khan mu, aziz s, iqtidar k, zaher gf, alghamdi s, gull m. (2022) a two-stage classification model integrating feature fusion for coronary artery disease detection and classification. multimedia tools and applications, 81(10): 13661-13690. https://doi.org/10.1007/s11042-021-10805-3 [3] shah sms, shah fa, hussain sa, batool s. (2020) support vector machines-based heart disease diagnosis using feature subset, wrapping selection and extraction methods. comput. electr. eng., 84: 106628. https://doi.org/10.1016/j.compeleceng.2020.106628 [4] mohanty m, dash m, biswal p, sabut s. (2021) classification of ventricular arrhythmias using empirical mode decomposition and machine learning algorithms. prog. artif. intell., 10(4):489504. https://doi.org/10.1007/s13748-021-00250-6 [5] muhammad lj, algehyne ea. (2021) fuzzy based expert system for diagnosis of coronary artery disease in nigeria. health and technology, 11(2): 319-329. https://doi.org/10.1007%2fs12553-021-00531-z [6] nasarian e, abdar m, fahami ma, alizadehsani r, hussain s, basiri me, zomorodimoghadam m, zhou x, pławiak p, acharya ur, tan rs, sarrafzadegan s. (2020) association between work-related features and coronary artery disease: a heterogeneous hybrid feature selection integrated with balancing approach. pattern recognit. lett., 133: 33-40. https://doi.org/10.1016/j.patrec.2020.02.010 [7] apostolopoulos id, groumpos pp. (2020) non-invasive modelling methodology for the diagnosis of coronary artery disease using fuzzy cognitive maps. comput. methods biomech. biomed. eng., 23(12): 879-887. https://doi.org/10.1080/10255842.2020.1768534 [8] ma c, wei s, chen t, zhong j, liu z, liu c. (2020) integration of results from convolutional neural network in a support vector machine for the detection of atrial fibrillation. ieee trans. instrum. meas., 70(2504610): 1-10. https://doi.org/10.1109/tim.2020.3044718. [9] chen x, cheng z, wang s, lu g, xv g, liu q, zhu x. (2021) atrial fibrillation detection based on multi-feature extraction and convolutional neural network for processing ecg signals. comput. methods programs biomed., 202: 106009. https://doi.org/10.1016/j.cmpb.2021.106009 [10] kumari cu, murthy asd, prasanna bl, reddy mpp, panigrahy ak. (2021) an automated detection of heart arrhythmias using machine learning technique: svm. mater. today proc., 45(2): 1393-1398. https://doi.org/10.1016/j.matpr.2020.07.088 [11] li h, wang x, liu c, zeng q, zheng y, chu x, yao l, wang j, jiao y, karmakar c. (2020) a fusion framework based on multi-domain features and deep learning features of phonocardiogram for coronary artery disease detection. comput. biol. med., 120: 103733. https://doi.org/10.1016/j.compbiomed.2020.103733 [12] nguyen qh, nguyen bp, nguyen tb, do tt, mbinta jf, simpson cr. (2021) stacking segment-based cnn with svm for recognition of atrial fibrillation from single-lead ecg recordings. biomed. signal process. control, 68: 102672. https://doi.org/10.1016/j.bspc.2021.102672 [13] jahmunah v, ng eyk, san tr, acharya ur. (2021) automated detection of coronary artery disease, myocardial infarction and congestive heart failure using gaborcnn model with ecg signals. comput. biol. med., 134: 104457. https://doi.org/10.1016/j.compbiomed.2021.104457 [14] tseng lm, tseng vs. (2020) predicting ventricular fibrillation through deep learning. ieee access, 8: 221886-221896. https://doi.org/10.1109/access.2020.3042782 [15] panigrahy d, sahu pk, albu f. (2021) detection of ventricular fibrillation rhythm by using boosted support vector machine with an optimal variable combination. comput. electr. eng., 91: 107035. https://doi.org/10.1016/j.compeleceng.2021.107035 84 iium engineering journal, vol. 24, no. 2, 2023 ramaiah and srikantegowda https://doi.org/10.31436/iiumej.v24i2.2698 [16] çınar a, tuncer sa. (2021) classification of normal sinus rhythm, abnormal arrhythmia and congestive heart failure ecg signals using lstm and hybrid cnn-svm deep neural networks. comput. methods biomech. biomed. eng., 24(2): 203-214. https://doi.org/10.1080/10255842.2020.1821192 [17] chen tm, huang ch, shih es, hu yf, hwang mj. (2020) detection and classification of cardiac arrhythmias by a challenge-best deep learning neural network model. iscience, 23(3): 100886. https://doi.org/10.1016/j.isci.2020.100886 [18] chang kc, hsieh ph, wu my, wang yc, chen jy, tsai fj, shih es, hwang mj, huang tc. (2021) usefulness of machine learning-based detection and classification of cardiac arrhythmias with 12-lead electrocardiograms. can. j. cardiol, 37(1): 94-104. https://doi.org/10.1016/j.cjca.2020.02.096 [19] cai w, chen y, guo j, han b, shi y, ji l, wang j, zhang g, luo, j. (2020) accurate detection of atrial fibrillation from 12-lead ecg using deep neural network. comput. biol. med., 116: 103378. https://doi.org/10.1016/j.compbiomed.2019.103378 [20] rai hm, chatterjee k. (2022) hybrid cnn-lstm deep learning model and ensemble technique for automatic detection of myocardial infarction using big ecg data. appl. intell., 52(5):5366-5384. https://doi.org/10.1007/s10489-021-02696-6 [21] baral s, alsadoon a, prasad pwc, al aloussi s, alsadoon oh. (2021) a novel solution of using deep learning for early prediction cardiac arrest in sepsis patient: enhanced bidirectional long short-term memory (lstm). multimedia tools and applications, 80(21-23): 3263932664. https://doi.org/10.1007/s11042-021-11176-5 [22] sun l, wang y, he j, li h, peng d, wang y. (2020) a stacked lstm for atrial fibrillation prediction based on multivariate ecgs. health inf. sci. syst., 8(1): 19. https://doi.org/10.1007/s13755-020-00103-x 85 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 97 towards a scalable scientific data grid model and services azizol abdullah1, mohamed othman1, md nasir sulaiman1, hamidah ibrahim1, abu talib othman2 1faculty of computer science and information technology universiti putra malaysia, 43400 serdang, selangor, malaysia 2 abstract: scientific data grid mostly deals with large computational problems. it provides geographically distributed resources for large-scale data-intensive applications that generate large scientific data sets. this required the scientist in modern scientific computing communities involved in managing massive amounts of a very large data collections that are geographically distributed. research in the area of grid has given various ideas and solutions to address these requirements. however, nowadays the number of participants (scientists and institutions) that are involved in this kind of environment is increasing tremendously. this situation has lead to a problem of scalability. in order to overcome this problem we need a data grid model that can scale well with the increasing number of users. peer-to-peer (p2p) is one of the architectures that is a promising scale and dynamism environment. in this paper, we present a p2p model for scientific data grid that utilizes the p2p services to address the scalability problem. by using this model, we study and propose various decentralized discovery strategies that intend to address the problem of scalability. we also investigate the impact of data replication that addresses the data distribution and reliability problem for our scientific data grid model on the propose discovery strategies. for the purpose of this study, we have developed and used our own data grid simulation written using parsec. we illustrate our p2p scientific data grid model and our data grid simulation used in this study. we then analyze the performance of the discovery strategies with and without the existence of replication strategies relative to their success rates, bandwidth consumption and average number of hop. keywords: scientific data grid, peer-to-peer, data grid model, data discovery universiti kuala lumpur 50250 kuala lumpur, malaysia e-mails: {azizol, mothman, nasir, hamidah}@fsktm.upm.edu.my abutalib@unikl.edu.my 1. introduction in modern scientific communities, the number of researchers involved in managing massive amounts of very large data collections through a geographically distributed environment is increasing. they need an infrastructure that can provide services to support their requirements to create a high-performance computing environment. recently, research in the area of grid has given various ideas and solutions to address these requirements. however, as the numbers of participants (scientists and institutions) that involve in this collaboration environment keep increasing with the awareness of the iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 98 benefit from grid implementation, we are now facing with a new problem on how to provide a scalable infrastructure with scalable services for this environment. it is very difficult task to provide a scalable infrastructure with scalable services that can support high-performance computing environment. as discussed by venugopal et al. [27], currently there are four different data grid model that have being manifested. however, these models are not scale when the number of user increased since they are based on centralized architecture. over the last few years, the peer-to-peer (p2p) network has become a major research topic. the success of p2p networks was originally boosted by some very popular file sharing applications (e.g., napster). it seems that the p2p network has provides a scalable file sharing environment. we argued that, the issues of scalability in grid might also be solved by using p2p model and p2p services since these two: the grid and p2p computing represents the same notion of sharing resources available at the edge of the internet but with different purpose and target users. a data grid system connects a collection of geographically distributed computer and storage resources that may be located in different parts of a country or even in different countries, and enables user to share data and other resources [1]. recently, there are a few research projects directed towards the development of data grid such as particle physics data grid (ppdg) [2], grid physics network (griphyn) [3], the china clipper project [4], and storage request broker (srb) [5] which are aim to build scientific data grid that enable scientists sitting at various universities and research labs to collaborate with one another and share data sets and computational power. the size of the data that needs to be accessed on those data grid is on the order of terabytes today and is soon expected to reach petabytes. as an example, the large hadron collider (lhc) experiment [12] at cern is producing terabytes of raw data a year, and by 2008, this experiment will produce petabytes of raw data a year that needs to be pre-processed, stored, and analyzed by teams comprising 1000s of physicists around the world. through this process, more derived data will be produced and 100s of millions of files will need to be managed and stored at more than 100s of participating institutions. off course, the number of participations will increase and there is a need to provide a more scalable environment that could support this requirement. in scientific environments, even the data sets are created once and then remain reads only, but the data sets usage often leads to creation of new files, inserting a new dimension of dynamism into a system [13, 14]. ensuring efficient access to such huge and widely distributed data is a serious challenge and critical to network and data grid designer. the major barrier to supporting fast data access in a data grid system are high latencies of wide area network (wans) and the internet, which impact the scalability and fault tolerance of total data grid systems. there are a number of research groups investigating a number of data replication approaches on the data distribution for data grid, in order to improve its ability to access data efficiently [17-20]. in this study, we used a different approach in addressing the scalability problem by proposing a scientific data grid model based on peer-to-peer (p2p) and this model used p2p services. using this model we then study various decentralized discovery strategies which the heart of this model. in this paper, we also investigate the data replication approaches for data distribution to address the data distribution and reliability problem for our scientific data grid model and study the impact of these approaches on the propose discovery strategies. to evaluate the model and selected discovery strategies, we have developed our own data grid simulation using iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 99 parsec. the simulation used to generate different network topologies to study the impact of discovery strategies on the cost of locating data and the data access on the overall scientific data grid. the paper is organized as follows. section 2 gives an overview of previous work on discovery strategies. in section 3, we describe our scientific data grid model. section 4 describes the simulation study and our simulation results. finally, we present a brief conclusion and future directions in section 5. 2. related works in this section, we discussed more on discovery since discovery is a core grid functionality that enhances the accessibility of data in our proposed model. support for handling and discovering resource capabilities already exist in some metacomputing system such as globus [21] and legion [22]. in globus, the globus resource allocation manager (gram) acts as a resource broker is responsible for resource discovery within each administration domain, which works with an information service, and a co-allocator for monitoring current state of resources, and managing an ensemble of resources respectively. in legion system, resources and tasks are describe as a collection of interacting objects. a set of core object, enable arbitrary naming of resources based on legion object identitifers (loids) and legion object addresses (loa). specialized services such as binding agents and context objects are provided to translate between arbitrary resource name and its physical location – enabling the resource discovery to be abstracted as a translation between loids and physical resource location. in condor [23], resource describes their capabilities as an advertisement, which is subsequently matched with an advertisement describing the needs of an application. most of these strategies based on a centralized approach, which may not be as scale. in a large and dynamic environment such as grid, the discovery service should be decentralized in order to avoid potential computation bottlenecks at a point and be more scale. in the last couple of years, peer-to-peer (p2p) system became fashionable [6-9, 11]. they emphasize two specific attributes of resources sharing communities: scale and dynamism. most of existing p2p systems such as gnutella, freenet, can [15] and chord [16] provide their own discovery mechanisms and focus on specific data sharing environment and, therefore on specific requirements. as example, gnutella emphasis on easy sharing and fast file retrieval, but with no guarantees that files will always be located. in freenet, the emphasis is on ensuring anonymity. can and chord guarantee that files are always located but accepting increased overhead for file insertion and removal. in scientific collaboration, the typical uses of shared data in scientific collaboration have particular characteristics: group locality – users tend to work in a group and use the same set of resources (data sets). the newly produced data sets will be of interest to all users in the group. time locality – the same users may request the same data multiple times within short time intervals [10]. however, the discovery mechanisms that are proposed in existing p2p systems such as gnutella, can, chord, etc., do not attempt to exploit this behavior. iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 100 a large amount of work on p2p discovery mechanisms has been done either in structured and unstructured p2p system [15, 16, 24-26]. in this paper, we focus our work on unstructured p2p scientific data grid system that will answer one of the questions that have been raised up by the authors in [10]. the question that the most interest to us is how do we translate the dynamics of scientific collaborations in self-configuring network protocols such as joining the network, finding the right group of interests, adapting to changes in user’s interest, etc.? this is relevant and challenging in context of selfconfiguring p2p networks. the services that are provided by unstructured p2p system could be the answer for this question, where it does not rely on a specific network topology and supports the discovery in arbitrary forms. the unstructured p2p provides more scale and dynamism for scientific data grid environment. we have proposed and developed an unstructured p2p scientific data grid model which is discussed in the next section. 3. the p2p data grid model a variety of models are in place for the operation of a data grid. these data grid models are manifest in different ways in different systems. the model is the manner in which data sources are organized in a system. these are dependent on the source of data, whether single or distributed, the size of data and the mode of sharing [27]. four of the common models are monadic, hierarchical, federation and hybrid. in this section, we only illustrate our proposed model which provides a generic infrastructure to deploy p2p services and applications. figure 1 shows our proposed model for a scientific data grid that will support scientific collaboration. this model is specified as unstructured p2p model where, peers could be any network devices and in our implementation, the peers can include pcs, servers and even supercomputers. each peer operates independently and asynchronously from all other peers and it can be self-organized into a peer group. peer group contains peers that have agreed upon a common set of services, and through this peer group, peer can discover each other on the network. once a peer joins a group it uses all the services provided by the group. peers can join or leave the group at anytime that they want. in this model, once a peer joins the group, all the data sets that are shared by other peers in the group will be available to him/her. peers can also share any of their own data sets with other peers within the group. a peer may belong to more than one group simultaneously. in this scientific communities data-sharing model, we try to provide the same concept as the analogy of electrical power grid, where the users or scientists (in our case is peers) can access their required data sets without knowing which peers deliver the data sets. in other words, they can execute their applications, obtain the remote data sets (did not concerned with the provider) and then wait for the results. this will be done by the discovery service. our focus in this research is to propose a decentralized discovery strategy for scientific data grid that addresses the scalability problem and also reliability problem. iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 101 fig. 1: p2p model for scientific data grid. 4. the simulation study the presented results were obtained with simulation of only read requests without any background traffic in network and the stream of requests for the scientific data grid. our simulation is written in parsec simulation language. parsec is a c-based discreteevent simulation. the simulator consists of three parts. the first part is the entity that is responsible for creating the rest of entities: the entities that simulating the network nodes and network layer. it also reads all the inputs needed for the simulation. the second part is the network layer, which comprises of two entities: the entity that simulates a network forwarding protocol and the entity that simulates the distance vector multicast routing protocol. the third part is the entity that simulates the various nodes in the scientific data grid. the scientific data grid simulation is developed to identify suitable resource discovery strategies and mechanism for p2p scientific data grid model. starting a simulation first involves specifying the topology of the grid, including the number of network nodes, how they are connected to each other and the location of the files across various nodes. the bandwidth of each link is not specified in this simulation model in order to simplify the model. we assumed that all links have the same bandwidth. in this simulation model, various file requests will be triggered originating according to file access patterns to be simulated. in this study, a file access pattern is generated randomly. the request will be forwarded to the selected neighbour nodes using the information in the routing table in each nodes. before it forwards the request to several neighbor nodes, it iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 102 will check the file required and submit the request if the node has the requested file. in this case, the simulator will record the hop count for the successful request. if not, it will forward the request to other nodes until its time-to-live (ttl) for the request expired. there are various proposed strategies and mechanism to discover or locate the resources in distributed system. we have studied and compared different discovery strategies using this simulation. through this simulation, various parameters such as hop count, success rates, response time and bandwidth consumption will be measured. however, in this paper, we just show only the hop count measurement. the simulation was first run on the access patterns that were generated randomly. table 1 is a sample access pattern file randomly generated during simulation. this being the worse case scenario, more realistic access pattern that contained varying amounts of temporal and geographical locality will be generated in future study. table 1: a sample access pattern file. 5. experiments and results in a scientific data grid system, several factors influence the performance of discovery mechanism; the network topology, resource frequency and resource location. however, in these studies, we will only focus on the last two factors. in this section, we show the simulation results of the discovery strategies performance with and without the existence of replication strategies. we then show the results on the impact of data replication strategies that we proposed to address the data distribution and reliability problem for our scientific data grid model, on the propose discovery strategies. currently, in our simulation, we used generated random flat networks topology consisting of 20 220 nodes. we placed the data file ourselves randomly, and measured data access cost in average number of hop, success number of request and bandwidth consumption. however, in this paper we only show a few of the experiment results. in this simulation study, we assumed that the overlay network graph topology does not change time file name requestor node 20 file1 1 39 file2 5 70 file2 6 75 file3 3 90 file1 2 92 file2 3 98 file3 5 iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 103 during the simulation as to maintain simplicity. in this study, four discovery schemes have been model and studied. the study was focused on the discovery and also replication aspects that would improve the performance of data discovery strategy. in a flooding-based protocol, nodes flood an overlay network with queries to discover a data file. in a request forwarding technique, nodes will forward the queries to the selected neighbor by utilizing information range from simple forwarding hints to exact object locations. the discovery strategies that we have modeled in this simulation included flooding(f), random neighbour(rn), learning flooding(learningf) and learning random neighbour (learningrn). we have run a number of simulations by creating two different scenarios. in the first scenario, we assumed that no replicas are created at the beginning and during the simulation. in the second scenario, we created replicas at the beginning of simulation. this scenario is to study the impact of replication on the discovery strategies. figure 2 shows a graph representing the data access cost in average number of hop for topologies with different number of nodes without replication for four different discovery strategies. as shown by fig. 2, the performance of all four strategy is worst when the number of nodes increases in the collaboration network. we expect that in real scientific data grid environment, it will become worst as this strategy does not scale well when the number of nodes increases. the strategy based on flooding technique might give optimal results in a network with a small to average number of nodes. fig. 2 also shows that the performance of random neighbour discovery strategy is worst compared to other discovery strategies where the number of hops reaching nearly 200 hops to reach to an object in a network topology that consist 160 nodes. average number of hops vs number of nodes 0 50 100 150 200 250 20 40 60 80 100 120 140 160 180 200 number of nodes a ve ra ge n um be r o f h op s flooding random neighbor learningrn learningf fig. 2: average number of hop in different number of nodes. iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 104 figure 3 shows a graph representing the data access cost in term of the number of success queries for topologies with a different number of nodes with and without replication using flooding discovery strategy. the results show that the number of success queries increase when the data is replicated in the collaboration network. the number of replica that created in the network can gives a better performance to discovery strategies as shown by fig. 3 and fig. 4. fig. 3: number of success queries for flooding mechanism. fig. 4: the 100 nodes network topology with various numbers of replicas. iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 105 the results from fig. 4 show that when the number of replica increase, the number of success queries also increase. for discovery strategy that is based on random, it shows that this strategy can perform better when more data is replicated in the collaboration network. however, we need to monitor and maintain the optimum number of replica that should be replicated in the network in order to prevent other problems such as the storage usage problem etc. bandwidth consumed vs number of nodes 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 20 40 60 80 100 120 140 160 180 200 number of nodes b an dw id th flooding random neighbor learningrn learningf fig. 5: bandwidth consumption for four different discovery mechanisms. figure 5 shows a graph representing the bandwidth consumption for different topologies with different number of nodes without replication using four different discovery strategies. the results show that both flooding-based discovery strategies used more bandwidth to flood the queries. the bandwidth consumption increase accordingly when the number of node increase. however, by having a little bit of checking process for learning flooding strategy, it shows that we have slightly reduced the bandwidth consumed by the strategy. it is also the same with the learning random strategy. 6. conclusion and future work we have addressed the problem of scalability in discovery process for scientific data grid by proposing decentralized discovery strategies (learning flooding and learning random neighbour). we also have addressed the issue of having a scalable scientific data grid model by proposing p2p scientific data grid model. we have described our p2p model for scientific data grid environment and our simulation study. although the model is conceptually simple, it has provided a scalable service that could be remarkably useful for a scientific data grid environment that is based on p2p. we believe that with a very simple simulation experiment that we have done on our model using our scientific data grid simulation, it shows that this approach can be used to support good services for iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 106 data discovery in a large-scale unstructured scientific collaboration environment. it also represents an interesting approach to data management in scientific data grid through our study on replication impact to discovery strategy. our results show that, for a scientific data grid environment with large population of users, we need a discovery mechanism that could give the shortest time to discover and locate data resources, it also provide the guarantees required by collaborators and, with low bandwidth consumption, and also scalable. in our future work, we will study other strategies to discover or locate the resources in decentralized environment. various replication strategies will be incorporated as to support more dynamic scientific data grid scenario and also to address the reliability problem. references [1] chervenak, a., foster, i., kesselman, c., salisbury, c., tuecke, s. the data grid: towards an architecture for the distributed management and analysis of large scientific data sets. journal of network and computer applications. (2000). [2] ppdg: particle physics data grid, http://ppdg.net [3] griphyn : grid physics network, http://www.griphyn.org [4] johnston, w., lee, j., tierney, b., tull, c.,millsom, d. the china clipper project: a data intensive grid support for dynamically configured, adaptive, distributed, highperformance data and computing environments. in proceeding of computing in high energy physics 1998, chicago (1998). [5] srb: storage request broker, http://www.npaci.edu/dice/srb [6] gnutella website, http://www.gnutella.wego.com [7] the free network project website, [8] napster website, http://freenetproject.org http://www.napster.com [9] konspire website, http://konspire.sourceforge.net [10] iamnitchi, a., ripeanu, m., foster, i. locating data in (small-world?) peer-to-peer scientific collaborations. 1st [11] gong, l. project jxta: a technology overview. sun microsystems, inc. april 25, (2001). international workshop on peer-to-peer systems, cambridge, massachusetts, march (2002). [12] lhcthe large hadron collider website, http://lhc-new-homepage.web.cern.ch/lhc-new-homepage/ [13] loebel-carpenter, l., lueking, l., moore, c., pordes, r., trumbo, j., veseli, s., terekhov, i., vranicar, m., white, s. and white, v. sam and the particle physics data grid. in proceedings of computing in high-energy and nuclear physics. beijing, china. (2001) [14] lueking, l., loebel-carpenter, l., merritt, w., moore, c. the do experiment data grid – sam. c.a. lee(ed.): grid 2001, lecture notes in computer science, vol 2242. springerverlag berlin heidelberg (2001). 177-184 [15] ratnasamy, s., francis, p., handley, m., karp, r., shenker, s. a scalable contentaddressable network. in sigcomm 2001, san diego, usa.( 2001). http://ppdg.net/� http://www.griphyn.org/� http://www.npaci.edu/dice/srb� http://www.gnutella.wego.com/� http://freenetproject.org/� http://freenetproject.org/� http://www.napster.com/� http://konspire.sourceforge.net/� http://lhc-new-homepage.web.cern.ch/lhc-new-homepage/� iium engineering journal, vol. 10, no. 2, 2009 abdullah et al. 107 [16] stoica, i., morris, r., karger, d., kaashoek, m. f., balakrishnan, h. chord: a scalable peerto-peer lookup service for internet applications. in sigcomm 2001, san diego, usa. (2001). [17] ranganathan, k. and foster, i. identifying dynamic replication strategies for a high performance data grid. in proceedings of the international grid computing workshop. denver. (2001) [18] ranganathan, k. and foster, i. design and evaluation of replication strategies for a high performance data grid. . in proceedings of computing in high-energy and nuclear physics. beijing, china. (2001) [19] stockinger, h., samar, a., allcock, b., foster, i., holtman, k., tierney, b. file and object replication in data grids. in proceedings of the tenth international symposium on high performance distributed computing. ieee press. ( 2001). [20] vazhkudai, s., tuecke, s., foster, i. replication selection in the globus data grid. in proceedings of the first ieee/acm international conference on cluster computing and the grid. pp. 106-113, ieee computer society press. (2001). [21] foster, i., kesselman, c. globus: a metacomputing infrastructure toolkit. intl j. supercomputer applications [22] grimshaw, a., lewis, m., ferrari, a., karpovich, j. architectural support for extensibility and autonomy in wide-area distributed objectsystems. in , 11(2) (1997)115-128 [23] frey, j., tannenbaum, t., foster, i., livny, m., tuecke, s. condor-g: a computation management agent for multi-institutional grids. in proceedings of the tenth ieee symposium on high performance distributed computing (hpdc10) san francisco, california, august 7-9. (2001). proceedings of the 2000 network and distributed system security symposium (ndss2000). (2000) [24] gkantsidis, c., mihail, m., saberi, a. hybrid search schemes for unstructured peer-to-peer networks. proc. of ieee infocom’05, miami, usa (2005). [25] lv, q., cao, p., cohen, e., li, k., shenker, s.: search and replicating in unstructured peerto-peer networks. proc. of 16th [26] crespo, a., garcia-molina, h.: routing indices for peer-to-peer systems. proc. of int. conf. on distributed computing systems(icdcs’02), vienna, austria (2002). annual acm int. conf on supercomputing (isc’02), new york, usa (2002). [27] venugopal, s., buyya, r., ramamohanarao, k., a taxonomy of data grids for distributed data sharing, management and processing. in: acm computing surveys, vol. 38(1), pp. 1– 53. acm press, new york, usa, 2006. tunable bandpass filter using rf mems switches 2.1 one mems bridge parallel with the resonator 2.2 two mems bridge parallel with the resonator 2.3 one mems bridge perpendicular to the resonator 2.4 mems bridges parallel and covering all the resonators acknowledgement references keywords : quantum cryptography, quantum key distribution, decoy state protocol, optical communications 2. experimental setup influence of polarization mode dispersion on the effect of cross-phase modulation in intensity modulation-direct detection wdm transmission system introduction system model theoretical analysis 3.1 modulation of the probe field results and discussion conclusion acknowledgement references towards a scalable scientific data grid model and services introduction related works the p2p data grid model the simulation study experiments and results conclusion and future work references anomalous electrodeposition of fe-ni alloy coating from simple and complex baths and its magnetic property application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 a review on software-defined networking enabled iot cloud computing sumit badotra, surya narayan panda chitkara university institute of engineering and technology, chitkara university, punjab, india. *corresponding author: sumit.badotra@chitkara.edu.in (received: 8th april 2019; accepted: 24th july 2019; published on-line:2nd december 2019) abstract: making use of internet of things (iot) is becoming the necessity of today’s life. the data collected and stored through iot devices comes from the cloud and therefore cloud computing is acting as a backbone for supporting iot. but it is easy to forget that the cloud is not completely digital in some areas of the world and there is a need for a data centre where data storage can be achieved. cloud data centres are facing many difficulties and issues because they are using traditional methods of networking. this is where software defined networking (sdn) has come into view; where it has changed the way traditional networks are operated. for example, the separation of the intelligence of the network devices within the data path can be useful in making networks agile and manageable. this paper aims to provide problem areas in the networking used by the cloud data centres and the role of sdn to overcome these issues. platforms for providing the experimental setup for collaboration between sdn and cloud will ultimately be beneficial in setting up the sdnenabled iot cloud, and this is also discussed with the open research problems. abstrak: penggunaan internet benda (iot) menjadi keperluan kepada kehendak hari ini. data yang dikumpul dan disimpan melalui peranti iot berasal dari awan dan oleh itu pengkomputeran awan bertindak sebagai tulang belakang bagi menyokong iot. tetapi, satu perkara yang dilupakan adalah bahawa awan itu tidak sepenuhnya digital, di suatu tempat dalam dunia ini, terdapat keperluan pada pusat data di mana penyimpanan data boleh dicapai. pusat data awan menghadapi banyak masalah dan isu kerana ianya menggunakan kaedah rangkaian tradisional. di sinilah perisian definisi perangkaian (sdn) dipandang; ia telah mengubah cara rangkaian tradisional dikendalikan. sebagai contoh, pemisahan kecerdasan peranti rangkaian dengan laluan data berguna bagi membuat rangkaian pintar dan boleh diurus. kajian ini bertujuan bagi menyediakan ruang masalah dalam rangkaian yang digunakan oleh pusat data awan dan peranan sdn dalam mengatasi masalah ini. platform persediaan eksperimen bagi kerjasama sdn dan awan akhirnya bermanfaat dalam menubuhkan pengaktifan-sdn awan iot, juga turut dibincangkan dalam kajian ini berkenaan masalah penyelidikan terbuka. keywords: internet of things (iot); software defined networking (sdn); data center networks; cloud computing 1. introduction internet of things (iot) and cloud computing are strongly related to each other. data transferred to various iot devices comes from data centres. iot is not all about how to connect various devices to the internet to get the information but how to analyse the data 105 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 to get an intelligent answer to a query. analysis of the data can only be possible if it is being stored at a data centre. then, the iot device can make a decision based on a previous data decision. for example, a smart watch is not only smart because it is connected to the internet but because it is making use of some cloud where the data is stored, and analysing that cumulative data and making a smart decision. cloud computing has emerged in such a simple way that its acceptance is universal. the computing that has been facilitated by cloud computing has eliminated several problems while providing services to the shoppers like direct investment, minimizing operational expenses, the handiness of on-request computing resources, protractible scaling, and creating pay-peruse [1]. as the utility of this computing model is expanding, it should be matched with a supplier of cloud with a similar brokering system that is dynamic for hosting its application [1]. the application supplier can lease resources used for computing from the cloud supplier by just clicking on a mouse at regular intervals and using their application without direct payment. with a dynamic adjustment (either increasing or decreasing) of the amount of virtualized infrastructure resources such as virtual machines (vms), the extensibility and flexibility in the cloud atmosphere is achieved [2]. to give versatile support of their shoppers, cloud suppliers work with varied information centres over totally different locations with virtualized quality provisioning. substantial giant information centres are comprised of thousands of switches interfacing unnumbered servers [3]. each server will serve varied application demands from varied shoppers by utilizing virtualization advances that have improved readiness and asset capability that were not previously in the network resources [3]. as of now, cloud shoppers will lease virtualized process assets, i.e., vms (virtual machines), and virtualized storage from different cloud suppliers that are allotted for the shopper. be that as it may, the system quality virtualization innovation remains an extended method being employed within business public clouds [4]. servers are allotted to totally different customers if the mass or total requested size from shoppers doesn't exceed server limit. cloud shoppers accept inquiring for some littler measured resources than the limit of the entire server, and a server will offer varied virtual machines [5]. these virtual machines connect to the customer through varied system switches and switches. so as to transfer the traffic among varied vms effectively and with information efficiency, network centres are established. because the data centre network (dcn) interfaces a huge range of servers, the system can have better quality, which makes it exhausting to administrate and scale within the standard systems administration view. in customary systems, every system switch has its own specific management explanation that solely chooses its conduct based on the info obtained from its neighbours [6]. the traditional system approach is wasteful with regards to the information centre of the cloud, where a better thickness provided by varied virtual machine servers that increasingly change over time [5, 6]. in order to overcome the disadvantages of traditional networks like measurability problems, inflexibility, etc. [7] different cloud information centres have started accepting the software-defined networking (sdn) thought in their dcns [7, 8]. with the help of sdn, provisioning of incorporated centralized management logic with a perspective of the full system at the centralized controller will form dynamic changes on the conduct of the system [9, 10]. the network will likewise be modified by the controller, which is well suited to the more dynamic nature of the service provided by the cloud [11, 12]. large suppliers of clouds, google for example, formally received the sdn plan in their information centres [13]. there is a tremendous rise in the rate of iot devices and to accommodate the growth of this rate, the cloud data centre has to expand its functionality 106 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 in order to provide the best services to every user. so, there is a need to implement the new architecture of cloud networking to enable innovation and continue the functionality and services of cloud. in this paper, each cloud computing and sdn are considered for examination purposes. the main contribution of this paper is to explore the challenges and issues before and after introduction of sdn in iot and cloud computing for future remedies. the remainder of this research paper is structured as follows: in section ii related literature is discussed along with the issues in the cloud data centre network with a brief introduction of sdn. in section iii and iv comprehensive review of the state of art, including on-going projects and research, motivating sdn-enabled iot cloud computing is given. section v is comprised of various evaluation methods that can be used as a platform for performing experiments in sdn-enabled iot cloud computing. section vi explores the spectrum of challenges and obstacles in traditional networks, followed by concluding observations in section vii. 2. background although several surveys and taxonomies are conferred in sdn and cloud computing contexts, each of them presents their own drawbacks within the space. toosi et al. [14] did a survey specializing in interconnected cloud computing. this research paper discussed various abilities in the context of multiple information centres and elaborately discussed every approach to work for cloud information centres that were interconnected. this paper had a separate section where it explained various networking challenges for inter-cloud connections, however, the main focus was on the broader problem of desegregation of multiple cloud information centres from the perspective of a cloud broker. mastelic et al. [15] additionally conferred a review on the potency of cloud energy for computing. in cloud computing, a scientific class of energy consumption has been instructed with respect to factors like software and hardware systems infrastructure in clouds. the author additionally discussed the networking aspect, accenting the information centre networking (dcn), end-user network, and inter-data-centre network. a detailed survey was done on various aspects of energy potency in networks, but the article was lacking with respect to the context of sdn. jararweh et al. [16] discussed in depth about software-defined clouds that specialized in networking, security, systems, and storage. however, his paper emphasized the system design instead of an individual analysis of sdn clouds. azodolmolky et al. [17] additionally proposed an innovative software-defined network. sdn can be applied to a number of challenges and will be utilized in future deployments as an economical solution along with cloud computing networking as a possible contributor of a software system outlined network. some analysis results on the performance of the area unit are presented in this paper. yen et al. [18] initially established an association in nursing sdn that is based on a cloud computing atmosphere via openflow switches, controller packages, and open supply. then, it explained the practicality of the power saving openflow controller to supply load equalization and observance mechanisms. to prove the feasibility of their planned design, they additionally developed a model of sdn queuing and estimated its analytical resolution for the chances of a steady-state. the result obtained from the experiment showed that the atmosphere based on sdn gave qos-bonded services for cloud computing. 107 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 before starting an investigation of sdn-empowered cloud computing, the fundamentals of cloud computing are discussed and that’s why the cloud information centres areas unit are represented. during the following section, we try to briefly discuss cloud computing, dcn, and sdn. 2.1 cloud computing cloud computing has come up as a typically acknowledged registering worldview worked around centre ideas [19], as an example, elimination of forthright venture, the diminishment of operational prices, on-request process resources, versatile scaling, and putting in compensation for every utilization arrange action for information innovation and computation administrations [20]. cloud computing has given economy to ability through financially savvy and versatile it profit worldview. the specialist additionally outfits its benefits, the pay-as-you-utilize estimating model for example, and flexibility to reinforce their nature of administration and to minimize their price [20]. in cloud condition, skill and flexibility will be accomplished by more decreasing or increasing virtualized foundation assets, e.g. vms. in fact, virtualization had distended the efficiency and limit of cloud information centres to a degree that ancient system standards cannot offer [21 22]. figure 1 shows the varied features of cloud computing. fig. 1: features of cloud computing. the numerous service models of cloud computing enable varied administrations like platform-as-a-service (paas), software-as-a-service (saas), infrastructure-as-aservice(iaas), and network-as-a-service (naas) [23]. in saas, benefits for the outside provider has various applications that can later be made accessible to the shoppers online [24-25]. the naas profit model will incorporate elastic and broadened virtual private network (vpn), transfer speed for the asking, custom steering, multicast conventions, security firewall, intrusion detection system, wide area networking (wan), content monitoring and separation, and antivirus [26-28]. there’s no commonplace determination with respect to what's incorporated into naas and its executions can shift. platform-as-aservice (paas) may be a cloud computing model in which an outsider provider conveys instrumentation and programming devices for the main half to those needed for application advancement to shoppers over the web [29]. in paas, the supplier has the 108 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 instrumentation and programming framework [30-33]. thus, paas allows its shoppers to put in in-house instrumentation and programming to form or run another applications [34]. figure 2 demonstrates the various administration models of cloud computing. fig. 2: models of cloud. 2.2 problem area in the cloud data centre network (dcn) cloud computing has been well received and generally utilized everywhere. to keep pace with its rapid adoption, service providers must build an ever increasing number of data centres, placing them all around to diminish dormancy to the most extreme conceivable degree for worldwide customers [35]. in cloud situations, flexibility and versatility can be accomplished by expanding or diminishing virtualized framework assets such as virtual machines, yet there are a few issues in overseeing cloud framework on the iaas level while considering both systems administration asset provisioning and configuring. a large number of networks are making use of a cloud foundation for themselves for dealing with these offices and associating them together. however, the present networking approach utilized in cloud data centre systems is becoming a hurdle to scaling up data centres. in straightforward words, it can neither be effectively organized nor adaptable [36]. with a specific end goal to give cloud benefits, the supplier should construct and keep up at least one vast scale cloud data centre where countless physical hosts are associated through a huge number of system switches [37]. with the high complexity of network connections on a huge scale, the provider needs to think about the dcn with an alternate point of view from the traditional system. subsequently, it puts an expanding request on the networks and the systems as well [36-37]. 2.3 software defined networking sdn is a novel approach in the area of networking [38]. the basic norm behind sdn is the segregation of the data plane and the control plane. in traditional networking both the intelligence and the forwarding plane are coupled inside proprietary hardware. this increases the complexity and decreases the expandability of the network [39]. with the introduction of sdn in networking, the whole concept of managing the networks has been changed, thereby making them programmable networks that allow the network 109 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 administrator to change the traffic flow from one switch to another with few lines of code. figure 3 shows the layered architecture of sdn: a) physical layer: it is the layer that includes the infrastructure being used in the network like switches, routers, etc. b) control layer: it is the main layer where the sdn controller resides and provides various network services and provisioning [40]. c) application layer: sdn architecture’s topmost layer is the application layer. it includes all applications like firewall, load balancer, etc. [38, 39]. d) api’s (application programming interface): to provide the communication between various layers there are some well-defined api’s such as southbound api (e.g. openflow protocol) and northbound api (e.g. rest). [40]. fig. 3: architecture of sdn. since the bond between sending equipment (or forwarding plane) and control logic has been separated in the case of sdn, so it provides more options to institutions and researchers for establishing new system administration conventions, traffic administration, virtualization, and programming advancements [41]. it prompted the presentation of openflow in which aggregate consequences of various associations are and turn into an accepted standard convention for sdn controllers. numerous controllers have been presented and effectively created in light of openflow such as ryu, floodlight, ryu, pox, open daylight etc. sdn has likewise opened up inventive open doors in transit of building up the controlling rationale of systems [41, 42]. in traditional systems, the control plane is exclusively created by substantial switch merchants, for example vendors such as juniper or cisco, that are combined to equip network hardware and hence make the network devices vendor-specific [41-43]. as the sending equipment is isolated and completely maintained by the sdn controller, programming with respect to sdn based network, various control logic can be combined and executed since it takes after sdn standard, for e.g., openflow. figure 4 demonstrates the correlation design of traditional network administration and sdn. in this way, sdn has encouraged advancements in the 110 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 improvement of different type of system intelligence or the control logic that might have been abundantly restricted in the approach used by conventional systems [43, 44]. fig. 4: network architecture of traditional networks. 2. sdn enabled cloud computing combining sdn and cloud gives birth to new methods and possibilities through which new interfaces automatically become programmable [45]. although there has been a tremendous rise in the field of cloud computing, those that are playing the vital role of managing cloud networks are facing a significant challenges on which the overall performance is dependent [46-47]. the issues in cloud networks include inflexibility, vendor-specific firewalls, scalability, manageability, etc. consequently, cloud networks need a cloud infrastructure in which the aforementioned disadvantages are absent. in the future of networking sdn is an emerging model; with its basic principle of separation of the intelligence of the networks with the network, hardware with improved flexibility and scalability hence makes cloud networks programmable which increases the manageability and agility [48]. out of all the issues in cloud networks, scalability is one of the main issues that need to be considered. sdn is the solution that can be used to upgrade the scalability of the cloud and fulfil the need of the hour. sdn can furnish a new architecture which supports the dynamism in network architecture and then further transforms the usual cloud networks into prosperous provider delivery platforms [49-50]. this is the reason for introducing sdn into the cloud. making use of sdn in cloud computing can be referred to as sdnenabled cloud computing. the sdn based cloud is a new type of cloud in which sdn is introduced and network control is at one single place [51]. from centralized sdn controller, instructions to move the traffic from one place to another is provided to other networking devices [52-53]. in the cloud based on sdn, cloud computing extends from server virtualization and centralization as nicely as storage virtualization and centralization to community virtualization and centralization. recently, clouds based on sdn have attracted first-rate attention [54]. when the sdn based cloud is compared with the traditional network used in the cloud, it has many advantages in terms of quality of service (qos), vm orchestration, etc. for the purpose of allocation, a required bandwidth is needed. this requirement of qos for all the priority cloud users can be met by the sdn based cloud that uses an open vswitch [53]. sdn based networks are not only limited to provide the qos but also live vm management in which the server can interrupt or exploit the information from one end to another. it is also believed that if sdn is implemented in the cloud it can offer new opportunities for network security to be enhanced since cloud-based sdn provides faster reaction and greater flexibility when the condition is getting revised [55]. 111 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 3.1 need for software defined cloud data centres (sdn-dc) to conquer the deficiencies of traditional networks, cloud data centres began embracing the sdn idea in dcn [51]. sdn offers a centralized control plane with a perspective of the whole system. with the help of the controller, it can make use of progressive change in the network. the need for dynamic flow of data from sender to receiver in the cloud environment and its data centres is well suited to sdn because of its centralized controller that can easily dynamically alter the flow of data in the network. on the basis of traditional networking used in dcn architecture, sdn-dc takes over from conventional systems administration hardware with sdn-empowered gadgets [52]. when sdn is implemented in dc, each system’s administration that is a part of that data centre is fitted for implementing the features of sdn and then can convey all the aforementioned advantages to the cloud data centre [53]. sdn-empowered cloud computing (sdn-cloud or sdn-empowered clouds) specified to sdn-dc, as well as inter-cloud organizing that consumes the sdn utilization over various data centres and wan. in this way, sdn benefits can be connected to internetworking domains [54, 55]. a more extensive term sdn-dc has been proposed by jararweh et al. [8] and buyya et al. [7] in which the network infrastructure is also software defined rather than only defining the networking. the approach was to construct a completely mechanized cloud server farm enhancing configurations, that was powerful and self-governing. buyya et al. [7] expanded the idea of virtualization from a virtualized server to every other component in cloud data centres. the centre innovations to empower sdn-dc to incorporate server virtualization, sdn, arrange virtualization, and virtual middle boxes. with advances, the reconfiguration and adjustment of physical assets in sdn-dc has turned out to be more achievable and easier to be executed. the suggested architecture was executed and assessed in the simulation environment. jararweh et al. [8] likewise considered a framework concentrating on different parts of sdc including capacity, organizing, data centres, virtualization, and security. it assembled an exploratory setup for sdn-dc with the examined components in the study to explain the viability of the proposed programming defined cloud architecture. sdn-dc is more realistic as it is suggested for research purposes and has not yet been investigated broadly. 3.2 sdn-enabled cloud computing architecture sdn empowered architecture is separated into three layers. figure 5 explains the abstract architecture of cloud computing empowered by sdn, based on the literature [46, 53-55]. the sdn controller controls the system related capacities, which are associated with the director of the cloud through apis that are north-bound. sdn highlights such as arranging topology disclosure, virtual system administration; organizing checks and dynamic system designs are empowered through the controller of sdn. different types of sdn controller can be practical to expand its adaptability through intercommunicating, with the help of east-west-bound apis. cloud resources consist of systems and process administration assets. the cloud administrator convinces hosts to run vms on a hypervisor, though organizing assets like switches are overseen by the sdn controller by refreshing switches of sending tables through south-bound apis (e.g. openflow). note that the sdn controller also manages functions of networking in hosts for examples, virtual switches for vm traffic management and network virtualization. 112 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 fig. 5: sdn-enabled cloud architecture. recently, mayoral et al. [56] provided the structure of the cloud with a single sdn controller as well as numerous controllers. the framework arranged the administration of a data centre with the sdn capacity. keeping in mind the end result to discover the differences between one or more controllers in data centres, the author had assessed the openstack [57] architecture and opendaylight with respect to sdn. similarly, the author had also proposed a conclusion to end arrangement of cloud architecture and system assets that oversee the two assets in distributed cloud data centres [58]. virtual foundations in clouds are powerfully assigned and overseen through the chief. the vm distribution issues were displayed as a mapping figure with switch parameters and arranged joins. additionally, a set of rules for the calculation of locating the base number of hosts with enough limits was incorporated and chose the shortest way between the hosts. the design of the organization was approved on an exact testbed with openvswitch and openstack [57], while the calculation was done in simulation. fichera et al. [59] exhibited in a detailed testbed setup for the organization of sdn crosswise over the edge, iot spaces, and cloud in 5g benefits. the foundation was comprised of isolated orchestrator(s) for the sdn, cloud, and iot [60]. the sdn orchestrator oversees the cloud and iot arrangements as well as the transport organized between them. over individual orchestrators, the administration orchestrator gets direct benefits provisioning for applications with respect to the client’s prerequisites. the proposed framework was examined in a testbed which comprised of onos (open networking operating system) controller, openstack cloud and mininet for the edge arrangement. the control orchestration protocol (cop) was suggested by specialists with respect to different organizations to allow overseeing heterogeneous control planes of sdn and cloud [60]. while openflow means controlling of messages between switches and the sdn controller as the controller southbound interfaces, cop is accountable for organizing among sdn controllers in various system and in addition controllers of cloud working north of controllers. cop brought together transport api for arranging diverse transport in the inter-cloud condition. this convention gives a deliberation of asset topology disclosure, provisioning and way calculation. it was approved through 2 proof-of-idea tests for organizing asset recovery and provisioning [60]. 113 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 4. sdn based iot cloud the boom of iot and the quick enhancement of related applied sciences create an extensive connection of “things.” cloud computing is a field for creating big storage statistics and analysis. iot is attractive on its own, but the enormous amount of data coming from iot devices, its storage, big data statistics, and analysis must be performed by cloud computing. real innovation will only come if iot and cloud computing combine. the aggregation of both cloud computing and iot will enable new services for monitoring and processing data. for example, sensory information from iot devices can be uploaded and stored with cloud computing. this data can later be used for statistical analysis and decision making. in truth, cloud computing and iot are tightly coupled and are closely related to each other in a similar way that an automobile and gasoline are related. the strength produced with the aid of gas (the iot) runs the vehicle (cloud computing). iot is no longer solely about connecting random devices nearby and making robots. iot is an imaginative and prescient tool whereby we are able to talk to gadgets near us in such a way that we can make informed decisions based totally on the statistics accrued by means of these devices. one of the vital desires of cloud providers is to provide availability to their customers. to supply versatile guide of their clients, cloud vendors work with more than a few fact facilities over distinct geolocations with virtualized asset provisioning. substantial massive records centres are comprised of heaps of switches interfacing countless servers. every server can serve a number of utility needs from more than a few consumers by making use of virtualization advances, which have been increased inconceivably in preparation and capacity belongings for the most recent few many years yet not in network resources. as of now, cloud clients can lease virtualized processing assets, i.e., virtualized storage, and virtual machine from various cloud providers that are fixed surely for the client. be that as it may, the machine asset virtualization innovation is nevertheless a lengthy way from being used in industrial public clouds. therefore, it can be concluded that as the data from iot devices is coming in a huge manner, we need a cloud infrastructure in such a way that it has the capability to handle the rate of growth of the network. sdn has the capability to achieve this. therefore, if sdn is implemented in the cloud it can increase the capability, efficiency of cloud storage and hence this cloud is called an sdn based iot cloud. 4.1 issues in sdn-based iot cloud a wide variety of gadgets enabled with iot which are used to supply these applications, consisting of actuators, sensors and cellular devices. communication among devices with one another is done through an integrated community that may additionally be defining the media type i.e. wireless or wired. it constructs the iot in more necessary theme in its existence in daily practices which offers with the circumstances and the surrounding occasions such as fitness care, commercial agency administration, factories, automation, climate forecasting and many greater areas. imagine the amount of records generated by means of 10 such government places of work and the quantity of computing power wanted to manage this information. here, cloud computing comes into play. hence the records gathered via iot units is stored and processed on the cloud and primarily based on our learning and processing of that information choices like building renovation, electrical faults, building lifespan is detected. the iot is generating an extraordinary quantity of data, which in turn places a notable pressure on the internet 114 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 infrastructure. as a result, businesses are working to locate methods to alleviate that stress and resolve the facts problem. another problem is heterogeneitymeaning that iot objects are changing in their properties and characteristics. as the numbers of devices are increasing day by day different vendors are coming into play to provide the services to various users. devices that are communicating and getting the services are from different vendors is very hard to manage. the need to combine sdn and iot is to compile and resolve many types of issues that will be propagated as the iot network grows. by making use of sdn, in an iot network, the iot controller, which is a high-level module, will interact with the centralized sdn controller for planning and organizing the network and performing the functions related to the iot. 4.2 sdn-based iot cloud architecture sdn-empowered architecture is separated into 3 layers. figure 6 demonstrates the summary shapes of simple sdn-empowered cloud computing structure obtained from the literature. system-related capacities are managed by the sdn controller, which is related to the director of the cloud via northbound apis. sdn highlights, for example, organize topology disclosure, prepare checking, virtual machine administration and dynamic system designs, are empowered via the sdn controller. various sdn controllers can be sensible to lengthen adaptability through the ability to intercommunicate through the potential of east-west-bound apis. the cloud property consists of buildings and manner administration assets. hosts are managed by the network administrator of the cloud for running vms on a hypervisor, although organizing property like switches is overseen using the sdn controller through clean sending of tables in switches with the resource of southbound apis. it is very important to understand the fact that the sdn controller manages features of networking in hosts, for example, for community virtualization, vm visitor’s administration, and digital switches. fig. 6: sdn-based iot cloud. 115 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 4.3 good features of sdn for offering protection in sdn-enabled iot and cloud computing separation of the control plane from the data plane: sdn decouples the intelligence of the network and management plane which constitutes the networking devices. hence it permits setting up, besides troubles of large-scale attack and safety experiments. the high configurability of sdn not only allows the network administrator to have clarity among the digital networks but also how to enable experiments on a true environment. centralized controller and its vision: the sdn controller has a full vision and control over the network including traffic monitoring, shaping, switches flow table updating etc. centralized manipulation of sdn controller allows dynamically resisting threats and attacks as well. analysis of traffic: network traffic can be examined on the basis of evaluation which is a software-based and which is ultimately enables the innovation, as it is possible to enhance the capabilities to change the usage of any technique which is a software-based. analysis of the network traffic can be carried out in a real-time environment using desktop and getting to know algorithms used, backup databases and any other specific software program tool. dynamic updating the flow tables: flow tables of switches can be dynamically updated through a centralized sdn controller which further helps to prevent much security threats in the network. 5. evaluation method and technology for quickening improvement and advancement of sdn-empowered cloud computing, toolboxes and devices are required to manufacture a testbed for testing sdn and openflow frameworks in a cloud data centre. the testbed also has the ability to quantify the vitality utilization to assess proposed algorithms. in this section, observational and simulation techniques are clarified as shown in fig. 7. fig. 7: evaluation method. 5.1 simulation platforms for cloud simulation is the first and initial tool for new research and experimental setups. real infrastructures are utilized to archetype the performance of the application under certain conditions like patterns of workload, reliability, etc. one of the major examples of 116 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 invariable frameworks is microsoft azure, amazon ec2, etc. therefore, this makes the transcription of results authentic and extremely considerable. on the other hand, it is timeconsuming and unvaried to re-configure the parameters across a large-scale. there are some restrictions for the developers as the environment of the cloud is not in the control of them under certain circumstances. thus, archetype practices in scaling, depending as well as repeating is impossible to execute in the real-world surroundings. an alternative tool that can open up the probability to examine the hypothesis in a manageable environment is a simulation tool. it can also easily recreate the outputs. it organizations get remarkable benefits from these kinds of tools. the simulation platform gives a controlled and reproducible condition for assessment effortlessly of change and setup. for cloud computing, a number of simulation tools have been introduced to evaluate new ways to deal with controlling and overseeing the cloud server farm and different type of situations. cloudsim [61] is a prominent cloud test system executed in java, giving a discrete occasion-based simulation equipped for mimicking cloud server, vms, intermediaries, and hosts. different scenarios can be executed in cloudsim, including the vm position approach, vm relocation arrangements, facilitating strategy and other server farm administration strategy [61]. it likewise bolsters workload reproduction executing in the vms. with its simple to-utilize discrete occasionbased design, extra components can be added to send and get re-enactment occasions and in addition, stretching out the recent elements to give additional usefulness. as far as there is a concern of network events there is no support available by cloudsim in details [61]. to satisfy the lack or unavailability of system reproduction capacity of cloudsim, networkcloudsim [62] is acquainted with re-enacting applications with organizing correspondence assignments. extra system components are included networkcloudsim, including system switches and connections that get arrange occasions and ascertain evaluated organize transmission time. in spite of the fact that networkcloudsim [62] incorporates broad system usefulness to mimic server farm system and various applications for message transferring within a data centre, the use of sdn in the experiment execution of cloudsim is clearly not supported [62]. greencloud [63] is another ns-2 [64] a based system which is based on a simulation that catches the vitality part of various cloud data centres comprising registration and correspondence of components. with the joining of ns-2 [64], which can catch the system design precisely on the bundle level, greencloud [63] can likewise give exact system comes about. the recreation substances incorporate has and switches with control utilization models, for example, dvfs. workload models are likewise predefined and given in the system to three sorts of occupations, e.g., figure concentrated, information escalated, and adjusted. in ns-2 there is an availability of simulated environment which helps to provide a comprehensive framework with respect to clouds but there is no support for evaluation of sdn based applications. 5.2 emulation platform for sdn networks in order to create the network virtual host, switches and controller links between them to create a network emulated is used called as mininet [65] emulator. standard linux network software is run by mininet hosts, and mininet switches support openflow protocol for the purpose of communication and highly flexible custom routing and ultimately creating the networks which are software defined. mininet not only is a good platform which is useful in providing support to research and developing applications but it is also helpful in making prototypes of networks, debug the networks and then perform testing on them. with the help of mininet, a complete network including topologies, 117 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 server, and everything can be emulated and created in a single laptop. mininet is the best emulation platform to emulate sdn networks in the absence of real hardware [66]. for sdn support in cloudsim, cloudsimsdn [67] was as of late acquainted with empower mimicking sdn highlights, for example, flexible transfer speed distribution or dynamic system setup. cloudsimsdn [67] is aimed to provide and simulate the highlighted features of sdn that further can be transferred in cloud data centres. utilizing cloudsimsdn centralized sdn controller can be actualized inside the test system to imitate the conduct of the controller to reduce the unpredictability of copying the openflow controller in the recreation [67]. despite the fact that it gives just basic outcomes in systems administration reproduction, the disentangled engineering furnishes basic outcomes etc. with the help of sdn features in a very small period of time [67]. teixeira et al. [68] proposed collaboration of python-based sdn openflow controller pox with mininet to support simulation and making use of sdn features in cloud computing. to organize the network topologies mininet is used to imitate them information activity and then organizing topologies within a data centre in which there is already a presence of openflow sdn controller. by collaborating pox and mininet, it helps to give handy outcomes and then preparing to-utilize programming. but still, this simulation tool suffers from many cons with respect to help or need in cloud-highlights, for example, characterizing different vm writes or execution of heterogeneous application workloads at the host through simulation. 5.3 evaluation method for collaborating both sdn and cloud to overcome the disadvantages occurred in various simulations and emulation tools discussed above. cloudsimsdn [67] has accomplished the task of combining sdn and cloud together. it is a new simulation tool that provides the framework for sdn networks and cloud. on top of cloudsim simulator, this new simulation tool is built. cloudsimsdn [67] includes the configuration and dynamic management of the resources which are managed and configure in a cloud data centre through a single point of control that is the sdn controller. the designing and formulation of this framework is done in such a way that it has the ability to perform the evaluation of all the resource management policies and strategies and ultimately which are to be used and appropriate for various sdn-ready cloud data centres [67]. with the help of cloudsimsdn simulation is performed of various cloud data centres, machines, switches in the network, links in between the network, and topologies (virtual) in network. this simulation is performed in order to calculate the approximated values of performance metrics which ultimately guarantees the quality of service and less energy consumption to satisfy the needs of the environment conservation [67]. 5.4 real platform openstackemu [57] is providing a platform for the consolidation of a network using emulation with sdn and openstack. ono and odl (opendaylight) [69] are the largest open-source sdn controllers that are making it possible for the sdn to join with openstack by means of modules. modules in the openstack suite such as neutron can be designed to utilize as an alternate to the sdn controller rather than utilizing neutron's own particular capacities. 118 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 6. challenges to sdn based cloud despite the fact that sdn-based cloud demonstrates numerous great highlights, it faces a few difficulties that must be considered, including execution, accessibility, and versatility security. although numerous examinations have explored the utilization of sdn innovation in cloud computing, there are as yet a few perspectives that have not been investigated exhaustively [70-71]. 6.1 execution execution refers to the system hub for the preparing pace considering both latency and throughput [72]. the strategy for sdn was to deal with new packets which bring the network programmability. but, at the same time, it produces execution issues. the authors [73] had explained that nowadays controllers cannot deal with a huge number of flows in connections of 10 gbps. so the question is how to keep programmability which is requiring for additional examination and to enhance execution. 6.2 accessibility the duration or the time in which the framework of sdn is in running condition is called accessibility. in the sdn network as there is a dependency on the single centralized controller. though it brings the programmability, on the other hand, it also brings a challenge with respect to accessibility. one of the advantages that the traditional distributed network architecture is comprised of is that if a switch fails, the accessibility of the system does not affect and still can be looked for [74]. but on the other hand in the sdn network if a single point of control i.e. sdn controller fails the whole network collapses and then the accessibility of the system might be lost completely. 6.3 scalability it is the ability to increase the network infrastructure so that it can easily incorporate the demand or need for network growth. then centralized single sdn controller can be converted into a bottleneck of versatility [75]. by introducing peer-with-peer or distributed controller foundation it may share the communication weight to the controller. it may be, a general system view is required to coordinate the correspondences between the controllers utilizing the westward and eastward apis. behind controller adaptability, there are some other versatility concerns including the overhead of flow setup and flexibility to failures. one of the basic issues that need to be addressed is the scalability of the sdn controller [77]. sdn controller accumulates data from the whole system and then handles each and every individual network switch individually; this process makes the controller adaptable and keeps the single point of failure at the controller. in the cloud, this entanglement can become a critical issue because of the size multiple-sided quality of dcn and the normal sla for the supplier [77]. the sdn controller for the cloud dcn can without much of a stretch turn into a solitary purpose of disappointment as controllers in the dcn can be over-burden because of the gigantic number of network switches. the aforementioned issue can be handled by disseminating controllers or by implementing a proactive approach while communicating between the sdn controller and switch [77]. 6.4 virtualization previously, nfv is provided by middle boxes, which are embedded with dedicated hardware, such as load balancer, firewall and intrusion detectors. these dedicated and vendor specific hardware devices are meant to perform the single task only and they don’t 119 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 allow the network administrator to reconfigure their codes and hence hardware inflexibility is there which ultimately reduces the cost-effectiveness. many researchers have already attempted to alter the hardware of middle boxes with a series of sdn switches which are embedded with specific controller programs [5]. 6.5 security as compared to traditional networking sdn brings separation of intelligence of the sdn network constitutes in the control plane and network devices from the data plane. due to this, there is an increase in the rise of security attacks [78]. security investigation has demonstrated that the sdn system endures numerous security dangers, including: 1) unapproved get to, e.g., the unapproved controller gets to or unauthenticated application get to. 2) information spillage, e.g., flow control disclosure (side station assault on input cushion) sending strategy revelation (parcel handling timing examination), 3) alteration in the information, e.g., modification in flow run to alter bundles [78-79]. 4) noxious applications, e.g., false run addition controller commandeering. 5) issues in configuration e.g., absence of tls (or other verification strategies) reception strategy requirement. 6) denial of service, e.g., while providing communication between switch-controller there may occur a switch or controller table flooding [80]. for various available open cloud providers, the most important aspect that needs to be addressed is security. while accessing the cloud services user’s information is an important factor. although security in cloud data centres has been explored broadly with multiple methodologies, collaborating sdn into it can make it vulnerable [81]. so, research can be directed towards providing security to the sdn enabled cloud data centres [82-83]. 6.7 energy efficiency cloud data centres are consuming a huge amount of electricity which is increasing very rapidly. in 2013, 91 billion kilowatt-hours energy was consumed by us data centres, which is more than enough to power all households in nyc for 2 years. it is even expected that by 2020 it will be increased to approximately 140 billion kilowatt-hours which will cost the us $13 [7] billions annually. therefore to improve energy efficiency while computing the cloud is becoming a most important research problem in both academics and in industries. there are already many researchers who are working in this area to optimize energy efficiency [7]. with the recent introduction of sdn, the technology of joint optimization is feasible and it can be explored in order to save maximum energy and therefore providing best qos [7, 84]. 6.8 network function virtualization dcn is comprised of many numbers of devices, these devices communicate with each other through multiple switches and devices and virtualization of the network in it is quite difficult because of the complexity of the network. there are gaps which are found while realizing virtualization of the network in clouds, which can be diminished by making of sdn. although traditional networking technologies as vpn and vlan not only accepted by industry is making use of them. but by combining sdn with the traditional methods can take even more flexibility, programmability, and security to 120 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 clouds. thus for further research, virtualization of the network can be explored in a cloud data center. 6.9 system function virtualization there are gaps in acknowledging virtualization of the system in the cloud, which can be feasible with the coordination of sdn [7]. though the customary systems administration advancements, like vpn and vlan has been broadly embraced in industry, co-ordination of sdn with the conventional technologies can bring much better execution and more adaptability to the cloud. along with sdn, streams among vms can be controlled more finely all the powerfulness and adaptability by adjusting the evolving activity. progressively, switches can be continuously arranged in the supervision of the controller, which can direct the whole network. therefore, virtualization of the network for sla network guarantee is possible can be investigated in cloud data centres and introducing research in [7, 84]. 7. final remarks and conclusion use of iot devices is increasing day by day. the foundation behind cloud networks, cloud computing, is making use of large networks to fulfil user demands. the cloud network is growing at a very fast pace but by making use of traditional networks, cloud networking is suffering from inflexibility, less manageability, and vendor specificity. to overcome the situation, sdn can be used in cloud data centre networks. sdn not only achieves programmability, agility, manageability but removes the barrier of vendorspecific by using the principle of separating the control plane and data plane. the job of the network administrator to overlook the network and managing the network can be easily achieved. in this paper, an overview of traditional networking used in cloud computing with its disadvantages and how sdn can improve its functionality is described. this paper discussed the related work in this collaboration various limitations and advantages of their work is also surveyed. in order to implement cloud and sdn, this paper would be contributing to researchers. various simulation and emulation platforms for performing the experiments are also discussed. at last research directions towards sdn based cloud are also provided. references [1] senyo, p. k., effah, j., & addae, e. (2016). preliminary insight into cloud computing adoption in a developing country. journal of enterprise information management, 29(4), 505–524. [2] buyya, r., yeo, c. s., venugopal, s., broberg, j., & brandic, i. (2009). cloud computing and emerging it platforms: vision, hype, and reality for delivering computing as the 5th utility. future generation computer systems, 25(6), 599-616. [3] senyo, p. k., addae, e., & boateng, r. (2018). cloud computing research: a review of research themes, frameworks, methods and future research directions. international journal of information management, 38(1), 128-139. [4] bayramusta, m., & nasir, v. a. (2016). a fad or future of it? : a comprehensive literature review on the cloud computing research. international journal of information management, 36(4), 635–644. [5] son, j., & buyya, r. (2018). a taxonomy of software-defined networking (sdn)-enabled cloud computing. acm computing surveys (csur), 51(3), 59. 121 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 [6] al-fares, m., loukissas, a. and vahdat, a., (2008), august. a scalable, commodity data center network architecture. in acm sigcomm computer communication review,vol. 38, no. 4, pp. 63-74. [7] buyya, r., calheiros, r.n., son, j., dastjerdi, a.v. and yoon, y., (2014), september. software-defined cloud computing: architectural elements and open challenges. in advances in computing, communications and informatics (icacci, 2014 international conference on (pp. 1-12). ieee. [8] jararweh, y., al-ayyoub, m., benkhelifa, e., vouk, m. and rindos, a.,( 2016). software defined cloud: survey, system and evaluation. future generation computer systems, 58, pp.56-74. [9] kreutz, d., ramos, f.m., verissimo, p.e., rothenberg, c.e., azodolmolky, s. and uhlig, s., (2015). software-defined networking: a comprehensive survey. proceedings of the ieee, 103(1), pp.14-76. [10] badotra, s. and singh, j., (2017). a review paper on software defined networking. international journal of advanced research in computer science, 8(3). [11] mckeown, n., anderson, t., balakrishnan, h., parulkar, g., peterson, l., rexford, j., shenker, s. and turner, j., (2008). openflow: enabling innovation in campus networks. acm sigcomm computer communication review, 38(2), pp.69-74. [12] lantz, b., heller, b. and mckeown, n., (2010), october. a network in a laptop: rapid prototyping for software-defined networks. in proceedings of the 9th acm sigcomm workshop on hot topics in networks (p. 19). acm. [13] vahdat, a., clark, d. and rexford, j., (2015). a purpose-built global network: google's move to sdn. queue, 13(8), p.100. [14] toosi, a.n., calheiros, r.n. and buyya, r., (2014). interconnected cloud computing environments: challenges, taxonomy, and survey. acm computing surveys (csur), 47(1), p.7. [15] mastelic, t., oleksiak, a., claussen, h., brandic, i., pierson, j.m. and vasilakos, a.v., (2015). cloud computing: survey on energy efficiency. acm computing surveys (csur), 47(2), p.33. [16] jararweh, y., al-ayyoub, m., benkhelifa, e., vouk, m. and rindos, a., (2016). software defined cloud: survey, system and evaluation. future generation computer systems, 58, pp.56-74. [17] azodolmolky, s., wieder, p. and yahyapour, r., (2013), june. sdn-based cloud computing networking. in transparent optical networks (icton), 2013 15th international conference on (pp. 1-4). ieee. [18] yen, t.c. and su, c.s., (2014), april. an sdn-based cloud computing architecture and its mathematical model. in information science, electronics and electrical engineering (iseee), 2014 international conference on (vol. 3, pp. 1728-1731). ieee. [19] buyya, r., broberg, j. and goscinski, a.m. eds., (2010). cloud computing: principles and paradigms (vol. 87). john wiley & sons. [20] grover, j. and sharma, m., (2014), july. cloud computing and its security issues—a review. in computing, communication and networking technologies (icccnt), 2014 international conference on (pp. 1-5). ieee. [21] yang, h., & tate, m. (2012). a descriptive literature review and classification of cloud computing research. communications of the association for information systems, 31(1), 2. [22] kaur, s. and singh, a., (2012). the concept of cloud computing and issues regarding its privacy and security. international journal of engineering research & technology (ijert), 1(3). [23] choo, k.k.r., (2010). cloud computing: challenges and future directions. trends and issues in crime and criminal justice, (400), p.1. [24] zhang, q., cheng, l. and boutaba, r., (2010). cloud computing: state-of-the-art and research challenges. journal of internet services and applications, 1(1), pp.7-18. [25] kumar, d.k., rao, d.g.v. and rao, d.g.s., (2012). cloud computing: an analysis of its challenges & security issues. international journal of computer science and network (ijcsn), 1(5). 122 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 [26] dogra, n. and kaur, h., (2013). cloud computing security: issues and concerns. international journal of emerging technology and advanced engineering, 3(3). [27] al-fares, m., loukissas, a. and vahdat, a., (2008), august. a scalable, commodity data center network architecture. in acm sigcomm computer communication review (vol. 38, no. 4, pp. 63-74). acm [28] clos, c., (1953). a study of non blocking switching networks. bell system technical journal, 32(2), pp.406-424. [29] guo, c., wu, h., tan, k., shi, l., zhang, y. and lu, s., (2008), august. dcell: a scalable and fault-tolerant network structure for data centers. in acm sigcomm computer communication review (vol. 38, no. 4, pp. 75-86). acm. [30] guo, c., lu, g., li, d., wu, h., zhang, x., shi, y., tian, c., zhang, y. and lu, s., (2009). bcube: a high performance, server-centric network architecture for modular data centers. acm sigcomm computer communication review, 39(4), pp.63-74. [31] zhang, z., deng, y., min, g., xie, j. and huang, s., (2017). exccc-dcn: a highly scalable, cost-effective and energy-efficient data center structure. ieee transactions on parallel and distributed systems, 28(4), pp.1046-1060. [32] bilal, k., malik, s.u.r., khalid, o., hameed, a., alvarez, e., wijaysekara, v., irfan, r., shrestha, s., dwivedy, d., ali, m. and khan, u.s., (2014). a taxonomy and survey on green data center networks. future generation computer systems, 36, pp.189-208 [33] chen, t., gao, x. and chen, g.,( 2016). the features, hardware, and architectures of data center networks: a survey. journal of parallel and distributed computing, 96, pp.45-74. [34] xia, w., zhao, p., wen, y. and xie, h., (2017). a survey on data center networking (dcn): infrastructure and operations. ieee communications surveys & tutorials, 19(1), pp.640-656. [35] bari, m.f., boutaba, r., esteves, r., granville, l.z., podlesny, m., rabbani, m.g., zhang, q. and zhani, m.f., (2013). data center network virtualization: a survey. ieee communications surveys & tutorials, 15(2), pp.909-928. [36] he, t., toosi, a. n., & buyya, r. (2019). performance evaluation of live virtual machine migration in sdn-enabled cloud data centers. journal of parallel and distributed computing, 131, 55-68. [37] abts, d., marty, m.r., wells, p.m., klausler, p. and liu, h., (2010). energy proportional datacenter networks. acm sigarch computer architecture news, 38(3), pp.338-347. [38] amarasinghe, h., jarray, a. and karmouch, a., (2017), may. fault-tolerant iaas management for networked cloud infrastructure with sdn. in communications (icc), 2017 ieee international conference on (pp. 1-7). ieee. [39] nunes, b.a.a., mendonca, m., nguyen, x.n., obraczka, k. and turletti, t., (2014). a survey of software-defined networking: past, present, and future of programmable networks. ieee communications surveys & tutorials, 16(3), pp.1617-1634. [40] alsaeedi, m., mohamad, m. m., & al-roubaiey, a. a. (2019). toward adaptive and scalable openflow-sdn flow control: a survey. ieee access, 7, 107346-107379. [41] bilal, r., & khan, b. m. (2019). software-defined networks (sdn): a survey. in handbook of research on cloud computing and big data applications in iot (pp. 516536). igi global. [42] t karakus, m., & durresi, a. (2017). a survey: control plane scalability issues and approaches in software-defined networking (sdn). computer networks, 112, 279-293. [43] kim, h. and feamster, n.,(2013). improving network management with software defined networking. ieee communications magazine, 51(2), pp.114-119. [44] jarraya, y., madi, t. and debbabi, m., (2014). a survey and a layered taxonomy of software-defined networking. ieee communications surveys & tutorials, 16(4), pp.19551980. [45] azodolmolky, s., wieder, p. and yahyapour, r., (2013). cloud computing networking: challenges and opportunities for innovations. ieee communications magazine, 51(7), pp.54-62. [46] banikazemi, m., olshefski, d., shaikh, a., tracey, j. and wang, g., (2013). meridian: an sdn platform for cloud network services. ieee communications magazine, 51(2), pp.120127. 123 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 [47] priya, i. d., & silas, s. (2019). a survey on research challenges and applications in empowering the sdn-based internet of things. in advances in big data and cloud computing (pp. 457-467). springer, singapore. [48] yan, q., yu, f.r., gong, q. and li, j., (2016). software-defined networking (sdn) and distributed denial of service (ddos) attacks in cloud computing environments: a survey, some research issues, and challenges. ieee communications surveys & tutorials, 18(1), pp.602-622. [49] jain, r. and paul, s.,( 2013). network virtualization and software defined networking for cloud computing: a survey. ieee communications magazine, 51(11), pp.24-31. [50] ma, y.w., chen, y.c. and chen, j.l., (2017), february. sdn-enabled network virtualization for industry 4.0 based on iots and cloud computing. in advanced communication technology (icact), 2017 19th international conference on (pp. 199202). ieee. [51] li, f., cao, j., wang, x., sun, y. and sahni, y., (2017), june. enabling software defined networking with qos guarantee for cloud applications. in 2017 ieee 10th international conference on cloud computing (cloud) (pp. 130-137). ieee. [52] bruschi, r., davoli, f., lago, p., lombardo, a., lombardo, c., rametta, c. and schembra, g., (2017). an sdn/nfv platform for personal cloud services. ieee transactions on network and service management, 14(4), pp.1143-1156. [53] papagianni, c., androulidakis, g. and papavassiliou, s., (2014), february. virtual topology mapping in sdn-enabled clouds. in network cloud computing and applications (ncca), 2014 ieee 3rd symposium on (pp. 62-67). ieee. [54] alhazmi, k., shami, a. and refaey, a., (2017). optimized provisioning of sdn-enabled virtual networks in geo-distributed cloud computing datacenters. journal of communications and networks, 19(4), pp.402-415. [55] nguyen, t. g., phan, t. v., nguyen, b. t., so-in, c., baig, z. a., & sanguanpong, s. (2019). search: a collaborative and intelligent nids architecture for sdn-based cloud iot networks. ieee access, 7, 107678-107694. [56] buyya, r., yeo, c.s., venugopal, s., broberg, j. and brandic, i., (2009). cloud computing and emerging it platforms: vision, hype, and reality for delivering computing as the 5th utility. future generation computer systems, 25(6), pp.599-616. [57] son, j., dastjerdi, a.v., calheiros, r.n. and buyya, r., (2017). sla-aware and energyefficient dynamic overbooking in sdn-based cloud data centers. ieee transactions on sustainable computing, 2(2), pp.76-89. [58] pajila, p. b., & julie, e. g. (2019, february). detection of ddos attack using sdn in iot: a survey. in intelligent communication technologies and virtual mobile networks (pp. 438-452). springer, cham. [59] martínez, r., mayoral, a., vilalta, r., casellas, r., muñoz, r., pachnicke, s., szyrkowiec, t. and autenrieth, a., (2017). integrated sdn/nfv orchestration for the dynamic deployment of mobile virtual backhaul networks over a multilayer (packet/optical) aggregation infrastructure. journal of optical communications and networking, 9(2), pp.a135-a142. [60] openstack foundation. (2018). open source software for creating private and public clouds. retrieved from https://www.openstack.org/ [61] mayoral, a., munoz, r., vilalta, r., casellas, r., martínez, r. and lópez, v., (2017). need for a transport api in 5g for global orchestration of cloud and networks through a virtualized infrastructure manager and planner. ieee/osa journal of optical communications and networking, 9(1), pp.a55-a62. [62] fichera, s., gharbaoui, m., castoldi, p., martini, b. and manzalini, a., (2017), july. on experimenting 5g: testbed set-up for sdn orchestration across network cloud and iot domains. in network softwarization (netsoft), 2017 ieee conference on (pp. 1-6). ieee. [63] stallings, w. (2015). foundations of modern networking: sdn, nfv, qoe, iot, and cloud. addison-wesley professional. [64] calheiros, r.n., ranjan, r., beloglazov, a., de rose, c.a. and buyya, r., (2011). cloudsim: a toolkit for modeling and simulation of cloud computing environments and 124 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 evaluation of resource provisioning algorithms. software: practice and experience, 41(1), pp.23-50. [65] badotra, s., & singh, j. (2017). a review paper on software defined networking. international journal of advanced research in computer science, 8(3). [66] kliazovich, d., bouvry, p. and khan, s.u., (2012). greencloud: a packet-level simulator of energy-aware cloud computing data centers. the journal of supercomputing, 62(3), pp.1263-1283. [67] network simulator ns-2. retrieved from http://www.isi.edu/nsnam/ns/ [68] ahn, g. j., gu, g., hu, h., & shin, s. (2019, march). sdn-nfv security 2019 preface. in sdn-nfv 2019-proceedings of the acm international workshop on security in software defined networks and network function virtualization, co-located with codaspy 2019 (p. iii). [69] riley, g. f., & henderson, t. r. (2010). the ns-3 network simulator. in modeling and tools for network simulation (pp. 15-34). springer, berlin, heidelberg. [70] son, j., dastjerdi, a.v., calheiros, r.n., ji, x., yoon, y. and buyya, r., (2015), may. cloudsimsdn: modeling and simulation of software-defined cloud data centers. in cluster, cloud and grid computing (ccgrid), 2015 15th ieee/acm international symposium on (pp. 475-484). ieee. [71] teixeira, j., antichi, g., adami, d., del chiaro, a., giordano, s. and santos, a., (2013), october. datacenter in a box: test your sdn cloud-datacenter controller at home. in software defined networks (ewsdn), 2013 second european workshop on (pp. 99-104). ieee. [72] badotra, s. and singh, j., (2017). open daylight as a controller for software defined networking. international journal of advanced research in computer science, 8(5). [73] bhushan, k. and gupta, b.b., (2017). security challenges in cloud computing: state-ofart. international journal of big data intelligence, 4(2), pp.81-107. [74] bhushan, k., & gupta, b. b. (2019). distributed denial of service (ddos) attack mitigation in software defined network (sdn)-based cloud computing environment. journal of ambient intelligence and humanized computing, 10(5), 1985-1997. [75] sezer, s., scott-hayward, s., chouhan, p.k., fraser, b., lake, d., finnegan, j., viljoen, n., miller, m. and rao, n., (2013). are we ready for sdn? implementation challenges for software-defined networks. ieee communications magazine, 51(7), pp.36-43. [76] jarschel, m., oechsner, s., schlosser, d., pries, r., goll, s. and tran-gia, p., (2011), september. modeling and performance evaluation of an openflow architecture. in proceedings of the 23rd international teletraffic congress (pp. 1-7). international teletraffic congress. [77] pandya, b., parmar, s., saquib, z. and saxena, a., (2017), march. framework for securing sdn southbound communication. in innovations in information, embedded and communication systems (iciiecs), 2017 international conference on (pp. 1-5). ieee. [78] yan, q., yu, f. r., gong, q., & li, j. (2015). software-defined networking (sdn) and distributed denial of service (ddos) attacks in cloud computing environments: a survey, some research issues, and challenges. ieee communications surveys & tutorials, 18(1), 602-622. [79] sezer, s., scott-hayward, s., chouhan, p.k., fraser, b., lake, d., finnegan, j., viljoen, n., miller, m. and rao, n.,(2013). are we ready for sdn? implementation challenges for software-defined networks. ieee communications magazine, 51(7), pp.36-43. [80] yeganeh, s.h., tootoonchian, a. and ganjali, y., (2013). on scalability of software-defined networking. ieee communications magazine, 51(2), pp.136-141. [81] jantila, s. and chaipah, k., (2016). a security analysis of a hybrid mechanism to defend ddos attacks in sdn. procedia computer science, 86, pp.437-440. [82] dargahi, t., caponi, a., ambrosin, m., bianchi, g. and conti, m., (2017). a survey on the security of stateful sdn data planes. ieee communications surveys & tutorials, 19(3), pp.1701-1725. [83] wang, b., zheng, y., lou, w. and hou, y.t., (2015). ddos attack protection in the era of cloud computing and software-defined networking. computer networks, 81, pp.308-319. 125 iium engineering journal, vol. 20, no. 2, 2019 badotra and panda https://doi.org/10.31436/iiumej.v20i2.1130 [84] negru, c., mocanu, m., cristea, v., sotiriadis, s. and bessis, n., (2017). analysis of power consumption in heterogeneous virtual machine environments. soft computing, 21(16), pp.4531-4542. 126 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <feff004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 143-887-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 mohd akil tan et. al 77 characterization of materials by vibration technique m. h. mohd akil tan, n. l. tajul lile, f. mat and s. yaacob school of mechatronic engineering, universiti malaysia perlis (unimap), ulu pauh, 02600 perlis, malaysia. hilmanakil@yahoo.com abstract: this paper presents an experimental investigation of two different kinds of plates of materials namely glass and stainless steel by experimental modal analysis. the materials are excited by an impact hammer to perform resonant vibration where the characteristics of the resonance are acquired. one most important characteristic is the natural frequency where it is known that different material having undergone resonant vibration exhibit different specific natural frequencies to it. the natural frequencies and corresponding mode shapes are used as the parameters of determining the structural properties of these materials. the vibration analysis is done using the lms instruments and software where frequency response function (frf) measurement technique is employed in determining the natural frequencies. the structural properties are established based on the obtained natural frequencies and geometries of the materials using the expression from available literature. the elastic moduli obtained for glass and stainless steel are 66.08 gpa and 193.26 gpa. abstrak: kertas ini membentangkan kajian mengenai dua bahan plat yang berbeza iaitu kaca dan keluli tahan karat dengan menggunakan analisis ragaman eksperimental. getaran resonans dijalankan dengan menguja bahan-bahan tersebut dengan tukul hentaman dimana ciri-ciri tertentu diperolehi. frekuensi asli merupakan satu daripada ciri utama, dimana ianya diketahui bahawa bahan yang berbeza akan mengalami getaran resonans yang menghasilkan frekuensi asli tertentu. frekuensi asli dan bentuk ragam yang berpadanan digunakan sebagai parameter dalam menentukan sifat-sifat struktur bahan ini. analisis getaran dijalankan dengan menggunakan peralatan lms dan teknik ukuran perisian fungsi frekuensi sambutan (frequency response function (frf)) untuk menentukan frekuensi asli. sifat-sifat struktur ditentukan berdasarkan frekuensi asli dan bahan geometri, yang diperolehi daripada pengungkapan bahan sumber bacaan yang sedia ada. modulus keanjalan yang diperolehi untuk kaca adalah 66.08 gpa dan untuk keluli tahan karat adalah 193.26 gpa. keywords: modal analysis; resonant vibration; natural frequency; nondestructive testing; frf measurement; glass; stainless steel; young’s modulus. 1. introduction the study of materials characterization is important in knowing more about the behavior of the materials so that the utilization of the materials could be varied and used to the utmost potential. knowledge of materials characterization is widely applied in the area of failure analysis to prevent engineering breakdown especially the very much undesirable catastrophic and cascading ones. in the area where safety, reliability and quality control are highly iium engineering journal, special issue, mechanical engineering, 2011 mohd akil tan et. al 78 considered, the continuous development of analysis technique and measurement technology for materials characterization becomes inevitable. one prominent aspect of materials characterization is the determination of elastic properties for materials by investigating the corresponding elastic constants namely young’s modulus (e), and poisson’s ratio (v). as meticulously reviewed in [1], various techniques have been developed for characterizing materials by their elastic properties. these variation of techniques could be classified into two major methods: static and dynamic. static methods are based on determination of specimen’s stress and strain during standard mechanical testing. the specimens need to conform to certain specific shape and size for testing. one example of such test is the tensile test using universal testing machine (utm) where the specimens are shaped like a dog bone to specific length and thickness. graph of stress and strain is plotted from the test and used to determine the mechanical behaviour of the specimens. the desired e is attained from the slope of the linear region of the stress-strain graph. the test often requires a certain range of deformation of the specifically sized and shaped specimen for measurement of e. it is a destructive test as the specimens are usually tested until failure or reaches plastic region hence can no longer be used for further investigation. meanwhile, dynamic methods are nondestructive methods allowing variation in specimens’ shapes and dimensions. materials could be repeatedly tested through range of temperatures and conditions. there are two types of dynamic methods namely ultrasonic method and resonant method. ultrasonic method involves the quantification of transit time of wave propagation through materials while resonant method involves the measurement of natural frequencies and the associated modal shapes to acquire the desired elastic constants. resonant method or modal vibration testing has been widely favoured as the method of testing due to the fact that it is easy to be implemented and does not require expensive equipments. astm e 1876-09 [2] provided the procedures for determining elastic properties from the measured impulse excitation of vibration. however the standard only applies to specimens with structural shapes of beams, rods and disks. as highlighted in [1], simple structures like beam and rod are easier for direct determination of elastic constants from modal testing to be applied compare to complex structures like plates and shells. many researches have been done for finding the most proper procedure for the determination of elastic properties of rectangular plates from modal vibration technique [3-8]. the procedure proposed in [3] seems very feasible and reliable and hence it has been employed in our experiment. this paper presents the modal analysis of square plates from different materials for determination of elastic constants e and v. the results are then compared to the one attained from mechanical testing and theoretical values to evaluate the precision of such procedure. 2. overview of specimens two types of materials had been tested. it consisted of stainless steel and glass. both materials were cut to square plates of 250mmx250mmx3mm and were marked with nine nodes on the surfaces; as shown in fig. 1. the stainless steel is an austenitic stainless steel iium engineering journal, special issue, mechanical engineering, 2011 mohd akil tan et. al 79 having properties similar to the 304 type while the glass is the ordinary sheet glass normally used for windows making. fig. 1: schematic representation of a specimen with nodes position. 3. experimental modal analysis the experimental modal analysis was carried out using the dynamic application group (dag) technologies (malaysia) sdn. bhd. [9] instruments using the lms international [10] software where frequency response function (frf) measurement technique is employed in extracting the natural frquencies. for this particular research the modal analysis is done using the method of impact hammer test. this single fixed output testing method which is further described in [11] is one of the most favoured methods for modal testing as it is economical, fast and undemanding in terms of resonance investigation the specimens were impacted to nine different nodes which were already allocated on the surface of the materials (fig. 1). for each node, the frf curve was plotted so that the observation of resonant frequency behavior could be performed thoroughly. the natural frequencies of the plates were then determined from the accumulation of frf curve behavior of all nodes along with corresponding mode shapes by modal analysis. careful observation should be done in determining the desired natural frequencies where all frf of every node should be studied because a peak of natural frequency could appear in one node but not the other as depicted in fig. 2-5. the selection of the right frequencies is the essential step in determining the value of frequency ratio hence the values of the elastic constants. iium engineering journal, special issue, mechanical engineering, 2011 mohd akil tan et. al 80 fig. 2: frf for the first node of stainless steel. fig. 3: frf for the sixth node of stainless steel. iium engineering journal, special issue, mechanical engineering, 2011 mohd akil tan et. al 81 fig. 4: frf for the first node of glass. fig. 5: frf for the sixth node of glass. the obtained natural frequencies were then exploited for the procedure outlined in [3] using the formula presented in the same paper: ܧ = ସ଼ గమ ቀ௙ ఒ ቁ ଶ ௠௔య(ଵି௩మ) ௕௧య (1) iium engineering journal, special issue, mechanical engineering, 2011 mohd akil tan et. al 82 where e and v are the elastic constants, f is the natural frequency, m is the mass of the material, a and b are the width and length of the sides of the plate, where in this case a = b, t is the thickness, and λ is a non-dimensional factor obtained from the table presented in [3] as well. 4. results table 1: dimensions, mass and natural frequencies of materials. dimensions,a x b x t (m3) mass,m (kg) f1 (hz) f2(hz) f3(hz) f4 (hz) stainless steel 0.25 x 0.25 x 0.003 1.490 156.126 233.258 264.016 400.887 glass 0.25 x 0.25 x 0.003 0.468 165.439 227.142 279.802 428.809 table 2: elastic constants of materials. frequency ratio, fj/fi v λi λj ei(gpa) ej(gpa) stainless steel f3/f1 1.691 0.224 1.430 2.419 189.81 189.81 f3/f2 1.132 0.178 2.113 2.391 198.04 198.04 f4/f3 1.518 0.212 2.412 3.662 191.92 191.92 mean values 0.205 193.26 glass f3/f1 1.691 0.224 1.430 2.419 66.99 66.99 f3/f2 1.232 0.293 1.993 2.456 62.59 62.58 f4/f3 1.533 0.198 2.403 3.683 68.67 68.67 mean values 0.238 66.08 table 3: comparison between experimental and theoretical values. materials parameters experimental theoretical [12] stainless steel e (gpa) 193.26 193 v 0.205 0.3-0.31 glass e (gpa) 66.08 50-90 v 0.238 0.18-0.3 iium engineering journal, special issue, mechanical engineering, 2011 mohd akil tan et. al 83 5. remarks from the results presented in table 1-2, it could be seen that the acquired natural frequencies for glass are generally higher than that of stainless steel for every matching mode value. this is due to the fact that the frequency of material is in inverse proportion of mass where in this case, glass, which has lower mass gives higher corresponding frequencies compared to stainless steel. from the comparison table between the experimental modal analysis testing and theoretical values (table 3), it could be seen that the values for e for both materials are in the range of the theoretical ones but the values for v for stainless steel doesn’t really comply to the theoretical value. this may be due to the fact that the ratio of length over thickness, a/t does not equal or exceed 100 as mentioned in [3]. this discrepancy could however be avoided in the future by carefully selecting the dimensions for the plates. due to the advantages that this technique has including the ease of use, inexpensive and convenient way of conducting the procedure, it is not a surprise that this technique has been increasingly favoured to be adopted in industries and laboratories. besides being a nondestructive type of method with great precision, there is a very high probability that the use of such technique would only continue to grow with more research and exploration of how to employ it to future practicability. 6. conclusion this paper presented the use of experimental modal analysis technique in determining the elastic constants for square plates. it was found that the values obtained from this technique are in great precision with the theoretical values despite some inconsistency due to avoidable poor selection of specimens’ dimensions. for future work, this modal vibration technique which provides the knowledge of natural frequencies relationship to properties of materials would be best integrated with the use of artificial intelligence algorithm system such as artificial neural network especially in the area of pattern recognition where some preliminary works could be done in order to create a system of materials identification for easier assessment of characterization of materials. acknowledgement the malaysian ministry of higher education (mohe) kindly provided funding for the research through the "fundamental research grant scheme" (frgs) no 9003-00222. references [1] l. pagnotta, “recent progress in identification methods for the elastic characterization of materials,” international journal of mechanics, 2008, vol. 2, n. 4, pp. 129-140. [2] astm standard e1876-09, “standard test method for dynamic young’s modulus, shear modulus, and poisson’s ratio by impulse excitation of vibration,” astm international, west conshohocken, pa, 2003, doi: 10.1520/e1876-09, www.astm.org. iium engineering journal, special issue, mechanical engineering, 2011 mohd akil tan et. al 84 [3] m. alfano, l. pagnotta, “determining the elastic properties of isotropic materials by modal vibration testing of rectangular thin plates,” journal of sound and vibration, vol. 293, 2006, pp. 426-439. [4] a.w. leissa, vibration of plates (nasa sp-160), us government printing office, washington, dc, 1969. [5] m.d. waller, vibration of free rectangular plates. proceedings of the physical society, london 72 (1949), pp. 277–285. [6] f. moussu, m. nivoit, determination of elastic constants of orthotropic plates by a modal analysis/method of superposition, journal of sound and vibration, volume 165, issue 1, 22 july 1993, pp 149-163. [7] s.f. hwang, c.s. chang, “determination of elastic constants of materials by vibration testing,” composite structures, vol. 49, 2000, pp 183-190. [8] l.r. deobald, r. f. gibson, “determination of elastic constants oforthotropic plates by modal analysis/rayleigh-ritz technique,” journal of sound and vibration, vol. 124, 1988, pp. 269283. [9] dynamic application group (dag) technologies (malaysia) sdn. bhd, malaysia, www.dagtech.com.my. [10] lms international nv, belgium, www.lmsintl.com. [11] brian j. schwarz & mark h. richardson, ‘experimental modal analysis’, application note vibrant technology, inc., (1999) [12] matweb – material property data www.matweb.com. nomenclature a length m b width m t thickness m m mass kg e young’s modulus gpa v poisson’s ratio f frequency hz λ frequency factor application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 182 an analytical technique to obtain higher-order approximate periods for the nonlinear oscillator md sazzad hossien chowdhury1*, md. alal hosen2, mohammad yeakub ali3 and ahmad faris ismail4 1 department of science in engineering, kulliyyah of engineering, international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia. 2 department of mathematics, rajshahi university of engineering and technology, rajshahi-6204, bangladesh 3 department of manufacturing and material engineering, 4 department of mechanical engineering, kulliyyah of engineering, international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia. *corresponding author: sazzadbd@iium.edu.my (received:4th june 2018; accepted: 21st sept2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.943 abstract: in this paper, an analytical technique has been proposed to obtain higherorder approximate periods for the nonlinear oscillator with the square of the angular frequency depending quadratically on the velocity which is based on the harmonic balance method (hbm). analytical investigation of the appeared set of nonlinear algebraic equations is usually cumbersome, which is addressed by the proposed technique in a novel way. in this paper, this limitation is eradicated and provides desired results without much numerical complexity. additionally, a new suitable truncation formula has been introduced in which the approximate periods measure much better results than existing periods. the proposed technique is applied to the benchmark nonlinear oscillatory problem where the square of the angular frequency depends quadratically on the velocity to illustrate its novelty, reliability, and wider applicability. it is remarkably improtant to note that, using the proposed technique, a third-order approximate period gives an excellent agreement as compared with the exact ones. abstrak: kertas cadangan ini membincangkan tentang teknik analitikal bagi menghasilkan tempoh anggaran lebih tinggi pada sistem bukan linear dengan kuasa dua frekunsi angular halaju kuadratik, iaitu bergantung pada kaedah imbangan harmoni (hbm). penyelidikan analitikal pada set persamaan algebra bukan linear selalunya adalah rumit, iaitu dibincangkan secara teknik cadangan baru. kertas ini, menghapuskan kekurangan ini dan menghasilkan keputusan tanpa banyak kerumitan numerik. selain itu, formula baru yang ringkas dan sesuai ini diperkenalkan dengan tempoh anggaran ukuran keputusan lebih bagus daripada tempoh sedia ada. teknik yang dicadangkan ini digunakan sebagai penanda aras pada masalah osilator bukan linear dengan frekunsi angular halaju kuadratik bagi memperlihatkan kebaharuan, kebergantungan dan keluasan pada kegunaannya. pengunaan kaedah ini adalah sangat luar biasa. keywords: approximate periods; truncation principle; harmonic balance method; nonlinear oscillator; analytical technique iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 183 1. introduction nonlinear oscillations have important aspects for areas including physical sciences, mechanical structures, engineering and other disciplines [1,2] which appear mathematically in the form of nonlinear differential equations (ndes). the solution procedure of obtaining approximate solutions of linear differential equations is comparatively easy and well established. in contrast, the solution procedure of obtaining approximate solutions of ndes remains less available to this day. it is often more difficult to get an analytic approximation than a numerical one. a few nonlinear systems can be solved explicitly, and the numerical methods especially the most well-known runge-kutta fourth order method are frequently used to calculated approximate solutions. however, in stiff differential equations and chaotic differential equations, the numerical schemes do not always give accurate results, thus presenting a big challenge to numerical analysis. in this situation, many researchers have shown an intensifying interest in the field of analytical approximate techniques. the most widely used analytical technique for solving nonlinear equations associated with oscillatory systems is the perturbation method [3-6], which is the most versatile tool available in nonlinear analysis of engineering problems, and it is constantly being developed and applied to ever more complex problems. however, the standard perturbation methods have many limitations, and they do not yield for strongly nonlinear oscillators. as a result, to overcome this shortcoming, in recent years, a large variety of modified perturbation techniques are commonly used in nonlinear systems, especially for strongly nonlinear oscillators. there modified methods include optimal homotopy asymptotic method [7], homotopy perturbation method [8-10], modified homotopy perturbation method [11], modified he’s homotopy perturbation method [12-14], modified lindsted-poincare method [15], he’s modified lindsted-poincare method [16], and modified multiple time scale method [17]. in the recent past, some other approximation techniques have been investigated. these techniques include the he’s max-min approach [18], elliptic balance [19], algebraic [20], the differential transform approach [21], he’s frequency-amplitude formulation [22], iteration [23], the variational approach [24], energy balance [25-29] methods, and the rational harmonic balance method [30]. all have been paid much attention in order to determine periodic solutions of strongly nonlinear oscillatory problems. in fact, to the best of our knowledge, in the energy balance method and some other methods, there is no clear idea to obtain higher-order approximate solutions. moreover, only first-order approximation has been considered, which does not provides sufficient accuracy. in this situation, an analytical technique has been proposed based on the harmonic balance method [31-38] to obtain approximate periods to the nonlinear oscillator with the square of the angular frequency depending quadratically on the velocity. the higher-order approximate period (mainly third-order approximation) has been obtained. the proposed technique not only provides accurate results but is also more convenient and efficient for solving more complex nonlinear oscillatory problems. moreover, using a suitable truncation formula gives approximate periods that are very near to the next higher-order approximation and avoids a lot of calculation. this is the main advantage of the proposed technique presented in this article. the rest of this paper is organized as follows: in section 2, we give the outline of the solution approaches of the harmonic balance method. in section 3, we implement the harmonic balance method to the nonlinear oscillator with the square of the angular frequency depending quadratically on the velocity. the results and a detailed discussion have been explained extensively in section 4. concluding remarks are given in section 5. iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 184 2. solution approaches consider a general second-order nonlinear differential equation and initial conditions as follows: ]0)0(,)0([),,( 0 2 0  xaxxxfxx   (1) where ),( xxf  is a nonlinear function such that ),(),( xxfxxf   , 00  and  is a constant. a periodic solution of eq. (1) can be assumed as ))9cos()7cos()5cos()3cos()cos(( 0 tztwtvtutax   (2) where 0a ,  and  are constants. if  vu1 , then the solution to eq. (2) easily satisfies the initial conditions given in eq. (1). substituting eq. (2) into eq. (1) and expanding ),( xxf  in a fourier series, reduces it to an algebraic identity 2 2 2 2 0 0 0 1 0 3 0 [ ( ) cos( ) ( 9 ) cos(3 ) ] [ ( , , ) cos( ) ( , , ) cos(3 ) ] a t u t f a u t f a u t                   (3) by comparing the coefficients of equal harmonic terms of eq. (3), the following nonlinear algebraic equations are obtained. ,)25(,)9(,)( 5 22 03 22 01 22 0 fvfuf   (4) using the first equation, 2  is eliminated from all the remaining equations of eq. (4). thus, eq. (4) takes the following form ),25(24),9(8, 15 2 013 2 01 2 0 2 fvfvfufuf   (5 ) substituting  vu1 , and then simplifying, second-, thirdequations of eq. (5) takes the following form.  ),,,,,,,(),,,,,,,( 00020001  vuagvvuagu (6) where ,, 21 gg exclude, respectively, the linear terms of ,, vu . whatever the values of 0 ,  and 0a , there exists a parameter 1),,( 000  a , such that ,, vu are expandable in the following power series in terms of 0 as  ,, 2 0201 2 0201   vvvuuu (7) where  ,,,,, 2121 vvuu are constants. finally, substituting the values of ,, vu from eq. (7) into the first equation of eq. (5), the approximate angular  is determined. this completes the determination for the approximate periods obtained by the relation  2 t . iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 185 3. numerical example consider a nonlinear oscillator which was studied in [6,15,31-32] as: 0)1( 2  xxx  (8) in eq. (2), a second-order approximate solution of eq. (8) is ))3cos()cos(( 0 tutax   (9) substituting eq. (9) along with u 1 into eq. (8), then simplifying and equating the coefficients of )cos( t and )3cos( t to zero, the following residuals are obtained. .034/74/594/ ,02/74/112/4/1 322 0 222 0 22 0 222 0 322 0 222 0 22 0 222 0 2   uauauauua uauauauua   (10) from the first equation of eq. (10), it becomes ).2/74/112/4/1/()1( 32 0 22 0 2 0 2 0 2 uauauauau  (11) substituting eq. (11) into the second equation of eq. (10), the nonlinear algebraic equation of u is obtained as: 32/),28/321451( 2 00 432 0 22 0 auuauuuu  . (12) therefore, the power series solution of eq. (12) in terms of 0 is  3 0 2 0 2 00 )/3239(5 au (13) substituting the value of u from eq. (13) into eq. (11) and then simplifying the secondorder approximate angular frequency results in: , 81924096 3 256 3 8 1 8 0 6 0 4 0 2 0           aaaa  (14) and using the relation  2 t , the second-order approximate period of eq. (8) is:           65536 7 40962568 12 8 0 6 0 4 0 2 0 2 aaaa t (15) considerable calculation is saved and improved results are obtained if we use the truncation principle in eq. (10). the higher-order terms of u greater than second-order have no effect on the value of the unknowns u and  . so, we may ignore greater than secondorder terms of u ; but half of the second-order terms are considered. this is called the truncation principle. after using the truncation principle, eq. (10) can be transformed into .08/74/594/ ,08/112/4/1 222 0 22 0 222 0 222 0 22 0 222 0 2   uauauua uauauua   (16) iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 186 from the first equation of eq. (16), it can be easily written as )8/112/4/1/()1( 22 0 2 0 2 0 2 uauauau  . (17) substituting 2  into the second equation of eq. (16), the nonlinear algebraic equation of u is reduce to: )2/322/2151( 32 0 22 0 uauuuu  (18) where 0 is given in eq. (12). the power series solution of eq. (18) in terms of 0 is:  3 0 2 0 2 00 )/322/71(5 au (19) substituting the value of u from eq. (19) into eq. (17) the second-order approximate angular frequency becomes:           16777216 2065 131072 35 16384256 3 8 1 10 0 8 0 6 0 4 0 2 0 aaaaa  (20) and the approximate period of oscillation in using the truncation principle is:           131072 15 6144 6.5 2568 12 8 0 6 0 4 0 2 0 2 aaaa t truc  (21) by the same mathematical manipulation as stated above, the higher-order approximations have been obtained using the proposed technique. in this paper, a third-order approximation is 𝑥(𝑡) = 𝑎0 𝑐𝑜𝑠(𝜔𝑡) + 𝑎0𝑢(𝑐𝑜𝑠(3𝜔𝑡) − 𝑐𝑜𝑠(𝜔𝑡)) + 𝑎0𝑣(𝑐𝑜𝑠(5𝜔𝑡) − 𝑐𝑜𝑠(𝜔𝑡)) (22) substituting eq. (22) into eq. (8), then simplifying and equating the coefficients of )cos( t , )3cos( t and )5cos( t equal to zero, the related equations are 0 2/52/254/114/7 ,02/ 334/74/594/ ,0 2/74/112/4/1 22 0 22 0 2322 0 222 0 22 0 22 0 22 0 322 0 222 0 22 0 222 0 2 322 0 222 0 22 0 222 0 2          uvavavvuauaua uva vauauauauua vv uauauauua      (23 ) from the first equation of eq. (23), it can be written as: ).4/34/112/4/1/()1( 2 0 22 0 2 0 2 0 2  vavuauauavu (24) with the help of eq. (24), 2  is eliminated from the second and third equations of eq. (23) and then simplifying, the nonlinear algebraic equations of u and v are obtained as: iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 187 ),31161328/321451( 2432 0 22 0  vuuvvuuauuuu  (25) ),3932313415187( 222432 0  uvvvuuvvuuuuv  (26) where 96/ 2 00 a and 0 is given in eq. (12). the algebraic relation between 0 and 0 is: 3/ 00  (27) therefore, eq. (26) takes the form: 3/)3932313415187( 222432 0  uvvvuuvvuuuuv . (28) the power series solution of eq. (25) and eq. (28) in terms of 0 are:  3 0 2 0 2 00 )/323/26(5 au , (29)  4 0 2 0 3 0 2 0 )3/44827/2194(9/1662/7 av . (30) substituting the values of u and v from eqs. (29)-(30) into eq. (24), the third-order approximate angular frequency is:           3538944 161 2359296 305 6144256 3 8 1 10 0 8 0 6 0 4 0 2 0 aaaaa  . (31) thus, the third-order approximate period of eq. (8) is:           262144 55.0 6144 5 2568 12 8 0 6 0 4 0 2 0 3 aaaa t  . (32) the third-order approximation of eq. (22) measures a more correct result when a suitable truncation principle is used. using the truncation principle, eq. (23), takes the following form: .04/5 2/252/4/114/7 ,04/3 2/34/74/594/ ,04/154/3 4/74/112/4/1 22 0 22 0 2322 0 222 0 22 0 22 0 22 0 322 0 222 0 22 0 222 0 22 0 22 0 2 322 0 222 0 22 0 222 0 2       uva vavvuauaua uvava uauauauua uvavavv uauauauua       (33) the first equation of eq. (33), can be written as: ).4/34/112/4/1/()1( 2 0 22 0 2 0 2 0 2  vavuauauavu (34) by using the same mathematical manipulation discussed above, the nonlinear algebraic equations of u and v are: iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 188 ),715132/321451( 2432 0 22 0  vuuvvuuauuuu  (35) ),20278213187( 222432 0  uvvvuuvvuuuuv  (36) where 0 and 0 are given in eqs. (25)-(26). the power series solution of eqs. (35)-(36) in terms of 0 are:  4 0 2 0 3 0 2 0 2 00 )3/12169/804()/323/26(5  aau , (37)  4 0 2 0 3 0 2 0 )3/44827/2281(9/1662/7 av . (38) substituting the values of u and v from eqs. (37)-(38) into the eq. (34), the third-order approximate angular frequency by using truncation principle is:           56623104 263 2359296 53 6144256 3 8 1 10 0 8 0 6 0 4 0 2 0 aaaaa  , (39)           262144 4.27 6144 5 2568 12 8 0 6 0 4 0 2 0 3 aaaa t truc  . (40) 4. results and discussion the accuracy of the approximate periods has been illustrated by comparing with the exact period ext that is stated in [6]. for this nonlinear problem, the exact period is           10485760 133 262144 7 6144 5 2568 12 10 0 8 0 6 0 4 0 2 0 aaaaa t ex . (41) the secondand third-order approximate periods obtained by applying truncation and without truncation principle to the nonlinear oscillator are defined in eq. (8).           65536 7 40962568 12 8 0 6 0 4 0 2 0 2 aaaa t , (42)           262144 55.0 6144 5 2568 12 8 0 6 0 4 0 2 0 3 aaaa t  . (43) in the case of truncation principle:           131072 15 6144 6.5 2568 12 8 0 6 0 4 0 2 0 2 aaaa t truc  , (44)           262144 4.27 6144 5 2568 12 8 0 6 0 4 0 2 0 3 aaaa t truc  . (45) iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 189 comparing all the approximate periods, the accuracy of the proposed analytical technique using the truncation principle is better than without the truncation principle. it is highly remarkable that, using the truncation principle, the third-order approximate period gives almost the same result as the exact period. high accuracy period and very simple solution procedure reveal the novelty and reliability of the proposed harmonic balance method. the advantages of the proposed technique include its simplicity and computational efficiency, and the ability to objectively find better agreement in third-order approximate period by applying the truncation principle. 5. conclusion in this paper, an analytical technique has been proposed based on the harmonic balance method to determine approximate periods to the nonlinear oscillator with the square of the angular frequency depending quadratically on the velocity. the solution procedure of the proposed technique is very simple and straightforward. in the presented problem, the approximate periods obtained using the proposed technique shows much better agreement with the corresponding exact period. it is noted that, the third-order approximate period obtained using the truncation principle is almost identical compared with the numerically obtained exact period. high accuracy of the approximate periods obtained from the problem reveals the versatility of the proposed technique in solving strongly nonlinear classes of problems. it can be concluded that the proposed technique is a better and efficient alternative to the existing lindstedt–poinare´ perturbation-based method and classical harmonic balance method for approximating solutions for strongly nonlinear classes of problems. acknowledgement the authors would like to thank the ministry of higher education (mohe), malaysia for financial support under the project frgs 14-156-0397. the authors also express their gratitude to the reviewers for their useful suggestions and comments which significantly improved the original manuscript. references [1] leissa aw. (1993) vibration of plates, washington dc: acoustical society of america. [2] chopra ak. (1995) dynamic of structures, theory and application to earthquake engineering, new jersey: prentice-hall, usa. [3] nayfeh ah. (1973)perturbation methods, jhon wiley, new york, usa. [4] elmas n, boyaci h. (2014) a new perturbation technique in solution of nonlinear differential equations by using variable transformation. applied mathematics and computation, 227:422-427. [5] azadak, hosen ma, rahmanms. (2012) a perturbation technique to compute initial amplitude and phase for the krylov-bogoliubov-mitropolskii method. tamkang journal of mathematics, 43(4):563-575. [6] belendeza, belendezt, hernandeza, gallegos, ortunom,neippc. (2007) comments on “investigation of the properties of the period for the nonlinear oscillator 0)1( 2  xxx  ”. journal of sound and vibration, 303(3-5):925-930. [7] belendez a, hernandez a, belendez t, neipp c, marquez m. (2007) asymptotic representation of the period for the nonlinear oscillator. journal of sound and vibration, 299(1-2):403-408. [8] marincaa v, herisanu n. (2010) determination of periodic solutions for the motion of a particle on a rotating parabola by means of the optimal homotopy asymptotic method. journal of sound vibration, 329(9):1450-1459. iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 190 [9] belendez a. (2009) homotopy perturbation method for a conservative 3/1 x force nonlinear oscillator. computers & mathematics with applications, 58(11-12):2267-2273. [10] leung ayt, guo zj. (2009) homotopy perturbation for conservative helmholt-duffing oscillator. journal of sound and vibration, 325(1-2):287-296. [11] he jh. (2004) the homotopy perturbation method for nonlinear oscillators with discontinuities. applied mathematics and computation, 151(1):287-292. [12] suleman m, wu q. (2015) comparative solution of nonlinear quintic cubic oscillator using modified homotopy perturbation method. advances in mathematical physics, article id 932905:5. [13] belendez a, pascual c, belendez t, hernandez a. (2009) solution for an anti-symmetric quadratic nonlinear oscillator by a modified he’s homotopy perturbation method. nonlinear analysis, 10(1):416-427. [14] belendez a, pascual c, ortunom, belendez t, gallego s. (2009) application of a modified he’s homotopy perturbation method to obtain higher-order approximations to a nonlinear oscillator with discontinuities. nonlinear analysis, 10(2):601-610. [15] ganji ss, ganji dd, karimpour s, babazadeh h. (2009) applications of a modified he's homotopy perturbation method to obtain second-order approximations of the coupled twodegree-of-freedom systems. international journal of nonlinear sciences and numerical simulation, 10(3):303-312. [16] ozis t, yildirima. (2007) determination of periodic solution for a 3/1 u force by he’s modified lindstedt-poincare method. journal of sound vibration, 301(1-2):415-419. [17] razzak ma, alammz, sharif mn. (2018) modified multiple time scale method for solving strongly nonlinear damped forced vibration systems. results in physics, 8:231-238. [18] azami r, ganji dd, babazadeh h, dvavodi ag, ganji ss. (2009) he’s max-min method for the relativistic oscillator and high order duffing equation. international journal of modern physics b, 23(32):5915-5927. [19] alex ez, rodríguez ca, romero om. (2012) application of the elliptic balance method to a nonlinear singular oscillator. applied mathematics and computation, 218(22):1111211117. [20] akbari m, ganji dd, ahmadi a, kachapi shh. (2014) analyzing the nonlinear vibrational wave differential equation for the simplified model of tower cranes by algebraic method. frontiers of mechanical engineering, 9(1):58-70. [21] huseyin t, murat s. (2018) a local differential transform approach for the cubic nonlinear duffing oscillator with damping term. scientia iranica, available online from 20 january. [22] younesian d, askari h, saadatnia z, yazdi mk. (2010) frequency analysis of strongly nonlinear generalized duffing oscillators using he’s frequency-amplitude formulation and he’s energy balance method. computers & mathematics with applications, 59(9):32223228. [23] razzak ma. (2017) a simple new iterative method for solving strongly nonlinear oscillator systems having a rational and an irrational force. alexandria engineering journal, in press. [24] yildirim a, askari h, yazdi mk, khan y. (2012) a relationship between three analytical approaches to nonlinear problems. applied mathematics letter, 25(11):1729-1733. [25] razzak ma,rahmanmm. (2015) application of new novel energy balance method to strongly nonlinear oscillator system. results in physics, 5:304-308. [26] molla mhu, alam ms. (2017) higher accuracy analytical approximations to nonlinear oscillators with discontinuity by energy balance method. results in physics, 7:2104-2110. [27] askari h, saadatnia z, esmailzadeh e, younesian d. (2014) multi-frequency excitation of stiffened triangular plates for large amplitude oscillations. journal of sound and vibration, 333(22):5817-5835. [28] younesian d, askari h, saadatnia z, yazdi mk. (2012) analytical approximate solutions for the generalized nonlinear oscillator. applicable analysis, 91(5):965-977. [29] hosen ma, chowdhury msh, ali my, ismail af. (2017) an analytical approximation technique for the duffing oscillator based on the energy balance method. italian journal of pure and applied mathematics, 37:455-466. iium engineering journal, vol. 19, no. 2, 2018 chowdhury et al. 191 [30] yamgoue sb, bogning jr, jiotsa ak, kofane tc. (2010) rational harmonic balance-based approximate solutions to nonlinear single-degree-of-freedom oscillator equations. physicascripta, 81:035003. [31] beatty j, mickens re. (2005) a qualitative study of the solution to the differential equation 0)1( 2  xxx  . journal of sound and vibration, 283:475-477. [32] mickens re. (2006) investigation of the properties of the period for the nonlinear oscillator 0)1( 2  xxx  . journal of sound and vibration, 292(3-5):1031-1035. [33] mickens re. (1986) a generalization of the method of harmonic balance. journal of sound and vibration, 111:515-518. [34] hosen ma, chowdhury msh. (2015) a new analytical technique based on harmonic balance method to determine approximate periods for duffing-harmonic oscillator. alexandria engineering journal, 54(2):233-239. [35] hosen ma. (2014) approximate solutions of the equation of motion's of the rigid rod which rocks on the circular surface without slipping. ain shams engineering journal, 5(3):895899. [36] hu h. (2006) solution of a quadratic nonlinear oscillator by the method of harmonic balance. journal of sound and vibration, 293(1-2):462-468. [37] chowdhury msh, hosen ma, ahmad k, ali my, ismail af. (2017) high-order approximate solutions of strongly nonlinear cubic-quintic duffing oscillator based on the harmonic balance method. results in physics, 7:3962-3967. [38] hosen ma, chowdhury msh. (2015) a new reliable analytical solution for strongly nonlinear oscillator with cubic and harmonic restoring force. results in physics, 5:111-114. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 203 study of mesh quality improvement for cfd analysis of an airfoil farah aqilah, mazharul islam1*, franjo juretic2 , joel guerrero3, david wood4 and farid nasir ani5 1 department of mechanical and production engineering, ahsanullah university of science and technology, dhaka-1208, bangladesh 2 creative fields ltd, dragutina golika 63, 10000 zagreb, croatia 3 dicat, university of genova, 1, via montallegro, 16145 genova italy 4 department of mechanical and manufacturing engineering, schulich school of engineering, university of calgary t2n1n4, canada 5 faculty of mechanical engineering, universiti teknologi malaysia, johor, malaysia *corresponding author: mazharul.islam.mpe@aust.edu (received: 27th feb 2018; accepted: 19th nov 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19i2.905 abstract: airfoils generate lift in engineering applications such as for airplanes, wind turbines, automotive spoilers, etc. for accurate cfd analysis of airfoils, the quality of the mesh is of paramount importance, especially when dealing with turbulent flows commonly encountered in real life applications. currently there are different tools that are available to improve the quality of the mesh required for cfd studies. this paper describes a study to assess the significant of the quality of the mesh on cfd analyses of naca 23012 airfoil by using selected open source tools. the turbulence is modeled using the well-known k-ω shear stress transport model. for validation, results have been compared with experimental datasets which were obtained from “tag stuttgart #1” tunnel. abstrak: sayap pesawat dapat menghasilkan daya angkat dalam aplikasi kejuruteraan seperti kapal terbang, turbin angin, spoiler automotif, dan sebagainya. kualiti pada jaringan adalah amat penting bagi mendapatkan analisa cfd yang tepat pada sayap pesawat, terutamanya apabila berhadapan situasi aliran turbulen sebenar. pada masa ini terdapat pelbagai perisian bagi meningkatkan mutu jaringan dalam kajian cfd. kertas kerja ini membentangkan satu kajian bagi menilai kepentingan kualiti jaringan pada analisis cfd bagi sayap pesawat naca 23012 dengan menggunakan sumber terpilih perisian terbuka. model turbulen dibangunkan mengguna pakai model k-ω shear stress transport (sst) yang terkenal. bagi pengesahan, keputusan uji kaji telah dibandingkan dengan set data yang diperoleh dari terowong "tag stuttgart #1”." key words: naca 23012, openfoam, cfmesh, mesh quality, fvm, cfd 1. introduction airfoils are widely used for different engineering applications like airplanes, wind turbines, automotive spoilers, etc. simulating the aerodynamic performance of airfoils at different angles of attack (aoa) is essential for most engineering applications which rely iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 204 on the lift (l) to drag (d) ratio. with the improvement in computing hardware and parallel algorithms, researchers and industry are increasingly relying on cfd simulations. the airfoil naca 23012 [1] has been chosen in the present study with airfoil chord length c = 1m. naca 23012 is interesting for some cfd analyses due to is high aerodynamic performance at low flying velocities. it develops high maximum lift coefficient (clmax) and high stall angle (αstall). according to reference [1] , its geometric characteristics are as follows:  thickness: 12%  maximum thickness position: 30%  maximum chamber: 1.83%  maximum chamber position: 13% in the present work, the incompressible reynolds-averaged navier-stokes (rans) equations are numerically approximated by using the open source finite volume solver openfoam [2]. in the present research, a parametric cfd study of the flow around a naca airfoil have been conducted and the significance of mesh quality on prediction of lift and drag coefficients have been discussed. 2. mesh quality in cfd simulations, the accuracy of the solutions are highly dependent upon on the quality of the mesh. there are several mesh quality metrics, some of the most critical parameters are orthogonality, skewness, smoothness (also termed as uniformity, growth factor, growth rate or change in cell size) and aspect ratio. it should be noted that the present study is done for two dimensional situations only. according to reference [3] "skewness has an adverse effect on the accuracy of interpolation on the face, non-orthogonality increases the error of the approximation of the surface-normal gradient, and nonuniformity reduces the order of the approximation of the surface-normal gradient to first order". interested readers can consult references [4]–[7] for more information about mesh quality and influence these parameters for successful cfd analysis. brief explanation regarding each parameters that affect the mesh quality is described below as stated in reference [8]. 2.1. non-orthogonality fig. 1 shows a simple representation of mesh non-orthogonality. by definition, mesh non-orthogonality is the angular deviation of the vector s (located at face center f) from vector d connecting the two adjacent cell centers p and n. mesh non-orthogonality mainly affects the diffusive terms as it adds diffusion to the solution [8]. fig. 1 mesh orthogonality iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 205 2.2. skewness according to reference [8], mesh skewness is the deviation of vector d that connects the two adjacent cells for example p and n from the face center, f as shown in fig. 2. it mainly adds diffusion to the solution and affects convective terms of the solution [8]. fig. 2 mesh skewness 2.3. smoothness smoothness (also known as expansion rate or growth rate) is the ratio of transition in size between cells. further explanation is as illustrated in fig. 3. large transition ratios between cells add diffusion to the solution [8]. fig. 3 smoothness 2.4. aspect ratio mesh aspect ratio is the ratio between ∆x and ∆y as shown in fig. 4. high ar will smear the gradients, therefore it adds numerical diffusion to the solution [8]. fig. 4 mesh aspect ratio iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 206 3. methodology to demostrate the importance of mesh qualiy on the solution accuracy, we conducted a parametric study using open source tools. different stages of the study and the tools used are shown in fig. 5. fig. 5 methodology of investigation 3.1. geometry preparation the initial stage in a cfd study is preparation of the geometry. to prepare the geometry of the computational domand aaround a naca 23012 airfoil, we used gnu octave [9] and a script was written following the guidelines given in reference [10]. to generate the geometry, this script used the following inputs:  angle of attack (aoa)  y+  reynolds number  mach number  temperature  n  bump among these parameters,“bump“ and “n“ vector are critical for generating good quality meshes around airfoils. a brief description about these two parameters are given below as decribed in [10]. 1. bump: defines the degree of grid concentration around leading and trailing edge of the airfoil. when bump=1 the cell length is uniformly distributed along the airfoil contour. when bump>1 the grid are concentrated along the midchord of the airfoil. if bump is between 0 and 1, the grid will be concentrated around the edges. the quality of mesh varies with the value of bump [10]. 2. n1: refers to the number of hexahedra cells along the airfoil chord [10]. 3. n2: refers to the number of grid which is normal to the chord and inside a semiellipse closely enclosing the airfoil [10]. 4. n3: refers to the number of elements located at the horizontal leading edge-inlet and trailing edge-outlet [10]. iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 207 5. n4: similar to n3 but applied to the vertical gaps between the airfoil and the top/bottom walls defining the box [10]. 6. specified yplus (y+) : the value of y+ mesh variable specified at the beginning of the analysis. y+ value of 50 is use for the analyses. in this study, geometry files for generating computational domains around a naca 23012 airfoil have been prepared for two different angles of attack which are 0o and 10o. fig. 6 shows the computational domains of the analyses. (a) (b) fig. 6 computational domains of cases: (a) aoa=0o; (b) aoa=10o 3.2. meshing the geometrical data file generated by the script is then used to generate mesh using an open-source software, gmsh [11]. the mesh files from gmsh can be converted into the openfoam mesh format using the “gmshtofoam“ command in the openfoam environment. tables 1 and 2 show selected input parameters which can alter the quality of the meshes. numerous meshes with different qualities have been investigated and only the selected ones are presented in these tables. after preparing the meshes, the quality of each iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 208 mesh have been assessed using the “checkmesh“ command in openfoam and the key quality related parameters are listed in tables 1 and 2. table 1: input and output for gmsh for aoa = 0o mesh id inputs outputs bump n1 n2 n3 n4 maximum aspect ratio maximum nonorthogonality maximum skewness m13 1 400 40 30 30 665.06 69.25 1.35 m14 1 500 40 30 30 664.88 69.25 1.35 m19 10 500 40 30 30 664.88 75.90 2.85 m20 20 500 40 30 30 664.88 78.29 3.58 m21 30 500 40 30 30 664.88 79.29 4.04 m22 0.0001 500 40 30 30 664.8795 78.28 4.28 m23 0.001 500 40 30 30 664.8795 76.11 3.01 m24 0.01 500 40 30 30 664.8795 71.62 1.75 table 2: input and output for gmsh for aoa = 10o mesh id inputs outputs bump n1 n2 n3 n4 maximum aspect ratio maximum nonorthogonality maximum skewness u14 1 500 40 30 30 665.1764 71.95165 1.7937 u15 1 500 40 30 30 332.5241 70.41457 1.867064 u16 1 500 40 30 30 3325.454 73.03355 1.908497 u17 1 500 40 30 30 1662.638 73.38908 1.817821 u18 1 500 40 30 30 1109.237 73.68965 1.838289 u19 1 500 40 30 30 169.8483 69.90738 1.27191 u20 1 500 40 30 30 169.8483 70.11737 1.334913 u22 0.0001 500 40 30 30 665.1764 78.28807 4.288395 u30 0.0001 500 40 30 30 332.5241 81.46802 4.287458 to determine the quality of the mesh, the output parameters which are maximum aspect ratio (ar), maximum non-orthogonality and maximum skewness of mesh have been considered. for an ideal mesh, the maximum ar should be closer to 1 and the maximum skewness should be as low as possible. also, the maximum mesh non-orthogonality should be less than 70%. the high quality mesh case (mesh id: m14 and u14) and the low quality mesh case (mesh id: m22 and u22) were simulated and the resulting aerodynamic coefficients were compared to experimental data [12]. iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 209 3.3. cfd solutions in this study, we used the open-source numerical library openfoam version 3.0.1 [2], which is a collocated unstructured finite volume solver. the cfd cases were run in a linux (ubuntu 14.04 lts) platform with 4 processor, maximum speed of 2.59ghz and a total of 12gb of ram memory. for turbulence modelling, we used the well validated k-ω sst turbulence model of menter with wall functions [13]. the flow is specified to be incompressible subsonic flow with turbulence intensity (ti) is set to be 0.02% with reynolds number (re) of 1x106 and mach number (m2) of 0.04. the cases is solved using the second order unbounded gradient discretization scheme. each case described in tables 1 and 2, is solved using a method that is at least second order accurate in space. the cases were run until the quantities of interest did not show any oscillations. 3.4. post-processing the results obtained with openfoam were analyzed using the post-processing software paraview [14]. also, quantities of interests (such as the residuals, lift and drag coefficient), were plotted using gnuplot [15]. to show the wake topology, we used the line-integral convulation technique (lic), implemented in paraview [14]. this technique, generates high density streamlines plots in two-dimensional view [16]. the lic technique to show wake topology in this study is more preferable compared to the traditional streamlines technique due to its visualization feature of condense lines which shows the development of wake structure much clearer. 4. results and discussion in the present study, several meshes were investigated at angle of attack, aoa, of 0° and 10o and the best mesh (in terms of mesh quality and its suitability to resolve the physics involve) was selected for subsequent detailed analysis at different aoa. to perform the steady flow simulations, the simplefoam solver (which uses the simple algorithm for pressure-velocity coupling) was used. the results obtained from openfoam are compared with experimental results adopted from experimental study at stuttgart tunnel #1 in reference [12]. the experimental was carried out in a wind tunnel at six reynold numbers ranging from 700,000 to 3,000,000 using a naca 23012 at ti of 0.02%. to setup the case in openfoam, proper turbulence related parameters were calculated for a turbulence intensity of 0.02% in order to match the experimental results. table 3 and 4 show the aerodynamic coefficient of the analysed case studies. table 3: aerodynamic coefficient for cases aoa = 0o aerodynamic coefficient m14 m22 experimental [12] lift coefficient (cl) 0.1271 0.03116 0.15 drag coefficient (cd) 0.01203 0.01113 0.0071 table 4: aerodynamic coefficient for cases aoa = 10o aerodynamic coefficient u14 u22 experimental [12] lift coefficient (cl) 1.0501 0.9388 1.13 iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 210 drag coefficient (cd) 0.02447 0.02007 0.0156 m14 and u14 are the studies using good quality mesh for aoa=0o and aoa=10o cases respectively as mentioned before. it can be seen that the obtained results closely matched the experimental results. it can also be seen that although the drag coefficient doesn’t show much effect, lift coefficient shows significant difference. in the present study, a wall function has been used to resolve the boundary layer around the naca airfoil. however, modeling drag forces for flow over airfoils in cfd analysis is quite challenging and better results are expected from transition and turbulence models. fig. 7 and 8 show the convergence of cd and cl value of the analysis. it can be seen that a better-quality mesh, m14 and u14 (denoted by the red line) converges faster at approximately 500 time-steps compared to m22 and u22. fig 7 convergence of the cd and cl value for case aoa=0 o over time steps and comparison to the experimental data fig. 8 convergence of the cd and cl value for case aoa=10 o over time steps and comparison to the experimental data even with the same computational capability and flow solution, m14 and u14 cases took lesser run time compared to both m22 and u22 case. this shows that with low quality mesh, it is likely to obtain acceptable results but at a cost of increased computation time. keep in mind that non-orthogonality, skewness and non-uniformity only cause problems in the regions with high gradient variation. therefore, in this case, mesh quality does not affect drag value much for all 4 cases. iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 211 fig. 9 and 10 show the post-processing result from both case analysis of aoa=0o and aoa=10o using the line-integral convolution (lic) technique of visualization. it can be observed that there is no wake structure developed from both of the cases. fig. 9 lic visualization for case aoa = 0o fig. 1o lic visualization for case aoa = 10o 5. conclusion in this article, the effect of mesh quality on the lift and drag coefficients was studied. from the results obtained, it is concluded that the mesh quality plays an important role on the reliability, accuracy and convergence speed of the solution. it was observed that nonorthogonality and skewness has a strong influence on the solution outcome, and these values need to be keep as low as possible, which is difficult, especially for industrial meshes. from the study, we can see that lift and drag coefficient value closely matched the experimental value when using a good quality mesh. although, drag value for low quality mesh shows an acceptable agreement with the experimental result, lift value differs significantly. it may be due to the cells with high mesh non-orthogonality and high skewness is at an area where does not affect cd. iium engineering journal, vol. 19, no. 2, 2018 aqilah et al. 212 acknowledgement the authors are grateful to the ministry of higher education malaysia for the ru grant, vot 05h25 and research management center, utm for the financial and management support. preparation of the article was also partly supported by the research initiative grant scheme (rigs) funded by the ministry of higher education (mohe) malaysia. also, the preparation of the article was partly supported by the canadian natural sciences and engineering research council (nserc) and the enmax corporation under the industrial research chairs program. references [1] the foam house [http://the-foam-house5.webnode.es/products/chapter-4-airfoil-case/] [2] openfoam [https://www.openfoam.com] [3] juretić f. and gosman a. d. (2010) error analysis of the finite-volume method with respect to mesh type. numer. heat transf. part b fundam., 57(6): 414–439. [4] juretic f. (2004) error analysis in finite volume cfd. phd thesis, university of london, department of mechanical engineering. [5] knupp p. m. (2008) remarks on mesh quality, 46th aiaa aerospace sciences meeting and exhibit. [6] katz a. and sankaran v. (2011) mesh quality effects on the accuracy of cfd solutions on unstructured meshes, j. comput. phys., 230(20):7670–7686. [7] baker t. j. (2005) mesh generation: art or science?, prog. aerosp. sci., 41(1):29–63. [8] openfoam introductory course material: module 3. [http://www.wolfdynamics.com/ourservices/training/openfoam-intro-training.html?id=50]. [9] gnu octave [https://www.gnu.org/software/octave/about.html]. [10] airfoil simulations a little contribution for meshing [http://codesaturne.org/forum/viewtopic.php?f=10&t=957]. [11] gmsh: a three-dimensional finite element mesh generator with built-in preand postprocessing facilities [http://geuz.org/gmsh/]. [12] miley s. j. (1982) a catalog of low reynolds number airfoil data for wind turbine applications”, prepared by department of aerospace engineering, texas a&m university for rockwell international corporation, usa. [13] menter f. r., kuntz m., and langtry r. (2003) ten years of industrial experience with the sst turbulence model, turbul. heat mass transf., 4:625–632. [14] paraview [https://www.paraview.org]. [15] gnuplot [http://www.gnuplot.info]. [16] knowles r. d., finnis m. v., a. j. saddington, and knowles k. (2006) planar visualization of vortical flows, proc. inst. mech. eng. part g j. aerosp. eng., 220(6): 619–627. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 307 role of substrate binding on the protein dynamics of an endoglucanase from fusarium oxysporum at different temperatures abdul aziz ahmad 1 , ibrahim ali noorbatcha 1 and hamzah mohd. salleh 2 1 bioprocess and molecular engineering research unit (bpmeru), department of biotechnology engineering, 2 international institute for halal research and training (inhart), international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. * corresponding authors:hamzah@iium.edu.my, ibrahiman@iium.edu.my (received:15 th feb 2018 ; accepted:1 st june 2018 ; published on-line:5 th june 2018) https://doi.org/10.31436/iiumej.v19i1.894 abstract: thermostability is an important requirement for protein function, and one goal of protein engineering is improvement of activity of the enzymes at higher temperatures, particularly for industrial applications. computational approaches to investigate factors influencing thermostability of proteins are becoming researchers’ choice. this study investigates the influence of substrate binding on the protein dynamics by comparing the molecular dynamics simulations of substrate-enzyme complex against un-bound enzyme, using endoglucanase i from fusarium oxysporum. endoglucanase-substrate complex was prepared by docking and molecular dynamics simulations were carried out at three different temperatures, 313 k, 333 k and 353 k. our finding shows that the secondary structures for substrate-enzyme complex show more fluctuations relative to un-complexed structure. the same trend was observed for solvent accessible surface area and radius of gyration. at the highest temperature studied (353 k), the substrate-enzyme complex form showed the highest fluctuations. the fluctuations around the active site regions reach a minimum at the optimum temperature, compared to the other structural regions and other temperatures. abstrak: kestabilan (ketahanan) terhadap haba merupakan keperluan yang penting untuk fungsi protin, salah satu matlamat kejuruteraan protin adalah penambahbaikan aktiviti enzim pada suhu yang tinggi khususnya untuk aplikasi industri. kini para penyelidik memilih kaedah komputasi, bagi mengkaji faktor yang mempengaruhi kestabilan terhadap haba. kajian ini menyelidik pengaruh ikatan substrat pada protin dengan membandingkan simulasi molekular dinamik diantara substrat-enzim kompleks dan enzim sahaja, menggunakan endoglucanase i dari fusarium oxysporum. kompleks endoglucanase-substrat disediakan melalui kaedah docking dan simulasi molekular dinamik dilakukan pada suhu 313 k, 333 k dan 353 k. kajian kami menunjukkan struktur sekunder bagi substrat-enzim kompleks kurang stabil berbanding enzim sahaja. pola yang sama bagi luas permukaan boleh dicapai pelarut (sasa) dan jejari gyrasi. pada suhu tertinggi dikaji (353 k), substrat-enzim kompleks paling tidak stabil. pada suhu optimum, kadar ubah-ubah sekitar amino asid aktif adalah minimum berbanding struktur dan suhu lain. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 308 keywords: thermostable enzymes; thermostability factors; ligand-enzyme complex; fusarium oxysporum endoglucanase; molecular dynamics simulations 1. introduction thermostable cellulases are highly sought after in the production of biofuels as the digestion requires thermostable enzymes to achieve economically feasible process. thermostable cellulases allow the use of increased substrate concentration as the substrate viscosity decreases. this improves product yields, reduces capital and processing costs such as increased reaction rate, increased solubility of reactants and reduced contaminating microbial growth [1-3]. thermostability of enzymes is temperature dependent phenomena. computational approach to investigate factors influencing thermostability are becoming researchers tool as it enables them to understand the interactions at near and beyond melting temperatures at atomic detail. currently, molecular dynamics (md) simulation is the only method available to understand the dynamics of enzymes at higher temperature. furthermore, insilico method is relatively cost effective compared to wet-lab experiments. initially researchers used enzyme structures with no ligand complexed in md simulations [4-8]. however, this is not the actualenvironment when the enzymes are in action. nowadays, more researchers are simulating ligand-enzyme complexed structures to study the effects of complexation on the dynamical behavior [9-11] of the enzymes at different temperatures. here md simulations wereused to investigate the impact of enzyme-substrate binding on thermostability. cellotetraose was chosen to represent substrate based on our previous report [12]. root mean square deviation (rmsd) of the whole protein, secondary structure, radius of gyration and solvent accessible surface area (sasa) were analyzed and discussed. 2. system setup an endoglucanase (eguia) from fusarium oxysporum available in our laboratory (originally provided by s.g. withers, university of british columbia, vancouver, canada) is used for modelling in this work. the molecular structure of eguia is not known. however, eguia is found to have 99.5% sequence identity with the crystal structure from protein data bank with (pdb id: 3ovw) with two mutations at r41h and s216n. hence the structure of eguia was obtained using homology modelling by comparing with the available crystal structure from protein data bank [13]. the cellotetraose ligand was docked to the eguia using biomedcache 6.1 (fujitsu) software [14]. docking was performed as described in our previous report [12]. the docked structure of the enzyme is shown in fig. 1. the two structures were denoted as eguia for the enzyme with no ligand bound and eguia-cellotetraosecomplex for cellotetraose bound enzyme. charmm-gui website was used to generate protein structure file (psf) (www.charmm-gui.org). both systems were solvated using approximately 24,063 tip3p water molecules in arectangular box of (102×90×90 å); the box dimensions ensured that any protein atom was at least 20 å away from the wall of the box.the net charge of the systems was balanced with one cl ion to produce a neutral system. all md simulations (mds) were performed with nanoscale molecular dynamics (namd) software package (version 2.11) [15]. charmm 22 force field parameters for iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 309 protein and nucleic acids including cmap corrections which contained in charmm forcefield (top_all27_prot_lipid.inp) obtained from http://www.ks.uiuc.edu/research/namd was used for enzyme simulations and charmm36 force field parameters for enzyme-substrate complex simulations. fig. 1: cartoon representation of eguia based on secondary structure. the substrate (cellotetraose) is represented as cpk in red color. non-covalent van der waals interactions were cut off at 12 å. particle mesh ewald (pme) was used to calculate long range electronic interactions. the integration timestep is 1 fs. the velocity quenching (5000 time step) and conjugate gradient (50,000 timestep) algorithms were used to perform energy minimization. after energy minimization, md simulation were performed for 35,000 time step (at 313 k), 40,000 (at 333 k and 353 k) to heat the system and then followed by equilibration for 200,000 time step (pressure 1 atm) with periodic boundary conditions. langevin thermostat and barostat were used to control temperature and pressure.the attainment of minimum energy during energy minimization and the constant temperature during equilibration is verified by the asymptotic behavior of these properties. the equilibrated structures were subjected to 20 ns production runs in npt (isothermal-isobaric ensemble). structures were saved every 0.001 ns for analysis. 3. results and discussion the docking scores of cellobiose (a disaccharide) and cellotetraose (a tetrasaccharide) were evaluated. cellotetraose showed stronger binding compared to cellobiose. the reasons for the stronger interactionson the binding characteristics are mainly due to hydrogen bonds. five hydrogen bonds were observed between cellotetraose compared to three hydrogen bonds with cellobiose [12]. the docked eguia-cellotetraose structure was used in the md simulation. root mean square deviation (rmsd) is used to evaluate structural deviations from the initial protein structure (i.e., to estimate the protein intactness) [16]. the stability of the protein relative to its conformation can be determined by the deviations produced during the course of its simulation. the smaller the deviations, the more stable the protein structure [17]. the behavior of the enzyme and the complex was monitored at three different temperatures. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 310 rmsd of backbone atoms (c, n, cα) from the initial structure (the structure after equilibration step) were calculated for the entire simulation trajectory at 313 k, 333 k and 353 k. the rmsd of backbone atoms are illustrated in fig. 2. in general, the temperature dependence of the fluctuations can be expected to represent the stability of overall structure when the temperature is increased. it is found that the rmsd of backbone atoms of the enzyme-substrate complex is higher than eguia which indicates that the structure is becoming less stable at higher temperatures. at high temperature, the rmsd has tendency to diverge to larger values for the complex as well as eguia. while the rmsd of complex at 313 k was higher than 333 k, it remains almost constant after 3ns with slight variations. after 8 ns, rmsd of complex at 333 k, increases dramatically from 1.6 å to 2.5 å at 20 ns. rmsd of complex at 353 k was lower than 313 k and 333 k for the initial 4ns, but was the highest until 18 ns before reaching the same rmsd value with 333 k complex. fig. 2: backbone rmsd of eguia and enzyme-substrate complex plotted as a function of md time at 313 k, 333 k and 353 k fitted with trendline of polynomial degree 5. black solid (enzyme-substrate complex at 353 k), black dash (eguia at 353 k), red solid (enzyme-substrate complex at 333 k), red dash (eguia at 333 k), blue solid (enzyme-substrate complex at 313 k), and blue dash (eguia at 313 k). the changes in the backbone rmsd values are expected to affect the structure of the active site and hence the activity of the enzyme. the rapid divergence of rmsd of enzyme-substrate complex at higher temperature compared to eguia under same conditions seems to suggest that the enzyme-substrate complex would lose its activity at higher temperatures, much more easily compared to eguia. the backbone rmsd of eguia at 333 k was the least among the three temperatures studied here implying that the structure at this temperature deviate less from the corresponding equilibrium structure thus maintaining the integrity of the active site structure and hence the activity. it should be noted that the optimum temperature for the activity of this enzyme is around 333 k. however, the rmsd of the enzyme-substrate complex does not show such a trend and the fluctuations increases as the temperature is increased. perhaps the rmsd of the complete backbone of the enzyme-substrate complex may not be a good indicator of the thermostability of the enzymes, as the temperature response of the active site region is more crucial rather than the whole enzyme structure in determining the thermostability. hence for better understanding of the thermostability it is necessary to analyze the rmsd of the secondary structure components at different temperatures. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 311 rmsd of secondary structure components are shown in fig. 3. for all helices, the rmsd was around 1.5 å for all except for enzyme-substrate complex at 353 k which increased from 1.5 å to 2.3 å at 7.5 ns to 12.5 ns. however, for alpha helices a different phenomenon was observed, the enzyme (with no ligand) showed higher rmsd. the 333 k eguia was the highest for the entire simulation. complex at 353 k was the lowest. the rmsd of 3_10 helices was more violent at 353 k. it is interesting to note that at 333 k enzyme and complex of 3_10 helices was maintained at zero. relative to any other individual secondary structure element, influence of one helix is more dominant on the stability and organization of a protein [18]. thirteen parts of bridge beta showed a different behavior compared to extended beta-sheet as illustrated in fig. 3. fig. 3: rmsd time evolutions of secondary structure’s backbone atoms (c,cα and n). reference frame is the initial frame, to. black solid (enzyme-substrate complex at 353 k), black dash (eguia at 353 k), red solid (enzyme-substrate complex at 333 k), red dash (eguia at 333 k), blue solid (enzyme-substrate complex at 313 k) and blue dash (eguia at 313 k). in general, betasheets of eguia are more stable than helices. coil and turn shows a similar pattern of rmsd for the entire 20 ns. as expected, coil and turns showed higher rmsd due to flexible nature. this finding is consistent with our previous report [6]. in reality, coil is not a true secondary structure; it is the class of conformations that show absence of regular secondary structure. relationship between stability and activity of enzymes is maintained by underlying conformational flexibility. in thermophilic enzymes, a decrease in flexibility causes low enzyme activity. it can be seen that even though the iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 312 rmsd changes differently for different secondary structure components, for beta sheets (excluding bridge beta sheets) the fluctuations at 333 k for the both the un-bound enzyme and the enzyme-susbtrate complex is the lowest among the fluctuations at other temperatures. as shown in fig. 1, the substrate is surrounded by beta sheets and the temperature at which the beta sheets structures are maintained will preserve the active site. the highest temperature at which the active site is retained will be the optimum temperature for the enzyme activity. the current simulations reveal that even though the substrate binding on the enzyme can influence the dynamics of the different parts of the enzymes differently, the fluctuations around the active site (beta sheets in this case) around the optimum temperature is distinctly maintained thus offering an avenue for further exploration for enhancing the thermostability of the enzymes. the accessible surface of a molecule is the part of the molecular surface that is exposed to the solvent [19]. the solvent accessible surface areas (sasa) of atoms are related to hydrophobicity and folding process of proteins. the folding process is usually accompanied by a significant decrease in sasa value [20]. sasa is higher for enzymesusbtrate complex than eguia (enzyme only) at the corresponding temperatures (fig.4). the sasa for both the enzyme and the enzyme-substrate complex are larger at higher temperatures, implying the presence of the substrate at the active site do not change the temperature dependence of sasa. at 313 k, sasa of eguia is the least although in the increasing trend after 10 ns. it is interesting to note that at the end of simulation (20 ns), eguia and complex had the same sasa. except at 313 k, the sasa at 353 k and 333 k increased sharply after 15 ns. this may be an indication that the enzyme starts to unfold at these temperatures. fig. 4: sasa of complex and eguia. black solid (enzyme-substrate complex at 353 k), black dash (eguia at 353 k), red solid (enzyme-substrate complex at 333 k), red dash (eguia at 333 k), blue solid (enzyme-substrate complex at 313 k) and blue dash (eguia at 313 k). radius of gyration (rg) were calculated for the 20 ns simulation time and depicted in fig. 5. in general, all the structures maintained its rg between 20.5 to 21.0 å except for enzyme-substrate complex at 353 k which showed a steady increment beyond 21.0 å. radius of gyration is an indicator of protein structure compactness [21]. eguia and enzyme-substrate complex maintained its structure at all temperatures studied except for enzyme-substrate complex at 353 k, at which the compactness has decreased (increase in rg). iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 313 fig. 5: radius of gyration of complex and eguia. black solid (enzyme-substrate complex at 353 k), black dash (eguia at 353 k), red solid (enzyme-substrate complex at 333 k), red dash (eguia at 333 k), blue solid (enzyme-substrate complex at 313 k) and blue dash (eguia at 313 k). 4. conclusion md simulations are carried out at three different temperatures to study the impact of ligand binding on the thermal stability of an endoglucanase, eguia. it is found that even though the fluctuation of the overall structure of the enzyme and the enzyme-substrate complex changes at higher temperatures, there is a tendency to maintain the compactness with minimum rmsd around the active site region of the enzyme. this remarkable ability of the active site region determines the optimum temperature for the enzyme activity of endoglucanase. the simulation findings should be validated experimentally. however, care should be taken in extending this argument for other enzymes. for enzymes with flexible active site, such as protein kinases [22], a much longer simulation is necessary to confirm this trend. acknowledgement this research was supported by fundamental research grant scheme (frgs 13-0700311) from the ministry of higher education, malaysia. references [1] bornscheuer ut, huisman gw, kazlauskas rj, lutz s,moore jc,robins k. (2012) engineering the third wave of biocatalysis.nature, 485:185-194. [2] zamost bl, nielsen hk, starnes rl. (1991) thermostableenzymes forindustrial applications. journal of industrial microbiology, 8:71-81. [3] kim hs, leqat, kim yh.(2010) development of thermostable lipase b from candida antarctica (calb) through in silico design employing b-factor androsettadesign. enzyme and microbial technology, 47(1-2):1-5. [4] noorbatcha ia, waesoho s, salleh hm. (2012) structural and dynamics behavior of native endoglucanase from fusarium oxysporum. australian journal of basic and applied sciences, 6(1):89-92. [5] akcapinar gb, venturini a, pier luigi martelli pl, casadio r, sezerman uo. (2015) modulating the thermostability of endoglucanase i fromtrichoderma reesei using computational approaches. protein engineering, design and selection, 28(5):127-135. iium engineering journal, vol. 19, no. 1, 2018 ahmad et al. 314 [6] noorbatcha ia, khan am, salleh hm. (2010) molecular dynamics studies of human βglucuronidase. american journal of applied sciences, 7(6):823-828. [7] purmonen m,valjakka j,takkinen k, laitinen t, rouvinen j. (2007) molecular dynamics studies on the thermostability of family 11 xylanases. protein engineering, design and selection, 20(11):551-559. [8] karjiban ra, rahman mba, basri m, salleh ab, jacobs d, wahabha. (2009) molecular dynamics study of the structure, flexibility and dynamics of thermostable l1 lipase at high temperatures. protein j., 28:14-23. [9] zhang pp, zhao l, long sy, tian p. (2015) the effect of ligands on the thermal stability of sulfotransferases: a molecular dynamics simulation study. j. molecular modeling, 21:1-7 [10] maximilian cjce, espinola jg, lamoureux g,pelletier jn. (2017)substrate-specific screening for mutational hotspots using biased molecular dynamics simulations. acs catalysis, 7: 6786-6797. [11] azam ma, jupudi s. (2017) insight into the structural requirements of thiophene-3carbonitriles-based murf inhibitors by 3d-qsar:molecular docking and molecular dynamics study. j. receptors and signal transduction,37(5):522-534. [12] noorbatcha ia, ahmad aa, salleh hm. (2014)molecular docking of cellobiose and cellotetraose into an endoglucanase i from fusarium oxysporum. j.pure and applied microbiology, 8:791-796. [13] berman hm, westbrook j, feng z, gilliland g, bhat tn, weissig h,shindyalov in,bourne pe. (2000) the protein data bank . nucleic acids research, 28: 235-242. [14] cacheworksystem pro version 7.5.0.85, copyright © 2000-2006 fujitsu limited, © 19892000 oxford molecular ltd. [15] jamescp, rosemary b, wei w, james g, emad t, elizabeth v, christopherc, robertds, laxmikant k, klaus s. (2005) scalable molecular dynamicswith namd.j. comp. chem., 26:1781-1802. [16] monhemi h, housaindokht mr, nakhaei pa. (2015) effects of natural osmolytes on the protein structure in supercritical co2: molecular level evidence, j. chem. phys. b 119:10406–10416. [17] imlimaong a, pritish kv & utkarsh r. (2016) structural insights into conformational stability of both wild-type and mutant ezh2 receptor. scientific reports. 6:34984 [18] richardson j s. (1981) the anatomy and taxonomy of protein structure. [http://kinemage.biochem.duke.edu/teaching/anatax/html/anatax.2a.html] [19] shucheng l , yuan l, shuai l, andi d, mengna l, hongwu j, jing g, jiming h (2017) molecular dynamics simulation of the interaction between dense-phase carbon dioxide and the myosin heavy chain. journal of co2 utilization, 21:270–279 [20] norhayati y, nor hak, adam tcl, abu bs, raja nzar and mohd sma. (2017) the role of solvent-accessible leu-208 of cold-active pseudomonas fluorescens strain ams8 lipase in interfacial activation, substrate accessibility and low-molecular weight esterification in the presence of toluene. molecules 2017, 22(8) [21] lobanov my, bogatyreva ns, galzitskaya ov. (2008) radius of gyration as an indicator of protein structure compactness.molecular biology. 42(4):623-628. [22] meharena hs, fan x, ahuja lg, keshwani mm, mcclendon cl, chen am, adams ja, taylor ss, et al. (2016) decoding the interactions regulating the active state mechanics of eukaryotic protein kinases. plosbiology 14(11):e2000127 http://www.tandfonline.com/doi/full/10.1080/10799893.2017.1360354 http://www.tandfonline.com/doi/full/10.1080/10799893.2017.1360354 http://www.tandfonline.com/doi/full/10.1080/10799893.2017.1360354 http://www.tandfonline.com/toc/irst20/37/5 http://kinemage.biochem.duke.edu/teaching/anatax/html/anatax.2a.html https://link.springer.com/journal/11008 iium engineering journal, vol. 16, no. 1, 2015 haque et al. 9 aerostatic and aerodynamic modules of a hybrid buoyant aircraft: an analytical approach anwar u. haque, waqar asrar, ashraf a. omar, erwin sulaeman and mohamed j.s. ali department of mechanical engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. waqar@iium.edu.my (received 29 november 2014; accepted 25 february 2015; published on line 29 may 2015) abstract: an analytical approach is essential for the estimation of the requirements of aerodynamic and aerostatic lift for a hybrid buoyant aircraft. such aircraft have two different modules to balance the weight of aircraft; aerostatic module and aerodynamic module. both these modules are to be treated separately for estimation of the mass budget of propulsion systems and required power. in the present work, existing relationships of aircraft and airship are reviewed for its further application for these modules. limitations of such relationships are also discussed and they provide a starting point for better understanding of design methodology of such aircraft. abstrak: pendekatan beranalisis penting dalam perkiraan keperluan aerodinamik dan daya angkat aerostatik bagi sesebuah pesawat hibrid timbulan. pesawat ini mempunyai dua modul berbeza untuk mengimbang berat pesawat; modul aerostatik dan aerodinamik. kedua-dua modul ini perlu dikaji secara berasingan untuk perkiraan jisim anggaran sistem dorongan dan kuasa yang diperlukan. buat masa ini, hubungan yang sedia ada antara pesawat dan kapal udara dikaji semula untuk aplikasi seterusnya bagi kedua-dua modul ini. kekurangan hubungan ini juga diperbincangkan dan seterusnya merupakan titik permulaan untuk lebih memahami metadologi reka bentuk pesawat sedemikian. keywords: aerostatic lift; aerodynamic lift; hybrid bouyant aircraft; drag polar. 1. introduction knowledge regarding the aerodynamic characteristics of a flying vehicle forms the backbone in starting the conceptual design work. aerodynamic data, especially the drag force predicted by experimental techniques can be highly reliable. unfortunately the experimental data bank is limited for hybrid buoyant (hb) aircrafts, which differ with conventional airships in terms of generation of aerodynamic lift, takeoff and landing characteristics, as well as the structural anatomy. airships usually fly at a constant altitude and use vertical takeoff and landing technology (vtol) to avoid angle of attack. the concept of hybrid and its meanings for airships and aircrafts are not yet clear. this is because the term “hybrid” is not solely related with the lift generated by the hull body itself and/or by single or multiple wings, but it is also linked with the propulsion system used by them. depending on the type of propulsion system, a general consensus does exist about various types of hybrid airships, but “there is no authoritative definition of it”. similar to an aircraft, a hybrid buoyant is a buoyant aerial vehicle in which the propulsion system is hybrid. a buoyant aircraft can take off and land either by using the landing gears or vtol, or both. the exact estimation of lift by the hull is also challenging. relative to iium engineering journal, vol. 16, no. 1, 2015 haque et al. 10 the wing, the hull span will be quite small. as a result, the applicability of empirical relationships used for estimating the lift generated by the wing [1-3], becomes questionable as such relationships are derived for high aspect ratio tapered wings.[4] a good solution to this issue of lifting the fuselage, will be to carry out numerical flow simulations [5] to find out the value of total drag and lift force. however, numerical simulations take a long time and there is a need to look back at the existing analytical relationships of aircraft and airships for their utilization in the estimation of aerodynamic properties hence the need to merge such existing relationships for aerostatic as well as aerodynamic modules of hb aircraft. 2. modules of a hybrid buoyant aircraft in hb aircrafts, aerostatic lift is produced by the lifting gas which is stored in gas cells. the concept of gas cells comes from rigid airships in which several gas cells are arranged along the longitudinal axis of hull of airship which are free to expand and contract due to variation in atmospheric properties of air [6, 7]. the hull’s outer skin is made a certain fabric material, which requires an internal pressure to maintain its aerodynamic shape, especially when the lifting gas shrinks during the descent flight segment. the shape of the hull can be in the shape of an airfoil such that additional aerodynamic lift is generated by the hull from the beginning of ground roll in the take-off segment. moreover, similar to a winged airship; a wing can be attached with such a hull to generate partial lift. in this way; there are two different modules, which are to be treated separately to obtain information about the aerostatic as well as aerodynamic behavior of such aircrafts. in the following sections, these modules are discussed focusing on the further utilization of such analytical relationships. 2.1 aerostatic module in airships, aerostatic lift comes from lifting gas [8], aerodynamic lift arises from the contour of hull at certain angle of attack and power static lift originates from the propellers of stol engines. aerostatic lift, which remains constant till pressure height[9], is estimated for a given volume of gas cell inside the envelope by applying archimedes principle [10] which is expressed as eq. (1): = ( − ) (1) the densities of the air and gas are defined (eq. 2) according to clapeyron equation for ideal gas [7]; in which and are absolute pressure and temperature of air/gas. as per airship’s design standard [11], thelifting capacity of helium gas is about 1.05 kg/m3, against its density equal to0.1785 kg/m3 with 96% purity at sea level condition. = (2) forlifting gas cells, required volume, shape of individual gas cell, properties of material and its allocated space inside the hull are required. for non-rigid airships and blimps, shape of the outer contour is maintained by keeping the internal pressure in the envelope for maintaining the shape [10]. but the volume of the lifting gas is dependent on altitude and temperature of lifting gas itself. for example, superheating, due to sun heat will cause a change in buoyant lift ∆ and according to ideal gas law, change in volume can be represented as eq. (3) [12]: iium engineering journal, vol. 16, no. 1, 2015 haque et al. 11 ∆ = ∆ (3) where is equal to  and its value forhelium gas at 0oc is 0.1832 and is the temperature of gas.traditionally, control of the internal pressure is done by using airinflated bladders within the envelope, known as ballonets [7]. this concept is also both directly and indirectly applicable to hb aircrafts as well. for example, similar to airships, it can be applied to make hb aircrafts heavy by getting the air from surrounding air. moreover, for a constant altitude condition, the weight also decreases with burning of fuel and the control surfaces may/do not compensate for the decrease in the overall lift requirement of the aircraft. for ballonets [1], it is first required to find out the percent fullness (% ) for the additional required volume of hull. the structural anatomy of non-rigid and semi-rigid airships are not rigid enough to maintain the aerodynamic shape of the outer hull and ballonets help in maintaining the outer contour during the descent segment of flight. ballonets are used to compress the expansion of lifting gas in gas bags; the required extra volume for which can be estimated by using eq. (4), [1]: % = = (4) and are the values of atmospheric pressure and temperature, respectively at the defined height pressure. sl denotes the atmospheric conditions corresponding to sea-level or the altitude from where hb aircraft will take-off. once the volume of lifting gas at sealevel is calculated, this value is then divided by percent fullness to get the required volume of ballonets. 2.2 aerodynamic module in this module, aerodynamic contour of wing and hull is discussed. in order to get a first order aerodynamic response of then wing and hull of an hb aircraft, only three major parameters are required, i.e. the reference area, zero-lift drag coefficient and airfoil selection. 2.2.1 selection of airfoils similar to aircraft design, airfoil is the heart of aircraft and one of the major constraints for its selection is the ) required for aerodynamic lift. for this purpose, an initial estimation of ) is required, which will provide guidelines for selection of airfoil maximum lift coefficient, . as a first guess, required lift for level flight is estimated by taking ) equal to and similar to aircraft design one can take ) equal to 0.9 . the term is used here to cater for the effects of mass of air in ballonets in gross takeoff weight[1]. is the weight corresponding to gross takeoff mass, excluding the mass of lifting gas and apparent mass 2.2.2 wing sizing the wing is the most important component of an aircraft and low drag and high lift wing is always desirable. for a hb aircraft, the primary function of the wing is to generate sufficient aerodynamic lift to balance obtained from initial assumption of buoyancy ratio (eq. 2). with the progress of the science of aerodynamics, now there are a number of low fidelity panel method based software like javafoil [13], xflr [14], etc., available for iium engineering journal, vol. 16, no. 1, 2015 haque et al. 12 estimation of the lift in quite less time as compared with any cfd solver. based on the initial sketch, the wing can be designed at conceptual level. in this way projected area of the wing can be obtained for its first order approximation. this digit can further be refined after calculating the wing loading for which complete aerodynamic analysis is required. for a hb aircraft, wing loading is defined here as . for aircrafts, wing loading is usually referred to takeoff conditions [1] and the same holds good for hb aircraft as well. 2.2.3 aerodynamic contour design for hull as with any other airship and aircraft, the major contribution of drag for an hb aircraft is also due to the hull. a general expression for the hull’s drag for hb aircrafts can be calculated as the sum of zero-lift drag and induced drag, which is expressed as eq. (5): = + (5) where, for airships and hybrid airships can be estimated by using eq. (6). this expression is obtained from the trend plot of experimental data of body of revolution (without tail), body of revolution and hybrid (with tails), lifting bodies and of aircrafts [12]. moreover, in this equation is defined in terms of projected planform area: = −0.0145 1 + 0.182 1 − 0.514 1 + 0.838 1 − 0.053 (6) if the hull is aerodynamically lofted to have a shape somewhat of a cambered airfoil then it will contribute more towards induced drag and use of above mentioned relationship is still open to question. for aircrafts, induced drag of fuselage is not calculated separately as major lift is coming from the wings attached with fuselage. on the other hand, nonrigid, semi-rigid and even rigid airships were designed from hull of body of revolution and have no aerodynamic lift at zero angle of attack [15] due to symmetric shape of hull. because standard shapes of bodies of revolution can only produce lift when it is at certain angle of attack, therefore drag due to lift exists due to the hull as lift is generated for > 0[12]. for aircrafts [16], empirical relationships used for the estimation of induced drag always cater for the aspect ratio of wing as it is reference lifting surface for calculation of lift and drag. induced drag formula available in most of the references related to aircraft design [1], [3], [16–18] is based on prantdl’s lifting line theory, applicable to high aspect ratio wings; whereas the application of the same for estimating the induced drag of hull by considering the hull as low aspect ratio wing will be erroneous. the only realistic solution of this issue at the moment is to perform some numerical simulation to estimate lift as well as total drag. similar to a fuselage of an aircraft, zero-lift drag or parasite drag of hull consists mainly of skin friction drag, which can be calculated by considering a calculated flat-plate skin friction coefficient, , and form factor, that estimates the pressure drag due to viscous separation [2]. this estimation is done for major aerodynamic components of aircraft, and is given by eq. (7): , , = , . . , (7) iium engineering journal, vol. 16, no. 1, 2015 haque et al. 13 this equation is used for calculating the drag of other components of hb aircraft by the build-up method. for the estimation of wetted area of hull of a hb aircraft there are different calculation possibilities [2],16], out of which the one suggested for airships [1] is shown as eq. (8). , = . . . 1 − 2 / 1 + 1 (8) the form factor for estimation of drag coefficient of fuselage of aircraft eq. (9),[2] and of hull [18]are shown below as eq. (11) and (12) respectively. out of them, suggested one for hull of hb aircraft is eq. (9), but with a correction factor of 0.85 [1]: = 1 + 60 + 400 (9) = 1 + 1.5 ( ) + 7 (10) = 3. . 1 + 1.5 ( ) + 7 ( ) (11) it is well known that friction coefficient for turbulent flow is mainly dependent on the reynolds number and mach number and can be calculated by using eq. (12) [2],16]: , = 0.455 (log ) . (1 + 0.144 ) . (12) finally the drag force of hull, which accounts for inviscid as well as viscous drag due to lift is expressed as eq. (13); = . _ + _ (13) 2.2.4 aerodynamic lift and drag coefficients in a reference of hybrid airship [19], the aerodynamic lift coefficient is defined similar to an airplane, eq. (14): = (14) ina reference of hybrid airship [19], total lift coefficient isexpressed in terms of ) and ) as eq. (15), [19]. = = ) + ) (15) where, variable is defined by eq. (16) [19]: iium engineering journal, vol. 16, no. 1, 2015 haque et al. 14 = (16) it can be observed from eq. (15) that changes with altitude. however, if the gas cells are free to expand then has to remain constant till pressure height. moreover, the aerostatic as well as aerodynamic lift is non-dimensionalized by , eq. (15). from aerodynamic point of view, if the shape is invariant then there will be no contribution of buoyant lift towards the aerodynamic lift. these relationships are not suitable for any analysis work related to hb aircraft and aerostatic lift force can be balanced with some % of gross takeoff weight; described as ‘dead weight lift’ [20] and its corresponding mass as ‘dead mass’, represented by . also, definition of reference area is not fully explored. for a hb aircraft can be defined as the sum of the planform projected area of hull and wing , which is the area of wing outside the hull. = + (17) induced drag of a hb aircraft can be represented by eq. (18) and zero lift drag or pressure drag can be estimated by using the built up method of aircraft [1]. , = − (18) = + + + (19) in eq. (19), ‘k’ is the total induced drag coefficient due to wings , canards and lifting hull . this term accounts for inviscid as well as viscous drag due to lift. is for minimum and for conventional airships its value is approximately equal to zero due to low camber hull. the zero lift drag of the empennages and wing can be calculated with the same procedure as for the hull, eq. (7). the wetted area depends on the geometrical characteristics of the empennage and is estimated by using eq. 20[2]: = 2 1 + 0.25( / ) 1 + 1 + (20) where, is equal to ( / ) /( / ) and represents the taper ratio. similarly, the wetted area of wings, ventral and canards can be found by using the above mentioned equations. 2.2.5 drag polar equation as the aerodynamic lift is totally generated by the lifting surface, the total drag and its coefficient is given by eq. (21), [12]: = + − (21) usually, airships have no or very small camber, and will be equal to zero [12]. the same holds good for a hb aircraft with a low camber wing attached with the nonlifting hull. total drag of such configurations can be represented by using eq. (22). however, the drag polar equation for a configuration of hb aircraft designed using a lifting hull can be approximated by using eq. (23) [5]: iium engineering journal, vol. 16, no. 1, 2015 haque et al. 15 = 1 2 + − (22) = ( ) _ + − + (23) analytical relationships of airships and aircrafts, which were discussed above will give a starting point for the conceptual design work of hb aircrafts. unfortunately, at present the wind tunnel testing of such aircrafts is quite rare. but like conventional aircrafts, it is perceived that the aerodynamic data obtained from wind tunnel testing can be utilized in future for the correction of existing analytical relationship like form factor, induced drag factor of hull. unfortunately, except estolas aircraft, experimental data for estimation of aerodynamic characteristics of such unconventional aircrafts is not available. it is perceived that whenever the design methodology for different versions of hb aircraft, starting from a light passenger aircraft to a very high payload cargo type is available, then the existing relationships will be a starting point for the design work. 3. conclusion remarks flying characteristics of hb aircrafts will be a merger of aircraft and airship technology due to lift augmentation, i.e. lift generated by buoyancy and due to pressure difference. since the aerostatic lift remains constant till pressure altitude; therefore its coefficient has to remain constant. aerostatic lift is independent of the weight, and volume is the only parameter of concern. the inflation and deflation of the ballonets depends on exact estimation of pressure height. there are no existing historical trends available for initial estimation of lift generated by an aerodynamically lofted hull. numerical simulations will be required to get a first-hand account of the coefficient of drag. it can be perceived that the existing analytical relationships of aircraft and airship will provide a starting point to develop the design methodology of hb aircrafts. acknowledgement the support of the ministry of science, technology and innovation (mosti), malaysia, under the grant 06-01-08-sf0189 is gratefully acknowledged. references [1] raymer d. (2012) aircraft design: a conceptual approach, 5th edition. american institute of aeronautics and astronautics, inc., washington, dc. [2] nita m, scholz d. (2013) from preliminary aircraft cabin design to cabin design to cabin optimisation-part i, u.p.b. sci. bull., series d, 75(3). .http://www.fzt.hawhamburg.de/pers/scholz/opera/opera_pub_upb-sci-bull-d-75-3_13-07-01.pdf, [retrieved 4 november. 2014] [3] grant ce, leland nm. (2013)fundamentals of aircraft and airship design: volume ii, aircraft design. american institute of aeronautics and astronautics, aiaa.. [4] lowry jg, polhamusec. (1957) a method for predicting lift increments due to flap deflection at low angles of attack in incompressible flow. naca-tn-3911 1957.http://www.naca.central.cranfield.ac.uk/reports/1957/naca-tn-3911.pdf [retrieved 2 december. 2014] [5] haque au, asrar w, omar aa, sulaeman e, ali jm. (2014) conceptual design of a winged hybrid airship,” in 21st aiaa lighter-than-air systems technology conference, aiaa– 2014–2710. iium engineering journal, vol. 16, no. 1, 2015 haque et al. 16 [6] ardema m, flaig k. (1980) parametric study of modern airship productivity. nasa tm81151. [7] konstantinov l. (2003) the theory of gas and airships theory. tech. sci. j. mod. aerostatic probl., pp. 1–21. http://www.fplgenerator.free.fr/aero/airship, [retrieved 17 december. 2014] [8] khoury ga. (2012) airship technology, vol. 10. cambridge university press. [9] burgess cp. (1927) airship design, university press of the pacific, honolulu, hawaii. [10] khoury ga, gillett jd. (1999) airship technology. cambridge univ. press, new york. [11] faa regulations (2001) regulations on airship design criteria. faa p-8110-2. [12] carichner ge, nicolai lm. (2013) fundamentals of aircraft and airship design: volume ii, airship design. american institute of aeronautics and astronautics, aiaa. [13] hepperle m. (n.d.) javafoil users guide. pp. 1–34, http://www.mh-aerotools.de, [retrieved 17 march. 2014] [14] deperrois ca. (2001) about stability analysis using xflr5, http://www.xflr5.com, [retrieved 10 feb. 2014] [15] hoerner, s. f. (1965). fluid–dynamic drag, hoerner fluid dynamics, bakersfield, ca. in library of congress catalog card (no. 64-19666) [16] roskam j. (1990) airplane design. kansas: roskam aviation and engineering corporation. [17] anderson jd. (1999) aircraft performance and design. mcgraw–hill, boston. [18] gudmundsson s. (2013) general aviation aircraft design: applied methods and procedures. butterworth-heinemann. [19] zhang ks, han zh, song bf. (2010) flight performance analysis of hybrid airship: revised analytical formulation.j. aircr., 47(4):1318–1330. [20] prentice jt, barry e, beilock re, phillips aj. (2005) the rebirth of airships. transp. res. forum, 44(1):173–190. [21] gamaleyev a. (2012) estolas project description. http://www.estolas.eu/. [accessed: 6 march, 2014] nomenclature = aspect ratio = buoyancy ratio = aerodynamic lift coefficient of hb aircraft at the cruise condition = maximum aerodynamic lift coefficient of hb aircraft = coefficient of aerodynamic lift of hbaircraft for the minimum drag ( ) _ = zero-lift drag coefficient hbaircraft, less of the hull = zero-lift drag coefficient of hybrid buoyant aircraft = coefficient of minimum drag of hbaircraft hb = hybrid buoyant k = drag due to lift factor = aerostatic lift, (n) ) = maximum aerodynamic lift, (n) gtmm = total mass corresponding to gross takeoff mass, (kg) q = dynamic pressure, (n/m2) r = universal gas constant, (j/mol. k) ref s = reference area, (m2) , = wetted area of hull, (m 2) vol = volume, (m3) iium engineering journal, vol. 16, no. 1, 2015 haque et al. 17 = velocity, (m/sec) = density, (kg/m3) = finenss ratio of hull a = air application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 culinary recommendation application based on user preferences using fuzzy topsis faried effendy*, barry nuqoba, taufik information system study program, department of mathematics, faculty of science and technology, universitas airlangga, surabaya, indonesia. *corresponding author: faried-e@fst.unair.ac.id (received: 28th november 2018; accepted: 29th may 2019; published on-line:2nd december 2019) abstract: culinary tourism is the experience of finding and enjoying unique and impressive food and drinks in a new region. each region has a unique food flavor and can be the right choice for culinary tourists who want to try new experiences regarding taste. differences in tourist preferences in choosing culinary regions sometimes become obstacles in finding a suitable place. price, distance, facilities, menu variations, and halalness are some of the things that tourists consider in choosing culinary locations. therefore, it is essential to accommodate tourist preferences to produce appropriate recommendations because the characteristics of tourists in determining their favorite culinary places are very subjective and varied. this study aims to develop a culinary recommendation system based on user preferences using fuzzy topsis as a recommendation method. ten criteria can be selected, and their weight value determined by the user. the final result of the recommendation system is an alternative culinary location ranking and map location, along with detailed culinary location information. result evaluation shows that the system is suitable and useful for users. this study proposes some new criteria that have not been used in other research. abstrak: pelancongan masakan merupakan pengalaman mencari dan menikmati makanan dan minuman yang unik dan menarik di sesebuah daerah. setiap daerah mempunyai rasa unik makanan dan boleh menjadi pilihan tepat untuk pelancong yang ingin mencuba pengalaman baru mengenai rasa. perbezaan pilihan pelancong dalam memilih tempat masakan kadang-kadang menjadi halangan dalam mencari tempat sesuai. harga, jarak, kemudahan, variasi menu, dan makanan halal merupakan beberapa faktor yang dilihat pelancong dalam memilih lokasi kulinari. oleh itu, sokongan cadangan untuk pelancong membuat pilihan adalah penting kerana pilihan makanan adalah sangat subjektif dan berbeza-beza. kajian ini bertujuan bagi membangunkan sistem cadangan masakan mengikut pilihan pengguna dengan menggunakan kaedah fuzzy topsis. sepuluh kriteria boleh dipilih mengikut keutamaan. matlamat akhir sistem ini adalah sebagai pilihan lain bagi pilihan lokasi makanan dan lokasi peta bersama maklumat terperinci lokasi masakan. keputusan menunjukkan sistem ini sesuai dan berguna untuk pengguna. kajian ini mencadangkan beberapa kriteria baru yang tidak digunakan oleh penyelidik lain. keywords: recommender system; fuzzy topsis; culinary ranking; user preferences; gis 1. introduction tourism is a complex multidimensional sector that influences the relevance of other areas in tourism activities. tourism is all activities related to the tourist, and its multidimensional and multidisciplinary nature emerges as a manifestation of the needs of 163 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 every person and country as well as interactions between tourists and the local community, fellow tourists, the government, regional government and entrepreneurs [1] indonesia is actively developing the tourism industry, especially for surabaya, as one of the metropolitan cities in indonesia, also focusing on increasing the visits of both local and foreign tourists. various efforts have been made, starting from city park beautification, city corner cleaning, growing tourist destinations, and many other things. surabaya is famous as a city with a variety of culinary destinations that present many colors and choices for tourists who want to enjoy culinary treasures in surabaya. however, some obstacles are encountered by tourists, including lack of knowledge about culinary locations in surabaya and different preferences in determining culinary location. the selection of culinary destinations has many criteria, such as price, location, convenience, type of menu, and others [2]. the choice is also subjective, meaning that each tourist has different preferences in choosing culinary destinations. according to [3], if data attributes of an alternative are not adequately served, contain uncertainties or inconsistencies, the usual multiple attribute decision making (madm) method cannot be used. based on these problems, it is necessary to have a decision support system (dss) with geographic information system (gis), so that the system can provide automatic recommendations on culinary tourism. dss allows users to make decisions more quickly and carefully by combining hardware, software, and decision processes [4]. there have been many studies discussing decision support systems (dss) culinary recommendations [2, 5, 7]. web and mobile-based applications have also been made to facilitate culinary connoisseurs in finding the nearest culinary location. however, most web and mobile apps focus more on distance and rating, so other criteria such as convenience, a variety of menus, prices, and halalness were rarely used as filters or additional rules. the concept of combining dss and gis is now growing. the method in dss is used to analyze the inputted data, and gis is used to display location information in the form of mapping. the advantages of dss in analyzing data and the advantages of gis in delivering information are combined, making this system better when used [8]. this culinary selection problem requires the consideration of multiple factors and can be categorized as a multi-criteria decision-making problem. fuzzy topsis is one of the multi-criteria decision-making methods used to find optimal alternatives from several alternatives with certain criteria. fuzzy is used in linguistic criteria that have uncertainty, while topsis is used to get the best alternative. fuzzy topsis is easy to use, can take into account all types of criteria (subjective and objective), rational logic, and is easy to understand for practitioners. the calculation process is straightforward, the concept allows the pursuit of the best alternative criteria described in mathematics in a simple way, and essential weights can be entered easily [9, 10]. this study aims to design a mobile application that makes it easier for surabaya tourists to choose the destination for culinary locations based on their preferences. criteria to be selected include convenience, menu variation, price, distance, parking area, facilities, service, and halalness. 2. related work several criteria were used to determine tourist destinations according to tourist considerations [11]. the analytic hierarchy process (ahp) method is used as a method for analyzing data to determine the priority of tourist destinations in the talaud islands. promotional patterns that are still traditional for tourism in the talaud islands are 164 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 considered to be still inefficient. therefore a web-based system is needed that can become an effective promotional media so that it can increase tourist enthusiasm. developing the concept of a combination of gis with multi-criteria was also used to determine the location of the industry in the vojvodina area [12]. the use of the idea can provide a location determination solution by analyzing several influential factors. gis in this study is used as an approach to spatial decision making to determine the location of the industry. other research has applied the merge of fuzzy multi-attribute decision making (fmadm) and geographic information system (gis) [13]. the incorporation of fmadm and gis is done to identify and evaluate the application of ecotechnology. the process carried out is to determine the use of ecotechnology methods that are suitable for riverbank walls. feasibility evaluation refers to specific criteria provided by local area experts. the results of the study show that gis can provide convenience for users to obtain information regarding geographical problems. a research was conducted by taroreh et al. [14] to determine the location of tourism development in the poso region using feedback from the community (feedback). the poso region has natural tourism that is attractive to tourists but still has not been developed; the development carried out by the government is based on feedback and input from the community. the results of this study indicate that this system can provide a solution for the government to develop tourism. some research [15] used location-based services (lbs) to help tourists find restaurant locations and specific culinary menus. lbs is a service that can send data and information that contains current location information about the user's presence or information that projects several locations of mobile users. lbs is applied as a part of architecture consisting of five components, such as mobile devices, communication networks, positioning components (gps), provider services, applications, and data providers. services delivered include map areas, weather conditions, traffic flow conditions, tour guides, shopping information, and so on. lbs requires a precise location to produce useful information. afnarius et al. [16] have built a culinary tourism search application in west sumatra based on the mobile geographic information system. the development of this application aims to help tourists get information about culinary tours in west sumatra. the app is built using the php programming language, basic4android, and google maps. the database used in the application is postgresql. however, the application still needs to add additional features, such as uploading photos to social networks, accounts for users, and adding new culinary locations. geotagging is a procedure for adding geographic metadata information on different media such as adding geographic information on images, audiovisuals, internet sites, sms messages, qr codes, and rss in the form of geospatial metadata [17]. generally, the information added consists of gps geographic coordinates, location (address), description of data from the place. the difference between previous research projects lies in the criteria, data analysis, and methods used. this study uses the concept of combining dss with gis to create an auto recommendation system, which applies the fuzzy topsis method. this application is expected to help tourists in surabaya determine the location of a culinary destination and be able to display the route to the desired culinary tour. 165 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 3. method 3.1 data and information collection survey and literature studies are conducted to find out what criteria are considered by tourists when choosing culinary destinations. at this stage, 50 respondents would select and verify the criteria obtained from literature studies. this verification is used to determine the factors that influence based on user needs. after confirmation, criteria derived will be used as the criteria for selecting culinary destinations in the system. furthermore, the results of data collection on culinary destinations are used as an alternative in the system. five culinary experts will assess all of these alternatives. 3.2 fuzzy topsis as ranking method the recommendation system works by ranking culinary destinations according to user preferences using the fuzzy topsis method. following are the ranking steps using the fuzzy topsis method [18]: step 1: categorizing positive and negative ideal criteria: at this stage, predetermined selection criteria will be grouped in the categories of positive and negative ideal criteria. step 2: determine fuzzy numbers for weighting criteria and assessment of culinary destinations: at this stage, linguistic variables and tfn (triangular fuzzy number) are associated with establishing the importance weight matrix for each criterion and performance rating for each alternative culinary destination. step 3: determine importance weights: at this stage, the importance of each of the criteria used in the system will be determined. the level of importance of the criteria will be denoted by the formula: (1) step 4: construction of decision matrix: at this stage, the performance rating of each alternative culinary destination will be determined. the decision matrix that is constructed contains alternative m, n criteria, and k experts. the decision matrix can be denoted by [10]: (2) where (3) step 5: normalization of decision matrix: the decision matrix obtained in step 4 will be normalized. there is a difference in the normalization technique on the ideal positive criteria (benefit) and negative ideal (cost). normalized decision matrices can be denoted by: (4) where (5) for benefit criteria. (6) for cost criteria. 166 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 step 6: weighting decision matrix: a normalized decision matrix will be multiplied by the level of importance/weight of the criteria obtained in step 3. the weighted decision matrix can be denoted by: (7) step 7: determining fuzzy positive ideal solution (fpis) and fuzzy negative ideal solution (fnis): determine fpis and fnis for each criterion: (8) (9) where: (10) step 8: calculating the distance of each alternative to fpis and fnis: at this stage, the distance of each alternative that will be ranked against fpis and fnis will be calculated using the formula: (11) (12) step 9: calculating the relative proximity to ideal solutions: calculate the distance of the total criteria of each alternative to fpis and fnis so that x then calculate the proximity relative to the ideal solution with the formula: (13) step 10: ranking: sort the results of closeness relative to the ideal solution obtained in the previous step from the largest to the smallest value; the higher the value, the better the alternative. 4. results 4.1 data and information collection from the results of data collection and processing, the final results are in the form of criteria that are considered when tourists choose culinary destinations. the full criteria can be seen in table 1. all criteria will be used as calculation criteria in the fuzzy topsis method. filter criteria are the criteria used to filter out alternative culinary destinations that will be recommended to suit the user's wishes. for the halal criteria, if a user wants a halal culinary destination, then alternative culinary destinations that will be recommended are alternative culinary destinations with halal menus. the criteria for filters that are not selected will not be a filter for the system; for example, if the halal criteria are not chosen, then all the culinary destinations which have a halal menu and not will be an alternative culinary destination that will be recommended. 167 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 table 1: final result criteria code criteria type c1 comforts linguistic c2 menu variation linguistic c3 area of place crisp c4 distance crisp c5 parking area linguistic c6 facility linguistic c7 service linguistic c8 price crisp c9 halal crisp, filter c10 menu linguistic linguistic criteria are non-exact criteria and will be used as criteria given by five experts. criteria that have a type of crisp value will not be assessed again to facilitate the assessment of alternatives to be carried out by experts. experts do not need to repeat the assessment of alternative culinary tourist destinations on specific criteria that already have exact numbers. 4.2 fuzzy topsis as ranking method step 1: results that have been obtained from the assessment criteria will be grouped into two types of criteria, namely the criteria of benefit and cost. the criteria to be taken are five criteria, namely c1 (convenience), c2 (menu variation), c3 (place area), c8 (price), and c10 (menu type). for the calculation example, five criteria will be taken, namely c1 (convenience), c2 (menu variation), c3 (place area), c8 (price), and c10 (menu type). categorizing the assessment criteria can be seen in table 2. table 2: grouping of positive and negative ideal criteria criteria type c1 ideal positive solution c2 ideal positive solution c3 ideal positive solution c8 ideal positive solution c10 ideal positive solution step 2: fuzzy numbers that will be used for weighting criteria, and evaluating each alternative can be seen in tables 3 and 4. 168 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 table 3: importance rating importance rating linguistic variables tfns very low (vl) 0 0 0.1 low (l) 0 0.1 0.3 medium low (ml) 0.1 0.3 0.5 medium (m) 0.3 0.5 0.7 medium high (mh) 0.5 0.7 0.9 high (h) 0.7 0.9 1 very high (vh) 0.9 1 1 table 4: assessments rating assessments rating linguistic variables tfns very poor (vp) 0 0 1 poor (p) 0 1 3 medium poor (mp) 1 3 5 fair (f) 3 5 7 medium good (mg) 5 7 9 good (g) 7 9 10 very good (vg) 9 10 10 step 3: the next step is to choose the importance level of the criteria. the level of importance of the criteria is in the form of linguistic variables that will be converted into fuzzy numbers. for example, this calculation will use the following criteria: c1: "very high" c2: "very high" c3: "very high" c8: "medium" c10: "medium-high" so the results are as shown in table 5. table 5: importance of weight matrix criteria tfn l m u c1 0.9 1 1 c2 0.9 1 1 c3 0.9 1 1 c8 0.3 0.5 0.7 c10 0.5 0.7 0.9 step 4: in this stage, performance ratings are given by each expert (p) to each alternative to building a decision matrix. the performance rating given by each expert is a linguistic variable. the linguistic variable will then be converted into fuzzy numbers. experts (p) only provide performance ratings against assessment criteria that are not crisp numbers. the performance 169 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 rating for criteria in the form of crisp numbers will be taken directly from the data specifications of culinary destinations. the performance rating given by experts will be aggregated because experts number more than one person. the aggregation calculations for a1 on c1 are as follows: for k = 3 in criterion c1 for alternative a1, for example, a = a1 and b = c1 for criteria that have crisp values, fuzzy numbers will not be used, but the form of the criteria value will be changed to tfn. for example, criterion c3 (area of place) has a value of 8; it will be converted into the form of tfn to (8,8,8). this is done to equalize crisp numbers into calculations using the tfn. step 5: at this stage, the normalization of the decision matrix will be carried out. the formula used to normalize depends on the type of criteria that have been grouped in step 1. calculation of normalization of the decision matrix on positive ideal criteria is as follows: for i = 5 on c1 belongs to the alternative a1, for example a = a1 and b = c1: so that while for the negative ideal criteria, normalization of decision matrices can be calculated as follows: for i = 5 on c8 belongs to alternative a1, for example a = a1 and b = c8: so that step 6: then, the normalized decision matrix will be weighted multiplied by the importance of weights obtained in step 3. weighting the decision matrix can be calculated as follows: for criterion c1 in alternative a1, for example, a = a1 and b = c1: step 7: fpis and fnis have their respective values: dan 170 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 step 8: at this stage, each alternative in the weighted decision matrix will be calculated: the distance to the ideal fuzzy positive solution (fpis) and the negative fuzzy ideal solution (fnis). alternative distances to fpis and fnis for positive ideal criteria can be calculated as follows: for c1 and c2 on a1, suppose: so that the distance between fpis and fnis can be seen in tables 6 and 7. table 6: alternative distance to fpis criteria a1 a2 a3 a4 a5 c1 0.47 0.44 0.79 0.79 1.51 c2 0.44 1.03 0.41 0.47 1.03 c10 1.1 1.27 1.1 0.95 1.12 c3 2 1.5 2.76 2 2 c8 1.56 0.9 1.44 1.65 1.86 distance 5.57 5.14 6.5 5.86 7.52 table 7: alternative distance to fnis criteria a1 a2 a3 a4 a5 c1 2.53 2.56 2.21 2.21 1.49 c2 2.56 1.97 2.59 2.53 1.97 c10 1.9 1.73 1.9 2.05 1.88 c3 1 1.5 0.24 1 1 c8 1.44 2.1 1.56 1.35 1.14 distance 9.43 9.86 8.5 9.14 7.48 171 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 step 9: the distance of each alternative to the ideal positive fuzzy solution and the ideal negative fuzzy solution will be calculated for the proximity of the ideal solution so that the results can be seen in table 8. alternative closeness to the ideal solution can be calculated as follows: for alternative a1, where a = a1 so that table 8: proximity to ideal solutions distance a1 a2 a3 a4 a5 di+ 5.57 5.14 6.5 5.86 7.52 di9.43 9.86 8.5 9.14 7.48 di+ di+ 15 15 15 15 15 si 0.629 0.657 0.567 0.609 0.499 step 10:at this stage, an alternative closeness to the ideal solution will be ranked based on the values obtained to determine the best alternative. the higher the value obtained by the alternative, the better. ranking results can be seen in table 9. table 9: alternative ranking results ranking alternative point 1 a1 0.657 2 a2 0.629 3 a4 0.609 4 a3 0.567 5 a5 0.499 4.3 implementation the user of this application can input directly into a text box on what kind of food they want; then they can choose such criteria that they prefer and its importance criteria. there are seven levels of importance criteria that can be selected (very low, low, medium low, medium, medium high, high, and very high). the application will display the culinary places that meet the condition and rank it from the highest to lowest; the rank image is displayed from left to right. the app will also view the map and how to reach that place when the picture is clicked. the application image can be seen in fig. 1. 4.4 system testing to test the system, black-box testing was used to validate the system in making recommendations by comparing the results of expectations (expert judging) with system output. we used 20 different tests, that cover different criteria, and their weight and calculates the score value with the formula: (14) 172 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 table 10 shows number 1 of 20 test cases that have been done; overall result evaluation shows that this system scored 75%, meaning that there were 15 cases that had the same result between system output and expert judgment. fig. 1: the application. table 10: recommendation results test case criteria weight system output experts 1 price distance service medium very high medium rank: 1.bakso p.jan 2.bakso cak bagong 3.bakso jenggot 4.bakso bringas 5.bakso cak man rank: 1.bakso p.jan 2.bakso cak bagong 3.bakso jenggot 4.bakso bringas 5.bakso cak man 4.5 system evaluation the system evaluation aims to determine the performance accuracy of the fuzzy topsis method as a decision support system for selecting culinary locations. system evaluation will be carried out by measuring user satisfaction with the system. the users were application users and experts who conduct culinary location selection. the categories used in the evaluation questionnaire are usability, accuracy, functional completeness, performance, and subjective assessment of users of the system as a whole (overall). each category asked in the questionnaire will calculate the mos (mean opinion score) value. mos calculations are used to conclude the ratings given by the user. the application is said to be useful if it has a value of 3 to 4. mos formula can be seen below: (15) where r is the individual rating of subject n for stimulus or n related factor. 173 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 this application was evaluated by twenty end-users and five experts; evaluation results show that usability, completeness, accuracy, performance, and overall category each scored 3.5, 3.5, 3.5, 3.65, and 3.6. the mos results for each category are then calculated with mos so that the overall system score is obtained. the calculation for the overall system score is as follows: from the results of the system score calculation, it was found that twenty-five system users gave a value of 3.55 from the total value of 4. therefore, it can be concluded that the system is useful. 5. conclusion the decision support system with the fuzzy topsis method helps users by identifying the essential criteria in the process of selecting culinary destinations. these criteria were the convenience, a variety of menu, price, distance, parking area, facilities, services, area, halal, and type of menu. in these criteria, there are three types of values, namely linguistic, crisp, and filter. linguistic use for criteria that are not exact values, crisp values use for criteria in the form of exact values, while filter values use for optional type criteria, which serve as an alternative filter for culinary destinations. the user's level of importance then determines the non-filter criteria. the level of importance of the criteria and assessment of alternative culinary destinations is processed by the fuzzy topsis method, and the system will display five culinary destinations with the best ranking as recommendations to users as the best culinary destination choice according to their preferences. decision support systems that are built have a high impact on solving the problem of choosing culinary destinations by providing recommendations on culinary destinations that suit the needs and preferences of users. this is evidenced by the results of a system testing and evaluation, which shows that 75% of system output has the same result as expected result, and the user considers the features provided in the decision support system with the topsis fuzzy method worth 3.55 out of 4. in this study, the app is built with minimal features for end-users so that for further development, it is recommended that this application also has a user-based community where all users can post a review, comments, and also rate so that the performance rating of each alternative can be determined. this feedback can be related to culinary destinations so that this application can be an effective and unbiased platform for people who need culinary destinations recommendation. references [1] haneef sk. (2017) a model to explore the impact of tourism infrastructure on destination image for effective tourism marketing. (thesis). uk: university of salford manchester. [2] maharani s, hatta hr, merdiko g. (2014) decision support system of culinary recommendations using ahp and topsis methods with map visualization. in bali international seminar on science and technology (bisstech) ii 2014 (p. c3.2-1-c3.26). bali. [3] kusumadewi s. (2006) fuzzy multi-attribute decision making (fuzzy madm). yogyakarta: graha ilmu. 174 iium engineering journal, vol. 20, no. 2, 2019 effendy et al. https://doi.org/10.31436/iiumej.v20i2.1023 [4] turban e. (2010) decision support and business intelligence systems 9th. prentice-hall press upper saddle river, nj, usa ©2010. [5] suteja br, guritno s. (2017) a recommendation system for culinary tourists in jogjakarta based on collaborative filtering. in 2017 second international conference on informatics and computing (icic) (pp. 1–4). jayapura, indonesia: ieee. [6] huda aa, hantono bs, widyawan. (2015) sistem rekomendasi restoran dengan pendekatan ekstraksi fitur pada menu makanan. in seminar nasional teknologi informasi dan komunikasi 2015 (sentika 2015) (pp. 285-290). yogyakarta. [7] pinandito a, fanani l, brata kc. (2015) alternatives weighting in analytic hierarchy process of mobile culinary recommendation system using fuzzy. arpn journal of engineering and applied sciences, 10(19), 8791–8798. [8] halim i, arep h, kamat sr, abdullah r, omar ar, ismail ar. (2014) development of a decision support system for analysis and solutions of prolonged standing in the workplace. safety and health at work, 5(2), 97–105. https://doi.org/10.1016/j.shaw.2014.04.002. [9] azizi a, aikhuele do, souleman fs. (2015) a fuzzy topsis model to rank automotive suppliers. procedia manufacturing, 2(february), 159–164. https://doi.org/10.1016/j.promfg.2015.07.028. [10] nadaban s, dzitac s, dzitac i. (2016) fuzzy topsis: a general view. procedia computer science, 91(itqm), 823–831. https://doi.org/10.1016/j.procs.2016.07.088. [11] taluay, h. r., seminar, k. b., & monintja, d. r. (2015). development of web-based tourism decision support system in talaud island regency. international journal of information technology and business management, 39(1), 36-45. [12] rikalovic a, cosic i, lazarevic d. (2014) gis based multi-criteria analysis for industrial site selection. procedia engineering, 69: 1054-1063. https://doi.org/10.1016/j.proeng.2014.03.090. [13] chou wc, lin wt, lin cy. (2007) application of fuzzy theory and promethee technique to evaluate suitable ecotechnology method : a case study in shihmen reservoir watershed, taiwan, 1, 269–280. https://doi.org/10.1016/j.ecoleng.2007.08.004 [14] taroreh aa, tanaamah ar, fibriani c. (2014) decision support system feasibility of tourism resort in poso district used 360 degree method. international journal of computer science issues, 11(2): 201-207. [15] brimicombe a, c li. (2009) location-based services and geo-information engineering. singapore: faboulus printers pte ltd. [16] afnarius s, ningsih vm, frihandana d. (2014) pembangunan aplikasi wisata kuliner sumbar berbasis mobile geographic information system. prosiding seminar ilmiah nasional komputer dan sistem intelijen, 8(kommit): 354-360. [17] annisa ns, dwi s. (2012) perancangan dan pembangunan perangkat fitur geotagging. jurnal teknik pomits, 1(1): 1-6. [18] yayla y, ozbek a, yildiz a. (2012) fuzzy topsis method in supplier selection and application in the garment industry. fibres and textiles in eastern europe, 20: 20-23. 175 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <feff0633062a062e062f0645002006470630064700200627064406250639062f0627062f0627062a002006440625064606340627062100200648062b062706260642002000410064006f006200650020005000440046002006450646062706330628062900200644063906310636002006480637062806270639062900200648062b06270626064200200627064406230639064506270644002e00200020064a06450643064600200641062a062d00200648062b0627062606420020005000440046002006270644062a064a0020062a0645002006250646063406270626064706270020062806270633062a062e062f062706450020004100630072006f00620061007400200648002000410064006f00620065002000520065006100640065007200200036002e00300020064806450627002006280639062f0647002e> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <feff005500740069006c0069007a00610163006900200061006300650073007400650020007300650074010300720069002000700065006e007400720075002000610020006300720065006100200064006f00630075006d0065006e00740065002000410064006f006200650020005000440046002000610064006500630076006100740065002000700065006e007400720075002000760069007a00750061006c0069007a006100720065002000640065002000ee006e00630072006500640065007200650020015f0069002000700065006e00740072007500200069006d007000720069006d006100720065006100200064006f00630075006d0065006e00740065006c006f007200200064006500200061006600610063006500720069002e00200044006f00630075006d0065006e00740065006c00650020005000440046002000630072006500610074006500200070006f00740020006600690020006400650073006300680069007300650020006300750020004100630072006f0062006100740020015f0069002000410064006f00620065002000520065006100640065007200200036002e003000200073006100750020007600650072007300690075006e006900200075006c0074006500720069006f006100720065002e> /rus <feff04180441043f043e043b044c043704430439044204350020044d044204380020043f043004400430043c043504420440044b0020043f0440043800200441043e043704340430043d0438043800200434043e043a0443043c0435043d0442043e0432002000410064006f006200650020005000440046002c0020043f043e04340445043e0434044f04490438044500200434043b044f0020043d0430043404350436043d043e0433043e0020043f0440043e0441043c043e044204400430002004380020043f043504470430044204380020043104380437043d04350441002d0434043e043a0443043c0435043d0442043e0432002e00200421043e043704340430043d043d044b043500200434043e043a0443043c0435043d0442044b00200050004400460020043c043e0436043d043e0020043e0442043a0440044b0442044c002c002004380441043f043e043b044c04370443044f0020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e00300020043b04380431043e00200438044500200431043e043b043504350020043f043e04370434043d043804350020043204350440044104380438002e> /sky <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> /slv <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> /suo <feff004b00e40079007400e40020006e00e40069007400e4002000610073006500740075006b007300690061002c0020006b0075006e0020006c0075006f0074002000410064006f0062006500200050004400460020002d0064006f006b0075006d0065006e007400740065006a0061002c0020006a006f0074006b006100200073006f0070006900760061007400200079007200690074007900730061007300690061006b00690072006a006f006a0065006e0020006c0075006f00740065007400740061007600610061006e0020006e00e400790074007400e4006d0069007300650065006e0020006a0061002000740075006c006f007300740061006d0069007300650065006e002e0020004c0075006f0064007500740020005000440046002d0064006f006b0075006d0065006e00740069007400200076006f0069006400610061006e0020006100760061007400610020004100630072006f0062006100740069006c006c00610020006a0061002000410064006f00620065002000520065006100640065007200200036002e0030003a006c006c00610020006a006100200075007500640065006d006d0069006c006c0061002e> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 eshev et al. https://doi.org/10.31436/iiumej.v21i2.1329 influence of wind waves on the flow in flowing reservoirs sobir samatovich eshev, alisher normurodovich khazratov*, ashraf rasul o’gli rahimov and shahboz alisher o`gli latipov “operation of hydraulic structures and pumping stations” department, karshi engineering economics institute, karshi, uzbekistan *corresponding author: khazratov@gmail.com (received: 4th january 2019; accepted: 18th february 2020; published on-line: th july 2020) abstract: methods are given for calculating the formation of wind waves in flowing reservoirs, taking into account oncoming and associated currents and the limitation of acceleration by the banks. abstrak: kaedah diberikan bagi mengira pembentukan gelombang angin dalam takungan aliran, dengan mengambil kira arus datang dan aliran berkaitan dan kekurangan pecutan pada tebing. keywords: wave action; spectral component; method of characteristics; acceleration length; wave beam 1. introduction additional factors that determine the generation of wind waves at large watercourses (flowing reservoirs, large rivers, and large canals) in comparison to the open sea are the current and the limited acceleration by the coasts. the combined effect of both factors was studied in [1-10]. we will review the corresponding theory that underlies the methodology for calculating the formation of wind waves on watercourses. for wind waves on a large-scale flow, the main dynamic equation is the conservation equation, which with respect to the problem under consideration can be written as: act n n n r k q t r k , (1) where: rtkrs /,,t,k,rn (2) spectral density of the wave action tkrs ,, is the spatial amplitude spectrum of the waves, r – is the frequency corresponding to the spectral component yx kkk , at the point yxr , at time t in the reference frame moving with the flow velocity tru , . the principle of conservation of wave action is valid for waves in a moving environment, was established by bretherton, garret in 1969 [9], and was developed for waves on water by uizem. in the one-dimensional case, equation (1) is simplified as follows: 125 iium engineering journal, vol. 21, no. 2, 2020 eshev et al. https://doi.org/10.31436/iiumej.v21i2.1329 act n x n k n q t t x t k . (3) characteristics of equation (3): 0 ag x c t k k t x , (4) where gac is the absolute group velocity, ag grc c u . in accordance with (3) and (4), the condition on the characteristics has the form: ag act n n c q t x . (5) in the steady state, when sufficient time is reached, the wave action ceases to depend on time, but is only a function of acceleration. moreover, equation (5) takes a very simple form: ag act n c q x . (6) therefore, using the method of characteristics and dividing the variables in equation (6), we can write the solution of equation (3) in the following implicit form: 0 0 x agx dx c n actn dn q , (7) where 0 0 xx nn (8) is a boundary condition. under the initial condition 0x , the wave factor 0n corresponds to 0 0x n , in a certain section x , the wave factor n corresponds x n . since the group velocity at constant depth and flow velocity does not depend on the coordinate, the right-hand side of equation (7) is reduced to: 0 x 0 0 agx dx c ag x x t t c , (9) where 0tt is the propagation time of waves with a group velocity from the boundary alignment. from (7) and (9) it follows that the following coordinate transformation (for 00x ) is: 0 0 x x g ag g ag cx x or c c c (10) where 0gc , the group velocity on still water, gives a wave action value )(xn equal to )(0 xn at the acceleration distance x along the flow, which is the amount of wave action 126 iium engineering journal, vol. 21, no. 2, 2020 eshev et al. https://doi.org/10.31436/iiumej.v21i2.1329 on the take-off run x on still water. thus, relation (10) determines the effective acceleration length for wind waves in the flow. the definition of the effective acceleration length for waves in a flow was considered in more detail in [6], where, in particular, it was shown that if the angle between the wind and current vectors is equal to , then the effective acceleration length is determined by the relation: cosx x 0 uc c gr g , (11) where grc is the group velocity of the waves in the coordinate system associated with the flow. the concept of the effective acceleration length for waves in a flow gives the correct qualitative tendency for the influence of the flow on the development of waves. indeed, in deep water ucc gga 0 and in the associated stream ( 0u ) it follows from (10) that 1/ xx , i.e. effective acceleration length is less than actual. on the contrary, in the opposite flow ( 0u ) it follows from (10) that 1/ xx , i.e. effective acceleration length is greater than the actual geometric length. such a flow effect corresponds to the data obtained in aero hydrodynamic channels [11–13], where the wind waves in the passing current are less and are more in the opposite flow than in the absence of the flow, in other equal conditions. the effective acceleration length can be determined from equation (11), in which it is necessary to set the value of the relative group velocity. for this, the experimental dependence for the frequency of the maximum of the wave spectrum in the coordinate system of the flow can be used [13]: 354,0 2 * * 939,0 u gx g fu pr , (12) where *u is the wind friction velocity in a fixed coordinate system. if we go in relation (12) to the wind speed and the average frequency in the spectrum using the following relations [14]: pffuw 17,125 * , (13) then the expression (12) takes the form: 354,0 2 * 28,14 u gx g wr , (14) where r is the average relative circular frequency. then for the average group speed we get: 354,0 2 *4 44,0 u gxw c gr . (15) for the effective acceleration length, from the relation (11) the following implicit equation is obtained: 127 iium engineering journal, vol. 21, no. 2, 2020 eshev et al. https://doi.org/10.31436/iiumej.v21i2.1329 354,0 2 354,0 cos 44,0 4 1 w gx w u x xx x . (16) the numerical solution of equation (16) is shown in fig. 1. in fig. 1a, the solution relates to the associated flow, when 0/cos wu and 1/ xx . figure 1b shows the solution for the oncoming flow: 0/cos wu and 1/ xx . the curves in fig. 1 clearly demonstrate how important the flow factor can be, which can increase or decrease the acceleration length, especially at limited acceleration lengths. fig. 1: the dimensionless acceleration length for wind waves in the flow: a) on the passing flow, b) on the oncoming flow. the introduction of an effective acceleration length allows the following formulas of goin-soyuzmorniiproekt [5] to be used to calculate the average height and period of waves in flows [5]: 625,0 2 5,023 8,02 2 5,0232 21,3 100,61 1 1 625,0 100,61 1 116,0 w hg w tg wgx wgd th wgxw hg r , (17) gx/w21 10 100 a 1000 0.4 0.6 0.8 1ucosa/w= 0 0,01 0,025 0,05 0,075 0,1 0,125 0,15 10 100 1000 1 1.5 2 2.5 б gx/w2 ucosa/w= 0,1 0,075 0,05 0,01 0 128 iium engineering journal, vol. 21, no. 2, 2020 eshev et al. https://doi.org/10.31436/iiumej.v21i2.1329 where rt is the period of waves in a moving coordinate system (in the flow system), d is the water depth at acceleration. as shown in [5], dependences (17) are consistent for the absence of flow with a large amount of data from field measurements of waves. when predicting wind waves in limited water areas (large rivers, canals, reservoirs, or the coastal zone of the sea), it is necessary to take into account the limitation of acceleration by the coastline. this factor in conditions of narrowness or complex configuration of the coastline can be no less important than the current. the principle of taking into account the influence of the coastline on acceleration limitation is known. for the coastal zone of the sea, the corresponding techniques are given in [15]. for estuaries, straits, and canals that can be approximated in plan by a rectangle, a technique for accounting for the limited channel width is given in [16]. the effective acceleration length is also used, which we will call effective to limit acceleration. the latter value is determined by the integration of the acceleration lengths measured from the design point to the intersection with the coastline, along the angle between the local and general directions of the wind speed: xddxp x f , (18) where ’ is the raster of angles of the effective wave-forming action of the wind, p( ) – is the weight function. the effective wave formation raster is set at 90 degrees on both sides of the general direction for the complex outline of the coastline and from 30 to 90 degrees in the case of watercourses. the type of weight function depends on the distribution of wind speed in the directions and on local conditions. so with ’=300 and p( )=1, we get a solution often used for channels: x b arctgtg x b x b x b arctgtg x f 22 1 ln 22 317,1 422 1 ln 6 , (19) where b is the channel width. the form of the function (19) is shown in fig. 2. fig. 2: the influence of the relative width of the channel on the acceleration of waves. 10,001 0.01 0.1 0 0.2 0.4 0.6 0.8 1f/x b/x 129 iium engineering journal, vol. 21, no. 2, 2020 eshev et al. https://doi.org/10.31436/iiumej.v21i2.1329 2. methodology the calculation method, taking into account the influence of both the current and the complex configuration of the coastline, is as follows and is used further to calculate the size of wind waves in the region of the investigated transition. the principles of the technique are described in detail in [7,8]. the algorithm is a generalization of the method of calculating wind waves with a complex coastline configuration. from the calculated point with an interval of 22.5 degrees on both sides of the main beam with number n = 1, additional rays with numbers 4,3,2n are drawn. then, for each beam, the effective acceleration length along the stream is determined: n i ix x x 1 , (20) where is the length of the calculated section, (x / x) i is determined by formula (16), in which the corresponding projection of the flow velocity takes part. the beam continues until it crosses the shoreline. in the case of relatively small accelerations, we can neglect the curvature of the wave beam and use relation (20) for the beam as a whole. further, for each wave beam, the average wave height is calculated according to the first formula (17), the average wave height for the studied water area is determined by weighted averaging in accordance with the recommendations [13]: 2 1 2 4 2 4 2 3 2 3 2 2 2 2 2 1 5,31321251,0 hhhhhhhh . (21) then, according to the second formula (17), the average wave period is determined. to move from the average height and period of the waves to the height and period of the specified provision, the system uses the distribution function of the heights of the wind waves in the form of the rayleigh distribution, which is assumed to be valid for effective acceleration. in particular, to determine the height and period of significant waves, the following ratio can be applied: ss tthh 9,0625,0 . (22) as measurements show, for the oncoming flow, there is a feature related to the initial acceleration section. in this area, the generated wind waves propagate along the downstream, and in the wind, i.e. groups of waves propagate upstream. it is natural to assume that for a given wave the length of the initial section is determined by the relation: cosucgr , (23) that, using expression (15) for group velocity, can be written as: 0cos 44,0 4 354,0 2 354,0 w gx w u x x . (24) if we solve equations (24) and (16) together for a ray in the opposite flow, then we can take into account the effect of the initial section. 130 iium engineering journal, vol. 21, no. 2, 2020 eshev et al. https://doi.org/10.31436/iiumej.v21i2.1329 3. results and conclusion the developed methodology is confirmed by field measurements made at the karakum channel (on the 110-120 km section of the canal) by the authors of the report, as well as by the saniiri measurement data on several central asian channels [6]. for an idea of the ranges of the comparison, the author’s measurement data along with the calculation data are presented in table 1. the table shows that a comparison of the results of calculating the heights of the wind waves with the measurement data give a good ratio. table 1: comparison of wind wave height calculation results with measurement data acceleration length [m] channel width [m] water depth [m] wind speed [m / s] flow velocity [m] mass [kg] measured estimated 256 134 4.6 5.3 -0.42 4.5 4.3 258 134 4.6 6.9 -0.42 5.8 6.7 258 134 4.6 4.1 -0.42 3.3 3.0 795 167 3.8 5.7 0.42 6.0 6.1 795 167 3.8 5.8 0.42 6,3 6.2 137 55 3.2 9.4 -0.55 8.0 5.8 198 55 3.2 6.1 -0.55 5.6 3.7 180 50 2.1 15.8 -0.53 14.0 14.0 125 50 2.1 17.2 -0.53 13.0 11.0 180 50 2.1 6.0 -0.53 1.6 1.5 it can be concluded that when calculating the formation of wind waves on a stream in flowing reservoirs, large and small rivers, and large channels, the proposed calculation method can be used. the proposed methods have scientific justification and allow you to get the results needed to estimate the turbidity fields during dredging, determine the safe depth of the pipeline, predict possible erosion along the route, and calculate the wave deformation of the bottom and coastal slopes of the watercourse. the presented calculation methods and models can be applied to various areas of large watercourses or the coastal zone of the sea for the scientific justification of works on the construction of crossings by pipelines. references [1] atazhanov a, kantargi ig, sapova no. (1989) development of a method for predicting wind waves on streams. proceedings of the vnii vodgeo, m., vodgeo, 40-45. [2] zairov hi, listrova pp, masumov rr. (1986) prediction of wind wave elements in large channels. hydraulic engineering, 12:44-46. [3] kantargi ig (1987) a method for predicting wind waves on streams. tr. vnii vodgeo, m, vodgeo, 60-68. [4] kantargi ig, dreisis yui., chebotkevich vo. (1987) the forecast of wind waves in large canals and flowing reservoirs. hydraulic engineering and land reclamation, 2: 24-27. [5] krylov yum., strekalov ss, tsyplukhin vf. (1976) wind waves and their impact on structures. leningrad, gidrometeoizdat. [6] mass ei, kantargi ig. (1988) method for calculating wind waves in large channels. water resources, 1:60-67. 131 iium engineering journal, vol. 21, no. 2, 2020 eshev et al. https://doi.org/10.31436/iiumej.v21i2.1329 [7] mass ei, kantargi ig. (1986) recommendations for the calculation of wind waves and sediment transport in large channels. central scientific research institute of scientific research, 1986, pp 1-63. [8] rzhanitsyn na, altunin vs, voynich-syanozhentsky tg, mass ei, debolsky vk, kantargi ig and others. recommendations for the hydraulic calculation of large channels. gknt ussr, soyuzgiprovodkhoz, (1986), pp 1-153. [9] bretherton fp, garret cjr. (1969) wave trains in inhomogeneous moving media. proc. roy. soc. a, 302: pp 1-529. [10] kato h, tsuruya h, doi t, mijarari y. (1976) experimental study of wind waves generated on water currents. 2nd report, rep. port harbor res. inst., 15(4):3-46. [11] kato h, tsuruya h, terakawa h. (1981) experimental study of wind waves generated on water currents. 3rd report. wave forecasting methods and its experimental confirmation. rep. port harbor res. inst., 20(3):94-129. [12] kato h, tsuruya h. (1978) experimental study of wind waves generated on currents. proc. 16th coastal eng. conf. asce, 1:742-755. [13] mitsuyasu h, rikiishi. (1975) on the growth of duration-limited wave spectra. rep. res. inst. appl. mech., kuishi univer., v. 23, 31-60. [14] us army (1984) shore protection manual v. 2, 4th ed., coast. eng. res. center, washington, d.c. [15] wood amm. (1969) coastal hydraulics. pitman press, both. [16] willis dh. (1978) sediment load under waves and current. proc. 16th int. conf. on coastal eng. august 27-september 3, 1978; hamburg, germany. 132 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <feff004b00610073007500740061006700650020006e0065006900640020007300e400740074006500690064002c0020006500740020006c0075007500610020005000440046002d0064006f006b0075006d0065006e00740065002c0020006d0069007300200073006f00620069007600610064002000e4007200690064006f006b0075006d0065006e00740069006400650020007500730061006c006400750073007600e400e4007200730065006b0073002000760061006100740061006d006900730065006b00730020006a00610020007000720069006e00740069006d006900730065006b0073002e00200020004c006f006f0064007500640020005000440046002d0064006f006b0075006d0065006e0074006500200073006100610062002000610076006100640061002000760061006900640020004100630072006f0062006100740020006a0061002000410064006f00620065002000520065006100640065007200200036002e00300020006a00610020007500750065006d006100740065002000760065007200730069006f006f006e00690064006500670061002e> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <feff004b00e40079007400e40020006e00e40069007400e4002000610073006500740075006b007300690061002c0020006b0075006e0020006c0075006f0074002000410064006f0062006500200050004400460020002d0064006f006b0075006d0065006e007400740065006a0061002c0020006a006f0074006b006100200073006f0070006900760061007400200079007200690074007900730061007300690061006b00690072006a006f006a0065006e0020006c0075006f00740065007400740061007600610061006e0020006e00e400790074007400e4006d0069007300650065006e0020006a0061002000740075006c006f007300740061006d0069007300650065006e002e0020004c0075006f0064007500740020005000440046002d0064006f006b0075006d0065006e00740069007400200076006f0069006400610061006e0020006100760061007400610020004100630072006f0062006100740069006c006c00610020006a0061002000410064006f00620065002000520065006100640065007200200036002e0030003a006c006c00610020006a006100200075007500640065006d006d0069006c006c0061002e> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 ali et al. https://doi.org/10.31436/iiumej.v21i1.1206 diabetes classification based on knn ameer ali1*, mohammed alrubei2, laith falah mohammed hassan1, mohannad al-ja'afari1 and saif abdulwahed2 1najaf technical institute, al-furat al-awsat technical university, 31001 al-najaf, iraq. 2al-furat al-awsat technical university, 31001 al-najaf, iraq, 3al-furat al-awsat technical university, 31001 al-najaf, iraq. *corresponding author: inj.ame7@atu.edu.iq (received: 26th july 2019; accepted: 7th december 2019; published on-line: 20th january 2020) abstract: diabetes is a life-threatening syndrome occurring around the world; it can have huge complications and is documented by large amounts of medical data. therefore, attempts at early detection of this disease took a large area of research and many methods were used to deal with diabetes. in this paper, different types of knn algorithm have been used to classify diabetes disease using matlab. the dataset was generated by the criteria of the american diabetes association. for the training stage, 4900 samples have been used by the classifier learner tool to observe the results. then, 100 of the data samples were used for the test. the results show that the knn types (fine, weighted, medium and cubic) give high accuracy over the coarse and the cosine methods. fine knn is considered the most suitable according to its accuracy of classified samples. abstrak: penyakit kencing manis adalah sindrom penyakit ancaman nyawa yang berlaku di seluruh dunia dan ia mempunyai data perubatan yang besar serta komplikasi tinggi. oleh itu, cubaan dalam mengesan awal penyakit ini mempunyai potensi luas dalam kajian dan banyak kaedah telah digunakan bagi mengkaji penyakit kencing manis. dalam kajian ini, pelbagai jenis algoritma knn telah digunakan bagi mengelas penyakit kencing manis menggunakan matlab. setdata dihasilkan berdasarkan kriteria kesatuan kencing manis amerika. pada peringkat latihan, sebanyak 4900 sampel telah digunakan oleh pelatih alat pengelasan bagi memantau dapatan kajian. kemudian, 100 daripada sampel data telah digunakan bagi ujian. keputusan menunjukkan jenis knn (halus, berat, sederhana dan kubik) lebih tepat berbanding kaedah kasar dan kosinus. knn halus di dapati lebih sesuai berdasarkan ketepatan sampel pengelasan. keywords: diabetes; knn; classification machine learning 1. introduction diabetes disease is chronic and widespread in the world. it occurs by disorder in insulin secretion that causes an irregular increase in glucose level. spread of this disease has been observed in due to unhealthy diets [1]. generally, a higher probability of diabetes infection correlates to various factors such as female gender, age over 35, and persons with unhealthy weight [2]. many methods have been produced for diagnosis of different types of diseases, which used intelligent algorithms to classify, cluster, and diagnose these diseases. support vector machine (svm) used as a classifier to diagnose diabetes based on a medical dataset [3,4,5]. bayes theorem used to classify prediction accuracy in diabetes data with a data set delivered from diabetes 130-us hospitals [6]. decision tree and naïve bayes algorithms presented to analyse and classify the patterns in order to 175 iium engineering journal, vol. 21, no. 1, 2020 ali et al. https://doi.org/10.31436/iiumej.v21i1.1206 diagnose the diabetes disease [7]. coupling methods: likelihood ratio test, joint clustering, and classification based data presented from boston medical center, in order to diagnose diabetes [8]. fasting plasma glucose used to predict and diagnose type 2 diabetes based on two machine-learning algorithms: logistic regression and naive bayes classifier [9]. fuzzy logic also presented system to diagnose diabetes based on five layers [10]. convolution neural network used to diagnose many diseases belonging to the diabetes family using [11]. in this paper, six types of knn algorithms have been used to investigate its ability to classify glucose levels. the organization of this paper is arranged as follows: the description of knn algorithms and their distance equations are presented in section two. section three presents the dataset criteria for diabetes. the discussion of results for knn algorithms has been explained in section four to identify which type of knn is more suitable. finally, the conclusion of this experiment has been introduced in section five. 2. k-nearest neighbours (knn) the classification is a type of supervised machine learning. the knn is one of the classification techniques that is commonly used to classify data input into pre-defined classes (k) [12]. it was proposed by cover and hart in 1968. the straightforward mechanism of the knn algorithm is to compute the euclidean distance function between pre-defined classes and each varying sample. after that, the knn algorithm chooses the minimum nearest neighbours according to each category. the samples are assigned to their category based on the nearest k neighbours. there are many versions of distance function between the samples. in this paper, the most commonly used is the euclidean distance, expressed in eq. (1) [13]. (1) where is the number of values in each sample vector, and , are input samples. six types of knn have been chosen to classify the dataset. their details are described as follows [14]: fine knn takes one neighbour to distinguish the sample data, while the medium knn takes more neighbours than fine knn for distinction. this type will cause a low distinction feature to the algorithm. the coarse knn takes more neighbours than medium knn, which leads to the lowest distinction feature amongst the three types. the cosine knn uses a cosine distance metric as in eq(2). the cubic knn uses a cubic distance metric as in eq(3). the weight knn uses a distance weight as in eq(4). the last three types have the same number of neighbours as medium knn [15]. (2) (3) (4) when the numbers of neighbours are decreased, the accuracy of the classifier increases. this will increase the complexity of the classifier model, but does not guarantee that the out-of-samples will be classified correctly [16]. 176 iium engineering journal, vol. 21, no. 1, 2020 ali et al. https://doi.org/10.31436/iiumej.v21i1.1206 3. diabetes criteria the dataset presents amounts for each of the variables based on the criteria, such as glucose before food and glucose after food of an object. each value or amount is called as a datum. the criteria used in this research are summarized in table 1. the objective of these criteria is to generate a dataset to diagnose diabetes in humans. based on a personal dataset, such as (hb a1c test, fasting test, and random test), it tries to decide if a human subject has diabetes, based on whether its values are normal or not. diabetes criteria are already in public domain, thanks to the american diabetes association standards [17]. table 1: diabetes criteria [17] hb a1c a fasting (fpg) b random (pg) c response y 5-5.9 a0 90-119 b0 140-199 c0 normal (0) 6-6.5 a1 120-140 b1 200-250 c1 neuropath (0.25) 6.6-7 a2 141-180 b2 251-300 c2 retinopathy (0.5) 7.1-7.5 a3 181-250 b3 301-350 c3 nephropathy (0.75) 7.6-8 a4 251-600 b4 351-500 c4 heart disease (1) the diagnosis of diabetes is based on glucose and plasma; either the 2-h plasma glucose (2-h pg) value after a 75-g oral glucose tolerance test or the fasting plasma glucose (fpg). a1c (threshold ≥6.5%) is added as a third option in the diagnosis. the a1c test uses a diabetes control that is certified by the national glycohemoglobin standardization program. the relationship between the a1c and the risk of retinopathy, as with fpg and 2-h pg, were shown in epidemiological data. the compatibility between the 2-h pg tests with fpg and between a1c with glucose-based tests are <100%. the a1c and oral glucose tolerance have several benefits to the fpg, including greater convenience and less daily disturbances during stress and sickness [17,18]. 4. results in this experiment, we will train the classifier using the sample data generated from table 1. each training sample has four values. the first three values are input samples that indicate hb a1c, fasting (fpg), and random (pg). the fourth one is the response. then the classifier was tested using out-of-sample data to calculate the accuracy of the distinction. table (2) summarizes the parameters of the experiment. table 3 shows the accuracy prediction speed and training time for all knn types using 4900 input samples. for the accuracy, fine knn, weighted knn, medium knn, cubic knn, cosine knn, and coarse knn have been arranged according to their performance. in addition, according to the mathematical computation distance, the maximum training time was taken by the cosine knn while the medium knn takes the least training time. thus, the prediction speed (observation/second) is maximum for fine knn and minimum for cosine knn. 177 iium engineering journal, vol. 21, no. 1, 2020 ali et al. https://doi.org/10.31436/iiumej.v21i1.1206 table 2: simulation parameters no. coefficient description 1 fine knn k=1 2 medium knn k=10 3 coarse knn k=100 4 cosine knn k=10 5 cubic knn k=10 6 weighted knn k=10 7 number of training samples 4900 8 number of testing samples 100 9 training tool classification learner using matlab table 3: experiment outcome information preset accuracy training time prediction speed fine knn 99.9% 0.54411 sec 200000 obs/sec medium knn 98.4% 0.26525 sec 100000 obs/sec coarse knn 74.3% 0.46863 sec 43000 obs/sec cosine knn 85.6% 0.69376 sec 25000 obs/sec cubic knn 98.2% 0.47105 sec 52000 obs/sec weighted knn 99.8% 0.27984 sec 110000 obs/sec the pre-trained classifier tested 100 random out-of-sample data to check the distinction capability, which it is enough to cover the reliability of the classifier over all classes. as expected, the numbers of classification errors are 0, 0, 19, 16, 2, and 0 for fine knn, medium knn, coarse knn, cosine knn, cubic knn, and weighted knn, respectively. figure 1 shows the confusion matrix for each of the knn types. in each model in fig. 1, the diagonal of green squares represents the correct prediction ratio of the predict classes over true classes while the red squares give the incorrect class ratio. the ratio of each square is associated with the disparity of the colours. the white squares are empty for samples from the training stage. the results show the magnitude of decision ratio between the true value and the prediction value. fine, medium, cubic, and weighted give the best decision while coarse and cosine give high failure ratios. figure 1 shows that the fine knn classifier is the most preferable because it gives 100% accuracy for normal, neuropath, and retinopathy classes and <1% for nephropathy and heart disease. 178 iium engineering journal, vol. 21, no. 1, 2020 ali et al. https://doi.org/10.31436/iiumej.v21i1.1206 fig. 1: the confusion matrix for different types of knn. 5. conclusion the dataset of diabetes has been classified using different types of knn algorithms. the simulation results show that fine, medium, cubic, and weighted knn types have a superior performance over coarse and cosine. the classifier model of all knn types required less than 0.7 sec to predict the target. in addition, it can be said that the fine knn cubic knn cosine knn coarse knn medium knn fine knn weighted knn 179 iium engineering journal, vol. 21, no. 1, 2020 ali et al. https://doi.org/10.31436/iiumej.v21i1.1206 algorithm is suitable to solve the diabetes classification problem with higher accuracy than other types. references [1] t.karthikeyan, k.vembandadsamy. (2015). an analytical study on early diagnosis and classification of diabetes mellitus. international journal of computer application,7:2250-1797. [2] catherine c. cowie, keith f. rust,danita d. byrd-holt, edward w. gregg, earl s. ford, linda s. geiss, kathleen e. bainbridge, judith e. fradkin. (2010). prevalence of diabetes and high risk for diabetes using a1c criteria in the us population in 1988–2006. diabetes care, 33: 562-568. [3] v. anuja kumari, r.chitra. (2013). classification of diabetes disease using support vector machine. international journal of engineering research and applications,3:1797-1801. [4] longfei han, beijing, senlin luo, jianmin yu, limin pan, songjing chen. (2013) rule extraction from support vector machines using ensemble learning approach: an application for diagnosis of diabetes. ieee,19:2168-2194. [5] nahla h. barakat, andrew p. bradley, mohamed nabil h. barakat (2010). intelligible support vector machines for diagnosis of diabetes mellitus. ieee,40:2168-2194. [6] subhankar manna, malathi g. (2017). performance analysis of classification algorithm on diabetes healthcare dataset. international journal of research granthaalayah,5:260-266. [7] aiswarya iyer, s. jeyalatha, ronak sumbaly (2015). diagnosis of diabetes using classification mining techniques. international journal of data mining & knowledge management process (ijdkp),5:1-14. [8] theodora s. brisimi, tingting xu, taiyao wang, wuyang dai, william g. adams , ioannis ch. pasc halidis(2018). predicting chronic disease hospitalizations from electronic health records: an interpretable classification approach. ieee,106:1-18. [9] bum ju lee, boncho ku, jiho nam, duong duc pham, jong yeol kim (2014). prediction of fasting plasma glucose status using anthropometric measures for diagnosing type 2 diabetes. ieee,18:555-561. [10] chang-shing lee, senior member, mei-hui wang (2011) a fuzzy expert system for diabetes decision support application. ieee,41:139-153. [11] yuliang liu, quan zhang, geng zhao, zhigang qu, guohua liu, zhiang liu, yang an (2018). detecting diseases by human-physiologicalparameter-based deep learning. ieee,7: 2169-3536 [12] shichao zhang, xuelong li,ming zong, xiaofeng zhu, ruili wang (2017). efficient knn classification with different numbers of nearest neighbors. ieee,29:1-12. [13] mehdi zekriyapanah gashti (2018). a modified model based on flower pollination algorithm and k-nearest neighbor for diagnosing diseases. iium engineering journal, 19:144157. [14] jenifer mariam johnson and anamika yadav(2016). fault detection and classification technique for hvdc transmission lines using knn, second international conference on ict for sustainable development, goa, 1-2 july 2016. [15] jaime vitola , francesc pozo, diego a. tibaduiza, maribel anaya (2017). a sensor data fusion system based on k-nearest neighbor pattern classification for structural health monitoring applications. sensors, 17. [16] asad hussain, sajjad ahmed ghauri, m. farhan sohail,sheraz a. khan, ijaz mansoor qureshi. (2016). knn based classification of digital modulated signals. iium engineering journal, 17: 71-82. 180 iium engineering journal, vol. 21, no. 1, 2020 ali et al. https://doi.org/10.31436/iiumej.v21i1.1206 [17] american diabetes association (2014). standards of medical care in diabetes 2014 ,diabetes care 37: s14-s80. 181 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <feff004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 159-993-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zain et al. 11 bioethanol production by calcium alginate-immobilised st1 yeast system: effects of size of beads, ratio and concentration m. m. zain, n. t. kofli and s. r. s. yahya department of chemical and process engineering faculty of engineering and built environment, universiti kebangsaan malaysia, 43600 bangi, selangor, malaysia. masni.roszaime@gmail.com abstract: immobilized yeast-cell technology posses several advantages in bioethanol production due to its potential to increase the ethanol yield by eliminating unit process used. thus, process expenses in cell recovery and reutilization can be minimised. the aim of this study is to investigate the influence of three parameters (substrate concentrations, size of alginate beads and ratio of volume of beads to volume of medium) on local isolated yeast (st1) which immobilized using calcium alginate fermentation system. the most affected ethanol production by calcium alginateimmobilised st1 yeast system were ratio of volume of the beads to the volume of substrate and concentration of lbs. highest theoretical yield, 78% was obtained in st1alginate beads with the size of beads 0.5 cm, ratio volume of beads to the volume of lbs media 0.4 and 150 g/l concentration of lbs. abstrak: teknologi sel yis pegun memiliki beberapa kelebihan dalam penghasilan bioetanol kerana ia berpotensi meningkatkan pengeluaran etanol dengan menyingkirkan unit proses yang digunakan. maka, proses pembiayaan dalam perolehan sel dan penggunaan semula boleh dikurangkan. tujuan kajian ini adalah untuk mengkaji pengaruh tiga parameter (kepekatan substrat, saiz manik alginat dan nisbah isipadu manik terhadap isipadu bahantara) ke atas sel tempatan terasing (local isolated yeast (st1)) yang dipegun menggunakan sistem penapaian kalsium alginat. penghasilan etanol yang paling berkesan dengan menggunakan sistem yis st1 kalsium alginat-pegun adalah dengan kadar nisbah isipadu manik terhadap isipadu substrat dan kepekatan lbs. kadar hasil teori tertinggi iaitu 78% didapati menerusi manik alginat-st1 dengan saiz manik 0.5 cm, nisbah isipadu 0.4 terhadap perantara lbs dan kepekatan lbs sebanyak 150 g/l. keywords: immobilization; bioethanol; calcium alginate 1. introduction the production of bioethanol as an alternative fuel by fermentation of sugar has been increasing due the growing demands, which is expected to produce high and good yield of ethanol [1-4]. isolating and inoculating selected potential yeasts and alternative economic evaluation for ethanol production has become popular topic amongst researchers. immobilization applied the cells entrapped inside the inert support meanwhile separation of bioethanol from the medium should be easier and cost saving since it is omitting a unit procedure than those of free cells while retaining their desired catalytic activities for repeated and continuous use [5-7] which created possibility for the cells to be reused. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zain et al. 12 calcium alginate matrix entrapment has been approached widely in the immobilization of bacteria, yeast fungi, algae in many different bioprocesses, such as wastewater treatment, vinegar production, and ethanol production due to the simplicity of this method, it is nontoxic, less expensive, reversible, and has good mechanical properties [6, 8, 9]. sodium alginic is a linear polysaccharide extracted from many strains of brown algae and seaweed and solidification of sodium alginate occur in calcium chloride solution by displacement of sodium ion [10, 11]. most east-asian countries have their own traditional fermented food and an alcoholic beverage which is produced at household or cottage industry scales [12, 13]. for malaysia, which consist of multiple races, produced various fermented foods and amongst the popular are tapai and tuak. tapai is a food made from tapioca (cassava), glutinous rice, rice or banana can be eaten raw after few days of fermentation with ragi. similar to indonesian tape ketan (black rice fermentation), malaysia tapai is partially liquefied, sweet sour and mildly alcoholic rice paste served as dessert or snack. whereas tuak is rice wine for native peoples (especially in sarawak) usually serve during special and important occasions. tuak is prepared similarly like tapai but in longer fermentation period, resulting in greater liquefaction of the rice and consumed as an alcoholic beverage. since both tapai and tuak production a must of fermented rice, this process is referred as tape fermentation [13-15] but in local language is called tapai fermentation. there are many reported studies that using manipulating unsterilized juice as a substrate on bioethanol production [16, 17]. local brown sugar (lbs), also known as ‘gula merah’ in malay is the names of jaggery, a traditional unrefined sugar consumed in asia, africa, latin america and caribbean [16, 18] it is a natural sweetening substance made by concentrating sugarcane juice without any preservatives and colourings. the ultimate objective of this study is to investigate the influence of three parameters (substrate concentrations, size of alginate beads and ratio of volume of beads to volume of medium) on local isolated yeast (st1) which immobilized using calcium alginate fermentation system. st1 strain is isolated from starter ragi from sarawak which is used in preparation of traditional fermented food, tapai and tuak. local brown sugar (lbs) is a natural sweetening substance made by concentrating sugarcane juice without any preservatives and colourings. it is normally used in preparing cakes, syrups and desserts and sold cheaply at the local market. the usage of local yeast in production of ethanol has to be explored to enrich the culture collection as well as a novel way in ethanol production. 2. materials and methods 2.1 microorganism the starter ragi is bought at the local market in kuching, sarawak (malaysia). the starter ragi is dry flattened circular cakes, about 3-5 cm in diameter, prepared from rice flour and packed in small plastic bag. it was subcultured, screened and isolated on sabouraud agar [19] to produce a single colony. the strain selected was named as st1 and was kept on ypd medium/agar at 4˚c. 2.2 substrate cheap local brown sugar (lbs) was used as medium. it was bought at the local supermarket in a packed plastic. preparation of medium followed the method by bravo and gonzales [18]. the composition of the medium is lbs (100-200 g/l) which was diluted and filtered with addition of 5.19 g/l (nh4)2so4, 1.53 g/l kh2po4 and 0.55 g/l iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zain et al. 13 mgso4. ypd medium is commercialised medium for yeast consist of : yeast extract 10 g/l, peptone 20 g/l and dextrose 20 g/l. 2.3 cell immoblisation st1 cells were grown at 30˚c for 10 hours. 150 ml culture broths were harvested by centrifuge at 13 000rpm for 5 minutes. 50 ml of this growth medium was mixed with an equal volume (1:1,v/v) of 4% (w/v) na-alginate (sigma, a-2033) solution. a 100 ml aliquot of alginate-cell suspension containing 2% na-alginate (unless otherwise stated) was added dropwise to 1000 ml of 2% cacl2 with a syringe [20]. alginate drops solidified upon contact with cacl2, forming beads and thus entrapping yeast cells. the beads were allowed to harden for 30 min and then were washed with sterile saline solution (0.85% nacl) to remove excess calcium ions and cells. 2.4 fermentation st1-alginate beads fermentation was carried out in 250 ml flask supplemented with 150 ml local brown sugar as a media. three variables parameters were chosen to investigate their affect on bioethanol production performance; size of the alginate-st1 beads, ratio of the beads to the substrate and concentration of lbs. two selected size of the beads, 0.3 cm and 0.5 cm in diameter were form using different nozzles and kept in 0.2% yeast extract until use. the volume of the beads was measured by cylinder measurement in order to investigate the ratio of volume of beads to volume of substrate. the immobilized yeast was incubated in 30˚c with agitation at 75 rpm to avoid breakage. 2.5 analytical method ethanol and glucose concentrations were determined using biochemical analyzer, ysi select (yellow spring ltd.). 3. results and discussion 3.1 immobilisation the most common forms are round small beads about 0.3 to 5 mm in diameter, and the small diameter beads are generally preferred because of the favourable mass transfer characteristics for the entrapped cells [6] and stability due avoid damage occurs. the effect of bud-like shape of alginate bead on the surface area was not investigated and all beads were assumed to be spheres. at this diameter and alginate concentration used (2 wt %), the beads were fully active, flexible and hard enough to stand mild agitation and have a good stability [10]. figure 1 showed the observation by scanning electron microscope for st1-alginate beads. 3.2 effects of size of beads the effect of alginate-st1 beads size in lbs fermentation was studied. the beads with diameter 0.3 cm and 0.5 cm were prepared by using different nozzles and the fermentation was carried out in 50 g/l and 150 g/l concentration of lbs and the result is shown in fig. 2 and 3. the ethanol production curve is identical to both 0.3 and 0.5 mm beads size and the highest ethanol production (8.2 g/l) was obtained with cell entrapped in 0.5 cm ca-alginate beads. in fact, immobilization fermentation considered mass transfer phenomena as smaller beads has more surface area available for mass transfer of substrate through the beads [6, 11]. however, since the beads are rigid, the agitation rate has to be low to prevent the beads breakage but small beads also tend to attach among themselves. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zain et al. 14 (a) (b) fig. 1: scanning electron microscopy of immobilized yeast cell (a) & (b). fig. 2: fermentations profile for two different size using 150 g/l lbs. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zain et al. 15 fig. 3: fermentations profile for two different size using 50 g/l lbs. 3.3 effects of ratio (beads : substrate) the amount of beads to the substrate was investigated using ratio of the volume of beads to the volume of the substrate to evaluate the effect of the surface-volume ratio beads to substrate for bioethanol production. the experiment was conducted in two chosen ratio; 0.2 and 0.6 where ratio 0.2 represented 30 ml of beads in 150 ml lbs media and 0.6 represented 90 ml of beads in 150 ml lbs media. the graph in fig. 4 and 5 showed the ethanol production was highest at ratio 0.6. this maybe due to the fact that the amount of beads used was higher than at ratio 0.2. more beads in a solution making large area for mass transfer resulted in better ethanol production. fig. 4: fermentations profile for two different ratio size in 150 g/l lbs. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zain et al. 16 fig. 5: fermentations profile for two different size in 50 g/l lbs. 3.4 effects of concentration lbs the effect of concentration lbs on ethanol fermentation by immobilized st1 strain was studied. two concentrations of lbs, 50 g/l and 150 g/l were chosen, and the experiment was conducted in different size of beads (0.3 cm and 0.5 cm) and the results illustrated in fig. 6 and 7. the glucose was consumed almost 99% for both concentrations at 6 th hour fermentation. the maximum ethanol production were achieved using 150 g/l lbs for both sizes of beads (0.2 and 0.6 mm) at 8 g/l and 8.2 g/l respectively. interestingly, glucose content in 50 g/l lbs and g/l lbs when initially measured was in the range of 2.6-3 g/l and 7.8-10.7 g/l respectively. the theoretical yield [20] from the experiments were then calculated and showed in fig 8. as expected, the higher the glucose concentrations, higher concentration of bioethanol being produced resulted in highest theoretical yield obtained (67%). fig. 6: fermentations profile for concentration of 50 g/l and 150 g/l lbs using 0.3 cm beads. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zain et al. 17 fig. 7: fermentations profile for concentration of 50 g/l and 150 g/l lbs using 0.5 cm beads. fig. 8: theoretical yield (%) and maximum ethanol profile for overall parameters. table 1a and 1b showed the summary of overall fermentation profiles. the highest theoretical yield, 78% was obtained in st1-alginate beads with the size of beads 0.5 cm, ratio volume of beads to the volume of lbs media 0.4 and 150 g/l concentration of lbs. the three variables parameter indicated that affected to the bioethanol production, but the alternative effect between these three parameters should not be neglected [21]. table 1a: summary of fermentation profile for all parameters. size of beads 0.3 cm ratio (beads: substrate) 0.2 0.4 0.6 concentration of lbs (g/l) 50 150 50 150 50 150 ethanol (g/l) 2.63 8.18 2.35 6.58 5.94 8.02 theoretical yield (%) 65 67 65 68 23 46 iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zain et al. 18 table 1b: summary of fermentation profile for all parameters. size of beads 0.5 cm ratio (beads: substrate) 0.2 0.4 0.6 concentration of lbs (g/l) 50 150 50 150 50 150 ethanol (g/l) 2.94 8.63 2.61 7.53 4.9 7.44 theoretical yield (%) 57 64 51 78 34 54 4. conclusions it was concluded that higher ethanol production rates could be achieved by increasing concentration of lbs media and amount of beads in fermentation. however, the effect between three variables need to investigated further. the highest theoretical yield, 78% was obtained in st1-alginate beads with the size of beads 0.5 cm, ratio volume of beads to the volume of lbs media 0.4 and 150 g/l concentration of lbs. acknowledgement the research is funded by university research grant (code: ukm-gup-btt-07-25-165) which is duly acknowledged by authors. references [1] s. hiyasori, k. jun, f. yasuya, m. takeshi, b. yohei, u. mitsuyosi, s. eiichi, f. hideki, and k. akihiko, “direct production of ethanol from raw corn starch via fermentation by use of a novel surface-engineered yeast strain codisplaying glucoamylase and α-amylase,” applied and environmental microbiology, pp. 5037-5040, august 2004. [2] b.v.v ratnam, m. n. rao, m. d. rao, s.s. rao, s.s. and c.ayyana, “optimization of fermentation conditions for the production of ethanol from sago starch using response surface methodology,” world journal of microbiology & biotechnology, vol. 19, pp. 523526, 2003. [3] h. fukuda, a. kondo, and s. tamalampudi, “ bioenergy: sustainable fuels from biomass by yeast and fungal whole-cell biocatalysts,” biochemical engineering journal, vol 44, pp. 212, 2009. [4] s. nikoloc, l. mojovic, d. pejin, m. rakin, and v. vucuvic, “ improvement of ethanol fermentation of corn semolina hydrolyzates with immobilized yeast by medium supplementation” food technol. biotechnol., vol 47, pp 83-89, 2009. [5] m. rakin, l. mojovic, s. nikolic, m. vukasinovic, and v. nedovic, “bioethanol production by immobilized sacharomyces cerevisiae var. ellipsoideus cells,” african journal of biotechnology vol.8(3):464-471, 2009. [6] margaritis, and p. m. kilonzo, “production of ethanol using immobilized cell bioreactor systems,” application of cell immolisation bioetechnology, vol. 8b, pp.375-401, 2005. [7] m.a.a da cunha, a. converti, j.c. santos, and silva, s.s. “yeast immobilization in lentikats : a new strategy for xylitol bioproduction from sugarcane bagasse,” world j. microbiol. biotechnol., vol.22(1), p : 65-72, 2006. [8] r.l.c. giordano, p.c. hirano, l.r.b goncalves, w.s. netto, “study of biocatalyst to produce ethanol from starch” applied biochemistry and biotechnology,pp 84-86, 2000. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology zain et al. 19 [9] r.a. peinado, j.j moreno, j.m. vilalba, j.a.g. reyes, j.m. ortega, and j.c. mauricio, “yeast biocapsules: a new immobilization method and their applications,” enzyme and microbial technology, vol. 40, pp.79-84, 2006. [10] g. najafpour, h. younesi, and k. s. k. ismail, “ethanol fermentation in an immobilized cell reactor using saccharomyces cerevisiae,” bioresource technol., vol. 92, pp. 251-269, 2004. [11] y. goksungur, and n. zorlu, “production of ethanol from beet molasses by ca-alginate immobilised yeast cells in a packed-bed reactor,” turk j. biol., vol.25, pp. 265-275, 2001. [12] n.t.p dung, f.m. rombouts and m.j.r. nout, “characteristic of some traditional vietnamese starch-based rice wine fermentation starters (men),” food science and technology, vol. 40(1), pp. 130-135, 2007. [13] i.n. sujaya, s. amachi, k. saito, a. yokota, k. asano, and f. tomita, “specific enumeration of lactic acid bacteria in ragi tape by colony hybridization with specific oligonucleotide probes,” world journal of microbiology & biotechnology, vol.18, pp. 263270, 2002. [14] k.h. streinkraus, indigenous fermented food in which ethanol is a major product. in handbook of indigenous fermented food, 2 nd ed.steinkraus, k.h.:365-508. new york: marcel dekker, 1996. [15] t. c. cronk, k. h. steinkraus, l. r. hackler, and l.r. mattick, “indonesian tape ketan fermentation,” applied and environmental microbiology, pp. 1067-1073, 1977. [16] c.s. rathnasabapathy, s.m. basha and r. dhanasekar. enhanced production of glutathione from candida utilis using palm jaggery. int. j. chemtech res.,1(4): 1137-1144. [17] j. yu, x. zhang, and t. tab, “optimization of media conditions for the production of ethanol from sweet sorghum juice by immobilized saccharomyces cerevisiae,” biomass and bioenergy, vol. 33, pp. 521-526, 2009. [18] a.k. rajvanshi, and n. nimbkar. sweet sorghum r and d at the nimbkar agricultural research institute (nari). proceedings of first european seminar on sorghum for energy and industry, toulouse, france, 1-3, april 1996. pp: 356-362. [19] a.p. koehler, k.c. chu, e.t.s houang, and a.f.b. cheng, “simple, reliable and costeffective yeast identification scheme for the clinical laboratory,” j. of clinical microbiol., vol.37 (2), pp. 422-426, 1999. [20] p. bravo, and g. gonzales, “continuous ethanol fermentation by immobilized yeast cells in a fluidised-bed reactor,”j. chem. technol. biotechnol., vol. 52, pp. 127-134, 1991. [21] g. dragone, d. p. silva, and j.b.a. silva, “factors influencing ethanol production rates at high-gravity brewing” swiss society of food science and technology, vol 37, pp 797-802, march 2004. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 daud et al. https://doi.org/10.31436/iiumej.v21i2.1227 cutting tool performance in turning of al 7075-t651 aluminium alloy nur sofwati daud @ ab aziz1, natasha a. raof1*, abdul rahman a.ghani2, aishah najiah dahnel1, suhaily mokhtar1, nor khairusshima muhamad khairussaleh1 1department of manufacturing and materials engineering, international islamic university malaysia, kuala lumpur, malaysia. 2production technology, german malaysian-institute, kuala lumpur, malaysia. *corresponding author: natashar@iium.edu.my (received: 28th august 2019; accepted: 22nd january 2020; published on-line: th july 2020) abstract: recently, almost 70% of a commercial jetliner’s airframe is made of aluminium alloys. it is predicted that the application of aluminium alloy is to increase up to 65% by the year 2025. they are typically used because of their high strength to weight ratio. however, there are some drawbacks during machining aluminium alloy such as the adhesion wear and built-up edge (bue) formation that can shorten tool life. as the tool wears, the machining performance, surface roughness, and cutting tool life are affected significantly. a lot of studies were conducted in order to minimize this critical issue. this project presents a study of the cutting tool performance of an uncoated carbide tool in dry turning operation on al 7075-t651, in which the tool wear rate, volume of material removed, wear mechanism, and surface roughness were investigated. the machining tests were conducted on a cnc lathe machine to obtain the tool wear and surface roughness of the machined work piece. the average flank wear was measured using a digital microscope, whereas the wear mechanism was observed using a scanning electron microscope (sem). the average surface roughness (ra) was measured using a surface roughness tester. the cutting time for this experiment was fixed at 40 minutes and all the results were analysed within this time range to evaluate the tool performance in the turning of al 7075-t651. the results revealed that the tool performs better at low cutting speed, 250 m/min, by reducing the tool wear rate by 33%. the cutting speed of 250 m/min also contributed to 71% higher volume of material removed during the machining tests. the dominant type of wear found was flank wear, while the main principal of wear mechanism is adhesion. at higher cutting speed, the surface roughness was improved. based on the results, it can be concluded that high cutting tool performance is achieved when low tool wear growth rate, high volume of material removal, and low surface roughness during turning operation are obtained. abstrak: kebelakangan ini, hampir 70% kerangka pesawat udara komersil diperbuat daripada aloi aluminium. penggunaan aloi aluminum ini dijangka meningkat sehingga 65% pada tahun 2025. ia biasa digunakan kerana nisbah kekuatan kepada berat yang tinggi. walau bagaimanapun, terdapat beberapa kekurangan semasa pemesinan aloi aluminum ini iaitu pemakaian pelekat dan pembentukan binaan tepi (bue) yang mengurangkan jangka hayat mata alat. apabila mata alat menjadi haus, prestasi mesin, kekasaran permukaan, dan jangka hayat mata alat pemotong terjejas dengan ketara. banyak kajian telah dijalankan bagi mengurangkan isu kritikal ini. projek ini mengkaji prestasi mata alat pemotong karbida tidak bersalut dalam operasi mesin larik kering pada al 7075-t651, di mana kadar haus mata alat, kuantiti bahan yang dibuang, mekanisme haus dan kekasaran permukaan telah diselidiki. ujian pemesinan dijalankan pada mesin 177 iium engineering journal, vol. 21, no. 2, 2020 daud et al. https://doi.org/10.31436/iiumej.v21i2.1227 cnc mesin larik bagi mendapatkan kadar haus mata alat dan kekasaran permukaan material yang dimesin. purata haus pengapit mata alat diukur dengan menggunakan mikroskop digital, manakala mekanisme haus dipantau menggunakan mikroskop elektronik pengimbas (sem). purata kekasaran permukaan (ra) diukur menggunakan alat penguji kekasaran permukaan. tempoh masa pemotongan bagi eksperimen ini telah ditetapkan pada 40 minit dan semua keputusan telah dianalisa dalam tempoh masa ini bagi menilai prestasi mata alat dalam melarik al 7075-t651. hasil menunjukkan prestasi mata alat lebih baik pada kelajuan pemotongan rendah, 250 m/min dengan mengurangkan kadar haus mata alat sehingga 33%. kelajuan pemotongan 250 m/min juga menyumbang kepada 71% peningkatan ke atas jumlah bahan yang dibuang semasa ujian pemesinan. jenis haus yang dominan telah ditemui pada pengapit mata alat, manakala mekanisme haus yang utama adalah lekatan. pada kelajuan pemotongan yang tinggi, kekasaran permukaan didapati lebih baik. berdasarkan keputusan, dapat disimpulkan bahawa prestasi mata alat pemotong yang bagus dapat dicapai apabila kadar haus mata alat adalah rendah, jumlah penyingkiran bahan yang tinggi dan kekasaran permukaan yang rendah semasa operasi pelarikan dijalankan. keywords: tool wear; cutting tool performance; surface roughness; wear mechanism; al 7075 1. introduction aluminium alloy is one of the common metal alloys used to manufacture products in industries such as automotive, aircraft, sporting equipment, food packaging, and building construction. various applications of aluminium products include bicycle frame, rudder of aircraft, truck frames, kitchen utensils, and food wrapper [1]. it is favoured in industry owing to the excellent combination of high strength-to-weight ratio and excellent mechanical properties such as hardness and good machinability found in various series of aluminium alloy [2]. aluminium alloy consists of different elements with different chemical compositions where the aluminium is the dominant component with different main alloying elements. different alloy elements in the composition of aluminium alloys determine its characteristics and properties. among the aluminium alloy groups, al 7075 containing 5.6% zinc in weight of aluminium was marked as the highest strength of aluminium alloy with 570mpa tensile strength, comparable to other steels [3]. the research claimed that, aluminium alloy has its drawbacks in machining operation despite its high machinability. the formation of a built-up edge (bue) tends to affect the machined surface and alter the cutting tool geometry. bue also tends to increase the tool wear significantly [3]. thus, numerous studies were conducted in order to minimize the problem encountered during machining aluminium alloy and solve the critical issues. recently, many studies were done on aluminium alloy to investigate its machinability. researchers are looking into various machining parameters on some criteria such as tool life, chip formation, and surface roughness to provide a vast overview on the machinability of aluminium alloys [4]. nevertheless, research on the cutting tool analysis and performance is a bit lacking compared to the study on the surface integrity and optimization of cutting conditions especially for turning operations. most of the research concentrated on the milling operation. therefore, further studies on this problem are necessary, particularly in turning operations. this study aims to evaluate the cutting tool performance in terms of tool wear rate, wear mechanism, volume of material removed, and the quality of machined surface in dry turning al 7075-t651 aluminium alloy using kw10 kyocera uncoated carbide tool. 178 iium engineering journal, vol. 21, no. 2, 2020 daud et al. https://doi.org/10.31436/iiumej.v21i2.1227 2. methodology 2.1 workpiece and cutting tool material the workpiece material used in the machining tests was 100 mm x 200 mm al 7075t651 cylindrical bar. t651 is the tempered designation in which the material is solution heat treated, stress relieved, and artificially aged. the chemical composition and mechanical properties of the work material are given in table 1 and table 2, respectively. table 1: chemical composition of al 7075 (%wt) si fe cu mn mg cr zn ti others 0.04 0.10 1.3 0.07 2.3 – 2.4 0.10 6.7 – 6.8 0.05 balance table 2: mechanical properties of al 7075 properties values tensile strength (ksi) 78 85 yield strength (ksi) 68 – 78 elongation (%) 7 – 12 the cutting tool used was a kw10 kyocera uncoated carbide tool with the iso designation tngg 160408ah. this cutting tool is suitable for use in cutting non-ferrous material such as al 7075 for medium to finishing operations. the tool holder was selected according to the cutting tool with the iso designation mtjnr 2525m-16. 2.2 machining experiments the turning operation was conducted in dry conditions using a romi m420 cnc lathe machine. the parameters and values used in the experiment are shown in table 3. table 3: parameters used in the experiment parameters value cutting speed (m/min) 250, 450 feed rate (mm/rev) 0.05 depth of cut 1.0 the average tool flank wear, was measured using a dino-lite edge digital microscope at 227x magnification at each 1 minute of the cutting time. the turning operation was then stopped when the cutting time reached 40 minutes. the recorded data was used to determine the tool flank wear progression with cutting time and tool wear rate for both cutting speeds. the wear also was used to calculate the volume of material removed within 40 minutes of machining time. when 40 minutes of cutting time was achieved, the average surface roughness of workpiece (ra) was measured using a mitutoyo surftest surface roughness tester. the surface roughness of both cutting speeds were recorded and analysed. then, the cutting tool was examined under scanning electron microscope (sem) jeol jsm-5600 in order to determine the type of wear and wear mechanism that occurred during the machining operation. 179 iium engineering journal, vol. 21, no. 2, 2020 daud et al. https://doi.org/10.31436/iiumej.v21i2.1227 3. results and discussion 3.1 effect of cutting speed on tool wear rate and volume of material removed figure 1 shows the progression of flank wear versus cutting time for turning al 7075t651 using kw10 uncoated carbide tool at cutting speed of 250 m/min and 450 m/min, while other parameters are kept constant, as tabulated in table 3. the average flank wear of uncoated carbide tool increased with the increase in cutting time within 40 minutes of cutting time. fig. 1: comparison of tool average flank wear progression versus cutting time at cutting speeds 250 m/min and 450 m/min in dry condition (f = 0.05mm/rev, d = 1.0 mm). although similar trends of flank wear were observed, it is noted that at 40 minutes of machining time, the uncoated carbide tool used at 450 m/min had 50% higher average flank wear which is 0.090 mm compared to 0.060 mm of when cutting at 250 m/min. due to that, it can be concluded that the uncoated carbide tool wears rapidly at high cutting speed especially on the flank face. this might be caused by the high intensity of cutting temperature at high cutting speed because of the rubbing of the tool and the machined surface and the sliding of the chip along the tool’s rake face. this is supported with the findings by other researchers that were reviewed by [5], who stated that the increment of cutting speed results in higher rate of material deformation at the cutting zone, which consequently elevates the degree of heat generation hence accelerating the tool wear formation. the graph presented in fig. 1 has a similar trend to the tool wear growth curve that was reported in [6]. for 40-minutes machining time, the two phases of wear progression trend, which are break-in period and steady-state wear regions, can be observed. the rate of tool wear growth for each phase at both cutting speeds was calculated as shown in table 4. the rate of flank wear growth using a kw10 uncoated carbide tool in the first phase is higher than the second phase and the tool wear rate is relatively high at higher cutting speed (450 m/min). this means that the wear occurred rapidly in the first phase, especially at high cutting speed. this rapid increment was due to the increase in the tool’s material removal resulting from the elevation of the machining temperature. this result is aligned with the findings reported by [6] that some of tool materials can be removed easily when the cutting edge experienced high cutting temperature due to the high cutting speed. 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0 5 10 15 20 25 30 35 40 45 a ve ra ge f la nk w ea r, v b av e (m m ) cutting time, t (min) v= 450 m/min v= 250 m/min 180 iium engineering journal, vol. 21, no. 2, 2020 daud et al. https://doi.org/10.31436/iiumej.v21i2.1227 table 4: the rate of flank wear growth using uncoated carbide tool rate of flank wear growth tool wear progression phase v = 250 m/min v = 450 m/min break-in period (first phase) 2.375e-3 3.636e-3 steady-state wear region (second phase) 0.774e-3 1.28e-3 the varied cutting speeds also have an influence on the volume of material removed in the turning operation. the volume of material removed was calculated using eq. (1) at the same average flank wear, which is 0.060 mm. (1) at cutting speed 250 m/min, the volume of material removed was found to be 507 461.46 mm3 for 40 minutes of machining time ( = 0.060 mm), whereas the volume of material removal at cutting speed 450 m/min for 11 minutes of machining time ( = 0.060 mm) was 296 161.71 mm3. the lower speed (250 m/min) has 71% higher volume of material removal with longer cutting time compared to the high cutting speed (450 m/min). according to rao [8], they stated that the relationship between tool life and cutting speed affects the decrease of material removal rate (mrr). mrr is the volume of material removed per unit time. hence, it can be decided that, the decrease of mrr leads to a decrease in material removal volume as the volume of material removed is directly proportional to mrr. 3.2 tool wear and wear mechanism table 5 shows the views of wear area for the kw10 uncoated carbide tool used in the machining test for 40 minutes under sem. from table 5, it can be noted that the flank wear, crater wear, and nose wear were found on the cutting tool edges for both cutting speeds within 40 minutes of the turning operation of al 7075-t651 using kw10 uncoated carbide under dry conditions. the flank wear occurred at the front relief and side relief faces, whereas the crater wear was formed at the rake face. the nose wear was formed at the nose area of the tool.flank wear is the main type of wear observed in this machining experiment. the friction caused by the rubbing action of the tool and the machined surface resulted in high cutting temperature; thus, the flank wear formation was promoted [9]. despite both cutting conditions having similar types of wear, the severity in tool wear formation differed. with the increment of cutting speed, the flank wear was affected and increased significantly. the main wear mechanism observed in this study was adhesion wear mechanism. it was formed due to the high cutting temperature at the tool-chip interface during machining of aluminum alloy. the heat generation was influenced by the cutting speed. however, the effect of the cutting speed on the adhesion wear mechanism is not severely affected as the flank wear does. adhesion wear was formed due to the welding of the workpiece material which was concentrated at the rake, front relief, and side relief faces. the cutting temperature that was generated in both conditions was predicted to be high enough to melt the work material at the cutting interface. the welded material was then developed to form bue. the tearing of unstable bue from the cutting tool surface caused a small quantity of tool material to be removed. the frequent building and breaking away of bue increased the high wear rate 181 iium engineering journal, vol. 21, no. 2, 2020 daud et al. https://doi.org/10.31436/iiumej.v21i2.1227 [7]. the result was in agreement with the findings reported by jurado et al. [9], as the adhesion wear occurred when material was transferred by chip onto the tool surface and modified the cutting conditions. table 5: the views of wear area for kw10 uncoated carbide tool used in machining test at cutting speed at v = 250 m/min and v = 450 m/min after 40 minutes of cutting time 3.3 effect of cutting speed on surface roughness the surface roughness of the machined workpiece was measured to evaluate the cutting tool performance of the uncoated carbide tool in turning al 7075-t651. fig.2 shows the relationship between cutting speed and average surface roughness (ra) at 40 minutes of cutting time. v = 250 m/min v = 450 m/min n os e f ro nt r el ie f f ac e si de r el ie f f ac e crater wear nose wear adhesion adhesion adhesion adhesion flank wear adhesion flank wear adhesion crater wear nose wear 182 iium engineering journal, vol. 21, no. 2, 2020 daud et al. https://doi.org/10.31436/iiumej.v21i2.1227 fig. 2: the average surface roughness (ra) of the machined surface of al 7075t651 for cutting speeds 250 m/min and 450 m/min using the kw10 uncoated carbide tool at t = 40 minutes in dry conditions (f = 0.05mm/rev, d = 1.0 mm). referring to fig. 2, the best surface finish was achieved at high cutting speed with 0.132 μm within 40 minutes of cutting time. the surface roughness value produced decreased as the radius of chip curl increased with the increment of the cutting speed. figure 3 shows the difference in degree of chip curl produced at cutting speed = 250 m/min and 450 m/min in turning al 7075-t651. fig. 3: chips produced in turning al 7075-t651 using a kw10 uncoated carbide tool under dry conditions, f = 0.05 mm/rev, d = 1 mm at, (a) v = 250 m/min, and (b) v = 450 m/min. a high surface roughness was obtained due to this low radius of chip curl, which tends to tangle and accumulate around the machined surface and scratches the freshly cut workpiece. consequently, the surface roughness increases as the accumulation of chips caused the unevenness in the machined surface. similar findings were discussed by [10], 0 0.04 0.08 0.12 0.16 0.2 200 250 300 350 400 450 500a ve ra ge s ur fa ce ro ug hn es s, r a (μ m ) cutting speed, v (m/min) f = 0.05 mm/rev, d = 1.0… b) a) 183 iium engineering journal, vol. 21, no. 2, 2020 daud et al. https://doi.org/10.31436/iiumej.v21i2.1227 the radius of the chip curvature increased with increase in the cutting speed which led to chips wrapping around the cutting tool, tool holder, and workpiece. 4. conclusion from the analysis on the cutting tool performance of kw10 uncoated carbide tool in turning al 7075-t651, the following can be concluded: the tool at lower cutting speed (250 m/min) performed better in having lower average tool wear rate within 40 minutes of operation. the percentage of average tool wear reduction was about 33% when turning at cutting speed 250 m/min compared to 450 m/min. a rapid wear growth rate was achieved in the first phase (break-in phase) especially at a high cutting speed. the tool wear rate at cutting speed 250 m/min is 34%-40% slower than the tool wear rate at 450 m/min in both phases (break-in and steadystate wear phases). the rapid increment was due to the high intensity of cutting temperature at higher cutting speed. at the same average flank wear measurement, vbave = 0.6 mm, the low cutting speed (250 m/min) produced about 71% higher volume of material removed compared to high cutting speed (450 m/min), in which high volume of material removed may increase the machining productivity. the most significant type of wear observed on the cutting edges in both conditions at 250 m/min and 450 m/min is the flank wear. the severity in tool wear formation increased with the increment of cutting speed. the main wear mechanism identified was adhesion during the turning operation at both cutting speeds. the welded material on the cutting edge caused the adhesion to form in all conditions. the building and tearing of bue promotes higher tool wear. the kw10 uncoated carbide tool used in turning al 7075-t651 at cutting speed 450 m/min performed better than at 250 m/min in producing low surface roughness due to the high radius of chip curl. it has low tendency for the chip to tangle around the freshly cut surface of the workpiece and leave scratches and marks on it. acknowledgements this project is supported by the government of malaysia and the international islamic university malaysia under these research grants, frgs/1/2018/tk03/uiam/03/4 and rigs17-157-0732. references [1] ng ch, yahaya sn, majid aa. (2017) reviews on aluminum alloy series and its applications. academia journal of scientific research, 708–716. [2] das dk, mishra pc, sahoo ak, ghosh d. (2015) experimental investigation on cutting tool performance during turning aa 6063 using uncoated and multilayer coated carbide inserts. international journal of machining and machinability of materials, 17(3/4):277. [3] santos mc, machado ar, sales wf, barrozo mas, ezugwu eo. (2016) machining of aluminum alloys: a review. international journal of advanced manufacturing technology, 86(9–12):3067–3080. 184 iium engineering journal, vol. 21, no. 2, 2020 daud et al. https://doi.org/10.31436/iiumej.v21i2.1227 [4] kouam j, songmene v, balazinski m, hendrick p. (2015) effects of minimum quantity lubricating (mql) conditions on machining of 7075-t6 aluminum alloy. the international journal of advanced manufacturing technology, 79(5–8):1325–1334. [5] santos mc, machado ar, barrozo mas. (2018) temperature in machining of aluminum alloys. temperature sensing. [6] sv alagarsamy nr. (2014) analysis of influence of turning process parameters on mrr & surface roughness of aa7075 using taguchi’s method and rsm. international journal of applied research and studies, volume 3(4):1–8. [7] zagórski i, warda t. (2018) effect of technological parameters on the surface roughness of aluminium alloys after turning. advances in science and technology research journal, 12(2):144–149. [8] rao cj, sreeamulu d, mathew at. (2014) analysis of tool life during turning operation by determining optimal process parameters. procedia engineering, 97:241–250. [9] jurado dg, martínez jmv, gámez aj, batista m, puerta fj, marcos m. (2017) analysis of secondary adhesion tool wear effects on surface roughness in dry turning process of uns a92024 aluminium alloy. international journal of mechatronics and manufacturing systems, 10(1):23. [10] xu d, feng p, li w, ma y, liu b. (2014) research on chip formation parameters of aluminum alloy 6061-t6 based on high-speed orthogonal cutting model. international journal of advanced manufacturing technology, 72(5–8):955–962. 185 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <feff004c006900650074006f006a00690065007400200161006f00730020006900650073007400610074012b006a0075006d00750073002c0020006c0061006900200069007a0076006500690064006f00740075002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c0020006b006100730020007000690065006d01130072006f00740069002000640072006f01610061006900200075007a01460113006d0075006d006100200064006f006b0075006d0065006e0074007500200073006b00610074012b01610061006e0061006900200075006e0020006400720075006b010101610061006e00610069002e00200049007a0076006500690064006f0074006f0073002000500044004600200064006f006b0075006d0065006e00740075007300200076006100720020006100740076011300720074002c00200069007a006d0061006e0074006f006a006f0074002000700072006f006700720061006d006d00750020004100630072006f00620061007400200075006e002000410064006f00620065002000520065006100640065007200200036002e003000200076006100690020006a00610075006e0101006b0075002000760065007200730069006a0075002e> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <feff04180441043f043e043b044c043704430439044204350020044d044204380020043f043004400430043c043504420440044b0020043f0440043800200441043e043704340430043d0438043800200434043e043a0443043c0435043d0442043e0432002000410064006f006200650020005000440046002c0020043f043e04340445043e0434044f04490438044500200434043b044f0020043d0430043404350436043d043e0433043e0020043f0440043e0441043c043e044204400430002004380020043f043504470430044204380020043104380437043d04350441002d0434043e043a0443043c0435043d0442043e0432002e00200421043e043704340430043d043d044b043500200434043e043a0443043c0435043d0442044b00200050004400460020043c043e0436043d043e0020043e0442043a0440044b0442044c002c002004380441043f043e043b044c04370443044f0020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e00300020043b04380431043e00200438044500200431043e043b043504350020043f043e04370434043d043804350020043204350440044104380438002e> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 1, 2019 rahman et al. pll-based 3φ inverter circuit for microgrid system operated by electrostatic generator tawfikur rahman, s. m. a. motakabber * , muhammad ibn ibrahimy and ahm zahirul alam department of electrical and computer engineering international islamic university malaysia, po box 10, kuala lumpur 50728, malaysia. * corresponding author: amotakabber@iium.edu.my (received: 29 th jan 2019; accepted: 27 th march 2019; published on-line: 1 st june 2019) https://doi.org/10.31436/iiumej.v20i1.1071 abstract: a current source control based pll (phase lock loop) technique is one of the most efficient methods for modern 3φ synchronized grid power systems. when an inverter circuit is driven by an electrostatic generator with wind power, it encounters some problems, such as static and dynamic turn-on-off switching losses, unbalanced source voltage, low continuous current, higher frequency harmonic distortion, phase angle imbalance, etc. to solve these problems, a series of connected switching inverter modules technique is proposed. it is not only a traditional inverter system, but it also works as a low-frequency ripple current inverter with lower switch losses. a new topology of phase synchronous inverter (psi) is designed using a pll current source controller. the input voltage source of the psi is a high dc voltage from an electrostatic generator (esg). the modified esg is capable of generating the hvdc and a continuous moderate amount of current. the proposed switching topology of the inverter is able to control the microgrid power as well as reduce the dynamic and static switching loss. it also reduces the high-frequency harmonic distortion and improves the phase angle error. the output lcl lowpass filter scheme of the inverter is designed to reduce the total harmonic distortion of 1.62%. the psi circuit is designed and simulated using matlab software. in the developed system, the input voltage of 8 k𝑉dc, microgrid frequency of 50hz, switching frequency of the carrier of 10 khz, and modulation index of 0.85 are considered to be implemented. the proposed novel microgrid connected psi switching module design technique has significantly enhanced the power stability. the overall system efficiency improved by 95.52%. abstrak: sumber-arus terkawal berdasarkan teknik pll (fasa litar kunci) adalah satu kaedah cekap bagi sistem moden tenaga grid selaras 3φ. apabila litar songsang (inverter) digerak menggunakan penjana elektrostatik bersama tenaga angin, ia mengalami masalah seperti kehilangan tenaga statik dan dinamik suis hidup-mati, sumber voltan yang tidak seimbang, kurang arus terus, gangguan harmoni frekuensi tinggi, ketidak-seimbangan sudut fasa, dan sebagainya. bagi menyelesaikan masalah ini, teknik modul suis bersiri dihubung bersama inverter telah dicadangkan. ini bukan semata-mata teknik lama sistem inverter, tetapi ia juga berfungsi sebagai arus tidak tetap frekuensi-rendah dengan kurang kehilangan tenaga pada suis inverter. topologi baru fasa inverter tetap (psi) ini telah direka menggunakan kawalan sumber arus pll. sumber voltan masuk psi ini telah digunakan daripada voltan dc tinggi penjana elektrostatik (esg). esg yang diubah suai ini dapat menghasilkan hvdc dan arus terus yang sederhana. topologi suis inverter yang dicadang ini dapat mengawal kuasa mikrogrid 177 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. serta mengurangkan kehilangan dinamik dan statik suis. ia juga mengurangkan gangguan harmoni frekuensi tinggi dan memperbaiki ketidak-seimbangan sudut fasa. skim tapisan signal keluar yang rendah pada lcl inverter ini direka bagi mengurangkan total gangguan harmoni sebanyak 1.62%. litar psi ini direka dan disimulasi menggunakan perisian matlab. dalam sistem yang dibangunkan ini, 8 kvdcvoltan masuk, 50hz frekuensi mikrogrid, 10 khz frekuensi suis angkutan dan 0.85 indeks modulasi telah dipertimbangkan untuk kegunaan. teknik baru modul suis psi mikrogrid bersambung yang dicadangkan ini mempunyai kepentingan dalam menstabilkan kuasa dan memperbaiki kecekapan sistem keseluruhan sebanyak 95.52%. keywords: psi; pll; current controller; pwm controller; inverter switching topology; output lcl filter; microgrid 1. introduction a microgrid is a small area power transmission and distribution system that is connected to three-phase synchronous inverters. these are well known to simplify esg and universally create sustainable power usage [1,2]. generally, the pll-based current controller topology is used to control the reactive and active power flow of microgrid systems as described in [2]. the study of current and voltage control strategies of the 3φ microgrid-connected, phase-synchronous inverter system is detailed in [3]. it is described as a high voltage and low current microgrid power regulator that is simplified by pllbased current regulator or voltage control with pwm system [3]. high voltage and low current regulator for 3φ microgrid coupled voltage control with pwm are described in, [4-5]. the regulators are applied synchronously, turning in the reference frame utilizing a dc regulator, pi regulator or in a-b-c to d-q-0 frame employed deadbeat regulator or hysteresis regulator. a pll based current regulator system executed in the synchronously turning reference frame is designed in [6]. these papers assume the inverter input voltage from esg and balance the microgrid voltage and current to microgrid networks. however, with the improvement of the inverted output current study in the area of a microgrid, increasing microgrid current and low higher harmonic frequency distortion is the focus of study. the voltage source pll based current regulator for microgrid associated dc to ac inverters is described in [7-8] and the output lcl filter is detailed in [9-10]. in these papers, twin synchronous pll based current and dc voltage regulators are designed and various types of switching regulator are utilized to create a high voltage and low current regulator in the case of unstable microgrid circumstances. however, the design techniques deal with equal unstable (nonappearance of zero order factor) and stable 3φ inverter output lcl filter connection between the psi and microgrid. a lowpass grid synchronous lcl filter is involved to decrease the low order harmonic frequency distorted current that is a 50 hz fundamental frequency [11]. the inverter dc capacitance of the source side is improved in injected ripple current. however, it could be complicated to maximize the size and weight of the system. alternatively, by including a suitable logic and switching controller circuit, the energetic power is diverted to additional loading energy elements [12]. the loading element of the inverter dc source side of the active power of the filter can carry out a unique low-frequency distorted compensator that is in sequence with the novel inverter. the total energy from the input inverter side can remain constant by appropriately monitoring the current of the additional phase terminal [13]. while these approaches can successfully overpower the input frequency ripple current, the additional inverter switches and circuits may lead to an increase in cost, power losses, and regulator difficulty [14]. 178 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. in this paper, the 3φ psi with pll based current control in a-b-c to d-q-0 frame is used to reduce the switching loss and increase the output current due to the esg produced ma current [15]. a pll with zero-crossing based regulator is designed to simplify the dc voltage and current regulator as traditional in the a-b-c to d-q-0 frame [12]. that regulator is also designed in a-b-c to d-q-0 reference frame to eliminate the requirement of software pll in the regulator construction. furthermore, the proposed regulatory approach is invariant with admiration to the central frequency of the microgrid [16]. the proposed switching regulator technique has utilized the current and voltage references that the method is defined in [3]. in addition, a grid synchronous lcl lowpass filter is usually utilized to reduce switching loss and reduction ripple, to improve the phase angle error, and to increase the inverter system efficiency [17]. the inverter must be synchronized, and noise should be reduced in terms of its output voltage and current waveform because the inverter performance depends on noiseless power quality and power density. therefore, the output filter is used to couple the inverter and microgrid for synchronization purposes by reducing the higher harmonic distortion. the effective current and voltage tracking by the voltage source controller with pwm confirms suitable microgrid current and voltage flow along with input dc ripple current and pure sinusoidal microgrid waveform. the study of the proposed regulator and inverter output lcl filter are provided and acceptable simulations are also carried out to show the overall system efficiency of the proposed systems. 2. design of a psi interface with microgrid systems conventionally, this inverter circuit consists of three half h-bridge single-phase inverter switches each connected to one of the three load terminals. for the preliminary control system, the operation of the solid state or mechanical three phase switches are synchronized in order for one switch to work at each 60º of the fundamental output waveform. fig. 1 illustrates the block diagram of a 3φ psi with an electrostatic generator and a microgrid system. fig. 1: proposed esg powered psi circuit for 3φ microgrid systems. the efficient specifics of the diagram are investigated in [3]. to the existing microgrid systems, this represents some significant improvements like power quality, bulky line-frequency transformer, power density, high controllability, flexibility, and high 179 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. efficiency, etc. the psi connected micro-grid technology is a capable solution to integrate a lot of energies and energy storage systems, which calls for more controllable and more flexible smart grids [12]. on the power delivery level, the voltage-source inverter, currentsource inverter, zero voltage source inverter, voltage direct-current transmission systems are a developing technology to integrate small static power such as offshore pv or wind farms coupled electrostatic generator systems. in the modern world, energy demand is one of the most important key factors in every sector of our daily life. conventionally, the electromagnetic system is employed to create electrical energy. however, esg can also be utilized to produce high electrical static dc voltage. the main drawback of such generators is their limited and specific applications in the power generation and distribution systems. however, the esg-based inverter system can overcome these limitations by converting dc to ac electrical power. 4. mathematical analysis of 3φ psi systems three-phase inverters are widely utilized for microgrid systems because of rising power demand, developing the power quality, and the potential benefits to end users. to simplify the psi design of the microgrid connected esg, fig. 1 shows the shortened model and that model is further demonstrated in fig. 2. it is distinguished that the input dc sources link mutual point “o” is isolated from 3φ microgrid neutral point “n”. two input sources are taken such as +𝑉𝐷𝐶 /2 and −𝑉𝐷𝐶 /2. the mutual point “o” is connected to the two input dc sources. the inductor of the inverter side as well as the microgrid side is distorted and harmonics. the line current of each phase is written as analysis given in [3]: 𝐿𝑎 𝑑𝑖𝐶𝑎 𝑑𝑡 + 𝑅𝑎 𝑖𝐶𝑎 = 𝑣𝑖𝑛𝑣𝑎 − 𝑣𝑚𝑔𝑎 (1) 𝐿𝑏 𝑑𝑖𝐶𝑏 𝑑𝑡 + 𝑅𝑏 𝑖𝐶𝑏 = 𝑣𝑖𝑛𝑣𝑏 − 𝑣𝑚𝑔𝑏 (2) 𝐿𝑐 𝑑𝑖𝐶𝑐 𝑑𝑡 + 𝑅𝑐 𝑖𝐶𝑐 = 𝑣𝑖𝑛𝑣𝑎 − 𝑣𝑚𝑔𝑐 (3) where, 𝑣𝑖𝑛𝑣 𝑎, 𝑣𝑖𝑛𝑣 𝑏 and 𝑣𝑖𝑛𝑣 𝑐 are the specific psi output voltage regarding the microgrid neutral “n” point while 𝑣𝑚𝑔 𝑎, 𝑣𝑚𝑔 𝑏 and 𝑣𝑚𝑔 𝑐 are the individual microgrid voltages regarding the microgrid “n” point, correspondingly. in this case, microgrid neutral point “n” is isolated from the two input dc sources mutual point “o”, the three phase currents can be followed as: 𝑖𝐶𝑎 + 𝑖𝐶𝑏 + 𝑖𝐶𝑐 = 0 (4) subtracting eq. (3) from (1) and (2) using eq. (4), resulting eq. with line quantities are derived: 𝐿𝑎 𝑑𝑖𝐶𝑎 𝑑𝑡 + 𝐿𝑎 𝑑 (𝑖𝐶𝑎 + 𝑖𝐶𝑏 ) 𝑑𝑡 + 𝑅𝑐 (𝑖𝐶𝑎 + 𝑖𝐶𝑏 ) + 𝑅𝑎𝑖𝐶𝑎 = 𝑣𝑖𝑛𝑣𝑎𝑐 − 𝑣𝑚𝑔𝑎𝑐 (5) 𝐿𝑎 𝑑𝑖𝐶𝑏 𝑑𝑡 + 𝐿𝑐 𝑑 (𝑖𝐶𝑎 + 𝑖𝐶𝑏 ) 𝑑𝑡 + 𝑅𝑐 (𝑖𝐶𝑎 + 𝑖𝐶𝑏 ) + 𝑅𝑏 𝑖𝐶𝑏 = 𝑣𝑖𝑛𝑣𝑏𝑐 − 𝑣𝑚𝑔𝑏𝑐 (6) 180 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. where, 𝑣𝑖𝑛𝑣 𝑦𝑦 and 𝑣𝑚𝑔 𝑦𝑦 are consistent psi and microgrid phase voltages respectively. therefore, the independent states space equation, for example, 𝑖𝐶𝑎= 𝑦1 and 𝑖𝐶𝑏 = 𝑦2 and solving eq. (5) and (6) the resulting eq. are initiated [3-4]. 𝑑𝑦1 𝑑𝑡 = 𝑎11𝑦1 + 𝑎12𝑦2 + 𝑏11𝑣𝑖𝑛𝑣 𝑎𝑐 + 𝑏12𝑣𝑖𝑛𝑣 𝑏𝑐 + 𝑚1 𝑑𝑦2 𝑑𝑡 = 𝑎21𝑦1 + 𝑎22𝑦2 + 𝑏21𝑣𝑖𝑛𝑣 𝑎𝑐 + 𝑏22𝑣𝑖𝑛𝑣 𝑏𝑐 + 𝑚2 (7) eq. (7) has been improved eq. (8). 𝑑𝑦1 𝑑𝑡 = 𝑎11𝑦1 + 𝑎12𝑦2 + 𝑥1 + 𝑚1 𝑑𝑦2 𝑑𝑡 = 𝑎21𝑦1 + 𝑎22𝑦2 + 𝑥2 + 𝑚2 (8) the inputs control 𝑥1 and 𝑥2 are specified in relations phase to phase voltages 𝑉𝑖𝑛𝑣 𝑎𝑏 and 𝑉𝑖𝑛𝑣 𝑏𝑐 as represented in eq. (8). [ 𝑥1 𝑥2 ] = [ 𝑏11 𝑏12 𝑏21 𝑏22 ] [ 𝑣𝑖𝑛𝑣 𝑎𝑐 𝑣𝑖𝑛𝑣 𝑏𝑐 ] (9) ⇒ [ 𝑣𝑖𝑛𝑣 𝑎𝑐 𝑣𝑖𝑛𝑣 𝑏𝑐 ] = [ 𝑏11 −𝑏12 −𝑏21 𝑏22 ] 𝑏11𝑏22−𝑏12𝑏21 [ 𝑥1 𝑥2 ] (10) where 𝑥1 and 𝑥2 are observed as the trouble inputs to the state space eq. demonstrated in eq. (6) and (7). 5. design of a control method for 3φ psi topology two dc voltage sources connected in series may be implemented using one psi. the logic switching control circuit must produce zero-crossing gate pulses from the twodifferent reference signals. the pulse signal is sent to the igbt module. it can produce three-terminal phase voltages, namely 𝑣𝑎𝑜 , 𝑣𝑏𝑜 and 𝑣𝑐𝑜 which are square-waves. during the operating period, the circuit has six different states. three modules drive each state. when a module is turned on, another module turns off. the load voltage is regulated from zero to its maximum by changing the angle ψ. in addition, the lcl lowpass filter is used to convert square waves into a modified sine wave with low frequency higher harmonic distortion. figure 2 shows the psi power circuit block diagram of the 3φ microgrid connected esg system. form the eq. (7) and (8), it is observed that the 3φ microgrid connected esg system consists of two conditions, 𝑦1 and 𝑦2. 181 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. fig. 2: shortened psi circuit of the 3φ microgrid connected esg systems. considering a positive definite function [5] as demonstrated in eq. (11). 𝑈 = 𝑒 𝑒𝑇 2 (11) where e is the error array highlighted in eq. (11). e = [ 𝑒1 𝑒2 ] = [ 𝑦′1 − 𝑦1 𝑦′2 − 𝑦2 ] (12) where, 𝑦′1 and 𝑦′2 are the following references of 𝑦1 and 𝑦2 respectively. at first, assuming no disturbances, such as 𝑚1= 𝑚2= 0: applying eq. (8), u is the first-time derivative exposed in eq. (13). 𝑑𝑈 𝑑𝑡 = 𝑒𝑇 [ 𝑑𝑦1 ′ 𝑑𝑡 − 𝑎11𝑦1 − 𝑎12𝑦2 − 𝑥1 𝑑𝑦2 ′ 𝑑𝑡 − 𝑎21𝑦1 − 𝑎22𝑦2 − 𝑥2 ] (13) the finding of the stability of the lyapunov function method must be a negative function as given in eq. (14). 𝑑𝑈 𝑑𝑡 = −𝑒𝑇 τ 𝑒 (14) 𝜏 = [ 𝜓1 0 0 𝜓2 ] (15) where, 𝜓1and 𝜓2 are the positive quantity. comparing eq. (13) and (14), the control variables are resolved as followed by eq. (16) and (17). 𝑥1 = 𝑑𝑦1 ′ 𝑑𝑡 − 𝑎11𝑦1 − 𝑎12𝑦2 + 𝜓1𝑒1 (16) 𝑥2 = 𝑑𝑦2 ′ 𝑑𝑡 − 𝑎21𝑦1 − 𝑎22𝑦2 + 𝜓2𝑒2 (17) 182 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. secondly, assuming microgrid voltage disturbance such as 𝑚1≠𝑚2≠ 0: the first derivative is considered of lyapunov function u and employing state space eq. (8) and the input array as demonstrated in eq. (16 and 17), eq. (18) is written. 𝑑𝑈 𝑑𝑡 = 𝑒𝑇 𝑑𝑒 𝑑𝑡 (18) = [ −𝑒1𝜓1 −𝑚1 −𝑒2𝜓2 −𝑚2 ] (19) if both eq. 20 and 21’s conditions are justified, then eq. (19) is first derived from the lyapunov function (u). this function is negative and definite in the absolute error designed 𝑒1𝑏 and 𝑒2𝑏 of e1 and e2 correspondingly. 𝜓1 > |𝑚1|𝑚𝑎𝑥 𝑒1𝑏 (20) 𝜓2 > |𝑚2|𝑚𝑎𝑥 𝑒2𝑏 (21) therefore, the design of the control law presented in eq. 16 and 17 is enough to push the state-error into the error designed 𝑒1𝑏 and 𝑒2𝑏. the inverter parameter uncertainty is solved by selecting appropriate gain which are 𝜓1 and 𝜓2. fig. 3 shown in the pll based psi switching controller. fig. 3: the matlab block diagram of the psi switching controller. the controller includes three synchronous pulse voltages to operate the series switching module. two modules are connected to one terminal. every terminal is determined like the next and lagged by 2𝜋 3 degree interval. each switching module drives for 180°. from eq. 20 and 21, it is observed that during the functioning period, the circuit is eight different switching logic states while two logic states are considered. the conducting period is called blanking time. three switches drive in each state. when a switch is opened, another switch is closed. this drives a new current path and a new circuit logic state. 183 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. 6. design of the psi output lcl filter a three-pole lowpass filter is presented to reduce the ripple current of the switches and improve the phase oscillations [10]. the designed filter is utilized to reduce dc ripple and noise. figure 4 presents the lowpass filter, where inductor linv is interconnected with the inverter side while inductor lmg is corporate with the microgrid-side and cf1 is a capacitor. equations 22 and 23 define the base capacitance and impedance and both parameters’ relation refer to the percentage of the base values [7-9]. 𝐶𝑏𝑎𝑠𝑒 = 1 𝜔𝑚𝑔𝑍𝑏𝑎𝑠𝑒 (22) 𝑍𝑏𝑎𝑠𝑒 = 𝑈𝑛 2 𝑃𝑛 (23) where, 𝑉𝐿−𝐿 and 𝑉𝑝 are inverter output voltage, 𝑓0 is microgrid frequency, pn is nominal power, 𝑓𝑠𝑤 is switching frequency. fig. 4: schematic diagram of the lcl lowpass filter. maximum 5% power factor sweeping is taken to design the filter capacitance that percentage is performed by the microgrid. that factor indicates the system base impedance is adjusted to 𝐶𝑓1= 0.05cbase. another researcher is taken a higher power factor to compensate for the inductive reactance of the filters [9-10]. ∆𝑖𝐿𝑚𝑎𝑥 = 𝑉𝐷𝐶 6𝑓𝑠𝑤 𝐿𝑖𝑛𝑣 (24) the filter is designed in such a way that ripple current would be 15% calculated by ∆𝑖𝐿𝑚𝑎𝑥 =0.15 𝑖𝑚𝑎𝑥 (25) for phase voltage 𝑉𝑝ℎ the 𝑖𝑚𝑎𝑥 and 𝐿𝑖𝑛𝑣 can be written by eq. (26) and eq. (27) 𝑖𝑚𝑎𝑥 = √2 𝑃𝑛 3𝑉𝑝ℎ (26) 𝐿𝑖𝑛𝑣 = 𝑉𝐷𝐶 6𝑓𝑠𝑤 ∆𝑖𝐿𝑚𝑎𝑥 (27) 184 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. the ratio (r) is constant for both sides of the inductor. therefore, 𝐿𝑚𝑔 = 𝑟𝐿𝑖𝑛𝑣 (28) 𝑅𝑓 is the damping resistor that is incorporated with the series capacitor to reduce the ripple current on the switching frequency [8-11]. 𝑘1 represents the 20% attenuation factor. lcl filter capacitance value is found out by the following eq. (32). therefore, 𝐿𝑚𝑔 = √1/𝑘1 2 + 1 𝐶𝑓 𝜔𝑠𝑤 2 (29) 𝜔𝑟𝑒𝑠 =√ 𝐿𝑖𝑛𝑣+𝐿𝑚𝑔 𝐿𝑖𝑛𝑣𝐿𝑚𝑔𝐶𝑓1 (30) 15𝑓𝑚𝑔 < 𝑓𝑟𝑒𝑠 < 0.5𝑓𝑠𝑤 (31) 𝑅𝑓 = 1 3 𝜔𝑟𝑒𝑠 𝐶𝑓1 (32) if the output lowpass filter inverter side inductor of 𝐿𝑖𝑛𝑣 and microgrid side inductor of 𝐿𝑀𝐺 is considered constant, then their ripple current is not surpassed. however, the microgrid inductor of 𝐿𝑀𝐺 can have a large set of values. based on microgrid lcl lowpass filter, the ratio of 𝑅𝑀𝐺 𝑋𝑀𝐺 varies according to the high voltage line microgrid configuration with wires length and conditions. it is also consisted of the leakage inductance of the inductors, whereas the filter capacitor value produced a small amount of error which depends on capacitor accuracy. typically, the small value of the capacitors have an accuracy varying between 5% and 20%. thd is the rms value of the total higher harmonics current [7-9], divided by the rms value of its fundamental current, where the equation is as follows: 𝑀 = 𝐻𝑎𝑟𝑚𝑜𝑛𝑖𝑐 𝑀𝑎𝑔𝑛𝑖𝑡𝑢𝑑𝑒 √2 (33) %𝑇𝐻𝐷 = √∑ 𝑀𝑖 2𝑛 𝑖=2 𝑀1 (34) where, mi is rms value of the harmonic magnitude corresponding to the i th harmonic. 7. experimental setup to attain the improved design, series switching based psi switching modules were constructed utilizing 40wr21 igbt with a 4n35 optocoupler, controlling the required input 8𝑘𝑉𝐷𝐶 static dc voltage. in this case, series switching igbt modules are regulated using an arduino uno microcontroller. in addition, e55/28/21-n87 cores with 400000 turns, coil length of 127 mm and coil diameter of 32 awg, achieving the required 0.5 h inductance value. the output lcl filter was implemented using three inductors of 0.5 h / 1 a with the plastic resistance of 164 ω connected in inverter side, three capacitors of 2.5 µf and three inductors of 0.45 h / 1 a with the plastic resistance of 164 ω connected in microgrid side. 185 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. (a) (b) fig. 5: prototype half phase psi circuit, (a) 3d, (b) pcb layout. 8. results and discussion 8.1 simulated results and discussion the psi circuit demonstrated in fig. 2 along with a control structure that is illustrated in fig. 5 is simulated by matlab2016a /simulink. for both switching turn-on and turnoff conditions and considered ic current is 400 a, then energy loss may be 500 mj at 25 c, however, in the case of 125 c, energy loss is 600 mj. from the igbt on-state characteristics, it is observed that when 𝑉𝐶𝐸 is 3.25v then current 𝐼𝐶 500a while 𝑉𝐶𝐸 is equal to 4.5 v then 𝐼𝐶 current should be same, 500 a. fig. 6: turn on and off switching energy of the igbt. in addition, the diode reverse recovery energy and diode on-state characteristics are presented in fig. 6. for both 25 c and 125 c, energy loss is gradually increased from the current 50 a to 450 a. in the case of 450 a, energy loss approximately 200 mj at 25 c whereas energy loss is 330 mj at 125 c. fig. 9 shows that the diode is forward current at 25 c and 125 c. if the current is almost 500 a, the maximum 𝑉𝑓, voltage is found 2.4 v and 2.7 v voltage, respectively. 186 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. fig. 7: turn on and off switching energy diode. in order to simulate the increased inverter output current using a series switching strategy with pll based current controller from eq. 20 and 21, the conventional voltage source control method is modified and presented in fig. 3. the pwm switching frequency of the psi is kept at 𝑓𝑤𝑠 = 10 khz. the parameters of the proposed control are applied in the simulation, proportional gain of the current loop 𝐾𝑝=0.3, an integral gain of the current loop 𝐾𝑖=20, proportional gain of the dc-link voltage loop 𝐾𝑉𝑑𝑐 p =7, an integral gain of the dc-link voltage loop 𝐾𝑉𝐷𝐶 i =800, nominal dc voltage 8k𝑉𝐷𝐶, sampling time 5×10 -6 s and the number of sampling per cycle is 3240 to generate the inverter output voltage and current. the distorted output voltage and current waveform of the psi are shown in fig. 8. it is clearly seen that the voltage is 𝑉𝑎𝑏𝑐 = 5443𝑉𝑟𝑚𝑠 and the current is 𝐼𝑎𝑏𝑐 = 282.8 a (rms) whereas the fundamental frequency is 50 hz. (a) (b) fig. 8: inverter output waveforms, (a) voltage, (b) current. 187 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. the output lcl filter is carried out in a microgrid connected psi based on eq. 9 and 10, in order to demonstrate the concert under pll based current control. the microgrid voltage and current waveform with the filtering condition are shown in fig. 9 (a) and (b). in this case, the microgrid output voltage and current are around 8 k𝑉𝑟𝑚𝑠 and almost 26.22 a (rms), respectively, considering fundamental frequency 50 hz. an fft analyzer based on eq. 33 is used to analyze % thd. without the filtering condition, the thd of the inverter output injected voltage and current are shown in fig. 10 (a) and (b). it is observed that the inverter output phase voltage (𝑉𝑎 rms) and current (𝐼𝑎 rms) are -7.09db (thd = 43.90%) and -7.08db (thd = 43.95%), respectively. (a) (b) fig. 9: microgrid waveform, (a) voltage vabc , (b) current iabc. (a) (b) fig. 10: fft analysis of the inverter output, (a) voltage va , (b) current (ia). 188 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. microgrid harmonic spectrum of injected voltage and current with filtering conditions are shown in fig. 11 (a) and (b). it is seen that injected voltage and current are -35.87 db and -35.76 db, respectively. so, the microgrid output thd voltage and current are 1.61% and 1.62%. (a) (b) fig. 11: fft analysis for microgrid (a) voltage va and (b) current (ia). figure 12 shows the microgrid magnitude and phase waveform. in this case, the systems are used the switching frequency of 10 khz, duty cycle 85%, sample per cycle of 3240 and microgrid fundamental frequency of 55 hz. it should be noted that the microgrid voltage phase angles with the filtering condition are 𝑉𝑎𝑏-𝑉𝑏𝑐 of 4.39, 𝑉𝑏𝑐 -𝑉𝑐𝑎 of 124.50, 𝑉𝑐𝑎-𝑉𝑎𝑏 of -115.78, correspondingly. the without-filtering condition, the inverter output voltages are 𝑉𝑎𝑏-𝑉𝑏𝑐 of 34.39, 𝑉𝑏𝑐 -𝑉𝑐𝑎 of 154.50, 𝑉𝑐𝑎-𝑉𝑎𝑏 of -85.78, respectively. however, the magnitude and phase of the lcl output phase to ground 𝑉𝑎𝑏𝑐 is almost the same as 𝐼𝑎𝑏𝑐 . fig. 12: the microgrid output voltage magnitude and phase. 189 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. finally, the simulated result has shown that the proposed inverter phase is almost equal to the microgrid phase of the designed pll based synchronization technique and therefore the phase error is only 4.39 8.2 experimental results and discussion to establish the experimental set-up, the control switching frequency is set to 10 khz of the microcontroller and the input reference voltage 𝑉𝐷𝐶 was performed to 8k𝑉𝐷𝐶 from the electrostatic generator. based on the switching controller, the inverter output voltage and current waveform without filtering conditions are almost the same as simulated results as demonstrated in fig. 13. (a) (b) fig. 13: output waveforms of the psi, (a) voltage, (b) current. it is clearly seen that the experimental results of the inverter output voltage and current are 4 kv peak and 400 a peak, respectively. after filtering, the microgrid voltage and current are around 6 kv and 30 a peak which is almost similar to simulated results as depicted in fig. 14. according to fig. 14, it is observed that both waveforms are cut the same point of 0.02 s which is 50 hz of fundamental microgrid frequency. similarly, it should be renowned that the experimental results are attained without damping technique. the inverter output voltage and current thd is equal to 44% without filtering condition, while the microgrid voltage and current thd is almost equal to 2% with filtering condition. as represented in fig. 15, the voltage and current frequency distortion and the thd value are decreased utilizing microgrid based lowpass lcl output filter. moreover, the gained microgrid voltage and current thd is less than <5% which meets microgrid code requirements. figure 15 shows the fft analysis of the measured inverter and microgrid voltages and currents. from these figures, the largest near fundamental and switching frequency voltage and current harmonic components are equal to 43.98% on the inverter 190 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. side and 1.67% on the microgrid side. therefore, the higher frequency harmonic attenuation rate of δ is equal to 26%. (a) (b) fig. 14: the voltage and current of the microgrid (a) simulated, (b) experimental. (a) (b) fig. 15: fft analysis of microgrid current, (a) simulated, (b) experimental. figure 16 illustrates the output waveforms of the microgrid line to line voltage of 𝑉𝑎 𝑀𝐺 with respect to the microgrid line to line current of 𝑖𝑎 𝑀𝐺 during steady state operation. in this case, the power factor is close to the unity power factor then the 191 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. microgrid output voltage and current are in phase. however, these odd frequency harmonics ripple could be avoided then the dc ripple current come from sensors harmonic and the peripheral current control loop of the static high voltage dc of 𝑉𝐷𝐶. in conclusion, it is found that a pll based synchronous controller provides high performance with minimized switching loss, reduced harmonic distortion and synchronized phase angle. fig. 16: magnitude and phase of the microgrid. in addition, the lowpass lcl microgrid filter offers high filtering performances with losses, synchronization, size, weight, and cost. also, the experimental results are relatively similar to those gained in simulated results. finally, it should be known that the experimental results specify the psi switching performances and reliability of the designed pll based synchronous controller with lowpass microgrid lcl output filter to reduce the loss and increase the system’s overall efficiency. 9. conclusions the finding shows that, a series of switch-based igbt/diode psi is designed and the proposed control system is simulated and experimental. the main influence of this design to integrate the psi with the microgrid system by connecting the lcl filter with the aid of a pll based current controller. the psi output current is increased by connecting igbt/diodes switches in series and the stability of the system is improved. it is observed that the total harmonics distortion is 1.61 % thd and phase angle is 4.35°, which is lower than maximum permissible distortion (<5% thd and <5°) as per requirements of ieee standard. the psi output voltage and current of the thd are reduced from 44% to 2% which is 42% thd of reduced in both cases. on the other hand, simulated and experimental results show the analysis of pll based pwm control system. the psi phase angle is developed from 34.39° to 4.35° which is 30% improved in the psi output voltage which shows the overall psi system efficiency is 95.61%. thus, the proposed psi inverter system can be implemented in large power systems and long power transmission and destitution systems as well. acknowledgments this research has been supported by the malaysian ministry of education through the fundamental research grant scheme under the project id: frgs19-054-0662. 192 iium engineering journal, vol. 20, no. 1, 2019 rahman et al. references [1] rahman t., motakabber, s. m. a., & ibrahimy, m. i. (2016, july). phase synchronous inverter for microgrid system. in 2016 international conference on computer and communication engineering (iccce) (pp. 167-171). ieee. [2] huangfu y, pang s, nahid-mobarakeh b, guo l, rathore ak, gao f. (2018). stability analysis and active stabilization of on-board dc power converter system with input filter. ieee trans. on industrial electronics, 65(1):790-799. [3] gomes cc, cupertino af, pereira ha. (2018). damping techniques for grid-connected voltage source converters based on lcl filter: an overview. renewable and sustainable energy reviews, 81:116-135. [4] dasgupta s, mohan sn, sahoo sk, panda sk. (2013). lyapunov function-based current controller to control active and reactive power flow from a renewable energy source to a generalized three-phase microgrid system. ieee trans. on industrial electronics, 60(2):799-813. [5] rahman t, ibrahimy mi, motakabber sm, mostafa mg. (2014). three phase three-layer phase synchronous inverter for microgrid system. in computer and communication engineering (iccce), pp 44-47. [6] cao y, xu y, li y, yu j, yu j. (2017). a lyapunov stability theory-based control strategy for three-level shunt active power filter. energies, 10(1):112. [7] rahman t., motakabber, s. m. a., & ibrahimy, m. i. (2017). a zero crossing pwm controller of a full bridge single phase synchronous inverter for microgrid systems. international journal of engineering and information systems, 1(6), 202-211. [8] yue y, chen y, luo a, ma f, xu q, he z. (2017). robust predictive dual-loop control method based on lyapunov function stability and energy equilibrium though double-core processors for active power filter. international journal of electrical power & energy systems, 89:69-81. [9] rahman t, ibrahimy m i, motakabber s m a. (2017). synchronization of output voltage waveforms in phase synchronous inverter with lcl filter for smart grid systems. in 3rd international conference on science and social research, pp. 6-7. [10] costa bl, bacon vd, da silva sa, angélico ba. (2017). tuning of a pi-mr controller based on differential evolution metaheuristic applied to the current control loop of a shuntapf. ieee trans. on industrial electronics, 64(6):4751-4761. [11] rahman t, motakabber sm, ibrahimy mi. (2016) design of a switching mode three-phase inverters. in computer and communication engineering (iccce), pp.155-160. [12] jayalath s, hanif m. (2017). generalized lcl-filter design algorithm for grid-connected voltage-source inverter. ieee trans. on industrial electronics, 64(3):1905-1915. [13] rahman t, motakabber s m a, ibrahimy m i. (2016). low noise inverter for polyphase microgrid system. in computer and communication engineering (iccce), pp172-176. [14] abdelrahem, m., hackl, c. m., & kennel, r. (2018). finite position set-phase locked loop for sensorless control of direct-driven permanent-magnet synchronous generators. ieee transactions on power electronics, 33 (4), 3097-3105. [15] rahman t., motakabber, s. m. a., ibrahimy, m. i., & rahman, m. w. (2017). an enhanced zero crossing based hvac phase synchronous inverter for electrostatic generator in microgrid systems. indonesian journal of electrical engineering and informatics (ijeei), 5(4), 285-294. [16] mondal, a., & illindala, m. s. (2018). improved frequency regulation in an islanded mixed source microgrid through coordinated operation of ders and smart loads. ieee transactions on industry applications, 54(1), 112-120. [17] rahman t, motakabber sma, ibrahimy mi. (2017). design and simulation of a pwm based phase synchronous inverter for utility grid systems with 20 km feeder line. scientific research journal, 14(2):17-34. 193 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 new approach to predict fecal coliform removal for stormwater biofilter applications sai hin lai1*, chun hooi bu1, ren jie chin2*, xiang ting goh3 and fang yenn teo4 1 department of civil engineering, faculty of engineering, universiti malaya, 50603 kuala lumpur, malaysia. 2 department of civil engineering, lee kong chian faculty of engineering and science, universiti tunku abdul rahman, 43000 kajang, malaysia. 3 department of parasitology, faculty of medicine, universiti malaya, 50603 kuala lumpur, malaysia. 4 department of civil engineering, faculty of engineering, university of nottingham (malaysia campus), 43500 semenyih, malaysia. * corresponding author: laish@um.edu.my; chinrj@utar.edu.my (received: 21st august 2021; accepted: 26th march 2022; published on-line: 4th july 2022) abstract: fecal coliform removal using stormwater biofilters is an important aspect of stormwater management. a model that can provide an accurate prediction of fecal coliform removal is essential. therefore, feedforward backpropagation neural network (fbnn) and adaptive neuro-fuzzy inference system (anfis) models were developed using a range of input features, namely grass type, the thickness of biofilter, and initial concentration of e. coli, while the estimated final concentration of e. coli was the output variable. the anfis model shows a better overall performance than the fbnn model, as it has a higher r2-value of 0.9874, lower mae and rmse values of 3.854 and 6.004 respectively, and a smaller average percentage error of 14.2%. hence, the proposed anfis model can be served as an advanced alternative to replace the need for laboratory work. abstrak: penyingkiran kolifom tinja menggunakan turas biologi (bioturas) air hujan merupakan aspek penting dalam pengurusan air hujan. model yang dapat menunjukkan anggaran tepat tentang penyingkiran kolifom tinja adalah penting. oleh itu, model rangkaian suapan neural perambatan belakang (fbnn) dan sistem adaptasi inferen neurofuzi (anfis) telah dibentukkan menggunakan pelbagai ciri input, iaitu jenis rumput, ketebalan bioturas dan kepekatan awal e. coli, manakala anggaran kepekatan akhir bagi e. coli merupakan hasil pembolehubah. model anfis menunjukkan peningkatan keseluruhan yang lebih baik berbanding model fbnn, kerana ia mempunyai nilai r2 yang lebih tinggi iaitu 0.9874, nilai mae dan rmse yang lebih rendah iaitu sebanyak 3.854 dan 6.004 masing-masing, dan ralat peratusan purata yang lebih kecil sebanyak 14.2%. oleh itu, model anfis yang dicadangkan boleh dijadikan alternatif awal bagi menggantikan keperluan kerja makmal. keywords: artificial intelligence; biofilters; fecal coliform; neural network; stormwater 1. introduction biofiltration systems such as swale and bio-detention systems are increasingly popular low-energy treatment technologies for improved stormwater management, e.g. increase of 45 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 infiltration, reduction of peak flow, improvement of water quality and increase of surrounding aesthetic value. stormwater biofilters can be defined as vegetated vertical infiltration systems that can achieve runoff volumes and contaminant load reductions for urban environments [1]. they have shown promising yet variable removal of fecal microorganisms [2-4]. fecal coliform bacteria are a group of bacteria that are passed through the fecal excrement of humans, livestock, and wildlife and they are the indicator bacteria. the most common member of fecal coliform bacteria is escherichia coli. vegetation and filter media depth may affect the capability of stormwater biofilters in removing fecal coliform. in the past two decades, researchers from around the world have experimented with biofilters using different design elements to investigate the biofiltration system in removing fecal coliform [5-10]. these studies reported that vegetation type or filter media depth caused variable bacteria removal performance. a previous study in australia reported that biofilters planted with native grasses (paspalum conjugatum and buchloe dactyloides) and shrubs (melaleuca incana, leptospermum continentale) showed improved e. coli removal, possibly due to reduced infiltration rates in vegetated biofilter systems. in addition, the leaf or seed extracts of l. continentale demonstrated potential antibacterial activity against e. coli [7]. with regards to filter media depth, it was reported that e. coli concentration decreased with increasing filter media depth [7]. nevertheless, there is no data available for the influence of native vegetation and filter media depth on microbial removal by stormwater biofilters in malaysia. therefore, in this study, the effect of biofilter designs (i.e., vegetation type, media thicknesses), as well as the inflow concentration in fecal coliform removal, are investigated to fill the gap of knowledge. artificial intelligence (ai) appears as a popular tool in providing the solution to complex non-linear problems and its application on issues relevant to environmental and hydrological researches has been widely seen, i.e. application of artificial neural networks (ann), fuzzy logic and adaptive neuro-fuzzy systems (anfis) for the solution of water/ wastewater and air pollution-related environmental problems [11], integration of ann and genetic algorithms (ga) for water quality modelling [12], implementation of machine learning classification to detect simulated increases of de facto reuse and urban stormwater surges in surface water [13], performance prediction of stormwater biofilters in heavy metal removal and risk mitigation using multilinear regressions (mlr), neural network (nn), and random forest (rf) [14], etc. therefore, this study aims to introduce the use of feedforward backpropagation neural network (fbnn) and adaptive neuro-fuzzy inference system (anfis) to predict the final concentration of fecal coliform for different conditions of stormwater biofilters. the proposed model can serve as an advanced method to replace the need for laboratory work. this study is innovative as it adds value to the current development of ai applications in improving stormwater management systems. 2. materials and methods 2.1 experimental works in this study, four native plants, namely cow grass (axonopus compressus), pearl grass (axonopus compressus, dwarf), philippine grass (zoysia matrella), and japanese grass (microstegiumvimineum) were selected. the biofilter columns were set up as shown in fig. 1. 46 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 fig. 1: the setup of biofilter columns used in this study. the main constituent that forms the filter media was washed river sand. four different depths were fixed in the sand columns, which are 150 mm, 250 mm, 350 mm and 450 mm. with respect to each depth, the recorded average hydraulic conductivity was 60.2, 47.1, 35.4 and 25.4 mm/hr, respectively. the values fell within the ranges recommended by urban stormwater management manual of malaysia (msma) [15]. one month before conducting the experiments, the biofilter columns were planted with native vegetation for the plants to mature. an amount of 80 l of water was collected from a local pond to act as stormwater in the experiments. four liters of water were poured into every biofilter column and the filtered water was collected. the analysis was carried out for the number of remaining indicator bacteria. a vacuum pump was then used to further filter the collected water sample through sterile nitrocellulose membrane filters. the membrane filters had characteristics of 0.45 µm pore size and 47 mm diameter. the membrane was transferred to a sterile petri dish with an absorbent pad (millipore, bedford, ma, usa) containing lauryl sulfate membrane medium (oxoid, hampshire, uk) agar plates. the plate was sealed with parafilm and incubated at 30 °c for 4 hours to resuscitate the growth of bacteria before further incubation at 44.5 °c for 14 hours. fecal coliform that formed yellow colonies were counted and expressed as colony-forming units (cfu) per 100 ml (cfu/100 ml). the water samples collected before and after the filtration were termed inflow and outflow concentration respectively. the removal efficiency of the biofilter columns can be obtained using eq. (1). log 𝑟𝑒𝑚𝑜𝑣𝑎𝑙 = 𝑙𝑜𝑔10 𝐼𝑛𝑓𝑙𝑢𝑒𝑛𝑡 𝑝𝑎𝑡ℎ𝑜𝑔𝑒𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 𝑝𝑎𝑡ℎ𝑜𝑔𝑒𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 (1) 2.2 architecture of the feedforward backpropagation neural network (fbnn) model data used in this study can be retrieved from the authors’ previous work [10]. feedforward backpropagation neural network (fbnn), as shown in fig. 2, has been 47 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 commonly used in different fields of applications, particularly in developing non-linear mathematical/prediction models [16-17]. fig. 2. the general architecture of the fbnn model. the net values at each hidden neuron (with first pattern inputs and random weight and bias) are presented as [16]: 𝑛𝑒𝑡𝑣𝑎𝑙𝑢𝑒𝑗 = ∑ 𝑤𝑖𝑗 𝑥𝑗 + 𝑏𝑗 𝑛 𝑖=1 (2) where 𝑛𝑒𝑡𝑣𝑎𝑙𝑢𝑒𝑗 is net input to node i in hidden or output layer, 𝑥𝑗 are the inputs to node i (or output of the previous layer), 𝑤𝑖𝑗 are the weights representing the power of the relationship between the ith node and jth node, n is the number of nodes and 𝑏𝑗 is the bias related to node j. the transfer function is required to activate the neurons. in this research study, the sigmoid function is chosen as the activation function. ℎ𝑗 = 1 1+𝑒 −𝑛𝑒𝑡𝑣𝑎𝑙𝑢𝑒𝑗 (3) where ℎ𝑗 is the output node of j and is an element of the inputs to the nodes in the next layer. the net values at the output layer and output neuron values are calculated by eqs. (4) and (5) respectively. 𝑛𝑒𝑡𝑣𝑎𝑙𝑢𝑒 = ∑ 𝑤𝑘 ℎ𝑘 + 𝐵 𝑚 𝑘=1 (4) 𝑜𝑢𝑡𝑝𝑢𝑡 𝑛𝑒𝑢𝑟𝑜𝑛 𝑣𝑎𝑙𝑢𝑒𝑠 = 1 1+𝑒 −𝑛𝑒𝑡𝑣𝑎𝑙𝑢𝑒 (5) where b is the bias. in this study, the inputs for the fbnn model were grass type, the thickness of the biofilter, and the initial concentration of e. coli. the expected resulting output of the model is the final concentration of e. coli. the architecture of the feedforward backpropagation neural network (fbnn) for the final e. coli concentration prediction is shown in fig. 3. in addition, data sorting is one of the crucial procedures in developing any fbnn model. this is to ensure the smoothness of the overall process and to obtain a model with a respectively high level of accuracy. a proper size of training-testing data is required so that the model can learn enough possible input-output patterns [18-19]. there is no fixed guideline while setting the training to testing ratio. however, it was normally suggested to set the training dataset within the range of 60% to 80% while the remaining 20% to 40% becomes the testing dataset [20-21]. since this study is considered as very first attempt to introduce the application of artificial intelligence in predicting the final concentration of 48 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 fecal coliform with respect to different conditions of stormwater biofilters, the upper limit of 80% is selected so that the developed model will be provided with the most possible input-output patterns. fig. 3: the architecture of the fbnn model. the number of hidden layers and the transfer function were set as one and a sigmoid function, respectively [21]. this is mainly due to its performance achievement in the prediction and forecasting model. meanwhile, the training algorithm is selected as levenberg-marquardt (trainlm), since it is suited for function fitting (nonlinear regression) problems [22-24]. while designing the architecture of the fbnn, the determination of the number of hidden neurons is one of the main challenging tasks. this is due to the sensitivity of the networks to the number of hidden neurons. underfitting problems may appear if there are too few neurons while overfitting issues may arise if there are too many neurons. therefore, it is important to choose a proper number of neurons [25]. for this study, the hidden neurons were set within the ranges of 2 to 19. 2.3 architecture of adaptive neuro-fuzzy inference system (anfis) model the integration of different techniques to form a hybrid ai model becomes the main trend of the development of ai applications. adaptive neuro-fuzzy inference system (anfis) is a technique that integrates both neural networks and fuzzy logic principles within a single framework. this may strengthen the ability of the model to reach a higher level of accuracy [26-28]. a basic anfis architecture is presented in fig. 4 [29-31]. fig. 4: the general architecture of anfis. 49 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 two rules were used in the method of “if-then” for takagi-sugeno fuzzy model, as shown in the following: rule 1: if x is 𝐴1 and y is 𝐵1, then 𝑓1 = 𝑝1𝑥 + 𝑞1𝑦 + 𝑟1 (6) rule 2: if x is 𝐴2 and y is 𝐵2, then 𝑓2 = 𝑝2𝑥 + 𝑞2𝑦 + 𝑟2 (7) where 𝐴1, 𝐴2, 𝐵1 and 𝐵2 are the membership functions for each input x and y (part of the premises), f1and f2 are the outputs within the fuzzy region specified by the fuzzy rule, while 𝑝1, 𝑞1, 𝑟1, 𝑝2, 𝑞2 and 𝑟2 are linear parameters in partthen (consequent part) of takagisugeno fuzzy inference model [26]. anfis architecture consists of five layers excluding the input layer (layer 0). the description of each layer is shown as follows [26]: 1. layer 0: it is an input layer that has n nodes, where n is the number of inputs to the system. 2. layer 1: it is the fuzzification layer. every node in this layer adapts to a function parameter. the output from each node is a degree of membership value that is given by the input of the membership functions. the typical membership function is shown below: µ𝐴(𝑥) = 1 1+| 𝑥−𝑐𝑖 𝑎𝑖 | 2𝑏𝑖 (8) where 𝑎𝑖, 𝑏𝑖 and 𝑐𝑖 are parameters for the function. the parameters in this layer are defined as premise parameters. 3. layer 2: every node in this layer is a fixed or nonadaptive node. the output is the product of all the incoming signals. each node in this layer represents the fire strength for each rule. t-norm operator with general performance, such as the and, is used to obtain the output: 𝑂2𝑖 = 𝑤𝑖 = µ𝐴𝑖 (𝑥) ∗ µ𝐵𝑖 (𝑦), 𝑖 = 1, 2 (9) 4. layer 3: it is the normalization layer. each node in this layer is fixed. each node is a calculation of the ratio between the i-th rules firing strength and the sum of all rules’ firing strengths. the result is known as the normalized firing strength. the strength of all rules is normalized by: 𝑂3𝑖 = �̄�𝑖 = 𝑤𝑖 ∑ 𝑤𝑖𝑖 (10) 5. layer 4: it is a layer of adaptive nodes. every node in this layer is an adaptive node to output, with a node function defined as: 𝑂4𝑖 = �̄�𝑖 𝑓𝑖 = �̄�𝑖 (𝑝𝑖 𝑥 + 𝑞𝑖 𝑦 + 𝑟𝑖 ) (11) where �̄�𝑖 is the normalized firing strength from the third layer and (𝑝𝑖 𝑥 + 𝑞𝑖 𝑦 + 𝑟𝑖 ) is a parameter in the node. the parameters in this layer are referred to as consequent parameters. it is assumed in eq. (11) that all the universe of discourse for all input variables can be defined using the selected type of the membership functions, and the final output is computed using the regression parameters for each rule r. the regression parameters are the premise parameters in eq. (11) which define the shape of the selected type of the membership function for each input variable. consequently, the training process aims at tuning the premise and consequence parameters to achieve the desired output. 50 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 6. layer 5: it is an output layer whose function is the summation of net outputs of the nodes in the fourth layer using the formula as shown: ∑ 𝑤𝑖 𝑓𝑖𝑖 = ∑ 𝑤𝑖𝑓𝑖𝑖 ∑ 𝑤𝑖𝑖 (12) while determining the input and output features as well as sorting data for anfis model development, a procedure that is similar to the fbnn model development was followed. the input features were made up of grass type, the thickness of stormwater, and the initial concentration of e. coli, while the output feature was the final concentration of e. coli, as depicted in fig. 5. the number of membership function (mf) was set as three. in order to tune the patterns of the anfis network, the hybrid optimization method, which is the combination of backpropagation and least square-type approaches, was selected. the models were trained using different input membership functions, i.e. trimf, trapmf, gbellmf, gaussmf, gauss2mf, pimf, dsigmf and psigmf, and output membership function, i.e. constant and linear membership function. fig. 5: the architecture of the anfis model. 2.4 model performance evaluation the commonly used analyses for model performance evaluation are coefficient of determination (r2), mean absolute error (mae), mean squared error (mse), root mean squared error (rmse), and percentage error (% error). these are the relevant important indicators to show the suitability of the developed model in predicting the final concentration of e. coli. r2 = ( 𝑛 ∑ 𝑥𝑖𝑦𝑖−∑ 𝑥𝑖 ∑ 𝑦𝑖 √𝑛 ∑ 𝑥𝑖 2−(∑ 𝑥𝑖)²√𝑛 ∑ 𝑦𝑖 2−(∑ 𝑦𝑖)² ) 2 (13) mae = ∑|𝑦𝑖 − 𝑥𝑖 | 𝑛 (14) 51 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 rmse = √ 1 𝑛 ∑(𝑦𝑖 − 𝑥𝑖 )² (15) percentage error = |𝑇𝑟𝑢𝑒 𝑣𝑎𝑙𝑢𝑒 − 𝑃𝑟𝑒𝑑𝑖𝑐𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒| 𝑇𝑟𝑢𝑒 𝑣𝑎𝑙𝑢𝑒 × 100% (16) where n is the number of data pairs, x is the observed variable, y is the predicted variable. 3. results and discussion 3.1 experimental works as shown in fig. 6, the removal capability of cow grass on a 450 mm depth river sand column together with 150 mm of topsoil and 100 mm of gravel drainage layer revealed the highest fecal coliform mean log removal (2.4 log) compared to other biofilter columns. it agrees with the findings in barrett et al. [32] and chandrasena et al. [5] which indicated that vegetated biofilters improved fc removal. fig. 6: mean log removal of fecal coliform of four vegetations vs four filter media. planting of grasses, sedges, and shrubs in bioretention systems not only fulfils an esthetic purpose but also improves pathogen removal [33-35]. in the present study, cow grass was found to be more suitable to use in stormwater biofilters because the survival rate of cow grass was the highest compared to pearl, philippine, and japanese grass. the bigger root mass of cow grass improved the removal rates of fc due to its effect on biofilter retention time. it is hardy and able to grow with minimal to no fertilizer. the physical appearance of pearl grass is similar to cow grass but it has shorter, rounder, and thicker leaves. pearl grass needs more water compared to cow grass to grow and is less hardy. as for philippine grass, it needs regular trimming about once every 2 weeks. meanwhile, japanese grass blades are softer, shorter, and compact. they grow rather slowly, require frequent watering, and in dry soil, they tend to die off. 52 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 apart from vegetation type, the physiochemical nature of filter media in biofilters plays a significant role in microbe removal [36-37]. in this study, the major component that constituted the filter media was washed river sand, offering an effective and low-cost means of treating stormwater. the finding is in-line with the previous studies which reported that sand filters showed satisfying outputs on fecal coliform removal in stormwater treatment [5]. barrett et al. [32] reported that austin sand filters achieved high fc (85%) and e. coli removal (97.1%) in an experiment to test for biofiltration performance. in terms of depth, the biofilter with 150 mm media depth exhibited an inconsistent performance in removing fecal coliform. this may be mainly because the preferential flow was more prone to occur in lower media depth due to the intermittent wet-drying cycle. it was found that, in order to achieve > 1 log fecal coliform removal, 250 mm should be the minimum media depth required. on the other hand, the mean fc removal at 350 mm depth filter was slightly higher than the 250 mm depth filter but it exceeded 2 log for all types of biofilter columns at 450 mm depth filter. 3.2 models development 3.2.1 fbnn models the proposed fbnn models, which were developed with a range of hidden neurons from 2 to 19, were evaluated using the selected statistical analyses. however, since there were so many developed models, only the selected models were presented in this paper. table 1 depicts the performance of all the developed fbnn models from the aspect of r2, mae, rmse and average percentage error (% error). based on the common theory, a higher r2-value indicates that the model has a higher ability to explain all the variance within the model. in this case, the highest r2-value is 0.9285, as shown in model iv. table 1: statistical performance of the selected fbnn models with respect to the different number of neurons model number of neurons r2 mae rmse i 14 0.8646 6.014 9.926 ii 15 0.0650 27.850 65.771 iii 16 0.8910 5.107 9.194 iv 17 0.9285 4.204 7.322 v 18 0.9249 4.512 7.423 vi 19 0.0630 57.487 122.191 while evaluating the performance of a fbnn model, a smaller error value is always favorable. this is because the smaller the calculated value, the better the accuracy of the estimated output. from the aspect of mae and rmse, model iv achieves the lowest values, displaying a value of 4.204 and 7.322, respectively. all the above-discussed aspects indicate that model iv is the best-performed model. the appropriateness of model iv to predict the final e. coli concentration is further verified using the average percentage error. percentage error is another common indicator. fig. 7 contains the average percentage error of the selected fbnn models. model iv shows the lowest average percentage error (27.5%), indicating that it has the highest level of accuracy among the examined models. 53 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 fig. 7: the average error of the developed fbnn models. overall, model iv appears as the most suitable fbnn model to predict the final e. coli concentration for the stormwater biofilters application. this is because it has the highest r2value (0.9285), the lowest values of mae (4.204) and rmse (7.322), and the smallest average percentage error (27.5%). 3.2.2 anfis models a total number of 16 anfis models were developed, and their respective performances are contained in table 2. in terms of r2-value, if the value is near 1, indicating that the observed values and the predicted values have a strong linear relationship. in other words, the observed values and predicted values are almost similar if the r2-value approximates 1. referring to table 2, the highest r2-value is 0.9874. on the other hand, the models with the output linear membership function (model ii, iv, vi, viii, x, xii, xiv, and xvi), in general, show a better performance than the models with constant output membership function. therefore, it can be deduced that the output linear membership function is more suitable for the development of the anfis model to deal with the stormwater biofilters application. in this case, model iv displays the lowest mae and rmse values. table 2: performance in terms of r2, mae and rmse for the developed anfis models. models nmfs mfti mfto r2 mae rmse i 3 trimf constant 0.7994 11.397 23.885 ii 3 trimf linear 0.9112 7.820 15.866 iii 3 trapmf constant 0.7994 11.397 23.885 iv 3 trapmf linear 0.9874 3.854 6.004 v 3 gbellmf constant 0.8231 11.260 22.428 vi 3 gbellmf linear 0.9217 7.665 14.892 vii 3 gaussmf constant 0.7909 11.451 24.394 viii 3 gaussmf linear 0.9215 7.706 14.908 ix 3 gauss2mf constant 0.7784 11.471 25.126 x 3 gauss2mf linear 0.9216 7.626 14.910 xi 3 pimf constant 0.7714 11.597 25.534 xii 3 pimf linear 0.9214 7.688 14.927 xiii 3 dsigmf constant 0.7709 12.328 25.502 xiv 3 dsigmf linear 0.9215 7.630 14.915 xv 3 psigmf constant 0.7726 12.253 25.406 xvi 3 psigmf linear 0.9218 7.629 14.892 0 50 100 150 200 250 300 350 400 450 500 i ii iii iv v vi a v e ra g e p e rc e n ta g e e rr o r (% ) fbnn model 54 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 from the perspective of average percentage error, model iv has achieved the lowest value if compared with other investigated models, recording at 14.2%, as shown in fig. 8. in other words, it can achieve an average accuracy of around 86%. in general, no guideline was set for the range of acceptable error in certain engineering applications. however, a smaller error is always preferable. as this is the first attempt to introduce the use of anfis in predicting the final e. coli concentration for stormwater biofilters application, such an average accuracy is encouraging. fig. 8. average percentage error of the anfis model. in short, model iv is the model with the best performance while evaluating through the series of analytical analyses. it exhibits the highest r2-value of 0.9874, the lowest mae and rmse of 3.854 and 6.004 respectively, and the smallest average percentage error of 14.2%. 3.2.3 ai models comparison this study investigates both fbnn and anfis as the advanced methods to predict the final e. coli concentrations. after conducting the performance evaluation through a series of statistical analyses, the best-performed model for each approach was identified. table 3 shows the comparison of the selected model in terms of r2, mae, rmse and average percentage error. table 3: comparison between the best-performed fbnn and anfis model model r2 mae rmse average percentage error fbnn model iv 0.9285 4.204 7.322 27.5 anfis model iv 0.9874 3.854 6.004 14.2 among all the examined statistical indicators, anfis model iv achieved a better performance than that of fbnn model iv. overall, it shows an improvement from fbnn to anfis. the most significant enhancement can be seen from the aspect of the average percentage error. the value has been reduced from 27.5% to 14.2%, showing an improvement of around 50%. the architecture of the best-performed anfis model is therefore described as follows: • network inputs: grass-type, the thickness of biofilters, initial e. coli concentration 0 5 10 15 20 25 30 35 40 i ii iii iv v vi vii viii ix x xi xii xiii xiv xv xvi a v e ra g e p e rc e n ta g e e rr o r (% ) anfis model 55 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 • network output: final e. coli concentration • number of membership functions: 3 • input membership function: trapmf • output membership function: linear • optimization method: hybrid 4. conclusions the main purpose of this study was to develop an artificial intelligence (ai) model to serve as an alternative to predict the final e. coli concentration in the application of stormwater biofilters in stormwater management practices. both feedforward backpropagation neural network (fbnn) and adaptive neuro-fuzzy inference system (anfis) models have seen their application in different fields of study, especially while dealing with non-linear regression problems. both techniques are appropriate for this task because it has the capability to learn the relationships between input-output variables for a complex physical relationship and hence provide an output with a considerably high level of accuracy. in this study, it is found that a single-layer feedforward backpropagation neural network (fbnn) with 17 hidden neurons to be the most suitable model for the final e. coli concentration prediction. meanwhile, the anfis model with the number of membership function of 3, input trapmf membership function and output linear membership function has shown the best performance among the examined models. the selection of the models was supported by the results of a range of statistical analyses. the selected fbnn model and anfis model were then further compared using the same series of statistical analyses to investigate their appropriateness to achieve the main goal of this study. in conclusion, the anfis model appears as the more suitable model for the final e. coli concentration prediction after comparing it with the selected fbnn model. in short, anfis is an effective tool to provide a more accurate simulation of the non-linear behavior between the final e. coli concentration and the factors affecting it. with such a model, it allows the user to determine the final e. coli concentration and thereby the removal percentage of the biofilters application by inserting the relevant input parameters into the model. since this study is seen as the first attempt to implement the artificial intelligence techniques in predicting the final coliform concentration under different stormwater biofilter conditions, two basic techniques (bpnn and anfis) were chosen for the model development. to further enhance the model performance in terms of accuracy and effectiveness, the integration of optimization algorithms such as genetic algorithm (ga), ant colony algorithm (aco), etc. to the proposed model can be performed. acknowledgements this work was supported by university of malaya under postgraduate research grant (ppp) (grant no. 4576). the authors would like to thank the faculty of engineering, university of malaya for providing space to conduct the biofilter column experiments and department of parasitology, faculty of medicine, university of malaya for the laboratory facilities and technical assistance provided for their experiments. 56 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 references [1] payne eg, fletcher td, cook pl, deletic a, hatt be. (2014) processes and drivers of nitrogen removal in stormwater biofiltration. crit. rev. environ. sci. technol., 44: 796-846. [2] kanda r, kishimoto n, hinobayashi j, hashimoto t, tanaka s, murakami y. (2017) influence of temperature and cod loading on biological nitrification-denitrification process using a trickling filter: an empirical modeling approach. int. j. environ. res., 11: 71-82. [3] samhan sa, al-sa'ed rm, mahmoud nj. (2007) removal of pathogenic microorganisms in pilot‐scale uasb‐septic tanks and albireh urban wastewater treatment plant in palestine. water int., 32: 798-809. [4] wang r, li x, feng y, tariq f, li k, wei y, . . . chen l. (2019) removal of formaldehyde from the air with a suspended growth bioreactor. int. j. environ. res., doi:https://doi.org/10.1007/s41742-019-00228-2 [5] chandrasena gi, pham t, payne eg, deletic a, mccarthy dt. (2014) e. coli removal in laboratory scale stormwater biofilters: influence of vegetation and submerged zone. j. hydrol., 519: 814-822 [6] li y, mccarthy dt, deletic a. (2016) escherichia coli removal in copper-zeolite-integrated stormwater biofilters: effect of vegetation, operational time, intermittent drying weather. ecol. eng., 90: 234-243. [7] chandrasena gi, shirdashtzadeh m, li y, deletic a, hathaway, jm, mccarthy dt. (2017) retention and survival of e. coli in stormwater biofilters: role of vegetation, rhizosphere microorganisms and antimicrobial filter media. ecol. eng., 102: 166-177. [8] galbraith p, henry r, mccarthy dt. (2019) rise of the killer plants: investigating the antimicrobial activity of australian plants to enhance biofilter-mediated pathogen removal. j. biol. eng., 13: 52. [9] hunt wf, smith jt, jadlocki sj, hathaway jm, eubanks pr. (2008) pollutant removal and peak flow mitigation by a bioretention cell in urban charlotte, n.c. j. environ. eng., 134: 403-408. [10] bu ch, lai sh, goh xt, chong wt, chin rj. (2021) influence of filter media depth and vegetation on faecal coliform removal by stormwater biofilters. water environ. j., 35: 181189. [11] yetilmezsoy k, ozkaya b, cakmakci m. (2011) artificial intelligence-based prediction models for environmental engineering. neural netw. world, 3: 193-218. [12] chau, k-w. (2006) a review on integration of artificial intelligence into water quality modelling. mar. pollut. bull., 52: 726-733. [13] thompson ka, dickenson er. (2021) using machine learning classification to detect simulated increases of de facto reuse and urban stormwater surges in surface water. water res., 204: 117556. [14] fang h, jamali b, deletic a, zhang k. (2021) machine learning approaches for predicting the performance of stormwater biofilters in heavy metal removal and risk mitigation. water res., 200: 117273. [15] did malaysia (2012) urban stormwater management manual for malaysia 2nd edition. kuala lumpur, department of irrigation and drainage malaysia. [16] chin rj, lai sh, shaliza i, wan zurina wj, ahmed elshafie ah. (2019) new approach to mimic rheological actual shear rate under wall slip condition. eng. comput., 35: 1409-1418. [17] deng b, chin rj, tang y, jiang c, lai sh. (2019) new approach to predict the motion characteristics of single bubbles in still water. appl. sci., 9: 3981. [18] alimissis a, philippopoulos k, tzanis cg, deligiorgi d. (2018) spatial estimation of urban air pollution with the use of artificial neural network models. atmos. environ., 191: 205-213. [19] zhang y, chen h, yang b, fu s, yu j, wang z. (2018) prediction of phosphate concentrate grade based on artificial neural network modeling. results phys., 11: 625-628. [20] akter t, desai s. (2018) developing a predictive model for nanoimprint lithography usingartificial neural networks. mater. des., 160: 836-848. [21] chin rj, lai sh, shaliza i, wan zurina wj, elshafie a. (2019) rheological wall slip velocity prediction model based on artificial neural network. j. exp. theor. artif. intell., 31: 659-676. 57 iium engineering journal, vol. 23, no. 2, 2022 lai et al. https://doi.org/10.31436/iiumej.v23i2.2173 [22] pham dt, sagiroglu s. (2001) training multilayered perceptrons for pattern recognition: a comparative study of four training algorithms. int. j. mach. tools manuf., 41: 419-430. [23] demuth h, beale m. (2014) neural network toolbox for use with matlab user's guide version 4. natick, ma, the mathworks inc. [24] sharma b, venugopalan k. (2014) comparison of neural network training functions for hematoma classification in brain ct images. iosr j. comput. eng., 16: 31-35. [25] alsmadi mk, omar kb, noah sa (2009) back propagation algorithm: the best algorithm among the multi-layer perceptron. int. j. comput. sci. netw., 9: 378-383. [26] chin rj, lai sh, shaliza i, wan zurina wj, elshafie a. (2020) anfis-based model for predicting actual shear rate associated with wall slip phenomenon. soft comput., 24: 96399649. [27] ghasemi e, kalhori h, bagherpour r. (2016) a new hybrid anfis–pso model for prediction of peak particle velocity due to bench blasting. eng. comput., 32: 607-614. [28] korotkikh v, korotkikh g (2008) on principles in engineering of distributed computing systems. soft comput., 12: 201-206. [29] jang js (1993) adaptive network-based fuzzy inference system. ieee trans. syst. man cybern. syst., 23: 665-685. [30] jang js, sun ct. (1997) neuro-fuzzy and soft computing: a computing approach to learning and machine intelligence, englewood cliffs, new jersey, prentice hall. [31] jang js, sun ct, mizutani e. (1997) a computational approach to learning and machine intelligence. neuro-fuzzy and soft computing. upper saddle river, new jersey, prenticehall. [32] barrett me, limouzin m, lawler df. (2013) effects of media and plant selection on biofiltration performance. j. environ. eng., 139: 462-470. [33] read j, fletcher td, wevill t, deletic a. (2009) plant traits that enhance pollutant removal from stormwater in biofiltration systems. int. j. phytoremediation, 12: 34-53. [34] kim mh, sung cy, li mc (2012). bioretention for stormwater quality improvement in texas: removal effectiveness of escherichia coli. sep. purif. technol., 84: 120-124. [35] li yl, deletice a, alcazar l, bratieres k, fletcher td, mccarthy dt. (2012) removal of clostridium perfringens, escherichia coli and f-rna coliphages by stormwater biofilters. ecol. eng., 49: 137-145. [36] hermawan aa, chang jw, pasbakhsh p, hart f, talei a. (2018) halloysite nanotubes as a fine grained material for heavy metal ions removal in tropical biofiltration systems. appl. clay sci., 160: 106-115. [37] sileshi r, pitt r, clark s. (2016) prediction of flow rates through various stormwater biofilter media mixtures. proceedings of the world environmental and water resources congress, west palm beach. 58 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. rans k-ω simulation of 2d turbulent natural convection in an enclosure with heating sources mehdi ahmadi, seyed ali agha mirjalily* and seyed amir abbas oloomi department of mechanical engineering, yazd branch, islamic azad university, yazd, iran. *corresponding author: saa_mirjalily@iauyazd.ac.ir (received: 13th dec 2018; accepted: 24th feb 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.1040 abstract: this study is conducted to investigate turbulent natural convection flow in an enclosure with thermal sources using the low-reynolds number (lrn) k-ω model. this enclosure has a cold source with temperature tc and a hot source with temperature th as thermal sources, other walls of the enclosure are adiabatic. the aim of this study is to predict the effect of change in rayleigh number, repositioning of cold and hot sources, and thermal sources aspect ratio on the flow field, temperature, and rate of heat transfer. to achieve this aim, the equations of continuity, momentum, energy, turbulent kinetic energy, and kinetic energy dissipation are employed in the case of 2d turbulence with constant thermo-physical properties except the density in the buoyancy term (boussinesq approximation). to numerically solve these equations, the finite volume method and simple algorithm are used. according to the modeling results, the most optimal temperature distribution in the enclosure is seen when the hot source is below the cold source. with decreasing distance between hot and cold sources, heat transfer rate increases. the maximal heat transfer rate is derived via study of the heating sources aspect ratio. in constant positions of cold and hot sources on a wall, the heat transfer rate increases with increasing rayleigh number (ra=109-1011). abstak: kajian ini dijalankan bagi mengkaji perubahan semula jadi aliran perolakan dalam tempat tertutup dengan sumber haba menggunakan model k-ω nombor reynoldsrendah (lrn). bekas tertutup ini mempunyai dua sumber haba iaitu sumber sejuk dengan suhu tc dan sumber panas dengan suhu th, manakala dinding lain bekas ini adalah adiabatik. tujuan kajian ini adalah bagi mengesan perubahan nombor rayleigh, mengubah sumber sejuk dan panas dan nisbah sumber haba kepada kawasan aliran, suhu dan halaju perubahan haba. bagi mencapai tujuan tersebut, persamaan sambungan, momentum, tenaga, tenaga kinetik perolakan, dan pengurangan tenaga kinetik telah dilaksanakan dalam kes perolakan 2d dengan sifat fizikal-haba berterusan (malar) kecuali isipadu terma keapungan (anggaran boussinesq). bagi menyelesaikan persamaan ini secara berangka, kaedah isipadu terhad dan algorithma mudah telah digunakan. berdasarkan keputusan model, suhu distribusi optimal dalam bekas tertutup dilihat apabila sumber panas adalah kurang daripada sumber sejuk. dengan pengurangan jarak antara sumber panas dan sejuk, kadar pertukaran haba meningkat. kadar pertukaran haba maksima telah diperoleh melalui kajian nisbah aspek sumber pemanasan. kadar pertukaran haba bertambah dengan bertambahnya nombor rayleigh (ra=109-1011), pada posisi tetap sumber sejuk dan panas pada dinding bekas. keywords: heat transfer; turbulent natural convection; k-ω model; enclosure 229 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. 1. introduction many numerical and experimental studies have been conducted on natural convection flows. in the last two decades, many studies have sought to achieve quantitative data on the processes of flow convective heat transfer and its association with many applications inside enclosures [1-2]. the most important and most frequently investigated section of these convections is a rectangular enclosure filled with dry air and two vertical walls at two different temperatures [3-6]. in a rectangular enclosure with height h, heat is naturally transferred from the hot wall to the cold wall through the formation of a vortex with slow movement. the movement of the vortex is considered the engine of heat transfer from hot source to cold source. flow intensity is expressed by rayleigh number, ra=gβδth3 /αʋ, where, h is the enclosure height, β is coefficient of thermal expansion, δt is temperature difference between vertical walls, and α and ʋ are thermal and molecular diffusivities of fluid. depending on the rayleigh number, the flow can be classified as turbulent or laminar [7-9]. a rayleigh number of less than 108 represents laminar flow, and the transient of laminar flow to turbulent occurs at ra=108-1010[10]. natural convection in enclosure was first experimented by elder [11] and then giel and schmidt [12]. in these experiments, water was used instead of air. cheesewright [13] studied the mean velocity, center temperature, and turbulent variations in natural convection flow in an air-contained enclosure with temperature difference between the walls. he used a standard k-ε model with wall functions to simulate turbulent convection flow in an enclosure with a radiator. in addition, he used the wall functions to calculate kε but did not use them to measure velocity and temperature. the selected model made a good prediction of the average flow, which was consistent with previous studies but was weak for modeling turbulence; the rayleigh number of the enclosure was constant in his study and was considered 3*1010 with length to height ratio of the enclosure of 1:5. dafa alla and bets [6] studied natural convection flow in a high enclosure with length/height ratio of 1:14 and the rayleigh number 8.3*105. in this experiment, a laser velocity meter was used to measure velocity and velocity variations and thermocouple to measure temperature and temperature variations. olsen et al [14] conducted a study on natural convection flow in an air-conditioning enclosure with a small model and rayleigh number of 1010. the length/height ratio of the enclosure was approximately 1:3. they illustrated the measured flow and temperature in the center and boundary layer. unlike previous studies, two lateral lobes were seen in these experiments, this study was a rare study on an enclosure with virtually real dimensions. chen [15] used different reynolds models of stress (rms) to calculate the natural, forced, and mixed convection flows in the enclosure. modeling results demonstrated that the efficiency of different rms approaches to simulate convection flow in the enclosure were equal and consistent with the mean flow derived in experimental calculations, but turbulence values were not predicted appropriately. ince and launder [16] studied natural convection flow in a square enclosure with hot right surface and cold left surface and upper and lower adiabatic surfaces. they managed to develop a model to resolve turbulent flow with rayleigh numbers ranging from 106 to 1010. hanjealic and vasc [17] used threeequation k-ε-ɵ and four-equation v1-ε-ɵ-εɵ and low reynolds number (lrn) to calculate turbulent convection flow in different empty and partitioned enclosures. the rayleigh number in their studies varied between 1010 and 1012, which is compatible with rayleigh numbers in real indoors. mean temperature and velocity derived for these models have displayed relatively acceptable consistency with experimental values. sigey et al. [18] 230 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. used launder and sharma k-ε model with the wall functions and considered the rayleigh number of the enclosure 1011 in their experiments. their model was found to optimally predict the flow inside the enclosure; and the values of velocity and temperature derived for all regions of the enclosure were highly consistent with the experimental values. ji [19] discussed the modelling of natural convection in air cavities using four turbulence models. regarding the cited studies, we set the aims of the present study. the results of resolving this question can be used in induced buoyancy flows, heat transfer of free convection, and designing and assessing different technical and engineering uses especially designing the systems of central heating and air conditioning. following the studies of these researchers, in the present paper we investigate turbulent natural convection flow in an enclosure with thermal sources using the low-reynolds number (lrn) k-ω model. the aim of this study is to predict the effect of change in rayleigh number, repositioning of cold and hot sources and thermal sources aspect ratio on the flow field, temperature, and rate of heat transfer that have been seen less in previous studies. the geometry of this paper is an enclosure that has a cold source with temperature tc and a hot source with temperature th as thermal sources that are placed on the left wall of enclosure, the other walls are adiabatic. subsequently, to achieve the desired results, the rayleigh number varies between 109-1011. 2. model and simulation 2.1 mathematical model fig. 1: the geometry of problem. in the present study, natural convection flow is studied in a 2d enclosure seen in fig. 1. the temperatures of the cold and hot sources are tc and th, respectively, and other parts are assumed insulated. the aim of this study is to predict the effect of change in rayleigh number, repositioning of cold and hot sources, and heating sources aspect ratio on the basic parameters of flow and temperature. therefore, first, the flow field and fluid temperature in the enclosure are determined using a numerical solution, and then the nusselt number, mean velocity, and temperature are calculated in different sections of the enclosure. to achieve this purpose, turbulent flow in the 2d enclosure is examined. the numerical solution of the question is conducted using a simple algorithm and the computer program is written using fortran language. henkes et al. [20] studied the concepts of the critical rayleigh number of enclosures' layers using natural convection flow. the critical rayleigh number was derived around 1011 for upper reynolds models and approximately 109 for lower ones. if the rayleigh number is less than 108, the flow is laminar, if the rayleigh number is bigger than 1010, the flow is turbulent, and if the rayleigh number is 108-1010, the flow is transient [8, 21]. therefore, the rayleigh number in the question of interest is 109-1011 and therefore convection flow in the enclosure is 231 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. transient. given the operating conditions of the enclosure, the indoor flow can be laminar or turbulent. this study investigates turbulent flow. 2.1.1 the equations of natural convection flow in the enclosure turbulent flow field in an enclosure is derived by continuity, momentum, and energy equations. to include buoyancy effects, a boussinesq approximation was used. air density, except for buoyancy sentence, is constant and is calculated according to the gases law, and its effects were included in the momentum equation. the enclosure's air was assumed to be incompressible and newtonian (pr=0.71), and dynamic viscosity was calculated through the sutherland formula. the equations governing continuity, momentum and energy can be expressed as follows [22]: 0)( j j u x (1) )t-()()( refiji j i jjj ji tguu x u xx p x uu (2) )-( )( i jjj jp tu x t k xx tuc (3) where u, p, and t represent velocity, pressure, and mean time temperature, respectively. in addition, there are number of high-ranking statements as tuuu iji , in reynolds averaging equations, namely, reynolds stress and turbulent heat transfer, respectively. we conducted turbulent modeling to use the equations of appropriate transfer in order to model these statements. 2.1.2 two-equation model k-ω there are different turbulence models to solve turbulent flow equations. here, a standard two-equation model k-ω was used in this study. in this model, in addition to a turbulence kinetic energy equation k, an additional differential model solves for energy dissipation. wilcox [23] extended low reynolds model k-ω to simulate a transient area as illustrated below. to describe the field and determine turbulence rate in a steady flow, the equations of kinetic energy and those of energy dissipation are generally as follows according to the above formulated hypotheses: (4) (5) (6) k jk t j kk j j s x k x p x ku )( )( s x k x p x u j t jj j )( )( k fct 232 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. (7) (8) constants used in this model are as follow [23]: (9) (10) in this model, three damping functions 1,, fff k are added to k-ω equations. these functions become small in low reynolds areas and tend to 1 in high reynolds areas. (11) 2.1.3 boundary conditions generally, boundary conditions to solve the equations are as follow: on the enclosure's walls: temperature boundary conditions consider constant on hot and cold surfaces: ht=t ct=t for adiabatic walls: 2.2 solution procedure the equations that have already been derived can be used to calculate temperature field and velocity parameters. to conduct calculations in this study, the finite volume is used to discretize the partial differential equations with structural grid [24,25]. a quick scheme is employed for the convection terms in the momentum equations and in the thermal energy equation. the convection term in the turbulence transport equations is discretized using the hybrid upwind-central scheme. to increase the accuracy of discretization, a second order van leer accuracy method is used [26]. in addition, it j i x u 2 ijtk sp j t t k s t gg 2 j x )( 2 1 i j j i ij u u u u s kfc kkk 2 2c kk gs k p k fcp 11 kgk cs 3 0.1c 09.0kc 92.11c 075.02c 0.03c 3.1 9.0t 0.2k 6 1 6 025.0 t t r r f 11 7.2 1 7.2 1.0 f r r f t t 4 4 ) 8 (1 ) 8 (278.0 t t k r r f krt 0kvu 0y2 2 6 yc 00yy t 0 t 0xx 233 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. demonstrates that without using damping function gk and using the combined method, the results will lead to solving the laminar flow in the enclosure. a simple algorithm is used for the mixed solution of velocity-pressure field, the iterative line-by-line tdma procedure and the strongly implicit procedure (sip) are used for the pressure correction equation [27]. to ensure achievement of a steady state, an appropriate under-relaxation technique is used. due to the use of a low reynolds number model to solve the velocity field, it requires a sufficient number of grid points to be in the near-wall boundary layer. special attention has thus been paid to the grid refinement, particularly for computing the buoyancy-driven enclosure flow. in fact, to achieve convergence in the solution equations in this problem, the first approximate grids to the wall should be placed in the near-wall region to resolve the wall-damping effect, this is not necessary for grids farther from the wall [28]. 2.3 grid study running the prepared computer code and considering the high accuracy of solutions, especially near the walls and fluid phase boundaries that cause serious change in some parameters, it is necessary to review the effect of varying the number of grid points on the flow parameters. to achieve this purpose, an enclosure with geometrical specs h=w, h1=h5=0.125h, h2=0.2h, h3=0.25h, and h4=0.3h (fig.1) was used and the rayleigh number was considered 1011 and pr=0.71. the average nusselt number of the hot source was determined according to different numbers of the grid points (table 1). as can be seen in table 1, the difference between the values obtained using the 100*100 grid and the 110*110 grid are very small and negligible. thus, a non-uniform grid of 110*110 is selected to run the program. table 1: average nusselt number of hot source according to the numbers of grid points (ra=1011) number of nodes average nusselt of the hot source surfaces 50*50 149.8120 60*60 161.1375 70*70 178.0820 80*80 184.7461 90*90 188.6720 100*100 194.5231 110*110 194.5301 2.4 validation to investigate the performance of the computer code in a 2d turbulent state, a comparison was made with two previous studies [5, 16]. in this study, a square enclosure was used with horizontal insulated walls and vertical walls with different temperatures. the cold wall was placed to the right and the hot wall was placed to the left. to solve the equation of turbulent convection flow, a low reynolds turbulent model k-ω was used. figures 2 and 3 illustrate the comparison between the results of this study and other studies in this regard. as observed, the obtained results are highly consistent with those of other studies. the difference is at most 1.65% for the average nusselt number and 1.87% for vertical velocity, which are negligible. to insure the performance of the present model, in another validation we compare the present model with other turbulence models carried 234 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. out by ji [19]. as we can see in fig. 4, the present model is in good agreement with the others in reference. as the results indicated, the present model is potent to simulate flow in the enclosure at the turbulent and transient stages. fig. 2: variations in the average nusselt number of heating sources with constant temperature according to changes in rayleigh number. fig. 3: variations in vertical velocity according to increase in distance from hot wall. 235 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. fig. 4: numerical comparison between the present model and the reference models [19]. 3. results and discussion 3.1 turbulent convection flow in 2d enclosure after the performance of the computer code was ensured and appropriate network selected, different runs were conducted at different states. all calculations for air were conducted with pr= 0.71 and constant geometry enclosure h=w. rayleigh number varied between 109 and 1011. in the following sections, the effects of change in rayleigh number, heat source position, and heating sources aspect ratio on the rate of heat transfer, isothermal lines, mean velocity in the enclosure, and the maximum values of velocity parameters were investigated. 3.1.1 the effect of rayleigh number in this section, we changed rayleigh number only. geometrical specs h=w, h1=h5=0.125h, h2=0.2h, h3=0.25h, and h4=0.3h were considered constant. we investigated the effects of changes in these conditions in any state and illustrated them. figure 5 indicates isothermal lines and streamlines in this state for different rayleigh numbers. as illustrated, in 2d turbulent flow inside the enclosure, there was a cold area at the bottom of the enclosure and a hot area at the top. with increasing rayleigh number from 109 to 1011, this condition intensified such that at rayleigh number 1011, we observed a cooling area besides the right vertical wall. in the area between cold and hot sources, we observed a large heating stress. further examination of temperature profiles demonstrated that as the rayleigh number increased, the flows of high and low temperatures between the heating sources mixed better, which caused a more uniform temperature profile at higher rayleigh numbers compared to lower ones. regarding the streamlines, as fig. 5 illustrates, in all states, there are numerous vortices in the enclosure. most large vortices form in the area close to hot and cold sources in the middle of the enclosure. besides the large vortices, we observed several small vortices in the corners of the enclosure that form due to the flow separation in the area near to the wall. next, we examined the effect of change in rayleigh number on the heat transfer rate in terms of mean and local nusselt numbers on the heating sources. figures 68 illustrate the heat transfer rate on hot and cold sources in terms of local and mean nusselt numbers. as observed, with increasing rayleigh number, local and mean nusselt numbers increased in the enclosure. this can be explained by increased velocity parameters due to strengthened buoyancy forces. it is noteworthy (fig. 8) that because the cold source was bigger than the hot source, its mean nusselt number that represented the heat transfer rate was lower. to make a more accurate comparison, the results are tabulated in table 2. in addition to the mean nusselt numbers of hot and cold sources, the maximum parameters of velocity and mean fluid velocity shown in table 2. table 2: comparison of temperature and flow parameters for different rayleigh numbers in turbulent flow. ra num,h num,c vmean umax vmax 109 50.907 -49.38 0.0148 0.106 0.225 5*109 98.615 -74.306 0.0273 0.101 0.227 1010 110.33 -84.96 0.0281 0.0901 0.230 5*1010 138.10 -107.95 0.0284 0.0894 0.231 1011 195.53 -120.65 0.0287 0.0883 0.234 236 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. fig. 5: isothermal lines (right) and streamlines (left) at different rayleigh numbers. fig. 6: the effect of changes in local nusselt number on hot source for different rayleigh numbers. 237 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. fig. 7: the effect of changes in the absolute local nusselt numbers on cold source for different rayleigh numbers. fig. 8: the mean nusselt number of heating sources according to changes in rayleigh number. as shown in table 2, with increasing rayleigh number, maximum horizontal velocity in the enclosure (umax) increased. due to increased rayleigh number, this finding is attributed to the acceleration of the fluid velocity in the area between the heating sources due to mixture of cold and hot fluid flows following increased rayleigh number that in turn causes increase in mean temperature in the enclosure. 3.1.2 positions of cold and hot sources take into consideration the enclosure illustrated in fig. 1. in this section, we changed the value of h4, the distance between the two sources. other geometrical specs h1=h5, h2=0.2h, h3=0.3h, and h4=0.3h were assumed constant. in addition, rayleigh number was considered 1011. in addition to repositioning cold and hot sources on a wall, we also placed the two sources on two opposite walls and then compared heat transfer rates in terms of nusselt number. fig.9 illustrates isothermal and stream lines in these states. as stream lines in this figure demonstrate, it was observed that the fluid movement was specified by cell flow in which the upward hot flow jet next to the hot source entered the downward cold source jet next to the cold source. the two flows mixed with each other in the distance between them and the hot flow transferred its heat to the cold flow.tracing the stream lines when both sources were placed on a single wall, multiple vortices filled 238 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. the entire enclosure. with decreasing distance between the heating sources, the number of vortices on the top of the enclosure increased. however, when the two heating sources were placed on two opposite walls, several big standing vortices were observed. as isothermal lines in fig. 9 illustrate, when the distance between the two sources decreases, hot air above hot source mixes well with cold air and so, the cold source and the cold air fails to penetrate the enclosure. as a result, a more uniform temperature dissemination occurred in the enclosure. when the two sources were placed on two opposite walls, hot air above the hot source does not mix well with cold air beside the cold source and the cold air could penetrate the enclosure such that low temperature fluid on the bottom of the enclosure assembled with the high temperature fluid on the top of the enclosure. therefore, the air temperature became less uniform compared to when the two heating sources were placed on a single wall. as illustrated in fig.10, the rate of heat transfer from cold source to hot source was estimated in terms of mean nusselt number. as fig.10 shows, with increasing distance between the sources, the rate of heat transfer from heating sources into the enclosure declined, but these changes were negligible possibly due to decreased velocity parameters in the enclosure. fig. 9: isothermal (right) and stream (left) lines in different positions of hot and cold sources (ra=1011). 239 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. according to fig. 11, with increasing distance between the sources, maximum horizontal velocity (umax) and maximum vertical velocity (vmax) in the enclosure decreased. this observation can be attributed to the movements of the fluid on the heating sources and the interaction of high temperature fluid with low temperature fluid in the distance between the heating sources. to make a more accurate comparison, the above results were tabulated in table 3. in addition, table 3 compares the heat transfer rate between hot and cold sources on two opposite walls. as it can be observed, when the heating sources were placed on two opposite walls, mean nusselt number increased dramatically, which can be attributed to the regular vortex movement of the fluid in which fluid neighboring the hot source went upward and fluid neighboring the cold source went downward in the enclosure. because the two heating sources were placed on two opposite walls, the two fluid flows reinforced each other, which led to increased mean velocity of fluid movement in the enclosure. with an increase in mean velocity in the enclosure, the heat transfer rate increased because of the fluid movement. fig. 10: changes in mean nusselt number of hot and cold sources according to changes in distance between heating sources (ra=1011). fig. 11: changes in maximum parameters of velocity in enclosure according to changes in distance between heating sources (ra=1011). table 3: comparison of heat and flow parameters for different rayleigh numbers in turbulent flow. 3.1.3 the effect of hot and cold sources aspect ratio assume an enclosure illustrated in fig. 1. in this section, the length of source is considered constant, h2=0.2h. by changing the length of the cold source, h4, we studied the effect of changes in the heating sources aspect ratio. other geometrical specs, h3=0.3h and h1=h5, were assumed constant and the rayleigh number was considered to be 1011. as stream lines in the graphs on the left side of fig. 12 illustrate, the fluid movement was determined by vortex flow in which the fluid moves upward in parallel with the hot surface and moves downward in parallel with the cold surface. with the change in cold positions of thermal sources num,h num,c vmean umax vmax placed on single wall h3=0.4h 193.08 -121.46 0.0271 0.0855 0.269 placed on single wall h3=0.2h 195.61 -124.78 0.0286 0.0915 0.245 placed on single wall h3=0.1h 196.98 -128.12 0.0963 0.125 0.209 placed on two opposite walls h3=0.2h 212.04 -161.77 0.2108 0.1716 0.281 240 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. and hot sources aspect ratio, no marked changes occurred in the stream lines. in all states, two large vortices were formed approximate to the heating sources and the central areas of the enclosure and multiple small vortices formed in the corners of the enclosure. as isothermal lines in the graphs on the right side of fig.12 illustrate, with an increase in the heating sources aspect ratio, no marked changes occurred in the isothermal lines. cold fluid that moved alongside gravity acceleration faced hot fluid that moved in the opposite direction of the gravity acceleration in the distance between the two sources such that in all states, a cold area is seen at the bottom, next to the cold source, a hot area is seen at the top, next to the hot source, and an area with uniform temperature profile in the wide central area of the enclosure. fig. 12: isothermal (right) and stream (left) lines in different aspect ratios of cold source to hot source (ra=1011). 241 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. fig. 13: changes in mean temperature according to heating sources aspect ratio (ra=1011). the studies of changes in heating sources aspect ratio on the heat transfer rate indicated that with an increase in the ratio of the length of the cold source to that of the hot source, the heat transfer rate underwent an increasing trend, which can be attributed to the increased parameters of flow in the enclosure. it was also demonstrated that with decreasing aspect ratio, the maximum velocity parameters umax and vmax in the enclosure decreased, which in turn caused a decrease in mean temperature in the enclosure. as illustrated in fig. 13, with increasing aspect ratio, mean dimensionless temperature in the enclosure decreased, which can be explained by the increased area of the cold source that causes a decrease in temperature in the enclosure. table 4: the comparison of heat transfer rate and flow parameters in different heating sources aspect ratio in turbulent flow. 4. conclusion based on the calculations carried out in this research, the numerical results allow a better understanding on the influence of heating source arrangement within a turbulent natural convection flow in an enclosure. the influence on fluid flow and heat transfer was identified for the different arrangement of the heating sources within the enclosure. some general conclusions are presented below. in constant positions of hot and cold sources on a wall, if the rayleigh number increased, the mean nusselt number of both heating sources, maximum flow function, and maximum velocity parameters increased. study of different positions of hot and cold sources with constant aspects and temperature difference indicated that the dimensionless heat transfer rate increased with a decrease in the distance between the hot and cold sources on a single wall. if the two sources were placed on two opposite walls, a dramatic increase occurred in mean nusselt number and mean temperature in the enclosure. however, because the distribution of the temperature profile is not uniform, the optimal position of the hot and cold sources is on a single wall with short distance. sources aspect ratio ah× hm, nu ac× cm, nu meanv maxu maxv h4/h2=2 42.21 -42.44 0.0314 0.205 0.298 h4/h2=1.5 38.74 -38.33 0.0296 0.165 0.278 h4/h2=1 35.56 -36.15 0.0214 0.0105 0.248 h4/h2=0.5 27.14 -28.11 0.019 0.0951 0.199 242 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. study of different heating sources aspects ratio with constant temperature difference and distance indicated that with an increase in sources aspect, the dimensionless heat transfer rate increased and mean temperature in the enclosure decreased. references [1] kadem s, lachemet a,younsi r, kocaefe d. (2011). 3d-transient modeling of heat and mass transfer during heat treatment of wood. international communications in heat and mass transfer, 38(6): 717-722. [2] laguerre o, benamara s, remy d, flick d. (2009). experimental and numerical study of heat and moisture transfers by natural convection in a cavity filled with solid obstacles. international journal of heat and mass transfer, 52(25-26): 5691-5700. [3] calcagni b, marsili f, paroncini m. (2005). natural convective heat transfer in square enclosures heated from below. applied thermal engineering, 25(16): 2522-2531. [4] tian ys, karayiannis tg. (2000). low turbulence natural convection in an air filled square cavity part ii: the turbulence quantities. international journal of heat and mass transfer, 43(6): 867-884. [5] ampofo f, karayiannis tg. (2003). experimental benchmark data for turbulent natural convection in an air filled square cavity. international journal of heat and mass transfer, 46(19): 3551-3572. [6] dafa alla aa, betts pl. (1996). experimental study of turbulent natural convection in a tall air cavity. experimental heat transfer, 9(2): 165-194. [7] penot f, skurtys o, saury d. (2010). preliminary experiments on the control of natural convection in differentially-heated cavities. international journal of thermal sciences, 49(10): 1911-1919. [8] chen w, liu w. (2004). numerical and experimental analysis of convection heat transfer in passive solar heating room with greenhouse and heat storage. solar energy, 76(5):623-633. [9] saury d, rouger n, djanna f, penot f. (2011). natural convection in an air-filled cavity: experimental results at large rayleigh numbers. international communications in heat and mass transfer, 38(6): 679-687. [10] barakos e, mitsoulis g, assimacopoulos d. (1994). natural-convection flow in a square cavity revisitedlaminar and turbulent models with wall functions. international journal for numerical methods in fluids, 18(7): 695-719. [11] elder jw. (1965). turbulent free convection in a vertical slot. j. fluid mechanics, 23(1): 99111. [12] giel pw, schmidt w. (1986). experiment study of high rayleigh number natural convection in an enclosure. 8th international heat transfer conference, 4: 1459-1464. [13] cheesewright r. (1968). turbulent natural convection from a vertical plane surface. j. heat transfer, 90(1): 1-6. [14] olsen da, glicksman lr, ferm hm. (1990). steady state natural convection in an empty and partitioned enclosure at high rayleigh numbers. j. heat transfer, 112(3): 640-647. [15] chen q. (1996). prediction of room air motion by reynolds-stress models. building and environment, 31: 233-244. [16] ince nz, launder be. (1989). on the computation of buoyancy-driven turbulent flows in rectangular enclosures. international journal of heat and fluid flow, 10(2): 110-117. [17] hanjealic k, vasc e. (1993). computation of turbulent natural convection in rectangular enclosure with algebraic flux model. interntional journal of heat and mass transfer, 36(14): 3603-3624. [18] sigey jk, gatheri fk, kinyanjui m. (2004). numerical study of free convection turbulent heat transfer in an enclosure. energy conversion and management, 45(15-16): 2571-2582. [19] ji y. (2014). cfd modelling of natural convection in air cavities. cfd letters, 6(1): 1531. 243 iium engineering journal, vol. 20, no. 1, 2019 ahamdi et al. [20] henkes rawm, van der vlugt ff, hoogendoom ff. (1991). natural convection flow in a square cavity calculated with low-reynolds-number turbulence models. international journal of heat and mass transfer, 34(2): 377-388. [21] penot f, skurtys o, saury d. (2010). preliminary experiments on the control of natural convection in differentially-heated cavities. international journal of thermal sciences, 49(10): 1911-1919. [22] versteeg hk, malalasekera w. (2007). an introduction to computational fluid dynamics. the finite volume method approach, pearson education limited, usa, 2th ed. [23] [23] wilcox dc. (1994). simulation of transition with a two-equation turbulence model. aiaa journal, 32(2): 247-255. [24] davidson l, farhanieh b. (1991). calc-bfc: a finite-volume code employing collocated variable arrangement and cartesian velocity components for computation of fluid flow and heat transfer in complex three-dimensional geometries. report 92/4, department of thermo and fluid dynamics, chalmers university of technology, gothenburg, sweden. [25] ahmadi m. (2017). natural convective heat transfer in a porous medium within a two dimension enclosure. iium engineer journal, 18(2): 196–211. [26] van leer b. (1974). towards the ultimate conservative difference scheme: monotonicity and conservation combined in a second order scheme. journal of computational physics, 14(4): 361-370. [27] ahmadi m, khosravi farsani a. (2018). cfd simulation of non-newtonian two-phase fluid flow through a channel with a cavity. thermal science, online first. doi:10.2298/tsci180102151a [28] hoffmann ka, chiang st. (1993). computational fluid dynamics for engineers. engineering education system, wichita, usa. nomenclature w width of the enclosure in x-direction m h height of the enclosure in y-direction m t temperature °c th hot temperature °c tc cold temperature °c p pressure pa x, y cartésien coordinats u, v cartesian velocities m.s-1 cp specific heat capacity at constant pressure j/kg.k k turbulent kinetic energy g acceleration of gravity m/s² i) greek symbols kinematic viscosity m².s-1 density kg/m3 ω specific dissipation rate of k μ dynamic viscosity pa.s fluid thermal diffusivity m².s-1 ii) dimensionless numbers ra rayleigh number, (= g β (th-tc) h3 / α) nu local nusselt number, (= hconv h/k) num average nusselt number, )( danu pr prandtl number, (= /α) 244 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <feff04180437043f043e043b043704320430043904420435002004420435043704380020043d0430044104420440043e0439043a0438002c00200437043000200434043000200441044a0437043404300432043004420435002000410064006f00620065002000500044004600200434043e043a0443043c0435043d04420438002c0020043f043e04340445043e0434044f044904380020043704300020043d04300434043504360434043d043e00200440043004370433043b0435043604340430043d0435002004380020043f04350447043004420430043d04350020043d04300020043104380437043d0435044100200434043e043a0443043c0435043d04420438002e00200421044a04370434043004340435043d043804420435002000500044004600200434043e043a0443043c0435043d044204380020043c043e0433043004420020043404300020044104350020043e0442043204300440044f0442002004410020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e0030002004380020043f043e002d043d043e043204380020043204350440044104380438002e> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <feff005500740069006c0069006300650020006500730074006100200063006f006e0066006900670075007200610063006900f3006e0020007000610072006100200063007200650061007200200064006f00630075006d0065006e0074006f0073002000640065002000410064006f00620065002000500044004600200061006400650063007500610064006f007300200070006100720061002000760069007300750061006c0069007a00610063006900f3006e0020006500200069006d0070007200650073006900f3006e00200064006500200063006f006e006600690061006e007a006100200064006500200064006f00630075006d0065006e0074006f007300200063006f006d00650072006300690061006c00650073002e002000530065002000700075006500640065006e00200061006200720069007200200064006f00630075006d0065006e0074006f00730020005000440046002000630072006500610064006f007300200063006f006e0020004100630072006f006200610074002c002000410064006f00620065002000520065006100640065007200200036002e003000200079002000760065007200730069006f006e0065007300200070006f00730074006500720069006f007200650073002e> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <feff004200720075006b00200064006900730073006500200069006e006e007300740069006c006c0069006e00670065006e0065002000740069006c002000e50020006f0070007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740065007200200073006f006d002000650072002000650067006e0065007400200066006f00720020007000e5006c006900740065006c006900670020007600690073006e0069006e00670020006f00670020007500740073006b007200690066007400200061007600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020005000440046002d0064006f006b0075006d0065006e00740065006e00650020006b0061006e002000e50070006e00650073002000690020004100630072006f00620061007400200065006c006c00650072002000410064006f00620065002000520065006100640065007200200036002e003000200065006c006c00650072002e> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 215-820-2-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology haziyamin and ezureen 133 isolation of lactic acid bacteria from malaysian non-broiler chicken (gallus gallus) intestine with potential probiotic for broiler feeding tengku haziyamin tengku abdul hamid and ezureen ezani department of biotechnology, kulliyyah of science, international islamic university malaysia, kuantan campus, jalan istana, bandar indera mahkota, 25200, kuantan, pahang, malaysia. haziyamin@iium.edu.my abstract: probiotic supplement can function as substitute for antibiotics especially in the broiler chicken feeding which can form an integral part of organic farming. broiler forms one of an important protein source in south east asia. lactic acid bacteria (lab) are important inhabitants of animal intestine and are useful source of probiotic microorganisms. non-broiler chicken could be an ideal source of probiotic microorganisms that can be utilized for large scale broiler feeding. our studies have successfully identified, through morphological and biochemical tests, 11 lab isolates from gastrointestinal tract of local non-broiler chicken (gallus gallus). these isolates have the ability to utilize lactose as part of their metabolism process and all showed negative reactions on catalase test. out of the eleven (11) isolates, three (3) isolates were gram-positive cocci and remaining isolates were of gram-positive bacilli. three isolates (e4, e11 and e17) showed at least 10 mm inhibitory effects on disc diffusion test against pathogenic bacteria salmonella typhimurium. the partial 16s rrna gene sequencing showed that one isolate (e17) has 89% similarity with lactobacillus rhamnosus. these lab strains isolated from malaysian domestic non-broiler chicken gastrointestinal tract can potentially be used as a component for probiotics formulation in poultry feeding. abstrak: makanan tambahan probiotik boleh berfungsi sebagai pengganti antibiotik terutamanya dalam pemakanan ayam pedaging yang akan membentuk bahagian kamiran dalam penternakan organik. ayam pedaging merupakan sumber protein penting di asia tenggara. bakteria asid laktik (lactic acid bacteria (lab)) merupakan penghuni penting dalam usus haiwan dan merupakan sumber penting dalam mikroorganisma probiotik. ayam bukan pedaging sesuai dijadikan sumber mikroorganisma probiotik agar dapat digunakan sebagai pemakanan ayam pedaging secara besar-besaran. kajian telah berjaya mengenal pasti, melalui kaedah morfologi dan uji kaji biokimia, 11 lab diasingkan daripada salur gastrousus ayam bukan pedaging (gallus gallus). pencilan ini berupaya menggunakan laktosa sebagai sebahagian daripada proses metabolisma dan semuanya menunjukkan kesan negatif terhadap ujian katalase. daripada sebelas (11) pencilan, tiga (3) pencilan adalah kokus gram-positif dan pencilan yang lainnya adalah basilus grampositif. tiga pencilan (e4, e11 dan e17) menunjukkan sekurang-kurangnya 10 mm kesan rencatan terhadap ujian resapan cakera terhadap bakteria patogen salmonella typhimurium. sebahagian daripada urutan gen 16s rrha menunjukkan bahawa satu pencilan (e17) mempunyai 89% persamaan dengan lactobacillus rhamnosus. strain lab ini diasingkan daripada salur gastrousus ayam tempatan bukan pedaging, sesuai digunakan sebagai komponen untuk rumusan probiotik dalam pemakanan ayam-itik. keywords: lactic acid bacteria; probiotic; non-broiler chicken; lactobaccilus rhamnosus iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology haziyamin and ezureen 134 1. introduction the variable use of probiotics as a daily supplement has become a popular routine in commercial poultry feeding, particularly following antibiotic treatment. lactic acid bacteria or labs are the most common microbes employed as probiotics and these strains are usually of lactobacillus sp, bifidobacterium sp and enterococcus sp [1]. two principal kinds of probiotic bacteria, the members of the genera lactobacillus and bifidobacterium, have been studied in detail [2]. these are gram-positive lactic acidproducing bacteria that constitute a major part of the normal intestinal microflora in animals and humans. these friendly bacteria play key role in enhancing the resistance to colonization by potentially pathogenic organisms in the gut. bacterial food-borne diseases in chicken are the major problem affecting the productivity in poultry industry. commonly, the control of this disease is based on the administration of antibiotics. meanwhile, the use of antibiotic as growth promoter is so extensive in poultry and pig industries [3,4]. however, such treatment could develop resistant bacteria [5,6] and result in antibiotic residues leftover in chicken which is a potential hazard to public health. furthermore, the normal microflora which is beneficial to chicken may also be killed or inhibited due to the administration of antibiotics [7] and a new approach of using probiotic is gaining acceptance [8]. in the recent years, there are great interests in the use of probiotic in poultry feeding to improve disease resistance and growth performance. probiotic bacteria competed with the pathogen for nutrient, stimulated the immune system [7] and showed good colonizing and antagonistic properties against the pathogens [9]. however, the proper probiotic supplements are relatively expensive, and different studies have used different plethora of lab species and strains. in some countries, successful probiotic supplement could be subjected to trade secret and consequently, commercially available probiotics formulation may not contain the most appropriate strains or doses. as a result, the extensive use of probiotic is not quantitative and economically ineffective at the larger scale. due to the lab diversity and poorly understood interactions between the microbes and intestine, determining the correct types and quantity of probiotics are the biggest challenge [10]. non-broiler chicken could be a good source of probiotic for broiler feeding. malaysian non-broiler chicken referred as ‘ayam kampung’ is usually fed with household foods, and these are usually free of antibiotic. in this work, lab strains from the intestinal tissue of non-broiler chickens were screened and characterized. it is hope that the isolated lab can potentially be used as supplement to the young or growing broiler. 2. materials and methods a selected non-broiler chicken was slaughtered and it intestinal tissues was dissected and collected. the intestinal tissue was cut and suspended into 5 ml phosphate buffered saline pbs buffer and briefly vortexed. the tissue was grinded until homogenised and the solution kept as a stock. this was serially diluted in pbs and each dilution was plated on mrs agar followed by incubation at 37 °c overnight, anaerobically. mrs broth and media contained 1.0 % peptone, 0.8% meat extracxt, 0.4 yeast extract, 2.0% glucoase, 0.5 % sodium acetate, 0.1 % tween 80, 0.2 % dipotassium hydrogen phosphate, 0.2 % triammonium citrate, 0.02 % magnesium sulfate and 0.005 % manganese sulfate. single colonies were sub-cultured and kept in 80 %v/v glycerol and stored at -80°c for future identification processes. gram staining, lactose utilization test, catalase tests were carried iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology haziyamin and ezureen 135 out on the selected colonies. in lactose utilization test, lactose and few drops of bromocresol purple was added into nutrient agar (na). genomic dnas were extracted from 11 isolated lactic acid bacteria strain. dna was extracted using method as outlined in the protocol on dneasy® blood and tissue extraction kit (qiagen). the 16s ribosomal gene was amplified by pcr using the universal primers pa forward (5’-agagtttgatcctggctcag-3’) and pe reverse (5’ccgtcaattcctttgagttt-3’). the pcr products were then loaded in 1.0 % agarose gel for electrophoresis and visualized on under uv transilluminator. for detection of antimicrobial activity, a disc diffusion method was used. sterile filter discs (12 mm) were dipped into the culture broth (mrs broth) of lactic acid bacteria, incubated for 42 hours and placed on solidified nutrient agar na (oxoid) which was seeded with 12 to 14 hours cultures of salmonella typhimurium (pathogenic bacteria). the plates were stored at 4 °c for 3 to 4 hours to permit diffusion, and finally incubated at 37 °c for 14 to 16 hours. disc dipped in uninoculated mrs broth was served as control. zones of inhibition observed were then measured [11, 12]. disk impregnated in 0.4 mg/ml streptomycin was taken as control. 3. results and discussion all isolates appeared positive in lactose utilisation test. these bacteria were able to ferment lactose to produce lactic acid that lowers the ph of the media that, in turn, changed the purple indicator dye to yellow indicative of fermentation activities (fig. 1a). gram reaction and morphology studies showed that out of eleven (11) isolates, three (3) isolates were gram-positive bacilli and eight (8) isolates were gram-positive cocci (table 1 and fig. 1b). in the antimicrobial test, all eleven (11) isolates produced antimicrobial compound that were active against pathogenic bacteria salmonella typhimurium strains. this was indicated by the formation of clear inhibitory zones near the diffusion spots (fig. 2). as also shown in table 1, sample e4, e11 and e17 produced more that 10 mm (12-15 mm) diameter zones of inhibition; while all other samples produced less than 10 mm zone of inhibitions. several factors could cause these inhibitions. other than the production of organic acid, the antagonistic activity of lab towards pathogens was also due to the production of bactericidal substances like bacteriocins [1]. 1a 1b fig. 1: a) lactic acid bacteria changed the agar from purple to yellow indicative for lactic acid fermentation and formation of lactate; b) morphology and gram staining of isolate 17 showing gram positive coccobacilli (oil immersion, 1000x magnification). iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology haziyamin and ezureen 136 table 1: biochemical and morphological test for isolates from chicken intestine. isolates gram reaction shape catalase lactose zone of inhibition* e2 + cocci + + e4 + cocci + ++ e10 + bacilli + + e11 + cocci + ++ e12 + cocci + + e14 + cocci + + e15 + cocci + + e17 + bacilli + ++ e18 + cocci + + e19 + cocci + + e24 + bacilli + + *using salmonella thyphimurium as indicator + < less than 10 mm ++> more than 10 mm fig. 2: lactic acid bacteria against salmonella typhimurium strains in disk diffusion method. zone of inhibitions form surrounding the disk impregnated with sample lab cultures e4, e11, e24 and e17. as shown in table 2, the result ribosomal rrna sequence from one of the sample (isolate e17) produced 1.5 kb fragment (fig. 3). the sequence indicated 89 % similarity to lactobacillus rhamnosus gg (atcc 53103) (table 2). the other closely similar sequences were lactobacillus plantarum followed by other common lab, lactobacillus casei and others. lactobacillus rhamnosus gg was isolated from healthy human intestinal tract. this strain has however, established clinical health effects to human that prevents urogenital tract infection from pathogens, human diarrhea [13-15] and respiratory infections risk in children zone of inhibition control e11 e17 e4 e iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology haziyamin and ezureen 137 [16]. it was shown that a strong antimicrobial activity of lactobacillus rhamnosus gg against salmonella typhimurium is due to the accumulation of lactic acid produced [17]. the usefulness of lactobacillus rhamnosus strain in formulating probiotic feeding was previously suggested [1]. fig. 3: the polymerase chain reaction amplification of ribosomal rna gene using rrna universal primer . lane m in 1 kb ladder (fermentas). lane number 1 to 9 correspond to genomic sample from the 9 of the isolates, of which lane 9 is for isolate e17. table 2: the ncbi blast hit list for rrna sequence from sample e17 isolate. strain from ncbi databse reference score e-value lactobacillus rhamnosus gg nc 013198.1 477 1e-133 lactobacillus plantarum nz acgz01000098.1 473 2e-132 lactobacillus plantarum jdm1 nc 012984.1 473 2e-132 lactobacillus plantarum wcfs1 nc 004567.1 472 6e-132 lactobacillus rhamnosus lms2-1 nz aciz01000148.1 472 6e-132 lactobacillus rhamnosus hn001 nz abwjo1000068.1 472 6e-132 lactobacillus rhamnosus lc705 nc 013199.1 472 6e-132 lactobacillus casei bl23 nc 010999.1 472 6e-132 lactobacillus casei atcc334 nc 008526.1 472 6e-132 lactobacillus salivarius atcc 11741 nc 007929 459 5e-128 lactococcus lactis kf 147 nc 013656.1 361 1e-98 4. conclusion in this work, we have successfully isolated lactic acid bacteria (lab) strain from the gastrointestinal tract of malaysian domestic non-broiler chicken. this isolated bacteria demonstrated common probiotic properties. out of 25 isolates, 11 isolates have the ability to utilize lactose as part of their metabolism process, all showed negative reactions towards 1.5 kbp sample e17 m 1 2 3 4 5 6 7 8 iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology haziyamin and ezureen 138 catalase test and active against pathogenic bacteria salmonella typhimurium. three out of the 11 isolates were gram-positive cocci and remaining 8 isolates were gram-positive bacilli. based on ribosomal rna sequencing, one of the isolated bacilli have 89% similarity to lactobacillus rhamnosus. while this strain was established it uses as probiotic in yogurt and dairy product, it was also shown to be pathogenic in some other circumstances. from this study, the isolated strains could potentially be used as probiotics in poultry feeding formulation. acknowledgement the authors wish to thank international islamic university malaysia for financial assistance in this work (iium endownment fund, edw b0905-282). references [1] karimi torshizi m. a., rahimi sh., mojgani n., esmaeilkhanian s. and grimes j. l.. screening of indigenous strains of lactic acid bacteria for development of a probiotic for poultry. asian–aust. j. anim. sc. 2008 21(10); 1495 – 1500 [2] tannock, g. (2005). probiotics and prebiotics: where are we going? norfolk, uk: caister academic press. [3] celik k, okan f, and denli m. effect of dietary probiotic, organic acid and antibiotic supplementation to diet on broiler performance and carcass yield. 2003. pak. j. nutr., 2(2): 8991 [4] charles, ow and duke, s. the response of laying hens to dietary fermentation products and probiotic-antibiotic combinations. poultry sci. 57: 1125 [5] langhout p (2000). new additives for broiler chickens, 1978. feed mix. 18(6); 24-27 [6] stavric s., b. buchanan, and t.m. gleeson. intestinal colonization of young chicks with escherichia coli o157:h7 and other verotoxin-producing serotypes. 1993. j. appl. bacteriol. 74:557–563. [7] edelman s., b. westerlund-wikstrom, s. leskela, h. kettunen, n. rautonen, j. apajalahti, and t. k. korhonen. (2002). in vitro adhesion specifity of indigenous lactobacilli within the avian intestinal tract 2001. appl. environ. microbiol. 68:5155–5159. [8] reid, g.. the scientific basis for probiotic strains of lactobacillus. 1999. appl. environ. microbiol. 65:3763–3766. [9] aswathy, r. g., ismail b., john r. p., nampoothiri k. m. evaluation of the probiotic characteristics of newly isolated lactic acid bacteria. 2008. appl biochem biotechnol. 151:244-55. [10] britt, r. r.. bacteria vs. bacteria: the new fight against salmonella. retrieved on august 27, 2009, from http://www.livescience.com/health/060317_good_bacteria.html. [11] apella, m.c., gonzalez, s.n., nader de macias, m.e., romero, n. & oliver, g. . in vitro studies on the inhibition of the growth of shigella sonnei by lactobacillus casei and lactobacillus acidophilus. 1992. j. appl. bacteriol., 73, 480-483. [12] hamadan, j. & mikolajcik, e.m. acidolin: an antibiotic produced by lactobacillus acidophilus. 1974. j. antibiot., 27, 631-636. [13] canaani, r. b.; cirillo, p., terrin, g., cesarano, l., spagnuolo, m. i., de vincenzo, a., albano, f., passariello, a., de marco, g., manguso, f., guarino, a. probiotics for treatment of accute diarrhoea in children: randomised clinical trial of five different preparations. 2007. brit. med. j. 335 (7615): 340. [14] österlund, p., ruotsalainen, t., korpela, r., saxelin, m., ollus, a., valta, p., kouri, m., elomaa, i., joensuu, h.. lactobacillus supplementation for diarrhoea related to chemotherapy of colorectal cancer: a randomised study. 2007. brit. j. cancer. 97 (8): 1028-34. [15] guandalini, pensabene, l., zikri, m. a., dias, j. a., casali, l. g., hoekstra, h., kolacek, s., massar, k., micetic-turk, d., papadopoulou, a., de sousa, j. s., sandhu, b., szajewska, h., iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology haziyamin and ezureen 139 weizman, z. lactobacillus gg administered in oral rehydration solution to children with acute diarrhea: a multicenter european trial. 2000. j. pediatr. gastroenterol. nutr. 30 (1): 5460. [16] hatakka, savilahti, e., pönkä, a., meurman, j. h., poussa, t., näse, l., saxelin, m., korpela, r. effect of long term consumption of probiotic milk on infections in children attending day care centres: double blind, randomised trial. 2001. brit. med. j. 22 (7238): 1327. [17] sigrid c.j. de keersmaecker, tine l.a. verhoeven, jos desair, kathleen marchal, jos vanderleyden, and istván nagy. strong antimicrobial activity of lactobacillus rhamnosus gg against salmonella typhimurium is due to accumulation of lactic acid. 2006. microbiol. lett. 256 (1): 89-96 iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 137 influence of die angles on the microhardness of aluminum alloy processed by equal channel angular pressing ali a. aljobouri1 and nurulakmal mod. sharif2 1faculty of arts and sciences, alabiar branch, univ. of garyounis, benghazi, libya. 2school of materials and mineral resources engineering usm, 14300, nibong tebal, penang, malaysia. abstract: the die geometry has a massive effect on the plastic deformation behavior during pressing of material processed by equal channel angular pressing (ecap) method; subsequently the properties of the processed material are strongly dependent on the die design. two categories of designed and manufactured dies are used for equal channel angular pressing, a 1200 sharp angle ( ψ = 00) and a 900 round–cornered ( ψ = 20 0) dies. this produce strain per pass through both dies of ~0.7 and ~1.05 respectively. the microhardness is developed in al-si alloy during ecap using route bc. the microhardness is increased by a factor of >1.5 after only 1 pressing for both dies. the microhardness increases slightly up to 8 passes, to increase by a factor of ~2.6 through the 1200 sharp angle die, while it is increased by a factor of ~3 after 8 passes by using the 900 roundcornered die, compared to the microhardness of the cast workpiece. in addition, the microhardness values are essentially identical across each eca pressed workpiece on both x and y planes. keywords: ecap, al alloy, microhardness, mmicrostructure 1. introduction severe plastic deformation methods have been the subject of intensive investigations in recent years [1]. extremely high amount of deformation can be introduced by several different ways such as compressed torsion [2], cyclic extrusion compression [3], high pressure torsion (hpt) [4], accumulative rolling banding process (arb)[5], and equal channel angular pressing(ecap) [6,7]. the latter process, which is invented by segal et al. [8], is one of the most promising and interesting ways due to its capability of producing large, fully dense samples containing ultrafine (or nanometer scale) grain size of various metals and their alloys by repeating the process while maintaining the original cross section of the workpiece. deformation in ecap occurs at the shear plane, which is lying at the intersection of the two equal cross-sectional channels of the die, as shown in fig. 1, where φ is the internal angle between the two intersecting channels, and ψ is the angle defining the outer arc of curvature at the point of intersection of the two channels [9]. iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 138 fig. 1: angles for equal channel angular pressing and ecaped workpiece. as the material crosses the intersection of the channel, it experiences a shear deformation that induces a shear strain. subsequently, the strain ε , after one cycle is ε =                   ψ+ φ ψ+      ψ+ φ 3 22 cos 22 cot2 ec ………………………………… (1) since in each passage through the die the same strain is accumulated, the following equation represents a more general relationship allowing one to calculate the strain value of the workpiece during ecap for an n number of passes. ε n= n                   ψ+ φ ψ+      ψ+ φ 3 22 cos 22 cot2 ec …………………………. (2) according to equation (2), the magnitude of the equivalent strain depends upon the values of φ and ψ angles, where it decreases with the increase of both angles. the equivalent strain during ecap can decrease from the maximum of 1.15 at minimum value of ψ =00, to the minimum of 0.907 at the maximum value of ψ =900, when the channel angle is fixed as φ =900. nakashima and co-workers [10] processed high purity aluminum (99.99%) at room temperature using route bc, with the ψ angle fixed to 20 0, and with internal channels angles ( φ ) of 900, 112.50, 1350 and 157.50, producing a strain of 1.05, 0.71, 0.47 and 0.23 per pass, respectively. therefore, the channel angle φ has more influence on the strain generated during ecap than the die corner angle ψ [11-13]. iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 139 since the material emerges from the die without any change in the cross sectional area, it is possible to rotate the workpiece around its longitudinal axis between consecutive passes, creating different ecap routes. it is possible to define four distinct processing routes a, ba, bc and c, which are classified by how the workpiece is rotated with respect to the die for each subsequent pass. route a: in this route the workpiece is not rotated between consecutive pressings. route b: routes ba and bc where the subsequent rotations are made in the sequence of (900, 00, 900, 00) or ( ± 900) and (900, 1800, 2700, 3600) or (+900), respectively. in other words, in route b the workpiece is rotated by 900 between each pressing, where route ba denotes rotations in alternate directions between each two consecutive pressing, and route bc denotes rotations in the same direction between each two consecutive pressing. route c: denotes a rotation of 1800 between each two consecutive pressing. table 1 summarizes these four fundamental ecap routes. most researchers have reported that route bc leads to an enhanced rate of grain refinement and a more isotropic equiaxed submicron grain structure, compared to other deformation routes with a 900 die angle [14-16]. table 1: rotation angles and directions for four fundamental processing routes [17]. number of pressings route 1 2 3 4 5 6 7 8 a 0° 0° 0˚ 0˚ 0˚ 0˚ 0˚ 0˚ ba 0° +90° 90° +90° 90° +90° 90° +90° bc 0° +90° +90° +90° +90° +90° +90° +90° c 0° 180° 180° 180° 180° 180° 180° 180° ecap can be used to produce large amounts of porosity free and impurity free bulk of ultrafine grained (ufg) materials with high-angle grain boundaries (hagbs) [18]. the hardness of a material is generally related to the grain size through a hall-petch equation [19] of the form hν =h0 + khd 2 1− ………………………………………………………... (3) iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 140 where h0 and kh are appropriate constants associated with the hardness measurements. this equation established that the hardness or the strength of the material increases with decreasing grain size. in the present study, ecap with different die angles was used to achieve two objectives. first, to investigate the feasibility of obtaining ultrafine grain sizes of al-si alloy through the use of ecap technique at room temperature. second, to achieve significant increasing in microhardness properties of eca pressed al-si alloy at room temperature. 2. methods and experiments x-ray fluorescence (xrf) equipment was used to determine the chemical composition of the material. the material used in this study was identify as an aluminum alloy containing 98 wt. % al, 1.3 wt. % si, 0.3 wt. % mg, 0.18 wt. % fe, 0.023 wt.% cu, 0.019 wt. % mn, 0.017 wt. % zn, 0.014 wt. % ga, and 0.011 wt. % ti. the material was subjected to severe plastic deformation using ecap at room temperature in order to investigate the effect of ecap on the microhardness properties of this alloy. each of the ecap dies designed for this study consisted of two blocks of skd 11 tool steel, bolted together to give a die with two channels having an equal circular cross-section with the diameter of 10 mm. the two channels of the two dies intersected at the angles ( φ ) of 1200, with ( ψ ) of 00 and ( φ ) of 900, with ( ψ ) of 200. workpieces were prepared by melting al-si alloy billets and cast into a circular sand molds (φ 15 mm x 150 mm).the cast ingots were machined by lathe machine with cooling oil to overcome the machining effect. the machined rods with dimensions of (φ 10 mm x 50 mm) became suitable for pressing by ecap facility. prior to ecap, the surface of the workpieces was polished using sic abrasive papers with grades 100, 230, 400, 600, 800, 1000 and 1200 to reduce the friction between the workpiece and the die wall. universal testing machine (utm) was used to press the workpiece through the dies. the workpiece enters the die through a vertical channel, passes through the shearing plane at the point of intersection of the two parts of the channel, and then emerges from the die through the horizontal or exit channel. route bc is selected in this experiment by rotating the workpiece 900 in the same sense around its longitudinal axis between each two consecutive passing for the end of producing an equiaxed grain structure with high angle grain boundaries. many researchers used this route to create a homogeneous ultrafine grained aluminum alloy [20, 21]. grease was used as a lubricant in the extrusion for more friction reduction. the model of the scanning electron microscope (sem) used in this study was supra 35vp field emission (fe-sem). the average grain and subgrain sizes was taken from measurements made directly from the sem photomicrographs using the linear intercept method (at least 5 different places on a sample were measured). iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 141 following ecap process, the workpieces were sliced from an x-plane (perpendicular to the longitudinal axis of the pressed workpiece) and a y-plane (the side-viewed plane parallel to the longitudinal axis of the workpiece) to a thickness of 2 mm from the middle section of the workpieces after each pass, using a diamond cutter with oil as lubricant. the sectioned samples were cold-mounted using epoxy resin and then they were polished to become suitable for the scanning electron microscope (sem) as well as for microhardness measurements. 3. results and discussion one of the most important indications of mechanical properties improvement is a microhardness measurement. the microhardness values for the present study were determined using a microhardness tester with pyramidal indenter, and were taken by applying a load of 300 g for 8 seconds on the x and y-planes samples. the spacing between points both in x and y-planes was 0.9mm as shown in fig. 2. twelve separate measurements were taken at a diametric line from the bottom to the top on each workpiece. the vickers microhardness value was determined by taking the average of the twelve measurements on the workpiece. (a) (b) fig. 2: sketch of pyramidal vickers indentations on (a) x-plane, (b) y-plane. the microhardness on the x-plane and the y-plane had the same tendency to increase with the number of passes. the microhardness was increased by a factor of >1.5 due to the highly deformed state, after one pass through the die with φ =1200 and ψ =00, as clearly shown by comparing the indentations sizes in fig. 3 and fig. 4. figure 4 also shows that the microstructure of al-si alloy was homogeneous before the ecap, and that the grains had a size of approximately 60-70 µ m. subsequently, the microhardness increased slightly iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 142 up to 8 pressings as shown in fig. 5. the drastic increase of microhardness after the pressing is due to the reduction in the grain size from 70 µ m for cast workpiece to ~ 200 nm for ecaped workpiece after six passes (shown in fig. 6), as well as by the density increase of dislocation when the number of passes is increased for route bc [22]. fig. 3: sem photomicrograph showing microstructures of the al-si alloy as cast (x 200 marker 200 µ m). fig. 4: sem photomicrograph showing microstructures of the al-si alloy after 1 pass on the y-plane using a die with φ =1200 and ψ =00 using route bc. iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 143 c a s t a la ll o y 1 p x 1 2 0 1 p y 2 p x 2 p y 3 p x 3 p y 4 p x 4 p y 5 p x 5 p y 6 p x 6 p y 7 p x 7 p y 8 p x 8 p y 0 20 40 60 80 100 120 number of passes h v ( k g /m m 2 ) fig. 5: the average values of vickers microhardness (hv) for the cast and ecaped alsi workpieces on the x and y planes, showing alongside the number of passes through the die with φ =1200 and ψ =00. (p: pass, x: x-plane and y: y-plane). fig. 6: sem photomicrograph showing microstructures of the al-si alloy pressed through the die with φ =1200 and ψ =00 using route bc; after 2 passes on the x-plane. figures 7 and 8 show that there is no significant difference in microhardness across the cross section of the eca pressed workpiece on the x and y-planes respectively. the individual microhardness measurements are shown in fig. 9 for the x and y-planes after four passes through the die. it is apparent from this figure that there is some scatter in the individual datum points. although all of the individual points lie within a reasonably narrow band, and are consistent with the presence of a reasonable degree of homogeneity iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 144 throughout the workpiece. but there is a little increase of microhardness values at the top surface of the workpiece due to high deformation at the inner angle of the die [23]. hardness measurements for eca pressed workpieces made by means of a die with φ =900 and ψ =200 show that the value of vickers microhardness is essentially identical across the workpiece on both x and y planes as shown in fig. 10 and fig. 11, respectively despite the lack of a fully homogeneous microstructure revealed by the presence of some elongated grains, as shown in fig. 12. this shows that the structure yields an equal amount of strain throughout the whole workpiece. this result is in consistent with the results obtained by chang et al. [24] and shin et al. [25] on 6061 al alloys. 0 20 40 60 80 100 0 2 4 6 8 10 12 distance (mm) h v ( k g /m m 2 ) as cast al-alloy 1px 120 3px 120 5px 120 8px 120 fig. 7: vickers microhardness at x-plane for cast al-si alloy, 1, 3, 5 and 8 passes through the die with φ =1200 and ψ =00 from the bottom (near to ψ ) to the top (near to φ ) of the workpiece. . 0 20 40 60 80 100 120 0 2 4 6 8 10 12 distance (mm) h v ( k g /m m 2 ) as cast al-alloy 1py 120 3py 120 5py 120 8py 120 fig. 8: vickers microhardness at y-plane for cast al-si alloy, 1, 3, 5 and 8 passes through the die with φ =1200 and ψ =00 from the bottom (near to ψ ) to the top (near to φ ) of the workpiece. iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 145 0 10 20 30 40 50 60 70 80 90 0 2 4 6 8 10 12 distance (mm) h v ( k g /m m 2 ) 4p ex 120 4p ey 120 4p mx 120 4p my 120 fig. 9: vickers microhardness from the bottom to the top of the al-si workpiece at two locations for 4 passes through the die with φ =1200 and ψ =00 on the x and y planes. (e: end of the workpiece that is in touch with the plunger) ;( m: middle of the workpiece); (x: x-plane and y: y-plane); (p: pass). it can be seen that the hv values of the workpieces increased significantly during deformation. the average microhardness of the workpieces after six pressings increased almost three times compared to that of the cast workpiece as shown in fig. 13. according to equation (1) this result is in agreement with the changes in microstructure where the microhardness increases with decreasing grain size. it is easy to noticed the reduction in the grain size from 70 µ m for cast sample to ~ 150 nm in fig. 12 for ecaped sample after 7 passes. another cause for the increase of microhardness is the generation of high dislocation density, which occurred with the shear deformation in the initial grain and the large number of structural defects [26]. a comparison between fig. 5 and fig. 13 shows higher values of microhardness in the latter figure. this is in accordance with the finite element method analysis conducted by luis perez et al. [27], where maximum strains and high friction conditions were reached for sharper inner angle. as well as, the dislocation density in the right angle die is higher than that in the obtuse angle die. which is attributed to the larger strain rate in the right angle die than that in the obtuse angle die [28]. iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 146 0 20 40 60 80 100 120 0 2 4 6 8 10 12 distance (mm) h v ( k g /m m 2 ) 2px 90 20 4px 90 20 6px 90 20 8px 90 20 cast al-alloy fig.10: vickers microhardness (hv) profiles at x-plane along the transverse distance from the bottom (near to ψ ) to the top (near to φ ) of the cast, 2, 4, 6 and 8 ecaped alsi alloy workpieces through the die with φ =900 and ψ =200. 0 20 40 60 80 100 120 0 2 4 6 8 10 12 distance (mm) h v ( k g /m m 2 ) as cast al-alloy 2py 90 20 3py 90 20 5py 90 20 8py 90 20 fig.11: shows the vickers microhardness (hv) profiles at y-plane along transverse distance from the bottom (near to ψ ) to the top (near to φ ) of the cast, 2, 3, 5 and 8 ecaped al-si alloy workpieces through the die with φ =900 and ψ =200. iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 147 fig.12: microstructure of eca pressed al-si alloy after 7 passes through the die with φ =900 and ψ =200, using route bc. 4 p y 5 p x 6 p x 7 p x 8 p y c a s t a la ll o y 2 p x 2 p y 3 p x 3 p y 4 p x 5 p y 6 p y 7 p y 8 p x 0 20 40 60 80 100 120 number of passes h v ( k g /m m 2 ) fig. 13: the average values of vickers microhardness (hv) for the cast and ecaped al-si workpieces at the x and y-planes shown alongside the number of passes through the die with φ =900 and ψ =200. (p: pass, x: x-plane and y: y-plane). iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 148 4. conclusion significant increase in microhardness is obtained after the first pressing through the ecap dies. it increases by a factor of >1.5 when compared to the microhardness of the cast workpiece. after the first pass, the microhardness increases slightly up to 8 passes in both dies, where it is increases by a factor of ~2.6 when using the die with φ =1200, and by a factor of ~3 when the die with φ =900 is used. thus, it is well established that the microhardness of ultrafine-grained materials (pressed workpieces) is higher than the microhardness of similar materials with large grain size (cast workpiece). the microhardness has the same tendency to increase at x and y-planes with the number of passes. no significant difference is noticeable in microhardness across the cross-section of the eca pressed workpieces on x and y planes. references [1] azushima a., kopp r., korhonen a., yang d.y., micari f., lahoti g.d., groche p., yanagimoto j., tsuji n., rosochowski a., yanagida a. (2008), severe plastic deformation (spd) processes for metals. cirp annals manufacturing technology 57, 716–735. [2] valiev r.z. (1997). structure and mechanical properties of ultrafine grained metals. mater. sci. eng. a234-236, 59-66. [3] korbel a., richert m., richert j. (1981) the effects of very high cumulative deformation on structure and mechanical properties of aluminium. proceedings of second riso international symposium on metallurgy and material science, roskilde, september 14–18, 445–450. [4] lowe t.c. and valiev r.z. (2000). producing nanoscale microstructures through severe plastic deformation. jom 52, 4, 27. [5] lee s.h., saito y., tsujib n., utsunomiya h., sakai t., (2002). role of shear strain in ultragrain refinement by accumulative roll-bonding (arb) process. secripta materialia 46,4,281-285. [6] segal v.m. (2002) severe plastic deformation: simple shear versus pure shear.materials. science and engineering a 338(1–2):331–344. [7] valiev r.z., estrin y., horita z., langdon t.g., zehetbauer m.j., zhu y.t. (2006). producing bulk ultrafine-grained materials by severe plastic deformation. jom 58(4):33– 39. [8] segal v. m., reznikov v.i., drobyshevkiy a.e. and kopylov v.i. (1981). plastic working of metals by simple shear. russian metall. 1, 99-105. [9] iwahashi, y., wang j., horita z., nemoto m. and langdon t. g., (1996). principle of equal channel angular pressing of ultra-fine grained materials. scripta mater. 35, 143-146. [10] nakashima k., horita z., nemoto m. and langdon t. j. (1998). influence of channel angle on the development of ultrafine grains in ecap. acta mater. 46, 1589-1599. [11] prangnell p.b., harris c., and. roberts s.m., (1997). finite element modeling of equal channel angular extrusion. scripta mater. 37, 983-989. [12] semiatin s.l., delo d.p., and shell e.b., (2000). the effect of material properties and tooling design on deformation and fracture during equal channel angular extrusion. acta mater. 48, 1841-1851. iium engineering journal, vol. 11, no. 2, 2010 ali a. aljobouri et al. 149 [13] basavaraj v. p., chakkingal u., kumar t.s.p.(2009). study of channel angle influence on material flow and strain inhomogeneity in equal channel angular pressing using 3d finite element simulation. journal of materials processing technology 209, 89–95. [14] iwahashi y., horita z., nemoto m. and langdon t.g. (1997). an investigation of microstructural evolution during ecap. acta metall. mater, 45, 4733-4741. [15] iwahashi y., horita z., nemoto m. and langdon t.g. (1998). the process of grain refinement in equal-channel angular pressing. acta mater. 46, 3317–3331. [16] oh-ishi k., horita z., furukawa m., nemoto m., langdon t.g. (1998). optimizing the rotation conditions for grain refinement in ecap. metall. mater. trans. 29a 2011-2013. [17] furukawa m., iwahashi y., horita z., nemoto m., langdon t.g., (1998). the shearing characteristics associated with equal-channel angular pressing. mater. sci. eng. a257, 328332. [18] sun p.l., kao p.w., chang c.p. (2004), high angle boundary formation by grain subdivision in equal channel angular extrusion. scripta materialia 51, 565–570. [19] furukawa m., iwahashi y. horita z., nemoto m., tsenev n.k., valiev r.z. and langdon t.g. (1997). structural evolution and the hall-petch relationship in an al-mg-li-zr alloy with ultra-fine grain size. acta mater. 45, 4751-4757. [20] sabirov i., estrin y., barnett m.r., timokhina i., hodgson p.d. (2008). tensile deformation of an ultrafine-grained aluminum alloy: micro shear banding and grain boundary sliding. acta materialia 56, 10, 2223-2230. [21] sabirov i., barnett m.r., estrinb y., and hodgson p.d. (2009). the effect of strain rate on the deformation mechanisms and the strain rate sensitivity of an ultra-fine-grained al alloy. scripta materialia 61 (2009) 181–184. [22] atef rebhia, thabet makhlouf, nabil njaha, yannick championb, jean-philippe couziniéb (2009). characterization of aluminum processed by equal channel angular extrusion: effect of processing route. materials characterization 60, 1489-1495. [23] kim h.s., hong s.i., seo m.h. (2001). effects of strain hardenability and strain rate sensitivity on the plastic flow and deformation homogeneity during equal channel angular pressing. j. mater. res. 16, 856. [24] chang s.y., lee k.s, choi s.h., shin d.h., (2003). effect of ecap on microstructure and mechanical properties of a commercial 6061 al alloy produced by powder metallurgy. j. alloy and compounds 354, 216-220. [25] shin d.h., park j.j., kim y.s. and park k.t. (2002). constrain groove pressing and its application to grain refinement of aluminum. mater. sci. eng. a328, 98-103. [26] liu z. y., liang g. x., wang e. d., and wang z. r. (1998). the effect of cumulative large plastic strain on the structure and properties of a cu–zn alloy. mater. sci. eng. a 242, 137– 140. [27] luis perez c.j., gonzales p. and garces y. (2003). equal channel angular extrusion in a commercial al-mn alloy. j. mater. process. tech. 134-144, 506-511. [28] hosseini e., kazeminezhad m. (2009). the effect of ecap die shape on nano-structure of materials. computational materials science 44, 962–967 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 physicochemical and functional properties of composite flours based on mocaf and tempeh flour for making cookies dita kristanti* and woro setiaboma 1 research center for food technology and processing, national research and innovation agency, yogyakarta, 55861, indonesia. 2 research center for appropriate technology, national research and innovation agency, subang, 41213, indonesia. * corresponding author: dita.kristanti@gmail.com (received: 24th november 2021; accepted: 27th april 2022; published on-line: 4th july 2022) abstract: gluten and casein free cookie products are increasingly in demand by consumers. gluten and casein free cookies were made using mocaf as a substitute for gluten-free flour and tempeh flour as a casein-free protein source. the characteristics of a good cookie composite flour made from mocaf and tempeh flour need to be known. the purpose of this study was to determine the physicochemical and functional properties of a cookie composite flour based on mocaf and tempeh flour. the composite flour was mixed by dry mixing. the composite flour formulations were: c0 (100% wheat flour); c1 (100% mocaf); c2 (75% mocaf and 25% tempeh flour); c3 (50% mocaf and 50% tempeh flour); c4 (25% mocaf and 75% tempeh flour) and c5 (100% tempeh flour). the results showed that addition of tempeh flour increased the ash, protein, fat, minerals, a* value, b* value, and water absorption capacity. the addition of tempeh flour was proven to reduce moisture content, carbohydrates, lightness, and whiteness index value. the cookie composite flour made from 75% mocaf and 25% tempeh flour had a gelatinization profile similar to 100% wheat flour, so this formula was recommended as a cookie composite flour. abstrak: produk kuki bebas gluten dan kasein semakin meningkat dalam permintaan pengguna. kuki bebas gluten dan kasein dibuat menggunakan mocaf sebagai pengganti tepung bebas gluten dan tepung tempe sebagai sumber protein bebas kasein. ciri-ciri tepung komposit biskut yang baik diperbuat daripada tepung mocaf dan tempeh perlu diketahui. tujuan kajian ini adalah untuk menentukan sifat fizikokimia dan fungsian bagi tepung komposit biskut berasaskan tepung mocaf dan tempeh. tepung komposit telah dicampur dengan adunan kering. formulasi tepung komposit ialah c0 (100% tepung gandum); c1 (100% mocaf); c2 (75% mocaf dan 25% tepung tempeh); c3 (50% mocaf dan 50% tepung tempeh); c4 (25% mocaf dan 75% tepung tempeh) dan c5 (100% tepung tempeh). hasil kajian menunjukkan penambahan tepung tempeh meningkatkan kadar abu, protein, lemak, mineral, nilai a*, nilai b*, dan kapasiti penyerapan air. penambahan tepung tempeh terbukti dapat mengurangkan kandungan lembapan, karbohidrat, ringan, dan nilai indeks keputihan. tepung komposit biskut yang diperbuat daripada 75% mocaf dan 25% tepung tempe mempunyai profil gelatinisasi yang serupa dengan 100% tepung gandum, jadi formula ini disyorkan sebagai tepung komposit biskut. keywords: casein free; composite flour; cookies; gluten free; mocaf; tempeh flour 20 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 1. introduction cookies are a type of biscuit that are relatively crunchy and have a dense texture. the ingredients that are often used to make cookies are wheat flour and soft sugar, starch, skim milk, egg yolks, shortening, and emulsifier. most cookies produced and consumed in indonesia use wheat flour as a main ingredient. the demand for wheat flour in indonesia is relatively high for the food industry. this is a serious problem since wheat flour cannot be produced in indonesia, so it needs to be imported. in general, low protein wheat flour (8-9%) is a raw material for cookies that has advantages of gluten and gliadin protein contents compared to other flours. the gluten protein plays a role in providing rigidity while gliadin protein provides sticky properties. the expansion of dough volume is not required in the process of making cookies so it is possible to use gluten-free flours and thus make cookies from local commodity flours. local commodity flour can be used as an alternative source to replace wheat flour as an effort to strengthen food security in indonesia. modified cassava flour (mocaf) is a fermented flour from cassava. the use of mocaf flour as a partial or whole substitute in baked products has been widely carried out. the sensory evaluation of baked products made from mocaf was more acceptable than baked products made from wheat flour [1]. however, the low protein content of mocaf caused the protein of baked products from mocaf to be lower than baked products made from wheat flour [1]. kristanti et al. [2] reported that mocaf contained 11.54% moisture content, 1.12% ash, 0.55% protein, 4.81% fat, and 81.96% carbohydrate. tempeh is a vegetable protein source in food that is made from fermented soybeans. enzyme hydrolysis occurs during fermentation, which causes improvements in texture, flavor, and aroma. according to reyes-bastidas et al. [3], fermentation affected the reduction of anti-nutrients and increase in nutritional value in tempeh through enzyme hydrolysis. the addition of tempeh flour caused an increase in protein in cookies [1] and instant baby porridge [2]. omosebi and otunola [4] reported that the proximate composition of the tempeh flour consists of 44.27-44.85% protein, 0.38-0.42% crude fiber, 16.45-17.12% fat, 5.60-5.72% ash, 2.50-3.00% moisture content, and 33.52-32.57% carbohydrate. mocaf and tempeh flour were used for cookie composite flour production in this study. cookies made from mocaf flour and tempeh are glutenand casein-free. autism is a disorder in which the body cannot digest gluten and casein proteins, this occurs because the body does not produce the dipeptidylpeptidase iv enzyme. therefore, cookies made from mocaf and tempeh flour are expected to be used as alternative foods for autism sufferers. composite flour is made from two or more flours to get the desired material characteristics for a product. research on the characteristics of composite flour with a mixture of mocaf and tempeh flour or soybean flour in noodles [5] and biscuits [6] have been carried out. the combination of flour in cookie composite flour will affect the dough and final product characteristics. chandra et al. [7] reported that the physicochemical properties of a dough were determined by an interaction between the composition, structure, and molecular changes of the combined components. the purpose of this study was to determine the physicochemical (proximate, mineral, and color) and functional properties (swelling power, solubility, water and oil absorption capacity, emulsion activity and stability, and gelatinization profile) of composite flour based on mocaf and tempeh flour for cookie products. 21 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 2. methodology 2.1 material modified cassava flour (mocaf) was obtained from “tanjung siang” small and medium enterprises (sme) in subang, indonesia. tempeh was obtained from sme of koperasi tahu tempe indonesia (kopti) in subang. the tapioca was bought from a local market in subang. 2.2 tempeh flour process fresh tempeh was sliced with a thickness of 10-20 mm. tempeh slices were steamed at a temperature of 85 °c for 10 minutes to deactivate the enzymes and fungi in the tempeh. the steamed tempeh slices were drained then dried at 50 °c for ± 5 hours. the dried tempeh slices were ground and sieved using a 40 mesh sieve [1]. the nutritional content of tempeh flour that was used in this study was 10.78% moisture content, 1.10% ash, 45.25% protein, 35.18% fat, and 7.63% carbohydrate [2]. 2.3 cookie composite flour process the process of cookie composite flour was carried out by weighing mocaf, tempeh flour, and tapioca according to the compositions shown in table 1. these composite flour formulas had been used to make cookies in previous studies [1]. the tapioca in this formula was used to produce cookies with a sturdy structure. all the ingredients were mixed by dry mixing using a mixer (philips hr 1559, china) and then stored in plastic for analysis. table 1: the composition of cookie composite flour formula formula wheat flour (g) mocaf (g) tempeh flour (g) tapioca (g) c0 100 5 c1 100 5 c2 75 25 5 c3 50 50 5 c4 25 75 5 c5 100 5 where c0 (100% wheat flour), c1 (100% mocaf), c2 (75% mocaf and 25% tempeh flour), c3 (50% mocaf and 50% tempeh flour), c4 (25% mocaf and 75% tempeh flour), c5 (100% tempeh flour). 2.4 physicochemical properties analysis proximate analysis, including moisture and ash contents, were analyzed by gravimetric method [8]; protein was obtained by dumas method using dumaster buchi d-480, switzerland; fat was determined using the soxhlet method, and carbohydrate was calculated by the difference method [8]. the mineral content of calcium (ca), iron (fe), zinc (zn), and magnesium (mg) were analyzed using flame atomic absorption spectrometry (aas) gbc type 933aa. the color properties (l*, a*, b* values) of cookie composite flour were measured using the nh310 chromameter using the cie method. the degree of whiteness (whiteness index) was calculated using equation (1). whiteness index = 100 − √((100 − 𝐿) 𝑥 2) + (𝑏 𝑥2) + (𝑐 𝑥 2) (1) 22 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 2.5 functional properties analysis the functional properties include swelling power, solubility, water absorption capacity (wac), oil absorption capacity (oac), emulsion activity, emulsion stability, and gelatinization profile. each sample (200 mg) was added to 10 ml of distilled water then homogenized using a vortex mixer vm-300 (gemmy industrial corp., taiwan). the homogenous sample was heated at a temperature of 95 °c for 30 minutes in a water bath (gsl, d-30938 burgwedel, type 1086, germany). the samples were centrifuged (thermo scientific type sl 40r centrifuge) at 3000 rpm for 15 minutes to separate the gel and supernatant. the gel was weighed to determine the swelling power, while the supernatant was placed in a constant beaker glass then dried using an oven at a temperature of 105 °c until constant weight to determine the solubility. swelling power and solubility were calculated using eqs (2) and (3). swelling power ( 𝑔 𝑔 ) = (w2 − w3) w1 (2) solubility (%) = w4 w1 𝑥 100% (3) where w1 = sample weight (g), w2 = gel + centrifuged tube weight (g), w3 = sample + centrifuged tube weight (g), w4 = dry supernatant weight (g). water and oil absorption capacity analysis were referred to in chandra et al. [7] with a modification. each sample (1 g) was added to 10 ml of distilled water or soybean oil then homogenized using a vm-300 vortex mixer. the homogenous sample was allowed to stand at room temperature (30±2 °c) for 30 minutes. the samples were centrifuged (sl 40r centrifuge) at 3000 rpm for 15 minutes to separate the precipitate and supernatant. the supernatant was decanted, while the precipitate and the centrifuge tube were weighed. the water and oil absorption capacity were calculated using eq. (4). water or oil absorption capacity (%) = w2 w1 𝑥 100% (4) where w1 = sample weight (g), w2 = natant weight emulsion capacity and stability analysis were referred to in chandra et al. [7] with a modification. each sample (500 mg) was added with 5 ml of distilled water and 5 ml of soybean oil then homogenized with a vortex mixer. the samples were centrifuged at 3000 rpm for 15 minutes. emulsion capacity was expressed as a percent ratio between the height of emulsion layer and mixture solution. after measurement, the emulsion was heated at 80 °c for 30 minutes in a water bath. the samples were then cooled at room temperature for 15 minutes and centrifuged at 3000 rpm for 15 minutes. emulsion stability was expressed as a percent ratio between the height of the emulsion layer mixture solution after the heating process. gelatinization profile was analyzed using a perten instruments rapid visco analyser (rva), tec master (sweden) with the std1 method. the operating conditions of the rva were a standard sample weight (3.5 g); standard water weight (25 g), and base water content (14%). the weighed sample and distilled water were heated and maintained at 50 °c for 1 minute, the temperature then increased to 95 °c in 4 minutes and maintained at 95 °c for 3 minutes. furthermore, the temperature cooled again to 50 °c in 4 minutes and maintained at 50 °c for 2 minutes. the rotational speed in the initial time (10 seconds) was 960 rpm, then reduced and maintained at 160 rpm throughout the test. the temperature at peak viscosity was expressed as gelatinization temperature (p temp), the 23 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 highest viscosity was expressed as peak viscosity (pv), the final viscosity after being maintained at 95 °c was expressed as hot paste viscosity (hpv), breakdown viscosity (bd) was expressed as the result reduction of pv with hpv, the final viscosity after being maintained at 50 °c was expressed as cold paste viscosity (cpv), the setback viscosity (sb) was expressed as the result of the reduction of cpv with hpv, the stability ratio (sr) was expressed as hpv divided by pv, and the ratio setback (sbr) was expressed as cpv divided by hpv [9]. 2.6 statistic analysis the data were analyzed using the ibm spss statistics 20 program. the data was analyzed with one-way analysis of variance (anova) followed by duncan's test at a significance level of p<0.05. all data were shown as mean with standard deviation. 3. results and discussion the chemical properties of the cookie composite flour are shown in table 2. the increase in addition of tempeh flour significantly (α<0.05) decreased moisture content and carbohydrate, however increased the ash, protein, and fat of the cookies composite flour. these results supported the previous research in that an addition of tempeh flour caused a decrease in moisture content and carbohydrate and an increase in protein and fat of cookies made from tempeh flour and mocaf [1]. a study by yulianti et al. [5] showed that the percentage increase of tempeh flour had the effect of increasing protein but had no effect on moisture content, ash, or fat of pasta composite flour. the protein and fat of these cookie composite flours were contributed by the tempeh flour. tempeh flour contained 45.25%db protein and 35.18% fat [2]. omosebi and otunola [4] reported that protein and fat content of the tempeh flour were 44.27-44.85% and 16.45-17.12%, respectively. table 2: the chemical composition of cookie composite flour samples chemical composition (%db) moisture ash protein fat carbohydrate c0 13.870.11a 0.590.02f 12.950.07e 1.450.02e 71.150.17b c1 10.110.05b 1.140.04e 1.870.05f 0.720.02f 86.140.09a c2 8.940.18c 1.240.06d 13.980.43d 7.200.03d 68.750.54c c3 7.630.15d 1.400.01c 25.690.46c 13.380.12c 52.080.47d c4 6.560.09e 1.790.08b 37.220.09b 19.470.11b 35.010.06e c5 5.450.10f 2.600.11a 48.090.11a 25.590.12a 18.290.20f values are expressed as mean ± standard deviation. the means in the same raw with different letters were significantly different at p < 0.05. the treatments code were c0 (100% wheat flour), c1 (100% mocaf), c2 (75% mocaf and 25% tempeh flour), c3 (50% mocaf and 50% tempeh flour), c4 (25% mocaf and 75% tempeh flour), c5 (100% tempeh flour). the zinc (zn), calcium (ca), and magnesium (mg) content of cookies composite flour were significantly (α<0.05) increased in line with the increase in percent addition of tempeh flour (figure. 1). these results supported the research results of kristanti et al. [1], where the mineral content (fe, zn, ca and mg) of tempeh mocaf cookies increased with the enhancement of percent tempeh flour. the mineral contents of tempeh flour were quite high, especially iron at 0.011-0.014%, calcium at 0.19-0.21%, and zinc at 0.00460.0050% [4]. 24 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 fig. 1: the mineral concentration of cookies composite flour. the treatments code were c0 (100% wheat flour), c1 (100% mocaf), c2 (75% mocaf and 25% tempeh flour), c3 (50% mocaf and 50% tempeh flour), c4 (25% mocaf and 75% tempeh flour), c5 (100% tempeh flour). the lightness (l* value) and whiteness index of cookies composite flour were significantly (α <0.05) decreased with the addition of tempeh flour (table 3). the decrease in the value of l* and whiteness index showed that the color of cookie composite flour tended to be darker. however, the a* and b* values were significantly (α <0.05) increased with the addition of tempeh flour. the a* and b* values showed in a range between 0-60, this indicated that the color of cookie composite flour tended to be reddish or yellowish. the color properties of cookie composite flour were influenced by the color of the tempeh flour. the c5 cookie composite flour (100% tempeh flour) had a lowest l* value and whiteness index, and had highest a* and b* values. table 3: the color properties of cookie composite flour. samples chemical composition l* a* b* whiteness index c0 68.180.86a 1.220.03f 9.040.11e 57.920.77a c1 65.100.97b 1.340.02e 7.540.11f 56.220.84b c2 63.530.64c 2.750.02d 10.530.11d 50.250.55c c3 60.010.23d 3.460.04c 12.480.14c 44.070.05d c4 56.510.42e 4.400.12b 14.480.27b 37.640.04e c5 52.380.23f 6.150.09a 15.990.10a 30.240.18f values are expressed as mean ± standard deviation. the means in the same raw with different letters were significantly different at p < 0.05. the treatment codes were c0 (100% wheat flour), c1 (100% mocaf), c2 (75% mocaf and 25% tempeh flour), c3 (50% mocaf and 50% tempeh flour), c4 (25% mocaf and 75% tempeh flour), c5 (100% tempeh flour). the results of this study supported previous research, where the value of l* and whiteness index decreased, while the values of a* and b* increased along with the increase f e bc e d c d c b c b bc b a b a a a 0 5 10 15 20 25 30 zn ca mg m in e ra l c o n se n tr a ti o n (m g /1 0 0 g ) c0 c1 c2 c3 c4 c5 25 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 in the percentage of tempeh flour in cookies [1]. yulianti et al. [5] reported that an increase in the percentage of tempeh flour had an effect on decreasing the whiteness value of pasta composite although it was not significantly different. the addition of soy flour was shown to reduce the l* value in the bakery composite flour [6,9]. the water and oil absorption capacity of cookie composite flour from mocaf and tempeh flour (c1, c2, c3, c4, and c5) were significantly (α <0.05) higher than wheat flour (c0). the increase in an addition of tempeh flour significantly (α <0.05) increased wac, but had no effect on oac (figure. 2). the tempeh used in the tempeh flour process was made from soybeans. the results of julianti et al. [10] studies showed that wheat flour had a lower wac and oac than composite flour from sweet potato, maize, soybean and xanthan gum. the increase of soybean concentration did not been affect the wac and oac of bakery composite flour [9,10]. the wac and oac of tempeh flour were 2.612.77 g/g and 0.96-0.98 g/g [4]. fig. 2: the water and oil absorption capacity of cookie composite flour. the treatment codes are c0 (100% wheat flour), c1 (100% mocaf), c2 (75% mocaf and 25% tempeh flour), c3 (50% mocaf and 50% tempeh flour), c4 (25% mocaf and 75% tempeh flour), c5 (100% tempeh flour). wac and oac are the important parameters for bakery products. wac was related to the viscosity of an ingredient, important in the development process, and maintaining the consistency of bakery products [11]. aremu et al. [12] reported that oil had a function of retaining and enhancing taste, and extending the shelf life of bakery products. protein affects the wac and oac of a material, it consists of hydrophilic and hydrophobic groups. the hydrophilic groups can interact with water, while the hydrophobic groups can interact with oil. swelling power and solubility of the cookie composite flour can be seen in fig. 3. swelling power of c1, c2, and c3 cookie composite flour were significantly (α <0.05) higher than wheat flour (c0). solubility of c1, c2, c3, c4, and c5 cookies composite flour were significantly (α <0.05) higher than wheat flour (c0). the increase in the addition of tempeh flour was generally significant (α <0.05) in reducing the swelling power of the cookie composite flour. the increase in addition of soybeans caused a decrease in swelling power of composite flour of bakery products [9,10]. high protein e b d a c a c a b a a a 0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00 water absorption capacity oil absorption capacity w a te r a n d o il a b so rp ti o n c a p a c it y ( % ) c0 c1 c2 c3 c4 c5 26 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 content in cookie composite flour may cause starch granules to adhere to the protein matrix, thereby limiting the interaction between starch and water. it is thought to cause a decrease in swelling power. the decrease in solubility of cookie composite flour was thought to be caused by a destruction of starch granules after the gelatinization process so that they were not strong enough to hold water. fig. 3: the swelling power and solubility of cookie composite flour. the treatment codes are c0 (100% wheat flour), c1 (100% mocaf), c2 (75% mocaf and 25% tempeh flour), c3 (50% mocaf and 50% tempeh flour), c4 (25% mocaf and 75% tempeh flour), c5 (100% tempeh flour). the results of this study showed that the emulsion activity and stability of cookie composite flour were significantly different (α<0.05) between treatments (figure. 4). the greater the proportion of tempeh flour, the lower the emulsion activity and stability. this was possible because the protein content of cookie composite flour affects the formation of hydrophilic and hydrophobic bonds in the emulsion. the quality and quantity of protein content was not proven to affect the formation of the emulsion. the emulsion formation and stability were determined by protein denaturation and unfolding to form hydrophilic and hydrophobic surfaces [13]. the gelatinization profile of the cookie composite flour is shown in table 4. the results showed that the gelatinization temperature of c0, c1, c2, and c3 cookie composite flours were not significantly different (α<0.05), while c4 and c5 cookie composite flours were not read (error). the increase in the proportion of tempeh flour significantly (α <0.05) decreased the pv, hpv, bd, cpv, sb, and sr values, while it also showed a significantly (α<0.05) increased sbr value for the cookie composite flour. the results of this study were in line with previous research. a study by tharise et al. [9] reported that gelatinization temperature of wheat flour was not significantly different with bakery composite flour. the pv, hpv, bd, and cpv values of wheat flour were significantly lower than that of bakery composite flour with added soybean flour [9]. according to yulianti et al. [5] results studies, the increase in the addition of tempeh flour had an effect of reducing the pv, cpv, and sb values, increasing the gelatinization temperature and bd, but had no effect on the hpv value of the composite flour. the increase in the addition of soybean flour to bakery composite flour had the effect on decreasing the pv, hpv, bd, cpv, and sb values, increasing the sr and sbr values, but had no effect on d f c a a db b e c f e 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 swelling power solubility s w e ll in g p o w e r a n d s o lu b il it y ( g /g / % ) c0 c1 c2 c3 c4 c5 27 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 the gelatinization temperature [9,10]. ratnawati et al. [6] reported that an addition of soybean flour increased the sb value and decreased the pv, bd, and hpv values of biscuit composite flour. fig. 4: the emulsion activity and stability of cookie composite flour. the treatment codes are c0 (100% wheat flour), c1 (100% mocaf), c2 (75% mocaf and 25% tempeh flour), c3 (50% mocaf and 50% tempeh flour), c4 (25% mocaf and 75% tempeh flour), c5 (100% tempeh flour). changes in the gelatinization profile, such as a decrease in the value of pv, hpv, bd, cpv, sb, and sr might cause by the high protein and fat content of cookie composite flour (table 2). high protein content of flour might limit the interaction between starch and water, thereby inhibiting the starch gelatinization process. the swelling process of starch granules was inhibited which might cause a decreasing of viscosity [14]. fat content in the ingredients had been shown to inhibit the starch gelatinization process. fat might form a complex bond with amylose, which is hydrophobic, so that it had the effect of inhibiting the binding of water and reducing the viscosity of the material. the amylose and starch content in the composite flour also affected the gelatinization process of starch. in general, the gelatinization profile of c2 cookies composite flour was similar to that of wheat flour (c0), especially the db, sb, sr, and sbr values. the decrease in bd and cpv in c2 cookies composite flour indicated the ability to form a gel after the cooking process was followed by cooling and gel resistance to maintain consistency during the stirring process. according to devi et al. [15] studies, the gelatinization profile wheat flour variety h5 490, which was of a good quality for making cookies, had lower pv, hpv, cpv, and sb values than wheat flour variety hd 2967, which was of a poor quality. the gelatinization profiles of wheat flour varieties h5 490 included pv, hpv, bd, cpv, sb, and the gelatinization temperature were 3050 cp, 2343 cp, 707 cp, 3762 cp, 1419 cp, 80.70 °c, respectively [15]. based on the devi et al. [15] study, c2 cookie composite flour had a good gelatinization profile, so this formula was recommended as a cookie composite flour. a ab b a c a c c d c d d 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 emultion activity emultion stability e m u ls io n a c ti v it y a n d s ta b il it y ( g /g ) c0 c1 c2 c3 c4 c5 28 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 table 4: the gelatinization profile of cookie composite flour samples gelatinization profile p temp. pv hpv bd cpv sb sr sbr c0 73.13±5.47a 3267.67±122.07b 3140.00±115.54b 747.33±102.84b 2451.33±194.88b 816.33±98.55a 0.98±0.00b 0.77±0.04c c1 71.85±0.43a 3798.00±26.16a 5609.33±26.16a 2492.33±44.47a 3117.00±27.51a 681.00±37.03b 1.48±0.01a 0.56±0.01f c2 72.75±0.09a 2670.00±43.03c 2668.00±29.31c 798.00±12.00b 1870.00±18.19c 800.00±27.87a 1.00±0.01b 0.70±0.00d c3 73.82±0.38a 1336.00±7.55d 980.67±30.57d 118.67±25.15c 862.00±9.85d 474.00±6.08c 0.73±0.02c 0.88±0.02b c4 err 330.67±4.51e 234.67±4.51e 17.00±0.00d 217.67±4.51e 113.00±0.00a 0.71±0.00c 0.93±0.00b c5 err 42.67±1.53f 26.33±1.53f 3.00±0.00d 23.33±1.53f 19.33±2.31d 0.62±0.04d 0.89±0.01a values are expressed as mean ± standard deviation. the means in the same raw with different letters were significantly different at p < 0.05. the treatment codes are c0 (100% wheat flour), c1 (100% mocaf), c2 (75% mocaf and 25% tempeh flour), c3 (50% mocaf and 50% tempeh flour), c4 (25% mocaf and 75% tempeh flour), c5 (100% tempeh flour). 29 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 4. conclusion the increase in addition of tempeh flour has been shown to increase the ash, protein, fat, minerals (zn, ca, mg), and water absorption capacity as well as decrease the moisture content, carbohydrates, lightness value, and whiteness index of cookie composite flour. the gelatinization profile of cookie composite flour made from 75% mocaf and 25% tempeh flour was similar to 100% wheat flour, so this formula was recommended as a cookie composite flour. the characteristics of recommended cookie composite flour were moisture content (8.94%), ash (1.24%), protein (13.98%), fat (7.20%), carbohydrates (68.75%), zinc (1.32 mg / 100 g), calcium (3.90 mg / 100 g), magnesium (20.17 mg / 100 g), lightness value (63.53), whiteness index (50.25), swelling power (13.84 g/g), solubility (11.22%), wac (188.77%), oac (117.85%), breakdown viscosity (798.00 cp), and setback viscosity (800.00 cp). acknowledgement this research was funded by the indonesian institute of sciences through science and technology program for regions (iptekda) 2019. the authors would like to thank the research center for appropriate technology-indonesian institute of sciences for providing facilities to conduct this research. the authors would also like to thank all organoleptic panelists who have taken the time to help carry out this research. references [1] kristanti d, setiaboma w, herminiati a. (2020) physicochemical and organoleptic characteristics of mocaf cookies with tempeh flour additions. biopropal ind., 11: 1-8. [2] kristanti d, herminiati a, yuliantika n. (2021) the physicochemical properties of mocafbased baby instant. j. ris. teknol. ind., 15: 12-22. [3] reyes-bastidas m, reyes-fernández e, lópez-cervantes j, milán-carrillo j, loarca-piña g, reyes-moreno c. (2010) physicochemical, nutritional and antioxidant properties of tempeh flour from common bean (phaseolus vulgaris l.). food sci. technol. int., pp. 427-434. [4] omosebi mo, otunola et. (2013) preliminary studies on tempeh flour produced from three different rhizopus species. int. j. biotechnol. food sci., 1: 90-96. [5] yulianti le, sholichah e, indrianti n. (2019) addition of tempeh flour as a protein source in mixed flour (mocaf, rice and corn ) for pasta product. iop conference series: earth and environmental science, 251(1): 012037. [6] ratnawati l, desnilasari d, kumalasari r, surahman dn. 2020 characterization of modified cassava flour (mocaf)-based biscuits substituted with soybean flour at varying concentrations and particle sizes. food res., 4: 645-651. [7] chandra s, singh s, kumari d. (2015) evaluation of functional properties of composite flours and sensorial attributes of composite flour biscuits. j. food sci. technol., 52: 3681–3688. [8] aoac (1995) official methods of analysis of the association of official analytical chemist, 14 ed. airilington, aoac inc. [9] tharise n, elisa j, nurminah m. (2014) evaluation of physico-chemical and functional properties of composite flour from cassava, rice, potato, soybean and xanthan gum as alternative of wheat flour. int. fiood res. j., 21: 1641-1649. [10] julianti e, rusmarilin h, ridwansyah, yusraini e. (2017) functional and rheological properties of composite flour from sweet potato, maize, soybean and xanthan gum. j. saudi soc. agric. sci., 16: 171-177. [11] niba ll, bokanga mm, jackson fl, schlimme ds, li bw. (2001) physicochemical properties and starch granular characteristics of flour from various manihot esculenta (cassava) genotypes. food chem. toxicol., 67: 1701-1705. 30 iium engineering journal, vol. 23, no. 2, 2022 kristanti and setiaboma https://doi.org/10.31436/iiumej.v23i2.2234 [12] aremu mo, olaofe o, akintayo et. (2007) functional properties of some nigerian varieties of legume seed flours and flour concentration effect on foaming and gelation properties. j. food technol., 5: 109-115. [13] raikos v, neacsu m, russell w, duthie g. (2016) comparative study of the functional properties of lupin, green pea, fava bean, hemp, and buckwheat flours as affected by ph. food sci. nutr., 2: 802-810. [14] kaushal p, kumar v, sharma hk. (2012) comparative study of physicochemical, functional, antinutritional and pasting properties of taro (colocasia esculenta), rice (oryza sativa) flour, pigeonpea (cajanus cajan) flour and their blends. lwt food sci. technol., 48: 59–68. [15] devi a, sindhu r, khatkar bs. (2019) morphological, pasting, and textural characterization of starches and their sub fractions of good and poor cookie making wheat varieties. j. food sci. technol., 56: 846-853. 31 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 characterization and melt spinning of poly (lactic acid)/poly (ethylene glycol) blends nur atiqah mohd akhir1, maizatulnisa othman1 yose fachmi buys2, norhashimah shaffiar1, dzun noraini jimat1 and sharifah imihezri syed shaharuddin1* 1 department of mechanical engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia 2 department of mechanical engineering, faculty of engineering, university of malaya, 50603 kuala lumpur, malaysia * corresponding author: shaimihezri@iium.edu.my (received: 15th february 2020; accepted: 14th june 2020; published on-line: 4th january 2021) abstract: in this study, melt blended compositions of pure pla with additions of polyethylene glycol (peg) up to 30 wt% were prepared. fourier-transform infrared spectroscopy (ftir), differential scanning calorimeter (dsc), and thermogravimetric analysis (tga) were used to investigate the properties of pla/peg blends, such as structural, thermal, and morphological properties. the results showed that further increments of peg cause the -oh group of pla/peg blends to show a broad peak, indicating that there is hydrogen bonding interaction between peg and pla chains. dsc result revealed that the addition of peg decreases the glass transition temperature from 57 °c to 46 °c and crystallization temperature from 107 °c to 87 °c. such trends suggest enhanced chain mobility of pla chains. tga thermograms showed that further additions of peg into pla resulted in a consistent shift to lower temperature and decrease in thermal stability. optical microscopy (om) and scanning electron microscopy (sem) observations of the melt spun pla/peg microfibers revealed that the diameter of the microfibers averaged between 15 to 80 microns. abstrak: kajian ini menganalisa komposisi adunan lebur pla asli bersama tambahan polietilena glikol (peg) sebanyak 30%. penjelmaan fourier spektroskopi inframerah (ftir), kalorimeter pengimbasan pembezaan (dsc) dan analisis termogravimetri (tga) telah digunakan bagi mengkaji sifat-sifat adunan pla/peg, seperti struktur, terma dan sifat-sifat morfologi. keputusan menunjukkan penambahan peg seterusnya menyebabkan kumpulan -oh campuran pla/peg memberikan puncak yang lebar, ini menunjukkan ada interaksi ikatan hidrogen antara rantaian peg dan pla. keputusan dsc menunjukkan penambahan peg mengurangkan perubahan gelas dari 57 °c kepada 46 °c dan suhu kristalisasi dari 107 °c kepada 87 °c. trend ini mencadangkan peningkatan pergerakan rangkaian pada rantaian pla. termogram tga menunjukkan dengan penambahan berterusan peg ke dalam pla menghasilkan penurunan konsisten pada suhu dan pengurangan kestabilan haba. pemerhatian mikroskop optik (om) dan mikroskopi elektron penskanan (sem) mikrofiber spun lebur pla/peg menunjukkan purata diameter mikrofiber ini antara 15 ke 80 mikron. keywords: microfiber; poly lactic acid (pla); polyethylene glycol (peg); melt spinning 201 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 1. introduction the advancement of biodegradable polymers, particularly aliphatic polyester, has attracted curiosity and a great deal of interest among researchers due to their potentials as high performance biomedical and environment-friendly material [1,2]. examples of aliphatic polyester are poly (lactic acid) (pla), poly(glycolic acid) (pga), and poly(caprolactone) (pcl) [3]. in recent years, pla has received considerable attention due to biodegradability and biocompatibility properties [4]. pla is one of the renewable resources that are rich in starch such as beetroots, corn, and potato [5] and allowed by the us food and drug administration (fda) for internal consumption [6,7]. pla is a suitable candidate to be utilized for biomedical applications since the degradation product of pla is non-toxic [8]. pla possesses excellent mechanical properties and good physical properties such as high strength, thermoplasticity, and great processability [2,9]. there are various processing methods such as extrusion, injection molding, blow molding, thermoforming, and fiber spinning that pla can go through to produce the desirable end product; solid shape, film, or fiber [13,14]. however, pure pla has a stiff chain back-bone that restricts its plasticity [12] and causes low deformation at break and high modulus [13]. the stiffness of pla can be improved by blending with other biocompatible plasticizers [14]. plasticizer is used to increase flexibility and processability of matrix material [15]. common examples of plasticizer are polyethylene glycol (peg), polycaprolactone pcl, acetyl triethyl citrate and partial fatty acid esters [16]. in this study, polyethylene glycol (peg) is used to improve pla properties since it is non-toxic, miscible and biodegradable [17]. phuphuak et al. [18] and pillin et al. [19] stated that plasticizing pla with peg facilitates the chain mobility of pla which results with improved ductility and drawability of the blends. thus, these pla/peg blends can be melt spun into microfiber and potentially be used in biomedical application such as for wound dressings and sutures. one of the manufacturing processes used to produce fibers is the melt spinning method. the melt spinning method does not require the use of solvents during the drawing process [20], is low in cost, and allows for continuous production of fiber [21]. the polymer material is melted into viscous liquid through the heater at the spinneret and then rapidly solidifies upon extrusion. in this paper, pla and peg were mixed at different compositions via melt blending method and were melt spun into microfiber. 2. materials and methods 2.1 materials a pellet form of poly (lactic acid) was purchased from nature works llc (usa) grade 3052d natureworks ingeo tm biopolymer. polyethylene glycol flake was purchased from merck (darmstadt, germany). 2.2 preparation of pla/peg blends the pla pellets were placed in a drying oven at 50 °c for an hour to remove moisture before being melt blended with peg. the pla/peg compositions and their sample code are described in table 1. pla, peg, and pla/peg blends were mixed in an internal mixer (haake polylab rheomix) for 10 minutes at 170 °c mixing temperature with speed of 50 rpm. pla, peg, and pla/peg melt blended were then crushed using a crusher machine (hitop, m sy-20) 202 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 into smaller pieces. the crushed pla, peg, and pla/peg blends acquired were then again dried in an oven for minimum an hour at temperature 50 ℃ to reduce the moisture contents. table 1: composition of pla/peg blends sample used in this study 2.3 characterization of melt blended compositions 2.3.1 thermal property a) differential scanning calorimetry (dsc) the thermal property test was conducted using a sapphire dsc (perkin elmer instruments, usa). the dsc was conducted for 2 samples for each composition that were measured in the range of 5–10 mg. thermograms were obtained when the samples were heated at a temperature of 25 °c – 200 °c at a rate of 10 °c/min in a nitrogen environment. the glass transition temperature (tg), crystallization temperature (tc), melting temperature (tm), melting enthalpy (δhm), and crystallization enthalpy (δhc) of the studied compositions were investigated. the crystallinity degree were also obtained based on equation 1, xc (%) = ((δhm-δhc )⁄(δho-w) x 100 % equation (1) where;δhm = melting enthalpy of the pla δhc = crystallization enthalpy of the pla δho = melting enthalpy of 100% crystalline pla homopolymer 93.6 j/g [21] w = wt % of pla b) thermal gravimetric analysis (tga) tga was conducted using a simultaneous thermal analyzer (sta7300) (hitachi high technologies, usa) to determine the thermal property of the pla, peg, and pla/peg blends. the test was carried out under air atmosphere, heated at room temperature to 600 °c and a rate of 5 °c/min. the initial degradation temperature (tᵢ) and the final degradation temperature (tf) were noted and investigated. 2.3.2 structural property fourier-transform infrared spectroscopy (ftir) was carried out using an ftir spectroscopy spectrum 100 (perkin elmer, usa) to characterize the presence and intensity of the functional groups of the studied compositions. the analysis was conducted in the range of 600 cm-1 to 4000 cm-1 with a resolution of 4 cm-1 and a scanning frequency of 16 per sample. 203 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 2.4 melt spinning and characterization of pla/peg microfiber microfibers of pla/peg were drawn using an in-house built melt spinning tower. the microfibers were spun at a spinning temperature of 150 °c – 160 °c and at a spinning speed of 430 rpm. an olympus microscope (bx41m, uk) was used to observe the diameter of the melt spun microfibers with a magnification of 20x. the fiber cross-sections were observed using a scanning electron microscope (jeol jsm-it 100, japan). the fiber samples were cut and placed on a double-sided carbon adhesive stub and coated with palladium using a polaron sc7620. 3. results and discussion 3.1 fourier-transform infrared (ftir) analysis figure 1 shows the (ftir) peaks of the pla, peg, and pla/peg blends. table 2 represents the peak assignments and wave numbers for the samples. fig. 1: ftir spectra of various pla/peg blends used in this study. table 2: ftir spectra of various pla/peg blends used in this study. 204 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 the pla backbone structure consists of the carbon chain of the carbonyl group (c=o) while peg structural arrangement is made of c-o-c bonds. the ir spectra of the carbonyl group (c=o) of pla appears at the frequency region of 754-756 cm-1 and 1746–1754 cm1. meanwhile, for peg, the c-o-c group appears at the frequency of 1095 cm-1. the pla showed peaks of the asymmetrical ch3 and symmetrical ch3 at 2995 cm -1 and 2942 cm-1, respectively. it was observed that as the incorporation of peg increases above 10 wt %, the stretching for asymmetrical ch3 became invisible (refer table 2). the ftir graph showed a strong methylene/methyl band (ch2/ch3) at 1470 cm -1 and a weak methyl band (1380 cm1), plus a band between 725–720 cm-1 (methylene rocking vibration). the presence of these bands indicates the existence of linear aliphatic structure in the form of long chains. this is attributed to the crystallinity and the formation of a backbone structure with a high amount of regularity in the pla/peg blends [22]. the spectra showed only one significant peak of the c-h stretching band. the peak that correlates to c-h stretching became more intense as the amount of peg wt% increased. the pla and peg were melt blended at a temperature of 170 ºc and a study by sarasua et al. [23] suggested that such melt blending process may have resulted in a stronger c-h interaction. the presence of oh functional groups in the pla structure was confirmed by the presence of a broad peak at 3422 cm−1. the c-h stretch vibrations for methyl (–ch3) and methyne (–ch) in pla and peg structure, respectively confirm that both compounds are organic-based compounds that contain at least one aliphatic fragment or center. it can be seen that with further increments of peg wt%, the incorporation of peg increases, and the -oh group of pla/peg blends showed an increasingly broader peak. thus, it is proposed that interaction of the hydrogen bonds between the two polymers [24,25] have occurred in the pla/peg blends. similar observations were also deduced by chieng et al. [9]. the author suggested [9] that the hydrogen bonding may have occurred due to intermolecular interaction between the oxygen that is fixed to the carbonyl (c=o) in pla structure and the hydroxyl (–oh) terminal group present in the peg molecular structure. 3.2.1 differential scanning calorimetry (dsc) analysis the thermogram characteristics are shown in figure 2 and information on glasstransition temperatures (tg), crystallization temperatures (tc), and melting temperatures (tm) are tabulated and presented in table 2. table 2: the thermal properties of various pla/peg compositions used in this study based on dsc analysis. 205 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 fig. 2: characteristics of dsc thermograms of various pla/peg compositions used in this study. the tg, tc and tm values of pure pla are observed at 57 °c, 107 °c, and 155 °c, respectively. as peg is added to pla, the resultant pla/peg blends exhibited a trend of decreasing tg values compared to pure pla. the decreasing tg trend with further peg additions indicates enhanced chain mobility of pla backbones [2,15,26]. furthermore, peg is formed based on a chain structure that allows greater degree of flexibility compared to the chain structure of pla [16]. thus, the peg chains may be able to occupy the intermolecular spaces between pla polymer chains to form hydrogen bonding [17,27]. the ftir result (figure 1) also showed a strong intensity correlated to hydroxyl bonding with further increments of peg wt %. the decreasing tg trend was also consistent with the studies by hashim et al. [27] and pivsa et al. [2]. the improved mobility of the blends with peg addition facilitates the crystallization event to occur at lower temperatures. moreover, table 2 shows that the blend’s crystallinity (xc) increases as the concentration of peg increases up to 25 wt % indicating that a good plasticization effect from peg. however, as peg was added at 30 wt %, the crystallinity of the pla/peg blend slightly decreased to 1.3%. a comparable trend of decreasing crystallinity degrees was also obtained by li et al. [17] and was proposed due to the separation of the peg phase in the blend. it is observed that the further increments of peg into pla decrease the melting temperature by 3-4 °c. a similar tm trend was also observed by chieng et al. [28]. 3.2.2 thermogravimetric analysis (tga) the tga was performed to identify the thermal properties of the studied compositions. table 3 shows relevant data of the tga thermogram for initial degradation temperature (tᵢ) and final degradation temperature (tf) of these blends. the tga thermograms of pla, peg, and pla/peg blends in the range of 40 °c to 450 °c are shown in figure 3. it was observed that the studied compositions experienced a single weight-loss behavior. the tᵢ of pure pla occurred at 323 °c. it is known that pla has hydroxyl end groups in the main chain of its molecular structure. according to song [29] and maiza [26], hydroxyl end 206 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 groups will be critically affected during thermal degradation due to chain-scission which leads to decreasing thermal stability of pla. table 3: the ti and tf obtained from tga for various pla/peg compositions in this study fig. 3: tga thermograms for various pla/peg compositions used in this study. pure peg only experiences a weight loss of 60% as the temperature reaches 400°c and tf at 510 °c. comparable study by zhang et al. [12] reported that peg with different (high and low) molecular weight affects the thermal stability of a polymer blend and concluded that high molecular weight of peg requires extra energy to undergo chain scission due to the longer chain thus indicates higher thermal stability. septevani & bhakri [30] and silverajah et al. [31] proposed that the long polymer chain of peg functioned as a surface protector of the polymer blends. the presence of the protective layer impedes the permeability of volatile degradation products out from the blend and slows down the degradation of the blend. further increments of peg wt% into pla resulted with a trend of decreasing tᵢ temperatures. other studies have also observed similar trend [12,16]. according to chieng et al. [28], peg chains scatter themselves around pla chains and break the polymerpolymer interactions that led to a decrease in thermal stability. it is necessary to identify the temperature region where thermal degradation will commence to avoid decrease in physical and mechanical properties at the melt spinning temperature for the studied compositions [31]. 207 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 3.3 pla/peg fibers 3.3.1 morphological study the surface morphologies and diameter of melt spun fibers are depicted in the optical microscope (om) micrographs at 20x magnifications in fig. 4. table 4 shows the average fiber diameter for the pla and pla/peg fibers. fig. 4: om micrographs of the melt spun microfiber for various pla/peg compositions used in this study. 208 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 it can be observed from table 4 that the increase of peg wt % led to a trend of decreasing fiber diameter from 112 µm to 15 µm. it was therefore deduced that the increase in chain mobility (as evidenced in dsc result) further reduced the viscosity of the pla/peg blends at the melt-spinning temperature of 150 °c – 160 °c. this, in turn, exerted an increase in the degree of flexibility and workability [32] which enables much thinner fibers to be drawn. the om images (figure 4) revealed that the melt spinning process produces clear, bead-free, and uniform pla and pla/peg microfibers. the surface and cross-section morphologies of pla/peg fibers are depicted in scanning electron microscopy (sem) micrographs at 500x magnifications in fig. 5. fig. 5: sem micrographs at 500x magnification of the melt spun microfiber for various pla/peg compositions used in this study. 209 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 table 4: measured diameter obtained via om for the melt spun pla/peg microfiber the sem micrographs of melt spun pla and pla/peg fibers at spinning temperature 150 °c – 160 °c revealed that all the fibers produced were circular cross-section in shape. pla fiber has a smooth, uniform morphology, and larger fiber diameter than pla/peg fibers. with increasing peg wt%, it was revealed that the surface of the fiber transitions from smooth to slightly rough. such rough surface condition is proposed due to thermally induced phase separation of pla and peg. mohamed [33] and buttaro et al. [34] explained that the tendency for phase separation increases during melt spinning due to its processing conditions such as the distance from the spinneret to take-up wheels and the spinning temperature. similar surface condition was also noted by clarkson et al. [35] on microfiber produced via melt spinning method. 4. conclusion in this study, the effect of peg addition was structurally and thermally characterized via ftir, dsc, tga, and sem. ftir results suggest that the intermolecular reaction occurring between hydrogen and oxygen and the carbonyl (c=o) in the pla structure reacts with hydroxyl (–oh) terminal group in the peg molecular structure. such interactions were indicated by the increasing broad peak of –oh group as peg composition in pla/peg blend increased. the crystallinity degrees of pla/peg blends showed increasing trend up to 25 wt % peg indicating a good plasticization effect from peg. tga results revealed that the addition of peg into pla lowers the ti and tf of pla/peg. this is attributed to the poor thermal stability of peg. the melt spinning method was then used to successfully produce bead-free and uniform pla/peg microfibers. the mechanical performance of these melt drawn fibers will be investigated in the next phase of this study. acknowledgment this work was fully supported by the international islamic university malaysia, iium (rigs17-052-0627). the authors would like to express their deepest gratitude to facilities and technical assistance provided by the international institute for halal research and training (inhart), iium. references [1] farah tmn, nadia aa. (2014) study the mechanical and thermal properties of biodegradable polylactic acid/poly ethylene glycol nanocomposites. international journal of application or innovation in engineering & management, 3(1): 459-464. [2] weraporn p, kazunori f, keiichiro n, yuji a, hitomi a, hideki y. (2016) the effect of poly (ethylene glycol) as plasticizer in blends of poly (lactic acid) and poly (butylene succinate). journal of applied polymer science, 133(8): 1-10. 210 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 [3] mariya s, olya s, nevena m, iliya r, george a. (2007) preparation of plla/peg nanofibers by electrospinning and potential applications. journal of bioactive and compatible polymers, 22(1): 62-76. [4] gupta ap, vimal k. (2007) new emerging trends in synthetic biodegradable polymers polylactide: a critique. european polymer journal, 43(10): 4053-4074. [5] ching wl, chun hy, yueh sc, tsung ch, jia hl and wen hh. (2008) manufacturing and properties of pla absorbable surgical suture. textile research journal 78(11): 958-965. [6] yangling c, shaobo d, paul c, roger r. (2009) polylactic acid (pla) synthesis and modifications: a review. frontiers of chemistry in china, 4(3): 259-264. [7] cynthia dce, ricardo ja, jarbas mr, roberto fsf and ricardo gs. (2012) synthesis and characterization of poly(d, l-lactide-co-glycolide) copolymer. journal of biomaterials and nanobiotechnology, 3: 208-225. [8] lin x, bo w, guang y and mario g. (2006) poly(lactic acid)-based biomaterials: synthesis, modification and applications. in biomedical science, engineering and technology. edited by prof. dhanjoo n. ghista. intech; pp 248-282. [9] buong wc, nor ai, wan mzwn, mohd zh. (2014) poly(lactic acid)/poly(ethylene glycol) polymer nanocomposites: effects of graphene nanoplatelets. polymers, 6(1): 93-104. [10] jong-whan r, amar km, sher ps, perry kwg. (2006) effect of the processing methods on the performance of polylactide films: thermocompression versus solvent casting. journal of applied polymer science, 101(6):,3736-3742. [11] muhammad aas, wan awar, rohah am. (2014) effect of different solvents on the thermal, ir spectroscopy and morphological properties of solution casted pla / starch films. malaysian journal of fundamental and applied sciences, 10(1): 33-36. [12] jianming z, shiwei w, yuhui q, qian l. (2016) effect of morphology designing on the structure and properties of pla/peg/abs blends. colloid and polymer science. 294(11):1779–1787. [13] hu y, rogunova m, topolkaraev v, hiltner a, baer e. (2003) aging of poly(lactide)/poly (ethylene glycol) blends. part 1. poly(lactide) with low stereoregularity. polymer, 44(19): 5701-5710. [14] aswini km, smita m, sanjay kn. (2014) properties and characterization of biodegradable poly (lactic acid) (pla)/poly(ethylene glycol) (peg) and pla/peg/organoclay. j. thermoplast. compos. mater., 29(4): 443-463. [15] savitha s, girija b, ravichandran k. (2018) effect of polyethylene glycol on mechanical, thermal, and morphological properties of talc reinforced polylactic acid composites. materials today: proceedings, 5(1): 1591-1598. [16] saddys rl, bernabe lr, monica ap, florence ps. (2012) poly(ethylene glycol) as a compatibilizer and plasticizer of poly(lactic acid)/clay nanocomposites. high performance polymers, 24(4): 254-261. [17] feng jl, shui dz, ji zl, jun zw. (2015) effect of polyethylene glycol on the crystallization and impact properties of polylactide-based blends. polymer advanced technologies, 26: 465475. [18] yupin p, yong m, philippe z, suwabun c. (2013) balancing crystalline and amorphous domains in pla through star-structured polylactides with dual plasticizer / nucleating agent functionality. polymer, 54:7058-7070. [19] isabelle p, nicolas m, yves g. (2006) thermo-mechanical characterization of plasticized pla: is the miscibility the only significant factor? polymer, 47(13): 4676-4682. [20] nor ai, wan mzwn, maizatulnisa o, khalina a, kamarul ah. (2010) poly (lactic acid) (pla)-reinforced kenaf bast fiber composites: the effect of triacetin. journal of reinforced plastics and composites, 29(7): 1099-1111. [21] gupta vb, kothari vk. manufactured fibre technology, first edit. chapman & hall, 1997. [22] kurniawan y, yohanes ap, setyo p, bruce aw, hadi kp, titi cs. (2016) infrared and raman studies on polylactide acid and polyethylene glycol-400 blend. aip conference proceedings. 1725, 020101. [23] jose-ramon s, nerea lr, alberto la, emilio m. (2005) stereoselective crystallization and specific interactions in polylactides. macromolecules, 38(20): 8362-8371. 211 iium engineering journal, vol. 22, no. 1, 2021 mohd akhir et al. https://doi.org/10.31436/iiumej.v22i1.1364 [24] yong j, xin-yao y, tao l, mei-yun z, jin-huia l, xing-jiu h. (2013) peg aggregation templated porous zno nanostructure: room temperature solution synthesis, pore formation mechanism, and their photoluminescence properties. crystengcomm., 15(18): 3647-3653. [25] decai l, yang j, shanshan l, xiaojing l, jiyou g, qifeng c, yanhua z. (2018) preparation of plasticized poly (lactic acid) and its influence on the properties of composite materials. plos one, 13(3): 1-15. [26] mounira m, mohamed tb, guilhem q, valerie mn. (2015) biobased additive plasticizing polylactic acid (pla). polimeros, 25(6): 581-590. [27] norazlina h, kamala r, santhoshini s, kamal yusoh. (2015) effect of processing method on thermal behavior in pla/peg melt blending. advanced materials research, 1134: 185190. [28] buong wc, nor ai, wan mzwn, mohd zh. (2013) plasticized poly (lactic acid) with low molecular weight poly (ethylene glycol): mechanical,thermal and morphology properties. journal of applied polymer science, 130(6): 4576-4580. [29] yan ps, de yw, xiu lw, ling l, yu zw. (2011) a method for simultaneously improving the flame retardancy and toughness of pla. polymer advanced technologies, 22(12):2 2952301. [30] athanasia as, samsul bi. (2017) plasticization of poly (lactic acid) using different molecular weight of poly ( ethylene glycol ). in proceedings of the 3rd international symposium on applied chemistry: 23–24 october 2017; jakarta, indonesia. volume 1904. issue 1. [31] giita s, nor ai, norhazlin z, wan mzwy and hazimah ah. (2012) mechanical, thermal and morphological properties of poly(lactic acid)/epoxidized palm olein blend. molecules. 17(10): 11729–11747. [32] melissa gav, mariana as, lucielen os, marisa mb. (2011) natural-based plasticizers and biopolymer films: a review. european polymer journal. 47(3):254–263. [33] khayet m. (2015) melt spinning. encyclopedia of membranes. [34] larissa. mb, erin d, margaret wf. (2014) phase separation to create hydrophilic yet nonwater soluble pla/pla-b-peg fibers via electrospinning. journal of applied polymer science, 131(19): 1-7. [35] caitlyn mc, sami meaa, reaz c, shoumya ns, james s, gregory s, volkan o, jeffrey py. (2019) melt spinning of cellulose nano fibril/polylactic acid (cnf/pla) composite fibers for high stiffness. appllied polymer material, 1:160-168. 212 iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 225 a linear relationship between the tensile, thermal and gas barrier properties of mape modified rubber toughened nanocomposites n.a. jamal1, h. anuar1 and s.b.a. razak2 1department of manufacturing and materials engineering, faculty of engineering, international islamic university malaysia, po box 10, kuala lumpur, 50728, malaysia 2crop improvement and protection unit, production development division, rubber research institute malaysia (rrim), 47000, sungai buloh, selangor darul ehsan, malaysia e-mail: ayuni_jamal@yahoo.com abstract: the nanocomposites with the application of compatibilizer agent were developed aiming to enhance the tensile, crystallization as well as gas barrier properties. nanocomposites based on high density polyethylene (hdpe), ethylene propylene diene monomer (epdm) and organophilic montmorillonite (ommt) clays were prepared via melt compounding followed by compression molding. the addition of clay as well as compatibilizer agent (maleic anhydride polyethylene (mape)) considerably improved the tensile properties of nanocomposites systems. the largest improvement in mechanical and thermal properties occurred at clay loading levels of 4% (2-8 wt %) with mape system. interestingly, the increased in tensile properties also resulted in improvement in thermal and gas barrier properties. based on the optimum finding in tensile test, differential scanning calorimeter analysis (dsc) and gas barrier analysis were evaluated at 4 vol% of ommt. dsc analysis revealed that the gas barrier property of nanocomposite was influenced by the crystalline percentage of nanocomposite. along with crystalline percentage, the crystallization temperature, tc and melting temperature, tm were also improved with the presence of ommt and mape agent. the d-spacings of the clay in nanocomposites was monitored using x-ray diffraction (xrd) and the extent of delamination was examined by transmission electron microscope (tem). the wide angle of xrd patterns showed the increased of interplanar spacing, d of clay layers, indicating enhanced compatibility between polymer matrix and ommt, with the aids of mape agent. tem photomicrographs illustrated the mixed intercalated and partial exfoliated structures of the nanocomposites with ommt and mape agent. keywords: organophilic montmorillonite; tensile properties; thermal property; maleic anhydride polyethylene; gas barrier 1. introduction polymer layered silicate (pls) has replaced the traditional used of macro and micro fillers that have been used for years and successfully made breakthroughs in glass fiber reinforced polymers [1-2]. this is because the used of conventional fillers required larger iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 226 amount than silicate in which resulting in additional of cost. unlike fiber reinforcing polymer composites that often trade one propitious quality for another, nanocomposites provide opportunity to tailor the constituent properties towards optimal material behavior without compromise. different types of filler or reinforcement can be incorporated into polymer blending system but the selection of silicate layered is more preferable. it should be noted that small amounts of well dispersed natural clay can lead to environmental friendly and inexpensive plastic composites with improved specialized properties and thus produce a new class of lightweight materials. however, as stated by marian and janusz (2007), thermodynamic immiscibility or incompatibility of most polymers is a serious barrier to processing of polymer matrix with nano filler which results in poor mechanical properties. a common approach to alleviate this problem involves the addition (or the in situ formation) of an interfacial active agent, or so called compatibilizer, to the blend [4]. crosslinking agents or so called compatibilizer agents have been applied for years due to their ability to improve both physical and chemical interaction between polymer matrix and filler. this leads to better mechanical and thermal properties. for decades, the flexible packaging consumption has grown rapidly in united states (us) including europe and japan. in contrast to malaysia, fabrication of individual or composite material with superior barrier property is still at a critical stage. an innovation to enhance barrier property of material produced is by developing polymer nanocomposite technology which holds the key to future advances in flexible packaging. a majority of consumer products use polymeric materials or composite materials as packaging. it is widely known that, polymer composites (hdpe/epdm) possess good water vapor barrier properties. however, it is easily permeated by oxygen, carbon dioxide, and hydrocarbons. thus, the necessity of developing more effective gas barrier polymers has given rise to different strategies to incorporate and optimize the features from several components. most schemes to improve the gas barrier properties involve either the addition of higher barrier plastics via a multilayer structure (processing techniques) or by introducing filler with high aspect ratio in the polymer matrix. polymer nanocomposites which are constructed by dispersing a filler material into nanoparticles that form flat platelets are an ideal system for the gas barrier application. these platelets are then distributed into a polymer matrix, creating multiple parallel layers which force gases to flow through the polymer in a torturous path, forming complex barriers to gases and water vapor [5]. as more tortuosity is present in a polymer structure, higher barrier properties can be obtained. once these tiny flat platelets are dispersed into the plastic, they create a path that gases must follow to move through the material thus greatly slowing their transmission [6]. therefore, nanocomposites would ease the transition between current packaging with metal layers and glass containers to flexible pouches or rigid plastic structures. although a lot of work has been done on elastomer blends, studies on the blends of epdm and hdpe with the addition of clay as filler as well as its ability as gas barrier resistance are meager. the development of this nanocomposite system is aimed to vary the existing research done in this area as well as being a future and important reference particularly in enhancing barrier property of nanocomposite. iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 227 2. experimental 2.1 materials homopolymer high density polyethylene (hdpe) (melt index 3-6 g/10min, density 900 kg/cm3) supplied by cementhai chemicals group, thailand and ethylene propylene diene monomer (epdm) supplied by centre west sdn bhd, malaysia were used as the base polymer matrix. mape-polybond@ 3009 obtained from uniroyal chemical company was used as a coupling agent to improve surface adhesion. commercially available organophilic montmorillonite (ommt) surface modified with 15-35 wt% octadecylamine and 0.5 wt% aminopropyltriethoxysilane obtained from sigma-aldrich group, malaysia was used as reinforcing agent to prepare the nanocomposites. 2.2 compounding melt blending of hdpe (70 vol%), epdm rubber (30 vol%), mape agent (3 vol%) and the ommt of different loading (2, 4, 6 and 8 vol%) was carried out in an internal mixer (thermo haake rheomix 600p). prior to mixing, the matrix polymer and the nanoclays were dehumidified in a dry oven at 110 �c for a period of 1 hr. 2.3 specimen preparation subsequently, the blended samples were compression molded as per astm-f-412 using a compression molding machine at a temperature range of 135–155 �c, with 8 ton metric pressures for 14 min. 3. characterization techniques 3.1 mechanical properties test specimens for analyzing the mechanical properties were initially conditioned at 23 ± 1 �c and 55 ± 2 % rh for 24 hr prior to testing. these conditioned specimens were subjected to mechanical testing and an average from the five testing measurements was reported. the corresponding standard deviation along with the measurement uncertainty value for the experimental data showing maximum deviation was also included. 3.2 tensile test specimens with dimensions of 125 × 1 × 1 mm3 were subjected to a tensile test as per astm f412, using instron 5567 machine with 5 kn load. a crosshead speed of 50 mm/min and a gauge length of 60 mm were set at room temperature. 3.3 differential scanning calorimeter (dsc) dsc of each sample was performed using perkin elmer dsc 7. samples with weight between 7 to 9 mg were used for the analysis. measurements of glass transition temperature, tg and crystallization temperature, tc were recorded as a function of iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 228 temperature in the range of -80 ºc and 200 °c with heating rate of 10 °c/min. the crystallinity (%) of nanocomposites was determined using the following relationship: (% crystallinity) xc = ∆hf /∆hof × 100 where ∆hf and ∆hof are enthalpy of fusion of the system and enthalpy of fusion of perfectly (100%) crystalline hdpe, respectively. for ∆hof (hdpe) a value of 277 j/g was used for 100% crystalline hdpe homopolymer [7]. 3.4 gas barrier test: oxygen transmission rate (o2tr) o2tr of nanocomposites was analyzed in mocon ox-tran 2/20 devices in accordance to the astm d3985 standard method. specimens having circular shape with thickness of 1 mm and diameter of 130 mm were conditioned in a desiccator at room temperature for a minimum of 48 hours. the test conditions used to determine the o2tr of nanocomposites were 23 °c and 0% rh with nitrogen flow rate of 20 ml/min. the resulting permeability was recorded as cm3/m²/day. 3.5 morphology a. transmission electron microscope (tem) the morphology of the nanocomposites was observed using a jeol jem 2010 electron microscope with an accelerating voltage of 100 kv. ultrathin specimens of 100 nm thickness were cut from the middle section of the compression molded bar using a reichert ultracut microtome. the specimens were collected on a trough filled with water and placed on a 200 mesh grid. b. x-ray diffraction analysis (xrd) x-ray diffractograms of ommt and the nanocomposites were recorded using shimadzu 6000 (japan), x-ray crystallographic unit equipped with nickel filtered cu kα radiation source operated at 40 kv and 40 ma. the basal spacing or d001 reflection of the samples was calculated from bragg’s equation by monitoring the diffraction angle 2θ from 2 to 10�. 4. results and discussion 4.1 tensile strength and modulus the effect of different clay loading on control, mape and eb irradiated systems is demonstrated in fig. 1 and 2. it is observed that the tensile strength and modulus for all nanocomposite system began to increase up to 4 vol% of ommt. as clay loading exceeded 4 vol%, the tensile strength and modulus of all system were found to decrease. similar improvement was also reported by previous researchers in their works on any polymer/organo clay nanocomposites [8-9]. the primary causes for such improvement was attributed to the presence of immobilized or partially mobilized polymer phases as a iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 229 consequence of interaction of polymer chains with organic modification of the clays and large number of interacting molecules due to the dispersed phase volume ratio characteristic of largely intercalated and exfoliated clay platelets as evidenced by tem micrographs. the tensile strength and modulus of both pristine composites and nanocomposites were further improved with mape agent, as evidenced in fig.1 and 2. an increased of 33.79% and 21.52% in tensile strength and modulus were observed for mape system as compared to control one, (only 30.66% and 19.52% increment in tensile strength and modulus with 4 vol% ommt). this increased was believed due to accomplish a larger interlayer distance as the molecular structure of mape contains anhydride group highly attracted to ommt sheets and a longer non polar fragment attracted to the hdpe/epdm matrix. moreover, the addition of mape into polymer matrix tends to decrease the free volume, which showed its compatibilizing effect [10]. this can be attributed to the penetration of both polar and non polar segments in the compatibilizer. 4.2 elongation at break it can be seen that a moderate increment of the elongation at break with initial incorporation of 2 vol% organoclay loading and followed by a sudden dropping of elongation at break upon 6 vol% loading of organoclay is presented in fig. 3. similar results were also reported by premphet and paecharoenchai (2001) as well as pramanik and srivastava (2003). the improvement in elasticity may be attributed to the plasticizing effects of the ommt gallery and to their contribution to the formation of dangling chains, but also probably due to conformational effects at the clay and matrix interface [13]. in contrast, the reduction in elongation at break with addition of organoclay implied that the nanocomposites became more brittle as compared to the unfilled polymer matrix. further 9.8% reduction in elongation at break at optimum clay loading of 4 vol% was observed for mape system. this is believed due to the mape reduced chain slippage on the surface of the fillers by the reaction both of filler and matrix. as a result, the elongation at break of the mape nanocomposite decreased. fig. 1: the tensile strength of control and mape systems with different clay loading (%). iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 230 fig. 2: the tensile modulus of control and mape systems with different clay loading (%). fig. 3: the elongation at break of control and mape systems with different clay loading (%). 4.3 differential scanning calorimeter analysis (dsc) the effect of ommt loading and mape compatibilizer on the crystallization temperature, tc, melting temperature, tm and crystallinity content, xc of nanocomposite systems were analyzed by dsc thermograms. the tc, xc, tm, and heat of fusion, ∆h values for all nanocomposites are outlined in table 1. the dsc thermograms of heating scan (tm, xc and ∆h) for unfilled polymer matrix and nanocomposite at 4 vol% clay loading are presented in fig. 4 and 5, respectively. moreover, the dsc thermograms of iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 231 cooling scan (tc) for unfilled polymer matrix and nanocomposites at 4 vol% clay loading are demonstrated in fig. 6 and 7. all the heating and cooling scans show only one endothermic as well as exothermic peak, but some differences in the peak temperatures can be revealed. durmus et al. (2007) mentioned that a single crystallization peak observed for the nanocomposite system could be attributed to the compatibility of the polymer matrix and nano clay. this indicates that the presence of multiple peaks (possibly attributed to β and γ phases) in the nanocomposite system may be due to the presence of either imperfect or small size crystallites [15]. as shown in fig. 5 and 7, the tm and tc values for all nanocomposites were shifted towards the higher temperature range. the ∆h values were also increased as compared to the unfilled polymer matrix (table 1). similar observations were also reported by previous researchers [16-17]. the addition of ommt at optimum level of 4 vol% increased the tm values for all nanocomposite system. the increased in tm values signifies that the crystal thickness in nanocomposites is more perfect than polymer matrix [17]. similar improvement pattern was observed for tc and xc values, which suggest that the crystallization mechanism of neat polymer matrix was enhanced. the nucleation mechanism is responsible for the growth of crystals in nanocomposites. this is because ommt silicates acted as a heterogeneous nucleating agent has increased the overall crystallization rate and the crystalline fraction. as evidenced in fig. 7, the presence of ommt narrowed the width of the crystalline peak. therefore, it can be concluded that the narrow pattern of the crystallization peaks also indicate an increase in crystallization rate of polymer matrix chains. mingliang and demin (2009) stated that the strong interaction exists between polymer matrix molecules and the layers of organoclay has resulted in immobilizing of some polymer matrix as organoclay easily absorb the polymer molecules segments. these immobilized molecules of polymer matrix contribute to the crystallization process of nanocomposite; therefore, the crystallization of polymer matrix molecules has occurred at higher temperature, thus increasing the tc values of nanocomposite systems. a considerable improvement were observed with mape where the values of tm, tc, ∆h and xc were increased about 6.3 °c, 1.8 °c, 9.4 °c and 6.84 %, respectively (as shown in table 1). the increasing in tc and xc suggested that both ommt and carboxyl group of mape has heterogeneous nucleation effect on the macromolecules segments of polymer matrix [17, 19]. moreover, a study done by xu et al. (2002) found that the melted polymer matrix macromolecule segments can be easily attached to the surface of the ommt particle, which leads to the crystallization of polymer matrix molecules at a higher crystallization temperature. besides that, the difference of tc between control and mape systems indicates heterogeneous nucleus effects of mape and a synergetic effect between mape and ommt on the crystallization behavior of polymer matrix. table 1: dsc results for unfilled composites and nanocomposite systems. systems ommt tm (°c) tc (°c) ∆∆∆∆h (j/g) xc (%) control 122.5 113.8 110.9 40.04 mape 126.9 116.5 124.7 45.02 control 4 vol% 131.8 115.7 120.5 43.5 mape 4 vol% 132.8 118.7 134.1 48.41 iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 232 fig. 4: melting endotherms of unfilled polymer matrix for control and mape systems. fig. 5: melting endotherms of nanocomposites at 4 vol% clay loading for control and mape systems. iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 233 fig. 6: crystallization exotherms of unfilled polymer matrix for control and mape systems. fig. 7: crystallization exotherms of nanocomposites at 4 vol% clay loading for control and mape systems. 4.3 gas barrier testing: oxygen transmission rate (o2tr) a protection of samples produced against the gas permeation is measured by using the oxygen transmission rate technique (o2tr). the effect of clay loading at 4 vol% as well crosslinking techniques on the oxygen (o2) permeability is summarized in table 2. as evident from table 2, the o2 permeability significantly decreased with clay loading whereas the introduction of crosslinking techniques further reduced the value of o2 permeability. it should be noted that the lower the permeation, the better the barrier. for iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 234 table 2: oxygen transmission rate (o2tr) of unfilled composites and nanocomposites with control and mape systems. control mape unfilled composites 52.8 51.7 nanocomposites at 4 vol% 52.6 50 48.5 49 49.5 50 50.5 51 51.5 52 52.5 53 53.5 o x y g e n t ra n sm is si o n r a te ( c m 3 /m 2 /d a y ) unfilled composites nanocomposites at 4 vol% the control system without mape treatment, no enhancement in o2 permeability was observed. such result is consistent with the result obtained in section 4.3, where the higher the crystallinity percentage, the lower the value of o2 transmission. this is because the crystal regions are impervious to water and oxygen transmission whiles the amorphous regions are diffused easily by water and oxygen molecules. this concept readily account for the general observations that gas permeability is reduced by increasing the crystallinity and by decreasing the amorphous phase density. in the context of gas transportation, the nanocomposite is considered to consist of a permeable phase (polymer matrix) in which non permeable nano platelets are dispersed [21]. in general, there are three main factors that influence the permeability of a nanocomposite which are the volume fraction of the nano platelets, the orientation of nano platelets relative to the diffusion direction as well as the aspect ratio [21]. low fractions of clays which affect the reduction of the polymer matrix volume are required to achieve equivalent properties in comparison with the traditional composites. therefore, a decrease of the solubility is expected in the nanocomposite due to the reduced polymer matrix volume, as well as a decrease in diffusion due to a more tortuous path for the diffusing molecules. in addition, the nanoclay layers are believed can act as a trap to preserve the active oxygen foragers in the polymer while reducing the rate of oxygen transmission. on the other hand, the degree of dispersion of the nano platelets is determined by the degree of delamination of the clay which will introduce a tortuous path for a diffusive penetration for gasses. the presence of ommt loading at 4 vol% enhanced the o2 permeability of mape system. the gas barrier property for mape system with the aids of ommt loading was slightly improved from 51.7 cm3/m2/day to 50 cm3/m2/day. this is believed due to the increasing of compatibilizer polarity which reduced the o2 permeability. in this system, iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 235 the used of mape agent has expanded the role of ommt filler by creating longer tortuous path by improving the surface interactions between the anhydride group of compatibilizer and the oxygen in the surface of the nanolamellae. note that the clay layers themselves are impermeable to oxygen, thus the introduction of mape provided greater barrier resistance towards the oxygen penetration due to the increased in the degree of crystallinity as evidenced in dsc analysis. as a result, the amorphous parts which are the only pathway for oxygen permeation became less and this led to enhance oxygen barrier property. 4.4 x-ray diffraction analysis (xrd) the changes in the interlayer distance of clay can generally be elucidated using xrd. the peak was blunted, after compounding the polymer matrix with optimum clay loading of 4 vol%, indicating that most of the clay is still in the original stacking condition. it is evident that the diffraction peak for control system was present at the position of 2θ = 3.570�, corresponding to d-spacing of 24.73 å. as 3 vol% of mape was added, the (001) peak still appeared, but its intensity was obviously lowered. this suggests that the diffraction peak of mape system has shifted toward lower angle, which was obtained at 2θ = 3.218� corresponding to d-spacing of 28.72 å. lei et al. (2006) mentioned that in the presence of compatibilizer agent, mape molecules could enter and penetrate the galleries between clay layers resulting in broadening of xrd peak. this is believed due to the strong driving force as the clay was premixed with mape, which originated from the strong hydrogen bonding between the maleic anhydride group (or cooh group generated from the hydrolysis of the maleic anhydride group) and the oxygen groups of the silicates [7]. as evidenced in fig. 8, with mape, some clay are still kept in the original stacking condition. however, the shifting in the diffraction peak to lower 2θ value may not necessary offer evidence for the complete exfoliation, it may also indicate for mixed ommt structure of intercalation and exfoliation as well as ordered or disordered intercalation, which has been confirmed by tem examination. fig. 8: xrd patterns of control and mape systems at 4 vol% of clay loading. iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 236 4.5 transmission electron microscope (tem) the nanometer scale dispersion of the treated clays ommt within the polymer matrix is further validated with tem images as depicted in fig. 9 and 10, respectively. the lighter region represents hdpe part, dark region represents epdm part whereas the dark lines corresponding to silicate layers (ommt). the tem images of nanocomposites prepared with treated clay (ommt) revealed mixed nano morphology. individual silicate layers along with two to three layer stacks were found to be intercalated in the polymer matrix for control system as compared to mape systems as evidence in fig. 9. in the case of control system, the non-uniform of ommt agglomerates was easily detected. moreover, it can be seen that the dispersion of the clay particles was poor and many large aggregates (in microns) were observed. however, in the case of mape system as shown in fig. 10, mixed intercalation and partially exfoliation of the clay platelets within the polymer matrix were observed. fig. 9: tem micrograph of control nanocomposites. fig. 10: tem micrograph of mape nanocomposites. iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 237 5. conclusion the effects of mape compatibilizer as a crosslinking agent on the tensile, thermal and barrier properties of nanocomposites were investigated in the current study. the findings are then summarized as below: • a good balance of properties in terms of stiffness and strength was achieved at 4 vol% ommt content. • surface modification through the use of mape has enhanced the interfacial adhesion between the ommt particles and polymer matrix thus enhanced the tensile, crystallization and gas barrier properties of unfilled and filled nanocomposites systems. • as ommt was introduced into the nanocomposite system, the value of xc, tc and tm were significantly increased along with decreased in o2tr value as clay particles were able creating more tortuous path due to its impermeable nature towards gases. • the introduction of crosslinking agent significantly enhanced the gas barrier property as well as crystallization behaviors indicating crosslinking network was successfully created in the nanocomposite system. references [1] w. j. cho, h. m. park, w. k. lee, c. s. park. environmentally friendly polymer hybrids part 1: mechanical, thermal, and barrier properties of thermoplastic starch/clay nanocomposites, j. mat. sci. (38), 909–915, 2003. [2] s. b. hamid and m. a. yarmo. perspective in nanotechnology in malaysia scenario. national symposium on science and technology. ukm, 2003. [3] z. marian and d. janus. effects of electron radiation and compatibilizers on impact strength of composites of recycled polymers. polymer testing (26), 903-907, 2007. [4] m.a. paul, m. alexandre, p. degee, c. henrist, a. rulmont and p. dubois. new nanocomposite materials based on plasticized poly(l-lactide) and organo-modified montmorillonites: thermal and morphological study. polymer (44), 443–450, 2003. [5] t. defosse matthew. innovative barrier technologies boost viability of pet beer bottles. modern plastics, 26-27, 2000. [6] p. demetrakakes, “nanocomposites raise barriers, but also face them: clay-based additives increase the barrier qualities of plastics, but obstacles to commercialization must be overcome”. nanocomposite materials. retrieved from http://www.findarticles.com, 2002. [7] y. lei, q. wu, and m.g. clemons. preparation and properties of recycled hdpe/clay hybrids. journal of applied polymer science (103), 3056-3063, 2006. iium engineering journal, vol. 11, no. 2, 2010 n.a. jamal et al. 238 [8] q.t. nguyen and d.g. baird. “preparation of polymer–clay nanocomposites and their properties. advances in polymer technology, (25), 270-285, 2006. [9] s. pavlidoua and c.d. papaspyridesb. a review on polymer–layered silicate nanocomposites. progress in polymer science (33), 1119-1198, 2008. [10] q.x. zhang, z.z. yu, m. yang, j. ma and y.w. mai. “multiple melting and crystallization of nylon-66/montmorillonite nanocomposites. j. polym. sci. polym. phy. (41), 2861–2870, 2003. [11] k. premphet and w. paecharoenchai. quantitative characterization of dispersed particle size, size distribution, and matrix ligament thickness in polypropylene blended with metallocene ethylene-octene copolymers. journal of applied polymer science (82), 2140-2149, 2001. [12] m. pramanik and s.k. srivastava. eva/clay nanocomposite by solution blending: effect of aluminosilicate layers on mechanical and thermal properties. macromolecular research, (11), 260-266, 2003. [13] i. aravinda, p. alberta, c. ranganathaiah, j.v. kurianb and s. thomas, “compatibilizing effect of epm-g-ma in epdm/poly(trimethylene-terephthalate) incompatible blend. polymer (45), 4925–4937. 2004. [14] a. durmus, m. woo, a. kasgoz, c.w. macosko and m. tsapatsis, “intercalated linear low density polyethylene (lldpe)/clay nanocomposites prepared with oxidized polyethylene as a new type compatibilizer: structural, mechanical and barrier properties. european polymer journal (43), 3737–3749, 2007. [15] m. bousmina, s.s. ray and j. bandyopadhyay. thermal and thermo-mechanical properties of poly(ethylene terephthalate) nanocomposites. j. ind. eng. chem, (13), 614-623, 2007. [16] j.w. lim, a. hassan, a.r. rahmat and m.u. wahit. mechanical behaviour and fracture toughness evaluation of rubber toughened polypropylene nanocomposites. plastics, rubber and composites, (35), 37-46, 2006. [17] t.y. tsai. templated synthesis of nanoparticles, nanoporous materials and nanowires. chemical information monthly, (14), 59－69, 2000. [18] g. mingliang and j. demin. preparation and properties of polypropylene/clay nanocomposites using an organoclay modified through solid state method. journal of reinforced plastics and composites, (28), 228-230, 2009. [19] s.y. lee, i.a. kang, g.h. dohl, w.j. kim, j.s. kim, h.g. yoon and q. wu. thermal, mechanical and morphological properties of polypropylene/clay/wood flour nanocomposites. express polymer letters, (2), 78–87, 2008. [20] w.b. xu, g.d. liang, w. wang, s.p. tang, p.s. he and w.p. pan. poly(propylene)poly(propylene) -grafted maleic anhydride-organic montmorillonite (pp-pp-g-mahorg-mmt) nanocomposites ii: nonisothermal crystallization kinetics. j. appl. polym. sci. (88), 3093. 2003. [21] k.b. anil and vijayabaskar. electron beam curing of elastomers. lancas bulletin, (4), 5-8, 2005. iium engineering journal, vol. 11, no. 2, 2010 tanay dey et al. 239 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 1, 2019 azmi et al. augmentative and alternative communication method based on tongue clicking for mute disabilities muhammad amirul amin azmi, nik nur wahidah nik hashim* and hazlina md. yusof department of mechatronics engineering, faculty of engineering, international islamic university malaysia, po box 10, kuala lumpur 50728, malaysia. *corresponding author: niknurwahidah@iium.edu.my (received:22nd nov 2018; accepted:22nd jan 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.1021 abstract: this paper presents a pilot study for a novel application of converting tongue clicking sound to words for people with the inability to speak. 15 features of speech that are related to speech timing patterns, amplitude modulation, zero crossing and peak detection were extracted. the experiments were conducted with three different patterns using binary support vector machine (svm) classification with 10 recordings as training data and 10 recordings as development data. peak size outperformed all features with 85% classification rate for pattern p1-p3 whereas multiple features produced 100% classification rate for p1-p2 and p2-p3. a gui based system was developed to validate the trained classifier. multiclass svm were constructed based on the best features obtained from binary svm classification outcome, namely peak size and skewness amplitude modulation, and then tested on 15 recordings. the gui based multiclass svm obtained a satisfying performance of 67% correct classification of the test data set. abstrak: kertas ini membentangkan panduan kajian kepada aplikasi terkini dalam menukar bunyi klik pada lidah kepada perkataan untuk orang yang mempunyai kehilangan upaya dalam bertutur. 15 ciri khas berkaitan pertuturan adalah pola masa, modulasi nilai tertinggi, tiada titik persilangan dan nilai terpilih yang dikesan. eksperimen telah dijalankan dengan tiga corak berlainan menggunakan perduaan mesin vektor sokongan (svm) klasifikasi dengan 10 rakaman sebagai data terlatih dan 10 rakaman sebagai data yang dibina. saiz tertinggi yang melebihi semua ciri-ciri pada 85% kadar klasifikasi dilihat pada corak p1-p3, sedangkan ciri-ciri pelbagai telah terhasil pada 100% kadar klasifikasi p1-p2 dan p2-p3. sistem berdasarkan gui telah dibina bagi menilai ciri terlatih. kelas pelbagai svm telah dibina berdasarkan ciri-ciri terbaik dan dihasilkan daripada klasifikasi perduaan svm, iaitu saiz tertinggi dan modulasi saiz tertinggi tidak linear, dan telah diuji dengan 15 rakaman. kelas pelbagai svm yang didapati melalui gui ini adalah memberangsangkan iaitu 67% klasifikasi adalah tepat pada set data yang diuji. keywords: mute; speech; alternative communication; classification; features 1. introduction normally, people who suffer from hearing disability will also experience the inability to talk (mute). according to the world federation of the deaf, it is estimated that there are 70 million people with hearing and mute disabilities in the world [1]. in malaysia, according to the ministry of women, family and community development, the number of people 119 iium engineering journal, vol. 20, no. 1, 2019 azmi et al. with hearing and mute disabilities is around 3,771 people [2]. in the context of face-to-face conversation, there are several conventional methods used by people with hearing and mute disabilities to communicate with the public, such as american sign language (asl), mobile applications, and writing or typing. asl is a complex communication method used by the deaf and mute people through hand and body gestures. the disadvantage of asl is that the resulting signals are often different from one speaker and another due to different backgrounds of hearing loss. the use of sign language also limits the transfer of information due to the components required to use sign language being limited to hand gestures, arm gestures, and facial expressions. the use of sign language is also limited in dark conditions as the receiver cannot see any movement of the signal using the finger or hand clearly, in turn, further affecting the smoothness of the communication being carried out. although mobile applications are considered to be a popular alternative communication method, the majority of the population that suffers the disabilities cannot afford to own a decent smart phone. transmission of information using a mobile application will not be as efficient as a normal conversation when communicating face to face. similarly, communication through typing and writing are not effective due to limited transmission of information at one time and the inability to communicate at farther distances or remotely. the aim of this project is to convert tongue clicking sounds to speech. each and every physiological characteristic of human beings is unique and will never be identical to one another, this fact leads to the foundational hypothesis of this research, which is that each tongue clicking sounds are unique in their own way. this study aimed to achieve the following objective. first, to identify the features in tongue clicking sounds that could distinguish different patterns. second, to classify the different tongue clicking sounds and associate them with a particular speech. third, to develop a system that converts tongue clicking sounds to speech. based on these objectives, the following question arises: what is the best feature to use for a speaker recognition application? this question will be explored further throughout this research. this research will not only benefit the deaf and mute but also benefits the people who will be communicating with them. companies or organizations will be more confident to rely on the deaf and mute in certain areas and it also encourages them to actively engage with the surrounding communities. this proves that communication aids to people with disabilities are indispensable and will greatly benefit everyone if realized. 2. previous work people with conditions related to disorders of motor speech control and language disorders due to brain injury require some kind of augmentative and alternative communication (aac). however, depending on the type of disorders and the level of physical and cognitive capabilities, the use of aac varies from one person to another. the development of aac is currently at the stage of producing, at most, 25 words per minute with inefficient response time. this section briefly reviews the existing method of aac. 2.1 asl to speech conversion in work by [9], the idea to translate finger spelling (sign) to speech using recognition and synthesis technique was proposed. two modules will be used in this project to make sure that a finger spelling (gesture) recognition module and a text-to-speech synthesis module can perform properly. 120 iium engineering journal, vol. 20, no. 1, 2019 azmi et al. this research identified that the sensor-based system is more accurate than the visionbased system. the sensor-based system only uses tactile sensors, flex sensors, and an accelerometer that significantly lower the cost as compared to the vision-based system that requires a camera with image processing as a portable device. the sensor-based system also provides a fast response in recognizing the gestures and thus reduces the computational time in real-time applications. 2.2 asl identification using microsoft kinect the research by [7] incorporates microsoft kinect as a vision-based approach for utilizing a picture processing technique as well as an additionally implanted frameworkbased approach where a sensor is placed on a hand glove for acknowledgment of the hand motions. they describe the process as independent of lighting conditions, which means that the image can be captured in full light or low light due to the processing data coming from the depth sensor, which is used for skeletal data. 2.3 breathing to speech conversion a breath control device was first initiated by [3] at the google science fair where a prototype using an arduino microcontroller was developped. the device translates breathing into electrical signals using a mems microphone where it detects varying intensity level or timing patterns of the user’s exhale. these variations were represented as dots and dashes that were then associated with the morse code to spell out words that were synthesized into voice. another study in [4] designed a device specifically for patients on ventilator support with the aim to support those with severe speech impairment and loss of motor functionality. the device captured breathing patterns and extracted features such as frequency variations, intensity, and phase. these feature patterns were then used to train the system and once recognized, each pattern was associated with synthesized words and phrases. the device was tested on seven healthy people with no speech impairment with each person producing 10 repetitions of three unique breathing patterns. the device was reported to have a mean reliability of 90% with the range of values being between 73% and 100%. researchers in [10] introduced communication by breathing device driven by a beltmounted breath-mouse that was improvised based on the dasher mouse gesture language. dasher is an alphabetical library based on the language model that predicts the probability of each letter in a given context. it allows a user to write any sentence using a mouse, touchscreen, or gaze tracker as the steering command. novice dasher users were reported to write 6.0 ± 1.3 words per minute with an average of 2.0% error in spelling. 2.4 eye blink-based alternative communication a device that converts eye blinks to english alphabet morse code was developed by [5]. the device used an ir led-sensor module attached to an eyeglass to recognize eye blinks. the sensor detected two levels of signals based on the amount of reflected light when the eyes were closed and open. measurements were fed into an arduino atmega 328p. short blinks were translated into dots and longer blinks were translated into dashes. the device took an average of three seconds to convert the blinking patterns to an english alphabet morse code. 3. methodology 3.1 data collection and pre-processing as an initial investigation, we would like to see if it is possible to distinguish between 121 iium engineering journal, vol. 20, no. 1, 2019 azmi et al. different tongue clicking patterns. thus, for database a, five different tongue clicking patterns from a single person were recorded using a tascam dr-05 with a 44.1 khz sampling rate. the patterns differed based on the number of clicks but with consistent pauses. for example, pattern one is one clicking, pattern two is a double click, and so on. we collected 30 recordings for training data and 30 recordings for development data to validate the classifiers trained using the training data. to further validate the classifier, we collected 15 recordings from 5 different people where each recorded three patterns of tongue clicking. table 1 shows the number of recorded tongue clicking patterns. the recordings were made in a closed room with each sound being recorded within 10 to 40 seconds depending on the tongue clicking patterns. table 1: database for collected tongue clicking patterns clicking pattern number of clicks number of training data number of development data number of test data pattern1 (p1) 4 10 10 5 pattern2 (p2) 1 10 10 5 pattern3 (p3) 5 10 10 5 figure 1 shows the recorded tongue clicking sound for five different patterns. speech signals were edited manually using audacity and saved as a separate .wav files labeled p1_1 to p1_10 and repeated for all p2 and p3 recordings. in the pre-processing stage, each speech signal can be decomposed in the form of voiced, unvoiced, and silence segments. each signal was then divided into 40 ms frames to satisfy quasi-periodic analysis where each frame was determined to be either a voiced, unvoiced, or silence segment using the method in [8]. fig. 1: tongue clicking signals for each pattern. (a) p1, (b) p2, and (c) p3. 122 iium engineering journal, vol. 20, no. 1, 2019 azmi et al. 3.2 feature extraction a total of 15 features of speech that are related to speech timing patterns, amplitude modulation, zero crossing and peak detection were extracted. a. speech timing pattern (transition matrix) audio consisting of voiced, unvoiced, and silence segments were marked as 1, 2, and 3, respectively. the variation happens during the timing pattern of the speech. here, the variations were captured in in the form of transition from one state to another state. interestingly, these states were interchangeable depending on the set of probabilities concerning the states. the probability is simply estimated using a discrete-time markov process as further discussed in [6]. the transition matrix elements were sequenced into one row vector {t11, t12, t13, t21, t22, t23, t31, t32, t33}. for example, t12 represents the probability of transitioning from the voiced state to unvoiced state within one signal. only pause and voiced transition parameters, which are {t11, t13, t31 and t33}, were used hereafter due to the fact that they are most related to the tongue clicking sound. b. root mean square amplitude modulation (rms am) the envelope of the waveform was determined based on the analysis of the root mean square amplitude modulation, also known as ‘the square-law envelope detector’, as shown in fig. 2. the input signal was squared and sent through an averaging represented by a lowpass filter. an averaging is a crude low-pass filter with a gain of 1. by squaring the signal, the input signal was demodulated using itself as the carrier wave. the square root was then taken in order to reverse the scaling distortion from squaring the signal and to characterize a more accurate statistical measure. seven rms am statistical measurements were extracted for each signal which included minimum, maximum, range, variation, average, skewness, kurtosis, and coefficient of variation. fig. 2: block diagram representing the square-law envelope detector. c. zero crossing rate zero crossing rate calculates the value of times in a given time interval/frame that the amplitude of the speech signal crosses through a value of zero. d. absolute peak detection the matlab built-in function for peak detection produced peak detection for both positive and negative peaks as demonstrated in fig. 3. for each signal, two features were gathered. the peak size represents the total absolute peak detection and peak average represents the average absolute peak. in summary, the 15 features were: 4 features from transition parameters {t11, t13,, t31, t33} 7 features from root mean squared amplitude modulation {minimum, maximum, range, variation, average, skewness, kurtosis, and coefficient of variation} zero-crossing rate peak average and peak size 123 iium engineering journal, vol. 20, no. 1, 2019 azmi et al. fig. 3: example of peak detection for one tongue clicking pattern. 3.3 construction of multiclass svm using binary svm the analysis of classification for database a were conducted using the built-in binary svm function in matlab (svmtrain) that accepts two parameters, training data and class label, to identify the optimum feature combination that would produce the highest pairwise classification rate. the binary svm classification was then used to construct a multiclass svm classifier to classify between three tongue clicking patterns of p1, p2 and p3. figure 4 shows the block diagram for the constructed multiclass svm using a binary svm classifier. fig. 4: construction of multiclass-svm using binary-svm. each binary classifier used features that were shown to have the highest percentage when trained and tested using database a. the features selected were peak size and skewness. the result produced either output p1 (labeled=1), p2 (labeled=2), or p3 (labeled=3). then the majority of the output of the three binary classifiers was calculated. each pattern was then associated with a certain sentence and speech sound such as ‘hello’ for p1, ‘good morning’ for p2, and ‘nice to meet you’ for p3. 4. results and discussion 4.1 analysis using training and development data the binary svm classifier was trained using the training data and the performance using the development data was analyzed. the best combination of features was limited to 124 iium engineering journal, vol. 20, no. 1, 2019 azmi et al. only one and two features in order to prevent over-modelling with the small number of samples. table 2 shows the result of the best feature for one combination binary-svm classification for p1-p2, p2-p3 and p1-p3 pairwise analysis. table 2: binary-svm percentage of correctness for one feature classification class classification % features p1 100 peak size, t31, max am, range am, skewness am, kurtosis am p2 100 (%all) 100 p2 70 peak size p3 100 (%all) 85 p1 100 peak size, peak average, max am, range am, kurtosis am p3 100 (%all) 100 for the two-feature combinations, due to a high classification percentage that produced a greater than 90% correct classification, the results are represented in the form of highest frequency of each feature as a contributor to the high percentage of correctness. figures 5, 6 and 7 show the results for each pairwise classification of p1-p2, p2-p3 and p1-p3. fig. 5: result for each feature contribution to the highest two-feature combination for p1-p2. fig. 6: result for each feature contribution to the highest two-feature combination for p2-p3. 125 iium engineering journal, vol. 20, no. 1, 2019 azmi et al. fig. 7: result for each feature contribution to the highest two-feature combination for p1-p3. the x-axis represents the 15 features extracted and y-axis represents the frequency of occurrence for the feature to contribute the highest percentage of binary-svm classification (90% and above) when combined with the other features. 4.2 analysis using testing data after performing the analysis for oneand two-feature combinations using the binary svm classification, the best two features that were chosen for use in the multiclass svm classification were peak size and skewness. for differentiating p2-p3 and p1-p3, peak size was used. peak size was observed to produce good results when analyzed using the binary svm classification, whether by itself or combined with another for two-feature combination, in order to differentiate the pattern of clicking sound. for differentiating p1-p2, the combination of peak size and skewness was used. these features were randomly chosen among the other features that produce good classification for creating the gui. in this part, tongue clicking patterns produced by five subjects were used as a testing input. results for the test classification are shown in fig. 9(a) and 9(b). a graphical user interface (gui) was developed for the conversion of tongue clicking sound to words as shown in fig. 8. fig. 8: the gui for the conversion of tongue clicking sound to words. 126 iium engineering journal, vol. 20, no. 1, 2019 azmi et al. there are three main sections that have been designed in the gui to operate this system. the first section is an input by real-time recording from the user using the microphone of the laptop. the second section is an input by uploading the tongue clicking sound of the user that is already stored in the file. the third section is the two features chosen from previous analysis. when the user clicks on peak and amplitude modulation (skewness), the values are the feature extracted from the input provided by the user through section one or two. (a) (b) fig. 9: successful rate on multiclass svm classification for (a) five user inputs and (b) each pattern. in fig. 9, the trained classifier was able to recognize 100% of input from user 1, 67% correct identification from user 2 to 4 and 33% correct identification for user 5. a moving average was then applied to the peak size threshold to improve the classification result and the success rate for all five user inputs produced 67% correct identification as illustrated in fig. 10(a) and 10(b). fig. 10: successful rate on multiclass svm classification with moving average filter for (a) five user inputs and (b) each pattern. even though the overall percentage result for all five user input is the same, the success rate on the pattern is different for p1 and p3. p3 gives a higher success rate without moving average filter while p1 gives higher percentage successful rate with moving average filter. 127 iium engineering journal, vol. 20, no. 1, 2019 azmi et al. 5. conclusion in conclusion, the method of converting tongue clicking sounds to speech is novel in the field of aac. however, a higher number of samples and a pre-trained tongue clicking session before collecting samples might increase the rate of detection. besides using only two features (peak size and skewness) other features have yet to be analyzed and used for training the classifier. acknowledgement this work is supported by the fundamental research grant scheme (frgs16-030-0529) from the ministry of education (moe), malaysia. references [1] world federation of deaf, retrieved december 10, 2018, from https://wfdeaf.org/ [2] statistik pendaftaran oku. retrieved december 10, 2018, from http://www.data.gov.my/data/ms_my/dataset/statistik-pendaftaran-oku [3] dilbagi a. (2014). talk breathes new life into the alternative communication device market. available at: http://newatlas.com/talk-morse-code-speech/33042/. [4] kerr d, bouazza-marouf k, gaur a, sutton a, green r. (2016). a breath controlled aac system. journal of communication matters, 30(3): 11-13. [5] mukherjee k, chatterjee d. (2015). augmentative and alternative communication device based on eye-blink detection and conversion to morse-code to aid paralyzed individuals, int. conf. on communication, information and computing technology (iccict), pp. 1-5. doi: 10.1109/iccict.2015.7045754 [6] nik nur wahidah nh, wilkes m, salomon r, meggs j, and france dj. (2016). evaluation of voice acoustics as predictors of clinical depression scores, journal of voice, 31(2): 256.e1-256.e6. [7] nagori np, malode v. (2016). communication interface for deaf-mute people using microsoft kinect. int. conf. autom. control dyn. optim. tech., pp. 640-644. [8] ozdas a, shiavi rg, silverman se, silverman mk, wilkes dm. (2004). investigation of vocal jitter and glottal flow spectrum as possible cues for depression and near-term suicidal risk. ieee trans. biomed. eng., 51(9): 1530-1540. [9] vijayalakshmi p, aarthi m. (2016). sign language to speech conversion. fifth int. conf. recent trends inf. technol., pp. 1-6. [10] shorrock th, mackay jc, ball cj. (2004). efficient communication by breathing, proceedings of the first international conference on deterministic and statistical methods in machine learning, pp. 88-97. doi: 10.1007/11559887_5 128 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <feff005500740069006c006900730065007a00200063006500730020006f007000740069006f006e00730020006100660069006e00200064006500200063007200e900650072002000640065007300200064006f00630075006d0065006e00740073002000410064006f006200650020005000440046002000700072006f00660065007300730069006f006e006e0065006c007300200066006900610062006c0065007300200070006f007500720020006c0061002000760069007300750061006c00690073006100740069006f006e0020006500740020006c00270069006d007000720065007300730069006f006e002e0020004c0065007300200064006f00630075006d0065006e00740073002000500044004600200063007200e900e90073002000700065007500760065006e0074002000ea0074007200650020006f007500760065007200740073002000640061006e00730020004100630072006f006200610074002c002000610069006e00730069002000710075002700410064006f00620065002000520065006100640065007200200036002e0030002000650074002000760065007200730069006f006e007300200075006c007400e90072006900650075007200650073002e> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <feff004200720075006b00200064006900730073006500200069006e006e007300740069006c006c0069006e00670065006e0065002000740069006c002000e50020006f0070007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740065007200200073006f006d002000650072002000650067006e0065007400200066006f00720020007000e5006c006900740065006c006900670020007600690073006e0069006e00670020006f00670020007500740073006b007200690066007400200061007600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020005000440046002d0064006f006b0075006d0065006e00740065006e00650020006b0061006e002000e50070006e00650073002000690020004100630072006f00620061007400200065006c006c00650072002000410064006f00620065002000520065006100640065007200200036002e003000200065006c006c00650072002e> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 118 a new spectrum and energy aware routing protocol in cognitive radio sensor networks sara moshtaghi and sayyed majid mazinani* 1 department of electrical engineering, imam reza international university, mashhad, iran * corresponding author: smajidmazinani@imamreza.ac.ir (received: 25th april 2018; accepted: 30th july 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.927 abstract: cognitive radio sensor network (crsn) is a new generation of communication systems that wants to solve the overcrowded spectrum utilization of the unlicensed bands. it has combined sensor networks and cognitive radio technology, so it has the challenges of energy restriction of sensors and also dynamic spectrum access of the cognitive radio network. on the other hand, considering both of these challenges in the routing protocol plays a basic role in network performance and we can’t apply the routing protocols that have been proposed for wireless sensor networks and cognitive radio networks, separately, in the crsn. therefore, this article has tried to provide a new spectrum and energy-aware routing protocol in which the source is able to choose the most stable route in the aspect of node residual energy or spectrum access probability. not only can considering the nodal residual energy and spectrum access in the route discovery process avoid repetitive link failure, but it also can increase the network lifetime. this protocol has been compared with esac, scr, erp, and ser. the result of this comparison has shown that our protocol reduces end-to-end delay, control overhead, throughput, and lifetime in comparison to other protocols, especially in small-scale networks. abstrak: rangkaian sensor radio kognitif (crsn) adalah generasi baru sistem telekomunikasi bagi menyelesaikan masalah kesesakan pada pemakaian band spektrum tidak berlesen. ianya adalah kombinasi rangkaian sensor dan teknologi radio kognitif. oleh itu, ia mempunyai cabaran sekatan tenaga pada sensor dan kemasukan spektrum secara dinamik pada rangkaian radio kognitif. pada masa sama, dengan mengambil kira keduadua cabaran pada protokol rangkaian ini telah memainkan peranan asas pada prestasi rangkaian dan kami tidak boleh mengguna pakai protokol rangkaian yang telah diguna pakai pada rangkaian sensor tanpa wayar dan rangkaian radio kognitif secara asing dalam crsn. oleh itu, artikel ini cuba menyediakan spektrum baru dan pengawasan tenaga pada protokol rangkaian, di mana sumber boleh memilih laluan rangkaian yang stabil dengan mengambil kira pada aspek baki tenaga nod atau kebarangkalian akses spektrum. selain itu, ianya dapat mengelakkan kegagalan laluan berulang juga menambahkan jangka hayat rangkaian. protokol ini telah dibandingkan dengan esac, scr, erp dan ser. perbandingan keputusan menunjukkan protokol ini mengurangkan kelewatan hujung-kehujung, mengawal kesesakan, mambaiki jumlah penghantaran dan menambah tempoh hayat berbanding protokol lain, khususnya pada rangkaian skala kecil. keywords: spectrum; energy; routing; cognitive radio; sensor networks iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 119 1. introduction the huge growth of the wireless services during the past few years has resulted in many spectrum scarcity challenges. in order to improve usage in the face of these challenges, cognitive radio (cr) has emerged as the next generation of wireless communication systems. the idea for cognitive radio technology was developed by mitola [1] for the first time and defined as a form of wireless communication in which a user can intelligently sense and analyze its environment and choose the best transmission strategy. in other words, the unlicensed or secondary user (su) can detect the available empty wireless spectrum which is owned by a licensed or primary user (pu) and then opportunistically exploits it without interference to the pus. to avoid any interruption to pus, the unlicensed user must be able to sense the channel correctly and make sure that it is vacant. furthermore, the su has to leave the channel as soon as the pu begins its activity in it. though dynamic spectrum allocation in cr networks can improve the efficiency spectrum, it can create many challenges in routing and quality of service. spectrum awareness is one of the main challenges in these networks [2,3] and it should be considered in the routing protocol of cr networks. ignoring the spectrum access probability of sus may cause many route failures and consequently, impose a lot of overhead and delay on the network. today, wireless sensor networks (wsns) are put to use in many applications such as area monitoring or healthcare monitoring. sensor nodes are mainly supplied with energyconstrained batteries. so, resource limitations are the main challenge for the lifetime of this network. the energy depletion happens when the nodes communicate with each other. reaching to the lowest allowed nodal energy level, that node cannot participate in subsequent data delivery and so is named a dead node. a dead node can badly affect the efficiency of the network. it can cause many problems such as link failure, delay in data delivery, further energy consumption, and more [4]. therefore, it is necessary to pay attention to nodal energy in the routing protocol. a lot of studies have been carried out in the wsn field focusing on the energy of sensor nodes. in most of these works, different routing protocols have been suggested for a variety of wireless networks, including wireless sensor networks (wsns), wireless mesh networks (wmns), and mobile ad-hoc networks (manets) [5], but only a few works have considered cr features in routing wireless networks [6-8]. in this paper, we have proposed a new routing protocol considering spectrum and energy awareness in cognitive radio sensor networks (crsn). the source node in our protocol can choose the route that is the most stable in the aspect of nodal residual energy or spectrum access. this means that route selection is done so that its nodes have more residual energy for sending data and this causes the nodes’ energy to last much longer, in other words, there are fewer dead nodes. link failure will thus be reduced and consequently, throughput and lifetime will be increased. also, choosing the route with the most spectrum access improves the quality of the route and decreases link failure. so, our routing protocol improves the quality of service (qos) such as throughput, end-to-end delay, overhead… especially in some small-scale networks. in general, small scale wsns (ss-wsns) are used for surveillance in small areas. they are deployed in industry to control machines, in smart homes to control electrical appliances, and in healthcare [9]. in the small-scale area, flat-based routing is more suitable than hierarchical-based in some aspects. for example, forming clusters and then starting routing takes more time than route discovery in the flat routing protocol. the rest of the article is organized as follows: in section 2, we introduce some related works. subsequently, in section 3 we present our system model and its assumption. in iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 120 section 4, we explain our routing protocol in detail. the simulation performance results and comparison are presented in section 5. finally, we conclude the paper in section 6. 2. related work routing for cr ad hoc networks is mainly divided into three types: on-demand routing (reactive), table-driven routing (proactive), and hybrid. in proactive routing, all routes are discovered and kept even if they are not needed. for this purpose, a periodic message is required to be sent for updating the route table. this causes lots of overhead. an example of this type is dynamic source routing (dsr) [10] protocols. in reactive routing protocols, routes discover and compute only if they are demanded. eliminating the periodic message in this type has resulted in a reduction of overhead and bandwidth usage. perhaps the most common and important of these protocols is ad hoc on-demand distance vector (aodv) [11]. this protocol consists of two phases of route discovery and route maintenance. hybrid routing is a combination of the two mentioned protocols. routing also can be divided into three categories depending on the network structure: flat-based, hierarchical-based and location-based [12]. in flat-based routing, nodes are distributed uniformly through the network and they have the same role. in the hierarchical structure, the network forms clusters so that nodes play different roles. for example, the nodes with more residual energy are selected as the cluster head. this energy consumption will be reduced in the large-scale network. however, this routing method also has some drawbacks such as complexity, delay (as mentioned before), and too much overhead of clustering, that cause some flat routing protocols to act better than hierarchical ones, especially in the small-scale network. routing in crsns has many challenges. on one hand, energy constraint in wireless sensors supplied by batteries should be considered and on the other hand, it is a problem of dynamic spectrum access of cognitive radio. also, improvement of quality of service parameters is attempted. many studies in recent years have proposed to solve the challenges of routing in cognitive radio and wireless sensor networks separately. but only a few works have been done for the challenges of crsns. esca [13] is an event-driven spectrum-aware clustering routing protocol. clusters just form when an event happens and they are kept until all data about the event is sent to the sink. the routing process has tried to maximize the available channel between each node and its one-hop and two-hop neighbours. though spectrum access is considered in this routing protocol, ignoring nodal energy increases route failure and it imposes a delay on the network. in scr [14] a cluster-based spectrum aware routing protocol is proposed. it is not event-driven and clusters are created and kept when the network begins to work until it is dead. even though energy and spectrum access are considered in this protocol, keeping clusters during the simulation period imposes much energy consumption to the network and so this protocol is not suitable for wsn networks in which sensors are supplied with batteries. energy-aware event-driven routing protocol (erp) [15] forms clusters in a reactive manner. this protocol makes energy consumption less than scr and esca because of its on-demand feature. also, it is spectrum-aware, which leads to less end-to-end delay and also increases throughput due to decreased route failure. this approach is based on clustering and as mentioned above, clustering especially for small-scale networks is too iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 121 complex and imposes more delay for route discovering. furthermore, energy consumption may be a need in some clustering routing protocols. the spectrum and energy aware routing protocol ser [16] is a routing protocol which is proposed for cognitive radio networks. it is based on dsr protocol and selects a route in which the nodal minimum residual energy is higher and has the minimum hop count. considering just the node with the minimum energy in selecting the route and neglecting other nodal energy frequently increased link failure probability. for example, we suppose the route is selected with this metric and link failure happens during data sending duration. if local reparation, which is discussed in this article, is used, the same nodes participate in the route again and because we don’t consider their energy, each time a new route failure may happen. 3. system model 3.1 assumptions of our routing protocol we have assumed a wireless sensor network in which sus are sensors with cognitive radio capability that are uniformly distributed. sus and pus simultaneously exist in this network but functional details of pus are not considered. each su can access different channels depending on its position and time. the state of a channel can be obtained from one of the sensing approaches, for example [17-19]. the details of this are beyond the scope of our work. we have considered that each su knows its (x, y) location with localization protocols such as gps or any other ones [20,21]. also, the fixed location of the sink is known for all of the su sensors. therefore, each node can figure out the distance between itself and the destination. we have supposed that su knows its own current residual energy as well as residual energy, location and free available channels of its one-hop and two-hop neighbours [22]. also, it can calculate the minimum pu appearance probability (pmin) for all the common channels between itself and its neighbour using [15,23,24]. we also have considered that each time that pu begins to use the channel, it sends a public announcement message that every su that is in the transmission range of the pu will hear and will be aware of how long the channel is busy. this protocol is a new version of aodv routing protocol and as mentioned above, because of the elimination of the periodic beacon messages that are sent for updating table routes, overhead is reduced in this kind of routing protocol. the proposed protocol can be employed both in multi-route and single-route routing. in multi-route routing, data packet fragments are transmitted through different routes and therefore, the end-to-end delay is decreased. in single-route routing, it is possible to choose only one route from among the discovered routes to send the data and the other ones are reserved as backup routes. in this approach, single-route routing is simulated. we consider n number of cr sensors and that each cr user has access to l+1 data channel(s). from among these channels, l belongs to the pu while sus opportunistically use it and 1 channel is used as the common control channel which is available only to the sus, that is, the pu is not permitted to use it. [16] it has been assumed that each su has access to the available license channels via csma/ ca protocol. from the viewpoint of su, the channel has three states: iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 122 off: it is free of any pus or sus on: is used by pus or other sus temporarily on: the channel is temporarily used by an su. this channel might be used for data transmission on a specific link.[16] two kinds of control data packets are sent for route discovery including route request (rreq) control data packet and route reply (rrep) packet. another control packet that is called a route error (rerr) is used when link failure happens. we will explain the proposed routing process in two phases: route discovery and route maintenance. route discovery also includes two processes: route request and route reply. 3.2 route discovery in our proposed protocol 3.2.1 route request: when a source node has a data for the sink, it needs to discover a route to the sink. so the source starts the routing process by filling a control packet, which is called route request (rreq), and its field is shown in table 1. table 1: the fields of rreq packet fields description reqid unique route request number sid address of the source node did address of the destination node eth the threshold of nodal energy seres sum of the residual energy of all participating nodes in the route. �̅�min the minimum average of the probability of appearance probability of pus in the route. hc hop count fig. 1: the example of routing for sus in our protocol. when the fields of the packet are filled, the source sends the packet to all of its competent one-hop neighbours and this process is repeated until the packet is received by the sink. for example in fig. 1 node a is the source node and node s is the sink. iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 123 b is one of the competent neighbours of a if it satisfies the eq. (1) and eq. (2): eb > eth (1) dsa > dsb (2) eq. (1) means the residual energy of node b should be more than a determined minimum threshold energy (eth) for receiving the request packet from node a. in other words, by eq. (1) we can eliminate the nodes with too little residual energy from participating in the route. consequently, the probability of link failure and overhead are decreased and the network lifetime is improved. also, by knowing the location of the sink and its neighbour, each node can figure out the euclidean distance of itself and its neighbour to the sink (dsa, dsb) . so, node b should be nearer to the sink than node a to be considered as the competent neighbour. in fig. 1 we can see that node b is a competent neighbour but node n and r are not. because node n is farther from the sink than node a and also the residual energy of node r is lower than the threshold level. eq. (2) avoids making a loop and also reduces end-to-end delay. each relay node that receives the packet changes some parts of the fields by its information and sends it, as mentioned above, to its competent neighbours. these changes in fields of request packet are explained in detail as follows: • the source node s initiates to make an rreq packet and at the same time sets a timer. this timer is going to measure the time of route discovery. • node s puts its residual energy in the field of seres. each node that receives the rreq packet sums its residual energy (ec) with the current number of the field seres and puts it in this field again. thus, when the rreq packet gets to the sink, it can calculate the sum of the residual energy of all nodes in every route. • as mentioned above, each node is aware of its neighbours’ free channel. so if there are more than one common free channel between rreq sending and receiving nodes, the sending node should choose a common channel that has the minimum pu appearance probability (p). in this way, the probability of link failure will be decreased during the sending data period and consequently, due to avoiding reroute, end-to-end delay and energy consumption will be reduced. moreover, throughput and network lifetime will be increased. after choosing a channel for sending the rreq packet, the sending node compares the (p) of that channel with the amount of field (𝑃min) in the rreq packet and if it is smaller (𝑃 ≤ 𝑃min), supersede with the amount of field 𝑃min (𝑃 = 𝑃min) and if it isn’t, it will remain with no changes. thus when the sink receives the rreq packet, it can calculate the (𝑃min) in every route separately. • each time the rreq packets are sent, one unit is added to the hop count and it is brought in the (hc) field of rreq packet. this process has been shown in flowchart 1 for node c in route1. 3.2.2 route reply after receiving the first request packet, the destination starts a timer and receives rreq packets until the timer expires. it is assumed that the sink gets the most q packets and discards the rest even if the timer expires. the sink is responsible for averaging the residual energy of all nodes in the route by eq. (3). 𝐴𝐸 = 𝑆𝐸𝑟𝑒𝑠/𝐻𝐶 (3) iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 124 flowchart 1: route request process for node c. in other words, ae is the approximate average of nodal energy in the route. so for every route, there is a unique ae and �̅�min. the sink should create a packet which is called route reply (rrep) for each route and ae and �̅�min of each route are considered separately in the rrep packet of that route. the fields of this packet are shown in table 2. table 2: the fields of rrep packet. fields description reqid unique route reply number sid address of the source node did address of the destination node ae average of nodal energy in the route �̅�min the minimum average of the probability of appearance probability of pus in the route ne the number of nodes whose residual energy are lower than average energy troute time is needed for route discovery rrep packet of each route sends back through that route to the source node (s). the intermediate nodes in the route get the rrep packet and change it with their information. some of these important changes have been stated in the following: • each relay node that receives the rrep packet compares its residual energy (ec) with the amount of field ae. if it is lower than ae, then the node adds one unit to the amount of field ne (with zero initial value). it can be seen in flowchart 2. when the rrep reaches to the source node (s), the amount of the ne field shows the iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 125 number of nodes in which their residual energy are lower than average energy of all nodes through the route. in other words, this shows the number of nodes of which residual energy is in crisis situation. in this way, we pay attention to the energy of each node in the route separately. • when the rrep packets reach the source node, (s), the required time for the route discovery is written in the packet of that route by the source. after the time of receiving the first rrep packet, the source waits until the next t time and gets all the rrep packets which reach in this time span and after that, each rrep packet reached is discarded. • after receiving all the rrep packets, the source should calculate ne̅̅̅̅ for every packet using eq. (4). this parameter (ne̅̅̅̅ ) shows the stability of the route in the aspect of residual energy of all nodes in that route. lower ne̅̅̅̅ causes less route failure probability and more stability of the route; so it improves the throughput and the lifetime of the network. note that n=hop count (hc). 𝑁𝑒̅̅ ̅̅ = 𝑁𝑒 𝑁 (4) as said before, the 𝑃min for each route is available in the rrep packet of that route. more 𝑃min causes more stability and less link failure probability in that route and so it increases the throughput of the network. also, it reduces end-to-end delay because of eliminating extra rerouting processes. 3.2.3 selecting route finally, a route should be chosen from all of the discovered routes [25]. selection of a route depends on the priority of the source node(s) and it is done using eq. (5). ui = α 𝑃min +(1 − α) 1 𝑁𝑒̅̅ ̅̅ (5) the selecting route process is done as follows: • if the source (s) node wants to choose a more stable route from the aspect of channel access, it should choose 0.5 < 𝛼 ≤ 1 first and then calculate ui for all of the discovered routes. the route which has the maximum amount of ui is selected. (if 𝛼 = 1, only �̅�min is important). • if the source prefers to choose the more stable route from the aspect of residual energy of all its nodes, it should consider 0 ≤ 𝛼 < 0.5 and then the route with the maximum amount of ui is selected for sending data. (if 𝛼 = 0 ,so just 𝑁𝑒̅̅ ̅̅ is important for the source) • if two factors of channel access and residual energy of nodes are equally important for the source, α should be considered 0.5 and then selected the maximum amount of ui. • so the route with the maximum amount of ui is selected and the other discovered routes are kept as backup routes. • after selecting route (i), the data packet should be sent through that route (i). the troute should be inserted in the data packets. for example, in fig. 1, we suppose that for the source node (s) two routes to the destination have been discovered. iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 126 if we consider that both nodal residual energy and channel access are equally important for the source node, it should choose 𝛼 = 0.5 . u1=0.5*0.3+0.5*7/6=0.73 u2=0.5*0.4+0.5*7/3=1.35 as one can see, the amount of metric u for the route 1 and 2 are 0.73 and 1.35, respectively. so the source should choose route 1 for sending data. this process is shown in flowchart 2 for source node s in route 1 and with 𝛼 = 0.5. flowchart 2: selecting the route for the source node. one can see that the most stable route in the aspect of energy and spectrum access has been selected. in this approach, by considering the residual energy of all nodes participating in a route, the probability of complete depletion of nodal energy during sending data is reduced. consequently, link failure and the necessity for rerouting is lower, and then delay and energy consumption are decreased and throughput and lifetime are increased. the selected route has the minimum precedence probability of pus, so it can improve throughput and delay too. 3.2.4 route maintenance link failure can have several reasons such as starting activity of pus in the channel, channel inaccessibility, energy exhaustion of nodes, node mobility, etc. the sender node becomes aware of the failure when it does not receive the ack message. for instance, if the link fails while node a is transmitting a packet to node h, node a does not receive the ack message of packet delivery to node h. in this situation our protocol has proposed: iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 127 node a should understand why link failure has happened. • if the link failure is for the sake of the appearance of pu in the channel, the su will sense it by sensing method and as it was supposed, it can predict how long it takes for pu to regain the channel. therefore, it searches between its one-hop neighbours to find a shortcut route that with one additional node gets to node b. in fig. 2 one sees both nodes p and q can join nodes a and b. for choosing between route a-qh and a-p-h node a should do the eq. 5 and choose the shortcut route which has the maximum ui. for this point, a should get the amount of pmin and (ne̅̅̅̅ ) for each route by knowing about its one-hop neighbours and their channel, as mentioned before. after selecting the shortcut route, sending data continues through that route. as our approach has considered the residual energy of each node in the route, merging the shortcut route with the original selected route makes the most stable route again. fig. 2: the example of route maintenance for sus in our protocol. • if the link failure is because of energy depletion of node h, node h is dead, so node a cannot utilize the first approach. in this situation, node a searches between its two-hop neighbours to find a shortcut route to get to node i. as one can see by using the shortcut route a-q-t-i node a can send its packet through route 2 again. like approach1 if there is more than one shortcut route to node i, node a should select the route with the maximum ui. • we consider that link failure has been created by the pu’s activity and there is not any shortcut route to retain route. as mentioned before, in the route discovery process, needed time for discovery has been calculated and has been included in the data packet. when pu starts its activity in the channel node, node a will know how long pu will stay in the channel. so it compares the time (which should be waiting to regain the channel) with a required time of route discovery troute (as included in the data packet). if the waiting time is less than that of troute, it keeps the packet until the pu leaves the channel so that node a can restart its activity and transmit the packet. however, if waiting time is more than troute, node a will discard the packet and will send the route error (rerr) packet back to the source to notify it of link failure and to restart route discovery. • if the link failure is not caused by pu’s activity, node a will send the packet to node h for k times, and if it still does not receive the ack message, it will send the rerr packet for the source in order to use the backup route or even restart route discovery. as mentioned before, in the selecting route process, when one route is selected iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 128 among all the discovered routes for sending data, another route among all discovered routes, which has the most ui is used as the backup route. 4. performance evaluation our protocol was compared with esac and scr and erp and ser. firstly, our protocol is designed for small-scale areas (smart home, healthcare,) and in these areas, it improves the performance of the network. secondly, as mentioned before, clustering, especially for the small-scale networks, is too complex and imposes more delay for route discovery. also, energy consumption may be needed in some clustering routing protocols. so, in the aspect of quality of service parameters such as delay and overhead our protocol is better than esac and scr and erp especially in small-scale areas. 4.1 simulation setting we intend to simulate a square area in which m stationary pus are uniformly active. table 3 illustrates the simulation configuration parameters. table 3: simulation parameters parameter nominal value network dimension 150 m ×150 m number of cr sensor nodes 150 number of pu 20 sink location (50,50) the threshold of nodal energy 0.6 joule sensing range 10 m initial node energy 100 joule channel bandwidth 512 kbps packet size 256 byte packet rate 5 packets/s initial placement of nodes uniform random simulation time 1000 s each pu operates on l channels. the details of the pu operation are not within the scope of this paper. however, the pu operation is modelled on the on/off process. if the pu occupies a channel it is in on state while the su cannot access the channel. the sus can utilize the channel only when pus is in off state and the channel is free. as it was mentioned, we assumed each time pu appears in the channel, that the node su that is in the pu’s sensing range can be aware how long it stays in the channel (the pu is on). the cr users have the same rate of message generation with exponentially distributed random intergeneration time. the transmission and receiving energies for the data packet are 6.6 and 4.6 respectively, and for the control packet they are about 0.75 mg and 0.52 mg, respectively. we compared our protocol with esac and scr and erp using the following metrics [15]: • packet delivery ratio: the total number of packets received at the sink to the total number of packets sent from all the source nodes during the simulation. • network throughput: the total number of bytes received at the sink per unit time. the higher amount of these two metrics shows more reliability of the routing protocol and better performance of the network. iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 129 • end-to-end delay: the time a message takes from its generation to the final arrival at the sink. at the end of the simulation, we should take the average end-to-end delay for all packets which are received by the sink. the lower this metric, the less link failure and better quality of routing protocol. • network lifetime: the time between the start of the simulation to the moment the first node energy exhausts and dies. more amount of this metric declares less energy consumption of network. also, it shows better performance of the routing protocol. • normalized routing overhead: the number of transmitted packets except for data packets (control packets, beacon packets, etc...) to the total number of the delivered packets to the destination. 4.2 simulation results figure 3(a) shows the packet delivery ratio variation. it is obvious that with increasing level of pu, occupancy delivery ratio has decreased for each of the five protocols. as one can see ser and esac have the minimum delivery rate because they have not considered the pu appearance in the channel during the route selection. our approach and erp and scr have considered pu activity and so, they nearly have the same high delivery rate. figure 4(a) has shown an increasing number of su causing a drop in delivery ratio. also in our protocol, variation in rate until 180 secondary users are nearly fixed and a bit higher than others. but with increasing the number of su from 180, delivery rate suddenly decreases and gradually its rate falls below other protocols. figure 3(b) displays the comparison of throughput among the five protocols. ser shows less throughput than others. since the route selection process in this protocol may cause frequent route failure, the throughput of esac is better than ser. but still, it is much lower than the other three protocols. erp, scr and our protocol have better performance. in a lower number of pus, our protocol has better performance. as one can see in fig. 4(b), with increasing the number of sus, throughput will be decreased. with a lower number of sus, the throughput of our protocol is better than others. figure 3(c) has compared end-to-end delay with increasing pu in five protocols. as it is obvious, our protocol and erp and scr act nearly the same. while due to considering pu activity of route selection, they are much better than ser and esac. as it can be seen in fig. 4(c), in a lower number of su, the delay of our protocol is much less than other protocols. in ser and esac, the appearance probability of pu in the route discovery process has been neglected. also in ser protocol, energy consideration is done in a way that causes frequent route failure and imposes too much delay on the network. it is also a driven-table protocol so it naturally has a high delay. in scr, however, it has noted pu activity in route discovery, but clusters are created in the whole time of simulation even if no event has happened and it is the main reason that scr has more delay than erp. it can be seen in the lower number of su that our protocol has less delay than erp. because clustering in erp is too complex and causes more delay than flat routing. the comparison of network lifetime in five protocols is displayed in fig. 3(d). we can see that with increasing the occupancy percentage of the pu, the network lifetime has decreased but meanwhile, our protocol and erp have outperformed the others. in fig. 4(d) we show that our protocol in the lower number of sus has a higher lifetime than other protocols. being aware of energy as well as considering pu activity in our protocol causes less route failure and consequently, less retransmission or rerouting. therefore, it has less nodal energy consumption. also, maintaining the route in our protocol is such that it has the minimum energy consumption. in other words, energy balancing, which was considered in selecting the route in our protocol, leads to increased network lifetime. another reason that iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 130 erp and our protocol have better network lifetime is that nodes with lower energy than the threshold of energy cannot participate in the routing process. (a) (b) (c) (d) (e) fig. 3: effect of channel usage percentage by pus on (a) packet delivery ratio, (b) throughput, (c) end-to-end delay, (d) network lifetime, (e) control overhead. 0 10 20 30 40 50 60 70 80 90 100 1 0 2 0 3 0 4 0 5 0 6 0 7 0 p a c k e t d e li v e ry r a ti o ( % ) channel usage percentage by pus 0 100 200 300 400 1 0 2 0 3 0 4 0 5 0 6 0 7 0 t h ro u g h p u t ( k b ) channel usage percentage by pus ser esac erp scr our protocol 0 0.2 0.4 0.6 0.8 1 1 0 2 0 3 0 4 0 5 0 6 0 7 0 e n d -t o -e n d a v e ra g e p a c k e t d e la y ( s) channel usage percentage by pus ser esac erp scr our protocol 0 100 200 300 400 500 1 0 2 0 3 0 4 0 5 0 6 0 7 0 n e tw o rk l if e ti m e ( s) channel usage percentage by pus ser scr erp esac our protocol 0 2000 4000 6000 8000 10000 12000 14000 1 0 2 0 3 0 4 0 5 0 6 0 7 0 c o n tr o l o v e rh e a d channel usage percentage by pus ser esac erp scr our protocol iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 131 (a) (b) (c) (d) (e) fig. 4: effect of number of sus on (a) packet delivery ratio, (b) throughput, (c) end-to-end delay, (d) network lifetime, (e) control overhead. 5. conclusion in this paper, we have proposed a new routing protocol considering spectrum and energy awareness in cognitive radio sensor networks (crsn). the protocol tries to choose the most stable route in the aspect of nodal residual energy or spectrum access probability for sending data. as can be seen in section 5 of this paper, our proposed protocol has 30 40 50 60 70 80 90 100 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 2 4 0 p a c k e t d e li v e ry r a ti o ( % ) number of sus ser esac erp scr our protocol -50 50 150 250 350 450 3 5 7 0 1 0 5 1 4 0 1 7 5 2 1 0 2 4 5 t h ro u g h p u t ( k b ) number of sus ser esac erp scr our protocol 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 2 4 0 e n d -t o -e n d a v e ra g e p a c k e t d e la y (s ) number of sus ser esac erp scr our protocol 50 100 150 200 250 300 350 400 450 500 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 2 4 0 n e tw o rk l if e ti m e ( s) number of sus ser esac erp scr our protocol 0 1000 2000 3000 4000 5000 6000 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 o v e rh e a d number of sus ser esac erp scr our protocol iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 132 improved the quality of service parameters such as delay and throughput. this is mainly because our protocol considers the energy of all nodes participating in the route. also, it pays attention to spectrum access probability of each node in the route. finally, we believe our protocol, especially in a small area, can be useful and it can improve the performance of the network. references [1] mitola j. (1999) software radio architecture: a mathematical perspective. ieee journal on selected areas in communications., 17(4):514-538. [2] li b, li d, wu qh, li h. (2009) asar: ant-based spectrum aware routing for cognitive radio networks. in wireless communications & signal processing: november 2009; wcsp 2009. international conference on.ieee; pp 1-5. [3] shi y, hou yt, kompella s, sherali hd. (2011) maximizing capacity in multi-hop cognitive radio networks under the sinr model. ieee transactions on mobile computing., 10(7):954967. [4] song y, he x, binsack rv. (2017) energy aware routing protocol for cognitive radio networks. wireless sensor network., 9(03):103. [5] saleem y, salim f,rehmani mh. (2015) routing and channel selection from cognitive radio network’s perspective: a survey. computers & electrical engineering., 42:117-134. [6] tang f, tang c, yang y, yang lt, zhou t, li j, guo m. (2017) delay-minimized routing in mobile cognitive networks for time-critical applications. ieee transactions on industrial informatics., 13(3):1398-1409. [7] oey ch, christian i, moh s. (2012) energy-and cognitive-radio-aware routing in cognitive radio sensor networks. international journal of distributed sensor networks., 8(12):636723. [8] sarma hkd, bhuyan b, dutta n. (2013) an energy balanced routing protocol for cognitive wireless sensor networks. in world congress on engineering & computer science: october 2013; san francisco, usa. [9] chouikhi s, el korbi i, ghamri-doudane y, saidane la. (2015) a survey on fault tolerance in small and large-scale wireless sensor networks. computer communications., 69:22-37. [10] clausen t, jacquet p. (2003) optimized link state routing protocol (olsr)., (no. rfc 3626). [11] royer em, perkins ce. (1999) multicast operation of the ad-hoc on-demand distance vector routing protocol. in proceedings of the 5th annual acm/ieee international conference on mobile computing and networking: august 1999; acm; pp 207-218. [12] al-karaki jn, kamal ae. (2004) routing techniques in wireless sensor networks: a survey. ieee wireless communications, 11(6), 6-28. [13] ozger m, akan ob. (2013). event-driven spectrum-aware clustering in cognitive radio sensor networks. in infocom, 2013 proceedings ieee: april 2013; ieee; pp 1483-1491. [14] shah, ga, akan, ob. (2013). spectrum-aware cluster-based routing for cognitive radio sensor networks. in communications (icc), 2013 ieee international conference on: june 2013; ieee; pp 2885-2889. [15] tabassum m, razzaque ma, miazi mns, hassan mm., alelaiwi a, alamri a. (2016) an energy-aware event-driven routing protocol for cognitive radio sensor networks. wireless networks., 22(5):1523-1536. [16] kamruzzaman sm, kim e, jeong dg. (2011) spectrum and energy aware routing protocol for cognitive radio ad hoc networks. in communications (icc), 2011 ieee international conference on: june 2011; ieee; pp 1-5. [17] lo bf, akyildiz if. (2013) reinforcement learning for cooperative sensing gain in cognitive radio ad hoc network. wireless networks (springer)., 19(6):1237-1250 [18] singh jsp, rai mk, singh j, kang as. (2014) trade-off between and and or detection method for cooperative sensing in cognitive radio. in advance computing conference (iacc), 2014 ieee international: february 2014; ieee; pp 395-399. iium engineering journal, vol. 19, no. 2, 2018 moshtaghi and mazinani 133 [19] singh jsp, singh r, rai mk, singh j, kang as. (2015) cooperative sensing for cognitive radio: a powerful access method for shadowing environment. wireless personal communications., 80(4):1363-1379. [20] langendoen k, reijers n. (2003) distributed localization in wireless sensor networks: a quantitative comparison. computer networks., 43(4):499–518. [21] xiao b, chen l, xiao q, li m. (2010) reliable anchor-based sensor localization in irregular areas. ieee transactions on mobile computing., 9(1):60-72. [22] dutta p, culler d. (2008) practical asynchronous neighbor discovery and rendezvous for mobile sensing applications. in proceedings of the 6th acm conference on embedded network sensor systems: november 2008; acm; pp 71-84. [23] xing x, jing t, cheng w, huo y, cheng x. (2013) spectrum prediction in cognitive radio networks. ieee wireless communications., 20(2):90-96. [24] sharma m, sahoo a. (2010) residual white space distribution-based opportunistic channel access for cognitive radio enabled devices. sigcomm computer communication review., 40(4):427–428. [25] singh jsp, rai mk. (2018) crop: cognitive radio routing protocol for link quality channel diverse cognitive networks. journal of network and computer applications., 104: 48-60. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 dynamic modeling of a single-link flexible manipulator robot with translational and rotational motions dermawan dermawan1,2*, hammada abbas1, rafiuddin syam1, zulkifli djafar1 and abdul kadir muhammad2 1department of mechanical engineering, hasanuddin university, gowa-makassar, indonesia. 2department of mechanical engineering, state polytechnic of ujung pandang, makassar, indonesia *corresponding author: dermawan@poliupg.ac.id (received: 26th august 2019; accepted: 27th november 2019; published on-line: 20th january 2020) abstract: the flexible manipulator is widely used in space robots, robot arm, and manufacturing industries that produce micro-scale products. this study aims to formulate the equation of motion of a flexible single-link manipulator system that moves translationally and rotationally and to develop computational codes with the finite-element method in performing dynamic simulation on the vibration of the flexible manipulator system. the system of the single-link flexible manipulator (slfm) consists of an aluminium beam as a flexible link, a clamp part to hold the link, a dc motor to rotate the drive shaft, a trajectory to transfer the link in translational motion, and a servo motor to rotate the link. computational codes in time history response (thr) and fast fourier transform (fft) processing were developed to identify the dynamic behaviour of the link. the finite-element method and newmark-beta are used in simulating the slfm. simulation using the finite-element method has displayed dynamic behaviour through a graph of fft on free vibration and thr graph on forced vibration by the excitation force due to the translational and rotational motions of the system. fft has also generated natural frequency values as (f) 8.3 [hz]. for translational and rotational motions, lateral deformation gets the maximum deviation at the value 0.0077 [m] and the minimum deviation -0.0085 [m] at t = 0 [s]. while at time t = 0.5 [s] due to the existence of the excitation force at the time, the maximum deviation at the value -0.009 [m], and the minimum deviation -0.0085 [m]. abstrak: pemanipulasi fleksibel banyak digunakan dalam robot angkasa, lengan robot, dan industri pembuatan yang menghasilkan produk skala-mikro. kajian ini bertujuan mengformulasi persamaan pergerakan sistem manipulasi pautan-tunggal fleksibel yang bergerak secara realisasi dan putaran dan bagi membina kod pengkomputeran dengan kaedah unsur-terhingga dalam membuat simulasi dinamik pada getaran sistem manipulasi fleksibel. sistem manipulasi pautan-tunggal fleksibel (slfm) terdiri daripada alur aluminum sebagai pautan fleksibel, bahagian pengapit bagi memegang pautan, motor dc bagi memutar pandu aci, trajektori bagi memindahkan pautan dalam gerakan realisasi, dan motor servo bagi memutar pautan. kod pengkomputeran dalam sambutan respons masa (thr) dan proses penjelmaan fourier pantas (fft) telah dibina bagi mengenal pasti kelakuan dinamik pada pautan. kaedah unsur-terhingga dan beta-newmark telah digunakan dalam simulasi slfm. simulasi menggunakan kaedah unsur-terhingga menunjukkan kelakuan dinamik melalui graf fft pada bebas getaran dan graf thr pada getaran paksaan melalui ujaan paksa bagi membentuk realisasi dan gerakan putaran pada sistem. fft juga menghasilkan nilai frekuensi semula jadi sebagai (f) 8.3 [hz]. bagi 228 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 realisasi dan gerakan putaran, sisihan perubahan bentuk maksimum ialah pada nilai 0.0077 [m] dan sisihan minimum -0.0085 [m] pada t = 0 [s]. sementara pada masa t = 0.5 [s] bergantung pada ujaan paksa yang hadir pada masa tersebut, sisihan maksimum ialah pada nilai -0.009 [m], dan sisihan minimum ialah -0.0085 [m]. keywords: dynamic modelling; single-link flexible manipulator; finite-element method; time history response; translational and rotational motions 1. introduction in industrial applications and robotic systems, single-link flexible manipulators (slfm) are expected to work optimally during operation. researchers who study flexible manipulators for space can be found in many reputable journals, such as [1-6]. for the application of space robots, a manipulator robot is designed to lift relatively small objects such as rock samples and remove existing obstacles so that the manipulator must be able to carry out operations with better positioning accuracy. lower weight aims to save load capacity and reduce the cost of rocket launches and reduce energy consumption. slfm has limitations with frequent vibrations that cause system performance to be interrupted. therefore, further research is needed to describe the dynamic conditions of the slfm. several studies have investigated the performance and control system of the slfm. qiu [7] reviewed two main parts of the flexible cartesian manipulator (fcm), explicitly the control algorithm and validated it with the experiment. the fcm used fiberglass colophony material. the fcm experiment only displayed translational motion along the y-axis (o-yo). conversely, shin and rhim [8] conducted modelling with the newtonian approach to horizontal translational motion (o-x-o) on the flexible link. the modelling result showed the effect of lateral vibration and dynamic stiffness at varying frequencies of the beam. yang et al. [9] designed an observation using partial differential equations (pde) using kinetic energy and potential energy methods to predict vibration, unlimited dimensional condition by only requiring practical measurement values from a boundary position. from the simulation result, the vibration can be removed using pd control. the research done by ata et al. [10] is somewhat different. they used an euler bernoulli approach on slfm, where a flexible beam is considered rigid and marked by a straight line that extends from point o to the end of the beam, called a virtual link (vl), which is perpendicular to the tangent vector line. the beam on vl moves rotationally. still, on the slfm, muhammad et al. [12-15] carried out comprehensive simulations and experiments with the fem, pd, and af control approaches to vibration on the slfm. they [16-18] also added a piezoelectric actuator on aluminium-based links, which generate stress on two degrees of freedom (dof). meanwhile, mahto [18], still in the rotation movement of the slfm, has investigated it using the finite-element method (fem) approach with five dof assuming the link manipulator as a euler-bernoulli beam. a myriad of investigations on the flexible manipulator using fem in analysing vibration has been reported in the literature such as essential modelling replacement in control algorithm [19], a multi-link flexible robotic manipulator with a smart piezoelectric transducer [20], vibration control of a single-link flexible composite manipulator [21]. finite-element modelling with the piezo-integrated structure using hamiltonian principles [22], and free vibration analysis on a thin-plate [23]. based on several studies, in general, they researched the slfm system with just one motion: translation or rotation. if the slfm is applied in industry, it generally uses two movements simultaneously, that is to say, translational and rotational motions. the problem is the lack of research that combines 229 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 translational and rotational motions of the slfm system, which results in inaccurate positioning. therefore, this research will to do a more in-depth study. several similarities were also identified with existing research, such as the use of lagrange’s equation, kinetic energy, and potential energy to derive the equation of motion [24]. the difference is, bien's work focuses on the combination of translational and rotational movements of a two-link manipulator, where the first link moves horizontally, and the second link moves rotationally. dermawan et al. [25] have found the equation of translational movement in slfm using the finite-element method. research from muhammad et al. [17] as the primary reference in this research, that has formulated the equation of rotational motion at slfm, becomes interesting to develop by combining translational and rotational movements. the purpose of this study is to formulate the equation of motion and compose computational codes by fem on the slfm system that moves translationally and rotationally. this research used fem in carrying out dynamic simulations of the slfm system. the results of the simulation showed the vibration dynamics of the order by displaying a time history response (thr) and fast fourier transform (fft) processing of the system. 2. dynamic modelling based on the kinematic model of the slfm that moves translationally, as shown in fig. 1, the position vector of point p moves translationally at the o-y coordinate. the link moves translationally in the horizontal direction at the coordinates o-yp as far as y, and vp is the lateral deformation to point p. the base of the link experiences a positive displacement on the y-axis as now as o-y, the positive x-axis at position xp = xp, and the end of the link is a position vector p. the position vector r (x,t) at point p on the link at t = t, is represented in the o-x-y coordinates. fig. 1: the position vector of point p on the link that moves translationally. the position vector of point p in the o-x-y coordinates is( , ) = ( , ) + ( , ) , (1) where; ( , ) = , (2)( , ) = + . (3) 230 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 the velocity vector of point p in the coordinates o-x-y is given witḣ ( , ) = ̇ ( , ) + ̇ ( , ) . (4) 2.1 equation of motion using the finite-element method fig. 2: the translational coordinate of the link. this paper uses the finite-element method approach, where each partition on the link is presently divided into several elements. the aim is to find out the mass matrix (m) and the stiffness matrix (k), that will be used to simulate the dynamics of the system. the system dynamics model is a cantilever structure that is partitioned into six elements and six-node points. fig. 2 show the translational coordinate x-y divided by one-dimension and twonode elements with four boundary conditions together at node i and i+1. an element of the link is shown in fig. 3. the finite-element has two dof, called the lateral deformation of the i-th element ( ) and slope ( ). the physical properties of the system consist of the length of the link (li), the cross-sectional area of the link (si), and the moment of inertia (ii). each element has mechanical properties, namely young's modulus and mass density, which are denoted by ei and i. the nodal displacement vector is expressed by = [ , , , ], (5) with = + + + . (6) fig. 3: nodal displacement of the link. node i+1 node i y xi x vi i vi+1 i+1ei, i, ii, si, li, 231 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 in the discretization process, the equation of translational motion can be achieved as follows; acceleration of p can be written bẏ . ̇ = ̇ + ̇ + ̇ + 2 ̇ ̇ . (7) the general articulation of kinetic energy (t), with (v) being the velocity, can be expressed by = ∫ . . (8) kinetic energy (ti) of the system is given by = ∫ . ̇ . ̇ . . (9) so that kinetic energy of translation motion (tit) for the system can be written as= ̇ + ̇ + ̇ ̇ + ̇ ̇ , (10) wherė ̇ = [6 6 − ]. (11) the potential energy (ui) of the system is= . (12) the dissipation function (ri) of the system is= ̇ . (13) the mathematical model of a dynamic system using the lagrange’s equation is written with ̇ − ̇ + ̇ + ̇ = . (14) if we substitute variables from eq. (14) as follows:̇ − ̇( ) + + ̇ + ̇ = . (15) furthermore,̈ − ̈( ) + ̇ + = 0. (16) so that the equation of motion for the i-th element gives̈ + ̇ + = ̈ ( ) . (17) m a t r i x m i , c i , k i , a n d ̈ ( ) are the mass matrix, damping matrix, stiffness matrices, and excitation forces of the dc motor, respectively. matrix mi, ci, ki is an element of the equation contained in eq. (17) is a representation of; = ⎣⎢⎢ ⎡ 1562254−13 22413−3 5413156−22 −13−3−224 ⎦⎥⎥ ⎤ , (18) 232 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 = ⎣⎢⎢ ⎡ 126−126 64−62 −12−612−16 62−64 ⎦⎥⎥ ⎤ , (19) = . . (20) while the translational motion of the force vector is= − {6, , 6, − } . (21) the length of the i-th element is the length from the first element to i, with the symbols li and l1+i. equation of translational motion of the slfm with i-th element based on boundary conditions is written with;̈ + ̇ + = ̈( ) . (22) the kinetic energy of rotational motion (tir) of the system has been formulated in [11] as follows = ̇ + ̇ ̇ + ̇ + ̇ ̇ . (23) and then the rotational force vector is written witḧ( ) = 30 + 9 , 5 + 2 , 21 , −5 + 3 . (24) equation of motion of the i-element is written by [12],̈ + ̇ + ( − ̇ ( ) ) = ̈( ) . (25) w h e r e ̈( ) the respective excitation forces. to find the kinetic energy of the system, kinetic energy caused by translational and rotational motions is obtained by combining kinetic energy from translational motion and rotational motion so that the kinetic energy of translational and rotational motions ( ) of the system will be obtained;= + . (26) from the discretization result of the kinetic energy of translational and rotational motions, then by substituting eq. (10) and (23) into eq. (26) becomes= ̇ + ̇ + ̇ + ̇ ̇ − ̇ − ( ̇ + ̇ ) ̇ . (27) applying lagrange’s equation, then substitution eq. (27) to eq. (14) gives2 ̇ − ( ̇ + ̇ − ̇ + + ̇ = 0, (28)2 ̈ − ̈ + ̈ + ( − ̇ ) + ̇ = 0. (29) from the results of discretization using lagrange’s equation, the equation of translational and rotational motions for the i-element becomes2 ̈ + ̇ + ( − ̇ ) = ̈ + ̈ . (30) finally, the equation of translational and rotational motions of the system can be written 233 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 2 ̈ + ̇ + ( − ̇ ) = ̈ + ̈ . (31) 3. computational model fig. 4: physical model of the slfm. figure 4 shows the physical model of the slfm robot. the slfm consists of an aluminium beam, a track of the link, a clamp-part, a servo motor to rotate of the link, and a dc motor to make translational motion using a ball screw mechanism. the link, including the clamp-part, is more rigid than the link alone. furthermore, at the end of the link, an accelerometer is installed to detect vibration that occurs in the system. figure 5 shows an illustration set-up of the slfm system. on the microcontroller, there is a switch to regulate translational and rotational motions on the slfm system. the switch consists of on-off buttons, translational motion, translational and rotational motions, and direction of movement. there is a usb connector for connecting the vibration sensor accelerometer to a computer program. fig. 5: illustration set-up of the slfm. 234 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 table 1: physical parameters of the slfm. property symbol value total length [m] l 3.30 × 10-1 length of the link [m] li 3.00 × 10-1 breadth of cross section [m] bi 2.50 × 10-2 height of cross section [m] hi 1.00 × 10-3 cross-section area of the link [m2] si 1.95 × 10-5 cross-section area moment of inertia around iaxis of the link [m4] ii 2.75 × 10 -12 young’s modulus of the link [n/m2] ei 7.00 × 1010 the mass density of the link [kg/m3] ρi 2.70 × 103 the viscous damping ratio of the link α 0.10 × 10-3 4. results 4.1 time history response on free vibration figure 6 shows the time history response of lateral deformation vp on free vibration. the lateral deformation was simulated using impulse force as an external force. in this section, the dc motor and servo motor have not moved. the computational code has been generated at a nodal point six on the thr of lateral deformation. the minimum deviation is at the value -0.009 [m], and the maximum difference is 0.0078 [m]. fig. 6: thr on the free vibration of the slfm. 4.2 fast fourier transform processing the results obtained from simulation with free vibration on the system, are then transferred by the fft process to get the value of the natural frequency of the magnitude. figure 7 shows the result of a simulation of the natural frequency of the slfm system. the fft graph shows that the natural frequency (f) is 8.3 [hz]. when compared using the calculation method, a natural frequency of the order obtained is 9.1 [hz], so it can be concluded that the simulation results can be validated correctly. la te ra l d ef or m at io n, v p [m ] time, t [s] 235 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 fig. 7: the natural frequency of the slfm. 4.3 time history response with excitation force on translational motion figure 8 shows the thr of lateral deformation with the excitation force of the slfm system on the translational motion. computational codes on thr of lateral deformation were developed based on the formulation explained in the previous section. in the calculation, the motor rotates the shaft within 2.5 seconds. this simulation calculates at a nodal point six of the link using the excitation force. the dc motor was operated within 2.5 seconds. it can be seen that the lateral deformation gets the minimum deviation at the value 0.0035 [m], and the maximum difference is 0.0032 [m] at t = 0 [s] and t = 0.5 [s] due to the existence of the excitation force at the time, the minimum deviation at the value 0.0037 [m]. the maximum deviation is 0.0034 [m]. fig. 8: thr on the system with excitation force experienced translational motion. 4.4 time history response with excitation force on translational and rotational motions the simulation results of translational and rotational motions obtain thr of lateral deformation using excitation forces on the system, as shown in fig. 9. in this simulation, the dc motor for translational motion and servo motor rotates the link by the angle of π/2 radians (90 degrees) within 2.5 seconds. it can be seen that the lateral deformation gets the maximum deviation is at the value 0.0077 [m], and the minimum difference is 0.0085 [m] at t = 0 [s]. while, at time t = 0.5 [s] due to the existence of the excitation force at the time, the maximum deviation at the value 0.009 [m], and the minimum difference is -0.0085 [m]. 8.30 0 0.5 1 1.5 2 2.5 3 0 50 100 150 200 frequency, f [hz] m ag ni tu de 236 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 fig. 9: thr on the slfm with excitation force experienced translational and rotational motions. 5. discussion this study focuses on the discretization of equations of motion in slfm systems using fem. when compared with research that has been done by muhammad et al. [17], the results of simulations and experiments of rotational motion have the same tendency as shown on the thr graph. the damping factor and physical parameters determine vibration characteristics. the difference is that this study has installed vibration control in the system so that it produces smaller vibrations and voltages. therefore, for further research, validation of the simulation results with the experimental method, and appropriate vibration control is needed to obtain high position accuracy. 6. conclusion this study has presented the dynamic modelling of the single-link flexible manipulator robot. the equation of motion for the single-link flexible manipulator that includes translational and rotational motion has been formulated using the finite-element method and the lagrange equation. the computational code has been successfully developed and used in system dynamics simulations. the results are presented in the order of time history response and natural frequency with the fft processing. for the translational and rotational motions, the lateral deformation is higher when compared to translational motion, and this is due to the presence of two kinetic energies that occur in the system, namely translational kinetic energy and rotational kinetic energy. this research indicates that vibrations that arise in slfm that move translationally and rotationally are more significant when compared to the individual translational motion or rotational motion, due to the influence of the simultaneous movements that occur in the system. the presented dynamic model ignores the coupling effect and the action of the motor, therefore, this system requires experiment validation and vibration control for industrial applications and robotics. references [1] sabatini m, gasbarri p, monti r, palmerini gb (2012). vibration control of a flexible space manipulator during on orbit operations. acta astronaut. 73: 109–121. https://doi.org/10.1016/j.actaastro.2011.11.012. [2] nanos k, papadopoulos eg (2015). on the dynamics and control of flexible joint space manipulators. control engineering practice. 45: 230–243. https://doi.org/10.1016/j.conengprac.2015.06.009. la te ra l d ef or m at io n, v p [m ] time, t [s] 237 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 [3] meng d, wang x, xu w, liang b (2017). space robots with flexible appendages: dynamic modeling, coupling measurement, and vibration suppression. journal of sound and vibration. 396: 30-50. https://doi.org/10.1016/j.jsv.2017.02.039. [4] gasbarri p, pisculli a (2015). dynamic/control interactions between flexible orbiting spacerobot during grasping, docking and post-docking manoeuvres. acta astronaut. 110: 225-238. https://doi.org/10.1016/j.actaastro.2015.01.024. [5] borovin gk, lapshin v (2018). motion planning of a space robot. in iop conference series: materials science and engineering paper. doi:10.1088/1757-899x/468/1/012020. [6] xu w, meng d, chen y, qian h, xu y (2014). dynamics modeling and analysis of a flexiblebase space robot for capturing large flexible spacecraft. multibody system dynamics. 32: 357-401. doi:10.1007/s11044-013-9389-0. [7] qiu zc (2012). adaptive nonlinear vibration control of a cartesian flexible manipulator driven by a ballscrew mechanism. mechanical systems and signal processing. 30: 248–266. http://dx.doi.org/10.1016/j.ymssp.2012.01.002. [8] shin h, rhim s (2015). modeling and control of lateral vibration of an axially translating flexible link. journal of mechanical science and technology. 29: 191–198. http://dx.doi.org/10.1007/s12206-014-1226-8. [9] yang h, liu j, lan x (2015). observer design for a flexible-link manipulator with pde model. journal of sound and vibration. 341: 237–45. https://doi.org/10.1016/j.jsv.2014.12.033. [10] ata aa, fares wf, sa’adeh my (2012). dynamic analysis of a two-link flexible manipulator subject to different sets of conditions. procedia engineering. 41: 1253–1260. https://doi.org/10.1016/j.proeng.2012.07.308. [11] muhammad ak, okamoto s, lee jh (2014). computer simulations on vibration control of a flexible single-link manipulator using finite-element method. in the nineteenth international symposium on artificial life and robotics 22-24 january 2014; beppu, japan. pp. 381-386. [12] muhammad ak, okamoto s, lee jh (2015). finite element analysis for active-force control on vibration of a flexible single-link manipulator. international journal on smart material and mechatronics (ijsmm). 2(2):106-109. [13] muhammad ak, okamoto s, lee jh (2014). comparison of proportional-derivative and active-force controls on vibration of a flexible single-link manipulator using finite-element method. artif life robotics. 19: 375–381. https://doi.org/10.1007/s10015-014-0186-5. [14] muhammad ak, okamoto s, lee jh (2015) active-force control on vibration of a flexible single-link manipulator using a piezoelectric actuator. in: transactions on engineering technologies. edited by yang gc, ao si, huang x, castillo o. springer, dordrecht ; pp 1– 15. doi:https://doi.org/10.1007/978-94-017-9588-3_1. [15] muhammad ak, okamoto s, lee jh (2014). comparisons of proportional and active-force controls on vibration of a flexible link manipulator using a piezoelectric actuator through calculations and experiments. engineering letters. 22(3): 8. [16] muhammad ak, okamoto s, lee jh (2016). comparison between the one piezoelectric actuator and the two ones on vibration control of a flexible two-link manipulator using finite element method. international journal of mechanical engineering 5(1): 27-44. 238 iium engineering journal, vol. 21, no. 1, 2020 dermawan et al. https://doi.org/10.31436/iiumej.v21i1.1254 http://www.iaset.us/view_archives.php?year=2016&jtype=2&id=67&details=archives. [17] muhammad ak, okamoto s, lee jh (2014). computational simulations and experiments on vibration control of a flexible link manipulator using a piezoelectric actuator. in proceedings of the international multiconference of engineers and computer scientists imecs 2014. 1: 12-14 march 2014; hong kong. [18] mahto s (2014). shape optimization of revolute-jointed single link flexible manipulator for vibration suppression. mechanism and machine theory. 75: 150–160. https://doi.org/10.1016/j.mechmachtheory.2013.12.005. [19] dubay r, hassan m, li c, charest m (2014). finite element based model predictive control for active vibration suppression of a one-link flexible manipulator. isa transactions. 53(5): 1609–19. https://doi.org/10.1016/j.isatra.2014.05.023. [20] halim d, luo x, trivailo pm (2014). decentralized vibration control of a multi-link flexible robotic manipulator using smart piezoelectric transducers. acta astronautica. 104(1): 186– 196. https://doi.org/10.1016/j.actaastro.2014.07.016. [21] yavuz ş, malgaca l. karagülle h (2016). vibration control of a single-link flexible composite manipulator. composit structur. 140: 684–691. https://doi.org/10.1016/j.compstruct.2016.01.037. [22] parashar sk, von wagner u, hagedorn p (2013). finite element modeling of nonlinear vibration behavior of piezo-integrated structures. computers & structures. 119: 37–47. https://doi.org/10.1016/j.compstruc.2012.12.026. [23] kadıoğlu f, tekin g (2018). mixed finite element formulation for the free vibration analysis of viscoelastic plates with uniformly varying cross-section. international journal of mechanical engineering and robotics research 7(2): 235–239. https://doi.org/10.18178/ijmerr.7.3.235-239. [24] bien dx, my ca, khoi pb (2018). dynamic modeling and control of a flexible link manipulators with translational and rotational joints. vnu journal of science: mathematics – physics. 34(1): 52–66. https://doi.org/10.25073/2588-1124/vnumap.4240. [25] dermawan d, abbas h, syam r, djafar z, muhammad ak (2019). finite element analysis on vibration of a flexible single-link manipulator moved translationally. iop conference series: materials science and engineering. 619(1): 012050. https://doi.org/10.1088/1757899x/619/1/012050. 239 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <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> /eti <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> /fra <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> /gre <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> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <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> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. grease quality issues on middle voltage switchgear: corrosivity, resistivity, safety and ageing mohd sabri mahmud1*, sanuri ishak2, mohd najib razali1, mohd aizudin abdul aziz1 and musfafikri musa1 1faculty of chemical and natural resources engineering, universiti malaysia pahang, tun razak highway, gambang, 26300 kuantan, pahang, malaysia. 2tenaga nasional berhad research sendirian berhad, no. 1 research institute area, jalan ayer itam, 43000, kajang, selangor, malaysia. *corresponding author: mohdsabri@ump.edu.my (received: 22nd sept 2018; accepted: 27th april 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.995 abstract: grease products recommended by oem for conventional 11kv switchgears are generally trusted. some disadvantages might however exist among them or their supply could be insufficient and lead to use of non-oem-recommended grease. this paper reports analysis methods to evaluate both types of grease that were recently used in the switchgears at local electrical distribution stations owned by tenaga nasional berhad. hardened, greenish and severely irritating greases probably caused by incompatible compounding, electrochemical reaction, and hazardous components, respectively, were among common problems faced by workers. eight physical tests and four chemical tests were conducted on 10 grease samples using thermogravimetry, switchgear rig, gas chromatography and infrared spectroscopy besides other equipment and standard methods. grease stability, oil bleeding, flammability of grease droplet and dropping point were among the characteristics determined in the analyses. the results reveal copper corrosion, chemical change, instable and inconsistent grease, and toxics in grease, which surprisingly included the oem-recommended one. abstrak: produk gris yang disyorkan oleh pengeluar peralatan asal (oem) bagi gearsuis konvensional 11 kv secara umumnya dipercayai ramai. kemungkinan terdapat kekurangan pada produk-produk tersebut ataupun bekalan gris mereka yang tidak mencukupi telah mendorong kepada penggunaan gris yang tidak disyorkan oleh oem. kaedah analisis kajian ini melaporkan tentang kedua-dua jenis gris yang kebelakangan ini digunakan oleh tenaga nasional berhad pada gear-suis di stesen pencawang elektrik. gris mengeras, berlumut dan menjengkelkan mungkin disebabkan oleh sebatian bahan yang tidak sesuai, tindak balas elektrokimia dan komponen yang tidak selamat, masing-masing adalah antara masalah yang dihadapi oleh para pekerja. lapan ujian fizikal dan empat ujian kimia telah dijalankan pada 10 sampel gris menggunakan termogravimetri, pemakai gearsuis, kromatografi gas dan spektroskopi inframerah selain alatan lain dan kaedah-kaedah piawai. antara ciri-ciri yang dikaji dalam analisis ini adalah kestabilan gris, sifat lelehan minyak, sifat mudah terbakar titisan gris dan takat rendah gris. hasil kajian mendapati gris ini menyebabkan tembaga terhakis, sifat kimia berubah, sifat gris yang tidak stabil dan mudah berubah, dan juga beracun memberi kejutan kerana pihak oem tetap mengesyorkan gris jenis ini. keywords: switchgear grease; switchgear corrosion; grease analysis; grease corrosivity; grease resistivity; grease safety and ageing 216 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. 1. introduction characterization of grease for mechanical bearing components is well developed. various tests were standardized to check bearing life, friction, fretting and false brinelling, noise, and grease life [1]. the lubricating grease for electrical connection however needs additional testing because the grease will be on the contact surface for a long time facing various room conditions, air humidity, and heat from electricity. the switchgear grease should have heat stability to withstand inconsistent temperature due to electrical resistance, unexpected arcing and friction. it must also be consistent for years and not harden as the switching movement is very seldom and involves high electric potential. the electric potential may initiate undesired electrochemical reaction due to charged or sub-charged components of grease that would lead to corrosion and greenish staining on the switchgear part, as shown in fig. 1. fig. 1: corrosion and greenish stain on the switchgear part. compounding of a grease is usually confidential. oem-recommended greases are generally expensive and produced on a specific purpose and equipment. when the technology employed in the equipment becomes obsolete, production of grease may also be reduced or cease. investigating the content of a grease is normally tedious because it involves derivation of unknown complex chemicals from both solid and liquid phases. the use of analytical equipment for chemical property such as ftir, gas chromatography and thermogravimetry helps consumers profile the content of both phases and plan for replacement frequency and stocking. issues of corrosion, safety and health, and lubrication defect necessitate chemical analysis to determine the functional group, chemical species and composition, and elementary composition. this study employed grease tests that were related to the complaints raised by the personnel of the electric company. physical property under hot environment, electric resistivity, and chemical property are the focus of the experiments. the temperature was set between 50 – 110 oc from the highest temperature of the switchgear (90 oc) in order to accelerate reactions – decomposition, oxidation, reduction, and transformation. some of the tests were not from any standard methods and all runs were carried out more than once to ascertain the results. the brands of the 11-kv switchgears employed in local power distributors were electrical power engineering (epe), schneider, abb, tamco, siemens/item, and toshiba. 217 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. 2. materials and methods 2.1 materials heptane (99%), k2co3, na2so4, hydrochloride acid reagent (37%) were supplied by merck. 10 grease samples were tested. eight samples were obtained from tenaga nasional berhad research, of which 3 were oem-recommended and 5 were non-oemrecommended for use in their electric power distributors. however, the brands of the greases are confidential and the terms ‘oem’ and ‘noem’ denote oem and non-oem recommended greases, respectively, which are all followed by numbers. the final 2 samples were non-oem recommended greases proposed by universiti malaysia pahang and are denoted by prop and followed by numbers. 2.2 thermogravimetric analysis evaporation of volatile components and decomposition indicate the stability of the grease. the samples were analyzed using a ta instruments tga q500 based on the astm e2550 method. the analysis was conducted under inert conditions using nitrogen gas blanketing. a few milligrams of sample were put in a pan and heated under a 10 oc/min program from ambient temperature to 800 oc. the tga analysis under isothermal conditions at 150oc was also carried out for 3 hours to estimate the grease ageing. the data was integrated via qnx/platinumtm software to generate plots of weight and derivative weight lost versus temperature. 2.3 10-day heating as an extension to the thermogravimetric analysis, the stability of the grease samples was further studied by observing their weight lost in an oven from 50 oc to 150 oc for 10 days. the samples were also graded by penetration and bleeding tests. 2.4 dropping point and fire test the first drop of grease liquid at a particular temperature was determined manually following the steps described in astm d556 using 2 thermometers, a pyrex tube, fabricated cups, and an oven. the samples were put on the internal wall of the cup while the thermometer was inserted into a tube inside the same cup without touching the sample. the other thermometer was put outside the cup but inside the oven. the temperature of the oven was increased at 2 oc intervals. ten minutes were allocated to allow the samples to reach the desired temperature. as the grease dropped, the experiment was stopped and one third of the temperature difference between tube and oven was calculated as the variance of the dropping point. the test was repeated three times. the droplet was further tested for flammability using a bunsen burner and a glass rod at ambient temperature. after 5 seconds of being in the flame, the presence (or lack) of a fire or flash was observed and recorded. 2.5 oil bleeding test an skf grease test kit was employed to analyze oil bleeding of the samples as per astm d4950. a quantity of 0.5 g of grease was put on a piece of blotter paper. after two hours at 60 oc, oil that was released from the sample appeared as stain on the paper. the area of the stain was measured and the values were then interpreted according to nlgi standard. fig. 2 illustrates the test. 2.6 penetration the consistency of the grease was measured using the cone penetration test (astm d217). the cone was dropped into the grease by a koehler k19500 penetration test and 218 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. the depth of penetration was measured in tenths of a millimeter. the depth of the penetration indicated how thin the grease consistency was, as per nlgi classification. fig. 2: bleeding test. 2.7 contact resistance resistance of switchgear contact (ohms or siemens per meter) was tested by measuring the resistance of electrical connections. this test was specifically to evaluate electrical connections made in the presence of the grease samples by checking contact resistance. two sensing cables (using the same polarities to existing cables) on two sides of the contacts were connected to the targeted object as close as possible, as illustrated in fig. 3. fig. 3: connection diagram for circuit breaker (close position). the variation of no more than 20% from the result for a fresh sample, compared using similar connections, is acceptable based on measurement of the resistance of the circuit/main circuit [2]. the resistivity of the grease was tested by applying it to the 11kv contacting arm using fresh samples, and those samples were heated at 150 ºc for 24 hours. the difference of contact resistance without grease, fresh samples, and prolonged-heated samples were compared. 2.8 corrosivity greenish grease indicates a possibility of copper corrosion on the switchgear arms. a clean copper strip was coated with each sample and was kept in the oven and furnace under 100 oc, 150 oc, and 200 oc for several days following the astm d4048 method. the resulting colors of the strips were interpreted according to the standard codes by a same person at all times, in to avoid bias. 2.9 chemical analysis functional groups were analyzed by using a nicolet is5 ftir spectrometer equipped with id7 atr, which was supplied by thermo fischer scientific, usa. alkane, carbonyl group, and hydroxyl group are among the common functional groups that usually exist in the grease. the sample was scanned from 4000 cm-1 to 600 cm-1 wavelength. 219 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. chemical species in the grease were analyzed using gas chromatography (gc) equipped with a mass spectrometer detector (gc-ms). in chromatographic analysis, lubricant and additive organic liquid were dissolved using heptane for safety reasons since its solubility is comparable to hexane. the procedure presented by synder et al. [3] was therefore referred with some modification. five grams of grease was stirred in a beaker with 100-ml of heptane for 20 min. the polar compound of soap, salt, and ionic complex that settled at the bottom of the beaker was next separated using filter paper, glassware, and a vacuum pump. the cake of undissolved material was peeled away using a spatula when it was dry. one gram of the cake was mixed with 100-ml methanol and 1 ml of concentrated hcl at 60 oc in a flask was agitated on a hot plate stirrer for 20 min for derivatization of methyl esters. next, the substrate was washed with a 200-ml beaker of water to remove remaining methanol and the acid at room temperature in a separating funnel at least thrice. one hundred ml of heptane was finally added to extract methyl esters. the heptane-enriched layer was then taken using a pipette and transferred to a test tube containing k2co3 and na2so4. the heptane solution from extraction of the lubricant and methyl esters derived from thickeners were both analyzed in an agilent gc-ms equipped with an agilent db-1 dimethylpolysiloxane column using helium as the carrier gas. the injections of samples were at 250 oc and the detector temperature was set at 280 oc. the oven was under a program of 65 oc for 3 min, subsequent ramping of temperature of 20 oc/min and a final condition of 250 oc for 5 min were set. the components were identified using the spectrometer library of elements. elemental analysis was also conducted to check the existence of metals in the samples. an agilent icp-ms 7500a was used to determine common salt and metal-based additives such as lithium, aluminum, potassium, calcium, chromium, strontium and metals that were lower electropositive than copper, that were added to grease such as molybdenum and silver. the rate of plasma was 15 ml/min. the flow rates of auxiliary, carrier gas, and sample uptake were 0.8 ml/min under auto detection mode. elements inside the samples were all derived using nitric acid solution. 3. results and discussion 3.1 corrosive and safety corrosion of the samples of copper strip coated with grease was performed at three oven temperatures at different periods, resulting in various colors of stain. although the effect of friction due to the corroded surface of copper-made arms of switchgear is minor, the corrosion roughened the contact surface and produced an uneven copper oxide layer that increased the resistance to electric current [4]. table 1 shows the colors coded as per astm standards and molybdenum element. noem3 and noem4 did not oxidize copper. four samples corroded resulting in totally black copper strips i.e. oem2, noem2, noem5 and prop1 after 3 and 2 days in 150 oc and 200 oc oven, respectively, while other greases only caused tarnishing. noem2 did not corrode at 100 oc for 6 days. this result indicates that, even though the grease was recommended by oem, the metal compound (cation) existing in the grease was less electropositive than copper metal and would lead to oxidation of copper at high temperature. this finding is similar to what el-daly and turky [5] reported when two greases of unknown compounds were analyzed using the copper strip test. icpms analysis further confirmed the presence of low electropositive metal of molybdenum in 4 corrosive grease samples, i.e. oem1, oem2, noem4 and prop1 as shown in table 3. presence of molybdenum may corrode and thus resist switch operations [6]. the other two 220 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. corrosive grease samples, noem2 and noem5, did not have molybdenum result by icpms. table 1: results of corrosion, dropping point and penetration samples astm copper strip corrosion standard* mo (bpm) dropping point (oc) fire test penetration (nlgi) 100oc in 6 days 150oc in 3 days 200oc in 2 days fresh heated in 10 days oem1 1a 1b 3a 2 295 not ignited 3 3 oem2 4c 4c 4c 1506 198.8 ignited and flashed 2 3 oem3 2d 2d 3b 258.3 not ignited 1 1 noem1 1a 3b 3b 207.1 not ignited 2 2 noem2 1b 4c 4c >344 not ignited 2 2 noem3 1a 1a 2c >344 ignited and flame sustained 3 3 noem4 1a 1a 2c 137.1 not ignited 00 00 noem5 4c 4c 4c 327.3 not ignited 1 1 prop1 4c 4d 4d 2150 150 not ignited 2 3 prop2 1a 3b 3c 230 not ignited 2 2 * 1a-1b: slight tarnish, 2a-2e: moderate tarnish, 3a-3b: dark tarnish and 4a-4c: corrosion table 1 also shows the other results. dropping point analysis reveals that noem4 liquefied below 150 oc. a droplet might contain flammable liquid that could cause electrical arcing and fire. painstaking testing was subsequently conducted to determine flammability of the droplet (mixing of lubricant and other compounding fluid from the dropped grease) shows that oem2 and noem3 could catch fire at room temperature. although they were physically buttery and medium solid as indicated by nlgi grade, liquid dropped from these grease samples at high temperature may cause fire in the switchboard and can therefore be considered as class b fires that require use of chemicals to extinguish the fire [7]. chemical identity of grease components were determined from the ftir results within 70% sensitivity. as can be seen in fig. 4, all of them contained alkane where transmittance percentage of the peaks stretching of ch2 and ch3 were within 725 – 720 cm-1, 3000 – 2840 cm-1 and 1450 – 1375 cm-1 wavelength, which were probably attributed to lubricant and aliphatic chain of soaps [8]. c=o and c=c were present in oem3, noem1 and prop1, stretching from 1650 to 1600 cm-1. other functional groups detected in the spectra were integrated by the omnic software to propose species of chemicals for each grease as listed in table 2. similarly, the samples heated at 150 oc for 10 days were analyzed and were compared. thickening the bundle of peaks alumino silicate, kaolin clays, and aliphatic compounds bound with sulfoxide, halogen, acrolein aldehydes, phosphates, and vinyl olefins were found. 3 samples, i.e. noem2, noem3 and prop1, changed after 10 days treatment of 10 oc/day heating and were probably involved with the reaction. this deteriorated the consistency of the grease. although other grease samples did not have the functional groups, their color became dark and black, as particularly shown by the best grease in fig. 5, indicating that there was change of chemical property in the same functional group. this results similarly reported by jiabao et al. [9] where physical property of their tested greases changed without considerable change in the chemical property, was analyzed using ftir. 221 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. fig. 4: ftir results for all grease samples. fig. 5: oem1 after 10 days at (a) ambient temperature – no change, and (b) 150 oc after elevated 10 oc/day for 10 days – dark. (a) (b) 222 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. table 2: results of predicted group of chemicals and comparison of ftir spectra between temperature conditions samples ambient temperature treated remark oem1 aliphatic hydrocarbons aliphatic hydrocarbons no change oem2 aliphatic hydrocarbons aliphatic hydrocarbons no change oem3 trans olefins aliphatic hydrocarbons trans olefins aliphatic hydrocarbons no change noem1 aliphatic hydrocarbons aliphatic hydrocarbons no change noem2 aliphatic hydrocarbons, aliphatic alpha halogen ketones, kaolin clays/ alumino silicates aliphatic hydrocarbons, aliphatic acrolein aldehydes inorganic phosphates changed noem3 aliphatic hydrocarbons, aliphatic sulfoxides aliphatic hydrocarbons, aliphatic primary amines changed noem4 aliphatic hydrocarbons terminal vinyl olefins aliphatic hydrocarbons terminal vinyl olefins no change noem5 aliphatic hydrocarbons perluorinated alkanes aliphatic hydrocarbons, perfluorinated alkanes no change prop1 aliphatic hydrocarbons perfluorinated alkanes, aliphatic carboxylic acid salts changed prop2 aliphatic hydrocarbons kaolin clays/ alumino silicate aliphatic hydrocarbons kaolin clays/ alumino silicate no change lubricant and fame derived from thickeners and additive were analyzed in the gcms. colloidal aqueous layer was present during extraction using heptane in the sample preparation of noem2, noem3 and prop1, which was probably attributed to emulsion of short-chain methyl esters that dissolved in water. gc-ms analysis results revealed possible chemical compounds. among the generic compound of lubricants such as paraffin oils and mineral oils [10], and specific chemical names for aliphatic hydrocarbon, alkane, etc. mentioned in the ftir analysis, hazardous chemicals were also identified by comparing with components in a mass spectrometry library. all grease contained fatty acid alkyl ester where the alkyl probably came from methyl, ethyl, or butyl groups. bis(4octylphenyl)amine, that may cause irritation, was detected at 23 % and 24 % with detection quality (qual) greater than 90 % in oem1 and oem3. butylated hydroxytoluene, that is carcinogenic if swallowed or introduced through wounds, was found with 98% qual in oem3. icp-ms is very sensitive and could measure elements below 10 ppm, as shown in table 3 [11]. metal from contamination of abrasion or corrosion of the contact surface or container can be detected by icp-ms better than icp-oes and icp-aas. oem1, oem2 and noem1 were clearly lithium-based greases. argentum, which normally exists in metal form, was detected in oem2 and prop2. aluminum was detected in all grease while calcium was not detected in oem1 and noem3. aluminum and calcium are normally present in salt or complex form and mixture of thickeners will be incompatible if both compounds exist abundantly in the same grease [6] as evidenced by separate liquid in noem4 and prop2 containers. strontium was found in all grease whereas kalium was found the same except in noem3. no barium was found in any grease samples. 223 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. table 3: concentration of argentum and other elements in ppm in grease samples grease li al k ca cr sr ag ba mo oem1 1321.5 23 25 32 2 2 oem2 1322.1 17 22 1.3 3838 1506 1506 oem3 0.9 510 19 4 133 noem1 488.7 30 23 1 37 noem2 0.7 19 24 9 4587 noem3 0.2 7879 80 noem4 1.0 2574 45 5450 70000 154 noem5 0.2 1525 25 1 77 prop1 1.2 20 26 5 2327 2150 2150 prop2 1.0 969 22 1866 1202 3.2 resistance of grease resistance of real switchgear under 11-kv potential was compared between fresh and heated grease (150 oc for 24 hours) using different contact switch arms. blank tests were also carried out for each grease before the grease was applied, to get initial resistance. all analyses were repeated at least twice and the average values were recorded. all grease samples showed changes in resistance. as can be seen in table 4, the highest difference in resistance (in /m) between blank and fresh grease was 16 % in oem1, which is still below the 20% limit. in the other comparison between fresh and heated samples, the resistance of oem3-applied switchgear increased 14%, which was worse than the non-oem recommended greases. although these values were lower than 20%, in the long term, the oem3 might increase in resistance and cause switchgear heating [6]. therefore the greases that showed dropping trends are preferable in the aspect of conductivity. table 4: contact resistance result grease contact resistance – measured on 1 contact to 1 joint without grease ( ) fresh grease ( ) % difference without grease ( ) heated grease ( ) % difference oem1 77.7 90.3 16 58.3 64.5 11 oem2 82.5 93.43 13 62.6 62.0 -1 oem3 70.7 70.2 -1 80.7 91.2 13 noem1 73.1 85.8 17 80.9 84.6 5 noem2 73.4 78.2 7 87.6 75.3 -14 noem3 72.6 71.3 -2 60.5 56.8 -6 noem4 83.5 87.7 5 69.2 59.2 -14 noem5 75,2 69.3 -8 60.4 71.2 18 prop1 72.1 78.1 8 71.7 63.6 -11 prop2 70.4 76.7 9 67.5 74.4 10 3.3 ageing of grease ageing of the grease samples was determined based on thermogravimetric analysis, stability, oil bleeding, and dropping point. switchgear movement does not involve high temperature like mechanical devices. nonetheless, heat that could degrade the grease might be produced from electrical resistance while switching and also because of hotspots [6]. the 224 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. highest temperature that local switchgears could reach was reportedly 90 oc without considering the hotspot due to arcing [12]. thus, decomposition of grease is possible when this condition prolonged for several months before the grease is replaced. the results of the thermogravimetric study under inert conditions, shown in fig. 6, for all grease samples demonstrate decomposition profiles of the samples in elevated temperature. generally, all greases except prop1 started decomposition at about 200 oc. fig. 6(a) shows the profiles for 3 oem-recommended greases. the single drop that occurred until 10 – 1 wt% indicates homogeneity between lubricant and other grease components in forming collective vaporization and decomposition. fig. 6(b) and 6(c) illustrate the decomposition profile for 5 non-oem-recommended greases. only noem1 and noem2 had the single drop. noem2, noem3 and noem4 had more than 15 wt% non-composing materials, probably thickener and additive made from metal-based compounds, as previously evidenced in the icp-ms data. the results for prop1 and prop2 in fig. 6(d) show that prop1 had separate decomposition temperature between lubricant and other components. prop2 had a single decomposition trend that is likely similar to oem2. fig. 6: tga results indicating weight drop and derivative weight as the function of temperature. further study of heating at 10 oc/day is presented in fig. 7. all sample weight data shows dropping trends similar to their weight drop in tga results in fig. 6, especially prop1 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 20 40 60 80 100 120 0 200 400 600 800 d er iv . w ei gh t ( % /o c ) w ei gh t ( % ) temperature (oc) oem1 wt oem2 wt oem3 wt oem1 dwt (a) -0.5 0 0.5 1 1.5 2 2.5 0 20 40 60 80 100 120 0 200 400 600 800 d er iv at iv e w ei gh t ( % /o c ) w ei gh t ( % ) temperature (oc) noem1 wt noem2 wt noem3 wt noem1 dwt noem2 dwt noem3 dwt (b) -0.5 0 0.5 1 1.5 2 0 20 40 60 80 100 120 0 200 400 600 800 d er iv at iv e w ei gh t ( % /o c ) w ei gh t ( % ) temperature (oc) noem4 wt noem5 wt noem4 dwt (c) -0.2 0 0.2 0.4 0.6 0.8 1 1.2 0 20 40 60 80 100 120 0 200 400 600 800 d er iv at iv e w ei gh t ( % /o c ) w ei gh t ( % ) temperature (oc) prop1 wt prop2 wt prop1 dwt prop2 dwt (d) 225 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. that dropped to 80 wt% after 10 days at 150 oc. the drop greater than 20 wt% is not a stable grease [5]. fig. 7: weight of grease sample after 10 days of heating at 10 oc/ day. fig. 8: isothermal tga of 4 samples. isothermal tga analysis of selective samples at 150 oc in fig. 8 reveals a trend of weight decrease that can be projected to estimate the final weight. the declination of sample weight can be expressed as exponential decay in eq. (1) where the fitness for all data, r2 > 99 %, was significant. from the values of constants in table 5, a denotes the final weight of the sample or residue at the infinity shows an excellent result, which is 98.4 wt%. nonrecommended greases also had fairly comparable results having residue greater than 90 wt%. the ageing of the grease is more apparent on the parameters that correspond to time. the rate of non-linear declination, or degradation, of the samples can be identified from multiplication of b and c, which is the derivation constant of the exponential equation. oem1 has the lowest rate and noem3 showed 5.6 times faster rate implying that noem3 might need to be replaced more frequently due to relatively fast decay. from this method of analysis, planning of grease replacement can be made when low performance grease is used. expm a b ct (1) table 5: parameters of exponential decay of sample weight. samples a (wt%) b (wt%) c (/min) b*c 104 (wt%/min) oem1 0.9839 0.0155 0.0144 2.23 oem2 0.9544 0.0423 0.0122 5.16 noem3 0.9246 0.0719 0.0175 12.58 noem5 0.9258 0.0735 0.0130 9.56 table 6 tabulates the results of the bleeding test and a comparison between fresh grease and the 10-day-heating grease. the circle area of stain, s, and its change due to the heat treatment was calculated using eqs. (2) and (3). oem1 shows excellent consistency with difference of 39.81 %. the bleeding of oem1 was not from molten grease as evidenced 0 20 40 60 80 100 120 140 160 180 92% 93% 94% 95% 96% 97% 98% 99% 100% 101% 0 100 200 te m pe ra tu re (o c) w ei gh t ( % ) time (min)oem1 oem2 noem3 noem5 temp 226 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. from the dropping point test. other greases show negative values, which imply the potential of hardness of the grease increases. from the list of the grease samples oem1 is therefore preferable. (2) (3) table 6: circle area (mm2) of oil from grease in the bleeding tests grease fresh 10-day heated % diff oem1 438.6 612.4 39.81 oem2 967.3 604.65 -37.49 oem3 1005.9 785 -21.96 noem1 706.7 500.9 -29.33 noem2 717 589.3 -17.81 noem3 855.9 643.8 -24.78 noem4 1167.1 110.1 -90.57 noem5 733.7 301.4 -58.92 prop1 1976.7 16.5 -99.17 prop2 1035.2 910.8 -12.02 4. conclusion analysis methods of electrical-switch-lubricating grease were the focus of this study. grease samples from the local electric power distributor and our institution were analyzed to meet the requirement of switchgear grease. unstiffened, conductive, inert, and unhazardous grease is desired for lubricating electricity connections at switchgears of middle voltage of 11 kv. thermogravimetry, dropping point, burning, oil bleeding, penetration, resistivity, corrosivity, chromatography, mass spectrometry, and ir spectrometry were the analyses conducted to select the best one. oem1 was identified as having excellent properties. it showed single dropping weight at temperatures greater than 200 oc, a high dropping point, inflammable drop, consistent bleeding value, consistent grease property (nlgi reading), good conductivity without producing a metal oxide layer, no hazardous chemicals, and compatible metal elements. for all other grease, the consumer needs to manage usage and stocking, such as frequent replacement of grease according to the ageing prediction, wearing proper personal protective equipment (ppe), and obtaining work permits to face the possibility of grease or switching failure. acknowledgements the authors would like to express their gratitude and appreciation for the financial support from the ministry of higher education (mohe), malaysia for the fundamental research grant scheme (frgs kpt – rdu160129, reference number: frgs/1/2016/tk02/ ump/03/2 entitled rheological and structural characterization of emulsified modification bitumen synthesized from industrial wastes). the supports from the faculty of chemical and natural resources engineering and universiti malaysia pahang, malaysia are also acknowledged. special gratitude is additionally expressed to our collaboration from the government-linked-company, tenaga nasional berhad via its research institute, tnb 227 iium engineering journal, vol. 20, no. 1, 2019 mahmud et al. research sendirian berhad on their sponsorship to this study under purchase order no. 20784104. references [1] lugt pm. (2016). modern advancements in lubricating grease technology. tribology international, 97:467-477. [2] iec, high-voltage switchgear and controlgear, in part 1: common specifications for alternating current switchgear and controlgear. (2017): international electrotechnical commision. [3] snyder ca, mayotte d, donahue cj. (2006). analysis of the thickening agents in automotive greases by gc-ms. journal of chemical education, 83(6): 902. [4] de los santos valladares l, salinas dh, dominguez ab, najarro da, khondaker si, mitrelias t, barnes chw, aguiar ja, majima y. (2012). crystallization and electrical resistivity of cu2o and cuo obtained by thermal oxidation of cu thin films on sio2/si substrates. thin solid films, 520(20): 6368-6374. [5] el-adly, r.a. and g.m. turky (2018) comparative study between prepared electrical grease and the imported one. egyptian journal of petroleum, 27 (2):209-213. [6] chudnovsky b. (2008) lubrication manual: lubrication instructions for major manufacturers' medium voltage and low voltage circuit breakers, switches and switchgear. lubrication instructions for major manufacturers' medium voltage and low voltage circuit breakers, switches and switchgear, ed. 6. us: square d company. [7] crippin jb. (2015). types of fires, ed. m.m. houck. academic press. [8] hurley s, cann pm. (1999). ir spectroscopic analysis of grease lubricant films in rolling contacts, in tribology series, dowson d et al., editors. elsevier. pp. 589-600. [9] jiabao p, yanhai c, jinyong y. (2015). effect of heat treatment on the lubricating properties of lithium lubricating grease. rsc advances, 5(72):58686-58693. [10] carre dj, bauer r, fleischauer pd. (1982). chemical analysis of hydrocarbon grease from spin bearing tests. asle transactions, 26 (4): 475-480. [11] takahashi j, kasahara k. (2013). analysis of inorganic impurities in lubricating oils by icpms. application note. agilent technology url: http://hpst.cz/sites/default/files/attachments/5991-3263en-analysis-inorganic-impuritieslubricating-oils-icp-ms.pdf as accessed on 28/3/2019. [12] zhang x, granhaug o, hall g. (2015). data model for overheat prediction of mediumvoltage switchgear. in 23rd international conference on electricity distribution. lyon: cired. 228 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <feff04180437043f043e043b043704320430043904420435002004420435043704380020043d0430044104420440043e0439043a0438002c00200437043000200434043000200441044a0437043404300432043004420435002000410064006f00620065002000500044004600200434043e043a0443043c0435043d04420438002c0020043f043e04340445043e0434044f044904380020043704300020043d04300434043504360434043d043e00200440043004370433043b0435043604340430043d0435002004380020043f04350447043004420430043d04350020043d04300020043104380437043d0435044100200434043e043a0443043c0435043d04420438002e00200421044a04370434043004340435043d043804420435002000500044004600200434043e043a0443043c0435043d044204380020043c043e0433043004420020043404300020044104350020043e0442043204300440044f0442002004410020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e0030002004380020043f043e002d043d043e043204380020043204350440044104380438002e> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <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> /eti <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> /fra <feff005500740069006c006900730065007a00200063006500730020006f007000740069006f006e00730020006100660069006e00200064006500200063007200e900650072002000640065007300200064006f00630075006d0065006e00740073002000410064006f006200650020005000440046002000700072006f00660065007300730069006f006e006e0065006c007300200066006900610062006c0065007300200070006f007500720020006c0061002000760069007300750061006c00690073006100740069006f006e0020006500740020006c00270069006d007000720065007300730069006f006e002e0020004c0065007300200064006f00630075006d0065006e00740073002000500044004600200063007200e900e90073002000700065007500760065006e0074002000ea0074007200650020006f007500760065007200740073002000640061006e00730020004100630072006f006200610074002c002000610069006e00730069002000710075002700410064006f00620065002000520065006100640065007200200036002e0030002000650074002000760065007200730069006f006e007300200075006c007400e90072006900650075007200650073002e> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <feff30d330b830cd30b9658766f8306e8868793a304a3088307353705237306b90693057305f002000410064006f0062006500200050004400460020658766f8306e4f5c6210306b4f7f75283057307e305930023053306e8a2d5b9a30674f5c62103055308c305f0020005000440046002030d530a130a430eb306f3001004100630072006f0062006100740020304a30883073002000410064006f00620065002000520065006100640065007200200036002e003000204ee5964d3067958b304f30533068304c3067304d307e305930023053306e8a2d5b9a3067306f30d530a930f330c8306e57cb30818fbc307f3092884c3044307e30593002> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <feff004e006100750064006f006b0069007400650020016100690075006f007300200070006100720061006d006500740072007500730020006e006f0072011700640061006d0069002000730075006b0075007200740069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c002000740069006e006b0061006d0075007300200076006500720073006c006f00200064006f006b0075006d0065006e00740061006d00730020006b006f006b0079006200690161006b006100690020007000650072017e0069016b007201170074006900200069007200200073007000610075007300640069006e00740069002e002000530075006b00750072007400750073002000500044004600200064006f006b0075006d0065006e007400750073002000670061006c0069006d006100200061007400690064006100720079007400690020007300750020004100630072006f006200610074002000690072002000410064006f00620065002000520065006100640065007200200036002e00300020006200650069002000760117006c00650073006e0117006d00690073002000760065007200730069006a006f006d00690073002e> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <feff004200720075006b00200064006900730073006500200069006e006e007300740069006c006c0069006e00670065006e0065002000740069006c002000e50020006f0070007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740065007200200073006f006d002000650072002000650067006e0065007400200066006f00720020007000e5006c006900740065006c006900670020007600690073006e0069006e00670020006f00670020007500740073006b007200690066007400200061007600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020005000440046002d0064006f006b0075006d0065006e00740065006e00650020006b0061006e002000e50070006e00650073002000690020004100630072006f00620061007400200065006c006c00650072002000410064006f00620065002000520065006100640065007200200036002e003000200065006c006c00650072002e> /pol <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> /ptb <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> /rum <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> /rus <feff04180441043f043e043b044c043704430439044204350020044d044204380020043f043004400430043c043504420440044b0020043f0440043800200441043e043704340430043d0438043800200434043e043a0443043c0435043d0442043e0432002000410064006f006200650020005000440046002c0020043f043e04340445043e0434044f04490438044500200434043b044f0020043d0430043404350436043d043e0433043e0020043f0440043e0441043c043e044204400430002004380020043f043504470430044204380020043104380437043d04350441002d0434043e043a0443043c0435043d0442043e0432002e00200421043e043704340430043d043d044b043500200434043e043a0443043c0435043d0442044b00200050004400460020043c043e0436043d043e0020043e0442043a0440044b0442044c002c002004380441043f043e043b044c04370443044f0020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e00300020043b04380431043e00200438044500200431043e043b043504350020043f043e04370434043d043804350020043204350440044104380438002e> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 formalization of the cotton drying process based on heat and mass transfer equations yunusova sayyora toshkenboyevna1*, halmatov davron abdalimovich2, atajonov muhiddin odiljonovich1 and huzanazarov ulugbek olimovich2 1department of information processing and control systems, tashkent state technical university, tashkent, uzbekistan 2tashkent institute of textile and light industry, tashkent, uzbekistan *corresponding author: yunusova_sayyora@mail.ru (received: 17th april 2020; accepted: 9th may 2020; published on-line: 4th july 2020) abstract:the paper deals with the construction of a mathematical model of the cotton drying process, taking into account the thermal and mass transfer properties of raw cotton components. to determine changes in the temperature of the fibre and raw cotton seeds, the application of fourier's law is proposed. the mathematical dependence of the change on the humidity of the cotton fibre and seeds along the length of the drum is determined. the rational value of the heat agent consumption in the process of drying raw cotton is also determined. research methods are based on the provisions of modern trends in management theory and identification. mathematical models are constructed using analytical methods and equations that describe the physical properties of an object. methods for constructing a mathematical model usually rely on experimental methods, in particular, the method of acceleration curves, and as a result, the mathematical description becomes a priori inaccurate. it is shown that the mathematical model used is quite adequate for the dynamics of a real object, fully describes it, and characterizes it over the entire range of changes. the analysis of the developed mathematical model based on simulation showed the adequacy of the obtained mathematical dependence of the temperature regime of the cotton drying process with the consumption of heat agent. abstrak: kajian ini membincangkan tentang penciptaan model matematik bagi proses pengeringan kapas, dengan mengambil kira terma dan sifat-sifat pindah jisim komponen kapas mentah. bagi mendapatkan perubahan suhu fabrik dan biji benih kapas mentah, penggunaan hukum fourier telah dicadangkan. kebergantungan matematik pada perubahan kelembapan fabrik kapas dan biji benih sepanjang drum telah diperolehi. nilai bersesuaian menggunakan ejen haba dalam proses pengeringan kapas kering mentah didapati. kaedah kajian berdasarkan tren moden dalam teori pengurusan dan pengenalpastian. model matematik dibina dengan menggunakan kaedah analisis dan persamaan yang menerangkan ciri-ciri fizikal pada objek. kaedah bagi membina model matematik selalunya bergantung pada kaedah eksperimen, khususnya, kaedah pecutan melengkung, dan hasilnya, penyataan penaakulan matematik menjadi tidak tepat. model matematik yang digunakan adalah cukup bagi objek dinamik sebenar, dengan penerangan penuh dan perincian ke atas keseluruhan perubahan. analisis model matematik yang terhasil berdasarkan simulasi, dilihat cukup kebergantungan matematik terhasil melalui proses pengeringan kapas pada aturan suhu dengan ejen haba. keywords: raw cotton; mass transfer; fibers; heat exchange; drying drum; process; differential equations; temperature 256 iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 1. introduction raw cotton, as an object of drying, refers to capillary porous-colloidal, heterogeneous materials. its main components are fiber, skin, and seed core. the structure of the fiber refers to capillary-porous materials. due to the structure of raw cotton, the removal of moisture from the core is slow and depends on many factors. depending on the humidity between the skin and the seed core, air layers are formed, the size of which depend on the maturity and humidity of the seeds. with the presence of an air layer, the process of heat and mass exchange between the skin and the seed core changes significantly, due to the formation of additional resistance to the movement of moisture and heat between the components of raw cotton [1]. the intensification of heating of porous materials, in particular the drying of raw cotton, is determined by the laws of heat and substance transfer inside the body (internal heat and mass transfer) and between the surface of the body and the environment (external heat and mass transfer). to properly understand the mechanism of these processes under thermal influence, it is necessary to develop a thermophysical model of raw cotton that describes the heat and mass exchange processes between the components (fiber and seeds) and the thermal agent (heated air). when exposed to heat, the thermodynamic equilibrium in the material is disturbed, resulting in internal heat and mass transfer processes associated with the transfer of heat and matter (moisture) in the raw cotton components. in this case, the exchange processes can be implemented: due to surface heat and mass transfer; -internal convective heat exchange between raw cotton components according to newton's law, according to which the flow of heat and matter will be proportional to the difference in temperature and moisture of each component; internal convective heat and mass exchange between the material components and the heated air mass (heat agent); transfer of heat and moisture as a result of flow movement in the pores of raw cotton; transfer of heat and moisture by diffusive phenomena occurring in each component of the material in the air. when creating a control system for the technological processes of raw cotton processing, it is necessary to use the entire arsenal of modern theory and practice of automatic control and management, and in addition, it is necessary to have information about the behaviour of the technological control object under the influence of control actions. effective management of processes and industrial facilities is possible when the main characteristic features inherent in the object are presented in the form of a mathematical description [2-4]. the development of a control system for the process of cotton processing that can provide the required quality of management in the conditions of rapid changes in the parameters of processed raw cotton with changes in environmental indicators is an urgent scientific and technical task. the solution to this problem will significantly improve the quality of management of technological process parameters. to solve this problem, the processing raw cotton is functionally decomposed into subprocesses, the structure of which changes over time depending on such factors as changes 257 iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 in the quality requirements of cotton fibre and raw cotton source material, as well as on the operating modes of aggregates, changes in technological regulations, and production situations. the complexity of mathematical modelling of the technological process is caused by the insufficient level of development of the theory, the presence of a large number of factors that affect the course of the process, the difficulty of assessing the objective relationship between a set of disturbing factors, as well as the non-stationary parameters of the technological object and their weak observability in real time [4,5]. these factors determine the formalization of the processes, taking into account the main parameters that define it. it is known that the process of cotton processing consists of interrelated sub-processes, the technological parameters of which significantly affect the quality of the produced preproduct-cotton fibre. at the same time, the most important among them is the process of drying raw cotton [6-8]. 2. finding solutions method based on the analysis of the functioning of the drying drum, the facts of the existence of functional relationships of each parameter with others are revealed and subsets of interrelated parameters are formed based on these features. the subsets obtained in this way are combined into a common set (set) of interrelated parameters and divided into groups of input parameters u(t), output у(t), variable states х(t), and the drying process. the input parameters of the drying process include: raw cotton consumption 1ugc , fuel consumption 2ugt , humidity of raw cotton 3uc , air flow4ugb , air temperature5utb ,air humidity6ub . the output parameters of the object are: cotton humidity at the outlet of the drum `1yx , temperature of cotton at the exit of the drum 2yt x , output of cotton from the drum3ygx temperature of the waste heat agent40 yt , and humidity of the selected heat agent50 y output of the selected heat agent6yga . in this case, the number of variable state parameters selected: dehumidifier in the drum1xb temperature in the drum2xtb , all cotton in the drum3xgb , heat agent temperature4xta , heat agent consumption5 xga , and humidity of the heat agent6xa . using the method proposed in this paper [5-9] we will make differential equations of heat and mass transfer processes in each phase of raw cotton. select the volume of the material v bounded by the surface s and denote by ilij jj , and 2ij accordingly, the flow of moisture in the form of liquid (i=l) and steam (i=2) through the surface s, through ilij uu , and 2iu corresponding to the moisture content in each component. changing the moisture content iju in volume v occurs due to the derivative t uij internal moisture exchange between components according to newton's law. according to the law of conservation of mass of a substance a second change in the moisture content of a material in volume v is equal to the amount of liquid entering this volume per unit of time, both due to its inflow through the surface s, and due to its receipt from sources [10-14]. 258 iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 find expressions for the vectors .ijj for this purpose, we use fourier's law, according to which the flow vector will be collinear to the gradient of changes in moisture and temperature. ),~()()( k k mik k mikik gradtagraduapj where )(k mia and )(~ k mia are the transfer coefficients. given all this, the differential equations for the total mass of transport in the fiber-seedair system are presented as )];~([ )-()-()-()-( 1 )( 1 )( 1 31 )( 132112 )( 31132112 gradtagraduadiv ttcttcuucuuc t u l m l m tt l (1) )];~([ )-()-()-()-( 2 )2( 2 )2( 2 32 )( 232112 )( 32231212 2 2 gradtagraduadiv ttcttcuucuuc t u mm tt (2) )],~([ )-()-()-()-( 3 )3( 3 )3( 3 23 )( 231313 )( 23231313 3 3 gradtagraduadiv ttcttcuucuuc t u mm tt (3) where ,+= 232323 bac ,+= )( 23 )( 23 )( 23 ttt ba ,+= lklklk bac = )(t lkc ,+ )()( t lk t lk ba ,= 1011 ρmρ ,= 2022 ρmρ ,= 3033 ρmρ ,10ρ 20ρ and 30ρ true densities of fibres, seeds, and air, respectively. taa 1212 , mass transfer and heat transfer coefficients between fibres and seeds for liquid moisture, taa 1313 , mass transfer and heat transfer coefficients between fibres and air, taa 2323 , coefficients of mass exchange and heat exchange between seeds and air (drying agent),)(23 )( 13 )( 12231312 ,,,,, ttt bbbbbb similar coefficients for vaporous moisture, ,+= 21111 uuu ,+= 22212 uuu 32313 += uuu total mass of moisture transfer for the fibre system, seeds and air, respectively, ,+= )( 2 )( 1 )( k m k m k m aaa . ~+~=~ )( 2 )( 1 )( k m k m k m aaa 3. solving the problems the system of equations (1) – (3) describes the process of mass transfer in raw cotton components under the known law of change in the temperature of the fiber, for which we use fourier's law. heat consumption for heating components, as well as heat exchange between components: );-()-(-)( 3113211211 )1( 11 1 11 ttttirgradtdivt u c (4) );-()-()( 3223211212 )2( 22 2 212 ttttirgradtdivt u c (5) ),-()-()( 3223311313 )3( 23 3 33 ttttirgradtdivt u c (6) 259 iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 where with k and )( kr coefficients of thermal conductivity and specific heat of transformation (for fibre (k=1), for seeds (k=2)) and air (k=3), ijα coefficients of internal heat exchange between fibres and seeds (i=1, j=2), air and fibres (i=1, j=3) and air and seeds (i=2, j=3). the power of the source when transferring vaporous moisture will be equal to 2111 = ii and is determined from the condition ,0= 21 t u which gives )].()]()()([)( 31 )( 1321 )( 123113211212121 ttbttbuubuubjdivi tt (7) substituting (1) in equation (4), using the expression (7), we get )].()(()([)( )(]~)([)( 31 )( 1321 )( 12311321121 )1( 3113 21121 )1( 21 )1( 21 )1( 11 1 11 ttbttbuubuubrtt ttgradtagraduadivrgradtdiv t t c tt mm (8) similarly, we have )];-()-(-()-([)-( -)-(]~)([)( 32 )( 2312 )( 12322312122 )2( 3223 21122 )2( 22 )2( 22 )2( 22 2 22 ttbttbuubuubrtt ttgradtagraduadivrgradtdiv t t c tt mm (9) )].-()-(-()-([ )-()-(]~)([)( 23 )( 2313 )( 13232313133 )3( 322321123 )3( 23 )3( 23 )3( 33 3 33 ttbttbuubuubr ttttgradtagraduadivrgradtdiv t t c tt mm (10 ) equations (1)-(3), (8)-(10) for known densities kρ , heat capacity kc and transfer coefficients ,~,,, )()()( kmi k mi k k aarλ mass transfer coefficients ikik ba , and heat exchange ik t ik t ik αba ,, )()( form a closed system for determining the moisture content and temperature of the fiber ( 11,tu ), seeds' ( 33 ,tu ). introducing the coefficients of the phase transformation of a liquid into steam iik εε , and thermogradient coefficients according to iik δδ , the formulas , + = 1212 12 12 ba b ε , + = 1313 13 13 ba b ε , + = 2323 23 23 ba b ε ,= )1( )1( 2 1 m m a a ε ,= )2( )2( 2 2 m m a a ε ;)3( )3( 2 3 m m a a ,= 12 )( 12 12 c с δ t ,= 13 )( 13 13 c с δ t ,= 23 )( 23 23 c с δ t , ~ = )1( 2 )1( 2 1 m m a a δ , ~ = )2( 2 )2( 2 2 m m a a δ )3( 2 )3( 2 1 ~ = m m a a δ and considering the one-dimensional transfer case (flat case n=0, cylindrical symmetry n=1 and the case of spherical symmetry n=2) give the equation (1)-(3), (8)-(10) to mind )];([)]()[( 3 )( kiikki lk iki i i i i i m i i ttuucx t x u a x n xt u (11) 260 iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 ;)]()[)( )]()[())(( 3 1 3 1 )( )()( k kiikki k ikiki i kiik i i i i i mi i i i ii ttuucrtt x t x u a x n x r x t x n xt t c (12) where i=1, 2, 3, c21= c12, c32=c23, 2332 = εε , ,= 2121 αα .= 2332 αα to integrate equations (11) and (12), the following initial, boundary, and symmetry conditions must be met: constuu ii == 0 at t=0 0)()1()( )( ci i ciciicicicic uurttax t at x=r, 0)()( ciic i ic i mc uux t a at x=r, 0,0 x t x u ii at x=0, where icic i mcicic a ,,,, )( boundary values of thermal conductivity , density, substance diffusion coefficient, thermogradient coefficient and phase transformation criterion for the i-th phase, icic ηα , coefficients of heat and mass transfer of the i-th phase with the external environment, tc and uc-values of temperature and humidity of the external environment. for a moving medium, the time derivative operator t replaced by the full derivative operator using the formula ,+= x v tdt d where iv is the velocity of transport of medium particles. then the transport equations (11) and (12) for a moving medium can be written as: )];-(-[-)]()[()( 3 1 )( kiikki k iki i i i i i m i i i i ttuucx t x u a x n xx u v t u (13 ) )],-()-[)( )]()[())(()( 3 1 )( 3 1 )()( kiikkiik k iki i ki k ik i i i i i mi ii i i i i ii ttuucrtt x t x u a x n x r x t x n xx t v t t c where iv is the speed of movement of fibres (i=1), seeds (i=2) and air (i=3) in the case of a one-dimensional (n=0) stationary transfer mode ,0( t u i 0= t u i ) at constant values of travel speeds ,0 constvv ii thermal and mass transfer parameters of raw cotton components [11-17]. ,== 0 constρρ ii ,== )()( 0 constaa im i m ,== 0 constλλ ii ,== 0 constδδ ii ,== 0 constεε ii ,== 0)()( constrr ii constcc ii == 0 have 261 iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 ;)]-(-[-)( 3 1 2 2 2 2 )( k kiikkiik i i i i ii ttuu d td d ud lu d ud (14) 3 1 3 1 2 2 2 2 11 )()( ),-(-[-)(( k ki k ikkiik i i iiii ttuu d td d td k d td (15) where ,= 0t t t ,= 0u u u ,= 0 )( i ii lv a γ ,= 0 )( i m i i a a lu ,= 0 00 u tδ ρ ini ,= 0 2 i ik ik v lc λ ,= 0 0 u tδ ρ ikik ,+1= 00 )( 11 iniii i luρkεk ,= 00 )( 12 iii i lukεk ,= 00 00 )( 0 tc ur k i i i ,= 0 ikiikik εkλθ ,+= ikikikik ρθβσ ,= 0 2 ii ik ik aλ la β 0 00 0 ,= t ρc λ a ii i i i 0u initial (equilibrium) values of temperature and moisture of any component (for example, air) of raw cotton. the system in eq. (14) and (15) are integrated under the following boundary conditions niiini uutt =,= by ,0=ξ (16) 0)-()1()-( ciicicicic i uutt t at ,1=ξ (17) 0)-( ciic i ni i uuv tu at ,1=ξ (18) where ,= l x ξ ,= 0i ic ic λ la β ,= 00 00 )( ii i ic ic atc lurη μ ,= )0( 0 0 m ic ic a luη v ,= 0t t t nini ,= 0u u u nini ni c c tu u u 0 = and niu set values of temperature =i and moisture of the o-th component in the crosssection .0=x as an example, consider the process of drying raw cotton in a dryer in a drum, where the fibres and seeds move at the same speed 02010 and equal in size 300 q . the research is carried out using the following initial data, corresponding to the properties of the real properties of raw cotton and the parameters of the dryer [6]: 1,0,,1.0 ,10,20,20,150,20,20,10,20 0302015.01312231312 32132100 kkkppp uuutttuт nnnnnn the maximum values of seed moisture are 20% at the beginning of the drum, i.e. before drying, and at the end, i.e. at the end of drying %5.17 . the pattern of removing moisture from the fibre differs significantly from similar patterns corresponding to seeds. at the beginning and end of the drying process the fibre humidity has the following limits 20% и 12%. based on equation. (14) and (15), a computational model of the cotton drying process has been developed (fig. 1), which characterizes the dependence of changing parameters. simulation experiments were conducted to study the properties of these dependencies.the 262 iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 calculations were performed in the matlab system. the transition process graphs are shown in fig. 2. fig.1: modelling scheme of static mode of raw cotton drying process (with distributed parameters). fig. 2: graphs of the transition process. to calculate the processes in the computational model, the following are entered: 87565 431211 ,,, ,,,, kkkkkk kkkkxlk comparing the results, we conclude that the seeds at the exit of the drum have a humidity of 17,5%, and fiber – 12%. the moisture content of the seed is 2.5%, and that of the fibre 263 iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 is 8%, which means that to intensify the drying of raw cotton seeds, it is necessary to improve the access of heated air to their surface. it follows that in order to obtain high-quality fibre and seeds, it is proposed to maintain the seed temperature at the exit of the drum at about 50% of the input temperature. 4. conclusion a dynamic mathematical model of the drying process is constructed, which determines the regularities of changes in the moisture content of fibre and seeds, which depend not only on the humidity of the original cotton, but also on the consumption of the supplied heat agent. verification of the adequacy of the developed model is carried out by comparing real data with the result of simulation modelling. thus, a mathematical model of the raw cotton drying process is obtained, which allows us to determine the dynamic properties of the control system and choose rational modes of operation of aggregates with optimal control of the entire process and increase production productivity without compromising the natural properties of cotton fibres and seeds. acknowledgements i thank you for giving me such an opportunity to work under your iium engineering journal. huge thanks to my supervisor dr i.h. sidikov for providing me great insight and knowledge, for his continuous encouragement and for providing me with many of his valuable time. i would also like to thank my friends muhiddin atajonov, and others who have given me moral support and stayed with me at the university for many days. without their support, i could not have spent so much time and effort on my article. finally, i thank goes to the tashkent state technical university, department of "information processing and control systems" staffs for their support and taking me to the next level in my studies. references [1] cotton: world statistics. bulletin of the international cotton advisory committee, ny, november 2015.http://www.icac.org., http://www.usda.gov. [2] parpiev a.p, mamatov a.z, usmankulov a.k. (2000) maximum permissible temperatures in the drum dryer. izvestiyavuzov, 1:35-36. [3] usmankulov a. (2002) improving the efficiency of the drying process of raw cotton in a drum dryer, diss. for the degree of candidate of technical sciences tashkent; pp128. [4] mamatov a.z. (1995) modeling of raw cotton drying technology to improve the quality of fiber, diss. on competition of a scientific degree. doctor of technical sciences tashkent; pp 248. [5] siddikov i.x, umurzakova d.m. (2019) features of automatic control of technological parameters of water level in the drum steam boilers, journal of southwest jiaotong university,54(3):1-10. doi:10.35741/issn.0258-2724.54.3.1. [6] siddikov i.x, umurzakova d.m. (2019) mathematical modeling of transient processes of the automatic control system of water level in the steam generator, universal journal of mechanical engineering, 7(4):139-146. doi:10.13189/ujme.2019.070401. [7] siddikov i.x, umurzakova d.m. (2019) adaptive neuron-fuzzy regulating system of the temperature mode of the drum boiler. international journal of advanced research in science, engineering and technology, 6(1) 7869-7872. (2019). [8] siddikov i.x, umurzakova d.m, bakhrieva h.a. (2020) adaptive system of fuzzy-logical regulation by temperature mode of a drum boiler // iium engineering journal 21(1):182-192. https://doi.org/10.31436/iiumej v 2lil.1220. 264 iium engineering journal, vol. 21, no. 2, 2020 toshkenboyevna et al. https://doi.org/10.31436/iiumej.v21i2.1456 [9] yunusova s.t. (2013) on the formalization of the optimization criterion of the cleaning process of raw cotton to tashkent state technical university. bulletin. 3:35-40. [10] sidikov i.h, atajonov m.o, yunusova s.t, nashvandova. g.m. (2020) adaptive analytical control of technological parameters based on the probability method of oil refining installations, european science review, scientific journal, 1(2):78-83 https://doi.org/10.29013/esr-20-1.2-78-83. [11] kholmatov d. a, yunusova s. t. setmetov n. u, khuzhanazarov u. o. (2014) information and algorithmic technological monitoring system algorithmic processes processing of raw cotton., wcis-eighth world conference on intelligent systems for industrial automatic. toshkent .261-264 [12] siddiqov ih, yunusovа st, izmailovа nr. (2018) algorithm for optimization of the membership function of the fuzzy control model on the basis of the probabilistic approach. wcis – 2018, tenth world conference on intelligent systems for industrial automation october 25-26, tashkent, uzbekistan, 251-254 [13] yunusova st. (2019) fuzzy logic model of temperature control of a drying unit based on a probabilistic approach. collection of reports of the republican scientific and practical conference on "innovations in the development of information and communication technologies" april 15-17. [14] kholmatov da, yunusova st, setmetov nu, khuzhanazarov uo. (2019) software tool monitoring process of processing raw cotton. international journal of advanced research in science, engineering and technology, 6(2): 8140-8143. [15] igamberdiyev h.z, yusupbekov a.n, zaripov o.o,sevinov j.u. (2017) algorithms of adaptive identification of uncertain operated objects in dynamical models. procedia computer science.120. 854-861. doi: 10.1016/j.procs.2017.11.318. [16] sidikov i.h, atajonov m.o, atajonova s.b. (2019) fuzzy-situational diagnostics of technological safety of petrochemical plants, 4(7):182-186. doi:10.33564/ijeast. 2019.v04i07.030 265 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <feff004f0076006500200070006f0073007400610076006b00650020006b006f00720069007300740069007400650020006b0061006b006f0020006200690073007400650020007300740076006f00720069006c0069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400650020006b006f006a00690020007300750020007000720069006b006c00610064006e00690020007a006100200070006f0075007a00640061006e00200070007200650067006c006500640020006900200069007300700069007300200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e006100740061002e0020005300740076006f00720065006e0069002000500044004600200064006f006b0075006d0065006e007400690020006d006f006700750020007300650020006f00740076006f007200690074006900200075002000700072006f006700720061006d0069006d00610020004100630072006f00620061007400200069002000410064006f00620065002000520065006100640065007200200036002e0030002000690020006e006f00760069006a0069006d0020007600650072007a0069006a0061006d0061002e> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <feff30d330b830cd30b9658766f8306e8868793a304a3088307353705237306b90693057305f002000410064006f0062006500200050004400460020658766f8306e4f5c6210306b4f7f75283057307e305930023053306e8a2d5b9a30674f5c62103055308c305f0020005000440046002030d530a130a430eb306f3001004100630072006f0062006100740020304a30883073002000410064006f00620065002000520065006100640065007200200036002e003000204ee5964d3067958b304f30533068304c3067304d307e305930023053306e8a2d5b9a3067306f30d530a930f330c8306e57cb30818fbc307f3092884c3044307e30593002> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <feff005400650020006e006100730074006100760069007400760065002000750070006f0072006100620069007400650020007a00610020007500730074007600610072006a0061006e006a006500200064006f006b0075006d0065006e0074006f0076002000410064006f006200650020005000440046002c0020007000720069006d00650072006e006900680020007a00610020007a0061006e00650073006c006a006900760020006f0067006c0065006400200069006e0020007400690073006b0061006e006a006500200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e0074006f0076002e0020005500730074007600610072006a0065006e006500200064006f006b0075006d0065006e0074006500200050004400460020006a00650020006d006f0067006f010d00650020006f00640070007200650074006900200073002000700072006f006700720061006d006f006d00610020004100630072006f00620061007400200069006e002000410064006f00620065002000520065006100640065007200200036002e003000200074006500720020006e006f00760065006a01610069006d0069002e> /suo <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> /sve <feff0041006e007600e4006e00640020006400650020006800e4007200200069006e0073007400e4006c006c006e0069006e006700610072006e00610020006f006d002000640075002000760069006c006c00200073006b006100700061002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400200073006f006d00200070006100730073006100720020006600f60072002000740069006c006c006600f60072006c00690074006c006900670020007600690073006e0069006e00670020006f006300680020007500740073006b007200690066007400650072002000610076002000610066006600e4007200730064006f006b0075006d0065006e0074002e002000200053006b006100700061006400650020005000440046002d0064006f006b0075006d0065006e00740020006b0061006e002000f600700070006e00610073002000690020004100630072006f0062006100740020006f00630068002000410064006f00620065002000520065006100640065007200200036002e00300020006f00630068002000730065006e006100720065002e> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 adaptive development of svsf for a featurebased slam algorithm using maximum likelihood estimation and expectation maximization heru suwoyo1,3, yingzhong tian1,2, wenbin wang 4, long li 1,2, andi adriansyah 3*, fengfeng xi5, guangjie yuan1,2 1 school of mechatronic engineering and automation,shanghai university, shanghai, china 2 shanghai key laboratory of intelligent manufacturing and robotics, shanghai university, shanghai, china 3 department of electrical engineering, universitas mercu buana, jakarta, indonesia 4 mechanical and electrical engineering school, shenzhen polytechnic, guangdong, china 5 department of mechanical aerospace, and industrial engineering, ryerson university, toronto, canada *corresponding author: andi@mercubuana.ac.id (received: 18th march 2020; accepted: 23rd october 2020; published on-line: 4th january 2021) abstract: the smooth variable structure filter (svsf) has been considered as the robust estimator. like other filters, the svsf needs an accurate system model and known noise statistics to approximate the posterior state. unfortunately, the system cannot be accurately modeled, and the noise statistic is unknown in the real application. for these reasons, the performance of svsf might be decreased or even led to divergence. therefore, the enhancement of svsf is required. this paper presents an adaptive svsf. initially, svsf is smoothed. to provide the ability to estimate the noise statistic, asvsf is then derived based on maximum likelihood estimation (mle) and expectation-maximization (em). additionally, the unbiased noise statistic is also approached. however, its covariance is complicatedly formulated. it might cause a negative definite symmetric matrix. therefore, it is tuned based on the innovation covariance estimator (ice). the asvsf is designed to solve the online problem of simultaneous localization and mapping (slam). henceforth, it is termed as the asvsf-slam algorithm. the proposed algorithm showed better accuracy and stability compared to the conventional algorithm in terms of root mean square error (rmse) for both estimated path coordinate (epc) and estimated map coordinate (emc). abstrak: penapis struktur bolehubah lembut (svsf) telah dianggap sebagai penganggar teguh. seperti penapis lain, svsf memerlukan model sistem yang tepat dan statistik hingar yang diketahui bagi menganggar keadaan posterior. malangnya, sistem tidak dapat dimodelkan dengan tepat dan statistik hingar tidak diketahui dalam aplikasi sebenar. atas sebab-sebab ini, prestasi svsf mungkin berkurangan, bahkan berbeza. oleh itu, memperbaharui svsf adalah perlu. kajian ini adalah mengenai svsf mudah suai. pada awalnya, svsf dilembutkan. bagi menyediakan keupayaan anggaran statistik hinggar, asvsf dihasilkan terlebih dahulu berdasarkan anggaran kemungkinan maksimum (mle) dan maksimum-harapan (em). tambahan, statistik hinggar yang tidak berat sebelah juga dibuat. walau bagaimanapun, rumusan formula kovarians ini adalah kompleks. ini mungkin menyebabkan matriks simetri menjadi negatif. oleh itu, ia diselaraskan berdasarkan penganggar kovarians inovasi (ice). asvsf dibina bagi menyelesaikan masalah dalam talian penempatan dan pemetaan serentak (slam) dalam talian. oleh itu, ia disebut sebagai 269 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 algoritma asvsf-slam. algoritma yang dicadangkan ini menunjukkan ketepatan dan kestabilan yang lebih baik berbanding algoritma konvensional dari segi ralat punca min kuasa dua (rmse) bagi kedua-dua koordinat anggaran laluan (epc) dan anggaran koordinat peta (emc). keywords: slam, asvsf, mle, em, ice 1. introduction it has been stated that the role of a consistent map of a complex environment can significantly help the robot to conduct the navigation task [1], [2]. however, the robot is commonly blind from this environment. therefore, the robot should be completed to construct the map used to navigate itself and concurrently locate the position of the robot used [1] for the initial base of the mapping task. theoretically, it is known as simultaneous localization and mapping (slam) problem) [3]–[6]. due to this widespread problem's challenges, the slam has been attracting much attention from different researchers. as the manner to fulfill the objective to estimate the robot path and static map, the estimation based on the probability principle has been frequently proposed, such as extended kalman filter (ekf) [5]–[9]. the use of ekf has been limited because of the consistency issue [10]. for this reason, the smooth variable structure filter (svsf) [10]–[13] is often chosen as the alternative filtering method of ekf. the svsf is relatively considered a new predictorestimator that adopts the sliding mode [13]–[15]. the switching gain is utilized as a way to reach the convergence by forcing the estimated values to always on the boundary of the truth estimates. similar to the former implementation of ekf, which keeps the noise statistic to be invariant under the step increment, svsf has been proven to successfully solving the featurebased online slam problem [16]–[19]. fundamentally, the svsf requires the accurate system model and known characteristic of the noise statistic. unfortunately, these orders are often unavailable. therefore, it still poses a risk of divergence and filter degradation quality [18], [20]. in order to cover this possibility, its conventional form needs to modify and enhance [21]– [24]. the most effective way to improve is by adaptively approximating the unknown parameters based on the offline batch estimation. generally, it can significantly tune the gain of svsf [7], [15], [20], [22]. the use of this approach has been proven when used as the manner to improve the ekf [7], [8], [23], [25]–[29], unscented kalman filter (ukf) [18], [30]–[34], and cubature kalman filter (ckf) [24], [34]–[37]. there are some types of the method can be adopted, and two of them are used in this experiment, maximum likelihood estimation (mle) [7], [18], [31], [38]–[41] and the working principle of expectationmaximization (em) [7], [40]–[43]. the process of obtaining the suboptimal solution under these creations seem to unobservable. for this reason, the improved svsf expanded based on the one-step smoothing point is involved [7], [20], [44]. it is adopted to proceed with the derivation process under mle [15]. these processes aim produces the time-varying formulation relative to the noise statistic and its covariances. it gives the form with high complexity; thus, it is compactly reduced. however, it was not strong enough to guarantee positive definite covariance. accordingly, the innovation covariance estimation (ice) [7], [25], [38], [45], [46]is involved. then it is further implemented as the feature-based slam algorithm of a wheeled mobile robot. the rest parts of this paper are organized as follows. section ii presents the formulation of svsf. section iii presents the adaptive svsf with mathematical derivation. the first solution calculated using the mle and em, the enhanced svsf, the unbiased mle-estimator, its time270 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 varying, and the addition of ice. section iv presents all the prerequisites to build the slam algorithm as well as presents the feature-based online slam algorithm referring to the proposed method. section v presents a discussion about the results. section vi presents the conclusion. 2. classical smooth variable structure filter given a nonlinear gaussian system as shown below, { 𝑥𝑘 = 𝑓(𝑥𝑘−1, 𝑢𝑘) + 𝜔𝑘−1 𝑧𝑘 = ℎ(𝑥𝑘) + 𝜈𝑘 (1) where 𝑘 is the discrete time index, 𝑥 ∈ ℝ𝑛 refers to the state vector, 𝑢 is the control vector, and 𝑧 ∈ ℝ𝑚 is the measurement vector. meanwhile, ω ∈ ℝ𝑛 is the additive noise following the process and ν ∈ ℝ𝑚 is the additive noise of the measurement. therefore, once 𝑓(. ) and ℎ(. ) are assumed as the transition and measurement function, respectively, the characteristic noise of eq. (1) is expressed as follows { 𝐸[𝜔𝑘] = 𝑞𝑘, 𝐶𝑜𝑣[𝜔𝑘, 𝜔𝑗] = 𝑄𝑘𝛿𝑘𝑗 𝐸[𝜈𝑘] = 𝑟𝑘, 𝐶𝑜𝑣[𝜈𝑘, 𝜈𝑗] = 𝑅𝑘𝛿𝑘𝑗 𝐸[𝜔𝑘, 𝜈𝑗] = 0 (2) where 𝛿 is well-known as the kronecker delta function. meanwhile, 𝐸[. ] is term used to indicate the expectation or mean and 𝐶𝑜𝑣[, ] is used to indicate the covariance term. once eq. (1) and eq. (2) are described, the summary of svsf are chained as follows [12] �̂�𝑘|𝑘−1 = 𝑓(�̂�𝑘−1|𝑘−1, 𝑢𝑘) + 𝑞 (3) 𝑃𝑘|𝑘−1 = 𝐹𝑃𝑘−1|𝑘−1𝐹 𝑇 + 𝑄 (4) 𝑒𝑧,𝑘|𝑘−1 = 𝑧𝑘 − ℎ(�̂�𝑘|𝑘−1) − 𝑟 (5) 𝜓 = ((|𝑒𝑧,𝑘|𝑘−1|𝑎𝑏𝑠 + 𝛾|𝑒𝑧,𝑘−1|𝑘−1|𝑎𝑏𝑠 ) ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿  −1 𝐻𝑃𝑘|𝑘−1 −1 𝐻𝑇(𝐻𝑃𝑘|𝑘−1𝐻 𝑇 + 𝑅) −1 ) −1 (6) 𝑠𝑎𝑡[𝜓−1𝑒𝑧,𝑘|𝑘−1̿̿ ̿̿ ̿̿ ̿̿ ̿] = { 1 𝜓−1𝑒𝑧,𝑘|𝑘−1̿̿ ̿̿ ̿̿ ̿̿ ̿ −1 𝜓−1𝑒𝑧,𝑘|𝑘−1̿̿ ̿̿ ̿̿ ̿̿ ̿ ≥ 1 , 1 < 𝜓−1𝑒𝑧,𝑘|𝑘−1̿̿ ̿̿ ̿̿ ̿̿ ̿ < −1 𝜓−1𝑒𝑧,𝑘|𝑘−1̿̿ ̿̿ ̿̿ ̿̿ ̿ ≤ −1 (7) 𝐾𝑘 𝑆𝑉𝑆𝐹 = 𝐻+ {(|𝑒𝑧,𝑘|𝑘−1|𝑎𝑏𝑠 + 𝛾|𝑒𝑧,𝑘−1|𝑘−1|𝑎𝑏𝑠 ) ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿̿ ̿ ∘ 𝑠𝑎𝑡[𝜓−1𝑒𝑧,𝑘|𝑘−1̿̿ ̿̿ ̿̿ ̿̿ ̿]} [𝜓 −1𝑒𝑧,𝑘|𝑘−1̿̿ ̿̿ ̿̿ ̿̿ ̿] −1 (8) �̂�𝑘|𝑘 = �̂�𝑘|𝑘−1 + 𝐾𝑘 𝑆𝑉𝑆𝐹𝑒𝑧,𝑘|𝑘−1 (9) 𝑃𝑘|𝑘 = (𝐼 − 𝐾𝑘 𝑆𝑉𝑆𝐹𝐻)𝑃𝑘|𝑘−1(𝐼 − 𝐾𝑘 𝑆𝑉𝑆𝐹𝐻)𝑇 + 𝐾𝑘 𝑆𝑉𝑆𝐹𝑅𝑘𝐾𝑘 𝑆𝑉𝑆𝐹𝑇 (10) 𝑒𝑧,𝑘|𝑘 = 𝑧𝑘 − ℎ(�̂�𝑘|𝑘) (11) where, 𝑃 represents the state error covariance matrix, 𝐹 refers to the jacobian matrix of 𝑓(. ) and 𝑒𝑧 is innovation of measurement error. the sign of . ̿̿ ̿̿ ̿̿ refers to the diagonal term, γ refers to the constant indicating the convergence rate 0 < γ𝑖𝑖 ≤ 1, ψ refers to the boundary 271 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 layer width, 𝑄 ∈ ℝ𝑛𝑥𝑛 correspondences to the covariance matrix of the noise statistic relative to the process and 𝑅 ∈ ℝ𝑚𝑥𝑚 correspondences to the covariance matrix of the noise statistic relative to the measurement and 𝐻 is jacobian matrix of the measurement. meanwhile, the sign of .+ and ∘ are used to indicate the function of the pseudo-invers and schur matrix multiplication, respectively. the stability of svsf and its convergence to the existence of the subspace are satisfied if the absolute error about the posterior is smaller than the prior one [11], [12], [47]–[49]. mathematically, it can be described as follows |𝑒𝑧,𝑘−1|𝑘−1|𝑎𝑏𝑠 > |𝑒𝑧,𝑘|𝑘|𝑎𝑏𝑠 (12) 3. adaptive smooth variable structure filter assuming eq. (1) contains the unknown parameters θ = (𝑞, 𝑟, 𝑄, 𝑅); then, using the maximum likelihood estimation, its estimates θ̂ can be calculated as follows �̂�𝑀𝐿𝐸 = arg maxθ{𝑙𝑛[𝐿(𝑞, 𝑟, 𝑄, 𝑅|𝑍𝑘, 𝑋𝑘)]} (13) note that the likelihood function of θ is 𝐿(𝑞, 𝑟, 𝑄, 𝑅|𝑍𝑘, 𝑋𝑘), which can be expanded as 𝐿(𝑞, 𝑟, 𝑄, 𝑅|𝑍𝑘, 𝑋𝑘) = 𝑝(𝑍𝑘, 𝑋𝑘|𝑞, 𝑟, 𝑄, 𝑅) = 𝑝(𝑋𝑘|𝑞, 𝑄, 𝑟, 𝑅)𝑝(𝑍𝑘|𝑋𝑘, 𝑞, 𝑟, 𝑄, 𝑅) (14) since 𝑋𝑘 = [𝑥0, … , 𝑥𝑘], 𝑍𝑘 = [𝑧1, … , 𝑧𝑘], and eq. (1) refers to the first-order of the markov process, the factorized form of eq. (14) is 𝑝(𝑍𝑘, 𝑋𝑘|𝜃) = 𝑝[𝑥0] ∏ 𝑝[𝑥𝑖|𝑥𝑖−1, 𝑞, 𝑄] ∏ 𝑝[𝑧𝑖|𝑥𝑖, 𝑟, 𝑅] 𝑘 𝑖=1 𝑘 𝑖=1 (15) next, by considering that the prior knowledge complies with gaussian distribution, then eq. (15) can be rewritten as follows 𝑝(𝑍𝑘, 𝑋𝑘|𝑞, 𝑟, 𝑄, 𝑅) = 1 (2𝜋) − 𝑘(𝑛+𝑚)+𝑛 2 |𝑃0| − 1 2|𝑄| − 𝑘 2|𝑅| − 𝑘 2 × exp {− 1 2 [‖𝑥0 − �̂�0‖𝑃0 −1 2 + ∑‖𝑥𝑖 − 𝑓(𝑥𝑖−1) − 𝑞‖𝑄−1 2 𝑘 𝑖=1 + ∑‖𝑧𝑖 − ℎ(𝑥𝑖) − 𝑟‖𝑅−1 2 𝑘 𝑖=1 ]} (16) then by taking logarithm eq. (16), it yields ln[𝐿(𝑞, 𝑟, 𝑄, 𝑅|𝑍𝑘, 𝑋𝑘)] = − 𝑘(𝑛 + 𝑚) + 𝑛 2 𝑙𝑛(2π) − 1 2 𝑙𝑛(|𝑃0|) − 𝑘 2 𝑙𝑛(|𝑄|) − 𝑘 2 𝑙𝑛(|𝑅|) − 1 2 [‖𝑥0 − �̂�0‖𝑃0 −1 2 + ∑‖𝑥𝑖 − 𝑓(𝑥𝑖−1) − 𝑞‖𝑄−1 2 𝑘 𝑖=1 + ∑‖𝑧𝑖 − ℎ(𝑥𝑖) − 𝑟‖𝑅−1 2 𝑘 𝑖=1 ] (17) 272 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 3.1. expectation-maximization (em) estimation according to eq. (1) – eq. (17) and aiming to estimate noise statistics about the process and measurement together with the corresponding covariances, the principle of expectationmaximization is involved. estimating particular function based on em are done by taking the expectation of the objective function, and sequentially maximizing its result [7], [40]–[43]. 3.1.1. expectation process (e-step) the expectation process can be done by first taking the conditional expectation and sequentially equating the result to zero, as shown below. 𝐸[ln[𝐿(𝑞, 𝑟, 𝑄, 𝑅|𝑍𝑘, 𝑋𝑘)]] = − 𝑘(𝑛 + 𝑚) + 𝑛 2 𝑙𝑛(2𝜋) − 1 2 𝑙𝑛(|𝑃0|) − 𝑘 2 𝑙𝑛(|𝑄|) − 𝑘 2 𝑙𝑛(|𝑅|) − 1 2 𝐸 [‖𝑥0 − �̂�0‖𝑃0 −1 2 + ∑‖𝑥𝑖 − 𝑓(𝑥𝑖−1) − 𝑞‖𝑄−1 2 𝑘 𝑖=1 + ∑‖𝑧𝑖 − ℎ(𝑥𝑖) − 𝑟‖𝑅−1 2 𝑘 𝑖=1 ] (18) now by supposing that 𝐶 = − 𝑘(𝑛 + 𝑚) + 𝑛 2 𝑙𝑛(2𝜋) − 1 2 𝑙𝑛(|𝑃0|) − 1 2 𝐸 [‖𝑥0 − �̂�0‖𝑃0 −1 2 ] (19) and applying eq. (19) into eq. (18), the compact form of eq. (18) can be written as follows 𝐸[ln[𝐿(𝑞, 𝑟, 𝑄, 𝑅|𝑍𝑘, 𝑋𝑘)]] = 𝐶 − 𝑘 2 𝑙𝑛(|𝑄|) − 𝑘 2 𝑙𝑛(|𝑅|) − 1 2 𝐸 [∑‖𝑥𝑖 − 𝑓(𝑥𝑖−1) − 𝑞‖𝑄−1 2 𝑘 𝑖=1 + ∑‖𝑧𝑖 − ℎ(𝑥𝑖) − 𝑟‖𝑅−1 2 𝑘 𝑖=1 ] (20) it is known that by definition ‖𝑎‖ 𝑏−1 2 = 𝑎𝑇𝑏−1𝑎. therefore, by applying the identity tr(𝑎𝑇𝑎) = tr(𝑎𝑎𝑇), eq. (20) can be calculated as 𝐸[ln[𝐿(𝑞, 𝑟, 𝑄, 𝑅|𝑍𝑘, 𝑋𝑘)]] = 𝐶 − 𝑘 2 𝑙𝑛(|𝑄|) − 𝑘 2 𝑙𝑛(|𝑅|) − 1 2 ∑ 𝐸 𝑘 𝑖=1 {𝑡𝑟[𝑄−1(𝑥𝑖 − 𝑓(𝑥𝑖−1) − 𝑞)(𝑥𝑖 − 𝑓(𝑥𝑖−1) − 𝑞) 𝑇]} − 1 2 ∑ 𝐸 𝑘 𝑖=1 {𝑡𝑟[𝑅−1(𝑧𝑖 − ℎ(𝑥𝑖) − 𝑟)(𝑧𝑖 − ℎ(𝑥𝑖) − 𝑟) 𝑇]} (21) 3.1.2. maximization process (m-step) up to this point, the unknown parameters relative to the noise can be approximated by maximizing 𝐸[ln[𝐿(𝑞, 𝑟, 𝑄, 𝑅|𝑍𝑘, 𝑋𝑘)]]. it can be done by calculating its partial derivative concerning all elements of the unknown parameter 𝜃 and equating it to zero. correspondingly, the suboptimal of 𝜃 are determined as follows 273 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 �̂�𝑘 = 1 𝑘 ∑ 𝑥𝑖|𝑘 − 𝑓(𝑥𝑖−1|𝑘) 𝑘 𝑖=1 (22) �̂�𝑘 = 1 𝑘 ∑ 𝑧𝑖 − ℎ(𝑥𝑖|𝑘) 𝑘 𝑖=1 (23) �̂�𝑘 = 1 𝑘 ∑(𝑥𝑖|𝑘 − 𝑓(𝑥𝑖−1|𝑘) − 𝑞)(𝑥𝑖|𝑘 − 𝑓(𝑥𝑖−1|𝑘) − 𝑞) 𝑇 𝑘 𝑖=1 (24) �̂�𝑘 = 1 𝑘 ∑(𝑧𝑖 − ℎ(𝑥𝑖|𝑘) − 𝑟)(𝑧𝑖 − ℎ(𝑥𝑖|𝑘) − 𝑟) 𝑇 𝑘 𝑖=1 (25) according to eq. (22) – eq. (25), it can be evaluated that the multistep smoothing term of 𝑥𝑖|𝑘 and 𝑥𝑖−1|𝑘 seems unobservable. therefore, as the effort to proceed derivation process and prevent solution from inefficiency, 𝑥𝑖|𝑘 and 𝑥𝑖−1|𝑘 are respectively replaced by 𝑥𝑖|𝑖 and 𝑥𝑖−1|𝑖. thus, the new forms of suboptimal solutions are obtained as �̂�𝑘 = 1 𝑘 ∑ 𝑥𝑖|𝑖 − 𝑓(𝑥𝑖−1|𝑖) 𝑘 𝑖=1 (26) �̂�𝑘 = 1 𝑘 ∑ 𝑧𝑖 − ℎ(𝑥𝑖|𝑖) 𝑘 𝑖=1 (27) �̂�𝑘 = 1 𝑘 ∑(𝑥𝑖|𝑖 − 𝑓(𝑥𝑖−1|𝑖) − 𝑞)(𝑥𝑖|𝑖 − 𝑓(𝑥𝑖−1|𝑖) − 𝑞) 𝑇 𝑘 𝑖=1 (28) �̂�𝑘 = 1 𝑘 ∑(𝑧𝑖 − ℎ(𝑥𝑖|𝑖) − 𝑟)(𝑧𝑖 − ℎ(𝑥𝑖|𝑖) − 𝑟) 𝑇 𝑘 𝑖=1 (29) although the suboptimal formulation relative to the noise statistics are calculated already, they contain the lack of estimates values, 𝑥𝑖−1|𝑖, which is unavailable from the original form of svsf. for this reason, the svsf is smoothed and improved using a one-step smoothing point [7], [15], [20]. using eq. (3) – eq. (10), one lag smoothed values �̂�𝑘−1|𝑘 and its covariance 𝑃𝑘−1|𝑘 are computed as follows �̂�𝑘−1|𝑘 = �̂�𝑘−1|𝑘−1 + 𝐾𝑘 𝑆𝑉𝑆𝐹�̂�𝑧,𝑘|𝑘−1 (30) 𝑃𝑘−1|𝑘 = (𝐼 − 𝐾𝑘 𝑆𝑉𝑆𝐹𝐻)𝑃𝑘−1|𝑘−1(𝐼 − 𝐾𝑘 𝑆𝑉𝑆𝐹𝐻)𝑇 + 𝐾𝑘 𝑆𝑉𝑆𝐹𝑅𝑘𝐾𝑘 𝑆𝑉𝑆𝐹𝑇 (31) instead of using the prior �̂�𝑘−1|𝑘−1, in this point �̂�𝑘−1|𝑘 in eq. (30) is applied into the transition function f(.) in eq. (3); then, the svsf is essentially smoothed and improved already. moreover, once eq. (30) and eq. (31) are determined, the estimated values �̂�𝑘|𝑘 and 𝑃𝑘|𝑘 can be computed. it is noted that the prediction steps in eq. (3) and eq. (4) of the second step are using the following definition. �̂�𝑘|𝑘−1 = 𝑓(�̂�𝑘−1|𝑘, 𝑢𝑘) + 𝑞 (32) 274 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 𝑃𝑘|𝑘−1 = 𝐹𝑃𝑘−1|𝑘𝐹 𝑇 + 𝑄 (33) now, the estimate values 𝑥𝑖−1|𝑖 in the sequence forms of eq. (22) – eq. (25) can be replaced by eq. (30). 3.2. unbiased estimate noise statistic up to this point, it seems to have clear derived formulation, but the simplification shown in eq. (26) – eq. (29) might reduce the quality as well as leads to bias condition. for this reason, the unbias estimation is approached to guarantee the optimality of eq. (26) – eq. (29). this stage can be sequentially conducted as follows; by definition, it is known that 𝑥𝑖 − 𝑓(𝑥𝑖−1|𝑖) = 𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1 + 𝑞 (34) now, by substituting eq. (34) into 𝑧𝑖 − ℎ(𝑥𝑖|𝑖) 𝑧𝑖 − ℎ(𝑥𝑖|𝑖) = 𝑧𝑖 − ℎ(𝑥𝑖|𝑖−1 + 𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1) = (𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑒𝑧,𝑖|𝑖−1 + 𝑟 (35) then the equivalent form of eq. (26) – eq. (29) are respectively presented as follows �̂�𝑘 = 1 𝑘 ∑ 𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1 + 𝑞 𝑘 𝑖=1 (36) �̂�𝑘 = 1 𝑘 ∑(𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑒𝑧,𝑖|𝑖−1 + 𝑟 𝑘 𝑖=1 (37) �̂�𝑘 = 1 𝑘 ∑ 𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 𝐾𝑖 𝑆𝑉𝑆𝐹𝑇 𝑘 𝑖=1 (38) �̂�𝑘 = 1 𝑘 ∑(𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 (𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑇 𝑘 𝑖=1 (39) since the innovation 𝑒𝑧,𝑘|𝑘−1 and its covariance 𝑒𝑧,𝑘|𝑘−1𝑒𝑧,𝑘|𝑘−1 𝑇 are the parts on the process and measurement noise estimator, it is clear to have 𝑒𝑧,𝑖|𝑖−1 = ℎ(�̃�𝑖|𝑖−1) + 𝑣𝑖 − 𝑟 (40) and the expectation of the innovation error 𝑒𝑧,𝑘|𝑘−1 as well as its corresponding covariance 𝑒𝑧,𝑘|𝑘−1𝑒𝑧,𝑘|𝑘−1 𝑇 are respectively obtained as follows 𝐸[𝑒𝑧,𝑘|𝑘−1] = 0 (41) 𝐸[𝑒𝑧,𝑘|𝑘−1𝑒𝑧,𝑘|𝑘−1 𝑇 ] = 𝐻𝑃𝑘|𝑘−1𝐻 𝑇 + 𝑅 (42) therefore, the expectation of all the suboptimal eq. (36) – eq. (39) are 𝐸[�̂�𝑘] = 𝑞𝑘 (43) 𝐸[�̂�𝑘] = 𝑟𝑘 (44) 275 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 in order to obtain the expectation form of the error covariance noise statistic for both the process and measurement, the joseph covariance form is used. 𝑃𝑖|𝑖 = 𝑃𝑖|𝑖−1(𝐼 − 𝐾𝑖 𝑆𝑉𝑆𝐹𝐻) = 𝑃𝑖|𝑖−1 − 𝑃𝑖|𝑖−1𝐾𝑖 𝑆𝑉𝑆𝐹𝐻 (45) it is clear, once the unbiased estimates are also satisfiying 𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 = 𝐻𝑃𝑖|𝑖−1𝐻 𝑇 + 𝑅, therefore, the following forms are determined 𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 = 𝐻𝑇𝑃𝑖|𝑖−1 (46) (𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 ) 𝑇 = 𝐻𝑃𝑖|𝑖−1 (47) then all expectation values of 𝜃 relative to the error matrices are 𝐸[�̂�𝑘] = 1 𝑘 ∑(𝐹𝑃𝑖−1|𝑖−1𝐹 𝑇 + 𝑄)𝐻𝑇𝐾𝑖 𝑆𝑉𝑆𝐹𝑇 𝑘 𝑖=1 (48) 𝐸[�̂�𝑘] = 𝑅𝑘 + 1 𝑘 ∑ 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹𝐻𝑃𝑖|𝑖−1𝐻 𝑇 − 𝐻𝑃𝑖|𝑖−1𝐻 𝑇 𝑘 𝑖=1 (49) up to this point, the expectation of all the noise statistic are obtained. note that, 𝑞𝑘, 𝑟𝑘, 𝑄𝑘, 𝑅𝑘 in eq. (46) – eq. (49) and eq. (36) – eq. (39) are the representation of eq. (26) – eq. (29), respectively. hence, the unbiased noise statistic properties can be calculated as follows �̂�𝑘 = 1 𝑘 ∑ 𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1 + 𝑞 𝑘 𝑖=1 (50) �̂�𝑘 = 1 𝑘 ∑(𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑒𝑧,𝑖|𝑖−1 + 𝑟 𝑘 𝑖=1 (51) �̂�𝑘 = 1 𝑘 ∑ (𝐹𝑃𝑖−1|𝑖−1𝐹 𝑇 + 𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 𝐾𝑖 𝑆𝑉𝑆𝐹𝑇) 𝐻𝑇𝐾𝑖 𝑆𝑉𝑆𝐹𝑇 𝑘 𝑖=1 (52) �̂�𝑘 = 1 𝑘 ∑(𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 (𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑇 − 𝐻𝑃𝑖|𝑖−1𝐻 𝑇 + 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹𝐻𝑃𝑖|𝑖−1𝐻 𝑇 𝑘 𝑖=1 = 1 𝑘 ∑(𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 (𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑇 𝑘 𝑖=1 − (𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝐻𝑃𝑖|𝑖−1𝐻 𝑇 (53) 3.3. time-varying unbiased noise statistic once, the unbiased form are calculated, the time-varying forms can also be calculated. according to eq. (50) – eq. (53), they are respectively expressed as follows �̂�𝑘 = �̂� + 1 𝑘 (𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1) (54) 276 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 �̂�𝑘 = �̂� + 1 𝑘 ((𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑒𝑧,𝑖|𝑖−1) (55) �̂�𝑘 = �̂� 𝑘 − 1 𝑘 + 1 𝑘 (𝐹𝑃𝑖−1|𝑖−1𝐹 𝑇 + 𝐾𝑖 𝑆𝑉𝑆𝐹𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 𝐾𝑖 𝑆𝑉𝑆𝐹𝑇) 𝐻𝑇𝐾𝑖 𝑆𝑉𝑆𝐹𝑇 (56) �̂�𝑘 = �̂� 𝑘 − 1 𝑘 + 1 𝑘 ((𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑒𝑧,𝑖|𝑖−1𝑒𝑧,𝑖|𝑖−1 𝑇 (𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝑇 − (𝐼 − 𝐻𝐾𝑖 𝑆𝑉𝑆𝐹)𝐻𝑃𝑖|𝑖−1𝐻 𝑇) (57) where �̂�, �̂�, �̂�, and �̂� are 𝑞𝑘−1, 𝑟𝑘−1, 𝑄𝑘−1, and 𝑅𝑘−1, respectively. moreover, as an effort to keep its stability, the exponential 1 𝑘 in eq. (54) – eq. (57) are replaced with the weighting coefficient 𝑑𝑘 [7], [15], [18], [22], [30], [37]. additionally, the use of innovation covariance estimator (ice) is involved to depress the posibility of negative definite matrices eq. (56) – eq. (57). then, the final formulation for covariance matrices relative to the noise statistic of the process and measurement are expressed as follows �̂�𝑘 = (1 − 𝑑𝑘)�̂�𝑘−1 + 𝑑𝑘 (𝐹𝑃𝑘−1|𝑘−1𝐹 𝑇 + 𝐾𝑘 𝑆𝑉𝑆𝐹𝐼𝐶𝐸𝑘𝐾𝑘 𝑆𝑉𝑆𝐹𝑇) 𝐻𝑇𝐾𝑘 𝑆𝑉𝑆𝐹𝑇 (58) �̂�𝑘 = (1 − 𝑑𝑘)�̂�𝑘−1 + 𝑑𝑘 ((𝐼 − 𝐻𝐾𝑘 𝑆𝑉𝑆𝐹)𝐼𝐶𝐸𝑘(𝐼 − 𝐻𝐾𝑘 𝑆𝑉𝑆𝐹)𝑇 − (𝐼 − 𝐻𝐾𝑘 𝑆𝑉𝑆𝐹)𝐻𝑃𝑘|𝑘−1𝐻 𝑇) (59) once, the adaptive svsf is designed with addition of the smoothing formulation (see eq. (1) – eq. (12) and eq. (32) – eq. (33)) and the time-varying of the noise statistic eq. (54) – eq. (55) and eq. (58) – eq. (59), the adaptive svsf-based slam algorihtm can also be designed. the design involves all the configuration and completeness that have been introduced in [15]. it is noted that this involvement includes the motion model, direct point-based observation, and inverse point-based observation. accordingly, the compact pseduo-code of this algorithm can be described as follows: algorithm asvsf-based slam require : initial state estimate, covariance, convergence rate, and initial error 1: loop 2: prediction step: if proprioceptive data is available 3: propagate the state estimate 4: compute the jacobian of f(.) 5: propagate the covariance relative to the state 6: update: if the observation data is available 7: compute the innovation sequence error 8: calculate gain 9: update the state, and covariance 10: compute the noise statistic 11: endloop 4. result and discussion in order to validate its stability, the proposed method is realistically simulated before it is compared to the conventional one. all the parameters relative to the robot configuration are adopted from turtlebot2, as stated below. 𝑊𝑟 = 33𝑐𝑚, 𝑑𝑙𝑠 = 14𝑐𝑚, γ = 15𝑒 − 2, 𝑒𝑧,0 = [0.1; 0.5π/180] furthermore, the initial state and its error covariance are defined as follows. 277 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 �̂�0 = [ 0 0 ( 35π 180 ) ] , 𝑃0 = [ (1.5)2 0 0 0 12 0 0 0 ( 2.5π 180 ) 2 ] it is also assumed, the robot is also completed with a 2d-lidar used to get the measurement data, distance and bearing. according to the initial noise statistics, there would be two different simulation cases presented in this paper. • first test the initial process and measurement noise are considered as follows �̂�0 = [ 0.03 ( π 180 ) ] , �̂�0 = [ 0.2 ( 3π 180 ) ] , �̂�0 = [ 0.032 0 0 ( π 180 ) 2] , �̂�0 = [ 0.22 0 0 ( 3π 180 ) 2 ] these noises will be executed once initially, and for the next iteration, they will be recursively provided by the proposed algorithm. to validate the effectiveness and robustness of the proposed method some comparative results are presented as follows. fig. 1. performance of different slam-based algorithm (first test) fig. 1 demonstrates different filter performances in solving the slam problem of wheeled mobile robots. it verifies that the proposed method's properness is satisfied with locating the robot position and mapping the features. graphically, it is hard to evaluate the difference, so that fig. 2 and fig. 3 are presented. fig. 2 shows that the proposed method has been successfully presenting the better-estimated path than then svsf-slam algorithm. although the small difference between isvsfslam, asvsf-mle-em cannot be observed from this figure. so that to ease our analysis, table 1 is presented. additionally, the algorithms mentioned above are also compared in terms of rmse for the estimated map. fig. 3 demonstrates that the proposed method has been reducing the rmse given by the svsf-slam algorithm. thus, it can be noted that the asvsf-slam based on mle-em has been successful in upgrading the quality of the classical method. 278 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 moreover, according to fig. 3, the effectiveness of one-step smoothing has been proven to stably the svsf-slam algorithm. fig. 2. rmse of estimated path coordinate of different slam-algorithm (first test) fig. 3. rmse of estimated map coordinate of different slam-algorithm (first test) 279 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 table 1: rmse of different slam-based algorithm (first test) slam-based algorithm x-epc [cm] y-epc [cm] 𝛉-epc [rad] x-emc [cm] y-emc [cm] svsf 5.5823 9.7952 0.1045 11.2296 14.4148 isvsf 5.4492 2.5447 0.0985 7.5200 14.2128 asvsf 4.2798 2.3807 0.0989 15.4925 13.5943 • second test the initial process and measurement noise are considered as follows. �̂�0 = [ 0.08 ( 5π 180 ) ] , �̂�0 = [ 0.8 ( 3π 180 ) 2 ] , �̂�0 = [ 0.082 0 0 ( 5π 180 ) 2 ] , �̂�0 = [ 0.82 0 0 ( 3π 180 ) 2 ] in the second case, the initial noise statistics both for process and measurement were increased. it aims to examine the stability of the proposed algorithm under an uncertain predetermined noise statistic. fig. 4. performance of different slam-based algorithm (second test) similarly, fig. 4 also demonstrates different filter performances in solving the slam problem of wheeled mobile robots. it also verifies that the proposed method's properness is satisfied with locating the robot position and mapping the features even there is an increment of small additive noise to both the process and measurement. according to fig. 5, it can be noted that the increment of the defined noise statistic has no effect on the proposed method stability. it is shown by its ability to reduce rmse of the svsf-slam algorithm. at this point, it can be stated that the proposed method can guarantees stability better than the classical one. next, to validate the proposed algorithm stability, the different approaches in estimating map are compared (see fig. 6). fig. 6 illustrates that the stability of the proposed method in mapping the feature is satisfied even after increasing the statistics of the initial noise. according to fig. 6, the proposed method also presents better quality compared with the svsf-slam algorithm. the 280 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 effectiveness of one-smoothing is again proven, referring to its best achievement in estimating the map. similarly, to clearance the differences in the simulation results discussed above, table 2 is presented. fig. 5 rmse of estimated path coordinate of different slam-algorithm (second test) fig. 6. rmse of estimated map coordinate of different slam-algorithm (second test) 281 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 table 2: rmse of different slam-based algorithm (second test) slam-based algorithm x-epc [cm] y-epc [cm] 𝜽-epc [rad] x-emc [cm] y-emc [cm] svsf 5.9065 10.0448 0.1099 10.8078 13.6891 isvsf 5.3109 2.6691 0.0989 7.7296 7.2725 asvsf 3.2337 2.5043 0.0985 10.8512 11.1995 according to table 1 and table 2, the smallest rmse is shown by the isvsf-based slam algorithm. it verifies that the one-step smoothing technique has been successfully enhancing the classical svsf without losing the svsf characteristic. however, since it can estimate the noise statistic, its performance cannot guarantee effectiveness when applied in the real application. regarding these differences, the proposed method has been presenting excellent performance. • third test asvsf-slam algorithm based on mle-em with and without ice in order to evaluate the existence of innovation covariance estimation, the following figures (see fig. 7 and fig. 8) are presented. these results refer to the initial noise statistic as defined in the second test above. fig. 7. rmse of estimated path coordinate of different slam-algorithm (third test) fig.7 confirms that the simplification of the first formulated covariance of the measurement noise statistic does not negatively affect the final solution. it can be proven as well in fig. 8. 282 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 fig. 8. rmse of estimated map coordinate of different slam-algorithm (third test) at this point, it can be noted that the differences depicted by fig. 7 and fig. 8 verify that the innovation covariance estimator (ice) has been successfully reducing rmse of the original asvfv-slam algorithm. to ease our analysis, table 3 is also presented table 3: rmse of different slam-based algorithm (second test) asvsfslam-based algorithm x-epc [cm] y-epc [cm] 𝜽-epc [rad] x-emc [cm] y-emc [cm] without ice 3.1637 2.4950 0.0985 20.9206 18.3115 with ice 3.2337 2.3807 2.5043 10.8512 11.1995 according to table 3, the proposed method with ice has been showing better performance compared to other algorithm in term of rmse of epc and emc 5. conclusion this paper presents a proposed method termed as asvsf-slam based on mle-em creation. the contributions can be summarized as follows; improving the normal svsf based on a one-step smoothing method, providing an ability to estimate the noise statistic to normal svsf, providing the time-varying unbiased noise statistic; completing the recursive unbiased noise statistic with innovation covariance estimation. following all the stages and validating the asvsf-slam algorithm's performance in terms of rmse has been proving the robustness and effectiveness of the proposed method. additionally, by referring to the convergence result, which is shown by its performance in different and increment of the initially predetermined noise statistic, the proposed method guarantees the stability compared to the conventional one. 283 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 acknowledgement research was supported by special plan of major scientific instruments and equipment of the state (grant no.2018yff01013101), national natural science foundation of china (61704102), the iiot innovation and development special foundation of shanghai (2017gyhlw01037) and project named “key technology research and demonstration line construction of advanced laser intelligent manufacturing equipment” from shanghai lingang area development administration, shanghai university, and mercu buana university, jakarta, indonesia. references [1] suwoyo, h., tian, y., deng, c., & adriansyah, a. (2018). improving a wall-following robot performance with a pid-genetic algorithm controller. proceeding of the electrical engineering computer science and informatics, 5(1), 314-318. [2] adriansyah, a., suwoyo, h., & tian, y. (2019). jurnal teknologi improving robot. 3, 119–126. [3] afshari, h. h., gadsden, s. a., & habibi, s. (2017). gaussian filters for parameter and state estimation: a general review of theory and recent trends. signal processing. https://doi.org/10.1016/j.sigpro.2017.01.001 [4] ahmed, r., el sayed, m., gadsden, s. a., tjong, j., & habibi, s. (2016). artificial neural network training utilizing the smooth variable structure filter estimation strategy. neural computing and applications, 27(3), 537–548. https://doi.org/10.1007/s00521-015-1875-2 [5] akhlaghi, s., zhou, n., & huang, z. (2018). adaptive adjustment of noise covariance in kalman filter for dynamic state estimation. ieee power and energy society general meeting, 2018january, 1–5. https://doi.org/10.1109/pesgm.2017.8273755 [6] al-shabi, m., & habibi, s. (2011). iterative smooth variable structure filter for parameter estimation. isrn signal processing, 2011(1). https://doi.org/10.5402/2011/725108 [7] bailey, t. (2002). mobile robot localisation and mapping in extensive outdoor environments. philosophy, 31(august), 212. https://doi.org/10.1016/s0921-8890(99)00078-0 [8] bailey, t., & durrant-whyte, h. (n.d.). simultaneous localisation and mapping ( slam ): part ii state of the art. 1–10. [9] bar-shalon, y., li, x.-r., & kirubarajan, t. (n.d.). estimation with applications to tracking and navigation. [10] benzerrouk, h., nebylov, a., & salhi, h. (2016). quadrotor uav state estimation based on highdegree cubature kalman filter. ifac-papersonline. https://doi.org/10.1016/j.ifacol.2016.09.060 [11] chen, s., shi, z., & ding, j. (2017). application of the 2nd-order smooth variable structure filter algorithm for sins initial alignment. 2017 forum on cooperative positioning and service, cpgps 2017, (1), 43–49. https://doi.org/10.1109/cpgps.2017.8075095 [12] choset, h., lynch, k., hutchinson, s., kantor, g., burgard, w., kavraki, l., & thrun, s. (2006). principles of robot motion, theory, algorithms and implementations, by howie choset et al., mit press, 2005. xix + 603 pp., index, isbn 0-262-03327-5, 433 references (hb. £38.95) . robotica, 24(2), 271–271. https://doi.org/10.1017/s0263574706212803 [13] demim, f., nemra, a., & louadj, k. (2016). robust svsf-slam for unmanned vehicle in unknown environment. ifac-papersonline. https://doi.org/10.1016/j.ifacol.2016.10.585 [14] fethi, d., nemra, a., louadj, k., & hamerlain, m. (2018). simultaneous localization, mapping, and path planning for unmanned vehicle using optimal control. advances in mechanical engineering, 10(1), 1–25. https://doi.org/10.1177/1687814017736653 [15] gadsden, s. a., al-shabi, m., arasaratnam, i., & habibi, s. r. (2014). combined cubature kalman and smooth variable structure filtering: a robust nonlinear estimation strategy. signal processing, 96 (part b), 290–299. https://doi.org/10.1016/j.sigpro.2013.08.015 [16] gadsden, s. andrew, & afshari, h. h. (2015). a review of smooth variable structure filters: recent advances in theory and applications. asme international mechanical engineering 284 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 congress and exposition, proceedings (imece), 4a-2015. https://doi.org/10.1115/imece201550966 [17] gadsden, s. andrew, habibi, s. r., dunne, d., & kirubarajan, t. (2011). combined particle and smooth variable structure filtering for nonlinear estimation problems. fusion 2011 14th international conference on information fusion, 1552–1559. [18] gadsden, s. andrew, & lee, a. s. (2017). advances of the smooth variable structure filter: square-root and two-pass formulations. journal of applied remote sensing. https://doi.org/10.1117/1.jrs.11.015018 [19] gadsden, stephen andrew. (2011). smooth variable structure filter theory and application.pdf. mcmaster university. [20] gao, b., gao, s., gao, l., & hu, g. (2016). an adaptive ukf for nonlinear state estimation via maximum likelihood principle. iceiec 2016 proceedings of 2016 ieee 6th international conference on electronics information and emergency communication, (4), 117–120. https://doi.org/10.1109/iceiec.2016.7589701 [21] gao, b., gao, s., hu, g., zhong, y., & gu, c. (2018). maximum likelihood principle and moving horizon estimation based adaptive unscented kalman filter. aerospace science and technology. https://doi.org/10.1016/j.ast.2017.12.007 [22] gao, w., li, j., zhou, g., & li, q. (2015). adaptive kalman filtering with recursive noise estimator for integrated sins/dvl systems. journal of navigation, 68(1), 142–161. https://doi.org/10.1017/s0373463314000484 [23] gao, z., mu, d., zhong, y., gu, c., & ren, c. (2019). adaptively random weighted cubature kalman filter for nonlinear systems. mathematical problems in engineering, 2019. https://doi.org/10.1155/2019/4160847 [24] grisetti, g. (2004). towards a phd thesis on simultaneous localization and mapping. 1–38. retrieved from http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.106.4683&amp;rep=rep1&amp;type =pdf [25] habibi, b. s. (2007). structure filter. proceedings of the ieee, 95(5). [26] he, j., chen, y., zhang, z., yin, w., & chen, d. (2018). a hybrid adaptive unscented kalman filter algorithm. international journal for engineering modelling, 31(3), 51–65. https://doi.org/10.31534/engmod.2018.3.ri.04d [27] huang, y., zhang, y., xu, b., wu, z., & chambers, j. a. (2018). a new adaptive extended kalman filter for cooperative localization. ieee transactions on aerospace and electronic systems, 54(1), 353–368. https://doi.org/10.1109/taes.2017.2756763 [28] kim, k. h., lee, j. g., & park, c. g. (2009). adaptive two-stage extended kalman filter for a fault-tolerant ins-gps loosely coupled system. ieee transactions on aerospace and electronic systems, 45(1), 125–137. https://doi.org/10.1109/taes.2009.4805268 [29] kim, t., wang, y., sahinoglu, z., wada, t., hara, s., & qiao, w. (2014). state of charge estimation based on a realtime battery model and iterative smooth variable structure filter. 2014 ieee innovative smart grid technologies asia, isgt asia 2014, 132–137. https://doi.org/10.1109/isgt-asia.2014.6873777 [30] laviola, j. j. (2003). a comparison of unscented and extended kalman filtering for estimating quaternion motion. proceedings of the american control conference, 3, 2435–2440. [31] levitan, e., & herman, g. t. (1987). a maximum a posteriori probability expectation maximization algorithm for image reconstruction in emission tomography. ieee transactions on medical imaging, 6(3), 185–192. https://doi.org/10.1109/tmi.1987.4307826 [32] li, z., yang, w., & ding, d. (2017). time-varying noise statistic estimator based adaptive simplex cubature kalman filter. mathematical problems in engineering, 2017. https://doi.org/10.1155/2017/5349879 [33] mohamed, a. h., & schwarz, k. p. (1999). adaptive kalman filtering for ins/gps. journal of geodesy, 73(4), 193–203. https://doi.org/10.1007/s001900050236 [34] outamazirt, f., fu, l., lin, y., & abdelkrim, n. (2016). a new sins/gps sensor fusion scheme for uav localization problem using nonlinear svsf with covariance derivation and an adaptive boundary layer. chinese journal of aeronautics. https://doi.org/10.1016/j.cja.2016.02.005 285 iium engineering journal, vol. 22, no. 1, 2021 suwoyo et al. https://doi.org/10.31436/iiumej.v22i1.1403 [35] shao, x., he, b., guo, j., & yan, t. (2016). the application of auv navigation based on adaptive extended kalman filter. oceans 2016 shanghai. https://doi.org/10.1109/oceansap.2016.7485592 [36] suwoyo, h., deng, c., tian, y., & adriansyah, a. (2018). improving a wall-following robot performance with a pid-genetic algorithm controller. international conference on electrical engineering, computer science and informatics (eecsi), 2018-octob, 314–318. https://doi.org/10.1109/eecsi.2018.8752907 [37] thrun, s. (2002). probabilistic robotics. communications of the acm, 45(3), 52–57. https://doi.org/10.1145/504729.504754 [38] tian, y., suwoyo, h., wang, w., & li, l. (2019). an asvsf-slam algorithm with timevarying noise statistics based on map creation and weighted exponent. mathematical problems in engineering, 2019, 28–34. https://doi.org/10.1155/2019/2765731 [39] tian, y., suwoyo, h., wang, w., mbemba, d., & li, l. (2019). an aekf-slam algorithm with recursive noise statistic based on mle and em. journal of intelligent and robotic systems: theory and applications. https://doi.org/10.1007/s10846-019-01044-8 [40] wan, e. a., & van der merwe, r. (2000). the unscented kalman filter for nonlinear estimation. ieee 2000 adaptive systems for signal processing, communications, and control symposium, as-spcc 2000, 153–158. https://doi.org/10.1109/asspcc.2000.882463 [41] wang, hairong, deng, z., feng, b., ma, h., & xia, y. (2017). an adaptive kalman filter estimating process noise covariance. neurocomputing. https://doi.org/10.1016/j.neucom.2016.10.026 [42] wang, hongjian, fu, g., li, j., yan, z., & bian, x. (2013). an adaptive ukf based slam method for unmanned underwater vehicle. mathematical problems in engineering, 2013. https://doi.org/10.1155/2013/605981 [43] wang, x., song, b., liang, y., & pan, q. (2017). em-based adaptive divided difference filter for nonlinear system with multiplicative parameter. international journal of robust and nonlinear control, 27(13), 2167–2197. https://doi.org/10.1002/rnc.3674 [44] woo, r., yang, e. j., & seo, d. w. (2019). a fuzzy-innovation-based adaptive kalman filter for enhanced vehicle positioning in dense urban environments. sensors (switzerland), 19(5). https://doi.org/10.3390/s19051142 [45] yang, j. n., pan, s., & huang, h. (2007). an adaptive extended kalman filter for structural damage identifications ii: unknown inputs. structural control and health monitoring, 14(3), 497–521. https://doi.org/10.1002/stc.171 [46] yang, jann n., lin, s., huang, h., & zhou, l. (2006). an adaptive extended kalman filter for structural damage identification. structural control and health monitoring, 13(4), 849–867. https://doi.org/10.1002/stc.84 [47] yi, b., kang, l., tao, s., zhao, x., & jing, z. (2013). adaptive two-stage extended kalman filter theory in application of sensorless control for permanent magnet synchronous motor. mathematical problems in engineering, 2013. https://doi.org/10.1155/2013/974974 [48] yong, s., chongzhao, h., & yongqi, l. (2009). adaptive ukf for target tracking with unknown process noise statistics. 2009 12th international conference on information fusion, fusion 2009, (1), 1815–1820. [49] yu, f., sun, q., lv, c., ben, y., & fu, y. (2014). a slam algorithm based on adaptive cubature kalman filter. mathematical problems in engineering, 2014. https://doi.org/10.1155/2014/171958 [50] zeng, z., zhang, s., xing, y., & cao, x. (2014). robust adaptive filter for small satellite attitude estimation based on magnetometer and gyro. abstract and applied analysis, 2014. https://doi.org/10.1155/2014/159149 286 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 mustafina et al. https://doi.org/10.31436/iiumej.v21i1.1180 numerical algorithm for finding optimal initial concentrations of chemical reactions svetlana mustafina1*, andrey antipin1, evgenia antipina1, elena odinokova2, larisa tuchkina2, konstantin kolyazov2, and sofia mustafina1 1dept. mathematics and information technology, bashkir state university, ufa, russia 2dept. information technology and management systems, moscow state university of technologies and management, moscow, russia. *corresponding author: mustafina_sa@mail.ru (received: 16th june 2019; accepted: 19th october 2019; published on-line: 20th january 2020) abstract: this article is devoted to the problem of developing methods for mathematical modelling in the sphere of optimal planning in a chemical experiment. in the article, the problem of finding the optimal ratio for initial concentrations of substances is formulated in general terms and an algorithm for solving this problem is constructed basing on the method of artificial immune systems. the developed algorithm for finding the optimal initial concentrations of substances allows solving the problem of experiment planning in chemistry at the computational experiment stage. in this case, the solution of the optimization problem found with its help does not depend on the choice of the initial approximation. the algorithm was tested for the industrially meaningful process of benzilidenebenzilamine synthesis for which the optimum values of the initial concentrations were calculated in order to obtain maximum yield of the reaction product. abstrak: artikel ini ditujukan untuk masalah mengembangkan kaedah pemodelan matematik dalam bidang perancangan optimum dalam percubaan kimia. dalam artikel itu, masalah mencari nisbah optimum untuk konsentrasi awal bahan digubal secara umum dan algoritma untuk menyelesaikan masalah ini dibina berdasarkan kaedah sistem imun buatan. algoritma yang dibangunkan untuk mencari kandungan konsentrasi awal yang optimum membolehkan menyelesaikan masalah perancangan percubaan dalam kimia pada peringkat percubaan pengkomputeran. dalam kes ini, penyelesaian masalah pengoptimuman yang didapati dengan bantuannya tidak bergantung pada pilihan permulaan awal. algoritma ini telah diuji untuk proses sintesis benzilidenebenzilamin yang bermakna industri yang mana nilai-nilai optimum kepekatan awal dikira untuk mendapatkan hasil maksimum produk reaksin. keywords: chemical kinetics; artificial immune systems; initial concentration 1. introduction the solution to many problems in chemistry and chemical technology is associated with complex and expensive experiments. in the study of the chemical process at the computational experiment stage, it is advisable to identify its main regularities because of the complexity of the initial raw materials’ compositions and the low content of valuable components in them. in this regard, the actual task is to develop methods for optimal planning of the experiment, which allow saving time and material resources for conducting a full-scale experiment. 167 iium engineering journal, vol. 21, no. 1, 2020 mustafina et al. https://doi.org/10.31436/iiumej.v21i1.1180 the development of computer technology and information technology allows the use of mathematical methods in the planning of the chemical experiments. the methods of mathematical modelling allow the determination of optimal concentrations of reagents to obtain the best yield of the final product and significantly reduce the cost of substance synthesis. the calculation of the initial concentrations of the reactants in a chemical reaction is made by searching for an extremum of the function for calculating the dynamics of the substance concentrations during the chemical experiment. the significant drawbacks of most numerical methods for finding the extremum of functions are the difficulties in achieving convergence of the process, which depends on the choice of the initial approximation. currently, metaheuristic optimization methods are widely used, which make it possible to efficiently find a global optimum in a reasonable time [1-3]. their important feature is the ability to overcome the local extremum point of the target function in the search process. therefore, they allow finding better solutions in comparison with classical heuristics [4-7]. among the metaheuristic algorithms, the method of artificial immune systems is distinguished. its advantage is the presence of a memory mechanism. the memory mechanism makes it possible to use information about previously found best solutions, thereby increasing the efficiency of global search. an important feature of the method of artificial immune systems is the independence of the optimization problem solution from the initial approximation [8-10]. 2. formulation of the problem let us formulate in general terms the problem of finding the optimal ratio for initial concentrations of substances. a mathematical model for the dynamics of substance concentrations is a system of ordinary differential equations ( , ( ), ), dx f t x t t dt (1) with initial conditions 0(0) , 1, ,i ix x i n (2) where 1 2( ) ( ( ), ( ), , ( ))nx t x t x t x t is the vector of the concentrations of the reacting substances, f (t, x(t), t) is continuous together with their partial derivatives of the function, ],0[ 2tt is the time of reaction, and t is the reaction temperature [11]. at the initial moment of time, substances are interconnected by some ratio: 1 1(0) : : (0) : : .n nx x (3) it is required to find the ratio for initial concentrations of substances, which ensures the extremum of optimality criterion 2 1 ( ) ( ) . n i i i q x x t extr (4) the optimality criterion expresses the maximum yield of the target products or the minimum impurity content depending on the coefficients i (positive or negative). you 168 iium engineering journal, vol. 21, no. 1, 2020 mustafina et al. https://doi.org/10.31436/iiumej.v21i1.1180 can also specify some economic criterion, then the coefficients i are the cost coefficients of the reagents. 3. the algorithm for the method of artificial immune systems to calculate optimal initial concentrations of substances the method of artificial immune systems simulates the functioning of a living organism immune system, designed to destroy foreign bodies and improve the fight against them. consider the main concepts of the method. an antigen is an alien substance from which the body tries to protect itself with antibodies. an antibody is a substance that recognizes and destroys an antigen [12]. a memory cell is an immune cell that accumulates data about new antibodies that can recognize an antigen. the target function of the optimization problem is called the fitness function [13,14]. as a function of fitness, we used the maximum yield of the target reaction product at the final moment of the reaction. this required the solution of a direct kinetic problem with a given ratio for the initial concentrations of the initial substances, that is, the solution of a system of differential equations (eq. (1)) with initial conditions (eq. (2)). we modified the algorithm to solve the problem of finding the optimal initial concentrations of the components in the reacting mixture. as a population of immune cells, we introduced sets of initial concentrations of substances 1 2 (0) ( (0), (0), , (0)), 1, ,j j j jnx x x x j k where k is the number of immune cells in the population. to calculate the value of the fitness function ( )q x , it is necessary to know the concentration of reagents at the final point in time. to do this, we introduced a block for solving a direct kinetic problem into the algorithm. the problem of finding the minimum of the target function ( )q x was reduced to the problem of finding the maximum by replacing the sign in front of the function with the opposite one: *( ) min ( ) max [ ( )].q x q x q x if q(x) was positive then q(x*)<0. we formulated this algorithm. step 1. the creation of an initial population for the starting substance concentrations. set the number of immune cells in the population k, the number of parental cells for the selection r_sel, the number of cells in the population with the worst value of the fitness function n_bad, the maximum number of iterations i_max, the clone operator parameter n_cl, the mutation parameter m, the iteration counter num = 0. randomly set the values of k cells of the initial population (0), 1, ,jx j k 0 (0) 1.jx step 2. calculation of fitness function values. for sets (0)jx calculate the value of fitness function ( )jq x , by solving a direct kinetic problem for each immune cell. that is, at this step it is necessary to find a numerical solution to the system of differential equations (eq. (1)) with the initial 169 iium engineering journal, vol. 21, no. 1, 2020 mustafina et al. https://doi.org/10.31436/iiumej.v21i1.1180 conditions (eq. (2)) by an explicit or implicit method. the initial conditions of the system (eq. (2)) are the immune cell. step 3. cloning. select r_sel parent cells from the population (a set of antibodies), which correspond to the best values of fitness function ( )q x . generate n_cl clones for each cell. step 4. mutation. for each parent cell generate random numbers [0,1],l 1 [0,1 (0)], j ih x 2 [0, (0)], j ih x 1, .i n perform a mutation of its clones by the rule: if 0, 5,l then 1(0) : (0) , s s i ix x h m else 2(0) : (0) , s s i ix x h m where 1, _ ,s n cl m – mutation parameter. step 5. calculation of fitness function values. for each mutant clone calculate the value of the fitness function by eq. (4). step 6. selection and transition to a new population. for each parent cell, find the mutant clone with the lowest value of the fitness function. compare its value with the value of the fitness function of the parent cell. in the new population, leave the parent cell or replace it with a mutant clone with the best fitness function value. step 7. renewal of a population. in the population, find n_bad cells with the lowest value of fitness function ( )q x . replace these cells with new ones, randomly generated in the interval [0,1), and calculate the value of the fitness function ( )q x for them. increase the iteration counter: num= num + 1. step 8. checking the conditions for the end of search. if num<i_max, then go to step 3, else finish the search and go to step 9. step 9. selection of optimal concentrations of substances from the population. as a solution to the problem of finding the optimal concentrations of substances, select the cell with the highest fitness function value from the last population. the developed algorithm was implemented as a software tool in the visual programming environment delphi. 4. computational experiment based on the formulated algorithm, we calculated the optimal ratio of the initial concentrations for the reaction of the benzylidenebenzylamine synthesis in order to obtain the maximum yield of the reaction product. the mechanism of the chemical reaction for the synthesis of benzylidenebenzylamine in the presence of a catalyst 3 26fecl h o is represented by a set of stages [15]: 170 iium engineering journal, vol. 21, no. 1, 2020 mustafina et al. https://doi.org/10.31436/iiumej.v21i1.1180 1 2 3 4 3 5 6 5 1 7 8 8 6 9 , , , , x x x x x x x x x x x x x x (5) where x1 – benzylamine (c7h9n), x2 – carbon tetrachloride (ccl4), x3 – chlorobenzylamine (c7h8ncl), x4 – chloroform (chcl3), x5 – 1-phenylmethanimine (c7h7n), x6 – hydrogen chloride (hcl), x7 – benzylidenebenzylamine (c14h13n), x8 – ammonium (nh3), x9 – ammonium chloride (nh4cl). the speed of each stage is determined according to the law of mass action: 1 1 1 2 2 2 3 3 3 5 1 4 4 8 6 , , , , k x x k x k x x k x x (6) where ix is the concentration of the i-th substance ( 1, 9i ) (mole fraction), jk is the rate constant of the j-th reaction stage 1, 4 ,j calculated according to the arrhenius equation 0( ) exp , j j j e k t k rt where jе is the energy of activation of the j-th stage (kj/mol), t is the reaction temperature (к), and r is the universal gas constant (8,31 j/(mol∙к)). the matrix of stoichiometric coefficients of substances ( )ij ( 1, 4,i 1, 9j ) is given in table 1. table 1: matrix of stoichiometric coefficients of the reaction of synthesis of benzylidenebenzylamine ω1 ω2 ω3 ω4 x1 -1 0 -1 0 x2 -1 0 0 0 x3 1 -1 0 0 x4 1 0 0 0 x5 0 1 -1 0 x6 0 1 0 -1 x7 0 0 1 0 x8 0 0 1 -1 x9 0 0 0 1 δ 0 1 0 -1 since there are nonzero elements among the elements of the last line , the reaction proceeds with a change in the reaction volume [16, 17]. then the kinetic model of the reaction is a system of differential equations: 171 iium engineering journal, vol. 21, no. 1, 2020 mustafina et al. https://doi.org/10.31436/iiumej.v21i1.1180 ),,( ,9,1, ),(),( txf dt dn i n txfxtxf dt dx n niii (7) with initial conditions: 0(0) , 1, 9, (0) 1,i ix x i n (8) where n is the variable reaction volume, 4 1 , 1, 9,i ij j j f w i 4 9 1 1 ,n j ij j i f w 0 j jw c is the values of rate of reaction stages ( 1, 4j ) (h-1), and с0 is the initial total concentration of substances (mol/l). the functions ( , ),nf x t ( , )if x t ( 1,9)i have the form: 1 1 3 2 1 3 1 2 4 1 5 2 3 6 2 4 7 3 8 3 4 9 4 2 ( , ) ( , ) ( , ), ( , ) ( , ), ( , ) ( , ) ( , ), ( , ) ( , ), ( , ) ( , ) ( , ), ( , ) ( , ) ( , ), ( , ) ( , ), ( , ) ( , ) ( , ), ( , ) ( , ), ( , ) ( ,n f x t w x t w x t f x t w x t f x t w x t w x t f x t w x t f x t w x t w x t f x t w x t w x t f x t w x t f x t w x t w x t f x t w x t f x t w x t 4) ( , ).w x t (9) the initial substances of the reaction are benzylamine (x1) and carbon tetrachloride (x2), the concentrations of which are related by the ratio: 1 2(0) (0) 1.x x for other substances (0) 0,ix 3, 9.i since the target substance of the reaction scheme is benzylideneaniline (x7), the optimization problem is formulated as follows: find the ratio for the initial concentrations 1 2(0) : (0)x x of the source substances x1 and x2, at which at the final time of the reaction the maximum yield of benzylidenebenzylamine x7 is reached, i.e. 7 2( ) ( ) max.q x x t the solution of this problem was obtained at the temperature 23t c and the time of the reaction was 2 4t h. the solution of the system (eq. (7)) with initial conditions (eq. (8)) was obtained by the implicit euler method. the result of the calculation obtained the optimal ratio for the initial concentrations of the source substances was: 1 2(0) : (0) 0,51: 0, 49.x x (10) the maximum yield of the reaction (benzylideneaniline) was 0,013 mole fractions. 172 iium engineering journal, vol. 21, no. 1, 2020 mustafina et al. https://doi.org/10.31436/iiumej.v21i1.1180 figure 1 shows the dynamics of the benzylidenebenzylamine concentration at optimal initial concentrations. fig. 1: dynamics of the optimal concentration of benzylidenebenzylamine. 5. conclusions consider the solution of a direct kinetic problem for the reaction scheme (eq. (5)) with arbitrary sets for initial concentrations of substances. according to table 2, the maximum concentration of benzylidenebenzylamine is observed at a specific ratio of the source substances (eq. (10)). this confirms the correct operation of the algorithm. table 2: dependence of the concentration of benzylidenebenzylamine 7x from the ratio of source substances 1x and 2x x1, mole fraction x2, mole fraction x7, mole fraction 0.1 0.9 0.004 0.2 0.8 0.008 0.3 0.7 0.010 0.4 0.6 0.012 0.51 0.49 0.013 0.7 0.3 0.011 0.8 0.2 0.009 0.9 0.1 0.005 thus, the developed algorithm for finding the optimal initial concentrations of the initial substances makes it possible to solve the problem of planning an experiment in chemistry at the stage of a computational experiment. the solution of the optimization problem will be found for any set of values of the initial concentrations of substances, since the work of the artificial immune systems method does not depend on the initial approximation. acknowledgement the reported study was funded by rfbr according to the research project no 17-47020068 and project no. 13.5143.2017 / 8.9. 173 iium engineering journal, vol. 21, no. 1, 2020 mustafina et al. https://doi.org/10.31436/iiumej.v21i1.1180 references [1] goldberg d. (1989) genetic algorithms in search, optimization and machine learning. addison-wesley, usa. [2] holland jn. (1975) adaptation in natural and artificial systems. ann arbor, michigan: univ. of michigan press. [3] stepashina ev. (2014) optimization the financial performance of enterprise on neural network model. information systems and technologies, 5: 34-42. [4] igel c, hansen n, roth st. (2007) covariance matrix adaptation for multi-objective optimization. evolutionary computation, 15(1): 1-28. [5] mahdavi m. (2007) an improved harmony search algorithm for solving optimization problems. applied mathematics and computation, 188(2): 1567-1579. [6] herrera f, lozano m, verdegay jl. (1998) tackling real-coded genetic algorithms: operators and tools for the behavior analysis. artificial intelligence review, 12(4): 265-319. [7] lee ks, geem zw.(2005) a new meta-heuristic algorithm for continuous engineering optimization: harmony search theory and practice. computer methods in applied mechanics and engineering, 194: 3902-3933. [8] ishida y, hirayama h, fujita h, ishiguro a, mori k. (1998) immunity-based systemsintelligent systems by artificial immune systems. corona pub. co., japan. [9] sedova na, sedov va, bazhenov ri. (2018) analysis of emergency level at sea using fuzzy logic approaches. advances in intelligent systems and computing, 658: 314-322. [10] antipin af. (2013) a computer-aided system for designing multidimensional logic controllers with variables representing a set of binary logic arguments. automation and remote control, 74(9): 1573-1581. [11] mustafina sa, vaytiev va, stepashina ev. (2014) search the kinetic parameters of the reduced scheme of a-methylstyrene dimerization reaction. arpn journal of engineering and applied sciences, 9(7): 1118-1120. [12] de castro l, timmis j. (2002) an artificial immune network for multimodal function optimization. proceedings of ieee congress on evolutionary computation, 1: 669-674. [13] panteleev av, metlitskaya dv. (2012) applying of the method of the synthetic immune systems in a problems of searching comditional extremum of the function. civil aviation high technologies, 184: 54-61. [14] antipin af. (2015) improving response time of real time control systems based on multidimensional interval-logical controllers. automation and remote control, 76(3): 480486. [15] stepashina ev, baitimerova ai, mustafina sa. (2011) the software package for the computer aided procedure of qualified mechanism of chemical reactions based on drgep method. bashkir chemical journal, 18(3): 112-115. [16] vaytiev va, stepashina ev, mustafina sa. (2013) identification of a mathematical model of the reduced scheme of α-methylstyrene dimerization reaction. european journal of natural history, 6: 30-32. [17] sedov va, sedova na. (2014) modelling collision avoidance actions in closest approach zones by means of neural networks. asia-pacific journal of marine science & education, 4(2): 104-111. 174 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <feff0054006f0074006f0020006e006100730074006100760065006e00ed00200070006f0075017e0069006a007400650020006b0020007600790074007600e101590065006e00ed00200064006f006b0075006d0065006e0074016f002000410064006f006200650020005000440046002000760068006f0064006e00fd006300680020006b0065002000730070006f006c00650068006c0069007600e9006d0075002000700072006f0068006c00ed017e0065006e00ed002000610020007400690073006b00750020006f006200630068006f0064006e00ed0063006800200064006f006b0075006d0065006e0074016f002e002000200056007900740076006f01590065006e00e900200064006f006b0075006d0065006e0074007900200050004400460020006c007a00650020006f007400650076015900ed007400200076002000610070006c0069006b0061006300ed006300680020004100630072006f006200610074002000610020004100630072006f006200610074002000520065006100640065007200200036002e0030002000610020006e006f0076011b006a016100ed00630068002e> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <feff04120438043a043e0440043804410442043e043204430439044204350020044604560020043f043004400430043c043504420440043800200434043b044f0020044104420432043e04400435043d043d044f00200434043e043a0443043c0435043d044204560432002000410064006f006200650020005000440046002c0020043f044004380437043d043004470435043d0438044500200434043b044f0020043d0430043404560439043d043e0433043e0020043f0435044004350433043b044f04340443002004560020043404400443043a0443002004340456043b043e04320438044500200434043e043a0443043c0435043d044204560432002e0020042104420432043e04400435043d04560020005000440046002d0434043e043a0443043c0435043d044204380020043c043e0436043d04300020043204560434043a04400438043204300442043800200437043000200434043e043f043e043c043e0433043e044e0020043f0440043e043304400430043c04380020004100630072006f00620061007400200456002000410064006f00620065002000520065006100640065007200200036002e00300020044204300020043f04560437043d04560448043804450020043204350440044104560439002e> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 108 anomalous electrodeposition of fe-ni alloy coating from simple and complex baths and its magnetic property m.a. islam and m. moniruzzaman department of materials and metallurgical engineering bangladesh university of engineering and technology dhaka-1000, bangladesh e-mails: aminul03211@yahoo.com, mmoniruzzaman@mme.buet.ac.bd abstract: electrodeposition of fe-ni thin films has been carried on copper substrate under various electrodeposition conditions from two simple and six complex baths. sulfate baths composing of niso4. 7h2o, feso4.7h2o, h3bo3 and na2so4 keywords: anomalous electrodeposition, fe-ni coating, complexing agent, current density, magnetic property. 1. introduction alloy electrodeposition technologies can extend tremendously the potential of electrochemical deposition processes to provide coatings that require unique mechanical, chemical and physical properties [1]. there has been a great research interest in the development and characterization of iron-nickel (fe-ni) thin films due to their operational capacity, economic interest, magnetic and other properties [2]. due to their unique low coefficient of thermal expansion (cte) and soft magnetic properties, fe-ni alloys have been used in industrial applications for over 100 years [3]. typical examples of applications that are based on the low cte of fe-ni alloys include: thermostatic bimetals, glass sealing, integrated circuit packaging, cathode ray tube, shadow masks, membranes for liquid natural gas tankers; applications based on the soft magnetic properties include: read-write heads for magnetic storage, magnetic actuators, magnetic shielding, high performance transformer cores. comprise the simple baths whereas complex baths were prepared by adding ascorbic acid, saccharin and citric acid in simple baths. the effect of bath composition, ph and applied current density on coating appearance, composition, morphology and magnetic property were studied. wet chemical analysis technique was used to analyze the coating composition whereas sem and vsm were used to study the deposit morphology and magnetic property respectively. addition of complexing agents in plating baths suppressed the anomalous nature of fe-ni alloy electrodeposition. coatings obtained from simple baths were characterized by coarse grained non-smooth surface with/without microcracks onto it whereas those from complex baths were fine grained with smooth surfaces. satisfactory saturation magnetization value of 131.13 emu/g in coating was obtained from simple bath. coatings obtained from complex baths did not show normal magnetization behavior. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 109 fe-ni electrodeposition exhibits the phenomenon of anomalous codeposition. this term introduced by brenner is being used to describe the preferential deposition of the less noble metal, fe, to the more noble metal, ni. in other words, the reduction of nickel is inhibited while the deposition of iron is enhanced when compared with their individual deposition rates. thus electrodeposition of fe-ni alloys has attracted considerable attention because of its special characteristic nature and wide range of unique properties. attempts have been made but there are several explanations of this phenomenon and the mechanism is not yet well understood. grande and talbot [4] proposed the monohydroxide, feoh+ and nioh+, as the charge transfer species. it is found that the monohydroxide of the less noble metal is favored in aqueous solution. they reported that the ph at the cathode is not high enough for formation of metal hydroxide precipitates, fe(oh)2 and ni(oh)2, which are unlikely to be key species in the codeposition. this model worked well for the fe-ni system, but was unable to fully characterize ni-co or co-fe codeposition [5]. matlosz [6] proposed the competitive adsorption phenomena between fe and ni during electrodeposition and reported that the inhibition of ni is related solely to the differences in kinetic constants for fe and ni as single metals. bertazzoli et al. [7] reported the inhibition of the early stage nucleation and growth of the noble metal in the presence of the less noble metal. moreover, the effects of electrodeposition conditions and complexing agent additives on the magnetic properties of deposits have received little attention so far. in the present study we investigated in detail the effects of electrodeposition conditions and addition of complexing agents on quality and magnetic properties of fe-ni deposit. 2. experimental procedure commercial copper sheets of 50 mm × 15 mm × 1 mm were used as substrates (cathode) and platinum foil of 35 mm × 15 mm × 0.4 mm was used as anode in this investigation. the cu substrates were degreased, mechanically and electrochemically cleaned by maintaining polishing with emery papers, pickling, rinsing and acid dipping process. schematic of the electrodeposition set up is illustrated in fig. 1. fig. 1: schematic of the set-up used for electrodeposition. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 110 both simple and complex baths were used. analytical reagent grade chemicals and deionized water were used to prepare baths. sulfate baths composing of niso4. 7h2o, feso4 .7h2o, h3bo3 and na2so4 bath identification in varying composition comprise the simple baths. complex baths were prepared by adding ascorbic acid, saccharin and citric acid in varying composition to the simple baths. details of the simple and complex bath compositions are shown in table 1a and table 1b respectively. table 1a: simple bath compositions. bath concentration (g/l) ni/fe ratio b1 niso4. 7 h2o feso4. 7 h2o h3bo : 28.1 : 27.8 : 12.4 3 1.04 b2 niso4. 7 h2o feso4. 7 h2o h3bo3 na2so : 15.5 : 5.6 : 12.4 : 49.7 4 2.84 table 1b: complex bath compositions. bath identification principal ingredients (g/l) complexing ingredients (g/l) ni/fe ratio ascorbic acid saccharin citric acid b-3a niso4.7h2o feso4.7h2o h3bo3 na2so4 h2so : 28.1 : 27.8 : 12.4 : 49.7 : 9.8 4 1.5 1.5 2.1 1.04 b-3b 2.0 3.0 4.2 b-3c 3.0 4.5 8.4 b-4a niso4.7h2o feso4.7h2o h3bo3 na2so4 h2so : 28.1 : 27.8 : 12.4 : 49.7 : 9.8 4 ─ ─ 4.2 1.04 b-4b 2.0 ─ 4.2 b-4c ─ 3.0 4.2 all depositions were carried out at room temperature and at constant current densities viz. 20, 30, 40, 50, 60, 70, 100, 120 and 140 ma/cm2. each deposition was continued for a predetermined time period of 2 hours and without any stirring action. the ph value of bath solution before and after every deposition was measured and the change of ph was recorded. chemical analysis of the deposit was carried out by the conventional wet method. weight of the electrodeposited sample was taken first (say w1). the deposit was allowed to dissolve in 40 c.c. aqua rezia solution (hcl : hno3 = 3:1). precaution was taken here so that hcl and hno3 do not react with the substrate. the sample was rinsed with tap water, dried in acetone and weighted (say w2). so, w = w1 w2 gives the weight iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 111 of the deposit dissolved in aqua rezia solution. this solution was treated chemically to analyze the percentage of ni and fe content in it. scanning electron microscopy (sem) was used to study the morphology of fe-ni alloy coatings. magnetic properties of the fe-ni films were measured by a vibrating sample magnetometer (vsm). the vsm was carefully calibrated using the standard calibration sample of nickel with 99.999% purity. the calibration was done at an applied magnetic field of 2500 oe and a temperature of 20oc. hysteresis loops were generated using a sweep time of 20 minutes and a maximum field of 2500 oe. the dimensions of the fe-ni coating samples used in the vsm measurements were 3mm × 4mm. the sample was fixed to a small sample holder located at the end of a sample rod mounted in an electromechanical transducer. the transducer is driven by a power amplifier which itself is driven by an oscillator at a frequency of 90 hz. so, the sample vibrates along the z axis perpendicular to the magnetizing field. the induced signal in the pick-up coil system is fed to a differential amplifier. the output of the differential amplifier is subsequently fed into a tuned amplifier and an internal lock-in amplifier receives a reference signal supplied by the oscillator. the output of this lock-in amplifier, or the output of the magnetometer itself, is a dc signal proportional to the magnetic moment of the sample and is obtained from the digital readout. 3. results and discussion 3.1 electrodeposition of fe-ni alloy coating the fe-ni films were deposited from eight different baths. two of them were simple baths containing the main ingredients niso4, feso4, na2so4, h3bo3 of varying composition with different ni/fe ratio in each bath (table 1a). another six were complex baths containing ascorbic acid, saccharin and citric acid in varying concentration as complexing agents in addition with the main ingradients. effect of individual complexing agent on coating can be obtained from baths b-4a, b-4b and b-4c whereas combined effect of complexing agents on coating can be obtained from baths b-3a, b-3b and b-3c (table 1b). the bath ph and applied current density had a profound effect on the nature of fe-ni alloy deposit. the deposit quality was identified by visual inspection. uniform, adherent and bright coatings from all the baths were obtained at higher ph range with lower current density and at lower ph range with higher current density. an applied current density of 100 ma/cm2 produced blackish rough deposit from bath b-3a having electrolyte solution ph of 1.85 while uniform, adherent and bright coatings were obtained from the same bath b-3a at current density of 30 ma/cm2 and ph 1.85 of the bath. figure 2 shows a contrast between the good coating and blackish rough deposit whereas fig. 3 represents the ph and current density matching for uniform and bright deposition of fe-ni coatings from complex baths b-3a and b-3b. similar trend was also observed in all other complex as well as simple baths. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 112 (a) (b) fig. 2: coatings obtained from bath b-3a; (a) uniform, adherent, bright coating and (b) blackish rough coating. (a) (b) fig. 3: relation between ph and current density for bright deposition obtained from baths (a) b-3a and (b) b-3b. no deposition was seen in cases the ph < 1.90 for simple baths and ph < 1.00 for complex baths. from baths with ph less than these lower limit, deposit could form only near the edges while major portion of the substrate surface remained bare. at this low ph, fe-ni plating baths became too corrosive and therefore the newly deposited fe-ni alloy is chemically attacked and dissolved. at the mid portion of the sample where current density is lower than the average, rate of this chemical attack is higher than the deposition rate. on the other hand, at areas near the edges which receive more current than the average, the deposition rate is higher than the rate of chemical attack. as a result, significant amount of deposit could only be seen near the edges at ph < 1.90 for simple baths and ph < 1.00 for complex baths [8]. no good deposition was obtained at a current density > 120 ma/cm2 for simple baths and > 140 ma/cm2 for complex baths. at these higher current densities deposited coating tend to peeling due to developing of stress. thus, no electrodeposition was carried out at any current density > 120 ma/cm2 and 140 ma/cm2 0 10 20 30 40 50 60 70 80 90 100 1 2 3 ph of bath solution c ur re nt d en si ty (m a /c m2 ) for simple and complex baths respectively. 1.85 1.31 1.17 0 20 40 60 80 100 120 140 160 1 2 3 ph of bath solution c ur re nt d en si ty (m a /c m2 ) 1.78 1.31 1.00 iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 113 3.2 chemical analysis of the deposit chemical analysis of the coatings was carried out by the conventional wet method. feni films obtained at different current density from baths with varying ni/fe ratio show the variation of ni content in it. electrodeposition was performed at room temperature with no agitation where current density had been varied from 50 to 120 ma/cm2 for simple baths b-1 and b-2 while from 20 to 140 ma/cm2 for complex baths b-3a, b-3b, b-3c, b-4a, b4b and b-4c. fe content of the coatings was also analyzed to check the co-deposition of fe-ni alloy in the coating. the results thus obtained confirm the co-deposition of fe-ni alloy in it. percentage ni in the deposit as a function of applied current density is shown in fig. 4 for simple baths and in fig. 5 for complex baths. neglecting a small deviation, an increase of % ni in the deposit with increasing applied current density is observed for simple baths while the reverse trend is seen for complex baths. bath b-2 contains higher ni/fe ratio in its electrolyte composition than the other baths. the highest ni content in the deposit was measured 21.80 wt% for bath b-2 while 15.11 wt% for bath b-1 at the same current density of 120 ma/cm2. this is supported by the alloy deposition principle that an increase in the metal percentage (or ratio) of a parent metal in an alloy plating bath results in an increase in its percentage (or ratio) in the deposit [9]. moreover, the electrolyte conductance increases as a result of addition of na2so4 in bath b-2 and consequently it significantly increased ni2+ in the deposit if compared with bath b-1 [9]. decrease in ni content with increasing current density is observed in coatings obtained from complex baths (fig. 6). however, 47.52 wt% ni content obtained from complex bath b-3b was the highest than those obtained from all the simple as well as complex baths studied. also, the minimum ni content (26.19%) of coatings obtained from all complex baths is higher than the maximum ni content (21.80%) of those obtained from simple baths. ni/fe ratio in all the baths except bath b-2 is 1.04. figure 6 shows the %ni in the coating deposited from simple bath b-1 and complex baths b-3a, b-3b and b-3c at the same current density of 50 ma/cm2 5 7 9 11 13 15 17 19 21 23 25 40 60 80 100 120 140 current density (ma/cm2 ) % n i i n co at in g b-1 b-2 . higher %ni in 25 35 45 20 70 120 current density (ma/cm2) % n i i n co at in g b-3a b-3b b-3c l fig. 4: effect of current density on %ni in coating deposited from simple baths. ni/fe ratio in baths b1 and b-2 is 1.04 and 2.84 respectively. fig. 5: effect of current density on % ni in coating deposited from complex baths b-3a, b-3b and b-3c. ni/fe ratio in these baths is 1.04. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 114 coatings deposited from complex baths than from simple baths is observed. the standard electrode potential for reduction of pure ni2+ (-0.257 v) is relatively more positive than that of fe2+ (-0.447 v). according to normal deposition theory, an element with a higher positive standard electrode potential is expected to deposit preferentially than the one with a less positive standard electrode potential [10]. again according to brenner’s definition of anomalous codeposition [11], the less noble metal (here fe) is deposited preferentially and its percentage in the deposit become higher than that in electrolytes. in general, the anomalous codeposition is attributed to hydrogen evolution (the side reaction of metal reduction at the cathode surface) that depletes protons and results in increasing the local concentration of hydroxyl ions [9]. this increase in hydroxyl ion, however, leads to the formation and adsorption of metal monohydroxide ions or metal hydroxides on cathode surface, favoring the anomalous codeposition. according to the model proposed by gangasingh et al. [12], the formation of feoh+ and nioh+ m near the cathode has a critical role in the occurrence of anomalous deposition phenomena. but, higher %ni (more noble) in coatings deposited from complex baths than the simple bath (fig. 6) concludes that addition the complexing agents suppresses the anomalous nature of the fe-ni alloy electrodeposition. ph of the complex baths was as low as 2 which might prevent the generation of hydroxide and therefore could suppress the anomalous characteristics of feni coatings. typical reactions which may take place during the deposition of metals having a negative standard electrode potential are as follows [13]: +n + ne(i) → m …………………………………….......... metal deposition 2h+ + 2e→ h2 (ii) ………………………………………. hydrogen evolution 2h2o + 2e → 2oh(iii) …………………………………....... water decomposition xm+n + yh2o → mx(oh) y (xn-y)+ + yh+ (iv) ………………...... hydrolysis of metal ion mx(oh)y (xn-y)+ + (xn-y)h2 o → xm(oh)n + (xn y)h + (v) ….. precipitation of hydroxide • electrochemical reactions (ii) and (iii) tend to consume h+ or generate oh• reactions (iv) and (v) tend to produce h . hence, when they take place at the cathode, the ph of the cathode will increase. + • when the ph near the surface becomes such that hydrolysis and precipitation reactions occur, any further ph rise will be slowed by reactions (iv) and (v). and will counteract the ph rise at the cathode produced by reactions (ii) and (iii). • if the hydrolysis reaction (iv) is not able to slow the ph rise, the deposit may contain hydroxide inclusions because of reaction (v). ni electrodeposition proceeds via a nickel monohydroxide species (nioh+) or the surface ph may reach values at which nickel hydroxide [ni(oh)2] would precipitate at the surface and would inhibit metal deposition [14]. so, complexing agent was supposed to enhance the hydrolysis reaction producing nioh+ effect of different complexing agents on %ni in the deposit is shown in fig. 7. addition of ascorbic acid and citric acid shows a major impact (bath b-4b) to increase during electrodeposition which might increase the ni content of the coatings from baths b-3a, b-3b and b-3c. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 115 0 5 10 15 20 25 30 35 40 45 1 2 3 4 bath ide ntification % n i i n co at in g b-1 b-3a b-3b b-3c %ni in the deposit than addition of saccharin with citric acid (bath b-4c) or only with citric acid in the bath b-4a. ascorbic acid prevents oxidation of ferrous to ferric ions [15] in the bath and thus the ni content of the films was higher. the reaction mechanism may be proposed as following [16-18]: h2o + 2e→ h2 + oh(vi) .................................................... ......................... fe2+ + 2(oh)→ fe(oh)2 (vii) ...................................................................... fe(oh)2 + oh→ fe(oh)3(ads) (viii) .............................................................. fe(oh)3(ads) + fe(oh)n (3-n)+ + 3e→ fe + noh(aq) + fe(oh)3(ads) (ix) ..... according to these reactions, if fe(oh)2 is inhibited to convert to fe(oh)3, then fe(oh)3 the influence of current density, bath composition and ph on the morphology of fe-ni coatings was evaluated by scanning electron microscope (sem). the topographies of feni coatings were analyzed concerning their uniformity, porosity and the presence of was not able to act as a positive catalyst to produce fe. so, inhibition of ferrous to ferric ions might increase the ni content of the coatings obtained from bath b-4b by reducing fe content of the deposited films. saccharin increases the ni content of the films. citric acid increases the side reaction rate [19] that decreases the alloy current efficiency due to the increase of the hydrogen ions adsorption which consequently, might decrease the ni content in coatings. 3.3 morphology of the coating 26 27 28 29 30 31 32 33 1 2 3 bath identification % n i i n co at in g b-4b b-4c b-4a a=ascorbic acid s=saccharin c=citric acid c s+c a+c fig. 6: percentage ni deposited from simple bath b-1 and complex baths b-3a, b-3b and b-3c. all these baths contain same ni/fe ratio of 1.04 and the depositions were carried on at 50 ma/cm2. fig. 7: effect of complexing agent on % ni in coating deposited from complex baths b-4a, b-4b and b-4c. all depositions were carried on at 30 ma/cm2. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 116 cracks. figure 8 shows sem images of fe-ni alloy coatings obtained from simple bath b2 at different current density. grains are roughly spherical and average grain size decreased with increasing current density. thus structure of the fe-ni coatings is strongly influenced by current density. myung et al. [20] reported similar observations to binary fe-ni thin films. it is known that high current density give rise to a high degree of adatoms saturation at the electrode surface [21] and high degree of adatoms decreases the grain size. elezovi et al. [22] reported that the stress changes in the fe-ni films on varying deposition current density may mainly be attributed from the changes of the average grain sizes. as the average grain sizes decreased with increasing current density, the deposit stress might be increased. thus morphology of the fe-ni alloys is characterized by the presence of microcracks. in this study, stressed films at high current density revealed the presence of sharp line microcracks distributed over the deposits [fig. 8(b), 8(c)]. the detail mechanisms of stress changes by varying the deposited current density have yet not been clear. morphology of the deposits can be controlled by using electrolytes containing complexing agent/agents with proper compositions. for complexing agent, the crystallization of the electrodeposited layer is very important, since it influences directly the structure of the deposit and therefore its properties [23]. crystallization occurs either by the buildup of old crystals or by the formation and growth of new ones. these two processes are in competition and can be influenced by different factors. high surface diffusion rates, low population of adatoms and low over-potentials are factors enhancing the buildup of old crystals. on the contrary, low surface diffusion rates, high population of 20 µm (a) 20 µm (b) 20 µm (c) fig. 8: sem images of the deposit obtained from simple bath b-2 at current density of (a) 50 ma/cm2, (b) 100 ma/cm2 and (c) 120 ma/cm2. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 117 adatoms and high over-potentials on the surface enhance the creation of new nuclei [24]. from the sem observations, it can be said that addition of complexing agent of 2.0 g/l ascorbic acid, 3.0 g/l saccharin and 4.2 g/l citric acid in bath b-3b increased nucleation rates that helped to form crack-free, uniform and fine grained structures as is seen in fig.9. 3.4 magnetic properties of fe-ni coating soft magnetic thin films with high saturation magnetization are highly desired in a wide range of applications from magnetic write heads to high frequency inductors. however, soft magnetic thin-film materials with a saturation magnetization >21 kg and a low coercivity <1 oe are still not available. discovering new soft magnetic materials with very high saturation magnetization still remains to be a major challenge [25]. the magnetic anisotropy and coercivity are important properties of soft magnetic materials which find applications in the magnetic recording and reading technology [26]. the demand of saturation magnetization for soft magnetic materials is increasing steadily and that the saturation magnetization 135 emu/g is satisfactorily acceptable for the write head materials [27]. magnetization loops of the fe-ni films deposited from various simple and complex baths were measured using a vibrating sample magnetometer (vsm). the variation of saturation magnetization (ms) with %ni of coatings from simple baths is shown in table 2. 20 µm (a) 20 µm (b) 20 µm (c) fig. 9: sem images of the deposit obtained from complex bath b-3b at current density of (a) 50 ma/cm2, (b) 100 ma/cm2 and (c) 140 ma/cm2. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 118 table 2: the saturation magnetization (emu/g) and %ni obtained from simple baths. bath identification ms % ni (emu/g) b-1 131.13 9.38 125.56 10.38 118.38 11.09 b-2 104.92 15.21 94.34 16.12 68.32 21.80 as shown here, the saturation magnetization (ms) for bath b-1 is higher than that of films for bath b-2. the coating containing 9.38% ni displays the highest saturation magnetization and it decreases with increase in ni content of the coating. figure 10 shows saturation magnetization curves of fe-ni films for bath b-1. the ms-h (saturation magnetization vs applied field) curves clearly show that the curves are mostly straight lines with small easy axis coercivity of about <1 oe which might occur by domain translation and rotation. when the applied field is along the easy axis, the net magnetization of the films should be zero after removal of the field due to the formation of an equal amount of antiparallel domains. fe-ni films deposited from simple bath showed a (a) 9.38% ni coating (b) 10.38% ni coating m s -150 -100 -50 0 50 100 150 -3000 -2000 -1000 0 1000 2000 3000 h (oe) m ( e m u /g ) 131.13 emu/g -150 -100 -50 0 50 100 150 -3000 -2000 -1000 0 1000 2000 3000 h (oe) m ( e m u /g ) 125.56 emu/g -150 -100 -50 0 50 100 150 -3000 -2000 -1000 0 1000 2000 3000 h (oe) m ( e m u /g ) 118.38 emu/g fig. 10: magnetization curves of feni coatings obtained from simple bath b-1. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 119 (c) 11.09% ni coating nearly ideal behavior, fe-ni films deposited from simple bath showed a nearly ideal behavior, with a well-defined uniaxial anisotropy. this shows that the uniaxial anisotropy, which is dependent on the film microstructure such as grain size, preferred orientation and stress, is mostly confined in-plane [28]. the saturation magnetization curves of fe-ni coatings obtained from bath b-2 are shown in fig. 11. the highest saturation magnetization is seen 104.92 emu/g among the coatings obtained from bath b-2. similar results that magnetic saturation decreases with increasing %ni content in coatings and the uniaxial anisotropy is mostly confined in plane were observed for coatings obtained from bath b-1 as well as bath b-2. thus no major difference in magnetic saturation property is found due to the variation of bath composition in simple baths. (a) 15.21% ni coating (b) 16.12% ni coating (c) 21.80% ni coating the change in saturation magnetization (ms) of the as-deposited fe-ni coatings obtained from simple baths is shown in fig. 12 as a function of %ni of the films. the fast decreasing ms with the increasing %ni within the lower range ni content (9-11%) and relatively slow decreasing ms with the increasing %ni within the higher range ni content (15-22%) was observed. the saturation magnetization of the fe-ni coating is shifted to higher saturation magnetization values with increasing fe content in it which is expected as magnetic moment of pure fe (221.9 emu/g) is greater than that of pure ni (57.5 emu/g) [29]. the saturation magnetization of these fe-ni thin films is apparently limited by that of pure iron which is 221.9 emu/g. -150 -100 -50 0 50 100 150 -3000 -2000 -1000 0 1000 2000 3000 h (oe) m ( e m u /g ) 94.34 emu/g -150 -100 -50 0 50 100 150 -3000 -2000 -1000 0 1000 2000 3000 h (oe) m ( e m u /g ) 104.92 emu/g -80 -60 -40 -20 0 20 40 60 80 -3000 -2000 -1000 0 1000 2000 3000 h (oe) m ag n et ic s at u ra ti o n (e m u /g ) 68.32 emu/g m (e m u/ g) fig. 11: magnetization curves of the fe-ni coatings deposited from simple bath b-2. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 120 magnetization curves of the films obtained from complex baths did not show normal magnetization behavior. figure 13 shows the magnetization curve of 44.13% ni coating deposited from complex bath b-3a. curves obtained from all other complex baths were of similar pattern. the unusual pattern might be due to the structural and compositional characteristics in the thin films. coatings from simple baths are characterized by coarsegrained with some microcracks onto it but those from complex baths are characterized by fine-grained smooth deposits. magnetic softness of polycrystalline thin films is an extrinsic property of the magnetic materials, and is closely related to the structural and compositional characteristics in the thin films [30-32]. these characteristics can also affect anisotropy and magnetostriction, which are in turn correlated with the magnetic softness. thus the structural and compositional characteristics of the thin films, such as grain size, crystallographic texture, strain and stress state may change the magnetization property of coatings obtained from complex baths. however, it is still not well established how these structural characteristics affect the magnetic softness [33]. it would be of great scientific as well as technological interests to make this alloy soft while keeping its saturation magnetization at high level simultaneously. 4. conclusions electrodeposition of fe-ni thin films has been carried on copper substrate under various electrodeposition conditions from simple as well as complex baths. the influence of plating parameters on appearance, anomalous characteristics, morphology and magnetic properties of fe-ni coating is investigated. the electrolytic composition, current density and ph of depositing baths are considered as varying parameters in this work. the conclusions drawn from the study are: 1. bright and smooth fe-ni coating can be deposited from higher current density with lower ph value or higher ph value with lower current density both from simple and complex baths. 62 64 66 68 70 72 74 8 13 18 23 % ni in coating m s (e m u/ g) b-1 b-2 -30 -20 -10 0 10 20 30 -3000 -2000 -1000 0 1000 2000 3000 h (oe) m a g n e ti c s a tu ra ti o n ( e m u /g ) m s (e m u/ g) fig. 12: variation of magnetization saturation with ni content for simple baths. fig. 13: magnetization curve of 44.13% ni coating deposited from complex bath b-3a. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 121 2. addition of ascorbic acid, saccharin, citric acid as complexing agents in the plating bath suppresses the anomalous nature of fe-ni alloy electrodeposition. complexing agents are supposed to enhance hydrolysis reaction producing nioh+ which, in turn, favors ni deposition. on the contrary, formation of ni(oh)2 3. variation of applied current density affected deposit compositions differently for simple and complex baths. percentage ni into the coating increased with increasing current density for simple baths whereas the reverse occurred for complex baths. precipitate at the cathode surface inhibits ni deposition in simple baths. 4. the morphology of the fe-ni films obtained from simple baths is characterized by coarse-grained, non-smooth surface with presence of microcracks onto it. on the contrary, coatings from complex baths are fine-grained with smooth surfaces. 5. the saturation magnetization (ms) of the electrodeposited fe-ni coating is found to decrease with increasing ni content which is in good agreement with suppression of ferromagnetic character of the films. the highest saturation magnetization is seen 131.13 emu/g among the coatings studied which is very close to the acceptable limit (135 emu/g). coating obtained from complex baths did not show normal magnetization behavior. the morphological and compositional characteristics of coating might interfere the magnetization nature of it. acknowledgements the authors thank the directorate of advisory, extension and research services (daers), buet for sanctioning fund to make this research work successful. the assistance of dr. a.k.m. abdul hakim and dr. sheikh manjura hoque of bangladesh atomic energy commission with the vsm analysis is gratefully acknowledged. references [1] d. landolt, j. electrochem. soc. vol. 149, s9, 2002. [2] h. li and f. ebrahimi, mater. sci. eng., vol. 93, 347, 2003. [3] g. beranger, f. duffaut, j. morlet and j.f. tiers, ″the iron-nickel alloys″, lavoisier publishing, new york, 1996. [4] w.c. grande and j.b. talbot, j. electrochem. soc. vol. 140, 669, 1993. [5] k.y. sasaki and j.b. talbot, j. electrochem. soc. vol. 142, 775, 1995. [6] m. matlosz, j. electrochem. soc. vol. 140, 2272, 1993. [7] r. bertazzoli and d. pletcher, electrochim. acta vol. 38, 671, 1993. [8] m. moniruzzaman and a.s.m.a. haseeb, proceedings, ieb, rajshahi, bangladesh, 113, 1995. [9] a. brenner, ″electrodeposition of alloys″, academic press, london, vol. 1, 1963. [10] m. m. abu-krisha, a. m. zaky and a. a. toghan, j. corr. sci. and egg., vol. 7, 2005. [11] a. brenner, ″electrodeposition of alloys″, academic press, new york, vol. 2, 1963. iium engineering journal, vol. 10, no. 2, 2009 islam and moniruzzaman 122 [12] d. gangasingh and j.b. talbot, j. electrohem. soc., vol. 138, 3605, 1991. [13] m. matlosz, j. electrochem. soc., vol. 140, 2272, 1993. [14] h. deligianni and l. t. romankiw, j. res. develop., vol. 37, 85, 1993. [15] j. matulis and r. slizys, electrochem. acta., vol. 9, 1177, 1964. [16] r. d. shull and e. d. siegel, nist activities in nanotechnology in r&d status and trends, 1998. [17] m. el-hilo, k. o. grady and r. w. chantrell, j. appl. phys., vol. 76, 6811, 1994. [18] r. d. shull, r. d. mcmichael and j. j. ritter, nanostructured mater., vol. 2, 205, 1993. [19] b. n. popov, k. m. yin and r. e. white, j. electrochem. soc., vol. 140, 1321, (1993). [20] l. sathlerb and k. barmak, ″hardness analysis of fe-ni alloy produced from sulphate electrolytes″, j. materials research, vol. 6, 299-302, 2005. [21] n. v. myung, d. y. park, d. e. urgiles and t. george, electrochim. acta., vol. 49, 4397, 2004. [22] n. elezovi, b.n. grgur, n.v. krstajic and v.d. jovic, j. serb. chem.. soc., vol. 70, no. 6, 879, 2005. [23] a. r. marder and a. m. flaman, ″characterization of copper-zinc alloys produced in sulphate electrolytes″, j. materials research, vol. 8, 285-299, 2004. [24] f. ebrahimi and h. q. li, ″structure and properties of electrodeposited nanocrystalline fcc ni-fe alloys″, j. rev. adv. mater. sci., vol. 5, 134-138, 2003. [25] n. x. sun and s. x. wang, ″soft high saturation magnetization (fe 0.7 co 0.3)1x n x [28] m. s. flores, g. ciapetti, j. l. gonzalez-carrasco, m. a. montealegre, m. multigner, s. pagani and g. rivero, thin films for inductive write heads″, vol. 36, 2506, 2000. [26] m. bedir, o. f. bakkaloglu, i. h. kkarahan and m. oztas, j. of phys., indian academy of sciences, vol. 66, 1093, 2006. [27] g. herzer, j. appl. phys., vol. 26, 1397, 1990. j. of mat. sci., vol. 15, 559, 2004. [29] d. l. grimmett, m. schwartz and k. nobe, j. electrochem. soc., vol. 137, 3414, 1990. [30] g. herzer: j. appl. phys., vol. 26, 1397, 1990. [31] h. akihiko and y. shimada: j. appl. phys., vol. 67, 6981, 1990. [32] b. d. cullity, ″introduction to magnetic materials″, wesley, 1972. [33] m. takahashi, y. takahashi and h. shoji, j. of ieee transactions, usa, vol. 37, 2179, 2002. http://www.ingentaconnect.com/content/klu/jmsm;jsessionid=rlkyd2fvoqd8.alice� http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=20� tunable bandpass filter using rf mems switches 2.1 one mems bridge parallel with the resonator 2.2 two mems bridge parallel with the resonator 2.3 one mems bridge perpendicular to the resonator 2.4 mems bridges parallel and covering all the resonators acknowledgement references keywords : quantum cryptography, quantum key distribution, decoy state protocol, optical communications 2. experimental setup influence of polarization mode dispersion on the effect of cross-phase modulation in intensity modulation-direct detection wdm transmission system introduction system model theoretical analysis 3.1 modulation of the probe field results and discussion conclusion acknowledgement references towards a scalable scientific data grid model and services introduction related works the p2p data grid model the simulation study experiments and results conclusion and future work references anomalous electrodeposition of fe-ni alloy coating from simple and complex baths and its magnetic property application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 unwearable multi-modal gestures recognition system for interaction with mobile devices in unexpected situations hanene elleuch1*, ali wali1, anis samet2, adel m. alimi1 1 research groups in intelligent machines lab (regim-lab), university of sfax, national engineering school of sfax (enis), bp 1173, sfax, 3038, tunisia 2sifast: software and computing services company, sfax 3003, tunisia *corresponding author: hanene.elleuch@ieee.org (received: 26th september 2018; accepted: 14th august 2019; published on-line:2nd december 2019) abstract: in this paper, a novel real-time system to control mobile devices, in unexpected situations like driving, cooking and practicing sports, based on eyes and hand gestures is proposed. the originality of the proposed system is that it uses a real-time video streaming captured by the front-facing camera of the device. to this end, three principal modules are charged to recognize eyes gestures, hand gestures and the fusion of these motions. four contributions are presented in this paper. first, the proposition of the fuzzy inference system in the purpose of determination of eyes gestures. second, a new database has been collected that is used in the classification of open and closed hand gesture. third, two descriptors have been combined to have boosted classifiers that can detect hands gestures based on adaboost detector. fourth, the eyes and hand gestures are erged to command the mobile devices based on the decision tree classifier. different experiments were assessed to show that the proposed system is efficient and competitive with other existing systems by achieving a recall of 76.53%, 98 % and 99% for eyes gesture recognition, detection of fist gesture, detection of palm gesture respectively and a success rate of 88% for eyes and hands gestures correlation. abstrak: kajian ini mencadangkan satu sistem masa nyata bagi mengawal peranti mudah alih, dalam keadaan tak terjangka seperti sedang memandu, memasak dan bersukan, berdasarkan gerakan mata dan tangan. kelainan sistem yang dicadangkan ini adalah ia menggunakan masa nyata video yang diambil daripada peranti kamera hadapan. oleh itu, tiga modul utama ini telah ditugaskan bagi mengenal pasti isyarat mata, tangan dan gabungan kedua-dua gerakan. empat sumbangan telah dibentangkan dalam kajian ini. anggaran pertama bahawa isyarat gerak mata mempengaruhi sistem secara kabur. kedua, pangkalan data baru telah dikumpulkan bagi pengelasan isyarat tangan terbuka dan tertutup. ketiga, dua pemerihal data telah digabungkan bagi merangsangkan pengelasan yang dapat mengesan isyarat tangan berdasarkan pengesan adaboost. keempat, gerakan mata dan tangan telah digunakan bagi mengarah peranti mudah alih berdasarkan pengelasan carta keputusan. eksperimen berbeza telah dijalankan bagi membuktikan bahawa sistem yang dicadang adalah berkesan dan berdaya saing dengan sistem sedia ada. keputusan menunjukkan 76.53%, 98% dan 99% masing-masing telah dikesan pada pengesanan gerak isyarat mata, genggaman tangan dan tapak tangan, dengan kadar 88% berjaya mengesan gerak isyarat mata dan tangan. keywords: eye gesture recognition, hand gesture detection, multimodal interaction, fuzzy inference system, human-computer interaction 142 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 1. introduction nowadays, mobile devices are considered like a ubiquitous computer. no matter where the user is, he can access any information and use it to do anything that he/she wants; capturing photos, paying an invoice, accessing emails, etc. today, the consumption of mobile devices is changing due to the continuous evolution of the hardware as well as the software. however, the question of how providing the most suitable mode of interaction with these devices has not been really solved. all these years, the mobile human-computer interaction is based on one way: the touchscreen. in fact, the touchscreen is simple, clear and intuitive. however, the limits of this mode are clearly visible when using mobile devices in unexpected situations such as moving, driving or using one hand while the other is busy [1], etc. besides, the minimization of on-screen targets causes occlusions. to cope with these issues, many solutions are proposed to extend mobile human-computer interaction modalities by introducing natural ways of communications like eyes, hands, and voice. eyes and hands are the most intuitive way of communication. eyes are our first channel of communication with the surrounding environment. they play an important role in expressing needs and expressional emotions. also, hands play an important role in nonverbal communication with the purpose of sending messages correctly. for the ubiquitous interaction with mobile devices, it is clear that eyes and hands have many advantages compared to voice because of the background noise that can affect the quality of communication, on the one hand, and on the other hand, gestures are independent of language and do not require any previous knowledge. several solutions are presented to extend the ways of interaction with mobile devices. some of these solutions focus on eye tracking by using eeg [2], eog [3, 4] and eye tribe [5]. other solutions focused on hand gestures recognition are based on gloves [6, 7]. all these solutions require the addition or modification of the device, which is considered as a barrier to adoption and generalization. in contrast, most mobile devices already contain cameras. for this reason, an image-based solution can be more efficient for eye tracking as well as for the hand gesture recognition at one and the same time. in this paper, a new mobile human-computer interaction system based on eyes and hands' gestures was proposed for a medical application used by doctors to manipulate patients’ information during a surgical intervention. the input of this system is a real-time video captured from the front-facing camera of the device. two modules are responsible for each modality's gestures. the first module aims to recognize eyes gestures from the captured video. the user's face and his eyes are detected first and then the pupils are determined and tracked. a fuzzy inference system is deployed to recognize the pupils' motions. in this work, the main goal is detecting 8 motions in different directions: right, left, up, down, right-up, left-up, right-down, left-down. in addition to these movements, this module can also detect blinks. the second module aims to recognize hand gestures from the input video. viola and jones’ algorithm is used to detect 2 gestures: fist and palm. to achieve this goal, a new dataset is collected and used for the training phase. a couple of descriptors are combined to improve the accuracy. the recognized gestures coming from different modules are combined and fused in a separate module to execute actions to monitor mobile devices. this system is evaluated by conducting a study on volunteers in real life conditions, the results obtained are promising. the remainder of this paper is organized as follows: in section 2, the relevant work was detailed in studying the unimodal and multi-modal interaction systems. in section 3, the proposed system is presented and each module is detailed. in section 4, an assessment is conducted for the purpose of evaluating this system. in this section also, a description of the 143 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 experiments of each module separately and then the whole system. finally, the paper is concluded and an example of application is suggested to prove the practical aspect of the proposed system. 2. related work many research works introduced eyes and hands as alternative modalities to control devices. in this section, the related work was cited that included eyes and hands as the only modality and their combination in the human-computer interaction. 2.1. natural user interface based on unimodal interaction systems eye-based interaction is deployed as an important input modality. gaze estimation is used to determine the point-of-regard on the screen of mobile devices [8,9,10,11 ,12]. wood and bulling [8] combines cascade classifiers and a shape-based approach for eyes centers detection, limbus ellipse fitting and limbus back projection for gaze estimation. pino and kavasidis [9] used haar classifier and camshift to detect and track eyes respectively. the authors estimated the gaze by determining a correlation between the centroid of eyes rectangle and the user’s gaze. [10] proposed a dataset for unconstrained gaze estimation for mobile devices. these works proved their robustness by achieving competitive results, however, they suffered from many limits like the execution time and the need of learning phase and calibration preprocessing. eyes gestures are also used to interact with mobile devices. [13] proposed a new eyes gestures recognition system for mobile devices. the algorithm is based on image processing algorithms to detect and track the user's eyes from video captured from the device. a face detector based on viola and jones algorithm is responsible for detecting the face. another module tracked the detected face. an eye detector detected the eyes from the face which have been tracked using an eye tracker. the eyes gesture recognition is assured by using template-matching. other methods are also deployed. miluzzo et al. [11] used contour detection to localize the eyes in their system presented eyephone that combines blinks detection and gaze’s estimation to command mobile devices. in [14], the authors proposed an eye gesture input interaction system for smartphones dedicated for people with als. this system recognizes gestures by using template-matching but a calibration step is necessary to use this system for the first time. in [15], the authors proposed a system of eyes gestures recognition. this system recognizes 8 gestures to communicate with mobile devices without any additional peripheries. hands gestures are widely used in the human-computer interface. meng et al. [16] presented a new system of hand gesture recognition. the hand detection is assured by using skin color detection algorithm and static approach image to separate the hand from the background. the hand gesture recognition is assured by determining the fingers' number and the angle formed between the fingers. this step is based on hand contour detection and fingertips and palm center extraction. the authors proposed the deployment of cloud computing to solve the problem of the slow processing time. prasuhn et al. [17] proposed a hog-based hand gesture recognition system deployed on the mobile device and applied it to american sign language (asl). a hand detection area based on the skin color algorithm is first applied. the hand shape features are computed by using the hog descriptor [18]. the recognition step is assured by finding the best matching between the target image and images from the database. song et al. [19] presented a new system of interaction with mobile devices based on hands gestures. the detection step is based on skin color technique and the recognition phase is assured by the random forest algorithm. the experiments showed promising results. in [20], the author proposed a new system of interaction with mobile devices based on static hands gestures. this system is based on skin color for hand 144 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 segmentation and svm for the recognition phase. the hand detection in all these works is based on skin color detection. this technique was proved as a robust method; however, it causes many false positive detections and occlusions with the face region. the response time for [16] and [17] is relatively high. for this reason, [16] deploys a cloud server for the computation part to have more rapid execution time. [16] and [17] are the only systems developed for mobile devices. however, these systems did not treat the case of the face occlusion and the dynamic hand gesture recognition. [16] did not present the recognition results so the robustness of his method cannot be determined. on the other hand, [17] proved that the recognition rate of their system is only 47%. besides, this system's algorithm is not totally developed on the device, but it is based on a client-server configuration that made the need of the internet indispensable for the operation process. in this paper, a real-time hand gesture recognition based on the camera was proposed. it is running entirely in the device and it can detect hands gesture without any confusion with user's face and any other body part. 2.2. natural user interface based on multi-modal interaction systems many systems are proposed with different combinations of modalities. gaze and hand gesture were the most popular. many research works focused on the combination of these modalities in user-computer interaction. chatterjee et al. [21] used these modalities for the purpose of building an interactive mode with a computer, a series of leds and a mobile robot. each modality is captured by a specific periphery: eye tribe tracker for gaze tracking and leap motion for recognizing hand gestures. the authors conducted a study to test the efficiency of these modalities applied differently in various scenarios. hales et al. [22] presented a system of object manipulation through gaze and hand gestures. a specific glass assured gaze tracking and a vision-based module assured the recognition of hand gestures. the assessment of this system proved that the combination of these modalities is natural and promising. pouke et al. [23] presented a model of interaction based on gaze and hand gesture for 3d virtual space on tablet devices. the gaze tracking is assured based on corneal reflexion technique and the hand gesture recognition is based on the accelerometer sensor and machine learning algorithms. the author proposed to use the gaze for selecting objects and hand gesture for the manipulation of these objects. yoo et al. [24] evoked the issue of interaction with a large screen cannot be efficient with the traditional tools of interaction like mouse and keyboard cannot be efficient. to this end, the authors presented a new system of human-computer interaction based on gaze and hand gestures. these works proved the efficacy of multi-modal interaction in comparison with gaze only or hand only gestures. however, in all these works the modalities are treated separately and there is no interaction between them. besides, these modalities are captured by specific sensors that require adding specific peripheries to the devices. in this work, eyes and hands gestures modalities are proposed without any additional peripheries. the capture of these modalities is assured by the camera already provided in the mobile device. 3. architecture of the proposed system: multimob the proposed system aims to interact with mobile devices through eyes and hands gestures by providing the possibility to do actions like click, swipe etc. through natural modalities instead of touch way. to this end, the input of this system is a real-time video 145 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 captured from the camera of the devices. there are not any additional peripheries. this system is composed of three main modules. the system overview is presented in fig.1. the first module is responsible for detecting eyes’ regions and then capturing eyes positions for each frame and recognizing gestures. the second module is responsible for the detection and recognition of static hands gestures and uses it to the recognition of dynamic hands gestures. static hand gestures and eyes gestures resulting from each of these two subsystems are used in the third module and combined in several ways with the purpose of building a new vocabulary to launch final actions that control the device such as click, rotate, wipe etc. in this system, the possibility to use one or more modality is given, the multimodal gestures fusion system is active only when the user chooses to not use eyes gestures and hands gestures only. in the other case, the user can execute specific actions with the corresponding modality. fig 1 system overview 146 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 3.1. eyes gesture recognition for mobile devices this subsystem is composed of successive steps. face and eyes detectors based on viola and jones algorithm [25] are launched for each given frame. the eye detector indicates if the eyes are open or closed. if the eyes are detected as open, the next sub-module is launched. the pupil’s detection is based on the reduction of the region of interest (roi) in the eye and the determination of the darkest zone in the eyes [26]. once the pupils are detected, the eye gestures recognition sub-module will determine and extract the positions of pupils. these positions in the next step will be provided as inputs for a fuzzy inference system to recognize the corresponding motion. 3.1.1. face and eyes detection in the beginning, this module detects the user's face. this detection is assured by the viola and jones algorithm. this classifier, known by its ability to be running in real-time conditions, is provided by the opencv library [27] that achieves a true detection rate of 98.5% [28]. the face region is extracted and used as a location for eyes detection. the classification is based on boosted cascade haar-like features. in fact, the determination of eyes regions includes also a classification about the state of the eyes to determine if they are open or closed. eyes blink is an involuntary reflex. this motion is intuitive and very rapid. the duration of the blink is on average between 100 ms and 400 ms [4]. for this reason, to differentiate between the spontaneous and the intentional blinks, a threshold is fixed, fixed at 500 milliseconds, of eye's closing duration. any blink that lasts for a time longer than this threshold is considered as an intentional blink. 3.1.2. eyes’ gestures recognition once the eyes’ region is detected, a reduction of this zone is required. in fact, the result eyes zone contains several parts of the eyes like the eyelid. this part is not needed to detect the pupils; for this reason, the first step in this sub-module is keeping only the small part of the iris and its surrounding. in this roi, a pupil detector is charged to localize the pupils. in fact, the pupils are characterized by their common features. the pupils are the darkest zone in the eyes. so, to find the pupil’s zone, a search of the darkest pixel is applied, once the pupil is localized a tracking task is launched by the template matching [26, 15]. eye gesture recognition is defined in this work as the motion of pupils in a specific direction. in this module, the target gestures to be detected are the movements of the eyes to the lowing directions: right, right up, up, up left, left, left down, down and down right direction. these gestures have been chosen because they are simple and do not tire the eyes. however, the determination of each gesture cannot be precise. there is an overlap between 2 consecutive gestures for instance between left and left down like fig.2 shows. to solve this issue, a fuzzy-based approach for the classification of eyes' motions based on pupils tracking was proposed. 147 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 fig 2 eyes gestures the recognition of the eye’s gestures used basically the pupils’ position extracted from each frame. the variation of these positions in successive frames is exploited in the motion's classification. this variation is computed as shown in the following equations: (1) (2) where dx and dy are the variations between 2 pupils' positions p1 and p2 at the x and y-axis respectively computed in pixels. in fact, the eyes are naturally in continuous variation. so, any movement that is lower than a specific threshold valthreshold cannot be taken in consideration of. the sign of the value of dx and dy can be precise in the next step presented by the pseudo-code in fig. 3 a fuzzy inference system (fis) based on a set of rules to assure the phase of eyes gestures recognition as presented in fig.4. these rules are defined in a natural way according to the directions of dx and dy; for example, if there is a variation on the x-axis without any variation on the y-axis, the final direction is right. the fis used in this approach is a the mamdani type because there are many outputs so, it is the most intuitive and suitable in this case. the fuzzification of the inputs and the outputs variables is presented in fig.5, fig.6, and fig.7. fig 3 pseudo-code of defining the sign of dx and dy 148 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 fig 4 fuzzy rules of eyes gesture recognition fig 5 fuzzification of the input variable dx 2.1. hands gesture recognition for mobile devices the second system aims to recognize hands gestures. a system of hand gesture recognition is developed. it is based on the 2 types of gestures: the static and the dynamic ones. the definition of the static hand gesture is the stationary posture of a hand formed by fingers and the dynamic hand gesture as the succession of consecutive hand positions. 149 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 fig 6 fuzzification of the input variable dy fig 7 fuzzification of the output variable gesture 2.1.1. static hand gesture recognition to recognize hand gestures, independent classifiers were created for each gesture based on viola and jones algorithm [25]. these detectors are based on images converted in the grayscale. a cascade of strong classifiers is obtained by threshold on scalar features [28] using the adaboost algorithm. for this system, two hand gestures were chosen: fist (closed hand) and palm (opened hand). to ensure having the highest success recognition rate, 3 classifiers were created for each gesture based on haar-like, lbp, and hog descriptors. dataset: for the training, 7716 and 7611 positive images for the fist and the palm, respectively and 12933 negative images collected from our private dataset [29] and other 150 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 different public databases [30,31] were used. for the collection of this dataset, 21 volunteers have participated. the images collected are in indoor conditions with different backgrounds and hands positions. a low resolution of 72 dpi is used. the parameters of each window are described in the following table: table 1 parameters of hand gestures detectors to have the highest success rate, a test of our classifiers is conducted according to three descriptors on 200 images for the closed hand and 200 images for the opened hand. the recall, the precision and the false positive per image (fppi) were computed. a reminder of the metrics ‘equations related to the recall, the precision, and the fppi is presented in the following equations: (3) (4) (5) where tp, fp, and fn are respectively the value of the true positive, false positive, and false negative of the detection rate. to determine these values, a bounding-box-based representation of the ground truth and the detected hand gestures are created. the pascal criterion [32] is applied. it is based on the computation of the bounding bow overlap (boi) of the detected bounding box (di)and the ground truth (gi) as in this equation: (6) a tn detection is obtained if the value of (boi) exceeds the value of the threshold. an fp detection is determined when a bounding box is detected and the value of (boi) is less than the threshold. an fn is obtained when there is no bounding box detected although the hand gesture is visible. the test results for the fist and the palm detection are shown in tables 2 and 3, respectively. to improve our obtained results, the used descriptors are combined with the purpose of increasing the true detection rate and decreasing the false detection. so, the common region of each bounding box of the two descriptors is computed by using eq. 6. if the result is more than 0.5, the number of tp is increased and the result is the union of the two bounding boxes. windows stages fist detector [32,33] 5 palm detector [42,32] 5 151 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 table 2 recall, precision and fppi values of the fist detection recall (%) precision (%) fppi hog 98 62.61 0.585 haar 100 26.49 2.775 lbp 100 38.24 1.615 table 3 recall, precision and fppi values of the palm detector recall (%) precision (%) fppi hog 90 50.04 0.885 haar 98.5 18.97 4.2 lbp 100 35.14 1.845 to have the best result, all possibilities of combinations are tested and the results are presented in tables 4 and 5 for the fist and the palm gesture, respectively. table 4 recall, precision and fppi of the fist detector for each combination of descriptors recall (%) precision (%) fppi hog+haar 98.5 98.5 0.015 hog+lbp 97.5 97.5 0.025 haar+lbp 94 94 0.09 table 5 recall, precision and fppi of the palm detector for each combination of descriptors recall (%) precision (%) fppi hog+haar 91 93.84 0.06 hog+lbp 99 96.11 0.04 haar+lbp 79.5 85.94 0.145 152 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 (a) fist detection results on some examples from our dataset (b) fist detection results on some examples from nus dataset fig. 8 fist detection results these tables show that the high result is obtained by the combination of hog and haar for the fist detection and hog and lbp for the palm detection. to check the robustness, these classifiers are tested on a public database nus [33]. 200 images from this database have been tested for each open and closed hand. the recall, precision and fppi found are respectively: 95%, 93.59% and 0.065 for the fist and 96%, 97.46% and 0.025 for the palm. these results are promising mainly in comparison with the work of [34] that achieves 94,36% of success rate. fig. 9 and fig. 8 presented the detection result for each palm and 153 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 fist gesture for both our database and nus database. in fact, the detection is successful in several cases as fig. 8 and fig. 9 show; there are simple and complex backgrounds and there are pictures captured in outdoor and indoor conditions. this static hand gesture recognition is the same regardless of the color skin, the gender and the size of the hand. (a) palm detection results on some examples from our dataset (b) palm detection results on some examples from nus dataset fig. 9 palm detection results 154 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 2.1.2. dynamic hand gesture recognition the second module developed in this system is the dynamic hand gesture recognition. in fact, a dynamic hand gesture is a sequence of static hand gestures. as the dynamic hand gesture is a natural way of communication, there is a need to differentiate between the intentional one and the gesture used to execute a command. for this reason, vocabulary is built to define each gesture with the commands. the dynamic hand gesture is composed by a sequence of static hand postures that determine the beginning and the end of one gesture. a tree of vocabulary is presented in fig.10 to recognize three gestures that each one is responsible for executing a command: a click, a drag, and a drop. all motions begin with the initial gesture which is the opened hand and are finished with the same gesture. click: the user must open his hand, close it and open it again in a duration that does not exceed the minimal time tmin. drag: the user should open and close his hand for a duration more than the minimal time tmin then a tracking module is responsible for following the hand's position. drop: is executed once the user opens his hand after the drag action. fig. 10 dynamic hand gestures vocabulary 2.2. multi-modal fusion based gestures for interaction with mobile devices the hands and eyes are in related movements. these couple modalities have an important role in the enhancement of the efficiency of controlling mobile devices. the coupled modalities provide for us additional information that can serve in the separation between the intentional and natural motions [35]. 155 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 to this end, the fusion of gestures recognized by the previous modules specific for eyes and hands gestures is proposed. in fact, the fusion domain is divided into three levels: data, feature and decision levels [36]. data-level fusion is applied in the phase of receiving information captured from all available inputs. it aims to conserve all this information. however, in this type of fusion, the pre-processing step is absent and so the generated noise cannot be eliminated [36]. feature-level fusion combines the features generated from each input modality. basically, this fusion's category requires that the generated features' vectors have the same representation. this condition cannot be available in many cases particularly when the input modalities have different natures. decision-level fusion is the most used thanks to its capability to operate with different types of modalities. the final decision is taken based on the local decision generated from each modality. in comparison with other fusion levels, decision-level fusion has not any constraint of invariance input or vectors' representation because each module analyses its related modality separately. the comparison of these fusion-levels leads us to use the decision-level fusion. this is the most convenient in our case. in fact, the eyes and hands gesture recognition modules are captured from the same camera. however, each module analyzed the captured video and generated a decision regarding each modality. the variety of the decisions classified by each module, the ability to fuse them and the respect of the real-time conditions are the important constraints that specify the tool used for the decision fusion step. the decision tree is one of the most known techniques in the supervised classification. it is characterized by its simplicity in analyzing and interpreting thanks to its flexibility in the determination of the input variables and the rules used for the classification task. the fusion module takes 3 attributes as inputs, one from eyes gestures and two from hand gestures with the purpose of executing actions to command mobile devices. it is noteworthy that the hands gesture recognition module has 2 classes: palm and fist and the eyes gesture recognition module has 9 classes: right, right up, up, left up, left, left down, down, right down and blink. for the fusion module, a choice is made to consider that the right, right up and right down as right direction and left, left up and left down as left direction. as final decisions, 6 classes are defined: long press, rotate, click, zoom, swipe in the right and swipe in the left. table 6 details how these decisions are organized. table 6 training table of eye and hand gestures fusion module eye gesture hand gesture 1 hand gesture 2 decision blink close close long press right close close rotate left close close rotate up close close rotate down close close rotate blink open open zoom right open open swipe in right left open open swipe in right up open open swipe in left down open open swipe in left right open close click left open close click 156 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 up open close click down open close click right close open click left close open click up close open click down close open click 3. experimental results and discussion in this part, the twofold system is evaluated with the purpose of validating its robustness. to this end, we used an android-based tablet for the deployment of our system. this device has an android version of 4.2.1 running on nvidia tegra 3 quad-core and a 2 go of ram. the front-facing camera has a 2 megapixels resolution. 3.1. eyes gesture recognition for mobile devices in this module, these libraries are used: opencv [27] image processing and fuzzy lite libraries [37] for the classification. 8 participants aged between 25 and 31 years, who are unfamiliar with eyes gestures recognition systems, volunteered to test our system. first, each participant is asked to sit in front of the tablet and save a distance between 25 and 40 cm to keep the whole face captured by the camera. then, they are asked to close their eyes and move it in the 8 directions. to validate this module, different metrics are computed: the sensitivity, the false positive rate (fpr) defined by these equations: (1) ( 2) ( 3) where the value of tp, fn, fp, tn are computed as in this way: there is a tp when a correct eyes gesture is recognized. there is a fn when none or a false eyes gesture is recognized. there is a fp when an eyes movement is detected but there is no gesture. there is a tn when there is no gesture is detected and the user keeps his eyes in a stationary position. the result of this assessment and a comparison with the most related work are presented in table 7. table 7 the result of eyes gesture recognition module accuracy [%] sensitivity [%] fpr [%] our system 76.53 85 27 vaitukaitis et al. [13] 60.0 28.3 17.6 this assessment showed promising results achieved by our system. in comparison with related work, the proposed system attained 76.53% of accuracy while [13] achieved 60%. 157 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 another test is conducted to investigate the material consumption of this module. the measurement of the physical resources consumption of ram and cpu is computed. the rapidity of our developed algorithm can be induced in the number of frames per second (fps). the results are presented in table 8. table 8 computation of ram and cpu consumption ram cpu fps our system 90 40 24 miluzzo et al.[11] 56.51 65.4 as shown in table 8, our subsystem consumes 90% and 40% of ram and cpu, respectively. these numbers showed the limit of this module in terms of ram consumption. it is noteworthy that this module consumes ram much more than the system proposed by [11], in the contrast to cpu. besides, this module proved the fact that it can be running in real-time condition by achieving 24 fps. it is so far advantageous when compared with similar systems [13] and [38] which had lower than 15 fps. 3.2. hands gesture recognition for mobile devices for this module, a study is conducted on 10 volunteers that they never use any touchless application based on eyes and hands gestures. this test is repeated in two scenarios depending on the external environment and the user's state whether he is sitting or walking: scenario 1: the user is in laboratory conditions and takes the tablet when he is sitting. scenario 2: the user is in outdoor conditions and takes the tablet when he is walking. in this evaluation, each participant is asked to move one hand with the purpose of executing actions corresponding to the vocabulary presented in the subsection 3.2.2. the initial hand position is palm gesture. the results of this experiment are shown in table 9. table 9 experiment result for dynamic hand gesture recognition scenario 1 scenario 2 click 100% 90% drag+drop 100% 100% the experiment results prove that the recognition of the dynamic gesture reaches 100% in scenario 1 and 90% in scenario 2 for both motions. in fact, these results depend on the performance to the recognition of the static and dynamic gestures. the error coming from the static gesture causes automatically an error in the dynamic gesture. 158 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 3.4. multi-modal fusion based gestures for interaction with mobile devices to validate our approach in this module, a study is conducted on 5 volunteers aged between 24 and 30 years. each participant is asked to operate the tablet to execute the proposed actions. fig.11 shows that our module can achieve promising results. the success rate attains 100% for long press and zoom actions and 80% for others. indeed, the results of fusion's gestures are due mainly to the result of eyes and hands gestures modules. note that every error of the eye’s gestures recognition or in the hand gestures recognition modules causes a decision error. fig. 11 experiment results of multi-modal fusion based gestures subsystem 4. conclusion in this paper, a new system for mobile hci based on eyes and hands gesture recognition is presented. this system uses the eyes’ gestures to execute commands based on detection of the eyes and gaze direction. for the hand gesture recognition, two independent classifiers are created and dedicated to fist and palm gesture. a combination of different descriptors is used to have the highest success rate and the minimum false detection. from the static gestures, dynamic gestures are created. they are based on precise vocabulary to execute commands. to evaluate our system, a study is conducted on 10 participants in two different scenarios for each eye and hands gesture. the experimental assessment showed that this system can reach promising results. to study the feasibility of the proposed system, an application for medical uses is developed. this application provides the doctor with the possibility to consult and manipulate a patient's medical images and information that he can need during the surgical intervention. 159 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 actually, the surgeon cannot touch anything that is not sterilized during the surgery; also his hands are busy all the time. as a consequence, he is obliged to use touchless ways to interact with his device. first, the doctor chooses the modality that he/she wants to use to control his/her devices. then, he/she can swipe the medical images and the patient’s information by using their eyes with a blink and an eye movement. the hand gestures can serve to move a cursor to provide the manipulative actions in the application like clicking on buttons etc. acknowledgment the research leading to these results has received funding from the ministry of higher education and scientific research of tunisia under the grant agreement number lr11es48. the research and innovation are performed in the framework of a thesis mobidoc financed by the eu under the program pasri. references [1] nagamatsu t, yamamoto m, sato h. (2010). mobigaze: development of a gaze interface for handheld mobile devices. in proceedings of extended abstracts on human factors in computing systems, pp: 3349-3354. [2] samadi m r h, cooke n. (2014). eeg signal processing for eye tracking. in proceedings 22nd european signal processing conference. pp. 2030-2034 [3] dhuliawala m, lee j, shimizu j, bulling a, kunze k, starner t, woo w. (2016). smooth eye movement interaction using eog glasses. in proceedings of the 18th acm international conference on multimodal interaction, 307-311. doi: 10.1145/2993148.2993181. [4] bulling a, ward ja, gellersen h, troster g. (2011). eye movement analysis for activity recognition using electrooculography, ieee transactions on pattern analysis and machine intelligence, 33(4):741-753 [5] theeyetribe [http://www.theeyetribe.com/] [6] chen p, wang p, wang j, yao y. (2017). design and motion tracking of a strip glove based on machine vision. neurocomputing. doi: https://doi.org/10.1016/j.neucom.2017.03.098. [7] dipietro l, sabatini a m, dario p. (2008). a survey of glove-based systems and their applications. ieee transactions on systems, man, and cybernetics, part c (app/lications and reviews) 38(4): 461-482. doi: 10.1109/tsmcc.2008.923862 [8] wood e, bulling a. (2014) eyetab: model-based gaze estimation on unmodified tablet computers. in proceedings of the symposium on eye tracking research and applications, pp: 207-210 [9] pino c, kavasidis i. (2012). improving mobile device interaction by eye tracking analysis. in proceeding of federated conference on computer science and information systems. pp:11991202. [10] huang q, veeraraghavan a, sabharwal a. (2017). tabletgaze: dataset and analysis for unconstrained appearance-based gaze estimation in mobile tablets. in machine vision and applications. 28(5): 445-461. doi: 10.1007/s00138-017-0852-4 [11] miluzzo e, wang t, campbell a t. (2010). eyephone: activating mobile phones with your eyes. in proceedings of the second workshop on networking, systems, and applications on mobile handhelds, pp: 15-20. [12] iqbal n, lee h, lee s y. (2013). smart user interface for mobile consumer devices using model-based eye-gaze estimation. in ieee transactions on consumer electronics, 59(1): 161166 [13] vaitukaitis v, bulling a. (2012). eye gesture recognition on portable devices. in proceedings of the 2012 acm conference on ubiquitous computing, pp: 711-714 160 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 [14] zhang x, kulkarni, h, morris m r. (2017). smartphone-based gaze gesture communication for people with motor disabilities. in proceedings of the 2017 chi conference on human factors in computing systems. pp: 2878-2889. [15] elleuch, h., wali, a., samet, a., alimi, a.m. (2016). a real-time eye gesture recognition system based on fuzzy inference system for mobile devices monitoring. in proceedings of international conference on advanced concepts for intelligent vision systems, pp. 172-180. [16] meng x, cheung c m, ho k l, lui k s, lam e y, tam v. (2012). building smart cameras on mobile tablets for hand gesture recognition. in proceeding of sixth international conference on distributed smart cameras, pp: 1-5 [17] prasuhn l, oyamada y, mochizuki y, ishikawa h. (2014). a hog-based hand gesture recognition system on a mobile device. in proceedings of ieee international conference on image processing, pp. 3973-3977 [18] dalal n, triggs b. (2005). histograms of oriented gradients for human detection, ieee computer society conference on computer vision and pattern recognition, 1:886-893 [19] song j, soros g, pece f, fanello s r, izadi s, keskin c, hilliges o. (2014). in-air gestures around unmodified mobile devices. in proceedings of the 27th annual acm symposium on user interface software and technology, pp: 319-329 [20] elleuch, h., wali, a., samet, a., alimi, a.m. (2015). a static hand gesture recognition system for real time mobile device monitoring. in proceedings of the 15th international conference on intelligent systems design and applications (isda), pp. 195-200. [21] chatterjee i, xiao r , harrison c. (2015). gaze+ gesture: expressive, precise and targeted free-space interactions, proceedings of the 2015 acm on international conference on multimodal interaction, 131-138 [22] hales j, rozado d, mardanbegi d. (2013). interacting with objects in the environment by gaze and hand gestures. in proceedings of the 3rd international workshop on pervasive eye tracking and mobile eye-based interaction; pp: 1-9 [23] pouke m, karhu a, hickey s, arhippainen l. (2012). gaze tracking and non-touch gesture based interaction method for mobile 3d virtual spaces. in: proceedings of the 24th australian computer-human interaction conference, pp. 505-512 [24] yoo b, han j j, choi c, yi k, suh s, park d, kim c. (2010). 3d user interface combining gaze and hand gestures for large-scale display. in proceedings of extended abstracts on human factors in computing systems, pp: 3709-3714 [25] viola p, jones m j. (2004). robust real-time face detection. international journal of computer vision. 57(2): 137-154 [26] elleuch h, wali a, alimi a m. (2014). smart tablet monitoring by a real-time head movement and eye gestures recognition system. in proceedings of international conference on future internet of things and cloud (ficloud); pp. 393-398. [27] opencv [http://www.opencv.org/] [28] gonzalez-ortega d, diaz-pernas f, martinez-zarzuela m, anton-rodriguez m, diezhiguera j, boto-giralda d. (2010). real-time hands, face and facial features detection and tracking: application to cognitive rehabilitation tests monitoring. journal of network and computer applications. 33(4): 447-466 [29] rehg [http://www.regim.org/publications/databases/rehg/] [30] mit [ http://web.mit.edu/torralba/www/indoor.html] [31] memo a, zanuttigh p. (2018). head-mounted gesture controlled interface for humancomputer interaction. multimedia tools and applications. 77(1): 27-53. doi: 10.1007/s11042016-4223-3. [32] everingham m, van gool l, williams c k, winn j, zisserman a. (2010). the pascal visual object classes (voc) challenge. international journal of computer vision. 88(2): 303-338 [33] nus [https://www.ece.nus.edu.sg/stfpage/elepv/nus-handset/] [34] pisharady p k, vadakkepat p, loh a p. attention based detection and recognition of hand postures against complex backgrounds. international journal of computer vision.101(3) :403419 161 iium engineering journal, vol. 20, no. 2, 2019 elleuch et al. https://doi.org/10.31436/iiumej.v20i2.1000 [35] elleuch h, wali a, alimi m a, samet a. (2017). interacting with mobile devices by fusion eye and hand gestures recognition systems based on decision tree approach. in ninth international conference on machine vision, pp: 103-410. [36] dumas b, lalanne d, oviatt s. (2009). multimodal interfaces: a survey of principles, models and frameworks. human machine interaction. 5440:3-26. doi: https://doi.org/10.1007/978-3-642-00437-7_1 [37] fuzzylite [http://www.fuzzylite.com/] [38] skodras e, fakotakis n. (2015). precise localization of eye centers in low resolution color images. image and vision computing. 36: 51-60 162 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <feff004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 158-761-1-ed-1 completed.docx iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 132 computational investigation on csf flow analysis in the third ventricle and aqueduct of sylvius edi azali hadzri1, ahmad lufti abdul ghani1, amir hamzah shamsudin1, kahar osman1,mohammed rafiq abdul kadir1and azian abd aziz2 1faculty of mechanical engineering, university technology malaysia, 81310 skudai, johor, malaysia 2department of radiology, kulliyyah of medicine, international islamic university malaysia, 25200, kuantan, malaysia. arezareli@gmail.com.my abstract: in this study, a three dimensional (3d) model of the third ventricle and aqueduct of sylvius derived from mri scans was constructed by using computational fluid dynamics (cfd) modeling. cerebrospinal fluid(csf) can be modeled as a newtonian fluid and its flow through the region of interest (roi) was visualized using engineering fluid dynamics (efd).the constructed roi was regarded as rigid walled and only steady state flow was able to be defined due to the limitations of current software. different flow rate was simulated at the foramen of monro and a small stenosis was modeled at the middle of the aqueduct of sylvius at a fixed location. this was made corresponding to normal patients with variation of csf flow rate physiologically and abnormal patients with tumor causing obstruction to or within the aqueduct of sylvius, respectively. due to the small dimensions of the roi geometry, gravity and complex external gravity that acted upon it was considered to be neglected. the results show as the flow rate increase, the pressure drop of csf in the roi proportionally increased. for normal csf flow rate, the presence of stenosis in the aqueduct demonstrates a significant increased pressure drop. abstract: dalam kajian ini, model tiga dimensi (3d) untuk ventrikel ketiga dan akueduk sylvius, yang terhasil daripada pengimejan resonans magnetik telah dikonstruksi menggunakan permodelan perkomputeran dinamik bendalir (computational fluid dynamics (cfd)). cecair serebrospinal (cerebrospinal fluid (csf)) dimodelkan sebagai bendalir newtonan dan alirannya melalui kawasan kepentingan (region of interest (roi)) digambarkan menggunakan dinamik bendalir kejuruteraan (engineering fluid dynamics (efd)). kawasan kepentingan yang dikonstruksi dianggap sebagai dinding tegar dan hanya aliran keadaan tunak yang dapat ditakrifkan berdasarkan pengehadan perisian komputer terkini. kadar aliran yang berbeza disimulasikan di foramen monro dan laluan stenosis yang kecil dimodelkan di tengah-tengah akueduk sylvius di satu lokasi yang telah ditetapkan. kaedah ini dijalankan terhadap pesakit normal dengan variasi pada kadar aliran csf, serta pesakit abnormal yang mempunyai tumor, penyebab sekatan terhadap atau melinkungi akueduk sylvius. disebabkan oleh ukuran geometri roi kecil, tarikan graviti dan graviti luar kompleks yang bertindak ke atasnya diabaikan. keputusan menunjukkan bahawa apabila kadar aliran meningkat, susutan tekanan csf di dalam roi meningkat dengan berkadar. untuk kadar aliran csf yang normal, kehadiran stenosis di dalam akueduk membuktikan pertambahan susutan tekanan yang ketara. keywords: cerebrospinal fluid; cfd; magnetic resonance image; human ventricular system iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 133 1. introduction the cerebrospinal fluid (csf) is contained within and surrounds the brain and spinal cord [1]. it suspends the brain through its buoyancy force and protects it from impact on the cranial vault walls in cases of sudden head motion. the csf further serves as an intermediary between blood and nervous tissue, providing the latter with nutrients and removing waste products. within the skull, the cerebrospinal fluid is enclosed in the ventricles and the subarachnoid space [1]. the ventricles are four cavities interconnected by pathways. the two lateral ventricles are situated within the cerebral hemispheres. they communicate by way of the foramen of monro with the third ventricle located in the median sagittal plane of the cerebrum. the fourth ventricle is connected to the third through the aqueduct of sylvius .csf is secreted from the bloodstream mainly in the choroid plexi of the brain ventricles at a rate of approximately 0.7 ml/min[2].a pulsatile motion, governed primarily by the cardiac cycle, is superimposed upon the steady flow caused by the csf production; the interaction between the cardiovascular and the csf systems is not fully understood. traditionally, it was accepted that the csf is drained mainly through the arachnoid villus system in the superior sagittal sinus. when there is an imbalance between the formation and absorption of csf, an excess of csf will accumulate within the ventricles resulting in hydrocephalus. this will cause increased intracranial pressure, which leads to increase pressure onto the brain substance. this pressure increase depends on the degree of the hydrocephalus, which in turn is affected by the cause of the hydrocephalus. the causes of hydrocephalus can be due to excessive csf production e.g. by a choroid plexus papilloma or from impairment or obstruction of csf absorption. hydrocephalus can cause death if not treated in a timely manner. the treatment of hydrocephalus include placement of a shunt catheter that can drain csf from the ventricular spaces. currently employed shunts contained valves that open when a given preset pressure threshold is reached. this is a very crude approach; a more sophisticated shunt that actively regulates the flow or pressure could potentially lead to much better results for the patients well-being. this justifies the need for a better understanding of the human ventricular system, an integral part of which is the csf flow and pressure dynamics within the ventricles. in children, a phenomenon where the ventricular systems is large or prominent but the children are asymptomatic can occur in which no surgical intervention is necessary and the ventricular size will attain the normal appearance as they grow older. this condition is termed benign enlargement of the subarachnoid spaces. however this condition can be confusing and of concerned particularly to a non-pediatric radiologists as to whether it is a hydrocephalus or otherwise. there are basically three approaches to obtain the ventricular flow pattern. they are invivo measurements using, e.g., mri velocimetry, cfd (computational fluid dynamics) simulations and experimental methods using a physical model of the ventricular system, while anatomical mri scans can achieve excellent spatial and temporal resolution (e.g. the geometry reconstruction of the ventricular system in [3]), velocimetric mri scans do not reach the same level of detail. typical resolution (voxel size) of the latter is of the order of 0.5mm; which is insufficient to accurately capture the csf flow pattern in the human ventricles, where important feature sizes are in the range of 1.5 mm (thickness of the 3rd ventricle, connection between ventricle chambers). while the resolution can be theoretically enhanced by increasing measurement time, this is not viable for in vivo measurements as the required resolution would lead to prohibitively long scan times. extensive cfd simulations iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 134 have been carried out in [3], where anatomical mri scans were used to obtain the ventricle geometry. in this study, cfd was used to perform the same simulation that utilized local patients mri scans. 2. research methodology 2.1 model generation structural mr imaging to define the ventricle and aqueduct boundaries was performed on a healthy female volunteer on a high field clinical imaging system (philips medical system 1.5t) by 256×256 resolution. the recorded pixel size was 0.7183.the successful scanned images were transferred electronically to an mri conversion software called amira. this is integrated 3d image processing and editing software that allows mri data to be converted into other suitable formats. for computational analysis, amira uses threshold separation to capture various individual region in an mri slice and was used to identify the contrast between csf and brain material. the best setting for the contrast identification was between 57 until 303. after thresholding, the crude roi (region of interest-consist of 3rd ventricle, aqueduct of sylvius and 4th ventricle) was then undergo several steps to correct errors that resulted from the process. by morphology operations, the model was dilated for 1 pixel and anatomical wall surrounding the roi was successfully fabricated by using boorlean operations. the generated model was then transferred to another software package called magics under remesh tab. this software was used to make major alteration such as holes patching , geometry correction and volume reconstruction.2 flow inlet at foramen of monro was artificially created. finished model was saved into stl format to be exported to another cfd software for flow analysis and stenosis modeling purpose. 2.2 numerical methods the model was exported to the cfd package efd (engineering fluid dynamics), a meshing program that allowed the stl file to be converted from a wall fabricated hollow model into a volume filled with tetrahedral cells.a computational domain was automatically set at 0.013 × 0.036 × 0.034 dimensions.mininum gap sizes of 0.1 mm and a total number of 122909 mesh (47345 fluid cells and 75564 partial cells) was succesfully incoporated within the domain.for fluid volume of 1682.7mm3,estimated meshing density was 73mm-3.due to the computer capabality limitation and time restriction, the effects of grid resolution on the results was not being performed.the volume mesh is comparable to the numerical solution of the fluid flow. using efd, the boundary conditions were applied to the model with foramina of monro modeled as uniform flow rate inlets while the inferior end of aqueduct modeled as static pressure outlets. in the same software, csf flow dynamics in the roi was calculated by solving the navier-strokes equations that govern 3d flow in incompressible fluids assumptions. the model was set up as a rigid, non-slip with zero velocity walled, steady state model, despite the known flexibility of the roi and the pulsatile nature of csf. gravity and external hydronamics pressure effect was not incorporated into this model and therefore buoyancy has been ignored in the navier-stokes equations. the fluid was modeled as csf with a density of 1005 kg/m3 and the flow modeled as laminar as it is secreted at very low velocities and therefore possess a low reynolds number. using the same software, a small stenosis was modeled at fixed location and with different sizes along the aqueduct narrow channel to iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 135 resemble actual aqueduct blockage that leads to hydrocephalus. fig. 1: a normal geometry that constructed from mri scans, consist of third ventricle, aqueduct of sylvius and fourth ventricle. fig. 2: a stenosed aqueduct was modeled on the geometry. 2.3 boundary conditions by using efd software, the stl format model was converted into sldprt format and the boundary condition for every inlet and outlet are defined. flow rates defined in each cases are computed based on the findings by linninger [4]. iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 136 table 1: parameters for 3rd ventricle and 4th ventricle. 3. results and discussion we assumed that the both sides of the foramen of monro possess the same flow rate. a normal uniform flow rates inlets were designate at various flow rate to resembles normal and hydrocephalus conditions.0.1166 ml/s (0.7 ml/min) was regarded as normal flow rate based on the friese [2] findings and the others parameter was referred to linninger [4]. fig. 4: streamlines and pressure distribution in roi for normal cases: a) 0.0108 ml/s, and b) 0.01167 ml/s. fig. 5: streamlines and pressure distribution in roi for hydrocephalus cases: c) 0.0162 ml/s, and d) 0.0189 ml/s. based on fig. 4 and fig. 5, inlets pressure was at its maximum value and while the csf flow through down to the inferior end of the aqueduct of sylvius, the pressure decreasing and parameter incompressible flow flow rate (ml/s) 0.0081,0.108,0.011667.0.0135, 0.0162,0.0189 static/outlet pressure 500 pa density 1005 kg/m3 stenosis location aqueduct of sylvius (a) (b) (c) (d) iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 137 reached its lowest value. we can see as the flow rate increases, the artificial flow tends to fulfil the region of interest as much as possible. since the wall of the model regarded as rigid, the expansion of the model was neglected. fig. 6: graph for pressure distribution for normal case. 499.8 500 500.2 500.4 500.6 500.8 501 501.2 0 0.01 0.02 0.03 0.04 0.05 0.06 0.0081ml/s 0.0108ml/s normal pressure distri bution for normal strength iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 138 fig. 7: graph for pressure distribution for hydrocephalus case. based on the shown graph, as the csf flow reach at aqueduct of sylvius at nearly 0.025m from the foramen of monro and flow through along it at approximately 0.01 m, we can see a sharp pressure drop indicating that the narrow channel of the aqueduct does the effect to the flow characteristic. it has been found that pressure drop were present between the foramen of monro and the inferior end of the aqueduct of sylvius. in fig. 4, 0.65 pa and 0.72 pa of pressure drop were successfully recorded. these results can be acceptable for normal patient based on the findings by aroussi [5]. while for hydrocephalus cases in figure 5, the pressure drop recorded at 0.82 and 1.21 pa. the latter figure show slightly higher than 1.0 pa as it can be regarded as the boundary value for the normal cases based on jacob [6] findings. we can concluded that as the inlets flow rate increases, so does the drop in the region of interest which match to helen`s [7] work on her research on hypothesis for hydrocephalus. a normal model was generated while the stenosis model was taken to be of the normal aqueduct shape, but reduced in size with approximately 10% to 80% with an increment of 10% in reduced cross-sectional areas. a normal flow rate was defined at the inlets. the results are shown in fig. 8 and fig. 9 whereas the total pressure drop for each stenosis size is shown in fig. 10. 499.5 500 500.5 501 501.5 502 0 0.01 0.02 0.03 0.04 0.05 0.06 normal 0.0135ml/s 0.0162ml/s 0.0189ml/ss ta tic p re ss ur e (p a) length (m) iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 139 fig. 8: streamlines and pressure distribution in roi with 50% stenosis size (3 pa of pressure drop). fig . 9: streamlines and pressure distribution in roi with 80% stenosis size (181 pa of pressure drop). iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 140 fig. 10: graph for pressure distribution in roi for each stenosis size. in fig. 8 and 9, the shape of the stenosed aqueduct is the same as that of the normal aqueduct, only of smaller dimensions. as expected, the flow decreases for a given pressure difference as the aqueduct narrows. the flow was obviously obstructed by the blockage that only a small volume of csf managed to drive flow through the narrowed aqueduct. based on the graph on figure 10,we can see that as the stenosis size increase, the pressure drop increase. the sharp fall that begins at the inferior end of the foramen of monro and along the aqueduct demonstrates that the csf was accelerating. since the stenosis is not modelled based on the actual shape and the exact location of it is still undefined, we assumed that the obtained result remain ambiguous. but as the results fall within the range that found in jacobson [8] and parkkola [9] work, we come to an agreement that the results are acceptable. as all the results were the outcome from a rigid walled roi, non-pulsatile nature flow of csf, excluded gravity and external hydrodynamics pressure from the surrounded brain tissues, these result represents a crude approach for the quantification of the pressure in the third roi. although the results seem not to abide the accurate medical findings by other practitioners and researchers, they can be served as groundwork for further studies. 3. conclusion cfd simulations was used to obtain ventricle geometry from anatomical mri scans. in efd, various flow rates were artificially defined at inlets and stenosed aqueduct was modeled within the domain of the geometry. the results show as the flow rate increase, the pressure drop of csf in the roi proportionally increased. for normal csf flow rate, the presence of iium engineering journal, special issue, mechanical engineering, 2011 hadzri et al. 141 stenosis in the aqueduct demonstrates a significant increased pressure drop. with further refinement and input based on the clinical information gathered from patients with hydrocephalus and their treatment outcome the information obtained from this study can be useful to aid in the design of medical devices that can be used to monitor or treat hydrocephalus. it would also be interesting to explore further to see if a simple method or software can be designed to help radiologists distinguish between hydrocephalus and benign enlargement of the subarachnoid spaces. acknowledgement this research was fully supported by grant number 79414 from the faculty of medical engineering and health science of university technology malaysia. references [1] davson, h., and segal, m. b., 1996, physiology of the csf and blood-brain barriers, crc press, boca raton. [2] friese, s., klose, u., and voigt, k., 2002, “zur pulsation des liquor cerebrospinalis,”klin. neurorad. 12, pp. 67–75. [3] v. kurtcuoglu, m. soellinger, p. summers, k. boomsma,d. poulikakos, p. boesiger, and y. ventikos.,(2007).computational investigation of subject-specific cerebrospinal fluid flow in the third ventricle and aqueduct of sylvius. journal of biomechanics, 40(6):1235–1245. [4] a. andreas a. linninger michalis xenos, david c. zhu, mahadevabharath r. somayaji, srinivasa kondapalli,(2007) cerebrospinal fluid flow in the normal and hydrocephalic human brain. ieee transactions on biomedical engineering, vol. 54, no. 2. [5] a.aroussi , (2006 ). 3d visualization of cerebrospinal fluid flow within the human central nervous system. [6] jacobson e.e flecther , (1996),fluid dynamics of cerebral aqueduct,pediatric neurosurgery 24,229-236. [7] helen williams,(2008). a unifying hypothesis for hydrocephalus, chiari malformation,syringomyelia,anencephaly and spina bifida. [8] e.e jacobson,d.f. flectherm.k. morgan,(1999)computer modelling of cerebrospinal fluid flow dynamics of aqueduct stenosis. medical & biological engineering & computing, vol 37 ,59-63. [9] parkkola rk, komu mes, kotilainen em, valtonen so, thomsen c, gideon p (2000), csf flow in patients with dilated ventricles studied with mr imaging. eur radiol ;10:1442–6. microsoft word 1075-article text-6991-1-18-20191018.docx susanti et al. 1dept. of civil engineering, universitas sriwijaya, palembang, indonesia. 2dept. of civil engineering, institut teknologi bandung, bandung, indonesia. 3dept. of civil engineering, politeknik negeri bandung, bandung, indonesia. *corresponding author: bettysusanti0401@gmail.com (received: 2nd february 2019; accepted: 30th july 2019; published on-line:2nd december 2019) abstract: abstrak: keywords: life-cycle cost; maintenance; performance-based contract; road; traditional contract 57 susanti et al. . output and performance-based road contract 58 susanti et al. 59 susanti et al. 60 susanti et al. 61 susanti et al. 62 susanti et al. balai pelaksanaan jalan nasional 63 susanti et al. 64 susanti et al. 65 susanti et al. 66 susanti et al. , proceedings: the 67 susanti et al. , , , , . , 68 susanti et al. 69 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 1051-article text-7380-2-9-20191209 193 194 195 196 197 198 199 200 201 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <feff004f0076006500200070006f0073007400610076006b00650020006b006f00720069007300740069007400650020006b0061006b006f0020006200690073007400650020007300740076006f00720069006c0069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400650020006b006f006a00690020007300750020007000720069006b006c00610064006e00690020007a006100200070006f0075007a00640061006e00200070007200650067006c006500640020006900200069007300700069007300200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e006100740061002e0020005300740076006f00720065006e0069002000500044004600200064006f006b0075006d0065006e007400690020006d006f006700750020007300650020006f00740076006f007200690074006900200075002000700072006f006700720061006d0069006d00610020004100630072006f00620061007400200069002000410064006f00620065002000520065006100640065007200200036002e0030002000690020006e006f00760069006a0069006d0020007600650072007a0069006a0061006d0061002e> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 228-1053 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 141 the reduction of stress concentration in a uni-axially loaded infinite width rectangular isotropic/orthotropic plate with central circular hole by coaxial auxiliary holes jain n.k. department of applied mechanics, national institute of technology, raipur (c.g.)-492010, india. nkjmanit@rediffmail.com, nkjnitrr@rediffmail.com abstract: a comprehensive plane stress finite element study is made for reduction of stress concentration factor (scf) in a uni-axially loaded infinite width rectangular isotropic/orthotropic plate with central circular hole. the finite element formulation is carried out by the ansys package. with the help of present work, stress concentration can be reduced up to 24.4 % in an isotropic and 31 % in an orthotropic plate by introducing four coaxial auxiliary holes on either side of main hole. the study reveals that the introduction of these holes helps to smooth flow of the tensile stresses passes through the main hole and results, a reduction in stress concentration factor. with such reduction in maximum stress levels, the improvement in fatigue life of a component can be significant. abstrak: satu kajian komprehensif tentang unsur terhingga telah dibuat keatas factor pemusatan tegangan bagi plat isotropic/ortotropik segi empat tepat lebar infinit yang dimuat secara uni-aksial berlubang pusat bulat. rumusan unsur finit telah dibuat menggunakan pakej ansys. dengan kajian masa kini, pemusatan tegangan dapat dikurangkan sehingga 24.4 % dalam plat isotropik and 31 % dalam plat ortotropik dengan membuat empat lubang auksiliari sepaksi di kedua belah lubang utama. kajian ini menunjukkan penggunaan empat lubang ini telah melicinkan aliran tegasan tegangan melalui lubang utama. ini mengakibatkan pengurangan factor pemusatan tegangan. dengan pengurang tahap tegangan maksimum ini peningkatan hayat kelesuan komponen boleh menjadi signifikan. keywords: stress concentration factor; finite element method; plate; composite 1. introduction an infinite width rectangular isotropic/orthotropic plate with central circular hole have found widespread applications in various fields of engineering such as aerospace, marine, automobile and mechanical. stress concentration arises from any abrupt change in geometry of plate under loading. as a result, stress distribution is not uniform throughout the cross section. failures such as fatigue cracking and plastic deformation frequently occur at points of stress concentration. hence, for the design of a plate with central circular hole, stress concentration factor plays an important role and accurate knowledge of stresses and stress concentration factor at the edges of hole under in plane or transverse loading are required. analytical solutions are available in the literature for prediction of iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 142 scf in different types of abrupt changes in shape, but there are limited methods for reduction in scf. meguid [1] presented a technique for reducing stress concentration factor by introducing defence hole system in a uni-axially loaded plate with two coaxial holes by finite element method, where reduction in scf ranging from 7.5 to 11 % maximum have been achieved. but to achieve the maximum possible reduction, these auxiliary holes have to be introducing very near to the original holes, which is not practically possible in all cases. giare et al. [2] presented a method for the reduction of stress concentration around the main hole in an isotropic plate by using a ring of composite material around the main hole, method is not suitable for all designing conditions and also no techniques were presented for reduction in scf for orthotropic plate. providakis and sotiropoulos [3] have developed a boundary element approach to the reduction in stress concentration factor in visco-plastic plates by multiple holes. tenchev et al. [4] presented a design procedure for reducing stress concentration around holes in laminated composite by increasing the thickness in this area. younis [5] investigated by reflected photoelasticity method that the assembly stress contributes to reducing stresses around the holes in a plate. mahiou and bekaou [6] studied for local stress concentration and for the prediction of tensile failure in unidirectional composites. toubal et al. [7] studied experimentally for stress concentration in a circular hole in composite plate. wu and mu [8] analysed stress concentrations for isotropic/orthotropic plates and cylinders with a circular hole by finite element method. peterson [20] has developed good theory and charts on the basis of mathematical analysis and presented excellent mythology in graphical form for evaluation of stress concentration factors, but no techniques were presented for reduction of scf. this paper is concerned with the reduction of scf in isotropic and orthotropic infinite width rectangular plates with central circular hole under in-plane static loading. in general stress concentration factor can be reduced up to 12-18 % by two coaxial auxiliary holes on either side of the main hole, to achieve the maximum possible reduction; these auxiliary holes are to be introducing very near to the original hole, which is not practically possible. it has been seen that the reduction in scf at the edges of main hole become directly proportional to diameter of auxiliary holes, increasing the diameter of auxiliary holes results in reduction of normal stress (σx) at the edges of main hole, but this is also accompanied by an increase of σx at the edges of auxiliary holes. at a certain diameter of auxiliary holes, σx at the edges of auxiliary holes attained more than σx at the edges of main hole i.e. maximum value of σx is shifted from edges of main hole to edges of auxiliary holes. this problem can avoid by introducing two more coaxial holes on either side of first two coaxial holes and the diameter of first two auxiliary holes can increase more. this results more reduction in stress concentration. the work has been done firstly for isotropic plates, and then study is further expanded for orthotropic plates. this work is most appreciated in aerospace and marine industry where the introduction of holes will not only reduce the stress concentration around main hole, but also reduce the weight of the components. this study will also provide guidelines technique to designer for reduction of stress concentration up to maximum level. 2. description of problem iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 143 to study the influence of auxiliary holes upon the stress concentration around the main hole, three models a, b and c are described in fig. 1, where model a is basic model (a plate with central circular hole of diameter d), model b is modification of model a (plate with two coaxial auxiliary holes of diameter d1, numbered as auxiliary hole 1) and model c is modification of model b (plate with four coaxial auxiliary holes) i.e. two more coaxial auxiliary holes of diameter d2 (numbered as auxiliary hole 2) are created in model b. the centre distance between main hole and auxiliary hole 1 is taken as x and the centre distance between auxiliary hole1 and auxiliary hole 2 is taken as 0.8 x. all the details of dimensions are described in fig 1. a plate under in-plane static uniformly distributed load of p, is analyzed by finite element method for d/a ratio of 0.1, where a is plate width. the dimensions are selected such a way that it can be considered as infinite width plate. (a) model a (basic plate with central circular hole of diameter d ). (b) model b (c) model c fig. 1: details of three models analysed in this study. 3. finite element analysis iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 144 an eight nodded quadrilateral element with element length of 1 mm was selected and used through out the study. each node has two degrees of freedom, making a total 16 degrees of freedom per element. in order to construct the graphical image of the geometries of the different models of plate examined using the ansys (advanced engineering simulation), it was necessary to input the basic geometric elements such as points, lines and arcs. due to the symmetric nature of different models investigated, it was only necessary to discretize and analyse the one quarter of the problem of each model for finite element analysis. main task in finite element analysis is selection of suitable element type. number of checks and convergence test are made for selection of suitable element type from different available element. results were then displayed by using post processor of ansys programme. 4. results and discussion numerical results are presented for isotropic and orthotropic plates with central circular hole under in-plane static loading. the scf is calculated on nominal area in all cases. the reduction in scf is achieved firstly for isotropic plates and then work is extended for orthotropic plates. 4.1 isotropic plate in the basic model (model a) maximum stress concentration is always occurred at the edges of main hole. at the edges of main hole; normal stress in xdirection (σx) is placed 3.003 times of p and scf (calculate at nominal area) is appeared as 2.70, which is very close to theoretical value of 2.72. stress concentration at the edge a is reduced by two coaxial auxiliary holes of diameter d1 in model b. the analysis for reduction in stress concentration at the edges of main hole has been done for different centre distances of main hole and auxiliary hole 1. it was very necessary to analyse, the influence of auxiliary holes on stress concentration around main hole as well as around of auxiliary holes. in model b, edges of main hole (edge a) and edges of auxiliary hole 1 (edge b) are zone of stress concentration. table 1 shows the effect of d1/d on σx/p at the edges a and b for x/d=1.2, 1.5, 1.8 and 2.0 respectively in model b. for all cases of x/d, results illustrate clearly that increasing d1/d results in continuously reduction of stress concentration at the edges of main hole, but this is also accompanied by an increase in stress concentration at the edges of auxiliary holes. the following observations can be made from table 1. for x/d=1.2; increasing d1/d from 0.4 to 0.85 results in reduction of σx/p at edge a from 2.895 to 2.451, this is also accompanied by an increase of σx/p at edge b from 2.058 to 2.435. but when d1/d increases from 0.85 to 0.86, σx/p is increased from 2.435 to 2.441 at edge b and attained more than σx/p at edge a i.e. maximum value of σx is shifted from edge a to edge b. the critical value of d1/d is 0.85 for this case. table 1: variation of σx/p at the edges of main hole and auxiliary hole 1 with d1/d for different values of x/d in model b. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 145 x/d=1.2 x/d=1.5 x/d=1.8 x/d=2.0 d1/d edge a edge b d1/d edge a edge b d1/d edge a edge b d1/d edge a edge b 0.40 2.895 2.058 0.40 2.892 2.320 0.40 2.904 2.503 0.40 2.912 2.598 0.60 2.747 2.215 0.60 2.751 2.439 0.60 2.779 2.581 0.60 2.800 2.645 0.80 2.521 2.407 0.80 2.551 2.507 0.70 2.698 2.589 0.70 2.728 2.660 0.84 2.466 2.436 0.82 2.530 2.523 0.74 2.663 2.606 0.76 2.681 2.666 0.85 2.451 2.435 0.84 2.505 2.537 0.78 2.626 2.600 0.78 2.664 2.661 0.86 2.437 2.441 ------------0.80 2.607 2.609 0.80 2.646 2.661 if d1/d increases beyond critical value, maximum stress concentration occurs at edge b and increases with increase of d1/d. for x/d=1.5; increasing d1/d from 0.4 to 0.82 results in reduction of σx/p at edge a from 2.892 to 2.530, this is also accompanied by an increase of σx/p at edge b from 2.320 to 2.523. but when d1/d increases from 0.82 to 0.84, σx/p is increased from 2.523 to 2.537 at edge b and attained more than σx/p at edge a i.e. maximum value of σx is shifted from edge a to edge b. the critical value of d1/d is 0.82 for this case. for x/d=1.8; increasing d1/d from 0.4 to 0.78 results in reduction of σx/p at edge a from 2.904 to 2.626, this is also accompanied by an increase of σx/p at edge b from 2.503 to 2.600. but when d1/d increases from 0.78 to 0.80, σx/p is increased from 2.600 to 2.609 at edge b and attained more than σx/p at edge a i.e. maximum value of σx is shifted from edge a to edge b. the critical value of d1/d is 0.78 for this case. for x/d=2.0; increasing d1/d from 0.4 to 0.78 results in reduction of σx/p at edge a from 2.912 to 2.664, this is also accompanied by an increase of σx/p at edge b from 2.598 to 2.661. but when d1/d increases from 0.78 to 0.80, σx/p at edge b is attained more than at edge a i.e. maximum value of σx is shifted from edge a to edge b. the critical value of d1/d is 0.78 for this case. table 2 shows the effect of d1/d and d2/d on σx/p at the edges a, b and c for x/d=1.2, 1.5, 1.8 and 2.0 respectively in model c. for all cases of x/d, model c is prepared by creating two more coaxial auxiliary holes in model b (with critical value of d1/d). the following observations can be made from table 2. for x/d=1.2; increasing d2/d from 0.4 to 0.74, while maintaining the d1/d unchanged as 0.85 (critical value in model b), results in reduction of σx/p at edge a from 2.434 to 2.359, this is also accompanied by a decrease of σx/p at edge b from 2.362 to 2.142 and an increase of σx/p at edge c from 1.943 to 2.343. but when d2/d increases beyond 0.74, σx/p at edge c is attained more than σx/p at edge a i.e. maximum value of σx is shifted from edge a to edge c. again, increasing d1/d from 0.85 to 0.92, while maintaining the d2/d unchanged as 0.74, results in reduction of σx/p at edge a from 2.359 to 2.271, this is also accompanied by an increase of σx/p at edge b from 2.142 to 2.241 and a decrease of σx/p at edge c from 2.343 to 2.255. for x/d=1.5; increasing d2/d from 0.4 to 0.7, while maintaining the d1/d unchanged as 0.82 (critical value in model b), results in reduction of σx/p at edge a from 2.507 to 2.454, this is also accompanied by a decrease of σx/p at edge b from 2.440 to 2.226 and an increase of σx/p at edge c from 2.226 to 2.448. but when d2/d increases beyond 0.7, σx/p iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 146 at edge c is attained more than σx/p at edge a i.e. maximum value of σx is shifted from edge a to edge c. again, increasing d1/d from 0.82 to 0.90, while maintaining the d2/d unchanged as 0.7, results in reduction of σx/p at edge a from 2.454 to 2.369, this is also accompanied by an increase of σx/p at edge b from 2.226 to 2.330 and a decrease of σx/p at edge c from 2.448 to 2.365. for x/d=1.8; increasing d2/d from 0.4 to 0.6, while maintaining the d1/d unchanged as 0.78 (critical value in model b), results in reduction of σx/p at edge a from 2.603 to 2.574, this is also accompanied by a decrease of σx/p at edge b from 2.520 to 2.421 and an increase of σx/p at edge c from 2.461 to 2.563. but when d2/d increases beyond 0.6, σx/p at edge c is attained more than σx/p at edge a i.e. maximum value of σx is shifted from edge a to edge c. again, increasing d1/d from 0.78 to 0.88, while maintaining the d2/d unchanged as 0.6, results in reduction of σx/p at edge a from 2.574 to 2.482, this is also accompanied by an increase of σx/p at edge b from 2.421 to 2.474 and a decrease of σx/p at edge c from 2.563 to 2.457. table 2: variation of σx/p at the edges of main hole, auxiliary hole 1 and auxiliary hole 2 with d1/d and d2/d for different values of x/d in model c. x/d d1/d d2/d edge a edge b edge c 1.2 0.85 0.40 2.434 2.362 1.943 0.85 0.60 2.400 2.257 2.181 0.85 0.70 2.371 2.181 2.281 0.85 0.74 2.359 2.142 2.343 0.88 0.74 2.324 2.195 2.297 0.90 0.74 2.298 2.205 2.282 0.92 0.74 2.271 2.241 2.255 1.5 0.82 0.40 2.507 2.440 2.226 0.82 0.60 2.476 2.333 2.400 0.82 0.70 2.454 2.226 2.448 0.84 0.70 2.433 2.279 2.415 0.86 0.70 2.413 2.308 2.411 0.90 0.70 2.369 2.330 2.365 1.8 0.78 0.40 2.603 2.520 2.461 0.78 0.60 2.574 2.421 2.563 0.80 0.60 2.557 2.431 2.537 0.82 0.60 2.539 2.440 2.518 0.86 0.60 2.502 2.467 2.474 0.88 0.60 2.482 2.474 2.457 2.0 0.78 0.40 2.642 2.587 2.585 0.78 0.50 2.631 2.539 2.583 0.78 0.56 2.623 2.514 2.616 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 147 0.80 0.56 2.606 2.521 2.599 0.82 0.56 2.590 2.532 2.579 0.84 0.56 2.574 2.539 2.542 0.86 0.56 2.556 2.546 2.536 for x/d=2.0; increasing d2/d from 0.4 to 0.56, while maintaining the d1/d unchanged as 0.78 (critical value in model b), results in reduction of σx/p at edge a from 2.642 to 2.623, this is also accompanied by a decrease of σx/p at edge b from 2.587 to 2.514 and an increase of σx/p at edge c from 2.585 to 2.616. but when d2/d increases beyond 0.56, σx/p at edge c is attained more than σx/p at edge a i.e. maximum value of σx is shifted from edge a to edge c. again, increasing d1/d from 0.78 to 0.86, while maintaining the d2/d unchanged as 0.56, results in reduction of σx/p at edge a from 2.623 to 2.556, this is also accompanied by an increase of σx/p at edge b from 2.514 to 2.546 and a decrease of σx/p at edge c from 2.616 to 2.536. figure 2 illustrates the variation of scf at the edges of main hole (edge a) in model b and c with d1/d for different values of x/d. these are maximum scf in plate, attaining at the edges of main hole. fig. 2: effects of d1/d on scf at the edges of main hole (edge a) in model b and c. in model b, scf is reduced up to 2.21, 2.28, 2.36 and 2.4 for x/d = 1.2, 1.5, 1.8 and 2.0 respectively. where, in model c, scf is reduced up to 2.04, 2.13, 2.23 and 2.3 for x/d = 1.2, 1.5, 1.8 and 2.0 respectively. figure 3 shows the % reduction in scf at the edges of main hole in model b and c with d1/d for different values of x/d. in model b; 18.39, 15.75, 12.57 and 11.31 % reduction in scf is achieved for x/d = 1.2, 1.5, 1.8 and 2.0 respectively. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 148 fig. 3: effects of d1/d on % reduction in scf at the edges of main hole (edge a) in model b and c. where, in model c; 24.39, 21.13, 17.36 and 14.90 % reduction in scf is achieved for x/d = 1.2, 1.5, 1.8 and 2.0 respectively. results indicate clearly that maximum possible % reduction in scf in model c is almost 6.0 % greater than model b for all values of x/d. it has been observed that maximum possible % reduction in scf decreases with increase of x/d in model b and c both. 4.2 orthotropic plate thirteen different composite materials are selected for analysis of influence of auxiliary holes in model b and c, upon reduction of stress concentration around main hole in an orthotropic plate. scf in model a and % reduction in scf in model b and c for x/d=1.2 and 1.5, are listed in table 3. the elastic properties of different composite materials used in study are also listed in table 3. table 3: scf in model a and achieved % reduction in scf in model b and c for orthotropic plates. material type e1 e2 g12 µ scf % reduction in scf x/d=1.2 x/d=1.5 model b model c model b model c e-glass/epoxy 39 8.6 3.8 0.28 3.816 21.13 29.60 19.36 27.15 s-glass/epoxy 43 8.9 4.5 0.27 3.789 21.20 29.58 19.40 27.10 woven glass/epoxy 29.7 29.7 5.3 0.17 3.169 19.83 27.11 17.61 24.23 kelvar/epoxy 87 5.5 2.2 0.34 5.017 18.70 29.42 17.73 27.95 carbon/epoxy 142 10.3 7.2 0.27 4.488 20.81 30.55 19.52 28.60 carbon/peek 131 8.7 5 0.28 4.696 20.11 30.27 18.96 28.51 carbon/epoxy 177 10.8 7.6 0.27 4.637 20.46 30.48 19.27 28.66 carbon/polyimide 216 5 4.5 0.25 5.384 17.97 29.15 17.18 27.95 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 149 graphite/epoxy 294 6.4 4.9 0.23 5.585 16.89 28.28 16.13 27.26 boron/epoxy 201 21.7 5.4 0.17 4.889 18.80 29.36 17.77 27.83 boron/aluminum 235 137 47 0.3 3.169 20.08 27.20 17.82 24.28 sic/al 204 118 41 0.27 3.175 20.10 27.23 17.84 24.31 sic/ceramic 121 112 44 0.2 2.783 18.73 24.95 16.17 21.74 the reduction in scf is calculated with critical value of d1/d and d2/d of isotropic plate. following observations can be made from these results. for x/d=1.2; in case of model b, reduction in scf is between the range of 17 to 21 % for all materials, maximum in case of s-glass/epoxy with 21.20 % and minimum in case of graphite/epoxy with 16.89 %. in case of model c, reduction in scf is between the range of 25 to 31 % for all materials, maximum in case of carbon/epoxy (as4/3501-6) with 30.55 % and minimum in case of sic/ceramic with 24.95 %. for x/d=1.5; in case of model b, reduction in scf is between the range of 16 to 20 % for all materials, maximum in case of carbon/epoxy (as4/3501-6) with 19.52 % and minimum in case of graphite/epoxy with 16.13 %. in case of model c, reduction in scf is between the range of 22 to 29 % for all materials, maximum in case of carbon/epoxy (im6sc1081) with 28.66 % and minimum in case of sic/ceramic with 21.74 %. 5. conclusion the reduction in scf depends on diameter and position of auxiliary holes in isotropic or orthotropic plates, two parameters x/d and d1/d in model b and three parameters x/d, d1/d and d2/d in model c influence the reduction in scf. for an isotropic plate; in case of model c, maximum reduction in scf is achieved for x/d=1.2 as 24.39 %, where, in case of model b, maximum reduction in scf is achieved for x/d=1.2 as 18.39 % only. for a convenient design, for x/d=1.5, up to 21.13 % reduction in scf can be achieve in model c, but in case of model b, it can be only 15.75 %. in case of orthotropic plate; maximum reduction in scf is between the range of 25.0 to 31.0 % for different materials in model c, where in model b, maximum reduction in scf is between the range of 17.0 to 21.0 % for different materials. it has been observed that maximum possible % reduction in scf decreases with increase of x/d in model b and c both, for isotropic and orthotropic plates. it has been also seen that maximum possible reduction in scf in an orthotropic plate depends on elastic constants. in case of orthotropic materials like graphite epoxy, kelvar/epoxy, carbon/polyimide, where scf is approaching more than 5.0, reduction in scf can be achieved more than 28.0 % in model c, where in model b, reduction in scf can be achieved up to 18.0 % only. for an isotropic and an orthotropic plate, such reductions in maximum scf improve fatigue life of component. it must be remembered that only three parameters x/d, d1/d and d2/d in model c affect the reduction in scf, and these should be selected as per requirement and convenience of designer. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics jain 150 references [1] a meguid. ‘finite element analysis of defence hole system for the reduction of stress concentration factor in a uni-axially loaded plate with two coaxial holes’. engineering fracture mechanics, vol 25, issue 4, 1986, p 403. [2] g s giare and r shabahang. ‘the reduction of stress concentration around the hole in an isotropic plate using composite material’. engineering fracture mechanics, vol 32, issue 5, 1989, p 757. [3] c p providakis and d a sotiropoulos. ‘a bem approach to the stress concentration reduction in visco-plastic plates by multiple holes’. computers & structures, vol 64, issue 14, 1997, p 313. [4] r t tenchev, m k nygard and a echtermeyer. ‘design procedure for reducing the stress concentration around circular holes in laminated composites’. composites, vol 26, 1995, p 815. [5] n t younis. ‘assembly stress for the reduction of stress concentration’. mechanics research communications, vol 33, 2006, p 837. [6] h mahiou and a bekaou. ‘local stress concentration and the prediction of tensile failure in unidirectional composites’. composites science and technology, vol 57, 1997, p 1661. [7] l toubal, m karama and b lorrain. ‘stress concentration in a circular hole in composite plate’. composite structures, vol 68, 2005, p 31. [8] h c wu and b mu. ‘on stress concentrations for isotropic/orthotropic plates and cylinders with a circular hole’. composites: part b, vol 34, 2003, p 127. [9] v g ukadgaonker and d k n rao. ‘a general solution for stress around holes in symmetric laminates under in-plane loading’. composite structure, vol 49, 2000, p 339. [10] k ting, k t chen and w s yang. ‘stress analysis of the multiple circular holes with the rhombic array using alternating method’. international journal of pressure vessels and piping, vol 76, 1999, p 503. [11] r a chaudhuri. ‘stress concentration around a part through hole weakening laminated plate’. computers and structures, vol 27, issue 5, 1987, p 601. [12] t k paul and k m rao. ‘stress analysis in circular holes in frp laminates under transverse load’. computers and structures, vol 33, issue 4, 1989, p 929. [13] g b sinclair. ‘on the effect on stress concentration of rounding the edge of a hole through plate’. international journal of mechanical sciences, vol 22, issue 12, 1980, p 731. [14] n troyani, c gomes and g sterlacci. ‘theoretical stress concentration factors for short rectangular plates with centered circular holes’. transactions of asme journal of mechanical design, vol 124, 2002, p 126. [15] t iwaki. ‘stress concentrations in a plate with two unequal circular holes’. international journal of engineering sciences, vol 18, issue 8, 1980, p 1077. [16] t k paul and k m rao. ‘finite element evaluation of stress concentration factor of thick laminated plates under transverse loading’. computers and structures, vol 48, issue 2, 1993, p 311. [17] m fillipini. ‘stress gradient calculations at notches’. international journal of fatigue, vol 22, issue 5, 2000, p 397. [18] x xiwu, s liangxin and f xuqi. ‘stress concentration of finite composite laminates with elliptical hole’. computers & structures, vol 57, issue 1, 1995, p 29. [19] x xiwu, s liangxin and f xuqi. ‘stress concentration of finite composite laminates weakened by multiple elliptical holes’. international journal of solids structures, vol 32, issue 20, 1995, p 3001. [20] r e peterson. ‘stress concentration design factors’. john wiley and sons, new york, 1966. [21] i m daniel and o ishai. ‘engineering mechanics of composite materials’. oxford university press, new york, 1994. [22] c t f ross. ‘advance finite element methods'. horwood publishing limited, chichester, 1998. compiled journal vol 12 no 2.pdf application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 habib et al. 158 a single lc tank based active voltage balancing circuit for battery management system a k m ahasan habib, s. m. a. motakabber*, muhammad ibn. ibrahimy and a. h. m. zahirul alam dept. of electrical and computer engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia *corresponding author: amotakabber@iium.edu.my (received: 19th feb 2018; accepted: 23rd may 2018; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.895 abstract: nowadays, battery operated vehicles and power tools are becoming popular due to their simple construction, compact structure, low operating and maintenance cost, moreover renewable energy utilization facility. a single series resonant active converter has been designed to balance the voltage level of electrical energy storage device (esd). to obtain the necessary operating voltage and current, many electric cells are combined together in series and parallel. a series battery balancing circuit can be used to improve the efficiency of each cell charging and discharging process and consequently increase the lifespan of the battery. a battery management system (bms) needs an efficient balancing circuit. this paper presents a high-speed single lc-tank dc to dc converter for electric cell balancing scheme. in this research, two 2s lipo battery has been used as energy storage device. the proposed voltage balancing circuit works by charging and discharging the charge storage device through a single series lc-tank circuit. experimental results show that the proposed balancing circuit can make 0 voltage difference from 800 mv, in 285 seconds and it is less time than the current system. abstrak: satu pengubah resonan sesiri telah direka bagi mengimbangi aras voltan pada kenderaan beroperasikan bateri dan pada mesin jana kuasa yang menjadi semakin popular. ini kerana strukturnya yang mudah dan kompak, kos operasi dan penyelenggaraan yang rendah, termasuk kemudahan penggunaan tenaga kitar semula dan sebagainya. bagi mendapatkan voltan dan arus operasi yang sesuai, banyak sel elektrik telah digabungkan bersama dalam gabungan sesiri dan selari. litar pengimbang bateri sesiri boleh digunakan bagi meningkatkan kecekapan setiap proses pengecasan dan penyahcas sel dan sekaligus meningkatkan jangka hayat sel. sistem pengurusan bateri (bms) memerlukan litar pengimbang yang cekap. kertas ini membentangkan tentang satu pengubah dc-dc tangki-lc berkelajuan tinggi berdasarkan skim pengimbang sel elektrik. oleh kerana supercapacitors bertindak seperti bateri boleh cas semula; penyelidikan ini telah mengguna pakai dua super-kapasitor dan bukan bateri boleh cas semula. baki voltan telah dikekalkan dengan mengecas dan menyahcas super-kapasitor menggunakan satu litar tangki-lc. dengan ini, masa pengimbang keseluruhan voltan dapat dikurangkan dan kecekapan litar dapat ditingkatkan. hasil eksperimen menunjukkan litar pengimbang yang dicadangkan dapat mengurangkan perbezaan voltan antara dua super-kapasitor dari 350 mv kepada 0 v dalam tempoh 284 saat, kurang daripada masa sistem sedia ada. keywords: voltage balancing; battery management system; electrical energy storage device; resonant converters; electric vehicles. iium engineering journal, vol. 19, no. 1, 2018 habib et al. 159 1. introduction the evs (electric vehicles) are becoming an important field of business interest in the automobile industries, because of the high price of fossil fuel, economic and ecological issues [1]. in the transportation sector, evs becoming emerging technology instead of conventional fossil fuel engine. it has proven, that many industries and combustion engines produce co2, co, no, etc. which is the main source of the greenhouse effect. evs would be solving the environmental and fuel energy issues that are correlated with zero-carbon emission policies. since most of the vehicles are using fossil fuel and producing huge amounts of co, co2 and others gas. the renewable energy sources are environmentfriendly, electricity can be generated by using this energy sources. electric vehicles (evs) use electricity without emitting the co, co2 and other gases, which will help in solving environmental and energy issues. the rechargeable battery and supercapacitor i.e., esd (energy storage device) provides continuous electrical power in electric motors to operate an ev. the esd such as supercapacitors or batteries are playing a vital part in the hybrid electric vehicle (hev), plug-in hev and ev to microgrid [2-4]. becouse, some small urban city and rural area are started to produce electricity by utilizing the renewable energy sources. they extracted the generated electricity by using microgrid system and charges their hev and ev battery from the microgrid. nowadays, li-ion (lithium-ion) and lipo (lithium polymer) battery are widely used in ev and portable power equipment due to its high-power capacity, high energy density, low memory effect, low self-discharge, lowtemperature impact, long life cycle etc. [5]. the voltage of a li-ion/lipo cell is relatively low. so, for a required load voltage and current, it is connected in series and parallel arrangement. evs and many systems use rechargeable battery packs such as li-ion, lipo, nicd etc. a battery pack is made by using many unit cells. the battery pack is charged and discharge during application, however at this time there is no guarantee, that each unit cell can be equally charged and equally discharge. as a result, few unit cells of the battery pack may be damaged within a short time and make the whole battery pack imbalance and useless. so, this is a big issue for using a rechargeable battery pack, when the pack is made by many unit cells. the manufacturers make the only unit cell and the users make their own customized size battery pack by using required numbers of the unit cell. in a battery pack, li-ion/lipo cells have some drawback, due to different manufacturing, environmental condition and purpose of using. when cells are overcharged then have a chance of the explosion, similarly, undercharged cell reduces its lifetime [6]. for an unbalance charging and discharging affect the capacity and efficiency of a cell is gradually reduced inside the battery pack [7-8]. the cell capacity, input/output current, balancing etc. issues can be overcome by using a battery management system (bms). the researchers are still working on battery charge balancing to improve battery cell performance [2, 9-10]. there are two types of battery charge balancing methods are used; namely, passive balancing method and active balancing method. in passive charge balancing method uses a resistor. as a result, the excess charge of the higher energy cell is dissipated by the resistor in the form of heat and to make a balance with the weaker cell. on the other hand, in the active charge balancing method, the excess charge from the higher energy cell is transferred to the lower energy cell through the inductor, capacitor, and transistor [8, 11-12]. in this paper, a single resonant lc-tank converter based cell to cell active balancing circuit has been proposed. the switching frequency of this circuit has been chosen same as the resonant frequency of the lc-tank circuit, so that, the charging or discharging time of the resonant can just to run half period of the resonant frequency.the proposed circuit uses iium engineering journal, vol. 19, no. 1, 2018 habib et al. 160 fewer numbers of components which, makes the circuit simple, compact, faster and inexpensive. 2. proposed balancing circuit and algorithm the proposed single lc resonant balancing circuit is shown in fig. 1. in this circuit, n numbers of esd are connected in series. the esd-1 and esd-n are associated with two mosfet switches, similarly, esd-2 and esd-(n-1) are associated with anti-series mosfet switches. all the mosfet switches are operated by a pwm signal. the resonant converter based circuit is worked as an active balancing circuit. to measure the cell voltage, a voltage status monitoring sensor has been used. each cell voltage of the battery is measured by using a voltage sensor and sends the information to a microcontroller as shown in fig. 1. fig.1: a basic block diagram of the proposed voltage balancing circuit. the proposed voltage balancing algorithm steps as follows: 1. system initialization 2. check the cell status by monitoring the sensor voltage 3. send the cell status to the microcontroller. if the cell voltages are equal: then goto step 2 else: cell voltages are not equal goto step 4 4. estimate the cell voltage and find out the highest and lowest voltage cells. iium engineering journal, vol. 19, no. 1, 2018 habib et al. 161 5. execute the highest and lowest cell voltage and goto step 4. 6. goto step 2 fig. 2: flowchart of the proposed voltage balancing algorithm 3. voltage balancing circuit working principle figure 3 shows a single resonant lc-tank converter based voltage balancing circuit and its working principle. the associated mosfet switches and the resonant tank are the basic balancing unit of this circuit. in this circuit, n-numbers of the cell are connected in series. initially, assume that the voltage of cell-1 is higher than the voltage of cell-2. during the balancing time, each cell goes through charge and discharge states. 3.1 working mode i: cell-1 voltage > cell-2 voltage charging state: in this state, all associate mosfet switches (ms) of cell-1 are on state and all associated mosfet switches (md) of cell-2 are off state. so, the cell-1, mosfet switches (ms) and lc-tank circuit from a closed loop, and current flows in the loop in the clockwise direction as shown in fig. 3(a). this time, the lc-tank circuit is stored energy by the cell-1. discharging state: in this state, all associate mosfet switches (ms) of cell-1 are off condition and all associate mosfet switches (md) of cell-2 are on condition. so, the iium engineering journal, vol. 19, no. 1, 2018 habib et al. 162 cell-2, mosfet switches (md) and the lc-tank circuit from a closed loop, and the current flows in the loop in the counter-clockwise direction as shown in fig. 3(b). in this situation, cell-2 is charged by the stored energy of the lc-tank circuit. (a) (b) (c) (d) fig. 3: voltage balancing process of the proposed circuit. 3.2. working mode ii: cell-2 voltage > cell-1 voltage in this mode, charging and discharging are just opposite of the working mode i, as shown in fig. 3 (c) and 3(d). for controlling the mosfet switches a pwm signal has been used as shown in fig. 4(a). an excess charge of the higher potential cell is transferred to the lower potential cell via a single series resonant lc-tank circuit as shown in fig. 4(a) and (b). the mosfet switches are turned on and off by the high and low voltages of the pwm signal respectively. the analysis of the circuit has been performed casewise based on the voltage condition of vcell-1 > vcell-2. case 1: the mosfet switches ms are on and md are off states, the series lc-tank circuit is connected with the cell-1 and makes a closed loop as shown in fig. 4(b). the cell-1 starts to discharge through the lc-tank circuit and store the energy in the tank circuit. iium engineering journal, vol. 19, no. 1, 2018 habib et al. 163 (a) (b) (c) fig. 4: equivalent circuit vcell-1 > vcell-2 the voltage of the cell-1 can be expressed as (1), 𝑉𝐶𝑒𝑙𝑙1 = 𝑅𝐶𝑒𝑙𝑙1 [−𝑖𝐶𝑒𝑙𝑙1 (𝑡) + 𝐿𝑟 𝑑[−𝑖𝐶𝑒𝑙𝑙1 (𝑡)] 𝑑𝑡 + 𝑅𝑐𝑟 [−𝑖𝑐𝑟 (𝑡)] (1) where, 𝑅𝐶𝑒𝑙𝑙1 is the internal resistance of the cell-1. the current in the lc-tank can be expressed as (2), 𝑖𝐿𝑟 (𝑡) = 𝑉𝐶𝑒𝑙𝑙1 𝑅𝐶𝑒𝑙𝑙1 − 𝑉𝐶𝑒𝑙𝑙1 𝑅𝐶𝑒𝑙𝑙1 𝑒 𝑅𝐶𝑒𝑙𝑙1 𝑅𝑐𝑟 𝐿𝐶 (𝑡−𝑡0) (2) where, 𝑖𝐿𝑟 (𝑡0) is the initial current, which increases by the switching time t. case 2: the mosfet switches, ms are off and md are on states, the series lc-tank circuit is connected with the cell-2 and makes a closed loop as shown in fig. 4(c). the lctank circuit releases its stored energy into the cell-2. the voltage of the cell-2 can be expressed as (3), 𝑉𝐶𝑒𝑙𝑙2 = −𝑖𝑣𝑐𝑒𝑙𝑙1 (𝑡)𝑅𝐶𝑒𝑙𝑙2 + 𝑉𝐿𝐶 (𝑡) (3) where, the lc-tank circuit voltage 𝑉𝐿𝐶 (𝑡) can be expressed as (4), 𝑉𝐿𝐶 (𝑡) = 𝐿𝐶 𝑑2𝑉𝐶(𝑡) 𝑑𝑡2 + 𝑉𝐶𝑒𝑙𝑙1 (𝑡) (4) the pwm signal allows for continuous voltage balance through the lc-tank circuit. the duty cycle and pulse timing of the pwm signal relation can be expressed as (5), 𝑖𝐿 𝐷𝑇 − 𝑖𝐿 (1 − 𝐷)𝑇 = 0 (5) where, d is the duty cycle and t is the switching time as shown in fig.4(a). 4. result and discussion a dc to dc converter based active voltage balancing circuit simulation has been established by using matlab simulink. a hardware prototyping has been developed to verify the design and effectiveness of the proposed voltage balancing circuit (as fig. 5.). in this experiment, two 2s lipo (lithium polymer) battery has been used, each battery pack has 1500 mah capacity at 7.5v. for experimental setup, initially, the lipo batteries have been made imbalance charge, which makes the battery voltages as 7.8v and 8.4v iium engineering journal, vol. 19, no. 1, 2018 habib et al. 164 respectively. the pwm signal has been generated by using an arduino microcontroller, which makes it easy to control the switching frequency and duty cycle. fig. 5: experimental setup of the proposed active voltage balancing circuit the main hardware components used in this experiment are listed in table 1 table 1: components and their values component value arduino microcontroller 2s lipo battery uno r3 1500mah, 7.5v mosfet switches 2n7000 (nmos) inductor 100 uh (sdr0403bourns) capacitor 220 uf figure 6 shows the ms and md gate voltage signals, lc-tank inductor current and capacitor voltage. it is observed that when the switching frequency (fs) and resonant frequency (fr) are same maximum energy has been stored in and released from the series lc-tank circuit. fig. 7 shows the charging and discharging effect of the lc circuit when the switching frequency is double of the resonant frequency. in this case, the inductor magnetizing current is not enough to achieve the soft switching and it occurs additional voltage stress in the switch. as a result, the circuit takes a long time for balancing the cell voltage. iium engineering journal, vol. 19, no. 1, 2018 habib et al. 165 fig. 6: simulation result waveforms with an internal resistor (when, fs = fr). fig. 7: simulation result waveforms with an internal resistor (when, fs =2fr). figure 8 shows the voltage balancing results. initially, the voltage difference between the two 2s lipo batteries was 800mv. the voltage difference reduced to 0 mv about 275 seconds by the operation of the balancing circuit. fig. 8: simulation results of the two 2s lipo battery voltage balancing scheme. iium engineering journal, vol. 19, no. 1, 2018 habib et al. 166 figure 9 illustrated the experimental circuit gate drive signal, lc-tank inductor current and capacitor voltage waveforms. the two 2s lipo batteries voltage balancing is shown in fig. 10. the initial voltage difference of the two 2s lipo batteries was 800 mv and after 285s this voltage difference developed to 0v, which is 10 seconds higher than the simulation results. fig. 9: gate driving signal, inductor current and capacitor voltage waveforms of the experimental circuit. fig. 10: the experimental result of the voltage balancing circuit. 5. conclusion the proposed design is a new topology of an active voltage balancing schemes for electrical energy storage devices. due to the simple structure, it is able to quickly adjust the cells voltage difference of a battery pack. the proposed voltage balancing circuit requires few components to construct, which will reduce its size and contribute to reducing its price. it is a simple design, easy to build and can operate faster. acknowledgment this research has been supported by the malaysian ministry of education through the fundamental research grant scheme (frgs) under the project id: frgs15-190-0431. references [1] iqbal h. (2011). electric and hybrid vehicles: design fundamentals, crc press. [2] frost d. f., & howey d. a. (2018). completely decentralized active balancing battery management system. ieee transactions on power electronics, 33(1):729-738. iium engineering journal, vol. 19, no. 1, 2018 habib et al. 167 [3] yu y., saasaa r., & eberle w. (2016). a series resonant circuit for voltage equalization of series connected energy storage devices. applied p elec conf and exp (apec) ieee, 1286-1291. [4] rahman, a., rashid, m., mohiuddin, a. k. m., & hawlader, m. n. a. (2015). nano-battery technology for ev-hev panel: a pioneering study. iium engineering journal, 16(2), 57-68. [5] li y., & han y. (2016). a module-integrated distributed battery energy storage and management system. ieee trans p elec., 31:8260-70. [6] mizanur r., khan s., hrairi m., rahman a., & habib s. (2014). a modularized battery charge equalizer in the application of electric vehicle. ieee international conference on smart instrumentation, measurement and applications (icsima 2014). [7] gong x., xiong r., & mi c. c. (2015). study of the characteristics of battery packs in electric vehicles with parallel-connected lithium-ion battery cells. ieee trans. ind. appl., 51(2):1872-1879 mar/apr 2015. [8] hoque m. m., hannan m. a., & mohamed a. (2016). voltage equalization control algorithm for monitoring and balancing of series connected lithium-ion battery. j renewable sustainable energy, 8(2):1-15. [9] hoque m. m., hannan m. a., mohamed a., & ayob a. (2017). battery charge equalization controller in electric vehicle applications: a review. renewable and sustainable energy reviews, 75:1363-1385. [10] habib a. a., motakabber s. m. a., & ibrahimy m. i. (2017). a series regeneration converter technique for voltage balancing of energy storage devices. indonesian journal of electrical engineering and computer science, 8(2):475-481. [11] zhang z., gui h., gu d. j., yang y., & ren x. (2017). a hierarchical active balancing architecture for lithium-ion batteries. ieee transactions on power electronics, 32(4):2757-2768. [12] li w., liao x., & gao z. (2016). a modular equalizer using buck/boost converters with snubber capacitors in series-connected supercapacitors. in industrial technology (icit), 2016 ieee international conference, 1904-1909. microsoft word 208-819-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 73 micro-sized particle production of momordica sp extract using spray dryer maizirwan mel, emirul adzhar yahya and mohd. rushdi abu bakar bioprocess and molecular engineering research unit, kulliyah of engineering, international islamic university malaysia. p.o. box 10, 50728 kuala lumpur malaysia. maizirwan@iium.edu.my abstract: spray drying is the most widely used industrial process involving particle formation and drying. it is highly suited for the continuous production of dry solids in either powder, granulate or agglomerate form from liquid feed-stocks as solutions, emulsions and pump able suspensions. therefore, spray drying is an ideal process where the end-product must comply with precise quality standards regarding particle size distribution, residual moisture content, bulk density, and particle shape. in this study, momordica sp extract product has been successfully spray dried into micro scale of powder particle and will be used as plant-based insulin. the process optimized using taguchi method with four factors and three levels has given a good quality of the product. the average of particle size was obtained at about 11 microns. abstrak: kering sembur digunakan secara meluas dalam proses industri yang melibatkan pembentukan zarah dan pengeringan. ia amat sesuai dalam penghasilan pepejal kering secara beterusan dalam bentuk serbuk, butiran atau gumpalan daripada simpanan suapan bendalir sebagai larutan, emulsi dan ampaian boleh dipam. maka, kering sembur adalah proses yang ideal apabila hasil akhir harus mematuhi piawaian kualiti yang tepat berkaitan dengan pengagihan saiz zarah, kandungan kelengsaan sisa, ketumpatan pukal dan bentuk zarah. dalam kajian ini, produk ekstrak momordica sp (dikenali juga sebagai peria katak) telah berjaya dikering sembur menjadi serbuk zarah berskala mikro dan akan digunakan sebagai insulin berasaskan tumbuhan. proses ini dioptimumkan dengan pengunaan kaedah taguchi empat faktor dan tiga peringkat, agar memberikan hasil produk yang berkualiti. kadar purata saiz zarah yang terhasil adalah lebih kurang 11 mikron. key words: micro-sized; particle; momordica sp; spray dryer 1. introduction momordica charantia also known locally as peria katak is an herb that helps regulate blood sugar levels and keeps body functions operating normally. it contains gurmarin, a polypeptide considered to be similar to bovine insulin, which has been shown in experimental studies to achieve a positive sugar regulating effect by suppressing the neural response to sweet taste stimuli. clinical studies for p-insulin was tested in a controlled clinical trial. in juvenile diabetics, the peak hypoglycemic effect was observed after 1-8 hrs and in patients with maturity onset diabetes; maximum fall in blood sugar level was noted after 12 hours [1]. the fruits and leaves of the plant contain two alkaloids, one of them being momordicine. the plant is reported to contain a glucoside, a saponin-like substance, a iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 74 resin with an unpleasant taste, an aromatic volatile oil and mucilage. the seeds contain an alkaloid and an anthelmintic principle in the germ; they also contain urease. the fruits, leaves and extracts of momordica charantia possess pharmacological properties and medicinal uses. it is useful as an emetic, purgative, in bilious affections, burning soles of the feet, as an anthelmentic, in piles, leprosy, jaundice, as a vermifuge, astringent in hemorrhoids, as a stomachic, antispasmodic, antioxytocic, hypoglycemic, antipyretic, mild hypotensive, and anorectic [2]. spray drying is the transformation of a liquid feed containing solids (dissolved and/or suspended) into a dried particular form. the solvent evaporates and a dry solid in the form of a powder is formed. the spray drying process is unique in being able to produce powders of specific particle size and moisture content. materials that are spray dried vary from plastics to ceramic materials, detergents, food products pharmaceuticals, agrochemicals, fruit and vegetables, cocaine to bone glue [3]. the application of the spray drying encapsulation technique is to prepare "dehydrated" powders of substances which do not have any water to dehydrate. for example, instant drink mixes are spray dries of the various chemicals which make up the beverage [4]. in this experiment, the most important criteria for spray drying are to maintain constant moisture content of the powder. this is required to meet legal standards and for maintaining a uniform quality of product. average operating conditions for spray drying of herbal extract powder will vary somewhat depending upon the dryer system used and must be adjusted to produce the desired uniform moisture can be controlled by changing the conditions. it was noted that the final moisture content is controlled by the relative humidity of the outlet air. if that value is too high, then the powder particles will absorb moisture rather than give moisture away.content. it is important to understand how the final moisture content. 2. materials and method 2.1 materials the extract of momordica charantia was provided by periwinkle science sdn.bhd. production process of the extract starts from receiving of raw materials which then followed by raw material processing, extraction process and gmp processes. from raw material handling, the received herbs was processed as soon as possible in order to avoid any damage or contamination of material. the next step was drying the herb. drying of herbs is important as to avoid microbial growth which then could damage the material. as for the herb under process, standard moisture content was set at below 10%. drying process was using oven dryer. for the oven drying, it was set up at 70˚ c for 4 hours. the raw material that already dried was processed in extraction plant in 4 hours duration with temperature of 110˚ c. the ratio used was 100 kg of raw material alongside with 1000 l of deionized water. the extraction plant itself, is supported by five support systems which are: electric boiler, cooling tower, compressor, deionized water, vacuum system. the extraction plant is divided by two main sections which are the extraction chamber and the concentration chamber. raw material was placed in the heating tank of the extraction chamber. at this stage, deionized water of quantity 10 times the raw material is iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 75 used (1000 l for 100 kg of raw material). at the end of the process, there were first discharge and second discharge. the discharge was the herbs extract diluted in water (liquid extract). it then pumped into storage tank (capacity: 2000 l). when it reached the storage tank, it was let to cool down to room temperature. the discharge from storage tank was pumped periodically into vacuum concentrating chamber. the periodic flow of discharge into concentrating chamber was manually controlled as the automatic controller is not efficient enough. this was to avoid risk of bubbles flowing into vacuum chamber. such condition will jeopardize the functionality of the vacuum system and even the extraction plant. the overall concentration process consumed 5 hours of time with 55° c of temperature. the gross yield of concentrating process is 4.4%. 2.2 equipment and instruments the equipments and instruments used in this study are pilot spray dryer (niro, mobile minor), moisture content analyzer, particle size analyzer and fesem (philip). 2.3 experimental design for process conditions the experiment was designed using statistica by taguchi method matrix, l9 [5]. there were 9 runs that carried out in this study. the parameter for each run is shown in table 1. table 1: spray dryer setting parameters and experimental results. prior to start up the spray dryer: prior to the start up the following was checked: 1) checked the centralizing of the two-fluid nozzle. for rotary atomizer, the liquid distributor and the atomizer wheel must be correctly mounted having the specified distance between them. the atomizer wheel was checked that they freely rotate, 2) checked rotation of the feed pump, 3) checked all connection for tightness. all gaskets were correctly mounted. no false air was sucked into the dryer system due to leakage around the duct connections, 4) the glass jars under the cyclone and drying chamber were check that fastened securely. the glass jar was clean and dry. the glass jar was preheated to prevent condensation in the jar during early stages of the drying process, 5) the silencer was checked and mounted on rotary atomizer, 6) the atomizer was then tightened. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 76 starting up procedure with rotary atomizer: the starting up procedure with rotary atomizer; 1) the power was switch on by turning on the main switch located on the front of the electric control panel, 2) the damper opened after the cyclone and the fan was start 3) the inlet temperature controller was set, 4) the heater was turn on, 5) the rotary atomizer started by turning the valve on. on the pneumatic control panel front slowly go to full speed, which reached after approximately 30 seconds. a gradually decreasing squealing sound was observed during acceleration. the air pressure indicated in the pressure gauge was kept constant, 6) the feed pump started slowly, when desired outlet temperature was passed by approximately 10°c on the outlet indicator, by pushing the button number 7 and pass distilled water to the atomizer until the required outlet temperature is stable, 7) switch from distilled water to product, 8) the outlet temperature adjusted by changing the amount of feed led through the feed pump, 9) the atomizer speed was keep constant in order to obtain a homogenous atomization. decreasing speed results in increasing particle size and vice versa. too large particles can result in wet chamber deposits. plant in operation: the drying operation was controlled by maintenance of the required outlet air temperature at a constant inlet temperature. for a given feed liquid of constant physical properties the outlet temperature was related directly to moisture content; decrease the temperature increase the moisture content. the outlet temperature was manually controlled by regulation of the pump speed. the outlet air temperatures do not change, once the feed rates has been adjusted. it was observed that alterations of viscosity and solids content of the product influenced the outlet air temperature. when the feed rate is too large it was likely that the powder already in the chamber absorbed moisture and stick to the chamber wall. the powder was collected in the glass jar mounted under the cyclone and under the chamber cone. it was important that the glass jar under the cyclone is exchanged before it becomes completely full. shutting down: the shutting down procedure are; 1) exchange the powder glass jar, 2) change the feed to distilled water, 3) keep the constant outlet temperature. decreasing temperature will result in absorption of excess water in the powder still being present in the chamber, 4) run with distilled water 5 to 10 minutes, 5) switch of the process gas heater, 6) switch off the pump, 7) after approximately 3 minutes switch off the atomizer device, 8) keep the fan running for at least 5 minutes to cool the plant down, 9) when outlet temperature is below 50°c the chamber roof can be opened pressing button 12 and 18 at the same time. be sure that no people are standing in reach of the chamber while lifting or lowering the roof, 10) remaining powder in the chamber can be swept down while the fan is still running to collect the particles in the cyclone, 11) switch off the fan, 12) turn off main switch. emergency shut down: this are the step that should be taken for emergency shut down; 1) turn of main switch, 2) if separate power supply to feed pump, turn it off, 3) stop atomizer, 4) do not open the chamber roof until the plant has cooled down, surfaces may be hot. cleaning: the atomizer wheel and the liquid distributor removed from the atomizer and cleaned immediately after operation. the atomizer was kept in its box when not in use. dry cleaning: the camber roof lifted and turned vertically upwards. when the roof was in upright position, the locking pin was inserted. this is safety precaution. the powder then brush down from the chamber walls and roof leaving the fan running. the powder then collected in the glass jars. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 77 wet cleaning: the fan was stopped and the electrical power supply switched off. demounted the glass jars. the interior of the chamber then wash down. precaution: the precaution step taken by removing the atomizer device before lifting the chamber roof. it was avoided spraying water directly on the instrument panel or the light fixture. 2.4 sample analysis total yield: the total quantities of the end product (the powder) were calculated by taking the final weight of the final product that is in powder form. this analysis carried out to find the best condition to produced maximum quantity of final product. moister content: the moister content of the powder were tested by using moister content analyzer. the systems were based on the percentage difference of the wet weight and the dry weight. moisture content (wet basis) was computed as mwb = mb – ma /mb, where mb = mass of powder before infrared treatment, ma = mass of powder after infrared treatment. for stability, this should be < 10% for herbal product. particle size: the extract powder collected from the spray dryer at the end and analyzed with particle size analyzer and fesem. this analysis was carried out to see the distribution of the particle size produced from the different set of parameters. 3. results and discussion referring to the experimental results in table 1, we can see that from all runs (1-9) that have been conducted, the quality of the final product varies for all the run. this shows that the changes in the control variable do affect the production of the final product either moisture content or size of product particle. run 1, 5 and 9 considered to be out of spec as the final quantity are too low that is below 1 gram thus no moisture content test has been conducted. 3.1 moisture content run 1, 5 and 9 were omitted from moisture content test. from the result, the inlet, outlet temperature and the atomic pressure significantly affect the moisture content of the final product. this is due to the concept that the initial contact between spray droplets and drying air controls evaporation rates and product temperatures in the dryer [4]. it was measured by weighing a quantity of dried powder, then subjecting it to infrared radiation to drive of all residual moisture and, watching its weight until it levels off. moisture content (wet basis) was computed as mwb = mb – ma /mb, where mb = mass of powder before infrared treatment, ma = mass of powder after infrared treatment. in the experiment, it was found that for outlet temperature, the condition was dependent upon liquid feed intake. if the feed intake is increased, the outlet temperature will be dropped. if the intake is reduced, the outlet temperature will increase and approach the inlet temperature. the outlet temperature will also be affected by the air flow rate. for a constant inlet temperature and constant feed intake, an increase in the air flow will raise the outlet temperature [6]. once in feed temperature has been set, feed rate is a function of desired moisture. if the feed rate is too high or the outlet temperature is too low, product moisture and bulk density will usually be higher. increased feed (fluid product) temperature can also increase the powder's bulk density by forming smaller spherical droplets or by de-aerating the fluid. dilution of the feed can have an identical effect. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 78 the problem of humidity or the moisture content was controlled by dropping the product from the single-stage dryer into a fluid bed dryer/cooler. most of the drying occurs within the spray-dryer, but the final moisture can be higher than in the single-stage dryer final drying occurs over more time and at a lower temperature in the fluid bed. energy costs can easily be decreased 15% to 20%, and product quality is more constant. an added benefit, due to the fluid bed, is the ability to re-wet and agglomerate if this type of product is needed. this technique had been applied to several dairy products, including skim-milk powder (low, medium and high heat); instantized skim-milk powder; whey powder; permeate; whey/fat blends; cheese powder; ice-cream powder; and whole-milk powder. air-to-air or air-to-liquid heat recuperators also could be used to recover energy from dryer and fluid-bed exit air to further reduce energy costs [6]. 3.2 the particle size distribution this experiment manages to study the particle size distribution of the powdered momordica charantia. it was found that the type of atomizer determines the size and sizes distribution of the drop and their trajectory and speed. in this experiment, rotary atomizer were used and the particles produced were relatively small (9-13 µ m) as shown in fig. 1. this atomizer can handle a wide variety of stream with different physical properties, and its large flow ports result in a negligible tendency to clog [7]. atomization is generally accomplished by one of three basic devices: a single-fluid (or pressure) nozzle, a two-fluid nozzle, or a rotary atomizer (also known as a spinning disc or a wheel). the single-fluid nozzle allows more versatility in terms of positioning with the spray chamber, so the spray angle and spray direction can be varied. fig. 1: sem-photograph of spray dried and agglomerated powder. since it was known from this experiment that particle size is partially depend on the feed rate, nozzles have more limitations in terms of product characteristics and operating rates. once the nozzle is in place, rate can only be varied by pressure; changing the orifice requires removing the nozzle. in high-volume operations, several nozzles are located within the chamber and positioned so constant evaporation conditions are maintained around each nozzle. for more viscous or abrasive feeds, two-fluid nozzles are utilized, with air being the second medium to move the feed and effectively atomize it. air can be mixed internally within the nozzle or externally to the nozzle. in situations in which small particle sizes might not be possible with a single-fluid nozzle, the two-fluid nozzle can iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 79 provide the necessary additional atomization however; this produces a much wider particle size range. during the experiment, it was also found that the physical properties of a powder are also very depending upon the total solids concentration of the liquid which was being dried. if the droplets are maintained at a constant size, then, the amount of solids will affect both the size and the density of the dry particles. the structure of a spray-dried particle is a hollow sphere, with the solids being a shell which surrounds a central vacuole. as the total solids of the feed increases, the shell becomes thicker and, as a consequence, the particle does not shrink as much during drying. similarly, as the air-filled vacuole decreases in size, the particle density increases. the increase in particle density has a pronounced influence on the efficiency of powder separation/collection by the cyclones, because these operate on the principle of a difference in the buoyant density difference between air and particles [8].. it is well-known in the spray-drying industry that drying a liquid of low solids content is the cause of very fine particles which are difficult to collect. it was identified that spray-drying was an energy-intensive process. for standard single-stage drying, the best way to control energy usage is raising the inlet temperature as high as possible, keeping outlet temperature as low as possible, taking full advantage of the energy introduced. the downside of this is potential degradation or discoloration of the product, and potential final moisture problems [6]. 3.3 effect of parameters on particle size forming figure 2 shows the means plot analysis on particle size of momordica dried product. this indicates the inversely proportional for all factors. the main factor that confers the smaller particle size was the outlet temperature which was the low level of outlet temperature. the second factor that may also influence the particle size of momordica dried product was the sample concentration where less concentration gives the smaller particle. then, smaller particle was also influenced by higher pressure and medium level of inlet temperature. the incline line at atomization pressure means higher atomization pressure is better. the decline line at feed concentration means lower feed concentration is better. fig. 2: means plot of factors on product particle size. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 80 table 2: the correlation analysis between inlet temperature and outlet temperature. table 3: the correlation analysis between inlet temperature and pressure. table 4: the correlation analysis between inlet temperature and sample concentration. table. 5: the correlation analysis between outlet temperature and sample concentration. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 81 table 6: the correlation analysis between pressure and sample concentration. 3.4 the variables (factors) correlations referring to table 2-6, the correlation between the controlled parameter and the measured parameter, the combination factors inlet temperature and pressure gives the significant affect on the final product as shown at p value of 0.076599. changes in the temperature and pressure level produced a very significant difference to the quality of the final product. by using temperature 150 o c and pressure of 5.5 bars, it would yield a better product in term of quantity and quality. as explained by blei [9] the product moisture and particle size is always relevance with temperature. 4. conclusion this study has identified the best condition to improve and optimize the spray drying condition leading towards a high quality of powdered momordica sp and producing the standard optimum moisture content (<10%). by controlling the parameters especially temperature and pressures lead to better quality of the product. this experiment was successful to identify the best condition for producing a best end product base on the quality. from the result obtained, the average particle size is 11.1 µm at optimum condition with inlet temperature of 150˚c, outlet temperature of 70˚c, atomic pressure of 4.5 bars and at least sample concentration (1x) yield the best result both on the moisture content and the particle yield. acknowledgement we would like to acknowledge the kulliyyah of engineering especially the department of biotechnology engineering, international islamic university malaysia for the support of this project. references [1] b draznin., d leroith, molecular biology of diabetes: autoimmunity and genetics; insulin synthesis and secretion. humana press, new jersey. 1994. [2] ol johnson, w jaworowicz, jl cleland, l bailey, m charnis, e duenas, c wu, d shepard, s magil, t last, ajs jones, sd putney. herbal: the pharmacological properties of momordica charantia. pharm. res.; 14:730-735. 1997. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mel et al. 82 [3] toba, t., abe s., arihara k. and adachi s. spray drying technology and the concepts. agric. biol. chem., 50, 2673-2674. 1986. [4] p. menn, g. schulte, k. bauckhage, experimental investigation of high pressure spray drying nozzle performance at industrial operating conditions’, proc. 9 th international conference on liquid atomization and spray systems, july 13-17, sorrento, italy,2001. [5] v n nair, taguchi's parameter design: a panel discussion, technometrics. vol. 34, pp127-161. 1992 [6] j.g.p. verhey, vacuole formation in spray powder particles. 1. air incorporation and bubble expansion. neth. milk dairy j. 26: 187-202. 3. 1972 and 1973. [7] i filkova, and a.s mujumdar, industrial spray drying system, in handbook of industrial drying, mujumdar, a.s., ed., marcel dekker, new york, vol. 1, part ii chapter 9, 263-300, 1995. [8] t. j. buma, and s. henstra, particle structure of spray-dried caseinate and spraydried lactose as observed by a scanning electron microscope. neth. milk dairy j. 25: 278-281. 1971 [9] s. blei, m. sommerfeld, lagrangian modeling of agglomeration during spray drying processes’, proc. 9 th international conference on liquid atomization and spray systems, july 13-17, sorrento, italy. 1999. microsoft word 217-959-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology ahmad et al. 153 zinc-laccase biofuel cell abdul aziz ahmad 1 , raihan othman 2 , faridah yusof 1 and mohamad firdaus abdul wahab 1 1 biotechnology engineering department, 2 science in engineering department, faculty of engineering, international islamic university malaysia p.o. box 10, 50728 kuala lumpur, malaysia. raihan@iium.edu.my abstract: a zinc-laccase biofuel cell adapting the zinc-air cell design features is investigated. a simple cell design configuration is employed: a membraneless single chamber and a freely suspended laccase in a quasi-neutral buffer electrolyte. the cell is characterised according to its open-circuit voltage, polarization profile, power density plot and discharge capacity at constant current. the biocatalytic role of laccase is evident from the polarization profile and power output plot. performance comparison between a single chamber and dual chamber cell design is also presented. as anticipated, a single chamber cell design possesses lower power output as compared to the dual chamber cell design due to probably the charge leakage phenomenon. the biofuel cell possesses an open-circuit voltage of 1.2 v and delivered a maximum power density of 0.9 mw/cm 2 at current density of 2.5 ma/cm 2 . these characteristics are comparable to biofuel cell utilising a much more complex system design. abstrak: sel bio-bahan api zink-laccase dengan adaptasi daripada ciri-ciri rekabentuk sel zink-udara telah dikaji. sel dengan konfigurasi rekabentuk yang mudah digunapakai: ruangan tunggal tanpa membran dan laccase diampaikan secara bebas di dalam elektrolit pemampan quasi-neutral. sel dicirikan berdasarkan voltan litar terbuka, profil polarisasi, plot ketumpatan kuasa dan kapasiti discas pada arus malar. peranan laccase sebagai biopemangkin adalah amat ketara daripada profil polarisasi dan plot ketumpatan kuasa. perbandingan prestasi di antara sel dengan rekabentuk ruangan tunggal and dwi-ruangan turut diketengahkan. seperti dijangkakan, sel dengan rekabentuk ruangan tunggal menunjukkan kuasa keluaran yang lebih rendah jika dibandingkan dengan rekabentuk dwi-ruangan kemungkinan disebabkan fenomena cas bocor. sel bio-bahan api ini mempunyai voltan litar terbuka 1.2 v dan memberikan ketumpatan kuasa maksima 0.9 mw/cm 2 pada ketumpatan arus 2.5 ma/cm 2 . ciri-ciri ini adalah sebanding dengan sel bio-bahan api yang menggunapakai rekabentuk sel yang jauh lebih rumit. keywords: biofuel cell; single chamber; zinc anode; enzyme; oxidoreductase 1. introduction one of the major fields of research in response to the need for preserving the environment is the research and development in renewable energy source to ease dependence on fossil fuel. biofuel cell (bfc) is a potential clean energy substitute for fossil fuel. it is a clean, non-polluting, renewable energy source and producing benign byproduct as it produces energy – fondly dubbed as the nature’s solution. biofuel cell can be classified as an offspring of fuel cell technology. unlike conventional fuel cells, biofuel cells utilize biological catalysts, either as they occur in microorganisms, or as isolated proteins rather than precious metals for the oxidation and reduction processes of fuel iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology ahmad et al. 154 source [1]. main types of biofuel cells depend on biocatalysts used. microbial biofuel cells (mfc) employs whole living cells (microorganisms) whereas enzymatic biofuel cells (efc) employs enzymes (functional proteins) [2]. efcs have several positive attributes with respect to energy conversion, namely, the use of renewable catalysts, ability to operate at room temperature and physiological ph, and possess much higher power densities as compared to mfc. in addition, enzymes have the added advantage of catalysing specific and defined reactions [3, 4]. the bfc system, however, is rather complex. the anolyte and catholyte of a bfc comprises of specific organic fuel or substrate, biocatalyst and electronophores or electron transfer mediators. besides, each anolyte and catholyte requires a unique buffer condition for its optimum condition. therefore, in this work we replaced the anolyte of a glucose oxidase-laccase bfc with an electropositive zinc metal producing a hybrid bfc – zinclaccase biocatalytic system. consequently, it reduces the complexity of the bfc system, simplifies the design and makes the handling of the cell easier. in addition, we employed a simple design configuration – membraneless, single chamber cell and freely suspended laccase in buffer electrolyte. unlike most prototypes of bfc which were tested under controlled or simulated conditions [5, 6], the zinc-laccase cell developed in the present work was left to operate under open ambient surrounding. yet, as shall be described succeedingly, its power density output is found comparable to biocatalytic cell employing much more complex system design and operating under controlled conditions. laccase belongs to the blue-multicopper oxidase family. laccases (benzenediol:oxygen oxidoreductase, ec 1.10.3.2) are extracellular that use molecular oxygen to oxidize various aromatic and non-aromatic compounds by a radical catalysed reaction mechanism [7]. due to its specific affinity towards oxygen, laccase is one of the industrial enzymes widely used in oxidative processes such as bioremediation, delignification, dye or stain bleaching, plant fibre modification, biosensors, biofuel cells, ethanol production etc. [8]. 2. experimental section 2.1 cell design and components the cell comprised of zinc foil (99.9 %, 250 µ m thick) as the anode and a commercially available air electrode sheet as the cathode. the air electrode consisted of laminated structures of fibrous carbon supported by a nickel mesh. the air-side of the electrode was covered with a gas permeable, hydrophobic, teflon membrane. the air electrode served both as the cathodic current collector as well as to feed ambient oxygen continuously into the system through its porous structure. the highly specific laccase reaction enables the use of a membraneless single compartment design. cell was also constructed using dual chamber configuration. cellophane and polypropylene polymeric separators were each utilized as the ionic exchange membrane. fig. 1 depicts the photograph of the home-made, both the single and dual chamber cell designs, fabricated from acrylic boards. 2.2 electrolyte formulation the electrolyte consisted of laccase and syringaldazine in potassium dihydrogen phosphate buffer. laccase from rhus vernicifera (120 unit activity, u/mg) was sourced from sigma-aldrich. laccase served as the biocatalyst for oxygen reduction, whereas syringaldazine was the phenolic substrate for laccase. table 1 summarizes the electrolyte formulation used. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology ahmad et al. 155 fig. 1: single and dual chamber cell designs. table 1: electrolyte formulation of zinc-laccase biocatalytic cell. electrolyte component stock final reaction mix concentration volume used concentration potassium phosphate buffer 1100 µ l 100 mm 36.5 mm potassium phosphate catalyst: laccase from rhus vernicifera 250 µ l 100 u/ml 25 units laccase substrate: syringaldazine in methanol 150 µ l 0.216 mm 0.01 mm syringaldazine total 1500 µ l syringaldazine solution was prepared in absolute methanol. the electrolyte was prepared fresh in cold deionised water before each run. laccase was assayed spectrophotometrically at 530 nm based on the following oxidative reaction to estimate the unit activity prior to electrolyte preparation. syringaldazine + o2 laccase oxidized syringaldazine + 2h2o (eq. 1) this method was adopted from [9]. figure 2 depicts the spectrophotometer scan of laccase/syringaldazine oxidative reaction in the 400-800 nm range which reaffirms the maximum absorbance detection at 530 nm. 2.3 electrochemical characterization the zinc-laccase biofuel cell was characterized based on its open-circuit voltage (ocv), polarization profile, power density plot and galvanostatic discharge capacity. an eco chemie autolab potentiostat/galvanostat pgstat302n was utilized for the electrochemical tests. all experiments were conducted at room temperature. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology ahmad et al. 156 fig. 2: spectrophotometer scan of laccase/syringaldazine oxidative reaction. a polarization profile is essentially a v-i plot i.e. the variation of operating voltage as a function of discharge current. theoretically, the plot is a horizontal straight line with an abrupt vertical line drop which marks the cell ceases to operate. the existence of internal resistance, concentration gradient and activation energy of each half electrode reaction resulted in the ‘polarization’ of the v-i profile. power density plot can be subsequently obtained by measuring the cell power output, p (product of v and i) at each particular discharge current. based on the p-i plot, the maximum power that the cell could deliver is readily obtained. cell discharge capacity is a measure of the total charge quantity that an electrochemical cell could supply. it is measured in ampere-hour or miliampere-hour (mah) unit capacity, � � �� � (eq. 2) id is the constant discharge current and t is the total discharge duration. the energy output of the cell can be obtained from the product of id and the area under the discharge plot (operating voltage vs. time) energy output, � � �� �� � �� �� �� �� �� �� (eq. 3) an is the area under the discharge plot, vop(t) is the instantaneous operating voltage of the cell, and ∆� � �� � �� is the discharge duration. an can be estimated using the riemann’s sum approximation �� � ∑ ∆� � ��� � �� � (eq. 4) n is the number of data points, ∆� is the interval between data points, and � �� � is the midpoint value between data point i-1 and i � � 1,2,3, … � i.e. the average cell potential value between successive data points. 3. results and discussion 3.1 electrochemical characterization the zinc-laccase biofuel cell registered an ocv of 1.2 v. the highest ocv for glucose oxidase-laccase biofuel cell was reported by zebda and co-workers [10] i.e. 0.95 v. they incorporated multi-walled carbon nanotubes (mwcnts) into the compressed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology ahmad et al. 157 bioelectrode which served as a direct electrical wiring for glucose oxidase (gox) and laccase. thus, we have demonstrated that by substituting gox with an electronegative zinc anode and merely employing freely suspended laccase, a biofuel cell with highest ocv was achieved. further refinement of the zinc-laccase system which includes laccase immobilization, electrically wired laccase, utilization of mediator etc would definitely improve the ocv. fig. 3: polarization profile of zinc-laccase biofuel cell employing different laccase loading. fig. 4: power density plots of zinc-laccase biofuel cell employing different laccase loading. figure 3 and 4 illustrate the polarization profile and the power density plot of zinclaccase biofuel cell, respectively. the cell was tested with 25 u laccase, 50 u laccase and 0 u laccase i.e. a negative control cell. the polarization profiles and power density plots clearly substantiate the biocatalytic role of laccase. a marked enhancement was observed 0 0.2 0.4 0.6 0.8 1 1.2 0 5 10 15 20 p o te n ti a l / v i /ma 0u 50u 25u 0 0.5 1 1.5 2 2.5 3 3.5 4 0 5 10 15 20 p o w e r / m w i /ma 0u 25u 50u iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology ahmad et al. 158 with the inclusion of laccase into the electrolyte and further improvement was noticed as the quantity of laccase was doubled. note that from the power density plot, a maximum power output is obtained at 8 ma discharge current i.e. 2.8 mw and 3.6 mw for 25 u laccase and 50 u laccase respectively. figure 5 shows the discharge capability of zinc-laccase biofuel cell performed at constant current of 0.25 ma, 0.5 ma and 1.0 ma. all cells employed 25 u laccase. the resulting cell capacity was 3.7 mah, 5.9 mah and 4.5 mah, respectively. cell capacity is an empirical quantity which is dependent on discharge current. the polarization profile of fig. 3 can be used to gauge the capability of the cell to discharge at higher current density. fig. 5: discharge curves of zinc-laccase biofuel cell. 3.2 single chamber and dual chamber design analysis one of the unique features of functional proteins or enzymes is their highly specific reaction. this characteristic permits the use of a membraneless, single compartment zinclaccase biofuel cell design [11]. however, the simple membraneless, single chamber design is at the expense of a reduced power output. when zinc oxidizes into zinc ions, the electrons released should be channelled to the air electrode or cathodic current collector through the external circuit. these electrons are in turn utilized to reduce oxygen molecules. in the absence of an ionic exchange membrane in a single chamber design, these electrons could be passed directly to laccase to reduce dissolved oxygen. a phenomenon termed as current or charge leakage. in order to investigate the charge leakage phenomena in the present membraneless cell configuration, a zinc-laccase system with dual chamber design was also investigated. two types of ionic exchange membrane were tested i.e. cellophane and polypropylene. cellophane membrane is commonly used for biofuel cells of dual chamber design [15, 16]. polypropylene membrane, on the other hand, is normally employed in lithium and proton secondary cells. both cells were discharged at a constant current of 0.5 ma. figure 6 displays the results. zinc-laccase system using cellophane separator showed better discharge profiles; the operating voltage was higher for most of the discharge duration and the discharge lasted slightly longer. polypropylene separator seemed not suitable for use in zinc-laccase system; the cell could only be discharged at 5 µa. by comparing the area under the discharge curve, the single chamber zinc-laccase cell delivered 15.2 j of energy while utilizing cellophane resulted in 10 % energy output enhancement i.e. 16.8 j. thus, 0 0.2 0.4 0.6 0.8 1 1.2 0 500 1000 1500 p o te n ti a l / v time / min 1ma 0.25ma 0.5ma iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology ahmad et al. 159 the occurrence of charge leakage was observed in the membraneless, single chamber cell design. fig. 6: discharge performance comparison between dual chamber cell and single chamber (membraneless) cell. 3.4 zinc-laccase biofuel cell performance analysis reports in the literature on zinc-laccase biocatalytic system are scarce and to the best of our knowledge the only published work is by smolander and co-workers [13]. they coupled zinc anode with laccase biocathode. the biocathode consisted of a mixture of laccase from t. hirsuta, abts electron mediator (2,2’ azino-bis(3-ethylbenzthiazoline-6sulfonic acid)), and mwcnts, in succinate buffer of ph 4.5. the zinc-laccase system operated under humidity controlled conditions and oxygenated electrolyte in double chamber design utilizing cellophane, nafion or whatman 1 filter paper as separator. they observed a higher ocv of 1.45 v for the zinc-laccase system. the optimum cell configuration possessed a maximum power density around 10 µw/cm 2 at discharge current of 39 µa/cm 2 , obtained under humidity controlled condition and closed system. on the other hand, the present work studied an open zinc-laccase system in which an air electrode was utilized to permit direct air (oxygen) access to the system, and the cell was left to operate under open ambient conditions. basically the system design resembles zinc-air cell which employed laccase as the oxygen reduction catalyst. furthermore, we adopted a much simpler design: membraneless (single-chamber cell) and freely suspended laccase (not immobilized) in quasi-neutral buffer electrolyte. we obtained a maximum power density an order of magnitude higher i.e. 0.9 mw/cm 2 at current density of 2.5 ma/cm 2 (based on 25 u laccase formulation, 2.8 mw maximum power and electrode size of π x 1 cm 2 ). direct comparison of discharge capacity is not possible since they characterized the cell under constant load of 2.2 kω. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology ahmad et al. 160 4. conclusion a zinc-laccase biofuel cell adapting the zinc-air cell design configuration has been investigated. unlike most biofuel cells, the cell operated under open ambient conditions. a single chamber, membraneless cell design was utilized. laccase biocatalyst was left to be freely suspended (i.e. not immobilized) in quasi-neutral potassium dihydrogen phosphate buffer (ph 6.5) electrolyte. despite its simple design features and operated not under controlled conditions, the zinc-laccase system studied demonstrated power output of comparable performance to biofuel cell system utilizing a much more complex design – immobilized enzyme and electron transfer mediator, controlled temperature and humidity, oxygenated electrolyte etc. the present biofuel system demonstrated attractive features to be further developed. acknowledgement the authors gratefully acknowledge the international islamic university malaysia for the funding of this project through the iium research endowment fund (edw b 0902-227). references [1] palmore gt, whitesides gm: microbial and enzymatic biofuel cells. acs sym ser 1994, 566:271–290. [2] minteer sd, liaw by, cooney mj: enzyme-based biofuel cells. curr opin biotech 2007, 18:228–234. [3] bond dr, lovley dr: evidence for involvement of an electron shuttle in electricity generation by geothrix fermentans. appl environ microbiol 2005, 71:2186–2189. [4] bullen ra, arnot tc, lakeman jb, walsh fc: biofuel cells and their development. biosens bioelectron 2006, 21:2015–2045. [5] habrioux a, merle g, servat k, kokoh kb, innocent c, cretin m, tingry s: concentric glucose/o2 biofuel cell. j electroanal chem. 2008, 622:97–102. [6] mano n, kim hh, zhang y, heller a: an oxygen cathode operating in a physiological solution. j am chem soc 2002, 124:6480–6486. [7] thurston cf: the structure and function of fungal laccases. microbiology 1994, 140:19–26. [8] alcalde m: laccases: biological functions, molecular structure and industrial applications. in industrial enzymes. edited by polaina j and maccabe ap. netherlands: springer; 2007:461–476. [9] ride j: the effect of induced lignification on the resistance of wheat cell walls to fungal degradation. physiol plant pathol 1980:187–196. [10] zebda a, gondran c, le goff a, holzinger m, cinquin p, cosnier s: mediatorless high-power glucose biofuel cells based on compressed carbon nanotube-enzyme electrodes. nat commun 2011, 2:370. [11] heller a: potentially implantable miniature batteries. anal bioanal chem. 2006, 385:469–473. [12] sakai h, nakagawa t, tokita y, hatazawa t, ikeda t, tsujimura s, kano k: a high-power glucose/oxygen biofuel cell operating under quiescent conditions. energy environ sci 2009, 2:133–138. [13] smolander m, boer h, valkiainen m, roozeman r, bergelin m, eriksson j-e, zhang xc, koivula a, viikari l: development of a printable laccase-based biocathode for fuel cell applications. enzyme microb tech 2008, 43:93–102. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 influence of fibreglass mesh on physical properties of lightweight foamcrete anisah mat serudin, md azree othuman mydin* and abdul naser abdul ghani school of housing, building and planning, universiti sains malaysia, 11800, penang, malaysia *corresponding author: azree@usm.my (received: 12th april 2020; accepted: 27th september 2020; published on-line: 4th january 2021) abstract: this research project was designed to investigate the influence of fibremesh on the durability properties of lightweight foamcrete (lfc). the fibremesh, categorized as a synthetic fibre (man-made fibre), was used for this study. it poses a continuous fibre with warp and weft structure that was used as confinement material in this investigation where four different weights per area (g/m2) of the fibremesh were observed namely, 110 g, 130 g, 145 g, and 160 g. three experimental tests were involved in this preliminary study: porosity, water absorption, and drying shrinkage test. all the specimens were confined with 1-layer fibremesh at a constant density of 1100kg/m3 of lfc and the result was compared with the control (unconfined lfc). the 160 g/m2 of fibremesh significantly improved the physical properties of lfc where 13.8%, 20%, and 57.4% enhancement was obtained for the porosity, water absorption, and drying shrinkage result, respectively. abstrak: projek penyelidikan ini dijalankan bagi menyiasat kesan pengunaan jejaring sabut pada sifat ketahanan konkrit ringan berbusa (lfc). jejaring sabut yang digunakan dalam kajian ini adalah jejaring gentian kaca tahan-alkali yang dikategorikan sebagai serat sintetik yang juga dikenali sebagai fabrik tekstil. ia mempunyai serat yang panjang dan bersambung dengan struktur yang lekuk dan renda yang digunakan sebagai penambahbaikan bagi konkrit ringan berbusa. terdapat empat berat jejaring sabut yang diuji iaitu 110 g, 130 g, 145 g, dan 160 g. tiga jenis eksperimen bagi kajian awal ini iaitu keliangan, penyerapan air, dan pengecutan pengeringan. semua spesimen dibalut dengan 1 lapisan jejaring sabut pada 1100kg/m3 lfc dan data yang diperoleh dibandingkan dengan spesimen yang tidak dibalut dengan gentian kaca berjejaring. jejaring sabut 160 g/m2 meningkatkan sifat fizikal konkrit ringan berbusa di mana 13.8%, 20%, dan 57.4% peningkatan diperoleh bagi keliangan, penyerapan air, dan pengecutan pengeringan, masing-masing. keywords: foamed concrete; property; fibremesh; confinement 1. introduction from ancient times, concrete has been well known as the most popular material utilized in the worldwide construction industry. it is used in construction work to fulfil the high demand for housing, high-rise building, infrastructure, etc. this is because concrete is resistant to deterioration compared to wood, and it is also easier to build in several forms. presently, the application of an air cell system becomes one of the preferable technologies to be used in a construction project due to its benefits. it is getting more attention since it has the ability to reduce the size of the foundation and structural dead load due to its low 23 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 density, thus minimizing operating costs and labour use [1,2]. it is also acknowledged as a sustainable building material [3,4]. high flowability concrete, namely, lightweight foamcrete (lfc) has a varied range of density and can be constructed to any desired application such as wall panels, slabs, or other load-bearing building elements, lightweight concrete block, void filling, etc. [5]. the density of lfc typically ranges between 300 kg/m3 to 1600 kg/m3 [6] which is 20% and up to 85% of its volume filled with air-void. these air-voids were created by the introduction of foam into the cement slurry or mortar causing its unit weight (density) to be lower than that of normal concrete where the density ranges between 2240 kg/m3 and 2400 kg/m3 [7]. however, when a high volume of foam is added into the mortar, more airvoids will be created in the mortar slurry, thereby inducing a higher porosity, water absorption, and shrinkage in the lfc. according to shabbar et al. [8], 60 to 90% of lfc volume is pore space where the pore size and microstructure influenced its physical properties. kurpińska and ferenc [9] also reported that the high percentage of porosity in lfc is due to the void contents of the composite being higher, while hilal et al. [10] clarified that the higher percentage of porosity is obtained at the lower density of lfc. besides, thakrele [11] also mentioned that water absorption is higher because of the higher air content in the lfc. in addition, the major drawbacks of this lfc material are the high drying shrinkage behaviour, which is 4 to 10 times higher than normal weight concrete [12]. rai and kumar [13] verified that this happened due to the no coarse aggregate used in the mixture that resulted in the high drying shrinkage obtained, which will lead to the low strength characteristic of lfc. many researchers have done the study of enhancement of the properties of lfc by the inclusion of short fibres such as sisal fibres [14], kenaf fibres [15-17], oil palm fibres [15,18], polypropylene fibres [15,16], and ar-glass and steel fibres [15]. however, some of the materials have a negative impact on the long-term performance of lfc such as deterioration of natural fibre [19], and corrosion of the reinforcing steel [20]. thus, in this research, authors have explored the potentiality of continuous fibres, namely, fibremesh, as an enhancement to the properties of lfc, this has not being practiced yet in such types of concrete. in this research, the authors examined the influence of different weight per area (g/m2) of fibremesh-confined lfc to improve its porosity, water absorption, and drying shrinkage performance since it is correlated to the mechanical properties of the composite. the fibremesh used in this research is alkali-resistant (ar) fibremesh with four different weights per area (g/m2) which were 110 g, 130 g, 145 g, and 160 g. this type of fibremesh is more flexible, easy to handle, cheaper, and has higher performance compared to others (carbon, aramid, etc.). 2. material preparation to prepare the lfc mix, four (4) common materials were utilized in the production: cement, sand, water, and stable foam. furthermore, four different weights per area (g/m2) of fibremesh were utilized in this study, namely, 110 g, 130 g, 145 g, and 160 g. all the results obtained from respective lfc specimens confined with 1-layer of the different weights per area of fibremesh were compared to the control specimens (lfc without any reinforcement). for this particular research, ordinary portland cement (opc) was used which is in accordance with the specifications of type 1 portland cement in astm c15004 [21]. sand particle size utilized in this research is less than 1.18mm diameter with the specific gravity of 2.74 and fineness modulus of 1.35. the grading limits are according to astm c778-06 [22]. fine aggregate is suitable for producing the lfc since the coarse aggregate caused the existence of bigger pores and created an inconsistent mix that affected the lfc properties. the presence of water is necessary to mix the cement and fine 24 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 aggregate to form the cement slurry through chemical reaction which will lead to the hardened of mortar paste. tap water (free from any harmful substance) was used which complied with the standard stated in astm c1602-c05 [23]. foam was added to control and obtain a desirable density for the lfc. in this study, a protein-based foaming agent, namely, noraite pa-1 was used to produce a stable foam. 1kg of foaming agent was diluted into 30 l of water. 3. mix proportion and experimental setup 3.1 mix design based on the previous research, there are many factors that influence the behaviour of lfc such as the density of lfc, the water to cement ratio, the binder to cement ratio, the type of filler, the type of foaming agent, the inclusion of fibre, etc. thus, to obtain comparable results, the mix design of lfc was fixed, as shown in table 1. besides, the density of lfc was the major factor that would affect the performance of lfc, so that in this research it was maintained at 1100 kg/m3. since the application of lfc can be categorized into structural, semi structural, and non-structural, the intermediate application is more suitable to be chosen for preliminary study. table 1: mix design of lfc mixes confined with fibremesh sample weights per area of fibremesh [g/m2] mix density of lfc [kg/m3] mix ratio of lfc mix proportions of lfc, kg/m3 cement/ sand water/ cement cement sand water control 1100 1:1.5 0.45 410.79 616.18 184.86 110 g 110 1100 1:1.5 0.45 410.79 616.18 184.86 130 g 130 1100 1:1.5 0.45 410.79 616.18 184.86 145 g 145 1100 1:1.5 0.45 410.79 616.18 184.86 160 g 160 1100 1:1.5 0.45 410.79 616.18 184.86 fig. 1: physical features of the fibremesh. as mentioned by [24], 0.45 of water to cement ratio produced an lfc with a reasonable workability. thus in this research, it was fixed at 0.45. the filler to cement ratio was fixed to 1:1.5 as demonstrated in previous study [15-16, 18, 25-28]. furthermore, four different weights of fibremesh, namely, 110 g, 130 g, 145 g, and 160 g per area (g/m2) were used in this observation. the data obtained from this research would 25 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 be useful for the construction sector or other researchers that are interested in the application of fibremesh in lfc since it has not been documented yet. figure 1 shows the physical features of the fibremesh and its physical properties is detailed in table 2. table 2: physical properties of fibremesh properties weight of woven fiberglass mesh (g/m2) 110 130 145 160 mesh size 4.0 x 5.0 mm 4.0 x 5.0 mm 4.0 x 5.0 mm 4.0 x 5.0 mm colour white white white white coating type alkali resistant alkali resistant alkali resistant alkali resistant mass (g/m2) 110±3 130±3 145±3 160±3 ignition point 391ºc (735.8ºf) 394ºc (741.2ºf) 398ºc (784.4ºf) 404ºc (759.2ºf) melt point 154ºc (309.2ºf) 156ºc (312.8ºf) 158ºc (316.4ºf) 160ºc (320.0ºf) tensile strength (mpa) 1195 1250 1325 1407 elongation at break (%) 4.15% 3.75% 3.41% 3.07% compliance astm c1116-02 astm c1116-02 astm c1116-02 astm c1116-02 quality assured facility iso 9001:2008 iso 9001:2008 iso 9001:2008 iso 9001:2008 3.2 water absorption test the water absorption test was determined as prescribed in bs 1881-122 [29]. cylindrical-shaped specimens (75 mm ø x 100 mm h) were used in this study. at the aging day of the test, 3 specimens were unwrapped and oven-dried for 72 hours. then, the weights of the cooled oven-dried specimens were recorded as wd, and they were fully submerged in a water tank for 30 minutes (refer fig. 2). next, a dry cloth was used to remove any excess water present on the test specimens and their weight was recorded in a saturated condition ws. the water absorption was expressed in percentage, wa, and calculated using equation (1). the average of these 3 specimens was taken as the final result for the water absorption test. 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑊𝑊𝑎𝑎𝑎𝑎𝑎𝑎𝑊𝑊𝑎𝑎𝑊𝑊𝑎𝑎𝑎𝑎𝑛𝑛 (%), 𝑊𝑊𝑎𝑎 = � 𝑊𝑊𝑠𝑠−𝑊𝑊𝑑𝑑 𝑊𝑊𝑑𝑑 � × 100% (1) where, ws = saturated surface dry weight wd = oven-dried weight (a) (b) fig. 2 :water absorption test. (a) lfc specimens were fully submerged in a water tank, (b) side view of lfc specimen. 26 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 3.3 porosity test the porosity test was conducted based on the method described in rilem [30]. this test was determined by the immersion method into a vacuum desiccator and tested on day 28. the purpose of this test was to determine the percentage of air-voids in the lfc specimens confined with different weights per area (g/m2) of fibremesh. as mentioned by previous researchers, lfc (without any reinforcement) possesses a high porosity compared to the lfc specimens with reinforcement. thus, the confinement of fibremesh in the lfc will decrease the percentage of porosity contained. therefore, 3 specimens of lfc, with a diameter of 45 mm and height of 50 mm, were placed in an oven to remove moisture for 72 hours or until no changes in weight were recorded. then, the specimens were cooled and their weights recorded as wdry. the specimens were fully immersed in the vacuum chamber for 72 hours or up until no visible bubbles appeared. the weights of the specimens in water (ws,w) and in air (ws,a) were recorded. figure 3 shows the setup of the vacuum desiccator for the test, while eq. (2) was used to measure the percentage of porosity in lfc. the average value of the 3 specimens was recorded as the final result for the total porosity test. 𝑇𝑇𝑎𝑎𝑊𝑊𝑊𝑊𝑇𝑇 𝑎𝑎𝑎𝑎𝑊𝑊𝑎𝑎𝑎𝑎𝑎𝑎𝑊𝑊𝑝𝑝 (%) = � 𝑊𝑊𝑠𝑠,𝑎𝑎−𝑊𝑊𝑑𝑑𝑑𝑑𝑑𝑑 𝑊𝑊𝑠𝑠,𝑎𝑎− 𝑊𝑊𝑠𝑠,𝑤𝑤 � × 100% (2) where, ws,a = weight of saturated sample in air wdry = weight of oven-dried sample ws,w = weight of the saturated sample in water fig. 3: porosity test. 3.4 shrinkage test drying shrinkage test was measured via mitutoyo brand digital indicator with 298 mm of reference bar and it was performed according to astm c157/c157m [31], where 3 prism specimens with size of 75 x 75 x 285 mm were installed with a pair of steel screws and cap nuts. after demoulding, lfc specimens were placed in the length comparator, as seen in fig. 4, and rotated anti-clockwise to obtain the data. the readings were taken and recorded as,(li). li is the corrected initial comparator reading. then, the steps were repeated for the next testing ages, which were at days 1, 3, 7, 14, 21, 28, and 56. these readings were recorded as lx, where x represents the test at the subsequent ages. the drying shrinkage was calculated using eq. (3), where the corrected comparator 27 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 reading was equal to the specimen comparator reading minus the reference bar comparator reading. 𝐷𝐷𝑊𝑊𝑝𝑝𝑎𝑎𝑛𝑛𝐷𝐷 𝑎𝑎ℎ𝑊𝑊𝑎𝑎𝑛𝑛𝑟𝑟𝑊𝑊𝐷𝐷𝑊𝑊, (mm) = �𝐿𝐿𝑥𝑥−𝐿𝐿𝑖𝑖 285 � × 100% (3) where, lx = corrected comparator reading li = corrected initial comparator reading x = day test fig. 4: setup for drying shrinkage test. 4. results and discussion 4.1 porosity the porosity test was conducted using the vacuum saturation approach in accordance to rilem. as verified by hilal et al. [10], this method provides the most appropriate means of accurately assessing the porosity of lfc compared to mercury intrusion porosimetry (mip) and apparent porosity techniques. this is because the mip method only determines the entrained pores with diameters of less than 400 µm, while the apparent porosity approach is unsuitable as the contribution of water absorption is only applied for the capillary pores, which depend on the paste content, and the entrained pores (air-voids) do not take part in this test as they are not interlocked [10]. as shown in fig. 5, the control specimen showed the highest porosity when compared with the other specimens, which had been confined with different weights per area (g/m2) of fibremesh. the porosity decreased as the weight per area (g/m2) of the fibremesh increased. as illustrated in table 3, the porosity decreased from 5.7% to 13.8% when the lfc specimens were confined with 110 g/m2 to 160 g/m2 of fibremesh, respectively. this was due to the confinement effect of the fibremesh which had reduced the rate of the water penetrated into the air void 28 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 of lfc on the same day the measurements were taken. the presence of the fibremesh impeded the water movement into the paste phase of the lfc. this explained the reason for the control specimen having a higher porosity compared to all the other specimens. besides, from the previous studies, no research has yet been done to investigate the porosity of lfc confined by fibremesh. in this experimental investigation, it was observed that the lfc that was confined with fibremesh showed the same decreasing pattern for porosity as with the inclusion of fibres (short fibres such as sisal, kenaf, oil palm, polypropylene, steel, etc.). for instance, based on a study conducted by zamzani [27], the inclusion of 0.1% to 0.6% of cocos nucifera linn. (cnf) fibre by volume fraction in lfc (1450 kg/m3) was able to decrease the porosity from 3% to 13% at day-28 compared to the control. this result was approximately similar to the result obtained in the current research, where the confinement of lfc with 110 g/m2 to 160 g/m2 improved the porosity by 5.7% to 13.8% compared to the control, which was without any confinement. therefore, the confinement of the lfc specimens with 160 g/m2 of fibremesh showed the best result as it reduced the porosity up to 13.8%, as obtained in this research. fig. 5: porosity of lfc specimens confined with different weights per area (g/m2) of fibremesh at day-28. table 3 percentage decrease in porosity for confined lfc specimens compared to the control specimen specimen percentage decrease (%) 110 g 5.7 130 g 10.4 145 g 13.4 160 g 13.8 4.2 water absorption water absorption occurs as a result of capillary pores in the lfc cement paste [32]. figure 6 shows the water absorption capacity of the lfc specimens confined with different weights per area of fibremesh and of the control specimen as a reference sample. overall, the control specimen possessed a relatively high-water absorption capacity 50.8 47.9 47.1 45.5 43.8 40 42 44 46 48 50 52 control 110g 130g 145g 160g po ro si ty (% ) control 110g 130g 145g 160g 29 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 compared to the specimens confined with fibremesh. theoretically, the water absorption happened due to the process whereby the concrete absorbed or drew water into its pores and capillaries [33]. it could be seen that the higher weight per area of fibremesh contributed to a greater reduction in the water absorption capacity of all the specimens that were tested in this research. as shown in table 4, the water absorption capacity of the specimens confined with 110, 130, 145, and 160 g/m2 of fibremesh decreased by 6.5%, 7.6%, 14.1% and 20.0%, respectively when compared to the control specimen. the reduction in the water absorption capacity of the lfc specimens was due to the enclosed fibremesh array that managed to prevent the penetration of water into the cement matrix. besides, fibremesh possesses a hydrophobic characteristic where it provides an alternative solution for inhibiting the diffusion of water molecules into a cement matrix, which is contrary with the behaviour of natural fibres that tended to attract water due to their hydrophilic nature [17]. thus, this investigation proved that the 160 g/m2 of fibremesh led to a reduction in the water absorption properties of lfc. fig. 6: water absorption capacity of lfc specimens confined with different weights per area (g/m2) of fibremesh at day-28. table 4: percentage decrease in water absorption capacity for confined specimens compared to the control specimen specimen percentage decrease (%) 110 g 6.5 130 g 7.6 145 g 14.1 160 g 20.0 4.3 drying shrinkage amran et al. [1] claimed that the drying shrinkage in lfc is ten times higher compared to normal weight concrete because of the absence of coarse aggregates. according to cheah et al. [32], drying shrinkage occurs in a cement matrix due to the evaporation of internal free water from the concrete or mortar in the hardened state to the surrounding environment. based on the test results shown in fig. 7, the control specimen exhibited a 17.0 15.9 15.7 14.1 13.6 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 control 110g 130g 145g 160g w at er a bs or pt io n (% ) control 110g 130g 145g 160g 30 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 higher drying shrinkage compared to the other specimens. this was because the confinement of fibremesh reduced the drying shrinkage behaviour in lfc specimens as the fibremesh was able to maintain the water content and delay the evaporation of the internal moisture, hence lessening the drying shrinkage behaviour. falliano et al. [34] also proved that unreinforced specimens exhibit a shrinkage that decreases with increasing dry density. besides, namsone et al. [35] also stated that the addition of fibre can reduce the risk of shrinkage and stabilize the fresh mix. there was a significant improvement in the drying shrinkage behaviour of the lfc specimens confined with fibremesh, as displayed in table 5. when the lfc specimen was confined with 110 g/m2 of fibremesh, the drying shrinkage behaviour was enhanced by 34.4% compared to the control specimen. the improvement of the drying shrinkage behaviour rose as the weight per area of the fibremesh increased. consequently, 160 g/m2 of fibremesh showed the best drying shrinkage prevention, where the drying shrinkage was reduced up to 57.4% compared to the control specimen. fig. 7: drying shrinkage of lfc specimens confined with different weight per area (g/m2) of fibremesh. table 5: percentage decrease of drying shrinkage for confined specimens compared to the control specimen. specimen percentage decrease (%) 110 g 34.4 130 g 42.6 145 g 47.5 160 g 57.4 5. conclusion in this preliminary study, the influence of fibremesh on the physical properties of lfc with a density of 1100 kg/m3 was investigated. based on the results obtained, the following conclusions can be drawn: • overall, the confinement of fibremesh significantly enhanced the physical properties of lfc. 0 0.1 0.2 0.3 0.4 0.5 0.6 0 10 20 30 40 50 60 d ry in g sh ri nk ag e (m m ) days contro 110g 130g 145g 160g 31 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 • obviously shown in the three experiment tests (porosity, water absorption, and drying shrinkage), the confinement of 160 g of fibremesh resulted in improvement of the physical properties of lfc. • it is proven that the weight per area of fibremesh influenced the physical properties of lfc. • as recommendation for future study, authors suggest to investigate the effect of different types of textile fibres such as carbon, aramid, basalt, etc., to be utilized as confinement material for lfc since it is not covered in this research. they also suggested cost effectiveness analysis between the mentioned textile fabrics to examine which materials give greater benefits to the construction sector. acknowledgement the authors would like to thank universiti sains malaysia for their funding of this research through the bridging grant: grant no: 304/ppbgn/6316230. references [1] amran yhm, farzadnia n, ali aaa. (2015). properties and applications of foamed concrete; a review. construction and building materials, 101: 990-1005. https://doi.org/10.1016/j.conbuildmat.2015.10.112 [2] fu y, wang x, wang l, li y. (2020). foam concrete : a state-of-the-art and state-of-thepractice review. advances in materials science and engineering. https://doi.org/10.1155/2020/6153602 [3] moon as, varghese v, waghmare ss. (2015). foam concrete as a green building material. international journal for research in emerging science and technology, 2(9): 2532. [4] siram kkb, raj ka. (2013). concrete + green = foam concrete. international journal of civil engineering and technology (ijciet), 2(2): 1-24. [5] sari kam, sani arm. (2017). applications of foamed lightweight concrete. matec web of conferences, 97: 1-5. https://doi.org/10.1051/matecconf/20179701097 [6] jalal md, tanveer a, jagdeesh k, ahmed f. (2017). foam concrete. international journal of civil engineering research, 8(1): 1-14. retrieved from https://www.ripublication.com/ijcer17/ijcerv8n1_01.pdf [7] hedjazi s. (2019). compressive strength of lightweight concrete. in intechopen:1-18. https://doi.org/10.5772/intechopen.88057 [8] shabbar r, nedwell p, wu z. (2018). porosity and water absorption of aerated concrete with varying aluminium powder content. international journal of engineering and technology, 10(3): 234-238. https://doi.org/10.7763/ijet.2018.v10.1065 [9] kurpińska m, ferenc t. (2017). effect of porosity on physical properties of lightweight cement composite with foamed glass aggregate. itm web of conferences, 15: 06005. https://doi.org/10.1051/itmconf/20171506005 [10] hilal aa, thom nh, dawson ar. (2014). pore structure and permeation characteristics of foamed concrete. journal of advanced concrete technology, 12: 535-544. https://doi.org/10.3151/jact.12.535 [11] thakrele mh. (2014). experimental study on foam concrete. international journal of civil, structural, environmental and infrastructure engineering research and development, 4(1): 145-158. [12] elrahman ma, el madawy me, chung sy, sikora p, stephan d. (2019). preparation and characterization of ultra-lightweight foamed concrete incorporating lightweight aggregates. applied sciences (switzerland), 9(7): 1-12. https://doi.org/10.3390/app9071447 [13] rai a, kumar m (2017). experimental study on compressive and split tensile strength of foamed concrete using stone dust. international research journal of engineering and 32 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 technology(irjet), 4(5): 1377-1382. retrieved from https://www.irjet.net/archives/v4/i5/irjet-v4i5269.pdf [14] dhanunjaya g, dadapeer abs, rafi dm. (2018). an experimental study on the durability properties of foam concrete with addition of natural fibers. international journal of scientific research in science and technology, 4(2): 529-536. [15] awang h, ahmad mh. (2014). durability properties of foamed concrete with fiber inclusion. international journal of civil, structural, construction and architectural engineering, 8(3): 273-276. [16] hanizam a, mohammed a, ahmad mh. (2015). influence of kenaf and polypropylene fibres on mechanical and durability properties of fibre reinforced lightweight foamed concrete. journal of engineering scinece and technology, 10(4): 496-508. https://doi.org/10.4028/www.scientific.net/amr.626.404 [17] mahzabin ms, hock lj, hossain ms, kang ls. (2018). the influence of addition of treated kenaf fibre in the production and properties of fibre reinforced foamed composite. construction and building materials, 178: 518-528. [18] musa m. (2019). investigation of durability, thermal and mechanical properties of oil palm empty fruit bunch (efb) fibre strengthen lightweight foamed mortar (lfm). master thesis. universiti sains malaysia. [19] bentur a, mindess s. (2007). fibre reinforced cementitious composites. in a. bentur & s. mindess (eds.), taylor & francis (2nd edition). https://doi.org/10.1016/00104361(79)90446-4 [20] memon ia, jhatial aa, sohu s, lakhiar mt, hussain z. (2018). influence of fibre length on the behaviour of polypropylene fibre reinforced cement concrete. civil engineering journal, 4(9): 2124-2131. https://doi.org/10.28991/cej-03091144 [21] astm c150-04 (2004). standard specification for portland cement c150-04. annual book of astm standards, 4(2): 1-8. [22] astm c778-06 (2006). standard specification for standard sand c778-06. annual book of astm standards. retrieved from http://www.who.int/csr/don/03-june-2016-oropoucheperu/en/ [23] astm c1602-c05 (2006). standard specification for mixing water used in production of hydraulic cement concrete c1602. annual book of astm standards. [24] talaei s, jafari m, tarfan s, hashemlou h. (2014). the effect of ratio of aggregate to cement paste volume on structural lightweight concrete strength , viscosity , density and cost. research journal of environmental and earth sciences, 6(9): 443-450. [25] coker eb, sadiku s, aguwa ji, abdullahi m. (2016). study of the strength characteristics of protein-based lightweight foamed concrete with cement partially replaced with rice husk ash. nigerian journal of technology, 35(4): 699-706. https://doi.org/10.4314/njt.v35i4.2 [26] suhaili ss, mydin mao. (2020). potential of stalk and spikelets of empty fruit bunch fibres on mechanical properties of lightweight foamed concrete. international journal of scientific and technology research, 9(3): 3199-3204. [27] zamzani nm. (2019). characterization of durability and engineering properties of cocos nucifera linn fibre (cnf) reinforced foamcrete and its performance at elevated temperatures. master thesis. universiti sains malaysia. [28] zulkarnain f. (2011). strength and durability properties of lightweight foamed concrete for housing construction. master thesis. universiti sains malaysia. [29] bs 1881-122 (2011). testing concrete part 122 method for determination of water absoprtion bs1881-122. british standard institution. https://doi.org/10.1017/cbo9781107415324.004 [30] rilem (1984). absorption of water by concrete by immersion under vacuum. in rilem (ed.), rilem recommendations for the testing and use of constructions materials: 36-37. https://doi.org/doi: 10.1617/2351580117.018 [31] astm c157/c157m (2005). standard test method for length change of hardened hydraulic-cement mortar and concrete. annual book of astm standards: 1-10. 33 iium engineering journal, vol. 22, no. 1, 2021 mat serudin et al. https://doi.org/10.31436/iiumej.v22i1.1446 [32] cheah cb, lim js, ramli mb. (2019). the mechanical strength and durability properties of ternary blended cementitious composites containing granite quarry dust (gqd) as natural sand replacement. construction and building materials, 197(november 2018): 291-306. https://doi.org/10.1016/j.conbuildmat.2018.11.194 [33] jung ct, kwong t h, boon kh. (2018). water absorption and drying shrinkage of recycled foamed aggregate concrete. malaysian journal of civil engineering, 30(3): 482-492. [34] falliano d, de domenico d, ricciardi g, gugliandolo e. (2019). compressive and flexural strength of fiber-reinforced foamed concrete: effect of fiber content, curing conditions and dry density. construction and building materials, 198: 479-493. https://doi.org/10.1016/j.conbuildmat.2018.11.197 [35] namsone e, korjakins a, sahmenko g, sinka m. (2017). the environmental impacts of foamed concrete production and exploitation. iop conference series: materials science and engineering, 251(1). https://doi.org/10.1088/1757-899x/251/1/012029 34 1. introduction 2. material preparation 3. mix proportion and experimental setup 3.1 mix design 3.2 water absorption test 3.3 porosity test 3.4 shrinkage test 4. results and discussion 4.1 porosity 4.2 water absorption 4.3 drying shrinkage 5. conclusion acknowledgement references application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 microwave irradiation optimization for efficient lignin removal from cocoa shell waste using alkali farah hafidzah ahmad1, nurhamizah ibrahim1, mohd sabri mahmud1, waleed ali1, mohd bijarimi mat piah1, suriyati salleh2, and said nurdin3 1 department of chemical engineering, college & natural resources engineering, 2 faculty of chemical and process engineering technology, universiti malaysia pahang, gambang, 26300 kuantan, pahang, malaysia 3 chemical engineering department, faculty of engineering-syiah kuala university, darussalam, bandar acheh, 23111 indonesia * corresponding author: mohdsabri@ump.edu.my (received: 10th september 2020; accepted: 5th march 2021; published on-line: 4th july 2021) abstract: this paper reports a study to determine the optimum conditions of microwave in assisting alkali treatment for removing lignin from cocoa shell waste (csw). the csw was mixed with 5% of naoh solution at the ratio of 1: 10 of weight to volume of the alkaline before being irradiated in a microwave oven. various microwave powers (200-400 w), temperature settings (60-80 °c) and irradiation times (10-20 min) were tested on 15 samples set by the box-behnken design. the lignin removal was analysed using a 72% sulfuric acid treatment method. a quadratic equation was employed to the response surface and statistical analysis conducted to confirm the adequacy of the model. the plots show that the optimum microwave conditions are 400 w, 76 °c and 19 min, which were capable to remove 86.57% of lignin. thermogravimetric analysis and micrographs revealed different decomposition temperature of lignin and morphology of extensively-pored surface of treated csw, respectively. abstrak: kajian ini berkaitan penentuan keadaan optimal ketuhar gelombang mikro bagi membantu membuang lignin daripada sisa kulit biji koko (csw) menggunakan rawatan alkali. csw dicampurkan dengan larutan naoh 5 % pada nisbah 1:10 berat kepada isipadu larutan alkali sebelum campuran dipanaskan ke dalam ketuhar gelombang mikro. pelbagai ujian dibuat pada ketuhar gelombang mikro seperti tenaga (200-400 w), suhu ketuhar (60-80 °c) dan masa pemanasan (10-20 min) ke atas 15 sampel mengikut reka bentuk box-behnken. kadar pembuangan lignin ditentukan dengan menggunakan kaedah rawatan larutan asid sulfurik berkepakatan 72%. persamaan kuadratik telah digunakan ke atas permukaan respon dan analisis statistik telah dilakukan bagi memastikan kesesuaian model. plot-plot menunjukkan keadaan optima ketuhar gelombang mikro adalah pada 400 w, 76 °c dan 19 min iaitu berupaya menyingkirkan sebanyak 86.57% lignin. analisis thermogravimetri dan mikrograf masing-masing menunjukkan perbezaan suhu penguraian lignin dan morfologi permukaan csw yang dirawat didapati berliang dengan banyaknya. keywords: cocoa shell waste; microwave assisted; alkali treatment; lignin removal; non-wood fibers; response surface methodology 21 iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 1. introduction by-product discarded from food industries may harm environment in large quantities [1]. cocoa (theobroma cacao) shell waste (csw) is an example of the by-products that is usually used, among others, for dietary, food additives, fuel burning, or fertilizer in order to prevent accumulation [2–6]. an alternative approach to add value is by utilizing csw as non-wood for bio-composite preparation. however, there is a drawback that needs to be considered since csw is mainly composed of cellulose, lignin, hemicelluloses, pectin, and wax. weak binding between fiber and polymer due to moisture absorption [7], low impact strength [8], faced dimension instability for fibers composites [9] and low microbial resistance [10] of csw application are reported that are mainly caused by the presence of hydroxyl groups from lignin in its fiber. therefore, reduction of lignin is essentially required. pre-treatment using alkali is a vital step in converting the lignocellulosic material into less wood material. several studies suggested the use of microwave heating to accelerate the pre-treatment process due to some advantages over conventional heating [11,12]. in particular, microwave-assisted alkaline pre-treatment for hydrolysis and fermentation increase cellulose breakdown and the activity of the reactions [13]. interface of fibers with lower hydroxyl group will bond with matrix better and enhance strengths of the composites [9,14]. sodium hydroxide (naoh) is an effective alkaline in breaking down lignin structure [15,16] that leads to an increase in surface area and pore volume in the substrate. meanwhile, microwave radiation results in rapid heating due to interaction between an irradiated object and electromagnetic field [17,18]. thus, this high efficiency of treatment eases the implementation [19,20] of breaking down lignocellulosic material bonding. several studies reported on the optimization of treatment process parameters for other agricultural wastes. for instance, sombatpraiwan et al. [17] conducted microwave –assisted on cassava rhizome by varying microwave power (300-900 w), irradiation time (5-15 min), and naoh concentration (3%–7% w/v). it was found that optimal conditions for lignin removal were 840 w microwave, 9 min, and 3% w/v naoh. lai et al. [21] found that 22.38% lignin removal was optimal at 900 watt, 100 ºc, and 80 min from a two-level factorial analysis on the range of microwave power, temperature and heating duration range spanning from 500 to 900 watt, 80 to 100 °c and 40 to 80 min on oil palm trunk. the aim for this study is to determine optimal microwave–assisted alkali treatment condition on csw. the pre-treatment parameters are microwave power, temperature setting and irridiation time, which were varied between 200 – 400 w and 60 – 80 ℃ for 10 – 20 min, respectively. this treatment was optimized by using the box–behnken design (bbd), response surface methodology (rsm). 2. materials and methods 2.1 assisted alkali treatment csw samples were mixed to 5 % of naoh at 1: 10 according to the ratio of sample weight to volume of the alkaline. the microwave was set to the ranges of 200 – 400 w, 60 – 70 ℃ and 10 – 15 min for power, temperature and time of irradiation, respectively. all these treatment conditions were designed based on bbd using design expert software version 7. after the treatment, mixtures were filtered to recover solid residue. the residue was rinsed with distilled water to remove the alkali solution and followed by the addition of 5 % 22 iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 acetic acid solution in dropwise. then, the slightly acidic residue was rinsed again with distilled water until neutral ph was achieved. the treated csw was dried at 105 °c until constant weight was achieved. 2.2 experimental design bbd was used to optimize microwave parameters as the factor in assisting the caustic removal of lignin from csw via 15 experiments in random order with three replications at the centre point. the design of experiment was of three-factor and two-level factorial box– behnken design (bbd) [17]. the three factors were microwave power (x1), temperature (x2), and treatment time (x3) with low, moderate, and high levels factor as represented by −1, 0, and 1 as shown in table 1. percentage of lignin removal was the response variable. 3d surface plots were generated through fitting of a quadratic polynomial between the factors and the response. table 1 experimental levels of three independent variables factors units factor levels -1 0 1 microwave power w 200 300 400 temperature setting °c 60 70 80 irradiation time min 10 15 20 2.3 lignin removal determination two grams of untreated / treated csw samples were mixed with 15 ml of 72% sulphuric acid in a flask. the mixtures were vigorously stirred at ambient temperature for 2 hours. then, hot distilled water was added to the mixtures to reduce acid concentration up to 4%. the mixture was heated immediately in a water bath at 100 °c. after 4 hours, the csw was filtered and rinsed with hot distilled water to neutralize ph before it was dried at 105 °c until constant weight was achieved. the amounts of lignin removal for all the samples were determined by using equation (1). initial csw sample treated csw sample lignin removal % = 100% initial csw sample −  (1) 2.4 analyses of thermogravimetry and morphology the degradation of the treated csw sample was measured by thermogravimetric analysis (tga) using the hitachi sta-7200 thermal analyser. csw samples (5 g) were placed in alumina pan and heated from ambient temperature up to 1000 °c at a heating rate of 10 °c min-1 under nitrogen flow blanketing. the sample weights were obtained as a function of temperature. the effect of treatment on surface morphology of csw were observed via scanning electron microscopy (sem). the plate with csw samples was and placed at leo 1450 vp sem for the analysis with magnifications of 5000 times. 3. results and discussion 3.1 effect of process parameters on lignin removal box-behnken design (bbd) was used to determine the samples and plot the responses surface. fifteen runs were carried out to obtain the results in table 2. in particular, experimental run#8 (400 w, 70 °c, 20 min) achieved the highest lignin removal, while run#14 (200 w, 70 °c, 10 min) obtained the lowest one. 23 iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 table 2: lignin removal of csw samples using different process parameters run microwave power level temperature level irradiation time level lignin removal (%) experimental lignin removal (%) predicted 1 +1 -1 0 63.07 66.06 2 0 -1 -1 61.79 57.54 3 0 +1 -1 54.47 53.80 4 +1 +1 0 83.01 82.42 5 -1 0 +1 50.19 48.94 6 0 -1 +1 61.43 62.14 7 0 +1 +1 64.17 68.41 8 +1 0 +1 86.34 82.69 9 0 0 0 73.52 69.86 10 -1 +1 0 33.75 30.76 11 -1 -1 0 43.97 44.55 12 +1 0 -1 74.67 75.93 13 0 0 0 67.12 69.86 14 -1 0 -1 32.87 36.52 15 0 0 0 68.94 69.86 the effect of three process variables on lignin residue was generally significant as confirmed by the high r2 value (r = 0.97). the quadratic equation established the level of lignin removal as a function of different microwave power, temperature setting and irradiation time. all the terms regardless of their significance are included in equation (2). after considering the significance of the terms, equation (3) was obtained where the symbols were denoted as a = microwave power, b = temperature setting and c = irradiation time. lignin removal (%) = (2) lignin removal (%) = (3) fig. 1(a) shows the actual experimental data versus predicted data of lignin residue (%) which was generated from the quadratic equation model. the normal probability plot was also presented in fig. 1(b). the plot indicates that the internal studentized residual (different between actual and predicted data) follow a normal distribution and form an approximately linear line. table 3 summarizes the f-test and p-value that were used to assess the significance of the coefficients of the model for respective parameters and the interaction strength among the parameters. p-values that are less than 0.05 indicate significance of model terms, which are shown by a, c, ab, a2 and b2. oppositely, the values greater than 0.1 indicates their insignificance. the "lack of fit f-value" (lof) of 2.61 implies that the lof is not significant relative to the pure error, thus good model, which means the terms are adequate to fit the model. meanwhile, the fitness, r2 and further-refined fitness, adj r2 are 0.970 and 69.86 + 18.29*a + 0.64*b + 4.79*c + 7.54*a*b – 1.41*a*c + 2.51*b*c – 6.68*a2– 7.23*b2 – 2.16*c2 -239.48403 + 0.098481*a + 7.17353*b + 0.88321*c + 7.53792e-003*a*b– 2.83000e-003*a*c + 0.050258*b*c – 6.67972e-004*a2 -0.072318*b2 0.086456*c2 24 iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 0.916, respectively, which indicate that the estimated model that fits the experimental data is reasonable. fig. 1(a) shows the actual experimental data versus predicted data of lignin residue (%) which was generated from the quadratic equation model. the normal probability plot was also presented in fig. 1(b). the plot indicates that the internal studentized residual (different between actual and predicted data) follow a normal distribution and form an approximately linear line. table 3: statistical analysis source of variation sum of squares degree of freedom mean square f value p-value probability model 3461.364 9 384.596 17.970 0.0027a a-microwave power 2676.254 1 2676.254 125.049 < 0.0001a b-temperature 3.302 1 3.302 0.154 0.7106b c-time 183.792 1 183.792 8.588 0.0326a ab 227.281 1 227.281 10.620 0.0225a ac 8.009 1 8.009 0.374 0.5675b bc 25.259 1 25.259 1.180 0.3269b a^2 164.746 1 164.746 7.698 0.0392a b^2 193.104 1 193.104 9.023 0.0300a c^2 17.249 1 17.249 0.806 0.4105b residual 107.008 5 21.402 lack of fit 85.259 3 28.420 2.613 0.2888b pure error 21.750 2 10.875 correction total 3568.373 14 r² 0.970 adj r² 0.916 value of p-value < 0.0500 indicate model terms are significant asignificant bnot significant fig. 1: (a) correlation of normal probability of internal studentized residuals, and (b) actual conversions and values predicted by model. 25 iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 3.2 effect of individual parameters: microwave power, temperature setting and irradiation time on lignin removal the effects of three microwave parameters on the alkaline treatment of csw are shown in fig. 2. the lignin removal was improved significantly by the increase of microwave power from 200 w to 400 w in fig. 2(a). in particular, csw treatment at 80 °c for about 20 minutes increased the lignin removal up to 40% by raising microwave power from 200w to 250w. these results indicate that the microwave power probably help break down the structure of csw. however, upon increase of temperature and time at 200 w microwave power, the lignin removal only slightly changed as shown in fig. 2(b) and (c). upon the increase of temperature from 60 °c to 70 °c, the lignin removal approximately increased up to 14% and reach similar percent removal started from 75°c to 80 °c when csw exposing 400w of irradiation for about 20 minutes. lignin removal on csw at 400 w irradiation and temperature setting about 80°c which varying irradiation time was apparently not effective. based on the observation in fig. 2(c), the percentage of lignin removal only improved 7% when the time was increased from 10 to 15 minutes and as of beyond 15 minutes the lignin removal started to decline as the percentage removing was too small. since the longer irradiation time was less effective for reducing the lignin content, shorter duration would be more economical due to low power consumption [21]. duan et al. [22] had studied the effects of microwave temperature, microwave time, and hydrochloric acid concentration on characteristics and pyrolysis behaviour of lignin. their results show that microwave temperature applied the most significant influence on lignin conversion at 600 w. thus, at high microwave power, temperature is elevated. response surface area reveals the effect of temperature at different microwave power. fig. 2: (a) effect of various individual parameters: microwave power, (b) temperature setting and (c) irradiation time on the lignin removal from csw. one parameter was varied while others are kept constant at their centre point. 26 iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 3.2.1 response surface of lignin removal figure 3 illustrates the plots of interaction between the three microwave parameters on the lignin removal from csw. these plots exhibit correlation between two variables, with one variable fixed at various levels. the increase of lignin removal had been affected dominantly by the increase of microwave power and temperature as compared to irradiation time. these results conform to the finding made by vardhini et al. [23] on banana fibre. among the interaction between respective parameters, the irradiation time was observed to be less effecting in achieving the objective of removing lignin. furthermore, combination of high microwave power and temperature significantly increased the lignin removal. overall, the microwave parameters that maximally removed lignin from the csw under caustic mixture for this study (fig. 2a, b, and c) were 400 w, 76 °c and 19 min where 86.57% lignin was removed. further increase of microwave power and temperature may find an optimum point but the study was continued due to the limitation of our microwave oven. fig. 3: rsm 3d plots of interaction between (a) microwave power and temperature, (b) microwave power and irradiation time and (c) microwave temperature and irradiation time in removing lignin from csw in the presence of naoh. 3.2.2 thermogravimetric analysis (tga) thermogravimetric analyses were performed to observe any change in thermal degradation profile of csw after the treatment. fig. 4 exhibits the tga result of raw csw and treated csw. the weight of both samples firstly dropped until the temperature 120°c due to removal of unbound and bound water [24] or also known as drying period [25]. when heating temperature reached 230 °c, components which are believed [26] hemicellulose and cellulose started to decompose. finally, different dropping trend possessed by raw csw at higher temperature indicating that lignin content in the treated csw has been decreased [26]. after analysis, it was found that the residual weight of raw csw 11% lower compare to raw csw. when the treated fibres were subjected to heat, less chars were generated and resulting in lower amount of residual weight [27]. 3.2.3 scanning electron microscopy (sem) 27 iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 the changes in morphology of csw were observed using scanning electron microscopy (sem). fig. 5 shows the significant effect of microwave of the alkali treatment of csw. the surface of treated csw in fig. 5(b) seems rougher as compared to un-treated csw in fig. 5(a). the result is supported by the study carried out by pua et al. [28] who found similar morphology result when they treated cocoa pod husk (cph) using the same alkaline. during their treatment, hemicellulose component including lignin had been removed and left mesoporous structure on the surface. the rough surface may provide more surface area for adhesion. fig. 4: thermogravimetric analysis result for both csw. fig. 5: sem image with 2000 magnification for (a) untreated csw sample and (b) treated csw sample. 3. conclusion a microwave-assisted alkali treatment process is an alternative approach in quickly breaking the structure and removing lignin from csw for preparation of bio composites. this approach is simple, easy and rapid. the results are successfully modelled using boxbehnken design in the response surface methodology. the maximum removal of lignin up to 86.57% was obtained at the microwave power, temperature and irradiation time of 400 watt, 76 ºc, and 19 min, respectively. removal of components within lignin decomposing temperature and change of csw surface were shown by tga and sem analyses, respectively. residue 19.4% residue 8.3% raw csw treated csw 10 m 10 m 28 iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 acknowledgement the authors are thankful for financial assistance by ministry of higher education, malaysia under research grants number: frgs/1/2016/tk02/ump/02/6 (rdu160126), lembaga koko malaysia, jerantut, pahang, malaysia for material supply, universiti malaysia pahang under the grant number pgrs1903125 and faculty of chemical and process engineering technology laboratory staff, ump for technical support and facilities. references [1] balentic jp, ačkar đ, jokic s, jozinovic a, babic j, miličevic b, ubaric d, pavlovic n. (2018) cocoa shell: a by-product with great potential for wide application. molecules, 23 (6): 1-14. doi: 10.3390/molecules23061404. [2] handojo l, triharyogi h, indarto a. (2019) cocoa bean shell waste as potential raw material for dietary fiber powder. int j recycl org waste agric., 8: 485-491. doi: 10.1007/s40093-019-0271-9 [3] jokić s, gagić t, knez e, ubarić d, kerget m. (2018) separation of active compounds from food by-product (cocoa shell) using subcritical water extraction. molecules, 23(6): 1408. doi: 10.3390/molecules23061408 [4] fioresi f, vieillard j, bargougui r, bouazizi n, fotsing pn, woumfo ed, brun n, mofaddel n, le derf f. (2017) chemical modification of the cocoa shell surface using diazonium salts. journal of colloid and interface science, 494: 92-97. doi: 10.1016/j.jcis.2017.01.069. [5] foon cs, may cy, liang yc, ngan ma, basiron y. (2005) palm biodiesel: gearing towards malaysian biodiesel standards. palm oil developments (pod) 42: 28-34. [6] rojo-poveda o, barbosa-pereira l, zeppa g, stévigny c (2020) cocoa bean shell—a byproduct with nutritional properties and biofunctional potential. nutrients 12(4): 1-29. doi: 10.3390/nu12041123. [7] mohammed l, ansari mnm, pua g, jawaid m, islam ms. (2015) a review on natural fiber reinforced polymer composite and its applications. int j polym sci. 243947. doi: 10.1155/2015/243947 [8] balaji a, karthikeyan b, sundar raj c (2015) bagasse fiber – the future biocomposite material: a review. int. j. chemtech res, 7 (1): 223-233. [9] sood m, dwivedi g. (2018) effect of fiber treatment on flexural properties of natural fiber reinforced composites: a review. egypt j pet., 27(4): 775-783. doi: 10.1016/j.ejpe.2017.11.005 [10] husseinsyah s, marliza mz, selvi e. (2014) biocomposites from polypropylene and corn cob: effect maleic anhydride grafted polypropylene. advances in materials research, 3(3): 129-137. [11] laghari sm. isa mh, abdullah a, laghari aj, saleem h. (2014) microwave individual and combined pre-treatments on lignocellulosic biomasses. iosr j eng., 4(2): 14-28. doi: 10.9790/3021-04261427 [12] nomanbhay sm, hussain r, palanisamy k. (2013) microwave-assisted alkaline pretreatment and microwave assisted enzymatic saccharification of oil palm empty fruit bunch fiber for enhanced fermentable sugar yield. journal of sustainable bioenergy systems, 3(1): 7-17. doi: 10.4236/jsbs.2013.31002. [13] kucharska k, rybarczyk p, hołowacz i, łukajtis r, glinka m, kamiński m. (2018) pretreatment of lignocellulosic materials as substrates for fermentation processes. molecules 23(11): 1-32. doi: 10.3390/molecules23112937. [14] rajesh m, pitchaimani j, rajini n. (2016) free vibration characteristics of banana/sisal natural fibers reinforced hybrid polymer composite beam. procedia engineering, 144: 1055-1059. doi: 10.1016/j.proeng.2016.05.056. 29 iium engineering journal, vol. 22, no. 2, 2021 ahmad et al. https://doi.org/10.31436/iiumej.v22i2.1608 budiyono, wicaksono a, rahmawan a, hawali abdul matin h, gumilang kencana wardani l, djoko kusworo t, sumardiono s. (2017) the effect of pretreatment using sodium hydroxide and acetic acid to biogas production from rice straw waste. matec web conf. doi: 10.1051/matecconf/201710102011 [16] modenbach aa, nokes se. (2014) effects of sodium hydroxide pretreatment on structural components of biomass. transactions of the asabe, 57(4): 1187-1198. doi: 10.13031/trans.57.10046. [17] sombatpraiwan s, junyusen t, treeamnak t, junyusen p. (2019) optimization of microwave‐assisted alkali pretreatment of cassava rhizome for enhanced enzymatic hydrolysis glucose yield. food and energy security (october 2018): e00174. doi: 10.1002/fes3.174. [18] agu os, tabil lg, meda v, dumonceaux t, mupondwav e. (2019) pretreatment of crop residues by application of microwave heating and alkaline solution for biofuel processing: a review. renew resour biorefineries. doi: 10.5772/intechopen.79103 [19] ethaib s, omar r, mazlina m, radiah a, syafiie s, harun my. (2016) effect of microwave-assisted acid or alkali pretreatment on sugar release from dragon fruit foliage. int. food res. j., 23 (suppl): s149-s154 [20] safari a, karimi k, shafiei m. (2017) dilute alkali pretreatment of softwood pine: a biorefinery approach. bioresource technology, 234: 67-76. doi: 10.1016/j.biortech.2017.03.030. [21] lai l, idris a, yusof nm. (2014) lignin extraction from oil palm trunk by microwavealkali technique. malaysian journal of fundamental and applied sciences, 10(2): 59-64. [22] duan d, ruan r, wang y, liu y, dai l, zhao y, zhou y, wu q. (2018) microwaveassisted acid pretreatment of alkali lignin: effect on characteristics and pyrolysis behavior. bioresour. technol., 251: 57-62. doi: 10.1016/j.biortech.2017.12.022 [23] vardhini kjv, murugan r, selvi ct, surjit r. (2016) optimisation of alkali treatment of banana fibres on lignin removal. indian journal of fibre and textile research, 41: 156-160. [24] yang h, yan r, chen h, zheng c, lee dh, liang dt. (2006) in-depth investigation of biomass pyrolysis based on three major components: hemicellulose, cellulose and lignin. energy & fuels, 20(1): 388-393. doi: 10.1021/ef0580117. [25] sushmitha d, suranai s. (2019) microwave-assisted alkali-peroxide treated sawdust for delignification and its characterisation. in: waste valoris. recycl. singapore, springer singapore. pp 527–537. [26] waters cl, janupala rr, mallinson rg, lobban ll. (2017) staged thermal fractionation for segregation of lignin and cellulose pyrolysis products: an experimental study of residence time and temperature effects. journal of analytical and applied pyrolysis, 126: 380-389. doi: 10.1016/j.jaap.2017.05.008. [27] yew bs, muhamad m, mohamed sb, wee fh. (2019) effect of alkaline treatment on structural characterisation, thermal degradation and water absorption ability of coir fibre polymer composites. sains malaysiana, 48(3): 653-659. doi: 10.17576/jsm-2019-4803-19. [28] pua fl, sajab ms, chia ch, zakaria s, rahman ia, salit ms. (2013) alkaline-treated cocoa pod husk as adsorbent for removing methylene blue from aqueous solutions. journal of environmental chemical engineering, 1(3): 460-465. doi: 10.1016/j.jece.2013.06.012. 30 [15] application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 treble search optimizer: a stochastic optimization to overcome both unimodal and multimodal problems purba daru kusuma*and ashri dinimaharawati computer engineering, telkom university, bandung, indonesia * corresponding author: purbodaru@telkomuniversity.ac.id (received: 28 december 2022; accepted: 18 march 2023; published on-line: 4 july 2023) abstract: today, many metaheuristics have used metaphors as their inspiration and baseline for novelty. it makes the novel strategy of these metaheuristics difficult to investigate. moreover, many metaheuristics use high iteration or swarm size in their first introduction. based on this consideration, this work proposes a new metaheuristic free from metaphor. this metaheuristic is called treble search optimizer (tso), representing its main concept in performing three searches performed by each member in each iteration. these three searches consist of two directed searches and one random search. several seeds are generated from each search. then, these searches are compared with each other to find the best seed that might substitute the current corresponding member. tso is also designed to overcome the optimization problem in the low iteration or swarm size circumstance. in this paper, tso is challenged to overcome the 23 classic optimization functions. in this experiment, tso is compared with five shortcoming metaheuristics: slime mould algorithm (sma), hybrid pelican komodo algorithm (hpka), mixed leader-based optimizer (mlbo), golden search optimizer (gso), and total interaction algorithm (tia). the result shows that tso performs effectively and outperforms these five metaheuristics by making better fitness scores than sma, hpka, mlbo, gso, and tia in overcoming 21, 21, 23, 23, and 17 functions, consecutively. the result also indicates that tso performs effectively in overcoming unimodal and multimodal problems in the low iteration and swarm size. abstrak: dewasa ini, terdapat ramai metaheuristik menggunakan metafora sebagai inspirasi dan garis dasar pembaharuan. ini menyebabkan strategi baharu metaheuristik ini susah untuk dikaji. tambahan, ramai metaheuristik menggunakan ulangan berulang atau saiz kerumunan dalam pengenalan mereka. berdasarkan penilaian ini, kajian ini mencadangkan metaheuristk baharu bebas metafora. metaheuristik ini dipanggil pengoptimum pencarian ganda tiga (tso), mewakilkan konsep utama dalam pemilihan tiga pencarian yang dilakukan oleh setiap ahli dalam setiap ulangan. ketiga-tiga carian ini terdiri daripada dua pencarian terarah dan satu pencarian rawak. beberapa benih dihasilkan dalam setiap carian. kemudian, carian ini dibandingkan antara satu sama lain bagi mencari benih terbaik yang mungkin berpotensi menggantikan ahli yang sedang digunakan. tso juga direka bagi mengatasi masalah pengoptimuman dalam ulangan rendah atau lingkungan saiz kerumunan. kajian ini tso dicabar bagi mengatasi 23 fungsi pengoptimuman klasik. eksperimen ini tso dibandingkan dengan lima kekurangan metaheuristik: algoritma acuan lendir (sma), algorithma hibrid komodo burung undan (hpka), pengoptimum campuran berdasarkan-ketua (mlbo), pengoptimuman carian emas (gso), dan algoritma jumlah interaksi (tia). dapatan kajian menunjukkan tso berkesan menghasilkan dan lebih baik daripada kelima-lima metaheuristik dengan menghasilkan pemarkahan padanan terbaik berbanding sma, hpka, mlbo, gso, dan tia dalam mengatasi fungsi 21, 21, 23, 23, dan 17, secara 86 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 berurutan. dapatan kajian juga menunjukkan tso turut berperanan efektif dalam mengatasi masalah modal tunggal dan modal ganda dalam iterasi rendah dan saiz kerumunan. keywords: optimization; metaheuristic; swarm intelligence; unimodal; multimodal 1. introduction metaheuristics is a popular tool extensively used in various optimization problems. many optimization studies from a wide range of subjects use metaheuristics, such as in smart farming [1], path planning for autonomous robots [2], traffic forecasting [3], power systems [4], electric vehicle charge scheduling [5], and so on. today, hundreds of metaheuristics exist and are ready to be used in any optimization problem. this circumstance becomes one of several reasons why metaheuristic is so popular. moreover, there are optimization studies that hybridize a metaheuristic with other methods, whether they are metaheuristics or exact methods. because metaheuristics are flexible in overcoming various optimization problems and easy to modify, there are many studies on hybridizing metaheuristics. in general, this massive development of metaheuristics comes from two reasons. the first reason is that various things can be used as inspiration for searching mechanisms, especially nature. many metaheuristics use nature, especially animal behavior, as their inspiration and transform it into an optimization or searching strategy. several shortcoming metaheuristics that use animal behavior as their inspiration, such as the komodo mlipir algorithm (kma) [6], northern goshawk optimizer (ngo) [7], marine predator algorithm (mpa) [8], hybrid pelican komodo algorithm (hpka) [9], coati optimization algorithm (coa) [10], cheetah optimizer (co) [11], chameleon swarm algorithm (csa) [12], and so on. several metaheuristics used the term leader to represent the reference during the directed search, such as mixed leader-based optimizer (mlbo) [13], random selected leader-based optimizer (rslbo) [14], hybrid leader-based optimizer (hlbo) [15], and so on. meanwhile, several metaheuristics declared their main concept or strategy for their name rather than using metaphors, such as total interaction algorithm (tia) [16], golden search optimizer (gso) [17], average and subtraction-based optimizer (asbo) [18], and so on. the second reason is that no metaheuristic is suitable or superior in overcoming any optimization problem, as stated in the no-free-lunch theory. each strategy has its strengths and weaknesses. in other words, no metaheuristic can accommodate all strategies. there are several critiques following the massive development of new metaheuristics. first, many metaphor-based metaheuristics use their metaphor as a novelty or contribution. however, through the investigation of the algorithm and mathematical model, their method is slightly different from the previous ones [19]. second, many studies proposing new metaheuristics exploited their ability to outperform the previous metaheuristics rather than highlighted their distinct mechanics in a clear explanation [19]. besides, the performance of many metaheuristics is investigated in the high iteration or swarm in their first appearance. moreover, these circumstances need to be clarified in several studies proposing a new metaheuristic. for example, ngo uses the behavior of the northern goshawk as metaphor and the maximum iteration is set to 1,000 during the evaluation [7]. the maximum iteration is also set to 1,000 in the first introduction of asbo [18]. in the first introduction of gso, the maximum iteration is set to 1,000 while the swarm size is set to 30 [17]. unfortunately, the performance of these metaheuristics has not been investigated in the low swarm and low iteration circumstance. 87 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 the objective of this work is to promote a new simple and metaphor-free swarmbased metaheuristic that works effectively with a low iteration number and swarm size. this metaheuristic is called a treble search optimizer (tso) which comes from the three searches performed in the algorithm. these searches include two directed searches and one random search. the global optimal member and one randomly selected member become the references in these two directed searches. meanwhile, the random search focuses on finding a better member near or around the corresponding member. in tso, each member performs all these three searches in every iteration, which means tso does not implement segregation of roles. one best seed is selected in every search, so three seeds from three searches are generated by a corresponding member in every search. then, the best seed becomes the final seed as a substitute for the current corresponding member. based on this explanation, below are the novelties and contributions of this work. 1) this work promotes a novel swarm-based metaheuristic that is free from using metaphors, named treble search optimizer (tso). 2) tso was designed to overcome the optimization problem in the low iteration and swarm circumstance. 3) tso performs three searches (two directed searches and one random search) where several seeds are generated from each search. 4) the performance of tso is investigated using 23 classic functions to overcome. 2. related works investigating the existing metaheuristics is the first and main critical step in proposing a new metaheuristic. within this investigation, it is very important to highlight the distinction, novelty, or uniqueness of the metaheuristic. this step is also important because there are hundreds of metaheuristics already in existence. proposing a new metaheuristic without investigating the existing ones, especially the shortcoming ones, may end with proposing a metaheuristic like the existing ones. this investigation is also important because a new metaheuristic can be developed by modifying or hybridizing several existing metaheuristics. investigating a metaheuristic can be performed by classifying the metaheuristic based on several parameters. first, a metaheuristic should be classified as whether it uses metaphors. as mentioned, a metaphor-based metaheuristic should be rigorously investigated to address its distinct approach by abstracting the metaphor. second, the algorithm and mathematical model following the algorithm should also be reviewed. after that, several parameters can be used to classify the metaheuristic, such as the number of searches, segregation of roles, and so on. in many shortcoming metaheuristics, implementing multiple search strategies has become more popular rather than performing a single search strategy, as shown in table 1. the main reason is that there is not any single search that can guarantee finding the optimal member. using the global best member or the best member among the swarm becomes the most popular option so that this member is used in many swarm-based metaheuristics, such as kma [6], hpka [9], asbo [18], and so on. some other metaheuristics use local best member for their reference, such as in mpa [8], gso [17], and so on. meanwhile, there are also metaheuristics using the other members within the swarm as their reference, such as in tia [16], ngo [7], and so on. even moving toward 88 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 the best member may guide the entire swarm toward the local optimal entrapment because the global best member lies somewhere else in the search space. table 1: list of shortcoming metaheuristics no metaheuristic metaphor segregation of roles number of searches maximum iteration swarm size 1 kma [6] komodo dragon yes 4 5,000 evaluations 5, 20-200 2 ngo [7] northern goshawk no 2 1,000 20-80 3 hpka [9] pelican and komodo dragon yes 4 200 20 4 mpa [8] marine predator yes 5 500 50 5 co [11] cheetah yes 3 12x105 evaluations 6 6 coa [10] coati no 3 200, 1,000 n/a 7 hlbo [15] leader no 2 1,000 n/a 8 mlbo [13] leader no 1 n/a n/a 9 rslbo [14] leader no 1 n/a n/a 10 asbo [18] no 3 1,000 20-80 11 gso [17] no 1 1,000 30 12 tia [16] no 1 50 10 13 this work no 3 40 5 the list of swarm-based shortcoming metaheuristics is displayed in table 1. table 1 consists of five pieces of information related to the corresponding metaheuristics. the first information is the metaphor used in the metaheuristic. the second information is whether the corresponding metaheuristic implements the segregation of roles. the third information is the number of searches implemented in the corresponding metaheuristic. the fourth information is the maximum iteration set in the first appearance of the corresponding metaheuristic. the fifth information is the swarm size set in the first appearance of the corresponding metaheuristic. there are 14 things that could be improved in metaheuristics in table 1. the last row of table 1 presents the attributes of tso to give a clear view regarding the novelty and position of this work. table 1 presents many areas for improvement in the metaheuristic's use of metaphors, especially animals. some metaheuristics use the term leader while others do not use a metaphor. most metaheuristics do not perform segregation of roles so that in these metaheuristics, all members perform all searches adopted in the corresponding metaheuristic. besides, most shortcoming metaheuristics perform multiple searches rather than a single search. in their first appearance, many metaheuristics are challenged to overcome optimization problems in the high maximum iteration or swarm size. based on this explanation, the opportunity to propose a new swarm-based metaheuristic that is metaphor-free implements multiple searches and is challenged to overcome problems in the low maximum iteration and low swarm size is still open. 3. model tso is built based on two approaches. first, tso performs three searches where each output will be compared to find the best output. second, there are multiple seeds generated in every search so that the best seed among these seeds will be chosen to compete with other selected seeds from other searches mentioned in the first approach. 89 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 algorithm 1: treble search optimizer (tso) 1 output: sb 2 for all s in s 3 initialize s using eq. (1) 4 update sb using eq. (2) 5 end for 6 for t=1 to tmax 7 for all s in s 8 select ss using eq. (3) 9 for j=1 to nc 10 generate c1, c2, c3 using eq. (4), eq. (5), eq. (6) 11 end for 12 select cs1, cs2, cs3 using eq. (7), eq. (8), eq. (9) 13 select cf using eq. (10) 14 update s using eq. (11) 15 update sb using eq. (2) 16 end for 17 end for c1 first search seed c2 second search seed c3 third search seed c1 set of first search seed c2 set of second search seed c3 set of third search seed cs1 selected seed among first search seeds cs1 selected seed among second search seeds cs3 selected seed among third search seeds cf final seed f objective function nc number of seeds s member s set of members sb global best member ss selected member su upper boundary sl lower boundary t iteration tmax maximum iteration u uniform random ur real uniform random number ui integer random number in tso, each corresponding member performs three searches which are two directed searches and one random search. the first directed search generates several seeds along the way, the corresponding member toward the global best member. the second directed search generates seeds relative to a selected random member within the swarm. in the second directed search, these seeds may be in the direction of the corresponding member toward the selected member or away from the selected member. this choice depends on the quality of the corresponding member and the randomly selected member. the first direction occurs if this randomly selected member is better than the corresponding member. otherwise, the second direction takes place. in the third search, several seeds are generated around the corresponding member. as a metaheuristic, tso consists of two phases: initialization and iteration. in the initialization, all members are uniformly randomized within the search space. meanwhile, the iteration phase represents the improvement where three searches are performed. at the end of the process, the global best member becomes the final member, i.e., the algorithm 90 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 output. the best seed is then chosen in every search. it means that there are now three selected seeds from three searches. then, these seeds will compete among each other so that the best seed among these three seeds becomes the final seed. this final seed is then compared with the corresponding member. this final seed substitutes the corresponding member only if this final seed is better than the current corresponding member. otherwise, the corresponding member remains static at the end of this iteration. this concept is then transformed into an algorithm and mathematical model. the mathematical model is displayed in eq. (1) to eq. (11). the formalization of tso is displayed in algorithm 1. below are annotations used in algorithm 1 and the following mathematical model. the visualization of tso is presented in fig. 1. fig. 1: flowchart of treble search optimizer. 𝑠 = 𝑈𝑟(𝑠𝑙, 𝑠𝑢) (1) 𝑠𝑏′ = { 𝑠, 𝑓(𝑠) < 𝑓(𝑠𝑏) 𝑠𝑏,𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 (2) 𝑠𝑠 = 𝑈(𝑆) (3) 𝑐1 = 𝑠 + 𝑈𝑟(0,1)(𝑠𝑏 − 𝑈𝑖(1,2)𝑠) (4) 𝑐2 = { 𝑠 + 𝑈𝑟(0,1)(𝑠𝑠 − 𝑈𝑖(1,2)𝑠) 𝑠 + 𝑈𝑟(0,1)(𝑠 − 𝑈𝑖(1,2)𝑠𝑠) (5) 𝑐3 = 𝑠 + 0.1𝑈𝑟(−1,1)(𝑠𝑢 − 𝑠𝑙) (6) 𝑐𝑠1 = 𝑐1 ∈ 𝐶1 ∧ 𝑚𝑖𝑛(𝑓(𝑐1)) (7) 91 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 𝑐𝑠2 = 𝑐2 ∈ 𝐶2 ∧ 𝑚𝑖𝑛(𝑓(𝑐2)) (8) 𝑐𝑠3 = 𝑐3 ∈ 𝐶3 ∧ 𝑚𝑖𝑛(𝑓(𝑐3)) (9) 𝑐𝑓 = 𝑐, 𝑚𝑖𝑛(𝑐1, 𝑐2,𝑐3) (10) 𝑠′ = { 𝑐𝑓, 𝑓(𝑐𝑓) < 𝑓(𝑠) 𝑠, 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 (11) below is the detailed explanation of eq. (1) to eq. (11). the global best member becomes the final solution. lines 2 to 5 represent the initialization phase. lines 6 to 17 represent the iteration phase. equation (1) describes that the initial member is uniformly randomized between the lower and upper boundary, i.e., search space. equation (2) describes that the corresponding member substitutes the current global best member if this corresponding member is better than the current global best member. equation (3) describes randomly selecting a member among the set of members. equation (4) describes that the seed of the first search is generated along the way from the corresponding member toward the global best member. equation (5) describes that the seed of the second search is generated based on the relation between the corresponding member and the randomly selected member. equation (6) describes that the seed of the third search is generated near the corresponding member. equations (7) to eq. (9) describes that the best seed is selected from among seeds in every search. equation (10) describes that the best seed among these three selected seeds becomes the final seed. equation (11) describes that the final seed substitutes the current corresponding member if this final seed is better than the current corresponding member. 4. results this section presents the experiment performed to evaluate the performance of tso and its result. there are two experiments regarding this work. the first experiment is performed to evaluate the performance of tso in overcoming a set of benchmark functions and the performance comparison between tso and the sparing metaheuristics. the second experiment is performed to evaluate the hyperparameter of tso. the 23 classic functions are chosen as the benchmark functions. these 23 classic functions are chosen based on several reasons. the first reason is that these functions represent various problems with specific circumstances and challenges. the second reason is that these functions are very popular, so they are chosen in many studies proposing a new metaheuristic. these functions can be categorized into three groups: seven high-dimension unimodal functions, six high-dimension multimodal functions, and ten fixed-dimension multimodal functions. these functions also represent problems with various search spaces, from narrow to large ones. in the first experiment, tso is compared with five shortcoming metaheuristics: sma, hpka, mlbo, gso, and tia. these metaheuristics are chosen mainly because they are new. in their first appearance, these metaheuristics outperformed many previous metaheuristics. sma outperformed many metaheuristics, such as the whale optimization algorithm (woa), moth-flame optimizer (mfo), grey wolf optimizer (gwo), bat algorithm (ba), sine cosine algorithm (sca), particle swarm optimization (pso), firefly 92 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 algorithm (fa), multi-verse optimizer (mvo), salp swarm algorithm (ssa), ant lion optimizer (alo), and differential evolution (de) [20]. hpka outperformed four metaheuristics: gwo, mpa, kma, and poa [9]. mlbo outperforms several metaheuristics, such as pso, genetic algorithm (ga), teaching-learning based optimizer (tlbo), gwo, emperor penguin optimizer (epoa), and so on [13]. gso outperformed four metaheuristics: gravitational search algorithm (gsa), sca, tunicate swarm algorithm (tsa), and gwo [17]. tia outperformed five sparing metaheuristics: pso, marine predator algorithm (mpa), gso, directed pelican algorithm (gpa), and driving trainingbased optimizer (dtbo) [16]. table 2: the simulation result of the first experiment function average fitness score sma hpka mlbo gso tia tso 1 6.6663x104 6.2570x104 2.2305x104 6.0029x104 0.0000 0.0000 2 0.0000 0.0000 1.1222x1051 7.5089x1069 1.7930x1055 0.0000 3 2.1289x105 2.0975x105 5.7327x104 1.7531x105 0.0316 0.0000 4 8.2362x101 7.9015x101 4.7480x101 5.6846x101 0.0000 0.0000 5 1.7908x108 1.9984x108 1.9085x107 1.2710x108 4.8879x101 4.8803x101 6 6.9099x104 6.9444x104 2.1638x104 5.9789x104 9.4253 8.2081 7 1.6824x102 1.3522x102 1.6547x101 9.2918x101 0.0122 0.0021 8 -6.2418x103 -5.9791x103 -3.9934x103 -4.3938x103 -2.3210x103 -4.6397x103 9 5.4539x102 5.6253x102 4.4459x102 5.1443x102 0.0000 0.0000 10 1.9750x101 1.9947x101 1.6483x101 1.9463x101 0.0000 0.0000 11 6.2192x102 7.1348x102 1.9505x102 5.3193x102 0.0087 0.0000 12 4.6092x108 3.3887x108 8.1216x106 2.2263x108 0.8217 0.6182 13 1.1149x109 8.5180x108 5.0042x107 4.7534x108 3.0902 2.8085 14 1.1963x101 1.3565x101 7.6193 1.1118x101 7.5131 3.7733 15 0.0106 0.0111 0.0141 0.0277 0.0046 0.0006 16 -0.8973 -0.8722 -0.9689 -0.9862 -1.0219 -1.0314 17 0.9389 0.7064 0.4966 0.8170 1.7409 0.3986 18 8.0109x101 2.2714x101 9.8071 2.6717x101 1.7821x101 3.0137 19 -0.0455 -0.0387 -0.0486 -0.0193 -0.0495 -0.0495 20 -2.7549 -2.7309 -2.8287 -2.5539 -2.3823 -3.2980 21 -2.9231 -4.0803 -2.8597 -2.7178 -4.1103 -8.2464 22 -3.7697 -3.0703 -2.8335 -3.3707 -3.4117 -7.6623 23 -3.5599 -2.8837 -2.3017 -3.1063 -2.5551 -8.8215 in the first experiment, several parameters are set based on a certain value. the swarm size is set to 5, which represents the low swarm. the maximum iteration is set to 40, which represents low iteration. the dimension is set to 50, which represents a highdimension problem. in hpka, all searches have equal opportunity. the result is displayed in table 2, while the superiority of the tso compared with the other metaheuristics based on the group of functions is displayed in table 3. in table 2, the best score is written in bold font. meanwhile, the floating-point accuracy is set to 10-4 so that a score less than 104 is rounded to 0. table 2 indicates the excellent performance of tso in terms of finding the optimal global member and producing the best scores among the metaheuristics. tso could find the optimal global member of seven functions: sphere, schwefel 2.22, schwefel 1.2, schwefel 2.21, rastrigin, ackley, and griewank. meanwhile, tso could also find the 93 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 member near the global optimal member of three functions: kowalik, six hump camel, and branin. tso also performed the best of 22 functions out of 23 functions. however, several metaheuristics also performed the same value in six functions. these six functions are sphere, schwefel 2.22, schwefel 2.21, rastrigin, ackley, and hartman 3. tia performed the same value in five functions (sphere, schwefel 2.21, rastrigin, ackley, and hartman 3), while sma and hpka performed the same value in schwefel 2.22. table 3 indicates the superiority of tso among other competing metaheuristics in all groups of functions. tso was better than sma, hpka, mlbo, gso, and tia in overcoming 21, 21, 23, 23, and 17 functions, respectively. it means that tso was superior to mlbo and gso. tso was superior to sma and hpka. meanwhile, tso was still superior to tia, although tia is the most challenging metaheuristic to beat. this result indicates the superiority of tso in overcoming all three kinds of problems: highdimension unimodal problems, high-dimension multimodal problems, and fixeddimension multimodal problems. table 3: tso superiority among other metaheuristics based on group of functions group number of functions sma hpka mlbo gso tia 1 6 6 7 7 4 2 5 5 6 6 4 3 10 10 10 10 9 total 21 21 23 23 17 the second experiment was performed to evaluate the sensitivity or hyperparameter. there were three parameters evaluated in this experiment: maximum iteration, swarm size, and the number of seeds. this experiment was performed by implementing tso to overcome 23 classic functions with several values of these parameters. the maximum iteration in the first sub-experiment was set at 10, 20, and 30. the result is displayed in table 4. in the second sub-experiment, the swarm size was set at 10, 15, and 20. the result is displayed in table 5. in the third experiment, the number of seeds was set to 3, 6, and 9. the result is displayed in table 6. table 4 indicates that all functions have achieved an acceptable member in the low iteration. in almost all functions, the result produced by tso in the low iteration circumstance was still competitive compared with the result produced by other metaheuristics, as seen in table 2. moreover, convergence was achieved in the early iteration in nine functions (schwefel 2.22, schwefel, penalized, penalized 2, shekel foxholes, six hump camel, branin, hartman 3, and hatman 6). among these nine functions, one function was a high dimension unimodal function, two functions were highdimension multimodal functions, and six functions were fixed-dimension multimodal functions. table 5 indicates that the increase in swarm size after five members is insignificant in improving the member quality in almost all functions. stagnancy occurred in nine functions because the optimal global member was achieved. stagnancy also occurred in five functions, although a globally optimal member had yet to be achieved. less significant improvement occurred in nine functions. table 4: performance of tso with several values of maximum iteration 94 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 function average fitness score tmax = 10 tmax = 20 tmax = 30 1 2.6467 0.0001 0.0000 2 0.0000 0.0000 0.0000 3 7.7478x102 1.3350 0.0034 4 1.8470 0.0259 0.0003 5 1.3821x102 4.8819x101 4.8819x101 6 1.1822x101 8.0214 8.1741 7 0.0193 0.0043 0.0019 8 -4.0668x103 -4.2352x103 -4.6166x103 9 3.5869x101 0.0024 0.0000 10 0.7767 0.0020 0.0000 11 0.5366 0.0060 0.0035 12 0.7894 0.6502 0.6806 13 3.2482 2.9358 2.8653 14 4.4341 4.9429 3.6936 15 0.0017 0.0006 0.0005 16 -1.0304 -1.0309 -1.0308 17 0.3989 0.3984 0.3984 18 6.6955 3.0042 3.0079 19 -0.0495 -0.0495 -0.0495 20 -3.2050 -3.239 -3.2961 21 -5.7886 -7.2599 -7.9212 22 -5.8045 -7.1234 -7.5447 23 -6.1753 -6.9030 -7.8198 table 5: performance of tso with several values of swarm size function average fitness score n(x) = 10 n(x) = 15 n(x) = 20 1 0.0000 0.0000 0.0000 2 0.0000 0.0000 0.0000 3 0.0000 0.0000 0.0000 4 0.0000 0.0000 0.0000 5 4.8717x101 4.8717x101 4.8713x101 6 6.8744 6.4879 6.2007 7 0.0007 0.0005 0.0004 8 -5.7240x103 -5.2949x103 -5.3398x103 9 0.0000 0.0000 0.0000 10 0.0000 0.0000 0.0000 11 0.0000 0.0000 0.0000 12 0.4685 0.4531 0.3879 13 2.6890 2.5259 2.4414 14 2.4780 1.1478 1.0927 15 0.0014 0.0004 0.0004 16 -1.0316 -1.0316 -1.0316 17 0.3981 0.3981 0.3981 18 3.0015 3.0000 3.0000 19 -0.0495 -0.0495 -0.0495 20 -3.3071 -3.3038 -3.3137 21 -9.2349 -9.4629 -9.6812 22 -9.6167 -1.0084x101 -1.0193x101 23 -9.1412 -1.0034x101 -1.0293x101 table 6: performance of tso with several values of number of seeds 95 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 function average fitness score n(c) = 3 n(c) = 6 n(c) = 9 1 0.0000 0.0000 0.0000 2 0.0000 0.0000 0.0000 3 0.0005 0.0000 0.0000 4 0.0000 0.0000 0.0000 5 4.8850x101 4.8775x101 4.8775x101 6 8.5787 7.7692 7.4645 7 0.0033 0.0012 0.0005 8 -4.4692x103 -4.6142x103 -4.8921x103 9 0.0000 0.0000 0.0000 10 0.0000 0.0000 0.0000 11 0.0000 0.0000 0.0000 12 0.7405 0.6131 0.5368 13 2.9124 2.7398 2.7218 14 4.7629 5.9951 3.5355 15 0.0023 0.0015 0.0013 16 -1.0310 -1.0310 -1.0316 17 0.3987 0.3986 0.3982 18 3.0053 3.0007 3.0009 19 -0.0495 -0.0495 -0.0495 20 -3.2625 -3.2822 -3.2983 21 -8.0977 -6.3341 -8.3292 22 -7.0566 -8.3640 -7.9018 23 -6.5042 -8.6724 -8.5935 table 6 indicates that the increase in the number of seeds was less sensitive to the improvement of the performance of tso. the average fitness score tended to fluctuate or remain static in almost all problems. meanwhile, the less significant improvement occurred in six functions (penalized, shekel foxholes, branin, quartic, shekel 5, shekel 7, and shekel 10). 5. discussion this section presents an in-depth evaluation of the relation between the result and the findings. this discourse is divided into four parts. the first part is a discourse related to the performance of the tso and the linkage with the chosen exploitation-exploitation strategy. the second part is a discourse regarding the hyperparameter evaluation. the third part is a discourse related to the algorithm complexity of tso. the fourth part is a discourse related to the limitation of this work, especially the metaheuristic. the first discourse is related to the evaluation of the experiment result. tso performed effectively in overcoming the 23 classic functions. its performance was superior in all groups of these functions. based on the superior result in overcoming unimodal functions, tso performed exploitation effectively. moreover, tso was also good at performing exploration based on the superior result in overcoming multimodal functions, whether they were high-dimension multimodal functions or fixed-dimension multimodal functions. the performance gap between tso and the sparing metaheuristics was also broad, especially in overcoming high-dimension functions. this gap needs to be more comprehensive in overcoming fixed-dimension functions. 96 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 the superiority of tso proves that the strategy implemented in tso is better than the strategy implemented in the sparing metaheuristics. first, implementing multiple searches is proven better than a single search because each has its strengths and weaknesses. second, each member needs to perform multiple searches in every iteration. third, the tournament-based approach was better than the sequential-based approach. the second discourse is related to the sensitivity analysis of the hyperparameter. this work evaluated three parameters: maximum iteration, swarm size, and the number of seeds. in general, the increase in maximum iteration improves the quality of the member. in the low maximum iteration, increasing maximum iteration improves the member mostly in overcoming the unimodal functions. on the other hand, the increase in the maximum iteration is less significant in improving the quality of the member. on the contrary, the swarm size does not improve the member quality in overcoming unimodal functions. the increase in swarm size improves the member quality, mostly in overcoming the multimodal functions. however, this improvement is also insignificant because the nearoptimal or optimal global member has been found in the low maximum iteration and low swarm size circumstances. increasing the number of seeds improves the quality of members in overcoming several functions. these functions can be found in both unimodal and multimodal functions. however, the improvement could be more significant. the third discourse is related to algorithm complexity. the complexity of tso can be displayed as o(3tmax.n(x).n(c)). based on this presentation, the complexity is linear to one of three parameters: the maximum iteration, swarm size, or the number of seeds. fortunately, the computational process of tso is still competitive because the acceptable member has reached a low maximum iteration, low swarm size, and a low number of seeds. the fourth discourse is related to the limitation of the algorithm and this work. there are several limitations regarding this algorithm and this work. first, tso still needs to find the final member, the optimal global member or near-optimal member in overcoming six functions. these six functions are two high-dimension unimodal functions (rosenbrock and step), three high-dimension multimodal functions (schwefel, penalized, and penalized 2), and one fixed-dimension multimodal function (hartman 3). this fact strengthens the no-free-lunch theory. although tso is superior among the sparing metaheuristics, there are still problems where tso needs to find the optimal global member. meanwhile, there is an opportunity to find the optimal global member for these functions by setting the system to high maximum iteration and swarm size. however, this scenario was not performed in this work as its focus is on the low maximum iteration and low swarm size. this limitation can be used as a baseline to improve the current form of tso so that the improved version can overcome these six functions in future studies. this work has a limitation on implementing tso in overcoming theoretical optimization problems only. in some studies, the proposed metaheuristic has been challenged to overcome the theoretical problems only, while in other studies, the metaheuristic has also been challenged to overcome practical problems. 6. conclusion the development and evaluation of a new swarm-based metaheuristic, treble search optimizer (tso) has been introduced in this paper. referring to its name, the central concept of tso is performing three searches: two directed searches and one random search. each member in every iteration performs these three searches. several seeds are generated from each search. the experiment result presents that tso performed 97 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 effectively in overcoming 23 classical functions. tso outperformed five shortcoming metaheuristics chosen as the sparing metaheuristics in this work. tso was better than sma, hpka, mlbo, gso, and tia in overcoming 21, 21, 23, 23, and 17 functions, respectively. tso could find the optimal global member of seven functions in low maximum iteration and low swarm size circumstances. when the swarm size was set to moderate, there were three more functions where tso can find their optimal global member. tso also performed the best member of 22 functions out of 23 functions. future studies can be conducted in several ways. improvement is still open for tso, especially in finding the optimal global member of the six functions that tso still needs to find in this work. more theoretical experiments should be performed to enrich the investigation of the strengths and weaknesses of tso. moreover, future studies can also be performed by implementing tso to overcome many kinds of practical optimization problems. acknowledgment this work was financially supported by telkom university, indonesia. references [1] ramezanpour mr, farajpour m. (2022) application of artificial neural networks and genetic algorithm to predict and optimize greenhouse banana fruit yield through nitrogen, potassium and magnesium. plos one, 17(2): e0264040. https://doi.org/10.1371/journal.pone.0264040. [2] thammachantuek i, ketcham m. (2022) path planning for autonomous mobile robots using multi-objective evolutionary particle swarm optimization. plos one, 17(8): e0271924. https://doi.org/10.1371/journal.pone.0271924. [3] sivakumar r, angayarkanni sa, ramana ryv, sadiq as. (2022) traffic flow forecasting using natural selection based hybrid bald eagle search-grey wolf optimization algorithm. plos one, 17(9): e0275104. https://doi.org/10.1371/journal.pone.0275104. [4] hoballah a, azmy am. (2023) constrained economic dispatch following generation outage for hot spinning reserve allocation using hybrid grey wolf optimizer. alexandria engineering journal, 62: 169-180. https://doi.org/10.1016/j.aej.2022.07.033. [5] sowmya r, sankaranarayanan v. (2022) optimal scheduling of electric vehicle charging at geographically dispersed charging stations with multiple charging piles. international journal of intelligent transportation systems research, 20: 672-695. https://doi.org/10.1007/s13177022-00316-2. [6] suyanto, ariyanto aa, ariyanto af. (2022) komodo mlipir algorithm. applied soft computing, 114: 108043. https://doi.org/10.1016/j.asoc.2021.108043. [7] dehghani m, hubalovsky s, trojovsky p. (2021) nortehrn goshawk optimization: a new swarm-based algorithm for solving optimization problems. ieee access, 9: 162059-162080. doi: 10.1109/access.2021.3133286. [8] faramarzi a, heidarinejad m, mirjalili s, gandomi ah. (2020) marine predators algorithm: a nature-inspired metaheuristic. expert systems with applications, 152: 113377. https://doi.org/10.1016/j.eswa.2020.113377. [9] kusuma pd, dinimaharawati a. (2022) hybrid pelican komodo algorithm. international journal of advanced computer science and applications, 13(6): 46-55. https://dx.doi.org/10.14569/ijacsa.2022.0130607. [10] dehghani m, montazeri z, trojovska e, trojovsky p. (2023) coati optimization algorithm: a new bio-inspired metaheuristic algorithm for solving optimization problems. knowledgebased systems, 259: 110011. https://doi.org/10.1016/j.knosys.2022.110011. 98 iium engineering journal, vol. 24, no. 2, 2023 kusuma and dinimaharawati https://doi.org/10.31436/iiumej.v24i2.2700 [11] akbari ma, zare m, azizipanah-abarghooee r, mirjalili s, deriche m. (2022) the cheetah optimizer: a nature-inspired metaheuristic algorithm for large-scale optimization problems. scientific reports, 12: 10953. https://doi.org/10.1038/s41598-022-14338-z. [12] braik ms. (2021) chameleon swarm algorithm: a bio-inspired optimizer for solving engineering design problems. expert systems with applications, 174: 114685. https://doi.org/10.1016/j.eswa.2021.114685. [13] zeidabadi fa, doumari sa, dehghani m, malik op. (2021) mlbo: mixed leader based optimizer for solving optimization problems. international journal of intelligent engineering and systems, 14(4): 472-479. doi: 10.22266/ijies2021.0831.41. [14] zeidabadi fa, dehghani m, malik op. (2021) rslbo: random selected leader based optimizer. international journal of intelligent engineering and systems, 14(5): 529-538. doi: 10.22266/ijies2021.1031.46. [15] dehghani m, trojovsky p. (2022) hybrid leader based optimization: a new stochastic optimization algorithm for overcoming optimization applications. scientific reports, 12: 5549. https://doi.org/10.1038/s41598-022-09514-0. [16] kusuma pd, novianty a. (2023) total interaction algorithm: a metaheuristic in which each agent interacts with all other agents. international journal of intelligent engineering and systems, 16(1): 224-234. doi: 10.22266/ijies2023.0228.20. [17] noroozi m, mohammadi h, efatinasab e, lashgari a, eslami m, khan b. (2022) golden search optimization algorithm. ieee access, 10: 37515-37532. https://doi.org/10.1109/access.2022.3162853. [18] dehghani m, hubalovsky s, trojovsky p. (2022) a new optimization algorithm based on average and subtraction of the best and worst members of the population for solving various optimization problems. peerj computer science, 8: e910. https://doi.org/10.7717/peerj-cs.910. [19] swan j, adriaensen s, brownlee aei, hammond k, johnson cg, kheiri a, krawiec f, merelo jj, minku ll, ozcan e, pappa gl, garcia-sanchez p, sorensen k, vob s, wagner m, white dr. (2022) metaheuristics in the large. european journal of operational research, 297(2): 393-406. https://doi.org/10.1016/j.ejor.2021.05.042. [20] li s, chen h, wang m, heidari aa, mirjalili s. (2020) slime mould algorithm: a new method for stochastic optimization. future generation computer systems, 111: 300-323. https://doi.org/10.1016/j.future.2020.03.055. 99 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 91 power quality improvement with cascaded multilevel converter based statcom mahdi heidari1*, abdonnabi kovsarian2 and s. ghodratollah seifossadat2 1 department of electrical engineering, university of zabol, zabol, iran 2 department of electrical engineering, shahid chamran university of ahvaz, ahvaz, iran. * corresponding author: m.heidari@uoz.ac.ir (received: 1st oct 2017; accepted: 22nd feb 2018; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.873 abstract: static synchronous compensators (statcom) are increasingly implemented in power systems. moreover, cascaded multilevel converters (cmc) are more frequently taken in consideration because of their strong capabilities. in this paper, the design and simulation of a multilevel statcom for voltage regulation of load is presented. design of the passive components, active and reactive power controller, and balancer of capacitor voltage are parts of proposed system design. the pole placement method was used for the design of the controller. simulation results with matlab/simulink show good performance of voltage regulation in full load and dynamic load conditions. abstrak: penyelaras pengimbang statik (statcom) semakin dilaksanakan dalam sistem kuasa. selain itu, penukar pelbagai aras tingkatan (cmc) lebih diutamakan kerana mempunyai banyak kelebihan. dalam kajian ini, reka bentuk dan simulasi bertingkat statcom bagi pelbagai voltan beban dibentangkan. reka bentuk komponen pasif, penyelenggara kuasa aktif dan reaktif dan pengimbang voltan kapasitor adalah sebahagian daripada sistem yang dicadangkan. bagi reka bentuk penyelenggara, kaedah penempatan titik telah digunakan. hasil simulasi melalui matlab/simulink menunjukkan keputusan yang baik pada regulasi voltan pada beban penuh dan pada keadaan beban dinamik. keywords: cascaded multilevel converter; statcom; power quality; voltage regulation; pole placement 1. introduction in a deregulated power system, market and business are key factors in the design and operation of the network and lead to effective and efficient operation of the power system at all three levels: generation, transmission, and distribution. therefore, power quality is of great importance, more so than any other issue, reactive dynamic power control is especially important in urban and local areas. flexible ac transmission systems (facts) are ac transmission systems combined with power electronics-based controllers that perform control of load flow and increase stability by controlling one or more system parameters such as voltage, phase angle, and impedance [1]. among the facts controllers, parallel controllers, due to cost issues, iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 92 have shown their capabilities in a wide range of issues from transmission to distribution levels [2]. these controllers increase the power transmitted from transmission lines and improve the voltage profile along a line with an appropriate control of reactive power. in addition, parallel controllers can improve transient stability and cause the damping of power oscillations during an error [1]. using high-speed power converters, parallel controllers can be used in distribution for applications such as voltage regulation [3], voltage balancing, reducing flicker, and mitigating voltage sag [4]. basically, all parallel controllers inject an additional current to the system at the point of common coupling (pcc). parallel controller impedance that is connected to the pcc, creates a changing current. as long as the injected current has  90 phase difference with voltage, parallel controllers can only produce or absorb changing reactive power [2]. parallel controllers include two groups: static reactive power (var) compensators (svc) and static synchronous compensators (statcom) [5]. svc attracts or produces controllable reactive power by connecting the inductor or capacitor to or from the power system and therefore svc is very slow for problems with rapid transition states. using the semiconductor equipment with shutdown feature, power converters can be used at higher switching frequencies and provide faster response. this has caused voltage source converters (vsc) to be an important part of facts controllers, creating a parallel controller known as statcom, with its single-line diagram illustrated in fig. 1 [1]. voltage source converter lossc f x power system pcc o i o v pccv fig. 1: single-line diagram of statom. among the structures of power converters that have been recently introduced, multilevel converters are useful structures that can be used in high power applications such as facts devices. several structures of multilevel converters are presented, most notably diode clamed multilevel converter (dcmc) [6], flying capacitor multilevel converter (fcmc) [7], generalized p2-cell multilevel converter (p2mc) [8], cascaded multilevel converter (cmc) [7], reversing voltage multilevel converter (rvmlc) [9], and modular multilevel converter (m2mc) [10]. with these converters, switches with lower nominal power can be used in medium voltage [2]. among the diverse structures provided, the cascaded multilevel converter (cmc) has a possible and useful structure for reactive power compensation without voltage unbalancing [2, 11]. cascaded multilevel converters are made with a number of identical h-bridge converters [12]. the modular structure not only simplifies the construction of the hardware, but also the overall system on power capability enables flexibility. moreover, it has far fewer components compared to other structures and all its components are the same for any number of levels [5, 13]. a statcom structure based on cmc is shown in fig. 2. several studies were performed on cmc-based statcom for improving dynamic response and stabilization of dc capacitor voltage [2, 5, 11]. according to the advantages of multilevel converters in power quality applications and cmcs in particular, this paper recaps the design and simulation of cmc-based multilevel statcom for load voltage regulation. compared to the previous control strategies [14-17], the proposed method has iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 93 a higher performance for power quality improvement and is comparatively easy and has high practical value with easy hardware implementation. in the second section, investigation of factors affecting passive components of cmc-based multilevel statcom and its power circuit design to regulate the load voltage is done. the control algorithm, statcom control system design and modeling of the test system and multilevel statcom based on cmc are conducted in the third section and test system and cmc-based multilevel statcom in the fourth section with the matlab/simulink software is simulated. finally, conclusion is provided in the fifth section. fig. 2: cmc based statcom. 2. cmc-based multilevel statcom power circuit design for the load voltage regulation 2.1 nominal reactive power design of statcom the test system is shown in fig. 3 and its characteristics are given in table 2 in the appendix. in this test system, constant and switchable loads are fed through a feeder and the purpose of applying statcom is to regulate the load voltage in nominal value. cascaded multilivel converter c s v n distribution substation s r sl pcc v l r ll distribution feeder fixed load switch switchable load statcom lsw l lsw r f l f r filter jqp  fig. 3: test system. an v cn v bn v l l l o c c c c c c c c c   1c v   2c v   cn v   bn v  an v   cn v a i b i c i 1c i 2c i cn i iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 94 assuming a full load condition and placement of statcom equivalent circuit in the test system shown in fig. 4, the statcom nominal reactive power is designed for the load voltage regulation. by writing the kcl equation at pcc, we will have: (1) ji jxr v r v jxr vv to tto t ll pcc loss pcc ss spcc      3 by putting numerical values from table 2, the voltage pccv can be obtained by: (2) )6108.01144.2()5636.06574.57( ijiv pcc  since the purpose of applying statcom is to regulate the load voltage, voltage magnitude pccv must be equal to supply voltage and therefore nominal current and reactive power of the statcom is obtained by: (3) aiiiv pcc 1264)6108.01144.2()5636.06574.57( 22  (4) var230412643  statcom q fig. 4: equivalent circuit of test system and statcom. 2.2 design of passive components of statcom the passive components in a statcom system are dc capacitors and a fl reactor. since passive components of a statcom system have a significant impact on system performance, design, and the factors affecting the dc capacitor, the reactor size will be detailed here. 2.2.1 dc capacitor design factors that affect the capacitance are voltage ripple [18], modulation index [19], harmonic distortion in output current and voltage of converter [20], and voltage overshoot [19]. the minimum value of dc capacitance is determined by overshoot and voltage ripple, while the maximum value is limited by cost. given the low rate of harmonics in the converter output voltage, dc capacitance is designed as follows [21]: (5) dc dc v q c   iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 95 where dcv is the maximum allowed voltage ripple of the capacitor voltage and q is the charge of the capacitor. maximum ripple voltage takes place in π/2 from each period. thus, charge of the capacitor is in the form of eq. (6): (6) f i dtftiq rms rms ..2 )2cos(..2 2 0      that rmsi effective value of the converter current and f is frequency of system. by combining eqn. (5) and (6), dc capacitance value is obtained. (7) dc rms dc vf i c   ...2  by inputting nominal values of the test system, multilevel statcom, and 10% allowed ripple of voltage, dc capacitance is obtained at 12 mf. 2.2.2 factors affecting the size of reactor the reactor is the second passive component in statcom. the purpose of using the reactor is firstly the filtering of converter current harmonics, and secondly as reactive power coupler, i.e. the cause of reactive current. factors that affect the size of the reactor are the converter output current harmonic distortion [22], performance range of the converter [23], and dynamic response of the system [24]. the minimum value of the reactor is determined by current harmonic distortion and the maximum value is determined by performance range of the converter and cost. it is assumed for reactor design that the multilevel statcom output voltage and current is sinusoidal and the reactor resistance is ignored. thus, inductance of the reactor is defined as follows [21]: (8) rms rms dc rms rms o f i v vn i v v x     2 . 2 max where maxov the maximum output voltage of the converter cmc, n is the number of hbridge converters in each phase, rmsv is the effective phase voltage of the system, and rmsi is the effective current of system. by inputting nominal values of the test system and multilevel statcom, the inductance of the reactor is obtained as mhl f 2.2 . because the reactor resistance is neglected, reactor resistance is 0.1 of the reactor reactance and is placed equal to  1.01.0 ff xr . 3. control algorithm and cmc based statcom control system design 3.1 active and reactive power control algorithm according to the theory of instantaneous reactive power that was presented by akagi et al. in 1983 [25, 26], active and reactive power exchanged between power and statcom systems are defined as follows: (9) qpccqdpccd ivivp  iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 96 (10) qpccddpccq ivivq  if we put 0pccqv in the above equations, the equations are as follows: (11) dpccd ivp  (12) qpccd ivq  as can be seen in these equations, active and reactive power is controlled by di and q i respectively. in fact, active and reactive power control is carried out completely independently. if the statcom produces reactive power, then qi will be negative and if statcom attracts reactive power, qi will be positive. similarly, if the statcom produces active power, then di will be positive and if statcom attracts active power, di will be negative [27]. 3.2 cmc based statcom control system design figure 5 shows the multilevel statcom controller. in this controller, first, voltages of pccav , pccbv and pcccv , and currents of ai , bi and ci can be changed to pccdv , pccqv , di and qi using park’s transformation matrix. angle in park’s transformation matrix is obtained by phase-locked loop (pll). figure 6 shows a block diagram of pll [28]. according to the block diagram and description of previous section, pccqv is first compared by zero value and the difference between these two is given to pi controller. since reference coordination is synchronous, the pi controller output is summed with  120 . by integrating the obtained value, angle  is obtained. n distribution substation distribution feeder load switch 7 level cmc pwm generator dq abc pcca v pccb v pccc v pll  pccabc v pccdq v dq abc a i b i c i abc i dq i 2 22 pccqpccd vv  + )120cos( )120cos( )cos(         mie mie mie cref bref aref + +  q i +  d i+ + q i d i +  q d d d d q qd d d ddmi 1 22 tan     s k k 2 1  s k k 2 1  s r s l l r ll s r s l l r ll sa v s r s l lr ll lsw r lsw l lsw r lsw l lsw r lsw lswitch switch sb v sc v  dc v  dc f v l  dc f v l f l f r f l f r f l f r 1/3 1/3 1/3 1/3 1adc v 2adc v 3adc v 1bdc v 2bdc v 3dcb v 1cdc v 2cdc v 3cdc v 1dc v 2dc v 3dc v dc v s k k 4 3  s k k 6 5   rms v rms v fig. 5: multilevel statcom controller. iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 97 fig. 6: block diagram of pll [28]. since the purpose of applying multilevel statcom is voltage regulation, the effective voltage in pcc is compared with the desired value in the loop q and is given to the pi controller. pi controller output is the reactive current value that multilevel statcom should produce or attract. in other words, the current is the reference value of q i . then, qi is compared with the reference value of itself and is given to the pi controller. the controller output forms switching function of q axis. in loop d, the average capacitor voltage is initially compared with the reference value and is given to the pi controller. the pi controller output is the active current value that multilevel statcom should produce or attract. in other words, the current is reference value of di . then, di is compared with the reference value of itself and is given to the pi controller. the controller output forms switching function of d axis. when switching functions of axes d and q were obtained, their amplitude and angle are estimated. these values are initial amplitude and phase of reference signals of pspwm. to determine the coefficients 1 k , 2 k , 3k , 4k , 5k and 6k of pi controllers, the closed loop equations are obtained based on the test system, multilevel statcom, and controller. equations (13) and (14) are the average model of cmc based statcom [5] and open loop state equations of the studied system and multilevel statcom in abc coordination.          njid c v crdt dv i l r v l dv ldt id abc t abcjdc lossj dc abc f f pccabc f abcdc f abc ,...,1,.. .3 1 . 1 1 . 1    (13) (14)                  abc t abcdc loss dc abc f f pccabc f abcdc f abc abcsabclabclabc l l pccabc l labc sabc s s pccabc s sabc s sabc i.d .c v .crdt dv i. l r v l d.v l n dt id iiii l r v ldt id i l r v l v ldt id to t to t to t        3 11 1 , 1 11 iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 98 in these equations:            c b a abc i i i i  ,            c b a abc d d d d  ,            cj bj aj abcj d d d d  and            pccc pccb pcca pccabc v v v v  . also, to tl r and to tl l are load resistance and inductance respectively in full load condition (constant and switchable load on the circuit). by multiplying the eqn. (14) in park transformation matrix, open-loop model in dqo coordination is obtained as eqn. (15). since the test system was a three-phase three-wire, the axis o is ignored. (15)                                                                      dq t dqdc loss dc dq f f f f pccdq f dqdc f dq dqsdqldqldq l l l l pccdq l ldq sdq s s s s pccdq s sdq s sdq id c v crdt dv i l r l r v l dv l n dt id iiii l r l r v ldt id i l r l r v l v ldt id to t to t to t to t to t        . .2 1 . 1 1 . , 1 11       in these equations sdi , sqi , di , qi and dcv are state variables, dd and qd are control variables, sdv and sqv are input variables, respectively. the state variables in these equations are         qdqddcqdsqsd ddiiviiiix . by linearization of equations at the operating point and applying a pole placement method for designing pi controllers, the gains of pi controllers are obtained to achieve optimal response and damping as 1.0 1 k , 100 2 k , 13 k , 304 k , 5.05 k and 1006 k to achieve optimal response and damping. table 1 shows eigenvalues of the test system and multilevel statcom with or without controller. table 1: eigenvalues of system in full load condition. eigenvalues of system, multilevel statcom and controller eigenvalues of system and multilevel statcom j8071666 j34.38437.242  j17.84204.862  j5.40491.159  j38.37835.221  43.31 78.33 j68.2344.14  iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 99 because of different carrier signals, unbalancing usually occurs in capacitor voltage. in practice, this unbalance increases due to the lack of uniformity in components. therefore, we need a balanced capacitor voltage. figure 7 shows the block diagram of the voltage capacitor balancer [29]. each of the capacitor voltages is compared with its nominal value and is given to the pi controller. the controller output changes the angle that is deduced from the angle of reference signal related to its h-bridge converter. + +  dc v 3,2,1 ,,,   j cbaiijdc v pi ij  ij  m pwm generator fig. 7: block diagram of capacitor voltage balancer [29]. 4. simulation in this section, simulation of the system is presented using the matlab/simulink software. 4.1 simulation in full load condition in a full load condition, both constant and switchable loads are in circuit. a 7 level cmc converter with pspwm control method was implemented. figure 8 shows pspwm switching control for a 7 level cmc converter. figure 9 shows the output voltages of the cmc converter. figures 10 and 11 respectively show the load voltages and effective phase voltages in the pcc. as can be seen, effective voltage of the load is regulated with good speed and accuracy at the nominal value of 45.5 volts, which reflects the good performance of the controller. fig. 8: pspwm switching control for the 7 level cmc converter. fig. 9: output voltages of the cmc converter. figures 12 and 13 respectively show the output current of a multilevel statcom and current of the q axis )( qi . as can be seen, multilevel statcom is capable of injecting reactive current in less than 200 msec. figure 14 shows the fft analysis of iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 100 output current of multilevel statcom. as can be seen from the figure, the total harmonic distortion of the output current is 3.82%, which is less than 5% to meet the ieee 519 standard. the average voltage of the capacitors is shown in fig. 15. the average voltage of the capacitors is fixed completely at the nominal value of 25 volts. fig. 10: load voltages. fig. 11: effective phase voltage in the pcc. fig. 12: output current of the multilevel statcom. fig. 13: current of the q axis )( qi . fig. 14: fft analysis of output current of the multilevel statcom. fig. 15: average voltage of the capacitors. iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 101 4.2 simulation in dynamic conditions in this case, a constant load is in the circuit. at the time of 500 msec, a switchable load enters the circuit and finally, the switchable load is output from the circuit at the time of 1 second. figures. 16 and 17 show effective phase voltage in the pcc and current of the q axis )( qi respectively. as can be seen, effective voltage of load is regulated with good speed and accuracy at the nominal value of 45.5 volts, which reflects the good performance of the controller in dynamic conditions. fig. 16: effective phase voltage in the pcc. fig. 17: current of the q axis )( qi . 5. conclusion remarks in this paper, the design and simulation of a multilevel statcom to regulate load voltage are provided. among conventional multilevel converters, the cascade multilevel converter was chosen for use in the statcom due to fewer components and the simplicity of control. for the cascade multilevel converter output voltage control, the phase-shifted sinusoidal pulse width modulation method (pspwm) was selected due to a better harmonic spectrum and simplicity of producing the switching angles. a cascaded multilevel converter statcom design was presented in two parts. in the first part, the multilevel statcom to regulate load voltage in the test system was designed and its nominal reactive power was obtained. also, design of multilevel the statcom passive components, based on cascade multilevel converter, was presented in this section. due to the factors that affect the size of these components, design of these components was conducted optimally. in the second part, the multilevel statcom control system was designed. the design by pole placement method to achieve the optimal dynamic properties was performed. to balance the voltage of the capacitors, a voltage balancer was added to the control system. the simulation results showed dynamic and steady state responses of the control system at full load and dynamic conditions with good speed and accuracy in the nominal value by balancing and stabilizing the voltage of capacitors. the proposed method has a higher performance for power quality improvement and is comparatively easy and possesses a high practical value with easy hardware implementation. iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 102 references [1] hingorani ng, gyugyi l. (2000) understanding facts, ieee press. [2] sirisukprasert s, huang aq, lai j.-s. (2003) modeling, analysis and control of cascadedmultilevel converter-based statcom. power engineering society general meeting, 25612568. [3] xu y, li f. (2014) adaptive pi control of statcom for voltage regulation. ieee transactions on power delivery, 29(3):1002-1011. [4] elnady a, salama mm. (2005) unified approach for mitigating voltage sag and voltage flicker using the dstatcom. ieee transactions on power delivery, 20(2):992-1000. [5] sirisukprasert s. (2004) the modeling and control of a cascaded-multilevel converter-based statcom. virginia tech. [6] rodriguez j, lai j-s., peng fz. (2002) multilevel inverters: a survey of topologies, controls, and applications. ieee transactions on industrial electronics, 49(4):724-738. [7] lai j-s, peng fz. (1996) multilevel converters-a new breed of power converters. ieee transactions on industry applications, 32(3):509-517. [8] peng f. z. (2001) a generalized multilevel inverter topology with self voltage balancing. ieee transactions on industry applications, 37(2): 611-618. [9] najafi e, yatim a, samosir a. (2008) a new topology-reversing voltage (rv) for multilevel inverters. in power and energy conference, 604-608. [10] siemaszko d, antonopoulos a, ilves k, vasiladiotis m, ängquist l, nee h-p. (2010) evaluation of control and modulation methods for modular multilevel converters. in power electronics conference (ipec), 746-753. [11] liang y, nwankpa c. (1999) a new type of statcom based on cascading voltage-source inverters with phase-shifted unipolar spwm. ieee transactions on industry applications, 35(5):1118-1123. [12] rashid mh. (2009) power electronics: circuits, devices, and applications. pearson education india. [13] khomfoi s, tolbert lm. (2007) multilevel power converters. power electronics handbook, 451-482. [14] tavana mr, khooban mh, niknam t. (2017) adaptive pi controller to voltage regulation in power systems: statcom as a case study. isa transactions, 66:325-334. [15] park j, yu j, kim j, kim m, kim k, han s. (2016) frequency/voltage regulation with statcom with battery in high voltage transmission system. ifac-papersonline, 49(27):296-300. [16] wang k, crow ml. (2011) power system voltage regulation via statcom internal nonlinear control. ieee transactions on power system, 26(3):1252-1262. [17] augustine a, paul e, prakash rd, balakrishna bm, xavier r. (2016) voltage regulation of statcom using fuzzy self tuning pi controller. international conference on circuit, power and computing technologies (iccpct). [18] hannan ma. (2012) effect of dc capacitor size on d-statcom voltage regulation performance evaluation. przegląd elektrotechniczny, 88(12a):243-246. [19] min z, yiwei z, libing c. (2014) dc capacitor voltage control strategy for the cascaded statcom. open automation and control systems journal, 6:1415-1425. [20] pulikanti sr, konstantinou g, agelidis vg. (2012) dc-link voltage ripple compensation for multilevel active-neutral-point-clamped converters operated with she-pwm. ieee transactions on power delivery, 27(4):2176-2184. [21] hawley jc. (2004) the modeling and simulation of a cascaded three-level converter-based sssc. virginia polytechnic institute and state university. [22] cetin a. (2007) design and implementation of a voltage source converter based statcom for reactive power compensation and harmonic filtering. middle east technical university. iium engineering journal, vol. 19, no. 1, 2018 heidari et al. 103 [23] gultekin b, ermis m. (2013) cascaded multilevel converter-based transmission statcom: system design methodology and development of a 12 kv±12 mvar power stage. ieee transactions on power electronics, 28(11):4930-4950. [24] zhang jl. (2011) the design of statcom control system. in applied mechanics and materials, 1631-1635. [25] akagi h, kanazawa y, fujita k, nabae a. (1983) generalized theory of instantaneous reactive power and its application. electrical engineering in japan, 103(7):58-66. [26] heidari m. (2015) improving the power quality of wind power plants through modifying the instantaneous active and reactive power theory. international journal of renewable energy research, 5(3):722-731. [27] heidari m, kovsarian a, seifossadat s. (2011) detailed analysis of cascaded multilevel converter based statcom. international review on modelling and simulations, 4(2):507-516. [28] yang z. (2007) digital controller design for cascaded-multilevel-converter based statcom systems. [29] peng fz, lai j-s, mckeever jw, vancoevering j. (1996) a multilevel voltage-source inverter with separate dc sources for static var generation. ieee transactions on industry applications, 32(5):1130-1138. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 forecasting of infection prevalence of helicobacter pylori using regression analysis komiljon usarov1, anvarjon ahmedov1, mustafa fatih abasiyanik2 and ku muhammad na’im ku khalif1 1 centre for mathematical sciences college of computing & applied sciences of computer science universiti malaysia pahang, 26300 kuantan, pahang, malaysia. 2 pritzker school of molecular engineering, the university of chicago, edward h. levi hall, 5801 south ellis avenue chicago, illinois 60637, usa. * corresponding author: ukomiljon@gmail.com (received: 27th july 2021; accepted: 16th november 2021; published on-line: 4th july 2022) abstract: global warming may have a significant impact on human health because of the growth of the population of harmful bacteria such as helicobacter pylori infection. it is crucial to predict the prevalence of a pathogen in a society in a faster and more costeffective way in order to manage caused disease. in this research, we have done predictive analysis of h. pylori infection spread behavior with respect to weather parameters (e.g., humidity, dew point, temperature, pressure, and wind speed) of istanbul based on a database from istanbul samatya hospital. we developed a forecasting model to predict h. pylori infection prevalence. the goal is to develop a machine learning model to predict h. pylori (hp) related infection diseases (e.g., gastric ulcer diseases, gastritis) based on climate variables. the dataset for this study covered years from 1999 to 2003 and contained a total of 7014 rows from the samatya hospital in istanbul. the weather information related to those years and location, including humidity (h), dew point (d), temperature (t), pressure (p) and wind speed (w), were collected from the following website: https://www.wunderground.com. in this paper we analyzed the forecasting model, which was used to predict h. pylori infection prevalence, by non-linear multivariate linear regression model (mlrm). we applied the non-linear least square method of minimization for the sum of squares to find optimal parameters of mlrm. multiple regression method was used to determine the correlation between a criterion variable and a combination of predictor variables. it was established that the hp infection disease is most influenced by humidity. hp prevalence is modelled using the multiple regression method equation, the average h, d, t, p, and w were the most important parameters to deviation of the datasets (testing dataset was 17% and 18% for training dataset). this showed that the statistical model predicts the hp prevalence with about 83% accuracy of the testing data set (11 months) and 87% accuracy of the training data set (42 months). based on the proposed model, monthly infection can be predicted early for medical services to take preventative measures and for government to prepare against the bacteria. in addition, drug producers can adjust their drug production rates based on forecasting results. abstrak: pemanasan global mungkin mempunyai kesan langsung terhadap kesihatan manusia kerana pertambahan populasi bakteria merbahaya seperti infeksi h. pylori. adalah penting bagi mengesan kehadiran patogen dalam masyarakat bagi mengawal penularan penyakit dengan cepat, dan melalui kaedah kurang mahal. kajian ini berkaitan analisis ramalan penularan infeksi h. pylori secara langsung terhadap parameter cuaca (cth: kelembapan, titik embun, suhu, tekanan, kelajuan angin) di istanbul berdasarkan data dari hospital samatya istanbul. kajian ini membentuk model ramalan bagi menjangka 183 iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 penyebaran infeksi h. pylori. matlamat adalah bagi mencipta model pembelajaran mesin bagi mengjangka penyakit berkaitan infeksi h. pylori (hp) (cth: penyakit ulser gastrik, gastrik) berdasarkan pembolehubah cuaca. dari tahun 1999 ke 2003, set data telah digunakan bagi mempelajari di mana sejumlah 7014 baris dari hospital samatya di istanbul. informasi berkaitan tahun-tahun tersebut dan lokasi mengenai kelembapan (h), titik embun (d), suhu (t), tekanan (p) dan kelajuan angin (w) dikumpul dari laman sesawang https://www.wunderground.com. kajian ini mengguna pakai model ramalan bagi meramal kelaziman infeksi h. pylori, melalui model regresi berkadaran multivariat tidak-berkadaran (mlrm). kaedah kuasa dua terkecil tidak linear digunakan bagi pengurangan jumlah ganda dua bagi mencapai parameter optimum mlrm. kaedah regresi gandaan digunakan bagi mencari persamaan antara kriteria pembolehubah dan gabungan pembolehubah ramalan. dapatan menunjukkan infeksi penyakit hp adalah disebabkan oleh faktor kelembapan. penyebaran hp dimodel menggunakan persamaan kaedah regresi gandaan, purata h, d, t, p dan w adalah parameter terpenting bagi sisihan data latihan iaitu sebanyak 17% dan 18% bagi set data latihan. ini menunjukkan model statistik menjangkakan penyebaran hp adalah sebanyak 83% adalah tepat pada set data yang diuji (selama 11 bulan) dan 87% tepat pada set data latihan (selama 42 bulan). berdasarkan model yang dicadangkan ini, infeksi bulanan dapat di jangka lebih awal bagi membendung servis kepada perubatan dan kerajaan bersiap-sedia memerangi bakteria ini. tambahan, prosedur jumlah ubatan dapat dihasilkan lebih atau kurang daripada jumlah ubatan berdasarkan dapatan ramalan. key words: h. pylori; infectious disease prediction; multivariate linear regression 1. introduction helicobacter pylori is highly prevalent in approximately 50% of the world’s population [1], causes inflammation in the stomach and leads to chronic gastritis, peptic ulcer diseases (pud), gastric ulcers (gu), duodenal ulcers (du), and eventually gastric cancer in the human stomach [1,2,3]. in the united states, about 10% of the population will develop a duodenal ulcer at some point in their lives. peptic ulcer disease affects about 4 million people annually in the world [4]. the occurrence of peptic ulcer disease is similar in men and women. approximately 11%-14% of men and 8%-11% of women will develop peptic ulcer disease in their lifetime. the mortality rate for peptic ulcer disease is approximately one death per 10,000 cases. the mortality rate due to ulcer hemorrhage is approximately 5%. according to globocan 2018 data, stomach cancer is the 3rd most deadly cancer with an estimated 783,000 deaths in 2018 [5]. it causes high cost to society and even brings on high risk to human lives. the prediction of h. pylori prevalence has essential impact on the minimizing of the transmission of h. pylori related infectious diseases, which is a core function of public health law. laws can be affected that prevent prevalence of the infection, but it is crucial to know early about the infection prevalence using forecasting models. the literature consists of some interesting research work related to forecasting models for infections such as malaria, scarlet fever, chickenpox [5] combining big data and neural networks. moreover, there are some articles about predictions based on environmental factors which have a great impact on the prevalence of the infections. for instance, song et al. built a time series model based on eight climate variables to predict hand, foot, and mouth disease [6]. in addition, lu et al. showed that average daily sunshine time correlated positively with h. pylori infection [1]. previous studies showed that using climate variables can be more accurate and efficient to predict infection prevalence. 184 iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 since there is no prediction model for h. pylori disease prevalence, we set a goal to design forecasting model for h. pylori prevalence based on the following environmental factors: humidity, dew point, temperature, and wind speed by using outstanding machine learning tools such as multivariate linear regression model (mvlr). this model will enable market players (e.g., doctors, government, pharmaceutical firms, etc.) to take sufficient precautions before outbreaks. ultimately, by building the forecasting model, we have proven that it is possible to predict the h. pylori infection prevalence and to know early information about the spread of the infection. it gives a chance to act for prevention procedures against the infection, which leads not only to reducing the prevalence of the infection, but it also minimizes social costs for the public and saves many people’s lives. furthermore, it can increase hospital services for patients and drug producers can develop drugs based on the demand of the patients. 2. materials and methods 2.1 research data from the original dataset from 7014 patients, only non-null values of clo attribute were selected, leaving 4388 patients between 1999 to 2003 in the samatya hospital in istanbul, turkey, which includes 48 attributes such as visiting date, gastritis cancer, du, gu, gastritis, abdominal pain, stomachache, and clo results. the ages were divided into below 20, 20-30, 30-40, 40-50, 50-60, and above 60 years old, representing 2%, 13%, 19%, 24%, 21% and 30% of the total dataset, respectively. more than half of patients were above 50 years old. cases were 16% of du, 18% of deformative pylorus, 19% of (peptic ulcer) (pu), 27% of deformative bulbus, 41% of erosive duodenitis, 46% of feel pain, 58% hp infected, 22% stomachache, 93% of pangastritis and 99% of gastritis of the patients. in addition, there were 51% male and 49% female patients. the bacterial infection of each patient was detected by a special test called clo and patients with a positive clo test were assumed to be infected (table 1). table 1: baseline and outcome clinical characteristics of h. pylori patients parameters 4388 of patients (%) percentage from total patients female 2247 (51%) male 2141 (49%) pain 2015 (46%) hp 2547 (58%) pangastritis 4087 (93%) erosive duodenitis 1811 (41%) gastritis 4347 (99%) weather data (wd), (humidity the concentration of water vapor present in the air, dew point the temperature to which air must be cooled to become saturated with water vapor, temperature a degree of heat or cold the can be measured using a thermometer in degrees on the fahrenheit, celsius, and kelvin scales, pressure or air pressure the force per unit of area exerted on the earth's surface by the weight of the air above the surface, wind speed or wind flow speed a fundamental atmospheric quantity caused by air moving 185 iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 from high to low pressure, usually due to changes in temperature) including humidity (%), dew point (°f) (https://en.wikipedia.org/wiki/dew_point), temperature (°f), pressure (hg), wind speed (mph) was obtained from historical data by average daily information in the https://www.wunderground.com/history website, joined with the visitor date attribute. the joined data was transformed into a monthly dataset using sum of hp and mean of humidity, dew point, temperature, pressure, wind speed aggregate functions. the final data contains v (number of visitors), hp (sum of hp), h (mean of humidity), d (mean of dew point), t (mean of temperature), p (mean of pressure), w (mean of wind speed) attributes and 53 months of observed rows (see table 2). all of this was performed using google colab notebook (https://colab.research.google.com/) and python3 (https://www.python.org/) machine learning libraries (https://scipy.org/) on google’s cloud tpu server. the dataset above was divided into a train subset and a test subset with a ratio of 80% and 20%, respectively. it means that all 53 months of rows were split into 42 months of rows of training data subset and 11 months of rows of testing data subset. 2.2 method the following multivariate linear regression model was used to forecast hp based on table 2 data: 𝑦 = 𝑓(𝐻, 𝐷, 𝑇, 𝑊) = 𝛽1𝑠𝑖𝑛 2(𝜌1𝐻 + 𝜌2)𝑠𝑖𝑛 2(𝜌3𝑇 + 𝜌4) + 𝛽2𝑠𝑖𝑛 2(𝜌5𝐻 + 𝜌6)𝑠𝑖𝑛 2 (𝜌7𝑇 + 𝜌8) + 𝛽3𝑠𝑖𝑛 4(𝜌9𝐷 + 𝜌10)𝑠𝑖𝑛 4(𝜌11𝑊 + 𝜌12) + 𝛽4𝑠𝑖𝑛 4(𝜌13𝐷 + 𝜌14)𝑠𝑖𝑛 4(𝜌15𝑊 + 𝜌16) + 𝛽5𝑠𝑖𝑛(𝜌17𝐻 𝐷 + 𝜌18) + 𝛽6 (1) where: 𝑦 dependent variable (𝐻p – the number patients who had positive clo infection test), 𝐻 the average of humidity (%) 𝐷 the average of dew point (of) 𝑇 the average of temperature (of) 𝑊 the average of wind speed (mph) 𝜌1−18 non-linear regression coefficients, 𝛽1−5 regression coefficients, 𝛽6 constant. 2.3 the algorithms in order to determine which 𝜌1−18and 𝛽1−6 vector paraments give the best fit to the data, the sum of squares of the residuals is minimized. the residuals are defined for each observed data-point as 𝜀𝑖 = 𝑦𝑖 − 𝑓(𝐻𝑖 , 𝐷𝑖 , 𝑇𝑖 , 𝑊𝑖 ) (2) where 𝑦𝑖 is the number of the total infected per month by h. pylori in the given region. we perform the leastsq command (nonlinear least square solver) in scipy in python from scipy.org. 2.4 mvlr assumptions in order to achieve validity of the tests of hypothesis (like t-test, f-test) and to enhance that ols estimators are the best linear unbiased estimator (blue), it needs to follow four base assumptions: 186 iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 1. the relationship between the dependent variable and the independent variables is linear. 2. the residuals are independent. 3. homoscedasticity. 4. normality of residuals with mean equals to zero. the durbin-watson statistic (dw) was used to check that residuals are independent. if dw is between 1.65 and 2.35, there is no autocorrelation. if dw is between 1.21 and 1.65 or between 2.35 and 2.79, the test is inconclusive [7]. homoscedasticity is a word used for the “constant variance” assumption. the regression model assumes that the residuals have the same variance throughout. when this assumption is violated, the problem is called “heteroscedasticity,” or changing variance. we used the breusch – pegan and white test to check it. errors need to be a normal probability distribution. this makes no difference to the estimates of the coefficients, or the ability of the model to forecast. but it does affect the f and t-tests and confidence intervals. we used more testing algorithms such as jarque–bera test (jb), shapiro-wilk test, d’agostino’s k-squared test, anderson-darling test because it is a very important assumption to rate the model. 3. results and discussion 3.1 statistical analysis in table 2, the four-year hospital statistics show the average monthly infection rate was 58% among average monthly visitors (78 ± 44) of 45.1 patients among average 78.4 visitors per month in four years. it is shown that more than half of visitors were infected by h. pylori infection. table 2: statistics of monthly data count mean std min 25% 50% 75% max total visitors 53 78.4 44 1 49 81 100 190 total hp 53 45.1 25 0 26 47 60 113 humidity (°f) 53 72 8.7 54 68 72 78 92 wind speed (mph) 53 9.8 2.2 3.5 8.7 10 11 17 dew point (°f) 53 50.6 12 22 44 50 60 73 temperature (°f) 53 61.2 13 36 52 61 72 82 n=53, which is the total number of months in the study correlations of attributes for both data sets can be seen in table 3. h attribute negative correlates to total hp. d and t were correlated positive with 0.10 and 0.15 respectively. table 3: correlations between given variables for monthly transformed data total hp h w d t total hp 1.00 -0.25 -0.02 0.10 0.15 h -0.25 1.00 0.14 -0.30 -0.53 w -0.02 0.14 1.00 -0.14 -0.12 d 0.10 -0.30 -0.14 1.00 0.96 t 0.15 -0.53 -0.12 0.96 1.00 187 iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 the box plot graph shows that for 5 years the number of visitors was close each month of year in january, february and september. however, in june and july there was very high difference between the number of visitors for each year. while the infected number of patients was very close in january, february, and august, there was a wide spread of numbers and the highest number of the infected patients with hp in april, june, and july (fig. 1). (a) (b) fig. 1: the box plot for total visitors (a) and the hp infected patients in percentage among visitors (b) are demonstrated by months. we found various behaviors of the independent variables, such as the number of visitors and the number of hp infected patients, in different climate conditions. according to the given dataset, the behavior of the independent variables was maximized, when weather temperature was 75-80 of, the humidity was 75%-80%, the pressure was between 29.8 mmhg and 30 mmhg, the wind speed was between 9 mph and 10 mph, and the dew point was between 45 of and 50 of, 60 of and 65 of. all of those factors were significant since null hypothesis were rejected (p<0.05) (fig. 2). (a) (b) (c) (d) 188 iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 fig. 2: for monthly average data, hp positive and negative factors are represented by forecast weather variables: temperature (a), humidity (b), pressure (c), wind speed (d), dew point (e). in addition, the behavior of the independent variables was highly impacted for the 4550 years old patients (p-value<0.05) (fig. 3). moreover, the number of clo infected patients grew until 50 years old, and it began to drop after that. fig. 3: the positive and negative clo factors are represented by age of the patients. here we studied monthly and yearly statistics for nv and nc. nv and nc were more in june and september (p-value<0.05 each) than other months. also, it is significant for march and august where there were p-values < 0.05 (fig. 4a). there was strong growth of the number of visitors and clo patients between 1999 and 2002 and it reached a peak in 2002 (it is significant for 2002, p-value<0.05) and dropped significantly in 2003. note that there were no records for last two months in 2003 (november and december of data in 2003 (fig. 4b). fig. 4: the positive and negative clo factors are represented by month (a) and year (b). 3.2 model using eq. (2) we obtained optimal parameters of eq. (1) the proposed model described for hp infection prevalence by the below mathematical formula: (e) (a) (b) 189 iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 𝑦 = 𝑓(𝐻, 𝐷, 𝑇, 𝑊) = 31.1237𝑠𝑖𝑛2(3.7370𝐻 − 121.6778)𝑠𝑖𝑛2(2.9952𝑇+112.3183) + 68.2460𝑠𝑖𝑛2(7.1261 𝐻 + 0.2939)𝑠𝑖𝑛2 (8.8473 𝑇+17.8187) + 72.6059𝑠𝑖𝑛4(12.4216 𝐷-15.3039)𝑠𝑖𝑛4(12.4320 𝑊+27.8774)+ 70.2747𝑠𝑖𝑛4(16.9445 𝐷+20.2464)𝑠𝑖𝑛4(18.7481 𝑊+21.9338) + 19.8196𝑠𝑖𝑛(22.0029 𝐻𝐷+12.7998) + 1.6339 (3) the mvrm was obtained with a training subset of data. this formula predicts the accuracy with coefficient of determination (r2) equal to 87% and 83% for train data (42 months) and test data (11 months), respectively (fig. 4). and adjusted r2 is 85% which is high. it means that the correlation coefficient between the observed value of the dependent variable and the forecast value based on the regression model was high. anova table showed that the value of f statistic was 48.36 and the significance of f was zero which is less than the critical value (p<0.001). the null hypothesis was rejected. it means that the model is significant. 3.3 regression assumptions the proposed model was linear by 𝛽1−6 coefficients. it gives us the first assumption true. dw test was 1.998 which lies between 1.65 and 2.35. therefore, there is no autocorrelation between residuals and predicted values (fig. 5b). thus, the model held 2 assumptions. the breusch–pegan test showed that the null hypothesis was not rejected (p>0.05), meaning that the model holds 3 assumptions. it can be seen in fig. 5a. by the qq plot, which easily proves that it is homoscedasticity. the last assumption is also true for the given model and the mean of residuals is zero. in addition, jarque–bera(jb), shapiro-wilk, d’agostino’s ksquared, anderson-darling tests rejected null hypothesis (p>0.05) which means the residuals are normally distributed (fig. 5c). (a) qq plot. (b) independence of residuals. (c) distribution of residuals. fig. 5: residuals analysis. 3.1 forecast results the forecasts result of training and testing data were represented by fig. 6, where it was separated by a grey vertical line. by date (month, year) and the number of clo are represented by x-axis and y-axis, respectively. actual data is in blue color, training data is in green and testing data is in red color. the forecasting data started from november, 2002 until october 2003, which means that almost all 1-year forecasts are highly accurate. we calculated lower and upper prediction intervals using upper prediction interval 𝐔𝐏𝐈𝒊 = �̂�𝑖 + 𝑧√mse lower prediction interval 𝐋𝐏𝐈𝒊 = �̂�𝑖 − 𝑧√mse (4) 190 iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 where: mean squared error (mse) = 1 𝑛 ∑(𝑦𝑖 − �̂�𝑖 ) 2 (5) 𝑧 =1.645, the forecasted data with a 90% prediction interval (6) prediction intervals for train data and test data 𝐔𝐏𝐈𝒊 and 𝐋𝐏𝐈𝒊 are represented by green dot line and red dot line, accordingly with 90% probability (𝑧 = 1.645). (fig. 7a and fig. 7b). fig. 6: true train and test data and its forecasts. (the grey line is separator between train and test data). fig. 7: train data prediction with a 90% prediction interval (𝑧 =1.645, mse = 79.29) for mvrm in (a), test data prediction with a 90% prediction interval (𝑧 =1.645, mse = 124.13) for mvrm in (b.) (a) (b) 191 iium engineering journal, vol. 23, no. 2, 2022 usarov et al. https://doi.org/10.31436/iiumej.v23i2.2164 4. conclusions in this paper, we proposed non-linear mvrm to predict the prevalence of h. pylori infection prevalence based on the patients records of the hospital. if average monthly climate variables are introduced, the model predicts the number of h. pylori infection related to the given month’s average climate variables. the proposed model uses to find patterns of h. pylori infection behavior based on the mean of humidity, dew point, temperature, and wind speed of months. our researched showed that only the forecasting model achieves more accurate results by using the combinations of the given climate variables. since the infectious disease is a social problem, it can impact not only personal health, but can also cause widespread damage. therefore, this research is being conducted to minimize social cost by predicting the prevalence of the h. pylori infection. the aim of this study was to design a forecasting model to predict h. pylori infection, which does not exist in the research papers yet, by using various input climate variable techniques based on nonlinear mvrm with high accuracy. for this reason, we used non-linear least square method to find the regression coefficients of the model. the proposed model is significant since it holds four base assumptions of mvrm and gives 83% and 87% accuracy for training and testing dataset, respectively. the proposed model helps to conduct precise predictive analysis of h. pylori infection prevalence for 1 year based on the dynamics of climate variables. keeping in mind importance of climate variables in the forecast modelling of h. pylori infection prevalence we found high correlation between the climate factors and the prevalence. this model gives high accurate early forecast results which can be used by hospitals or governments to do early prevention acts against the infection prevalence, since it is critical to safe life of people and reduce cost in society. the proposed model is not only giving highly accurate results, but also it is easy to use by excel or sample calculators. the obtained results of prediction analysis of h. pylori infection prevalence can be extended to the region with a similar climate condition. in further research, the model can be improved with different regions of databases and climate factors and also to check weather to possibly simplify mathematical formula of the proposed model by reducing the climate variables. references [1] lu c, yu y, li l, yu c, xu p. (2018) systematic review of the relationship of helicobacter pylori infection with geographical latitude, average annual temperature and average daily sunshine. bmc gastroenterology, 18(1): 50. [2] tang my, chung ph, chan hy, tam pk, wong kk. (2019) recent trends in the prevalence of helicobacter pylori in symptomatic children: a 12-year retrospective study in a tertiary centre. journal of pediatric surgery, 54(2): 255-257. [3] peek jr rm, blasser mj. (1997) pathophysiology of helicobacter pylori-induced gastritis and peptic ulcer disease. the american journal of medicine, 102(2): 200-207. [4] thorsen k, søreide ja, kvaløy jt, glomsaker t, søreide k. (2013) epidemiology of perforated peptic ulcer: age-and gender-adjusted analysis of incidence and mortality. world journal of gastroenterology, 19(3): 347. [5] rawla p, barsouk a. (2019) epidemiology of gastric cancer: global trends, risk factors and prevention. przeglad gastroenterologiczny, 14(1): 26. [6] song y, wang f, wang b, tao s, zhang h, liu s, ramirez o, zeng, q. (2015) time series analyses of hand, foot and mouth disease integrating weather variables. plos one, 10(3): e0117296. https://doi.org/10.1371/journal.pone.0117296 192 https://doi.org/10.1371/journal.pone.0117296 microsoft word 1030-article text-6979-3-9-20191025 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 comparison study of stainless steel cyclic voltammograms in various natural media addition: product and voltage efficiency isana supiah yosephine louise*, endang widjajanti laksono, dewi yuanita lestari1 chemical education department, mathematics and science faculty, yogyakarta state university, yogyakarta, indonesia *corresponding author: isana_supiah@uny.ac.id (received: 4th december 2018; accepted: 4th july 2019; published on-line:2nd december 2019) abstract: the cyclic voltammogram is widely used to analyse the electrolysis process. the use of various media, namely rambutan seed flour (nephelium lappaceum), mango seed flour (mangifera indica), breadfruit leaf powder (artocarpus altilis), peria extract (momordi charantia) and aloe vera extract (aloe vera), in this study is to deliberately mimic the occurrence of those media in wastewater produced by several industries. the electrolysis analysis on the presence of several media would minimize the preparation steps on wastewater utilization for generating hydrogen as renewable energy. the research looks at the potential of wastewater as the raw material for the electrolysis process. in this research, stainless steel cyclic voltammograms were studied on water electrolysis. the electrolysis was done in base solution and adding various media, such as rambutan seed flour (nephelium lappaceum), mango seed flour (mangifera indica), breadfruit leaf powder (artocarpus altilis), peria extract (momordi charantia) and aloe vera extract (aloe vera) in various concentrations, 0 10 g per litter of water. by reviewing the activity of a stainless steel electrode to decompose water molecules, the media generally caused the occurrence of covering by relatively large molecules around the electrode surface, resulting in decreased activity of the stainless steel electrodes. the optimum condition occurred with the addition of breadfruit leaf powder in all treatments with similar electrode activity as much as 1.68. the result could be implemented in a wastewater electrolysis processes containing the media to generate hydrogen gas. abstrak: voltammogram berkitar banyak digunakan bagi menganalisis proses elektrolisis. dalam kajian ini pelbagai jenis media telah sengaja digunakan seperti tepung biji rambutan (nephelium lappaceum), tepung biji mangga (mangifera indica), serbuk daun sukun (artocarpus altilis), ekstrak peria (momordi charantia) dan ekstrak lidah buaya (aloe vera), bagi memimik terjadinya media-media tersebut dalam sisa air buangan yang terhasil daripada beberapa industri. analisis elektrolisis pada pelbagai media dapat mengurangkan langkahlangkah persiapan pada penggunaan sisa air bagi menghasilkan hidrogen sebagai tenaga boleh baharu. penilitian kajian ini bertumpu pada potensi sisa air sebagai bahan kasar bagi proses elektrolisis. kajian ini adalah tentang elektrolisis air voltammogram berkitar pada keluli tahan karat. proses elektrolisis telah dilakukan pada larutan dasar dan dengan menambah pelbagai media, seperti tepung biji rambutan (nephelium lappaceum), tepung biji mangga (mangifera indica), serbuk daun sukun (artocarpus altilis), ekstrak petola (momordi charantia) dan ekstrak lidah buaya (aloe vera) dalam pelbagai kepekatan, 0 10 gram pada setiap liter air. penurunan aktiviti elektrod keluli tahan karat telah disebabkan oleh aktiviti elektrod keluli tahan karat yang mengurai molekul air dan diliputi molekul-molekul besar pada permukaan 1 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 elektrod. keadaan optimum telah berlaku dengan penambahan serbuk daun sukun pada semua rawatan dengan aktiviti elektrod serupa sebanyak 1.68. dapatan kajian dapat digunakan dalam proses elektrolisis sisa air yang mengandungi media bagi menghasilkan gas hidrogen. keywords: voltammogram; stainless steel; media; electrode activity; efficiency 1. introduction the voltammetry method is favourable for synthesis, analysis, and characterization or application, namely linear and cyclic voltammetry. in cyclic voltammetry, the same potential was applied on continuous time measurement for the electric current recording [1-5]. furthermore, an electric current is plotted against a potential (voltammogram) which can be used as a basis for analysing samples. for the same sample measured under similar conditions, it will have a similar voltammogram. otherwise, when the modified state is applied, it will give a different voltammogram. the electrolysis of water will provide a typical cyclic voltammogram with differences occurring for electrodes and media changes. hence, it could be used to study the efficiency of the electrolysis process. water molecules can be decomposed to hydrogen and oxygen gases by electrolysis. the electrolysis process depends on the type of electrolyte, the type of electrode, current, and time used [6-10]. hydrogen is a well-known renewable energy source with its environmentally friendly property. hydrogen gas production by electrolysis of water has relatively lowefficiency [11]. therefore, it is necessary to strive for a condition of electrolysis of water with high efficiency in hydrogen gas production and voltage efficiency. to produce safe, environmentally friendly, and cheap hydrogen it needs an effort to meet energy demand, given the increasing rarity of fossil fuels and their non-renewability. one of the methods to increase efficiency is through modification of the electrodes. the preparation, characterization, and application of stainless steel electro-catalyst electrodes for producing hydrogen gas had been reported by isana et al. [12]. the voltammogram pattern of the stainless steel/fe-co-ni electrolysis in base solution had been analysed by [13] and the reaction of hydrogen evolution in the stainless steel/fe-co-ni electrode [14] showed that the ternary electrode has relatively better catalytic activity than binary and single electrodes. the reaction of hydrogen evolution in fe-co/s, fe-ni/s and co-ni/s electrodes [15] showed that stainless steel coated electrodes with binary metals have relatively better catalytic activity than stainless steel electrode. meanwhile, islam [16] evaluated the surfaces of fe-ni films on various coating bath media and concluded the morphology that is characterized by a coarse-grained and non-smooth surfaces with the presence of micro-cracks on it is superior. other studies by hairin et al. [17] and salim [18] showed that high surface area is produced from the coating using the electrodeposition method. another method to increase efficiency is conducted on the batch solution manipulation of water electrolysis. the temperature thermogram against the time of electrolysis of various brands of salt solution using carbon electrodes showed the diversity of thermograms, which differed with each brand that had been studied by isana [19]. another study on well water from various places with stainless steel electrodes indicated that each well water has different electrolysis behaviour [20]. furthermore, the splitting of water molecules in a cornstarch medium had been reported, as well as in the medium of mocaf [21], in the ipomoea batatas l flour medium [22], in dahlia bulbs flour [23, 24], in the bitter melon medium [25], and in mango 2 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 seed flour [26] showing that there was covering at the surface of the electrode by the flour. both the production of hydrogen and catalytic activity were relatively dependent on the media. the modification of batch solution can be beneficial on either improving the quality of water electrolysis or utilizing the wastewater of several industries containing several media. to study the effect of media addition in the water electrolysis process, research was carried out on the electrolysis of water in base solutions by using stainless steel electrodes in various media. the media used in this research were rambutan seed flour (nephelium lappaceum), mango seed flour (mangifera indica), breadfruit leaves powder (artocarpus altilis), peria extract (momordi charantia) and aloe vera extract (aloe vera). the major chemical compositions in the media from various studies are described in table 1 and illustrated in fig. 1. the problem formulation is (1) how does the activity of the stainless steel electrode affect the process of decomposition of water in various media based on the cyclic voltammogram? (2) how does media concentration affect the decomposition of a water molecule? (3) what is the value of the decomposing water molecule to produce hydrogen and oxygen gases in various media at the optimum condition? table 1: major composition of media in water electrolysis using stainless steel media carbohydrate fatty acids crude protein amylose reference rambutan seed flour 87.04% 10.07% 32.14% [27] mango seed flour 64.23% 12.00% 4.95% [28] breadfruit leaves powder 50.00% 22.45% [29] peria extract 18.02% [30] aloe vera extract 61.68% 11.21% [31] (a) (b) (c) (d) (e) fig. 1: (a) rambutan and seed, (b) mango and seed, (c) breadfruit leave, (d) peria and (e) aloe vera. 2. materials and methodology the equipment used here included glassware for preparation, an electrolysis tube, and a edaq echem voltammeter. the materials used were nitric acid, acetone, and nahco3 (merck). other materials such as stainless steel grades s-430 (thickness 1.2 mm, width 3 mm, 3 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 and length 110 mm), platinum electrodes, and ag/agcl electrodes were equipped as part of the electrolysis apparatus. the solvents, such as distilled water and aquabides, were produced locally in laboratory, while the media of rambutan seed flour, mango flour, breadfruit powder, peria extract, and aloe vera extract were prepared and extracted from the local market. several processes such as rinsing, drying, size reduction, and 100-mesh screening were used in the flour production of the media. meanwhile, aloe vera extract was obtained by crushing the raw material using a blender followed by a filtration process. fig. 2: edaq echem voltammeter equipment in this study. nahco3 (5 g) was poured into one litre of water to make a base solution of mother liquor. mother solution was added with each media with various concentrations under constant stirring for 1 hour. the concentration of the media varied from 0 to 10 g per 1 liter of water. electrolysis of water was carried out by using stainless steel electrodes and various media. meanwhile, the edaq echem voltammeter (fig. 2) was used to analyse the voltammetry during the electrolysis of water using multiple media. furthermore, cyclic voltammetry was conducted twice for each sample to ensure data reliability. the edaq echem have recorded the value of anodic-cathodic peak current and anodic-cathodic peak potential of the cyclic voltammogram data file experiment, which was further analysed to gain production efficiency and voltage efficiency. production efficiency was calculated based on a comparison of the cathodic current peak with or without media, as shown in eq. 1. meanwhile, voltage efficiency was compared; observed as the voltage at the cathodic peak condition, for every treatment and the treatment without media as shown in eq. 2. furthermore, the electrolysis activity is expressed in eq. 3 as comparing product efficiency and voltage efficiency. (1) (2) (3) 4 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 where thermodynamic voltage is 1.229 v at standard temperature and pressure. 3. results and discussion the stainless steel voltammogram in various media can be seen in fig. 3. based on the stainless steel cyclic voltammogram, the cathodic current peak and potential for each system of mass of media versus the efficiency of products are presented in fig. 4 and voltage efficiency in fig. 5 in various media such as rambutan seed flour, mango seed flour, breadfruit leaves powder, peria extract, and aloe vera extract. the efficiency of hydrogen product and the voltage efficiency in various media from the cyclic voltammogram are summarized in table 2. meanwhile, product efficiency and voltage efficiency also were drawn in figs. 4 and 5 to compare influences with each other. furthermore, the activity of electrolysis was shown in table 3 with the comparison of product efficiency and voltage efficiency in various media. from voltage efficiency, we can calculate the product efficiency using a comparison of voltage efficiency with or without media in every treatment. -2.00e-01 -1.00e-01 0.00e+00 1.00e-01 2.00e-01 3.00e-01 4.00e-01 -1.5 -1 -0.5 0 0.5 1 1.5 -4.00e-01 -2.00e-01 0.00e+00 2.00e-01 4.00e-01 6.00e-01 8.00e-01 -1.5 -1 -0.5 0 0.5 1 1.5 -6.00e-01 -4.00e-01 -2.00e-01 0.00e+00 2.00e-01 4.00e-01 6.00e-01 8.00e-01 -1.5 -1 -0.5 0 0.5 1 1.5 -6.00e-01 -4.00e-01 -2.00e-01 0.00e+00 2.00e-01 4.00e-01 6.00e-01 8.00e-01 -1.5 -1 -0.5 0 0.5 1 1.5 i ( m a) i ( m a) i ( m a) i ( m a) e (v) e (v) e (v) e (v) (a) (b) (c) (d) 5 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 fig. 3: cyclic voltammogram of stainless steel in various media: (a) rambutan seed flour, (b) mango seed flour, (c) breadfruit leaves powder, (d) peria extract, (e) aloe vera extract, and (f) without media. tabel 2: the efficiency of hydrogen product and voltage efficiency in various media no. system product efficiency (%) voltage efficiency (%) rsf msf blp pe ave rsf msf blp pe ave 1 0 g 100.0 100.0 100.0 100.0 100.0 67.4 59.2 59.6 59.3 59.8 2 1 g 74.3 46.6 97.4 61.6 62.3 55.2 48.7 58.0 58.6 60.0 3 2 g 69.7 34.8 96.3 38.1 58.3 53.5 44.7 57.4 57.7 59.1 4 3 g 49.6 35.5 100.8 53.2 51.0 54.4 43.8 60.0 58.7 59.7 5 4 g 59.8 30.8 102.2 56.5 48.4 53.5 43.9 60.9 58.7 59.5 6 5 g 72.7 36.1 98.9 55.7 40.2 53.5 47.0 58.9 56.1 59.6 7 6 g 67.4 34.0 95.0 55.1 36.2 55.2 46.6 56.6 56.6 59.2 8 7 g 68.7 26.7 98.1 21.3 36.0 54.4 50.7 58.4 56.1 59.2 9 8 g 53.4 30.4 95.6 19.5 22.8 53.5 47.2 57.0 54.4 59.1 10 9 g 40.7 36.7 99.5 48.5 25.5 54.4 46.3 59.2 53.6 59.2 11 10 g 40.6 35.6 96.5 35.8 27.7 53.5 47.4 57.4 49.9 59.3 rsf: rambutan eed flour, msf: mango seed flour, blp: breadfruit leaves powder, pe: peria extract, and ave: aloe vera extract cyclic stainless steel voltammograms in various media can be used to study the activity of the stainless steel electrode on decomposition of water molecules to form hydrogen and oxygen gases. the comparison between product gained, and the voltage efficiency is the best method to represent the activity of the stainless steel electrode on decomposition of water molecules to form hydrogen and oxygen gases. randles-sevcik’s equation describes that the peak current for a reversible system is affected by electron stoichiometry (n), electrode area (a, cm2), diffusion coefficient (d, cm2/s), concentration (mol/cm3), and scan rate ( , v/s) as shown at eq. 5. thus, the concentration of the product is affecting the peak current of cyclic voltammetry. voltage efficiency is the value of energy used to produce hydrogen and oxygen gas compared to the initial condition without any addition of the media. (5) -4.00e-01 -2.00e-01 0.00e+00 2.00e-01 4.00e-01 6.00e-01 8.00e-01 -1.5 -1 -0.5 0 0.5 1 1.5 -4.00e-01 -2.00e-01 0.00e+00 2.00e-01 4.00e-01 6.00e-01 8.00e-01 -1.5 -1 -0.5 0 0.5 1 1.5 i ( m a) e (v) (e) e (v) i ( m a) (f) 6 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 fig. 4: the efficiency of hydrogen product of various media. fig. 5: the voltage efficiency of various media, solid and dotted line indicated major and minor y-axis respectively. regarding voltage efficiency, the addition of rambutan seed flour and mango seed flour showed decreasing result. meanwhile, the other media did not significantly impact voltage efficiency. the result of the hydrogen product yield, ranked from relatively high efficiency to relatively small efficiency, is as follows: breadfruit leaves powder, rambutan seed flour, peria extract, aloe vera extract, and mango seed flour. when viewed from energy consumption, illustrated with voltage efficiency, the sequence becomes: mango seed flour, rambutan seed flour, peria extract, breadfruit leaf powder, and aloe vera extract. the most unfavourable 0 20 40 60 80 100 120 0 2 4 6 8 10 p ro du ct io n e ffi ci en cy , % media added, g rsf msf blp pe ave 40.0 45.0 50.0 55.0 60.0 65.0 70.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 0 2 4 6 8 10 v ol ta ge e ffi ci en cy , % system blp pe ave rsf msf 7 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 medium to decompose water molecules into hydrogen and oxygen gases was the aloe vera extract. from table 3, it can be concluded that the bigger the value, the better the activity of the stainless steel electrode is. the calculation using least significant difference was conducted to analyse the significance of the activity of electrolysis value. in general, the media caused the covering surface of the electrode because of its relatively large molecules, resulting in decreased activity of the electrode, as presented in fig. 6 (b). from eq. 4, it can be shown that the presence of media can disturb the diffusivity (d, cm2/s) because the media are covering the electrode. interestingly, the addition of breadfruit leaves powder gave an unusual trend, as shown in fig. 6 (a). those graph tendencies are strongly believed to be the result of the polymer structure in the media that had not covered the electrode. the polymer occurrence in every media affects the interaction between the surface of the electrode and the polymer itself influences the electrode activity. tabel 3: activity of electrolysis in various media no system activity of electrolysis rsf msf blp pe ave 1 0 g 1.49b 1.70a 1.68a 1.69a 1.68a 2 1 g 1.35b 0.96b 1.68a 1.06b 1.04b 3 2 g 1.31b 0.78c 1.68a 0.66c 0.99b 4 3 g 0.92c 0.82c 1.68a 0.91c 0.86c 5 4 g 1.12b 0.71c 1.68a 0.97b 0.82c 6 5 g 1.36b 0.77c 1.68a 1.00b 0.68c 7 6 g 1.23b 0.73c 1.68a 0.98b 0.62c 8 7 g 1.27b 0.53c 1.68a 0.38c 0.61c 9 8 g 1.00b 0.65c 1.68a 0.36c 0.39c 10 9 g 0.75c 0.80c 1.68a 0.91c 0.44c 11 10 g 0.76c 0.76c 1.68a 0.72c 0.47c rsf: rambutan seed flour, msf: mango seed flour, blp: breadfruit leaves powder, pe: peria extract, and ave: aloe vera extract a,b, and c show significance group. fig. 6: the activity of electrolysis in various media; (a) unusual trend and (b) usual trend. 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 0 5 10 a ct iv ity o f e le ct ro ly si s media added, g blp 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 0 5 10 a ct iv ity o f e le ct ro ly si s media added, g msf ave rsf pe (a) (b) 8 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 the optimum condition occurred when the electrolysis activity is highest. it is obtained when the production efficiency is high, and the voltage efficiency is low. the higher the cathodic current peak, the higher hydrogen production is, so that the higher the activity of the electrode; and the lower the potential, the lower the voltage efficiency. that is the best condition to decompose water molecules into hydrogen and oxygen gases. therefore, the optimum condition from this research occurred with the addition of breadfruit leaves powder for which the electrolysis activity was constant around 1.68. 4. conclusion the activity of stainless steel electrodes in the decomposition of a water molecule into hydrogen and oxygen gases in various media varied greatly. the optimum conditions for water molecule decomposition into hydrogen and oxygen gases were achieved by adding breadfruit leaves powder at every system with similar activity of electrolysis around 1.68. the addition of various media, regularly, could not improve the electrode activity, but the addition of breadfruit leaves powder could stabilize the electrode activity. the results could give an illustration and initial data to the generalization of hydrogen gas using the electrolysis process in wastewater mainly containing flour media. acknowledgement the authors send gratitude to the university for the facilities and support during the research. references [1] fricke, k., harnisch, f., and schröder, u., 2008, on the use of cyclic voltammetry for the study of anodic electron transfer in microbial fuel cells, energy & environmental science, 1(1): 144-147. [2] karlberg, g., jaramillo, t., skulason, e., rossmeisl, j., bligaard, t., and nørskov, j.k., 2007, cyclic voltammograms for h on pt (111) and pt (100) from first principles, physical review letters, 99(12): 126101. [3] kissinger, p.t. and heineman, w.r., 1983, cyclic voltammetry, journal of chemical education, 60(9): 702. [4] van benschoten, j.j., lewis, j.y., heineman, w.r., roston, d.a., and kissinger, p.t., 1983, cyclic voltammetry experiment, j. chem. educ., 60(9): 772. [5] rountree, e.s., mccarthy, b.d., eisenhart, t.t., and dempsey, j.l., evaluation of homogeneous electrocatalysts by cyclic voltammetry, acs publications, 2014. [6] bard, a.j., faulkner, l.r., leddy, j., and zoski, c.g., 1980, electrochemical methods: fundamentals and applications, wiley new york, [7] de nora, o., de nora, v., and spaziante, p.m., electrolysis cells, google patents, 1977. [8] denora, o., electrolysis cell, google patents, 1986. [9] olivares-ramirez, j., campos-cornelio, m., godínez, j.u., borja-arco, e., and castellanos, r., 2007, studies on the hydrogen evolution reaction on different stainless steels, international journal of hydrogen energy, 32(15): 3170-3173. 9 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 [10] stojić, d.l., marčeta, m.p., sovilj, s.p., and miljanić, š.s., 2003, hydrogen generation from water electrolysis—possibilities of energy saving, journal of power sources, 118(12): 315-319. [11] zeng, k. and zhang, d., 2010, recent progress in alkaline water electrolysis for hydrogen production and applications, progress in energy and combustion science, 36(3): 307326. [12] isana syl, w.t., agus kuncaka and triyono, 2016, preparation, characterization and application of stainless steel/fe, co, ni electrocatalyst electrodes, j. chem. & cheml. sci., 6 (11)1151-1160. [13] isana, s., trisunaryanti, w., and kuncaka, a., 2012, studies on the hydrogen evolution reaction on fe-co-ni, iosr journal of applied chemistry, 6-10. [14] louise, i.s.y., 2014, stainless steel/fe-co-ni sebagai elektro katalis pada reaksi evolusi hidrogen, [15] isana s. y. l., w.t., agus k., triyono, studies on the hydrogen evolution reaction on fe-co/s, fe-ni/s and co-ni/s electrodes, the international post graduate conference on science and mathematics 2013, convention hall, e-learning building, universiti pendidikan sultan idris, malaysia, 2013. [16] islam, m., 2009, anomalous electrodeposition of fe-ni alloy coating from simple and complex baths and its magnetic property, iium engineering journal, 10(2): 108-122. [17] hairin, a.n., othman, r., ani, m.h., and saputra, h., 2011, high discharge rate electrodeposited zinc electrode for use in alkaline microbattery, iium engineering journal, 12(5): 115-122. [18] salim, w.w.a.w., benoudjit, a., guthoos, h.f.a., and arris, f.a., 2017, pedot: pssmodified platinum microelectrodes for measurement in aqueous media: effect of polymer surface area on long-term anodic peak current stability, iium engineering journal, 18(2): 11-15. [19] isana, s., variasi temperatur dan waktu pada elektrolisis larutan garam dapur berbagai merk, seminar nasional kimia, 2009. [20] isana, s., perilaku sel elektrolisis air dengan elektroda stainless steel, prosiding seminar nasional kimia dan pendidikan kimia, yogyakarta, 2010, pp. 1-9. [21] louise, y.a.a.a.i.s.y., reaksi evolusi hidrogen menggunakan media tepung mocaf dengan elektroda stainless steel/fe-co-ni, jurusan pendidikan kimia, universitas negeri yogyakarta, 2016. [22] isana s. y. l., s., heru pratomo, voltamogram siklik stainless steel dalam media tepung ubi jalar (ipomoea batatas l) (cyclic voltammogram of stainless steel in ipomoea batatas l flour), seminar nasional kimia, jurusan pendidikan kimia fmipa universitas negeri yogyakarta, yogyakarta, indonesia, 2016. [23] isana, s., yuanita, d., and pratomo, h., 2015, pemecahan molekul air dengan menggunakan media tepung umbi dahlia (dahlia pinnata), jurnal sains dasar, 4(2): 173-178. [24] isana, s., yuanita, d., sulistyani, a., and pratomo, h., voltammogram of stainless steel/fe-co-ni electrode on water electrolysis in base condition with dahlia pinnata tuber starch media, american institute of physics conference series, 2017. [25] isana s. y. l., h.p.a., sulistyani, dan lathifa h., the efficiency of hydrogen production from water electrolysis with bitter melon as a media using stainless steel/fe-co-ni 10 iium engineering journal, vol. 20, no. 2, 2019 yosephine louise et al. https://doi.org/10.31436/iiumej.v20i2.1030 electrode, basic and applied sciences interdisciplinary conference (basic), universitas indonesia, jakarta, indonesia, 2017. [26] isana s. y. l., s., dan nur a. r., breaking of h2o in mango seed flour medium with stainless steel/fe-co-ni electrode, basic and applied sciences interdisciplinary conference (basic), universitas indonesia, jakarta, indonesia, 2017. [27] eiamwat, j., wanlapa, s., sematong, t., reungpatthanapong, s., phanthanapatet, w., hankhuntod, n., and kampruengdet, s., 2015, rambutan (nephelium lappaceum) seed flour prepared by fat extraction of rambutan seeds with sc-co2, isan journal of pharmaceutical sciences, 10138-146. [28] okpala, l. and gibson-umeh, g., 2013, physicochemical properties of mango seed flour, nigerian food journal, 31(1): 23-27. [29] oladipupo, a.a. and abiodun, t.g., 2014, phytochemical analysis and antimicrobial effect of chrysophillum albidum leave extract on gastrointestinal tract pathogenic bacteria and fungi in human, journal of applied chemistry, 71-5. [30] yuwai, k.e., rao, k.s., kaluwin, c., jones, g.p., and rivett, d.e., 1991, chemical composition of momordica charantia l. fruits, j. agric. food chem., 39(10): 1762-1763. [31] scala, k.d., vega-gálvez, a., ah-hen, k., nuñez-mancilla, y., tabilo-munizaga, g., pérez-won, m., and giovagnoli, c., 2013, chemical and physical properties of aloe vera (aloe barbadensis miller) gel stored after high hydrostatic pressure processing, food science and technology, 33(1): 52-59. 11 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice 404 not found application of digital cellular radio for mobile location estimation khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 radiation dose delivered by 125i, 103pd and 131cs and dose enhancement by gold nanoparticle (gnp) solution in prostate brachytherapy: a comparative analysis by monte carlo simulation hamda khan1, umair aziz2*, zafar ullah koreshi2 1department. of mathematics, national university of computer and emerging sciences, islamabad, pakistan. 2department of mechatronics engineering, air university, islamabad, pakistan. *corresponding author: umair.aziz@mail.au.edu.pk (received: 10th april 2019; accepted: 1st august 2019; published on-line:2nd december 2019) abstract: the energy deposition and radiation dose from commonly used radioisotopes, 125i,103pd, and 131cs, used for brachytherapy of cancers is estimated using monte carlo (mc) simulations. to enhance the dose, gold nanoparticle (gnp) solutions are injected into the tumor; this results in more effective and shorter therapy duration. it is thus important to estimate the dose enhancement factor (def) achievable by a radioisotope. the research presented in this paper thus focuses on a comparative analysis of radioisotopes. to estimate the radiation dose, the monte carlo n-particle code mcnp5 was used for a coupled photon-electron simulation of radiation transport from radiation emanating from seeds of radioisotopes implanted in the prostate at positions prescribed to deliver effective doses to the tumor while protecting neighbouring vital organs such as the rectum and urethra. the quantities tallied were the energy deposition (f6 tally) and the pulse heights (*f8 tally) in specified energy bins. the energy deposited in the tumor was used to estimate the absorbed dose to the prostate incorporating the transformations of the radioisotopes during decay. the absorbed dose was subsequently estimated for a gnp-tissue solution with a concentration of 25 mg au/g of prostate tissue, modelled as a homogenous mixture. from the simulations, it was found that the lifetime absorbed dose is ~96 gy from 98 seeds, each of 0.31 mci, of 125i; ~102 gy, from 115 seeds, each of 1.4 mci, of 103pd, and ~90 gy from 131cs seeds replacing 103pd seeds of the same initial activity. the main advantage of 131cs, over 125i and 103pd, is observed in the larger dose rate (~26 cgy/hr) delivered initially i.e. in the first few days which is 1.5 and 5.7 times higher than that for 103pd and 125i. the absorbed dose for 125i, 103pd and 131cs increases to ~245, ~130, ~187 gy respectively with gnp-tissue solution of 25 mg au/g tissue. from the analysis, it is found that while the lifetime absorbed dose of all three radioisotopes is of the same order, there are advantages in using 131cs; these advantages are further quantified. abstrak: pemendapan tenaga dan dos sinaran radiasi daripada radioisotop yang biasa digunakan, 125i,103pd, dan 131cs, digunakan bagi terapibraki kanser dianggar menggunakan simulasi monte carlo (mc). bagi meningkatkan dos, larutan partikel nano emas (gnp) telah disuntik ke dalam tumor; ini lebih memberi kesan dan mengurangkan masa terapi. oleh itu, adalah penting menganggar faktor dos penggalak (def) dapat dicapai dengan radioisotop. kajian ini mengfokuskan pada analisis perbandingan radioisotop. bagi menganggarkan dos radiasi, kod monte carlo n-partikel mcnp5 telah digunakan pada simulasi pasangan foton-elektron pengangkutan radiasi daripada 176 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 pancaran radioaktif benih radioisotop yang ditanam dalam prostat pada posisi yang disebut bagi mencetuskan dos penghantaran yang berkesan pada sel tumor. dalam masa sama melindungi organ penting seperti rektum dan uretra. kuantiti diselaras dengan pemendapan tenaga (selaras f6) dan ketinggian denyut (selaras *f8) dalam aras tenaga sebenar. tenaga yang dienap dalam sel tumor ini telah digunakan bagi menganggarkan dos serapan pada prostat dengan menggabungkan transformasi radioisotop ketika susutan. dos yang diserap telah kemudiannya dianggarkan bagi larutan tisu-gnp dengan ketumpatan 25 mg au/g tisu prostat, dimodelkan sebagai campuran homogen. daripada simulasi, dapatan kajian menunjukkan dos diserap sebanyak ~96 gy daripada 98 benih, setiap satu daripada 0.31 mci, 125i; ~102 gy, dari 115 benih, setiap 1.4 mci, dari 103pd, dan ~90 gy daripada benih 131cs menggantikan benih 103pd pada pemulaan aktiviti yang sama. keistimewaan utama adalah 131cs, ke atas 125i dan 103pd, telah dilihat dalam kadar dos lebih besar (~26 cgy/hr) dikeluarkan pada pemulaannya iaitu dalam beberapa hari pertama iaitu 1.5 dan 5.7 kali lebih tinggi daripada 103pd dan 125i. dos yang diserap pada 125i, 103pd dan 131cs bertambah kepada ~245, ~130, ~187 gy masingmasing dengan larutan tisu-gnp sebanyak 25 mg au/g tisu. hasil analisis menunjukkan penyerapan seumur hidup dos diserap pada ketiga-ketiga radioisotop dalam aturan yang sama, ini adalah keistimewaan menggunakan 131cs; keistimewaan ini akan terus diuji pada masa depan dan diukur kuantitinya. keywords: monte carlo; simulation; medical; prostate cancer therapy; gold nanoparticles; dose enhancement 1. introduction cancer cases globally are expected to grow from 14.1 million in 2012 to 24 million by 2035 [1, 2] with the top three: lung [3], prostate [4-6], and colorectal cases accounting for over 47% of all cancers in men. the treatments for cancer, in order of general preference, are chemotherapy, surgery, and radiation therapy. in the case of recurrent cancers however, brachytherapy is the preferred treatment due to its localized and noninvasive effects. for brachytherapy, radioisotopes with energy <50 kev, such as 125i and 103pd sources [7-9] with typical implants of 50-80 metallic seeds encasing isotopes, are used as low dose rate (ldr) [10] therapies for the treatment of prostate cancer, uveal melanomas and brain tumours. the dose is estimated by a number of computer codes such as egsnrc, geant[11], penelope [12] and mcnp [13] based on monte carlo (mc) methods [14]. further improvements in the effectiveness of brachytherapy are being considered by the injection of gold nanoparticles through fenestrations of cancer cells. the particle size requirements are in the nanoscale range (~10-9 m) which is comparable with the diameter of an atom (~10-10 m) [15, 16]. for mc simulations in brachytherapy, it has been demonstrated that def is a function of the source energy and concentration of gnp solution [17-20], while the size of gnps is not so important (above the k-edge energy). thus, in this work, a homogenous model with considerable savings on the computational effort, required for a full heterogeneous model, is used to extract crucial information on the def resulting from the presence of gold in small concentration while mcnp has the capability of modelling very detailed heterogeneous configurations. this paper considers a homogenous model solely for the purpose of carrying out a comparative study for the dose delivered to a prostate tumour by 125i, 103pd and 131cs and particularly the enhancement of radiation dose due to the presence of gold. 177 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 the ultimate goal of brachytherapy is to deliver maximum dose to the tumour while minimizing collateral damage to the normal tissue and for maximizing the def, there is still no consensus on the optimal size, shape and distribution of gnps. however, experimental and pre-clinical evidence for mouse tumours, showing a 1-year survival rate of 86% following a dose of 26 gy with 1.9 nm intravenously administered gnps vs 20% for tumours not laden with gnps [15], indicate that nanotechnology offers promising improvements in brachytherapy. the radioisotope cesium-131 (131cs), was introduced to brachytherapy in 2004 [21] and in the first five years it was used in about 3000 prostate implants yielding the required dose in less time compared with 125i and 103pd due to its shorter half-life and high energy, as shown in table 1. table 1: energy and half-life of 125i, 103pd and 131cs radionuclide e (kev) t1/2 (days) 103pd 20.8 17 125i 35.49 59.4 131cs 29-30.4 9.7 typically,125i is used with a radiation dose of 145 gy or more conforming to the prescribed dose of 145 gy suggested by the american association of physicists in medicine task group 64 [22]. while all three are low-energy sources, so that their dose would not extend to normal tissue in nearby organs [23], one of the main advantages of 131cs is that it offers an initial dose rate of ~32 cgy/h at the periphery [24] which is 1.5 and 4 times higher than that from 103pd and 125i respectively. this initial dose rate advantage is a vital radiobiological parameter for rapidly growing tumours [25] as well as for slow-growing tumours such as prostate adenocarcinomas. a set of clinical recommendations for prescribed doses, on the basis of 1200 prostate implants [26] indicated that the high initial dose rate of 131cs caused more intense urinary and rectal complication but they also resolved more quickly than that for 125i and 103pd. that study also found that the drop in prostate-specific antigen levels from 131cs, with a maximum follow-up of just over three years and median follow-up of 23 months, were equivalent to that from other isotopes. such promising results from 131cs extended its use to gynecological malignancies [27] and to brain radiotherapy [28] from which it was demonstrated that this treatment was well-tolerated and safe for patients. 2. materials and methods 2.1 monte carlo simulation the monte carlo code mcnp5 is used to carry out a coupled photon-electron simulation of radiation transport in the range 1 kev-100 mev to estimate the radiation dose distribution for prostate tumor brachytherapy. the radioisotope sources considered are 125i, 103pd and 131cs in the form of ‘seeds’ modelled as point sources. for 125i, 98 seeds each of 0.31 mci and for 103pd 115 seeds each of 1.4 mci were spatially distributed in the tumour tissue, as shown in fig. 1 [29] for data given for two patients with different size prostates. the placement of needles takes into account a number of factors including the location of vital organs surrounding the prostate, such as the bladder, urethra, and rectum. 178 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 for simulating the effect of 131cs, the 103pd seeds were replaced by 131cs seeds of the same initial activity and spatial distribution. the energy deposition track length estimation tally f6 and the pulse height tally *f8 are both used for estimating energy deposition to get reliable estimates in case of a few interactions in a region of interest. the simulation is repeated with gold-tissue solution; material compositions for both simulations are listed in table 1. the photon and electron data for both tissue and gold are based on endf/b-vi (release 8). in mcnp the “detailed physics” simulation incorporates coherent (thomson) scattering and fluorescent photons produced from photoelectric absorption. electrons produced from photon collisions are transported in a “condensed history” method that accumulates the effects of many individual collisions into single steps sampled probabilistically. the effects of such artefacts for electron transport have been investigated [30-32] with egsnrc, geant and penelope codes and in some cases “large discrepancies” (>3%) have been found between mcnp5 dose distributions and the ‘reference codes’ concluding that mcnp5 electron transport calculations are not accurate at all energies and in every medium by general clinical standards. it can thus be anticipated that mcnp5 may differ due to its inadequate low-energy treatment of electron transport. authors of [33] have carried out electron transport comparisons of mcnpx, penelope and egsnrc, for electrons of 20-450 kev in water, lead, and tungsten. these comparisons were focused on bremsstrahlung, energy deposition in matter, electron ranges and production of secondary electrons by gamma radiation. fig. 1: placement of 25 needles with 98 seeds of 125i in the x-y plane. -5 -4 -3 -2 -1 0 1 2 3 4 5 -5 -4 -3 -2 -1 0 1 2 3 4 5 125i seeds x(cm) y (c m ) 179 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 fig. 2: placement of 29 needles of 115 seeds of 103pd/131cs in the x-y plane. the f6 tally for dose from mcnp is converted from mev/g to yield the dose rate in gy/hr by using the activity as shown below. 2.2 activity and transformations the activity of a radioisotope is and the number of transformations in an interval is thus (1) thus the ‘infinite-time’ transformations i.e. the number of disintegrations integrated over the time interval is . the absorbed dose is computed as follows: (2) where is the initial activity, n is the number of radioisotope seeds, and is the energy pulse height (*e8) tally (mev) and m is the mass of the tumor (g). thus, the absorbed dose varies directly with the energy deposition and source, which in turn depends on the number of transformations i.e. the product of initial activity and halflife. -5 -4 -3 -2 -1 0 1 2 3 4 5 -5 -4 -3 -2 -1 0 1 2 3 4 5 103pd seeds x(cm) y (c m ) 180 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 3. results mcnp simulations were carried out on an intel(r) core (tm) i7-2620m cpu @ 2.70ghz with an installed memory of 8.00 gb (3.24 gb usable) and 32-bit operating system with windows 7 professional. the runtime for each simulation of 107 source particles was 35.60, 51.1 and 41 minutes for 125i, 103pd and 131cs, respectively the time-dependent transformations and activities of 125i, 103pd and 131cs, for an initial activity of 1 mci each, are shown in fig. 3. the basic hypothesis for effectiveness of each isotope arises from its half-life. this factor results in a longer decay time for 125i while faster decay rates of 103pd and 131cs translate into lifetime transformations of 2.74 × 1014, 7.84 × 1013 and 4.47 × 1013 for 125i, 103pd and 131cs respectively which clearly illustrate the slow build-up, but higher dose from 125i after ~ six months compared with the much faster effects of 103pd and 131cs. there is hence a saturation in activities for 103pd and 131cs with the implications that the effect of these two isotopes is seen much faster than that for 125i. figure 4 shows the absorbed dose for 125i (initial activity 0.31 mci, 98 seeds distributed as illustrated in fig. 1), 103pd and 131cs (both of initial activity 1.4 mci 115 seeds distributed as illustrated in fig. 2) which indicates that 131cs is clearly the best in terms of delivering the highest and fastest dose to the tumour, reaching 50 gy in the first 10 days and 100 gy when gnps in a solution of 25 mg/g tissue are injected in the tumour. the absorbed dose on a longer timescale, however, is highest for 125i with gnp solution but exceeds that from 131cs after about three months. for the sake of comparison, when all seeds are of equal initial activity (1.4 mci) and placed in the configuration of fig. 2, it is seen in fig. 5 that the highest absorbed dose for both cases, with and without gnpsolution, is the highest at 117 gy and ~283 gy respectively but after ~250 days). thus for a given requirement, 125i exceeds the 103pd dose in about 200 days; higher doses for stronger tumours can thus not be treated by 131cs and 103pd unless they are used in conjunction with gold solutions. fig. 3: transformations and activity of 125i, 103pd and 131cs each of initial activity 1 mci. 0 20 40 60 80 100 120 140 160 180 0 1 2 3 4 x 10 14 125i 125i 103pd 103pd 131cs 131cs t ra n sf o rm a tio n s time (days) 0 20 40 60 80 100 120 140 160 180 0 2 4 x 10 7 0 20 40 60 80 100 120 140 160 180 0 1 2 3 4 x 10 7 0 20 40 60 80 100 120 140 160 180 0 1 2 3 4 x 10 7 a ct iv ity ao=1 mci 181 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 fig. 4: absorbed dose (gy) as a function of time (days) in prostate tissue from 98 seeds each of 0.31 mci of 125i, 115 seeds each of 1.4 mci of 103pd and 115 seeds each of 1.4 mci 131cs (replacing 103pd seeds). fig. 5: absorbed dose (gy) as a function of time (days) in prostate tissue from 125i, 103pd and 131cs (115 seeds each of 1.4 mci distributed as in fig. 2) on a shorter time scale, the differences between all three isotopes is seen from the absorbed dose rates shown in fig. 6 showing a clear advantage of 131cs over the first ~300 hours exceeding 5.7 times and 1.5 times that of 125i and 103pd respectively in the initial period and falling gradually, as shown in fig. 7. levelling off is found to be ~300 and ~400 hours respectively for 103pd and 125i. 10 -1 10 0 10 1 10 2 10 3 0 50 100 150 200 250 time (days) a bs d os e (g y) 125i 125i gnp 103pd 103pd gnp 103cs 103cs gnp 10 -1 10 0 10 1 10 2 10 3 0 50 100 150 200 250 300 time (days) a bs d os e (g y) 125i 125i gnp 103pd 103pd gnp 103cs 103cs gnp 182 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 fig. 6: absorbed dose rate (gy/hr) as a function of time (hours) in prostate tissue from 98 seeds each of 0.31 mci of 125i, 115 seeds each of 1.4 mci of 103pd and 115 seeds each of 1.4 mci 131cs (replacing 103pd seeds). fig. 7: relative absorbed dose rate (gy/hr) of 131cs (relative to 125i and 103pd) as a function of time (hours) in prostate tissue from 98 seeds each of 0.31 mci of 125i, 115 seeds each of 1.4 mci of 103pd and 115 seeds each of 1.4 mci 131cs (replacing 103pd seeds). the lifetime dose delivered by the three sources considered is shown in table 2. the absorbed dose for 125i, 103pd and 131cs increases from 96.30, 102.21 and 90 gy to ~245, ~130, ~187 gy with gnp-tissue solution of 25 mg au/g tissue. these results are in line 10 0 10 1 10 2 10 3 10 4 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 time (hours) a bs d os e r at e (g y/ hr ) 125i 103pd 103cs 10 0 10 1 10 2 10 3 10 4 0 1 2 3 4 5 6 time (hours) r el . a bs d os e r at e of 13 1 c s 103pd 125i 183 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 with the decay rates of the three isotopes which favour 125i in terms of energy but result in a slow dose delivery. the dose enhancement with gold gnp-tissue found in these simulations is the effect of both source energy of each radioisotope and the solution concentration. the important photon interaction for high-z materials such as gold is the photoelectric effect for which the cross-section varies as so that low energy and high-z are desirable for dose enhancement which is localized to the tumor due to the short range of photoelectrons and auger electrons in the surrounding medium which for electrons of energy 0.1 mev is ~100 microns in water and ~15 microns in gold so that the effect of gold will require thin layers (of the order of to utilize the energy of photoelectrons in water. at this energy, the photoabsorptions were estimated to be ~13.5% of all interactions. thus, the increases found in this work are a measure of the photon interaction in each radioisotope. as shown in table 2, the highest dose achievable is ~245 gy by 125i, and lesser doses by 103pd and 131cs for 25 mg au/g tissue. when the configuration of fig. 2 is used for all three sources of 1.4 mci each, the f6 and f8 tallies for 125i increase to 1.82733 × 10-5 (0.0011) mev/g and 1.24662 × 10-3 (0.0016) mev respectively, as depicted in fig. 5. table 2: lifetime absorbed dose (gy) to prostate tumour due to 125i, 103pd and 131cs. the second result in f6, f8 and abs. dose columns refer to tissue with 25 mg au/g tissue homogenous mixture source t1/2 (d) a0 (mci) e(kev) nseeds tr=a0/ (s-1) f6 (rel. err.) (mev/g) f8 (rel. err.) (mev) abs. dose* (gy) 125i 59.4 0.31 35.49 98 8.5 × 1013 1.73548 × 10-5 (0.0011) 4.30593 × 10-5 0.0012 1.183 × 10-3 (0.0016) 3.0087 × 10-3 0.0010 96.30 244.91 103pd 17 1.4 20.8 115 1.1 × 1014 1.21460 × 10-5 (0.0018) 1.50096 × 10-5 0.0019 8.2786 × 10-4 (0.0015) 1.0511 × 10-3 0.0014 102.21 129.77 131cs 9.7 1.4 30.4 115 6.3 × 1013 1.88145 × 10-5 (0.0012) 3.79186 × 10-5 (0.0013) 1.2803 × 10-3 (0.0015) 2.64847 × 10-3 0.0010 90.17 186.57 *for an organ mass 16.3634 g 4. conclusions from the simulations, it was concluded that: lifetime absorbed dose is ~96 gy from 98 seeds, each of 0.31 mci, of 125i, ~102 gy, from 115 seeds, each of 1.4 mci, of 103pd, and ~90 gy from 131cs seeds replacing 103pd seeds of the same initial activity, there is a saturation in the activities of 103pd and 131cs with the implications that the effect of these two isotopes is much faster than that of 125i, the main advantage of 131cs, is the larger initial dose rate (~26 cgy/hr) for the first few days, which is 1.5 and 5.7 times higher than that for 103pd and 125i, 184 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 with a gnp-tissue mixture, the dose enhancement factors in 125i, 103pd and 131cs are 2.5, 1.26 and 2.1 respectively which give another edge to 131cs, for a specified dose, 125i exceeds 103pd by about 200 days; higher doses for stronger tumours can thus not be treated by 131cs and 103pd unless they are used in conjunction with gold solutions. this work has shown results for three candidate radioisotopes in their effectiveness for the treatment of tumours. the basic hypotheses to determine their effectiveness were their radiation energy and half-life. the monte carlo simulations carried out in this work have elaborated the effect of radiations from three isotopes and found substantially higher time of treatment, as well as stronger radiation dose with 125i than for 103pd and 131cs. funding this research did not receive any specific grant from funding agencies in the public, commercial, or not-forprofit sectors. references [1] common cancer types, national cancer institute [https://www.cancer.gov/types/commoncancers] [2] worldwide cancer data, world cancer research fund. [https://www.wcrf.org/dietandcancer/cancer-trends/worldwide-cancer-data] [3] yu e, lewis c. (2018) lung cancer brachytherapy. current cancer therapy reviews, 14(2): 137-148. doi: 10.2174/1573394714666180208145420. [4] blanchard p, pugh tj, swanson da, mahmood u, chen hc, wang x, graber wj, kudchadker rj, bruno t, feeley t, frank sj. (2018) patient-reported health-related quality of life for men treated with low-dose-rate prostate brachytherapy as monotherapy with 125iodine, 103-palladium, or 131-cesium: results of a prospective phase ii study. brachytherapy, 17( 2): 265-276. doi: 10.1016/j.brachy.2017.11.007. [5] rice sr, olexa g, hussain a, mannuel h, naslund mj, amin p, kwok y. (2019) a phase ii study evaluating bone marrow-sparing, image-guided pelvic intensity-modulated radiotherapy (imrt) with cesium-131 brachytherapy boost, adjuvant chemotherapy, and long-term hormonal ablation in patients with high risk, nonmetastatic prostate cancer. american journal of clinical oncology, 42(3): 285-29. doi: 10.1097/coc.0000000000000520. [6] fahmi mr, hashikin na, yeong ch, guatelli s, ng kh, malaroda a, rosenfeld ab, perkins ac. (2019) evaluation of organ doses following prostate treatment with permanent brachytherapy seeds: a geant4 monte carlo simulation study. journal of physics: conference series, 1248(1): 012049-012049. doi: 10.1088/1742-6596/1248/1/012049. [7] radioisotopes in medicine, world nuclear association [https://www.worldnuclear.org/information-library/non-power-nuclear-applications/radioisotopesresearch/radioisotopes-in-medicine.aspx] [8] park ds. (2012) current status of brachytherapy for prostate cancer. korean journal of urology, 53(11): 743-749. doi: 10.4111/kju.2012.53.11.743. [9] lechtman e, mashouf s, chattopadhyay n, keller bm, lai p, cai z, reilly rm, pignol jp. (2013) a monte carlo-based model of gold nanoparticle radiosensitization accounting for increased radiobiological effectiveness. physics in medicine and biology, 58(10): 30753087. doi: 10.1088/0031-9155/58/10/3075. [10] stish bj, davis bj, mynderse la, mclaren rh, deufel cl, choo r. (2018) low dose rate prostate brachytherapy. translational andrology and urology, 7(3): 341-356. doi: 10.21037/tau.2017.12.15. [11] allison j, amako k, apostolakis j, araujo h, arce dubois p, asai m, barrand g, capra r, chauvie s, chytracek r, cirrone gap, cooperman g, cosmo g, cuttone g, daquino gg, donszelmann m, dressel m, folger g, foppiano f, generowicz j, grichine v, guatelli s, 185 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 gumplinger p, heikkinen a, hrivnacova i, howard a, incerti s, ivanchenko v, johnson t, jones f, koi t, kokoulin r, kossov m, kurashige h, lara v, larsson s, lei f, link o, longo f, maire m, mantero a, mascialino b, mclaren i, mendez lorenzo p, minamimoto k, murakami k, nieminen p, pandola l, parlati s, peralta l, perl j, pfeiffer a, pia mg, ribon a, rodrigues p, russo g, sadilov s, santin g, sasaki t, smith d, starkov n, tanaka s, tcherniaev e, tome b, trindade a, truscott p, urban l, verderi m, walkden a, wellisch jp, williams dc, wright d, yoshida h. (2006) geant4 developments and applications. ieee transactions on nuclear science, 53(1): 270-278. doi: 10.1109/tns.2006.869826. [12] salvat f, josé m, sempau j. (2011) penelope 2011: a code system for monte carlo simulation of electron and photon transport. nuclear energy agency, doc(2011)5. https://www.oecd-nea.org/science/docs/2011/nsc-doc2011-5.pdf [13] briesmeister jf. (2000) mcnp: a general monte carlo n-particle transport code. version 4c, la-13709-m. https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/la-13709m [14] kalos mh, whitlock pa. (2008) monte carlo methods. wiley-blackwell, 2008, pp. 203203. [15] jain s, hirst dg, o'sullivan jm. (2012) gold nanoparticles as novel agents for cancer therapy. the british journal of radiology, 85(1010): 101-113. doi: 10.1259/bjr/59448833. [16] chatterjee dk, wolfe t, lee j, brown ap, singh pk, bhattarai sr, diagaradjane p, krishnan s. (2013) convergence of nanotechnology with radiation therapy-insights and implications for clinical translation. translational cancer research, 2(4): 256-268. doi: 10.3978/j.issn.2218-676x.2013.08.10. [17] lechtman e, chattopadhyay n, cai z, mashouf s, reilly r, pignol jp. (2011) implications on clinical scenario of gold nanoparticle radiosensitization in regards to photon energy, nanoparticle size, concentration and location. physics in medicine and biology, 56(15):4631-4647. doi: 10.1088/0031-9155/56/15/001. [18] mesbahi a, jamali f, garehaghaji n. (2013) effect of photon beam energy, gold nanoparticle size and concentration on the dose enhancement in radiation therapy," bioimpacts : bi, 3(1): 29-35. doi: 10.5681/bi.2013.002. [19] asadi s, vaez-zadeh m, masoudi sf, rahmani f, knaup c, meigooni as. (2015) gold nanoparticle-based brachytherapy enhancement in choroidal melanoma using a full monte carlo model of the human eye. journal of applied clinical medical physics, 16(5): 344-357. doi: 10.1120/jacmp.v16i5.5568. [20] banoqitah e, djouider f. (2016) dose distribution and dose enhancement by using gadolinium nanoparticles implant in brain tumor in stereotactic brachytherapy. doi: 10.1016/j.radphyschem.2016.06.002. [21] kehwar ts. (2009) use of cesium-131 radioactive seeds in prostate permanent implants. journal of medical physics, 34(4): 191-193. doi: 10.4103/0971-6203.56077. [22] yu y, anderson ll, li z, mellenberg de, nath r, schell mc, waterman fm, wu a, blasko jc. (1999) permanent prostate seed implant brachytherapy: report of the american association of physicists in medicine task group no. 64. medical physics, 26(10): 20542076. doi: 10.1118/1.598721. [23] awan sb, hussain m, dini sa, meigooni as. (2008) historical review of interstitial prostate brachytherapy," vol. 5. http://ijrr.com/article-1-345-en.pdf [24] yaparpalvi r. et al. (2007) is cs-131 or i-125 or pd-103 the “ideal” isotope for prostate boost brachytherapy?– a dosimetric view point. international journal of radiation oncology*biology*physics, 69(3): s677-s678. doi: 10.1016/j.ijrobp.2007.07.2038. [25] armpilia ci, dale rg, coles ip, jones b, antipas v. (2003) the determination of radiobiologically optimized half-lives for radionuclides used in permanent brachytherapy implants. international journal of radiation oncology, biology, physics, 55(2): 378-385. [online]. available: http://www.ncbi.nlm.nih.gov/pubmed/12527051. [26] bice ws, prestidge br, kurtzman sm, beriwal s, moran bj, patel rr, rivard mj, cesium advisory g. (2008) recommendations for permanent prostate brachytherapy with 131cs: a 186 khan et al. iium engineering journal, vol. 20, no. 2, 2019 https://doi.org/10.31436/iiumej.v20i2.1136 consensus report from the cesium advisory group. brachytherapy, 7(4): 290-296. doi: 10.1016/j.brachy.2008.05.004. [27] wooten ce, randall m, edwards j, aryal p, luo w, feddock j. (2014) implementation and early clinical results utilizing cs-131 permanent interstitial implants for gynecologic malignancies. gynecologic oncology, 133(2): 268-273. doi: 10.1016/j.ygyno.2014.02.015. [28] wernicke ag, smith aw, taube s, yondorf mz, parashar b, trichter s, nedialkova l, sabbas a, christos p, ramakrishna r, pannullo sc, stieg pe, schwartz th. (2016) cesium131 brachytherapy for recurrent brain metastases: durable salvage treatment for previously irradiated metastatic disease. journal of neurosurgery, 126(4): 1212-1219. doi: 10.3171/2016.3.jns152836. [29] usgaonker sr. (2004) mcnp modeling of prostate brachytherapy and organ dosimetry. [online]. available: https://oaktrust.library.tamu.edu/handle/1969.1/305. [30] almansa jf, guerrero r, al-dweri fmo, anguiano m, lallena am. (2006) dose distribution in water for monoenergetic photon point sources in the energy range of interest in brachytherapy: monte carlo simulations with penelope and geant4. [online]. available: http://fm137.ugr.es/photonpointsources/ [31] archambault jp, mainegra-hing e. (2015) comparison between egsnrc, geant4, mcnp5 and penelope for mono-energetic electron beams. physics in medicine and biology, 60(13): 4951-4962. doi: 10.1088/0031-9155/60/13/4951. [32] koivunoro h, siiskonen t, kotiluoto p, auterinen i, hippeläinen e, savolainen s. (2012) "accuracy of the electron transport in mcnp5 and its suitability for ionization chamber response simulations: a comparison with the egsnrc and penelope codes. medical physics, 39(3): 1335-1344. doi: 10.1118/1.3685446. [33] šídlová v, trojek t. (2010) testing monte carlo computer codes for simulations of electron transport in matter. applied radiation and isotopes, 68(4-5): 961-964. doi: 10.1016/j.apradiso.2009.12.019. 187 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 improve the efficiency of the power transmission system using the genetic algorithm to determine the optimum location and facts devices husam hasan mohammed1*, hiba zuhair abdul kareem1, and wafaa mohammed ridha2 1department of electronic technologies, 2department of computer systems, babylon technical institute, al-furat al-awsat technical university,51015, babylon, iraq *corresponding author: husam171984@gmail.com husam10@atu.edu.iq (received: 23rd october 2019; accepted: 4th january 2020; published on-line: 4th july 2020) abstract: as the world's energy consumption increases, the expansion of the energy system becomes increasingly important. however, the creation of new transmission lines requires excessive costs and time if the same transmission capacity is to be added to the existing network. today's electrical networks are faced with high risks of voltage instability and real power losses. this development tends to occur due to the lack of reactive control power (rpl) in heavily stressed operating conditions caused by increased demand for loads and the rapid development of power systems worldwide. this paper has adopted the setting of facts (flexible ac transmission system) devices as additional control parameters for reducing transmission losses in power system static types of two facts devices consisting of svc (static var compensators) while the tcsc (thermistor controlled series compensator) is included in the issue formulation. during this paper, the proposed algorithm was to determine the optimal placement of power network devices by genetic algorithm to manage reactive power, reduce losses, increase the transmission capacity and power lines, and help simulate the ieee 24 bus control system and also the position of facts devices. abstrak: apabila penggunaan tenaga dunia semakin meningkat, penambahan sistem tenaga sangat penting. walau bagaimanapun, penciptaan talian penghantaran terkini memerlukan kos yang berlebihan dan had masa jika kapasiti penghantaran yang sama digunakan dengan lebih tinggi. dalam rangkaian elektrik hari ini, unit ini berhadapan dengan risiko ketidakstabilan voltan dan putus bekalan tenaga. penambahan sistem tenaga ini cenderung berlaku disebabkan kekurangan kuasa kawalan reaktif (rpl) dalam keadaan beban operasi yang besar disebabkan oleh peningkatan beban permintaan dan perkembangan pesat sistem kuasa di seluruh dunia. kertas ini telah mengguna pakai peranti facts (sistem penghantaran ac fleksibel) sebagai parameter kawalan tambahan bagi mengurangkan kehilangan penghantaran dalam sistem kuasa statik dua peranti facts yang terdiri daripada svc (pemampas var statik) manakala tcsc (pemampas siri termistor kawalan) adalah termasuk dalam perumusan isu. dalam kertas kerja ini, algoritma yang dicadangkan adalah penempatan optimum peranti rangkaian kuasa oleh algoritma genetik bagi mengurus kuasa reaktif juga mengurangkan kerugian dan meningkatkan kapasiti penghantaran dan kabel elektrik dan membantu menyerupai 133 iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 sistem kawalan bas ieee 24 dan juga kedudukan peranti facts di mana ia terbukti berkesan. keywords: facts devices; genetic algorithms; svc; tcsc; optimal location 1. introduction reducing oil and gas reservoirs and increasing energy consumption worldwide have encouraged researchers to consider optimizing generation and energy transmission in power grids to increase efficiency and improve plant utilization, reduce losses, and preserve the environment. studies show that facts technology has increased transmission capacity, reduced losses of power and load density, and improved reliability, performance and control by maintaining the voltage profile and affecting transmission parameters [1]. in recent years, reactive power control and loss reduction in power systems are performed through optimal location of facts devices using smart algorithms. genetic algorithm (ga) is one of the computer science exploration techniques used to find approximate solutions for optimization of exploration problems [2]. facts devices were first presented by electric power research institute (epri) in 1990 in the usa [3]. these devices not only increase system loadability but also control power to a great extent. they are also able to improve system stability due to their high speed [4]. 2. power losses for solving this problem, continuous variables such as generator bus voltage, and discrete variables such as parallel switching size and facts series devices are used, and the objective function is to reduce the power network loss index. the real power loss ( ) in transmission networks is calculated as the following [5]: where, is the number of the branches of the power system, is the loss of a branch, is the conductance of the branch k. and voltages at the beginning and end of the branch. is the power angle difference between bus. the constraints that are considered for this problem include nonlinear equality of power flow equations and the linear inequality of various parameters [6] as the following: the equation (2) and (3) follow the following constraints[6] 134 iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 where and are active and reactive powers of bus. and are active and reactive consumption powers of bus . and are real and imaginary parts of component ij of admittance matrix of the network. is the number of buses of the network. is the set of buses of the generator. indices min and max are minimum and maximum value of each parameter. is the number of shunt var compensation . 3. the model of svc the static var compensator (svc) parallel compensator is a static capacitance/inductance with susceptance of bsvc shown in fig. 1, which is, modelled as a variable susceptance in parallel with bsvc at bus i. the reactive power injected to bus of svc is described as follows[7]: where v is the amplitude of the voltage for the bus that svc is connected to. the main task of svc is to regulate voltage of the bus, which is done by controlling reactive power injection at that point. as shown in fig. 1, the equivalent circuit of svc can be represented as a variable susceptance [8]. fig. 1: the static var compensator (a) basic structure (b) model.. the new admittance of the system after installing svc in the i bus can be expressed by the following matrix: where, is the admittance of the system without svc. for constant active power and vrms source voltage, the required capacitive reactive power varies before and after the capacitive compensator is installed: as the value of bcap capacitive susceptance is given by the following equation: and capacitance required in farad is calculated as follows: [2] 135 iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 4. the model of thyristor controlled series compensator tcsc the tcsc is a capacitive reactance compensator that consists of a series capacitor bank shunted by a thyristor-controlled reactor. the basic conceptual tcsc module comprises a series capacitor, c, in parallel with a thyristor controlled reactor fig. 2a [9]. the tcsc compensator is a static reactor capacitance with the impedance of jxc with susceptance of bsvc shown in fig. 2b [9]. the thyristor is modelled with a nonlinear resistance that is controlled by firing angle [10]. current of inductance and voltage of capacitance are selected as two variables in state space. fig. 2: thyristor controlled series compensator presentation: (a) basic structure, (b) model. xij is the line reactance, rij is the line resistance, jbjo , jbio are load susceptance of half of the line at bus i and bus j of the line. the difference between the line susceptance before and after tcsc installation is as follows: the new admittance of the system after connecting tcsc between the and bus can be expresseing by the following matrix: 136 iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 where, is the admittance of the system without tcsc. eq. (17) shows new reactance of the line after installing tcsc. where, is the reactance of the line without tcsc and the is in the range of 5. the proposed method one of the most important advantages of intelligent methods is that there is no specific space to find the best solution. among the intelligent methods, we can mention simulated annealing (sa) [11], tabu search method (ts) [12] and particle swarm optimization technique [13]. we decided in this paper to use the method of ga. ga uses one of the natural darwin’s selection principles for finding an optimal formula to predict or match patterns [14]. in summary, it is said that ga is a programming technique that employs genetic evolution to solve problems. the summary of a genetic algorithm is as follows: beginning: create n chromosomal population randomly (appropriate solutions to the problem). valuation: assess the fitness f (x) of each chromosome x in the population. new population: create a new population. repeat steps below to complete the new crowd. choice: choose two chromosomes (parents) according to their fitness from the crowd. the higher the chances, the better the chances of being chosen. combination: combine the possibility of combining parents (probability crossover) to form new children (offspring). mutations: a mutation occurs with the probability of children mutation in each locas (position on the chromosome). accepting: include new children in the new population. replacement: use the new population created for the algorithm process the main objective of this work is to find the best place for the facts devices, their types, and their values. special coding was developed to achieve parameters (location, type, value). the first string represents the location of the facts devices, where it contains the numbers of lines. as for the second string, it is to determine the type of facts devices added. the value of the added device is determined by the last string, which is between 0 and 1 where 0 represents the minimum, and 1 represents the maximum. the real value of the facts device can be calculated using the following equation: where and are respectively the maximum and the minimum setting value of the facts device, and is the normal value. the initial population of the system depends on the following parameters: the number of facts devices that are selected as optimal types of facts devices that will be determined represents the number of special settings for each device represents the number of individuals of the population. 137 iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 at each of the three stages is created: in the first string, a set of numbers of branches of the network are randomly placed. the second step is to draw random numbers indicating the types of devices and placed in the second string in the third step, the values of the devices are chosen randomly within the possible limits. the objective function will be calculated for each individual population previously configured and the objective function in this paper is the effect of the facts devices in the power system. a slice will be allocated in the roulette wheel for each individual population. the size of the slide is proportional to each individual and the appropriate individual will occupy a larger slice, as in fig. 3. the wheel will be rotating many times and after the wheel stops, the individual to which it refers will be selected. fig. 3: arrangement of 2 facts devices (a) individual, (b) roulette wheel to select individuals. 6. determine the location and value of the facts devices with the genetic algorithm (ga) first, initial conditions are considered for system loads. this initial condition might be based on the basic load of the system. for generator buses (except reference bus), an initial active power proportionate to the load is determined. the power flow program is executed. the power flow program might diverge due to excess increase in load condition of the system. in this case, the previous load condition is considered as the maximum load condition and step 6 is performed. ga and the employed devices are used to define the objective function (reducing losses). real genetic program is executed. the algorithm represents optimal size and location of tcsc and svc and the considered index through iterative and random selection. the program is finished. 7. simulation and results in this section, location of svc and tcsc in a standard ieee 24-bus system is investigated using ga and the results are presented. performance of the system is first 138 iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 investigated in the absence of facts devices and then in the presence of these devices. figure 4 shows the single-line diagram of the ieee 24-bus system. this network has 38 transmission lines which are assumed to have no problems in terms of thermal capacity [15]. in this network, there are 10 generator buses where bus 23 is considered as the slack bus, 10 pv bus and 13 pq buses. in this network, it is assumed that initial load of the system is 2700 mw and 549.474 mvar. during execution of the program, as system load increases, this ratio is preserved. fig. 4: single-line diagram of the ieee 24-bus system. 7.1 losses index in ieee 24-bus system without installing facts devices loss index in 24-bus system without installing facts devices is 225.68 mva using ga. 7.2 losses index by installing svc at ieee 24bus as it is known, when svc is installed in this system, considering all buses of the system, there would be 24 possible locations for svc. encoding region of the location is considered as 24 integers from 1 to 24. after using real ga, it is seen that considering bus 10 as the optimal bus with a capacity of 225.69 mvar, loss index is reduced to 218.786 mva. 7.3 losses index by installing tcsc in the ieee 24-bus system as mentioned before, there are various methods for controlling tcsc. among these methods, controlling power flowing through line, controlling phase angle at the ends of the line, and constant compensation of transmission line reactance can be mentioned. in this study, constant compensation of transmission line is used to establish steady state conditions. if all lines of this system are considered, there would be 38 possible locations 139 iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 for tcsc. encoding region would be 38 integers from 1 to 38. compensation percentage using tcsc is 60%. after using real ga, it is seen that considering line 27 which is between buses 15 and 24 as the optimal location of tcsc with magnitude of 0.581, loss index is reduced to 208.865 mva. 7.4 losses index by installing a combination of svc and tcsc in the ieee 24-bus system in this case, installing a combination of tcsc and svc is studied and its results are compared with each other. after using real ga, it is seen that considering line 27, which is located between buses 15 and 24, as the optimal location for installing tcsc with magnitude of 0.581 and bus 10 as the best location for installing svc with capacity of 225.69mvar, loss index is reduced to 201.765mva. the voltage profile curve for ieee 24-bus system is shown in fig. 5 to fig. 7. fig. 5: voltage profile of buses (1-8) for the ieee 24-bus system. fig. 6: voltage profile of buses (9-16) for the ieee 24-bus system. fig. 7: voltage profile of buses (17-24) for the ieee 24-bus system. 0.9 0.92 0.94 0.96 0.98 1 1.02 b1 b2 b3 b4 b5 b6 b7 b8 v o lt a g e (p .u ) bus no facts with svc with tcsc with svc & tcsc 0.9 0.92 0.94 0.96 0.98 1 1.02 1.04 b9 b10b11b12b13b14b15b16 v o lt a g e (p .u ) bus no facts with svc with tcsc with svc & tcsc 0.92 0.94 0.96 0.98 1 1.02 b1 7 b1 8 b1 9 b2 0 b2 1 b2 2 b2 3 b2 4 v o lt a g e (p .u ) bus no facts with svc with tcsc with svc & tcsc 140 iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 when referring to fig.5-7, we notice a significant improvement in the voltage profile of buses after installing a combination of svc and tcsc. for example, the bus voltage number 5 was 0.9668 before the installation of svc and tcsc, but it became 1.0018 and by installing svc in this system, voltage profile of load buses at bus 10 increases significantly. table 1: comparing loss index before and after devices in ieee 24-bus system with svc and tscswith tcscwith svcwithout factscase svc bus 10 tcsc line 27line 27bus 10--location 225.69 mvar 0.581 0.581225.69 mvar--size 201.765 mvar208.865 mva218.786 mva225.68 mvalosses after using the proposed ga method to find the best location and value for svc and tcsc we find that the losses in the system decreased a lot and when looking at table 1. we find that the losses became 201.765 mva after installing tcsc and svc after it was 225.68mva without facts devices. in other words, this index was improved. 8. conclusion in order to study simulation, genetic algorithm is implemented on a sample bus of an ieee 24-bus system with real coding and the obtained results are discussed along with corresponding diagrams and tables. obtained results show that considering loss index and installing svc in both systems, voltage profile of load buses increases significantly. furthermore, considering loss index and installing a combination of svc and tcsc in both systems, voltage profile of load buses increases. by installing a combination of svc and tcsc, loss index becomes lower compared to when no such device is installed, svc is installed, or tcsc is installed, which shows improvement of this index. references [1] dazahra mn, elmariami f, belfqih a, boukherouaa j.( 2016) optimal location of svc using particle swarm optimization and voltage stability indexes. international journal of electrical and computer engineering, 6(6):2581. [2] mirjalili s. (2016) dragonfly algorithm: a new meta-heuristic optimization technique for solving single-objective, discrete, and multi-objective problems. neural computing and applications, 27(4):1053-1073. [3] jordehi ar. (2016) optimal allocation of facts devices for static security enhancement in power systems via imperialistic competitive algorithm (ica). applied soft computing, 48:317-328. [4] darabian m, jalilvand a. (2017) a power control strategy to improve power system stability in the presence of wind farms using facts devices and predictive control. international journal of electrical power & energy systems, 85:50-66. [5] nwohu mn, isah a, usman au, sadiq aa. (2016) optimal placement of thyristor controlled series compensator (tcsc) on nigerian 330kv transmission grid to minimize real power losses. international journal of research studies in electrical and electronics engineering, 2:18-26. [6] raj s, bhattacharyya b.( 2018) optimal placement of tcsc and svc for reactive power planning using whale optimization algorithm. swarm and evolutionary computation, 141 iium engineering journal, vol. 21, no. 2, 2020 mohammed et al. https://doi.org/10.31436/iiumej.v21i2.1273 40:131-143. [7] yu m, xie h, song w, wang h, he j, xin h. ( 2017) impact of svc control mode on voltage abnormal oscillation in wind power influx area. autom electr power syst, 41(1):7378. [8] sen d, ghatak sr, acharjee p. (2019) optimal allocation of static var compensator by a hybrid algorithm. energy systems, 10(3):677-719. [9] zare k, hagh mt, morsali j.( 2015) effective oscillation damping of an interconnected multi-source power system with automatic generation control and tcsc. international journal of electrical power & energy systems, 65:220-230. [10] sahoo dk, sahu rk, sekhar gtc, panda s. (2018) a novel modified differential evolution algorithm optimized fuzzy proportional integral derivative controller for load frequency control with thyristor controlled series compensator. journal of electrical systems and information technology, 5(3):944-963. [11] sodeifian g, sajadian sa, ardestani ns. (2017) experimental optimization and mathematical modeling of the supercritical fluid extraction of essential oil from eryngium billardieri: application of simulated annealing (sa) algorithm. the journal of supercritical fluids, 127:146-157. [12] martí r, martínez-gavara a, sánchez-oro j, duarte a. (2018) tabu search for the dynamic bipartite drawing problem. computers & operations research, 91:1-12. [13] babu ts, rajasekar n, sangeetha k. (2015) modified particle swarm optimization technique based maximum power point tracking for uniform and under partial shading condition. applied soft computing, 34:613-624. [14] gubin a v, borzunov dy, marchenkova lo, malkova ta, smirnova il. (2016) contribution of ga ilizarov to bone reconstruction: historical achievements and state of the art. strategies in trauma and limb reconstruction, 11(3):145-152. [15] kia m, nazar ms, sepasian ms, heidari a, siano p.( 2017) optimal day ahead scheduling of combined heat and power units with electrical and thermal storage considering security constraint of power system. energy, 120:241-252. 142 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <feff005500740069006c006900730065007a00200063006500730020006f007000740069006f006e00730020006100660069006e00200064006500200063007200e900650072002000640065007300200064006f00630075006d0065006e00740073002000410064006f006200650020005000440046002000700072006f00660065007300730069006f006e006e0065006c007300200066006900610062006c0065007300200070006f007500720020006c0061002000760069007300750061006c00690073006100740069006f006e0020006500740020006c00270069006d007000720065007300730069006f006e002e0020004c0065007300200064006f00630075006d0065006e00740073002000500044004600200063007200e900e90073002000700065007500760065006e0074002000ea0074007200650020006f007500760065007200740073002000640061006e00730020004100630072006f006200610074002c002000610069006e00730069002000710075002700410064006f00620065002000520065006100640065007200200036002e0030002000650074002000760065007200730069006f006e007300200075006c007400e90072006900650075007200650073002e> /gre <feff03a703c103b703c303b903bc03bf03c003bf03b903ae03c303c403b5002003b103c503c403ad03c2002003c403b903c2002003c103c503b803bc03af03c303b503b903c2002003b303b903b1002003bd03b1002003b403b703bc03b903bf03c503c103b303ae03c303b503c403b5002003ad03b303b303c103b103c603b1002000410064006f006200650020005000440046002003ba03b103c403ac03bb03bb03b703bb03b1002003b303b903b1002003b103be03b903cc03c003b903c303c403b7002003c003c103bf03b203bf03bb03ae002003ba03b103b9002003b503ba03c403cd03c003c903c303b7002003b503c003b103b303b303b503bb03bc03b103c403b903ba03ce03bd002003b503b303b303c103ac03c603c903bd002e0020002003a403b1002003ad03b303b303c103b103c603b10020005000440046002003c003bf03c5002003b803b1002003b403b703bc03b903bf03c503c103b303b703b803bf03cd03bd002003b103bd03bf03af03b303bf03c503bd002003bc03b50020004100630072006f006200610074002003ba03b103b9002000410064006f00620065002000520065006100640065007200200036002e0030002003ba03b103b9002003bd03b503cc03c403b503c103b503c2002003b503ba03b403cc03c303b503b903c2002e> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <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> /slv <feff005400650020006e006100730074006100760069007400760065002000750070006f0072006100620069007400650020007a00610020007500730074007600610072006a0061006e006a006500200064006f006b0075006d0065006e0074006f0076002000410064006f006200650020005000440046002c0020007000720069006d00650072006e006900680020007a00610020007a0061006e00650073006c006a006900760020006f0067006c0065006400200069006e0020007400690073006b0061006e006a006500200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e0074006f0076002e0020005500730074007600610072006a0065006e006500200064006f006b0075006d0065006e0074006500200050004400460020006a00650020006d006f0067006f010d00650020006f00640070007200650074006900200073002000700072006f006700720061006d006f006d00610020004100630072006f00620061007400200069006e002000410064006f00620065002000520065006100640065007200200036002e003000200074006500720020006e006f00760065006a01610069006d0069002e> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 study of productivity improvement of manual operations in soya sauce factory zaharah wahid1*, mohd radzi che daud2 and kartini ahmad1 1department of science in engineering, 2department of manufacturing and materials engineering, faculty of engineering, internation islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. *corresponding author: zaharahwahid@iium.edu.my (received: 27th september 2019; accepted: 28th october 2019; published on-line: 20th january 2020) abstract: today with a rapidly changing world and markets, smes are facing a critical challenge to remain competitive in the business market. in this paper, a case study of the smes food industry is presented. work study methodology was embedded in the strategy to improve the productivity of the soya sauce enterprise. the sample size required for the study was calculated and random observations were determined through a work sampling technique to achieve a 95% confidence level. the result from this study reveals that work sampling data can be used as a reliable estimation for identification of any potential bottleneck as well as idle time in the factory. the process flowchart at the filling and capping terminal were examined and the travelling distance was optimized to 12.5 feet from original distance of 17 feet. the modified plant layout significantly improves the people flow, production material handling, work safety, space utilization, and better working conditions. the survival of smes is critical as this sector contributes 38.3% to malaysian‘s gross domestic productivity (gdp). thus, these findings demonstrated that enhancing the productivity of sme food industries is effective through a work study. however, the successful adoption of this approach is mostly because of top administrative involvement and the participation of all staff members. abstrak: pada hari ini, dengan perubahan pesat dunia dan pasaran, smes berhadapan cabaran getir bagi terus tetap berdaya saing dalam pasaran perniagaan. kajian ini membincangkan berkaitan kes kajian smes dalam industri makanan. kaedah kajian kerja telah diguna pakai dalam strategi bagi meningkatkan pengeluaran sos soya. saiz sampel yang diperlukan bagi kajian ini dikira dan pemerhatian rawak diperoleh melalui teknik persampelan bagi memperolehi 95% tahap yakin diri. hasil keputusan kajian menunjukkan data persampelan boleh digunakan sebagai anggaran boleh percaya bagi mengklasifikasi kemungkinan kesesakan dan juga masa terbiar dalam kilang. proses carta alir pada terminal isian dan penutup telah diperiksa dan jarak perjalanan dioptimumkan pada 12.5 kaki dari jarak asal iaitu 17 kaki. ubah suai susun atur kilang dapat memperbaiki dengan ketara aturan pekerja, pengendalian bahan pengeluaran, keselamatan kerja, pengunaan ruang tempat kerja dan persekitaran tempat kerja yang lebih bagus. kemandirian smes adalah sangat kritikal kerana sektor ini menyumbang 38.3% kepada keluaran malaysia dalam negara kasar (kdnk). oleh itu, hasil kajian menunjukkan peningkatan produktiviti industri makanan smes adalah berkesan menerusi kajian ini. walau bagaimanapun, keberhasilan kaedah ini berpunca daripada keterlibatan pentadbiran dan seluruh anggota pekerja. keywords: food industry; work study; sustainability; time study; productivity 202 iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 1. introduction small and medium enterprises (smes) in malaysia are regarded as the growth engine that drives the local economy as this sector contributed 38.3% to the gross domestic product (gdp) of this country. to completely realise their potential, the government has given high importance to supporting the development of smes. however, as per the statistics released by the malaysian productivity centre (mpc) 2014/2015, even though the government has put efforts to increase productivity, smes’ productivity growth (3.5%) has only slightly improved in malaysia, [1]. currently, with the establishment of the trans-pacific partnership agreement (tppa), smes in malaysia are expected to face higher competition due to free trade. to stay competitive, the smes have to be a lot more effective and thus yield a higher productivity. it is therefore of great importance not only to the individual enterprises but also for the country’s economic sustainability as a whole. deploying work study is a key strategy to boost smes’ growth and enhance productivity. managers often fail to recognise early the need to change their management practices and execution of production operations. they lack knowledge and professionalism. they are hampered by high production costs. because of capital shortage, these firms are weak in market niche researches and r&d activities. hence, there is an urgent need to respond to the challenges facing the smes. to alleviate this problem, deploying work studies is key strategy to achieving high yields and efficiency. this project will assist the entrepreneur to implement work study techniques through training and consultation efforts. in japan, soya sauce production occurs on a small scale. since 1950, the manufacturing process has been studied and modernized using modern production control methods such as using microorganisms in the fermentation process [2]. however, in malaysia, most soya sauce factories operate on a small scale partly due to the factors mentioned earlier. this work study is comprised of method study and work measurement. the former involves minimisation of the work content and setting a single best way to execute a job. it is implemented to decrease manufacturing costs by saving on cycle time pertaining to the operation [3-6]. the latter deals mostly with investigation of ineffective time associated with a job, and setting time standards to execute an operation by conforming to the standard method [7]. this also results in a systematic investigation pertaining to all factors that can impact the production efficiency and economy pertaining to the case being studied, which effectively allows achieving productivity gains [8]. productivity enhancement can be achieved by getting rid of inefficient methods, decreasing work content as well as effectively making use of manpower, machines, and materials. also, it can be realised in multiple ways, such as by decreasing the production unit cost or decreasing the production work content, by increasing the products’ valueadded content [8-14], by line balancing with respect to the production line, or via combination of all of these [9-10,15]. enhancement of productivity can be defined as a continuous improvement process that is applicable to many kinds of activities [7-8,11,1617]. when harnessing more profit via the same types of resources, increasing productivity is regarded as a key issue [18]. enhancing productivity also results in customer satisfaction, time and cost reduction, as well as delivery of products [19]. productivity involves an effective relationship in order to determine method output, product prices, method utilisation, work in process, on-time delivery, and inventory levels [4]. vergeer [5] regarded productivity as a driver for profit. assessing the entire process allows for the establishment of further best practices as well as optimum productivity, which also helps to decrease the cycle time. since the 203 iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 bottom line is affected by cycle time, assessing the process and determining consistency in best practices will aid in enhancing the overall business operations [9]. as per [6-10], decrease in cycle time has a cascading impact on the value as well as worth. with decrease in cycle times, there is equally an increase in output. it has been shown that there is considerable enhancement in production throughput with decrease in order-to-delivery cycle time. seemingly, long cycle times result in higher cost, high inventory as well as poor customer service. because of these facts, this study focuses on manpower utilisation and production cycle time. these days, a key element to successful management is reduction in cycle time [10]. the work study has been extensively employed in the manufacturing industry and in various other fields [11,14,18-19]. as per the literature, work study’s application is not limited to manufacturing industries and can also be used in service sectors such as the hospitality sector [20-21]. some recent works have considered new areas pertaining to improvement in productivity and layout planning with regards to smes food industry as well as the hospitality sector [20-24]. this study recommends a work study approach that can be used to devise an efficient strategy to attain sustainability in smes, which in turn can function as a means to improve both process efficiency and product quality, thereby enhancing productivity. the factory setup comprises a manual assembly system, in which the work in progress (wip) item undergoes manual transportation through its processes. the scope of the research includes the general factory layout at the filling area and the manual operation line of the 630 ml soya sauce bottle. the problems that the enterprise runs into include the unbalanced operation at each workstation that impacts the smooth functioning of the production line. the objectives of the study are to (a) assess the work performance of the existing operations with regards to manpower utilisation and production cycle time; (b) recommend a new operational layout design; and (c) analyse and compare the performance of the new and current operations. 2. method in this research, the work study technique was employed at the soya sauce 630 ml bottle operation line where the problems occurred. cycle time reduction, manpower utilization, and plant layout were the main focus in this study as they impact the bottom line of the company. 2.1 analysis method this section outlines a systematic approach for recording, observing, and critically analysing the existing linked problems and processes. the approach also serves as a means for improving productivity, as shown in table 1. process charts were created after identification and selection of the operations or activities. a process chart provides an outline of the process and records the key events in a sequence, as well as captures all aspects of the job. every operator’s movement was recorded against time measured. this approach helps to identify the best pattern of movements for an operator that leads to minimum effort and optimum time consumption. it also enables finding the most economical route of movement. 204 iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 table 1: analysis method item how analysis line balance time study time analysis method study work improved work sampling no proper layout process flow and routing analysis material flow in order to balance the work team, the line balancing approach was implemented, so that the idle time on the filling machine and workers could be detected. this in turn resulted in the optimisation of work distribution between machines and workers. to improve the performance at the 630 ml bottle operation line, the layout was also redesigned. figure 1 shows the process flow of the soya sauce 630 ml bottle operation line. table 2 presents the breakdown of the operators based on the operation. in this assembly line, the total number of operators engaged was seventeen. fig. 1: flow process chart of soya sauce 630 ml bottle line. figure 2 presents the flow diagram of the existing manual operation line. trolleys were used for transportation between workstations. the workstations were about six feet apart. at the filling workstation, there were three filling barrels with one trolley between the filling barrels on which to place the filled bottle. once the trolley was filled, it would be transported to the capping workstation. the capped bottle was placed back on the trolley on completion of the capping operation. thereafter, it goes through a manual labelling operation. table 2: breakdown of the operator based on the operation workstation number of operator filling 6 capping 2 labelling 6 tying 3 total 17 7. tying 6. labelling 5. capping 4. filling 3. cooling 2. blending and heating of caramel and sugar 1. heating of soya sauce extract 205 iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 fig.2: flowchart of soya sauce 630 ml bottle line. 3. data collection and analysis work sampling is one of the work measurement techniques employed in this study to find the percentage occurrence of a certain activity by statistical sampling and random observations. an established standard procedure was adopted before the study was performed. various authors [24-26] recommended that the use of the sampling method is an effective way to detect idle time or unproductive work. according to [20] now more than 40,000 mainly industrial engineers are trained in work sampling due to its effectiveness and accuracy. 3.1 estimation of number of observations required the method of work sampling was employed at the filling terminal to determine the ineffective time/idle time of the operator. a pilot study was performed with 80 observations to measure the idle time of the operators and processes. from the result of this primary examination, it was found that 7.5% of the time was idle time, 92% of the time was filling time and 0.5% of the time was for other work. determining the number of observations entailed assigning a limit of precision of ± 5% at 95% confidence level to the percentage of operation idle time. the following formula was employed. n = [4p (100-p)] / l = [4 x 7.5 (92.0)] / 25 =111 where, p (% of idle time) = 7.5; l (limits of accuracy) = 25; 111 actual observations were made and the following results were obtained. filling = 66.66% 206 iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 idle time = 16.27% other work = 17.12% n = [4 x 16.27 (66.66) ] / 25 = 385 therefore, required observations needed are 385 to achieve the desired level of accuracy. one of the basic foundations of statistical sampling theory is the concept that the larger the sample size, the results will be more accurate [20, 26-27]. [28] reported that work sampling as a method improves plant efficiency and increase productivity. filling = 68.57% idle time = 23.38% other work = 8.05% hence the % of idle time was 23.4 ± 5. work sampling technique was also used at the capping workstation to determine the operator idle time. causes of idle time at the capping workstation are waiting for the bottle, transfer of trolleys, transfer of bottles, talking/looking, and not at working place. the preliminary results are as following: observation, n = 27 capping = 55.56% idle time = 37.01% other work = 7.41% to determine the number of observations required to give a limit of accuracy of ± 5% at 95% confidence level in the percentage of operation idle time. n = [ 4 x 37.03 (63) ] / 25 = 373 actual observation of n = 373 capping = 65.19% idle time = 29.35% other work = 5.46% hence the % of idle time at the capping workstation was 29.35 ± 5. 4. results and discussion the work sampling approach was employed at both the filling and capping workstations to determine the productive and nonproductive element or idle time in the operation. it is basically a statistical technique where large numbers of observations are made. the purpose of this analysis is to take action to eliminate the problem. at the filling workstation, a sample size of 385 total observations was made to achieve 95% accuracy. the result of the examination indicated that the idle time of the operator was 23.4% with bounds of accuracy of 5%. similarly, 29.35% idle time of the operator was found at the capping workstation based on a sample size of 373 observations made as discussed in section 3.1. this study discovered that the root causes were mostly attributed to the general factory layout at the filling area and the manual operation line of the 630 ml soya sauce bottle and it results in wasted time and unnecessary movements such as transferring the 207 iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 trolleys from one workstation to another, which cause a delay or slow down the production line. the manual operations demand intensive engagement of manpower however, the extent of manpower engagement and utilisation is still low. in addition, documentation of any standard operating procedure was not in existence and as a result, the operators perform work based on their individual styles, which results in added work content that were not value added activities. hence, the productivity could potentially be increased by an enormous amount based on the above factors. a study by [18, 25, 27-28] revealed that the use of work sampling enhanced the production capacity. a study by [26] also showed that it is simple and inexpensive to perform. based on the data collected, the idle time is higher at the capping workstation as compared to the filling workstation. the cycle time of these processes were measured and calculated. these analyses automatically confirmed where the bottlenecks or capacity constraints are in the process line. this bottleneck causes delay or slows down the operation system so it needs to be solved urgently. this is a major obstacle faced by this enterprise as most of the jobs are performed manually. according to [12] a bottleneck is one of the significant problems encountered by most smes. subsequently the improvement action has been established and implemented using a semi-automatic filling machine having 6 nozzles, which is essential. only a single worker was needed to work at this workstation compared to the existing operational conditions. the bottleneck is eliminated by the installation of the semi-automatic filling machine. thus, the time of one processing cycle was decreased, which in turn increases the efficiency of the whole system and improves the earnings. the small investment for this semi-automatic filling machine was recuperated in 3 months. the quantity of sauce loaded in the bottle was more consistent and easy to control and monitor. this improvement leads to better product quality and quantity. underutilisation of the human resources was reduced. using a semi-automatic process will benefit the firm with respect to productivity and will also solve the issue of manpower employment since the labour turnover is fairly high. hence, the imbalance between the capping and the filling workstations was eliminated. this result was parallel with the result obtained by [11,19,29]. the existing process flowchart was critically studied. the layout was rearranged by minimising the transit time between each workstation. using systematic layout planning a modified process flowchart was presented and the travel distance was reduced to 12.5 feet which was originally 17 feet. the cycle time for each operation is very much related to the transit times from one workstation to the next workstation. the number of trolleys involved was reduced from 5 to 3. figure 3 displays the proposed new process flowchart of the soya sauce (630 ml) operation line. [18,24,28,] reported that increasing productivity by reducing cycle time in the assembly lines of the automotive industry. the modified design layout and simplified process flowchart minimised the unnecessary movements of the operators, as shown in fig. 3. it also improved the safety and the flow of the material on the workstation floor. similar findings were also revealed by [8,18]. [29] reported that systematic layout planning and design layout is an influential factor in a company’s performance to support the streamlined process of production. furthermore, it provides better working conditions for the operators. these workstations are now connected to each other through a conveyor belt. the work elements at both workstations were reduced. thus, time required to complete the final product was substantially reduced in comparison to the time taken in the current operational conditions. thus, there was an increase in the output in less time and the results of this study support the findings of [26]. 208 iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 fig. 3: proposed improvement flow diagram of soya sauce (630 ml) operation line. fig. 4: the overall factory layout at the filling area. figure 4 presents the overall factory layout at the filling area which was quite congested due to the limitation of floor area. an improved layout was proposed so that a centralized bottle rinsing workstation could be achieved. as compared to the existing layout, the workstations were all over the factory. the improved layout design allowed feeding of the bottle to be centralized. [16, 18, 22, 27,29] also showed that the optimization of production layout was achieved and improve product flow and plant layout efficiency. 5. conclusion the deployment of the system proposed in the study at the capping and filling workstations have a significant impact on the productivity of the soya sauce factory. the 1. bottle feeder 2.inspection(sensory) 3.& 4. capper operator (manual) 5. & 6. top label (manual) 7.8,9. bottom label operator (manual 10 &11. tying/packing operator e e e m ept y m t e e m p t y b o t t l e 3 1 1 1 1 1 1 1 1 1 5 6 2 8 7 4 9 11 1 10 209 iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 layout of the factory was optimised, the bottleneck was eliminated, the production capacity was improved, and the return on investment (roi) was 3 months. moreover, even the transportation was decreased from 5 to 3 trolleys with no delay in the assembly line. the standard operating process was well established by using the new proposed outline. new policies and observation schedules were introduced to keep up the improvement in the process. thus, this study demonstrated that work study techniques are suitable tools to be implemented for productivity improvements. however, the successful adoption of this approach is mostly because of the top administration involvement and the participation of all the members of the staff. references [1] malaysian, productivity corporation. (2017) mpc productivity report 2016/2017. [2] desmond ko’t. (2019) role of microorganism in soya sauce production. advances in applied microbiology, 108: 45-113. [3] lakwinder ps. (2016) work study and ergonormics. cambridge university press. [4] baines a. (1997) productivity improvement. work study. mcb university press 46: 49-51. [5] vergeer r, kleinknecht a. (2014) do labour market performs reduce labour productivity growth? a panel data analysis of 20 oecd countries (1960-2004). international labor review (153):365-593. [6] hiten patel scs. (2014) review on cycle time reduction in industries. journal of emerging technologies and innovative research, 1(7):955-956. [7] kansel m, yagmahan b, emel e. (2017). determination of standard times for process improvement: a case study. global journal of business, economics and manag., 7(1):6268. [8] hezekiah oa, olasunkanmi a, ayoola ab. (2018) review of method study approach to productivity gain: a muti-case study of portable water producing factory. researchgate 3(2):1-6. [9] macías-jiménez ma, romero-conrado ar, acosta-fontalvo lc, coronado-hernández jr. (2019) application of work study to process improvement: fruit nectar case. in proceedings of the 18th international conference on computer information systems and industrial management: 19-21 september 2019; belgrade, serbia. edited by khalid s, ritupama c, valentina j. springer international; pp 1-43. [10] moktadir ma, ahmed s, zohra ft, sultana r. (2017) productivity improvement by work study technique: a case on leather products industry of bangladesh. ind. eng manag. j., (6):207. [11] chisosa, d.f., chipambwa, w.(2018) an exploration of how work study techniques can optimize production in zimbabwe’s clothing industry. j. text. apparel technol. manag., 10: 1-11. [12] jaffrey v, mohamed nmzn, rose anm. (2017) improvement of productivity in low volume production industry layout by using witness simulation software. material science and engineering, vol.257. [13] singh mp. (2016) improvement in process industries by using work study methods: a case study.ijmet426-436. [14] ozor pa, olua c, (2015) productivity improvement of small and medium scale enterprises using lean concept: case study of bread factory. european journal of business and management (7): 73-84. [15] ojaghi, y., et al. ( 2015) production layout optimization for small and medium scale food industry. procedia cirp, (26): 247-251. [16] ali naqvi sa, et al. (2016) productivity improvement of a manufacturing facility using systematic layout planning. cogent engineering, 3(1): 1207296. [17] wanniarachchi wnc, gopura rc, punchihewa h. (2016) development of a layout model suitable for the food processing industry. journal of industrial engineering. 2:1-8. 210 iium engineering journal, vol. 21, no. 1, 2020 wahid et al. https://doi.org/10.31436/iiumej.v21i1.1237 [18] malashree p, kulkarni, vn, gaitonde vn, sahebagowda m. (2018) an experimental study on productivity improvement using work study and ergonomics. international j. of darshan inst. on engineering research and emerging technologies, 7(1):31-36. [19] shravan s r, nilesh p, ujjainwala f, amit p. (2018) productivity improvement through work sampling in a ceramic tiles manufacturing industry: a case study. international j. for science research & development, 6(8): 662-670. [20] martinec t, skec s, savsek t, perisic mm.(2017) work sampling for the production development: a case study of a supplier in european automotive industry. advances in production engineering & manag., 12(4): 375-387. [21] gaurav g, verma ds.(2019) optimization of plant layout in manufacturing industry. ijrte 8(2): 41-47. [22] buchmeister b, palcic,i. (2017) implementation of correlation analysis to work sampling results. in proceedings of the 28th daaam, international symposium,0029-0034, vienna, austria; pp.29-34. [23] sidharth sr. (2019) study and analysis of performance evaluation of the low level employees in tourism and hospitality: case of five star hotel in mussoorie, uttarakland. international journal of research and analytical review 6(1): 359-270. [24] kunica z. (2018). optimization of the plant layout in the production of the special transformers: case study. fme transactions, 46: 285-290. [25] dhanashree r, madhuri k, pranjali c, raichurkar pp. (2018) enhancing efficiency and productivity of garment industry by using different techniques. international journal on textile engineering and processes. 4(1): 5-8. [26] bogert a, edwards w, jalali f, aqlan f. (2018) process improvement and layout optimization in a forging company. proceedings of the international conference on industrial engineering and operations management, 1162-1170 [27] suhardi b, juwita e, astuti rb. (2019) facility layout improvement in sewing department with systematic layout planning and ergonomics approach. cogent engineering, 6(1): retrieved from https://doi.org/10.1080/23311916.2019.1597412. [28] srijit krisnan a., sarang dev, rahul suresh, a. sumesh and ramesh kumar, k. (2018) bottleneck identification in a tyre manufacturing plant using simulation analysis and productivity improvement. 5(11)3:24720-24730. [29] wilson rn, charles m. (2017) process mapping and optimization of the process flows of a furniture manufacturing company in zimbabwe using machine distance matrices. procedia manufacturing 8:447-454. 211 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <feff004b00610073007500740061006700650020006e0065006900640020007300e400740074006500690064002c0020006500740020006c0075007500610020005000440046002d0064006f006b0075006d0065006e00740065002c0020006d0069007300200073006f00620069007600610064002000e4007200690064006f006b0075006d0065006e00740069006400650020007500730061006c006400750073007600e400e4007200730065006b0073002000760061006100740061006d006900730065006b00730020006a00610020007000720069006e00740069006d006900730065006b0073002e00200020004c006f006f0064007500640020005000440046002d0064006f006b0075006d0065006e0074006500200073006100610062002000610076006100640061002000760061006900640020004100630072006f0062006100740020006a0061002000410064006f00620065002000520065006100640065007200200036002e00300020006a00610020007500750065006d006100740065002000760065007200730069006f006f006e00690064006500670061002e> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <feff005500740069006c0069007a00610163006900200061006300650073007400650020007300650074010300720069002000700065006e007400720075002000610020006300720065006100200064006f00630075006d0065006e00740065002000410064006f006200650020005000440046002000610064006500630076006100740065002000700065006e007400720075002000760069007a00750061006c0069007a006100720065002000640065002000ee006e00630072006500640065007200650020015f0069002000700065006e00740072007500200069006d007000720069006d006100720065006100200064006f00630075006d0065006e00740065006c006f007200200064006500200061006600610063006500720069002e00200044006f00630075006d0065006e00740065006c00650020005000440046002000630072006500610074006500200070006f00740020006600690020006400650073006300680069007300650020006300750020004100630072006f0062006100740020015f0069002000410064006f00620065002000520065006100640065007200200036002e003000200073006100750020007600650072007300690075006e006900200075006c0074006500720069006f006100720065002e> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice comparative metagenomics analysis of palm oil mill effluent (pome) using three different bioinformatics pipelines iium engineering journal, vol. 20, no. 1, 2019 parman et al. comparative metagenomics analysis of palm oil mill effluent (pome) using three different bioinformatics pipelines adibah parman1, mohd noor mat isa2, farah fadwa benbelgacem1, ibrahim ali noorbatcha1 and hamzah mohd. salleh3 1bioprocess & molecular engineering research unit (bpmeru), department of biotechnology engineering, kulliyyah of engineering, international islamic university malaysia, 2malaysia genome institute, jalan bangi, 43000 kajang, selangor, malaysia 3international institute for halal research and training (inhart), international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. *corresponding authors: ibrahiman@iium.edu.my, hamzah@iium.edu.my (received: 9th march 2018; accepted: 25th jan 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.909 abstract: the substantial cost reduction and massive production of next-generation sequencing (ngs) data have contributed to the progress in the rapid growth of metagenomics. however, production of the massive amount of data by ngs has revealed the challenges in handling the existing bioinformatics tools related to metagenomics. therefore, in this research we have investigated an equal set of dna metagenomics data from palm oil mill effluent (pome) sample using three different freeware bioinformatics pipelines’ websites of metagenomics rast server (mg-rast), integrated microbial genomes with microbiome samples (img/m) and european bioinformatics institute (ebi) metagenomics, in term of the taxonomic assignment and functional analysis. we found that mg-rast is the quickest among these three pipelines. however, in term of analysis of results, img/m provides more variety of phylum with wider percent identities for taxonomical assignment and img/m provides the highest carbohydrates, amino acids, lipids, and coenzymes transport and metabolism functional annotation beside the highest in total number of glycoside hydrolase enzymes. next, in identifying the conserved domain and family involved, ebi metagenomics would be much more appropriate. all the three bioinformatics pipelines have their own specialties and can be used alternately or at the same time based on the user’s functional preference. abstrak: pengurangan kos dalam skala besar dan pengeluaran data ‘next-generation sequencing’ (ngs) secara besar-besaran telah menyumbang kepada pertumbuhan pesat metagenomik. walau bagaimanapun, pengeluaran data dalam skala yang besar oleh ngs telah menimbulkan cabaran dalam mengendalikan alat-alat bioinformatika yang sedia ada berkaitan dengan metagenomik. justeru itu, dalam kajian ini, kami telah menyiasat satu set data metagenomik dna yang sama dari sampel effluen kilang minyak sawit dengan menggunakan tiga laman web bioinformatik percuma iaitu dari laman web ‘metagenomics rast server’ (mg-rast), ‘integrated microbial genomes with microbiome samples’ (img/m) dan ‘european bioinformatics institute’ (ebi) metagenomics dari segi taksonomi dan analisis fungsi. kami mendapati bahawa mgrast ialah yang paling cepat di antara ketiga-tiga ‘pipeline’, tetapi mengikut keputusan analisa, img/m mengeluarkan maklumat philum yang lebih pelbagai bersama peratus identiti yang lebih luas berbanding yang lain untuk pembahagian taksonomi dan img/m 1 iium engineering journal, vol. 20, no. 1, 2019 parman et al. juga mempunyai bacaan tertinggi dalam hampir semua anotasi fungsional karbohidrat, amino asid, lipid, dan koenzima pengangkutan dan metabolisma malah juga paling tinggi dalam jumlah enzim hidrolase glikosida. kemudian, untuk mengenal pasti ‘domain’ terpelihara dan keluarga yang terlibat, ebi metagenomics lebih bersesuaian. ketiga-tiga saluran ‘bioinformatics pipeline’ mempunyai keistimewaan mereka yang tersendiri dan boleh digunakan bersilih ganti dalam masa yang sama berdasarkan pilihan fungsi penggun. keywords: bioinformatics pipeline; metagenomics analysis; mg-rast; img/m; ebi; metagenomics; palm oil mill effluent 1. introduction in the last few decades, metagenomics has become one of the crucial tools in mining the hidden microbial treasure without the use of conventional laboratory culture techniques. metagenomics involves the study of genetic material extracted from the diverse microbial population of environmental samples. the early stage of genomics relied on the standard laboratory cultivation method which is insufficient to identify the entire microbial population as compared to metagenomics. furthermore, the change in biotechnology development within this era, such as inexpensive next-generation sequencing (ngs) technologies, high throughput screening technique for metagenomics library and advances in bioinformatics tools, have left a huge impact in the field of metagenomics [1]. illumina is the most widely used ngs platform in metagenomics studies. the illumina system has advantages to other ngs platforms in terms of its high throughput sequencing at an economical price with high accuracy (> 99%) reads [2]. the illumina platform could initially only produce a short-read sequence length which has gradually been improved to a readable length and consequently made it more popular compared to the other platforms in ngs tools [2]. this fast evolution by ngs technologies allows researchers to achieve more variety of data with a high level of detailed sequencing results. ngs has also been developed continuously and rapidly, starting from its launch in 2006, resulting in the accumulation of massive amounts of sequences [2]. hence, several bioinformatics tools for metagenomics annotation are needed to accurately analyze the enormous amount of data. palm oil mill effluent (pome) is a colloidal suspension of the final stage effluent in the palm oil industry production. the composition of pome includes 95-96% water, 4-5% total solids, and 0.6-0.7% oil [3]. besides that, the raw pome also contains significant concentrations of carbohydrates, proteins, nitrogenous compounds, lipids, and minerals that enable this effluent to be used in various biotechnological applications like fermentation media, production of antibiotics, bio-insecticides, polyhydroxyalkanoates (pha), organic acids, enzymes, and hydrogen [3]. the present study attempts to make a comparative bioinformatics analysis of pome’s sample metagenome constructed using different automated bioinformatics pipelines of mg-rast, img/mer, and ebi metagenomics to evaluate their accuracy in the taxonomical assignment and functional annotation for future research directed to the industrial application. metagenome rapid annotation using subsystem technology (mg-rast) is a free web-based server with a fully automated system that provides sequence alignment, gene prediction, structural and functional annotation, comparative metagenomics and archiving services [4]. it was launched at the argonne national library in 2007 to address the computational needs of huge metagenomics data production analysis [5]. this 2 iium engineering journal, vol. 20, no. 1, 2019 parman et al. bioinformatic pipeline is being used by researchers around the world with the analysis record of over 250,000 datasets with 100 tera-basepairs of dna being successfully and completely analyzed to date [6]. besides, it also has a graphical user interface (gui) that allows the researcher to study the composition of microbial communities with their specific function [6]. mg-rast is also one of the bioinformatics pipelines that allows the submission of raw sequence data in the fastq, fasta, and sff format which will then be normalized and processed until annotation is completed by several integrated bioinformatic tools [6]. the integrated microbial genomes with microbiomes (img/m) is quite similar to mg-rast, which can also examine the taxonomy and function or metabolic potential of microbiomes [7]. img/m is a metagenomics data management system supported by the doe-jgi metagenome annotation pipeline (map v.4) which allows the submission of fasta or fastq format assembled and unassembled 454, illumina, and pacbio nucleotide sequences [8]. in early 2016, all these unassembled reads could no longer be accepted; meanwhile the sequence data generated outside jgi has been limited to the fasta format in assembled data formed only. until now, img/m still supports the external submission of assembled genomes only with the condition that the metagenomes submission and metadata have to be registered with genomes online database (gold) version 5 [9]. european bioinformatics institute (ebi) metagenomics is an expanding metagenomics analysis and archiving resource that uses the european nucleotide archive (ena) data scheme developed by the european molecular biology laboratory (embl). ena is needed for the initial submission and archiving purposes in a long-term period storage for reuse in the future [10]. besides, ebi metagenomics is a free web-based server that enables users to perform analysis on large scale platforms from ion torrent, roche 454, and illumina metagenomic sequence data [11]. similar to mg-rast and img/m, ebi metagenomics also has an established standardized system and analysis pipeline that includes a variety of analytical and visualization tools in generating the analysis of taxonomic and functional features of user-submitted sequence [12]. a comparison of mg-rast to qualitative insights into microbial ecology (qiime) based on 16s rrna method found qiime to be more accurate in term of taxonomic assignment compared to mg-rast [13]. when mg-rast was compared to qiime but with mothur as an additional bioinformatic tool, the results showed that qiime was again the fastest compared to the other two [14]. qiime is a bioinformatic tool used by ebi metagenomics version 3.0 to perform the taxonomical annotation that currently is being replaced with mapseq in ebi metagenomics version 4.0. even though in previous research qiime produced a better result, it lacks the facility to manage, store, and analyze the metagenomics data. in this work, we provide a comparative analysis of the metagenomics data using a fully automated bioinformatics pipeline that integrates the work of management, analysis, storage, and sharing of metagenomics projects [15] instead of analysis of 16s rrna data only. the three bioinformatics pipelines, namely mg-rast, img/m, and ebi metagenomics are chosen because within the existing web resources in metagenomic studies, the three bioinformatics tools are highly rated in terms of ease in data uploading, online user support availability, analysis spectrum, citation, and storage capacity [16]. hence, this research will only focus on the metagenomics analysis by these three bioinformatic pipelines: mg-rast, img/mer, and ebi metagenomics. these three tools, especially mg-rast, have been used repeatedly to analyze many metagenome sequencing datasets from a variety of sources. in the present work, we compare the 3 iium engineering journal, vol. 20, no. 1, 2019 parman et al. analysis result of the same input data using the common three web-based automated bioinformatics pipelines of mg-rast, img/mer, and ebi metagenomics to evaluate their accuracy in taxonomy and functional annotation on the microbial diversity and several functional genes contain in pome. 2. materials and methods 2.1 collection of samples and creation of metagenomics libraries pome samples were collected from felda palm industries sdn. bhd. of kks mempaga, pahang, malaysia. after sample collection, the metagenomic dna was extracted using meta-g-nome™ dna isolation kit (epicentre, u.s), sheared, endrepaired, ligated to pcc1fos fosmid vector and phage-mediated transfection to surrogate host epi300t1 resistant e.coli to perform the cloning of metagenomic dna grown in lb agar with the recommended antibiotic. the libraries (>100,000) were constructed by preparing 384-well transparent microplates with lb broth and 20% glycerol and each colony were inoculated from lb agar to the microplates and of glycerol media and stored at -80 oc. 2.2 high throughput screening and next-generation sequencing (ngs) colonies from each plate were inoculated to 384-well microplates filled with lb broth with antibiotic and inducer (respective to their positions in the library plates). screening buffer (potassium acetate) and lysis mix (10% triton x-100, 100 mm tris and 10 mm edta) were added to break open the cells and methylumbelliferyl-β-dglucopyranoside (muglc), methylumbelliferyl-β-d-cellobioside (muc) and chlorocoumarin-xylobioside (ccx) fluorogenic substrates were added to each well. after an overnight incubation, the plates were screened using a microplate reader for the presence of celluloseand xylan-degrading enzymes. the relative fluorescence units given by the microplate reader were changed to robust z-score to select the high rated hits. robust z-score was calculated for each microplate independently and results of all plates (109,834 clones) were combined to select the 100 high rated clones [17,18] and sent for illumina hiseq2000 next-generation sequencing (ngs) at the malaysia genome institute (mgi), bangi, selangor. 2.3 post-processing of ngs data initial raw data of ngs in the fastq format had undergone sequence quality trimming and short read removal by solexaqa++ program [19]. the fosmid vector and internal control phix sequences were removed using bowtie2 [20]. the high-quality sequences were assembled with velvet based on the de bruijn graph algorithm to organize the sequences in contigs. velvet is a new strategy developed to merge very short reads in combination with read pairs to produce useful assemblies [21]. 2.4 metagenomics analysis using three bioinformatics pipelines the same dataset of assembled data from pome’s ngs results with fasta format was uploaded into three automated bioinformatics pipelines of mg-rast, img/m, and ebi metagenomics. these free web-based bioinformatic pipelines were automatically run after submission of the file with related metadata. the details on the uploading method, databases, and system included are summarized in table 1. 4 iium engineering journal, vol. 20, no. 1, 2019 parman et al. 2.4.1 mg-rast the fasta format file and metadata were uploaded in the upload segment of mgrast. the metadata was also uploaded using microsoft excel template prior to the submission. throughout the process, the percentage of analysis and process done could be seen in the progress segment. in mg-rast, the file had undergone the quality control for data hygiene first and before proceeding with feature identification of coding dna sequence (cds) using fraggenescan. this database could predict the dna coding region of higher than 75 bp. the similarity searches on taxonomic classification in mg-rast were conducted using the blast-like alignment tool (blat) that is used to find sequence hits in seven taxonomic categories. for functional annotation, m5nr was used by providing non-redundant integration of several databases like seed, kegg, genbank, img, uniprot, and eggnogs [6]. table 1: technical comparison of mg-rast, img/m, and ebi metagenomics mg-rast img/m ebi metagenomics analysis duration 5 h 21 mins 5 days 22 h 46 mins 3 days license open-source open-source open-source current version 4.0.3 4.570 pipeline version 4.0 website http://metagenomics.anl .gov/ https://img.jgi.doe.gov/m/ https://www.ebi.ac.uk/m etagenomics/ association gold & doe-jgi map ena primary usage gui gui gui feature identification rrna & cds (fraggenescan) crispr, trna, rrna & cds prediction (genemark, prodigal, metageneannotator, fraggenescan) rrna & cds (fraggenescan, prodigal) homologybased algorithm blat blast, hmmer, usearch functional annotation uniprot, img/m, cogs, eggnogs, kegg, seed, string cogs, pfam, ko, ec, metacyc, kegg comparing cds using interproscan taxonomic annotation blat blast comparing rrna using mapseq 2.4.2 img/m to submit our own data for metagenomics analysis in img/m, we used the integrated microbial genomes with microbiomes for expert review (img/mer). img/m has been associated with gold v.5 and doe’s joint genome institute (jgi). the initial step involved is by login to img/mer and then registering the project metadata at gold prior to uploading the data at jgi. after completion of data submission, the quality control (qc) pre-processing like trimming and removing sequences shorter than 150 bp would take 5 iium engineering journal, vol. 20, no. 1, 2019 parman et al. place. next, the genes prediction of crispr, trna, rrna, and cds was conducted using several databases like genemark, prodigal, metageneannotator, and fraggenescan. finally, the functional annotation was completed by associating the protein-coding genes with the cog, pfam, ko, ec, metacyc, and kegg [8]. 2.4.3 ebi metagenomics (emg) to analyze the data from pome’s ngs results using ebi metagenomics, the data file needs to be uploaded to the european nucleotide archive (ena) using either webin uploader, filezilla client-server, or aspera. in this research, filezilla client-server was utilized, which is easier to use compared to the other methods and has been used widely by many researchers. after qc and filtering out ncrna reads, the cds of proteins were predicted using fraggenescan for short reads and prodigal for longer reads or assembled ones. in ebi metagenomics, mapseq was used for taxonomic classification by assigning taxonomy and otu classification to rrna sequence. in the meantime, interproscan was also used for functional annotation by predicting the domains and classifying them into families using a compilation of several databases like pfam, tigrfam, prints, prosite patterns, and gene3d. finally the functional results were produced in gene ontology (go). 3. results and discussion to ensure the similar type of dataset for data comparison, the file in fasta format with assembled form has been selected for this research. the assembled format is used instead of the raw sequence because one of the bioinformatics pipelines, img/m cannot process the unassembled reads if they are generated outside the joint genome institute (jgi) [9]. the data was submitted to get a clear result related to the taxonomic and functional annotation involving pome dna metagenome sample. specifically, the results of major phylum and genus distribution existing in pome will represent the taxonomic classification. on the other hand, major functional annotation and glycoside hydrolase enzyme present in pome’s metagenomics dna results will represent the functional annotation part of this research. overall, mg-rast was found to be the quickest in 5 hours 20 minutes (table 1) compared to img/m and ebi metagenomics. however, qiime was the quickest compared to mg-rast and mothur [14]. on the contrary, mg-rast is the quickest in this research, even though qiime was included in ebi metagenomics system version 3.0. in this condition, qiime is not a stand-alone system, and ebi metagenomics also involves other bioinformatic tools like fraggenescan, prodigal, and interproscan which explains the slowness of ebi metagenomics containing qiime compared to mg-rast. figure 1(a) showed the results of major phylum distribution present in effluent of felda palm oil mill, mempaga, pahang by each bioinformatic pipelines. all three bioinformatic pipelines have similar dominant phylum of proteobacteria and firmicutes with mg-rast 73.7% and 25.3%, img/m 48% and 28%, and ebi metagenomics 67% and 33%, respectively. the difference can be seen in img/m er with additional dominant phylum of actinobacteria (12%), dsdna viruses (5%), and bacteroidetes (4%). in this phylum composition, img/m er appeared to be more diverse and details compared to the other two bioinformatics pipeline. mg-rast using a blat algorithm while img/m er used blast which is the most commonly used bioinformatics tool for sequence similarity analysis. besides that, img/m could provide the percent identities greater than 30% which ensured the larger amount of results produced, while the setting in mg-rast is only for the percent identities of 60% and above. 6 iium engineering journal, vol. 20, no. 1, 2019 parman et al. for genus distribution result, the comparison table only involves mg-rast and img/mer as shown in fig. 1(b). ebi metagenomics was excluded because no details genes distribution could be detected except staphylococcus. the latest version of ebi metagenomics pipeline 4.0 uses mapseq framework for taxonomic classification whichallows the metagenomic analysis of reference based rrna only. consequently, only small amount of 16s rrna could be found in this sequence and finally bring the limitation of staphylococcus as an output. on the contrary, the other two pipelines of mg-rast and img/m, besides rrna as reference-based, they also used coding dna sequence (cds) of protein as the reference which results thousands of cds can be found from the data submission. fig. 1: (a) phyla distribution of palm oil mill effluent (pome) computed by each tool and (b) major genus distribution in pome analyzed by mg-rast and img/m only. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 g en es a nn ot at ed (x 10 ^3 ) taxonomic hits (genus) mg-rast img/ mer 0% 20% 40% 60% 80% 100% 120% mg-rast img/m er emg ph yl a r el at iv e a bu nd an ce (% ) dsdna viruses proteobacteria firmicutes cyanobacteria chlamydiae bacteroidetes actinobacteria (a) (b) 7 iium engineering journal, vol. 20, no. 1, 2019 parman et al. the major genus found in mg-rast in fig. 1(b) is similar to img/mer which are pseudomonas, staphylococcus, serratia, escherichia, burkholderia, yersinia, and salmonella. from the same figure too, the quantity of major genes found in all mgrast’s genus is greater than img/m, and the total number of the genus found in mgrast initially also is greater than img/m. soleimaninanadegani and manshad‘s work on pome reported that they found bacillus, micrococcus, pseudomonas and staphylococcus genus in pome sample [22]. this finding explains the existence of pseudomonas and staphylococcus as one of the major genus found in pome while the other genus like serratia, burkholderia, yersinia, and salmonella are new findings in this research. besides that, all the genus are identified under the family of firmicutes and proteobacteria which also explain the two families as the main families present in pome. for functional annotation, several major categories of functional annotation can been extracted from the results obtained by each pipeline which are transport and metabolism of nucleotide, lipid, inorganic ion, coenzyme, carbohydrate, and amino acid as shown in fig. 2. raw pome contains a high concentration of carbohydrate, protein, nitrogenous compounds, lipids, and minerals [23], which explains why in all three pipelines’ analysis of the metabolism that lipid, carbohydrate, amino acid, inorganic ion, and coenzyme are among the highest annotated reads of functional annotation. once again, img/m has the highest number of annotated reads nearly in all the functional categories. fig. 2: major functional annotation of palm oil mill effluent (pome) analyzed by mg-rast, img/m, and ebi. all the glycoside hydrolase enzymes analyzed by each pipeline are listed in table 2 in order for future research related to the study of useful glycoside hydrolases related to pome. the pome glycoside hydrolase enzymes identified by bioinfomatics tools suggest that pome can be a potential local source for novel enzymes and future potential enzymes for industrial applications. the blank spaces of ebi metagenomics part (table 2) probably occurred because ebi metagenomics used interproscan in functional annotation. interproscan is a database that works by classifying the cds into respected families and also by predicting any important domains and sites related to protein sequence [24]. therefore, the output result of ebi metagenomics will be more related to predicted domains and families rather than the protein or enzyme names. 0 200 400 600 800 1000 1200 1400 1600 amino acid transport and metabolism carbohydrate transport and metabolism coenzyme transport and metabolism inorganic ion transport and metabolism lipid transport and metabolism functional annotation ebi img/m mg-rast 8 iium engineering journal, vol. 20, no. 1, 2019 parman et al. table 2: total number of enzyme glycoside hydrolase (ec 3.2.1.-) in palm oil mill effluent (pome) identified by mg-rast, img/m er, and ebi metagenomics enzyme id enzyme name mg-rast img/m ebi ec 3.2.1.1 alpha-amylase 1 2 5 ec 3.2.1.14 chitinase 4 12 ec 3.2.1.141 malto-oligosyltrehalose trehalohydrolase 2 ec 3.2.1.17 lysozyme 1 ec 3.2.1.20 alpha-glucosidase 1 3 ec 3.2.1.21 beta-glucosidase 1 3 ec 3.2.1.23 beta-galactosidase 2 2 7 ec 3.2.1.26 beta-fructofuranosidase 3 3 ec 3.2.1.4 cellulase 3 1 2 ec 3.2.1.52 beta-n-acetylhexosaminidase 11 5 ec 3.2.1.85 6-phospho-beta-galactosidase 1 1 ec 3.2.1.86 6-phospho-beta-glucosidase 4 4 2 ec 3.2.1.93 alpha,alpha-phosphotrehalase 1 2 2 28 33 30 4. conclusions throughout the results of taxonomic and functional annotation of palm oil mill effluent (pome) dna metagenomics sample, img/m could be seen to provide a better analysis result compared to the other pipelines. img/m could give a diverse phylum result as it involves a much wider range of percent identity. besides that, this bioinformatics pipeline also is the one with the highest in nearly all major functional annotation of carbohydrate, amino acid, lipid and coenzyme transport and metabolism as well as the highest in the total number of glycoside hydrolase enzymes contained in pome. on the other hand, the other two pipelines of mg-rast and ebi metagenomics also have their own specialties. these two bioinformatic tools allow the submission of raw data compared with img/m, which is limited to the assembled one only. mg-rast is also good for obtaining data analysis in a short period as it uses the blat system which is 500 times faster for nucleic acid sequence alignment and 50 times faster for protein sequence alignment than other famous existing tools including the one being used in img/m and ebi metagenomics server [25]. next, ebi metagenomics is more suitable for a deeper understanding of the protein families and domains involved in any specific sequence rather than focusing on taxonomical annotation. in conclusion, all the three bioinformatics pipelines have their own specialty that the researcher needs to know in detail so that the specific bioinformatic pipeline can be used based on individual functional interest 9 iium engineering journal, vol. 20, no. 1, 2019 parman et al. acknowledgment the authors would like to thank ministry of education, malaysia for giving the financial support through the fundamental research grant scheme (frgs) with project id frgs 13-086-0327. besides that, the authors also deeply grateful to malaysia genome institute (mgi) for the technical assistance in analyzing the metagenomic data of pome. the authors also would like to express their appreciation to professor s.g. withers and dr hong ming (chemistry department, university of british columbia, vancouver, canada) for providing substrates used for the high-throughput screening of this work. references [1] kumar s, krishnani kk, bhushan b, and brahmane mp. (2015) metagenomics : retrospect and prospects in high throughput age, vol. 2015. [2] mincheol k, lee kh, yoon sw, kim bs, chun j, and hana y. (2013) analytical tools and databases for metagenomics in the next-generation sequencing era, 11(3): 102-113. [3] abdullah n and sulaiman f. (2013) the oil palm wastes in malaysia, biomass now – sustain. growth use, pp. 75-100. [4] meyer f, paarmann d, souza md, olson r, glass em, kubal m, edwards ra. (2008) the metagenomics rast server – a public resource for the automatic phylogenetic and functional analysis of metagenomes, 8: 1-8. https://doi.org/10.1186/1471-2105-9-386. [5] tang w, bischof j, desai n, mahadik k, gerlach w, harrison t, meyer f. (2014) workload characterization for mg-rast metagenomic data analytics service in the cloud. 2014 ieee international conference on big data (big data), 56-63. https://doi.org/10.1109/bigdata.2014.7004394. [6] wilke a, gerlach w, harrison t, paczian t, trimble wl, & meyer f. (2016) mg-rast manual for version 4, revision 1. [7] markowitz vm, chen ima, chu k, szeto e, palaniappan k, pillay m, kyrpides nc. (2014) img/m 4 version of the integrated metagenome comparative analysis system. nucleic acids research, 42(d1): 568-573. https://doi.org/10.1093/nar/gkt919. [8] huntemann m, ivanova nn, mavromatis k, tripp hj, paez-espino d, tennessen k, kyrpides nc. (2016) the standard operating procedure of the doe-jgi metagenome annotation pipeline (map v . 4). standards in genomic sciences, 1: 1-5. https://doi.org/10.1186/s40793-016-0138-x. [9] chen ima, markowitz vm, chu k, palaniappan k, szeto e, pillay m, kyrpides nc. (2017) img/m: integrated genome and metagenome comparative data analysis system. nucleic acids research, 45(d1): d507-d516. https://doi.org/10.1093/nar/gkw929. [10] hunter s, corbett m, denise h, fraser m, gonzalez-beltran a, hunter c, sansone s. (2014) ebi metagenomics — a new resource for the analysis and archiving of metagenomic data, 42: 600-606. https://doi.org/10.1093/nar/gkt961. [11] denise h, mitchell a, bucchini f, cochrane g, denise h, hoopen p, finn rd. (2016) ebi metagenomics in 2016 an expanding and evolving resource for the analysis and archiving of metagenomic data ebi metagenomics in 2016 an expanding and evolving resource for the analysis and archiving of metagenomic data, (november 2015). https://doi.org/10.1093/nar/gkv1195. [12] mitchell al, scheremetjew m, denise h, potter s, tarkowska a, qureshi m, finn rd. (2017) ebi metagenomics in 2017: enriching the analysis of microbial communities, from sequence reads to assemblies. nucleic acids research, 46(d1): d726-d735. https://doi.org/10.1093/nar/gkx967. [13] d’argenio v, casaburi g, precone v, & salvatore f. (2014) comparative metagenomic analysis of human gut microbiome composition using two different bioinformatic pipelines. biomed res int, 325340. https://doi.org/10.1155/2014/325340. 10 iium engineering journal, vol. 20, no. 1, 2019 parman et al. [14] plummer e, twin j. (2015) a comparison of three bioinformatics pipelines for the analysis of preterm gut microbiota using 16s rrna gene sequencing data. j. proteomics & bioinformatics, 8(12): 283–291. https://doi.org/10.4172/jpb.1000381. [15] oulas a, pavloudi c, polymenakou p, pavlopoulos ga, papanikolaou n, kotoulas g, iliopoulos i. (2015) metagenomics: tools and insights for analyzing next-generation sequencing data derived from biodiversity studies. bioinformatics and biology insights, 9: 75-88. https://doi.org/10.4137/bbi.s12462. [16] dudhagara p, bhavsar s, bhagat c, ghelani a, bhatt s, & patel r. (2015) web resources for metagenomics studies, 13: 296–30. [17] malo n, hanley ja, cerquozzi s, pelletier j, & nadon r. (2006) statistical practice in highthroughput screening data analysis. nature biotechnology, 24(2): 167-175. https://doi.org/10.1038/nbt1186. [18] birmingham a, selfors lm, forster t, wrobel d, kennedy cj, shanks e, shamu ce. (2009) statistical methods for analysis of high-throughput rna interference screens. nat methods, 6(8): 569-575. https://doi.org/10.1038/nmeth.1351. [19] cox mp, peterson da, & biggs pj. (2010) solexaqa: at-a-glance quality assessment of illumina second-generation sequencing data. bmc bioinformatics, 11: 485. https://doi.org/10.1186/1471-2105-11-485. [20] langmead b, & salzberg sl. (2013) fast gapped-read alignment with bowtie 2. nature methods, 9(4): 357-359. https://doi.org/10.1038/nmeth.1923.fast. [21] zerbino dr, birney e. (2008) velvet manual version 1.1. genome research, 18(5): 821829. https://doi.org/10.1101/gr.074492.107. [22] soleimaninanadegani m, manshad s. (2014) enhancement of biodegradation of palm oil mill effluents by local isolated microorganisms. international scholarly research notices, 1-8. https://doi.org/10.1155/2014/727049. [23] habib mab, yusoff fm, phang sm., ang kj, & mohamed s. (1997) nutritional values of chironomid larvae grown in palm oil mill effluent and algal culture. aquaculture, 158(1-2): 95-105. https://doi.org/http://dx.doi.org/10.1016/s0044-8486(97)00176-2. [24] finn rd, attwood tk, babbitt pc, bateman a, bork p, bridge aj, mitchell al. (2017) interpro in 2017-beyond protein family and domain annotations. nucleic acids research, 45(d1): d190-d199. https://doi.org/10.1093/nar/gkw1107. [25] kent wj. (2002) blat — the blast -like alignment tool. genome research, 12: 656664. https://doi.org/10.1101/gr.229202. 11 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <feff004200720075006700200069006e0064007300740069006c006c0069006e006700650072006e0065002000740069006c0020006100740020006f007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400650072002c0020006400650072002000650067006e006500720020007300690067002000740069006c00200064006500740061006c006a006500720065007400200073006b00e60072006d007600690073006e0069006e00670020006f00670020007500640073006b007200690076006e0069006e006700200061006600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020004400650020006f007000720065007400740065006400650020005000440046002d0064006f006b0075006d0065006e0074006500720020006b0061006e002000e50062006e00650073002000690020004100630072006f00620061007400200065006c006c006500720020004100630072006f006200610074002000520065006100640065007200200036002e00300020006f00670020006e0079006500720065002e> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 characteristics of leachate upon hydrothermal treatment processing: case study of ampang district municipal solid waste leachate hadi purwanto1*, siti salwa khamis1, hamzah mohd salleh2, alya naili rozhan1, mohamed abd rahman1 and rashidi othman3 1 department of manufacturing and materials engineering, faculty of engineering, 2 international institute for halal research and training, 3 herbarium unit, department of landscape architecture, faculty of architecture and environmental design, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. * corresponding author: hadi@iium.edu.my (received: 5th october 2021; accepted: 22nd february 2022; published on-line: 4th july 2022) abstract: municipal solid waste (msw) leachate is a hazardous liquid produced from decomposition of solid waste with high amount of organic matter and ammonia-nitrogen with obnoxious smell. this study aimed to investigate the behavior of msw leachate when subjected to hydrothermal treatment using an autoclave set up at below water critical points (temperatures of 100 °c, 150 °c, and 200 °c at 0.1 mpa, 0.4 mpa and 1.6 mpa, respectively) with 15 min and 60 min holding time. physicochemical characterization of the setup at 200 °c and 1.6 mpa at 60 min holding time indicates a feasible parameter when materials that caused the dark color and obnoxious smell were almost completely removed. over 99% of chemical oxygen demand and ammonia nitrogen was eliminated when treated with hydrothermal treatment and yielded a condensed liquid product that complied with permissible limits set by the national water quality standard malaysia and the world health organization for wastewater discharges for irrigation purposes. chromatographic analysis indicated that most of the organic compounds present in the raw leachate was removed. this processing is believed to be an environmentally friendly method that can treat msw leachate rapidly, and it has the potential to be used as an effective alternative to existing leachate treatment technologies. abstrak larut lesap daripada sisa pepejal perbandaran merupakan cecair merbahaya yang berlaku semasa penguraian sisa pepejal dengan jumlah bahan organik dan ammonianitrogen yang tinggi dengan bau menjengkelkan. kajian ini bertujuan bagi mengkaji sifat larut lesap ini apabila melalui rawatan hidroterma menggunakan autoklaf yang ditetapkan di bawah titik kritikal air (suhu 100 °c, 150 °c, dan 200 °c pada 0.1 mpa, 0.4 mpa dan 1.6 mpa masing-masing) dengan tempoh masa 15 minit dan 60 minit. sifat fizikal kimia yang dirawat pada suhu 200 °c, 1.6 mpa selama 60 minit menunjukkan satu parameter yang boleh dilaksanakan apabila warna gelap dan bau yang menjengkelkan hampir dikurangkan sepenuhnya. lebih 99% ammonia nitrogen disingkirkan apabila dirawat dengan rawatan hidrotherma dan menghasilkan air bersih yang mematuhi had yang dibenarkan oleh piawaian kualiti air kebangsaan malaysia (nwqsm) dan pertubuhan kesihatan sedunia (who) bagi pelupusan air sisa pepejal bagi tujuan pengairan. analisis kromatografi menunjukkan bahawa sebahagian besar sebatian organik yang terdapat dalam larut resap telah disingkirkan. pemprosesan ini diyakini merupakan kaedah mesra 205 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 alam yang dapat merawat dengan cepat, dan berpotensi digunakan sebagai alternatif efektif untuk teknologi rawatan larut lesap sedia ada. keywords: municipal solid waste; leachate; hydrothermal; organic compound 1. introduction the recent economic, demographic, and technological development of society have led to an increase in the production of municipal solid waste (msw), which consequently causes a waste disposal problem. landfills are the most widely used method to dispose msw since it is simple, feasible and cost effective; it minimizes carbon dioxide (co2) and controls methane (ch4) and leachate emissions [1] especially in sanitary landfills. however, the conventional landfilling method has a lot of negative impacts on the environment. open msw dumpsites nowadays have become looming hotspots for water, air, and land pollution [2]. as waste generation increased, more waste would be dumped into landfill that would simultaneously lead to an increase in landfill leachate generation. unfortunately, waste is still being wantonly discarded in open dumps all over the world, while the substantial resources spent in remediation suggest that landfill leachate is a significant source of groundwater pollution [3]. in malaysia, act 672, gazetted in 2007, is the law that deals with solid waste and public cleansing management. the plans and strategies formulated in line with act 672 were projected to bring about huge transformation in msw management in the country. however, the authorities face a huge challenge in the implementation of the national policy regarding msw management [4]. the strategies to reduce waste to be sent to landfill do not seem to produce the expected results. landfill is still the main msw disposal approach [5] and solid waste sent to landfill is increasing every year [6]. landfill leachate generally contains organic matter (biodegradable, but also refractory to be biodegraded), ammonia-nitrogen (nh3-n), heavy metals, and chlorinated organic compounds and inorganic salts [7]. the main concern about those compounds in environmental matrices is that they are hazardous and of difficult decomposition by soil and aquatic microorganisms [8]. inhabitants who live near the dumps are particularly at risk of consuming contaminated water. domestic water use for drinking, bathing, or washing in nearby areas may lead to exposure to volatile organic compounds (vocs) [9], mercury [10], polychlorinated biphenyl (pcbs) [11], or polyaromatic hydrocarbon (pahs) [12]. a laboratory analysis by griffith et al. [13] identified 593 sites in the us where contaminated groundwater was used for drinking purposes. in the state of new jersey for example, leachate from the site of lipari landfill has migrated into nearby streams and lakes adjacent to a residential area and contaminated most of the water pathways causing an increase in the proportion of low-birth-weight babies (2.5 kg) and lowering the birth weight for the population living closest (within 1 km radius) to the landfill. studies on leachate demonstrate that it contains compounds such as pahs, alkenes, ketones, esters, alcohols [14], phthalates, phenols and nitrogen compounds [15], carboxylic acids, amines, amides, aldehydes and carbohydrates [16]. these pollutants have accumulative, threatening, and detrimental effects on the survival of aquatic life forms, ecology, and food chains leading to enormous problems in public health including carcinogenic effects, acute toxicity, and genotoxicity [12,17-19]. solid waste landfills are often reported to have serious and recurring leachate contamination issues, and the pollution is caused by the design of the landfill and existing leachate treatment system that are not able to fully accommodate the increasing volume of solid waste received [20]. biological processing is usually carried out to remove the contaminants, especially the organic contents and total kjeldahl nitrogen (tkn) in the form 206 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 of ammonium – from leachate, to meet the compliance limits before being discharged into the environment [21]. conventional biological treatment process usually consists of two stages: denitrification and nitrification. however, the conventional pathway involves higher operational cost due to the requirement of high amounts of oxygen during the nitrification when pure oxygen is used to supplement the air system and carbon during the denitrification process [22]. the most common approach to leachate treatment involves biological and physical or chemical leachate treatment in combinations. leachate contains recalcitrant to biological process substance that cannot be treated using either one of the processes alone. all the contaminants make the treatment of leachate complex and expensive [23]. advanced oxidation process (aop) has gained importance over the past few years due to its potential to biologically destruct resistant organic molecules and micro pollutants, enhancing the quality of discharge waters from secondary treatment units [24]. of all the aops, the hydrothermal oxidation process (suband super-critical) has received particular attention for its complete conversion without producing any harmful intermediates [25]. aop is also referred to as hydrothermal treatment process. hydrothermal treatment below the critical points of water has been widely employed for the solubilization, extraction, and liquefaction of target materials [26]. subcritical water has hydrolytic and pyrolytic reaction characteristics, which result from a decrease in the dielectric constant and increase in the ion product of water at temperatures and pressures below and near 374 °c and 22.1 mpa [2728] . most researchers have focused on solubilization and extraction to recover valuable organic compounds such as glucose and organic acids [27,29-31]. some researchers have dealt with hydrothermal treatment as pretreatment prior to fermentation, gasification, composting, and other processes [26,32-35]. many have focused on treatment using supercritical water, which is the process that occurs in water above its critical points [3641]. only a few researchers focus on treating msw leachate by employing hydrothermal treatment below the critical points water. kirmizakis et al. [42] employs hydrothermal treatment below the critical points water to treat landfill leachate at temperatures in the range of 100 ºc to 374 ºc but requires chemicals as a catalyst for the treatment. in this work, hydrothermal treatment below critical points condition was performed to treat msw leachate samples from the area of ampang district, selangor, malaysia. physicochemical characteristics of the leachate samples such as color, odor, ph, chemical oxygen demand (cod), ammonia-nitrogen (nh3-n) and the organic compound composition of the leachate were mainly investigated. the experimental results were then compared with the standard discharge limit by the national water quality standard malaysia (nwqsm) and the world health organization (who) at the permissible limits for contaminants present in wastewater discharges for irrigation purposes. 2. materials and method 2.1 material fresh msw leachate was collected from several garbage trucks for municipalities in the area of ampang district, selangor owned by kdeb waste management sdn bhd (kdebwm) for the sampling. each garbage truck had a temporary leachate storage tank below it, which allowed excess liquids in the msw to infiltrate and accumulate in the tank. msw leachate sample went directly from the tank into container. collected msw leachate was filtered using a 1.5 mm mesh to remove solid particles and was stored at 4 ºc. 207 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 2.2 hydrothermal treatment processing setup fig. 1 shows the laboratory-scale experimental apparatus for the hydrothermal treatment. the reactor was loaded up to ¾ volume of the reactor. raw msw leachate (50 ml) and 130 ml distilled water were put in a batch type autoclave reactor and sealed. saturated steam and pressure were set at 100-200 ºc and 0.1-1.6 mpa depending on working temperature. the reactor was held for 15 min or 60 min after reaching all the setup conditions. the reactor was quenched with cooling water at room temperature in the condenser to terminate further reactions from occurring after the intended holding time. the clean liquid was collected as the product of the hydrothermal treatment and the inorganic particles that had settled at the bottom of the reactor were discharged. fig. 1: laboratory-scale experimental apparatus for the hydrothermal treatment. 2.3 physicochemical analysis the parameters for characterization were chosen according to the leachate pollution index (lpi) that provides an overall pollution potential of a landfill site in identifying whether the msw leachates are hazardous or not. physicochemical parameters were analyzed for color, odor, ph, chemical oxygen demand (cod), and ammonia-nitrogen (nh3-n) composition. color and odor were observed according to the physical appearance of the sample and indicated using sensorial technique by smelling the samples respectively. ph was analyzed using a ph meter, cod was determined by the colorimetric method, and nh3-n was measured by the salicylate method (385 hach dr/3900 spectrophotometer) using the apha standard methods [43]. the removal percentage of cod and nh3-n was computed based on following equation: 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑜𝑓 𝑟𝑒𝑚𝑜𝑣𝑎𝑙 (%) = ((𝑋𝑖 − 𝑋𝑓)/𝑋𝑖) ∗ 100% where percentage removal represents percentage of cod and nh3-n removed from raw msw leachate, 𝑋𝑖 refers to average initial raw reading of cod and nh3-n before treatment, and 𝑋𝑓 is the average final reading of cod and nh3-n after treatment. 208 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 2.3.1 ph sampling the ph values were measured immediately after the samples were taken from the garbage truck. three representative samples from each garbage truck were put into glass closed containers. the fresh sample was stirred, and ph meter electrode was placed in the leachate sample and measurement recorded when the readings stabilized. the electrode was rinsed several times with distilled water and blotted dry before placing into the sample. the same steps were followed for ph measurements of treated leachate. 2.3.2 chemical oxygen demand (cod) a high range cod digestion reagent vial was used for the sample concentration up to 15000 mg/l range like msw leachate. the leachate sample was made homogenous by gently swirling and inverting the container several times for 30 sec, before 0.2 ml leachate was pipetted into the cod digestion reagent vial. the vial was capped tightly, rinsed with deionized water, and wiped clean with paper towel. the vial was inverted gently several times to make sure the content was mixed and was placed into the 150 °c preheated drb 200 reactor for two hours. a blank sample was prepared with 0.2 ml deionized water instead of the leachate. after 20 minutes, the drb 200 reactor was turned off. both sample and blank vials were gently inverted before allowing them to cool down to room temperature. measurements were made with a spectrophotometer set at 620 nm wavelength. 2.3.3 ammonia nitrogen (nh3-n) the blank sample was prepared by filling the sample cell with 10 ml deionized water, followed by the leachate sample preparation by filling the cell with 10 ml leachate sample. both were filled with ammonia salicylate reagent powder pillow (hach malaysia sdn bhd), and the cells were inverted to dissolve the reagent well. after three minutes of reaction time, both cells were filled with ammonia cyanurate powder pillow. the cap was closed, and cells were shaken to mix well. after 15 min, the green color formed in the presence of nh3-n was measured at 655 nm. 2.4 organic compound composition the organic compound composition was determined based on the standard apha method [43]. samples were prepared according to turki et al. [44] with slight modifications. sample (0.01 g) was brought to 1 ml volume with ethanol and filtered (0.2 µm nylon membrane) prior to gas chromatography – mass spectrometry (gc-ms) analysis using a hp-5ms fused silica capillary column (30 m × 250 μm i.d. and 0.5 μm film thickness; agilent technologies). the gc oven temperature was programmed as follows: 80 °c held for 2 min and raised at 10 °c/min to 250 °c (held for 10 min). helium was the gas carrier, and the flow rate was set at 1.07 ml/min. the sample injection (1.0 μl) was set on a splitless mode at 250 °c with solvent delay of 4 min. detection was conducted by a mass selective detector with electron impact ionization at 70 ev, in selected ion monitoring mode. ms transfer line temperature was at 250 °c, and the ms was operated in full scan in electron ionization mode with an electron multiplier voltage of 1588 v. the mass scanning was set to be of a range of m/z 40 to 500. the semi-quantification and the removal of persistent compounds in each stage of the process were performed by comparing the corrected areas of specific peaks to the peak area. 209 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 3. results and discussion 3.1 physicochemical characteristics msw raw leachate was a dark-cloudy colored liquid (brown and black), very acidic, offensive, and sometimes had a very pervasive smell. the ph of the samples collected from several garbage trucks owned by kdebwm during the transportation of the msw to the landfill were between 3.00–3.54 (average of 3.27). the cod ranges between 47000–55000 mg/l in raw leachate samples (average of 51000 mg/ml) and the nh3-n varied between 2950–4042 mg/l in the raw leachate samples (average of 3496 mg/l). the ph of the samples when subjected to hydrothermal treatment as a function of temperature is shown in fig. 2. the ph of hydrothermal treatment from 15 min to 60 min holding time was maintained within acceptable range limit. table 1: the physicochemical characteristics of msw leachate from ampang district, selangor no. parameter raw leachate hydrothermal treated nwqsm standard* nwqm standard* 100 °c, 0.1 mpa, 15 min 150 °c, 0.4 mpa, 30 min 200 °c, 1.6 mpa, 60 min 1 color dark brown, cloudy very light yellow, clear light yellow, clear almost transparent, clear 2 odor obnoxious less obnoxious less obnoxious no odor 3 ph 3.00-3.54 4.00-4.03 5.00-5.20 5.00-5.05 5.0-8.0 6.5-8.5 4 cod (mg/l) 47000-55000 7800-8800 230-248 48-52 100 250 5 nh3n (mg/l) 2950-4042 2301-2809 12.8-15.9 0.20-0.21 2.7 *discharge standard at class iv for irrigation. the result shows that with the increasing ph value, cod and nh3-n showed decline, and organic compounds in the treated leachate became significantly simpler than raw msw 4.01 4.78 4.814.42 5.10 4.924.81 5.23 5.02 0 1 2 3 4 5 6 100 150 200 p h temperature (°c) 15 min 30 min 60 min fig. 2: effect of temperature on ph change after hydrothermal. treatment. 210 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 leachate, as can be seen in table 1. raw leachate is a potentially hazardous material to lifeforms because biochemically it exhibited low ph, high cod, and high nh3-n. among the three set up parameters, temperature of 100-200 ºc, pressure of 0.1-1.6 mpa and holding time of 15 min or 60 min, the conditions of 100 °c, 1.6 mpa and 15 min holding time yielded condensed treated leachate that is characterized by very light yellow and clear liquids with some obnoxious smell. only 30% of nh3-n and 84% of cod was eliminated when treated with hydrothermal treatment that required further treatment to reach permissible limits. the conditions of 200 °c, 1.6 mpa with 60 min holding time provided the highest hydrothermal treatment performance on the raw msw. under these conditions, the final condensed liquid, which is clear and without any obnoxious smell (table 1), complies with the national water quality standard malaysia (nwqsm) and the world health organization (who) standards at the permissible limits for contaminants presents in wastewater discharges for irrigation purposes. percentage removal of cod and nh3-n under minimum and maximum condition of hydrothermal treatment is shown in table 2, calculated based on equation in section 2.3. treatment at 100° c, 0.1 mpa with 15 min holding time causes 84% of cod and only 30% of nh3-n to be degraded and removed. treatment at higher temperature and longer holding time of 200 °c, 1.6 mpa with 60 min results in removal of over 99% of cod and nh3-n. the results indicate that the hydrothermal treatment has significant impact on the reducing of organic substances in the leachate to meet the standard content in the wastewater discharging for irrigation purposes. table 2: percentage removal of cod and nh3-n no. parameter percentage removal 100 °c, 0.1 mpa, 15 min 200 °c, 1.6 mpa, 60 min 1 cod (mg/l) 84% 99% 2 nh3-n (mg/l) 30% 99% 3.2 organic compound composition a large number of organic compounds were identified in gc-ms based on a query mass spectrum with reference mass spectrum in the library of pahs and pcbs. there were no detectable pcbs in msw raw and treated leachate samples. table 3 shows the list of pahs found in the tested raw msw samples. pahs distribution data for the raw msw leachate showed major contribution of low molecular weight pahs (2-3 rings) molecular structures such as 2-fluorobiphenyl, 4-terphenyl-d4, naphthalene-d8, phenanthrene-d10, etc. besides, there was also minor presence of higher molecular weight pahs (4-6 rings) structures such as chrysene-d10, perylene-d12, chrysene, 3-methylchloanthrene, benzo(b)fluoranthene, benzo(k)fluoranthene, and benzo(a)pyrene. compounds that have more rings are much more stable and may hardly experience losses due to weathering processes such as solubilization, evaporation/ volatilization and natural biodegradation. the presence of benzo(a)pyrene consisting of five fused benzene rings for example, even at the smallest composition, in the distribution data of the leachate is enough to be of concern and requires effective efforts to eliminate it. immediate steps should be taken to limits its spread to the environment. this is because this compound is highly hazardous and is listed as a group 1 carcinogen by the international agency for research on cancer, iarc [45]. benzo(a)pyrene is hazardous to human health because it will attack the nervous system, immune system, and reproductive system, react and bind to dna, and result in mutations and eventually cancer in the body [46-48]. 211 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 the compounds of concern in msw leachate are those that are potentially hazardous, belonging to xenobiotic organic compounds including pahs and halogenated organics like the pcbs. pah organic pollutants are the most long-lived families of toxic chemicals. pahs are strongly hydrophobic and lipophilic as well as have the propensity to accumulate in the tissue of any living thing [49] that can undergo long range transport and move into otherwise pristine environments. pcbs are toxic persistent organic pollutants that are harmful to humans and the environment due to their lipophilic characteristic and not easily degraded in the environment. both pahs and pcbs are therefore the focus of the msw leachate analysis. the elimination of pahs and pcbs in treated leachate is important to avoid undesirable adverse effects on human health. table 3: list of pahs found in raw msw leachate no rt (min) compound % pahs detected % pcbs detected 1 7.16 2-fluorobiphenyl 12.66867 nd 2 10.89 4-terphenyl-d4 11.98621 nd 3 6.09 naphthalene-d8 8.62133 nd 4 9.31 phenanthrene-d10 7.87956 nd 5 8.66 chrysene-d10 7.49305 nd 6 4.5 phenol-d5 7.41990 nd 7 6.34 phenanthrene-d10 6.91754 nd 8 11.94 chrysene-d12 6.78624 nd 9 5.39 nitrobenzene-d4 6.53955 nd 10 3.6 2-fluorophenol 6.37875 nd 11 7.83 acenaphthene-d10 4.64253 nd 12 4.85 1,2-dichlorobenzene-d4 3.66190 nd 13 13.28 perylene-d12 3.65857 nd 14 8.61 2,4,6-tribromophenol 2.47231 nd 15 4.85 1,4-dichlorobenzene-d4 2.47227 nd 16 9.89 benzyl butyl phthalate 0.33581 nd 17 5.24 3&4-methylphenol 0.03793 nd 18 8.84 di-n-butyl phthalate 0.00669 nd 19 11.97 bis(2-ethylhexyl) phthalate 0.00368 nd 20 11.97 di-n-octyl phthalate 0.00368 nd 21 12.52 7,12-dimethyl benz(a)anthracene 0.00340 nd 22 7.86 diethyl phthalate 0.00201 nd 23 11.97 chrysene 0.00181 nd 24 7.69 acenaphthylene 0.00175 nd 25 12.4 3-methylchloanthrene 0.00114 nd 26 6.08 4-chlorophenol 0.00073 nd 27 6.11 naphthalene 0.00064 nd 28 11.92 benz(a)anthracene 0.00059 nd 29 12.93 benzo(b)fluoranthene 0.00057 nd 30 4.65 2-chlorophenol 0.00054 nd 31 12.96 benzo(k) fluoranthene 0.00041 nd 32 13.22 benzo(a)pyrene 0.00023 nd rt (retention time); nd (not detected) the chromatograms of raw msw leachate and two hydrothermally treated leachates at 200 °c are shown in fig. 2. the behavior of the chemical changes on the organic loads in the leachate during hydrothermal treatment can be seen clearly in the changes of chromatogram peaks. most compounds, especially pahs, existed in raw leachate, went missing when held at 200 °c, 1.6 mpa with 15 min of holding time. but some new compounds that are hazardous to environment like benzene, nitroso-, 2-pyrrolidinone, secbutyl nitrite, and cetene appeared. this means exposing raw leachate with hydrothermal treatment at 15 min of holding time has removed pahs and the reaction may cause the derivatives of new compounds from pahs of smaller molecular weight and change their molecular structure. for example, benzene, nitrosois a single-ring benzene structure that 212 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 derives from the existence of benzene. improper setup parameters in hydrothermal process may result in some hazardous compounds appearing. however, in this case, the compounds that appeared were selectively less reactive and not stable due to their lower molecular weight. fig. 2: the chromatograms of raw msw leachate (bottom) and hydrothermally-treated leachate at 200 °c held for 15 min (middle) and 60 min (top), respectively. as the treatment holding time increased, the intensity and/or peak abundance became smaller. as indicated earlier, the conditions of 200 °c, 1.6 mpa with 60 min holding time showed the highest performance for the hydrothermal treatment of raw msw leachate. under these conditions, there was no detectable presence of pahs but there were new compounds with significant peak intensity corresponding to alpha-amyrin, lupeol, and eicosane. all these compounds come from the lipid family and do not have any record of being hazardous compounds by the globally harmonized system of classification and labelling of chemicals (ghs) report. lipids formed from the process are believed to be the natural oils that come out from the hydrothermal processing of msw leachate in a hot and pressurized environment. hydrothermal liquefaction of organic content in the leachate may happen along the treatment in the thermochemical conversion of the organics into liquid fuels. temperature and pressure that is set in a closed reactor causes a thermal depolymerization process converting the wet organics, and other macromolecules, into a crude-like oil result. the hydrothermal conversion of leachate into clean water involves the process of vaporization, condensation, and collection of condensate product (clean water). leachate is a mixture of liquids containing organic and inorganic components. the hot and pressurized conditions vaporize the leachate and cause compounds in the mixture to break-up into smaller fragments, some of which are dissolved in water. the organic matter that makes 6.00 8.00 10.00 12.00 14.00 16.00 20.00 22.00 60 min 15 min raw area of pahs distribution in raw msw leachate 213 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 leachate hazardous are converted into simpler dissolved compounds during the process and the gaseous species was collected as clean water following condensation. inorganic components were collected as residues of the process. 4. conclusion characteristics and behavior of raw municipal solid waste leachate sampled from the ampang district, selangor, malaysia were experimentally investigated under hydrothermal treatment at various temperatures. the fresh raw leachate was dark brown and black color cloudy liquid that was potentially hazardous with average ph, cod and nh3-n of 3.27, 51000 mg/l, and 3496 mg/l. the decrease in the area of intensity in the gc-ms chromatograms reflects the removal of compounds from the raw leachate and their greatly reduced quantity after the hydrothermal treatment. treatment at 15 min holding time is insufficient to cause the compounds in the leachate to be degraded and removed which is inferred from peak areas comparison in the chromatograms for treated and raw leachate. treatment at longer holding time of 60 min and higher temperature appear to cause more compounds to be removed. most compounds were removed from the leachate sample that was hydrothermally treated at 200 °c, 1.6 mpa and 60 min, thus giving favorable parameters: 99% of cod and nh3-n were removed over raw leachate and complied with the national water quality standard malaysia and the world health organization standards for permissible limits for contaminants present in wastewater discharges for irrigation use. the results indicated that proper parameter setup on hydrothermal treatment cause an effective conversion of poisonous aromatic and complex organic compounds in the leachate into clean water so that burden to the environment can be reduced. it would provide a potential solution to leachate problems and reduce water pollution if the proposed process was implemented to process leachate on an industrial scale. acknowledgement this work was supported by the ministry of higher education malaysia through fundamental research grant scheme (frgs/1/2019/tk10/uiam/02/2). references [1] ramírez-sosa dr, castillo-borges er, méndez-novelo ri, sauri-riancho mr, barcelóquintal m, marrufo-gómez jm. (2013) determination of organic compounds in landfill leachates treated by fenton–adsorption. waste management, 33(2): 390-395. https://doi.org/10.1016/j.wasman.2012.07.019 [2] peter ae, nagendra ss, nambi im. (2019) environmental burden by an open dumpsite in urban india. waste management, 85, 151-163. https://doi.org/10.1016/j.wasman.2018.12.022 [3] christensen th, kjeldsen p, bjerg pl, jensen dl, christensen jb, baun a. (2001) albrechtsen h.-j. r.; heron g. biogeochemistry of landfill leachate plumes. appl. geochem, 16, 659-718. https://doi.org/10.1016/s0883-2927(00)00082-2 [4] manaf la, samah maa, zukki nim. (2009) municipal solid waste management in malaysia: practices and challenges. waste manag 29: 2902-2906. https://doi.org/10.1016/j.wasman.2008.07.015 [5] abas ma, wee st. (2014) the issues of policy implementation on solid waste management in malaysia. int j conceptions manag soc sci 2(3): 12-17. [6] mahidin dsdmu. (2020) department of statistics malaysia press release: compendium of environment statistics, malaysia 2020. dep stat malaysia 2015(2) [7] li w, zhou q, hua t. (2010) removal of organic matter from landfill leachate by advanced oxidation processes: a review. international journal of chemical engineering. 214 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 https://doi.org/10.1155/2010/270532 [8] nascimento filho id, von mühlen c, caramão eb. (2001) china ddp despachante de frete marítimo taxas transporte da para saba/em todo o mundo. química nova, 24(4): 554-556. https://doi.org/10.1590/s0100-40422001000400017 [9] hamar gb, mcgeehin ma, phifer bl, ashley dl. (1996) volatile organic compound testing of a population living near a hazardous waste site. journal of expo anal environ epidemiol 6(2): 247-255. [10] reif js, tsongas ta, anger wk, mitchell j, metzger l, keefe tj, tessari jd, amler r. (1993) two-stage evaluation of exposure to mercury and biomarkers of neurotoxicity at a hazardous waste site. journal of toxicol environmental health, 40(2-3): 413-422. https://doi.org/10.1080/15287399309531808 [11] stehr-green pa, burse vw, welty e. (1988) human exposure to polychlorinated biphenyls at toxic waste sites: investigations in the united states. arch environ health 43(6): 420-424. https://doi.org/10.1080/00039896.1988.9935861 [12] moraes pb, bertazzoli r. (2005) electrodegradation of landfill leachate in a flow electrochemical reactor. chemosphere, 58(1): 41-46. https://doi.org/10.1016/j.chemosphere.2004.09.026 [13] griffith j, duncan rc, pellom ac. (1989) cancer mortality in u.s. counties with hazardous waste sites and ground water pollution. arch environmental health, 44(2): 69-74. https://doi.org/10.1080/00039896.1989.9934378 [14] sang ym, gu qb, sun tc, li fs. (2008) color and organic compounds removal from secondary effluent of landfill leachate with a novel inorganic polymer coagulant. water science and technology, 58(7): 1423-1432. https://doi.org/10.2166/wst.2008.446 [15] marttinen sk, kettunen rh, rintala ja. (2003) occurrence and removal of organic pollutants in sewages and landfill leachates. science of the total environment, 301(1-3): 1-12. https://doi.org/10.1016/s0048-9697(02)00302-9 [16] monje-ramirez i, de velasquez mo. (2004) removal and transformation of recalcitrant organic matter from stabilized saline landfill leachates by coagulation–ozonation coupling processes. water research, 38(9): 2359-2367. https://doi.org/10.1016/j.watres.2004.02.011 [17] park jy, batchelor b. (2002) a multi-component numerical leach model coupled with a general chemical speciation code. water research, 36(1): 156-166. https://doi.org/10.1016/s0043-1354(01)00207-x [18] gajski g, oreščanin v, garaj-vrhovac v. (2012) chemical composition and genotoxicity assessment of sanitary landfill leachate from rovinj, croatia. ecotoxicology and environmental safety, 78: 253-259. https://doi.org/10.1016/j.ecoenv.2011.11.032 [19] mukherjee s, mukhopadhyay s, hashim ma, sen gupta b (2015) contemporary environmental issues of landfill leachate: assessment and remedies. critical reviews in environmental science and technology, 45(5): 472-590. https://doi.org/10.1080/10643389.2013.876524 [20] hemananthani s. (2017) minister: leachate contamination must be addressed. the star. https://www.thestar.com.my/news/nation/2017/07/10/a-very-dirty-dirty-headache-ministerleachate-contamination-must-be-addressed/ [21] hoang vy, jupsin h, le vc, vasel jl. (2012) modeling of partial nitrification and denitrification in an sbr for leachate treatment without carbon addition. journal of material cycles and waste management, 14(1): 3-13. https://doi.org/10.1007/s10163-011-0033-x [22] show pl, pal p, leong hy, juan jc, ling tc. (2019) a review on the advanced leachate treatment technologies and their performance comparison: an opportunity to keep the environment safe. environmental monitoring and assessment, 191(4): 1-28. https://doi.org/10.1007/s10661-019-7380-9 [23] wang k, li l, tan f, wu d. (2018) treatment of landfill leachate using activated sludge technology: a review. archaea, 2018: 1-10. article id 1039453. https://doi.org/10.1155/2018/1039453 [24] du x, zhang r, gan z, bi j. (2013) treatment of high strength coking wastewater by supercritical water oxidation. fuel, 104: 77-82. https://doi.org/10.1016/j.fuel.2010.09.018 [25] reddy sn, nanda s, hegde ug, hicks mc, kozinski ja. (2015) ignition of hydrothermal 215 https://doi.org/10.1590/s0100-40422001000400017 https://doi.org/10.1080/15287399309531808 https://doi.org/10.1016/j.chemosphere.2004.09.026 https://doi.org/10.1080/00039896.1989.9934378 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 flames. rsc advances, 5(46): 36404-36422. https://doi.org/10.1039/c5ra02705e [26] hwang i-h, aoyama h, matsuto t, nakagishi t, matsuo t. (2012) recovery of solid fuel from municipal solid waste by hydrothermal treatment using subcritical water. waste management, 32(3): 410-416. https://doi.org/10.1016/j.wasman.2011.10.006 [27] kang k, quitain at, daimon h, noda r, goto n, hu hy, fujie k. (2001) optimization of amino acids production from waste fish entrails by hydrolysis in sub and supercritical water. the canadian journal of chemical engineering, 79(1): 65-70. https://doi.org/10.1002/cjce.5450790110 [28] brunner g. (2009) near critical and supercritical water. part i. hydrolytic and hydrothermal processes. the journal of supercritical fluids, 47(3): 373-381. [29] ren lh, nie yf, liu jg, jin yy, sun l. (2006) kinetics study on photochemical oxidation of polyacrylamide by ozone combined with hydrogen peroxide and ultraviolet radiation. journal of environmental sciences, 18(4): 660-664. [30] watchararuji k, goto m, sasaki m, shotipruk a. (2008) value-added subcritical water hydrolysate from rice bran and soybean meal. bioresource technology, 99(14): 6207-6213. https://doi.org/10.1016/j.biortech.2007.12.021 [31] lamoolphak w, de-eknamkul w, shotipruk a. (2008) h production and characterization of protein and amino acids from silk waste. bioresource technology, 99(16): 7678-7685. https://doi.org/10.1016/j.biortech.2008.01.072 [32] eley mh, guinn gr, bagchi j. (1995) cellulosic materials recovered from steam classified municipal solid wastes as feedstocks for conversion to fuels and chemicals. applied biochemistry and biotechnology, 51(1): 387-397. https://doi.org/10.1007/bf02933442 [33] sawayama s, inoue s, minowa t, tsukahara k, ogi t. (1997) thermochemical liquidization and anaerobic treatment of kitchen garbage. journal of fermentation and bioengineering, 83(5): 451-455. https://doi.org/10.1016/s0922-338x(97)82999-6 [34] kato a, matsumura y. (2003) hydrothermal pulping of wet biomass as pretreatment for supercritical water gasification studies using cabbage as a model compound. journal of the japan institute of energy, 82: 97-102. https://doi.org/10.3775/jie.82.97 [35] papadimitriou ek, barton jr, stentiford ei. (2008) sources and levels of potentially toxic elements in the biodegradable fraction of autoclaved non-segregated household waste and its compost/digestate. waste management & research, 26(5): 419-430. https://doi.org/10.1177/0734242x08088697 [36] onwudili ja, williams pt. (2007) hydrothermal catalytic gasification of municipal solid waste. energy and fuels, 21: 3676-3683. https://doi.org/10.1021/ef700348n [37] marrone pa, hong gt. (2007) supercritical water oxidation. environmentally conscious materials and chemicals processing, 385-453. https://doi.org/10.1002/9780470168219.ch13 [38] gidner a, stenmark l. (2001) supercritical water oxidation of sewage sludge–state of the art. in proceedings of the ibc’s conference on sewage sludge and disposal options: 26-27 march 2001; birmingham, england; 1-16. elsevier karlskoga. [39] cocero mj, martín a, bermejo md, santos m, rincón d, alonso e, fdez-polanco f. (2003) supercritical water oxidation of industrial waste from pilot to demonstration scale. in proceedings of the 6th international symposium on supercritical fluids: 28-30 april 2003; versailles, france. [40] behnia i. (2013) treatment of aqueous biomass and waste via supercritical water gasification for the production of ch4 and h2. master thesis. the university of western ontario, chemical and biochemical engineering department. [41] veriansyah b, kim jd. (2007) supercritical water oxidation for the destruction of toxic organic wastewaters: a review. journal of environmental sciences, 19(5): 513-522. https://doi.org/10.1016/s1001-0742(07)60086-2 [42] kirmizakis p, tsamoutsoglou c, kayan b, kalderis d. (2014) subcritical water treatment of landfill leachate: application of response surface methodology. journal of environmental management, 146: 9-15. https://doi.org/10.1016/j.jenvman.2014.04.037 [43] apha (2005) standard methods for the examination of water and wastewater. stand methods. https://doi.org/isbn 9780875532356 [44] turki n. (2013) determination of organic compounds in landfill leachates treated by 216 https://doi.org/10.1016/j.jenvman.2014.04.037 iium engineering journal, vol. 23, no. 2, 2022 purwanto et al. https://doi.org/10.31436/iiumej.v23i2.2196 coagulation-flocculation and fenton-adsorption. journal of environmental science toxicology food technology, 7(3): 18-25. https://doi.org/10.9790/2402-0731825 [45] baan r, gross y, straif k. (2009) a review of human carcinogens-part f: chemical agents and related occumations. the lancet oncology, 10(12): 1143-1144. [46] mccallister mm, maguire m, ramesh a, aimin q, liu s, khoshbouei h, aschner m, ebner ff, hood db. (2008) prenatal exposure to benzo(a)pyrene impairs later-life cortical neuronal function. neurotoxicology, 29(5): 846-854. [47] clark rs, pellom st, booler b, ramesh a, zhang t, shanker a, maguire m, juarez pd, patricia mj, langston ma, lichtveld my, hood db. (2006) validation of research trajectory 1 of an exposome framework: exposure to benzo(a)pyrene confers enhanced susceptibility to bacterial infection. environmental research, 146: 173-184. [48] ramesh a, inyang f, lunstra dd, niaz ms, kopsombut p, jones km, hood db, hills er, archibong ae. (2008) alteration of fertility endpoints in adult male f-344 rats by subchronic exposure to inhaled benzo(a)pyrene. experimental and toxicologic pathology, 60(4-5): 269280. [49] vane ch, kim aw, beriro dj, cave mr, knights k, moss-hayes v, nathanail pc. (2014) polycyclic aromatic hydrocarbons (pah) and polychlorinated biphenyls (pcb) in urban soils of greater london, uk. applied geochemistry, 51: 303-314. https://doi.org/10.1016/j.apgeochem.2014.09.013 217 https://doi.org/10.9790/2402-0731825 https://doi.org/10.1016/j.apgeochem.2014.09.013 untitled iium engineering journal, vol. 21, no. 2, 2020 omar et al. https://doi.org/10.31436/iiumej.v21i2.1388 preparation and characterizations of latex/filler nanocomposites mohamad firdaus omar1,2, nuriah mohamad2 and fathilah binti ali1* 1department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2top glove sdn. bhd., r&d centre, lot 64593, jalan dahlia ku/8, 41050 klang, selangor *corresponding author: fathilah@iium.edu.my (received: 9th march 2020; accepted: 14th june 2020; published on-line: 4th july 2020) abstract: latex compounding which incorporates various types of clays as filler to the rubber can significantly give reinforcement in the rubber matrix when rubber/clay nanocomposites are formed, but the filler agglomerates. thus, study was conducted by using kaolin clay as the filler in the rubber nanocomposites with silane coupling agent to functionalize the surface of the filler. this study was done in order to investigate the mechanical properties of various functionalized kaolin in latex nanocomposites, to prepare various ratios of kaolin to rubber, and to characterize mechanical, thermal and morphological properties of the kaolin in latex nanocomposites. to achieve these, six types of silane coupling agents was used for kaolin filler surface functionalization purpose during the filler’s incorporation in latex compounding. the optimized coupling agent, usi7301 (γ-chloropropyltrimetoxysilane) – with tensile strength value of 32.77 mpa, elongation at break value of 632.589 % and force at break value of 6.737 n – was used to further functionalize kaolin filler in different ratios so as to achieve the optimum mechanical, thermal and morphological properties of the filler in the polymer matrix. universal tensile machine was used to analyze the mechanical properties of the nanocomposites, while the scanning electron microscopy (sem) and differential scanning calorimetry (dsc) were used to observe the morphological and thermal properties of the nanocomposites, respectively. the results showed that reducing the total solids content (tsc) of kaolin filler to 26 % somehow showed the optimized properties of the nanocomposites, giving 34.00 mpa tensile strength, 576.494 % elongation at break and 6.564 n force at break. rough surface morphology was observed under sem suggesting the occurrence of phase separation between the hydrophilic filler and the hydrophobic rubber matrix. in the dsc plot, sample with usi-7301 and with functionalized kaolin filler 26 % tsc showed glass transition temperature shifted to lower region compared to normal nitrile rubber. the reinforcement of nanocomposites formed will not only enhance the properties of the nanocomposites, but is also economically feasible thus brings advantages to the industry. abstrak: penyebatian lateks yang menggabungkan pelbagai jenis tanah liat sebagai pengisi dalam getah dapat memberi pengukuhan dalam matriks getah dengan ketara apabila nanokomposit getah / tanah liat terbentuk, tetapi pengisi mengagregat. oleh itu, kajian dijalankan dengan menggunakan tanah liat kaolin sebagai pengisi dalam nanokomposit getah dengan ejen gandingan silan untuk menambah-fungsi permukaan pengisi tersebut. kajian ini dilakukan untuk mengenalpasti sifat mekanik pelbagai kaolin (yang berfungsi) dalam nanokomposit lateks, untuk menyediakan pelbagai nisbah kaolin terhadap getah, dan untuk mencirikan sifat mekanik, haba dan morfologi kaolin dalam nanokomposit lateks. untuk mencapainya, enam jenis ejen gandingan silan digunakan 230 iium engineering journal, vol. 21, no. 2, 2020 omar et al. https://doi.org/10.31436/iiumej.v21i2.1388 untuk tujuan menambah-fungsi permukaan pengisi kaolin semasa penggabungan pengisi dalam penyebatian lateks. ejen gandingan silan yang paling optimum, usi-7301 (γ-silan kloropropiltrimetoksi) dengan nilai kekuatan tegangan 32.77 mpa, nilai pemanjangan ketika pemutusan 632.589% dan kekuatan daya ketika pemutusan 6.737 n digunakan dengan lebih lanjut untuk menambah-fungsi pengisi kaolin dalam nisbah yang berbeza untuk lebih mencapai sifat mekanikal, haba dan morfologi optimum pengisi dalam matriks polimer lateks. mesin tegangan universal digunakan untuk menganalisis sifat mekanik nanokomposit, sementara mikroskopi elektron pengimbasan (sem) dan kalorimetri pengimbasan berbeza (dsc) digunakan untuk menganalisa sifat morfologi dan haba nanokomposit tersebut. hasil kajian menunjukkan bahawa pengurangan jumlah kandungan pepejal (tsc) pengisi kaolin kepada 26% menunjukkan sifat optimum nanokomposit, dengan kekuatan tegangan 34.00 mpa, pemanjangan ketika pemutusan sebanyak 576.494% dan daya ketika pemutusan sebanyak 6.564 n. morfologi permukaan kasar diperhatikan di bawah sem dan ia menunjukkan berlakunya pemisahan fasa antara pengisi hidrofilik dan matriks getah hidrofobik. dalam plot dsc, sampel dengan usi7301 dan dengan pengisi kaolin yang difungsikan dengan 26% tsc menunjukkan suhu peralihan kaca beralih ke kawasan yang lebih rendah berbanding getah nitril biasa. pengukuhan nanokomposit yang terbentuk bukan sahaja akan meningkatkan sifat nanokomposit, tetapi juga dapat dilaksanakan secara ekonomi sehingga memberi banyak kelebihan kepada industri. key words: rubber; latex; filler; nanocomposites; silane coupling agent 1. introduction the incorporation of clay with natural rubber has been commonly investigated in the past few years because of the structure of the nanoparticles exhibited that can significantly give reinforcement towards rubber/clay nanocomposites when the two materials are mixed [1]. due to its improved physical or mechanical properties, thermal stability, gas permeability and so on, these rubber/clay nanocomposites have gained so much attention, especially in the rubber industry. compared to unfilled rubber compounds, these rubber/clay nanocomposites are generally better in properties as mentioned. as the name suggests, nanocomposites are lighter in terms of weight and significantly is low cost. there are several methods on how these nanocomposites could be formed; which include melt intercalation [2], in-situ polymerization process [3], intercalation of solution [4], and also the compounding of latex [5]. latex compounding and melt mixing methods have been combined and rampantly used especially in the rubber industry [5], since it is considerably more environmental-friendly because no organic solvents are present in the system and has high compatibility with the system that is currently used in industries. the idea of latex compounding is that, during the initial stage of the process, the clay interlayer spacing is increased. during this stage, monomers form polymers due to the clay dispersion in the water that was happening and thus intercalation of matrix will happen within the widened spacing of the clay [6]. however, because nanocomposite itself is in nano-scale, agglomerations of particles of the filler tend to happen and therefore, the adhesion and compatibility of the filler with the polymer matrix need to be enhanced. it was proposed in this project that silane coupling agent could help in modifying the filler surface so as to induce a strong interaction between the polymer and filler, by silanization process. this process is significant in order to introduce reactions on the surface of hydroxyl (–oh) groups abundant on the mineral (filler) 231 iium engineering journal, vol. 21, no. 2, 2020 omar et al. https://doi.org/10.31436/iiumej.v21i2.1388 surface with the coupling agent [7]. therefore, surface-functionalized filler was created in this project and believed to have improved the properties of the polymer from its matrix. in this study, kaolin filler was used as the main material, surface-functionalized with six coupling agents separately in order to investigate the best type of coupling agent to be employed in its latex compounding to produce synthetic rubber gloves. furthermore, the surface-functionalized filler at the optimized coupling agent type – would then be prepared with different ratios or total solids content (tsc) to find the best optimized ratio or tsc for the filler for improved mechanical, morphological and thermal properties of the rubber produced. the importance of this study is to improve the mechanical properties of synthetic rubber that will be produced with the incorporation of surface functionalized latex/filler nanocomposites from kaolin clay as the main ingredient for filler. from the past recent studies, it has been shown that kaolin filler could be one of the contributing agents in rubber production, during the latex compounding procedure. the present study is carried out in order to achieve the objectives as follows; to prepare kaolin clay surface functionalized with different functionalization agents incorporated with nitrile butadiene rubber (nbr) synthetic rubber and to investigate the mechanical properties of the various functionalized kaolin filler in latex nanocomposites, to prepare various ratios or tsc of kaolin filler to latex based on the optimized functionalized kaolin, and to characterize mechanical, thermal and morphological properties of the optimized kaolin filler in latex nanocomposites. 2. materials and methods 2.1. materials carboxylated nitrile butadiene rubber latex (nbr latex) was used as the core material to produce the rubber samples. kaolin clay was used as the main constituents for kaolin filler for the latex/filler nanocomposites purpose. for functionalization of the filler, six (6) silane coupling agents of product names usi-2301, usi-7301, usi-7311, usi-1212, usi1302 and usi-5301 were used for the surface functionalization of kaolin filler. after characterized by tensile test, usi-7301 has the highest elongation at break value, thus chosen to be the optimized sample. then, this coupling agent is used for surface functionalization of kaolin filler to be diluted to different ratios or tsc. the raw chemicals for the kaolin filler preparation as well as latex compound preparation as in table 1 and table 2 together with the aforementioned coupling agents in were obtained from top glove sdn. bhd via avidco asia pacific sdn. bhd. as top glove’s main supplier for chemicals that were purchased from china. 2.2. kaolin filler preparation the ingredients were mixed in a tank and stirred to produce a homogenous mixture and left to mature for 24-36 hours. kaolin filler of appropriate mass to be used in few sets of latex compounding was made and a small portion of the filler was taken and diluted where necessary for latex compounding procedure (table 1). 232 iium engineering journal, vol. 21, no. 2, 2020 omar et al. https://doi.org/10.31436/iiumej.v21i2.1388 table 1: ingredients in preparing kaolin filler ingredient (chemical) mass percentage (%) ph adjuster < 4 dispersing agent 1 – 5 wetting agent < 1 thickener 1 – 2 antifoam < 1 water 60 – 65 calcined kaolin clay 35 2.3. latex compounding tsc, measured in percentage, was measured as the remaining weight of sample after drying, expressed in terms of the original weight of the wet sample as in eq. 1. tsc % = (weight of dry sample+container)-(weight of empty container)(weight wet sample+container)-(weight empty container) × 100 % (1) the dosage of each chemical was measured in phr. in rubber industry, it is common to use this term to demonstrate the amount of chemicals needed to be incorporated with the raw latex for compounding purpose. thus, the mass of each chemical with regards to their given dosage values in phr unit was as in eq. 2. chemical mass (kg) = ( ) × ( ) × × 100 % (2) table 2 shows the chemical formulation for the production of nitrile gloves with required dosage (phr) of each chemical. nbr latex, as the main ingredient for the synthetic glove samples production was initially stirred in the compounding tank based on its required amount. then, the chemicals as in table 2 were mixed with the raw latex. the compounded latex was then stirred for maturation purpose for 24-36 hours. the tsc of the compounded latex will then be checked upon maturation for clarification. the mixture was further diluted with water if necessary. then, the samples were produced by hand-dip procedure in the production line. table 2: formulation of nbr latex added with kaolin filler and coupling agent ingredient (chemical) tsc (%) dosage (phr) nbr latex 44.5 100 kaolin filler 35.0 (variable in second objective) 7.0 coupling agent 100 0.3 ph adjuster 25 1.4 – 2.0 vulcanizing accelerator 50 0.2 – 0.8 vulcanizing agent 60 0.8 – 1.4 vulcanizing activator 60 1.0 – 1.6 wax 49 0.5 – 1.0 wetting agent 25 0.2 – 0.4 antifoam 10 0.02 – 0.06 233 iium engineering journal, vol. 21, no. 2, 2020 omar et al. https://doi.org/10.31436/iiumej.v21i2.1388 2.4. methods of testing and characterizations the nitrile glove samples were produced in the factory’s production line by hand-dip procedure. hand-dip was done by plugging out of the hand-shapped ceramic mould before the latex dip process to be dipped in the lab scale-made compounded latex for 8-10 seconds before plugging in back to the production line. the ceramic mould temperature shall maintain its temperature in between 55 to 70 °c throughout the hand-dip process. the dipped moulds shall undergone processes such as leaching, chlorination, drying and cuffbeadrolling before stripping of the samples. then, the glove samples were cut into dumbbell-shape by using the pneumatic cutter before tested for tensile properties (tensile strength, elongation at break, force at break). universal tensile machine (model: al-3000) from top glove company was used for this purpose. scanning electron microscope (sem) was used to observe the morphological properties of the samples. the fractured surface of the samples was observed with field emission sem (fesem) (joel, jfc-1600) from iium, after the tensile test was done. the fractured samples were initially cut to an approximately 4 mm × 4 mm square shape and placed on the sample holder with the fractured surface facing upward. the microphotographs of the samples were generated at the magnification ×2300. thermal properties of the samples were analyzed by using differential scanning calorimetry (dsc) (mettler toledo dsc 3) from top glove, with heating rate of 10.0 °c/min, temperature range of -75 °c to 350 °c nitrogen gas, and a one-time heat process. the samples were cut into an approximately 2.0 mg. 3. results and discussion 3.1. tensile properties 3.1.1 sample tensile properties with different silane coupling agents figure 1 shows tensile properties (tensile strength and elongation at break) for rubber samples incorporated with kaolin filler functionalized with different silane coupling agents. it can be seen that the samples have the highest average tensile strength after the incorporation of usi-7311 (chloro family) silane coupling agent at 35.47 mpa, while the average tensile strength is the lowest with usi-1302 (amino family) silane coupling agent at only 28.24 mpa, when they were compared with the control samples. this could be due to the stronger bonding between the matrix and nanoparticles presented in the samples with usi-7311 compared to others [8]. usi-7301 of chloro family has elongation at break value of 632.589 % as well as considerably high tensile strength of 32.77 mpa. here, polymer chains are believed to cross-link with each other that eventually strengthen the polymeric structure. occasionally, the event leads to higher stress needed to elongate and rupture the sample that gives high elongation at break value [9]. the tested samples generally conform to the astd d639 standard requirement of minimum tensile strength and elongation at break of 14 mpa and 500 % respectively. 234 iium engineering journal, vol. 21, no. 2, 2020 omar et al. https://doi.org/10.31436/iiumej.v21i2.1388 figure 1: tensile properties of rubber with kaolin filler functionalized with different silane coupling agent. 3.1.2 sample tensile properties with different tsc of kaolin filler the best optimized silane coupling agent used for the 35 % kaolin filler is of type usi7301 with tensile strength value of 32.77 mpa and elongation at break value of 632.589 %. this silane was further used to be incorporated with kaolin filler of various tsc values (35, 32, 29, 26 and 23 %). figure 2 shows the results for tensile properties (tensile strength and elongation at break) for rubber samples incorporated with different ratios or tsc kaolin filler functionalized with usi-7301 silane coupling agent. from figure 2, all sets showed increase in the rubber’s tensile strength relatively with filler addition at decreasing solids content. theoretically, better spreading of the silane coupling agent used throughout the filler surface occurs here since the solids content is lower to achieve better silane spreading on the filler surface, thus the rubber’s tensile strength improved [10]. the average elongation at break for the samples at 35 % tsc of filler is much lower than the ones with lower tscs, and 23 % tsc of kaolin filler loadings with the highest elongation at break value of 587.248 %. at this kaolin filler’s tsc, it is believed that the polymer chains gives better cross-link with each other and stronger the polymeric structure which in turns giving higher stress needed to elongate and rupture the sample [8]. figure 2: tensile properties of rubber with optimized silane coupling agent in different ratios (tsc) of kaolin filler. 235 iium engineering journal, vol. 21, no. 2, 2020 omar et al. https://doi.org/10.31436/iiumej.v21i2.1388 3.2. morphological properties four (4) samples as follows were taken for characterization under sem to analyze their surface morphology and filler behavior in the rubber matrix, respectively: (i) rubber sample without fillers, (ii) rubber sample with kaolin filler but without silane coupling agent, (iii) rubber sample with kaolin filler functionalized with usi-7301 silane, and (iv) rubber sample with kaolin filler of 26 % tsc functionalized with usi-7301. figure 3 shows fesem analysis on the four samples under 2300× magnification. as can be observed from figure 3, the surfaces can be justified to be smooth in figure 4 (a) and (b), but rough in (c) and (d). with the presence of silane coupling agent usi-7301 (figures 4 (c) and (d)), a better adhesion between kaolin filler and rubber matrix were believed to happen here. kaolin filler well wetted by the rubber matrix and the pulled out of filler from rubber matrix is minimum [11]. these figures also show that the surface has many tear lines with branching. this type of failure indicates strong adhesion between filler and rubber matrix. however, the film is rougher than the control rubber sample with more pronounced undulating curves. particles are very obviously accompanied by cracks and grooves. the formation of surface cracks suggests the occurrence of phase separation between the hydrophilic filler and the hydrophobic rubber matrix [12]. (a) (b) (c) (d) figure 3: sem images of the control (a, b) and the optimized samples (c, d) at ×2300 magnification. 3.3. thermal properties the same 4 samples were taken for characterization in analyzing their thermal properties by using dsc. the results were based on the use of dsc on graph plotting. table 3 shows the results of thermal analysis of the samples, with respective glass-transition temperatures (tg). 236 iium engineering journal, vol. 21, no. 2, 2020 omar et al. https://doi.org/10.31436/iiumej.v21i2.1388 table 3: tg values of samples in dsc analysis. sample tg value (°c) decomposition temperature (°c) rubber sample without fillers -20.67 244.88 rubber sample with kaolin filler but without silane coupling agent -19.62 241.80 rubber sample with kaolin filler functionalized with usi-7301 silane -20.98 240.19 rubber sample with kaolin filler of 26 % tsc functionalized with usi-7301 -20.80 236.30 from the results in the dsc curve tabulated in table 3, on further heating the samples, the sudden shifting down of the 4 curves indicate that there is more heat flow. the onset temperature value for sample with usi-7301 silane has the absolute tg value of -20.98 °c. thus, there is more in the heat capacity of the sample compared to the others. in contrast, the sample without silane coupling agent functionalizing the filler has the lowest absolute tg value -19.62 °c. apparently, all the samples had gone through glass transition, and the change in heat capacity is more on the sample with usi-7301. however, the change doesn't occur suddenly, but takes place over a temperature range. the curve also had shown no crystallization peak, which means the polymer cannot form crystals. apparently, for nitrile rubber, it is amorphous, thus the samples will not show any crystallization or any melting behavior [13, 14]. towards the end of the plots, the highest decomposition temperature is for the sample containing no filler, at 244.88 °c, and the lowest decomposition temperature 236.30 °c achieved for the samples with kaolin filler tsc of 26 % functionalized with usi-7301 silane coupling agent. the samples are rendered safe to be used for handling materials at relatively high temperature. 4. conclusion in this study, one of the fillers that have the potential to be further employed and commercialized in rubber or polymer industry – the kaolin filler, from its clay based – was prepared and characterized with silane coupling agent and optimized. usi-7301 silane coupling agent was taken to be the optimized functionalization agent with tensile strength value of 32.77 mpa and elongation at break value of 632.589. optimized content of 26 % tsc kaolin filler in the rubber composites has exhibited tensile strength value of 34.00 mpa and elongation at break value of 576.494 %. usi-7301 and kaolin filler tsc of 26 % showed rough surface morphology with glass transition temperature of -20.98 °c and -20.80 °c respectively. this sample can further be explored for its potential in the gloves production. acknowledgement the corresponding author would like to thank iium faculty of engineering and top glove sdn. bhd. and its r&d department for the supports in accomplishing this project. not to forget, also thanks to top glove’s main chemical and equipment suppliers for this project for samples preparation and characterizations. top glove company, the world’s largest rubber glove manufacturer had also provided space in their production line for the samples’ production. 237 iium engineering journal, vol. 21, no. 2, 2020 omar et al. https://doi.org/10.31436/iiumej.v21i2.1388 references [1] mohd nor, n. a., muttalib, s. n., & othman, n. (2016). synthesis of natural rubber/palygorskite nanocomposites via silylation and cation exchange. nanoclay reinforced polymer composites, 261-289. doi:10.1007/978-981-10-1953-1_12a. [2] lu, m., zhou, j., wang, l., zhao, w., lu, y., zhang, l., & liu, y. (2010). design and preparation of cross-linked polystyrene nanoparticles for elastomer reinforcement. journal of nanomaterials, 2010, 1-8. doi:10.1155/2010/352914. [3] okamoto, m., morita, s., taguchi, h., kim, y. h., kotaka, t., & tateyama, h. (2000). synthesis and structure of smectic clay/poly(methyl methacrylate) and clay/polystyrene nanocomposites via in situ intercalative polymerization. polymer, 41(10), 3887-3890. doi:10.1016/s0032-3861(99)00655-2. [4] paul, p. k., hussain, s. a., bhattacharjee, d., & pal, m. (2013). preparation of polystyrene– clay nanocomposite by solution intercalation technique. bulletin of materials science, 36(3), 361-366. doi:10.1007/s12034-013-0498-4. [5] tan, j., wang, x., luo, y., & jia, d. (2012). rubber/clay nanocomposites by combined latex compounding and melt mixing: a masterbatch process. materials & design, 34, 825-831. doi:10.1016/j.matdes.2011.07.015. [6] mohd nor, n. a., muttalib, s. n., & othman, n. (2016). synthesis of natural rubber/palygorskite nanocomposites via silylation and cation exchange. nanoclay reinforced polymer composites, 261-289. doi:10.1007/978-981-10-1953-1_12. [7] tatou, m., genix, a., imaz, a., forcada, j., banc, a., schweins, r., … oberdisse, j. (2011). reinforcement and polymer mobility in silica–latex nanocomposites with controlled aggregation. macromolecules, 44(22), 9029-9039. doi:10.1021/ma2012893 [8] nassar, a., & nassar, e. (2013). study on mechanical properties of epoxy polymer reinforced with nanosic particles. nanoscience and nanoengineering, 1(2), 89–93. https://doi.org/10.13189/nn.2013.010201. [9] nair, k. p., nair, a. b., & joseph, r. (2014). carboxylated acrylo nitrile butadiene rubber latex/kaolin nanocomposites: preparation and properties. composite interfaces, 21(6), 571583. doi:10.1080/15685543.2014.899198. [10] takatoh, k., sakamoto, m., hasegawa, r., koden, m., itoh, n., & hasegawa, m. (2005). alignment technology and applications of liquid crystal devices, 90-95. boca raton: crc press. [11] alkadasi, n. a., sarwade, b. d., hundiwale, d. g., & kapadi, u. r. (2004). studies on the effect of titanate coupling agent (2.0%) on the mechanical properties of flyash-filled polybutadiene rubber. journal of applied polymer science, 93(3), 1293-1298. doi:10.1002/app.20548. [12] a. ndabigengesere, k. b. narasiah, and k. subraimanian. “quality of water treated by coagulation using moringa oleifera seeds,” water res. vol. 32, no. 3, pp. 781-791, 1998. [13] song, q., tan, z., zhang, y., sha, l., deng, x., deng, y., … yang, l. (2014). do the rubber plantations in tropical china act as large carbon sinks? iforest biogeosciences and forestry, 7(1), 42-47. doi:10.3832/ifor0891-007. [14] shanks, r. a., & kong, i. (2013). general purpose elastomers: structure, chemistry, physics and performance. advanced structured materials, 11-45. doi:10.1007/978-3-642-20925-3_2. 238 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <feff005500740069006c0069006300650020006500730074006100200063006f006e0066006900670075007200610063006900f3006e0020007000610072006100200063007200650061007200200064006f00630075006d0065006e0074006f0073002000640065002000410064006f00620065002000500044004600200061006400650063007500610064006f007300200070006100720061002000760069007300750061006c0069007a00610063006900f3006e0020006500200069006d0070007200650073006900f3006e00200064006500200063006f006e006600690061006e007a006100200064006500200064006f00630075006d0065006e0074006f007300200063006f006d00650072006300690061006c00650073002e002000530065002000700075006500640065006e00200061006200720069007200200064006f00630075006d0065006e0074006f00730020005000440046002000630072006500610064006f007300200063006f006e0020004100630072006f006200610074002c002000410064006f00620065002000520065006100640065007200200036002e003000200079002000760065007200730069006f006e0065007300200070006f00730074006500720069006f007200650073002e> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <feff0041006e007600e4006e00640020006400650020006800e4007200200069006e0073007400e4006c006c006e0069006e006700610072006e00610020006f006d002000640075002000760069006c006c00200073006b006100700061002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400200073006f006d00200070006100730073006100720020006600f60072002000740069006c006c006600f60072006c00690074006c006900670020007600690073006e0069006e00670020006f006300680020007500740073006b007200690066007400650072002000610076002000610066006600e4007200730064006f006b0075006d0065006e0074002e002000200053006b006100700061006400650020005000440046002d0064006f006b0075006d0065006e00740020006b0061006e002000f600700070006e00610073002000690020004100630072006f0062006100740020006f00630068002000410064006f00620065002000520065006100640065007200200036002e00300020006f00630068002000730065006e006100720065002e> /tur <feff0130015f006c006500200069006c00670069006c0069002000620065006c00670065006c006500720069006e0020006700fc00760065006e0069006c0069007200200062006900e70069006d006400650020006700f6007200fc006e007400fc006c0065006e006d006500730069006e0065002000760065002000790061007a0064013100720131006c006d006100730131006e006100200075007900670075006e002000410064006f006200650020005000440046002000620065006c00670065006c0065007200690020006f006c0075015f007400750072006d0061006b0020006900e70069006e00200062007500200061007900610072006c0061007201310020006b0075006c006c0061006e0131006e002e0020004f006c0075015f0074007500720075006c0061006e002000500044004600200064006f007300790061006c0061007201310020004100630072006f006200610074002000760065002000410064006f00620065002000520065006100640065007200200036002e003000200076006500200073006f006e00720061006b00690020007300fc007200fc006d006c0065007200690079006c00650020006100e70131006c006100620069006c00690072002e> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 145-951 vetted iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics marini and ismai 21 torsional deformation and fatigue behaviour of 6061 aluminium alloy m. marini and a. b. ismail school of materials and mineral resources engineering, university sanis malaysia, 14300 nibong tebal, penang, malaysia. marini.marno@gmail.com abstract: torsional deformation and fatigue behaviour of both solid and thin-walled tubular specimens made from as-received and heat treated 6061 aluminium alloy were studied. 6061 aluminium alloy have been widely used as a candidate material in automobile, aerospace, aircraft and structural application because of their superior mechanical properties such as high strength to weight ratio, good ductility and others. the differences in cyclic deformation and fatigue behaviours between round and solid specimens where a stress gradient exist, and thin-walled tubular specimens where a uniform stress state is commonly assumed, are also discussed. von mises and tresca criteria has been used to predict the monotonic and cyclic deformation curve and compared to the torsional data obtained from the experiment. both tresca and von mises fit the experimental curve but tresca estimation shows a curve that fits the experimental curve better than the von mises fatigue life of the specimens were recorded and presented in the s-n curve and shows that heat treated t6 alloy exhibit higher fatigue life and fatigue strength compared to the as-received alloy. through fractographic analysis, failure criteria of fracture surfaces were observed and discussed. abstrak: ubah bentuk kilasan dan kelakuan lesuk edua-dua specimen berbentuk rod dan tiub berdinding nipis yang diperbuat daripada aloi aluminium 6061 seperti yang diterima dan dirawat haba adalah dikaji. aloi aluminium 6061 digunakan secara meluas sebagai bahan di dalam aplikasi bidang aeroangkasa, automobil, pesawat udara, danstruktural kerana mempunyai sifat-sifat mekanikal yang hebat seperti berkekuatan tinggi bagi nisbah berat, kemuluran yang tinggi dan lain-lain.perbezaan ubah bentuk kitaran dan kelakuan lesu di antara spesimen berbentuk rod dimana wujudnya kecerunan tegasan dengan spesimen tiub berdinding nipis di mana diandaikan keadaan tegasan adalah seragam juga dibincangkan. kriteria von mises dan tresca digunakan untuk meramalkan ubah bentuk lengkung monotonik dan kitaran yang kemudian dibandingkan dengan data kilasan yang diperolehi dari eksperimen. kedua-duatresca dan von mises menunjukkan lengkung yang menepati lengkung eksperimen tetapi anggarantresca memberikan lengkung yang lebih menepati lengkung eksperimen jika dibandingkan dengan von mises. hayat lesu spesimen yang kemudian direkodkan dan ditunjukkan dalam bentuk lengkung s-n menunjukkan bahawa aloi t6 yang dirawa tmempamerkan hayat lesu dan kekuatan lesu yang lebih tinggi berbanding aloi seperti yang diterima.melalui analisis fraktografi, kriteria kegagalan permukaan patah diperhatikan dan dibincangkan. keywords: fatigue; 6061 aluminium alloy; torsional deformation; fractography iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics marini and ismai 22 1. introduction 6061 aluminium alloy finds various usages as structural application and welded assemblies including truck components, aircraft, automotive parts, marine applications and others. this alloy shows great promise for more applications [1]. 6061 aluminium alloy is a heat treatable, wrought al-mg-si alloy. it is well known for its superior mechanical properties such as good ductility, high strength to weight ratio and others. it also has capability to resist cracks because of one of its properties which is high toughness. it can be considered as a potential candidate material for automobile and aerospace sectors where high crack arrest capabilities and high strength with reduced weight will contribute to crash worthy design of automobiles and aircrafts structure [2]. fatigue is the principal cause of premature failure of engineering components where it can be subjected to cyclic stresses during service condition which may locally exceed the yield strength of particular material. this situation led to the demand for increasing vehicle safety that becomes a matter of concern [3, 4]. failure of bus drive shaft and power transmission shaft are some examples of torsional fatigue failures [5, 6]. the objectives of this paper are to study the cyclic deformation behaviour of 6061 aluminium alloy and the response of cyclic torsion to the morphology of fracture. the different in fatigue life for the heat treated and different specimen geometry also have 2. experimental procedure 2.1 material and specimens the material used in this investigation was a 6061 as-received aluminium alloy and with t6 heat treatment. the specimens were machined into round solid specimen and tubular specimen shown in fig. 1. the specimen were heat treated into precipitation hardening (t6). for solid specimens, solution heat treatment was performed at 530 °c for 55 minutes followed by water quenching while for tubular specimen, solution heat treatment was performed at 530°c for 35 minutes. aging treatment was carried at 175 °c for 8 hours. the chemical composition and the mechanical properties are shown in table 1 and 2, respectively. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics marini and ismai 23 fig. 1: geometry and dimension of the specimens used in the torsional fatigue. (a) solid specimen. (b) thin-walled tubular specimen. table 1: chemical composition of the 6061 as-received and 6061-t6 aluminium alloy. 6061 al alloy mg si fe cu mn as-received 0.66 0.58 0.18 0.20 0.0075 t6 0.72 0.67 0.31 0.36 0.0630 table 2: monotonic torsional mechanical properties of the 6061 as-received and 6061-t6 aluminium alloy. 6061 al alloy as-received t6 ultimate strength, τu (mpa) 160.27 211.77 yield strength, τy (mpa) 146.30 192.95 modulus, g (gpa) 15.87 18.59 strength coefficient, k0 (mpa) 202.64 258.05 strength hardening exponent, n0 0.063 0.048 2.2 experiments and results (a) (b) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics marini and ismai 24 a test resource instruments (tr1) with servo-hydraulic axial–torsion load frame was applied for the fatigue experiments using the solid and tubular specimens. the machine is capable of exerting a 50 kn axial force and a 1000 nm torque on test specimens. the testing system is equipped under environment of mtl7 basic software with 2350 controller, computer control, and data acquisition. the operating frequency for fatigue tests is 1 hertz and tests took from 2 hours to 4 days. all tests were performed in load control, and conformed to astm e2207. all tests were controlled using the computer and conducted in the ambient air. torque and shear strain value were recorded during the first ten cycles of the fatigue test in order to determine the initial cyclic hardening or softening of the specimens. failure of the specimens has been determined when the sample breaks and separate into two pieces and this situation most likely to occur on the solid specimen. for specimens that do not separate into two pieces, the specimens was considered to have failed when there is either 5% or 10% force drop from the previously recorded torsional peak loads. monotonic torsion test were conducted in order to obtain the monotonic properties of the material. cycles to failure were recorded when the specimen failed. the fractured surface of every specimen has been observed under the scanning electron microscopy. 3. results and discussion 3.1 monotonic and cylic deformations from measured torsional loading and specimen dimensions, shear stress (τ) for solid and tubular specimen was calculated. 0.02% offset method were used on the monotonic shear stress strain curve in order to determine the shear yield strength, (τy). shear modulus (g) was determined by calculating the slope of the elastic region from the monotonic shear stress-strain curve obtained. the relation between true shear stress (τ) – shear strain (γ) that has been plotted was described by ramberg – osgood equation: γ � γ� � γ� � � � � � � � � (1) from equation (1), shear strength coefficient or material constant, ko and strain hardening exponent, no describe the monotonic shear stress-plastic strain relationship. value of ko and no can be determine from the intercept and slope of the best line fit to the data plotted on a log-log scale of true shear stressplastic strain curve. common yield criteria which are von mises and tresca criterion has been used to predict the shear stressstrain behavior of the material and compared to the torsional data obtained from the experiment. the prediction was made by using the ramberg-osgood equation, based on von mises and tresca criterion respectively: ko = k�1�� �����/� and no = n (2) ko = k�k��� 2 �� � and no = n (3) iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics marini and ismai 25 figure 2 shows the comparison between experimental monotonic torsion curve with von mises and tresca criterion. from this figure, it can be seen that both tresca and von mises fit the experimental curve but tresca estimation shows a curve that fits the experimental curve better than the von mises. the tresca criterion assumes that the yielding and plastic deformation will occur when the shear stress on the plane of maximum shear reaches a critical value where the mechanism of plastic deformation occur due to the slip of crystal planes [7, 8]. fig. 2: comparison between experimental monotonic torsion curve with von mises and tresca criterion for 6061 aluminium alloy. from the torsion fatigue test data, the behaviour of cyclic torsional deformation was obtained. using the ramberg-osgood type equation, the cyclic shear stress-strain behaviour can also be characterized [7]. one of the most important fatigue characteristics for the major part of the fatigue life is the plastic stress-strain response of the material which have been characterizes from the basic stress-strain curve. by plotting the stable torsional stress amplitude against the torsional plastic strain on a logarithmic scale, the strain hardening exponent and strength coefficient have been determined. figure 3 and 4 show the cyclic stress-strain curves for both alloys and table 3 indicate the parameters obtained. from the figures, we can see that both alloy were cyclically hardened, this is due to the low dislocation densities in this alloy. but in hard materials such as steels, it will become cyclically soften. shear strain, mm/mm 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 s h e a r s tr e s s , m p a 0 50 100 150 200 250 300 experimental torsion curve tresca von mises iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics marini and ismai 26 fig. 3: comparison between monotonic and cyclic stress-strain curve for as-received 6061 aluminium alloy fig. 4: comparison between monotonic and cyclic stress-strain curve heat treated 6061-t6 aluminium alloy. table 3: cyclic stress-plastic strain parameters for as-received 6061 aluminium alloy. 6061 al alloy as-received t6 cyclic hardening coefficient, k` (mpa) 257.532 301.505 cyclic hardening coefficient, n` 0.055 0.034 3.2 torsional and fatigue behaviour on solid and tubular specimen shear strain, mm/mm 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 s h e a r s tr e s s , m p a 0 50 100 150 200 250 300 experimental torsion curve tresca von mises shear strain, mm/mm 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 s h e a r s tr e s s , m p a 0 50 100 150 200 250 300 experimental torsion curve tresca von mises iium engineering journal, vol. 12, no. 6, 201 under torsional cyclic loading, the life for solid specimens were longer compared to the tubular specimen because surface growth toward the center of the specimen and slowly g fig. 5. so, there is more material through which crack can solid specimen last longer and also due to the stress gradient toward the center of the specimen fig. 6, we can also found that for the specimens that were heat treated into t6 condi gives longer fatigue life compared to the as heat treatment process that greatly affects be related to an increasing the hardness and strength of this all fig. 5: fractograph showing overall appearance of fracture surface. fig. 6: s-n curve fatigue life for both solid and tubular as 0 50 100 150 200 250 300 10 t o r si o n a l s tr e ss , m p a g journal, vol. 12, no. 6, 2011: special issue in science and ethics marini 27 nder torsional cyclic loading, the life for solid specimens were longer compared to because of the crack which retarded crack growth due to the sub surface growth toward the center of the specimen and slowly growing inward as . so, there is more material through which crack can grow inward and this makes a solid specimen last longer and also due to the stress gradient effect which lower the stress specimen cross section and led to a longer fatigue life , we can also found that for the specimens that were heat treated into t6 condi gives longer fatigue life compared to the as-received specimens. this is due to the solution process that greatly affects the fatigue properties of this alloy the hardness and strength of this alloy [9]. fractograph showing overall appearance of fracture surface. n curve fatigue life for both solid and tubular as-received and heat treated 6061 aluminium alloy. 100 1000 10000 100000 1000000 log cycle to failure, nf solid ar tubular ar : special issue in science and ethics marini and ismai nder torsional cyclic loading, the life for solid specimens were longer compared to of the crack which retarded crack growth due to the subrowing inward as shown in inward and this makes a which lower the stress cross section and led to a longer fatigue life [7]. from , we can also found that for the specimens that were heat treated into t6 condition his is due to the solution the fatigue properties of this alloy which might fractograph showing overall appearance of fracture surface. received and heat treated 6061 iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics marini and ismai 28 3.3 analysis of fatigue fracture surfaces figures 5 and fig.7-10 show torsional fatigue fracture surface features from this investigation. figure 5 shows the overall appearance of fracture surfaces which shows peak and valley fracture surface that pointing towards the middle of the specimen. the crack initiation stage of fatigue was called stage i. crack initiates from the surface of the specimen where the shear stresses values gives the highest level but there is no indication of initiation sites observed. when the crack initiated, the local stress increased, different states of stress were formed around the fatigue crack initiation and the crack begin to propagate when the local shear stress exceeded the shear strength of the material [10]. figure also shows that cracks propagate toward the center of the specimen. this fracture surface also called “starry” pattern fracture surface [11]. crack propagation which is stage ii occur when the crack has progressed a small distance from the surface of the specimen. smooth specimens that were subjected to torsional fatigue loading will proceed to mode ii after crack initiation stage. this means that crack initiation occurred on the planes where the largest shear stress amplitude exist. when the shear crack reached a threshold value, which was a function of the material and number of cycles to failure, crack branching would occur, and the crack would propagate in the same direction [10, 12]. figure 7 shows shear dimples fracture surface resulting from torsional fatigue loading. this fracture surface describes ductile fracture that formed through a process which called void coalescence. slip is the cause of plastic deformation of material that occurred between the voids. since this slip extends to the free surface of the void, then slip traces form shown in fig. 8. voids are initiated by fracture of the particles. it were formed at second-phase particle which is mg2si due to the separation of material internally will combine to develop the fracture surface after that, the connecting material will continue to deform by slip, allowing the voids to expand and connect along the fracture path. some particles lies in the dimples of the mating fracture surface shown in fig. 9 while some of them fell out during separation of the fracture surface, so that in the fractograph some dimples are empty [2, 13, 14]. fig. 7: fractograph showing shear dimples fracture surface resulting from torsional loading. iium engineering journal, vol. 12, no. 6, 201 fig. 8: fractograph showing slip traces (arrows) on the side of the dimples. fig. 9: fractograp figure 10 shows that the fracture surface contained ductile striation. striations formed during crack propagation stage. aluminium alloy can change the local spacing. when a fatigue crack approaches such particles, it is briefly retarded if the particle permits intact or is accelerated if the particle cleaves fig. 10: fractograph showing typical ductile striation in fatigue fractures. g journal, vol. 12, no. 6, 2011: special issue in science and ethics marini 29 fractograph showing slip traces (arrows) on the side of the dimples. fractograph showing dimples with particle lying inside. s that the fracture surface contained ductile striation. striations formed during crack propagation stage. large second-phase particles and inclusions in 6061 aluminium alloy can change the local crack growth rate resulting in fatigue striation hen a fatigue crack approaches such particles, it is briefly retarded if the particle permits intact or is accelerated if the particle cleaves [2, 10]. fractograph showing typical ductile striation in fatigue fractures. : special issue in science and ethics marini and ismai fractograph showing slip traces (arrows) on the side of the dimples. s that the fracture surface contained ductile striation. striations formed phase particles and inclusions in 6061 crack growth rate resulting in fatigue striation hen a fatigue crack approaches such particles, it is briefly retarded if the fractograph showing typical ductile striation in fatigue fractures. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics marini and ismai 30 stage iii which is the final overload fracture was the final stage in fatigue crack propagation stage. in this specimen, since the cracks propagate towards the center of the specimen, the final rupture appeared to be at the center of the specimen shows central fibrous fracture. from the analysis, it also indicates that the material was adequate for the low applied stresses because of the final fracture of the surface area become smaller compared to the initial total area [9]. 4. conclusion remarks from the results and analysis that have been presented in the paper, the following concluding remarks can be drawn. a. tresca estimation provided the best predictions when predicting torsional monotonic and cyclic behaviour. it shows a curve that fits the experimental curve better than the von mises criterion. b. from the comparison of both monotonic and cyclic shear stress-strain curve, both alloys tend to harden when cyclic torsional loading were applied to them. c. solid specimens give longer fatigue life compared to tubular specimens due to stress gradient effect. heat-treated specimens also give longer fatigue life compared to the as-received specimens due to the solution heat treatment process that improves the fatigue properties. d. it was observed that crack initiate at the surface of the specimens and then propagate towards the center of the cross sectional area of the specimens. it also observed that, the final fracture surface area have been decreased compared to the total area. this shows that the material were suitable for the applied stress. acknowledgement the authors express their thanks to the universiti sains malaysia and usm fellowship for supporting this work. references [1] j. r. d. a. joseph r. davis, aluminum and aluminum alloys: asm international, 1993. [2] b. f. jogi, p. k. brahmankar, v. s. nanda, and r. c. prasad, "some studies on fatigue crack growth rate of aluminum alloy 6061," journal of materials processing technology, vol. 201, pp. 380-384, 2008. [3] u. sánchez-santana, c. rubio-gonzález, g. mesmacque, a. amrouche, and x. decoopman, "effect of fatigue damage induced by cyclic plasticity on the dynamic tensile behavior of materials," international journal of fatigue, vol. 30, pp. 1708-1719, 2008/11// 2008. [4] u. sánchez-santana, c. rubio-gonzález, g. mesmacque, and a. amrouche, "effect of fatigue damage on the dynamic tensile behavior of 6061-t6 aluminum alloy and aisi 4140t steel," international journal of fatigue, vol. 31, pp. 1928-1937, 2009/12// 2009. [5] d. duffner, "torsion fatigue failure of bus drive shafts," journal of failure analysis and prevention, vol. 6, pp. 75-82, 2006. iium engineering journal, vol. 12, no. 6, 2011: special issue in science and ethics marini and ismai 31 [6] s. k. bhaumik, r. rangaraju, m. a. parameswara, m. a. venkataswamy, t. a. bhaskaran, and r. v. krishnan, "fatigue failure of a hollow power transmission shaft," engineering failure analysis, vol. 9, pp. 457-467, 2002. [7] d. mcclaflin and a. fatemi, "torsional deformation and fatigue of hardened steel including mean stress and stress gradient effects," international journal of fatigue, vol. 26, pp. 773784, 2004. [8] g. b. m. darrell f.socie, multiaxial fatigue. warrendale, pa: society of automotive engineers, inc., 2000. [9] r. sadeler, y. totik, m. gavgali, and i. kaymaz, "improvements of fatigue behaviour in 2014 al alloy by solution heat treating and age-hardening," materials & design, vol. 25, pp. 439-445, 2004. [10] h. x. e. bayraktar, f. ayari, c. bathias, "torsional fatigue behaviour and damage mechanisms in the very high cycle regime," archives of materials science and engineering, vol. 43, pp. 77-86, 2010. [11] d. j. wulpi, understanding how components fail, 2nd edition ed.: asm international, 1999. [12] c. makabe and d. f. socie, "crack growth mechanism in precracked torsional fatigue specimens," fatigue & fracture of engineering materials & structures, vol. 24, pp. 607-615, 2001. [13] a. c. charlie r.brooks, metallurgical failure analysis: mcgraw-hill, inc., 1993. [14] j. g. cowie and f. r. tuler, "comparison of shear and tensile fracture in high strength aluminum alloys," international journal of fracture, vol. 47, pp. 229-239, 1991. nomenclature g shear modulus gpa ko material constant no strain hardening coefficient greek letters τ shear stress mpa γ shear strain γe elastic shear strain γp plastic shear strain iium engineering journal, vol. 12, no. 6, 2012: special issue in science and ethics marini and ismail 32 223 iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 13 evaluation of sustainable development indicators with fuzzy topsis based on subjective and objective weights n. z. nang idayu and a. lazim mathematics department, faculty of science and technology, universiti malaysia terengganu (umt), 21030, kuala terengganu, terengganu, malaysia. idayu_zahari@yahoo.com, lazim_m@umt.edu.my abstract: sustainable development aims at improving and maintaining the wellbeing of people and the ecology. however, this paper focuses only on the ecological aspects. the selection of the proper ecological protection determinant plays a very important role in improving the environment of malaysia. this paper will propose a method from wang and lee (2009), and yong (2006) which applies a fuzzy topsis method -based on subjective and objective weights – to make the required selection. four alternatives will be tested which are: prevent pollution (a1), conservation (a2), well-manage (a3), and public awareness (a4). along with these, four criteria need to be considered: water quality factor (c1), land integrity factor (c2), air quality factor (c3), and biodiversity factor (c4). finally, a numerical example of ecological protection determinant selection is used to illustrate the proposed method. abstrak: pembangunan lestari bermatlamat memperbaiki dan mengekalkan kesejahteraan rakyat serta ekologi. walau bagaimanapun, kertas kajian ini hanya memberi tumpuan kepada aspek-aspek ekologi. pemilihan penentu perlindungan serta keselamatan bagi aspek ekologi memainkan peranan yang amat penting dalam meningkatkan kualiti alam sekitar di malaysia. kertas kajian ini telah menggunakan kaedah wang dan lee (2009) dan yong (2006) yang mengaplikasikan kaedah topsis kabur berdasarkan pemberat subjektif dan objektif. terdapat empat alternatif yang akan diuji iaitu: pencegahan pencemaran (a1), pemuliharaan (a2), pengurusan yang baik (a3), kesedaran orang awam (a4). selain itu, terdapat empat kriteria yang perlu dipertimbangkan: faktor kualiti air (c1), faktor kualiti tanah (c2), faktor kualiti udara (c3), faktor kepelbagaian biologi (c4). kesimpulannya, contoh pengiraan untuk memperoleh penentu pemilihan perlindungan ekologi telah digunakan bagi menunjukkan kaedah yang dicadangkan. keywords: sustainable development; ecological factors; subjective and objective weight; fuzzy topsis 1. introduction the concept of sustainable development is a challenge of growing combination between a range of environmental issues and human being issues. environmental and human development problems have multiplied and changed day after day [1]. the issues of sustainable development have been discussed about 70 decades ago among experts and researchers and their objectives still remain the same until today. the important objectives which always been considered including: restart growth; changing the quality of growth; iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 14 meeting essential needs for jobs, food, energy, water and cleanliness; ensuring a sustainable level of population; and merging environment and economics in decision making [2]. there are many definition of sustainable development were used but the most accepted definition is that from the world commission of economic development [3]. it is known as bruntland commission which refers the sustainable development as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”. sustainable development is a difficult concept to define using mathematical terms. experts and decision makers were proposed many methods such as human development index, ecological footprint, and time series analysis to measure and evaluate sustainable development. one of method that can be used to evaluate sustainable development is fuzzy topsis (technique for order performance by similarity to ideal solution) based on subjective and objective weights. fuzzy topsis is one of a famous method in multiple criteria decision making (mcdm). mcdm refers to solving problems in which the data are imprecise and fuzzy. according to chen & hwang, in fuzzy mcdm, ratings and weights presentation are always performed by fuzzy number [4, 5]. the main advantage using mcdm method is its ability to consider a large number of sustainable development attributes. fundamentally, there are two techniques of weighting methods, subjective and objective weights. subjective weights refer to the consideration of expert evaluation while objective weights obtain by solving mathematical models without considering decision makers preferences. the objective of this paper is to evaluate and ranking weights of sustainable development indicators with fuzzy topsis approach based on subjective and objective weights. the rest of this paper is organized as follows: in section 2, we briefly review about basic definition of fuzzy topsis and related works of fuzzy topsis. in section 3, we briefly review about fuzzy topsis based on subjective/ objective weights approaches. in section 4, we illustrate the proposed approach with numerical examples. in the final section some conclusions are drawn. 2. preliminaries in this section, a review of basic definition of fuzzy topsis, subjective and objective weights approaches as well as related works of fuzzy topsis are presented prior defining sustainable development. definition 1: let a set � be non-empty and finite. � fuzzy set � on � is an expression given by [6]: � � �� �, � ���, ��� � |� � �� (1) where: � � � �0,1� is the membership function of the fuzzy set �; � ��� � �0,1� is the membership of � � � in �. definition 2: a triangular fuzzy numbers �� can be defined by a triple ��, �, �� as shown below: iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 15 fig.1 a triangular fuzzy number �� ��� ��� � ��� �� 0, � � � !"#!" , � $ � $ �%! %!# , � $ � $ �0, � � � & (2) definition 3: the graded mean integration representation of triangular fuzzy number �� � ��1, �2, �3� is defined as: )*�� + � ,��, . 4��0 . �1� (3) let �� � ��,, �0, �1� and 23 � �,, �0, �1� be two triangular fuzzy numbers. so, the graded mean integration representation from both �� and 23 can be obtained as follows: )*�� + � ,��, . 4��0 . �1� (4) )*23 + � ,��, . 4��0 . �1� (5) 2.1 related work of fuzzy topsis there are a variety of criteria techniques within multiple criteria decision making (mcdm) method. mcdm method which is famous among experts and researchers are the total sum (ts), the simple additive weighting (saw) method, the ahp, the data development analysis (dea), the outranking approaches electre and promethee, and the topsis method [7]. the concept of this method is based on the chosen alternative with the shortest distance from the positiveideal solution (or the best possible alternative) and the longest distance from the negativeideal solution (or the worst possible alternative). the benefits of this concept include; (a) its intuitively appealing logic, (b) its simplicity and directness, (c) its computational efficiency, and (d) its ability to measure the relative performance of the alternatives with respect to individual or all evaluation criteria in a simple mathematical form. the vector normalization which is the method chooses the alternative with the largest value of 456 were given in eq. (4). iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 16 456 � 7∑ 9:; <=;>∑ <=;?@=ab !c;de ?f;ab 7∑ 9:; <=;>∑ <=;?@=ab !c;6e ?f;ab g7∑ 9:; <=;>∑ <=;?@=ab !c;de ?f;ab (6) or it chooses the alternative with the least value of 45! formulated as in eq. (5). 45! � 7∑ 9:; <=;>∑ <=;?@=ab !c;6e ?f;ab 7∑ 9:; <=;>∑ <=;?@=ab !c;6e ?f;ab g7∑ 9:; <=;>∑ <=;?@=ab !c;de ?f;ab (7) where h �h � 1, … , j� and k �k � 1, … , l� are index numbers for the alternative and attributes m5 � nop mphqon rs nop kno �nnth�unp �v5 � nop �nnth�unp t�nhlq srt hno �wnptl�nhxp’z kno �nnth�unp x56 � nop [rzhnhxp \ h]p�w x�wup srt kno �nnth�unp x5! � nop lpq�nhxp \ h]p�w x�wup srt nop hno �nnth�unp there are few studies that have been carried out by researchers in developing fuzzy topsis method. chen and hwang [4,5] found a new technique of topsis by transforming hwang and yoon’s [7] method into a fuzzy case. triantaphyllou and lin developed topsis method into a fuzzy version based on fuzzy arithmetic operation that leads to a fuzzy relative closeness for each alternative [8]. this new version offers a fuzzy relative closeness for each alternative which the closeness is badly imprecise and over stressed because of the reason of fuzzy arithmetic operations. besides, abo-sinha and abou-el-enien [9] used topsis by expanding this method for solving largescale multiple objective programming problems involving fuzzy parameters. chen [10] proposed the rate of each alternative as well as the weight of each criterion using linguistic terms; can be expressed in triangular fuzzy numbers. after that, he suggested to calculate the distance between two triangular fuzzy numbers using a vertex method for topsis. 3. fuzzy topsis approach with subjective and objective weight 3.1 determination of subjective weight a judgment tasks mostly requires a decision maker to integrate information from several sources to arrive at a single judgment about certain criterion. therefore, to acquire a satisfying decision making result, the decision-maker need to construct different expert opinion. the subjective weight method is determined based on expert’s evaluation. the overall evaluation of each decision maker is calculated. it will be applying in some mathematic methods such as eigenvector method, mathematical programming models and weighted least squares method. iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 17 3.2 determination of objective weight the objective weight methods are determined by solving mathematical models automatically without any consideration of the decision maker’s preferences. there are two techniques of objective method could be apply including a modified weighted least square method [11] and entropy. according to deng et al., objective weighting approaches is particularly applicable for situations where reliable subjective weights cannot be obtained [12]. the entropy method is based on information theory. there is such attribute does not help in differentiating alternatives where a small weight is assigned to an attribute if it has similar attribute value across alternatives. for this paper, the shannon entropy will be applied for objective weights approach. it is a measure of uncertainty in information formulated in terms of probability theory. we extend shannon’s concept to use entropy measure as weighting calculation method. definition 4: the entropy h(x) of a discrete random variable x is defined [13] as, ^��� � \ ∑ [*�v5 +wrq0 [��v5 �_!,5`a (8) ^��� � \ ∑ [v5 wrq0 [v5_!,5`a (9) in this paper, we recommended a method from wang and lee [11] and yong [8] that proposed a fuzzy topsis approach integrates subjective and objective weights to calculate the weight of each sustainable development indicators. this approach will give benefit to the decision makers’ expertise and entail endusers into a whole decision making process. the steps of fuzzy topsis algorithm can be expressed as follows: step 1: construct a decision matrix assume there j alternatives �v�h � 1,2, … , j� to be evaluated against l selection criteria 4v �h � 1,2, … , l�. subjective assessments are to be made by decision makers (dm) to determine: (a) the weighting vector b � �m1, m2, … , mk, … , ml�, and; (b) the decision matrix � � c�v5 , h � 1,2, … , j; k � 1,2, … , le, using the linguistic terms given in table 1. the weighting vector w represents the relative importance of n selection criteria 45 �k � 1,2, … , l� for the problem. the decision matrix � � c�v5 , h � 1,2, … , j; k � 1,2,…,l represents the utility ratings of alternative �h with respect to selection criteria 4k. given the weighting vector w and decision matrix �, the objective of the problem is to rank the entire alternative by giving each of them an overall utility with respect to a selection criteria. the decision matrix can be expressed as follows: f � 4, 40 g 4h�,�0i�j k �,,�0,i�j, & �,0�00i�j0 ……l… & �,h�0hi�jhm (10) iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 18 b � �m, , m0, … mh � (11) step 2: both subjective and entropybased objective weighting methods were used. (a) subjective: determine the dm’s weight for each criterion, b� � ,h *∑ m5nh5`, +, k � 1,2, … , l (12) (b) objective: objective weights determined using entropy measure. the decision matrix needs to be normalized for each criterion 45 �k � 1,2, … , l� to gain the projection value of each criterion: )v5 . )v5 � =;∑ =;@=ab (13) after normalized the decision matrix, the entropy value, ej calculated as, p5 � \o ∑ ln )v5 h5`, r=; (14) k is a constant, let o � *wl�j�+!,the degree of divergence di of the basic information of each criterion 45 �k � 1,2, … , l� calculated as ]5 � 1 \ p5 (15) the value ]5 represents the inherent contrast intensity of 45 . the higher the ]5 is, the more important the criterion 45 is for the problem. the objective weight for each criterion can be obtained b5 � s;∑ stftab (16) step 3: the aggregate weights for each criterion wj calculated as follow: �3v5 � ,h *∑ �uv5nhn`, +, h � 1,2, … , j (17) step 4: the decision matrix is obtained to identify the kth criteria with respect to hth alternative v3 � �t̃v5 �j x , vv5 � b�5 y�3v5 (18) step 5: normalize the decision matrix in order to make each criterion value is limited between 0 and 1, so that each criterion is comparable. the initial data with respect to each criterion will be normalized by dividing the sum of criterion value. for fuzzy data denoted by triangular fuzzy number as *�v5 , �v5 , �v5 +, the normalized values are calculated as follows: t̃v5 � z{"=;%=;| , #=;%=;| , %=;%=;| }~ , k � � (19) t̃v5 � z{"=;%=;d , #=;%=;d , %=;%=;d }~ , k � 4 (20) iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 19 �5g � j��v �v5 hs k � � (21) �5g � j��v �v5 hs k � 4 (22) step 6: the overall performance evaluation for each alternative is calculated by multiplying the aggregate weights for each normalized criterion. �3 � �xuv5 �j x , h � 1,2, … , j; k � 1,2, … , l (23) where, xv5 � c=;>∑ �c=;�?@=ab (24) step 7: the positive ideal solution �g and negative ideal solution �! are determined. the weighted normalized values for each criterion are sorted in descending order. �g � �xu,g, xu0g, … , xuxg� (25) �! � �xu,!, xu0!, … , xux!� (26) step 8: the distance from the positive ideal solution and the negative ideal solution are calculated for each alternative. according to bojadziev and bojadziev (1995), the distance between two triangular fuzzy numbers �, � ��,, �,, �,� and �0 � ��0, �0, �0� is calculated as ]��,, �0� � >,1 ���, \ �0�0 . ��, \ �0�0 . ��, \ �0�0� (27) ]vg � >∑ �xuv5 \ xu5g�0h5`, , h � 1,2, … , j (28) ]v! � >∑ �xuv5 \ xu5!�0h5`, , h � 1,2, … , j (29) step 9: the closeness coefficient (cc) is calculated. rank each cc of each alternative in descending order. the alternative with higher cc value will be the best choice. 44v � s=ds=|gs=d , h � 1,2, … , j (30) 4. numerical example in this section, we provide a numerical example to test the ability of the proposed method from wang and lee [11] and yong [14]. a selection of ecological protection determinant can be calculated as a multiplecriteria decision making problem in which alternative are the practice of ecological control measures to be selected and attributes are those criterion under consideration. a government desires to select the best alternative for the ecological protection determinant in order to improve quality of environment in malaysia. after preliminary screening, four alternatives: prevent pollution ��,�, conservation ��0�, well-manage ��1�, public awareness ���� have remained in the candidate list. there are four criteria need to be considered: i) water quality factor (c1), ii) land quality factor �40�, iii) air quality factor �41�, iv) biodiversity factor �4�� iium engineering journal, vol. 13 no. 1, 2012 f � 4, 40 4�,�0�1�� k 882915.6 & 12.55.411.721 32 1134 fig. 2 the linguistic variables for each criterion. step 1: the linguistic variables developed by chen and hwang illustrated in fig. 2. the triangular fuzzy number used to express criterion. the terms of “very low” to “very high” is the range of linguistic expressions. table 1: fuzzy linguistic terms and correspondent fuzzy numbers for each criterion. importance abbreviation very low low medium low medium medium high high very high fig. 3: the fuzzy linguistic variables for each alternative. step 2: similar to the step 1, the linguistic terms and fuzzy number are decided. the linguistic terms expression is “very poor” to “very good” will be the r fuzzy number. journal, vol. 13 no. 1, 2012 ida 20 41 4�3291134 & 1773115.9m fig. 2 the linguistic variables for each criterion. variables developed by chen and hwang [4] illustrated in fig. 2. the triangular fuzzy number used to express importance for each criterion. the terms of “very low” to “very high” is the range of linguistic expressions. table 1: fuzzy linguistic terms and correspondent fuzzy numbers for each criterion. abbreviation fuzzy number graded mean integration importance weight of the criterion vl (0, 0, 0.2) 0.0333 l (0.05, 0.2, 0.35) 0.2000 ml (0.2, 0.35, 0.5) 0.3500 m (0.35, 0.5, 0.65) 0.5000 mh (0.5, 0.65, 0.8) 0.6500 h (0.65, 0.8, 0.95) 0.8000 vh (0.8, 1, 1) 0.9667 fig. 3: the fuzzy linguistic variables for each alternative. to the step 1, the linguistic terms and fuzzy number are decided. the linguistic terms expression is “very poor” to “very good” will be the range of its triangular idayu and lazim (31) are used as importance for each criterion. the terms of “very low” to “very high” is the range of linguistic expressions. table 1: fuzzy linguistic terms and correspondent fuzzy numbers for each criterion. graded mean integration for the importance weight of the criterion 0.0333 0.2000 0.3500 0.5000 0.6500 0.8000 0.9667 to the step 1, the linguistic terms and fuzzy number are decided. the ange of its triangular iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 21 table 2: fuzzy linguistic terms and correspondent fuzzy number for each alternative importance abbreviation fuzzy number graded mean integration for the ratings very poor vp (0, 0, 2) 0.3333 poor p (1.5, 2, 3.5) 2.1667 medium poor mp (2, 3.5, 5) 3.5000 fair f (3.5, 5, 6.5) 5.0000 medium good mg (5, 6.5, 8) 6.5000 good g (6.5, 8, 9.5) 8.0000 very good vg (8, 10, 10) 9.6667 step 3: the criterion’s weight rated by decision maker according to linguistic terms. table 3: the importance weights of the attributes criteria decision maker (dm) �� �� �� �� �� ml h m vh �� l vh vh vh �� mh vh m m �� h vl mh ml step 4: based on the assessment values in table 3, fuzzy weights of each decision maker’s attribute is computed. table 4: the aggregated fuzzy weights criteria average fuzzy number �� (0.5, 0.66, 0.74) �� (0.1, 0.8, 0.84) �� (0.5, 0.66, 0.76) �� (0.34, 0.45, 0.61) the decision-makers weight for each criterion shown as follows: table 5: the dm’s weights for each criterion criteria dm’s weight ���� �� 0.6333 �� 0.7500 �� 0.6400 �� 0.4333 iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 22 step 5: according to table 3, crisp projection for each criterion in table 6 is derived. table 6: each criterion projection value criteria decision maker (dm) �� �� �� �� �� 0.3500 0.8000 0.5000 0.9300 �� 0.2000 0.9300 0.9300 0.9300 �� 0.6500 0.9300 0.5000 0.5000 �� 0.8000 0.0700 0.6500 0.3500 step 6: we calculate p5 , ]5 , and m5 according to eq. (14) to (16) respectively. according to table 7, it is clearly identified that 40 is the most important criterion. table 7: entropybased weights (m5 ) for each attributes c �� �� �� �� 0.94366 0.05634 0.12603 �� 0.72409 0.27591 0.61722 �� 0.92050 0.07950 0.17784 �� 0.96473 0.03527 0.07890 step 7: the importance of each decisionmaker described by linguistic weighting variables as shown in table 8. for the benefitrelated criteria and costrelated criteria, the rate is calculated based on the graded mean integration representation shown as follows: 4, 40 41 4��,�0�1�� � 5.37506.20845.08343.0833 & 6.54173.50003.12505.7500 5.08346.12504.29176.8750 &6.12504.95834.66676.6250� table 8: the initial decision-maker rating table criteria candidates decision maker �� �� �� �� �� �� �� �� �� a1 a2 a3 a4 f g vg mp f f p vp g vg mp mp mp p f f 5.0000 8.0000 9.6667 3.5000 5.0000 5.0000 2.1667 0.3333 8.0000 9.6667 3.5000 3.5000 3.5000 2.1667 5.0000 5.0000 �� a1 a2 g mp f vp vg p mp g 8.0000 3.5000 5.0000 0.3333 9.6667 2.1667 3.5000 8.0000 iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 23 a3 a4 f f vp mg p mp f g 5.0000 5.0000 0.3333 6.5000 2.1667 3.5000 5.0000 8.0000 �� a1 a2 a3 a4 f g f mg vg f vg g p g p f mp mp vp g 5.0000 8.0000 5.0000 6.5000 9.6667 5.0000 9.6667 8.0000 2.1667 8.0000 2.1667 5.0000 3.5000 3.5000 0.3333 8.0000 �� a1 a2 a3 a4 f vp p vg f g mp vg mg f g p g mg f f 5.0000 0.3333 2.1667 9.6667 5.0000 8.0000 3.5000 9.6667 6.5000 5.0000 8.0000 2.1667 8.0000 6.5000 5.0000 5.0000 step 8: the decision matrix and the normalized decision matrix will be calculated by applying eq. (18) to (24). i) the decision matrix 4, 40 41 4��,�0�1�� � 3.40403.93183.21931.9527 & 4.90632.62502.34384.3125 3.25343.92002.74674.4000 &2.65402.14842.02212.8706� ii) the normalized decision matrix 4, 40 41 4��,�0�1�� � 0.53020.61240.50140.3041 & 0.66120.35380.31590.5812 0.44750.53920.37780.6052 &0.54190.43860.41290.5361� step 9: determined the positiveideal solution (pis) and negative-ideal solution (nis) according to eq. (7) and (8). the distance of each alternative from the positiveideal solution (pis) and the negativeideal solution (nis) is calculated respectively. �g � �x,g, x0g, … , xhg� � �0.6124,0.6612,0.6052,0.5861� (32) �! � �x,!, x0!, … , xh!� � �0.3041,0.3159,0.3778,0.4129� (33) table 9: the distance measurement alternative �g �! �� 0.1832 0.4380 �� 0.3473 0.3510 �� 0.4618 0.1973 �� 0.3185 0.3900 iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 24 step 10: finally, the closeness coefficient of each alternative is calculated. table 10: closeness coefficient table alternative cc ranking �� 0.7051 1 �� 0.5026 3 �� 0.2993 4 �� 0.5505 2 according to table 10, the ranking order of four candidates is ��ф��ф��ф��. the best alternative would be �� which the symbol of ‘ф’ means ‘is preferred to’. in this paper, the easy way to obtain fuzzy number is through applied the graded mean representation method [15]. it is very efficient and useful because it helps decreases the computation load for resulting steps of the proposed method. 5. conclusion the multicriteria decision making problem will be used when there is a group of decisionmakers. among many famous mcdm methods, fuzzy topsis is the best way. it is a practical technique to rank or choose the best alternative in their computation. it is an attractive way because the limited subjective input is needed from the decisionmaker. the advantage of using this method is that its ability to find the best alternative promptly [16]. in this paper, the proposed method is used to calculate weight of each criterion and find the best alternative for the ecological protection determinant. in addition, the distance between positiveideal solution and negativeideal solution is easily determined without ranking fuzzy number because the graded mean representation method is applied. acknowledgement the authors thank the ministry of higher education, malaysia for financing this research (fundamental research grant scheme, no.59148). references [1] j. holmberg, and s. karlsson, “on designing socio-ecological indicators, in svedin, u. and hägerhäll-aniansson, b. (eds.)”, society and environment: a swedish research perspective, kluwer academic publishers: dordrecht, 1992. [2] g. p. glasby, “concept of sustainable development: a meaningful goal”, the science of the total environment. vol. 159. uk: elsevier, 1995. 67-80. [3] world commission on environment and development (wced), “our common future”, , oxford: oxford university press, 1987. [4] s. j. chen and c. l. hwang, “fuzzy multiple attribute decision making methods and applications”, berlin : springer verlag, , 1992. [5] s. j. chen, & c.l hwang, “fuzzy multiple attribute decision making”, lecture notes in economics and mathematical system series”, vol. 375 new york: springer-verlag, 1992. [6] l. a. zadeh, “fuzzy sets”, information and control, 8 (1965): 33853. 8 august. 2014. iium engineering journal, vol. 13 no. 1, 2012 idayu and lazim 25 [7] c. l. hwang, & k. s. yoon, “multiple attribute decision making: methods and applications”, berlin: springer-verlag, 1981. [8] e. triantaphyllou, and c. t. lin, “development and evaluation of five fuzzy multiattribute decisionmaking methods”, international journal of approximate reasoning, 14. (1996): 281-310. 8 august. 2014. [9] m. abosinna and t. h.m abouelenien, “an interactive algorithm for large scale multiple objective programming problems with fuzzy parameters through topsis approach”, applied mathematics and computation, 177.2 (2005): 515-527. 8 august. 2014. [10] t. c. chen, “extensions of the topsis for group decisionmaking under fuzzy environment”, fuzzy sets and systems, 114. (2000):1-9. 8 august. 2014. [11] t. c. wang, and h. d. lee, “developing a fuzzy topsis approach based on subjective weights and objective weights”, expert systems with application. 36. (2009):8980-85. 8 august. 2014. [12] h. deng, c. h. yeh, & r. j willis, “inter-company comparison using modified topsis with objective weights”, computers and operations research. 27. (2000):963-73. 8 august. 2014. [13] c.e. shannon, “a mathematical theory of communication”, journal of bell system and technology. 27. (1948):379-423, 623-59. 8 august. 2014. [14] d. yong, “plant location selection based on fuzzy topsis”, the international journal of advance manufacturing. 28. (2006):839-44. 8 august. 2014. [15] c. c. chou, “the canonical representation of multiplication operation on triangular fuzzy numbers”, international journal of applied mathematics and computer science 45. (2003):1601-10. 8 august. 2014. [16] c. parkan, and m. l. wu, “on the equivalence of operational performance measurement and multiple attribute decision making”, international journal of production research 35.11 (1997):2963-88. 8 august. 2014. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 investigation of magnetic properties for different coil sizes of dynamic wireless charging pads for electric vehicles (ev) syasya azra zaini, siti hajar yusoff*, amira aziera abdullah, sheroz khan, faridah abd rahman and nadia nazieha nanda department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, p.o box 10, 50728 kuala lumpur, malaysia *corresponding author: sitiyusoff@iium.edu.my (received: 14th march 2019; accepted: 22nd october 2019; published on-line: 20th january 2020) abstract: electric vehicles (ev) have been introduced in the recent years due to public awareness of the effect of gas emission from traditional cars and the extinction of petroleum natural resources. for charging ev, dynamic wireless charging is considered in this paper. this is because it is more convenient and saves charging time since it charges the electric vehicle while moving. the main challenge of this process is to maintain a high amount of power transfer from primary to secondary coil. one of the factors contributing to a good power transfer is the size of the coil [1]. there are various designs of coil for wireless charging of electric vehicles (ev). among the most common designs are circular pad (cp), rectangular pad (rp), double-d pad (ddp), and double-d quadrature pad (ddqp). in this paper, circular pad (cp) is chosen for use, due to its simplicity in design and good electrical and magnetic properties. three different coil pair sizes are tested to find the most suitable coil pair for the primary and secondary pads that has the maximum power transfer and is least sensitive to misalignment. the magnetic properties have been investigated to obtain the highest value of magnetic flux. the geometry design of the pads and simulation was done using comsol multiphysics software. from the simulation, it was found that the unsymmetrical coil pair gives high magnetic strength when the outer diameters of the primary and secondary coils have the same value. abstrak: kenderaan elektrik (ev) telah diperkenalkan sejak beberapa tahun ini hasil kesedaran awam tentang kesan pembebasan gas dari kenderaan lama dan pengurangan sumber asli petroleum. kajian ini berkaitan pengecas dinamik tanpa wayar bagi mengecas ev. ini kerana pengecas ini lebih sesuai dan jimat masa mengecas kerana kenderaan elektrik dicas ketika bergerak. cabaran utama proses ini adalah mengekalkan pemindahan tenaga yang tinggi daripada gegelung primer kepada gegelung sekunder. salah satu faktor bagi mendapatkan pemindahan tenaga yang tinggi adalah saiz gegelung wayar [1]. terdapat pelbagai bentuk gegelung bagi mengecas kenderaan elektrik (ev) tanpa wayar. antaranya adalah pad membulat (cp), pad segiempat tepat (rp), pad berganda-d (ddp), dan pad kuadratur berganda-d (ddqp). kajian ini telah menggunakan pad membulat (cp) kerana reka bentuknya yang ringkas dan ia mempunyai sifat elektrikal dan magnatik yang baik. tiga pasang gegelung berbeza telah diuji bagi mendapatkan pasangan gegelung pad primer dan sekunder yang paling sesuai di mana ianya mempunyai pemindahan tenaga maksima dan paling kurang sensitif pada ketidakjajaran. sifat magnet telah diuji bagi mendapatkan nilai fluks magnet tertinggi. rekabentuk geometri pad dan simulasi telah dijalankan menggunakan perisian multifizik comsol. hasil simulasi mendapati pasangan gegelung yang tidak simetri telah menghasilkan kekuatan magnetik tertinggi apabila diameter luaran gegelung primer dan sekunder mempunyai nilai sama. 23 iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 keywords: eletric vehicle (ev); magnetic properties; wireless power transfer; inductive charging; circular coil 1. introduction electric vehicles (ev) have been introduced in 2012 due to public awareness of the effect of gas emission from traditional cars and the extinction of petroleum natural resources [2]. malaysia’s government also supports electric vehicles by offering full exemption of tax for ev. besides, the fact that ev and plug-in hybrid ev produce smaller carbon dioxide (co2) than traditional vehicles and lower the cost of ownership over lifetimes has attracted manufacturers and researchers alike to study more about this topic [3]. in developed countries, ev sales are rising rapidly due to their advantages. in wireless charging systems, several components are needed to ensure that power is transferred efficiently from the grid to the car battery, as shown in fig. 1. the wireless charging process will begin from the dc input, which is the main source power. then, the dc power will pass through an inverter and compensation to convert it from dc to ac power. for wireless charging, the transmitter coil and receiver coil are used as a medium to transmit and receive power using an air gap channel. after that, the received power will go through the same process with the help of a converter before reaching the car battery. many types of converter can be used, such as ac/ac matrix converters [4,5], t-type direct converters, and many more. fig. 1: basic block diagram of wireless charging ev system [6]. there are various designs of coil for the wireless charging of electric vehicles (ev). among the most common design are circular pad (cp), rectangular pad (rp), double-d pad (ddp), and double-d quadrature pad (ddqp) [7,8]. each of the pad designs has its own benefit for its specific requirements and applications. among the designs are: a) circular pad (cp) circular pad design is the most widely used due to its simplicity in design and manufacturing [9]. besides that, cp design also has good electrical and magnetic properties to transfer power efficiently [10]. in terms of misalignment, cp design has the same tolerance in all directions [8] due to its circular shape. however, researchers are still trying to reduce the misalignment effect in order to improve the performance of wireless charging. polarized circular pads have mostly been implemented in static ev charging applications [8]. despite that, cp has a problem with the increasing of the air gap. this is because the diameter of the coil will get four times larger when the air gap increases once. this is due to the 1:4 ratio of the primary flux path and diameter of coil [8,11]. due to this limitation, other designs of coil were introduced. 24 iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 b) rectangular pad (rp) rectangular pad (rp) is another basic coil design for wireless charging. it is suitable in dynamic charging due to its cost effectiveness. besides that, rp is also popular because of its capability to transfer power and its reasonable cost of materials [12]. in order to optimize the power transfer between coils, a ferrite bar has been used and attached to the rectangular coil. wang et al. tested a variety of lengths of ferrite bar on the rectangular coil in order to improve the coupling coefficient and mutual inductance between two coils [13]. from the simulation, it can be concluded that longer ferrite bars can transfer more power than shorter bars. c) double-d pad (ddp) besides circular and rectangular pad, double-d pad (ddp) is also among the popular designs for wireless ev charging. this is due to a better performance and it interoperability with different secondary topologies [7]. even though ddp has a higher tolerance of misalignment, it only covers the horizontal component. therefore, the double-d quadrature pad (ddqp) was invented to have a high tolerance in both horizontal and vertical components [8]. the ddqp design is a combination of dd pad and rectangular pad (rp). this pad has high misalignment tolerance especially when it is placed at the secondary side [14]. nonetheless, this design leads to increased costs due to the increase in number of coils. figure 2 below shows the design of ddp and ddqp coils. fig. 2: different charging pads (a) cp (b) rp (c) ddp (d) ddqp. among many pad designs, circular couplers are the most usable because of their magnetic properties [15]. however, different sizes of circular pad would give different performance in terms of magnetic properties. therefore, this paper would design and discuss different pairs of circular-circular coil pads that give highest magnetic strength between the primary and secondary coils. this paper is organized as follows: section ii presents the methodology consisting of the design for each coil pair. then, section iii discussed the simulation results using comsol multiphysics software. finally, the paper concludes in section iv. 25 iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 2. methodology in this project, three different circular pairs of coils have been investigated to decide which pair gives the maximum power transfer. the secondary coil, or the receiving side, is set to the same value in all three designs, while the primary, or transmitting side, is varied to compare the effect on power transfer. proper matching of coil parameters such as the diameter of the primary and secondary coils, distance between two coils, and mutual inductance between them, allow the maximum power transmission through the link. therefore, this paper proposed the best design for circular coils in order to obtain high magnetic strength. in all coil pairs, ‘p’ represents the primary coil and ‘s’ represents the secondary coil. detailed explanations about the three different coils will be discussed below. a) -s for this type of coil, the inner diameter as well as the outer diameter of primary coil are kept smaller than the secondary coil. b) -s for this coil-pair, the inner diameter of the primary coil is kept smaller than the inner diameter of the secondary coil and the outer diameter of the primary coil is kept the same as the outer diameter of the secondary coil. c) -s for this type of coil pair, the outer diameter of primary coil is larger than secondary coil and diameter of inner primary coil is less than inner diameter of secondary coil. table 1 listed the value parameters that were used in this project. figure 3 also shows a clear illustration of the three coil pairs designed. the primary coil is placed at the bottom, whereas secondary coil is placed at the top in order to replicate a real ev system. for real ev, the primary coil is attached to the road while the secondary coil attached below the car. table 1: geometry parameters of designed coils coil (cm) (cm) 28 21.4 24 6 28 12 32 12 secondary coil primary coil a) p1-s b) p2-s c) p3-s fig. 3: different coil pairs. 26 iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 figure 4 below shows the primary and secondary coil sketch in comsol multiphysics before running the simulation. the air gap between the primary coil and secondary coil is fixed at 16 cm. fig. 4: primary and secondary coil drawn in comsol multiphysics. after the simulations for all three pairs were done, another simulation is performed to vary the inner diameter while fixing the outer diameter for the best primary coil. the coil design that gives the highest magnetic field norm and magnetic flux density norm will be simulated again by varying the inner diameter of primary coil in order to find the most suitable parameter for the primary coil. 3. simulation results there are three designs of coil pair that were tested in the comsol multiphysics software. each coil has a fixed number of turns, n, and an air gap with no misalignment condition. the secondary coil is also fixed for all the three tests. the diameter of the secondary coil is chosen based on the best design achieved from aditya [1]. the diameter of the primary coil is the only varying parameter for this simulation. the simulation results are shown below. 3.1 magnetic field characteristic in each coil pair, different values of magnetic field have been identified. the figures below show the behaviour of magnetic fields around the coils. the red colour indicates a strong magnetic field while the blue colour indicates the lowest field strength. in each simulation, there is a colour legend that states the maximum and minimum magnetic fields. different ranges of colour show different values of magnetic field inside the coil. table 2 shows the magnetic field characteristics for all coil pairs. this simulation is done to observe the behaviour of the magnetic fields between the primary and secondary coils. from the simulation, it can be seen that the behaviour of the magnetic fields is quite similar for all pairs since there are no misalignments involved. however, table 2 only shows the behaviour of the magnetic fields. in order to know the magnitude of magnetic fields, the magnetic fields norm have been simulated. the maximum normal magnetic field value for the first, second, and third pairs are 9.82 × 10 (a/m), 1.0 × 10 (a/m) and 9.64 × 10 (a/m), respectively. normal magnetic fields represent the magnitude for the magnetic fields between two coil pairs. table 3 shows the magnetic field norms for each coil pair. primary coil secondary coil 27 iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 table 2: the magnetic field behaviour for each coil pair table 3: the magnetic field norms for each coil pair (a) p1-s coupling (a) p1-s coupling (b) p2-s coupling (b) p2-s coupling (c) p3-s coupling (c) p3-s coupling from the table above, p2-s gives the highest magnetic field norm with 1.0 × 10 a/m. so, high magnetic strength between p2-s coils will provide better power transfer between the primary and secondary coils. there is no specific range of magnetic field and magnetic flux density needed for good performance of wireless charging. however, a magnetic field induces electrical charge movement, producing an electric current. therefore, a high value of magnetic field and magnetic flux density produces more current and thus improves the charging process for the electric vehicle (ev). 28 iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 3.2 magnetic flux density characteristic table 4 below shows the simulation of the magnetic flux density for all three coil pairs. the blue colour around the coil represents the air environment. table 4: the magnetic flux density norm for each coil pair p1-s p2-s p3-s the simulation shows that the p2-s coupling pair gives the highest magnetic flux density norm, which is 1.3 t. the strengths of the magnetic flux density norms in descending order are p2>p3>p1. therefore, the p2-s coil pair is chosen for use in ev charging since it has high strength of magnetic field and magnetic flux density norm between the two coils. 3.3 simulations varying the inner diameter of coils in the previous simulation, -s has been proven to provide the highest magnetic field norm and magnetic flux density. therefore, in this section, the p2-s design is further simulated to find the most suitable parameter for the primary coil. the inner diameter for the coil is varied between 12 cm, 16 cm, and 20 cm while maintaining the outer diameter of 28 cm. table 5 shows the value of varying the inner diameter. table 6 shows the simulation results for the coil by varying the inner diameter of the primary coil. the parameter for the coil was shown in table 1. from the simulation results, it can be seen that the magnetic field behaviour for larger inner diameter of primary coil is higher. it can be seen p2c-s has more arrows compared to the other two designs. 29 iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 arrows inside the coil and air region indicate the amount of magnetic field flow between the two coils. the sphere line in this simulation represents the air region. furthermore, as the magnetic field arrow increases, the magnetic flux density value also increases. as can be seen from table 6, p2c-s has the highest magnetic flux density value of 1.67 t. therefore, p2c-s will produce the highest power transfer between primary and secondary coils. table 5: geometry parameters varying the inner diameter for coils coil (cm) (cm) 28 21.4 28 12 28 16 28 20 table 6: simulation results varying the inner diameter for coils coil pair magnetic field behaviour magnetic flux density − − − 30 iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 according to the international commission on non-ionizing radiation protection (icnirp) 2010 guidelines, the reference level for magnetic fields is 27 μt for frequencies between 3 khz to 10 mhz [16, 17]. however, the value achieved from this simulation is in the range of 1.3 t to 1.67 t and it exceeds the reference level. therefore, it shows that several improvements need to be done before it can be used by the public. high magnetic flux density is useful to increase the effectiveness of power transfer. but, if the value exceeds the maximum value set by icnirp, it might be harmful for the public. 4. conclusion this paper has successfully investigated the effect of unsymmetrical pad couplers on the magnetic flux density in air environment. three pairs of unsymmetrical pad couplers were designed and simulated using comsol multiphysics software in order to analyse the magnetic properties for each pair. the primary coil is varied by the diameter of the coil while secondary coil’s parameter is kept constant. from the results, similar values of the coil’s outer diameter will give a strong magnetic field and magnetic flux density. the simulation done in comsol multiphysics shows that the second coil pair ( -s) that has an outer diameter of 28 cm has the highest magnetic field and magnetic flux density norm, which is 1.0 × 10 a/m and 1.3 t, respectively. another simulation was done to find the best inner diameter of the primary coil ( ). the results show that -s gives the highest magnetic flux density of 1.67 t. therefore, high magnetic field and magnetic flux density will provide high power transfer between the primary and secondary coils. thus, the -s coil pair is chosen for use in ev wireless charging. however, further research can explore a coil pair that is safe for use by the public and obeys the standards given by icnirp. acknowledgement this work was partially supported by ministry of higher education malaysia (kementerian pendidikan tinggi) under fundamental research grant scheme (frgs) number frgs17-038-0604. references [1] k. aditya, v. k. sood, and s. s. williamson. (2017) magnetic characterization of unsymmetrical coil pairs using archimedean spirals for wider misalignment tolerance in ipt systems. ieee transaction on transportation electrification, 3(2): 454–463. [2] r. bosshard and j. w. kolar. (2016) inductive power transfer for electric vehicle charging. ieee power electronics magazine: 22–30. [3] malaysian green technology corporation "low carbon mobility" [https://www.greentechmalaysia.my/services/low-carbon-mobility/] [4] s. yusoff, l. de lillo, p. zanchetta, and p. wheeler. (2012) predictive control of a direct ac/ac matrix converter power supply under non-linear load conditions. 15th international power electronics and motion control conference expo. epe-pemc 2012 ecce europe: 1–6. [5] s. yusoff, l. de lillo, p. zanchetta, p. wheeler, p. cortés, and j. rodríguez. (2012) predictive control of a direct ac/ac matrix converter for power supply applications. 6th iet international conference on power electronics, machines and drives (pemd 2012): a92– a92. [6] p. s. r. nayak and d. kishan. (2018) performance analysis of series/parallel and dual side lcc compensation topologies of inductive power transfer for ev battery charging system. front. energy: 1–14. https://doi.org/10.1007/s11708-018-0549-z [7] c. liu, c. jiang, c. qiu. (2017) overview of coil designs for wireless charging of electric 31 iium engineering journal, vol. 21, no. 1, 2020 zaini et al. https://doi.org/10.31436/iiumej.v21i1.1108 vehicle. ieee pels workshop on emerging technologies: wireless power transfer (wow): 15–18. [8] a. ahmad, m. s. alam, s. member, and r. chabaan. (2018) a comprehensive review of wireless charging technologies for electric vehicles. ieee transaction on transportation electrification, 4(1): 38–63. [9] m. mohammad and s. choi. (2018) optimization of ferrite core to reduce the core loss in double-d pad of wireless charging system for electric vehicles. conference proceedings ieee applied power electronics conference and exposition (apec): 1350–1356. [10] a. tejeda, c. carretero, j. t. boys, and g. a. covic. (2017) ferrite-less circular pad with controlled flux cancelation for ev wireless charging. ieee transactions on power electronics, 32(11): 8349–8359. [11] m. budhia, g. covic, and j. boys. (2010) a new ipt magnetic coupler for electric vehicle charging systems. iecon proceedingsindustrial electronics conference: 2487–2492. [12] w. chen, c. liu, c. h. t. lee, and z. shan. (2016) cost-effectiveness comparison of coupler designs of wireless power transfer for electric vehicle dynamic charging. energies journal: 113. [13] s. wang, y. guo, and d. dorrell. (2017) analysis of rectangular ev inductive charging coupler. 12th ieee conference industrial electronics and applications: 285–291. [14] l. xiang, y. sun, z. ye, z. wang, and s. zhou. (2016) combined primary coupler design and control for ev dynamic wireless charging system. ieee pels workshop on emerging technologies: wireless power, wow 2016: 174–179. [15] m. budhia, s. member, j. t. boys, g. a. covic, and s. member. (2013) development of a single-sided fluxmagnetic coupler for electric vehicle ipt charging systems. ieee transactions on industrial electronics, 60(1): 318–328. [16] s. li and c. c. mi. (2014) wireless power transfer for electric vehicle applications. ieee journal of emerging and selected topics in power electronics, 3(1): 4–17. [17] k. a. grajski, r. tseng, and c. wheatley. (2012) loosely-coupled wireless power transfer: physics, circuits, standards. ieee mtt-s international: 9–14. 32 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <feff004f0076006500200070006f0073007400610076006b00650020006b006f00720069007300740069007400650020006b0061006b006f0020006200690073007400650020007300740076006f00720069006c0069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400650020006b006f006a00690020007300750020007000720069006b006c00610064006e00690020007a006100200070006f0075007a00640061006e00200070007200650067006c006500640020006900200069007300700069007300200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e006100740061002e0020005300740076006f00720065006e0069002000500044004600200064006f006b0075006d0065006e007400690020006d006f006700750020007300650020006f00740076006f007200690074006900200075002000700072006f006700720061006d0069006d00610020004100630072006f00620061007400200069002000410064006f00620065002000520065006100640065007200200036002e0030002000690020006e006f00760069006a0069006d0020007600650072007a0069006a0061006d0061002e> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <feff004c006900650074006f006a00690065007400200161006f00730020006900650073007400610074012b006a0075006d00750073002c0020006c0061006900200069007a0076006500690064006f00740075002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c0020006b006100730020007000690065006d01130072006f00740069002000640072006f01610061006900200075007a01460113006d0075006d006100200064006f006b0075006d0065006e0074007500200073006b00610074012b01610061006e0061006900200075006e0020006400720075006b010101610061006e00610069002e00200049007a0076006500690064006f0074006f0073002000500044004600200064006f006b0075006d0065006e00740075007300200076006100720020006100740076011300720074002c00200069007a006d0061006e0074006f006a006f0074002000700072006f006700720061006d006d00750020004100630072006f00620061007400200075006e002000410064006f00620065002000520065006100640065007200200036002e003000200076006100690020006a00610075006e0101006b0075002000760065007200730069006a0075002e> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <feff04180441043f043e043b044c043704430439044204350020044d044204380020043f043004400430043c043504420440044b0020043f0440043800200441043e043704340430043d0438043800200434043e043a0443043c0435043d0442043e0432002000410064006f006200650020005000440046002c0020043f043e04340445043e0434044f04490438044500200434043b044f0020043d0430043404350436043d043e0433043e0020043f0440043e0441043c043e044204400430002004380020043f043504470430044204380020043104380437043d04350441002d0434043e043a0443043c0435043d0442043e0432002e00200421043e043704340430043d043d044b043500200434043e043a0443043c0435043d0442044b00200050004400460020043c043e0436043d043e0020043e0442043a0440044b0442044c002c002004380441043f043e043b044c04370443044f0020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e00300020043b04380431043e00200438044500200431043e043b043504350020043f043e04370434043d043804350020043204350440044104380438002e> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 the effects of cerium promoter on the performance of cobalt-based catalysts in fischer tropsch synthesis for liquid fuel production firas khaleel al-zuhairi1, wafaa abdul kadhim 2, ahmed lateef khalaf3* and mohd hasbi ab rahim4 1petroleum technology department, 2nanotechnology & advanced material research center (namrc), university of technology, baghdad, iraq 3department of computer engineering techniques, al-ma’moon university college, baghdad, iraq 4faculty of industrial sciences & technology, universiti malaysia pahang, gambang, pahang, malaysia *corresponding author: ahmed.l.khalaf@almamonuc.edu.iq received: 28th april 2019; accepted: 13th march 2020; published on-line: 4th july 2020) abstract: an intensive work of fischer-tropsch synthesis (fts) on a cobalt-based catalyst supported with cerium as a promoter was presented. the influence of space velocity and inlet gas feed ratio on fts reaction performance was studied for the synthesized catalysts. incipient wetness impregnation method was utilized to synthesis both unpromoted (25%co/γ-al2o3) and cerium promoted (1%ce-25%co/γ-al2o3) catalysts. the proposed catalysts were examined by n2 adsorption and temperatureprogramed reduction (tpr). the performance of ce-promoted and unpromoted cobaltbased catalysts in fts was assessed in terms of activity and selectivity to desired products (c5+). the obtained results revealed that the addition of cerium by impregnation notably favours the reducibility of cobalt oxides by reducing the reduction temperature. in addition, the promoted catalysts exhibited higher activity and selectivity toward desired products at low space velocity and high inlet gas feed ratio as compared with the unpromoted catalysts. in conclusion, a cerium based cobalt catalyst considered as a suitable candidate to be used in gas to the liquid conversion process. abstrak: kajian intensif sintesis fischer-tropsch (fts) adalah tentang pemangkin berasas kobalt bersama penggalak cerium. pengaruh tindak balas fts pada halaju ruang dan nisbah suapan gas masuk dikaji menggunakan pemangkin yang disintesis. kaedah impregnasi insipien basah telah digunakan bagi mensintesis pemangkin bukan penggalak (25%co/γ-al2o3) dan penggalak cerium (1%ce-25%co/γ-al2o3). pemangkin ini diuji dengan penjerapan n2 dan pengurangan suhu terprogram (tpr). hasil tindak balas penggalak-ce dan bukan penggalak berasas kobalt dalam fts diperiksa dari segi aktiviti dan pemilihan hasil (c5+). tindak balas menunjukkan dengan penambahan cerium melalui kaedah impregnasi dengan ketara mengurangkan kobalt oksida bersama pengurangan suhu. di samping itu, pemangkin penggalak menunjukkan aktiviti dan pemilihan ke arah hasil pada halaju ruang dan nisbah suapan gas masuk yang tinggi berbanding dengan pemangkin bukan penggalak. kesimpulan, pemangkin kobalt berasas cerium dianggap sesuai sebagai pemangkin sintesis bagi digunakan dalam proses penukaran gas ke cecair. keywords: catalyst, cerium promoter, fischer-tropsch synthesis, gtl, syngas; 1 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 1. introduction over the past few decades, natural gas has been considered a plentiful and cleanest natural fuel that should be altered to liquid form to prevent safety hazards and to reduce transportation costs [1]. natural gas, methane (ch4) is commonly employed to produce synthesized gas (syngas) via different techniques, such as partial oxidation [2], steam reforming [3], and auto-thermal reforming [4]. recently, the gas-to-liquid technique (gtl) has been considered one of the most efficient processes that is mainly used to convert natural gas into a syngas intermediate through a fischer-tropsch (ft) synthesis technology [5]. in general, the gtl process produces oil crudes that contain different fractions of useful hydrocarbons that can be amended and segregated to different types of necessary transportation sector fuels [6], in the presence of solid catalysts. because of their high c5+ selectivity, excellent activity, and ability to work at low operating temperatures (between 200 and 250 ºc), co-based catalysts are in the limelight recently as an effective catalyst for attaining heavy hydrocarbons in ft synthesis [7, 8]. thus, it is of a great necessity to improve the efficiency of co-based catalysts. many researches have demonstrated that adding different promoters and loadings to the catalyst assists in improving the selectivity and activity of the catalyst towards c5+ contents. guo et al. [9] reported that adding a small amounts of lanthanum to the co/γ-al2o3 catalyst could enhance the performance of the catalyst in terms of selectivity, activity, and co reducibility to heavy hydrocarbons. co reducibility was significantly increased by adding different loading of silver to the co-based catalyst [10]. furthermore, the addition of silver helps in decreasing the reduction temperatures by up to 100 °c and increasing the co reduction, dispersion, and electronic properties. another study by pedersen et al. [11] employed manganese (mn) as a promoter for a co-based catalyst supported by γ-al2o3. they found that mn enhanced the intrinsic co catalyst activity, co dispersion, and selectivity to c5+ species due to its stable effect on the adsorption of co, c, h, o, chx, thereby decreasing the co dissociation barrier. rare earth elements were also utilized to improve the performance of the co-based catalyst supported by al2o3, sio2, tio2, zro2, and cnts [12, 13]. among all the discussed promoters, co-based catalysts promoted with cerium (ce) attained excellent performance in ft synthesis technology due to its ability to facilitate the dissociation of co, weaken the interaction between support and co and improve the activity, c5+ selectivity and the olefin/paraffin ratio of the co-based catalyst [13-15]. although many studies have been conducted on ce as a promoter for co-based catalysts, there are great opportunities in further investigating the influence of reaction conditions on the ceriumpromoted cobalt-based catalyst in fts reactions. herein, we thoroughly study and evaluate the effects of reaction conditions (space velocity and h2/co ratio) on the cerium-promoted co-based catalyst in terms of fts activity and product selectivity. the developed catalyst shows excellent results as compared with those of the un-promoted cobalt-based catalyst. 2. materials and methods 2.1 catalysts preparation incipient wetness impregnation method was employed to synthesize the co-based catalysts supported by γ-al2o3 (axens) according to the method reported by trépanier et 2 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 al. [16]. initially, the support (γ-al2o3) was calcined in airflow at 500 ºc for 4 h. after cooling down the temperature to room temperature (25 ºc), sequential impregnation with continuous stirring in aqueous solutions of cobalt (ii) nitrate hexahydrate (co(no3)2.6h2o) was performed at ambient temperature. then, 25 % of co by weight was laden to the mixture and left to dry for 12 h at 110 ºc and then calcined at 400 °c for 6 h beneath airflow with a degree of temperature increase 2°c/min to attain 25 co/γ-al2o3 reduced catalyst. to obtain the ce promoted catalyst, 1wt. % of ce promoter was added to 25 co/γal2o3 dried un-calcined catalyst by the co-impregnation in an aqueous solution of cerium nitrate hexahydrate (ce(no3)2.6h2o) and dried overnight for 12 h at 110 ºc. later, the catalyst was calcined at 400 °c for 6 h with a heating rate of 2 °c/min under airflow. the developed catalysts were labelled as co0 and co1 representing unpromoted and ce promoted co-based catalysts, respectively. 2.2 catalyst characterization the calcined prepared catalysts were characterized by temperature-programed reduction (tpr) and n2 physisorption. the temperature-programed reductions were accomplished to decide the reducibility of metal oxides to metallic using a tp-5000 analyser fitted with a quartz tubular reactor and tcd. a 50 mg of each sample was exposed to a continuous argon gas flow at rate of 1.8 l/h containing 5 % of h2 with heating temperature ranging from 25 °c to 900 °c with increments of 10 °c per min. n2 physisorption isotherm analysis was done using the micromeritics asap-2020 system, to estimate the bet surface area, pore-volume, and the average pore radius for the γ-al2o3 and catalysts. 2.3 fischer-tropsch reaction (ftr) as aforementioned, the ftr process was utilized to convert synthesized gas to liquid fuel (high molecules weight hydrocarbons). the activity and selectivity of the developed catalysts were investigated in a fixed-bed flow reactor made from a stainless steel metal with internal diameter of 10 mm. two grams of the promoted and unpromoted co-based was loaded in the centre of the reactor and fixed between two quartz beads, then heated under argon gas to reduction temperature, the reduction was conducted by (5% h2-95%ar) gas mixture to convert the forms of metal from oxide to the metallic. after finishing the reduction, the reactant gases mixtures (h2 and co) were introduced to the reactor with a desired flow rate using a mass flow controller (brooks 5850) fitted with a pid controller. the ft reactions were conducted at a temperature of 230 ºc and pressure of 15 bar with different space velocity (sv) in the range of 2 8 l/h.gcat. (with increments of 2) and different feed gas ratio (h2/co) of 1 to 2 (with increments of 0.5). the output stream from the reactor was lowered to atmospheric pressure by a control valve (bpr) and then went over two traps. the first one was at 100 ºc and the other was 0 ºc to condense the products. the compositions of products in a gas and liquid phase were analysed online and off-line using a gas chromatograph (gc-shimadzu-2014) equipped with (tcd and fid) and varian cp 3800 equipped with fid, respectively. 3. results and discussion 3.1 catalyst characterization the tpr profiles for the unpromoted (25%co/γ-al2o3) and promoted (1%ce25%co/γ-al2o3) calcined catalysts are illustrated in fig. 1. three reduction peaks are 3 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 clearly observed for the un-promoted co-based catalyst. the reduction of co3o4 to coo (co3+ →co2+) and coo to co metal (co2+ →co0) can be allocated at 350 ºc and 577 ˚c, respectively [17]. while, the weak peak noticed around 702 ˚c can be attributed to the reduction of cobalt aluminate compounds [18]. on the other hand, the catalyst promoting with 1% ce has robustly influenced the tpr profile, as revealed in fig. 1, where the first and second peaks obviously shifted to lower temperature, at 252 ºc and 527 ºc, respectively, due to the significant easy reduction of coo to co metal along with the low interaction between co ions and the al2o3 support [19, 20]. as a result, the third peak related to cobalt aluminate compounds observed in the un-promoted catalyst disappeared. in addition, the tpr outcomes confirmed that the selected reduction parameters (5% h295% ar) mixture by rate of flow 1.8 l/h at 570 ºc for 10 h) were appropriate for reducing the cobalt oxides into cobalt metal insuite apparatus prior to the ft reaction. table 1 listed the results of single point pore volume, bet surface area (sa) and pore size for the calcined support (γ-al2o3), co0, and co1 catalysts. from the table, it can be noticed that the sa of γ-al2o3, co0, and co1 were found to be 145, 95.2 and 94.6 m2/g, respectively. fig. 1: tpr profiles for the un-promoted (25%co/γ-al2o3) and promoted (1%ce-25%co/γ-al2o3) calcined catalysts. table 1: bet surface area and pore volume for the developed catalysts catalyst symbol bet sa (m2/g) pore volume (cm3/g) pore size (nm) γ-al2o3 145 0.542 6.8 25%co/γ-al2o3 co0 95.2 0.276 4.9 1%ce-25%co/γ-al2o3 co1 94.6 0.265 4.7 sa for the support was 145 m2/g which plunged to 95.2 m2/g for the unpromoted catalyst, the 25% of co corresponds to 34% co3o4. according to the obtained cobalt oxide percentage, the theoretical value of the bet surface area catalyst was approximately 95.6 m2/g for the un-promoted catalyst. the theoretical and experimental bet surface area values were more closed owing to the minimum pore plugged by cobalt species [21]. adding the ce promoter causes a small decrement in the surface area. in addition, the pore volume and pore size for the γ-al2o3 were 0.542 cm3/g and 6.8 nm, respectively, that 4 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 decreases to 0.276 cm3/g and 4.9 nm, accordingly, for co0. pore volume and pore size were slightly altered in co1. these results are in good agreement with the results reported by gnanamani et al. [22]. 3.2 fischer-tropsch synthesis production of liquid fuels by ft synthesis process is considered as one of the most important techniques used to tackle the problem of fuel shortage in the transport sector [23]. to investigate the influences of space velocity and inlet feed ratio (h2/co) on the activity of unprompted and ce promoted catalysts and their selectivity toward liquid fuels production, number of experiments of fischer-tropsch reaction were conducted at a temperature of 230 ºc, pressure of 15 bar, and different space velocity and inlet feed ratios (h2/co). after steady-state condition of about 8 to 9 h, the percentage of carbon monoxide conversion (%xco) and product selectivity (%) were examined. 3.2.1 influence of space velocity on catalyst performance figure 2 shows that the co conversion (%xco) as a function of space velocities of the developed catalysts (co0 and co1) ranges from 2 to 8 l/h. gcat. with different h2/co ratios between 1 and 2 for each sv at operating temperature and applied pressure of 230 ºc and 15 bar, respectively. the obtained results demonstrated that the co conversion sharply decreased when sv increased thereby, the residence time of reaction decreased. thus, co conversion and chain growth decrease, which assures the rapid increase in the formation of low molecular weight hydrocarbons (ch4 and c2-c4) and the decrease in production of high molecular weight hydrocarbons (c5+) [24]. fig. 2: effect of space velocity on carbon monoxide conversion for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c, and h2/co= 1, 1.5, and 2. the selectivity of the developed catalysts (co0 and co1) toward ch4, c2-c4 hydrocarbons, c5+, and co2 are demonstrated in fig. 3(a-d). it is evident that the product selectivity of both catalysts against ch4, c2-c4 hydrocarbons, and co2 increased proportionally with sv while the desired product (c5+) decreased. this is because an increase in sv leads to a significant decrease in the residence time of reaction, thereby decreasing the co conversion, which is in agreement with the results reported in [24]. figure 3a shows that the selectivity of co0 and co1 toward co2 were very small (< 3). this can be attributed to the little activity of water-gas shift mainly obtained by the co 5 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 based catalyst [25, 26]. furthermore, the promoted co-based catalysts exhibited an excellent co conversion and c5+ selectivity by decreasing the sv due to the presence of ce promoter which aids in increasing the amount of chemisorbed hydrogen and weakening the strong bond of co–h [27]. table 2 summarized the obtained results. fig. 3: (a) effect of sv on co2 selectivity for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c and h2/co ranging from 1 to 2. fig. 3: (b) effect of sv on ch4 selectivity for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c and h2/co ranging from 1 to 2. fig. 3: (c) effect of sv on c2-c4 selectivity for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c and h2/co ranging from 1 to 2. 6 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 fig. 3: (d) effect of sv on c5+ selectivity for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c and h2/co ranging from 1 to 2. 3.2.2 influence of inlet feed ratio (h2/co) on catalyst performance the effect of inlet feed ratio (h2/co) on the developed catalysts (co0 and co1) has been thoroughly investigated in terms of %xco and selectivity at operating temperature of 230 ºc and under a pressure of 15 bar with different sv, as shown in fig. 4 and fig. 5 and listed in table 2. table 2: catalytic performance of co-based catalysts during co hydrogenation catalyst sv (l/hr. gcat.) h2/co ratio %xco %selectivity ch4 c2-c4 c5+ co2 25%co/γ-al2o3 (co0) 2 1 29.8 9.65 14.12 75.12 1.11 1.5 39.5 8.6 11.53 78.82 1.05 2 47.8 6.23 8.74 84.1 0.93 4 1 20.4 10.02 15.88 72.68 1.42 1.5 30.2 8.75 13.9 76.14 1.21 2 41.5 7.41 11.27 80.17 1.15 6 1 14.7 12.7 15.6 70.25 1.45 1.5 21.6 10.76 14.68 73.02 1.54 2 27.8 9.95 13.15 75.31 1.59 8 1 9.8 19.58 16.9 60.81 2.71 1.5 11.2 16.42 15.47 65.48 2.63 2 20.1 15.64 14.86 67.35 2.15 1%ce-25%co/γ-al2o3 (co1) 2 1 40.8 5.13 9.77 84.68 0.42 1.5 49.4 4.67 7.54 87.48 0.31 2 61.9 3.26 4.89 91.64 0.21 4 1 28.1 7.84 10.23 81.03 0.9 1.5 35.7 7.66 8.54 82.93 0.87 2 53.5 5.34 6.9 87.25 0.51 6 1 18.5 9.59 10.97 78.19 1.25 1.5 29.5 9.41 8.45 80.97 1.17 2 41.6 8.75 7.12 83.07 1.06 8 1 16.5 12.05 11.6 74.95 1.4 1.5 21.4 11.31 9.41 77.97 1.31 2 30.2 10.84 8.61 79.29 1.26 7 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 fig. 4: effect of h2/co ratio on co conversion for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c and sv= 2, 4, 6 and 8 l/h. gcat.. fig. 5: (a) effect of h2/co ratio on co2 selectivity for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c and sv= 2, 4, 6 and 8 l/h. gcat.. fig. 5: (b) effect of h2/co ratio on ch4 selectivity for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c and sv= 2, 4, 6 and 8 l/h. gcat.. 8 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 fig. 5: (c) effect of h2/co ratio on c2-c4 selectivity for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c and sv= 2, 4, 6 and 8 l/h. gcat.. fig. 5: (d) effect of h2/co ratio on c5+ selectivity for the ce-promoted and unpromoted cobalt catalysts at p = 15 bar, t= 230 °c and sv= 2, 4, 6 and 8 l/h. gcat.. 4. conclusion in conclusion, the performance of ft synthesis reaction for unpromoted and cepromoted cobalt-based catalysts was investigated based on space velocity and inlet gas feed ratio reaction conditions. the relevant results demonstrated that the addition of ce promoter remarkably enhances the reducibility of cobalt oxides by decreasing the reduction temperature. in addition, ce promoted co-based catalysts show a significant c5+ selectivity and co conversion ascribed to the high reducibility of co that provides huge number of active sites for the reactant species. for both co catalysts, the results exhibited that the reaction properties have strongly affected the catalysts’ activity and products’ selectivity, consequently, improved c5+ selectivity with low water–gas shift reaction activity were observed at high h2/co ratio and low space velocity. thus, ce based co catalyst is considered to be a suitable candidate for use in the gas to liquid conversion process. references [1] hall kr. (2005) a new gas to liquids (gtl) or gas to ethylene (gte) technology. catalysis today, 106(1-4): 243-246. [2] singha rk, shukla a, yadav a, konathala lns, bal r. (2017) effect of metal-support interaction on activity and stability of ni-ceo2 catalyst for partial oxidation of methane. applied catalysis b: environmental, 202: 473-488. 9 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 [3] kim h, jang w, yoo s, shim j, jeon k, na h, lee y, jeon b, bae jw, roh h.(2018) low temperature steam reforming of methane using metal oxide promoted ni-ce0.8zr0.2o2 catalysts in a compact reformer. international journal of hydrogen energy, 43(1): 262-270. [4] shahhosseini hr, saeidi s, najari s, gallucci f. (2017) comparison of conventional and spherical reactor for the industrial auto-thermal reforming of methane to maximize synthesis gas and minimize co2. international journal of hydrogen energy, 42(31): 19798-19809. [5] ma w, jacobs g, pendyala vrr, sparks de, shafer wd, thomas ga, maclennan a, hu y, davis bh. (2018) fischer-tropsch synthesis. effect of kcl contaminant on the performance of iron and cobalt catalysts. catalysis today, 299: 28-36. [6] bao b., el-halwagi m. m., elbashir n. o.(2010) simulation, integration, and economic analysis of gas-to-liquid processes. fuel processing technology, 91(7): 703-713. [7] mousavi s, zamaniyan a, irani m, rashidzadeh m.(2015) generalized kinetic model for iron and cobalt based fischer–tropsch synthesis catalysts: review and model evaluation. applied catalysis a: general, 506: 57-66. [8] zhu c, bollas gm.(2018) gasoline selective fischer-tropsch synthesis in structured bifunctional catalysts. applied catalysis b: environmental, 235: 92-102. [9] guo q, huang j, qian w, zhang h, ma h, ying w. (2018) effect of lanthanum on zr– co/γal2o3 catalysts for fischer–tropsch synthesis. catalysis letters, 148(9): 2789-2798. [10] rahmati m, huang b, schofield lm, fletcher th, woodfield bf, hecker wc, bartholomew ch, argyle md. (2018) effects of ag promotion and preparation method on cobalt fischer-tropsch catalysts supported on silica-modified alumina. journal of catalysis, 362: 118-128. [11] pedersen eø, svenum i-h, blekkan ea.(2018) mn promoted co catalysts for fischertropsch production of light olefins–an experimental and theoretical study. journal of catalysis, 361: 23-32. [12] zeng s, du y, su h, zhang y. (2011) promotion effect of single or mixed rare earths on cobalt-based catalysts for fischer–tropsch synthesis. catalysis communications, 13(1): 6-9. [13] he l, zhang y, fan m.(2015) development of composited rare-earth promoted cobalt-based fischer–tropsch synthesis catalysts with high activity and selectivity. applied catalysis a: general, 505: 276-283. [14] pardo tf., cabrera s, sanchez dm., boutonnet m.(2017) ce-promoted co/al2o3 catalysts for fischer–tropsch synthesis. international journal of hydrogen energy, 42(15): 9754-9765. [15] de lima aep, de oliveira dc. (2017) in situ xanes study of cobalt in co-ce-al catalyst applied to steam reforming of ethanol reaction. catalysis today, 283:104-109. [16] trepanier m, tavasoli a, dalai ak, abatzoglou n.(2009) co, ru and k loadings effects on the activity and selectivity of carbon nanotubes supported cobalt catalyst in fischer–tropsch synthesis. applied catalysis a: general, 353(2): 193-202. [17] jacobs g, ji y, davis bh, cronauer d, kropf aj, marshall cl.(2007) fischer–tropsch synthesis: temperature programmed exafs/xanes investigation of the influence of support type, cobalt loading, and noble metal promoter addition to the reduction behavior of cobalt oxide particles. applied catalysis a: general, 333(2): 177-191. [18] hilmen a, schanke d, holmen a. (1996) tpr study of the mechanism of rhenium promotion of alumina-supported cobalt fischer-tropsch catalysts. catalysis letters, 38(3-4): 143-147. [19] chu w, chernavskii pa, gengembre l, pankina ga, fongarland p, khodakov ay. (2007) cobalt species in promoted cobalt alumina-supported fischer–tropsch catalysts. journal of catalysis, 252(2): 215-230. [20] osa ar, lucas ad, valverde jl, romero a, monteagudo i, coca p, sáncheza p.(2011) influence of alkali promoters on synthetic diesel production over co catalyst. catalysis today, 167(1): 96-106. [21] osa ar, lucas ad, romero a, valverde jl, sáncheza p. (2011) fischer–tropsch diesel production over calcium-promoted co/alumina catalyst: effect of reaction conditions. fuel processing technology, 90(5): 1935-1945. 10 iium engineering journal, vol. 21, no. 2, 2020 al-zuhairi et al. https://doi.org/10.31436/iiumej.v21i2.1150 [22] gnanamani mk, jacobs g, graham um, pendyala vrr, martinelli m, lennan am, hu y, davis bh. (2017) effect of sequence of p and co addition over silica for fischer-tropsch synthesis. applied catalysis a: general, 538: 190-198. [23] dry me.(1999) fischer–tropsch reactions and the environment. applied catalysis a: general, 189(2): 185-190. [24] zhang l, chu h, qu h, zhang q, xu h, cao j, tang z, xuan j. (2018) an investigation of efficient microstructured reactor with monolith co/anodic γ-al2o3/al catalyst in fischertropsch synthesis. international journal of hydrogen energy, 43(6): 3077-3086. [25] pendyala vrr, jacobs g, bertaux c, khalid s, davis bh.(2016) fischer–tropsch synthesis: effect of ammonia on supported cobalt catalysts. journal of catalysis, 337: p. 8090. [26] tristantini d ,lögdberg s, gevert b, borg ø, holmen a. (2007) the effect of synthesis gas composition on the fischer–tropsch synthesis over co/γ-al2o3 and co–re/γ-al2o3 catalysts. fuel processing technology, 88(7): 643-649. [27] xu d, li w, duan h, ge q, xu h. (2005) reaction performance and characterization of co/al2o3 fischer–tropsch catalysts promoted with pt, pd and ru. catalysis letters, 102(34): 229-235. [28] storsæter s, tøtdal b, walmsley jc, tanem bs, holmen a. (2005) characterization of alumina-, silica-, and titania-supported cobalt fischer–tropsch catalysts. journal of catalysis, 236(1): 139-152. [29] visconti cg, ballova z, lietti l, tronconi e, zennaro r, forzatti p. (2010) advances in fischer–tropsch synthesis. catalysts and catalysis, crc press taylor francis group, new york. 11 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <feff004f0076006500200070006f0073007400610076006b00650020006b006f00720069007300740069007400650020006b0061006b006f0020006200690073007400650020007300740076006f00720069006c0069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400650020006b006f006a00690020007300750020007000720069006b006c00610064006e00690020007a006100200070006f0075007a00640061006e00200070007200650067006c006500640020006900200069007300700069007300200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e006100740061002e0020005300740076006f00720065006e0069002000500044004600200064006f006b0075006d0065006e007400690020006d006f006700750020007300650020006f00740076006f007200690074006900200075002000700072006f006700720061006d0069006d00610020004100630072006f00620061007400200069002000410064006f00620065002000520065006100640065007200200036002e0030002000690020006e006f00760069006a0069006d0020007600650072007a0069006a0061006d0061002e> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <feff004200720075006b00200064006900730073006500200069006e006e007300740069006c006c0069006e00670065006e0065002000740069006c002000e50020006f0070007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740065007200200073006f006d002000650072002000650067006e0065007400200066006f00720020007000e5006c006900740065006c006900670020007600690073006e0069006e00670020006f00670020007500740073006b007200690066007400200061007600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020005000440046002d0064006f006b0075006d0065006e00740065006e00650020006b0061006e002000e50070006e00650073002000690020004100630072006f00620061007400200065006c006c00650072002000410064006f00620065002000520065006100640065007200200036002e003000200065006c006c00650072002e> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <feff0041006e007600e4006e00640020006400650020006800e4007200200069006e0073007400e4006c006c006e0069006e006700610072006e00610020006f006d002000640075002000760069006c006c00200073006b006100700061002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400200073006f006d00200070006100730073006100720020006600f60072002000740069006c006c006600f60072006c00690074006c006900670020007600690073006e0069006e00670020006f006300680020007500740073006b007200690066007400650072002000610076002000610066006600e4007200730064006f006b0075006d0065006e0074002e002000200053006b006100700061006400650020005000440046002d0064006f006b0075006d0065006e00740020006b0061006e002000f600700070006e00610073002000690020004100630072006f0062006100740020006f00630068002000410064006f00620065002000520065006100640065007200200036002e00300020006f00630068002000730065006e006100720065002e> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 effect of spinning parameters on pla/ppc/curcumin microfiber diameter: an investigation via response surface methodology sharifah imihezri syed shaharuddin1*, amirul akmal fauzan1, mohamad faris izzudin mohamad jazi1, nur atiqah mohd. akhir1, maizatulnisa othman1, nor khairushima muhamad khairussaleh1, norhashimah shaffiar1 and zaimah hasan2 1 department of manufacturing and materials engineering, kulliyyah of engineering international islamic university malaysia, gombak, malaysia 2mechanical engineering department, college of engineering, universiti tenaga nasional, kajang, malaysia . *corresponding author: shaimihezri@iium.edu.my (received: 16th january 2020; accepted: 4th march 2020; published on-line: 4th july 2020) abstract: the initial phase of this study was to investigate the effect of polypropylene carbonate (ppc) additions in polylactic acid (pla)/curcumin (cur) blends. it was observed that the presence of curcumin particulates behaved as a reinforcement filler for ppc additions up to 30 wt%. a specific composition was then invested to find the correlation between the fiber diameter and melt-spinning process parameters using central composite design (ccd), a subset of response surface methodology (rsm). results showed that the spinning temperature had a greater effect than the spinning speed on the diameter of pla/ppc/curcumin fiber. the response model indicated a good correlation between experimental and predicted values since the anova analysis demonstrated high fvalue of model adequacy at 10.34, non-significant lack of fit, precision adequacy of 9.94 and r2 value of 0.80. therefore, this model can be used in a future study to establish the processing parameters for controlled fiber production. abstrak: fasa awal kajian ini adalah bagi mengkaji kesan penambahan karbonat polipropilin ke dalam campuran asid prolaktik (pla)/kurkumin (cur). didapati kehadiran zarah-zarah kurkumin bertindak sebagai pengisi bantuan pada penambahan ppc sehingga 30 wt%. komposisi tertentu kemudian dikaji bagi mencari kaitan diameter fiber dan parameter proses putaran-cair menggunakan rekaan komposit utama (ccd), dan subset metodologi gerak-balas permukaan (rsm). keputusan menunjukkan suhu putaran berpengaruh besar berbanding kelajuan putaran pada diameter fiber pla/ppc/kurkumin. model yang bertindak balas ini menunjukkan kaitan yang baik antara eksperimen dan nilai yang dijangka kerana analisis anova menunjukkan nilai-f yang tinggi pada 10.34 kecukupan model, tidak-ketara kurang padanan, kecukupan ketepatan pada 9.94 dan nilai r2 sebanyak 0.80. oleh itu, model ini boleh digunakan pada kajian akan datang bagi menghasilkan parameter proses pengeluaran fiber kawalan. keywords: poly(lactic acid); curcumin; poly(propylene carbonate); fiber; rsm 197 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 1. introduction poly(lactic acid) (pla) biopolymer has been extensively studied for biomedical applications due to its high mechanical strength and modulus [1]. pla can be used with non-toxic and non-carcinogenic effects in the human body [2,3] since its by-products such as lactic acid and its short oligomers, h2o and co2, are internally metabolized. however, brittleness has been one of its main drawbacks since it limits the flexibility of the polymer [4]. the physical properties of pla can be attuned for specific applications by blending (solvent or melt blending techniques) [5] with biodegradable polymers such as polypropylene carbonate (ppc) [6]. ppc is produced through a copolymerization process of co2/propylene oxide (po) [7]. the resulting copolymer chains are comprised of homopolymer propylene oxide and alternating carbon dioxide and propylene segments [8]. despite the similar chemical structure between pla and ppc [9]., ning et al. [10] and ma et al. [11] studies on pla/ppc blends suggested that the two polymers are partially miscible when mixed. curcumin, a naturally active compound derived from turmeric (curcuma longa), is well known for its antibacterial, antitumor, and antioxidant properties [12-14]. antimicrobial agent derived from natural sources does not display typical side effects as observed for synthetically produced chemicals [15]. in-vivo and in-vitro studies revealed that curcumin promotes bioactivities by inducing cell apoptosis, inhibiting cell proliferation, anti-cell adhesion and motility, and imparting anti-microbe properties [16]. pla membranes loaded with curcumin (1-5 wt %) have been previously reported [17.18]. the incorporation of bioactive particulates into polymer fiber, however, affects the strength of the fiber with increasing particulate content [19]. thus, one of the greatest challenges in manufacturing these novel therapeutic-eluting fibers lies in attaining considerable drug amounts and therapeutic properties without compensating the suture’s mechanical and release kinetic properties. response surface methodology is prevalently used to develop a mathematical loworder polynomial expression by approximating physical experimental data [20]. one of the main advantages of rsm is the ability to establish a true relationship between the dependent variable or response (y) and a range of independent variables (x). rsm also gives a low standard of error and thus has been considered as a reliable optimization tool [21]. previously, rsm has been employed in an abundant number of works to study the correlation between process/materials and fiber properties that were produced via the melt spinning process [22,23] as well as the electrospinning process [20,24,25].. this study was spurred by our previous success in the melt-spinning of pla/curcumin microfiber [26]. however, the addition of curcumin filler into pla resulted in a more viscous blend and the resultant melt-spun fibers were also found to be brittle and lack the desired flexibility. thus, this study aims to address the brittle issue of pla/curcumin by adding plasticizer such as ppc. the resultant polymer blends were characterized via tensile test. a specific composition with reasonable strength and modulus was then selected to investigate the interactive effects of the melt spinning process parameters (spinning speed and spinning temperature) on the fiber diameter using rsm. this work provides a processing route for mass production of biodegradable fibers containing therapeutic agents that can potentially be used for suture, ligament reconstruction, and in self-reinforced composite [27,28]. 198 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 2. methodology 2.1 materials preparation pla (ingeotm biopolymer 3052d) from natureworks (usa), ppc (qpac 40) from empower materials (malaysia) and curcumin (pahang pharmacy sdn. bhd., malaysia) were dissolved in chloroform (r&m chemicals, united kingdom). before the solvent blending process, both pla and ppc pellets were dried at 70°c and 40°c respectively for 2 hours in an oven. the pla/curcumin/ppc blends at different weight % ratios as shown in table 1 were dissolved in chloroform at a ratio of 1:10 and stirred for 1 hour at room temperature. the completely dissolved mixture was then poured into a tray. the polymer blend solutions were reduced into thin films once the chloroform has fully evaporated. table 1: composition of pla/curcumin/ppc used in this study. code ratio (wt.%) pla curcumin ppc pla_cur_ppc 10 89 1 10 pla_cur_ppc 20 79 1 20 pla_cur_ppc 30 69 1 30 pla_cur_ppc 40 59 1 40 pla_cur_ppc 50 49 1 50 2.2 tensile test thin films were cut according to the astm d882 dimension of 50 mm x 10 mm x 0.80 mm with an extra 10 mm at both ends for clamping purposes. the tests were performed using a shimadzu universal tensile machine (ags-10k nxd) at a crosshead speed of 20 min/mm and a load cell of 5kn. the average and standard deviation of tensile strength, modulus and percent elongation were calculated from the load-elongation curve based on 5 samples. 2.2 mutivariate design of experiment before determining the design space, the range of available spinning speed as well as the temperature range for continuous fiber spinning was determined. the in-house built mini fiber drawing tower has the capacity to spin fiber from 250 to 390 rpm. preliminary experimental works showed that the intended composition can be successfully drawn/spun within a melt viscosity region corresponding to 160 °c – 173 °c. in this study, central composite design (ccd) which is a subset of rsm was used to develop the regression model. the model represents the response of fiber diameter (y) for two design factors or independent variables represented by x1, spinning temperature and x2, spinning speed. the total number of runs suggested by ccd was based upon the following equation: n= 2k + 2k + n0 (eq. 1) where 2k = represents the two-level factorial points, k= axial points located at “± k” from the centre points of experimental domain n0 = central point replicates. the 2k (axial points) is used during screening and readability for variance of model prediction and the n0 (central points) is very crucial to obtain an independent estimate of the 199 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 design experimental error [29]. the design factors or independent variables (in this study, k=2 for spinning temperature and spinning speed) were considered at two levels; low (-) and high (+) as shown in table 2. therefore, the total number of proposed experiments is 13 based on: 2k (22 = 4: factorial points) + 2k (2x2 = 4 axial points) + 5 (n0 = 5 replications). fig. 1 shows the schematic of the experimental design. the ccd design matrices in coded/uncoded values for the design of experiment are listed in table 3. the anova analysis and statistical values were determined using design expert software (version 6.0.8). table 2: ccd coded and uncoded values of the input variables for the experimental design codes levels variables lowest 2 low -1 center 0 high 1 highest 2 (x1) spinning temperature (°c) 157 160 166.5 173 176 (x2) spinning speed (rpm) 221 250 320 390 419 fig. 1: schematic diagram of central composite design (ccd) with 22 factorial design based on x1(spinning temperature) and x2 (spinning speed) variables. table 3: ccd design matrices in coded and uncoded values for the design of experiment of melt spinning process. run no. design factor in coded value design factor in uncoded value x1 x2 spinning temperature (°c) spinning speed (rpm) 1 0 2 166.5 221 2 1 1 173 390 3 -1 1 160 390 4 -1 -1 160 250 5 2 0 176 320 6 2 0 157 320 7 0 0 166.5 320 8 0 2 166.5 419 9 0 0 166.5 320 10 0 0 166.5 320 11 0 0 166.5 320 12 0 0 166.5 320 13 1 -1 173 250 200 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 2.3 melt-drawn spinning setup the fibers from pla_cur_ppc 30 were spun via an in-house built melt spinning process as shown in the schematic representation in fig. 2. in this process, the crushed thin film was melted above the melting temperature for extrusion through a circular shaped orifice at the nozzle and then stretched into monofilament fiber by the speed of the take-up rotating wheel. the fibers were rapidly cooled by the ambient air as they emerged from the nozzle. the melt spinning process used is also known as vertical spinning since no mechanical means such as extruder is used to force the flow through the nozzle. instead, the polymer moves simply by the force of gravity. fig. 2: schematic representing the melt spinning experimental setup. 2.3 fiber morphology the diameter of pla_cur_ppc 30 fibers was measured via optical microscope (bx41m) (olympus microscopes, uk). the diameter was taken as an average of 20 different fibers for each composition. the resulting fiber physical structure was then observed via scanning electron microscope (sem) (jeol, jsm-it 100; japan) with 200x magnifications at 10 kv. all fibers were prepared by sputter coating with palladium using polaron sc7620. 3. results and discussion 3.1 tensile test the amount of filler particulates significantly affects the ease of processing and quality of the fibers obtained [26]. in this study, the amount of curcumin was limited to only 1 wt% since previous studies [26,30] had shown that increasing the curcumin content corresponds with a further decrease in strength. the tensile test was performed to determine the effect of ppc on pla/curcumin blend. in this study, it can be seen from fig. 3 that the strength was maintained as ppc was incorporated up to 30 wt %. however, previous studies have shown that there was an immediate decrease in strength and modulus when ppc was incrementally added into neat pla [9,31,32]. thus, it is postulated that the observed strength retention was attributed to the presence of curcumin particulate that had behaved as a reinforcing filler [33,34]. ppc also has an inherently lower tensile strength in comparison to pla [35]. thus, further 201 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 additions of ppc (>30 wt%) are believed to have weakened the intermolecular strength of the polymer blend which subsequently cancelled the curcumin reinforcement effect [11,31]. a comparison between fig. 4 and fig. 5 revealed that the elongation % trend is inversely proportional to young’s modulus trend. it is also observed that at 30 wt% ppc, reversal trend occurred for both modulus and elongation. other than the contribution of young’s modulus of each constitutive polymer in the blend, other factors may have contributed to the observed modulus and elongation trend such as phase morphology and selective localisation [11]. in most cases, the major constituent in the polymer blend will form the continuous phase whilst the minor constituent will form as scattered spherical droplets [36]. sem studies on binary pla/ppc system [37,38] revealed that at 30 wt% ppc addition, the blend resembles typical sea-island morphology in which the pla phases coalesce together and surround the ppc droplets. at 50 wt% ppc, the existing sea-island morphology is transformed into co-continuous morphology. consequently, the ppc phase progressed from droplets into elongated and interconnected structures. particulates or fillers added into the polymeric blend may be dispersed at the phase interphase or in either phase of the multi-component blend. studies have shown that during mixing, particulates behave in a manner of selective localization whereby the particulates prefer to move and reside in the polymer phase that has sufficiently low viscosity [39,40]. such selective localization tendency induces better particulate dispersion and has been observed in various systems of filler/matrix composites [42,42]. fig. 3: tensile strength properties of pla/curcumin/ppc blends. fig. 4: young’s modulus properties of pla/curcumin/ppc blends. fig. 5: elongation at break properties of pla/curcumin/ppc blends. thus, it is proposed that the parallel increase of young’s modulus with the increasing amount of ppc (inversely proportional effect on elongation %) up to 30 wt% ppc, encourages better curcumin dispersion in the ppc phase since it is less viscous than pla. the presence of these particulates impedes the slippage movement of ppc molecular chains. a study by ning et al. [10] on pla/ppc/carbon black (cb) particulate blend also revealed 202 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 that greater particle dispersion was achieved in the ppc phase. at 40 wt% ppc, the size of the ppc droplets further increases [38] and the modulus drops drastically by 85% whilst the elongation % increased tremendously by 400%. further additions of ppc at 50 wt% decrease the elongation % of the blend. a similar drop in elongation % was also observed by gao et al. [37]. hence, it is proposed that the localization of curcumin particles in the cocontinuous phase has contributed to the decrease in elongation %. in this work, pla_cur_ppc 30 was selected as a case study for rsm due to its reasonably high strength and modulus properties. 3.2 anova analysis and response model fabrication of biopolymer fiber via the melt spinning process offers a simple, efficient and economical approach since solvent-free monofilament fiber can be manufactured at a fairly high rate [43,44]. theoretically, the region of melt viscosity suitable for most polymer processing such as extrusion and melt spinning varies from 102 pa s to 105 pa s [44]. the obtained responses (fiber diameter) for the ccd design matrices are tabulated in table 4. table 4: design factors in coded and uncoded values and their responses. run no. design factor in coded value design factor in uncoded value response x1 x2 spinning temperature (°c) spinning speed (rpm) average fiber diameter (μm) 1 0 2 166.5 221 26.2 2 1 1 173 390 28.7 3 -1 1 160 390 14.7 4 -1 -1 160 250 28.5 5 2 0 176 320 36.7 6 2 0 157 320 30.4 7 0 0 166.5 320 25.6 8 0 2 166.5 419 21.1 9 0 0 166.5 320 23.5 10 0 0 166.5 320 26.3 11 0 0 166.5 320 27.9 12 0 0 166.5 320 28.4 13 1 -1 173 250 39.4 the initial anova analysis for the design factors for pla_cur_ppc 30 is shown in table 5. the constructed response model was evaluated for its suitability to represent the experimental data based on the following criteria; model adequacy, lack-of-fit test, precision adequacy, and r2 value. the p-value statistically represents the significance measures of each design factor or parameter in explaining the variability for the response model. the parameter is considered to have an adequate or significant effect if its p-value is lower than 0.05 (p<0.05 degree of confidence limit). the f-value for ‘model adequacy’ of 6.20 implies that the response model is significant and there is only a 1.65% chance that a “model f-value” this large could occur due to noise. the result also shows that the f-values for both terms (spinning temperature x1 and spinning speed x2) was significantly effective on the response trend with probability values of nearly 99%. the quadratic terms (x1²) were also significantly effective with a probability of more than 96%. however, the quadratic term, x2² and cross-product term x1x2 were greater than the significance level of p = 0.05 and thus have no significant impact on 203 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 the response trend. the p-value for the lack-of-fit test was not significant at 0.06 (p > 0.05), hence it was deduced that the model was able to satisfactorily fit the data. the signal-tonoise ratio or “adequacy precision” for the response model indicates an adequate signal at 9.032 since a value greater than 4 is highly desirable. table 5: initial analysis of variance based on two design factors (spinning temperature, spinning speed) for the melt spinning process of pla_cur_ppc 30 the initial fitted second-order equation for the response and design factors is as follows: y= 26.34+ 4.23x1 – 3.96x2 + 3.41x1² 1.54x2² + 0.78x1x2 (eq. 2) where y is the average fiber diameter, and x1 and x2 respectively represent the coded terms for spinning temperature and spinning speed. both negative and positive signs respectively represent antagonistic effect and synergistic effect. the insignificant terms of x2² and crossproduct term x₁x₂, were removed and anova analysis was performed for the second time, yielding the results shown in table 6. table 6: reduced analysis of variance based on two design factors (spinning temperature, spinning speed) for the melt spinning process of pla_cur_ppc 30. the reduced fitted second-order equation for the response and design factors is as follows: y’= 25.27+ 4.23x1 – 3.96x2 + 3.61x1² (eq. 3) the f-value for ‘model adequacy’ in y’ increases to 10.34, with a 0.28% chance that the f-value obtained may occur due to noise. the ‘lack-of-fit” value was not significant at 0.08 (p>0.05) and the adequacy precision is 9.941. the increase of p-values for the reduced model, y’ for ‘lack-of-fit and the increase of adequate precision respectively means that the model is now better fitted and has a higher signal-to-noise ratio. the correlation coefficient, r2 is a criterion that is obtained from the fitted linear plot for a set of predicted values versus observed values and is used to evaluate the ability of the model to predict the result. the value of r2 for the final response model in this study statistically indicates that the model source f value p value temperature: x1 11.66 0.0112 speed: x2 10.25 0.0150 x1² 6.60 0.0370 x2² 1.34 0.2844 x₁x₂ 0.20 0.6713 model adequacy 6.20 0.0165 lack of fit 6.15 0.0559 adequate precision (ratio>4) = 9.032 r2 = 0.8157 source f value p value temperature: x1 12.28 0.0067 speed: x2 10.81 0.0094 x1² 7.94 0.0201 model adequacy 10.34 0.0028 lack of fit 4.68 0.0801 adequate precision (ratio>4) = 9.941 r2 = 0.7752 204 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 can explain reasonably well up to approximately 80% of the variation in the fiber diameter due to the two design factors. the f-value associated with the x1 term (spinning temperature) is higher than the x₂ term (spinning speed) and thus comparatively has a more significant effect on the response model (fiber diameter). kong et al. [45] had also observed the pronounced effect of temperature on fiber diameter since it directly influences the physiochemical properties (melt viscosity, surface tension) of the polymer blend. on its own, ppc lacks the viscous flow necessary to produce continuous fiber due to its terminal chain of hydroxyl groups [46]. thus, the addition of ppc is expected to lower the melt viscosity of the pla/curcumin blend in this study [10]. hypothetically, it was anticipated that the fabrication of nano-sized fibers of this composition may be slightly difficult since polymer melts are more viscous [45] in the order of one magnitude in comparison to the viscosity of polymer solutions [47]. fig. 6 depicts an approximately linear probability plot and thus supports the condition that the error terms were distributed normally. the plot of predicted results against observed results is shown in fig. 7. it can be seen from the graph that there is a satisfactory correlation between the diameter of the fiber with spinning temperature and spinning speed. fig. 8 visualizes the contoured plot of the predicted mean fiber diameter due to the effect of spinning temperature and spinning speed. the propitious condition for fiber fabrication via melt spinning process dictates that both the gravitational force and elongation force provided by the spinning speed must be able to overcome the combined forces exerted by viscosity and surface tension [48]. it can be seen that at any given spinning temperature, the fiber diameter decreases with increasing spinning speed due to the increasing elongation stress. it was also observed that at any constant spinning speed, the diameter of the fiber progressively increases with increasing temperature. in general, the increase in spinning temperature lowers the surface tension. as a result, the cohesive forces between the molecules to resist the increasingly fluidic polymer flow from the gravitational force and elongation force decrease. eventually, more volume of the polymer is drawn which leads to an increase in the fiber diameter. a similar correlation effect between spinning temperature and fiber diameter was also observed by ko et al. [48]. the contour plot suggests that the optimum range of temperature and speed to draw thin microfiber occur within the spinning temperature region of 160-163 oc and 285 rpm340 rpm respectively. fig. 6: studentized residuals and normal percentage probability plot for the melt spinning of pla_cur_ppc 30 fibers. fig. 7: plot of observed values versus the predicted values obtained from the reduced fitted regression line obtained for 205 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 the melt spinning of pla_cur_ppc 30 fibers. fig. 8: contour plot in the design space for y’ (fiber diameter) with respect to x1 (spinning temperature) and x2 (spinning speed) for pla_cur_ppc 30 fiber. fig. 9. plot of standard error of design in the design space for y’ (fiber diameter) with respect to x1 (spinning temperature) and x2 (spinning speed) for pla_cur_ppc 30 fiber. fig. 9 represents the standard error estimation based on several numbers of observations made at the centre point (0,0) (aslan, 2007) of the two-factor ccd approach. if the number of observations/replicates at the centre point is too high, then the farther points from the centre will yield a rapid increase in standard error estimations (clark & williges, 1973). on the contrary, if the number of replicates is too low at the centre point, this would yield a reversing effect in which the error estimation would be greater at the centre compared to other data points. having a constant error contour throughout the design space is highly desirable as this would justify that the error estimate calculated at the centre point is a good representative of the error estimate throughout the design space. it can be observed from fig. 9 that the error estimation is not the same throughout the experimental domain. the standard error is reasonably uniform over a large design space near the centre and the error contours slowly increase as the data points reach the design space boundaries which suggest that the response model may not deliver accurate predictions for diameter governed by extreme values of the design space. 3.3 fiber morphology the fiber diameter measured using optical microscope revealed that they averaged between 15 to 40 microns (see fig. 10). fig. 11 shows the fiber bundle from each test run observed via sem. it was also noted that there was irregular formation of bead-like structure on the lateral surface of the fiber as shown in fig. 12. it is postulated that such surface condition occurred due to the partial dispersion of curcumin particles in the pla/ppc blend. a similar textured or bead-like surface effect was also obtained for melt-spun fibers from the polypropylene/soy particle blend [51] and the polypropylene/talc blend [52]. contrary to the perception that such textured surface is undesirable, this bead-like surface is actually a unique feature because it imitates the tactile feel of the irregular cross-section and highly crenulated structure of natural fibers such as those found in cotton [51]. 206 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 fig. 10: sem images (200x) of pla_cur_ppc 30 fiber spun at each ccd design matrice. fig. 11: images of randomly taken fiber diameter measured via optical microscope for pla_cur_ppc 30 fiber. 207 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 fig. 12: sem image showing the irregular formation of bead-like structure on the lateral surface of the fiber. 4. conclusion this study revealed that the substantial inclusion of ppc up to 30 wt % into pla/curcumin blends did not result in appreciable change in strength due to the reinforcement effect of curcumin. the modulus values increased due to favourable dispersion of curcumin in the less viscous ppc, which aids in constraining the polymer chain movement. however, further additions of the more flexible ppc at 40 wt% were accompanied by an increasing toughness and vice versa effect in strength and modulus. pla_cur_ppc 30 was then identified for further study via rsm. it was concluded from the response model that spinning temperature had a more dominant effect on the fiber diameter in comparison to spinning speed due to its direct influence on the surface tension and melt viscosity. the response model also indicated a good correlation between experimental and predicted values based on all the criteria defined in this study. acknowledgements this work was fully supported by international islamic university malaysia, iium (rigs17-052-0627). the authors would like to express their deepest gratitude to facilities and technical assistance provided by international institute for halal research and training (inhart), iium. references [1] lyu s, untereker d. (2009) degradability of polymers for implantable biomedical devices. int. j. mol. sci., 9:4033-4065. [2] xiaon l, wang b, yang g, gauthier m. (2011) poly(lactic acid)-based biomaterials: synthesis, modification and applications. biomedical science, engineering and technology, intech, croatia. [3] casalini t, rossi f, castrovinci a, perale g.(2019) a perspective on polylactic acid-based polymers use for nanoparticles synthesis and application. front. bioeng. biotechnol., 7:1-16. [4] liu l, wei h, wang z, li q, tian n. (2018) simultaneous enhancement of strength and toughness of pla induced by miscibility variation with pva. polymers, 10(10):1178. [5] saini p, arora m, kumar mr. (2016) poly(lactic acid) blends in biomedical applications. adv. drug deliv., 107: 47-59. 208 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 [6] qin sx, yua cx, chen xy, zhoua hp, zhao lf (2018) fully biodegradable poly(lactic acid)/poly(propylene carbonate) shape memory materials with low recovery temperature based on in situ compatibilization by dicumyl peroxide. chinese j ploym sci., 36:783-790. [7] gao l, huang m, wu q, wan x, chen x, wei x, yang w, deng r, wang l, feng j. (2019) enhanced poly(propylene carbonate) with thermoplastic networks: a cross-linking role of maleic anhydride oligomer in co2/po copolymerization. polymers., 11:1467-1479. [8] wang s, huang y, liao b, lin g, cong g, chen l. (1997) structure and properties of poly(propylene carbonate). int j polym ch. 3(2):131-143. [9] yao m, deng h, ma f, wang k, zhang q, chen f, fu q. (2011) modification of poly(lactic acid)/poly(propylene carbonate) blends through melt compounding with maleic anhydride. polym lett, 5(11):937-949. [10] ning w, xingxiang z, jiugao y, jianming f. (2008) partially miscible poly(lactic acid)blend-poly(propylene carbonate) flled with carbon black as conductive polymer composite. polym int., 57:1027–1035. [11] ma x, yu j, wang n. (2006) compatibility characterization of poly(lactic acid)/poly(propylene carbonate) blends. j polym sci phys., 44(1):94-101. [12] aggarwal b, sung b. (2009) pharmacological basis for the role of curcumin in chronic diseases: an age-old spice with modern targets. trends pharmacol sci., 30(2):85-94 [13] prasad s, tyagi ak, aggarwal bb. (2014) recent developments in delivery, bioavailability, absorption and metabolism of curcumin: the golden pigment from golden spice. cancer res treat., 46(1):2-18. [14] ramalingam n, natarajan ts, rajiv s. (2015) preparation and characterization of electrospun curcumin loaded poly(2-hydroxyethyl methacrylate) nanofiber--a biomaterial for multidrug resistant organisms. j. biomed. mater. res. part a, 103(1):16-24. [15] morais ds, guedes rm and lopes ma. (2016) antimicrobial approaches for textiles: from research to market. materials, 9(6):498. [16] xia f, chun z, dong-bo l, jun y, hua-ping l. (2013) the clinical applications of curcumin: current state and the future. curr. pharm. des., 19(11):2011-2031. [17] yan c, jie l, yuqin w, yanna f, hongbo w, weidong g. (2012) preparation and blood compatibility of electrospun pla/curcumin composite membranes. fiber polym., 13(10):1254-1258. [18] chen y, lin j, fei y, wang h, gao w (2010) preparation and characterization of electrospinning pla/curcumin composite membranes. fiber polym., 11(8):1128-1131. [19] weldon cb, tsui jh, shankarappa sa, nguyen vt, ma m, anderson dg, kohane ds. (2012) electrospun drug-eluting sutures for local anesthesia. j control release, 161:903-909. [20] yördem os, papila m, mencelog˘lu y. (2008) effects of electrospinning parameters on polyacrylonitrile nanofiber diameter: an investigation by response surface methodology. mater design, 29:34-44. [21] mohamed oa, masood sh, bhowmik jl. (2015) optimization of fused deposition modeling process parameters: a review of current research and future prospects. adv manuf., 3(1):4253. [22] ghoreishian sm, fereydooni a, nasser s, asadolahi t, beigpour n, ghoreishian m. (2017) optimization of melt-spinning parameters of poly(ethylene terephthalate) partially oriented multi-filament yarn in an industrial scale: central composite design approach. fiber polym., 18:1280-1287. [23] garnier l, duquesne s, casetta m, lewandowski m, bourbigot s (2010) melt spinning of silane–water cross-linked polyethylene–octene through a reactive extrusion process. react funct polym., 70(10):775-783. 209 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 [24] shu ying g, jie r. (2005) process optimization and empirical modeling for electrospun poly(d,l-lactide) fibers using response surface methodology. macromol mater eng., 290 (11):1097-1105. [25] dhura b, saraswathy n, maheswaran r, sethupathi p, vanitha p, vigneshwaran s, rameshbabu v. (2013) electrospinning of curcumin loaded chitosan/poly (lactic acid) nanofilm and evaluation of its medicinal characteristics. front mater sci., 7(4):350–361. [26] sharifah iss, qairol aab, noor azlina h, nor khairusshima mk (2017) thermal, structural and mechanical properties of melt drawn curloaded poly(lactic acid) fibers. procedia eng., 184:544-551. [27] yuan x, mak af, kwok kw, yung bk, yao k. (2001) characterization of poly(l-lactic acid) fibers produced by melt spinning. j app polym sci., 81:251-260. [28] pawar rp, tekale su, shisodia su, totre jt, domb aj (2014) biomedical applications of poly(lactic acid). recent pat regen med., 4:40-51. [29] behera sk, meena h, chakraborty s, meikap bc. (2018) application of response surface methodology (rsm) for optimization of leaching parameters for ash reduction from lowgrade coal. int. j. min. sci. technol., 28 (4):621-629. [30] shah saa, imran m, lian q, shehzad fk, athir n, zhang j, cheng j. (2018) curcumin incorporated polyurethane urea elastomers with tunable thermomechanical properties. react funct polym., 128:97-103. [31] yu c, zhao r, wang h. (2018) mechanical property of pla/ppc blends. int j trend res dev., 5(2):206-208. [32] liu h, zhang j. (2011) research progress in toughening modification of poly(lactic acid). j polym sci pol phys., 49:1051-1083. [33] liu y, cai y, jiang x, wu j, le x. (2015) molecular interactions, characterization and antimicrobial activity of curcumin-chitosan. food hydrocoll., 52:564-572. [34] kim dk, kim ji, sim br, khang g. (2017) bioengineered porous composite curcumin/silk scaffolds for cartilage regeneration. mater sci eng c., 78:571-578. [35] muthuraj r, mekonnen t. (2018) recent progress in carbon dioxide (co2) as feedstock for sustainable materials development: co-polymers and polymer blends. polymer, 145:348-373. [36] deng y, yu c, wongwiwattana p, thomas nl. (2018) optimising ductility of poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends through co-continuous phase morphology. j polym environ., 26:3802-3816. [37] gao j, bai h, zhang q, gao y, chen l, fu q. (2012) effect of homopolymer poly(vinyl acetate) on compatibility and mechanical properties of poly(propylene carbonate)/poly(lactic acid) blends. polym lett., 11:860–870. [38] haneef inhm, shaffiar nm, buys yf, hamid m, shaharuddin sis. (2018) morphologies and mechanical properties of polylactic acid / polypropylene carbonate (pla/ppc) blends by solvent casting method. in proceedings of the international conference biotechnology engineering : september 19-20, kuala lumpur. [39] mofokeng j, luyt a. (2015) morphology and thermal degradation studies of melt-mixed poly(lactic acid) (pla)/poly(ε-caprolactone) (pcl) biodegradable polymer blend nanocomposites with tio2 as filler. polym test, 45:93-100. [40] nocke a, wolf m. (2012) nanoparticle-based resistors and conductors in bio and nano packaging techniques for electron devices: advances in electronic device packaging. springer-verlag, berlin. [41] kim sy, noh yj, yu j. (2015) thermal conductivity of graphene nanoplatelets filled composites fabricated by solvent-free processing for the excellent filler dispersion and a theoretical approach for the composites containing the geometrized fillers. compos part a appl sci manuf., 69:219-225. 210 iium engineering journal, vol. 21, no. 2, 2020 sharifah et al. https://doi.org/10.31436/iiumej.v21i2.1336 [42] wu d, zhang y, zhang m, yu w. (2009) selective localization of multiwalled carbon nanotubes in poly(ε-caprolactone)/polylactide blend. biomacromolecules, 10:417-424. [43] asmatulu r, khan ws. (2019) synthesis and applications of electrospun nanofibers. elsevier, amsterdam. [44] vlachopoulos j, strutt d. (2003) the role of rheology in polymer extrusion. in proceedings of the extrusion minitec and conference: from basics to recent developments: 26th october 2004, du¨sseldorf; pp 107–132. [45] kong c, jo k, jo hknk. (2009) effects of the spin line temperature profile and melt index of poly(propylene) on melt-electrospinning. polym eng sci., 49(2):391-396. [46] m. niaounakis (2015) biopolymers: applications and trends, elsevier, oxford. [47] nayak r, padhye r, kyratzis il, truong yb, arnold l. (2013) effect of viscosity and electrical ccnductivity on the morphology and fiber diameter in melt electrospinning of polypropylene. text res., 83(6):606-617. [48] ko j, jun s, lee jk, lee pc, jun mb. (2015) effects of molecular weight and temperature on fiber diameter of poly(ε-caprolactone) melt electrospun fiber. j. korean soc manuf technol eng., 24(2):160-165. [49] aslan n. application of response surface methodology and central composite rotatable design for modeling the influence of some operating variables of a multi-gravity separator for coal cleaning. fuel, 86(5-6):769-776. [50] clark c, williges rc. (1973) response surface methodology central-composite design modifications for human performance research. human factor, 15(4):295-310. [51] guzdemir o, ogale aa. (2019) influence of spinning temperature and filler content on the properties of melt-spun soy flour/polypropylene fibers. fibers, 7(10):83-101. [52] tascan m, nohut s. (2016) melt-spun talc-filled polypropylene fibers and yarns with higher thermal shock resistance. text res j., 87(1):31-45. 211 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <feff0633062a062e062f0645002006470630064700200627064406250639062f0627062f0627062a002006440625064606340627062100200648062b062706260642002000410064006f006200650020005000440046002006450646062706330628062900200644063906310636002006480637062806270639062900200648062b06270626064200200627064406230639064506270644002e00200020064a06450643064600200641062a062d00200648062b0627062606420020005000440046002006270644062a064a0020062a0645002006250646063406270626064706270020062806270633062a062e062f062706450020004100630072006f00620061007400200648002000410064006f00620065002000520065006100640065007200200036002e00300020064806450627002006280639062f0647002e> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <feff0054006f0074006f0020006e006100730074006100760065006e00ed00200070006f0075017e0069006a007400650020006b0020007600790074007600e101590065006e00ed00200064006f006b0075006d0065006e0074016f002000410064006f006200650020005000440046002000760068006f0064006e00fd006300680020006b0065002000730070006f006c00650068006c0069007600e9006d0075002000700072006f0068006c00ed017e0065006e00ed002000610020007400690073006b00750020006f006200630068006f0064006e00ed0063006800200064006f006b0075006d0065006e0074016f002e002000200056007900740076006f01590065006e00e900200064006f006b0075006d0065006e0074007900200050004400460020006c007a00650020006f007400650076015900ed007400200076002000610070006c0069006b0061006300ed006300680020004100630072006f006200610074002000610020004100630072006f006200610074002000520065006100640065007200200036002e0030002000610020006e006f0076011b006a016100ed00630068002e> /dan <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> /deu <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> /esp <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> /eti <feff004b00610073007500740061006700650020006e0065006900640020007300e400740074006500690064002c0020006500740020006c0075007500610020005000440046002d0064006f006b0075006d0065006e00740065002c0020006d0069007300200073006f00620069007600610064002000e4007200690064006f006b0075006d0065006e00740069006400650020007500730061006c006400750073007600e400e4007200730065006b0073002000760061006100740061006d006900730065006b00730020006a00610020007000720069006e00740069006d006900730065006b0073002e00200020004c006f006f0064007500640020005000440046002d0064006f006b0075006d0065006e0074006500200073006100610062002000610076006100640061002000760061006900640020004100630072006f0062006100740020006a0061002000410064006f00620065002000520065006100640065007200200036002e00300020006a00610020007500750065006d006100740065002000760065007200730069006f006f006e00690064006500670061002e> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <feff004e006100750064006f006b0069007400650020016100690075006f007300200070006100720061006d006500740072007500730020006e006f0072011700640061006d0069002000730075006b0075007200740069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c002000740069006e006b0061006d0075007300200076006500720073006c006f00200064006f006b0075006d0065006e00740061006d00730020006b006f006b0079006200690161006b006100690020007000650072017e0069016b007201170074006900200069007200200073007000610075007300640069006e00740069002e002000530075006b00750072007400750073002000500044004600200064006f006b0075006d0065006e007400750073002000670061006c0069006d006100200061007400690064006100720079007400690020007300750020004100630072006f006200610074002000690072002000410064006f00620065002000520065006100640065007200200036002e00300020006200650069002000760117006c00650073006e0117006d00690073002000760065007200730069006a006f006d00690073002e> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <feff004200720075006b00200064006900730073006500200069006e006e007300740069006c006c0069006e00670065006e0065002000740069006c002000e50020006f0070007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740065007200200073006f006d002000650072002000650067006e0065007400200066006f00720020007000e5006c006900740065006c006900670020007600690073006e0069006e00670020006f00670020007500740073006b007200690066007400200061007600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020005000440046002d0064006f006b0075006d0065006e00740065006e00650020006b0061006e002000e50070006e00650073002000690020004100630072006f00620061007400200065006c006c00650072002000410064006f00620065002000520065006100640065007200200036002e003000200065006c006c00650072002e> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 107-665-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 saeid and chia 57 investigation of thermal performance of air to water heat exchanger using nanofluids nawaf h. saeid and tan heng chia department of mechanical, materials & manufacturing engineering, the university of nottingham malaysia campus, jalan broga, 43500 semenyih, selangor, malaysia. nawaf.saeid@nottingham.edu.my abstract: in the present study the three-dimensional numerical simulation is selected as a tool to investigate the effectiveness of a cross flow heat exchanger. water is selected to be mixed with nano-particles and flow inside a circular pipe while a pure air is flowing across it. numerical simulations is carried out under laminar flow for both water and air sides. the thickness of the pipe is neglected in the present preliminary study. from the physics of the problem, the governing parameters can be determined as: the reynolds, the type and the volume fraction of the nono-fluid. the effect of these governing parameters is studied and the results are presented. the results show significant enhancement of heat transfer with introduction of nano-particles, such as titanium-oxide (tio2) nano-powder, compared to the pure base fluid. the accuracy of the results presented in the present study depends on the accuracy of the effective properties of the nano-fluids, which are taken from the open literature. abstrak:dalam kajian ini, simulasi tiga dimensi berangka digunakan untuk mengkaji keberkesanan penukar haba aliran silang. air dipilih untuk dicampurkan dengan zarah bersaiz nano dan dialirkan di dalam paip berbentuk bulat, sementara udara tulen mengalir melaluinya. simulasi berangka dijalankan di bawah aliran lamina untuk kedua-dua belah air dan udara. ketebalan paip diabaikan di dalam kajian permulaan ini. dari sudut permasalahan fizik, parameter pengawal imbang boleh ditentukan sebagai: nombor reynolds, jenis dan isipadu pecahan bendalir nano. kesan parameter pengawal imbang ini dikaji dan keputusannya dibentangkan. keputusan menunjukkan peningkatan pemindahan haba yang ketara dengan penggunaan zarah bersaiz nano seperti serbuk titanium oksida (tio2), berbanding dengan bendalir tulen. ketepatan keputusan kajian ini bergantung kepada ketepatan sifat-sifat efektif bendalir nano yang dirujuk daripada sumber maklumat terdahulu. keywords:heat exchanger; nanofluids; effective thermal properties 1. introduction it is well known that metals in solid form have thermal conductivities that are higher than fluids. for example, thermal conductivity of copper at room temperature is about 700 times greater than that of water. even oxides such as alumina (al2o3), titanium oxide (tio2) which are good insulators compared to metals have high thermal conductivities compared to water [1]. conventionally, when heat transfer fluids do not have the capacity to cool the mechanical iium engineering journal, special issue, mechanical engineering, 2011 saeid and chia 58 machinery fast enough, an alternative is to use a metallic solid with several times the heat transfer capacity of the base fluid as a heat dissipating medium. in conventional cases, the suspended particles are of micrometer or even millimeter dimensions. this can give higher heat transfer rates, compared with common base fluids, but the large suspended particles in the fluid present problems such as sedimentation of particles, erosion of channel walls, fouling and increased pressure drop in the flow channel [2]. therefore, fluids with large suspended particles have little practical application in enhancing heat heat transfer process. in comparison, nano-particles submerged in fluids (termed nanofluids) are more desirable because of their considerably smaller size, better stability and rheological properties, and higher thermal conductivities compared with microfluids, and there is no penalty in pressure drop [3]. besides that, nanofluids are also very stable and have no additional problems, such as sedimentation, erosion, additional pressure drop and non-newtonian behaviour due to tiny size of nanoelements and low volume fraction of nanoelements required. investigations on adding nano-particles to the base fluid to enhance heat transfer have been carried out by many researchers [4-10] either experimentally or by numerical simulation. in these studies, they concluded that nanoparticles can remarkably enhance the thermal performance of base fluids by about 20-30%. the present paper is considering the numerical simulation investigation of the thermal performance of the air to water heat exchanger in cross flow using nanofluids. 2. mathematical model the mathematical model in the present study is using single phase model with the assumption that the nanofluid is single and continuous fluid phase. parameters such as density, thermal capability, thermal conductivity and viscosity are varied in single phase flow. the governing equations are: conservation of mass (continuity equation) 0         z w y v x u (1) conservation of momentum (navier-stokes equation)                                2 2 2 2 2 2 z u y u x u dx dp z u w y u v x u u nfnf (2)                                2 2 2 2 2 2 z v y v x v dy dp z v w y v v x v u nfnf (3)                                2 2 2 2 2 2 z w y w x w dz dp z w w y w v x w u nfnf (4) conservation of energy                                2 2 2 2 2 2 z t y t x t k z t w y t v x t uc nfpnfnf (5) where u,v, w (m.s-1) are the velocity components in the x,y and z direction respectively, ρnf (kg.m-3) is density of nanofluid, µnf (kg.m-1.s-1) is the viscosity of nanofluid, p (n.m-2) is iium engineering journal, special issue, mechanical engineering, 2011 saeid and chia 59 the pressure, t (k) is temperature, knf (w.m-1.k-1) is the thermal conductivity of nanofluid, and cpnf (j.kg-1.k-1) is the heat capacity of nanofluid.the properties of the nanofluid are calculated using the following equation:   sfnf  1 (6)   pspfpnf ccc  1 (7) where the subscripts f and s stands for fluid and soild respectively. for effective thermal conductivity, there are few conventional equationssuch as hamilton-crosser [4] maxwell [4]. for viscosity, there are also some conventional equations such as einstein’s [5], brickman [5]. he et al [7] derived the following equations for viscosity and thermal conductivity, which are adopted in the present study. nanofluid thermal conductivity:   fnf kk 182.462.125 2  (8) nanofluid viscosity:   fnf  162.421.199 2 (9) where  is in percentage of volume fraction = volume of the nano-particles/total volume, ௣௙is the heat capacity of baseܥ ,௦is the density of nanoparticleߩ ,௙is the density of base fluidߩ fluid, ܥ௣௦is the heat capacity of nanoparticle, ݇௙ is the thermal conductivity of base fluid, ߤ௙is the viscosity of base fluid. the properties of the nanofluid components used in the present study are given in table 1 [4][11]. table 1: properties of the tio2nano particles [4][11]. properties air water tio2 particles density, ρ (kg.m-3) 1.03 997.746 4850 specific heat capacity, cp (j.kg -1.k-1) 1009 4180.2 544.25 thermal conductivity, k (w.m-1.k-1) 0.0241 0.60192 7.44 dynamic viscosity, ߤ (kg.m-1.s-1) 1.94 x 10-5 0.96172 x 10-3 3. numerical method and validation tests the solution domain is considered as two regions. the inner region is the horizontal pipe with negligible thickness. the pipe is subjected to an external cross flow in a duct, which represnts the outer region. the nanofluid is flowing inside the pipe and a pure air is flowing in the duct across the pipe. the air duct is meshed by splitting the total volume into 3 volumes as shown in fig. 1. air duct is meshed using element of hex/wedge with copper type. for the pipe, boundary layer mesh is produced with the setting of first row at 0.01mm, growth factor = 1.1, rows =15 with 96 mesh edge at θ direction and 28 mesh edge at radial direction. the iium engineering journal, special issue, mechanical engineering, 2011 saeid and chia 60 face is then mesh using tri element with pave type. this is to ensure that the mesh spacing gradually increase from wall to centre of pipe. specific continuums are created for both volumes of air and water. fig. 1: mesh geometry for internal and external domains. dimensions (air duct = 100mm×30mm×300mm; pipe radius =5mm and length =300mm) fluent 6.3 [12] is used as a tool for numerical solution of the governing equations based on finite-volume method. the governing equations were discretized using quick scheme for convection-diffusion formulations with simplec velocity-pressure coupling algorithm. convergence is satisfied with a minimum residual of 10-5. initial temperature for water is set to 293 k and for air it is set to 323k. initial velocity for both cross flow and normal flow is calculated from the desired re. in all the following simulations the reynolds number for the internal and external flows is based on the pipe diameter and has the same value which is selected to be in the laminar flow regime. to test the present numerical method, the results are compared with the results of the pure water flow in pipes and external air flow across the pipe. the performance of the cross flow heat exchanger is evaluated based on the calculation of the nusselt number, which is defined as: nfk hd nu  (10) where d is the diameter of the pipe, knf is the thermal conductivity of the nanofluid and h is the local heat transfer coefficient calculated from  avww ttqh  where qw is the heat flux at the wall of the pipe, tw is the wall temperature and tavis the average temperature across tube diameter. the comparison of the variation of nusselt number along the pipe with different references at re= 900 is shown in fig. 2a for pure water flow. for the air flow across the pipe, fig. 2b shows the comparison of mean nu around the cylinder surface with naca [13] experiment result with re= 38900. in this case a turbulence model is needed since the reynolds number is high. the k-kl-ω turbulence model [12] is used to generate the results depicted in fig. 2b. iium engineering journal, special issue, mechanical engineering, 2011 saeid and chia 61 (a) (b) fig. 2: (a) variation of nu along the pipe with re= 900 for pure water [7][8], (b) comparison of mean nu around the cylinder surface with naca [11] experiment result with re= 38900. in fig. 2(a), it can be seen that the trend of simulated results with re=900 is almost same as the experiment result, he et al. [7] simulation and shah’s equation [8]. the present simulation results for pure water show that the nusselt number at the end of the pipe is 5.43. the difference in the values of nu between the present results and the experimental result is about 7.7%. this difference in nu at outlet of the pipe is about 6.63 compared with he et al [7] simulation results. therefore, it can be conclude that the simulation is validated. the results presented in fig. 2(b) show the accuracy of the present numerical method to predict the mean nusselt number around the surface of the cylinder in cross flow situation compared with naca [13] experimental results. 4. results and discussion parametric study is carried out by varying reynolds number of the water in the range 500,1000, 1500 and 2000 and nano-fluid volume fraction in the range of  = 0.6%, 1.5%, 3%, 6% and 10%. figures 3(a) and 3(b) show the nusselt number record highest increment at the inlet due to large temperature difference and gradually decrease and come to a constant at the fully developed region. furthermore, from fig 3(a), heat transfer coefficient increases as reynolds number increase with a constant volume fraction of tio2 0.6%. on the other hand, heat transfer also increase as volume fraction of tio2 increases at constant reynolds number re=1000 as shown in fig 3(b). the increment of volume fraction from 0.6%-1.5% has recorded enhancement of nusselt number at about 6.5%. this happens because thermal conductivity of the nanofluid is increased from 0.62205 (w.m-1.k-1) to 0.66452 (w.m-1.k-1) as volume fraction increase. 4 6 8 10 12 14 16 0 50 100 150 200 250 n us se lt n um be r z/d,m experiment result shah equation result he simulation result present simulation result 0 50 100 150 200 250 0 20 40 60 80 100 120 140 160 180 n u m ea n θ o naca experimental result present simulation result iium engineering journal, special issue, mechanical engineering, 2011 saeid and chia 62 (a) (b) fig. 3: nusselt number variation along the pipe with (a) different reynolds numbers, (b) different volume fractions of tio2 nano-fluid at re=1000. figure 4(a) shows that the nusselt number increases as the reynolds number increases. the value of nusselt number is about 139.515 at re = 2000 which is about 49% higher than that at re = 500. this is due to the separation happens at about 120o for re = 500 and it happens at about 98o as reynolds number increases to re = 2000. the results presented in fig. 4(b), shows that the nusselt number increases as volume fraction of nano-fluid tio2 increase. the nusselt number for each volume fraction comes to a minimum value at angle of about 108°due to separation of the flow. beyond this angle to 180°, the values of the nusselt number show slight increment. hence, most of the heat transfer is occur between 0-100°. (a) (b) fig. 4: nusselt number variation at mid-span of cylinder with (a) tio2 of volume fraction 0.6% flow at different reynolds numbers, (b) different volume fractions of tio2 nano-fluid at with re=1000. finally, the isotherms for both inner and outer regions are shown in fig. 5. these results are generated for laminar cross flow of hot air over a pipe of nano-fluid (0.6% tio2 – water) flow with re = 1000. the inlet conditions are as follows: inlet water temperature 295k, inlet z/d 0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 25 30 n u re=500 re=1000 re=1500 re=2000 z/d 0 20 40 60 80 100 120 0 5 10 15 20 25 30 n u z/d,m tio2-0.6% tio2-1.5% tio2-3% tio2-6% tio2-10% water 0 20 40 60 80 100 120 140 160 0 50 100 150 200 n u ss e lt n u m b e r ɵ° re=1000 re=500 re=1500 re=2000 re=500 re=1500re=1000 re=500 0 20 40 60 80 100 120 140 160 180 0 50 100 150 200 n u ss el t n u m b er ɵ° water tio2 -0.6% tio2 -1.5% tio2 -3% tio2 -6% tio2 -10% iium engineering journal, special issue, mechanical engineering, 2011 saeid and chia 63 water velocity 0.0974 m/s, inlet air temperature 323k, inlet air velocity 1.8835 m/s. the isotherms for the internal pipe flow show the increase of the water temperature as the hot air flow over the pipe. on the external air side the isotherms which indicate the separation point are shown at inlet, outlet, and mid-span across the pipe. fig. 5: isotherms for inner and outer regions at re = 1000 for 0.6% tio2 water nanofluid. 5. conclusions the present simulation results show that the convective heat transfer process can be significantly improved by introducing nano-particles such as tio2 in base fluid. the present simulation results show the enhancement in the convection heat transfer by either increase the reynolds number or the nano-particles volume fraction. however, higher volume fraction will cause higher wall shear stress which may need more energy to pump the nano-fluid in the cylindrical pipe and also may cause abrasion of the cylinder wall which causes corrosion, scaling, and clogging of the pipe. the accuracy of the present results depends on the accuracy of the effective properties of the nano-fluids, which are taken from the open literature. references [1] s. lee, s. li, s. choi “measuring thermal conductivity of fluids containing oxide nanoparticles“. asme j. heat transfer, vol. 121, 280-289, 1999. [2] v. trisaksri and s. wongsies “critical review of heat transfer characteristics of nanofluids“. renewable and sustainable energy review, vol. 11, 512-523, 2007. [3] w. daungthongsuk and s. wongwises “a critical review of convective heat transfer of nanofluids“. renewable and sustainable energy review, vol. 11, 797-817, 2007. [4] y. xuan and q. li “heat transfer enhancement of nanofluids“. int. j. heat fluid flow, vol. 21, 58-64, 2000. [5] c.t.nguyen, g.roy, c. gauthier, n. galanis “heat transfer enhancement using al2o3-water nanofluid for an electronic liquid cooling system“. applied thermal enginnering, vol. 27, 15011506, 2007. iium engineering journal, special issue, mechanical engineering, 2011 saeid and chia 64 [6] d.s. wen and y.l. ding “experiment investigation into convective heat transfer of nanofluids at the entrance region under laminar flow conditions“. int. j. heat and mass transfer, vol. 47, 5281-5288, 2004. [7] y. he, y. men,y. zhao, h. lu, y. ding “numerical investigation into the convective heat transfer of tio2 nanofluids flowing through a straight tube under the laminar conditions“. applied thermal engineering, vol. 29,1965-1972, 2009. [8] r.k. shah “thermal entry length solutions for the circular tube and parallel plates”. in: proceedings of the 3rd national heat and mass transfer conference, indian institute of technology, bombay, i (paper hmt-11-75), 1975. [9] c.t.nguyen,f.des, n.galanis, g. roy, t. mare, s. boucher, h.a.mintsa, “viscosity data for al2o3water nanofluidhysteresis: is the heat transfer enhancement using nanofluids reliable?“. international journal of thermal sciences vol. 47, 103-111, 2008. [10] z.w.ding,s.c.cheah,n. h.saeid, “parametric study of heat transfer enhancement using nanofluids“. proceedings of icee 2009 3rd international conference on energy and environment, 7-8 december 2009, malacca, malaysia, pp. 348-352, 2009. [11] f.p. incropera, and d.p. dewitt, “fundamentals of heat and mass transfer“, 6th edition, wiley.(2006). [12] fluent 6.0 documentation. [13] e.schmidt and k.venner “heat transfer over the circumference of a heated cylinder in transverse flow“. techical memorandum no 1050, naca, 1941. microsoft word 209-818-2-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology nur aimi et al. 83 effect of rhizopus oryzae fermentation on kenaf-based polylactic acid’s monomer nur aimi mohd nasir 1 , mohd adlan mustafa kamalbahrin 1 , nurhafizah seeni mohamed 1 , hazleen anuar 1 , maizirwan mel 2 , and rashidi othman 3 1 department of manufacturing and materials engineering, 2 department of biotechnology engineering, faculty of engineering, 3 faculty of architecture and environmental design, international islamic university malaysia. hazleen@iium.edu.my; maizirwan@iium.edu.my; rashidi@iium.edu.my abstract: kenaf biomass is the potential as raw materials used to produce polylactic acid’s monomer which is lactic acid via fermentation by rhizopus oryzae. kenaf biomass’ structure is complex due to its lignin and cellulose content. this matter had encouraged it to undergo pretreatment process as the initial step before fermentation process can be done. in this paper, kenaf biomass was treated with dilute sulphuric acid (h2so4) to hydrolyze the cellulose content in it as well as to convert the cellulose into glucosea carbon source for rhizopus to grow. then, the fermentation process was carried out in shake flask for 3 days at ph 6. several conditions for fermentation process had been chosen which were 25 o c at 150 rpm, 25 o c at 200 rpm, 37 o c at 150 rpm and 37 o c at 200 rpm. in this fermentation process, 0.471 g/l, 0.428 g/l, 0.444 g/l and 0.38 g/l of lactic acid was produced respectively. sample at 25 o c at 200 rpm produced maximum amount of lactic acid compared to others. abstrak: biojisim kenaf berpotensi sebagai bahan mentah dalam penghasilan monomer asid polylactic (poliester alifatik termoplastik diterbitkan daripada sumber boleh diperbaharu seperti kanji jagung) yang merupakan asid laktik menerusi penapaian oleh rhizopus oryzae (sejenis fungus yang hidup dalam jirim organik yang telah mati). struktur biojisim kenaf adalah kompleks disebabkan kandungan lignin dan selulosanya. hal ini menyebabkan ia perlu melalui proses pra-rawatan sebagai langkah awal sebelum proses penapaian dijalankan. dalam kertas ini, biojirim kenaf dirawat dengan asid sulfurik (h2so4) yang dicairkan untuk menghidrolisis kandungan selulosa di dalamnya di samping menukar selulosa menjadi glukosa – sumber karbon bagi tumbesaran rhizopus. kemudian, proses penapaian dijalankan di dalam kelalang goncang selama 3 hari pada ph 6. beberapa ciri proses penapaian telah dipilih iaitu 25 o c pada 150 rpm, 25 o c pada 200 rpm, 37 o c pada 150 rpm dan 37 o c pada 200 rpm. dalam proses penapaian ini, 0.471 g/l, 0.428 g/l, 0.444 g/l dan 0.38 g/l asid laktik dihasilkan secara berturut. sampel pada 25 o c pada 200 rpm menghasilkan kadar asid laktik yang maksimum dibandingkan dengan yang lainnya. keywords: kenaf biomass; pre-treatment; lactic acid; rhizopus oryzae; fermentation 1. introduction the environmental pollutions and global warming caused by the petroleum polymer and the variation price of oil had encouraged several researchers to find solution to the iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology nur aimi et al. 84 issue. polylactic acid has the answer. polylactic acid (pla) derived from its monomer which is lactic acid (la). lactic acid (iupac systematic name: 2-hydroxy propanoic acid) is a biochemical value added product which has a remarkable applications in industries. industrial development has significantly increased interest in lactic acid. there are two ways to produce lactic acid, which are chemical synthesis and biological fermentation. the chemical synthesis method was found to be not economical because of the expensive used of petrochemical. in contrast, the biological fermentation offer the low cost of substrate and low energy consumption as well as low energy consumption [1, 2]. lactic acid bacteria or aerobic microorganisms are commonly used in industry because of its high growth and high product yield which involved complex substrate and product recovery. in contrary, rhizopus oryzae fungus can overcome the problems in bacterial fermentation [3]. rhizopus can produce pure l (+)-lactic acid from complex carbohydrates from agriculture plant and biomass with a simple substrate. it is an anaerobic microorganism which needs oxygen to grow and indirectly produce lactic acid. because of that, several factors of fermentation must be considered such as incomplete substrate, temperature and agitation speed. commercially, lactic acid is via biological fermentation is derived from food sources such as beet sugar, potato, corn and barley malt [4, 5]. however, these sources are not economical especially for a long term. it has to compete with the food value which results to the expensive prices. these sources also were not sustainable and green technology. on the basis of these reasons, many researchers are looking forward for a new source that is renewable, sustainable and cheap is important. kenaf (hibiscus cannabinus l) could be candidate of choices because of its inexpensive crop, warm season annual fibre, herbaceous plant and widely available for its renewable carbon sources. it has wide application especially for its bast. in this paper, we are using kenaf biomass which was basically an agro residues obtained from the processing of kenaf fibre in order to separate core and bast. kenaf is a lignocellulosic material which contains high lignin (15-23 %) and high cellulose (3757%) composition. this is similar to its biomass which has a complex structure results the difficultness of the microorganism to degrade it. thus, it has to undergo pre-treatment process to remove or modify cellulose into fermentable carbon sources. there are many types of pre-treatment which had been investigated by several researchers for more than decades such as chemical pre-treatment [6, 7]. in earlier work, we studied the best solvent used for the pre-treatment process [6]. it was reported that dilute sulphuric acid (h2so4) hydrolysis provide highest glucose conversion for kenaf biomass under optimum condition. sufficient glucose, oxygen requirements and condition’s temperature are the crucial factor for rhizopus oryzae to be a promising lactic acid producer. thus, in this paper, the influence of temperature and agitation speed for the fermentation process via kenaf biomass based glucose by rhizopus oryzae was studied. 2. materials and methodology 2.1 kenaf biomass and its pre-treatment process kenaf natural fibre industry sdn bhd, kelantan, malaysia was one of the factories supplied kenaf biomass for this research. previously, 2 g, 3 g and 4 g of kenaf biomass were added in dilute sulphuric acid (h2so4) solution and conducted in a temperature 140 o c, 160 o c and 180 o c for 10 min, 35 min and 60 min respectively [6]. the experiment for this hydrolysis process was designed using design expert software 6.08. anuar et al. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology nur aimi et al. 85 reported that the optimum glucose attained when the mass of biomass is 2 g at 60 min and 180 o c. in this study, we are trying to use such condition to produce better yield of lactic acid. several replicates of pre-treated kenaf biomass which are at the mass of 2 g in 60 min and 180 min were prepared. 2.2 microorganism and medium rhizopus oryzae was isolated originally from the bread and grown in potato dextrose agar (pda) and stored at 37 o c for 2 days. the fermentation medium used was potato dextrose broth (pdb) which consists of potato starch (4 g/l) and dextrose (20 g/l). the medium was autoclaved at 121 o c for 30 min. glucose obtain from pre-treatment process was autoclaved separately and then added to 20 ml sterile pdb. the initial ph of the media in the shake flask was adjusted to ph 6 by adding sodium hydroxide (naoh). 2.3 lactic acid production via fermentation in this study, the fermentation process was done in a shake flask. initially, it begin with the collection of the growth spores of rhizopus oryzae using l-loop by extracting it with distilled water and added it into 250ml erlemenyer shake flask. next, the mixture of the sterilized medium and hydrolyzed glucose were added into it and was then incubated for 3 days. in order to yield maximum lactic acid via rhizopus oryzae, the influence temperature and oxygen transfer rate which is agitation speed were chosen. for fermentation design, the statistica 7 software two levels full factorial design was chosen. the experimental design consists of 4 runs. an average of three replicates for each experiment was conducted. the experimental design can be illustrated in table 1. after fermentation, the obtained of lactic acid was analyzed using high pressure liquid chromatography (hplc) agilent 1101. table 1: experimental design with two varied conditions. run 1 to 4 temperature ( o c) 25 and 37 speed (rpm) 150 to 200 3. results and discussion 3.1 effect of kenaf biomass on lactic acid production statistical analysis was done for the fermentation to be run in the varied temperature and agitation speed. temperature between 25 o c and 37 o c were chosen in order to compare the growth of rhizopus oryzae between the room temperature and human body temperature. note that, rhizopus oryzae can grow in a temperature range between 25 o c to 45 o c [8]. the temperature of 45 o c had not been chosen since it is beyond the growth temperature of rhizopus. rhizopus will die during that time. the growth of rhizopus was then aided with the agitation speeds which were between 150 rpm and 200 rpm to show whether agitation speed will influence the production of lactic acid or not. all data recorded were analyzed and plotted on the graph after three (3) days of fermentation in shake flask. during fermentation process, glucose consumption was analyzed since glucose is the carbon substrate for lactic acid production. as for that, in this study, glucose content from pdb was added with hydrolyzed glucose from kenaf biomass to give more carbon substrate to rhizopus to produce lactic acid. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology nur aimi et al. 86 fig. 2: lactic acid analysis. figure 2 shows the rate of lactic acid production during fermentation period. in this graph, sample at 25 o c in 200 rpm produced the highest concentration of lactic acid which is 0.471 g/l at the end of its production. whereas for the sample at 25 o c in 150 rpm and sample at 37 o c in 150 rpm , the values of lactic acid concentration are 0.428 g/l and 0.444 g/l respectively. lactic acid produced at 37 o c in 200 rpm results the lowest concentration compared to the other sample. it was 0.38 g/l during that condition in 72 hours of fermentation process. fig. 3: interaction between temperature and speed with production of lactic acid obtain from statistica 7 software. as illustrated in fig. 3, when the agitation speed is increased and the temperature is lower, the production of lactic acid is increased. at 25 o c, rhizopus cell tend to grow faster with the aid of faster agitation speed which is at 200 rpm. even though the cell grows faster in 25 o c, the cell will not growth effectively in the low agitation speed condition which is at 150 rpm. this could be due low agitation speed will not enhance the growth of rhizopus to produce lactic acid. for fermentation process at 37 o c, the rhizopus oryzae tend to grow smoothly but at the same time, some of it may died, thus produced low concentration of lactic acid. this matter was enhanced by the agitation speed of process, iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology nur aimi et al. 87 where the faster the speed of agitation, the lower the lactic acid produced at high temperature which is at 37 o c. naranong and poochareon claimed that the values of specific growth rate increased with increasing the agitation rate demonstrating that growth was dependent on oxygen supply. as in the case of agitation rate 200 rpm production, yield of llactic acid was higher than those obtained at the agitation rate of 150 rpm. this was due to the medium homogeneity and higher transfer rates of substrate and oxygen resulting from more thorough mixing [9]. in addition, an increase in agitation rate also increased oxygen supply in the medium which promoted not only rhizopus growth but also lactic acid production. 4. conclusion remarks in this paper, we found that rhizopus oryzae has the capability to produce lactic acid using kenaf biomass as the raw materials. the production of lactic acid is influenced by temperature and agitation speed of shake flask. the highest lactic acid production is sample which produced at 25 o c in 200 rpm. further investigation will be required to produce maximum lactic acid especially for industrial usage. acknowledgement this work was supported by comstech-twas grant. thank to the staff of department of biotechnology engineering and department of manufacturing and materials engineering, iium as a whole. references [1] zhang, z.y., jin bo., and joan m. k. 2007. mini review: production of lactic acid from renewable materials by rhizopus fungi. biochemical engineering journal 35: 251–263 [2] pandey, a., soccol c.r. rodrigues-leon j., and nigam. p. 2001. solid fermentation in biotechnology: fundamental and applications, asiatech publishers new delhi [3] thongchul. n (2005). lactic acid production by immobilized rhizopus oryzae in rotating fibrous bed bioreactor.(doctoral dissertation, the ohio state university) [4] narayanan.n., roychoudhury. p.k., and srivastava .a. 2004. l(+) lactic acid fermentation and its product polymerization. electronic journal of biotechnology, vol.7 no.2. retrieved from http://www.ejbiotechnology.cl/index.php/ejbiotechnology/article/view/v7n2-7/520 [5] maas. r.h.w., bakker .r. r, mickel.j. l. a., visser .d, jong. e.d., gerrit. e. and ruud.a.w. 2008. lactic acid production from lime-treated wheat straw by bacillus coagulans: neutralization of acid by fed-batch addition of alkaline substrate, appl microbiol biotechnol 78:751–758 [6] anuar, h., mel, m. and seeni mohamed.n. 2010. sugar hydrolysis of kenaf fibre for utilization in lactic acid production. patent no. : pi 2010005191 [7] kumar, p., barret. d.m., delwiche, m.j., stroeve,p. (2009). methods of pretreatment lignocellulosic biomass for efficient hydrolysis and biofuels production. ind.eng.chem res article asap . doi: 10.1021/ie801542g. [8] sparringa. r.a., kendall.m.,westby.a., and owens j.d. 2002. effect of of temperature, ph, water activity and co2 concentration on growth of rhizopus oligosporus nrrl 2710. journal of applied microbiology, 92, 329–337 [9] naranong. n and poochareon.d. 2001. production of l-lactic acid from raw cassava starch by rhizopus oryzae nrrl 395. kasetsart j. (nat. sci.) 35 : 164 170 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 numerical study of argon effect on nitrogen separation from air by pressure swing adsorption abdulbasit hassan mahdi1, suhaib shwish salih1*, heba sa’ady ayuob1, and tushar ghosh2 1tikrit university, college of engineering, department of chemical engineering, salahaldin, iraq. 2 department of nuclear science & engineering institute, university of missouri-columbia, missouri, united states. *corresponding author: sss43b@mail.missouri.edu (received: 19th june 2019; accepted: 30th september 2019; published on-line: 20th january 2020) abstract: a mathematical model was used to design four modes of two-bed pressure swing adsorption (psa) process to investigate argon presence in the feed mixture. the effect of operating parameters such as cycle time, pressure equalization, adsorption pressure, and purging flow rate was investigated. the model was validated with experimental data of nitrogen separation from the air by a single bed adsorber on carbon molecular sieve (cms). a good agreement with experimental data is obtained. in the psa process, higher purity of nitrogen (99.7%) was detected by mode 4 when the feed mixture was free of argon (o2: 21%, n2:79%). while the nitrogen purity was only 98.0% in the state of argon presence in the feed mixture (o2: 21%, n2: 78%, ar: 1%). the results showed that the cycle time had insignificant effect whereas the pressure equalization and purging at low vacuum pressure had a significant effect on the process performance. abstrak: model matematik digunakan bagi membina empat mod terdiri daripada tekanan dua-turus proses penyerapan buai (psa) bagi menyiasat kehadiran argon dalam campuran pakan. kesan parameter beroperasi seperti masa kitaran, penyamaan tekanan, tekanan penyerapan, dan kadar aliran penyingkiran disiasat. model matematik tersebut disiasat melalui data eksperimen pemisahan nitrogen dari udara melalui penyerapan turus tunggal pada penapis molekular karbon (cms). data eksperimen yang bagus diperoleh. dalam proses psa, mod keempat menghasilkan ketulenan nitrogen (99.7%) lebih tinggi apabila campuran pakan bebas argon (o2: 21%, n2:79%). sementara itu, ketulenan nitrogen hanya 98.0% apabila terdapat kehadiran argon dalam campuran pakan (o2: 21%, n2: 78%, ar: 1%). kajian menunjukkan masa kitaran memberi kesan tidak signifikan sementara penyamaan tekanan dan penyingkiran pada tekanan vakum rendah mempunyai kesan signifikan terhadap prestasi proses. keywords: nitrogen separation; psa; argon; model simulation 1. introduction gaseous nitrogen is used extensively in many industries such as vessel inerting applications, electronics, metals, and food industries due to its inert properties [1]. a variety of separation processes are used to produce commercial nitrogen such as cryogenic distillation, adsorption separation, and membrane separation processes. psa is one of the most important process in the field of gas separation [2-4]. a carbon molecular sieve 1 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 (cms) is used as an adsorbent for nitrogen separation from air due to the difference in the kinetic adsorption of oxygen and nitrogen [5-7]. since oxygen is faster than nitrogen to diffuse into the cms, a kinetic selectivity is created, which allows reaching nitrogen purities as high as 99.999%. the demand for high nitrogen purity, over 99%, in a low and medium amount in the industrial sector has urged a lot of companies to produce nitrogen from atmospheric air by psa process [8]. zeolite x-type and perovskite-type ceramic were used as adsorbents instead of the cms sieve for nitrogen separation from air at high pressure [9-12]. in the last decades, the psa process was investigated experimentally and theoretically in many studies [13,14]. for instance, a simple linear driving force (ldf) model was created to simulate a single bed psa process for nitrogen separation from the air on cms. the feed mixture was assumed to be (o2: 21%, and n2:79%) [15]. the effect of bed length and pressurizing rate on the single bed psa performance was studied carefully. the higher performance of the process was observed with a bed length over 1.3 m. the effect of the adsorption/desorption rate constants of oxygen on the nitrogen separation was evaluated through a simulation process and found that the purity varied significantly with cycle time [8,16]. operating parameters such as feed flow, purge flow, cycle time, adsorption pressure, and bed length on the psa process performance was studied experimentally and theoretically [17]. higher purity of nitrogen was observed at short adsorption time. no significant effect of adsorption pressure over 4 bar on the process performance was observed. about 97.6% of nitrogen purity was detected using atmospheric air as a feed [2,3]. the purity was improved from 96% to over 99% by adding a deoxo reactor to the psa process. the feed mixture only consisted of oxygen and nitrogen [18]. many previous studies assume that the feed mixture only consists of o2 and n2, but real air consists of argon as well. so, the main objective of this study is to investigate the effect of argon presence in the feed mixture and operating parameters on the nitrogen purity. a mathematical model is introduced to study the nitrogen separation from the air by single bed adsorber on a cms sieve. then, it is employed to design four configurations of the two-bed psa process to deeply investigate the process and compare the four modes. 2. modeling and simulation a theoretical study is employed to investigate the nitrogen separation from atmospheric air by psa process. the numerical study was applied to the following processes: a) single bed adsorber to study the breakthrough time. b) two-bed psa process with the four different configurations as shown in table 4. the first design of the psa process is represented by the skarstrom cycle, which involved four steps: pressurizing, producing, depressurizing, and purging steps. different modifiers are added such as purging by vacuum pump, pressure equalization, and product pressurizing, to improve the performance of the psa process. the numerical study of the psa process was carried out using a simulation program. finite difference method (fdm) is employed, and axial dimension is discretized into 50 nodes. the purity of oxygen or nitrogen is used as an indication of the process performance. the following assumptions are considered in the numerical study: 1feed mixture assumed to be (o2:21%, n2:78%, ar:1%, and o2:21%,n2:79%). 2 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 2ideal gas law is applied. 3isothermal system. 4the flow pattern is described by the axial dispersion plug flow model. 5radial concentration is neglected. 6mass transfer transport is described by a linear driving force (ldf). 7 adsorption equilibrium is fitted with the langmuir equation. 8pressure drop along the bed is represented by the darcy equation. overall mass balance: component (i) mass balance: boundary conditions of each step of the psa process are presented in table 1. the boundary conditions of well-known danckwerts are applied [19]. the adsorption isotherm and adsorption rate parameters of n2, o2, and ar on cms are presented in table 2. the operating parameters of the single bed adsorber are presented in table 3. the operation parameters of other modes of psa process are presented in table 4. table 1: applied boundary conditions in the simulation process. cycle step concentration ( ) velocity (u) pressurizing (pre) ( |z=0=u(ci|z=0ci|z=0+) ( |z=l=0 u|z=0 = ufeed u|z=l= 0 adsorption (ads) ( |z=0=u(ci|z=0ci|z=0+) ( |z=l=0 u|z=0 = ufeed depressureequalization (depequ) ( |z=0=0 ( |z=l=0 u|z=0 = 0 depressurizing (dep) ( |z=0=0 ( |z=l=0 u|z=l= 0 purging (pur) ( |z=l=u(ci|z=l+ ci|z=l-) -dl( |z=0=0 u|z=l= upurge pressure-equalization (preequ) ( |z=0=u(ci|z=0ci|z=0+) ( |z=l=0 u|z=0=0 initial conditions: (z, 0) = ; (z, 0) = ideal gas law: 3 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 the adsorption rate is described by the ldf equation with concentration-dependent diffusivity: where: the ldf coefficient has been estimated from the fitting between the mathematical model and experimental data of single bed adsorber from the literature survey. the predicted values are presented in table 2. the adsorption isotherm for multi-components (oxygen, nitrogen, and argon) are predicted by the langmuir equation to the n-component mixture: where: table 2: adsorption equilibrium and adsorption rate parameter [20]. parameters o2 n2 ar k1*10 3(mol/g) 5.817 × 10-3 1.130 × 10-2 9.556 × 10-3 k2*10 5(mol/g) -7.512 × 10-6 -2.80 × 10-5 -2.101 × 10-5 k3*10 5(1/kpa) 7.984 × 10-6 30.89 × 10-5 6.566 × 10-5 k4 (k) 1444 359.7 773.8 ( ) 0.248 0.001 0.0071 darcy’s equation used to predict pressure drop: where : u is the superficial gas velocity. table 3: adsorbent and common parameters were used in the single bed process. adsorbent cms type pellet pellet density (kg/m3) 800 bed voidage (ε) 0.30 adsorption bed length (m) 1 diameter (m) 0.0254 ambient temperature (oc) 25 adsorption pressure (bar) 7 product flow rate (liter/min) 1 4 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 the performance of the psa process is indicated by the purity and recovery of nitrogen according to the following equations: table 4: operated conditions of the four modes of the psa process. the psa modes pressure (bar) product flowrate (liter/min) purge flowrate (liter/min) vacuum purging (bar) cycle step time (sec) 2-bed 4-step (mode 1) 2-9 0.1-5 1-6 no pre ads dep pur 5 20 5 20 5 30 5 30 5 40 5 40 5 50 5 50 5 60 5 60 5 70 5 70 5 80 5 80 2-bed 4-step with vacuum purging (mode 2) 7 0.1-1 1-3 yes pre ads dep vacpur 5 80 5 80 2-bed 6-step with equalization pressure (mode 3) 7 0.1-1 1-6 no pre ads depeq dep pur preeq 5 80 5 5 80 5 2-bed 6-step with equalization pressure and vacuum purging (mode 4) 0.1-1 1-3 yes pre ads depeq dep vacpur preeq 5 20 5 5 20 5 5 30 5 5 30 5 5 40 5 5 40 5 5 50 5 5 50 5 5 60 5 5 60 5 5 70 5 5 70 5 5 80 5 5 80 5 5 90 5 5 90 5 5 100 5 5 100 5 3. results and discussion 3.1 single bed adsorber the breakthrough curve of oxygen at the product end of the single bed adsorber for nitrogen separation from the air on cms is shown in fig. 1. the effluent flow rate is 1 5 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 liter/min. the breakthrough time occurred at 100 s. thereby, the oxygen purity gradually increased until it reached a stable purity of about 20%. the mass transfer zone (mtz) is very wide due to the effect of axial dispersion during the pressurizing and producing steps. the predicted results are in good agreement with experimental data obtained by abdelrahman [3]. figure 2 represents the effect of product pressurizing pressure on the breakthrough time and the amount of nitrogen produced. a little improvement in the breakthrough time and in the amount of nitrogen produced was noticed. that is because the adsorption isotherm of oxygen and nitrogen are closer to each other on the cms at equilibrium state. so increasing in the product pressurizing pressure leads to increase in the partial pressure of nitrogen in the bed and the most porosities of the adsorbent (cms) are filled by nitrogen. therefore, little increases in the breakthrough time may be attributed to increases in adsorbent capacity with pressure and decreased axial dispersion effects. fig. 1: fitting between the predicted results and experimental data of oxygen breakthrough curve in the product end of single bed adsorber. fig. 2: effect of product pressurizing pressure on the breakthrough time and amount of produced nitrogen in single bed adsorber. 6 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 3.2 two bed psa process 3.2.1 effect of the ternary feed mixture figure 3 represents the effect of the argon presence in the feed mixture on the performance of the 2-bed 6-step psa process (mode 3) at 7 bar pressure, 80 s adsorption time, 1-4 liter/min purge flow rate, and 0.1 liter/min product flow rate. higher purity of nitrogen, over 99% is observed in the state of a binary feed mixture (o2/n2) than a ternary feed mixture (o2/n2/ar), where the maximum purity was about 95%. according to the ldf coefficient values, oxygen diffuses faster than nitrogen and argon through the cms porosity, therefore the purity of nitrogen in the product end could not be higher than the purity of the psa process with the binary feed mixture. most studies obtained high purity of nitrogen, over 99% when they handled a binary feed mixture. fig. 3: effect of argon presence in the feed mixture on the performance of mode 3 of psa processes. 3.2.2 effect of adsorption pressure figure 4 shows the effect of adsorption pressure (2-9 bar) on the product purity of 2bed 4-step psa processes (mode 2), at purge flow rate of 1 liter/min, product flow rate of 1 liter/min, and adsorption time of 40 s. the purity of nitrogen and argon are increased with increasing adsorption pressure, due to increase in the adsorption capacity of the cms to adsorb more oxygen. the same trend is detected with the argon component. only oxygen is adsorbed by cms, therefore the purity of nitrogen in the product could not be higher due to the argon presence in the feed mixture. fig. 4: effect of adsorption pressure on the purity of the nitrogen and argon in the mode 2 of the psa process. 7 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 3.2.3 effect of adsorption time figure 5 shows the effect of adsorption time in the range of 40-250 s with two different feed mixtures, at adsorption pressure of 7 bar, purge flow rate of 1 liter/min, and product flow rate of 1 liter/min. nitrogen purity increased with increasing adsorption time until 100 s and then decreased slightly or kept stable. nitrogen separation on cms is kinetically controlled. increase in the adsorption time over 100 s leads to the system approaching an equilibrium state, causing decreases in the nitrogen purity or keeping it stable. at short adsorption time, the time is not enough to adsorb the whole oxygen molecule by cms. maximum uptake is obtained at nearly 100 s. maximum purity (98%) is detected by mode 3 without argon presence in the feed mixture, while it dropped to 92% with argon presence in the feed mixture. the production of nitrogen purity by mode 3 regardless of feed mixture components binary or ternary is higher than mode 1. this may be attributed to the effect of the pressure equalization step in mode 3, which contributed to reducing the axial dispersion effect during the pressurizing step. moreover, the rapid diffusion of oxygen into the cms led to the adsorption of oxygen rather than argon and nitrogen, where the diffusion rate constant of oxygen is higher than nitrogen and argon as shown in table 2. cms is a kind of adsorbent material with pore sizes in the range of 3-5 ao, while the diameter of oxygen is (3.46 ao), diameter of nitrogen is (3.64 ao) and the diameter of argon is (3.43 ao). all these reasons lead to kinetic separation of air on cms. despite the smaller diameter of argon than other components, low partial pressure of argon in the feed mixture and small diffusion rate constant reduced argon diffusion in the state of the ternaryfeed mixture. this phenomenon was observed by jee [20] when they used two ternary feed mixtures (o2/ar/n2; 95:4:1 and 90:4:6 vol%) for gas separation on cms. nitrogen recovery increased with increasing adsorption time, where the product flow rate increased with increasing the adsorption time. the results are in a good agreement with lacava [16], farooq [21], and mostamand [2]. fig. 5: effect of the adsorption time on the performance of two modes of psa process. 3.2.4 effect of purge flowrate figure 6 shows the effect of purge flow rate for all modes of psa process on the purity of nitrogen at adsorption time of 80 s, adsorption pressure of 7 bar, and product flow rate of 1 liter/min. in all modes, nitrogen purity was approximately kept constant or decreased slightly with increased purge flow rate until 2 liter/min, and it then decreased 8 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 dramatically. the gas used in the purging step is represented as part of the product flow rate during the adsorption step and is enriched with nitrogen. increasing it over 2 liter/min causes an increase in vapor pressure of nitrogen, after displacing oxygen out of the bed and adsorbing it by cms. so in the next cycle, nitrogen purity will inevitably drop, because most cms porosity is filled with nitrogen during the purging step. in addition, both the depressurizing step and low purge flowrate (< 1 liter/min) were enough to expel adsorbed oxygen from cms porosity. the most out of purge flow rate is observed at low purge flow rate. the results are in agreement with farooq [21], and abdel-rahman [3], and in disagreement with mostamand [2]. fig. 6: effect the purge flow rate on the four modes of the psa process. fig. 7: effect of vacuum pressure on the performance of two modes of the psa processes. 3.2.5 effect of vacuum pressure figure 7 shows the effect of vacuum pressure on the effluent nitrogen purity at adsorption pressure of 7 bar, purge flow rate of 1 liter/min, product flow rate of 0.1 liter/min, and adsorption time of 80 s. all processes have the same trend. high nitrogen purity is detected at a low vacuum pressure (0.0001 bar) and then decreased slightly with increasing vacuum pressure. purging the adsorbent at low vacuum pressure has a significant effect to clean the adsorbent during the purging step. increases of vacuum pressure lead to sufficient desorption of cms to prepare it for the next cycle. maximum purity, over 99% is observed by mode 4 with the binary feed mixture, while low purity of about 98% is observed with the same mode (mode 4) with the ternary feed mixture. the nitrogen purity produced by mode 4 with a feed mixture that is free of argon is higher than mode 4 with ternary feed mixture and mode 2. this may be attributed to the faster rate of diffusion of oxygen than nitrogen and argon on cms, the presence of the pressure equalization step, and the purging step at low vacuum pressure, where they contributed to 9 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 improving the process performance. it is important to consider the argon presence in the feed mixture, and operation steps to design the psa unit to produce high purity nitrogen from atmospheric air. 4. conclusions the mathematical model of single bed adsorber is in good agreement with experimental data. the breakthrough time and amount of nitrogen product are increased slightly with increases in product pressurizing pressure. for the psa process, high purity of nitrogen was not available when argon was present in the feed mixture. high purity of nitrogen over 99% was observed by mode 4 when the feed mixture was free of argon, while the purity decreased to 98% with presence of argon in the feed mixture. also, the same trend was detected by mode 3, where the purity decreased from 98% to 92% when argon was considered in the feed mixture. only oxygen is adsorbed by cms from the feed mixture (o2: 21%, n2 :78%, ar: 1%). for different psa modes, the equalization step in mode 3, and the equalization step with purging step under vacuum pressure in mode 4 are useful to increase the nitrogen purity to 99% in comparison with other modes (mode 1 and mode 2) where the nitrogen purity was about 90%. the best arrangement of all modes from higher to lower nitrogen purity is as follows: mode 4, mode 3, mode 2, and mode 1. for operation parameters, the purities of argon and nitrogen in the product stream increased with increases of adsorption pressure due to increases in adsorption capacity of cms sieve to adsorb more oxygen. in all modes, the purity of nitrogen increased a few percent between adsorption times of 50 – 100 s. also, the purity of nitrogen decreased about 4% with increases of purge flow rate from 1 to 6 liter/min, and optimum purge flow rate was between 1 and 2 liter/min. acknowledgement the authors would like to thank the chemical engineering department at the university of tikrit, iraq for allowing them working in their laboratories. references [1] nicholas af, mohd zh , zulkarnain z, tumirah k. (2019) activated carbon for shape stabilized phase change material. technology and applications of carbon nanomaterials, 279-308. [2] mostamand a, mofarahi m. (2011) simulation of a single bed pressure swing adsorption for producing nitrogen. in international conference on chemical, biological and environment sciences (iccebs'2011) bangkok. [3] abdel-rahman za, mhdi ah, auob hs. (2016) parametric study for nitrogen separation from air by pressure swing adsorption using carbon molecular sieve. tikrit journal of engineering science. 23 (2), 1-9 [4] carreon ma. (2018) molecular sieve membranes for n2/ch4 separation. journal of material research, 33(1): 32-43. [5] lemcoff no. (1999) nitrogen separation from air by pressure swing adsorption. studies in surface science and catalysis. 120: 347-370. [6] reid cr, o’koye ip, thomas km.( 1998) adsorption of gases on carbon molecular sieves used for air separation. spherical adsorptives as probes for kinetic selectivity. 14(9): 2415-2425. 10 iium engineering journal, vol. 21, no. 1, 2020 mahdi et al. https://doi.org/10.31436/iiumej.v21i1.1182 [7] vivo-vilches jf, agustín fp, francisco jm, francisco c, christophe s , ana mr, alexander f, alirio er. (2018) from carbon molecular sieves to vocs filters: carbon gels with tailored porosity for hexane isomers adsorption and separation, microporous and mesoporous materials, 270: 161-167. [8] shirley ai, lemcoff no. (2002) air separation by carbon molecular sieves. adsorption. 8: 147–155. [9] kim j-d. ( 1995) production of high-purity nitrogen from air by pressure swing adsorption on zeolite x. separation science and technology, 30: 347-368. [10] reynolds sp, ebner ad, ritter ja. (2006) enriching psa cycle for the production of nitrogen from air. ind. eng. chem. res., 45: 3256-3264. [11] yang j, lee ch. (1998) adsorption dynamics of a layered bed psa for h2 recovery from coke oven gas. aiche journal, 44: 1325-1334. [12] xu m, wu hc, lin ys, deng s. (2018) simulation and optimization of pressure swing adsorption process for high-temperature air separation by perovskite sorbents. chemical engineering journal, 354: 62-74. [13] mate via, dobladez jad, alvarez-torrellas s, larriba m, rodriguez am. (2019) modeling and simulation of the efficient separation of methane/nitrogen mixtures with [ni3 (hcoo) 6] mof by psa. chemical engineering journal, 361: 1007-1018. [14] moran a, talu o. (2018) limitations of portable pressure swing adsorption processes for air separation. industrial & engineering chemistry research, 57(35): 11981-11987. [15] farooq s, ruthven dm. (1990) a comparison of linear driving force and pore diffusion models for a pressure swing adsorption bulk separation process. chemical engineering science, 45: 107 – 115. [16] lacava ai, lemcoff no. (1996) single bed pressure swing adsorption process to generate high purity nitrogen. gas separation & purification , 10(2): 113-115. [17] makarem ma, mofarahi m, jafarian b, lee ch. (2019) simulation and analysis of vacuum pressure swing adsorption using the differential quadrature method. computers & chemical engineering, 121: 483-496. [18] vaduva m, stanciu v. (2006) separation of nitrogen from air by selective adsorption of carbon molecular sieves. u.p.b. sci. bull., 68: 2-10. [19] jee jg, lee j-s, lee ch. (2001) air separation by a small-scale two-bed medical o2 pressure swing adsorption. industrial & engineering chemistry research, 40: 3647-3658. [20] jee jg, kim mb, lee ch. (2005) pressure swing adsorption processes to purify oxygen using a carbon molecular sieve. chemical engineering science, 60: 869 882. [21] farooq s, rathor mn, hidajat k. (1993) a predictive model for a kinetically controlled pressure swing adsorption separation process, chemical engineering science, 48(24): 4129– 4141. 11 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <feff0041006e007600e4006e00640020006400650020006800e4007200200069006e0073007400e4006c006c006e0069006e006700610072006e00610020006f006d002000640075002000760069006c006c00200073006b006100700061002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400200073006f006d00200070006100730073006100720020006600f60072002000740069006c006c006600f60072006c00690074006c006900670020007600690073006e0069006e00670020006f006300680020007500740073006b007200690066007400650072002000610076002000610066006600e4007200730064006f006b0075006d0065006e0074002e002000200053006b006100700061006400650020005000440046002d0064006f006b0075006d0065006e00740020006b0061006e002000f600700070006e00610073002000690020004100630072006f0062006100740020006f00630068002000410064006f00620065002000520065006100640065007200200036002e00300020006f00630068002000730065006e006100720065002e> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 analysis and correlations of dimensionless numbers relevant to orifices’ cavitating flow abdul-fattah mohammed ali1,2 and mohanad jasim mohammed-ridha1* 1department of environmental engineering, university of baghdad, baghdad, iraq 2department of oil and gas refining engineering, al-farabi university college, baghdad, iraq *corresponding author: muhannadenviro@coeng.uobaghdad.edu.iq (received: 5th december 2019; accepted: 13th may 2020; published on-line: 4th july 2020) abstract: the aim of this work was to establish a general design basis for pilot-scale units to treat textile dyeing wastewater containing recalcitrant organic chemicals by hydrodynamic cavitation (hc) using orifices of various geometries. relevant tabulated data available in the literature were analyzed and correlated to obtain universal relationships to this end. in spite of extensive effort, most of the obtained correlations were system-specific, which still can be used for design using their respective orifice geometries as demonstrated. however, one salient general relationship links the pipe’s dimensionless loss coefficient (klp) to the pipe’s reynolds number (rep), encompassing all data under consideration, which may serve as an additional design option to optimize such units. the implication of this relationship is a lower upstream pressure (p1) value with an increase in pipe diameter while using the same specified orifice and achieving the same desired cavitation number (cv). the ratio of p1 value in the larger pipe to its value in the smaller pipe is a function of the smaller pipe diameter (ds) to the larger pipe diameter (dl) ratio: (p1 in dl) / (p1 in ds) = (ds /dl)2.33. a lower p1 value will increase the cavitation yield by decreasing the expended energy, especially if the required number of passes is large. additionally, the variation of the orifices’ hole loss coefficient (klh) with the ratio of the holes area to the pipe cross-sectional area (ah/ap) for cavitating flow is compared with that for non-cavitating/incipient cavitation flow reported in the literature. abstrak: tujuan kajian ini diadakan bagi mereka bentuk dasar umum unit skalapandu bagi merawat pewarnaan air buangan tekstil yang mengandungi kimia organik rekalsitran daripada peronggaan hidrodinamik (hc) menggunakan orifis pelbagai geometri. data berjadual berkaitan yang ada dalam kajian lepas dianalisa dan dikaitkan bagi mendapatkan kaitan universal hingga akhir. walaupun pelbagai usaha telah dijalankan, banyak kaitan didapati mengguna pakai sistem-tertentu, di mana boleh digunakan bagi mereka cipta menggunakan geometri orifis yang ditunjukkan. walau bagaimanapun, bagi menghubung kait pekali langsung tanpa dimensi (klp) kepada paip nombor reynolds (rep), meliputi semua data di bawah pertimbangan, di mana membantu pilihan rekaan tambahan bagi mengoptimum unit tersebut. implikasi hubungan ini adalah nilai tekanan hulu sungai bawah (p1) dengan penambahan diameter paip dengan menggunakan orifis sama yang sebenar dan mendapati nombor peronggaan yang sama diingini (cv). nisbah nilai p1 dalam paip besar kepada nilai paip kecil adalah berkadaran pada nisbah diameter paip kecil (ds) kepada diameter paip besar (dl): (p1 dalam dl) / (p1 in ds) = (ds /dl)2.33. 41 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 nilai p1 yang lebih kecil akan menambah jumlah peronggaan dengan pengurangan tenaga pengembangan, terutama jika nombor laluan yang diperlukan adalah besar. tambahan, variasi orifis pekali langsung lubang (klh) dengan nisbah keluasan lubang kepada ruang keratan-rentas paip (ah/ap) bagi alur rongga dibandingkan dengan bukan rongga / permulaan rongga alur telah dilapor dalam kajian keywords: hydrodynamic cavitation; orifice geometry; cavitation numbers; upstream pressure; loss coefficients 1. introduction hydrodynamic cavitation (hc) is a well-established technique for a variety of applications including the treatment of wastewater containing pharmaceuticals [1], insecticides [2], phenolic compounds [3], and textile dyes [4-8]. hc is usually combined with the addition of an oxidizing agent (h2o2, naocl, etc.) or with acoustic cavitation to achieve an acceptable cavitation yield (cy) which is defined as the cavitation effect per unit energy supplied to the system. over the last two decades, many hc research studies have been published, some with detailed tabulated data. their size-scale ranged from 1 l lab units to 50 l pilot ones. various devices were used to induce hc in these units such as single-/multi-hole orifices, venturis, stator-rotor equipment, etc. the operational mode was batch-wise based either on fixed time or on a specified number of passes (turnovers) where the wastewater volume was recirculated many times through the hc device to achieve an acceptable cy. this could be hundreds of times, lasting over two hours depending on the system’s flow rate (e.g. 260 passes lasting 130 min [7]). single-/multi-hole orifices as hc inducing devices are simpler to manufacture and install than other alternatives which explain their wide use in hc studies. their hole size generally ranges from 1 to 5 mm with multi-hole counts of 8, 16, 20, 25, or 33, although some studies used sizes and counts outside these values. the pipes in which the aforementioned orifices were placed had inside diameters ranging from 4 to 53 mm. the results obtained in all previously published hc studies were system-specific; a generalized or unifying approach were markedly lacking. reviews stated only general trends based on the published works. consequently, it is difficult to make practical use of available information, specifically a priori design of a functional wastewater-treating hc unit, save adopting a given system with all its particulars. the present work is an attempt at a unifying approach, relying entirely on tabulated data from a number of published research studies. the outcome of this endeavor was only partially productive as will be illustrated later by the obtained results. this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. 2. geometrical details and references of orifices whose hc published data were used in this work two categories of published data were excluded from the analysis and correlations performed in this study. the first concerned orifices with a hole size of one mm or less, whether singleor multi-hole ones. one mm holes or smaller are difficult/expensive to produce locally while ensuring their integrity (sharp edge, lack of burrs, etc.). the second category concerned a hc system in which the fully-recovered orifice’s downstream pressure (p2) was higher than atmospheric pressure (i.e. p2 > one atm. abs. or zero gage). 42 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 data with p2 > 0 gage did not match those with p2 ≈ 0 gage. table 1 gives the details of the orifices whose hc data were used in this work along with their references. the data of testud et al. [10] and that of mancuso et al. [7] were excluded due to p2 values being greater than one atm. abs. as pointed out earlier. it should be stressed that all the hc data of the references cited in table 1 are relevant to pilot-scale units with p2 ≈ one atm. abs. hence, all the obtained correlations of this work are only relevant to such systems. table 1: geometrical details and references of orifices whose hc data were employed in the analysis and correlations of this work. hole dia. [mm] no. of holes pipe i.d [mm] ah/ap reference 2 1 25.4 6.2x10-3 [6] 2 1 25 6.4x10-3 [9] 2 1 19 0.011 [8] 2 1 19 0.011 [17] 2 8 38 0.02216 [11] 2 8 38 0.02216 [4] 2 33 38 0.0914 [11] 2 33 38 0.0914 [4] 3 1 25.4 0.01395 [6] 3 1 19 0.02493 [17] 3 16 38 0.099723 [11] 3 16 38 0.099723 [4] 3 20 38 0.12465 [11] 3 20 38 0.12465 [4] 5 8 38 0.1385 [11] 5 8 38 0.1385 [4] notes: (i) ah/ap is the ratio of the total area of holes to the cross-sectional area of the pipe. (ii) thicknesses of orifices in table 1 references were not mentioned, apart from pawar et al. [9] which was 4 mm leading to an aspect ratio of 2 (aspect ratio = orifice thickness/hole dia.). (iii) hc data listed in table 1 references are extensive and can be referred to; they shall not be repeated in this article. (iv) a 4-mm single hole orifice datum from madhu et al. [6] was excluded due to lack of 4-mm multi-hole data. 3. dimensionless numbers relevant to orifice’s cavitating flow and their inter-relationships 3.1 cavitation number or index there are several definitions for this parameter, the two most widely used ones are cv and σ (notations used are similar to those in the cited references) defined as follows: cv = (p2 – pv) / (0.5 ρl uo2) and σ = (p2 – pv) / (p1 – p2) where p1, p2 are the orifice’s upstream and fully-recovered downstream pressures, respectively. pv is the liquid-vapor pressure and ρl is its density, both at the operating temperature. uo is the average liquid velocity at the orifice’s hole (single hole or one hole in a multi-hole geometry). cavitating flow occurs when the value of cv (or σ) is usually ˂ 1, with an increase in cavitation intensity as the value of the index is lowered. very low values of the index (˂ 43 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 0.1) may induce a regime called supercavitation which is counterproductive and should be avoided. a modification of cv (called cvprime) was introduced and used by vichare et al. [11] and sivakumar and pandit [4] as a unifying approach for comparison of hc data of orifices with various multi-hole geometries. cvprime was defined as: cvprime = cv / [(total perimeter of holes/perimeter of pipe)] 3.2 flow head loss coefficients and reynolds numbers two dimensionless flow head loss coefficients were used in this work. their definitions are: klh = (p1 – p2) / (0.5 ρl uo2) and klp = (p1 – p2) / (0.5 ρl up2) klh is based on the hole’s dynamic pressure, whereas klp is based on the pipe’s dynamic pressure with up being the average flow velocity in the pipe. additionally, two reynolds numbers were used, one based on the hole average velocity and the other one on the pipe average velocity: reo = ρl uo do / μl and rep = ρl up d / μl where do and d are the hole diameter and the pipe inside diameter, respectively. μl is the liquid dynamic viscosity at the operating temperature. 3.3 inter-relationships among the aforementioned dimensionless numbers klh is related to klp by (maynes et al. [12]) eq. (1): klh= (ah/ap)2 klp (1) and rep is related to reo by eq. (2): rep= reo [n (ah/ap)]0.5 (2) where n is the number of holes in the orifice (hole count) and ah/ap is the ratio of the total area of holes to the pipe cross-sectional area as pointed out earlier. additionally, σ is related to cv by eq. (3): σ= cv / klh (3) the relationships represented by eqs. (1) to (3) can be easily obtained by considering the given definitions of the dimensionless numbers involved. the orifices’ hc tabulated data of table 1 references constituted experimental values of p1, cv, uo, ah/ap, flow rate, and temperature. p2 values were either given or calculated using the above relationships, where it was confirmed that its value was virtually one atm. abs. in all cases. eq. (3) was used to calculate the corresponding σ values. 4. specific correlations of orifices’ cavitating flow dimensionless numbers and their utility in design cavitating flow is a complex phenomenon that is still not-well understood and whose theoretical basis has not been fully established. consequently, an empirical approach is usually adopted (burzio et al. [18]). accordingly, eqs. (4) to (18) are empirical; only 44 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 characterized by values of the determination coefficient r2 ˃ 0.9. furthermore, the data upon which they are based (table 1) lacked standard deviation bounds which compromise their accuracy. notwithstanding these limitations, the equations are of use in a priori design of hc pilot-scale units (as elucidated in section 4.5) where plus or minus 5% off specification is usually acceptable. table 2 expounds the types of correlations employed and equations designation as related to five orifice geometries. two other geometries pertaining to the 2mm and 3mm single hole orifices were excluded from the said correlations due to their trend-lacking scattered data. additionally, eqs. 13 to 15 were also excluded from table 2 because they represent a test for cvprime as a unifying parameter. table 2: types of correlation, equations designation and corresponding orifice geometries correlation type 2mm-8h 2mm-33h 3mm-16h 3mm-20h 5mm-8h klh vs. reo eq. (4) ------------------eq. (5) -------- klh vs. cv eq. (6) ------------------eq. (7) -------- σ vs. reo eq. (8) eq. (9) ------------------eq. (10) σ vs. cv eq. (11) eq. (12) eq. (16) eq. (17) eq. (18) notes: (i) in the design procedure, the value of cv is initially assumed depending on the application (see sec. 4.5) which leads to the calculation of reo. (ii) for a selected geometry, klh or σ is then determined from an appropriate equation(s) leading to the value of p1 (a prime design parameter). (iii) there are 4 choices to accomplish note (ii) for 2mm-8holes, 3 choices for 3mm-20holes, 2 choices for either 2mm-33holes or 5mm-8holes, but only one choice for the 3mm-16holes geometry. 4.1 klh vs reo correlations for this category, only two specific correlations were obtained as shown in fig. 1. fig. 1: klh vs reo/104. klh = 0.4964 – 0.019 (reo/104) (4) (2mm-8holes, 5 ≤ reo/104 ≤ 13, r2 = 0.9368) klh = 0.2482 (reo/104) – 0.1876 (5) (3mm-20holes, 4.5 ≤ reo /104 ≤ 8, r2 = 0.9594) y = 0.2482x 0.1867 r² = 0.9594 y = -0.019x + 0.4964 r² = 0.9368 0 0.5 1 1.5 2 2.5 0 2 4 6 8 10 12 14 16 18 klh re0/104 5mm8 holes 3mm16 holes 3mm20 holes 2mm8 holes 2mm33 holes 45 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 the trends of eqs. (4) and (5) are opposite to one another. the 2mm-8holes klh decreases with increasing reo (ah/ap = 2.2%) whereas the 3mm-20holes klh increases (ah/ap = 12%). also shown in fig. 1 are the data of the 2mm-33holes (ah/ap = 9.1%) and the 5mm-8holes (ah/ap = 13.85%). the former reflects an increasing-decreasing trend, whilst the latter depicts a clearly non-linear increasing trend for reo > 16x104. maynes et al. [12] had shown an increasing klh trend with increasing uo for two multi-hole orifices with ah/ap values of 22% and 44% which they attributed to cavitating flow, since according to their results for non-cavitating flow klh was constant and independent of uo. any explanation for the above observations would be premature at this stage. 4.2 klh vs cv correlations the following specific correlations were obtained for this category. klh = 1.0192 cv + 0.2095 (6) (2mm-8holes, 0.045 ≤ cv ≤ 0.56, r2 = 0.9956, fig. 2) klh = 0.862 cv-0.567 (7) (3mm-20holes, 0.3 ≤ cv ≤ 0.75, r2 = 0.9681, fig. 3) fig. 2: klh vs cv 2mm-8holes. fig. 3: klh vs cv 3mm-20holes. y = 1.0192x + 0.2095 r² = 0.9956 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 klh cv 2mm8 holes y = 0.862x-0.567 r² = 0.9681 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 klh cv 3mm20 holes 46 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 the trends represented by eqs. (6) and (7) are opposite to one another. for each geometry, the above trend is the reverse of its klh vs reo trend [eqs. (4) and (5)]. hence, klh increases with increasing cv for the geometry of the 2mm-8 holes [eq. (6)] whereas it decreases for the 3mm-20holes one [eq. (7)]. 4.3 σ vs reo correlations for this category, the following specific relationships were obtained: σ = 0.8139 – 0.0159 (reo/104) (8) (2mm-8holes, 3.7 ≤ reo/104 ≤ 13, r2 = 0.9095, fig. 4) σ = 1.0317 – 0.1757 (reo/104) (9) (2mm-33holes, 3 ≤ reo/104 ≤ 5, r2 = 0.9644, fig. 4) σ = 65.504 (reo/104)-2.027 (10) (5mm-8holes, 9 ≤ reo/104 ≤ 17.5, r2 = 0.9559, fig. 5) equations (8) to (10) indicate a decreasing trend of σ with increasing reo for different geometries. this was expected since higher reo values imply higher p1 values making σ smaller since p2 and pv are fixed, [σ = (p2 – pv)/(p1p2)]. fig. 4: σ vs reo/104 for 2 mm-8, 33holes. fig. 5: σ vs reo/104 for 5mm-8holes. y = -0.0519x + 0.8139 r² = 0.9095 y = -0.1757x + 1.0317 r² = 0.9644 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 σ reo/104 2mm8 holes 2mm33 holes y = 65.504x-2.027 r² = 0.9559 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 9 10 11 12 13 14 15 16 17 18 σ reo/104 5mm8 holes 47 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 4.4 σ vs cv or cvprime correlations specific correlations linking the two most widely-used definitions of cavitation number were as follows: σ= 1.016 cv0.5509 (11) (2mm-8 oles, 0.045 ≤ cv ≤ 0.56, r2 = 0.9647, fig. 6) σ = 0.6848 cv – 0.0262 (12) (2mm-33 holes, 0.35 ≤ cv ≤ 0.75, r2 = 0.9799, fig. 6) fig. 6: σ vs cv for 2mm-8, 33holes. the two geometries of eqs. (11) and (12) were combined by a single σ vs cvprime correlation: σ = 0.9478 cvprime + 0.0593 (13) (2mm-8, 33 holes, 0.1 ≤ cvprime ≤ 0.45, r2 = 0.9388, fig. 7) fig. 7: σ vs cvprime for combined 2mm-8, 33holes. y = 1.016x0.5509 r² = 0.9647 y = 0.6848x 0.0262 r² = 0.9799 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.2 0.4 0.6 0.8 σ cv 2mm8 holes 2mm33 holes y = 0.9478x + 0.0593 r² = 0.9388 0 0.1 0.2 0.3 0.4 0.5 0.6 0 0.1 0.2 0.3 0.4 0.5 σ cvprime 2mm8 holes 2mm33 holes 48 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 equation (13) is the only case where cvprime acted as a unifying parameter. consequently, two additional σ vs cv specific relationships were deduced for imaginary geometries of 2mm-16holes and 2mm-20holes: σ = 1.1255 cv + 0.0593 (14) (2mm-16holes, 0.0842 ≤ cv ≤ 0.379) σ = 0.9004 cv + 0.0593 (15) (2mm-20holes, 0.1053 ≤ cv ≤ 0.477) additionally, the following specific σ vs cv correlations were obtained: σ = 0.5995 cv – 0.0081 (16) (3mm-16holes, 0.37 ≤ cv ≤ 1.15, r2 = 0.9602, fig. 8) σ = 1.2227 cv – 0.206 (17) (3mm-20holes, 0.3 ≤ cv ≤ 0.75, r2 = 0.9936, fig. 8) σ = 1.2676 cv (18) (5mm-8holes, 0.15 ≤ cv ≤ 0.55, r2 = 0.9732, fig. 9) equations (11) to (18) reflect a trend of increasing σ with increasing cv for the various orifice geometries. this trend was also expected since an increase in cv value means a lower uo value which entails a lower p1 value leading to an increase in the value of σ. fig. 8: σ vs cv for 3mm-16, 20holes. yan and thorpe [13] derived a theoretical equation linking σ to cv for a single hole orifice. their relationship included the orifice’s discharge coefficient cd , its contraction coefficient cc , and ah/ap . it was not possible to compare eqs. (11) to (18) with their equation because cd and cc were not given for the orifices under consideration in this work. estimating the values of cd and cc from correlations available in the literature would be uncertain since they are related to the aspect ratio, which is also missing for all the multi-hole orifices of table 1. y = 0.5995x 0.0081 r² = 0.9602 y = 1.2227x 0.206 r² = 0.9936 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 σ cv 3mm16 holes 3mm20 holes 49 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 fig. 9: σ vs cv for 5 mm-8holes. 4.5 outline of a priori design procedure utilising the specific correlations (a) initially an appropriate cv value for the intended application is chosen, e.g. for wastewater containing bio-refractory organic dyes, a suitable range is 0.2 ≤ cv ≤ 0.4 (rajoriya et al. [19]) (b) since cv = (p2 – pv)/(0.5 ρl uo2), uo can be determined after an operating temperature is set, fixing the values of pv, ρl, and μl. hence the value of reo can be established. (c) after selecting an orifice geometry, one or more correlation may be used to calculate either klh or σ from which the value of p1 can be determined. this p1 value is based on 38 mm (1.5 inch) pipe diameter (see table 1). (d) the 38mm-based p1 value can be lowered by specifying a larger pipe diameter, e.g. 53mm (2 inch) according to the findings of sec. 5 below. (p1 – p2) represents the main pressure drop of the system whose volumetric flow rate (q) can be calculated from the value of uo and the selected geometry leading to the estimation of the system’s total pressure drop (∆p). (e) a centrifugal pump whose best efficieny point (bep) matches the system’s q-∆p point should be employed. conversely, if a pump is already available, an appropriate cv value, the ensuing p1 and reduced p1 values, and selected geometry should be manipulated to achieve the pump’s bep-system’s q-∆p match. 5. general klp vs rep correlation and its implications figure 10 shows a plot of klp vs. rep for all the hc data of the orifices listed in table 1, including the single hole data which were excluded from the specific correlations of sec. 4 due to their trend-lacking scatter. it is noteworthy that four pipe sizes are included in fig. 10 with a range of 19 ≤ i.d. ≤ 38 mm, which is in contrast with the specific correlations where only a single pipe size of i.d = 38 mm was involved. the unifying characteristic of klp vs rep is clear, resulting in the following general correlation eq. (19): klp = 4228.5 (rep/104)-1.6707 (19) {(rep/104) ≤ 18, r2 = 0.9353} y = 1.2676x r² = 0.9732 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.1 0.2 0.3 0.4 0.5 0.6 σ cv 5mm8 holes 50 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 retrieving the definitions of klp = (p1p2)/(0.5 ρl up2) and rep = (ρl up d)/μl, fig. 10 indicates that increasing rep by increasing up, which can only come about by increasing p1 reduces klp in a nearly exponential decay manner. if the definitions of klp and rep are substituted into eq. (19) and noting that (p1 – p2) may be replaced by p1 as gage pressure, then eq. (19) can take the following form: p1 = 1.0185x105 ρl-0.6707 μl1.6707 up0.3293 d-1.6707 (20) where p1 has units of bar gage. fig. 10: klpvs rep/104 for all single and multi-hole orifices. if for a specific orifice geometry and a desired cv value, two pipes are considered (in which the specified orifice is to be installed in one of them) one pipe with a smaller inside diameter ds and the other with a larger inside diameter dl , then the application of eq. (20) and the equation of continuity (conservation of mass flow rate) for the two pipes will result in the following ratio eq. (21): (see appendix a), (p1 in dl pipe / p1 in ds pipe) = (ds / dl)2.33 (21) hence, a lower value of p1 is required to obtain the desired cv value by installing the specified orifice in a larger i.d pipe compared to a smaller i.d. pipe. it is emphasized that this result is limited to the applicability range of eq. (19) and the data upon which it is based. an additional advantage of using a relatively larger inside diameter pipe is the lower pressure drop in the system, apart from the orifice’s pressure drop (p1 – p2), especially when the required number of passes is large. this will have a positive effect on the expended energy and consequently on the cavitation yield. a possible drawback of lowering p1 value by using a larger inside diameter pipe is the ensuing decrease in the value of the cavity collapse pressure given by the following empirical correlation [14-16] eq. (22). pcollapse = 7527 [100 (ah/ap)]-2.55 p12.46 ro-0.8 do2.37 (22) which is related to the cavitation yield by eq. (23): y = 4228.5x-1.671 r² = 0.9353 1 10 100 1000 10000 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 klp rep/104 3mm-16 holes 3mm20 holes 3mm single hole 2mm8 holes 2mm33 holes 2mm-single hole 5mm8 holes 51 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 cy = k ( pcollapse )w (23) where ro is the initial cavity size, k and w are constants whose values depend on the system’s particulars (device geometry, operating parameters, type of reaction). however, the possible negative effect of lower p1 value may be partially or totally offset by the decrease in the value of ah/ap with a larger inside diameter pipe and/or the value of w being positive or negative. applying eq. (22) with ds or dl leads to: (pcollapse in dl pipe)/(pcollapse in ds pipe) = (ds/ dl)0.632 (24) 6. comparison with findings of maynes et al. [12] maynes et al. [12] showed a graphical representation of klh vs ah/ap in which data points pertaining to 16 multi-hole orifices of their work plus data points from three references were all bounded by two theoretical models, namely eqs. (25) and (26): (klh)detached = [cc-1 – (ah/ap)]2 (25) (klh)attached = 2 [1(ah/ap) – cc-1] + cc-2 + (ah/ap)2 (26) these models were derived by testud et al. [10] for single hole orifice using bernoulli’s principle and conservation of momentum for non-cavitating flow. eq. (25) is relevant to a thin orifice where the flow does not reattach within the hole, whereas eq. (26) is for a thick orifice where the flow is reattached. cc value for eq. (25) was determined from busemann theoretical relation cited by maynes et al. [12] (a function of ah/ap ) whilst for eq. (26) it was given a fixed value of 0.75. maynes et al. emphasized that all the shown data were non-cavitating/incipient-cavitation points. however, the two included points from testud et al. are developed cavitation results (one for a single hole and the other for multi-hole orifices with aspect ratios of 0.64 and 4.67, respectively). fig. 11: klh vs ah/ap for all single and multi-hole orifices. figure 11 is a reproduction of maynes et al. [12] presentation where the upper line represents eq. (25) and the lower line eq. (26). the plotted points are all the data of table 0 0.5 1 1.5 2 2.5 3 3.5 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 klh ah/ap 2mm single hole 2mm8 holes 2mm33 holes 3mm16 holes 3mm20 holes 3mmsingle hole 5mm8 holes testud et al.-mulitholes testud et al. -single hole eq. 26 eq. 25 52 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 1 plus all the developed cavitation results of testud et al. [10]. hence, all the points in fig. 11 are cavitating flow results. the 2 mm and 3 mm single hole points having very small ah/ap values lie mainly below or in-between the bounds representing eqs. (25) and (26). as for the multi-hole orifices data and that of testud et al. [10], there seems to be a trend with increasing value of ah/ap starting below the lower bound (2mm-8holes), then inbetween the two bounds and finally back to the lower bound (5mm-8holes). it is therefore concluded that results falling in-between these two bounds are not necessarily noncavitating/incipient cavitation data and could very well be developed cavitation results. 7. conclusions correlations represented by eqs. (4) to (12) and eqs. (16) to (18), although specific to their respective orifice geometries, can be used to design and/or predict the performance of pilot-scale hc units for wastewater treatment. this includes a priori determination of p1 and (p1 – p2) values for the desired cv value using a specific orifice geometry. furthermore, they can be used to design systems to suit available pumps in order to obtain operating points at or very close to the pump’s best efficiency points. this will increase the cavitation yield by lowering the value of the expended energy. the pipe’s loss coefficient klp and the pipe’s reynolds number rep were the only dimensionless parameters that unified all the hc data of orifices of various geometries and pipe sizes in a single general correlation with r2 = 0.9353. this resultant correlation, eq. (19), implies that for the same specified orifice geometry and desired cv value, using a relatively larger pipe inside diameter entails a reduction in the value of the required upstream pressure p1. the ratio of p1 value in the larger pipe to its value in the smaller pipe is a function of the ratio of the smaller pipe diameter (ds) to the larger pipe diameter (dl): (p1 in dl) / (p1 in ds) = (ds / dl)2.33. a lower p1 value will increase the cavitation yield by decreasing the expended energy especially if the number of passes is large. however, a lower p1 value will also decrease the value of the cavity collapse pressure which may affect the cavitation yield negatively, positively, or not at all depending on ah/ap variation and on constants whose values are system-specific. the findings of maynes et al. [12] that non-cavitating/incipient cavitation orifices’ klh vs ah/ap data fall in-between two theoretical models, eqs. (25) and (26), are not exclusive. orifices’ cavitating flow results may also behave likewise, but with a discernible trend. references [1] braeutigam p, franke m, schneider rj, lehmann a, stolle a, ondruschka b. (2012) degradation of carbamazepine in environmentally relevant concentrations in water by hydrodynamic-acoustic cavitation (hac). water res., 46:2469-2477. [2] patil pn, bote sd, gogate pr. (2014) degradation of imidacloprid using combined advanced oxidation processes based on hydrodynamic cavitation. ultrason. sonochem., 21:1770-1777. [3] pradham aa, gogate pr. (2010) removal of p-nitrophenol using hydrodynamic cavitation and fenton chemistry at pilot scale operation, chem. eng. j., 156:77-82. [4] sivakumar m, pandit ab. (2002) wastewater treatment: a novel energy efficient hydrodynamic cavitational technique. ultrason. sonochem., 9:123-131. [5] saharan vk, pandit ab, kumar pss, anandan s. (2012) hydrodynamic cavitation as an advanced oxidation technique for the degradation of acid red 88 dye. ind. eng. chem. res., 51:1981-1989. 53 iium engineering journal, vol. 21, no. 2, 2020 ali and ridha https://doi.org/10.31436/iiumej.v21i2.1306 [6] madhu gm, thomas a, deepak s, preetham hs, rajanandam ks. (2015) escalation of degradation of malachite green and methyl violet using hydrodynamic cavitation using different orifice geometry. int. j. env. sci., 5(4):880. [7] mancuso g, langone m, laezza m, andreottola g. (2016) decolourization of rhodamine b: a swirling jet-induced cavitation combined with naocl. ulatrason. sonochem., 32:1830. [8] rajoriya s, bargole s, saharan vk. (2017) degradation of reactive blue 13 using hydrodynamic cavitation: effect of geometrical parameters and different oxidizing additives. ultrason. sonochem., 37:192-202, doi:http://doi.org/10.1016/j.ultsonch.2017.01.005 [9] pawar sk, mahulkar av, pandit ab, roy k, moholkar vs. (2017) sonochemical effect induced by hydrodynamic cavitation: comparison of venturi/orifice flow geometries. aiche journal, 63(10):4705-4716. [10] testud p, moussou p, hirschberg a, auregan y. (2007) noise generated by cavitating single-hole and multi-hole orifices in a water pipe. j. fluids and structures, 23:163-189. [11] vichare n p, gogate pr, pandit ab. (2013) optimization of hydrodynamic cavitation using a model reaction. chemical engineering technology, 23:683-690. [12] maynes d, holt gj, blotter j. (2013) cavitation inception and head loss due to liquid flow through perforated plates of varying thickness. j. fluids eng., 135: 031302-1— 031302-11. [13] yan y, thorpe rb. (1990) flow regime transitions due to cavitation in the flow through an orifice. int. j. multiphase flow, 16 (6):1023-1045. [14] gogate pr, pandit ab. (2000) engineering design methods for cavitation reactors ii: hydrodynamic cavitation. aiche j., 46 (8):1641-1649. [15] gogate pr, shirganokar iz, sivakumar m, senthilkumar p, vichare np, pandit ab. (2001) cavitation reactors: efficiency assessment using a model reaction. aiche j., 47 (11):2526-2538. [16] gogate pr, pandit ab. (2005) a review and assessment on hydrodynamic cavitation as a technology for the future. ultrason. sonochem., 12:21-27. [17] carpenter j, badve m, rajoriya s, george s, saharan vk, pandit ab. (2017) hydrodynamic cavitation: an emerging technology for the intensification of various chemical and physical processes in a chemical process industry. reviews in chemical engineering, 33(5):433-468. https://doi.org/10.1515/revce-2016-0032. [18] burzio e, bersani f, caridi gca, vesipa r, ridolfi l, manes c. (2020) water disinfection by orifice-induced hydrodynamic cavitation. ultrasonics-sonochemistry, 60, 104740: 1-13. [19] rajoriya s, carpenter j, saharan vk, pandit ab. (2016) hydrodynamic cavitation: an advanced oxidation process for the degradation of bio-refractory pollutants. rev. chem. eng., 32: 379-411. appendix a the mass flow rate and volumetric flow rate (q) will be the same in both dl and ds pipes, therefore, p1 in dl pipe = 1.0185x105 ρl-0.6707 μl1.6707 (4q/πdl2)0.3293 dl-1.6707 p1 in ds pipe = 1.0185x105 ρl-0.6707 μl1.6707 (4q/πds2)0.3293 ds-1.6707 dividing: (p1 in dl pipe / p1 in ds pipe) = ( dl-0.6586 dl-1.6707 ) / ( ds-0.6586 ds-1.6707 ) = dl-2.33 / ds-2.33 = (ds / dl)2.33 54 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <feff04180441043f043e043b044c043704430439044204350020044d044204380020043f043004400430043c043504420440044b0020043f0440043800200441043e043704340430043d0438043800200434043e043a0443043c0435043d0442043e0432002000410064006f006200650020005000440046002c0020043f043e04340445043e0434044f04490438044500200434043b044f0020043d0430043404350436043d043e0433043e0020043f0440043e0441043c043e044204400430002004380020043f043504470430044204380020043104380437043d04350441002d0434043e043a0443043c0435043d0442043e0432002e00200421043e043704340430043d043d044b043500200434043e043a0443043c0435043d0442044b00200050004400460020043c043e0436043d043e0020043e0442043a0440044b0442044c002c002004380441043f043e043b044c04370443044f0020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e00300020043b04380431043e00200438044500200431043e043b043504350020043f043e04370434043d043804350020043204350440044104380438002e> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <feff04120438043a043e0440043804410442043e043204430439044204350020044604560020043f043004400430043c043504420440043800200434043b044f0020044104420432043e04400435043d043d044f00200434043e043a0443043c0435043d044204560432002000410064006f006200650020005000440046002c0020043f044004380437043d043004470435043d0438044500200434043b044f0020043d0430043404560439043d043e0433043e0020043f0435044004350433043b044f04340443002004560020043404400443043a0443002004340456043b043e04320438044500200434043e043a0443043c0435043d044204560432002e0020042104420432043e04400435043d04560020005000440046002d0434043e043a0443043c0435043d044204380020043c043e0436043d04300020043204560434043a04400438043204300442043800200437043000200434043e043f043e043c043e0433043e044e0020043f0440043e043304400430043c04380020004100630072006f00620061007400200456002000410064006f00620065002000520065006100640065007200200036002e00300020044204300020043f04560437043d04560448043804450020043204350440044104560439002e> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 monitoring and control system with a client-server model based on internet of things (iot) sri ratna sulistiyanti, f.x. arinto setyawan*, sri purwiyanti, helmy fitriawan and adam rabbani adnan 1 department of electrical engineering, faculty of engineering, universitas lampung, bandar lampung, indonesia * corresponding author: fx.arinto@eng.unila.ac.id (received: 25th august 2020; accepted: 25th september 2020; published on-line: 4th january 2021) abstract: safety and comfort are needs for all human beings. meanwhile, the crime rate is increasing. therefore, a remote monitoring and control system is needed. this research offers a home monitoring and control system with a client-server model using nodemcuesp-12e. the equipment design can be used to monitor the condition of the house through sensors installed in each room. home monitoring includes motion detection using a motion sensor, detection of the condition of the house door using a magnetic sensor, and remote door locking using a solenoid. the system can be operated offline or online using an android smart phone. the communication model used for client-server over the transport layer protocol is user datagram protocol (udp), so the server can communicate simultaneously on two clients. the fastest average response time is 0.653 seconds. the communication model between a server and a cloud uses transmission control protocol (tcp) so that the data sent or received by the server through the internet is more reliable. the cloud used is firebase which has real-time database facilities and historical data. when online, sensor response time average is the fastest on an android at 3.898 seconds, response time control is the fastest average on a client at 7.157 seconds and the control response time average is the fastest on an android at 9.495 seconds. abstrak: keselamatan dan keselesaan merupakan keperluan penting untuk manusia. sementara itu kadar jenayah pula kian meningkat. oleh itu, kita perlu pemantauan jarak jauh dan sistem kawalan. kajian ini merupakan sistem kawalan dan pemantauan rumah dengan model pelanggan-pelayan menggunakan nodemcuesp-12e. peralatan yang dibina boleh digunakan bagi mengawasi keadaan rumah melalui sensor yang dipasang dalam setiap bilik. pemantauan rumah adalah termasuk pengesan gerakan menggunakan sensor gerakan, pengesan keadaan pintu rumah menggunakan sensor magnet, dan pengunci pintu jarak jauh menggunakan solenoid. sistem ini boleh digunakan secara luar atau dalam talian menggunakan telefon pintar android. model komunikasi yang digunakan pada pelanggan-pelayan menggunakan protokol lapisan pengangkutan adalah protokol datagram pengguna (udp), oleh itu pelayan dapat berkomunikasi secara terus dengan dua pelanggan pada purata masa respon terlaju sebanyak 0.653 saat. model komunikasi antara pelayan dan awan adalah menggunakan protokol kawalan penghantaran (tcp), dengan harapan data dapat dihantar dan diterima oleh pelayan melalui internet dengan lebih kebolehpercayaan. awan yang digunakan adalah firebase yang mempunyai kelengkapan pengkalan data waktu nyata dan data sejarah. melalui keadaan dalam talian, purata masa sensor bertindak balas adalah paling laju pada android sebanyak 3.898 saat, purata kelajuan kawalan masa bertindak balas pada pelanggan adalah 7.157 saat dan purata masa kawalan tindak balas adalah paling laju pada android sebanyak 9.495 saat. 93 iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 keywords: iot; client-server; control; monitoring; android; nodemcu esp-12e 1. introduction home is where we live to meet daily needs. along with the development of current times, many are using electronic systems inside their houses or buildings. home security technologies in use today are often web-based, so home security monitoring only occurs when the owner opens the web address. homeowners do not know the condition of their house directly, so that when there is a danger, unwanted events cannot be prevented in a timely manner. one solution for checking security conditions and home control each time it is needed is a tool that can monitor the application via smartphone with an internet connection using the concept of the internet of things (iot) so that users can know the state of the home anytime and at any distance via the internet. the concept of iot is where objects can communicate with other objects or any embedded sensors connected through an internet network [1]. one of the services used in the concept of the iot is firebase. firebase is a cloud service provider (csp) and a backend as a service (baas) owned by google which allows users to store data and read data in real time [2,3]. as a result of using these technologies, features don’t need to be built from scratch and focus can shift to easily developing iot-based applications without the need to create a cloud. previous research has been carried out by nama, who designed a surveillance system over the internet using a bcm 2835 microcontroller and sent notifications via a short message service [4], and despa, who designed smart monitoring of electrical quantities based on single board computer bcm2835 [5]. other research was conducted by nurfaif who designed a smart home using raspberry pi through the global system for mobile communication (gsm) network [6]. other research has also been carried out by kodali whose home security system uses the cc3200 it microcontroller. the system works on a single microcontroller with sensors via cables and sends notifications via telephone calls [7]. subsequent research was carried out by malche who designed a monitoring system via the mqtt-based internet web [8]. this research, designed to make home security maintained by monitoring the condition of a house, turning on the blower when there was lpg gas, locking the door electronically, and controlling the electric light in each room through the android application over the internet (online) or a local network (offline). 2. the proposed system this research uses firebase to facilitate the communication of mobile and web applications. firebase is a cloud service provider offered by google to facilitate the development of mobile and web applications. firebase has real-time database facilities and historical data. the block diagram of the monitoring and control equipment designed through this research is shown in fig. 1. the client consists of some sensors, each of which is connected to nodemcu esp12e. client 1 is the mc-38 magnetic sensor and hc-sr505 motion sensor, client 2 is a hcsr505 motion sensor, and client 3 is a hc-sr501 motion sensor and mc-06 gas sensor. each client is connected to nodemcu esp-12e which then connects to a server in the form of nodemcu sp-12e as well. 94 iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 fig. 1: block diagram of system design. 2.1 internet of things internet of things is a concept where certain objects have the ability to transfer data through the internet [1]. this process does not require interaction from humans to humans or humans to a computer but can run automatically with the program. the constituent elements of iot are artificial intelligence, sensors, connectivity, and various devices that are small in size. control and monitoring from very long distances can be done using iot through the internet network. sensors on the client side feel the phenomena that occur around them and send data to the microcontroller to be processed into information. information from the microcontroller is then sent through the internet to the user's smartphone. smartphone users can provide actions in the form of controlling remotely. iot devices can be connected to cameras installed in various locations in the city [9]. cameras can be used for traffic monitoring, security for example, at banks, or face recognition to assist police. iot applications in the health sector are used for remote monitoring and emergency notification systems [10]. this remote monitoring can range from monitoring blood pressure, heart rate, to sophisticated devices, namely monitoring special implants. 2.2 firebase firebase is a cloud service provider (csp) and a backend as a service (baas). firebase is the solution offered by google to simplify mobile and web application development [2]. this solution means that features don’t need to be developed from scratch and focus can be placed on easily developing iot-based applications without the need to create a dedicated cloud. firebase has many sdks that allow it to integrate with android, ios, javascript, c++ to unity. 2.3 client-server client-server is a work arrangement in accessing a server on a particular network between client and server. data communications on the client-server are a range of interfaces that function as a place to run database applications. a client-server network is a computer network architecture where the client device will process the request for data, and the server has the task of responding in the form of data to the request [7]. the communication model of client and server network systems is shown in fig. 2. client 1 used for controlling solenoid door locks in order to unlock and lock the doors, monitor motion, and monitor the condition of the door on the front porch of the house. client 1 can be installed at the front door of the house. the goal is to be able to open and 95 iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 close the door remotely and notify the homeowner if there is someone in front of the house. client 2 is used to control the lights in the living room and monitor the movements in the house. client 2 can be installed in the living room and used to monitor if there are people in the house. fig. 2: client-server network block diagram. fig. 3: local network block diagram. 3. experimental results in this research, a comparison is made between the time response of the equipment in responding to commands when using either a local network or the internet. the response time is determined using a stopwatch. a local network is a communication network using a wi-fi connection that gives commands to equipment over a maximum distance of only 10 meters. communication or commands to equipment using the internet network can be done from anywhere with unlimited distance. figure 3 shows a block diagram of a local network where communication is done between an android mobile and equipment via a wifi ap. 3.1 client 1 data response time on client 1 on the local network is shown in table 1. the response time is the delay of the action that occurs on the sensor when given a command through the local network. data is taken from five attempts with the initial conditions of both the door being closed or the door being open. table 1: response time client 1 and android on the door with a magnetic sensor (mc-38) when offline no. response time of android (seconds) the initial state of the door the final state of the door 1 2.24 closed open 2 3.55 closed open 3 2.88 closed open 4 2.65 closed open 5 1.65 closed open 6 1.78 open closed 7 2.91 open closed 8 3.28 open closed 9 2.69 open closed 10 1.58 open closed table 1 shows the response time for magnetic sensor (mc-38) given the state of the door with certain conditions on the local network or offline. response time where the client sends data or sensor feedback results to the server and the server data or sensor results broadcast feedback to android wifi ap via a network. the value of the response time average for android is 2.521 seconds. 96 iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 on the server, the data is processed in the form of json data type and then the sensor or result data broadcasts feedback to the wifi ap. the android listens to data from the server via the wifi ap network and receives the sensor results data. on android applications, each client listens to data sensor results from the server via wifi ap. the client had an arranged time span to send data or sensor feedback results to the server with a range of 1000 ms and span of time servers for broadcast data or sensor feedback results to wifi ap i.e. 1000 ms. so, the total minimal time span required from the client to the android application through the local network or offline is 1000 ms. there exists a delay in response time because when the client sends to the server. if the server is not processing data at that time, such as when it is still processing data from the cloud, this creates a span of 300ms for client listening. when a server sends broadcast data to android, android receives data every 1000ms and processes data from the firebase cloud conditions. table 2 shows android data response time on client 1, for magnetic sensors (mc-38) given the state of the door with a particular condition on the internet network or online. the android response time is where the client sends data or sensor feedback results to the server and the server is writing data to the sensor or the results of the feedback to the cloud through a network of wifi ap firebase. the value of the response time average android is 4.373 seconds. table 2. response time client 1 and android on the door with a magnetic sensor (mc38) when online no. response time of android (seconds) the initial state of the door the final state of the door 1 4.04 closed open 2 5.77 closed open 3 2.84 closed open 4 4.54 closed open 5 3.61 closed open 6 5.25 open closed 7 5.99 open closed 8 4.76 open closed 9 2.47 open closed 10 4.46 open closed on the server, the data results of the sensors or feedback received from the client is processed in the form of json data type and, if the data changes, then the server writes the results of sensor data or feedback to the firebase network through cloud wifi ap. the android app reads sensor data from each client from the cloud firebase. the client has an arranged time span to send data or sensor feedback results to the server with a 1000 ms range and the span of time the server to write data or sensor feedback results to the cloud through a network of wifi ap firebase with a 4000 ms range. so, the total minimal time span required from the client to the internet network through the android application or online is 4000 ms. there exists a delay in response time, because when the client sends data to the server at the time of that time, the server is still processing the data from the cloud and 300ms for listening span client and when the server sends a broadcast data to android. android receives data every 1000 ms and processes data from the cloud conditions firebase. 97 iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 the android data response time on client 1 for motion sensors (hc-sr505) was given to the condition of the moving objects on the local network or offline and online shown by table 3. the response time of the android is where the client sends data or sensor feedback results to the server and the server data or sensor results broadcast feedback to android wifi ap via a network. in this research, data retrieval is carried out 10 times when the motion sensor senses the object moving. the value of the android response time average is 2.3 seconds for a local network and 4.753 seconds. the android app reads sensor data of each client from the cloud firebase. the client has arranged a time span to send data or sensor feedback results to the server with a 1000 ms range and the span of time for the server to write data or sensor feedback results to the cloud through a network of wifi ap firebase is 4000 ms range. so, the total minimal time spans required from the client to the internet network through the android application or online is 4000 ms. table 3: response time client 1 and android on the sensor motion (hc-sr505) when online there exists a delay in response time because when the client sends data results of a sensor to the server, the server is still processing the data from the cloud and the server has a server listening span of 300 ms. when the server sends data from the cloud conditions, firebase and android are reading data from a cloud firebase every 1000 ms. table 4 shows data for the response time of client 1 and android, when the solenoid door lock is executed with open and closed conditions on the local network or offline. the client response time is faster than android because the response time of the client is the response time span between the android data giving instructions to the server through a network access point (ap) wifi broadcast and the server data instructions to the client via the wi-fi network server. while the response time on android is the response time of a client after the process and the android listening time. android listening time process is a time span of listening data from the server via the wifi ap network. the value of the average client response time is 0.653 seconds and the value of the android response time averages is 4.108 seconds. on the server, data and instructions from android are treated in the form of json data and then the instruction data is sent to the broadcast client, so the client receives the instruction data and executes it. the server has an arranged span to send data to the client with an instructions range of 500 ms. so the minimum range of client response time via local network or offline is 500 ms. no. response time of android when offline (seconds) response time of android when online (seconds) 1 3.8 4.45 2 1.85 5.75 3 3.02 3.54 4 3.09 5.08 5 2.64 5 6 1.85 4.32 7 1.29 3.54 8 1.78 5.62 9 2.03 4.52 10 1.65 5.71 98 iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 table 4: response time client 1 and android on the solenoid door lock when offline no. response time of client (seconds) response time of android (seconds) the initial state of the lamp the final state of the lamp 1 0.85 4.19 closed open 2 0.8 3.84 closed open 3 0.6 4.47 closed open 4 0.61 3.36 closed open 5 0.53 3.8 closed open 6 0.74 6.15 open closed 7 0.6 3.95 open closed 8 0.66 3.95 open closed 9 0.54 3.39 open closed 10 0.6 3.98 open closed on android, the client sends data measurement results or feedback data to a server with a span that is 1000 ms, the server listening to the client is set up with a span that is 300 ms, and server processes the data of each client in the form of json data then server broadcast to android apps via the ap with wifi within 1000 ms. so the minimum range of response time from android to the server to the client and that client to the server through a local network to the android or offline is 1500 ms. the existence of a delay in response time is because when android data sends instructions to a server, the server is still processing the data from the cloud, a 300ms listening client span, and the time for the server to send broadcast data to android. the android application receives data every 1000ms and the server processes the data to the cloud conditions firebase. when the client next sends the feedback data to the server, the server is still processing the data from the cloud and the server has a span of 300ms for client listening. when a server sends a broadcast data to android, android receives data every 1000 ms. table 5: response time client 1 and android on the solenoid door lock when online no. response time of client (seconds) response time of android (seconds) the initial state of the lamp the final state of the lamp 1 7.85 14.73 closed open 2 10.19 16.71 closed open 3 6.8 13.79 closed open 4 7.85 14.39 closed open 5 6.87 12.95 closed open 6 5.88 10.28 open closed 7 8.24 15.03 open closed 8 6.94 11.44 open closed 9 8.82 12.1 open closed 10 8.58 13.81 open closed table 5 shows data of the response time of a client and android for client 1, when the solenoid door lock executes commands with open and closed conditions over the internet network or online. the response time of the client is faster than the android response time because the response time on the client is the response where the time span between android writes instruction data to the firebase cloud, the server reads the firebase cloud, and the server broadcasts the instruction data to the client via the wifi server network. while the response time on android is the response time after the client response time process, the 99 iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 server time process writes instruction data to the firebase cloud, and the android time process reads the firebase cloud. the average response time of the client is 7.802 seconds and the average response time of the android is 13.523 seconds. 3.2 client 2 client 2 is a controller for living room lights and monitoring of moving objects in the house. table 6 and table 7 shows the data for the response time of a client and android on client 2, when executed with the final state of a particular lamp through the local network (offline) and internet (online). the average client response time for the living room lights is 0.986 seconds and the average value of the android response time is 3.719 seconds on the local or offline network. while the average client response time for a living room lamp is 7.157 seconds and the average value of android response time is 9.495 seconds on the internet or online. table 6: response time to client 2 and android on the living room light when offline no. response time of client (seconds) response time of android (seconds) the initial state of the lamp the final state of the lamp 1 1.19 3.44 off on 2 0.93 2.62 off on 3 0.73 2.87 off on 4 1.12 4.61 off on 5 0.79 3.1 off on 6 1 4.83 on off 7 1.19 3.26 on off 8 0.73 4.71 on off 9 1.12 4.99 on off 10 1.06 2.76 on off table 7: response time to client 2 and android on the living room light when online no. response time of client (seconds) response time of android (seconds) the initial state of the lamp the final state of the lamp 1 8.57 11.58 off on 2 7.19 9.38 off on 3 7.46 9.56 off on 4 6.74 9.12 off on 5 6.67 8.77 off on 6 5.96 8.51 on off 7 8.82 11.07 on off 8 8.25 10.33 on off 9 5.69 8.16 on off 10 6.22 8.47 on off table 8 shows the android data response time on client 2, when the motion sensor (hcsr505) found the condition of a moving object when used on a local network and the internet. response time of the android on the local network is the time response when the client sends data or sensor feedback results to the server and the server data or sensor results broadcast feedback to android wifi ap via a network. the value of the android response time on the local network is 1.411 seconds. 100 iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 android response time on internet network is response time where the client sends data or sensor feedback results to the server and the server is writing data to the sensor or the results of the feedback to the firebase network through cloud wifi ap. on the server the data results of the sensors or feedback received from the client are processed in the form of json data type and, if the data changes, then the server writes data the results of sensor or feedback to the cloud through a network of wifi ap firebase. the value of the response time averages android using the internet network is 3.898 seconds table 8: response time to client 2 and android on the sensor motion (hc-sr505) when offline and online 3. conclusion on the designed system, client response time for offline usage is faster than online. the offline use does not require an internet network and is done only through wifi ap communication with android mobile. online use requires an internet network to communicate with firebase, which takes longer. the average response time of the magnetic sensor on client 1 for offline usage is only 2.521 seconds while online usage takes 4.373 seconds. the average response time of the motion sensor on client 1 for offline usage is only 2.3 seconds while online usage takes 4.753 seconds. the average response time of the solenoid on the client-side for offline usage is only 0.653 seconds and on android side is 4.108 seconds while online usage takes 7.802 seconds on the client-side and 13.523 seconds on the android-side. for lamp control on client 2, the average response time takes 0.986 seconds on the client-side and 3.719 seconds on the android side on offline use, while online usage takes 7.157 seconds on the client-side and 9.495 seconds on the android side. the average response time of the motion sensor on client 2 for offline usage is only 1.411 seconds while online usage takes 3.898 seconds. for further research, more sensors such as gas sensors, visual sensors (cameras), temperature sensors, and voltage sensors need to be added to provide more safety for the user. acknowledgement thank you to the ministry of research, technology and higher education, directorate general of research and development, directorate of research and community service for the funds provided through the ppupik scheme. no. response time of android on local network/offline (seconds) response time of android on internet network/online (seconds) 1 1.58 3.74 2 1.19 4.83 3 1.33 3.35 4 1.06 3.68 5 1.45 3.37 6 0.92 3.73 7 1.85 3.89 8 1.57 4.4 9 1.39 3.99 10 1.77 4 101 iium engineering journal, vol. 22, no. 1, 2021 sulistiyanti et al. https://doi.org/10.31436/iiumej.v22i1.1596 references [1] minerva r, biru a and rotondi d. (2015) towards a definition of the internet of things (iot). in proceeding ieee internet initiative: 1-86. [2] moroney l. (2017) the definitive guide to firebase. a press, california, google. [3] zuhelmi tp, sulistiyanti sr, setyawan fxa, adnan ar. (2019) smart home controlling and monitoring system using multiboard client-server internet of things (iot). journal of engineering and scientific research, 1(2): 69-73. [4] nama gf (2013) the design of an internet connection monitoring system at lampung university based on a mini single board computer bcm2835. (rancang bangun sistem monitoring sambungan internet universitas lampung berbasis mini single board computer bcm2835). in proceeding national seminar on science & technology v: 73-83. [5] despa d, kurniawan a, komarudin m, mardiana, nama gf. (2015) smart monitoring of electrical quantities based on single board computer bcm2835. in proceeding of the 2nd international conference on information technologies, computer, and electrical engineering (icitacee 2015):315-320. [6] nurfaif mb, sulistiyanti sr, komarudin m, nama gf (2017) telemetry and tele-control of electronic appliances for smart-home-system. in proceeding international symposium on electronics and smart devices (isesd):18-23. [7] kodali rk (2016) iot based smart security and home automation system. in proceeding international conference on computing, communication and automation (iccca):12861289. [8] malche t (2017) internet of things (iot) for building smart home system.in proceeding international conference on i-smac palladam-2017:65-70. [9] bharati ts. (2019) internet of things (iott: a critical review. international journal of scientific & technology research, 8:227-232. [10] madhavia mvdns, hemalathaa k, sairamb pvs, rajani d. (2016) healthcare applications of the internet of things (iot): a review. proceedings of 3rd international conference on emerging technologies in computer science & engineering (icetcse 2016):205-213. 102 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 word segmentation of output response for sign language devices nor farahidah za’bah*, ahmad amierul asyraf muhammad nazmi, amelia wong azman department of electrical and computer engineering, kulliyyah of engineering, international islamic university malaysia, kuala lumpur, malaysia *corresponding author: adah510@iium.edu.my (received: 22nd march 2020; accepted: 11th june 2020; published on-line: 4th july 2020) abstract: segmentation is an important aspect of translating finger spelling of sign language into latin alphabets. although the sign language devices that are currently available can translate the finger spelling into alphabets, there is a limitation where the output is stored in a long continuous string without spaces between words. the system proposed in this work is meant to be used together with a text-generating glove device. the system used text input string and the string is then fed into the system, one character at a time, and then it is segmented into words that is semantically correct. the proposed text segmentation method in this work is by using the dynamic programming and back-off algorithm, together with the probability score using word matching with an english language text corpus. based on the results, the system is able to properly segment words with acceptable accuracy. abstrak: segmentasi adalah aspek penting dalam menterjemahkan ejaan bahasa isyarat ke dalam huruf latin. walaupun terdapat peranti bahasa isyarat yang menterjemahkan ejaan jari menjadi huruf, namun begitu, huruf-huruf yang dihasilkan disimpan dalam rentetan berterusan yang panjang tanpa jarak antara setiap perkataan. sistem yang dicadangkan di dalam jurnal ini akan diselaraskan bersama dengan sarung tangan bahasa isyarat yang boleh menghasilkan teks. sistem ini akan mengambil rentetan input teks di mana huruf akan dimasukkan satu persatu dan huruf-huruf itu akan disegmentasikan menjadi perkataan yang betul secara semantik. kaedah pembahagian yang dicadangkan ialah segmentasi yang menggunakan pengaturcaraan dinamik dan kaedah kebarangkalian untuk mengsegmentasikan huruf-huruf tersebut berdasarkan padanan perkataan dengan pengkalan data di dalam bahasa inggeris. berdasarkan hasil yang telah diperolehi, sistem ini berjaya mengsegmentasikan huruf-huruf tersebut dengan berkesan dan tepat. key words: segmentation, sign language, algorithm 1. introduction sign language is the main language used by deaf people around the world. however, there is always a gap between them and people without disability, since communication is a problem between them. sign language is a necessity for people with hearing problems to communicate and interact with others. for non-disabled people, learning sign language is optional. even if they learn sign language, it is difficult for them to be able to grasp it well as they do not use it frequently unless they are around the deaf community. this is the reason why a sign language device is needed. the device may help to improve communication and reduce the language barrier between them. in order to solve this problem, numerous research and studies were performed to make a sign language device possible. although there are many research papers on the topic, there are still many challenges and still there are no perfect solutions for translating sign language into other languages due to various constraints. 153 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 one of the biggest challenges in making a sign language device is the segmentation issue [1]. this issue is faced differently based on the types of input for the device. for example, camera-based sign language devices must be able to detect the hand sign made by the user correctly to ensure a proper translation [1]. glove-type devices [2][3], on the other hand, are based on digital text output but face issues to segment the text and sentences properly. therefore, it is difficult for these devices to determine what kind of output to produce and what the user intends to do, without a proper segmentation system. currently, a glove-type device that can produce character output based on hand signs is being researched. however, it is not working properly as it faces the text segmentation issue. all the alphabet character outputs from the device are stored in a long continuous string of text without spaces. for example, if the user intends to say “word of the day”, the output that will be produced is ‘wordoftheday’. therefore, in order to split this string, word segmentation needs to be performed to ensure that the output is correct and will be understood by humans [4]. there are a number of segmentation systems proposed using different approaches and algorithms to improve the accuracy of the output due to the challenges faced in many areas such as language translation and spelling correction. table 1 shows a summary of some previous work on segmentation. table 1: summary of some previous work on segmentation reference application input technique g. a. rao, p. kishore [1] sign language translation video captured with camera used gaussian filtering for pre-processing and segmentation. then, hand and head contour are segmented with morphological subtraction. peter norvig [4] word segmentation, spelling correction text input, url proposed a general method of word segmentation based on google n-gram dataset using python programming. w. jiang [5] word segmentation text input from user proposed a method of word segmentation using dynamic programming to improve performance. divide and conquer algorithm is introduced so there will be no maximum length character limit for the input. s. n. nawaz [6] word segmentation urdu text proposed word segmentation model using conditionalrandom field (crf) algorithm. d. tanaya and m. adriani [7] language transcription text in javanese script and latin character used a dictionary-based model with maximal matching algorithm modified with additional steps. performed character statistics on the dictionary to improve the output score. s. srinivasan, s. bhattacharya [8] web-domain and hashtag segmentation capturing url from website and twitter hashtag from twitter api used multiple corpora from different sources to improve the accuracy of segmentation and used dynamic programming to implement inference algorithm. y. bassil, m. alwani [9] spelling correction for optical character recognition (ocr) optical character recognition (ocr) output text proposed an error correction algorithm based on google spelling suggestion. the output from ocr will be fed to google search engine and triggers “did you mean” feature if there is at least one error. google search is capable of segmenting words properly in case the ocr output text has spacing error. s. p. panda and a. k. nayak [10] speech recognition system voice recorded in .wav file proposed a model that performs segmentation at syllable boundaries using vowel offset point (vop) identification and zero-crossing rate (zcr) technique. 154 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 reference application input technique y. bassil, m. alwani [11] error correction for automatic speech recognition (asr) asr output text an error correction algorithm based on bing spelling suggestion. the output of asr will be fed to bing search engine as an input. s. s. chawathe [12] word segmentation sanskrit text proposed a dictionary-based model with dynamic programming to match the input with the dictionary word with the inclusion of aho-corasick algorithm 2. methodology 2.1. overview for the proposed word segmentation system, three main components are required as shown in fig. 1; the text input, the processing algorithm that contains the text dictionary, and the output. while the input and output are simple and self-explanatory, the processing algorithm involves some steps and procedures in order to process the data and produce the intended output. this will be discussed in the next section. fig. 1. block diagram for the word segmentation model for the input, a text-generating glove device is used to produce the alphabet characters to be fed into the system. however, in this work, a keyboard input will be used to emulate the glove device to produce the alphabet characters when the wearer makes a proper hand sign. since the glove can only produce alphabet characters, all the non-alphabet keyboard keys such as “spacebar”, “enter”, “backspace” and all non-alphabet keys will be ignored. the flowchart for the model is illustrated in fig. 2. since the “enter” key is ignored, the string will be continuously fed into the system every time a character is added. secondly, for the processing of the input, python programming language will be used to write and implement the segmentation algorithm. also, for this work, a preinstalled dataset called text corpus will be used as the word library for the word matching mechanism. this text corpus is used to provide a vocabulary of words to the processor and “guide” the system with the correct words for segmentation. this is similar to the work done by jiang [5] and jenks [13] on the general word segmentation algorithm. for the output, it will be directly shown on display as soon as a character is added into the string. when the user stops entering an input for more than 3 seconds, the system will reset the input in order to allow the user to enter the next line of strings. 155 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 set timer to 3 seconds user enters characters into the system using the keyboard add character into a single input variable segmentation process starts – where the input will be matched with the words stored in the text corpus. display the output on the screen, and the timer is set to 3 seconds again if user enters another character in less than 3 seconds, the previous output is reset and the character is added to the first string of characters and segmentation process starts again fig. 2. flowchart of the segmentation system 2.2. segmentation algorithm there are some steps involved in implementing the word segmentation system, which involves the division of characters into possible words and then matching the words with the words contained in the text corpus. this part takes place after the input string is being fed into the processor. 2.2.1. dynamic programming the process of matching strings with words inside the text corpus is performed using dynamic programming. dynamic programming is a well-known method used in programming to solve complex problems by breaking them into smaller and simpler subproblems. in the case of word segmentation, a long continuous string entered by the user is split into two substrings by matching the string with the proper word inside the text corpus [5]. the first string will be the matched word and the latter will become the character strings that are not yet processed. then, the system recurs multiple times until the last character of the string, then splitting it into possible words, as shown in fig. 3. if no word can be found due to typing error, it will either separate the string into single character or simply return the input as the output. 156 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 fig. 3. dynamic programming example 2.2.2. word matching algorithm using probability score after the division of characters, the process of matching strings with words inside the text corpus is done using a word matching algorithm. basically, when the user enters a string, the system will try to match the string with the words contained in the dictionary. using a word dictionary is one of the common ways for creating a word segmentation model [7]. if the model finds a matched word, then that part of the string will be segmented. then, the process is iterated until it reaches the end of the string. the matching algorithm will also rely on the probability of the word as well as the whole sentence. as shown in fig. 4, the frequency is stored together with the word in the dictionary. if there are multiple ways of segmenting the string, it will prioritize the word with higher probability. also, longer words will be prioritized compared to shorter words. for example, the string “strawberry” will be segmented as “strawberry” instead of “straw” and “berry” although these two words are stored in the dictionary, and “berry” has a higher probability compared to “strawberry”. this is because the system will consider the total probability of the string, which is the multiplication of probability for each word [4]. in theory, it can be calculated by using equation 1 [4] shown below. p (w1: ) = π = 1: p (w | (w1: −1) (1) equation 1 is highlighted in norvig [4] states that, based on the context of a particular word, the probability of a sequence of words [p (w1: is the product of the probabilities of all the preceding words [π = 1: p (w | (w1: −1)] within the same context. it means that, for example, using a 5-word sequence – “honesty is the best policy” the probability of this word sequence would be the product of each word given the four previous words. 157 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 fig. 4. the word ‘instagram’ and its frequency is obtained using a search engine 2.2.3. back-off algorithm for every word segmented, the algorithm will check whether there is any bigram probability for the next word to occur. a bigram dataset is used in the system to ensure better accuracy of the segmentation. however, since there are chances that the probability of the bigram is zero, a back-off algorithm is included in the system to ensure no error in probability calculation due to multiplication by zero [4]. the back-off algorithm will simply ignore the bigram probability and continue the segmentation using unigram probability, or the probability for every single word. however, one of the disadvantages in implementing this is that the system will take a longer time to match each word in the unigram database, whereas if the bigram probability score is included, the computation time may be shorter. 2.2.4. text corpus text corpus (plural: corpora) is a huge collection of structured text stored in electronic form. it is used as a dataset for the word matching process so that the string input can be segmented into the correct output. in this work, the text corpus is massively important because the matching word will solely rely on it for segmentation purposes. in order to obtain a highly accurate output, a huge file of text corpus or multiple collection of corpora is required. therefore, the corpus is taken from the google n-gram dataset where it contains billions of words that are collected by google’s users around the world, which is stored in multiple ways; a single word (unigram), 2-word phrase (bigram), 3-word phrase (trigram) and so on. since the file size of the n-gram corpus is so big that it may consist of hundreds of gigabytes of memory, this work only considers the unigram and the bigram database. however, it is not difficult since all this data is provided by norvig [4] and is also being used for other word segmentation models. fig. 5 shows some of the words contained in the unigram and bigram dataset. this text corpus also contains the word frequency for each word for the purpose of increasing accuracy to determine the correctness of a word for a certain input. as shown in fig. 3, “home” and “homes” are both valid words that are the candidates for the output. here, the probability is calculated to ensure that the word with the higher probability is chosen. the term “homes and” generally has higher word frequency compared to “home sand”, hence the former is chosen. 158 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 fig. 5. unigram and bigram count inside the text corpus [4] 3. result and analysis 3.1. python programming python coding was developed specifically for word segmentation systems. it involves the process of loading the text corpora -unigram as well as bigram textto improve the accuracy of word segmentation. when the user starts the program, it will automatically load all these three text files into the program and store every word and its frequency in the dictionary. this is completed in a couple of seconds when the program is executed. then, the user can start entering the text using a keyboard. since this work is specifically made for the sign language device, it is programmed to accept only lower-case alphabet characters and numbers. all other buttons and symbols will be ignored, including the spacebar, enter, and delete buttons. if the user presses these keys, nothing will happen. however, for required functions such as ‘moving to next line’ or spacing between words, a delay time of 3 seconds is used as described in fig. 2. fig. 6 illustrates the graphical interface of the segmentation program. when the program is executed, two windows will be opened; one for the main windows for displaying the input and output and the other is to display the timer. 159 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 fig. 6. the graphical interface of the segmentation program by referring to fig. 6, when a user enters the string “thisisawordsegmentationprogram”, the program will automatically split the text and generate a correctly spaced text output. however, as mentioned earlier, the system will accept the input per character and the segmentation process occurs simultaneously as the user continues to key in the character. if the whole process were to be displayed, it would show a list of outputs as illustrated in fig. 7, where it illustrates that during the segmentation process, the segmentation output may change while user enters the input; such as “word” and “words”. this behavior is caused by the change of probability score of the whole sentence during the process. the system will choose the highest probability score for the whole sentence as the chosen output. 3.2. challenges in the segmentation system while testing the system, some errors in segmentation may occur due to the following issues. 3.2.1. incorrect input one of the reasons for error in segmentation is the user may enter an incorrect character and due to the continuous mode of the system, the incorrect character will be stored in the string. as the system can neither delete the character in the string nor have any kind of error correction mechanism, a timer is used to tackle this issue as shown in fig. 8. it shows that a user needs to wait for 3 seconds to allow a timeout, at which the system will reset the input and output of the system and move to the next line where the user can basically start again. however, the incorrect string or word will still be displayed and hence, this might not be an efficient way to fix the incorrect input error. 160 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 fig.7. the word segmentation process flow fig. 8. the output of the segmentation process after timeout 3.2.2. missing words in corpus another limitation of the system is the database used in this work. although it contains 330,000 unigram words and around 250,000 bigram phrases, many highly specific words such as scientific terms and specific words like “instagram” are not available because the text corpora used were compiled in 2009. the system will also have issue in detecting uncommon human names and places, as these are too specific. however, there are only a handful of words that are not stored in the corpora and it rarely needs 161 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 to be updated. nevertheless, a function to add words into the unigram or bigram corpus is added in the system. it is done simply by adding the word “addunigram” into the unigram file. when the system detects the user entering “addunigram”, it will interrupt the segmentation process, triggering a popup window that allows the user to key in the word and its frequency, as shown in fig. 9 and 10 fig. 9. the system does not recognize the word ‘instagram’ and by using the command addunigram, a pop-up windows appears to key in the word and its frequency fig. 10. the system now recognizes the word ‘instagram’ 162 iium engineering journal, vol. 21, no. 2, 2020 za’bah et al. https://doi.org/10.31436/iiumej.v21i2.1408 4. conclusion in this work, a text segmentation algorithm for sign language was implemented using python programming. the system is able to segment a string of characters correctly for all the input strings tested and thus, it is proven that the system is working properly as a word segmentation system for english words. although, the system is unable to segment some specific words such as long scientific terms and special nouns, this can be fixed by adding a function to add words into the text corpus together with its frequency. one of the main limitations of this work is that the system is made specifically for a text-generating glove device assuming that it will only generate single alphabet characters. as of now, the system is not able to detect and process hand gestures in sign language that represents phrases such as “hello” and “thank you”. another observation is that the system can be a bit slow in producing the output if the string is too long (more than 30 characters) as it has to go through the words in the text corpus. future work is required to address this challenge and in addition, the system may also include creating corpora for other languages that use latin alphabets, such as the malay language. references [1] g. a. rao, p. kishore (2016) sign language recognition system simulated for video captured with smart phone front camera, international journal of electrical and computer engineering (ijece), vol. 6, no. 5, p. 2176 [2] boon giin lee and su min lee (2019) smart wearable hand device for sign language interpretation system with sensors fusion, ieee sensors journal pp (99):1-1 [3] ahmad zaki shukor et al, (2015) a new data glove approach for malaysian sign language detection, procedia computer science, vol. 76, pp 60-67 [4] norvig, peter (2009), natural language corpus data [5] w. jiang (2015), word-segmentation [http://pypi.org/project/wordsegmentation] [6] sadiq nawaz khan et al, (2018) urdu word segmentation using machine learning approaches, international journal of advanced computer science and applications(ijacsa), 9(6) http://dx.doi.org/10.14569/ijacsa.2018.090628 [7] d. tanaya and m. adriani (2016), dictionary-based word segmentation for javanese, procedia computer science, vol. 81, pp. 208–213 [8] s. srinivasan, s. bhattacharya, r. chakraborty (2012), segmenting web-domains and hashtags using length specific models, in proceedings of the 21st acm international conference on information and knowledge management, oct 2012, maui. [9] y. bassil, m. alwani (2012), ocr post-processing error correction algorithm using google online spelling suggestion., journal of emerging trends in computing and information sciences, vol. 3, no. 1 [10] s. p. panda, a. k. nayak (2015), automatic speech segmentation in syllable centric speech recognition system, international journal of speech technology, vol. 19, no. 1, pp. 9–18 [11] y. bassil, m. alwani (2012), post-editing error correction algorithm for speech recognition using bing spelling suggestion, international journal of advanced computer science and applications, vol. 3, no. 2 [12] s. s. chawathe (2018), lexical text segmentation using dictionaries, 2018 ieee 8th annual computing and communication workshop and conference (ccwc) [13] jenks, g. (2017), python word segmentation [http://grantjenks.com/docs/wordsegment] 163 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <feff004c006900650074006f006a00690065007400200161006f00730020006900650073007400610074012b006a0075006d00750073002c0020006c0061006900200069007a0076006500690064006f00740075002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c0020006b006100730020007000690065006d01130072006f00740069002000640072006f01610061006900200075007a01460113006d0075006d006100200064006f006b0075006d0065006e0074007500200073006b00610074012b01610061006e0061006900200075006e0020006400720075006b010101610061006e00610069002e00200049007a0076006500690064006f0074006f0073002000500044004600200064006f006b0075006d0065006e00740075007300200076006100720020006100740076011300720074002c00200069007a006d0061006e0074006f006a006f0074002000700072006f006700720061006d006d00750020004100630072006f00620061007400200075006e002000410064006f00620065002000520065006100640065007200200036002e003000200076006100690020006a00610075006e0101006b0075002000760065007200730069006a0075002e> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <feff004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <feff005400650020006e006100730074006100760069007400760065002000750070006f0072006100620069007400650020007a00610020007500730074007600610072006a0061006e006a006500200064006f006b0075006d0065006e0074006f0076002000410064006f006200650020005000440046002c0020007000720069006d00650072006e006900680020007a00610020007a0061006e00650073006c006a006900760020006f0067006c0065006400200069006e0020007400690073006b0061006e006a006500200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e0074006f0076002e0020005500730074007600610072006a0065006e006500200064006f006b0075006d0065006e0074006500200050004400460020006a00650020006d006f0067006f010d00650020006f00640070007200650074006900200073002000700072006f006700720061006d006f006d00610020004100630072006f00620061007400200069006e002000410064006f00620065002000520065006100640065007200200036002e003000200074006500720020006e006f00760065006a01610069006d0069002e> /suo <feff004b00e40079007400e40020006e00e40069007400e4002000610073006500740075006b007300690061002c0020006b0075006e0020006c0075006f0074002000410064006f0062006500200050004400460020002d0064006f006b0075006d0065006e007400740065006a0061002c0020006a006f0074006b006100200073006f0070006900760061007400200079007200690074007900730061007300690061006b00690072006a006f006a0065006e0020006c0075006f00740065007400740061007600610061006e0020006e00e400790074007400e4006d0069007300650065006e0020006a0061002000740075006c006f007300740061006d0069007300650065006e002e0020004c0075006f0064007500740020005000440046002d0064006f006b0075006d0065006e00740069007400200076006f0069006400610061006e0020006100760061007400610020004100630072006f0062006100740069006c006c00610020006a0061002000410064006f00620065002000520065006100640065007200200036002e0030003a006c006c00610020006a006100200075007500640065006d006d0069006c006c0061002e> /sve <feff0041006e007600e4006e00640020006400650020006800e4007200200069006e0073007400e4006c006c006e0069006e006700610072006e00610020006f006d002000640075002000760069006c006c00200073006b006100700061002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400200073006f006d00200070006100730073006100720020006600f60072002000740069006c006c006600f60072006c00690074006c006900670020007600690073006e0069006e00670020006f006300680020007500740073006b007200690066007400650072002000610076002000610066006600e4007200730064006f006b0075006d0065006e0074002e002000200053006b006100700061006400650020005000440046002d0064006f006b0075006d0065006e00740020006b0061006e002000f600700070006e00610073002000690020004100630072006f0062006100740020006f00630068002000410064006f00620065002000520065006100640065007200200036002e00300020006f00630068002000730065006e006100720065002e> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 212-986-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jamal et al. 109 production of biosurfactant in 2l bioreactor using sludge palm oil as a substrate p. jamal, m.z. alam, e.a. zainuddin and w.m.f.w. nawawi bioenvironmental engineering research unit (beru), department of biotechnology engineering, faculty of engineering, international islamic university malaysia (iium), p.o. box 10, 50728 kuala lumpur, malaysia. jparveen@iium.edu.my abstract: in this study, sludge palm oil was utilized as a raw material for process optimization in a stirred tank bioreactor for the biosurfactant production. optimized parameters include temperature, agitation and aeration while the ph and media compositions such as nano3, nacl, feso4, meat extract, and glucose have been fixed from the previous study. the design of this research was made by using the designexpert software (2 level factorial design). surface tension was used as indirect indicator for biosurfactant production. after model validation, yield of biosurfactant was found to be highest when surface tension was at its lowest value (<24 mn/m) at temperature of 30 0 c , agitation 300 rpm and around 0.5 vvm of aeration with percentage error less than 10% between observed value and predicted value. the finding in this research can be applied to produce biosurfactant in large amount from the less expensive material such as sludge palm oil by using the same optimized model equation. abstrak: dalam kajian ini, enapcemar kelapa sawit digunakan sebagai bahan mentah untuk pengoptimuman proses dalam bioreaktor bagi penghasilan biosurfactant. parameter yang dioptimumkan termasuk suhu, pergolakan dan pengudaraan manakala ph dan komposisi media seperti nano3, nacl, feso4, ekstrak daging, dan glukos telah ditetapkan daripada kajian sebelumnya. reka bentuk kajian ini telah dilakukan dengan menggunakan perisian design expert (2 level factorial design). tegangan permukaan digunakan sebagai penunjuk tidak langsung untuk penghasilan biosurfactant. selepas pengesahan, hasil biosurfactant didapati terbanyak apabila tegangan permukaan pada nilai terendah (<24 mn/m) pada suhu 30 0 c, pergolakan 300 rpm, dan sekitar 0.5 vvm pengudaraan dengan margin perbezaan kurang daripada 10% antara nilai sebenar cerapan dan nilai yang diramalkan. penemuan dalam kajian ini boleh digunakan untuk menghasilkan biosurfactant dalam jumlah yang besar dari bahan yang murah seperti enapcemar kelapa sawit dengan menggunakan model optimum yang sama. keywords: biosurfactant; sludge palm oil; process optimization; factorial design 1. introduction nowadays, the usage of surfactant is very popular in various fields. examples of an area that have been utilized this compound includes cosmetics, pharmaceuticals, petroleum, petrochemicals, food, beverages, environmental control, and agrochemicals [1]. current worldwide surfactant markets estimates around us$9.4 billion per annum, and their demand is expected to increase at a rate of 35% toward the end of the century [2]. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jamal et al. 110 however, the emergence of biosurfactant, which have the capability to reduce surface and interfacial tension with low toxicity, with high specificity and biodegradability, led to an increasing interest on these microbial products as alternatives to chemical surfactants. biosurfactants are microbial compounds with a pronounced surface activity that can exhibit a wide variety of chemical structures, such as glycolipids, lipopeptides, polysaccharide protein complexes, protein-like substances, lipopolysaccharides, phospholipids, fatty acids and neutral lipids [3]. nevertheless, biosurfactants are still unable to compete with chemically synthesized surfactants in the market. this may be due to their high production costs in relation to inefficient bioprocessing method available, poor strain productivity and the need to use of expensive substrates [4]. despite possessing many commercially attractive properties and clear advantages compared to their synthetic counterparts, the production of microbial surfactants on a commercial scale has not been realized because of their low yields and high production costs. moreover, biosurfactants are difficult to produce as cost effective for several reasons such as overproducing strains of bacteria are rare and those found generally display a very low productivity so that complex media need to be applied [5]. in this study, production of biosurfactant was initiated by optimizing the growth of the potential biosurfactant producers as the factor of several process parameters such as temperature, agitation and, aeration in 2 l bioreactor. 2. material and methods 2.1 microorganisms and raw materials the pseudomonas aeruginosa involved in this study has been previously isolated from hydrocarbon contaminated site and cultured on nutrient agar for future usage [6]. this isolated bacterium was assumed to be able to degrade hydrocarbon from the sample. the raw material (sludge palm oil) have been collected from oil palm industry, dengkil, malaysia. it was then stored in an oven at 60ºc to ensure the sludge maintain its liquid form. 2.2 mineral salt medium the compositions of the media in 1 l working volume were: glucose (4%), meat extract (0.075%), feso4 (0.01%), sodium nitrate (0.04%), nacl (0.01%) and sludge palm oil (2%). the media was pre-autoclaved at 121 o c and 101.3 kpa for 15 min. 2.3 inoculum preparation for stirred tank bioreactor a fresh single pure colony of each bacterial isolate was transferred aseptically from agar plate into liquid medium using a sterile wire loop and incubated in a rotary shaker at 37 o c and 300 rpm for 6 hours. the 100 ml inoculum is used since the working volume is 1 l. 2.4 du nouy methodology surface tension measurement was measured using a ksv sigma 702 tensiomenter. all measurements were made on the cell-free broth obtained by centrifuging the culture at 10000 rpm for 15 min. ten milliliter of each cell free broth was transferred into a clean 20 ml beaker and placed onto the tensiometer platform. a platinum wire ring was submerged into the solution and then slowly pulled through the liquid-air interface, to measure the surface tension (mn/m). between each measurement, the platinum wire ring was rinsed with water and flamed with bunsen burner. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jamal et al. 111 2.5 optimization study for process conditions optimization of process condition was done using three factors that were temperature ( o c), agitation (rpm), and aeration (vvm) in order to determine the optimum conditions for the maximum yield of biosurfactant by using stirred tank bioreactor. other parameters such as ph and media compositions used in the process were fixed according to the optimum value of production of biosurfactant based on the previous study. the experimental design was selected from design-expert software (2 level factorial) for determination of optimum process conditions for production of biosurfactant. ten experiments were conducted and the range of which has been shown in table 1. table 1: the range of parameters used for design of experiment. factors level -1 1 temperature ( o c) 30 40 agitation (rpm) 100 300 aeration (vvm) 0.5 2.0 3. results and discussion the time needed to achieve the maximum concentration of biosurfactant is correlated indirectly with the surface tension reduction. thus, surface tension was used as a main response due to the fact there was a big difference between iterations. lowering of surface tension is directly correlated to higher biosurfactant concentration. table 2 presents the design matrix of the variables along with the surface tension as a response. table 3 shows the statistical results obtained after analyzing by design expert. analysis of variance (anova) was performed in order to find the effect and contribution of each variable. both fisher variation ratio (f-value) and p-value from anova were used to confirm the significance of variables studied. data were best fitted by the following equation (eq. 1): y = 26.13 – 0.66 a – 0.94 b – 0.92 c + 1.29 ab – 0.62 ac (1) where y is the predicted response (surface tension) and a, b, c are the coded values for temperature, agitation and aeration respectively. during the experiment, the surface tension reached the lowest values at run 10 where temperature = 30 0 c, agitation = 100 rpm, aeration = 2.0 vvm. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jamal et al. 112 table 2: 2 level factorial experimental design matrix with observed and predicted values of surface tension. run factor 1 temperature celsius factor 2 agitation rpm factor 3 aeration vvm surface tension mn/m observed predicted 1 35 200 1.25 27.21 27.37 2 30 300 2.00 23.78 24.26 3 40 100 0.50 25.33 24.85 4 40 300 2.00 29.21 28.73 5 40 300 0.50 24.45 24.29 6 40 100 2.00 28.84 29.32 7 30 300 0.50 26.82 26.66 8 30 100 0.50 24.13 24.80 9 35 200 1.25 25.47 24.80 10 30 100 2.00 23.43 23.59 table 3: analysis of variance (anova) for response surface quadratic model. source sum of square degree of freedom mean square f-value prob>f model 33.75 5 6.75 10.55 0.0404* a 3.45 1 3.45 5.39 0.1030 b 7.09 1 7.09 11.08 0.0448* c 6.72 1 6.72 10.50 0.0478* ab 13.39 1 13.39 20.94 0.0196* ac 3.09 1 3.09 4.83 0.1155 curvature 2.85 1 2.85 4.45 0.1254 residual 1.92 3 0.64 lack of fit 1.02 2 0.51 0.57 0.6841 pure error 0.90 1 0.90 corrected total 38.49 9 *p value < 0.05 indicate the model term is significant r = 0.9727, r 2 = 0.9462, cv = 3.09% anova was used to determine the relative importance of various factors/ parameters. both fisher variation ratio (f-value) and p-value (prob>f) from anova were used to confirm the significance of variables studied. the greater f-value indicated that the variables explained adequately the variation in the data about its mean, and the estimated variable effects were real. small p-values were associated with a larger f-value because they imply that the effects were much greater than its standard error. the smaller the magnitude of the p-value, the more significant is the corresponding coefficient [7]. values of "prob > f" which is 0.0404 and less than 0.0500 indicate model terms are significant. in this case b, c, ab is significant model terms. values greater than 0.1000 indicate the model terms are not significant. in this case, a and ac are not significant. the "curvature f-value" of 4.45 implies the curvature as measured by difference between the average of the center points and the average of the factorial points in the design space iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jamal et al. 113 is not significant relative to the noise. there is a 12.54% chance that a "curvature fvalue" this large could occur due to noise. the "lack of fit f-value" of 0.57 implies that the lack of fit for the model is not significant relative to the pure error. the correlation measures for the estimation of the regression equation are the multiple correlation coefficients and the determination coefficient (r 2 ). the value of r 2 = 0.9462 indicated that only 5.38% of total variations were not explained by the model. since the closer the value of r 2 is to 1, the better is the correlation between the observed and the predicted values. the value of r 2 was satisfied because it indicated that the lackof-fit of this model was “not significant”. then, a lower value of cv = 3.09% signified a greater reliability of the experiments performed and indicated that the model can be used to navigate the design space. the model provided few solutions for optimum process conditions with predicted minimal surface tension. thus, in order to verify this model prediction, more experiments were carried out using the optimized medium. only two of them were chosen to validate the accuracy and precision of the optimized model. table 4 shows the results from validation experiments in term of observed and predicted surface tension. table 4: results for validation experiments. run temperature agitation aeration surface tension (mn/m) observed predicted 1 30 300 0.58 23.57 24.82 2 30 300 0.53 23.44 24.84 the surface tension achieved experimentally under the statistically optimum conditions: 23.57 mn/m (run 1), which was close to the 24.82 mn/m, predicted by the model with 5.03% error difference between observed and predicted value. run 2 also showed small percentage error at 5.63%. by comparing with another study which utilized oily substrate, it was observed that the result obtained in this research was in accordance with the result obtained by using olive oil mill effluent and frying oil as a substrate that gave surface tension of 30 mn/m and 32-34 mn/m respectively [8]. due to low percentage error between observed and predicted value, the optimized model equation can be used to develop further studies for biosurfactant production that will utilize sludge palm oil at larger scale. 4. conclusion the present work demonstrated the effect of three process conditions namely temperature, agitation rate and aeration towards biosurfactant production. two level factorial with 3 full factorials design from statistical software package design-expert (version 6.0.8, stat-ease, minneapolis, usa) was used to design the process conditions and for analyzing the experiment. the analysis of experiment was conducted and the equation, which described the model, was used to find the optimized value of process conditions. after validation study, the optimized process conditions was found at temperature 30 0 c, agitation of 300 rpm with 0.58 vvm aeration with corresponding surface tension of 23.57. since malaysia is one of the main palm oil producers in the world, this project provides a ground in an effective way for the management of palm oil sludge as well as to produce a cost effective valueable product.this bioreactor scale study iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology jamal et al. 114 offered the basis of scale up for the production scale of biosurfactant before proceeding to industrial scale. references [1] n. kosaric. “biosurfactant in industry”. pure appl. chem., vol 64, no. 11, 1731-1737, 1992. [2] j. d. desai and i.m. banat. “microbial production of surfactants and their commercial potential”. microbiol. mol. biol. rev., vol 61, no.1, 47-64, 1997. [3] l. r. rodrigues, j. a. teixera, h. c. mei, and r. olievera. “physiochemical and functional characterization of a biosurfactant produced by lactococcus lactis”. colloids and surface b, vol. 49, 78-85, 2006. [4] s. s. cameotra and r. s. makkar. “synthesis of biosurfactants in extreme conditions”. appl. microbiol. biotechnol., vol 50, 520-529, 1998. [5] a. fiechter. “biosurfactant: moving towards industrial application”. trends biotechnol., vol 10, 208-217, 1992. [6] n. fathiah, production of biosurfactant using microbial fermentation, final year project thesis, biochemical and biotechnology engineering, international islamic university malaysia, malaysia, 2007. [7] w. m. f. w. nawawi, p.jamal, and m. z. alam, “utilization of sludge palm oil as a novel substrate for biosurfactant production”. bioresource technol., vol 101, no. 23, 9241-9247, 2010. [8] v. pruthi and s. s. cameotra. “production of a biosurfactant exhibiting excellent emulsification and surface active properties by serratia marcescenes”. world j. microbiol. biotechnol. vol 13, 133-135, 1997. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 nitrogen and phosphorus removal efficiency of three helophytes in constructed surface flow wetlands for urban wastewater treatment abdeslam ennabili1,2*and michel radoux2** 1mhea® international network, nobressart, belgium 2 department of process engineering, superior school of technology, sidi mohamed ben abdellah university, fez, morocco. *corresponding author: abdeslam.ennabili@usmba.ac.ma **died on june 3, 2017 received: 22nd july 2019; accepted: 13th march 2020; published on-line: th july 2020) abstract:nutrient absorption is a function, among others, aimed at macrophytes for wastewater treatment. in this work, typha angustifolia, phragmites australis, and sparganium erectum were multi-annually compared in secondary and tertiary treatment of urban wastewater under mediterranean climate. phragmites shows higher growth in height and density during the vegetative period of 1.83-2.09 cm.d-1 and 29-49 times the planting density, respectively. aerial biomass records 52.2-54.3, 38.1-41.0, and 19.4 t dw.ha-1 in phragmites, typha, and sparganium in the same order. the underground biomass fluctuates depending on the rooting vigour from 1.45 t dw.ha-1 for sparganium to 44.49 t dw.ha-1 for phragmites in tertiary treatment. nitrogen and phosphorus aerial mineralomasses are more important in phragmites (787 kg n.ha-1) and typha (107 kg p.ha-1) in secondary treatment. phragmites is, by far, the most cumulative of n and p in its underground part. the n and p retention by the vegetated mesocosms apparently has overall relationship with n-nh4+ and p-po43-. compared to mesocosm input, phragmites assimilates one’s maximum of 6.39% n in its aerial tissues and 7.86% p in the underground ones, whereas typha records maxima of 14.8% n and 33.6% p in its aerial part with respect to corresponding mesocosm removal. abstrak:penyerapan nutrien adalah satu fungsi, antara lain, bertujuan untuk makrofit merawat sisa air. kajian ini menggunakantypha angustifolia, phragmites australis dan sparganium erectumbagi membandingkan pelbagai-jenis rawatan sekunder dan tertiar sisa air bandar pada iklim mediterranean. phragmites menunjukkan pertumbuhan tertinggi dalam ketinggian dan ketumpatandalam tempoh vegetatif iaitu 1.83-2.09 cm.d1dan 29-49 kaliketumpatan penanaman, masing-masing. rekod biojisim udara mencatatkan 52.2-54.3, 38.1-41.0, dan 19.4 t dw.ha-1 dalam phragmites,typha, dan sparganium pada susunan sama. biojisim bawah tanah berubah-ubah bergantung kepada kekuatanakar dari 1.45 t dw.ha-1 untuk sparganium hingga 44.49 t dw.ha-1 untuk phragmites dalam rawatan tertiar. nitrogen dan fosforus mineralomassa udara adalah lebih penting untukphragmites (787 kg n.ha-1) dan typha (107 kg p.ha-1) dalam rawatan sekunder. phragmites, setakat ini, paling kumulatif bagi n dan p pada bahagian bawah tanah. pembendungan n dan p oleh mesokisme tumbuh-tumbuhan secara nyata berkaitan dengan n-nh4+ dan p-po43-. berbanding input mesokisme,phragmites mengasimilasi maksimum pada n 6.39% tisu udara dan p 7.86% bahagian bawah tanah, manakala typha mencatatkan maksima n 14.8% dan p 33.6% pada bahagian udara dengan penyingkiran mesokisme sepadan. 25 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 keywords:wastewater; constructed wetland; surface flow; nitrogen; phosphorus 1. introduction the use of native macrophytes in constructed wetlands for wastewater treatment has often considered the biology of the species, particularly its life cycle, the tolerance of relatively high pollutant loads, a high productivity of valuable biomass, and local criteria such as climate, wastewater quality, and operating facilities of the treatment process [1-3]. macrophytes obviously contribute directly or indirectly to the wastewater treatment process [3,4], and the direct absorption of nutrients is one of the desired functions in this regard. harvesting aerial biomass of helophytes at the end of the growing season could enhance their productivity during the following season, and generally further increase the retention of nutrients, including nitrogen and phosphorus [5, 6]. the macrophytes most commonly used in the world in constructed surface flow wetlands (csfw) correspond to species of typha, scirpus, schoenoplectus, phragmites, juncus and eleocharis genera [3], in addition to canna, cyperus, paspalum and iris for mediterranean countries [7]. in mediterranean morocco, three helophytes were selected and tested in urban wastewater treatment within the framework of the "mhea® experimental centre of m'diq (nw of morocco)" project, financed by the walloon region through the agence de la francophonie [8-10], typha angustifolia l., phragmites australis (cav.) trin. ex steud. and sparganium erectum l. these three species have been tested around the world to treat municipal, agricultural, industrial, and drainage waters [3]. based on overall treatment performance, the experiments carried out in this respect focused on the development and optimization of new extensive wastewater treatment technologies, adapted to the regional climatic and socio-economic conditions (mhea® processes), with three successive stages each composed of an artificial ecosystem or mesocosm [10]. this work specifically exposes for the first time a multi-year comparison of the three helophytes (t. angustifolia, p. australis and s. erectum) in secondary and tertiary treatments of urban wastewater, based on development descriptors with annual harvesting of biomass, and their direct contribution to the nitrogen and phosphorus removal in csfw. 2. materials and methods 2.1 mesocosms by imitating their respective habitats in natural or polluted environments, t. angustifolia (t), p. australis (pr), and s. erectum(s), were grown separately, just before the vegetative period (vp), at a density of 10 rhizomatous fragments per m2 in mesocosms by simulating macrophyte bioreactors: 2.2 m3 of wet volume, including 1.8 m3 of substrate and 0.4 m3 of surface water, and an identical non-planted pond was designed for comparison. the substrate used consists of washed river sand with a particle size of about 38% (diameter <2 mm), 31.6% (2-5 mm), 30% (>5 mm) and 0.4% (<80 μm). the feeding of these mesocosms in pre-treated wastewater is done semi-continuously and in translation (csfw). the three planted mesocosms are compared beforehand as secondary treatment, then in the presence of a control (non-planted mesocosm); the mesocosms with t or pr are compared in secondary and tertiary treatments (table 1). 26 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 the climate prevailing in the experimental site is of mediterranean type: rainfall of 523 to 683 mm (1999-2002), average daily temperatures of 14°c to 26°c, maximum of the warmest months of about 35 °c (july and august), and minimum of the coldest months above 7°c (december and january). the strongest winds are recorded during the months of september (w-e), and november-december (s-n), with negative transient effects of salt spray and plant collapse. water losses due to mesocosm evapotranspiration vary with planting type and treatment stage, from 5.28 to 19.0% of inlet flow (table 2). table 1: characteristics of inlets feeding mesocosms per treatment stage. sources: [11-12]; unpublished data. mesocosms group secondary inlets (i2) tertiary inlet (i3) t. angustifolia(t2) p. australis(pr2) s. erectum(s2) unvegetated control (l2) t. angustifolia(t2) p. australis(pr2) unvegetated control (l3) t. angustifolia(t3) p. australis(pr3) dco (mg o2.l-1) 402.9±236.2 292.2±148.9 34.81±14.63 dbo5 (mg o2.l-1) 115.8±51.94 110.3±57.95 32.67±16.54 tn (mg n.l-1) 39.48±9.446 38.65±9.906 22.60±8.332 tp (mg p.l-1) 6.769±1.908 6.803±2.553 4.896±1.525 t (°c) 22.0±5.57 22.0±5.65 20.1±4.43 ph 8.24±0.58 8.07±0.61 7.48±0.19 o2 (mg.l-1) 10.9±13.2 10.7±10.3 5.29±7.42 conductivity (μs.cm-1) 1043.8±92.463 991.49±105.19 1136.9±120.23 on the other hand duckweed coming to settle in unplanted mesocosms, or in those planted after biomass harvesting, were regularly removed. diptera and coleoptera spontaneously succeed in the aquatic and aerial mesocosm compartments, with an affinity of cladocera and gastropoda for the first, and hemiptera and hymenoptera for the second. furthermore, the mosquito fish [gambusia affinis (baird and girard, 1853), poeciliidae] was introduced throughout the vp into each of the three mesocosms in secondary treatment: t, pr and into the un-vegetated one. table 2: water balance in mesocosms per treatment stage. sources: [11-12]; unpublished data. mesocosm group inlet flow (l.d-1) evapotranspiration (mm.d-1) retention time (d-1) secondary treatment t. angustifolia(t2) 186.2±21.87 16.03±10.91 2.351±0.296 p. australis(pr2) 170.8±19.17 25.92±13.90 2.673±0.311 s. erectum(s2) 210.2±23.60 23.55±13.39 2.152±0.272 unvegetated control (l2) 243.0±39.22 12.84±17.86 1.810±0.407 t. angustifolia(t2) 217.7±42.16 16.80±19.79 2.096±0.592 p. australis(pr2) 224.9±50.46 16.03±17.53 2.072±0.715 tertiary treatment unvegetated control (l3) 132.9±20.72 22.45±6.19 3.430±0.565 t. angustifolia(t3) 137.1±21.37 16.57±11.36 3.254±0.642 p. australis(pr3) 144.4±22.50 27.47±10.91 3.244±0.629 2.2 experimental monitoring water samples are taken on each mesocosm inlet and outlet approximately every two weeks for analyses of nitrogen compounds (total nitrogen, ammonium, nitrates and nitrites) and phosphorus ones (total phosphorus and orthophosphates). in addition, water samples were also collected to quantify phytoplankton, and macrophyte development parameters were measured. 27 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 2.2.1 nitrogen total nitrogen (tn) and total non-particulate nitrogen (tnf) are determined after digestion of the sample in an alkaline medium (naoh) in the presence of persulfate whereby the nitrogen compounds convert to nitrates. undigested persulfate is reduced by sodium metabisulfite. nitrates react with chromotropic acid in a strong acid medium (h2so4) to form a yellow complex with maximum absorbance at 410 nm. two ranges are proposed by the hach firm: the low range (0.2-25 mg n.l-1) and the high range (7-150 mg n.l-1). ammonium ions (nh4+) are determined according to the nessler method on filtered samples. the hardness of the sample is complexed by a mineral stabilizer. the polyvinyl alcohol, a dispersing agent, helps to form a yellow colour with the nessler reagent in the presence of the ammonium ions. the colouring developed is proportional to the concentration of ammonia. the reading is at 425 nm for a concentration range 0.05 to 2.5 mg n.l-1. nitrite ions (no2-) are determined according to the sulfanilamide method whose principle is the formation of a diazonium compound by the reaction of nitrites with sulfanilamide. this compound gives, by coupling with n-(1-naphthyl)-ethylenediamine dichloride, a red-mauve colour measured at 540 nm. the range used is 0.003 to 0.3 mg n.l-1. nitrate ions (no3-) are reduced by cadmium to nitrite ones which react in acidic medium with sulfanilic acid to form an intermediate diazonium salt. the latter reacts with gentisic acid and forms an amber colour determined at 500 nm for the high range (0-30 mg n.l-1) and at 400 nm for the medium range (0-5 mg n.l-1). for the low range (0-0.5 mg n.l1), the diazonium reagent reacts with chromotropic acid and develops a yellow colour measured at 507 nm. 2.2.2 phosphorus total phosphorus (tp) and total non-particulate phosphorus (tpf) are oxidized as orthophosphate ions in acidic medium in the presence of persulfate. two ranges are used: (i) the low range (0-3.5 mg p.l-1) for which orthophosphate reacts with molybdate in an acid medium to produce a phosphomolybdic complex which, in turn, is reduced by ascorbic acid giving an intense molybdenum blue coloration determined at 890 nm; (ii) the high range (0-100 mg p.l-1) for which the phosphomolybdic complex forms in the presence of vanadium the yellow vanadomolybdophosphoric complex measured at 420 nm. orthophosphate ions (po43-) react, in acid medium, with the ammonium molybdate producing the molybdophosphoric acid. this complex is then reduced by the amino acid reagent to form the blue-molybdenum intensely coloured to determine at 530 nm. the method range is 0 to 9.8 mg p.l-1. 2.2.3 phytoplankton according to the algae density in mesocosms, an adequate volume is taken at a depth of 10 cm. the phytoplankton biomass was evaluated by the chlorophyll-a determination in accordance with the spectrophotometric method specified in standard methods [13]. 2.2.4 helophytes macrophyte development parameters include stem density and height, biomass production, and n and p contents in their tissues. at the end of the vp the aerial part of each helophyte is cut above the water level, and its dead parts are collected separately to estimate respectively the above-ground biomass, and the necromass inside the mesocosm. 28 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 in addition during each vp, cuttings of the plant aerial part beyond mesocosms were sometimes required because of accessibility. at the end of the 3rd vp, the mesocosms are emptied, and the rhizomes and roots of the middle 3rd are gently recovered and washed on stacked sieves with a regressive mesh for the estimation of the underground biomass. representative subsampling of collected biomass is adopted, and the following analytical steps (drying, grinding, and n and p determination) were conducted according to ennabili et al. [14]. 2.3 analytical methods data are presented depending on three periods: vegetative period (vp), vegetative rest (vr) and “vp+vr”. the one-way analysis of variance (anova) of normal distribution data was performed using the statistica software, v.5, otherwise only averages and standard deviations were calculated using microsoft excel software. 3. results and discussion 3.1 helophyte development 3.1.1 growth pr develops more in height especially in tertiary treatment (pr3), successively followed by t and s (table 3). these values greatly exceed those previously reported in t, pr, and s grown in constructed wetlands, under polluted environments, or those developed in greenhouses, specifically 1.79-2.50 m for pr, 0.90-1.99 m for t and 0.91 m for s [1518], and are close to those underlined in natural or polluted environments, 3.2-3.5 m for pr, 2.8 m for t and 1.70 m for s [6,14]. table 3: growth characteristics and above (a-) and underground (u-) biomass of helophytes studied per treatment level. mesocosms t2 t3 pr2 pr3 s2 height (m) 3.47±0.59 3.15±0.49 3.90±0.87 4.45±0.71 1.96±0.98 stems.m-2 86±52 38±24 494±217 289±140 79±31 fertile stems (%) 17.58 ±14.00 43.59 ±67.48 20.43 ±10.61 17.49 ±8.044 34.78 ±26.65 a-dry weight (% wet weight) 19.47 ±4.969 19.60 ±4.623 39.33 ±1.343 43.13 ±3.721 15.17 ±6.536 a-biomass (t dw.ha-1) 41.009 ±13.785 38.098 ±15.286 54.284 ±30.850 52.209 ±36.400 19.436 ±12.125 a-necromass (t dw.ha-1) 5.850 ±5.459 6.220 ±7.269 7.310 ±9.914 2.745 ±3.627 9.075 ±10.60 a-partial pre-cutting (t dw.ha-1) 0.951 ±0.369 0.927 ±0.773 4.021 ±2.396 3.413 ±3.787 0.538 ±0.371 net productivity (t dw.ha-1.y-1) 59.895 ±4.2172 52.428 ±20.601 70.113 ±65.025 50.098 ±54.739 22.272 ±6.6706 u-biomass (% ww) 6.80 18.47 22.20 22.27 6.78 u-biomass (t dw.ha-1) 4.363 7.998 25.008 44.486 1.454 "u/a-biomass" ratio 0.22 0.34 0.38 0.65 0.04 the average growth rate during the vp is 1.83-2.09, 1.48-1.63 and 0.92 cm.d-1 for p, t, and s in the same order, vs. 0.77-1.9 cm.d-1 underlined in pr by zheng et al. [6] and zhang et al. [17]. the shoot collapse is spectacular in s especially during the "augustoctober" period as it was noted in a polluted environment by ennabili and gharnit [19], due to the cumulated effect of sludge discharge and wind. asaeda et al. [20] point out that 29 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 collapsed shoots disappear in 40-60 days and constitute a large fraction of the floating organic matter. horizontal stems of pr sometimes robustly branch out from rhizomes during fruiting (july), reaching 9 m in length with an average of 3 sprouts.m-1 (september), and becoming rhizome once into the inlet piped water of mesocosms. aquatic stolons are also observed in t during the flowering-fruiting period. typically more apparent at the mesocosm margins, stem density at the end of vp increased by about 29-49, 3.8-8.6, an 7.9 times for pr, t, and s, respectively, compared to the initial planting, exceeding for pr the range of 130-175 plants.m-2 (17-18 times the planting density) highlighted by zheng et al. [6], and the 107 plants.m-2 cited in a polluted environment [15]. the increased rates of "post-planting density" obtained by this author in greenhouse approach noted in this work, 53.0 and 8.47 times the planting density of pr and s respectively, but substantially different from that of t (21.9 times). those high values of densities are related, inter alia, to the high tillering rate in these species, particularly 15, 6 and 3 sprouts.plant-1, respectively for pr, t, and s [15], and to the annual cut of helophyte aerial parts [6]. although peak flowering occurs in september, secondary flowering cohorts are noted along the vp: t (april, june-august), pr (april, august), and s (april-may, july-august, october). the flowering rate is likely to vary inversely with the treatment stage, contrary to pr (table 3), and it is negatively affected in s by the shoot collapse just before flowering. however, this species completes more than one development cycle per vp, with a maximum of 3 during the 3rd year of mesocosm functioning. in addition, s seeds massively germinate from the mesocosm bottom or on water surface (fig. 1). in addition, the sucking of s is also more remarkable in the canopy openings created by the shoot collapse in mid-summer. fig. 1: seed germination and development of s. erectum. fp, floating plantlets; fs, floating seeds; ep, emergent plantlets. moreover, the root bed is thicker in pr, followed successively by t and s, and overwhelmingly achieves about 107, 56.7 and 20.6 cm deep from the level of substrate in the mesocosm middle part, respectively (fig. 2). liffen et al. [21] found that the biomass of s roots and rhizomes was highest at a depth of 0-10 cm, with a gradual decrease to 2025 cm. rhizomes and roots of pr go through the whole mesocosm substrate, forming root plaques at the bottom, and oxygenating the full height of the mesocosm bed except a slightly anoxic intermediate layer in appearance. the oxygen release from the pr roots in the rhizosphere is qualitatively marked by a reddish colour, associated with the oxidized 30 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 forms of iron [4]. pr rhizomes sometimes damage the mesocosm outlet by penetrating duct junctions. 3.1.2 biomass the above-ground biomass of helophytes is found to be slightly disadvantaged in tertiary treatment, with lower hydraulic loads (table 2) and nutrients (table 1), and ranges from 19.44 t dw.ha-1 for s2 to 52.21-54.28 t dw.ha-1 for pr2, according to the lignification gradient, especially dry weights (dw) of 15.2 to 39.3-43.1% of the wet weight (ww) in the same order (table 3). which corresponds to a production in vp of about 0.193, 0.179, 0.255, 0.245 and 0.091 t dw.ha-1.d-1 for t2, t3, pr2, pr3 and s2, vs. 0.14, 0.16 and 0.10 reported by ennabili [15] in glasshouse, respectively for t, pr and s. fig. 2: side view of dewatered mesocosm substrate after three vegetation periods. b, mesocosm bottom; r, rhizome; r, root; s, sand; spli, “sand/plant litter” interface. disregarding the role of study conditions, the aboveground biomass values obtained exceed those underlined in pr (5.40-37.2 t dw.ha-1, vs. 52.2-54.3 t dw.ha-1) [6,14-16,18, 22-25], were similar to those reported for t (7.76-33.0 t dw.ha-1, vs. 38.1-41.0 t dw.ha-1) [14-15,18,26], and were part of the range of values highlighted in s [14-15,20-21]. the above-ground biomass during three successive years with harvesting of helophyte aerial parts at the end of each vp shows that pr has a relative stability of production in tertiary treatment, a resilience for pr and s in secondary treatment, while the t biomass increases in the first two years and falls steeply in the third year compared to the 3-year average (fig. 3). the positive impact of harvesting on biomass production has been demonstrated in pr [6,25]. due to non-harvesting of biomass de los reyes et al. [26] showed that the t biomass improved by about 39 to 48% in the 3rd year for the aboveground and below-ground parts respectively, suggesting an inadequacy of medium and long-term harvest for these species growing in csfw. the partial cut of helophytes for accessibility along the vp exports from 0.075 t dw.ha-1 for s2 to 4.021 t dw.ha-1 for pr2. the specific necromass collected after harvesting is higher for s (9.075 t dw.ha-1), due especially to the shoot collapse, followed in descending order by those of pr2, t3, t2 and pr3 (table 3), which would probably be a source of mesocosm enrichment during the forthcoming seasons. the net aboveground 31 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 productivity varies from more than 22 t dw.ha-1.year-1 for s to over 70 t dw.ha-1.y-1 for pr in secondary treatment (table 3), exceeding the estimated total biomass by maucieri et al. [27] in pr (49.2-58.9 ±9.1 t dw.ha-1) in csfw for agricultural wastewater treatment. as far as the underground biomass, it fluctuates from 1.454 t dw.ha-1 for s to 44.486 t dw.ha-1 for pr in tertiary treatment, approximately 4 to 65% of the respective aboveground biomasses (table 3). these values overlap with those underlined for pr (16.0-29.7 t dw.ha1, vs. 25.0-44.5 t dw.ha-1) [14-15,23], but are outperformed by those reported for t (12.334.95 t dw.ha-1, vs. 4.36-8.00 t dw.ha-1) and s (6.49.48-23.5 t dw.ha-1, vs. 19.4 t dw.ha-1) [14-15, 21, 26]. fig. 3: annual aboveground biomass in relation to the 3-year average one. the above-ground biomass apparently is more favoured in csfw (u/a of 0.04 to 0.65 depending on the species and the treatment stage) in comparison with the underground biomass (table 3), contrary to the ratios obtained in polluted environments: 1.62, 1.62 and 0.55 for t, pr and s in the same order [14]. however, by referring to the biomass averages obtained in these species from the same source by the same authors, and considering the harvest conditions at the end of each vp, csfw systematically favour the aboveground biomass production (fig. 4). the underground biomass is also favoured but with a lower intensity in pr and t in tertiary treatment. 3.1.3 mineralomass the n/p contents in aerial tissues of helophytes are more apparent in pr and t in secondary treatment, specially 787 kg n.ha-1/89.6 kg p.ha-1, and 670 kg n.ha-1/107 kg p.ha-1 in the same order. the lowest rates for these two nutrients were recorded in t in tertiary treatment (table 4). as regards the underground mineralomass pr is the most cumulative of n and p, apparently due to its high underground biomass in csfw. -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 p2 p3 t2 t3 s2 d ev ia tio n fr om th e 3ye ar ( y ) a ve ra ge helophytes y(n) y(n+1) y(n+2) 32 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 fig. 4: helophyte above-(a) and underground (u) biomass in relation to naturalpolluted sites [14] and csfw (the present study). table 4: nitrogen and phosphorus contents and mineralomass in above (a-) and underground (u-) parts of helophytes studied per treatment level. mesocosms t2 t3 pr2 pr3 s2 a-n (%) 1.64± 0.83 0.92± 0.25 1.45± 0.85 1.26± 0.47 1.90± 0.29 a-p (%) 0.26± 0.10 0.16± 0.08 0.17± 0.05 0.13± 0.01 0.45± 0.13 u-n (%) 1.23 0.62 1.00 1.08 1.08 u-p (%) 0.21 0.14 0.19 0.23 0.19 a-n (kg n.ha-1) 670.49±225.38 348.60±139.87 787.12±447.33 657.84±458.64 368.31±229.76 a-p (kg p.ha-1) 106.62±35.840 59.052±23.693 89.569±50.903 67.872±47.320 86.490±53.955 u-n (kg n.ha-1) 53.669 49.589 250.08 480.45 15.703 u-p (kg p.ha-1) 9.1629 11.197 47.515 102.32 2.7625 compared to the dw, the n/p contents in helophyte tissues intersect those reported by other authors in pr, except the low values of n in the underground part (table 4), respectively 1.10-3.11/0.09-0.27% dw of the aerial part, and 1.44-1.73/0.22-0.32% dw of the underground one [2, 5-6,14,18]. for t and s the values underlined by other works are 1.94/0.09-0.17% and 1.94/0.35% dw of the aerial tissues, and 1.04/0.15% and 1.73/0.55% of the aerial tissues in the same order [14,18]. the mineralomass values reported by other studies clearly distinguish the n/p aboveground mineralomasses of pr (658-787 kg n.ha-1/68-90 kg p.ha-1), vs. 111-502 kgn.ha-1/17-37.4 kg p.ha-1 [6, 14, 16, 24, 25, 27-29], and show an harmony of its n/p underground mineralomasses (250-480 kg n.ha-1/48-102 kg p.ha-1) vs. 503.3 kgn.ha1/32.02-76.9 kg p.ha-1 [6,14]. when compared with other authors, the n/p aboveground mineralomasses of t and s are similar (table 4), vs. 74-420 kgn.ha-1/20-55 kg p.ha-1 for t and 251-300 kgn.ha1/45.3-50 kg p.ha-1 for s [14, 26, 28, 29-31], while the n/p belowground ones are largely disadvantaged in this respect (table 4), vs. 310-822 kgn.ha-1/5-147 kg p.ha-1 for t and 124.3 kgn.ha-1/39.5 kg p.ha-1 for s [14,26]. 3.2 phytoplanktonic chlorophyll-a the chlorophyll-a content in mesocosm water varies widely throughout the growing cycle. in secondary treatment and as compared to t and s (fig. 5), the pr-mesocosm generally reduces more phytoplankton (0.0171±0.0200 mg chlorophyll-a.l-1) and especially during the vr (0.0066±0.0069 mg.l-1); this fact is more apparent in the t-1 -0.5 0 0.5 1 1.5 t2 t3 p2 p3 s2 d ev ia tio n fr om th e na tu ra lpo llu te d si te s helophytes a u 33 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 mesocosm in the vp (0.0174±0.0196 mg.l-1). in tertiary treatment, the pr-mesocosm forcefully reduces phytoplankton (0.0038±0.0105 mg.l-1), compared to a lesser role of tmesocosm, and an algae enrichment of the un-vegetated one (fig. 5). this particular behaviour of the pr-mesocosm is apparently in relation with, among other things, its leaf canopy more developed throughout the year. in addition to the indirect role of helophyte shading on phytoplankton contraction, authors have shown allelopathic interferences of macrophytes with phytoplankton development. for example, extracts of leaves, stems and rhizomes of pr can have negative effects on the growth of freshwater phytoplankton, microcystis and scenedesmus [32]. t and its allelochemicals can control phytoplankton blooms in eutrophic waters [33]. cyanobacteria can also produce effective allelochemicals that interfere with the growth of competitive cyanobacteria and algae [34]. fig. 5: chlorophyll-a content of mesocosm inlet (i) and outlets (june 99-sep.00). 3.3 nitrogen and phosphorus removal efficiency in secondary treatment, the pr-mesocosm has an advantage for the retention of tn, tnf and nh4+ in comparison with the t and s ones (table 5), but it’s similar to tmesocosm and the non-planted one (l) for tn and tnf (table 6). in tertiary treatment, it generates the best tn removal, and aggregates with l for tnf and nh4+, and with l and i (mesocosm inlet) for po43-(table 7). sand t-mesocosms would be of interest for the retention of no3and no2-in secondary and tertiary treatments in the same order (table 5 and 7). the l-mesocosm shows significant removal of nh4+and tpf respectively in secondary and tertiary treatments, and generates similar concentrations of no3-and po43-to those of i in secondary treatment (tables 6 and 7). depending on the i-water quality, planting of mesocosms apparently has no effect on the retention of no3-and po43in secondary treatment, and of po43-in tertiary treatment (tables 5, 6 and 7). the impact of the vp on the n and p retention likely has a general relationship with the direct plant uptake of n-nh4+ and po43-, but remains without clear trend for tnf, no2-, no3and tpf (tables 5, 6 and 7), seemingly due to other factors such as bacterial activity, substrate composition, hydraulic retention time, etc. 0 0.02 0.04 0.06 0.08 0.1 0.12 c hl or op hy lla (m g/ l ) inlets and outlets of mesocosms 34 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 table 5: nitrogen and phosphorus contents (mg.l-1) of inlet and outlets of t-, pr-, and s-mesocosms (secondary treatment; jan. 99 – sep. 00). inlet outlets anova significance (p<0.05) i2 t2 pr2 s2 f-ratio f-prob. effet tn 39.5±9.45 a 31.6±8.33 b 22.8±10.36 c 31.2±8.96 b 21.37 0.0000 *** vp 38.3±9.39 a 31.6±8.07 b 22.9±10.74 c 30.1±8.56 b 13.62 0.0000 *** vr 42.5±9.35 31.5±9.37 22.6±9.77 34.0±9.79 tnf 26.6±8.09 a 25.7±6.91 a 19.0±7.67 b 25.5±10.36 a 6.597 0.0003 *** vp 26.0±8.83 a 26.3±7.16 a 19.5±7.85 b 25.7±10.54 a 3.852 0.0117 * vr 28.1±6.02 24.1±6.28 17.9±7.48 24.8±10.4 nh4+ 21.6±5.89 a 21.0±8.06 a 13.3±6.20 b 20.5±7.59 a 12.89 0.0000 *** vp 21.4±5.67 a 22.4±6.37 a 14.1±5.70 b 21.1±6.12 a 12.55 0.0000 *** vr 22.0±6.74 17.3±11.1 11.2±7.26 18.7±10.9 no20.016±0.021 0.014±0.020 0.019±0.018 0.008±0.008 vp 0.022±0.024 0.017±0.024 0.014±0.012 0.008±0.009 vr 0.005±0.005 0.008±0.007 0.030±0.023 0.007±0.006 no30.252±0.236 a 0.340±0.317 a 0.217±0.214 a 1.056±1.894 b 3.318 0.0243 * vp 0.235±0.192 0.278±0.273 0.149±0.090 0.141±0.102 vr 0.278±0.303 0.432±0.372 0.320±0.301 2.428±2.477 tp 6.77±1.91 a 7.05±1.54 a 6.53±1.81 a 7.00±1.61 a 0.782 0.5058 ns vp 7.00±1.72 a 7.31±1.30 a 7.02±1.73 a 7.20±1.68 a 0.242 0.8671 ns vr 6.13±2.32 6.34±1.97 5.19±1.33 6.47±1.32 tpf 3.88±1.75 5.09±2.07 4.18±1.95 4.87±1.77 vp 4.27±1.56 5.64±1.64 4.60±1.88 5.11±1.81 vr 2.95±1.90 3.72±2.43 3.17±1.81 4.28±1.62 po432.15±1.83 a 3.77±2.78 b 2.77±2.21 a 4.06±2.12 b 6.264 0.0004 *** vp 2.15±1.81 3.89±2.84 2.71±2.30 4.11±2.22 vr 2.18±1.99 3.45±2.71 2.93±2.03 3.92±1.90 for each variable, means followed by the same letter are not significantly different at 5%. non-significant (ns), significant (*), and very highly significant (***) effects. the n/p retention in helophyte tissues compared to the i-mesocosm vary sharply and reaches maxima of 6.39%/7.86% in pr for the aboveground/underground parts (fig. 6), whereas by referring to the n/p removal rate by the corresponding mesocosms, t recorded maxima of 14.8%/33.6% for the aboveground (fig. 7), suggesting a greater retention of n and p by the pr-mesocosm compared to the t-one, contrary to the confirmation of song et al. [18] for p. fig. 6: nitrogen and phosphorus retention in plant tissues in relation to the corresponding mesocosm inlet. 35 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 table 6: nitrogen and phosphorus contents (mg.l-1) of inlet and outlets of l-, t-, and pr-mesocosms (secondary treatment; may 01 – sep. 03). inlet outlets anova significance (p<0.05) i2 l2 t2 pr2 f-ratio f-prob. effet tn 38.7±9.91 a 32.6±9.46 b 31.4±9.17 b 28.5±9.35 b 11.18 0.0000 *** vp 41.0±10.2 a 34.7±10.3 b 33.7±9.44 b 29.8±10.1 b 7.289 0.0001 *** vr 34.9±8.38 a 29.1±6.77 b 27.7±7.52 b 26.4±7.81 b 5.053 0.0030 ** tnf 29.1±8.78 a 23.8±7.64 b 23.0±8.25 b 25.6±8.13 b 6.209 0.0005 *** vp 31.3±9.29 a 25.0±8.17 b 23.9±9.33 b 27.6±8.02 b 4.756 0.0035 ** vr 25.9±6.91 a 21.9±6.47 a 21.5±6.13 a 22.5±7.43 a 1.889 0.1377 ns nh4+ 23.8±7.57 a 18.2±6.73 b 21.3±9.00 a 22.8±8.39 a 5.756 0.0008 *** vp 26.0±7.97 a 19.4±7.28 b 23.2±10.4 a 25.6±8.55 a 4.881 0.0029 ** vr 19.8±4.77 a 16.0±5.10 a 17.8±4.23 a 17.8±5.35 a 2.156 0.0993 ns no20.023±0.045 0.037±0.042 0.023±0.044 0.015±0.032 vp 0.023±0.042 0.030±0.035 0.022±0.042 0.010±0.022 vr 0.022±0.050 0.049±0.050 0.026±0.050 0.023±0.043 no32.80±1.82 a 2.62±2.16 a 3.91±2.03 b 3.85±1.73 b 7.301 0.0001 *** vp 3.28±2.00 a 3.31±2.31 a 4.43±2.29 b 4.39±1.80 b 3.530 0.0165 * vr 1.98±1.10 a 1.43±1.13 a 3.00±1.00 b 2.91±1.10 b 10.81 0.0000 *** tp 6.80±2.55 a 6.57±2.76 a 5.96±2.37 a 6.03±2.07 a 1.731 0.1612 ns vp 7.75±2.53 a 7.72±2.71 a 6.75±2.51 a 6.84±1.93 a 1.936 0.1261 ns vr 5.12±1.55 a 4.54±1.31 a 4.55±1.18 a 4.58±1.42 a 0.910 0.4398 ns tpf 4.20±1.87 a 3.84±2.09 a 4.59±2.23 a 4.47±1.83 a 1.653 0.1779 ns vp 4.95±1.69 a 4.67±2.09 a 5.22±2.48 a 5.09±1.90 a 0.510 0.6756 ns vr 2.88±1.39 2.36±1.01 3.46±1.02 3.36±1.04 po432.94±2.01 a 2.71±2.16 a 4.02±2.15 b 3.95±1.84 b 6.751 0.0002 *** vp 3.47±2.22 a 3.40±2.31 a 4.59±2.42 b 4.52±1.94 b 3.300 0.0221 * vr 2.00±1.08 a 1.48±1.11 a 3.03±0.99 b 2.94±1.08 b 10.86 0.0000 *** for each variable, means followed by the same letter are not significantly different at 5%. non-significant (ns), significant (*), highly significant (**), and very highly significant (***) effects. for the whole plant, pr assimilates in its tissues 10.9% n and 13.1% p compared to the i-mesocosm load. these values of n/p accumulated in aboveground plant tissues are far below than those obtained by de los reyes et al. [26] in t (29.6% n) and zheng et al. [6] in pr (16.2-17.04% n). besides, t is more effective in the n retention in its aerial tissues in secondary treatment and p in the whole plant in secondary treatment. pr offers more efficiency of n absorption in its aerial part in secondary treatment and n and p in its underground part in tertiary treatment. the underground part of pr retains at most 5.23% n and 15.1% p of the general elimination rate of the corresponding mesocosm, and can be released progressively because of tissue death and decomposition during the forthcoming seasons. the s necromass in water is valued at up to 2.94% n and 7.96% p the general retention of the corresponding mesocosm, and will recover more rapidly in the treatment system given the relatively rapid decomposition of its collapsed shoots [31]. 4. conclusion this work focused on the monitoring of t. angustifolia, p. australis and s. erectum grown in constructed surface flow wetlands for urban wastewater treatment in a mediterranean climate, based on growth and functional criteria, and allowed an interspecific comparison under the same growing conditions on the one hand, and within each species by reference to natural-polluted environments on the other hand. 36 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 table 7: nitrogen and phosphorus contents (mg.l-1) of inlet and outlets of l-, t-, and pr-mesocosms (tertiary treatment; jan. 99 – sep. 00). inlet outlets anova significance (p<0.05) i3 l3 t3 pr3 f-ratio f-prob. effet tn 22.8±8.45 a 12.4±6.10 b 12.9±6.42 b 7.45±5.96 c 35.80 0.0000 *** vp 24.4±9.38 a 14.2±6.65 b 15.4±6.34 b 7.68±4.92 c 24.23 0.0000 *** vr 20.1±5.97 9.53±3.66 8.73±3.97 7.07±7.56 tnf 17.7±5.29 a 7.26±3.92 b 10.4±6.02 c 5.84±4.41 b 43.00 0.0000 *** vp 18.4±5.39 a 6.88±3.57 b 12.0±6.23 c 5.56±3.68 b 36.29 0.0000 *** vr 16.3±5.01 8.00±4.56 7.38±4.37 6.38±5.69 nh4+ 14.0±4.81 a 3.17±2.23 b 7.30±4.51 c 2.74±2.54 b 82.06 0. 0000 *** vp 15.2±4.27 a 3.42±2.57 b 8.53±4.81 c 2.99±2.63 b 68.87 0.0000 *** vr 11.18±4.92 2.61±1.05 4.73±2.45 2.38±2.35 no20.065±0.053 0.121±0.090 0.021±0.034 0.024±0.028 vp 0.073±0.064 0.116±0.099 0.020±0.040 0.018±0.025 vr 0.051±0.018 0.132±0.073 0.024±0.022 0.035±0.030 no30.779±0.598 a 0.743±0.951 a 0.448±0.731 a 0.245±0.344 a 2.694 0.0519 ns vp 0.679±0.653 0.428±0.773 0.122±0.047 0.132±0.114 vr 0.929±0.507 1.214±1.044 0.936±0.996 0.413±0.497 tp 4.94±1.52 4.24±1.81 4.46±1.56 3.82±1.81 vp 5.49±1.48 4.75±2.08 5.13±1.49 4.41±1.99 vr 4.14±1.17 3.48±0.81 3.50±1.04 3.01±1.06 tpf 3.05±1.42 2.31±1.09 3.15±1.30 2.66±1.71 vp 3.40±1.30 2.38±1.09 3.56±1.24 3.11±1.85 vr 2.46±1.47 2.18±1.13 2.47±1.15 1.90±1.10 po432.32±1.39 a 2.17±0.93 a 3.07±1.30 b 2.26±0.84 a 5.360 0.0015 ** vp 2.41±1.33 2.29±0.97 3.43±1.31 2.49±0.78 vr 2.14±1.56 1.91±0.80 2.29±0.92 1.77±0.79 for each variable, means followed by the same letter are not significantly different at 5%. non-significant (ns), highly significant (**), and very highly significant (***) effects. fig. 7: nitrogen and phosphorus retention in plant tissues in relation to the corresponding mesocosm efficiency. in mediterranean climate the phragmites mesocosm is more effective in plankton reduction especially in tertiary treatment, compared to a lesser role of the typha and sparganium ones. by helophyte harvesting at the end of each vegetative period, there is relative stability of biomass production by phragmites in tertiary treatment, resilience for phragmites and sparganium in secondary treatment, while typha increases biomass 37 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 production the first two years and falls steeply the third year. moreover, the aerial biomass of the three helophytes seems to be slightly disadvantaged in tertiary treatment. given the development magnitude of its underground biomass, phragmites is by far the most cumulative of nitrogen and phosphorus in this part, in addition to the indirect benefit of substrate oxygenation, an interesting aspect for wastewater treatment. phragmites also accumulates more nitrogen in its aboveground part in secondary treatment, and the nitrogen and phosphorus in its underground part in tertiary treatment. in secondary treatment typha shows a specific interest in the assimilation of nitrogen in aerial tissues, and phosphorus in the whole plant. acknowledgement this study was carried out as part of the mhea® project, achieved in m’diq (nw of morocco) via the agence de la francophonie (walloon region-morocco). references [1] radoux m. (1989) epuration des eaux usées par hydrosère reconstituée. trib. cebedeau, 42(8):62-68. [2] greenway m. (2003) suitability of macrophytes for nutrient removal from surface flow constructed wetlands receiving secondary treated sewage effluent in queensland, australia. water sci. technol., 48(2):121-128. https://doi.org/10.2166/wst.2003.0101 [3] vymazal j. (2013) emergent plants used in free water surface constructed wetlands: a review. ecol. eng., 61(part b):582-592. https://doi.org/10.1016/j.ecoleng.2013.06.023 [4] brix h. (1997) do macrophytes play a role in constructed treatment wetlands? water sci. technol., 35(5):11-17. https://doi.org/10.2166/wst.1997.0154 [5] greenway m, woolley a. (1999) constructed wetlands in queensland: performance efficiency and nutrient bioaccumulation. ecol. eng., 12(1-2):39-55. https://doi.org/10.1016/s09258574(98)00053-6 [6] zheng y, wang xc, ge y, dzakpasu m, zhao y, xiong j. (2015) effects of annual harvesting on plants growth and nutrients removal in surface-flow constructed wetlands in northwestern china. ecol. eng., 83:268-275. https://doi.org/10.1016/j.ecoleng.2015.06.035 [7] korkusuz ea. (2005) manual of practice on constructed wetlands for wastewater treatment and reuse in mediterranean countries; avkr 5 technical report med-reunet ii (inco-ct2003-502453): agbar foundation barcelona. [8] ezzahri j, ennabili a, ater m, radoux m. (2001) epuration des eaux usées urbaines : expérimentation sous climat méditerranéen (m’diq, nord-ouest du maroc). ann. chim. sci. mat., 26:s297-311. [9] ezzahri j, ennabili a, radoux m (2010) artificial ecosystems for wastewaters treatment under mediterranean conditions (morocco). biol. divers. conserv. 3/2:145-150. retrieved from http://www.biodicon.com/yayinlananmakaleler/7.15.pdf [10] radoux m, cadelli d, nemcova m, ennabili a, ezzahri j. (2003) optimisation of extensive wastewater treatment systems under mediterranean conditions (morocco): compared purification efficiency of artificial ecosystems. in wetlands: nutrients, metals and mass cycling; vymazal, j., ed. backhuys publishers: leiden, nl, pp. 143-168. [11] ennabili a. (1999) végétation hygrophile du maroc méditerranéen: écologie, socio-économie et rôle potentiel dans l’épuration des eaux usées. phd thesis. university of liege, department of environmental sciences and management. [12] ezzahri j. (2005) optimisation de l'épuration naturelle des eaux usées domestiques urbaines dans le contexte climatique et socio-économique du nord du maroc (m'diq). phd thesis. university of liege, department of environmental sciences and management. 38 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 [13] standard methods. (1995) standard methods for the examination of water and wastewater, 19thedn, american public health association/american water works association/water environment federation: washington d.c. [14] ennabili a, ater m, radoux m. (1998) biomass production and npk-retention in macrophytes from wetlands of the tingitan peninsula. aquat. bot. 62(1):45-56. https://doi.org/10.1016/s0304-3770(98)00075-8 [15] ennabili a. (2008) régénération in vivo de macrophytes originaires des zones humides du maroc méditerranéen. rev. assoc. forum nord maroc, 2-3:116-124. retrieved from http://revue-afnm.org/b2e/numero-2-3/regeneration-in-vivo-de-macrophytes [16] abou-elela si, golinielli g, abou-taleb em, hellal ms. (2013) municipal wastewater treatment in horizontal and vertical flows constructed wetlands. ecol. eng., 61(part a):460468. https://doi.org/10.1016/j.ecoleng.2013.10.010 [17] zhang j, sun h, wang w, hu z, yin x, ngo hh, guo w, fan j. (2017) enhancement of surface flow constructed wetlands performance at low temperature through seasonal plant collocation. bioresour. technol., 224:222-228. https://doi.org/10.1016/j.biortech.2016.11.006 [18] song u, waldman b, park js, lee k, park sj, lee ej. (2018) improving the remediation capacity of a landfill leachate channel by selecting suitable macrophytes. j. hydro-environ. res., 20:31-37. https://doi.org/10.1016/j.jher.2018.04.005 [19] ennabili a, gharnit n. (2003) effets d’aménagements du littoral tétouanais (nord-ouest du maroc) sur la végétation hygrophile (spermatophyta). acta bot. barc., 48:199-216. [20] asaeda t, rajapakse l, kanoh m. (2010) fine sediment retention as affected by annual shoot collapse: sparganium erectum as an ecosystem engineer in a lowland stream. river res. appl., 26(9):1153-169. https://doi.org/10.1002/rra.1322 [21] liffen t, gurnell am, o’hare mt. (2013) profiling the below ground biomass of an emergent macrophyte using an adapted ingrowth core method. aquat. bot., 110:97-102. https://doi.org/10.1016/j.aquabot.2013.05.008 [22] asaeda t, rajapakse l, manatunge j, sahara n. (2006) the effect of summer harvesting of phragmites australis on growth characteristics and rhizome resource storage. hydrobiologia, 553:327-335. https://doi.org/10.1007/s10750-005-1157-6 [23] maddison m, soosaar k, mauring t, mander ü. (2009) the biomass and nutrient and heavy metal content of cattails and reeds in wastewater treatment wetlands for the production of construction material in estonia. desalination, 246(1-3):120-128. https://doi.org/10.1016/j.desal.2008.02.040 [24] boyd mc, brown mt, brandt-williams s. (2015) addressing pollutant load reduction goals for impaired waterbodies through biomass harvest of gulf coast type phragmites australis (common reed). wetlands ecol. manage., 23:519-533. https://doi.org/10.1007/s11273-0159406-6 [25] tanaka tst, irbis c, kumagai h, inamura t. (2016) timing of harvest of phragmites australis (cav.) trin. ex steudel affects subsequent canopy structure and nutritive value of roughage in subtropical highland. j. environ. manag., 166:420-428. https://doi.org/10.1016/j.jenvman.2015.10.055 [26] de los reyes cp, villamar ca, neubauer me, pozo g, vidal g. (2013) behavior of typha angustifolia l. in a free water surface constructed wetlands for the treatment of swine wastewater. j. environ. sci. health, part a: toxic/hazard. subst. environ. eng., 48(10):1216-224. https://doi.org/10.1080/10934529.2013.776852 [27] maucieri c, salvato m, tamiazzo j, borin m. (2014) biomass production and soil organic carbon accumulation in a free water surface constructed wetland treating agricultural wastewater in north eastern italy. ecol. eng., 70:422-428. https://doi.org/10.1016/j.ecoleng.2014.06.020 [28] borin m, tocchetto d. (2007) five year water and nitrogen balance for a constructed surface flow wetland treating agricultural drainage waters. sci. total environ., 380(1-3):38-47. https://doi.org/10.1016/j.scitotenv.2006.12.039 39 iium engineering journal, vol. 21, no. 2, 2020 ennabili and radoux https://doi.org/10.31436/iiumej.v21i2.1207 [29] li eh, li w, wang xl, xue hp, xiao f. (2010) experiment of emergent macrophytes growing in contaminated sludge: implication for sediment purification and lake restoration. ecol. eng., 36(4):427-434. https://doi.org/10.1016/j.ecoleng.2009.11.009 [30] das sc, tanaka n (2007) estimating nitrogen budgets of typha angustifolia by considering the regrowth shoot productivity and nitrogen content after harvesting aerial organs in different growing seasons. landsc. ecol. eng., 3:99-108. https://doi.org/10.1007/s11355007-0024-1 [31] asaeda t, rashid mh. (2015) nutrient retention associated with phenological features in sparganium erectum stands in a lowland stream. river res. appl., 31(2):207-215. https://doi.org/10.1002/rra.2733 [32] chicalote-castillo d, ramírez-garcía p, macías-rubalcava ml. (2017) allelopathic effects among selected species of phytoplankton and macrophytes. j. environ. biol., 38(special issue):1221-227. http://dx.doi.org/10.22438/jeb/38/6(si)/07 [33] zhang tt, hu w, zhang d. (2012) allelopathic effect of typha angustifolia l. on phytoplankton. adv. mater. res.-switz., 383-390:3724-728. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.3724 [34] gross em. (2003) allelopathy of aquatic autotrophs. crit. rev. plant sci., 22(3-4):313-339. https://doi.org/10.1080/713610859 40 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <feff004200720075006b00200064006900730073006500200069006e006e007300740069006c006c0069006e00670065006e0065002000740069006c002000e50020006f0070007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740065007200200073006f006d002000650072002000650067006e0065007400200066006f00720020007000e5006c006900740065006c006900670020007600690073006e0069006e00670020006f00670020007500740073006b007200690066007400200061007600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020005000440046002d0064006f006b0075006d0065006e00740065006e00650020006b0061006e002000e50070006e00650073002000690020004100630072006f00620061007400200065006c006c00650072002000410064006f00620065002000520065006100640065007200200036002e003000200065006c006c00650072002e> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <feff0041006e007600e4006e00640020006400650020006800e4007200200069006e0073007400e4006c006c006e0069006e006700610072006e00610020006f006d002000640075002000760069006c006c00200073006b006100700061002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400200073006f006d00200070006100730073006100720020006600f60072002000740069006c006c006600f60072006c00690074006c006900670020007600690073006e0069006e00670020006f006300680020007500740073006b007200690066007400650072002000610076002000610066006600e4007200730064006f006b0075006d0065006e0074002e002000200053006b006100700061006400650020005000440046002d0064006f006b0075006d0065006e00740020006b0061006e002000f600700070006e00610073002000690020004100630072006f0062006100740020006f00630068002000410064006f00620065002000520065006100640065007200200036002e00300020006f00630068002000730065006e006100720065002e> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice lipase immobilization on fibers grafted with polyglycidyl methachrylate iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. lipase immobilization on fibers grafted with polyglycidyl methachrylate ma’an fahmi rashid alkhatib1* nik adlin bahrudin1, hamzah mohd. salleh2, mohamed mahmoud elsayed nasef3, teo ming ting4 1 department of biotechnology engineering, faculty of engineering, 2 international institute for halal research and training (inhart), international islamic university malaysia, po box 10, kuala lumpur 59728, malaysia53100 gombak, selangor, malaysia. 3 chemical engineering department, universiti tecknologi petronas, 32610 seri iskandar, perak, malaysia. 4 radiation processing technology division, malaysia nuclear agency, bangi, 43000 kajang, selangor, malaysia. * corresponding author: maan@iium.edu.my (received:27th sept 2018; accepted:20th dec 2018; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.1002 abstract: lipase enzyme originated from wheat germ was immobilized on nylon -6 grafted with polyglycidyl methachrylate (pgma). the immobilization of enzyme experiments were designed and studied using face centred central composite design (fcccd) under response surface methodology (rsm). prior to immobilization, the polymer was activated with diethyl amine/ethanol to introduce an amine functional group to facilitate covalent bonding with the enzyme. the immobilized and free enzymes were characterized for effect of temperature and ph on enzyme activity, stability, storage and reusability as well as kinetics studies. anova revealed that optimum lipase activity of 0.287 u/ml was achieved at immobilization time of 5 h, ph of 6 and 1.0 mg/ml for enzyme concentration. the optimum temperatures and ph for immobilized and free enzymes were 45 °c and 35 °c, and 8 and 7, respectively. the immobilized enzyme showed higher stability compared to free enzyme. the immobilized enzyme retained 18% of its activity after being recycled 8 times. in a storage stability test, immobilized lipase was able to retain 70% of its activity after being stored for 30 days, while free enzyme activity dropped to 15 % after 20 days of storage. abstrak:enzim lipase telah dihasilkan daripada mikroorganisma pegun gandum di atas nilon -6dan digraf bersama poliglisidel methakrilet (pgma). enzim pegun ini direka dan dikaji secara eksperimen menggunakan reka bentuk campuran pusat pada permukaan (fcccd) di bawah kaedah tindak balas permukaan (rsm). sebelum menjadi pegun, polimer ini telah diaktifkan dengan dietil amine/ethanol bagi menghasilkan kumpulan fungsi amine bagi membantu ikatan kovalen atom pada enzim. enzim pegun dan bebas ini telah dikategorikan mengikut kesan enzim ke atas suhu, aktiviti enzim ke atas kesan ph, kestabilan, keboleh-simpanan dan keboleh-gunaan balik, serta ujian tindak balas kinetik. anova membuktikan bahawa aktiviti optimum enzim lipase ini adalah sebanyak 0.287 u/ml telah terhasil selama 5 jam pegun, pada ph 6 dan kepekatan enzim sebanyak 1.0 mg/ml. suhu dan ph optimum, pada enzim pegun dan enzim bebas ini adalah pada 45 °c dan 35 °c, dan ph 8 dan 7, masing-masing. enzim pegun ini menunjukkan lebih stabil daripada enzim bebas. enzim pegun dilihat kekal 18% daripada aktivitinya selepas 8 kali ulangan. melalui ujian kestabilan simpanan, enzim lipase pegun dapat mengekalkan 70% 12 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. daripada aktivinya selepas disimpan selama 30 hari, manakala aktiviti enzim bebas telah menurun kepada 15% selepas 20 hari dalam simpanan. keywords: immobilization; enzyme; lipase; optimization; fcccd; rsm; fibers; nylon; stability; reusability; kinetics study 1. introduction lipases (triacylglycerol ester hydrolase, ec 3.1.1.3) play an important role in industry. their capability to break triacylglycerols down to fatty acids and glycerol make them the most promising in biodiesel production using transesterification of oils. lipase is also used in food and flavour making, drug synthesis, and perfumery and cosmetics [1]. due to the shortcomings of free enzymes, such as having low stability, non-reusability and difficulty in separation from the products, immobilization technology is introduced to overcome these drawbacks. immobilization of enzymes is the most frequently used method to convey the needed characteristics of conventional heterogeneous catalysts into biological catalysts [2]. various mechanisms are applied to immobilize enzymes such as covalent binding physical adsorption, ionic interaction, or entrapment [3]. numerous benefits are conceivable through immobilization including improved stability, reusability, ease in separation of final products, greater control in catalysis [4], considerable cost benefits for industrial processes [5], and the ability to stop the reaction quickly by removing the enzyme from the reaction solution [6]. among many supports, immobilization on polymer support has gained more interest. polymer supports have good mechanical properties, can be produced in mass quantities and can be easily modified for immobilization with maintained stability [7,8]. several studies showed that lipase enzymes have been immobilized on different types of support including chitosan beads [9], electrospun cellulose nanofiber membrane [10] sepabeads® [11], ferric silica nanocomposite [12] and octyl and cyanogen bromide (cnbr) agarose beads [13]. radiation-induced graft polymerization (rigp) is a useful method to functionalize various polymer materials [14]. nylon-6, which is also known as polycaprolactam and polyamide 6, possesses excellent mechanical and physical properties and has become the most widely used synthetic polymer for fibres [15]. introducing functional groups on the nylon-6 polymer surface with rig can introduce new chemical characteristics to the polymer while its main properties remain unchanged [16] making it promising candidate for enzyme immobilization. in this study, lipase enzyme was immobilized onto the nylon-6 grafted polyglycidyl methachrylate (pgma) with covalent linkage. three conditions, namely, reaction ph, reaction time, and enzyme/support ratio were optimized using response surface methodology (rsm) and face centred central composite design (fcccd). the optimum temperature and ph, thermal stability, storage stability and reusability, as well as kinetic parameters were determined. 2. materials and methods 2.1 material nylon-6 polymer was purchased from reliance sdn. bhd. gma, polyoxyethylene sorbitanmonolaurate or tween-20 and diethyl amine (dea) were purchased from sigma aldrich (usa). lipase (solid form, 5-15 units/mg protein) from wheat germ was also procured from sigma-aldrich (usa). all reagents used were of analytical grade or higher 13 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. and used as procured. 2.2 synthesis and activation of polymer nylon-6-grafted with pgma was synthesized by radiation-induced emulsion graft copolymerization. typically, nylon-6 samples were placed in a pe zipper bags which were purged using purified n2, sealed and irradiated using an electron beam accelerator (eps 3000) to a total dose of 10 kgy. the deoxygenated grafting solution was transferred to an ampoule containing irradiated polymer. pgma grafted onto nylon-6 with grafting yield of 280% was obtained using grafting solution containing a mixture of 5 wt% of gma and 0.5 wt% of tween 20 in di water with reaction time 3 hours at 40 oc. nylon-6-grafted with pgma was introduced with the amine group where the pgma-fiber was treated with diethyl amine/ethanol solution (1:1, v/v) at 40 °c for 4 hours with 100 rpm agitation. the aminated fiber was taken out of the solution using forceps and washed several times with absolute ethanol then dried for 2 hours at 60 °c in oven. after the drying process, the amine group density was calculated by eq. (1) [14]: 𝐴𝑚𝑖𝑛𝑒 𝑔𝑟𝑜𝑢𝑝 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 ( 𝑚𝑚𝑜𝑙𝑒 𝑔𝑟𝑎𝑚 − adsorption) = [ (𝑊𝑓−𝑊𝑔) 𝑊𝑓 ] × ( 1000 mw ) (1) where wg and wf are the weights of nylon-6 grafted pgma before and after amination and mw is the molecular weight of diethyl amine. the aminated fiber then was soaked in hydrochloric acid solution (1m) followed by sodium hydroxide solution (1m) overnight. then, the aminated fiber underwent oven drying for 2 hours at 60 °c and was stored in a desiccator to avoid moisture. 2.3 statistical optimization for lipase immobilization statistical optimization is a practical approach for studying several factors associated with the production process. this method is commonly used in reducing the number of experiments and for quick screening of the experimental field. statistical evaluation of the data from an appropriately designed set of experiments can demonstrate the form of interaction between the parameters. in this study, design expert software (version 7.0.0) has been chosen to analyse the process parameters that influence the immobilization of lipase. a 3-factor and 3-level face centered central composite design (fcccd) under rsm was employed in this study. the effect of immobilization time (x1), immobilization ph (x2), and enzyme/support ratio (x3) on lipase activity was evaluated at immobilization time of 210 h; ph of 6-8; and an enzyme concentration of 0.4-1.0 mg/ml. analysis of variance (anova) results were used to analyse the statistical data. this analysis included the fischer’s f-test, p-value (which is used to indicate statistical significance for each of the coefficients tested and is also important to understand the pattern of the mutual interactions between the parameters), and the coefficient of determination r2 (that measures the fit of the regression model). a value of r2 closer to 1 indicates there are outstanding correlations between the independent variables. the αlevel was set at 0.05 intervals, a p-value which is less than this value indicates that the model terms are significant. 14 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. 2.4 immobilization of lipase enzyme immobilization of lipase onto polymer support was carried out by immersing 20 mg of activated polymer in various concentrations of lipase (0.4 mg/ml, 0.7 mg/ml and 1.0 mg/ml) in a phosphate buffer solution (pbs) (50 mm, ph 7) and the mixture was incubated at 2837 °c with 100 rpm agitation for different times (2, 6, 12 h). protein concentration in final solution was measured by bradford protein assay [17]. the amount of lipase immobilized was calculated based on the difference in lipase initial and final concentrations. the recovery efficiency (re) was defined as “the percentage of enzymes on the polymer by detecting the protein concentration before and after immobilization” [18]. the re value is calculated according to eq. (2): 𝑅𝐸 = 𝐶𝑝,𝑜−𝐶𝑝,𝑟 𝐶𝑝,𝑜 × 100% (2) where, cp,o is the protein concentration of added lipase (mg protein/ml); cp,r is the protein concentration of lipase in the solution and washed water after immobilization (mg protein/ml). 2.5 measurement of lipase activity the activity of lipase enzyme was found by employing p-nitrophenyl palmitate (p-npp) as a substrate. stock solution consisted of 28 mg of dissolved p-npp in 100 ml of triton x100 and 1.7 ml of 1% sodium dodecyl sulfate while stirring. then the solution mixture was heated on a hot plate until the solution become clear and no turbidity was seen. to start the enzymatic reaction, 1 ml of p-npp stock solution was incubated with 1 ml of 0.1 m trishcl (ph 8.2) and 20 mg immobilized enzyme at 37°c for 30 min. then, 1 ml naoh (1 m) was added to stop the enzyme reaction. the molar extinction coefficient for p-nitrophenol is 15,000 m-1cm-1 at 311 nm. manifestly, one unit (u) of enzyme activity is defined as the amount of enzyme that liberates 1 mmol p-nitrophenol per minute under assay condition. 2.6 effect of temperature and ph on enzyme activity the immobilized enzyme (20 mg matrix) was placed in phosphate buffer (0.1 m, ph 7) and assayed for residual lipase activity at different temperatures (25 65°c). for ph, the same amount of enzyme was assayed in 0.1 m pbs at ph range of (5-9). 2.7 stability profile of immobilized lipase the ph stability of immobilized lipase was studied by incubating the enzyme for 30 minutes without addition of substrate in buffers of varying ph in the range of (5-12). after the incubation period, the residual enzyme activity was evaluated. residual activities were calculated as the ratio of the activity of immobilized enzyme after incubation to the activity at the optimum reaction ph. thermal stability of immobilized lipase was tested by incubating the immobilised enzyme at varying temperatures in the range of 20–60 °c for 30 minutes at ph 7 and determining the activity at its optimum reaction temperature. relative residual activity was measured by setting the highest activity at 100%. 2.8 reusability of immobilized lipase immobilized lipase was washed thrice with pbs (50 mm, ph 7) to remove residual substrate. enzyme activity was assayed at 45 °c for up to eight times. the residual activity was determined by taking the first activity cycle as 100%. 15 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. 2.9 storage study immobilized lipase and free lipase were stored in pbs (50 mm, ph 7) at 4 °c for up to 30 days. the remaining activity was measured on a weekly basis. 2.10 kinetics study kinetic parameters of immobilized and free lipase were performed in phosphate buffer (50 mm, ph 7) at 45 °c. to evaluate the value of kinetic parameters which are km and vmax, the concentration of p-npp substrate was varied in the range (0.1-3.0 mm). a few plots were utilized to determine km and vmax of the enzyme. the best fitted plot was selected from the highest r2 value. 3. results and discussion 3.1 optimization of lipase immobilization the optimization of the lipase immobilisation on nylon-6 polymer was conducted using response surface methodology (rsm) under face centred central composite design (fcccd). the agitation was set up at 100 rpm and temperature of 37°c. the highest immobilized lipase activity was 0.222 u/ml obtained at ph 7, 6 hrs immobilization time, and enzyme concentration of 0.70 g/ml. the lowest activity of 0.004 u/ml was at ph 7, 6 hrs immobilization time, and enzyme concentration of 0.40 mg/ml. the effect of each factor and its interactions were calculated using a design expert program (version 7.0.0, stat–ease inc., usa). as the data was fitted with several models and consequently investigated using analysis of variance (anova), the results showed that the quadratic polynomial model is the most acceptable to describe immobilization of lipase. the mathematical prediction model for immobilization of lipase was derived (eq. (3)) under anova test as below 𝑌 = −1.00 + 0.052𝑥1 − 0.19𝑥2 + 0.37𝑥3 − 0.18𝑥1𝑥2 − 0.42𝑥1𝑥3 − 0.12𝑥2𝑥3 − 0.52𝑥2 2 − 0.27𝑥3 2 (3) where 𝑥1 is immobilization ph, 𝑥2 is the immobilization time and 𝑥3 is the enzyme concentration. anova results are shown in table 1. the model f-value of 11.60 implies the model is significant. there is only a 0.02% chance that a "model f-value" this large could occur due to noise. values of "prob > f" less than 0.05 indicate model terms are significant. meanwhile, lack of fit value (0.1088) was insignificant with respect to pure error. this indicated a good and reliable model. thus, it could be used as a target response. the coefficient of determination (r2=0.894) also indicated good correlation between the independent variables. figure 1 shows the 3d plot of the interaction between enzyme concentration and time. it can be observed that there is increase in enzyme activity with concentration; however, the highest enzyme activity is attained at medium time. at longer immobilization time the activity decreases substantially. 16 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. fig. 1: 3d surface plot of enzyme concentration and time vs enzyme activity table 1 analysis of variance (anova) for immobilized enzyme source f value p-value prob > f remarks model 11.6 0.0002 significant a-ph 0.3 0.6216 b-time 2.5 0.1436 c-concen. 9.0 0.0120 ab 1.5 0.2519 ac 7.9 0.0168 bc 0.8 0.3774 b2 24.9 0.0004 c2 6.8 0.0244 lack of fit 2.9 0.1088 not significant r2 0.89 3.2 model validation for immobilized lipase optimization the accuracy of the model was validated under the optimal conditions obtained from fcccd. the response (enzyme activity) was set at maximum. the validation test was performed by choosing three random runs according to table 2. based on the validation test, since the model is significant, lack of fit is insignificant and percentage error is low, it could be concluded that the model was reliable and reproducible. table 2 validation test on optimization of immobilized lipase parameters immobilized enzyme activity (u/ml) ph time (h) enzyme concen (mg/ml) pred exper error (%) 7 4.94 0.90 0.145 0.133 9.49 7 4.99 0.90 0.146 0.130 12.00 7 5.03 0.90 0.145 0.125 15.87 3.3 optimum temperature and ph of immobilized lipase activity assay the optimum temperature for free lipase was at 35 °c whereas for immobilised lipase, the maximum activity was at 45 °c as shown in fig. 2. the optimum temperature profile of 17 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. the immobilized lipase was broader compared to the free lipase. this may be due to the decrease in conformational mobility of immobilized lipase because of the covalent bonding between the enzyme and polymer [19]. the free lipase lost almost 60% of its activity when exposed to temperatures above 35 °c. this low residual activity may be attributed to a significant amount of enzyme being denatured when exposed to elevated temperature [20]. free lipase is denatured when heated at above 45 °c [21]. other studies supported improved thermostability of the immobilized lipase as compared to free enzyme including [10] and [21]. fig. 2: optimum temperatures for both immobilized and free lipase. fig. 3: optimum ph for both immobilized and free lipase. the optimum ph for free lipase was at ph 7, as shown in fig. 3. this may result from the ionization states of several groups on amino acid chains that result in suitable conformation of lipase molecules [22]. after immobilization, the maximum activity was observed at ph 8. this alkaline shift could be an effect from the alteration in the microenvironment of the enzyme caused by immobilization on the support system [17]. 3.4 thermal stability of immobilized lipase figure 4 shows the thermal stability of immobilized and free lipase. it can be seen that when increasing the temperature to 55 °c, the immobilized enzyme retained 74% of its activity compared to free lipase, which dropped to 18% residual activity. this result indicated that the immobilized enzyme was more stable than its free counterpart at higher 0 20 40 60 80 100 120 20 30 40 50 60 70r e la ti v e a c ti v it y ( % ) temperature (°c) immobilized lipase free lipase 0 20 40 60 80 100 120 6 7 8 9 1 0 1 1 1 2 r e la ti v e a c ti v it y ( % ) ph immobilised enzyme free enzyme 18 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. temperatures. zhu and sun [19] proposed that enhanced thermal stability was a result of covalent attachment, which limited conformational change and disallowed the denaturation process of the immobilized lipase at higher temperature. for free enzyme, high temperature might interrupt the globular structure of the proteins thus leading to the denaturation [23]. fig. 4: thermal stability of immobilized and free lipase. 3.5 ph stability of immobilized lipase figure 5 compares ph stability of immobilized and free lipase. it can be clearly seen that immobilized lipase has better ph stability within the alkaline region, from ph 8 to ph 12. pahujani et al. [24] reported that the immobilized lipase was fairly stable within ph 7.5 – 9.5. lipase from a mutant strain of cornebacterium sp. was immobilized and has been found stable at ph 8 [25]. according to [19], the multipoint attachment mechanism limits the undesired conformation against environment changes. this improves ph stability of the immobilized lipase. fig. 5: ph stability of immobilized and free lipase. 3.6 reusability of immobilized lipase figure 6 shows the effect of repeated use on the activity of immobilized lipase. in this study, the reusability test was conducted up to 8 cycles. the first cycle of this test was set as 100% and the residual activity of each cycle was calculated based on it. according to fig. 6, immobilized lipase retained 78% of its residual activity up to 4 cycles. after 8 cycles, the 0 20 40 60 80 100 25 35 45 55 65 r e la ti v e a c ti v it y ( % ) temperature (°c) immobilized enzyme free enzyme 0 20 40 60 80 100 6 7 8 9 10 11 12 r e la ti v e a c ti v it y ( % ) ph immobilized enzyme free enzyme 19 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. residual activity dropped to 18%. previous study reported that lipase immobilized on cnbractivated–sepharose 4b retained full activity even after 13 cycles [26]. huang et al. [22] reported that the remaining activity of lipase immobilized on the cellulose fibrous membrane dropped to 30% after 8 cycles. the activity of immobilized enzyme tends to decrease with repeated use. the loss of activity could be related to the inactivation of enzyme by continuous use and the leakage of protein from the polymer support. this can be improved by providing a stronger attachment mechanism in order to increase the recyclability. fig. 6: reusability of immobilized lipase. 3.7 storage stability of immobilized lipase the stability of immobilized and free lipase was compared with respect to storage time. both free and immobilized lipases were stored at 4 °c for 35 days then the activities of both enzymes were determined. the immobilized lipase was found to retain 70 % of its residual activity after 30 days of storage. on the other hand, after 20 days of storage at 4 °c, the activity of free lipase solution dropped to 15% of its original activity (fig. 7). according to [19] free enzyme solution undergoes rapid reductions in catalytic activity during storage, making it difficult to recover the enzyme from the reaction mixture after catalytic reactions. this result shows the great potential of the polymer used in this study as a support for enzyme immobilization. fig. 7: storage stability test of immobilized and free lipase. 100 93 83 78 53 45 35 18 0 20 40 60 80 100 1 2 3 4 5 6 7 8 r e si d u a l a c ti v it y ( % ) no. of cycle 0 20 40 60 80 100 0 7 14 21 28 35 r e la ti v e a c ti v it y ( % ) storage time (days) immobilized enzyme free enzyme 20 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. 3.8 kinects study for the kinetics study of immobilized and free lipase enzyme, a lineweaver-burk plot best fitted the data (fig. 8). it was found that both vmax and km for immobilized lipase were reduced compared to the free enzymes. vmax and km values obtained were 0.012 mm/min and 7.250 mm for immobilized lipase, and 0.024 and 10.321 for free lipase, respectively. the lower value of km for immobilized lipase enzyme compared to free enzyme indicates a stronger and more efficient binding of substrate. vmax, on the other hand, exemplifies how quick the reaction is catalyzed by the enzyme. lower vmax for the immobilized enzyme designates lower enzyme rate. this is commonly observed since the enzyme having lower activity after the immobilization process is caused by the lower accessibility of substrates towards the immobilized enzyme’s active site [19]. fig. 8: lineweaver–burk plot for immobilized lipase. 4. conclusions lipase enzyme was successfully immobilized on nylon-6-grafted with pgma. the optimum immobilization conditions were determined using rsm fcccd. immobilized enzyme showed higher stability at wide range of temperature and ph. immobilized lipase retained 70% of its activity when stored for 35 days at 4°c, while free lipase lost 70% after 14 days. the immobilized lipase retained 78% of its activity after 4 cycles. this proposed immobilized enzyme-polymer system has potential in applications such as biodiesel production from oil. acknowledgment the authors wish to acknowledge the financial support from a research grant (frgs 14162-0403) obtained under the fundamental research grants scheme, ministry of higher education (mohe), malaysia. the authors are also grateful to hazimah akbar tajudin for her valuable input on statistical analysis in this manuscript. references [1] hung tc, giridhar r,chiou sh, wu wt. (2003). binary immobilization of candida rugosa lipase on chitosan. j. mol. catal. b enzym., 26: 69-7.8 [2] won k, kim s, kim kj, park hw, moon sj. (2005). optimization of lipase entrapment in ca-alginate gel beads. process biochem., 40: 2149-2154. 0 500 1000 1500 2000 2500 0 2 4 1 /v , m in /m m 1/[s], mm-1 21 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. [3] yujun w, jian x, guangsheng l, youyuan d. (2008). immobilization of lipase by ultrafiltration and cross-linking onto the polysulfone membrane surface. bioresour. technol., 99: 2299-2303. [4] singh bd. (2009). biotechnology: expanding horizons. india kalyani [5] alkhatib m. (2011). enzymatic hydrolysis of oil palm empty fruit bunch using immobilized cellulase enzyme. african j. biotechnol., 10: 18811-18815. [6] alkhatib m, alam z, mohammed r. (2012). statistical modelling optimisation of cellulase enzyme immobilisation on functionalised multi-walled carbon nanotubes for empty fruit bunches degradation. aust. j. basic appl. sci., 6: 30-38. [7] bowers ld, carr pw. (1976). applications of immobilized enzymes in analytical chemistry. anal. chem., 48: 544a–559a. [8] lu j, toy ph. (2009). organic polymer supports for synthesis and for reagent and catalyst immobilization. chem. rev., 109: 815-838. [9] chiou sh, wu wt. (2004). immobilization of candida rugosa lipase on chitosan with activation of the hydroxyl groups. biomaterials. 25: 197-204. [10] huang x-j, chen p-c, huang f, ou y, chen m-r, xu zk. (2011). immobilization of candida rugosa lipase on electrospun cellulose nanofiber membrane. j. mol. catal. b enzym., 70: 95-100. [11] prlainović nž, knežević-jugović zd, mijin dž, bezbradica di. (2011). immobilization of lipase from candida rugosa on sepabeads®: the effect of lipase oxidation by periodates. bioprocess biosyst. eng., 34: 803-810. [12] tran dt, chen cl, chang js. (2012). immobilization of burkholderia sp. lipase on a ferric silica nanocomposite for biodiesel production. j. biotechnol. 158: 112-119. [13] manoel ea, dos santos jcs, freire dmg, rueda n, fernandez-lafuente r. (2015). immobilization of lipases on hydrophobic supports involves the open form of the enzyme. enzyme microb. technol. ,71: 53-57. [14] nasef mm, güven o. (2012). radiation-grafted copolymers for separation and purification purposes: status, challenges and future directions. prog. polym. sci., 37: 1597-1656. http://dx.doi.org/10.1016/j.progpolymsci.2012.07.004 [15] liu y, cui l, guan f, gao y, hedin ne, zhu l, fong h. (2007). crystalline morphology and polymorphic phase transitions in electrospun nylon-6 nanofibers. macromolecules. 40: 6283-6290. [16] nasef mm, abbasi a, ting tm. (2014). new co2 adsorbent containing aminated poly(glycidyl methacrylate) grafted onto irradiated pe-pp nonwoven sheet. radiat. phys. chem., 103: 72-74. http://dx.doi.org/10.1016/j.radphyschem.2014.05.031 [17] bradford mm. (1976). a rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. anal. biochem., 72: 248254. [18] liu c-h, lin y-h, chen c-y, chang j-s. (2009). characterization of burkholderia lipase immobilized on celite carriers. j. taiwan inst. chem. eng., 40: 359-363. [19] zhu j, sun g. (2012). lipase immobilization on glutaraldehyde-activated nanofibrous membranes for improved enzyme stabilities and activities. react. funct. polym., 72: 839845. [20] yu cy, li xf, lou wy, zong mh. (2013). cross-linked enzyme aggregates of mung bean epoxide hydrolases: a highly active, stable and recyclable biocatalyst for asymmetric hydrolysis of epoxides. j. biotechnol., 166: 12-19. doi: 10.1016/j.jbiotec.2013.04.015 [21] yuce-dursun b, cigil ab, dongez d, kahraman mv, ogan a, demir s. (2016). preparation and characterization of sol-gel hybrid coating films for covalent immobilization of lipase enzyme. j. mol. catal. b enzym., 127: 18-25. [22] huang xj, chen pc, huang f, ou y, chen mr, xz. (2011). immobilization of candida rugosa lipase on electrospun cellulose nanofiber membrane. j mol catal b-enzym., 70: 95100. [23] gupta k, jana ak, kumar s, jana mm. (2015). solid state fermentation with recovery of amyloglucosidase from extract by direct immobilization in cross linked enzyme aggregate 22 http://dx.doi.org/10.1016/j.progpolymsci.2012.07.004 http://dx.doi.org/10.1016/j.radphyschem.2014.05.031 iium engineering journal, vol. 20, no. 1, 2019 alkhatib et al. for starch hydrolysis. biocatal. agric. biotechnol., 4: 486-492. http://dx.doi.org/10.1016/j.bcab.2015.07.007 [24] pahujani s, kanwar ss, chauhan g, gupta r. (2008). glutaraldehyde activation of polymer nylon-6 for lipase immobilization: enzyme characteristics and stability. bioresour. technol., 99: 2566-2570. [25] roy n, ray l, chattopadhyay p. (2004). production of lipase in a fermentor using a mutant strain of corynebacterium species: its partial purification and immobilization. indian j. exp. biol., 42: 202-207. [26] dosanjh, n s and kaur, j (2002). immobilization, stability and esterification studies of a lipase from a bacillus sp. biotechnol. appl. biochem., 36: 7-12. 23 http://dx.doi.org/10.1016/j.bcab.2015.07.007 microsoft word 160-668-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 al-nassar and hawwa 142 wave scattering at a tapered free end of an elastic plate yagoub n. al-nassar and muhammad a. hawwa department of mechanical engineering, king fahd university of petroleum and minerals dhahran 31261, saudi arabia. ynassar@kfupm.edu.sa abstract: this paper focuses on the interaction of sh elastic waves in a plate with a tapered free end. the plate is modeled as a semi-infinite elastic structure, which was assumed to have traction-free surfaces. the results of the analysis based on mode matching are presented for various combinations of normalized frequencies and angles of free end inclination. the reported observations form important guidelines for the interpretation of experimental data when using horizontally polarized wave as a mean for nondestructive evaluation of elastic plates. abstrak: kertas kerja ini adalah khusus berkenaan interaksi gelombang anjal sh di dalam plat yang mempunyai hujung bebas yang tirus. plat ini dimodelkan sebagai satu struktur elastik separa tak terhingga, yang diandaikan mempunyai permukaan nirgeseran. keputusan analisis berdasarkan mod pemadanan dibentangkan untuk pelbagai kombinasi frekuensi ternormal dan sudut kecondongan hujung bebas. pemerhatian yang dibentangkan memberi panduan penting dalam menginterpretasi data eksperimental penggunaan gelombang berkutub mendatar sebagai satu kaedah penilaian tanpa musnah plat anjal. keywords: elastic plates; ultrasonic wave scattering; nondestructive evaluation 1. introduction the non-destructive testing (ndt) of materials become more important and demanding as they are used in safety critical applications such as aircraft primary structure. a decisive method for evaluating the condition of plate structures is the utilization of ultrasonic wave scattering due to the presence of inclusion or inclusions and defects such as cracks and flaws. methods of solution of scattering problem vary from classical approach such as mode matching and variational techniques to numerical techniques such as finite elements and boundary elements approach or combination of numerical formulation with a wave function expansion technique. there is an extensive literature on the studies of scattering of elastic waves in plates due to inclusion, cracks, or weldments. among these, the work of sabbagh et. al. [1] who has analyzed scattering of sh waves. in their approach, it is assumed that the plate wave guide admits a single mode only and all the higher modes in the waveguide are neglected. abduljabbar et. al. [2] studied the diffraction of sh waves in a plate by arbitrary defects where finite element formulation and a wave function expansion technique is employed. koshiba et al. [3] have analyzed sh wave scattering using similar approach. in their analysis, they have taken the number of normal modes and the number of nodal points iium engineering journal, special issue, mechanical engineering, 2011 al-nassar and hawwa 143 along the interface to be independent. datta et al. [4] and fortunko et al. [5] studied the diffraction of sh waves by edge crack and planar defects using low –frequency and medium and long wavelength. to the author knowledge, the scattering of sh waves by an inclined edge of an elastic plate has not been reported. recently, an interest is raised in the reflection of elastic waves from inclined free edges of elastic plates. wilkie-chancellier et al. [6-8] performed finite element analyses and laser interferometer / vibrometer experiments on the reflection of the sₒ, aₒ, and a1 lamb modes from an inclined edge of elastic plates having different values of the bevel angle. they proved that the edge mode was the resonance of different complex modes. galán and abascal [9] used a hybrid finite-element / boundary element technique to study lamb mode conversion at inclined or perpendicular free edges of elastic plates for frequencies beyond the first cutoff frequency. in this paper, a mode matching technique is used to investigate the scattering of sh waves due to impinging on a tapered end of an elastic plate. mode matching procedure is followed along a fictitious boundary inside the plate while satisfying the continuity of displacement and stresses condition. a stress-free condition is satisfied at the inclined surfaces of the plate. numerical integration leads to a system of linear algebraic equations for the reflection coefficient of the scattered field. 2. problem formulation let us consider a plate shown in fig. 1. the plate is assumed to be elastic of uniform thickness, 2h, and has traction-free surfaces. two regions can be identified and these are plate region, 1, and wedge region, 2. the two regions are assumed to be separated by a fictitious boundary. fig. 1: plate geometry. in the plate region, 1, the total displacement field, wt, can be written as wt = winc + wref (1) where the superscripts inc and ref in the above equation stand for incident and reflect field, respectively. incident field, winc, consists of a single propagating mode propagating in the negative x-direction. the incident field is assumed to be time harmonic wave, and given by the following expression )txk(j i inc ie) h yi cos(aw    2 (2) iium engineering journal, special issue, mechanical engineering, 2011 al-nassar and hawwa 144 where k and  are wavenumber and frequency, respectively. the relationship between these two quantities is given by the following expression  2 2 2 2 kh c h n          . the reflected field, wref, is generally composed of a number of reflected modes (propagating and non-propagating modes) in the plate region. the reflected field (scattered) takes the following expression )txk(j l l l ref le) h yl cos(bw       20 (3) the displacement field in wedge region, 2, is given by 0 cos( ) ( , ) n tr j t n n s n n r w c j e c               (4) where  is the wedge angle and cs is the shear velocity, (g/)1/2. g and  stand for the shear modulus and density, respectively. note that the solution in the wedge perfectly satisfies the traction free boundary conditions at the two surfaces 1 and 2. imposing the continuity of displacement and stress along the fictitious boundary, 3, gives wt |plate = wtr |wedge , r = r , 0     t |plate = tr |wedge , r = r , 0     where wtr is the displacement field in the wedge. the stress field, t, is given by t|plate = (inc + ref) |plate but the shear stress,, takes the following form  = xz nx + yz ny where nx and ny are the direction cosine of the outward unit normal vector n along the boundary 3. it remains to choose weight functions of the form cos( ),w m f     0,1, 2, ,m n  (5) then, the above boundary conditions lead to the following equations: cos( )0 sin( ) cos( ) 2 cos( ) 2 i l jk x i l jk x l x rl y r i a y e h l b y e h                     0 cos( ) ( , ) n n n s r r n n r c j c               (6) iium engineering journal, special issue, mechanical engineering, 2011 al-nassar and hawwa 145 cos( ) 2 sin( ) 2 2 i i x jk x i y i jk y n ha e i i y n h h                   0 cos( ) 2 sin( ) 2 2 l l xl jk x l l y l jk y n hb e l l y n h h                  0 cos( ) ( , ) n n n s s r r n n r c j c c                (7) where primes indicate differentiation with respect to r (i.e., d(..)/dr). by letting reflected modes l=n. these continuity equations can be integrated through the angle of the wedge after multiplying them with a set of weight functions. by this way, it leads to a set of algebraic equations (3n equations) in which the coefficients, bl, cn, and dn can be determined after setting intensity of the incident wave, ai, to be one. 3. results and discussion a semi-infinite plate of a homogeneous, isotropic, linearly elastic material is considered. the elastic plate is made of stainless steel and has a density and a shear modulus of 7.8 g/cm3 and 0.81 x1011 pa, respectively. a time-harmonic sh wave propagates in the plate and is incident upon the inclined end of the plate. since the end of the plate is considered to be stress free, the wave scattering problem reduces to determining the formed reflected wave field. only the traveling modes have the capability of carrying the incident wave energy back into the plate. these traveling modes are supplemented by a series of end modes, which are associated with purely imaginary wave numbers, in order to satisfy a traction-free end conditions. the number of modes, n, in the wave expansion function has been chosen to be 15 modes as to include all the propagating and non-propagating ones. the accuracy of the results is determined by studying the error norm in the energy balance. in order to understand wave scattering, a single sh mode is incident on the free end of the plate and reflected sh modes are examined.. two cases are considered; in the first, the zeroth symmetric mode is incident on the edge at selected frequencies and in the other, the first antisymmetric mode is incident on the edge at the same range of frequencies. the results are presented in terms of the energy content of the reflection modes for the two cases. the inclined free end of the plate is allowed to take various angles of inclination. figures 2 and 3 show the energy ratio (en / etotal) of the reflected sh modes from the incidence of the zeroth sh mode over the full range of angles of inclination as functions of the normalized frequencies, ω = (2ωh/πc), of 1.5. iium engineering journal, special issue, mechanical engineering, 2011 al-nassar and hawwa 146 fig. 2: the energy ratio (en / etotal) of the reflected sh modes (symmetric). fig. 3: the energy ratio (en / etotal) of the reflected sh modes (anti-symmetric). figures 4 and 5 show the energy ratio (en / etotal) of the reflected sh modes from the incidence of the zeroth sh mode over the range the normalized frequencies from 1 up to 2. figures 6 and 7 show corresponding results, (en / etotal), for the case when the first sh mode is incident on the free edge. fig. 4: the energy ratio (en / etotal) of the reflected sh modes (symmetric). iium engineering journal, special issue, mechanical engineering, 2011 al-nassar and hawwa 147 fig. 5: the energy ratio (en / etotal) of the reflected sh modes (symmetric). fig. 6: the energy ratio (en / etotal) of the reflected sh modes (anti-symmetric). fig. 7: the energy ratio (en / etotal) of the reflected sh modes (anti-symmetric). from the presented figures, one can report the following observations: 1. mode conversion of sh modes occurs if the end of the plate is tapered at low normalized frequency (e.g., ω = 1.5, where two propagating modes only) and for certain inclination angles. 2. at certain inclination angles, total (or most of) reflection energy is carried by the-incident mode itself, which increases the possibility of standing wave formation. iium engineering journal, special issue, mechanical engineering, 2011 al-nassar and hawwa 148 3. there are, however, other inclination angles that leads to the formation of reflected fields comprised of non-incident modes. hence, the ultrasonic field in the plate becomes multimodal in nature. 4. concluding remarks the study reported here deals with a single incident mode only. these curves of the reflection coefficients may be very useful in practical nondestructive testing. in an actual experiment the incident disturbance will be due to a time dependent source. then the field, in the frequency domain, will be made of multiple propagating modes. using the outcome results, in terms of reflection coefficients, it would be possible to find the total scattered field by summing up the modal contributions. in addition, the reported results could be used as reference information base as a perfectly edged blade with no cracks or defects. also, this study shows that there are some critical angles of inclination in which the incident mode (symmetric or anti-symmetric is totally reflected in an inversely fashion. in other words, an incident symmetric mode reflected into an anti-symmetric mode and vice versa. acknowledgement the authors would like to acknowledge the support offered by king fahd university of petroleum and minerals. references [1] h. a. sabbagh and t. f. krile, “finite element analysis of elastic waves scattering from discontinuities”. ultrason symp. proc.,pp 216 ,1973. [2] z. abduljabbar , s. k. datta, and a. h. shah, “diffraction of horizontaly polarized shear waves by normal cracks in a plate”, j.appl. phys., vol. 52, pp 461,1983. [3] m. koshiba, h .morita, and m. suzuki, “finite element analysis of discontinuity problem of sh modes in an elastic plate-wave guide”, electronic. lett., vol. 17, pp 480 1981. [4] s. k. datta, a. h. shah, and c. m. fortunko, “diffraction of medium and long wavelength horizontaly polarized shear waves by edge crack”, j. appl. phys., vol 53, pp 2895, 1982. [5] c. m. fortunko, r. b. king, and m. tan, “nondestructive evaluation of planar defects using low-frequency shear horizontal waves”, j. appl. phys., vol. 55, pp 3450 1982. [6] n. wilkie-chancellier, h. duflo, a. tinel, and j. duclos, ``energy balance in the conversion of a lamb wave at a bevelled edge”, acta acustica united with acustica 90-1, pp. 77-84, 2004. [7] n. wilkie-chancellier, h. duflo, a. tinel, and j. duclos, “experimental study and signal analysis in the lamb wave conversion at a bevelled edge”, ultrasonics 42-1, pp. 377-381, 2004. [8] n. wilkie-chancellier, h. duflo, a. tinel, and j. duclos, “numerical description of the edge mode at the beveled extremity of a plate”, journal of the acoustical society of america 117-1, pp. 194-199, 2005. [9] j. m. galán and r. abascal, , “lamb mode conversion at edges. a hybrid boundary elementfinite-element solution”, journal of the acoustical society of america 117-4i, pp. 1777-1784. 2005. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 using similarity degrees to improve fuzzy mining association rule based model for analyzing it entrepreneurial tendency endang supriyati1*, mohamad iqbal2, tutik khotimah2 1informatic department, universitas muria kudus, central java, indonesia. 2electrical engineering department, universitas muria kudus, central java, indonesia . *corresponding author: endang.supriyati@umk.ac.id (received: 27th february 2019; accepted: 18th august 2019; published on-line:2nd december 2019) abstract: higher education has great potential in producing new startups in the it (information technology) field. many choices influence students to become it entrepreneurs. association rule can be used to obtain a model by analysing data so that it can be used to make a rule to the it entrepreneurship-student model, but the association algorithm has disadvantages in handling large datasets. we propose reducing candidate itemsets using degrees of fuzzy similarity. the membership function in fuzzy sets can be used to measure the quality of rules obtained. the purpose of this study is to improve the algorithm by evaluating the similarity of candidate itemsets to get a good quality rule. this research method has 2 phases, namely (1) calculating the membership function with similarity itemset and (2) applying fuzzy mining association rule. phase 1 has several steps, including: preparation of a transaction database, the taxonomy process, and identification of similar itemset. phase 2 has several steps as well. the first is defining membership functions, and the last is a fuzzy mining fuzzy association rule. in this study, a questionnaire was distributed to 1225 students who were members of the it entrepreneurship program. the results of this study were reduced into 823 itemsets and produced an it entrepreneurship rule model. abstrak: pendidikan tinggi mempunyai potensi besar dalam menghasilkan permulaan baru dalam bidang it. banyak pilihan mempengaruhi pelajar bagi menjadi usahawan-it. kaedah bersekutu boleh digunakan bagi mendapatkan model dengan menganalisa data supaya ianya dapat digunakan menjadi model kepada pelajar keusahawanan-it, namun algoritma bersekutu mempunyai kelemahan dalam mengendalikan dataset yang besar. kami mencadangkan pengurangan bilangan set item menggunakan tahapan persamaan kabur. fungsi ahli dalam set kabur dapat digunakan bagi mengukur kualiti aturan yang diperoleh. tujuan kajian ini adalah bagi meningkatkan algoritma dengan menilai persamaan set item calon bagi mendapatkan aturan kualiti yang baik. kaedah penyelidikan ini mempunyai 2 peringkat, iaitu (1) mengira fungsi ahli dengan set item persamaan dan (2) menerapkan aturan perlombongan bersekutu kabur. peringkat 1 mempunyai beberapa langkah, iaitu: urus niaga pangkalan data, proses taksonomi, identifikasi set item yang sama. tahap 2 mempunyai beberapa langkah, iaitu: menentukan fungsi keahlian, dan akhirnya, aturan perlombongan bersekutu. dalam kajian ini, soal selidik telah diedarkan kepada 1225 pelajar yang menjadi ahli program keusahawanan it. dapatan kajian menunjukkan pengurangan nombor dataset kepada 823 set item dan menghasilkan model aturan teknologi keusahawanan it. keywords: fuzzy mining; association rule; similarity degrees; it entrepreneurial 78 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 1. introduction data mining technology is widely used to analyse large amounts of data, including classification, clustering, and association. the association algorithm is a classic association algorithm and widely used. classic association algorithms look for relationship patterns between one or more itemsets in the dataset. this algorithm is famous for finding highfrequency patterns. this frequent itemset pattern is used to compile associative rules [1]. frequent itemsets play an important role in determining the pattern of associations. a frequent itemset is able to detect problems to determine patterns in the dataset [2]. the main key to the association algorithm is in the iteration stage in the database. each iteration produces a frequency pattern to get the support value of each item. the association algorithm can reduce the number of candidates whose support must be calculated by removing unnecessary objects and attributes to get minimum attributes, and this algorithm has a better performance than the classic association algorithm [3]. research on improvement of association algorithms has been carried out, all aimed at improving algorithm performance, i.e. to reduce the calculation time of candidate items by duplicating the frequent itemset to build the next candidate item [4]. some paths are used to improve the association algorithm [5-8]: (1) reduction of transactions, transactions that do not contain the itemset are often deleted from the itemset candidates, (2) hashing tables to calculate the occurrence of set items, (3) partitioning each itemset often must be in one partition. fuzzy theory can be used to improve the association algorithm. the basic idea comes from dividing quantitative values into a crisp set that will weaken or overestimate the specified limit. fuzzy sets can solve problems by allowing membership to be in different sets. reference [9] applied the fuzzy association rule mining algorithm to find associated relationship information. mining fuzzy rules may lead to the discovery of more general and important knowledge from the data [10-12]. the focus of this study is the reduction of data by measuring the similarity of items in the transaction. this measurement of similarity uses the average distance between items. distance measurement for similarity is used for decision making based on certain criteria. therefore the measure of similarity must be able to distinguish similarities from fuzzy sets so as not to overlap [13,14]. after the process of measuring similarity, is used to reduce the dataset. the contain members whose membership value is not less than value. the selection of will have an effect on the results. the selection of the appropriate is based on the previous experience of the decision maker and/or the case under study [15-17] association algorithms are used to analyse data to obtain a model, but association algorithms have disadvantages in handling large datasets. we propose reducing candidate set items using degrees of fuzzy similarity. the focus of this study is the reduction of datasets by measuring the similarity of items based on distance in the dataset with fuzzy similarity degrees. 2. method there are 2 phases in this research, namely the phase of seeking membership functions, then the phase of the fuzzy mining association rule. the first phase consists of (1) transaction database, (2) taxonomy process, (3) identification of similarity items, the second phase consists of (4) defining membership functions (mfs), (5) fuzzy mining and (5) fuzzy association rule. figure 1 describes the research method. 79 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 fig. 1: research method. 2.1 transaction database in this process, the activities carried out include collecting and using historical data to find order, patterns, or relationships in the dataset. the dataset used in this study were 1225 itemsets. the dataset used for this research came from questionnaire survey data of students who took part in entrepreneurship programs at muria kudus university. table 1: the dataset of participant id case t1 md, ai, eb t2 md, e t3 dg, eb, el, em -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- t873 se, d,wd,md,dg,p,eb t874 ai,eb t875 wd,dg,p,eb in table 1, the values t1, t2, t3, ..., t1225 are the ids of students participating in the program, students are given a survey to choose the knowledge that will be used to pioneer into independent it entrepreneurs. these choices are mobile development (md), software engineering (se), database (d), web development (wd), artificial intelligence (ai), robotics (r), mechanics (m), electric (e), e-marketing (em), graphics design (dg), photography (p), e-learning (el), e-business (eb). 2.2 taxonomy process relevant taxonomy items are usually predetermined and can be represented as tree hierarchies. figure 2 is a picture of the it entrepreneurship taxonomy. this taxonomy was built based on a combination of computer science taxonomy [18-21] and the concept of 80 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 entrepreneurship [22,23]. in this taxonomy, engineering students can see the opportunity to use it and engineering to be more innovative, be able to share knowledge, and utilize technology to develop their businesses. fig. 2: taxonomy of it-entrepreneurship. 2.3 similarity identification the euclidean distance formula (1) is used to measure the distance between items. euclidean distance is the most common use of distance. euclidean distance examines the root of square differences between coordinates of a pair objects. if ) and ) then the distance is given by: . (1) finding distance between several points can be reached by the average formula (2). if distance and sample then the distance is given by (2) for example, to calculate the similarity item in table 2, t1 is measured against cases md, ai, and eb. the measurement of the distance of md to ai, md to eb, ai to the eb is carried out using the euclidean formula. the third result of the distance is then calculated on average. 2.4 fuzzy membership function once the similarity between elements is known, the next step is to calculate the degree of fuzzy membership in similarity. a fuzzy set is a set containing elements that have varying degrees of membership in the set. fuzziness is characterized by its membership function. the membership function is a curve that describes the mapping from input to membership level between 0 and 1. through the membership function that has been compiled, the input values become fuzzy information that is useful later for fuzzy processing. the membership function , is the usual fuzzy set a defined as: (3) where [0,1] shows real value intervals from 0 to 1. while notations are the elements of fuzzy set a, notation is the value of the degree of membership in a. a is usually represented as follows: (4) the membership function used is a triangle curve and a linear curve. membership in fuzzy sets has different curve shapes [24]. fuzzy sets can also be defined by assigning a continuous function to describe the membership either analytically or graphically. some commonly used membership functions are shown in fig. 3. 81 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 fig. 3: the membership function of distance similarity. the triangular membership function in fig. 4 be expressed as: (5) in the linear curve, the fuzzy set consists of 2 states, namely linear up and linear down. for the linear down, the straight line starts from the value of the domain with the highest degree of membership on the left side, then moves down to the value of the domain that has a lower degree of membership with the membership function: (6) in linear rise, the increase in the set starts at the domain value that has zero membership degree [0] moves to the right towards the value of the domain that has a higher degree of membership with the membership function: (7) 2.5 fuzzy mining mining is a technique for extracting process models from an execution log. fuzzy mining can be applied to very large and unstructured logs. [24,25] in this stage, data on fuzzy distance similarity is collected. in table 2, the similarity item represents near, middle, and far similarity. 2.6 fuzzy association rule fuzzy logic is used as data mining which involves calculations based on predictions and clustering. fuzzy logic data mining algorithms are not only able to analyse data but also to develop accurate results that are easy to implement. threshold value is a domain threshold value based on the membership value for each domain, where α-cut has 2 conditions: weak α-cut can be expressed as: , strong can be stated as: μ (x) <α. in this paper the fuzzy association rule algorithm is: 82 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 1. the main candidates are generated based on similarity 2. fuzzy operations are carried out to obtain fuzzy mining 3. reduction of candidates with 4. fuzzy rules are built using fuzzy support and confidence. fuzzy set operations are used to combine and modify fuzzy sets. the value of membership as a result of the operation of two sets is often known as fire strength or . several fuzzy operations [26] are used in this study to get associative linguistic rules, namely: (i) intersection of two fuzzy sets a and b are denoted a∩b, the membership function is as follows: (8) (ii) union two fuzzy sets a and b are denoted a b, the membership function is as follows: (9) table 2: fuzzy mining of itemsets id case distance similarity near middle far t1 md, ai, eb 6.30 0.00 0.90 0.10 t2 md, e 2.24 1.00 0 0 t3 dg, eb, el, em 3.82 0.73 0.27 0 ---------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------- t48 se, d 2.45 1.00 0.00 0.00 t49 e, r, ai 2.49 1.00 0.00 0.00 t50 wd, md, ai 4.41 0.53 0.47 0.00 the minimum criterion is used to find the intersection of these sets and take the minimum membership value. however, different decision agents may have different perceptions for the fuzzy operation. the min operation is used for near and middle similarity, and does not use far similar values which are of course not very similar. it is determined that α–cut is 0.3, hence only id with a value of α –cut ≥ 0.3 in the near set will be processed into the association algorithm. -cut determination decision, based on the author's decision. if the -cut is large or too small, the data entering the association algorithm becomes large or too small, and there is increased probability that the results do not represent optimal results. the near and middle sets are chosen because the level of proximity is stronger than the other. table 3 contains the results of the intersection operation on the fuzzy set. 83 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 table 3: intersection fuzzy set id case distance similarity near middle far near ∩ middle t1 md, ai, eb 6.30 0.00 0.90 0.10 0.00 t2 md, e 2.24 1.00 0.00 0.00 0.00 t3 dg, eb, el, em 3.82 0.73 0.27 0.00 0.27 ------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------ t48 se, d 2.45 1.00 0.00 0.00 0.00 t49 e, r, ai 2.49 1.00 0.00 0.00 0.00 t50 wd, md, ai 4.41 0.53 0.47 0.00 0.47 3. results 3.1 processing data the object of the study was 1225 engineering faculty students consisting of 560 women and 665 men, aged 19-22 years. students are required to give a value between 1-9 on the questionnaire items used in entrepreneurship. students are asked to write material that is mastered and provide an assessment of their interests, level of difficulty, and material needs on the market. questionnaire results were then averaged. the students have participated in an entrepreneurship program held by the university for 1 year. the questionnaire results are averaged as shown in table 4. table 4: results in the average value of questionnaire attribute difficulty interest market mobile develpoment (md) 9 9 7 sofware engineering (se) 7 9 8 database (d) 5 8 9 web development (wd) 7 8 8 artificial inteligent (ai) 9 4 5 robotic (r ) 9 4 5 mechanic (m) 8 8 7 electric ( e ) 8 7 7 e-marketing (em) 3 9 9 design graphics (dg) 3 4 7 photography (p) 2 4 5 e-learning (el) 4 6 6 e-business (eb) 4 9 9 3.2 similarities by calculating distance in this step, each data is calculated by the euclidean distance formula. table 5 describes the results of calculating the similarity of distance between data. 84 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 table 5: results of calculation of the similarity of distance between data id case distance similarity t1 md, ai, eb 6.30 t2 md, e 2.24 t5 md t8 md, em 6.00 t10 ai, eb 8.12 t12 se, d, wd, eb 2.26 t13 se, d, wd, md, dg, em, p, eb 1.87 t16 dg, ai, eb 8.60 t18 md, p 7.40 t25 se, wd, ai, eb 8.40 t26 r, ai, m, e 2.94 t31 dg, p 2.24 3.3 degree of membership from the calculation of distance similarity, the value of membership is sought with fuzzy theory. distance variables are divided into three sets, namely near, middle, and far. table 6 is the result of calculating fuzzy values, representing the itemset similarity. table 6: results of calculation of fuzzy values id case distance similarity near middle far t1 md, ai, eb 6.30 0.00 0.90 0.10 t2 md, e 2.24 1.00 0 0.00 t3 dg, eb, el, em 3.82 0.73 0.27 0.00 t4 md, em, eb 4.13 0.62 0.38 0.00 t5 md 0.00 0 0.00 t6 se, d, wd, ai, p 4.51 0.50 0.50 0.00 t7 wd, md, dg, p, eb 5.83 0.06 0.94 0.00 t8 md, em 6.00 0.00 1.00 0.00 t9 se, d, wd, md, dg, p, eb 5.21 0.26 0.74 0.00 t10 ai, eb 8.12 0.00 0.29 0.71 t11 ai, e 3.74 0.75 0.25 0.00 t12 se, d, wd, eb 2.26 1.00 0.00 0.00 3.4 fuzzy mining process after the process of calculating the degree of membership from the distance of similarity. the next process performs an intersection operation such as step 2.6. distance is represented in terms of near, middle and far. in this case the intersection operation is near and middle. far term is not used, because the distance between items is far apart. table 7 is 85 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 the result of fuzzy operations on fuzzy mining. fuzzy intersection operations are used to find the minimum value between itemset membership degrees. table 7: the result of fuzzy operations on fuzzy mining id case distance similarity near middle far near ∩ middle t1 md, ai, eb 6.30 0.00 0.90 0.10 0.00 t2 md, e 2.24 1.00 0 0.00 0.00 t3 dg, eb, el, em 3.82 0.73 0.27 0.00 0.27 t4 md, em, eb 4.13 0.62 0.38 0.00 0.38 t5 md 0.00 0 0.00 0.00 t6 se, d, wd, ai, p 4.51 0.50 0.50 0.00 0.50 t7 wd, md, dg, p, eb 5.83 0.06 0.94 0.00 0.06 t8 md, em 6.00 0.00 1.00 0.00 0.00 t9 se, d, wd, md, dg, p, eb 5.21 0.26 0.74 0.00 0.26 t10 ai, eb 8.12 0.00 0.29 0.71 0.00 t11 ai, e 3.74 0.75 0.25 0.00 0.25 t12 se, d, wd, eb 2.26 1.00 0.00 0.00 0.00 3.5 fuzzy association rule before running this algorithm, the minimum support parameter or the percentage of occurrence of a rule must be set first. minimum confidence or percentage of occurrence of rules for the appearance of the antecedent must also be set. the value depends on the researcher. rules are presented in antecedent consequent. 3.5.1 first implementation in the first experiment, all of the 1225 itemsets were used, after several tests, the values of support = 0.5 and min confidence = 0.4 were obtained. the rules discovered where : fig. 4: results of the fuzzy mining association rule algorithm. in fig. 4, three rules have an antecedent software engineering and consequent robotic. they are associations (think correlation) not necessarily causally related, so be very careful about interpreting association rules. 86 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 3.5.2 second implementation this experiment determined a strong alpha α-cut ≥0.3, after several test, the value of min support was 0.6 and min confidence = 0.5. from the initial 1225 itemsets, it was reduced to 823 itemsets with an α-cut. in this study, we focused on reducing the number of items included in the a priori algorithm using α-cut. the rules discovered were: fig. 5: results of the fuzzy mining association rule algorithm. in fig. 5 that algorithm presented 5 rules learned from the dataset. the number associated with the antecedent is absolute coverage in the dataset (in this case a number out of a possible total of 823). the number next to consequent is the absolute number of instance that matches the antecedent and the consequent. in this case, no rule has confidence (number of antecedent divided by number matching consequent) less than 0.96. 4. conclusion knowledge extraction in databases is a way of extracting knowledge in the form of rules. this rule expresses association relationships between various data, certain data items associated with other data items. in this study euclidean distance is used to measure the proximity or similarity itemset. fuzzy membership functions are used to obtain fuzzy mining. fuzzy logic operation was performed to reduce the size of the dataset, with α-cut. the results of this study are the reduction of the number of dataset from 1225 itemsets to 823 itemsets and to produce an it entrepreneurship rule model. acknowledgement this research received funding from ministry of research, technology and higher education of the republic of indonesia, through entrepreneurship development program in 2018. references [1] lin, x. (2014) mr-apriori: association rules algorithm based on mapreduce. in software engineering and service science (icsess), 2014 5th ieee international conference on., pp. 141-144. [2] kumar ks, chezian rm. (2012) a survey on association rule mining using apriori algorithm. international journal of computer applications (ijca), pp. 47-50. 87 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 [3] patel b, chaudhari vk, karan rk, rana yk. (2011) optimization of association rule mining apriori algorithm using aco. international journal of soft computing and engineering, vol.1, no.1. pp 24-26. [4] al-maolegi m, arkok b. (2014) an improved apriori algorithm for association rules. international journal on natural language computing (ijnlc) vol.3, no.1. pp 21-29. [5] kaur j, madan n. (2015) association rule mining: a survey. international journal of hybrid information technology, vol.8, no.7. pp 239-242. [6] kumar cp, anjaiah p, patil s, lingappa e, rakesh m. (2017) mining association rules from no-sql data bases using map-reduce fuzzy association rule mining algorithm. international journal of applied engineering research, vol.12, no.2. pp. 10472-10476. [7] yuan, x. (2017). an improved apriori algorithm for mining association rules. in aip conference proceedings, pp 1-6. [8] helm bl, hahsler pddm. (2007) fuzzy association rules. vienna university of economics and business administration. [9] verma sk, thakur rs. (2017) fuzzy association rule mining based model to predict students' performance. international journal of electrical & computer engineering. vol.3, no.4. pp.2223-2231 [10] moustafa a, abuelnasr b, abougabal ms. (2015) efficient mining fuzzy association rules from ubiquitous data streams. alexandria engineering journal, 54(2): 163-174. [11] imran a, vladimir k, viktor l, olga m. (2017) fuzzy methods and algorithms in data mining and formation of digital plan-schemes in earth remote sensing. procedia computer science, 120:120-125. [12] johanyak zc, kovács s. (2005) distance based similarity measures of fuzzy sets. proceedings of sami,pp 1-12 [13] liao h, xu z, zeng xj. (2014) distance and similarity measures for hesitant fuzzy linguistic term sets and their application in multi-criteria decision making. information sciences, 271: 125-142. [14] liu hw. (2005) new similarity measures between intuitionistic fuzzy sets and between elements. mathematical and computer modelling, 42(1-2): 61-70. [15] wong kw, gedeon t, tikk d. (2000) an improved multidimensional alpha-cut based fuzzy interpolation technique, international conference on artificial in science and technology, pp 1-6. [16] mendel jm. (2017) type-2 fuzzy sets. in uncertain rule-based fuzzy systems. springer, pp. 259-306. [17] wrapper h, meijer h. (1997) a taxonomy for computer science. technical report csir9713 [18] sujatha r, bandaru r, rao r (2011) taxonomy construction techniques –issues and challenges. indian journal of computer science and engineering,vol.2, no.5. pp 661-671. [19] ibrahim a. (2004) fuzzy logic for embedded systems applications. elsevier science. [20] salatino aa, thanapalasingam t, mannocci a, osborne f, motta e. (2018) the computer science ontology: a large-scale taxonomy of research areas. in international semantic web conference, springer, pp. 187-205. [21] masapanta-carrión s, velázquez-iturbide j á. (2018) a systematic review of the use of bloom's taxonomy in computer science education. in proceedings of the 49th acm technical symposium on computer science education, pp. 441-446. [22] dimapilis h. (2013) are we ready for technopreneurhip? a study on selected local entrepreneur within the city. research congress, de la salle, universty manila, pp:1-7. [23] amante ad, ronquillo ta. (2017) technopreneurship as an outcomes-based education tool applied in some engineering and computing science programme. australasian journal of engineering education, 22(1): 32-38 [24] hong tp, lee yc, wu mt. (2014) an effective parallel approach for genetic-fuzzy data mining. expert systems with applications, 41(2): 655-662. [25] michael h. (2005) applied fuzzy aritmatic an introdution with engineering applications. springer. 88 iium engineering journal, vol. 20, no. 2, 2019 supriyati et al. https://doi.org/10.31436/iiumej.v20i2.1096 [26] cho m, song m, yoo s. (2014) a systematic methodology for outpatient process analysis based on process mining. in asia-pacific conference on business process management, springer, pp. 31-42. 89 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <feff005500740069006c006900730065007a00200063006500730020006f007000740069006f006e00730020006100660069006e00200064006500200063007200e900650072002000640065007300200064006f00630075006d0065006e00740073002000410064006f006200650020005000440046002000700072006f00660065007300730069006f006e006e0065006c007300200066006900610062006c0065007300200070006f007500720020006c0061002000760069007300750061006c00690073006100740069006f006e0020006500740020006c00270069006d007000720065007300730069006f006e002e0020004c0065007300200064006f00630075006d0065006e00740073002000500044004600200063007200e900e90073002000700065007500760065006e0074002000ea0074007200650020006f007500760065007200740073002000640061006e00730020004100630072006f006200610074002c002000610069006e00730069002000710075002700410064006f00620065002000520065006100640065007200200036002e0030002000650074002000760065007200730069006f006e007300200075006c007400e90072006900650075007200650073002e> /gre <feff03a703c103b703c303b903bc03bf03c003bf03b903ae03c303c403b5002003b103c503c403ad03c2002003c403b903c2002003c103c503b803bc03af03c303b503b903c2002003b303b903b1002003bd03b1002003b403b703bc03b903bf03c503c103b303ae03c303b503c403b5002003ad03b303b303c103b103c603b1002000410064006f006200650020005000440046002003ba03b103c403ac03bb03bb03b703bb03b1002003b303b903b1002003b103be03b903cc03c003b903c303c403b7002003c003c103bf03b203bf03bb03ae002003ba03b103b9002003b503ba03c403cd03c003c903c303b7002003b503c003b103b303b303b503bb03bc03b103c403b903ba03ce03bd002003b503b303b303c103ac03c603c903bd002e0020002003a403b1002003ad03b303b303c103b103c603b10020005000440046002003c003bf03c5002003b803b1002003b403b703bc03b903bf03c503c103b303b703b803bf03cd03bd002003b103bd03bf03af03b303bf03c503bd002003bc03b50020004100630072006f006200610074002003ba03b103b9002000410064006f00620065002000520065006100640065007200200036002e0030002003ba03b103b9002003bd03b503cc03c403b503c103b503c2002003b503ba03b403cc03c303b503b903c2002e> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <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> /slv <feff005400650020006e006100730074006100760069007400760065002000750070006f0072006100620069007400650020007a00610020007500730074007600610072006a0061006e006a006500200064006f006b0075006d0065006e0074006f0076002000410064006f006200650020005000440046002c0020007000720069006d00650072006e006900680020007a00610020007a0061006e00650073006c006a006900760020006f0067006c0065006400200069006e0020007400690073006b0061006e006a006500200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e0074006f0076002e0020005500730074007600610072006a0065006e006500200064006f006b0075006d0065006e0074006500200050004400460020006a00650020006d006f0067006f010d00650020006f00640070007200650074006900200073002000700072006f006700720061006d006f006d00610020004100630072006f00620061007400200069006e002000410064006f00620065002000520065006100640065007200200036002e003000200074006500720020006e006f00760065006a01610069006d0069002e> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 162-872-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 149 automatic extraction of ferromagnetic particle from nonhomogeneous solid-solid mixture m.f. ismail, m.o. reza, a.a. rokoni and m.a.r. sarkar department of mechanical engineering, bangladesh university of engineering and technology, bangladesh. farhadananda.128@gmail.com abstract: separation of magnetic particles in sand processing is very important for many industrial purposes. this paper presents an automation process to separate the magnetic particles from a non-homogeneous solid-solid mixture (sea sand). here a magnetic force is created by changing the electric field and thus the particles are separated from the mixture of sand automatically. here such a simple and cost effective design is prsented which can automatically take the the mixture as input and give the refined and separated product as output continuously. abstrak: pengasingan zarah-zarah bermagnet dalam pemprosesan pasir penting untuk pelbagai tujuan industri. kertas ini membentangkan proses pengautomatikan untuk mengasingkan butir-butir bermagnet dari pepejal tak homogen – campuran pepejal (pasir pantai). di sini, daya magnet dihasilkan dengan menukarkan medan elektrik dan seterusnya butir-butir ini terasing daripada campuran pasir dengan sendirinya. kaedah yang mudah dan rekaan keberkesanan kos ini secara langsung mengambil campuran tersebut sebagai input dan memberikan hasil bertapis dan terpisah sebagai output dengan berterusan. keywords: magnetic particle; automation; non-homogeneous solid-solid mixture; magnetic force; continuously 1. introduction magnetic separation is a process in which magnetically susceptible material is extracted from a mixture using a magnetic force. this separation technique is used here to separate magnetic particles from non-homogeneous solid-solid mixture such as sea sand. engineers and researchers frequently need to carry out numerous experiments within a very short time. a highly automated system widens the scope of achieving an efficient result in a short period of time. sand is an available natural resource. in sand there are good percentage of ferromagnetic materials such as iron and other valuable particles. these materials have very wide range of uses not only in industrial case but also in various constructive and laboratory works. another very important point is to note that due to high percentage of iron present in the sand, many countries import sand for glass industries. it is known that the presence of iron in natural sand mixture increases the brittleness of glass [1]. so the target of this system is to refine the sand mixture and separate the ferromagnetic material from the mixture. this automated system is used to separate magnetic particles industrially. when minerals are placed in a magnetic field, there are three reactions which may occur. first, they are attracted iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 150 to the magnetic field. second, they are repulsed by the magnetic field. and third, no noticeable reaction to the magnetic field [2] occurs. particles that are attracted to the magnetic field are called magnetic. but, there are two classifications of magnetic particles, strongly magnetic particles, such as iron and magnetite, and weakly magnetic particles, such as chromite and ilmenite. strong magnetic particles may be easily separated with a separator having a low intensity magnetic field of 400-600 gauss (0.04-0.06t) [3]. paramagnetic particles (weakly magnetic) require a higher intensity magnetic field to separate them, generally ranging from 6,000 to 20,000 (0.6 to 2t) gauss (1t =104 gauss). particles that are repulsed by a magnetic field are called diamagnetic. a line of separators called eddy current separators [4], takes advantage of the diamagnetic particles, separating them from other material. when product, such as aluminum, passes over the eddy current, the spinning magnets inside the shell generate an eddy current in the aluminum thus creating a magnetic field around the piece of aluminum. the polarity of the magnetic field of the aluminum is the same as the rotating magnets, causing the aluminum to be repelled away from the separator. an eddy current is defined as the currents caused by voltages induced by changing flux, and tend to oppose the change of the flux. 2. objectives the objectives of this system are to separate the magnetic particles from a solid-solid non-homogeneous mixture (sea sand) so that it can be used industrially and also to reduce the cost of separating process. 3. mechanical components the hardware part of the system covers the whole electrical system. the total mechanical structure is developed by the wood with shafts and steel plates, which gives a pictorial view of the whole separating process (fig. 1). fig. 1: model of the overall system. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 151 3.1 wood wood has been used here to develop the overall system. the wooden blocks are used to make the structure. 3.2 super enamel wire, bearing and copper wire super enamel wire (fig. 2) is used for magnetization. windings of the steel plates for electromagnet are made by this wire. here ball bearing (fig. 3) is used. it’s been used in the crossing bar to reduce vibration and to rotate smoothly for creating an uniform magnetic field. it helps to rotate the shaft with the help of a motor. insulated copper wire was used as the connecting wire. fig. 2: enamel wire. fig. 3: ball bearing. 4. electrical components electrical arrangement is also very important for this system. the electrical system is briefly described here. 4.1 gear motor and limit switch two gear motors are used here each of them rated 24v and 3amp. a limit switch is used to demagnetize the coil when the gate is closed. 4.2 ic ne555 ne-555 is an integrated circuit. it is a timer ic. it is highly stable for generating accurate time delay or oscillation. it can operate both as mono stable and astable multi vibrator [5]. in a mono stable mode, it can produce accurate time delay from microseconds to hours. in the astable mode, it can produce rectangular waves with a variable duty cycle. the ic ne-555 timer consists of two comparators, a flip-flop, a discharge transistor and a resistive voltage divider (fig. 4). iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 152 fig. 4: pin diagram of ne555. 4.3 cd 4013 the cd4013b dual d flip-flop is a monolithic complementary mos (cmos) integrated circuit constructed with nand p-channel enhancement mode transistors. each flip-flop has independent data, set, reset, and clock inputs and ``q'' and ``q'' outputs. these devices can be used for shift register applications, and by connecting ``q'' output to the data input, for counter and toggle applications. the logic level present at the ``d'' input is transferred to the q output during the positive-going transition of the clock pulse. setting or resetting is independent of the clock and is accomplished by a high level on the set or reset line respectively. maximum speed of operation is 5 mhz, voltage vcc 4.5 to 15 v, current (vcc = +5 v) 3 to 6ma, maximum o/p current 200ma, power dissipation 600mw [5]. the cd 4013 can be used as a frequency divider in which the output is half the input frequency (fig. 5). it can also be used in toggle mode (this is exactly the same as a frequency divider) where the output toggles on then off after each clock (input pulse) [5]. fig. 5: pin diagram of 4013. 4.4 h-bridge the h-bridge (fig. 6) is a special types of circuit by which the gear motor can be operated in clockwise or anti-clockwise direction. here tip 122, tip 127 and bc 547 transistors are used. in the figure terminal a and b are connected with 4013. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 153 fig. 6: circuit schematic of h-bridge. 5. design methodology the efective and simple mechanical design is an important part of this system. the whole mechanical part can be divided into three modules to make the description easier. the description of the three modules with diagrams is given below. 5.1 module 1 module 1 (fig. 7) consists of a container to store non homogeneous solid-solid mixture. it was specially designed to deliver mixture discontinuously with a controlled flow rate. it delivers sand on the rotating electro-magnet of module 2. the flow is controlled by a gate which is connected directly to the shaft. power transmitted to this shaft from gear motor through gear and pinion. a circuit was used to inverse the rotation of the motor after a certain time interval for opening and closing of the gate. again, module 1 is directly connected to module 3 and controls the direction of its movement. fig. 7: schematic of module 1. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 154 5.2 module 2 the module 2 (fig. 8) consists of an electro-magnet which rotates due to the rotation of gear and pinion. four steel sheets were connected to the shaft each within 90 degree separation and winding was given on each sheet for magnetizing it. for a certain time it remains magnetized and gets demagnetized for a while and thus this cycle of magnetizationdemagnetization continues. when magnetized, the rotating electro-magnet attracts the ferromagnetic particles present in the mixture. they get attached with the electro-magnet plates while filtered mixture was collected in a separate space. after a certain period of time, sand flow is stopped from module 1. at the same time the steel plates get demagnetized and the ferro-magnetic materials loose the attachment with these plates. then module 3 is to collect the separated ferro-magnetic materials and filtered sand in different container. fig. 8: schematic of module 2. fig. 9: schematic of module 3. 5.3 module 3 in module 3 (fig. 9), a steel plate is connected to the shaft which is supported by the bearing and can rotate freely. this rotation is controlled completely by module 1. a wire connects the gate of module 1 with one side of the steel plate of module 3. normally, the plate stays inclined on one side because of extra weight on that side. so when the gate remains open, sand falls on the electro-magnet and then goes through the inclined plate to the filtered sand collector. again, when the gate is closed, due to the tension of the wire the plate becomes inclined on the other side. and at the same time the electro-magnet loose attraction iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 155 and falls through the steel plate to the ferromagnetic magnetic material collector. thus the cycle of path changing continues. 6. circuit configuration a very simple circuit is used here. this circuit is basically divided into three parts. part 1 is a timer circuit while part 2 is an h-bridge and part 3 is a switch which is used to demagnetize the electro-magnet when the gate is closed or open. 6.1 part 1 in the 1st part, ne 555 ic and cd 4013 are used. ne 555 has 8 pin. it is a timer ic which generates square wave pulse after a definite time interval. the time interval can be changed by changing the capacitance in pin 5 and pin 2.cd 4013 ic is a counter ic. it is a dtype flip-flop. it also generates square wave in pin1 and pin 2. when pin1 is on, pin 2 is off and vice versa. that means it gives output 1 0 or 0 1. 6.2 part 2 the part 2 is an h-bridge which changes the rotation of the motor at a certain interval. it consists of 6 transistors. among them, 2 are tip 122, 2 are tip 127 and 2 are bc 547. the rotation control of the gear motor for the h-bridge is described belowthere are four switching elements within the bridge. these four elements are often called, high side left, high side right, low side right, and low side left (when traversing in clockwise order). the switches are turned on in pairs, either high left and lower right, or lower left and high right, but never both switches on the same side of the bridge. if both switches on one side of a bridge are turned on it creates a short circuit between the plus and minus terminals (fig. 10). fig. 10: gear motor control in both directions by h-bridge. 6.3 part 3 it consists of a limit switch. the switch contains three pin. it is used to demagnetize the electro-magnet when the gate is closed. normally the switch remains on. when the gate of the container is closed, it hits the switch and it makes the circuit open. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 156 7. system evaluation this magnetic separation method exploits the difference in behavior of particles in magnetic fields. this separation process is controlled more or less by four parameters. they areintensity of magnetic field, particle magnetic susceptibility, effective medium viscosity and particle velocity. in the international unit system (si) magnetic susceptibility is dimensionless and is denoted as . more frequently [6] a specific magnetic susceptibility (w) is used and is defined as in (1): w =  /  (1) here,  is the density of the material. the specific magnetic susceptibility w is expressed in cm3/g. there are other forms of susceptibilities including molar magnetic susceptibility m. materials, which are repelled from the magnetic field are called diamagnetic and have negative values of the magnetic susceptibility. particles attracted towards greater intensity of the magnetic field are called paramagnetic. magnetic separation is based on principle that the force (f) acting [7] on a particle is given by the simplified form (2)          x h hmf xxwx 0 (2) where, f – magnetic force, n 0 – magnetic permeability of vacuum w – specific magnetic susceptibility, cm3/g m – mass of particles, g h – magnetic field intensity, a/m x h x   – field gradient, a/m2 the paramagnetics are further divided into such categories as true paramagnetic, ferromagnetic, and ferri and anti-ferromagnetic. their affiliation is determined by the behavior in changing magnetic field [8] (fig. 11) and temperature [9] (fig. 12). magnetization is expressed by m [10] (3). m =.w. h (3) here four separate rectangular current carrying coils (sheets) are used. the magnetic field produced for this separation process is around 0.1 t. the field can easily be increased by increasing the number of rectangular sheets as well as the coils. the magnetic separation process consists of several steps (fig. 13). in every step [11] different types of mineral fractions [12] are produced (fig. 14). iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 157 fig. 11: magnetization versus magnetic field for different materials. fig. 12: magnetic susceptibility versus temperature for different materials. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 158 fig. 13: separation steps of sand at different magnetic field strength. fig. 14: different types of mineral fraction in sand processing. to use the purified sand for the industrial purpose it is necessary to determine titanium and iron content in the different types of fractions. mineral fractions are decomposed by fusion with khso4 at 800 oc and then dissolved in 20% h2so4 acid for further chemical assessment [13]. in sand (unpurified) generally two types of oxides are available [14]-iron and titanium oxides (ilmenite and chromite). the magnetic susceptibility of chromite (fig.15) and ilmenite (fig.16) increases with increasing of iron content. fig. 15: magnetic susceptibility versus iron content at lower temperature for chromite. fig. 16: magnetic susceptibility versus iron-content (at lower temperature) for ilmenite. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 159 fig. 17: impurity versus output product in percentage by weight. ilmenite (fetio3) has the magnetic susceptibility of 200–1500x10–6 cm3/g. the magnetic susceptibility of iron (feo) and titanium (tio2) oxides are respectively +7200 and +5.9 cm3/mole. velocity as well as the size of the particles is also important parameters for magnetic separation. a low velocity enables the magnetic field to capture and hold a particle, whereas a high velocity causes only a deflection and no capture. this effect is more important as magnetic susceptibility decreases. in figure 17 the data is shown for the % impurity (measured in weight) vs. % refined product (sand). it can also be seen that high feed rate multiple pass is more effective than the moderate feed rate single pass. here a gear-pinion (fig. 17) mechanism is introduced to control the velocity of the particles by setting the sand container at a certain angle. with this mechanism the container position is controlled by a connecting rod. particles size less than 355m is economical for the separation technique [15]. fig. 18: velocity control of the particles by changing the angle of the container. the magnitude of the magnetic force of a particle in a magnetic field depends in part upon the magnetic susceptibility of the particle. if two minerals of equal volume but different iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 160 susceptibilities are exposed to the same magnetic field and field gradient, the resulting difference in magnetic forces will result in a separation of the particles if enough time is allowed. magnetic separation is generally a low cost method of recovery, unless high intensity separators are required. the electro-magnetic high intensity separators that produce 20,000 gauss (2t), is expensive. however, iron oxides and titanium oxides can be easily separated from sea sands by this magnetic separation process. because for this separation process magnetic fields only around 3,000 gauss (0.3t) is needed [16] and so it is inexpensive. but when looking for a process to recover valuable minerals, magnetic separation should not be overlooked, if some of the material is magnetic or para-magnetic. because that time a huge magnetic field around 2t is needed. 8. conclusion here the concentration is to reduce the cost for separating the magnetic particles in sand processing. this automated magnetic separation system is fabricated with a simple mechanical design using locally available materials. that is why the process reduces the cost as well as increases the efficiency. acknowledgement this work was supported by control and instrumentation lab of bangladesh university of engineering and technology (buet). references [1] u.o. häfeli, w. schütt, j. teller, et al. (eds), “scientific and clinical applications of magnetic cariers”, new york, 1997. [2] j. svoboda, “magnetic methods for the treatment of minerals”, elsevier, 1987, pp.692. [3] journal of magnetism and magnetic materials, 262 (2003), pp. 269–279. [4] r. m. staude , z. schlett , m. lungu and d. baltateanu, “a new possibility in eddy-current separation”, minerals engineering, 15(2002),pp. 287-291. [5] http://www.alldatasheet.com. [6] journal of magnetism and magnetic materials, 262 (2003): 269–279 [7] u. k. veeramachaneni , r.l. carroll , “magnetic particle motion in a gradient field” , proceedings of the comsol conference 2007, boston [8] xun-fang sun, xiao-shu fang, yao-hong lu, “strength of materials”, people's education publisher, beijing. sept. 1964 [9] n. ali, i.s. dubenko, i.y. gaidukova , a.s. markosyan , v.e. rodimin, "temperature induced magnetic instability in the itinerant co subsystem of the er1-xyxco3 compounds", physics b 281&282 (2000), pp. 696-698. [10] journal of applied physics, vol. 93, no. 1015, may 2003. [11] n. fraunholcz, p.c. rem and p.a.c.m. haeser, “dry magnus separation, minerals engineering”, 2002, pp. 45–51. [12] j. mendham, r.c. denney, j.d. barnes and m.j.k. thomas, “textbook of quantitative chemical analysis”, 6th edn , england, 2000, pp. 669–670. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 161 [13] p.g. jeffery and d. hutchison, “chemical method of rock analysis”, 3rd edn., pergamon, oxford, 1981, pp. 21–22, pp. 346–348 [14] m. dobbins, j. domenico and p. dunn, “a discussion of magnetic separation technique for concentrating ilmenite and chromite ores”, international heavy minerals conference, southern african mining and metallurgy,2007, pp. 197-204. [15] f. frass , “magnetic separation of minerals of low susceptibiity and small particle size”, bumines ic 8383, 1968, pp. 11-12. [16] u.t. andres, “magnetohydrodynamic and magnetohydrostatic methods of mineral seperation”, wiley,1976, pp. 206-218. iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 improvement of problematic soil using crumb rubber tyre nurain asrin saparudin1, norhidayu kasim1*, kamarudin abu taib2, wan nur aifa wan azahar1, nur aisyah kasim3 and maisarah ali1 1 civil engineering department, international islamic university of malaysia, po box 10, 50728 kuala lumpur, malaysia. 2 civil engineering department, national university of malaysia, selangor, malaysia. 3 civil engineering department, mara university of technology, selangor, malaysia. * corresponding author: ayukasim@iium.edu.my (received: 16th january 2022; accepted: 26th march 2022; published on-line: 4th july 2022) abstract: construction on problematic soil that has low bearing capacity, low shear strength, high compressibility, and high water-content will interfere with the smooth construction process and will affect time and cost due to repetitive maintenance. pavement built on problematic soil as its subgrade is exposed to pavement failures, such as fatigue cracking, longitudinal cracking, and pumping, owing to swelling or shrinkage due to moisture variation and differential settlement. therefore, improvement of the ground needs to commence so as to improve its load bearing capacity, in order to sustain the load on top of it. consequently, the main aim of this study is to determine the effectiveness of crumb tyre rubber mixed with soil samples as one of the soil stabilisation techniques and to establish the optimum usage percentage of crumb tyre rubber as a stabiliser. clayey sand soil was mixed with 5%, 10% and 15% of crumb tyre rubber by weight of the soil sample and was tested for physical properties, such as particle size distribution and plasticity index. in obtaining the changes in strength, mixed clayey sand-crumb tyre rubber samples were subjected to compaction and california bearing ratio (cbr) tests. the results showed that the increment of crumb tyre rubber percentage as an additive, increased the cbr value and therefore enhanced the strength of the modified soil. however, the crumb tyre rubber stabiliser affected the optimum moisture content and maximum dry density of the modified samples by decreasing their values. the optimum percentage of crumb tyre rubber mixture was found to be 10% by weight at the end of this study. these findings indicate that the measured crumb tyre rubber is suitable for supporting the clayey sand soil for the subgrade of pavement construction. abstrak: pembinaan di atas tanah bermasalah yang mengandungi kapasiti galas rendah, kekuatan ricih rendah, kebolehmampatan tinggi dan kandungan air tinggi akan mengganggu kelancaran proses pembinaan dan akan menjejaskan kekangan masa dan wang akibat penyelenggaraan berulang. jalan raya yang dibina di atas tanah yang bermasalah akan mengalami kegagalan turapan seperti keretakan, rekahan membujur dan pengepaman, disebabkan oleh subgrednya terdedah kepada pembengkakan atau pengecutan akibat perubahan kelembapan dan pemendapan berbeza. oleh itu, penambah baikan tanah perlu dilakukan bagi mencapai kapasiti galas beban lebih baik untuk menampung beban di atasnya. oleh itu, tujuan utama kajian ini adalah bagi menentukan keberkesanan serpihan tayar getah yang dicampur dengan sampel tanah sebagai salah satu teknik penstabilan tanah dan menentukan peratusan optimum penggunaan tayar getah sebagai penstabil. tanah pasir liat sebagai bahan utama dalam kajian ini dicampur dengan 5%, 10% dan 15% serbuk tayar getah mengikut berat sampel tanah dan telah diuji sifat fizikalnya, seperti taburan saiz zarah dan indeks keplastikan. perubahan dalam kekuatan ditentukan dengan cara menggaul sebatian sampel tayar getah bersama pasir tanah liat dan 72 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 diuji dengan eksperimen pemadatan dan ujian nisbah bearing california (cbr). dapatan kajian menunjukkan bahawa penambahan peratusan serbuk tayar getah sebagai bahan penstabil telah meningkatkan nilai cbr dan sekaligus meningkatkan kekuatan tanah yang diubah suai. walau bagaimanapun, penstabil tayar getah mempengaruhi kandungan lembapan optimum dan ketumpatan kering maksimum sampel yang diubah suai dengan nilai berkurang. pada akhir kajian ini, peratusan optimum bancuhan serbuk tayar getah yang diperolehi adalah sebanyak 10% berat sampel. dapatan ini menunjukkan bahawa tayar getah remah adalah sesuai dalam menyokong tanah pasir liat bagi subgred pembinaan turapan. keywords: california bearing ratio; crumb rubber tyre; ground improvement; problematic soil 1. introduction in geotechnical work applications, the existing ground will normally form the foundation of the building and road structure. weak and poor ground conditions cause delays in completing the project and incur huge additional costs. the poor soil often consists of a soft type of soil, such as clay, silt, or peat soil, which have the possibility for differential settlement to occur and are prone to flooding. ground improvement is important to overcome the poor performance of the site area in order to fulfil the project specification. one of the methods for the improvement of soil is adding a biopolymer mixture, such as rice husk ash, wood ash, crumb rubber tyre and banana fibre to the soil. biopolymer mixtures are natural polymers created by living organisms and are viewed as environmentally friendly and reasonable materials. therefore, numerous researchers have carried out research work related to the utilisation of biopolymer mixed with the soil to enhance the stability of the soil. ample works have succeeded in their findings. the effectiveness of adding crumb tyre rubber has been found in some research works carried out by banzibaganye [1]. shredded rubber tyre with two types of sand and, as a result, the materials produced showed a decrease in weight, adequate stability, low settlement, better drainage, and the preservation of energy and resources. the utilisation of the stabiliser also enabled proper waste disposal and tyre management that subsequently led to a positive effect on the environment [1]. the use of crumb rubber as a stabiliser substantially lessened the burden of waste tyre disposal and encouraged the establishment of an economical method for soil stabilisation purposes [2]. therefore, this initiative also contributed to the reduction of construction costs and would lead to a cleaner environment without worrying about environmental degradation due to the improper disposal of solid waste tyre. rubber tyres posed serious negative effects on the environment, health and aesthetics due to the huge quantity of rubber tyre waste. these non-biodegradable materials are often left to pile up in disposal sites, and provide a conducive place for mosquito breeding, as well as posing a fire risk [3]. as a result, it is advantageous to investigate crumb tyre rubber, as soil stabiliser material because it is one of the options for converting waste tyres for beneficial use. according to al-neami [4], the specific gravity test, compaction test, direct shear test, and california bearing ratio (cbr) test were conducted to identify the properties of the mixed soil-crumb tyre rubber. as a result, when the percentage of crumb rubber increased, the specific gravity, dry density, and optimum content also decreased. however, the shear strength and cbr value increased. the author also mentioned that lateral earth stress on retaining walls was reduced when using the tyre chips as fill material [4]. besides, hambirao and rakaraddi [5] stated that the compressive strength of mixed cement-crumb tyre rubber 73 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 increased from 74 kpa to 201 kpa for 2% cement replacement and 246 kpa and 328 kpa for 4% and 5% cement replacement, respectively, by adding waste tyre rubber chips. the cement replaced by 5% of rubber tyres had the highest compressive strength. ravichandran et al. [2] analysed the properties of mixed clay-crumb tyre rubber by carrying out a compaction test and cbr test. based on the compaction test, increase in the percentage of crumb rubber resulted in a decrease of maximum dry density and optimum moisture content of the clay. however, the cbr value increased when the addition of crumb tyre rubber was added up to 10% [2]. furthermore, singh et al. [6] mentioned that the strength of soil increased with no effect on the strain when the percentage of crumb rubber was increased. the value of unconfined compressive strength increased for soil at 20% mixture of crumb rubber. based on the presented literature, the objective of this research was to determine the effectiveness of crumb tyre rubber when blended with clayey sandy soil. generally, clayey sand attributes provide significant engineering properties and have high plasticity, cohesiveness, high water absorbency, high compressibility, and low shear strength, which makes the soil unsuitable for construction. the clayey sand properties were improved by the application of 5%, 10%, and 15% of the soil weight in each testing standard. laboratory testing was performed to test the physical properties of soil samples, as well as to investigate the additive’s performance in improving the efficiency of soil samples. from the data collection and analysis, the optimal percentage design of crumb tyre rubber to be mixed with the soil samples in order to produce an excellent mixture proportion for practical purposes could be established. additionally, the crumb tyre rubber mixtures were observed to be aligned with the specification for road works (jkr/spj/2014) set by the malaysian public works department (pwd), whereby the recommendation for pavements in traffic class t2 until t5 is not to be less than 5%. while, for large traffic volume, such as traffic class t4 and t5, the required minimum subgrade strength of 12% cbr value should be ascertained [7]. 2. methodology 2.1 desktop study a desktop study was carried out to identify the best soil stabiliser and to select a suitable site to collect weak soil samples. the crumb tyre rubber was chosen as a soil stabiliser for this study because of its performance in terms of improving the properties of the soil sample, such as reducing the dry density, specific gravity, and optimum moisture content. this is due to the lightweight crumb rubber tyre properties and its ability to decrease the lateral earth pressure of retaining walls when it is used as a fill material [8,9]. furthermore, tiwari et al. [10] stated that the crumb tyre rubber had a partial gluey attribute that could stick the materials together for long-term hardiness. meanwhile, keerthi and doodala [11] assumed that the flexibility of rubber tyres and their adaptability to nature, combined with the properties of difficult decomposition and flammability, drew the attention of geotechnical engineering researchers. 2.2 sample collection and preparation the soil samples collected for this study were weak ground soil with a soft texture and cohesive soil properties that primarily consisted of clay, clay loam, sandy clay loam, and so forth. the soil sample was collected from the sungai pusu riverbank at the international islamic university malaysia (iium), gombak campus, as shown in fig. 1. 74 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 fig. 1: location of soil sample collected. the crumb tyre rubber, which was processed and supplied by yong fong rubber industries sdn bhd in port klang, selangor, was the other main material used in this study. unwanted elements other than granular rubber were sorted and eliminated during the processing. the granular rubber was shredded into various sizes according to its functional ability. this research used 40 mesh sizes of crumb tyre rubber, as depicted in fig. 2, to provide decent interlocking properties between the tyre rubber and soil sample. the crumb tyre rubber was added, consisting of 5%, 10%, and 15% by weight of samples for each testing standard. fig. 2: 40 mesh of crumb tyre rubber. as the soil samples were taken from three different spots in the selected areas, the average result for each sample is considered to represent the type and properties of weak ground. table 1 simplified the ratio of soil samples and crumb tyre rubber to be prepared for the experimental study. table 1: percentage of soil sample and crumb tyre rubber with sample label soil percentage [%] crumb tyre rubber percentage [%] soil sample cs-clayey sand 100 0 cs-cr0 95 5 cs-cr5 90 10 cs-cr10 85 15 cs-cr15 2.3 particle size distribution a particle size distribution test was carried out to determine the grading characteristics of soil samples with a range of different sizes and shapes. in this investigation, two methods 75 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 were used in finding the particle size distribution: sieve analysis and hydrometer test. sieving analysis is commonly used to determine the particle size distribution of the coarse, large-sized particles, while hydrometer test is used for the finer size of particle that passes the 75 µm sieve. the results of this testing will be plotted on a particle size distribution curve to indicate the percentage of the finer and coarser particles within the soil sample. sieve analysis was conducted in this study to find the distribution of particles larger than 75 µm or 0.0075 mm and it was performed for the three raw soil samples collected from three separate points. the mechanical shaker, sieve stack, electronic weighing balance, and prepared samples were important apparatus and materials in conducting the test. prepared samples that had been oven-dried were poured into a series of sieve stacks in the mechanical shaker. the mechanical shaker was left operating for about 5 to 10 minutes to separate the soil particles into their appropriate sizes in each stacker. retained soil on every stack was weighed and recorded to enable the particle size distribution graph to be plotted, which is the diameter of the particle versus the percentage of the passing particle. sample preparation and test procedures for this sieve analysis complied with the requirements of the american society for testing and materials (astm) c136 standard. a hydrometer test was conducted to determine the finer particle size distribution of soil that passed a 0.075 mm sieve. the hydrometer test is more effective when dealing with finer grain size of soil samples compared to sieve analysis. it is impracticable to design the sieving stack with such a small hole. this test was also conducted due to the presence of clay in the soil samples and the standard procedure of this test was based on the astm d7928 standard. in this study, prepared soil samples that passed a 0.075 mm sieve were selected, and about 37.5 gm of the sample was mixed with distilled water in a graduated cylinder and allowed to suspend. the hydrometer reading was taken by observing the meniscus formed by the suspension and the hydrometer stems to the nearest 0.0001 according to the standard elapsed time reading schedule and the temperature reading was taken periodically. moreover, the reading for zero correction and meniscus correction were performed to avoid systematic errors. the zero correction and meniscus correction for this test were 0.9980 and 0.0002, respectively. the results from this test were then averaged to understand the properties of the samples, as illustrated in the particle size distribution graph. both results were combined and plotted on one graph of the particle size distribution curve. 2.4 atterberg limits test the atterberg limits test was performed to describe the consistency and plasticity behaviour of the soil samples in which the soil changes between solid, semi-solid, plastic and liquid states. the liquid limit (ll) results and plastic limit (pl) values could be obtained from the test. the difference between both values resulted in the plasticity index (pi) value, which measured the plasticity properties of the soil sample and provided the soil samples classification. the procedure of this experiment precisely followed the requirements, as stipulated in the astm d4318 standard. the pl value is the measurement of soil water content at the boundary between the semi-solid state and plastic state. it was determined by rolling the soil sample into a thread of 3.2 mm diameter on a flat glass surface by hand without breaking the sample. consequently, the soils were mixed with crumb tyre rubber, consisting of 0%, 5%, 10% and 15% by weight of samples and underwent the process of rolling until the soil disintegrated under pressure and could not be moulded into a 3.2 mm diameter measurement. the completed rolled soil samples were placed in a container and weighed. lastly, the water content was determined the next day after drying the samples in an oven at 105 ºc. 76 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 the ll test is to identify the ability of water content in the soil that changes the soil properties from plastic to liquid states. this test was measured using the casagrande cup method. the samples were moistened with about 25 drops of water prior to laying them in the casagrande cup and cutting the soil into a v-shaped line in the centre using flat grooving tools with a gauge. the mechanical casagrande cup was raised and dropped from a height of 10 mm at the rate of two drops per second. the process was repeated until the cutting section joined at about 13 mm in length. the number of drop-offs required to connect the cutting edge should be counted, which should be between 15 and 35 drops. connected samples were taken and weighed. next, water content was obtained after drying the sample in the oven at 105 ºc for 18 to 24 hours. the pi measures the plasticity properties of the soil sample. the plasticity index value could be calculated from the difference between the ll index and pl index as stated in eq. (1). pi = ll pl (1) 2.5 proctor compaction test the proctor compaction test is the procedure of densification of soil to decrease the air voids. in this present study, the test investigated the soil samples by mixing of crumb tyre rubber to identify its compaction attributes of the optimum moisture content and maximum dry density [12]. the standard procedure for this experiment was according to the astm d698 standard. the soil samples were thoroughly mixed with crumb tyre rubber consisting of 5%, 10%, and 15% by weight of the prepared soil samples, together with the calculated amount of water. the moist crumb tyre rubber-soil mixture was inserted into an empty mould in three layers. uniformly distributed, 25 blows were imposed on the surface of each layer using a 2.6 kg rammer. some of the compacted layers were extracted to test for the moisture content of the soil sample by oven-drying the soil sample overnight. based on the data collected from the experiment, a chart was drawn between the water content and dry density to achieve maximum dry density and optimum water content. the findings can be used to develop test samples for the cbr test. 2.6 california bearing ratio (cbr) test the cbr test was performed to decide the cbr value by accomplishing a laboratory load penetration test, as specified in the astm d1883 standard procedure. the cbr value indicated the mechanical strength of the soil sample and crumb tyre rubber mixtures due to the applied pressure from a plunger on the top surface of the soil. a higher cbr value indicates harder soil that can withstand more load. in this research, prepared samples were taken at about 5 kg in weight for every sample and blended evenly with 0%, 5%, 10% and 15% of the crumb tyre rubber. an amount of water was added to the mixture according to the result obtained in the proctor compaction test. the modified soil was then poured into a mould in five layers and each layer was compacted with 56 evenly distributed blows from a 4.89 kg hammer. the cbr is the proportion of force per unit area required to infiltrate a soil sample using a round hammer at a rate of 1.25 mm/min. the compacted modified soil in the mould was positioned on the cbr machine for data collection of the plunger force that the soil could bear. from the cbr results, a graph was produced. the percentage of crumb tyre rubber that best illustrated the effect of the added crumb tyre rubber on the soil was plotted against the cbr value in order to determine the ideal percentage of added crumb tyre rubber. the cbr 77 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 value was used as an index of soil strength and bearing capacity. eq. (2) was used to calculate the cbr value. cbr(%) = load carried by specimen load carried by standard specimen x100 (2) where, load carried by standard specimen: for 2.5 mm penetration = 13.2 kn for 5.0 mm penetration = 20 kn 3. results and discussions the soil samples collected from the riverside of sungai pusu were mixed with crumb tyre rubber with different percentages by weight (0%, 5%, 10%, and 15%) and were tested in several experiments based on a standard procedure. before mixing, the weights of the soil sample and crumb rubber tyre were calculated in order to prepare for the soil-rubber tyre mix proportion that was utilised in the sieve analysis, hydrometer test, atterberg limits, standard proctor compaction, and cbr tests. the goal of the investigation was to verify the effectiveness of crumb tyre rubber as soil sample stabilisers. 3.1 particle size distribution before determining the result of the particle size distribution percentage, the three samples collected from the chosen areas were subjected to two tests, which were the sieve analysis and the hydrometer test. the results from the two experiments were combined to plot the particle size distribution graph, as mentioned in the previous chapter. from the curve, the dissemination percentage of the particles could be divided into four categories: gravel, sand, silt, and clay. the particle size distribution graph for the parent soil is shown in fig. 3. fig. 3: particle size distribution graph. the particle size percentage of each category was tabulated in table 2. table 2 clearly showed that the highest particle percentage was sand (84.54%), followed by clay, gravel and silt, which were 6.99%, 5.51% and 2.96%, respectively. 78 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 table 2: percentage of particle size distribution type of particle percentage from total amount [%] gravel (>2 mm) 5.51 sand (0.06 2 mm) 84.54 silt (0.002 0.06 mm) 2.96 clay (<0.002 mm) 6.99 based on the particle distribution graph, uniformity coefficient, cu and coefficient of gradation, cc for the soil samples were calculated and resulted in values of 5.81 and 0.86, respectively. as the sample retained more than 50% of the no. 200 sieve, the soil was categorised as coarse-grain clayey sand according to the unified soil classification system (ucss) (astm test designation d2487). the values of cu and cc indicated that the soil sample was poorly graded sand and prone to settlement and had problematic water-clog areas. in order to have good interlocking between poorly graded soil and crumb tyre rubber, the waste tyre had to endure the mechanical machine grinding process and passing through standard size to achieve finer and more uniform particles of the crumb tyre rubber [4]. 3.2 atterberg limits test the ll test and pl test were conducted in order to determine the plasticity index of the soil samples and crumb tyre rubber mixtures. the atterberg limits test results for the soil samples are illustrated in table 3. table 3: atterberg limit results soil sample liquid limit [%] plastic limit [%] plasticity index cs-cr0 63.9 41.4 22.5 cs-cr5 44.2 27.7 18.6 cs-cr10 44.0 26.5 17.5 cs-cr15 25.5 9.8 15.7 based on the results shown in table 3, analysis was performed on the soil characteristic identification related to the plasticity traits. it was identified that cs-cr0 was characterised as clay with high plasticity (ch), while the modified soil that contained 5% and 10% of crumb tyre rubber was found to be clay with intermediate plasticity (ci), followed by cscr15, which was identified as clay with low plasticity (cl). the results showed that the soil-crumb tyre rubber combination exhibited a lower plasticity state and a higher add-on amount of the additive might lead to an enhanced shear strength of the altered soil compared to the basic soil. overall, it could be seen that ll, pl and pi were all increased as the percentage of crumb tyre rubber content increased. the results corresponded with a previous study by sarvade and shet [13]. this pattern revealed that the properties of the crumb rubber tyre, as an additive contributed positively to the changes in the consistency of the soil with varying moisture content. 3.3 standard proctor compaction test the compaction test was carried out for the soil samples supplemented by a crumb tyre rubber of size 40 mesh in different mix percentages to determine and compare the optimum moisture content (omc) and maximum dry density (mdd). heavy tamping using a rammer with a weight of 2.6 kg applied with 25 blows was distributed over the surface of each layer. 79 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 the outcome of the standard proctor compaction test for the samples were tabulated in table 4 according to the percentage of the additives mix. table 4: result of compaction test soil sample cs-cr0 cs-cr5 cs-cr10 cs-cr15 optimum moisture content [%] 16.18 17.32 17.13 14.74 maximum dry density [mg/m3] 1.64 1.63 1.54 1.57 figures 4 and 5 define the omc and mdd graph of the sample with their percentages of modification, respectively. the pattern showed an increasing trend in moisture content up to a particular point and began to decrease thereafter. fig. 4: optimum moisture content graph. figure 4 showed the trend of moisture content increasing until 7% of the crumb tyre rubber and decreasing afterwards. however, there was a difference between the percentage of omc at 5% and 10% crumb tyre rubber, which were recorded at 17.32% and 17.13%, respectively. further addition of stabiliser to the samples showed a decline in omc until the lowest value was at about 14.74%, similar to the results obtained by vasavi et al. [14]. this was due to the excessive amount of rubber that caused a disruption and led to a disturbance in the mixture's ability to absorb [15]. the results of the mdd were clarified in fig. 5, whereby generally the curve demonstrated a declining trend with the addition of more crumb tyre rubber. the decrease might be due to the benefit possessed by crumb tyre rubber as a fine and light material capable of holding 1.02 to 1.27 of specific gravity [16]. furthermore, mohammed et al. [3] supported the decrease of the crumb tyre rubber dry density of the modified soil mainly due to the density of the crumb tyre rubber that was found to be lower than that of raw dune sand [3] and it was considered as a lightweight fill material based on its nature [8]. this argument was bolstered by ravichandran et al. [2], who found that the lower specific gravity of crumb rubber led to a low maximum dry density. however, the cs-cr15 sample had slightly increased the dry density to about 0.03 mg/m3.overall, the maximum dry density value of the modified sand-crumb tyre rubber did not show significant differences from the original soil. the differences were in the range of 1.54 to 1.64 mg/m3. 80 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 fig. 5: maximum dry density graph. fig. 6: compaction curve. figure 6 illustrates the compaction curve that consists of the dry density-moisture content relationship with the altered percentage of crumb tyre rubber at 0%, 5%, 10%, and 15%. overall, there was a substantial increase in dry density along with an increase in moisture content of about 16% and the graph declined subsequently. both parameters of mdd and omc revealed minimal differences, with the values varying from 1.68 mg/m3 to 1.77 mg/m3 and 15.09% to 17.45%, respectively. additionally, the graph displayed that by adding the crumb tyre rubber, the maximum dry density of the modified soil was lower compared to the parent clayey sand sample. this was because the weight of the crumb tyre rubber, which was originally known to be light, affected the density of the modified soil. 3.4 california bearing ratio (cbr) test the results for force on the plunger versus penetration of the cbr test for the clayey sand sample with the addition of 0%, 5%, 10%, and 15% crumb tyre rubber is illustrated in fig. 7. the figure demonstrates that the origin sample, as well as the modified sample showed a mounting curve through the experiments. it could be seen from the graph that the most obvious positive rising trend was the cs-cr10 sample which had 10% of the crumb tyre rubber. this positive trend was also proven by al-neami [4], who stressed that generally, the curve for reinforced sand samples increased as the percentage of crumb rubber and soil increased because the mixture tends to create bonds between them, leading to the fact that the modified mixture was able to sustain more load compared to raw soil. moreover, the stress applied over the soil surface was dispersed and distributed evenly towards the crumb tyre rubber and the soil. increasing the crumb tyre rubber quantities 81 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 resulted in less stress being held within the soil. furthermore, al-bared et al. [17] agreed in their studies that soil samples supplemented with crumb tyre rubber could enhance the cbr value and be directed towards the reduction of pavement thickness and project costs. fig. 7: california bearing ratio result. fig. 8: effect of percentage of crumb rubber added on cbr value. to sum up the graph of crumb tyre rubber -soil mixtures with the cbr value relationship, it could clearly be seen that the rising trend in cbr value for the clayey sand samples was steadily persistent up to 10% of the crumb tyre rubber mixture, as shown in fig. 8. the increase in the trend of cbr value was due to the small difference between the sizes of soil and the sizes of rubber crumb that produced a decent interlocking between them, and thus, could fill in the air void. consequently, this factor resulted in the higher strength of the soil to withstand an applied load. however, the upward trend started to decrease after further addition of crumb rubber. according to juliana et al. [7], the fall pattern was due to the presence of higher crumb rubber content that might cause greater compressibility in the mixture. the highest cbr value achieved was approximately 17 at 10% of crumb rubber addition, while the lowest cbr value belonged to the raw clayey sand sample, which was at 6. this showed that all mixtures (cs-cr0, cs-cr5, cs-cr10 and cs-cr15) had satisfied the minimum condition of pwd‘s standard. furthermore, from the above illustration, it could be stated that the optimum percentage of adding rubber crumb to the soil was 10% by weight in order to improve the weak soil. this was because the highest peak of each sample was achieved when the addition of 10% 82 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 crumb tyre rubber to the samples was accomplished by the weight of the samples in each testing standard. 4. conclusion this study was conducted to design the most suitable and ultimate functional samples out of a mixture of crumb tyre rubber stabiliser and clayey sand. crumb tyre rubber was expected to improve the problematic soil sample in terms of their strength properties. the type of collected soil samples was coarse-grained clayey sand, which was classified as poorly graded sand. the sample was found to be unsuitable for construction purposes due to its poorly graded soil properties, whereby the soil was lacking in terms of interlocking capabilities between the particles. besides, clayey sand, as well as poorly graded soil have higher compressibility and permeability compared to well-graded soil. based on the tested results of crumb tyre rubber -soil sample mixtures, the following conclusions could be drawn. the addition of 0%, 5%, 10% and 15% of crumb rubber tyre to the soil samples showed the increasing trend in the omc of up to 7% and decreased afterwards, while mdd of the modified soil remained moderately declined. this was due to the lightweight properties of the crumb tyre rubber that filled the void between the soil particles. by referring to the california bearing ratio test, the graph of cbr value versus percentage addition of crumb tyre rubber indicated that the addition of the crumb tyre rubber tended to increase the cbr value, as well as cause the strength of the soil to increase. however, as the cbr value increased up to 10% of the crumb tyre rubber added to the soil, and further addition until 15% of the crumb rubber tyre showed a downward trend in the cbr value. it could be concluded that the optimum percentage usage of crumb rubber tyre added to the soil sample for soil stabiliser purposes was 10%. importantly, the cbr value for all the mixtures fulfilled the minimum pwd‘s requirement (jkr/spj/2014) of 5% cbr value. for further investigations, more experiments and testing could be carried out to determine the efficacy of the crumb tyre rubber and soil mixture, such as the pycnometer test, shrinkage limit test, oedometer test, direct shear test, etc., besides using other stabilising agents for the mixing materials. acknowledgement the research was carried out under the fundamental research grant scheme (frgsracer) project racer/1/2019/tk01/uiam//1 provided by the ministry of higher education, malaysia. the authors wish to thank all the staff of the international islamic university malaysia research management centre and yong fong rubber industries sdn bhd, pelabuhan klang, selangor for providing the soil samples and crumb rubber tyre, respectively. references [1] banzibaganye g. (2014) investigation into the use of waste tyre shreds for reinforcement of sandy soils in south africa. master’s thesis, university of cape town, south africa. [2] ravichandran pt, prasad as, krishnan kd, rajkumar prk. (2016) effect of addition of waste tyre crumb rubber on weak soil stabilisation. indian journal of science and technology, 9(5): 1-5. 83 iium engineering journal, vol. 23, no. 2, 2022 saparudin et al. https://doi.org/10.31436/iiumej.v23i2.2293 [3] mohammed bs, adamu m, shafiq n. (2017) a review on the effect of crumb rubber on the properties of rubbercrete. international journal of civil engineering and technology, 8(9): 599-615. [4] al-neami ma. (2018) stabilization of sandy soil using recycle waste tire chips. international journal of geomate, 15(48): 175-180. doi: 10.21660/2018.48.180228 [5] hambirao gs, rakaraddi dpg. (2014) soil stabilization using waste shredded rubber tyre chips. iosr journal of mechanical and civil engineering, 11(1): 20-27. [6] singh s, dhiman u, sharma r. (2017) soil stabilization using scrap rubber tyre. international research journal of engineering and technology (irjet), 4(5):3157-3161. [7] juliana i, fatin ar, rozaini r, masyitah mn, khairul ah, nur shafieza a. (2020) effectiveness of crumb rubber for subgrade soil stabilization. iop conference series: materials science and engineering, 849. doi: 10.1088/1757-899x/849/1/012029 [8] zutting dv, naktode pl. (2020) soil stabilization by using scrap tire rubber. international journal of engineering research and technology (ijert), 9(6): 1382-1388. [9] kaur mr, singh ed. (2019) tyre rubber powder as a soil stabilizer. international research journal of engineering and technology (irjet), 6(6): 1786-1791. [10] tiwari v, modi a, diwan p. (2019) soil stabilization using with waste crumb rubber tire. journal for innovative development in pharmaceutical and technical science, 5(5): 28-31. [11] keerthi ck, doodala s. (2018) stabilization of black cotton soil by using grounded rubber powder. international research journal of engineering and technology (irjet), 119(17): 311-322. [12] prasad as, ravichandran pt, annadurai r, rajkumar prk. (2014) study on effect of crumb rubber on behavior of soil. international journal of geomatics and geosciences, 4(3): 579584. [13] sarvade pg, shet pr. (2012) geotechnical properties of problem clay stabilized with crumb rubber powder. bonfring international journal of industrial engineering and management science, 2(4): 27-32. doi: 10.9756/bijiems.1671 [14] vasavi bs, prasad dsv, prasad acsv. (2016) stabilization of expansive soil using crumb rubber powder and cement. international journal of innovative research in technology (ijirt), 2(8): 26-31. [15] daud n, yusoff z, muhammed a. (2015) ground improvement of problematic soft soils using shredded waste tyre. jordanian international civil engineering conference (jicec06), 6: 1-5. [16] tasalloti a, chiaro g, murali a, banasiak l. (2021) physical and mechanical properties of granulated rubber mixed with granular soils—a literature review. sustainability (switzerland), 13(8) :4309. doi: 10.3390/su13084309 [17] al-bared mam, marto a, latifi n. (2018) utilization of recycled tiles and tyres in stabilization of soils and production of construction materials -a state-of-the-art review. ksce journal of civil engineering, 22(10): 3860-3874. 84 microsoft word 234 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering m. nor et al. 61 feasibility analysis of free space earth to satellite optical link in tropical region norhanis aida m. nor, md. rafiqul islam and wajdi al-khateeb electrical and computer engineering department, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. aniss_aida@yahoo.com abstract: free space optics (fso) becomes a great attention because of the chances in transmitting data up to 2.5gbps. there are a lot of advantages offered by fso such as easily deployment with saving time and cost and no electromagnetic interference. in spite of the advantages, fso has an uncontrolled drawback which is highly sensitive to atmospheric phenomena because uses air as tranmission medium. current studies and researches are only focusing on fso terrestrial link with short path length and based on data from temperate region. therefore, this paper is aiming to provide feasibility analysis of fso link from earth to satellite especially low earth orbit (leo) based on atmospheric data in tropical region. the analysis will include the losses from geometrical attenuation, absorption, scintillation, haze attenuation, and rain attenuation. abstrak: ruang bebas optik (free space optics (fso)) mendapat perhatian kerana kebolehannya memancarkan data pada kelajuan tinggi. di sebalik kelebihannya, fso amat sensitif terhadap fenomena atmosfera kerana ia menggunakan udara sebagai perantara transmisi. penyelidikan dan kajian terkini hanya memfokus kepada jalinan darat fso dengan kepanjangan jarak pendek dan bergantung kepada kawasan tenang. oleh itu, kertas ini menyasarkan untuk memberikan analisis kebolehlaksanaan jalinan fso dari bumi ke satelit terutamanya orbit rendah bumi (low earth orbit (leo)) bergantung kepada data atmosfera di kawasan tropika. analisa termasuklah kehilangannya akibat pengecilan geometri, penyerapan, kelipan, pelemahan jerebu dan pelemahan hujan. keywords: feasibility; free space optics; availability; atmospheric attenuation; beam divergence angle; elevation angle 1. introduction fso is an emerging technology that has a great chance to compliment the traditional wireless communications and offers some inherent advantages compared to microwave links. the advantages include higher bandwidth, lack of use cable, and require no license spectrum. further, the systems are small, lightweight, have compact dimensions, and low power consumptions which result in big cost savings [1]. however, because fso uses air as the tranmission channel, the system is very sensitive to poor weather conditions which include absorption, turbulence, and scattering due to presence of aerosols, smoke, dust, rain, fog, and snow. in temperate region, the most influence condition is because of fog which the attenuation may raise more than 300 db/km in heavy fog [2]. in tropical region, rain is become main consideration because it occur throughout the year. attenuation will be the most critical factor for longer fso links especially to implement it in space. currently, iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering m. nor et al. 62 most studies and researches centred on temperate region and terrestrial link. there are very limited resources to implement fso link from earth to satellite. thus, this research will be concentrating on implementing fso link from earth to satellite especially in tropical region. therefore, the goal of this paper is to predict the availability of performing fso from earth to satellite especially low earth orbit (leo) satellite by analyzing attenuations that degrade the link under tropical atmospheric conditions. although it is impossible to change the physics of the atmosphere, it is possible to take advantage on the parameters by choosing the wavelength, receiver capture surface, elevation angle, and beam divergence angle accordingly. the atmospheric phenomena will be quantified by geometrical attenuation, haze attenuation, rain attenuation, absorption, and scintillation. since there are no standard equations has been derived for fso earth-to-satellite link, effort has been made to integrate prediction models derived for fso terrestrial link and microwave earthto-satellite link. 2. fso propagation in the atmosphere the purpose of this section is to introduce a theoretical basis of the losses that occur during the propagation of a fso system. the losses containing the losses from atmosphere which are absorption, scintillation, rain attenuation, and haze attenuation as well as geometrical attenuation. 2.1 geometrical attenuation geometrical attenuation is loss that occurs due to beam diverges which result detector receives less signal power. this attenuation is the only parameter that is independent to the atmospheric condition. the loss can be calculated using eq. (1) [3]. (1) where sd is surface area of transmit beam at range d, scapture is receiver capture surface (m 2 ), θ is beam divergence angle (mrad), and d is emitter-receiver distance (km). divergence will determine how much signal will be collected at the receiver end. therefore, in order to have low geometrical losses, it is suggested to have small beam divergence angle and bigger receiver capture surface to concentrate all incoming light to the receiver. 2.2 absorption absorption is caused by many different types of gaseous in the atmosphere, the dominant one being water vapor, which is the wavelength region used for wireless optical links[2]. absorption along earth to space path for the frequency between 150 thz and 375 thz, and the elevation angle above 45 o can be calculated using eq. (2) where τ' is the extinction ratio from he (height of the earth station above mean sea level in km), θ is the elevation angle, and λ is wavelength in µ m [4]. (2) 2.3 scintillation scintillation is the fluctuations in the detector signal as a result of random variations in the refractive index of the turbulent atmosphere along the channel [5] that increase the iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering m. nor et al. 63 amount of spreading beam. according to [4] and [6], the strength of scintillation is measured in terms of the variance of the beam amplitude and can be calculated by using eq. (3) where is turbulence profile (m -2/3 ), ho is height of earth station above ground level (m), h is height above ground-level (m), and z is effective height of the turbulence which typically 20km (3) 2.4 haze attenuation haze is one of local weather that gives significant impact on fso communications. according to [7], haze is caused by tiny particulates suspended in the atmosphere which diminished horizontal visibility at high concentrations. haze attenuation can be calculated by using beer’s law equation [8]; (4) (5) where l is measurement distance occured (km), v is visibility (km), λ is wavelength (nm), σ is specific attenuation coefficient per unit of length, and q is size of distribution of diffusing particles based on kim and kruse model [9]. 2.5 rain attenuation rain is classified under non-selective scattering since the drop size is much larger than the wavelengths. in malaysia, rain is a dominant mechanism of signal loss and distortion because it occurs almost year-round and most instances the rainfall rate is much higher than temperate region. rain intensity is the parameter used to locally describe the rain and based on [10], average rain intensity for malaysia exceeding 0.01% of the year is 120 mm/hr. according to [3], specific rain attenuation of optical link based on db/km is given in eq. (6) where r is rain intensity (mm/hr) and carbonneau model is used as the reference for the k and α value which are 1.076 and 0.67 respectively. (6) in order to calculate long-term statistics of the slant-path rain attenuation, 10 steps provided in itu-r p.618-9 [11] is followed. 3. results and analysis in order to check the availability of the link,each of the attenuation has been calculated and analyzed by using matlab and excel software by varying elevation angles and percentage of time. there are some fixed parameters that is considered in the calculation which is based on the fso equipment that already been installed in kulliyyah of engineering, international islamic university malaysia (iium), gombak campus. the parameters include λ=850 nm, beam divergence=2 mrad, and receiver capture surface = 32 cm. 3.1 attenuation analysis iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering m. nor et al. 64 specific attenuation caused by geometrical, absorption, scintillation, haze, and rain with respect to elevation angle for 0.01% of an average year is shown in table 1. few assumptions has been made to calculate the attenuations which are haze attenuation calculation based on measurement distance, l=20 km due to the average depth of troposphere in tropical region [12], and visibility range for slant path=10km according to researh done by [13]. then, to calculte absorption, height of earth station above mean sea level, he=0.06 km taking iium as the reference, and ground wind speed=1.5 m/s for scintillation calculation. table 1 shows that when the elevation angle increases, each of the attenuation will decreases accordingly, result in lower total attenuation when it reach 90 degree elevation angle. however, the range of the total attenuation for 99.99% availability is still quite high which is in between 300-1100 db, make it impossible to establish the link to leo satellite. therefore, the availability needs to be reduced in order to have lower attenuation to make the link feasible. note that, scintillation and absorption contribute only small portion of attenuation when compared to rain and geometrical loss. table 1: calculated attenuations for different elevation angles. elevation angle (degree) types of attenuation total attn. (db) geometrical (db) absorption (db) scintillation (db) haze (db) rain (db) 10 88.63 17.72 1.26 111.06 905.81 1124.5 20 82.74 8.99 0.67 56.39 507.11 655.9 30 79.44 6.15 0.48 38.57 374.88 499.5 40 77.26 4.78 0.38 30.01 311.03 423.5 50 75.73 4.01 0.32 25.17 275.22 380.5 60 74.67 3.55 0.29 22.27 253.89 354.7 70 73.96 3.27 0.27 20.52 241.23 339.2 80 73.55 3.12 0.26 19.58 234.48 331.0 90 73.42 3.08 0.25 19.28 232.36 328.4 figure 1 shows the difference of total attenuation between several values of percentage of time with respect to the elevation angle. six different percentages has been selected in order to determine the total losses occur during data propagation which is 0.001%, 0.01%, 0.05%, 0.1%, 0.5%, and 1% of percentage time which equivalent to 99.999%, 99.99%, 99.95%, 99.9% and 99.5%, and 99.0% availability respectively. previous data in table 1 shows the specific value of total attenuation for 99.99% availability is impossible to establish not to mention 99.999%. consideration can be made if the availability is reduced to 99.9% and below which the attenuation is lower than 500db. more discussions about the availability are presented in next section. 3.2 availability of the link system availability is the probability that the system works correctly at the time t[2]. the availability of a fso link system mainly depend on the power link budget and the local climate conditions as it is the measure of optical signals can penetrate atmospheric attenuation in different weather conditions. there are few parameters that can be varied iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering m. nor et al. 65 and need to be concerned in order to make the link between earth and satellite is feasible which are transmitted power, receiver sensitivity, beam divergence angle, and elevation angle. since the total attenuation is quite high during rain, so tranmitted power and sensitivity values are set to maximum which are 40dbm and -90dbm respectively due to combat the total attenuation occured during the signal tranmission. 10 20 30 40 50 60 70 80 90 0 500 1000 1500 2000 2500 total attenuation from earth to leo satellite(db) vs elevation angle (degree) for different percentage of time elevation angle (degree) a tt e n u a ti o n ( d b ) 0.001% 0.01% 0.05 0.1% 0.5% 1% fig. 1: total attenuation vs elevation angle for different percentage of time. figure 2 presents the power received at different availability for different beam divergence angle during clear air and hazy days. during clear air, haze and rain are neglected and only scintillation, absorption, and geometrical loss is considered in the calculation. from fig. 2(a), it is clearly shows that, when 40dbm power is transmitted, receiver will capture all the signals even though beam divergence increases until 5mrad with total losses is in the range between 40-120db. for example, for beam=0.1mrad, fso system can operate with a 48.42db link margin with received power=-41.56db and penetrate the losses relatively unhindered. in addition, fig. 2(b) describes about power received during hazy days. sensitivity is still set up to -90dbm and if the signals are above the limit, means the signal will be captured by the receiver. from the graph, receiver can receive signals if the elevation angle is above 30 degree for all beam divergence angles. however, the elevation angle can be improved if the beam angle is reduced up to 0.1mrad onwards. therefore, during clear air and hazy days, there are possibilities to transmit fso signal from earth to leo satellite. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering m. nor et al. 66 fig. 2: power received (dbm) vs elevation angle (degree) for different beam divergence angle during clear air and during hazy days. moreover, fig. 3 describes about the effect of elevation angles to the availability and power received for different beam divergence angle during all types of attenuations occur including haze and rain. three different beam angles are set which are 0.01, 0.1, and minimum elevation angle will be indicated as the point of reference in order to establish the link. from the figure, it is possible to have link at beam angle=1mrad but with availability less than 99.5% with minimum elevation angle is 50 degree. better consideration can be made if the beam angle is lower than 0.01mrad, as at 0.01mrad, power will be received at elevation angle 30 degree and above at 99.3% availability. therefore in order to maintain percentage of availability and to make all elevation angles possible to use, one need to cogitated lower beam divergence angle. fig. 3: power received (dbm) vs availability for different elevation angles at certain values of beam divergence angle. last but not least, in order to see the effect of beam divergence angle to the power received and the availability, an elevation angle at 70 degree was chosen as the benchmark and red line which is receiver sensitivity is set to -90 as the limit. from the fig. 4, it is clearly presents that, the maximum availability the link can be established is 99.7% with beam divergence needed to decrease up to 0.05mrad. the link will be impossible is one look at the availability above 99.9% even though beam divergence is set up to smaller value like 0.01mrad. if the system needs to tolerate the angle of beam divergence, it can be increased up to 3mrad with the availability of 99.0%. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering m. nor et al. 67 fig. 4: power received vs availability for different beam divergence angle at θ=70 o . 4. conclusion fso is a growing technology that offers high data rates which is suitable for future near-earth, solar system, and space applications. this paper has estimated the availability of fso system from earth-to-satellite in tropical region . total attenuation is calculated by adding all the attenuations contibuted by absorption, scintillation, geometrical, rain, and haze. from the analysis, there are three main parameters that can be compensated for each other which are availability, elevation angles, and beam divergence angles. furthermore, attenuations during rain is very high which contributes significantly the availability of the link. for example, at elevation angle 60 degree, rain attenuation at 0.001% is 513.1db, 0.01% is 253.9db, 0.1% is 104.5db, and 1.0% is 20.47db. fso link is feasible to establish from earth to satellite if the availability is set to 99.5% with elevation angle higher than 40 degree and beam divergence angle is lower than 0.01mrad. if one need to decrease the elevation angle, beam divergence angle need to decrease or to increase transmit power for same availability. it is recommended to design the feasible link with availability 99.0% and beam divergence angle 0.01mrad in order to have lower elevation angles which is 30 degree. this result can be as a benchmark in designing fso system for earth-to-space. references [1] m. toyoshima, “trends in laser communications in space”, space japan review, no. 70, october / november 2010. [2] e. leitgeb, m. gebhart, and u. birnbacher, “optical networks, last mile access and applications”. journal of optical and fiber communication reports, 2005, rep 2, p 56-85. [3] prediction methods for the design of terrestrial free-space optical links. recommendation itu-r p.1814. [4] international telecommunication union. (2003). prediction methods required for the design of earth-space systems operating between 20 thz and 375 thz. recommendation itu-r p.1622. [5] a. k. majumdar, “free space laser communication performance in the atmospheric channel”. j. optic. fiber commun., pp. 345-396, 2005. [6] international telecommunication union. (2003). propagation data required for the design of earth-space systems operating between 20 thz and 375 thz. recommendation itu-r p.1621-1. [7] malaysian meteorological department website [online], retrieved november 11, 2011 http://www.met.gov.my/index.php?option=com_content&task=view&id=70&itemid=160&l ang=english iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering m. nor et al. 68 [8] m. achour, “simulating atmospheric free space optical propagation part 1, rainfall attenuation”, proc. spie, 2002. [9] o. bouchet, h. sizun, c. boisrobert, f. de fornel, p. favennec, free-space optics: propagation and communication. uk: iste ltd, 2006. [10] international telecommunication union. (2003). characteristics of precipitation for propagation modeling. recommendation itu-r p.837-4. [11] international telecommunication union . (2007). propagation data and prediction methods required for the design of earth-space telecommunication systems. recommendation itu-r p.618-9. [12] wikipedia site (n.d.) [online]. available: http://en.wikipedia.org/wiki/troposphere [13] m.s. awan, marzuki, e. leitgeb, b.hillbrand, f. nadeem, m.s. khan, “cloud attenuations for free space optical links”, iwssc, 2009. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 computational fluid dynamics modeling of microchannels cooling for electronic microdevices jonathan fábregas 1, henry santamaría1, edgardo buelvas1, saul pérez1, carlos díaz1, javier carpintero2, ricardo mendoza3 and jennifer villa2* 1 faculty of engineering, universidad autónoma del caribe, colombia 2 department of civil and environmental, universidad de la costa, calle 58 #55-66, 080002 barranquilla, atlántico, colombia 2 energy department, universidad de la costa, calle 58 #55-66, 080002 barranquilla, atlántico, colombia *corresponding author: jvilla27@cuc.edu.co (received: 13th june 2021; accepted: 13th october 2021; published on-line: 4thjanuary 2022) abstract: a simulation of the cooling of electronic devices was carried out by means of microchannels, using water as a coolant to dissipate the heat generated from a computer processor, and thus stabilize its optimum operating temperature. for the development of this study, computational fluid mechanics modeling was established in order to determine the temperature profiles, pressure profiles, and velocity behavior of the working fluid in the microchannel. in the results of the study, the operating temperatures of the computer processor were obtained, in the ranges of 303 k to 307 k, with fluid velocities in the microchannels of 5 m/s, a pressure drop of 633.7 kpa, and a factor of safety of the design of the microchannel of 15. from the results, the improvement of the heat transfer in a cooling system of electronic devices was evidenced when using a coolant as a working fluid compared to the cooling by forced air flow traditional. abstrak: simulasi penyejukan alatan elektronik telah dibina menggunakan saluran mikro, di samping air sebagai agen penyejuk bagi menghilangkan haba yang terhasil dari pemproses komputer, dan penstabil pada suhu operasi optimum. kajian ini mengenai model komputasi mekanik bendalir bagi menentukan profil suhu, profil tekanan, dan halaju perubahan bendalir dalam saluran mikro. dapatan kajian menunjukkan suhu operasi pemproses komputer adalah pada julat suhu 303 k sehingga 307 k, dengan halaju bendalir dalam saluran mikro adalah pada kelajuan 5 m/s, penurunan tekanan sebanyak 633.7 kpa, dan faktor keselamatan 15 bagi reka bentuk saluran mikro. ini menunjukkan terdapat kenaikan pemindahan haba bagi sistem penyejukan alatan elektronik ini, terutama apabila cecair digunakan sebagai penyejuk haba berbanding kaedah tradisi iaitu dengan mengguna pakai aliran udara sebagai agen penyejuk. keywords: computational fluids dynamics; microchannels; processor; cooling 1. introduction at present, there is a growing demand for greater performance in electronic devices and for reliability in the level of heat rejection, which make it necessary to create alternatives for the removal of heat and which in turn are much more efficient. therefore, some alternatives have been presented to solve this problem by developing research using 384 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 microchannels (mc). belhardj et al. [1] used mc with a phase change fluid to improve heat transfer in the cooling of processors. chen and ding [2] analyzed the performance of cooling devices using mc with working fluids of water and nanofluids. their results showed adequate behavior with the two proposed alternatives. moreover, chiu et al. [3] studied the effect of the mc geometry and the pressure used in the heat transfer. it was found that a higher pressure drop improved the heat transfer coefficient. bosi et al. [4] designed a series of mc modules with different channel separation configurations to study the cooling phenomenon of a silicon pixel detector system. in addition, brinda et al. [5], in their study, propose a series of mc in a stepped form with a rectangular cross-section to increase the area of the walls, which decreases the thermal resistance and increases the heat transfer coefficient. naqiuddin et al. [6] carried out a study applying the technology of mc for the cooling of electronic chips, adapting the principles of straight channels by a segmented method. modeling was developed for this research by computational fluid dynamics (cfd) and the statistical method of taguchi-gray to optimize the system according to the required specifications. in other studies, zhang et al. [7] worked in mc using the effect of the model k-e turbulent in three types of cross-section for the mc. they used circular, trapezoidal, and rectangular sections, comparing the results obtained in terms of heat transfer and mechanics of the fluid, establishing the best design in terms of performance. naqiuddin et al. [8] conducted a study on the recent technological advances in electronic systems that use mc systems. in their study, they emphasized the importance of geometry, fluid mechanics, fluid type, phase change, and the applications of the same to improve heat dissipation. kirsch and thole [9] evaluated the behavior of mc developed by additive metal fabrication methods with simulated profiles through computational tools, comparing the effect on the performance of the device in the tests performed, highlighting the influence of the roughness present on the surfaces of the elements manufactured with respect to the change of the shape of the profiles. yue et al. [10] developed a study by cfd modeling of the segment of a steam turbine separated by mc varying the filling ratio of the refrigerant, finding the optimum operating percentages, and establishing a method to simplify the experiments. a more complete review of the main applications that use cfd for physical phenomena modeling associated with heat transfer and fluid movement can be found in studies by hnaien et al. [11] where they compared several turbulence models using computational mechanics to simulate the interaction of parallel jets, highlighting better predictions in the results when using the standard k ε model. mohammed [12] reviewed literature focusing on the use of cm and nanofluids in both experimental and numerical designs, showing in his findings the improvement of heat transfer from devices because of increasing pressure drop. mohd and parashram n. [13] in their study used numerical techniques to predict the behavior of the dimensionless nusselt number, through cfd simulations where the turbulence model sst gamma-theta has greater precision in convergence. aqilah et al. [14] performed a mesh effect study on cfd simulations of the aerodynamic profile in an airfoil, indicating the importance of mesh quality when comparing results with experimental studies. drăgan [15] conducted a performance study of a centrifuge compressor using cfd software to simulate fluid behavior and heat transfer in equipment with optimized design under different operating conditions. 385 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 thome [16] conducted a review study of the effect of boiling in mc devices, for cfd simulations and experiments with two-phase flows, and evaluated the behavior of heat transfer in mc when boiling. talimi et al. [17] conducted a review on numerical simulation research in small channels in which the hydrodynamic and heat transfer characteristics in non-boiling gas-liquid and liquid-liquid slug flows were studied for circular and noncircular channels. bagheri-esfe and manshadi [18] developed a code for cfd simulations estimating the behavior of flow fields to design a wind tunnel. azizi et al. [19] studied gas-solid heat transfer in risers using two-fluid cfd modeling to evaluate the effect of bed angle and particle feed velocity. villegas et al. [20] used a coupling of computational tools, applying cfd to represent the friction-stir welding phenomenon. culun et al. [21] developed a synergistic analysis in cfd of heat transfer of impinging multi jets, evaluating parameters such as the geometry of the jet holes, their arrangement, the density of the jets through spanwise and streamwise directions, and the type of confinement. elsamni et al. [22] used cfd to study the characteristics of laminar flow in a semi-circular duct and the effect of the reynolds number on the hydrodynamic development length and the friction factor, and subsequently compared them with straight and curved ducts. thus, computational modeling through cfd software of the design of the device with mc system starts from the advances of the computational technology of last generation processors, which require a heat removal system that satisfies the conditions for its performance over maximum efficiency. traditional propeller heatsinks have been in the market for many decades obtaining a good performance in their operation, but as the technology of the processors increases, the system must meet their maximum operation demands. mc technology has had a great impact on cooling processes with good results. based on these studies and technologies, the design and modeling of a device that satisfies the conditions of the last generation processor is generated. in this study, a cooling system of an electronic device is evaluated, using water as the working fluid in a mc system, considering the heat transfer and the physical modeling involved in this case, in order to compare the operating temperature of the device with traditional forced airflow cooling. finally, the safety factor of the mc design is verified in the numerical analysis. 2. materials and method the development and application of phenomena associated with the behavior of cm technology are described by its formulation of mathematical models, as explained below, considering that the modeling equations were made with the use of ansys® software. it begins with a description of the physical phenomena that govern the system. similarly, the boundary conditions for heat conduction and the thermodynamic relationship of the working fluid with convection heat transfer are exposed. the external and internal working fluids were studied through the logarithmic mean temperature difference to establish the change of temperature in the exchange device system. from the description of the heat transfer model, the variables involved in the process are established to use a computational tool where these values will be entered. previously, a cad (computer-aided design) model was developed. then, an ansys cfx tool was used to evaluate the energy, continuity, moment, and turbulence models to obtain the results. 386 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 2.1 physical modeling the heat transfer phenomenon to which the mc cooling device is subjected, together with the working fluid and heat dissipation in the computer processor, requires a mathematical model to describe its behavior. therefore, the following numerical formulations are established. heat input from processor to mc device is: , (0, )cpu d s cpu q t t k a y  = −  (1) where kd is the thermal conductivity of the solid material with which the device mc was designed, cpuq is the heat generated by the processor, ,s cpua is the surface area of contact between the processor and the device mc. consequently, the liquid used for cooling inside the mc is water, and the heat transfer rate of the coolant without phase change is described with equations (2-3): 2 2 2 , 2 , 2 , ln,( ) ( )h o ph o h o out h o in h o mc s mc mcq c m t t h a t= − =  (2) , 2 , 2 ln, , , 2 , , 2 ln in h o out h o mc s prom out h o s prom in h o t t t t t t t     −   =    −     −    (3) assuming in the first stage of calculation the surface temperature of the mc as average temperature. where 2h om is the mass flow of the coolant (water) and 2ph oc is the specific heat, , 2in h ot and , 2out h ot are the coolant inlet and outlet temperatures in the mc, ,s promt is the average temperature on the surface of the mc, ln,mct is the average log temperature of the mc, mch is the coefficient of heat transfer by internal convection in the mc. for obtaining the coefficient of heat transfer by convection the number of nusselt nu is calculated by dittus-boelter equation (4). for the turbulent regime: 0.8 2 0.023 re pr nmc d d h o h d nu k = = (4) for the laminar regime with constant heat flux, and the laminar regime with an average surface temperature of constant mc, given the dimensions of the mc, the nusselt number is: 4.12; 3, 308; 61.144 / req ts dnu nu f= = = (5) where 2h ok is the thermal conductivity of the coolant liquid (water), dd is the hydraulic diameter before the test section at the entrance, f is the friction factor and the reynolds number represented by dd is calculated according to equations (6-7): re dvd v = (6) 4 c d a d p = (7) 387 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 where v represents the velocity of the coolant (water), v is the kinematic viscosity of the coolant (water), ca is the area of the cross-section located before the test zone and p is the perimeter of this. the heat generated around the mc device is represented by the equation (8): ( ) ( ) ( ) 4 4 2, , , ,d t l t k h t l t t t l t t y    − = −  + −      (8) where 2,h  is the coefficient of free heat transfer of the material of the device mc with the air environment of the surroundings, t is the environment air temperature of the surroundings,  is the stefan-boltzmann coefficient for radiation,  is the emissivity of the surface of the mc device. figure 1 describes the system developed. fig. 1: representation of the cooling system with the use of mc. 2.2 computational model the design of the mc cooling device was generated because of the size specifications of the last generation processor studied. that is, a compact device made of commercial aluminum that consists of an internal fluid inlet of 3.8 mm in diameter, the constitution of the series of mc of height 0.9 mm and width 0.5 mm, a fluid outlet of 3.8 mm in diameter, as shown in fig. 2. fig. 2: geometric representation of the cooling device by mc. figure 3 shows the volumetric meshing of the system in which the size of the elements is stipulated for a minimum of 0.015 mm and a maximum of 0.3 mm with a growth rate of 1.2, obtaining an element quality of 82 % indicating a good mesh, for a ratio of 369,995 nodes and 1,047,186 elements in the microchannel system. these meshing data are selected by performing different meshing independence tests according to a response variable, obtaining an error percentage of 0.6%. 388 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 the input boundary condition is assigned by the velocity variables and the ambient temperature of 298.15 k of the water domain, the velocity is calculated by the flow and the transverse area of the input. the boundary condition of the mc cooling device domain presents a set of variables in the initial state, the initial temperature of the medium at 298.15 k, free convection of the medium with the aluminum material at 25 w/m2k. the processor generates a heat flux corresponding to its maximum operation consumption on the surface or base of the mc cooling device and this corresponds to 22,849 w/m2 by equation (1). fig. 3: volumetric mesh of the microchannel section. therefore, the models applied to the system consist of the movement of the working fluid and the heat transfer between the contact interfaces and the environment, for which, the computational models of momentum conservation, energy conservation, and turbulence models for fluid movement are shown in equations (9) to (12). momentum conservation: ( ) ( ) ( )tv vv p v v g f t       + = − +  + + +   (9) where  is the density of the fluid,  is the dynamic viscosity, p is the pressure, is the dynamic viscosity of the fluid, v is the velocity of the fluid. ( ) ( ) ( ) ( )eff hv e v e p p k t s t     + + + =   +  (10) the equation (10) represents the energy conservation of the system, where the variable effk is the coefficient of effective thermal conductivity, and hs represents the energy of the potential chemical system. turbulence model k-ε: ( ) ( ) ij k b m k i i k i k k ku g g y s t x x x            + = + + + − − +           (11) ( ) ( ) 2 1 2 1 3 i j z z b z j j z j s ku c s c c c g s t x x kk v                 + = + + − + +        +    (12) 389 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 where kg represents the turbulence generation of the kinetic energy due to the average velocity gradient, my represents the contribution of the incompressible turbulence of fluctuating expansion to the general dissipation rate, and bg is the generation of turbulence due to the floating kinetic energy. due to defined boundary conditions and interface domains, a convergence criterion of 1e-04 is established to start the cfd software solver. table 1 presents the boundary conditions applied to the computational model with the process conditions. table 1: boundary conditions conditions value initial temperature 298.15 k heat flux 22.849 kw/m2 pump's rotational speed 100 – 2000 rpm external heat transfer coefficient of the microchannel 25 w/m2k external environment temperature 298.15 k inlet and outlet pipe area 11.341 mm2 the cross-sectional area of the microchannel 1.45 m2 3. results and discussion the transfer models that govern the design of the mc system were indicated in the modeling of the device. the design was generated from two aluminum materials for the mc device with water as the cooling liquid. the mc cooling device was generated based on the size specifications of the studied computer processor, that is, a compact device using mc in series, the boundary conditions assigned by the variables of velocity and ambient temperature of the water domain, and the limit conditions of the mc cooling device presenting a set of variables in an initial state such as ambient temperature. after the cfd software solution process was complete, the temperature, pressure, and velocity profiles were rendered for analysis purposes. the reading of results was presented in two specific areas, the interior of the mc and the contact surface of the processor-cooling device in planes, therefore, the results of the study carried out are shown in fig. 4 and 5. fig. 4: temperatures profiles: a) region of mc, b) region of processor-cooling device contact. 390 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 figure 4 shows the distribution by contours of the temperature in the device and inside the mc, from which it can be noted that the coolant reached a working temperature of approximately 306 k, while the solid-body reached a temperature of 307.5 k and a minimum temperature of 304 k located in the inlet zone of the coolant to the system. these results of mc temperature profiles were compared with those proposed by naqiuddin et al. [6], moradikazerouni et al. [23], and abdollahi et al. [24]. it was observed that the temperature differences were greater by up to 5 k according to the simulation conditions demonstrating that the operating principle of liquid cooling is adequate to maintain the working conditions of the electronic element, meaning the processor. fig. 5: profiles in the mc region: a) speed of the cooling fluid, b) pressure in the cooling fluid. in fig. 5, the velocity and pressure profiles corresponding to the working fluid inside the mc are observed, from which it can be seen that for the flow rate established when using equation (9), the operating pressure at the beginning of the conduit is 633.7 kpa and the speed reached by the liquid in the mc is 0.5 m/s. this relationship shows that increasing the fluid velocities requires a greater pressure range so that the flow parameters remain at the working condition that is required by the processor in terms of temperature. this velocity result is within the range of results obtained by chiu et al. [3] on hydraulic simulations in the cfds of microchannels used as heatsinks. when graphing, there is a line along the length of the device, these represent the temperature curves in two regions, which appear as a result of the system temperature is stabilized from 299 k to 306.4 k together with the mc and the temperature in the region of contact of the device with the processor from 304.5 k to 307.4 k, in the range of the optimum operating temperature of the processor as seen in fig. 6. 391 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 fig. 6: temperature curves: a) region of mc, b) region of contact processor-cooling device. the analysis of the behavior of the stabilized temperature in the computer processor was carried out, varying the range of angular velocity from the water pumping system to the mc device, thus obtaining characteristic curves that allowed choosing the best range of speeds to model. figure 7 shows the graphs of the temperature profile reached in the computer processor, for each point of variation of the angular velocity in the pumping system. it is observed that the angular velocity ranges between 500 rpm and 1000 rpm do not represent a significant variation in the temperature obtained in the computer processor, so this range of velocity is a good option to model the process. fig. 7: temperature & flow rates curves: a) region of processor, b) region of contact processorcooling device. 392 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 once the fluid dynamic behavior of the working liquid inside the mc system has been evaluated, a multiphysics coupling is made in the simulation software, by importing the pressures reached inside the mc system by the working fluid, in order to analyze in a structural mechanics tool, the stresses caused by this pressure on the walls of the mc. figure 8 shows the pressure vectors transferred to the structural mechanics' tool. fig. 8: pressure imported from cfd tool to structural mechanics' tool. upon obtaining the results of the temperature and pressure profiles the coupling between computational tools was performed to determine the effect caused by the pressures reached by the working fluid and the stress it causes on the mc surfaces. the magnitude of the stresses applied to the mc surfaces was obtained using commercial aluminum as the device material, in addition to estimating the safety factor to evaluate the feasibility of manufacturing a physical design under these working conditions. these results are shown in fig. 9. fig. 9: design contours: a) security factor, b) von mises stress. figure 9 can be analyzed to reveal the maximum applied stress for the pressure conditions generated for the cooling of the electronic processor device. the maximum 393 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 applied stress is 1.38 mpa with a safety factor of 15 granting design reliability for the use of a wide field of pressures used for cooling electronic devices. sreehari and sharma [25] carried out research about the thermal performance in mc using water as the working fluid. the effect of three types of surface engraving that were modeled were compared (rectangular coil, u-curvature coil, and v-shaped coil) and subjected to computational and experimental study. these microchannel systems have a rectangular cross-section with dimensions of 0.6 mm x 0.3 mm using heat flux of 10 kw/m2, 20 kw/m2, and 30 kw/m2. the results have shown an acceptable deviation between the experimental and numerical results with a maximum value of 11%. the rectangular coil behaved similarly to the device analyzed in the present investigation. 4. conclusion the main motivation for carrying out this study was the fact that the usual working temperatures of a cpu range between 328.15 k and 343.15 k when using the traditional dissipation system for air ventilation, which affects the performance of the device, causing forced labor. on this basis, the following conclusions are drawn when liquid cooling is used in a microchannel-type device. the main result is that the variables analyzed in the study such as fin geometry and mc distribution influence the heat transfer less than the flow rate used. for low flow rates, the temperature tends to exceed the normal operating range of the system, which implies that the design of the device must have the corresponding mechanical properties for the pressure range in the mc, as well as the supply hoses and the pumping device. the results of the simulation of the system were analyzed and it was observed that the behavior of the mc cooling device, when the processor is at its maximum use in operations, maintains an optimum working temperature in an average range of 307 k. it should be noted that the value depends on the conditions of fluid entry, such as the flow rate. it is concluded that at a lower flow rate than the one used in the fluid, the behavior of the temperature exceeds the range of 313 k, which is still suitable for optimal operation for the studied processor which establishes a limit of operation at 333 k and critical state at more than 373 k. the design of the device is suitable for its operation since it has a safety factor of 15 for optimal process conditions using commercial aluminum material, which is a light material and good conductor. the mesh size was evaluated with respect to the temperature reached by the contact surface with the computer processor. varying the number of elements in the mesh from a default value of 320,775 to 1,047,186, obtaining an error percentage between samples of 0.6%, which is an acceptable value for the reliability of the simulation. this study consisted of analysis using computational tools to simulate the explained phenomenon. validations were carried out with works published by various authors applying similar simulation techniques. the experimental validation of the design will be carried out in future studies. references [1] belhardj s, mimouni s, saidane a, benzohra m. (2003) using microchannels to cool microprocessors: a transmission-line-matrix study. microelectronics journal, 34(4): 247–253. https://doi.org/10.1016/s0026-2692(03)00004-1 394 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 [2] chen ch, ding cy. (2011) study on the thermal behavior and cooling performance of a nanofluid-cooled microchannel heat sink. international journal of thermal sciences, 50(3): 378–384. https://doi.org/10.1016/j.ijthermalsci.2010.04.020 [3] chiu hc, jang jh, yeh hw, wu ms. (2011) the heat transfer characteristics of liquid cooling heatsink containing microchannels. international journal of heat and mass transfer, 54(1–3): 34–42. https://doi.org/10.1016/j.ijheatmasstransfer.2010.09.066 [4] bosi f, balestri g, ceccanti m, mammini p, massa m, petragnani g, ragonesi a, soldani a. (2011) light prototype support using micro-channel technology as high efficiency system for silicon pixel detector cooling. nuclear instruments and methods in physics research, section a: accelerators, spectrometers, detectors and associated equipment, 650(1): 213–217. https://doi.org/10.1016/j.nima.2010.12.187 [5] brinda r, joseph daniel r, sumangala k. (2012) ladder shape micro channels employed high performance micro cooling system for ulsi. international journal of heat and mass transfer, 55(13–14):3 400–3411. https://doi.org/10.1016/j.ijheatmasstransfer.2012.03.044 [6] naqiuddin nh, saw lh, yew mc, yusof f, poon hm, cai z, thiam hs. (2018) numerical investigation for optimizing segmented micro-channel heat sink by taguchi-grey method. applied energy, 222: 437–450. https://doi.org/10.1016/j.apenergy.2018.03.186 [7] zhang y, wang s, ding p. (2017) effects of channel shape on the cooling performance of hybrid micro-channel and slot-jet module. international journal of heat and mass transfer, 113: 295–309. https://doi.org/10.1016/j.ijheatmasstransfer.2017.05.092 [8] naqiuddin nh, saw lh, yew mc, yusof f, ng tc, yew mk. (2018) overview of microchannel design for high heat flux application. renewable and sustainable energy reviews, 82: 901–914. https://doi.org/10.1016/j.rser.2017.09.110 [9] kirsch kl, thole ka. (2018) isolating the effects of surface roughness versus wall shape in numerically optimized, additively manufactured micro cooling channels. experimental thermal and fluid science, 98: 227–238. https://doi.org/10.1016/j.expthermflusci.2018.05.030 [10] yue c, zhang q, zhai z, ling l. (2018) cfd simulation on the heat transfer and flow characteristics of a microchannel separate heat pipe under different filling ratios. applied thermal engineering, 139: 25–34. https://doi.org/10.1016/j.applthermaleng.2018.01.011 [11] hnaien n, marzouk ks, ben ha, jayb j. (2016) numerical study of interaction of two plane parallel jets. international journal of engineering, 29(10): 1421–1430. https://doi.org/10.5829/idosi.ije.2016.29.10a.13 [12] mohammed ha, bhaskaran g, shuaib nh, saidur r. (2011) heat transfer and fluid flow characteristics in microchannels heat exchanger using nanofluids: a review. renewable and sustainable energy reviews, 15(3): 1502–1512. https://doi.org/10.1016/j.rser.2010.11.031 [13] mohd umair s, parashram gulhane n. (2016) on numerical investigation of non-dimensional constant representing the occurrence of secondary peaks in the nusselt distribution curves. international journal of engineering, transactions a: basics, 29(10):1 431–1440. https://doi.org/10.5829/idosi.ije.2016.29.10a.00 [14] aqilah f, islam m, juretic f, guerrero j, wood d, nasir ani f. (2018) study of mesh quality improvement for. iium engineering journal, 19(2): 203–212. https://doi.org/https://doi.org/10.31436/iiumej.v19i2.905 [15] drăgan v. (2017) centrifugal compressor efficiency calculation with heat transfer. iium engineering journal, 18(2): 225–237. [16] thome jr. (2004) boiling in microchannels: a review of experiment and theory. international journal of heat and fluid flow, 25(2): 128–139. https://doi.org/10.1016/j.ijheatfluidflow.2003.11.005 [17] talimi v, muzychka ys, kocabiyik s. (2012) a review on numerical studies of slug flow hydrodynamics and heat transfer in microtubes and microchannels. international journal of multiphase flow, 39: 88–104. https://doi.org/10.1016/j.ijmultiphaseflow.2011.10.005 [18] bagheri-esfe h, manshadi md. (2018) a low-cost numerical simulation of a supersonic windtunnel design. international journal of engineering, transactions a: basics, 31(1): 128–135. https://doi.org/10.5829/ije.2018.31.01a.18 [19] azizi k, keshavarz moraveji m. (2017) computational fluid dynamictwo fluid model study of gas-solid heat transfer in a riser with various inclination angles. international journal of 395 https://doi.org/10.1016/j.rser.2017.09.110 iium engineering journal, vol. 23, no. 1, 2022 fábregas et al. https://doi.org/10.31436/iiumej.v23i1.2113 engineering, transactions a: basics, 30(4): 464–472. https://doi.org/10.5829/idosi.ije.2017.30.04a.02 [20] villegas jf, guarín am, unfried-silgado j. (2019) a coupled rigid-viscoplastic numerical modeling for evaluating effects of shoulder geometry on friction stir-welded aluminum alloys. international journal of engineering, transactions b: applications, 32(2): 184–191. https://doi.org/10.5829/ije.2019.32.02b.17 [21] culun p, celik n, pihtili k. (2018) effects of design parameters on a multi jet impinging heat transfer. alexandria engineering journal, 57(4): 4255–4266. https://doi.org/10.1016/j.aej.2018.01.022 [22] elsamni oa, abbasy aa, el-masry oa. (2019) developing laminar flow in curved semicircular ducts. alexandria engineering journal, 58(1): 1–8. https://doi.org/10.1016/j.aej.2018.03.013 [23] moradikazerouni a, afrand m, alsarraf j, mahian o, wongwises s, tran md. (2019) comparison of the effect of five different entrance channel shapes of a micro-channel heat sink in forced convection with application to cooling a supercomputer circuit board. applied thermal engineering, 150: 1078–1089. https://doi.org/10.1016/j.applthermaleng.2019.01.051 [24] abdollahi a, mohammed ha, vanaki sm, osia a, golbahar haghighi mr. (2017) fluid flow and heat transfer of nanofluids in microchannel heat sink with v-type inlet/outlet arrangement. alexandria engineering journal, 56(1): 161–170. https://doi.org/10.1016/j.aej.2016.09.019 [25] sreehari d, sharma ak. (2019) on thermal performance of serpentine silicon microchannels. international journal of thermal sciences, 146: 1-14. https://doi.org/10.1016/j.ijthermalsci.2019.106067 396 microsoft word 231 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering nor hairin et al. 115 high discharge rate electrodeposited zinc electrode for use in alkaline microbattery a.l. nor hairin 1 , raihan othman 2 , mohd hanafi ani 1 and hens saputra 3 1 department of manufacturing and materials engineering, 2 department of science in engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. 3 pusat teknologi industri proses, badan pengkajian dan penerapan teknologi (bppt), jl. m.h. thamrin no. 8, jakarta 10340, indonesia. raihan@iium.edu.my abstract: high discharge rate zinc electrode is prepared using the electrodeposition process. the electrolytic bath consists of zinc chloride as the metal source and ammonium chloride as the supporting electrolyte. the concentration of the supporting electrolyte is varied from zero until 4 m, while the concentration of zinc chloride is fixed at 2 m. the aim is to produce a porous zinc coating with an enhanced and intimate interfacial area per unit volume. these characteristics shall contribute towards reduced ohmic losses, improved active material utilization, and subsequently producing high rate capacity electrochemical cell. nitrogen physisorption at 77 k is used to measure the bet surface area and pore volume density of the zinc electrodeposits. the electrodeposited zinc electrodes are then fabricated into alkaline zinc-air microbattery measuring 1 cm 2 area x ca. 305 µ m thick. the use of inorganic mcm-41 membrane separator enables the fabrication of a compact cell design. the quality of the electrodeposited zinc electrodes is gauged directly from the electrochemical performance of zinc-air cell. zinc electrodeposits prepared from electrolytic bath of 2 m nh4cl produces the highest discharge capacity. abstrak: elektrod zink dengan kadar discas tinggi telah dihasilkan dengan proses saduran elektrokimia. takungan elektrolit terdiri daripada zink klorida sebagai sumber logam dan ammonium klorida sebagai elektrolit sokongan. kepekatan elektrolit sokongan diubah daripada sifar hingga 4 m, sementara kepekatan zink klorida ditetapkan pada 2 m. ini bertujuan untuk mendapatkan saduran zink yang poros dengan luas permukaan per unit isipadu dan sentuhan antaramuka yang dipertingkatkan. ciri-ciri ini akan menyumbang terhadap pengurangan kehilangan disebabkan kerintangan, pertambahan dalam gunapakai bahan aktif dan akhirnya menghasilkan sel elektrokimia berprestasi tinggi. physisorpsi nitrogen pada 77 k telah digunakan untuk mengukur luas permukaan bet dan isipadu liang saduran zink. saduran zink kemudiannya dijadikan elektrod bagi bateri mikro zink-udara beralkali dengan saiz 1 cm 2 luas x ca. 305 µm tebal. penggunaan membran tak organik mcm-41 membolehkan pembuatan sel dengan rekabentuk padat. kualiti elektrod saduran zink telah dinilai secara lansung daraipada prestasi elektrokimia sel zink-udara. saduran zink yang disediakan daripada takungan elektrolit 2 m nh4cl menghasilkan kapasiti discas tertinggi. keywords: zinc electrodeposition; high discharge rate electrode; mcm-41 separator; zinc-air cell; alkaline microbattery iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering nor hairin et al. 116 1. introduction electrodeposition is one of the most commonly practiced industrial techniques for the fabrication of zinc coatings [1-3]. it is an effective and fast technique to obtain a coating of desired material for a variety of applications. the thickness of the coating can easily be controlled and even the material properties can be pre-designed. thus, zinc electrodeposition has been extensively investigated under various operating conditions depending on the application considered or the aims chosen. variety of applications of zinc coating include as corrosion protective coating, to provide decorative surface layers for materials, to alter the technological properties of materials, and to reduce cost of materials [4-6]. in this work, zinc electrodeposits are prepared from an acidic chloride bath of various electrolytic formulations. the aim is to produce a porous zinc coating with an enhanced and intimate interfacial area per unit volume. these characteristics shall contribute towards reduced ohmic losses, improved active material utilization, and subsequently producing high rate capacity zinc anode for use in alkaline cell, in particular zinc-air microbattery. though there were numerous work done on properties of zinc coatings and mostly utilizing cyclic voltammetry as the main tool [7-9], our approach is to gauge the electrodeposited zinc anode directly from the performance of the electrochemical cell. 2. experimental 2.1 electrolytic cell and bath formulation a two-electrode configuration electrolytic cell was adopted for the electrodeposition process. the working electrode was zinc foil (99.9 %) and the counter electrode was copper foil. both electrodes were mounted on a home-made acrylic board clamp with an exposed square window (1 cm x 1 cm) for electrodeposition area. the electrode spacing was fixed at 30 mm. the bath formulation composed of zinc chloride (zncl2) as the metal source and ammonium chloride (nh4cl) as the supporting electrolyte. the concentration of the supporting electrolyte was varied from 1 to 4 m, while the concentration of zinc chloride was fixed at 2 m. total electrolyte volume was maintained at 80 ml. during electrodeposition no electrolyte agitation was attempted. electrodeposition was performed at a constant current of 0.1 a for duration of 1.5 hours. an ecochemie (the netherland) potentiostat/galvanostat (pgstat302n, autolab) was used. 2.2 physical characterization of zinc electrodeposits nitrogen physisorption gas chromatography was utilized to measure the bet surface area and pore volume density of the zinc electrodeposits. the sorption isotherms of nitrogen at 77 k were determined in a pressure range p/p 0 from 0.001 to slightly below 1.0. an autosorb-1 (quantachrome) instrumentation was used. 2.3 fabrication of zinc-air cell and electrochemical characterizations zinc electrodeposits prepared from all electrolytic bath formulations were used as the anode and assembled into zinc-air cell. compact, planar zinc foil was also utilized for reference purposes. a commercially available air electrode sheet was utilized as the cathode. the air electrode consisted of laminated fibrous carbon structure supported by a nickel mesh. the airside of the electrode is covered with semi permeable hydrophobic teflon membrane to permit air access. we employed inorganic mcm-41 membrane as the iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering nor hairin et al. 117 cell separator. it also served as the electrolyte reservoir due to its porous nature and hydrophilic property. mcm-41 membrane was applied onto the electrodeposited zinc anode by dip-coating technique. details on the membrane preparation and its properties can be referred to the work of saputra and co-workers [10]. the cell electrolyte was 6 m potassium hydroxide (koh). figure 1 illustrates the as-synthesized zinc-air cell structure and its dimensions. fig. 1: as-synthesized zinc-air cell structure. zinc-air cells utilizing the electrodeposited zinc anode were characterized according to the polarization profile, power density output and galvanostatic discharge performance. the aim was to evaluate directly various qualities of zinc electrodeposits from the electrochemical cell performance. 3. results and discussion table 1 highlights the results of the nitrogen physisorption measurement i.e. the bet surface area and pore volume density of the zinc electrodeposits. firstly, note that the deposition spot was 1 cm x 1 cm square area. thus considering 0.25 mm zinc foil used as the working electrode as an example, and considering zinc density of 7.14 g cm -3 , the apparent specific surface area of the zinc foil is 0.056 m 2 g -1 . by using electrodeposition method, the specific surface area of zinc coatings is now more than 300 m 2 g -1 which clearly demonstrates the advantage of electrodeposition method. electrolytic bath with 3 m nh4cl produced zinc electrodeposits with the highest specific surface area i.e. 379 m 2 g -1 . on the other hand, electrolytic bath formulation with 2 m-nh4cl produced the most porous zinc electrodeposits i.e. with pore volume density of 0.227 cm 3 g -1 which is equivalent to 62 % porosity. figure 2 illustrates the polarization profiles of zinc-air cell employing the electroplated zinc anode. the profile of zinc-air cell utilizing a compact, planar zinc foil as anode is also shown. cells employing electroplated zinc anode showed superior profiles, in particular the high discharge rate capability. using compact zinc foil, the limiting iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering nor hairin et al. 118 current of the cell was 13 ma and the value markedly increased to more than 50 ma (i.e. between 52 – 55 ma) when electroplated zinc anode was utilized. limiting current is the table 1: bet surface area and pore volume density of zinc electrodeposits as a function of nh4cl content. electrolytic bath composition bet surface area (m 2 /g) pore volume density (cm 3 /g) zncl2 (g/l) (2 m) nh4cl (g/l) molarity (m) 273.0 0 0 351.37 0.211 273.0 53.5 1 349.61 0.2216 273.0 107.0 2 350.69 0.2273 273.0 160.5 3 379.54 0.2215 273.0 214.0 4 331.93 0.2108 maximum discharge current that can be supplied by a cell prior to an abrupt voltage drop. for zinc-air cell the abrupt drop occurs when the operating voltage reaches the value around 0.8 –0.9 v. the highest limiting current obtained was from zinc electrodeposits of 3 m-nh4cl bath i.e. 55 ma. though the difference between the highest and lowest limiting current density value seems small, i.e. 3 ma, note that the cell size was 1 cm x 1 cm. if the apparent cell area is increased by ten times for example to 33 mm x 33 mm, then the anticipated difference of 30 ma would be quite substantial. figure 3 depicts the corresponding power output density plot of the cells obtained from polarization profiles of fig. 2. power output of the cell was measured from the product of discharge current and the subsequent operating voltage. by using electroplated zinc anode, the maximum power density output was enhanced from 13 mw cm -2 to 55 mw cm -2 , a fourfold increment. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering nor hairin et al. 119 fig. 2: polarization profiles of zinc-air cell. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering nor hairin et al. 120 fig. 3: power output density plot of zinc-air cell. figure 4 illustrates the discharge capacity performance of zinc-air cells utilizing electroplated zinc anode of various electrolytic formulation. the cells were rated at 20 ma of constant discharge load. cell employing compact zinc foil could not be discharged at 20 ma load, refer to fig. 2 of the polarization profile for cell using compact zinc foil as the anode. the discharge curves of fig. 4 denote the distinct profile of zinc-air cell; a flat discharge curve with an abrupt voltage drop at the end of discharge [11]. this is mainly attributed to the fact that as the electropositive oxygen reactant is not stored within the electrochemical system, the changes in the internal resistance of the cell is small thus producing a rather flat discharge profile [12]. the cell utilizing zinc electrodeposits of 2 m-nh4cl electrolytic bath produced the highest discharge capacity of 34.5 mah i.e. 2 hour 15 min discharge duration. fig. 4: discharge capacity of zinc-air cell employing electrodeposited zinc anode of various electrolytic bath formulations. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering nor hairin et al. 121 electrodeposition for all electrolytic bath formulations was performed at fixed charge quantity of 540 c. each bath formulation produced unique zinc electrodeposits as indicated by the nitrogen physisorption measurement (table 1). this is the key attribute of electrodeposition technique. table 2 highlights the zinc electrodeposits mass gain from each bath formulation. although the quantity of nh4cl supporting electrolyte was varied from zero until 4 m, the variation in the mass gain was not significant i.e. less than 1 %. yet, the effect of quality of electrodeposits on zinc-air cell discharge capacity in particular, was substantial as displayed in fig. 4. on the other hand, the variation in the limiting current was less prominent than the discharge capacity. table 2: zinc electrodeposits mass gain from all electrolytic bath formulations. bath composition nh4cl content (m) zinc electrodeposits mass gain (g) 0 0.1846 1 0.1837 2 0.1832 3 0.1848 4 0.1832 4. conclusion high surface area and porous zinc anode were prepared through electrodeposition from an acidic zncl2-nh4cl electrolytic bath formulation. the bet surface area of the electrodeposits was in excess of 330 m 2 g -1 and the electrode porosity was at least 60 %. zinc-air microbattery measured 1 cm 2 area x ca. 305 µ m thick, utilizing the electrodeposited zinc anode, was able to deliver a maximum limiting current density of 55 ma cm -2 . it produced an optimum discharge capacity of 34.5 mah rated at 20 ma. acknowledgement the international islamic university malaysia funded this project through the research matching grant scheme (rmgs 09-09). the authors gratefully acknowledge the financial support. references [1] c.n. panagopoulos, k.g. georgarakis and s. petroutzakou, “sliding wear behaviours of zinc-cobalt alloy electrodeposits”. j. mater. process. technol., 160, 234-244, 2006. [2] m. paunovic and m. schlesinger, fundamentals of electrochemical deposition, a wiley– interscience publication, new york (1998). [3] a. m. alfantazi and d.b. dreisinger, “the role of zinc and acid concentrations in the electrolyte on the zinc electrowinning from industrial sulfate-based electrolyte”, j. appl. electrochem., 31, 641-646, 2001. [4] r. ramanauskas, “structural factor in zn alloy electrodeposit corrosion”, appl. surf. sci.153 53-64, 1999. [5] kim, b.n. popov and k.s.chen, “synthesis and characterization of mno2 based mixed oxides as supercapacitors”, j. electrochem. soc., 150, 1505, 2003. [6] b. veeraraghavan, b. haran, s. prabu and b. popov, “corrosion protection of steel using non-anomalous ni-zn-p alloys”, j. elctrochem. soc., 150, b131, 2003. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering nor hairin et al. 122 [7] c. chi-chung hu and c. yuan chang, “anodic stripping of zinc deposits for aqueous batteries: effects of anions, additives, current densities, and plating modes”, mater. chem. phys., 86, 195-203, 2004. [8] i. zouari and f. lapicque, “an electrochemical study of zinc deposition in a sulfate medium”, electrochim. acta, 37, 439-446, 1992. [9] southampton electrochemistry group, instrumental methods in electrochemistry, ellis horwood ltd., england (1993) pg.178. [10] h. saputra, r. othman, a.g.e. sutjipto and r. muhida, “mcm-41 as a new separator material for electrochemical cell: application in zinc–air system”, j. mem. sci., 367, 152157, 2011. [11] r. othman, a.h. yahaya and a.k. arof, “zinc-air cell employing porous zinc electrode fabricated from zinc-graphite-natural biodegradable polymer paste”, j. applied electrochem, no 32, 1347-1353, 2002. [12] s.f. bender, j. w. cretzmeyer and t.f. reise in: handbook of batteries, linden (editor) 2nd ed., mcgraw-hill, inc (1995). application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 mechanical and thermal conductive properties of natural and synthetic cellulose reinforced epoxy composites omran a. shabeeb1, dawood s. mahjoob2, hamid m. mahan2 and muammel m. hanon2,3* 1 middle technical university, electrical engineering technical college, 10022 baghdad, iraq. 2 middle technical university, baqubah technical institute, 32001 diyala, iraq. 3 mechanical engineering doctoral school, szent istván campus, mate university, 2100 gödöllő, hungary. * corresponding author: sharba.muammel.m.hanon@phd.uni-szie.hu (received: 11th september 2021; accepted: 24th november 2021; published on-line: 4th july 2022) abstract: natural and synthetic cellulose-based composites have been used widely as they have many advantages, the most significant of which are lightweight, durable, strong, flexible, and resistant to corrosion. although several studies have reviewed the characteristics of these composites, only limited research has investigated combining both natural and synthetic cellulose together. in this study, the thermal and mechanical properties of epoxy resin reinforced with different additives (sawdust and industrial cellulose) will be explored. to do this, four samples of different materials were prepared at room temperature. the first sample consisted of 100% epoxy, whilst the next sample contained 95 wt.% epoxy and 5 wt.% industrial cellulose. the third sample contained 95 wt.% epoxy and 5 wt.% natural cellulose (sawdust), and the final sample contained 95 wt.% epoxy, 2.5 wt.% natural cellulose and 2.5 wt.% industrial cellulose. the findings indicated that mechanical properties and thermal insulation can be enhanced by adding natural cellulose to the mixture. compared to the pristine epoxy, the improvement ratios for mechanical properties were as follows: tensile strength 25%, impact strength 16.6%, and hardness 6.9%, while the results were negative for bending resistance (3.9% less). in terms of thermal properties, the sawdust/epoxy composite showed better insulation (29% higher) than neat epoxy resin. these promising findings suggest the proposed composite can be a good alternative in numerous applications such as automotive parts and building construction that require superior mechanical characteristics and thermal insulation. abstrak: komposit semula jadi dan sintetik berasaskan selulosa telah banyak digunakan secara meluas kerana ia mempunyai banyak faedah, dan yang paling penting ianya ringan, tahan lama, kuat, fleksibel dan tahan hakisan. walaupun terdapat banyak kajian telah dilakukan pada ciri-ciri yang terdapat pada bahan komposit ini, terdapat kurang kajian dilakukan ke atas gabungan bersama kedua-dua bahan semua jadi dan sintetik selulosa. kajian ini adalah tentang suhu dan ciri-ciri mekanikal damar epoksi yang diperkukuhkan dengan pelbagai bahan tambahan seperti serbuk gergaji dan selulosa industri. bagi menghasilkan bahan kajian ini, empat sampel dari bahan berbeza disediakan pada suhu bilik. sampel pertama terdiri daripada epoksi 100%, sementara sampel berikutnya mengandungi epoksi 95 wt.% dan selulosa industri sebanyak 5 wt.%. sampel ketiga mengandungi epoksi 95 wt.% dan 5 wt.% selulosa semula jadi (dari serbuk gergaji), dan sampel terakhir mengandungi epoksi 95 wt.%, dan selulosa semula jadi 2.5 wt.% dan selulosa industri 2.5 wt.%. dapatan kajian menunjukkan ciri-ciri mekanikal dan penebat suhu boleh dipertingkatkan dengan menambah selulosa semula jadi dalam campuran. jika dibandingkan dengan epoksi asal, nisbah penambah baikan bagi ciri-ciri mekanikal adalah 193 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 seperti berikut: kekuatan tegangan 25%, kekuatan hentaman 16.6% dan kekerasan adalah sebanyak 6.9%, sementara dapatan kajian adalah negatif bagi rintangan ketika membengkok (iaitu berkurang sebanyak 3.9%). dari segi ciri-ciri haba, komposit serbuk gergaji/epoksi menunjukkan sebagai penebat yang baik (meningkat 29%) berbanding damar epoksi bersih. penemuan yang bagus ini menunjukkan, komposit yang di cadangkan ini dapat menjadi alternatif terbaik dalam pelbagai kegunaan seperti bahagian-bahagian automotif dan pembinaan bangunan yang memerlukan peningkatan ciri-ciri mekanikal dan penebat haba. keywords: natural composites; sawdust; mechanical properties; thermal conductivity; cellulose 1. introduction environmental awareness has led researchers to reconsider the design of engineering products for the construction, packaging, future, and vehicle industries. polymer elements have become favorable parts for numerous applications due to their excellent characteristics [1]. in recent times, increasing attention has been paid to the use of a modified thermoset polymer [2]. epoxy resins are polymeric or semi-polymeric materials that are part of the thermosets group and are widely used in composite materials [3]. moreover, epoxy resin has become more popular than alternative products due to its beneficial properties, such as high chemical, thermal, electrical, and mechanical strength [4]. multiple materials can be mixed to create a composite substance that has a unique combination of properties [5]. epoxy resin modification is thus an innovative approach to polymer material production [6]. this material can be used to support other materials, which has enabled many workers to improve their properties in this field and to accomplish desired targets [7–9]. recently, polymers have been reinforced with small amounts of strong fillers, as this can substantially enhance the mechanical and thermal properties [10–14]. it is thus sensible to seek other economically friendly raw materials (fillers) that could strengthen the properties of such products [15]. modified epoxy resins are often used nowadays because they have great thermal, mechanical, and electrical properties when used to manufacture natural fiber-reinforced composites [16]. as they are environmentally safe and userfriendly, natural fibers are one of the most important components added to epoxy resin [17]. unlike normal engineering fibers (such as glass, aramid, or carbon), natural fibers are widely usable, sustainable, recyclable, and cost-effective sources of fibers [18]. natural materials, when compared to man-made materials, can provide a good combination of favorable properties, such as rigidity, strength, and low weight [19]. natural fibers are also less harmful to the environment than synthetic fibers. natural fibers are less erosive, which means that as they wear off, the devices' performance may not be affected, and they have a more hospitable manufacturing environment than synthetic fibers [20–22]. studies exploring the topic demonstrate that sawdust can be added to polymer matrices from various sources, including trees, cellulosic powders, microcrystalline cellulose, natural fibers, and other waste materials produced during woodworking and food processing [23]. composite materials are made up of two or more materials that have completely separate characteristics and do not dissolve or mix with one another [24]. by combining precise amounts of materials with inherited properties, new materials with modified and better properties can be created [25]. a chunk of wood is made up of long cellulose fibers that are held together by a chemical called lignin [26]. the overlapping materials are lightweight and provide excellent thermal and electrical insulation. thus, in recent years, they have become increasingly more popular in various fields [27,28]. natural fiber 194 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 insulation is arguably the most practical way to produce environmentally friendly composites. numerous studies have investigated natural fiber-reinforced composites. in recent years, polymer composites have been studied in great depth [29,30] and sawdust has been found to serve as an insulator, slowing heat flow and conduction. this ultimately enhances its capacity to isolate [31]. it has recently been discovered that, by adding a small quantity of strong fillers to polymers, the mechanical and thermal performance of the composites can be significantly improved [32]. given their great insulation capacity, these composites can be applied for a variety of purposes. for instance, they can be used to fill the spaces between the interior and exterior sections of walls, or the floor, roof, ceiling, or insulation boards. moreover, they can be used to manufacture aircraft and automobile parts and furniture. they are thus beneficial in many industries, including transport and even medicine [33]. plenty of materials (natural and synthetic) have been investigated as reinforcements for polymer composites, as shown by the literature reviewed above. however, the additives utilized to form composites have not yet been fully covered, and there is still much to explore. combining both natural and synthetic cellulose together in one composite was rarely inspected. therefore, the present study aims to determine the effect of various combinations of additives, which are made from natural cellulose (sawdust) and industrial cellulose, on the mechanical properties (through tensile, flexural, impact, and hardness tests) and the thermal conductivity of composites, where epoxy is the matrix material. to the best of our knowledge, the combinations of additives utilized here have never been studied before. 2. experimental work 2.1 material properties epoxy resin (er) was used as a matrix material for the composites prepared. epoxy is created by combining the liquid resin and an appropriate hardener. the ratio for resin to hardener is typically 2 to1, which enables the substance to cure perfectly. the epoxy resin used in this study was obtained from sky bahrain and contained the sikadur-52 hardener. the specifications of the epoxy, as per the manufacturer, are presented in table 1. table 1: specifications of epoxy resin used in the study tensile strength (mpa) modulus of elasticity (mpa) percent elongation (%) density (g/cm3) water absorption (%) shear strength (mpa) flexural strength (mpa) 37 1800 7 1.1 1.5 29.6 63 industrial cellulose (ic), which is made up of carbon, oxygen, and hydrogen, is a very intricate carbohydrate. properties of cellulose – [(c6h10o5)n]: many properties are determined by the extent of polymerization, the chain length, and the number of glucose molecules that make up the polymer molecule. cellulose is tasteless, odorless, and chiral, as well as being both insoluble and biodegradable, and appears in the form of white powder. the physical, mechanical, and thermal properties of the industrial cellulose are tabulated in table 2. 195 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 table 2: specifications of industrial cellulose tensile strength (mpa) modulus of elasticity (mpa) percent elongation (%) density (g/cm3) water absorption (%) flexural strength (mpa) thermal conductivity (w/m-k) specific heat capacity (j/g.ºc) 22.1 – 41.4 1005 – 1850 3.7 – 25 1.17 – 1.21 1.3 –1.8 29 – 55.8 0.17 – 0.33 1.26 – 1.67 the natural cellulose (nc) used is sawdust that is produced during the process of sawing wood (type jam wood). this sawdust was collected from the carpentry workshop of the baquba technical institute, middle technical university, iraq. it was then sifted using a sieve with apertures of 50 μm to obtain very fine particles (see fig. 1a). fig. 1: (a) physical appearance of natural cellulose (sawdust), (b) digital electric laboratory mixer, and (c) physical appearance of specimens (type er+nc) after testing. 2.2 preparing the polymer composite four square glass molds measuring (130 mm * 130 mm * 5 mm) were used in this experiment. to create casting samples, four polymeric compounds were prepared. these were made up of a base material epoxy resin mixed with a hardener at a mixing ratio (2:1). once mixed, additives from industrial and natural cellulose were added to the composites for reinforcement (proportions presented in table 3). the mixing process was carried out utilizing a digital electric laboratory mixer (see fig. 1b) at room temperature and lasted 15 minutes. subsequently, samples were left for a day and then placed in an oven for 5 hours (a) (b) (c) 196 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 at 60 °c. the primary reason for doing this was to eliminate internal stresses, tangle the chains in the mixture and harden and depressurize the sample [34]. table 3: designation and composition of composites sample no. reinforcement % cellulose (c) epoxy (e) sawdust (n) er 100 er+ic 5 95 er+nc 95 5 er+nc+ic 2.5 95 2.5 2.3 testing physical (thermal conductivity and hardness) and mechanical (tensile, bending, and impact) properties tests were performed on the polymeric compound samples. all experiments were carried out at room temperature, in accordance with american standards (astm). a cnc router machine was used to cut three samples of each polymeric compound to the required dimensions. the physical appearance of specimens (of one composite) is shown in fig. 1c. regarding the physical properties’ testing, lee's disc (type griffin and george, england) was used to assess the thermal conductivity of the samples as per astm-d7340. the sample (disc) was sandwiched between the discs of the test setup. the heater was turned on, and the thermostat was adjusted to the desired temperature. in essence, thermal conductivity refers to a material's resistance to thermal transfer, which reflects the amount of heat that flows through it directly or indirectly. for each polymeric composition, three samples were tested for thermal conductivity. the sample's hardness was determined according to the astm d2240 using a durometer hardness tester (also known as the shore d hardness tester) due to the low hardness of the polymeric compounds. when the indenter is forced into the testing material, the amount of resistance is measured and shown on a digital screen (scale). the key reason for performing the hardness test is to determine whether the material is suitable for use under specific conditions. for each polymeric compound, the hardness test was performed on three samples, during which the average readings for each sample were taken. in terms of the testing of the mechanical characteristics, the sample tensile tests were carried out at room temperature using the universal testing equipment (see fig. 2a) in accordance with astm d638-type 1. thus, a 5 mm/min crosshead speed was used. for each polymeric compound, the tensile test was carried out on three samples, and, during the process, the average results were recorded. during the tensile test, specimens were tightened adequately to avoid sliding. the flexural test of the samples was done in accordance with (astm-d790) and was measured using the universal hydraulic press, as the experimental setup seen in fig. 2b. the two supports grip the specimen firmly, and the span length between them is 65 mm. the samples were tested with a loading rate of 2 mm/min. the flexural strength values are determined by the average of three bending tests. as illustrated in fig. 2c, a charpy impact test was performed in accordance with astm-e23 to evaluate the impact strength of the developed composites. a pendulum was used to break the unnotched specimen, with the test piece held tightly at each end. it is very important to perform a mechanical shock test to ensure that a material is safe. in this test, the extent to which a material is resistant to sudden shocks is evaluated. all specimens’ dimensions used in the tests are shown in fig. 3. 197 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 fig. 2: experimental setup of mechanical tests (a) tensile, (b) flexural, and (c) impact. thermal conductivity test specimen (astm-d7340) hardness test specimen (astm-d2240) tensile test specimen (astm-d638, tape 1) bending test specimen (astm-d790) impact test specimen (astm-e23) fig. 3: sample’s dimensions of physical and mechanical properties tests. 3. results and discussion 3.1 physical properties: thermal conductivity the conductivity can be influenced by the existence of interfacial layers, free volume, and gaps or cracks within the inner structure. when fillers are loaded as particles during the sample's preparation, they might generate gaps because air voids (created while mixing) are loading pin (a) (b) (c) supports force specimen pendulum 198 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 unable to escape due to the particles. therefore, all specimens containing particles were found to reduce the thermal conductivity of composites as compared to the pristine epoxy. as wood is a heat-insulating material, the sample with the polymeric compound (er+nc) had the lowest thermal conduction efficiency (see fig. 4) and hence provided the best thermal insulation. when compared to the epoxy resin specimen (the reference specimen), the improvement rate was 29%. this indicates that the presence of wood contributed to reducing the thermal conductivity of composites due to owning less thermal conductivity than epoxy as well as being in a form of particles within the matrix. the tendency of the results obtained agrees with the findings of a previous study [35]. they reported that adding 10 wt.% of wood dust to a composite reduces the composite's heat conductivity by around 67.1% compared to the neat epoxy resin. fig. 4: relationship between thermal conductivity and the proportions of additives to epoxy. 3.2 physical properties: hardness (shore d) figure 5 shows that the epoxy sample (er+nc) reinforced with natural cellulose (sawdust) has the best hardness. this is because the natural cellulose particles in the composite are arranged in a uniform pattern. this strengthens the bonds in the polymeric chain. this is because adding natural cellulose to the compound impedes cracks formation during the preparation, which increases the bonding of the atoms, and thus increases the hardness value. fig. 5: relationship between hardness and the proportions of additives to epoxy resin. these findings suggest that indentation can be avoided through strong bonding. thus, the improvement rate for this (er+nc) sample was 6.9% higher than the reference sample. on the other hand, the hardness of the (er+ic) was reduced by 6.1%. according to homkhiew et al. [36], the shore d hardness of composites (rubberwood sawdust reinforced 199 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 thermoplastic natural rubber) increases as the amount of wood sawdust increased. they attributed this to the fact that wood sawdust has a far greater hardness than the matrix material (thermoplastic elastomer), and that adding wood particles reduces the elasticity or flexibility of polymer chains, which results in stiffer composites. this is in good agreement with the outcomes of the current study. 3.3 mechanical properties: tensile strength the best tensile strength was identified (see fig. 6) in the polymeric compound sample that was reinforced with natural cellulose (er+nc) and this is due to the fact that the particles in sawdust join the fibers and strengthen the bonds between atoms. this is because sawdust, when loaded, serves as a barrier to interference movement inside the base material, decreasing the chance of plastic deformation [37]. as a result of this strong adhesive property, an improvement rate of 25% was achieved in comparison to the epoxy resin reference sample. however, the tensile strength of the (er+ic) sample was found to be nearly 20% worse. according to kumar et al. [38], wood dust (as filler) has good characteristics because it improves the mechanical properties of the polymeric resin. they stated that 10 wt.% fill provides the best tensile properties. fig. 6: relationship between tensile strength and the proportions of additives to epoxy resin. 3.4 mechanical properties: flexural strength the flexural strength of materials was measured in order to determine their capacity to withstand bending forces. the test results for the four samples revealed that the sample (er+ic) prepared with industrial cellulose was the least resistant (36.4% lower) in comparison to the pure epoxy resin reference sample. however, as fig. 7 shows, the sample (er+nc) containing natural cellulose (sawdust) produced essentially identical results to the epoxy resin samples. this means that, even after the additive materials were added, there was no improvement in flexural strength. this can be ascribed to a lack of adhesion at the filler/matrix contact. furthermore, as the particle-matrix interface is stressed, the number of microcracks increases, causing the crack to widen and fracture to occur. as a result, adding sawdust to the polymer matrix did not result in an improvement in flexural strength. other researchers have disclosed similar outcomes [35]. 200 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 fig. 7: relationship between flexural strength and the proportions of additives to epoxy. 3.5 mechanical properties: impact strength the findings are presented in fig. 8. it is evident that the polymeric compound sample (er+nc) reinforced with natural cellulose (sawdust) demonstrated the best impact strength. this is owing to the robust cohesion that exists between the sawdust and the epoxy. as a consequence, sawdust particles increase the amount of energy needed to break the sample. this energy is defined by the interface bonding's strength between the reinforcing materials' surfaces and the polymeric mix composite material's components [39]. thus, a 16.6% improvement was achieved in this sample compared to the reference sample. on the other hand, the impact strength of the (er+ic) sample was found to be reduced by 16.2%, whilst that of the (er+nc+ic) sample was reduced by 2%. fig. 8: relationship between impact strength and the proportions of additives to epoxy. 4. conclusions based on the experiments carried out in this study, the following conclusions have been made. 1physical properties: • the thermal conductivity tests revealed that the polymeric sample with the best thermal insulation was the (er+nc) sample containing 95% epoxy and 5% sawdust. this sample was found to be 29% more effective than the pure epoxy reference sample (er). 201 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 • sawdust was found to be most effective in the hardness tests. this was evident from the polymeric compound (er+nc) sample which had the best hardness test results with an improvement rate of 69%. 2mechanical properties • the findings of the tensile test also favored the (er+nc) polymeric sample, as it showed the highest tensile strength with an improvement rate of 25%. • the (er+ic) sample was found to have the lowest bending strength in the bending test (which was 36.4% lower than the reference test), whereas the polymeric compound (er+nc) sample seemed to have a bending resistance similar to that of the pure epoxy resin (er) sample. • the findings of the impact test also showed that the sample containing epoxy and sawdust had the highest impact strength and was 16.6% better than the reference sample. moreover, the findings of this work indicate that sawdust can be employed as a costeffective and environmentally friendly reinforcer in polymeric compounds. this could be beneficial to many industries. moreover, different types of wood and mixing ratios can be employed to achieve optimal mechanical and thermal properties. acknowledgements the researchers extend their sincerest gratitude to the staff of electrical engineering technical college and baqubah technical institute / middle technical university (mtu) in baghdad, iraq, as well as the materials engineering department at the university of technology in baghdad, iraq. references [1] hanon mm, marczis r, zsidai l. (2020) impact of 3d-printing structure on the tribological properties of polymers. ind lubr tribol, 72(6): 811-818. https://doi.org/10.1108/ilt-052019-0189 [2] abdellaoui h, bensalah h, echaabi j, bouhfid r, qaiss a. (2015) fabrication, characterization and modelling of laminated composites based on woven jute fibres reinforced epoxy resin. mater des, 68: 104-113. https://doi.org/10.1016/j.matdes.2014.11.059 [3] bello sa, agunsoye jo, hassan sb, kana mgz, raheem ia. (2015) epoxy resin based composites, mechanical and tribological properties: a review. tribol ind, 37(4): 500-524. [4] paluvai nr, mohanty s, nayak sk. (2014) synthesis and modifications of epoxy resins and their composites: a review. polym plast technol eng, 53(16): 1723-1758. https://doi.org/10.1080/03602559.2014.919658 [5] verma d, gope pc, shandilya a, gupta a, maheshwari mk. (2013) coir fibre reinforcement and application in polymer composites: a review. j mater environ sci, 4(2): 263-276. [6] bismarck a, baltazar-y-jimenez a, sarikakis k. (2006) green composites as panacea? socio-economic aspects of green materials. environ dev sustain, 8(3): 445-463. https://doi.org/10.1007/s10668-005-8506-5 [7] müller k, bugnicourt e, latorre m, jorda m, sanz ye, lagaron jm, miesbauer o, bianchin a, hankin s, bölz u, pérez g, jesdinszki m, lindner m, scheuerer z, castelló s, schmid m. (2017) review on the processing and properties of polymer nanocomposites and nanocoatings and their applications in the packaging, automotive and solar energy fields. nanomaterials, 7(4): 74. https://doi.org/10.3390/nano7040074 [8] akter t. (2006) manufacturing of biocomposite shell mimetic via the powder compaction method. 202 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 [9] khoee s, hassani n. (2010) adhesion strength improvement of epoxy resin reinforced with nanoelastomeric copolymer. mater sci eng a, 527(24-25): 6562-6567. https://doi.org/10.1016/j.msea.2010.07.013 [10] qi s, li c, huang y. (2006) preparation of sic hybrid phenolic resin composites. in: aiaa 57th int. astronaut. congr. iac 2006. pp 5237-5240 [11] hanon mm, alshammas y, zsidai l. (2020) effect of print orientation and bronze existence on tribological and mechanical properties of 3d-printed bronze/pla composite. int j adv manuf technol, 108(1-2): 553-570. https://doi.org/10.1007/s00170-020-05391-x [12] mahan hm, mahjoob d, mahmood ki. (2018) mechanical properties of alumina nanoparticles and glass fiber, kevlar fiber reinforced composites. j eng appl sci, 13(21): 90969100. https://doi.org/10.3923/jeasci.2018.9096.9100 [13] ismail m, rejab mrm, siregar jp, mohamad z, quanjin m, mohammed aa. (2020) mechanical properties of hybrid glass fiber/rice husk reinforced polymer composite. mater today proc, 27: 1749-1755. https://doi.org/10.1016/j.matpr.2020.03.660 [14] ismail m, rejab mrm, siregar jp, muhamad z, quanjin m. (2020) tensile properties of hybrid woven glass fibre/palf reinforced polymer composite. in: proc. 4th int. manuf. eng. conf. 5th asia pacific conf. manuf. syst. (imec-apcoms 2019). springer-singapore, putrajaya, malaysia, pp 448-454 [15] chen h, ginzburg vv, yang j, yang y, liu w, huang y, du l, chen b. (2016) thermal conductivity of polymer-based composites: fundamentals and applications. prog polym sci, 59: 41-85. https://doi.org/10.1016/j.progpolymsci.2016.03.001 [16] abdul-hussein ab. (2019) effect of industrial powder on mechanical properties of glass fiber reinforced epoxy composite. iraqi j phys, 12(25): 8-24. https://doi.org/10.30723/ijp.v12i25.300 [17] kumar ss. (2020) effect of natural fiber loading on mechanical properties and thermal characteristics of hybrid polyester composites for industrial and construction fields. fibers polym, 21(7): 1508-1514. https://doi.org/10.1007/s12221-020-9853-4 [18] girijappa ygt, rangappa sm, parameswaranpillai j, siengchin s. (2019) natural fibers as sustainable and renewable resource for development of eco-friendly composites: a comprehensive review. front mater, 6: 226. https://doi.org/10.3389/fmats.2019.00226 [19] xiao m, feng b, gong k. (2002) preparation and performance of shape stabilized phase change thermal storage materials with high thermal conductivity. energy convers manag, 43(1): 103-108. https://doi.org/10.1016/s0196-8904(01)00010-3 [20] chandramohan d, marimuthu. (2011) a review on natural fibers. int j res rev appl sci, 8(2): 194-206. [21] chand n, fahim m. (2008) tribology of natural fiber polymer composites. cambridge, england, woodhead publishing ltd, elsevier. https://doi: 10.1533/9781845695057 [22] hameed is, mahan hm, hameed as. (2020) microwave power absorption evaluation of river shell particles reinforced polyester composite. period polytech electr eng comput sci, 64(2): 192-199. https://doi.org/10.3311/ppee.14263 [23] mohan n, senthil p, vinodh s, jayanth n. (2017) a review on composite materials and process parameters optimisation for the fused deposition modelling process. virtual phys prototyp, 12(1): 47-59. https://doi.org/10.1080/17452759.2016.1274490 [24] swain ptr. (2013) physical and mechanical behavior of al2o3 filled jute fiber reinforced epoxy composites. int j curr eng technol, 2(2): 67-71. https://doi.org/10.14741/ijcet/spl.2.2014.13 [25] deng s, zhang j, ye l, wu j. (2008) toughening epoxies with halloysite nanotubes. polymer (guildf), 49(23): 5119-5127. https://doi.org/10.1016/j.polymer.2008.09.027 [26] waliszewska b, mleczek m, zborowska m, goliński p, rutkowski p, szentner k. (2019) changes in the chemical composition and the structure of cellulose and lignin in elm wood exposed to various forms of arsenic. cellulose, 26(10): 6303-6315. https://doi.org/10.1007/s10570-019-02511-z [27] tanaka t, montanari gc, mülhaupt r. (2004) polymer nanocomposites as dielectrics and electrical insulationperspectives for processing technologies, material characterization and future applications. ieee trans dielectr electr insul, 11(5): 763-784. 203 iium engineering journal, vol. 23, no. 2, 2022 shabeeb et al. https://doi.org/10.31436/iiumej.v23i2.2182 https://doi.org/10.1109/tdei.2004.1349782 [28] shaari n, jumahat a, yahya kh, sulaiman mf. (2014) impact resistance of woven fiber reinforced polymer composites. adv environ biol, 8(3): 2662-2668. [29] cicala g, cristaldi g, recca g, latteri a. (2010) composites based on natural fibre fabrics. woven fabr eng, 17:317–342. https://doi.org/10.5772/10465 [30] peças p, carvalho h, salman h, leite m. (2018) natural fibre composites and their applications: a review. j compos sci, 2(4): 66. https://doi.org/10.3390/jcs2040066 [31] surin vg, mogilevskii bm, chudnovskii af. (1972) effect of additives on the thermal conductivity of cyclohexane. j eng phys, 23(1): 904-905. https://doi.org/10.1007/bf00826269 [32] abenojar j, tutor j, ballesteros y, del real jc, martínez ma. (2017) erosion-wear, mechanical and thermal properties of silica filled epoxy nanocomposites. compos part b eng, 120: 42-53. https://doi.org/10.1016/j.compositesb.2017.03.047 [33] yin j, li g, he w, huang j, xu m. (2011) hydrothermal decomposition of brominated epoxy resin in waste printed circuit boards. j anal appl pyrolysis, 92(1): 131-136. https://doi.org/10.1016/j.jaap.2011.05.005 [34] mahan hm, farhan mm, shaalan tg. (2019) studying some mechanical properties of river shell particle polymer matrix composite. j southwest jiaotong univ. doi: 10.35741/issn.02582724.54.4.17 [35] al-shabander bm. (2013) investigation of flexural properties and thermal conductivity for wood dust filled epoxy. j al-nahrain univ sci, 16(3): 104-109. https://doi.org/10.22401/jnus.16.3.14 [36] homkhiew c, rawangwong s, boonchouytan w, thongruang w, ratanawilai t. (2018) composites from thermoplastic natural rubber reinforced rubberwood sawdust: effects of sawdust size and content on thermal, physical, and mechanical properties. int j polym sci, 2018: 1-11. https://doi.org/10.1155/2018/7179527 [37] hosseinizand h, sokhansanj s, lim cj. (2018) co-pelletization of microalgae chlorella vulgaris and pine sawdust to produce solid fuels. fuel process technol, 177: 129-139. https://doi.org/10.1016/j.fuproc.2018.04.015 [38] kumar r, kumar k, sahoo p, bhowmik s. (2014) study of mechanical properties of wood dust reinforced epoxy composite. procedia mater sci, 6: 551-556. https://doi.org/10.1016/j.mspro.2014.07.070 [39] dinesh s, kumaran p, mohanamurugan s, vijay r, singaravelu dl, vinod a, sanjay mr, siengchin s, bhat ks. (2020) influence of wood dust fillers on the mechanical, thermal, water absorption and biodegradation characteristics of jute fiber epoxy composites. j polym res, 27(1): 9. https://doi.org/10.1007/s10965-019-1975-2 204 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 10 synthetic antimicrobial agent and antimicrobial fabrics: progress and challenges norashikin mat zain1*, john olabode akindoyo1,2 and mohammad dalour hossen beg1 1 faculty of chemical and natural resources engineering, universiti malaysia pahang, lebuhraya tun razak 26300 gambang kuantan, pahang, malaysia. 2 school of materials & mineral resources engineering,engineering campus, universiti sains malaysia,14300 nibong tebal, pulau pinang, malaysia. * corresponding author: shikin@ump.edu.my (received: 26th april 2018; accepted: 25th sept 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19i2.929 abstract: recently, there is a strengthening requirement for antimicrobial fabrics that are resistant to pathogens, offer greater hygiene, and are protective in an active lifestyle. synthetic compounds have been applied to impart antimicrobial properties to the fabrics. in this paper, synthetic antimicrobial agents, namely quaternary ammonium compounds (qacs), polyhexamethylene biguanide (phmb), triclosan, and n-halamine are discussed along with their mechanisms of action. research has been done on synthetic antimicrobial treatment of fabrics; the tested microorganisms used to determine their efficiency and durability are summarized. it is also found that although synthetic antimicrobial agents have excellent strength to kill the microorganisms, some of these antimicrobial agents are harmful and have adverse effects on the environment, safety, and health. identification of these problems will provide future challenges to overcome and improve the techniques used for antimicrobial treatment of the fabrics. based on the infromation presented herein, it is recommended that subsequent studies should consider the use of antimicrobial agents that are either obtained from plant sources or from microorganisms. on the other hand, nanotechnlogy should be explored for production of antimicrobial agents in further studies based on its potential to facilitate the production of environmentally benign antimicrobial agents. abstrak: kebelakangan ini, permintaan terhadap fabrik antimikrobial bagi mencegah jangkitan patogen, penjagaan kebersihan dan perlindungan bagi gaya hidup yang aktif semakin meningkat. sebatian sintetik telah diguna pakai bagi menambah sifat antimikrobial pada fabrik. di dalam artikel ini, agen antimikrob sintetik yang dinamakan sebagai sebatian ammonium kuater (qac), polyhexamethylene biguanide (phmb), triclosan dan n-halamine serta mekanisma tindak balasnya telah dibincangkan. penyelidikan telah dijalankan terhadap fabrik yang dirawat menggunakan agen antimikrob sintetik. mikroorganisma yang digunakan bagi menentukan kecekapan dan daya tahan turut diringkaskan. keputusan menunjukkan agen antimikrobial sintetik mempunyai tindak balas yang sangat baik untuk membunuh mikroorganisma, namun sebahagian agen antimikrobial ini berbahaya dan mempunyai kesan buruk terhadap alam sekitar, keselamatan dan kesihatan. melalui kaedah kenal pasti masalah, ia dapat memberi solusi dan membaiki teknik rawatan antimikrobial pada fabrik pada masa iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 11 hadapan. hasil keputusan dan perbincangan menunjukkan kajian seterusnya harus menimbang penggunaan agen antimikrobial yang diperoleh dari sumber tumbuhan. selain itu, nanoteknologi harus diterokai bagi pengeluaran agen antimikrobial berdasarkan potensinya yang mesra alam. keywords: antimicrobial; fabrics; microorganisms; efficiency; synthetic antimicrobial agent 1. introduction the use of antimicrobial agents on fabrics dates back to ancient times when the egyptians used spices and herbs to preserve mummy wrappings [1]. the first antimicrobial fabric was developed by lister in 1867 [2]. today there is global suffering due to some serious illnesses caused by harmful microorganisms [3]. interestingly, antimicrobial fabrics have been used in different applications such as pharmaceutical, medical, engineering, agricultural, and food industries [4]. besides that, consumers’ attitude towards hygiene and active lifestyle has created a rapidly increasing demand for a wide use of antimicrobial fabrics [5]. it is well known that fabrics in contact with infected skin can serve as a carrier for fungi and bacteria, thereby facilitating their propagation. therefore, there is the need for fabrics with potent antimicrobial properties. in essence, explorations of antimicrobial fabrics for their antibacterial and antifungal activities are required to assess the clinical potential of fabrics for odor, skin problem prevention and to avoid microorganisms’ cross contamination [6]. so, there is a growing worldwide interest in the use of antimicrobial fabrics [7,8]. this would help to curtail the challenges hitherto associated with spread and propagation of microorganisms through fabrics. a microorganism is an organism that is microscopic and which can only be seen under a microscope [9]. a right temperature, moisture, dust, and receptive surface offer perfect environments for microorganism growth on fabric surface [10]. in good conditions, bacteria and fungi can propagate within a very short time. these microorganisms can obtain sufficient food through perspiration and other body secretions, skin particles, and fats [11]. although microorganisms can be beneficial in some ways, they can also be seriously unsafe to both fabrics and humans. in fact, it has been observed that the microorganisms that may be found on fabrics can become disease causatives to those wearing such fabrics. they can also lead to decay of fabric quality; for example, bacteria such as staphylococcus aureus on the underwear causes odour, escherichia coli causes odour and ulcers on the skin, and fungi such as aspergillus niger weakens and decolorizes clothing [12]. trouser legs and pockets can habour bacillus, staphylococcus epidermis and micrococcus. clothing in the inguinal and perineal areas soiled by urine often stimulates the growth of brevibacterium ammoniagenes, e. coli, and proteus mirabilis, causing diaper rash and infections [13]. it is noteworthy that these pathogens cannot be eliminated by simple laundering. reportedly, fungi, trychophyton rubrum, which is the causal organism of athlete´s foot, survives laundering at low temperatures around 30 °c and after washing, it was found that this fungi had spread to the other fabrics [14]. other potential adverse effects of microorganisms on fabrics include the possible loss of functional properties like elasticity and tensile strength as well as deterioration of the fabrics, especially cotton and wool [15]. deterioration of fabrics is usually caused by filamentous fungi, with only a few being caused by bacteria. these microorganisms can cause several problems to humans, from unpleasant odor to physical irritation, allergy, toxic responses, infection, and iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 12 dangerous diseases [11]. considering these undesirable phenomenon, scientists continue to search for antimicrobial agents that can help to mitigate the problems [9]. the effectiveness of fabrics to destroy microorganisms is determined based on the antibacterial or antifungal activity by measuring the colonies of the microorganisms before and after the treatment. durability of the fabrics will be tested by measuring the antibacterial or antifungal activities against repeated laundering. it is usually challenging work to obtain fabrics that have both high antibacterial/antifungal activity as well as high durability to laundering. this is coupled with the fact that environmental, health, and safety aspects of the use of antimicrobial agents must be considered [4,16]. in fact, the use of some antimicrobial agents has been discontinued because of their harmful effects to the human body and the environment [17,18]. to date, a number of synthetic chemicals have been applied to impart antimicrobial properties unto the fabrics. almost all synthetic antimicrobial agents used on fabrics are biocides [4]. to the best of the authors’ knowledge, there is no summarized report on the beneficial and adverse effect of synthetic antimicrobial agents on fabrics. therefore, this paper presents a summary of synthetic antimicrobial treatment of fabrics, their efficiency and durability as tested on different types of microorganisms, their advantages, and the adverse effect of application of these agents. progress on antimicrobial fabrics is also provided, as well as recommendations for future research. 2. emergence of antimicrobial agents the general public has become more aware of the effects of antimicrobial agents on health. this has largely contributed to the increasing demand for antimicrobial agents in different fields [19]. it is well known that fabrics produced from natural fibers can serve as a good medium for the proliferation of pathogenic microorganisms due to their high moisture retaining ability and wide large surface area [20,21]. in addition, temperature and nutrients such as dead skin cells, stains, and secretions such as sweat on the fabrics can facilitate the rapid growth of different bacteria and fungi [10]. likewise, the presence of microorganisms can degenerate the fabrics in form of colour stains, unpleasant odours, discoloration, higher tendency for cross contamination, or fabric deterioration [15]. it can also result in allergic responses in the fabric users as well as other potential health related issues. these make it necessary to prevent possible undesirable occurrences through the use of antimicrobial agents [10,19]. 3. synthetic antimicrobial agents microorganisms generally have outer cell walls that are made up of polysaccharides. this polysaccharide wall is responsible for maintaining the cellular integrity of the cell components as well as protecting the cell from external factors [22]. next to the polysaccharide wall is a membrane that hosts the intracellular components alongside several enzymes, as well as nucleic acids. all the genetic details of the organism are stored in the nucleic acids whereas the enzymes help to facilitate different chemical reactions within the cell [22]. all these components need to be properly functional in order to sustain the growth and survival of the organism. therefore, antimicrobial agents work by attacking and damaging the cell wall, or disrupting the normal iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 13 functionalities of the organism’s cell [22]. although there could be different classifications of antimicrobial agents, it is generally agreed that they can be grouped as either biocides or biostats. biocides are substances that kill microorganisms while biostats function by inhibiting the growth and proliferation of microorganisms [4], and their mechanisms of action are closely related to the amount of active substances imparted unto the antimicrobial fabric [4]. based on literature, the most commonly used synthetic antimicrobial agents for fabrics are quaternary ammonium compounds (qacs), polyhexamethylene biguanide (phmb), triclosan and n-halamines. the mechanism of action of these four classes of antimicrobial agents have been presented in this section as representative antimicrobial agents for fabrics. 3.1 quaternary ammonium compounds (qacs) quaternary ammonium compounds (qacs) are molecules with at least one hydrophobic hydrocarbon chain connected to a positively charged nitrogen atom as shown in fig. 1. the other alkyl or aryl groups are frequently short chain substituents such as methyl or benzyl groups [23]. fig. 1: representative structure of quaternary ammonium compounds (qacs). qacs are outstanding antimicrobial agents [24]. the antimicrobial activity of qacs ensues from both ionic and hydrophobic connections between the qac and components of the microbial cell wall which often leads to cell death or malfunction in cellular processes [25]. factors such as charge density, molecular size, and molecular mobility determines the ability of a qac to bind to the bacterial cell wall and/or cell membrane, thereby interrupting its normal function [26]. usually, qacs would attack the phospholipid components of the membrane, by irreversibly binding to them. this would lead to impaired membrane permeability, causing membrane deformation, leakage of low-molecular-weight intracellular material, and disruption of the proton motive force [27]. 3.2 polyhexamethylene biguanide the structure of polyhexamethylene biguanide (phmb) is shown in fig. 2. phmb is another antimicrobial agent which is mainly used in food, medicine, water industries, and others. fig. 2: structure of polyhexamethylene biguanide. phmb has been applied onto fabrics to avoid microbial growth. phmb is a water-soluble, positively charged polymer, with broad-spectrum antimicrobial effects toward gram-positive n n n nh h h ch3 n h ch3 nh iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 14 and gram-negative bacteria, fungi, and yeast [28,29]. its composition is a mixture of polymeric biguanides of structure [(ch2)6.nh.c (=nh).nh.c.nh–]n, where n can vary from 2 to 40, resulting in a molecular mass range from 400 to 8000 [30]. the antibacterial action of phmb upon e. coli has been studied and it is found that growth inhibition and antibacterial activity increased with increasing levels of phmb-polymerization [31]. in another vein, studies have reported that phmb, which at a physiological ph acts like a polycation, only interacts with negatively charged, acidic phospholipids, whereas neutral phospholipids were not affected [32]. this concept describes both the broad spectrum antimicrobial activity and the low mammalian toxicity of phmb [33]. generally, the antibacterial and antifungal activity of phmb is based on its ability to induce phospholipid phase separation and cause loss of membrane function in bacteria or yeast [34]. 3.3 triclosan another notable antimicrobial agent is triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol). triclosan (5-chloro-2-(2,4-dichlorophenoxy)-phenol) (fig. 3) is a stable, chlorinated phenolic and liphophilic compound [35-37]. it is a potent antibacterial and antifungal compound that is generally used in personal care products, plastics, and fabrics [38]. triclosan acts as a site directed, very potent enzyme inhibitor by mimicking its natural substrate [39]. it has hydroxyl-halogenated derivate of two phenolic groups connected by various bridges, and is more effective against gram-positive bacteria than gram-negative bacteria [40]. triclosan is fairly insoluble in aqueous solutions, unless the ph is alkaline, and readily soluble in most organic solvents. it is chemically stable and can be heated up to 200oc for up to 2 h [41]. triclosan acts on microbial growth generally by inhibiting fatty acid biosynthesis through blocking of lipid biosynthesis in addition to acting together with amino acid residues of the enzyme-active site within a membrane [41]. fig. 3: structure of triclosan 3.4 n-halamines a group of compounds containing one or more nitrogen-halogen covalent bond, known as n-halamine have also been reported to exhibit antimicrobial properties [42]. these compounds are formed by the halogenation of imide, amide, or amine groups [43]. compared with inorganic halogens (e.g., chlorine or bromine), organic n-halamines are more stable, less corrosive, and have much less tendency to generate halogenated hydrocarbons [44]. the bactericidal action of n-halamines is believed to be a chemical reaction involving the direct transfer of positive halogens from the n-halamines to appropriate receptors in the bacterial cells [45]. that is, in n-halamine structures with a general formula of n(r1r2)-x where (x = cl or br), the strength of the n-x bond is significantly influenced by r1 and r2. if r1 and r2 are electron-donating groups (in the case of amine n-halamines), they will tend to destabilize any developing negative charge on n as x+ leaves the molecule and the stability will increase, thereby decreasing the antimicrobial properties [46]. similarly, electron-withdrawing groups iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 15 attached to nitrogen (in the case of amide and imide n-halamines) would decrease the stability but increase the antimicrobial function [43]. the oxidative halogen is transferred to a microorganism through direct contact, the rate of which depends upon the strength of the n-x bond, which in turn is related to the structure of the n-halamine molecule [47]. 4. advantages and disadvantages of synthetic antimicrobial agents based on the different degree of problems that can possibly be associated with the use of antimicrobial agents, researchers have noted that an ideal antimicrobial agent should combine different salient properties [48]. it should not present adverse toxicity to humans, it should exhibit a wide spectrum of antimicrobial potency, it should not lead to damage of the inherent fabric properties, it should be able to withstand fabric production procedures, and the antimicrobial durability should be stable throughout the fabric’s use life [10]. the importance of antimicrobial agents and antimicrobial fabrics cannot be gainsaid. however, is it generally required that their durability and benefits should not trigger subsequent potential risks to humans and the environment. therefore, safety assessment of these materials is always necessary. this can be possible by equally assessing the benefits and risks associated with the use of any antimicrobial agent or antimicrobial fabric [48]. 4.1 advantages of synthetic antimicrobial agents the ultimate reason for the use of antimicrobial agents in fabrics is to curtail infections arising from pathogenic microorganisms [49]. it is well known that the transmission of infectious diseases is more rampant in hospitals and other locations related to public health. this can be prevented or reduced if antimicrobial fabrics are used by workers instead of normal fabrics [50]. the antimicrobial agents can help to protect antimicrobial fabric users from pathogens on one hand as well as sustaining the quality of the fabric on the other hand [4,48]. different synthetic antimicrobial agents have been tested on fabrics. they have powerful antimicrobial activity, as indicated by their effectiveness and durability. the benefits of using synthetic antimicrobial agents are presented in table 1. 4.2 disadvantages of synthetic antimicrobial agents several antimicrobial agents have been applied to fabrics as can be seen from the very many articles on the subject [49,56-61]. in order to facilitate the good performance of these antimicrobial agents, different chemical are often used [56]. these include organometallics, slow iodine-releasing substances (iodo-phors), inorganic salts, anionic group bearing heterocyclics, phenols, thiophenols, urea and its compounds, nitro compounds, amines, and derivatives of formaldehyde and others [15,19,20,56]. however, reports show that a large proportion of these chemicals do not easily degrade in nature and poses high toxicity to humans [49,56]. on the other hand, those that easily decompose may constitute a nuisance to the environment [62,63]. iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 16 table 1: the benefits of using synthetic antimicrobial agents synthetic antimicrobial agent benefits reference qacs strong antimicrobial agent and have a broad spectrum of antimicrobial activity. [51] phmb highly effective antimicrobial agents and have low toxicity to human cells. [52,53] triclosan it has demonstrated immediate, persistent, broad-spectrum antimicrobial effectiveness against bacteria, fungi and virus. [54] n-halamine compounds capable of providing fast and total kill against a wide range of microorganisms without causing resistance from microorganisms and can be used for long term disinfection. [43,55] therefore, it is established that although synthetic antimicrobial agents can be very effective against a wide range of microorganisms as well as have durable effect on fabrics, there are causes for concern due to health hazards and environmental pollution [64-66]. this is because most of these agents have toxic effects and cannot easily degrade in nature [56,67, 68]. among the four classes of antimicrobial agents reported herein, the adverse effects of phmb and n-halamines are mild and possibly negligible. a summary of the main disadvantages of the two other classes (triclosan and qacs) are highlighted in table 2. 5. challenges in the production of antimicrobial fabrics one major challenges faced with the use of antimicrobial agents is how to sustain the antimicrobial durability of the modified fabric [10]. this is due to the fact that during its use life, fabrics would normally be exposed to several actions such as washing, drying, wear, ironing, and so on. therefore, it is important to assess the antimicrobial durability of modified fabrics. unfortunately, assessment of durability is a complex and time-consuming task compared with normal antimicrobial tests [10]. this is a major challenge to assessment of antimicrobial reliability of modified fabrics. in general, durability of antimicrobial fabrics can be broadly classified as either temporary antimicrobial fabric or durable antimicrobial fabric. although temporary antimicrobial fabric is easier to produce, their antimicrobial potency is often lost during laundering processes [50]. this is because there is a close relationship between antimicrobial properties and concentration of active substances in the antimicrobial fabric. thus laundering activities, as well as leaching of active components into the environment, can cause the concentration of active components to drop below the level required for proper actions. one major problem associated with this is that it can lead to antimicrobial resistance [4]. in order to ensure antimicrobial durability through conventional techniques, several steps are usually involved such as neutralization, functionalization, curing, and so on. these steps are very expensive, time demanding, and most often not environmentally friendly [67]. in addition, they often lead to decreases in properties of the antimicrobial fabric such as softness, appearance, and tensile and abrasive properties [67]. these have often posed serious challenges to production of durable antimicrobial fabrics. iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 17 5.1 temporary antimicrobial fabrics temporary antimicrobial fabrics are easy to produce because they do not demand rigorous processes. however, their antimicrobial potency is easily lost after washing. as such, temporary antimicrobial fabrics generally refer to the group of fabrics that tend to lose their antimicrobial performance after only a few washing cycles. these antimicrobial fabrics are generally undesirable, which makes it a less important subject of discussion [50]. 5.2 durable antimicrobial fabrics one of the major requirements of an ideal antimicrobial fabric is durability. hence, it is often necessary that the fabric should manifest good durability throughout its use life. however, this is usually a grave challenge for researchers due to the fact that fabrics are normally subjected to several actions including washing, wear, ironing, and drying during the period of their use [10]. in addition, considering the complications surrounding the evaluation of durability, only few studies have focused on durability compared to the several studies available on antimicrobial activity [10]. more often than not, washing durability is one of the notable parameters used for evaluating the antimicrobial performance of fabrics. this denotes the quantity of the antimicrobial potency which is able to withstand repeated washing processes. notably, a group of n-halamine compounds have been reported suitable to provide durable antimicrobial properties onto fabrics. the antimicrobial properties of these compounds are said to be highly durable and even rechargeable [50]. in fact, they are said to be non-toxic [83], and the mode of their action is through oxidation of amino acids leading to inactivation of the microorganisms’ cells within a short period of contact [83,84]. interestingly, in a recent study, novel antimicrobial cotton fabric with desirable durability was prepared through a process that involves the physical absorption, followed by chemical bonding of modified polyhexamethylene guanidine (phmg) onto the cotton surface [85]. in their study, they assessed the antimicrobial performance of the modified cotton fabrics through the shaking flask method whereas laundering durability was used to evaluate the non-leaching properties [85]. it was inferred from the research that the interaction between the modified fabric and molecules of the antimicrobial agent plays notable roles in determining the durability of the fabric [85]. iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 18 table 2: disadvantages of using synthetic antimicrobial agent effects explanation reference ecotoxicity and environmental effect triclosan is a widely employed antimicrobial agent that has been found as a contaminant in rivers and lakes [69,70] exposure to sunlight causes the breakdown of triclosan and the formation of toxic polychlorinated dioxins [22] qacs also have toxicity effect against the environment, and their effects are short lived because of the difficulty of controlling their rate of diffusion [71,72] skin irritation and effect of exposure wearing treated fabrics with triclosan can lead to sensitization and skin irritation such as itching [22,73] triclosan has been detected in human breast milk, at levels ranging from 0 to 2100 lg/kg lipid, in serum and in urine [37,74-77] laboratory studies have documented that triclosan disrupts thyroid systems in rats and frogs [38,78,79] bacteria resistance wearing treated fabrics with some synthetic antimicrobial; agents in a continuous manner can cause bacteria resistance [22] the release of qacs from the fabrics into the surroundings could have destructive impacts on living organisms in water because they can affect susceptible bacteria, thereby potentially selecting resistant bacteria [80] moreover, it was recently reported that the presence of qacs in qac-polluted environments contributes to the induction of antibiotic resistance of bacteria which is currently an alarming human health concern [81] furthermore, triclosan blocks bacterial lipid biosynthesis which leads to concern for possible development of bacterial resistance [39,82] iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 19 6. synthetic antimicrobial fabric treatment to date, a number of synthetic antimicrobial agents have been applied to impart antimicrobial properties to the fabrics. the summary of different types of synthetic antimicrobial agents tested on different types of fabrics, the tested microorganisms, efficiency, and durability are presented in table 3. it can be inferred that cotton and wool impregnated with qacs exhibited excellent antimicrobial activity. the cotton fabrics with qacs show antimicrobial activity even after 30 laundry cycles. however, nylon impregnated with qacs shows low durability against laundering. on the other hand, phmb shows low antimicrobial activity on cotton fabrics. in contrast, non-woven fabrics and cotton treated with triclosan displayed good antimicrobial activity. notably, knitted cotton displayed good antimicrobial activity even after 50 laundry cycles. in another vein, cotton fabrics impregnated with nhalamine show less antimicrobial activity. however, the antimicrobial resistance of the cotton with n-halamine is generable by regular laundry exposure to chlorine bleach and can withstand more than 50 standard machine washes without deterioration. in summary, qacs exhibit excellent antimicrobial activity against different types of bacteria while triclosan and nhalamine exhibit excellent durability against laundering. however, pbhb impregnated fabric shows less effectiveness of antimicrobial activity. 7. future trends in antimicrobial fabric it is well established that most synthetic antimicrobial agents are obtained from petrochemical-based sources involving the use of different hazardous organic solvents that pose threats to both human and environmental health [99-102]. it is also well known that antimicrobial potency is not the only important property in antimicrobial fabrics, but there is a need to consider environmental and human health during their use [4]. therefore, high importance is being placed on, and attention is recently being concerted towards, the use of environmentally friendly, non-toxic, antimicrobial agents [99]. the main benefit of this approach is that natural antimicrobial agents do not elicit any observable health related problems both at production stage and during the use life of the antimicrobial fabrics [99, 103]. however, there are concerns about the antimicrobial durability of naturally modified antimicrobial fabrics. on a general note, antimicrobial fabrics may be obtained through chemical or physical incorporation of antimicrobial agents onto the fabrics [50]. chemical incorporation of antimicrobial agents onto fabrics is often a good way to ensure lasting durability of the antimicrobial fabric. however, it is very important that the antimicrobial agents should be incorporated onto the fabric through covalent bond [4,50]. this would help to maintain the integrity of the environment. the antimicrobial fabrics produced through this means have been observed to be environment due to non-release of toxic substances into the environment, a condition common with conventional antimicrobial fabrics [4]. the new trend in antimicrobial fabrics is therefore focused on the use of products that contain covalently bound active agents unlike the leaching-prone conventional antimicrobial fabrics. initially, use of nanoparticles and nanocomposites was thought to be a way forward. these inorganic nanoparticles are believed to be capable of opening new modern opportunities iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 20 for antimicrobial fabrics [67,104]. in fact, there is evidence for the safety of this approach. however, recent public awareness on health care has increased the concerns on possible side effects of new technologies on human and environmental health [67]. progress in research has led to the use of natural bioactive antimicrobial agents of plant origin [4, 67]. these types of antimicrobial fabrics have been observed to be non-toxic, safe, and human and environmentally friendly [4]. therefore, in order to facilitate antimicrobial durability of naturally derived antimicrobial fabrics, series of methods are being used to impart the active agents onto the fabric [105-107]. in a recent study, natural herbal extracts from azadirachta indica was used to impart antimicrobial properties onto fabrics without the incorporation of any additives [108]. antimicrobial potency of the treated fabrics was tested against escherichia coli and staphylococcus aureus. it was reported that treated fabrics did not only manifest desirable antimicrobial property, but it also revealed good washing durability as well as improved uvresistance properties. the notable active compounds present in the natural nanoparticle extract of the leaves includes nimbolide, mahmoodin, nimbidin, isomargolonone, margolonone, and margolone [108]. all of these have been reported to contribute to the antimicrobial properties of this extract [108]. in another study, antimicrobial fabrics were produced from natural extracts from nerium oleander, trigonella foenum graecum, and curcuma longa. phytochemical analysis of the extract obtained from nerium oleander showed that the extract contains different compounds, which are mainly alkaloids, flavonins, proteins, saponins, tannins, and other aromatic acids [106]. the extract from trigonella foenum graecum contains alkaloids, flavonins, proteins, saponins, tannins, aromatic acids and reducing sugars. on the other hand, analysis of the extract from curcuma longa contains alkaloids, flavonins, terpenoids, plobatinins, saponins, tannins, and other aromatic acids [109]. interestingly, it was found that the antimicrobial fabric obtained from these extracts manifested efficient anitimicrobial activity against different tested pathogenic microbes [109]. similarly, among other progressive studies, there has been a report on possible establishment of a new generation of environmentally compliant antimicrobial fabrics based on natural extracts from polygonum cuspidatum, namely resveratrol (res) [110]. all these studies point to the fact that researchers are turning towards the possibility of replacing synthetic chemicals based on antimicrobial agents with more naturally-based products. iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 21 table 3: studies of synthetic antimicrobial agents used for the development of antimicrobial fabrics and efficiency towards microorganisms biocide fabric tested microorganism effectiveness durability reference quaternary ammonium compounds (qac)s cotton staphylococcus aureus the treated fabrics displayed very effective antimicrobial activity showing 99.9% of reduction in the number of bacteria na [86] wool staphylococcus aureus bacillus pumilus the wool samples showed good antimicrobial activity na [87] cotton staphylococcus aureus escherichia coli when the concentration of antimicrobial agent exceeded 70 ppm, the antimicrobial activity increased to more than 99.99% for both bacteria even after 30 cycles of washing, the antimicrobial activity of the cotton fabrics remained at a high level [88] nylon escherichia coli the fabrics treated with more than 4% quaternary ammonium salt showed much better antimicrobial activity with results of 90% bacterial reduction the fabric treated in 2% salt solution started to lose the function after six washes and showed less than 90% potency on e. coli. it continued to deteriorate after eight washes, and finally became non-antimicrobial after ten washes [89] wool escherichia coli the treated fabrics shows excellent antimicrobial functions after 10 times of washing, the treated fabrics could still provide about 70% of antimicrobial activity [90] polyhexamethylene biguanide (phmb) cotton staphylococcus aureus as increasing quantities of phmb were applied to cotton, bacterial growth on the cotton reduced until there were no growth at ideal concentrations na [91] iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 22 table 3: continued biocide fabric tested microorganism effectiveness durability reference triclosan non-woven fabrics staphylococcus aureus escherichia coli microbiological tests indicated the high antimicrobial activity of the triclosanloaded microspheres against both microorganisms na [92] cotton escherichia coli when the triclosan concentration was increased from 3 to 5 wt % in the film it inhibited bacterial growth na [93] cotton staphylococcus aureus atcc 6538 escherichia coli atcc 35218 antimicrobial activity decreased somewhat after the use of polycarboxylic acid and triclosan. it caused a change in the ph level of the solution from basic to acidic and affected the mechanism of triclosan inhibition adding polycarboxylic acids to the fabrics containing triclosan enhanced the durability against laundering [40] knitted cotton staphylococcus aureus escherichia coli the antimicrobial properties of raw fabrics was significantly increased after triclosan treatment and it was found to be more effective against s. aureus than e. coli the antimicrobial resistant of the fabrics can withstand up to 50 laundry cycles [41] n-halamine compounds cotton and cotton blend fabrics staphylococcus aureus escherichia coli test results show uniformly high antimicrobial activity on both pure cotton and cotton blends. there were no significant differences in antimicrobial functions against the tested species between the fabrics used such as poly/cotton and pure cotton fabrics the antimicrobial resistance are generable by regular laundry exposure to chlorine bleach and can withstand over 50 standard machine washes without deterioration [94] cotton staphylococcus aureus escherichia coli the samples possessing amine halamine structures demonstrated relatively slower antimicrobial functions than those of the 1,3-dimethylol-5,5-dimethylhydantoin (dmdmh) treated ones after three cycles of washing, the sample containing only amine halamine exhibited the best durability, whereas the dmdmh-treated fabrics lost some of the antimicrobial activity resulting from the loss of the active imide halamine bonds [95] iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 23 table 3: continued. biocide fabric tested microorganism effectiveness durability reference n-halamine compounds cotton escherichia coli k 12 a 5-logarithmic reduction of escherichia coli in a contact time of 5 to15 minutes makes the acycilic halamine cotton as powerful as cyclic halamine cotton the active chlorine contents on halamine samples did not decrease after two or three accelerated washes as compared with one without accelerated washing. [96] nomex®, kermel and pbi/kevlar synthetic fabric staphylococcus aureus escherichia coli the nomex sample provided 6 log reduction to 106–107 cfu/ml of escherichia coli after 60 minutes of contact. the kermel and pbi/kevlar samples demonstrated only a 3 log reduction, even after 120 min of contact. a similar trend is also observed in the antibacterial tests against staphylococcus aureus after 10 rounds of bleach/wash 15 times/bleach cycles, the antibacterial properties of the samples were essentially unchanged, indicating that the antimicrobial properties of the grafted samples were regenerable. [97] nomex® and kevlar synthetic fabric escherichia coli atcc 15597 staphylococcus aureus atcc 6538 it can be seen clearly that the fabrics can provide a total kill of 106-107 cfu/ml bacteria at a contact time of only 10 min after 10 washes, few changes can be detected in their antimicrobial efficacies. after rebleaching, the chlorinated fabrics regenerated the antimicrobial resistance. [98] na = not available iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 24 8. conclusion and recommendations antimicrobial agents imparted onto fabrics play an important role in preventing discomfort and odour and reducing the risk of skin infections caused by fungi and other pathogenic bacteria. however, using triclosan and qacs can cause environmental and health concerns whereas phmb and n-halamine are still good alternatives to impart the antimicrobial properties onto the fabrics. in view of these phenomena and the adverse effect caused by triclosan and qacs, it is recommended that further research should be done to discover new alternatives involving the use of non-toxic ingredients in producing fabric products with potent antimicrobial properties. there should be intensive research on using nanotechnology as a new method to develop antimicrobial fabrics. the development of nanotechnology allows for discovering the antimicrobial properties of metal and metal oxide nanoparticles that can be applied to develop antimicrobial fabrics. in general, the antimicrobial potency of synthetic antimicrobial agents can be very high compared to natural antimicrobial agents. in fact, synthetic antimicrobial agents can exhibit a wide combination of salient properties compared with natural antimicrobial agents. this is coupled with the fact that the production and application of synthetic antimicrobial agents and antimicrobial fabrics can be highly cost effective. however, there is still the lingering problem of possible human toxicity and possible sacrifice of the environment’s integrity. it is therefore recommended that further research should tend towards the use of antimicrobial agents obtained either from plant sources or from microorganisms. although the efficiency of naturally derived antimicrobial agents is lower compared to synthetic antimicrobial agents at the moment, there is room for improvement. rigorous research in this area would help to ensure that the next generation of antimicrobial agents are safe to be used for humanrelated applications as well as ecologically friendly. acknowledgement the authors would like to thank universiti malaysia pahang for financial support and the government of malaysia for providing slab scholarship during the study. references [1] akira a. functional fibers and finishes for humans. senisha, inc: osaka, japan 1995. [2] sun g, worley sd. (2005) chemistry of durable and regenerable biocidal textiles. journal of chemical education, 82:60. [3] esteban-cubillo a, pecharromán c, aguilar e, santarén j, moya js. (2006) antibacterial activity of copper monodispersed nanoparticles into sepiolite. j. materials science, 41:52085212. [4] simoncic b, tomsic b. (2010) structures of novel antimicrobial agents for textiles a review. textile research journal, 80:1721-1737. [5] gouveia ic. (2010) nanobiotechnology: a new strategy to develop non-toxic antimicrobial textiles for healthcare applications. j. biotechnology, 150:349. [6] hammer tr, mucha h, hoefer d. (2012) dermatophyte susceptibility varies towards antimicrobial textiles. mycoses, 55:344-351. [7] song l, zheng w, jian-cheng q, jin-hui w, tao t, li-li h, et al. (2011) one-pot fabrication and antimicrobial properties of novel pet nonwoven fabrics. biomedical materials, 6:045009. [8] montazer m, pakdel e, behzadnia a. (2011) novel feature of nano-titanium dioxide on textiles: antifelting and antibacterial wool. j. applied polymer science, 121:3407-3413. iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 25 [9] balachandra nair r, ramachandranna pc. (2010) patenting of microorganisms: systems and concerns. j. commercial biotechnology 16:337-347. [10] zhang y, xu q, fu f, liu x. (2016) durable antimicrobial cotton textiles modified with inorganic nanoparticles. cellulose, 23:2791-2808. [11] yu q, wu z, chen h. (2015) dual-function antibacterial surfaces for biomedical applications. acta biomaterialia, 16:1-13. [12] montazer m, afjeh mg. (2007) simultaneous x-linking and antimicrobial finishing of cotton fabric. journal of applied polymer science, 103:178-185. [13] wasif a, laga s. (2009) use of nano silver as an antimicrobial agent for cotton. autex res j, 9:5-13. [14] sajitz m, grohmann j. (2011) hygiene effects of bleach systems in laundry detergents. söfw-journal, 137. [15] zhang s, yang x, tang b, yuan l, wang k, liu x, et al. (2018) new insights into synergistic antimicrobial and antifouling cotton fabrics via dually finished with quaternary ammonium salt and zwitterionic sulfobetaine. chemical engineering journal, 336:123-132. [16] benn tm, westerhoff p. (2008) nanoparticle silver released into water from commercially available sock fabrics. environmental science & technology, 42:4133-4129. [17] percival sl, bowler pg, russell d. (2005) bacterial resistance to silver in wound care. journal of hospital infection, 60:1-7. [18] cha j, lee wb, park cr, cho yw, ahn c-h, kwon ic. (2006) preparation and characterization of cisplatin-incorporated chitosan hydrogels, microparticles, and nanoparticles. macromolecular research, 14:573-578. [19] iyigundogdu zu, demir o, asutay ab, sahin f. (2017) developing novel antimicrobial and antiviral textile products. applied biochemistry and biotechnology, 181:1155-1166. [20] lim s-h, hudson sm. (2004) application of a fiber-reactive chitosan derivative to cotton fabric as an antimicrobial textile finish. carbohydrate polymers, 56:227-234. [21] yazhini kb, prabu hg. (2015) antibacterial activity of cotton coated with zno and znocnt composites. applied biochemistry and biotechnology, 175:85-92. [22] gao y, cranston r. (2008) recent advances in antimicrobial treatments of textiles. textile research journal, 78:60-72. [23] garcıá mt, ribosa i, guindulain t, sánchez-leal j, vives-rego j. (2001) fate and effect of monoalkyl quaternary ammonium surfactants in the aquatic environment. environmental pollution 111:169-175. [24] song j, kong h, jang j. (2011) bacterial adhesion inhibition of the quaternary ammonium functionalized silica nanoparticles. colloids and surfaces b: biointerfaces, 82:651-656. [25] majumdar p, lee e, gubbins n, stafslien sj, daniels j, thorson cj, et al. (2009) synthesis and antimicrobial activity of quaternary ammonium-functionalized poss (q-poss) and polysiloxane coatings containing q-poss. polymer, 50:1124-1133. [26] majumdar p, he j, lee e, kallam a, gubbins n, stafslien sj, et al. (2010) antimicrobial activity of polysiloxane coatings containing quaternary ammonium-functionalized polyhedral oligomeric silsesquioxane. j. coatings technology and research, 7:455-467. [27] mcdonnell g, russell ad. (1999) antiseptics and disinfectants: activity, action, and resistance. clinical microbiology reviews, 12:147-179. [28] krebs fc, miller sr, ferguson ml, labib m, rando rf, wigdahl b. (2005) polybiguanides, particularly polyethylene hexamethylene biguanide, have activity against human immunodeficiency virus type 1. biomedicine & pharmacotherapy, 59:438-445. [29] tang y, zhao y, wang h, gao y, liu x, wang x, et al. (2012) layer-by-layer assembly of antibacterial coating on interbonded 3d fibrous scaffolds and its cytocompatibility assessment. j. biomedical materials research part a, 100a:2071-2078. [30] pinto f, maillard jy, denyer sp, mcgeechan p. (2010) polyhexamethylene biguanide exposure leads to viral aggregation. j. applied microbiology, 108:1880-1888. [31] broxton p, woodcock pm, gilbert p. (1983) a study of the antibacterial activity of some polyhexamethylene biguanides towards escherichia coli atcc 8739. j. applied bacteriology, 54:345-353. iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 26 [32] ikeda t, ledwith a, bamford ch, hann ra. (1984) interaction of a polymeric biguanide biocide with phospholipid membranes. biochimica et biophysica acta (bba) – biomembranes, 769:57-66. [33] rosin m, welk a, kocher t, majic-todt a, kramer a, pitten fa. (2002) the effect of a polyhexamethylene biguanide mouthrinse compared to an essential oil rinse and a chlorhexidine rinse on bacterial counts and 4-day plaque regrowth. j. clinical periodontology, 29:392-399. [34] allen mj, white gf, morby ap. (2006) the response of escherichia coli to exposure to the biocide polyhexamethylene biguanide. microbiology, 152:989-1000. [35] lozano n, rice cp, ramirez m, torrents a. (2010) fate of triclosan in agricultural soils after biosolid applications. chemosphere, 78:760-766. [36] paul kb, hedge jm, devito mj, crofton km. (2010) short-term exposure to triclosan decreases thyroxine in vivo via upregulation of hepatic catabolism in young long-evans rats. toxicological sciences, 113:367-379. [37] adolfsson-erici m, pettersson m, parkkonen j, sturve j. (2002) triclosan, a commonly used bactericide found in human milk and in the aquatic environment in sweden. chemosphere, 46:1485-1489. [38] zorrilla lm, gibson ek, jeffay sc, crofton km, setzer wr, cooper rl, et al. (2009) the effects of triclosan on puberty and thyroid hormones in male wistar rats. toxicological sciences 107:56-64. [39] levy cw, roujeinikova a, sedelnikova s, baker pj, stuitje ar, slabas ar, et al. (1999) molecular basis of triclosan activity. nature, 398:383. [40] orhan m, kut d, gunesoglu c. (2009) improving the antibacterial activity of cotton fabrics finished with triclosan by the use of 1,2,3,4-butanetetracarboxylic acid and citric acid. journal of applied polymer science, 111:1344-1352. [41] orhan m, kut d, gunesoglu c. (2007) use of triclosan as antibacterial agent in textiles. j. fibre and textile research, 32:114-118. [42] kocer hb, cerkez i, worley sd, broughton rm, huang ts. (2011) cellulose/starch/hals composite fibers extruded from an ionic liquid. carbohydrate polymers, 86:922-927. [43] worley sd, williams de, crawford ra. (1988) halamine water disinfectants. critical reviews in environmental control, 18:133-175. [44] chen z, sun y. (2006) n-halamine-based antimicrobial additives for polymers:  preparation, characterization, and antimicrobial activity. industrial & engineering chemistry research, 45:2634-2640. [45] kaminski jj, bodor n, higuchi t. (1976) n-halo derivatives iii: stabilization of nitrogenchlorine bond in n-chloroamino acid derivatives. j. pharmaceutical sciences, 65:553-557. [46] braun m, sun y. (2004) antimicrobial polymers containing melamine derivatives. i. preparation and characterization of chloromelamine-based cellulose. j. polymer science part a: polymer chemistry, 42:3818-3827. [47] akdag a, okur s, mckee ml, worley sd. (2006) the stabilities of n−cl bonds in biocidal materials. j. chemical theory and computation, 2:879-884. [48] windler l, height m, nowack b. (2013) comparative evaluation of antimicrobials for textile applications. environment international, 53:62-73. [49] cheng x, ma k, li r, ren x, huang ts. (2014) antimicrobial coating of modified chitosan onto cotton fabrics. applied surface science, 309:138-143. [50] ren x, kocer hb, worley sd, broughton rm, huang ts. (2009) rechargeable biocidal cellulose: synthesis and application of 3-(2,3-dihydroxypropyl)-5,5-dimethylimidazolidine2,4-dione. carbohydrate polymers, 75:683-687. [51] kawabata n, nishiguchi m. (1988) antibacterial activity of soluble pyridinium-type polymers. applied and environmental microbiology, 54:2532-2535. [52] müller g, kramer a. (2008) biocompatibility index of antiseptic agents by parallel assessment of antimicrobial activity and cellular cytotoxicity. j. antimicrobial chemotherapy, 61:1281-1287. iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 27 [53] wiegand c, abel m, ruth p, hipler u-c. (2009) hacat keratinocytes in co-culture with staphylococcus aureus can be protected from bacterial damage by polihexanide. wound repair and regeneration, 17:730-738. [54] jones rd, jampani hb, newman jl, lee as. (2000) triclosan: a review of effectiveness and safety in health care settings. american journal of infection control, 28:184-196. [55] tsao tc, williams de, worley sd. (1990) a new disinfectant compound. industrial & engineering chemistry research, 29:2161-2163. [56] fu x, shen y, jiang x, huang d, yan y. (2011) chitosan derivatives with dual-antibacterial functional groups for antimicrobial finishing of cotton fabrics. carbohydrate polymers, 85:221-227. [57] lu g, wu d, fu r. (2007) studies on the synthesis and antibacterial activities of polymeric quaternary ammonium salts from dimethylaminoethyl methacrylate. reactive and functional polymers, 67:355-366. [58] du w-l, niu s-s, xu y-l, xu z-r, fan c-l. (2009) antibacterial activity of chitosan tripolyphosphate nanoparticles loaded with various metal ions. carbohydrate polymers, 75:385-389. [59] kocer hb, akdag a, ren x, broughton rm, worley sd, huang ts. (2008) effect of alkyl derivatization on several properties of n-halamine antimicrobial siloxane coatings. industrial & engineering chemistry research, 47:7558-7563. [60] li r, hu p, ren x, worley sd, huang ts. (2013) antimicrobial n-halamine modified chitosan films. carbohydrate polymers, 92:534-539. [61] gouda m, ibrahim na. (2008) new approach for improving antibacterial functions of cotton fabric. j. industrial textiles, 37:327-339. [62] docherty km, kulpa jcf. (2005) toxicity and antimicrobial activity of imidazolium and pyridinium ionic liquids. green chemistry, 7:185-189. [63] rai m, yadav a, gade a. (2009) silver nanoparticles as a new generation of antimicrobials. biotechnology advances, 27:76-83. [64] joshi m, ali sw, purwar r, rajendran s. (2009) ecofriendly antimicrobial finishing of textiles using bioactive agents based on natural products. [65] grillitsch b, gans o, kreuzinger n, scharf s, uhl m, fuerhacker m. (2006) environmental risk assessment for quaternary ammonium compounds: a case study from austria. water science and technology, 54:111-118. [66] singh r, jain a, panwar s, gupta d, khare sk. (2005) antimicrobial activity of some natural dyes. dyes and pigments, 66:99-102. [67] dastjerdi r, montazer m. (2010) a review on the application of inorganic nano-structured materials in the modification of textiles: focus on anti-microbial properties. colloids and surfaces b: biointerfaces, 79:5-18. [68] takai k, ohtsuka t, senda y, nakao m, yamamoto k, matsuoka j, et al. (2002) antibacterial properties of antimicrobial-finished textile products. microbiology and immunology 46:75-81. [69] kolpin dw, furlong et, meyer mt, thurman em, zaugg sd, barber lb, et al. (2002) pharmaceuticals, hormones, and other organic wastewater contaminants in u.s. streams, 1999−2000:  a national reconnaissance. environmental science & technology, 36:12021211. [70] singer h, müller s, tixier c, pillonel l. (2002) triclosan:  occurrence and fate of a widely used biocide in the aquatic environment:  field measurements in wastewater treatment plants, surface waters, and lake sediments. environmental science & technology, 36:49985004. [71] kenawy e-r, abdel-hay fi, el-shanshoury ae-rr, el-newehy mh. (1998) biologically active polymers: synthesis and antimicrobial activity of modified glycidyl methacrylate polymers having a quaternary ammonium and phosphonium groups. j. controlled release, 50:145-152. [72] cakmak i, ulukanli z, tuzcu m, karabuga s, genctav k. (2004) synthesis and characterization of novel antimicrobial cationic polyelectrolytes. european polymer journal, 40:2373-2379. iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 28 [73] bhargava hn, leonard pa. (1996) triclosan: applications and safety. american journal of infection control, 24:209-218. [74] dayan ad. (2007) risk assessment of triclosan [irgasan®] in human breast milk. food and chemical toxicology, 45:125-129. [75] hovander l, malmberg t, athanasiadou m, athanassiadis i, rahm s, bergman, et al. (2002) identification of hydroxylated pcb metabolites and other phenolic halogenated pollutants in human blood plasma. archives of environmental contamination and toxicology, 42:105-17. [76] calafat am, ye x, wong l-y, reidy ja, needham ll. (2008) urinary concentrations of triclosan in the u.s. population: 2003–2004. environmental health perspectives, 116:303307. [77] wolff ms, teitelbaum sl, windham g, pinney sm, britton ja, chelimo c, et al. (2007) pilot study of urinary biomarkers of phytoestrogens, phthalates, and phenols in girls. environmental health perspectives, 115:116-121. [78] crofton km, paul kb, devito mj, hedge jm. (2007) short-term in vivo exposure to the water contaminant triclosan: evidence for disruption of thyroxine. environmental toxicology and pharmacology, 24:194-197. [79] veldhoen n, skirrow rc, osachoff h, wigmore h, clapson dj, gunderson mp, et al. (2006) the bactericidal agent triclosan modulates thyroid hormone-associated gene expression and disrupts postembryonic anuran development. aquatic toxicology, 80:217227. [80] ioannou cj, hanlon gw, denyer sp. (2007) action of disinfectant quaternary ammonium compounds against staphylococcus aureus. antimicrobial agents and chemotherapy, 51:296-306. [81] gaze w, abdouslam n, hawkey p, wellington e. (2005) incidence of class 1 integrons in a quaternary ammonium compound-polluted environment. antimicrobial agents and chemotherapy, 49:1802-1807. [82] mcmurry lm, oethinger m, levy sb. (1998) triclosan targets lipid synthesis. nature, 394:531. [83] cerkez i, worley s, broughton r, huang t. (2013) antimicrobial coatings for polyester and polyester/cotton blends. progress in organic coatings, 76:1082-1087. [84] ahmed aesi, wardell jn, thumser ae, avignone‐rossa ca, cavalli g, hay jn, bushell me. (2011) metabolomic profiling can differentiate between bactericidal effects of free and polymer bound halogen. j. applied polymer science, 119:709-718. [85] li z, chen j, cao w, wei d, zheng a, guan y. (2018) permanent antimicrobial cotton fabrics obtained by surface treatment with modified guanidine. carbohydrate polymers, 180:192-199. [86] son y-a, kim b-s, ravikumar k, lee s-g. (2006) imparting durable antimicrobial properties to cotton fabrics using quaternary ammonium salts through 4aminobenzenesulfonic acid–chloro–triazine adduct. european polymer journal, 42:30593067. [87] diz m, infante mr, erra p, manresa a. (2001) antimicrobial activity of wool treated with a new thiol cationic surfactant. textile research journal, 71:695-700. [88] kim hw, kim br, rhee yh. (2010) imparting durable antimicrobial properties to cotton fabrics using alginate–quaternary ammonium complex nanoparticles. carbohydrate polymers, 79:1057-1062. [89] kim yh, sun g. (2001) durable antimicrobial finishing of nylon fabrics with acid dyes and a quaternary ammonium salt. textile research journal, 71:318-323. [90] zhu p, sun g. (2004) antimicrobial finishing of wool fabrics using quaternary ammonium salts. journal of applied polymer science, 93:1037-1041. [91] kawabata a, taylor ja. (2007) the effect of reactive dyes upon the uptake and antibacterial efficacy of poly(hexamethylene biguanide) on cotton. part 3: reduction in the antibacterial efficacy of poly(hexamethylene biguanide) on cotton, dyed with bis(monochlorotriazinyl) reactive dyes. carbohydrate polymers, 67:375-389. iium engineering journal, vol. 19, no. 2, 2018 mat zain et al. 29 [92] goetzendorf-grabowska b, królikowska h, gadzinowski m. (2004) polymer microspheres as carriers of antibacterial properties of textiles: a preliminary study. fibres & textiles in eastern europe, 12:62-64. [93] lu j, hill ma, hood m, greeson df, horton jr, orndorff pe, et al. (2001) formation of antibiotic, biodegradable polymers by processing with irgasan dp300r (triclosan) and its inclusion compound with β-cyclodextrin. j. applied polymer science, 82:300-309. [94] sun y, sun g. (2001) novel regenerable n-halamine polymeric biocides. iii. grafting hydantoin-containing monomers onto synthetic fabrics. j. applied polymer science, 81:1517-1525. [95] qian l, sun g. (2004) durable and regenerable antimicrobial textiles: improving efficacy and durability of biocidal functions. j. applied polymer science, 91:2588-2593. [96] liu s, sun g. (2006) durable and regenerable biocidal polymers:  acyclic n-halamine cotton cellulose. industrial & engineering chemistry research, 45:6477-6482. [97] sun y, sun g. (2003) novel refreshable n-halamine polymeric biocides: grafting hydantoin-containing monomers onto high performance fibers by a continuous process. journal of applied polymer science, 88:1032-1039. [98] sun y, sun g. (2004) novel refreshable n-halamine polymeric biocides:  n-chlorination of aromatic polyamides. industrial & engineering chemistry research, 43:5015-5020. [99] kasiri mb, safapour s. (2014) natural dyes and antimicrobials for green treatment of textiles. environmental chemistry letters, 12:1-13. [100] kasiri mb, khataee ar. (2011) photooxidative decolorization of two organic dyes with different chemical structures by uv/h2o2 process: experimental design. desalination, 270:151-159. [101] kasiri mb, aleboyeh h, aleboyeh a. (2008) degradation of acid blue 74 using fe-zsm5 zeolite as a heterogeneous photo-fenton catalyst. applied catalysis b: environmental, 84:915. [102] safapour s, seyed-esfahani m, auriemma f, ruiz de ballesteros o, vollaro p, di girolamo r, et al. (2010) reactive blending as a tool for obtaining poly(ethylene terephthalate)-based engineering materials with tailored properties. polymer, 51:4340-4350. [103] sivakumar v, vijaeeswarri j, anna jl. (2011) effective natural dye extraction from different plant materials using ultrasound. industrial crops and products, 33:116-122. [104] chen q, shen x, gao h. (2006) one-step synthesis of silver-poly(4-vinylpyridine) hybrid microgels by γ-irradiation and surfactant-free emulsion polymerisation. the photoluminescence characteristics. colloids and surfaces a: physicochemical and engineering aspects, 275:45-9. [105] joshi m, ali sw, rajendran s. (2007) antibacterial finishing of polyester/cotton blend fabrics using neem (azadirachta indica): a natural bioactive agent. journal of applied polymer science, 106:793-800. [106] haufe h, muschter k, siegert j, böttcher h. (2008) bioactive textiles by sol–gel immobilised natural active agents. j. sol-gel science and technology, 45:97-101. [107] boh b, knez e. (2006) microencapsulation of essential oils and phase change materials for applications in textile products. [108] subramani k, murugan v, kolathupalayam shanmugam b, rangaraj s, palanisamy m, venkatachalam r, et al. (2017) an ecofriendly route to enhance the antibacterial and textural properties of cotton fabrics using herbal nanoparticles from azadirachta indica (neem). j. alloys and compounds, 723:698-707. [109] selvam rm, athinarayanan g, nanthini aur, singh ajar, kalirajan k, selvakumar pm. (2015) extraction of natural dyes from curcuma longa, trigonella foenum graecum and nerium oleander, plants and their application in antimicrobial fabric. industrial crops and products, 70:84-90. [110] pinho e, henriques m, oliveira r, dias a, soares g. (2010) development of biofunctional textiles by the application of resveratrol to cotton, bamboo, and silk. fibers and polymers, 11:271-276. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 robust tuning of power system stabilizer parameters using the modified harmonic search algorithm hiba zuhair abdul kareem1, husam hasan mohammed1*, and ameer aqeel mohammed 2 1 department of electronic technologies, 2 department of computer systems, babylon technical institute, al-furat al-awsat technical university,51015, babylon, iraq *corresponding author: husam171984@gmail.com (received: 24th october 2019; accepted: 18th march 2020; published on-line: 4th january 2021) abstract: power system stabilizer is used to improve power system low frequency oscillations during small disturbances. in large scale power systems involving a large number of generators, psss parameter tuning is very difficult because of the oscillatory modes’ low damping ratios. so, the pss tuning procedure is a complicated process to respond to operation condition changes in the power system. some studies have been implemented on pss tuning procedures, but the harmony search algorithm is a new approach in the pss tuning procedure. in power system dynamic studies at the first step system total statues is considered and then the existed conditions are extended to the all generators and equipment. generators’ pss parameter tuning is usually implemented based on a dominant operation point in which the damping ratio of the oscillation modes is maximized. in fact the psss are installed in the system to improve the small signal stability in the system. so, a detailed model of the system and its contents are required to understand the dynamic behaviours of the system. in this study, the first step was to linearize differential equations of the system around the operation point. then, an approach based on the modified harmony search algorithm was proposed to tune the pss parameters. abstrak: penstabil sistem kuasa digunakan bagi meningkatkan sistem kuasa ayunan frekuensi rendah semasa gangguan kecil. dalam sistem kuasa berskala besar yang melibatkan sebilangan besar penjana, penalaan parameter pss adalah sangat sukar kerana nisbah corak ayunan redaman yang rendah. maka, langkah penalaan pss adalah satu aliran rumit bagi mengubah keadaan operasi sistem kuasa. beberapa kajian telah dilaksanakan pada prosedur penalaan pss, tetapi algoritma harmony search merupakan pendekatan baru dalam prosedur penalaan pss. dalam kajian sistem kuasa dinamik ini, langkah pertama adalah dengan memastikan status total sistem dan keadaan sedia ada diperluaskan kepada semua penjana dan peralatan. parameter penalaan generator pss biasa dilaksanakan berdasarkan titik operasi yang dominan di mana nisbah corak ayunan redaman dimaksimumkan. malah pss dipasang di dalam sistem bagi meningkatkan kestabilan isyarat kecil dalam sistem. oleh itu, model terperinci sistem dan kandungannya diperlukan bagi mengenal pasti perihal sistem dinamik. kajian ini, dimulai dengan melinear sistem persamaan pembezaan pada titik operasi. kemudian, pendekatan berdasarkan algoritma harmony search yang diubah suai telah dicadangkan bagi penalaan parameter pss. keywords: power system stabilizer (pss); power system; harmonic search algorithm 47 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 1. introduction small-signal fluctuation stability is a major issue for power system security and reliability. these fluctuations affect the power system’s natural damping [1]. pss, if welltuned, will have the ability to function properly in the system [2]. although these stabilizers have a simple and robust structure, their configuration, even with computer simulation or field testing, involves a highly skilled process for system parameters [3]. these parameters are not readily available and may, during normal operation of the power system, change the values of the parameters [4]. these parameters cannot be measured directly so they should be well estimated [5]. recently, several heuristic search algorithms have been proposed for tuning, pss parameters, such as tab search [6] evolutionary programming [7], and particle swarm optimization (pso) [8] were suggested to evaluate the pss parameters. however, these methods failed to determine precise parameters when the system has a specific objective function with a large-scale number of parameters. 2. problem formulation the power system can be described using a set of first-order nonlinear differential equations[8]: �̇� = 𝑓(𝑥,𝑢) (1) where �̇� or 𝑥 is the state variables vector, and 𝑢 is the vector of input variables.the linearized models of a power system can be used to design the power system stabilizers. therefore, the state equation of the power system with stabilizers can be written as [9]: ∆�̇� = 𝐴∆𝑋 + 𝐵𝑈 (2) ∆𝑦 = 𝐶∆𝑋 + 𝐷∆𝑈 (3) where ∆ represents small changes, 𝑋 is the state vector of order n, 𝑦 is the output vector of order m, 𝑈 is the input vector of order r, 𝐴 is a square matrix of states of size n, 𝐵 represents a control matrix with size n × r, 𝐶 refers to the output matrix with size m × n, 𝐷 is the leading matrix with the size m × r. a traditional lead-lag compensator pss is utilized in this study. the transfer function of the pss is described by the following equation [10]: 𝑉𝑖 = 𝐾𝑖 𝑠𝑇𝜔 1+𝑇𝜔 (1+𝑠𝑇1𝑖) (1+𝑠𝑇2) (1+𝑠𝑇3𝑖) (1+𝑠𝑇4) ∆𝜔𝑖 (4) where 𝑉𝑖 is the output signal for pss at 𝑖th machine, 𝐾𝑖 the stabilizer gain, 𝑇𝜔 represents the time constant, ∆𝜔𝑖 speed deviation of 𝑖th machine from the synchronous speed. 3. objective functions the objective functions are formulated by tuning the pss parameter and there are three different objective functions that have been used in many studies to set parameters, which will be discussed below: a) the damping factor can be considered as the first objective as follows [11]: 48 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 ( max 1≤𝑞≤𝑛𝑞 𝜎𝑞) 𝑦 (5) ( max 1≤𝑞≤𝑛𝑞 𝜎𝑞 − 𝜎0) 𝑦 (6) ( max 1≤𝑞≤𝑛𝑞 𝜎𝑞 − 𝜎0) 1 + ( max 1≤𝑞≤𝑛𝑞 𝜎𝑞 − 𝜎0) 2 + ⋯( max 1≤𝑞≤𝑛𝑞 𝜎𝑞 − 𝜎0) 𝑛𝑦 (7) 𝑀𝑖𝑛𝐹1 = ∑ ( max 1≤𝑞≤𝑛𝑞 𝜎𝑞 − 𝜎0) 𝑦 𝑛𝑦 𝑦=1 (8) where, 𝑛𝑦 are the all operating statuses of the test system, 𝑛𝑞 denotes the number of eigenvalues under 𝑛𝑦, 𝜎𝑞 is the damping factor , 𝜎0 is damping factor constant .when the 𝐹1 ( 𝜎𝑞 is defined as damping factor) is less than or equal to zero, the response for the maximum damping factor ( max 1≤𝑞≤𝑛𝑞 ) is less than or exactly equal to the expected value 𝜎0,[12]. b) the damping ratio can be considered as the second objective as follows [13]: 𝑀𝑖𝑛𝐹2 = ∑ (𝜁0 − min 1≤𝑞≤𝑛𝑞 𝜁𝑞) 𝑦 𝑛𝑦 𝑦=1 (9) where 𝜁0 represents the predicted damping ratio constant, and 𝜁𝑞 represents the damping ratio. when 𝐹2 is less than or equal to zero, the response is the minimum damping ratio(s) ( min 1≤𝑞≤𝑛𝑞 𝜁𝑞) are more than or exactly the value of 𝜁0 [14]. c) the damping ratio and damping factor can be considered as the third objective as follows [15]: 𝑀𝑖𝑛𝐹3 = ∑ ( max 1≤𝑞≤𝑛𝑞 𝜎𝑞 − 𝜎0) 𝑦 + 𝛼∑ (𝜁0 − min 1≤𝑞≤𝑛𝑞 𝜁𝑞) 𝑦 𝑛𝑦 𝑦=1 𝑛𝑦 𝑦=1 (10) where 𝛼 is the weight for combining both damping ratio and damping factor. 4. proposed objective function the objective functions f1, f2, and f3 produce high frequency or low frequency, which may reduce the life of system devices [16].therefore, we can overcome the disadvantages mentioned earlier through the following equation [17] : 𝑋 = −(𝜎−𝜎0) √(𝜎−𝜎0) 2+𝜔2 × 100% (11) 𝑀𝑖𝑛𝐹4 = ∑ (𝑋0 − min 1≤𝑞≤𝑛𝑞 𝑋𝑞) 𝑦 𝑛𝑦 𝑦=1 (12) 49 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 where x: the constant value for the prospective damping scale xq: the damping scale for the qth eigenvalue the following equations present the constraints of the pss parameter design model [18]: { 𝐾𝑚𝑖𝑛 ≤ 𝐾 ≤ 𝐾𝑚𝑎𝑥 𝑇1𝑚𝑖𝑛 ≤ 𝑇1 ≤ 𝑇1𝑚𝑎𝑥 𝑇2𝑚𝑖𝑛 ≤ 𝑇2 ≤ 𝑇2𝑚𝑎𝑥 𝑇3𝑚𝑖𝑛 ≤ 𝑇3 ≤ 𝑇3𝑚𝑎𝑥 𝑇4𝑚𝑖𝑛 ≤ 𝑇4 ≤ 𝑇4𝑚𝑎𝑥 } (13) 5. the proposed algorithm harmonic search algorithm is one of the simplest and most up-to-date methods, which is the process of finding the optimal solution to the problem. this method was used for the first time in 2001 [19]. harmony search is inspired by the process of jazz musicians to find the optimal solution. in this algorithm, each solution is called a harmonic and is represented by a vector (n). this algorithm contains the following steps [20]: a) primary generation (initial initialization) in the first step, the optimization problem is indicated by the relationship. also, at this step, the harmony memory size (hms) is calculated. 𝑀𝑖𝑛:{𝑓(𝑥)|𝑥 ∈ 𝑋} (14) 𝑆𝑢𝑏𝑗𝑒𝑐𝑡 𝑡𝑜 ∶ 𝑔(𝑥) ≥ 0 ℎ(𝑥) = 0 (15) where: 𝑓(𝑥) is the objective function, ℎ(𝑥) and 𝑔(𝑥) are the functions of equal and unequal constraints respectively. also in this step, the hs algorithm parameters are specified. these parameters are [21] : 1) harmony memory size (hms), or the number of solution vectors in the harmony memory. 2) harmony memory considering rate (hmcr), hmcr ∈ [0,1]. 3) pitch adjusting rate (par) ∈ [0,1]. 4) stopping criterion or number of improvisations (ni) b) primary harmonic memory determination at this step, the harmony matrix (hm) is created from a large number of solution vectors that are created randomly[22]. 𝐻𝑀 = [ 𝑥1 1 𝑥2 1 … 𝑥𝑁−1 1 𝑥𝑁 1 𝑥1 2 𝑥2 2 … 𝑥𝑁−1 2 𝑥𝑁 2 ⋮ 𝑥1 𝐻𝑀𝑆−1 𝑥1 𝐻𝑀𝑆 ⋮ 𝑥1 𝐻𝑀𝑆−1 𝑥2 𝐻𝑀𝑆 ⋮ ⋯ ⋯ ⋮ 𝑥1 𝐻𝑀𝑆−1 𝑥𝑁−1 𝐻𝑀𝑆 ⋮ 𝑥1 𝐻𝑀𝑆−1 𝑥𝑁 𝐻𝑀𝑆 ] (16) c) new harmonic production based on improvisation d) a new harmonic vector 𝑥′(𝑥1 ′ ,𝑥2 ′ ,…. . ,𝑥𝑁 ′ )is produced based on three rules that it describes as improvised: 1) harmony memory considering rate (hmcr) 50 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 2) sound regulation 3) random selection e) updating harmony memory: if the new harmonic vector is better than the worst harmonic vector based on the selected target function, the new harmony is placed inside and the worst harmonic is left out of the set. f) check the stopping criterion: when the termination criterion is satisfied, the calculations are completed, otherwise, steps 3 and 4 are repeated. 6. modified harmony search (mhs) the disadvantages of the hs method are the use of par and bandwidth, bw, constant values, which makes it difficult to set up these parameters. another disadvantage of the hs is that the number of repetitions for which the algorithm needs to find the optimal solution is not appropriate [23]. if par is small and bw is large, the algorithm's performance is weak hence increased ni improvements are required to find that optimal solution fig. 1. fig. 1: a) change of par with iteration number, b) change of bw with iteration number 3-or 4. the initial iteration of the hs has large bw and small par , which leads to increase the entire solution space of the search algorithm. these values are appropriate for subsequent replies in order to locally search. mhs is similar to hs, with a little difference in that par and bw parameter values are dynamically generated in each individual iteration according to the following relationships [24]: 𝑃𝐴𝑅(gn) = 𝑃𝐴𝑅𝑚𝑖𝑛 + 𝑃𝐴𝑅𝑚𝑎𝑥 − 𝑃𝐴𝑅𝑚𝑖𝑛 𝑁𝐼 × 𝑡 (17) where, par(t) = pitch adjusting rate for each iteration 𝑃𝐴𝑅𝑚𝑖𝑛= minimum pitch adjusting rate 𝑃𝐴𝑅𝑚𝑎𝑥= maximum pitch adjusting rate 𝑁𝐼 = number of solution vector iteration 𝑡 = iteration number 51 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 𝑏𝑤(𝑡) = 𝑏𝑤𝑚𝑎𝑥 × 𝑒 [ 1𝑛[ 𝑏𝑤𝑚𝑖𝑛 𝑏𝑤𝑚𝑎𝑥 ] 𝑁𝐼 ×𝑡] (18) where, 𝑏𝑤(𝑡) = bandwidth for each iteration 𝑏𝑤𝑚𝑖𝑛= minimum bandwidth 𝑏𝑤𝑚𝑎𝑥= maximum bandwidth 7. pss design and simulation results in this study, the mhs algorithm is used to obtain the optimal design of the pss parameters for the system of four generators shown in fig. 2 [25] and compare results with other techniques (harmony search, classic approach). . fig. 2: single-line diagram of the 4-generator system. 7.1 case 1: the stability of four-generators without pss in this case, the system was tested after the fault at bus-3 without pss to demonstrate the effect of pss on the stability of this system. according to table 1, the system is unstable. from figures 3 and 4, it is observed that the rate of voltage changes and oscillation of the generator’s speed are very high and the system is practically unstable. table 1: the four-generator data without pss generators eigenvalues frequencies damping ratios 1,2,3,4 ±3.994j 0.6354 -0.0134 3,4 ±7.274j 1.1577 0.0668 1,2 ±7.323j 1.655 0.0658 52 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 fig. 3: the bus voltage changes after the fault at bus-3 without pss fig. 4: generator speed changes after the fault at bus-3 without pss. 7.2 case 2: the stability of four-generators with pss based on (mhs) in this case, pss is installed on each generator which will guarantee stability of the system and restrain unwanted oscillations. thus, the pss parameter is set based on the (mhs) algorithm. the results of the modified harmonic search for the parameters are presented in table 2. from fig. 5 and fig. 6 it is clear that the oscillations due to disturbances are completely repressed and the dynamic state of the system improved. all this happened only after installation of the pss. figure 7 explains the convergence of the objective function with mhsa and hsa. from this figure, it is clear that mhsa shows superior performance over hsa. the proposed method obtained the solution after 210 iterations while the hsa reached the solution after 300 iterations. this speed in finding the optimal solution is very important in the stability of the system. table 2: optimal designed parameters of mhs generator 4t 3t 2t 1t wt k 1 0.01 0.08 0.01 0.07 10 100 2 0.02 0.1 0.02 0.09 10 127 3 0.01 0.1 0.01 0.1 10 148 4 0.02 0.08 0.02 0.12 10 95 53 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 fig. 5: voltage changes on the bus number 3 with pss. fig. 6: generator speed changes after the fault at bus 3 with pss. fig. 7: convergence characteristics of hsa and mhsa techniques. furthermore the above results are compared with those presented in [26] for the 4generator system. in this reference, the parameters were obtained using the sensitivity analysis method. table (3) shows the results of the special system values with stabilizer in the two studies. from fig. 8-9 and table 3, it is very clear that the performance of the pss 54 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 designed using mhsa is far better compared to the pss designed using sensitivity approach (tsa) and harmony search. fig. 8: voltage changes at bus 3 after fault in the three-phase system. fig. 9: the changes of the first generator speed. table 3: eigenvalues of the system 4 generators for modified harmony search method and trajectory sensitivity approach generators eigenvalues frequencies damping ratios mhs -2.138±j5.738 0.856 0.397 -2.714±j6.736 0.891 0.391 -1.130±j4.214 0.637 0.268 trajectory sensitivity approach (tsa)[26] -1.938±j5.738 0.913 0.319 -2.165±j5.936 0.945 0.343 -0.530±j3.504 0.558 0.149 8. conclusion transient and small-signal stability are critical in power system operation and control studies due to their impact on consumers. thus power system stabilizers could be used to solve this issue. a modified harmonic search algorithm was proposed to tune the pss parameters to overcome the drawbacks of the previously suggested algorithms. the mhs results show that adjusted stabilizers have improved performance. the proposed method was applied to a system of four generators. the mhs algorithm results were compared 55 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 with the results of the sensitivity analysis method, which was previously suggested for this purpose. the comparison indicates the superiority of this algorithm to obtain the optimal parameters to set the stabilizer. references [1] elazim sma, ali es. (2016) optimal power system stabilizers design via cuckoo search algorithm. international journal of electrical power & energy systems.75:99-107. [2] chitara d, niazi kr, swarnkar a, gupta n. (2018) cuckoo search optimization algorithm for designing of a multimachine power system stabilizer. ieee transactions on industry applications.54(4):3056-3065. [3] chaib l, choucha a, arif s. (2017) optimal design and tuning of novel fractional order pid power system stabilizer using a new metaheuristic bat algorithm. ain shams engineering journal.8(2):113-125. [4] radmehr m, mohammadjafari m, ghadisahebi mr. (2018) loc-pss design for improved power system stabilizer. journal of applied dynamic systems and control.1(1):47-54. [5] ray pk, paital sr, mohanty a, eddy fys, gooi hb. (2018) a robust power system stabilizer for enhancement of stability in power system using adaptive fuzzy sliding mode control. applied soft computing.73:471-481. [6] ali es. (2014) optimization of power system stabilizers using bat search algorithm. international journal of electrical power & energy systems.61:683-690. [7] pattanaik jk, basu m, dash dp. (2019) dynamic economic dispatch: a comparative study for differential evolution, particle swarm optimization, evolutionary programming, genetic algorithm, and simulated annealing. journal of electrical systems and information technology.6(1):1. [8] sambariya dk, prasad r. (2015) optimal tuning of fuzzy logic power system stabilizer using harmony search algorithm. international journal of fuzzy systems.17(3):457-470. [9] kumar a. (2015) power system stabilizers design for multimachine power systems using local measurements. ieee transactions on power systems.31(3):2163-2171. [10] bouchama z, essounbouli n, harmas mn, hamzaoui a, saoudi k. (2016)reaching phase free adaptive fuzzy synergetic power system stabilizer. international journal of electrical power & energy systems.77:43-49. [11] islam nn, hannan ma, shareef h, mohamed a. (2017)an application of backtracking search algorithm in designing power system stabilizers for large multi-machine system. neurocomputing.237:175-184. [12] ke d, chung cy. (2016) design of probabilistically-robust wide-area power system stabilizers to suppress inter-area oscillations of wind integrated power systems. ieee transactions on power systems.31(6):4297-4309. [13] soliman hm, yousef ha. (2015) saturated robust power system stabilizers. international journal of electrical power & energy systems.73:608-614. [14] yaghooti a, buygi mo, shanechi mhm. (2015) designing coordinated power system stabilizers: a reference model based controller design. ieee transactions on power systems.31(4):2914-2924. [15] farah a, guesmi t, abdallah hh, ouali a. (2016) a novel chaotic teaching–learning-based optimization algorithm for multi-machine power system stabilizers design problem. international journal of electrical power & energy systems.77:197-209. [16] soliman m. (2015) robust non-fragile power system stabilizer. international journal of electrical power & energy systems.64:626-634. [17] rahmatian m, seyedtabaii s. (2019) multi-machine optimal power system stabilizers design based on system stability and nonlinearity indices using hyper-spherical search method. international journal of electrical power & energy systems.105:729-740. [18] peres w, júnior ics, passos filho ja. (2018) gradient based hybrid metaheuristics for robust tuning of power system stabilizers. international journal of electrical power & 56 iium engineering journal, vol. 22, no. 1, 2021 abdul kareem et al. https://doi.org/10.31436/iiumej.v21i2.1276 energy systems.95:47-72. [19] wang g-g, gandomi ah, zhao x, chu hce. (2016) hybridizing harmony search algorithm with cuckoo search for global numerical optimization. soft computing.20(1):273-285. [20] gao k-z, suganthan pn, pan q-k, chua tj, cai tx, chong c-s. (2016) discrete harmony search algorithm for flexible job shop scheduling problem with multiple objectives. journal of intelligent manufacturing.27(2):363-374. [21] rezaie h, kazemi-rahbar mh, vahidi b, rastegar h. (2019 )solution of combined economic and emission dispatch problem using a novel chaotic improved harmony search algorithm. journal of computational design and engineering.6(3):447-467. [22] wang l, hu h, liu r, zhou x. (2019) an improved differential harmony search algorithm for function optimization problems. soft computing.23(13):4827-4852. [23] j. yi, l. gao, x. li, and j. gao, ‘an efficient modified harmony search algorithm with intersect mutation operator and cellular local search for continuous function optimization problems’, applied intelligence, vol. 44, no. 3, pp. 725–753, 2016. [24] yi j, gao l, li x, gao j.( 2016) an efficient modified harmony search algorithm with intersect mutation operator and cellular local search for continuous function optimization problems. applied intelligence.44(3):725-753. [25] c. canizares et al., ‘benchmark models for the analysis and control of small-signal oscillatory dynamics in power systems’, ieee transactions on power systems, vol. 32, no. 1, pp. 715–722, 2016. [26] yuan sq, fang dz. (2009) robust pss parameters design using a trajectory sensitivity approach. ieee transactions on power systems.24(2):1011-1018. 57 the analysis of liquefaction phenomenon of the flexible pavement using seismic iium engineering journal, vol. 20, no. 1, 2019 kusumawardani et al. the analysis of liquefaction phenomenon of the flexible pavement using seismic monitoring equipment rini kusumawardani*, untoro nugroho, sri handayani and mareta aspirilia fananda soil mechanics laboratory, civil engineering department, universitas negeri semarang, semarang, indonesia. *corresponding author: rini.kusumawardani@mail.unnes.ac.id (received: 4th dec 2018; accepted: 15th march 2019; published on-line: 1st june 2019) https://doi.org/10.31436/iiumej.v20i1.9031 abstract: liquefaction phenomenon is generally caused by high dynamic vibrations in a very short duration. this article investigated the behavior of dynamic vibrations caused by vehicles on the road. this study employed the hvsr (horizontal vertical spectral ratio) with an accelerometer. the result of dynamic vibration generated by the passing vehicle or the micro tremor / micro seismic vibration was recorded by seismic monitoring devices. this seismic monitoring equipment converted vibration into natural frequency (f0) and amplification (a0) using geopsy software. the result of hvsr (horizontal vertical spectral ratio) was the soil vulnerability index (kg). the results of this study indicated that the three parameters above were then analyzed with the assumption that if the amplification value (a0) was higher and associated with a lower natural frequency value (ƒ0) with a high vulnerability index (kg), then the area had potential liquefaction, with laboratory research results in the form of granular gradation testing as the supporting data. therefore, the results of the analysis and the laboratory work lead to the conclusion that the study area of majapahit street has potential for liquefaction. abstrak: fenomena pencairan umumnya disebabkan oleh getaran dinamik tinggi dalam tempoh singkat. artikel ini mengkaji fenomena getaran dinamik yang disebabkan oleh kenderaan di jalan raya. kajian ini menggunakan hvsr (nisbah spektral menegak mendatar) dengan alat pengukur pecutan. hasil getaran dinamik yang dihasilkan oleh kenderaan yang lalu-lalang atau gegaran mikro / getaran seismik mikro telah direkodkan oleh alat pemantauan seismik. alat pemantauan seismik ini mengubah getaran kepada frekuensi semula jadi (f0) dan amplifikasi (a0) menggunakan perisian geopsy. hasil hvsr (nisbah spektral menegak mendatar) ini adalah indeks kelemahan tanah. keputusan kajian ini menunjukkan bahawa tiga parameter di atas kemudiannya dianalisa dengan anggapan bahawa jika nilai amplifikasi (a0) adalah lebih tinggi dan nilai frekuensi semulajadi (ƒ0) lebih rendah dengan indeks kelemahan yang tinggi (kg), maka kawasan ini mempunyai potensi pencairan. penyelidikan makmal yang dilakukan pada kajian ini berupa ujian tingkatan granular sebagai data sokongan. oleh itu, hasil analisis dan ujian makmal menunjukkan lokasi penyelidikan ini iaitu jalan majapahit mempunyai potensi pencairan akibat lalu lintas kenderaan. keywords: liquefaction; flexible pavement; soil vulnerability index (kg); seismic monitoring; hvsr (horizontal vertical spectral ratio) method 70 iium engineering journal, vol. 20, no. 1, 2019 kusumawardani et al. 1. introduction the liquefaction phenomenon is the behavior of collapsed soil that occurs over a short period of time that is caused by dynamic load [1]. according to legrans [2], liquefaction is a condition where the soil experiences continuous deformation at residual stresses or low residual resistance caused by the formation of high pore pressure that decreases effective pressure. the increase in pore water pressure that causes liquefaction can be caused by static or cyclic stresses, and the possibility of liquefaction depends on the number of pores, the relative density, and total pressure. soil mass suddenly experiences a transition from a solid state to a liquid state or has a major consistency like a liquid. one of the main requirements for liquefaction includes the presence of dynamic load on loose sandy soil (not dense) that is saturated with water. however, some studies assume that liquefaction is only triggered by earthquakes [3-5]. the impact of liquefaction itself could trigger a problem in the structure of singleor multi-storey buildings and also the pavement structure. the liquefaction phenomenon, as illustrated on fig. 1, occurred in 2011 as the result of the earthquake in christchurch, new zealand. the liquefaction phenomenon caused all pavements to be submerged by water and sand boiling to occur. fig. 1: the impact of liquefaction in christchurch, new zealand [6]. kusumawardani [7,8] argues that the liquefaction potential can also occur in vibrations that have a low frequency but occur repeatedly over a long time. her study was continued in the following year by analyzing the behavior of soil particle vibrations due to vehicle types [9] and thickness of the pavement [10]. the acceleration of soil particles in subgrade was examined by 3-way review (x, y and z). the analysis results showed positive correlation between vehicle type, pavement thickness and acceleration. these parameters have contributed to the behavior of the soil particle acceleration that it passes through. changes in the behavior of particle acceleration caused the load of passing vehicles affected the performance of the flexible pavement system. the flexible pavement system resisted the load of the passing vehicle and then transmitted the load from the top layer to the layer below. the soil vibrations caused by traffic, industry, and human activity on the earth's surface are called micro tremor vibrations. micro tremor data can be analyzed using the hvsr (horizontal to vertical spectral ratio) method [19]. when the 71 iium engineering journal, vol. 20, no. 1, 2019 kusumawardani et al. vehicle passed, the soil particles under the pavement moved from their original position to find their stability. the illustration of particle movements under the pavement is contained in fig. 2. the loading from the vehicle passage is assumed to be dynamic loading. soil, as a propagation medium for a dynamic wave, has dynamic properties that show the ability of the soil to support a dynamic load. the soil could collapse when the effective soil decreases as an effect of dynamic load to the soil mass particles. this raises the assumption that liquefaction can be caused by the load of passing vehicles. fig. 2: illustration of soil particle movement due to vehicle load passed [9]. 2. study of literature 2.1 the soil vulnerability index (kg) the soil vulnerability index is a parameter used in identifying a vulnerable area against strong soil motion [11]. this parameter shows the soil resistance index against deformation for receiving seismic and dynamic loads. to figure out the index, the horizontal to vertical spectral ratio (hvsr) method is generally used [12]. this method compares the ratio of the horizontal components to the vertical components of the micro tremor signal spectrum [13]. the micro tremor signal is obtained from the accelerometer data installed in the field that consists of three components: vertical (z), horizontal x (north-south) and horizontal y (east-west). the fast fourier transform (fft) algorithm was used to analyze the results of field measurement. the comparison value of horizontal and vertical components (h/v) was obtained using hvsr analysis. the result was represented in the h/v amplitude versus frequency curve (fig. 3). the curve in fig. 3 shows the predominant frequency value and amplification factor, which was then used to calculate the soil vulnerability index (kg) using the following equation: (1) 72 iium engineering journal, vol. 20, no. 1, 2019 kusumawardani et al. where, kg is soil vulnerability index, ag is soil amplification, f0 is natural frequency (hz) and vb is wave velocity (m/s 2). fig. 3: the h/v amplitude versus frequency curve was obtained by using hvsr analysis [14]. 2.2 micro-seismic data a load that occurs repeatedly that can cause liquefaction is also called a micro seismic vibration. micro seismic vibration itself is soil vibration caused by traffic, industry, and human activity on the earth's surface. sources of soil vibrations caused by natural factors such as the interaction of wind and building structures, earthquakes, currents, and long period ocean waves can also affect micro seismic vibrations [15]. micro seismic vibration is a natural vibration (ambient vibration) that could come from two main sources: natural and human factors [13]. records of soil motion always contain ambient vibration (micro seismic). it shows that the soil is never really in a state of silence without vibration. all energy sources generate seismic waves such as the sea and continuous meteorological disturbances. therefore, they become a background of noise at all times [16]. 3. methodology of research 3.1 study area the location of the study was majapahit street, semarang, central java which can be seen in fig. 4. in this location, the occurrence of road damage was detected annually. this area is known as busy area traffic in semarang city. the numbers of passing vehicles, variations in the type of vehicles passing and the type of pavement are the parameters in this study. some field investigation was conducted during the research, there was manual traffic counting and installation of a set of acceleration equipment. the study area was selected considering the ease of access, heavy traffic flow, and ease of data retrieval. 3.2 field investigation field investigation at the location of the study was aimed at looking at the pavement condition of the road to be examined and determining the position of seismic monitoring equipment. the equipment placement model was based on previous research, where the sensor devices were embedded under the pavement. variations in the placement of sensor devices and the thickness of pavement were carried out to determine the behavior of particles caused by traffic loads [7,17]. during the testing, the accelerometer was placed beneath the pavement. the illustration of the investigation field can be seen in fig. 5(a). 73 iium engineering journal, vol. 20, no. 1, 2019 kusumawardani et al. the peak traffic hour was selected for the equipment installed during data retrieval. by combining with a set of video cameras to capture the type of passing vehicle, the correlation of the passing vehicle type and the micro tremor data was obtained. fig. 4: map of the study location. fig. 5: installation of the accelerometer in the field. 3.3 geopsy this software, which is popular in the geophysics field, processes the field investigation data obtained from acceleration recording. when the data processing is running, several windows appeared that indicated the three-directional signal obtained accelerometer (a) placement model for equipment (b) equipment installation during the research 74 iium engineering journal, vol. 20, no. 1, 2019 kusumawardani et al. (fig. 6). the information suggested by geopsy is recording time, number of signals, and frequency. after finished the analysis process, the result of the geopsy is the spectrum that described the natural frequency (f0) and soil amplitude (a0) of the study area. fig. 6: geopsy result data. 4. results and discussion 4.1 average daily traffic fig. 7: number of vehicles during peak hours at majapahit street. in order to obtain the vehicle's average daily traffic data on majapahit street, a three day survey was conducted to obtain the traffic characteristics in the study area. this preliminary investigation was carried out to determine the estimated peak hours on the study area. the data of numbers of vehicles during peak hours was obtained by an observation for 48 hours with a 15 minute observation interval. from fig. 7, it can be concluded that the peak hours on majapahit street usually occurred in the morning hours, (08.00-09.00). data was gathered for 1 hour by preparing seismic monitoring sensor equipment to record waves every 5 minutes. 4.2 natural frequency (f0), amplification (a0) and soil vulnerability index (kg) the natural frequency is the frequency that often appears or the frequency of the rock layer. it indicates the type and characteristics of the rock in the study area. high frequency values reflect more massive rock material such as andesite breccia rock, while low n um be r o f v eh ic le s 75 iium engineering journal, vol. 20, no. 1, 2019 kusumawardani et al. frequency values indicate sediment at the location of study where there is topsoil or clay on the surface. the low frequency value confirms that the location experiences damage caused by severe vibration [12]. the value of soil amplification can increase if the rock has experienced deformation (weathering, folding or faulting) that changes the physical properties of the rock. in the same area, the amplification value varies according to the level of deformation and weathering of the rock [18]. in nakamura [13], the value of soil amplification is related to the ratio of the contrast impedance of the surface layer to the layer below. figures 8 and 9 are micro tremor data and h/v graphs obtained at the location of the study. recapitulation of the results of natural frequency analysis, amplification, and vulnerability of soil at the location of the study can be seen in table 1. fig. 8: the micro tremor data display at majapahit street after being processed using geopsy software. fig. 9: the display of h/v graph at majapahit street with the results of natural frequency (f0) 2,35329 and amplification (a0) 0,288553. 76 iium engineering journal, vol. 20, no. 1, 2019 kusumawardani et al. 5. conclusion the study of the analysis of liquefaction potential on flexible pavement using seismic monitoring equipment concluded these following results: a) the results of the micro tremor data from seismic monitoring equipment were in the form of natural frequency (f0) and amplification (a0). the two parameters were processed using the hvsr (horizontal to vertical spectral ratio) method to generate the soil vulnerability index of each location of the study. b) to analyze the liquefaction potential at the location of the study, it is assumed that the higher amplification value (a0) leads to the greater value of the soil vulnerability index (kg) in the location associated with the low natural frequency value (f0). these parameters indicated liquefaction potential. c) from the location of the study, the results of 1 hour of data collection using seismic monitoring equipment were then processed and analyzed. it was concluded that the location of the study had the potential for liquefaction. references [1] kusumawardani r, suryolelono k, suhendro b, rifa’i a. (2013). dynamic behaviour of yogyakarta’s sand under cyclic triaxial testing. international journal of civil & environmental engineering, 13(2): 23-28. [2] legrans, roski (2016). liquifaction study based on standard penetration test in belang coast beach south minahasa. jurnal tekno, 14(65): 37-48. [3] bird jf, boulanger rw, idriss im. (2005). engineering geology | liquefaction. reference module in earth systems and environmental sciences. encyclopedia of geology. pages 525-534. [4] idriss im, boulanger rw. (2006) semi-empirical procedures for evaluating liquefaction potential during earthquakes. journal soil dynamics and earthquake engineering, 26: 115130. [5] idriss im, boulanger rw. (2015). 2nd ishihara lecture: sptand cpt-based relationships for the residual shear strength of liquefied soils. journal soil dynamics and earthquake engineering, 68: 57-68. [6] woodford k. (2011). understanding the christchurch earthquake : building image. download from https://keithwoodford.wordpress.com/2011/02/27/understanding-thechristchurch-earthquake-building-damage/ [7] kusumawardani r, suryolelono kb, suhendro b, rifa'i a. (2016). the dynamic response of unsaturated clean sand at a very low frequency. international journal of technology, 7(1): 123-131. [8] kusumawardani r, suryolelono kb, suhendro b, rifa’i a. (2014). the loading frequency effects of yogyakarta sand under cyclic triaxial testing. international journal of civil & environmental engineering, 14(2): 7-12. [9] kusumawardani r, nugroho u, lashari l, fansuri mh, mindiastiwi t, yuniarti w, hilmi, af. (2017). investigation of subgrade particles acceleration due to dynamic loading. aceh international journal of science and technology, 6(3): 97-103. [10] kusumawardani r, nugroho u, fansuri mh, mindiastiwi t, yuniarti w, hilmi as. (2018). the impact of vehicle load inducing vibrations on the subgrade soil particle acceleration. journal of engineering science and technology 13 (6): 1440-1450. [11] karyono (2016). kajian kerentanan tanah berdasarkan analisis hvsr di daerah semburan lumpur sidoarjo dan sekitarnya, jawa timur, indonesia. jurnal meteorologi dan geofisika 17(1): 61-68 77 iium engineering journal, vol. 20, no. 1, 2019 kusumawardani et al. [12] putri ra. (2017). mapping of earthquake microzonation in solok area, west sumatera based on microtremor investigaton hsvr (horizontal to vertical spectral ratio). final year project. universitas lampung, lampung, indonesia. [13] nakamura y, sato t, nishinaga m. (2000). local site effect of kobe based on microtremor measurement. proceeding of the sixth international conference on seismic zonation eeri, palm springs california [14] galliot (2016) hv toolbox hv. geopsy.org [15] petermans t, devleeschouwer x, pouriel f, rosset p. (2006). mapping the local seismic hazard in the urban area of brussels, belgium. proceeding of iaeg 2006 paper no 424. [16] febriani y, daruwati i, rindi gh. (2013). analisis nilai peak ground acceleration dan indeks kerentanan seismic berdasarkan data mikroseismik pada daerah rawan gempabumi di kota bengkulu. edu research 2(2): 85-90. [17] nugroho u, kusumawardani r, yuniarti w, hilmi as. (2017). analysis of esal factor on flexible pavement at weleri ring road, indonesia. aip conference proceedings 1818, 020037 (2017); doi: 10.1063/1.4976901 [18] arifin ss. (2014). determination of earthquake prone area based on amplification hsvr microtremor and dominant period analysis in liwa area. jurnal geofisika eksplorasi, 2(1): 30-40. [19] lestari fp, pujiastuti d, arifin h. (2016). vulnerability indeks analysis in padang area (case study west padang and kuranji. jurnal fisika unand, 5(1):42-46. 78 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <feff004f0076006500200070006f0073007400610076006b00650020006b006f00720069007300740069007400650020006b0061006b006f0020006200690073007400650020007300740076006f00720069006c0069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400650020006b006f006a00690020007300750020007000720069006b006c00610064006e00690020007a006100200070006f0075007a00640061006e00200070007200650067006c006500640020006900200069007300700069007300200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e006100740061002e0020005300740076006f00720065006e0069002000500044004600200064006f006b0075006d0065006e007400690020006d006f006700750020007300650020006f00740076006f007200690074006900200075002000700072006f006700720061006d0069006d00610020004100630072006f00620061007400200069002000410064006f00620065002000520065006100640065007200200036002e0030002000690020006e006f00760069006a0069006d0020007600650072007a0069006a0061006d0061002e> /hun <feff0045007a0065006b006b0065006c0020006100200062006500e1006c006c00ed007400e10073006f006b006b0061006c002000fc007a006c00650074006900200064006f006b0075006d0065006e00740075006d006f006b0020006d00650067006200ed007a00680061007400f30020006d00650067006a0065006c0065006e00ed007400e9007300e900720065002000e900730020006e0079006f006d00740061007400e1007300e10072006100200061006c006b0061006c006d00610073002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b006100740020006b00e90073007a00ed0074006800650074002e002000200041007a002000ed006700790020006c00e90074007200650068006f007a006f007400740020005000440046002d0064006f006b0075006d0065006e00740075006d006f006b00200061007a0020004100630072006f006200610074002000e9007300200061007a002000410064006f00620065002000520065006100640065007200200036002c0030002d0073002000e900730020006b00e9007301510062006200690020007600650072007a006900f3006900760061006c0020006e00790069007400680061007400f3006b0020006d00650067002e> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <feff004e006100750064006f006b0069007400650020016100690075006f007300200070006100720061006d006500740072007500730020006e006f0072011700640061006d0069002000730075006b0075007200740069002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c002000740069006e006b0061006d0075007300200076006500720073006c006f00200064006f006b0075006d0065006e00740061006d00730020006b006f006b0079006200690161006b006100690020007000650072017e0069016b007201170074006900200069007200200073007000610075007300640069006e00740069002e002000530075006b00750072007400750073002000500044004600200064006f006b0075006d0065006e007400750073002000670061006c0069006d006100200061007400690064006100720079007400690020007300750020004100630072006f006200610074002000690072002000410064006f00620065002000520065006100640065007200200036002e00300020006200650069002000760117006c00650073006e0117006d00690073002000760065007200730069006a006f006d00690073002e> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 performance analysis on dynamic wireless charging for electric vehicle using ferrite core siti hajar yusoff*, amira aziera abdullah, nadia nazieha nanda and ahmed samir abed badawi department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia *corresponding author: sitiyusoff@iium.edu.my (received: 18th october 2020; accepted: 15th july 2021; published on-line: 4thjanuary 2022) abstract: the technology of dynamic wireless power transfer (wpt) has been accepted in the electric vehicle (ev) industry. recently, for a stationary ev charging system, the existence of a ferrite core improves power efficiency. however, for dynamic wireless charging, the output power fluctuates when the ev moves. two main obstacles that must be dealt with is air-gaps and misalignment between the coils. this paper investigates clear design guidelines for fabrication of an efficient resonant inductive power transfer (ript) system for the ev battery charging application using a ferrite core. two different geometry shapes of ferrite core, u and i cores, will be investigated and tested using simulation and experimental work. the proposed design was simulated in jmag 14.0, and the prototype was tested in the laboratory. the expected output analysis from these two techniques was that the power efficiency of the ferrite pair should first be calculated. from the analysis and experimental results, it is seen that the pair of ferrite cores that used a u shape at the primary and secondary side provides the most efficient coupling in larger air-gap ript application with 94.69% on simulation jmag 14.0 and 89.7% from conducting an experiment. abstrak: teknologi alih kuasa wayarles (wpt) dinamik telah diterima pakai dalam kenderaan elektrik (ev). baru-baru ini, kewujudan teras ferit dalam sistem pengecasan pegun ev dapat meningkatkan kecekapan kuasa. namun, kuasa pengecasan ini akan berubah apabila ev bergerak bagi sistem pengecasan wayarles secara dinamik. dua halangan utama yang harus ditangani adalah ketidakjajaran dan jarak antara dua gegelung. kajian ini merupakan garis panduan yang jelas mengenai rekaan fabrikasi dan kecekapan sistem alih kuasa induktif resonan (ript) bagi aplikasi pengecasan bateri ev menggunakan teras ferit. dua bentuk geometri teras ferit, iaitu teras u dan i telah dikaji dan diuji menggunakan simulasi dan eksperimen. rekaan ini telah disimulasi menggunakan jmag 14.0 dan prototaip diuji di dalam makmal. kedua-dua teknik ini diharapkan dapat menghasilkan kecekapan kuasa yang sama. dapatan kajian menunjukkan kedua-dua teras ferit pada sisi primer dan sekunder berbentuk u mempunyai gandingan paling efisien bagi jarak paling besar antara 2 gegelung menggunakan aplikasi ript dengan 94.69% simulasi jmag 14.0 dan 89.7% secara eksperimen. keywords: dynamic wireless charging; inductive wireless charging; ferrite core; electric vehicle (ev) 46 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 1. introduction an electric vehicle (ev) is an automobile vehicle that operates entirely on electricity without the emission of gases typical of conventional cars. the working principle is straightforward and plays a role in preventing environmental degradation. evs can be associated with the use of an electric motor for propulsion and powering by electricity, either by plug-in, battery, or solar panel sources. this vehicle is not a new concept but was instead developed in the mid-18th century. however, during the 20th century, evs became obsolete because of their limited driving range and high price compared to gasoline-powered vehicles. it is expected that by 2050, the number of vehicles on the road is expected to reach up to 2.5 billion [1]. regarding the future transport significance, evs are considered the likely replacement for internal combustion engine-driven vehicles. evs can reduce carbon discharges by reducing co2 emissions, air pollution, and reliance on imported fuel [2]. the government of malaysia also encourages electric cars by providing a total ev tax exemption [3]. due to this, ev technology has captured the world’s attention. many researchers have realized the significance of ev; thus, intense studies have been reported on this technology. evs have rechargeable batteries onboard, as shown in fig. 1. the power source no longer uses oil or gas and eliminates emissions since evs are 100% electrical transportation. instead, their source of power comes from a battery pack. this battery pack is charged using a wireless power transfer method. the primary transmitter coil acts as a transmitter to transmit the power from a primary to a secondary. the vehicle’s pick-up coil acts as the receiver, also known as the secondary, in order to charge the battery pack. referring to fig. 1, the fully charged battery pack acts as the energy source to drive the traction motor inside the vehicle. as with gas emission transports, the battery pack of an ev needs to be recharged first. fig. 1: electric vehicle (ev) system model [4]. battery recharging for ev can be done in three different ways, as stated by [5]: 1) static charging; 2) quasi-dynamic charging; 3) dynamic charging. 47 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 contactless charging or wireless charging is a new technology for ev power transfer. charging is done using a wireless power transmitter and receiver to supply continuous power to the ev. a few years back, evs only used static wireless charging (swc), where the vehicle needed to stay in the charging area throughout the recharge time. the problem or limitation in this technology is that the vehicle can only be charged when parked or in stationary modes such as parked in car parks and garages, or waiting at traffic lights [6]. the significant issues in public acceptance of ev correlate to its high battery cost and limited driving range. the lithium-ion battery is widely used as the primary power source for the ev’s drivetrain due to its high specific energy (100-265 w/kg) and specific power density (250340 w/kg) compared to other battery technologies. despite its superior characteristics, such a battery still adds considerable weight and size to the vehicle. for example, nissan leaf’s 24 kwh battery pack weighs around 200 kg. in addition to high weight and size, the estimated price for an ev is about double that of its gasoline counterparts, with nearly half of the cost going toward the battery alone [7]. the limited driving range is an even more significant obstacle to the market penetration than the vehicles’ higher cost. for example, gasoline vehicles can go over 500 km before refueling, which takes about 2-3 minutes at a filling station located every few kilometers. on the other hand, most evs can only go about 100-200 km before requiring another round of recharging that can last from about 30 minutes to more than 12 hours [8]. besides this, charging stations are not as readily available as fuel stations. these limitations of static charging evs has awakened researcher interest in a new dynamic charging method. the power transmission coil concept is used by the wpt method to transfer electric power from the primary grid source to energize the ev [9]. for a dynamic wpt, the vehicle needs to be charged while moving. thus, the significant problem of high-power loss is encountered. this high-power loss is due to significant air gaps and misalignment between the primary and secondary pads [10]. when the loss is significant, the efficiency of power transfer is low. much research has been done to mitigate the mentioned problem [11,12]. however, none have come out with the optimal solutions and high-power efficiency. the other problem related to power loss is also due to low magnetic flux density. as the air-gap increases or misalignment occurs between the primary and secondary pad, the magnetic flux density is also reduced. magnetic flux density is proportionally related to the induced current, thus directly affecting the power produced. as a result, low power transfer is due to having low magnetic flux density in primary and secondary coils. some researchers have suggested including a ferrite core inside the primary and secondary coils. however, the design of the ferrite core is still an open issue. adding an unsuitable ferrite core design can lead to unwanted additional weight and an increase in the manufacturing cost. that is why, even today, these problems are still in open research. the research in this paper builds upon the improvements of previous research on novel ferrite cores [13] in wireless charging for ev applications. in this paper, inductive wireless power transfer (iwpt) uses coils embedded in the roadway and the vehicles. the ipt system consists of a pair of loosely coupled coils as transmitter and receiver. when the current flows through the coils, the magnetic field will be generated and thus will provide a wireless power transfer [14]. figure 2 shows the inductive wireless power transfer system. 48 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 fig. 2: inductive wpt system [15]. 2. methodology this section will discuss the proposed methodology used in designing the wireless charging system. figure 3 shows the steps involved: calculation of coil parameters, identification of core shape, experimentation, and evaluation of results obtained. next, subsection 2.1 will discuss the process of design and simulation using jmag designer 14.0. finally, subsection 2.2 is the preparation of experimental work. in this study, the u and i ferrite core characteristics were investigated using two techniques. the first technique used a simulation on jmag designer 14.0. the simulation work was crucial for obtaining magnetic flux density for each pair of ferrite cores. six designs of ferrite core, as shown in table 1, were run in this simulation. in addition, air-gaps of 1 cm and 2 cm with no misalignment was tested on all pairs of the ferrite cores. fig. 3: steps for designing inductive charging coupler. the second technique used in this paper conducted an experiment to obtain the results from the prototype. the experiment was conducted in the university laboratory. from the simulation and experiment analyses, the power efficiency results were compared to each other in order to select the combination of ferrite cores that gave greatest power transfer. the calculation of parameters was first calculated, as discussed in [16]. in this paper, the power required for the ev was ratioed down to 16.7 w. in an actual application, 36 kw of power would be required. table 2 shows the parameters used in this study. table 2 lists the primary and secondary voltages, primary and secondary currents, load resistor, primary and secondary inductances, mutual inductance, and primary and secondary capacitors. figure 4 shows the flowcharts for the a) first and b) second technique, for simulation in jmag designer 14.0 and experimental work. by using the jmag software, the magnetic flux of each ferrite pair was measured. for the u ferrite core’s shape, there are three possible ways to wind the copper coil around the u core. therefore, this study focused on winding the copper coil around the u core. table 3 shows the winding method around the u shape. the three different winding methods were examined only for the u shape, while the coil was simply wound at the central limb for the i core. coil parameters core shape experimentation evaluation 49 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 next, the final part of this study experimented on six pairs of ferrite cores. the experiment varied the air-gap from 1 cm with 0 cm to 5 cm misalignment. section 3 will show the performance evaluation of each pair. table 1: six pair of ferrite core pair 1: primary u ferrite core and secondary coil pair 4: primary i ferrite core and secondary coil pair 2: primary coil and secondary u ferrite core pair 5: primary coil and secondary i ferrite core pair 3: primary and secondary u ferrite core pair 6: primary and secondary i ferrite core table 2: calculated parameters for wpt system parameters values 𝑽𝒑,𝒓𝒎𝒔 12 v 𝑽𝒔,𝒓𝒎𝒔 5 v 𝑰𝑷,𝒓𝒎𝒔 1.39 a 𝑰𝒔,𝒓𝒎𝒔 3.33 a 𝑹𝑳 1.5 ω 𝑳𝑷 330.72 μh 𝑳𝒔 36.65 μh m 22.0 μh 𝑪𝒑 113.3 nf 𝑪𝒔 1022.4 nf secondary side primary side secondary side primary side secondary side primary side secondary side primary side secondary side primary side secondary side primary side 50 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 fig. 4: flowchart of a) first technique b) second technique. table 3: winding method for u shape no. winding method for u shape illustration 1 central winding: the copper coil is winding at the center of the u ferrite core. 2 edge separate winding: the copper coil is winding separately at two edges of the u ferrite core. 3 edge together winding: the copper coil is winding in one direction only at the edge of the u ferrite core. 2.1 simulation using jmag 14.0 table 4 displays the geometry editor for six ferrite core pairs created in jmag 14.0 before running the simulation. 51 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 the blue, red, and yellow colors in all figures are indicated as follows: 1. the blue color indicates ferrite core at primary side 2. red color is the secondary side. 3. yellow color indicates the winding of the copper coil. table 4: simulation using jmag designer 14.0 2.2 experimental setup the wireless power transfer circuit was constructed before conducting the experiment. transmitter and receiver circuits were constructed using fritzing software. figure 5 shows the construction of the transmitter (primary circuit), while fig. 6 shows the receiver (secondary circuit). 3. results this section contains two subsections to evaluate the obtained results. subsection 3.1 will discuss the simulation results from running the design in jmag designer. in this subsection, two main parts to run the simulation in jmag designer software will be discussed. the first part is crucial for the u ferrite core to identify the most suitable method to wind the copper coil around the u ferrite core. this part is crucial because the u shape’s secondary primary secondary primary secondary primary secondary primary secondary primary secondary primary 52 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 geometric design creates many possibilities to wind the coil, unlike the i ferrite core. therefore, three different methods were investigated to choose the best winding to create high magnetic flux. after a few tests, the best coil winding was identified: method 2, edge separate winding. then, the six pairs of ferrite cores listed in table 1 were simulated using this software. finally, among the six pairs, one pair was selected as the best ferrite core pair for the wpt system. the selection mainly focused on the highest magnetic flux produced. fig. 5: transmitter or primary circuit. fig. 6: receiver or secondary circuit. 3.1 simulation using jmag 14.0 software table 5 shows the magnetic flux density of six pairs of the ferrite cores. the simulation of the jmag designer provided a color region to indicate the strongest or weakest areas around the coil, u, and i ferrite cores. for all results of the three pairs, the color scale regions are shown together, with the strongest point identified. note that all the simulation pairs are at a 1 cm air-gap. 53 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 table 5: magnetic flux density for six pairs of ferrite core pair 1 pair 4 pair 2 pair 5 pair 3 pair 6 all six proposed design pairs in this study have been simulated using jmag designer. the magnetic flux obtained for each pair is shown in fig. 7. overall, as the air-gap between primary and transmitter increased, lower magnetic flux was produced. this result is because more flux leakages are created as the distance between the two sides increases. thus, the best pair with high magnetic flux is pair 3, in which the u ferrite core is located at the primary and secondary sides. fig. 7: magnetic flux density for six coil pair designs. 0.00e+00 5.00e-04 1.00e-03 1.50e-03 2.00e-03 2.50e-03 3.00e-03 3.50e-03 0 1 2 f lu x d e n si ty ( t ) airgap (cm) magnetic flux density versus airgap ( u and i ferrite core) pair 1 pair 2 pair 3 pair 4 pair 5 pair 6 54 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 the electric power efficiency was calculated and plotted for all six pair designs, as shown in fig. 8. in this simulation result, a pair of u ferrite cores at both the primary and secondary sides, known as pair 3, offered the best power efficiency among the other pairs, followed by pair 5. at 0 cm air-gap, the power of efficiency of this pair was 90.3 %. by increasing the air-gap to 1 cm, the power efficiency was about 94.69 %. however, if the air-gap was increased to 2 cm, the power efficiency dropped to a level similar to the other pairs. meanwhile, pair 6 showed good performance when there was no air-gap. surprisingly, it showed rapid drops when the air-gap increased to 1 cm and slowly fell at the 2 cm airgap. the performance of power efficiency pair 1 and pair 2 was almost the same throughout the air-gap. the lowest efficiency pair was the primary i ferrite core and secondary coil, known as pair 4. the power efficiency was consistently below 60 % in every air-gap. comparing the graph of magnetic flux versus air-gap from the fig. 7 and power efficiency versus air-gap in fig. 8, shows that the relationship between magnetic flux and power produced is directly proportional. therefore, a pair design must have a high magnetic flux density to serve maximum power transfer. fig. 8: power efficiency with varies air-gap for six coil pair. 3.2 experimental results this section evaluated the collected results for all pairs of u and i ferrite cores. the main case was the performance of all tested pairs while varying the misalignment at a 1 cm air-gap. in this experiment, a mini prototype was built to test the proposed designs in this study. even though the standard air-gap for a real ev is 8 cm until 10 cm, an air-gap of 1 cm was used in this experiment as a starting development for the ev charging system. figure 9 shows the percentage of power transfer versus misalignment between the primary and secondary sides. the highest power transfer delivered was from pair 3 (the u ferrite core at the primary and secondary side) with 94.69%, followed by pair 5 at 89.7%. as shown in table 1, these two pairs use ferrite cores at both sides, primary and secondary. therefore, it shows that the existence of a ferrite core in the system improves the power transfer. then, pairs 1 and 6 have the same amount of power transfer at 15 mm misalignment with 51% of power transfer. while pairs 2 and 4 have an equal amount of power delivered, which is 49.7% at 10 mm misalignment. overall, the power transfer delivered showed a constant decrease from 0 mm to 50 mm misalignment. as the distance between primary and secondary increased, more flux leakage occurred and reduced the power obtained at the primary side. 40 50 60 70 80 90 100 0 1 2 p o w e r e ff ic ie n cy ( % ) airgap (cm) power efficiency versus airgap pair 1 pair 2 pair 3 pair 4 pair 5 pair 6 55 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 fig. 9: power efficiency at 1 cm air-gap. figure 10 shows the final prototype of this project. the experiment was conducted in the laboratory with the equipment provided. a 1 v dc voltage was supplied to the primary circuit and transferred to the secondary circuit. the figure below labels the power supply and oscilloscope to calculate the power obtained, and the primary and secondary sides of the system. as discussed previously, the best pair of ferrite cores is pair 3. as shown in fig. 10, the proposed design of pair 3 is a u ferrite core at both the primary and secondary sides. fig. 10: pair 3, best pair of u ferrite core. to conclude, the best pair design was pair 3, which is the primary and secondary u ferrite core. the u ferrite core can reduce the leakage of magnetic flux and experience high magnetic flux density, as shown in fig. 7. the magnetic flux density for this pair is the highest among all the pairs, which is 3.00e-03 t. since this pair had a high magnetic flux density, the power transfer efficiency was also high. figure 9 shows that pair 3 with high magnetic flux density also had high power transfer, which was 94.69 %. therefore, the u shaped ferrite core is excellent for a wireless charging system because of its better magnetic flux distribution and reduced flux leakage. the design of the u ferrite core can reduce the flux leakage by feeding back the magnetic fluxes into the core and to the secondary side 0 20 40 60 80 100 0 10 20 30 40 50 p e rc e n ta g e ( % ) misalignment (mm) power efficiency vs misalignment for 1 cm airgap pair 1 pair 2 pair 3 pair 4 pair 5 pair 6 56 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 [17]. therefore, it is proven that the pair design of u ferrite cores at the primary and secondary sides was the best design that gave high magnetic flux and led to the maximum power efficiency of wpt, as mentioned by pathipati et al. [13]. the extension of this research is that there is a pair where the ferrite core is not at both sides simultaneously. previous research by pathipati et al. [13], who also investigated the ferrite core, proposed that all the designs have a ferrite core in both the primary and secondary sides. instead of using a ferrite core at both sides, this thesis investigated a different pair if one of the sides was a copper coil and the other was a ferrite core. running the jmag designer and experiment test showed the lower power efficiency pair was pair 4, the primary i ferrite core and the secondary coil. this result was due to high magnetic flux and power transfer leakage occurring without the ferrite core at the secondary side. here, table 6 lists the comparison of power transfer obtained from these two techniques. the first technique was to obtain the magnetic flux density produced between the primary and secondary sides by running jmag designer 14.0. the second technique was by experimenting with obtaining power transfer for each pair of the ferrite cores. in both techniques, pair 3 showed a high performance compared to other pairs. the different power efficiency from the experiment and jmag designer software was about 4.99 %. this slight difference in power efficiency was due to equipment limitations, inductance values, and other factors that led to the error. table 6: power efficiency of pair 3 in simulation and experiment test method jmag designer experiment p efficiency (%) 94.69 89.7 static wireless charging allows the recharging process to take place once the vehicles is located above the charging plate and must be static. dynamic wireless charging is better suited to recharging the battery pack while in motion. however, the biggest elements that must be tolerated with the dynamic wireless charging system is air-gap and misalignment. even though many studies show the effectiveness of a wireless pad design using ferrite cores, they rarely proposed an effective method to solve the problems by varying the geometric shape of the ferrites. the misalignment between the primary and secondary coils has an impact on the dynamic charging system performance. among them are the power fluctuation from the transmitter to the receiver coils if the ev is moving. this power fluctuation also means that the coupling coefficient changed with motion. meanwhile, for static charging, even with misalignment, the power fluctuation did not occur as the ev stayed in one place during the charging process. therefore, the coupling coefficient stayed constant until the ev was fully charged. 4. conclusion in this paper, a prototype of a wireless charging system for evs was developed. before conducting the experiment, a literature review and simulation work were first carried out. then, six pairs of ferrite cores were proposed in this study to select which pair showed better delivered power. the observation showed that the reduction of power transfer was caused by increasing the distance between the primary and secondary sides. the performance of the system in this study was that it can produce 1.8 w of delivered power. although the prototype’s performance was prolonged to charge the real ev charging system, this paper has proven that power can be transferred from one medium to another wirelessly using the inductive coupling principle. 57 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 acknowledgement this work was partially supported by the ministry of higher education malaysia under iium-ump-uitm sustainable research collaboration grant 2020 (srcg) number srcg20-049-0049. references [1] kumar pp, abd halim a. (2018) electric-based national car proposal being developed. the malaysian reserve, https://themalaysianreserve.com/2018/07/26/electric-based-national-carproposal-being-developed/ [2] tian y, li d, tian j, xia b. (2016) a comparative study of state-of-charge estimation algorithms for lithium-ion batteries in wireless charging electric vehicles. ieee pels workshop on emerging technologies: wireless power, wow 2016, no. 2016, pp. 186–190. doi: 10.1109/wow.2016.7772089 [3] zaini sa, yusoff sh, abdullah aa, khan s, abd rahman f, nanda nn. (2020) investigation of magnetic properties for different coil sizes of dynamic wireless charging pads for electric vehicle (ev). iium engineering journal, 21(1): 23–32. doi: https://doi.org/10.31436/iiumej.v21i1.1108 [4] pathipati v. k., azeez n. a., aditya k., williamson s. s., dohmeier and botting n. c. (2016) performance analysis of a high-efficiency multi-winding wireless ev charging system using u-u and u-i core geometries, 2016 ieee transportation electrification conference and expo (itec): pp. 1-8. doi: 10.1109/itec.2016.7520243. [5] ahmad a, alam ms, chabaan r. (2017) a comprehensive review of wireless charging technologies for electric vehicles. ieee transactions on transportation electrification, 4(1): 38–63. doi: 10.1109/tte.2017.2771619. [6] panchal c, stegen s, lu j. (2018) review of static and dynamic wireless electric vehicle charging system. international journal engineering science and technology, 21(5): 922937. doi: 10.1016/j.jestch.2018.06.015 [7] aditya k, williamson s. (2019) design guidelines to avoid bifurcation in a series-series compensated inductive power transfer system. ieee transactions on industrial electronics, 66(5): 3973–3982. doi: 10.1109/tie.2018.2851953 [8] how long does it takes to charge an electric car? (2016) pod point, 2016. https://podpoint.com/guides/driver/how-long-to-charge-an-electric-car [9] nanda nn, yusoff sh, toha sf, hasbullah nf, roszaidie nas. (2020) a brief review: basic coil designs for inductive power transfer. indonesian journal of electrical engineering and computer science, 20(3):1703–1716. doi: 10.11591/ijeecs.v20.i3.pp1703-1716. [10] national academy of engineering (2018) frontiers of engineering: reports on leading-edge engineering from the 2017 symposium, the national academies press, , washington, dc. 37-46. https://doi.org/10.17226/24906. [11] varikkottil s, febin daya jl. (2019) estimation of optimal operating frequency for wireless ev charging system under misalignment. electronics (switzerland), 8(3) :342. https://doi.org/10.3390/electronics8030342. [12] kalwar ka. (2017) a design method for developing a high misalignment tolerant wireless charging system for electric vehicles. journal of the international measurement confederation (measurement). doi: https://doi.org/10.1016/j.measurement. 2017.12.013 [13] pathipati vk, azeez na, aditya k, williamson ss, dohmeier n, botting c. (2016) performance analysis of a high-efficiency multi-winding wireless ev charging system using u-u and u-i core geometries. ieee transportation electrification conference and expo, itec 2016. doi: 10.1109/itec.2016.7520243. 58 iium engineering journal, vol. 23, no. 1, 2022 yusoff et al. https://doi.org/10.31436/iiumej.v23i1.1663 [14] wan noor nadira wan fauzi, mohamad syafiq mazli, sheroz khan, khairil azhar adnan, ezzidin hassan aboadla, majdee tohtayong, mashkuri yaacob (2018) beaming of inductive field with an asymmetric four-coil resonator for wireless power transfer, 2018 7th international conference on computer and communication engineering (iccce). 301-305. https://doi.org/10.1109/iccce.2018.8539312. [15] patrick p. mercier, anantha p. chandrakasan (2015) ultra-low-power short-range radios, springer, cham. 343-375. https://doi.org/10.1007/978-3-319-14714-7 [16] aditya k, sood vk, williamson ss. (2017) magnetic characterization of unsymmetrical coil pairs using archimedean spirals for wider misalignment tolerance in ipt systems. ieee transactions on transportation electrification, 3(2): 454–463. doi: 10.1109/tte.2017.2673847. [17] panchal c., lu j. and stegen s. (2013) investigation of magnetic flux distribution of ev wireless charging systems, 2013 asia-pacific symposium on electromagnetic compatibility (apemc). 1-4. doi: 10.1109/apemc.2013.7360652. 59 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 rainwater harvesting quality assessment and evaluation: iium case study nassereldeen ahmed kabbashi1, mohammed saedi jami1, nour hamid abdurahman2 and noor illi mohamad puad1 1department of biotechnology engineering, faculty of engineering, international islamic university malaysia, p.o box 10, 50728 kuala lumpur, malaysia 2 faculty of chemical and natural resources engineering. universiti malaysia pahang, gambang, pahang, malaysia. *corresponding author: nasreldin@iium.edu.my (received: 11th april 2019; accepted: 16th october 2019; published on-line: 20th january 2020) abstract: this study focuses on rainwater harvesting quality at the faculty of engineering, international islamic university malaysia (iium). as development is progressing over the years in malaysia, there is also an increasing number of environmental issues and those issues are getting worse day by day. at present, malaysia is blessed with plentiful annual rainfall that represents approximately 314 mm of monthly rainfall but there is no evidence that this rainwater is redirected for daily usage. to pursue a more sustainable development, rainwater harvesting has been recognized as one innovative solution. the iium gombak campus is located in a hillside area that is a suitable study area to perform rainwater harvesting, which can be used as an alternative water supply in the future and reduce utility bills for water used on the campus. firstly, a suitable study area for rain water harvesting around koe, iium was determined before collection of data to determine the storage capacity needed. this study includes the estimation of rainwater quantity that can be harvested in one year. the quality of rainwater in terms of biochemical oxygen demand (bod), chemical oxygen demand (cod), ph, total suspended solid (tss), turbidity, and microbial count were studied. data analysis showed that the values of bod, cod, ph, tss, turbidity, and microbial count were in the range of 2 3.2 mg/l, 22.5 – 42.5 mg/l, 5.9 6.5, 20 mg/l, 9 -11 ntu, and between 200 260 cfu/ml, respectively. this indicates that the harvested rainwater is acceptably clean but not suitable to be used as drinking water. abstrak: fokus kajian ini adalah pada kualiti air hujan yang ditadah di fakulti kejuruteraan, universiti islam antarabangsa malaysia (uiam). sejajar dengan pembangunan pesat di malaysia, isu alam sekitar juga semakin bertambah dan menjadi semakin teruk hari ke hari. pada masa sama, ketika ini malaysia dirahmati dengan hujan yang mencurah setiap tahun, dengan kuantiti bulanan sebanyak 314 mm air hujan dan tidak ada bukti penggunaan air hujan ini bagi kegunaan harian dsb. bagi memenuhi keperluan kelangsungan pembangunan, penadahan air hujan dikenal pasti sebagai satu penyelesaian inovatif. kampus uiam gombak terletak di kawasan pinggiran bukit yang sesuai bagi menjalankan kajian tadahan air hujan. ianya boleh digunakan sebagai bekalan air alternatif pada masa depan dan mengurangkan bil utiliti bekalan air dalam kampus. terlebih dahulu, kawasan kajian yang sesuai dikenal pasti berdekatan fakulti kejuruteraan, uiam bagi mengumpul air hujan sebelum data dikumpulkan bagi mengenal pasti kapasiti pengumpulan yang diperlukan. kajian ini juga menganggar kuantiti air hujan yang boleh ditadah dalam satu tahun. kualiti air hujan dikaji dari segi keperluan oksigen biokimia 12 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 (bod), keperluan oksigen kimia (cod), ph, jumlah pepejal terampai (tss), kekeruhan dan bilangan mikrob. analisis data mendapati nilai bod, cod, ph, tss, kekeruhan dan bilangan mikrob berada dalam julat 2 3.2 mg/l, 22.5 – 42.5 mg/l, 5.9 6.5, 20 mg/l, 9 11 ntu dan antara 200 -260 cfu/ml, masing-masing. ini menunjukkan air hujan yang ditadah adalah boleh diterima sebagai bersih tetapi tidak sesuai dijadikan sebagai air minuman. keywords: rainwater harvesting; water quality analysis; moringa oleifera; disinfectant 1. introduction water harvesting is a practice that has been used to increase the effectiveness of water and make use of it. water harvesting systems direct water, from a great normal watershed or man-made collection, into a small puddling basin. the water can then be stored in subversive tanks or be used directly for irrigation or family purposes. in the modern period, water harvesting has been neglected, particularly in developed countries, due to technical achievements in the fields of water treatment and distribution. but, in recent years, water harvesting in modern-urban environments has turned into an essential practice. municipal areas are being cemented and built, resulting in the decrease of groundwater renewal area. as a result, a great quantity of good water that rains over the municipality is inhibited from refreshing aquifers as it is absorbed into the public drainage system. the water crisis is hitting a current civilization that already needs to decrease its major expenditures: energy utilization and water use. the sometimes indiscriminate utilization of water wealth flies in the face of water deficiencies and scarcity occurring in several countries. less than 1% of the water on the globe is potable. the water from rain, melting snow, and fog has always been considered to have important potential to contribute to supply, even though these types of water need to be treated in order to meet the legal requirements for consumption, with chemical, microbiological, and sometimes accurate bacteriological reports. the most important factor in the planet’s wellbeing report card is the quality and quantity of potable water reserves: partial accessibility, patchy distribution, and rising contamination levels are growing concerns aggravated by booming world population, increased use per capita, water mismanagement and the lowering of water aquifers due to unnecessary removal. ruhela [1], declared that fresh surface water is routinely restocked by rainfall, but added that the one factor that most determines the availability of good and sufficient fresh water supply is the ever-increasing population. in malaysia, wong [2] highlighted that in november and december, during the north-east monsoon, malaysia received the maximum rainfall for the year. the difference in temperatures in certain places, for example cold temperatures in central asia, will result in a change in atmospheric pressure that causes strong winds and heavy rainfall on the east coast of peninsular malaysia near the south china sea. the maximum average rainfall recorded in one month is 314 mm in december, which represented 14 percent of the average rainfall for one year. this proves that malaysia is blessed by a sufficient, accessible supply of fresh water. rainwater harvesting is a process for inducing, collecting, storing, and conserving local surface run off water for various purposes such as drinking, washing, and irrigation. there are 3 types of surfaces that allow the process of harvesting rainwater: rooftops, water bodies, and storm drains [3]. several factors that need to be considered before implementing water harvesting are rainfall intensity and distribution, the type of soil and the depth of soil, water resources, infrastructure and socio-economic conditions, environmental and ecological impacts, and the terrain and topography profile [4]. 13 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 water quality, on the other hand, generally refers to the characteristics and condition of water according to certain units of measurement. water is divided into a few classes based on its usage and it can be determined to be good and safe for use if it meets the minimum requirements set by the department of environment (doe) of malaysia. in malaysia for instance, water harvesting can fulfill two purposes: to stockpile surplus water owing to rain and to supplement established water sources, usually during periods of water deficiency [2]. during droughts, water harvesting is vital to meet domestic water requirements for human use. whether rainwater harvesting technology is used as the source of non-potable or potable water, it can be managed to supplement existing sources. in addition, the fast expansion of population is another factor aggravating water shortages. a sluggish economy paired with water scarcity causes the need for potable or non-potable water for drinking and sanitation to proportionally increase. there are a few treatments that can be used to treat the rainwater harvested from the roofs, such as filtration and uv treatment [6]. moringa oleifera seeds can be used as a disinfectant that can remove microbes in water and act as a coagulant [7]. the main objective of this study is to estimate the volume of rainwater that can be harvested from the roof of one building (e0) at the faculty of engineering, iium over the course of one year. an additional aim is to analyze and characterize the harvested rainwater in terms of bod, cod, ph, tss, turbidity and microbial count to determine its suitable application or usage. 1.1 present rainwater harvesting (rwh) rwh consists of rainwater collection from large surfaces, mainly rooftops [8,9,10], and storage of the water under or above ground in reservoirs. based on the water quality, which is mainly affected by the quality and state of the water collection surfaces and the delivery systems, the water can be used for drinking, domestic uses, and irrigation. rwh is a renewable source of clean water that is ideal for domestic and small scale agricultural uses and the greater attraction of a rainwater harvesting system is its low cost, accessibility, and simple maintenance at the household level [11]. rwh can promote significant water saving in residences in different countries. for an example, in germany, herrmann [12] reported that a potential saving of potable water in a house might vary from 30% to 60%, depending on the demand and size of the rainwater collection area. in newcastle, australia, rwh would save 60% of potable water [13] and in brazil, ghisi [14] concluded that a potential water saving by using water harvesting was in the range of 34% to 92%, with an average of 69%. abdulla [11] indicated a potential water saving of up to 20% of drinking water by applying rwh at urban environment in jordan. 1.2 water quality analysis water from any source, whether harnessed or harvested from ground water or rainwater, has its own quality. therefore, it is important to begin by analyzing the water’s quality before it can be used for drinking or for irrigation. there are many variables that make up the water quality analysis such as the total suspended solid, the chemicals present, and the oxygen demand of the water tested. it is important to determine the water quality so that a proper water treatment process can be carried out to fulfill the specific water quality requirement for a specific usage. these requirements have been set by either the department of the environment (doe) or ministry of health (moh) in malaysia. in malaysia, juahir et al [15] asserted that, according to malaysia’s doe (1997), there are six variables that need to be included in water quality data to develop a water quality index. these six variables are dissolved oxygen (do), biochemical oxygen demand (bod), chemical oxygen demand (cod), suspended solids (ss), ammonical nitrogen (an) and ph. the standard 14 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 requirement of the doe for different types of water class is shown in table 1 and the applications allowed for each class are shown in table 2. table 1: doe water quality index classification* parameter unit class i ii iii iv v ammonical nitrogen mg/l < 0.1 0.1 – 0.3 0.3 – 0.9 0.9 – 2.7 > 2.7 biochemical oxygen demand mg/l < 1 1 – 3 3 – 6 6 – 12 > 12 chemical oxygen demand mg/l < 10 10 -25 25 – 50 50 – 100 > 100 dissolved oxygen mg/l > 7 5 – 7 3 – 5 1 – 3 < 1 ph > 7 6 – 7 5 – 6 < 5 > 5 total suspended solid mg/l < 25 25 50 50 150 150-300 > 300 (*adapted from the national water quality standards) table 1: doe water quality index classification* class uses class i conservation of natural environment. water supply i practically no treatment necessary. fishery i very sensitive aquatic species. class iia water supply ii conventional treatment. fishery ii sensitive aquatic species. class iib recreational use body contact. class iii water supply iii extensive treatment required. fishery iii common, of economic value and tolerant species; livestock drinking. class iv irrigation class v none of the above. (*adapted from the national water quality standards) 2. materials and methods this study was conducted in three parts according to the objectives of the project. the e0 building in the faculty of engineering was set as the study area where the rainwater was harvested. a high density polyethylene (hdpe) tank with down pipes and conveyance pipes, depending on the site assessment and calculation of water demand, were installed in the e0 building to collect and store the harvested rainwater. 2.1 preparation of water storage tank fresh rainwater was the main raw material for this study and it was collected from the roof of iium’s faculty of engineering building (e0). a downpipe which connected with gutter of the roof was chosen to install a high density polyethylene (hdpe) tank for the rainwater storage. figure 1 shows the location of the rainwater harvest at iium. 15 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 fig. 1: the study area (adapted from https://www.google.com.my/maps). a downpipe (fig. 2) that connected with the gutter of the roof was used to harvest the rainwater. an hdpe tank holding roughly 80 gallons was purchased together with 3 inch polyvinyl chloride (pvc) lay-flat flexible water hose pipe for the installation of the tank. the tank was installed with a pvc water tap to collect the samples in the e0 building near the staff parking area. fig. 2: roof rainwater harvesting system. 2.2 estimation of the rainwater quantity the external length and width of the e0 building beneath the roof were measured, and divided into several individual rectangles. the tank was designed to meet the necessary water demand throughout the dry season. eq. (1) was used to obtain the required storage capacity: required storage capacity= demand dry period (1) the average volume of rainwater collected in an hour of rain was calculated based on eq. (2). (2) 16 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 where vr = amount of water that can be harvested (m3); i = rainfall intensity (mm); hra = catchment area (m2); c = runoff coefficient. the volume of rainfall that can be harvested from iium was estimated using eq. (1). eq. (2) can be interpreted as the volume of rainfall that can be harvested per hour and is based on the area of catchment, the rainfall intensity, and the runoff coefficient. since this study focused specifically on rainwater harvesting by roof catchment, the data for the surface area of the roof at faculty of engineering e0 building and the entire roof of iium were obtained from the development division of iium (table 3). table 3: total surface area of roof in iium location surface area of the roof (m2) faculty of engineering 19,302 iium (gombak campus) all faculties, mahallah’s and other buildings in iium 726,986 the runoff coefficient was determined from the roof’s material. different types of material used for the roof will have different runoff coefficients. table 4 shows the runoff coefficient for the roof catchment area. based on table 4, the runoff coefficient for roof in iium was set to 0.80 since it is made of tiles. table 4: the runoff coefficient for roof catchment (unep, 2009) roof’s material runoff coefficients tiles 0.8 – 0.9 corrugated metal sheets 0.7 – 0.9 the rainfall intensity data was obtained from the on-line hydrological data from the department of irrigation and drainage malaysia for klang gate dam area. from the cumulative rainfall data, the average rainfall intensity in a month is between 100-200 mm/hour taken in december as the reference. figure 3 illustrates the hyetograph obtained for cumulative rainfall per hour for a period of a month. fig. 3: hyetograph of rainfall in klang gate dam station (obtained from http://infobanjir.water.gov.my). 17 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 2.3 sample collection and analysis samples were taken from a downpipe in the e0 building for every 5 minutes of rainfall over a 30-minute period. the samples were analyzed according to the parameters selected (bod, cod, ph, tss, turbidity and microbial count). the bod and cod test were conducted according to the standard operating procedure by the american public health association (apha). the concentration of cod in the water was analyzed using a spectrophotometer at the 600 nm wavelength. in addition, digestion solution and sulfuric acid reagent were prepared prior to the cod analysis. the sample’s ph and turbidity were both analyzed by hach ph meter and turbidity meter. microbial count was measured by incubating the 100 l samples in nutrient agar for 48 hours at 37 c. 2.4 preparation of moringa oleifera seeds dry seeds of moringa oleifera were bought from a local supplier before the wings and coat of the seeds were separated manually. the seeds were grounded into powder form using a domestic blender and sieved through a 210 μm sieve. the powdered form of moringa oleifera seeds was defatted using a soxhlet extractor. about 10 g of powdered seeds was placed in the thimbles and 170 ml of hexane was poured into the thimbles as well as the solvent. it was run for 90 minutes and the powdered seeds in the thimbles were dried and weighed. the defatted powder was added into a beaker containing 1000 ml of distilled water. the solution was mixed using a stirrer at 85 rpm for different periods of mixing time set for experiment optimization [16]. 2.4.1 optimization of disinfectant preparation the disinfectant preparation procedure was optimized based on two factors, the dosage of powdered seed (mg/ml) and the mixing time. the mixing speed was fixed at 85 rpm. design expert software was used to for experimental design and statistical analysis using a response surface methodology (rsm). the percentage of bacterial removal was set as the response of this study. the dosage of seeds in the beaker was varied from 2.75 mg/ml to 3.75 mg/ml while the mixing time was varied from 21 minutes to 41 minutes [16]. 2.4.2 treatment of rainwater using moringa oleifera in each optimization run, 1 ml of moringa oleifera extracts was added into 10 ml of rainwater sample. a blank sample was prepared as the control by adding 10 ml of rainwater without any disinfectant. the mixture was mixed and incubated without agitation for 2 hours. each sample was diluted with distilled water before it was pipetted onto the agar in a petri dish. it was then incubated at 37 °c for 48 hours. the bacterial count was calculated and the data of each run was compared with the control. 3. results and discussion 3.1 estimation of rainfall quantity the volume of rainfall that can be harvested at iium was estimated using eq. (1). the equation stated that the volume of rainfall that can be harvested per hour is calculated based on the area of catchment, the rainfall intensity and the runoff coefficient. the study was done specifically on rainwater harvesting by roof catchment, thus, the data for the surface area of the roof in the faculty of engineering and the entire iium roof was obtained. the estimated volume of rainwater that can be harvested in the faculty of engineering and the entire iium (gombak campus) is 37000 m3 per year and 1395 103 m3 per year, respectively.the result was in line with a study carried out in sarawak that reported that water demand for their study was 4.32 m3 per day. 18 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 3.2 water quality analysis the bod obtained was in the range of 2.0 – 3.2 mg/l. contamination that occurred on the roof and along the downpipe by elements such as dried leaves, dead animals, or animal waste, contributed to the high bod. this is due to the consumption of dissolved oxygen in the water by the bacteria that degrade these contaminants. it may also be due to the contamination occurring along the downpipe being flushed exponentially in the first few minutes of rainfall. the concentration of cod was in the range of 22.5 – 42.5 mg/l. since iium is located near the karak highway, pollutants from the vehicles contribute to the high concentration of cod as well as chemicals from bird droppings and chemicals from the roof itself. the amount of tss is contributed from the impurities that formed on the catchment roof and along the downpipe to the rainwater harvesting tank. the average concentration of tss in the rainwater collected was 20 mg/l. the readings of concentration of tss for every five minutes of samples were quite similar and since there are not many impurities in the rainwater harvested, the concentration of tss is low. figure 4 shows the concentration of bod, cod, and tss in the rainwater against the times of sampling. the ph of the rainwater harvested in iium was in the range of 5.9 – 6.5. the ph value changed after a few minutes of rainfall where a low ph value was recorded in the first 10 minutes. the result indicates the rainwater is acidic in the early minutes of rainfall. this is because the first flush of rainfall carries the trapped carbon dioxide gas from vehicle activities as well as other gases in the air [4]. the average turbidity of rainwater was rather low, in which the highest recorded turbidity for harvested rainwater was 11.21 ntu. the low turbidity indicates that the clarity of rainwater is high since there are less particles or matter suspended in the water [1]. microbial count was performed with the aim to determine the existence of microbial matter in the harvested rainwater. the recorded microbial count in 1 ml of water sample is in the range of 200 – 260 colony-forming units (cfu). this is the result of two major contamination sources: animals and the environment of the catchment area itself. these include the waste produced by birds or animals and dead organisms [6]. fig. 4: the graph of water quality against time. 3.3 optimization of disinfectant preparation the optimization was done for the preparation of the disinfectant by using design expert 6.0.8. two factors were tested by using central composite design (ccd) under rsm. the aim of the optimization is to obtain the highest percentage of microbial removal 0 10 20 30 40 50 0 5 10 15 20 25 30 35 c on ce nt ra ti on (m g/ l) time (minutes) bod (mg/l) cod (mg/l) tss (mg/l) 19 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 by varying the mixing time and the dosage use in the preparation of disinfectant. a total of 10 runs with two central points were set for the experiment, as shown in table 5. table 5: experimental design for optimization run mixing time (min) dosage (mg/ml) microbial removal (%) 1 21 3.25 65.9 2 41 3.25 59.5 3 31 2.75 65.4 4 41 3.75 65.4 5 31 3.75 66.8 6 31 3.25 65.9 7 21 3.75 67.3 8 21 2.75 77.1 9 41 2.75 54.1 10 31 3.25 66.3 from the data obtained, anova was used to represent the relationship between the parameters and the response as well as the effect of individual parameters. the final equation obtained from anova is as in eq. (3): microbial removal (%) = + 65.37 – 5.22a +0.48b +5.28ab (3) where, a and b are the mixing time (in minutes) and the dosage (mg/ml), respectively. the model is significant, as the model f-value was 18.23. furthermore, the value of prob > f was less than 0.05, thus proving the model was significant. the r-squared for the model was 0.9011, which means that 90.11% of total variation in microbial removal is attributed to the experimental value. figure 5 shows the effect of both mixing time and dosage during the preparation of moringa oleifera as disinfectant on the microbial removal during treatment of rainwater. de-fatted powdered seeds of moringa oleifera at 2.75 g/liter of distilled water and 21 minutes of mixing time was able to achieve the best percentage of microbial removal of 75.38%. according to suarez [17], around 2 mg/ml of moringa oleifera used had the highest inhibition, which is acceptable. fig. 5: effect of mixing time and dosage on microbial removal in 3-d. 4. conclusion in this study, the three main objectives were to estimate the volume of rainwater that can be harvested in a year, to characterize the rainwater harvested, and to treat the rainwater using moringa oleifera. the volume of rainwater that can be harvested from the roof at 20 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 iium is 1395 × 103 m3 per year. analysis done on bod, cod, ph, tss, turbidity, and microbial count indicates that the rainwater complies with the class iii standard in the water quality index set by the doe. the rainwater harvested from the rooftop is non-potable and is not safe to consume as drinking water but it is suitable to be used for gardening, flushing, or cleaning processes. from the data obtained, the quality of rainwater harvested from the rooftop improved as the time increased. this proved the importance of having a first-flush concept on the rainwater harvesting system. the treatment process using moringa oleifera as disinfectant improved the quality of the rainwater in terms of removing some of the microbial component. an amount of 2.75 mg/ml of seeds dissolved and mixed with distilled water at 85 rpm for 21 minutes is the optimum parameter to prepare the disinfectant. harvested rainwater in koe-iium still needs another type of treatment to improve and utilize the water for more than cleaning and flushing. from the study conducted, there are a few recommendations that could be made for further study. first, analyze and compare the quality of the rainwater harvested from roof catchment and harvested directly from the sky by prepare an open tank to collect the rainwater. furthermore, install a first-flush device along the downpipe so that the quality of the rainwater store in the tank is improved. references [1] ruhela, m., bhutiani, r., & anand, a. (2004) rain water harvesting. journal-geological society of india, 85(9): 1259-1261. retrieved from http://www.currentscience.ac.in/cs/downloads/article_id_085_09_1259_1261_0.pdf. [2] wong, c. l., venneker, r., uhlenbrook, s., jamil, a. b. m., & zhou, y. (2009) variability of rainfall in peninsular malaysia. hydrology and earth system sciences discussions, 6(4): 5471– 5503. https://doi.org/10.5194/hessd-6-5471-2009. [3] prinz, d., & singh, a. (2000) technological potential for improvements of water harvesting. gutachten für die world commission on dams, retrieved from http://web.stanford.edu/~cbauburn/basecamp/dschool/homeproject/water_harvesting_improve ments_technology.pdf. [4] evans, c. a., coombes, p. j., & dunstan, r. h. (2006) wind, rain and bacteria: the effect of weather on the microbial composition of roof-harvested rainwater. water research, 40(1): 37– 44. https://doi.org/10.1016/j.watres.2005.10.034. [5] boers, t. m., & ben-asher, j. (1982) a review of rainwater harvesting. agricultural water management, 5(2): 145–158. https://doi.org/10.1016/0378-3774(82)90003-8. [6] despins, c., farahbakhsh, k., & leidl, c. (2009) assessment of rainwater quality from rainwater harvesting systems in ontario, canada. journal of water supply: research and technology aqua, 58(2): 117–134. https://doi.org/10.2166/aqua.2009.013. [7] bichi, m. h., agunwamba, j. c., & muyibi, s. a. (2012) optimization of operating conditions for the application of moringa oleifera (zogale) seeds extract in water disinfection using response surface methodology, 11(92): 15875–15887. https://doi.org/10.5897/ajb12.1341. [8] liaw, c. h., & chiang, y. c. (2014) dimensionless analysis for designing domestic rainwater harvesting systems at the regional level in northern taiwan. water (switzerland), 6(12): 3913– 3933. https://doi.org/10.3390/w6123913. [9] sharma, a.k., begbie, d. and gardner, t. (2015) rainwater tank systems for urban water supply: design, yield, energy, health risks, economics and social perceptions. iwa publishing, london. [10] charters, f. j., cochrane, t. a., & o’sullivan, a. d. (2016) untreated runoff quality from roof and road surfaces in a low intensity rainfall climate. science of the total environment, 550: 265–272. https://doi.org/10.1016/j.scitotenv.2016.01.093. 21 iium engineering journal, vol. 21, no. 1, 2020 kabbashi et al. https://doi.org/10.31436/iiumej.v21i1.1139 [11] fayez abdulla & a.w. al-shareef. (2009) roof rainwater harvesting systems for household water supply in jordan. desalination. 243(1-3):195-207. https://doi.org/10.1016/j.desal.2008.05.013 [12] herrmann t, schmida u. (2000) rainwater utilization in germany: efficiency, dimensioning, hydraulic and environmental aspects. urban water, 1(4): 307-316. [13] cook, s., sharma, a. and chong, m. (2013) performance analysis of a communal residential rainwater system for potable supply: a case study in brisbane, australia. water resources management, 27: 4865-487. [14] ghisi e. (2006) potential for potable water savings by using rainwater in the residential sector of brazil. building and environment, 41(11): 1654-1666. [15] juahir, h., zain, s. m., yusoff, m. k., hanidza, t. i. t., armi, a. s. m., toriman, m. e., & mokhtar, m. (2011) spatial water quality assessment of langat river basin (malaysia) using environmetric techniques. environmental monitoring and assessment, 173(1–4): 625–641. [16] bichi, m. h., agunwamba, j. c., & muyibi, s. a. (2012) optimization of operating conditions for the application of moringa oleifera (zogale ) seeds extract in water disinfection using response surface methodology, 11(92): 15875–15887. https://doi.org/10.5897/ajb12.1341. [17] suarez m, entenza j, doerries c, meyer e, bourquin l, sutherland j, marison i, moreillon p, mermod n (2003) expression of a plant-derived peptide harboring water-cleaning and antimicrobial activities. biotech bioeng 81(15):13–20. retrieved from https://www.researchgate.net/publication/237077424_genetic_diversity_and_population_stru cture_of_moringa_oleifera 22 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <feff004200720075006b00200064006900730073006500200069006e006e007300740069006c006c0069006e00670065006e0065002000740069006c002000e50020006f0070007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e00740065007200200073006f006d002000650072002000650067006e0065007400200066006f00720020007000e5006c006900740065006c006900670020007600690073006e0069006e00670020006f00670020007500740073006b007200690066007400200061007600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020005000440046002d0064006f006b0075006d0065006e00740065006e00650020006b0061006e002000e50070006e00650073002000690020004100630072006f00620061007400200065006c006c00650072002000410064006f00620065002000520065006100640065007200200036002e003000200065006c006c00650072002e> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <feff0041006e007600e4006e00640020006400650020006800e4007200200069006e0073007400e4006c006c006e0069006e006700610072006e00610020006f006d002000640075002000760069006c006c00200073006b006100700061002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400200073006f006d00200070006100730073006100720020006600f60072002000740069006c006c006600f60072006c00690074006c006900670020007600690073006e0069006e00670020006f006300680020007500740073006b007200690066007400650072002000610076002000610066006600e4007200730064006f006b0075006d0065006e0074002e002000200053006b006100700061006400650020005000440046002d0064006f006b0075006d0065006e00740020006b0061006e002000f600700070006e00610073002000690020004100630072006f0062006100740020006f00630068002000410064006f00620065002000520065006100640065007200200036002e00300020006f00630068002000730065006e006100720065002e> /tur <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> /ukr <feff04120438043a043e0440043804410442043e043204430439044204350020044604560020043f043004400430043c043504420440043800200434043b044f0020044104420432043e04400435043d043d044f00200434043e043a0443043c0435043d044204560432002000410064006f006200650020005000440046002c0020043f044004380437043d043004470435043d0438044500200434043b044f0020043d0430043404560439043d043e0433043e0020043f0435044004350433043b044f04340443002004560020043404400443043a0443002004340456043b043e04320438044500200434043e043a0443043c0435043d044204560432002e0020042104420432043e04400435043d04560020005000440046002d0434043e043a0443043c0435043d044204380020043c043e0436043d04300020043204560434043a04400438043204300442043800200437043000200434043e043f043e043c043e0433043e044e0020043f0440043e043304400430043c04380020004100630072006f00620061007400200456002000410064006f00620065002000520065006100640065007200200036002e00300020044204300020043f04560437043d04560448043804450020043204350440044104560439002e> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 237 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering manshor et al. 79 observation on responsive ocv variation of zinc-air cell with relative humidity content hanisah manshor1, raihan othman2, anis nurashikin nordin3 mohd hanafi ani1 and hens saputra4 1 department of manufacturing and materials engineering, 2 department of science in engineering, 3 department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. 4 pusat teknologi industri proses badan pengkajian dan penerapan teknologi (bppt) jl. m.h. thamrin no. 8, jakarta 10340, indonesia. raihan@iium.edu.my abstract: zinc/mcm-41/air cell, in its dry form without the electrolyte, demonstrates humidity sensing property. a good linear correlation between the cell’s open circuit voltage (ocv) and the relative humidity content is observed. the system possesses the potential to be developed into a low cost microhumidity sensor. an ultra thin cell of thickness not more than 40 µm has been fabricated and its use as a humidity sensor is substantiated. abstrak: sel zinc/mcm-41/udara, dalam keadaan kering tanpa elektrolit, menunjukkan sifat pencirian kelembapan. voltan litar terbuka sel didapati menunjukkan korelasi linear yang baik terhadap kandungan kelembapan relatif. sistem ini berpotensi untuk dibangunkan menjadi penciri kelembapan mikro yang murah. sel yang amat nipis dengan ketebalan tidak melebihi 40 µm telah difabrikasi and kegunaannya sebagai penciri kelembapan dibuktikan. keywords: zinc-air cell; mcm-41 membrane; humidity sensor; microsensor 1. introduction the development of low cost micro-humidity sensors requires specific considerations of microfabrication technology and processing techniques due to the complexities associated with humidity measurement. the relatively complex post-processing techniques employed to integrate the humidity sensitive material within the microstructure of the humidity sensor contributed towards high cost of such devices [1-2]. in this paper, we report a preliminary observation on humidity sensing behaviour of zinc-air microbattery of less than 40 µm thick. the open circuit voltage (ocv) of the electrochemical cell is found responsive with the ambient humidity variation. most importantly the construction of the microbattery merely requires the fabrication of a threelayered structure i.e. zinc, mcm-41 and carbon, which is highly compatible with microelectronics fabrication. interestingly, no addition of caustic electrolyte, which is commonly the case for zinc-air system, is needed. these characteristics show promising prospects for the zinc-air microsystem to be further explored and developed as a novel microhumidity sensor. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering manshor et al. 80 2. experimental method 2.1 zinc-air microbattery components and construction an electrochemical cell in principle consists of an anode and a cathode in an ionic conducting medium or electrolyte. a physical contact between the anode and cathode is prevented by placing an ionic exchange membrane or separator between them. zinc-air cell belongs to the metal-air electrochemical system in which an electropositive metal element is coupled with the electronegative oxygen of the ambient air. normally a carbonbased air electrode is used as the oxygen reaction site. in this work, zinc served as the anode, an inorganic mcm-41 membrane as the separator, and a carbon layer functioned as the air cathode. details of characterization of mcm-41 as a separator material can be referred to the work of saputra et al. [3]. zinc was prepared from an electrodeposition technique from an acidic chloride bath (2 m zinc chloride electrolyte). a two-electrode configuration was used. zinc was deposited onto copper foil (10 µm) at a constant current of 100 ma for 10 minutes. an ecochemie (the netherland) potentiostat/galvanostat (pgstat302n, autolab) was used. mcm-41 material was prepared from a parent solution consisted of cetyltrimethyl ammonium bromide (ctab), tetraethylorthosilicate (teos), hydrochloric acid (hcl), distilled water (h₂o) and ethanol (c2h5oh), with molar ratio formulation of 0.05 ctab, 1.0 teos, 0.5 hcl, 25 c2h5oh and 75 h2o. ctab served as the cationic surfactant while teos was the silica source. the mixture of parent solution was stirred at about 200 rpm at 30°c for 1 hour. the electrodeposited zinc layer was then coated by mcm-41 membrane by spin coating technique (cee ® 200x precision spin coater). the spin speed was set to 2000 rpm for duration of 10 seconds. finally ctab template was removed from mcm-41 pore structure by leaching with etoh. this template removal process is named solvent extraction, which is reported as an alternative to heat treatment process [4]. this method was adapted because heat treatment process will cause the zinc electrodeposits to be oxidized. finally carbon paste was applied onto mcm-41 coated zinc anode as the air cathode. the carbon paste consisted of carbon particulate suspension (spi-chem tm ) in ethanol. normally catalytic compound such as manganese oxide is mixed with the air cathode as the oxygen reduction reaction is rate-limiting. however, in the present work no catalyst was added to the carbon paste as the fabricated cell was not required to deliver discharge current. once carbon paste was applied, the zinc-air cell ready to be tested. we did not incorporate any electrolyte into the fabricated cell. the cell was left to operate in its dry form. figure 1 illustrates the schematic diagram of the fabricated zinc-air microbattery and the photograph is shown in fig. 2. the area of the zinc electrodeposits was approximately 1cm². the distinct appearance of the copper foil of fig. 2 was due to mcm-41 coating i.e. the uncoated area appeared brighter. 2.2 material characterization the structural formation of mcm-41 was verified using small angle x-ray diffraction analysis (cu kα radiation, 2θ range of 1.5 10°, scan speed of 2°/minute). the microstructure images of zinc electrodeposits and mcm-41 membrane were observed using scanning electron microscope (jsm 5600) and feld-emmision scanning electron microscope (fe-sem) (jed-2100, jeol co. ltd.) respectively. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering manshor et al. 81 fig. 1: schematic illustration of zinc-air cell and its components. fig. 2: photograph of the fabricated ultra thin cell as microhumidity sensor. 2.3 ocv measurement and relative humidity monitoring ocv measurement of the zinc-air cell was conducted by eco chemie (the netherland) autolab galvanostat/potentiostat in open ambient surrounding. a commercial digital humidity sensor (lascar humidity el-usb-2) was placed in close proximity to the cell. both measurements were performed simultaneously for 19 hours. 5 mm iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering manshor et al. 82 3. results and discussion xrd analysis of fig. 3 confirms the structural formation of mcm-41 material. its hexagonal lattice structure is characterized by the dominant (100) peak and followed by three small diffraction peaks, as listed in table 1 [5-8]. mcm-41 material belongs to a group of mesoporous materials known as m41s. this class of material is characterized by its regular arrays of tunable uniform channels with large surface area. mcm-41 materials possess the high specific surface area and pore volume of about 1000 m 2 g -1 and 1 cm 3 g -1 respectively, very narrow pore size distribution (~2 nm) and very good thermal stability i.e. up to 900°c [5, 9, 10]. fig. 3: xrd pattern of the as-synthesized mcm-41 material. table 1 characteristic of mcm-41 x-ray diffractogram. hkl d / å 100 39.8 110 22.9 200 19.8 210 14.9 figure 4 displays the sem image of the electrodeposited zinc layer. the sem image was focussed at the boundary between the plated area and bare copper substrate in order to estimate the thickness. the thickness of the zinc layer was estimated around 30 µm. the zinc layer was in the form of granular deposits and the deposits seemed to be smooth and even. but most importantly the electrodeposits were non-dendritic. dendritic or tree-like deposits will cause premature electrochemical cell failure due to internal short-circuiting [11]. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering manshor et al. 83 fig. 4: sem micrograph of electrodeposited zinc layer. figure 5 shows fe-sem image of mcm-41 membrane encapsulating the zinc electrodeposits at 100,000 magnifications. the micrograph reveals the coarse, high surface area characteristics of the material. fig. 5: fe-sem micrograph of mcm-41 membrane. we noticed that the zinc/mcm-41/air cell in its dry form registered changing ocv readings over time. since the as-synthesized mcm-41 material is hydrophilic in nature, we suspected the variation in the ocv could be related to the changing humidity content of the ambient air. figure 6 highlights the measurement of relative humidity of our laboratory over a period of 19 hours and the corresponding variation of the ocv of the dry zinc/mcm-41/air cell. both profiles were similar, thus suggesting a direct correlation iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering manshor et al. 84 between the ocv values of the cell with relative humidity content. the curve for ocv variation is smoother since the potentiostat/galvanostat was able to record a five and a half digits voltage value. on the other hand, the digital humidity sensor could only measure the smallest variation of 0.5 %. fig. 7 is the correlation plot between the cell’s ocv and the relative humidity content. the linear trend of the plot further supports that a correlation between them could be established. as mentioned earlier, the use of a more accurate digital humidity sensor could substantiate a more significant correlation. fig. 6: ocv responds of cell as compared to relative humidity readings from digital humidity sensor. fig. 7: correlation between the cells’s ocv and the relative humidity content. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering manshor et al. 85 we attributed the observed humidity sensing behaviour of zinc/mcm-41/air cell to the hydrophilic property of mcm-41material [12, 13]. mcm-41 surface structure is covered with silanol groups (si-oh) formed during the synthesis of the material. while these groups serve as hydration site, the mesoporous phase of mcm-41 makes the structure accessible for water physisorption from the surrounding moisture [14, 15]. consequently, the adsorption-desorption of water molecules from zinc/mcm-41/air cell affected its ocv thus enables the system to be utilized as a novel micro humidity sensor. 4. conclusion a zinc/mcm-41/air cell possessed a humidity sensing property. we have fabricated an ultra thin cell of thickness not more than 40 µ m and demonstrated its use as relative humidity sensor. the cell consists merely of three thin layers of different materials and it’s free from any corrosive electrolyte since the cell is utilized in the dry form. hence its fabrication is very much compatible with microelectronics processing and highly potential to be further developed as a low cost microhumidity sensor. acknowledgement the international islamic university malaysia funded this project through the research matching grant scheme (rmgs 09-09). the authors gratefully acknowledge the financial support. references [1] h. shibata, m. ito, m. asakursa, and k. watanabe, “a digital hygrometer using a polyimide film relative humidity sensor”. ieee, vol. 45, no. 2, 564-569, 1996. [2] n. yamazoe and y. shimizu, humidity sensors: principles and applications, sensors and actuators, 10 (1986) 379-398. [3] h. saputra, et al., “mcm-41 as a new separator material for electrochemical cell: application in zinc-air system”. journal of membrane science 367, 152-157, 2011. [4] a. marcilla, et al., “template removal in mcm-41 type materials by solvent extraction: influence of the treatment on the textural properties of the material and the effect on its behaviour as catalyst for reducing tobacco smoking toxicity”. chemical engineering research and design, vol. 89, 2330-2343, 2001. [5] c. t. kresge, m. e. leonowicz, w. j. roth, j. c. vartuli and j. s. beck, ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism, nature 359 (1992) 710-712. [6] g. øye, j. sjöblom, m. stöcker, synthesis, characterization and potential applications of new materials in the mesoporous range, advances in colloid and interface science. elsevier 89 (2001) 439-466. [7] z. bayram-hahn, ba. grimes1, am. lind1, r skudas, kk. unger1, a galarneau, j iapichella, f. fajula, pore structural characteristics, size exclusion properties and column performance of two mesoporous amorphous silicas and their pseudomorphically transformed mcm-41 type derivatives, j sep sci 30:18 (2007) 3089-3103. [8] q. li, et al., “synthesis and characterization of mcm-41-supported ba2sio4 base catalyst”. microporous and mesoporous materials 59, 105-111, 2003. [9] j. s. beck, j. c. vartuli, w. j. roth, m. e. leonowicz, c. t. kresge, k. d. schmitt, c. t. w. chu, d. h. olson, e. w. sheppard, a new family of mesoporous molecular iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering manshor et al. 86 sieves prepared with liquid crystal templates, j. am. chem. soc. 114:27 (1992) 10834–10843. [10] r. ryoo and s. jun, “improvement of hydrothermal stability of mcm-41using salt effects during the crystallization process”. j. phys. chem. b 101, 317-320, 1997. [11] s. martirosyam, “zinc electrode with reduced dendritic propagation”. journal of power sources vol. 172, issue 2, 984-987, 2007. [12] p. j. branton, et al., “physisorption of argon, nitrogen and oxygen by mcm-41, a model mesoporous adsorbent”. j. chem. soc. faraday trans. vol. 90, no.19, 29652967, 1994. [13] k. a. northcott, et al., “the adsorption of divalent metal cations on mesoporous silicate mcm-41”. chemical engineering journal 157, 25-28, 2010. [14] p. innocenzi, et al., “electrical and structural characterisation of mesoporous silica thin films as humidity sensors”. sensors and actuators b 76, 299-303, 2001. [15] a. bearzotti, et al., “relative humidity and alcohol sensors based on mesoporous silica thin films synthesised from block copolymers”. sensors and actuators b 95, 107-110, 2003. microsoft word 219-719-3-ce completed-corrected iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mahamad maifiah et al. 171 molecular cloning of phytase gene from asuia279 and its expression in pichia pastoris system m. h. mahamad maifiah 1 , p. jamal 1 , t. nuge 1 , n. s. mohd dali 1 , a.s. meor hussin 2 ,abd-elaziem farouk 3 and h. mohd. salleh 1 1 bioprocess and molecular engineering research unit, department of biotechnology engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2 department of food technology, faculty of science and food technology, 43400, university putra malaysia, serdang, selangor, malaysia. 3 department of biotechnology, faculty of science, taif university, 21974 taif, al-hawiayah, p. o. box. 888, saudi arabia. hamzah@iium.edu.my; yumi@iium.edu.my abstract: phytases catalyze the hydrolysis of phytate (myo-inositol hexakisphosphate), one of the major storage form of phosphate in plants, with subsequent release of myo-inositol, phosphate and phytate-bound minerals. nonruminant animals such as chicken, swine and fish can’t use the organic phosphorus and minerals from their diet because there is no phytase activity in their digestive tract. phytate degrading enzyme is added to the animal feed diet to improve phosphorus availability from the dietary phytate and at the same time this lessen the phosphate pollution level in areas of intensive animal production as the phosphate would not be excreted out to the environment. asuia279, a bacterial strain isolated from malaysian soil has potentially shown good phytase activity. in the present work, the gene encoding for phytase has been amplified from the plasmid dna of recombinant asuia279(5) obtained from a previous study (unpublished data) by a polymerase chain reaction (pcr) methodology. the amplified phytase gene was extracted, purified then cloned into the ppiczαa plasmid and transformed into pichia pastorisx-33 strain for enzyme production. abstrak: fitase pemangkinan hidrolisis fitat (myo-inositol hexakisphosphate), merupakan salah satu cara penyimpanan utama fosfat dalam tumbuhan, dengan pelepasan berturut myo-inositol , fosfat dan galian terikat fitat. haiwan bukan ruminan seperti ayam, khinzir dan ikan tidak dapat memanfaatkan fosforus organik serta galian yang diperolehi daripada makanan kerana tidak mempunyai aktiviti fitase di dalam saluran pencernaan mereka. enzim pengecilan fitase dicampurkan ke dalam pemakanan haiwan untuk mempertingkatkan keperolehan fosforus dari fitat diet. pada masa yang sama ia dapat mengurangkan tahap pencemaran fosfat di kawasan yang terdapat penternakan haiwan secara intensif agar fosfat tidak dikumuhkan ke persekitaran. asuia279, satu strain bakteria yang diasingkan daripada tanih di malaysiamenunjukkan aktiviti fitase yang memberansangkan. buat masa kini, pengekodan gen fitase telah diperkuatkan dengan plasmid dna dari asuia279(5), rekombinan yang diperolehi daripada kajian terdahulu (data tak diterbitkan) berdasarkan kaedah tindak balas berantai polimerase (polymerase chain reaction (pcr)). gen fitase yang diperkuatkan, ditulenkan dan kemudian diklonkan menjadi plasmid ppiczαa dan berubah menjadi strain pichia pastorisx-33 untuk penghasilan enzim. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mahamad maifiah et al. 172 keywords: phytase;animal feed;pollution;polymerase chain reaction (pcr);pichia pastoris 1. introduction phytic acid, phytate (myo-inositol 1,2,3,4,5,6hexakisphosphate, ip6) and phytin can be referred as free acid, salt, and calcium/magnesium salt respectively [1]. the used of the terms has been used interchangeably but gives the same meaning that refer to phytate. phytate is the major storage form for phosphorus especially in cereal grains and legumes which represents almost 75% to 80% of phosphorus in nature [2]. phytase is an important enzyme that functions to sequentially hydrolyze myo-inositol hexakisphosphate into less phosphorylated myo-inositol derivatives and inorganic phosphate [3]. monogastric animals such as chicken, pig, fish as well as human do not have the ability to utilize and hydrolyze phytate into its intermediate products and phosphorus [4]. this undigested phytate together with additional inorganic phosphorus will be excreted out through their feces and this will contributes tophosphate pollution problem, eutrophication in areas of intensive livestock production [4]. in addition, phytate exhibits anti-nutritive effects as it happens to be a chelating agent and form complexes with significant multivalent metal ions mainly fe 2+ , zn 2+ , cu 2+ , mg 2+ , mn 2+ and ca 2+ which may cause mineral deficiency in animals and humans [2, 5]. the methylotrophic yeast, pichia pastoris system was attributed with several important advantages over prokaryotic and other eukaryotic expression system since it has powerful and tightly regulated alcohol oxidase 1 (aox1) promoter, performs many posttranslational modification of an eukaryotic system, for example protein folding, proteolytic processing and glycosylation [6, 7]. many works have been reported with successful overexpression of heterologous protein using the p. pastoris system [6]. chen et al..managed to enhance phytase activity level from 118 to 204 u/ml at the flask scale and 1880–4946 u/ml for high cell-density fermentation, respectively, by appropriately modifying the medium composition and fermentation strategy of escherichia coli phytase gene appa expressed in p. pastoris km71-61 strain [8]. the genetically engineered phytase of aspergillus niger sk-57 showed a 14.5-fold increase compared with its wild type strain produced at 6.1 g/l of phytase or 865 u/ml phytase activity [9]. fu et al. reported that the clone of phytase gene appa from yersinia kristeensenii in p. pastoris gs115 exhibited specific enzymatic activity of 2656 umg -1 [10]. furthermore, olazaran et al., 2010 reported on the cloning and expression of native gene encoding a bacillus subtilis phytase where the selected recombinant strain produced and secreted 0.82 u/ml of phytase activity after 48 h of methanol induction in shake flasks[11]. the objective of this study is to investigate the over expression pattern of phytase produced by asuia279 that was previously isolated from malaysian soil[12]. the phytase encoding gene from asuia279 was cloned into ppiczαa plasmid and expressed in p. pastorisx-33 strain. 2. materials and methods 2.1 bacterial strains, plasmids and chemicals all chemicals were analytical grade and commercially available. recombinant asuia279(5) (unpublished results) , one shot top10 competent cells (invitrogen). zero blunt topo (invitrogen) was used as cloning vector and ppiczαa vector (invitrogen) was used as expression vector, p. pastoris strain x-33. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mahamad maifiah et al. 173 2.2 cloning of phytase gene two primers were designed to cover the whole sequence of asuia279(5) phytase gene. the forward primer used wasesf2m (5’-ggtaccatgaaattcaaacc-3’) containing a kpn 1 site. a reverse primer that will remove stop codon formation at the cterminal of the target gene sequence was designed as hsrpns1 (5’tctagatacagcggttta3’) containing a xba1 site. the gene fragment encoding phytase was amplified from the recombinant plasmid ofasuia279(5) by a polymerase chain reaction (pcr) in a master cycler gradient machine (eppendorf) to obtain a size of 1.4 kb fragment and was then purified using qiaquick gel extraction kit (qiagen). the purified dna fragment was cloned into the zero blunt topo as cloning vector. the plasmid construct was transformed into one shot top10 competent cells. after digestion with the restriction enzyme kpn1/xba1, the fragment then was purified, ligated into the ppiczαa vector and transformed into one shot top 10 according to the manufacture’s protocol. the positive transformants were selected on low salt luria-bertani (lb) plates containing 25µg/ml zeocin. the positive colony was selected for sequencing analysis. 2.3 linearization of plasmid the positive plasmid was linearized with pmei and purified using qiaquick gel extraction kit (qiagen) for transformation into the expression host p. pastorisx-33. 2.4 preparation of competent cells the competent cell of p. pastorisx-33 was prepared according to the pichia easycomp. kit (invitrogen) manual prior to the transformation process. single colony of p. pastorisx-33 strain was grown overnight in 10 ml ypd (1% yeast extract, 2% peptone, 2% dextrose) broth media at 30 o c at 250 rpm. the overnight culture was diluted to an od600 of 0.1-0.2 by addition of ypd broth media. cells were grown at 30 o c at 250 rpm until the od600 reached 1.0. the cells were then pelleted by centrifugation at 500 x g for 5 minutes at room temperature and the supernatant was discarded. the cell pellet was resuspended in 10 ml of solution i without further incubation and centrifuged at 500 x g for 5 minutes at room temperature. the supernatant was discarded. the cell pellet was resuspended in 1 ml of solution i and aliquoted of about 50 µl of the prepared competent cells into labeled 1.5 ml microcentrifuge tubes. the prepared x-33 hosts were stored in 80 o c. 2.5 transformation into p. pastorisx-33 by easycomp protocol highly concentrated and linearized pichia ppiczαa expression plasmid (4 µl) was added to the x-33 competent cells. solution ii (1 ml) was added to the mixture and then mixed by vortexing or inverting up and down the tube. the transformation reaction was incubated for 1 hour at 30 o c and mixed every 15 minutes by vortexing the tube. the cells were heat shocked in a 42 o c water bath for 10 minutes. the cells were split into 2 microcentrifuge tubes (~ 500ul per tube) and 1 ml ypd medium was added to each tube. after incubation at 30 o c for 1 hour, the cells were centrifuged at 3000 x g for 5 minutes at room temperature and the supernatant was discarded. cells from each tube were resuspended in 500 µl of solution iii and the resuspended cells were combined. the tube was centrifuged at 3000 x g for 5 minutes and the supernatant was discarded. the cell pellet obtained was resuspended in 120 µl of solution iii and plated on ypds (1% yeast extract, 2% peptone, 2% dextrose, 1 m sorbitol, 2% agar) agar plate containing 50 µg/ml zeocin. the plate was incubated for 2 to 4 days at 30 o c. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mahamad maifiah et al. 174 2.6 selection of high copy number of multiple integrant phytase strain the resistant zeocin colonies that grew on the plate were further selected by plating the clones on ypds plate with incremental zeocin concentration of 100, 200, 500 and 1000 µg/ml of zeocin to obtain recombinant pichia strains that possess high copy number of multiple integrants. the selected positive transformants were indicated as hsuia279(5h)ax. clones that survived on plate with 1000 µg/ml of zeocin concentration were subjected to direct pcr screening by preheating treatment of colony pcr to determine if the gene of interest has integrated into the pichiagenome. 2.7 fermentation and phytase expression study single colony of recombinant hsuia279(5h)ax was inoculated into 50 ml of bmgy media (1% yeast extract, 2% peptone, 1.34% yeast nitrogen base (ynb), 4 x 10 5 % biotin, 1% glycerol, supplemented with 100 µg/ml of zeocin) in a 250 ml shake flask as a starter culture for 24 hour. the starter culture (1%) was inoculated into 100 ml of bmgy media supplemented with 100 µg/ml of zeocin in a 250 ml shake flask. the culture was grown at 30 o c and 250 rpm for 24 hour (od600~1.0). the cells were centrifuged at 3000 x g for 5 minutes at room temperature. the supernatant was decanted and the pellet was resuspended in 10 ml bmmy media (1% yeast extract, 2% peptone, 1.34% ynb, 4 x 10 -5 %,) to induce the expression of phytase by 1% methanol. the culture was transferred into 100 ml shake flask and continues to grow for 3 days. methanol (1 %) was added to the cultures of every 24 hours to maintain the induction and 1 ml of the cultures were collected and centrifuged at maximum speed for 3 minutes. the supernatants were collected and concentrated by a concentrator amicon® ultra-15. the supernatant were checked for protein expression and purity by coomassie-stained sodium dodecyl sulfate (sds)-polyacrylamide gel (page) 12% electrophoresis. this step was repeated every 24 hours for four days (24 hr, 48 hr, 72 hr, 96 hr). 2.8 phytase activity assay phytate-degrading activity was carried out in a total volumeof 40 µl containing 25 µl of 0.1 m sodium acetate buffer, ph 4.5, 10 µl of 1.03 mm sodium phytate, ph 4.5 and 5 µl of phytase sample. the assay mixture was incubated for 30 minutes at 50 o c. the liberated phosphate was measured with a slight modification of the ammonium molybdate method [13]. freshly prepared stop solution was added into the mixture that basically contains acetone: 5 n sulphuric acid (h2so4): 10 mm ammonium molybdate (2:1:1 v/v) and 10 µl citric acid. the control was prepared by adding the stop solution prior to adding the enzyme into the assay mixture. the phytase activity was calculated from the average of at least three phytase assay measurements. phytase activity (unit/ml) = (1) where od of volume total, differences in od reading of volume total; t, time of incubation (min); d, thickness of the microplate reader (0.59 cm); ɛ, extinction coefficient (0.3094 µmol/ml.cm). 3. results and discussion the plasmid, asuia279(5) was amplified by pcr using designed primers with deletion of stop codon at the c terminus of the expressed protein to allow binding of the iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mahamad maifiah et al. 175 secreted protein during the purification stage. the amplified fragment was successfully purified and cloned into pcrii-blunt-topo cloning vector. highly concentrated, digested and purified plasmid was ligated into the ppiczαa expression vector and transformed into top 10 e. coli plated on low salt lb with 25 µg/ml zeocin. one positive colony was selected from the plate after being confirmed by restriction enzyme digestion with kpn1 and xba1. the amino acids sequence revealed 99% homology with the referred sequence of asuia279 (5) (unpublished) with polyhistidine tag sequence at the c terminal (fig. 1). 5 mkfkpltlafaalfplcllaaapqveryvvtfpqedhvvysgnyasafpnglpvgvgsgl 60 a5 mkfkpltlafaalfplcslaaapqveryvvtfpqedhvvysgnyasafpnglpvgvgsgl 60 ***************** ****************************************** 5 lflrkegddlifatvtdrgpnadspkmgkqeskifaspeytplmmtirvskdqaqasdpm 120 a5 lflrkegddlifatvtdrgpnadspkmgkqeskifaspeytplmmtirvskgqaqasdpm 120 ***************************************************.******** 5 plhddqgnisglplpagligatnelalndalqtltgdkrgldtegitpdgkggywlcdey 180 a5 plhddqgnisglplpagligatnelalndalqtltgdkrgldtegitpdgkggywlcdey 180 ************************************************************ 5 gpfiihvdasgailakhgpqagkgeegvagglpniikwrqpnrgfegltrmpdgriiaav 240 a5 gpfiihvdasgailakhgpqagkgeegvagglpniikwrqpnrgfegltrmpdgriiaav 240 ************************************************************ 5 qstldidgktkntarftrlvsfdpatgktamygypididvykkakdakigdivalddhri 300 a5 qstldidgktkntarftrlvsfdpatgktamygypididvykkakdakigdivalddhri 300 ************************************************************ 5 llieqggdknktmrnriyvvdlsnatdlstldntqppefddaeklnargvklatkqlavd 360 a5 llieqggdknktmrnriyvvdlsnatdlstldntqppefddaeklnargvklatkqlavd 360 ************************************************************ 5 lrelgwqqekaeglalidsqtlavindndfglqsellepqgdkkamddynvdgkghltld 420 a5 lrelgwqqekaeglalidsqtlavindndfglqsellepqgdkkavddynvdgkghltld 420 *********************************************:************** 5 gkpvaskigikplektasqnelwvikldkpl----------------------451 a5 gkpvaskigikplektasqnelwvikldkplyleqkliseedlnsavdhhhhhh 474 fig 1: comparison of amino acid sequences between hsuia279(5h)a gene and the asuia279(5) gene. the expected size of phytase gene without addition of his-tag is 48.71 kda while with the addition of his6x-tag is 51.48 kda after calculated from primary structure analysis of expasy proteomics server. the plasmid was linearized by pme1 to effectively integrate the gene into the aox1 locus of the p. pastoris genome. the purified plasmid was transformed into x-33 pichia strain by easycomp method and plated on ypd agar with 25µg/ml zeocin. transformants that grew on the plate were picked and replated on 100µg/ml, 500µg/ml, and 1000µg/ml zeocin successively. the results showed that the transformants contain multicopy numbers of expression cassettes in the genome as they grew on high concentration of zeocin(fig. 2). the existence of the expression cassettes in their genome will lead to over expression of high concentration of heterologous phytase [14]. in addition, the integration process of the vector will increase the stability of the expression recombinant [15]. ten of the transformants were subjected to colony pcr in order to verify the presence of the phytase gene and its integration into p. pastoris genome. the result shows that there are two bands after done the colony pcr reaction (fig. 3). a ~2.2 kb band size appeared to be the aox1 gene of p. pastoris strain using the aox1 primers while a ~1.9 kb band size represents the hsuia279(5h)ax phytase gene. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mahamad maifiah et al. 176 fig. 2: growth of zeocin resistant p. pastoris x-33 transformants on ypd plate with zeocin concentration of (a) 100µg/ml zeocin, (b) 200 µg/ml zeocin and (c) 1000 µg/ml zeocin after 2 days of incubation period respectively. fig. 3: colony pcr of clone 1 to 10. two bands represent the transformant’s phytase gene (1.9 kb) and aox1 gene (2.2 kb) of p. pastoris strain using the aox1 primers. c indicatescontrol which is plasmid clone before it was transformed into pichiax-33 strains. recombinant phytase, hsuia279(5h)ax was expressed in p.pastoris x-33 strain as secreted protein after fermentation in medium bmgy and bmmy in shake flask cultures after methanol induction. culture supernatants collected after 24 hrs, 48 hrs, 72 hrs and 96 hrs were concentrated by a concentrator amicon® ultra-15 and then analyzed on sdspage (fig. 4). phytase was successfully expressed and detected from the recombinant hsuia279(5h)ax culture supernatant at 24 hours interval during 4 days fermentation while no protein was observed from the wild type of p. pastoris x-33 strain. phytase expression was increasingly enhanced from day 1 till day 4. the highest extracellular phytase expression occurred after 96 hrs fermentation period. the secreted recombinant phytase detected on sds-page show apparent molecular weight of 55 kda which was slightly greater than the predicted size of primary sequence (51 kda). this is probably the result of glycosylation that normally occurs in protein translational modification for yeast secreted proteins. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mahamad maifiah et al. 177 fig. 4: sds-page analysis of the expressed crude phytase enzyme. lane 1-4 is phytase expression after24, 48, 72 and 96 hour induction respectively with 0.5% methanol induction. lane a-d represents control study which is wild type x-33 at the same conditions after 24, 48, 72 and 96 hour induction with 0.5% methanol. the recombinant clone gave activity of 17.004 u/ml after 48 hours of incubation period under the current growth conditions. p. pastoris would secrete very little amount of native proteins, while secrete the huge amount of heterologous protein of interest [16]. this would be an advantage for protein recovery and purification processes. 4. conclusion the cloning of the phytase enzyme from asuia279 into the p. pastoris system would be a significant consideration for a cost effective measure to produce a high yield and activity enzyme for animal feed application. acknowledgements this research work is funded by biotech research project from the ministry of science, technology and innovation (mosti) malaysia, (grant project no. 07-01-08-eib011). the authors also thanked dr. farah diba abu bakar for valuable discussions. references [1] r. angel, n.m. tamim, t. j. applegate,a. s. dhandu, l. e. ellestad. “phytic acid chemistry: influence on phytin-phosphorus availability and phytase efficacy”. j. appl. poult. res. 11:471–480, 2002. [2] b.c. oh, w.c. choi,s. park,y.o. kim,t.k. oh. “biochemical properties and substrate specificities of alkaline and histidine acid phytases”. appl microbiol biotechnol 63: 362– 372, 2004. [3] x. wang,s. upatham,w. panbangred,d. isarangkul,p. summpunn,s. wiyakrutta,v. meevootisomd. “purification, characterization, gene cloning and sequence analysis of a phytase from klebsiella pneumoniae subsp. pneumoniae xy-5”.scienceasia30: 383-390, 2004. [4] j. dvorakova “phytase: sources, preparation and exploitationreview”. folia microbiol. 43 (4), 323-338, 1998. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mahamad maifiah et al. 178 [5] s. haefner,a. knietsch,e. scholten,j. braun, m. lohscheidt,o. zelder. “biotechnological production and applications of phytases”.appl microbiol biotechnol 68: 588–597, 2005. [6] g.p.l. cereghino,j.l. cereghino,c. ilgen, j.m. cregg. “production of recombinant proteins in fermenter cultures of theyeast pichiapastoris”.current opinion in biotechnology, 13:329–332, 2002. [7] a.l. zhang,j.x. luo,t.y. zhang,y.w. pan, y.h. tan,c.y. fu,f.z. tu. “recent advances on the gap promoter derived expression system of pichia pastoris”. mol biol rep 36:1611–1619, 2009. [8] c.c. chen,p.h. wu,c.t. huang,k.j. cheng. “a pichia pastoris fermentation strategy for enhancing the heterologous expression of an escherichia coli phytase”. enzyme and microbial technology. 35, 315–320, 2004. [9] a.s. xiong,q.h. yao,r.h. peng,p.l. han,z.m. cheng,y. li.“high level expression of a recombinant acid phytase gene in pichia pastoris”.journal of applied microbiology, 98: 418–428, 2005. [10] d.fu,h. huang,h. luo,y. wang,p. yang, k. meng,y. bai,n. wu,b. yao.“a highly phstable phytase from yersinia kristeensenii: cloning,expression, and characterization”. enzyme and microbial technology, 42: 499–505, 2008. [11] m.g. olazara´n,l.r. blanco,j.g.c. trevin˜o,j.a.g. lo´pez, j.m.v. salvado.“expression of a bacillus phytase c gene in pichia pastoris and properties of the recombinant enzyme”. applied and environmental microbiology. 5601–5608, 2010. [12] anis shobirin, m. h., farouk, a., greiner, r., salleh, h. m. and ismail, a. f. “phytatedegrading enzymes production by malaysian soil bacteria”. world journal of microbiology and biotechnology 23, 1653-1660, 2007. [13] j.k. heinonen, and r.j. lahti “a new and convenient colorimetric determination of inorganic orthophosphate and its application to the assay of inorganic pyrophosphatase”. anal biochem 113:313–317, 1981. [14] n.t. xuan,m.t. hang,v.n. thanh. “cloning and over expression of an aspergillus niger xp phytase gene (phya) in pichia pastoris”. world academy of science, engineering and technology 56, 2009. [15] j.l. cereghino andj.m. cregg“heterologous protein expression in the methylotrophic yeast pichia pastoris”. fems microbiology reviews 24: 45-66, 2000. [16] y. bin,z. chunyi,w. jianhua,f. yunliu. “recombinant pichia pastoris overexpressing bioactive phytase”.science in china (series c). vol. 41: no. 3, 1998. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 fvs-technology: intellectual search tools bahodir muminov boltayevich*and ulugbek bekmurodov bakhrom ugli fundamentals of informatics department tashkent university of information technologies named after muhammad al-khwarizmi, tashkent, uzbekistan * corresponding author: mbbahodir@gmail.com (received: 10th march 2020; accepted: 29th september 2020; published on-line: 4th january 2021) abstract: it is enough to have 3 basic stages of the modules in the spd of a diversified corporate network: (f) the method of submitting the request, i.e. the method of forming the expression of the information needs of the system user (s) the function of the correspondence of the electronic resource to the request degree of compliance with the request and the found electronic resource; (v) method of presenting electronic resources. combining these three stages for models, methods, and software modules of the aml, is referred to as fsv technology (fsv platform, fsv framework). fsv technology is an instrumental software platform based on a client-server architecture, integration and modification of models, and methods and algorithms of aml in the information environment of corporate networks. the following architecture has been developed for the fsv technology proposed for the search index in data retrieval systems. abstrak: tiga peringkat asas modul adalah cukup dalam pelbagai rangkaian korporat spd iaitu: (f) kaedah penyerahan permintaan, kaedah membentuk ungkapan keperluan maklumat pengguna sistem (s) fungsi surat-menyurat sumber elektronik bagi permintaan tahap pematuhan permintaan dan sumber elektronik yang dijumpai; (v) kaedah penyampaian sumber elektronik. gabungan tiga peringkat model, kaedah dan modul perisian aml, dipanggil teknologi fsv (platform fsv, rangka fsv). teknologi fsv adalah platform perisian instrumen berdasarkan seni bina pelanggan-pelayan, integrasi dan pengubah suaian model, kaedah-kaedah dan algoritma aml dalam persekitaran maklumat dalam rangkaian korporat. seni bina ini telah di bina bagi teknologi fsv yang dicadangkan bagi indeks carian dalam sistem dapatan data. keywords: intellectual search; fvs technology; information resource; search module; program module 1. introduction in the world to meet the needs of the population in electronic resources, information is given great attention to the creation of intelligent data search systems in corporate networks of information and resource centers. technologies of using information resources, the number of which is increasing every day, are one of the important issues of today. in this regard, including special attention is paid to improving the technology of searching and processing data based on semantic and fuzzy rules in corporate networks, database design and logical knowledge. the world conducts research work aimed at creating data retrieval systems, database design and semantic knowledge, creating and improving software modules and algorithms 118 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 for mining, search, data storage in corporate networks. in this regard, the important tasks are the design, development of models, methods for searching and processing data, creating software for building data retrieval systems in fuzzy and stochastic information environments of corporate networks. modern technologies that do not replace many years of experience and highly qualified specialists, are designed to significantly improve the quality and efficiency of its work. this was discussed at the international forum held and dedicated to modern intellectual systems. as it was noted, the modern it industry all over the world is going through a new stage of its development. the catalyst for this process is the latest technology that can solve problems that have traditionally been considered creative. the forum discussed trends in the development of modern intellectual systems, their implementation in various sectors of the economy, the health sector. with the independence of the republic, special attention is paid to the formation of a database of information resource centers (ircs), on the creation of corporate information library systems, national content in raising the level of informatization of society based on intelligent management of hardware and software in information technologies. in this direction, the development of databases and software systems for logical search in data retrieval systems is included. the objectives for “... developing national content, improving the mechanisms for creating and promoting modern educational, scientific and educational information resources, multimedia products in the state language, meeting the needs of young people, ... introducing information and communication technologies ...” were defined. the implementation of this task, including the formation of electronic resources, the improvement of data mining systems, the development of a database of semantic data and knowledge in corporate information library systems, is one of the most important issues. in the world of creating electronic resources, modeling processes and creating highperformance control systems to study the issues of intelligent search and data processing, research is carried out in a number of priority areas, including the creation of intelligent software modules based on the theory of fuzzy sets in solving problems in the fields of computer science and library, creation of methods for analyzing, searching and storing data based on models and methods of data mining and text mining, big data, development of methods and algorithms for integrating systems data retrieval, creation of algorithms, methods for processing and searching full texts, creating databases of aggregate data of corporate information library systems, creating methods and algorithms for processing requests for artificial and natural languages, creating a knowledge base, a semantic core based on the principles of smart and seo, developing software and data retrieval models based on local language. studies have shown that issues related to information retrieval, the structure and properties of data, the formation and processing of queries, the creation of a semantic core, the identification of electronic resources rating, the development of models and methods for intelligent search, the presentation and processing of data in fuzzy and stochastic information environments of corporate information biotech systems are not well understood. the purpose of the research is the development of models, methods for searching and processing data in fuzzy and stochastic information environments, as well as the creation of software for corporate information library systems. 119 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 2. main chapter methods of forming queries, determining the rating and elements of data search in the corporate network are devoted to the questions of forming queries, determining the rating and elements of searching in fuzzy and stochastic information environments (nsns). a “search module” is a subsystem that, upon request, provides the most current ordered set of electronic resources, equipped with a user-friendly interface, including a database and statistical data. the search module in the corporate network consists of two main elements that are independent of each other: an indexing element and a search element. the user sees only the capabilities of the search item and uses it. the indexing element is used to create the appropriate form for the effective presentation of information when searching for the necessary data in the data retrieval system (dps). suppose that in the database are consistently given and are in the segment v = [1, n], n={0, 1, 2, 3, …} with dosid identifiers with the set v, which has n electronic resources: a) a quote (or reference) is a pair of ordinal electronic resources. ( ) 2, vi j  . i incoming link and j outbound link electronic resource. in the set v between the electronic resources from all the links we form the e set, the graph directed to the links can be called reference graphs g = (v,e). b) for example, g = (v,e) in this case the graph is the final set of vertices, e v v=  and i v , denote ( )i i the incoming set of links, and ( )o i the outgoing set of links denote as, then: ( ) ( ) | ,,i i e e e j vi j=  =  , ( ) ( ) | ,,i i e e e j vi j=  =  (1) c) if ( )o i and ( )i i do not exist and, then they are denoted as in this case   , the rating of the electronic resource i v equals 0. d) no electronic resource can provide its inbound links ( )i i and outbound links ( )o i to these links. the rating of incoming links ri and outgoing links ro is determined as follows: ( ) ( ) 1 ( ( )) ( ) i ii ri r count i i doc i i ii i ==   ( ) ( ( )) ( ) r count o i o i o o i =  (2) here ( ( ))count i i is the number of incoming, ( ( ))count o i the number of all outgoing links. using the expression given above (2), we determine the method of preliminary rating of an electronic resource using (3) an expression. ( ) / 2r r rd i o= + (3) expression (2) allows the definition of electronic resources with a high rating and select a set that is recognized as relevant based on the identification of the rating of electronic resources in corporate information library systems (icbs). 120 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 suppose that  iq q= a lot of requests and given to iq the corresponding to a variety of electronic resources  i ijr r= , 1... dj m= 1... qj n= . here dm – is the number of electronic resources viewed in the system, nq – is the number of requests in the system. the method of logical-semantic search for a couple of queries, we will write as follows. ( , ) | j i i j i j j r r f q q q q r  = = (4) here, a b denotes the relation and similarity of a with respect to b. j i j r r r the condition must be relevant. rule 1: if 0i jq q = , then in this case iq is not semantically related to jq , and is also considered not similar to each other. rule 2: if 1i jq q = , then in this case it is considered that iq , jq is completely semantically related and the similarity 1 is considered ( iq exactly similar). rule 3: if the expression (4) is equal i j= , then in this case 1i jq q = it is considered semantically related, the similarity is 1 (it is exactly the same). rule 4: if 0 | 1i jq q  , then iq in this case, it is considered that semantically equal jq and the similarity is calculated by the expression (4). the method of logical-semantic search (4) for all queries, we write as follows: 1 2 1 1 1 1 ( , ,..., ) | q q q q q n n n n j i n i j j i j i j r r f q q q q q r= = = =  = =  (5) here ∑ is the union of the elements of the set. (5) the expression allows you to create a base of semantic knowledge in the data retrieval system (dps). creating models, methods, and software for searching and processing data in fuzzy information environments, using the theory of fuzzy sets and using the linguistic variable model, defines the method for developing fuzzy queries in the data retrieval system (pds) as follows: 1) () – defined linguistic variable; 2) t() – we define a linguistically similar variable of a fuzzy set of terms; 3) x – for fuzzy sets of terms, we determine the set of values; 4) g() – defined in the set of fuzzy terms, characterized by logical and modifier outputs; 5) x – x defines the membership function of the set. when designing a parametric membership function, the set −x x is the linguistic variable of the corresponding object characteristic, the parametric design  –method of the membership function is an important element in the intellectualization capabilities of the data retrieval system (pds). x – in the membership function, enter 4 parameters and give the following definition: 121 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 proposition 5: if a, b, c, d parameters are taken from x – the set of values, then in this case the function is considered to be x(a,b,c,d) the membership function of the set of values x. proposition 6: in the membership function x(a,b,c,d), the parameters a, b, c, d among themselves must be in ascending order. so one of the conditions a < b or b < c or c < d must be constantly met. proposition 7: t() – the parameters of the membership function for each term of the set of fuzzy terms corresponding to linguistic variables t(), at least one distinguishing parameter must be introduced. it is recommended to use the choice of classes for the selection of membership functions corresponding to the linguistic variables of a fuzzy set in intelligent search and processing in a fuzzy information environment. when intelligently searching for data in a fuzzy information environment of corporate information library systems, the main problem is the creation and management of the semantic core. we give the definition of a semantic core for intelligent search and data processing. in a fuzzy information environment: the semantic core is a set of relationships recognized as relevant, relevant in content and essence to normalized terms and electronic inquiry. based on this definition, 3 methods have been developed for creating the semantic core of data retrieval systems in a fuzzy information environment. these include: • automatic construction of the semantic core as a result of search and processing. • creating a semantic core by processing the citation of links, data in electronic resources. • creating a semantic core with the help of expert groups. this method is carried out in version 2. a) creation of a semantic core by an expert by creating queries corresponding to an electronic resource. b) expert processing of the existing semantic core, cancellation, modification, creation by it of the relationship of the request with the electronic resource, if necessary. a model of the semantic core, based on the implementation of the control of the semantic core and 3 algorithms of methods for creating a semantic core, has been developed. to determine the relevance of the semantic core model 4 properties have been added to the semantic core. if in property 1 there is a semantic link of the electronic resource and the query is 1, otherwise it takes the value 0, property 2 activates n the total number of links, property 3 m the number of link-references. in a fuzzy information environment for intelligent search and data processing in the development of models and rules for fuzzy search, the core of the knowledge base will form a fuzzy query q in a variety of fuzzy queries q* (6) to form the rule condition as follows:  * * * *: , ,...,1 2f q q q q qn→ = (6) 122 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 in this case, i q  1i q  the term consists of a fuzzy pair of terms 2i q  and can be defined as 1 2 | i i q q   , and, 1...i n= , 2 2 i n q    , 2i q  2i q  is the number of fuzzy terms. conditions of the rule for the logical action "and" and 1 q  a pair of terms (6) we write as follows: 1 * * * * * 1 11 12 1 1, 12 ( ) ( ) ( ) ( ( )) x q q and q d and q t and a q= = = = (7) where * 1 ( )q q= 1q  q – is the pairing or non-pairing of the terms that make up the query, * 11 ( )q d= the semantic relation of the electronic resource d and term, 11 q  , * * 12 ( )q t= the presence or absence in the set of fuzzy terms t* of a database of fuzzy data 12 q  , * 12 ( ( )) x a q= * 11 ( )q d= , the weight а and the membership or nonmembership of the values of membership functions of fuzzy terms 12 q  . using this condition (7) we write as follows. optimally, the fuzzy rules are based on the mamdani method for intelligent data search in the data retrieval system. ( )* * * * *1 2 , 2 1 ( ) ( ) ( ) ( ( )) i n i i i i i x i i q q and q d and q t и a q r = = = = = → (8) if, on the basis of fuzzy rules, to write the set d of electronic resources in the knowledge base of rule (8), we obtain a system of fuzzy rules  1 2, ,..., md d d d= , m the number of electronic resources in the database. we introduce the concept of the knowledge base kernel for the definition method, a fuzzy term and modifier, parameters corresponding to the membership functions that have been developed and are constantly updated with the help of expert experts. the algorithm for the development of the knowledge base kernel, the idef1x model, and relationships in the model have been developed. for the formation of a variety of electronic resources that meet the requirements in a fuzzy information environment, idef0 models have been developed that describe the functional structure and functionality of category 3 related tools to create a knowledge base based on the knowledge base, semantic core, and processing fuzzy requests. creation and implementation of software for searching and processing data in the corporate network, is devoted to the development of technology and architecture of fsv, composite modules and models, for the effective operation of search modules in corporate information-library environments it is necessary to have several basic steps. 123 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 fig. 1: idef1x core model knowledge base. it is enough to have 3 basic stages of the modules of the search box in the data retrieval system of a multi-profile corporate network. these include: 1. (f) method of presenting the request, i.e. method of forming the expression of the information needs of the user system. 2. (s) the function of the correspondence of the electronic resource to the request, i.e. the degree of compliance with the query and the found electronic resource. 3. (v) method of presenting electronic resources. fig. 2: architecture of fsv technology for processing data. combining these three stages for models, methods and software modules of the aml, we call fsv technology (fsv platform, fsv framework). 124 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 fsv technology is an instrumental software platform based on a client-server architecture, integration and modification of models, methods and algorithms for searching and processing data in the information environment of corporate networks. the following architecture has been developed for the fsv technology proposed for the search index in data retrieval systems. in the development of the functional structure and idef models of the instrumental software module for query processing corporate networks request processing is divided into 2 stages. fig. 3: architecture of fsv technology for intellectual research. at stage i, requests are created in natural language, based on the request processing methods, artificially created requests, based on the ui (user interface) methods. the second stage, which is a recurrent sequence, is carried out by clearing additional and auxiliary terms, determining the type of query, creating indices of logical and fuzzy terms, of the zonal field. when creating idef models and functional structure of a software search and presentation software module. in the corporate network, an idef0 model was developed based on the methods, data retrieval system models in fuzzy and stochastic environments, traditional search, and s-er matching process. presentation v includes the processes of receiving a set of electronic resources, choosing a presentation method, determining the type of ui, providing constraints and filters and representing the set based on them, determining and controlling calls in the user’s electronic resources. fig. 4: search results and data processing for the parameter "speed". 125 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 fsv technology is integrated into such systems as: “armat ++” an automated system of information resource centers, “mobile-library” mobile software on library resources, “vlibrary” a virtual library of written cultural heritage of turkic peoples of central asia of the xix century (kazakhstan). for the experiment in marc21 format, you can use the iso2709 data exchange standard when exchanging data in corporate information library systems. therefore, more than 50,000 titles of various electronic resources and full texts were chosen. for comparison and analysis results, such parameters as “speed”, “number of found data”, “average relevance value” were selected and their results are given in the following figures (fig. 3 and fig. 4). fig. 5. search results and data processing for the parameter "average relevance". the results of the experiment show that high speed provides the user with, firstly, superfluous information, secondly, it is very difficult to satisfy the information needs, i.e. need to analyze a lot of data. although the search takes more time, but finding the necessary data indicates the effectiveness of search systems, since the analysis and limitation of redundant information saves 25%, sometimes up to 50% of the time of users. the implementation of the results. based on the software "armat ++", created on the basis of fsv technology, models, methods of searching and processing data in fuzzy and stochastic information media: • a method for determining a preliminary rating of an electronic resource based on references, a software module and an algorithm for designing parametric membership functions based on linguistic variables for fuzzy user requests, a software module, a method and algorithm for creating a knowledge base were introduced into the corporate networks of the main library of the academy of sciences (reference dated october 30 2017 no. 33-8 / 7293 of the ministry for the development of information technologies and communications). as a result of scientific research, there were opportunities to improve the efficiency of determining electronic resources rating by 30%, using high-rating resources when presenting resources to users, improving the efficiency of processing requests in the corporate network by 15%, increasing the efficiency of collecting, searching, processing and providing data by 12%. • a mathematical model of logical-semantic search, a software module and an algorithm for designing parametric membership functions based on a linguistic 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 exact requests s requests fuzzy requests armat++ (uzbekistan) ирбис (russian) armat (uzbekistan) «библиотека-2000» (russian) «руслан» (russian) “libermedia” (france) «aleph» (israel) vtls (usa) 126 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 variable for fuzzy user requests, a model, methods, algorithms and a software module for creating a semantic core (reference from october 30, 2017 no. 33-8 / 7293 of the ministry for the development of information technologies and communications). the results of the research allowed to increase the choice of resources that meet the requirements described in natural language by 30%, increase the efficiency of data search by 8%, reduce the number of corresponding electronic resources found by 2 times and increase accuracy by 30%. • an information retention algorithm with a recurrent relationship, a model, an algorithm and a software module of the semantic core, a model, an algorithm and a software module for creating a knowledge base were introduced into the information resource center of the intellectual property agency in accordance with rule m mamdani (reference dated october 30, 2017 no. 33-8 / 7293 of the ministry of information technology and communications development). the results of the research allowed to increase the efficiency of the formation and processing of the original data by 15%, increase the efficiency of data retrieval by 12%, increase the amount of data matching the requests by processing fuzzy thermal queries by 30% and reduce the amount of unnecessary data by 50%. • e-line press ltd. introduced a database project and idef-architecture architecture of fsv technology, developed to create a method and software module for determining a preliminary rating of an electronic resource based on links, a mathematical method of logical-semantic search, a data retrieval system (reference from october 30, 2017 no. 33-8 / 7293 of the ministry for the development of information technologies and communications). the results of the study allowed to increase the efficiency of determining the accuracy of the preliminary rating of scientific resources and periodicals by 1.5 times, increase the efficiency of creating a database by 20%, increase the efficiency of data search by 5%, reduce the number of corresponding resources found by 50% and improve their accuracy in 1.3 times. 3. conclusion remarks as a result of the scientific and practical work “models, methods of searching and processing data in fuzzy and stochastic information environments” the following results were obtained and the following main conclusions were made. for the evaluation of data retrieval systems, compliance with the criteria of accuracy and integrity, reducing search time, a logical-semantic search model was developed, which increased the search efficiency by 5%. it can serve to study the issues of indexing sets of predefined ers and queries, building their semantic links, optimizing search speed based on criteria and mathematical methods for searching and processing data in multidisciplinary and multi-stage information resources. the algorithm and software module for determining the relationship between the parameters of parametric membership functions, the choice of fuzzy terms corresponding to the classes of membership functions in the methods of intelligent search and data processing have been developed. improved processing of fuzzy requests by 22%. developed algorithms, software module and 3 ways on creation of a semantic core for data retrieval systems in a fuzzy information environment of corporate information library systems, as well as increased the amount of data matching the query, on 10%. idef0 and idef1x models for software modules of data retrieval systems in 127 iium engineering journal, vol. 22, no. 1, 2021 boltayevich and bakhrom ugli https://doi.org/10.31436/iiumej.v22i1.1389 corporate information library systems were developed. serves for use in related research with the design of the functionality of the instrumental software module for analysis, text processing and the development of idef models, with questions of indexing, compression, information security, the choice of technical means. the architecture, technologies fsv-software for creating a system for searching and processing data in corporate information library systems has been created. the results of introducing fsv technology into the armat ++ corporate information library system make it possible to increase the effectiveness of the “number of found data” by 7%, the average relevance value by 10%, and the search by 5%. references [1] anagnostopoulos a, andrei z, kunal p. (2006) effective search engine model. in proc. cikm, pp 208-217. [2] arlitsch k, obrien p, rossmann b. (2013) managing search engine optimization. journal of library administration, 53(2-3): 177-188. [3] azevedo c, iacob m, almeida j, van s, pires l, guizzardi g. (2015) archimate. information systems, 54: 235-262. [4] bhat na, ganaie sh. a. (20160 e-resources: y.s. parmar university of horticulture and forestry. collection building, 35(1): 16-21. [5] brock eo. (2016) declarative semantics of transactions in orm. information systems, 60:85-94. [6] cai f, rijke m. (2016) learning from homologous queries and semantically query auto completion. information processing & management, 52(4): 628-643. [7] muminov bb. (2014) methods of information retrieval and cash algorithms. itpa, 4-5 november, pp.194-196. [8] muminov bb. (2016) the model of logical semantic searching. proceedings of the uzbekjapan symposium on ecotechnologies, tashkent, pp 72-77. [9] newquist h. p. data mining: the ai metamorphosis // database programming and design. 1996. № 9. hp. (1996.) [10] muminov bb. (2016.), malumotlarni izlash usullari. fan va texnologiya,toshkent pg 276. [11] muminov bb. (2016.), data search methods. science and technology, tashkent pg 276. 128 microsoft word vol 12_no1_2011_june.doc iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 65 effect of fiber length variations on mechanical and physical properties of coir fiber reinforced cement-albumen composite (cfrcc) a. zuraida, s.norshahida, i. sopyan and h. zahurin department of manufacturing and materials engineering, faculty of engineering, international islamic university malaysia (iium), p.o. box 10, 50728 kuala lumpur, malaysia. e-mails: zuraidaa@iium.edu.my, adihahs_ron@yahoo.com abstract: this paper evaluated the effect of fiber length on the mechanical and physical performance of coir fiber reinforced cement-albumen composites (cfrcc). albumen protein was added as a binder and the coir fibers with the lengths of 0 (control cement composite), 2.5, 5, 10 and 20 mm was used as partial replacement of the cement mixture. flexural and compressive strength, bulk density, moisture content and water absorption were investigated. the experimental investigations revealed that increasing in length of fiber increase the flexural strength. incorporation of long fiber into the cement paste however, decreased the workability and thus introduced voids which resulted in low density. in fact, the water absorption and moisture content were also increased. abstrak: kerja ini menilai pengaruh panjang serat terhadap prestasi mekanik dan fizikal serat sabut diperkuatkan komposit simen-albumen (cfrcc). albumen protein ditambah sebagai bahan pengikat dan serat sabut dengan panjang 0(kawalan komposit simen), 2.5, 5, 10 dan 20 mm telah digunakan sebagai pengganti sebahagian dari campuran simen. kekuatan lenturan dan mampatan, ketumpatan, kadar kandungan air dan penyerapan air diselidiki. penyelidikan eksperimental mendedahkan bahawa peningkatan panjang serat meningkatkan kekuatan lentur. gabungan serat panjang ke dalam adunan simen bagaimanapun,menurunkan kebolehkerjaan dan menghasilkan rongga yang mengakibatkan kepadatan rendah. bahkan, penyerapan dan kandungan air juga meningkat. __________________________________________________________________ keywords: egg albumen, cement, coir fiber, biopolymer, matrix, composite iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 66 1. introduction the concrete industries in malaysia have been an active, integrated and growing. yet, the industry not stuck in the present but keen to seek out new markets, invest in the future and raise productivity and quality. it is generally known that ordinary cement based composites have been long occupied in industry because of it is relatively low price and uncomplicated in processing. even so, the concern now is therefore lies in creation towards environmental friendly with higher performance type of cement based composite. faced by these adversaries, cement industry promotes widespread application of best practices and technologies to reduce the amount of limestone calcinations, energy usage and emissions of carbon dioxide. hence, there should be greater utilization of ingredients, materials and systems that can improve the functionality and durability of cement products without destructing the environment. the search for alternative binder or cement replacement materials led to the discovery of the potential of using agriculture wastes. amongst the various types of residues from agriculture industry, coconut fiber is the most economical in terms of availability [1]. the use of coir fiber in cementitious material is assumed to be effective toward produce lightweight product. on the other hand, the employment of biopolymer in building material is expected to results in better processability, higher strength and reduction of final material brittleness. it is anticipated egg albumen will toughen and regulate the qualities of cement composite. it is timely that we have developed biopolymer-added cement composite with natural fiber as reinforcement. hence, the efforts currently is under way in producing lightweight cement composite with use of agriculture waste, coir fiber, and biopolymer, egg albumen in turn to reduce the use of portland cement which at the same time provide composite with better attributes. research has shown good prospects in terms of properties which are comparable to ordinary cement based composite. asasutjaritet al. [2] claimed that the effect of fiber length is inversely proportional to the mechanical properties. this opinion advocates that the short fiber become mineralized earlier than long fibers. in short fiber-reinforced composite, there are more end points which create facilities for the penetration of cement hydration products. consequently, the loss of flexibility of the fibers is accelerated. moreover, the longer the fiber length, the higher the water absorption since the incorporation of long coir fibers into the mix decreased the workability and increased void spaces. according to li et al. [3], short fibers of coir fiber-reinforced cementitious composite show better flexural strength than the long fibers. this is attributed to the long fiber that is neither well-dispersed nor straightened. as well, asasutjarit et al. [2] found that the composite samples having fiber lengths of 1-4 cm are likely to yield better mechanical properties. it is well understood that the fiber length plays an important role in the properties of fiber cement composites. in this present work, focus is placed on the influence of fiber length on mechanical and physical properties of cfrcc. evidence for fiber length variations on the flexural, compression, density, moisture content and water absorption are presented. iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 67 2. experimental procedures 2.1 materials locally produced duracem white portland cement (wpc) was obtained from duracem coating industries sdn. bhd., malaysia. as received cement powders were sieved in order to obtain a granular size below 500 µm. the body component contained in commercial wpc powders was identified precisely by fourier transform infrared (ftir) spectrometer (perkin elmer ft-ir, spectrum 100 series) using atr method. all spectra were measured in transmittance in the 4000 cm-1 – 380 cm-1 range. the brown colored and matured coir fiber used in this work was supplied by hk mega trading sdn. bhd, malaysia and the coir fibers were untangled to rip the fibers into an individual state. they were sieved to remove shorter fiber and contaminant. coir fibers were washed with clean tap water for 30 minutes and air-dried in oven at 60ºc for 8 hours before cut into required test length. the coir fiber was then subjected to ft-ir characterization to identify their chemical constituents. the major bands of coir fiber and their peak assignments to chemical bonds were identified precisely by ftir spectrometer (perkin elmer ft-ir, spectrum 100 series) using atr method. all spectra were measured in transmittance in the 4000 cm-1 – 380 cm-1 range. fresh eggs were supplied by ffm farms sdn. bhd., malaysia. egg white (albumen) in the liquid form was obtained by first breaking fresh egg and following complete removal of the adhering yolk by using egg separator. albumen solution was beaten for 3 minutes or until the entire albumen has been converted to froth. the albumen froth was allowed to settle in a covered container for 24 hours. then, the albumen drained through muslin. after settling for 24 hours and ageing for 1 day, it is a yellowish homogeneous liquid which indicates its readiness for use. thermal properties of albumen solution which underwent denaturation and aging process were examined using differential scanning calorimetry (dsc) (perkin elmer, sapphire) at 2°c/ min in the range 30-120°c. 2.2. composite fabrication in the cfrcc samples preparation, the fiber with the length of 0, 2.5, 5, 10 and 20 mm were added to the slurry of albumen and cement, and the ratio of albumen and fibercement was 65:35 (volume percent). they were mixed homogeneously in a laboratory mechanical mixer at a constant speed of 150 rpm. the mixture then poured into a mould and compacted by vibration. after moulding, the composites were allowed to settle in covered mould at a room temperature of 20 ± 2 ºc for 24 hours before demoulding. the samples were dried for another 35 days at ambient temperature of 20-25ºc and 60 % relative humidity. and finally, the physical and mechanical properties such as flexural and compressive strength, density, moisture content and water absorption were measured. 2.3 test method flexural strengths were measured under three point bend loadings with a span of 60 mm and at the deflection rate of 5 mm/min. flexural testing was conducted using universal testing machine (instron, model 5582) in accordance with astm c78.density was determined following the procedures described in astm c1161. the same specimen were weighted, dried in circulating oven to constant mass at 103 ± 2 ºc and reweighed. iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 68 while, absorption test required the mass of the specimen to be recorded before and after the specimen immersed in 20 ºc water for 1 hr in a water bath. 3. results and discussion 3.1 characterization of raw materials figure 1 shows the ftir spectra of as received cement powders. the remarkable absorption peaks of 1409, 873 and 712 cm-1 are observed. it is believed that these peaks were attributed to the vibration of carbon oxygen double bond in the carbonate ion. the two most prominent peaks at sharp absorptions of 873 and 712 cm-1 imply the presence of calcium carbonate, caco3 as the main element in the cement. the presence of caco3 compounds confirmed the existence of chalk, limestone, iron oxide and white clay in the powders. fig.1:ftir spectra of cement powder. iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 69 fig. 2 ftir spectra of coir fiber. as seen in fig. 2, the spectra revealed a strong band at 1030 cm-1 which is due to c-oc symmetric stretching dialkyl ether linkages and c-o stretching vibration in cellulose, hemicellulose and minor lignin contribution. large band of range between 3600-3100 cm-1 attributed by the polymeric association of the hydroxyl group and the bonded o-h stretching vibration exists in carbohydrates (cellulose + hemicellulose) and lignin is observed. region of absorption involving overlapping bands in the range of 1700-1100 cm-1 are due to c-c, c=c, oh, co, chn, c-o-c, ch aromatic linkages and bands at 2921 and 1442 cm-1 are due to vibration of chn(aliphatic and aromatic) which is present in carbohydrates and lignin. from the dsc traces in fig. 3, the existence of the endothermic peak determines the denaturation temperature of albumen. there were at least two endothermic peaks observed that attributed to the denaturation of conalbumin, and ovalbumin within the temperature range of 60-100ºc which confirmed the change occurring upon beating and aging of albumen. iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 70 fig. 3:dsc traces of denatured egg albumen. 3.2 ftir analysis the ftir spectra of coir fiber-reinforced cement-albumen composites are presented in fig. 4. the spectra indicated a vibration band of 1633 cm-1, which corresponds to the c=o stretching band of albumen. the spectra also exhibit the absorption peaks of 1409, 873 and 712 cm-1 which were attributed to the vibrations of carbon oxygen double bond in the carbonate ion of cement powders. the appearance of a strong band at 1030 cm-1is a vibration in cellulose, hemicellulose and a minor lignin contribution, while the one at 3341 cm-1 corresponded to cellulose. these indicate that each constituent in composite structure was thoroughly reacted and the hydration process was envisaged. iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 71 fig. 4: ftir spectra of coir fiber reinforced cement-albumen composite. 3.3 mechanical properties from fig. 5, it can be seen that the flexural strength of cfrcc increased with the increase of fiber length with the maximum of 6.719 mpa, for fiber length of 5 mm. it is hypothesized that cfrcc with longer fibers are able to bridge cracks more effectively and withstand higher load than cfrcc with shorter fibers. fiber with length less than 0.3 mm acts more as filler rather than as reinforcement when used in fiber-reinforced cement composite. although the amount of fiber loading was sufficient to provide strength, however it results inefficient fiber packing due to its higher volume fractions. khedari et al. [4] reported that short fibers are more difficult to align and pack densely compared to the long fiber. another strong reason that contributing to the low strength properties of the cfrcc is too short fibers allow a faster penetration on cement hydration. consequently the mineralization of the fiber accelerated the loss of flexibility of the fibers. similar effects have been observed by asasutjarit et al. [2]. furthermore, if the fiber is short, then the energy required to pull the fiber through the matrix is low and this can contribute to the dissipation of energy contained in the advancing crack. therefore, the crack continues through the sample and the material appears to be brittle [5]. the opposite effect, however was observed for composites with fiber length of 10 and 20 mm. longer fibers tend to ball up resulting in low workability and decline in strength. as can be seen (fig. 5), the flexural strength decreased to 5.417 and 6.036 mpa for composites reinforced with 10 and 20 mm fiber lengths respectively. iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 72 nevertheless, it is postulated that cfrcc specimens attained higher strength compared to cement-albumen composite without coir fiber. the strength is attributed by the presence of fiber, which provides stress transfer during the bending of composite specimen. fig. 5:flexural strength of cfrcc at different fiber length. figure 6 revealed typical failure mode of flexural test specimens. visual observation showed a macroscopic crack on the composite specimen. it can be seen that specimens with shorter fiber length were split into two pieces and some of the fibers debonded on both sides of the crack. in fact, sudden failure is observed in which the composites appeared to be fail in a brittle manner. this observation is in agreement to the flexural strength obtained in previous findings. for composites specimens reinforced with 5 mm length fibers, some of the fibers were still linked the two sides of cracks. this proved that the resistance to full separation of composite is provided by the fibers bridging across the cracked surface. this was interpreted as the highest failure forces which contribute to the rise in strength. nevertheless, composites with longer fibers (in this case, 10 mm and 20 mm) showed multiple cracking which were attributed to a continuous fall of load. at this point, the fibers tend to cluster together and resulting in an inadequate bond and fall in the strength. iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 73 fig. 6: photographs showing the fracture modes of cfrcc specimens under flexural stress. cfrcc samples experienced a drop off in compressive strengths with increasing fiber length as shown in fig.7. the compressive strength is inversely proportional to the fiber length. similar findings have been reported by khedari et al. [4]. it was found that as fiber length increased from 2.5 to 20 mm, the compressive strength dropped from 5.828 to 3.903 mpa. this is related to the fiber spacing in the cfrcc specimen. it is suggested that shorter fibers are aligned to be distant from each other which yield high density and strength. in contrast, longer fibers result in fiber cluster which then creates voids, low density and reduces strength. on the other hand, the cement-albumen composites exhibited higher compressive strength compared to cfrcc specimens. the mean compressive strength obtained was 16.316 mpa (fig. 7). a greater amount of cement in the mixture leads to denser product compared to the one reinforced with fiber resulted in higher compressive strength. 2.5 20 5 10 iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 74 fig. 7: compressive strength of cfrcc at different fiber length. 3.4 physical properties figure 8 illustrates the variation in density of composite as the fiber lengths increased in cement composite samples. the results indicate a slight drop off density as fiber length increases. it can be observed that the density decreased from 1.324 to 0.963 g/cm3 as the embedment length rose from 2.5 to 20 mm. this is due to the fact that the inclusion of long fibers into the composite blend decreased the packing, which lead to the disruption of fiber distribution and resulting in high void spaces. apparently, greater void contents yield low density composite. as mentioned by khedari et al. [4], short fibers are aligned and pack densely than the longer ones. on the other, cement-albumen composite obtained a maximum density of 1.257 g/cm3. this suggested that the inclusion of fibers into plain cement composite had little effect on the density. the density might be reduced slightly compared to cement-albumen composite. the effect of fiber lengths on moisture content properties of composite is depicted in fig. 9. for the fiber length in the range of 2.5 to 20 mm, the moisture content increased from 2.572 to 7.482 %. this relationship depended on voids volume present in the composite, which would account for the dominant effect on density, moisture content and water absorption. as mentioned previously, inclusion of long fibers into the composite might lead to the disruption of fiber distribution resulting in void spaces.on the basis of these results, specimens with low density have more void spaces which absorb more water and thus resulting in higher moisture content. while, it seems that the cement-albumen iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 75 composite specimens exhibited the least percentage of moisture content. cement composite that contained natural fibers generally seems to possess a high percentage of moisture content due to its hydrophilic nature. the effect of fiber lengths on water absorption properties of composite is depicted in fig. 10. longer fibers tend to increase the percentage of water absorption. the rate of water absorption increased from 3.024 to 16.021 % for 2.5 to 20 mm range of fiber lengths. as explained before, the rate of water absorption is greatly affected by the specimen’s density and void volumes. asasutjarit et al. [2] identified that the incorporation of long coir fibers into the mix decreased workability and increased the void space. consequently, the longer the fiber, the higher is the water absorption. this is in agreement with the findings by li et al. [6]. however, for cement-albumen specimens, the percentage of water absorption obtained was 29.778%. it is expected that without the presence of hydrophilic natural fibers, the percentage of water absorption should be lesser. over mixing might also results in foaming and subsequently resulted in occurrences of pores inside the specimen which was attributed by the entrapped air. therefore, more water was absorbed from surrounding. fig. 8: density of cfrcc at different fiber length. iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 76 fig. 9:moisture content of cfrcc at different fiber lengths. fig. 10: water absorption of cfrccat different fiber lengths. iium engineering journal, vol. 12, no. 1, 2011 zuraida et al. 77 4.0 conclusions a method for fabricating coir fiber reinforced cement albumen based composite were optimized. fiber length is one of the significant factors that affects the flexural strength, compressive strength, density, moisture content and water absorption properties of cfrcc. under conditions reported in this paper, longer fiber is found to be effective in increasing flexural strength. however, it diminished the compressive strength. inversely, the addition of shorter fiber into the matrix significantly reduces water density, moisture content and water absorption. it can be concluded that, for a given fiber type, length, orientation and volume concentration, the strength of composite was influenced by the bonding between all constituents resulted from distribution of the fiber in the cementalbumen paste. acknowledgements the authors would like to thank the ministry of science, technology and innovation (mosti) for the escience research fund (grant no. 03-01-08-sf0039), sirim bhd. for their technical help, technicians of faculty of engineering, iium and the research management centre (rmc) for their much commitment and assistance throughout this research. references [1] romildo, d., filho, t., ghavami, k., england, g. l., & scrivener, k., “development of vegetable fibre-mortar composites of improved durability”, cement and concrete composite, 25, 185-196, (2003). [2] asasutjarit, c., hirunlabh, j., khedari, j., charoencai, s., zeghmati, b., and cheul shin, u., “development of coconut coir based lightweight cement board”, j. of construction and building materials, 21: 277-288, 2007. [3] li, z., wang, l., & wang, x. a. “cement composites reinforced with surface modified coir fiber”, j. of composite materials, 41, 1445-1456, 2006. [4] khedari, j, suttidonk, b., pratinhong, n. &hirunlabh, j. “new lightweight composite construction materials with low thermal conductivity”, cement & concrete composite, 23, 65-70, 2001. [5] lindhagen, j.e. and berglund, l.a. “application of bridging law concepts to shortfiber composites part 1: dcb test procedures for bridging law and fracture energy”, composite science & technology, 6, 871-883, 2000. [6] li, y. mai, y.w. and ye, l., “sisal fiber and its composites: a review of recent developments”, composite science & technology, 11, 2037-2055, 2000. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 a review of road embankment stability on soft ground: problems and future perspective rufaizal che mamat1,3*, anuar kasa1, siti fatin mohd razali2 1centre of engineering and built environment education research (peka) 2smart and sustainable township research centre (sutra) faculty of engineering & built environment, universiti kebangsaan malaysia, 43600 bangi, selangor, malaysia. 3department of civil engineering, politeknik ungku omar, jalan raja musa mahadi, 31400 ipoh, perak, malaysia. *corresponding author: rufaizal.cm@gmail.com (received: 4th december 2018; accepted: 30th july 2019; published on-line:2nd december 2019) abstract: this paper presents an exhaustive review of the challenges faced in the construction of road embankments on soft ground and proposes a direction for future development. frequently used techniques for soft ground improvement are discussed. the factors that contribute to the stability of the road embankment are reviewed by approach, results of past studies, and historical cases. the findings show that settlement, slope stability, and soil bearing capacity are all challenges to constructing the road embankment. additionally, it is found that geometric data is a key factor in embankment design. preloading with prefabricated vertical drain (pvds) methods and lightweight fill were found to be widely used techniques in soft ground improvement. the information from this study can be used to develop design guidance systems, numerical modelling, and to give an overview and knowledge to other researchers who are or will conduct research in this field. finally, future perspectives for research are related to predictions of factors that affect the stability of road embankment with an artificial intelligence approach. abstrak: kertas ini membentangkan ulasan kajian menyeluruh mengenai cabaran yang dihadapi dalam pembinaan benteng jalanraya di atas tanah lembut dan mencadangkan ke arah pembangunan kajian masa depan. teknik-teknik penambahbaikan tanah lembut yang sering digunakan turut dibincangkan. faktorfaktor yang menyumbang kepada kestabilan benteng jalanraya diulas dengan pendekatan kepada kajian lepas dan sejarah kes. hasil kajian ini didapati bahawa enapan, kestabilan cerun dan keupayaan galas tanah merupakan cabaran dalam pembinaan benteng jalanraya. selain itu, ia didapati bahawa data geometri merupakan faktor penting kepada rekabentuk benteng. kaedah pra pembebanan dengan prefabrikasi saliran menegak (pvds) dan isian ringan didapati teknik yang popular digunakan dalam pembaikkan tanah lembut masa kini. maklumat dari kajian ini boleh digunakan untuk membangunkan sistem panduan reka bentuk, pemodelan berangka serta memberi gambaran dan ilmu kepada penyelidik lain yang sedang atau akan menjalankan kajian dalam bidang ini. akhir sekali, perspektif masa depan untuk penyelidikan berkaitan ramalan faktor-faktor yang mempengaruhi kestabilan embankment jalanraya dengan pendekatan kepintaran buatan. keywords: road embankment; soft grounds; stability factors; ground improvement 32 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 1. introduction in road construction, the embankment is used to increase the height of the road compared to the height of the surrounding area. it is a large earth structure and is often used in civil engineering applications related to infrastructure projects. the construction involves two essential construction components namely fill and foundation [1, 2]. these two components act as definitive parameters to analyse the embankment to find failure slope. hence, a deep understanding and interpretation of the behaviours of these components such as deformation mechanisms can produce the collapse mechanism of the embankment. embankment fill is defined as selected fill placed and compacted with proper specifications so that it can display the required engineering performance [3]. the characteristics of fill material, the degree of compaction and the factors affecting the workability are considered for best results in the construction of embankment fill. common fill materials are soil [4], natural aggregates [5] and lightweight filling material [6]. these fill materials must possess the required characteristics such as proper drainage to prevent saturation [7], good performance in compaction properties [8], compressibility [9], and shear strength [10]. even if the embankment fill has the best material properties, instability can occur if it is built on unstable soft ground or soil with properties needing improvement. the foundation serves as a placement for embankment structure and it may to be stable or unstable. the embankment foundation containing soft grounds is often a challenge for all engineers to ensure stability depending on the nature of the soil. soft ground with fine particles such as silt, clay, and peat have high moisture content and are located near or below the groundwater level [11]. these soils also have the characteristics of high compressibility, high plasticity, high sensitivity, low shear strength, and low permeability [11,12]. such features will lead to the problem of high settlement and low bearing capacity during postconstruction work. this will reduce the strength of workability and shorten the embankment’s lifespan [13]. it will also lead to bumpy road surface and damage, subsequently causing accidents to road users. embankment stability is critical in road construction. hence, before construction, the engineer must provide all geotechnical design reports and include drawings to be submitted to the relevant parties. the report shall state clearly the assumptions, parameter justifications and the methods used in the design to mitigate all issues or concerns. geometric data is a general requirement in the preparation of design drawings while data materials contain the engineering parameters of fill and foundation of the embankment. data materials are used in the engineering design of the embankment. the factor of safety (fos) calculation is used to assess the performance of the embankment to ensure constant stability. the design report contains stability analyses, settlement analyses, the design of porewater pressure and technical recommendations for ground improvement. embankments built on soft ground require the installation of monitoring instruments on site such as the inclinometer, settlement marker or rod settlement gauge and piezometer. the instrument will be monitored from time to time for the aid in the demonstration of compliance with minimum fos during construction. this paper reviews the literature on the challenges of embankment construction on soft ground and the latest techniques that are often used in improving soft ground. to achieve this objective, this paper has been divided into three sections. the first part deals with the factors that affect the embankment stability. the second part is about the factors affecting the design of the embankment, while the third is the latest soft soil improvement technique widely used with considerable aspects of sustainability, cost savings, and construction time. finally, the main conclusions and future perspectives will be presented. 33 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 2. the challenge of constructing embankments on soft ground soft ground has a high groundwater level and typically, it can be found near coastal areas. the soil profile consists of a layer of crust at the top followed by a soft soil layer of either limited or unlimited thickness underneath. this soil is brown from light to dark [11]. in general, soft soil such as clay is dominated by particles of less than 0.002 mm in size and is pliable. it is formed from a combination of clay and mud and with almost 50% clay content [11]. the structure of this soil is identified as being dispersed, flocculated, bookhouse, turbostratic, and cohesive [14]. soils are characterized by their physical, mechanical, chemical, and biological properties. soil with poor geotechnical properties, such as soft clay, requires improvement technique application. yalcin [15] investigated the effect of clay on a landslide in kanlica village, turkey. as a result of laboratory tests, clay was found to contain illite and montmorillonite, which produced low shear strength and high swelling potentials making it prone to landslide problems. this conclusion is also supported by ohlmacher [16], where the soil comprising mineral content such as illite has a high liquid limit contributing to very low strength parameters. instability problems such as lateral deformations and excessive settlement often occur in structural and geotechnical construction on soft soils [17]. the load generated by the embankment fill drives the increase in soil stress and pore water pressure leading to deformation mechanisms. this causes the load to be undrained, where the behaviour is similar to the viscous fluid that can lead to critical conditions against structures such as bearing capacity problems. however, a thick hard layer built on the top can absorb the load produced by the fill of embankment. an example of active embankment failure is the 1 km-long highway corridor located at the eisenhower tunnel, colorado, usa. a survey by the colorado transport department (cdot) found that frequent slope settlement and failure problems have occurred over the last four decades [18]. the instability of the embankment due to movements of the side ground should be carefully considered during the design process and during engineering projects around the embankment. the road damage incident that occurred in september 2010 at the port of tanjung priok, jakarta was caused by embankment instability [19]. the embankment was built on clay with high plasticity. the movement of side ground caused the road surface to crack. road embankment failure also happened in the northland region of new zealand [20], where the embankment was built on a soft soil characterized by a low strength with a highly sheared fabric. other reasons for the failure are settlement and continuous soil movement that led to slope failure. an embankment failure occurred during the construction of a four-lane expressway in st. stephen, new brunswick, canada across the usa border in july 2006, where failure was due to the rapid rate of construction and the intensity of loading for low-strength foundation soils [21]. the land in the foundation was composed of a soft marine clay layer which is a grey clay with a thickness of up to 15m. irsyam et al. [22] reported that a failure of the embankment slope occurred in cipularang toll road located in west java, indonesia. based on the record of slope monitoring indicators, the failure plane was due to low ground shear strength. parameters of soil shear strength at failure conditions, i.e., cohesion and friction angle, were 5 kpa and 130 respectively from the toe of the embankment to the top of the embankment at the median of the highway. additionally, a road connecting two villages, namely nata and pentalia in southwest cyprus suffered 340 m of severe cracks even though the road was still under construction. the incident began in january 2002 where the foundation ground was 34 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 composed of soft soil with high plasticity and low shear resistance [23]. the slope failure also occurred at the embankment due to high rates of rainfall. based on the case histories, it is clear that soil properties and rainfall are the cause of road embankment construction failures. to ensure embankment stability, the geotechnical design typically requires consideration of three factors namely: strength, deformation, and permeability or hydraulic conductivity. bearing capacity and slope stability are among the important elements in the strength factor. deformation is influenced by differential settlement, surface settlement, and lateral displacement of the ground while pore water pressure and seepage are elements affecting permeability. 2.1 bearing capacity bearing capacity is one of the necessary steps in the design of the embankment. it is the ability of the soil to bear the structural burden on the ground safely without any shear failure by accommodating a large settlement. this means that the foundation with shear failure involving general, local, or punching shear failure mechanisms will experience structure instability. davis and booker [24] have significantly contributed to understanding of the problem of clay-bearing capacity with increased strength with depth. over the last few decades, much research has emphasized that embankment instability is due to a possible loss of bearing capacity of the foundation soil [25, 26]. during soft soil failure under the embankment, the fill moves downward with part of the foundation soil as a rigid body [25]. several studies investigating the performance of the embankment on muar clay [27], bangkok clay [28], and matagami lacustrine clay [29] were performed with low bearing capacity. factors thought to influence bearing capacity have been explored in several studies. popescu et al. [30] studied the effects of random heterogeneity of soil properties on bearing capacity with various shear strength values. on the other hand, lehtonen et al. [31] investigated the effect of the trainload and the loading time on the embankment on soft soil. it is clear that careful study of the literature reveals that the soil shear strength, depth, and surcharges are the factors that influence the bearing capacity. a clear understanding of these factors is essential in the design of embankments on soft soils. over the past decade, some laboratory research projects have been conducted to investigate the soft soil performance based on the factors affecting bearing capacity. kim and lee [32] compared the bearing capacity of various sizes of gravel and sand. two types of samples were composed of gravel and sand of compaction piles. the results revealed that coarse particles had a high bearing capacity compared to fine particles. it clearly showed that particle size contributes to higher bearing capacity, and it is noted that each type of soil has different strengths. another study was performed with various strengths of soil stabilized by portland cement [33]. the results found that the higher the percentage of cement mixture, the higher the maximum dry density and bearing capacity. this implies that the strength and density of the soil are higher, resulting in a high bearing capacity. in order to improve soft soil bearing capacity, several researchers have suggested the application of basal reinforcement [34], chemical stabilization [11], and pile-supporting [35] in the embankment construction. however, cost, time and sustainable construction are the challenges of engineers choosing ground improvement techniques. a number of methods can be used to overcome this challenge with the 'limited life geotextiles' [36] approach as basal reinforcement of embankments and fly ash [37] as a soft soil foundation stabilization. 2.2 slope stability slopes are closely related to the height of an area, whereby the higher the area, the steeper the slope. the stability of the slope is an important aspect in embankment 35 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 construction due to its possible side effect of loss of human life and damage to property. a stable slope guarantees safety but otherwise, unstable slopes increase the risk of failure that can trigger landslides that cause the most damage and produce thousands of deaths every year and material losses of billions of dollars [38]. this is of increasing concern with this trend expected to continue in the next decade due to urbanization and development. thus, the challenging task for engineers is to make decisions by paying more attention to the importance of public safety. engineers need to understand the factors that led to the failure in order to assess slope stability. over the past decade, most research on slope failure was investigated and discussed based on studies and historical cases. ballantyne [39] reviewed the literature from the period and identified factors that influenced slope failure in scotland. a total of 740 incidents of landslides due to intense precipitation, engineering excavations, and mass weakening by fluctuating cleft-water pressures were studied. in 1993, over 800 slope failures were triggered by a rainstorm on lantau island, hong kong [40]. ohlmacher [16] reports that the landslide that occurred in 1995 damaged two us$ 400,000 homes in overland park, kansas. based on the investigation, the slope angle was the main factor contributing to the problem of landslides in the study area. davies [41] reported more than 50 slope failures in kenya caused by natural geological and geomorphological conditions, coupled with high rainfall. a landslide that occurred in wenchuan, china in 2008 was triggered by earthquakes and heavy rainfall [42]. several studies investigating the factors of stability were performed by experiment. xu et al. [43] studied gravity erosion on the steep loess slope by conducting a series of experiments in the laboratory to test slope stability against various geometry and rainfall rates. the analysis found that climate changes have significant influence over gravity erosion. yong et al. [44] described the dynamic processes of grain comminution through grain size distribution of soils. high dynamic properties are found in granular soil exposed to soil evolution and mass movements, which can cause instability. the effect of slope length and slope angle on stability was successfully investigated based on laboratory tests by kinnell [45]. based on the evidence presented in this section, it is clear that nature, humans, and slope geometry are factors affecting stability. landslides triggered by natural factors such as heavy rainfall and earthquake are the most common in the world. high intensity of rainfall is prone to contribute to weathering and rapid erosion of rock mass causing a reduction in the slope stability [45]. erosion agents such as surface runoff enter the cracks, eroding the slope carrying with it a mud and soil stream while runoff absorbed into the soil weakens the bonds between soil particles on the slope surface. the pore water pressure that exists between the soil particles will affect the strength of the soil structure. the earthquake phenomenon causes strong ground vibration that increases shear stress. the effect of the earthquake’s frequency and magnitude can overcome the force of adhesion to the ground and the retaining structure [42]. besides, the vibration causes the movement of ground particles to be more likely to move according to gravity. gravity is a force acting on the surface of the earth by pulling something towards the middle of the earth. material on a flat surface will not move due to gravitational attraction unless the surface is sloped or angled. slope excavation is the human factor required for the construction of building foundations and roads because suitable engineering sites do not exist. this activity triggers the movement of slope and ground vibration will cause disturbance that will slide the mass, which makes the deformation accelerate [46]. additionally, it will also destroy the 36 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 vegetation on the slope surface and consequently, the reinforcing effect of the vegetation will be lost and precipitation will infiltrate the slope crack on the surface. geometric factors such as slope angle are the main components of the slope for measuring stability. as the slope angle increases, the shear stress in the soil and erosion will also increase [45]. the low slope angle is expected to be stable due to low shear stresses [47]. conversely, with the increase in slope steepness, water infiltration decreases [48]. thus, the slope angle is suspected of playing a major role in the control of infiltration and erosion that affects slope stability. however, the slope stability problem varies between different geographical regions. for example, in european countries, slopes are exposed to varying temperatures and humidity, while in malaysia, they are exposed to heavy rainfall with an average annual rainfall of 2500 mm. lack of information on climate change, rainfall rates, and unpredictable clouding has caused engineers to fail to understand the mechanisms of slope failure. a detailed study is, therefore, needed and must be performed with appropriate technology to predict the parameters associated with slope failure factors. 2.2 settlement settlement is the total size of the vertical deformation on the soil surface. in theory, embankment settlement occurs when increased compressive stress is generated by baseload compression. this process will cause vertical and horizontal deformation of the soil foundation. besides changes in water content, soil mass and temperature can also distort soil. it is often associated with cohesive soil such as soft soil and can produce a large settlement for an extended period even under load [11]. during settlement, the ground transition at stress conditions is of its weight to the new state due to the extra load. the stress change caused by the additional load can produce a time-dependent accumulation of particle rolling, sliding, crashing, and elastic distortions in a limited influence zone beneath the loaded area. hence, significant and excessive impacts will affect the road surface, where a decrease in height will occur and may cause flooding during heavy rains. terzaghi [49] began the study of soft soil settlement. in theory, a settlement analysis comprises calculations of total and differential settlement, where total settlement is the magnitude of downward movement while the differential settlement is the vertical movement between two places. the total settlement consists of three modes, namely elastic, consolidation, and creep deposition. elastic settlement occurs due to the deformation of soil that is loaded without changes in water content and occurs within a short period [50]. it is also known as an undrained or immediate settlement. this type of settlement occurs instantaneously during the loading process with saturated soil that has low permeability and drainage ability. consolidation settlement occurs due to the consolidation of soil in which water is slowly expelled from the soil cavity [51]. during the consolidation process, the deformation of the soil occurs with volume reduction over a long period. creep or secondary compression is the same as compaction. it can occur when soil attempts to reposition itself in the cavity left by the water during consolidation settlement [52]. in the typical case, during embankment design, the computation of settlement involves elastic settlement and consolidation while post-construction involves creep. azzam and basha [53] assessed the impact of improvements in the parameter of cohesive soil shear strength by using a soil nailing technique to reduce settlement. brown to grey clay was taken from the middle delta of egypt and stabilized using steel flat bars as vertical soil nails. the sample is then compressed with an unconfined compression machine 37 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 with a low pressing rate. the study showed that increasing vertical inclusions significantly increases the shear strength and reduces settlement rates. studies on the effects of creep on the side deformation of soil and pore pressure below the embankment were performed by grimstad et al. [54]. the numerical method is used to investigate the embankment on the i95 motorway in north boston with a height of 12.2 m and built on boston blue clay. the study shows that an increase in creep rate also increases soil settlement, pore pressure, and lateral deformations. earthquakes can cause the settlement of saturated clay layers. this has been discussed in a study conducted by sato et al. [55] using a kaolinite clay sample, i.e. tokyo bay clay, and kitakyushu clay tested using uniform and irregular cyclic shear tests. the results of the study concluded that the atterberg limits affect the settlement rate and pore water pressure accumulation during earthquakes. accumulation and settlement of water pore pressure triggered by the friction cycle are measured by cumulative shear stress. to conclude, the studies conducted by the researchers clearly show that the type of soil, the underground conditions, the techniques to improve soil properties, and the soil drainage are factors that affect the settlement. differential value of settlement on the ground surface and uneven settlements can cause major problems such as a function of the uniformity and stiffness of the soil. as shown in fig. 1, it may be characterized as the distortion, i.e. the settlement over a horizontal distance. it occurs when the ground underneath the structure is unable to withstand the load, but the limitation to differential settlement is dependent on the application and site condition. fig. 1: definition of the differential of settlement [56]. one of the case histories occurred in bangkok where significant settlement happened in an area with 12-16 m of soft clay [57]. the 1.5 m to 2.5 m road embankment experienced total settlement of between 500 to 1000 mm in 10 years. dark grey soft and compressible recent marine clay and frequent flooding from the chao phraya river seem to be the major factors. a seven-story building was slanted during the mexico earthquake that took place in 1985 and continued until 2005, as reported by moghaddam and jayawickrama [58]. based on the results of the review and monitoring it was found that the building underwent a differential settlement leading to vertical inclinations ranging from 241 mm to 310 mm to the north, and 70 mm to 98 mm to the east. this problem is very closely related to the consolidation process of the base soil. apart from these factors, eccentricity in loading, groundwater extraction, and construction in the vicinity also contributed to this problem. there are four reasonable and commonly used methods to predict soft clay settlement. these are the conventional one-dimensional (1d), skempton and bjerrum [59], stress path and finite element methods. terzaghi [49] introduced the 1d conventional method aimed at estimating the compression of clay at a certain soil depth. it is now used to predict the magnitude and settlement rates. with the right soil compression and the measurement of a settlement horizontal distance area of differential settlement earth embankment 38 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 thin layer of soil in the laboratory under a single load dimension, engineers can successfully and accurately predict performance [60]. according to the theory, stratum compressible is divided into several layers, while the calculation of the initial vertical effective stress and vertical stress increase using the boussinesq stress [61] is based on the centre of each layer. at the end of the consolidation, when all excess pore water pressure is lost, the stress increase will become effective stress. the vertical strain of each layer can be obtained from the graph plotted between the void ratio with effective vertical stress as a result of the onedimensional (odometer) compression experiment. this method was used in the study of the settlement of road embankment prediction [62]. however, duncan [63] highlighted the limitations of this method; among others are the difference in the conditions between the field and the laboratory, the difference in load rates and tensions experienced by the soil between the laboratory and field, and the limitations found in 1d theory for threedimensional (3d) problems. in addition, there are insufficient resources and documentation on the selection of parameters and the use of theory to predict settlement of silt compared to clay [64]. skempton et al. [65] used 1d to calculate the total settlement of several buildings but admitted that undrained settlement is a significant parameter in the total settlement. as such, they used the elastic displacement theory to calculate the undrained settlement. the settlement forecasting in 3d has lower consistency compared to 2d due to pore pressure and the lower lateral deformation in 3d. they have thus put together a primary method to calculate the consolidation settlement caused by excessive dissipation of pore pressure. the settlement correction factors proposed in 1957 are dependent on geometric problems and pore pressure. this factor was also supported by bergado and teerawattanasuk [66] in their study that geometric effects should be considered as an important factor that could affect numerical simulation results. bergado et al. [67] used this method to predict the embankment settlement of the bangna-bangpakong highway that was constructed on bangkok soft clay. the study found that these methods provide reasonable estimates of long-term settlement. the stress path method was proposed by skempton [59] and developed further by poulos and davis [68]. it uses an uninterrupted sample under the appropriate underground depth to perform triaxial experiments under the appropriate initial in situ effective stresses. the purpose of vertical and horizontal stress without allowing drainage to be calculated is to determine vertical strain and excess pore pressure. when necessary, drainage was allowed, and applied stresses were adjusted to determine vertical stress and change in volume. the strain was then measured to obtain undrained settlement and consolidation. studies on the performance of the screw plate test to determine the properties of deformability and consolidation of bangkok clay was carried out by bergado et al. [67]. comparison of consolidation coefficients, non-flow and flow modulus between split and stress-path-controlled triaxial consolidation tests was performed. the findings of both experiments are similar to each other, implying the accuracy of the results to be sufficient for use for predictive purposes. although logical, the method is complicated because the initial vertical and horizontal effective stresses must be known, and it requires advanced experimental skills. isotropic and homogenous elasticity used to calculate the stress change and uncertainty in the accuracy of horizontal stresses exist. in addition, these experiments are highly costly and require a long time to conduct. in recent times, numerical methods have been well received for predicting settlements because finite elements are carried out on non-homogeneous anisotropic elastic materials. besides, it can handle nonlinear stress-strain behaviours of varying complexity. the engineers are more confident in the findings of finite elements because of its strength and 39 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 flexibility, without realizing that this package contains inherent idealization and assumptions. generally, the quality of data inputs plays an important role in determining the accuracy of the forecast. it is therefore important to evaluate and examine the constraints of the experiment as good control ensures high-quality data to be used for numerical analysis. it was clear that settlement forecasting methods have undergone a sophisticated revolution moving from the classic 1d to numerical methods. the latter is able to solve a variety of complex issues because the program is equipped with advanced parameters and testing ground. the available features with sophisticated computing technology have led to this method becoming popular for application and development. 3. embankment design the design of the embankment is extremely complex because it depends on the purpose of construction, the environment, and the ground foundation conditions. when designing an embankment, engineers must plan, define geometric data, and analyse stability. the road embankment especially consists of a series of compacted layers placed on top of each other until the subgrade surface level is reached. it is also known as structural embankment and is divided into two types: the unreinforced [69] and reinforced, [70] which serves to distribute traffic load to soil foundation. therefore, appropriate stability assessment and geometric data methods are essential to ensure the desired efficiency of construction. this section discusses three key aspects of geometric data, design, and analysis methods based on the recent literature. 3.1 design and analysis methods the majority of today's engineers and researchers model the embankment design using fem. it is a numerical method that aims to design and analyse various engineering problems of both practical or research. it is also useful for problems with complicated geometries, loadings and material properties where analytical solutions cannot be obtained. there are three types of finite elements that are often used, namely one-dimensional (line), twodimensional (plane), and three-dimensional (solid). from the literature, the use of twodimensional is the choice of many researchers in the study of embankment stability. plaxis [81], abaqus [82] and fast lagrangian analysis of continua (flac) [83] are the types of software used for analysis, testing, and design in geotechnical engineering. however, the use of flac is less common in the study of the road embankment. researchers and engineers more popularly use plaxis as it is friendlier in soil modelling to solve simple problems in complex strata. beyond that point, it can analyse all cases in geotechnical engineering including pile design [84], ground foundation [85], retaining wall [86], slope stability [87], and dam [88]. the driving force along the slopes that is greater than the resisting force restraining the movement of the slope is the basis of slope stability. force imbalances such as increased resisting force will fail. both forces are elements in slope design. the main driving force in most earth movements is gravity while the main resisting force is the material's shear strength. slope stability is evaluated by calculating and assessing the stability index, or the fos, defined as the ratio of ground resistance force along the failed surface to the instability force that illustrates the capabilities of a structure, such as an embankment [89]. duncan [90] also explains that fos is the ratio of real ground shear strength to the minimum shear strength required to prevent failure. theoretically, a fos value greater than 1 indicates a stable slope while a fos value equal to 1 implies that the slope is in equilibrium. 40 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 the slope stability analysis is divided into two, namely global and local stability. global stability refers to the overall stability of soil mass along the slip surface and in multiple failure mechanisms by providing a lower safety factor. a sloping surface can withstand soil stress. for long-term and short-term flows, fos ≥ 1.3 [91]. most slope stability analysis software available, such as slope/w, provides global fos calculations. the global fos calculation using the phi-c reduction method was performed by singh et al. [92] in the study of slope stability in nainital, india. iñeguez [93] in his study defines universal fos by using a strength level approach. he also calculates local fos using enhanced methods as the location of the most critical zone can be evaluated and used to guide the implementation of remedial measures. local fos are irregular and different at each point compared to conventional fos which assumes that it remains constant along the slip surface. in order to assess the stability of the slope, limit equilibrium (le) analysis is commonly employed to determine the fos by researchers and engineers. the le technique such as the ordinary method of slices [94], bishop simplified [95], spencer [96], and morgenstern-price [97] methods have been widely used in the slope stability analysis. the slicing technique is known as an uncertain static problem, solved by assuming a distribution of internal forces. as such, different assumptions can result in varied results. due to this inherent engineering practical weakness, fem is now a choice. some researchers have compared the results between le method and fem [98, 99], concluding that fem provides the best and most accurate fos result, as it is better able to explain the behaviour of soil stress and eliminate stress assumptions used in the le method. strength reduction method (srm) [100,101] and enhanced limit strength method (elsm) [102, 103] are popular methods used in fem although there are also ways to evaluate fos using stress calculated directly through finite element modelling. the srm has been used by zienkiewicz et al. [104] to calculate slope safety factors based on the mohr-coulomb model. most fos formulas used now are obtained from the mohr-coulomb failure criterion [105]. srm does not require assumptions on the form or location of the failure surface, because failures occur naturally through the zone in the soil mass where soil shear strength is unable to resist the applied shear stress [106]. this means that the critical slip surface is automatically obtained from the increased shear stress when the shear strength decreases. however, this method is unable to determine the position of the local minimum slip. elsm is a hybrid between the le method and fem introduced by kulhawy [107] as an independent assessment of the distribution of normal and shear stress along the assumed slip surface. normal and shear stresses from elasticity analysis are used to calculate the overall fos. in addition, this method uses fem to estimate the magnitude of the stress as well as to find the critical slip surface with minimum fos. elsm has the advantage over srm in terms of time, as some finite element analyses need to be conducted separately. besides, srm is best suited for global fos calculations while elsm is for local fos calculations. this is because local fos calculations along the potential failure surface cannot be considered in the srm procedure. 3.2 geometry analysis through fem requires the establishment of data in constitutive relationships and geometric modelling. geometric data namely height, crest width, and gradient of side slope are among the important parameters in the production of design drawings. engineers usually select the parameters based on their own experience. based on observations, most studies conducted by researchers use embankments that are 1.5 m in height, have a crest width of between 35 m and 40 m, and have a 1:1.5 gradient of side slope (vertical: horizontal). in addition, road design manuals in several countries are described in table 1. 41 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 most countries recommend embankment height of less than 6m to enable the verticalhorizontal side slope ratio of 1:1.5. table: various sources of standards for side slope and height embankment for design. height side slope (v:h) references 0 – 6 m 1:1.5 [108] 0 – 6 m 1:3 [109] 0 – 1 m 1:4 [110] 1 – 3 m 1:2 more than 3 m 1:1.5 0 – 1.5 m 1:8 (flat terrain) [111] 1:6 (rolling terrain) 1.5 m and over 1:6 (flat or rolling terrain) 1 m 1:1.5 [112] 2 m 1:2 3 m 1:2.5 based on literature reviews, geometric data such as crest width and side slope are reported to be too limited. researchers widely practice the study of critical [113–115], safe [116], and reasonable [117, 118] embankment height as they believe that these parameters are factors that contribute to embankment stability, which is supported by study findings. the study conducted by cui et al. [119] further supports this statement as it found that the height of the embankment affects the cumulative settlement of the subsoil. embankments built at an altitude of less than 1.5 m will lead to an increase in the speed of cumulative settlement of the subsoil. however, the determination of height depends on the soil foundation improvement and traffic load method or technique. studies conducted by almeida et al. [120] found that the result of fem analysis showed the difference in settlement of soil surface decreased when the height of the embankment increased. this proves that height is an important determinant of embankment stability. 3.3 height of embankment the height of the embankment is a problem often encountered during design and construction work. this is because the embankment built below the critical height can control the deformation and stability of the foundation. critical height is important to determine performance such as the workability of the embankment and the assessment of potential excessive settlement [121]. for example, surface damage is caused by uneven crest surface. this happens when the embankment is lower than the clear column spacing, leading to the differential settlement at the base of the embankment that can spread up to the crest of the embankment. according to mcguire [122], the minimum height for the column diameter and distance where differential settlement in the crest does not occur is known as the critical height. thus, the diameter and distance from the column are important factors that affect critical height. fagundes et al. [113] in their study used the calculations proposed by filz et al. [121], mcguire [119], and bs 8006 [123] to find that the critical height suitable for the construction of embankments built on soft soils strengthened by piles without reinforcements is 2.5 m. bhasi and rajagopal [114] found that the critical height with the effect of reinforcement modulus on maximum settlements is 5.6m. in this study, embankments stabilized using the geosynthetic reinforced pile method built on soft soils were analysed using the three-dimensional (3d) fem. the findings from chen jia et al. [124] on embankments stabilised by plastic tubes cast-in-place concrete piles found that the 42 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 critical height is 2.2 times the pile net spacing distance. the piles are driven by a distance of 1.0 to 1.5 m from one another. this means that the critical height is between 2.2 to 3.3 m. the three studies found that the critical height for the embankment built on soft soil and soil stabilized with piles is between 2.2 m and 5.6 m. however, there are very few studies on the critical height for embankments stabilized using other techniques such as vertical drains, preloading, grouting, and reinforcement. a lot of research regarding reasonable height was conducted on the qinghai-tibet highway (qth) and the qinghai-tibet railway (qtr). it was introduced by zhang et al. [125] to protect the underlying permafrost during construction. the freezing and defrosting cycle of soil can lead to a settlement on the embankment. hence, maintaining the magnitude of the embankment settlement to reasonable limits is key to ensure embankment stability [126]. the higher the embankment, the greater the differential settlement because an embankment that is not sufficiently high will lead to the freezing and defrosting cycle that affects tension and settlement. the foundation soil found along the highway and the railway is mostly silty clay, which is a type of soft ground. qth has a length of 1937 km and has a 632 km permafrost area. among the studies to determine the reasonable elevation of the embankment in qth were those carried out by wang et al. [117] and zhang et al. [127] who found, through site monitoring, that an embankment height of more than 4 m would lead to a reduction in the permafrost table. therefore, reasonable elevation shall be determined to a limited extent. wang et al. [117] have determined a reasonable embankment height for two typical geological sections along the qth. the findings of the analysis are obtained through the modified numerical method, with a reasonable embankment height implied of 1.63 m. this is a significant study because reasonable height is important for maintaining the thermal and mechanical stability of highways located in the cold areas. the qtr is 550 km long and has a permafrost area at an altitude of about 4500 m to 5000 m above sea level. yue et al. [126] and qi et al. [128] conducted analyses to obtain reasonable embankment of railroads in the permafrost state. the embankment should be built at a reasonable height of 4.0 m to reduce differential settlement [126]. the in-situ monitoring results in qi et al. [128] showed that the reasonable height is 3.0 m and has a positive impact on frozen soil protection and promotes the increase of the permafrost table under the embankment. a study on the optimum design of crushed stone layers with shading board over the railway embankment on warm perma-frost was done by g. li et al. [129] and found that the reasonable elevation is between 3.0 m to 5.0 m. the analysis of these findings is obtained through systematic numerical tests. the safe embankment height is dependent on the gain in strength of soft subsoil and target fos [130]. the study determines the height of each stage of construction based on increased shear strength to reach the fos of 1.25. through the iteration process, they have found the exact height of second-stage loading to be 3.02 m to achieve a total height of 5 m for the embankment. meanwhile, the study conducted by kasim et al. [116] concerning the safe height for the construction of the embankment on soft soil is summarised through the simulation results of plaxis version 8.2 software that the maximum height is 4.9 m to ensure its stability against excessive settlement. this is also supported by jin et al. [131], whereby increasing the height from 1.0 m to 4.0 m reduced the deformation value towards settlement. several factors affect the height of an embankment. we have reviewed critical, reasonable, and safe height, which have the same goal of ensuring embankment stability. overall, height determination depends on several factors. the diameter and distance 43 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 between planted pile stalks are factors that determine the critical height. permafrost is one of the most dangerous elements and affects the stability of the embankment in cold areas. this is due to uncontrolled thaw settlement, and frost heaving processes that can cause settling problems and longitudinal cracks on the embankment. according to wang et al. [132], embankment height is closely related to the problem. the reasonable height is interlinked with embankments built in areas prone to permafrost. therefore, the temperature of the permafrost is also a factor in determining a reasonable height. fos is the determinant of an embankment’s safe height. most studies conducted to determine the safe height use taylor's stability charts. the road design manual as in table 1 suggested embankment height of up to 6 m. however, there are also researchers who employ the height in their study as 2.0 m [133], 3.0 m [134], 4.0 m [135] and 5.0 m [102]. we can conclude from the literature that 1.5 m to 6.0 m is the height range in embankment design that is able to ensure stability. the same height range is appropriate for the study or design of embankments. this range is relevant and useful as a guide for young engineers and researchers in the prediction and design of embankments. 4. soft ground improvement an engineer must possess several strategies that may be adopted to achieve project goals when dealing with troubled ground conditions at the site. various methods exist to improve compressible soils commonly applied on-site including preloading, lightweight fill, geosynthetic reinforcement, over-excavation and replacement, vertical drains, rigid piles, and injection. as mentioned in the literature review, enhancing density, increasing shear strength, and reducing compressibility can help in promoting stability. on the other hand, influencing permeability also decreases groundwater flow to increase consolidation rates. despite the fact that existing methods may mitigate stability problems, selection factors need to be considered, such as sustainability, cost, and time of construction. all have become the topic of intense debate within the scholar community. thus, this section will review the application of preloading with pvds and geofoam as lightweight fill materials in the road embankment construction on soft ground by considering three selection factors. 4.1 preloading and prefabricated vertical drains preloading methods are categorized as static consolidation and are cost-effective and practical. they impose a temporary load to increase soil stress. this causes the substratum to densify and form stiffer support that will help reduce compressibility when the actual structure is built. this method commonly uses earth filled with a pre-determined height, and subsequent monitoring of settlement is conducted during a specific period until the deformation stops. dafalla [136] studied the performance of a stabilized soft ground settlement using the preloading and prefabricated vertical drains (pvds) method along the coast of the red sea of saudi arabia and found that medium hard silty sand was beneath the site surface. buildings and pedestrian pathways around the site have been damaged due to excessive settlement. the saudi ministry of municipal and rural affairs has proposed that this method is applied for the project. the site uses preloaded sand of 4.5 m to 6 m high for six months and was monitored every week. the study concluded that this method reduces 20 % to 50 % of total settlement with sufficient time to prevent deformation. it can increase the strength of soft soils by accelerating the consolidation process so that the ground is able to bear the load. therefore, sites with soft grounds are suitable for this method as they can be compressed in a relatively short time when loaded. pressures exceeding what is required are placed above the soil and allowed to settle until the predicted settlement is reached. when 44 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 the settlement has been reached, the excessive load is removed, and the service load is allowed on a strengthened foundation. recently, various innovations in this method have been created using modern technology. among the successful modernizations of this method is combining the use of vertical drains or pvds. variation of this method has been successfully applied in many construction projects worldwide requiring ground improvements and reclamation [137]. therefore, the theory, design, and construction methods for pvds are significant issues in the preloading or consolidation method. the practice of using horizontal drainage began to emerge with drainage and then evolved into pvds. kjellman [138] introduced a combination of two materials, namely wood, and cardboard in 1947. most pvds have a width of about 100 mm with a thickness of 3.0 m to 6.0 m made of corrugated plastic cores surrounded by geotextile filters or a layer of natural fibres. it serves as artificial drain lines to accelerate the draining of water in the ground so that the time taken for the soft soil consolidation and the removal of excess pressure in the water pore can be significantly reduced. the elimination of pore water pressure increases soil strength, which would enable it to sustain the load. da silva et al. [81] studied the impact of pvds installation on stability and embankment settlement. using back-analysis to find sufficient material model and calculation of values using elastic-viscoplastic (evp) through fem to four dikes on very soft clay, it was found that pvds very significantly accelerated settlement and increased fos. chu et al. [139] also conducted a study on the use of pvds on soft clay soil which has a high moisture content for land reclamation projects. evaluation of the consolidation effectiveness and suitability of the selected pvds was performed through a large-scale laboratory model. the results showed that the installation of pvds is very effective to accelerate the consolidation process. however, pvds performance may decline as the consolidation process takes place due to the quality of the material that is unable to sustain the biological and chemical reaction between the filter and the soil surface. besides, the soil undergoes a significant increase in undrained shear strength. it is clear from the above study findings that the installation of the preloading and pvds methods has advantages. a combination of both methods is efficient to be used in areas with soft ground. this method does not meet the green technology needs that emphasize the environmental impact of construction. this is because the surcharge fill usually involves cutting of high places such as hills, leading to various degrees of destruction and disasters. although there are alternatives undertaken and introduced by yang et al. [140], which use water as a surcharge, they are not suitable for areas with hot climates because the evaporation process will reduce the quantity of water and thus can affect the settlement monitoring readings. besides, there are preloading methods using vacuum pressure [141, 142], which only use surcharges such as minimal soil but still require soil transportation from sources elsewhere. this method is also highly costly because it involves the pumping and plastic pipes that are often exposed to leakage. therefore, environment-conscious methods should be developed based on the environmental and construction conditions of a particular location. 4.2 geofoam as lightweight fill material construction challenges on soft grounds and lack of suitable soil for reclamation work and environmental preservation led to a massive demand for innovative methods. the use of lightweight materials to replace fill material such as clay is an alternative. according to schaefer et al. [143], lightweight fills are divided into two categories: materials that behave and have the same properties as soil particles, and materials with unconfined compressive strength that possess properties that are similar to the cohesive soil as shown in table 2. the 45 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 unconfined compressive strength is directly related to the cast density of the mixture. in the report by stark et al. [144], geofoam unconfined compressive strength range is 160-173 kpa. cellular concrete consists of cement, aggregate, water, and air voids. its production needs to mix materials such as foaming agents that can produce 10-70% of the air content [145]. therefore, the unconfined compressive strength is dependent on the mixed material used. the material mixture used in cellular concrete as foam content + bottom ash [146], flue ash [147] and aluminium powder [148] produces a compressive strength of 0.8-5.2 mpa, 1.72.7 mpa and 0.9-7.9 mpa, respectively. table 2: lightweight fill materials categories [143]. granular lightweight fill materials lightweight fill materials with an unconfined compressive strength wood fiber blast furnace slag boiler slag fly ash expanded shale, clay and slate shredded tires geofoam cellular concrete the use of geofoam is well received because it is more practical as a readily-available source, and there are many manufacturers and suppliers around the world [149]. it has a density value of between 12 to 35 kg/m3 and was first used in the construction of road embankment in 1972 by the norwegian road authorities [150]. based on density, expanded polystyrene (eps) is divided into seven categories with the index oxygen volume of 24% as shown in table 3 [151]. it is produced in large light blocks and can be obtained in various sizes and resistance characteristics. it is made of expanded styrene formed through the process of expansion using pentane and steam [152]. the mechanical [153] and dynamic properties [154] of geofoam blocks were investigated in detail. the eps' light strength properties between surfaces were also investigated and found to be significant across two surfaces of the block [155]. in general, eps blocks are used to reduce overburden pressure and settlement problems. umashankar et al. [76] studied the settlement rates of landfill built on soft soils using two types of eps. the comparison of settlement concentration was done on eps with an elastic modulus of 1 and 10 mpa respectively. the analysis through flac on the embankment loaded following aashto specifications found that the maximum embankment settlement with eps elastic modulus of 10 mpa is between 1.8 cm and 2.0 cm while the elastic modulus eps 1 mpa is in the range of 15 cm to 16 cm. this demonstrates that the eps with a hard feature has the advantage of reducing the settlement problem. table 3. types of eps geofoam [151]. types density (kg/m3) flexural strength (kpa) eps12 11.2 69 eps15 14.4 172 eps19 18.4 207 eps22 21.6 240 the indiana department of transportation has recommended the use of the eps blocks for the borman highway reconstruction project near gary, indiana to reduce the load on soft grounds [156]. the ground in this area consists entirely of soft soils, as it is close to lake michigan. thirty-two truckloads of eps blocks were used in this project. michalowski 46 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 et al. [157] investigated the road embankment performance which is partially stabilized using the pile-supported method, that is controlled modulus columns of 400 mm in diameter and installed with square grid space of between 1.4 m to 2.0 m from one another and were installed in ground by up to 22.8 m deep [148]. the bulk of the embankment fill used the eps29 block and mounted on a 9.5 m thick organic clay foundation. the top layer of the eps block is protected with a 0.4 mm thick synthetic moisture resistant coating, while the end of the block is mounted with at 0.6 mm thick geomembrane. the results obtained through the calculation of settlement were consistent with the settlement of the pile group due to the use of eps which reduced the burden of the load. in another project, the utah transportation department in 2001 undertook the reconstruction of a 27-km i-15 highway over four years costing $1.4 billion in salt lake city [158]. a total of 100,000 m3 eps15 blocks are used in this project as a road embankment filling material. the widened i-15 alignment requires a large embankment of 8.0 m to 10.0 m above the soft soils that could potentially lead a primary consolidation settlement of more than 1.0 m. some sections of the highway experienced settlement due to the construction of the embankment and have damaged the utility lines across the road. this has led the design team to decide on the use of eps blocks in the project to maintain service without the need for relocation or work suspension, which could affect construction costs. after the project was completed, bartlett et al. [159] produced a design review report and performance assessment of the embankment for 10 years. the results obtained from the site show that the elastic compression and gaps between the two eps block faces yield about 1% vertical gradients as load distribution slabs. additionally, a total of 15 mm foundation ground settlement and 0.2 to 0.4% of creep cramps occur on the base soil during the post-construction period of 10 years under pressure levels of 20 to 35 kpa. long-term monitoring of creep deformation of the criteria of 50 years found that maximum pressure is about 1.5 to 1.7 %. the case history described above showed that the eps blocks functioned as a solution to the problem of excess settlement. its light weight reduces side loads or bearings borne by the base soil. although eps with various density characteristics is available to meet different strength requirements, cost-based selection and suitability of use should be considered. eps with high hardness or elastic modulus is useful for large loads. many researchers believe that using this method can reduce costs [76, 153, 157], but kim et al. [160] argued that the use of eps blocks requires a high cost in terms of installation and construction operations in road construction projects compared to plastic board drains and pvd. this is because even with the reduction in the quantity of soil used for the embankment, it still requires additional soil due to the same longitudinal grade as the original design. hence, the development of sustainable materials such as expanded cork granules and granite sludge, comparable to eps features and functions should be carried out. 5. discussion and future research development the initial objective of this study is to discuss the factors that contribute to the stability of road embankment on soft ground. based on surveys through literature and some historical cases, current studies have found that settlement, slope stability, and bearing capacity are important factors for the stability of the road embankment. therefore, it is clear that these factors are contributors to road damage as evidenced by the findings of a historical case investigation that has been reported by researchers [19-23]. however, an unexpected finding was that soil properties and rainfall rates also contribute to this problem. the rainfall rate depends on the weather conditions of the area or country. these two factors are the cause of the occurrence of sediment, failure of bearing capacity, and slope failure. one of the 47 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 issues emerging from this finding is that soft soil properties require a high cost for improvement. furthermore, these soil properties also require the installation of instruments and frequent lab and field tests during the design process. with the latest technology approaches such as artificial intelligence, it no longer requires excessive testing in the field or laboratory as it can predict the soil properties quickly and accurately. artificial neural network (ann), adaptive neuro-fuzzy inference system (anfis) and support vector machines (svm) are artificial intelligence methods that are widely used today. further work is required to develop a road embankment stability prediction system that includes the key aspects of settlement, soil bearing capacity, and slope stability based on soil properties. the second objective of this study is to discuss the factors affecting the design of road embankments. in this study, geometric data is found to have an important role in the design. this is because geometric data such as embankment height, side slope, and crest width should be determined before the analysis of stability is done. what is interesting from the literature is that most researchers are more interested in investigating the height of the embankment. three types of embankment height have been previously reported, which are critical [113, 124], safe [116], and reasonable height [117, 128]. however, most guidelines issued by enforcement agencies in many countries emphasize that slopes and side loads need to be complied with as stipulated. most of the existing guidelines are limited regarding side slope determination criteria based on the height of the embankment. this is an important issue for future research to develop new guidance that has critical, safe, and reasonable side slope criteria. moreover, the relationship between crest width, side slope, and embankment height may be investigated in the future to develop a standardized level or value range with critical, safe, and reasonable criteria. the final objective of this study is to discuss effective soft soil improvement techniques. based on literature and observations through some historical cases, preloading and prefabricated vertical drains [136, 138] and geofoam as lightweight fill materials [145, 146] are widely used today. the study found that both techniques are environmentally friendly. however, both of these techniques require a long construction time. the preloading and prefabricated vertical drains technique takes up 6-12 months for the soft ground to consolidate. installation of geofoam is very complicated and requires the construction of a linked network that takes a long time. this problem can lead to cost implications for construction. thus, this is an important issue for future research and development. 6. conclusion the main goal of the current study was to review the challenges faced in the construction of highway embankments on soft ground and suggest a direction for future development. this study has found that, generally, there are two major challenges that engineers need to face in the construction of road embankments on soft ground during the stability design and selection of improvement techniques. it also found three factors that engineers need to consider in the embankment stability analysis, i.e., bearing capacity, settlement, and slope stability. however, these factors depend on ground properties, rainfall rate, and earthquakes. additionally, more significant findings in current studies have found that research that has been reported on a side slope and crest width was limited compared to the height of the embankment. thus, future development studies need to be broadly comprehensible on these three geometric data by considering criteria such as critical, safe, and reasonable. in order to save construction time, this study found that the fem approach in determining settlement rates and slope stability is useful. the most obvious finding to 48 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 emerge from this study is that preloading with pvds and geofoam is widely applied as a soft soil improvement technique as it is environmentally friendly, cost-effective, and saves construction time. the findings from this study make several contributions to the current literature. first, it extends our understanding of the latest issues in the construction of embankments on soft ground. secondly, it adds to a growing body of literature on road embankment stability. finally, it identifies the gap in previous studies for the development of future studies. acknowledgement the authors wish to thank the centre of engineering and built environment education research (peka) and smart and sustainable township research centre (sutra), faculty of engineering at and built environment, universiti kebangsaan malaysia for providing the facility for this research work. besides, the appreciation also goes to the ministry of education, malaysia, for providing scholarships for the project. moreover, we are grateful to politeknik ungku omar for providing the opportunity to perform this project. references [1] arulrajah a, maghoolpilehrood f, disfani mm, horpibulsuk s. (2014) spent coffee grounds as a non-structural embankment fill material: engineering and environmental considerations. journal of cleaner production, 72:181-186. [2] yu z, jianhui z, xu z, xiaodong p, hongwei l, hao c. (2017) finite element analysis of embankment with soft foundation reinforced by geogrids. modern civil and structural engineering, 1(1):78-83. [3] watts k, charles a. (2015) building on fill: geotechnical aspects, third. garston, watford: building research establishment. [4] xue j feng, chen j feng. (2015) reinforcement strength reduction in fem for mechanically stabilized earth structures. journal of central south university, 22(7):2691-2698. [5] zhuang y, wang k. (2017) numerical simulation of high-speed railway foundation improved by pvd-dcm method and compared with field measurements. european journal of environmental and civil engineering, 21(11):1363-1383. [6] yu h, wang y, zou c, wang p, yan c. (2017) study on subgrade settlement characteristics after widening project of highway built on weak foundation. arabian journal for science and engineering, 42(9):3723-3732. [7] quang nd., dang sm. (2013) settlement calculation and back-analysis of soil properties for a test embankment on a soft clay ground improved by pvd and vacuum-assisted preloading at a site in vung tau, viet nam. springer series in geomechanics and geoengineering, 3:317-322. [8] li s, huang x, zeng c. (2017) performance of an embankment foundation with sand over clay : experimental and numerical analyses. international journal of geomechanics, 17(6):1-11. [9] nazir r, moayedi h, subramaniam p, gue s-s. (2017) application and design of transition piled embankment with surcharged prefabricated vertical drain intersection over soft ground. arab j sci eng. doi: 10.1007/s13369-017-2628-6. [10] yean-chin t, peir-tien l, kuan-seng k. (2016) construction control chart developed from instrumented trial embankment on soft ground at tokai of kedah, malaysia. procedia engineering, 143(ictg):548-555. [11] che mamat r. (2013) engineering properties of batu pahat soft clay stabilized with lime, cement and bentonite for subgrade in road construction. ms thesis, faculty of civil and environmental engineering, universiti tun hussien onn malaysia. [12] liu sy, cai gj, tong ly, du gy. (2008) approach on the engineering properties of lianyungang marine clay from piezocone penetration tests. marine georesources & 49 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 geotechnology, 26(3):189-210. [13] horpibulsuk s, wijitchot a, nerimitknornburee a, shen sl, suksiripattanapong c. (2014). factors influencing unit weight and strength of lightweight cemented clay. quarterly journal of engineering geology and hydrogeology, 47(1):101-109. [14] le tm, fatahi b, khabbaz h. (2012) viscous behaviour of soft clay and inducing factors. geotechnical and geological engineering, 30(5):1069-1083. [15] yalcin a. (2007) the effects of clay on landslides: a case study. applied clay science, 38(1-2):77-85. [16] ohlmacher gc. (2000) the relationship between geology and landslide hazards of atchison, kansas, and vicinity. current research in earth sciences, 244(3):1-16. [17] oser c, cinicioglu sf. (2017) embankment design method combining limit-state approach with stress-path application. international journal of geomechanics asce, 17(4):1-16. [18] lu n, wayllace a, oh s. (2013) infiltration-induced seasonally reactivated instability of a highway embankment near the eisenhower tunnel, colorado, usa. engineering geology, 162:22-32. [19] rahadian h, hendarto, prasetya b. (2011) the failure of road embankment over north java soft soil. in: geotech. eng. disaster mitig. rehabil. highw. eng. pp 224-232. [20] tatarniuk c, bowman et. (2012) case study of a road embankment failure mitigated using deep soil mixing. in: proc. fourth int. conf. grouting deep mix. american society of civil engineers, pp 471-482. [21] mills b, mcginn j. (2010) design, construction, and performance of a highway embankment failure repaired with tire-derived aggregate. transportation research record, (2170):90-99. [22] irsyam m, susila e, himawan a. (2007) slope failure of an embankment on clay shale at km 97+500 of the cipularang toll road and the selected solution. in: int. symp. geotech. eng. gr. improv. geosynth. hum. secur. environ. preserv. bangkok, thailand, pp 531-540. [23] hadjigeorgiou j, kyriakou e, papanastasiou p. (2006) a road embankment failure near pentalia in southwest cyprus. in: int. symp. stab. rock slopes open pit min. civ. eng. the south african institute of mining and metallurgy, cape town, pp 343-352. [24] davis eh, booker jr. (1973) the effect of increasing strength with depth on the bearing capacity of clays. géotechnique, 23(4):551-563. [25] michalowski rl. (1992) bearing capacity of nonhomogeneous cohesive soils under embankments. journal of geotechnical engineering, 118(7):1098-1118. [26] michalowski rl. (1993) bearing capacity of nonhomogeneous clay layers under embankments. journal of geotechnical engineering, 119(10):1657-1669. [27] indraratna b, balasubramaniam as, balachandran s. (1992) performance of test embankment constructed to failure on soft marine clay. journal of geotechnical engineering, 118(1):12-33. [28] eide o, holmberg s. (1972) test fills to failure on soft bangkok clay. in: spec. conf. perform. earth earth-supported struct. asce, lafayette, indiana, united states, pp 159180. [29] dascal o, tournier jp, tavenas f, rochelle p la. (1972) failure of a test embankment on sensitive clay. in: spec. conf. perform. earth earth-supported struct. asce, lafayette, indiana, united states, pp 129-158. [30] popescu r, deodatis g, nobahar a. (2005) effects of random heterogeneity of soil properties on bearing capacity. probabilistic engineering mechanics, 20(4):324-341. [31] lehtonen vj, meehan cl, länsivaara tt, mansikkamäki jn. (2015) full-scale embankment failure test under simulated train loading. géotechnique, 65(12):961-974. [32] kim bb, lee s. (2005) comparison of bearing capacity characteristics of sand and gravel compaction pile treated ground. ksce journal of civil engineering, 9(3):197-203. [33] lopez-querol s, arias-trujillo j, gm-elipe m, matias-sanchez a, cantero b. (2017). improvement of the bearing capacity of confined and unconfined cement-stabilized aeolian sand. construction and building materials, 153:374-384. [34] rowe rk, li al. (2005) geosynthetic-reinforced embankments over soft foundations. 50 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 geosynthetics international, 12(1):50-85. [35] hewlett wj, randolph mf. (1988) analysis of piled embankment. ground engineering, 21(3):12-18. [36] sarsby rw. (2007) use of ‘limited life geotextiles’ (llgs) for basal reinforcement of embankments built on soft clay. geotextiles and geomembranes, 25(4-5):302-310. [37] ozdemir ma. (2016) improvement in bearing capacity of a soft soil by addition of fly ash. procedia engineering, 143(ictg):498-505. [38] brabb ee. (1991) the world landslide problem. episodes, 14(1):52-61. [39] ballantyne ck. (1986) landslides and slope failures in scotland: a review. scottish geographical magazine, 102(3):134-150. [40] dai fc, lee cf, li j, xu zw. (2001) assessment of landslide susceptibility on the natural terrain of lantau island, hong kong. environmental geology, 40(3):381-391. [41] davies tc. (1996) landslide research in kenya. journal of african earth sciences, 23(4):541-545. [42] tang c, zhu j, qi x, ding j. (2011) landslides induced by the wenchuan earthquake and the subsequent strong rainfall event: a case study in the beichuan area of china. engineering geology, 122(1-2):22-33. [43] xu xz, liu zy, xiao pq, guo wz, zhang hw, zhao c, yan q. (2015) gravity erosion on the steep loess slope: behavior, trigger and sensitivity. catena, 135:231-239. [44] yong l, chengmin h, baoliang w, xiafei t, jingjing l. (2017) a unified expression for grain size distribution of soils. geoderma, 288:105-119. [45] kinnell pia. (2000) the effect of slope length on sediment concentrations associated with side-slope erosion. soil science society of america journal, 64(3):1004-1008. [46] hou q, wu g, li h, fan g, zhou j. (2019) large deformation and failure mechanism analyses of tangba high slope with a high-intensity and complex excavation process. journal of mountain science, 16(2):453-469. [47] duncan jm. (1996) soil slope stability analysis. in: turer ka, schuster ri (eds) landslides, investig. mitig. national research council, washington, dc, us., pp 337-371. [48] huat bbk, ali fh, low th. (2006) water infiltration characteristics of unsaturated soil slope and its effect on suction and stability. geotechnical & geological engineering, 24(5):1293-1306. [49] terzaghi k. (1925) erdbaumechanik. franz deuticke, leipzig and vienna . [50] kong x. (2016) prediction of subgrade settlement based fuzzy self adaptable method of artificial intelligence. 9th international symposium on computational intelligence and design, (7):144-147. [51] zou c, wang y, lin j, chen y. (2016) creep behaviors and constitutive model for high density polyethylene geogrid and its application to reinforced soil retaining wall on soft soil foundation. construction and building materials, 114:763-771. [52] zou l, wang s, lai x. (2013) creep model for unsaturated soils in sliding zone of qianjiangping landslide. journal of rock mechanics and geotechnical engineering, 5(2):162–167. [53] azzam wr, basha a. (2017) utilization of soil nailing technique to increase shear strength of cohesive soil and reduce settlement. journal of rock mechanics and geotechnical engineering, 9(6):1104-1111. [54] grimstad g, haji ashrafi ma, degago sa, emdal a, nordal s. (2016) discussion of ‘soil creep effects on ground lateral deformation and pore water pressure under embankments’. geomechanics and geoengineering, 11(1):86-93. [55] sato h, nhan tt, matsuda h. (2018) earthquake-induced settlement of a clay layer. soil dynamics and earthquake engineering, 104(may 2017):418-431. [56] lagatta md, boardman bt, cooley bh, daniel de. (1997) geosynthetic clay liners subjected to differential settlement. journal of geotechnical and geoenvironmental engineering, 123(5):402-410. [57] paveenchana t, arayasiri m. (2009) solving the problems of differential settlement of pavement structures in the bangkok area. in: geohunan int. conf. 2009. american society of civil engineers, changsha, hunan, china, pp 180-185. 51 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 [58] moghaddam rb, jayawickrama pw. (2017) general bearing capacity theory and soil extraction method for the mitigation of differential settlements. in: geotech. front. 2017. american society of civil engineers, orlando, florida, pp 314-323. [59] skempton aw, bjerrum l. (1957) a contribution to the settlement analysis of foundations on clay. géotechnique, 7(4):168-178. [60] bo mw, fabius m, chu j, a. arulrajah. (2011) predicting consolidation settlements using small strain, large-strain and stress path methods. in: proc. 17th int. conf. soil mech. geotech. eng. pp 3481-3485. [61] boussinesq mj. (1885) application des potentiels. gauthier-villars, paris [in french]: à l’étude de l’éqilibre et du movvement des solides elastiques. [62] disfani mm, arulrajah a, suthagaran v, bo mw. (2013) long-term settlement prediction for wastewater biosolids in road embankments. resources, conservation and recycling, 77:69-77. [63] duncan m. (1993) limitation of conventional analysis of consolidation settlement. journal of geotechnical engineering, 119(9):1333-1359. [64] carroll r. (2011) use of crs test to predict settlement in an irish silt. 21st eur. young geotech. eng. conf. rotterdam . [65] skempton aw, peck rb, macdonald dh. (1955) settlement analyses of six structures in chicago and london. proceedings institution of civil engineers, 4(4):525-542. [66] bergado dt, teerawattanasuk c. (2008) 2d and 3d numerical simulations of reinforced embankments on soft ground. geotextiles and geomembranes, 26(1):39-55. [67] bergado d., chong kc, daria pam, alfaro mc. (1990) deformability and consolidation characteristics of soft bangkok clay using screw plate tests. canadian geotechnical journal, 27(5): 531-545. [68] poulos hg, davis eh. (1963) triaxial testing and three dimensional settlement analysis. in: proc. 4th aust. new zeal. conf. sm fe, adelaide. pp 233-243. [69] chai j chun, shrestha s, hino t, uchikoshi t. (2017) predicting bending failure of cdm columns under embankment loading. computers and geotechnics, 91:169-178. [70] smith cc, tatari a. (2016) limit analysis of reinforced embankments on soft soil. geotextiles and geomembranes, 44(4):504-514. [71] buttling s, cao r, lau w, naicker d. (2018) class a and class c numerical predictions of the deformation of an embankment on soft ground. computers and geotechnics, 93:191203. [72] keller gr. (2016) application of geosynthetics on low-volume roads. transportation geotechnics, 8(april):119-131. [73] yapage n, liyanapathirana s. (2018) behaviour of geosynthetic reinforced column supported embankments. journal of engineering, design and technology, 16(1):44-62. [74] zhou wh, lao jy, huang y, chen r. (2017) group effect on soil arching in geogridreinforced pile-supported embankments. japanese geotechnical society special publication, 5(2):130-134. [75] hegde am, sitharam tg. (2015) effect of infill materials on the performance of geocell reinforced soft clay beds. geomechanics and geoengineering, 10(3):163-173. [76] umashankar b, mouli s, hariprasad c. (2015) settlement of embankment constructed with geofoam. in: iskander m, suleiman mt, anderson jb, laefer df (eds) int. found. congr. equip. expo 2015. american society of civil engineers, pp 161-170. [77] paolo di pietro. (2017) practical applications with geosynthetic mats reinforced with steel wire meshes to prevent embankment damage by burrowing large rodents and beavers. journal of civil engineering and architecture, 11(1):8-15. [78] chaiyaput s, bergado dt, artidteang s. (2014) measured and simulated results of a kenaf limited life geosynthetics (llgs) reinforced test embankment on soft clay. geotextiles and geomembranes, 42(1):39-47. [79] marto a, othman ba, kasim f, bakar i. (2012) comparison of field performance between bamboo-geotextile composite embankment and high strength geotextile embankment. advanced materials research, 587:77-80. [80] lal d, sankar n, chandrakaran s. (2017) effect of reinforcement form on the behaviour of 52 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 coir geotextile reinforced sand beds. soils and foundations, 57(2):227-236. [81] da silva em, justo jl, durand p, justo e, vázquez-boza m. (2017) the effect of geotextile reinforcement and prefabricated vertical drains on the stability and settlement of embankments. geotext geomembranes. doi: 10.1016/j.geotexmem.2017.07.001. [82] zhuang y, wang ky. (2016) finite-element analysis on the effect of subsoil in reinforced piled embankments and comparison with theoretical method predictions. international journal of geomechanics, 16(5):04016011-1–15. [83] parsa-pajouh a, fatahi b, vincent p, khabbaz h. (2014). trial embankment analysis to predict smear zone characteristics induced by prefabricated vertical drain installation. geotechnical and geological engineering, 32(5):1187-1210. [84] sheil bb, mccabe ba. (2014) a finite element-based approach for predictions of rigid pile group stiffness efficiency in clays. acta geotechnica, 9(3):469-484. [85] rezania m, nguyen h, zanganeh h, taiebat m. (2018) numerical analysis of ballina test embankment on a soft structured clay foundation. computers and geotechnics, 93:61-74. [86] xue jf, chen jf, liu jx, shi zm. (2014) instability of a geogrid reinforced soil wall on thick soft shanghai clay with prefabricated vertical drains: a case study. geotextiles and geomembranes, 42(4):302-311. [87] rabie m. (2014) comparison study between traditional and finite element methods for slopes under heavy rainfall. hbrc journal, 10(2):160–168. [88] ghafari a, nikraz hr, sanaeirad a. (2016) finite element analysis of deformation and arching inside the core of embankment dams during construction. australian journal of civil engineering, 14(1):13-22. [89] zhao l, yang f, zhang y, dan h, liu w. (2015) effects of shear strength reduction strategies on safety factor of homogeneous slope based on a general nonlinear failure criterion. computers and geotechnics, 63:215-228. [90] duncan jm. (1996) state of the art: limit equilibrium and finite-element analysis of slopes. journal of geotechnical engineering, 122(7):577-596. [91] kirkby w, pickett pe. (2018). geotechnical manual. texas department of transportation. [92] singh tn, verma ak, sarkar k. (2010) static and dynamic analysis of a landslide. geomatics, natural hazards and risk, 1(4):323-338. [93] iñeguez jb. (2016) enhanced limit method for slope stability analysis. electronic journal of geotechnical engineering, 21(26):10215-10232. [94] fellenius w. (1936) calculation of the stability of earth slope. in: trans. 2nd congr. large dams. washington, dc, us., pp 445-462. [95] bishop aw. (1955) the use of slip circle in the stability analysis of slopes. geotechnique, 5(1):7-17. [96] e. spencer. (1967) a method of analysis of the stability of embankments assuming parallel interslice forces. géotechnique, 17(1):11-26. [97] morgenstern nr, price ve. (1965) the analysis of the stability of general slip surfaces. géotechnique, 15(1):79–93. [98] liu sy, shao lt, li hj. (2015) slope stability analysis using the limit equilibrium method and two finite element methods. computers and geotechnics, 63:291-298. [99] guo t, he z. (2012) comparison of factor of safety of a roadway slope based on the limit equilibrium method and shear strength reduction method. in: geohunan int. conf. american society of civil engineers, hunan, china, pp 34-40. [100] luo n, bathurst rj, javankhoshdel s. (2016) probabilistic stability analysis of simple reinforced slopes by finite element method. computers and geotechnics, 77:45–55. [101] alemdag s, kaya a, karadag m, gurocak z, bulut f. (2015) utilization of the limit equilibrium and finite element methods for the stability analysis of the slope debris: an example of the kalebasi district (ne turkey). journal of african earth sciences, 106:134146. [102] liu kw, rowe rk. (2015) numerical modelling of prefabricated vertical drains and surcharge on reinforced floating column-supported embankment behaviour. geotextiles and geomembranes, 43(6):493-505. [103] ishii y, ota k, kuraoka s, tsunaki r. (2012) evaluation of slope stability by finite element 53 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 method using observed displacement of landslide. landslides, 9(3):335-348. [104] zienkiewicz oc, humpheson c, lewis rw. (1975) associated and non-associated viscoplasticity and plasticity in soil mechanics. géotechnique, 25(4):671-689. [105] sun c, chai j, xu z, qin y, chen x. (2016) stability charts for rock mass slopes based on the hoek-brown strength reduction technique. engineering geology, 214:94-106. [106] griffiths dv, lane p a. (1999) slope stability analysis by finite elements. geotechnique, 49(3):387-403. [107] kulhawy fh. (1969) finite element analysis of the behavior of embankments. the university of california at berkeley, california. u.s.a. [108] korea expressway corporation. (1996) road design manual, soil and foundation (in korean). korea expressway corporation. [109] public works department malaysia. (2010) guideline for slope design.. [110] ministry of work tanzania. (2011) road geometric design manual.. [111] texas department of transportation. (2014) roadway design manual.. [112] new jersey department of transportation. (2015) roadway design manual.. [113] fagundes d de f, almeida m de ss de, girout r, blanc m, thorel l. (2015) behaviour of piled embankment without reinforcement. proceedings of the institution of civil engineers geotechnical engineering, 168(6):514-525. [114] bhasi a, rajagopal k. (2014) geosynthetic-reinforced piled embankments: comparison of numerical and analytical methods. international journal of geomechanics, 15(5):1-12. [115] chen y, qi c, xu h, ng cww. (2013) field test research on embankment supported by plastic tube cast-in-place concrete piles. geotechnical and geological engineering, 31(4):1359-1368. [116] kasim f, marto a, othman ba, bakar i, othman mf. (2013) simulation of safe height embankment on soft ground using plaxis. apcbee procedia, 5:152-156. [117] wang s, qi j, liu f. (2016) study on the reasonable height of embankment in qinghai– tibet highway. geotechnical and geological engineering, 34(1):1-14. [118] lu z, wang h, yao h. (2014) method to determine height and water content of highway subgrade filled with fine grained soil materials. materials research innovations, 18(sup5):s5-5-s5-8. [119] cui x, zhang n, li s, zhang j, wang l. (2015) effects of embankment height and vehicle loads on traffic-load-induced cumulative settlement of soft clay subsoil. arabian journal of geosciences, 8(5):2487-2496. [120] almeida mss, riccio m, hosseinpour i. (2013) performance of a geosynthetic-encased column (gec) in soft ground: numerical and analytical studies. geosynthetics international, 20(4):252-262. [121] filz g, sloan j, mcguire mp. (2012) column-supported embankments: settlement and load transfer. geocongress 2012 geotech eng state art pract. doi: 10.1007/s13398-0140173-7.2. [122] mcguire mp. (2011) critical height and surface deformation of column-supported embankments. virginia polytechnic institute and state university, blacksburg, va. [123] bs 8006. (2010) code of practice for strengthened / reinforced soils and other fills. br stand inst. doi: bs 8006:1995. [124] chen jia f, hai bin w, bao ping a, zhang p, yang peng z. (2013) application of bp neural network embankment settlement prediction in seasonal frozen areas. in: 2013 4th int. conf. digit. manuf. autom. icdma 2013. pp 276-279. [125] zhang j, zhang m, lui y. (2006) study on the reasonable embankment height of qinghaitibet railway in permafrost regions. china railway science, 27(5):28-34. [126] yue z, ge j, li z, liu y. (2007) study on settlement of unprotected railway embankment in permafrost. cold regions science and technology, 48(1):24-33. [127] zhang j, zhang m, lui y. (2009) reasonable height of roadway embankment in permafrost regions. in: 14th conf. cold reg. eng. american society of civil engineers, pp 486-495. [128] qi c, wu q, wu j. (2007) analysis of thermal state of permafrost under high embankment along qinghai–tibet railway. chinese journal of rock mechanics and 54 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 engineering, 26(s2):4518-4524. [129] li g, li n, kang j, niu f, yu w, shi l, bi g. (2008) study on design optimization of a crushed stone layer with shading board placed on a railway embankment on warm permafrost. cold regions science and technology, 54(1):36-43. [130] sinha ak, havanagi vg, mathur s. (2007) inflection point method for predicting settlement of pvd improved soft clay under embankments. geotextiles and geomembranes, 25(6):336-345. [131] jin l, wang s, chen j, dong y. (2012) study on the height effect of highway embankments in permafrost regions. cold regions science and technology, 83-84:122-130. [132] wang s, chen j, qi j. (2009) study on the technology for highway construction and engineering practices in permafrost regions. sciences in cold and arid regions, 1(5):412422. [133] aljanabi qa, chik z, allawi mf, el-shafie ah, ahmed an, el-shafie a. (2018) support vector regression-based model for prediction of behavior stone column parameters in soft clay under highway embankment. neural computing and applications, 30(8): 2459–2469. [134] artidteang s, chaiyaput s, bergado dt, tanchaisawat t. (2015) embankment reinforced with limited life geotextiles on soft clay. ground improvement, 168(2):130-143. [135] zhuang y, wang k. (2017) finite element analysis on the dynamic behavior of soil arching effect in piled embankment. transportation geotechnics, 14:8-21. [136] dafalla ma. (2009) improvement of coastal silty sand of saudi arabia using preloading technique. in: geohunan int. conf. american society of civil engineers, changsha, hunan, china, pp 100-105. [137] chan kf, poon bm, perera d. (2018) prediction of embankment performance using numerical analyses – practitioner’s approach. computers and geotechnics, 93:163-177. [138] kjellman w. (1948) accelerating consolidation of fine grained soils by means of cardboard wicks. in: 2nd int. conf. soil mech. found. eng. rotterdam, pp 302-305. [139] chu j, bo mw, choa v. (2006) improvement of ultra-soft soil using prefabricated vertical drains. geotextiles and geomembranes, 24(6):339-348. [140] yang h, xiao j, he y. (2010) an economical, practical, and environmental friendly surcharge preloading method to improve soft ground of municipal road. in: geoshanghai int. conf. american society of civil engineers, pp 267-272. [141] sun l, gao x, zhuang d, guo w, hou j, liu x. (2018) pilot tests on vacuum preloading method combined with short and long pvds. geotextiles and geomembranes, 46(2):243250. [142] zhang z, ye gb, xu y. (2018) comparative analysis on performance of vertical drain improved clay deposit under vacuum or surcharge loading. geotextiles and geomembranes, 46(2):146-154. [143] schaefer vr, berg rr, collin jg, christopher br, dimaggio ja, filz gm, bruce da, ayala d. (2017) ground modification methods reference manual – volume i. u.s. dep. transp. fed. highw. adm. fhwa-nhi-16-027 i: [144] stark td, horvath js, leshchinsky d. (2004) guideline and recommended standard for geofoam applications in highway embankments. washington, d.c. [145] panesar dk. (2013) cellular concrete properties and the effect of synthetic and protein foaming agents. construction and building materials, 44:575-584. [146] onprom p, chaimoon k, cheerarot r. (2015) influence of bottom ash replacements as fine aggregate on the property of cellular concrete with various foam contents. advances in materials science and engineering, 2015:381704. [147] struhárová a, rouseková i. (2007) porous structure of cellular concrete and its impact on selected physicalmechanical properties of cellular concrete. slovak journal of civil engineering, 2:35-43. [148] hu w, neufeld rd, vallejo le, kelly c, latona m. (1997) strength properties of autoclaved cellular concrete with high volume fly ash. journal of energy engineering, 123(2):44-54. [149] marradi a, pinori u, betti g. (2012) the use of lightweight materials in road embankment construction. procedia social and behavioral sciences, 53(0):1000-1009. 55 iium engineering journal, vol. 20, no. 2, 2019 mamat et al. https://doi.org/10.31436/iiumej.v20i2.996 [150] elias v, welsh j, warren j, lukas r. (1999) ground improvement technical summaries. washington dc, us: department of transportation federal highway administration. [151] astm d6817 / d6817m-17. (2017) standard specification for rigid cellular polystyrene geofoam. astm int. doi: 10.1520/d6817_d6817m-17. [152] koerner rm. (2012) designing with geosynthetics, 6th ed. bloomington, in: xlibris corporation. [153] beju yz, mandal jn. (2017) expanded polystyrene (eps) geofoam: preliminary characteristic evaluation. in: procedia eng. pp 239-246. [154] trandafir ac, bartlett sf, lingwall bn. (2010) behavior of eps geofoam in stresscontrolled cyclic uniaxial tests. geotextiles and geomembranes, 28(6):514-524. [155] özer at, akay o. (2016) interface shear strength characteristics of interlocked eps-block geofoam. journal of materials in civil engineering, 28(4):04015156. [156] shong d, sutmoller n. (2011) project showcase: highway reconstruction on sof soils not a problem with geofoam. geosynthetics, 29(2):14-17. [157] michalowski rl, asce f, wojtasik a, duda a, florkiewicz a, park d, asce sm. (2018) failure and remedy of column-supported embankment : case study. journal of geotechnical and geoenvironmental engineering, 144(3):1-14. [158] newman mp, bartlett sf, lawton ec. (2010) numerical modeling of geofoam embankments. journal of geotechnical and geoenvironmental engineering, 136:290-298. [159] bartlett sf, lawton ec, farnsworth cb, perry mn. (2012) design and evaluation of expanded polystyrene geofoam embankments for the i-15 reconstruction project, salt lake city, utah. salt lake city,us. [160] kim t-h, lee hw, hong s-w. (2016) value engineering for roadway expansion project over deep thick soft soils. journal of construction engineering and management, 142(2):19. 56 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <feff004200720075006700200069006e0064007300740069006c006c0069006e006700650072006e0065002000740069006c0020006100740020006f007000720065007400740065002000410064006f006200650020005000440046002d0064006f006b0075006d0065006e007400650072002c0020006400650072002000650067006e006500720020007300690067002000740069006c00200064006500740061006c006a006500720065007400200073006b00e60072006d007600690073006e0069006e00670020006f00670020007500640073006b007200690076006e0069006e006700200061006600200066006f0072007200650074006e0069006e006700730064006f006b0075006d0065006e007400650072002e0020004400650020006f007000720065007400740065006400650020005000440046002d0064006f006b0075006d0065006e0074006500720020006b0061006e002000e50062006e00650073002000690020004100630072006f00620061007400200065006c006c006500720020004100630072006f006200610074002000520065006100640065007200200036002e00300020006f00670020006e0079006500720065002e> /deu <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> /esp <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> /eti <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> /fra <feff005500740069006c006900730065007a00200063006500730020006f007000740069006f006e00730020006100660069006e00200064006500200063007200e900650072002000640065007300200064006f00630075006d0065006e00740073002000410064006f006200650020005000440046002000700072006f00660065007300730069006f006e006e0065006c007300200066006900610062006c0065007300200070006f007500720020006c0061002000760069007300750061006c00690073006100740069006f006e0020006500740020006c00270069006d007000720065007300730069006f006e002e0020004c0065007300200064006f00630075006d0065006e00740073002000500044004600200063007200e900e90073002000700065007500760065006e0074002000ea0074007200650020006f007500760065007200740073002000640061006e00730020004100630072006f006200610074002c002000610069006e00730069002000710075002700410064006f00620065002000520065006100640065007200200036002e0030002000650074002000760065007200730069006f006e007300200075006c007400e90072006900650075007200650073002e> /gre <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> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice iium engineering journal chief editor ahmad faris ismail, iium, malaysia technical editor sany izan ihsan, iium, malaysia executive editor ahm zahirul alam, iium, malaysia associate editor nor farahidah za’bah, iium, malaysia language editor lynn mason, malaysia copy editor hamzah mohd. salleh, iium, malaysia malay translator nurul arfah che mustapha, iium, malaysia editorial board members abdullah al-mamun, iium, malaysia abdumalik rakhimov, iium, malaysia ali sophian, iium, malaysia erwin sulaeman, iium, malaysia hanafy omar, saudi arabia hazleen anuar, iium, malaysia konstantin khanin, university of toronto, canada ma'an al-khatib, iium, malaysia md zahangir alam, iium, malaysia meftah hrairi, iium, malaysia mohamed b. trabia, united states mohammad s. alam, texas a&m university-kingsville, united states mustafizur rahman, national university singapore, singapore ossama abdulkhalik, michigan technological university, united states othman o khalifa, iium, malaysia razi nalim, iupui, indianapolis, indiana, united states rosminazuin ab. rahim, iium, malaysia sharifah imihezri syed shaharuddin, iium, malaysia waqar asrar, iium, malaysia aims & scope of iiumengineering journal the iium engineering journal, published biannually (january and july), is a carefully refereed international publication of international islamic university malaysia (iium). contributions of high technical merit within the span of engineering disciplines; covering the main areas of engineering: electrical and computer engineering; mechanical and manufacturing engineering; automation and mechatronics engineering; material and chemical engineering; environmental and civil engineering; biotechnology and bioengineering; engineering mathematics and physics; and computer science and information technology are considered for publication in this journal. contributions from other areas of engineering and applied science are also welcomed. the iium engineering journal publishes contributions under regular papers and invited review papers. it also welcomes contributions that address solutions to the specific challenges of the developing world and address science and technology issues from an islamic and multidisciplinary perspective. referees’ network all papers submitted to iium engineering journal will be subjected to a rigorous reviewing process through a worldwide network of specialized and competent referees. each accepted paper should have at least two positive referees’ assessments. submission of a manuscript a manuscript should be submitted online to the iium-engineering journal website at http://journals.iium.edu.my/ejournal. further correspondence on the status of the paper could be done through the journal website. i ii international advisory committee a. anwar, united states abdul latif bin ahmad, malaysia farzad ismail, usm, pulau pinang, malaysia hanafy omar, saudi arabia hany ammar, united states idris mohammed bugaje, nigeria k.b. ramachandran, india kunzu abdella, canada luis le moyne, isat, university of burgundy, france m mujtaba, united kingdom mohamed ai-rubei, ireland mohamed b trabia, united states syed kamrul islam, united states tibor czigany, budapest university of technology and economics, hungary yiu-wing mai, the university of sydney, australia. published by: iium press, international islamic university malaysia jalan gombak, 53100 kuala lumpur, malaysia phone (+603) 6421-5014, fax: (+603) 6421-6298 whilst every effort is made by the publisher and editorial board to see that no inaccurate or misleading data, opinion or statement appear in this journal, they wish to make it clear that the data and opinions appearing in the articles and advertisement herein are the responsibility of the contributor or advertiser concerned. accordingly, the publisher and the editorial committee accept no liability whatsoever for the consequence of any such inaccurate or misleading data, opinion or statement. iium engineering journal issn: 1511-788x e-issn: 2289-7860 iii iium engineering journal volume 23, issue 1, january 2022 https:/doi.org/10.31436/iiumej.v23i1 table of contents editorial ......................................................................................................................................................... i civil and environmental engineering 1781: consolidation integrated buoyancy equation for soft ground improved with lightweight polyurethane foam................................................................................................... 1 diana che lat, ismacahyadi bagus mohamed jais, nazri ali, nor zurairahetty mohd yunus, nor hibatul wafi nor zarin and atiqah najwa zainuddin 1788: potential volumizing effect of the post-morph lime filler in attenuating concrete carbonation ..................................................................................................................................... 13 muhamad hasif hussin, mohd haziman wan ibrahim, nor hazurina othman, mohammed yahya mohammed al-fasih and mohd fadzil arshad 2119: critical success factors for bim implementation for power plant projects in malaysia ............................................................................................................................................................. 34 mohd azrul aziz, chee fui wong, nuzul azam haron, aidi hizami ales, raja ahmad azmeer raja ahmad effendi and ooi kuan tan electrical, computer and communications engineering 1663: performance analysis on dynamic wireless charging for electric vehicle using ferrite core ...................................................................................................................................... 46 siti hajar yusoff, amira aziera abdullah, nadia nazieha nanda and ahmed samir abed badawi 1744: design and analysis of a microstrip patch antenna at 7.5 ghz for x-band vsat application ........................................................................................................................................ 60 sarah yasmin mohamad, noralya fatin muzamil, norun farihah abdul malek, s.m.a. motakabber, rafidah abd malik and nurain izzati shuhaimi 1760: wavelet detail coefficient as a novel wavelet-mfcc features in text-dependent speaker recognition system .......................................................................................................... 68 syahroni hidayat, muhammad tajuddin, siti agrippina alodia yusuf, jihadil qudsi and nenet natasudian jaya 1783: in-idris: modification of idris stemming algorithm for indonesian text ............................. 82 febiarty wulan suci, nur hayatin and yuda munarko 1789: botnet detection using independent component analysis ..................................................... vi wan nur hidayah ibrahim, ali selamat and ondre krejcar 1802: color image retrieval based on fuzzy neural networks and swarm intelligence .......... vi baydaa ibraheem khaleel 1803: enhancement of stability on autonomous waypoint mission of quadrotor using lqr integrator control ........................................................................................................................ vi oktaf agni dhewa, tri kuntoro priyambodo, aris nasuha and yasir mohd mustafah 1807: maintain agent consistency iin surakarta chess using dueling deep network with increasing batch............................................................................................................................. vii rian adam rajagede 1822: development of rainfall forecasting model using machine learning with singular spectrum analysis .......................................................................................................................... vii pundru chandra shaker reddy, yadala sucharitha and goddumarri surya narayana 1825: classification model for breast cancer mammograms ......................................................... vii suzani mohamad samuri, try viananda nova, bahbibi rahmatullah, wang shir li and z.t. al-qaysi 2053: an immersive augmented reality system to study the efficiency of dynamic exit signage .............................................................................................................................................. vii azhar mohd ibrahim, muhammad arif kamaruddin andazni nabela wahid 2086: computationless palm-print verification using wavelet oriented zero-crossing signature .......................................................................................................................................... vii jitendra prabhakar chaudhari, hiren kantilal mewada, amit vinubhai patel, keyur kamaldasji mahant and alpesh dudabhai vala 2115: a study of channel and delay-based scheduling algorithms for live video streaming in the fifth generation long term evolution-advanced network ..................................... vii liza abdul latiff, huda adibah mohd ramli, ani liza asnawi and nur haliza abdulwahab 2135: detection traffic density with image processing using pin hole algorithm .................... vii mochamad aditya irawanto, casi setianingsih and budhi irawan materials and manufacturing engineering 1620: biodegradation of mango seed starch films in soil ................................................................ vii nur’aishah ahmad shahrim, norshahida sarifuddin, ahmad zahirani ahmad azhar and hafizah hanim mohd zaki 1693: experimental investigation of the influence of multi-recycling on the fracture behavior of post consumer high impact polystyrene from disposable cups evaluated by the j-integral approach ............................................................................................................... vii hanan el bhilat, hassan mabchour, houda salmi, abdelilah hachim and khalid el had 1769: effect of sterilization on mechanical and blood properties of medical grade polyvinyl chloride............................................................................................................................................ vii maryam poostchi and hamed bagheri 1816: magnetically modified sugarcane bagasse disordered carbon as a cadmium removal agent in water ................................................................................................................................ vii izzaty syahirah baharudin, noraini mohamed noor, ezzat chan abdullah, raihan othman and mubarak nasibab mujawar 1842: application of house of quality in the conceptual design of batik wax extruder and printer .............................................................................................................................................. vii nurul anissa mohd asri, abdul malek abdul hamid, norhashimah shaffiar, nor aiman sukindar, sharifah imihezri syed shaharuddin and farid syazwan hassan 1848: mechanical characterization of polyester/ e-glass fiber reinforced/mwcnts nanocomposites .............................................................................................................................. vii naguib g. yakoub 2114: evaluation of surface roughness and material removal rate in electrical discharge machining of al-alloy with 10%sic ........................................................................................... viii abbas fadhil ibrahim 2031: influence of ipns (vinylester / epoxy / polyurethane) on the mechanical properties of glass / carbon hybrid composites ............................................................................................. viii karjala santhosh priya, kuttynadar rajammal vijaya kumar,gopi suresh, rajesh ravi, chockalingam devanathan and chinathambi muthukaruppan meenakshi mechanical and aerospace engineering 1804: flow induced vibration in square cylinder of various angles of attack ........................ viii nur ain shafiza ramzi, lee kee quen, nur amira balqis mohd zainuri, hooi-siang kang, nor’azizi othman and keng yinn wong 1812: vehicle air conditioner (vac) control system based on passenger comfort: a proof of concept ............................................................................................................................................ viii suroto munahar, bagiyo condro purnomo, muhammad izzudin, muji setiyo and madihah mohd saudi 2113: computational fluid dynamics modeling of microchannels cooling for electronic microdevices ................................................................................................................................... viii jonathan fábregas, henry santamaría, edgardo buelvas, saul pérez, carlos díaz, javier carpintero, ricardo mendoza and jennifer villa 2138: comparative study on degradation of polylactic acid/ syzygium aromaticum composites ageing in outdoor environment and soil burial ............................................... viii salina budin, normariah che maideen, koay mei hyie, hamid yussof and halim ghafar 2146: numerical modelling of bird strike on a rotating engine blades based on variations of porosity density ............................................................................................................................ viii sharis-shazzali shahimi, nur azam abdullah, meftah hrairi, ameen top and ahmad faris ismail iv v 2156: maximizing output voltage of a piezoelectric energy harvester via beam deflection method for low-frequency inputs ............................................................................................ viii mohamad safiddin mohd tahir, noor hazrin hany mohamad hanif and azni nabela wahid mechatronics and automation engineering 1971: optimal piezoelectric shunt damper using enhanced synthetic inductor: simulation and experimental validation ..................................................................................................... viii muhamad nazri suhaimi, azni nabela wahid, norhidayati diyana nordin, and khairul affendy md nor vol23-n1-frontpage application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 nutrients and chemical oxygen demand (cod) removals by microalgae – bacteria co-culture system in palm oil mill effluent (pome) amirah samsudin, azlin suhaida azmi, mohd nazri mohd nawi, amanatuzzakiah abdul halim* department of biotechnology engineering, kulliyyah of engineering, international islamic university malaysia. p.o. box 10, 50728 kuala lumpur, malaysia, *corresponding author: amana@iium.edu.my (received: 3rd april 2019; accepted: 11th july 2019; published on-line:2nd december 2019) abstract: in malaysia, large amounts of waste known as palm oil mill effluent (pome) are generated during the production process of crude palm oil. conventionally, pome is treated using biological treatment that involves two processes; aerobic and anaerobic. these processes however, require long hydraulic retention time and produce methane and carbon dioxide (co2) that can cause environmental problems. alternatively, pome can be treated by a combination of microalgae and bacterial co-culture that requires a shorter treatment time and is environmentally friendly. in this study, a microalgae strain, chlorella vulgaris was co-cultured with a bacteria strain azospirillum brasilense in pome with an initial concentration of 1.9 106 cells/ml and 104 cfu/ml, respectively. the removal of chemical oxygen demand (cod) and nutrients (phosphorus and ammonium) were analyzed using standard methods, apha 1999. the effectiveness of the co-culture system in pome treatment under agitation and aeration conditions for nutrients and cod removals were studied. results show that the removal of ammonium by microalgae was much higher under the aeration condition (73.5%) compared to that of the agitation condition (34.4%) in pome. moreover, co-culture system exhibits better removal of ammonium, phosphorus, and cod (84%, 87.3% and 51.8%, respectively) compared to that in an axenic microalgae system (67%, 84.2% and 41.1%, respectively). the kinetic studies on the co-culture system and the nutrients removal were also conducted. the kinetic coefficients of maximum specific growth rate (μmax) and half-saturation coefficient (ks) obtained from lineweaver-burk plot were 0.192 d 1 and 27.32 mg/l, respectively. based on the findings obtained, the co-culture system could be implemented as an efficient and inexpensive alternative method for pome treatment. abstract: di malaysia, banyak bahan buangan kilang minyak kelapa sawit yang dikenali sebagai (pome) telah terhasil ketika proses penghasilan minyak kelapa sawit mentah. dahulu, pome dirawat menggunakan rawatan biologi yang terdiri daripada dua proses; erob dan anaerob. walau bagaimanapun, proses-proses ini memerlukan masa yang panjang bagi pengekalan hidraulik dan gas metana dan karbon dioksida (co2) telah terhasil yang menyebabkan masalah alam. sebagai alternatif, pome dapat dirawat dengan kombinasi mikroalga dan sistem bakteria ko-kultur melalui masa rawatan yang lebih pendek dan mesra alam. kajian ini, strain mikroalga, chlorella vulgaris telah di ko-kultur dengan strain bakteria azospirillum brasilense dalam pome dengan ketumpatan awal 1.9 106 sel/ml dan 104 cfu/ml masing-masing. penyingkiran kehendak oksigen secara kimia (cod) dan nutrisi (fosferus dan ammonium) telah dikaji menggunakan kaedah biasa, apha 1999. keberkesanan system ko-kultur dalam rawatan 22 iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 pome di bawah keadaan kisaran dan pengudaraan bagi nutrisi dan penyingkiran cod telah diselidiki. dapatan kajian menunjukkan penyingkiran ammonium menggunakan mikroalga lebih banyak melalui keadaan pengudaraan (73.5%) berbanding keadaan kisaran (34.4%) dalam pome. tambahan, system ko-kultur menunjukkan lebih bagus dalam penyingkiran ammonium, fosferus dan cod (84%, 87.3% dan 51.8%, masingmasing) dibandingkan dengan sistem mikroalga aksenik (67%, 84.2% dan 41.1%, masingmasing). kajian kinetik pada sistem ko-kultur dan penyingkiran nutrisi turut dijalankan. pekali kinetik kadar maksimum pertumbuhan sebenar (μmax) dan pekali separuh-penepuan (ks) telah diperolehi melalui plot lineweaver-burk iaitu 0.192 d⁻1 dan 27.32 mg/l, masingmasing. berdasarkan penemuan ini, sistem ko-kultur boleh dijalankan dengan cekap dan murah sebagai pilihan alternatif kepada rawatan pome. keywords: co-culture; microalgae; palm oil mill effluent; symbiotic; wastewater treatment 1. introduction malaysia is one of the largest producers and exporters of palm oil in the world. during the palm oil production process, huge amounts of wastewater, known as palm oil mill effluent (pome) consisting of various pollutants and nutrients, are generated [1]. pome contains a high concentration of phosphorus, organic nitrogen, and other nutrients. moreover, the biochemical oxygen demand (bod) and chemical oxygen demand (cod) content in pome are also high, reaching 100 times higher than municipal sewage [2]. hence, pome treatment is very crucial prior to discharge into natural water resources, such as rivers, which can cause water pollution and negatively affect aquatic life. pome has been treated using conventional methods (e.g. anaerobic and aerobic digestion). however, these methods produce co2 and methane which can lead to enviromental problems. furthermore, these conventional methods require long hydraulic retention time (hrt) and can take at least 20 days for the aerobic digestion process. as an alternative for pome treatment, utilization of microalgae has been introduced due to its ability to grow in robust environments and still remove various pollutants in wastewater such as phosphorus and nitrogen. it was also reported that bacteria known as microalgae growth promoting bacteria (mgpb) can be co-cultured with microalgae to improve the removal of nutrients [3-6]. moreover, this co-culture system shares a symbiotic relationship. the oxygen (o2) produced by microalgae during photosynthesis will be used by heterotrophic bacteria and the bacteria in return release co2 that can be consumed by microalgae for growth [7]. the aim of this study is to evaluate the efficiency of microalgae and bacteria species, chlorella vulgaris and azospirillum brasilense for nutrients (ammonium and phosphorus) and cod removals in partially treated pome under different cultivation conditions to replace the aerobic digestion process in the conventional pome treatment. the kinetics studies of the co-culture system were also determined. 2. methodology 2.1 raw materials and inoculum preparation a species of microalgae (chlorella vulgaris) and a bacteria strain (azospirillum brasilense) were used in this study. the microalgal strain and bacteria were purchased from universiti malaya, kuala lumpur and leibniz-institute dsmz, germany respectively. microalgae was grown in tris-acetate-phosphate (tap) medium at 25 c and 150 rpm in a rotary shaker and bacteria was maintained in nutrient media at 30±2 c and 120 rpm [3]. partially treated palm oil mill effluent (pome) (sample after anaerobic process) was 23 iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 collected from west mill sdn bhd, sime darby research centre, carey island, malaysia. partially treated pome was used because this study aims to replace the aerobic process and the amount of nutrients available were acceptable for microalgae to growth. sample obtained was stored in 5 l plastic containers and kept at 4 c to limit the activity of biodegradation process and prevent any contamination [7]. the ammonium, phosphorus and cod contents in partially treated pome are 162, 18, and 874 mg/l, respectively. 2.2 experimental set up microalgae and bacteria were cultivated in pome at 10% concentration (vmicroalgae – bacteria /vpome) in a 250 ml flask for 6 days and 25±2 c under 45 – 50 μmol photon m 2s 1 of illumination of white fluorescent light (alternate 12 h/12 h of light/dark periods) [7]. the initial concentrations of microalgae and bacteria were 1.9×106 cells/ml and 104 cfu/ml respectively [7]. two different cultivation conditions of microalgae – bacteria for pome treatment, agitation and aeration conditions, were tested. for the agitation condition, pome treatment was incubated in incubator shaker at 25 c and 150 rpm. for the aeration condition, a shake flask containing pome and microbes was connected to an air pump (1.8 l/min) to provide aeration to the treatment system. a sterilized 0.22 μm nylon filter was used to avoid contamination. during cultivation, 2 ml of algae suspension was collected for every 2 days and filtered using 0.45 μm nylon filter before it was analyzed for ammonium, phosphorus and cod using their respective method. the growth of microalgae and bacteria were also recorded. 2.3 analytical methods microalgae cell number was calculated by neubauer haemocytometer counting and bacterial concentrations were determined as colony forming units (cfu) on nutrient media agar plates. besides that, the standard methods for the examination of water and wastewater were used to analyse ammonium, phosphorus and cod removal [8]. ammonium content was analysed using phenate method while phosphorus content (ortophosphate) was analysed using ascorbic acid method and cod was analysed using closed reflux, colorimetric method [7]. 2.4 kinetics study based on the best growth conditions (agitation or aeration) in terms of cod and nutrient removal, batch kinetics studies were carried out by using approximately 1.9 106 cells/ml and 104 cfu/ml of microalgae and bacteria initial concentration, respectively. they were cultivated in partially treated pome at room temperature (25±2 c). pome was diluted to study the kinetics of different n/p ratios. the removals and the growth of microalgae were recorded and analyzed for six days of treatment. kinetics coefficient, maximum specific growth rate, μmax (d 1) and half-saturation coefficient, ks (mg/l) were determined using lineweaver–burk plot of 1/ μ vs. 1/s. 3. results and discussion 3.1 pome treatment in agitation and aeration conditions the characteristic of the partially treated pome sample collected is tabulated in table 1. 24 iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 34.4 95.3 54.0 73.5 93.0 50.5 0.0 20.0 40.0 60.0 80.0 100.0 ammonium phosphorus cod p er ce nt ag e of r em ov al , % components agitation aeration table 1: characteristic of partially treated pome parameters concentration (mg/l), except for ph and turbidity average concentration (mg/l) ph 7.5 – 8.5 8 cod 600 – 900 750 ammonium 160 – 250 205 phosphorus 10 – 30 20 total suspended solid 1120 – 1160 1140 total volatile solid 880 – 1170 1025 turbidity (ntu) 2755 – 2785 2775 oil and grease content 118 234 176 in this study, microalgae were grown in non-sterilized partially treated pome under agitation and aeration cultivation conditions. throughout the treatment, the ph of pome was observed and measured. at day 0, the ph of pome samples was 7.5 and it increased to 8.8 after six days of treatment in both conditions. the percentage of ammonium, phosphorus, and cod removal by agitation and aeration conditions in non-autoclaved partially treated pome are illustrated in fig. 1. fig. 1: percentage of ammonium, phosphorus, and cod removal in agitation and aeration conditions by axenic microalgae in a 250 ml flask containing 150 ml nonsterilized partially treated pome with 10% concentration (vmicroalgae – bacteria /vpome) for 6 days at 25±2 c and under 45 – 50 μmol photon m 2s 1 of illumination of white fluorescent light (alternate 12 h/12 h periods of light/dark). initial concentration of ammonium = 162 mg/l, phosphorus = 18 mg/l and cod = 874 mg/l. error bars represent one standard deviation about the mean (n = 3). based on fig. 1, the removal of ammonium in aeration condition is 73.5% which is higher compared to that in agitation condition which is 34.4%. the ammonium removal percentage was in line with the growth rate of c. vulgaris which were 0.356 d 1 and 0.176 d 1 for aeration and agitation system respectively. similar results were obtained whereby the microalgae cultivated with air supply (aerated) recorded higher growth rate compared to the microalgae grown in mixing shaker (non-aerated system) [9]. the optimum turbulence effect created by aeration system promotes better cell growth which consequently helps in the removal of the nutrients. moreover, under equal light intensity, air flux is produced as a result of the turbulence and creates different movement regimes of the cells within the media. adequate turbulence enhances mass transfer of nutrients to the microalgae cell and 25 iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 promotes gas exchange that overcomes the photo-oxidative effect as well as minimizing thick boundary layer between microalgae cell and the surrounding condition of unstirred suspension. in addition to that, sufficient system turbulence enhances the microalgae reproduction compared to the non-aerated medium, which can cause biomass accumulation [9]. although the removals of phosphorus and cod in the agitation system were higher compared to those in the aeration system, the difference was very small, i.e. less than 5%. results indicated that the aeration system offered better nutrient removal especially for ammonium removal. therefore, the aeration system was chosen to be used in the subsequent experiment. 3.2 axenic and co-culture systems in aeration condition a co-culture system (c. vulgaris and a. brasilense) was utilized in the partially treated pome treatment. in this case, sterilized partially treated pome was used with initial concentration of 874 mg/l, 162 mg/l and 18 mg/l of cod ammonium and phosphorus, respectively. the microalgae – bacteria growth conditions were at 0.77 g/l (1.9×106 cells/ml), 104 cfu/ml and day 1.52 for microalgae initial concentration, bacteria initial concentration and bacteria inoculation time, respectively. pome treatment was conducted in the aeration condition. the growth profiles of microalgae – bacteria and percentage of nutrients and cod removals in axenic and microalgae – bacteria co-culture systems are shown in fig. 2 (a) and 2 (b), respectively. (a) (b) fig. 2: (a) growth profiles of bacteria (a. brasilense), microalgae (c. vulgaris) in axenic system and microalgae (c. vulgaris and a. brasilense) in co-culture system (b) percentage of ammonium, phosphorus and cod removals in aeration condition by axenic microalgae and co-culture microalgae – bacteria in a 250 ml flask containing 150 ml sterilized partially treated pome with 10% concentration (vmicroalgae – bacteria/vpome) for 6 days at 25±2 c, under 45 – 50 μmol photon m 2s 1 of illumination of white fluorescent light (alternate 12 h/12 h periods of light/dark) and aerated. initial concentration of ammonium = 162 mg/l, phosphorus = 18 mg/l and cod = 874 mg/l. error bars represent one standard deviation about the mean (n = 3). figure 2 (a) shows that, co-culture of microalgae and bacteria enhanced the microalgae population. the specific growth rate of co-cultured microalgae was higher (0.570 d 1), compared to that of axenic microalgae (0.228 d 1). similar results were obtained by a study that reported that the growth of c. vulgaris was significantly enhanced when co26 iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 immobilized with a. brasilense bacteria under aeration conditions (1.8 l/min) [3]. it was also reported that some bacteria species enhance microalgae cells growth [10]. however microalgae and bacteria have a complex relationship. it depends on the species of microlagae and bacteria as well as the growth conditions themselves [5,11]. mutual symbiosis between microalgae and bacteria can be achieved if the species and conditions were optimum for both microorganisms. the results showed that bacteria promoted the growth of microalgae when the initial concentration was suitable (104 cfu/ml) and cultivated under aeration conditions. a study reported that, at low bacteria concentration (102 cfu/ml), the effect of bacteria in the co-culture system was not significant towards the removal of the nutrients. on the other hand, low nutrient removal was also recorded at maximum bacteria concentration (106 cfu/ml) due to the competition of the nutrients between the bacteria and microalgae. at these conditions, the bacteria growth rate was higher than the microalgae growth rate, hence the utilization of nutrients was dominated by the bacteria cells [7]. in addition, a. brasilense bacterium was able to grow well with microalgae and partially treated pome with specific growth rates of 2.264 d 1. besides getting oxygen from the microalgae’s photosynthesis process, the aeration process helps to promote gaseous exchange and enhances mass transfer of nutrients in the system. moreover, excess oxygen from microalgae photosynthesis can be released from the media in the aeration system [10]. based on fig. 2 (b), the co-culture system has significantly increased the removals of cod and nutrients after six days of treatment, especially for ammonium and cod removal. the presence of bacteria delivers positive effect to the system. higher percentage removals of ammonium, phosphorus and cod were obtained for co-cultured c. vulgaris system (84%, 87.3% and 53.4%, respectively) compared to that from axenic c. vulgaris system (67.3%, 84.2%, and 41.1%, respectively). these results show better removals of cod and nutrients compared to another study that reported that microalgae from chlamydomonas incerta species removed 67.35% of cod with initial concentration of 250 mg/l in pome in 28 days [1]. ammonium removal in this study was sligthly lower (84%) compared to the previous study, which used spirulina plantesis to achieve 96.5% removal from approximately 296 mg/l of initial concentration [2]. comparison of doe standard and results of removals achieved by this study is presented in table 2. table 2: doe standard b and final results of removals achieved by this study doe standard b this study initial concentration final concentration axenic and cocultured system axenic system co-cultured system cod (mg/l) 200 874 514.8 ± 37.32 407.3 ± 32.95 ammonium (mg/l) 20 162 53 ± 4.97 25.9 ± 5.3 phosphorus (mg/l) 10* 18 2.84 ± 0.39 2.29 ± 0.15 * doe standard b for sewage discharge into enclosed water body results obtained in this study showed that, microalgae – bacteria co-cultured system exhibits a good potential to be applied in pome treatment within six days of cultivation compared to aerobic digestion process that required at least 20 days of treatment with final concentration 200, 52 and 12 mg/l of cod, nitrogen and phosphorus respectively [1].the co-cultured system also proves that, it enhances the cod and nutrient removal in the 27 iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 treatment compared to the axenic system. however, further investigation has to be conducted to improve cod removal in order to achieve the standard set by doe, malaysia, prior to discharge treated pome into the river. heterotrophic bacteria is one of the microorganisms that have an important role in the reduction of cod content by breaking down the organic matter in the wastewater. isolation and growth characterization of heterotrophic bacteria in partially treated pome sample could be investigated further in order to find more efficient bacteria to improve cod removals in pome. 3.3 kinetics studies of microalgae growth and nutrients removal there are two important nutrients for microalgae growth: phosphorus (p) and ammonium (n). kinetics constants were determined to study the rate of nutrients uptake by the microalgae. in this study, nutrients removal rates were calculated by eq. (1) [12]. (1) where r represents the removal rate of nutrients (n or p), c0 and ci represent initial concentration of nutrients and nutrient concentration at time ti respectively and ti is the time when there is no significant change of nutrient concentration. the specific nutrient removal rate, ri was determined by dividing r by the initial cell density (c. vulgaris). in these kinetic studies, two pome samples with different n/p ratio were utilized. the n/p ratio of media used for pome 1 and pome 2 were 8.96 and 2.27 respectively. the specific nutrient removal rate, ri of ammonium and phosphorus for both samples are shown in table 3. table 3: specific nutrient removal rate of ammonium and phosphorus in pome 1 and pome 2 the specific ammonium removal rates, rn for c. vulgaris grown in pome 1 and pome 2 were 29.42 and 4.64 mg g 1d 1 with initial ammonium concentration (pome 1 = 167 mg/l, pome 2 = 22.6 mg/l). these results showed that high rn was achieved when initial concentration of ammonium introduced was high. these results were in agreement with a previous study whereby the specific n removal rates of chlorella sp. grown in media with 9 and 56 n/p were 1.8 and 3.8 mg mg 1 chl a d 1 respectively [12]. furthermore, the other study observed that the specific n removal rates increased from 0.5 to 3 mg mg 1 chl a d 1 when the initial concentration of nh4+-n increased from 13.2 mg/l to 410 mg/l in synthetic wastewater [12]. in this study, a similar pattern of results was obtained for specific phosphorus removal rates, rp. the rp increased from 1.18 to 3.41 mg g 1d 1 with the increase of phosphorus initial concentration from 9.96 to 18.06 mg/l. slightly higher p concentration in the primary effluent also led to higher rp. chlorella sp. obtained 0.25 and 0.15 mg mg 1chl a d 1 for the diluted sludge centrate and the primary effluent with initial p, 4.0 and 3.5 mg/l respectively [12]. first-order and second-order reactions were tested for both nutrients removal to find the reaction constant. the reaction constant for first-order and second-order was calculated by eq (2) and (3), respectively [13]. samples n/p ratio rn (mg g 1d 1) rp (mg g 1d 1) pome 1 8.96 29.42 3.41 pome 2 2.27 4.64 1.18 28 iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 (2) (3) where or and or represent the concentration of ammonium or phosphorus at time and , respectively and is the reaction constant. graphs were plotted for both order reactions and in this study, the removal of phosphorus and ammonium fitted most to the first-order reaction since r2 in first-order reaction for both pome were higher than r2 in second-order reaction, as shown in table 4. this result was in line with a study that reported that the phosphorus and nitrogen removal in their study fitted the first-order reaction very well [12]. based on the nutrient consumption, the yield of biomass was determined by eq. (4), [11]. (4) where y represents the yield of biomass linked to the consumption of nutrients (phosphorus, p or ammonium, n), c0 is the initial nutrient concentration, ci is the concentration of nutrients when there was no significant decrease of nutrients, xi represents c. vulgaris cell density with respect to the nutrient ci and x0 is the initial c. vulgaris cell density [11]. the yield of biomass based on specific nutrient consumption and first order reaction rate constants are shown in table 5. table 4: value of r2 for first and second order reaction sample first-order second-order r2, p r2, n r2, np pome 1 0.9305 0.9565 0.9231 pome 2 0.8741 0.9127 0.8052 table 5: kinetics parameters of nutrients removal for c. vulgaris in pome 1 and pome 2 the biomass yield based on n consumption, yn, for c. vulgaris cultivated in pome 1 was lower than the yield in pome 2 which were 0.01406 g mg 1 n and 0.1751 g mg 1 n respectively. a similar result was obtained for yp, 0.1213 g mg 1 p and 0.6886 g mg-1 p for c. vulgaris grown in pome 1 and pome 2, respectively. the ratio of yp/yn, indicates the amount of the ratio of n/p required (mg n consumed/mg p consumed) to produce the same unit amount of biomass. in this study, n/p ratio of pome 1 was almost double the n/p ratio of pome 2. theoretically, the chemical formula of microalgae is c106 h181o45n16p where n/p ratio is 7.2 [14]. the yp/yn for c. vulgaris cultivated in pome 1 was 8.62, which is close to this theoretical value. in this study, the final n and p concentration in pome 1 were 25.9 and 2.3 mg/l respectively. this case was similar to the result obtained by a study that stated that p was the limiting nutrient for microalgae grown in pome 1. thus, the kinetic coefficients of sample kp kn yn yp yp/yn pome 1 0.3685 0.3272 0.01406 0.1213 8.6231 pome 2 0.1271 0.1383 0.1751 0.6886 3.9327 29 iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 microalgae growing in pome 1 were determined using lineweaver-burk equation (eq. (5)), where μ is specific growth rate (d 1), μmax is the maximum specific growth rate (d 1), s is the concentration of limiting nutrient (mg/l) and ks is half-saturation coefficient (mg/l). experimental data were plotted as illustrated in fig. 3 [11]. (5) fig. 3: lineweaver-burk plot used to estimate kinetic coefficient. based on the linear fit line for this plot (fig. 3), the kinetic coefficients μmax and ks of p removal by c. vulgaris were determined to be μmax = 0.192 d 1 and ks = 27.32 mg/l (r2 = 0.973). 4. conclusion as a conclusion, higher removal of ammonium from pome was obtained under aeration conditions (73.5%) compared to that of agitation conditions (34.4%). in addition, the microalgae – bacteria co-culture system showed higher removal of ammonium, phosphorus, and cod in pome (84%, 87.3% and 51.8%, respectively) compared to that in the axenic microalgae system (67%, 84.2% and 41.1%, respectively). the kinetic coefficients obtained were μmax = 0.192d 1 and ks = 27.32 mg/l. the obtained data showed that this co-culture system has the potential to improve the current aerobic digestion process in the wastewater treatment. the long hrt required by the aerobic treatment can be shortened by replacing or integrating with this co-culture system. moreover, this system also promotes green technology and can be considered for future commercial use. however, for cod removal, further investigation on pome treatment is required in order to achieve the standard set by doe, malaysia, prior to discharge into the river. acknowledgment this research was supported by research initiative grant scheme (rigs15-144-0144) from the international islamic university malaysia and ministry of higher education, malaysia. references [1] kamyab h, fadhil m, keyvanfar a, abd mz. (2015) efficiency of microalgae chlamydomonas on the removal of pollutants from palm oil mill effluent (pome). energy procedia, 75: 2400-2408. [2] hadiyanto, marcelinus c, danny s. (2013) phytoremediation of palm oil mill effluent 30 iium engineering journal, vol. 20, no. 2, 2019 samsudin et al. https://doi.org/10.31436/iiumej.v20i2.1109 (pome) by using aquatic plants and microalgae for biomass production, j. environ. sci. technol., 6(2): 79-90. [3] de-bashan le, hernandez jp, morey t, bashan y. (2004) microalgae growth-promoting bacteria as ‘helpers’ for microalgae: a novel approach for removing ammonium and phosphorus from municipal wastewater. water res., 38(2): 466-474. [4] hernandez j, luz e, bashan y. (2006) starvation enhances phosphorus removal from wastewater by the with azospirillum brasilense. enzyme microb. technol, 38: 190-198. [5] mujtaba g, rizwan m, lee k. (2015) simultaneous removal of inorganic nutrients and organic carbon by symbiotic co-culture of chlorella vulgaris and pseudomonas putida. biotechnol. bioprocess eng., 20(6): 1114-1122. [6] delgadillo-mirquez l, lopes f, taidi b, pareau d. (2016) nitrogen and phosphate removal from wastewater with a mixed microalgae and bacteria culture. biotechnol. reports, 11: 18– 26. [7] samsudin a, azmi as, mohd nawi mn, abdul halim a. (2018) wastewater treatment by microalgae-bacteria co-culture system. malays. j. microbiol., 14(2): 131-136. [8] apha. (1999) standard methods for the examination of water and wastewater part 4000 inorganic nonmetallic constituents standard methods for the examination of water and wastewater. [9] gonzalez le, bashan y. (2000) increased growth of the microalga chlorella vulgaris when coimmobilized and cocultured in alginate beads with the plant-growth-promoting bacterium azospirillum brasilense. appl. environ. microbiol., 66(4): 1527-1531. [10] hariz hb, takriff ms. (2017) growth and biomass production of native microalgae chlorella sp ., chlamydomonas sp . and scenedesmus sp . cultivated in palm oil mill effluent (pome) at different cultivation conditions. transactions on science and technology, 4(3): 298-311. [11] wang m, kuo-dahab wc, dolan s, park c. (2014) kinetics of nutrient removal and expression of extracellular polymeric substances of the microalgae , chlorella sp. in wastewater treatment. bioresour. technol., 154: 131-137. [12] aslan s , kapdan ik. (2006) batch kinetics of nitrogen and phosphorus removal from synthetic wastewater by algae. j. ecol. eng., 8: 64-70. [13] levenspiel, o. (1999). interpretation of batch reactor data. (3rd ed.) in : chemical reaction engineering (pp.38-63). new york, usa: john wiley & sons. [14] grobbelaar, ju. (2007). algal nutrition mineral nutrition, amos, r. (1st ed.) in : handbook of microalgae culture (pp. 95-115). new jersey, usa: blackwell publishing ltd. 31 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <feff004c006900650074006f006a00690065007400200161006f00730020006900650073007400610074012b006a0075006d00750073002c0020006c0061006900200069007a0076006500690064006f00740075002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c0020006b006100730020007000690065006d01130072006f00740069002000640072006f01610061006900200075007a01460113006d0075006d006100200064006f006b0075006d0065006e0074007500200073006b00610074012b01610061006e0061006900200075006e0020006400720075006b010101610061006e00610069002e00200049007a0076006500690064006f0074006f0073002000500044004600200064006f006b0075006d0065006e00740075007300200076006100720020006100740076011300720074002c00200069007a006d0061006e0074006f006a006f0074002000700072006f006700720061006d006d00750020004100630072006f00620061007400200075006e002000410064006f00620065002000520065006100640065007200200036002e003000200076006100690020006a00610075006e0101006b0075002000760065007200730069006a0075002e> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <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> /slv <feff005400650020006e006100730074006100760069007400760065002000750070006f0072006100620069007400650020007a00610020007500730074007600610072006a0061006e006a006500200064006f006b0075006d0065006e0074006f0076002000410064006f006200650020005000440046002c0020007000720069006d00650072006e006900680020007a00610020007a0061006e00650073006c006a006900760020006f0067006c0065006400200069006e0020007400690073006b0061006e006a006500200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e0074006f0076002e0020005500730074007600610072006a0065006e006500200064006f006b0075006d0065006e0074006500200050004400460020006a00650020006d006f0067006f010d00650020006f00640070007200650074006900200073002000700072006f006700720061006d006f006d00610020004100630072006f00620061007400200069006e002000410064006f00620065002000520065006100640065007200200036002e003000200074006500720020006e006f00760065006a01610069006d0069002e> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 parallel process discovery using a new time-based alpha++ miner yutika amelia effendi1* and riyanarto sarno2 1information systems study program, department of engineering, universitas airlangga, surabaya, indonesia 2department of informatics, institut teknologi sepuluh nopember, surabaya, indonesia *corresponding author: yutika.effendi@vokasi.unair.ac.id (received: 3rd h june 2019; accepted: 26th october 2019; published on-line: 20th january 2020) abstract: a lot of services in business processes lead information systems to build huge amounts of event logs that are difficult to observe. the event log will be analysed using a process discovery technique to mine the process model by implementing some well-known algorithms such as deterministic algorithms and heuristic algorithms. all of the algorithms have their own benefits and limitations in analysing and discovering the event log into process models. this research proposed a new time-based alpha++ miner with an improvement of the alpha++ miner and modified time-based alpha miner algorithm. the proposed miner is able to consider noise traces, loop, and non-free choice when modelling a process model where both of original algorithms cannot override those issues. a new time-based alpha++ miner utilizing time interval pattern can mine the process model using new rules defined by the time interval pattern using a double-time stamp event log and define sequence and parallel (and, or, and xor) relation. the original miners are only able to discover sequence and parallel (and and xor) relation. to know the differences between the original alpha++ miner and the new one including the process model and its relations, the evaluation using fitness and precision was done in this research. the results presented that the process model obtained by a new timebased alpha++ miner was better than that of the original alpha++ miner algorithm in terms of parallel or, handling noise, fitness value, and precision value. abstrak: banyak sistem perniagaan perkhidmatan menghasilkan sejumlah besar log data maklumat yang payah dipantau. log data ini akan dianalisis menggunakan teknik proses penemuan bagi memperoleh model proses dengan menerapkan beberapa algoritma terkenal, seperti algoritma deterministik dan algoritma heuristik. semua algoritma ini memiliki kehebatan dan kekurangannya dalam menganalisis dan mencari log data ke dalam model proses. kajian ini mencadangkan time-based alpha++ miner baru yang merupakan pembaharuan dari algoritma alpha++ miner dan modified timebased alpha miner. algoritma baru ini dapat mempertimbangkan kesan bunyi, pusingan, dan pilihan tidak bebas ketika memodelkan model proses di mana kedua algoritma asal tidak dapat menggantikan isu tersebut. time-based alpha++ miner baru mengguna pakai pola interval waktu berjaya memperoleh model proses menggunakan peraturan baru berdasarkan pola interval waktu menggunakan log peristiwa waktu-ganda dan menentukan jujukan dan hubungan selari (and, or, dan xor). dibandingkan algoritma asal, ia hanya dapat menemukan jujukan dan hubungan selari (and dan xor). bagi membezakan alpha++ miner asal dan yang baru termasuk model proses dan kaitannya, penilaian menggunakan nilai padanan dan penelitian telah dijalankan dalam kajian ini. hasil kajian model proses yang diperoleh oleh time-based alpha++ miner baru, adalah lebih baik keputusannya berbanding menggunakan algoritma alpha++ 126 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 miner asal, berdasarkan hubungan selari or, bunyi kawalan, nilai padanan, dan nilai penelitian. keywords: alpha++ miner; business process model; parallel process; process discovery; process mining; time interval pattern 1. introduction collections of activities that produce services for organizations or companies are called business processes [1]. a lot of services are available in the organization, which requires a means to handle all the services in an efficient way. information systems were built to facilitate business processes and produce event logs as the documented business processes. due to the huge amount of event logs, they will be difficult to observe manually. well-documented business processes are important because they act as navigator for organizations to operate and analyse their business processes. obtaining the model of business processes from those event logs is becoming a concern in order to monitor and improve business processes easily and automatically. a process mining technique is a good choice to solve this issue [2]. process mining consists of several tasks; one of them is process discovery. it is a method to automatically construct a current business process and record variations to the process that occurred within an organization. because process discovery is a part of the process mining technique, the main goal becomes to discover the process models from an event log that describes the best behaviour of this business process implemented in an organization [3]. to carry out its duties properly, process discovery uses some well-known algorithms to help analyse the event log, such as the deterministic algorithm [4], consisting of alpha miner and its renewal versions; alpha+ miner, alpha++ miner, and modified time-based alpha miner [5], or the heuristic algorithm [4] i.e. heuristics miner and fuzzy miner. all of these algorithms have their own limitations and benefits in analysing the event log. in this research, the improvement of alpha++ miner and modified timebased alpha miner, which were the latest improvements on alpha miner related to parallel findings, are the main highlights. this research proposes a new time-based alpha++ miner algorithm to mine a process model along with its relations based on a time interval pattern. the new timebased alpha++ miner is an upgraded version of the alpha++ miner [6] and modified time-based alpha miner [5]. as a process discovery algorithm, the alpha++ miner algorithm can handle loop and non-free choice in a business process. this algorithm brings implicit dependencies out of a process model in a petri net form for showing nonfree choice conditions. as an expansion of alpha miner, the steps to discover the model is exactly the same, with the alpha miner algorithm using a single-time stamp event log. however, the disadvantages of alpha++ are that it cannot distinguish the differences between and and or in parallel relations and still use sequential relations between activities to obtain a business process. in other words, the alpha++ algorithm can only determine whether the relations of business processes are sequential and parallel (and, xor) in a sequential way. on the other hand, a modified time-based alpha miner, usually known as a mtbam algorithm, is the latest update from alpha miner which uses time-based information in discovering the process model using a double-time stamp event log. this algorithm can discover sequence and parallel and, or, xor relation. however, this algorithm cannot mine length one loop (l1l), length two loop (l2l), and 127 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 non-free choice in the event log to be modelled in a business process. loop and non-free choice are included in the issues of process discovery. each issue of process discovery implies that the process discovery cannot present the overall information of an event log in a process model. the similarity between the two algorithms is that they do not consider the noise traces in the event log when obtaining a process model. to cover the shortcomings of the alpha++ miner and mtbam algorithm, an improvement of the alpha++ miner that utilizes time interval pattern is proposed in order to be able to discover process models, including discovering loop, non-free choice, as well as their sequential and parallel relations (and, or, xor) by determining new rules so that the business process cannot only be discovered in a sequential way. in addition, the new one can override noise traces when modelling a process model. to compare our method with the original alpha++ miner, fitness and precision will be presented as evaluation of the discovered process models in the experimental result. the paper is arranged in structured way. section ii is for related work, while in section iii the authors will explain the proposed method; a new time-based alpha++ miner with time interval pattern. discussion related to experimental results is put in section iv and section v will provide the conclusion to this paper. 2. literature review 2.1 process mining process mining is a study where data mining and machine learning are connected, then do analysis in business processes implemented in an organization. as a popular technique, process mining is always used to observe standard operating procedure (sop) based on event log run in the organization. the overview of process mining and its tasks is shown in fig. 1. as shown in the figure, process mining consists of several tasks, namely discovery, conformance, and enhancement [4]. first task is called process discovery. it is a method to automatically construct a current business process and occurrences of variations to the process that happened in an organization. because process discovery is a part of the process mining technique, discovering the process models from an event log that describes the best behaviour of the business process implemented in an organization becomes its main goal. a lot of process discovery techniques are suggested. several of them are alpha algorithm and heuristics miner algorithm. the goal of process discovery techniques is not only representing models that show the relations of activities. the other goal is discovering the social network between resources in business processes. conformance checking is the second task in process mining. it compares the behaviour captured in the process model and the behaviour captured in the event log. the value of conformance checking is higher if the process model captures more of the behaviour in the event log. it divides into four criteria: fitness, precision, simplicity, and generalization. the last task of process mining is enhancement. an enhancement extends or improves the process model which contains the information of the event log. there are two types of enhancement. first one is repairing a process model and the second one is extending the process model which refers to the information described in event log, such as durations or allocations. figure 2 shows the simple explanation of the three tasks in process mining. 128 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 fig. 1: mind map of process mining. fig. 2: the explanation of three tasks in process mining. 2.2 event log in the process mining technique, the event log becomes the main input. all three tasks of process mining consider that information systems are capable of recording events. an event log contains several processes. each process recorded in the event log is called a case. usually, a case is symbolized by a number in the event log and consists of a series of ordered events. the event log records several pieces of information about the event, such as activity, time stamp, and resource. activity indicates the name of the ordered event. time stamp indicates the time when the ordered event occurred. resource indicates the person who is doing the event. process mining might use those pieces of information to provide the best understanding of the real processes. table 1 shows a piece of the event log. this event log shows the selection acceptance of a journal. as shown, there are two types of processes. the first process is acceptance of a journal, which is displayed in case 1. the second process is rejection of a journal, which is displayed in case 2. in fact, not all event logs record only three types of information, like in table 1. there are several event logs that record other information to describe the process clearly. based on the time stamp, the event log can be divided into single-time stamp event log and double-time stamp event log. 129 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 table 1: an example of event log 2.2.1 single-time stamp event log initially, the single-time stamp event log is a form of general event log. the characteristic of the single-time stamp is to only have one time stamp for each activity. the most common time stamp recorded in the event log is a finish time. both alpha algorithm [7] and heuristics miner algorithm [8] use single-time stamps to analyse the business processes. an example of the single-time stamp event log is shown in table 1. 2.2.2 double-time stamp event log in some cases, using the single-time stamp event log makes the analysis of business processes difficult. it is because the single-time stamp only records the finish time of the activities, while sometimes the analysis needs to use both of the time stamps of activities to obtain a complete version of the process model. this matter is the reason that doubletime stamp event logs appeared. some algorithms use a double-time stamp event log to determine the model, such as heuristics miner with interval time [9] and modified timebased alpha miner [5]. the characteristic of the double-time stamp is to have a start time and a finish time. because the two time stamps are recorded, they can help solving parallel processes in process mining. this research will use a double-time stamp event log to model the business process. 2.3 existing algorithm of process discovery in process discovery, issues appeared during the implementation to discover the model. this becomes the main concern in process discovery. many algorithms are proposed to handle the issues. the algorithms are divided into two principal categories, namely deterministic algorithms consisting of alpha, alpha+, alpha++, and heuristic algorithms consisting of heuristics miner, heuristics miner with time interval, and fuzzy miner. all of these algorithms have their own limitations and excellences in analysing the event log to model the business processes. therefore, process discovery in terms of modifying the algorithms becomes the most challenging task for researcher. deterministic algorithms define reproducible results [10]. a concept of deterministic algorithms is that behaviours of inputs become behaviours of results. it means that this algorithm delivers all behaviours of event log in the process model. alpha algorithm is a 130 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 deterministic algorithm and it has several modifications, such as alpha+ and alpha++ algorithm. 2.3.1 alpha algorithm alpha algorithm is the first algorithm used in process discovery. it develops causality of activities based on the event log. the event log used in alpha algorithm is a single time-stamped event log. the alpha algorithm focuses on the workflow process and is displayed in the form of workflow-nets, which are also part of petri nets [7]. to build a process model using alpha algorithm [4], the first step is to list all activities that are recorded in the event log. next, a set of beginning activities and a set of last activities are created. a set of beginning activities contains activities that are recorded first for some cases. meanwhile, a set of last activities consists of activities that occur as end activities of some cases. in the third step, several tuples are created. in the fourth step a set of tuples is obtained from the third step by taking the activities as well as the set inclusion [7]. the fifth step is listing places that connect activities in every tuple constructed, based on the fourth step. the last step is to connect places with their respective activities and a petri net is formed. alpha algorithm is a basic algorithm and easy to apply. however, alpha algorithms have some disadvantages. alpha algorithm cannot deal with short loop, long loop, invisible task, and non-free choice. because alpha algorithm cannot handle several issues, other deterministic algorithms appear to improve alpha algorithm. those algorithms are alpha+ algorithm and alpha++ algorithm. 2.3.2 alpha+ algorithm alpha+ algorithm is an advanced form of alpha algorithm. alpha+ focuses on dealing with short loop conditions [4,5,11]. both alpha and alpha+ algorithms do not consider noise in the event log. this algorithm assumes that all information in the event log is correct in order to build an output model, usually presented in a petri-net form. to obtain a petri net using alpha+ algorithm, there are several steps that must be followed [11]. the first step is to list all of activities based on the event log. the second step is to list activities that have dependency relations with itself (have one loop condition). the third step is to create a set of activities that do not consist of one loop activities. the fourth step is to create a set of arcs that connect one loop activities. the fifth step is to discover a workflow net from a set of activities from the third step. the sixth step is combine the fifth step and the fourth step to build a petri net. it can be concluded that alpha+ algorithm cannot deal with skip conditions. the other disadvantage of alpha+ algorithm is that it cannot override noise traces when modelling a process. 2.3.3 alpha++ algorithm alpha++ algorithm is also an expansion of the alpha algorithm. it offers a method for handling non-free choice. this algorithm also brings implicit dependencies out of the process model in a petri net form for showing non-free choice conditions. the alpha++ algorithm states that this algorithm is able to discover explicit and implicit dependencies between tasks. alpha++ algorithm has several steps to mine non-free choice conditions [12]. an outline of the steps is determining possible implicit dependencies between activities and reducing the possible implicit dependencies by several steps. the obtained implicit dependencies will be added in a process model as the output of the alpha++ algorithm. the alpha++ algorithm has the same disadvantages as the alpha+ algorithm. however, 131 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 the alpha++ algorithm has an extra advantage. that is handling non-free choice conditions. 2.3.4 modified time-based alpha algorithm modified time-based alpha algorithm (mtbam) is the latest update on the deterministic algorithm [5]. this algorithm uses time-based information from a doubletime stamp event log to discover the model. not only is it able to take advantage of the double-time stamp event log, but it is also able to define or relationships in a process model. however, although this algorithm can overcome some of alpha miner’s weaknesses, it still cannot discover loops, non-free choices, and it also cannot override noise traces when modelling a process. 3. research method this section presents the event log, temporal pattern and integrated discovery approach for discovering business processes in this research. 3.1 differentiation of parallel relations of activities a process model has relations to connect all activities. relations in the process model consist of a sequence and parallel relations. sequence relation is a relation to connect one activity to another activity directly. parallel relations are divided into and, xor, and or. each parallel relation will be presented in petri nets form as in table 2. table 2: parallel relations presented in petri nets almost all algorithms in process discovery can distinguish and and xor relations correctly, but not or relations. or relations have high possibilities of appearing in the process model, but a lot of algorithms have difficulty in classifying or relations. many algorithms will construe or relations into xor or and whereas these two relations are very different from the function of the or relation. 3.2 a new time-based alpha++ miner with time interval pattern a new time-based alpha++ miner algorithm will be introduced in this section. this algorithm is divided into three steps: defining the double-time stamp event log, determining the sequence relation, classifying the parallel relation, defining the loop condition and non-free choice, and the last, establishing the process model. 3.2.1 defining the double-time stamp event log the double-time stamp event log will be used as an input in this research. however, if there is only a single-time stamp provided in an organization, using the technique explained in [5], a single-time stamp event log can be converted into a double-time stamp event log. after it is obtained, the next step is to determine the relations. in this step, we will pay attention to noise traces in the event log. the event log will be processed without 132 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 noise, with 10% noise, with 30% noise, and with 50% noise. we separate the discovery process based on noise traces because they will affect the obtained process model as well as the fitness and precision values. 3.2.2 determining the relations as explained in section 3.1, relations in process model consist of sequence and parallel and, or, xor relations. however, besides those relations, there are conditions wherein the activities proceed to themselves again or return to the previous activity rather than advance to the next activity. this is known as a loop condition [13]. other than that, non-free choice is also an issue to be solved. the inability to identify a non-free choice process is one of the issues in discovering process models. this is because several processes implement non-free choice. for example, consider the selection of provinces and cities in software systems. usually, the choice of cities appears appropriate to the selected province. the city cannot be chosen if it is not a part of the selected province. it means that the selection of provinces and cities is a non-free choice process. this research proposes definitions to determine the sequence and parallel relations from an event log considering noise traces by utilizing a time interval pattern. the definitions in the proposed algorithm are: definition 3.1 there are event log (el) and trace ( ) wherein el. the types of time interval pattern between activity x and activity y; x (xs, xf) and y (ys, yf), according to which x,y el can be classified into before, meet, is-started-by, is-completed-with, overlap, contain, and equal. definition 3.2 based on event log (el), trace ( ) and activities x,y el, the relations of process models both sequential and parallel can be distinguished as follows: notrelated, yx # iff xyyx sequence, yx iff xyyx parallel, yx || iff }@{ yxyxyxyxyxxyyx f and, yx iff yx || and there is no yx in in el or, yx iff yx || and there is yx in in el xor, yx iff yx || if there is only x or y in in el 3.2.3 establishing a process model this research proposed how to discover process models using a new time-based α++ miner algorithm. there are 10 steps in this proposed algorithm to obtain the process model. step i. a double-time stamp event log is an input step ii. define place (before and after), start activities, end activities, loop, nonfree choice, relations, and rule numbers in time interval pattern ii.1 steps to determine the loop: (1) where: : loop : activity : transition between activities 133 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 : workflow of process model ii.2 steps to set the rules in the time interval pattern the model of time interval pattern is based on a double-time stamp to mine the process model. [14] introduced the use of time-based process mining algorithms. in her research, the definition of a time-based process mining algorithm consists of before and meets, overlaps, contains, is-finished-by, equals, and starts. in this research, we specify and categorize an improvement of time interval pattern between activities in business processes. we divide the sequence relations into before and meet, whereas parallel relations become is-started-by, is-completed-with, overlap, contain and equal. table 3 presents the rules and the relations proposed in this research. table 3: rules of determining activity relations by algorithm with hmm number rules relations 1 before : wherein yx iff sf yx sequence 2 meet : wherein yx iff sf yx sequence 3 is-started-by : wherein yx f iff fsssff xyyxyx parallel 4 is-completed-with: wherein yx iff ffss yxyx parallel 5 overlap: wherein yx iff ffsf yxyx parallel 6 contain:wherein yx @ iff ffsfss yxxyyx parallel 7 equal: wherein yx iff ffss yxyx parallel ii.3 steps to specify the parallel relations: xor relation if avg ppm ≤ min asr in el, then xor (2) or relation if min asr ≤ avg ppm ≤ avg asr in el, then or (3) and relation if avg asr ≤ avg ppm in el, then and (4) where: min asr : minimum value of all sequential relations in el avg asr : average of all sequential relations in el 134 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 avg ppm : average of parallel relations with the same parent activity in process model (the frequency of each activity is both directly and indirectly followed by another activity) step iii. generate process models by following these steps: iii.1 generate set of transition }|{ tttt ll (5) iii.2 generate set of input )}(|{ firsttttt li (6) iii.3 generate set of output )}(|{ lasttttt lo (7) iii.4 generate the places },{}),(|{ ),( lllbal oiybapp (8) step iv. display the final result of business process in petri net [15] ),,()( lll ftpl (9) where: α : a business process in petri net form p : place in the business process, it is symbolized by circle shape and named as p1, p2, p3, etc. t : transition in the business process, it shows the activities with square shape f : function in the business process, function means an arc. f = {p x t} means the arc connects the place (p) and transition (t) step v. evaluation of the process model using fitness and precision [16,17]. 4. results and discussion the experimental results will present the process model to prove that our new approach can mine business processes using a new time-based alpha++ miner algorithm utilizing a time interval pattern. 4.1 case study and event log a) case study the experiment data are business processes in a textile industry where the event log is generated from pt. xyz, a yarn production company in jakarta, indonesia. the business processes of pt. xyz consist of 11 activities as described in table 4. the pieces of the event log from pt. xyz are shown in table 5. the process model will be presented in a petri net form [15,18]. b) data set the case study uses a double-time stamp event log that has information including case id, activities, start time, and finish time. this event log contains 50 cases in four conditions. these conditions are event log without noise, event log with 10% noise, event log with 30% noise, and event log with 50% noise. the event log after being processed using the proposed method explained in section 3 in this experiment is presented in table 6. 135 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 table 4: lists of activities activities activity code used in this experiment getting-good-receive a opening-blending-bale b opposing-spike c blowing-air d striking-cotton e carding f framing-drawing g framing-roving h combing i framing-ring j winding-cone k table 5: part of event log table 6: event log after being processed using proposed method place (before) place (after) start activities finish activities relation rule number pp1 pp2 a b sequence 2 pp2 pp3 b c,d parallel 5 pp3 pp4 c,d e parallel 5 pp4 pp5 e f sequence 1 pp5 pp6 f g,h parallel 6 pp6 pp7 g,h i parallel 7 pp7 pp8 i j sequence 1 pp8 pp8 j j sequence 2 pp8 pp9 j k sequence 1 pp9 pp10 k e 1 4.2 experimental results based on the event log in table 5, there are sequence and parallel activities in the business processes of pt. xyz. all activities are in sequence relations except for: opposing-spike, blowing-air, framing-roving, and framing-drawing. activities of opposing-spike and blowing-air are parallel following rule number 5 according to section 136 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 3, meanwhile activities framing-drawing and framing-roving follow rule number 6 (contain) and 7 (equal) respectively. therefore, four of them are parallel relations. by implementing a new time-based alpha++ algorithm for parallel processes utilizing a time interval pattern as explained in section 3 and by following all steps, the final process model is described in fig. 3. the type of parallel relations in the process model after (2), (3), and (4) are applied, are also shown in table 7. fig. 3: process model obtained by using proposed algorithm. table 7: relations of process model generated by proposed algorithm place (before) place (after) start activities finish activities relation pp1 pp2 a b sequence pp2 pp3 b c,d parallel and pp3 pp4 c,d e parallel and pp4 pp5 e f sequence pp5 pp6 f g,h parallel or pp6 pp7 g,h i parallel or pp7 pp8 i j sequence pp8 pp8 j j sequence pp8 pp9 j k sequence pp9 pp10 k e the evaluation by the proposed algorithm was also tried out in event logs that contain 10% noise, 30% noise, and 50% noise. the percentage of noise shows the total of cases that are noise in the event log. for example, 10% noise means that 10% of all cases restored in the event log are noise. based on the experiments, the process models from those event logs are the same as the process model displayed in fig. 3. this research also presents the results of the same case study and event log processed by the original alpha++ algorithm in order to compare and prove that our proposed algorithm can discover the process model better than that of the original alpha++ miner. the process model of the alpha++ miner will be obtained using prom [19,20], a process mining tool to accelerate the process discovery. fig.4 shows the resulting process model and table 8 presents the result of its relations. 137 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 fig. 4: process model obtained by applying alpha++ miner. table 8: relations of process model generated by original algorithm start activities finish activities relation a b sequence b c,d parallel and c,d e parallel and e f sequence f g,h parallel xor g,h i parallel xor i j sequence j j sequence j k sequence k e the results presented in fig. 4 and table 8 show that alpha++ miner cannot define an or relation in a process model and considers it as an xor relation. the reason for this is that the original alpha++ miner has difficulties in interpreting the or relation and is only able to define either and or xor relations, so it automatically construes or relations into xor or and if there is an or relation in the process model, whereas these two relations are very different from the function of or relation. 4.3 evaluation of the business processes the quality of an algorithm can be measured from the results of that algorithm. in the data mining context, especially clustering and classification, the proposed algorithm is measured based on the obtained classes of respective data. the accuracy, recall, and precision are mostly used criteria to measure the quality of data mining algorithms. process mining also has several criteria to measure the quality of algorithms [4,16]. there are fitness, precision, generalization, and simplicity. our proposed algorithm for parallel processes utilizing time interval pattern is evaluated by measuring fitness and precision value. 138 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 the definition of fitness is the total number of cases in the event log displayed in the process model. fitness is measured using the formula explained in [15]. [15] reviewed that there are two ways to calculate the fitness of an obtained process model. the first way measures the fitness by calculating the percentage of activities that can be generated in the process model. the second way is by calculating the percentage of traces that can be represented in the process model. this evaluation uses the second way to calculate fitness. the equation of the second way is shown in (10). fitness ct t n n (10) table 9: the details of fitness and precision of the proposed algorithm process model of event log fitness precision nct nt result nctm ntm result event log without noise 50 50 1 16 16 1 event log with 10% noise 45 50 0,9 16 16 1 event log with 30% noise 35 50 0,7 16 16 1 event log with 50% noise 25 50 0,5 16 16 1 the precision measures how many traces in process model occur in the event log. the precision can be calculated from the total of correct traces divided by the total of all traces that are generated from process model. the correct traces are combination traces that are generated from the process model and occur in the event log. the equation of precision is shown in (11). precision= ctm tm n n (11) this evaluation measures the quality of the proposed algorithm based on the process models, as shown in fig. 3. the calculation details of fitness using (10) and precision by applied (11) of the proposed algorithm are presented in table 9. the final fitness and precision of the proposed algorithm as well as the original algorithm for parallel processes are shown in table 10. based on table 10, the proposed algorithm for parallel processes has relatively high fitness and high precision to produce a process model from the event log without noise or with noise of 10%, 30%, and 50% compared with the original alpha++ miner itself. table 10: the comparison of fitness and precision from both proposed and original algorithm algorithm fitness precision a new time-based alpha++ miner 0.7 1 original alpha++ miner 0.6 0.83 139 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 5. conclusions the conclusions for this paper are as follows: • this research paper focused on introducing a new approach to mine parallel business processes using a time interval pattern that was implemented in alpha++ miner algorithm. the proposed method defined seven types of time interval patterns which included both sequence and parallel relations and grouped them into rules. • a new time-based alpha++ algorithm was an upgraded version of alpha++ miner algorithm. compared to original alpha++ miner algorithm, the improved algorithm could detect sequence and parallel time stamp using time interval pattern and identifies them as sequence and parallel processes, discovered loop, determined non-free choice, and also distinguished and, or, xor relations in a correct way. meanwhile, alpha++ miner algorithm was not able to define the differences between or and xor in parallel relations according to the results of the experiment. • the experimental results proved that our new process discovery approach could mine the business processes with parallel and and or relations, which could not be obtained by the original alpha++ miner algorithm. in addition, the results of fitness and precision also clearly stated that a new time-based alpha++ also gave better results rather than that of the original alpha++ miner algorithm. references [1] sienou a, karduck ap, lamine e, pingaud h. (2018) business process and risk models enrichment: considerations for business intelligence. ieee international conference on ebusiness engineering. doi: 10.1109/icebe.2008.123 [2] peña mr, bayona-oré s. (2018) process mining and automatic process discovery. 7th international conference on software process improvement (cimps). doi: 10.1109/cimps.2018.8625621 [3] saylam r, sahingoz ok. (2013) process mining in business process management: concepts and challenges. international conference on electronics, computer and computation (icecco). doi: 10.1109/icecco.2013.6718246 [4] van der aalst wmp. (2011) process mining: discovery, conformance and enhancement of business processes. springer science and business media. http://dx.doi.org/10.1007/978-3642-19345-3 [5] effendi ya, sarno r. (2018) modeling parallel business process using modified time-based alpha miner. international journal of innovative computing, information and control, 14(5). doi: 10.24507/ijicic.14.05.1565 [6] wen l, van der aalst wmp, wang j, sun j. (2007) mining process models with non-freechoice constructs. data mining and knowledge discovery, 15(2):145-180. [7] van der aalst wmp, weijters t, maruster l. (2004) workflow mining: discovering process models from event logs. ieee transactions on knowledge and data engineering, 16(9):1128-1142. [8] weijters ajmm, van der aalst wmp, alves de medeiros ak. (2006) process mining with the heuristic-miner algorithm. technische universiteit eindhoven, tech. rep. wp, 166:1-34. [9] burattin a, sperduti a. (2010) heuristics miner for time intervals. european symposium on artificial neural networks computational intelligence and machine learning, d-side publi., isbn 2-930307-10-2. [10] gehrke n, werner m. (2013) process mining. das wirtschaftwachstum, 42(7):934-943. 140 iium engineering journal, vol. 21, no. 1, 2021 effendi and sarno https://doi.org/10.31436/iiumej.v21i1.1173 [11] alves de medeiros ak. (2004) process mining: extending the α-algorithm to mine short loops. eindhoven, netherland: beta working paper series, wp 113, eindhoven university of technology, eindhoven. [12] wen l, van der aalst wmp, wang j, sun j. (2007) mining process models with non-freechoice constructs. data mining and knowledge discovery, 15(2):145-180. [13] sarno r, effendi ya, haryadita f. (2016) modified time-based heuristics miner for parallel business processes. international review on computers and software (irecos), 11 (3):249260. http://doi.org/10.15866/irecos.v11i3.8717 [14] sutrisnowati ra, bae h, dongha l, minsoo k. (2014) process model discovery based on activity lifespan. international conference on technology innovation and industrial management, pp.137-156. http://dx.doi.org/10.1016/j.eswa.2014.05.055 [15] effendi ya, sarno r. (2018) implementation of the semantic web in business process modeling using petri nets,” international conference on information and communications technology (icoiact). doi: 10.1109/icoiact.2018.8350724 [16] effendi ya, sarno r. (2018) conformance checking evaluation of process discovery using modified alpha++ miner algorithm. international seminar on application for technology of information and communication, pp. 435 – 440. doi: 10.1109/isemantic.2018.8549770. [17] burattin a, maggi fm, sperduti a. (2016) conformance checking based on multi-perspective declarative process models. expert systems with applications, 65:194-211. doi: 10.1016/j.eswa.2016.08.040 [18] ishihara k, hiraishi k. (2001) the completeness of linear logic for petri net models. logic journal of the igpl, 9(4):549 567. doi: 10.1093/jigpal/9.4.549 [19] de cnudde s, claes j, poels g. (2014) improving the quality of the heuristics miner in prom 6.2. expert system with application, 41:7678-7690. [20] van dongen bf, verbeek hmw, van der aalst wmp, de medeiros aka, weijters ajmm. (2005) the prom framework: a new era in process mining tool support. 26th international conference applications and theory of petri nets (icatpn). doi: 10.1007/11494744_25 141 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <feff0633062a062e062f0645002006470630064700200627064406250639062f0627062f0627062a002006440625064606340627062100200648062b062706260642002000410064006f006200650020005000440046002006450646062706330628062900200644063906310636002006480637062806270639062900200648062b06270626064200200627064406230639064506270644002e00200020064a06450643064600200641062a062d00200648062b0627062606420020005000440046002006270644062a064a0020062a0645002006250646063406270626064706270020062806270633062a062e062f062706450020004100630072006f00620061007400200648002000410064006f00620065002000520065006100640065007200200036002e00300020064806450627002006280639062f0647002e> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice a comparative study on treatment technologies for sewage reclamation: a focus on the disinfection process iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 a comparative study on treatment technologies for sewage reclamation: a focus on the disinfection process noorini izzati mohamad mazuki1, teow yeit haan1,2* and abdul wahab mohammad1,2 1department of chemical engineering and process, 2research centre for sustainable process technology (cespro), faculty of engineering and built environment, universiti kebangsaan malaysia, 43600 ukm bangi, selangor darul ehsan, malaysia *corresponding author: yh_teow@ukm.edu.my (received: 24th september 2019; accepted: 8th april 2020; published on-line: 4th july 2020) abstract: selection of suitable disinfection technology is necessary with regards to wastewater reclamation goals. in this work, the performance of various disinfection technologies single disinfection units and integrated disinfection systems on local sewage was studied for non-potable reuse. disinfection units used as stand-alone units include ultraviolet (uv) disinfection, chlorination, microfiltration (mf), and ultrafiltration (uf). the integrated disinfection system consists of uv or chlorination as the primary disinfection unit incorporated with either mf, uf, multi-media or granular activated carbon as pre-treatment. the performance of these disinfection units and integrated processes were evaluated based on the percentage of removal of biochemical oxygen demand, chemical oxygen demand, total suspended solids, ammoniacal nitrogen, nitrate nitrogen, phosphorus, escherichia coli, and trihalomethane in bench-scale disinfection systems. the single unit of pes20kda membrane and the integrated disinfection system of uf-cl showed the most effective treatment among single disinfection units and integrated systems, respectively. the results showed that almost all disinfection units and integrated disinfection processes were useable for restricted and unrestricted area non-potable applications according to united state environmental protection agency (us epa) water reuse guidelines and managed to fulfil singapore grey water quality for recycling. abstrak: pemilihan teknologi penyahjangkitan kuman yang sesuai adalah perlu selaras dengan matlamat pemulihgunaan air buangan. kajian ini adalah tentang prestasi pelbagai teknologi penyahjangkitan kuman unit tunggal penyahjangkitan kuman dan sistem penyahjangkitan kuman bersepadu pada air sisa kumbahan tempatan dikaji bagi penggunaan semula air minuman. unit tunggal penyahjangkitan kuman yang digunakan mempunyai penyahjangkitan kuman ultraungu (uv), pengklorinan, mikro penurasan (mf), dan ultra penurasan (uf). manakala, sistem penyahjangkitan kuman bersepadu terdiri daripada uv atau pengklorinan sebagai unit penyahjangkitan kuman utama yang digabungkan bersama samada dengan mf, uf, multi-media atau karbon teraktif berbutir sebagai proses pra-rawatan. prestasi unit tunggal penyahjangkitan kuman dan prosesproses bersepadu dinilai berdasarkan pada peratus penyingkiran keperluan oksigen biokimia, permintaan oksigen kimia, jumlah pepejal terampai, nitrogen ammonia, nitrogen nitrat, fosforus, escherichia coli, dan trihalometana dalam sistem penyahjangkitan kuman berskala-makmal. unit tunggal penurasan ultra membran pes20kda dan sistem penyahjangkitan kuman bersepadu uf-cl menunjukkan masing80 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 masing paling efektif dalam rawatan unit tunggal dan sistem penyahjangkitan kuman bersepadu. keputusan menunjukkan bahawa hampir semua unit tunggal penyahjangkitan kuman dan proses penyahjangkitan kuman bersepadu boleh diguna pakai bagi aplikasi terhad dan tidak terhad mengikut garis panduan penggunaan semula air sisa rawatan yang ditetapkan oleh agensi pelindungan alam sekitar amerika syarikat (us epa) dan kualiti kitar semula air sisa singapura. keywords: sewage reclamation; single disinfection unit; integrated disinfection system; water reuse; escherichia coli 1. introduction sewage reclamation has been widely practiced in various regions around the world, in line with increasing water demand and public awareness related to safe and clean water issues. meanwhile, various studies are still on-going on the potential of wastewater reclamation and reuse in malaysia. in early 2015, malaysia faced water shortages that affected more than seven million users in the klang valley, due to drought which led to the reduction of the water level at the sungai selangor dam [1]. this issue indicates the importance of sustainable water management since there is no guarantee of constant water supply even for high rainfall countries. about 4,500 mld of sewage equivalent to 25% of national potable water is being treated in indah water konsortium (iwk) sewerage treatment plant (stp) in malaysia per day with 96.7% sanitation coverage available in urban areas [2-4]. hence, sewage effluent should be considered as a valuable resource and can provide important positive trade-off to overcome the water crisis in this country. sewage in malaysia is commonly allowed to undergo preliminary, primary, and secondary treatments before being discharged into the environment. typically, centralized stps produced high-quality final discharge effluent that is well below the department of environment (doe) malaysia standard a limit [5]. given the intent to promote the reuse of treated sewage, which is considered to be a green technology initiative, the treated effluent could be used as a water resource for non-potable applications. however, the raw effluent is unsafe for direct use as it still contains high concentration of pathogens (both salmonella spp. and escherichia coli (e. coli) that were present at 105 cfu/100 ml in malaysia sewage discharged effluent) [6]. therefore, it is important to disinfect the final discharge effluent prior to its supply to end users to lower the risk of biological hazard. chlorination and ultraviolet (uv) processes are the most extensively used disinfection technologies. chlorination has been widely investigated in the past several decades for wastewater applications. despite numerous advantages offered by chlorination, its potential generation of carcinogenic disinfection by-products (dbps) has made it a less favourable disinfectant [7]. on the other hand, the adoption of uv light for wastewater disinfection has grown significantly to compete with chlorination since it would not produce toxic treated effluent, is safe in operation, and has a small footprint [8,9]. today, thousands of municipalities in north america have converted from chemical-based disinfection technology such as chlorine gas to uv [10]. as the efficiency of chlorination and uv disinfection varied depending on the characteristics of sewage’s discharged effluent, both systems were suggested to be coupled with an advanced technology that could act as a physical pre-treatment prior to the primary disinfection process in order to enhance the effectiveness of chlorination or uv disinfection and improve the quality of the treated effluent to meet with the stringent wastewater reuse limit established by united state environmental protection agency (us 81 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 epa) and by other countries [11]. membrane filtration and adsorption process could be applied as the pre-treatment to reduce the colloidal and particulate constituents in wastewater to enhance the effectiveness of the primary disinfection unit. adsorption technology using granular activated carbon (gac) is a good option for the removal of macro-contaminants. gac could perform dual functions as an adsorbent and filter to the influent. its ability as a macrofilter-adsorbent medium has attracted strong interest from many parties to utilize at various wastewater treatment plants [12-15]. on the other hand, membrane filtration applying a physical separation mechanism in its operating process is well-known to be able remove microbial and contaminants in sewage. microfiltration (mf) and ultrafiltration (uf) are the membranes commonly used to remove microorganisms and turbidity. the selection on the feasible disinfection technology must be done accordingly, suitable to the target sewage reclamation’s objective. unfortunately, there are still limited numbers of studies that provide technical feasibility information on the implementation of disinfection technology in malaysia for sewage reclamation. hence, this research aims to study and evaluate the performance of various commercially available single disinfection units and integrated disinfection systems on malaysia sewage for non-potable water reuse applications. 2. materials and methods 2.1 sampling of final discharge effluent effluent used in this study was collected from a secondary effluent discharge drain at stp located in selangor, malaysia. currently, the plant operates up to secondary treatment using sequencing batch reactor (sbr) system. the raw effluent discharged from this plant was stipulated under standard b limits based on the department of environment (doe) standard. characterization of raw effluent was done immediately after each sampling to ensure the reliability of the measurements. in this study, 30 l volume of sample was required for each experiment. hence each experiment was conducted using different batches of raw effluent. 2.2 materials a calcium hypochlorite [ca(clo)₂] tablet manufactured by tosoh corporation, japan was used as the chlorine source. four different types of commercial flat sheet membranes: two mf membranes and two uf membranes were used in this study. hvlp00010 and pvdf021m membranes having membrane pore size of 0.45 μm and 0.2 μm were used to represent the mf membranes, respectively. meanwhile, pvdf1001m and pes20kda membranes having molecular weight cut-off (mwco) at 100 kda and 20 kda each were selected to represent uf membranes, respectively. gac (mesh size: 8×30, iodine value: 1000 to 1200 mg/g, ash content: < 3%) synthesized by laju carbon products sdn. bhd, malaysia was used as the adsorbent for pre-treatment prior to the disinfection process. environ multi-media (emm) capsule (height: 6 cm, diameter: 2 cm) acted as the housing for gac was supplied by envirosource (m) sdn. bhd, malaysia. 2.3 bench-scale integrated disinfection system the single disinfection units involved in this study include uv, chlorination, mf, and uf. whereas, for integrated disinfection processes, uv disinfection and chlorination acted as the primary disinfection unit incorporated with mf, uf, emm or gac as the pretreatment unit. 82 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 figure 1 shows the schematic diagram of the bench-scale integrated disinfection system comprising of mf/uf-chlorination and mf/uf-uv. fig. 2 shows the schematic diagram of a bench-scale integrated disinfection system comprising of gac/emmchlorination and gac/emm-uv. fig. 1: schematic diagram of bench-scale integrated disinfection system (mf/ufchlorination and mf/ufuv) with sampling points: (1) at feed tank (2) at discharge point after the membrane unit (3) at uv disinfection tank (4) at chlorine contact basin. fig. 2: schematic diagram of bench-scale integrated disinfection system (gac/emm column-chlorination and gac/emm column–uv) with sampling points: (1) at feed tank (2) at discharge point of gac/emm column (3) at uv disinfection tank (4) at chlorine contact basin. 2.3.1 preliminary study preliminary study was conducted for uv disinfection and chlorination to investigate the optimum uv dosage and chlorine dosage in treating raw effluent. the selection of optimum uv dosage and chlorine dosage was determined at the condition when there was no e. coli detected in the treated effluent. a) uv disinfection uv exposure time in treating raw effluent was varied for 5 minutes, 30 minutes, 60 minutes, 120 minutes, and 180 minutes while the intensity of uv lamp was kept constant at 15 watts. 83 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 b) chlorination chlorine dosage applied for the raw effluent ranged from 0 mg/l to 30 mg/l while the contact time for chlorine treatment was kept constant at 30 minutes. 2.3.2 disinfection technology a) gac gac/emm adsorption column was filled with gac at a filling ratio of 0.5. next, the raw effluent was fed into gac/emm adsorption column from the top at constant flow rate of 50 l/day with empty bed contact time (ebct) at 12.73 minutes. b) emm emm capsules used for emm pre-treatment were half-filled with gac and closed tightly. emm pre-treatment was carried out in a gac/emm adsorption column where the emm capsules were used to replace gac in adsorption column at a filling ratio of 0.5. subsequently, the raw effluent was fed into the gac/emm adsorption column from the top at constant flow rate of 50 l/day. the pre-treated raw effluent was then transferred to the primary disinfection unit for further treatment. c) membrane filtration the commercial flat sheet membrane was cut into a rectangular shape (19.1 cm × 14.0 cm) with membrane effective surface area of 155 cm2, laid on top of the cross-flow stainless steel membrane test cell unit and clamped tightly. operating pressure for both mf and uf membranes was 2 bar. the permeate flux (j) was determined using eq. (1): (1) where v is the permeate volume (l), a is the membrane effective surface area (m2), and t is the permeation time (h). d) uv disinfection uv disinfection was carried out in the uv disinfection tank by immersing a 15 watt uv-c lamp (dolphin kw, china) at the centre of uv disinfection tank. the effective exposure area for uv disinfection was 0.3 m in diameter and 0.3 m in height. the intensity of uv light at 254 nm was measured using the pm100d optical power and energy meter with s120vc photodiode (thorlabs, germany) after the low-pressure uv-c lamp was switched on for 30 minutes. uv exposure time in single uv disinfection unit and integrated uv disinfection system was based on the results obtained from the preliminary study for uv disinfection. the applied uv dosage was calculated using eq. (2) and eq. (3) [16, 17]. (2) (3) where is the uv-c intensity per unit area (mw/cm2), is the uv exposure time, is the uv-c incident irradiance (mw/cm2), is the depth of the raw effluent perpendicular to the uv lamp, and is the uv-c transmittance at 254 nm with cell path length of 1 cm. io is constant at 0.475 mw/cm². 84 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 e) chlorination the chlorination process was carried out in a chlorination tank for 30 minutes. the chlorine dosage added to the single chlorination unit and integrated chlorination system was according to the results obtained from the chlorination preliminary study. next, the treated raw effluent was added with 4 w/w% of na2s2o5 solution for de-chlorination purposes after 30 minutes of chlorination process. 2.4 water quality analysis efficiency of commercially available disinfection units and integrated disinfection processes in treating the raw effluent was assessed based on the treated effluent quality. the measured parameters included temperature, ph, biochemical oxygen demand (bod5), chemical oxygen demand (cod), total suspended solids (tss), ammoniacal-nitrogen (nh3-n), nitrate-nitrogen (no3-n), phosphorus (p), e. coli, and trihalomethanes (thm). the percentage of removal for each parameter was calculated using eq. (4): (4) where and are the specific parameter’s concentration in the feed water sample and treated effluent, respectively. the measurement for each sample was tested in triplicates. 3. results and discussion 3.1 characterization of the raw effluent the characteristics of the raw effluent samples were summarized in table 1. the data was obtained from 17 samples to minimize analytical error. the raw effluent contained a high quantity of e. coli in that had far exceeded the water reuse standard for any nonpotable applications. high quantity of e. coli has high potential to be a health hazard. hence, direct use of the raw effluent for any purpose is not suggested without an appropriate disinfection treatment. on the other hand, the wide range of the raw effluent quality indicated the need for a pre-treatment process prior to the primary disinfection unit for better disinfection performance. table 1: characteristics of the raw effluent samples parameter unit effluent quality temperature °c 21.93-28.90 ph 7.05-8.21 tss mg/l 2-21 nh3-n mg/l 10.00-24.03 no3-n mg/l 0.02-1.11 p mg/l 0.50-3.71 cod mg/l 27-59 thm μg/l 112.00-246.98 e. coli cfu/100 ml 608-635000 bod5 mg/l 4-8 85 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 3.2 preliminary study 3.2.1 uv disinfection two raw effluent samples: sample 1 with low number of e. coli (~700 cfu/100 ml) and sample 2 with high number of e. coli (~26000 cfu/100 ml) were sampled at different sampling periods and used as the feed water samples for the uv disinfection preliminary study. figure 3 depicted the results obtained from the uv disinfection preliminary study. as shown in fig. 3, 5 minutes of uv exposure time is sufficient to totally disinfect e. coli in sample 1. for 5 minutes of uv exposure time, 28.14 mws/cm² of uv dosage has been transmitted with average uv transmittance (uvt) of 72.27%. previous study conducted by wahid et al (2012) reported that the uv dosage needed to inactivate 1-3 log of e. coli in secondary wastewater effluent was in the range of 27.80 – 83.40 mws/cm² [18]. hence, uv dosage of 28.14 mws/cm² used in this study was in good agreement for the uv dosage applied for disinfection. however, 5 minutes of uv exposure time is not able to produce e. coli free effluent for sample 2. 500 cfu/100 ml e. coli still remained in the treated effluent after exposure to 5 minutes of uv light. hence, the uv exposure time was further prolonged. by referring to fig. 3, 30 minutes of uv exposure time is required to fully disinfect raw effluent which contained a high quantity of e. coli (4.4 log). the uv dosage applied for 30 minutes of exposure time was 168.86 mws/cm². it was in line with the finding obtained by anastasi et al (2013), where 40-80 mws/cm² of uv dosage was required to inactivate 1.7-1.9 log e. coli from secondary treated effluent [19]. hence, approximately 160 mws/cm² of uv dosage is required to inactivate 4 log of e. coli in raw effluent. as a conclusion for the uv disinfection preliminary study, uv dosage of 28.14 mws/cm2 produced from 5 minutes of uv exposure time is sufficient for effluent containing low quantity of e. coli. on the other hand, uv dosage of 168.86 mws/cm2 produced from 30 minutes of uv exposure time is recommended to be applied for the single uv disinfection unit, where high uv radiation was required to penetrate through the effluent with low water quality or having huge quantity of e. coli. fig. 3: effect of uv exposure time towards e. coli removal for different raw effluent quality. 0 5000 10000 15000 20000 25000 30000 0 5 30 60 120 180 n o. o f e . c ol i( c fu /1 00 m l) uv exposure time (minutes) sample 1 sample 2 86 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 3.2.2 chlorination the raw effluent samples underwent a chlorination breakpoint study to determine the optimum chlorine dosage applied for the single disinfection unit and subsequently, the integrated disinfection system. figure 4 showed the chlorination curve profile for both the raw effluent and the samples pre-treated with gac, emm, mf, and uf. as presented in fig. 4, the chlorination curve profile for a single chlorination unit showed a typical “hump-and-dip” pattern. the “hump” zone with a peak appeared at 15 mg/l chlorine dosage corresponded to the formation of chloramines compounds in chlorinated raw effluent after chlorine reacted with inorganic reducing compounds [20]. chloramine compounds were formed through the oxidation-reduction and substitution reactions between hypochlorite available in ca(clo)2 (chlorine source in this study) and ammonia or ammonia-like compounds, such as amines groups, present in the raw effluent [20]. the destruction of chloramine compounds subsequently occurred at higher chlorine dosage as the chlorination curve profile switched to the “dip zone”. the ammonia or ammonia-like compounds were oxidized by chlorine and produced nitrogen-free gas [21]. this phenomenon caused the concentration of residual chlorine in raw effluent to decline. fig. 4: chlorination curve profile for (a) raw effluent and (b) pre-treated raw effluent. 0 50000 100000 150000 200000 250000 300000 350000 0 1 2 3 4 5 0 5 10 15 20 25 30 35 n o. o f e . c ol i( c fu /1 00 m l) r es id ua l c hl or in e (m g/ l) chlorine dosage (mg/l) cl e. coli (a) 0 200 400 600 800 1000 0 1 2 3 4 5 6 7 0 5 10 15 20 25 n o. o f e . c ol i( c fu /1 00 m l) r es id ua l c hl or in e (m g/ l) chlorine dosage (mg/l) gac mf emm uf e. coli uf (b) 87 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 the minimum point of the “dip zone” in the chlorination curve profile is known as the chlorination breakpoint. it indicated the minimum chlorine dosage required in a chlorination process to react with organic and inorganic substances contained in the water sample and to disinfect the bacteria as it contained persistent chloramines that had not yet been destroyed. by referring to the chlorination curve profile in fig. 4(a), the chlorination breakpoint for the single chlorination unit is 20 mg/l. the feasibility of using 20 mg/l chlorine dosage to disinfect raw effluent in the single chlorination unit is confirmed with the absence of e. coli in the treated effluent after 30 minutes of chlorination contact time. on the contrary, a distinct chlorination curve profile was observed for the raw effluent pre-treated with gac, emm, mf, and uf in fig. 4(b) where no chlorination breakpoint was detected. pre-treatment using gac, emm, mf, and uf was expected to improve the quality of the raw effluent, thus reducing the chlorine dosage to react with reducing compounds, ammonia, and nitrogenous organics in the pre-treated effluent. referring to chlorination curve profile in fig. 4(b), no e. coli was detected in pre-treated raw effluent dosed with 5 mg/l of chlorine after 30 minutes chlorination contact time. hence, 5 mg/l of chlorine dosage is recommended to treat the pre-treated raw effluent in the integrated disinfection system that had been pre-treated with gac, emm, mf, or uf. 3.3 performance study of the single disinfection unit table 2 summarizes the treated effluent quality for single disinfection unit, while fig. 5 shows the performance of the single disinfection unit on each measuring parameters. as shown in fig. 5, most of the single disinfection units achieved outstanding performance on e. coli removal where no e. coli was detected in the treated effluent. the uv dosage (168.86 mws/cm2) and chlorine dosage (20 mg/l) determined from preliminary study were effective in producing treated effluent free with e. coli. similarly, mf and uf membranes that have smaller pore diameter than the size of e. coli (2.1 μm in length and 0.6 μm in width) also successfully acted as barrier to prevent the penetration of e. coli and suspended solids (> 0.45 μm) through the membrane filtration unit [22]. the performance of mf and uf membranes in removing particulate matters such as e. coli and tss from feed water is not affected by feed water quality. both mf and uf membranes used in this study showed a superior performance for tss removal where the percentage of removal was 100%. meanwhile, no significant tss removal was observed for chlorination and uv disinfection. this is expected since the mechanism of both chlorination and uv disinfection are just to destroy pathogens in the feed water sample. unfortunately, the pvdf021m membrane failed to achieve total removal of e. coli in treated effluent even though its membrane diameter was smaller than that of the hvlp00010 membrane. this is because the pvdf021m membrane has a very porous surface morphology as compared to other commercial flat sheet membranes used in this study (depicted in fig. 6). on the other hand, although the hvlp00010 membrane has a membrane pore diameter that is larger than the pore diameter of the pvdf021m membrane, the gridded morphology structure of the hvlp00010 membrane provided a better trapping capability than the hvlp00010 membrane, where the e. coli was not able to penetrate through the membrane with non-straight channels. the trend of cod removal is analogous to tss removal where membrane filtration has shown predominant impact compared to chlorination and uv disinfection. similar trend is observed for both cod and tss removal since cod is considered as part of tss. according to falsanisi et al. [23] the reduction of cod from feed solution using a membrane filtration process is attributed to the retaining of organic compounds by molecular sieving mechanism. it is surprising that the pvdf021m membrane (mf 88 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 membrane) rejects a higher percentage of cod than the pvdf1001m membrane and the pes20kda membrane (uf membranes) with smaller membrane pore diameters. high permeate flux of the pvdf021m membrane could be the reason for this phenomenon. high permeate flux of the pvdf021m membrane contributed to fast development of a fouling layer on top of the pvdf021m membrane surface. the developed fouling layer acted as an additional barrier to the pvdf021m membrane, eventually leading to higher removal efficiency by prohibiting more organic matter from passing through the membrane. meanwhile, no significant cod removal was observed for chlorination and uv disinfection. table 2: raw effluent quality after treated with single disinfection unit obtained from two samples. parameter unit mf uf uv chlorination hvlp00010 pvdf021m pvdf1001m pes20kda temperature °c 26.27±2.67 24.49±1.29 26.05±0.75 27.13±2.03 27.08±0.82 22.96±0.41 ph 7.55±0.53 7.82±0.13 7.56±0.38 7.82±0.19 7.58±0.11 7.42±0.14 tss mg/l 0±0 0±0 0±0 0±0 15±4 12±5 nh3-n mg/l 10.37±1.23 13.09±1.15 12.22±1.58 9.71±1.23 18.96±1.78 13.65±1.04 no3-n mg/l 0.83±0.28 0.55±0.27 0.93±0.19 0.79±0.28 1.55±0.57 0.33±0.23 p mg/l 0.87±0.11 2.18±1.13 0.76±0.13 1.60±0.11 3.51±0.36 1.99±0.18 cod mg/l 20±0 15±3 20±2 18±4 43±1 57±8 thm μg/l na na na na na 223.84±49.84 e. coli cfu/100 ml nd < 1 341±176 nd < 1 nd < 1 nd < 1 nd < 1 bod5 mg/l 2±0 4±1 1±0 1±0 2±1 1±0 0 20 40 60 80 100 nh -n no -n p cod bod pe rc en ta ge o f r em ov al ( % ) parameter pvdf1001m pe s20kda hvlp00010 pvdf021m uv chlorination fig. 5: performance of single disinfection unit. with regards to the bod5 removal illustrated in fig. 5, the pvdf021m membrane contributed to the lowest bod5 removal, followed by uv disinfection, hvlp00010 membrane, pvdf1001m membrane, chlorination, and pes20kda membrane with the removal percentage of 39.38, 58.70, 69.24, 77.95, 84.79, and 86.28%, respectively. low 89 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 bod5 removal by the pvdf021m membrane is probably due to large membrane pore diameter and non-gridded structure of the membrane. hence, the trapping capability of the pvdf021m membrane towards e. coli is the weakest among the other membranes. whereas, the pes20kda membrane with the smallest membrane pore diameter is most vulnerable for the rejection of microorganisms among other membranes. meanwhile, the average removal of bod5 concentration by uv disinfection could have been influenced by the presence of activated e. coli after uv disinfection. the presence of residual organic substrate that has not been removed during uv disinfection supported the regrowth of e. coli in the treated effluents. in contrast, chlorination accomplished considerably high bod5 removal, which proved its capability as an oxidizing agent to oxidize organic compounds. in addition, unlike uv disinfection, microorganisms that have been inactivated by chlorination cannot undergo major repair mechanisms of damaged cells. fig. 6: (a) surface morphology and (b) cross-sectional micrographs of flat sheet commercial membranes at the magnification of 3000x and 300x, respectively. (a) (b) hvlp00010 pvdf021m pvdf1001m pes20kda 90 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 on the other hand, single disinfection units used in this study were not able to achieve a high percentage of nutrient (nh3-n, no3-n, and p) removal. generally, both mf and uf membranes are not effective for the removal of dissolved natural organic matter (nom), where the hydrodynamic particle size of dissolved nom is smaller than the mf and uf membrane pore diameters [24]. however, the slight removal of the nutrients could be attributed to nitrogen-containing anions (no3-) and orthophosphate (po4³-) that are possibly rejected due to the partial repulsion caused by the negatively charged membranes. membrane surface charge was indicated by the surface zeta potential value presented in fig. 7 [25]. as presented in fig. 7, all flat sheet commercial membranes used in this study were negatively charged and increased at the trend of pvdf021m < pvdf1001m < pes20kda < hvlp00010. although the hvlp00010 membrane is a mf membrane with larger pore diameter, the segmented morphology of the hvlp00010 membrane has provided good trapping capability to the membrane in improving its rejection efficiency. meanwhile, uv radiation, which only affects the pathogens, is not able to contribute in nutrient removal. chlorination showed a better performance on nutrient removal as compared to uv radiation in which the percentage of removal for nh3-n, no3-n, and p was 15.71, 36.00, and 8.67%, respectively. still, the percentage of removal of nh3-n, no3-n, and p is still not as high as expected. theoretically, the destruction of chloramine by free chlorine at chlorination breakpoint concentration will release nitrogen (n2) gas and allowed for the oxidation of nh3. however, there is only a slight “dip” zone in the chlorination curve profile for our study. as a result, less chloramine was destructed by the limited available free chlorine, resulting in slight removal of nh3-n and no3-n (15.71 and 36.00% of removal, respectively). the effectiveness of the chlorination process is always compensated by the coupling of carcinogenic disinfection by-products such thm [26]. table 3 showed the concentration of four thm compounds including chloroform (chcl3), bromodichloromethane (chbrcl2), dibromochloromethane (chbr2cl), and bromoform (chbr3) presented in raw effluent and chlorination treated effluent. high concentration of chcl3 in the feed solution has contributed to the high concentration of chcl3 in the treated effluent after the chlorination process, exceeding the ministry of health (moh) malaysia guidelines. thus, the utilization of chlorination treated effluent could be risky and harmful. therefore, pre-treatment prior chlorination is necessary where a suitable pretreatment method is expected to reduce the thm value of feed solution. fig. 7: membrane surface charge for the commercial flat sheet membranes. -25 -20 -15 -10 -5 0 hvlp00010 pvdf021m pvdf1001m pes20kda ze ta p ot en tia l ( m v ) membrane 91 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 table 3: thm concentration in raw effluent, chlorination treated effluent, and moh guidelines compound raw effluent [μg/l] chlorination treated effluent [μg/l] moh guidelines [μg/l] chcl3 213.70±33.07 222.02±51.66 200 chbrcl2 0.45±0.24 1.11±1.11 100 chbr2cl 0.28±0.28 0.65±0.65 100 chbr3 0.61±0.61 0.07±0.07 60 among the single disinfection units, the pes20kda membrane with the smallest membrane pore diameter had shown the highest rejection in most of the parameters where the percentage of removal for e. coli, tss, cod, bod5, nh3-n, no3-n, and p was recorded as 100.00, 100.00, 49.77, 86.28, 9.80, 27.88, and 42.27%, respectively. since pes20kda membrane filtration unit was able to remove part of the nutrients and suspended solids, it was used as the pre-treatment coupled with either uv disinfection or chlorination unit (primary disinfection process) in integrated disinfection system to further enhance the effectiveness of the primary disinfection process and to improve the water quality of the treated effluent. 3.4 performance study of the integrated disinfection system table 4 and table 5 summarize the treated effluent quality from the integrated disinfection system using chlorination as primary disinfection unit and treated effluent quality from the integrated disinfection system using uv as primary disinfection unit. meanwhile, the performance of both integrated disinfection systems is illustrated in fig. 8. table 4: treated effluent quality from integrated disinfection system using chlorination as primary disinfection unit obtained from two samples. parameter unit uf-cl gac-cl emm-cl influent effluent influent effluent influent effluent temp. °c 25.67±2.93 25.03±1.97 23.12±0.12 22.90±0.80 26.17±2.93 22.10±0.60 ph 7.70±0.18 7.20±0.04 7.33±0.11 7.69 ±0.05 7.21±0.22 7.13±0.38 tss mg/l 2±0 0±0 4±2 1±1 4±1 2±1 nh3-n mg/l 12.08±2.08 1.92±1.79 11.50±3.80 7.25±4.45 7.76±7.54 6.00±6.00 no3-n mg/l 0.70±0.39 1.13±0.00 1.10±0.00 0.62±0.47 0.74±0.32 0.80±0.31 p mg/l 1.63±1.13 1.70±0.02 1.99±1.21 3.82±0.15 2.05±1.15 1.75±0.87 cod mg/l 35±2 23±5 31±1 15±1 63±31 27±0 thm μg/l 215.04±34.20 171.81±2.73 215.04±34.20 161.52±37.04 215.04±34.20 177.44±2.54 e. coli cfu/ 100 ml 9004±8396 nd < 1 26850±26150 nd < 1 22276±4276 nd < 1 bod5 mg/l 7±1 0±0 5±1 0±0 3±1 0±0 with regards to the e. coli removal presented in fig. 8, almost all integrated disinfection systems are successful in producing treated effluent with no e. coli contamination. this result indicated that 5 mg/l chlorine dosage and 58.43 mws/cm2 uv dosage determined from preliminary study are able to disinfect all e. coli detected in raw effluent with the assistance of a pre-treatment unit. it is known that the performance of chlorination and uv disinfection greatly depends on the turbidity of the feed solution [27]. as mentioned by winward et al (2008), the removal of tss constituents from water 92 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 samples could reduce the shielding effect which restricted the chlorine from accessing the cellular components of e. coli [28]. similarly, low tss content in the water sample allow the direct transmittance of uv light towards the targeted microorganisms for disinfection purposes. hence, pes20kda, gac, and emm pre-treatment units which help to reduce the tss content in raw effluent had eventually helped in increasing the efficiency of chlorination and uv disinfection processes in integrated disinfection systems. table 5: treated effluent quality from integrated disinfection system using uv as primary disinfection unit obtained from two samples. parameter unit uf-uv gac-uv emm-uv influent effluent influent effluent influent effluent temp. °c 25.67±2.93 26.35±2.25 26.17±2.93 22.10±2.00 26.17±2.93 26.50±2.80 ph 7.70±0.18 7.63±0.17 7.21±0.22 7.54±0.29 7.21±0.22 7.59±0.32 tss mg/l 2±0 0±0 4±1 1±1 4±1 3±2 nh3-n mg/l 12.08±2.08 6.72±0.62 7.76±7.54 5.60 ±5.60 7.76±7.54 7.07±7.07 no3-n mg/l 0.70±0.39 1.11±0.01 0.74±0.32 0.11±0.07 0.74±0.32 0.66±0.46 p mg/l 1.63±1.13 0.42±0.91 2.05±1.15 2.21±1.35 2.05±1.15 0.97±0.82 cod mg/l 35±2 23±2 63±31 50 ±40 63±31 56±27 e. coli cfu/100 ml 9004±8396 nd < 1 35500±17500 nd < 1 22276±4276 9±9 bod5 mg/l 7±1 2±1 3±1 3±1 3±1 1±1 fig. 8: performance of integrated disinfection system. as a comparison for tss removal, the uf membrane is the most promising pretreatment unit that had greatly reduced the tss content in raw effluent through sieving effect. therefore, greatest tss removal is achieved by the integrated disinfection system using the uf membrane as a pre-treatment unit. the performance of an integrated disinfection system on tss removal is followed the trend of emm < gac < uf. emm and gac pre-treatment units use the same type of adsorbent. however, the percentage of tss removal for the emm pre-treatment unit is slightly lower as compared to the gac 0 20 40 60 80 100 tss nh₃-n no₃-n p cod bod₅ pe rc en ta ge o f r em ov al ( % ) parameter uf-cl gac-cl emm-cl uf-uv gac-uv emm-uv e. coli 93 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 pre-treatment unit due to the loose packing of adsorbents in the emm column. fewer adsorption sites are available for the attachment of suspended solids, thus contributing to lower efficiency of the emm pre-treatment unit. with regards to the cod removal presented in fig. 8, the integrated disinfection system using chlorination as primary disinfection unit revealed higher cod removal as compared to the integrated disinfection system using uv as primary disinfection. besides, it is found that the trend of cod removal by integrated disinfection system using uv as primary disinfection unit is analogous to the trend of tss removal. hence, with higher tss removal by uf membrane filtration unit, greater cod removal is observed for ufuv. however, a different trend of cod removal is observed for the integrated disinfection system using chlorination as a primary disinfection unit, where the cod removal is decreased in the sequence of emm-cl < gac-cl < uf-cl. this trend basically depends on chlorine demand needed by the system. high removal efficiency of uf pre-treatment towards organic matters has contributed to higher quality of pre-treated effluent. with the same chlorine dosage in each integrated disinfection system using chlorination as a primary disinfection system, there will be excess free residual chlorine in uf-cl. this will eventually lead to higher cod value in uf-cl as the excess free residual chlorine is part of the factor contributing to cod concentration. whereas, for emm and gac pretreatment where the efficiency is not so high, the remaining organic matter in the pretreated effluent are bonded with free chlorine, therefore greatly reducing the cod concentration in the treated effluent. for bod5 removal, all integrated disinfection systems using chlorination as a primary disinfection unit successfully resulted in treated effluent with high bod5 removal. the bod5 removal followed the trend of emm-cl < gac-cl < uf-cl. high removal of bod5 by integrated disinfection systems using chlorination as the primary disinfection unit is due to the effectiveness of the pre-treatment unit and also the chlorination process, where the chlorination process is able to disinfect the microorganisms contained in the raw effluent. comparatively, integrated disinfection systems using uv as a primary disinfection unit had lower bod5 removal than integrated disinfection systems using chlorination as a primary disinfection unit. this is because although uv has the function of disinfecting the microorganisms in the raw effluent, its efficiency is not as high as chlorination. on the other hand, low percentage removal of bod5 for gac-uv is influenced by the high p content in gac-uv treated effluent. high p content in treated effluent will speed up eutrophication, support the microorganisms (recovered e. coli or non-disinfected pathogens) for cell synthesis and energy transport, thus accelerating the microbial activity to consume more do and lower the bod5removal [29,30]. with regards to nutrient (nh3-n, no3-n, and p) removal as depicted in fig. 8, a wide range of nutrient removal was obtained by the integrated disinfection systems used in this study. the percentage of nh3-n, no3-n, and p removal was at the range of 8.90-84.15, 0.00-85.55, and 0.00-18.36%, respectively. the percentage of nutrient removal greatly depended on the pre-treatment efficiency and dosage applied in the primary disinfection unit. uf-uv presented the greatest nh3-n removal among integrated disinfection system using uv as primary disinfection. nitrification process (depicted in eq. (5)) is expected to occur during pre-treatment of uf-uv. long membrane filtration time increased the do level in pre-treated effluent due to continuous flow of retentate back to the inlet tank. with the added oxygen into the effluent, nh3-n is converted into no3-n. (5) 94 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 this postulation is supported by the addition of no3-n content in treated effluent by uf-uv and uf-cl, in which no no3-n removal was achieved. whereas, gac and emm pre-treatment showed inconsistent performance in treating nutrients. this could be because gac and emm are insufficient in providing effective adsorption sites for the nutrient adsorption. however, more activated carbon contained in the gac column provided larger effective adsorption sites for the nutrients to adsorb onto it and therefore had greater adsorption capacity as compared to the emm column. comparatively, the integrated disinfection system using chlorination as primary disinfection unit generally exhibited higher nh3-n removal than integrated disinfection system using uv as primary disinfection unit. the addition of ca(ocl)2 in the chlorination process has increased the oxidation level in pre-treated effluent [10]. hence, a higher amount of nh3-n was removed from the raw effluent through the nitrification process (as indicated by eq. (5)). with regards to p removal, only a low amount of p is able to be removed by integrated disinfection systems using emm as pre-treatment. although much research reported that gac has the capability to adsorb p, the leaching of p from the gac surface into treated effluent due to weak physical attachment of p onto the gac surface during its synthesis process has opposed the removal of p from raw effluent. however, p leaching effect was less significant in the emm pre-treatment unit as the gac content in the emm column was less than that of the gac column. meanwhile, the inconsistent p removal by integrated disinfection system using uf as a pre-treatment unit could be due to the pes20kda membrane surface defect. as compared to single the disinfection unit, the integrated disinfection system using chlorination as a primary disinfection unit is able to reduce the thm content in the treated effluent. this could be attributed to the existence of a pre-treatment unit in the integrated disinfection system. pre-treatment such as uf, gac, and emm manage to remove part of thm and nom from raw effluent either by physical sieving mechanism or adsorption. nom is the precursor for thm formation [31]. lower thm concentration in pre-treated effluent and less nom for the further formation of thm will therefore reduce the thm concentration in treated effluent from the integrated disinfection system using chlorination as a primary disinfection unit. the treated effluent from the integrated disinfection system using chlorination as primary disinfection unit is able to comply with moh guidelines. thus, the treated effluent is safe for recycle and reuse purposes. 3.5 treated effluent quality compared to water reuse guidelines to date, no water reuse guideline has been developed by malaysian authorities to facilitate the recycling and reuse of treated water in malaysia. attributed to this, several water reuse guidelines presented in table 6 united states environmental protection agency (us epa) water reuse guidelines and singapore grey water quality were chosen as the benchmark to determine the adaptability of treated water quality for reuse purposes [11,32]. the us epa water reuse guidelines is an international guideline that has been widely recognized for water reuse in restricted area applications and unrestricted area applications. as these us epa water reuse guidelines might not be representative of the asia climate, singapore grey water is a water reuse program tailored strictly for flushing of water closets and urinals, general washing (excluding high pressure jet washing and general washing at market and food establishments), irrigation (excluding irrigation sprinklers), and cooling tower makeup water [32]. 95 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 table 6: water reuse guidelines parameter us epa [11] singapore grey water [32] restricted area unrestricted area ph 6-9 6-9 6-9 bod5 [mg/l] ≤ 30 ≤ 10 < 5 cod [mg/l] turbidity [ntu] ≤ 2 < 2 tss [mg/l] ≤ 30 ≤ 5 e. coli [cfu/100 ml] nd fecal coliform [cfu/100 ml] ≤ 200 nd no3-n [mg/l] nh3-n [mg/l] total thms [μg/l] table 7: adaptability of treated effluent from each system for water recycling and reuse system usepa singapore grey waterrestricted area unrestricted area hvlp00010 pvdf021m pvdf1001m pes20kda chlorination uv uf-uv gac-uv emm-uv uf-cl gac-cl emm-cl table 7 summarizes the adeptness of treated effluent from each system for water recycling and reuse. as presented in table 7, almost all treated effluent from single disinfection complied with the us epa water reuse guidelines at restricted areas except for the final effluent given by the pvdf021m membrane. this means that treated effluents from the hvlp0010 membrane, pvdf1001m membrane, pes20kda membrane, chlorination, and uv disinfection are suitable for reuse as irrigation water (restricted area), agricultural reuse (food crops commercially processed and non-food crops), landscape impoundments, and construction. however, only treated effluents by the hvlp0010 membrane, pvdf1001m membrane, and pes20kda membrane are able to meet us epa water reuse guidelines for unrestricted areas. these treated effluents have added value for urban reuse, recreation, and agricultural purposes (food crops commercially processed and food crops not commercially processed). uv and chlorination are only recommended for restricted area applications due to the presence of high tss content in treated effluent. whereas, permeate filtered from the pvdf021m membrane did not comply with us epa water reuse guidelines for both unrestricted areas and restricted areas. there was still a high number of e. coli (341 ± 176 cfu/100 ml) 96 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 remaining in the treated effluent after filtering with the pvdf021m membrane. for integrated disinfection systems, almost all integrated disinfection systems complied with us epa water reuse guidelines for unrestricted area applications except the integrated disinfection system of emm-uv due to the presence of e. coli. the adaptability of treated effluent with singapore grey water quality presented the same trend as its adaptability with us epa water reuse guidelines for restricted area. all disinfection units and integrated disinfection systems complied with the parameter range except the pvdf021m membrane, and integrated disinfection system of emm-uv. although single pvdf021m membrane and integrated disinfection system of emm-uv compiled with ph and bod5 parameters of the singapore grey water quality, high e. coli content in treated effluents make them fail to comply. thus, treated effluent from these disinfection systems are not recommended for grey water reuse purposes [32]. 4. conclusion the pes20kda membrane with the smallest membrane pore diameter was the most effective single disinfection unit with the highest rejection in most of the parameters where the percentage of removal for e. coli, tss, cod, bod₅, nh₃-n, no₃-n, and p were 100.00, 100.00, 49.77, 86.28, 9.80, 27.88, and 42.27%, respectively. almost all single disinfection units complied with the us epa water reuse guidelines at restricted areas for the application of irrigation (restricted area), agricultural reuse (food crops commercially processed and non-food crops), landscape impoundments, construction, and industrial reuse except the pvdf021m membrane filtration unit. additionally, high quality treated effluent by the hvlp0010 membrane, pvdf1001m membrane, and pes20kda membrane are able to meet singapore grey water quality, and us epa water reuse guidelines at unrestricted area for urban reuse, recreation, and agricultural (food crops commercially processed and food crops not commercially processed) purposes. all integrated disinfection systems were effective in disinfecting the raw effluent where almost all of it achieved 100% e. coli removal in treated effluent. comparatively, the integrated disinfection system using chlorination as primary disinfection unit has better performance than the integrated disinfection system using uv as primary disinfection unit. uf-cl is the preferable integrated system for the greatest removal of most of the parameters from raw effluent. the percentage of removal for e. coli, tss, cod, bod5, nh3-n, no3-n, and p by uf-cl is 100.00, 100.00, 36.32, 97.74, 84.15, 0.00, and 0.00%, respectively. all integrated disinfection systems complied with the us epa water reuse guidelines for restricted area application. however, only integrated disinfection systems of emm-uv did not manage to fulfil the singapore grey water quality, and us epa water reuse guidelines for unrestricted area applications. acknowledgements the authors wish to gratefully acknowledge the financial support of this work by indah water konsortium (iwk) sdn. bhd. (kk-2018-005) and dana penyelidikan strategik 97 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 (kra-2017-06). the authors also wish to acknowledge fuel sel institute, ukm for sem analysis. references [1] mohamed rmsr, nazmi am, arief mm, hashim mka. (2016) conventional water filter (sand and gravel) for ablution water treatment, reuse potential, and its water savings. j. sustain. dev, 9:35–43. doi:10.5539/jsd.v9n1p35 [2] academy of sciences malaysia. (2015) study on the current issues and needs for water supply and wastewater management in malaysia. volume 2. kuala lumpur. retrieved from https://issuu.com/asmpub/docs/wswm_volume_2 [3] alternative water resource to potentially reduce water footprint [http://ensearch.org/wpcontent/uploads/2013/10/paper-11-alternative-water-resources-as-apotential-to-reduce-water-footprint.pdf] [4] cleaning the unseen [https://www.thestar.com.my/news/nation/2016/12/04/cleaning-theunseen-from-the-tidak-apa-attitude-of-users-to-financial-gaps-former-indah-water-konsor/] [5] looking for water [https://www.thestar.com.my/news/environment/2014/06/16/lookingfor-water/] [6] wahid ma, tanaka h. (2012) potential implementation of wastewater reclamation and reuse in malaysia urban area. int. sustain. civ. eng. j., 1(1):75–83. [7] abarnou a, miossec l. (1992) chlorinated waters discharged to the marine environment chemistry and environmental impact. an overview. sci. total environ., 126:173–197. doi:10.1016/0048-9697(92)90490-j [8] turtoi m. (2013) ultraviolet light potential for wastewater disinfection. ann. food sci. technol., 14(1):153–164. retrieved from https://www.researchgate.net/publication/264002288_ultraviolet_light_potential_for _wastewater_disinfection [9] rodriguez-chueca j, ormad mp, mosteo r, sarasa j, ovelleiro jl. (2015) conventional and advanced oxidation processes used in disinfection of treated urban wastewater. water environ. res., 87(3):281–288. doi:10.2175/106143014x13987223590362 [10] uv disinfection for wastewater [http://www.trojanuv.com/applications/wastewater] [11] u.s. environmental protection agency. (2004) guidelines for water reuse. washington. [12] grover d, zhou j, frickers p, readman j. (2011) improved removal of estrogenic and pharmaceutical compounds in sewage effluent by full scale granular activated carbon: impact on receiving river water. j. hazard mater, 185(2-3):1005–1011. doi:10.1016/j.jhazmat.2010.10.005 [13] kim sd, cho j, kim is, vanderford bj, snyder sa. (2007) occurrence and removal of pharmaceuticals and endocrine disruptors in south korean surface, drinking, and waste waters. water res, 41(5):1013–1021. doi:10.1016/j.watres.2006.06.034 [14] margot j, kienle c, magnet a, weil m, rossi l, de alencastro lf, abegglen c, thonney d, chevre n, scharer m, barry da. (2013) treatment of micropollutants in municipal wastewater: ozone or powdered activated carbon? sci total env, 461:480–498. doi:10.1016/j.scitotenv.2013.05.034 [15] gonzalez o, bayarri b, acena j, perez s, barcelo d. (2016) treatment technologies for wastewater reuse: fate of contaminants of emerging concern. in advanced treatment technologies for urban wastewater reuse the handbook of environmental chemistry. volume 45. edited by fatta-kassinos d, dionysiou d, kummerer k. cham, springer; pp 5–38. [16] morowitz hj. (1950) absorption effects in volume irradiation of microorganisms. science, 111(2879):229–230. doi:10.1126/science.111.2879.229-a [17] hallmich c, gehr r. (2010) effect of preand post-uv disinfection conditions on photoreactivation of fecal coliforms in wastewater effluents. water res, 44: 2885–2893. doi:10.1016/j.watres.2010.02.003 98 iium engineering journal, vol. 21, no. 2, 2020 mohamad mazuki et al. https://doi.org/10.31436/iiumej.v21i2.1245 [18] wahid ma, kim i, yamashita n, tanaka h, baki a. (2012) uv based process for e. coli and coliphage in secondary effluent for wastewater reclamation and reuse. inst. eng. malaysia, 73:18–24. retrieved from https://www.myiem.org.my/content/iem_journal_2012-361.aspx [19] anastasi em, wohlsen td, stratton hm, katouli m. (2013) survival of escherichia coli in two sewage treatment plants using uv irradiation and chlorination for disinfection. water res, 47(17):6670-6679. doi:10.1016/j.watres.2013.09.008 [20] march jg, gual m. (2007) breakpoint chlorination curves of greywater. water environ. res, 79(8):828–832. doi:10.2175/106143007x156736 [21] jorgensen se. (1993) breakpoint chlorination. in the removal of nitrogen compounds from wastewater. edited by halling-sorensen b, jorgensen se. netherlands, elsevier science publishers; pp. 295–304. [22] martins jm, majdalani s, vitorge e, desaunay a, navel a, guine v, daian jf, vince e, denis h, gaudet jp. (2013) role of macropore flow in the transport of escherichia coli cells in undisturbed cores of a brown leached soil. environ. sci. process. impact, 15(2):347–356. doi:10.1039/c2em30586k. [23] falsanisi d, liberti l, notarnicola m. (2009) ultrafiltration (uf) pilot plant for municipal wastewater reuse in agriculture: impact of the operation mode on process performance. water, 1:872–885. doi:10.3390/w2040872 [24] ang wl, mohammad aw, hilal n, leo cp. (2015) a review on the applicability of integrated/hybrid membrane processes in water treatment and desalination plants. desalination, 363: 2–18. doi:10.1016/j.desal.2014.03.008 [25] mandzy n, grulke e, druffel t. (2005) breakage of tio2 agglomerates in electrostatically stabilized aqueous dispersions. powder technology, 160(2):121-126. doi:10.1016/j.powtec.2005.08.020 [26] shah ad, mitch wa. (2012) halonitroalkanes, halonitriles, haloamides, and nnitrosamines: a critical review of nitrogenous disinfection byproduct formation pathways. environ. sci. technol., 46:119–131. doi:10.1021/es203312s [27] farrell c, hassard f, jefferson b, leziart t, nocker a, jarvis p. (2018) turbidity composition and the relationship with microbial attachment and uv inactivation efficacy. sci. total environ., 624:638–647. doi:10.1016/j.scitotenv.2017.12.173 [28] winward gp, avery lm, stephenson t, jefferson b. (2008) chlorine disinfection of grey water for reuse: effect of organics and particles. water res., 42:483–491. doi:10.1016/j.watres.2007.07.042 [29] phosphorus and water. [http://water.usgs.gov/edu/phosphorus.html] [30] zhang y, zhang g, wang p, wang q. (2017) disinfection of municipal secondary effluents with microwave-induced electrodeless ultraviolet irradiation for water reuse. j. chem. technol. biotechnol., 92(5):1017–1025. doi:10.1002/jctb.5077 [31] hua g, yeats s. (2010) control of trihalomethanes in wastewater treatment. florida water resour. j., april. retrived from https://www.fwrj.com/techarticles/0410 fwrj_tech1.pdf [32] technical guide for greywater recycling system [https://www.pub.gov.sg/documents/greywatertech.pdf] 99 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <feff04180441043f043e043b044c043704430439044204350020044d044204380020043f043004400430043c043504420440044b0020043f0440043800200441043e043704340430043d0438043800200434043e043a0443043c0435043d0442043e0432002000410064006f006200650020005000440046002c0020043f043e04340445043e0434044f04490438044500200434043b044f0020043d0430043404350436043d043e0433043e0020043f0440043e0441043c043e044204400430002004380020043f043504470430044204380020043104380437043d04350441002d0434043e043a0443043c0435043d0442043e0432002e00200421043e043704340430043d043d044b043500200434043e043a0443043c0435043d0442044b00200050004400460020043c043e0436043d043e0020043e0442043a0440044b0442044c002c002004380441043f043e043b044c04370443044f0020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e00300020043b04380431043e00200438044500200431043e043b043504350020043f043e04370434043d043804350020043204350440044104380438002e> /sky <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> /slv <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> /suo <feff004b00e40079007400e40020006e00e40069007400e4002000610073006500740075006b007300690061002c0020006b0075006e0020006c0075006f0074002000410064006f0062006500200050004400460020002d0064006f006b0075006d0065006e007400740065006a0061002c0020006a006f0074006b006100200073006f0070006900760061007400200079007200690074007900730061007300690061006b00690072006a006f006a0065006e0020006c0075006f00740065007400740061007600610061006e0020006e00e400790074007400e4006d0069007300650065006e0020006a0061002000740075006c006f007300740061006d0069007300650065006e002e0020004c0075006f0064007500740020005000440046002d0064006f006b0075006d0065006e00740069007400200076006f0069006400610061006e0020006100760061007400610020004100630072006f0062006100740069006c006c00610020006a0061002000410064006f00620065002000520065006100640065007200200036002e0030003a006c006c00610020006a006100200075007500640065006d006d0069006c006c0061002e> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 210-1075-1-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 89 determination of igf-1-producing cho-k1 growth phases using gcms-based global metabolite analysis s.e.m. saberi, y.z.h-y. hashim, v. packeer mohamed, m. mel, r. ahmad-raus and a. amid department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. s.ezrina@hotmail.com abstract: mammalian cell lines, in particular cho-k1 is vital for the multibillion dollar biotechnology industry. the majority of large scale bioprocessing of commercially valuable protein biopharmaceuticals is produced using this type of cell. an ideal mammalian cell system as host for biologics production should retain efficient use of energy sources in order to boost productivity at minimum cost. various analyses such as cell counting and monitoring of specific biochemical responses are used to provide data to enable bioprocess control in order to achieve the ideal system. our study aimed to see whether global metabolite analysis using gas chromatography mass spectrometry (gcms) would be a potential alternative approach in providing data for bioprocess control. in this study, we analyzed metabolites of cho-k1 cells at different growth phases using gcms. cho-k1 cells producing insulin like growth factor-i (igf1) were obtained from atcc. cells were grown in t-flask and incubated at 37°c/ 5% co2 until 70-80% confluent in rpmi 1640 media. samples (cells and spent/conditioned media) were taken at designated intervals for routine cell counting (trypan blue dye exclusion method); glucose, glutamine and lactate determination (ysi 2700); igf-1 production (elisa kit r&d sstems, inc); and global metabolite analysis (gcms). conditioned media from each time point were spun down before subjecting into gcms. data from gcms was then transferred to simca p+12.0 for chemometric evaluation using principal component analysis (pca). the first component, pc1 results was able to explain 36% of the variation of the data with clear separation between exponential phase and other phases (initial and death phase). this suggests that gcms-based global metabolite analysis has the ability to capture cell growth behaviour and offered insights of factors that may influence the biological system. abstrak: produk yang berupa sel kekal mamalia, terutamnya cho-k1 adalah penting dan menguntungkan industri bioteknologi. majoritinya pemprosesan protein biofarmaseutikal secara besar-besaran dihasilkan dengan menggunakan sel jenis ini. sistem sel mamalia yang ideal sebagai hos untuk penghasilan produk ubatan harus mengekalkan penggunaan sumber tenaga secara efisien untuk meningkatkan produktiviti pada kos yang minima. pelbagai analisa seperti penghitungan sel dan pemerhatian tindak balas biokimia tertentu digunakan untuk memberikan data dan untuk menentukan bioproses terkawal untuk mendapat sistem yang ideal. kajian ini dijalankan untuk mengkaji sama ada analisa metabolit global menggunakan spektrometri jisim kromatografi gas (gas chromatography mass spectrometry (gcms)) boleh berpotensi sebagai pendekatan alternatif dalam membekalkan data untuk kawalan bioproses. dalam kajian ini, metabolit sel cho-k1 dikaji pada peringkat tumbesaran berbeza menggunakan gcms. sel cho-k1 menghasilkan insulin seperti faktor pertumbuhan-i (igf1) didapati daripada atcc. sel dibesarkan dalam kelalang-t dan dieramkan pada iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 90 37°c/ 5% co2 sehingga 70-80% konfluen dalam perantara rpmi 1640. sampel (sel dan perantara yang digunakan/dilazimkan) diambil kiraan pada selang masa yang telah ditetapkan untuk sel rutin (kaedah eksklusi pencelup trypan blue), glukosa, glutamin dan penentuan laktat (ysi 2700); penghasilan igf -1 (kit elisa r&d sstems, inc); dan analisa global metabolit (gcms). perantara yang dilazimkan dari setiap poin masa dikurangkan kelajuannya pada setiap pusingan sebelum dianalisa secara gcms. data daripada gcms kemudiannya dipindahkan ke simca p+12.0 untuk taksiran kemometrik menggunakan analisis komponen utama (principal component analysis (pca)). keputusan komponen pertama, pc1 berupaya menjelaskan variasi 36% data dengan pengasingan jelas antara fasa eksponen dan fasa-fasa lain (fasa permulaan dan fasa akhir). ini menunjukkan bahawa analisa metabolit global berasaskan gcms mampu menjelaskan tingkah laku pertumbuhan sel dan memberikan pemahaman tentang faktorfaktor yang mempengaruhi sistem biologikal. keywords: cho-k1 cells; insulin growth factor -1 (igf-1); metabolomics; metabolite profile; pca; gcms 1. introduction animal cell lines have been used extensively for the production of a variety of therapeutics and prophylactic protein products including hormones, cytokines, enzymes, monoclonal antibodies, recombinant glycoproteins, viral vaccines and blood clotting factors. mammalian cells are generally capable of secreting functionally active proteins with correct folding and post-translational modifications, unlike bacterial or yeast systems [2]. although many simple proteins can be produced using rdna in bacterial cultures, more complex proteins that are glycosylated (carbohydrate-modified) require animal cells as host system. the natural surroundings of mammalian cells (biochemical, physiological and physiochemical) directly affect the growth of cells and their metabolism. a battery of analyses is routinely performed to provide data for bioprocess control in the desire to achieve the ideal. this includes determination of the concentration of target bioproducts and cell counting. however, these analyses require repeated sampling at multiple time points which may lead to high cost and potential contamination. each type of analysis is very specific and has its own procedure with different consumables and apparatus which also incur cost. metabolomics (metabolome analysis) refers to the in-depth analysis of metabolites [3]. gcms-based metabolomics is used to reveal important metabolic pathway by surveying large number of metabolites that may not be picked up by standard metabolic analyses and hence provide a starting point for further detailed study. gcms also work as an excellent starting point for a non-hypothesis driven way, analyze and quantify as many metabolites as possible and generate data sets that can be used for biomarker discovery [1]. there are various analytical instrument platforms for metabolomics approach, namely nuclear magnetic resonance (nmr) spectroscopy, mass spectrometry, chromatographic and column separation, vibrational spectroscopies such as fouriertransform infrared (ftir) and hyphenated instruments such as gas chromatography mass spectrometry (gcms) and liquid chromatography mass spectrometry (lcms) [4]. nmr increases the analytical reproducibility and simplicity of sample preparation but it is relatively insensitive compared to mass spectrometry technique [13]. meanwhile, gas chromatography (gc) coupled to mass spectrometry (ms) offers high chromatic iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 91 resolution but requires chemical derivatization for many biomolecules. only volatile chemicals can be analyzed without derivatization. ms is designed to separate gas ions according to their m/z (mass to charge ratio) value. gcms measures mass of analytes and give information about chemical structures including metabolites. while lcms requires no derivatization of samples and gives excellent throughput, gcms covers a wider range of global metabolites compared to lcms [14]. in addition, metabolite identification by gcms is simplified when standardized retention indices and mass spectra are registered in a database. global metabolite analysis studies generate complex data from gcms mass spectra, which are hard to summarize and visualize without appropriate tools. the use of chemometric tools, e.g., principal component analysis (pca) and partial least-squares to latent structrures (pls) are therefore of great importance as these include efficient, validated, and robust methods for modelling information-rich biological data. the pca model can indicate systematic trends within the data, i.e., clustering, time trends, etc. metabolomics has been used in a wide range of fields, including diagnostic marker search and etiology analysis in medical treatment, biomarker search for revealing efficacy and toxicity in drug manufacturing, and quality control in food processing [3]. metabolomics also being used in plant science [4], yeasts-related research [5] and increasingly used in nutrition research [6]. although metabolomics have been applied to the mammalian system in relation to disease diagnosis and therapeutic efficacy, preclinical drug safety assessment and pharmacology [7], it has been applied to a lesser extent in the mammalian cell culture/bioreactor area [4, 8]. as the number of therapeutic proteins produced by mammalian cell cultures in the pharmaceutical industry continues to increase, the need to improve productivity and ensure consistent product quality during process development activities becomes more significant. while the focus here is on the extracellular metabolite of cho-k1 cell cultures, this methodology is generally applicable to quantitating intracellular concentrations and can be extended to other mammalian cell lines, as well as platforms such as yeasts, fungi, and escherichia coli [16]. gcms has proven to be an effective tool for metabolites identifications and quantifications in mammalian cell lines due to its excellent resolution, sensitivity, separation capacity, and its ability to generate a mass spectrum for each compound, allowing separation and detection of many metabolites [9-11]. in this study, we use gas chromatography coupled to mass spectrometry together with chemometric tools to investigate whether gcms-based approach can identify the growth phases of cells in culture using spent media. this would offer alternative to bioprocessing monitoring in particular using non-invasive technique. 2. materials and methods 2.1 media and reagents rpmi 1640 media were obtained from cellgro (herndon, va usa); other reagents include fetal bovine serum, (gibco – invitrogen, south america); accutase in dulbecco's phosphate-buffered saline, dpbs 0.5 mm edta (innovative cell technologies, inc); phosphate buffered saline, (sigma-aldrich). 2.2 cell line iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 92 the cho-k1 cell line, (atcc ccl-61 tm ) was obtained from american type culture collection (atcc). 2.3 cell culture and growth assessment stocks of cho-k1 cells were revived in 25 cm 2 t-flask in 5 ml rpmi 1640 with 10% fbs (v/v). after several passages, the cells were then subcultured in 75 cm 2 t-flask (15 ml) for 3-4 days with a seeding density 2.0 x 10 5 cells ml -1 , 37°c/ 5% co2. cells were prepared in separate t-flask for each time point for three independent experiments. samples were taken at 8-hourly intervals for routine cell counting (trypan blue dye exclusion method), biochemical responses and metabolite analysis. 2.4 biochemical/standard analysis supernantant were collected for glucose, glutamine and lactate concentration analyses. these analyses were carried out at all designated time points (8-hourly intervals) in each condition. all experiments were carried out with 3 biological replicates for each experimental condition. conditioned media were collected for glucose, lactate and glutamine concentrations at designated time points. determination was carried out using biochemical analyzer ysi 2700. 2.5 igf-1 protein analysis conditioned media were separated from cells by centrifugation at 1400 rpm in 5 minutes. the expression of igf-1 protein was then studied using elisa kit (r&d systems, inc.) based on manufacturer instructions. 2.6 gcms analysis gcms analysis was performed on a 7890a gc system (agilent technologies) coupled to a 5975c inert xl msd. samples of supernatant (spent media) were spun down and injected (splitless mode, 10:1) onto a hp-5ms ultra inert (agilent technologies; 250 µm x 30 m x 0.25 µm film thickness) using helium (1.2 ml/min) as the carrier gas. components were separated by isothermal chromatography for 1 min at 60°c, followed by an increase to 325°c. mass spectra were acquired in positive ion mode using electron impact ionisation at 70 ev. the injector, ms source and ms quad temperatures were set at 250, 230 and 150°c respectively. 2.7 multivariate data analysis multivariate data analysis was conducted in simca-p+12.0. pca scores plot of gcms data from the spent media of cho-k1 was generated. in this study, the principle component analysis was based on the top 50% library-matching of metabolites (qual), given by the retention time. peak areas with low intensity were rejected. 3. results and discussion all experiments were carried out at 3 biological replicates for each experimental condition. cell growth and behaviour were observed under various conditions using standard analyses and gcms-based metabolomics approach. 3.1 cho-k1 cell growth iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 93 cho-k1 cell cultures were monitored every 8 hours for growth and viability. these data represent the average cell viability for 96 hours. cultures were seeded at a density of 2 x 10 5 cells/ml in 15 ml media. the cell growth of cho-k1 is shown in fig. 1. the highest saturation density of cho-k1 is 9.70 x 10 5 cells/ml at 80 th hour. the doubling time of cho-k1 cells is 29 h at specific growth rate of 0.02 cells h -1 . it can be seen in the graph that there is no lag phase in cell growth of cho-k1. 3.2 biochemical/standard analysis in mammalian cell culture, both glucose and glutamine can be utilized as the carbon sources to provide energy for cell growth through the catabolic pathway, and to transform to precursors or intermediates for synthesis of cellular components. while these components are vital for the mammalian cells to grow, the metabolites produced upon consumption of these components result in toxic waste products (metabolites) such as lactate [15]. figure 2 showed the trend of glucose and glutamine consumption as well as lactate production during the cho-k1 cell growth. fig.1: cell growth of cho-k1 cell. i=early log phase, ii=early mid log phase, iii=mid log phase, iv=late log phase, v=death phase. fig. 2: (a) concentration of glucose, (b) concentration of glutamine, (c) concentration of lactate during cho-k1 cell growth. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 94 the amount of glucose in the cell culture formulations is 2.0 g/l. in this culture, it can be seen that glucose was totally consumed after 64 hours. the high concentration of glucose is usually used because cells at high density consume a lot of glucose and the growth and maintenance of mammalian cells depend on glucose availability [19]. meanwhile, the trend of glutamine consumption was similar to glucose. when glucose levels are low and energy demands are high, cells can metabolize amino acids for energy. glutamine is one of the most readily available amino acids for use as energy source and it is a major source of energy for many rapidly dividing cell types in vitro. as the glucose concentration is decreased, glutamine becomes the sole energy source for cultured cells. the concentration of glutamine is regulated by the presence of glucose [17]. while glucose and glutamine are vital for the mammalian cells to grow, the metabolites produced upon consumption of these components result in toxic waste products (metabolites) such as lactate [15]. figure 2 shows that cell growth was reduced after 72 hours with the increase in lactate during the exponential phase. 3.3 igf-1 protein analysis figure 3 shows that the igf-1 concentration increased during the exponential phase and decreased after the highest saturation density point. but these analyses (biochemical/standard/igf-1 protein analyses) are difficult to promise us the concrete results in future as biomarker in culture system since the amount of consumption and accumulation of substrates in a cell growth will change associated/non-associated with the different growth culture environment setting. fig. 3: igf-1 production (pg/ml) in cho-k1 cell growth. 3.4 multivariate analysis figure 4 shows gcms data analysed by pca. the score plot shows that there were clear groupings of the samples in a pattern which relates to the time of sampling (growth phases). principle component 1 (pc1) explained 36% variation of the data while pc2 only explained 15% of the variation. based on pc1, samples were discriminated into (a) exponential phase and (b) early, late log and death phase. pc1 is most probably refers to the abundance of metabolites. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 95 interestingly, based on pc2, early log phase (i) and mid log phase (iii) – a, are grouped together while early-mid log (ii), late log (iv) and death phase (v) b are in one group. the mass spectra of group a and b were shown in fig. 6. we are currently analysing the phenomena to further understand the system in study. fig. 4: principle component analysis of the gcms spectra from secreted metabolites in cho-k1 cells. interestingly, based on pc2, early log phase (i) and mid log phase (iii) – a, are grouped together while early-mid log (ii), late log (iv) and death phase (v) b are in one group. the mass spectra of group a and b were shown in fig. 6. we are currently analysing the phenomena to further understand the system in study. figure 5 shows mass spectra at each phase of growth. there are two main dimensions of which the spectra can be analyzed. one is the complexity where the number of peak increases as the culture aged. the second dimension is related to abundance of compounds. however, in this study it is oserved that each phase revealed similar metabolites but with different abundance. the abundance of compounds increased at later stages of growth. this is in contrast to a study of yeast metabolomic footprinting where yeast culture footprints were simple at initial stages and became more complex at later stages allen et al. [18]. gcms-based metabolomics approach using spent media as samples is a potentially valuable tool in providing biomarker for the purpose of monitoring cell culture growth and product formation. this is particularly useful for large scale production where invasive technique such as cell counting from adherent cells are not favourable. online monitoring could be designed to complement bioreactor system where spent media is being sampled at designated time for subsequent analysis using gcms. in this study, it was identified that the highest abundance of compound throughout all phases is 2-cyclohexen-1-one, 2-methyl-5-(1-methylethenyl)-, (s)which is a terpenoid compound detected at 16.20 minute (cas number 057397-12-3). iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 96 fig. 5: mass spectra of global metabolite of cho-k1 cells at different growth phases: early-log [i], early – mid log [ii], mid log [iii], late log [iv] and death [v]. fig. 6: a – early-mid log [ii] and mid log [iii] phase spectra, (c) b – early-log [i], late log [iv] and death [v] phase spectra. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 97 although common biochemical analyses such as determination of glucose, glutamine and lactate concentration are routinely performed alongside cell counting, these analyses have not been able to describe the growth phases of cells as clearly as being shown by the pca results (fig. 5). pertaining to the detection of terpenoid as the highest concentration of compound in the culture, it suggests that this compound could be used as a biomarker to predict growth phase of a similar culture system without having to conduct cell counting and other common biochemical analyses. the biomarker can also be used to predict product formation. for instance, the cho-k1 cells in this study produced insulin-like growth factor 1 (igf-1) with the highest level found at 64 h (data shown in fig. 3). therefore the optimal level of terpenoid at 56 h would serve as a cue to the igf production thus enable on-time downstream processing such as harvesting of igf-1. to this end, global metabolite analysis offers the benefits of using a single method of analysis as compared to a battery of specific analyses targeting specific compounds in the quest to maintain efficiency of cell culture system and give insights on how to improve the system when necessary. 4. conclusion the growth phases of igf-1-producing cho-k1 were clearly identified using gas chromatography coupled to mass spectrometry together with bioinformatics tools pca to monitor changes in the levels of metabolites. the gcms based global metabolite analyses may enable and provide novel insights into the biological system under study. acknowledgement this research is funded by iium research matching grant scheme (rmgs). we would like to thank everyone who contributed to this research. references [1] goodacre, r., seetharaman, v., dunn, w.b., harrigan, g.g., kell, d.b.,“metabolomics by numbers: acquiring and understanding global metabolite data” [2] castilho, l.r., moraes, a.m., augusto, e.f.p, butler, m., “animal cell technology: from biopharmaceuticals to gene therapy”. taylor & francis group, new york (2008), p. 30. [3] yuki, s., katsuhiro, n., shuichi, k., novalina, l., hui-loo, l.c., haruhiko, m., “profiling of japanese green tea metabolites by gcms”. shimadzu [4] khoo, s.h.g., al-rubeai, m., “review: metabolomics as a complementary tool in cell culture”. biotechnology aplication biochemistry, portland press ltd (2007), 47: p. 71-84. [5] pope, g.a.m., d.a., defernez, m., aroso, m.a.a.m., fuller, l.j., mellon, f.a., dunn, w.b., brown, m., goodacre, r., kell, d.b., marvin, m.e., louis, e.j., roberts, i.n., “metabolic footprinting as a tool for discriminating between brewing yeasts”. yeast (2007), 24: p. 667-679. [6] gibney, m., “metabolomics in human nutrition: opportunities and challenges”. american journal of clinical nutrition (2005), 82: p. 497-503. [7] lindon, j.c.n., j.k., holmes, e., “the handbook of metabonomics and metabolomics”. (2006), amsterdam: elsevier. [8] kuystermans d, k.b., swiderek, h., al-rubeai, m., "using cell engineering and omic tools for the improvement of cell culture processes”. cytotechnology (2007), 53: p. 3-22. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology saberi et al. 98 [9] fernandez, c., fransson, u., hallgard, e., spegel, p., holm, c., krogh, m., warell, k., james, p., mulder, h., “metabolomic and proteomic analysis of a clonal insulin-producing β-cell line (ins-1 832/13)”. journal of proteome research (2008), p. 400-411. [10] takeda, s., sim, p. g., horrobin, d. f., sanford, t., chisholm, k. a., simmons, v., “mechanism of lipid peroxidation in cancer cells in response to gamma-linolenic acid (gla) analyzed by gc-ms(i): conjugated dienes with peroxyl (or hydroperoxyl) groups and cell-killing effects”. anticancer res (1993), p. 193-199. [11] wojciech, f., andreas, s., anna, f., clemens, a., jochen, s., wolfram, m., anton, a., jakob, t., “td-gc-ms analysis of volatile metabolites of human lung cancer and normal cells in vitro”. cancer epidemiol biomarkers prev (2010), p. 182. [12] sellick, c.a., knight, d., croxford, a.s.,maqsood, a.r., stephens, g.m., goodacre, r., dickson, a.j., “evaluation of extraction processes for intracellular metabolite profiling of mammalian cells: matching extraction approaches to cell type and metabolite targets”. metabolomics (2010), 6: p. 427 – 438. [13] griffin, j.l., “metabonomics: nmr spectroscopy and pattern recognition analysis of body fluids and tissues for characterisation of xenobiotic toxicity and disease diagnosis”. curr opin chem biol 7 (5): 648–54. [14] silas, g.v.b., sandrine, m., mats, a., jorn, s., jens, n., “mass spectrometry in metabolome analysis”. mass spectrometry reviews (2005), 24, 613– 646. [15] provost, a.b., g., “dynamic metabolic modeling under the balanced growth condition”. journal of process control, (2004). 14: p. 717-728. [16] scott, a. b., anli o., jennifer p., tim, a. s., tongtong, w., a. k., fermentanomics: monitoring mammalian cell cultures with nmr spectroscopy. j. am. chem. soc., 2010, 132 (28), pp 9531–9533. [17] http://www.sigmaaldrich.com/lifescience/cell-culture/learning-center/mediaexpert/glutamine.html [18] allen, j., davey, h.m., broadhurst, d., heald, j.k., rowland, j.j., oliver, s.g., kell, d.b., “highthroughput classification of yeast mutants for functional genomics using temetabolic footprinting”. nat. biotech. 2003, 21(6), pp 692-696 microsoft word 3_v17no2_compiled_v3_26nov16.docx iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 1 co-production of lactic acid and ethanol using rhizopus sp. from hydrolyzed inedible cassava starch and leaves azlin suhada azmi*, nurlisa yusuf, dzun noraini jimat, and noor illi mohamad puad department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. *corresponding author: azlinsu76@iium.edu.my (received: 5th jan. 2016; accepted: 19th aug. 2016; published online: 30th nov. 2016) abstract: production of lactic acid and ethanol from inedible cassava starch and leaves was investigated. prior to fermentation, hydrolysis of the starch and leaves was conducted. hydrolysis was optimized by manipulating at three levels each four particular factors, namely acid concentration, starch concentration, temperature, and reaction time. maximum glucose yield of 0.96 g/g was obtained when 2.5% (w/v) of cassava leaves with 2.5% (w/v) of starch was hydrolyzed using 0.20 m nitric acid at 160 oc of temperature for 10 min. the potential of hydrolyzed cassava starch and leaves was then investigated for lactic acid production using fungal rhizopus sp. the fermentation process was then conducted in a shake flask by varying four factors at three levels each. maximum lactic acid and ethanol yields of 0.95 g/g and 0.52 g/g, respectively, were achieved at different optimum conditions. lactic acid production was found to be linked to a decrease in ethanol production. design expert v6.0.8 was used to aid in the design of the experiment using taguchi’s methodology. abstrak: pengeluaran asid laktik dan etanol dari kanji dan daun ubi kayu tidak boleh dimakan telah dikaji. sebelum penapaian, hidrolisis kanji dan daun telah dijalankan. hidrolisis telah dioptimumkan dengan memanipulasi pada tiga peringkat setiap empat faktor tertentu, iaitu kepekatan asid, kepekatan kanji, suhu, dan masa tindak balas. hasil glukosa maksimum 0.96 g/g dihasilkan bila 2.5% (w/v) daun ubi kayu telah dihidrolisiskan dengan 2.5% (w/v) kanji menggunakan 0.20 m asid nitrik pada suhu 160 oc selama 10 min. potensi kanji dan daun ubi kayu dihidrolisis kemudiannya disiasat untuk pengeluaran asid laktik dengan menggunakan kulat rhizopus sp. proses penapaian kemudian dijalankan di dalam kelalang bergoncang dengan mengubah empat faktor di setiap tiga tahap. hasil maksimum asid dan etanol laktik adalah sebanyak 0.95 g/g dan 0.52 g/g, masing-masing, telah dicapai pada keadaan optimum yang berbeza. pengeluaran asid laktik didapati mempunyai kaitan dengan pengurangan pengeluaran etanol. design expert v6.0.8 telah digunakan untuk membantu dalam reka bentuk eksperimen menggunakan kaedah taguchi. keywords: cassava leaves; cassava starch; ethanol; lactic acid; rhizopus sp. 1. introduction numerous investigations on the development of biotechnological processes for lactic acid production have been performed to make the process both more efficient and economical. one attempt has been made to start production with cheap raw materials, for iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 2 the economical production of lactic acid with low levels of contaminants, high production rate and yield, fermentation with little or no pre-treatment, and year-round availability [1]. among starchy materials, cassava root is one of the candidates suitable for lactic acid production. it is cheap, has year-round availability, and is a high and efficient carbohydrate producer under suboptimal conditions of uncertain rainfall, infertile soil, and limited input encountered in the tropics [2]. cassava leaves are one of the byproducts from the cassava root harvesting process. their yield can amount to as much as 60 tons of wet leaves or 12 tons of dried leaves per hectare [3]. the leaves are usually discarded as waste after harvesting the roots, which are themselves under-researched and under-utilized. depending on the varieties, cassava leaves are rich in protein (14-40% dry matter), vitamin b1, b2, c and carotenes [4] and have a good amino acid content. they are also a good source of minerals, particularly calcium, magnesium, phosphorus, iron, and zinc [5]. these are the essential mineral sources for microorganism growth in a fermentation system. however, the leaves contain two cyanogenic glucosides, namely linamarin and lotaustralin. these compounds may be decomposed by linamarase, a naturally occurring enzyme in cassava, liberating hydrogen cyanide (hcn) [6]. fungal rhizopus species have been recognized as potentially suitable candidates for lactic acid production. rhizopus sp. has the ability to utilize starch-based materials [7, 8], although fungus such as rhizopus oryzae preferred glucose compared to other carbon sources [9, 10]. rhizopus strains also grow better in nitrogen-limited environments than lactic acid producing bacteria [11]. besides lactic acid, this fungus also produces ethanol, which may be beneficial later during the separation steps of these two products. the use of cassava leaves as a co-substrate to cassava starch for fermentation has great advantages for the production of lactic acid. the starch is available all year round and the leaves have adequate content of minerals for lactic acid production with rhizopus sp. thus, this study investigated the potential of inedible cassava starch and its leaves for lactic acid production and other byproducts such as ethanol using fungal rhizopus sp. in the fermentation process. the objectives of this research were as follows: i) to optimize the hydrolysis process of cassava starch and leaves for the maximum production of glucose and ii) to optimize the fermentation process for the maximum production of lactic acid. 2. materials and methods 2.1 preparation of cassava leaves and starch inedible cassava tubers and leaves were obtained from a cassava plantation in selangor, malaysia. the cassava tuber was peeled and washed with water and then cut into small pieces. it was then dried on perforated trays in a vacuum oven (memmert, germany) at 80 ºc for 24 hours. finally, the dried slices were grounded into powder and this powder was stored in a microwavable container for further use. cassava leaves were also dried in the vacuum oven at 80 ºc for 24 hours to remove water and cyanide. after that, the dry leaves were ground into powder before storing in a container for further use. 2.2 hydrolysis process a concentration of 2.5% (w/v) of cassava leaves was mixed with varying concentrations of tuber starch from 1.5% to 3.5% (w/v). nitric acid (merck, usa) was also prepared at different concentrations (0.12–0.20 m) for the hydrolysis process, which iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 3 was conducted in an oven (memmert, germany) at different temperatures (140–180 oc) for several minutes (10–30 min). the supernatant was then separated from the biomass, via centrifugation, in order to analyze the glucose using high performance liquid chromatography, hplc (waters, usa). hydrolysates prepared at selected conditions were used for fermentation (section 2.4). 2.3 microorganism and culture conditions rhizopus sp. was isolated from ragi tapai [12] and grown on potato dextrose agar (pda) under an incubation temperature of 37 oc for 7 days. the produced spores were collected, using l-loop, by shaving and extracting it with 25 ml of sterilized distilled water and filtering the mixture through sterilized filter paper. urea and nitrogen-phosporus-potasium (npk) at a ratio of 15-15-15 were prepared in distilled water at 0.8% and 0.09%, respectively, in a 150 ml shake flask. the medium was then sterilized at 121 oc for 30 min and later cooled to room temperature. after that, the spore suspension was inoculated in the medium and placed in an incubator shaker (infors ag, switzerland) at 37 ºc, 200 rpm, for 25 min. 2.4 fermentation process prepared inoculum was added into the hydrolyzed medium from section 2.2 and the ph was adjusted to different values (5–7) using hydrochloric acid and sodium hydroxide (merck, usa). then, it was incubated at different agitation speeds (150–350 rpm) and temperatures (25–35 oc) in an incubator shaker (infors ag, switzerland). fermentation took place within 5 days. 2.5 glucose, lactic acid, and ethanol analysis concentrations of glucose, lactic acid, and ethanol were determined from the supernatants obtained from section 2.4 and were analyzed using supelcogel c-610h column or ic-paktm ion exclusion column (sigma-aldrich, usa) with sh-1011p precolumn (sigma-aldrich, usa) on an hplc equipped with a refractive index (ri) detector. the column was eluted at 75 oc with 0.5 mm sulfuric acid at 1.0 ml·min−1. the glucose yield, x, was based on eq. (1): = 1.11 · (1) where g is the glucose concentration from the hydrolysis process and s is the starch concentration. the value of 1.11 is the correction factor as a result of the increase in total solids during glucose production [13]. yields of lactic acid and ethanol were based on eq. (2). = ℎ / ( / ) (2) 2.6 design of experiment (doe) a standard orthogonal array of l9 (34) was selected to examine a four-factor system. the l9 (34) array consisted of 9 runs requiring a fraction of the full factorial design of 81 runs. all the runs in this work involved the corresponding combination of levels to which the factors in the experiment were set. the experimental results were analyzed to independently extract the main effects of the factors. iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 4 3. results and discussion 3.1 optimization of the hydrolysis process table 1 shows an l9 orthogonal array of doe for hydrolysis process using taguchi methods. taguchi methods were chosen for the experiment because they provide an alternative to standard factorial designs. from the table, the maximum and minimum glucose yields were obtained from run 2 and run 7, respectively. the maximum and minimum values were respectively equivalent to 0.90 g/g and 0.26 g/g of starch-glucose conversion. the maximum concentration was obtained when 2.5% (w/v) of starch with 2.5% (w/v) leaves were hydrolyzed at a temperature of 140 oc using 0.16 m of hno3. the minimum concentration of glucose was obtained when 1.5% (w/v) of starch with 2.5% (w/v) of leaves (fixed amounts for all runs) were hydrolyzed at same temperature (140 oc) using 0.12 m of hno3. hno3 was used in this study, to take the advantage of the nitrogen content from the acid for the later fermentation process. table 1: glucose yield resulting from the hydrolysis of cassava starch and leaves run acid concentration starch concentration temperature time (min) yield (g/g) (m) (w/v %) (°c) 1 0.16 1.5 180 20 0.47 2 0.16 2.5 140 30 0.90 3 0.14 3.5 140 20 0.69 4 0.14 2.5 180 10 0.87 5 0.14 1.5 160 30 0.44 6 0.12 2.5 160 20 0.76 7 0.12 1.5 140 10 0.26 8 0.12 3.5 180 30 0.52 9 0.16 3.5 160 10 0.76 table 2: anova for the selected factorial model for optimization of the hydrolysis process source sum of degree of mean f value prob>f squares freedom square model 0.38 6 0.063 210.12 0.0047 acid conc.(a) 0.064 2 0.032 106.78 0.0093 starch conc.(b) 0.31 2 0.16 519.11 0.0019 temp.(c) 2.467e-3 2 1.233e-3 4.11 0.1957 residual 6.00e-4 2 3.000e-4 cor total 0.38 8 std dev. = 0.48 r-sq = 99.84% r-sq(adj) = 99.38% pred r-square = 96.79% to analyze the hydrolysis process, analysis of variance (anova) for the selected factorial model was conducted on the glucose yield and the results are presented in table 2. the analysis indicates that the model is significant, with two of the factors contributing significantly (p < 0.05) to the model. concentration of starch was the most significant factor affecting glucose concentration followed by the concentration of acid. this was iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 5 expected, since higher starch concentration resulted in higher glucose hydrolyzed from it. maximum glucose concentration was obtained when 2.5% (w/v) of cassava starch was used, and the concentration reduced when the starch concentration was at 3.5% (w/v), as shown in fig. 1. it may be concluded that the starch concentration of 2.5% (w/v) is the optimum concentration for this study. fig. 1: one factor plots of glucose yield (g/g) versus a: acid concentration (m), b: starch concentrations (%(w/v)) and c: temperature (oc), respectively. figure 1 shows that the glucose yield increased as the concentration of hno3 increased. the optimum concentration of hno3 was not determined at this stage. however, it was further analyzed using one-factor-at-time (ofat) and the results are plotted in fig. 2. the analysis was carried out at different acid concentrations ranging from 0.16 m to 0.22 m, while other parameters were kept constant. the ofat for the hydrolysis process was performed using equal amounts of cassava leaves and starch (i.e. 2.5% (w/v) each), and hydrolyzed at a temperature of 160 ºc for 10 minutes. these were the optimized values obtained during hydrolysis using the taguchi method, as previously shown in fig. 1. hydrolysis time did not contribute to the model and did not significantly affect glucose yield. thus, 10 min was selected for the ofat analysis. the highest yield of glucose of 0.96 g/g was later obtained at 0.20 m hno3. this was an improved yield of 7% compared to that previously obtained at 0.90 g/g. fig. 2: yield of glucose at different acid concentrations for ofat analysis. the hydrolysis process was validated to prove that the regression model is reliable. the hydrolysis process was done using two sets of process conditions, and the observed glucose concentration values were compared to predicted values for confirmation, as shown in table 3. the percentage difference between actual and predicted values is 11% to 14%; proving that the experiment is repeatable at an acceptable range. 0 0.2 0.4 0.6 0.8 1 0.16 0.18 0.2 0.22 yi el d of g lu co se (g /g ) acid concentration (m) iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 6 table 3: validation of the hydrolysis process run acid concentration starch concentration temperature concentration of glucose (g/l) (m) (g) (°c) actual predicted 1 0.14 2.5 160 22.01 25.01 2 0.16 2.5 160 22.68 26.35 3.2 optimization of the fermentation process 3.2.1 lactic acid production fermentation media consists of 2.5% (w/v) cassava leaves that were prepared using optimized conditions from the hydrolysis process (hydrolyzed using 0.2 m hno3 at a temperature of 160 oc for 10 min). rhizopus sp. was inoculated into the media for lactic acid production. to optimize the fermentation process, the design of experiment (doe) consists of a l9 orthogonal array of taguchi method analyzing four factors with three levels. the studied factors were ph, inoculum size, temperature, and agitation speed. maximum accumulation of lactic acid and ethanol concentrations were recorded as shown in table 4. generally, constant lactic acid concentrations were obtained after 36 hours of cultivation. the maximum yields of lactic acid and ethanol based on initial glucose concentration were obtained from run 2 and 4 at 0.95 g/g and 0.52 g/g, respectively. table 4: lactic acid and ethanol concentrations from nine set of runs. run ph inoculum size (spore/ml) agitation (rpm) temperature (°c) lactic acid (g/g) ethanol (g/g) 1 7 104 150 35 0.41 0.16 2 5 104 200 30 0.95 0.02 3 5 103 150 25 0.39 0.00 4 7 103 250 30 0.29 0.52 5 5 105 250 35 0.05 0.32 6 6 104 250 25 0.23 0.23 7 6 103 200 35 0.09 0.02 8 7 105 200 25 0.06 0.06 9 6 105 150 30 0.09 0.00 the analysis of variance (anova) for lactic acid of the selected factorial model is presented in table 5. the model f-value implies that the model was significant. in this case, inoculum size (b) was the only significant model term with the lowest p-values (0.0098) among the studied factors. agitation and temperature of the fermentation process did not significantly affect lactic acid production. however, the optimum level may be determined from one factor plot of lactic acid with respect to inoculum dilution, agitation speed, and temperature (fig. 3). from the figure, the optimum levels for inoculum size, agitation, and temperature were 104/ml, 150 rpm, and 30 °c, respectively. iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 7 table 5: anova for the selected factorial model for optimization of lactic acid yield source sum of degree of mean f value prob>f squares freedom square model 378.32 6 63.05 43.68 0.0225 ino. size (b) 291.22 2 145.61 100.88 0.0098 agitation (c) 33.25 2 16.62 11.52 0.0799 temp (d) 53.85 2 26.93 18.66 0.0509 residual 2.89 2 1.44 cor total 381.20 8 std dev. = 1.20 r-sq = 99.24% r-sq(adj) = 96.97% pred r-squared 84.67% fig. 3 one factor plots for lactic acid with respect to b: inoculum size, c: agitation speed, and d: temperature, respectively. the maximum yield of lactic acid was attained with the initial inoculum size of 104/ml. the same result was also reported by others where maximum lactic acid was produced at low initial inoculum size; around 103104/ml [14, 15]. it was also reported that the size of inoculum influenced the morphology of the rhizopus fungus [15-18]. when the size of the inoculum was below 105/ml, they produced a mycelia floc while larger sizes resulted in the formation of pellet or clump mycelia. in this study, mycelia floc was observed and the morphology might have influenced the oxygen transfer and produced different concentrations of lactic acid. rhizopus sp. requires oxygen supply during aerobic fermentation on order to produce lactic acid as the main product [19]. agitation is important for proper distribution of oxygen in a shake flask. the agitation speed for rhizopus sp. growth ranged from 100 rpm to 400 rpm [20]. results obtained from this study have shown that the lowest agitation speed of 150 rpm produced the maximum amount of lactic acid. this might be due to the sensitivity of rhizopus sp. to agitation speed which also had been observed by mohd nasir et al. [21] and tanyildizi et al. [22]. rhizopus fungus can grow in a fermentation temperature ranging between 25 to 45 oc [8, 23, 24]. as with growth, lactic acid production is also dependent on the temperature. as previously mentioned, the optimum temperature for maximum lactic acid yield was at 30oc. similar results were also reported by huang et al. [23, 25] when they fermented potato wastewater using rhizopus arrhizus. in their study, biomass was decreased when temperature increased. control of initial ph is important for high lactic acid yield since ph value will drop during its production to around ph 2.4 [25]. the ph is an important factor to be controlled and monitored in any fermentation process. calcium carbonate is commonly added to neutralize lactic acid during fermentation. in this study, no neutralizing reagent was used. iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 8 however, cassava leaves used in this study contained a detected amount of magnesium (5  10-3 – 7.5  10-3 g/g) in dried cassava leaves and traces of iron and zinc (data not shown). magnesium might have some effect as a neutralizing agent and in controlling the ph. however, it was found that ph had no significant effect on lactic acid yield in this study. nevertheless, the range selected in this study (ph value of 5.0 to 7.0) is the favorable ph range for high lactic acid yield [8, 23]. 3.2.2 ethanol production unlike lactic acid bacteria, rhizopus sp. also produces byproducts such as ethanol. the maximum and minimum yields of ethanol conversion were obtained from runs 4 and 3, respectively, as shown in table 4. generally, when ethanol production is high, lactic acid yield will be lower. the increase in lactic acid production was coupled with a reduction of biomass and byproducts [19]. table 6: anova for the selected factorial model for optimization of ethanol yield source sum of degree of mean f value prob>f squares freedom square model 0.49 6 0.082 25.74 0.0379 ph(a) 0.10 2 0.052 16.33 0.0577 agitation (c) 0.36 2 0.18 57.39 0.0171 temp (d) 0.022 2 0.011 3.48 0.2230 residual 6.349e-3 2 3.175e-3 cor total 0.50 8 std dev. = 0.056 r-sq = 98.72% r-sq(adj) = 94.89% pred r-squared 74.11% fig. 4: one factor plots for ethanol with respect to a: ph, c: agitation speed, and d: temperature, respectively. anova, as presented in table 6, shows that agitation was the only factor that significantly affected (p < 0.05) ethanol production. it is interesting to note that, the highest agitation of 250 rpm produced the highest ethanol yield (fig. 4). this was not expected, since ethanol has been reported to be produced more in the absence of oxygen or in oxygen-limited cultures [11, 19, 26]. however, this result coincided with lactic acid production where the lowest agitation produced the highest lactic acid yield. the only explanation of this phenomenon is that during high speed agitation, rapid oxygen utilization for initial growth of spores produced mycelia and rapidly reduced oxygen levels in the flask. in the shake flask, there was no aeration to supply oxygen. this created an anaerobic environment, or oxygen-limited environment, and produced more ethanol than lactic acid. temperature and ph did not significantly affect ethanol production. however, from the graph shown in fig. 4, maximum ethanol was achieved at a temperature of 35 oc iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 9 and a ph of 7. as mentioned, there is an inverse relationship between lactic acid and ethanol production, as 35 oc corresponds to the lowest lactic acid yield (fig. 3). 4. conclusions two process optimizations, namely hydrolysis and fermentation, were successfully performed using the taguchi method. glucose production was optimized for maximum yield through dilute acid hydrolysis. four factors were studied: acid concentration, starch concentration, temperature, and reaction time, with optimized levels at 0.2 m, 2.5% (w/v), 160 oc and 10 min, respectively. the same concentration of 2.5% (w/v) cassava leaves was employed during the hydrolysis process. fermentation was then optimized by varying four factors at three levels each for lactic acid and ethanol production. factors were inoculum size, agitation speed, ph, and temperature. production of lactic acid had an inverse relationship with the production of ethanol which required a different culture environment for optimum yield. high yields of lactic acid were obtained at inoculum size, temperature, and agitation speed of 104/ml, 30 oc and 150 rpm, respectively. on the other hand, maximum ethanol yield was attained at the temperature, agitation speed, and ph of 35 oc, 250 rpm, and 7, respectively. this study shows the potential of using cassava leaves as one of the nutrient sources in microbial fermentation, while reducing waste accumulation problems caused by the root harvesting process. acknowledgements the authors would like to thank mr. kok keong lim for supplying cassava raw materials for this research. references [1] wee y-j, kim j-n, ryu h-w. (2006) biotechnological production of lactic acid and its recent applications. food technol. biotechnol.,44:163-72. [2] fregene m, puonti-kaerlas j. (2002) cassava biotechnology. cassava: biology, production and utilization. 10:179-207. [3] lim kk. (2011) project consultant from kibartek sdn bhd. 2011. [4] fasuyi ao. (2005) nutrient composition and processing effects on cassava leaf (manihot esculenta, crantz) antinutrients. pak j nutr., 4:37-42. [5] ravindran v. (1992) preparation of cassava leaf products and their use as animal feeds. roots, tubers, plantains and bananas in animal feeding. fao animal production and health paper. [6] cereda m, mattos m. (1996) linamarin: the toxic compound of cassava. j. venomous anim. toxins., 2:6-12. [7] taskin m, ortucu s, unver y, arslan np, algur of, saghafian a. (2013) l-lactic acid production by rhizopus oryzae mbg-10 using starch-rich waste loquat kernels as substrate. starch stärke, 65:322-329. [8] zhang zy, jin b, kelly jm. (2007) production of lactic acid from renewable materials by rhizopus fungi. biochem. eng. j., 35:251-263. [9] bulut s, elibol m, ozer d. (2004) effect of different carbon sources on l(+) -lactic acid production by rhizopus oryzae. biochem. eng. j., 21:33-37. [10] park ey, anh pn, okuda n. (2004) bioconversion of waste office paper to l (+)-lactic acid by the filamentous fungus rhizopus oryzae. bioresour. technol., 93:77-83. [11] soccol c, marin b, raimbault m, lebeault j-m. (1994) potential of solid state fermentation for production of l (+)-lactic acid by rhizopus oryzae. appl. microbiol. biotechnol., 41:286-290. iium engineering journal, vol. 17, no. 2, 2016 azmi et al. 10 [12] azmi as, ngoh cg, mel m. (2013) prediction of significant factors in the production of ethanol by ragi tapai co-culture using taguchi methodology. afr. j. biotechnol., 10:18331841. [13] widiasa in, wenten ig. (2009) saccharification of native cassava starch at high dry solids in an enzymatic membrane reactor. reaktor,12:129-136. [14] xiao z, wu m, beauchemin m, groleau d, lau pc. (2011) direct fermentation of triticale starch to lactic acid by rhizopus oryzae. ind. biotechnol.,7:129-134. [15] büyükkileci ao, hamamcı h, yucel m. (2006) lactate and ethanol productions by rhizopus oryzae atcc 9363 and activities of related pyruvate branch point enzymes. j. biosci. bioeng.,102:464-466. [16] kossen n. (2000) the morphology of filamentous fungi. history of modern biotechnology ii: springer, 1-33. [17] liao w, liu y, frear c, chen s. (2007) a new approach of pellet formation of a filamentous fungus–rhizopus oryzae. bioresour. technol., 98:3415-3423. [18] wu x, jiang s, liu m, pan l, zheng z, luo s. (2011) production of l-lactic acid by rhizopus oryzae using semicontinuous fermentation in bioreactor. j. ind. microbiol. biotechnol., 38:565-571. [19] meussen bj, de graaff lh, sanders jp, weusthuis ra. (2012) metabolic engineering of rhizopus oryzae for the production of platform chemicals. appl. microbiol. biotechnol., 94:875-886. [20] naranong n, poocharoen d. (2001) production of l-lactic acid from raw cassava starch by rhizopus oryzae nrrl 395. the kasetsart j (nat sci)., 35:164-170. [21] nasir nam, kamalbahrin mam, mohamad n, anuar h, mel m, othman r (2011). effect of rhizopus oryzae fermentation on kenaf-based polylactic acid’s monomer. iium eng. j.,12(4):83-87. [22] tanyıldızı mş, bulut ş, selen v, özer d. (2012) optimization of lactic acid production with immobilized rhizopus oryzae. afr. j. biotechnol.,11:8546-8552. [23] huang lp, jin b, lant p, zhou j. (2005) simultaneous saccharification and fermentation of potato starch wastewater to lactic acid by rhizopus oryzae and rhizopus arrhizus. biochem. engin. j., 23:265-276. [24] thongchul n, navankasattusas s, yang s-t. (2010) production of lactic acid and ethanol by rhizopus oryzae integrated with cassava pulp hydrolysis. bioprocess and biosystems engineering, 33:407-416. [25] huang lp, jin b, lant p, zhou j. (2003) biotechnological production of lactic acid integrated with potato wastewater treatment by rhizopus arrhizus. j. chem. technol. biotechnol., 78:899-906. [26] skory cd. (2003) induction of rhizopus oryzae pyruvate decarboxylase genes. curr. microbiol., 47:59-64. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 1 purification and partial characterization of l-asparaginase enzyme produced by newly isolated bacillus sp dzun noraini jimat*, intan baizura firda mohamed, azlin suhaida azmi and parveen jamal department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. *corresponding author: jnoraini@iium.edu.my (received: 18 th march 2016; accepted: 13 th nov. 2017; published on-line: 1 st dec. 2017) abstract: a new bacterial producing l-asparaginase was successfully isolated from sungai klah hot spring, perak, malaysia and identified as bacillus sp. it was the best lasparaginase producer as compared to other isolates. production of l-asparaginase from the microbial strain was carried out under liquid fermentation. the crude enzyme was then centrifuged and precipitated with ammonium sulfate before being further purified by chromatographic method. hitrap deae-sepharose fast flow ion exchange chromatography followed by separation on superose 12 gel filtration were used to obtain pure enzyme. the purified enzyme showed 10.11 u/mg of specific activity, 50.07% yield with 2.21 fold purification. the purified enzyme was found to be dimer in form, with a molecular weight of 65 kda as estimated by sds-page. the maximum activity of the purified l-asparaginase was observed at ph 9 and temperature of 60 o c. abstrak: kajian penyelidikan ini telah berjaya menghasilkan enzim l-aspraginase daripada bakteria-bakteria baru yang diambil dari kolam air panas, sungai klah, perak, malaysia dan ia dikenal pasti sebagai bacillus sp. teknik isolasi bakteria ini adalah teknik terbaik dalam menghasilkan enzim l-asparaginase berbanding teknik-teknik lain. penghasilan enzim ini dibuat menerusi proses fermentasi. kultur bakteria yang diperolehi diempar dan diikuti presipitasi menggunakan ammonium sulfat sebelum proses penulenan seterusnya dilakukan menggunakan kaedah kromatografi. kolum penukaran ion jenis hitrap deae-sepharose fast flow diikuti dengan pemisahan oleh gel superose 12 telah digunakan untuk mendapatkan enzim l-asparaginase yang tulen. hasil kajian mendapati enzim tulen yang diperolehi mempunyai aktiviti spesifik sebanyak 10.11 u/mg daripada 50.07% enzim yang dihasilkan dan berjaya mencapai 2.21 kali ganda tulen dari enzim tanpa proses penulenan. enzim tulen yang diperolehi didapati dalam bentuk “dimer“ dengan berat molekular sebanyak 65 kda yang ditentukan menerusi sds-page. enzim ini juga menunjukkan aktiviti yang tinggi pada ph 9 dan suhu 60 o c. keywords: bacillus sp.; l-asparaginase; ion exchange chromatography; gel filtration chromatography; partial characterization 1. introduction l-asparaginase is one of the important enzymes in therapeutic treatment as well as the food industry. it is also known as asparagine aminohydrolase. l-asparaginase is a generic iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 2 denomination for enzymes that catalyse the transformation of l-asparagine into their respective acid and ammonia [1]. as reported by dominika et al. [2], biochemical and kinetic properties of enzymes vary with the genetic nature of the microbial strain. l-asparaginase possesses anti-tumour activity and is accepted as chemotherapeutic agents. this enzyme is used as an effective treatment for acute lymphoblastic leukemia, lymphosarcoma and tumor cells or others that are related to tumor therapy in combination with chemotherapy [3]. it is mainly used in the treatment of leukemia in children. as described by dominika et al. [2] and borah et al. [4], l-asparagine acts as an important amino acid for the growth of tumour cells. l-asparaginase, lowering the concentration of l-asparagine, retard the growth of cancer cells. they require an external amino acid because they cannot synthesize asparagine by the enzyme asparagine synthetase. the application of l-asparaginase as a drug in the treatment of leukemia is to reduce and eliminate the amount l-asparagine in the blood and subsequently involves monitoring the level of the corresponding amino acid in blood of treated leukemia patients. besides therapeutic treatment, l-asparaginase also has a significant role in the food industry. as mentioned in previous studies, the level of acrylamide in baked and fried food products (i.e. fried potato) is reduced by the action of l-asparaginase [1]. acrylamide is known as a cancer causing agent. it presents in heat-derived (fried and baked) foods and contains some reducing sugar. other studies reported that the contents of acrylamide should be reduced since it is proven to be neurotoxic, genotoxic, carcinogenic, and toxic to reproductive system [5]. as discussed by [3], acrylamide is formed by the result of a maillard reaction, which is a heat-induced reaction. heat-induced reactions between the αamino group of the free amino group of the free amino acid l-asparagine and carbonyl groups of reducing sugar like glucose can derive acrylamide. l-asparaginase helps in hydrolysing asparagine, which in turn significantly reduces the formation of the substance. nowadays, researchers all around the world are interested in studying the production of thermostable l-asparaginase from various sources. thermostable enzymes are considered to be of biotechnological and industrial interest as their enhanced stability at elevated temperatures could greatly reduce enzyme replacement costs or permit processes to be carried out in such conditions. the thermostable enzymes are proven to have many advantages over the mesophilic enzymes. it has been reported that l-asparaginase can be produced from several sources such as bacteria, fungi, and animal [6]. a large number of thermophilic microorganisms, especially bacteria, capable of producing the thermostable l-asparaginase have been reported globally. most of the levels of enzyme activity produced by microbial strains from a natural environment are low and need to be elevated or increased for industrial production. the level of enzyme production by one microorganism differs with other microorganisms. moreover, levels differ in terms of both composition and properties. l-asparaginase from microbial sources must be purified before it can be characterized in terms of physical and biological characteristics. it is important to remove all contaminants and impurities present in the crude enzyme. enzyme purification is an important downstream processing step in manufacturing biopharmaceutical products where all the contaminants and impurities need to be removed. normally, biopharmaceuticals require exceptional purity, making downstream processing a critical step of the overall processes. the selected purification methods must be simple, easy, and adaptable, particularly in large scale. the common purification step that has been applied in protein purification is combination of precipitation (fractionation/salting out) in order to precipitate out the protein. several chromatographic methods are added to the precipitation as polishing steps. iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 3 therefore, the present work aims to purify and characterize the asparaginase from a local newly isolated strain of bacillus sp. the enzyme was purified using conventional steps of purification. then, the purified enzyme was partially characterized in terms of ph and temperature stability. 2. materials and methods 2.1 microorganism one liter of modified m9 medium containing: na2hpo4.2h2o, 6.0 g; kh2po4, 3.0 g; nacl, 0.5 g; l-asparagine, 5.0 g; 1 m mgso4.7h2o, 2.0 ml; 0.1 m cacl2.2h2o, 1.0 ml ; 20% glucose stock, 10.0 ml; agar 20.0 g was prepared and supplemented with 3 ml phenol red as an indicator. the medium was adjusted to ph 7 and autoclaved at a temperature of 121 o c. one hundred microliters of collected water (from the hot spring) was plated onto the agar medium and gently streaked. then, the plates were incubated at a temperature of 50 o c for 48 hrs. the isolated bacteria, which produced l-asparaginase, were screened based on a wide formation of a pink zone around the colonies on the plates (qualitative assay) as well as a concentration of released ammonia (quantitative assay). the potential bacteria that produced the highest enzyme activity (based on release of ammonia) were selected for further studies. the selected bacterial strain was confirmed as bacillus sp. by 16s rrna gene sequencing. a single colony of the strain was cultured a few times to obtain a pure strain. the pure culture of bacillus sp. was maintained and preserved in nutrient agar at 4 o c and stock culture (contained glycerol) at -20 o c. 2.2 production of l-asparaginase from bacillus sp. under submerged fermentation two percent (1.46×10 8 cfu/ml) of inoculum (bacillus sp.) were inoculated into 50 ml of media: na2hpo4.2h2o, 6.0 g; kh2po4, 3.0 g; nacl, 0.5 g; l-asparagine, 5.0 g; 1 m mgso4.7h2o, 2.0 ml; 0.1 m cacl2.2h2o, 1.0 ml; 20% glucose stock, 10.0 ml was placed in 250 ml erlenmeyer flasks and incubated at 50 o c at 150 rpm for 48 hrs. the medium without innoculum was used as a control. each experiment was done in triplicates. the culture broth was collected after 48 hrs for determination of l-asparaginase activity and protein concentration. 2.3 l-asparaginase assay the bacteria cultures were harvested by centrifugation at 6,000 rpm for 15 min. sample of enzyme extract (0.1 ml) was mixed with 0.2 ml of 0.05 m tris-hcl (ph 8.6), followed by 1.7 ml of 0.01 m l-asparagine then the mixture sample was incubated for 10 min at 37 o c. trichloroacetic acid (0.5 ml of 1.5 m solution) was added to the mixture in order to stop the reaction. after that, the mixture was centrifuged at 10,000 rpm, then 0.5 ml of the supernatant was diluted to 7 ml with distilled water together with 1 ml of nessler reagent. after 10 min, the absorbance was measured at 480 nm. the optical density (od) readings were then compared to standard curve of ammonia. one unit (u) of lasparaginase was defined as that amount of enzyme which liberating 1 µmol of ammonia per minute at 37 o c under the assay conditions. 2.4 protein concentration concentration of protein was determined by mixing the 1.50 ml protein reagent (pierce™ 660 nm protein assay reagent) with 0.10 ml of sample. the sample was the supernatant that was taken after centrifuging the culture at 6,000 rpm for 15 minutes. after adding the protein reagent into the sample, the od was measured at 660 nm. then, the ods were compared to a standard curve of bovine serum albumin (bsa) concentration. iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 4 2.5 purification of l-asparaginase 2.5.1 ammonium sulfate precipitation the crude enzyme (supernatant) was prepared by centrifuging the cell cultures at 10,000 rpm for 15 min at 4 o c. ammonium sulfate powder was added into the supernatant at 4 o c (slowly stirred) to bring it to 90% ammonium sulfate saturation. then, the precipitated protein was centrifuged at 10,000 rpm for 15 min at 4 o c. the precipitated protein was dissolved in a minimal volume (2-3 ml) of 0.05 m tris-hcl, ph 8.5. then, the dialysis was conducted to remove the excess ammonium salt present in the protein solution by putting this protein in a dialysis bag. principally, the protein was left retained in the dialysis bag while allowing water and salt to permeate out of the bag. after that, this dialysis bag was immersed in a bulky volume of buffer (0.05 m tris-hcl, ph 8.5) and agitated for 24 hours at 4 o c. 2.5.2 ion exchange chromatography using hitrap diethylaminoethyl (deae) sepharose fast flow one milliliter of the dialysate from the previous step was filtered through 0.45 µm filter prior to loading into hitrap™ deae sepharose fast flow chromatography column (dimension: 0.7 x 2.5 cm; volume: 1 ml; bead size: 45-165 µm). two buffer solutions were used in ion exchange chromatography; 0.05 m tris-hcl, ph 8.5 (start buffer) and 0.05 m tris-hcl, ph 8.5 with 1 m nacl, ph 8.5 (elution buffer). the column was equilibrated with 0.05 m tris-hcl, ph 8.5 at 1 ml/min prior to use. then, the enzyme was eluted by the elution buffer, 0.05 m tris-hcl, ph 8.5 with 1 m nacl, ph 8.5) at a flow rate of 1 ml/min and 2 ml fractions were collected. the fractions with the highest peak were pooled together. then, the fractions were analysed for determination of lasparaginase activity and protein concentration. 2.5.3 gel filtration using superose® 12 the pooled fractions with high l-asparaginase activity from the previous step (section 2.5.2) were further purified using superose® 12 (dimension: 1 x 30–31 cm; volume: approximately 24 ml); optimal separation range (globular proteins): 1-300 kda; average particle size: 11 μm). the column was equilibrated with 0.05 m tris-hcl (ph 8.5) at 0.8 ml/min. the protein elution was done with same buffer at a flow rate of 0.8 ml/min and 1 ml fractions were collected. the fractions with the highest peak were pooled together. then, the fractions were analysed for determination of l-asparaginase activity and protein concentration. 2.6 characterization of l-asparaginase 2.6.1 determination of molecular weight using sds-page sodium dodecyl sulfate polyacrylamide gel electrophoresis (sds-page) was used to estimate the molecular weight of the purified l-asparaginase. in the present work, the method was adopted from gupta et al. [7]. a 12% resolving or separating gel, ph 8.8 (sterilized distilled water: 1.7 ml; 30% degassed acrylamide: 2.0 ml, resolving buffer: 1.25 ml; 10% sds: 50 μl; 10% ammonium persulfate: 50 μl; temed: 5 μl) and 4% stacking gel, ph 6.8 (sterilized distilled water: 3.05 ml; 30% degassed acrylamide: 0.65 ml, stacking buffer: 1.25 ml; 10% sds: 50 μl, 10% ammonium persulfate: 50 μl; temed: 10 μl) were prepared. the casting frames were set (two glass plates were clamped together in the casting frames) on the casting stands. an appropriate amount of separating gel solution was filled into the gap between the glass plates. water was filled on the top of the separating gel in order to check for any leakage between the glasses and to avoid bubbles. iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 5 after separating gel was polymerized, the stacking gel solution was poured until overflow. then, the well-forming comb was inserted without trapping air under the teeth. the comb was taken out after complete gelation of the stacking gel. after that, the 1x running buffer was poured into the inner chamber until the buffer surface reached the required level in the outer chamber. ten microliters of samples were mixed with 2 µl of sample buffer (loading buffer) and the mixture was heated at 95 o c (denaturing the samples) for 10 min. next, 10 µl of prepared samples were loaded into each well. the protein marker (thermo scientific pre-stained protein ladder 10-170 kda) was loaded into the first lane. the equipment was operated after everything was set up correctly. the voltage was set at 120 v. when the dye reached to the bottom of the gel, the supplied power was turned off and the gel unit was removed from the electrophoresis unit. the plates were gently separated with the help of a spatula and the gel was carefully transferred into the staining solution for staining overnight. next, it was destained for 7 hours. the molecular weight of the l-asparaginase was measured with reference to the standard markers used. protein bands were visualized by staining with coomassie r-250 blue. 2.6.2 effect of ph on stability of enzyme activity the effect of ph on the stability of l-asparaginase activity was determined by incubating the purified enzyme in buffers with various ph values. purified l-asparagin ase (100 µl) was incubated with 0.2 ml of buffer solutions (different ph) in the absence of substrate (l-asparagine) for 24 hours at 4 o c. the buffer solutions were 0.05 m sodium acetate-acetic acid (ph 4 and ph 5), 0.05 m sodium phosphate (ph 6 and ph 7), 0.05 m tris-hcl (ph 8 and ph 9) and 0.05 m glycine-naoh (ph 10). after that, 1.7 ml of 0.01 m l-asparagine was added into the solutions and the activity of l-asparaginase was determined under assay conditions. 2.6.3 effect of temperature on stability of enzyme activity the temperature stability of l-asparaginase was determined by incubating 100 µl of purified enzyme at different temperatures (30, 37, 40, 50, 60, 70 and 80 o c) for 60 minutes. then, the enzyme activity was measured after adding 1.7 ml of substrate under assay conditions. 3. results and discussion a summary of enzyme activity and yield of purified l-asparaginase from bacillus sp. is shown in table 1. the specific activity before purification was 4.58 u/mg. upon precipitation with ammonium sulfate, the specific activity was found to be increased by 1.33 fold with a yield of 98.07% and the total protein content was found to be decreased by 1.36 fold. enzyme activity was slightly loss (2.13%) at this stage. it indicated some contaminant proteins were removed by the salting out process. the precipitated enzyme was then purified by ion exchange chromatography (iec) through a hitrap deaesepharose fast flow column that was eluted in 50 mm tris-hcl and 1 m nacl, ph 8.5 at a flowrate of 1.0 ml/min. in this step, l-asparaginase was purified to 1.58 fold with a yield of 69.62% and specific activity of 7.21 u/mg. a typical elution profile of enzyme from the deae-sepharose ion exchange column (fig. 1) shows one distinct major peak at fraction numbers 5 to 6. high enzyme activity was located at the fraction numbers. both fractions were pooled and tested for l-asparaginase quantitative activity. the fractions containing high enzyme activity were then applied to superose 12 gel filtration column. the activity was located in peak 2. after ion exchange chromatography, only 1.5% of the total protein from crude extract was eluted (2.26 fold decreased), but the specific activity was found to iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 6 be increased by 2.21 fold. the specific activity after the gel filtration column was 10.11 u/mg. the specific activity of purified l-asparaginase of bacillus sp. obtained in the present study was 7.21 u/mg. it was 28% less than previous study which was also performed via two chromatography steps (13.97 u/mg) with 36.204% yield [7]. another study reported a recovery of 18.46% with a specific activity of 69.43 u/mg of an extracellular l-asparaginase from mucor hiemalis [8]. table 1: summary of purification steps of newly isolated bacillus sp. producing lasparaginase. sample l-asparaginase activity (u/ml) protein concentration (mg/ml) specific enzyme activity (u/mg) % yield fold purification crude enzyme extract 0.19 0.03 0.041 0.00871 4.57 100 1 ammonium ppt (90% saturation) 0.18 0.008 0.030 0.0417 6.10 98.07 1.33 hitrap deae-sepharose fast flow column – ion exchange chromatography 0.13 0.031 0.018 0.00565 7.21 69.62 1.58 superose 12 column gel filtration 0.09 0.0171 0.009 0.0076 10.11 50.07 2.21 fig. 1: elution profile of l-asparaginase from deae-sepharose chromatography column. gel filtration chromatography (gfc) was performed as a polishing step in purification. superose 12 column was used in this chromatography step on a fast protein liquid chromatography to confirm whether the purified protein was composed of a mixture of other higher molecular weight aggregates or lower monomer forms in addition to the native tetramer state. in the present work, a superose 12 column (ge healthcare) was equilibrated with 50 mm tris-hci ph 8.5 and 2 ml of the purified asparaginase was loaded onto the column and eluted at a flow rate of 1.0 ml/min. in fig. 2, the elution diagram of the size exclusion of the purified enzyme also revealed a single peak at a absorbance at 280nm fraction number iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 7 fraction number of 19 confirming that it was a pure preparation. previous studies reported the fact that a single sharp peak on the elution diagram refers to the pure target protein [9]. fig. 2: elution profile of asparaginase from superose 12 chromatography column. the sds-page analysis of the purified l-asparaginase from bacillus sp. as illustrated in fig. 3 revealed a protein band migrating at approximately 65 kda. three bands were observed in sds-page after ion exchange chromatography. and after gel filtration chromatography, only one band was observed. from the protein band observed, it can be claimed that the enzyme was purified to near homogeneity (lane 3). the purified enzyme showed a single band in sds-page gel indicated that it was homogenous [9]. generally, l-asparaginase is known as a tetramer protein molecule [10]. tetramer protein is built up of four protein subunits. the similar protein structure of escherichia coli lasparaginase was discovered by jha et al.[11]. in the present study, l-asparaginase from bacillus sp. was observed to have dimer form of protein. fig. 3: sds-page analysis of purified l-asparaginase from bacillus sp. lane 1: partial purification by ammonium sulfate precipitation; lane 2: eluted fraction contains asparaginase obtained from hitrap deaesepharose fast flow ion exchange chromatography; lane 3: eluted fraction contains asparaginase obtained from gel exclusion by superose 12 column chromatography. absorbance at 280nm fraction number iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 8 figure 4 shows that the l-asparaginase activity secreted by the isolated bacillus sp. was stable at ph 9 after 1 hour incubation at 37 o c. the highest enzyme activity (0.20±0.044 u/ml) was recorded at this ph condition. it seems that the highest enzyme activity was found at the alkaline condition. it was similar to what has been reported by most recent researchers. they found that most of l-asparaginase activities from microbial strains are stable at alkaline environment. the enzyme activity was still comparable and good at ph 8 and ph 10 even though it was slightly lower than activity at optimum ph (ph 9). it is in accordance with the previous studies, the l-asparaginase activity as well as enzyme yield, regardless their sources (l-asparaginase produced by any microbial strains) were found to be low when the enzyme was incubated at ph below and above its optimum ph [9]. based on the obtained result, it is clear that enzyme activity was very low when the enzyme was incubated in buffers with acidic condition (ph 4-6). this acidic condition probably affected the active site of this enzyme which led to its low activity. as reviewed by other studies, the stability of this enzyme at a wide range of ph is dependent on its sources [11]. previous studies reported that enzymes‘ surface exhibit a large number of basic and acidic groups that get ionized depending on surrounding ph condition [8]. fig. 4: effect of ph on l-asparaginase activity. in general, bacillus sp. is characterized as a bacteria species that grow well in moderate environment; they are known as mesophiles. mesophiles grow best in moderate temperature, typically between 20 and 45 o c. figure 5 shows the bacteria that grow in that moderate temperature still can produce the asparaginase which is stable at high temperature (60 o c). the recorded l-asparaginase activity was 0.170±0.01 u/ml. lasparaginase activity at high temperature (40 o c to 80 o c) is higher than enzyme activity at normal environment (30 o c 40 o c). different sources of the l-asparaginase enzymes may have different stabilities of temperature which due to dissimilarity of their amino acid sequences and structures. denaturation and degradation of proteins or enzymes is likely to occur at temperature above 80 o c. both may cause loss of enzyme activity. it was further explained by [12], the extracellular and cell-bound thermophilic enzymes (i.e., saccharidases and proteases) are highly stable and therefore optimally active at temperatures above, or sometimes far above, the host organism’s optimum growth temperature. they reported that at a temperature of 117 o c, thermococcus litoralis amylopullulanase was optimally active even though its optimum growth temperature was 88 o c. it is still not understood whether all thermophilic proteins can be expressed in a mesophilic environment or not. only fewer than 10% of all the thermophilic enzymes obtained by e. coli have been found to poses stability, catalytic, or structural properties distinct from the enzyme‘s purified from the native organism. other studies reported that thermostable l-asparaginase were produced by escherichia coli and pseudomonas 0 0.05 0.1 0.15 0.2 0.25 0.3 4 5 6 7 8 9 10 l-asparaginase activity (u/ml) p h l-asparaginase activity 50mm sodium acetate acetic acid 50mm sodium phosphate 50mm tris-hcl 50mm glycine-naoh iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 9 aeruginosa since the enzyme was found to be maximally active at 55 o c and the lasparaginase retained 98% activity [9]. fig. 5: effect of temperature on activity of purified l-asparaginase activity. 5. conclusion and recommendations in summary, l-asparaginase from local, newly-isolated bacillus sp. has been purified by a combination of precipitation and chromatography steps. the purified enzyme showed 10.11 u/mg specific activity, 50.07% yield with 2.21 fold purification. the molecular weight of this purified enzyme is 66 kda in the form of a dimer. this l-asparaginase is stable at a ph of 9 and temperature of 60 o c. its considerable stability at wide ph range and high temperature make it advantageous for use in biotechnological industries. the antitumor activity of l-asparaginase from the bacillus sp. should be further examined in order to increase its value and its properties as a potential anticancer enzyme. later, it could be commercialized in malaysia as an alternative drug to be used in therapeutic treatment, especially against leukemia, after a few polishing steps are done. it is also recommended to investigate the production of the desired enzyme in a bioreactor or on a large scale. acknowledgement this project was funded by a research acculturation grant scheme (rags 12-003-0003) by the ministry of higher education, malaysia. references [1] asthana sn, azmi w. (2003) microbial l-asparaginase : a potent antitumour enzyme. indian j biotechnol., 2:184-194. [2] borek d, jaskólski m. (2001) sequence analysis of enzymes with asparaginase activity. acta biochim pol., 48(4): 893-902. [3] prakasham rs, rao cs, rao rs, lakshmi gs, sarma pn. (2007) l -asparaginase production by isolated staphylococcus sp. – 6a : design of experiment considering interaction effect for process parameter optimization., 102:1382-1391. doi:10.1111/j.1365-2672.2006.03173.x. 0 0.05 0.1 0.15 0.2 0.25 30 40 60 80 l-asparaginase activity (u/ml) t e m p e r a tu r e (º c ) l-asparaginase activity iium engineering journal, vol. 18, no. 2, 2017 jimat et al. 10 [4] borah d, sangra a, shahin l.(2012) production , purification and process optimization of l-asparagines ( an anticancer enzyme ) from e . coli , from sewage water. int j pharm pharm sci.,4(4):560-563. [5] sunitha m, ellaiah p, devi rb. (2010) screening and optimization of nutrients for lasparaginase production by bacillus cereus mntg-7 in smf by plackettburmann design. african j microbiol res., 4(4):297-303. [6] kumar nsm, shimray ca, indrani d. (2013) reduction of acrylamide formation in sweet bread with l -asparaginase treatment. food bioprocess technol., 7(3):741-748. doi:10.1007/s11947-013-1108-6. [7] patro kr, gupta n. (2012) extraction, purification and characterization of lasparaginase from penicillium sp. by submerged fermentation,3(3) :30-34. doi:10.5897/ijbmbr11.066. [8] thakur m, lincoln l, niyonzima fn, more ss. (2013) isolation, purification and characterization of fungal extracellular l-asparaginase from mucor hiemalis. j biocatal biotransformation., 2(2):1-9. [9] jois s, chandru s, lakshmikantha ry, satwadi pr. (2013) study on production, purification and characterisation of l-asparaginase from escherichia coli and pseudomonas aeruginosa. int j pharm chem biol sci. ,3(3):565-570. [10] sanches m, krauchenco s, polikarpov i. (2007) structure , substrate complexation and reaction mechanism of bacterial asparaginases. curr chem biol., 1(1):75-86. [11] jha, s. k.;pasrija, d.; sinha, r.k.; singh, h.r.; nigam, v.k.; vidyarthi as. (2012) microbial l-asparaginase: a review on current scenario and future aspect. int j pharm sci res., 3(9):3076-3090. [12] vieille c, zeikus gj, vieille c. (2001) hyperthermophilic enzymes : sources , uses , and molecular mechanisms for thermostability hyperthermophilic enzymes : sources , uses , and molecular mechanisms for thermostability. microbiol mol biol rev., 65(1):1-43. doi:10.1128/mmbr.65.1.1. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 statistical analysis of growth conditions of newly isolate bacillus sp. producing l-asparaginase dzun noraini jimat1*, intan baizura firda mohamed1, azlin suhaida azmi1 and azura amid2 1department of biotechnology engineering, kulliyyah of engineering,international islamic university malaysia (iium), p.o. box 10, 50728 kuala lumpur, malaysia. 2international institute for halal research and training, international islamic university. malaysia (iium), p.o. box 10, 50728 kuala lumpur, malaysia. *corresponding author: jnoraini@iium.edu.my (received: 4th february 2019; accepted: 13th june 2020; published on-line: 4th july 2020) abstract: the concentrations of nutrient elements together with several physical parameters were screened to find out the significant factors for the production of lasparaginase from newly isolated strain, bacillus sp. from sg klah, hot spring, perak. then, the significant factors were optimized for enhancing l-asparaginase production from the bacterium strain. two statistical designs, two level factorial design and face centered composite design (fccd), design expert @version 8.0 were employed in screening and optimization of the process variables, respectively. the results for all experiment runs were analyzed by analysis of variance (anova). peptone (nitrogen source) concentration and temperature were found as significant factors, positively influenced the production of lasparaginase. the two factors were then optimized to increase the desired enzyme production. the optimum peptone concentration and the temperature were found at 1.4 g/l and 30ºc, respectively. the l-asparaginase production under optimized conditions increased from 0.15±0.023 u/ml to 0.19 ± 0.03 u/ml. the kinetic studies showed that the biomass production dropped after 24 hours while l-asparaginase activity is active and positively increased until the fermentation period ended. abstrak: kepekatan unsur-unsur nutrien bersama-sama dengan beberapa parameter fizikal telah diteliti untuk mengetahui faktor-faktor penting untuk pengeluaran l-asparaginase dari spesis baru diasingkan, bacillus sp. dari kolam air panas tempatan. kemudian, faktor penting dioptimumkan untuk meningkatkan pengeluaran l-asparaginase daripada bakteria tersebut. two level factorial design dan face centered composite design (fccd), design expert @version 8.0 telah digunakan dalam penyaringan dan pengoptimuman pembolehubah proses dalam kajian ini. keputusan untuk semua eksperimen dianalisis dengan analisis varians (anova). kepekatan dan suhu peptone (sumber nitrogen) didapati sebagai faktor penting, secara positif mempengaruhi pengeluaran l-asparaginase. kedua-dua faktor ini dioptimumkan untuk meningkatkan pengeluaran enzim yang dikehendaki. kepekatan peptone dan suhu optimum didapati masing-masing pada 1.4 g / l dan 30ºc. pengeluaran lasparaginase di bawah keadaan yang dioptimumkan meningkat dari 0.15 ± 0.023 u / ml kepada 0.19 ± 0.03 u/ml. kajian kinetik menunjukkan bahawa pengeluaran biojisim menurun selepas 24 jam manakala aktiviti l-asparaginase aktif dan meningkat secara positif sehingga tempoh penapaian berakhir. keywords: bacillus sp., l-asparaginase activity, screening, optimization, peptone, temperature 67 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 1. introduction l-asparaginase catalyzes the hydrolysis of l-asparagine into l-aspartic acid and ammonia. l-asparaginase is widely used in food industry as an acrylamide reducing agent especially in baked and fried food products [1] as when the temperature in processing food is getting higher, the acrylamide compound is formed [2]. this enzyme is also known as a microbial therapeutic approach for cancer treatment [3]. this enzyme helps in reducing the amount of l-asparagine present in patients’ blood by hydrolyzing the amino acid to two end products in leukemic cells [4]. tumor cell needs l-asparagine to build proteins. however, these cells cannot synthesize its own l-asparagine because of the absent or low expression of asparagine synthase in the cells. therefore, the cells use exogenous l-asparagine that obtains from the human diet to meet its needs. this enzyme is also used as a diagnostics biosensor for monitoring asparagine levels in leukemia [4]. l-asparaginase serves to destroy all the l-asparagine that does not manage to get synthesized in a tumor cell or that comes from the other sources [5]. l-asparaginase is an important component for cancer therapy, but it still has some limitations for clinical utility due to its side effect, short half-life and low-level enzyme production [6]. the current microbial strains producing l-asparaginase that are used for therapeutic are from escherichia coli and erwinia sp. [7]. the therapeutic response of l-asparaginase from these bacteria strains usually occurs with the evidence of toxicity [8]. a native form of the enzyme has a short half-life [9]. the fast progress of clinical resistance (the failure of cancer to shrink after treatment) is the key problem of l-asparaginase usage in treating acute leukemia. a long term administration of l-asparaginase into patients may cause the production of the corresponding antibody in the tissues. this condition may result in anaphylactic shock or neutralization of the drug effect. it was found that different types of microbial strains exhibit different biochemical and kinetic properties of l-asparaginase [10]. previous studies have discovered new strains that able to produce asparaginase such as helicobacter pylori [11, 12], serratia marcescens [13, 14] and basidiomycetes, flammulina velutipes [15]. however, alternative l-asparaginase sources are a necessity to meet a great demand that is expected in the coming years. it is because microbes are preferable sources than animals and plants due to their fast and easily grow and low-cost of culture nutrient requirements [16]. thus, this study aimed to screen the significant factors in enhancing l-asparaginase production by newly isolated bacillus sp. obtained from our previous study [17]. the significant factors were then optimized to maximize enzyme production. the growth kinetic of the bacterial strain under optimum conditions was investigated. in this study, face-centered central composite design (fccd) from response surface methodology (rsm) using design expert @version 8.0 was selected as through this approach optimum values could be discovered effectively within the designated range of the independent variable. furthermore, a previous study reported that the effect of several process variables on the prediction of the optimum response yield could be observed as well [18]. 2. materials and methods 2.1 microorganisms a bacteria strain producing l-asparaginase from bacillus sp. was used in the present study. the wild strain of bacillus sp. was isolated previously from sg. klah, hot spring, perak [17]. the pure bacterial strain was maintained in glycerol stock at -20ºc to preserve it. then it was subcultured on nutrient agar before use. the culture plates were then stored at 4ºc and subcultured every two weeks. 68 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 2.2. identification of the isolate bacteria molecular identification using 16s rrna gene sequencing analysis was performed by 1st base molecular biology services. blast program was used to identify the gene sequence. 2.3. inoculum preparation a bacteria suspension was prepared from 24 hours old culture grown on modified m9 agar medium as described by gulati and co-workers (1997) [19]. this modified m9 medium containing (per 1000 ml of distilled water): na2hpo4.2h2o, 6.0 g ; kh2po4, 3.0g ; nacl, 0.5 g ; l-asparagine, 5.0 g ; 1m mgso4.7h2o, 2.0 ml ; 0.1m cacl2.2h2o, 1.0 ml ; 20% glucose stock, 10.0 ml ; agar 20.0 g at ph 7. a colony from the culture plates was suspended in 5 ml of sterile liquid m9 medium. it was grown overnight at 37˚c. 2.4. cultivation of newly isolates, bacillus sp. sterilized modified m9 media (50 ml) was inoculated with 2% (1.46 x 108 cfu/ml) of inoculums (bacillus sp.) which placed in 250 ml erlenmeyer flasks and incubated at 37˚c at 150 rpm for 48 hours. the uninoculated medium was used as a control. the same experiment was carried out in three times. l-asparaginase activity was determined by taking the culture broth sample after 48 hours of incubation time. 2.5.l-asparaginase assay the collected sample cultures were analyzed as described in previous studies [17, 19]. the bacteria cultures were harvested by centrifugation at 6,000 rpm for 15 min. a mixture of 0.1 ml sample of enzyme extract with 0.2 ml of 0.05m tris-hcl (ph 8.6), 1.7 ml of 0.01m lasparagine was incubated for 10 min at 37˚c. 5 ml of 1.5m trichloroacetic acid (tca) was added to the mixture to stop the reaction. this mixture was centrifuged at 10,000 rpm for clarification then 0.5 ml of the supernatant was diluted to 7 ml with distilled water and treated with 1 ml of nessler reagent and left for 10min. the absorbance of color changes was measured at 480 nm. the optical density (od) readings were then compared to the standard curve of ammonia. one unit (u) of l-asparaginase was defined as that amount of enzyme which liberating 1μmole of ammonia per minute at 37ºc under the assay conditions. 2.6.protein concentration protein concentration was determined using reagent (pierce™ 660nm protein assay reagent) and compared to a standard curve of bovine serum albumin (bsa) concentration as described by bradford, (1976)[21]. 2.7.screening of carbon and nitrogen concentrations and operating culture conditions by two-level factorial design two-level factorial designs, design expert @version 8.0 was applied for screening of significant concentration of carbon and nitrogen sources. based on the previous part of our study [17], it was found that sucrose and peptone positively enhanced the l-asparaginase activity from the used bacterial strain, bacillus sp. the concentrations of the two nutrient components were screened together with the other culture operating conditions such as ph, inoculum sizes, agitation speed, and temperature to determine the most significant parameters for l-asparaginase production by the strain. sucrose and peptone were supplemented at certain 69 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 concentrations into the production medium as reported in the previous study [22]. the design contains 32 experimental runs where the factors were taken at two levels (high and low values) as illustrated in table 1. table 1: controllable factors and their coded levels for screening the significant factors using two-level factorial design factor code variable levels -1(low) +1(high) carbon (g/l) a 1.50 3.00 nitrogen (g/l) b 1.50 3.00 temperature (ºc) c 37 60 ph d 5 9 agitation speed (rpm) e 150 250 inoculum sizes (%) f 2 3.5 2.8.optimization of significant factors using face centered composite design (fccd) from response surface methodology (rsm) face centred composite design (fccd) from response surface methodology (rsm) using design expert @version 8.0 was employed to optimize the response (enzyme activity) which was influenced by the independent variables such as medium components (carbon and nitrogen sources) and operating parameters (ph, inoculum sizes and agitation speed). the significant factors were selected based on the results obtained in section 2.7. all results were analyzed by anova and validated. 3.0. results and discussion the most potent isolate (i3) with high potential for lasparaginase production was selected and identified using 16s rrna gene sequence analysis for classification and to further confirm the subspecies level. fig. 1. pcr products for 16s rrna gene sequence (m: dna marker; -ve: pcr non template control (water); +ve: dna extracted from e.coli ; i3: isolated strain) 70 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 based on fig. 1, a single band of the dna appeared between 1000 and 1500 bp sequence. the result revealed a single band of amplified dna products of approximately 1373 base pairs was recorded. the complete sequence data of the 16s ribosomal rna gene were aligned and analyzed for finding the closest homologous microbes. the gene sequence was compared to nucleotide databases using the blast program. fig. 2. a phylogenetic tree of i3 strain. neighbor-joining tree based on 16s rrna gene sequences showing the positions of the selected strain. a phylogenetic tree (fig. 2) was constructed by taking the sequences obtained in the blast search. it was constructed to illustrate the evolutionary relationship between the unknown strains and the most closely related strains of species of the genus. as illustrated in fig. 2, i3 strain was clustered into two major clades. the analysis of 16s rdna sequences showed the sequences of the selected strain that very closely related to bacillus sp. therefore, based on fig. 2, i3 isolate was identified as bacillus anthracis. the sequence of the selected strain was most closely related to bacillus anthracis strain ames with a sequence similarity of 98%. sucrose and peptone were found as the best nutrients to boost l-asparaginase activity based on our previous study [17]. the varied concentration of the two elements together with four operating parameters like temperature, agitation speed, ph, and inoculum sizes were screened to investigate the significant factors influencing l-asparaginase activity from the bacillus sp. strain. the experiment was designed under two-level factorial designs. the concentration of nutrients elements is vital to enhance bacterial growth as well as metabolites production during the fermentation process. 71 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 fig. 3. pareto chart of significant variables the most significant factors were determined based on the analyzed results shown by the pareto chart (fig. 3). the factors that are above bonferroni limit, factor b (peptone concentration), and c (temperature) are the most significant factors. the factors that are between bonferroni and t-value limit line can be considered as significant too. meanwhile, the parameters which are below the t-value limit line are insignificant factors and those variables can be ignored. the concentration of peptone and temperature enhanced l-asparaginase activity. table 2: analysis of variance (anova) for the screening of significant factors sources sum of squares df mean square f value p-value prob >f model (significant) 0.46 16 0.029 11.03 < 0.0001 a: carbon 0.011 1 0.011 4.36 0.0543 b: nitrogen 0.12 1 0.12 46.72 < 0.0001 c: temperature 0.097 1 0.097 37.02 < 0.0001 d: ph 0.01 1 0.01 3.92 0.0664 e: agitation speed 8.91e-03 1 8.91e-03 3.4 0.0849 f: inoculum sizes 2.16e-03 1 2.16e-03 0.83 0.3776 r2 0.9217 adjusted r2 0.8381 predicted r2 0.6436 72 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 table 2 shows a summary of the anova analysis. the f-value of the model was 11.03 and its p-value was < 0.0001 which was less than 0.05 implies the model was significant. all of the values of p-value or prob > f less than 0.05 indicate model terms are significant whereas the values greater than 0.1 indicate the model terms are not significant. the p-values were the indicator of the importance of each correlation among the tested variables [23]. as shown in the pareto chart, factor b (peptone concentration; nitrogen source) and c (temperature) were important factors since the p-value for that variable were less than 0.05 while the others were greater than 0.05. table 3: controllable factors and their coded levels for the face centered composite design (fccd) factor code variable levels -1(low) +1(high) peptone (g/l) a 1.00 2.00 temperature (oc) b 30 40 in present work, face centered composite design (fccd) from (rsm) was employed to optimize the effective parameters with a minimum number of trials. this method helps to analyze the interaction between the tested parameters. the two significant factors obtained from the previous experiment were optimized. the low (-1) and high (+1) levels of each variable were designated respectively as illustrated in table 3. high and low levels of the substrate may lead to the fluctuation of the yield of the process [14]. as illustrated by them, the decreased l-asparaginase activity was due to the substrate inhibition when the substrate used in a high level. meanwhile, when a low level of substrate is used, it may decrease the yield because of less nutrient availability for microbial growth and metabolite synthesis. ph 7 was selected as previous studies revealed that the ph condition was the most suitable for the growth of any bacillus sp.[24]. the same observation also found for the isolate streptomyces abr2 at this ph of 7.0 [25]. while inoculum size and agitation speed were fixed at 2% and 150rpm respectively. both factors were insignificantly influenced to the culture, thus, the lowest level value was used in the optimization condition of the culture. the complete experimental results are listed in table 4. table 4: experimental results of fccd run peptone (g/l) temperature (oc) l-asparaginase activity (u/ml) protein concentration (mg/ml) specific activity (u/mg) 1 1.00 40.00 0.13 ±0.082 0.02±0.012 6.5 2 1.50 35.00 0.16±0.129 0.01±0.098 16.0 3 1.50 30.00 0.15±0.054 0.02±0.120 7.5 4 1.50 40.00 0.16±0.100 0.02±0.011 8.0 5 1.00 30.00 0.13±0.024 0.01±0.044 13.0 6 1.00 35.00 0.13±0.071 0.01±0.004 13.0 7 2.00 40.00 0.07±0.090 0.01±0.011 7.0 8 1.50 35.00 0.17±0.110 0.01±0.014 17.0 9 1.50 35.00 0.19±0.010 0.01±0.068 19.0 10 2.00 30.00 0.11±0.017 0.02±0.049 5.5 11 1.50 35.00 0.18±0.018 0.01±0.113 18.0 12 2.00 35.00 0.06±0.032 0.02±0.012 3.0 13 1.50 35.00 0.20±0.013 0.01±0.002 20.0 73 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 table 5: analysis of variance (anova) for optimization of response function anova for the quadratic model for optimization process parameters is shown in table 5. the model f-value of 22.02 implies the model is significant. the values of the p-value less than 0.05 reflect that the model terms were significant. in this case, a and a2 were significant variables. values more than 0.1000 show the model terms are not significant. the lack of fit of the model is not significant indicated that it was reasonable for the present work. the cv value is also considered as an important value since it determines the reproducibility of the model and helps to determine statistical reliability. the estimation is less accurate when the cv ratio is large. if the value is less than 15%, the model reliability is good. in the present work, the cv value was 12.33 showing reliability and reproducibility of the model. the accuracy of the model developed can be determined by the r2, adjusted r2, and standard deviation values. r2 or known as the coefficient of determination is a number indicates how well data fit a statistical model. generally, when the r2 value is closer to 1, the linear regression fits the data is better. based on table 5, the r2 value for the model was 0.8801. the predicted r2 of 0.7228 was in reasonable agreement with the adjusted r2 of 0.8402. the value of the “adeq precision” obtained was 10.824. this value measures the signal to noise ratio. the ratio of 10.824 indicated an adequate signal. thus, the model could be used to navigate the design space. a multiple regression analysis was used to relate the response of l-asparaginase activity (y) with the two variables studied using a second-order polynomial. it can be represented by the following equation of (1) in terms of coded factors: y = -0.36398 + 0.81268a 9.04033x10-4 b 0.28758a2 (1) in eq. (1), the coded factors a and b represent peptone concentration and temperature, respectively. a positive sign in front of the a-code represents good effect, while negative sign in front the b code can be deduced as a bad effect on the response function (y). the positive value of the main effect denotes that higher activity of the enzyme would result in at a higher level of the factor whereas a factor with negative sign denotes that its lower level would provoke higher l-asparaginase activity. previous studies confirmed that when the effect of a factor was positive, an increase in the value of the enzyme activity efficiency was observed [23]. besides, a coefficient close to zero value means that the factor has little impact or no sources sum of squares df mean square f value p-value prob >f model (significant) 0.021 3 6.860e-003 22.02 0.0002 a: peptone conc. 3.758e-003 1 3.758e-003 12.07 0.0070 b: temperature 1.226e-004 1 1.226e-004 0.39 0.5460 a2 0.017 1 0.017 53.61 < 0.0001 residual 2.803e-003 9 3.115e-004 lack of fit (not significant) 2.081e-003 5 4.162e-004 2.30 0.2194 c.v (%) 12.33 r2 0.8801 adjusted r2 0.8402 predicted r2 0.7228 74 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 impact on the response. the a term of peptone concentration had the highest effect indicating that it was the most important component for l-asparaginase production. the linear term of peptone concentration (a) has a higher effect value than the square term (a2), indicating that the variable has more influence on enzyme production. it means that any alteration in the level could influence the production in a significant manner. based on the above equation, the coefficient of b (temperature) is close to zero. only peptone concentration influenced lasparaginase activity produced by the strain positively. fig. 4. a three-dimensional response surface plot showing the effect of peptone and temperature on the l-asparaginase activity. the contour plot and three-dimensional (3d) graph are used to show the interaction between the involved variables. the curvature observed in a three-dimensional surface plot represents the prominent effect of peptone concentration on l-asparaginase activity (fig. 4). the plot reveals that peptone concentration is proportional to the l-asparaginase activity. it seems like up to certain limits, the increased concentration of peptone will improve the enzyme activity. the activity of l-asparaginase was the highest at the middle level of peptone and lower level of temperature. the contour is slightly inclined towards temperature indicating that nitrogen source concentration; peptone was a slight influenced on temperature. fig. 3 demonstrated that peptone at a concentration range of 1.40-1.50 g/l is optimum (middle level). the contour is elliptical indicating that both were independent of each other. the predicted l-asparaginase activity for a particular set of operating culture conditions was numerically showed in the same fig. 4. based on the analysis of the contour plot, lasparaginase activity increases to a maximum value with the increasing level of peptone to 1.40 g/l where the temperature was at its lower level (30°c). further increment of the variables beyond the previously mentioned level shows an inhibitory effect on enzyme activity. 75 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 table 6: optimum-operating conditions for maximizing l-asparaginase peptone concentration (g/l) temperature (°c) l-asparaginase activity (u/ml) percentage difference (%) predicted experimental 1.41 30.00 0.183 0.19 ± 0.03 3.83 model validation was performed according to the condition generated by the software. the optimal values of parameters are as follows: peptone concentration 1.41 g/l and temperature 30°c, with corresponding l-asparaginase production at 0.183 u/ml (as shown in table 6). the validation experiments were performed (triplicates) to find out the experimental results for enzyme activity. on conducting the experiments under these conditions, 0.19 ± 0.03 u/ml of l-asparaginase activity was recorded. according to saeed gholamian and co-worker, the optimum temperature for growth of bacillus sp. and l-asparaginase production was 37°c [24]. deshpande and co-workers found that the addition of peptone into the medium growth favored maximum enzyme production by streptomyces ginsengisoli [26]. other studies reported that the presence of peptone enhanced the growth of bacillus sp. because it increased the dry weight of the cell and shortened the lag period where the bacteria are adjusting to the new environment and [27]. while farag and co-workers reported that l-asparagine was the best nitrogen source for the new fungal isolate, a. terreus [28]. the maximum growth of the bacterial strain and lasparaginase activity were recorded at the temperature. the experimental results were compared to the predicted l-asparaginase activity and the percentage error was calculated. it found that the values given by the software were following by with the experimental values with a small percentage difference (3.83%). fig. 5. a graph showing the correlation between cell dry weight (g/l) and l-asparaginase activity at different interval times. the relationship between biomass concentration and l-asparaginase activity within 48 hours fermentation is shown the fig. 5. the biomass concentration was increased gradually with the culture duration from 2 to 30 hours. at the 30th hour of incubation, it showed the maximum (7.8 g/l) biomass production. the biomass concentration sharply declined beyond 30 hours toward 48 hours. in this study maximum, l-asparaginase metabolite production occurred at the 76 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 end of the exponential growth phase. the l-asparaginase production declined to indicate its accumulation after a certain period of growth [29]. it found that the specific rates are high in the early part of the fermentation and later it declined steadily as the fermentation proceeds due to the disappearance of nutrients and the accumulation of toxic products. 4.0. conclusion peptone concentration and temperature were the most influential parameters in stimulating l-asparaginase activity from bacillus sp. the optimal conditions for l-asparaginase activity were at 30ºc with 1.41 g/l of peptone concentration. the l-asparaginase production under optimized conditions increased from 0.15±0.023 u/ml to 0.19 ± 0.03 u/ml. this study showed that the optimization of l-asparaginase production has been successfully achieved through face centred composite design (fccd) of response surface methodology (rsm). references [1] cachumba jjm, antunes faf, peres gfd, brumano lp, santos jcd, silva ssd. (2016) curent applications and different approaches for microbial l-asparaginase production. brazilian j microbiol, 47s:77–85. https://doi.org/http?//dx.doi.org/10.1016/j.bjm.2016.10.004 [2] kumar nsm, shimray ca, indrani d. (2014) reduction of acrylamide formation in sweet bread with l -asparaginase treatment. food bioprocess technol, 7:741–748. https://doi.org/10.1007/s11947-013-1108-6 [3] amena s., vishalakshi n., prabhakar m., dayanand a. lk. (2010) production, purification and characterization of l-asparaginase from treptomyces gulbargensis. brazilian j mocrpbiology, 41:173–178. https://doi.org/doi 10.1590/s1517838220100001000025 [4] verma n, kumar k, kaur g, anand s. (2007) l-asparaginase: a promising chemotherapeutic agent. crit rev biotechnol, 27:45–62. https://doi.org/doi:10.1080/07388550601173926 [5] jha, s k, pasrija d., sinha rk, singh hr, nigam vk vas. (2012) microbial lasparaginase: a review on current scenario and future prospects. int j pharm sci res, 3:3076–3090. https://doi.org/http://dx.doi.org/10.13040/ijpsr.0975-8232.3(9).307690 [6] zuo s, zhang t, jiang b, mu w. (2014) recent research progress on microbial lasparaginases. appl microbiol biotechnol, 99:1069–1079. https://doi.org/10.1007/s00253-014-6271-9 [7] pieters r, hunger sp, boos j, rizzari c, silverman l, baruchel a, goekbuget n, schrappe m, pui c. (2011) l-asparaginase treatment in acute lymphoblastic leukemia. cancer, 117:238–249 . https://doi.org/10.1002/cncr.25489 [8] jha sk, pasrija d., sinha rk, singh hr, nigam vk, vidyarthi as. (2012) microbial l-asparaginse: a review on current scenario and future prospects. int j pharm sci res, 3:3076–3090 [9] jain r, zaidi ku, verma y, saxena p. (2012) l-asparaginase : a promising enzyme for treatment of acute lymphoblastic leukiemia. people’s j sci res, 5:29–35 [10] prakasham rs, hymavathi m, rao cs. (2010) evaluation of antineoplastic activity of extracellular asparaginase produced by isolated bacillus circulans. appl biochem biotechnol, 160:72–80 . https://doi.org/10.1007/s12010-009-8679-8 77 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 [11] shibayama k, takeuchi h, wachino j ichi, mori s, arakawa y. (2011) biochemical and pathophysiological characterization of helicobacter pylori asparaginase. microbiol immunol, 55:408–417. https://doi.org/10.1111/j.1348-0421.2011.00333.x [12] cappelletti d, chiarelli lr, pasquetto mv, stivala s, valentini g, scotti c. (2008) helicobacter pylorilasparaginase: a promising chemotherapeutic agent. biochem biophys res commun, 377:1222–226. https://doi.org/doi:10.1016/j.bbrc.2008.10.118 [13] agarwal a, kumar s, veeranki vd, kumar æ. (2011) effect of chemical and physical parameters on the production of l -asparaginase from a newly isolated serratia marcescens sk-07. letter in applied microbiology, 52:307–313. https://doi.org/10.1111/j.1472-765x.2011.03006.x [14] ghosh s, murthy s, govindasamy s, chandrasekaran m. (2013) optimization of lasparaginase production by serratia marcescens (ncim 2919) under solid state fermentation using coconut oil cake. sustainable chemical process, 1(9):1–8 . https://doi.org/doi: 10.1186/2043-7129-1-9 [15] eisele n, linke d, bitzer k, na’amnieh s, nimtz m, berger rg. (2011) the first characterized asparaginase from a basidiomycete, flammulina velutipes. bioresour technol, 102:3316–3321 . https://doi.org/10.1016/j.biortech.2010.10.098 [16] lopes am, oliveira-nascimento l de, ribeiro a, tairum ca, breyer ca, oliveira ma de, monteiro g, souza-motta cm de, magalhães p de o, avendaño jgf, cavacopaulo am, mazzola pg, rangel-yagui c de o, sette ld, converti a, pessoa a. (2017) therapeutic l-asparaginase: upstream, downstream and beyond. crit rev biotechnol, 37:82–99 . https://doi.org/10.3109/07388551.2015.1120705 [17] jimat dn, baizura i, mohamed f, azmi as, zainudin z. (2015) isolation and characterization of thermophilic bacteria producing l-asparaginase from malaysia hotspring and enzyme activity using different carbon and nitrogen sources. j appl sci agric, 10:69–77 [18] ahmad t, danish m, kale p, geremew b, adeloju sb, nizami m, ayoub m. (2019) optimization of process variables for biodiesel production by transesterification of flaxseed oil and produced biodiesel characterizations. renew energy, 139:1272–1280. https://doi.org/10.1016/j.renene.2019.03.036 [19] gulati r, saxena rk, gupta r. (1997) a rapid plate assay for screening l -asparaginase producing. lett appl microbiol, 24:23–26 [20] jimat dn, mohamed ibf, azmi as, jamal p. (2017) purification and partial characterization of lasparaginase enzyme produced by newly isolated bacillus sp. iium eng j, 18:1–10 https://doi.org/10.31436/iiumej.v18i2.654 [21] bradford mm. (1976) a rapid and sensitive method for the quantitation microgram quantities of protein utilizing the principle of protein-dye binding. anal biochem, 72:248–254 [22] hymavathi m, sathish t, brahmaiah p, prakasham rs. (2010) impact of carbon and nitrogen sources on l-asparaginase production by isolated bacillus circulans (mtcc 8574 ): application of saturated plackett-burman design. chem biochem eng q, 24:473–480 [23] mungi h, carvalho r, ilegar s. (2014) optimization of l-asparaginase production form pseudomonas fluorescens by response surface methodology. int j curr microbiol appl sci, 3:350–362 [24] gholamian, s.; gholamian, s.;nazemi, a.;nargesi mm. (2013) optimization of culture media for l asparaginase production by newly isolated bacteria , bacillus sp. gh5 1. microbiology, 82:856–863 . https://doi.org/10.1134/s0026261714010032 [25] sudhir ap, dave br, trivedi ka, subramanian rb. (2012) production and 78 iium engineering journal, vol. 21, no. 2, 2020 jimat et al. https://doi.org/10.31436/iiumej.v21i2.1351 amplification of an l-asparaginase gene from actinomycete isolate streptomyces abr2. ann microbiol, 62:1609–1614 . https://doi.org/10.1007/s13213-011-0417-0 [26] deshpande n, choubey p, agashe m. (2014) studies on optimization of growth parameters for l-asparaginase production by streptomyces ginsengisoli. the scientific world journal, :1–6 . https://doi.org/10.1155/2014/895167 [27] fooladi j, sajjadian a. (2010) screening the thermophilic and hyperthermophilic bacterial population of three iranian hot-springs to detect the thermostable α-amylase producing strain. iran j microbiol, 2:49–53 [28] farag am, hassan sw, beltagy ea, el-shenawy ma. (2015) optimization of production of anti-tumor l-asparaginase by free and immobilized marine aspergillus terreus. egypt j aquat res, 41:295–302 . https://doi.org/10.1016/j.ejar.2015.10.002 [29] thaer, t.a. and ellaiah p. (2013) l-asparaginase production by a streptomycete and optimization of production parameters. j pharm biomed sci, 29:859–869 79 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <feff0633062a062e062f0645002006470630064700200627064406250639062f0627062f0627062a002006440625064606340627062100200648062b062706260642002000410064006f006200650020005000440046002006450646062706330628062900200644063906310636002006480637062806270639062900200648062b06270626064200200627064406230639064506270644002e00200020064a06450643064600200641062a062d00200648062b0627062606420020005000440046002006270644062a064a0020062a0645002006250646063406270626064706270020062806270633062a062e062f062706450020004100630072006f00620061007400200648002000410064006f00620065002000520065006100640065007200200036002e00300020064806450627002006280639062f0647002e> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <feff00560065007200770065006e00640065006e0020005300690065002000640069006500730065002000450069006e007300740065006c006c0075006e00670065006e0020007a0075006d002000450072007300740065006c006c0065006e00200076006f006e002000410064006f006200650020005000440046002d0044006f006b0075006d0065006e00740065006e002c00200075006d002000650069006e00650020007a0075007600650072006c00e40073007300690067006500200041006e007a006500690067006500200075006e00640020004100750073006700610062006500200076006f006e00200047006500730063006800e40066007400730064006f006b0075006d0065006e00740065006e0020007a0075002000650072007a00690065006c0065006e002e00200044006900650020005000440046002d0044006f006b0075006d0065006e007400650020006b00f6006e006e0065006e0020006d006900740020004100630072006f00620061007400200075006e0064002000520065006100640065007200200036002e003000200075006e00640020006800f600680065007200200067006500f600660066006e00650074002000770065007200640065006e002e> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 space mapping of hip and wrists motions for different transfer distances in manual material handling task radin zaid radin umar1,2*, fatin ayuni mohd azli lee1, muhammad naqiuddin khafiz1, nadiah ahmad1,2, nazreen abdullasim3 1fakulti kejuruteraan pembuatan, 2center of smart system and innovative design, 3fakulti teknologi maklumat dan komunikasi, universiti teknikal malaysia melaka, malaysia *corresponding author: radinzaid@utem.edu.my (received: 16th july 2019; accepted: 9th march 2020; published on-line: th july 2020) abstract: manual material transfer tasks are common in occupational settings. repetitive lifting tasks usually involve twisting and bending which are associated with occupational lower back injuries. one of the approaches to reduce bending and t wi st i ng is to separate the distance between lifting origin and destination, which will encourage lifters to step and turn entire bodies. however, adding lifting distances is likely to af f ect space usages and requirements. a study was conducted to investigate how the transfer distances influence space usage during the lifting task. raw data of hip and hand wr i st s motion of 26 male subjects during transfer in 4 different distances were captured using x-sens motion capture system. mvn studio software was used to process and extract positional data. tabulated space mapping revealed limited hip movement and semicircular shaped hand motions for short transfer distances. the pattern changes into a more stretched-curve shape as the distance increases. overall, it was observed that shorter transfer distance caused participants to adopt more twisting and less bending postures, while further transfer distances resulted in more bending and less twisting. this study may provide industrial practitioners with information to design a space requirement for manual material transfer tasks. abstrak: kerja-kerja pemindahan barang secara manual adalah biasa dalam persekitaran kerja. kerja-kerja mengangkat barang yang kebiasaannya melibatkan badan membengkok dan berpusing boleh menyebabkan kecederaan tulang belakang. salah sat u cara bagi mengurangkan risiko ini adalah dengan memisahkan jarak antara tempat asal dan tempat tuju pemindahan barang. pemindah barang digalakkan untuk melangkah dan memusingkan seluruh badan. namun, cara ini menyebabkan penggunaan ruang yang banyak. satu kajian telah dijalankan bagi mengkaji bagaimana jarak pemindahan bar ang mempengaruhi penggunaan ruang ketika kerja-kerja pemindahan. data asal pergerakan pinggul dan pergelangan tangan daripada 26 subjek lelaki ketika pemindahan barang pada 4 jarak berbeza diperolehi menggunakan sistem rakaman gerakan x-sens. peri si an mvn studio digunakan bagi memproses dan mengekstrak data ini. ruang pemetaan berjadual mendedahkan pergerakan pinggul yang terhad dan pergerakan tangan berbentuk separa bulat pada jarak pemindahan terdekat. corak ini berubah kepada bentuk lengkung memanjang apabila jarak bertambah. keseluruhannya, jarak pindahan yang kurang menyebabkan para peserta lebih terdedah kepada postur memusingkan badan berbanding membengkok, sementara jarak yang jauh menyebabkan peserta lebih membengkok berbanding memusingkan badan. kajian ini memberikan maklumat unt uk 164 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 penggiat industri mereka cipta keperluan ruang bagi kerja-kerja pemindahan barang secara manual. keywords: space mapping; ergonomics; manual material handling; transfer distance 1. introduction application of ergonomic principles has shown good results in increasing productivity and decreasing health issues [1]. ergonomics consideration in early stage s o f w o rk pla c e design has been shown to yield better outcomes compared to considerations at later design stages. front end ergonomics involves looking into interfaces between workers and workplace elements such as workstation, task, and work environment. one of the components of front-end ergonomics is the evaluation of work layout, which spe c ific ally looks into space requirements. manual material handling (mmh) activities are one of the most common tasks in workplaces. high frequency and long duration of exposure to mmh, especially in the industry that still relies on manual labour, can directly impact the workers as they are more likely to be exposed to ergonomic risk factors related to mmh activities [2]. multiple studies have discussed potential methods to minimize ergonomic risk factors due to mmh such as training [3], assisting devices [4], and workplace layout design [5,6]. however, there have been publications suggesting limited effectiveness of training for preventing lower back pain [7,8]. assisting devices may also minimize ergonomic related risks, however high tech devices may come at a cost, and there might be resistance to adopt them due to unfamiliarity and slowing down the processes [9]. workplace layout and space play a direct role in influencing workers’ movements and postures. poor layout and limited space may contribute to poor work postures for the workers [10]. lavender and johnson [6] argued that consideration of good workplace layout allows some degree of control on asymmetric lifting behaviour. in a n o th er s tu d y , mehta et. al. [5] outlined that separating the origin of the lift station and the destinatio n a t a certain distance may nurture workers to step and turn their whole body which m a y h e lp reduce bending and twisting during the manual handling activity. it wa s suggested that distancing the location between lifts can limit the twisting of body. in an experimental study conducted in the united states of america, lavender & johnson [6 ] re v ea le d th a t lateral bending and twisting of the spine were minimized when a separation dista nc e o f 1 meter was created between the lift’s origin and the destination. poor work postures in combinations of repetitive and long exposure durations can increase risks o f e rgo no m ics issues like sprain, strain, and work-related musculoskeletal disorders [11,12]. therefore, a good design that focuses on optimizing interaction between workplace setup and w o rk ers can contribute to increased efficiency and productivity in a workplace [13]. in workstation design options to control ergonomic risk factors, existing ergo n o mic s guidelines have been primarily focused on space clearances. there have also been generic guidelines on manual material handling activities [14,15] than can be referred prior to th e design process. however, there has not been much information that specifically focuses on space requirement for manual material handling tasks. the objective of this study is to capture and map the hip and wrist motions during the manual material handling task. specifically, box transfer processes of different transfer distances and their e ffe c t o n th e space requirement during the handling task have been selected as the focus of s tu dy . it is envisioned that space mapping of motions during manual material handling tasks can provide engineers and designers with space requirement information during the fron t -e nd 165 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 manual material handling workstation design process. thus, a deeper s tu d y f oc u sin g o n interaction of workers and their space requirement may provide insights that can be utilized in the front-end design of workplaces. 2. methodology 2.1 overview a randomized repeated design of experiment was conducted to map the space requirement behaviours of different transfer distances during manual handling a c tiv itie s . space mapping data was collected through th e use of 3d body motion capture system xsens (xsens technologies, netherlands). the system consisted of accelerometers that captured acceleration data at a sampling frequency of 30 data per second. the raw acceleration data were then converted into velocity data, and then positional data through a series of customized programming algorithms developed using processing software. 2.2 subject participants 26 healthy male participants, age ranging from 23 -24 years old (mean = 23.88, sd=0.35) were recruited in this study. the subjects were screened to ensure that they were free of any history of musculoskeletal disorders or prior injuries that could affect th e w a y they performed the tasks of interest. other exclusion criteria include any injury within th e past 12 months that caused them to restrict any work or non -work activity, and e x is te n ce of current pain or other musculoskeletal symptoms. 2.3 data collection each subject signed consent forms and filled demographic data before wearing the xsens sensor-integrated suit. the subject was then asked to transfer boxes of fixed weigh t (10.9 kg) between two stations, the heights of which were set so that the beginning and ending heights were at the 5th percentile of malaysian population elbow height (0.913 m ) [16]. lifting load and height were controlled to minimize their effect on experimental outcomes. each subject was briefed on the simulated task, before being asked to p ra c tic e transferring the boxes. after the practice session, subject was asked to continuously transfer 4 boxes in 4 different transfer distances of 0.50 m, 0.75 m, 1.00 m, and 1.25 m, a s shown in fig. 1. no specific instructions were given with regard s to transf e r te c hn iqu e s. figure 2 shows an example of one subject performing the box transfer task. fig. 1: workstation setup (left), top view of experimental setup (right). 166 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 fig. 2: subject wearing motion capture system performing the box transfer task at 0.5 m distance set up. 2.4 data processing and analysis 2.4.1 image analysis raw data from the xsens motion capture system were extracted and visualized in mvn studio software (xsens technologies, netherlands). the 3d simulation was run f or each subject to observe obvious trends and patterns on postural behaviours. screen captures were taken at the 4th cycle at both origin and destination of lifting for the purpose of image analysis. the observation of 4th cycle data is to represent work postures d u ring continuous transfer, as well as to allow subjects to be more at ease as task familia riz a tio n started to take place. 2.4.2 space mapping analysis positional data of the hip and right and left wrists were obtained for each subject. these positional data, in x and y planes were extracted using cinema 4d software (maxon computer gmbh, germany) that were then tabulated and mapped using microsoft excel. the tabulation allows an overview of the motions from the top view. ea c h d a ta w a s colour-coded to differentiate between the body parts (hip, right wrist, and left w ris t), a n d between transfer distances (0.5 m, 0.75 m, 1.0 m, and 1.25 m). 2.4.3 analysis on width requirements the maximum width distance requirements of each cycle from all transfer dis ta nc e s , across all subjects, were captured through identification of furthest positio na l d a ta in a n excel file. descriptive statistics were used to analyse the differences in width requirements and consequently, in the area used by each subject. repeated anova measures were conducted using a jasp statistics package (wagenmakers, amsterdam) to see if there were significant differences on width requirements between different tra n s fe r d is ta n ce s . mauchly's test was used for sphericity assumption. a post hoc comparison test was performed using bonferroni correction to analyse the pairwise comparisons of experimental conditions. 167 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 3. results 3.1 image analysis qualitative analysis was conducted through observation of images captured using mvn studio software. it was conducted to identify the relation between bending and twisting postures with transfer distance from different subjects. figure 3 a n d 4 s h o w th e bending postures whereas fig. 5 and fig. 6 show twisting postures of one of the su b je cts . both were captured during the box lifting and placing at four different distan ce s . fo r th e twisting posture, the images were captured from the top view. it can be seen that the small transfer distance caused the subject to adopt more twisting but less bending p o s tu re . th e observation was opposite for greater transfer distances. fig. 3: forward bending of a subject during th e start of box lifting (origin) at four different transfer distances: (a) 0.50 m, (b) 0.75 m, (c) 1.00 m, and (d) 1.25 m. fig. 4: forward bending of a subject during the start of box placement (destination) at four different transfer distances: (a) 0.50 m, (b) 0.75 m, (c) 1.00 m, and (d) 1.25 m. fig. 5: lower back twisting of a subject during the start of box lifting (origin) at four different transfer distances: (a) 0.50 m, (b) 0.75 m, (c) 1.00 m, and (d) 1.25 m. 168 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 fig. 6: lower back twisting of a subject during the start of box placement (destination) at four different transfer distances: (a) 0.50 m, (b) 0.75 m, (c) 1.00 m, and (d) 1.2 5m. 3.2 space mapping analysis in order to see the patterns of hip and wrist motions, graphs were plotted based on t h e maximum and minimum points of the hip and wrists for all subjects. figu re 7 s h o w s th e graphs of space mapping data for one subject at different transfer dis ta nc e s w h ile fig. 8 shows the graphs of space mapping of hip and wrists positional data for all s ubjects during the material handling activity. the starting point of each subject is facing th e p o sitiv e x axis from the origin. fig. 7: space mapping of wrists and hip motion of manual transfer for subject 23 at 0.50 m, 0.75 m, 1.00 m, and 1.25 m transfer distances. 169 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 it can be seen from the space mapping analysis that more space wa s u tiliz e d d u ring the transfer as the transfer distances increased. the hip movements in 0.5 m transfer distance were seen to be localized in the same area, between 20 cm in bo th x a n d y a x is . as the transfer distance increased, the hip movements were seen to be distributed over larger areas. at 1.25m transfer distance, the hip movements were shown to be th e la rge s t compared to other distances, as shown in fig. 8. a similar tren d was observ e d w ith b o th right and left wrist movements. the space mapping data shows that movements of hip, right wrist, and left wrist occupied larger areas as the transfer distances increased from 0.5 m to 1.25 m. in addition to the larger occupied area , it can also be seen that different transfer distances affected the movement direction and shape. as transfer distance increased, the hip tended to move further in the y axis direction. in terms of wrists, the movements expended from a semi-circular shape into stretched-out semi-circular shape. fig. 8: mapping of (a) hip, (b) right wrist, and (c) left wrist movements for all 26 subjects at 0.50 m, 0.75 m, 1.00 m, and 1.25 m transfer distances. 3.3 analysis on width requirements the positional data involved to map the top view of hip and wrist motions were x an d z points. the maximum value, average, and standard deviation of width a t e a c h tra n s fe r distance from all subjects were calculated and tabulated in table 1. the values showed 170 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 increase in space width from the shortest (0.50 m) to greatest (1.25 m) tran s fe r d is ta n ce . figure 9 shows the graph of width average for subject 23. mauchly's test showed good sphericity assumption (p=0.129), which indic ated that the variances of the differences were equal. repeated anova measures showed that there was a significant effect of transfer distances (p<0.001) on width require m e nts . th e post hoc bonferroni test to analyse the pairwise comparisons between the tr ansfer distances showed significant differences between 0.5 m vs 1.25 m, and 0.75 m v s 1 . 2 5 m at alpha=0.05. the width requirements for transfer distances between 0.5 m vs 0.75 m, 0.50 m vs 1.0 m, and 1.0m vs 1.25m were not statistically significant, as sh own in table 2. it should be noted that the 0.75 m vs 1.0 m transfer distance showed marginal significance (p=0.055). fig. 9: width requirements of wrists and hip motion of manual transfer for different distances for subject 23. 171 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 table 1: maximum value, mean and standard deviation of width requirements for all subjects (n=26) at different transfer distances. transfer distance (m) width requirements (cm) maximum mean standard deviation 0.50 92.02 74.84 10.26 0.75 93.73 74.18 8.81 1.00 109.41 78.95 12.07 1.25 108.02 83.42 14.01 table 2: post hoc analysis to compare significance differences in width requirements between transfer distances. comparison of transfer distances mean difference standard error t p bonferroni 0.5 m 0.75 m 0.654 1.818 0.360 1.000 1.0 m -4.111 2.060 -1.996 0.342 1.25 m -8.586 2.660 -3.228 0.021* 0.75 m 1.0 m -4.765 1.686 -2.827 0.055 1.25 m -9.240 2.502 -3.693 0.007* 1.0 m 1.25 m -4.474 2.089 -2.142 0.253 note: * signifies statistical significant difference 4. discussion comparing images visualized from mvn studio software, it was found that the 0.50m transfer distance encourages twisting the most, compared to longer transfer distances. the limited space and clearance encouraged subjects to stand relatively static a t one place and twist the body while transferring the box. when the transfer distance increased, subjects were able to make some movements while transferring the box causing less possession of twisting, but it was observed that bending posture was more prominen t. in general, hip movement is more dynamic at larger space but the hip position is still within the same relative area (not spread around). this indicates that the subjects tended to move more but were still standing on the same spot. in order to complete the transfer task, subjects tended to bend more during lifting and placing the box in order to reach the stations. the positional data of hip and wrists for different transfer distances during manual transfer were mapped to give an overview of the space requirements. ov era ll, th e re s u lt showed that in the shortest setup (0.5 m), hip positional data are mostly lo c a liz e d in o n e area, while the wrist motions are in a semi-circular shape. the relatively static hip data suggested that the subjects were adopting twisting motion during the transfer proc e ss . a s the transfer distances increased, the curve pattern for hip and wrists positional data stretched out and resulted in a more stretched curve pattern. this suggests more d y n a mic motions occur during the transfer process, comprising of both body movements and bending, compared to primarily twisting movements in the shortest setup at 0.5 m transf er distance. body postures during material handling can be influenced by the distance between the lifting origin and the destination stations. findings from this study show that the magnitude of lower back bending increases as the transfer distance increases. this result is in agreement with a study by metha et al. [5] which found that the increase of s e pa ra tion 172 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 distance might increase forward flexion of the spine. this posture pose may happen due to the tendency of the workers to reach rather than stepping toward to the destination station. the authors added that longer transfer distance can also increase physio logic a l c o s t a n d transfer time of the handlers. meanwhile, if the transfer distances between the o rigin a n d destination stations were too close to each other, workers were more likely to adopt a twisting motion due to limited space and clearances. in another study, kuorinka and ilk k a [10] also found that limited workspaces and clearances may result in workers adopting incorrect material handling methods. overall, results in this study are aligned to f in d ings from other researchers that suggest increase in lower back bending magnitude, and decrease in lower back twisting magnitude, as the transfer distances increased. h o w ev er, the detailed analyses on these trends were not the primary focus of this m a n u s crip t. th e detailed measurement, analysis, and description on the trends of lower back b e nd in g a n d twisting during different transfer distances had been documented in the authors’ other manuscript. the principle of correct manual carrying is by holding the object as close to the b o d y as possible while keeping the back straight [15]. a study conducted by d o la n e t a l. [1 7 ] found that the activity of lifting a weight that is farther in front of the body a s o n e o f th e parameters contributing to a substantial increment in ex tensor moment of the spine. extensor moment is the tension in the thin muscle groups running at every side of the vertebral column of the body, and can be an indirect measure of the compressive force acting on the spine. in addition, multiple studies have established that lower back bendin g and twisting cause biomechanical load on lower back, hence increasing the risk for lo w e r back pain [18,19]. for example, a case study in malaysian automotive manufacturing company reported that lower back pain is the highest prevalence of msd among w o rk e rs [20]. the authors claimed that the workers were found to perform the mmh tasks with improper work postures and incorrect techniques. poor handling, in combination with poor postures may affect the function and efficienc y of muscle forces. muscle forces are increased when there are asymmetrical postures during bending and twisting of lower back [21]. the asymmetry in muscle activity occurs due to generation of mechanic al s tif f ne s s by different sets of muscles for spine stabilization process, and this may eventually lead to unequal stress concentrations on the different component structures of the spine. cholewicki and mcgill [22] in a lumbar spine modelling study showed that re d u c tion in passive joint and muscle stiffness in various postures may affect mechanic al s ta b ility o f the spine, consequently increasing the risk of development of chronic back pain. marras and granata [18] reported that bending and twisting can cause compres sio n al and shear force loadings on spine discs. compressive force and shear force exerted on th e intervertebral discs increase as the velocity and acceleration of the trunk inc re a se , w h ic h may happen due to sideways bending and twisting activities. during material handling tasks, the gravitational f orce, initial force of body segments and hand load nota b le to l5 s1 of spine may cause the upper body to torque-tilt at the lumbosacral (l5-s1) joint [2 3 ]. this torque depends on the motion of the spine and on the acceleration of the body segments, as well as the load. as such, transfer distances at two extremes (too short or to o far away) would increase risks to musculoskeletal strain. an appropriate transfer dis ta nc e that can balance between bending and twisting would reduce biomechanical load, musculoskeletal strain, and ultimately risks to musculoskeletal disorders or injuries. ev e n though many industries have been providing supporting devices and techniques on prop e r material handling to their workers, they may not be effective enough in p re v en tin g b a c k pain among workers [24]. as such, practitioners may also include consideration of 173 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 appropriate transfer distance as it can influence the magnitude of bending and twisting activities in manual handling tasks. the positional data showed that the different transfer distances may also affect w id th requirements, consequently the overall space requirement. the data across subjects showed similar width requirements between 0.5 m and 0.75 m transfer distances (m e a n = 74.84 cm, sd =10.26 cm for 0.5 m, and mean = 74. 18 cm, sd= 8.81 cm for 0.75 m). these two transfer distances encourage more twisting, due to limited clearance. a s s u c h , this might result in the subjects to naturally pulling the box close to the body during the transferring process of both 0.5 m and 0.75 m transfer distances, hence explaining why the width requirements were similar. as the transfer distance increases, the data trend suggests that the width requirement increases as well (mean = 78.95 cm, sd =12.07 cm for 1 . 0 m , and mean = 83.42 cm, sd= 14.01 cm for 1.25 m). at further transfer d is ta nc e , th e b o d y posture seems to shift from primarily twisting to twisting plus forward bending. as subjects were bending forward, the hands naturally extended out in an ef fort to s p a n th e reaching distances. this is likely to explain the extension of the width requirements in further transfer distances. the repeated measures anova found that there were significant differences in width requirements between transfer distances of 0.5 m vs 1.25 m, and 0.75 m vs 1.25 m at alpha=0.05. since width requirements for transfer distances of 0.5 m and 0.75 m were similar, it can be argued that 0.75 m transfer distance does not take significantly larger areas than 0.5 m, but at the same time provide larger clearance between the tra n s fe rs. o n the other hand, the 1.25 m transfer distance showed significant difference in width requirement as compared to 0.5 m, 0.75 m, and 1.0 m transfer distances, whic h in d ica te s that it will take larger space area. when translated to area requireme nts, 1.25 m transfer distance on average consumed 64% larger area than 0.5 m, 46% larger area th a n 0 . 7 5 m , and 24% larger area than 1m transfer distances. larger space area requirement resulte d in additional real estate, which indirectly translated to high er capital and costs. as such, it can be interpreted from data obtained in this study that the optimum transfer distance m a y be between 0.75 and 1.0 m. in this range, there is a middle ground in which the lif te rs d o not have to adopt extreme twisting and f orward bending. in addition, the differences in width requirements are marginal. this can provide the trade-off between postural adoption and space requirements when performing the manual transfer task. it should be noted th a t study by lavender and johnson [6] suggest that twisting and lateral moveme n t w o u ld b e minimized when the transfer distances were between 1 and 1.25 meters. th e d iffe ren ce s may come due to experimental setups, measures, and subject populations. 5. conclusion this study provides a visual mapping of hands and hip movements of manual transfer at four different distances, 0.50 m, 0.75 m, 1.00 m and 1.25 m. based o n o b s erv atio n o f twisting and bending of subjects in motion capture software, and through visualiza tio n o f hip and hand wrists motion top view mapping, it can be seen that the pattern of the hip motion changes from mostly static to more dynamic movements as the distance increas e s . in addition, patterns for wrists motions change from a semi-circular shape to a more stretched semi-circular shape as the transfer distance increases. shorter tran s fe r d is ta nc e encourages low back twisting while minimizing bending, whereas the increase of tra n s fer distance reduces the magnitude of low back twisting while individuals adopt more bending postures. as such, the motions of the hip and wrists during the manual h a n dlin g p ro c e s s were affected by the transfer distance. in addition, the study also found that transfer 174 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 distances affect space requirements. as transfer distance increases, the data trend sugges ts that the width requirement also increases, due to shifting from primarily twisting to twisting plus forward bending. forward bending and arm extension were adopted by subjects to increase their reaching range in further transfer distances, which consequ en tly affect the space requirements. the study suggests that the optimum transfer dista nc e m a y be between 0.75 and 1.0 m, in which there is a balance between extreme twisting and bending. in summary, it can be concluded that the difference in transf er distance does affect the space requirement as well as the postures possessed during manual handling activity. this provides guidance for engineers in designing workplace lay ou ts a s w e ll a s space requirements related to manual transfer tasks, especially in the early engineering design stage. acknowledgements the authors are grateful to the malaysian government, universiti teknikal malaysia melaka (utem) for supporting this study. the study is partially funded by research gra n t industri (irmg) / ergoworks / 2019 / fkp-cossid / i00037. the authors acknowledge lee poh yan and nur izzati azri for their contributions in this study. references [1] duly j, neumann wp. (2009) ergonomic contributions to company strategies. applied ergonomics, 40(4):745-752. [2] coenen p, gouttebarge v, van der burght as, van dieën jh, frings-dresen mh, van der beek aj, burdorf a. (2014) the effect of lifting during work on low back pain: a health impact assessment based on a meta-analysis. occupational and environmental medicine, 71(12): 871-877. [3] deros bm, daruis ddi, rosly al, aziz ia, hishamuddin ns, hamid nha, roslin sm. (2017) ergonomic risk assessment of manual material handling at an automotive manufacturing company. press academia procedia, 5:317-324. [4] mital a. (2017) guide to manual materials handling, london. [5] mehta jp, kim th, weiler mr, lavender sa. (2014) effects of transfer distance on spine kinematics for de-palletizing tasks. j. of occupational and environmental hygiene, 11(1):18. [6] lavender sa, johnson m. (2009) is there a transfer distance that minimizes twisting and bending motions of the spine?. in proceedings of the human factors and ergonomics society annual meeting, 53(14):882-882. [7] lavender sa, lorenz ep, andersson gb. (2007) can a new behaviorally oriented training process to improve lifting technique prevent occupationally related back injuries due to lifting?. spine, 32(4):487-494. [8] daltroy lh, iversen md, larson mg, lew r, wright e, ryan j, liang mh. (1997) a controlled trial of an educational program to prevent low back injuries. new england j. of medicine, 337(5):322-328. [9] karwowski w. (2005) ergonomics and human factors: the paradigms for science, engineering, design, technology and management of human-compatible systems. ergonomics, 48(5):436-463. [10] kuorinka i, lortie m, gautreau m. (1994) manual handling in warehouses: the illusion of correct working postures. ergonomics, 37(4):655-661. [11] shamsuddin ka, ani mnc, ab-kadir ar, osman mh. (2014) analysis on the workrelated musculoskeletal disorders (wmsd’s) based on ergonomic study in case of industry study. international j. of engineering research, 3(4):190-195. 175 iium engineering journal, vol. 21, no. 2, 2020 radin umar et al. https://doi.org/10.31436/iiumej.v21i2.1197 [12] yahya nm, zahid mno. (2018) work-related musculoskeletal disorders (wmds) risk assessment at core assembly production of electronic components manufacturing company. in iop conference series: materials science and engineering, 319(1):012036. [13] kazmierczak k, neumann wp, winkel j. (2007) a case study of serial-flow car disassembly: ergonomics, productivity and potential system performance. human factors and ergonomics in manufacturing & service industries, 17(4):331-351. [14] cheung z, feletto m, galante j, waters t, centers for disease control and prevention. (2007) ergonomic guidelines for manual material handling. in niosh publication, 2007131. [15] department of occupational safety and health. (2018) guidelines for manual material handling at workplace 2018, malaysia. [16] mohamad d, deros bm, ismail ar, daruis ddi. (2010) development of a malaysian anthropometric database. in conference on manufacturing technology and management. [17] dolan p, earley m, adams ma. (1994) bending and compressive stresses acting on the lumbar spine during lifting activities. j. of biomechanics, 27(10):1237-1248. [18] marras ws, granata kp. (1997) the development of an emg-assisted model to assess spine loading during whole-body free-dynamic lifting. j. of electromyography and kinesiology, 7(4):259-268. [19] plamondon a, denis d, delisle a, larivière c, salazar e, irsst mmh research gr oup. (2010) biomechanical differences between expert and novice workers in a manual material handling task. ergonomics, 53(10):1239-1253. [20] deros bm, daruis dd, ismail ar, sawal na, ghani ja. (2010) work-related musculoskeletal disorders among workers' performing manual material handling work in an automotive manufacturing company. american j. of applied sciences, 7(8):1087. [21] pope mh, andersson gbj, broman h, svensson m, zetterberg c. (1986) electromyographic studies of the lumbar trunk musculature during the development of axial torques. j. of orthopaedic research, 4(3):288-297. [22] cholewicki j, mcgill sm. (1996) mechanical stability of the in vivo lumbar spine: implications for injury and chronic low back pain. clinical biomechanics, 11(1):1-15. [23] jager m, luttmann a. (1992) the load on the lumbar spine during asymmetrical bi-manual materials handling. ergonomics, 35(7-8):783-805. [24] verbeek jh, martimo kp, karppinen j, kuijer ppf, viikari-juntura e, takala ep. (2011) manual material handling advice and assistive devices for preventing and treating back pain in workers. cochrane database of systematic reviews, (6). 176 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <feff04180437043f043e043b043704320430043904420435002004420435043704380020043d0430044104420440043e0439043a0438002c00200437043000200434043000200441044a0437043404300432043004420435002000410064006f00620065002000500044004600200434043e043a0443043c0435043d04420438002c0020043f043e04340445043e0434044f044904380020043704300020043d04300434043504360434043d043e00200440043004370433043b0435043604340430043d0435002004380020043f04350447043004420430043d04350020043d04300020043104380437043d0435044100200434043e043a0443043c0435043d04420438002e00200421044a04370434043004340435043d043804420435002000500044004600200434043e043a0443043c0435043d044204380020043c043e0433043004420020043404300020044104350020043e0442043204300440044f0442002004410020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e0030002004380020043f043e002d043d043e043204380020043204350440044104380438002e> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <feff0054006f0074006f0020006e006100730074006100760065006e00ed00200070006f0075017e0069006a007400650020006b0020007600790074007600e101590065006e00ed00200064006f006b0075006d0065006e0074016f002000410064006f006200650020005000440046002000760068006f0064006e00fd006300680020006b0065002000730070006f006c00650068006c0069007600e9006d0075002000700072006f0068006c00ed017e0065006e00ed002000610020007400690073006b00750020006f006200630068006f0064006e00ed0063006800200064006f006b0075006d0065006e0074016f002e002000200056007900740076006f01590065006e00e900200064006f006b0075006d0065006e0074007900200050004400460020006c007a00650020006f007400650076015900ed007400200076002000610070006c0069006b0061006300ed006300680020004100630072006f006200610074002000610020004100630072006f006200610074002000520065006100640065007200200036002e0030002000610020006e006f0076011b006a016100ed00630068002e> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <feff03a703c103b703c303b903bc03bf03c003bf03b903ae03c303c403b5002003b103c503c403ad03c2002003c403b903c2002003c103c503b803bc03af03c303b503b903c2002003b303b903b1002003bd03b1002003b403b703bc03b903bf03c503c103b303ae03c303b503c403b5002003ad03b303b303c103b103c603b1002000410064006f006200650020005000440046002003ba03b103c403ac03bb03bb03b703bb03b1002003b303b903b1002003b103be03b903cc03c003b903c303c403b7002003c003c103bf03b203bf03bb03ae002003ba03b103b9002003b503ba03c403cd03c003c903c303b7002003b503c003b103b303b303b503bb03bc03b103c403b903ba03ce03bd002003b503b303b303c103ac03c603c903bd002e0020002003a403b1002003ad03b303b303c103b103c603b10020005000440046002003c003bf03c5002003b803b1002003b403b703bc03b903bf03c503c103b303b703b803bf03cd03bd002003b103bd03bf03af03b303bf03c503bd002003bc03b50020004100630072006f006200610074002003ba03b103b9002000410064006f00620065002000520065006100640065007200200036002e0030002003ba03b103b9002003bd03b503cc03c403b503c103b503c2002003b503ba03b403cc03c303b503b903c2002e> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <feff005400650020006e006100730074006100760069007400760065002000750070006f0072006100620069007400650020007a00610020007500730074007600610072006a0061006e006a006500200064006f006b0075006d0065006e0074006f0076002000410064006f006200650020005000440046002c0020007000720069006d00650072006e006900680020007a00610020007a0061006e00650073006c006a006900760020006f0067006c0065006400200069006e0020007400690073006b0061006e006a006500200070006f0073006c006f0076006e0069006800200064006f006b0075006d0065006e0074006f0076002e0020005500730074007600610072006a0065006e006500200064006f006b0075006d0065006e0074006500200050004400460020006a00650020006d006f0067006f010d00650020006f00640070007200650074006900200073002000700072006f006700720061006d006f006d00610020004100630072006f00620061007400200069006e002000410064006f00620065002000520065006100640065007200200036002e003000200074006500720020006e006f00760065006a01610069006d0069002e> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 bouzenita et al. 42 the islamic ethics of mitochondria transplantation anke iman bouzenita 1 *, mohamed elwathig s. mirghani 2,3 and irwandi jaswir 2,3 1 department of islamic sciences, college of education, sultan qaboos university, oman. 2 bioprocess and molecular engineering research unit, department of biotechnology engineering, 3 international institute for halal research and training international islamic university malaysia, jalan gombak, 50728 kuala lumpur, malaysia. *corresponding author: anke_b_@hotmail.com (received: 5 th sept. 2016; accepted: 5 th may 2017; published on-line: 1 st dec. 2017) abstract: biotechnology has opened a new chapter with the advent of mitochondria transplantation for cell-based therapy. mitochondrial transplantation has successfully led to birth; however, cytoplasmic transplantation has caused apprehension since the mixing of human ooplasm from two different maternal sources may generate mitochondrial dna (mtdna) heteroplasmy in the offspring. most islamic legal verdicts on human cloning and somatic cell transfer are explicit as to its prohibition, due to the change of creation, mixing of lineage and other evaluations. is mitochondria transplantation equivalent to human cloning in that genetic information is proliferated and does it, therefore, take the same legal rule? are there possible benefits (maṣāliḥ) for medical treatment that may render mitochondria transplantation permissible, or are possible harms (mafāsid) overweighing? or is it a completely different procedure, taking a different rule? the paper will investigate into these questions and discuss the dimensions of islamic ethics on the issue. abstrak: bioteknologi telah membuka ruang baru pada perkembangan pemindahan mitokondria terapi berasaskan-sel. pemindahan mitokondria telah berjaya menghasilkan kelahiran; walau bagaimanapun, pemindahan sitoplasmik telah membawa kepada masalah lain, ini kerana percampuran telur manusia (ooplasm) daripada dua induk wanita yang berbeza bakal menghasilkan mitokondrial dna (mtdna) yang pelbagai (heteroplasmy) dalam jalur keturunan. kebanyakan undang-undang islam ke atas klon manusia dan sel pemindahan somatik adalah jelas dan nyata larangannya. ini disebabkan oleh perubahan pada ciptaan, percampuran dalam keturunan, dan pelbagai tanggapan lain. adakah pemindahan mitokondria sama dengan klon manusia dalam informasi genetik dibiakkan dan adakah, dengan ini membawa kepada peraturan undang-undang yang sama? adakah kemungkinan kebaikan (maṣāliḥ) pada rawatan perubatan akan menyebabkan pemindahan mitokondria dibenarkan, atau kemungkinan keburukan (mafāsid) lebih berat? atau adakah prosedur itu benar-benar berlainan, sehingga menyebabkan hukum berbeza digunakan? kertas ini akan mengkaji persoalan-persoalan ini dan membincangkan tentang isu ini dari sudut etika islam. keywords: mitochondria; organelle; heteroplasmy; dna; genome; islamic ethics; harms (mafāsid); benefits (maṣāliḥ) iium engineering journal, vol. 18, no. 2, 2017 bouzenita et al. 43 1. introduction the mitochondrion (plural mitochondria) is a large organelle found in the cytoplasm of all plant and animal (eukaryotic) cells. mitochondrial proteins vary depending on the tissue and the species. in humans, 615 distinct types of protein have been identified from cardiac mitochondria. the mitochondrial proteome is thought to be energetically regulated and the mitochondrion has its own independent genome, containing 37 genes. its inheritance is haploid; mitochondria are inherited through the maternal side only. mitochondria (mt) are known as "the powerhouse of the cell" because they provide most of the chemical energy in the cell. they are also involved in other tasks in the living cells such as cellular respiration, cellular differentiation, cell death, maintaining control of the cell cycle and cell growth. mitochondria have been implicated in several diseases, including mitochondrial disorders, cardiac dysfunction, heart failure and autism [1]. mitochondria transplantation may take place on the embryonic level, before or after in vitro fertilization of an egg cell, or through the transplantation of unhealthy mitochondria in adult human cells. while the first scenario has in variations already taken place but has been legally endorsed after heated debates by the uk as the only state in 2015, the second scenario is, to our knowledge, still in a trial phase. both scenarios need to be evaluated within an islamic legal and ethical framework. 2. the procedure embryonic mt transplantation intends to replace the dysfunctional, unhealthy mt of the intended mother, who is the only mt carrier, with the healthy mtdna of a female donor. this may happen in two ways: (i) maternal spindle transfer (mst), where the mt of the affected egg cell is exchanged with healthy donor mitochondria before fertilization. this happens by removing the nucleus from the egg cell of the mother-to-be, then inserting this nuclear dna into an enucleated donor egg with healthy mitochondria. after in vitro fertilization with the father‟s sperm, the embryo can be implanted into the mother‟s womb, resulting in a baby with ndna from each mother and father and mtdna from a female donor, the “third parent”; and (ii) pronuclear transfer (pnt) which takes place after fertilization, where the parental dna (the zygote) is transferred from a cell with unhealthy mt to a fertilized donated egg with healthy mtdna from the “third parent” that is vacated of its zygote [2]. meanwhile, the adult mt transfer has, to our knowledge, so far taken place in vitro only. elliott et al. have shown that the introduction of normal epithelial mitochondria into human cancer cells inhibit proliferation and increase drug sensitivity. for example, the introduction of normal mammary mitochondria into human breast cancer cells inhibits cancer cell proliferation and increases the sensitivity of the human breast cancer cell line (mcf-7) to the anticancer drugs such as doxorubicin, abraxane, and carboplatin. these results support the role of mitochondrial dysfunction in cancer and suggest the possible use of targeted mt for cancer therapeutics. the in-vivo scenario could be to insert healthy donor mt into cancerous cells to enhance reception of anticancer drugs, stop tumor growth or kill cancerous cells [3, 4]. 3. islamic evaluation the primary concerns regarding genetic engineering involving embryos and ivf procedures from the islamic perspective are the illicit mixing of progeny, establishment of doubtful parenthood and changing of creation. actual known and expectable harms (mafāsid) and benefits (maṣāliḥ) will also be discussed. iium engineering journal, vol. 18, no. 2, 2017 bouzenita et al. 44 3.1 mixing of ansāb (lineage) recent research on the actual role of mtdna suggests that many discoveries are yet to be expected, it is, therefore, premature to decide on the lacking importance of mtdna for genetics [5]. the donor mtdna may account for a minor percentage of the child‟s dna [6], but it is clearly traceable. the status of the donor with regard to the child is, therefore, unclear, is she a mother, comparable to a foster mother, are her own children related to the mtdna recipient? the introduction of dna other than that of husband and wife who are legally married to each other and alive at the time of ivf and implantation of the embryo into the wife‟s uterus disturbs a very complex system with regard to legal rules of marriage, procreation, inheritance, the social system at large. the identity and descent of the created child become unclear. an analogy to organ transplantation is faulty as organ transplantation (of blood, heart, and kidney) does not change the recipient‟s dna. the transplantation of reproductive organs (testicles, ovaries) is not permissible due to the mixing of descent [7]. in addition to the mixing of dna (nuclear and mitochondrial) from different parents which is part of both mst and pnt procedures, pnt also involves the destruction of the zygote of a donor egg. adult mt transplantation therapy seems unobjectionable with regard to a possible mixing of lineage provided that no harm is involved for donor and recipient. the main question would be in how far a mitochondria transplantation in, say, an adult breast cancer patient affects her germ line. since progeny is already established for this patient, there seems to be no concern of a possible mixing of ansāb. it may, in fact, be comparable to a blood transfusion and could fall under the permissibility of medical treatment if it realizes benefits for the preservation of life. the case is still subject to scrutiny. 3.2 alternatives the existence of alternatives is vital to decide whether a case can be described as a necessity (ḍarūrah) from the islamic point of view. an acute case of a necessity that renders the prohibited lawful (al-ḍarūrah tubīḥ al-maḥẓūrah) could be claimed with the imminent danger of losing life and limbs to oneself or a family member. the existence of alternatives (here: in treatment) defies this. mtdna transplantation as a “therapy” for infertility or to avoid unhealthy offspring is not a therapy for already existing human beings, but projected to births planned in the future. searching for less objectionable ways of therapy is mandatory. 3.3 actual and possible harms warding off harm has priority over acquiring benefit (dar’u l-mafsadah awlā min jalb al-maṣlaḥah). the consideration of actual known and expectable possible harms is, therefore, essential and may, if prevailing, be given priority over possible benefits, bringing a prohibition closer than permission [8]. the possibility of mt heteroplasmy and malignant genetic modification through mtdna transplantation is not sufficiently researched. preliminary research results seem to defy the idea [6], but more clinical trials with long-term observation will be needed. the average number of mothers transmitting mtdna defects in the uk has been estimated at 150, for the us at 778 per year [9]. but not all affected carriers of unhealthy mtdna will choose and be subject to this treatment, due to the risks for themselves and their offspring [10]. it is however not a benefit for the entire society, but rather for a small number. it is possible to expect that the procedures involved („harvesting‟ donor eggs, transplanting the mt, ivf procedures) are costly and may defer funds from the research for other healing techniques [11]. a major concern that is not generally discussed involves the donation of egg cells. they need to be free from mt dysfunctions, and a large number of donor eggs need to be procured. donating women iium engineering journal, vol. 18, no. 2, 2017 bouzenita et al. 45 need to undergo fertility treatment with known side effects. the commodification of human eggs is to be expected [11]. in addition, the availability of this “treatment” may turn into a „moral obligation‟ or even pressure to use it and not give birth to children with genetic defects anymore. 3.4 actual and possible benefits (maṣāliḥ) at first glance, the therapeutic results and prospects of mt transplantation seem to be promising in that embryos resulting from the procedure are healed of the mtdna defect and the healing effect is passed on to their offspring. embryonic mtdna transplantation, however, involves an impermissible mixing of lineage (ansāb) through involving a third genetic parent. possible benefits cannot outweigh this prohibition. with the rise in discoveries on the functioning of the mitochondria and their role in diverse diseases, more therapeutic uses not involving embryonic transfer may be found. the maṣlaḥah involved in protecting and enhancing human life, however, is still in the stage of probability and not yet attested to. it affects a small group of people and is not a common benefit to society at large, one of the conditions that need to be met for the consideration of maṣlaḥah in rendering the prohibited lawful [12]. 4. conclusion in conclusion, genetic therapy, and the mt transplantation that belongs to it, may seem and be propagated as a promising cure for manifold diseases. however, the change of the genetic blueprint in a way that involves genetic material of a donor, leading to a „threeparent-baby‟ is analogous to human cloning in that it 1) defies sunnat al-zawjiyah, the creation of human beings from pairs, 2) genetic material of a donor who is not legally married to the father of the embryo is fused if only to a small extent – and passed on to the next generations, therefore the nasab (progeny) of that embryo as well as its relation to the donor and her family and descendants is doubtful, with manifold effects on the islamic legal rules regarding, marriage, descent, inheritance, and others. it is premature to completely exclude unwanted side effects and expectable harms at this stage. the expectable harms with regard to embryonic mtdna transplantation seem to exceed possible benefits. in addition, the existence of prohibiting evidence with regard to the introduction of a third parent renders the procedure illegal. as to mt transplantation in adults from adult donor mitochondria, there is still a need to assess possible harms and benefits. references [1] chan dc. (2006) mitochondria: dynamic organelles in disease, aging, and development. cell, volume 125(7):1241–1252. [2] baylis f. (2013) the ethics of creating children with three genetic parents, reproductive medicine online 26: 531-534. [3] elliott rl, jiang xp, head jf. (2012) mitochondria organelle transplantation: introduction of normal epithelial mitochondria into human cancer cells inhibits proliferation and increases drug sensitivity. breast cancer research and treatment, 136:347-354. [4] elliott rl, jiang xp, head jf. (2014) mitochondria organelle transplantation: the mitochondrion, “an intracellular organelle for cell-based therapy” opinion commentary. international journal of applied science and technology, 4(5):158-162. [5] new scientist: three-parent babies: it‟s more messy than we thought. 17 september 2014, https://www.newscientist.com/article/mg22329871-600-three-parent-babies-its-more-messythan-we-thought/ iium engineering journal, vol. 18, no. 2, 2017 bouzenita et al. 46 [6] barritt ja, brenner ca, matter he, cohen j. (2001) mitochondria in human offspring derived from ooplasmic transplantation. human reproduction 16:513-516. [7] imana (islamic medical association of north america) (1967) islamic medical ethics (publication 2), section 4: f organ donation and transplantation. available at: https://c.ymcdn.com/sites/www.imana.org/resource/resmgr/files/publication2.pdf [8] al-suyūṭī, j. (2007) al-ashbāh wa l-naẓā‟ir fī qawā c id wa furū c fiqh al-shāfi c iyyah, beirut, dar al-kutub al-„ilmiyyah. [9] gorman gs, grady jp, and turnbull dm. (2015) mitochondrial donation – how many women could benefit? the new england journal of medicine, 372:(9) 885-887. [10] baylis f. (2015) the truth about mitochondrial replacement, impact ethics. [11] stammers t. (2015) the ethics of mitochondrial transfer. lecture was given at the first international bioethics conference, sultan qaboos university, muscat, oman, march 2015. [12] al-ghazālī aḥ. (1997) al-musṭaṣfā fī c ilm al-uṣūl. beirut. https://www.ncbi.nlm.nih.gov/pubmed/?term=gorman%20gs%5bauthor%5d&cauthor=true&cauthor_uid=25629662 https://www.ncbi.nlm.nih.gov/pubmed/?term=grady%20jp%5bauthor%5d&cauthor=true&cauthor_uid=25629662 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 kareem et al. https://doi.org/10.31436/iiumej.v20i2.1006 no reference quality of hazy images depending on transmission component estimation hana hasan . kareem1, esraa gatea. daway2, hazim gatea. daway3 1department of physics, college of education, mustansiriyah university, baghdad, iraq. 2department of medical instrumentation techniques engineering, bilad alrafidain university college, baghdad, iraq. 3department of physics, college of science, mustansiriyah university, baghdad, iraq. *corresponding author: hazimdo@uomustansiriyah.edu.iq (received: 6th october 2018; accepted: 30th july 2019; published on-line:2nd december 2019) abstract: the research aim is to measure the quality of hazy images using a noreference scale based on the transmission component and wavelet transform (tcwt) by calculating the histogram in the high and low (hl) component. the system is designed to capture several images at different levels of distortion from little to medium to high and the quality is studied in the transmission component. this measure is compared with the other no-reference measurements as a haze distribution map based haze assessment (hdmha) and entropy by calculating the correlation coefficient between the no reference measurements and the reference scale universal quality index (uqi). the results show that the proposed algorithm tcwt is a good measure of the quality of hazy images. abstrak: kajian ini bertujuan bagi mengukur kualiti imej berjerebu dengan menggunakan skala tiada-rujukan berdasarkan komponen transmisi dan penukaran signal gelombang (tcwt) dengan mengira komponen tinggi dan rendah (hl) histogram. sistem ini dicipta bagi mengumpul imej pada tahap berbeza dari takat selerakan paling rendah kepada paling tinggi dan kualiti imej diselidik dalam komponen transmisi. ukuran ini dibandingkan dengan ukuran tiada-rujukan lain sebagai peta selerak berjerebu (uqi). keputusan menunjukkan algoritma kualiti imej berjerebu tcwt yang dicadangkan adalah berkualiti baik.. keywords: no reference quality; wavelet transform; hazy images; transmission 1. introduction the atmosphere reacts to light due to the atmosphere’s composition under steady conditions. the atmosphere includes a variety of different molecules and small types of suspended particles, called aerosols [1]. as such, the primary problem presented is the distortion of aerial imaging by these particles. aerosols, by definition, are very fine liquid or solid particles suspended (in the air) in the atmosphere with a very low fall speed. their size mostly lies between 10−2 m and 100 μm. furthermore, dust, fog, haze, drizzle, smoke, rain, and snow are some of the examples of aerosols [2]. the majority of aerial images have been taken under bad conditions and thus, need a quality scale. the quality scale provides a pointer on the degree of deformation as well as the degree of improvement. correspondingly, the image quality assessment is a hot spot in the field of image processing. 70 iium engineering journal, vol. 20, no. 2, 2019 kareem et al. https://doi.org/10.31436/iiumej.v20i2.1006 in the classified image quality assessment (iqa) [3], the two main categories are fidelity and intelligibility of the image. the fidelity is described as deviation level between the evaluated image and a standard image. the intelligibility is the image’s ability to provide related information to people or a computer. the image quality measure can be estimated by quantitative measurement of the combination of the two classes. currently, iqa is segregated into (i) the subjective estimation method, and (ii) the objective estimation method. the previous method uses people's subjective sense in order to evaluate the quality level of the images while the latter simulates perception technique of human visual system (hvs) in order to measure it. several corresponding existing approaches are known as fullreference (fr), reduced-reference (rr), and no-reference (nr). among these methods, the full reference method is based on hvs [4,5], structural similarity measurement (ssim) [6] ,and universal quality index (uqi) [7], which were developed a long time ago and were subsequently applied in several areas. in general, the no reference iqa method can be divided into two categories [8]: (i) algorithms developed for specific types of distortion, such as blur [9], jpeg and jpeg2000 compression [10,11], and noise [12] and (ii) non-distortion specific algorithms. moorthy and bovik [13] proposed a two-step framework (biqi) for no reference iqa based on natural scene statistics, which did not require any prior knowledge of the distorting process, once trained, as evidenced by tang et al. [14]. another research [15] proposed the method to determine no reference image quality by depending on the entropy (ent) of the first derivative of the lightness. furthermore, an evaluation of the histogram of the edge regions in [16] suggested that the no reference measure, which depends on the range channel (rgb) of the image, is defined and the haze distribution map (hdm) that is extracted from the hazy image and then the haze assessment metric hdm-based haze assessment (hdmha) is designed according to the hdm using google earth maps. 2. proposed algorithm to measure the quality of the hazy images in real visual systems, the effects of the haze in the scene rely on the haze density level and coverage area of the haze. increasing the density of the haze and increasing the area covered by haze, leads to an increased distortion in the resulting image. the proposed method, thus, depends on the estimation the transmittance components from the image. following which, a wavelet transform of this component is calculated. the wavelet transform is further analyzed by calculating the histogram. 2.1 estimating the transmission in a single image distorted by haze, an optical transmission (t) can only be evaluated depending on the hazy image [17-19]. in the calculation, possibly, an atmospheric light (a) value may be given. thus, by superimposition, the transmission in a local patch r(x) is constant. we denote the patch’s transmission to have the min value in the local patch r(x) on the haze image. the transmission is, thereby, given by [20]: (1) in this equation, the term is dark channel of the haze image. an optional is to keep a very small amount of haze for distant objects, depending on the constant (0< ≤1). in this study, we have used , as in [18]. figure 1 illustrates the transmission for the flower images using equation (1). 71 iium engineering journal, vol. 20, no. 2, 2019 kareem et al. https://doi.org/10.31436/iiumej.v20i2.1006 fig. 1: the flower image and its transmission. 2.2 histogram of the hl component in the wavelet transform wavelet transforms are significantly beneficial tools for image processing; they have been used extensively in procedures involving image processing, data compression, and signal processing. figure 2 illustrates the wavelet transform for one level decomposition using a haar transform [21]. wherein, the quality scale is based on a conversion of transmission image rather than the original image, and the histogram is calculated for the hl component. figure 3 shows this transform for the original transmission image (free haze) and its histogram of the hl component. fig. 2: the wavelet transform for the flower image and its components. fig. 3: the wavelet transform for the transmission of the flower image with free haze and histogram of the hl component. transmission l h l h 72 iium engineering journal, vol. 20, no. 2, 2019 kareem et al. https://doi.org/10.31436/iiumej.v20i2.1006 figure 4 illustrates this transform for the transmission image (for haze images) and its histogram of the hl component. in the histogram distributions, we can see that the maximum value is inversely proportional to the haze ratio in the image, where this feature can be investigated in the creation of a blind-reference quality measure by using: (2) fig. 4: the wavelet transform for the transmission flower image with distortion by haze and histogram of a hl component. the increase in the haze ratio leads to a decrease in quality by reducing the q_tcwt factor while an increase in quality, leads to increased q_tcwt. the tcwt algorithm can be performed with the following procedure: 1. input hazy images ih(x, y). 2. estimate the transmission using eq. (1) to get th(x,y). 3. transform th(x, y) image by finding the wavelet transform for one level. 4. estimate the hl component from the wavelet transform to get thhl(x, y). 5. calculate the histogram for thhl(x,y). 6. compute the quality based on by using eq. (2). 3. universal quality index instead of using traditional error summation measurements, we can use a method referred to as universal quality index (uqi) to model any image distortion. [7]: , (3) where and are the mean of the original and processing (or hazy) images, and are the standard deviation between the original and processed (or noisy) images. is the covariance, which can be defined as[7]: ) (4) or 73 iium engineering journal, vol. 20, no. 2, 2019 kareem et al. https://doi.org/10.31436/iiumej.v20i2.1006 . (5) 4. results and discussion in this study, we have designed a system to measure the level of the haze (dust form), which distorts the color image. figure 5 shows the complete system, which contains a firm glass box, hene laser, fan, lux meter, camera stand, and camera. dust is raised by the fan in the box, whereby the lux meter immediately measures the laser intensity. while more dust is added into the box, the dust in the bottom of the box is stirred. after a short span of time, the dust settles at the bottom of the box, and once the dust has settled, images are taken from the camera a second time. the lux meter reads the intensity of the laser light, which decreases as the intensity of dust increases and increases according to the reduced density at the same time as the camera captures the images. during the course of the experiment, in the current study, 39 images were taken, each group contained 13 images (distorted from high to low by hazy) with size (1068*1040 pixel). subsequently, all the images were processed using a matlab program version 2013a. fig. 5: the system used to capture the hazy image with deformation levels from high to low. in this research, the reference measure values (uqi) of the hazy images was calculated as well as no-reference measures (ent, hdmhs, and tcwt) were computed for all measurements. these relationships are illustrated in figs. 7, 8 and 9 for all the group images. note, as apparent from all these relationships, the non-reference measure tcwt is closer to reference measure uqi, followed by hdmhs then ent. this behaviour is reflected in the correlation coefficients between the reference scale and non-reference measures. note that the greatest value of the correlation is 0.9864 because it is close to one for the tcwt as shown in table 1, and then correlation coefficients are lower in hdmhs and ent. 74 iium engineering journal, vol. 20, no. 2, 2019 kareem et al. https://doi.org/10.31436/iiumej.v20i2.1006 fig. 6: the first row represents some images in the first group, i.e., artwork images, the second row represents the second group, i.e., the pens images and the third row represents the second group, i.e., the flower images. all images were taken in about 27 to 203 lux. fig.7: the relationship between normalized quality measurements and normalized illuminance for the first group images. fig. 8: the relationship between normalized quality measurements and normalized illuminance for the second group images. 27 50 129 203 (lux) 75 iium engineering journal, vol. 20, no. 2, 2019 kareem et al. https://doi.org/10.31436/iiumej.v20i2.1006 fig. 9: the relationship between normalized quality measurements and normalized illuminance for the third group images. table 1: correlation coefficient between the reference measure (uqi) and nonreference measure for all image groups method first g. second g. third g. tcwt 0.9864 0.9857 0.9864 hdmhw 0.9798 0.9735 0.9798 ent 0.9686 0.9339 0.9686 5. conclusion in this research a non-reference scale tcwt was proposed to measure the quality of hazy images based on transmission. this measure is compared with the hdmhw and ent measurements by calculating the correlation coefficient. through the analysis of the results, we note that the tcwt is a suitable performance metric for measuring the quality of hazy images and a good proportion if it is comparable with other non-reference measures in the ent and hdmhw, because the proposed method has higher correlation (0.9864) compared to other methods. references [1] aber, j. s., marzolff, i., & ries, j. b. (2010). small-format aerial photography. boston: elsevier. 266. [2] murphy, b. l., and morrison, r. d. (2002). introduction to environ-mental forensics . san diego, ca: academic press. [3] abdou ie, dusaussoy nj. (1986) survey of image quality measurements. paper presented at proceedings of 1986 acm fall joint computer conference, ieee computer society press. pp71-78. [4] yu z, wu hr, winkler s, chen t. (2002) vision-model-based impairment metric to evaluate blocking artifacts in digital video. proceedings of the ieee, 90(1): 154-169. [5] nill nb, bouzas b. (1992) objective image quality measure derived from digital image power spectra. optical engineering, 31(4): 813-826. [6] wang z, bovik ac, sheikh hr, simoncelli ep. (2004) image quality assessment: from error visibility to structural similarity. ieee transactions on image processing, 13(4): 600-612. [7] wang z, bovik ac. (2002) a universal image quality index. ieee signal processing letters, 9(3): 81-84. [8] lu y, xie f, wu y, jiang z, meng r. (2015) no reference uneven illumination assessment for dermoscopy images. ieee signal processing letters, 22(5): 534-538. 76 iium engineering journal, vol. 20, no. 2, 2019 kareem et al. https://doi.org/10.31436/iiumej.v20i2.1006 [9] cao z, wei z, zhang g. (2014) a no-reference sharpness metric based on the notion of relative blur for gaussian blurred image. journal of visual communication and image representation, 25(7): 1763-1773. [10] corchs s, gasparini f, schettini r. (2014) no reference image quality classification for jpeg-distorted images. digital signal processing, 30: 86-100. [11] liang l, wang s, chen j, ma s, zhao d, gao w. (2010) no-reference perceptual image quality metric using gradient profiles for jpeg2000. signal processing: image communication, 25(7): 502-516. [12] liu m, zhai g, zhang z, sun y, gu k, yang x. (2014) blind image quality assessment for noise, paper presented at broadband multimedia systems and broadcasting (bmsb), 2014 ieee international symposium on, ieee, 1–5. [13] moorthy ak, bovik ac. (2010) a two-step framework for constructing blind image quality indices. ieee signal processing letters, 17(5): 513-516. [14] tang h, joshi n, kapoor a. (2011) learning a blind measure of perceptual image quality, paper presented at computer vision and pattern recognition (cvpr), 2011 ieee conference on, ieee. [15] thuy tuong nguyen, xuan dai pham, dongkyun kim and jae wook jeon, (2008,"automatic exposure compensation for line detection applications",ieee international conference on multisensor fusion and integration for intelligent systemsseoul, korea. [16] pan x, xie f, jiang z, shi z, luo x. (2016) no-reference assessment on haze for remotesensing images. ieee geoscience and remote sensing letters, 13(12): 1855-1859. [17] daway, h.g.; mohammed, f.s.; abdulabbas, d.a. (2016) aerial image enhancement using modified fast visibility restoration based on sigmoid function. adv. nat. appl. sci. 2016, 10 (11), 16–22 [18] he k, sun j, tang x. (2011) single image haze removal using dark channel prior. ieee transactions on pattern analysis and machine intelligence, 33(12): 2341-2353. [19] tan rt. (2008) visibility in bad weather from a single image, paper presented at computer vision and pattern recognition, 2008. cvpr 2008. ieee conference on, ieee. [20] wang z, feng y. (2014) fast single haze image enhancement. computers & electrical engineering, 40(3): 785-795. [21] gonzalez rc, woods re. (2002) digital image processing, edited, prentice hall new jersey 77 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <feff0633062a062e062f0645002006470630064700200627064406250639062f0627062f0627062a002006440625064606340627062100200648062b062706260642002000410064006f006200650020005000440046002006450646062706330628062900200644063906310636002006480637062806270639062900200648062b06270626064200200627064406230639064506270644002e00200020064a06450643064600200641062a062d00200648062b0627062606420020005000440046002006270644062a064a0020062a0645002006250646063406270626064706270020062806270633062a062e062f062706450020004100630072006f00620061007400200648002000410064006f00620065002000520065006100640065007200200036002e00300020064806450627002006280639062f0647002e> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <feff0054006900650074006f0020006e006100730074006100760065006e0069006100200073006c00fa017e006900610020006e00610020007600790074007600e100720061006e0069006500200064006f006b0075006d0065006e0074006f007600200076006f00200066006f0072006d00e100740065002000410064006f006200650020005000440046002c0020006b0074006f007200e90020007300fa002000760068006f0064006e00e90020006e0061002000730070006f013e00610068006c0069007600e90020007a006f006200720061007a006f00760061006e006900650020006100200074006c0061010d0020006f006200630068006f0064006e00fd0063006800200064006f006b0075006d0065006e0074006f0076002e002000200056007900740076006f00720065006e00e900200064006f006b0075006d0065006e0074007900200076006f00200066006f0072006d00e10074006500200050004400460020006a00650020006d006f017e006e00e90020006f00740076006f00720069016500200076002000700072006f006700720061006d00650020004100630072006f0062006100740020006100200076002000700072006f006700720061006d0065002000410064006f006200650020005200650061006400650072002c0020007600650072007a0069006900200036002e003000200061006c00650062006f0020006e006f007601610065006a002e> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 232 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering suriza et al. 45 analysis of rain effects on terrestrial free space optics based on data measured in tropical climate suriza a.z., islam md. rafiqul, wajdi al-khateeb and a.w. naji electrical and computer engineering department, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. rafiq@iium.edu.my abstract: free space optics (fso) shows a great alternative as the solution for last mile problem where fiber optics is unavailable due to deployment time and cost constraint. however, the feasibility of using fso system as communication link very much depends on local weather. since tropical region experiences heavy rainfall, rain with high intensity is expected to affect the fso link severely. few prediction models have been proposed by itu-r based on france and japan’s measurement. this paper has compared rain attenuation predicted by models and data measured in malaysia over free space optical links for one year period. prediction models are clearly unable to predict attenuation measured in tropical climate. abstrak: wayarles optik menjadi alternatif sebagai satu penyelesaian kepada masalah kesesakan terutama diakhir sesuatu talian dimana ianya tidak dapat diselesaikan dengan menggunakan gentian fiber akibat daripada kekangan masa pemasangan dan masalah kewangan. walaubagaimanapun, kejayaan untuk menggunakan wayarless optic ini amat bergantung kepada keadaan cuaca di sesuatu tempat. di rantau tropika hujan lebat sentiasa dialami, oleh itu hujan dengan kepadatan tinggi adalah dijangkakan lebih memberi kesan kepada talian wayarles optic ini. beberapa model yang telah dicadangkan oleh itu-r berlandaskan kepada pengumpulan data yang dibuat di perancis dan jepun. kertas kajian ini akan membandingkan antara model-model yang telah digunapakai dengan data yang dikumpulkan di malaysia selama setahun. jelasnya model yang telah digunapakai tidak dapat digunakan secara berkesan di rantau tropika. keywords: free space optics; rainfall rate; rain attenuation 1. introduction in telecommunication infrastructure, backbone network and last mile access is required to have efficient telecom and internet connectivity. with the existing connectivity gap, free space optics (fso) provides an excellent alternative. fso technology promise point-to-point, high speed communications links. it is a technology which offers the speed of fiber with the flexibility of wireless. available communication system like fiber which is the most reliable solution for optical communications is one of the backbones in most cities. however, the cost to digging and laying down the fiber cable are huge. furthermore, the time of deployments is also economically too expensive. it is also quiet difficult to relocate fiber cable once it is already been deployed [1,2]. however, local weather condition is the foremost limitation of fso link availability. the attenuation in atmosphere is unpredictable and can cause the attenuation from a few dbs to hundred of dbs per kilometer distance. in temperate region, the availability of fso iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering suriza et al. 46 link is limited by fog and heavy snow [3]. in tropical region like malaysia, rainy events can be experienced throughout the year. therefore, rain is an important factor of attenuation and distortion signals in receiver systems [4]. heavy rain is expected to be the limiting factor for fso link availability. recently, few prediction models have been proposed by itu-r based on france and japan’s measurement. the rain attenuation on fso links and corresponding rainfall intensity has been measured at iium for a period seven month from march 2011 to september 2011. this paper has compared attenuation predicted by models and those measured over free space optical links in malaysia. 2. rain attenuation prediction model rain attenuation prediction is normally referred as “specific attenuation” which means attenuation per unit length. in terahertz wave system like fso, rain attenuation is particularly severe and greatly dependent on various models of raindrop-size distribution [5]. the most commonly used raindrop size distributions that have been proposed are marshal and palmer [6]. marshal and palmer distribution proposed renowned empirical expression by fitting their data and the laws and parsons data. rain specific attenuation is represented by power law; refer to equation (1). � � �� � (1) where r is the rain rate in mm/hr, k and α are power law parameters. the power law parameters depend on frequency, rain drop size distribution and rain temperature. for the purpose of calculating the attenuation, it is adequate to assume that raindrops have spherical shape. this assumption makes k & α independent of polarization [7]. to model rain prediction attenuation in tropical weather condition, an approach adopted by itu-r is used. it is based on the relationship between the equally probable experimental rain rates and received level signal [8]. in itu-r methods, it is recommended that the rainfall needs to be measured at interval of 1 minute in order to determine the rain rate [9]. analysis on the effect of rain on fso link can be done by knowing the rain attenuation on fso links and corresponding rainfall intensity. the modeling of rain attenuation prediction can be done using two methods, namely empirical method and the physical method [10]. the empirical method is based on correlation between observed attenuation distribution and corresponding observed rain-rate distribution measured at 1 minute integration time [11, 12]. while the physical method is an attempt to use the physical behavior involved in the attenuation process. the prediction model that has been recommended by itu-r [13] is as in table 1 and other models that have been used for fso rain attenuation prediction is as in table 2 [6]. table 1: rain attenuation prediction model proposed by itu-r for fso. model origin author k α note carbonneau france itu-r [17] 1.076 0.67 temperate region japan japan itu-r [17] 1.58 0.63 temperate region iium engineering journal, vol. 12, no. 5, 2011: special issue table 2: rain attenuation prediction model for fs drizzle or light rain (joss) (r<3.8 mm/hr) mean rain (joss) (3.8 < r < 7.6 mm/hr) strong rain (storm) (joss) (r < 7.6 mm/hr) rain (marshal and charbonneau’s model proposed done in france [14]. however the measurement done was compare with rain intensity in tropical region. highest rain rate in measurement and (uk) [14]. however, in tropical region mm/hr. for japan’s model, the measurement seems rain rate. the most of the data concentrated below 50 mm/hr which is much lower than measured in malaysia. both models, t determining values of k and �. k and � values of marshal measured drop size distribution. in [1 distribution established for other countries may result in the prediction error when applied in tropical region. even though the analysis is done for microwave system but the application on drop size distribution is applied also in fso. paper is to investigate rain attenuation prediction model for fso under tropical weather condition using method recommended by itu 3. measurement setup rainfall data is measured using tipping bucket block e1, faculty of engineering, iium, malaysia bucket rain gauge and the data logger fig. 1: rain gauge and data logger block diagram the data is being logged device. rainfall amount is lo minute integration time. from the collected rain data, rain events are extracted and rain intensity of mm/hr is calculated. the fso link is installed ruqayyah in line of sight. since the transmission of the fso link is sending and receiving signal, the term to describe it is transceiver g journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics 47 rain attenuation prediction model for fso. attenuation relation drizzle or light rain (joss) (r<3.8 mm/hr) 0.509 r 0.63 mean rain (joss) (3.8 < r < 7.6 mm/hr) 0.319 r 0.63 strong rain (storm) (joss) (r < 7.6 mm/hr) 0.163 r 0.63 rain (marshal and palmer) 0.365 r 0.63 proposed values to predict the k & � based on measurement however the measurement done was for very low rain intensities compare with rain intensity in tropical region. the 5 mm/hr rain rate is in measurement and is considered exceptional in the united kingdom ]. however, in tropical region the highest rain intensity measured above 200 . for japan’s model, the measurement seems to be conducted up to 80 to 90 mm/hr the most of the data concentrated below 50 mm/hr which is much lower than measured in malaysia. both models, the higher rain rate is not in the consideration for �. marshal-palmer and joss distributions are developed by drop size distribution. in [15], it is mentioned clearly that the use of drop size stablished for other countries may result in the prediction error when applied tropical region. even though the analysis is done for microwave system but the application on drop size distribution is applied also in fso. therefore, the aim of this rain attenuation prediction model for fso under tropical weather condition using method recommended by itu-r with 1 minute integration time measurement setup rainfall data is measured using tipping bucket type rain gauge located at rooftop of block e1, faculty of engineering, iium, malaysia. the block diagram of the tipping bucket rain gauge and the data logger are as shown in fig. 1. 1: rain gauge and data logger block diagram. ged into the data logger before being transmit to the monitoring device. rainfall amount is logged by data logger [16] to the monitoring software with 1 minute integration time. from the collected rain data, rain events are extracted and rain lculated. fso link is installed between faculty of engineering block e1 and mahallah line of sight. since the transmission of the fso link is sending and receiving the term to describe it is transceivers. the distance of both transceivers is 800 m. 1 on science and ethics in engineering suriza et al. based on measurement for very low rain intensities 5 mm/hr rain rate is taken as the xceptional in the united kingdom the highest rain intensity measured above 200 80 to 90 mm/hr the most of the data concentrated below 50 mm/hr which is much lower than he higher rain rate is not in the consideration for palmer and joss distributions are developed by considering that the use of drop size stablished for other countries may result in the prediction error when applied tropical region. even though the analysis is done for microwave system but the therefore, the aim of this rain attenuation prediction model for fso under tropical weather r with 1 minute integration time. located at rooftop of . the block diagram of the tipping data logger before being transmit to the monitoring software with 1 minute integration time. from the collected rain data, rain events are extracted and rain faculty of engineering block e1 and mahallah line of sight. since the transmission of the fso link is sending and receiving of both transceivers is 800 m. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering suriza et al. 48 on both sides of transceivers there are four transmitters and four receivers. all are operated in 850 nm wavelength optical signals [17]. the management point of the link head is connected to pc interface via multipatch fiber cable to the monitoring device. the data point of the link head is connected to media converter as the source of the data transmission. the other side of the transceiver is loop backed using fiber cable. the effect of rain on the fso link, as shown in fig. 2, is monitored and the result for both rain event and fso power received level is analyzed and synchronized to find the link attenuation and rain intensity at the time the rain occurred. (a) (b) fig. 2: the effect of rainfall on fso link (a), and rain data taken from rain gauge (b), taken on 29 july 2011 between 4.40am to 7.40am. 4. results and analysis throughout the measurement, 96 raining events were collected and out of it 73 heavy raining events are considered for analysis. the other 23 observed raining events are discarded due to two obvious reasons. there are 18 events where rain gauge collected rain intensity but the fso link was unavailable. and other 5 events measured low rain intensity which has no effect to the fso link. all measured rain intensities and attenuation on fso link were synchronized based on the 1 minute’s integration time. for every rainy day and amount of rain is extracted out from the measured data. each rain event is compared to fso link’s received power level and the attenuation level due to the rain is extracted for each minute. the collected data was not considered for one year period, hence it is not adequate to represent statistical distribution. but the analysis is focused on to derive relationship between rain and its effects on fso signal. therefore, it is obvious that considering 73 events are adequate to produce correct results. a sample calculation of percentage of exceeded for is calculated and plotted. a sample graph for a month data is as shown in fig. 3. the same process is done for measured received power level (dbm) of fso link that attenuate due to the rainfall rate at the same time and the same date as the rain events with 1 minute integration. from the data, the attenuation due to rainfall is extracted and percentage of time exceeded is calculated and plotted as in fig. 4. the measured rain intensity and corresponding rain attenuation on fso link is estimated for equally probable at different percentage of time exceeded. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering suriza et al. 49 fig. 3: one month rain intensity (mm/hr) as a % of time exceeded measured on july 2011. fig. 4: one month rain attenuation on fso link (db) as a % of time exceeded measured on july 2011. the same process is repeated and done for all 73 measured rain events. the measured rainfall data against the attenuation of the link is plotted. the predicted rain attenuation using rain rate obtained from measurement and k and � values proposed by carbonneau, japan’s model, marshal-palmer and joss are estimated and compared with measured attenuation. the predicted and measured values are presented in fig. 5. it is obvious from the result in fig. 5, the prediction models which are proposed by marshal-palmer and joss based on rain drop size distribution underestimate measured attenuation at all rain intensities. on the other hand, model proposed by carbonneau, overestimate the measured attenuation for entire rain intensities. the differences are more than 10 db/km for higher rain rates; since the carbonneau model just considered very low rain intensity to develop k and �. hence these values seriously mislead the prediction for tropical region where intensity of rain is much higher than 10 mm/hr, most of the raining event. 0 50 100 150 200 250 300 0.001 0.01 0.1 1 r a in i n te n si ty ( m m / h r) % of exceeded 0 2 4 6 8 10 12 14 16 18 0.001 0.01 0.1 1 f s o li n k a tt e n u a ti o n ( d b ) % of exceeded iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering suriza et al. 50 fig. 5: comparison of measured rain attenuation and that predicted by prediction models using measured rain intensity. model proposed by japan overestimate the measured data even higher than that proposed by carbonneau model. the prediction goes more than 20 db/km for higher rain intensity which shows severe error. this model also estimate k and α values based on rain intensity much lower than 100 mm/hr. attenuation on free space optics occurred mainly due to scattering which seems not to increase exponentially with intensity of rain. that’s why the regression coefficients proposed based on very low rain intensity are unable to predict attenuation on fso in tropical region’s high intensity rainfall. 5. conclusion free space optics is severely affected by rain and it is a challenge to design a reliable fso link in tropical region. in order to investigate the effects of rain on fso, a link was installed in the faculty of engineering, international islamic university malaysia’s kuala lumpur campus. real time rain intensity and corresponding attenuation on fso link was measured concurrently for one year period. measured result was with that predicted by models proposed by itu-r based on france and japan’s measurement. both models overestimate the measurement severely. on the other hand, models proposed by other researchers based on drop size distribution of rain underestimate the measurement. hence it is recommended to study rain effects more details for designing fso links in tropical climate. acknowlegment the authors gratefully acknowledge ministry of science, technology and innovation (mosti), meteorological department of malaysia and mimos berhad for the support of the project. references [1] ramasarma, v. (2002). free space optics: a viable last-mile solution. bechtel telecommunications technical journal, 22-30. [2] bloom, s., korevaar, e., et al. (2003). understanding the performance of free space optics. journal of optical networking, 2( 6), 178. 0 10 20 30 40 50 60 0 50 100 150 200 250 300 350 experimental carbonneau japan msrshal-palmer joss iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering suriza et al. 51 [3] kim, i. i., mcarthur, b., et al. (2001). comparison of laser beam propagation at 785 nm and 1550 nm in fog and haze for optical wireless communications. optical wireless communications iii, proc. spie, 4214, 26-37. [4] md rafiqul, i. (2000). rain attenuation prediction for terrestrial microwave links based on rain rate and rain attenuation measurements in a tropical region. ph.d. thesis, university of technology malaysia, johor bahru. [5] ishii, s., sayama, s., et al. (2010). rain attenuation at terahertz. wireless engineering and technology, 1, 92-95. [6] marshall, j. s., & palmer, w. m. (1948). the distribution of raindrops with size. journal of meteorology, 5(4), 165-166. [7] zhang, w., & moayeri, n. (1999). power-law parameters of rain specific attenuation. retrieved 09 march, 2011. [8] emiliani, l. d., luini, l., et al. (2008). extension of itu-r method for conversion of rain rate statistics from various integration times to one minute. electronics letters, 44(8), 557558. [9] itu-r p.838, r. (1999). specific attenuation model for rain for use in prediction methods. [10] ojo, j. s., ajewole, m. o., et al. (2008). rain rate and rain attenuation prediction for satellite communication in ku and ka bands over nigeria. progress in electromagnetics research b, 5, 207-223. [11] crane, r. k., & robinson, p. c. (1997). acts propagation experiment: rain-rate distribution observations and prediction model comparisons. proceedings of the ieee, 85(6), 946-958. [12] zhou, x. x., lee, y. h., et al. (2009). conversion model of one-minute rainfall rate distribution in singapore. paper presented at the ieee antennas and propagation society international symposium, 2009 (apsursi '09). [13] itu-r p.1814, r. (2007). prediction methods required for the design of terrestrial free-space optical links. [14] carbonneau, t. h., & wisley, d. r. (1997). opportunities and challenges for optical wireless: the competitive advantage of free space telecommunications link in today's crowded marketplace. wireless technologies and systems: millimeter wave and optical, proc. spie, 3232, 119-128. [15] awang, m. a., & din, j. (2004, 5-6 oct. 2004). comparison of the rain drop size distribution model in tropical region. paper presented at the proceedings of rf and microwave conference, 2004 (rfm 2004). [16] nexsens technology. ichart environmental software. http://nexsens.com/featured/nexsens ichartf.htm [17] lightpointe. flightstrata. http://www.lightpointe.com/products/fs_155.cfm. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 ibrahim https://doi.org/10.31436/iiumej.v23i1.2114 evaluation of surface roughness and material removal rate in electrical discharge machining of al-alloy with 10% sic abbas fadhil ibrahim production engineering and metallurgy department, university of technology, baghdad, iraq * corresponding author: 70011@uotechnology.edu.iq (received: 18th june 2021; accepted: 14th september 2021; published on-line: 4thjanuary 2022) abstract: aluminum-based metallic matrix compounds are widely used in industrial and aircraft manufacturing due to their advanced characteristics, such as toughness and high strength resistance to weight ratio, etc. silicon carbide is an important industrial ceramic and it is the fourth hardest ceramic after diamond, boron nitride, and boron carbide. owing to its low fracture toughness, it is difficult to machine silicon carbide using traditional machining processes. electrical discharge machine can machine such materials irrespective of their hardness. aluminum alloy 6061 and 10% sic based-metal matrix composite were used as a workpiece that was produced by stir casting. in the experimental investigation, pulse current pc (10, 20, and 30 a), pulse on (pon) duration (100, 150, and 200 μsec), and pulse off (poff) duration (6, 12, and 24 μsec) were treated as the input variables. the output responses were surface roughness (sr) and material removal rate (mrr). the best value for surface roughness (ra) reached (1.032 µm) at pc (10 a), pon duration (100 μsec) and poff (15 μsec). also, the best result for the productivity of the process (mrr) reached (69.49 × 10-3 g/min) at pc (30 a) pon, (200 μsec) and (6 μsec) poff. therefore, the experimental outcomes were optimized for surface roughnes and material removal rate by adding 10% sic to aluminum alloy 6061. abstrak: sebatian matrik logam berasaskan aluminium telah digunakan secara meluas dalam industri pembuatan dan pesawat kerana ciri-cirinya yang canggih, seperti ketahanan dan daya rintangan yang tinggi kepada nisbah berat, dan lain-lain. silikon karbida adalah seramik industri yang penting dan ia merupakan seramik keempat terkuat setelah berlian, boron nitrida dan boron karbida. disebabkan ketahanan frakturnya yang rendah, adalah sukar bagi menghasilkan mesin silikon karbida menggunakan proses pemesinan tradisional. mesin pelepasan elektrik mampu menghasilkan mesin menggunakan bahan tersebut tanpa mengira kekerasan. aloi aluminium 6061 dan komposit matrik logam berasaskan sic 10% telah digunakan sebagai bahan kerja yang terhasil melalui tuangan kacauan. melalui penyelidikan eksperimen, detik arus pc (10, 20, dan 30 a), detik hadir (pon) berdurasi (100, 150, dan 200 μsec), dan detik henti (poff) berdurasi (6, 12, dan 24 μsec) dirawat sebagai pemboleh ubah input. respon pengeluaran adalah kekasaran permukaan (sr) dan kadar penyingkiran bahan (mrr). nilai terbaik bagi kekasaran permukaan (ra) telah mencapai (1.032 µm) pada pc (10 a), berdurasi pon (100 μsec) dan poff (15 μsec). tambahan, hasil terbaik bagi proses produktiviti (mrr) mencapai (69.49 × 10-3 g/min) pada pc (30 a) pon, (200 μsec) dan (6 μsec) poff. oleh itu, hasil eksperimen dioptimumkan bagi permukaan kasar dan kadar penyingkiran bahan dengan tambahan 10% sic ke aloi aluminium 6061. keywords: electrical discharge machining; roughness; material removal; al-alloy; sic 349 iium engineering journal, vol. 23, no. 1, 2022 ibrahim https://doi.org/10.31436/iiumej.v23i1.2114 1. introduction electrostatic discharge treatment is one of the most used unconventional manufacturing processes. thermoelectric power is used to remove the unwanted materials from the workpiece by a sequence of electrical sparks between on the workpiece and the electrode. electrical discharge happens between the workpiece and the electrode in a small gap that separates the undesirable metal from the original workpiece during melting and evaporation. the work piece and electrode must have electrical conductivity to create the spark [1]. the electrostatic discharge generates an impulse pressure by blasting an insulator to expel the molten particles. thus, the amount of material removed can be effectively controlled to produce a complex and precise machine element [2]. the removed material is incompletely discarded, and the remaining material collects to form drainage pits. as a result, the machined surface has small pores and cracks caused by a high temperature gradient which reduces the quality of the surface finish. there have been several published studies dealing with the surface finishing of edm materials. it was observed that several machining parameters affect the surface roughness, and it was difficult to determine the best surface quality that would result from any possible combination of parameters, such as the wear of the workpiece and the wear occurring at the corners of gr and cu materials observed after the average values of pulse current (pc) and pulse on time (pon). therefore, the generated sparks were concentrated in the middle of the machined area causing arcing and short circuit. investigations indicated that the edm output parameters increased with increasing pulse current, and the best curing rates were achieved using copper and aluminum electrodes [1, 3]. the advantage of edm compared to other traditional methods is the ability to penetrate very hard metals, the ability to machine complex shapes, and the reduction of distortion on fine features [2, 4, 5]. this technology is widely used to manufacture elements for critical parts, like the copier parts, gearboxes, etc. these components operate under the parameters of temperature and dynamic forces, thus high-strength materials are used, such as thermally hardened steel alloys, titanium-aluminum-tungsten-based alloys and others. metal matrix compounds (mmcs) are compound materials, such as alloys based on al, mg, or ti and stiffeners, like al2o3 molecules, sic, tib2, and tic [6,7]. mmcs provide support to the structure and distribute the load, while the particles or fiber stiffeners provide beneficial thermal performance, physical, or mechanical properties. they have high specific properties, such as light weight, high strength, high toughness, high durability, and excellent heat resistance. the evolution of mmcs leads to their use in the nuclear, aerospace, and automotive industries as an alternative to conventional materials. mmcs are created by different manufacturing processes, such as friction stir welding process, metal injection molding, pressure casting technology, mechanical alloying, and continuous binder powder coating [7,8]. conventional machines for mmcs offer relatively high engineering precision; therefore, due to the mechanical nature of the process, they generate excessive heat and that causes plastic deformation which in turn reduces the quality of the workpiece surface layer [9-11]. edm is a contactless process, and the processing powers are humble, therefore it is used for thin, fragile, and aspect ratio machines [12]. studies showed a selection of process variables, and fixing the appropriate range of parameters to machine every product decides the quality of the product. haris et al. [13] analyzed the effect of nozzle size and inlet pressure supplied on the flushing efficiency to avoid improper flushing and enhance the material removal rate in the edm process. rino et al. [14] investigated the effect of different types of electrode, including cu (ordinary electrode) and cu-ni (newly proposed graphitization catalyst electrode), on 350 iium engineering journal, vol. 23, no. 1, 2022 ibrahim https://doi.org/10.31436/iiumej.v23i1.2114 the electrical discharge machining performance, material removal rate and surface roughness. the copper-nickel electrode recorded a 35% better material removal rate than the copper electrode, though with a higher short-circuiting rate. copper-nickel also provided the lowest surface roughness value with 10% better than the best surface roughness produced by the copper electrode [14]. abdul-azeez et al. [15] studied the optimization of parameters for siliconized silicon carbide (sisic) on the output quality responses: mrr, tool wear rate (twr) and sr. face centered central composite (fccc) design was used in the experiment planning. pc and pon were found to be significant on all the responses. in addition to pc and pon, sv was also significant on mrr. pc-pon interaction is significant on mrr and twr, while pon-sv interaction is significant on ra. [15]. sulaiman et al. [16] investigated the surface characteristics of a functionally graded titanium (ti-6al-4v) alloy during (edm). the results showed an average micro-layer thickness of 24.47 μm with a current of 7.5 a when machined at -1600°c. also, an increase in the crack formation with the highest current of 7.5 a for the surfaces machined at subzero temperature was recorded for both the workpieces and electrode materials [16]. ahsan et al. [17] studied the effect of nickel powder mixed dielectric fluid on the electrical discharge machining performance of mild steel. peak current, tool/electrode diameter and concentration of powder were the process parameters. the process performance was measured in terms of material removal rate (mrr), tool wear rate (twr), and surface roughness (sr). according to them, increasing the current had a negative effect on both the twr and surface roughness in contrast, and the current increase had a positive effect on the mrr [17]. this study sought to evaluate the effect of the electrostatic discharge mechanism of an aluminum alloy with silicon carbide stiffeners. peak current, pulse on time, and pulse off time were chosen as process parameters, while the material removal rate and the surface roughness were chosen as process performance indicators. 2. experimental work the work material was made of aluminum alloy matrix (aa6061) and 10% silicon carbide, which was produced by stirring casting method. silicon carbide reinforced mmcs have high hardness, low density, high strength (also at high temperature), and high corrosion resistance. thus, aluminum alloy with silicon carbide parts are used in highly demanding applications (such as pistons and pressure arms). the composite porosity was about 5%, and the average grain size was 50 μm. the experiment was designed and analyzed using the screening method in minitab 19 software. also, three variables of factors, including the pulse current (pc), pulse on duration (pon), and the pulse off duration (poff) were selected for the investigation. the experimental works were conducted on a cm 323c edm machine, seen in fig. 1, with kerosene as the dielectric solution. a copper electrode was used as the tool material in the experimental work with (ϕ40 × 100 mm), seen in fig. 2, with its chemical composition shown in table 1. according to the design of experiments (doe) with screening method, the research consisted of thirteen tests. the machining conditions for experimental work are listed in table 2. the value of mrr was calculated from the weighting method. the workpiece sample was weighed before machining (wp1) and after machining (wp2), and the mrr was calculated from the following formula [18]: 𝑀𝑅𝑅 = 𝑊𝑝1 − 𝑊𝑝2 𝑇 (1) 351 iium engineering journal, vol. 23, no. 1, 2022 ibrahim https://doi.org/10.31436/iiumej.v23i1.2114 where, t represents the time of machining. the value of sr of the samples was measured by using a portable device (pocket surf), and the test was carried out in the laboratories of the university of technology, baghdad. fig. 1: edm (cm323c type). fig. 2: copper electrode tool. table 1: chemical composition of copper electrode material zn% pb% sn% au% si% bi% sb% te% cu% weight% 0.0029 <0.005 0.003 0.0004 0.010 0.003 0.033 0.015 rem table 2: machining conditions for experimental work 3. results and disscusion depending upon the experimental results given in table 3, the effect of the process parameters on the two responses that are (ra) and (mrr) using copper electrodes was analyzed by analysis of variance (anova) from screening approach with the help of factors of code consideration symbol grade 1 2 3 current (a) pc 10 20 30 pulse on duration (µs) pon 100 150 200 pulse off duration (µs) poff 6 12 24 electrode holder tank of dielectric edm table control unit 352 iium engineering journal, vol. 23, no. 1, 2022 ibrahim https://doi.org/10.31436/iiumej.v23i1.2114 minitab 19 software. according to the theory of experiment, the research was performed and a response surface full quadratic polynomial was selected. table 3: design of experiments and response result run order pc (a) pon (μsec) poff (μsec) ra (µm) mrr× 10-3 (g/min) 1 30 100 6 1.543 67.45 2 10 100 15 1.032 58.21 3 10 150 6 1.153 60.93 4 20 150 15 1.384 63.71 5 10 200 6 1.611 59.52 6 30 200 6 1.744 69.49 7 20 100 6 1.226 65.36 8 10 200 24 1.372 63.12 9 30 150 24 1.421 64.56 10 20 200 24 1.463 64.62 11 30 200 15 1.711 68.28 12 30 100 24 1.274 62.78 13 10 100 24 1.086 58.41 3.1 analysis of variance (anova) anova has been used to check the null hypothesis of the predicted data at a point of (95) per cent confidence and to test the defined dominant conditions and the efficacy of the second-order model for increasing the machining process reaction. fishers statistical test (f-test) tested the importance of the function, its strength. if p-value ≤ 0.05, the factor was concluded to have a statistically significant impact. tables 4 and 5 indicate the information of analysis of variance for the ra and mrr of edm process. the mathematical relation between the variables and the surface roughness and material removal rate was obtained from the non-linear regression models that are given in eqs. 2 and 3, respectively. table 4: analysis of variance (anova) for ra exporter degree of adj. sum. adj mean f-value p-value freedom square square model 4 0.57094 0.14273 21.45 0.000 linear 3 0.55352 0.184508 27.73 0.000 a 1 0.20707 0.207072 31.12 0.001 b 1 0.30276 0.302760 45.50 0.000 c 1 0.04369 0.043692 6.57 0.034 square 1 0.01741 0.017413 2.62 0.144 b*b 1 0.01741 0.017413 2.62 0.144 error 8 0.05323 0.006654 / / total 12 0.62417 / / / 3.2 predicted model of surface roughness the results for (ra) response were assessed, which were given in the analysis of variance in table 4 using the three levels of factors for the backward convert model for the minimum p-value. the f-value model (21.45) indicated that the model was significant. 353 iium engineering journal, vol. 23, no. 1, 2022 ibrahim https://doi.org/10.31436/iiumej.v23i1.2114 values of "prob> f" less than 0.05 imply the model terms are significant. in this case, a, b, c were significant model terms. the predicted final empirical equation is: ra = 1.401 + 0.01439 (pc) 0.00694 (pon) 0.00734 (poff) + 0.000035(pon)2 (2) the 3d graphs presented in fig. 3, 4, and 5 illustrate the effect of edm factors on the ra. figure 3 manifested that when using pulse current (10 a) and pulse over duration (100 μs), the lower sr was reduced when using copper electrodes and kerosene insulator to 1.032 μm, and the lower surface roughness occurred due to the interaction effects of low peak pc and low pon. the intensity of spark energy increased with pon, which resulted in recast layers and the formation of large craters on the machined surface tending to increase the surface roughness. kerosene dielectric produced a better surface finish than that of the distilled water dielectric, possibly due to the slow oxidation rate and the fine surface morphology. figure 4 depicts the 3d graphs of the ra using pulse current (10 a) and pulse duration (6 μs), and the lower ra obtained when using the values of 1.032 μm. figure 5 reveals the 3d graphs of ra using pulse over duration (100) and pulse duration (24 μs), and the lower ra obtained reached the value (1.086 μm). this is due to the long pulse duration that furnished good cooling effect and enough time for flushing away the molten material and debris from the gap between the workpiece and electrode. fig. 3: 3d plot for relationship between sr, pc, and pon. fig. 4: 3d plot for relationship between sr, poff, and pc. fig. 5: 3d plot for relationship between sr, poff, and pon. 3.3 predicted model of mrr in order to assess the outcomes of the material removal rate response in table 5 using the three levels of parameters, the f-value of 40.66 indicated that the pattern is significant. 354 iium engineering journal, vol. 23, no. 1, 2022 ibrahim https://doi.org/10.31436/iiumej.v23i1.2114 in this case, a, b, c, ac, bc were important model terms. the expected final empirical equation is: mrr = 56.32 + 0.5035 (pc) 0.0085 (pon) 0.204 (poff) 0.01199 (pc *poff) + 0.002276 (pon*poff) (3) in eqs. 2 and 3, it was also apparent that the coefficient of current amplitude was the most significant machining parameter and influence on the predicted (ra) and (mrr), respectively. higher pulse current values created melted craters on the surface of the workpiece, visible to the naked eye. table 5: analysis of variance (anova) for mrr exporter df adj ss adj ms f-value. p -value model 5 151.914 30.383 40.66 0.000 linear 3 129.792 43.264 57.89 0.000 a 1 104.782 104.782 140.21 0.000 b 1 16.435 16.435 21.99 0.002 c 1 8.575 8.575 11.47 0.012 2-way interactions 1 22.122 11.061 14.80 0.003 a*c 1 8.732 8.732 11.68 0.011 b*c 1 7.864 7.864 10.52 0.014 error 7 5.231 0.006654 / / total 12 157.145 0.747 / / the three-dimensional diagrams presented in fig. 6, 7, and 8 were used to evaluate and interpret the experimental group model. these numbers demonstrated the influence of edm factors on the mrr. figure 6 displays that the value of material removal rate increases with increasing pc (up to 30 a) and pon (up to 200 μsec) reaching the value of 69.49×10-3 g/min, due to higher pc, which produces maximum spark discharge power combined with higher thrust in the spark gap, which tends to heat the workpiece and cause melting and vaporization resulting in higher material removal rate. an increase in pon proportionally increases the spark or the amount of heat energy to transfer heat to the workpiece, which causes the melting of material resulting in higher mrr. figure 7 shows the 3d graphs of mrr using current (30 a) and pulse duration (6 μsec), and the maximum material removal rate obtained when using the value of 69.49 × 10-3 g/min, due the interaction between maximum current and lower pulse duration. figure 8 clarifies the 3d graphs for mrr using the pon (200) and poff (6 μsec), and the maximum material removal rate obtained when using the kerosene dielectric reached the value of 69.49×10-3 g/min. mrr increased after the increasing of pulse on time value due the increased energy density at the points of the electrical discharge instantaneously after the time of the discharge, and as a result, the plasma channel expanded continuously with the pon. the amount of heat energy generated was large and increased the dissolving and abrasive treatment to remove the successive layers from the surface of the workpiece, and this means that the productivity increased with the current and the pulse on time. 355 iium engineering journal, vol. 23, no. 1, 2022 ibrahim https://doi.org/10.31436/iiumej.v23i1.2114 fig. 6: 3d plot for relationship between mrr, pc, and pon. fig. 7: 3d plot for relationship between mrr, pc, and poff. fig. 8: 3d plot for relationship between mrr, pon, and poff. 4. conclusions the machining characteristics of al-alloy with 10% sic mmcs in electrical discharge machining (edm) were investigated with the help of the screening design method. it was found that the pulse current has a more significant influence on the sr and mrr than the other inputs, namely pon duration and poff duration. the values of the coefficients of correlation and the analysis of variance indicated a good statistical analysis for the non-linear regression models of the responses. the best value for the surface roughness (ra) reached (1.032 µm) at pulse current (10 a), pulse on duration (100 μsec) and pulse off (15 μsec). the best result for the productivity of the process (mrr) reached (69.49×10-3 g/min) at pc (30 a), pon (200 μsec) and poff (6 μsec). the desirability process elucidates that the best predicting response values were roughly the same as those obtained through the experiments as mentioned in the two items above, and this confirmed the results of the present work. references [1] bains p, sidhu s, payal h. (2016) fabrication and machining of metal matrix composites, ikg punjab technical university, 31: 553-573. [2] pramanik a, basak k, littlefair g, debnath s, prakash c, meinam s, deepak m, ramesh s. (2020),methods and variables in electrical discharge machining of titanium alloy – a review, heliyon, 6: 1-15. [3] manjunath p, sandeep k, jagadish danil y, khaled g. (2021) experimental analysis and optimization of edm parameters on hchcr steel in context with different electrodes and 356 iium engineering journal, vol. 23, no. 1, 2022 ibrahim https://doi.org/10.31436/iiumej.v23i1.2114 dielectric fluids using hybrid taguchi-based pca-utility and critic-utility approaches, metals, 11(419): 1-23. [4] smolentsev v. (1983) edm and electrochemical methods of processing materials, moscow: higher school. [5] yeliseyev y, savushkin b. (2010) edm of aerospace products ,moscow: moscow state technical university. [6] liao z., abdelhafeez a., li h., yang y., diaza o. g., and axinte d. (2019) state-of-theart of surface integrity in machining of metal matrix composites, international journal of machine tool manufacturing, 143:63-91. [7] kandpal b, kumar j, and singh h. (2014) production technologies of metal matrix composite: a review, international journal of research in mechanical engineering & technology, 4(2): 27-32. [8] manikandana k, ranjithkumarb p, kumarb d, palanikumarc k. (2020) machinability evaluation and comparison of incoloy 825, inconel 603 xl, monel k400 and inconel 600 super alloys in wire electrical discharge machining, journal of material research and technology, 9(6): 12260-12272. [9] uthayakumar m, kumaran t, khan a, skoczypiec s, bizon w. (2018) microdrilling of aa (6351)-sic-b4c composite using hybrid micro-ecdm process, journal of testing and evaluation, 48(4): 3073-3086. https://doi.org/10.1520/jte20180216. [10] gore s, patil g. (2018) wire electro discharge machining of metal matrix composites: a review. procedia manufacturing, 20:41-52. [11] skoczypiec s, machno m, bizon w. (2015) the capabilities of electrodischarge microdrilling of high aspect ratio holes in ceramic materials, management and production engineering review, 6(30):61-69. [12] sivasankar s, jeyapau r. (2012) application of grey entropy and regression analysis for modelling and prediction on tool materials performance during edm of hot pressed zrb2 at different duty cycles, procedia engineering, 38:3977-3991. [13] haris r, rasidi i, kee m, al emran i, zulafif r, worapong s. (2020) design and investigate of flushing system for electrical discharge machining (edm) application, international journal of integrated engineering, 12(2):218-225. [14] rino a, ahmad m, rahim m, rha h, sabri a, aziz n, ahmad t, al emran i, rasidi i. (2020) the influence of graphitization catalyst electrode in electrical discharge machining of polycrystalline diamond-finishing condition. international journal of integrated engineering, 12(2):211-217. [15] abdulazeez a, jafri r, ahmad a, hamidon m. (2017) optimization of electrical discharge machining parameters of sisic through response surface methodology. jurnal teknologi, 799(1):119-129. [16] sulaiman a, ahsan k, mohamed k. (2018) analysis of microlayer defects of a functionally graded titanium alloy by electrical discharge machining, engineering and applied science research, 45(1):17-22. [17] ahsan k, muataz f, mohiuddn a, nurfathhah a, mohd d. (2018) performance of electrical discharge machining (edm) with nickel added dielectric fluid. iium engineering journal, 19(1):215-222. [18] prasanna j, rajamanickam s, amit k, karthick g, sathya v. (2017) mrr and twr evaluation on electrical discharge machining of ti-6al-4v using tungsten: copper composite electrode, frontiers in automobile and mechanical engineering, iop conference series: materials science and engineering, pp. 197–208. 357 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 alang rashid et al. receiver operating characteristics measure for the recognition of stuttering dysfluencies using line spectral frequencies nahrul khair bin alang md rashid, sabur ajibola alim*, nik nur wahidah nik hashim and wahju sediono department of mechatronics engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. * corresponding author: moaj1st@yahoo.com (received: 23rd aug. 2015; accepted: 27th sep. 2016; published on-line: 30th may 2017) abstract: stuttering is a motor-speech disorder that has features in common with other motor control disorders such as dystonia, parkinson’s disease, and tourette’s syndrome. stuttering results from complex interactions between factors such as motor, language, emotions, and genetic systems. this study used line spectral frequency (lsf) for feature extraction, while using three classifiers for the identification purpose, multilayer perceptron (mlp), recurrent neural network (rnn) and radial basis function (rbf). the uclass (university college london archive of stuttered speech) release 1 was used as the database in this research. these recordings were from people of ages ranging from 12y11m to 19y5m, who were referred to clinics in london for assessment of their stuttering. the performance metrics used for interpreting the results are sensitivity, accuracy, precision, and misclassification rate. only m1 and m2 had below 100% sensitivity for rbf. the sensitivity of m1 was found to be between 40% & 60%, therefore categorized as moderate, while that of m2 falls between 60% & 80%, classed as substantial. overall, rbf outperforms the two other classifiers, mlp and rnn for all the performance metrics considered. abstrak: gagap adalah gangguan motor pertuturan, mempunyai ciri-ciri yang sama dengan lain-lain gangguan kawalan motor seperti dystonia, penyakit parkinson dan sindrom tourette. keputusan kegagapan daripada interaksi kompleks antara faktor-faktor seperti motor, bahasa, emosi dan genetik. kajian ini menggunakan frekuensi line spektral (lsf) untuk pengekstrakan ciri, semasa menggunakan tiga penjodoh untuk tujuan mengenal pasti, multilayer perceptron (mlp), rangkaian neural berulang (rnn) dan radial asas fungsi (rbf). the uclass (university college london arkib stuttered ucapan) melepaskan 1 digunakan sebagai pangkalan data dalam kajian ini. ini rakaman adalah dari orang-orang peringkat umur 12y11m untuk 19y5m, yang dirujuk kepada klinik di london untuk penilaian kegagapan mereka. metrik prestasi yang digunakan untuk mentafsir keputusan yang sensitif, ketepatan, ketepatan dan kadar misclassification. hanya m1 dan m2 mempunyai di bawah 100% kepekaan untuk rbf. kepekaan m1 didapati antara 40% & 60%, oleh itu dikategorikan sebagai sederhana, manakala m2 jatuh antara 60% & 80%, dikelaskan sebagai besar. secara keseluruhan, rbf melebihi performa dua penjodoh lain, mlp dan rnn untuk semua metrik prestasi dipertimbangkan. keywords: stuttering; dysfluencies; line spectral frequency; radial basis function 193 iium engineering journal, vol. 18, no. 1, 2017 alang rashid et al. 1. introduction stuttering is a neurological trait that may involve specific abnormalities of speech motor control in the human brain. stutterers experience reduced blood flow and decreased or increased electrical activity in areas of the brain associated with speech production. the cause of this malfunction is linked to the brain [1, 2]. stuttering is a severe complication focused on by speech pathologists [3, 4]. stuttering is primarily viewed as a motor-speech disorder, sharing features with other kinds of motor control disorders such as dystonia, parkinson’s disease, and tourette’s syndrome. however, there is evidence that linguistic factors also play a role in stuttering [5]. it was found that many complex interactions between the language and motor systems, have led researchers to believe that there is no single cause of stuttering. stuttering is the result of a complex interaction among numerous factors such as motor, language, emotional, and genetic systems. about 80% of stuttering occurrences automatically disappear. however, the remaining 20%, which is about 1% of the entire world’s population, have difficulties returning to normal speech [6]. stuttering has been found to more prevalent in males than females (by a ratio of 4:1) [1, 3, 4, 7]. stutterers and non-stutterers alike have speech disfluencies that can be gaffes or disturbances in the flow of words a speaker plans to say, but disfluencies are more observable in stutterers’ speech [8]. stuttered speech is rich in dysfluencies, usually repetitions. classical approaches to the analysis of dysfluencies are done over very short intervals, which is sufficient for recognition of simple repetitions of phonemes [9]. the usual practice in the stuttered speech recognition or dysfluency recognition reported in previous research findings was in form of identification accuracy. it is, however, essential to use metrics such as sensitivity, accuracy, precision and misclassification rate, which better analyze how a stuttered speech recognition system would behave in real life. these performance metrics form a part of the receiver operating characteristics (roc). this experiment serves as a furtherance of the previous experiments, gives further confidence in stuttering recognition research, and serves as a precursor to research on stuttered speech correction via reconstruction. 2. feature extraction line spectral frequency (lsf) is an alternative to the direct form predictor coefficients or the lattice form reflection coefficients for representing filter response. the direct form coefficient representation of the linear prediction coefficient (lpc) filters is not perfect for efficient quantization. nonlinear functions of the reflection coefficients are often used as transmission parameters in place of direct form coefficients. these parameters are preferable because they have a relatively low spectral sensitivity [10]. it has been found that the line spectral frequency (lsf) representation of the predictor is particularly well suited for quantization and interpolation. theoretically, this can be motivated by the fact that the sensitivity matrix relating the lsf-domain squared quantization error to the perceptually relevant log spectrum is diagonal [11]. the linear prediction polynomial 𝐴(𝑧) = 1 − ∑ 𝑎𝑘 𝑧 −𝑘𝑝 𝑘=1 can be expressed as 𝐴(𝑧) = 0.5[𝑃(𝑧) + 𝑄(𝑧)] [12]. where 𝑃(𝑧) = 𝐴(𝑧) + 𝑧−(𝑝+1) 𝐴(𝑧−1), 𝑄(𝑧) = 𝐴(𝑧) − 𝑧−(𝑝+1) 𝐴(𝑧−1), 𝑃(𝑧) is the vocal tract with the glottis closed, 𝑄(𝑧) is the vocal tract with the glottis opened, 𝐴(𝑧) is the lpc analysis filter of order p, and 𝑎𝑘 is the lpc coefficient. 194 iium engineering journal, vol. 18, no. 1, 2017 alang rashid et al. the roots of p and q lie on the unit circle in the complex plane. the roots alternate as they travel through the circle. the coefficients of p and q are real. as such, the roots occur in conjugate pairs and are the same as the lpc order. 3. classification 3.1 multilayer perceptron (mlp) multilayer perceptron (mlp) is one of many different types of existing neural networks. it comprises a number of neurons connected together to form a network. this network generally has three layers: the input layer, one or more hidden layer(s), and the output layer, with each layer containing multiple neurons [13]. a neural network is able to classify the different aspects of the behaviors of a data structure, understand what is going on at every instant of time, analyze whether it is correct or faulty, forecast what to do next, and give the desired response [14, 15]. 3.2 recurrent neural network (rnn) feed-forward multi-layer neural networks are unable to deal with time-varying information like time-varying spectra of speech sound. one way to cope with this problem is to incorporate feedback into the networks to provide them with the capacity to learn incoming time-varying information [16]. recurrent neural networks (rnn) have a feedback connection that is used to pass the output of a neuron in a certain layer to the previous layer(s). rnn have the ability to process short-term spectral features but yet respond to long-term temporal events [17]. however, rnn have limited memory, and underperform once the memory is surpassed [15]. 3.3. radial basis functions (rbf) radial basis function (rbf) networks are derived from the theory of function approximation. they are two-layered feed-forward networks, containing a hidden layer and an output layer. the hidden layer nodes implement a set of radial basis activation functions, while the output layer nodes compute the linear summation functions just as in mlp. the network training is divided into two phases: first the weights from the input to hidden layer are determined, then the weights from the hidden to output layer. the learning or training is very fast and the networks are very good at interpolation [18]. the response of the functions rises or falls monotonically with distance from their center and are controlled by local measurements [19]. 4. methodology the uclass (university college london archive of stuttered speech) release 1 was used as the database for this research. these recordings were from people of ages 12y11m to 19y5m, who were referred to clinics in london for assessment of stuttering. the recordings were all monologs [20]. all the samples were quantized at a bit rate of 16 bits. table 1 shows the age and sex of the 8 samples used for this experiment. each sample was divided into smaller bits of 10 seconds and 11 sub-samples for each sample. the relevant features were extracted from each sample using line spectral frequency (lsf). a three layer multilayer perceptron, a three layer recurrent neural network and a two layer radial basis function were used for the classification and identification. the neural networks were trained with 88 inputs, 8 outputs, and 215 neurons in the hidden layer. all the layers were trained with a scaled conjugate gradient type of back propagation algorithm, while the tangent sigmoid activation function was used for the 195 iium engineering journal, vol. 18, no. 1, 2017 alang rashid et al. computation of the weight in each layer. the rbf, however, uses the radial basis activation function for the hidden layer and linear activation function for the output layer. table 1: features of samples used age sex 1 15y2m f f1 2 17y2m f f2 3 15y11m f f3 4 12y11m f f4 5 16y4m m m1 6 17y9m m m2 7 19y5m m m3 8 16y9m m m4 mean 16y5m the confusion matrices of the designed systems were plotted. from the confusion matrix plot, the sensitivity, accuracy, precision, and the misclassification rate were computed as performance measures that are the receiver operating characteristics (roc). sensitivity measures the number of correctly identified samples, accuracy measures the degree of closeness between the predicted and actual values, precision measures the ability of the algorithm to reproduce the same output for the same set of inputs, and the misclassification rate measures the percentage of incorrectly identified samples with respect to the total number of samples. 5. results and discussion the results of the performance measures were used to evaluate the three systems, lsf-mlp, lsf-rnn and lsf-rbf. the results are given as percentages for sensitivity, accuracy, precision, and misclassification rate. they help to give a better understanding of the systems for further evaluation, recommendations, and implementation. the three classifiers used have different strengths and weaknesses which would in turn affect their eventual performance. for the interpretation of the results, the tool used is the statistical classification by best in 1981. it was used to describe the significance of the probability of any experiment. it is listed as follows: 0 0.20 (0 20%) – negligible, 0.20 0.40 (20 40%) – low, 0.40 0.60 (40 60%) – moderate, 0.60 0.80 (60 80%) – substantial & 0.80 1.00 (80 100%) – high. 5.1 sensitivity table 2 shows the sensitivity of the systems to each of the samples used. only m1 and m2 had below 100% sensitivity for rbf. the sensitivity of m1 was found to be moderate, while that of m2 was substantial. all the other samples were high. similarly, in the case of rnn, the sensitivities of f1, f2, m2, m3 and m4 were high, f3 and f4 were moderate, while m1’s sensitivity was negligible. furthermore, for mlp, the sensitivities of f1, f2 and m4 were high. while f3, m2 and m3, all had substantial sensitivity. m1’s sensitivity was moderate. it was observed that for the three classifiers considered, the sensitivity of sample m1 was the lowest. 196 iium engineering journal, vol. 18, no. 1, 2017 alang rashid et al. table 2: sensitivity mlp (%) rnn (%) rbf (%) f1 90.91 90.91 100 f2 100 90.91 100 f3 72.73 54.55 100 f4 36.36 45.45 100 m1 27.27 9.09 45.45 m2 72.73 90.91 72.73 m3 72.73 100 100 m4 100 100 100 5.2 accuracy table 3 shows the accuracies of the three systems under consideration. the accuracies for all the samples and classifiers are high. in the case of rnn, all the accuracies were 100% except for m1 and m2 whose accuracies were below 90% and 89.77% in both cases. similarly, for mlp, only f2 and m4 had accuracies that are exactly 100%. the accuracies of f1 and m3 fall between 90 and 100%, while the accuracies of the other samples are between 80 and 90%. furthermore, for rnn, the accuracies of only m3 and m4 are exactly 100%, the accuracies of f1 and f2 are between 90 and 100%, while the accuracies of the other fall between 80 and 90%. it could also be observed that m1 had the lowest accuracies for both mlp and rbf, while f3 had the lowest accuracy for rnn. table 3: accuracy mlp (%) rnn (%) rbf (%) f1 98.86 98.86 100 f2 100 97.73 100 f3 85.23 85.23 100 f4 88.64 87.5 100 m1 84.09 87.5 89.77 m2 89.53 88.64 89.77 m3 96.6 100 100 m4 100 100 100 table 4: precision mlp (%) rnn (%) rbf (%) f1 100 100 100 f2 100 90.91 100 f3 44.44 42.86 100 f4 57.14 50 100 m1 33.33 50 62.5 m2 57.14 52.63 57.14 m3 100 100 100 m4 100 100 100 197 iium engineering journal, vol. 18, no. 1, 2017 alang rashid et al. 5.3 precision the precision values of the systems can be seen in table 4. rnn had high precision for f1, f2, m3 and m4, and is categorized as high. the precisions of f3, f4, m1 and m2 are moderate. furthermore, for rbf, the values of the precision for all the samples are high, except for m1 and m2. the precision of m1 is substantial, while that of m2 is moderate. in addition, in the case of mlp, the accuracies of f1, f2, m3 and m4 are high. while f3, f4 and m2 have moderate accuracies, and m1’s accuracy is low. 5.4 misclassification rate the misclassification rates of lsf-mlp, lsf-rnn and lsf-rbf can be seen in table 5. it can be seen that all the values obtained are below 20%, putting them in the class of negligible. rnn had misclassification rates of 0% each for m3 and m4, while f1 and f2 had below 10% misclassification rate and the others were between 10 and 20%. similarly, mlp, both f2 and m4 had misclassification rates of 0%, while f1 and m3 have between 0 and 10% misclassification rates and the remaining fall between 10 and 20% misclassification rate. finally for rbf, except for m1 and m2, all the other samples had misclassification rates of 0%, while m1 and m2 had misclassification rates of 9.57% and 10.23% respectively. table 5: misclassification rate mlp (%) rnn (%) rbf (%) f1 1.14 1.14 0 f2 0 2.27 0 f3 14.77 12.79 0 f4 11.36 12.5 0 m1 15.91 12.5 9.57 m2 10.47 11.36 10.23 m3 3.41 0 0 m4 0 0 0 5.5 discussion it is expected that for a recognition system to work perfectly, the sensitivity, accuracy and precision should be high, while the misclassification rate should be negligible for each sample. lsf-rbf has high sensitivity to six out of the eight samples having high sensitivity, accuracy and precision, with negligible misclassification rates. rbf has the ability to generate as many as needed hidden neurons in order to effectively map the input to the output. this gives it better performance as compared with the mlp and rnn, where you have to specify a certain number of hidden neurons. as compared with the research conducted by [21], where 39 stuttered speech samples were used, 2 females (5%) and 37 males (95%), from uclass which is the same database used for this research. table 6: benchmark feature extractor number of coefficients frame length (ms) classifier percentage recognition (%) mfcc 15 40 svm 96.14 wlpcc 10 50 svm 96.02 198 iium engineering journal, vol. 18, no. 1, 2017 alang rashid et al. they used five feature extractors; lpc, linear prediction cepstral coefficient (lpcc), weighted linear prediction cepstral coefficient (wlpcc), perceptual linear prediction (plp) & mel frequency cepstral coefficient (mfcc) and k-nearest neighbour (knn), linear discriminant analysis (lda) & support vector machines (svm) as classifiers. lpc, lpcc, wlpcc and plp are lpc based feature extractors as seen in table 6. for mfcc, the best recognition of 96.14% was obtained with svm classifier, 15 mfcc coefficients and 40 ms frame length. the lpc-based feature extractors, wlpcc-svm had the best recognition of 96.02% at the 10th lpc order and 50 ms frame length. however, the difference between the current research and the study in [21] is that while the authors evaluated the system using overall system performance. this research was evaluated using the performance and behavior of the system to each test sample. 5. conclusion the findings of this experiment have been presented above and it was observed that the lsf-rbf performed well in terms of sensitivity, precision, accuracy and misclassification rate for all the samples except m1 and m2. rbf, on the overall, outperforms the two other classifiers, mlp and rnn, for all the performance metrics considered. mlp and rnn performed well for f1, f2, m3 and m4, while giving an average performance for the other samples. it can therefore be said that the lsf-rbf system has a bright future in terms of possible use in real life applications. references [1] awad s. (1997) the application of digital speech processing to stuttering therapy. in ieee sensing, processing, networking, instrumentation and measurement technology conference (imtc), pp1361-1367. [2] chee ls, ai oc, yaacob s. (2009) overview of automatic stuttering recognition system. in proceedings of international conference on man-machine systems, pp1-6. [3] chee ls, ai oc, hariharan m, yaacob s. (2009) automatic detection of prolongations and repetitions using lpcc. in international conference for technical postgraduates (techpos), pp1-4. [4] chee ls, ai oc, hariaran m, yaacob s. (2009) mfcc based recognition of repetitions and prolongations in stuttered speech using k-nn and lda. in ieee student conference on research and development and development (scored), pp146-149. [5] watkins k, smith s, davis s, howell p. (2008) structural and functional abnormalities of the motor system in developmental stuttering. brain, 131(1):50-59. [6] zhang j, dong b, yan y. (2013) a computer-assist algorithm to detect repetitive stuttering automatically. in international conference on asian language processing (ialp), pp 249-252. [7] manjula g, kumar m. (2014) stuttered speech recognition for robotic control. int. j. eng. innov. technol., 3(12):174-177. [8] hollingshead k, heeman p. (2004) using a uniform-weight grammar to model disfluencies in stuttered read speech: a pilot study. cslu, ohsu. available at www.cslu.ogi.edu/publications/ps/hollingshead04.pdf. [accessed: 20-jun-2016]. [9] pálfy j, pospichal j. (2012) pattern search in dysfluent speech. in ieee international workshop on machine learning for signal processing (mlsp), pp 1-6. [10] kabal p, ramachandran r. (1986) the computation of line spectral frequencies using chebyshev polynomials. ieee trans. acoust. speech signal process., 34(6):1419-1426. [11] kleijn wb, bäckström t, alku p. (2003) on line spectral frequencies. ieee signal process. lett., 10(3):75-77. [12] robinson t. (1998) speech analysis. [online]. available at http://svrwww.eng.cam.ac.uk/~ajr/speechanalysis/speechanalysis.html. [accessed: 20-jun-2016]. 199 iium engineering journal, vol. 18, no. 1, 2017 alang rashid et al. [13] kumar r, ranjan r, singh sk, kala r, shukla a, and tiwari r. (2009) multilingual speaker recognition using neural network. in proceedings of the frontiers of research on speech and music, frsm, pp1-8. [14] al-alaoui ma, al-kanj l, azar j, yaacoub e. (2008) speech recognition using artificial neural networks and hidden markov models. ieee multidiscip. eng. educ. mag., 3(3):7786. [15] haykin ss. (2009) neural networks and learning machines. pearson education upper saddle river. [16] ahmad am, ismail s, samaon df. (2004) recurrent neural network with backpropagation through time for speech recognition. in ieee international symposium on communications and information technology (iscit), 1:98-102. [17] ismail s, ahmad a. (2004) recurrent neural network with backpropagation through time algorithm for arabic recognition. in proceedings of the 18th european simulation multiconference (esm), pp 13-16. [18] bullinaria j. (2004) introduction to neural networks. university of birmingham, uk. [19] singla p, subbarao k, junkins j. (2007) direction-dependent learning approach for radial basis function networks. ieee trans. neural networks, 18(1):203-222. [20] howell p, davis s, bartrip j. (2009) the university college london archive of stuttered speech (uclass). j. speech, lang. hear. res., 52(2):556-569. [21] chong yf, hariharan m, chee ls, yaacob s, adom h. (2013) comparison of speech parameterization techniques for the classification of speech disfluencies. turkish j. electr. eng. comput. sci., 21:1983-1994. 200 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 ali et al. effect of minimum quantity lubrication on surface roughness in tool-based micromilling mohammad yeakub ali*, wan norsyazila jailani, mohamed abd rahman, muhammad hasibul hasan and asfana banu department of manufacturing and materials engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. *corresponding author: mmyali@iium.edu.my (received: 26th feb. 2016; accepted: 22nd jan. 2017; published online: 30th may 2017) abstract: cutting fluid plays an important role in machining processes to achieve dimensional accuracy in reducing tool wear and improving tool lifespan. the conventional flood cooling method in machining processes is not cost effective and consumption of huge amounts of cutting fluid is neither healthy nor environmentally friendly. in micromachining, flood cooling is not recommended to avoid possible damage to the microstructures. therefore, one of the alternatives to overcome the environmental issues is to use a minimum quantity of lubrication (mql) in the machining process. mql is ecofriendly and has an economical advantage in manufacturing costs. however, there is an observed lack of study on mql in improving machined surface roughness in micromilling. a study of the effects of mql on surface roughness should be carried out because surface roughness is one of the important issues in micromachined parts such as microfluidic channels. this paper investigates and compares surface roughness with the presence of mql and dry cutting in the micromilling of aluminium alloy 1100 using a dt-110 milling machine. the relationship between the depth of cut, feed rate, and spindle speed on surface roughness is also analyzed. the three machining parameters identified as significant for surface roughness with dry cutting are: depth of cut, feed rate, and spindle speed. for surface roughness with mql, it is found that spindle speed did not greatly influence surface roughness. the presence of mql provides a better surface roughness by decreasing the friction between tool and work piece. abstrak: cecair pemotongan memainkan peranan yang penting dalam proses pemesinan untuk mencapai ketepatan dimensi dalam mengurangkan kehausan alat dan mempertingkatkan jangka hayat alat. kaedah konvensional penyejukan banjir dalam proses pemesinan tidak efektif kos dan penggunaan jumlah cecair pemotongan yang besar adalah tidak sihat dan tidak mesra alam. dalam pemesinan mikro, penyejukan banjir tidak digalakkan untuk mengelakkan kerosakan kepada struktur mikro. oleh itu, salah satu alternatif untuk mengatasi isu alam sekitar adalah dengan menggunakan kuantiti pelinciran (mql) yang minimum dalam proses pemesinan. mql adalah mesra alam dan adalah lebih baik dari segi menjimatkan kos pembuatan. walau bagaimanapun, tidak banyak pengajian mengenai bagaimana mql dapat memperbaiki kekasaran dipermukaan mesin dalam pengisaran mikro. satu kajian mengenai kesan mql pada kekasaran di permukaan perlu dijalankan kerana kekasaran di permukaan adalah salah satu isu penting pada bahagian mikromesin seperti saluran microfluidic. kertas ini mengkaji dan membandingkan kekasaran permukaan dengan kehadiran mql dan pemotongan kering dalam pengisaran mikro aloi aluminium 1100 menggunakan mesin pengilangan dt-110. hubungan antara ketebalan pemotongan, kadar suapan dan kelajuan gelendong pada kekasaran permukaan 147 iium engineering journal, vol. 18, no. 1, 2017 ali et al. juga dianalisis. tiga parameter pemesinan yang dikenal pasti sebagai penting untuk mempengaruhi kekasaran pada permukaan dengan pemotongan kering adalah: ketebalan pemotongan, kadar suapan dan kelajuan gelendong. untuk kekasaran pada permukaan dengan mql, didapati bahawa kelajuan gelendong tidak kuat mempengaruhi kekasaran pada permukaan. kehadiran mql memberi kekasaran pada permukaan yang lebih baik dengan mengurangkan geseran antara alat dan bahan kerja. keywords: micromilling; minimum quantity lubrication (mql); surface roughness; dry cutting; metal working fluids (mwfs); microlubrication 1. introduction the increasing demands for miniaturized products, especially in the biomedical, electronics, and aerospace industries, have obliged manufacturers to fabricate complex micro-parts with high accuracy. one of the fast developing microfabrication methods is micropatterning, which has a broad application in cell biology and biodegradable implantable medical devices. the micropatterning method can be conducted by several micromachining processes such as electron beam etching, soft lithography, laser micromachining, micromilling, etc. micromilling is one of the flexible mechanical micromachining processes that are capable for producing three dimensional (3d) miniaturized parts. it is characterized by the mechanical interaction between a sharp edged microtool and a workpiece material. micromilling is similar to macro milling except for the tool size it employs [1-6]. micromilling can be used to drill holes, slots, and pockets on workpieces. however, the micromilling process leads to high friction between the tool and the workpiece, resulting in high temperature and damaging the dimensional accuracy and surface quality of the product. hence, in order to reduce these problems, avoid chips, and reduce the adhesion at the toolworkpiece interface, cutting fluids are used in the machining operation [7, 8]. without the cutting fluid, the temperature of the tool and the workpiece would increase since the heat carried away from the cutting zone would be decreased [9]. during the machining operation, cutting fluids or metalworking fluids (mwfs) are widely used. the main objectives are to cool and lubricate the machined surface, flush away the unwanted chips, and restrain corrosion. better tool life and better work quality with effective chip management are some of the advantages of the mwfs [10, 11]. due to these advantages, mwfs are seeing increased utilization in the machining industry. since most of the mwfs are petroleum-based oils, they need to be treated and disposed of every year and the cost to treat the waste is extensive. in addition, inadvertent environmental contamination, digestive system problems, cancer, and adverse respiratory effects in workers may result in the ineffective disposal of mwfs and cutting fluid toxicity [10]. exposure to large amounts of cutting fluid, through either inhalation of skin contact, will cause adverse effects [12]. thus, in order to protect the environment and lower costs, it is crucial to decrease the usage of mwfs in machining as much as possible and keep pace with green manufacturing. the more frequently used approaches to green manufacturing relating to mwfs are dry cutting and minimum quantity lubrication (mql) [11, 13]. the mql method has been accepted as a prominent alternative in machining because of its environmentally-friendly characteristics. however, it requires special machining and cutting tool setups [11, 13, 14]. mql, known as the “micro-lubrication” and “near-dry machining” [15, 16], refers to a small amount of cutting fluid (2-100 ml/hr) in the form of aerosol being delivered to the tool-to-workpiece interface. mql may also refer to use of cutting fluids in tiny quantities [12, 15, 17]. the lubricant does not recirculate through the 148 iium engineering journal, vol. 18, no. 1, 2017 ali et al. lubrication system since it is almost all evaporated at the point of application. yet, it is vital to ensure an efficient extraction of aerosol from the machine. in mql, the lubrication is obtained via the lubricant and the cooling is achieved by pressurized air that reaches the cutting surface. mql also helps to reduce the induced thermal shock and increases the workpiece surface integrity when the tool is at high pressure [15, 17]. the objective of this paper is to investigate and compare surface roughness with the presence of mql and dry cutting in micromilling of aluminum alloy 1100. the comparison between surface roughness in micromilling in mql and the dry cutting processes is presented. 2. experiment and measurement the micromilling operation in this experiment is conducted using a miniature machine known as integrated multi-purpose machine tools (dt-110, microtools inc., singapore). this machine has three travel axes which are the x, y, and z-axes, for greater flexibility and more accuracy. this machine is an ultra-precision milling machine with submicron accuracies. after machining the workpiece with a two flute end mill, surface roughness is measured by the mitutoyo surface test sj-400. a bluebe fk-type mql system is used in this experiment to apply mql. bluebe fktype is equipped with a highly accurate variable pump. it transfers air and lubricant to the nozzles which can be adjusted separately. lubricant consumption is as little as 4-8 ml per hour per nozzle and the lubricant spouting from the nozzles is barely visible. fig. 1 shows the miniature machine tools (dt-110) and the bluebe fk-type that are used in this research. the cutting fluid from nozzle is directed to the micro end mill. the lubrication that is used with the mql system is an accu-lube lb-2000 (lb-1). the accu-lube lb-2000 is natural-based fluid lubrication for mql. it is manufactured using non-toxic, renewable raw materials and biodegradable ingredients. then, it is extracted and blended on the basis of vegetable oils. it does not contain hazardous chemicals. therefore, it is environmentally safe and biodegradable. it is safe to be used with all metals without any damage [15]. the tool material that is used in this experiment is tungsten carbide. the use of tungsten carbide as a tool material is important because it has high hardness and strength at high temperatures [18]. the selected work material is aluminum alloy 1100. the dimension of the aluminum is 80 mm x 20 mm x 5 mm. it is selected because of its excellent comprehensive performance which is thermally stable, high strength and a lightweight microcomponent. the slotting of the workpieces are done with an end mill of 0.5 mm in diameter with two different depths of cut, feed rates, and spindle speeds as shown in table 1. after the preliminary tests, the machining is performed under different cutting conditions, as shown in table 1. for this experiment, the cutting parameters of depth of cut, feed rate, and spindle speed are chosen to be variable. design expert software with two factorial levels is used to analyze the surface roughness. from this model, eight experiments need to be conducted with varied parameters and levels. for dry cutting, the same cutting conditions are also applied as shown in table 1. 149 iium engineering journal, vol. 18, no. 1, 2017 ali et al. table 1: cutting conditions machining parameters values level-i level-ii a: depth of cut (mm) 0.05 0.15 b: feed rate (mm/min) 1 2 c: spindle speed (rpm) 2000 2800 machining length (mm) 12 work material aluminum alloy 1100 table 2: experimental results of surface roughness with dry cutting and mql no. a: depth of cut (mm) b: feed rate (mm/min) c: spindle speed (rpm) surface roughness with dry cutting (µm) surface roughness with mql (µm) 1 0.05 1 2000 0.10 0.14 2 0.15 1 2000 0.15 0.15 3 0.05 2 2000 0.19 0.18 4 0.15 2 2000 0.20 0.19 5 0.05 1 2800 0.17 0.12 6 0.15 1 2800 0.18 0.19 7 0.05 2 2800 0.21 0.18 8 0.15 2 2800 0.27 0.21 fig. 1: (a) integrated multipurpose machine tools (dt-110) and (b) minimum quantity lubrication system (bluebe fk). fig. 2: selected machined microchannels on aluminum alloy 1100. a b 150 iium engineering journal, vol. 18, no. 1, 2017 ali et al. 3. results and discussion figure 2 shows the eight machined workpiece microchannels after the machining process. table 2 shows the experimental result of surface roughness with dry cutting and mql of the micromilling process. the range of surface roughness with dry cutting is from 0.10 to 0.27 µm and for surface roughness with mql is from 0.14 to 0.21 µm. anova, as shown in table 3, of surface roughness in dry cutting showed a “model f-value” of 19.98 which shows the model is significant. there is only a 0.72% chance that the “model f-value” could occur due to noise. values of "prob > f" less than 0.05 indicate that model terms of depth of cut (a), feed rate (b), and spindle speed (c) are significant model terms. based on the table 3, feed rate (b) is the most significant parameter that affected the surface roughness with dry cutting followed by spindle speed (c) and depth of cut (a). the “pred r-squared” of 0.7498 is in reasonable agreement with the “adj rsquared” of 0.8905. the adjusted r-squared is particularly useful when comparing models with different numbers of terms. however, this comparison is done in the background when model reduction has taken place. “adeq precision” measures the signal to noise ratio. a ratio greater than 4 is desirable. thus, in this analysis, the ratio of 12.875 indicates that the “adeq precision” is an adequate signal. so, the model can be used to navigate the design space. table 3: anova of surface roughness with dry cutting source sum of squares df mean square fvalue prob > f model 0.016 3 5.246 e-003 19.98 0.0072 a-depth of cut 2.112e-003 1 2.112 e-003 8.05 0.0470 b-feed rate 9.112e-003 1 9.112 e-003 34.71 0.0041 c-spindle speed 4.512e-003 1 4.512 e-003 17.19 0.0143 residual 1.050e-003 4 2.625 e-004 cor total 0.017 7 pred r-squared 0.7498 adj r-squared 0.8905 adeq precision 12.875 figure 3a shows the contour plot between depth of cut (a) and feed rate (b) on surface roughness for dry cutting. from the graph, when depth of cut is 0.05 mm and feed rate is 1.25 mm/min, the surface roughness is 0.15 µm and while depth of cut is 0.15 mm and feed rate is 1.75 mm/min, the surface roughness is 0.22 µm. this shows that as the depth of cut and feed rate increase, higher surface roughness will result. the empirical model for ra surface roughness for dry cutting is shown by eqn. 1, where a = depth of cut (mm), b = feed rate (mm/min), and c = spindle speed (1000 rpm). (ra)dry = 0.093 + 0.33 a + 0.068 b + 0.06 c (1) anova, as shown in table 4, of surface roughness with mql showed an f-value for the model of 11.25. it indicates that the model is significant. there is only a little chance (3.76%) that the model f-value of 11.25 could occur due to noise. values of "prob > f" less than 0.05 indicate that the model terms are significant. in this case depth of cut (a) and feed rate (b) are significant model terms. based on table 4, feed rate (b) is the most significant parameter that affected the surface roughness with mql followed by the depth of cut (a). the “pred r-squared” of 0.5556 is not as close to “adj r-squared” of 0.8542 as 151 iium engineering journal, vol. 18, no. 1, 2017 ali et al. one might normally expect. “adeq precision” of 9.859 indicates that the signal to noise ratio is an adequate signal. fig. 3: three dimensional plot of depth of cut and feed rate on surface roughness in (a) dry cutting, and (b) cutting with mql. table 4: anova of surface roughness with mql source sum of squares df mean square fvalue prob > f model 6.000 e-003 4 1.500 e-003 11.25 0.0376 a-depth of cut 1.800 e-003 1 1.800 e-003 13.50 0.0349 b-feed rate 3.200 e-003 1 3.200 e-003 24.00 0.0163 c-spindle speed 2.000 e-004 1 2.000 e-004 1.50 0.3081 ac 8.000 e-004 1 8.000 e-004 6.00 0.0917 residual 4.000 e-004 3 1.333 e-004 cor total 6.400 e-003 7 pred r-squared 0.5556 adj r-squared 0.8542 adeq precision 9.859 design-expert plot surface roughnes s x = a: depth of cut y = b: feed rate actual factor c: spindle s peed = 2400.00 0.13 0.16 0.18 0.21 0.23 s ur fa ce ro ug hn es s 0.05 0.08 0.10 0.13 0.15 1.00 1.25 1.50 1.75 2.00 a: depth of cut b: feed rate design-expert plot surface roughnes s x = a: depth of cut y = c: spindle s peed actual factor b: feed rate = 1.50 0.15 0.16 0.18 0.19 0.20 s ur fa ce ro ug hn es s 0.05 0.08 0.10 0.13 0.15 2000.00 2200.00 2400.00 2600.00 2800.00 a: depth of cut c: spindle s peed a b 152 iium engineering journal, vol. 18, no. 1, 2017 ali et al. figure 3b shows the relationship between depth of cut and spindle speed on surface roughness in micromachining with mql. from the graph, when depth of cut is 0.05 mm and spindle speed is 2150 rpm, the surface roughness is 0.16 µm. when depth of cut is 0.15 mm and spindle speed is 2600 rpm, the surface roughness is 0.19 µm. these show that as depth of cut and spindle speed increase; higher surface roughness will result. the empirical model for ra surface roughness for micromilling with mql is shown by eqn. 2, where a = depth of cut (mm), b = feed rate (mm/min), and c = spindle speed (1000 rpm). the results show a similar outcome to the previous researcher’s investigation, where machining with mql gave better surface roughness compared to dry cutting [19]. (ra)mql = 0.17 0.9 a + 0.04 b – 0.038 c + 0.5 ac (2) 4. conclusions and recommendations through this research, the surface roughness of a machined part has been measured by a surface roughness tester. the values of surface roughness with dry cutting and mql have been compared. figure 4 shows the comparison of surface roughness between dry cutting and mql. the surface roughness with mql has lower values compared to surface roughness with dry cutting. this proves that the surface roughness with mql produces better surface roughness compared to dry cutting. the relationship among parameters has been analyzed. for dry cutting, depth of cut, feed rate, and spindle speed are significant factors for surface roughness while for mql, spindle speed is an insignificant factor and hence has a small influence towards the surface roughness. for further research, it is recommended that all parameters, such as cutting tool, workpiece materials, and vibration that could influence surface roughness and accuracy should be analyzed. in addition, an optimization of process parameters also should be carried out. fig. 4: comparison of ra surface roughness values obtained from dry milling and milling with mql. acknowledgement the authors would like to express their thanks to the ministry of higher education, malaysia for their financial support under the fundamental research grant scheme (frgs 14-156-0397). 153 iium engineering journal, vol. 18, no. 1, 2017 ali et al. references [1] cheng x, wang z, nakamoto k, yamazaki k. (2011) a study on the micro tooling for micro/nano milling. international journal of advanced manufacturing technology, 53:523533. [2] wang js, gong yd, abba g, chen k, shi js, cai gq. (2008) surface generation analysis in micro end-milling considering the influences of grain. microsystem technologies, 14(7):937942. [3] li km, wang sl. (2014) effect of tool wear in ultrasonic vibration-assisted micro-milling. proceedings of the institution of mechanical engineers part b journal of engineering manufacture, 228(6):874-855. [4] ucun i, aslantas k, bedir f. (2013) an experimental investigation of the effect of coating material on tool wear in micro milling of inconel 718 super alloy. wear, 300(1):8-19. [5] fink j, thery m, azioune a, dupont r, chatelain f, bornens m, piel m. (2007) comparative study and improvement of current cell micro-patterning techniques. lab on a chip, 7(6):672680. [6] kancharla vv, chen s. (2002) fabrication of biodegradable polymeric micro-devices using laser micromachining. biomedical microdevices, 4(2):105-109. [7] shahrom ms, yahya nm, yusoff ar. (2013) taguchi method approach on effect of lubrication condition on surface roughness in milling operation. procedia engineering, 53:594-599. [8] kajaria s, chittipolu s, adera s, hung wnp. (2012) micromilling in minimum quantity lubrication. machining science and technology, 16(4):524-546. [9] yerkes kl, dorian j. (1999) micro-cooler for chip-level temperature control. sae technical paper, 01-1404. [10] burton g, goo cs, zhang y, jun mb. (2014) use of vegetable oil in water emulsion achieved through ultrasonic atomization as cutting fluids in micro-milling. journal of manufacturing processes, 16:405-413. [11] zhong w, zhao d, wang x. (2010) a comparative study on dry milling and little quantity lubricant milling based on vibration signals. international journal of machine tools and manufacture, 50(12):1057-1064. [12] machado ar, wallbank j. (1997) the effect of extremely low lubricant volumes in machining. wear, 210(1):76-82. [13] superkar sd, clarens af, stephenson da, skerlos sj. (2012) performance of supercritical carbon dioxide sprays as coolants and lubricants in representative metalworking operations. journal of materials processing technology, 212(12):2652-2658. [14] machai c, iqbal a, biermann d, upmeier t, schumann s. (2013) on the effects of cutting speed and cooling methodologies in grooving operation of various tempers of β-titanium alloy. journal of materials processing technology, 213(7):1027-1037. [15] shaikh v, bouberi n, scharf tw. (2014) analyzing the effectiveness of microlubrication using a vegetable oil-based metal working fluid during end milling aisi 1018 steel. international journal of manufacturing engineering, 2014: 1-13. [16] biermann d, iovkov i. (2013) modelling and simulation of heat input in deep-hole drilling with drills and mql. procedia cirp, 8:87-92. [17] rakurty cs, vrela pi, balaji ak. (2013) effects of targeted minimum quantity fluid (mqf) application on surface integrity. procedia cirp, 8:461-467. [18] chae j, park ss, freiheit t. (2006) investigation of micro-cutting operations. international journal of machine tools and manufacture, 46(3-4):313-332. [19] okonkwo uc, okokpujie ip, sinebe je, ezugwu ak. (2015) comparative analysis of aluminium surface roughness in end-milling under dry and minimum quantity lubrication (mql) conditions. manufacturing review, 30(2): 1-11. 154 microsoft word 3_v17no2_compiled_v3_26nov16.docx iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 11 implementing ndn using sdn: a review of methods and applications shiva rowshanrad*, mohamad reza parsaei and manijeh keshtgari information technology department, shiraz university of technology, shiraz, iran. *corresponding author: shiva.rrad@gmail.com (received: 11th oct. 2015; accepted: 20t h jan. 2016; published on-line: 30th nov. 2016) abstract: in recent years, many claims have been made about the limitations of today’s network architecture, its lack of flexibility and its inability to respond to ongoing changes and increasing users demands. in this regard, new network architectures are proposed. software defined networking (sdn) is one new architecture that centralizes the control of network by separating control plane from data plane. this separation leads to intelligence, flexibility and easier control in computer networks. one of the advantages of this framework is the ability to implement and test new protocols and architectures in actual networks without any concern of interruption. named data networking (ndn) is another paradigm for future network architecture. with ndn the network becomes aware of the content, rather than just transferring it among end-points. ndn attracts researchers’ attention and is known as the potential future of networking and internet. providing ndn functionalities over sdn is an important requirement to enable the innovation and optimization of network resources. in this paper, a description of sdn and ndn are given, and methods for implementing ndn using sdn are introduced. various methods are compared from hardware methods requiring changes in switches, to software methods such as using proxies, to methods that take advantage of unusable ip header fields as ndn headers. the advantages and applications of implementing ndn over sdn for routing, virtualization, traffic management, data centers, and heterogeneous networks are also pointed out. abstrak: sejak beberapa tahun kebelakangan ini telah timbul banyak dakwaan mengenai batasan senibina rangkaian komputer hari ini, kekurangan fleksibiliti dan keupayaan untuk bertindak balas kepada perubahan yang berterusan dan permintaan pengguna yang semakin meningkat. dalam hal ini, seni bina rangkaian baru adalah dicadangkan. software defined networking (sdn) adalah salah satu daripada seni bina baru yang memusatkan kawalan ke atas rangkaian dengan mengasingkan satah kawalan dari satah data. pengasingan ini membawa kepada kecerdasan, fleksibiliti dan kawalan lebih mudah dalam rangkaian komputer. salah satu kelebihan rangka ini adalah keupayaan untuk melaksanakan dan menguji protokol dan seni bina baru dalam rangkaian sebenar tanpa sebarang gangguan. named data networking (ndn) adalah satu lagi paradigma untuk seni bina rangkaian masa depan. dengan ndn rangkaian mengetahui kandungan, bukan hanya memindahkannya antara mata akhir. ndn menarik perhatian penyelidik dan dikenali sebagai potensi masa depan bagi rangkaian dan internet. menyediakan fungsi ndn lebih dari isdn adalah satu keperluan yang penting bagi membolehkan inovasi dan pengoptimuman sumber rangkaian. dalam kertas ini mulanya kami menerangkan tentang sdn dan ndn, kemudian kami memperkenalkan kaedah untuk melaksanakan ndn menggunakan sdn. kami membandingkan methodes yang memerlukan perubahan perkakasan dalam suis, methodes perisian yang menggunakan proksi dan methodes menggunakan bidang pengepala ip yang tidak lagi boleh digunakan sebagai pengepala ndn. kami juga menunjukkan aplikasi dan iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 12 kelebihan mengguna ndn berbanding dengan sdn untuk routing, virtualisasi, pengurusan trafik, pusat data dan rangkaian heterogen. keywords: software defined networking; named data networking; future internet; openflow 1. introduction today’s network architecture was proposed between the 1960’s and 1970’s [1]. so far, there have been many changes in internet usage which require it to migrate to new network architectures. changes include new services and technologies such as cloud computing and big data, the diversity of it users, especially mobile users, etc. furthermore, current users tend care for their content and information rather than where and how to access such content [2, 3]. in recent years, new architectures and frameworks have been proposed and investigated to solve current network issues and limitations. as an example, software defined networking (sdn) is proposed to create highly programmable computer networks. in sdn, the separation of the control plane from data plane gives network operators the ability to introduce new protocols and services to the network without any changes in the network hardware or infrastructure [4]. one of the most popular ways to deploy sdn is by implementing it based on an open standard protocol, named openflow. in sdn/openflow, network devices are simple forwarders named openflow switches, while a centralized controller is responsible for making routing and control decisions [4, 5]. named data networking (ndn) is another paradigm for new network architecture which has recently attracted many researchers’ and academia’s attention. this architecture is proposed to solve current network issues such as high bandwidth cost due to point-topoint traffic and content delivery networks (cdns). there is a difference between today’s network principles and its applications. to deal with this difference, ndn introduces an architecture that focuses on content access and delivery instead of host-centric communication. ndn introduces services such as in-network caching and service classification based on content [6]. the functionalities and advantages of ndn can be truly realized when the network’s infrastructure is dedicated to this architecture. furthermore, to improve network operation and efficiency, there is a need for new solutions for deploying new architectures incrementally while they are compatible with current ip networks. therefore, developing ndn devices in current networks is an important issue. sdn brings the opportunity for innovations and development of new network architectures. this can be the mainspring of implementing ndn functionalities using sdn. sdn also facilitates the implementation of ndn without the need for new hardware, hence decreasing infrastructure expenses. in this paper, the methods and applications of implementing ndn using sdn are discussed. first, an overview of sdn and ndn are given in sectio n 2 and section 3 respectively. then, in section 4 existing methods for implementing ndn over sdn are explained and compared. in section 5, the applicatio n of ndn over sdn is introduced. finally, section 6 concludes the paper. iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 13 2. software defined networking in sdn, the control plane and data plane are separated, which makes the networks control more flexible. in current networks, routers include both control plane and data plane. the control plane is responsible for routing computation and decisions while the data plane is responsible for forwarding packets. in sdn, the control plane is centralized into a server called the controller. the controllers are modular network operating systems. new services such as monitoring and new routing protocols can be added to network by adding different software modules to the controller, hence analyzing and controlling network behaviour. for this purpose, the controller also needs to communicate with underlying switches using standard protocols such as openflow [4, 7]. figure 1 shows the sdn architecture which has three layers: an infrastructure layer consisting of openflow switches, a control layer in which the controller is placed, and an application layer in which business applications can be placed. aside from these three layers, there are two interfaces: the first is a southbound interface such as openflow which standardizes the communication between the infrastructure and control layers; the second is a northbound interface which is used for communication between the controller and application layers [2, 4]. fig. 1: sdn architecture. in the infrastructure layer, openflow switches are simple forwarders which communicate with the controller via openflow protocols. this communication is achieved through a secure channel such as secure sockets layer (ssl) or transport layer security (tls). the switches have one or more flow tables. each flow table consists of flow entries for forwarding flows. each entry includes three main parts [7, 8]:  matching field: the information of layer 2 to layer 4 header of packet, ingress port and metadata. this field is for matching the entries to arriving packet.  action: set of operations and instructions to be done on the packet after matching process. application layer business applications control layer infrastructure layer (openflow switches) network operating system northbound api southbound api (openflow) iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 14  counters: statistical information about a flow such as received and sent bytes/packets, dropped packets, or duration. the entries can be added, deleted, or updated by the controller through openflow messages. upon receiving a packet, the switch looks into the flow table to find a match based on the matching field. if a match is found, the specified action will be done on the packet and counters will be updated. if a table-miss happened, the switch will encapsulate the received packet as a packet-in message and send it to the controller for decision making. then the controller informs the switch about its decision using a packet-out message [4, 5]. 3. named data networking as mentioned before, in ndn, the concentration is on content delivery instead of physical location of content. this architecture is based on named content and does not recognize any host entity. also, in this framework, the contents have unique names similar to a url, instead of ip addresses. the names consist of human readable parts with different lengths [6, 8]. ndn has the functionality of in-network caching. upon receiving a data packet the router can cache it into its content store. the communication starts from the consumer via an interest packet which contains the request for desired content and its name. when an interest packet gets into a router, the router looks up the content store based on longest prefix matching (lpm) for the desired content. if the content is available, the router sends it to the consumer from the same interface that received the interest and discards the interest packet. if no content matches the interest packet, the router looks into another table called the pending interest table (pit) which contains the list of interests waiting for data. if the look up process was successful, the ingress interface of the interest packet will be added to the related table entity; otherwise the router will look in the forwarding information base (fib) table to forward the interest packet to the producer. if no related entity is found in fib, it means that the router neither has the content, nor knows how to get to it; so it discards the interest packet. the data packet follows the interest packet chain of entities in pits to get to the consumer [3]. 4. implementing ndn using sdn/openflow as mentioned before, ndn is a new network architecture proposed for solving limitations and issues in current networks. ndn has functionalities and advantages such as in-network caching, data-centric security (by signatures on all packets), multipath forwarding, self-regulation (by flow balancing between interest and data packets) [6, 9]. these functionalities have the greatest effect in the network when ndn infrastructure and devices are available in the network. one of the opportunities from adopting sdn is the ability to deploy and test new network architectures. implementing ndn using sdn makes it possible to define ndn’s functionality in the network without the need for new hardware, thereby decreasing infrastructure expenses. overcoming the weaknesses of ndn or optimizing its capabilities and resources, such as in-network storage, is another motivation for deploying ndn over sdn. many projects proposed different methods for implementing ndn over sdn. four groups of these methods will be investigated in this paper [1, 8, 10-15]:  changing openflow switches iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 15  use of hash functions to hash packet names into ip header fields  using proxy to communicate between of switch and ccnx (an ndn implementation reference, ccn stands for content centric network which is the earlier name of named data network)  using the ip option field of a packet as the name field in [1] an architecture named contentflow, is proposed which is shown in fig. 2. in this architecture the openflow switches must change to be able to process ndn packets and support its functionalities. fig. 2: contentflow architecture model [1]. the ccn node in fig. 2 is the modified openflow switch which is programmable through the network controller and supports ndn transactions. this node includes fib, pit, and content storage. the contentflow node is the controller that communicates with ccn nodes and the content server to manage the network. the ccn nodes transfer the copy of the contents they have, and their updated information, to the content server periodically. the controller can query the content list and their information from the content server. this gives the controller the ability to take a global view of the network. the content server is also responsible for making decisions about the location of content in the network and their caching duration in the ccn node [1]. the strong point of this architecture is that while it can deploy all functionalities of ndn, it also supports the advantages of sdn such as a centralized global view of the network from the controller. furthermore, it creates the ability to add new protocols and services to the network, independent of changing hardware devices, which is a strong advantage since ndn is still evolving and may face many changes. however, changing openflow switches to build ccn nodes is dependent on hardware changes that are time consuming and expensive. it is therefore better to use existing available elements as much as possible in ndn architecture testing phases. the problem is that sdn forwarding and routing is based on flows and their layer 2-4 header information, while ndn’s is based on content names. in [16] a method is proposed that is based on hashing content names in the ip packet’s address field. to implement this method, user datagram protocol (udp) and openflow 1.0 are used. the ndn packets are encapsulated into the payload part of udp packet. two different port numbers are dedicated to interest and data packets. this makes the nodes able to distinguish between these two ndn packets and also recognize ip packets from ndn packets; hence the switches can work with both ndn and ip iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 16 architectures. the ndn routers should be able to perform lpm on packet names, but there is no rule in openflow protocol for matching packet payloads. as a result, the names are hashed and placed into the ip field in the packets header. since each part of a name would be hashed into a 4 bit number, a name can consist of 8 parts at most. one problem occurs because the names in ndn can have different lengths, and studies show that 99.9 percent of names have fewer than 30 parts; so in most cases, 8 parts are insufficient. the collision probability is also dependent on the number of bits. the greater the number of bits for each part of the name, the lower the collision probability. this means that there is a tradeoff between the number of the parts and the number of bits for each part. a better solution is to consider openflow 1.3 for exploiting ipv6 or mac fields. this paper [16] uses software caching in the controller as in-network caching that clearly has a better performance than hardware caching in routers. instead of pit, fib, and content store, it considers a state flag in the controller for each packet [16]. although this method makes the controller aware of all content in the network, it doesn’t have the most important advantage of ndn architecture named “on-path caching”. on-path caching brings the contents closer to consumers, and lowers the bandwidth consumption and latency. however, on-path caching also has shortcomings. due to high content replication in nodes, the maximum amount of content that can be cached inside the domain is limited. to solve this issue in [11], a new strategy is proposed for “off-path caching” in ndn using sdn functionalities. this strategy lowers the content replication and increases the content hit-rate. for integrating sdn and ndn, this paper proposed a method in which the network switches are composed of an openflow switch and ccnx that communicate with each other via a proxy. the proxy maps the ccnx and openflow switches and hashes the ndn content names into fields that can be processed by openflow switches. the advantage of this method is that there is no need to change ccnx or openflow switches and the proxy can be updated easily. the openflow hardware cache can be used as fib while the ccnx daemon can be used as pit and content store. but the proxy can decrease the network performance due to extra operations it should do. for solving this issue, three modules where added to the controller. the first module is a measurement module that periodically identifies the most popular contents by querying the switches. the second module is an optimization module that finds the best location for caching content based on latency and congestion. the third module is a deflection module that builds a mapping between the hashed name of the content and the outgoing interfaces where it was cached. the evaluation results show that the proxy decreases the efficiency by only 5% in the worst case [11, 12]. in conet architecture, which is implemented over the ofelia test-bed, the ip option is used as the name field. due to the inability of openflow in processing ip options, the name is also hashed and tagged into the first 4 bytes of the udp header. as the conet packet is placed into the udp packet, the ip protocol is 17 for both the udp and conet packets. so , a reserved ip in ip destination field is used to distinguish between these two packets. two other reserved ip is also used for the interest and data packets of conet [10, 17, 18]. a detailed part of the conet architecture is shown in fig. 3. on receipt of an interest to the edge node of the system, if the requested data isn’t cached in any node, the interest will be routed to the appropriate destination which can be a system inner node in or edge node when the data belongs to an outer system. if the requested data is cached in a cache server, the interest will be routed to that server. when the data packet is routed to consumer, one of the switches will also send the data to be cached into a cache server. this should be done with the help of controller (nrs node). iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 17 the controller is also responsible for checking and ensuring that tags are unique in their domain. conet supports most of ndn’s functionalities such as digital signature for security and in-network caching. it also offers some other functionalities such as tcp congestion control [10, 17, 18]. fig. 3: conet architecture [17]. 5. advantages and applications in section 4 some methods for integrating sdn and ndn were discussed. in this section the advantages and applications of implementing ndn over sdn will be introduced. as mentioned before, one of the advantages of implementing ndn over sdn is to improve ndn’s functionalities, such as tcp congestion control optimization in ofelia. also in [19], a routing protocol is proposed for supporting mobility in ndn by means of a controller. this can be easily implemented in integrated architectures of sdn and ndn. in [20] another controller-based routing strategy for ndn is proposed. the simulation results show improvement up to 75% signalling efficiency and faster convergence time. in [21], a routing scheme called the sdn-based routing scheme for ccn (srcs) is proposed. the srcs architecture is a clean slate implementation of ndn and uses ndn messaging, while it uses the separation of control plane and data plane in sdn. the simulation result on ns3 shows the improvement of caching efficiency and a decrease in the number of messages compared to the default flooding strategy in the original ndn architecture. another case for improvement in ndn based on sdn is network and traffic management. in [22], a network management system is built on top of ndn by using sdn/openflow controller to manage traffic by focusing on traffic classification, labelling, shaping and queuing. another advantage of combining ndn and sdn is to improve performance of new technologies such as virtualization, cloud computing, etc. for example, odicn [23] is proposed for data centers. odicn is based on combining ndn and sdn/openflow. in this framework, the users can request content from different data centers while the controller can optimize the downloading efficiency based on its global view of topology and resources. the odicn controller has three main responsibilities: content locating, content optimal deployment, and path optimization. content locating can redirect users’ requests to the best (least cost) data center containing the requested content. content optimal deployment automatically deploys the contents to the other data centers according to the given principles for optimizing network performance; and path optimization and traffic balance are both done in spatial and temporal dimensions. in [24], the role of iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 18 virtualization, by use of sdn, in ndn is discussed. the authors outlined traffic optimization, traffic engineering, and caching management as the advantages of implementing ndn over sdn, especially for multimedia traffics. in [25], an ndn architecture is proposed in the sdn framework for heterogeneous networks such as sensor networks. the motivation of combining thes e two networks in this paper is the flexib le management and the ability for continuous evolution of network architectures in sdn, and also efficient data dissemination via name routing and in-network caching in ndn. a summary of mentioned advantages and applications is in table 1. table 1: application and advantages of implementing ndn using sdn paper application advantage offelia testbed [1718] tcp congestion control optimizing tcp congestion control in ndn j. torres et al. [19] controller-based routing supporting for mobility in ndn cros-ndn [20] controller-based routing signalling efficiency and faster convergence time in ndn srcs [21] controller-based routing caching efficiency, decrease in messaging q. sun et al. [22] centralized traffic management in ndn higher awareness, fairness, and low congestion m. chen et al. [23] deploying ndn in data centers using openflow obtaining content from data centers via its name, optimizing download efficiency in data centers, automatic and optimal deployment of content, load balancing in network links j. ren et al. [24] virtualization in ndn using sdn traffic optimization, traffic management, traffic engineering and cache management s. eum et al. [25] deploying ndn using sdn framework for heterogeneous networks such as sensor networks flexible management, efficient data dissemination, ability to evolve network incrementally 6. conclusion ndn is a new paradigm for dealing with various limitations of current network architecture and its applications. this new architecture focuses on “what” instead of “where”. it uses content naming and name-based routing instead of ip routing. but the current design of ndn still has some limitations and needs to grow. for exploiting and improving ndn functionalities, there is a need for dramatic changes to network devices deployed in current networks, which creates the challenge of ndn implementation. sdn is another new network architecture that decouples the control plane from the data plane and places it into a server called the controller. one of sdn’s advantages and promise is the ability of deploying and improving new architectures and protocols without concerns for hardware dependency and expenses. so much research and papers have been done in implementing ndn using an sdn framework. this paper explained and discussed some of these methods. advantages and applications of combining these new architectures iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 19 were also pointed out. the applications included traffic management, new routing schemes, virtualization, architectures for data centres and sensor networks. references [1] carvalho i, faria f, cerqueira e, abelem a. (2012) contentflow: an introductory routing proposal for content centric networks using openflow. api, 7th think-tank meeting. [2] open networking foundation. (2012) software-defined networking: the new norm for networks. onf white paper, available online: https://www.opennetworking.org/images/stories/downloads/sdn-resources/white-papers/wpsdn-newnorm.pdf, last accessed: 25 may 2015 [3] zhang l, estrin d, burke j, jacobson v, thornton jd, smetters dk, zhang b, tsudik g, claffy k, krioukov d, wang l, massey d, papadopoulos c, abdelzaher t, crowley p, yeh e. (2010) named data networking (ndn) project. avalilable online: http://nameddata.net/publications/techreports/, last accessed: 25 may 2015. [4] rowshanrad s, namvarasl s, abdi v, hajizadeh m, keshtgary m. (2014) a survey on sdn, the future of networking. j. adv. comp. sci. tech., 3:232-248. [5] openflow switch consortium. (2009) openflow switch specification version 1.0. 0., available online: https://www.opennetworking.org/images/stories/downloads/sdn-resources/onfspecifications/openflow/openflow-spec-v1.0.0.pdf, last accessed:25 may 2015 [6] jacobson v, burke j, zhang b, estrin d, zhang l, zhang b, tsudik g, claffy k, krioukov d, massey d, papadopoulos c, ohm p, abdelzaher t, shilton k, wang l, yeh e, uzun e, edens g, crowley p. (2013) named data networking (ndn) project. available online: http://named-data.net/publications/techreports/, last accessed: 25 may 2015 [7] nunes b, mendonca m, nguyen x, obraczka k, turletti t. (2014) a survey of softwaredefined networking: past, present, and future of programmable networks. communications surveys & tutorials, ieee, 1617-1634. [8] mckeown n, anderson t, balakrishnan h, parulkar g, peterson l, rexford j, shenker s, turner j. (2008) openflow: enabling innovation in campus networks. acm sigcomm comp. comm. rev., 38: 69-74. [9] zhang l, afanasyev a, burke j, jacobson v, crowley p, clafy k, papadopoulos c, wang l, zhang b. (2014) named data networking. acm sigcomm comp. comm. rev., 44:6673. [10] salsano s, blefari-melazzi n, detti a, morabito g, veltri l. (2013) information centric networking over sdn and openflow: architectural aspects and experiments on the ofelia testbed. computer networks, 57:3207-3221. [11] nguyen xn, saucez d, turletti t. (2013) efficient caching in content-centric networks using openflow. infocom 2013 student workshop. [12] nguyen xn, saucez d, thierry t. (2013) providing ccn functionalities over openflow switches. available online: https://hal.inria.fr/hal-00920554/, last accessed: 25 may 2015. [13] melazzi nb, detti a, pomposini m, salsano s. (2012) route discovery and caching: a way to improve the scalability of information-centric networking. ieee global communications conference (globecom), 2701-2707. [14] melazzi nb, detti a, mazza g, morabito g, salsano s, veltri l. (2012) an openflow-based testbed for information centric networking. future network & mobile summit (futurenetw), 2012. ieee, 1-9. [15] chanda a, westphal c, raychauldhuri d. (2013) content based traffic engineering in software defined information centric networks. proc. ieee infocom workshop nomen’13, 1-6. [16] ooka a, ata s, koide t, shimonishi h, murata m. (2013) openflow-based content-centric networking architecture and router implementation. future network and mobile summit (futurenetworksummit), 2013. ieee, 1-10 iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 20 [17] salsano s. (2013) ofelia: exotic final architecture and design. technical report, available online: http://netgroup.uniroma2.it/people/faculties/stefano-salsano/stefanosalsano-publication-list/, last accessed: 25 may 2015 [18] blefari-mellazzi n, detti a, morabito g, salsano s, veltri l. (2013) information centric networking over sdn and openflow: architectural aspects and experiments on the ofelia testbed. available online: http://netgroup.uniroma2.it/twiki/bin/view/netgroup/conet, last accessed 25 may 2015 [19] torres j, ferraz l, duarte o. (2012) controller-based routing scheme for named data network. technical report, electrical engineering program, coppe/ufrj. [20] torres j, duarte o. (year?) cros-ndn: controller-based routing strategy for named data networking. available online: http://www.gta.ufrj.br/ftp/gta/techreports/todu14a.pdf, last accessed 25 may 2015 [21] aubry e, silverston t, chrisment i. (2015) srsc: sdn-based routing scheme for ccn. ieee netsoft., londres, united kingdom. [22] sun q, wendong w, hu y, que x, xiangyang g. (2014) sdn-based autonomic ccn traffic management. globecom workshops,183-187. [23] chen m, weng x, wang x, xing c, zhang g. (2013) a mechanism of information-centric networking based on data centers. international conference in advanced cloud and big data (cbd), 40-45. [24] ren j, pentikousis k, westphal c, liu w, wang j. (2013) the role of virtualization in information centric network deployment. ieee cosmoc mmtc, 8:21-23. [25] eum s, jibiki m, murata m, asaeda h, nishinaga n. (2015) an icn architecture within the framework of sdn. available online: http://www.ieice.org/~icn/wp-content/uploads/2015/04/icn_kickoff_4.pdf, last accessed: 25 may 2015 microsoft word 0_vol_16_no_2_2015_special issue on energy_compiled.docx iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 69 investigation of pem fuel cell for automotive use a.k.m. mohiuddin, ataur rahman, mohamed fadhil chemani and mohd baihaqi zakaria department of mechanical engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia mohiuddin@iium.edu.my, arat@iium.edu.my, cbr1000_fadhil@yahoo.com, and scuderia889@gmail.com (received: oct. 30, 2015; accepted: nov.10, 2015; published on-line: nov. 30, 2015) abstract: this paper provides a brief investigation on suitability of proton-exchange membrane fuel cells (pemfcs) as the source of power for transportation purposes. hydrogen is an attractive alternative transportation fuel. it is the least polluting fuel that can be used in an internal combustion engine (ice) and it is widely available. if hydrogen is used in a fuel cell which converts the chemical energy of hydrogen into electricity, (nox) emissions are eliminated. the investigation was carried out on a fuel cell car model by implementing polymer electrolyte membrane (pem) types of fuel cell as the source of power to propel the prototype car. this pemfc has capability to propel the electric motor by converting chemical energy stored in hydrogen gas into useful electrical energy. pem fuel cell alone is used as the power source for the electric motor without the aid of any other power source such as battery associated with it. experimental investigations were carried out to investigate the characteristics of fuel cell used and the performance of the fuel cell car. investigated papameters are the power it develops, voltage, current and speed it produces under different load conditions. abstrak: kertas kerja ini memberikan penyelidikan ringkas tentang keserasian penukaran membran sel bahan api proton (pemfcs) sebagai punca kuasa untuk tujuan pengangkutan. hidrogen merupakan bahan api pengangkutan alternatif yang menarik. ia merupakan sumber bahan api yang banyak dan paling kurang mencemar yang boleh digunakan sebagai engin pembakaran dalaman (ice). penggunaan hidrogen dalam sel bahan api dapat menukarkan tenaga kimia hidrogen kepada elektrik, di mana pengeluaran (nox) dapat disingirkan. penyelidikan dijalankan ke atas model kereta sel bahan api dengan menggunakan jenis sel bahan api membran elektrolik berpolimer (pem) sebagai sumber tenaga untuk menjanakan kereta prototaip. penggunaan pemfc membolehkan penjanaan kuasa elektrik motor dengan menukarkan tenaga kimia yang terkandung dalam gas hidrogen sebagai tenaga elektrik yang berguna. sel bahan api pem secara sendirinya digunakan sebagai sumber tenaga kepada motor elektrik tanpa bantuan daripada sumber tenaga lain seperti bateri. penyelidikan eksperimental dijalankan untuk mengkaji sifat sel bahan api yang digunakan dan keupayaan sel bahan api kereta. parameter yang dikaji termasuklah tenaga yang dihasilkan, voltan, arus dan kelajuan yang terhasil daripada bebanan yang berbeza. keywords: fuel cell; automotive; proton exchange membrane; polymer electrolyte membrane; internal combustion engine iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 70 1. introduction motor vehicles account for 30% to 70% of emissions of all urban air pollutants (epa, 1991) [1], and up to 30% of emissions of carbon dioxide from the use of petroleum fuels [2]. in most countries of the world, ground transportation exclusively uses petroleum fuels. the vulnerable supply and price volatility in the world oil market have motivated researchers and policy makers to seek alternatives to gasoline and diesel fuel. hydrogen is an attractive alternative transportation fuel. it is the least polluting fuel that can be used in an internal combustion engine (ice) and it is available anywhere where water is available and is a clean source of power. the prospect of a clean, widely available transportation fuel has prompted much of the research on hydrogen fuels. hydrogen has been successfully demonstrated in experimental cars, buses and trucks [3-5]. if hydrogen is used in an internal combustion engine (ice), the only pollutant of concern is oxides of nitrogen (nox), which can be controlled to low levels. but if hydrogen is used in a fuel cell which converts the chemical energy of hydrogen into electricity, (nox) emissions are eliminated. a fuel is a device that converts chemical energy to direct current electrical energy. pem fuel cells use a proton conductive polymer membrane as electrolyte. pem stands for polymer electrolyte membrane or proton exchange membrane. sometimes they are also called polymer membrane fuel cells, or just membrane fuel cells. in the early days (1960s) they were known as solid polymer electrolyte (spe) fuel cells. this technology has drawn the most attention because of its simplicity, viability, quick start-up, and it has been demonstrated in almost any conceivable application, from powering a cell phone to a locomotive [6]. by converting an on-board fuel to electricity it could be effectively used to power an electric vehicle. as such, a fuel cell is an energy conversion device like an internal combustion engine. the objective of this work is to investigate the suitability of pemfc for automotive use through a fuel cell car prototype which will be powered by pem fuel cell. proton-exchange membrane fuel cells (pemfcs) are considered to be a promising technology for efficient power generation in the 21st century. pemfcs are one of the most promising clean energy technologies. pemfcs have certain potential advantages, such as portable applications, power generation, high efficiency, etc. [7, 8]. the key constituent of a pemfc is a dense proton-exchange membrane, which is responsible for proton migration from the anode to the cathode. hydrogen is catalytically oxidized in the anode to produce protons. the membrane is generally placed between two electrodes, i.e. between the anode and cathode. the protons thus produced can migrate from the anode to cathode where the protons react with oxygen to produce water and heat [9]. over the past few years, there have been intense efforts worldwide to develop low-cost pemfc systems. 2. fuel cell fuel cells are electrochemical devices that process hydrogen and oxygen to generate electric power, and water vapor comes out as their only by-product. figure 1 shows the basic operation of a fuel cell. hydrogen is channeled through fuel flow plates to the anode on one side of the fuel cell, while oxygen on the other side of the cell. at the anode, a platinum catalyst causes the hydrogen to split into positive hydrogen ions (protons) and negatively charged (electrons). the polymer electrolyte membrane (pem) allows only positively charged ions to pass through it to the cathode. the negatively charged electrons must travel along external circuit (load) to the cathode, creating an electrical current. at iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 71 the cathode, the electrons and positively charged hydrogen ions combine with oxygen to form water, which flows out of the cell [10]. fig. 1: fuel cell basic operation. there are four basic components in a single cell of pemfc and they are:  anode: it is the negative side of the fuel cell. it conducts the electrons that are freed from the hydrogen molecules and are used in an external circuit. channels etched into the anode disperse the hydrogen gas equally over the surface of the catalyst.  cathode: it is the positive side of the fuel cell and also contains channels that distribute the oxygen to the surface of the catalyst. it conducts the electrons back from the external circuit to the catalyst, where they can recombine with the hydrogen ions and oxygen to form water.  polymer electrolyte membrane: pem is a specially treated material that looks something like ordinary kitchen plastic wrap, only conducts positively charged ions and blocks the electrons. the pem is the key to the fuel cell technology. it must permit only the necessary ions to pass between the anode and cathode. other substances passing through the electrolyte would disrupt the chemical reaction.  catalyst: all electrochemical reactions in a fuel cell consist of two separate reactions, an oxidation half-reaction at the anode and a reduction half-reaction at the cathode. usually, the two half-reactions would occur very slowly at the low operating temperature of the pem fuel cell. each of the electrodes is coated on one side with a catalyst layer that speeds up the reaction of oxygen and hydrogen. it is usually made of platinum powder, very thinly coated onto carbon paper or cloth. the catalyst is rough and porous so that the maximum surface area of the platinum can be exposed to the hydrogen or oxygen. the voltage resulting from the reaction of the fuel (hydrogen) and oxygen varies with the load. due to their low output voltage it becomes necessary to stack many cells in series to realize a practical system. for low power applications, the number of cells that needs to be connected in series is small, but as power increases the number of cells that are required in the stack increases rapidly. for example, to produce 100 v fuel cell, the stack consists of 250 cells in series and to produce 300 v at full load, the fuel cell stack requires 750 cells in series. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 72 2.1 types of fuel cells there are many types of fuel cells that are currently being researched to make them commercially viable. some of them are polymer electrolyte membrane fuel cells (pemfcs), alkaline fuel cell (afcs), phosphoric acid fuel cell (pafcs), solid oxide fuel cell (sofcs), and molten carbonate fuel cells (mcfcs). a brief comparison of these fuel cells is given in table 1 [11]. table 1: comparison of fuel cell technology. fuel cell type polymer electrolyte membrane (pemfc) alkaline (afc) phosphoric acid (pafc) molten carbonate (mcfc) solid oxide (sofc) fuel h2 h2 h2 h2/co/reformate co, h2 oxidizer o2, air o2, air o2, air co2,o2, air o2, air common electrolyte hydrated polymeric ion exchange membranes mobilized or immobilized potassium hydroxide in asbestos matrix immobilized liquid phosphoric acid in sic immobilized liquid molten carbonate in lialo2 perovskites (ceramics) operating temperature 40 – 80 °c 65 – 220 °c 205 °c 650 °c 600 -1000 °c typical stack size 1kw-250kw 10-100kw 400w 300kw-3mw 1kw-2mw efficiency 60% (transportation) 35% (stationary) 60% 40% 50-60% 50-60% applications -backup power -portable power -distributed generation -transportation -specialty vehicle -military -space distributed generation -electric utility -distributed generation -auxiliary power -electric utility -distributed generation advantages -solid electrolyte reduce corrosion & electrolyte management problems -low temperature -quick start-up -cathode reaction faster in alkaline electrolyte, leads to high performance -low cost component -high temperature enable -increase tolerance to full impurities -high efficiency -fuel flexibility -can use variety of catalyst -suitable for chp -high efficiency -fuel flexibility -can use variety of catalyst -solid electrolyte -suitable for chp&chhp -hybrid/gt cycle challenges -expensive catalyst -sensitive to fuel impurities electrolyte management -pt catalyst -long start up time -high temperature corrosion and breakdown of cell components -long start up time -low power density high temperature corrosion and breakdown of cell components iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 73 2.2 transportation applications fuel cells could be used for many transportation applications, such as automobiles, buses, utility vehicles and scooters and bicycles. most automobile manufacturers have been developing fuel cell vehicles for at least a decade, and have demonstrated at least one prototype vehicle. the major reasons for developing automotive fuel cell technology are their efficiency, low or zero emissions, and fuel that could be reproduced from local sources rather than imported. some automobile manufacturers such as general motors, toyota, and honda are working on their own fuel cell technology. other automobile manufacturers such as ford, mazda, daimlerchrysler, mazda, hyundai, fiat, and volkswagen buy their fuel cells from fuel cell manufacturing companies. the types of fuel cells commonly used are the pemfc and the direct methanol fuel cell (dmfc). automotive fuel cells can have one or all of the following characteristics [11]: i) a fuel cell is sized to provide all of the power to a vehicle. a battery may be present for startup. ii) a fuel cell typically supplies a constant amount of power, so for vehicle acceleration and other power spikes, additional devices are typically switched on such as batteries, ultra or supercapacitors, and so on. iii) sometimes a fuel cell is used as the secondary power source. a system is set up where batteries power the vehicle, and the fuel cell just recharges the batteries when needed. iv) a fuel cell can run part or all of the vehicles electrical system. sometimes another engine is used for propulsion. 2.3 fuel cells selection for automotive application detailed study of different fuel cells characteristics helped us to select the correct type of fuel cell [12]. pemfc fuel cell shows the best characteristic to use in vehicle application [13]. the most important factors that make pemfc become the chosen fuel cell to be used in the prototype are [6]: a) high chemical stability: it is important in pem as the membrane plays the key role. if the polymer degrades, this will reduce the energy output of the fuel cell. if the membrane breaks, there will then be a path for the oxidant and the fuel to react directly. b) high proton conductivity: in the fuel cell, hydrogen ions must be able to easily reach the cathode and complete the electrochemical circuit. further, resistance (ohmic) polarization is a major contribution to voltage loss in the typical range of operating current densities. most of this resistance is due to resistance to ion flow in the membrane. the conductivity of a membrane is a function of the water content as well as the ion exchange capacity. c) low cost: apart from bi-polar plate material costs, nafiontm cost reduction is a major requirement of pemfc market penetration. it has been estimated that nafiontm will make up as much as 18 percent of the total cost of the cell. thus a lower cost material is desirable. d) thermal stability: it is referred to have a polymer membrane that is stable at higher temperature. if the polymer does not degrade at higher temperatures it will then become possible to operate the fuel cell at higher temperatures. currently pemfcs operate at 80 °c. at higher temperatures nafiontm becomes dehydrated and conductivity drops. a higher temperature would aid the kinetics of the cathode iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 74 reaction (which are current limiting), as well as reduce carbon monoxide poisoning of the anode catalyst. e) durability: apart from chemical and thermal stability, the membrane must be durable. a very strong material can allow for thinner membranes to be developed, which improve ion conductivity. more durable materials will also last longer. a criterion presented by reference sets the durability at 10 years for the pem. a separate durability criterion by the usdoe looks for durability of 5000 h for a 50 kw system used in a car. f) low expansion: with water uptake there is an inevitable expansion of the membrane. too much expansion of the membrane creates pressure on the bi-polar plates (which may consequently crack), and the plate may also buckle off which is detrimental for the fuel cell. 3. model car for investigation in this project we have assembled a fuel cell car prototype by implementing pem type of fuel cell as source of power to propel the prototype car. it has the capability to propel the electric motor by performing chemical reaction and converting chemical energy stored in hydrogen gas into useful electrical energy. in this fuel cell car prototype, pemfc alone is used as the power source to run the electric motor without any other power source [12]. 3.1 prototype selection the first step in developing the product was determining the type of the car. in this case, a remote control (rc) car model was chosen as the product. its movement can be controlled freely. there are different components in a rc car. the components are: chassis, suspension, drive train, tires, engine/motor, bearings, etc. 3.2 electric motor selection electric motor acts as an engine of the car substituting the internal combustion engine. there are several types of motors available in the market. to select the best suited motor for a rc car, it is essential to know the size of the model and amount of cells planned to be used. size of the rc vehicle will determine the size of motor needed to push the weight. for motors this is often best represented by the amount of weight of the motor itself. in this project, rs-540sh-6527 motor of capacity range 79 volt was chosen since it can propel the car with high speed and also can carry a load up to 4 kg. 3.3 fuel cell stack selection h-30 fcs-b30 pem fuel cell is selected to power the car model for its earlier mentioned advantages. range of voltage it produces must be equal or lower than that of the electric motor chosen to make the motor works in optimum performance and also to avoid overheating. if the voltage produced by fuel cell is lower than that needed by the motor, the motor will run slowly and not uniformly. this pem fuel cell can only stand for 0.5 bars. but hydrogen tank storage supplies the hydrogen at a pressure up to 10 bar. so to reduce this high pressure from hydrogen storage tank, a pressure regulator is used. 3.4 hydrogen storage tank selection in the development of fuel cell vehicles, hydrogen storage is the biggest remaining research problem according to the office of science and technology policy, executive office of the us president (january 2003). current hydrogen storage systems are inadequate to meet the needs of consumers in a fuel cell vehicle. existing and proposed technologies for hydrogen storage include (1) physical storage: pressurized tanks for gaseous hydrogen and pressurized cryo-tanks for liquid hydrogen; (2) reversible hydrogen iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 75 uptake in various metal-based compounds including hydrides, nitrides, and imides; (3) chemical storage in irreversible hydrogen carriers such as methanol; (4) cryo-adsorption with activated carbon as the most common adsorbent; and (5) advanced carbon materials absorption, including carbon nanotubes, alkali-doped carbon nanotubes, and graphite nanofibers. in this project, metal hydride hydrogen storage tank is used which is manufactured by horizon company called as hydrostiktm. metal hydride tank is a container loaded with hydrogen storage alloy powder, heat exchange parts, and gas transport components. the container body materials are generally aluminum alloy or stainless steel. hydrogen being stored at low pressure in the vessel, they provide a safe and reliable energy storage, particularly for portable applications, in-house and on-board storage. the weight is also low just 90g and can store about 10 l compressed hydrogen gas. 4. fuel cell car assembly figure 2 shows the model assembly based on material selection as mentioned above. fig. 2: final product, pem fuel cell car prototype. 5. results and discussion 5.1 experiment on pemfc performance experiments were carried out to detemine the performance of h30 pemfc. it was allowed to reach its maximum output before it was added to the fuel cell car prototype. besides that, the flowrate of hydrogen was measured to determine its consumption. progrmmable electronic load (e-load) machine model zvl300-150-40l was used to vary the load on the h30 pemfc. 5.1.1. experimental procedure 1 a) connect electric wire output of fuel cell to electrode of programmable electronic load machine. b) connect hydrogen supply to pressure regulator. c) setup the hydrogen supply to constant flow rate. d) record all the data obtain. e) plot the v vs i and p vs i graph. f) adjusting voltage by entering the value on the user panel button. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 76 5.1.2. result p = vi the power, p in the above equation is a function of time and is called the instantaneous power. thus the power absorbed or supplied by an element is the product of the voltage across the element and the current flow through it. if the power has a + sign, power is being delivered to be absorbed by the element. ohm’s law states that the voltage v across a resistor to be the resistance, r. (the resistance is a material property which can change if the internal or external conditions of the element are altered, e.g., if there are changes in the temperature). thus, v = ir for the first experiment, the current was set as a variable. the current was changed from the 1 a to 1.9 a. from the result, we got the high power as 13.448 w. for the second experiment, voltage was set as variable. the voltage was changed from 9.4 v to 7.5 v. this pemfc can supply until 9.4 v, even though the theoretical value is 8.4 v. the graph voltage versus current shows the voltage drops according to the current increase (fig. 3). this current shows the load applied to the pemfc. the capability of the pemfc will drop if the load applied to it is increased (fig. 4). fig. 3: voltage vs current plot. fig. 4: power vs current plot. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 77 5.1.3. experimental procedure 2 i) connect the flowmeter to the hydrogen supply system. ii) the output of flowmeter tube is connected to the fuel cell. iii) once fuel cell is running, collect the reading shown on the flowmeter. iv) take the reading every 1 min. v) compare the result with the supplier specification. fig. 5: h2 flow rate vs time plot. fig. 6: h2 flow rate vs voltage plot. figures 5 and 6 show that the flow rate of hydrogen does not change rapidly with the variation of voltage and time. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy mohiuddin et al. 78 6. conclusion pemfc powered vehicles could play a central role in future transportation systems. they produce only electricity, water and heat at the point of use. there has been great interest in hydrogen as a primary “energy carrier” displacing petroleum-based fuels. the present work shows the development of a prototype car powered by pem fuel cell. it shows the possibility to replace the conventional internal combustion engine with fuel cell. it is now a reality to think for fuel cell car though the present day technology it is little costlier. the performance of the fuel cell car prototype is interesting, eventhough it is not producing high performance but it produces zero emissions. futher research needs to be carried out to improve its performance. it is hoped that fuel cell vehicle will become the conventional vehicle in the future. it is because of their emissions that will cause no harm to the environment. the government should play an important role in the process of developing this zero emission vehicle. references [1] environmental protection agency (1991) office of air quality planning and standards. national air pollutant emissions estimates. epa-450/-4-91-004, research triangle park, north carolina, usa. [2] deluchi ma. (1991) emissions of greenhouse gases from the use of transportation fuels and electricity. anl/esd/tm-22, argonne national laboratory, argonne, illinois, usa. [3] buchner h, povet r. (1982) the daimler-benz hydride vehicle project. int j hydrogen energy, 7:259-266. [4] stewart wf. (1984) operating experience with a liquid hydrogen fueled buick and refueling system. int j hydrogen energy, 9:525-538. [5] grunenfelder nf, schucan t. (1989) seasonal storage of hydrogen in liquid organic hydrides: description of the second prototype vehicle. int j hydrogen energy, 14:579-586. [6] barbir f. (2005) pem fuel cells: theory and practice. elsevier academic press, new york. [7] devrim y, erkan s, bac n, eroglu i. (2009) preparation and characterization of sulfonated polysulfone/titanium dioxide composite membranes for proton exchange membrane fuel cells. int j hydrogen energy, 34:3467-3475. [8] zhang j, xie z, zhang j, tang y, song c, navessin t, et al. (2006) high temperature pem fuel cells. j power sources, 160:872-891. [9] yang c, costamagna p, srinivasan sj, benziger j, bocarsly ab. (2001) approaches and technical challenges to high temperature operation of proton exchange membrane fuel cells. j power sources, 103:1-9. [10] li x. (2006) principal of fuel cells. taylor & francis group, new york. [11] spiegel c. (2007) designing and building fuel cells. mcgraw-hill, new york. [12] mohiuddin akm, chemani mf, zakaria mb. (2014) design and investigation of a fuel cell car prototype. int. j. engineering systems modelling and simulation, 9 (¾):321-333. [13] thring rh. (2004) fuel cells for automotive applications. bury st edmunds, professional engineering pub. uk. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 177 detector response from thermal neutron activation of concealed explosives zafar ullah koreshi 1* and hamda khan 2 1 faculty of engineering, 2 faculty of basic and applied sciences, air university, islamabad 44000, pakistan. * corresponding author: zafar@mail.au.edu.pk (received: 18 th oct. 2016; accepted: 11 th feb. 2017; published on-line: 1 st dec. 2017) abstract: explosives concealed in small quatitites (~100 g), buried in landmines, or in baggage, can be detected by characteristic gamma rays produced by neutron activation. however, the detection response can be reduced by attenuation of the signal in the background medium. this paper carries out a monte carlo simulation, using mcnp5, to estimate the gamma signal spectrum and intesity degradation at a sodium iodide (nai) detector from a small sample of trinitrotoluene (tnt) explosive buried in limestone. it is found that the transmission across 25 cm of limestone is ~6% of the 2.2233 mev hydrogen signal and ~20% of the nitrogen signal. an empirical formula, obtained from mcnp re-runs, is used to estimate the signal strength from tnt, buried at 5-25 cm in limestone, for a californium source ( 252 cf) emitting 2.31 × 10 7 n/s. it is found that for tnt, mass in the range 0.1-3 kg, the signatures are in the range of 20-2000 s -1 from nitrogen and 24-2400 s -1 from hydrogen. these estimates can be used to determine the scanning time for an explosives detection system. abstrak: bahan letupan tersembunyi pada kuantiti sedikit (~100 g), yang ditanam di kawasan periuk api atau dalam beg, boleh dikesan melalui sinar gama yang dihasilkan melalui pengaktifan neutron. walau bagaimanapun, tindak balas yang dikesan dapat dikurangkan melalui pelemahan pada signal medium latar belakang. kertas ini mengguna pakai simulasi monte carlo, melalui mcnp5, bagi menganggarkan spektrum signal gama dan pengurangan keamatan pada pengesan sodium iodida (nai) daripada sedikit sampel bahan letupan trinitrotoluene (tnt) yang tertanam di lapangan periuk api. didapati penghantaran sejauh 25 cm pada batu kapur adalah ~6% pada signal hidrogen 2.2233 mev dan ~20% pada signal nitrogen. hasil formula empirik yang dijalankan semula keatas mcnp dan digunakan untuk menganggar kekuatan signal tnt, mendapati 5-25 cm telah tertanam dalam batu kapur, dengan punca kalifornium ( 252 cf) pada pengeluaran 2.31 x 10 7 n/s. berat tnt pada skala 0.1-3 kg, adalah sebanyak 202000 s -1 daripada nitrogen dan 24-2400 s -1 daripada hidrogen. anggaran ini boleh dipakai untuk memperolehi masa imbasan pada sistem pengesan bahan letupan. keywords: explosive detection; landmine detector; thermal neutron activation;monte carlo simulation; gamma signature 1. introduction with an estimated 110 million anti-personnel mines in about 70 countries [1,2], over 26,000 people are maimed or killed every year. it is thus both important and urgent to carry out studies which can lead to useful, efficient, field-portable systems. chemical iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 178 explosives, such as tnt and rdx, contain hydrogen (h), carbon (c), oxygen (o), and nitrogen (n) which can be identified along with their relative atomic compositions enabling identification using nuclear techniques such as fast neutron activation (fna) and thermal neutron activation (tna) [3]. such techniques have been under consideration since the 1960s [4-7] and explosives detection systems (eds) have been investigated and designed for detection of explosives concealed in vehicles [8], airport baggage [9], air cargo [10], land and sea containers [11, 12], as well as landmines [13-17]. landmine detection systems [18-28] are based on activation by sources such as 252 cf and use measurements of the 2.2233 mev and 10.829 mev gamma rays emitted from the h(n, ) and n(n, ) reactions respectively. some systems determine the c/o atom fraction with the 6.13 mev gamma-ray emitted in the reaction. typical capabilities include the identification of amounts as small as ~400 g of explosive in 10 minutes [22]. monte carlo simulation with mcnp [29] and experiments have been carried out [30-34] to optimize the performance of the neutron back-scattering technique (nbs) for a landmine system. typically, a californium 252 cf source emitting ~10 6 neutrons/s is needed for hand-held detection systems and ~10 7 neutrons/s for robotic detection systems. studies have also been carried out on the effects of source, moderator, and shielding [35-42]. another use of results from simulation has been in template-matching algorithms [43, 44] for efficient and fast matching of photon signatures from an interrogated volume. this work extends the previous works in this area which have been used to simulate neutron and gamma transport in landmine detection systems to estimate the signature quality for potential application in matching algorithms. a monte carlo simulation with mcnp5 [29] was carried out to determine the energy spectrum degradation and the reduction in intensity of gamma rays emitted from h(n, ) and n(n, ) reactions in soil consisting of limestone. from these estimates, and using proposed empirical formulae [45] the strength of the gamma-rays reaching the detectors was estimated. such information can be used to estimate the scanning time for field-portable landmine detection systems. 2. methodology and modeling monte carlo simulation was used to obtain fluxes and reaction rates in the explosive detection system, using the mcnp5 [29] to model a landmine detection system [45] shown in fig. 1 with physical data listed in table 1 and material composition in table 2. fig. 1: mcnp model of the landmine explosives detection system (scales in cm). iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 179 the neutron and photon fluxes and associated reaction rates from thermal neutron activation of a small (~ 200 g) sample of tnt were obtained. the system consisted of an anisotropic 252 cf source, labeled ‘s’, placed in a capsule in a moderator with the bf3 tubes, a sodium iodide (nai) detector, the soil, and the concealed sample. the ground considered was limestone ( g/cm 3 with composition of: c 12%, o 48% and ca 40%), which is common in many parts of the world. in a second model, a sphere of radius 25 cm of limestone with a point mono-energetic source at the origin is considered surrounded by sodium iodide detectors, as shown in fig. 2. table 1: physical data of the model source 252 cf linear moderator borated paraffin wax/water explosive trinitrotoluene (tnt) c6h2(no2)3ch3 photon detector sodium iodide (nai) radial moderator borated paraffin wax/water neutron detector bf3 gas detector cavity air/water/limestone table 2: composition of materials used (wi is the mass fraction) element and dry air: g/cm 3 0.75519 0.23179 0.00014 0.01288 borated paraffin wax: g/cm 3 0.14 0.83 0.01 0.02 limestone: g/cm 3 0.12 0.48 0.40 bf3: g/cm 3 0.143368 6.568e-3 0.850064 tnt: g/cm 3 0.022189 0.37016 0.185004 0.422648 fig. 2: gamma transport simulation model (s=source, d=detector, dimensions in cm) iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 180 a typical photon signal emanating from tnt, illustrating prominent h(n, ) and n(n, ) peaks, buried in limestone, is shown in fig. 3. it is the transport of these gamma rays which will be considered in the present work. fig. 3: typical signature from tnt explosive buried in limestone. based on the mcnp results for the model in fig. 1, a surface fitting of the gamma production in the buried tnt explosive was carried out to obtain an empirical formula of the form for the gamma production source term which is the reaction rate with units atom -1 cm -3 per source neutron. here, s is the neutron source strength (n/s), is the geometrical attenuation ⁄ , is the material attenuation and is a fitted function containing the burial depth d of explosive mass m. the fitted function is expressed as: ∑ , (i=1,2,3 and j=1,2,3) with coefficients listed in table 3. table 3: surface fitted coefficients for the gamma source from tnt explosive buried in a landmine. coefficient 1.962 × 10 -5 5.402 × 10 -6 7.851 × 10 -6 1.696 × 10 -6 9.949 × 10 -5 2.157 × 10 -5 -7.131 × 10 -7 -1.592 × 10 -7 -1.632 × 10 -6 -3.140 × 10 -7 -3.614 × 10 -5 -7.878 × 10 -6 1.569 × 10 -8 3.532 × 10 -9 -3.734 × 10 -8 -9.149 × 10 -9 9.013 × 10 -7 1.929 × 10 -7 1.951 × 10 -6 1.275 × 10 -7 2.1 energy spectrum degradation for photon transport in medium in order to estimate the quality of the transmitted signal, a monte carlo simulation is carried out for the gamma signatures from hydrogen and nitrogen shown in fig. 3. for detection of nitrogen in the signal, the 10.829 mev gamma ray is considered although its iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 181 intensity is ~47% relative to the 5.269 mev emission, but this is preferred in a counting system due to its high energy. the total intensity at a detector , located at a distance from the source, from both un-collided and collided rays, is written as a buildup factor [46] multiplied by the un-collided intensity. thus (1) while the intensity of the un-collided flux when a ray from the source, of intensity , reaches the detector after passing a thickness t of the medium is (2) where is the linear attenuation coefficient at source energy . there is a large body of data for point isotropic sources of photons in infinite homogenous media which accounts for compton-scattered and annihilation photons as well as for fluorescence and bremsstrahlung. a widely used form for the buildup factor is the geometric progress (gp) form: { (3) where ( ) in which the parameters depend on the gamma ray energy, the attenuating medium and the type of response. these are tabulated for attenuation in air, water, concrete, iron, and lead [46]. for this work, the mass attenuation coefficient ( ⁄ for limestone is calculated from the weight fractions (w) of c, o, and ca and the elemental coefficients [47] listed in table 4. from the elemental data, the mass attenuation coefficient of a compound such as limestone is given by ⁄ ∑ ( ⁄ ) (4) from which the intensity (eq. 2) can be calculated. table 4: mass attenuation coefficients for photons ⁄ (cm 2 /g) 2 mev 10 mev 15 mev carbon 0.12 4.442e-02 1.959e-02 1.698e-02 oxygen 0.48 4.459e-02 2.089e-02 1.866e-02 calcium 0.40 4.524e-02 2.839e-02 2.838e-02 iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 182 3. results the mcnp current tally, scoring the photon current leaving the sphere, is shown in figs. 4-6 for the total current and un-collided current of photons from hydrogen and neutron using third-order polynomials as fitting functions for 7 mc runs (at r= 2, 5, 10, 15, 20, 25, 30 cm). all simulations were carried out for 400,000 particles and used about 1 minute cpu time on intel(r) core(tm) i7-2620m cpu @ 2.70 ghz. fig. 4: photons from hydrogen transmitted versus sphere radius. figure 4 shows the total photon transmission and the un-collided (e> 2.2 mev) photon transmission, the ratios being the build-up b(r) described by eq. (1). these results can be used to obtain the coefficients in the gp form given by eq. (3). further, the excellent match of the mcnp f1 current tally estimates with the simple un-collided exponential attenuation modeled by eq. (2) is visible in figs. 4 and 5. fig. 5: photons from nitrogen transmitted as a function of the (limestone) sphere radius. 0 5 10 15 20 25 30 0 0.2 0.4 0.6 0.8 1 radius (cm) p h o to n s t ra n s m it te d mc: h fit: h mc: >2.2 mev fit: >2.2 mev exp 0 5 10 15 20 25 30 0 0.2 0.4 0.6 0.8 1 1.2 1.4 radius (cm) p h o to n s t ra n s m it te d mc: n fit: n mc: >10 mev fit: >10 mev exp iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 183 for a smaller sphere, the number of captures is much lower and consequently the photon creation by bremsstrahlung and fluorescence is also much less. however, these additional photons escape from the sphere and hence the transmitted number exceeds the number of source photons. it is also seen that the ‘un-collided’ signal (e> 2.22 mev) decreases exponentially with distance while the total signal falls off almost linearly. fig. 6: photon transmission (2.2233 mev: h and 10.8 mev: n). figure 6 shows that the more energetic 10.829 mev gammas from nitrogen have a much higher transmission across limestone. thus, while the reaction rate for the radiative capture reaction is much higher for h(n, ) reactions, the transmission balances out the signatures. fig. 7: energy spectrum of 2.2233 mev photons leaving the medium. 0 5 10 15 20 25 30 0 0.2 0.4 0.6 0.8 1 1.2 1.4 radius (cm) p h o to n s t ra n s m it te d n total h total n > 10.0 mev h > 2.22 mev 0 0.5 1 1.5 2 2.5 0.01 0.02 0.03 0.04 0.05 0.06 energy (mev) p h o to n s iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 184 figure 7 shows the energy spectrum of the 2.2233 mev photons leaving the limestone sphere. it is worth noting that only about 5.8% of the photons have source energy (about 8% e> 2 mev) while about 29.2% of the gammas leave the sphere. the degradation of the spectrum is thus over 90%. fig. 8: energy spectrum of 10.8 mev photons leaving medium. figure 8 shows the energy spectrum of the 10.8 mev photons leaving the limestone sphere. it is worth noting that only about 21.3% of the photons have source energy. the degradation of the spectrum is thus about 79%. fig. 9: photons from 10.8 mev point source crossing detector; mc results compared with solid angle estimate. figure 9 shows the mc results for photons crossing the 3.5 cm radius detector cylinder after passing through a 25 cm radius limestone sphere. each simulation was carried out for 400,000 particles and took approximately 1.4 minutes. the fraction crossing the limestone sphere was 0.658043 with a relative error of 0.0016. 0 2 4 6 8 10 12 -0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 energy (mev) p h o to n s 26 28 30 32 34 36 38 40 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 x 10 -3 detector distance (cm) p h o to n s mc f1(1) d/4 iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 185 now, using the empirical form for the gamma production and a source strength of the order of 10 7 n/s, the total gamma source in the concealed explosive for mass in the range of 0.1 3.2 kg at depths 5-25 cm, ranges from 100 – 10,000 photons/s from nitrogen and 400 40,000 photons/s from hydrogen [45]. using results from figs. 4 and 5, we have seen that only ~6% of the 2.2233 mev and ~20% of the 10.8 mev signals leave the ground. it is thus estimated that the hydrogen and nitrogen signatures are down to very low values e.g. 20–2000 s -1 from nitrogen and 24–2400 s -1 from hydrogen respectively (for the mass range 0.1–3 kg). thus, for efficient scanning, the scan time must be increased to match the resolution of the hardware. fig. 10: gamma production/transmission rate from radiative capture in the explosive. the gamma production and transmission rates for both h and n from 1 kg of tnt in limestone are shown in fig. 10 for a source strength of 2.31 10 7 n/s. this would be an estimate for the ‘un-collided’ signals leaving the medium. the detector signal would subsequently be obtained by multiplying the above by the solid angle subtended by the detector. 4. conclusions the main conclusions from this monte carlo simulation carried out for the landmine detection system based on neutron backscattering are  the energy spectrum is considerably attenuated and degraded with the depth of concealment in limestone in both hydrogen and nitrogen with only ~6% of the hydrogen signature and ~20% of the nitrogen signature being available for detection when the depth of concealment is 25 cm.  to effectively detect and characterize a concealed explosive in limestone, the scanning time can be estimated by matching the signature counts with the hardware. 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 3 3.5 x 10 4 depth (cm)  p ro d u c e d /t ra n s m it te d ( s1 ) mass = 1 kgp (h)  tr (2.2233 mev)  p (n)  tr (10.829 mev) iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 186 references [1] united nations, global issues, http://www.un.org/en/globalissues/demining/ last accessed 17 september 2016 [2] walsh ne, walsh ws. (2003) rehabilitation of landmine victims – the ultimate challenge, bulletin of the world health organization. 81(9):665-670. [3] gozani t. (2004) the role of neutron based inspection techniques in the post 9/11/01 era. nucl. instrum. methods phys. res. b. 213:460–463. [4] jordan ed. (1964) detecting hidden explosives using neutron beams patent no. us 3146349 a, aug 25, 1964. [5] bartko j. (1974) nuclear techniques for detecting the presence of explosives, patent no. us 3832545 a aug 27, 1974. https://www.google.com/patents/us3832545 [6] ettinger kv, brondo jh jr. (1989) detection of nitrogen in explosives, patent no. us 4851687 a, jul 25, 1989. https://www.google.com/patents/us4851687 [7] grenier g, coursant rh, rambaut m. (1992) apparatus for the detection of substances and in particular explosives by neutron irradiation thereof, patent no. us 5080856 a, jan 14, 1992. [8] koltick d, kim y, mcconchie s, novikov i, belbot m, gardner g. (2007) a neutron based vehicle-borne improvised explosive device detection system. nucl. instrum. methods phys. res. b 261:277-280. [9] gokhale pp, hussein ema. (1997) a 252 cf neutron transmission technique for bulk detection of explosives. appl radiat isot, 48:973-979. [10] runkle rc, white ta, miller ea, caggiano ja, collins ba. (2009) photon and neutron interrogation techniques for chemical explosives detection in air cargo: a critical review. nucl instrum methods phys res a. 603:510-528. [11] lehnert al, kearfott kj. (2015) a flag-based algorithm and associated neutron interrogation system for the detection of explosives in sea–land cargo containers. radiat phys chem, 112:13-21. [12] heider sa, dunn wl. (2015) a simulation study of fast neutron interrogation for standoff detection of improvised explosive devices. radiation physics and chemistry. 116:341–344, proceedings of the 9 th international topical meeting on industrial radiation and radioisotope measurement applications. [13] hussein ema, waller ej. (2000) landmine detection: the problem and the challenge. appl radiat isot, 53:557-563. [14] buffler a. (2004) contraband detection with fast neutrons. radiation physics and chemistry, 71(3-4):853–861. [15] kuznetsov av, osetrov p, stancl m (2006). detection of improvised explosives (ie) and explosive devices (ied) in detection and disposal of improvised explosives, h. schubert and a. kuznetsov, springer, netherlands, 7-25. [16] lanza rc. (2007) neutron techniques for detection of explosives in “counterterrorist detection techniques of explosives,” yinon, j., elsevier b.v., netherlands, 131-155. [17] whetstone zd, kearfott kj. (2014) a review of conventional explosives detection using active neutron interrogation. j radio nuc chem, 301:629-639. [18] viesti g, cinausero m, cufaro-petroni n, d’erasmo g, fabris d, fioretto e, r, lunardon m, lazzizzera i, nardelli g, nardulli g, nebbia g, palomba m, pantaleo a, pappalardo l, pesente s, prati p, prete g, reito s, sartori a, tecchiolli g, zavatarelli s, filippini v. (1999) the explodet project: advanced nuclear techniques for humanitarian demining. nucl instrum methods phys res a, 422:918-921. [19] viesti g, lunardon m, nebbia g, barbui m, cinausero m, d’erasmo g, palomba m, pantaleo a, obhođaš j, valković v. (2006) the detection of landmines by neutron backscattering: exploring the limits of the technique. appl radiat isot, 64:706-716. [20] cinausero m, lunardon m, nebbia g, pesente s, viesti g, filippini v. (2004) development of a thermal neutron sensor for humanitarian demining. appl radiat isot, 61:59-66. http://www.sciencedirect.com/science/article/pii/s0168583x03015908 http://www.sciencedirect.com/science/journal/0168583x/213/supp/c https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=ininventor:%22kamil+v.+ettinger%22 https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=ininventor:%22joseph+h.+brondo,+jr.%22 https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=ininventor:%22gerard+grenier%22 https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=ininventor:%22roger+h.+coursant%22 https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=ininventor:%22michel+rambaut%22 http://www.sciencedirect.com/science/article/pii/s0969804397000286 http://www.sciencedirect.com/science/article/pii/s0969804397000286 http://www.sciencedirect.com/science/journal/09698043 http://www.sciencedirect.com/science/journal/09698043 http://www.sciencedirect.com/science/article/pii/s0969806x15000808 http://www.sciencedirect.com/science/article/pii/s0969806x15000808 http://www.sciencedirect.com/science/journal/0969806x http://www.sciencedirect.com/science/journal/0969806x http://www.sciencedirect.com/science/journal/0969806x/112/supp/c http://www.sciencedirect.com/science/article/pii/s0969806x15001516 http://www.sciencedirect.com/science/article/pii/s0969806x15001516 http://www.sciencedirect.com/science/journal/0969806x http://www.sciencedirect.com/science/journal/0969806x/116/supp/c http://www.sciencedirect.com/science/article/pii/s0969804300002189 http://www.sciencedirect.com/science/article/pii/s0969806x04003068 http://www.sciencedirect.com/science/journal/0969806x http://www.sciencedirect.com/science/journal/0969806x http://www.sciencedirect.com/science/journal/0969806x/71/3 http://www.sciencedirect.com/science/article/pii/s0969804306000029 http://www.sciencedirect.com/science/article/pii/s0969804306000029 http://www.sciencedirect.com/science/article/pii/s096980430400082x iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 187 [21] csikai j, dóczi r, király b. (2004) investigations on landmine detection by neutron-based techniques. appl radiat isot, 61:11-20. [22] kuznetsov av, evsenin av, gorshkov iy, osetrov oi, vakhtin dn. (2004) detection of buried explosives using portable neutron sources with nanosecond timing. appl radiat isot, 61:51-57. [23] lunardon m, nebbia g, pesente s, viesti g, barbui m, cinausero m, d’erasmo g, palomba m, pantaleo a, filippini a. (2004) detection of landmines by using 14 mev neutron tagged beams. appl radiat isot, 61:43-49. [24] brooks fd, drosg m, buffler a, allie ms. (2004) detection of anti-personnel landmines by neutron scattering and attenuation. appl radiat isot, 61:27-34. [25] brooks fd and drosg m. (2005) the hydad-d antipersonnel landmine detector. appl radiat isot, 63:565-674. [26] takahashi y, misawa t, masuda k, yoshikawa k, takamatsu t, yamauchi k, yagi t, pyeon ch, shiroya s. (2010) development of landmine detection system based on the measurement of radiation from landmines. appl radiat isot, 68:2327-2334. [27] takahashi y, misawa t, pyeon ch, shiroya s, yoshikawa k. (2011) landmine detection method combined with backscattering neutrons and capture γ-rays from hydrogen. appl radiat isot, 69:1027-1032. [28] bergaoui a, reguigui n, gary ck, brown c, cremer jt, vainionpaa jh, piestrup ma. (2014) monte carlo simulation of explosive detection system based on a deuterium– deuterium (d–d) neutron generator. appl radiat isot, 94:118-124. [29] girard sm, shinn jb (2003) mcnp – a general monte carlo n-particle transport code, version 5, la-ur-03-1987, los alamos national laboratory, los alamos, nm. [30] maučec m and de meijer rj (2002) monte carlo simulations as a feasibility tool for nonmetallic land-mine detection by thermal-neutron backscattering. appl radiat isot, 56:837846. [31] mauc ec m, rigollet, c.(2004) monte carlo simulations to advance characterisation of landmines by pulsed fast/thermal neutron analysis. appl radiat isot, 61:35-42. [32] perot b, carasco c, bernard s, mariani a, szabo jl, sannie g, valkovic v, sudac d, viesti g, lunardon m., botosso c, nebbia g, pesente s, moretto s, zenoni a, donzella a, moszynski m, gierlik m, klamra w, tourneur pl, lhuissier m, colonna a, tintori c, peerani p, sequeira v, salvato m. (2008) measurement of 14 mev neutron-induced prompt gamma-ray spectra from 15 elements found in cargo containers. appl radiat isot, 66:421434. [33] uchai w, changkian s, zhu l, sun h. (2008) experiment on the performance of the neutron based explosives detection system using 252cf. suranaree j. sci. tech. 15:139147. [34] elsheikh n, viesti g, elagib i, habbani f. (2012) on the use of a (252cf–3he) assembly for landmine detection by the neutron back-scattering method. appl radiat isot, 70:643-649. [35] baysoy dy, subasi m. (2013) numerical evaluation of a landmine detection system based on the neutron back scattering technique. academic journals, 8:1424-1430. [36] hernández-adame pl, castro dm, rodriguez-ibarra jl, luevano mas, carrillo hrv. (2016) design of an explosive detection system using monte carlo method. appl radiat isot, available online 13 april 2016 [37] http://www.sciencedirect.com/science/article/pii/s0969804316301324 [38] elagib i, elsheikh n, alsewaidan h, habbani f. (2009) monte-carlo simulations of elastically backscattered neutrons from hidden explosives using three different neutron sources. appl radiat isot, 67: 39-45. [39] castro va, cavalieri ta, siqueira ptd, fedorenko gg, coelho prp, filho tm. (2011) mcnp simulation to study the bf3 detection efficiency, 2011 international nuclear atlantic conference – inac 2011 belo horizonte, m. g., brazil, october 24-28, 2011 associação brasileira de energia nuclearaben isbn:978-85-99141-04-5. [40] miri-hakimabad h, vejdani-noghreiyan a, panjeh h. (2008) improving the moderator geometry of an anti-personnel landmine detection system. appl radiat isot, 66:606-611. http://www.sciencedirect.com/science/article/pii/s0969804304000764 http://www.sciencedirect.com/science/article/pii/s0969804304000764 http://www.sciencedirect.com/science/article/pii/s0969804304000818 http://www.sciencedirect.com/science/article/pii/s0969804304000818 http://www.sciencedirect.com/science/article/pii/s0969804304000806 http://www.sciencedirect.com/science/article/pii/s0969804304000806 http://www.sciencedirect.com/science/article/pii/s0969804304000788 http://www.sciencedirect.com/science/article/pii/s0969804304000788 http://www.sciencedirect.com/science/article/pii/s0969804310001430 http://www.sciencedirect.com/science/article/pii/s0969804310001430 http://www.sciencedirect.com/science/article/pii/s0969804311000108 http://www.sciencedirect.com/science/article/pii/s0969804311000108 http://www.sciencedirect.com/science/article/pii/s0969804314002899 http://www.sciencedirect.com/science/article/pii/s0969804314002899 http://www.sciencedirect.com/science/article/pii/s0969804302000647 http://www.sciencedirect.com/science/article/pii/s0969804302000647 http://www.sciencedirect.com/science/article/pii/s096980430400079x http://www.sciencedirect.com/science/article/pii/s096980430400079x http://www.sciencedirect.com/science/article/pii/s096980430700379x http://www.sciencedirect.com/science/article/pii/s096980430700379x http://www.sciencedirect.com/science/article/pii/s096980430700379x http://www.sciencedirect.com/science/article/pii/s096980430700379x http://www.sciencedirect.com/science/article/pii/s096980430700379x http://www.sciencedirect.com/science/article/pii/s096980431200005x http://www.sciencedirect.com/science/article/pii/s096980431200005x http://www.sciencedirect.com/science/article/pii/s0969804316301324 http://www.sciencedirect.com/science/article/pii/s0969804316301324 http://www.sciencedirect.com/science/article/pii/s0969804316301324 http://www.sciencedirect.com/science/article/pii/s0969804316301324 http://www.sciencedirect.com/science/article/pii/s0969804316301324 http://www.sciencedirect.com/science/journal/09698043 http://www.sciencedirect.com/science/journal/09698043 http://www.sciencedirect.com/science/article/pii/s0969804308003722 http://www.sciencedirect.com/science/article/pii/s0969804308003722 http://www.sciencedirect.com/science/article/pii/s0969804308003722 iium engineering journal, vol. 18, no. 2, 2017 koreshi and khan 188 [41] metwally wa. (2015) multi-parameter optimization of a neutron backscattering landmine detection system, appl radiat isot, 105: 290-293. [42] koreshi z, khan h. (2016) optimization of moderator design for explosive detection by thermal neutron activation (tna) using a genetic algorithm, j nuc eng rad sci, 2: 031018. [43] ochbelagh rd, miri-hakimabad h, izadi-najafabadi r. (2007) the effect of source shield on landmine detection. iran j radiat res, 4:183-186. [44] loschke kw, dunn wi. (2010) detection of chemical explosives using multiple photon signatures. appl radiat isot, 68:884-887. [45] brewer rl, dunn wl, heider s, matthew c, yang x. (2012) the signature-based radiationscanning approach to standoff detection of improvised explosive devices, appl radiat isot, 70:1181-1185. [46] khan h, koreshi z, yaqub m (2017) design sensitivity studies of a landmine explosive detection system based on neutron backscattering using monte carlo simulation, nucl tech rad prot, xxxii:37-43. [47] cacuci dg. (2000) nuclear engineering handbook, springer. [48] national institute of standards and technology, u.s. department of commerce (nist), 2016. http://physics.nist.gov/physrefdata/xraymasscoef/tab3.html nomenclature n neutron w mass fraction b build-up factor cf californium 252 e energy i intensity m mass s source i) greek letters linear attenuation coefficient  gamma ray density ii) subscript 0 uncollided iii) superscript s scattered (collided) application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 system of automatic control of the level of steam power generators on the basis of the regulation circuit with smoothing of the signal umurzakova dilnoza maxamadjonovna* department of information processing systems and management, tashkent state technical university, 100097 tashkent, uzbekistan corresponding author: umurzakovadilnoz@gmail.com (received: 25th march 2020; accepted: 3rd september 2020; published on-line: 4th january 2021) abstract: the purpose of this article is to develop high-quality combined automatic control systems (acs) for the water level in the drum of steam boilers of thermal power plants (tpps), which can significantly improve the quality of regulation and increase the efficiency of tpps in a wide range of load changes. to improve the quality of water level control in the drum of steam generators of nuclear power plants with a pressurized watercooled power reactor (pwpr), it is proposed to use a combined automatic control system based on a control loop with a correcting pi-controller tuned to a symmetrical optimum, with smoothing the reference signal and device compensation of the most dangerous internal and external measurable disturbances. a technique has been developed for assessing the impact of changes in the quality characteristics of transients of combined self-propelled guns by the water level in the drum of steam boilers and steam generators on the safety, reliability, durability, and efficiency of thermal power equipment of thermal power plants. comparison was made of direct indicators of the quality of three acs (typical and three-pulse, digital system with an observer state, and the proposed combined acs). the simulation results of transients of the proposed and typical three-pulse selfpropelled guns confirmed the advantages of the first. abstrak: artikel ini bertujuan bagi membina sistem kombinasi automatik (acs) berkualiti tinggi bagi aras air dalam drum dandang stim tenaga terma logi kuasa (tpp). ini dapat meningkatkan mutu peraturan dan meningkatkan kecekapan tpp secara signifikan dengan pelbagai perubahan beban. bagi meningkatkan kualiti kawalan aras air dalam drum penjana wap loji kuasa tenaga nuklear dengan reaktor berpendingin air bertekanan (pwpr). gabungan sistem kawalan automatik berdasarkan gelung kawalan dengan pembetulan pi telah dicadangkan dan diselaraskan simetri secara optimum, dengan melancarkan isyarat rujukan dan pembetulan peranti dari gangguan yang boleh diukur dari dalam dan luar. satu teknik telah dibina bagi menilai kesan perubahan ciri kualiti transien gabungan berjentera pada aras air di tong dandang stim dan drum penjana wap pada keselamatan, kebolehpercayaan, ketahanan dan kecekapan peralatan tenaga terma loji janakuasa. perbandingan dibuat pada kualiti tiga acs (sistem digital khas dan tiga signal dengan keadaan pemerhati dan gabungan acs yang dicadangkan). hasil sistem simulasi transien yang dicadangkan dan tiga signal biasa berjentera mengesahkan kelebihan pada yang pertama. keywords: combined automatic control system; steam boiler drum; steam generator; controller; adaptive system; heat power industry 287 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 1. introduction currently widespread in the field of automation, heat and power processes in thermal and nuclear power plants (tpps and npps) received standard three-pulse automatic control systems (acs). as a result of their wide distribution, the problem of “technical contradiction” arises between the speed and stability of the system. the existing acs with the water level in the boiler drum and their modifications, which have become widespread at tpps and npps, but significant load changes turned out to be insufficiently effective. an increase in the steam production of boilers, the parameters of superheated steam at the outlet of the latter, as well as the need for boilers to operate in the peak and half-peak parts of the electrical loads of the power system, actualizes the problem of a significant increase in the quality of water level control in the drum in the entire range of load variation of heat power facilities during deep disturbances. a comparison of steam production technologies at tpps and npps shows that they are similar to each other: in essence, the difference is that the reactor and the primary circuit take on the role of the furnace in the boiler of tpps at nuclear power plants. therefore, the schemes for automatic control and regulation of nuclear power units in general coincide with the schemes for regulating power units of tpps. the similarity of steam and electricity production technologies at tpps and npps leads to the similarity of their automatic control and regulation schemes. one of the main acs of nuclear power plants that determine the safety and reliability of power units is self-propelled guns for the water level in the drum of the steam generator. despite attempts to use single-pulse level control systems in the drum of a steam generator of nuclear power plants [1], typical three-pulse self-propelled guns have currently gained maximum popularity at thermal power plants and nuclear power plants, which cannot provide the required quality level maintenance in the drum under deep load changes [2]. to eliminate this drawback, it is proposed to use a combined self-propelled gun for objects without self-leveling with the allocation of an equivalent external disturbance [3], which is characterized by increased fluctuations in the flow rate of feed water when disturbed by the steam flow. in [4], it was proposed to use combined self-propelled guns with a limitation of the maximum value of the corrective action at the output of the equivalent external disturbance compensation device. steam generators of npp with pressurized water power reactor (pwpr) are complex control objects, on the reliable operation of which safety depends and the reliability of the entire power plant. the main controllable parameter in the steam generator (sg) is the water level, which is subject to rigid requirements. inaccurate maintenance of the water level in the steam generator drum leads to an increase in humidity steam, increases the wear of the turbine blade and reduces the power of the power unit. the control of the water level in the drums of boilers of tpp and sg of npp is carried out by three-pulse acs [5,6]. 2. research methods a typical three-pulse acs with the water level in the boiler drum has the following disadvantages: • the presence of a static control error at the end of the transient process, first of all, when there is an external disturbance by the steam flow with the phenomenon of “level swelling”; 288 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 • the presence of three measurement sensors (level, steam, and feed water consumption); • large deviations of the water level in the boiler drum beyond the established limits with large load changes, which lead to the boiler shutdown by protection in case of overflow. fig. 1: typical three-pulse acs with water level in the drum: 1 boiler drum; 2 water economizer; 3 controller; 4 regulating feed valve; mcd manual control dial; h level water; fw d consumption of feed water; ss d superheated steam flow rate. the specified acs under deep disturbances in the system does not provide the required quality regulation, which leads to unloading or shutdown of the power unit and economic losses [7]. to improve the quality of the control of the steam generator pgv-1000 level at npp with pwpr a digital pi controller with one water level instead of three in the standard acs, which ensures an improvement in the quality of control in the case of external and internal disturbances in comparison with the typical system [8]. in this regard, the task of further improving the quality of comparison with the optimal acs with a state observer is based on express methods of structural and parametric optimization of dynamic systems of heat and power processes of npp and tpp with using the principles of the theory of invariance [9]. one of the implementation options for such systems is shown in fig. 2 [10]. fig. 2: scheme of implementation of the combined acs by the water level in the boiler drum. 289 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 the specified combined acs with the extraction of an equivalent external disturbance provides a decrease in the maximum dynamic error of regulation by the water level in the drum under external disturbance with steam consumption by 36% compared to a typical acs with differentiator. in this case, the time for working out the disturbance with the steam consumption is 200 s. to further improve the quality of maintaining the water level in steam generators of tpps based on standard controllers, it is proposed to use self-propelled guns based on a control loop with reference signal smoothing (fig. 3). designations adopted in fig. 3: ( )ty , ( )ty 1 respectively, the main (water level in the drum) and intermediate (feed water flow) controlled values; 1st x , 2st x assignment of intermediate and main controlled quantities; s st x 2 smoothed setpoint to the correction knob; ( )txc , ( )txr corrective and control effects; 1 f , 2 f internal and external disturbances; le k coefficient transmission; s e 1 − pure lag; transfer functions: ( )swle leading site of the object; ( )sw1 inertial section of the object; ( ) ( )swsw 32 − the difference between the inertial link and the ideal integrating link, which describes the dynamics of the phenomenon of “swelling” of the water level with increasing steam flow from the steam generator; ( )sw f cd 1 , ( )sw f cd 2 compensation devices for measured internal and external disturbances. fig. 3: structural diagram of the combined pgv-1000 steam generator automatic level control system with a correcting pi controller tuned to a symmetrical optimum, with a smoothing of the reference signal. the numerical values of the transfer functions developed by the combined acs of the level of the steam generator pgv-1000 tpp with wwpr-1000 are shown in the structural diagram of the simulation in fig. 4. 290 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 fig. 4: transient simulation modeling of combined acs with a water level in the pgv-1000 drum with a pi controller tuned to a symmetric optimum with smoothing of the reference signal. the following notation of transfer functions is accepted here: leading section: ( ) ; 15 2,1 1 + = + = ssт k sw le le le (1) inertial section: ( ) ( ) ; 3,30 19 0 11 1 s e eswsw s s − − ==  (2) inertial link of the first order: ( ) ; 120 038,0 1 2 2 2 + = + = ssт k sw (3) ideal integrating link: ( ) ; 67 1 3 2 3 ssт k sw == (4) stabilizing pi controller: ( ) ( ) ( ) ; 5 1583,01 1 11 1 s s sт stk sw i i c + = + = (5) corrective pi controller: ( ) ( ) ( ) ; 76 176797,01 2 22 2 s s sт stk sw i i c + = + = (6) smoothing filter: ( ) ( )( ) , 106,773,80 1381444 114 124 2 2 21 1 22 1 ++ ++ = ++ ++ = ss ss sts ss sw st f   (7) 291 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 where 2st t a dynamic tuning parameter aligning the order of the numerator and denominator of the filter transfer function; compensation devices for measured internal disturbance ( ) ; 15 52,1 1 1 111 +  = + = s s sт sтk sw d ddf cd (8) compensation devices for measured extreme external disturbance by steam flow: ( ) ( ) ( )  , 1064,1 3,30 67 1 120 038,0 1 3 1 32 2 +        − + = + −= s s ssst st swswsw st f cd (9) where 3st t a dynamic tuning parameter aligning the order of the numerator and denominator of the transfer differentiator of the device for compensating extreme external disturbances by the steam flow rate. it is required to form such an acs structure, which significantly (at times) will reduce the maximum permissible level control error when disturbed by the steam flow compared to a typical three-pulse aсs, to achieve complete invariance when working out the most dangerous measured internal disturbance, and also to eliminate large overshoot (up to 43.4%) when working out the jump in task 2st x , inherent acs with a correcting pi controller tuned to a symmetrical optimum [11]. in order to form the aсs structure that satisfies the given requirements, we will start by choosing the stabilization structure of the controller as the product of the inverse transfer function of the leading section and the transfer function of the open system in the form of an ideal integrating link taking into account (1) [12]: ( ) ( )  ( )( ) ( ) , 5 15 83,0 52,1 151 1 1 1 1 1 s s s s sтk st swswsw stle lenos stler + =  + = + == =− (10) where lest тt =1 parameter of dynamic adjustment of the stabilizing controller. in this case, the internal circuit of the system with a stabilizing controller during the completion of task 1st x can be replaced by a first-order inertial unit that plays the role of a quality criterion: ( ) . 1 1 1 1 + = st sw st st (11) if between the output of the correction and the input of the stabilizing controllers there is an amplifier with the transmission coefficient leam kk = , then the corrective action ( )txc will be equal to the regulating ( )tx r . as a result, the dual-circuit system turns into a singleloop system with a correcting controller and an inertial section of the object (2). if, at the same time, we select and measure the most dangerous internal disturbance 1 f using an additional sensor, the output of which is connected to the input of the compensation device for this disturbance, then the acs will have complete invariance with respect to 1 f if the following condition is satisfied [13]: ( ) ( ) .1 1 1 = swsw r f cd (12) 292 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 from where, taking into account (5), we obtain the transfer function of the compensation device for the measured internal disturbance in the form of a real differentiator: ( ) ( ) ( ) . 1 1 11 1 1 1 + == stk st sw sw ir i r f cd (13) for high-quality testing of internal unmeasured disturbances, the dynamic adjustment of the correcting pi controller should be performed at a symmetrical optimum with respect to the transfer function of the object (2) [14]: .764 12 st i ==  (14) .797,0 192 3,30 2 1 1 2 =  ==  in r k k (15) at the same time, with the high-quality processing of internal disturbances, the graph of the transition characteristic for the water level in the drum of the steam generator in relation to the task at the entrance to the correcting controller will have the following direct quality indicators: the first time of regulation st r 9,58191,33 11 ===  ; time of final entry into the tolerance band ± 2% st r 313195,16 2 == ; the maximum overshoot in this case will be 43.4% [15]. to eliminate overshoot and improve system performance when working out a task, a smoothing filter with a transfer function of this form is installed between the setter and the correction controller ( ) ( )( ) , 106,773,80 1381444 114 124 2 2 21 1 22 1 ++ ++ = ++ ++ = ss ss sts ss sw st f   (16) where 2st t a dynamic filter setting parameter that aligns the order of the numerator and denominator of the filter transfer function (16), with a decrease in the numerical value which increases the acs speed during mining 2st x . to improve the quality of working out extreme external disturbances during a planned change in the load of the power unit, we measure the steam flow rate with an additional sensor, the output of which is fed to the input of the external disturbance compensation device, the dynamics of which is described by the transfer function ( )sw f cd 2 . the output of the compensation device through the amplifying link le k is connected to the input of the stabilizing controller with the opposite sign. as a result, the invariance condition with a planned change in the load ( )ty with respect to the measured external disturbance takes the following form [16, 17]: ( ) ( ) ( ) ( )  .112 32 0 1 ssf cd eswsweswsw  −− −= (17) here, the delay link in the right-hand side of equality (17) is implemented programmatically in the automatic unit power generator, which, with a planned daily change in load, first generates the corresponding signal at the input to the external disturbance compensation device, and after the control action reaches the system output at time 1 =t , the power unit automatically switches to a different load level. in this case, the numerical value of 1  is adjusted as a function of the load of the power unit [18]. 293 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 taking into account (2) and (17), the transfer function of the external disturbance compensation device, as well as the physical implementation condition, will take ( ) ( ) ( )  , 1 3 1 32 2 + −= st st swswsw st f cd (18) where 3st t a parameter of dynamic adjustment of an external disturbance compensation device aligning the order of the numerator and denominator of the transfer function of the differentiator. 3. results and discussion transient graphs combined by an aсs combined with the water level in the pgv-1000 drum with a pi controller tuned to a symmetrical optimum under basic influences confirming the achievement of specified requirements are shown in fig. 5. fig. 5: graphs of transient processes of combined acs with the water level in the pgv-1000 drum with the adjustment controller set to a symmetric optimum: a testing the jump of the setting action 2st x ; b development of internal disturbance 1 f ; c development of external disturbance by steam flow * 2 f ; d changes in the control action ( )tx r during the development of an external disturbance by the steam flow rate; t is time. three combined aсs of the water level in the drum of the pgv-1000 steam generator for a planned load change and complete invariance with respect to the most dangerous internal disturbance with the measurement of the external disturbance by the steam flow 294 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 rate: aсs using the main feedback compensator during the processing of the driving signal, have been developed for steam generators of power units of pwpr tpps with pwpr; aсs with smoothing the reference signal and using a pi controller tuned to a symmetric optimum (so); acs based on optimal controllers. in these acss, the structure and dynamic settings of the stabilizing controllers due to the additional amplifier at the output of the correcting controller ensure the equality of the correcting ( )txc and control ( )txr actions, as well as the complete invariance of the development of internal perturbations and invariance accurate to  when working out external perturbations by the steam flow rate. direct indicators of the quality of transients of the two proposed acss in comparison with a typical three-pulse acs and digital acs with a state observer are shown in table 1. table 1: quality indicators of transients of the compared aсs name of acs quality indicators n yy bh str , m r x typical three-pulse aсs 0,034 83,6 160 0,454 digital aсs with state observer 0,031 76,0 130 +0,61 combined aсs with signal smoothing and the use of a pi controller (so) 0,016 41,0 200 +0,46 combined aсs based on optimal controllers 0,024 61,5 75 +0,475 from the analysis of the data in table 1 it follows that the proposed combined acs provides the best direct quality indicators in relation to a typical three-pulse acs, and digital acs with a state observer. the following notation has been adopted here: n yy the relative deviation of the water level in the drum from the nominal; bh absolute deviation of water level 13; r t regulation time; m r x the maximum value of the control impact. 4. conclusion the results of this research made it possible to formulate the following practical recommendations for improving the quality of drum water level control in steam boilers and steam generators: • refinement of task 2st x is carried out without overshoot. the control time is 200 s instead of 313 s without a smoothing filter. • when working out the measured internal disturbance, the complete invariance of the aсs is achieved. • the maximum dynamic level deviation in a combined acs using a pi controller tuned to a symmetrical optimum is 0.016 relative units, which corresponds to 41 mm of water, which is 2 times less than in a typical three-pulse acs. • the maximum change in the controller action in the combined acs decreased by 22.1% compared to the acs with a state observer 295 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 • the mathematical model for assessing the quality of acs transient processes the water level for partial and complete load shedding of the boiler can be used to clarify the settings for the operation of technological protections without carrying out field tests of the systems. references [1] siddikov ix, umurzakova dm, bakhrieva ha. (2020) adaptive system of fuzzy-logical regulation by temperature mode of a drum boiler. iium engineering journal, 21(1): 185192. https://doi.org/10.31436/iiumej.v21i1.1220. [2] siddikov ix, umurzakova dm. (2019) mathematical modeling of transient processes of the automatic control system of water level in the steam generator, universal journal of mechanical engineering, 7(4): 139-146. doi: 10.13189/ujme.2019.070401. [3] siddikov ix, umurzakova dm. (2019) synthesis of adaptive control systems of a multidimensional discrete dynamic object with a forecasting models. international conference on information science and communications technologies applications, trends and opportunities (icisct 2019). tashkent university of information technologies named after muhammad al-khwarizmi. –tashkent. 4-6 november, 2019. doi: 10.1109 / icisct47635.2019.9012033 [4] siddikov ix, umurzakova dm. (2019) neuro-fuzzy adaptive control system for discrete dynamic objects. international conference on information science and communications technologies applications, trends and opportunities (icisct 2019). tashkent university of information technologies named after muhammad al-khwarizmi. –tashkent. 4-6 november, 2019. doi: 10.1109/icisct47635.2019.9012027. [5] siddikov ix., umurzakova dm. (2020) fuzzy-logical control models of nonlinear dynamic objects // advances in science, technology and engineering systems journal, vol. 5, no. 4, 419-423 (2020). doi: 10.25046/aj050449. [6] demchenko va. (2001) avtomatizacija i modelirovanie tehnologicheskih processov ajes i tjes. odessa: astroprint, 308 s. [7] pletnev gp. (2007) avtomatizacija tehnologicheskih processov i proizvodstv v teplojenergetike: uchebnik dlja studentov vuzov. m.: izd. dom mjei, 352 s. [8] rotach, v. ya. (2008) the theory of automatic control. moscow: publishing house moscow power engineering institute, 396 p. [9] zhu x, zhang h, cao d, fang z. (2014) robust control of integrated motor-transmission powertrain system over controller area network for automotive applications, mechanical systems and signal processing, 58: 15-28. [10] zulfatman, rahmat mf. (2009) application of self-tuning fuzzy pid controller on industrial hydraulic actuator using system identification approach, international journal on smart sensing and intelligent systems, 2(2): 246-261. [11] das s, pan i, halder k, das s, gupta a. (2013) lqr based improved discrete pid controller design via optimum selection of weighting matrices using fractional order integral performance index, applied mathematical modelling: simulation and computation for engineering and environmental systems, 37(6): 4253-4268. [12] gasbaoui b, nasri a. (2012) a novel multi-drive electric vehicle system control based on multi-input multi-output pid controller, serbian journal of electrical engineering, 9(2): 279-291. [13] has z, muslim ah, mardiyah na. (2017) adaptive-fuzzy-pid controller based disturbance observer for dc motor speed control, in proceedings of the 2017 4th international conference on electrical engineering, computer science and informatics (eecsi), pp. 1-6, yogyakarta, september. [14] hu s, liang z, zhang w, he x. (2018) research on the integration of hybrid energy storage system and dual three-phase pmsm drive in ev, ieee transactions on industrial electronics, 65(8): 6602-6611. 296 https://doi.org/10.1109/icisct47635.2019.9012033 https://doi.org/10.1109/icisct47635.2019.9012033 https://doi.org/10.1109/icisct47635.2019.9012027 http://dx.doi.org/10.25046/aj050449 iium engineering journal, vol. 22, no. 1, 2021 maxamadjonovna https://doi.org/10.31436/iiumej.v22i1.1415 [15] iplikci s. (2010) a comparative study on a novel model-based pid tuning and control mechanism for nonlinear systems, international journal of robust and nonlinear control, 20(13): 1483-1501. [16] kumar smg, deepak j, anoop rk. (2010) pso based tuning of a pid controller for a high performance drilling machine, international journal of computer applications, 1(19): 12-18. [17] malwatkar gm, khandekar aa, nikam sd. (2011) pid controllers for higher order systems based on maximum sensitivity function, 2011 3rd international conference on electronics computer technology. [18] pelusi d. (2012) pid and intelligent controllers for optimal timing performances of industrial actuators, international journal of simulation: systems, science and technology, 13(2): 65–71. 297 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 sarima-lstm combination for covid-19 case modeling imam tahyudin1, rizki wahyudi2*and hidetaka nambo3 1 department of information system, universitas amikom purwokerto, purwokerto, indonesia 2 department of informatics, universitas amikom purwokerto, purwokerto, indonesia 3 artificial intelligence laboratory, kanazawa university, japan * corresponding author: rizkiw@amikompurwokerto.ac.id (received: 4th july 2021; accepted: 3rd december 2021; published on-line: 4th july 2022) abstract: the study of sarima method in combination with lstm is interesting to do. this combination method can be convincing and significant because the data collected is numerical and saved based on time. in addition, the proposed method can anticipate datasets, either linear or non-linear. based on several previous studies, the sarima method has the advantage of completing linear datasets while the lstm method excels in achieving non-linear datasets. also, both methods have been shown to have an accuracy value compared to some other methods. this study tried to combine the two through several stages of the first stage of applying the sarima method using fit datasets (linear data) then residual dataset (non-linear data) analysed using the lstm method. the result of the combination methods will be checked for the accuracy value. this research will be compared by using sarima and lstm methods separately. the dataset used as a trial is covid-19 patient data in the united states. the results showed that the combination of sarima-lstm method is better than either sarima or lstm alone with rmse of 0.33905765 and mae of 0.29077017. abstrak: gabungan kaedah kajian sarima dengan lstm adalah menarik untuk dikaji. gabungan kaedah ini meyakinkan dan penting kerana data yang dikumpulkan bersifat numerik dan disimpan berdasarkan waktu. selain itu, kaedah yang diusulkan ini dapat menerima set data, samada berkadar langsung atau tidak langsung. berdasarkan beberapa penelitian sebelumnya, kaedah sarima mempunyai faedah dalam melengkapi set data linear, sedangkan kaedah lstm berguna dalam mencapai set data tidak-linear. tambahan, kedua-dua kaedah ini terbukti memiliki nilai ketepatan lebih baik berbanding beberapa kaedah lain. kajian ini cuba menggabungkan keduanya melalui beberapa tahap. tahap pertama mengunakan kaedah sarima secara set data (data linear) kemudian baki set data (data tidak-linear) dianalisa menggunakan kaedah lstm. dapatan dari gabungan kedua-dua kaedah tersebut akan diperiksa nilai ketepatannya. kajian ini akan dibandingkan melalui kaedah sarima dan lstm secara berasingan. set data yang digunakan adalah merupakan data pesakit covid-19 dari amerika syarikat. dapatan kajian menunjukkan gabungan kaedah sarima-lstm memiliki nilai ketepatan yang lebih baik berbanding kaedah sarima secara berasingan, dan lstm dengan rmse adalah sebanyak 0.33905765 dan mae sebanyak 0.29077017. keywords: sarima; lstm; sarima-lstm; covid-19 patients 1. introduction the term sarima designates a seasonal autoregressive integrated moving average. one of the time series method's topics is this model. to handle problems involving timerun results, time series are frequently used. the time-series methodology is used in a 171 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 variety of domains, including the economics and financial turnaround results at hospitals [1-3]. a discussion of the time series method was held to complete the modelling of potential bioelectric plant data. using autoregressive (ar), moving average (ma), and arima models are one example. however, some of these models have not produced the best value. the average error rate for mean square error (mse) and the mean absolute error (mae) continues to be strong. although the average prediction accuracy is still about 75% [4-6]. therefore, this study aims to increase accuracy by using another time series model, sarima. in this study, the sarima method was combined with the lstm method. the combination of sarima with other methods is proven to have better accuracy results. among them is the combination of the sarima method with other methods, including the svm method, to predict the production value of the machine industry in taiwan [7]. the results showed that sarima hybrid accuracy with svm is better than with each method. other studies used hybrid arima with ann for forecasting pollution index in cities throughout southeast asia and further research used the same approach to predict tourists coming at minangkabau international airport [8]. the results showed the accuracy value of hybrid methods is better. subsequent research compared sarima and ann methods to predict power absorption in turkey’s electricity users [9]. after 12 weeks, the results showed that the ann method's mape value was 1.8% better than sarima because it had a mape of 2.6%. however, in certain conditions, such as the time after a holiday, the result is the opposite. another study combined sarima with svm, and then in analysis using clustering [10], this research was used to predict passengers at northern iranian stations. the result is a better mix of these approaches than the individual methods. as a result, the integrated approach outperforms the respective processes. additional research on the combination of svr-sarima models was done for tourist forecasting [11], for the best model's determination using the decision support system promethee ii. the result is the same combination method is better. thus, this study combined the sarima method with lstm. the sarima model successfully predicts a person's position for linear data set type better than the deep learning method [12], and also the sarima model has been tested with high accuracy of about 80% [13]. according to research, the long-short term memory (lstm) recurrent neural network on workload forecasting models for cloud datacentres has generated empirical results. the proposed method achieves high accuracy in prediction by reducing average squared errors by up to 3.17 x 10-3 [14]. therefore, we use both methods because both can solve problems for linear and non-linear data sets. in addition, this study will compare the sarima-lstm combination with each method separately. 2. method 2.1 arima model arima is a term derived from its parts: autoregressive (ar), integration (i), and moving average (ma) shape. in general, the arima models are classified into two types, namely non-traditional (non-seasonal) arima and seasonal arima models [15-17]. the arima model is as follows: arima (p,d,q). p represents the sum of ar values, d is the value of integration (i), and q is the ma value. in general, the arima model (p,d,q) can be seen from the model as follows: (1 1b.... pb p )(1 b) d yt = c + (1 + 1b..... + qb q ) et (1) 172 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 there are 3 main components in the model, the first being ar (p), (1-1b.... pb p ) (2) the second is differentiation through i (d), (1 b) d yt (3) the third was indeed ma (q), (1 + 1b..... + qb q )et (4) c, on the other side, is a constant value. 2.2 seasonal arima model the seasonal arima, or sarima model, is a model or shape that repeats itself at regular intervals. for stationary datasets, seasonality can be detected from the acf plot. if the acf visualization shows seasonal patterns, it will be done with a different solution [18-20]. in general, the seasonal arima equation is shown in eqn. 5. arima(p,d,q)(p,d,q)s (5) where (p,d,q) is the non-seasonal arima model index, while (p, d, q) is the seasonal arima model, and s is the number of periods on the seasonal model. for example, if arima (1,0,0), then the model follows the following eqns. 6 and 7: (1 1b)yt = c (6) where is byt = yt-1. so yt = c + 1yt-1 (7) to detect seasonal datasets, there are several chart techniques including sequential plots, seasonal plot subseries, multiple box plots, and autocorrelated plots. the study will use autocorrelated schemes to detect seasonality. one of the solutions for this autocorrelation plot is to use seasonal differential operators. 2.3 lstm long-short-term memory (lstm) is a form of rnn that consists of a collection of cells with features that allow them to memorize data sequences. data streams are captured and stored in cells. the cell then connects one module from the past to another, allowing data to be transmitted from several previous instances to the present. the data in every cell can be rejected, screened or started adding as a result of the gates in every cell in preparation for the cells that come after [19,21]. the gates focus on a neural network with sigmoidal shape layers, and the active cells either transfer data or discard it. each sigmoid layer generates a number between 0 and 1, indicating the sum of each data segment that must be permitted in every cell. more precisely, the estimated low value assumes that "nothing should be allowed to pass"; while forecast one shows that "let it all pass". every lstm has three types of gates that regulate a state for every cell: 1) forget gate produces a value between 0 and 1, with 1 denoting success. "fully save this"; whereas 0 says "ignore this." 2) memory gate the sigmoid layer, following either by the tanh layer, determines which of the cell's most recent data must be kept. the first sigmoid layer, known as 173 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 the "doorway layer," selects which values to modify. the tanh layer then generates a new candidate value vector, which can be added to the state. 3) the output gate determines what to make from each cell. the final value will be determined by the cell state as well as newly added filtered data. if the distance is vast, the rnn will be unable to predict the next result. consider the following text: "i go to work every day" and "i work hard at the office." the location's name is the next possible word for current knowledge, but deciding what kind of location to use is difficult. since there was some related knowledge in the previous period, rnn cannot learn to relate information. as a result, lstm is a solution for overcoming these flaws. lstms can study long-term dependencies. remembering information for a long time is the default behavior. some of the equations show this module as follows [22], [23]. 𝑟𝑡 = 𝑠𝑖𝑔𝑚(𝑊𝑥𝑟𝑥𝑡 + 𝑊ℎ𝑟 ℎ𝑡−1 + 𝑏𝑟 ) (8) 𝑧𝑡 = 𝑠𝑖𝑔𝑚(𝑊𝑥𝑧𝑥𝑡 + 𝑊ℎ𝑧ℎ𝑡−1 + 𝑏𝑧 ) (9) ℎ̃𝑡 = 𝑡𝑎𝑛ℎ(𝑊𝑥ℎ 𝑥𝑡 + 𝑊ℎℎ (𝑟𝑡 ⨀ℎ𝑡−1) + 𝑏ℎ ) (10) ℎ𝑡 = 𝑧𝑡 ⨀ℎ𝑡−1 + (1 − 𝑧𝑡 )⨀ℎ̃𝑡 (11) 2.4 combination of sarima method with lstm the steps of this combination are described in fig. 1. fig. 1: combination sarima-lstm model of covid-19 patient. based on fig. 1, the combination of the two methods is as follows: (1) prepare datasets; in this case, the dataset used is the covid-19 patient death data in a country affected by covid-19. (2) analysis process using the sarima model. the method includes the identification process. this process is checked using the box-jenkins process. that is the process of determining static data. the seasonal dataset is then examined by looking at the acf and pacf values. (3) if the dataset is seasonal, then the next step determines the best sarima model. (4) sarima fit model is forwarded for the forecasting process for linear components. while residual data is used for the forecasting process using the lstm method for non-linear components. (5) the last 174 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 step is the combined result of forecasting the two methods, further measuring mse values. 3. results and discussion 3.1 sarima model implementation in implementing the sarima method, covid-19 patients who died based on gender in the united states were used. the original data used as many as 1008 datasets but because many values were empty (missing value), the empty data was deleted. the net data was 711 datasets. the analysis process used r and minitab software. 3.1.1 identification as a dataset trial, male covid-19 patients' datasets were used. a plot of male covid-19 patients who died in the united states is shown in fig. 2. fig. 2: visual dataset of male covid-19 patients who died in the usa. following stationary check dataset of male covid-19 patients. a) stationary check of variety with cox box test results obtained as follows: fig. 3: visual dataset of male covid-19 patients who died in the usa. 24 /0 8/ 20 20 17 /0 8/ 20 20 03 /0 8/ 20 20 27 /0 7/ 20 20 13 /0 7/ 20 20 29 /0 6/ 20 20 15 /0 6/ 20 20 01 /0 6/ 20 20 18 /0 5/ 20 20 04 /0 5/ 20 20 13 /0 4/ 20 20 16000 14000 12000 10000 8000 6000 4000 2000 0 tanggal m a le time series plot of male 1.51.00.50.0-0.5-1.0 5000 4000 3000 2000 1000 lambda s t d e v lower c l upper c l limit estimate 0.11 lower c l 0.06 upper c l 0.15 rounded value 0.11 (using 95.0% confidence) lambda box-cox plot of male 175 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 because the value is still 0.11 should be worth 1. so, the transformation process is carried out as follows: fig. 4: cox box transformation. since the lambda value = 1 is stationary. it then checked stationary against the average by looking at its acf and pacf scores. b) stationary checks against averages by checking acf and pacf values based on acf and pacf lag, 1-3 images are still inside the significance interval. then it has been declared stationary against the average. fig. 5: acf. 5.02.50.0-2.5-5.0 0.55 0.50 0.45 0.40 0.35 0.30 lambda s t d e v lower c l upper c l limit estimate 1.00 lower c l 0.55 upper c l 1.39 rounded value 1.00 (using 95.0% confidence) lambda box-cox plot of maletrans1 7065605550454035302520151051 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 lag a u t o c o r r e la t io n autocorrelation function for maletrans1 (with 5% significance limits for the autocorrelations) 176 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 fig. 6: pacf. based on fig. 12, it appears that there is a trend. that is, there is an increase in the number of covid-19 patients who die per 10 datasets. therefore, the identification process is carried out further by differencing 3.1.2 estimation in this process, an analysis is carried out based on the sex of the male. fig. 7: dataset of covid-19 patients in the usa of the male gender. once the first differencing process trend is known lag=1, the model is formed with a non-seasonal model first by inspecting the graph autocorrelation function (acf) and partial autocorrelation function (pacf). the following acf and pacf charts were obtained: 1009080706050403020101 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 lag p a r t ia l a u t o c o r r e la t io n partial autocorrelation function for maletrans1 (with 5% significance limits for the partial autocorrelations) 11 /0 5/ 20 20 11 /0 5/ 20 20 04 /0 5/ 20 20 04 /0 5/ 20 20 04 /0 5/ 20 20 04 /0 5/ 20 20 27 /0 4/ 20 20 27 /0 4/ 20 20 27 /0 4/ 20 20 13 /0 4/ 20 20 13 /0 4/ 20 20 14000 12000 10000 8000 6000 4000 2000 0 tanggal d a t a male female variable time series plot of male, female 177 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 fig. 8: acf graph of male covid-19 patients in america non-seasonal arima models fig. 9: pacf graph of male covid-19 patients in america non-seasonal arima model. the acf chart shows the dying down as much as five lags. meanwhile, the pacf chart shows the cut-off pattern. thus, the non-seasonal arima model formed is arima (5,1,0). they are furthermore checking the non-seasonal arima model. the step to determine the seasonal arima model is the same as that performed to find the best model in non-seasonal arima by determining its acf and pacf charts. the seasonal value determines the difference. in this case, it is 10 because for every 10 datasets, there is a significant increase in covid-19 patient deaths. 3.1.3 model evaluation at this stage, checking the error value and other values. based on the output of the auto_arima, the evaluation value as follows. sarima (2,1,2)(0,0,2)12 next, check the error value and accuracy. here are the evaluation values obtained: 1009080706050403020101 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 lag a u t o c o r r e la t io n acf male 7065605550454035302520151051 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 lag p a r t ia l a u t o c o r r e la t io n partial autocorrelation function for male_lag1 (with 5% significance limits for the partial autocorrelations) 178 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 aic = 340.08 bic = 374.8 rmse = 0.44236361 mae = 0.33180744 these values are the best value when compared to other models. 3.1.4 forecasting based on fig. 10, the number of covid-19 patients who died of male gender in the usa, in general, decreased for the following forecasting result. the average difference is about 500 people. fig. 10: male covid-19 patient forecasting graph using sarima. 3.2 implementation of lstm and combination of sarima-lstm method this analysis used the parameters of batch size of 100, the look_back of seven data to previous, and the epoch for learning of 100. furthermore, for the forecasting process we split the data set with the composition of 80% training data and 20% testing data from the same data: male covid-19 patients in the usa. based on the analysis using lstm obtained an rmse value of 0.35847506 and mae of 0.29837463. based on rmse and mae results, the values are smaller than the sarima result, so it can be said that lstm is better than sarima. from fig 11, it appears that the number of covid-19 patients who died on average tends to decrease. fig. 11: graph forecasting male covid-19 patients using lstm method. 179 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 for the next test, the sarima method combined with lstm was done to determine how much accuracy through rmse and mae value obtained and prediction result. based on the calculation resulted that an rmse value was 0.33905765 and mae was 0.29077017. those results presented that the rmse and mae of combination sarima-lstm was better than the sarima and lstm methods (table 1). the results of combination sarima and lstm are seen in fig 12. this figure performed that the result is the best result because the predicted data is almost similar with real data. the number of covid19 suspected deaths decreased to near-zero. in addition, the table of comparison of rmse and mae are presented in table 1. this result presented that the combination of sarima and lstm is the best method for predicting the death of covid-19 patients in the usa. fig. 12: male covid-19 patient forecasting using sarima-lstm combination method table 1: the comparison of rmse and mae from sarima, lstm, and combination sarima-lstm parameters sarima lstm sarima-lstm rmse 0.44236361 0.35847506 0.33905765 mae 0.33180744 0.29837463 0.29077017 4. conclusion based on the results of the study, the combination sarima-lstm method is the best one. it performed better than the sarima or lstm methods separately. based on the results of general predictions using all three methods, there was a decrease in the number of male covid-19 patients who died in the usa on average. this research has the limitation of not explaining the mortality number of patients in every state within the usa. for future work, the analysis will be carried out using a combination of sarima – parcd methods. references [1] davis ra. (2014) introduction to statistical analysis of time series. department of statistics columbia university, pp. 1-24. 180 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 [2] borkowf cb. (2002) time-series forecasting. technometrics, 44(2): 194-195. https://doi.org/10.1198/tech.2002.s718. [3] schlüter t. (2012) knowledge discovery from time series (doctoral dissertation, universitäts-und landesbibliothek der heinrich-heine-universität düsseldorf). [4] chen ky, wang ch. (2007) a hybrid sarima and support vector machines in forecasting the production values of the machinery industry in taiwan. expert systems with applications, 32(1): 254-264. https://doi.org/10.1016/j.eswa.2005.11.027 [5] chi yn. (2021) time series forecasting of global price of soybeans using a hybrid sarima and narnn model: time series forecasting of global price of soybeans. data science: journal of computing and applied informatics, 5(2): 85-101. https://doi.org/10.4108/eai.2-8-2019.2290473 [6] ozozen a, kayakutlu g, ketterer m, kayalica o. (2016) a combined seasonal arima and ann model for improved results in electricity spot price forecasting: case study in turkey. in 2016 portland international conference on management of engineering and technology (picmet) (pp. 2681-2690). ieee. https://doi.org/10.1109/picmet.2016.7806831. [7] parviz l. (2020) comparative evaluation of hybrid sarima and machine learning techniques based on time varying and decomposition of precipitation time series. journal of agricultural science and technology, 22(2): 563-578. retrieved from: http://jast.modares.ac.ir/article-23-26018-en.html [8] abellana dpm, rivero dmc, aparente me, rivero, a. (2020) hybrid svr-sarima model for tourism forecasting using promethee ii as a selection methodology: a philippine scenario. journal of tourism futures. https://doi.org/10.1108/jtf-07-2019-0070 [9] tahyudin i, nambo h. (2018) comparison study of deep learning and time series for bioelectric potential analysis. in 2018 3rd international conference on information technology, information system and electrical engineering (icitisee) (pp. 79-83). ieee. https://doi.org/10.1109/icitisee.2018.8720998 [10] tahyudin i, nambo h. (2018) sarima model of bioelectic potential dataset. in international conference on big data, cloud and applications (pp. 367-378). springer, cham. https://doi.org/10.1007/978-3-319-96292-4_29 [11] kumar j, goomer r, singh ak. (2018) long short term memory recurrent neural network (lstm-rnn) based workload forecasting model for cloud datacenters. procedia computer science, 125: 676-682. https://doi.org/10.1016/j.procs.2017.12.087 [12] benvenuto d, giovanetti m, vassallo l, angeletti s, ciccozzi m. (2020) application of the arima model on the covid-2019 epidemic dataset. data in brief, 29: 105340. https://doi.org/10.1016/j.dib.2020.105340 [13] ceylan z. (2020) estimation of covid-19 prevalence in italy, spain, and france. science of the total environment, 729:138817. [14] zeroual a, harrou f, dairi a, sun y. (2020) deep learning methods for forecasting covid-19 time-series data: a comparative study. chaos, solitons & fractals, 140: 110121 [15] nist/sematech: seasonality (2012). http://www.itl.nist.gov/div898/ handbook/pmc/section4/pmc443.htm. accessed 23 september 2020 [16] qi c, zhang d, zhu y, liu l, li c, wang z, li x. (2020) sarfima model prediction for infectious diseases: application to hemorrhagic fever with renal syndrome and comparing with sarima. bmc medical research methodology, 20(1): 1-7. https://doi.org/10.1186/s12874-020-01130-8 [17] hamilton jd. (2020) time series analysis. princeton university press. [18] sherstinsky a. (2020) fundamentals of recurrent neural network (rnn) and long short-term memory (lstm) network. physica d: nonlinear phenomena, 404: 132306. https://doi.org/10.1016/j.physd.2019.132306 [19] reddy bk, delen d. (2018) predicting hospital readmission for lupus patients: an rnnlstm-based deep-learning methodology. computers in biology and medicine, 101: 199209. https://doi.org/10.1016/j.compbiomed.2018.08.029 [20] qi j, liu x, tejedor j. (2020) variational inference-based dropout in recurrent neural networks for slot filling in spoken language understanding. arxiv preprint arxiv:2009.01003 181 iium engineering journal, vol. 23, no. 2, 2022 tahyudin et al. https://doi.org/10.31436/iiumej.v23i2.2134 [21] li c, zhao l, cai b. (2020) size prediction of railway switch gap based on regarima model and lstm network. ieee access, 8, 198188-198200. https://doi.org/10.1109/access.2020.3034687 [22] z. liu et al., “entity recognition from clinical texts via recurrent neural network,” bmc med. inform. decis. mak., vol. 17, no. suppl 2, 2017, doi: 10.1186/s12911017-0468-7 [23] m. a. jishan, k. r. mahmud, a. k. al azad, m. s. alam, and a. m. khan, “hybrid deep neural network for bangla automated image descriptor,” int. j. adv. intell. informatics, vol. 6, no. 2, pp. 109–122, 2020. https://doi.org/10.26555/ijain.v6i2.499 182 microsoft word 235 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering kaderi et al. 69 observation on void formed in oxide scale of fe-cr-ni alloy at 1073k in dry and humid environments akbar kaderi 1 , ahmad zaki mohd zainal 1 , hanafi ani 1 and raihan othman 2 1 department of manufacturing and materials engineering, 2 department of science in engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. mhanafi@iium.edu.my abstract: void formation in oxide scale during high temperature oxidation is a common phenomenon. over a long period of time voids will affect the mechanical property of scales by influencing the cracking and spalling. voids formed in dry environment are different than that of formed in humid environment. with the presence of water vapor in humid environment the formation of void will increase, thus greater number of void compared to that in dry environment. fe-cr-ni alloy samples were exposed isothermally at 1073 k in air (��� = 0.21atm = 2.1 � 10 pa) and humid (air + steam) environments. xrd analysis done to all samples confirms that fe2o3, fe3o4, nicr2o4, fecr2o4, cr2o3 and nio phases exist in the scale. edx analysis done shows varying compositions of fe,cr,ni and o in outer and inner oxide scale, oxide scale/metal interface and metal. field emission scanning electron microscope (fe-sem) was used to investigate voids formed in the cross sections of the oxidized samples. volume fraction of voids in the oxide scale was calculated in accordance to the cross sectional area fraction of voids in the scale. it shows that fe-cr-ni alloy samples exposed in humid environment has as high as 71% more voids than that exposed in dry environment. it is concluded that the humid environment increased the number of void formed in the oxide scale, thus facilitates the exfoliation of protective scale during the high temperature oxidation. abstrak: pembentukan gelembung udara di dalam lapisan oksida ketika proses pengoksidaan di suhu tinggi merupakan satu fenomena biasa. pada satu jangka masa yang panjang gelembung-gelembung ini akan memberi kesan kepada sifat mekanikal oksida dengan mempengaruhi pembentukan keretakan dan pengelupasan oksida. gelembung udara yang terbentuk di dalam persekitaran kering berbeza daripada yang terbentuk di dalam persekitaran lembap. dengan adanya wap air, pembentukan gelembung akan bertambah berbanding yang terbentuk di dalam persekitaran kering. sampel aloi fe-cr-ni telah dioksidakan secara isoterma pada suhu 1073 k di dalam udara (��� = 0.21atm = 2.1 � 10 pa) dan lembap (udara + wap air). analisis pembelauan sinar – x (xrd) kepada semua sampel menunjukkan oksida yang terbentuk ialah fe2o3, fe3o4, nicr2o4, fecr2o4, cr2o3 dan nio. analisis penyebaran tenaga sinar – x (edx) menunjukkan komposisi fe, cr, ni dan o yang berubah ubah di lapisan oksida luar dan dalam, oksida/ antara muka logam dan logam. mikroskop imbasan elektron-pancaran medan (fe-sem) digunakan untuk meneliti gelembung di dalam oksida pada keratan rentas sampel. pecahan isi padu gelembung yang terbentuk pada oksida dikira dengan merujuk kepada pecahan luas keratan rentas pada oksida tersebut. sampel aloi fe-cr-ni yang dioksidakan di dalam persekitaran lembap iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering kaderi et al. 70 mempunyai kandungan gelembung udara 71% lebih banyak berbanding dengan yang dioksidakan di dalam persekitaran kering. kesimpulannya persekitaran lembap meningkatkan bilangan gelembung yang terbentuk di dalam lapisan oksida, sekaligus memudahkan pengelupasan oksida semasa pengoksidaan suhu tinggi. keywords: high temperature oxidatio;, fe-cr-ni alloy; void formation; quantitative analysis of voi;, dry environment; humid environment 1. introduction formation of voids in oxide scale especially in the proximity of metal/oxide interface or outer oxide scale/inner oxide scale interface is common in metals during high temperature oxidation. the formation will affect the oxidation mechanism and mechanical properties of the scale and also the metal itself. the tendency of voids to concentrate at outer oxide scale/inner oxide scale interface will result in spalling of the outer oxide scale [1]. voids within iron oxide scales and the iron-rich oxides formed on dilute fe-cr and fe-al alloys developed far more faster in the presence of water vapor. rahmel et al. [2, 3] have reported that presence of h2o(g) caused the scale to develop porosity. ehlers et. al. [4] observed that 9 mass% cr ferritic steels form rapidly growing scales of porous magnetite plus spinel during oxidation at 923 k in gases containing water vapor. contemporary literatures [2-6] on effect of water vapor on fe-cr or fe-al alloys mostly describe formation of voids in qualitative manner but few are attempting to study it quantitatively. understanding on the formation of voids quantitatively is very important because voids formation affect development of scales microsructure. maruyama et al. [7] proposed that void formation in a growing oxide scale during high temperature oxidation of a metal closely related with the divergence of ionic fluxes. further improvement of the treatment by ueda et. al. [8], by including all ionic fluxes into the calculation of the chemical potential distribution and quantitatively explained the position and the volume of voids formed in the magnetite scale. until recently, maruyama et al. [9] has successfully applied the quantitative estimation on the void formed in a single phase magnetite scale grown on iron substrate at 823 k in oxdizing environment containing oxygen partial pressure, ��� = 4.2 � 10 � � pa. however, most qualitative and quantitative studies on void formation cited earlier done in a strictly controlled oxidizing environment especially by lowering the ��� , so that only specific oxide scale grows on the metal substrate at specific temperature. therefore in this study, quantitative observation was focusing on void formed in a multiple oxide scale grown on fe-cr-ni alloy at 1073 k in normal air (��� = 0.21atm = 2.1 � 10 pa) and humid (air + steam) environment. 2. experimental methods 2.1 sample preparation of fe-cr-ni alloys fe-cr-ni alloys were prepared from high-purity fe (99.99%), cr (99.99%), ni (99.99%) plates by arc melting in ar gas. the alloys were further annealed for 86.4 ks at 1373 k in vacuum. after annealing the alloys were sliced into coupons of 1mm thick and the surfaces of the coupons were ground with emery paper up to #2000. then the samples were polished with 3µ m alumina paste to a mirror-like finish. the samples were cleaned iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering kaderi et al. 71 with acetone via ultrasonic agitation. the chemical composition of the alloys were analyzed through energy dispersive x-ray (edx). the chemical composition of fe-crni alloys are shown in table 1. table 1: chemical composition of fe-10 mass % cr-10 mass % ni alloy. element fe cr ni mass % 79.61 10.78 9.61 2.2 oxidation experiment of fe-cr-ni alloys figure 1 shows the experimental setup. the sample was placed at the isothermal zone of the furnace. an r-type thermocouple was placed at the isothermal zone beside the sample to monitor the temperature. the distance between the sample and the thermocouple is 5 mm. the isothermal zone is 30 mm in range. fig. 1: experimental setup for oxidation in humid condition at 1073 k. for the oxidation in dry environment, the sample was heated to 1073 k and held for 86.4 ks and 172.8 ks respectively in air. for the oxidation in humid environment, a boiler is placed directly below the furnace. the water vapor was channeled into the furnace once the heating process started. the continous supply of water to the boiler will ensure that the water vapor will be produced continously throughout the oxidation process. the oxidation process in humid environment was also hold for 86.4 ks and 172.8 ks respectivey. after oxidation, the samples are cooled to room temperature in the furnace. 2.3 phase identification oxide phases formed were analyzed by x-ray diffraction (xrd) using the divergence slit of 1 degree. the diffraction angle is from 20° to 80° and the scanning speed was 3.0000 °/min. the xrd patterns were compared with α-fe (jcpds 00-006-0696), feo (jcpds 00006-0615), fe2o3 (jcpds 01-085-0599), fe3o4 (jcpds 00-019-0629), nife2o4 (jcpds iium engineering journal, vol. 12, no. 5, 2011: special issue 01-074-1913), nicr2o4 (00-023 1479), and nio (jcpds 00-047 2.4 chemical composition of each o scale, inner oxide scale, inner oxide scale/ alloy the concentration of main elements of each samples after being oxidized were quantitatively determined by edx. the analysis was done on 4 spots; spot 1: outer oxide scale, spot 2: inner oxide scale, spot 3: metal/oxide interface and spot 4: metal. figure 2 shows an example of an area of a sample’s 4 spots being analyzed to determine the main elements concentration. fig. 2: an fe-sem micrograph shows the spots for edx analysis. 2.5 volume fraction of voids oxidized samples were mounted individually in resin. prior to mounting, 2 mm of each of sample was cross – samples after being cross-sectioned. the exposed cross ground up to #2000. then the samples were polished with 0.05 µ m alumina to a mirror like finish. fig. 3: schematics of samples after being cross surface morphology was observed by field emission scanning electron microscopy (fe sem). grids of uniformed size were traced on each images and area fraction of voids in the scale was measured. it was ass to the cross-sectional area fraction of voids in the scale applied by akiba et al. [11] substrate at 1373 k. g journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics 72 023-0432), fecr2o4 (jcpds 00-034-0140), cr 047-1049). omposition of each of main elements after oxidation: inner oxide scale/fe-cr-ni alloy interface a the concentration of main elements of each samples after being oxidized were by edx. the analysis was done on 4 spots; spot 1: outer oxide scale, spot 2: inner oxide scale, spot 3: metal/oxide interface and spot 4: metal. figure 2 shows an example of an area of a sample’s 4 spots being analyzed to determine the main sem micrograph shows the spots for edx analysis. f voids in the oxide scale oxidized samples were mounted individually in resin. prior to mounting, 2 mm of sectioned by diamond saw. figure 3 is a schematic of the sectioned. the exposed cross – section part of the samples was ground up to #2000. then the samples were polished with 0.05 µ m alumina to a mirror schematics of samples after being cross-sectioned. surface morphology was observed by field emission scanning electron microscopy (fe sem). grids of uniformed size were traced on each images and area fraction of voids in the scale was measured. it was assumed that the volume fraction of void in the scale equal sectional area fraction of voids in the scale [10]. the same assumption was [11], in order to calculate voids formed in nio grown of ni 1 on science and ethics in engineering kaderi et al. 0140), cr2o3 (00-038 outer oxide and fe-cr-ni the concentration of main elements of each samples after being oxidized were by edx. the analysis was done on 4 spots; spot 1: outer oxide scale, spot 2: inner oxide scale, spot 3: metal/oxide interface and spot 4: metal. figure 2 shows an example of an area of a sample’s 4 spots being analyzed to determine the main sem micrograph shows the spots for edx analysis. oxidized samples were mounted individually in resin. prior to mounting, 2 mm of diamond saw. figure 3 is a schematic of the section part of the samples was ground up to #2000. then the samples were polished with 0.05 µ m alumina to a mirrorsurface morphology was observed by field emission scanning electron microscopy (fesem). grids of uniformed size were traced on each images and area fraction of voids in umed that the volume fraction of void in the scale equal . the same assumption was , in order to calculate voids formed in nio grown of ni iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering kaderi et al. 73 3. results and discussion 3.1 phase identification by xrd and edx analysis figure 4 shows the xrd patterns of the sample surfaces.it was shown there is formation of fe2o3 in all samples. less intense and small peaks of cr2o3 and nio phase only detected for samples oxidized in dry environment. the formation of fecr2o4 and nicr2o4 spinels were observed in all samples. fe3o4 were also detected only in samples oxidized both in humid and dry environment. fig. 4: xrd patterns of samples in dry and humid environment at 1073 k after 86.4 ks and 172.8 ks. the edx profile was examined as shown in fig. 5a, b, c, and d. the metal/oxide scale interface for all samples were set at x = 0 µ m for the sake of easy observation. the elemental composition of fe in the outer scale is within a range of 67% 72%. the composition of o in the outer oxide scale is also substantial for all samples which are showing a range of 30 – 35%. correspond with the xrd pattern, the predomination of fe and o concentration in the outer scale can be explained by the presence of fe2o3 and fe3o4. the inner scale shows the element of fe as well as o has decreased. there are traces of ni and cr concentration in this inner scale compared to the outer scale. the inner scale is corresponding to the xrd pattern of nicr2o4 and fecr2o4. in the internal oxide zone (ioz), it was observed that the concentration of fe increased while the concentration of o is decreasing. the concentration of cr and ni also shows increment compared to that of in the inner scale zone. these suggested that spinel oxides of nicr2o4 and fecr2o4 formed in ioz region. finally, in the fe-cr-ni alloy region the concentrations of fe, cr, and ni are at their highest but the concentration of o is zero. the decreasing oxygen composition closer to the alloy and decreasing metal composition further away from the alloy was caused by the diffusion of metal ion and oxide ion under the influence of chemical potential gradients. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering kaderi et al. 74 fig. 5: edx profile of samples in dry and humid environment at 1073 k after 86.4 ks (a, b) and 172.8 ks (c, d). 3.2 volume fraction of voids in the oxide scale figure 6 shows the fe-sem micrographs of cross section of samples oxidized in dry and humid environment. voids are observed to be different from the inner oxide scale than that of outer oxide scale for all samples. larger size of voids are observed in the vicinity of outer oxide scale /inner oxide scale. smaller size of voids are observed to be congregated in the metal reservoir of inner oxide scale. for samples oxidized in dry environment, voids are spherical in shape. while samples oxidized in wet environment, voids are columnar in shape. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering kaderi et al. 75 fig. 6: fe-sem micrographs of cross section of samples oxidized in dry (a, b) and humid (c, d) environment at 1073 k after 86.4 ks (a, c) and 172.8 ks (b, d). figure 7 shows the volume fraction of voids in the inner oxide scale. the volume fraction of voids is in good agreement with the governing equation (1) proposed by maruyama [9]: the volume fraction of voids in scales, �� : �� � ����� �� ������ � (1) �� is volume fraction of voids in scale, ����� � is void formation in the scale during oxidation, ! is inner scale and " is outer scale. multiplication of the length,(l l) with 1 × 1 is to project the void formed into cubic dimension represented in a real oxide scale formed on the fe-cr-ni alloy. equation (1) shows the formation of voids is independent of time. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering kaderi et al. 76 fig. 7: the area fraction of voids in the inner oxide scale measured in the cross section of samples oxidized in dry and humid environment at 1073 k after 86.4 ks and 172.8 ks. figure 8 shows the volume fraction of voids in the outer oxide scale. however an anomaly occurred for volume fraction of voids in outer oxide scale of samples oxidized in dry environment. it was shown that the volume fraction of voids in outer scale increased with time. fig. 8: the area fraction of voids in the outer oxide scale measured in the cross section of the sample oxidized in dry and humid environment at 1073 k after 86.4 ks and 172.8 ks. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering kaderi et al. 77 nevertheless, the increases in volume fraction of voids for samples oxidized in humid environment shown in fig. 7 and 8 are phenomenal than that of samples oxidized in dry environment. the increase is ranging from 59% to 86%. it is interesting to note that the volume fraction of voids in outer oxide scale in this study are in a range of 0.06 to 0.29. studies on void formation in magnetite scale by maruyama [9] shows very small volume fraction of voids in a range of 0.05 to 0.06. meanwhile, nio scale on ni by akiba [11] shows volume fraction of voids less than 0.01. both studies were conducted in a controlled ��� environment. therefore, the fact that the oxidation for the current study was done in normal air with higher ��� has contributed to the formation of greater magnitude of void in the outer scale. 4. conclusion the void formation in oxide scales of fe-cr-ni alloy samples exposed isothermally at 1073 k in air (��� =0.21atm = 2.1 � 10 pa) and humid (air + steam) were investigated. it has been shown that the protective cr2o3 phases and nio phases occurred in samples oxidized in dry environment while non-protective fe3o4 phase occurred in all samples oxidized in dry and humid environment. the volume fraction of voids formed in inner scale increased by 84% for 86.4 ks and 86% for 172.8 ks when oxidized in humid environment. on the other hand, volume fraction of voids formed in outer scales increased by 76% for 86.4 ks and 59% for 172.8 ks when oxidized in humid environment. the oxygen partial pressure, ��� greatly influenced the volume fraction of voids formed in the oxide scale of fe-cr-ni alloy. hence the oxidation in air contributes greater formation of void than in controlled environment. acknowledgement the international islamic university malaysia funded this project through the research endowment grant b (edwb 0906-333) and the ministry of higher education malaysia funded this project through fundamental research grant scheme (frgs 0510-127). the authors gratefully acknowledge the financial support. references [1] r.j. ehlers, p.j. ennis, l. singheiser, w.j. quadakkers, and t. link. “significance of scale spalling for the lifetime of ferritic 9–10% cr steels during oxidation in water vapour at temperatures between 550 and 650 °c.” proceedings of the european federation of corrosion workshop. 2001. [2] a. rahmel, and j. tobolski. “einfluss von wasserdampf und kohlendioxid auf die oxidation von eisen in sauerstoff bei hohen temperaturen.” corrosion science 5.5 (1965): 333-340. [3] a. rahmel, and j. tobolski. “einfluß von wasserdampf und kohlendioxyd auf die oxydation von eisen-silicium-legierungen in sauerstoff bei temperaturen von 750 bis 1050°c.” werkstoffe und korrosion 16.8 (1965): 662-676 [4] j. ehlers, d.j. young, e.j. smaardijk , a.k. tyagi , h.j. penkalla , l. singheiser , w.j. quadakkers. “enhanced oxidation of the 9%cr steel p91 in water vapour containing environments.” corrosion science 48 (2006): 3428-3454 [5] j. śurek, e. wessel, l. niewolak, f. schmitz, t. -u. kern, l. singheiser, and w. j. quadakkers. “anomalous temperature dependence of oxidation kinetics during steam oxidation of ferritic steels in the temperature range 550–650 °c.” corrosion science 46.9 (2004): 2301-2317 iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering kaderi et al. 78 [6] l. mikkelsen, and s. linderoth. “high temperature oxidation of fe-cr alloy in o2-h2-h2o atmospheres; microstructure and kinetics.” materials science & engineering a, 361 (2003): 198-212 [7] t. maruyama, n. fukagai, m. ueda, and k. kawamura. “chemical potential distribution and void formation in magnetite scale formed in oxidation of iron at 823 k.” materials science forum 461-464 (2004): 807-814 [8] m. ueda, k. kawamura and t. maruyama. “void formation in magnetite scale formed on iron at 823 k -elucidation by chemical potential distribution-.” materials science forum 522-523 (2006) 37-44 [9] t. maruyama, and m. ueda. “void formation induced by the divergence of the diffusive ionic fluxes in metal oxides under chemical potential gradients.” journal of the korean ceramic society 47.1 (2010): 8-18 [10] w. d. kingery, h. k. bowen, and d. r. uhlmann. introduction to ceramics, second edition, pp. 526-530, wiley interscience publication, new york, usa 1976 [11] k. akiba, m. ueda, k. kawamura, and t. maruyama. “quantitative prediction of voids formation in a growing nickel oxide scale at 1373 k.” materials transactions 48.10 (2007): 2753-2761 252 iium engineering journal, vol. 14, no. 1, 2013 amara 15 optimizing phb and protease production by box behnken design amro abd-al-fattah amara 1,2 1 protein research department, genetic engineering and biotechnology research institute, mubarak city for scientific research and technological applications, alexandria, egypt. 2 microbiology division, pharmaceutical department, college of pharmacy, king saud university, riyadh, kingdom of saudi arabia. amroamara@web.de abstract: mixed culture is more suitable to adapt more flexible fermentation process and also to produce different product simultaneously. in this study, a mixed bacillus culture was investigated for their ability to produce the bioplastic "polyhydroxybutyrate" and both of the mesophilic and the thermophilic proteases, in one flask. box-behnken experimental design was used in this investigation. the produced amount of phb has been increased significantly. meanwhile there is a competition between phb and proteases. the maximum produced amount of phb using box-behnken design was 2.82 g/l/48 h with protease activity equal to 41.9 units/ml/48 h for thermophilic proteases and 99.65 units/ml/48 h for mesophilic proteases. excel solver was used for extraoptimization for the optimum conditions obtained from box-behnken experiments and its model. the maximum phb obtained after using excel solver was 2.88 g/l/48 h. the maximum mesophilic and thermophilic activities obtained at the same phb production conditions were 175.68 and 243.38 units/ml respectively. the model accuracy obtained from excel solver was 118.8%, which prove that the power of the experimental design in optimizing such complicated process. the strategies used in this study are recommended for the production of phb and different proteases simultaneously, using bacillus mixed culture. abstrak: kultur campuran adalah lebih sesuai bagi proses penapaian yang fleksibel dan ia boleh menghasilkan produk yang berbeza secara serentak. dalam kajian ini keupayaan menghasilkan "polyhydroxybutyrate" bioplastik serta mesofilik dan termofilik protease dalam satu flask oleh kultur bacillus campuran telah disiasat. eksperimen rekabentuk box-behnken telah digunakan. jumlah phb yang dikeluarkan meningkat dengan ketara dan terdapat persaingan antara phb dan protease. jumlah keluaran phb maksima menggunakan rekabentuk box-behnken adalah 2.82 g/l/48 jam dengan aktiviti protease sama dengan 41.9 unit/ml/48 jam untuk protease termofilik dan 99.65 unit/ml/48 h untuk protease mesofilik. solver excel telah digunakan untuk memperolehi kadar optimum tambahan dari keadaan optimum yang diperolehi dari experimen dan model box-behnken. phb maksimum diperolehi setelah menggunakan solver excel adalah 2.88 g/l/48 jam. aktiviti mesofilik dan termofilik maksima diperolehi daripada keadaan pengeluaran phb yang sama adalah 175.68 dan 243.38 unit / ml. ketepatan model diperolehi daripada solver excel adalah 118.8%, membuktikan kekuatan eksperimen tersebut bagi mengoptimumkan proses yang rumit. strategi yang digunakan dalam kajian ini adalah disyorkan bagi pengeluaran phb dan proteas berbeza secara serentak menggunakan kultur bacillus campuran. keywords: phb; proteases; mixed culture; box-behnken design. iium engineering journal, vol. 14, no. 1, 2013 amara 16 1. introduction bacteria-produced phb is approximately five to ten times more expensive than its competitors (e.g. polypropylene or polyethylene). although this natural product is promising, its price at the early production time is rather expensive [1]. the cheapest substrate cost is $0.22/kg (sugar) of pha while the cost of polypropylene is $0.185/kg [2]. the substrate cost affects the overall cost. when the phb productivity was increased from 1.98 to 3.2 g/h, the phb production cost was decreased from $5.37/kg to $4.91/kg [2]. in a laboratory fed-batch system using alcaligenes latus, the highest reported productivity was 4.94 g/h with cost about $2.6 kg [3]. thermostable enzymes can be produced by both of thermophilic and mesophilic microbes [4, 5]. bacilli and particularly bacillus licheniformis, bacillus subtilis and bacillus pumilus are the most used species [6]. molecular biology tools were used to increase the phb production. as an example random in vivo and in vitro mutageneses were performed [7-11]. experimental design is another versatile tool could be used for optimizing different parameters and conditions. in this study box-behnken design and excel solver were used to optimize the medium constituents[12]. phb and the proteases were subjected to the optimization processes. the different obtained results from the conducted experiments were analyzed statistically using excel 2000 and essential exp., version 2.205 software [13]. the results which have been obtained from box-behnken optimization in this study are promising. 2. materials and methods 2.1 microorganism five bacillus species were used in this study. they were isolated from the egyptian ecosystem and identified using standard criteria as bacillus subtilius, bacillus pumilus, bacillus thuringiensis, bacillus licheniformis and geobacillus stearothermophilus. they are grown routinely in lb medium (luria-bertani) [14] at 40-37 o c and maintained at 70 o c. the bacillus strains as mixed culture have been adjusted to have equal od600 (od600 = 0.025) (sterilize distilled water has been used to adjust the od). the used amount of each in the box-behnken design were: b. subtilius 100 µ l; b. pumilus 100 µ l; b. thuringiensis 10 µl; b. lichenifermis 10 µ l and geobacillus stearothermophilus 10 µ l. 2.2 cultivation medium the used medium has the following constituents: tryptone soy bean 10 mg; skim milk 10, 5.1 or 0.2 mg; lactose 2 g; glucose 2, 1.2 or 0.4 g; yeast extract 0.4, 0.24 or 0.08 g; kh2po4 0.01 g; feso4 solution 5 µl (12 mg/l); trace elements solution 5 µl/ml as described by pfenning [15] and kcl2 0.03 g (skim milk, glucose and yeast extract have been used in three different values represented as +1, 0 and -1 following box-behnken design). the trace elements and feso4 solution were sterilized each separately using 0.22 µm sterilize filter system. 2.3 preparation of equal cultures bacillus strains were pre-cultivated on lb agar plate for overnight at 37 o c. one loop from the fresh colonies from each bacillus strain was taken and inoculated to test tube contains 5 ml lb broth medium. the cultures incubated overnight at shaker incubator at 200 rpm and 37 o c. the od600 for each species was adjusted to 0.025 by adding sterilize distilled water to the culture under aseptic condition. iium engineering journal, vol. 14, no. 1, 2013 amara 17 2.4 shake flask fermentation condition phb and proteases production under the different experimental conditions were conducted using 250 ml erlenmeyer-flasks each containing 100 ml medium. the shaking rate was 250 rpm at 37 o c. the medium constituents were changed when randomized according to box-behnken design [12] as described in table 1 (see section 3.1). 2.5 proteases activities the protease activities of mesophilic and thermophilic proteases have been determined at 37 and 60 o c respectively by the method described by amara and serour [16]. 2.6 phb characterization the assay was spectrophotometrically (perkinelmer-uv/vis spectrometer lambda) performed after modification as described by law and slepecky to determine phb as crotonic acid [17]. two milliliters from each cultivation was centrifuged at 13000 rpm for 15 min. one milliliter of h2so4 then added to the precipitate, which contain the cells. the solution was incubated in 70 o c for 20 min. after cooling, 10 µl was taken and added to 990 µl of h2o and the absorbance of the solution was measured at 235 nm. the phb amount for each experiment was determined by calculating the amount of crotonic acid against crotonic acid standard curve reproduced from standard phb authentic sample. 2.7 box-behnken design the box-behnken experimental design, the model and anova analysis were carried out using the excel 2000 and essential exp., version 2.205 software [13]. box-behnken experimental design was used to optimize three variables represented at three levels high, medium and low, which are donated by +1, 0 and -1, respectively. they represent glucose (x1), skim milk (x2) and yeast extract (x3) g/l. the design contain fifteen experiments as in table 1. the phb produced from the different experiments were analyzed by multiple regression analysis. the created model was generated using the coefficient of each variable as described in detailed by amara and salem [18]. the various interactions between responses have represented in the surface plots. 2.8 excel solver optimization considering that phb is the main product, glucose (x1), skim milk (x2) and yeast extract (x3) were further optimized using microsoft excel 2000 solver to calculate the best yphb value. the experiment under mathematically calculated optimum glucose (x1), skim milk (x2) and yeast extract (x3) was practically conducted and the model accuracy was calculated using the following formula: �������� % �� � � � � ���������������� !����" # $ 100 (1) 3. results and discussion 3.1 box-behnken design glucose, skim milk and yeast extract have been randomized according to boxbehnken design while the other medium constituents as well as the amount of the used of each of the five bacilli are constant as described above. the amount of the produced phb, mesophilic and thermophilic proteases for each of the fifteen experiments were summarized in table 1. iium engineering journal, vol. 14, no. 1, 2013 amara 18 table 1: box-behnken experiments. exp. no. glucose skim milk yeast extract phb g/100 ml/48h measophilic protease units/ml/48hr thermophilic protease units/ml/48/hr 1 0 (1.2) 0 (5.1) 0 (0.24) 1.25 96.42 50.26 2 0 (1.2) 1 (10) -1 (0.08) 1.45 80.24 29.16 3 1 (2) -1 (0.2) 0 (0.24) 0.81 107.74 43.31 4 0 (1.2) 0 (5.1) 0 (0.24) 1.94 86.71 48.03 5 1 (2) 0 (5.1) -1 (0.08) 2.82 99.65 41.90 6 1 (2) 1 (10) 0 (0.24) 1.25 98.03 43.31 7 0 (1.2) -1 (0.2) 1 (0.4) 0.70 120.68 35.97 8 -1 (0.4) 1 (10) 0 (0.24) 1.49 102.89 27.14 9 0 (1.2) 1 (10) 1 (0.4) 1.01 115.83 21.27 10 1 (2) 0 (5.1) 1 (0.4) 0.99 114.21 25.99 11 -1 (0.4) 0 (5.1) -1 (0.08) 1.56 175.68 243.38 12 -1 (0.4) 0 (5.1) 1 (0.4) 1.12 151.42 74.13 13 0 (1.2) 0 (5.1) 0 (0.24) 1.21 112.59 194.45 14 0 (1.2) -1 (0.2) -1 (0.08) 1.13 135.24 219.12 15 -1 (0.4) -1 (0.2) 0 (0.24) 1.58 119.06 93.34 the best phb produced amount was in experiment number five and was equal to 2.82 g/10 µ l/48 hr with mesophilic and thermophilic proteases activities were 99.65 and 41.90 units/ml/48 hr respectively. in case of proteases production, experiment number eleven shows the highest mesophilic and thermophilic activities which are equal to 175.68 and 243.38 units/ml/48 hr respectively and the produced phb amount was equal to 1.56 g/100 ml/48 hr. each response was analyzed statistically using the multiple regression analysis test and the estimate, standard error, t statistic, p-value and coefficient % for each parameter was summarized (for each response) in tables 2 (phb), table 4 (mesophilic proteases) and table 6 (thermophilic protease). the model for each response was generated. the anova test for phb, mesophilic and thermophilic proteases were generated and the obtained results were summarized in tables 3, 5 and 7, respectively. 3.2 phb model phb = 1.46667 + 0.015* glucose + 0.182917* glucose* glucose + 0.1325* glucose * skim milk 0.3475* glucose* yeast extract + 0.1225* skim milk 0.367083* skim milk* skim milk 0.0025* skim milk* yeast extract 3 0.3925* yeast extract 0.0270833* yeast extract* yeast extract. the p-value in the anova table is greater or equal to 0.10. there is no a statistically significant relationship between the variables at the 90% or higher confidence level as in table 3. iium engineering journal, vol. 14, no. 1, 2013 amara 19 table 2: linear multiple regression analysis of the interaction between variables on phb response. parameter estimate standard error t statistic p-value confidence% constant 1.46667 0.278582 5.26476 0.0033 99.67 glucose 0.015 0.170596 0.087927 0.9333 6.67 glucose* glucose 0.182917 0.25111 0.728432 0.499 50.1 glucose*skim milk 0.1325 0.241259 0.549203 0.6065 39.35 glucose*yeast extract -0.3475 0.241259 -1.44036 0.2093 79.07 skim milk 0.1225 0.170596 0.718072 0.5049 49.51 skim milk* skim milk -0.36708 0.25111 -1.46184 0.2036 79.64 skim milk* yeast extract -0.0025 0.241259 -0.01036 0.9921 0.79 yeast extract -0.3925 0.170596 -2.30076 0.0697 93.03 yeast extract* yeast extract -0.02708 0.25111 -0.10785 0.9183 8.17 table 3: anova test for phb response. source sum of squares df mean square f-ratio p-value model 2.57144 9 0.285716 1.23 0.4321 residual 1.16412 5 0.232823 total (corr.) 3.73556 14 r-squared = 68.8369 percent; r-squared (adjusted for d. f.) = 12.7433 percent; standard error of est. = 0.482518; mean absolute error = 0.252444 table 4: linear multiple regression analysis of the interaction between variables on measophilic protease response. parameter estimate standard error t statistic p-value confidence % constant 98.5722 10.8994 9.04385 0.0003 99.97 glucose -16.177 6.67446 -2.42372 0.0598 94.02 glucose* glucose 15.3008 9.82454 1.55741 0.1801 81.99 glucose * skim milk 1.6177 9.43912 0.171383 0.8706 12.94 glucose * yeast extract 9.70623 9.43912 1.0283 0.351 64.9 skim milk -10.7173 6.67446 -1.60572 0.1692 83.08 skim milk* skim milk -6.94265 9.82454 -0.70666 0.5113 48.87 skim milk * yeast extract 12.5372 9.43912 1.32822 0.2415 75.85 yeast extract 1.41549 6.67446 0.212076 0.8404 15.96 yeast extract* yeast extract 21.3672 9.82454 2.17488 0.0816 91.84 iium engineering journal, vol. 14, no. 1, 2013 amara 20 table 5: anova test for mesophilic protease response. source sum of squares df mean square f-ratio p-value model 6764.39 9 751.598 2.11 0.2128 residual 1781.94 5 356.388 total (corr.) 8546.32 14 r-squared = 79.1497 percent; r-squared (adjusted for d.f.) = 41.619 percent; standard error of est. = 18.8782; mean absolute error = 9.47256 3.3 mesophilic protease model mesophilic protease = 98.5722 16.177* glucose + 15.3008* glucose* glucose + 1.6177* glucose* skim milk + 9.70623* glucose* yeast extract 10.7173* skim milk 6.94265* skim milk* skim milk + 12.5372* skim milk * yeast extract + 1.41549* yeast extract + 21.3672* yeast extract* yeast extract. the p-value from the anova analysis is greater or equal to 0.10, there is not a statistically significant relationship between the variables at the 90% or higher confidence level as in table 5. 3.4 thermophilic protease model thermophilic proteases = 97.58 35.435* glucose 12.9175* glucose* glucose + 16.55* glucose* skim milk + 38.335* glucose 33.8575* skim milk 32.8875* skim milk* skim milk + 43.815* skim milk* yeast extract 47.025* yeast extract + 11.6875* yeast extract* yeast extract. the p-value in the anova table is greater or equal to 0.10. there is not a statistically significant relationship between the variables at the 90% or higher confidence level as in table 7. table 6: linear multiple regression analysis of the interaction between variables on thermophilic protease. parameter estimate standard error t statistic p-value confidence% constant 97.58 38.5555 2.53089 0.0525 94.75 glucose -35.435 23.6104 -1.50082 0.1937 80.63 glucose * glucose -12.9175 34.7535 -0.37169 0.7254 27.46 glucose * skim milk 16.55 33.3901 0.495656 0.6412 35.88 glucose * yeast extract 38.335 33.3901 1.1481 0.3029 69.71 skim milk -33.8575 23.6104 -1.43401 0.211 78.9 skim milk* skim milk -32.8875 34.7535 -0.94631 0.3874 61.26 skim milk * yeast extract 43.815 33.3901 1.31222 0.2465 75.35 yeast extract -47.025 23.6104 -1.99171 0.103 89.7 yeast extract* yeast extract 11.6875 34.7535 0.336297 0.7503 24.97 iium engineering journal, vol. 14, no. 1, 2013 amara 21 table 7: anova test for thermophilic protease response. source sum of squares df mean square f-ratio p-value model 56789.3 9 6309.92 1.41 0.3669 residual 22297.9 5 4459.59 total (corr.) 79087.2 14 r-squared = 71.8059 percent; r-squared (adjusted for d.f.) = 21.0565 percent; standard error of est. = 66.7802; mean absolute error = 31.9153 fig. 1: response surface for skim milk and glucose effect in phb production. fig. 2: response surface for yeast extract and glucose effect in phb production. iium engineering journal, vol. 14, no. 1, 2013 amara 22 fig. 3: response surface for yeast extract and skim milk effect in phb production. fig. 4: response surface for skim milk and glucose effect in mesophilic protease production. iium engineering journal, vol. 14, no. 1, 2013 amara 23 fig. 5: response surface for yeast extract and glucose effect in mesophilic protease production. fig. 6: response surface for yeast extract and skim milk effect in mesophilic protease production. iium engineering journal, vol. 14, no. 1, 2013 amara 24 fig. 7: response surface for skim milk and glucose effect in thermophilic protease production. fig. 8: response surface for yeast extract and glucose effect in thermophilic protease production. iium engineering journal, vol. 14, no. 1, 2013 amara 25 fig. 9: response surface for yeast extract and skim milk effect in thermophilic protease production. 3.5 excel solver optimization the best level of the three variable as obtained from the maximum point of polynomial phb model was estimated using the solver function of microsoft excel 2000 tools and found to be for glucose = 2 g/100 ml, skim milk = 6.818 mg/100 ml and yeast extract = 0.08 g/100 ml, with a prediction calculated phb equal to 24.2 g/l/48 h. table 8: excel 2002 solver optimization for x1, x2 and x3. term glucose (x1) g/100 ml skim milk (x2) mg/100 ml yeast extract (x3) g/100 ml data minimum -1 (0.4) -1 (0.2) -1 (0.08) data average 0 (1.2) 0 (5.1) 0 (0.24) data maximum 1 (2) 1 (10) 1 (0.4) data solver 1 (2) 0.353571 (6.818) -1 (0.08) 3.6 confirming accuracy of model the y value which was calculated using microsoft excel is equal to 24.2 g/l/48 h. the in vivo experiments show that y value (phb) is 28.8 g/l/48 h. by calculating the model accuracy from the formula in material and methods section, the model accuracy % was 118.8%. the measophilic and thermophilic proteases activities determined to be 175.68% and 243.38 units/ml respectively. 4. discussion amara [7] suggests directing the research concerning the phb production to the medicinal applications. this will greatly encourage the investors to give phb researches iium engineering journal, vol. 14, no. 1, 2013 amara 26 more concern. however studies which were concerning with the reduction of the phb cost should not be stopped. this study introduces a new concept. it concern with the use of heterogeneous substrates and mixed bacillus culture to produce valuable products beside phb (the main product). mixed bacterial culture were used. thermophilic and mesophilic proteases were additionally produced under mesophilic condition. phb production is rather sensitive process usually conducted under nitrogen limitation and excess of carbon sources [7]. proteases, which are protein in nature require considerable amount of carbon and nitrogen sources to fit its amino acids' monomeric structure [4-6]. phb formed mainly from o2, h and c [7]. to minimize the conflict between the phb and proteases production conditions, box-behnken experimental design was used to map the points where phb and the proteases could be produced simultaneously. box-behnken design was used to optimize three of the used medium constituents. fifteen experiments were conducted according to the design. the three optimized medium constituents are glucose, skim milk and yeast extract. these three variables were selected based on literature review, experiments (data not shown) and basic science about phb and proteases productions [47]. the maximum phb amount was 2.82 g/100 ml/48 h as shown in experiment no 5 (table 1). in experiment no. 5, glucose was in its +1 value, skim milk was in its 0 value and yeast extract was in its -1 value. the amount of measophilic proteases was 99.65 units/ml and for thermophilic proteases was 41.90 units/ml in the same experiment. comparing the amount of proteases in experiment no 5 with that in experiments no 11 and 14 as well as the related amount of the produced phb prove that there is a conflict between the phb and proteases production. the linear multiple regression analysis of the data as in table 2 shows that under the experimental conditions, yeast extract was significant with confidence level equal to 93.03. the interaction between glucose and yeast extract as well as between skim milk and skim milk were effective with confidence level equal to 79.07 and 79.64 respectively. the glucose, which is the main carbon source for phb accumulation, was insignificant with confidence % equal to 6.67. this is due to the existence of substrates contain nitrogen such as the skim milk suppress the phb production. in the case of yeast extract which effect negatively on the phb production, this is agree with a well-proved criteria that phb produced under nitrogen limitation [7]. moreover, the amounts of the used glucose (0.4, 1.2 and 2g/l) is sufficient for phb production. in contrast, glucose gives confidence level % equal to 94.02 in case of mesophilic proteases. however, it is affect negatively on the mesophilic protease production. by analysis experiment number 11 which give the maximum mesophilic proteases activity {175.68 units/ml} the amount of the used glucose was in its minimal used amount (-1 value). it is concluded that glucose has a negative role in measophilic protease production and that the cell give a priority to proteases production over phb production. skim milk even it is not statistically significant but it is consider being effective and giving confidence level % equal to 83.08. however, skim milk is also negatively affect on the mesophilic protease production. it can be concluded that glucose which give a very low confidance level with phb production (6.67%) was concumed by the cell for producing proteases and that mixed culture is more able to produc proteases in low level of skim milk. high quantity of skim milk might interfere with the ability of the cells to produce proteases. nearly the same result obtained from statistical analysis of the themophilic proteases data where glucose gives confidence level % equal to 89.7. the maximum amount of thermophilic proteases was in experiment no 14 where the amount of glucose was at its 0 value. the anova test of each of phb, measophilic and thermophilic proteases which were insignificant prove that there is a chance for further optimization and that it is still a conflict between the used substrates. the response surface for the three calculated responces show different levels of interactions between the iium engineering journal, vol. 14, no. 1, 2013 amara 27 responces and agree with the statistical analysis of the box-behnken results. for extraoptimization, excel solver was used to optimize the model obtained from box-behnken experiments. the solver calculated y value was 2.42 g/100 ml/48 h. experimentally; the obtained y value was equal to 2.88 g/100 ml/48 h. this gives a model accuracy % equal to 118.8%. the amounts of mesophilic and thermophilic proteases have been improved and the produced amount equal to 144.94 and 158 units/ml respectively. it is important here to highlight that excel solver which optimize the model from blacket-burman design gives less calculated phb amount than that produced in experiment number five in box-behnken design. however experimentally it gives more phb. this might be explained that regression analysis could dilute the optimal result during fitting the best line pass through all the results. this problem should be considered by the mathematicians and perhaps can be solved by using manual fitting. the responses of various interactions between the variables and responses have been visualized as response surface as in figures from 1 to 9. the different response surface analysis results were agreed with the data obtained from the regression analysis and their models. it is important to highlight that there are some limitations concerning this study which did not included the environmental variables like ph, temperature and shaking rate. the fermentation process control is limited regarding to the use of flasks rather than using a fermentor. there are limitations in the size of the medium. those factors should be considered in further studies. meanwhile the results obtained from this study prove the powerful of the experimental design in optimizing complicated computational medium compositions. the use of mixed culture will improve the biotechnological process especially those deal with expensive products such as phb. the strategies included in this study are recommended to be used in optimizing complicated biotechnological process. references [1] j.w. moore, "degradable plastics". mod. plastics,. 69.13 (1992): 58-63. [2] b. kothuis, f. schelleman, "environmental economic comparison of biotechnology with traditional alternatives. (1998). 4. [3] s.y. lee, j. choi, "effect of fermentation of performance on the economics of poly(3hydroxybutylate) production by alcaligenes latus". polymer degradation and stability 59.1 (1998): 387-93. [4] j.k. lee, y.o. kim, h. k.y. kim, s. park, t.k. oh, "purification and characterization of a thermostable alkaline protease from thermoactinomyces sp. e79 and the dna sequence of the encoding gene".., bioscience biotechnology biochemistry, 40.6 (1996): 840-46. [5] s.r. salem, m.s.a. sabeb, a.a. amara, "optimization of thermophilic proteases production in bacillus mixed culture under mesophilic condition". world journal of agricultural sciences., 5.3 (2009): 375-83. [6] m, adams, michael ww, and robert m. kelly. "finding and using hyperthermophilic enzymes".. trends in biotechnology 16.8 (1998): 329-32. [7] a.a. amara, "polyhydroyalkanoates: from basic research and molecular biology to application". iium english journal.,. 9.1 (2008): 37-73. [8] a.a. amara, b.h. rehm, a. steinbuchel, "biopolymer overproduction by new mutants using simple methods for selection. daad-bioforum-berlin-grenzenlos forschen’’, daad, biotechnologische methoden,. (2001): 231-39. [9] .a. amara, a. steinbuchel, b.h rehm, "in vivo evolution of the aeromonas punctata polyhydroxyalkanoate (pha) synthase: isolation and characterization of modified pha synthases with enhanced activity".." applied microbiology and biotechnology 59.4-5 (2002): 477-82. iium engineering journal, vol. 14, no. 1, 2013 amara 28 [10] taguchi, a. maehara, k. takase, m. nakahara, h. nakamura, y. doi, ''analysis of mutational effects of a polyhydroxybutyrate (phb) polymerase on bacterial phb accumulation using an in vivo assay system''.." fems microbiology letters 198.1 (2001): 65-71. [11] s. taguchi, h. nakamura, t. hiraishi, i. yamato, y. doi, "in vitro evolution of a polyhydroxybutyrate synthase by intragenic suppression-type mutagenesis". journal of biochemistry 131.6 (2002): 801-06. [12] g, box, george ep, and donald w. behnken, ''some new three levels designs for the study of quantitative variables''. technometrics.,. 2.4 (1960): 455-75. [13] steppan, d. david, joachim werner, and r. p. yeater. ''essential regression and experimental design for chemists and engineers (software)'' [14] j. sambrook, e.f. fritsch, t. maniatis, ''molecular cloning: a laboratory manual'', 1989. [15] n. pfennig, ''rhodopseudomonas globiformis sp. nov., a new species of the rhodospirillaceae''.." archives of microbiology 100. (1974): 197-206. [16] a.a. amara, e.a. serour, ''wool quality improvement using thermophilic crude proteolytic microbial enzymes''. american-eurasian journal of agricultural & environmental sciences 3.4 (2008): 554-60. [17] j.h. law, r.a. slepecky, "assay of poly-b-hydroxybutyric acid". ."journal of bacteriology 82.1 (1961): 33-36. [18] a.a. amara, s.r. salem, amara, amro abd al fattah, and soheir r. salem ''logical and experimental design for phenol degradation using immobilized acinetobacter sp''. culture,.." iium engineering journal 11.1 (2010): 89-104. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 adaptive system of fuzzy-logical regulation by temperature mode of a drum boiler siddikov isamiddin xakimovich1, umurzakova dilnoza maxamadjonovna*1 and bakhrieva hurshida askarxodjaevna2 1department of information processing systems and management, tashkent state technical university, 100097 tashkent, uzbekistan 2department of multimedia technology, tashkent university of information technologies, 100200 tashkent, uzbekistan *corresponding author: umurzakovadilnoz@gmail.com (received: 13th august 2019; accepted: 14th october 2019; published on-line: 20th january 2020) abstract: the article discusses the creation of an adaptive system for managing dynamic objects based on neuro-fuzzy technology. this technology is used to actively identify and create temperature control algorithms for the superheated steam of a drum boiler in the presence of disturbances associated with a change in load. to solve this problem, the use of a fuzzy-logical controller is proposed. the rule base of this regulator is defined. a technique is proposed for determining the optimal number of neurons and the number of hidden layers. the neuro-fuzzy model of the controller is presented in the form of a multilayer neural network without feedback, which is characterized by a simple implementation in practice. the use of a fuzzy-logical controller gives the automatic control system the ability to maintain technological parameters at a given level in the presence of external disturbing influences, and also makes it possible to efficiently control the process. abstrak: artikel ini membincangkan rekaan sistem penyesuaian bagi mengurus objek dinamik berdasarkan teknologi neura-kabur. teknologi ini digunakan bagi mengenal pasti secara aktif dan mencipta algoritma kawalan suhu bagi stim melampau panas dalam drum dandang dengan kehadiran gangguan berkaitan perubahan beban. bagi menyelesaikan masalah ini, penggunaan pengawal logik-kabur telah dicadangkan. asas peraturan bagi pengaturan ini ditentukan. satu teknik dicadangkan bagi mendapat bilangan optima neuron dan bilangan lapisan tersembunyi. model neura-kabur pengawal ini dikemukakan dalam bentuk rangkaian neural berlapis tanpa suap balik, bercirikan praktik pelaksanaan mudah. penggunaan pengawal logik-kabur memberi sistem kawalan automatik kebolehan mengekalkan parameter teknologi pada tahap tertentu dengan kehadiran pengaruh gangguan luar, dan juga memberi kebolehan proses kawalan yang cekap. keywords: fuzzy model; pid-controller; neural networks; drum boiler; controller; adaptive system; temperature; heat power industry 1. introduction currently, in most industrial facilities, including heat and power facilities for process control, pid controllers have found wide application. about 90-95 % of the regulators currently in operation use the pid algorithm. the reasons for such popularity are their 182 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 simplicity of construction, clarity of operation, suitability for most practical tasks, and low costs. in existing thermal power facilities, a typical cascade system for superheated steam temperature control is used, which includes the control circuit of the proportional-integral (pi) regulator and the additional measurement loop of the auxiliary controlled variable formed in the signal conditioning unit. analysis of the operating characteristics of the superheater shows that the control object has a variable transport lag, its dynamic properties substantially depend on the oxygen content in the outgoing gases, contamination of heating surfaces, and regime factors load, type, and grade of fuel burned, condition of heating surfaces, excess air, etc. [2]. in addition, obtaining a mathematical model of superheated steam temperature is usually associated with approximation of acceleration curves obtained experimentally, as a result of which the mathematical description becomes a priori inaccurate. the study of scientific publications in the field of adaptive ars (automatic control systems) in dynamic systems [1,2] led to the conclusion that traditional methods of active identification and associated algorithms for calculating optimal settings for pi and pid controllers that analyse the complex frequency response of objects or the self-oscillation mode are widely used. it should be noted that for the considered acs of the temperature of the steam, the self-oscillation process is unacceptable due to the requirements of the technological regulations, since a deviation of the steam temperature from the norm can lead to premature wear of the turbine equipment. thus, the scientific problem arises of finding the optimal methods for identifying an object in cases of changes in its load and algorithms for calculating pi controller settings to ensure the expected transition process (by overshoot g <30%, attenuation degree, with minimum control time rt ) [1,2]. the use of pid-law in power engineering leads to an increase in the quality of regulation. with regard to the acs of the steam temperature, the use of the pid-law of regulation allows maintaining temperature fluctuations more accurately in the whole steam output range of the boiler unit, which is a top priority. the use of the pid algorithm is limited by the complexity of its setup. this is due to the peculiarity of acs operation with pid controllers: high sensitivity to deviation of their optimum settings and the impossibility of applying the step method for obtaining the type of transient process. a disadvantage of the known methods of setting the parameters of the pid controller is the incomplete information about the system stability margin and robustness. safety margin and robustness determines the reliability of the regulator. to consider these factors, an analysis is needed to change the dynamics of the control object and, in this case, obtain a transient response of the control object, model the control object taking into account the range of changes in dynamic characteristics, and go to settings that are close to optimal and do not need significant additional tuning. the algorithms of operation of automated control systems developed at the design stage, as a rule, differ significantly from the optimal values of the parameters of traditional regulators. this is due to the imperfection of mathematical models of objects. it is known that obtaining mathematical models of experimental control systems for operating complex objects is a difficult task. these difficulties are associated with the influence of external and parametric perturbations, some of which are non-stationary in nature and are not subject to control [3]. in this regard, it is necessary to use adaptive intelligent control systems for complex multi-mode dynamic objects, which include drum boilers, using neuro-fuzzy technology 183 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 and the necessary measure to improve the efficiency of production management in general. 2. research methods currently, scientific approaches associated with the use of intelligent systems [5, 6], based on the hybrid application of neural regulators and neural networks, have become widely popular in the theory of adaptive control, which prompted the emergence of a new scientific direction hybrid, or neuro-fuzzy networks (hn, nfn) [4]. consideration of this technology in relation to the identification and adaptation of the acs of the temperature of superheated steam is an important scientific task. the control parameters of the fuzzy pid controller include fuzzy parameters, fuzzy inference rules, and the resolution of the parameters of the fuzzy pid controller. based on the setup input and the feedback signal, the computer calculates the deviation and the current change in the deviation of the actual position and the theoretical position. it then processes the fuzzy reasoning according to a fuzzy rule. finally, the fuzzy parameters were processed by a fuzzy solution and output a proportional (p), integral (i), and differential (d) coefficients of the pid controller. as an object of regulation, we consider the automatic control system (acs) of the temperature of the superheated steam of a drum boiler [1, 2]. the task of controlling the superheater was to provide a predetermined temperature in the steam path of the boiler. the steam temperature is changed by increasing or decreasing the amount of water injected into the superheater to stabilize the set value of the steam temperature at the superheater outlet. to solve this problem, we will use intelligent control methods, in particular, the fuzzy logic method. this allows synthesis of process control systems in the class of neural network systems. the task is then to stabilize the controlled variable with a given quality of the transition process with incomplete information about the control object and to obtain invariance properties to external disturbing influences of the automatic control system. to solve the problem, it is necessary to [3]: 1. describe the control object and define its input and output parameters and disturbing influences. 2. choose the fuzzy inference algorithm that most fully determines the decisions made under the given conditions of the process. 3. synthesise a fuzzy controller, which is an integral part of an intelligent controller and provides the required qualitative and quantitative indicators of temperature control in the presence of disturbing influences. 4. investigate the obtained response surfaces of a fuzzy regulator under the conditions of the presence of disturbing influences and a pure delay characterizing the technological process. as a control object (fig. 1), we consider a superheater with a thermocouple. the transfer function obtained as a result of processing a family of acceleration curves [6], we write in explicit form as follows: 184 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 111 2 2 3 3 t m sasasa ek sv sy sw chct chct s fm (1) where s is a complex variable; sy and sv images of scalar functions of output and input of an object; k injection ratio; transport delay; 1a , 2a , 3a parameters of the characteristic equation of the function; swfm ; consttchct and constmchct time constant and static coefficient of a chromel-copel thermocouple. based on the technological regulations for a particular superheater, the interval of change of parameters is represented by the following relations: 3909600345600 ,6192020160 ,393244 ,2015 ,14145 ,6.48.2 333222 111 aaaaaa aaattt kkk chctchctchct (2) 321 ,,,,, aaathkcol chct , where the superscripts and are the values of the boundaries of the coefficients that determine the known set ; vector of unknown parameters. fig. 1: the main circuit control temperature superheater. the transfer function of the actuator (which moves the regulating body of the control object the valve), taking into account its inertia with respect to the object, will be described as stsu sv sw ca ca 1 , (3) where constтca is the time constant of the actuator. the structure of the adaptive controller, taking into account the neuron, is given in the form ; 10 2 sg st sk su (4) ;trttg (5) ; 1 1 , 0wtewe rteft 185 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 ;constrtr (6) ,tqtyrtyrte q where 2k and 0t the transmission coefficient and the time constant of the linear part of the adaptive controller; su control action; tg the output of the nonlinear part of the adaptive controller represented by a single neuron with a sigmoid activation function t and weighting coefficients w and 0w . the input of the neuron is a generalized regulation error te ; tr setting effect equal to the value *r in the stabilization mode; tyq generalized output control system of the form tqtytyq . the proposed system differs in that, in the control circuit, there is a single fuzzy-logic controller (flc) with two inputs and one output. the fuzzy controller is assigned the task of generating a control action in the range of variation of the dynamic regulation error and it is integral with respect to its threshold values. therefore, when synthesizing a fuzzy controller, we use the mamdani output algorithm [4] as the simplest one. although the mamdani algorithm is recommended for use in other areas (expert systems and decisionmaking systems), it can work effectively in the development of fuzzy process control systems. as you know, a fuzzy controller consists of three main blocks: the fuzzification block, the fuzzy output block and the defuzzification block. in the first block, it is necessary to fuzz the input signals, i.e. translate well-defined signals into fuzzy form. to do this, we first determine the number of fuzzy statements for each input signal, which will be operated by the flc knowledge base and is a meaningful component of the fuzzy output block. to fill an initially empty knowledge base, you must define a management goal. in this case, the goal of control is to maintain the technological parameter in a given range of deviations from the desired value in the event of controlled and uncontrolled disturbances. in this case, the more the deviation of the technological parameter from the threshold value increases, the greater should be the increment that changes the coefficient of transfer of the regulator. flc has two input signals: ;;,,"" max1 min 111 eeaerrore e ; ;;,,"error integral" max2 min 222 eeae e . for the 1e signal, we write the following statements: '' 1enb – «deviation of steam temperature is negatively large»; '' 1enm – «deviation of steam temperature is negatively average»; '' 1ens – «deviation of steam temperature is negatively small»; '' 1eze – «deviation of steam temperature near zero»; '' 1eps – «the deviation of the temperature of the steam is positively small»; '' 1epm – «temperature deviation of steam is positively average»; 186 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 '' 1epb – «deviation of steam temperature is positively large.»; then the term sets of the linguistic variable “error” can be defined as: 11111111 ,,,,,, eeeeeeee pbpmpszensnmnba . in the same way we will define a term a set of the linguistic variable “integral. error” as: 22222222 ,,,,,, eeeeeeee pbpmpszensnmnba . if we consider that flc has an output signal 21 , eefuzzyu , then its output linguistic variable can be represented as: maxmin ;,,"" uuacontrolu u , where ,,,,,,, uuuuuuuu pbpmpszensnmnba ; '' unb – «water consumption is negatively large»; '' unm – «water consumption is negative average»; '' uns – «negatively low water consumption»; '' uze – «water flow around zero»; '' ups – «positively low water flow»; '' upm – «water consumption is positively average»; '' upb – «positively large water flow». operating with the received input and linguistic variables, the goal of management will build a knowledge base for the fuzzy logic controller (table 1). choosing linguistic variables and making up the knowledge base of flc, you can proceed to the phase of fuzzification, the purpose of which is to establish the correspondence between the specific values of individual input and output variables of the fuzzy logic controller and the values of the membership functions of the corresponding thermal linguistic variables. at the end of this stage, the specific values of the membership functions for each of the linguistic terms should be defined. table 1 applies to all linguistic variables. table 1: values of membership functions for all linguistic variables 1e 2e 1enb 1enm 1ens 1eze 1eps 1epm 1epb 1enb 1enm 1enb unb unb unb unb unm uns uze unb unb 1enm unb unb unb unm uns uze ups unb unb 1ens unb unb unm uns uze ups upm unb unb 1eze unb unm uns uze ups upm upb unb unm 1eps unm uns uze ups upm upb upb unm uns 1epm uns uze ups upm upb upb upb uns uze 187 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 further, the mamdani output algorithm is used, which formally consists of the following: aggregation of sub-conditions in fuzzy rules. to find the degree of truth of the conditions of each of the rules, fuzzy logic operations are used. those rules, and the degree of truth that is non-zero, are considered active and are used for further calculations. activation of sub-conclusions in fuzzy rules is carried out according to the formula [5]: xcy ,min 1 , (7) where x is the term membership function, which is the value of some input variable; 1c the degree of truth of the sub-conclusions for each of the rules. accumulation of conclusions fuzzy rules of production. fuzzy sets are merged, corresponding to the terms of the subclasses belonging to the same output linguistic variables: xxx ee aadtteie 21 ,max , (8) where x ea 1 , x ea 2 are the membership functions of the merged fuzzy sets 1ea and 2ea . calculation of control variable values at the output of a fuzzy controller. to do this, it is necessary to find the function of belonging to a variable to a set formed as a result of executing output operations on sets included in the rule system (table 1). the membership functions for each of the sets ,,,,,,, uuuuuuuu pbpmpszensnmnba included in the fuzzy variable u ~ in the inference rules are defined as: edteuu eevr 1,21,11 ,min, ~min~ 1 , edteuu eevr 2,22,12 ,min, ~min~ 2 , edteuu eevr 3,23,13 ,min, ~min~ 3 , (9) edteuu eevr 4 9,24 9,14 9 ,min, ~min~ 3 . here, each of the 49 equations corresponds to one of the rules (table 1). the resulting membership function of the control action v~ , obtained after the application of all 49 rules, is found as the union of the membership functions of all rules: uuuu rrr ~,,~,~max~ 4 921 . (10) defusing output variables. now that the resulting membership function of the control action is obtained, the question arises as to which particular value of control action v~ should be chosen. if we use the probabilistic interpretation of the theory of fuzzy sets, it becomes clear that such a value can be obtained by analogy with the mathematical expectation of the control action in the form: 188 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 max min max min ~~/~~~ uduuduuu . (11) to determine the tuning values of the neuron weighting coefficients, we perform the following procedure, let’s set the mode of the system stabilization process described by the equations: gtmkky cachctq 1 2* , (12) ** 0 rg , (13) *,*,0 ref , 0*q , 0**** * yryre q , (14) where index * is the designation of the steady-state values of the corresponding variables. equations (12) (14) can be combined and represented identically as an expression *0 1 2* rtmkky cachctq , (15) which is often called the implicit reference model equation. in particular, from (15) it follows, taking into account the equality ** ryq , that the value const0 always exists and is determined by the expression chct ca mkk t 2 0 . (16) the adaptive fuzzy-logic controller is configured using the weighting coefficients of artificial neural networks, using the back-propagation error algorithm. in this case, the output signal of the neuron -th time is defined as ( ,2,1 ) e f 1 1 , (17) where eww0 . (18) thus we get a lot of output signals nnii ,,,,11 , (19) 2 0 2 2 1 2 1 e . (20) which is subject to the condition constryty t **lim , corresponds to the reference value of the output signal const0 , i.e. constnnn 0lim . in our case, the reference output will be (16), and the reference input will be 0*e . we formulate a measure of error, based on a comparison of signals (16) and (19), we define the half-sum of the squares of the differences for the correction of the weighting coefficient w , we will use the method of fastest descent, which is the most simple to implement. 189 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 dw de yww 1 , (21) where 0y determines the size of the correction step. here, it is necessary to take into account that e d de dwd dde dw de . (22) enter the designation d de , (23) get the algorithm for calculating the correction weights in the form eyww 1 . (24) here is calculated by the formula: .1 2 1 2 1 0 ' 0 2 0 2 f d d d d d de (25) taking into account (25), the algorithm for setting the weights of the neurons is as follows: eyww 11 00 (26) 11 000 yww . (27) finally, taking into account (16), we obtain: e mkk t yww chct ca 11 2 , (28) .11 2 00 chct ca mkk t yww (29) on the basis of the developed regulatory system, a simulation model was formalized and a computational experiment was performed in matlab [4,7]. 3. results and discussion analysis of transients (fig. 1) showed that with the influence of a parametric perturbation, the hybrid system has a shorter regulation time ( 1381rt s) compared to traditional adaptive acs ( 1632rt s), as well as overshoot hybrid acs %28trg traditional %50trg , the degree of attenuation of the hybrid 91,0 tr , traditional 68,0тр , i.e. the proposed hybrid acs is optimal and energy efficient. 190 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 fig. 2: transient processes along the control channel: 1-neuro-fuzzy acs (at nominal load), 2 neuro-transparent acs (when the load changes). 4. conclusion based on the obtained results, it can be concluded that the proposed intelligent adaptive acs temperature of superheated steam has the following advantages: the speed of the process of finding the optimal settings of the pi controller of the cascade acs with the possibility of approximation and extrapolation; smaller first deviation and time of the transition process regulation; the possibility of optimal functioning of the cascade acs in all modes of the steam drum boiler; the use of adaptive fuzzy-logic allows you to provide a fairly good quality control of the temperature of superheated steam. the possibility of using adaptation of various acs of tp, acs with pd, and pid regulators in the heat supply in the processes of adaptation. the results of the study showed that during the control of the temperature regime of the boiler unit, a developed adaptive system of fuzzy pid regulators has a faster response, higher regulatory accuracy, and the best functioning in stationary mode. it should be noted that when using an adaptive fuzzy pid regulator, the reconstitution is reduced by 20%, the control time of 35 seconds, degree attentiveness increased by 0.23, and the control regulation decreased by 15%, the dynamic characteristic of the adaptive control system with a fuzzy pid controller is improved. the performance of the control system of adaptive fuzzy system with pid by a regulator is much better than the digital pid controller and more energy-efficient. references [1] o’dwyer a. (2009) handbook of pi and pid controller tuning rules. 3rd edition. dublin: institute of technology; ireland, imperial college press. 529 p. [2] astrom kj. (2006) advanced pid control/ k. j. astrom, t. hagglund – isa (the instrumentation, systems, and automation society), 460 p. [3] demchenko va. (2001) automation and modeling of technological processes at nuclear power plants and thermal power plants / v. a. demchenko. odessa: astroprint. 308 p. 191 iium engineering journal, vol. 21, no. 1, 2020 xakimovich et al. https://doi.org/10.31436/iiumej.v21i1.1220 [4] kim t, maruta i, sugie t. (2008) robust pid controller tuning based on the constrained particle swarm optimization, automatica, 44(4): 1104-1110. [5] lu c, hsu c, juang c. (2013) coordinated control of flexible ac transmission system devices using an evolutionary fuzzy lead-lag controller with advanced continuous ant colony optimization, ieee transactions on power systems, 28(1): 385-392. [6] pelusi d. (2012) pid and intelligent controllers for optimal timing performances of industrial actuators, international journal of simulation: systems, science and technology, 13(2): 65-71. [7] pelusi d, mascella r. (2013) optimal control algorithms for second order systems, journal of computer science, 9(2): 183-197. [8] pletnev gp. (2007) automation of technological processes and productions in heatandpower engineering. 4th edition. moscow: publishing house moscow power engineering institute. -352 p. [9] rotach vy. (2008) the theory of automatic control. moscow: publishing house moscow power engineering institute. 396 p. [10] siddikov ix, iskandarov z. (2018) synthesis of adaptive-fuzzy control system of dynamic in conditions of uncertainty of information // international journal of advanced research in science, engineering and technology, 5(1): 5089-5093. [11] siddikov ix, umurzakova dm. (2019) features of automatic control of technological parameters of water level in the drum steam boilers, journal of southwest jiaotong university, 54(3): 1-10. doi: 10.35741/issn.0258-2724.54.3.1. [12] siddikov ix, umurzakova dm. (2019) mathematical modeling of transient processes of the automatic control system of water level in the steam generator, universal journal of mechanical engineering, 7(4): 139-146. doi: 10.13189/ujme.2019.070401. [13] sidikov ix, umurzakova dm. (2019) adaptive neuro-fuzzy regulating system of the temperature mode of the drum boiler // international journal of advanced research in science, engineering and technology, 6(1): 7869-7872. [14] soroko em, golden sections. (2006) processes of self-organizing and evolution in systems: introduction into the general theory of system harmonizing. moscow: komkniga. -264 p. 192 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <feff004b00e40079007400e40020006e00e40069007400e4002000610073006500740075006b007300690061002c0020006b0075006e0020006c0075006f0074002000410064006f0062006500200050004400460020002d0064006f006b0075006d0065006e007400740065006a0061002c0020006a006f0074006b006100200073006f0070006900760061007400200079007200690074007900730061007300690061006b00690072006a006f006a0065006e0020006c0075006f00740065007400740061007600610061006e0020006e00e400790074007400e4006d0069007300650065006e0020006a0061002000740075006c006f007300740061006d0069007300650065006e002e0020004c0075006f0064007500740020005000440046002d0064006f006b0075006d0065006e00740069007400200076006f0069006400610061006e0020006100760061007400610020004100630072006f0062006100740069006c006c00610020006a0061002000410064006f00620065002000520065006100640065007200200036002e0030003a006c006c00610020006a006100200075007500640065006d006d0069006c006c0061002e> /sve <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> /tur <feff0130015f006c006500200069006c00670069006c0069002000620065006c00670065006c006500720069006e0020006700fc00760065006e0069006c0069007200200062006900e70069006d006400650020006700f6007200fc006e007400fc006c0065006e006d006500730069006e0065002000760065002000790061007a0064013100720131006c006d006100730131006e006100200075007900670075006e002000410064006f006200650020005000440046002000620065006c00670065006c0065007200690020006f006c0075015f007400750072006d0061006b0020006900e70069006e00200062007500200061007900610072006c0061007201310020006b0075006c006c0061006e0131006e002e0020004f006c0075015f0074007500720075006c0061006e002000500044004600200064006f007300790061006c0061007201310020004100630072006f006200610074002000760065002000410064006f00620065002000520065006100640065007200200036002e003000200076006500200073006f006e00720061006b00690020007300fc007200fc006d006c0065007200690079006c00650020006100e70131006c006100620069006c00690072002e> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 dragan 225 centrifugal compressor efficiency calculation with heat transfer valeriu drăgan computational fluid dynamics department, incdt comoti, iuliu maniu 220d, sect. 6, bucharest, romania. corresponding author: drvaleriu@gmail.com (received: 11 th july 2016; accepted: 15 th june 2017; published on-line: 1 st dec. 2017 abstract: in this paper we present a case study of apparent performance variation of an optimized centrifugal compressor design when its metal parts are cold before the conjugated heat transfer between the fluid and parts reaches an energetic equilibrium. the methods used are numerical, using full viscous 3d computational fluid dynamics with heat transfer. three cases were considered, an adiabatic wall baseline, an all-blade cooling at 293 k and a more realistic stator row cooling at 293 k. results indicate an apparent yet erroneous isentropic efficiency reading increase beyond 100% which was to be expected due to the fluid cooling. however the isentropic and polytropic efficiencies could be estimated and were used to more accurately assess the performance of the compressor. power consumption decreased to approximately 97% of the original load while the pressure ratio was marginally increased. this alone does not, however, explain the non-physical efficiency readings, which are mainly due to the assumptions and manner under which the efficiency itself is calculated. the paper presents a more robust approach to measuring efficiency, regardless of the heat transfer within the turbomachinery itself. possible applications of the study may range from cold-start regime simulation to the optimization of inter-cooling setup or even flow angle control without mechanically actuated ogv. abstrak: kertas ini membincangkan tentang kajian kes ke atas perubahan jelas pada rekaan pemampat sentrifugal yang dioptimumkan ketika logam disejukkan – sebelum berlaku perubahan pemindahan haba ke atas bahagian tersebut antara keadaan cecair dan takat keseimbangan tenaga. kaedah yang digunakan adalah numerikal, dengan menggunakan pengiraan kelikatan penuh cecair 3d dinamik melalui perubahan tenaga. tiga kaedah telah diambil kira, iaitu: garis pemisah adiabatik, penyejukan pada semua bilah pada suhu 293 k dan pendekatan yang lebih realistik iaitu baris stator yang disejukkan pada suhu 293 k. keputusan mendapati kesalahan kenaikan bacaan yang jelas pada ketepatan bacaan isentropik melebihi 100% keputusan ini telah dijangka akan berlaku disebabkan oleh kesan penyejukan cecair. walau bagaimanapun, ketepatan isentropik dan politropik boleh dianggarkan dan telah digunakan untuk menilai ketepatan prestasi pemampat. penggunaan tenaga telah berkurangan sebanyak 97% daripada beban asal, sementara nisbah tekanan telah bertambah sedikit. perkara ini, walau bagaimanapun tidak dapat menjelaskan bacaan yang tepat pada perkara yang tidak bersifat fizikal, kebiasaannya berlaku disebabkan oleh andaian dan cara ketepatan bacaan itu dikira. kertas ini membentangkan pendekatan yang lebih mantap untuk mengukur ketepatan, tidak kira sama ada ketika pemindahan haba berlaku di dalam mesin turbo itu sendiri. aplikasi yang berkaitan kerja ini mungkin termasuk bermula dari simulasi rejim mulasejuk (cold-start), sehingga kepada antara persediaan penyejukan ataupun kawalan darjah aliran penyejukan tanpa mesin gerakan ogv. keywords: turbo machinery; centrifugal compressor; inter cooler; intra-cooler; sst iium engineering journal, vol. 18, no. 2, 2017 dragan 226 1. introduction industrial compressor designs typically include inter-cooling devices in order to reduce the mechanical work for compression and to increase the efficiency of the entire compression process [1, 2]. since space is always a limiting factor not only in aeroengines but also in industrial turbomachinery, an intracooler (i.e. a cooler within the stage itself) might reduce the size of the machine itself and/or improve the inter-stage cooling efficiency and reduce power consumption. defining efficiency proves to be difficult in applications where the heat transfer occurs either inside the rotary part, as is the case here, or in a very tight package inaccessible with temperature and pressure probes, as is the case in small turbochargers [3] or electronic appliances [4]. being unable to separate heat transfer effect from thermal effects associated with the compression (or, indeed expansion) presents a distinct problem which will be addressed herein. therefore, a novel approach to determining a more practical definition of isentropic and polytropic efficiency is developed. moreover, an argument is made regarding possible applications of these effects such as thermal flow control of both friction and flow angles this paper deals with such an industrial four stage compressor with a nominal air mass flow in excess of 4 kg/s. each stage has a centrifugal rotor, vaned diffuser crossover, discharge plenum and intercooler followed by a plenum to remove condensed moisture. figure 1 presents the schematic of a centrifugal compressor having its architecture topologically equivalent the one currently discussed in [5]. fig. 1: the generic configuration of the compressor discussed adapted from [5]. we will only refer to the last, high pressure stage, having a rotating speed of 3215 rad/s, an inlet temperature of 313 k, which is regulated by the previous stage intercooler, and a total inlet pressure of 800000 pa. the intercooler itself uses water at 293 k as a cooling agent which passes through a tubular circuit cooling the compressed air flowing out of the diffuser. typically intercoolers have been used to lower the temperature hence impeller shaft inlet duct for 4th stage cooling fluid ducts intercooler casing with integrated moisture vaned diffuser discharge volute iium engineering journal, vol. 18, no. 2, 2017 dragan 227 workload for the downstream compressor stage. in the cases presented herein, the cooling occurs during the actual compression process hence the assumption that an ideal process should be isentropic is no longer valid, leading to anomalous readings. the paper attempts to answer the question of how to monitor in an acceptable manner the efficiency of the compressor during start-up, when the metal parts affect the readings by essentially cooling the working fluid for a brief period of time. the sources of the anomalous efficiency readings and suggested corrective actions will be presented in the following sections. another question refers to the actual influence of cooling distribution across the stage in the overall power consumption and achieving the target pressure ratio. preliminary findings show that pressure ratios will not be adversely influenced by the infracooling and that power consumption may be slightly lowered particularly if the rotor is cooled. for this particular case study, a known optimized centrifugal compressor stage was considered [6]. the stage has been recently designed using a combination of an genetic algorithm [7] and an artificial neural network [8]. in paper [6], one of the conclusions reached was that the aerodynamic performance of the compressor cannot be significantly further increased by maintaining the conventional architecture of the compressor and that the thermodynamic losses were the limiting factor in improving its isentropic efficiency. one argument for the use of the stage is that it has also been manufactured and is currently in use, therefore experimentally confirming the cfd results obtained for the baseline. a secondary purpose of this paper is to examine the influence of rotor and stator cooling effect occurring with cold starts. during the initial experimentation phase a calculated efficiency exceeding 100% was obtained for a brief but sustained period of time during the starting. this was attributed not to faulty data acquisition since the efficiency reading eventually stabilized at the expected value for respective speed line. instead, an alternative explanation that the flow experienced a temporary cooling effect due to the fact that the compressor parts were at a temperature of 293 k, hence the total temperature of the outflow was influenced. 2. the computational fluid dynamics methodology for the cfd study, numeca's fine/turbo structured solver was used with a mesh having the properties described in table 1. the turbulence model chosen was the k-omega sst [9,10], due to its proven accuracy in various other turbomachinery applications [1113]. to simplify matters, the simulations were carried out using steady-state rans with constant temperature of 293 k at the cooled walls and adiabatic walls in all the others. prior to the simulation of the thermal transfer between the compressor walls and the working fluid, a grid sensitivity test was carried out. multiple mesh sizes were tested, monitoring both the global results such as total to total pressure ratio and efficiency as well as the quality of the interface between the rotating and stationary domain. the sensitivity study was started with a coarse mesh and its density was increased. due to the tip gap of the rotor, the topology of the blocking structure differs for the rotating and stationary domains. the mesh density was increased keeping the rotor and stator interface cells as closely synchronized as possible in order to minimize interpolation loss [14]. another parameter of interest was the isentropic efficiency difference on the two sides of the interface this is has a purely numerical cause and is due to a less than perfect approximation of the flow parameters in the interface model. the skewness, along with other mesh quality indicators, was also monitored in all meshes and the values were found iium engineering journal, vol. 18, no. 2, 2017 dragan 228 to be generally good, considering the complexity of the geometry. the few cells which are less than the typically recommended values for skewness are still above the minimal value accepted by the solver [14]. moreover, for heat transfer applications, a skewness level of the order used in the current simulations was considered acceptable [15], which present a mesh dependency study in which the maximum skewness of the fine mesh was 0.33 (*the actual value given was 0.57 but this is due to a converse definition of skewness which considers the perfect cell skewness at 0.00). table 1 presents the skewness of three representative meshes used for the grid sensitivity tests, the criterion is fully presented in [16] and is implemented by ansys in icem cfd [17]. as seen in table 2, the differences between the cfd results obtained with the fine mesh and the mesh which was used is lower than 0.0025, which is considered below the margin of error for typical rans simulations. three cases were simulated, the baseline – having all adiabatic walls, a fully cooled stage – having all walls with a constant temperature of 293 k and a final, more realistic case, having only the stator walls cooled to 293 k. in fig. 2 a meridional view of the computational domain is shown, comprising of compressor inlet, rotor, vaneless diffuser, vaned diffuser – which covers the 90° crossover, plenum space and outlet. note that in this case the actual intercooler which is downstream of the compressor is not modeled. table 1: mesh quality statistics for three of the meshes used for grid sensitivity checked with ansys icem-cfd skewness coarse mesh intermediate mesh fine mesh 1 531034 810691 1346979 0.95 233388 483557 600717.5 0.9 191381 286110 417272.5 0.85 122641 194958 253901.3 0.8 73621 135338 165965 0.75 92252 96458 177991.3 0.7 57797 64907 111066.3 0.65 21618 38638 36200 0.6 10428 19780 19460 0.55 4610 9543 7775 0.5 1817 2926 2109 0.45 511 405 292 0.4 166 305 0 0.35 16 200 0 0.3 0 54 0 0.25 0 0 0 0.2 0 0 0 0.15 0 0 0 0.1 0 0 0 0.05 0 0 0 total cells 1341280 2143870 3139729 iium engineering journal, vol. 18, no. 2, 2017 dragan 229 table 2: mass averaged total temperature and pressure taken at stage outlet and the isentropic efficiency calculated based on them. case fine mesh 403.7 1730020 0.850764 intermediate 403.454 1730350 0.853313 coarse mesh 402.6 1735020 0.864801 figure 3 presents a view of the surface mesh of a rotor and a stator flow channel; mesh smoothing was used to increase the orthogonality of the mesh as well as the growth ratio of the cells from the near wall cell to the periodic boundary. the mesh is conformal at the tip as well as at the periodic interfaces. although the notion of solution convergence depends heavily on the goals of the case and on the user's personal choice of criteria [18], certain general guidelines were employed in determining a stopping point to the simulations. thus, the residual values were monitored and stabilized at around 10-3.9, the pressure ratio fluctuations less than 0.3 %, and mass flow imbalance below 0.4% in all the three cases presented. fig. 2: flow channel of the stage considered, streamlines on medium mesh used. in terms of convergence, the several parameters which were continuously monitored during each run in order to insure that the relevant parameters have stopped evolving (i.e. their instantaneous values were fluctuating with a stable amplitude and frequency above the same average for almost 2000 iterations) before the case was considered converged. (a) rotor blades diffuser blades with 90° crossover vaneless diffuser space plenum space meridional view iium engineering journal, vol. 18, no. 2, 2017 dragan 230 (b) fig. 3: (a) the computational mesh used for the rotor, (b) the stator mesh and details. although perhaps not universally applicable, the mass flow imbalance is typically one of the most relevant parameter used in turbomachinery simulations for assessing the solution convergence, along with pressure ratio and isentropic efficiency. hence, fig. 4 presents the mass flow differences which were monitored for the three cases mentioned. isentropic efficiency in the case of turbomachinery is a parameter used to assess the extent to which the compression process (in this particular case) which is ideally considered to be isentropic reaches the ideal limit. therefore it is the expression of the isentropic, rather than polytropic, efficiency which gives the user the estimate power consumption. this is due to the fact that the standard assumption is that the compression process should be adiabatic. another way of looking at this is that the isentropic efficiency encompasses all losses (aerodynamic and thermodynamic) whereas the polytropic efficiency only accounts for the thermodynamic losses [19-22]. iium engineering journal, vol. 18, no. 2, 2017 dragan 231 fig. 4: mass flow for inlet/outlet for the three cases presented in the current paper. isentropic efficiency in the case of turbomachinery is a parameter used to assess the extent to which the compression process (in this particular case) which is ideally considered to be isentropic reaches the ideal limit. therefore it is the expression of the isentropic, rather than polytropic, efficiency which gives the user the estimate power consumption. this is due to the fact that the standard assumption is that the compression process should be adiabatic. another way of looking at this is that the isentropic efficiency encompasses all losses (aerodynamic and thermodynamic) whereas the polytropic efficiency only accounts for the thermodynamic losses [19-22]. in order to assess the isentropic efficiency, an alternative equation was used to eq. (2), since the total temperature (and enthalpy) was influenced by the heat transfer with the walls. ( ) (1) ( ) (2) the alternative isentropic efficiency definition used was deduced from the torque of the shaft and the total-to-total pressure ratio: (3) ̇ (4) ( ) (5) ̇ ( ) (6) based on this, an estimate of the isentropic efficiency was done by using the more relevant parameter of pressure ratio – which is less affected by the heat transfer, as it will be shown further on. hence, the proposed polytropic efficiency formulation is presented as: iium engineering journal, vol. 18, no. 2, 2017 dragan 232 ( ) ( ) (7) a note can be made regarding convergence time required for the cooled cases where a significantly higher number of iterations were necessary for the mass imbalance to drop below the 0.4% margin (which was set as a convergence criterion for all three cases). this is due to the more complex interactions between the flow and the walls in particular to the convection processes that occur in the turbulent boundary layer. also, the higher number of iterations required is due to the fact that, in order to stabilize the solver, a cfl number three times lower than for the baseline case was required for the cooled cases. 3. results and discussion due to the atypical nature of the flow simulations presented, the classical equation for isentropic efficiency normaly used in actual monitoring of operating compressors is not usable. this is due to the significantly lower outlet temperature which is in turn due to the heat transfer between the fluid and the compressor walls. as pointed out in [19-22], the isentropic efficiency is especially useful for turbomachinery designers in assessing the aerodynamic losses (rather than just the thermodynamic losses which are assessed by using the polytropic efficiency). therefore it is important to circumvent the faulty methodology for calculating isentropic efficiency and also to link it to measurable parameters which could be instrumented on real applications. one way to eliminate this inconvenience is to use the power consumption of the compressor in order to estimate the actual aerodynamic losses. equations (6) and (7) can be used to determine the isentropic and polytropic efficiency respectively in cases where heat transfer occurs between the working fluid and the machinery walls. a point must be made that a rigorous equation would have to factor the effort required by the cooling installation which should be considered a source of power loss. for the cases presented, however, the main question to be answered was how to eliminate the anomalous efficiency reading greater than one. hence heat transfer is not dependent on an external cooler and is hence effortless from a power consumption perspective. it is worth noting that heat transfer only lasts for a limited period of time, decreasing in intensity until the conjugated heat transfer between the metal parts and the working fluid reaches thermodynamic equilibrium and the walls behave overall adiabatically. as expected, the cases where cooling was applied along the stage displayed a higher efficiency and pressure ratio than the baseline which had adiabatic walls. this is in part related to the method in which the isentropic efficiency of the stage is calculated but it also has to do with the fact that the working fluid – having been cooled – requires less compression mechanical work. this having been said, the pressure ratio increased only slightly in the fully cooled case and the only visible differences were observed in the pressure ratio measured at the rotor-stator interface. however, in the fully cooled case, although minor pressure ratio increases were seen, the aerodynamic power consumption dropped to ~96.84% of the baseline –which could be significant. figure 5 presents the y+ distribution across the rotor geometry which is the same for the three cases studied. the plots confirm that the mesh size near the wall was in accordance with the prescriptions of k-omega models which require a less than one unit iium engineering journal, vol. 18, no. 2, 2017 dragan 233 y+. two aspects were monitored: the aerodynamic losses which could be accurately estimated through the polytropic efficiency and the thermodynamic process losses which could only be inferred from the modifications of the flow coefficient and the specific speed. an influence over the torque and pressure ratio was observed in both cases, as well as a reduction in the fluid deviation from the blade at the rotor outlet. tables 3 and 4 present the global parameters of interest for the three cases. for a more visual comparison, figure 6 presents a meridional average entropy distribution along the flow channel for the three cases. fig. 5: dimensionless wall height distribution of the first cell on the rotor for the three cases. slip factor, although apparently high – compared to other optimized compressors – is explainable due to the location at which it is measured. typical correlations [23-25] refer to the exact rotor outlet (in which the fluid has minimal slip), in our cases the measurements were taken in the middle of the distance separating the rotor from the vanes of the diffuser. therefore, as expected, both efficiency and slip factor measurements were below the values reported by typical optimized rotors. it was felt, however that the measurement point chosen was more representative for the rotor for the practical purpose of estimating the polytropic efficiency using eq.(7). table 3: global parameter synthesis for rotor-stator interface and stage rotor-stator interface adiabatic full stage cooling stator cooling only specific speed 0.4565088 0.4658891 0.467094 flow coefficient 0.6820208 0.6973607 0.682961 isent. eff. eq. (1) 0.9158536 1.0136014 0.9616 isent. eff eq. (6) n.a. 0.967467 0.925719 polyt. eff. eq. (2) 0.9250883 1.0120773 0.965853 polyt. eff. eq. (7) n.a. 0.97110685 0.93393505 slip factor 0.7516529 0.7678544 0.752223 power [w] 407086.69 394224.55 407086.7 press. ratio 2.3001112 2.33665 2.315713 axial thrust -44930 -44790 -45110 iium engineering journal, vol. 18, no. 2, 2017 dragan 234 fig. 6: entropy distribution along the flow channel adiabatic (top) full cooling (mid) and stator cooling (bottom). note how the entropy differs greatly from the case with and without cooling, although it is higher in the case in which the stator alone is cooled. this can be explained due to the high exposure surface aria between the fluid and the stator channel – which dominates the stage in terms of length. also significant influences were observed on the slip factor of the cooled rotor and also on the stage outlet flow angle of the fully cooled stage, where the specific speed is defined as: | | √ ̇ ( ) (8) iium engineering journal, vol. 18, no. 2, 2017 dragan 235 and the flow coefficient as: ̇√ ( ) | | √ (9) table 4: global parameter synthesis for the entire stage entire stage adiabatic full stage cooling stator cooling only isentropic efficiency eq. (1) 0.853 1.432 1.366967 isentropic efficiency eq. (6) n.a. 0.897 0.86861 polytropic efficiency eq. (2) 0.869 1.386 1.328 polytropic efficiency eq. (7) n.a. 0.908 0.882 flow angle (degrees from through flow direction) 47.67 56.52 46.2 pressure ratio (t-t) 2.194 2.212 2.211 outlet temperature 405.274 368.633 371.254 velocity magnitude 38.7874 47.2784 39.7024 5. conclusions simulations confirmed that the isentropic efficiency of the stage can be influenced by the heat transfer from the working fluid to the cold metallic parts of the compressor in its cold starting sequence. the paper presents a new approach, proposing new formulations for the total to total isentropic and polytropic efficiencies in order to eliminate the apparent greater than one efficiency. herein we take into consideration the consumed aerodynamic power and are therefore not prone to un-physical efficiency estimations. although, obviously not as high as estimated by eqs.(1) and (2), the efficiency of the cooled cases is higher than in the case of adiabatic walls, from the power consumption corroborated with the total pressure ratio. total temperature differences are comparable between the two cooled cases while in terms of power consumption, flow angle and absolute velocity, the most significant influence is seen only when the full stage is cooled. when the rotor is cooled the slip factor is significantly changed by the increased through flow velocity in the rotor due to less work necessary for compression. the same goes for the flow coefficient, surprisingly, since the surface aria of the stator has a much higher participation than that of the rotor. note that the correlations of polytropic efficiency with the flow coefficient [26] or [27], cannot be applied to the cases where there is heat transfer. flow angle influences set the premises of using thermal effects for small turbomachinery applications such as micro turbine engines where variable geometry would be prohibitive. iium engineering journal, vol. 18, no. 2, 2017 dragan 236 acknowledgement the author would like to acknowledge the support of the nrdi comoti for the current research as well as the particular contributions of eng. georgel vizitiu for the overall revamping efforts on the ccae 21-300 aerodynamics. references [1] teemu t-s, röyttä p, honkatukia j, backman j. (2010) predicting off-design range and performance of refrigeration cycle with two-stage centrifugal compressor and flash intercooler. international journal of refrigeration, 33(6):1152-1160. [2] xenos dp, cicciotti m, bouaswaig aef, thornhill nf, martinez-botas r. (2014) modeling and optimization of industrial centrifugal compressor stations employing data-driven methods, asme turbo expo 2014: turbine technical conference and exposition, volume 3b: oil and gas applications; organic rankine cycle power systems; supercritical co2 power cycles; wind energy düsseldorf, germany, paper no. gt2014-25089. [3] casey m, robinson c. (2013) a method to estimate the performance map of a centrifugal compressor stage, journal of turbomachinery, 135:021034-1. [4] dyson's challenges in turbomachinery design (white paper) (2016) numeca/conceptsnrec seminar: taking your turbomachinery design to the next level. [5] gerber td, clemons jd. (2014)centrifugal compressor having cooling system. united states patent application 20140356147 a1. [6] dragan v, malael i, gherman b. (2016) a comparative analysis between optimized and baseline high pressure compressor stages using tridimensional computational fluid dynamics. engineering, technology and applied science research, 6(4):1103-1108. [7] dragan v. (2014) aerodynamic reconfiguration and multicriterial optimization of centrifugal compressors-a cases study. incas bulletin, 6(4):41-49 . [8] safikhani h, khalkhali a, farajpoor m. (2011) pareto based multi-objective optimization of centrifugal pumps using cfd, neural networks and genetic algorithms. engineering applications of computational fluid mechanics, 5(1):37-48. [9] menter fr, langtry rb, likki sr, suzen yb, huang pg, völker s. (2006) a correlation based transition model using local variables part 1model formulation. asme journal of turbomachinery, 128(3):413-422. [10] de maesschalcka c, lavagnoli s, paniagua g, vinha n. (2014) aerothermodynamics of tight rotor tip clearance flows in high-speed unshrouded turbines., applied thermal engineering, 65(1-2):343-351. [11] borm o, kau h-p. (2012) unsteady aerodynamics of a centrifugal compressor stage: validation of two different cfd solvers, asme turbo expo turbine technical conference and exposition volume 8: turbomachinery [12] malael i, dumitrescu h, dumitrache a. (2011) methods for improve the performance of the turbomachines using the flow control, aip conf. proc. 1389, 1515. [13] rinaldi e, raspopov rs, colonna p, pecnik r. (2014) modeling curvature effects on turbulence transition for turbomachinery flows, vol 2b: turbomachinery [14] ** numeca fine/turbo 9.1 user manual [15] sundén b, brebbi ca. (2014) heat transfer xiii: simulation and experiments in heat and mass transfer, wit transatction on engineering sciences, wit press, 83:221. [16] bathe kj (1996) finite element procedures, prentice hall, new jersey 07632. [17] ** ansys icem cfd help manual (2012), ansys icem cfd 14.5,pp.425 [18] roache pj (1997) quantification of uncertainty in computational fluid dynamics. annu. rev. fluid. mech., 29:123-160. [19] walsh p, fletcher p. (2004) gas turbine performance, john wiley & sons. isbn:0-63206434-x, pp. 163 [20] boyce mp. (2012) gas turbine engineering handbook, elsevier, isbn: 987-0-12-3838421, pp.162 iium engineering journal, vol. 18, no. 2, 2017 dragan 237 [21] vogt d. (2007) course mj2429 efficienciesturbomachinery lecture notes, kth university [22] aungier rh. (2000) centrifugal compressors: a strategy for aerodynamic design and analysis. asme press. [23] harley p, spence s, filsionger d, dietrich m, early j. (2015) experimental and numerical benchmarking of an improved mean line modeling method for automotive turbocharger centrifugal compressors. asme proceedings radial turbomachinery aerodynamics, gt 2015-42175, [24] klausner e, gampe u. (2014) evaluation and enhancement of a one-dimensional performance analysis method for centrifugal compressors, volume 2d: turbomachinnery, isbn: 978-0-7918-4563-9 [25] dixon sl, hall ca. (2014)fluid mechanics, thermodynamics of turbomachinery – 7th edition, elsevier butterworth–heinemann, isbn: 0124159540 [26] casey mv, robinson cj. (2011) a method to estimate the performance of a centrifugal compressor stage proceedings of asme turbo power for land, sea and air, [27] rodgers c. (1991) the efficiencies of single-stage centrifugal compressors for aircraft applications, international gas turbine and aeroengine congress and exposition nomenclature specific heat at constant pressure [j/(mol∙k] impeller peripheral diameter ̇ fluid mass flow [kg/s] torque [n∙m] specific speed of the impeller power absorbed by the aerodynamic process [w] air gas constant [j/kg∙k] total inlet temperature [k] total temperature at considered outlet [k] adiabatic exponent (specific heat ratio) total temperature difference between considered outlet and inlet [k] total to total isentropic efficiency total to total polytropic efficiency total to total pressure ratio flow coefficient – angular velocity [rad/s] microsoft word 70-508-1-ce vetted complete cleaned_from the author iium engineering journal, vol. 12, no. 2, 2011 chin 1 study of liquid-liquid slug break up mechanism in a microchannel t-junction at various modified weber number jitkai chin department of chemical and environmental engineering, university of notitngham malaysia campus, jalan broga, 43500 semenyih, selangor darul ehsan, malaysia. jit-kai.chin@nottingham.edu.my abstract: the formation of immiscible liquid slugs shows various potential applications in different fields because of absolute control of the species both spatially and temporally, as well as enhanced mixing efficiency. although applications of droplet/slug based microfluidics have been widely demonstrated, the fundamental physics governing slug/ droplet break-up remains to be an area of active research. this study defines an effective weber number (weeff) that characterizes the interplay of interfacial tension, shear stress and dynamic pressure in the micro-channel. qualitative results show that, at relatively low weeff, hydrodynamic force plays an important role in slug breakup at the micro-channel t-junction. at intermediate weeff, both shear force and hydrodynamic force play an equally important role in slug break up. at relatively high weeff, shear force is dominant in slug break up at the t-junction. abstrak: pembentukan slug cecair likat tidak bercampur mempunyai potensi di dalam pelbagai bidang kerana daya kawalan mutlak spesis tersebut secara spasial dan temporal, serta kecekapan pencampuran. walaupun aplikasi titisan/ likat mikrofluida telah didemonstrasi secara meluas, kajian fizik asas yang menentukan pemecahan likat/ titisan masih menjadi bahan kajian yang aktif. kajian ini mentakrifkan nombor weber efektif (weeff) yang mengaitkan ketegangan antara permukaan, tekanan ricih dan tekanan dinamik di dalam saluran mikro. keputusan kualitatif menunjukkan bahawa, pada weeff yang rendah, daya hidrodinamik memainkan peranan penting dalam pemecahan likat di persimpangan t saluran micro. pada weeff perantaraan, daya ricih dan daya hidrodinamik memainkan peranan yang penting dalam pemecahan slug. pada weeff yang relatifnya tinggi, daya ricih adalah dominan di dalam pemecahan likat di persimpangan t. keywords: liquid-liquid slug break-up, modified weber number, hydrodynamic force 1. introduction slug forms spontaneously when two immiscible liquids are brought into contact in a t-junction micro-channel at appropriate flow rates. the potential application of slug-based microfluidics has been demonstrated since years ago and attracted attention from researchers because of the absolute control on species both spatially and temporally, as iium engineering journal, vol. 12, no. 2, 2011 chin 2 well as internal recirculation in the slug itself, induced by radial shearing along the channel enhances mass transfer that translates into a decrease of mixing time. although the technique has been widely demonstrated in various applications [1-6], the discussion in the mechanism of slug break up in an immiscible liquid-liquid phase is seldom reported. the present study experimentally observes the dynamic evolution of droplet interfaces and flow patterns that precede a slug break up event in a t-junction microchannel. interplay of interfacial tension, shear stress and pressure drop in driving the mechanism of break up at various flow rates were investigated. 2. theory slug break up has been studied for decades by carrying out experiments in millimetre scaled capillary tubes. although the scale discussed in the paper is larger than micrometer, some of the models and the ensuing understanding are relevant to the work. deformation of a droplet is affected by the external flow pattern and physical properties of both the disperse phase and the continuous phase [7]. force of inertia, shear stress, interfacial tension and viscosities ratio are the important parameters that act on the droplet which result in its deformation and break up. hence the weber number (we) was proposed to describe the phenomenon. investigation on droplet end-pinching and break up mechanism in large scale horizontal flow show that breakup of the two-phases flow is due to both shear stress and external pressure field applied by the continuous phase [8]. the imposed shear flow and interfacial tension act in opposite directions, in which imposed shear flow acts to deform the disperse phase while the interfacial tension tends to maintain its shape. the shear stress induces changes in the shape of the extruding disperse phase, causing the asymmetrical shape in disperse phase. the parameters laid the foundation for droplet and slug formations, which are simplified into two dimensionless numbers. the weber number, we and capillary number, ca, respectively are defined as: force linterfacia force inertia numberweber = γ ρ du we 2 = (1) tensionlinterfacia force viscous numbercapillary = γ µu ca = (2) several models are proposed for the disintegration of droplet and slug break up in a microchannel configuration. the size of droplet produced under external shear force is a product of the balance between the shear forces with laplace pressure [9], based on the derivation of viscosity, leading to equation 3. g r µ γ ~ (3) in which the shear rate is estimated from hagen poiseuille equation, iium engineering journal, vol. 12, no. 2, 2011 chin 3 d v g gap 2 ~ (4) further investigations show [2-3] that the slug formation at a microchannel t-junction is independent of ca but highly dependent of the flow ratio of the disperse phase to the continuous phase. their results also show that capillarity is no longer valid when ca >> 1 x 10 -3 , in which slug break up occurs further downstream in the main channel but not at the t-junction. further research reveals that slug break up is affected by viscosity of the continuous phase. these work shows that different shear forces applied at the interface might affect the range of each regime [3]. extensive work also suggests that hydrodynamic force is also one of the important parameters in producing slugs in microchannels, rather than shear stress acting at the liquid-liquid interface [10], which draws conclusion that liquid-liquid slug break up is due to higher magnitudes of hydrodynamic force. however, the experiment only focuses on moderate operating range in which steady slug formation occurs, neglecting slug formation in the disperse phase laminar flow region in the main channel downstream. notwithstanding, the result is consistent with the findings of ismagilov et al. [2-3], in which ca is not an appropriate parameter in characterisation of slug formation in microchannel since the flow dynamic is the most important factor in driving slug break up. in which case, the utilisation of we as a characterisation parameter is recommended. in addition, an effective viscosity is required in a two-phase system as both phases contribute to the shear stress. hence, a modified we is used for the characterisation, involving the effective viscosity, ρ; continuous phase velocity, vcont ; as well as the hydrodynamic diameter, dhyd; which is shown in equation 5. γ ρ hydconteff eff dv we 2 = (5) 2.1 interfacial tension as disperse phase slug grows in the main channel, the surface area of the disperse phase rear interface in the t-junction varies with time because of the different degree of tangential stress on it by the upstream continuous phase flow. the undefined contact line and unpredictable shape of the rear interface result in spatial and temporal interfacial force changes. hence, it is calculated based on the surface area estimated from images taken during experiment. assuming the shape of the slug is limited by the dimension of the channel and the cross sectional area of the microchannel equivalent to a bowl shape, the interfacial forces are equivalent to: ( ) 2 2 1 ~ 2 h hhwa w p π γ +−=       −∆ (6) (7) iium engineering journal, vol. 12, no. 2, 2011 chin 4 ( ) ( )       +−−       +−      +− 2 2*~ 2 2* 22 ~ 2 2 h hhw w f h hhw hw f πγ π γ γ γ (8) (9) 2.2 shear force similar to calculation of interfacial forces, the contact area between the immiscible phases is important in calculating the shear force. calculation of the shear force is difficult because it depends on the contact between both phases, based on images taken during the experiment. fτ= µga (10) 2.3 hydrodynamic force the hyrodynamic force including both the pressure drop along the main channel well as capillary force across interface, is shown in equation 11. cdishconth pppp ∆+∆+∆=∆ ,, (11) since it is not possible to measure pressure force along the flow direction, hagen poiseuille equation is used in estimating pressure drop along the channel in the flow direction, including both disperse phase slug and continuous phase slug, as shown in equation 12 and equation 13. from the pressure drop, forces acting at the rear interface are calculated by multiplying the pressure by the cross sectional area, as shown in fig. 1. contcont hyd cont disdis hyd dis toth conthdishtoth l d q l d q p ppp µ π µ π 44, ,,, 128128 +=∆ ∆+∆=∆ (12) (13) capillary pressure drop is calculated based on lucas-washburn equation, including the differences between the receding contact angle and the advancing contact angle, located at the front interface and the rear interface of the slug respectively, which are included in equation 14.               +−        +=∆ a h a w r h r w cap rrrr p θθθθγ cos 2 cos 2 cos 2 cos 2 (14) iium engineering journal, vol. 12, no. 2, 2011 chin 5 fig. 1: schematic description of liquid-liquid slug phase flow along the main channel. it is equivalent to a capillary flow in which the hydrodynamic pressure drop along the channel caused by each phase and the pressure drop across the interphase is calculated. the total hydrodynamic force is a combination of hydrodynamic pressure drop and capillary pressure drop over the cross sectional area of the channel, given in equation 15. ( ) ( )[ ]                             +−        ++         + =∆ ∆+∆= a h a w r h r w contcont hyd cont disdis hyd dis cap captotht rrrr l d q l d q ap ppaf θθθθγ µ π µ π cos 2 cos 2 cos 2 cos 2 128128 44 , (15) 3. experiment before the experiment, the properties of the chemicals are investigated. the experiment is carried out in a glass microchannel network fabricated with conventional wet etching method involving fluoric acid (hf) [11]. the channel has a bowl-shape dimension and consists of 2 simple t-junctions. however, only a junction was involved in this experiment. the top dimension of the channel is equivalent to 245 µ m while the height of the channel is equivalent to 50 µm. tetradecane and acetonitrile (sigma, 99% purity) are used as disperse phase and continuous phase respectively in this experiment. during experiment, the disperse phase is delivered from the side channel while the continuous phase is delivered into the main channel using standard syringe (bd plastic), driven by a syringe pump (ne-1000, new era pump system inc.). iium engineering journal, vol. 12, no. 2, 2011 chin 6 3.1 method the microchannel network was mounted onto a light inverted microscope platform before acetonitrile and tetradecane were injected into the device, driven by a syringe pump. the flowrate into the microchannel network is controlled from the digital panel on the syringe pump. velocities for disperse phase and continuous phase range from 1.5 – 9.0 mm/s and 4.8 – 21 mm/s. slug formed spontaneously when the liquid meet each other at the t-junction. images of the slug break up were recorded using a high speed camera system (redlake inc) mounted onto the microscope, as shown in figure 2. images are taken at rates ranging from 250 – 5000 fps, depending on the frequency of slug formation. image j, an image processing software, was used for analysis. different flow ratios were controlled by using different syringe sizes. for example for a flow ratio of 0.27, a syringe size of 2.5 ml was used as disperse phase while syringe size of 5 ml was used for the continuous phase. experiments were carried out with flow ratio of 0.35, 0.27 and 0.15 respectively, as shown in table 1. the flowrates were then adjusted accordingly while the process of image recording was repeated. fig. 2: schematic representation of (a) the setup for this experiment; (b) the glass microfluidic device with the continuous phase flowing along the main channel while the disperse phase from the side arm. both phases meet at the t-junction flowing downstream towards the outlet. (c) the dimension of the channel assumed to be a bowl shape, in which the cross sectional area is equivalent to a rectangular shape with a quarter circle at both ends. disperse phase syringe, ml continuous phase syringes, ml flow ratio 2 5 0.35 2 10 0.27 1 5 0.14 table 1: combinations of different bd standard plastic syringe size giving different flow ratios iium engineering journal, vol. 12, no. 2, 2011 chin 7 4. results and discussion surface tensions of acetonitrile and tetradecane are 28.46 mn/m and 25.97 mn/m respectively while the interfacial tension of acetotnitrile/tetradecane system is 15.84 mn/m. the measurements were carried out in a digital tensiometer (k10 st, kruss instrument). dynamic viscosities of tetradecane and acetonitrile are 2.27 and 0.38 mpas respectively [12]. advancing and receding contact angles of the tetradecane slug are measured from images taken during experiment. the ranges of angles are 125 o – 150 o and 40 o – 100 o respectively, depends on flowrate and flow ratio. slug lengths were measured from images taken throughout the experiment. the discussion below excludes flow ratio at 0.42 because of limitation of the high speed camera in which the images are not sufficiently sharp for measurement and calculation. 4.1 at relatively low weeff (weeff < 2.0 x 10 -4 ) at relatively low weeff and across different flow ratio, disperse phase was observed to have a clean snap off at the corner of the side and the main channel, as shown in fig. 3. symmetry of the disperse phase into the main channel is disturbed when it almost occupies the cross sectional area of the main channel (fig. 3a). the disperse phase then fully occupies the cross sectional area of the main channel and blocks it while elongating in the main channel (fig. 3b). throughout the process, rear interface in the junction is forced to change from convex in to a concave shape (fig. 3c), indicating pressure build up in upstream of the continuous phase. the pressure built up increases continuously while the rear interface is being displaced downstream. as the interface approaches the corner of the t-junction and just before breaking up, a thin but visible disperse phase connecting neck was generated between the disperse phase in the main channel and the disperse phase in the side channel (fig. 3d). however, the plane view thickness and the length of this connecting neck are relatively small and a clean snap off at the junction is reasonably assumed. due to the relatively short area available for shear and the explicit change in the shape of the rear disperse phase interface in the main channel, it is clearly shown that hydrodynamic plays an important role in slug break up at relatively low weeff flow. fig. 3: images of slug break up captured by high speed camera at weeff =8.8322 x 10 -5 and flow ratio of 0.35. the interval between images is 80 ms. clean snap-off takes place during slug break-up. 3(a) 3(b) 3(c) 3(d) iium engineering journal, vol. 12, no. 2, 2011 chin 8 4.2 at intermediate weeff (2.0 x 10 -4 < weeff < 5.5 x 10 -4 ) as the total flow rate is further increased, the disperse phase slug growth in the main channel is approximating to that at relatively low weeff (fig. 4a, 4b, 4c) but the increase flow rate in the disperse phase causes a connecting neck of the disperse phase to evolve into a short trail of thin laminar flow before breaking up a short distance downstream of the t-junction (fig. 4d). the thin laminar flow layer provides some surface area for shear to take place. analyses from images show that both hydrodynamic force and shear stress play important role in slug break up. fig. 4: slug break up at intermediate weeff , weeff = 5.0 x 10 -4 and flow ratio = 0.35. images were taken at interval of 20 ms. small connecting neck exists before slug breakup. 4.3 at relatively high weeff (weeff > 5.5 x 10 -4 ) as flow rates of both disperse phase and continuous phase are increased, the break up mechanism varies from previous cases. the continuous phase pushes the extruding disperse phase in the junction towards main channel downstream, before it can fully occupy the entire cross sectional area of the main channel. this causes increase in total contact area between both phases (fig. 5a, 5b). compared to low and intermediate weeff, the change of the shape of the rear interface in the t-junction was not obvious and the plane view rear interface in the t-junction and downstream main channel did not approximate to the top width of the microchannel (fig. 5c), at any time throughout the break up process. shear interaction between the disperse phase and the continuous phase in the main channel causes elongation of the disperse phase laminar flow region in the main channel while the slug breaks off from the laminar flow region (fig. 5d). fig. 5: slug break up at relatively high weeff , weeff = 1.18 x 10 -3 and flow ratio = 0.35. images were taken at interval of 36 ms. a large disperse phase laminar flow region formed downstream in the main channel. slug breaks up at the tip of the region in the main channel. 4(a) 4(b) 4(c) 4(d) 5(a) 5(b) 5(c) 5(d) iium engineering journal, vol. 12, no. 2, 2011 chin 9 the experimental data and calculation is summarised in table 2. it shows that hydrodynamic force is an important factor in slug break up at relatively low weeff. at intermediate weeff, both shear stress and hydrodynamic force are important for slug break up. at relatively high weeff, the break up is dominated by shear force between both phases in the main channel. flow ratio = 0.35 weeff 8.83 x 10 -5 2.28 x 10 -4 4.34 x 10 -4 9.89 x 10 -4 shear force, fτ 3.50 x 10 -11 1.67 x 10 -10 2.42 x 10 -10 4.51 x 10 -10 hydrodynamic force, fh+c 1.89 x 10 -5 5.00 x 10 -5 7.46 x 10 -5 8.36 x 10 -5 ratio of forces, fτ/ fh+c 1.86 x 10 -6 3.34 x 10 -6 3.24 x 10 -6 5.39 x 10 -6 flow ratio = 0.27 weeff 1.69 x 10 -4 2.22 x 10 -4 5.91 x 10 -4 8.88 x 10 -4 shear force, fτ 3.90 x 10 -11 1.04 x 10 -10 1.65 x 10 -10 2.40 x 10 -10 hydrodynamic force, fh+c 1.68 x 10 -5 2.44 x 10 -5 3.09 x 10 -5 3.21 x 10 -5 ratio of forces, fτ/ fh+c 2.32 x 10 -6 4.26 x 10 -6 5.34 x 10 -6 7.48 x 10 -6 flow ratio = 0.15 weeff 7.25 x 10 -5 1.13 x 10 -4 1.72 x 10 -4 2.88 x 10 -4 shear force, fτ 7.32 x 10 -11 9.04 x 10 -10 1.15 x 10 -10 2.69 x 10 -10 hydrodynamic force, fh+c 4.44 x 10 -5 6.21 x 10 -5 8.05 x 10 -5 7.55 x 10 -5 ratio of forces, fτ/ fh+c 1.65 x 10 -6 1.46 x 10 -6 1.43 x 10 -6 3.56 x 10 -6 table 2: calculation of force ratio according to weeff in different syringe combination giving different flow ratios in each flow ratio, weeff is increased by increasing in overall flowrates in both syringes. in flow ratio = 0.35, when weeff < 2.5 x 10 -4 , tetradecane slugs have clean snap off taken place at the corner of t-junction. as the weeff is increased, a disperse phase small trail starts to form at the corner. a disperse phase laminar flow region formed in the main channel as weeff is further increased. throughout the experiment, phenomena of clean snap off until failure of the slug formation at the t-junction is observed. in flow ratio = 0.27, the experiment starts with clean snap off of slug formation. however, a small trail is formed as increment in weeff is carried out. further increment in weeff causes the tetradecane slugs to be produced from the laminar flow region formed in the main channel. in third experiment, in which 1ml syringe is used in disperse phase while 5ml syringe is used in continuous phase to give flow ratio of 0.14, tetradecane slug formation takes place across a wide range from 7.25 x 10 -5 until 1.72 x 10 -4 . a trail is formed at the corner for slug formation as weeff is increased to 2.88 x 10 -4 . further increase in weeff results in the phenomenon failure at weeff = 7.23 x 10 -4 , however meaningful results are limited due to capability of the high speed camera. iium engineering journal, vol. 12, no. 2, 2011 chin 10 the preliminary study shows a general trend that the phenomena of slug formation in a tjunction, ie clean snap off, formation of a small trail at the corner and formation of a disperse phase laminar flow region depends on the weeff but independent of flow ratio. validation is carried out by plotting disperse phase slug length against weeff, as shown in fig. 6. it is found that slug length approaches infinity when weeff is extremely low. as weeff increases gradually, the slug length generated drops significantly until weeff ~1 x 10 4 . further increase in weeff has negligible effect on the slug length. the plots are similar to the trend in hagen poisuelle equation, with t showing that the slug length as an inverse function of pressure drop in the main channel. fig. 6 confirms the suitability of utilising weeff as characterising parameter especially at relatively low flow rate. fig. 6: plotting of relative disperse phase slug length to weeff. 5. conclusion understanding the fundamental physics of slug formation in a microchannel tjunction is important in exploring further potential application of the phenomenon into other fields. however the flow dynamic is always complicated and difficult to model with simulation any software available. although the experiment was carried out only with a single immiscible liquid-liquid system, the qualitative result and simplified analysis method still give a few important points about slug break up phenomenon in a microchannel t-junction. from the experimental work, it can be concluded that at relatively low weeff, (weeff < 2.0 x10 -4 ), in which disperse phase slug clean snap off occurs, the ratio of shear force to the hydrodynamic force is always less than 3.0 x 10 -6 . hydrodynamic force plays an iium engineering journal, vol. 12, no. 2, 2011 chin 11 important role in disperse phase slug break up at relatively low weeff with a clean snap off at the t-junction. at intermediate weeff, (weeff = 2.5 5 x10 -4 ), the force ratio is approximately 3.0 – 5.0 x 10 -6 . a small trail of disperse phase extruding into the main channel, resulting in both hydrodynamic force and shear force playing important role in slug break up. in the case when weeff > 5 x10 -4 , disperse phase slug breaks up from a laminar flow region in the main channel with the force ratio at approximately 4.5 – 6.0 x 10 -6 . large contact surface area of the disperse phase laminar flow region in the main channel provides large surface area for shear interaction between both phases. further analysis justifies the utilization of weeff as a characterizing parameter. 6. future work experimentations with different immiscible liquid-liquid systems are being carried out in verifying the model and establishing the theory for slug break up across different flow ratio and viscosity ratios. in addition, the use of a high speed camera which gives higher resolution and higher frames per second, fps, are useful in analysis. acknowledgement the author would like to acknowledge ministry of higher education malaysia (mohe) fundamental research grant scheme (frgs/2/2010/tk/unim/03/3) for funding the research project. references [1] burns, j. r., and ramshaw c., the intensification of rapid reactions in multiphase systems using slug flow in capillaries, lab-on-a-chip, 2001, 1, pp. 10–15 [2] song h., tice j. d., and ismagilov r. f., a microfluidic system for controlling reaction networks in time, angw. chem., 2003, pp. 768–772 [3] tice j. d., lyon a. d., and ismagilov r. f., effects of viscosity on droplet formation and mixing in microfluidic channels, analytica chimica acta 507, 2004, pp. 73–77 [4] niu, x.z., zhang, b., marszalek, r.t., ces, o., edel j.b., klug, d.r. and demello, a.j. droplet-based compartmentalization of chemically separated components in two-dimensional separations, chem. commun., 2009, 7(41), pp. 6159-6161 [5] mazutis, l. and griffiths, a.d., preparation of monodisperse emulsions by hydrodynamic size fractionation, applied physics letters, 2009, 95, pp. 20410304105 [6] srinivasan, v., pamula, v.k. and fair, r.b., an integrated digital microfluidic lab-on-achip for clinical diagnostics on human physicological fluids, lab-on-a-chip, 2004, 4, pp. 310-315 [7] hinze j., fundamentals of the hydrodynamic mehcanism of splitting in dispersion processes, aiche, 1955, 1, pp. 289–295 [8] zhang d. f., and stone h. a., drop formation in viscous flows at a vertical capillary tube, phys. fluids, 1997, 9, pp. 2234–2242 iium engineering journal, vol. 12, no. 2, 2011 chin 12 [9] thorsen t., roberts. r. w., arnold f. h., and quake s., dynamic pattern formation in a vesicle-generating microfluidic device, phy. rev. lett., 2001, pp. 4163–4166 [10] garstecki p., fuerstman m., stone h. a., whitesides g. m., formation of droplets and bubbles in a microfluidic t-junction – scaling and mechanism of break up, lab-on-a-chip, 2006, 437 [11] che-hisn lin, gwo-bin lee, yen-heng lin, and guan-liang chang, a fast prototyping process for fabrication of microfluidic systems on soda-lime glass, j. micromech. microeng., 2001, 11, pp. 726–732 [12] perry’s chemical engineers’ handbook, 1997 nomenclature re reynolds number we weber number ca capillary number eff effective ρ density, kg/m 3 l characteristic length, m u flow velocity, m/s µ viscosity, kg/m 2 s r radius, m h height of the channel, m w width of the channel, m dhyd hydraulic diameter, m g shear rate, cont continuous phase disp dispersed phase γ interfacial tension q volumetric flowrate, kg/m 3 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 potential of fabrication of durian skin fiber biocomposites for food packaging application through the electricity impact analysis hazleen anuar1*, siti munirah salimah abd rashid1, nurfarahin mohd nordin1, fathilah ali2, yose fachmi buys3, sabu thomas4, nur aimi mohd nasir1 and syazeven effatin azma mohd asri1 1 department of manufacturing and materials engineering, 2 department of biotechnology engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia 3 department of mechanical engineering, faculty of engineering, university of malaya, 50603 kuala lumpur, malaysia 4 school of energy materials and international and inter university centre for nanoscience and nanotechnology, mahatma gandhi university, priyadarshini hills, kottayam 686560, kerala, india * corresponding author: hazleen@iium.edu.my (received: 2nd november 2020; accepted: 17th march 2021; published on-line: 4th july 2021) abstract: as an effort to replace the petroleum-based polymers and reduce wasterelated environmental problems, biopolymers are the best candidate due to their renewable, biodegradable and commercially viable. initiative have been taken by developing durian skin fibre (dsf) reinforced polylactic acid (pla) biocomposites with the addition of epoxidized palm oil (epo). pla/dsf biocomposites were fabricated via extrusion and then injection moulded. the biocomposites were assessed for its life cycle by developing a system boundary related to its fabrication processes using gabi software. the life cycle assessment (lca) of pla/dsf biocomposites show that global warming potential (gwp) and acidification potential (ap) were the major impacts from pla/dsf biocomposite. for pla/dsf biocomposite, the results were 199.37 kg co2 equiv. gwp and 0.58 kg so2 equiv. ap. meanwhile, for pla/dsf/epo biocomposite, the results obtained were 195.89 kg co2 equiv. gwp and 0.57 kg so2 equiv. ap. the gwp and ap were contributed by the electricity used in the fabrication of biocomposites. these impacts were due to the usage of electricity, which contributed to the emission of co2. however, the pla/dsf/epo biocomposite had lower negative impacts because epo improved the workability and processability of the biocomposite, and hence, reduced the amount of energy required for production. it can be concluded that the plasticized pla/dsf biocomposite can be a potential biodegradable food packaging material as it has favourable properties and produces no waste. abstrak: biopolimer adalah terbaik dalam usaha mengganti polimer berasaskanpetroleum dalam mengurang masalah pencemaran-sisa. ini kerana biopolimer boleh diperbaharui, biodegradasi dan sangat maju secara komersial. inisiatif telah diambil dengan menghasilkan sabut kulit durian (dsf) bersama biokomposit asid polilaktik (pla) dengan penambahan minyak kelapa sawit terepoksi (epo). biokomposit pla/dsf direka melalui kaedah pemyemperitan dan acuan suntikan. biokomposit ini iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 dipantau kitar hidupnya dengan membina sistem sempadan berkaitan proses rekaan menggunakan perisian gabi. pengawasan kitar hidup (lca) biokomposit pla/dsf menunjukkan potensi pemanasan global (gwp) dan potensi pengasidan (ap) menyebabkan impak terbesar komposit pla/dsf. dapatan kajian menunjukkan 199.37 kg co2 bagi gwp dan 0.58 kg so2 bagi ap bagi biokomposit pla/dsf. sementara itu, dapatan kajian bagi biokomposit pla/dsf/epo adalah 195.89 kg co2 bagi gwp dan 0.57 kg so2 bagi ap. kedua-dua gwp dan ap adalah disebabkan oleh penggunaan elektrik dalam proses pembuatan biokomposit. ini adalah kesan daripada penggunaan elektrik, dan menyumbang kepada pembebasan co2. walau bagaimanapun, biokomposit pla/dsf/epo mempunyai kurang kesan negatif, kerana epo telah menambah baik kebolehkerjaan dan kebolehprosesan biokomposit, menyebabkan kurang tenaga yang diperlukan dalam proses pembuatan. kesimpulannya plastik biokomposit pla/dsf berpotensi sebagai bahan biodegradasi bagi pembungkus makanan kerana ianya mempunyai ciri-ciri yang diperlukan dan tidak menghasilkan sisa buangan. keywords: life cycle assessment; cradle-to-grave; durian skin fibre; plasticizer; food packaging; polylactic acid 1. introduction earth has ecosystem that consists of humans, plant life, ocean and natural resources. however, the development of engineering has resulted in resource depletion and environmental destruction. almost all food packaging including single use packaging are petroleum-based polymers that are undegradable in nature and when they are being dumped on the land and in the ocean; it leads to the production of smelly garbage or polluted water. these problems are crucial environmental issues that should not be taken lightly. food packaging provide protection to the food, to maintain the quality and safety of the food from the environment and other physical harm. food packaging is important when transporting the food from one place to another [1]. most food packaging is made from glass, cloth, metal, paper and polymers. polymers are the most common materials used in the food packaging industry due to their superior properties. the most commonly used plastics in packaging include polyethylene terephthalate (pet), polyvinyl chloride (pvc), polyethylene (pe), polypropylene (pp), polystyrene (ps) and polyamide [2,3]. the utilization of these polymers harms the environment and ecosystems via global warming and ozone layer depletion. this is due to the unwanted gas like carbon dioxide is released to the atmosphere. the degradation process of polymers takes many years to be completed. pp for example shows resistance to biodegradation since it is highly hydrophobic, high molecular weight, lacks an active functional group and has a continuous chain of repetitive methylene units [4]. 2. methodology the framework was conducted according to iso 14040 [5] and iso 14044 [6] which involve four phases; goal and scope definition, inventory analysis, impact assessment and interpretation using gabi software. 2.1 goal and scope definition the goal of this study is to assess the environmental impacts of food packaging made of pla/dsf in comparison with pla/dsf with the addition of epoxidized palm oil (epo) as a plasticizer. this comparison was to investigate the effect of epo on pla/dsf iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 on the environmental impact. the functional unit of this study was 50-unit biodegradable food packaging and the reference flow was 850 g for each pla/dsf and pla/dsf/epo biocomposite. the scope of this study was from the preparation of durian skin fibre, preparation of biocomposite and fabrication of biocomposite into food packaging before end-of-life disposal. the scope of impact assessment covered was global warming, acidification, eutrophication and ozone depletion. these impacts were chosen based on the impact on electricity usage as electricity was the main contributor and this could be the main cause for the climate change. the study covered the entire life cycle of pla/dsf and pla/dsf/epo biocomposite from cradle-to-grave. 2.2 system boundary the system boundary in this study includes the preparation of dsf, manufacturing of biocomposites and end-of-life stage. the preparation of dsf involves chopping and grinding, washing, drying and alkali treatment process while manufacturing of biocomposite covers extrusion and injection moulding. the inputs and outputs of each biocomposite food packaging manufacturing process was identified based on the inventory analysis elaborated later. from the information gathered in the inventory analysis, system boundaries for both biocomposites were determined. figures 1 and 2 show the schematic diagrams of input and output flow for pla/dsf and pla/dsf/epo biocomposites, respectively. 2.3 data sources and limitations in this study, the input and output data for preparation of dsf and fabrication of biocomposites were primary data which was collected during the process. the covered data consists of raw material (durian skin waste) and energy consumption for the fabrication of biocomposite. data on production of pla resin and epo was excluded as these two materials were bought from the supplier and delivered directly to the fabrication lab. the use phase also was neglected as this biocomposite still in prototype food packaging. 2.4 inventory analysis the inventory analysis was gathered which include the material and energy inputs, air emissions, solid waste emissions and waterbone emissions in the life cycle of the pla/dsf biocomposite with and without epo. it involved collecting quantitative data for every unit process in the system based on a functional unit of product. details of each phase starting from durian skin fibre preparation until end-of-life stage are explained next. 2.5 raw materials durian skins waste were collected from local markets and transported to iium. pla (grade 3052) was obtained from natureworks, china; epo was obtained from malaysian palm oil board; and databases for raw pla and epo were obtained from gabi software (which were compiled from a literature review by [7-10] for epo. the database for pla was obtained from a study by [11]. the composition of the biocomposite was observed based on the weight of the food packaging. the biocomposite was initially prepared for 1000 g including waste after injection moulded. from such preparation, the weight of a single food packaging was determined at 17 g whereas the total weight for 50 units of biocomposite food packaging was 850 g. compositions for each pla are shown in tables 1 and 2. iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 table 1: composition of pla/dsf biocomposite table 2: composition of pla/dsf/epo biocomposite material composition (%) weight for 1 unit (g) weight for 50 units (g) material composition (%) weight for 1 unit (g) weight for 50 units (g) pla 70 11.9 595 pla 65 11.05 552.5 dsf 30 5.1 255 dsf 30 5.1 255 total 100 17 850 epo 5 0.85 42.5 total 100 17 850 2.6 preparation of durian skin fibre (dsf) the durian skin was cut into smaller pieces and washed thoroughly with tap water to remove any dust and adhering particles. the skin was then dried at 70 °c for 24 h. the dried skin was ground to obtain fibre with 100 to 150 µm in length. the weight of the raw durian skin fibres used is approximately 300 g. sodium hydroxide (naoh) was used for alkali treatment of dsf. 2.7 preparation of biocomposites next, fabrication process of the biocomposite consists of extrusion using extruder (brabender, germany) and injection moulding processes using battenfeld hm 600/850 injection moulding machine. the temperature profile from barrel to die was 160 °c to 170 °c at 100 rpm screw speed. for injection moulding, the temperature was 165 °c to 180 °c for all four zones of the injection moulding machine and 45 s cooling time. finally, the biocomposite food packaging waste was exposed to the environment for end-of-life stage. 2.8 transportation transportation is referring to picking up the waste durian skins from petaling jaya, to laboratory at gombak, selangor, malaysia. transportation data required for conveying the product to the end user and to the transfer station was not available, because the process is assumed to have only evolved within the area of fabrication, which is iium. the total journey from iium gombak to petaling jaya and back to iium gombak is approximately 92 km. the transportation for obtaining the pla and epo were not included in this study since it was delivered to iium. both pla/dsf biocomposites were still in prototype, thus the distribution of the biocomposites to the consumer was not included for transportation. 2.9 electricity table 3 describes the total power and electricity utilized for each particular process in the production of pla/dsf and pla/dsf/epo biocomposites. table 3: power calculation of each machine used. machine total time utilised for 50 units (hours) total power (kwh) energy (mj) oven a) 24 b) 48 a) 36 b) 72 a) 129.6 b) 259.2 extruder 10 50 180 grinder 0.85 3.4 12.24 injection moulding 1.25 66.94 240.98 iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 2.10 end-of-life stage the pla/dsf and pla/dsf/epo biocomposite were exposed to the environment to observe their degradation time. both biocomposites took about five to six months to fully biodegrade. fig. 1: system boundary of pla/dsf biocomposite. fig. 2: system boundary of pla/dsf/epo biocomposite. iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 2.11 impact assessment the environment impact assessment was conducted to evaluate and analyse the possibility of activities in the inventory analysis and production of biocomposite food packaging whether to leave negative environmental impacts on the earth or not. for this examination, effects were measured up to the midpoint level. the midpoint level expects to cover ecological issues that stand close to the inventory and endpoint results. ecological impact categories, under the midpoint level, include carbon footprint, photochemical ozone formation, human toxicity, water footprint, ozone layer depletion, global warming, acidification, eutrophication, etc., depend on the intergovernmental panel on climate change (ipcc). among the impact listed, the last four contributed to the highest impact score and play a vital role in the lifecycle of pla/dsf biocomposite food containers. this study uses the recipe (1.08) life cycle impact assessment (lcia) method, run through gabi software, and based on iso 14040 framework [5] and iso 14044-guidelines and requirements [6]. 3. results and discussion the results are analysed for four major environmental impacts comprised of global warming potential, ozone layer depletion potential, acidification potential and eutrophication potential based on the impact in electricity usage as this could be the main cause for climate change. the environmental impacts evaluated was cradle-to-grave analysis started from raw materials, processing, manufacturing and end life of the product which was landfill. based on the impact score, global warming potential (gwp) possesses the highest impact score with 199.38 kg co2 equiv. for pla/dsf over pla/dsf/epo with 195.89 kg co2 equiv. these are followed by acidification potential (ap), with an impact score of 0.58 kg so2 equiv. for pla/dsf and 0.57 kg so2 equiv. for pla/dsf/epo. the remaining two impacts considered in this study produced very low values of impact score; which are deemed insignificant. for all four impacts considered in this study, pla/dsf showed a higher potential of environmental impacts than pla/dsf/epo biocomposites. this was as expected as biocomposite consists of epo that is bio-based and environmentally friendly plasticizer. according to [12], plasticizers made from natural sources incorporated into a bio-based polymer provide lower negative impacts to the environment. 3.1 global warming potential (gwp) the findings for global warming potential (gwp) are presented in table 4 and fig. 3 as percentage values. from table 4 and fig. 3, it can be seen that the injection moulding process had the highest contribution towards the global warming potential for both biocomposites. the process of pla/dsf showed a slightly higher percentage, at 33.08% over pla/dsf/epo at 31.70%. plasticizer, added to the composites, improved their workability, processability and flexibility, making them easier to be processed with reduced energy needed [13]. therefore, the percentage contribution of each biocomposites process towards gwp was different as epo was added at the beginning of the mixing process for the plasticized one. figure 3 clearly shows that the major contributors towards gwp are the drying, mixing and injection moulding processes of both biocomposites. these processes contribute up to 95.0% of the total gwp for both pla/dsf and pla/dsf/epo biocomposites. specifically, these processes require electricity to generate output (i.e., biocomposite food packaging). consumption of electricity highly contributed towards the iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 release of co2 gas. energy industries are a major source of greenhouse gases in malaysia [14,15]. global warming is mainly caused by the release of greenhouse gases into the environment; primarily co2. co2 emissions take up to 93.0% and the rest are other greenhouse gases, such as nitrous oxide and methane. [16] stated that the three crucial sources of fossil fuel, that highly affected the power generation operations in malaysia are natural gas, coal fuel and hydropower. however, hydropower that come from renewable energy sources used only small percentage as compared to other sources. emissions of greenhouse gases, mainly co2 from the burning of fossil fuels, cause environmental degradation and global warming. therefore, the more electricity utilised in the production of biocomposites raises the emission level of co2 gas to the environment; eventually contributing towards global warming. the amount of electricity used are high in the fabrication process due to the utilisation of various machines. fig. 3: percentage contribution of each process to gwp. table 4: percentage contribution of each process to gwp process % of gwp for each process (kg co2 equiv.) pla/dsf pla/dsf/epo collecting durian skin waste 0 0 transportation 0.016 0.016 chopping and washing 0.013 0.013 drying (24 h) 15.10 15.10 grinding 1.46 1.46 alkali treatment 3.51 3.51 drying (48 h) 20.30 20.30 mixing (extrusion) 26.52 27.90 shaping (injection moulding) 33.08 31.70 waste on landfill 0 0 recovery -2.43 -2.38 total gwp value of each type of biocomposite (including material recovery) (kg co2 equiv.) 199.38 195.89 iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 meanwhile, the process of chopping and washing of durian skins contributed less to the potential global warming, about 0.013%, for both biocomposites. this is because only tap water is used in the process and no greenhouse gases are emitted during fibre preparation. a previous study on environmental impact was done by [17] on tap water and compared with bottled mineral water. the study found that tap water imparted a lower environmental impact than bottled mineral water. in fig. 3, the resource column indicates that resource recovery is involved in the production process. the biocomposites are produced from bio-based materials that originated from plants, such as dsf and pla. carbon dioxide can be sequestered, as plants consume it, even though it is released during the production process [18]. in summary, gwp for pla/dsf/epo contributed less to global warming than pla/dsf biocomposite; with the potential of 195.89 kg co2 equiv. compared to 199.38 kg co2 equiv. 3.2 acidification potential (ap) table 5 and fig. 4 present the percentage of acidification potential of each process involved in the production process of both biocomposites. from table 5 and fig. 4, the injection moulding process shows significantly high potential to acidification as compared to other process, which is responsible for 30.51% of ap from pla/dsf biocomposite and 31.59% of ap from pla/dsf/epo biocomposite. similarly, the major contributors to ap of both biocomposites are from the processes that need electricity, namely injection moulding, extrusion and drying. the acidification potential of these processes includes electricity generated 97.15% of total ap for pla/dsf and 98.60% of total ap for pla/dsf/epo biocomposites including the grinding process. from the total ap for both biocomposites, more than 57% comes from the emission of nitrogen oxides, followed by sulfur dioxides at 41%. a small portion is made up of ammonia and nitrogen dioxides. this is due to the utilization of electricity during biocomposites fabrication. the ocean and the atmosphere absorb the toxic gases generated and hence acidity is increased. as a conclusion, even though the contribution of electricity to ap for pla/dsf/epo is higher than pla/dsf, the total ap of pla/dsf/epo is lower than that of pla/dsf. therefore, pla/dsf/epo causes less effect to the acidification as compared to pla/dsf biocomposite. fig. 4: percentage contribution of each process to ap. iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 table 5: percentage contribution of each process to ap 3.3 eutrophication potential (ep) eutrophication is one of several environmental impacts considered in this study; and showed a very low impact score. eutrophication is measured in terms of kg p equiv. as it is mainly caused by phosphorus and phosphate [19]. the lca leads to 8.29 x 10-5 kg p equiv. for pla/dsf and 6.95 x 10-5 kg p equiv. for pla/dsf/epo. table 6 and fig. 5 indicate the results generated from the study for eutrophication potential. figure 5 shows that the alkali treatment process for dsf displayed the highest potential to eutrophication; with 37.27% for both biocomposites. this process consumes sodium hydroxide, tap water and distilled water. the waste is then discharged through the sewage system before going directly into soil and water bodies, stimulates, and eventually causes eutrophication. when the waste yielded from the alkali treatment process is discharged, it unlocks the phosphate and phosphorus contained within the soil; thus, increasing the nutrients level of the soil. when the concentration levels of the nutrients are too high, they are carried by rain water into rivers and ground waters that subsequently flow into lakes and seas. [20] assured that wastewater is a contributor for eutrophication to occur; where it increases the amount of nitrogen and phosphorus transferred to water bodies. fig. 5: percentage contribution of each process to ep. process % of ap for each process (kg so2 equiv.) pla/dsf pla/dsf/epo collecting durian skin waste 0 0 transportation 0.02 0.02 chopping and washing 0.01 0.01 drying (24 h) 15.43 15.43 grinding 1.46 1.46 alkali treatment 2.67 2.67 drying (48 h) 21.81 21.43 mixing (extrusion) 28.09 27.39 shaping (injection moulding) 30.51 31.59 waste on landfill 0 0 total ap value of each type of biocomposite (kg so2 equiv.) 0.58 0.57 iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 table 6: percentage contribution of each process to ep process % of ep for each process (kg p equiv.) pla/dsf pla/dsf/epo collecting durian skin waste 0 0 transportation 0.05 0.05 chopping and washing 9.67 9.67 drying (24 h) 2.53 2.53 grinding 0.91 0.91 alkali treatment 37.27 37.27 drying (48 h) 16.16 16.16 mixing (extrusion) 18.51 17.43 shaping (injection moulding) 14.96 15.98 waste on landfill 0 0 total ep value of each type of biocomposite (kg p equiv.) 8.29 x 10 -5 6.95 x 10-5 the transportation process contributes the lowest impact to eutrophication. this is because transportation does not produce waste that is discharged to soil and water bodies, but contributes towards other environmental impacts through emissions of gases into the air. in conclusion, eutrophication is not affected by the life cycle of the biocomposites based on the low impact score of ep which is nearly zero. 3.4 ozone depletion potential (odp) ozone layer depletion, or ozone depletion potential (odp), for both biocomposites is further analysed and presented in table 7 and fig. 6. odp is considered as the negligible impact on the biocomposites in this study. this is due to the lowest impact score obtained; which was nearly zero. odp is the most insignificant impact from the food packaging industry. this is in agreement with a previous finding by [21] which showed that odp yields a very low impact score compared to other environmental impacts. fig. 6: percentage contribution of each process to odp. iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 table 7: percentage contribution of each process to odp process % of odp for each process (kg cfc-11 equiv.) pla/dsf pla/dsf/epo collecting durian skin waste 0 0 transportation 0 0 chopping and washing 0.01 0.005 drying (24 h) 0.13 0.14 grinding 23.19 12.71 alkali treatment 0.25 0.20 drying (48 h) 76.09 86.68 mixing (extrusion) 0.23 0.27 shaping (injection moulding) 0 0 waste on landfill 0 0 total odp value of each type of biocomposite (kg cfc-11 equiv.) 8.28 x 10-10 1.28 10-10 4. conclusion the fabrication of biocomposites food packaging causes significant global warming and acidification to occur. the impact scores are higher with almost 200 kg co2 equiv and 0.5 kg so2 equiv. pla/dsf produced higher impact compared to pla/dsf/epo for all categories. gwp and ap were not significantly difference but for ep and odp the impact difference between pla/dsf and pla/dsf/epo was almost 19%. this impact is due to generation of electricity throughout the production process. the highest emission was achieved by carbon dioxide with the highest percentage value. ozone layer depletion and eutrophication potential values were very low, almost zero. meanwhile, eutrophication only affected by the alkali process in the fabrication of biocomposites, which produces waste discharged into the soil and other water bodies. acknowledgement the authors wish to thank the ministry of higher education (mohe) malaysia for the funding provided through the fundamental research grant scheme (frgs/1/2019/tk05/uiam/02/2), research initiative grant scheme–post-doctoral fellow (rpdf18-010-0010) from the international islamic university malaysia (iium), department of science & technology (dst)-asean-india research training fellowship (rtf/2019/000083) for the equipment and facilities provided in making these studies a success. references [1] duncan tv. (2011) applications of nanotechnol. in food packaging and food safety: barrier materials, antimicrobials and sensors. j. of colloid and interface science, 363: 1-24. https://doi.org/10.1016/j.jcis.2011.07.017 [2] siracusa v. (2012) food packaging permeability behaviour: a report. int. j. of polym. sci., 1-11. https://doi.org/10.1155/2012/302029 [3] badmus aa, gauri s, ali ni, gomes c. (2015) mechanical stabilty of biobased food packaging materials. food sci. and quality management, 39: 41-48. https://doi.org/10.1016/j.jcis.2011.07.017 https://doi.org/10.1155/2012/302029 iium engineering journal, vol. 22, no. 2, 2021 anuar et al. https://doi.org/10.31436/iiumej.v22i2.1673 [4] xu x, jayaraman k, morin c, pecqueuxn. (2008) life cycle assess of wood-fibrereinforced polypropylene composites. j of mater. processing tech., 198: 168-177. https://doi.org/10.1016/j.jmatprotec.2007.06.087 [5] iso, 2006a. iso 14040: environmental management life cycle asses. – princ. and framew. int organization for standardization, genève, switzerland. [6] iso, 2006b. iso 14044: environmental management life cycle assess. – princ. and framew. int. organization for standardization, genève, switzerland. [7] subramaniam v, may cy, muhammad h, hashim z, tan ya, wei pc. (2010) life cycle assess.of the production of crude palm oil (part 3). j. of oil palm research, 22: 895-903. [8] schmidt jh. (2010) comparative life cycle assess. of rapeseed oil and palm oil. the int j. of life cycle assess., 15: 183-197. [9] flynn hc, canals lmi, keller e, king h, sim s, hastings a, smith p. (2012) quantifying global greenhouse gas emissions from land-use change for crop production. global change biology, 18: 1622-1635. https://doi.org/10.1111/j.1365-2486.2011.02618.x [10] choo ym, muhamad h, hashim z, subramaniam v, puah cw, tan y. (2011) determination of ghg contributions by subsystems in the oil palm supply chain using the lca approach. the int. j. of life cycle assess., 16: 669-681. [11] vink eth, davies s. (2015). life cycle inventory and impact assessment data for 2014 ingeotm polylactide production. industrial biotechnology, 11: 167-180. https://doi.org/10.1089/ind.2015.0003 [12] jusoh er, ismail mh, abdullah lc, robiah y, rahman wawa. (2012) crude palm oil as a bioadditive in polypropylene blown films. bioresources, 7: 859-867. [13] sanyang ml, sapuan sm, jawaid m, ishak mr, sahari j. (2016) effect of plasticizer type and concentration on physical properties of biodegradable films based on sugar palm (arenga pinnata) starch for food packaging. j. of food sci. and tech., 53: 326–336. [14] zaid sm, myeda ne, mahyuddin n, sulaiman r. (2015) malaysia’s rising ghg emissions and carbon 'lock-in' risk : a review of malaysian building sector legislation and policy. j. of surv., construction and property, 6: 1-1. [15] abdullah wsw, osman m, ab kadir mza, verayiah r. (2019) the potential and status of renewable energy development in malaysia. energies, 12(2): 2437. https://doi.org/10.3390/en12122437 [16] samsudin msn, rahman mm, wahid ma. (2016) power generation sources in malaysia : status and prospects for sustainable development. j. of adv. review on sci. research, 25: 11-28. [17] jungbluth n. (2006) comparison of the environmental impact of tap water vs. bottled mineral water. uster, switzerland: swiss gas and water association bull. [18] hervy m, evangelisti s, lettieri p, lee ky. (2015) life cycle assess. of nanocellulosereinforced advanced fibre composites. composites sci. and tech., 118: 154-162. https://doi.org/10.1016/j.compscitech.2015.08.024 [19] ortiz-reyes e, anex rp. (2018) a life cycle impact assess. method for freshw. eutrophication due to the transp. of phosphorus from agricultural production. j. of cleaner production, 177: 474-482. [20] de jonge vn, elliott m. (2001) eutrophication. encyclopedia of ocean sciences, 2: 852870. [21] la rosa ad, recca g, summerscales j, latteri a, cozzo g, cicala g. (2014) bio-based versus traditional polymer composites. a life cycle assessment perspective. j. of cleaner production, 74: 135-144. https://doi.org/10.1016/j.jclepro.2014.03.017 https://doi.org/10.1016/j.jmatprotec.2007.06.087 https://doi.org/10.1111/j.1365-2486.2011.02618.x https://doi.org/10.1089/ind.2015.0003 https://doi.org/10.3390/en12122437 https://doi.org/10.1016/j.compscitech.2015.08.024 https://doi.org/10.1016/j.jclepro.2014.03.017 microsoft word 4_vol17_no1_2016_(compiledversion_4).docx iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 49 removal of chromium from aqueous solution using locally available inexpensive taro and water hyacinth as biosorbent shahjalal khandaker1, ganesh chandra saha2, and mohammad al mamun miah3 1 department of textile engineering, 2 department of civil engineering, dhaka university of engineering and technology, gazipur-1700, bangladesh. 3 roads and highways department, ministry of transport and bridges, bangladesh. s.khandaker@duet.ac.bd; ganesh@duet.ac.bd; and almamuntangail@gmail.com (received: 09 jun. 2015; accepted: 13 oct. 2015; published on-line: 30 apr. 2016) abstract: in this investigation, locally available and inexpensive taro and water hyacinth were used as biosorbents to remove chromium from synthetic wastewater. the removal of this metal ion from water in the batch and column method have been studied and discussed. adsorption kinetics and equilibrium isotherm studies were also carried out. the material exhibits good adsorption capacity and the data follow both freundlich and langmuir models. scanning electronic microscopic image was also used to understand the surface characteristics of biosorbent before and after biosorption studies. effects of various factors such as ph, adsorbent dose, adsorbate initial concentration, particle size etc. were analyzed. the initial concentrations of chromium were considered 5-30mgl-1 in batch method and only 4mgl-1 in column method. the maximum chromium adsorbed was 1.64 mgg-1 and 4.44 mgg-1 in batch method and 1.15 mgg-1 and 0.75 mgg-1 in column method. batch and column desorption and regeneration studies were conducted. column desorption studies indicated that both of these biosorbents could be reused for removing heavy metals. results of the laboratory experiments show that the performance of taro and water hyacinth prove that they can effectively be used as low cost biosorbents for the removal of chromium from wastewater. abstrak: dalam penyiasatan ini, tumbuh-tumbuhan tempatan yang sedia ada dan murah iaitu taro dan air hyacinth telah digunakan sebagai biosorbents untuk menghapuskan kromium daripada air sisa sintetik. penyingkiran ion logam ini daripada air dalam kaedah kumpulan dan kaedah kolum telah dikaji dan dibincang. kajian kinetik penjerapan dan keseimbangan isoterma juga telah dijalankan. bahan ini menunjukkan kapasiti penjerapan yang baik dan data yang diperolehi adalah saperti data dari model freundlich dan langmuir. imej pengimbasan mikroskopik elektronik juga diambil untuk memahami ciri-ciri permukaan biosorbent sebelum dan selepas kajian biosorption..kesan beberapa faktor seperti ph, dos penjerap, kepekatan awal bahan terjerap, saiz zarah dan lain-lain telah dianalisa. kepekatan awal kromium adalah 5-30mgl-1 dalam kaedah kelompok dan hanya 4mgl-1 dalam kaedah kolum. kromium terjerap maksima ialah 1.64 mgg-1 dan 4.44 mgg-1 dalam kaedah kelompok dan 1.15 mgg-1 dan 0.75 mgg-1 dalam kaedah kolum. kajian penyaherapan dan pertumbuhan semula menggunakan kaedah kelompok dan kolum telah dijalankan. dalam kajian penyaherapan kolum menunjukkan bahawa kedua biosorbent ini boleh digunakan semula untuk menghapuskan logam berat. hasil daripada eksperimen makmal ini menunjukkan taro dan hyacinth air iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 50 adalah berkesan digunakan sebagai biosorbent kos rendah bagi penghapusan kromium dari air sisa. keywords: adsorption; chromium removal; taro; water hyacinth; batch method; column studies 1. introduction water pollution due to toxic heavy metals has been a major cause of concern for environmental engineers. the industrial and domestic wastewater is responsible for triggering severe damage to the environment and adversely affecting human health. the availability of non-biodegradable heavy metals in wastewater may lead to bioaccumulation with living organisms and may cause health complications to animals, plants and human beings [1]. moreover, toxic heavy metals can transfer from water and soil to plants through nutrients uptake and may come into the food chain. chromium can be severely poisonous to both plants and animals. it is also considered one of the acute toxic metal ions for its carcinogenic nature [2]. chromium mainly affects the liver, kidneys, and respiratory organs with hemorrhagic effects, dermatitis and ulceration of the skin due to prolonged exposure [3]. moreover, international agency for research on cancer (iarc) considered that toxic chromium can change the dna transcription process causing important chromosome abnormalities [4]. the toxicity of chromium depends on the forms of metal, quantity, and the ionic form. some industries discharge wastewater which contain two forms of chromium such as hexavalent and trivalent. the hexavalent form of chromium is comparatively more toxic than the trivalent form [2]. therefore, nowadays, like other harmful heavy metals, removal of chromium from wastewater following suitable approaches is being seriously considered. although subtraction of toxic metal ions from wastewater is a very challenging task with high treatment costs. a wide range of technologies have been established for removal of chromium from wastewater such as reverse osmosis, ion exchange, precipitation, electrolysis, adsorption, etc. [5]. among the various treatment processes, the adsorption process is being extensively applied by numerous researchers for the removal of heavy metal from waste stream [6-8]. adsorption is a surface phenomenon in which materials are extracted from one phase and concentrated at the surface of a second phase [34]. in the adsorption process, a considerable number of adsorbents have been investigated to remove heavy metals. these include starch xanthate [6], activated carbon [7-10], inorganic gels [11], low rank coals and related materials [12], giridih coal, singareni coal, crushed coconut shell [13], chitosan [14], peat [15], vermiculite [16], macro fungi v. volvacea [17], fontinalis antipyretica biomass [18], banana peel [19], rice husk [20], etc. in this study, attempts have been made to develop low cost bisorbents using taro and water hyacinth for removal of chromium from wastewater. taro and water hyacinth are locally available in bangladesh and fast spreading, cheap biosorbents. 2. experimental studies 2.1 materials preparation and characterization water hyacinth (eichhornia crassipes) and taro (colocasia esculenta) were collected from in and around dhaka university of engineering and technology, gazipur, bangladesh. the collected organisms were washed properly with deionized water to eliminate adhering foreign particles like sand and debris. the washed biomass was first air iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 51 dried for 24 h and then placed in an oven at 60°c to constant weight. the resulting materials were grounded, powdered by agate mortar and sieved to the preferred particle size before usage. the material was stored in a vacuum desiccator for further use. the water soluble matters of biosorbent was determined by taking 10 g of the biosorbent in contact with distilled water for 24 h and then biosorbent was separated from the water and dried at 40oc ± 2oc for 24 h and weighed. water soluble matters were reported as percentage of the original weight. specific gravity of the biosorbent was calculated by measuring the volume of water displaced by 7 g of the sorbent. mixture of biosorbent was boiled and materials were separated by filtration and then ph was measured by a ph meter (hach, usa). leaching characteristics were undertaken by conducting a leachability test and chemical oxygen demand (cod) was determined as per standard methods. moreover, biosorbents were characterized by scanning electronic microscope (sem) before and after chromium sorption. 2.2 batch method adsorption studies 2.2.1 kinetics of adsorption batch method was used for kinetics studies. five hundred milliliters of chromium solution (5 mgl-1, 10 mgl-1, 15 mgl-1, 20 mgl-1, 25 mgl-1, and 30 mgl-1) was taken in 1 l beaker. the exact initial concentration of chromium in solution was measured by atomic absorption spectrometer (aa-7000, shimadzu, usa) before starting the experiment. biosorbents (2 gl-1) were added and the solution was stirred (120 rpm) by a rotary shaker and the residual heavy metal concentration in solution was measured by taking 5 ml aliquots from the solution at predetermined contact time (5 min, 10 min, 15 min, 30 min, 45 min, 60 min, 90 min, 120 min, 180 min, 200 min, 300 min). however, among the initial kinetics studies, the equilibrium time of 3 h was found to be sufficient for the observed metal concentrations. the adsorption was estimated by employing the following expression [21]: % = ∁ ∁ ∁ × 100 (1) where, c0 = initial chromium concentration and ce = chromium concentration at equilibrium condition. 2.2.2 effect of ph and biosorbent dose upon adsorption the effects of solution ph on adsorption of chromium were investigated over a range of 3 to 10 and the ph was adjusted by 0.1 n hno3 and 0.1 n naoh. contact time was chosen as 3 h to study the effect of ph at room temperature (25 °c). moreover, the effect of biosorbent on chromium removal was studied with varying biosorbent dose from 1 to 5 gl1 in a 4 mgl-1 of chromium solution. 2.2.3 batch mode desorption studies batch desorption studies were conducted to verify the possibility of reusing the biosorbent. after 3 h contact time, biosorbent was separated from solution by using whatman filter paper and washed with distilled water to remove unadsorbed chromium and oven dried. the dried biosorbent was again reused maintaining a 2 gl-1 concentration for 3 h. 2.3 fixed bed column studies column studies (down flow mode) were conducted with distilled water spiked metals. a 63.15 mm id glass column was filled with the biosorbent. a bed depth of 80 mm was adopted and a study bed depth of 100 mm was maintained. porous stone was used to support iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 52 the biosorbent in the column. influent concentration was 4 mgl-1. the samples from effluent were collected periodically (15 to 30 min interval) and tested for metal concentration. the columns were run up to 3 h. column desorption studies were also performed in the same column and with the same biosorbent that was saturated with metal. after exhaustion of the column, the biosorbent was separated and washed with distilled water. the same biosorbent was utilized again in the column for desorption using 0.01 n hno3. 3. results and discussions 3.1 characteristics of the adsorbents the water soluble matters were 96% and 44% in taro and water hyacinth respectively. the specific gravity of taro was 0.70, whereas in water hyacinth this was 0.35. ph was measured in water hyacinth and taro were 4.80 and 3.90 and leaching as cod was 2094 mgl-1 and 5262 mgl-1 respectively. sem studies were performed to understand the physical nature and physical damage of biosorbent surface during adsorption. the sem pictures of biosorbent taro and water hyacinth before and after chromium uptake are shown in fig. 1(a), 1(b), 2(a), and 2(b). the images clearly indicate that the biosorbents are highly porous in nature which is a desirable characteristic of any adsorbent. fig. 1 (a): scanning electron micrograph of taro. fig. 1 (b): scanning electron micrograph of cr adsorbed taro. fig. 2 (a): scanning electron micrograph of water hyacinth. fig. 2 (b): scanning electron micrograph of cr adsorbed water hyacinth. iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 53 3.2 effect of particle size three different particles mean sizes such as 0.945 mm, 0.505 mm and 0.150 mm were considered for batch adsorption investigation. chromium uptake by the biosorbents for their different sizes with time is shown in fig. 3 and fig 4. the adsorption rates were initially rapid because of readily accessible sites for exchange adsorption. maximum cr uptake was observed by the sorbent mean size 0.505 mm for both taro and water hyacinth. therefore, the sorbent mean size 0.505 mm was considered for further experimentation. fig. 3: cr removal kinetics for different sizes of taro. fig. 4: cr removal kinetics for different sizes of water hyacinth. 3.3 effect of adsorbate initial concentration the metal removal efficiency is marginally increased for solution with same initial metal concentrations for any contact period. the variations of chromium uptake by the biosorbent for different initial cr concentrations with time are shown in fig. 5 and fig. 6. metal uptake often follows a two-step kinetics [22]. the same phenomenon was observed in the present studies. the adsorption rates were initially rapid because of higher number of available accessible sites for exchange adsorption, and due to the presence of higher solute concentration gradient. nearly 3%, 9%, 14%, 20%, 25%, 30% of total sorption at initial stage for metal concentrations of 5 mgl-1, 10 mgl-1, 15 mgl-1, 20 mgl-1, 25 mgl-1, 30 mgl1 respectively by taro. it is seen that the total sorption has been completed in around 60 min. fig. 5: bisorption kinetics of cr with different initial concentrations by taro. 0 5 10 15 20 25 30 35 0 30 60 90 120 150 180 r em ai ni ng c on ce nt ra ti on , gl -1 time (min) 5 ppm 10 ppm 15 ppm 20 ppm 25 ppm 30 ppm iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 54 fig. 6: bisorption kinetics of cr with different initial concentrations by water hyacinth. on the other hand, at the beginning about 4%, 11%, 14%, 19%, 25%, 30% of total sorption were for the cr concentration of 5 mgl-1, 10 mgl-1, 15 mgl-1, 20 mgl-1, 25 mgl1, 30 mgl-1 respectively by water hyacinth and virtually the sorption process was completed within 60 min. the uptake capacity increases with increase in initial concentration, which may be due to the availability of more number of cr (vi) ions in solution for adsorption. moreover, higher initial adsorbate concentration provided greater driving energy to overcome various mass transfer confrontations of the metal ions from the aqueous to the solid phase resulting in higher probability of collision between cr (vi) ions and the active sites [23]. 3.4 equilibrium studies when an adsorbent is in contact with an adsorbate, an apparent equilibrium is established between the adsorbate concentration in the liquid phase and that on the solid phase. this state is one of dynamic stability. the amount of adsorbate migrating onto the adsorbent is counterbalanced by the amount of adsorbate migrating back into the solution phase and should not be construed as a state of termination of adsorption. the adsorption equilibria can hence be modelled along the lines of a heterogeneous chemical reaction. langmuir and freundlich isotherms are widely used as equilibrium isotherm models to represent experimental data obtained from batch equilibrium studies [24]. 3.4.1 langmuir isotherm the langmuir theory shows controlling of extreme sorption abilities which denotes the first theoretical treatments of non-linear sorption, and has been effectively applied to an extensive range of systems [25]. the model assumes uniform energies of adsorption onto the surface and no transmigration of the adsorbate in the plane of the surface. graphically, it is represented by a plateau, an equilibrium saturation point where once a molecule conquers a site, no additional adsorption can happen [26-27]. the langmuir isotherm is presented by the following equation: = (2) where qmax and b are langmuir constants related to maximum adsorption ability and energy of adsorption respectively [28]. qe is the amount adsorbed (mgg-1); ce is the equilibrium concentration of the adsorbate (mgl-1). iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 55 when is plotted against , a straight line with slope is obtained. figure 7 and 8 show the adsorption isotherm of cr for taro and water hyacinth respectively. the value of the correlation coefficient r2 suggests that adsorption of chromium follows the langmuir isotherm. langmuir constants b, qmax and r2 value are given in table 1. table 1: langmuir isotherm coefficients metal name of biosorbent biosorbent size (mm) qmax (mg g-1) b r2 value chromium taro 0.505 1.64 0.03 0.99 water hyacinth 0.505 4.44 0.11 0.96 fig. 7: adsorption isotherm of cr absorbed onto taro. fig. 8: adsorption isotherm of cr absorbed onto water hyacinth. 3.4.2 freundlich isotherm the adsorption data of chromium were also analyzed by the freundlich model. the linear form of freundlich equation may be written as iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 56 log (qe) = log (k') + (1/n) log (ce) (3) where qe is the amount adsorbed (mgg−1), ce is the equilibrium concentration of the adsorbate (mgl−1), and k' and n are freundlich constants connected to adsorption capability and adsorption concentration, respectively [29]. when log (qe) is plotted against log (ce), a straight line with slope 1/n is obtained which shows that the adsorption of chromium follows a freundlich isotherm (fig. 9 and fig. 10), and values of k' and n are shown in table 2. table 2: freundlich isotherm coefficients metal name of bisorbents biosorbent size (mm) k´ (mg g-1) n r2 value chromium taro 0.505 28.44 0.66 0.98 water hyacinth 0.505 1.47 1.96 0.88 fig. 9: adsorption isotherm of cr absorbed by taro. fig. 10: adsorption isotherm of cr absorbed by water hyacinth. y = 1.5037x 1.4544 r² = 0.9803 -0.8 -0.4 0 0.4 0.8 0 0.25 0.5 0.75 1 1.25 1.5 lo g q e log ce freundlich isotherm iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 57 3.5 effect of ph the ph of the solution is an important factor which influences the uptake of metal ions by biosorbents in many ways. the effect of ph on metal adsorption is given in fig. 11 and fig. 12. the maximum uptake of chromium took place at ph 4.5 and 3.0 by taro and water hyacinth respectively. it is also apparent from the figures that the removal of chromium decreases from 19% (ph 4.5) to 10% (ph 6.0) and then increases to 15% (ph 10.0) for taro whereas for water hyacinth it is declined from 34% (ph 3.0) to 10% (ph 10). moreover, a similar trend for cr (vi) adsorption on activated carbon is described by mohammad et al. [30]. the higher adsorption of cr by taro and water hyacinth at low ph might be due to the neutralization of surface charge by a surplus of hydrogen ions. therefore, smoothing the diffusion of dichromate ions and their adsorption on the prepared adsorbent [31]. higher adsorption of chromium at low ph values might suggest that the mechanism of metal ion uptake is highly energetic to overcome the net electrostatic repulsion. fig. 11: effect of ph of adsorbate solution on cr by taro. fig. 12: effect of ph of adsorbate solution on cr by water hyacinth. fig. 13: effect of taro concentration on cr removal. fig. 14: effect of water hyacinth concentration on cr removal. 3.6 effect of biosorbent concentration the selected adsorbents were used at concentrations ranging from 1.0 to 5.0 gl-1 in batch adsorption method at 25° c. the cr uptake is found to increase rapidly with increasing concentration of biosorbent taro up to a dose of 4 gl-1 and for water hyacinth up to 3 gl-1 (fig. 13 and fig. 14). the number of available sites and exchanging ions for adsorption depends upon the amount of adsorbent in the adsorption process. the increase in the 0 5 10 15 20 25 0 1.5 3 4.5 6 7.5 9 10.5 % r em ov e ph 0 10 20 30 40 0 5 10 15 % r em ov e ph iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 58 removal efficiency can be attributed to the increased number of sites and exchangeable ions available for adsorption [30]. 3.7 batch desorption studies the desorption studies have been performed for cr using distilled water for both biosorbents and the results are presented in fig. 15 and fig. 16. it is clearly seen in figures that a marginal amount of chromium desorbed and there is some scope to further reuse these biosorbent for heavy metal removing. 3.8 column kinetic study the thomas model was used to analyze the column performance. the linearized form of the thomas model is given below [32]: ln − 1 = − (4) where ce, co = the effluent and inlet solute concentrations (mgl-1), qo = the maximum adsorption capacity (mgg-1), m = the total mass of the adsorbent (g), q = volumetric flow rate (ml min-1), v= the throughput volume (ml) and kt = the thomas rate constant (ml min1 mg-1). the kinetic coefficient, kt and the adsorption capacity of the bed, qo were determined from the plot of ln( −1) against v (fig. 17 and fig. 18). thomas rate constant, kt is dependent on flow rate, initial ion concentration and bed height. the maximum adsorption capacity, qo is increased with increase in flow rate and initial ion concentration but decreased with increase in bed height. the values of kt obtained in this work are similar to the ones obtained by sivakumar and palanisamy [33]. the value of regression coefficient (r2) indicates that the kinetic data conformed well to thomas model. figure 17 shows the results of the column study with distilled water spiked with chromium by biosorbent taro. column exhaustive capacity of distilled water spiked chromium shows values 1.15 mgg-1. figure 18 shows the results of column study with distilled water spiked with chromium by water hyacinth. column exhaustive capacity of distilled water spiked chromium shows values of 0.75 mgg-1. fig. 15: cr desorption kinetics with adsorbed biosorbent taro. fig. 16: cr desorption kinetics from adsorbed biosorbent water hyacinth. iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 59 fig. 17: column adsorption capacity for chromium by taro. fig. 18: column adsorption capacity for chromium by water hyacinth. 3.9 column regeneration and reuse studies column desorption studies were subsequently carried out after complete exhaustion of the adsorption column using 0.01 n hno3 solution and the metal concentration of the eluate was measured. it is observed from fig. 19 and fig. 20 for chromium that the desorption was judged to be successful if the previously adsorbed metal ions were recovered in a volume of less than 1.8 liters of taro and 3.5 liters of water hyacinth. this result indicates that these biosorbents could be reused in further heavy metal removal treatment from wastewater. fig. 19: desorption of chromium adsorbed taro. y = -0.002x + 1.1518 r² = 0.9011 -3 -2 -1 0 1 2 0 500 1000 1500 2000 ln [ (c o/ ce ) 1] throughput volume, ml thomas model y = -0.0006x + 0.7548 r² = 0.889 -1.5 -1.0 -0.5 0.0 0.5 1.0 0 500 1000 1500 2000 2500 3000 3500 ln [ (c o/ ce ) 1] throughput volume, ml thomas model 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0 300 600 900 1200 1500 1800 ef flu en t co nc en tr at io n, m gl -1 eluent volume, ml flow rate = 14 ml/min column id = 63.15 mm bed depth = 80 mm inf. concentration = 3.83 mg/l flow rate = 26 ml/min column id = 63.15 mm bed depth = 80 mm inf. concentration = 3.83 mg/l iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 60 fig. 20: desorption of chromium adsorbed water hyacinth. 4. conclusions the removal performance of chromium from wastewater using locally available, inexpensive taro and water hyacinth is quite good. the maximum chromium uptake by taro and water hyacinth were 1.64 mgg-1 and 4.44 mgg-1 respectively in batch method. on the other hand, uptake capacity of taro and water hyacinth in column studies was 1.15 mgg1 and 0.75 mgg-1 respectively. the results indicate that both langmuir and freundlich isotherms give good correlation of the present data for chromium. in column desorption studies, maximum release of chromium was found after passing 1.8 l 0.01 n hno3 in taro and 3.5 l in water hyacinth. the chromium removal efficiency was significantly influenced by the concentration of ph, adsorbate concentration and adsorbent dose. in view of all these findings, it may be concluded that these biosorbent are very useful, economic, and quite rapid. therefore, these bisorbent could be successfully used for the removal of chromium from wastewater and many other effluents. acknowledgement this work is performed under the financial support of higher education and quality enhancement project (heqep) cp-259, named, “industrial waste management & process efficiency” of university grants commission (ugc) of bangladesh. therefore, the authors are grateful to ugc. moreover, the authors are happy to acknowledge the contribution of the department of civil engineering, dhaka university of engineering & technology, bangladesh for allowing the use of their laboratory facilities for experimental work. references [1] ong s, seng c, lim p. (2007) kinetics of adsorption of cu (ii) and cd (ii) from aqueous solution on husk and modified rice husk. ejeafche., 6(2):1764-1774. [2] gupta vk, ali i. (2004) removal of lead and chromium from wastewater using bagasse fly ash—a sugar industry waste. j. colloid and interface sci., 271(2):321-328. [3] moore jw, subramaniam r. (2012) heavy metals in natural waters: applied monitoring and impact assessment. springer science & business media. [4] waghmare vh, chaudhari ue. (2014) removal of hexavalent chromium from aqueous solution by adsorption on commiphora myrrha bark. rasayan j. chem., 7(1): 16-19. [5] world health organization (2004) iarc working group on the evaluation of carcinogenic risks to humans, world health organization, and international agency for research on cancer. betel-quid and areca-nut chewing and some areca-nut-derived nitrosamines: iarc monographs on the evaluation of carcinogenic risks to human. 0 0.01 0.02 0.03 0 500 1000 1500 2000 2500 3000 3500 e ff lu en t co nc en tr at io n, m gl -1 eluent volume, ml iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 61 [6] wing re, doane wm, russell cr. (1975) insoluble starch xanthate: use in heavy metal removal. j. app. pol. sci., 19(3):847-854. [7] huang cp, ostavic fg. (1978) removal of cadmium (ii) by activated carbon. j. envir. engrg. asce, 104(5):863-873. [8] huang cp, wirth pk. (1982) activated carbon for treatment of cadmium wastewater. j. envir. engrg. div., asce, 108(6):1280-1299. [9] reed be, matsumoto mr. (1993) modelling cd adsorption in single and binary adsorbent (pac) systems. j. envir. engrg. div., asce, 119(2):332-348. [10] reed be, arunachalam s. (1994) use of granular carbon columns for lead removal. j. envir. engg. div., asce, 120(2):416-436. [11] srivastava sk, bhattacharjee g, sharma ak, oberoi ck. (1980) studies on the use of inorganic gels in the removal of heavy metals. water research, 14:113-115. [12] cullen gc, neil gs. (1982) removing metals from waste solutions with low rank coals and related materials. water research, 16(8):1357-1366. [13] bhattacharya ak, venkobachar c. (1984) removal of cadmium (ii) by low cost adsorbents. j. envir. engg. asce, 110:110-127. [14] jha in, iyengar l, rao. (1988) removal of cadmium using chitosan. j. envir. engrg. asce, 114(4):962-974. [15] chen xh, gosset t, thevenot. (1990) batch copper ion binding and exchange properties of peat. water res., 24(12):1463-1470. [16] das nc, bandyopadhyay m. (1991) removal of lead by vermiculite medium. app. clay sci.. 6(3):221-231. [17] osman ms. (1995) biosorption of heavy metals from water environment by macro fungi v. volvacea. ph. d. thesis, indian institute of technology, kharagpur, india. [18] martins rj, vilar vj, boaventura ra. (2010) removal of pb (ii) from wastewaters by fontinalis antipyretica biomass: experimental study and modelling. desalination and water treatment. 20(3):179-188. [19] ashraf ma, mahmood k, wajid a, maah mj, yusoff i. (2011) study of low cost biosorbent for biosorption of heavy metals. int. conf. food eng. biotechnology, 9:60-68. [20] rocha ls, lopes cb, borges ja, duarte ac, pereira e. (2013) valuation of unmodified rice husk waste as an eco-friendly sorbent to remove mercury: a study using environmental realistic concentrations. water, air, & soil pollution. 224(7):1-18. [21] milonjić sk, bošković mr, ćeranić ts. (1992) adsorption of uranium (vi) and zirconium (iv) from acid solutions on silica gel. sep. sci. tech., 27(12):1643-1653. [22] nathalie c, guilet r, deydier e. (2003) adsorption of cu (ii) and pb (ii) onto a grafted silica: isotherms and kinetic models. water research, 37(13):3079-3086. [23] pandey pk, sharma sk, sambi ss. (2010) kinetics and equilibrium study of chromium adsorption on zeolite nax. int. j. env. sci. tech., 7(2):395-404. [24] foo k, hameed bh. (2010) insights into the modeling of adsorption isotherm systems. chem. eng. j., 156(1):2-10. [25] rengaraj s, joo ck, kim y, yi j. (2003) kinetics of removal of chromium from water and electronic process wastewater by ion exchange resins: 1200h, 1500h and irn97h. j. hazardous mat., 102(2):257-275. [26] allen sj, mckay g, porter jf. (2004) adsorption isotherm models for basic dye adsorption by peat in single and binary component systems. j. coll. interface sci., 280(2):322-333. [27] demirbas e, kobya m, konukman aes. (2008) error analysis of equilibrium studies for the almond shell activated carbon adsorption of cr (vi) from aqueous solutions. j. hazardous mat., 154(1):787-794. [28] langmuir i. (1918) j. am. chem. soc., 40:1361. [29] weber wj. (1972) physicochemical processes for water quality control. wiley inter science. [30] mohammad a, rafaqat akr, siddiqu ba. (1996) studies on removal and recovery of cr (v1) from electroplating waste. water research, 30(6):1478-1482. [31] gupta vk, gupta m, sharma s. (2001) process development for the removal of lead and chromium from aqueous solutions using red mud an aluminum industry waste. water research, 35(5):1125-1134. iium engineering journal, vol. 17, no. 1, 2016 khandaker et al. 62 [32] kavak d, öztürk n. (2004) adsorption of boron from aqueous solution by sepirolite: ii column studies. illuslrararasi bor sempozyumu, 23:495-500. [33] sivakumar p, palanisamy pn. (2009) adsorption studies of basic red 29 by a nonconventional activated carbon prepared from euphorbia antiquorum l. int. j. chem. tech. res., 1(3):502-510. [34] othman mr, lee or, fernando wjn. (2006) gas adsorption and surface diffusion on 5˚a microporous adsorbent in transition and turbulent flow region. iium engineering journal, 7(1):1-12. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 effect of machining parameters on surface roughness, power consumption, and material removal rate of aluminium 6065-si-mwcnt metal matrix composite in turning operations savina jaddinagadhe puttaswamy* and raghavendra bommanahalli venkatagiriyappa department of mechanical engineering, jss academy of technical education, bangalore-560060, india * corresponding author: mailtosavin@gmail.com (received: 4th october 2020; accepted: 25th march 2021; published on-line: 4th july 2021) abstract: nanocomposites were prepared with al-6065-si and multi walled carbon nanotubes of 1 wt.% as reinforcement through the stir-casting method. fabricated nanocomposites were machined on a lathe machine using a tungsten carbide tool. the study investigated the multi-objective optimization of the turning operation. cutting velocity, feed, and depth of cut were considered for providing minimum surface roughness of the workpiece. also, the power consumed by the lathe machine with maximum metal removal rate was examined by surface response methodology. the design of experiments was developed based on rotational central composite design. analysis of variance was executed to investigate the adequacy and the suitable fit of the developed mathematical models. multiple regression models were used to represent the relationship between the input and the desired output variables. the analysis indicates that the feed is the most influential factor that effects the surface roughness of the workpiece. cutting speed and the depth of cut are two other important factors that proportionally influence the power consumed by the lathe tool as compared to the feed rate. abstrak: komposit nano disediakan bersama al-6065-si dan karbon nanotiub berbilang dinding sebanyak 1 wt.% sebagai bahan penguat melalui kaedah kacauantuangan. komposit nano yang terhasil melalui mesin pelarik ini menggunakan alat tungsten karbida. kajian ini merupakan pengoptimuman pelbagai objektif operasi pusingan. kelajuan potongan, suapan dan kedalaman potongan diambil kira sebagai pemberian minimum pada kekasaran permukaan bahan kerja. tenaga yang digunakan bagi mesin pelarik dengan kadar maksimum penyingkiran logam diteliti melalui kaedah tindak balas permukaan. rekaan eksperimen yang dibangunkan ini adalah berdasarkan rekaan komposit pusingan tengah. analisis varian telah dijalankan bagi mengkaji kecukupan dan penyesuaian lengkap bagi model matematik yang dibangunkan. model regresi berganda digunakan bagi menunjukkan hubungan antara input dan pembolehubah output yang dikehendaki. analisis menunjukkan pemberian suapan merupakan faktor mempengaruhi keberkesanan kekasaran permukaan bahan kerja. kelajuan pemotongan dan kedalaman potongan adalah dua faktor penting lain yang mempengaruhi kadar langsung ke atas tenaga yang digunakan oleh mesin pelarik dibandingkan kadar pemberian suapan. keywords: mwcnt (multi-walled carbon nanotube); power consumption; machining; cutting force; central composite design; response surface methodology iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 1. introduction carbon-nanotubes reinforced with ammc’s in the recent technological era are gaining high importance among various classes of composites. researchers have made attempts to produce mmcs with cnt as reinforcement material. core research on metals such as aluminum and aluminum alloy materials [1,2], due to their light weight, high strength composites, are sought for dynamic mechanical systems like aerospace industries, robotics and automobiles [3]. materials with high stiffness, modulus, strength, low density, and high specific surface are associated in carbon nanotubes as an ideal reinforcement [4]. the presence of hard mwcnt reinforcement and its abrasive nature affects the quality of the workpiece resulting in difficulty of machining and wear of the cutting tool [5]. the traditional machining process, if adopted in composite materials with appropriate tool design and the optimal operating conditions can resolve this difficulty. these raw materials are very expensive. in order to reduce their wastage during the final conversion of the composites into engineering products and to obtain the required geometrical parts, it becomes necessary to investigate and study the basic manufacturing and machinability of the material at the time of design of material and selection [6,7]. the machining of composites depends mainly on their various reinforcements and diverse matrix properties. the cutting tool will be alternatively in contact with the base metal and the reinforcing materials and hence the response obtained by the machining of composite materials can be completely different. thus, the cutting tool’s material, geometry, and wear resistance play critical roles for the machining of composite materials. correspondingly, the different machine operating parameters like the feed, cutting velocity, depth of cut, and other factors such as tool geometry, machining system stability, lubrication, and proper cutting tool selection, all play crucial roles [8]. considering these many factors, it becomes very difficult to attain fine surface finish and high metal removal rate (mrr). the feed, cutting speed and the depth of cut are those parameters that can be controlled, and proper selection of these parameters yields proper surface finish to the mmcs [9]. the machining operations are classified under two important categories: cutting and grinding process. process flexibility, yield time, high material removal rate and good surface finish are found to be salient features in the turning process. the proper prediction of cutting forces in the turning process is the primary task to achieve along with high dimensional accuracy and suitable machining system stability [10]. in the industry, metal removing processes are used to get the desired shape and dimension with precise quality. the process that removes metal at a higher rate and power consumed is considered to obtain an economical process [11]. measuring the power consumption in the metal-removal-bycutting-tool operation helps for designing machine components, increasing the life of the tool for high productivity, and managing the capacity required by the motor for machine. the objective of the research is to analyze the percentage contribution of machining parameters like feed, cutting velocity, and the depth of cut of the developed mmc on surface roughness, material removal rate, and power consumed using rsm. 2. experimental details 2.1 fabrication of mwcnt-si-al matrix of 1 wt.% by stir casting method the al-6065 ingot-castings were placed in the electric furnace and the temperature of the crucible in the furnace was raised and maintained at a temperature of 750 oc for about 20 minutes. this process was carried out to convert the material into a molten state. the iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 molten metal was stirred continuously for about 15 minutes. the cnt powder was slowly added into the molten metal. the stirring created a uniform mixture of the reinforced particle of 1 wt.% of mwcnt and 4% of silicon into molten mix. the molten metal was poured into the metal die and left for solidification. the sample of the specimen was considered for further machining processes [12]. 2.2 turning machine and the cutting conditions the experiments were conducted on a heavy-duty precision lathe machine as shown in fig. 1, with a tungsten carbide tool. the cutter being the single point cutting tool, fed right into the rotating workpiece and cut the material as chips. this process was carried out to create the desired shape. a full bridge strain gauge dynamometer was used to measure the cutting forces. this analog device is highly capable of measuring the cutting force while the turning operations are executed. this data of measured cutting force was utilized for further analysis [13]. the specimen of ø25mm ø75mm size were used for the experimentation. fig. 1: heavy-duty precision lathe machine. 2.3 design of experiment (doe) by response surface methodology (rsm) a group of statistical and mathematical techniques that helps in modelling and analysis of a problem is termed as rsm. the output or the response of it can be controlled and is affected by several input variables. the objective here is to determine the correlation between the responses and variables determined. rsm is one of several doe methods, which is efficient for analyzing and planning the problem when certain independent variables will influence the dependent variables or when several obtained responses should yield valid and objective conclusions. rotatable central composite design (ccd) and box-behnken design are the widely used and suitable types of rsm methods that are readily available for investigation purposes [14]. the embedded factorial design is not found in the box-behnken design and is an independent quadratic model. this design is normally incorporated while executing the non-sequential investigations. the design uses certain combinations for the treatment at the corners of the face center, the process space and at the center of the design body. the design requires three levels of each factor that are near to rotatable. as compared to the ccd methods, the box-behnken model has less capability for the orthogonal blocking [15]. thus, ccd methodology is the most commonly used technique iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 in case of the second-order response models. the ccd provides very few numbers of experiment and, with a rotatable feature, the optimal response can be obtained [16]. experimental independent variables along with their coded levels for the central composite design (ccd) are represented in table 1. table 1: experimental independent variables and their coded levels independent variable levels of variables low medium high cutting velocity (m/min) 30 50 70 feed (mm/rev) 0.2 0.3 0.4 depth of cut (mm) 0.5 0.85 1.2 2.4 surface roughness (ra) and its measurement ra is a subjective property that indicates surface roughness. it is measured in micrometers, and has a crucial characteristic that quantifies high frequency deviations from that of an ideal surface. ra is the arithmetic mean value. it is based on the mean of normal deviations from a nominal surface. it is generally specified over the “cut-off” length and is represented in eq. (1). 𝑅𝑎 = 1 𝑛 ∑ 𝑦𝑖 𝑛 𝑖=1 (1) where, ra is surface roughness, n is number of measurement points and yi is surface deviation at measurement point of ‘i’. from the observation, it is noted that the values obtained are affected by few factors and machining parameters. the commercially available surface profilometers feature a diamond stylus that travels over the workpiece surface to measure the surface roughness [17]. 2.5 power consumption (pc) a dynamometer is a measuring device used to measure tangential force from which power consumed by the machine can be calculated. the product of tangential force and the cutting velocity results in cutting power consumption (pc). it is represented by eq. (2). the experiments were conducted using ccd by rsm [18]. p = fz × v (2) where, p is power in kilowatts, fz is force in newton and v is cutting speed in meter per second. 2.6 metal removal rate (mrr) the metal that is removed per unit time is the mrr. the si unit of mrr is mm3sec-1. for every revolution associated with the material, a ring-shaped chip of the material is taken out. the mrr can be obtained using eq. (3). mrr = v × f × d (3) where, v is the cutting velocity in m/min, f is the feed in mm/rev, and d is the depth of cut in mm. iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 3. results and discussion 3.1 validation for surface roughness by response surface methodology the experiments were executed according to ccd, that was generated by response surface methodology (rsm) with three input variables: cutting speed (v), feed (f) and depth of cut (d). twenty experimental runs were executed with 95% confidence level. the readings of trial runs were measured for the surface roughness using the surface roughness tester measuring machine and the cutting force using the lathe tool dynamometer. the response output obtained for mrr, experimental ra, model ra, and % of error is tabulated in table 2. regression coefficients obtained from the experimental results are shown in table 3 for polynomial regression equation of surface roughness (ra). table 4 shows the corresponding analysis of variance and is obtained using minitab-14 software. table 2: experimental runs and surface roughness responses sl. no input variables output responses cutting velocity (v) feed (f) depth of cut (d) mrr (mm3 min-1) exp. (ra) model (ra) ra (diff.) % error 1 30 0.2 1.20 120.000 1.34 1.360 0.020 1.559 2 70 0.2 0.50 116.667 1.68 1.865 0.185 11.058 3 30 0.4 0.50 100.000 2.8 3.023 0.223 7.977 4 70 0.4 0.50 233.333 3.12 3.324 0.204 6.543 5 30 0.4 1.20 240.000 3.1 3.138 0.038 1.254 6 30 0.2 0.50 50.000 1.93 1.935 0.005 0.278 7 70 0.2 1.20 280.000 0.96 0.960 0.0008 0.093 8 50 0.3 0.85 212.500 3.86 3.918 0.058 1.527 9 50 0.3 0.85 212.500 3.91 3.918 0.008 0.229 10 50 0.3 0.85 212.500 3.87 3.918 0.048 1.265 11 70 0.4 1.20 560.000 2.89 3.109 0.219 7.587 12 50 0.3 0.85 212.500 3.84 3.918 0.078 2.056 13 17.34 0.3 0.85 73.695 2.86 2.786 0.073 2.583 14 50 0.4633 0.85 328.171 3.64 3.391 0.248 6.830 15 50 0.3 0.85 212.500 3.91 3.918 0.008 0.229 16 82.66 0.3 0.85 351.305 2.82 2.705 0.114 4.073 17 50 0.3 1.42155 355.388 2.41 2.407 0.002 0.088 18 50 0.3 0.27845 69.613 3.26 3.052 0.207 6.368 19 50 0.3 0.85 212.500 3.9 3.918 0.018 0.486 20 50 0.1367 0.85 96.829 0.71 0.748 0.038 5.472 table 3: estimated regression coefficients for ra in µm term coeff. se coeff. t p constant -8.1365 0.95560 -8.514 0.000 v 0.1049 0.01682 6.237 0.000 f 43.1855 3.57327 12.086 0.000 d 4.7344 0.95350 4.965 0.001 v2 -0.0011 0.00012 -9.384 0.000 f2 -69.3314 4.73106 -14.655 0.000 d2 -3.6393 0.38621 -9.423 0.000 v x f 0.0463 0.03039 1.522 0.159 v x d -0.0118 0.00868 -1.357 0.205 f x d 4.9286 1.73676 2.838 0.018 s = 0.171930 r2 = 98.53% r2 (pred.) = 88.95% r2 (adj.) = 97.21% iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 table 4: analysis of variance for ra in µm source df seq ss adj ss adj ms f p regression 9 19.8663 19.8663 2.20737 74.67 0.000 linear 3 9.2669 4.6496 1.54985 52.43 0.000 interaction 3 10.2385 10.2385 3.41282 115.45 0.000 square 3 0.3610 0.3610 0.12032 4.07 0.040 residual error 10 0.956 0.2956 0.02956 lack-of-fit 5 0.2913 0.2913 0.05826 68.01 0.000 pure error 5 0.0043 0.0043 0.00086 total 19 20.1619 the model developed was investigated using the analysis of variance technique. the value of the determination coefficient (r2 = 95.00%) specified that only the values that are less than the 5% of total variations were not explained by the developed model and this indicated the quality of the model’s fit. the value of the adjusted determination coefficient (adj. r2 = 0.9500) was high and specifies that the obtained model was highly significant. if p-value is less than f-value (p<f), it indicates that the model is highly significant. the results of ra as obtained using anova is represented in table 4. it describes the predictability of the obtained model for its surface roughness (ra) to be at a 99% confidence level. this is due to the average value of ‘p’ which is less than 0.0001. figure 2 shows that the experimental output, surface roughness (ra) is closer to the regression model obtained using rsm method. the r2 was found to be 98.53% and shows that the regression equation is highly reliable [21]. the lower value of ‘p = 0.01’ indicates the statistic significance of the model and concludes that the proposed model is a correct one. 0.300.150.00-0.15-0.30 99 90 50 10 1 residual p e r c e n t 4321 0.2 0.0 -0.2 fitted value r e s id u a l 0.20.10.0-0.1-0.2 8 6 4 2 0 residual f r e q u e n c y 2018161412108642 0.2 0.0 -0.2 observation order r e s id u a l normal probability plot versus fits histogram versus order residual plots for ra fig. 2: residual plots for ra in µm. residual plots for ra shown in fig. 2 have been analyzed and are discussed. the probability plot was used to check for the data normality. the distribution of the data points all along the normal line with very few outliers indicated that the data is normally distributed. the residual versus fitted values, as shown in the second plot, do not show any subsequent trends. this indicates the chosen rsm model fits well within the given dataset. the third plot of frequency verses residual illustrates the normal distribution of residuals that are produced by the model and assures that the assumptions made are reasonable and the choice of the model is appropriate. the residue verses observation order as depicted in the last plot iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 highlights the presence of random data points. the randomness in the plot shows the insignificant experimental order in comparison to first surface response (ra). a confidence level of 95% has been applied to rsm for ra. the statistical significance of the surface roughness has been measured and concluded based on all the factors and respective interactions which has a probability value or p-value to be less than 0.05. 3.2 optimized solution for surface roughness the lower values, the upper values and the final target values of ra responses are fed to the response optimizer tool of minitab by giving equal weightages. the description of the same is given in table 5. table 5: response optimization goal lower target upper weight import optimization of ra 0.71 1.1 3.91 1 1 cur high low1.0000 d optimal d = 1.0000 targ: 1.10 ra y = 1.1000 1.0000 desirability composite 0.2784 1.4215 0.1367 0.4633 17.340 82.660 f dv [50.0] [0.2214] [1.4215] fig. 3: predicted response for ra in µm. a significant solution of about 100% composite desirability is provided by the software. this is concluded from the analysis of data of experiments. about 50 m/min cutting velocity, 0.2214 mm/rev of feed rate, and 1.4215 mm of doc along with 1.1 µm of minimum surface roughness is reached. lower half of fig. 3 shows the of variation of ra along with focused input variables. the blue dotted lines indicate the pin-pointing desired optimal points [19]. 3.3 validation for power consumption by rsm the experiments were conducted using three input variables such as cutting speed (v), feed rate (f), depth of cut (d) for 20 experimental run and obtain the output responses as cutting forces (fz) in z direction, power consumption (pc), difference of power consumption and percentage error are shown in the table 6. the output of the experiments was measured using tool dynamometer for cutting forces and calculated the power consumption. regression coefficients are as shown in table 7 for polynomial regression equation of power consumption (pc) and table 8 shows the corresponding analysis of the variance. the anova results of the pc is shown in table 8. it indicates the obtained model for the surface roughness having probability of 99% confidence level. this is due to the average value of p-value, which is less than 0.0001. the r2 is 99.40% and provides a highly reliable regression equation [21]. iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 table 6: experimental run and power consumption results sl. no input parameters output responses cutting velocity (v) feed (f) depth of cut (d) fz (in n) pc (in w) y (pc) pc. (difference) % error 1 30 0.2 1.2 107.910 53.955 51.12824 2.82676 5.239107 2 70 0.2 0.5 49.050 57.225 55.38798 1.83702 3.21017 3 30 0.4 0.5 78.480 39.240 38.20172 1.03828 2.645973 4 70 0.4 0.5 88.290 103.005 107.0857 4.08072 3.961672 5 30 0.4 1.2 166.770 83.385 86.47904 3.09404 3.710547 6 30 0.2 0.5 49.050 24.525 27.37598 2.85098 11.62479 7 70 0.2 1.2 117.720 137.340 139.6482 2.30824 1.680676 8 50 0.3 0.85 127.530 106.275 105.5303 0.74475 0.700776 9 50 0.3 0.85 137.340 114.450 105.5303 8.91975 7.793578 10 50 0.3 0.85 127.530 106.275 105.5303 0.74475 0.700776 11 70 0.4 1.2 186.390 217.455 215.871 1.58396 0.728408 12 50 0.3 0.85 127.530 106.275 105.5303 0.74475 0.700776 13 17.34 0.3 0.85 137.340 39.691 39.13672 0.5545442 1.397144 14 50 0.4633 0.85 147.150 122.625 117.5362 5.088793954 4.149883 15 50 0.3 0.85 117.720 98.100 105.5303 7.43025 7.574159 16 82.66 0.3 0.85 127.530 175.694 167.6571 8.0367482 4.574292 17 50 0.3 1.42155 176.580 147.150 144.282 2.868011577 1.949039 18 50 0.3 0.27845 49.050 40.875 36.06505 4.809945647 11.76745 19 50 0.3 0.85 127.530 106.275 105.5303 0.74475 0.700776 20 50 0.1367 0.85 58.860 49.050 46.46107 2.588926864 5.278138 residual plots for pc shown in fig. 4 has been analyzed and is discussed. the probability plot is used to check for the data normality. the distribution of the data points all along the normal line with very few outliers indicates that the data is normally distributed. the residual versus fitted values, as shown in the second plot, do not show any subsequent trends. this indicates the chosen rsm model fits well within the given dataset. the third plot of frequency verses residual illustrates the normal distribution of residuals that are produced by the model and assures that the assumptions made are reasonable and the choice of the model is appropriate. the residue versus observation order, as depicted in the last plot, highlights the presence of random data points. the randomness in the plot shows an insignificant experimental order in comparison to first power consumption (pc). a confidence level of 95% has been applied to rsm for pc. table 7: estimated regression coefficients for pc in watts term coeff. se coeff. t p constant -43.838 29.576 -1.482 0.169 v -1.202 0.521 -2.308 0.044 f 342.726 110.593 3.099 0.011 d 13.983 29.511 0.474 0.646 v2 -0.002 0.004 -0.429 0.677 f2 -882.428 146.426 -6.026 0.000 d2 -47.010 11.953 -3.933 0.003 v x f 5.109 0.941 5.432 0.000 v x d 2.161 0.269 8.039 0.000 f x d 175.179 53.753 3.259 0.009 s = 5.32124 r2 = 99.40% r2 (pred.) = 97.00% r2 (adj.) = 98.86% iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 table 8: analysis of variance for 𝑃𝑐 in watts source df seq. ss adj. ss adj. ms f p regression 9 46840.3 46840.3 5204.47 183.80 0.000 linear 3 42495.3 575.7 191.90 6.78 0.009 interaction 3 1379.0 1379.0 459.68 16.23 0.000 square 3 2965.9 2965.9 988.65 34.92 0.000 residual error 10 283.2 283.2 28.32 lack-of-fit 5 149.5 149.5 29.90 1.12 0.453 pure error 5 133.7 133.7 26.73 total 19 47123.4 1050-5-10 99 90 50 10 1 residual p e r c e n t 200150100500 10 5 0 -5 -10 fitted value r e s id u a l 840-4-8 8 6 4 2 0 residual f r e q u e n c y 2018161412108642 10 5 0 -5 -10 observation order r e s id u a l normal probability plot versus fits histogram versus order residual plots for pc in watt fig. 4: residual plots for pc in watts. 3.4 optimized solution for power consumption the lower values, the upper values and the final target values of pc responses are fed to the response optimizer tool of minitab by giving equal weightages. the description of the same is given in table 9. table 9: response optimization for power consumption goal lower target upper weight import optimization of pc 24.525 40 217.455 1 1 fig. 5: predicted response for ra in µm. iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 minimum power consumption (pc) of 40 watts is obtained for a cutting velocity of 17.3407 m/min, feed rate of 0.3172 mm/rev and depth of cut of 1.4215 mm, as shown in the fig. 5. the lower half of fig. 5 shows the of variation of pc along with focused input variables [19]. 3.5 development of empirical models the relation between the input machining parameters and the output responses is developed by the mathematical models and thereby optimization of the machining process. rsm is an optimization procedure that produces a multi objective function model which can solve the optimization problem. the present study concentrates on the development of empirical models for the output responses, surface roughness (ra) and power consumption (pc) with regards to the input machining parameters in actual factors by using rsm. [20]. any further optimization of the machining process can be carried out using the developed models. the second order regression equations of the model that was developed are estimated by regression analysis. the following equations for ra and pc were obtained in terms of actual factors. the polynomial optimization equation of surface roughness (ra): the polynomial optimization equation of power consumption (pc): 4. conclusion this study presents an effective method for estimating the optimal turning operation parameters for surface roughness and power consumption using response surface methodology. the investigation shows that the control factors had varying effects on the response variable. the use of central composite design of response surface methodology was considered successful to obtain optimal responses. the results of power consumption (pc) as obtained using anova is represented in table 8. the average value of ‘p’ was less than 0.001 and hence the model obtained for power consumption to be at a 99% confidence level. fig. 4 shows that the output response is closer to the regression model obtained using rsm method. the surface roughness was mainly affected by the feed and the cutting speed. also, an increase in the feed rate resulted in higher surface roughness. it was also observed that the cutting speed varies inversely along with surface roughness, thereby increasing the surface finish of the workpiece. the observed anova response of the cutting velocity and depth of cut majorly influenced the power consumed by the machine. minimum surface roughness along with minimum power consumption was estimated using the optimized solution parameters. this demonstrates that the rsm can be successfully applied to obtain a maximum amount of information with the least number of experimental runs. this can be successfully implemented to obtain an effective second order polynomial and for optimizing the machining process. acknowledgements the authors wish sincere thanks to basheer ahmed mohamed, the managing director of sidhi vinayaka fab engineering pvt. ltd., peenya industrial area, bangalore, india, for providing us the research facilities and supporting us in handling the research work. iium engineering journal, vol. 22, no. 2, 2021 puttaswamy and venkatagiriyappa https://doi.org/10.31436/iiumej.v22i2.1640 references [1] esawai a, morsi k. (2007) dispersion of carbon nanotubes (cnts) in aluminium powder composites part-a applied science and manufacturing, 38: 646-650. [2] iijima s. (1991) helical microtubules of graphic carbon. nature, 354: 56-58. [3] bakshi sr, lahiri d, agarwal a. (2010) carbon nanotube reinforced metal matrix composites a review. international materials reviews, 55: 41-64. [4] liu zy, yu sj, xiao bl. (2012) effect of ball milling time on mechanical properties of carbon nanotubes reinforced aluminium matrix composites. composites part-a applied zcience and manufacturing, 43: 2161-2168. [5] baburaj e, senthil p, dhanapal p. (2018) investigation on influence of machining parameters on high speed phase milling of hybrid (lm0-sic-fly ash). composite int j pure and appl math, 118(20): 901-906. [6] stratford kn, audy j. (1997) indirect monitoring of machinability in carbon steels by measurement of cutting forces. j. mater processing tech, 67(1-3): 150-156. [7] teti r. (2002) machining of composite materials. cirp annals, 51(2): 611-634. [8] ranganath ms, vipin rsm. (2014) effect of cutting parameters on mrr and surface roughness in turning of aluminium-6061. int j adv res and innov, 2(1): 32-39. [9] parhad p, likhite a, bhatt j. (2015) the effect of cutting speed and depth of cut on surface roughness during machining of austempered ductile iron. transactions of the indian institute of metals, 68: 99-108. https://doi.org/10.1007/s12666-014-0439-y. [10] thangarasu sk, shankar s, thomas at, sridhar g. (2018) prediction of cutting force in turning process-an experimental approach, iconamma-2017, iop conf. series: materials science and engineering, 310: 012119. [11] patel mt, deshpande va. (2014) optimization of machining parameters for turning different alloy steel using cnc-review. int j innov res sci eng tech, 3(2): 2319-8753. [12] puttaswamy sj, venkatagiriyappa rb. (2020) investigation on influence of anionic surfactant for homogenisation of mwcnt in aluminium 6065 matrix. iium engineering journal, 21(2). https://doi.org/10.31436/iiumej.v21i2.1317 [13] thangarasu sk. (2018) prediction of cutting force in turning process-an experimental approach. iop conference series: materials science and engineering, 310: 012119. [14] samuel mk, chandrasekaran c, paarthasarathy b, kamalakkannan sd. (2013) prediction of surface roughness response in turning on cu graphite mmc fabricated through stir-casting method. ijetae, iessn 3(3): 2250-2459. [15] geo r, d’cotha js. (2014) effect of turning parameters on power consumption in en 24 alloy steel suing different cutting tools. int j eng res gen sci, 2(6): 2091-2730. [16] akcay h, anagun as. (2013) multi response optimization application on a manufacturing factory. mathematical and computational application, 18(3): 531-538. [17] kuttolamadom m, hamzehlouia s, mears l. (2010) effect of machining feed on surface roughness in cutting 6061 aluminum. sae int j mater manuf, 3(1): 108-119. https://doi.org/10.4271/2010-01-0218. [18] richard geo, jose sheril d’cotha (2014) effect of turning parameters on power consumption in en 24 alloy steel using different cutting tools, international journal of engineering research and general science, vol. 2, issue 6, october-november, issn 20912730. [19] singh bj, sodhi hs. (2014) parametric optimisation of cnc turning for al-7020 with rsm. int j operational research, 20(2): 180-206. [20] ramudu c, sastry mnp. (2012) analysis and optimization of turning process parameters using design of experiments. int j eng res appl, 2(6): 20-27. [21] lakshminarayanan ak, balasubramanian v. (2009) comparison of rsm with ann in predicting tensile strength of friction stir welded aa7039 aluminium alloy joints. transactions of nonferrous metals society of china, 19(1): 9-18. https://www.sciencedirect.com/science/journal/09240136/67/1 https://link.springer.com/journal/12666 https://link.springer.com/journal/12666 https://doi.org/10.31436/iiumej.v21i2.1317 https://www.sciencedirect.com/science/article/abs/pii/s1003632608602216#! https://www.sciencedirect.com/science/article/abs/pii/s1003632608602216#! https://www.sciencedirect.com/science/journal/10036326 https://www.sciencedirect.com/science/journal/10036326/19/1 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. direct power control of a dfig-based wind turbine under unbalanced grid voltage without rotor position sensor ali izanlo, sayyed asghar gholamian* and mohammad verij kazemi faculty of electrical and computer engineering, babol noshirvani university of technology, babol, iran. *corresponding author: gholamian@nit.ac.ir (received: 24th apr. 2016; accepted: 20th jun. 2016; published online: 30th may 2017) abstract: in this paper, the behavior of a doubly fed induction generator (dfig) is proposed under an unbalanced grid voltage and without using a rotor position sensor. there are two main methods that have been used for the detection of rotor position: use of a shaft sensor and use of a sensorless algorithm. in this paper the shaft sensor is eliminated and a position sensorless algorithm is used for estimating the rotor position. sensorless operation is more desirable than using shaft sensors, because shaft sensors have several disadvantages related to cost, cabling, robustness, and maintenance. also, during network imbalance, three selectable control targets are identified for the rotor side converter (rsc), i.e., obtaining sinusoidal and symmetrical stator currents, mitigation of active and reactive powers ripples and the cancellation of electromagnetic torque oscillations. the effectiveness of the proposed control strategy is confirmed by the simulation results from a 2-mw dfig system. it is concluded that the sensorless algorithm is able to produce results with similar accuracy to shaft sensor use and the sensorless algorithm can be used in practical applications. abstrak: dalam kertas ini, tingkah laku penjana induksi dua suapan (dfig) dicadangkan di bawah voltan grid tidak seimbang dan tanpa menggunakan sensor kedudukan rotor. dua kaedah utama telah digunakan untuk mengesan kedudukan rotor: penggunaan sensor shaf dan penggunaan algoritma tanpa sensor. dalam kertas ini sensor shaf dihapuskan dan kedudukan algoritma tanpa sensor digunakan untuk menganggarkan kedudukan rotor. operasi tanpa sensor jauh lebih baik dari menggunakan sensor shaf, kerana sensor shaf mempunyai beberapa kelemahan yang berkaitan dengan kos, pemasangan kabel, keteguhan, dan penyelenggaraan. juga, dalam ketidakseimbangan rangkaian, tiga sasaran kawalan yang boleh dipilih telah dikenal pasti untuk converter rotor sisi (rsc), iaitu, mendapatkan arus stator sinusoidal dan simetri, pengurangan kuasa riak aktif dan reaktif dan pembatalan ayunan tork elektromagnet. keberkesanan strategi kawalan yang dicadangkan disahkan oleh keputusan simulasi daripada sistem 2mw dfig. adalah dirumuskan bahawa algoritma tanpa sensor mampu menghasilkan keputusan dengan tepat sama seperti menggunakan sensor syaf dan algoritma tanpa sensor boleh digunakan dalam aplikasi praktikal. keywords: double fed induction generator (dfig); direct power control (dpc); unbalanced voltage; rotor position estimation 1. introduction wind energy has become an important source for electricity generation in many countries. it is expected that wind energy will provide about 10% of the world’s electrical energy in 2020. nowadays, many wind farms are based on dfig technology with 57 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. converters that have generator ratings of 20%-30%. in the global wind market, dfig has become one of the most popular configurations. dfig has several advantages including variable speed, four-quadrant active and reactive power operation capabilities, and decoupled active and reactive power control. it also allows the use of a partially rated converter which reduces system cost. a schematic diagram of the dfig-based wind energy conversion systems is shown in fig. 1 [1]. fig. 1: schematic diagram of dfig-based wind energy systems. the wind power system shown in fig. 1 consists of a dfig, where the stator winding is directly connected to the network and the rotor winding is connected to the network through a four-quadrant power converter comprised of two back-to-back pulse width modulation (pwm) voltage source inverters (vsi). usually, the controller of the rotor side converter regulates the electromagnetic torque and supplies part of the reactive power to maintain the magnetization of the machine. on the other hand, the controller of the supp ly side converter regulates the dc link voltage. traditionally, the techniques to control the rotor-side converter (rsc) and the grid-side converter (gsc) of dfig-based wind turbines include vector control (vc) and direct torque control (dtc) or direct power control. the direct power control (dpc) for dfig has been the focus of some studies [1][7] and proven to have several advantages over the conventional vector control strategy, such as simple implementation, fast dynamic response, and robustness to dfig parameter variations. in [1] a dpc strategy based on an optimal switching table that uses the estimated stator flux information was proposed. however, like a conventional dtc, dpc has a switching frequency that varies significantly with active and reactive power variations, the power controllers’ hysteresis bandwidth, and the machine operating speed (rotor speed). as a result, this method complicates the ac filter design because of its variable switching frequency. consequently, the dpc with space vector modulation (svm) [2] and predictive control [3, 4] has been proposed to achieve a constant switching frequency. sliding mode control (smc) strategy is an effective and high frequency switching control for nonlinear systems with uncertainties. it features simple implementation, disturbance rejection, strong robustness and fast responses. thus, a smc based dpc drive for dfig was proposed in [5]. paper [6] presents the comparison of three different strategies for the control of a dfig in wind energy conversion systems (wecs). these strategies are: vector control, direct torque control, and direct power control. in [7], switching vectors for the rotor side converter were selected from the optimal switching table using the estimated stator flux 58 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. position and the errors of the active and reactive power. in this reference, the increased number of voltage vectors with application of the discrete space vector modulation (dsvm) will be presented. then a new switching table in super-synchronous and subsynchronous frames will be proposed. a simple position-sensorless method for rotor side field oriented control of a wound rotor induction machine is described in [8]. the algorithm is based on axis transformation. compared to the other methods, it is more direct and the dependence on machine parameters is also largely reduced. for most of the studies reported, a symmetrical stator voltage supply was assumed even during network disturbance. however, both transmission and distribution networks can have “small” steady states and “large” transient voltage unbalances. if dfig control systems do not take into account the voltage unbalance, the stator currents can become highly unbalanced even with small voltage unbalances. the unbalanced currents create unequal heating on the stator windings. subsequently, the pulsations with double grid frequency will be generated in the stator output active and reactive power, which are harmful to the stability of the connected power grid. furthermore, the electromagnetic torque starts to oscillate at the double grid frequency, which will cause durative stress concussion to the rotor shaft and possible damage to the mechanical system of the wind turbine. it has been found that wind farms connected to distribution networks periodically experience voltage unbalances of greater than 2%, and this has caused a large number of trips. more recently, several authors have analyzed the generator behavior in this situation [9-14]. basically, the available unbalance control methods were based on the symmetrical component theory, which states that an unbalanced system is a combination of the positive and negative networks. in [9], a new algorithm for generating the power reference for dpc was presented. it was shown that the oscillation term of electromagnetic torque can be eliminated without any sequence extraction. in [10], an improved vector control for dfig under unbalanced grid voltage was proposed; two notch filters have been used to extract the positive and negative sequence of grid voltage. so according to a specified target like balanced stator currents, these components were applied to generate the reference rotor currents. in [11], an improved dpc strategy using two resonant controllers and a pi controller is proposed for maintaining constant stator power, to eliminate torque pulsation and to maintain sinusoidal stator current. the author in [12] introduced the unbalanced control strategy with the vector oriented control (voc) technique, in which the detrimental influence on the dfig system caused by negative component of the grid voltage was also analyzed. also, the system is designed to operate for different targets. the oscillation in power and torque are considerably reduced. in [13] and [14], a model for predictive direct power control with power compensation and three selective control targets was presented, -obtaining sinusoidal and symmetrical grid currents, removing active and reactive power ripples and mitigation torque oscillationin order to enhance the control flexibility and performance of the dfigs when the network is unbalanced. this paper describes an algorithm for sensorless control of a dfig-based wind turbine system under unbalanced grid voltage. this paper is organized as follows: section 2 describes the dfig modeling; the response of dfig under unbalanced condition is proposed in section 3 whereas the power compensation strategies are illustrated in section 4; the rotor position estimation strategy is presented in section 5; section 6 discusses the simulation results on a 2 mw dfig system to demonstrate the effect and performance of the proposed control algorithm; and finally, the conclusions are presented in section 7. 59 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. 2. dfig modeling the equivalent circuit of a dfig expressed in the stator stationary frame is shown in fig. 2. the mathematical equations for a dfig can be expressed as (1) (1)   d sv r is s s dt  (2)    d rv r i jr r r r r dt    (3)  l i l is s s m r (4)  l i l ir m s r r (5)  3 3*im =2 2        t p i p i ie s s s ss s     (6)  3 3*re =2 2        p v i v i v is s s s s s s    (7)  3 3*im =2 2        q v i v i v is s s s ss s   3. response of dfig under unbalanced grid voltage under unbalanced grid conditions, the system variables contain double frequency components additionally. with the conventional decoupled power control and with no additional control measures in place, the control is ineffective since the stator and grid currents exhibit significant low frequency harmonics. as a consequence, there are severe oscillations in torque, active and reactive power, and the dc link voltage. according to the symmetrical component theory, and assuming no zero sequence components, if the grid supply is unbalanced, any three phase quantity, e.g., voltage, current, or flux, can be separated into the positive and negative sequence components as in (9) (8) -( ) ( )       s s s s ss v v v v v j v vs    (9) -( ) ( )       s s s s ss i i i i i j i is    (10) -( ) ( )       s s s s ss js           substituting (8) and (9) into (6) and (7), we get (11) 1 2 3 4 3 ( ) 2    p p p p ps (12) 1 2 3 4 3 ( ) 2    q q q q qs where (13)    *1 3 3re .2 2        s s s s s s p v i v i v i    (14)    *2 3 3re .2 2        s s s s s sp v i v i v i    60 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. (15)    *3 3 3re .2 2        s s s s ss p v i v i v i   (16)    *4 3 3re .2 2        s s s s s s p v i v i v i    (17)    *1 3 3im .2 2        s s s ss s v i v i v iq    (18)    *2 3 3im .2 2        s s s ss sq v i v i v i   (19)    *3 3 3im .2 2        s s s s ss q v i v i v i   (20)    *4 3 3im .2 2        s s s ss s q v i v i v i   fig. 2: equivalent circuit of a dfig in the stator stationary frame. the pulsation terms p1, q1 and p2, q2 are constant at steady state, because they are composed by the same sequence product. however, terms p3, q3 and p4, q4 oscillate at twice the grid frequency pulsation, since they are composed of positive and negative sequence products. also with substituting the positive and negative sequence components of the stator current and flux into the expression (5), we obtain (21) 3 * * * *im 2                 t p i i i ie s s s s s s s s    in addition, stator flux can be expressed using the stator voltage from (1) as (22)    j r i vs s s s s   substituting the flux from expressions (22) in torque equation (21), we get (23) 2 23 * * * *re ( ) 2                      s s s s t p v i v i v i v i r i ie s s s s s s s s  according to the active power expression (11), the torque equation (23) becomes (24)   3 1 2 3 4 02      p t p p p p te s 61 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. where (25) 22 ( )0   t r i is s s it should be noted, in this study, that the dpc technique is adopted for both rsc and gsc, as enunciated in [1] and [15]. 4. response of dfig under unbalanced grid voltage in an unbalanced condition, reference powers are generated based on the expression of instantaneous powers that include the steady state, sinusoidal, and cosine components of active and reactive powers. reference powers for rsc can be generated based on different individual control targets such as minimizing the double frequency oscillations of sinusoidal or cosine terms of stator active or reactive power, electromagnetic torque, and negative sequence winding currents. in other words, in this section the following three objectives will be introduced and will be used target 1: eliminating the double frequency pulsations of stator active and reactive power to make the instantaneous stator active and reactive power constant. target 2: maintaining a constant electromagnetic torque in order to reduce the mechanical stress on the turbine system. target 3: balancing the stator current to ensure balanced heating in the three phase stator windings. 4.1 active and reactive power oscillation cancellation strategy (target 1) this control target is to allow the existence of negative sequence current components but eliminate the stator output active and reactive power ripples. in order to obtain constant active and reactive power, both of the reference must be kept constant, thus the active and reactive power ripples must be zero, i.e. [9] (26) 03 4 p p (27) 03 4 q q as a result, the required powers for compensation become (28) 1 2  constrefp p p p (29) 1 2  constrefq q q q according to (24) and (26), even if the stator active and reactive power pulsation can be removed by the unbalanced dpc, the torque pulsation will still exist. 4.2 torque oscillation cancellation strategy (target 2) this objective is to mitigate the torque oscillation when the network is unbalanced. according to (24), the torque oscillation can be eliminated by imposing the requirement [9] (30) 0 3 4 p p which results in an electromagnetic torque, such that: 62 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. (31)   3 1 2 02 p t p p te s    under this situation, the required power and the reference stator active power are related by the following expression: (32) 3 42 2   const constrefp p p p p since the condition for torque oscillation cancellation in (30) is not related to reactive power, no compensation is needed for the reactive power; in other words, qref=0. 4.3 sinusoidal and balanced stator current exchanged with grid (target 3) if p2 and q2 are added to the original power references to obtain the new power references, p1 and q1 can be forced to zero; that is, the negative sequence current is eliminated. in other words, i s and is have to be zero if p1 and q1 are to be maintained as zero. therefore, the compensating power pulsations become [13] (33) 4 constrefp p p (34) 4 constrefq q q in the above equation, pconst and qconst are equal to the original power references under the balanced grid voltage condition. 5. rotor position estimation strategy to increase the reliability of the grid synchronization process, it is important to implement the sensorless rotor position control. there are two main methods that have been used for the detection of the rotor position: 1) derived from a shaft sensor and, 2) derived from a sensorless algorithm. sensorless operation is more desirable than using a shaft sensor, because the shaft sensor has several disadvantages related to the cost, cabling between the sensor and the controller, robustness, and maintenance. the rotor current of dfigs is available for measurement, which is not possible in cage rotor induction machines. this provides more flexibility in designing sensorless control schemes for dfigs. seen from the stator coordinate system, (ir) makes an angle s . figure 3 shows the same rotor current makes an angle r with the rotor axis. the problem, therefore, is to compute s and r , so that  ( )  estm s r   can be determined. rotor current magnitude and unit templates of rotor currents aligned to rotor axis are calculated as [8] (35) 2 2= r r r i i i  (36) 2 cos = rr r i i  (37) 2 sin = r r r i i   63 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. the rotor current unit templates  cos ,sins s  aligned to the stator coordinate system has to be calculated. using previous unit template samples two phase rotor currents  ,r ri i  are converted into stator coordinates as (38)    ' [ ] [ ]* cos [ 1] [ ]* sin [ 1]   rs r m mrest esti k i k k i k k    (39)    ' [ ] [ ]* cos [ 1] [ ]* sin [ 1]   r m mrs rest esti k i k k i k k   where k is the present sample, (k-1) is the previous sample, the superscript ' indicates the intermediate variable. where  cos [ 1]m estk and  sin [ 1]m estk are the unit vectors of rotor position estimated in the previous sample. in terms of the stator and rotor currents, the stator flux magnetizing current (ims) in the stator coordinate system can be expressed as (40)  ' '[ ] 1 [ ] [ ]  ms s s rsi k i k i k   (41)  ' '[ ] 1 [ ] [ ]  sms s rsi k i k i k   (42) ' '2 '2 ms ms ms i i i  where  2 s s r m s rl l l l l is the stator leakage factor. the stator flux magnetizing current vector (ims) makes an angle of  90 with the stator axis. the expression of α, β components can be written as (43) sinms msi i  (44) cos  msmsi i  where (45) 2 2 sin   s s s v v v     (46) 2 2 cos   s s s v v v     fig. 3: phasor diagram for rotor position estimation strategy [8]. 64 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. using above ims and measured value of stator current (is), the rotor currents can be computed in the stationary frame as (47)  1  rs ms s si i i   (48)  1   srs ms si i i   (49) 2 2 sr rs rs i i i  the unit vectors of rotor current in stationary coordinate system are given by (50) sin  rs s s r i i   (51) cos  rss s r i i  equations (36-37) and (50-51) represent the unit vectors in the two reference frames, the former rotating at synchronous speed and, the latter at slip frequency. the unit vectors pertaining to the rotor position  ( )  estm s r   can now be easily computed (52)            cos cos cos cos +sin sin  m s r s r s rest       (53)            sin sin sin cos cos sin   m s r s r s rest       the unit vectors of slip angle are used in below equation for finding the stator flux vector in rotor reference frame. this is equation as: (54)       = cos sin rs s m ms est estj j      where the stator flux linkages are calculated as: (55)  = s s s sv r i dt   (56)  =  ss s sv r i dt   figure 4 shows the schematic diagram of the improved control scheme for sensorless dpc of grid connected dfigs when the network voltage is unbalanced. there are no reports related to the use of sensorless algorithms for dfig control when the network voltage is unbalanced. also, fig. 4 shows the proposed compensation methods for powers, torque, and stator current oscillation, as well as the rotor position estimation strategy under unbalanced grid voltage conditions. it can be seen from fig. 4, that the compensating powers are calculated according to eqn. (28), (29) or (32) or (33), (34), as shown in the dotted line block. a notch filter turned at double grid frequency has been adopted to extract positive and negative sequence stator current and voltage. the filter may involve some amplitude and phase errors that may worsen the control effect. however, since the notch filter is just used to calculate the compensating power and it lies out of the power control loop, the inherent defects caused by sequential decomposition, such as slow dynamic response and low bandwidth of the control loop, could be avoided. 65 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. fig. 4: the proposed schematic diagram of the sensorless dpc for dfig under unbalanced condition. 6. simulation results simulations of the proposed control strategy for a dfig based wind power generation system were carried out using matlab/simulink and fig. 5 shows the scheme of the implemented system. the dfig is rated at 2 mw with its parameters given in table 1. the nominal converter dc-link voltage was set at 1200 v. during simulation, the sampling frequency is 20 khz and the bandwidths of the active and reactive power hysteresis controllers are set at 4% of the rated generator power of 2 mw. table 1: parameters of the dfig simulated parameters value rated power 2 mw stator voltage 690 v stator/rotor turns ratio 0.3 rs 0.0108 pu rr 0.0121 pu (refers to the stator) lm 3.362 pu l σs 0.102 pu l σr 0.11 pu (refers to the stator) lumped inertia constant 0.5 number of pole pairs 2 66 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. the performance of the system will be analyzed under a steady-state operation condition. the grid voltage unbalance programmed for this experiment is shown in fig. 6 and its values are (vsa=555 v<00, vsb= 484.2 v<-1130, vsc=557.5 v<-2310). the dfig was assumed to be in speed control, meaning that the rotor speed is set externally, as the large inertia of the wind turbine results in a slow change of rotor speed. the stator active and reactive power references are set to 0.166 and 0.33 p.u. at a constant speed of 0.73 p.u. where the synchronous speed was defined as 1 unit. in the second half of the experiment, the behavior of the machine side magnitudes and the grid side magnitudes are presented when the system is commanded with the oscillation cancellation strategies, as proposed in section 4. before this, in the first half of the experiment, the cancellation strategies are disabled. fig. 5: scheme of the simulated system. as shown in the previous section, target 3 gives good attenuation of both torque and active power oscillation. for target 1, while the active power oscillation is greatly reduced, the torque pulsation is relatively large. similar observations can also be noticed for target 2. the selection of the control target is highly dependent on the design of the turbine system and the operation of the network. in fig. 7, target 1 (active and reactive power oscillation cancellation strategy) was selected as the control objective. in fig. 8, target 2 (electromagnetic torque oscillation cancellation strategy) was selected as the control objective. the second half, of fig. 8(a) shows the power tracking behavior in order to cancel the electromagnetic torque oscillation. figure 8(b) shows the current exchanged through the stator under these operation conditions. in the simulation results, a strong deterioration of the currents can be observed before 0.15 s. this fact is due to the oscillating behavior of the electromagnetic torque during this first half of the experiment. in addition, when the torque oscillation cancellation strategy is operating, the stator currents are unbalanced but sinusoidal. in fig. 9, target 3 of the power compensation scheme is implemented. as shown in fig. 9, there are oscillating components in both the active and reactive powers because of the two oscillating terms, p4 and q4, added to the original constant active and reactive powers. however, these eliminate the negative sequence current. as a result, the stator current becomes quite sinusoidal and symmetric, thus power quality is improved significantly. 67 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. simulation of the stator flux position in the rotor reference frame, for cases with and without the rotor position sensor, with constant rotor speed were carried out and the results are shown in fig. 10 (a) and (b) for rotor speeds of 1.2 and 0.8 p.u. respectively. also, fig. 10(c) shows the result of the proposed method operating with variable speed from 1.2 p.u. to 0.8 p.u. it can be seen that the stator flux position in the rotor reference frame can be correctly estimated and there is very little deterioration in system performance with the sensorless scheme. in the rotor position sensorless control investigation, the rotor encoder was still installed on the shaft, but its position output was not used in the system control. instead, it was used for comparison with the estimated stator flux position values. fig. 6: unbalanced grid voltage. fig. 7: simulation results comparison with [b] and without [a] rotor position sensor, with power compensation for target 1. (a) stator active, and reactive powers (p.u). (b) stator currents (p.u). (c) electromagnetic torque (p.u). s q s p s ps q 68 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. fig. 8: simulation results comparison with [b] and without [a] the rotor position sensor, with power compensation for target 2. (a) stator active, and reactive powers (p.u). (b) stator currents (p.u). (c) electromagnetic torque (p.u). fig. 9: simulation results comparison with [b] and without [a] rotor position sensor, with power compensation for target 3. (a) stator active, and reactive powers (p.u). (b) stator currents (p.u). (c) electromagnetic torque (p.u). s q s p s q s p s p s q s p s q 69 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. fig. 10: stator flux position in the rotor reference frame for with and without rotor position sensor under constant and variable rotor speed. (a) constant speed 1.2 (p.u). (b) constant speed 0.8 (p.u). (c) variable speed from 1.2 to 0.8 (p.u). 7. conclusion this paper has presented a new control strategy for dfig-based wind energy generation systems operating under unbalanced network conditions. this method used a simple position-sensorless algorithm to eliminate the rotor position sensor. the simulation results show the accuracy of the proposed rotor position estimation strategy in all relevant situations. also, stator active and reactive powers and generator electromagnetic torque have been fully defined under an unbalanced voltage supply, which indicates that significant pulsation at twice the supply frequency could exist. methods for providing enhanced system control and operation for dfig-based wind turbines during network unbalance i.e., power, torque, or stator current oscillation minimization, are identified. these three selectable control targets are used for compensation. references [1] lie xu, phillip cartwright. (2006) direct active and reactive power control of dfig for wind energy generation. ieee trans. energy conv., 21(3):750-758. [2] dawei zhi, lie xu. (2007) direct power control of dfig with constant switching frequency and improved transient performance. ieee trans. energy conv., 22(1):110-118. [3] dawei zhi, lie xu, barry w. williams. (2010) model-based predictive direct power control of doubly fed induction generators. ieee trans. power electron., 25(2):341-351. 70 iium engineering journal, vol. 18, no. 1, 2017 izanlo et al. [4] yongchang zhang, jiefeng hu, jianguo zhu. (2014) three-vectors-based predictive direct power control of doubly fed induction generator for wind energy application. ieee trans. power electron., 29(7):3485-3500. [5] jiabing hu, heng nian, bin hu, yikang he, zhu zq. (2010) direct active and reactive power regulation of dfig using sliding-mode control approach. ieee trans. energy conv., 25(4):1028-1039. [6] etienne tremblay, sergio atayde, ambrish chandra. (2011) comparative study of control strategies for the doubly fed induction generator in wind energy conversion systems: a dsp-based implemention approach. ieee trans. sustain. energy, 2(3):288-299. [7] mohammad verij kazemi, ahmad sadeghi yazdankhah, hossein madadi kojabadi. (2010) direct power control of dfig based on discrete space vector modulation. 35(5):1033-1042. [8] rajib datta, ranganathan vt. (2001) a simple position sensorless algorithm for rotor side field oriented control of wound rotor induction machine. ieee trans. ind. electron., 48(4):786-793. [9] gonzalo abad, miguel angel rodriguez, grzegorz iwanski, javier poza. (2010) direct power control of douby-fed-induction-generator-based wind turbine under unbalanced grid voltage. ieee trans. power electron., 25(2):442-452. [10] lie xu, yi wang. (2007) dynamic modeling and control of dfig-based wind turbines under unbalanced network condition. ieee trans. power syst., 22(1):314-323. [11] heng nian, yipeng song, peng zhou, yikang he. (2011) improved direct power control of a wind turbine driven doubly fed induction generator during transient grid voltage unbalance. ieee trans. energy conv., 26(3):976-986. [12] lie xu. (2008) coordinated control of dfig’s rotor and grid side converters during network unbalance. ieee trans. power electron., 23(3):1041-1049. [13] jiefeng hu, jianguo zhu, david g. dorrell. (2015) predictive direct power control of doubly fed induction generators under unbalanced grid voltage conditions for power quality improvement. ieee trans. sustain. energy, 6(3):943-950. [14] jiefeng hu, jianguo zhu, david g. dorrell. (2014) model-predictive direct power control of doubly fed induction generators under unbalanced grid voltage conditions in wind energy conditions. iet renew. power gener., 8(6):687-695. [15] toshihiko noguchi, hiroaki tomiki, seiji kondo, isao takahashi. (1998) direct power control of pwm converter without power-source voltage sensors. ieee trans. ind. applicat., 34(3):473-479. nomenclature , v vs r stator and rotor voltage vectors , i is r stator and rotor current vectors , r rs r stator and rotor resistance , l ls r  stator and rotor leakage inductance lm magnetizing inductance , s r  stator and rotor flux vectors , p qs s stator active and reactive powers te electromagnetic torque , , r s m   rotor, stator and slip speeds p number of pole pairs * donates the complex conjugate operation 71 http://www.sciencedirect.com/science/journal/09601481/35/5 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 higher derivative block method with generalised step length for solving first-order fuzzy initial value problems kashif hussain, oluwaseun adeyeye*and nazihah ahmad school of quantitative sciences, universiti utara malaysia, kedah, malaysia * corresponding author: adeyeye@uum.edu.my (received: 30th march 2022; accepted: 10th august 2022; published on-line: 4th january 2023) abstract: block methods have been adopted in studies for solving first and higher order differential equations due to its impressive accuracy property. taking a step further to improve this accuracy, researchers have considered the inclusion of higher-derivative terms in the block method, although this has been limited to the presence of one higher-derivative term in previous studies. hence, this article aims at better accuracy by introducing two higher-derivative terms in the block method. in addition, this article presents a scheme with generalised step length such that there is flexibility on the choice of step length when developing the block method. the generalised step length scheme is adopted to develop a three-step block method for solving first-order fuzzy initial value problems. its properties to ensure convergence and to show the region of absolute stability is investigated, and problems relating to charging and discharging of capacitor are considered. the absolute error shows the impressive accuracy of the three-step block method including obtaining the same values as the exact solution. therefore, in addition to the new generalised algorithm presented in this article, a new three-step method for solving linear and nonlinear first order fuzzy initial value problems is presented. abstrak: kaedah blok digunakan dalam banyak kajian untuk menyelesaikan persamaan pembezaan peringkat pertama dan peringkat tinggi kerana sifat ketepatannya yang baik. bagi meningkatkan ketepatan ini, penyelidik telah mengambil kira dengan memasukkan terbitan peringkat tinggi dalam kaedah blok, walaupun ini terhad pada satu sebutan terbitan peringkat tinggi dalam kajian sebelum. oleh itu, kajian ini bertujuan bagi mendapatkan ketepatan yang lebih baik dengan memperkenalkan dua sebutan terbitan peringkat tinggi dalam kaedah blok. tambahan, kajian ini memperkenalkan skema dengan panjang-langkah kaki biasa supaya terdapat kebolehlenturan pada pilihan langkah semasa membangunkan kaedah blok. skema ini diadaptasi bagi membangunkan kaedah blok tiga-langkah bagi menyelesai masalah nilai awal peringkat pertama secara rawak. ciri-ciri terperinci dikaji bagi memastikan penumpuan lingkungan kestabilan mutlak, dan masalah berkaitan pengecasan dan nyahcas kapasitor juga turut diambil kira. ralat mutlak menunjukkan ketepatan yang mengkagumkan pada kaedah blok tiga-langkah termasuk mendapatkan nilai yang sama seperti penyelesaian. oleh itu, tambahan pada algoritma ini, kaedah tiga-langkah bagi menyelesaikan linear dan tidak linear pada masalah nilai awal peringat pertama secara rawak diperkenalkan. keywords: fuzzy initial value problem; generalised steplength; block method; higher derivative; charging and discharging of capacitor 158 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 1. introduction the primary focus of numerical methods for solving fuzzy differential equations has been on presenting numerical methods with a higher level of accuracy. this includes providing a more accurate numerical solution for first order fuzzy initial value problems (fivps) of the form 0 0 0 '( ) ( , ( )), ( ) , [ , ]y x f x y x y x y x x x= =  . (1) numerous researchers have developed different numerical methods [1-6] to solve problems in the form of equation (1), however, the major problem encountered is that these existing numerical methods give a low level of accuracy in terms of absolute error due to order of the method used. specifically, researchers considered the use of linear multistep methods implemented in predictor-corrector mode (a non-self-starting approach with low accuracy) as seen in studies [7,8]. to improve the accuracy, block methods were introduced in [9-11] and better accuracy was observed than linear multistep methods. however, there is still a need for an improvement in the solution accuracy in terms of absolute error. hence, the motivation to develop block methods in this article with the presence of two higher derivative terms with the aim of obtaining better accuracy. in comparison to existing methods, the proposed method has the advantage of better accuracy, being self-starting, and flexibility in development and implementation of the block method. 2. preliminaries this section recalls some basic definitions which will be adopted in this article. triangular fuzzy number [12]. consider that ( ) 3, , , u v w u v w   . then the triangular fuzzy number, ( )m x is given as 0, , ( , , , ) , 0, x u x u u x v v u m x u v w w x v x w w v x w  −   − = −   −           . (2) the corresponding r-level set of the triangular fuzzy number is denoted as ( ) , ( ) , [0,1]rm u r v u w r w v r= + − − −  . (3) trapezoidal fuzzy numbers [12]. consider that ( ) 4, , , , u v w u v w     . then the trapezoidal fuzzy number ( )m x is given as 159 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 0, , ( , , , , ) 1, , 0, x u x u u x v v u m x u v w v x w w x w x w v x     −   − =   −   −            . (4) the corresponding r-level set of the trapezoidal fuzzy number is denoted as ( ) , ( ) , [0,1]rm u r v u r w r = + − − −  (5) some of the basic fuzzy definitions and notions that are not included in this section 2 are widely known. notions of fuzzy sets, functions and their operations, fuzzy derivatives, and zadeh’s extension theory can be retrieved from literature such as [13-16]. 3. methodology given that the first-order fivp of the form defined in eq. (1) be a mapping, : f f f → and 0 fy  , with r-level set ( )0 (0, ), (0, ) , [0,1] r r y y r y r r  . also, denote the approximation solution as ( ) ( )y(x , ) (x , r), (x , r) rr n n nr r y y = at points 0n x x nh= + , where 0 n n  and 0 x x h n − = . the generalized k-step block method with presence of second and third derivative in first-order form is stated below as, ( ) 2 ( ) 0 0 , 1, 2, 3,..., r k r d n n dv n v r d v r y y f k     + + = =    = + =        . (6) expanding eq. (6) gives the expression ( ) 00 01 1 0 10 11 1 1 20 21 1 2 , ..., ' ' , ..., ' '' '' '',..., r n v n k n k r n n n n k n k r n n k n k r f f f y f f f f f f y                   + + + + + + + + + + = + + + + + + + +             +   . (7) consider the taylor series expansions defined by [17]: ( ) 0 ( ) y( ; r) ( ; r) , 0,1,..., k ! r in r i n nr i r jh x jh f x j i=   + = =     , (8) ( ) 2 3 ( ) ( ) ( ) y( ; r) '( ; r) y''( ; r) y'''( ; r) .... y''( ; r) 2! 3! n! r n r n j n n n n n r r jh jh jh y x jhy x x x x +   = + + + + +    . (9) 160 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 applying these expansions in eqs. (8) and (9) to expand each term in eq. (7) results in obtaining the unknown coefficients dv  from 1 dv a b   − = , where 22 3 23 2 3 23 2 3 1 ( ) 2! 2! ( ) ( ) 3! 3! 2! 2! ( ) (3 2)! (3 2)! (3 1 1 1 ... 1 0 0 ... 0 0 0 ... 0 0 ... 1 1 ... 1 0 0 ... 0 0 ... 0 ... 1 1 ... 1 0 ... 0 ... 0 ... . . ... . . . ... . . . ... . . . ... . . . ... . . . ... . . . ... . . . ... . . . ... . 0 ... 0 kk k khh kh khh h khh h k k k h kh h kh h kh a ++ + + + + = 2 3 4 3 1 3 3 3 3 ( ) 2! ( ) 3! ( ) 4! ( ) ( ) ( ) ( ) )! (3 1)! 3 ! 3 ! (3 3)! , and . . . . ... 0 ... k k k k rr h h h kh h kh h k k k kr r h b      + + + +                    =                         the resultant values are substituted in eq. (7) to get the desired generalized k-step block method with the presence of second and third derivatives for solving first-order fivps. a more detailed explanation is given in the following subsection, where the generalised step length (k-step) block method scheme with presence of second and third derivatives is adopted to develop a three-step ( 3k = ) block method for first order fivps. 3.1 development of three-step block method to develop a three-step block method with second and third derivatives for first order fodes requires substituting 3k = in eq. (7) and then applying taylor series expansions in eqs. (8), (9). the unknown coefficients dv  are obtained as follows: 912523 001 2395008 23717 011 29568 5851 021 29568 35339 031 2395008 214943 101 3991680 10657 111 147840 10657 121 147840 5941 131 1330560 11369 3991680201 4423 88211 221 231 r r             − − −                   =                    7031 002 18711 302 012 231 71 022 231 178 032 18711 544 102 10395 32 112 1155 32 122 11 132 202 704 212 7453 443520 222 1513 3991680 232 , r r             − −                            =                                3849 003 9856 10935 013 9856 10935 023 9856 3849 033 9856 279 103 113 12355 92 13331185 17 6237 203 212 3465 213 19 3465 223 8 31185 233 , r r             −                            =                                9 49280 2187 49280 2187 49280 2799 49280 153 49280 2187 49280 2187 49280 153 49280 − −                                       . substituting the obtained coefficients in eq. (7) for 3k = , the three-step block scheme is derived as 161 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 1 2 3 2 1 1 2 3 3 1 2 912523 23717 5851 35339 2395008 29568 29568 2395008 214943 10657 10657 5941 3991680 147840 147840 1330560 11369 4423 7453 1513 3991680 88704 443523 3 n n n n n n n n n n n n n h f f f f y y h g g g g h m m m + + + + + + + + +   + − + +      = + − + − +    + − + 3 991680 r n r m +                                , 1 2 3 2 2 1 2 3 3 1 2 3 7031 302 71 178 18711 231 231 18711 544 32 32 92 10395 1155 1155 31185 17 212 19 8 6237 3465 3465 31185 n n n n n n n n n n n n n n h f f f f y y h g g g g h m m m m + + + + + + + + + +     + + + +            = + + − − +            + − +        r r  , 1 2 3 2 3 1 2 3 3 1 2 3 3849 10935 10935 3849 9856 9856 9856 9856 2799 2187 2187 2799 49280 49280 49280 49280 153 2187 2187 153 49280 49280 49280 49280 n n n n n n n n n n n n n n h f f f f y y h g g g g h m m m m + + + + + + + + + +    + + + +        = + − + − +        + + +      r r                    (10) the block method in eq. (10) has corrector form ( ) ( ) ( ) ( ) ( ) 0 1 0 1 2 0 1 3 0 1 y' y' y'' y'' y'' y''' r r r r n k n k n k n k n k n k r r r r r n k n k r a y a y h b b h c c h d d + − + − + − + − = + + + + + + where 23717 5851 35339 29568 29568 2395008 0 1 0 302 71 178 231 231 18711 10935 10935 3849 9856 9856 9856 1 0 0 0 0 1 0 1 0 , 0 0 1 , , 0 0 1 0 0 1 rr r w r r r a a b −          = = =                  10657 10657 5941 912523 214943 147840 147840 1330560 2395008 3991680 0 1 132 32 92 7031 544 1155 1155 31185 18711 10395 2187 2187 2799 3849 2799 49280 49280 49280 9856 49280 0 0 0 0 , 0 0 , 0 0 0 0 0 0 r r r r c b c − − − − − −             = = =                 , r r   4423 7453 1513 11369 2 288704 443520 3991680 3991680 0 119 8 17212 113465 3465 31185 6237 2187 2187 153 153 49280 49280 49280 49280 0 0 , , 0 0 , ' , 0 0 rr r r n n nn k n n k nn rr rr y f fd y y d y fy − − − − −− − −               = = = =                    162 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 1 2 1 2 1 1 '' '' ''' ''' 2 1 2 1 2 2 3 3 3 3 , , , , , ' . n k n k n k n k r r r r r r n n n n n n n n n n n nn k n k n n n n n nr r r r r r g g m m y f g g m m y fy y y y y y g g m m y f + − + − + − + − + + + − + − + ++ + + + + +                         = = = = = =                                     4. convergence properties this section will detail the convergence properties of the developed three-step secondthird derivative scheme. the following definitions are used: consistency, zero-stability, and region of absolute stability from [18]. these definitions for block methods in crisp form are adopted to the proposed method for fuzzy initial value problems to prove the convergence properties for the proposed method. 4.1 order and error constant the linear operator which is associated with equation (6) for the three-step block method is defined as: 2 3 ( ) 0 0 ( ( ), ) r d n n dv n v d v r l y x h y y f    + + = =    = − −        (13) ( )2 1 10 1 2 1( ( ), ) y( ) '( ) y''( ) ,..., ( ) ( ) r z z z z n n n z n z n r l y x h x hy x h x h y x h y x + + + = + + + + + . the order of this method is z if 0 1 2 ,...., 0 z = = = = = and 1z+ is the error constant. by using the definition of order and error constant, the developed block method has order 12z = with error constant 29609 23 9 28768836096000 32108076000 5637632000 , ,−  . so, the developed block method is consistent. 4.2 zero-stability the zero-stability of the proposed method is computed from 2 1 0 0 0 0 1 ( ) 0 1 0 0 0 1 ( 1) 0 0 0 1 0 0 1 r r p    = − = − =                     . the obtained roots satisfy the condition in [18]. hence, the proposed three-step block method is zero-stable. since the proposed method satisfies the properties of consistency and zero-stability for block methods, this implies that the method is convergent. 4.3 region of absolute stability the characteristic polynomial used to obtain the region of absolute stability of the developed block method is obtained as 1 2 3 4 0 0 0 0 det ( ) , r k k k k k j k j j k j j k j j k j j j j j r w a q b w q c w q d w q e w − − − − = = = =           − + + + + +                         .q h= 163 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 ( ) 9 8 7 6 5 3 2 9 8 7 6 5 52183 388873 231359 1549771 10104397 4 5805453 47 3 6 369600 910694400 546416649 40981248 45534720 68302080 12142592 44 2 157 109 179 589 4 21 369600 16800 221760 19008 5280 3960 1 q q q q q q q q q q q q q q q w r w  − + − + − + − − −   == + + + + + + 3 2 47 3 3 44 44 2 1 q q q w         + + +     . the region of absolute stability is determined by plotting the roots of the polynomial using a boundary locus approach, as shown in fig. 1. fig. 1: absolute stability region of three-step second-third derivative block method. 5. results and discussion this section details using the three-step block method to solve first-order linear and nonlinear fivps numerically and comparing the results to the exact solution. tables and graphs are being used to compare exact and approximate solutions. the following notations are utilised in this section. x-axis shows the value of approximation solution y-axis shows the value of r-level set ,y y are the exact solution of lower and upper bound respectively ,y y are the approximation solution of lower and upper bound respectively y y− absolute error of lower bound approximation y y− absolute error of upper bound approximation h is the stepsize example 1 [19]. consider the following crisp capacitor model ( ( )) 1 1 ( ) ( )c c g d u x u x u x dx rc rc = − + (14) with exact solution 164 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 ( ) ( ) . ( . ) . dx dx dx grc rc rc c u x u x k e e dx e rc − − −    = +      . (15) for the initial condition charging of the capacitor ( ) .[1 ] x rc c b u x u e= − , (16) while for the initial condition discharging of the capacitor ,0 ( ) . x rc c c u x u e= . (17) according to [4], the crisp equation can be modelled in a fuzzy form using the definition of fuzzy theory, which is given in section 2. the uncertain behaviour of a capacitor using the voltage, capacitance, or resistance of the circuit current is defined as triangular fuzzy numbers. 5.1 charging of a capacitor the exact and approximate solutions are presented at 4x s= . table 1 presents the accuracy for the lower and upper solutions of charging capacitor under dc condition with triangular fuzzy number. the corresponding graphs are shown in fig. 2. the specifications adopted are battery voltage 12v= , 0.25c f= (farads), (0) 0cu = , and resistance with triangular fuzzy number is (2 , 4 )r r r= + − . 5.2 discharging of a capacitor the exact and approximate solutions are presented at 4x s= . table 2 presents the accuracy for the lower and upper solutions of the discharging capacitor under dc condition with triangular fuzzy number. the corresponding graphs are shown in fig. 3. the specifications adopted as same as the charging of a capacitor scenario. table 1: lower and upper solutions for charging of capacitor problem in example 1 r y y y− y y y− 0 0.2 0.4 0.6 0.8 1 11.995974448465169 11.991669406884018 11.984728394383922 11.974496498029186 11.960417930928731 11.942064600074023 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 11.780212333335189 11.821937321808754 11.859076458515744 11.905917027388661 11.931188450176629 11.942064600074023 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 0.0e+00 table 2: lower and upper solutions for discharging of capacitor problem in example 1 r y y y− y y y− 0 0.2 0.4 0.6 0.8 1 0.00402555153483014 0.00833059311598270 0.01527160561607770 0.02550350197081452 0.03958206907126909 0.05793539992597728 4.336e-18 7.806e-18 8.673e-18 1.737e-18 1.008e-17 1.048e-17 0.21978766666481017 0.17806267819124583 0.14092354148425637 0.10850319025595753 0.08085536398902561 0.05793539992597728 8.3266e-17 8.3266e-17 1.9428e-16 2.2204e-16 8.3266e-17 1.5265e-16 165 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 fig. 2: example 1 at h=0.1, [0, 4], [0,1]x r  fig. 3: example 1 at h=0.1, [0, 4], [0,1]x r  in subsequent examples (examples 2 and 3), since the exact solution cannot be obtained analytically, the proposed method in this study is used to obtain the approximate solution. it is seen that the approximate solution shows a non-monotone behaviour as time increases. the approximate solution in tables 3 and 4 shows the lower and upper solutions using triangular fuzzy numbers. example 2. [20]. consider the following nonlinear fivp 2 2 '( ) cos( ), (0, ) ( , )y x xy y r r r = = − . table 3: lower and upper solution for example 2 r y y 0 0.2 0.4 0.6 0.8 1 0.61513329423446 0.62072922853453 0.62648141558304 0.63281743366655 0.64032241288569 0.6500044930335 2.81437834172917 1.31086566147775 0.74700523547913 0.68810151091971 0.66399579330793 0.65000449303352 166 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 example 3. [21]. consider the following nonlinear fivp 2 2 '( ) , (0, ) (0.1 0.1, 0.1 0.1 )y x x y y r r r= + = − − . table 4: lower and upper solution for example 3 r y y 0 0.2 0.4 0.6 0.8 1 0.24913567333881 0.26259107127145 0.28321967366284 0.30466869011884 0.32698805629646 0.35023184431536 0.48255938900528 0.45370358499704 0.42612209786584 0.39973233756115 0.37445870012445 0.35023184431536 in example 1, a crisp capacitor model was successfully solved using the proposed method with a fuzzy initial value, and the results were compared to the exact solution. the results are seen in table 1 and 2 with charging and discharging of the capacitor. these tables, showing the comparison between exact and approximate solution, indicate that the accuracy of the solution in terms of absolute error is quite impressive. the nonlinear examples 2 and 3, which cannot be solved exactly, are solved numerically by the proposed method. the obtained results are demonstrated in tables 3 and 4. although, example 3 was solved by [21] with homotopy perturbation method, where the authors solved crisp riccati equation with two defuzzification for fivps, their obtained results lie in the short time interval [0,0.5] which indicate that their proposed method is limited to the specific points with large amounts of mathematical complexity. 6. conclusion the major objective of this research is to enhance the solution accuracy in terms of absolute error for first order fivps. as a result, this article developed a generalised step length block method for first order fuzzy ordinary differential equations with the presence of second and third derivatives. because the algorithm can simultaneously construct block methods of step length k for solving first order fivps, the generalised technique is considered as extremely flexible. the sample block method with second and third derivatives scheme has proven to be a viable strategy with increased accuracy for solving both linear and nonlinear fivps. the method was developed using a linear block approach with low computational complexity, while also satisfying all convergence conditions for the block methods. the solution of the fivps as seen in the tables and graphs demonstrates the applicability of the three-step implicit block method for first order fivps. so, this generalised approach is suitable for developing block methods for first order fivps. references [1] ahmady n, allahviranloo t, ahmady e. (2020) a modified euler method for solving fuzzy differential equations under generalized differentiability. computational and applied mathematics, 39(2):1-21. doi: https://doi.org/10.1007/s40314-020-1112-1 167 https://doi.org/10.1007/s40314-020-1112-1 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 [2] kodal sevindir h, cetinkaya s, tabak g. (2018) on numerical solutions of fuzzy differential equations. international journal of development research, 8(9): 2297122979. doi: https://www.researchgate.net/publication/329737810 [3] ahmadian a, salahshour s, chan cs, baleanu d. (2018) numerical solutions of fuzzy differential equations by an efficient runge–kutta method with generalized differentiability. fuzzy sets and systems, 331: 47-67. doi: https://doi.org/10.1016/j.fss.2016.11.013 [4] jameel af, saleh hh, azmi a, alomari ak, anakira nr, man nh. (2022) efficient approximate analytical methods for nonlinear fuzzy boundary value problem. international journal of electrical & computer engineering, 12(2): 1916-1928. doi: https://doi.org/10.11591/ijece.v12i2.pp1916-1928 [5] maghool fh, radhy zh, mehdi ha, abass hm. (2019) simpson's rule to solve fuzzy differential equations. international journal of advanced research in science, engineering and technology, 6(10): 11306-11315. doi: https://www.researchgate.net/publication/337941473 [6] fariborzi araghi ma, barzegar kelishami h. (2021) numerical accuracy of the predictorcorrector method to solve fuzzy differential equations based on the stochastic arithmetic. fuzzy information and engineering, 12(3): 335-354. doi: https://doi.org/10.1080/16168658.2021.1880134 [7] shang d, guo x. (2013) adams predictor-corrector systems for solving fuzzy differential equations. mathematical problems in engineering, 2013(1): 1-12. doi: https://doi.org/10.1155/2013/312328 [8] allahviranloo t, abbasbandy s, ahmady n, ahmady e. (2009) improved predictor–corrector method for solving fuzzy initial value problems. information sciences, 179(7): 945-55. doi: https://doi.org/10.1016/j.ins.2008.11.030 [9] isa s, abdul majid z, ismail f, rabiei f. (2018) diagonally implicit multistep block method of order four for solving fuzzy differential equations using seikkala derivatives. symmetry, 10(2): 42-53. doi: https://doi.org/10.3390/sym10020042 [10] ramli a, abdul majid z. (2016) fourth order diagonally implicit multistep block method for solving fuzzy differential equations. international journal of pure and applied mathematics, 107(3): 635-660. doi: https://doi.org/10.12732/ijpam.v107i3.12 [11] mohd zawawi is, ibrahim zb, suleiman m. (2013) diagonally implicit block backward differentiation formulas for solving fuzzy differential equations. in aip conference proceedings, 1522(1), 681-687. doi: https://doi.org/10.1063/1.4801191 [12] barnabas b. (2013) fuzzy sets. in mathematics of fuzzy sets and fuzzy logic, pp. 1-12: springer. doi: https://doi.org/10.1007/978-3-642-35221-8_1 [13] zimmermann hj. (2010) fuzzy set theory. wiley interdisciplinary reviews: computational statistics, 2,(3): 317-320. doi: https://doi.org/10.1002/wics.82 [14] madan pl, ralescu da. (1983) differentials of fuzzy functions. journal of mathematical analysis and applications, 91(2): 552-558. doi: https://doi.org/10.1016/0022-247x(83)901695 [15] babakordi f, allahviranloo t. (2021) a new method for solving fuzzy bernoulli differential equation. journal of mathematical extension, 15(4): 1-20. doi: https://doi.org/10.30495/jme.2021.1704 [16] hashim ha, shather a., jameel af, saaban a. (2019) numerical solution of first order nonlinear fuzzy initial value problems by six-stage fifth-order runge-kutta method. international journal of innovative technology and exploring engineering, 8(5): 166-170. doi: https://www..net/2/publication/332141468 [17] sindu ds, ganesan k. (2017) an approximate solution by fuzzy taylor’s method. international journal of pure and applied mathematics, 113(13): 236-44. doi: https://acadpubl.eu/jsi/2017113-pp/articles/13/26.pdf [18] adeyeye o, omar z. (2019) direct solution of initial and boundary value problems of third order odes using maximal order fourth-derivative block method. in aip conference proceedings, 2138: 030002_1-030002_6. doi: https://doi.org/10.1063/1.5121039 168 https://www.researchgate.net/publication/329737810 https://doi.org/10.1016/j.fss.2016.11.013 https://doi.org/10.11591/ijece.v12i2.pp1916-1928 https://www.researchgate.net/publication/337941473 https://doi.org/10.1080/16168658.2021.1880134 https://doi.org/10.1155/2013/312328 https://doi.org/10.1016/j.ins.2008.11.030 https://doi.org/10.3390/sym10020042 https://doi.org/10.12732/ijpam.v107i3.12 https://doi.org/10.1063/1.4801191 https://doi.org/10.1007/978-3-642-35221-8_1 https://doi.org/10.1002/wics.82 https://doi.org/10.1016/0022-247x(83)90169-5 https://doi.org/10.1016/0022-247x(83)90169-5 https://doi.org/10.30495/jme.2021.1704 https://www..net/2/publication/332141468 https://acadpubl.eu/jsi/2017-113-pp/articles/13/26.pdf https://acadpubl.eu/jsi/2017-113-pp/articles/13/26.pdf https://doi.org/10.1063/1.5121039 iium engineering journal, vol. 24, no. 1, 2023 hussain et al. https://doi.org/10.31436/iiumej.v24i1.2380 [19] hohenauer w. (2018) hohenauer-physical modelling based on first order odes. doi: https://simiode.org/resources/4448 [20] ahmad mz, hasan mk, de baets b. (2013) analytical and numerical solutions of fuzzy differential equations. information sciences, 236: 156-167. doi: https://doi.org/10.1016/j.ins.2013.02.026 [21] jameel af, ismail aim. (2015) approximate solution of first order nonlinear fuzzy initial value problem with two different fuzzifications. journal of uncertain systems, 9(3): 221-229. doi: http://www.worldacademicunion.com/journal/jus/jusvol09no3paper06.pdf 169 https://simiode.org/resources/4448 https://doi.org/10.1016/j.ins.2013.02.026 http://www.worldacademicunion.com/journal/jus/jusvol09no3paper06.pdf microsoft word 2-faris-53.doc iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 17 experimental and numerical analysis of electronics heat sink ahmad f. ismail, mirghani i. ahmed, and yousif a. abakr department of mechanical engineering, faculty of engineering, iium, 53100, kuala lumpur, malaysia. e-mail: faris@iiu.edu.my abstract: cooling of electronic components continues to attract many research and development activities towards achieving an effective way of cooling. computational fluid dynamics (cfd) tools may be considered as a cheap substitute for expensive experimental testing methods. in this work the cooling of a simulated electronic board was modeled using fluenttm cfd software, and experimental procedures were followed to validate the estimated results, and to understand the factors that would affect the software capability to predict the actual measured values. results showed good agreement between the simulation and experimental results. the software was found to be capable to predict the exact values at the locations where the temperature values were similar to the board mean temperature. the maximum percentage error was found to be limited to 4.7%, and the capability of the software to estimate the exact measured values was found to be affected by the function of thermal wake generation. keywords: cfd, electronic cooling, heat sink, simulation. 1. introduction the progressive decrease of electronics device sizes and the higher processing rates resulted in an increasing rate of heat generation per unit surface area, which means increased cooling requirements. the possibility of electronic equipment failure increases with the increase of temperature. high thermal stresses resulting from temperature variations in the solder joints of electronic components mounted on circuit boards are major causes of failure. figure 1 shows the increasing rate of failure as the junction temperature increases. therefore, cooling has become increasingly important in the design and operation of electronic equipment. air-cooled forced convection cooling is the most used technique. fan speed control offers numerous benefits including reduced noise, low energy consumption and extended operating life of the fan. the need of cooling of electronic components was known since thomas edison discovered the vacuum diode in 1883. the new era of electronics started in 1958 by the invention of the silicon integrated circuit (ic). integrated circuits contain several  author for correspondence iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 18 components such as diodes, transistors, resistors, and capacitors in a single chip. the number of components per chip has been increasing steadily. electronic component suppliers estimate that for every 10 c rise of junction temperature, the device failure rate doubles [1]. when a device exceeds the maximum temperature, the semiconductor performance, life and reliability are tremendously reduced. therefore, enhancing the heat transfer rate from electronic devices became a very important research issue. fig. 1: the relation between the junction temperature and the failure rate.[1] modify solution parameters or grid no yes no set the solution parameters initialize the solution enable the solution monitors of interest calculate a solution check for convergence check for accuracy stop yes fig. 2: flow chart for solution procedure. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 19 studies of the cooling of electronic devices are based on the fluid flow around obstacles mounted on a wall base, on which the phenomenon of mixed convection is observed around the localized heat sources. many numerical and experimental studies were conducted previously [2]. heat transfer and flow characteristics of four heat source locations were studied by kennedy and zebib [3]. studies by kang et al. [4] found that heat transfer can be improved significantly by buoyancy-driven secondary flow. but the effect of thermal wake generation was not fully understood because of use of a single heat source. numerical study of the unsteady and transitional characteristics of mixed convection of airflow in a channel was conducted by huang and lin [5]. kerki et al. [6] showed the significant effect of the thermal boundary flow pattern on the secondary flow pattern and on the heat flow distribution over the surface. effects of the varying duct dimensions and obstruction dimensions on the convection from the surface of the heat generating obstructions to the airflow were studied experimentally by leung et al. [7]. choi and kim [8] proposed a “modified 5% deviation rule” to define the natural, mixed and forced convection regimes. chin et al. [9] investigated experimentally the optimum spacing problem in mixed convection. jubran and al-salaymeh [10] investigated experimentally the effects of using ribs to enhance the convective heat transfer. in most of the previous work the thermal wake generation, and the actual effect of buoyancy driven secondary flow has not been studied thoroughly. the impact of the transitional characteristics of mixed convection on the accuracy of the numerically predicted results has not been investigated. this paper will focus on the sensitivity of the cfd obtained results to the local conditions and try to define the parameters that will result in accurate estimations that approach the experimental results very closely. 2. numerical modelling the steady state heat convection of the air moving from the electronic components is found by considering the heat generated by the chips, the heat conducted through the board and the heat radiated to the surroundings. equation (1) shows the heat balance for a steady state condition, c t r lq q q q= (1) both the total amount of heat to be dissipated and the density of the air must be known. according to the first law of thermodynamics (conservation of energy) for a steady state and steady flow process, the total amount of heat dissipated in a system is determined as follows: tq h k e peº d + d + d (2) fluenttm cfd software is based on the finite volume method. in this technique, the equations of motion are treated in balance form for finite sized control volumes (cv). formal balance of a property transported with the fluid can be expressed by iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 20      dvsdddv t aav  aav unsteady convection diffusion generation (3) a 2d model was first constructed using gambit software. the geometry was modeled with an appropriate number of nodes assigned to each line. the nodes for the modules and the board were set to 0.5 since more computational effort is needed in this region to gain good results. finally the whole model was meshed using triangular element type. a total of 18983 nodes and 36467 elements were used to build up this model. the appropriate boundary conditions were set to the model. fig. 3 shows the 2d model before and after meshing. (a) model before mesh. (b) model after mesh. fig. 3: the 2-d modeling and mesh generation. due to the large number of nodes for modeling in 3d space, only sub-region of the total test rig was modeled. the modules, the board and the zone above them were chosen for the purpose of modeling as shown in fig. 4. a total of 43079 nodes and 185215 tetrahedral elements were used to build up this model. due to low air velocities involved, this problem has been considered as an incompressible flow. the segregated solver was selected for both cases. the maximum reynolds number based on the modules length is 1418, which mean laminar flow. the option to solve the energy equation was enabled because there is heat-generation. the property of the air was set to the default values. properties of aluminum block and the hard board were set according to the values used for heat transfer analysis. using a computer of pentium ii processor with a speed of 266 mhz, the program takes about two hours to finish the calculations. graphical residual plotting is shown in fig. 5, which shows the progress of the solution to convergence. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 21 fig. 5: residual plotting for convergence. 3. experimental setup the experimental apparatus is made of a wind tunnel of a rectangular section with a dummy electronic components mounted on a circuit board. electric heating elements were imbedded inside the dummy electronic components, and sets of thermocouples were used to read the surface temperature of the components. the setup arrangement is shown in fig. 6. isometric view of the test rig is shown in fig. 7. the setup consists of the test rig, dc power supply for electronic modules, brushless blower and a number of digital thermocouples. the design and the coordination assignments for the modules were constructed as in fig. 7. the test rig shown in fig. 8 is divided into eight zones of airflow impedance. the zones are numbered sequentially, following the direction of airflow. 3 digital thermocouples fan d c h eater d c supply fig. 6: experimental setup. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 22 abrupt contraction outlet flow straightener unit simulated circuit board simulated electronics modules y z x gradual contraction inlet fig. 7: isometric view of the test rig and its components. 1 3 2 4 5 6 7 8 fig. 8: side view of the test rig. temperature measurements were taken only for the modules of row one, three and five. temperatures of the modules in row two and four were approximated from the corresponding column. this procedure will be followed in the heat transfer analysis part. the heat transfer coefficient for each module was calculated from, ( )s ac ref q h a t t = (4) the temperature of the modules closer to the air exit is affected by the thermal wake phenomenon. the thermal wake happens when heat-generating components are placed along the flow stream direction. this function is defined as, i ref i ac ref t t t t q = (5) the volumetric maximum flow rate is taken as 11.8 10-3 m3/s. this is the maximum flow rate of the blower that will be used in the test rig. each zone in the test rig will be analyzed individually for cross-section area changes and head loss. details of zone 5, which contains the simulated board, are shown in fig. 9. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 23 fig. 9: zone 5 (isometric view). 4. experimental procedure natural convection heat transfer measurements were taken while the fan power supply is kept off. after turning on the power supply of the heater, enough time was allowed for the system to reach steady state condition. when the steady state condition was achieved (modules temperature does not change with time), the local temperatures of the modules were then recorded. similar procedure was then followed for the forced convection heat transfer measurements. then, the fan power supply is turned on and set at 4 volts. at steady state condition the temperature measurements of the two modules were recorded. similar procedures were followed to repeat the test for the different fan speeds. thermocouples were placed at different modules and test procedures were repeated again. a vane anemometer was placed at the exit of the blower to measure the air velocity for every set of applied fan speed. the system usually takes about 1 hour and 30 minutes to reach the steady state. 5. results from the measured data it was noticed that the modules in the middle column have a higher temperature relative to the other two columns. also the hottest module was the module at the middle of the board. this is mainly because of heat accumulated at the centre of the circuit board. in fig. 10 the average module surface temperatures were plotted at different positions along the board longitudinal axis. from this curve we can notice that the surface temperature is maximum at the middle of the board for the free convection condition. the position of the maximum surface temperature tends to change towards the direction of the exit as the air velocity increases. figure 11 shows the results of the variation of the modules surface temperature as the air speed is increased gradually. the curve is plotted for three different axial locations. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 24 at the free convection condition the modules temperature reaches values more than 80˚c, and when he air is forced to move at high velocities the temperature drops to less than 60˚c for the first row. free convection re = 495 re = 1006 re = 762 re = 1121 re = 1418 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 0 10 20 30 40 50 60 position along test rig axis (cm) s ur fa ce t em pe ra tu re (o c ) fig. 10: average modules surface temperature. fifth row third row first row 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 0 1 2 3 4 5 6 7 8 air velocity( m/s) b ot to m s ur fa ce t em pe ra tu re ( oc ) fig. 11: variation of the modules surface temperatures with air velocity. figure 12 shows the variation of local rate of heat removal by convection at different air velocities. from this figure we can see that as the air velocity exceeds a value of 4 m/s the rate of heat removed becomes almost uniform all through the circuit board, while for low velocities it increases from the inlet position towards the exit. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 25 first row second row third row fourth row fifth row 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 0 1 2 3 4 5 6 7 8 air velocity (m/s) lo ca l r at e of h ea r co nv ec tio n (w at t) fig. 12: variation of local rate of heat convection with air velocity. the percentage of the amount of heat removed by convection to the total amount of heat generated at the chip is shown on fig. 13. it can be noticed from this figure that at different axial locations the maximum value is around 90% while the minimum is slightly below 60%, which occurs at natural convection conditions. re = 1418 re = 1121 re = 1006 re = 762 re = 495 free convection 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90 0 10 20 30 40 50 60 position (cm) r at e of h ea t c on ve ct ed ( w at t) fig. 13: percentage of heat convected at different axial position. the overall thermal wake generation correlation for different reynolds number (rel) is shown in fig. 14. the thermal wake generation was found to be increasing at high constant rate up to the middle of the board, then the rate decreases and remains constant up to the end of the board regardless of the value of the reynolds number. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 26 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 1 2 3 4 5 no. of row ( di m en si on le ss ) re =495 re =762 re =1006 re = 1121 re =1418 fig. 14: thermal wake generation function. 0 10 20 30 40 50 60 450 650 850 1050 1250 1450 re l n u l row 1 row 2 row 3 row 4 row 5 fig. 15: forced convection correlation (local). it can generally be stated that the thermal wake generation function increases at the downstream region. comparing the thermal wake generation correlation for each case, we can notice that, the thermal wake effect is high for high values of reynolds number and vice versa. according to the dimensionless correlated data shown in fig. 15, the rate of cooling is highest near the air inlet position and decreases as it approaches the outlet. modules in the first row experiences better cooling and as the row number increases the cooling efficiency reduces. the reduction of the cooling rate is caused partially by the thermal wake generation. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 27 6. discussion the analysis and evaluation of the fluenttm cfd simulation results revealed a very good agreement with the obtained experimental results. comparison between the estimated and the actual modules surface temperatures is shown in fig. 16 and fig. 17 on which the estimated and the measured values are found to be very close. the error in the estimated values was found to be related to the values of the reynolds numbers and the axial position on the board. lower values of reynolds number were found to coincide with better estimates at locations near to the inlet. larger values of reynolds number were accompanied with better estimates of surface temperature at downstream regions. figure 18 shows the variation of the percentage error values as reynolds number increases. 313.00 323.00 333.00 343.00 353.00 363.00 373.00 10 15 20 25 30 35 40 45 50 axial distance (cm) te m p e r a tu r e ( k ) experimental values fig. 16: comparison between the cfd and the experimental results at re = 1006. 313.00 323.00 333.00 343.00 353.00 363.00 373.00 10 15 20 25 30 35 40 45 50 axial distance(cm) t e m p e r a t u r e (k ) experimental values fig. 17: comparison between the cfd and the experimental results at re = 1211. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 28 row 5 row 4 row 3 row 2 row 1 -5.00 -4.00 -3.00 -2.00 -1.00 0.00 1.00 2.00 3.00 4.00 5.00 6.00 400 600 800 1000 1200 1400 1600 reynolds number e r r o r % fig. 18: variation of the percentage error with reynolds number one of the interesting observations is the mode of change of the position at which the software estimated exactly the measured value of surface temperature. this position was noticed to change axially towards the downstream direction as reynolds numbers increases. this phenomenon is illustrated in fig. 19. in addition to this fact, the modules surface temperatures that were estimated exactly by the software as the measured experimental values were found to be approximately equal to the average board temperature. figure 20 shows the values of temperature at different positions when the cfd software succeeded to estimate exactly the measured values. 0 200 400 600 800 1000 1200 1400 1600 1800 0 10 20 30 40 50 60 axial position (cm) r ey no ld s nu m be r fig. 19: reynolds number at axial positions when the cfd software estimated the exact values of temperature. when the comparison was made taking reynolds number variation at fixed positions, the standard deviation was found to be increasing as reynolds number increases to a maximum value of 800, then it start to decrease further. this is illustrated in fig. 22. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 29 313 318 323 328 333 338 343 348 353 358 10 15 20 25 30 35 40 45 50 axial position(cm) te m pe ra tu re ( k ) fig. 20: values of temperature at axial position at which cfd and experimental results were equal. 1.55 1.6 1.65 1.7 1.75 1.8 1.85 10 15 20 25 30 35 40 45 50 axial distance (cm) e r r o r s ta n d a r d d e v ia ti o n fig. 21: standard deviation of the error at different axial locations. 0.00 0.50 1.00 1.50 2.00 2.50 3.00 400 600 800 1000 1200 1400 1600 reynolds number e rr or s ta nd ar d d ev ia tio n fig. 22: standard deviation of error at different reynolds number values. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 30 7. conclusion this work shows a combination of cfd and experimental investigation of a heatgenerating matrix that simulates the behavior of an electronic circuit board. initially the board was simulated using fluenttm cfd software, then the simulation results were validated experimentally. the estimated values of the surface temperature were found to be in good agreement with the actual measured values. the maximum percentage error was found to be 4.9 %, with a maximum standard deviation of 2.5 when considering different reynolds number, for the entire plate, and 1.7 when considering the local error variations at same locations. values of reynolds number, at which the software estimated exactly the measured values, were found to be increasing following the trend of thermal wake generation. this phenomenon may be related partially to the instability of the thermal boundary layer when the thermal wake exceeds a certain value with respect to different reynolds numbers. the local surface temperatures, at which the software was able to predict exactly the measured values, were found to be always the same values. and they were generally noticed to be very close to the mean temperature of the board. acknowledgement the authors would like to thank iium for funding this project. the authors would like also to thank m. farid m. ismail and hilmi f. bachok for their assistance in fabricating the experimental setup and running the cfd simulation. references [1] r. remsburg, “advanced thermal design of electronic equipment”, international thomson publishing, 1998. [2] f. p. incropera, “convection heat transfer in electronic equipment cooling”, journal of heat transfer, vol. 110, pp. 1097-1111, 1988. [3] k. j. kennedy, a. zebib, “combined free and forced convection between horizontal parallel plates: some case studies”, international journal of heat and mass transfer, vol. 26, pp. 471-474, 1990. [4] b. h. kang, y. jaluria, s. s. tewari, “mixed convection air cooling of an isolated rectangular heat source module on a horizontal plate”, asme proceedings of nat, heat transfer conference, pp. 59-66,. [5] c. c. huang, t. f. lin, “buoyancy induced flow transition mixed convective flow of air through a bottom heated horizontal rectangular duct”. international journal of heat and mass transfer, vol. 37, pp. 1235-1255, 1994. [6] k. c. kerki, p. s. sathyamurthy, s. v. patankar, “laminar mixed convection in a horizontal semicircular duct with axial nonuniform thermal boundary condition on the flat wall”, numerical heat transfer: part a, vol. 25, pp.171-189, 1994. iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 31 [7] c. w. leung, h. j. kang, “convective heat from simulated air-cooled printed-circuit board assembly on horizontal or vertical orientation”. international comm. heat and mass transfer, vol. 25, pp. 67-80, 1998. [8] c. y. choi, s. j. kim, “conjugate mixed convection in a channel: modified fivepercent rule”, international journal of heat and mass transfer, vol. 39, pp. 1223-1234, 1996. [9] s. chin, y. liu, s. f. chan, leung cw, t. l. chan, “experimental study of optimum spacing problem in the cooling of simulated electronic package”, journal of heat and mass transfer, vol. 37, pp. 251-257, 2001. [10] b. a. jubran, a. s. al-salaymeh, “heat transfer enhancement in electronic modules using ribs and (film-cooling-like) techniques”, journal of heat and fluid flow, vol. 17, pp. 148154, 1996. nomenclature a area (m2) h coefficient of heat convection (kw/m2k) s heat generation term (kj) tac modules actual temperature (k) ti modules initial temperature (k) tref reference temperature (k) q convective heat flow rate (kw) qc amount of heat convected by air (kj) ql amount of heat loss by conduction (kj) qr amount of heat loss by radiation (kj) qt total heat generated by the chip (kj) v volume (m3) h change of total enthalpy (kj) k.e change of kinetic energy (kj) p.e change of potential energy (kj)  species concentration (kg/kg) i thermal wake function  general field parameter  density (kg/m3) iium engineering journal, vol. 3, no. 2, 2002 a. f. ismail et al. 32 biographies ahmad f. ismail was born in kelantan, malaysia in 1966. he received his b. sc. degree in chemical engineering from the university of houston, texas in 1989, and a phd degree from rice university, texas in 1993. he is currently an associate professor at the department of mechanical engineering at the international islamic university malaysia (iium). dr. ismail's primary research interests are energy and environmental systems, computational fluid dynamics and heat transfer, combustion and pyrolysis, modeling and simulation, and digital image processing. mirghani i. ahmed was born in singa, sudan in 1956. he received his m sc. and phd degree in mechanical engineering from the budapest technical university hungary in 1987. from 1987 to 1989 he worked with the sudan university of science and technology as assistant professor he later joined ibm – canada as a research associate from 1989 to 1996. he is currently an associate professor at the department of mechanical engineering at the international islamic university malaysia (iium). dr. ahmed’s primary research interests are renewable energy, thermal comfort problems, electronic component cooling, modeling and simulation, computational fluid dynamics applications and heat transfer. yousif a. abakr was born in khartoum, sudan in 1962. he received his b. sc. degree in mechanical engineering and m.sc. degree from the university of khartoum in 1987 and 1995, respectively. he joined the energy research council, sudan as assistant researcher in 1987. he joined the sudan university of science and technology as a lecturer in 1991. currently, he is at the final stages of his phd study at the international islamic university, malaysia. his primary research interest is the renewable energy applications, combustion, evaporation and condensation, and computational fluid dynamics applications. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 aziz et al. optimum power scheduling of a community-based home energy management system muhammad adnan aziz1*, ijaz mansoor qureshi2, tanweer ahmad cheema1 and akram rashid2 1department of electronic engineering, isra university, islamabad campus, islamabad, 44000, pakistan. 2department of electrical engineering, air university, islamabad, 44000, pakistan. *corresponding author: m_adnanaziz@hotmail.com (received: 22nd mar. 2016; accepted: 9th sep. 2016; published online: 30th may 2017) abstract: in a smart grid (sg) scenario, domestic consumers can gain cost reduction benefit by scheduling their appliance activation time (aat) towards the slots of low charge. minimization in cost is essential in home energy management systems (hems) to induce consumers acceptance for power scheduling to accommodate for a demand response (dr) at peak hours. many proposed algorithms addressed the power scheduling for hems but community based optimization has not been the focus. this paper presents community based hems (chems) and targets the minimization of energy costs of the whole community while keeping a low peak to average ratio (par) and smooth power usage pattern (pup). objective of cost reduction is accomplished by finding most favorable aat by particle swarm optimization (pso) in conjunction with inclined block rate (ibr) approach and circular price shift (cps). simulated numerical results show that chems can save up to 45.3% electricity cost and achieve 37.98% reduction in par for a population size of 750 houses. abstrak: dalam senario smart grid (sg), pengguna domestik boleh mendapat manfaat pengurangan kos dengan menjadualkan masa pengaktifan perkakasan mereka (aat) ke arah slot caj rendah. pengurangan kos adalah penting dalam sistem pengurusan tenaga rumah (hems) untuk mendorong pengguna menerima konsep penjadualan kuasa untuk menampung sambutan permintaan (dr) pada waktu puncak. pelbagai algoritma telah dicadangkan untuk mengatasi isu penjadualan kuasa untuk hems tetapi cadangan in tidak menumpukan penyelesaian kepada pengoptimuman melibatkan komuniti. kertas kerja ini membentangkan hems (chems) berasaskan komuniti dan sasarannya adalah pengurangan kos tenaga seluruh komuniti sambil mengekalkan nisbah puncak kepada purata (par) yang rendah dan corak kegunaan tenaga (pup) yang lancar. objektif pengurangan kos tercapai dengan memperoleh aat paling baik menggunakan particle swarm optimization (pso) bersama dengan pendekatan kadar inclined block (ibr) dan circular price shift (cps). keputusan numerik simulasi menunjukkan bahawa chems boleh menjimatkan kos elektrik sehingga 45.3% dan mencapai pengurangan par sebanyak 37.98 % untuk saiz penduduk sebanyak 750 buah rumah. keywords: smart grid (sg); particle swarm optimization (pso); community based home energy management (chems); peak to average ratio (par); incline block rate (ibr) 43 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. 1. introduction implementation of demand response (dr) has been the prime focus of researchers targeting optimization of smart grids (sg) from the last five years. surges in power requirements at peak hours are inevitable due to evolution in domestic electrical appliance industry despite advances in renewable energy alternatives. residential load optimization is a major concern for power utility companies because it constitutes a considerable portion of the total power demand. domestic users’ lack of involvement is one of the hurdles in dr setup for peak load reduction [1]. additionally, electricity supply companies (esc) only run their base power production units and secondary units are operated if the power usage pattern (pup) of the whole grid crosses some threshold. sharp peaks in pup lead to higher peak to average ratios (par) and result in the need for sub power units to kick in. operation of sub units for a short span of time caused by frequent peaks in pup is a technical hassle for esc, therefore, smooth pup and reduced par is primary goal in demand side management (dsm). home energy management system (hems) is a principal solution for domestic dsm, which involves automated decisions for load optimization [2, 3]. a time-based electricity pricing scheme is an actively used tool for both cost and load curtailment [4, 5]. numerous strategies have been developed to curtail the power requirement based on dr. some of them rely on resident habits hence using load prediction models [3, 6, 7] to adjust scheduling, whereas others rely on pricing schemes and penalty terms [8, 9]. in hems optimization, the main goal is finding a suitable solution subject to the constraint of electricity par reduction. researchers have formulated a lot of home-based optimum solutions for this problem, some of them are based on game theory [10, 11], mixed integer linear programming [12], genetic algorithm (ga) [8, 13], non-dominated sorting ga [14], particle swarm optimization (pso) [15], gradient based repair pso [16], and artificial bee colony optimization [17]. literature available is based on minimizing the par and electricity cost of domestic consumers only based on dr signals. we believe that in a sg paradigm, optimization must be made with regard to small sized communities. a smaller community strengthens the case of sg because it offers relatively shorter paths for renewable energy sharing, which renders low line losses. when a set of houses in a community is subjected to an optimization algorithm, peaks in pup of whole community are anticipated. now if some of the houses have renewable energy sources around peaks, they must share their excess energy with houses of the same community due to two reasons: a) it can easily be distributed with less line losses, b) computationally less complicated for optimization algorithm to decide when and with whom to share the excess energy. in this paper, a community based home energy management system (chems) is proposed, which is better practical for renewable energy sharing between residents of close vicinity. the proposed scheme ensures a reduced par and smooth power usage pattern (pup) for sharp peaked pups with reduced electricity cost. chems is based on modification of electricity pricing scheme called circular shifted real time price (csrtp), which scatters consumer device operation slots to achieve reduced par. the remaining paper is structured as follows: section 2 shows the framework of chems. section 3 shows the proposed methodology of chems in conjunction with inclined block rate (ibr) and pso. in section 4, results are presented. section 5 is allocated to discussion and analysis, followed by the conclusion in section 6. 44 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. 2. framework of chems the main aim to develop chems is to lower electricity costs while keeping a reduced par. overall conceptual structure of chems is as shown in fig. 1. power is distributed from main grid (mg) to micro grids (mcg) and then each mcg delivers electricity to different communities of equal/variable no. of houses. mcgs can communicate to communities/houses through wired or wireless medium [18] to transmit dr signal. each house is connected to the mcg via an electricity management controller (emc) and a smart meter (sm). mcgs have arrangement called as an automatic metering infrastructure (ami) that can establish two way communications between esc and consumer. mcgs use ami to communicate demand response (dr) and other controlling signals to hems at peak load time. main grid (mg) micro grid 1 (mcg1) micro grid 2 (mcg2) micro grid n (mcgn)... community 1a (c1a) community 1b (c1b) community 1c (c1c) ... house 1a1 (hems1a1) house 1a2 (hems1a2) house 1a3 (hems1a3) ... cems1a chemsmcg1 fig. 1: chems conceptual diagram. a typical hems structure is shown is fig. 2. in a hems setup, there are two types of devices, one regarded as manually operated devices (mods) and other as automatically operated devices (aods). in this paper, we consider economizing the operation of aods only, as the operation timing of mods cannot be known a day ahead or prior to its operation. examples of mods are fluorescent lights, computers, television etc. such devices are operated manually by the users, hence cannot be used in power scheduling mechanisms. their power requirements can be used by the sm to be sent to the mcgs for dr computations. aod comprises the devices that can be activated without supervision, for example air conditioners, rice cookers, water pumps, etc. electricity management system (ems) is fed with the device operating timing (dot) of each aod at the start of the day. in this study, it is assumed that the dot of aods are previously identified and fed to the hems by the residents. dedicated interface devices (did), computers or smart phones can be used to provide the schedule of aods to ems, which can decide the activation of device operation based on the optimization algorithm. aforementioned knowledge of dots is used for scheduling electricity utilization individually at each user ems. ems can communicate and control aods through any currently available solutions such as zigbee, lonworks, z-wave, x10, insteon, knx or a wired communication link [18]. 45 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. solar panels air conditioner dish washerdryer washing machine electric heater rice cooker smart meter water pump emc aods electricity supply company ami wind mill electric iron ceiling fan television light bulbs mods did user fig. 2: hems structure. 3. proposed methodology of chems using pso, ibr and community based pricing this section presents the tactic for aods power scheduling based on pso combined with ibr and enhanced with csrtp to accommodate community electricity load curtailments. csrtp is only used to reduce par and make the pup smooth, unchanged rtp is used for electricity cost evaluation of all communities. an algorithm used for power scheduling aods is elaborated based on a real time price (rtp) model that charges different rates to each hour of the day. rtp data shown in fig. 3. is taken from ameren illinois power company [19]. in an rtp model, the electricity charge to residents is based on one-hour time slots. we have used this data with each hour divided into 6 timeslots of 10 minutes each, such division is made to increase the degree of freedom for power scheduling optimization. sub divisions of one hour into 6 time slots will result in a 144-slot day. any aod can operate for any number of sub divided time slots. for example, if a device has to run for 1.5 hours, it will consume 9 time slots. each hour can also be subdivided into further smaller time slots, but it is a tradeoff between better optimization results and computational complexity. smaller size of time slots produces better results as each aod has more possibilities of being staggered to numerous activation time slots (ats). a large number of candidate solutions for ats is a better prospect for cost and par reduction but more parameters for optimization consume enormous time for algorithm convergence. on the contrary, if we 46 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. / 6 / time slot i i p p power kw choose large size of time slots, ats opportunities are reduced, costs increased, and par is inevitable. fig. 3: real-time electricity prices. domestic users are supposed to provide the ems with the length and possible operating interval of each aod. nine devices are considered for a sample house, where some devices may or may not run, and some may run repeatedly on a given day of the month. pup of all devices will take the form given as a vector: (1) where consumption of power by ith device is given by: (2) each device has the power rating in the form of: (3) once the ems has received the ats, operation termination slot (ots), operation time length (otl), device operation time start (dots), and device operation time end (dote) of every device, it will create a power usage pattern (pup) of (1) for each aod using: (4) where 0 represents the aod being inactive and 1 represents the aod being active at corresponding time slot. ats of each device is constrained by the house resident defined limits as: (5) then the pup for whole house is calculated as: (6)  (1) (2) (144)i i i i ipup p p p p  / kwh i p power    0 , 1 i i i i i j ats j ots p j ats j ots       i i i i dots ats dote otl   i i pup pup    47 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. here we have summed up the power consumptions of aods. cost of electricity can be calculated by taking an inner product of (6) and rtp mapped onto 10 minutes time slot. the final objective function of problem at hand is given by: (7) we need to minimize (7) subject to (5). when this problem is subjected to any optimization technique, otl vector of aods looks for an optimum permissible slot in the day, and it tends to move towards lower rate slots. likewise all aods shift towards the time slots with lowest rates, which result in reduced electricity cost but also create higher par, which should be avoided. one solution to this problem is a penalty term, which is also used by researchers in the form of ibr [8]. 3.1 particle swarm optimization (pso) pso is an iterative process that initiates its optimization by assigning the initial values of particles and their velocities. pso is applied to this problem for optimization of all ats for a given house subject to the constraint of “otl must be covered up with in the range of dots and dote”. initial values of particles for this optimization are used as the provided dots. cost function is evaluated and the location of the best particle is saved. at the next iteration, new velocities are evaluated, followed by cost function assessment and best particle storage. this process is continued until a termination condition is reached. 3.2 inclined block rate (ibr) in an ibr approach if a pup crosses a threshold at any time slot, the rate in rtp is scaled with a factor for that particular time slot; otherwise if the pup remains below the predefined threshold, then the rates are unchanged. it works as a controller term to keep optimization parameters from making large par. consider the case represented in fig. 4. fig. 4: device ats constraints. the aod is shown in a rectangular block; its horizontal length shows the otl of the device, dots and dote marked as vertical lines. when this device is subjected to an optimization algorithm; its ats will tend to move towards dots as it will cover its dot over the slots of low electricity price (ep). if more than one device for a house operates around that specific slot, they will create a peak pup by converging towards the vicinity of lowest ep slot. same peak pups can also be created by other residents when they look 1   .rtpmin pup 48 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. to run their floating operating time (fot) based devices to run around the lowest ep slots. fot refer to those devices which have to run for a specific length of time once a day, e.g. water pumps, washing machines, and dryers. such situations can be controlled by implying ibr. 3.3 architecture of chems in a practical scenario of actual population, each added residence is a contributing factor towards a high/peaked par in extension to aforementioned aspects of par increments. an mcg providing electricity to a large set of consumers can be considered for clarification. the majority of the houses will cluster ats of their aods around the time slots of low ep when subjected to optimization through traditional hems. this will result in sharp peaks in overall pup for the corresponding mcg. the core reason for traditional hems to cluster aods is that each house is optimized independently without any information regarding cluster locations of neighboring residents. this phenomenon is not different for any of the available schemes in the literature. additionally, all of the houses cannot be optimized in one go. this is equivalent to one big house with a very large quantity of devices, which is not practically realizable from two points of views. i) penalty terms for pup crossing thresholds will not be applicable for separate houses. ii) a large quantity of ats timings will not allow the optimization algorithm to converge due to time limitations. chems is the solution for electricity cost and par reduction for large populations. conceptual setup of chems is shown in fig. 1. the whole set of users under one mcg is divided into several communities. each community consists of a small number of houses, that can be varied based on the objective. the pup of every house is optimized separately with application of pso, ibr, and csrtp. every community is offered the same rtp but with a small circular shift, which guides communities to shift their peak loads with small steps. when sharp peaks of individual communities are a small step apart, par is automatically reduced. this process ensures reduced par and smoothed pup. obtain parameters pi, dotsi, dotei and otli for each device evaluate pup of whole house according to eq. (6) calculate particle location and velocities generate parameters at si for all devices subject to constraint (5) rtp for community 1a evaluate fitness update particle and global best termination criteria reached? no end yes fig. 5: flowchart of whole optimization process of one house. 49 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. when the pup of an entire community set is optimized in this fashion, it results in a decreased and smooth curve. community a is done first and rest of the communities follow thereafter. let us consider the devices with dots and dote containing tsj, being taken as the lowest ep slot in the interval. when the ats of aods corresponding to community a are subjected to the optimization algorithm, a peak will be created at tsj. then comes the optimization of community b, which being offered a circular shifted rtp will find the lowest ep slot tsj shifted by k units and positioned at tsj+k. aods of community b will create a peak at tsj+k by occupying ats there. this process goes on with rest of the communities and results in a pup with reduced par for the whole mcg. flowchart for overall optimization process is depicted in fig. 5. 4. simulation results this section is dedicated for simulation results to prove the capability of chems to produce better results for large populations. as mods are operated at random by the residents, therefore, only aods are simulated for this demonstration. a maximum of 16 devices can be operated for one residence and a minimum of 8. some devices like rice cookers may be used more than once a day. a typical residence aod usage is depicted in table 1. table 1: typical residence usage of aods aod power (kwh) otl (time slots) operation slots (scattered b/w) air conditioner 1.2 4,6,8,… 30 to 144 electric heater 1.5 5,10,15,… 100 to 144 washing machine 0.5 4,8,10 1 to 70 clothes dryer 0.7 4,8,10 71 to 100 dishwasher 0.5 2,4,6 120 to 144 water pump 1 3,6,9 70 to 90 electric kettle 1.6 1,2 60 to 70, 90 to 110 rice cooker 0.5 2,4 1 to 30, 50 to 70, 95 to 110 for this research, all simulations are performed in matlab. pso optimization parameters are the swarm size of 100, minimum fraction for neighbors 0.25, number of variables equal to number of devices, tolerance value for relative change and termination after 3200 iterations. results are compared with optimization based on a standalone house with traditional rtp, hence it is called traditional hems. traditional hems is optimized with pso & ibr applied to each house, whereas, chems use a modified rtp scheme in addition to pso and ibr. in this modeling, we took a total of 500 and 200 houses with randomized loads based on table 1. altered population sizes were chosen to study the effects of community size on different populations. the community size directly affects the final pup, so different sizes of communities are considered and the outcomes are shown in fig. 6 for the population size of 500 houses. 6 10  50 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. fig. 6: simulation with 500 houses a) traditional hems optimization b), c), d), e), and f) chems with 10, 20, 30, 40, and 50 houses/community. fig. 7: simulation with 200 houses a) traditional hems optimization b), c), d), e), and f) chems with 10, 20, 30, 40, and 50 houses/community. 51 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. each sub-figure of fig. 6 consists of two graphs. one of them is common to all subfigures showing pup without any power scheduling. the second graph, in dotted form, is of pso with ibr only in fig. 6a. figure 6b, 6c, 6d, 6e, and 6f represent application of chems with community sizes of 10, 20, 30, 40, and 50 houses per community. the same procedure is repeated for the population size of 200 and shown in fig. 7. reduction in par is 12.22% and electricity cost is 47.1% for traditional hems when a population size of 500 houses is considered. whereas application of chems with 10% houses per community, par is reduced by 25.56% and electricity cost reduced by 45.94%. figures 6 and 7 show that rapid changes in pup are eliminated by application of chems for both population sizes. smaller community size means larger shifts in rtp and results in increased delay time for consumer device operations. therefore, small shifts are used in csrtp. results are evaluated for different sizes of communities but 10% houses per community is recommended to keep the device operation delay time as low as possible. complete results for population sizes of 200, 500 and 750 houses are summarized in table 2. from table 2 it is clearly evident that chems enhances results of optimization by pso applied in conjunction with ibr. chems lags by 1.05% form traditional hems in electricity cost reduction for population size of 200 houses and it leads traditional hems by 2.72% in par reduction. for a population size of 500 houses, chems lags by 1.17% from traditional hems in electricity cost reduction and leads it by 13.34% in par reduction. finally, for a population size of 750 houses, traditional hems is less than 2% better than chems in terms of cost reduction, however, chems outsmarts traditional hems based optimization by 25.08% when par reduction is considered. this trend shows that results of chems are enhanced with larger populations, which is the case of real world. chems produces best results in terms of par reduction with community sizes of 2% houses/community and optimal results for cost reduction are achieved with a community size of 10% houses/community. the tradeoff between electricity cost and par reduction can easily be managed using variable community size at times of peak power demand. par reduction takes priority when electricity power demand is higher than a threshold; hence smaller community size may be used by esc. large community size can be selected if cost reduction is at esc precedence. table 2: simulation with 200, 500 and 750 houses algorithm community based on number of houses (percentage) percentage par reduction electricity cost reduction percentage 200 houses 500 houses 750 houses 200 houses 500 houses 750 houses traditional hems with pso & ibr nil 14.74 12.22 11.93 47.08 47.11 47.26 chems with pso & ibr 2% 37.19 36.57 38.61 36.71 38.02 39.27 4% 27.21 37.97 34.15 41.78 41.45 40.76 6% 23.13 36.94 37.29 44 42.34 41.92 8% 18.59 37.13 37.23 45.46 44.56 43.97 10% 17.46 25.56 37.01 46.03 45.94 45.3 the rest of the comparisons of traditional hems with chems are based on 10% houses/community. figure 8 shows the comparison of par reduction capabilities against 52 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. different population sizes. par is almost the same for both chems and traditional hems up to a population size of 100 houses. when the population size is greater than 100, par is almost constant for traditional hems. chems reduced par with increase in population size after 100 houses and stabilized after 650 houses. par is reduced to 2 by chems, whereas traditional hems only reduced it to 2.9 from 3.3. fig. 8: par comparisons for population of 10 to 750 houses. fig. 9: percentage cost reduction for population of 10 to 750 houses. figure 9 shows the percentage cost reduction for both schemes. traditional hems is slightly better than chems from a percentage electricity price reduction point of view. some lag in cost reduction for the sake of better par is obvious because if all consumers cluster around low ep, then par reduction is limited as is the case of traditional hems optimization. 5. discussion and analysis this study has demonstrated a new approach of dsm that is based on division of population into communities. each community is offered a slightly different csrtp, which renders pup peaks to scatter around slots of low ep such that overall sharp peaks are eliminated. the algorithm presented does not require any modification in hardware setups available in literature. it can be implemented in hems schemes equipped with 53 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. zigbee and sensor network-based appliance control/communication architecture like [20, 21]. the main goal of par reduction is achieved with a supplementary benefit of smooth pup. pup is smoother with application of chems than traditional hems as shown in fig. 6 and fig. 7. chems offers more authority to esc for electricity load shaping and curtailment. esc can guide consumer ems to shift loads in par reducing manner seamlessly by csrtp. variation in community size allows esc to prioritize between par or cost reduction depending upon power generation constraint. 6. conclusions this paper has presented an arrangement for implementing dr in a manner that can easily incorporate the resource sharing factor of sg. it has demonstrated through simulated results that our proposed technique trims par exceptionally well and reduces electricity cost with a supplementary benefit of smooth pup. it is evident from fig. 6 and fig. 7 that the pup transitions are much smoother after optimization by chems. results summarized in table 2 show that the par reduction with chems is 24% better than traditional hems for a community size of 750 houses. figure 8 shows that chems can reduce par for large populations in contrast to traditional hems. cost reduction is almost equivalent as shown in fig. 9. additionally, the community-based setup is very suited to localized sharing of renewable energies within the community. references [1] rastegar m, fotuhi-firuzabad mf, aminifar f. (2012) load commitment in a smart home. appl. energy, 96:45–54. [2] pipattanasomporn m, kuzlu m, rahman s. (2012) an algorithm for intelligent home energy management and demand response analysis. ieee trans. smart grid, 3(4):2166-2173. [3] ozturk y, senthilkumar d, kumar s, lee g. (2013) an intelligent home energy management system to improve demand response. ieee trans. smart grid, 4(2):694-701. [4] lui tj, stirling w, marcy ho. (2010) get smart. ieee power energy magazine, 8(3):66– 78. [5] ipakchi a, albuyeh f. (2009) grid of the future. ieee power energy magazine, 7(2):52-62. [6] adika co, lingfeng w. (2014) autonomous appliance scheduling for household energy management. ieee trans. smart grid, 5(2):673-682. [7] abushnaf j, rassau a, górnisiewicz w. (2015) impact of dynamic energy pricing schemes on a novel multi-user home energy management system. electric power systems research, 125:124-132. [8] zhao z, lee wc, shin y, song kb. (2013) an optimal power scheduling method for demand response in home energy management system. ieee trans. smart grid, 4(3):13911400. [9] chavali p, yang p, nehorai a. (2014) a distributed algorithm of appliance scheduling for home energy management system. ieee trans. smart grid, 5(1):282-290. [10] deng r, yang z, chen j, asr nr, chow my. (2014) residential energy consumption scheduling: a coupled-constraint game approach. ieee trans. smart grid, 5(3):1340-1350. [11] mohsenian-rad ah, wong vws, jatskevich j, schober r. (2010) optimal and autonomous incentive-based energy consumption scheduling algorithm for smart grid. innovative smart grid technologies (isgt) gaithersburg md, 1-6. [12] hubert t, grijalva s. (2012) modeling for residential electricity optimization in dynamic pricing environments in smart grid, ieee trans. smart grid, 3(4):2224-2231. 54 iium engineering journal, vol. 18, no. 1, 2017 aziz et al. [13] khomami hp, javidi mh. (2013) an efficient home energy management system for automated residential demand response. environment and electrical engineering (eeeic) 307-312. [14] lin yh, tsai ms. (2015) an advanced home energy management system facilitated by nonintrusive load monitoring with automated multi objective power scheduling. ieee trans. smart grid, 6(4):1839-1851. [15] pedrasa maa, spooner td, macgill if. (2010) coordinated scheduling of residential distributed energy resources to optimize smart home energy services. ieee trans. smart grid, 1(2):134-143. [16] huang y, tian h, wang l. (2015) demand response for home energy management system. international journal of electrical power & energy systems, 73:448-455. [17] zhang y, zeng p, zang c. (2015) optimization algorithm for home energy management system based on artificial bee colony in smart grid. cyber technology in automation, control, and intelligent systems, international conference of the ieee, 734-740. [18] tariq m, zhou z, wu j, macuha m, sato t. (2012) smart grid standards for home and building automation. power system technology (powercon), international conference of the ieee, 1-6. [19] real-time pricing for residential customers, ameren illinois power co. (2015) [https://www2.ameren.com/retailenergy/realtimeprices.aspx] [20] han dm, lim jh. (2010) smart home energy management system using ieee 802.15.4 and zigbee. ieee trans. consumer electronics, 56(3):1403-1410. [21] han j, choi cs, park wk, lee i, kim sh. (2014) smart home energy management system including renewable energy based on zigbee and plc. ieee trans. consumer electronics, 60(2):198-202. nomenclature mod manually operated devices aod automatically operated devices dot device operating time ats activation time slot ots operation termination slot otl operation time length dots device operation time start dote device operation time end pup power usage pattern 55 https://www2.ameren.com/retailenergy/ application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 stemming impact analysis on indonesian quran translation and their exegesis classification for ontology instances fandy setyo utomo1,2*, nanna suryana2 and mohd sanusi azmi2 1department of information system, faculty of computer science, universitas amikom purwokerto, purwokerto, indonesia. 2center for advanced computing technology (c-act), faculty of information and communications technology, universiti teknikal malaysia melaka, melaka, malaysia. *corresponding author: fandy_setyo_utomo@amikompurwokerto.ac.id (received: 29th may 2019; accepted: 7th october 2019; published on-line: 20th january 2020) abstract: the current gap that appears in the quran ontology population domain is stemming impact analysis on indonesian quran translation and its exegesis (tafsir) to develop ontology instances. the existing studies of stemming effect analysis were performed in various languages, datasets, stemming methods, cases, and classifiers. however, there is a lack of literature that studies the stemming influence on instance classification for quran ontology with different datasets, classifiers, quran translations, and their exegesis in indonesian. based on this problem, our study aims to investigate and analyse the stemming impact on instance classification results using indonesian quran translation and their exegesis as datasets with multiple supervised classifiers. our classification framework consists of text pre-processing, feature extraction, and text classification stage. sastrawi stemmer was used to perform stemming operation in the text pre-processing stage. based on our experiment results, it was found that support vector machine (svm) with term frequency-inverse document frequency (tf-idf) and stemming operation owns the best classification performance, i.e., 70.75% for average accuracy and 71.55% for average precision in indonesian quran translation dataset on 20% test data size. while in 30% test data size, svm and tf-idf with stemming process own the best classification performance, i.e., 67.30% for average accuracy and 68.10% for average precision in ministry of religious affairs indonesia dataset. furthermore, in this study, it was also discovered that the backpropagation neural network has the most precision and accuracy reduction due to the negative impact of stemming operations. abstrak: jurang semasa yang muncul dalam domain populasi ontologi quran adalah punca analisis kesan bendungan pada terjemahan quran bahasa indonesia dan tafsir bagi membangunkan ontologi kata dasar. kajian lalu terhadap analisis kesan bendungan telah dijalankan dalam pelbagai bahasa, set data, kaedah bendungan, kes dan pengkelasan. walau bagaimanapun, terdapat kekurangan kesusasteraan yang mengkaji kesan bendungan dalam bidang pengkelasan ontologi quran dengan set data berbeza, pengkelasan, penterjemahan quran dan tafsir dalam bahasa indonesia. oleh itu, kajian ini bertujuan bagi menyiasat dan menganalisa kesan bendungan terhadap dapatan pengkelasan menggunakan terjemahan quran dan tafsir bahasa indonesia sebagai set data dengan pelbagai pengkelasan yang diselia. kaedah pengkelasan kajian ini terdiri daripada pra-pemprosesan teks, ciri pengekstrakan, dan peringkat pengkelasan teks. pembendung sastrawi digunapakai bagi menjalankan operasi pembendungan pada peringkat prapemprosesan teks. hasil eksperimen menunjukkan mesin vektor sokongan (svm), frekuensi dokumen terma frekuensi-berbalik (tf-idf) dan operasi pembendungan memberikan keputusan pengkelasan yang terbaik, iaitu purata ketepatan pada 70.75% dan 33 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 purata kejituan pada 71.55% terhadap 20% saiz data ujian penterjemahan quran dalam bahasa indonesia. sementara itu, svm, tf-idf dan proses pembendungan memberikan prestasi pengkelasan terbaik, iaitu, purata ketepatan pada 67.30% dan purata kejituan pada 68.10% terhadap 30% saiz data ujian dari set data kementerian hal ehwal agama indonesia. kajian ini juga mendapati rangkaian neural rambatan belakang menghasilkan pengurangan ketepatan dan kejituan yang paling tinggi disebabkan oleh kesan negatif operasi pembendungan. keywords: k-nearest neighbor; neural network; ontology learning; ontology population; support vector machine 1. introduction the quran (al-quran) is a muslim sacred book that contains god’s revelations received by the holy prophet muhammad (sallallahu 'alaihi wa sallam). this holy book contains knowledge, instruction, and scientific facts. quran consists of several thematic topics or themes such as morals, criminal law, private law, worship, previous nations, the quran, and faith. these topics aim to guide humankind to reach blessedness in the world and hereafter. the knowledge inside the holy quran n could be stored and represented by ontology. there are two approaches to build an ontology, i.e., non-automated and automated process [1]. this automatic process is also known as the ontology population. the nonautomated process is usually crafted by a human, such as an ontology engineer or expert in a particular domain, whereas the ontology population is a technique to build an ontology by learning the concepts, relationships, and instances from the text. the standard techniques to conduct the ontology population are lexico-syntactic patterns, classification based on similarity, supervised methods, and knowledge-based and linguistic methods [2]. in the ontology, instances are defined as members of a class [3–5]. based on earlier research by [6, 7, 8–10], they classified the quran verses based on thematic topics for the quran ontology. in their case, thematic topics are concepts or classes, while quran verses are the instances. based on their case, our study also adopts the definition of thematic topics as a class and quran verses as instances. the aim of instances classification is to map the quran verses into their themes in order for users to have knowledge and better understanding by seeing the entire picture of a particular topic in the quran. stemming is one of the phases in text pre-processing which applies a natural language processing technique for removing affixes from words in order to transform them into their stems [11–13]. the aim of the stemming operation in text classification is to reduce the dimensionality of feature space to provide efficiency within the text classification processing [14,15]. there are several previous studies that employed a stemming operation in the text pre-processing stage to support the instances classification process. studies by [16–18] performed verse classification for english quran translation by applying a stemming operation in the pre-processing stage. to classify the verses, research conducted by [16,17] used back-propagation neural network (bpnn) as a classifier, while [18] used three classifiers, i.e., support vector machine (svm), k-nearest neighbour (k-nn), and naive bayes (nb). however, their research did not study the stemming impact on classification results. a different approach to performing quran verse classification was conducted by [19]. in their experiment, they learned the impact of the stemming operation to classify the english quran verse translations using hamming loss as a measuring instrument. as a result, they found stemming was not able to improve multinomial naive bayes performance to classify the instances according to the topics. 34 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 to date, the study of stemming impact analysis on instance classification is still a gap that needs to be bridged in the quran ontology population research field. there is a lack of literature that studies the stemming impact on instance classification with different datasets, quran translations, and classifiers. based on this gap, our study aims to investigate and analyse the stemming impact on instance classification results on several datasets and supervised classifiers. our research contribution is to provide knowledge toward stemming impact on instance classification results in quran ontology population domain using indonesian quran translation and indonesian quran exegesis as the dataset. the rest of the paper is structured as follows: section 2 presents the study of related work. section 3 describes our research methodology. section 4 discusses our experiment results. finally, we conclude our study results in section 5. 2. related works study to investigate and analyse the stemming impact has been conducted by several previous researchers for some languages and cases. research by [20] explains the stemming effect on the arabic text classification. they used shereen khoja’s stemmer and term frequency-inverse document frequency (tf-idf) as a feature selection model. their dataset consisted of 1100 documents from trusted websites. then, they classified the entire document info 9 classes, i.e., agriculture, art, economics, health and medicine, law, politics, religion, science, and sports. naïve bayes, smo (sequential minimal optimization), and decision tree (j48) were used as classifiers. the dataset was split 66% for training data and 34% for test data. after two test modes using percentage split (ps) and k-fold cross validation (cv), it was found that stemming had a negative impact on the classification accuracy of the three classifiers. on ps and cv test mode, j48 had the most significant accuracy decrease from 76.3% to 64.2% in ps mode, and 69.69% to 62.6% in cv mode. similar research conclusion was also obtained by [21] in their research. they performed arabic text classification using three datasets that were taken from two trusted sources. the first dataset consisted of 1800 documents with six classes, the second dataset had 1500 documents with five classes, and the third dataset had 1200 documents with four classes. the datasets were split into 70% for training data and 30% for test data on each dataset. bag of words (bow) with sorted and ratio was used for feature selection. they applied the frequency ratio accumulation method (fram) as a classifier, while to transform the words into their root form, they employed information science research institute’s (isri) stemmer [22] and tashaphyne stemmer [23]. experimental results in the entire dataset demonstrated that stemming had a negative impact on the classification accuracy. the most significant accuracy decrease was found in the second dataset from 97.33% to 88.89% with the isri stemmer and 95.33% with the tashaphyne stemmer. besides arabic, other studies have studied stemmer impact in another language and dataset. research by [24] conducted an indonesian tweet classification using 2000 tweets divided into three datasets, i.e., a first dataset with 1500 tweets, second dataset with 1750 tweets, and third dataset with 2000 tweets. they classified the tweets into 2 classes, namely positive and negative tweets. there were 1074 positive and 926 negative tweets. support vector machine (svm) and naïve bayes were used as classifiers. to convert the words into their root form, they applied nazief and adriani’s algorithm. this algorithm is clearly described by [25] in their research. they used bow and tf-idf for feature selection in their study. experimental results on the three datasets demonstrated that stemming had a negative impact on the classification accuracy. the most significant accuracy decrease was seen in the third dataset with bow as a feature selection and naïve bayes as a classifier from 89% 35 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 to 85.5%. furthermore, a study by [19] conducted a multi-label classification on topics of quranic verses in english translation by shakir. they used bow for feature selection, multinomial naive bayes as a classifier, 5-fold cross-validation to evaluate the system, and hamming loss as a metric measurement. according to their experiment results, the classification rate without stemming was 0.125 of hamming loss, while it was 0.135 using stemming. based on their research results, it can be concluded that stemming has a negative impact on the classification accuracy. different results for english text classification were obtained by [26]. they classified the us congress data collection document with 60% for training data and 40% for test data. lovin, porter, yet another suffix stripper (yass), graph based stemmer (gras), statistic based stemmer (sns), and high precision stemmer (hps) were used as stemmers. as a result of text classification by svm using all stemmers, it was concluded that stemming had a positive impact on the classification accuracy. all stemmers could improve the precision, recall, and f-measure values. the most significant value increase was seen with porter as a stemmer from 62.1% to 68.3% for precision, 62.9% to 65.3% for recall, and 61% to 65.4% for f-measure. 3. methodology this section is structured as follows: sub-section 3.1 discusses the framework for instance classification in this study that was taken from earlier studies. sub-section 3.2 provides the collection of datasets used in this investigation. our experimental configuration is shown in sub-section 3.3. finally, the experiment test scenario is defined in sub-section 3.4. 3.1 framework adopted based on earlier studies by [19–21, 24, 26], we have adopted their framework for classifying quranic verses and quran exegesis instances in our studies. their framework includes several phases, i.e. text pre-processing, feature extraction, and text classification. figure 1 presents the instance classification framework in our research. the text preprocessing phase is presented in sub-section 3.1.1, whereas sub-section 3.1.2 describes the feature extraction and text classification phase. fig. 1: instances classification framework. 3.1.1 text pre-processing phase the pre-processing phase input is text from indonesian quran translation and their exegesis in indonesian. this phase is aimed at preparing the text in an appropriate format to be processed in the next step. first, it removes the number and punctuation from the text. then, to prevent ambiguity in term identification, any capital letters discovered are 36 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 substituted by lower case letters. common words deemed to have no significance are removed from the sentences in the stop word removal stage after the case-folding procedure. this stage used tala's stop word list [27] consisting of 757 words. moreover, in the tokenization phase, the sentence was then divided into words. tokenization is a process where the text is fragmented into an array of words. subsequently, the array of words is used as an input for the stemming phase. stemming is an operation to remove affixes from the word to convert into their root form. we applied sastrawi stemmer to perform stemming operation for the indonesian language text. this stemmer is accessible at https://pypi.org/project/sastrawi/. sastrawi has work procedures based on the fundamental concept from nazief and adriani's stemmer. this stemmer algorithm was described by asian in [25]. however, there are several modifications on sastrawi to optimize the stemming operation results. to remove any derivational suffixes, sastrawi has added the adopted foreign suffix rule {“-is,” “-isme,” “-isasi”} into the nazief and adriani’s stemmer origin rule. furthermore, sastrawi also has added and modified prefix disambiguation rules to remove complex derivational prefixes {“be-,” “te-,” “me-,” or “pe-”}. sastrawi stemmer is the optimization result from nazief and adriani's algorithm. this stemmer was improved by confix stripping (cs) algorithm, enhanced confix stripping (ecs) algorithm, and modified ecs algorithm [28-29]. table 1 shows the prefix disambiguation rules that have added and modified in the sastrawi stemmer. table 1: prefix disambiguation rules modified rules rule construct return modified by 5 bec1erc2… be-c1erc2… where c1!=’r’ sastrawi 12 mempe… mem-pe… [25] 14 men{c|d|j|s|t|z}… men-{c|d|j|s|t|z}… sastrawi 16 meng{g|h|q|k}… meng-{g|h|q|k}… [25] 17 mengv… meng-v... | meng-kv... | mengv-... where v=’e’ | me-ngv… sastrawi 18 menyv… meny-sv… | me-nyv… [30] 19 mempa… mem-pa… where a != ‘e’ [31] 29 pengc… peng-c… [31] 30 pengv… peng-v... | peng-kv... | (pengv-... if v=’e’) [31] 31 penyv… peny-sv… | pe-nyv… [30] deleted rules rule construct return deleted by 33 pecerv… per-erv… where c!={r|w|y|l|m|n} sastrawi new rules rule construct return added by 35 terc1erc2… ter-c1erc2… where c1 != ‘r’ [25] 36 pec1erc2… pe-c1erc2… where c1 != {r|w|y|l|m|n} [25] 37 cerv… cerv | cv [30] 38 celv… celv… | cv… [30] 39 cemv… cemv… | cv… [30] 40 cinv… cinv… | cv… [30] 41 kua… ku-a… sastrawi 42 kaua… kau-a… sastrawi based on table 1, the letter ‘c’ is a consonant; the letter ‘v’ is a vowel, and the letter ‘a’ means any letter. there are 40 prefix disambiguation rules on sastrawi stemmer, where 32 of these rules were taken directly from nazief and adriani’s stemmer, and about ten rules were from 32 rules in nazief and adriani’s stemmer that were modified by several sources. sastrawi stemmer has applied the procedure to solve the suffix removal failure that was adopted from [31], for improving the stemming results. this procedure was used to handle 37 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 the suffix removal problem that arises from the nazief and adriani’s stemmer. finally, the array of words that contain the key terms in the basic form is used as an input on the feature extraction stage. 3.1.1 feature extraction and text classification phase text feature extraction is a method for extracting and selecting text to represent it in a specific form. we used the bag of words (bow) and term frequency-inverse document frequency (tf-idf) model in this research to conduct feature extraction. bag of words is an extraction model that could represent text as an unordered set of words and ignore grammatical structure [32]. this model has the representation of a sparse vector that includes appearance for each word in a document. hereinafter, tf-idf is a statistical model representing the meaning of a word on a collection by comparing the occurrence of a word in a document with its appearance in another document [33]. mathematically, the tf-idf approach can be written in eq. (1) as follows: (1) where is the number of occurrences that term r appeared in a document c, n is the number of entire documents in the corpus, and is the number of documents in which term r appears. here is an example to describe the difference between bow and tf-idf. suppose our dataset consists of two quran verses taken from indonesian quran translation. these verses are: dan jika kamu ditimpa sesuatu godaan syaitan maka berlindunglah kepada allah (surah al-a'raf: 200) sesungguhnya syaitan itu tidak ada kekuasaannya atas orang-orang yang beriman dan bertawakkal kepada tuhannya (surah an-nahl: 99) after the stop word list and stemming operation are performed on the data set, these are the verses final results after both operations have been conducted. timpa goda syaitan lindung allah (surah al-a'raf: 200) sungguh syaitan kuasa orang orang iman bertawakkal tuhan (surah an-nahl: 99) the bow model was built for comparing a set of documents. based on the data set, the model has two rows, i.e. surah al-a'raf: 200 as v1 and an-nahl: 99 as v2. timpa goda syaitan lindung allah sungguh kuasa iman bertawakkal tuhan orang v1 1 1 1 1 1 v2 1 1 1 1 1 1 2 based on eq. (1), the bow model then modified into a tf-idf model. the model transformation result is shown below. timpa goda syaitan lindung allah sungguh kuasa iman bertawakkal tuhan orang v1 0,3 0,3 0 0,3 0,3 v2 0 0,3 0,3 0,3 0,3 0,3 0,6 finally, after feature extraction and selection has been conducted, further the bow and tf-idf data are divided into training and test sets. we employed the back-propagation 38 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 neural network (bpnn), support vector machine (svm), and k-nearest neighbor (k-nn) classifier to classify the instances. the instances are classified into one of the classes by those classifiers. we utilized three classes, i.e., morals, al-quran, and previous nation in our study that taken from thematic topics within al-quran cordoba [34]. 3.2 dataset collection we utilized two sources to create the dataset, i.e., the data from tanzil project (http://tanzil.net) to build the indonesian quran translation and quraish shihab exegesis corpus; and the data from the ministry of religious affairs indonesia (https://quran.kemenag.go.id/) to develop quran exegesis corpus. in our study, we utilized several quran surahs and thematic topics for developing corpus. table 2 presents the thematic topic number with their names and the total of quran verse, which is connected to their thematic topic that was used to develop our corpus. table 2: thematic topics and total of quran verses thematic topic id thematic topic name total of quran verses 1 morals 218 2 al-quran 183 3 previous nation 127 based on table 2, we employed 528 of quran verses from indonesia quran translation and their exegesis. table 3 presents the quran surah, a total of verses inside the surah, and their thematic topic that are utilized to build the corpus. table 3: surah name, total of verses, and their thematic topic topic id albaqarah ali imran annisa’ alan’am ala’raf attaubah annahl taha 1 51 40 47 13 21 28 14 4 2 59 29 25 20 16 8 18 8 3 13 28 12 10 37 4 5 18 sum 123 97 84 43 74 40 37 30 for this study, we utilized quran verses that are categorized by al-quran cordoba into a single thematic topic. we used two datasets, i.e. indonesian quran translation and quraish shihab exegesis corpus to observe stemming impact toward the accuracy level of the classifier on both datasets. 3.3 experimental setup we employed two operational frameworks to classify the instances. figure 2 presents the framework that utilized the bow approach for classification, while fig. 3 shows the framework that used tf-idf to classify the instances. 39 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 fig. 2: framework with bow approach. figure 2 shows that the bow model follows the feature extraction phase. furthermore, the data is divided into training and test feature data. the dimensions of both feature data will be presented in sub-chapter 3.4. for the text pre-processing stage, we used two scenarios, i.e., pre-processing without stemming operation and with the stemming process. as shown in fig. 3, bow model representation is converted into the tf-idf model. further, the tf-idf representation divided into training and test feature data. we developed the operational framework and tested the model performance in python programming environment. similar to the previous operational framework, we used two scenarios, i.e., pre-processing without stemming operation and with the stemming process on the text preprocessing stage. fig. 3: framework with tf-idf approach. 3.4 test scenario we applied several test data sizes to investigate and analyse the stemming operation impact on instance classification with different feature selection models, i.e., bow and tfidf. the test data size for each thematic topic is shown in table 4. 40 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 table 4: the size of the test data for each topic size of test data topic 1: morals (data) topic 2: al-quran (data) topic 3: previous nation (data) sum (data) 20% 44 37 25 106 30% 66 55 38 159 as shown in table 4, there are two test scenarios to investigate and analyse the impact of the stemming operation on instance classification performance. we utilized the precision, recall, and accuracy metric for measuring the classification results in this study. 3.5 metric for evaluation in this study, we used various evaluation metrics to measure classification results, i.e. average accuracy, average precision, precision, and recall. table 5 presents the metric for evaluation and their evaluation focus which is used in this research. table 5: the evaluation metric for instance classification metrics formula evaluation focus precision the ratio between the positive patterns that are correctly predicted from the total predicted data in a positive class recall measure the fraction of positive patterns that are correctly classified average accuracy the average effectiveness of all class from a classifier average precision the average of all class precision where tp is true positive, fp is false positive, fn is false negative, tpi are true positive for ci, tni are true negative for ci, fni are false negative for ci, and fpi are false positive for ci. in our experiment, we used average accuracy and average precision to measure the impact of the stemming operation in all approaches toward classification results for all datasets. while to measure the effect of stemming operation in all methods toward classification results for each theme within all datasets, we used the precision and recall metric. 4. results and analysis first, we utilized the indonesian quran translation (iqt) corpus as a dataset in our experiment. this experiment applied the test scenario based on table 4. figure 4 presents the experiment results for the average precision and average accuracy measurement in all approaches. 41 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 fig. 4: measurement average precision and average accuracy on iqt dataset. as shown in fig. 4, the stemming operation has a negative impact on bow/tf-idf with bpnn approaches for both test data sizes. however, the stemming process has a positive effect on the tf-idf with svm approach for both test data sizes. furthermore, on bow/tfidf with k-nn methods also have a positive impact from the stemming operation on 20% test data size. the tf-idf with svm and stemming approach has the highest average precision and average accuracy value on both test data sizes. hereinafter, figure 5 shows the experiment results with quraish shihab exegesis as a corpus. fig. 5: measurement average precision and average accuracy on the quraish shihab dataset. based on fig. 5, it can be concluded that the stemming operation has a negative impact for bow/tf-idf with bpnn approach and bow with svm approaches on 20% test data size. similar to the previous dataset, the bow/tf-idf with k-nn methods have a positive impact from stemming operation on 20% test data size. otherwise, the stemming process has a positive effect for bow/tf-idf with bpnn approach and bow with svm approaches on 30% test data size. also, the bow/tf-idf with k-nn methods has a negative effect from stemming operation on 30% test data size. furthermore, fig. 6 describes the experimental results with the ministry of religious affairs tafsir as a corpus. 42 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 fig. 6: measurement of average precision and average accuracy on ministry of religious affairs dataset. as shown in fig. 6, it was found that the stemming process has a negative impact on bow/tf-idf with bpnn/svm approaches on 20% test data size. furthermore, the stemming process also has a negative impact on bow/tf-idf with bpnn approaches on 30% test data size. while the bow/tf-idf with svm approaches on 30% test data size has a positive impact from stemming operation. figure 7 shows the performance measurement of classification results for morals class on iqt dataset with 20% and 30% test data size. fig. 7: (a) morals class on iqt corpus with 20% test data size; (b) morals class on iqt corpus with 30% test data size. as shown in fig. 7, it was found that the stemming operation has provided negative results for bow/tf-idf with bpnn and bow with svm approaches on both test data sizes since there is a decrease in precision value. however, the stemming process has provided positive results for tf-idf with svm and bow/tf-idf with k-nn approaches on both test data size since there is an increase in precision and recall value. 43 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 figure 8 presents the performance measurement of classification results for al-quran class on iqt dataset with 20% and 30% test data size. fig. 8: (a) al-quran class on iqt corpus with 20% test data size; (b) al-quran class on iqt corpus with 30% test data size. based on fig. 8, similar to the previous class, the stemming process has provided negative results for bow/tf-idf with bpnn and bow with svm approaches on both test data size since there is a decrease in precision value. while the stemming operation has provided positive results for tf-idf with svm and bow/tf-idf with k-nn approaches on 20% test data size since there is an increase in precision values. figure 9 describes the performance measurement of classification results for previous nation class on iqt dataset with 20% and 30% test data size. fig. 9: (a) previous nation class on iqt corpus with 20% test data size; (b) previous nation class on iqt corpus with 30% test data size. according to fig. 9, it was found that the stemming operation provides a negative impact for bow/tf-idf with bpnn and svm approaches on 20% test data size since there is a decrease in precision and recall values. 44 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 figure 10 describes the performance measurement of classification results for morals class on quraish shihab tafsir dataset, fig. 11 shows the results for al-quran class, while fig. 12 presents the results for the previous nation class. as shown in fig. 10, the stemming process provides a positive impact for bow/tfidf with k-nn and tf-idf with svm approaches on 20% test data size since there is an increase in precision and recall values. furthermore, fig. 11(a) shows that stemming operation provides a negative impact for bow/tf-idf with bpnn and bow with svm approaches since there is a decrease in precision values, otherwise fig. 11(b) presents that the stemming operation provides a positive impact for bow/tf-idf with bpnn and bow with svm approaches since there is an increase in precision and recall values. fig. 10: (a) morals class on quraish shihab tafsir corpus with 20% test data size; (b) morals class on quraish shihab tafsir corpus with 30% test data size. fig. 11: (a) al-quran class on quraish shihab tafsir corpus with 20% test data size; (b) al-quran class on quraish shihab tafsir corpus with 30% test data size. 45 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 fig. 12: (a) previous nation class on quraish shihab tafsir corpus with 20% test data size; (b) previous nation class on quraish shihab tafsir corpus with 30% test data size. figure 13 shows the performance measurement of classification results for morals class on ministry of religious affairs indonesia dataset, fig. 14 presents the results for al-quran class, while fig. 15 provides the results for the previous nation class. as shown in fig. 13(a), it was found that the stemming operation provides a negative impact for bow with bpnn/svm approaches since there is a decrease in precision and recall values. this result is inverse compared to classification results for al-quran class with bow, and bpnn/svm approaches, as shown in fig. 14(b). furthermore, the stemming process also provides a negative impact on all approaches to classify the instances in previous nation class, as shown in fig. 15(a) and (b). fig. 13: (a) morals class on ministry of religious affairs tafsir corpus with 20% test data size; (b) morals class on ministry of religious affairs tafsir corpus with 30% test data size. 46 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 fig. 14: (a) al-quran class on ministry of religious affairs tafsir corpus with 20% test data size; (b) al-quran class on ministry of religious affairs tafsir corpus with 30% test data size. fig. 15: (a) previous nation class on ministry of religious affairs tafsir corpus with 20% test data size; (b) previous nation class on ministry of religious affairs tafsir corpus with 30% test data size. 5. conclusions based on our experimental results, as shown in fig. 4 to fig. 6, it was found that the stemming operation provides positive outcomes for k-nn with bow approach to perform instance classification on 20% test data size. furthermore, in this test data size, it was also found that the stemming process supplies a negative influence for instance classification 47 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 with svm and bow, bpnn and bow, and bpnn with tf-idf. svm and tf-idf with stemming operation own the best classification performance, i.e., 70.75% for average accuracy and 71.55% for average precision in iqt dataset. while in the 30% test data size, it was found that stemming operation provides a negative impact on precision for k-nn with bow approach to classify the instances. however, the stemming process was able to provide a positive effect on accuracy for instance classification with svm and tf-idf. svm and tf-idf with stemming process own the best classification performance, i.e., 67.30% for average accuracy and 68.10% for average precision in ministry of religious affairs indonesia dataset. in this study, it was also discovered that the bpnn has the most average precision and average accuracy reduction due to the negative impact of stemming operations. acknowledgement the authors would like to thank the financial support from universitas amikom purwokerto; and center for advanced computing technology (c-act), faculty of information and communications technology, universiti teknikal malaysia melaka (utem) for their assistance in this research. references [1] utomo fs, suryana n, azmi ms. (2019). new instances classification framework on quran ontology applied to question answering system. telkomnika, 17(1): 139–146. http://dx.doi.org/10.12928/telkomnika.v17i1.9794 [2] cimiano p. (2006). ontology learning and population from text: algorithms, evaluation and applications. new york, springer science & business media. doi: 10.1007/978-0-38739252-3 [3] xian g, li j, kou y, luo t, huang y. (2018). construction and application of upper country ontology based on owl and skos. in proceedings of the 2nd international conference on computer science and application engineering: 22-24 october 2018; hohhot. pp 1–6. doi: 10.1145/3207677.3278056 [4] buranarach m, supnithi t, thein ym, ruangrajitpakorn t, rattanasawad t, wongpatikaseree k, lim ao, tan y, assawamakin a. (2016). oam: an ontology application management framework for simplifying ontology-based semantic web application development. international journal of software engineering and knowledge engineering, 26(1): 115–145. doi: 10.1142/s0218194016500066 [5] mitzias p, riga m, kontopoulos e, stavropoulos tg, andreadis s, meditskos g, kompatsiaris i. (2016). user-driven ontology population from linked data sources. in communications in computer and information science. volume 649. edited by ngonga ngomo ac., křemen p. prague, springer; 31–41. [6] hakkoum a, raghay s. advanced search in the qur’an using semantic modeling. (2015). in ieee/acs 12th international conference of computer systems and applications (aiccsa): 17-20 november 2015; marrakech. pp. 1–4. doi: 10.1109/aiccsa.2015. 7507259 [7] periamalai nsha, mustapha a, alqurneh a. (2016). an ontology for juz’ amma based on expert knowledge. in 7th international conference on computer science and information technology (csit): 13-14 july 2016; amman. pp. 1–5. doi: 10.1109/csit.2016.7549480 [8] zailani sam, omar na, mustapha a, rahim mha. (2018). fasting ontology in pillars of islam. indonesian journal of electrical engineering and computer science, 12(2): 562–569. doi: 10.11591/ijeecs.v12.i2.pp562-569 [9] ta’a a, abed qa, ali bm, ahmad m. (2016). ontology-based approach for knowledge retrieval in al-quran holy book. international journal of computational engineering research (ijcer) ontology-based, 6(3): 8–15. 48 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 [10] afifi m, safee m, saudi mm, pitchay sa, ridzuan f, basir n, saadan k, nabila f. (2018). hybrid search approach for retrieving medical and health science knowledge from quran. international journal of engineering & technology, 7: 69–74. doi: 10.14419/ijet.v7i4.15. 21374 [11] jabbar a, iqbal s, khan mug, hussain s. (2018). a survey on urdu and urdu like language stemmers and stemming techniques. artificial intelligence review, 49(3): 339–373. doi: 10.1007/s10462-016-9527-1 [12] jabbar a, iqbal s, akhunzada a, abbas q. (2018). an improved urdu stemming algorithm for text mining based on multi-step hybrid approach. journal of experimental and theoretical artificial intelligence, 30(5): 703–723. https://doi.org/10.1080/0952813x.2018.1467495 [13] kassim mn, jali shm, maarof ma, zainal a. (2019). towards stemming error reduction for malay texts. lecture notes in electrical engineering, 481: 13–23. doi: 10.1007/978-981-132622-6_2 [14] uysal ak, gunal s. (2014). the impact of preprocessing on text classification. information processing and management, 50(1): 104–112. http://dx.doi.org/10.1016/j.ipm.2013.08.006 [15] sharma d, jain s. (2015). evaluation of stemming and stop word techniques on text classification problem. international journal of scientific research in computer science and engineering, 3(2): 1–4. [16] hamed sk, ab aziz mj. (2018). classification of holy quran translation using neural network technique. journal of engineering and applied sciences, 13(12): 4468–4475. doi: 10.3923/jeasci.2018.4468.4475 [17] hamed sk, ab aziz mj. (2016). a question answering system on holy quran translation based on question expansion technique and neural network classification. journal of computer science, 12(3): 169–177. doi: 10.3844/jcssp.2016.169.177 [18] rostam nap, malim nhah. (in press). text categorisation in quran and hadith: overcoming the interrelation challenges using machine learning and term weighting. journal of king saud university computer and information sciences. https://doi.org/10.1016/j.jksuci.2019.03.007 [19] pane ra, mubarok ms, huda ns, adiwijaya. (2018). a multi-lable classification on topics of quranic verses in english translation using multinomial naive bayes. in proceedings of the 6th international conference on information and communication technology (icoict): 3-5 may 2018; bandung. pp. 481–484. doi: 10.1109/icoict.2018.8528777 [20] wahbeh a, al-kabi m, al-radaideh q, al-shawakfa e, alsmadi i. (2011). the effect of stemming on arabic text classification. international journal of information retrieval research, 1(3): 54–70. doi: 10.4018/ijirr.2011070104 [21] sallam rm, mousa hm, hussein m. (2016). improving arabic text categorization using normalization and stemming techniques. international journal of computer applications, 135(2): 38–43. doi: 10.5120/ijca2016908328 [22] taghva k, elkhoury r, coombs j. (2005). arabic stemming without a root dictionary. in proceedings of the international conference on information technology: coding and computing (itcc): 4-6 april 2005; las vegas. pp. 152–157. doi: 10.1109/itcc.2005.90 [23] tashaphyne: arabic light stemmer [https://pypi.org/project/tashaphyne/]. [24] hidayatullah af, ratnasari ci, wisnugroho s. (2016). analysis of stemming influence on indonesian tweet classification. telkomnika, 14(2): 665–673. doi: 10.12928/ telkomnika.v14i2.3113 [25] asian j. (2007). effective techniques for indonesian text retrieval. phd thesis. rmit university, school of computer science and information technology. [26] singh j, gupta v. (2017). a systematic review of text stemming techniques. artificial intelligence review, 48(2): 157–217. doi: 10.1007/s10462-016-9498-2 [27] tala fz. (2003). a study of stemming effect on information retrieval in bahasa indonesia. master thesis. universiteit van amsterdam, institute for logic, language and computation. [28] kusumaningrum r, adhy s, suryono s. (2018). wcloudviz: word cloud visualization of indonesian news articles classification based on latent dirichlet allocation. telkomnika, 16(4): 1752–1759. doi: 10.12928/telkomnika.v16i4.8194 49 iium engineering journal, vol. 21, no. 1, 2020 setyo utomo et al. https://doi.org/10.31436/iiumej.v21i1.1170 [29] darmawiguna igm, pradnyana ga, santyadiputra gs. (2019). the development of integrated bali tourism information portal using web scrapping and clustering methods. journal of physics: conference series, 1165(1): 1–10. doi: 10.1088/1742-6596/1165/1/ 012010 [30] tahitoe ad, purwitasari d. (2010). implementasi modifikasi enhanced confix stripping stemmer untuk bahasa indonesia dengan metode corpus based stemming. undergraduate thesis. institut teknologi sepuluh november (its), informatics engineering department. [31] arifin az, mahendra ipak, ciptaningtyas ht. (2009). enhanced confix stripping stemmer and ants algorithm for classifying news document in indonesian language. proceeding of international conference on information & communication technology and systems (icts). pp. 149-158. [32] schneider mj, gupta s. (2016). forecasting sales of new and existing products using consumer reviews: a random projections approach. international journal of forecasting, 32(2): 243–256. doi: 10.1016/j.ijforecast.2015.08.005 [33] chen g, xiao l. (2016). selecting publication keywords for domain analysis in bibliometrics: a comparison of three methods. journal of informetrics, 10(1): 212–223. http://dx.doi.org/10.1016/j.joi.2016.01.006 [34] kurnia i, sopian t, suryana y, makbul, nugraha s, al-ghifari, mm, abdullah r. (2012). alqur’an cordoba, 1st ed. bandung, cordoba: internasional indonesia. 50 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <feff04180437043f043e043b043704320430043904420435002004420435043704380020043d0430044104420440043e0439043a0438002c00200437043000200434043000200441044a0437043404300432043004420435002000410064006f00620065002000500044004600200434043e043a0443043c0435043d04420438002c0020043f043e04340445043e0434044f044904380020043704300020043d04300434043504360434043d043e00200440043004370433043b0435043604340430043d0435002004380020043f04350447043004420430043d04350020043d04300020043104380437043d0435044100200434043e043a0443043c0435043d04420438002e00200421044a04370434043004340435043d043804420435002000500044004600200434043e043a0443043c0435043d044204380020043c043e0433043004420020043404300020044104350020043e0442043204300440044f0442002004410020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e0030002004380020043f043e002d043d043e043204380020043204350440044104380438002e> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 experimental and finite element analysis of solvent cast poly(lactic acid) thin film blends sharifah imihezri syed shaharuddin*, abdul rahman mukhtar, nur atiqah mohd akhir, norhashimah shaffiar, maizatulnisa othman department of manufacturing and materials engineering, kulliyyah of engineering, international islamic university malaysia, kuala lumpur, malaysia. *corresponding author: shaimihezri@iium.edu.my (received: 21th march 2019; accepted: 14th july 2019; published on-line:2nd december 2019) abstract: a combined experimental and finite element analysis (fea) investigation was performed to study the effect of incorporating poly(propylene carbonate)(ppc) and curcumin on the mechanical properties of poly(lactic acid) (pla). in addition, the chemical interaction and morphological changes brought upon by each subsequent additive were also observed. the addition of ppc at 30 wt% into pla causes a decrease in strength and modulus by 51% and 68% respectively whilst inducing higher elongation by 74%. the resultant decrease in strength and modulus of the pla/ppc blend was recovered by adding a low weight percentage (1 wt%) of curcumin. the images of the fractured surfaces via scanning electron microscope (sem) revealed the brittle-ductilebrittle progression of pla due to the addition of ppc and curcumin which corroborates the findings from the tensile test. fourier-transform infrared spectroscopy (ftir) revealed that the addition of ppc by 30 wt % resulted in chemical interaction between the carbonyl groups of pla and ppc as the c=o peak of pla slightly shifted to a lower wavenumber. the presence of curcumin peaks however was found to be difficult to be identified in the pla/ppc/curcumin blend. the simulated results for the stress-strain profile using fea agreed well with the experimental tensile test profile with a relatively low percentage error of less than 6%. therefore, it was concluded that for these compositions, the developed model can be used for further simulation works to design biomedical devices. abstrak: gabungan penyelidikan secara eksperimen dan analisis unsur terhad (fea) telah dijalankan bagi mengkaji kesan campuran poli (propilen karbonat) (ppc) dan kurkumin pada sifat mekanikal poli (asid laktik) (pla). tambahan, interaksi kimia dan perubahan morfologi pada setiap penambahan berikutnya turut diperhatikan. penambahan ppc pada 30 wt% ke dalam pla menyebabkan pengurangan pada tenaga dan modulus sebanyak 51% dan 68% masing-masing sementara menyebabkan kenaikan pemanjangan sebanyak 74%. hasil pengurangan pada tenaga dan modulus campuran pla/ppc diseimbangkan dengan mencampurkan peratus kurkumin kurang berat (1 wt%). melalui mikroskop imbasan elektron (sem), didapati imej permukaan retak menunjukkan pla berturutan rapuh-mulur-rapuh disebabkan penambahan ppc dan kurkumin di mana ianya menyokong dapatan kajian ini melalui ujian kekuatan tegangan. spektroskopi inframerah jelmaan fourier (ftir) menunjukkan dengan penambahan ppc sebanyak 30 wt %, interaksi kimia antara kumpulan karbonil pla dan ppc pada puncak c=o pla telah berubah sedikit kepada nombor gelombang lebih kecil. walau bagaimanapun, kehadiran puncak kurkumin adalah sukar dikenal pasti dalam campuran pla/ppc/kurkumin. dapatan hasil simulasi pada profil strain-tekanan menggunakan fea adalah sama dengan ujian kekuatan tegangan dengan peratus ralat yang agak rendah iaitu kurang daripada 6%. 197 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 oleh itu, komposisi model yang dibangunkan ini adalah sesuai bagi meneruskan kerjakerja simulasi iaitu bagi mereka bentuk alat biomedikal. keywords: pla; ppc; curcumin; tensile; fea 1. introduction poly(lactic acid) (pla), recently, has been the main thermoplastic polymer candidate for applications that require tailored biodegradability feature such as in the biomedical as well as food and packaging industry [1]. the biomedical application of pla is due to its ability to fulfil complex requirements in terms of biodegradability, and thermoplastic processability [2, 3]. in comparison to other traditionally studied biodegradable polymers, pla is able to provide excellent features at low cost [4]. pla offers good thermal processability, thus, the polymer can be processed via various techniques such as injection moulding, film extrusion, blow moulding and fiber spinning. despite the polymer’s copious advantages, the application of pla has been restricted to a certain extent due to its inherent brittleness, hydrophobicity, poor heat resistance and poor degradation rate [5,6]. specifically, one of the main drawbacks of pla for biomedical application is attributed to its high brittleness [7], since it reduces the flexibility and plasticity [8] of the polymer. the brittleness of pla is a result of the formation of large spherulites due to its slow crystallization rates [9]. a simple and efficient method to modify the flexibility, strength, processability, and impact toughness of pla is by blending with various plasticizers such as poly(propylene carbonate) (ppc) [10,11], polyethylene glycol (peg) [12,7], glucosemonoesters , poly(vinyl acetate) (pvac) [13], and partial fatty acid esters. the biodegradable poly(propylene carbonate) (ppc) is synthesized from copolymerization of renewable co2 and propylene oxide (po) and is typically amorphous [14]. ppc has a chemical structure akin to that of pla as shown in fig. 1. the polymer offers good mechanical property, in particular ductility that could be used to improve the toughness of pla [11]. in comparison to pla, ppc has a relatively low glass transition temperature (around 35 °c) due to the lack of a strong polar group in its chain, therefore enabling the ppc chain segment to move easily [15]. hence, ppc displays a very flexible structure. the polymer‘s elongation at break is nearly 330%, which is at least five-fold greater in comparison to other polyesters [16]. (a) (b) fig. 1: the chemical structure of (a) polylactic acid, pla and (b) poly(propylene carbonate), ppc [11]. curcumin, an orange-yellow crystalline powder with a chemical structure shown in fig. 2 is prepared from solvent extraction followed by purification of ground rhizomes of turmeric [17]. curcumin is commonly used in various applications such as foods and cosmetics. due to its medicinal properties, there is a high tendency for curcumin to be used in medical applications for antibacterial, antitumor, and antioxidant purposes [18-21]. the bioactivities of curcumin such as anti-cell adhesion and motility, anti-angiogenesis and antimicrobe properties have been elucidated in in vivo/in vitro studies [22]. various curcumin/polymer blends have been electrospun into nanoscale fiber scaffolds or mats [21, 198 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 23]. several studies of wounded animals treated with pla/curcumin nanofiber mats have been noticed to undergo improved wound closure rates [24, 25] fig. 2: the chemical structure of curcumin [26]. thin films often experience very high stresses during service which leads to distortion or deformation [27]. finite element analysis (fea) provides insight in identifying critical locations of the device (high stress/strain regions), reduces design iterations/optimization, and reduces the need for bench-top testing; thereby reducing the cycle time during product development [28]. fea has been used not only to model the mechanical properties [29,30] but also degradation performances [31,32] of various materials. previously, flat tension specimens of various ceramic matrix composites and monolithic ceramics have been studied via fea for creep performance [33]. this work was prompted by the scarcity of fea study on flat thin films subjected to uniaxial tensile tests. the motivation for this study is twofold: first, to study the effect of ppc and curcumin addition on pla upon its structural, morphological and mechanical properties, and second, to simulate the mechanical effect of ppc and curcumin addition in the elastic and plastic region using fea (abaqus). 2. methodology 2.1 sample preparation pla (ingeotm biopolymer 3052d) was obtained from nature-works (usa) whilst ppc (qpac 40) was sourced from empower materials (malaysia). analytical grade chloroform (r&m chemicals, united kingdom) was used as solvent. the curcumin (livewelltm) used in this study was manufactured by pahang pharmacy sdn. bhd. (malaysia). both pla and ppc pellets were dried at 70 °c and 40 °c respectively for 2 hrs in an oven prior to being dissolved in chloroform. subsequently, pla, ppc and curcumin were prepared at different weight % ratios (pla:ppc -100:0, pla:ppc 70:30 and pla:ppc:curcumin; 69:30:1). both pla and ppc were dissolved in chloroform at the ratio of 1:10. upon complete dissolution, curcumin was then added and stirred for 1 hour. each blend was then poured into a teflon covered container and was left to dry for 24 hours at ambient temperature. 2.2 ftir analysis identification of the functional groups of the pla and pla/ppc blends were obtained by using tensor 27 ftir spectrometer (bruker, usa). the spectra were collected within 4000 – 600 cm-1 region with a resolution of 4 cm-1 and 16 scans. 2.3 morphological observation the surface of the fractured tensile test specimens were sputtered with palladium using a quorum sc7620 sputter coater in order to make the surface conductive prior to sem analysis. the resulting surfaces were then observed via intouch scope jsm-it100 (jeol). 2.4 tensile test 199 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 the fea simulations for the studied polymers were based on the stress-strain response of the materials conducted according to astm d882. thin films were cut according to the following dimensions of 50 mm × 10 mm × 0.80 mm with an extra 10 mm at both ends for clamping purposes as shown in fig. 3. the grey tabs in this figure represent the glued cardboard strips of the same size, by which the sample is clamped between machine grips. tensile tests were performed using a shimadzu universal tensile machine (ags-10k nxd) at a crosshead speed of 20 min/mm with a load cell of 5 kn. the average and standard deviation of the mechanical properties were calculated from the load-elongation curve based on 5 samples. fig. 3: preparation of test specimen for tensile test. 2.5 simulation model the fe model of the thin films were developed using abaqus software. the 3d model was discretized into a structured element mesh using 3d linear hexahedral elements (c3d8r) which resulted in total mesh and node values of 1562 and 700 respectively for all samples. a schematic representation of the tensile specimen as well as the boundary condition inflicted on the sample is shown in fig. 4. (a) (b) (c) fig. 4: (a) schematic representation of the specimen geometry (b) finite element mesh using 3d linear hexahedral elements (c3d8r) (c) boundary conditions for the simulation of the tensile test. in the actual tensile test, each specimen was clamped and displaced using hydraulic rigid grips. the additional length of 10 mm at each end of the sample functions as a grip length in which the top grip length will be displaced upward by the load cell whilst the bottom grip 200 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 length would be stationary. in order to replicate the experimental tensile test, the boundary and loading conditions were translated as follows [34]; the top grip length (10 mm) and sample test length (50 mm) were kept as fixed in all directions but unconstrained in the direction of the load applied. the top grip was loaded with an upward load of 5 kn. meanwhile, the bottom grip length had no degree of freedom. the average thickness of each sample was 0.8 mm. the constitutive material data for the elastic model in the simulation were defined by the experimental elastic modulus whilst poisson’s ratio was obtained from the literature [35] as shown in table 1. the plasticity model was included in the fea by defining the region of yield stress and corresponding plastic strain that were obtained from the experiment. there were no purposefully designed geometrical flaws such as notches or necking in the simulation model that would trigger localization of the specimen at any desired region. table 1: material properties used for the fea simulation element composition (wt%) young’s modulus (mpa) yield strength (mpa) poisson’s ratio neat pla 936 8.4 0.36 pla / plc (70:30 wt%) 156 3.5 0.36 pla / ppc / curcumin (69:30/1 wt%) 771 11.7 0.36 3. results and discussion 3.1 ftir figure 5 shows the ftir spectra of neat pla, ppc, and curcumin as well as their blends. the ftir detects the chemical interaction and compatibility between the molecular chains of different polymer blends by the shift and broadening of the absorption band [36]. the neat pla spectra shows characteristic stretching frequencies for c=o, –ch3 asymmetric, –ch3 symmetric, and c–o, at 1752 cm-1, 2995 cm-1, 2947 cm-1 and 1085 cm1, respectively. the ppc spectra shows the typical characteristic peaks at 2920 cm-1, 1746 cm-1, and 1235 cm-1 attributed to c-h bond stretching vibration, c=o bond stretching vibration and c-o stretching respectively. in the 3700 – 3100 cm-1 region, the absorption of neat ppc and pla is not identified due to the rarity of terminal o-h groups. the pla/ppc spectra in the high wavenumber region, (3100-2800 cm-1), relates to the -chstretching vibration, which shows similar absorption peaks as pristine pla. ma et al. [38] observed that the stretching vibration may shift with higher ppc loading dueto intermolecular interaction between c-h and o-cor between c-h and o=c-. pla is made from lactic acid and forms rich carbon chains that serve as the main functional group (c=o groups). the functional group is detectable at the frequency region of 1740-1750 cm-1 (denoted as ‘a’) [37]. the addition of 30 wt % ppc causes the c=o peak of pla at 1752 cm-1to slightly shift to a lower wavenumber cm-1 (by 3 cm-1). therefore, implying that the carbonyl groups may have taken part in the interaction between pla and ppc. such interaction could be between c-h…o=c-, c=o…o=c or c=o…o-c dipole-dipole interaction [38]. a more significant wavenumber shift of up to 11 cm-1 has been observed with higher ppc loading [38]. it was noted that there is no significant peak shift in the c-h bending (‘b’ region) as well as the c-o stretching vibration (‘c’ region). it was deduced that despite the similar chemical nature of pla and ppc, the addition of 30 wt% of ppc only resulted in chemical interaction between the carbonyl groups of these polymers. 201 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 fig. 5: fourier transform infrared (ftir) spectra of pla, ppc, pla/ppc, and pla/ppc/curcumin blends. curcumin can be distinguished by its phenolic o-h stretching band at 3508 cm-1 [26, 39]. other significant curcumin bands are the aromatic c-c band (1602 cm-1), olefinic c-h (1428 cm-1), asymmetric c-o-c (1026 cm-1) and phenolic c-o (1276 cm-1) [40, 39]. these significant peaks are found to be comparable and appear at 3507 cm-1, 1601 cm-1, 1428 cm1, 1026 cm-1 and 1274 cm-1 respectively. a sharp common peak at 1180 cm-1, assigned as phenolic c-o is observed in both curcumin and pla/ppc/curcumin, hence confirming the presence of curcumin in the blend. apart from the c-o phenolic peak, the lack of presence of other curcumin peaks observed in the pla/ppc/curcumin trace suggests that these curcumin peaks were either eclipsed by the more generous peaks of pla at that wavenumber range due to the higher weight % of pla [41]. the ftir samples for pla/ppc/curcumin were performed twice to confirm such a scenario. previously, chen et al. [42] reported that curcumin loading below 5% would not give any chemical reaction with pla. 3.2 tensile test the tensile test was conducted to investigate the mechanical effect of adding 30 wt% of ppc and 1% of curcumin at the expense of pla. figure 6 illustrates that the neat pla curve behaves linearly in the low strain, then starts to plastically deform in the region of 3% strain. the strain at break of neat pla in this study is 11.7% and is higher than the pla thin films studied by yao et al. [10]. aside from the grade of pla used, the difference in sample thickness, as well as testing speed [13], it is postulated that the strain value in this study may have also been affected by the sample preparation technique since the thin films in their study [10] were prepared by melt compounding. 202 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 fig. 6: stress-strain curves for neat pla, pla/ppc, and pla/ppc/curcumin. studies on pla/ppc blends by zao et al. [43] and yu et al. [44] suggest that the addition of 30 wt% of ppc creates the optimum blend after considering the resulting elongation and flexural and impact strength properties. in this study, the addition of 30 wt % of ppc into pla causes a decrease of strength and modulus by 51% and 68% respectively (table 2). the trend of decreasing tensile strength and young’s modulus upon blending of ppc into pla is well documented. studies by ma et al. [38] and zou et al. [43] show a decreasing trend in strength as well as of modulus with further loading of ppc. it is also seen that ppc contributes to the elastic component. as a result, a higher strain at break by 74% was achieved in the pla/ppc blend in this study. such an increase in strain value is manifested from the weak molecular chain interaction and the presence of plenty weak flexible, polar c–o–c bonds in the backbone structure of ppc [15, 43]. sun et al. [45] suggested that the transformation of pla from brittle to ductile nature indicates a good compatibility between pla and ppc as evidenced by the chemical interaction found in ftir. table 2: mechanical properties of neat pla, pla/ppc and pla/ppc/curcumin properties neat pla pla / ppc pla/ ppc/curcumin modulus (mpa) 481.3 ± 145.1 155.4 ± 26.9 726.7 ± 62.4 strength (mpa) 15.3 ± 2.8 7.4 ± 0.3 11.0 ± 1.1 strain at break (%) 11.7 ± 3.3 20.4 ± 1.4 2.4 ± 0.7 the addition of 1 wt % of curcumin significantly improves the strength and modulus of pla/ppc, hence suggesting that the curcumin particles act as reinforcement filler. the presence of curcumin creates resistance that reduces the mobility of internal pla/ppc structures and resulted in an enhanced stiffness property. however, the inclusion of filler also increases the polymer blends’ brittleness characteristics [46]. as seen here, when the pla/ppc/curcumin was subjected to tensile-mode deformation, the samples failed at very low tensile strain. the composition of curcumin was restricted to only 1 wt% in this study since previous study by the author [47] has shown a decreasing trend in strength with further curcumin additions. an obvious decrease in the tensile strength at higher filler content is 203 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 likely to occur as the filler-matrix interaction is replaced by the contact between particles as well as filler agglomeration [46, 48]. 3.3 surface morphology the photographs of the dried polymer blend films are shown in fig. 7. the addition of ppc into pla increases opacity whilst the addition of curcumin imparts yellowish hue due to the bioactive yellow pigment from curcumin with the following structure; 1,7-bis(4hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione. fig. 7: from left to right, fractured tensile test specimens of pla, pla/ppc, and pla/ppc/curcumin. the morphological structure of the pla blend was examined via sem, and the results are shown in fig. 8. the sem image of neat pla exhibited the fractured surface that occurs at different layers and at different parts of the sample. similar surface topography was observed from other studies [13, 49] that confirms the brittle nature of pla. the blending of ppc into pla creates a surface fracture that is much smoother with no visible aggregation. such effect signals good dispersion and homogeneity in the blended films. the transition of the pla and pla/ppc samples from rough to smooth surface are in agreement with the observations made from the mechanical properties, in which the neat pla progresses from a brittle to a ductile nature with the decrease in stiffness and an increase in strain values. in comparison, the addition of curcumin induces a much rougher fractured surface with a phase-separated morphology. it was observed that the dispersed curcumin particles created almost spherical and empty voids at the fractured surface. the change in the fractured surface of pla/ppc blend from smooth to rough correlates to the effect of filler particle addition that changes the pla/ppc from being ductile to a more brittle nature [46]. fig. 8: sem micrographs at 1000x magnification of the surfaces of the fractured (a) neat pla (b) pla/ppc (c) pla/ppc/curcumin films subjected to uniaxial tensile stress. 204 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 3.4 finite element analysis of the tensile test the results from fe simulations are compared to the experimental data in fig. 9 fig. 11. the graphs obtained show that the simulated stress-strain behaviour (overall shape) in the elastic and plastic region are in excellent agreement with the experimental data for all compositions studied. the damage criterion model was not implemented in this fea model, hence the simulation and experimental work are comparable up to the ultimate tensile strength (maximum stress) only. the convergence between the simulation and experimental results near the maximum stress value indicates the reliability of the model since the maximum stress value is generally used as a criteria in design. the accuracy of the experimental and simulated model was obtained by comparing the integrated area beneath the stress-strain curves. simulation performed using abaqus fea models described accurate results with a relatively low percentage error of 1% for both pla as well as pla/ppc and 6% for pla/ppc/curcumin. fig. 9: stress-strain curves obtained experimentally and via fea for neat pla. fig. 10: stress-strain curves obtained experimentally and via fea for pla/ppc. 205 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 fig. 11: stress-strain curves obtained experimentally and via fea for pla/ppc/curcumin. (a) (b) (c) fig. 12: contour plots of computed von mises stress along the specimen length for (a) neat pla, (b) pla/ppc blend and (c) pla/ppc/curcumin blend. figure 12 shows the distribution of von mises stress calculated by the finite element model based on young's modulus, poisson ratio, boundary conditions as well as applied load. similar topography of low to high von mises stress was obtained for all compositions studied. it can be seen from fig. 13 that the stress distribution is divided into three regions. the first region undergoes no stress since it is the area under grip length, and hence was not deformed. the second region, is noted as the transition phase in which the stress starts to increase. it is also noted that the fe model highlighted the highest von mises stress in this transition region between grip and gage length which may indicate the location that possibly initializes the fracture [33]. the model postulated that fracture may occur at either end of the grip length since there were no purposefully designed geometrical flaws such as notches or necking in the simulation model that would trigger localization of the specimen at any desired region. the fe model shows that the addition of ppc into pla increases the von mises stress scale from 1400 mpa to 300 gpa. whilst the addition of curcumin particles into pla/ppc blends resulted with reduced von mises stress distribution (640 mpa). the values for young's modulus used for the fe analysis were 936 mpa, 156 mpa and 771 mpa 206 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 for pla, pla/ppc and pla/ppc/curcumin respectively. the young’s modulus property influences the stress distribution and hence the elastic deformation of the model [50]. thus, as the young's modulus of the sample increases or decreases, correspondingly the upward tensile force respectively causes less or more stress due to the material’s resistibility to deformation. fig. 13: identified regions of von mises stress. 4. conclusion the ftir analysis illustrated that the chemical interaction, in particular between the carbonyl group (c=o), exists when ppc was added at 30 wt% into pla. despite the resultant decrease in strength and modulus, the strain at break increased by 74%. the drop in strength and modulus of pla/ppc blend was recovered by adding a low weight percentage of curcumin. however, the pla/ppc/curcumin blend failed at very low tensile strain which shows the increase in the brittle nature of the blend. in light of this observation, it was further confirmed by sem images that the addition of ppc and curcumin respectively increases its ductility and brittleness. the validation and the excellent agreement between the simulation and experimental results are important indices of the simulated model developed using abaqus. hence, this model can be used to predict the performance of complex design components based on pla/ppc/curcumin blends for biomedical applications. acknowledgement this work was fully supported by the international islamic university malaysia (iium), (rigs17-052-0627). the authors would like to express their deepest gratitude to facilities and technical assistance provided by the international institute for halal research and training (inhart), iium. references [1] suping l, darrel u. (2009) degradability of polymers for implantable biomedical devices. int j mol sci., 9 (10): 4033-4065. [2] kaojin w, satu s, julian xxz. (2017) a mini review: shape memory polymers for biomedical applications. front chem sci eng., 11(2): 143-153. [3] rajendra pp, sunil ut, suresh us, jalinder tt, abraham jd. (2014) biomedical applications of poly(lactic acid). recent pat regen med., 1(4): 240-251. [4] kotiba h, mosab k, yang hw, fawaz d, young gk. (2015) properties and medical applications of polylactic acid: a review. polym lett., 9(5):435–455. [5] broz m, david lv, newell rw. (2003) structure and mechanical properties of poly(d,llactic acid)/poly( -caprolactone) blends. biomat., 24:4181-4190. region 1 region 2 region 3 maximum von mises stress 207 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 [6] erin h, margaret f. (2014) increasing surface hydrophilicity in poly(lactic acid) electrospun fibers by addition of pla-β-peg co-polymers. j eng fiber fabr., 9(2):153164. [7] feng-jiao l, shui-dong z, ji-zhao l, jun-zhe w. (2015) effect of polyethylene glycol on the crystallization and impact properties of polylactide-based blends. polym. adv. technol., 26(5):465-475. [8] yanping l, hanghang w, zhen w, qian l, nan t. (2018) simultaneous enhancement of strength and toughness of pla induced by miscibility variation with pva. polymers, 10 (10):1178-1191 [9] ahmed mohamed e. (2014) the effect of additives interaction on the miscibility and crystal structure of two immiscible biodegradable polymers. polimeros, 24(1):9-16. [10] yao m, deng h, mai f, wang k, zhang q, chen f, fu q. (2011) modification of poly(lactic acid)/poly(propylene carbonate) blends through melt compounding with maleic anhydride. polym lett., 5(11):937-949. [11] sheng-xue q, cui-xiang y, xue-yang c, hai-ping z, lifen z. (2018) fully biodegradable poly(lactic acid)/poly(propylene carbonate) shape memory materials with low recovery temperature based on in situ compatibilization by dicumyl peroxide. chinese j polym sci., 36:783-790. [12] mihir s, ananda kumar r, vipul d, richard ag, stephen pm. (1997). biodegradable polymer blends of poly(lactic acid) and poly(ethylene glycol). j appl polym sci., 66:14951505. [13] wannapa c, varaporn t, jean-francois p, pamela p. (2012) effect of poly(vinyl acetate) on mechanical properties and characteristics of poly(lactic acid)/natural rubber blends. j polym environ., 21:450-460. [14] baherah b, yanwei m, fariba d (2015). antimicrobial packaging for biomedical applications from a biodegradable polymer in asia pacific confederation of chemical engineering congress 2015; melbourne, australia. [15] youhua t, xianhong w, xiaojiang z, ji l, fosong w. (2006) crosslinkable poly(propylene carbonate): high-yield synthesis and performance improvement. j polym sci., 44:53295336. [16] iman m, ali f, hesham b, sean ryan d, ali negahi s, fariba d. (2016) biomedical applications of biodegradable polyesters. polymers, 8(1):20-52. [17] dalbir s, sharma s, davinder pal singh o, idress ahmed w. (2010) effect of extraction parameters on curcumin yield from turmeric. j food sci. technol., 47(3):300-304. [18] david e r, biotechnology 2, global prospects, florida: crc press, 2011. [19] bharat a, bokyung s. (2009) pharmacological basis for the role of curcumin in chronic diseases: an age-old spice with modern targets. trends pharmacol sci., 30(2):85-94. [20] sahdeo p, amit tyagi k, bharat a. (2014) recent developments in delivery, bioavailability, absorption and metabolism of curcumin: the golden pigment from golden spice. cancer res. treat., 46(1): 2-18. [21] nithya r, tamil selvan n, sheeja r. (2015) preparation and characterization of electrospun curcumin loaded poly(2-hydroxyethyl methacrylate) nanofiber-a biomaterial for multidrug resistant organisms. j biomed mater res., 103(1):16-24. [22] xia f, chun z, dong-bu l, jun y, hua-ping l. (2013) the clinical applications of curcumin: current state and the future. curr pharm des., 19:11-13. [23] xiao-zhu s, gareth r w, xiao-xiao h, li-min z. (2013) electrospun curcumin-loaded fibers with potential biomedical applications. carbo polym., 94:147-153. [24] thuy thi t n, chiranjit g, seong gu h, tran dai l, jun seo p. (2013) characteristics of curcumin –loaded poly(lactic) nanofibers for wound healing. j mater sci, 48:7125-7133 [25] bhaarathi d, saraswathy n, ramasamy m, ponnusamy s, palanisamy v, sukumar v, venugopal r. (2013) electrospinning of curcumin loaded chitosan/poly (lactic acid) nanofilm and evaluation of its medicinal characteristics. front mat sci., 7(4):350-361. [26] heni r, yulia lie y, annisa r, noboyuki m. (2016) curcumin-loaded pla nanoparticles: formulation and physical evaluation. sci pharma., 84(1):191-202. 208 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 [27] li-mei j, yi-chun z, yongli h. (2010) elastic-plastic properties of thin film on elasticplastic substrates characterized by nanoindentation test. t nonferr metal soc., 20(12):2345-2349. [28] senthil e, ashley kelley j, jorgen b, virginia l g (2011). material modeling of polylactide, in simulia customer conference, barcelona, spain, 2011. [29] harpen l, ahmed i, felfel rm, qian c. (2012) finite element modelling of the flexural performance of resorbable phosphate glass fibre reinforced pla composite bone plates. j mech behav biomed mater., 15:13-23. [30] anna b, susana pf, jose-ramon s, wang w, peter em. (2015) computational bench testing to evaluate the short-term mechanical performance of a polymeric stent. cardio eng tech., 6(4):519-532. [31] andrea costa v, antonio t. m, rui miranda g, volnei t. (2011) material model proposal for biodegradable materials. procedia eng., 10:1597-1602. [32] joao silve s, james e m, kumbakonan rr. (2008) constitutive framework for biodegradable polymers with applications to biodegradable stents. asaio j., 54(3): 295301. [33] link re, garrell mg, albert s, edgar lc, ronald s. (2003) finite-element analysis of stress concentration in astm d 638 tension specimens. j test eval., 31(1):1-6. [34] mayank n, anurag d, misra r k, harlal singh m. (2014) tensile test simulation of cfrp test specimen using finite elements. procedia mat sci., 5:267-273. [35] jonathan t, jose c, justin k, ali pg. (2015). mechanical property optimization of fdm pla in shear with multiple objectives. jom., 67(5):1183-1193. [36] shuwen p, xiuyan w, lisong d. (2005) special interaction between poly (propylene carbonate) and corn starch. polymer composite, 26:37-41. [37] kurniawan y, yohanes aris p, setyo p, bruce a w, hadi karia p, titi candra s. (2015) infrared and raman studies on polylactide acid and polyethylene glycol-400 blend. in aip conference proceedings of the third international conference on advanced materials science and technology (icamst 2015): 6-7 oct 2015; semarang. edited by sutikno, khairurrijal, heru susanto, risa suryana, kuwat triyana and markusdiantoro, aip publishing; pp 0201011-0201016. [38] xiaofei m, jiugao y, ning w. (2006) compatibility characterization of poly(lactic acid)/poly(propylene carbonate) blends. j polym sci pt b., 44: 94-101. [39] rosana aparecida da s, mateus ferreira de s, daniela o, evandro b. (2016) preparation of curcumin-loaded nanoparticles and determination of the antioxidant potential of curcumin after encapsulation. polimeros, 26(3):207-214. [40] harshal ashok p, karde m, mundle n, jadhav p. (2014) phytochemical evaluation and curcumin content determination of turmeric rhizomes collected from bhandara district of maharashtra (india). med. chem., 4(8):588-591. [41] duong quang l, trang m, thi thu t n, thi ngoan n, thi cham b, nguyen hai b, thi bich h p, tran dai l, jun seo p. (2012) a novel nanofiber cur-loaded polylactic acid constructed by electrospinning. adv nat sci-nanosci., 3:1-5. [42] yan c, jie l, yanna f, hongbo w. (2010) preparation and characterization of electrospinning pla/curcumin composite membranes. fib polym., 11(8):1128–1131. [43] wei z, rongyuan c, guizhen z, haichen z. (2016) mechanical, thermal and rheological properties and morphology of poly (lactic acid)/poly (propylene carbonate) blends prepared by vane extruder. polym adv technol,. 27(11): 1430-1437. [44] cuixiang y, ruirui z, haiyue w. (2018) the mechanical property of pla/ppc blends. int j trend res dev., 5(2):206-208. [45] qirui s, tizazu m, manjusri m, amar m. (2016) novel biodegradable cast film from carbon dioxide based copolymer and poly(lactic acid). j polyms environ., 24(1):23-36. [46] nurdina abdul k, mariatti j, samayamutthirian p. (2009) effect of single-mineral filler and hybrid-mineral filler additives on the properties of polypropylene composites. j vinyl addit techn., 15(1):20-28. 209 iium engineering journal, vol. 20, no. 2, 2019 syed shaharuddin et al. https://doi.org/10.31436/iiumej.v20i2.1119 [47] sharifah imihezri s s, qairol a a b, noor azlina h, nor khairusshima mk. (2017) thermal, structural and mechanical properties of melt drawn curloaded poly(lactic acid) fibers. procedia eng., 184:544 551. [48] zhao w, xiangling l, min z, wei y, mingbo y. (2017). synthesis of an efficient processing modifier silica-g-poly (lactic acid)/poly (propylene carbonate) and its behavior for poly (lactic acid)/poly (propylene carbonate) blends. ind eng chem res., 56 (49):1470414715. [49] baki h. (2014). the properties of pla/oxidized soybean oil polymer blends. j polym environ., 22(2):200-208. [50] yongtao w, liming k, sizhuo s, yuxing d, zhong g, zhirui y, qigang z. (2013) finite element analysis on von mises stress distributions of si dsp. mater sci semicond process., 16(1):165-170. 210 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <feff0054006f0074006f0020006e006100730074006100760065006e00ed00200070006f0075017e0069006a007400650020006b0020007600790074007600e101590065006e00ed00200064006f006b0075006d0065006e0074016f002000410064006f006200650020005000440046002000760068006f0064006e00fd006300680020006b0065002000730070006f006c00650068006c0069007600e9006d0075002000700072006f0068006c00ed017e0065006e00ed002000610020007400690073006b00750020006f006200630068006f0064006e00ed0063006800200064006f006b0075006d0065006e0074016f002e002000200056007900740076006f01590065006e00e900200064006f006b0075006d0065006e0074007900200050004400460020006c007a00650020006f007400650076015900ed007400200076002000610070006c0069006b0061006300ed006300680020004100630072006f006200610074002000610020004100630072006f006200610074002000520065006100640065007200200036002e0030002000610020006e006f0076011b006a016100ed00630068002e> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <feff004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e004b006f0072007a0079007300740061006a010500630020007a00200074007900630068002000750073007400610077006900650144002c0020006d006f017c006e0061002000740077006f0072007a0079010700200064006f006b0075006d0065006e00740079002000410064006f00620065002000500044004600200070006f007a00770061006c0061006a01050063006500200077002000730070006f007300f300620020006e00690065007a00610077006f0064006e0079002000770079015b0077006900650074006c00610107002000690020006400720075006b006f00770061010700200064006f006b0075006d0065006e007400790020006600690072006d006f00770065002e00200020005500740077006f0072007a006f006e006500200064006f006b0075006d0065006e0074007900200050004400460020006d006f017c006e00610020006f007400770069006500720061010700200077002000700072006f006700720061006d0061006300680020004100630072006f00620061007400200069002000410064006f0062006500200052006500610064006500720020007700200077006500720073006a006900200036002e00300020006f00720061007a002000770020006e006f00770073007a00790063006800200077006500720073006a00610063006800200074007900630068002000700072006f006700720061006d00f30077002e> /ptb <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> /rum <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> /rus <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> /sky <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> /slv <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> /suo <feff004b00e40079007400e40020006e00e40069007400e4002000610073006500740075006b007300690061002c0020006b0075006e0020006c0075006f0074002000410064006f0062006500200050004400460020002d0064006f006b0075006d0065006e007400740065006a0061002c0020006a006f0074006b006100200073006f0070006900760061007400200079007200690074007900730061007300690061006b00690072006a006f006a0065006e0020006c0075006f00740065007400740061007600610061006e0020006e00e400790074007400e4006d0069007300650065006e0020006a0061002000740075006c006f007300740061006d0069007300650065006e002e0020004c0075006f0064007500740020005000440046002d0064006f006b0075006d0065006e00740069007400200076006f0069006400610061006e0020006100760061007400610020004100630072006f0062006100740069006c006c00610020006a0061002000410064006f00620065002000520065006100640065007200200036002e0030003a006c006c00610020006a006100200075007500640065006d006d0069006c006c0061002e> /sve <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> /tur <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> /ukr <feff04120438043a043e0440043804410442043e043204430439044204350020044604560020043f043004400430043c043504420440043800200434043b044f0020044104420432043e04400435043d043d044f00200434043e043a0443043c0435043d044204560432002000410064006f006200650020005000440046002c0020043f044004380437043d043004470435043d0438044500200434043b044f0020043d0430043404560439043d043e0433043e0020043f0435044004350433043b044f04340443002004560020043404400443043a0443002004340456043b043e04320438044500200434043e043a0443043c0435043d044204560432002e0020042104420432043e04400435043d04560020005000440046002d0434043e043a0443043c0435043d044204380020043c043e0436043d04300020043204560434043a04400438043204300442043800200437043000200434043e043f043e043c043e0433043e044e0020043f0440043e043304400430043c04380020004100630072006f00620061007400200456002000410064006f00620065002000520065006100640065007200200036002e00300020044204300020043f04560437043d04560448043804450020043204350440044104560439002e> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 enhancing sustainability index parameter using anfis computational intelligence model diah septiyana1,2*, mohamed abd. rahman1, tasnim firdaus mohamed ariff1, nor aiman sukindar1 and erry yulian triblas adesta3 1 department of manufacturing and material engineering, kulliyyah of engineering (koe), international islamic university malaysia (iium), selangor, malaysia. 2 department of industrial engineering, faculty of engineering, universitas muhammadiyah tangerang, banten, indonesia. 3 department of industrial engineering safety and health, faculty of engineering, universitas indo global mandiri (uigm), palembang, indonesia. *corresponding author: dee.septie@gmail.com (received: 8 march 2023; accepted: 18 may 2023; published on-line: 4 july 2023) abstract: the scarcity of water resource is an essential global issue in the 21st century. therefore, one of the sustainable development goals (sdg) was to ensure the availability and sustainable management of water and sanitation. to do this, it is necessary to assess whether or not the sdg has been followed using the sustainability index. however, there are a lot of sustainability indexes and many of them have the same problem, in which all sustainability index parameters have the same weightage. this problem shows us that every parameter in the sustainability index is equal, while in real life there is no equal parameter. in this paper a weightage for each parameter is proposed to enhance the sustainability index. the method to assess the sustainability index parameters was using a questionnaire by key experts in the water industry. using anfis computational intelligence, the result of the assessment was then fit to the frequent parameters that exist in other sustainability indexes. this proposed method can produce a ranking and weight for each sustainability index parameter and criteria. using this method, the weightage for each sustainability index parameter can be generated, such as environmental 0.301, engineering 0.214, economic 0.280, and social 0.205. abstrak: kekurangan sumber air merupakan isu global yang penting dalam abad ke-21. oleh itu, salah satu matlamat pembangunan mampan (sdg) adalah bagi memastikan ketersediaan dan pengurusan air dan sanitasi yang berterusan. bagi melaksanakan ini, adalah perlu untuk menilai sama ada sdg telah diikuti atau tidak menggunakan indeks kemampanan. walau bagaimanapun, terdapat banyak indeks kemampanan dan kebanyakannya mempunyai masalah yang sama, di mana semua parameter indeks kemampanan mempunyai pemberat yang sama. masalah ini menunjukkan kepada kita bahawa setiap parameter indeks kemampanan adalah sama, manakala dalam kehidupan sebenar tiada parameter yang sama. kajian ini merupakan cadangan wajaran pemberat bagi setiap parameter bagi meningkatkan indeks kemampanan. kaedah bagi menilai parameter indeks kemampanan adalah menggunakan soal selidik oleh pakar utama dalam industri air. menggunakan kecerdasan pengiraan anfis, hasil penilaian kemudiannya diselaraskan dengan parameter kerap yang wujud dalam indeks kemampanan lain. kaedah yang dicadangkan ini boleh menghasilkan pemeringkatan dan pemberat bagi setiap parameter dan kriteria indeks kemampanan. menggunakan kaedah ini, wajaran pemberat bagi setiap parameter indeks kemampanan dapat dijana, seperti persekitaran 0.301, kejuruteraan 0.214, ekonomi 0.280, dan sosial 0.205. keywords: sustainability index, computational intelligence, anfis, weightage, water industry. 258 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 1. introduction in 2022, indonesia's economy improved, with economic progress in both urban and rural areas. increased employment in the agricultural, manufacturing, transportation, and logistics services sectors contributed to poverty reduction [1]. likewise, in the tangerang region, indonesia, which has seen an increase in per capita income, the total population is also growing very fast. consequently, water needs also increase [2]. apart from having a positive impact, it also poses new challenges in terms of water availability in the future [3, 4]. water resources are key ecosystem components that sustain life and all social and economic processes. the scarcity of water resources is an essential global issue in the 21st century [3–6] adequate water availability is challenged by population growth, rapid urbanization, and climate change in meeting urban water needs [7, 8]. therefore, the second target of sdgs seeks to ensure the availability and sustainable management of water and sanitation until 2030, emphasizing the quality and sustainability of water resources in integrating and balancing the three dimensions of sustainable development such as economic, social, and environmental [9]. although there is an increasing trend toward using sustainability index to support plans for long-term, medium-term, and short-term sustainable development, the sustainability index is not infallible on its own. this has been the cause for creation of many new sustainability indices such as the swam index, the canadian water sustainability index, and many more [10, 11]. even though there have been some instances of success with the use of these new and current sustainability indices, they are not entirely relevant in all applications. this was brought on by some of the sustainability indices that were created for usage in particular nations or regions [12]. one could argue that there isn't a universal gauge of water sustainability. however, in the current sustainability index, the parameters don’t have weightage. the example of this can be seen in the wssi index. this implies a problem in the sustainability index foundation, in which evaluation components are considered to have equal weight, hence making sustainability measurement inaccurate. the aim of this paper is to develop the best sustainability index. to achieve that aim, the objective of this paper will be to combine input from various experts and computational intelligence methods [13]. there are many computational intelligence methods, such as neural network, fuzzy, and other [14–16]. however, in this paper anfis is prefered because it combines the fuzzy method with the neural network method [17]. this combined approach makes anfis preferable compared to the others. anfis is preferred due to its transparency in associations (reasoning to generate the membership functions and rules from a set of training data) to reach the optimal predicted value [18]. this paper proposed an anfis method to create differing weightage for every sustainability index parameter and create more accurate sustainability measurements. 2. method and design in this section, the method used in this research is explained. the technique used includes questionnaires with experts and anfis computational intelligence. 2.1. adaptive neuro fuzzy inference system (anfis) zadeh developed the foundation of fuzzy in 1975 based on linguistic variables and their application to approximate reasoning [19]. the fuzzy rule was subsequently created to model the qualitative elements of human knowledge (reasoning based on experience) and address the issue using those as its foundations [20] fuzzy logic is typically employed for control, including robot movement, and many others [21–24], however in reality, a fuzzy system can be applied to anything from detection to forecasting [25-26]. in 1985, takagi and sugeno 259 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 created fuzzy sugeno [27]. the fuzzy implications and reasoning system control were shown using this mathematical model [28–30]. the fuzzy sugeno equation can be seen in equations 1 through 6. 𝑂 1 𝑖 = µ𝐴𝑖 (𝑥) 𝑎𝑛𝑑 𝑂 1 𝑖 = µ𝐵𝑖 (𝑥), 𝑖 = 1, 2 (1) where: i = each node of anfis architecture. a, b= is the linguistic label. x = is the input to node i. (such as small, large, etc.). every membership function type is usable at this stage. however, to offer a maximum equal to 1 and a minimum equal to 0, generalized bell types were employed. hence: µ𝐴𝑖(𝑥) = 1 1 +( 𝑥−𝑐𝑖 𝑎𝑖 ) 2∗𝑏𝑖 (2) where: a,b,c= is the parameter set. by multiplying the two input signals, the second step contributes to the firing strength of fuzzy inference. this is represented by each node. 𝑂 2 𝑖 = µ𝐴𝑖 (𝑥). µ𝐵𝑖 (𝑥), 𝑖 = 1, 2 (3) the following phase involves applying normalization for each fuzzy inference firing. 𝑂 3 𝑖 = 𝑊𝑖 = 𝑊𝑖 𝑊1+𝑊2 , 𝑖 = 1, 2 (4) where: w= is the firing strength of the node. 𝑊𝑖= is the normalized firing strength of the node. the following phase involves a calculation based on the parameters of the rule consequent in the following phase: 𝑂 4 𝑖 = 𝑊𝑖 . 𝐹𝑖 = 𝑊𝑖 . (𝑃𝑖 𝑥 + 𝑄𝑖 𝑥 + 𝑅𝑖 𝑥 ) , 𝑖 = 1,2 (5) where: p,q,r = is the parameter set the final phase computes the overall output by adding up all of the input signals: 𝑂 5 𝑖 = 𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝑂𝑢𝑡𝑝𝑢𝑡 = ∑ 𝑊𝑖 . 𝐹𝑖 𝑛 𝑘=0 = ∑ 𝑊𝑖 .𝐹𝑖 𝑛 𝑘=1 ∑ 𝑊𝑖 𝑛 𝑘=1 (6) jang jyh shing roger created adaptive neuro fuzzy inference system (anfis) in 1993 based on fuzzy takagi sugeno's if-then rules [31]. the fuzzy inference system can adapt organically using the anfis approach based on its training data. the takagi-sugeno fuzzy inference system serves as the foundation for the artificial neural network technique that makes up anfis [32]. this method can combine the benefits of fuzzy logic and neural networks into a single framework: a collection of fuzzy if-then rules that can be learned to estimate nonlinear functions govern how this inference system operates. consequently, anfis is regarded as a universal estimator (universal assessor). equations 2 through 7 make up the core 260 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 algorithm used by anfis, which uses a fuzzy sugeno algorithm. jang then used gradient descent and chain rule to optimize its parameter. however, to do this, it must be aware of the error rate for data training for each node output, since anfis learns through chain rule and gradient descent. the anfis algorithm can be seen from equation 7 through equation 12: if the data training sets have p numbers of inputs and the i-th position node outputs define o𝑖 , then the error function may be calculated as follows: 𝐸𝑝 = ∑ (𝑇𝑚𝑝 − #𝐿 𝑚=1 𝑂 𝐿 𝑚𝑝 )2 (7) where: 𝐸𝑝 = is the error measure which is the sum of squared errors. 𝑇mp = is the m component from the p output target vector. o 𝐿 𝑚𝑝 = is the m component from the actual output vector that has been delivered by the p input vector. hence, the error rate can be calculated as: 𝜕𝐸𝑝 𝜕𝑂 𝑘 𝑖 𝑝 = ∑ 𝜕𝐸𝑝 𝜕𝑂 𝑘+1 𝑚 𝑝 𝜕𝑂 𝑘+1 𝑚 𝑝 𝜕𝑂 𝑘 𝑖 𝑝 #𝑘+1 𝑚=1 (8) where 1 ≤ k ≤ l-1 is the error rate of an internal node. it is expressed as the linear combination error rate of nodes in the next step. therefore, for all 1 ≤ k ≤ l and 1 ≤ i ≤ #(k), the 𝜕𝐸𝑝 𝜕o 𝑘 𝑖 𝑝 can be found using mathematical equations (7) and (8). thus, a parameter of the adaptive network α can be written as: 𝜕𝐸 𝜕𝛼 = ∑ 𝜕𝐸𝑝 𝜕𝑂∗ 𝜕𝑂∗ 𝜕𝛼𝑂∗𝜖𝑆 (9) where: s= shows the set of nodes whose output depends on α. derivative for overall error measurement e concerning α is: 𝜕𝐸 𝜕𝛼 = ∑ 𝜕𝐸𝑝 𝜕𝑂∗ 𝜕𝑂∗ 𝜕𝛼𝑂∗𝜖𝑆 (10) therefore, the updated mathematical equations for generic parameter α as follows: 𝛥𝛼 = −𝜂 𝜕𝐸 𝜕𝛼 (11) where: η = is a learning rate. the learning rate can be written as: 𝜂 = 𝑘 √∑ ( 𝜕𝐸 𝜕𝛼 )2𝛼 (12) where: k = is the step size or length of each gradient transition in the parametric space. 261 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 2.2. sustainability index assessment using questionnaire with key experts in the water industry the assessment of water supply sustainability might well be classified into three methodological methods that were established sequentially throughout time but are still in use today and are mutually supplemented, enhanced, and integrated [33]. sustainability development is defined by three interconnected components (environment, social, and economy), often known as aspects. since the focus of this study is water management sustainability, the assessment of its sustainability must include extra components such as engineering components related to its intrinsic features [33–35]. the engineering component is adapted to the operating conditions of the water treatment which may affect the management of water utilities and affect environmental, social, and economic aspects. furthermore, for this paper, the sustainability assessment framework is created by grouping key indications into four major components (engineering, environmental, economic, and social). the questionnaire's primary components are in connection with the water sustainability index's theoretical model. a literature review was used to construct the framework, which consists of an initial set of components, indicators, and threshold values based on sustainability theories, water management principles, and existing water sustainability indexes from the cwsi, wssi, wjwsi, wsi, and wpi. criteria in designing this conceptual framework are critical for reducing researcher bias. the questionnaire's contents include the respondents' importance ratings in the component/indicator/threshold values on a 4-point likert scale. where a value of 4 is 'very important', a value of 3 is 'important', a value of 2 is 'less important' and a value of 1 is 'very less important'. questionnaires were distributed to several key experts who have backgrounds related to drinking water companies in indonesia, especially piped drinking water in the tangerang area. the parameter that is assessed using questionnaires by key experts can be seen in table 1 below. table 1: sustainability index parameter used for questionnaire. component indicator sustainability index (existing) literature cwsi wssi wjwsi wsi wpi engineering water losses √ √ [36]–[42] operational and maintenance √ √ √ √ [40], [43]–[46] environment quality √ √ √ √ √ [42]–[44], [46]– [48] quantity √ √ √ √ √ [40], [43]–[46], [48]–[50] continuity √ √ √ √ √ [40], [43]–[46], [48]–[50] economic capital investment √ √ √ [46], [51], [52] cost recovery & operation and maintenance cost √ [46], [51], [52] ability to pay √ √ [43], [44], [48] social access for water supply √ √ √ √ √ [40], [42], [43], [46], [51] access for sanitation √ √ √ [42], [43], [46], [53], [54] 262 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 3. result and discussion the findings of this research are presented in this section. the first step would be to start with the survey results from important water industry operation specialists. the anfis computational intelligence used the survey results to provide values that fit the frequently occurring sustainable index parameter. the weightage and ranking for each parameter of the sustainable index are generated in this way. 3.1 questionnaire result from the experts the assessment of the water sustainability index was carried out with a key expert in the water industry. figure 1 shows the ranking of the sustainability index parameter as a result of using 10 parameters from different sustainability indices in table 1. (a) (b) (c) (d) fig. 1. water sustainability index assessment by key experts in the water industry. (a) engineering parameter, (b) environment parameter, (c) economic parameter, (d) social parameter. 3.2 anfis fitting model for questionnaire and frequent parameter sustainability index assisted by the anfis algorithm, a fitting model for the questionnaire result and frequent parameters that exist in most sustainability indices can be developed easily. the questioner data in table 1 is data training for anfis. thus, using equation 2 and equation 6, an anfis fitting model can be produced as shown in figure 2, table 2, table 3, table 4, and equation 13. in figure 2, the generalized bell membership function is used for anfis fuzzification model fitting. its membership function was formed by three parameters such as a, b and c. using those parameters, the visualization can be built such that parameter a defines the width of the membership function input, while parameter b defines the shape of the curve on either side of the midland, and parameter c defines the center point of the membership function. 263 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 fig. 2. anfis fuzzification fitting model for the questionnaire and frequent parameter sustainability index. table 2: anfis fuzzification fitting model for the questionnaire and frequent parameter sustainability index. fuzzification input a b c mf1 70.7 1.283 3.825 mf2 65.97 0.1787 136.1 table 3: anfis inference for sustainable index parameter weighting rule index rule firing rule output 1 if (input is mf1) then output is f1 2 if (input is mf2) then output is f2 table 4: anfis fitting model fuzzy constant output output constant index (fi) value 1 -2.484 2 5.234 thus, the fitting anfis model for the questionnaire and frequent parameters that exist in sustainability index can be seen in equation 13 below: = ∑ 1 1 +[( 𝑥−𝑐𝑖 𝑎𝑖 ) 2∗𝑏𝑖 ] + 1 1 +[( 𝑥−𝑐𝑖 𝑎𝑖 ) 2∗𝑏𝑖 ] 𝐹𝑖=1 𝑛 𝑛 𝑘=0 ∑ 1 1 +[( 𝑥−𝑐𝑖 𝑎𝑖 ) 2∗𝑏𝑖 ] + 1 1 +[( 𝑥−𝑐𝑖 𝑎𝑖 ) 2∗𝑏𝑖 ] 𝑛 𝑘=0 (13) where: x = input variables in this research were questionnaire. a, b, c= defines the width of the membership function input as a, while b defines the shape of the curve on either side of the midland, and c defines the center point of the membership function. 𝐹𝑖=1 𝑛 = defines the output variables’ constant level generated automatically by anfis based on the number of fuzzy rules/inferences. in this case, it refers to the parameter that often appears in the sustainability index. n= number of fuzzy rules/inferences. 264 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 using the fuzzy sugeno fitting model on equation 13, the weight for each sustainability index parameter was determined. however, the value was normalized so that it ranged between a minimum of 0 and maximum of 1. hence, calculating the total value of all fitting values from anfis is necessary to get this weight. the fitting value of each parameter will then be divided by the anfis's overall fitting value. this will establish the relative importance of each parameter which, when added together, will result in a value of 1. therefore, the normalized weightage for each sustainability parameter can be seen in table 5. table 5: sustainability index weight and ranking parameter result using anfis fitting. total criteria weight indicator index questionn aire score anfis fitting ranking normalize weight engineering (0.214) water losses e1 133 3,77 1 0,108 operational and maintenance e2 132 3,72 2 0,106 environment (0.301) quality e4 127 3,5 7 0,100 quantity e6 129 3,58 3 0,102 continuity s4 126 3,46 8 0,099 economic (0.280) capital investment e7 120 3,23 9 0,092 cost recovery & operation and maintenance cost e8 115 3,04 10 0,087 ability to pay e10 128 3,54 6 0,101 social (0.205) access for water supply s1 129 3,58 4 0,102 access for sanitation s2 129 3,58 5 0,102 by employing this technique, it can be seen that the environmental criteria have a higher weightage (0.301) than other criteria, such as engineering (0.214), economic (0.280), and social (0.205). the fact that this criterion has a higher weightage indicates that it is more crucial in achieving a high sustainability index. 3.3 enhanced sustainability index model using new sustainability parameter weightage each sustainability index such as cwsi, wssi, wjwsi, wsi, and wpi can easily be enhanced using this new sustainability index parameter weightage, one such example is by enhancing the development of wssi by odjegba [46]. the original wssi model can be seen on equation 14 below: 𝑊𝑆𝑆𝐼 = s𝑜𝑏𝑡 ms𝑜𝑏𝑡 𝑥 100 (14) where: s𝑜𝑏𝑡 = score obtained from observation. ms𝑜𝑏𝑡 = maximum score obtained from total parameter. assisted with new sustainability index parameter weightage, the enhanced wssi sustainability index can be seen in equation 15 below: wssi𝑒ℎ = ∑ p𝑖 . w𝑖 𝑛 𝑖 ∑ p𝑡𝑜𝑡 . w𝑖 𝑛 𝑖 𝑥 100 (15) wssi𝑒ℎ = enhanced wssi sustainability index p𝑖 = sustainability index parameter score obtained from observation, minimum 1 and maximum 5. w𝑖 = sustainability index parameter normalize weightage obtained from table 3. p𝑡𝑜𝑡= total sustainability index parameter score, maximum score for each parameter is 5. using this final form of enhanced wssi sustainability index, it can reach the original wssi score from 0 to 100 points. 265 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 4. conclusion the sustainability index has been enhanced using the new sustainability index parameter weightage in this paper. this sustainability index parameter weightage was in general form so it can be applied to the different sustainability indices. using a leading expert in the water operations questions, the popular sustainability index parameter from cwsi, wssi, wjwsi, wsi, and wpi was evaluated carefully. the outcome of this evaluation was then computed utilizing the computational intelligence of anfis to fit the frequent parameter seen in the other 5 sustainability indices before. the rank and weightage for each indicator and criterion sustainability index parameter can be proposed for engineering 0.214, economics 0.280, social 0.205, and the environment 0.301. it can be concluded that using the suggested method has successfully generated weightage for each sustainability index parameter, thus creating a better water sustainability index. references [1] world bank poverty & equity brief east asia & pacific – indonesia [https://databankfiles.worldbank.org/public/ddpext_download/poverty/987b9c90-cb9f4d93-ae8c-750588bf00qa/current/global_poveq_idn.pdf] [2] badan pusat statistik provinsi banten proyeksi penduduk provinsi banten 2010-2020 [https://banten.bps.go.id/publication/2015/03/31/a723ef5e69db53cfc3eca058/proyeksipenduduk-provinsi-banten-2010-2020.html] [3] e. iglesias and m. blanco (2008). new directions in water resources management: the role of water pricing policies. water resour res, 44. doi: 10.1029/2006wr005708. [4] q. tang (2020). global change hydrology: terrestrial water cycle and global change. sci china earth sci, 63:459–462. doi: 10.1007/s11430-019-9559-9. [5] n. w. arnell (1999). climate change and global water resources, global environmental change, 9:s31-s49. doi: 10.1016/s0959-3780(99)00017-5. [6] e. marris (2016). water scarcity’ affects four billion people each year, nature. doi: 10.1038/nature.2016.19370. [7] climate change adaptation vs mitigation : a fiscal perspective [https://www.lse.ac.uk/granthaminstitute/wp-content/uploads/2015/03/barrage_2015_ adaptation_mitigation_fiscal.pdf] [8] d. s. brookshire and d. whittington (1993). water resources issues in the developing countries. water resour res., 29:1883-1888, doi: 10.1029/92wr02988. [9] united nations the sustainable development goals report 2019 [https://unstats.un.org/sdgs/report/2019/the-sustainable-development-goals-report2019.pdf] [10] m. maiolo and d. pantusa (2019). sustainable water management index, swam_index. cogent eng., 6, doi: 10.1080/23311916.2019.1603817. [11] the canadian water sustainability index (cwsi): case study report [http://www.bibliotheque.assnat.qc.ca/01/mono/2006/03/842674.pdf] [12] i. juwana, b. j. c. perera, and n. muttil (2010). a water sustainability index for west java. part 1: developing the conceptual framework. water science and technology, 62:1629– 1640. doi: 10.2166/wst.2010.452. [13] i. juwana, b. j. c. perera, and n. muttil (2010). a water sustainability index for west java. part 1: developing the conceptual framework. water science and technology, 62: 1641– 1652. doi: 10.2166/wst.2010.453. [14] g. p. n. hakim et al. (2023). levenberg marquardt artificial neural network model for selforganising networks implementation in wireless sensor network. iet wireless sensor systems, 1–14. doi: 10.1049/wss2.12052. [15] s. r. utama, a. firdausi, and g. p. n. hakim (2022). control and monitoring automatic floodgate based on nodemcu and iot with fuzzy logic testing. journal of robotics and control (jrc), 3:14-17. doi: 10.18196/jrc.v3i1.11199. 266 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 [16] a. adriansyah, y. gunardi, b. badaruddin, and e. ihsanto (2015). goal-seeking behaviorbased mobile robot using particle swarm fuzzy controller. telkomnika, 13:528-538. doi: 10.12928/telkomnika.v13i2.1111. [17] j. s. r. jang (1993). anfis: adaptive-network-based fuzzy inference system. ieee trans syst man cybern., 23:665–685. doi: 10.1109/21.256541. [18] h. a. o. cruz, r. n. a. nascimento, j. p. l. araujo, e. g. pelaes, and g. p. s. cavalcante (2017). methodologies for path loss prediction in lte-1.8 ghz networks using neuro-fuzzy and ann. in sbmo/ieee mtt-s international microwave and optoelectronics conference: 27-30 august 2017; brazil. edited by aguas de lindoia. [19] l. a. zadeh (1975). the concept of a linguistic variable and its application to approximate reasoning. inf sci (n y), 8:199–249. doi:10.1016/0020-0255(75)90036-5. [20] n. yusof, n. bahiah, mohd. shahizan, and y. chun, “a concise fuzzy rule base to reason student performance based on rough-fuzzy approach,” in fuzzy inference system theory and applications, 2012. doi: 10.5772/37773. [21] g. p. n. hakim, d. septiyana, and s. iswanto (2022). survey paper artificial and computational intelligence in the internet of things and wireless sensor network. journal of robotics and control (jrc), 3:439–454. doi: 10.18196/jrc.v3i4.15539. [22] i. r. f. arif, a. firdausi, and g. p. n. hakim (2021). nebulizer operational time control based on drug volume and droplet size using fuzzy sugeno method. journal of robotics and control (jrc) 2:94-97. doi: 10.18196/jrc.2259. [23] g. p. n. hakim, r. muwardi, m. yunita, and d. septiyana (2022). fuzzy mamdani performance water chiller control optimization using fuzzy adaptive neuro fuzzy inference system assisted. indonesian journal of electrical engineering and computer science, 28: 1388~1395. doi: 10.11591/ijeecs.v28.i3. [24] g. p. n. hakim, d. septiyana, and s. iswanto (2022). survey paper artificial and computational intelligence in the internet of things and wireless sensor network. journal of robotics and control (jrc), 3:439–454. doi: 10.18196/jrc.v3i4.15539. [25] d. sahid and m. alaydrus. (2020) multi sensor fire detection in low voltage electrical panel using modular fuzzy logic. in 2nd international conference on broadband communications, wireless sensors and powering on 28-30 september; jakarta. pp 31-35. [26] g. p. n. hakim et al. (2022). near ground pathloss propagation model using adaptive neuro fuzzy inference system for wireless sensor network communication in forest, jungle, and open dirt road environments. sensors, 22:3266-3288 doi: 10.3390/s22093267. [27] t. takagi and m. sugeno (1985). fuzzy identification of systems and its applications to modeling and control. ieee trans syst man cybern, 15:116-132. doi: 10.1109/tsmc.1985.6313399. [28] c. h. chiu and y. f. peng (2019). design of takagi-sugeno fuzzy control scheme for real world system control. sustainability, 11. doi: 10.3390/su11143855. [29] x. tang, d. ning, h. du, w. li, and w. wen (2020). takagi-sugeno fuzzy model-based semi-active control for the seat suspension with an electrorheological damper. ieee access, 8: 98027-98037. doi: 10.1109/access.2020.2995214. [30] x. tang, d. ning, h. du, w. li, y. gao, and w. wen (2020). a takagi-sugeno fuzzy modelbased control strategy for variable stiffness and variable damping suspension. ieee access, 8: 71628-71641. doi: 10.1109/access.2020.2983998. [31] j. s. r. jang (1993). anfis: adaptive-network-based fuzzy inference system. ieee trans syst man cybern, 23:665–685. doi: 10.1109/21.256541. [32] j.-s. r. jang, c.-t. sun, and e. mizutani (1997) neuro-fuzzy and soft computing-a computational approach to learning and machine intelligence, prentice hall. [33] k. carden and n. p. armitage (2013). assessing urban water sustainability in south africa not just performance measurement. water sa, 39. doi: 10.4314/wsa.v39i3.1. [34] z. chen, h. h. ngo, and w. guo (2012). a critical review on sustainability assessment of recycled water schemes. science of the total environment, 426:13-31. doi: 10.1016/j.scitotenv.2012.03.055. 267 iium engineering journal, vol. 24, no. 2, 2023 septiyana et al. https://doi.org/10.31436/iiumej.v24i2.2810 [35] sustainability indicators and the assessment of urban water systems: seeking for a robust way forward [http://www.switchurbanwater.eu/outputs/pdfs/wp1-1_pap_sustainability _indicators_for_assessment_of_uws.pdf] [36] evaluation of sustainability index for urban water management system [http://www.ipcbee.com/vol4/58-icesd2011d30014.pdf] [37] t. al-washali, s. sharma, f. al-nozaily, m. haidera, and m. kennedy (2019). monitoring nonrevenue water performance in intermittent supply. water, 11. doi: 10.3390/w11061220. [38] l. j. n. jones, d. kong, b. t. tan, and p. rassiah (2021). non-revenue water in malaysia: influence of water distribution pipe types. sustainability, 13. doi: 10.3390/su13042310. [39] m. farley and s. trow (2003) losses in water distribution networks: a practitioner’s guide to assessment, london, iwa publishing. [40] a. adham, s. seeyan, r. abed, k. mahdi, m. riksen, and c. ritsema (2022). sustainability of the al-abila dam in the western desert of iraq. water, 14. doi: 10.3390/w14040586. [41] the canadian water sustainability index (cwsi): case study report [https://core.ac.uk/reader/80536600] [42] i. juwana, b. j. c. perera, and n. muttil (2009) conceptual framework for the development of west java water sustainability index,” in 18th world imacs congress and modsim09 international congress on modelling and simulation: interfacing modelling and simulation with mathematical and computational sciences on cairns, australia 13-17 july 2009: pp 3343-3349. [43] canadian water sustainability index [https://publications.gc.ca/collection/ph4-382007e.pdf] [44] linking technology choice with operation and maintenance in the context of community water supply and sanitation [https://apps.who.int/iris/handle/10665/42538]. [45] h. m. l. chaves and s. alipaz (2007). an integrated indicator based on basin hydrology, environment, life, and policy: the watershed sustainability index. water resources management, 21:883–895. doi: 10.1007/s11269-006-9107-2. [46] e. odjegba, g. oluwasanya, o. idowu, o. shittu, and g. brion (2020). sustainability indices and risk analysis of drinking water systems in southwest nigeria. journal of water supply: research and technology aqua, 69:591–603. doi: 10.2166/aqua.2020.002. [47] water safety plans managing drinking-water quality from catchment to consumer water, sanitation and health protection and the human environment world health organization geneva [https://apps.who.int/iris/handle/10665/42890]. [48] c. sullivan (2002). calculating a water poverty index. world dev, 30:1195–1210. doi: 10.1016/s0305-750x(02)00035-9. [49] d. koo, k. piratla, and c. j. matthews (2015). towards sustainable water supply: schematic development of big data collection using internet of things (iot). procedia engineering, 118:489-497. doi: 10.1016/j.proeng.2015.08.465. [50] c. o. de castro, ó. c. s. loureiro, a. v. santos, j. silva, and w. b. rauen (2017). water sustainability assessment for the region of curitiba. international journal of sustainable building technology and urban development, 184-194 doi: 10.12972/susb.20170016. [51] h. m. l. chaves and s. alipaz (2007). an integrated indicator based on basin hydrology, environment, life, and policy: the watershed sustainability index. water resources management, 21:883–895. doi: 10.1007/s11269-006-9107-2. [52] m. van den belt, t. bowen, k. slee, and v. forgie (2013). flood protection: highlighting an investment trap between built and natural capital. j am water resour assoc, 49: 681692. doi: 10.1111/jawr.12063. [53] c. dong, g. schoups, and n. van de giesen (2013). scenario development for water resource planning and management: a review. technological forecasting and social change, 4: 749761. doi: 10.1016/j.techfore.2012.09.015. [54] d. p. loucks (1997). quantifying trends in system sustainability. hydrological sciences journal, 42: 513-530. doi: 10.1080/02626669709492051. 268 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 the effects of supercritical carbon dioxide on the degradation and antimicrobial properties of pla biocomposite hazleen anuar1, siti nur e’zzati mohd apandi1, siti munirah salimah abd rashid1, fathilah ali2, yose fachmi buys3, mohd romainor manshor4, sabu thomas5, nur aimi mohd nasir1 1department of manufacturing and materials engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia 2department of biotechnology engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia 3department of mechanical engineering, faculty of engineering, university of malaya, 50603 kuala lumpur, malaysia 4food technology research centre, malaysian agriculture research and development institute (mardi), 43400 serdang, selangor, malaysia 5international and inter university centre for nanoscience and nanotechnology, mahatma gandhi university, priyadarshini hills, kottayam 686560, kerala, india *corresponding author: hazleen@iium.edu.my (received: 12th april 2019; accepted: 24th december 2019; published on-line: 20th january 2020) abstract:biopolymer products that is biodegradable presently attracting an attention from researchers and industry. the biodegradable packaging based on polylactic acid (pla), durian skin fibre (dsf), epoxidized palm oil (epo) and incorporated with cinnamon essential oil (ceo) as antimicrobial agent have been developed and showed to be a promising field of research. this paper reported the effects of supercritical carbon dioxide on the degradation and antimicrobial properties of pla biocomposite films produced via solvent casting. the biocomposites underwent supercritical carbon dioxide (scco2) treatment at two different conditions under 40 °c temperature and at 100 bar and 200 bar pressure. water absorption test showed that the untreated pla biocomposite absorbed most water as compared to treated pla biocomposite with scco2 at 5.1%. this is due to the hydrophilic nature of the fibre that absorbed water molecules. soil burial test showed that the treated pla biocomposite possessed the highest value of weight losses after 80 days with 97.8%. biocomposite with the presence of ceo demonstrated antimicrobial activity against both gram-positive and gram-negative bacteria. this showed that scco2 significantly improved the properties of pla biocomposite films. the supercritical fluid treatment of pla biocomposite could be an alternative for active packaging industries to ensure that the packaging product meets the requirement by consumers as well as being an eco-friendly product. abstrak: produk biopolimer yang biodegradasi pada masa ini menarik perhatian dari penyelidik dan industri. pembungkusan biodegradasi berasaskan polilaktik asid (pla), serat kulit durian (dsf), minyak kelapa sawit terepoksi (epo) dan ditambah dengan 212 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 minyak pati kayu manis (ceo) sebagai agen antimikrobial telah dibangunkan dan menjadi bidang penyelidikan. artikel ini melaporkan kesan karbon dioksida superkritikal terhadap sifat-sifat degradasi dan antimikrobik dari filem biokomposit pla yang dihasilkan melalui pemutus pelarut. biokomposit telah menjalani rawatan superkritikal karbon dioksida (scco2) pada dua keadaan yang berbeza di bawah suhu 40 °c pada 100 bar dan 200 tekanan bar. ujian penyerapan air menunjukkan bahawa biocomposite pla yang tidak dirawat menyerap kebanyakan air berbanding komposisi lain dengan 5.1%. ini disebabkan sifat hidrofilik serat yang menyerap molekul air. ujian penanaman dalam tanah menunjukkan bahawa biocomposite pla yang dirawat mempunyai nilai kehilangan berat tertinggi setelah 80 hari dengan 97.8%. biokomposit dengan kehadiran ceo menunjukkan aktiviti antimikrobial terhadap bakteria gram-positif dan gram-negatif. ini menunjukkan bahawa scco2 meningkatkan sifat-sifat filem biocomposite pla. rawatan cecair superkritikal pla biocomposite boleh menjadi alternatif bagi industri pembungkusan untuk memastikan produk pembungkusan memenuhi keperluan pengguna serta menjadi produk mesra alam. key words: polylactic acid, durian skin fibre, supercritical carbon dioxide, degradation properties, and antimicrobial activity. 1. introduction food packaging is a packaging that provides food for carriage, distribution, packing, trade and end-user to fulfil the consumer expectations. consumer requirements for secure, environment-friendly and high-quality packaging materials have been increased, and therefore the garbage disposal problems are being resolved [1]. plastics, papers, metals and glasses are some of the main packaging materials; however plastic packaging is typically used in food packaging. synthetic plastic packaging is crucial to be disposed and can be wasteful due to its compositions and elemental contents [2]. this waste material ends-up being discarded to landfills and the declining availability of land for this purpose [3]. realizing this situation, many food packaging manufacturer tried to reduce the reliance on synthetic plastics as well as maintain the quality of food. researchers have found a solution by developed biopolymers that easily degrade within a definite period, compared to nondegradable plastics. due to renewability, biodegradability and commercial viability, development of biodegradable materials is interesting in the food packaging sector, since it provides a replacement to the usage of synthetic products [4]. other than that, production of biopolymer products can be an initiative income in the agriculture industry. pla is one of the most promising candidates among the renewable source-based products, due to its availability, biocompatibility, excellent tensile strength, good process ability and biodegradability, which are a significant benefit from an environmental perspective. biodegradable films produced from starch crops are defined as odor-free, flavourless, and neutral as well as non-toxicity [5]. despite the benefit features, mechanical properties of pla are unsatisfactory for packaging applications due to brittleness. the reinforced pla matrix with natural fibre is believed to improve its mechanical performance [6]. compared to petroleum-based fibre, natural fibres are more environmentally friendly and potentially decrease the environmental problems due to the biodegradable properties. in order to produce biocomposites while preserving the green features, biopolymers must be reinforced with natural fibre [7]. natural fibres are also composed of low toxicity and cheap resources. durian skin fibre (dsf) has excellent features as reinforcement or filler in pla biopolymer [4, 8, 9]. durian or, its scientific name, durio zibethinus murray can be found 213 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 in southeast asian countries such as malaysia, thailand, indonesia and philippines. it is also recognised as the ‘king of fruits’. about 45-55 wt% of durian can be considered as waste including skin and seed because only 55-65 wt% of durian is flesh [9]. to preserve the green environment, the durian skin waste can be used to produce durian skin fibre (dsf). this attempt could help in reducing the environmental pollution by decreasing the number of organic wastes. besides, the processability of films can be increased with plasticizers that contribute to decreasing the glass transition temperature (tg) and enhance the polymer chain flexibility [10]. this plasticizer also might overcome specimen’s brittleness created by high intermolecular forces. some researchers acknowledge that the natural plasticizers are better, which can be found naturally extracted from animals, vegetable fats and plants oil [11, 12]. among the natural plasticizer, epoxidized palm oil (epo) is a favourable plant oil due to its characteristics like inexpensive, non-toxicity and availability as a renewable agriculture resource. nowadays, the safety issues of food are utterly worrisome in the world. handling food packaging safety is just significant at the consumer level because many of them have contaminated food if not keep properly [13]. hence, research in active food packaging could play a primary role in food security guarantee, comprehensively permitted with the industrial sector, farmers, producers, wholesalers, retailers, and government as well as consumer groups. due to the problems highlighted, there is a necessity to produce food packaging with an anti-microbial agent and preventing food contamination. bacteria and fungi are examples of active microorganisms which may have migrated through direct interaction between food and packaging material or via moisture from inside packaging layer to the food surface [14]. the movement activity of these compounds might interrupt the lifespan and quality of the product. active packaging materials in the presence of antimicrobial agents like essential oil may be considered as the contemporary advancement of functional packaging. this antimicrobial agent in biocomposite films can avoid almost all bacteria activities that affect the food contamination [15]. the production of essential oil can be exploited as a natural antimicrobials agent and can be used as one of the additives for food [1]. different types of essential oils show different significance functional group with own antimicrobial properties. the incorporation of essential oil in biocomposite material as secure antimicrobials is expected to be non-harmful for food product and human consumption. cinnamon has been used as a spice since long time ago. the major component of essential oil extraction is cinnamaldehyde group, a wellknown functional group because of its strong antioxidant and antibacterial activities [16, 17]. the combination of essential oils into viscous biocomposite solvents via solvent casting has some disadvantages mostly due to hydrophobic oil behaviour by epo and cinnamon essential oil (ceo) which make it difficult to become a homogeneous film. therefore, supercritical carbon dioxide (scco2) treatment is introduced in this study as the dispersion agent to employ pla biocomposite films. the scco2 process can present an effective and beneficial medium for polymer processing. the major benefits of polymer treatment with scco2 include processing at low temperatures, allowing a large amount of carbon dioxide (co2) into different kinds of a polymer including synthetic and biopolymer and rapidly complete solvent elimination from the final product [13]. besides its greener characteristics, scco2 is chemically inert, inexpensive, easily purchased, non-flammable and highly pure. co2 gas is a suitable solvent for non-polar constituents and dissolves in most polymer compounds [18]. in short, scco2 offers regulated product quality and safety as well as efficient time and energy management. to the best of the author’s knowledge, the study of supercritical carbon dioxide (scco2) 214 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 treatment on antimicrobial biodegradable food packaging material has not been investigated. therefore, in this study, pla biocomposite was produced through solvent casting. this paper also discusses the effects of scco2 on the anti-microbial, water absorption and soil degradation of pla/dsf biocomposite films. 2. experimental 2.1. materials pla in a pallet form was purchased from natureworks®, china. the grade of pla used was 4043d with a density of 0.998 g/cm3 and glass transition between range 57-61 °c. chloroform used as a reagent to dissolve the pla pallet was supplied by merck, malaysia. durian skin waste crops were obtained from a local market at sri gombak, kuala lumpur, malaysia. the dried skins were ground using blender and mill crusher before sieving over 100 to 250 μm to obtain durian skin fibre (dsf). epoxidized palm oil (epo) was obtained from the advanced oleochemical technology division of the malaysia palm oil board (mpob), bangi. cinnamon essential oil (ceo) was bought from it tech research (m) sdn. bhd. luria-bertani agar (lba) and luria-bertani broth (lhb) were purchased from a local supplier and escherichia coli strains were collected from the international islamic university malaysia (iium) under biotechnology laboratory. stock cultures of the studied bacteria were grown in lhb at 30 °c for 24 h prior to testing. 2.2. biocomposite preparation pla biocomposite film was produced via solution casting method. before beginning the experiment, all materials used were kept in an oven with temperature 40 °c for 24 h to avoid moisture absorption. then, 50 ml of chloroform liquid was measured and added into the mixture where the ratio between the pla mixture and chloroform was 1:10 to obtain 0.05 mm of film sheet thickness. fig. 1 (a) shows the mixture of pla and chloroform in the covered beaker. the detailed amount of composition for each sample was shown in table 1. the mixture was then mechanically stirred on a hot plate by using a magnetic stirrer until it reached the homogeneous phase. total weight of each sample was 5.1 g. the solution mixture is poured into the flat surface of a mould in fig. 1 (b). samples were dried after left at room temperature for 1 day as in fig. 1 (c). dried films were peeled off from the casting surface and stored inside desiccators at 25 ± 1 °c until further evaluation. 2.3. supercritical carbon dioxide (scco2) the pla biocomposite film underent supercritical carbon dioxide (scco2) method for 2 h at temperature 40 °c with different pressure at 100 bar (condition 1) and 200 bar (condition 2). the samples were impregnated with co2 through a supercritical carbon dioxide machine model waters (tap sfe biobotanical system, ipm) at international institute for halal research and training (inhart), international islamic university malaysia. the scco2 treatment was carried out into a vessel containing spores in suspensions or film. the co2 was impregnated into the pla biocomposite until the desired pressure was obtained. next, the co2 vent valve was immediately unlocked to stop extra reactions in the container. the depressurize time depends on the pressure at that condition. a) b) c) 215 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 fig. 1. the pla biocomposite film preparation via solution casting method a) the mixture was mechanically stirred on a hot plate, b) poured the sample in mould and c) samples were dried for 24 h before peel-off. table 1: the composition for each sample 2.4. testing method 2.4.1. water absorption analysis water absorption of the films was carried out as per astm d570. before immersed in water, the specimens were dried in an oven for 1 day, placed in a desiccator to get constant weight and subsequently weighted. each sample was immersed in the distilled water at room temperature until saturated weight was obtained. the weight of the samples was recorded every day for the first 14 days and once a week until the values are equilibrium. the water absorption (%) was calculated from the difference in weight and stated as the percentage increase of the initial weight as in eq. (1) [19]. (%) = 100 (1) where wi is a weight of the sample after immersion (g) and wo is the initial weight of the sample (g). all data were collected from averaged of five samples tested. impregnated film at difference condition and non-impregnated specimens were also tested for comparison. 2.4.2. soil burial degradation analysis soil burial degradation analysis of pla biocomposite was measured according to astm d5988. the dried thin film specimen of size 5 cm x 5 cm was prepared. the initial sample pla (g) dsf (g) epo (ml) ceo (ml) chloroform (ml) pla 100 wt% (5.10) 51.00 pla-dsf 97 wt% (4.94) 3 wt% (0.15) 51.00 pla-dsf-epo 93 wt% (4.68) 3 wt% (0.15) 5 wt% (0.26) 51.00 pla-dsf-epoceo 92 wt% (4.68) 3 wt% (0.15) 5 wt% (0.26) 1 wt% (0.05) 51.00 216 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 mass of each sample was weighted before buried in soil at a 5 cm from the soil surface. at these depths, aerobic degradation (action of microorganism) condition could be achieved. the experiment is conducted in an outside laboratory that was exposed to the environment and end for 80 days. the specimens were removed, washed with water, dried in an oven and weighed. the weight losses of the biocomposite sample were studied and recorded based on eq. (2). ℎ (%) = 100 (2) where wi is initial weight of specimen (g) and wf is the final weight of specimen (g). all samples were observed under scanning electron microscope (sem) before and after soil burial test. 2.4.3. antimicrobial test antimicrobial test used in this project was an inhibition zone test through the agar diffusion method. the sample films prepared beforehand were cut by using sterilized scissors. for this test, the films were cut into 6 mm diameter and were placed into microcentrifuged tubes. before place the film into an agar medium, the agar medium was inoculated with 100 μl of tested bacteria, s. aureus (positive gram) and e. coli (negative gram). biocomposite films were then placed on the cultured agar with bacteria. after 24 h to 36 h, the inhibition zone was remarked upon and measured at three different points by using a ruler to get precise average value. 2.4.4. gas chromatography gas chromatography (gc-tof/ms) was used to determine the presence of essential oil composition. the interface temperature for gc-ms is 220 °c. the temperature of the ion source is 200 °c and ionization energy is 70 v. the total ion monitoring (tic) will be used to detect composition in cinnamon essential oil. three replicates per each sample were analyzed. 3. results and discussion 3.1. water absorption analysis the water absorption test is important in food packaging since water or moisture contributes towards the deterioration of food products. the water absorption curves, which demonstrated the percentage of water uptake of the pla biocomposites in 30 days, are shown in fig. 2. water affected the specimen films, based on the components present in the biocomposite films. it could be observed that the specimens underwent scco2 presented lower water absorption in comparison to the untreated specimens. the results showed that the percentage of water absorption slowly increased over the time. based on fig. 2, the water uptake for all the specimens slowly increased during the initial days of the experiment and then levelled-off when it reached the equilibrium state. a similar behaviour was reported for the isolated soy protein (spi) and pla films, whereby the samples started to sharply swollen in the first minute and then began to slowly shrink due to solubilisation of the samples during the experiment [20]. the films achieved saturated after 18 days, as shown in fig. 2. in this present work, the pla-dsf blend without scco2 treatment absorbed the most water (5.1%) compared to the other compositions. the water absorption rate increased in the pla blend when dsf was added. dsf is hydrophilic because it comprises an abundance of hydroxyl groups that tend to attract water molecules [9]. in contrast, pla is a 217 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 hydrophobic polymer. the results for the impregnated pla-dsf sample for conditions 1 and 2 were 4.90% and 4.83%, respectively. these values corresponded to the formation of micro-porosities observed under sem in fig. 4 due to the release of scco2 from the polymer. the pressure applied during the scco2 treatment significantly influenced the water absorption. therefore, as the scco2 pressure increased, the water uptake decreased. the treated biocomposites under condition 2 at a higher pressure presented lower water absorption for all the samples compared to the biocomposites under condition 1. this behaviour is in agreement with the findings studied by souza et al. [21] where the cassava starch biocomposite films was impregnated by scco2. fig. 2. water absorption of pla biocomposite for a) untreated scco2, b) treated scco2 at condition 1 (100 bar) and c) treated scco2 at condition 2 (200 bar). the addition of hydrophilic fibre into the hydrophobic polymer causing swelling of the matrix [6]. swelling affects the bonding between the matrix and fibre, thereby, indirectly decreasing the mechanical properties of a biocomposite. the water uptake in the untreated biocomposite after 30 days was 2.09%, while for the treated sample it was 1.96% (condition 1) and 1.83% (condition 2). these findings could be due to the hydrophobic nature of the polymer [22]. pla also possesses good barrier properties against water absorption [20]. other than that, the presence of epo in the pla biocomposite reduced the amount of water absorbed compared to the pla biocomposite. it was shown that epo slightly affected the water uptake because epo functions as a plasticizer and exhibits a hydrophobic nature [23]. hence, the addition of epo resulted in a hydrophobic behaviour that tended to resist water molecules. the triglyceride oil compound present in palm oil enables samples to be insoluble in water as reported by seniha et al. [24]. 218 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 the effect of ceo on water absorption can be observed in fig. 2. a significant difference was detected in the sample impregnated with ceo, which presented a lower water uptake. after 30 days, an increase of about 3.15% in the total water uptake of the impregnated film under condition 2 was noted, as depicted in fig. 2(c), whereas for the film impregnated under condition 1, it was 3.47%, as shown in fig. 2(b). these results could be correlated to the scco2 treatment conditions. as shown in fig. 2(a), the pla-dsf-epo-ceo biocomposite without scco2 treatment exhibited a 3.66% increase, where the water absorption decreased with the addition of ceo. this showed that the presence of ceo in the biocomposite increased its hydrophobicity and subsequently, reduced its ability to absorb water molecules, which is an important improvement for packaging applications. nevertheless, the water absorption of the untreated and treated biocomposites varied insignificantly. the water uptake decreased slightly for the sample in the presence of cinnamaldehyde, a compound extracted from pure ceo, as evident in the gc analysis presented in fig. 7. the water barrier is a property that dominates potential applications of these plastics in the food industry. materials with a low ability to absorb water are required to protect food products against contact with water [20, 22]. 3.2. soil burial degradation analysis a soil burial degradation test was used to monitor weight loss of pla biocomposite sample. through the soil burial degradation test, the effects of an ordinary and real composting environment on the specimens without any enzymatic and composting resources could be studied. the biodegradability was tested using normal soil to mimic a real environment. the physical appearance was also observed to identify changes in the shape and size of the samples. after 60 days, the samples were observed under sem. the percentage of weight loss was evaluated using eq. (2). the weight loss of the untreated and scco2-treated pla biocomposites with different element contents after 80 days of composting are presented in fig. 3. the weight loss was affected by the absorption of moisture from the soil and the actions of microorganisms [25]. fig. 3 shows the weight loss of the pla biocomposite film after 80 days. the results revealed that the percentage of degradation for all the specimens increased with the time interval. the treated pla biocomposite under condition 2 (200 bar) shows higher degradability with a weight loss of 96.58%, while for the treated pla biocomposite under condition 1 (100 bar) and the untreated biocomposite the weight loss was 95.17% and 93.23%, respectively. the treated sample under condition 2 consisted of a more porous structure, which contributed to the increase in the degradation rate of the film. a similar trend had been reported in which the weight loss of the pla biocomposite increased with the existence of more pores within the blends [3]. porosity aids bacteria and microorganisms to move through the film as shown in the sem micrograph in fig. 5. additionally, the presence of natural fibre is believed to speed up the degradation of specimens due to poor adhesion between the matrix and reinforcement [6]. natural fibre is also more compatible with the surrounding environment, which leads to the degradation process. the high cellulose content in the fibre causes high water absorption, which has a synergistic effect on residual loss and improves the degradation rate of composites [5]. the lowest residual loss was exhibited by the unreinforced pla (65.37%), while the weight loss of the treated pla under condition 1 and condition 2 was 67.01% and 68.56%, respectively. these circumstances occurred due to the hydrophobic behaviour of the pla, which resulted in a lower water uptake, leading to a reduction in the degradation rate [7]. as such, in the soil burial test, the lower composition of pla resulted in an increase in the weight loss. however, pla decomposes better than petroleum-based matrices because of 219 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 its biodegradability [5]. biodegradable plastics will eventually degrade in landfills as they are made from natural resources [26]. other than that, epo reduced the percentage of weight loss of the pla biocomposite. based on fig. 3, the weight loss for the untreated sample with the added of epo was 76.72%. in addition, as compared to the untreated biocomposite, the treated biocomposite had an increment of about 2.87% and 3.56% in the degradation rate for condition 1 and 2, respectively. epo acts as a plasticizer to improve the flexibility of pla biocomposites. therefore, the porosity of the treated sample increased its degradation rate [10, 23]. fig. 3. weight loss of pla biocomposite for a) untreated sample, b) treated sample at condition 1 and c) treated sample at condition 2. the weight loss experienced by the untreated pla-dsf-epo-ceo biocomposite after 80 days was 85.18% (fig. 3(a)). this revealed that the degradability of the specimens dependent on the addition of ceo. there was a slight difference between the samples with and without ceo. the pla biocomposite film with ceo degraded faster in the soil compared to the pla-dsf-epo specimen. fig. 3(c) shows that the treated biocomposite (condition 2) with ceo degraded the fastest, followed by the treated biocomposite (condition 1) and untreated biocomposite. the presence of ceo in the pla biocomposites weakened the specimens. this caused the degradation rate of the pla biocomposite films to increase due to the weak bonding after buried in soil. furthermore, some additive elements inside the specimens might have migrated into the soil and helped in the degradation process [27]. 3.3. surface morphology 220 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 fig. 4 and 5 illustrate the surface micrographs for the untreated and scco2-treated pladsf-epo-ceo films before and after 60 days of the soil burial degradation test. this confirmed that various changes had taken place on the surface of the biocomposite films. the results for the sample without scco2 treatment are shown in fig. 4, while the findings for the treated samples under conditions 1 and 2 are presented in fig. 5. after the degradation process, more pores and visible ruptures on the surface were noted. fig. 4. the surface morphology for pla-dsf-epo-ceo films without treatment a) before and b) after 60 days of soil burial. fig. 5. the surface morphology for pla-dsf-epo-ceo films underwent scco2 treatment a) before degradation (condition 1), b) after degradation (condition 1), c) before degradation (condition 2) and d) after degradation (condition 2). the influence of scco2 treatment with degradation time on the biocomposites was observed under sem. more apparent physical changes had taken place within the surface of the biocomposites treated with scco2 compared to the samples without scco2. based on the observation, fig. 5(b) and (d) showed more ruptures than fig. 4(b). the surface of the untreated films was less disrupted unlike the treated samples after day 60. such changes in the treated samples were signs of the degradation of the pla biocomposite films. according to fig. 5, before the soil burial test, a high porosity was observed on the surface of the biocomposite after the scco2 treatment. in contrast, after the burial in soil, all the films were rough and had numerous holes on the surface. furthermore, the samples also physically changed. the weight loss results could be correlated with the sem micrographs, as shown in fig. 4 and 5. 221 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 3.4. antimicrobial analysis antimicrobial activity was investigated in two steps. firstly, the antimicrobial activity of the ceo was examined using the agar diffusion method. this preliminary study was carried out to evaluate the antimicrobial effect of pure ceo; the results are presented in fig. 6 (a-b). in the second step, ceo was incorporated into the pla film. the effect of the antimicrobial activity of ceo in the pla biocomposites was studied using the agar diffusion method and it was then tested against selected microorganisms. there is no agreement on the standard procedures to evaluate the effectiveness of antimicrobial activities [14]. an antimicrobial test was conducted after the pla biocomposites had been treated with scco2. the antimicrobial activities of the untreated pla biocomposite films incorporated with ceo against gram-positive (staphylococcus aureus) and gram-negative (escherichia coli) bacteria are shown in fig. 6. both bacteria represent the spoilage of the microorganism groups normally found in food products. the size of the inhibition zone around the disks determined the inhibitory activities of the specimen films [17]. although the preliminary results of bacteria inhibition were satisfactory, showing that a complete inhibition of bacteria can be achieved by increasing the amount of ceo, the pla biocomposites however became more brittle when the ceo content was increased. to overcome this problem, it was necessary to vary the content of the plasticizer. nevertheless, this study focused only on the incorporation of 1 wt% of ceo. the control samples without ceo negatively inhibit any of the tested bacteria, which resulted in no inhibition zones around the films. in fig. 6 (a–b), all the films of the control samples were unable to stop the growth of the pathogens. in fact, bacteria colonies were formed on the agar. this result agreed with the findings by ghasemlou et al. [28] on the plasticized corn starch films with essential oil. they reported that the control films negatively exhibited inhibition zone against the tested bacteria. this indicates that the main material used contained no antimicrobial agent, and therefore, the essential oil was incorporated into the polymer films. no clear zones appear show that the specimens were not inhibitory [17]. fig. 6 (e–f) shows the inhibitory effect of films containing 1 wt% ceo against gram positive (s. aureus) and gram negative (e. coli) bacteria. all the films incorporated with ceo inhibited the growth of the two tested bacteria. the 1 wt% concentration of ceo resulted in a significant inhibition, with a diameter of 15.1 ± 0.5 mm for e. coli and 12.5 ± 0.5 mm for s. aureus. these results were significantly different from that of the control specimens. in anuar et al. [1], the untreated pla biocomposite film with 1 wt% of ceo showed an inhibition area of 15.05 ± 0.5 mm for the bacillus subtilis (gram-negative) and 12.8 ± 0.5 mm for the s. aureus. there was a slight difference in the antimicrobial activity results between the treated and untreated samples. however, both samples still achieved the objective of inhibiting bacterial growth. this demonstrated that ceo had a strong antimicrobial activity towards both bacteria. the addition of 0.1 wt% of ceo to the pla film is adequate to decrease the growth of the s. aureus [14]. the results of the current study were in agreement with those who also noticed a higher antimicrobial effect among biodegradable films incorporated with ceo [15]. it is important to note that the antimicrobial activity of the pla film with ceo is based on preliminary studies that evaluated the antimicrobial activity of pure ceo, as in fig. 6 (c–d). 222 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 fig. 6. the inhibition zone of a) control sample without ceo in e-coli, b) control sample without ceo in s. aureus, c) pure ceo in e. coli, d) pure ceo in s. aureus, e) sample incorporated ceo in e-coli and f) sample incorporated ceo in s. aureus. table 2 lists the results of the inhibitory effect of ceo incorporated into the bio-based polymer, which was lower than that of pure essential oil. the same outcome is observed as reported on polyvinyl alcohol (pva)-cassava bagasse incorporated with essential oil [29,30]. according to santos et al. [29] and debiagi et al. [30], the processing surroundings caused a partial loss of the volatile components of the essential oil during the preparation of the biocomposite films. the gram-negative bacteria (e. coli) were more resistant than the gram-positive bacteria (s. aureus) towards the antibacterial treatment. the lower antimicrobial activity against gram-negative bacteria (e. coli) affects the external lipopolysaccharide wall close to the peptidoglycan cell wall. this limits the diffusion of hydrophobic compounds through the lipopolysaccharide layer. on the other hand, grampositive bacteria (s. aureus) have a thick layer of peptidoglycan that may function as a preventive barrier against certain essential oil compounds [28]. table 2: antimicrobial activity of pla biocomposite incorporated with ceo the active compound, cinnamaldehyde, expressed a high antimicrobial activity against gram-positive and gram-negative bacteria. the antimicrobial efficiency of essential oils is related to the concentration and proportion of the phenolic compound [30]. it is believed that the amount of ceo that is added has a role in increasing the inhibition zone of the bacteria. various researches have been carried out on essential oils incorporated into biocomposite films used in the food packaging industry. phenolic compounds disintegrate tested bacteria diameter of inhibitory zone (mm) control 1 wt% ceo pla biocomposite incorporated 1 wt% ceo s. aureus 0±0 35.3±0.5 12.5±0.5 e. coli 0±0 32.7±0.2 15.1±0.5 a) b) c) d) e) f) 223 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 the external cell membrane and mitochondria of bacteria, allowing them to become permeable, and leading to leakage of the cell wall. from the gas chromatography (gc) data on ceo presented in fig. 7, the presence of the main phenolic and terpenoid compounds effectively reduced the zone inhabited by the e. coli and s. aureus. the high content of cinnamaldehyde and α-eugenol in ceo through a gc analysis as reported by bongiovanni et al. [31]. ceo yielded good antibacterial activity compared to thyme and lemongrass oils, and better antibacterial activity than other essential oils like rosemary and oregano [32]. 3.5. gas chromatography about six different elements with varying retention times were detected via the gas chromatography (gc) analysis (fig. 7). the contents of the elements identified in pure ceo are tabulated in table 3. these elements were identified through a retention time and mass spectral library search. the relative amount of each constituent was calculated according to the gc peak area. as seen in table 3, the antimicrobial components were characterised by a dominant concentration of cinnamaldehyde (46.615%) and eugenol (16.345%). other main constituents included à-pinene (2.901%), 3-methyl-hepta-1,6-dien-3-ol (9.064%), trans-á-ocimene (8.709%), and á-phellandrene (0.865%), which acted as antibacterial and antifungal elements but were less effective in inhibiting the bacteria. most ceo components are phenolic in nature and are volatile, and also consist of trace levels of terpenes with antibacterial activity [33]. table 3: composition of element content in the pure cinnamon essential oil (ceo) r.t. (minutes) name compound area % quant s/n area mw structure molecular formula 6.84524 à-pinene 2.9105 3.8659 294004 136 c10h16 10.3362 3-methyl-hepta-1,6-dien-3-ol 9.0646 4.5627 915667 126 c8h14o 15.4335 trans-á-ocimene 8.7029 5.1193 879130 136 c10h16 8.90751 á-phellandrene 0.86546 2.5648 87425 136 c10h16 14.9643 eugenol 16.345 7.4453 1651138 164 c10h12o2 12.9065 cinnamaldehyde, (e)46.615 20.201 4708802 132 c9h8o cinnamaldehyde and eugenol combinations are already being used as disinfectants in hospitals, especially for medical devices [34]. the experimental test enabled the evaluation and comparison of antimicrobial activity against bacteria commonly found in food products. with these findings, it can be concluded that ceo is suitable and more effective against the tested bacteria since it presents a wider inhibition zone with a lower concentration. it was hypothesised that this result could be due to the presence of cinnamaldehyde as an active compound against both gram-positive and gram-negative bacteria. furthermore, this finding also presented an important approach in developing active packaging with a lower oh h o 224 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 concentration of active essential oil. many studies on the antimicrobial activity of active films incorporated with other essential oils have indicated their potential for use in food packaging. as such, the effectiveness of antimicrobial films activated with ceo should be considered by the food packaging industry. fig. 7. gas chromatography profile of cinnamon essential oil. 4. conclusion remarks the weight loss for pla biocomposite was increased due to the presence of more porosity in the biocomposites. the water absorption evident that scco2 treatment aids to reduce the water uptake of pla biocomposite due to plasticizing effect. the plasticizer decreased the moisture transfer between the food and packaging, thus improving the shelflife of packaged food. only 1 wt% ceo has optimized the antimicrobial properties for active food packaging application. besides that, the presence of aldehyde as a functional group in ceo was evident by using gc-ms/tof. the use of ceo is very significant in this research as an antimicrobial agent for the biocomposites film. based on the findings, scco2 could be an interesting alternative treatment in the food packaging industry as compared to the conventional method. acknowledgement the authors wish to thank the ministry of higher education (moe) for the funding provided through the fundamental research grant scheme (frgs16-003-0502), research initiative grant scheme – post-doctoral fellow (rpdf18-010-0010) from international islamic university malaysia (iium), department of science & technology (dst)-asean-india 225 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 research training fellowship (rtf/2019/000083) for the equipment and facilities provided in making these studies a success. references [1] anuar h, nur fatin izzati b, sharifah nurul inani sm, siti nur e’zzati ma, siti munirah salimah ab, ali fb, manshor mr. (2017) impregnation of cinnamon essential oil into plasticised polylactic acid biocomposite film for active food packaging. journal of packaging technology and research, 1(3): 149-157. [2] lithner d. (2011) environmental and health hazards of chemicals in plastic polymers and products. phd thesis. university of gothenburg, department of plant and environmental sciences. [3] thothong s, jarerat a, sriroth k, tantatherdtam r. (2013) degradation of porous starch granules and poly (butylene adipate-co-terephthalate) (pbat) blends: soil burial and enzymatic tests. advanced materials research, 651: 12-17. [4] nur aimi mn, anuar h, manshor mr, wan nazri wb, sapuan sm. (2014) optimizing the parameter in durian skin fiber reinforced polypropylene composites by response surface methodology. industrial crops and products, 54: 291-295. [5] yussuf aa, massoumi i, hassan a. (2010) comparison of polylactic acid/kenaf and polylactic acid/rise husk composites: the influence of the natural fibres on the mechanical, thermal and biodegradability. journal of polymers and the environment, 18(3): 422-429. [6] gunti r, ratna prasad av, gupta avssks. (2016) mechanical and degradation properties of natural fiber-reinforced pla composites: jute, sisal and elephant grass. polymer composites, 39(4): 1125-1136. [7] kumar r, yakubu mk, anandjiwala rdy. (2010) biodegradation of flax fibre-reinforced polylactic acid. express polymer letters, 4(7): 423-430. [8] wan nazri wb, ezdiani zn, romainor mm., erma ks, jurina j, noor fadzlina iza. (2014)effect of fibre loading on mechanical properties of durian skin fibre composite. journal tropical agriculture and food science, 42(2): 169-174. [9] manshor mr, anuarh, nur aimi nm, ahmad fitrie mi, wan nazri wb, sapuan sm, elshekeil ya, wahid mu. (2014) mechanical, thermal and morphological properties of durian skin fibre reinforced pla biocomposites. material and design, 59: 279-286. [10] ali f, awale fakhruldin rj, anuar h. (2016) plasticizing poly (lactic acid) using epoxidized palm oil (epo) for environmental friendly packaging material. malaysian journal of analytic sciences, 20(5): 1153-1158. [11] silverajah vsg, ibrahim na, yunus wm, hassan ha, woei cb. (2012) a comparative study on the mechanical, thermal and morphological characterization of poly (lactic acid)/epoxidized palm oil blend. international journal of molecular sciences, 13: 5878-5898. [12] chieng bw, ibrahim na, wan md zin wy, hussein mz. (2014) epoxidized vegetable oils plasticized poly (lactic acid): mechanical, thermal, and morphology properties. journal applied polymer science, 130: 4576-4580. [13] souza a, dias ama, sousa hc, tadini cc. (2013) cassava starch composite films incorporated with cinnamon essential oil: antimicrobial activity, microstructure, mechanical and barrier properties. lwt food science and technology, 54: 346-352. [14] qin y, yang j, xue j. (2015) characterization of antimicrobial poly (lactic acid)/ poly (trimethylene carbonate) films with cinnamaldehyde. journal of material science, 50(3): 1150-1158. [15] erdohan zö, belgizarc, turhan knb. (2013) characterization of antimicrobial polylactic acid-based films. journal of food engineering, 119(2): 308-315. [16] vazirian ma, alehabib s, hossein j, mohammad rf, toosi an, mahnaz k. (2015) antimicrobial effect of cinnamon (cinnamomum verum j. presl) bark essential oil in creamfilled cakes and pastries. research journal of pharmacognosy, 2(4): 11-16. [17] wu j, sun x, guo x, ge s, zhang q. (2017) physicochemical properties, antimicrobial activity and oil release of fish gelatin films incorporated with cinnamon essential oil. aquaculture and fisheries, 2(4): 185-192. 226 iium engineering journal, vol. 21, no. 1, 2020 anuar et al. https://doi.org/10.31436/iiumej.v21i1.1220 [18] milovanovic s, kuska r, skoric-lucic m, kalagasidis-krusic m, frerich s, zizovic, i, ivanovic j. (2016) swelling kinetics and impregnation of pla with thymol under supercritical co2 conditions. tehnika, 71(1): 16-20. [19] patpen p, russly ar, rosnita at, khalina a. (2015) mechanical properties and water absorption behaviour of durian rind cellulose reinforced poly (lactic acid) biocomposites. international journal on advanced science engineering information technology, 5(5): 343348. [20] gonzález a, alvarez i, cecilia i. (2013) soy protein poly (lactic acid) bilayer films as biodegradable material for active food packaging. food hydrocolloids, 33(2): 289-296. [21] souza a, goto geo, mainardi ja, coelho acv,tadini cc. (2014) impregnation of cinnamaldehyde into cassava starch biocomposite films using supercritical fluid technology for the development of food active packaging. carbohydrate polymers, 102: 830-837. [22] aranda-garciafj, gonzález-núñez r, jasso-gastinel cf, mendizábal e. (2015) water absorption and thermomechanical characterization of extruded starch/ poly (lactic acid)/ agave bagasse fibre bioplastic composites. international journal of polymer sciences, 2015: 1-7. [23] emad aja, wan md. zain wy, nor azowa i, mohd zaki ar. (2010) properties of epoxidized palm oil plasticized polylactic acid. journal material science, 45: 1942-1946. [24] seniha gf, yagci y, tuncereay. (2006) polymers from triglyceride oils. progress in polymer science, 31: 633-670. [25] amer zja, saeed aq. (2015) soil burial degradation of polypropylene/ starch blend. international journal of technical research and applications, 3(1): 91-96. [26] weng yx, jin yj, meng qy, wang l, zhang m, wang yz. (2013) biodegradation behaviour of poly (butylene adipate-co-terephthalate) (pbat), poly (lactic acid) (pla), and their blend under soil conditions. polymer testing, 32(5): 918-926. [27] lardjane n, belhaneche bn. (2009) migration of additives in simulated landfills and soil burial degradation of plasticized pvc. journal of applied polymer science, 111(1): 525-531. [28] ghasemlou m, aliheidari n, fahmi r, shojaee-aliabadi s, keshavarz b, cran mj, khaksar r. (2013) physical, mechanical and barrier properties of corn starch films incorporated with plant essential oils. carbohydrate polymers, 98(1): 117-1126. [29] santos sf, novales mg. (2012) essential oils from aromatic herbs as antimicrobial agents. current opinion in biotechnology, 23: 136-141. [30] debiagi f, kobayashi, renata kt, nakazatogp, luciano a, mali s. (2014) biodegradable active packaging based on cassava bagasse polyvinyl alcohol and essential oils. industrial crops and products, 52: 664-670. [31] bongiovanni v, colombo m, laura c, andrea t, daniela c. (2017) determining odour-active compounds in a commercial sample of cinnamomun cassia essential oil using gc-ms and gc-o. journal of chromatography & separation techniques, 8(1): 1-7. [32] gende l, floris i, fritz r, eguaras m. (2008) antimicrobial activity of cinnamon (cinnamon zeylanicum) essential oil and its main components against paenibacillus larvae from argentine. b. insectol, 61(1): 1-4. [33] adinew b. (2014) gc-ms and ft-ir analysis of constituents of essential oil from cinnamon bark growing in south-west of ethiopia. international journal of herbal medicine, 1(6): 2231. [34] goni p, lopez p, sanchez c, gomez lr, beceril r, nerin c. (2009) antimicrobial activity in the vapour phase of a combination of cinnamon and clove essential oils. food chemistry, 116: 982-989. 227 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <feff03a703c103b703c303b903bc03bf03c003bf03b903ae03c303c403b5002003b103c503c403ad03c2002003c403b903c2002003c103c503b803bc03af03c303b503b903c2002003b303b903b1002003bd03b1002003b403b703bc03b903bf03c503c103b303ae03c303b503c403b5002003ad03b303b303c103b103c603b1002000410064006f006200650020005000440046002003ba03b103c403ac03bb03bb03b703bb03b1002003b303b903b1002003b103be03b903cc03c003b903c303c403b7002003c003c103bf03b203bf03bb03ae002003ba03b103b9002003b503ba03c403cd03c003c903c303b7002003b503c003b103b303b303b503bb03bc03b103c403b903ba03ce03bd002003b503b303b303c103ac03c603c903bd002e0020002003a403b1002003ad03b303b303c103b103c603b10020005000440046002003c003bf03c5002003b803b1002003b403b703bc03b903bf03c503c103b303b703b803bf03cd03bd002003b103bd03bf03af03b303bf03c503bd002003bc03b50020004100630072006f006200610074002003ba03b103b9002000410064006f00620065002000520065006100640065007200200036002e0030002003ba03b103b9002003bd03b503cc03c403b503c103b503c2002003b503ba03b403cc03c303b503b903c2002e> /heb <feff05d405e905ea05de05e905d5002005d105e705d105d905e205d505ea002005d005dc05d4002005db05d305d9002005dc05d905e605d505e8002005de05e105de05db05d9002000410064006f006200650020005000440046002005d405de05ea05d005d905de05d905dd002005dc05ea05e605d505d205d4002005d505dc05d405d305e405e105d4002005d005de05d905e005d505ea002005e905dc002005de05e105de05db05d905dd002005e205e105e705d905d905dd002e0020002005e005d905ea05df002005dc05e405ea05d505d7002005e705d505d105e605d90020005000440046002005d1002d0020004100630072006f006200610074002005d505d1002d002000410064006f006200650020005200650061006400650072002005de05d205e805e105d400200036002e0030002005d505de05e205dc05d4002e> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <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> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <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> /rum <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> /rus <feff04180441043f043e043b044c043704430439044204350020044d044204380020043f043004400430043c043504420440044b0020043f0440043800200441043e043704340430043d0438043800200434043e043a0443043c0435043d0442043e0432002000410064006f006200650020005000440046002c0020043f043e04340445043e0434044f04490438044500200434043b044f0020043d0430043404350436043d043e0433043e0020043f0440043e0441043c043e044204400430002004380020043f043504470430044204380020043104380437043d04350441002d0434043e043a0443043c0435043d0442043e0432002e00200421043e043704340430043d043d044b043500200434043e043a0443043c0435043d0442044b00200050004400460020043c043e0436043d043e0020043e0442043a0440044b0442044c002c002004380441043f043e043b044c04370443044f0020004100630072006f00620061007400200438002000410064006f00620065002000520065006100640065007200200036002e00300020043b04380431043e00200438044500200431043e043b043504350020043f043e04370434043d043804350020043204350440044104380438002e> /sky <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> /slv <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> /suo <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> /sve <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> /tur <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> /ukr <feff04120438043a043e0440043804410442043e043204430439044204350020044604560020043f043004400430043c043504420440043800200434043b044f0020044104420432043e04400435043d043d044f00200434043e043a0443043c0435043d044204560432002000410064006f006200650020005000440046002c0020043f044004380437043d043004470435043d0438044500200434043b044f0020043d0430043404560439043d043e0433043e0020043f0435044004350433043b044f04340443002004560020043404400443043a0443002004340456043b043e04320438044500200434043e043a0443043c0435043d044204560432002e0020042104420432043e04400435043d04560020005000440046002d0434043e043a0443043c0435043d044204380020043c043e0436043d04300020043204560434043a04400438043204300442043800200437043000200434043e043f043e043c043e0433043e044e0020043f0440043e043304400430043c04380020004100630072006f00620061007400200456002000410064006f00620065002000520065006100640065007200200036002e00300020044204300020043f04560437043d04560448043804450020043204350440044104560439002e> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 effect of printing parameters and postcuring on mechanical properties of photopolymer parts fabricated via 3d stereolithography printing raffle raed diab, abass enzi and omar hashim hassoon department of production engineering and metallurgy, university of technology, baghdad, iraq * corresponding author: abass.m.jabber@uotechnology.edu.iq (received: 4 march 2023; accepted: 22 may 2023; published on-line: 4 july 2023) abstract: three-dimensional printing has recently come into the spotlight due to its promising potential to create physically three-dimensional parts or structures through computer-aided design. while there are many options for 3d printing methods, photopolymerization 3d printing has garnered much attention because of its high resolution. however, the mechanical properties of photopolymerized 3d printed parts can vary widely depending on the manufacturing parameters and post-processing settings used. this research focuses on studying the effect of printing variables on the mechanical properties of samples printed using a stereolithography machine (formlabs, form+3). three variables are used: layer thickness (25 and 50 μm), part orientation (x and z directions), and post-curing. also, eight groups of 3d-printed photopolymer specimens for twenty-four specimens are used for the tensile test results. the results showed the printing variables affected the mechanical properties of samples, which were proven by young's modulus, ultimate stress, and ultimate strain. abstrak: pencetakan tiga dimensi baru-baru ini menjadi perhatian kerana potensinya yang menjanjikan bagi mencipta bahagian atau struktur tiga dimensi secara fizikal melalui reka bentuk bantuan komputer. walaupun terdapat banyak pilihan bagi kaedah percetakan 3d, pencetakan 3d fotopolimerisasi telah mendapat banyak perhatian kerana resolusinya yang tinggi. walau bagaimanapun, sifat mekanikal bahagian bercetak 3d fotopolimer adalah pelbagai bergantung pada parameter pembuatan dan tetapan pasca pemprosesan yang digunakan. kajian ini memberi tumpuan kepada kesan pembolehubah cetakan terhadap sifat mekanikal sampel yang dicetak menggunakan mesin stereolitografi (formlabs, form+3). tiga pembolehubah digunakan: ketebalan lapisan (25 dan 50 μm), orientasi bahagian (arah x dan z), dan pasca pengawetan. juga, lapan kumpulan spesimen fotopolimer cetakan 3d untuk dua puluh empat spesimen digunakan bagi mendapatkan keputusan ujian tegangan. dapatan kajian menunjukkan pembolehubah cetakan mempengaruhi sifat mekanikal sampel, dibuktikan oleh modulus young, tegangan utama, dan tarikan utama. keywords: additive manufacturing; stereolithography; photocurable polymer; mechanical properties; post-curing 1. introduction 3d printing is one of the modern manufacturing methods that are gaining popularity because of the possibility of its use in various fields of engineering, medicine, and more. compared to other manufacturing methods, simple and complex parts can be easily 225 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 manufactured in record time using 3d printing. also, the manufacturing process’ waste and its cost are very limited in the printing process, which reduces the manufacturing cost [1]. according to the annual growth rate, 3d printing industry sales in 2020 reached more than 8 billion dollars in sales, equivalent to 14%. in 2013, the worldwide demand for 3d printing materials reached about 2 tons, which is anticipated to grow due to the increased use of printed products [2]. operating 3d printers and manufacturing is simple; anyone can efficiently handle the machines and manufacture parts. the manufacturing process begins with drawing the 3d part with one of the engineering drawing programs, such as solidworks. then the drawing is saved in stl file format. after that, the file is sent to the 3d printer to start the manufacturing process layer-by-layer after the required manufacturing process parameters are determined [3-7]. as shown in fig. 1, stereolithography is one of the most important methods of producing 3d parts with good quality. sla system uses a laser to polymerize a liquid resin and transform it into a solid part by a process called photopolymerization [8,9]. printing thinner layers results in more cohesion and higher mechanical properties, but it does so at the expense of increased construction time [10]. layers in stereolithography are kept in a semi-reacted "green state" with polymerizable groups between them because the polymerization reaction is incomplete, and that helps with layer-to-layer bonding by supplying layers for subsequent polymerization. at the same time, post-curing procedures are used to finish the reaction and covalently bind successive layers. after curing, uv is typically employed to complete polymerization by activating photoinitiators [11]. fig. 1: scheme of stereolithography 3d printer machine. researchers used an sla printer in previous work to produce samples with a wide range of print orientations and layer thicknesses [12]. aznarte et al. [13] examined how 3d printing variables affect the final mechanical properties of specimens created using digital light processing (dlp) 3d printing. design, printing, and testing in this research were done on several iso-compliant tensile test specimens. the effect of variables (layer thickness, exposure time, and part orientation) was examined for the elastic modulus, ultimate strain, ultimate tensile strength, and printing time, along with the economic impact of the researched factors regarding printing time. results presented design guidelines for vat photopolymerization procedures. khalid et al. [14] used the pr 48 photopolymer samples in this investigation using the form 2 sla printer. the elastic modulus and hardness of printed specimens with 50 and 100 μm resolutions were evaluated employing a nanoindentation testing machine at 0°, 45°, and 90° directions. uv was used to cure the samples, and the impact of uv curing duration was examined. results demonstrated that the elastic modulus and hardness for 100 μm print resolution and 0° orientation was greater if compared to 45° and 90° orientation by 35% and 390%, respectively. elastic modulus and 226 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 hardness for 0° direction were greater than 45° direction by 106%, and greater also for 90° orientation by 92% for 50 μm print resolution. the findings demonstrated that mechanical properties strongly depended on resolution, print direction, and uv curing time. agrawal [15] attempted to determine which orientation angle is best for which kinds of loads, specifically the fracture test and the dynamic mechanical analysis (dma) test. various mechanical property values were obtained during the inspection process. results showed the orientation angle had a significant impact on the examination process. an average of three samples were taken for each test to reduce the error. after considering the stress-strain and load-extension graphs, the researcher concluded that the orientation angle should be 0°. the parts manufactured using the sla system change their mechanical properties according to the selected variables of the printing process. therefore, some printed samples have poor mechanical properties due to the values of the used printing process variables, as the printing process variables have a significant impact on the mechanical properties of the produced samples. therefore, the work aim is to determine the effect of part orientation in the x and z axes, layer thicknesses of 25 and 50 μm, and post-curing on the mechanical properties of printed samples that are fabricated using the sla system. the specimens' elastic modulus, ultimate stress, and ultimate strain are evaluated and analyzed depending on tensile test results to recognize the variables' values that affect printed specimens' mechanical properties. 2. material and experimental details a detailed description presents the manufacturing process and sample preparation, where the material used in the printing process is explained, as well as the variables of the printing process, the preparation of the number of experiments that are completed, the preparation of samples, and the examination process for samples that are produced through the printing process by a tensile test device. 2.1 material clear resin is ideal for fluidics and mold making, optics, lighting, and any component needing translucency or displaying internal characteristics. it possesses several crucial characteristics, including quality. formlabs' precisely crafted clear resin captures a model's finest features. formlabs clear resin is excellent for quick prototyping and product development because it produces accurate, durable pieces, a glossy appearance, and the surface finish of the printed parts is smooth [15]. in the present investigation, specimens are printed with photocurable acrylic-based resin flgpcl4 (formlabs, ma, usa). 2.2 process parameters 3d printing is one of the basic methods for producing prototype parts. still, 3d printing is not considered one of the mass production methods due to the long production time, anisotropy, etc. in addition, some critical issues face the 3d printing process, including accuracy, curvature, anisotropy, and the formation of voids inside the manufactured parts. the properties of 3d printed parts are dependent on printing parameters such as temperature, 3d printer machine resolution, layer thickness, geometries, and printing orientations. therefore, one of the important points before the printing process is to focus on choosing the best process variables for printing to avoid defects in the manufactured parts [7,16-20]. in the current experimental study, there are three process parameters used. two printing parameters include layer thickness and part orientation, and the third parameter is postcuring. the layer thickness is one of the most critical variables of the printing process, which affects the quality of the produced surface and the mechanical properties of the 227 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 manufactured parts. increasing or decreasing the layer thickness affects the sample's strength. there are many directions for printing, and researchers focus on changing the direction of printing during the sample preparation process to obtain the best quality of the manufactured parts. part orientation is one of the most studied manufacturing characteristics. therefore, printing direction statistically impacts the mechanical properties of sla 3d-printed parts [21-23]. figure 2 shows the part's orientation for both the x-axis and z-axis. fig. 2: printing process directions. finishing, including washing and post-curing, are necessary when using sla printing because areas of uncured resin, whether between layers or on the surface, are considered weak points and damage the material's mechanical properties. the uv post-curing of sla printed resin can significantly improve the mechanical strength due to the complete curing of any leftover resin. in addition, the most significant improvement in properties occurs when the uv light is at the same wavelength that the sla printer uses to cure the resin, as each resin type has a specific wavelength for the curing process. therefore, the appropriate wavelength must be chosen to cure the resin for the best results [24]. immediately following the completion of the printing process, the supporting material is removed from the printed part and the part is soaked in isopropyl alcohol for 15 minutes. alcohol liquefies any uncured resin and cleans the surface of the components. before testing, materials were allowed to dry for 24 hours on a clean surface. post-curing is carried out for 50 minutes in a uv chamber, previously heated to 60 °c with a light source of 405 nm and 1.25 mw/cm, see fig. 3. fig. 3: tensile test specimens during the post-curing process in formlabs uv chamber (formcure). 228 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 2.3 experimental design sla technology generates 3d printed parts from a liquid (photopolymer) resin by employing a uv-light source to solidify the liquid substance (resin). to construct a 3dprinted object, a build platform is submerged in a tank of photosensitive thermoset polymeric resin. once the build platform is submerged, a uv light within the machine solidifies the material by mapping each layer of the object through the tank's bottom. after the light source has printed the layer, the platform rises to allow the swiping blade to apply a fresh coating of resin to the surface; this is continued layer-by-layer until the desired object is created [25]. table 1 represents all experimental variables and groups that will be used to print the specimens, to ensure that the results of the studies can be reliably replicated; each sample is printed three times. table 1: eight groups (a-h) of specimens with printing parameters symbol a b c d e f g h variables layer thickness (μm) 25 25 25 25 50 50 50 50 part orientation xaxis xaxis zaxis zaxis xaxis xaxis z axis zaxis post-curing green postcured green postcured green postcured green postcured 2.3.1 specimen preparation solidworks is used to make the 3d model of the specimens following astm d638 type iv. fig. 4 displays the astm-required dimensions of the specimen. slicing can build the model using any cad software and export it in a 3d printable file format (stl). each sla printer includes software to configure printing settings and split the digital model into layers for printing. once the part design is completed, the print preparation software transmits the instructions to the printer over a wireless or wired connection. for slicing, stl file software named formlabs preform (version 3.27.1) is used to slice the specimen into some layers. in addition, the factors are fed to printer software based on the process parameters used in this research. fig. 4: standard specimens according to astm d638 specimen dimensions (all units in mm) [26]. an sla machine (formlabs, form+3) is used in this research to produce the specimens. form+3 has a 50 μm resolution in the plane parallel to the printing surface (xy resolution) and a 10 μm resolution perpendicular to the printing surface (z resolution). figure 5 depicts 229 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 the machine and the necessary support structure for building the specimens in all directions. it was reported that the printer's maximum build dimensions were 145 x 145 x 185 mm. fig. 5: fabrication of tensile specimen (a) longitudinal direction (b) vertical direction (c) twenty-four specimens. 2.3.2 tensile testing a gester universal tensile testing machine is used to test the properties of the printed specimens, with a load cell capacity of 5kn with a crosshead speed of 1mm/min; see fig. 6. fig. 6: specimen placed inside the grips of the gester universal tensile testing machine. 3. results and discussion in this section, the tensile test results are shown and discussed. the section is separated into three subsections that discuss the effect of several elements on young’s modulus, ultimate stress, and ultimate strain, respectively. table 2 shows eight specimens for twentyfour groups representing a variety of process parameters. figure 7 shows the relationship between displacement (mm) and force (n) for green and cured samples. the curing process and layer thickness increased the tensile strength of the samples, taking into account the printing orientation. the cured samples had greater tensile strength than the green samples with decreased displacement because the material's behavior tends towards the sample's fragility. however, the green samples had more significant displacement than the cured samples. the tensile strength and displacement values change according to the printing variables, which indicate that the variables significantly impact tensile strength. (a) (b) (c) 230 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 table 2: tensile testing results for twenty-four specimens depending on the printing parameters and post-curing sample young's modulus e (mpa) average of modulus e (mpa) ultimate stress (mpa) average of ultimate stress (mpa) strain at break (xf) average of strain at break (xf) a1 1394.6 1301.961 46.019 44.892 0.109 0.108 a2 1135.883 43.956 0.099 a3 1375.4 44.700 0.116 b1 1626.75 1648.417 61.8238 57.5566 0.085 0.073067 b2 1659.25 55.423 0.0522 b3 1659.25 55.423 0.082 c1 1339.273 1326.479 48.248 49.217 0.085 0.106 c2 1336.182 47.766 0.104 c3 1303.983 51.638 0.13 d1 1818.5 1767.274 62.193 61.707 0.067 0.067333 d2 1784.75 62.112 0.066 d3 1698.571 60.815 0.069 e1 619.564 796.141 35.097 33.159 0.0635 0.0822 e2 916.933 35.416 0.049 e3 851.925 28.963 0.134 f1 1526 1487.119 56.990 57.307 0.057 0.064 f2 1347.8 54.248 0.076 f3 1587.556 60.684 0.059 g1 1236.167 1228.141 41.537 42.219 0.076 0.103333 g2 1309.333 44.778 0.113 g3 1138.923 40.342 0.121 h1 1794.5 1699.033 61.731 60.277 0.0625 0.0815 h2 1449.6 59.433 0.118 h3 1853 59.666 0.064 fig. 7: force displacement curves (a) green and cured samples with x-axis and 25 μm (b) green and cured samples with z-axis and 25 μm (c) green and cured samples with x-axis and 50 μm (d) green and cured samples with z-axis and 50 μm. (a (b ) (c) (d 231 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 3.1 effect of layer thickness, part orientation, and post-curing on young's modulus in this part, a detailed explanation, supported by values and figures, is given of the relationship between the variables of the specimens manufacturing process with young's modulus and manufacturing time. where it will be explained: 1. young's modulus vs. layer thickness for samples printed with x, 0° orientation & 25 μm, 50 μm thickness. 2. young's modulus vs. layer thickness for samples printed with z, 90° orientation & 25 μm, 50 μm layer thickness. young's modulus vs. layer thickness for samples printed with x, 0° orientation & 25 μm, 50 μm thickness: for the green specimens, the average elastic modulus produced with layer thicknesses of 25 μm and 50 μm was 1301.961 mpa, 796.141 mpa, respectively. the modulus decreased clearly by 50.582% when layer thickness was increased from 25 μm to 50 μm. for cured samples, the average elastic modulus of the printed specimens with layer thicknesses of 25 μm and 50 μm was 1648.417 mpa and 1487.119 mpa, respectively. the modulus dropped by 16.13% when layer thickness was increased from 25 μm to 50 μm). in addition, the results imply that the elastic modulus increased with a thin layer, and that happens because of the resin's exponential decay in the amount of light it transmits, increased curing speeds along the layer, and increased adhesion between layers [26]. the data also showed that curing significantly increased elastic modulus, as the elastic modulus of a green specimen that was printed with a layer thickness of 25 μm grew to 1648.417 (34.6456 %) mpa when cured. additionally, after curing, the elastic modulus of the green specimen, which was printed with a layer thickness of 50 μm (796.141 mpa), increased to 1487.119 mpa (69.09%). the elastic modulus of 25 μm samples was higher than that of 50 μm samples because they have a lower fraction of semi-reacted resin due to superior laser beam penetration through a thinner layer, see fig. 8 (a) & (b). fig. 8: young's modulus vs. layer thickness for (a) x, 0° green samples (b) x, 0° cured samples (c) z, 90° green samples (d) z, 90° cured samples. (c) (d) (a) (b) 232 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 young's modulus vs. layer thickness for samples printed with z, 90° orientation & 25 μm, 50 μm layer thickness: for green samples, the average elastic modulus for specimens produced with layer thicknesses of 25 μm and 50 μm was 1326.479 mpa and 1228.141 mpa, respectively. as can be seen, the modulus decreased by 9.8338 % when layer thickness was increased from 25 μm to 50 μm. for cured samples, the average elastic modulus of the specimens printed with layer thicknesses of 25 μm and 50 μm was 1767.274 mpa and 1699.033 mpa, respectively. as can be seen, the modulus dropped by 6.8241% when the layer thickness was increased from 25 μm to 50 μm. the elastic modulus of 25 μm samples was higher because they have a lower fraction of semi-reacted resin due to superior laser beam penetration through a thinner layer, see fig. 8 (c) &(d). for green samples, the modulus of elasticity with x-direction and layer thickness varying from 50 and 25 μm increased from 796.141 to 1301.961 (increased 63.533%), and for the z-direction increased from 1228.141 to 1326.479 mpa (increased 8%). for the cured sample, the modulus of elasticity with x-direction and layer thickness varying from 50 and 25 μm increased from 1487.119 to 1648.417 (increased 10.846%), and for z-direction increased from 1699.033 to 1767.274 mpa (increased 4.016%). therefore, the results showed that the modulus of elasticity with the xdirection is better than the z-direction in both green and cured samples (see fig. 9). fig. 9: young's modulus for (a) green samples (b) cured samples. results showed that the thinner layer had higher elastic modulus, and that happened due to the exponential decay of light intensity transmission of the resin and getting higher curing rates along the layers and higher adhesion between layers. 3.2 effect of layer thickness, part orientation, and post-cure on ultimate stress this part will explain the effect of the manufacturing process variables on the ultimate stress and printing time. where it will be explained: 1. ultimate stress vs. layer thickness for samples printed with x, 0° orientation & 25 μm, 50 μm thicknesses. 2. ultimate stress vs. layer thickness for samples printed with z, 90° orientation & 25 μm, 50 μm layer thicknesses. ultimate stress vs. layer thickness for samples printed with x, 0° orientation & 25 μm, 50 μm thicknesses: figure 10 (c) & (d) demonstrates that specimens with the thinnest layer thickness can tolerate more stress than those with thicker layers. this outcome can be attributed to the resin transmittance, which allows a thinner layer to cure to a greater extent (a) (b) 233 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 than a thicker layer. for green samples, the average ultimate stress for specimens produced with layer thicknesses of 25 μm and 50 μm was 44.892 mpa, and 33.159 mpa, respectively. for cured samples, the average ultimate stress of the specimens printed with a layer thickness of 25 μm and 50 μm was 57.5566 mpa and 57.307 mpa, respectively. ultimate stress vs. layer thickness for samples printed with z, 90° orientation, and 25 μm and 50 μm layer thickness: for green samples, the average ultimate stress for specimens produced with layer thicknesses of 25 μm and 50 μm was 49.217 mpa and 42.219 mpa, respectively. for cured samples, the average ultimate stress of the specimens printed with a layer thickness of 25 μm and 50 μm was 61.707 mpa and 60.277 mpa, respectively, see fig. 10 (c) & (d). fig. 10. ultimate stress vs. layer thickness for (a) x, 0° green samples (b) x, 0° cured samples (c) z, 90° green samples (d) z, 90° cured samples (e) green samples (f) cured samples. (e) (f) 234 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 for green samples, the ultimate stress with x-direction and layer thickness varying from 50 and 25 μm increased from 33.159 to 44.892 (increased 35.384%), and for z-direction increased from 42.219 to 49.217 mpa (increased 16.575%). for the cured sample, the ultimate stress with x-direction and layer thickness varying from 50 and 25 μm increased slightly from 57.307 to 57.556 (increased 0.004 %). for the z-direction, it increased slightly from 60.277 to 61.707 mpa (increased by 2.372%). therefore, the results showed that the ultimate stress with the xdirection is better than the z-direction in both green and cured samples; see fig. 10 (e) & (f). the specimens with thin layers withstand greater forces than those with thicker layers, resulting from laser transmittance and providing a higher degree of curing to a thin layer than a thicker layer. 3.3 effect of layer thickness, part orientation, and post-cure on ultimate strain the effect of manufacturing process variables on ultimate strain will be explained in this part. where it will be explained: 1. ultimate strain vs. layer thickness for samples printed with x, 0° orientation & 25 μm, 50 μm thickness. 2. ultimate strain vs. layer thickness for samples printed with z, 90° orientation & 25 μm, 50 μm layer thickness. ultimate strain vs. layer thickness for samples printed with x, 0° orientation & 25 μm, 50 μm thickness: for green samples, the average ultimate strain for specimens produced with layer thicknesses of 25 μm and 50 μm was 0.108 and 0.082, respectively. for cured samples, the average ultimate strain of the specimens printed with a layer thickness of 25 μm and 50 μm was 0.073 and 0.064, respectively, see fig. 11(a) & (b). ultimate strain vs. layer thickness for samples printed with z, 90° orientation & 25 μm, 50 μm layer thickness: for green samples, the average ultimate strain for specimens produced with layer thicknesses of 25 μm and 50 μm was 0.106, 0.103, respectively. for cured samples, the average ultimate strain of the specimens printed with a layer thickness of 25 μm and 50 μm was 0.0822 and 0.0815, respectively. by examining the results, the ultimate strain of the green samples was greater than that of the cured samples, see fig. 11 (c) & (d). for green samples, the ultimate strain with x-direction and layer thickness varying from 50 and 25μm increased from 0.0822 to 0.108 (increased 31.386%), and for zdirection, increased from 0.103 to 0.106 mpa (increased 2.912%). for the cured sample, the ultimate strain with x-direction and layer thickness varying from 50 and 25μm rose from 0.064 to 0.073 (increased 14.062%), and for z-direction decreased from 0.081 to 0.067 mpa (fallen 20.895%). therefore, the results showed that the ultimate strain with the xdirection is better than the z-direction in both green and cured samples; see fig. 11 (e) & (f). 4. conclusions in this study, the mechanical properties of 3d-printed photopolymers are examined and analyzed according to layer thickness, printing orientation, and post-curing. based on the analyzed properties of elastic modulus, ultimate stress, and ultimate strain used to evaluate the printed samples, the results demonstrated that printing parameters significantly impacted mechanical properties. the results show that mechanical properties increased in xorientation when the layer thickness varied from 50 to 25 μm in green printed samples. therefore, the x-axis samples exhibit improvement in tensile strength and elastic modulus and have more elongation to failure when printed layers change to be thinner compared to 235 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 printed samples in the z-axis. this could be due to the nature of the 3d printing procedure, which constructs a desired part layer-by-layer. when printing a new layer on the specimens, the additional uv-light exposure to previously printed layers will increase the polymerization of leftover unreacted monomers. fig. 11: ultimate strain vs. layer thickness for (a) x, 0° green samples (b) x, 0° cured samples (c) z, 90° green samples (d) z, 90° cured samples (e) green samples (f) cured samples. the interlayer fracture happens between the printed layers. in a thicker layer, the strength degraded faster in the specimen due to separation in the printed layers and increased interlayer stress. in contrast, the strength of specimens that are printed with a thin layer degraded slowly. furthermore, in the case of vertical layer printing, the number of layers was large and thin. the laser-exposed surface area was large, enhancing the mechanical performance, which is distinct from horizontal printing. 236 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 the post-curing conditions had apparent effectiveness. uv curing under high temperatures and curing time improved the mechanical properties in both the x-axis and zaxis and with various layer thicknesses. in the xdirection with 25 μm thickness, the elastic modulus increased by 26.61 % compared to the green samples. also, the elastic modulus of the cured samples printed with 25 μm thickness and in the zdirection increased by 33.23% compared to the green samples. the elastic modulus printed with 50μm thickness and in the x-axis increased by 86.791% compared to the green samples. also, the elastic modulus printed with 50 μm thickness and in the vertical direction increased by 38.341% compared to the green samples. in summary, there was an increase in ultimate stress values of the samples. for the ultimate strain, the green samples were generally higher than the cured samples, as the post-curing made the material behavior more brittle. according to the results obtained, the printing orientation, layer thickness, and post-curing of the build-direction of 3d printed samples play a role in improving and controlling the anisotropy of mechanical properties of the printed samples, which is considered a challenge that is faced in the additive manufacturing process. references [1] ponce de leon c, hussey w, frazao f, jones d, ruggeri e, tzortzatos s, mckerracher rd, wills rga, yang s, walsh fc. (2014) the 3d printing of a polymeric electrochemical cell body and its characterization. chemical engineering transactions, 41: 1-6. https://doi.org/10.3303/cet1441001. [2] chong s, chiu hl, liao yc, hung st, pan gt. (2015) cradle to cradle® design for 3d printing. chemical engineering, 45. https://doi.org/10.3303/cet1545279. [3] ngo td, kashani a, imbalzano g, nguyen ktq, hui d. (2018) additive manufacturing (3d printing): a review of materials, methods, applications and challenges. composites part b: engineering, 143: 172-196. https://doi.org/10.1016/j.compositesb.2018.02.012. [4] standard, a.s.t.m. (2012) standard terminology for additive manufacturing technologies. astm international f2792-12a, 1-9. https://doi: 10.1520/f2792-12a. [5] hod l, kurman m. (2013) fabricated: the new world of 3d printing. john wiley and sons, 2013. [6] ivanova o, williams c, campbell t. (2013) additive manufacturing (am) and nanotechnology: promises and challenges. rapid prototyping journal, 19 ( 5): 353-364. https://doi.org/10.1108/rpj-12-2011-0127. [7] quan z, wu a, keefe m, qin x, yu j, suhr j, byun jh, kim bs, chou tw. (2015) additive manufacturing of multi-directional preforms for composites: opportunities and challenges. materials today, 18 (9): 503-512. https://doi.org/10.1016/j.mtadv.2019.100045. [8] quan z, larimore z, wu a, yu j , qin x, mirotznik m, suhr j, byun jh, oh y, chou tw. (2016) microstructural design and additive manufacturing and characterization of 3d orthogonal short carbon fiber/acrylonitrile-butadiene-styrene preform and composite. composites science and technology, 126:139-148. https://doi.org/10.1016/j.compscitech.2016.02.021. [9] skliutas e, kasetaite s, jonušauskas l, ostrauskaite j, malinauska m. (2018) photosensitive naturally derived resins toward optical 3-d printing. optical engineering, 57(4): 041412041412. https://doi.org/10.1117/1.oe.57.4.041412. [10] janusziewicz r, tumbleston jr, quintanilla al, mecham sj, desimone jm. (2016) layerless fabrication with continuous liquid interface production. proceedings of the national academy of sciences. 113(42): 11703-11708. https://doi.org/10.1073/pnas.1605271113. [11] o’neil pf. (2018) internal void fabrication via mask projection micro-stereolithography: a rapid repeatable microfluidic prototyping technique. ph.d dissertation. dublin city university, 2018. 237 https://doi.org/10.3303/cet1441001 https://doi.org/10.1016/j.compositesb.2018.02.012 https://doi.org/10.1108/rpj-12-2011-0127 https://doi.org/10.1016/j.compscitech.2016.02.021 iium engineering journal, vol. 24, no. 2, 2023 diab et al. https://doi.org/10.31436/iiumej.v24i2.2778 [12] naik d, kiran r. (2018). on anisotropy, strain rate and size effects in vat photopolymerization based specimens. additive manufacturing, 23: 181-196. https://doi.org/10.1016/j.addma.2018.08.021. [13] e aznarte, ayranci c, qureshi aj. (2017) digital light processing (dlp): anisotropic tensile considerations. 2017 international solid freeform fabrication symposium. university of texas at austin. [15] agrawal s, ray h, kulat a, garhekar y, jibhakate r, singh s, bisaria h. (2023) evaluation of tensile property of sla 3d printed nextdent biocompatible class i material for making surgical guides for implant surgery. materials today: proceedings, 72: 1231-1235. https://doi.org/10.1016/j.matpr.2022.09.288. [16] lee cs, kim sg, kim hj, ahn sh. (2007) measurement of anisotropic compressive strength of rapid prototyping parts. journal of materials processing technology, 187: 627-630. https://doi.org/10.1016/j.jmatprotec.2006.11.095. [17] sh. ahn, m. montero, d. odell, s. roundy, and p. wright. (2002) anisotropic material properties of pused deposition modeling abs. rapid prototyping journal, 8: 248-257. https://doi.org/10.1108/13552540210441166. [18] mueller j, shea k, and daraio c. (2015) mechanical properties of parts fabricated with inkjet 3d printing through efficient experimental design. materials and design, 86: 902-912. https://doi.org/10.1016/j.matdes.2015.07.129. [19] chockalingam k, jawahar n, chandrasekhar u. (2006) influence of layer thickness on mechanical properties in stereolithography. rapid prototyping journal, 12: 106-113. https://doi.org/10.1108/13552540610652456. [20] rankouhi b, javadpour s, delfanian f, letcher t. (2016) failure analysis and mechanical characterization of 3d printed abs with respect to layer thickness and orientation. journal of failure analysis and prevention, 16 :467-481. https://doi.org/10.1007/s11668-016-0113-2. [21] quintana r, choi jw, puebla k, wicker r. (2010) effects of build orientation on tensile strength for stereolithography-manufactured astm d-638 type i specimens. the international journal of advanced manufacturing technolog, 46: 201-215. https://doi.org/10.1007/s00170-009-2066-z. [22] domínguez-rodríguez g, ku-herrera j, hernández-pérez a. (2018) an assessment of the effect of printing orientation, density, and filler pattern on the compressive performance of 3d printed abs structures by fuse deposition. the international journal of advanced manufacturing technology, 95: 1685-1695. https://doi.org/10.1007/s00170-017-1314-x. [23] rohde s, cantrell j, jerez a, kroese c, damiani d, gurnani r, disandro l, anton j, young a, steinbach d, ifju p. (2018) experimental characterization of the shear properties of 3d– printed abs and polycarbonate parts. experimental mechanics, 58: 871-884. https://doi.org/10.1007/s11340-017-0343-6. [24] zguris z. (2016) how mechanical properties of stereolithography 3d prints are affected by uv curing. formlabs white paper, 1-11. [25] kerns j. (2015) what’s the difference between stereolithography and selective laser sintering. machine design, 17. [26] astm international (2014) standard test method for tensile properties of plastics. astm international. 238 https://doi.org/10.1016/j.addma.2018.08.021 https://doi.org/10.1016/j.matpr.2022.09.288 https://doi.org/10.1016/j.jmatprotec.2006.11.095 https://doi.org/10.1108/13552540210441166 https://doi.org/10.1016/j.matdes.2015.07.129 https://doi.org/10.1108/13552540610652456 https://doi.org/10.1007/s00170-009-2066-z https://doi.org/10.1007/s00170-017-1314-x https://doi.org/10.1007/s11340-017-0343-6 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 270 a parametric study on control of flow separation over an airfoil in incompressible regime lakshmanan prabhu* and jonnalagadda srinivas department of mechanical engineering, national institute of technology, rourkela, odisha-769008, india. * corresponding author: prabhulakshmananr@gmail.com (received: 23rd dec 2016; accepted: 15th june 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.784 abstract: this paper presents the effects of airfoil geometry on flow separation behavior and obtains the transition patterns at a specific angle of attack. a strong adverse pressure gradient field is observed at the leading edge of the airfoil, and it results in a flow detachment. leading edge flow separation is studied along with the variation of skin friction coefficient over the airfoil. novelty in the approach is the development of a hybrid control scheme to delay the flow separation with blowing/suction of air (termed active control) over the airfoil together with the tapping of flow from the pressure side as in a classical passive control procedure. the active controller delays the flow separation, while the passive controller is used to reduce the drag coefficient significantly and increases the total performance of an airfoil. the effectiveness of these controls is examined by varying the control parameters including blowing/suction velocity, the position of the slot in terms of percentage of chord and size of the slot. all the numerical simulations are carried out using ansys-fluent software. a surrogate model is also developed to predict the aerodynamic characteristics conveniently without much computational effort. the outcome of this study reveals that the blowing/suction velocity has a higher influence in delaying the flow separation. abstrak: kertas ini membentangkan tentang kesan geometri aerofoil pada perubahan pemisah aliran udara dan memperoleh bentuk peralihan pada darjah yang tepat. terdapat tekanan kuat yang tidak sesuai pada kawasan kecerunan di hujung hadapan permukaan aerofoil, dan ini menyebabkan aliran udara terpisah. pemisah aliran udara pada hujung hadapan ini dikaji bersama koefisien geseran pada permukaan aerofoil. pendekatan baru pada kaedah ini adalah berkaitan pembangunan skim kawalan hibrid bagi melengahkan aliran pemisah udara melalui tiupan/sedutan udara (kawalan aktif) ke atas aerofoil bersama ketukan pada aliran dari tepi tekanan seperti mana prosedur klasik kawalan pasif. kawalan aktif ini melengahkan aliran pemisah udara, sebaliknya kawalan pasif telah digunakan bagi mengurangkan koefisien penangguhan dengan ketara dan menambahkan jumlah prestasi aerofoil. keberhasilan kawalan-kawalan ini dikaji dengan mengubah parameter kawalan termasuk kelajuan tiupan/sedutan udara, posisi slot berdasarkan peratusan garis temu dan saiz slot. semua simulasi-simulasi numerikal ini dijalankan menggunakan perisian ansys-fluent. model pengganti turut dibangunkan untuk menjangka ciri-ciri aero-dinamik dengan mudah tanpa usaha pengiraan yang banyak. keputusan kajian ini mendedahkan tentang kelajuan tiupan/sedutan udara berpengaruh besar dalam melambatkan pemisahan aliran udara. keywords: flow separation; aerodynamic characteristics; hybrid control; boundary layer; skin-friction coefficient iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 271 1. introduction airfoil sections are commonly found in several applications including the blades of turbo-machinery, wind turbines, aircraft wings, etc. flow fields around airfoil sections have a significant influence on the overall aerodynamic characteristics. in fact, the fluid flow over the surface will become stagnant due to the viscous effect between the airfoil surface and the fluid under a no-slip boundary condition. as the flow passes downstream of the airfoil, where the motion of the fluid particles is already retarded by the frictional effects, the further increase in pressure gradient leads to reduced velocity. further, moving in downstream, the fluid particle comes to a stop and leads to a reverse flow, this phenomenon leads the flow to separate from the airfoil surface and a wake region downstream of the surface is formed [1, 2]. the transition point in a flow from laminar to turbulent is identified using the coefficient of friction (cf), where it increases suddenly along the flow direction. over the last two decades, several studies focused on the flowcontrol techniques and airfoil design modifications [3-6]. the flow separation can be delayed; by augmenting the flow over an airfoil using various passive and active control solutions such as airfoils with air impingement, slats, and flaps. ghadimi et al. [7] studied the effect of altitude on parameters like transition point and flow separation. the influence of these parameters on the drag produced was also investigated. the introduction of waviness on the airfoil to delay the flow separation was reported by favier et al. [8]. to study the effect of waviness in depth, lin et al. [9] used sinusoidal waviness on a symmetrical airfoil in two types; one was waviness over the upper and lower surfaces and another one was with waviness on the trailing and leading edges. the bumpy surface at 80% of the chord of the airfoil also delayed the flow separation [10]. the mean reynolds stresses, as a key parameter for flow separation over an airfoil, was found by performing a study on the geometrical effects over the transition point and the flow separation [11]. more recently, belamadi et al. [12] studied the effect of the slot shape in passive control of airfoil aerodynamic characteristics, particularly the ratio of the width of the slot on suction and the pressure side of the airfoil. the vortex generator was used as a tool to enhance aerodynamic characteristics [13]. the passive controller works well enough to increase the stall angle with weight as a penalty and intricate design. to overcome these difficulties, the micro-mechanical and fluid system is used as an active controller that increases the stability in unsteady conditions. the continuously distributed porous surface on the airfoil was used to control the flow separation by applying the suction pressure under the porous surface [14]. the parametric study of the controller is very important to know which parameter has more significance on the delay of the flow separation. the location and angle of the controller were the most important parameters of the controller design in delaying flow separation [15-17]. the synthetic jet is an active controller that adds momentum to the flow without adding mass to it. gilarranz et al. [18] conducted an experimental investigation on a naca-0015 airfoil to delay the flow separation and increase the performance of an airfoil using the synthetic jet actuation. the flow separation delay over an airfoil with synthetic jet actuation was carried out numerically using large eddy simulation (les) by you and moin [19] and the results were compared with the experimental work performed by gilarranz et al. [18]. tang et al. [20] used two synthetic jet arrays in 23% and 43% of the chord to delay the flow separation. the experimental results show the first array was more efficient compared to the second array. the active controller was employed with different air blowing, such as pulsed and harmonic, to study its significance on delaying the separation [21]. then coflow jet (cfj) was employed to enhance the aerodynamic parameters and to increase the iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 272 stall angle [22]. genc and kaynak [23] controlled the laminar separation over an airfoil by using the blowing and suction through the hole along various locations on the chord. the result shows the smaller blowing and larger suction velocity ratio gives the better result irrespective of the position of the hole. the suction controller with multi-holes shows better aerodynamic performance against the single hole [24]. skarolek and karabelas [25] used a non-conventional active flow control scheme that results in excellent efficiency in aerodynamic characteristics before and after the flow separation. here the slots were provided on both suction and pressure side at the trailing edge, that blows the air perpendicular to the chord. the ansys tool is used to check, how the system performs before going for the prototype. ali and ahmed [26] used reynolds-averaged navier stokes (rans) based two equation turbulence model (k-ε), and the grid generation was based on the body-fitted coordinate system to identify the separation point over an airfoil surface. kuwahara and surugadai [27] predicted the flow around the airfoil using the multi-directional finite difference method to solve the navier-stokes equation, which leads to a computation approach much wider. most of the above works were employed with either passive or active control techniques for flow separation. recently, the hybrid control schemes have become more popular for their effectiveness in controlling flow separation. unlike existing hybrid methods for control of flow separation, the present approach considers a continuous blowing/suction jet impingement along with a passive controller using a slot that taps the flow from the pressure side and releases it just before the trailing edge to enhance the aerodynamic characteristics. initially, the conditions of flow separation are identified and the proposed concept of separation control is implemented on naca 0015 airfoil, to know its effectiveness. during the controller design, effects of controlling parameters such as blowing/suction velocity, the position of the slot in the percentage of chord and size of the slot on the aerodynamic performance of airfoil are studied. based on these studies, the surrogate models are developed based on two neural networks namely, general regression neural network (grnn) and radial basis function (rbf) network to predict the aerodynamic characteristics more accurately and relatively faster with parameters of the controller as an input. 2. methodology 2.1 hybrid control concept active controllers use the continuous blowing/suction of air through a slot using the external sources. a passive controller is a technique that does not use any external aid and the slot extends from the pressure side of the airfoil to the suction side. the combination of both active and passive controllers is termed as the hybrid controller. the passive control slot size effect studied by belamadi et al. [12] is used in combination with the nonconventional controller by skarolek and karabelas [25] in this work, but the blowing (passive) slot is placed only on the suction side, just ahead of the trailing edge as shown in fig. 1. the slot for the passive controller has a greater width on the pressure side and a lower width on the suction side. the slot position on the suction side is about three percent of the chord length from the trailing edge (t.e), and the width of the hole in terms of ratio of chord is 0.0133m. figure 1 shows the airfoil with slots for the active and passive controller. iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 273 fig. 1: hybrid controller design in airfoil. 2.2 artificial neural networks an artificial neural network is designed based on the biological neural system and it is widely used as a surrogate model in many engineering applications. of all neural networks (nn), the three-layer rbf and its variants, like pnn, grnn, cpn, etc., have become famous due to limited network parameters and reliability in giving output results. the rbf is one of the neural network tools [28] that is a feed-forward with three layers, one is input, the other is hidden or known as a radial basis layer, the last is the output layer. figure 2 shows the block diagram of the rbf. fig. 2: rbf neural network structure. the hidden layer comes with a non-linear rbf activation code. rbf represents a local effect and its range is identified by the center element and width. the output layer is the sum of the weighted outputs of the hidden layer defined below: )c,x(w)x(y  (1) where x is input vector, w is connection weight, c is central vector, and  is radial basis function which in most of the cases is gauss function defined by following equation:            2 2 cx 1 expcxg)c,x( (2) where  represents the width. the rbf is trained using the estimation of parameters such as centers, widths of rbf, and connection weights. 2.3 general regression neural networks the grnn is a combination of radial basis layer and a special linear layer [29]. grnn comes under probabilistic neural networks, and it is a simple one-pass algorithm with a parallel structure that requires only a few training sets compared to back propagation neural networks (bpnn). in addition, parameters such as the optimum iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 274 number of neurons, learning rate, and momentum are not required, as in bpnn. the biggest advantage is its ability to converge with few training sets and a smooth transition is observed from one value to another. grnn comes with four layers: the input, pattern, summation, and output layers as shown in fig. 3. fig. 3: grnn structure. the input layer consists of the same number as the features of a model and it will be passed to the pattern layer. next is the summation layer, consisting of two units where all nodes in the third layer are connected to both units. finally, the output layer is the quotient of two units in summation layer, which is given below:                          2 2 in 1i 2 2 i i n 1i 2 d exp 2 d expy xy (3) where yi is the connection weight between the first summation node and the i th node of the pattern layer, n is number of data samples,    iti i xxxxd  2 is euclidean distance between the weights and the input vector, and  is the spread parameter. figure 4 shows the flowchart of the methodology and it starts with the selection of an airfoil to identify the flow separation point, which in turn helps to identify the parameters such as slot size, location along the chord, and blowing/suction velocity (active controller). as a next step, aerodynamic characteristics are calculated using both active and hybrid controllers to find their effectiveness on the control of flow separation. then comes the training of surrogate models and its performance is compared with ansys fluent. 3. numerical simulation the baseline airfoil model employed in this work is naca 0015 with a chord of 0.375 m with a free stream velocity of 35m/s, leading to a reynolds number of (re)=8.96e5 and a turbulence intensity of 0.3 percent. the experimental data [18] is used to validate the results of the numerical simulation without controller. 2-d simulation is efficient in the studies where large amounts of simulation cases are needed for an investigation of the effect of aerodynamic parameters. all the flow studies are carried out using ansys fluent. the physical two-dimensional model in c-type domain with the iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 275 radius of 10c and width of 12c is shown in fig.5 and flow considered is incompressible and subsonic in nature. fig. 4: flowchart of the methodology. fig. 5: cfd physical modeling. when the flow passes around the airfoil, separation begins in absence of the controller at a certain angle of attack and free-stream velocity. when the controller comes to effect along with the freestream velocity, the air impingement or suction will take place through the inlet for the active controller, and the air will enter through the passive iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 276 controller inlet and exit via the outlet for the passive controller. the boundary conditions used in the simulation are as follows: 1) the simulation is performed in the standard atmospheric conditions. 2) the inlet and outlet are treated as velocity inlet and pressure outlet respectively. 3) the airfoil is treated as the wall with no slip boundary conditions. 4) the inlet for the active controller is considered to be the velocity inlet (blowing/suction of air). 5) the pressure side air will pass through the inlet for the passive controller and exit through the outlet of the passive controller. the general two-dimensional forms of continuity and momentum equations for an incompressible flow are described as; 0 y v x u       (4) 2 2 2 2 2 2 2 2 y v x v y p1 y v v x v u t v y u x u x p1 y u v x u u t u                                       (5) where u,v are velocity components, and p, υ, and ρ are pressure, kinematic viscosity, and density, respectively. the rans based turbulence model is used in this numerical simulation. the transitional k-kl-ω is a rans-based model, proposed by walters and cokljat [30] and this model is developed based on a turbulence k-ω model. the k-ω is a two-equation model in which the equations are used to identify the turbulent kinetic energy and the specific dissipation energy [30]. in two-equation models, the physics of transition of flow is missing. to overcome this, a k-kl-ω transition model was developed [30]. it predicts the development of a boundary layer and onset of the transition from laminar to turbulent. the model uses a three-equation eddy viscosity type: the transport equation for turbulent kinetic energy (kt), laminar kinetic energy (kl) and the inverse turbulent time scale (ω) as follows [30]:                       j t k t j ttnatk t x k x dkrrp dt dk t    (6)               j t j tnatk l x k x drrp dt dk l (7)                                             jj t x t x 3 t2 t3 2 2nat tw r k t 1 t d k ffccrr k 1 f c p k c d d (8) the stringent modeling near the wall model (airfoil) has to be carried out to study the turbulent flow problems. the first cell height (δy) from the wall must be identified by the appropriate dimensionless y+ value. the δy = 8.3e-06 mm for y+ = 1, and the enhanced wall treatment is used in this study. the residual convergence criterion is fixed to 10e-6 to achieve reliable results. iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 277 the meshing tool used is icem cfd, and the mesh type is a structured one with quadrilateral elements. the structured block, mesh, and magnified mesh over an airfoil are shown in fig. 6. (b) (c) fig. 6: (a) structured block, (b) mesh, and (c) magnified mesh over an airfoil. to proceed further in the analysis, the grid independence is carried out by varying the number of mesh points (m1=300, m2=400, and m3=500) over the airfoil and the respective aerodynamic characteristics at various aoa are shown in fig 7. the lift coefficient by all mesh points is more or less similar, but the drag coefficient by m1 has a large deviation compared to the other two. m2 and m3 give the closer aerodynamic coefficients with less error; approximately 4%. to reduce the computational time, m2 is selected for further numerical studies. fig. 7: grid independence study. the entire analysis is performed in a high performing computing machine in 16 nodes with a memory of 64 gb on an intel processor of 2 ghz speed. the average time taken for each simulation is around 128 minutes. figure 8 shows the aerodynamic coefficients obtained from the numerical simulation in comparison with experimental data [18]. iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 278 fig. 8: aerodynamic coefficients of naca 0015 airfoil by cfd for uncontrolled case in comparison with experimental value [18]. from the earlier work [18] it was experimentally found that the stall occurs at approximately 12.6o and a separation of flow takes place at 40% of the chord from the t.e. the flow separation starts at l.e over an airfoil at aoa=16.6o as shown in fig. 9. fig. 9: flow separation over an airfoil at aoa=16.6o. the present study focuses on the suppression/delay of the flow separation over an airfoil at aoa of 16.6o. the residual and aerodynamic coefficients convergence graphs of uncontrolled flow over a naca 0015 airfoil at an aoa 16.6o are shown in fig. 10 using numerical simulation and table 1 displays the aerodynamic characteristics values in comparison with available experimental results [18]. table 1: aerodynamic characteristics at aoa=16.6o uncontrolled case aerodynamic characteristics present simulation experimental [14] cl 0.90 0.85 cd 0.25 0.26 l/d 3.6 3.27 3.1 parametric study for the influence of parameters such as blowing velocity, and the position of the slot in the percentage of chord and size of the slot on the output factor, the aerodynamic characteristics are studied. fig. 1 shows the airfoil naca-0015 with a chord (c) of 0.375 m. the taguchi method is employed for three levels and three parameters, as given in table 2 and then the l9 (3*3) orthogonal array is used to find the possible number of experiments. as the essential objective is to maximize the efficiency of the airfoil in terms iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 279 fig. 10: convergence graph of residual and aerodynamic coefficients at aoa 16.6o for an uncontrolled case. of aerodynamic characteristics, one has to predict the best level of each factor. minitab 16 is used to carry out the taguchi method and the aerodynamic characteristics of 9 combinations are predicted using cfd, then fed into minitab to get the means graphs for analysis. the slot for the controller is placed at a different position along the chord with various width and blowing/suction velocities, as shown in table 2. table 2: parameters of the controller level blowing/suction velocity in [m/s] position of slot in % of c size of slot in [m] 1 17.5 10 0.0015 2 35 30 0.002 3 52.5 50 0.0025 3.2 active controller effect from fig. 9, it can be witnessed that for the control-off case, the flow separation starts below the 10 % of chord from the l.e and the active controller used is to mitigate the flow separation over an airfoil by continuous blowing/suction of air tangentially over the suction side of the airfoil and as a result, it lead to an improvement of aerodynamic characteristic. in fig. 11, pressure distribution over the baseline airfoil with active controller on cases, shows the rise in the peak on the suction side along with the increase iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 280 of pressure on the pressure side when compared to the airfoil with a control-off case. it shows the active controller has a global effect over the suction side pressure distribution. (a) (d) (b) (e) (c) (d) fig. 11: pressure distribution over a baseline airfoil naca 0015 with active controller on and off cases, (a), (b), (c) are blowing and (d), (e), (f) are suction (v1=17.5m/s, v2=35m/s, v3=52.5m./s, w1=0.0015m, w2=0.002, and w3=0.0025) iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 281 3.3 hybrid controller effect the combination of the active and passive controller is employed in this work. here the active controller is to mitigate the flow separation as mentioned earlier, but the work of the passive controller is to reduce the total drag instead of controlling the flow separation. figure 12 shows the pressure coefficient over a baseline airfoil naca 0015 with hybrid controller off and on cases. the flow over the suction side gets decelerated and the pressure starts rising on the upstream of the passive controller as the blowing of the air jet is carried out. the increase in the static pressure improves the l/d ratio by reducing the drag value. (a) (d) (b) (e) (c) (f) fig. 12: pressure distribution over a baseline airfoil naca 0015 with hybrid controller on and off cases, (a), (b), (c) are blowing and (d), (e), (f) are suction (v1=17.5 m/s, v2=35 m/s, v3=52.5 m/s, w1=0.0015 m, w2=0.002, and w3=0.0025) iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 282 the influence of each and every parameter is analyzed in detail. the l9 orthogonal array and aerodynamic characteristic of an airfoil for nine experiments is shown in table 3 and table 4. all the experiments show the improvement in aerodynamic characteristics. figure 13 shows the variation of parameters against means of mean and the parameter with a higher value of mean has a more significant influence on lift to drag ratio (l/d ratio). table 3: l9 orthogonal array-blowing s.no velocity in [m/s] position of slot in % of c size of slot in [m] blowing aerodynamic coefficients active hybrid cl cd l/d cl cd l/d 1 17.5 10 0.0015 0.87 0.225 3.9 0.887 0.205 4.3 2 17.5 30 0.002 1.03 0.181 5.7 1.02 0.158 6.5 3 17.5 50 0.0025 1.01 0.1974 5.1 0.977 0.1717 5.7 4 35 30 0.0015 1.14 0.161 7.1 1.156 0.133 8.7 5 35 50 0.002 1.11 1.84 0.6 1.043 0.1607 6.5 6 35 10 0.0025 1.08 0.133 8.1 1.18 0.0953 12.4 7 52.5 50 0.0015 1.211 0.181 6.7 1.127 0.15 7.5 8 52.5 10 0.002 1.4 0.1 14.0 1.52 0.0657 23.1 9 52.5 30 0.0025 1.29 0.143 9.0 1.32 0.12 11.0 table 4: l9 orthogonal array-suction s.no velocity in [m/s] position of slot in % of c size of slot in [m] suction aerodynamic coefficients active hybrid cl cd l/d cl cd l/d 1 17.5 10 0.0015 1.19 0.135 8.81 1.17 0.108 10.8 2 17.5 30 0.002 1.13 0.172 6.57 1.06 0.152 7.0 3 17.5 50 0.0025 1.023 0.202 5.06 1.02 0.182 5.6 4 35 30 0.0015 1.19 0.161 7.39 1.147 0.133 8.6 5 35 50 0.002 1.09 0.198 5.51 1.084 0.191 5.7 6 35 10 0.0025 1.48 0.069 21.45 1.49 0.0424 35.1 7 52.5 50 0.0015 1.11 0.198 5.61 1.09 0.191 5.7 8 52.5 10 0.002 1.55 0.061 25.41 1.54 0.033 46.7 9 52.5 30 0.0025 1.36 0.132 10.30 1.34 0.1109 12.1 first, the influence of velocity on mitigation of flow separation on a surface is taken as one of the primary parameters. the velocities of the jets considered are 0.5, 1, and 1.5 times of freestream velocity. both, active and hybrid controllers with jet velocity of 52.5 m/s shows a superior performance compared to other velocities, irrespective of other parameters. the jet velocity of 17.5m/s in the active and hybrid controllers leads to the increase in total performance, but with decreased cl value in active/hybrid blowing as shown in table. 3. for other cases, the cl value is increased and cd value is decreased. the performance of the system increases proportionally to the velocity of the jet, as shown in fig. 13. the width of the slot is taken as another parameter to study the controller effect. the slot sizes of 0.0015, 0.002, and 0.0025 m are considered. the slot of 0.002 m gives high iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 283 aerodynamic performance with the combination of jet velocity of 52.5 m/s and slot position of 10% of the chord in a blowing and suction case. as the slot size increases or decreases from the optimum value (0.002 m), the performance of the all controllers starts to decelerate, as shown in fig. 13. (a) (b) (c) (d) fig. 13: influence of parameters on active and hybrid control: (a), (b) are blowing active and hybrid, and (c), (d) are suction active and hybrid. the other key parameter of the controller effectiveness is the position of the controller slot. the position of slot at 10% of chord with a size of 0.002 m gives good aerodynamic characteristics at high blowing/suction velocity. this is possible because the flow separation starts at 10% of chord. when the position of slot moved aft, the efficiency of a controller decreases even with a high jet velocity and a slot size of 0.002 m, as shown in fig. 13. the optimum combination of parameters for delaying or mitigating the flow separation is the position of slot at 10% of chord with 0.002 m size, and jet velocity of 52.5 m/s. the aerodynamic characteristics are also statistically analyzed by analysis of variance (anova) to know the exact contribution of the parameters on the efficiency of the controllers. the output of anova is given in table 5, and it also shows that the velocity has a high significance in blowing and blowing hybrid controllers, followed by position of the slot. in suction and suction hybrid controllers the location of the slot has a significant influence, followed by the velocity parameter. the increase in l/d ratio through active and hybrid controllers (blowing/suction) are promising by delaying the flow separation over the suction side of the airfoil. iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 284 table 5: anova output analysis of variance for l/d-blowing control, using adjusted ss for test source df seq ss adj ss adj ms f p blowing velocity in m/s 2 37.815 37.815 18.907 3.86 0.206 width of hole in m 2 10.987 10.987 5.494 1.12 0.471 position of hole in % of c 2 11.053 11.053 5.527 1.13 0.47 error 2 9.801 9.801 4.901 analysis of variance for l/d-blowing hybrid control, using adjusted ss for test source df seq ss adj ss adj ms f p blowing velocity in m/s 2 105.32 105.32 52.66 2.42 0.292 width of hole in m 2 39.7 39.7 19.85 0.91 0.523 position of hole in % of c 2 69.61 69.61 34.81 1.6 0.385 error 2 43.53 43.53 21.76 analysis of variance for l/d-suction control, using adjusted ss for test source df seq ss adj ss adj ms f p suction velocity in m/s 2 78.03 78.03 39.02 2.43 0.292 width of hole in m 2 53.89 53.89 26.94 1.68 0.373 position of hole in % of c 2 297.11 297.11 148.55 9.25 0.098 error 2 32.11 32.11 16.06 analysis of variance for l/d-suction control, using adjusted ss for test source df seq ss adj ss adj ms f p suction velocity in m/s 2 288.24 288.24 144.12 1.63 0.381 width of hole in m 2 220.35 220.35 110.18 1.24 0.446 position of hole in % of c 2 1128.29 1128.29 564.15 6.37 0.136 error 2 177.1 177.1 88.55 the detailed analysis of the skin friction coefficient over a suction side in control off and on cases is carried out for velocity (blowing/suction) 52.5 m/s, slot width 0.002 m, and position of slot of 10% of chord. in the blowing case, the momentum is added to energize the fluid particles to overcome the retardation by boundary layer effect. figure 14 (a) shows the delay in the separation of flow over the suction side when blowing through the slot is carried out, and the skin friction increases in the blowing area. the separation point is located at 10% of the chord in the control off case and it is moved to 55% of chord from l.e in the control on case. the activation of the passive controller, along with blowing, leads to the movement of the separation point to 74% of chord and it is seen in fig. 14(c). when the controller is activated with suction, the momentum is diffused with an increase in skin friction coefficient on the suction side and it is identified, as shown in fig. 14(b), and the separation point is moved to 79% of chord. when the hybrid controller with suction is employed, the separation takes place at 80% of chord and it is shown in fig. 9(d). iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 285 (a) (b) (c) (d) fig. 14: skin friction coefficient over the suction side: (a) blowing, (b) suction (c) hybrid with blowing and (d) hybrid with suction (v3=52.5m./s, and w3=0.0025). figure 15 show the streamlines over the naca 0015 airfoil with control. in airfoil with the control off case, the flow gets separated near l.e and when control (velocity (blowing/suction)=52.5 m/s, hole width 0.002 m, and position of hole is 10% chord ) is on the flow separation over an airfoil gets delayed is seen in fig. 15. this shows the controller works effectively to delay the separation of flow over the suction side of an airfoil. 3.4 surrogate model the grnn and rbf are used as the surrogate models in this work. inputs for the training sets are the blowing/suction velocity, width of the slot, and the position of the slot from the leading edge and the output variable is the l/d ratio. the surrogate models are trained with training sets shown in table 3 and 4, for the blowing and suction case separately. the training time is around 20 seconds and the convergence trend of the rbf model is shown in fig. 16(a). here, a spread constant is taken as one and a matlab neural network toolbox is employed for training both networks. fig. 16 (b) shows the outputs computed from grnn against target values. iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 286 (a) (b) (c) (d) fig. 15: streamline flow over an airfoil: (a) blowing, (b) suction, (c) hybrid with blowing and (d) hybrid with suction. the identified results are shown in table 6, and they are in good agreement with those obtained from a conventional flow solver (ansys) outputs for a few test cases. performance wise, both the surrogate models are similar and rbf has bagged the best performer in blowing operations in terms of training speed and accuracy. these models can be used to optimize the parameters of the controller without redesigning the airfoil model in the software front end and saves a lot of computational time. (a) (b) fig. 16 (a) convergence plot of rbf neural network, and (b) grnn target versus output l/d ratio. iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 287 table 6: validation of surrogate models parameters l/d v=52.5 [m/s] blowing suction width= 0.0015 [m] rbf ansys grnn ansys rbf ansys grnn ansys position= 10 % of chord 14 14 13 14 25.83 21.42 25.83 21.42 4. conclusions the parametric analysis of a controller to minimize/delay the flow separation effect was carried out with blowing and suction of an air jet over an airfoil section. the flow regime was considered to be incompressible with a reynolds number of 8.96×105 and a chord length of the airfoil section of 0.375 m. the airfoil aerodynamic characteristics were analyzed by a transitional k-kl-ω solver in ansys fluent for the natural flow and then by employing active, and hybrid controllers. the hybrid controller comes with a combination of the active controller, which plays a role in delaying the flow separation and the passive controller to reduce the drag by increasing the static pressure upstream of the blowing slot, just ahead of trailing edge, over a suction surface. the active and hybrid controller efficiency were studied by varying the controller parameters including the blowing/suction velocity, slot width, and position of the slot. the number of experiments was reduced using a taguchi design of experiments, and anova was used to identify the most influencing parameters in performance of the controllers. the parametric study reveals that the velocity of the jet has more influence in comparison with the other two parameters in deciding the performance of blowing active and hybrid controllers. the position of the slot is found to be most influential in suction active and hybrid controllers. finally, surrogate models based on rbf and grnn were proposed to minimize the computational cost of a flow solver in understanding the effectiveness of the flow separation by varying the three controller parameters. the rbf outperforms in comparison with grnn in all cases in predicting the l/d ratio. references [1] currie ig. (2013) fundamental mechanics of fluids, crc press, boca raton. [2] anderson jd. (2011) fundamentals of aerodynamics, mcgraw hill, new york. [3] amitay m, glezer a. (2002) controlled transients of flow reattachment over stalled airfoils. int j heat fluid fl, 23(5):690-699. [4] duvigneau r, visonneau m. (2003) simulation and optimization of stall control for an airfoil with a synthetic jet. aerosp sci technol, 10(4):279-287. [5] rumsey cl, nishino t. (2011) numerical study comparing rans and les approaches on a circulation control airfoil. int j heat fluid fl, 32(5):847-864. [6] azim r, hasan mm, ali m. (2015) numerical investigation on the delay of boundary layer separation by suction for naca 4412. procedia eng, 105:329-334. [7] ghadimi p, rostami ab, jafarkazemi f. (2012) aerodynamic analysis of the boundary layer region of symmetric airfoils at ground proximity. aerosp sci technol, 17(1):7-20. [8] favier j, pinelli a, piomelli u. (2012) control of the separated flow around an airfoil using a wavy leading edge inspired by humpback whale flippers. comptes rendus mécanique, 340(1-2):107-114. iium engineering journal, vol. 19, no. 1, 2018 prabhu and srinivas 288 [9] lin yf, lam k, zou l, liu y. (2013) numerical study of flows past airfoils with wavy surfaces. j. fluids struct, 36:136-148. [10] faruqui sha, bari maa, emran m, ahsan f. (2014) numerical analysis of role of bumpy surface to control the flow separation of an airfoil. procedia eng, 90:255-260. [11] zhang w, cheng w, gao w, ravi s. (2015) geometrical effects on the airfoil flow separation and transition. comput. fluids, 116:60-73. [12] belamadi r, djemili a, ilinca a, mdouki r. (2016) aerodynamic performance analysis of slotted airfoils for application to wind turbine blades. j. wind eng. ind. aerodyn, 151:79-99. [13] fouatih om, medale m, imrine o, imine b. (2016) design optimization of the aerodynamic passive flow control on naca 4415 airfoil using vortex generators. eur j mech b-fluid, 56:82-96. [14] eppler r. (1999) airfoils with boundary layer suction, design and off-design cases. aerosp. sci. technol, 3(7):403–415. [15] jiao y, lu y. (2015) parameter optimization research on lift-enhancing of multi-element airfoil using air-blowing. procedia eng, 99:73–8. [16] zhao g, zhao q. (2014) parametric analyses for synthetic jet control on separation and stall over rotor airfoil. chin. j. aeronaut, 27(5):1051–1061. [17] chapin vg, benard e. (2015) active control of a stalled airfoil through steady or unsteady actuation jets. j. fluids eng, 137(9): 091103. [18] gilarranz jl, traub lw, rediniotis ok. (2005) a new class of synthetic jet actuators-part ii: application to flow separation control. j. fluids eng, 127(2):377-387. [19] you d, moin p. (2008) active control of flow separation over an airfoil using synthetic jets application to flow separation control. j. fluids struct, 24(8):1349–1357. [20] tang h, salunkhe p, zheng y, du j, wu y. (2014) on the use of synthetic jet actuator arrays for active flow separation control. exp. therm. fluid sci, 57:1–10. [21] wang l, li l, fu s. (2014) numerical investigation of active flow control on a pitching naca 0015 airfoil using detached-eddy simulation. procedia eng, 79:49–54. [22] hossain ma, uddin mn, islam mr, mashud m: enhancement of aerodynamic properties of an airfoil by co flow jet (cfj) flow. am. j. eng. res 2015, 4: 103–112. [23] genc ms, kaynak u. (2009) control of laminar separation bubble over a naca 2415 aerofoil at low re transitional flow using blowing/suction. in: 13th international conference on aerospace sciences and aviation technology: 26th-28th may, egypt. [24] shi y, bai j, hua j, yang t. (2015) numerical analysis and optimization of boundary layer suction on airfoils. chin. j. aeronaut, 28(2):357–367. [25] skarolek v, karabelas j. (2016) energy efficient active control of the flow past an aircraft wing: rans and les evaluation. applied mathematical modelling, 40(2):700-725. [26] ali is, ahmed ss. (2011) modelling of turbulent separation flow. world academy of science, engineering and technology, 76:866-876. [27] kuwahara k, surugadai s. (2000) direct simulation of a flow around an airfoil. available: http://www2.nagare.or.jp/jscfd/cfds14/pdf/b05-2.pdf. [28] guan x, zhu y, song w. (2016) application of rbf neural network improved by peak density function in intelligent color matching of wood dyeing. chaos, solitons &fractals, 89:485-490. [29] rooki r. (2016) application of general regression neural network (grnn) for indirect measuring pressure loss of herschel-bulkley drilling fluids in oil drilling. measrurement, 85:184-191. [30] walters dk, cokljat da. (2008) three-equation eddy-viscosity model for reynoldsaveraged navier–stokes simulations of transitional flow. j. fluids eng, 130(12):121401. https://fluidsengineering.asmedigitalcollection.asme.org/article.aspx?articleid=1478203 https://fluidsengineering.asmedigitalcollection.asme.org/article.aspx?articleid=1478203 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 robust and imperceptible watermarking on medical images using coefficient pair modification ledya novamizanti1,3*, andriyan bayu suksmono2,4, donny danudirdjo2,4, and gelar budiman3,4 1 electrical engineering and informatics, school of electrical engineering and informatics, institut teknologi bandung, bandung 40132, indonesia 2 school of electrical engineering and informatics, institut teknologi bandung, bandung 40132, indonesia 3 school of electrical engineering, telkom university, bandung 40257, indonesia 4 research collaboration center for quantum technology 2.0, bandung 40132, indonesia * corresponding author: ledyaldn@telkomuniversity.ac.id (received: 7th september 2022; accepted: 3rd october 2022; published on-line: 4th january 2023) abstract: sensitive data including medical images and electronic patient records (epr) have potential value in the era of big data and telemedicine applications. distribution of medical images and epr over public networks requires a high level of privacy and security. robust and imperceptible watermarking techniques are needed to provide copyright preservation for medical images and protect patient information security. this paper improves the technique of coltuc et al. by modifying the discrete cosine transform (dct) coefficient pairs in the watermark embedding formula. our proposed formula ensures that the difference between the two coefficients is at least 𝜁. if the difference between the two coefficients is less than 𝜁, then the new pixels are modified so that the difference is equal to 𝜁. the proposed method was evaluated on a variety of medical images, including x-ray, ct, us, mri, and colonoscopy, and compared to numerous robust watermarking techniques of the recent time. the experimental results demonstrate that the suggested method outperforms contemporary robust watermarking techniques in terms of imperceptibility, robustness, and security. the peak signal noise ratio (psnr) for all modalities of watermarked medical images exceeds 54 db, and the average psnr is approximately 56 db. the proposed method is outstanding compared to coltuc's method due to a 93% and 14% increase in bit error rate (ber) and normalized correlation (nc), respectively. our work is superior to various state-of-the-art robust watermarking techniques, allowing it to be employed effectively in medical applications. abstrak: data sensitif termasuk imej perubatan dan rekod pesakit elektronik (epr) mempunyai potensi nilai dalam era aplikasi data besar dan teleperubatan. pengedaran imej perubatan dan epr melalui rangkaian awam memerlukan tahap privasi dan keselamatan yang tinggi. teknik penanda air yang mantap dan tidak dapat dilihat diperlukan untuk menyediakan pemeliharaan hak cipta untuk imej perubatan dan melindungi keselamatan maklumat pesakit. kertas kerja ini menambah baik teknik coltuc et al. dengan mengubah suai pasangan pekali transformasi kosinus diskret (dct) dalam formula pembenaman tera air. formula yang dicadangkan kami memastikan bahawa perbezaan antara dua pekali adalah sekurangkurangnya 𝜁. jika perbezaan antara dua pekali kurang daripada 𝜁, maka piksel baharu diubah suai supaya perbezaannya sama dengan 𝜁. kaedah yang dicadangkan telah dinilai pada pelbagai imej perubatan, termasuk x-ray, ct, us, mri, dan kolonoskopi, dan dibandingkan dengan banyak teknik penanda air yang mantap pada masa terkini. keputusan eksperimen menunjukkan bahawa kaedah yang dicadangkan mengatasi teknik penanda air teguh 88 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 kontemporari dari segi ketidakjelasan, keteguhan dan keselamatan. nilai psnr untuk semua modalitas imej perubatan bertanda air melebihi 54 db, dan nilai purata psnr adalah lebih kurang 56 db. kaedah yang dicadangkan adalah cemerlang daripada kaedah coltuc kerana masing-masing peningkatan 93% dan 14% dalam ber dan nc. kerja kami lebih unggul daripada pelbagai teknik penanda air teguh terkini, membolehkan ia digunakan dengan berkesan dalam aplikasi perubatan. keywords: dct; imperceptible; medical image; robust; watermarking 1. introduction information and communication technology (ict) is essential to all sectors of society, including government, banking, education, health, agriculture, and transportation. ict integrates computer systems, digital data, communication devices, and the internet into one unified system. an important use of ict for effective quality health care is the electronic storage of medical data. the information in the electronic medical data storage, including: patient identities, diagnosis reports, doctor's consultations, hospital information where the image was created, and other helpful information, can be used anywhere and anytime [1-3]. medical data is susceptible and has great potential value in the era of big data because it is the most important basis for diagnosis in determining diagnostic methods and results [4,5]. through public networks like the internet, medical professionals frequently exchange digitally created medical images of patients created using various modalities. radiologists and doctors in the same field share these images for clinical interpretation [6]. medical professionals use telemedicine applications to remotely diagnose, evaluate, and treat patients via electronic communications. the program facilitates the transmission of medical images between two healthcare providers for improved diagnosis. however, medical image and epr delivery over public networks demand a high level of security [7]. modified, manipulated, or distorted medical data can cause incorrect diagnoses and severe health issues for everyone. in addition, the destruction and theft of medical images and identities can give rise to various legal and ethical concerns, including image retention and fraud, piracy, and illegal handling [1]. in contrast to financial institutions, which have robust data protection methods through two-factor authentication, medical records in healthcare systems are poorly protected. medical facilities must secure data from illegal actions such as hacking and virus intrusion, staff negligence, and the theft of medical records on purpose [3]. the transfer of data in an intelligent healthcare system while preserving privacy, integrity, authority, and security is a complex topic that requires additional consideration [4]. digital watermarking is a common approach for concealing digital information by masking signals [8] due to its additional qualities of robustness and imperceptibility. digital watermarking technology is becoming crucial for various fields since it offers a variety of compact solutions for numerous approaches and applications, such as cloud computing, electronic health, and the internet of things [2,11]. watermarking of digital images is allowed in two domains, i.e., the spatial domain and the frequency domain. in the spatial domain of watermarking technology, personal information is integrated directly into the cover image by modifying the pixel values [3,9]. in frequency domain watermarking, the cover image is first translated into the frequency domain, and then the hidden data is embedded by modifying the frequency coefficient value [3,9]. watermarking is also categorized based on the method of watermark extraction. non-blind techniques require both the host and the watermark image to extract the watermark. a semi-blind watermark requires a secret key and a watermarked image to extract the watermark. if only the secret key is required to extract the watermark, the 89 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 approach is known as blind watermarking [10]. based on the application, watermarking techniques can be classified as either robust or fragile [1,5]. the robustness of confidential information, and how the encoded information can withstand attacks conducted by attackers during data transmission, is the primary goal of robust watermarking [9]. robust watermarking is therefore widely used to preserve digital data's copyright. however, fragile watermarking [1] is used to identify the invader-damaged portions of the watermarked image, i.e., those regions of the image that were damaged during transmission. the integrity of digital data material is therefore verified using fragile watermarking. processing time for spatial domain-based watermarking is lower than for methods that embed data in the transformation domain. however, compared to transformationbased strategies, spatial domain-based approaches are less resistant to attacks [7]. two key requirements for creating effective watermarking methods are imperceptibility and robustness [6]. compared to watermarking in the spatial domain, watermarking in the frequency domain offers additional benefits. that is why many researchers use frequency domain watermarking techniques. dct is one of the widespread transformations and is often chosen in frequency domain watermarking techniques [6] because of its lower computational cost, high robustness and high compression [11]. in [12,13], the watermark was embedded by coltuc and chassery using the dct domain watermarking method. the image is divided into 8×8 blocks. next, dct for each block is determined. one bit of information entered into each block depends on the difference between the two coefficients of the mid-band frequency. for example, bit "1" is encoded if the difference is negative, and a bit "0" otherwise. if the relative size of each coefficient does not match the bit to be encoded, the coefficients are swapped. the interchange of these coefficients does not considerably alter the watermarked image because the midfrequency dct coefficients have almost identical magnitudes. however, this method can cause errors due to the rounding case of dct. as a result, not all watermarks can be extracted properly. coltuc’s method is improved by modifying the dct coefficient pairs in the watermark embedding formula. our proposed formula ensures that the difference between the two coefficients is at least 𝜁. if the difference between the two coefficients is less than 𝜁, then the new pixels are modified so that the difference is 𝜁. the new watermarking system on medical images based on the modification of dct coefficient pairs is proposed to achieve the following objectives: (1) to achieve good imperceptibility from watermarked images; (2) to provide intellectual property protection for medical images; (3) to preserve the safety of patient data [6]. 2. related works the discrete cosine transform (dct), which has energy compaction features, is frequently employed in watermarking approaches. dct can convert an image into a frequency band, which can be inverted to transform it back into the original image. following the dct process, the image pixels are turned into coefficients. direct current (dc) is represented by the first coefficient dct in the base array function's upper left corner, while the remaining coefficients represent alternating current (ac). since the ac is so crucial to an image, any modifications to the ac can significantly affect the image. on the other hand, slight adjustments to the image have little impact on the ac. 90 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 thanki et al. [14] developed a watermarking technique for medical images based on fast discrete curvelet transform (fdcut) and dct. the block-wise dct is applied to the medical image's high-frequency curvelet coefficient. a white gaussian noise (wgn) order is added to the original image's mid-band frequency coefficient in compliance with the watermark bit to create a watermarked medical image. images from x-rays, ultrasounds, mris, and computed tomography (ct) scans were utilized to evaluate how the suggested watermarking technique worked. the study results show that watermarks are more invisible in all types of medical images with psnr above 45 db. however, two uncorrelated wgn sequences generated during the embedding process are required to recover the watermark. therefore, only binary watermarks may be embedded using this technique; text-based epr data cannot be. another drawback is that the resulting watermark image always contains noise. novamizanti et al. [15] introduced the singular value decomposition (svd) method to medical image watermarking techniques based on fdcut and dct. watermark embedding by exchanging the singular value of the watermark and the host image result from the fdcut and dct transformations. the proposed algorithm has good imperceptibility with interval psnr values 53 db to 54 db. however, this watermarking scheme is semi-blind, where it is necessary to output svd results from the original watermark image at the extraction stage. this method is not resistant to blurring and geometry attacks. lei et al. [16] reported a robust image watermarking algorithm based on dct domain and qim. the host signal's medium and low-frequency dct coefficient is divided into two regions. then the watermark bit is embedded by quantizing the ratio of the two halves. according to experimental findings, this method is only superior against attacks of the common type. this algorithm has limited capacity, where a 512×512 image host can only accommodate a 128-bit watermark. then, the optimal parameter for each image is obtained as psnr of 41 db. zhu et al. [17] presented a robust image steganography algorithm for jpeg compression. firstly, a candidate dct coefficient unaffected by jpeg compression is chosen. second, the proposed distortion function gives each potential dct coefficient a cost. the error correction code and the syndrome trellis code help the method become even more robust and invisible. this algorithm's embedding capacity remains restricted to payloads between 0.01 and 0.1 bpnzac. for 512×512 image hosts, the proposed algorithm only produces psnr values with the interval 42 db to 47 db. rachmawanto et al. [18] designed an image watermarking algorithm using block-based dct, where the dc coefficient is chosen to keep the watermark resistance included. the beaufort cipher is used for the encryption process and the watermark distribution when inserted. the goal is to improve watermark security and imperceptibility aspects. generally, the spread spectrum watermarking technique uses pn sequence for watermark deployment. however, the proposed method is non-blind, where the cover image is still required for the watermark extraction process. an image watermarking technique based on dct was researched by byun et al. [19]. first, the dct coefficient for the specified location is determined. next, the variation value is calculated to adjust the coefficient under the embedding bit and quantization step. finally, the watermark bit is inserted directly into the pixel value without using a full-frame dct. according to the findings, the suggested watermarking technology offers less computing complexity and ensures robustness. a color host image with a size of 512×512 can only accommodate a watermark of 1024 bits, indicating that the embedding capacity of this technique is still constrained. the proposed method's average psnr is about 42 db. 91 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 ko et al. [20] reported a watermarking method based on the correlation of dct coefficients between blocks. the coefficient variance in the two blocks of dct is calculated and changed depending on the watermark bits to adjust this difference to a specified range. the level of the dct coefficient's modification is based on the dc coefficient and the median of the alternating current (ac) coefficient, which is ordered in zigzag order. the experimental findings demonstrate the robustness of the suggested technique against several single and combined attacks. for the lena watermarked image, only a psnr of 41.6 db is obtained. in addition, the resistance is weak against types of noise attacks, including ber is 17.06 for saltand-pepper noise and 9.98 for gaussian noise. a robust watermarking technique based on dct, speeded up robust features (surf), and perceptual hashing was proposed by nawaz et al. [21]. the watermark image is preprocessed to enhance its security using affine transformation with feature matrix and chaotic encryption technology. surf feature points are utilized to choose the dct region and extract scalable watermarks after geometric rectification during the extraction process. studies reveal that the algorithm efficiently defends against geometric and conventional attacks and can effectively maintain the security of images with an nc value higher than 90%. however, this paper does not report the psnr results from the watermarked images without attack. this technique utilizes a correlation function to confirm the similarity of the derived watermarks. hence scrambled data from the original watermark is still required at the watermark extraction stage. kumar et al. [22] presented a secure watermarking framework on medical images by applying intdct and svd. the differential evolution technique was used to determine suitable scaling factors by randomizing the watermark with the step space fill curve. in addition to the watermarked image, the 𝑈𝑊,𝑆,and 𝑉𝑊 values during insertion are also required for the watermark extraction process. the experimental findings demonstrate that the designed framework is robust to geometric attacks. fares et al. [23] introduced watermarking approaches based on dct and schur decomposition to protect medical images. integration is performed at the intermediate frequencies. according to the findings, the designed algorithm produces acceptable imperceptibility with psnr values at intervals 47 db to 49 db. however, capacity is limited, where a 1024×1024 image host can only accommodate a 1024-bit watermark. the suggested method is robust under some conventional attacks but, it is not resistant to geometric attacks, such as cropping and scaling. 3. preliminary in this section, the dct technique and the method of coltuc are presented and used in the proposed watermarking method. the energy compaction and redundancy removal properties of dct make this transformation popular in image processing, especially image watermarking. however, dct-based watermarking is prone to rounding errors. when this dct is applied to the coltuc’s method, which exchanges two dct coefficients to embed a watermark into the host image, the watermarking method is challenging in developing watermarking techniques, especially in medical images. 3.1 discrete cosine transform as one of the prominent transformation techniques, dct works by changing the image from the spatial to the frequency domain [13]. this technique has been used extensively in image processing. some of the outstanding properties of dct in image processing applications [24,25] include: 92 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 1. decorrelation can eliminate redundancy between neighboring pixels. 2. dct offers better energy compaction for correlated images. 3. separability and symmetry: transformation matrices can be computed offline, thus providing computational efficiency. 4. orthogonality: this property makes some reduction in pre-computing complexity. generally, the image is segmented into 8×8 pixel blocks. then, each of those blocks is subjected to a 2d-dct. mathematically, the 2d-dct transformation and the 2d-dct inverse for a block size of 8×8 can be seen in eq. (1) and (2), respectively, as follows: 𝐹(𝑢,𝑣) = 1 4 𝐶(𝑢)𝐶(𝑣)∑ ∑ 𝑓(𝑥,𝑦) 7𝑦=0 7 𝑥=0 𝑐𝑜𝑠( (2𝑥+1)𝑢𝜋 16 )𝑐𝑜𝑠( (2𝑦+1)𝑣𝜋 16 ) (1) 𝑓(𝑥,𝑦) = 1 4 𝐶(𝑢)𝐶(𝑣)∑ ∑ 𝐹(𝑢,𝑣)7𝑣=0 7 𝑢=0 𝑐𝑜𝑠( (2𝑥+1)𝑢𝜋 16 )𝑐𝑜𝑠( (2𝑦+1)𝑣𝜋 16 ) (2) with 𝐶(𝜔) = 1 √2 for 𝜔 = 0,and 𝐶(𝜔) = 1,for otherwise ; 𝐹(𝑢,𝑣) is the dct coefficient; 𝑓(𝑥,𝑦) is the pixel value in the spatial domain. there are two ways to apply dct to images: block-wise and without block-wise. dct separates the image into three frequency sub-bands, i.e., low (lf), middle/ mid (mf), and high (hf), in a block-wise approach. figure 1 shows the position of the dct coefficient with blocks of size (8×8) pixels. the 8×8 pixel block transformation yields 64 dct coefficients. the position of the upper left corner of the dct coefficient, 𝐹(0,0), is the dc component, and the other 63 coefficients are the ac component. the dc component represents the average color of the entire frequency-transformed region. thus, embedding data in dc components can cause visual artifacts that are visible to the normal human eye. embedding data is done in the mf coefficient region, because this region carries relatively less important image information than the hf and lf regions, and is less significant in perception. thus, data embedding in the mf region does not significantly affect image quality or communication performance [14,26]. fig. 1: the 2d discrete cosine transform (dct) coefficients with blocks of size (8×8) pixels. 3.2 coltuc’s method coltuc and chassery [12,13] applied the dct domain in the robust watermarking stage. firstly, the cover image 𝑋 is segmented into 8×8 blocks. next, dct is applied to each block. the two mf coefficients �̂�𝑎 and �̂�𝑏 in each dct block are chosen to insert one watermark bit 𝑤ϵ {0,1}, as follows [27]: 93 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 (�̂�𝑎 ′ , �̂�𝑏 ′ ) = { (�̂�𝑎, �̂�𝑏), 𝑖𝑓 �̂�𝑎 − �̂�𝑏 > 0 and 𝑤 = 1 (�̂�𝑏, �̂�𝑎), 𝑖𝑓 �̂�𝑎 − �̂�𝑏 ≤ 0 and 𝑤 = 1 (�̂�𝑎, �̂�𝑏), 𝑖𝑓 �̂�𝑎 − �̂�𝑏 ≤ 0 and 𝑤 = 0 (�̂�𝑏, �̂�𝑎), 𝑖𝑓 �̂�𝑎 − �̂�𝑏 > 0 and 𝑤 = 0 (3) with 𝑎 and 𝑏 being the two ac channel indexes. the index is the coordinates of the pixels. thus, the ac channel index represents the coordinates of the dct coefficients located in the ac component. for example, 𝑎=(2,3) and 𝑏=(3,2) are the selected ac channel indexes, so the two mf coefficients �̂�(2,3) and �̂�(3,2) are used to insert a watermark bit, as shown in fig. 1. by replacing �̂�𝑎 ′ and �̂�𝑏 ′ for the appropriate coefficients, the dct coefficients for 𝑌 are obtained. the watermarked image 𝑌 is then created by applying the inverse dct. for the decoding process, 𝑌 is segmented into 8×8 blocks. next, each block is converted using the dct technique. the embedded watermark for a coefficient pair of �̂�𝑎 and �̂�𝑏 is recovered as: if �̂�𝑎 − �̂�𝑏 > 0, then the bit watermark is 1, and 0 otherwise. one bit of information is entered into each block depending on the difference between the two coefficients of mf. the new coefficient value does not change if the difference is positive and the bit is "1", or the difference is negative, and the bit is "0". however, for other conditions, the positions of the two mf coefficients are swapped. the exchange of these coefficients does not change the watermarked image significantly because the mf of dct coefficients generally have almost the same magnitude. however, this condition is prone to extraction errors due to the rounding factor of dct, as shown in fig. 2(a). as a result, not all watermarks can be extracted properly. one solution is to select two mf coefficients �̂�𝑎 and �̂�𝑏 to embed a robust watermark. however, this method becomes impractical. 4. proposed method: watermarking images via modifying dct coefficient pair in this section, the modification of the insertion formula in coltuc’s method is described in subsection 4.1. the watermarking embedding step is presented in subsection 4.2, and the watermarking extraction step is presented in subsection 4.3. the watermarking framework for medical images is generally shown in fig. 3. first, a watermark in the form of an epr is hidden into a medical image, resulting in a 𝑌 watermarked image, and then sent through a communication channel. during transmission, the watermarked image undergoes various attacks, resulting in a medical image that is attacked as �̂�. the attacks can be in the form of noise and intentional and unintentional modifications. in the extraction process, only 𝑌 (for noise-free channel) or 𝑌 (for noise channel) is needed to restore the original watermark. thus, it can preserve medical images with copyright and maintain patient data security. this paper enhances the robust watermarking method coltuc et al. by modifying the dct coefficient pairs in the watermark embedding formula. the proposed formula ensures that the difference between the two coefficients is at least as much as 𝜁. if the difference between the two coefficients is less than 𝜁, then the new pixels are modified so that the difference is equal to 𝜁. this new watermarking system on medical images based on modifying the dct coefficient pair is suggested to obtain acceptable imperceptibility of watermarked images, impart data confidentiality of medical images, and preserve patient information privacy. 94 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 fig. 2: illustration of watermark embedding formula (a) coltuc’s method, (b) proposed. fig. 3: the framework of medical image watermarking. 4.1 modification of the watermark embedding formula in coltuc’s method the value of the mf coefficient of the dct generally has the same magnitude. after rounding operations to produce watermarked images and entering the decoding process, not all watermarks can be extracted correctly. we modified eq. (3) so that the watermarked host image has high imperceptibility, protects the copyright (watermark) embedded in medical images, and maintains the privacy of patient information. (�̂�𝑎 ′ , �̂�𝑏 ′ ) = { (�̂�𝑎, �̂�𝑏), 𝑖𝑓 �̂�𝑎 − �̂�𝑏 > 𝜁 and 𝑤 = 1 (�̅� + 𝜁 2 , �̅� − 𝜁 2 ) 𝑖𝑓 |�̂�𝑎 − �̂�𝑏| ≤ 𝜁 and 𝑤 = 1 (�̅� + 𝜁 2 , �̅� − 𝜁 2 ) 𝑖𝑓 �̂�𝑎 − �̂�𝑏 < −𝜁 and 𝑤 = 1 (�̂�𝑎, �̂�𝑏), 𝑖𝑓 �̂�𝑎 − �̂�𝑏 < −𝜁 and 𝑤 = 0 (�̅� − 𝜁 2 , �̅� + 𝜁 2 ), 𝑖𝑓 |�̂�𝑎 − �̂�𝑏| ≤ 𝜁 and 𝑤 = 0 (�̅� − 𝜁 2 , �̅� + 𝜁 2 ), 𝑖𝑓 �̂�𝑎 − �̂�𝑏 > 𝜁 and 𝑤 = 0 (4) the proposed formula ensures that the difference between the two mf coefficients, namely �̂�𝑎 and �̂�𝑏, is at least as much as 𝜁. if the distance between the two mf coefficients is less than 𝜁, then the new pixel is modified so that the difference in distance is as significant as 𝜁. 95 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 modification of the insertion formula of coltuc’s method through the dct coefficient pair can be seen in eq. (4) and then simplified to eq. (5). figure 2(b) presents the illustration of the proposed formula (�̂�𝑎 ′ , �̂�𝑏 ′ ) = { (�̂�𝑎, �̂�𝑏), if (�̂�𝑎 − �̂�𝑏 < −𝜁 and 𝑤 = 0) or (�̂�𝑎 − �̂�𝑏 > 𝜁 and 𝑤 = 1) ( �̂�𝑎+�̂�𝑏+(2𝑤−1)𝜁 2 , �̂�𝑎+�̂�𝑏−(2𝑤−1)𝜁 2 ), otherwise (5) with �̅� is the average of the two mf coefficients of the dct, namely �̂�𝑎 dan �̂�𝑏. 4.2 embedding stage the input of the watermarking embedding stage is a medical image 𝑋 as the host, and the output is a watermarked host image 𝑌. the sizes of 𝑋 and 𝑌 are m × m, while the size of 𝑊 is n × n. fig. 4(a) presents the watermarking embedding stage, and the detailed embedding steps are described as follows. 1. split 𝑋 into 8×8 non-overlapping blocks. 2. for each block, apply dct using eq. (1) so that it produces �̂�. 3. in each dct block, the two mf coefficients �̂�𝑎 and �̂�𝑏 are decisive in embedding onebit watermark 𝑤ϵ {0,1}. the robust watermark embedding formula is expressed in eq. (5). 4. the dct coefficient of 𝑌 is done as follows: �̂�𝑖 = { �̂�𝑖 ′, 𝑖𝑓 𝑖 𝜖 {𝑎,𝑏} �̂�𝑖, otherwise (6) 5. process the inverse dct using eq. (2), and a watermarked image is obtained. (a) (b) fig. 4: the proposed watermarking method using dct coefficient pair (a) embedding stage (b) extraction stage. 4.3 extraction stage the input of the watermarking extraction stage is the 𝑌 watermarked host image, and the output is the extracted watermark 𝑊∗. while, 𝑌 and 𝑊∗ sizes are m × m, and n × n, respectively. figure 4(b) presents the watermarking extraction stage, and the extraction steps in detail are described as follows. 1. split 𝑌 into 8×8 non-overlapping blocks. 96 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 2. apply dct to each block using eq. (1) so that it produces �̂�. 3. in each dct block, the two mf coefficients �̂�𝑎 and �̂�𝑏 become determinants in extracting the one-bit watermark 𝑤ϵ {0,1}. the robust watermark extraction formula is stated as follows. 𝑊∗ = { 1, if �̂�𝑎 − �̂�𝑏 > 0 0, otherwise (7) at the transmission is without noise, 𝑊∗ equals 𝑊. 5. results and discussion this section evaluates the effectiveness of the suggested robust and imperceptible watermarking technique. subjective visual observation and objective quantitative analysis are used to evaluate the proposed method. numerous attacks with varying parameters were performed to assess robustness further. finally, the proposed method's imperceptibility and robustness are compared to state-of-the-art works. this experiment uses the grayscale format and image sizes 512×512 of the host medical image. a total of five medical images from different modality types were used as test data, including mri, x-ray, computed tomography (ct), ultrasound (us), and colonoscopy. medical images were retrieved from the medpixtm medical image database [26] and cvcclinicdb database [28]. the host medical image modality used in the experiment is shown in fig. 5(a-e). meanwhile, the watermark is a random binary image whose size depends on the block size discussed in the previous section. for an 8×8 block, the amount of watermarks embedded into the original host medical image is (512×512)/(8×8)=4096 bits. in other words, blocks measuring 8×8 yield a watermark of size 64×64. the efficiency of the proposed method is thoroughly evaluated on two watermarking criteria, including imperceptibility and robustness. the performance metric for imperceptibility criteria uses peak signal noise ratio (psnr) [9]. the watermarked host image must be invisible to humans to guarantee information security. therefore, imperceptibility/ invisibility criteria are essential metrics in watermarking techniques. the psnr measures how visually similar the watermarked image and the original host are. both images should look the same, so there is no significant difference between the two. the similarity between the two images increases with increasing psnr values and vice versa. generally, the watermarked image is acceptable if the psnr is more than 37 db and the watermark is not discernible to the human visual system [29]. here, 𝑋 is the original host image, 𝑌 is the watermarked host image, and m×m is the host image size. mathematically, psnr (in db) is formulated as follows [11,15]. 𝑃𝑆𝑁𝑅 = 10 × 𝑙𝑜𝑔 2552× m × m ∑ ∑ (𝑿𝒊,𝒋−𝒀𝒊,𝒋) 2m 𝑗=1 m 𝑖=1 (8) the bit error rate (ber) and normalized correlation (nc) are the performance metric to evaluate a watermarking technique's robustness criteria. technically, ber measures the erroneous bit rate after the watermark extraction process. if the ber value is close to 0, then a few messages are lost, and vice versa. ideally, the value of ber should be 0. if eb is the amount of incorrectly decoded bits, and tb is the number of watermark bits, then ber can be calculated [14], [27] as eb tb⁄ . 97 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 fig. 5: five modalities of original medical image and a watermark (a) x-ray , (b) ct, (c) us, (d) mri, (e) colonoscopy, (f) watermark. principally, the nc measures the similarity between the original and extracted watermark images. the nc can be described mathematically by eq. (9). if the nc value is near 1, then the watermarking method is very robust. 𝑁𝐶 = ∑ ∑ 𝑊𝑖,𝑗 𝑊𝑖,𝑗 ∗n 𝑖−1 n 𝑖=1 ∑ ∑ 𝑊𝑖,𝑗 2n 𝑖−1 n 𝑖=1 (9) where 𝑊 and 𝑊∗ are the original watermark and extracted watermark images, respectively. n×n is the watermark image's size [14]. after applying the embedding and extraction processes, the proposed scheme's imperceptibility and robustness tests are carried out for varied medical images. 5.1 𝜁 parameter evaluation the proposed watermark embedding formula ensures that the difference between the two mf coefficients, namely �̂�𝑎 and �̂�𝑏, is at least 𝜁. if the distance between the two mf coefficients is less than 𝜁, then the new pixels are modified so that the distance difference is 𝜁. we changed the value of the 𝜁 parameter in the watermark embedding formula to get the psnr and expected robustness level. experiments were carried out on five types of medical images, i.e., x-ray, ct, us, mri, and colonoscopy. figure 6 presents the effect of the 𝜁 parameter on psnr and ber. figure 6(a) shows the relationship between 𝜁 and ber. higher 𝜁 results in lower ber. the criterion ber is 0 when 𝜁 ≥ 3. it means that the extracted watermark can be recovered very well. ber of 0 means there are no bit errors in watermark extraction. while fig. 6(b) shows the relationship between ber and psnr over 𝜁, which corresponds to fig. 6(a). the higher the 𝜁 value, the higher the resistance, but the lower the psnr. when the resistance condition is ideal, namely ber is 0, the psnr value ranges around 48 db to 59 db for the range of 𝜁 is 3 to 10. thus, 𝜁 determines the imperceptibility and robustness of the watermark embedding into the host medical image. 5.2 imperceptibility analysis for integrity and ensuring information security, watermarked host medical images must be imperceptible/ invisible to humans. figure 7 shows a watermarked host x-ray image when not under attack and the extracted watermark. the experiment was carried out when 𝜁 = 3. the psnr, ber, and nc results of each corresponding image are also shown in fig. 7. the watermarked image is acceptable because the psnr is more than 37 db, and the watermark is not discernible to the human visual system [30]. 98 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 (a) (b) fig. 6: evaluation of 𝜁 (a) the ber of extracted watermark (b) the trade-off between psnr and ber. fig. 7: imperceptibility and robustness performance. rows represent the extracted watermarked image and watermark along with their corresponding psnr, nc, and ber. columns represent type medical images, i.e., x-ray, ct, us, mri, and colonoscopy. based on fig. 7, the imperceptibility criterion of the suggested method is that all psnr of each watermarked medical image is greater than 54 db. the average psnr generated for the five watermarked medical image modalities is 56.3604 db. then, all extracted watermarks yielded ber is 0 and nc is 1 when the watermarked host image was not subjected to attack. it demonstrates that the method of watermarking is imperceptible. furthermore, the suggested approach satisfies both the subjective and objective standards for watermarking invisibility. when the watermarked host image is not subjected to an assault, extracted watermarks have a ber of 0 and an nc of 1. therefore, the process of watermarking has a high level of imperceptibility. thus, the suggested method satisfies both the subjective and objective requirements for watermarking invisibility. 5.3 robustness analysis 99 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 various watermarking attacks were applied to watermarked medical images to examine the robustness criteria of the proposed method. table 1 represents different attacks with parameter specifications used in the experiment. these attacks include compression, filtering, noise, histogram equalization, sharpening, and motion blur. in particular, compression attacks include jpeg and jpeg2000. jpeg compression parameters with quality factor (qf) 80 and jpeg2000 compression with compression ratio (cr) = 4 and 8. filter attacks consist of median, gaussian, average, and lowpass filters. the parameters in the filtering attack use a filter with a window size of 3×3. noise attacks include gaussian, salt & pepper, and speckle. the parameters in the noise addition attack are set by the variance or noise density of 0.001. parameters of motion blur attack with linear motion of the camera with pixels len = 7, with angle degrees theta = 4. at the same time, histogram equalization and sharpening use default parameters. table 1: various attacks with parameter specifications in experiments attack parameter specifications jpeg compression (jc) qf = 80, 90 jpeg2000 compression (j2k) cr = 8, 12 median filter (mf) 3×3 gaussian filter (gf) 3×3 average filter (af) 3×3 lpf 3×3 gaussian noise (gn) mean = 0, variance = 0.001 salt & peppers noise (sp) noise density = 0.001 speckle noise (sn) mean = 0, variance = 0.001 histogram equalization (he) sharpening (sh) motion blur (mb) len = 7, theta = 4 in the extraction stage, if the extracted watermark can recover from damaged watermarked images, then the watermarking method is said to be robust and secure. here, ber and nc performance metrics examine the robustness of the proposed method under various watermarking attacks. in addition, the result of the suggested scheme is compared with the existing techniques [15,17] for the same medical image dataset. the ber of extracted watermark on numerous watermarked medical images is shown in fig. 8. meanwhile, figure 9 presents the results of the extracted watermark from the attacked watermarked x-ray along with corresponding ber and nc. various attacks are rendered on watermarked medical images. these medical images include x-ray, ct, us, mri, and colonoscopy. on the extraction side, the extracted watermark image is expected to be recovered from the damaged watermarked medical image. based on fig. 8, jpeg compresses images without significantly altering their appearance. medical images with watermarks are compressed with jpeg using varying quality factors. then, the proposed method is used to extract the watermarked image. the experiments indicated that the proposed method performs well for all the medical images we tested on jpeg compression with qf > 80 and jpeg2000 compression with cr < 12. the extracted watermark can still be interpreted visually if ber < 0.3 [30]. on x-ray, ct, and colonoscopy images, watermarks can be extracted well even at jpeg compression with qf = 90 and jpeg2000 compression with cr = 12. remarkably, watermarks can be best extracted, with ber is 0 for all 100 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 compression parameters given in watermarked colonoscopy image. based on fig. 9, watermarks can be extracted well with ber of 0 and nc of 1 for jpeg compression attacks with qf = 90 and jpeg2000 with cr = 8, and 12 given to the attacked watermarked x-ray images. fig. 8: the ber of extracted watermarks when condition with attack. fig. 9: the bers and ncs of extracted watermarks from watermarked x-rays attacked. four filters, including the median, gaussian, average, and low pass, and three different noises, such as gaussian, salt & pepper, and speckle, are applied to watermarked medical images. afterward, the watermark image is extracted using the proposed method. the experiment results (fig. 8 and fig. 9) prove that the proposed method performs well for all medical images provided a filtering attack. remarkably, watermarks can be extracted very well with ber 0 for watermarked colonoscopy medical images subjected to average filter and lpf attacks. the experiment results also prove that the proposed scheme performs well for all medical images under the noise attack. remarkably, watermarks can be successfully extracted with a ber of 0 for all watermarked medical images subjected to speckle noise attacks. 101 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 a series of other attacks, such as histogram equalization, sharpening, and motion blur are also applied to watermarked medical images for endurance testing. based on the experiment results (fig. 8 and fig. 9), the proposed scheme performs well for all medical images given the three attacks. impressively, watermarks can be well extracted with a ber of 0 for all watermarked medical images given a sharpening attack. watermarks can also be extracted with a ber of 0 for motion blur attacks rendered in watermarked mri and colonoscopy images. 5.4 comparison of the proposed method with state-of-the-art work in fig. 10, the imperceptibility performance of the proposed method is compared with coltuc's method [13] and the recently developed watermarking method [14,15] for medical image identity protection. the watermark payload under the same conditions, which is 1 bit for every 64 pixels of the host medical image. the psnr value of the proposed method is compared with the related work. the methods are compared using 𝜁 = 3 and without watermarking attacks. the proposed scheme offers superior performance to the three existing schemes [13-15]. in the proposed method, the average psnr value of watermarked medical images is 56.3604 db. meanwhile, the mean of psnr for watermarked medical images from the [13-15] scheme are 50.5647 db, 48.3150 db, and 53.6184 db, respectively. it means that the insertion of watermark bits does not influence the watermarked medical image of the proposed method. the proposed method produces high imperceptibility over the the state-ofthe-art works [13-15]. fig. 10: comparison under different medical images and methods. specifically, table 2 summarizes the robustness performance of the proposed method compared to coltuc’s method [13] to evaluate how much contribution the proposed watermarking method makes. the host image used as test data is an x-ray. the suggested method performs well compared to the previous method against all types of watermarking attacks. in fact, the watermark can be extracted perfectly in a jpeg compression attack with qf = 90, jpeg2000 with cr = 8 and 12, speckle noise, and sharpening. the proposed method is outstanding from coltuc’s method [13], with the increase in ber and nc being 93% and 14%, respectively. table 2: comparison of bers and ncs of the proposed method to the coltuc’s method [13] in attacked watermarked x-ray attack ber nc 102 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 [13] proposed [13] proposed jpeg (qf=80) 0.2488 0.0056 0.8491 0.9888 jpeg (qf=90) 0.2493 0 0.8523 1 j2k (cr=8) 0.1177 0 0.9605 1 j2k (cr=12) 0.1626 0 0.9337 1 mf [3×3] 0.2842 0.0374 0.4059 0.9221 gf [3×3] 0.1492 0.0405 0.6942 0.9172 af [3×3] 0.0615 0.0208 0.8693 0.9563 lpf [3×3] 0.0625 0.0190 0.8673 0.9598 gn (0.001) 0.2261 0.0042 0.8644 0.9950 sp (0.001) 0.0173 0.0054 0.9877 0.9982 sn (0.001) 0.2146 0 0.8652 1 he 0.1060 0.0068 0.9237 0.9863 sh 0.0225 0 0.9843 1 mb 0.0603 0.0022 0.9706 0.9956 table 3: ncs comparison of the proposed method to the state-of-the-art [14,15] in attacked watermarked x-ray attack thanki [14] novamizanti [15] proposed jpeg (qf=80) 0.9282 0.8769 0.9888 jpeg (qf=90) 0.9806 0.8973 1 gn (0.001) 0.6377 0.9970 0.9950 sp (0.001) 0.7532 0.9473 0.9982 he 0.9708 0.8909 0.9863 sh 0.9674 0.9890 1 the proposed method is also compared with the recently developed watermarking methods [14,15] to maintain the privacy and protection of the epr as a watermark. host x-ray images were used as test data for all compared methods. watermarking in both techniques [14,15] was performed in the fdcut and dct domains. the extraction process of both methods is semiblind. the difference is the insertion of the watermarking technique [14] using the correlation sequence method. while in [15], the watermarking embedding technique uses the svd method. compared with the state-of-the-art works [14,15], the proposed method is superior in terms of resistance to jpeg compression attacks, sharpening, histogram equalization, and sharpening. in addition, on a jpeg compression attack with qf = 90 and sharpening, the watermark can be extracted perfectly. the proposed method modifies the dct coefficient pairs to embed a robust watermark. thus, the average result demonstrates that the suggested method outperforms the present scheme regarding imperceptibility, robustness, and security. the proposed approach can be part of a robust reversible watermarking scheme [31] due to the blind extraction stage of the proposed watermarking method. 3. conclusion this paper proposes a modification of the dct coefficient pair in the watermark embedding process. the proposed formula ensures that the difference between the two coefficients is at least as 𝜁. if the difference between the two coefficients is less than 𝜁, then the new pixels are modified so that the difference is equal to 𝜁. this simple watermarking 103 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 technique based on modifying dct coefficient pairs is offered to achieve high imperceptibility, provide intellectual property protection for medical images, and ensure patient data security. the suggested method was evaluated on different types of medical images, including x-ray, ct, us, mri, and colonoscopy, and compared to numerous robust watermarking techniques of the current work. the experimental results indicate that the suggested method outperforms various contemporary watermarking techniques regarding imperceptibility, robustness, and security. the psnr value for all categories of watermarked medical images exceeds 54 db, and the average psnr value is approximately 56 db. in terms of resistance to jpeg compression attacks, histogram equalization, and sharpening, the suggested method is superior to numerous state-of-the-art robust watermarking methods. future research could apply the presented technology to a robust reversible watermarking strategy and medical image protection for telemedicine applications. acknowledgement this research is part of l. novamizanti's dissertation research funded by the doctoral dissertation research grant from the ministry of research and technology of the republic of indonesia, file numbers: 083/e5/pg.02.00.pt/2022 and 343/it1.b07.1/spplppm/v/2022. the indonesian endowment fund for education (lpdp) scholarship and telkom university also partially funded this research. references [1] memon, na. alzahrani a. (2020) prediction-based reversible watermarking of ct scan images for content authentication and copyright protection. ieee access, 8: 75448-75462. doi: 10.1109/access.2020.2989175. [2] sajedi h, rahbar s. (2020) information hiding methods for e –healthcare. smart health, 15: 100104. doi: 10.1016/j.smhl.2019.100104. [3] ahmad gi, singla j, giri kj. (2021). security and privacy of e-health data. in multimedia security, springer singapore, pp. 199-214. [4] lanxiang c, wutong bai, zhiqiang yao. (2020) a secure and privacy-preserving watermark based medical image sharing method. chinese j. electron., 29(5): 819-825. doi: 10.1049/cje.2020.07.003. [5] magdy m, hosny km. (2022) security of medical images for telemedicine : a systematic review. multimed. tools appl., 81: 25101-25145. doi: 10.1007/s11042-022-11956-7 [6] alzahrani a, memon na. (2021) blind and robust watermarking scheme in hybrid domain for copyright protection of medical images. ieee access, 9: 113714-113734. doi: 10.1109/access.2021.3104985. [7] thakur s, singh ak, ghrera sp, mohan a. (2020) chaotic based secure watermarking approach for medical images. multimed. tools appl., 79: 4263-4276. doi: 10.1007/s11042-018-6691-0 [8] hassan b, ahmed r, li bo, hassan o. (2019) an imperceptible medical image watermarking framework for automated diagnosis of retinal pathologies in an ehealth arrangement. ieee access, 7: 69758-69775. doi: 10.1109/access.2019.2919381. [9] anand a, singh ak. (2021) watermarking techniques for medical data authentication : a survey. multimed. tools appl., 80: 30165-30197. doi: 10.1007/s11042-020-08801-0 [10] evsutin o, dzhanashia k. (2022) watermarking schemes for digital images : robustness overview. signal process. image commun., 100: 116523. doi: 10.1016/j.image.2021.116523. [11] saini d, ali m. (2020) a robust medical image watermarking framework based on svd and de in integer dct domain (workshop paper), pp. 373-378. doi: 10.1109/bigmm50055.2020.00064. [12] coltuc d, chassery jm. (2007) distortion-free robust watermarking: a case study. secur. steganography, watermarking multimed. contents ix, 6505: 65051n, doi: 10.1117/12.702445. 104 iium engineering journal, vol. 24, no. 1, 2023 novamizanti et al. https://doi.org/10.31436/iiumej.v24i1.2597 [13] coltuc d. (2007) towards distortion-free robust image authentication. j. phys. conf. ser., 77: 012005. doi: 10.1088/1742-6596/77/1/012005. [14] thanki r, borra s, dwivedi v, borisagar k. (2017) an efficient medical image watermarking scheme based on fdcut–dct. eng. sci. technol. an int. j., 20(4): 1366-1379. doi: 10.1016/j.jestch.2017.06.001. [15] novamizanti l, wahidah i, wardana npdp. (2020) a robust medical images watermarking using fdcut-dct-svd. int. j. intell. eng. syst., 13(6): 266-278. doi: 10.22266/ijies2020.1231.24 [16] lei m, liu x, wang m, yang y, qu z. (2018) robust image watermarking based on quantization index modulation in the dct domain. j. internet technol., 19(2): 507-514. doi: 10.3966/160792642018031902019. [17] zhu z, zheng n, qiao t, xu m. (2019) robust steganography by modifying sign of dct coefficients. ieee access, 7: 168613-168628. doi: 10.1109/access.2019.2953504. [18] rachmawanto eh, setiadi drim, sari ca, rijati n. (2019) imperceptible and secure image watermarking using dct and random spread technique. telkomnika (telecommunication comput. electron. control., 17(4): 1750-1757. doi: 10.12928/telkomnika.v17i4.9227. [19] byun sw, son hs, lee sp. (2019) fast and robust watermarking method based on dct specific location. ieee access, 7: 100706-100718. doi: 10.1109/access.2019.2931039. [20] ko hj, huang ct, horng g, wang sj. (2020) robust and blind image watermarking in dct domain using inter-block coefficient correlation. inf. sci. (ny)., 517: 128-147. doi: 10.1016/j.ins.2019.11.005. [21] nawaz sa, li j, bhatti ua, mehmood a, shoukat mu, bhatti ma (2020) advance hybrid medical watermarking algorithm using speeded up robust features and discrete cosine transform. plos one, 15(6): 1-21. doi: 10.1371/journal.pone.0232902. [22] kumar s, jha rk. (2019) fd-based detector for medical image watermarking. iet image processing, 13(10): 1773-1782 2019. doi: 10.1049/iet-ipr.2018.5485. [23] fares k, khaldi a, redouane k, salah e. (2021) dct & dwt based watermarking scheme for medical information security. biomed. signal process. control, 66: 102403. doi: 10.1016/j.bspc.2020.102403. [24] khayam sa. (2003) the discrete cosine transform (dct): theory and application. in information theory and coding, michigan state university, pp. 1-13. [25] hamidi m, haziti me, cherifi h, hassouni me. (2018) hybrid blind robust image watermarking technique based on dft-dct and arnold transform. multimed. tools appl., 77(20): 2718127214. doi: 10.1007/s11042-018-5913-9. [26] hernandez jr, amado m, perez-gonzalez f. (2000) dct-domain watermarking techniques for still images: detector performance analysis and a new structure. ieee trans. image process.,9(1): 55-68. doi: 10.1109/83.817598. [27] wang x, li x, pei q. (2020) independent embedding domain based two-stage robust reversible watermarking. ieee trans. circuits syst. video technol., 30(8): 2406-2417. doi: 10.1109/tcsvt.2019.2915116. [28] rahim t, novamizanti l, ramatryana ina, shin sy. (2021) compressed medical imaging based on average sparsity model and reweighted analysis of multiple basis pursuit. comput. med. imaging graph., 90: 101927. doi: 10.1016/j.compmedimag.2021.101927. [29] guo y, li bz., goel n (2017) optimised blind image watermarking method based on firefly algorithm in dwt-qr transform domain. iet image process, 11(6): 406-415. doi: 10.1049/iet-ipr.2016.0515 [30] budiman g, suksmono ab, danudirdjo d. (2020) compressive sampling with multiple bit spread spectrum-based data hiding. appl. sci., 10(12): 1-21. doi: 10.3390/app10124338. [31] novamizanti l, suksmono ab, danudirdjo d, budiman g. (2022) robust reversible watermarking using stationary wavelet transform and multibit spread spectrum in medical images. int. j. intell. eng. syst., 15(3): 343-354. doi: 10.22266/ijies2022.0630.29. 105 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 the optimization of growth condition of the bacteria producing cold-active proteolytic enzyme from the antarctic region muhammad asyraf abd latip1,2, noor faizul hadry nordin3*, siti aisyah alias4,7, jerzy smykla5, faridah yusof2, and mohd azrul naim mohamad6 1 mariculture research division, fisheries research institute langkawi, kompleks perikanan bukit malut, 07000 langkawi, kedah, malaysia 2 biotechnology engineering department, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur 3 international institute for halal research and training (inhart), block a, level 3, kict building, international islamic university malaysia, jalan gombak, 53100 kuala lumpur 4 institute of ocean and earth and sciences, c308, level 3, block c, institute for advanced studies building, 50603 kuala lumpur, malaysia 5 institute of nature conservation, polish academy of sciences, al. a. mickiewicza 33 pl-31-120 krakow, poland 6 department of biotechnology, kulliyyah of science, international islamic university malaysia, jalan sultan ahmad shah, bandar indera mahkota, 25200 kuantan, pahang, malaysia 7 national antarctic research centre, b303, level 3, block c, institute for advanced studies building, 50603 kuala lumpur, malaysia * corresponding author: faizul@iium.edu.my (received: 30th may 2022; accepted: 9th september 2022; published on-line: 4th january 2023) abstract: the growth conditions of bacteria producing cold-active protease isolated from an antarctic sample were screened using one-factor-at-time (ofat). then, crude protease of the strain was extracted during the late logarithmic phase for enzymatic assay. a strain that showed the highest enzyme activity was selected for optimization via response surface method (rsm). the parameters studied were incubation temperature (4 – 36 °c), ph media (4 – 10) and nacl concentration (0 – 8%). based on the ofat results, all eight strains showed the highest growth rate at 20 °c, ph 7 and 4% (w/v) nacl. the assay showed that the crude enzyme extracted from strain sc8 exhibited significantly higher activity (0.20 u and 0.37 u) than the positive control (0.11 u and 0.31 u) at -20 °c and 20 °c. rsm suggested that the optimized setting for growth of sc8 were at 20.5 °c, ph 6.83 and 2.05% (w/v) of nacl with the results of the bacterial growth rate value was 3.70 ± 0.06 x 106 cells/hr. optimal growth conditions of sc8 from this study are useful for the large-scale production of cold-active protease in future. abstrak: keadaan pertumbuhan bakteria yang menghasilkan enzim protease aktif sejuk daripada sampel antartika disaring menggunakan satu faktor pada masa (ofat). kemudian, enzim protease ini diekstrak pada lewat fasa logaritma untuk ujian enzimatik. strain yang menunjukkan aktiviti enzim tertinggi telah dipilih untuk tujuan pengoptimuman melalui kaedah permukaan tindak balas (rsm). parameter yang dikaji ialah suhu pengeraman (4 – 36 °c), ph media (4 – 10) dan kepekatan nacl (0 – 8%). berdasarkan ofat, kesemua lapan bakteria menunjukkan kadar pertumbuhan tertinggi pada 20 °c, ph 7 dan 4% nacl. hasil ujian enzimatik menunjukkan bahawa enzim protease yang diekstrak daripada sc8 mempamerkan aktiviti yang jauh lebih tinggi (0.20 u dan 0.37 u) daripada kawalan positif (0.11 u dan 0.31 u) pada -20 °c dan 20 °c. 27 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 rsm mencadangkan tetapan optimum untuk pertumbuhan sc8 adalah pada 20.5 °c, ph 6.83 dan 2.05% nacl dengan keputusan kadar pertumbuhan bakteria ialah 3.70 ± 0.06 x 106 sel/jam. keadaan pertumbuhan optimum sc8 daripada kajian ini bermanfaat untuk menghasilkan produk protease aktif sejuk secara besar-besaran pada masa hadapan. keywords: cold-active protease; antarctica; one factor at time; response surface method 1. introduction antarctica is located at the south pole of the earth and acknowledged as one of the world’s seven continents. this pristine place has recorded the lowest temperature on earth [1]. compared to the arctic, this continent encompasses solid land and is mostly covered with a thick snow layer. roughly, the environment of the antarctic is extremely cold and exposed to strong ultraviolet radiation [2]. its sediment and soil contain a low level of carbon and nitrogen sources, contaminated with toxic metal compounds, fluctuating salt concentration, and exposure to low oxygen levels [3-5]. although it looks like deserted terrain, a diverse microbial community has been discovered from its snows, soil, and sediment [6,7]. recently, several novel environmental bacteria species have been identified such as paenisporosarcina antarctica [8], labilibaculum antarcticum [9] and pseudomonas fildesensis [10]. throughout history, many conventional methods used catalysts to speed up the process, either chemically or biologically. nowadays, bio-catalyst-like enzymes have been accepted by communities. it has been widely used in daily life and industry. the discovery of novel enzymes has replaced the former catalyst and provides more convenient, ecofriendly and cost-effective processing. several enzymes have been successfully extracted from microorganisms originated from the antarctica regions [11-13]. one of the important enzymes is a protease. generally, this enzyme breaks down proteins or polypeptides into smaller subunits or single amino acids. microbial proteases have been widely used in many different industries including poultry, detergent, food and feed, leather, chemicals, waste management, medical, and research [14-16]. cold-active protease is an extremozyme that enables a system to run at lower temperature where the majority of the commercial or industrial enzymes require higher temperatures for efficient catalytic activity and denaturation process. consequently, introducing higher temperatures will always initiate an undesirable chemical reaction and loss of volatile compounds. thus, cold-active protease has potential as an alternative to overcome these limitations. however, isolating and growing microorganisms in the laboratory directly from a sample is very challenging, especially samples from an extreme environment. a lot of factors must be considered, and the best idea is to mimic the sample environment to prepare the media conditions. in short, optimization of several parameters is important to provide ideal growing conditions for the isolated bacteria. the basic parameters used in this study was incubation temperature, ph media, and salt concentration. based on previous studies, bacteria from the antarctic region at 4 36 °c, ph 4 10 and 0 8% nacl concentration was isolated [17]. experimental design for optimization was conducted through response surface method (rsm). initially, rsm was introduced by box & wilson [18] as a design of experiment for chemical processing and nowadays, the method has been widely applied in many areas. this system is supported by its regression analysis and allows us to investigate the effect and interaction of multiple variables on one or more responses [19]. in this study, we analyzed the growth conditions of isolated bacteria producing cold-active proteolytic enzymes from the antarctic region. 28 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 2. materials and methods 2.1 determination of bacteria growth phase previously, several bacteria that showed positive activity of cold-active extracellular protease on skim milk agar were isolated and stored in glycerol [20]. samples bb and rob were collected from moss communities, sample ros was moist soil covered with alga and cyanobacterial mats, and sample sc was composed at an abandoned skua nest. the parameters to be characterized for bacteria growth rate were incubation temperature, ph media, and sodium chloride concentration. for every experiment, the bacteria were cultured in 10 ml of preferred lb broth with the initial od600 set at 0.1 in a sterile 50 ml tube [21]. the culture was incubated for 24 hours with an orbital shake at 200 rpm. a preliminary experiment disclosed that the strain reached the late logarithmic phase after a 24-hour incubation period. later, bacteria were harvested during this phase to be incubated in skim milk media for enzymatic assay. after 24 hours incubation period, the final od600 of the culture bacteria was measured and the growth rate (cells x 10 6 /hr) was calculated based on the eq. (1): growth rate = od (final)−od(initial) 24 hours x 5,85 x 107 cells (1) 2.1.1 effect of temperature the first parameter to be characterized for bacteria growth rate was temperature while fixing the other parameters. the bacteria-producing cold-active proteolytic enzyme was incubated in lb broth at three different temperatures, 4 °c, 20 °c and 36 °c. the nacl concentration and ph of the media were maintained at 1% (w/v) and 7, respectively. 2.1.2 effect of ph different ph, i.e. 4, 7, and 10 of lb broth were prepared and autoclaved. the ph of the media was adjusted using hcl and koh. then, these media were used to characterize the growth rate of isolated strains. based on temperature optimization results, these bacteria were incubated at 20 °c and the nacl concentration of the media was kept constant at 1%. 2.1.3 effect of nacl concentration the last parameter to be characterized for bacteria growth rate was nacl concentration. lb broth media with 0%, 4%, and 8% of nacl concentration were prepared and autoclaved. the ph of this media was maintained at 7 and the bacteria culture was incubated at 20 °c. 2.2 proteolytic assay azo-casein (sigma aldrich) was used as a substrate to quantify the protease activity enzymatic assay as decribed by garcía-cano et al. [22]. for the enzymatic assay, 250 μl of 1% azocasein, 250 μl of 0.5 m tris and 250 μl of the crude enzyme from culture supernatant were added into 1.5 ml sterile tube and incubated at –20 °c, 20 °c, and 60 °c. before adding the crude enzyme, the assay was pre-incubated at mentioned temperatures for 10 minutes. for positive control, 0.2 units/ml of protease from the bovine pancreas (optimum temperature at 37 °c) was used. after 20 minutes, 500 μl of 25% of trichloroacetic acid (tca) was added to stop the reaction and centrifuged at 12,000 rpm for 30 minutes. this supernatant was transferred into a 1.5 ml cuvette and the absorbance was read at 340 nm. for blanks, only 250 ml of 1% azocasein and 250 μl of 0.5 m tris were incubated before adding 500 μl of 25% tca. then, 5 % of skim milk 29 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 media were added and centrifuged at 12,000 rpm for 30 minutes. the supernatant was transferred into a new cuvette and labelled as blank. the data represented as enzyme unit mean ± standard deviation (stdev). statistical analysis was calculated using one-way analysis of variance (anova), spss 26.0. the results were considered significant differences if the p-value was < 0.05. 2.3 response surface method (rsm) the bacteria strain that showed the fastest shifting of clear skim milk media and highest protease activity were selected and preceded with an optimization process using response surface method (rsm) [23]. the experiment was designed based on three-level parameters of face centered central composite design (fcccd) as in table 1. the response variable was the growth rate of the bacteria. the initial and final od600 of bacteria cultures were recorded and one unit of od600 corresponded to 5.85 x 10 7 cells. the culture was incubated for 24 hours with an orbital shake at 200 rpm. a total of 20 experimental runs were generated by the software design-expert® version 7.0.0 (stateease inc., minneapolis, mn) with six runs at center points included. table 1: independent variables and their corresponding levels for fcccd in a response to bacteria growth rate factor variables level -1 0 1 a temperature [°c] 4 20 36 b ph 4 7 10 c sodium chloride concentration [%, w/v] 0 4 8 response growth rate [a/hr] [cells x 106 cells/hr] 3. results from the previous study, the total amount of bacteria producing extracellular protease isolated from antarctica’s soils and sediments were 35 strains [20]. these strains were further tested on their capability to produce extracellular protease within 24 hours through halo zone formation around the colony on skim milk agar. therefore, 8 bacteria strains consisting of bb1, di25, rob8, ros7, ros8, sc8, s10, and sc11 were selected for further analysis for their growth conditions. experimental designs to analyze the growth rate conditions for each strain were carried out in a conventional one-factor-at-a-time (ofat) approach. this approach was performed by altering one parameter at a time and maintaining the other parameters, so that the impact of the altering parameters can be accessed. 3.1 effect of temperature on bacteria-producing cold-active proteolytic enzyme from the graph in fig. 1, the optimum temperature for growth rates for all bacteria was 20 °c. there was a significant difference observed in all isolated strains at different temperatures. all bacteria grew faster at 20 °c compared to 4 °c and 36 °c. 3.2 effect of ph on bacteria-producing cold-active proteolytic enzyme the second factor, ph has been found as the important factor affecting the bacteria growth rate. based on the graph in fig. 2, all strains showed the highest growth rate at neutral ph 7. besides, several strains can tolerate lower ph or acidic conditions such as bb1, rob1, ros7, ros8, sc8, sc10 and sc11. 30 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 fig. 1: effect of different temperature levels to bacteria growth rate. the ph of the media and nacl concentration were maintained at 7 and 1%, respectively. fig. 2: effect of different level of ph in a response to the bacteria growth rate. the incubation temperature and nacl concentration were maintained at 20 °c and 1%, respectively. 3.3 effect of nacl concentration on bacteria-producing cold-active proteolytic enzyme the concentration of sodium chloride (nacl) was considered an important factor as the coastal environment influenced the sample. all bacteria strains showed an optimum growth rate at 4% nacl concentration as in fig. 3. in the absence of nacl, the slower growth rate of these bacteria compared to 4% nacl was observed. however, with an increase in the concentration of nacl from 4% to 8%, the growth rate of the bacteria was significantly reduced. fig. 3: effect of nacl at different levels to the bacteria growth rate. the incubation temperature and ph of the media were maintained at 20 °c and 7, respectively. 0 0.02 0.04 0.06 0.08 bb5 di22 rob2 ros7 ros8 sc8 sc9 sc11 g ro w th r a te [ a /h r] bacteria strains 4 °c 20 °c 36 °c 0.00 0.02 0.04 0.06 0.08 bb5 di22 rob2 ros7 ros8 sc8 sc9 sc11 g ro w th r a te ( a /h r) bacteria strains 4 7 10 0 0.02 0.04 0.06 0.08 bb5 di22 rob2 ros7 ros8 sc8 sc9 sc11 g ro w th r a te [ a /h r] bacteria strains 0 %. 4 %. 8 %. 31 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 3.4 proteolytic assay change of white skim milk media to clear indicated that the bacteria produced extracellular protease to degrade the casein of milk. from the graph in fig. 4, the crude enzyme extracted from strains sc8 and ros8 showed higher proteolytic activity compared to other isolated bacteria. this indicates that the amount of protease produced was higher from both strains. in addition, both crude enzymes showed a significantly higher activity at -20 °c compared to the positive control. fig. 4: results of crude protease assay at three different temperatures. sc8 showed the highest proteolytic activity at the lowest temperature. * p < 0.05 3.5 optimization of growth conditions of bacteria producing cold-active proteolytic enzyme by response surface methodology (rsm) the growth rate of isolated bacteria sc8 was selected to be further optimized using response surface method (rsm). this strain showed the fastest shifting of clear skim milk media and the highest proteolytic activity at the lowest temperature. the result of rsm is shown in table 2. from the results, the bacteria growth rate was varied from 0.014 x 106 to 3.93 x 106 cells/hr. table 2: experimental design and results of face centered central composite design (fcccd). the experimental growth rate data represented as mean ± standard deviation (stdev). treatment number nacl [%, w/v] ph temp. [ºc] response growth rate [a/hr] bacterial growth rate [cells x 106/hr] 1 0 4 4 0.0469 ± 0.0005 2.74 ± 0.03 2 8 4 4 0.0242 ± 0.0204 1.42 ± 1.19 3 0 10 4 0.0385 ± 0.0002 2.25 ± 0.01 4 8 10 4 0.0195 ± 0.0009 1.14 ± 0.05 5 0 4 36 0.0408 ± 0.0003 2.39 ± 0.02 6 8 4 36 0.0305 ± 0.0009 1.78 ± 0.05 7 0 10 36 0.0425 ± 0.0007 2.49 ± 0.04 8 8 10 36 0.0275 ± 0.0018 1.61 ± 0.12 9 0 7 20 0.0597 ± 0.0100 3.49 ± 0.59 10 8 7 20 0.0506 ± 0.0211 2.96 ± 1.23 11 4 4 20 0.0525 ± 0.0008 3.07 ± 0.05 12 4 10 20 0.0563 ± 0.0008 3.29 ± 0.05 13 4 7 4 0.0476 ± 0.0046 2.78 ± 0.27 14 4 7 36 0.0541 ± 0.0198 3.16 ± 1.16 15 4 7 20 0.0671 ± 0.0082 3.93 ± 0.48 16 4 7 20 0.0604 ± 0.0077 3.53 ± 0.46 17 4 7 20 0.0576 ± 0.0073 3.37 ± 0.43 18 4 7 20 0.0661 ± 0.0070 3.87 ± 0.41 19 4 7 20 0.0563 ± 0.0079 3.29 ± 0.46 20 4 7 20 0.0632 ± 0.0069 3.70 ± 0.40 *sc8 *r… *sc8 0 0.2 0.4 0.6 0.8 -20 20 60e n z y m e u n it [ u ] temperature [ºc] protease bb5 di22 rob2 ros7 ros8 sc8 sc9 sc11 32 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 preliminary analysis showed that the highest growth rate was at the center of the design. based on the fit summary, the model suggested was quadratic because the sequential model sum of squares (type i) was significant and the lack of fit tests was insignificant. an insignificant lack of fit was good because the model should be fitted. the value of prob > f less than 0.05 indicated that the model terms were significant. from the analysis of variance (anova) in table 3, for the response surface quadratic model, the model f-value of 45.87 implied the model was significant. in this experiment, the concentration of nacl (a), temperature (c) and algebraic contribution (a2, b2, c2) were significant model terms. the multiple correlation coefficient of the model or r2 of 0.9574 meant that the regression prediction was capable of estimating 95 % fit to the actual data points. besides, the predicted r-squared of 0.9191 was in reasonable agreement with the adjusted r-squared 0.8051 because the difference was less than 0.2. the adequate precision greater than 4 (14.948) indicated an adequate signal. the final equation in terms of coded factors was generated as eq. (2): growth rate = 0,0622 − 0,0076 a − 0,0011 b + 0,0019 c − 0,0001 ab + 0,0021 ac + 0,0015 bc − 0,0077 a2 − 0,008487 b2 − 0,0120 c2 (2) table 3: analysis of variance (anova) for response surface quadratic model. source sum of squares degree of freedom f-value p-value model 2.096e-003 9 34.23 < 0.0001 a-nacl 1.568e-004 1 23.05 0.0020 b-ph 6.300e-005 1 9.26 0.0188 c-temp 2.704e-006 1 0.40 0.5484 ab 1.378e-005 1 2.03 0.1977 ac 1.513e-007 1 0.022 0.8857 bc 8.001e-005 1 11.76 0.0110 a2 3.110e-005 1 4.57 0.0698 b2 3.335e-004 1 49.02 0.0002 c2 2.791e-004 1 41.02 0.0004 residual 4.763e-005 7 lack of fit 3.570e-005 5 1.20 0.5135 pure error 1.193e-005 2 cor total 2.144e-003 16 the graphs were constructed by plotting the response against any two independent variables while maintaining the other variable at the optimal level. for this experiment, as in fig. 5, contour and the 3d surface graph showed the bacterial growth rate as a response was plotted at the z-axis, meanwhile, the xand y-axis were assigned for two different variables. higher growth rate was observed around 2% nacl at ph 7 (fig. 5a), 2% nacl at 20 °c (fig. 5b) and at ph 7 and 20 °c (fig. 5c). for optimization, the criteria were selected to maximize the bacterial growth rate while keeping all the variables in the range. the solution suggested by the design expert software to optimize the bacterial culture conditions were concentration of sodium chloride at 2.05% (w/v), ph of the solution at 6.83, and the incubation temperature at 20.5 °c. new experiments were conducted as post-analysis to validate these statistical models and regression equations. the experiments were run in triplicate under optimized variables as suggested previously. the predicted bacterial growth rate calculated by the software under these optimized variables was 3.75 x 106 cells/hr and the average observed experimental value was 3.70 ± 0.06 x 106 cells/hr. from these validation results, it 33 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 confirmed that the model was good enough because the error between predicted and actual value was only 1.2 %. fig. 5: 3d surface and contour graph showed the interaction of three independent variables with the response to the bacteria growth rate. 34 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 4. discussion generally, psychrophiles are microorganisms that can live under very low temperatures. the majority of these extremophilic organisms inhabit a permanently icecovered environment on earth. the word ‘living’ means that they can grow and reproduce under extremely low temperatures rather than hibernate. some researchers characterized these psychrophiles into two groups: obligate psychrophiles and psychrotolerant organisms. obligate psychrophiles referred to organisms with an optimum growth temperature of 15 ºc that cannot withstand higher temperatures of more than 20 ºc [24]. psychrotolerants are organisms that can withstand a broader range of temperatures between 0 °c to approximately 36 °c [25]. some researchers called them facultative psychrophiles or psychrotrophs and their maximal or optimal growth temperature was above 20 ºc [26,27]. based on the ofat, all isolated strains showed the fastest growth rate at 20 °c. these bacteria can be classified as psychrotolerant because they can live in a wide range of temperatures (4 – 36 °c). besides, these bacteria can tolerate up to 4 % nacl concentration indicating that their living environment was influenced by the coastal environment. on average, seawater contains a salt concentration of about 35 parts per thousand or about 3.5 % and the major sources of the salt are sodium and chloride [28]. wind effect brought seawater onto the ice and during the summer season, the ice melted and the salt was concentrated in the soils and sediments [29]. furthermore, the majority of the isolated strains can endure acidic conditions. this is possible because these strains were influenced by the surrounding environment at the collection point. researchers have reported that lower ph on antarctic soils and sediments from moss communities and wetlands were due to the accumulation of organic matter [30]. besides, birds’ nests and excrement created in situ unfavorable chemical reactions that led to acidic conditions of the soil and sediment [31]. an interesting aspect of these psychrophiles is their survivability is supported by the cold-adapted enzyme. they produce biocatalysts that are capable of working at very low temperatures. there were several theories on this unique characteristic of enzymes and the majority of the researchers claimed that flexibility of the protein structure is the main contributor [32]. comparison studies between psychrophilic and mesophilic enzymes showed that structural modification and adaptation remain obscure although both active sites are preserved [30]. some researchers claim that the amino acid composition affects the bonding between residues and the structural rigidity of the protein [22]. besides, loop modification vicinity to active site matched to the induced fit model for enzymatic reaction [24]. these strategies were designated to consume less energy during enzymatic reactions when a smaller amount of heat is available at low temperatures. in this case, crude enzymes extracted from sc8 and ros8 strains showed significantly higher protease activity than positive control at a lower temperature but gradually decreased at the higher temperature. this showed that increasing the flexibility of the enzyme adversely affected its thermostability [35]. cold active proteases have been extracted from various species of psychrophiles and the majority showed optimal activity at a temperature range between 30–40 ºc [36-39]. a thorough search on cold-active protease yielded the lowest optimal temperature at only 15 ºc [40,41]. in this experiment, strain sc8 showed the capability to produce extracellular protease faster and higher compared to the other strains. it has a high potential for bioprospecting in future. thus, we focused on this strain for growth rate optimization. initially, the term optimization for the ofat method was not accurate according to some scholars [42,43]. this is because changing one variable at a time could not estimate the interaction between 35 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 variables and might miss the optimal setting for each variable [44]. frequently, the ofat technique was used in the experiment objectively to identify the maximal or minimal effect [45]. maximal effect is the highest or greatest result’s magnitude whereas, the optimal effect is the most desirable condition for the model. yet, results from ofat could be applied as a screening method to determine significant high and low levels for each variable [46,47]. although the factorial method is best used as screening design in designexpert software before optimization using the response surface method, this ofat technique is lower in cost and easier to conduct. in this experiment, based on the rsm result in table 2, the fastest growth rate, 3.93 x 106 cells/hr, was treatment number 15 with variables set at 4% nacl, ph 7, and 20 ºc. however, the optimized growth rate-setting suggested was slightly different from the fastest growth rate setting. clarification on these results was rsm calculated the optimal setting for each variable or resource in the design to achieve maximized results. based on the validation results, the optimum bacterial growth rate at 2.05% of nacl, ph 6.83 and 20.5 °c was 3.70 x 106 cells/hr and it was only 5% to achieve the fastest result, 3.93 x 106 cells/hr. therefore, this model could achieve a higher response and save the usage of nacl by using the optimal setting recommended by rsm. 5. conclusion in conclusion, the isolated strains of bacteria-producing cold-active protease from the antarctica region in this experiment could be categorized as psychrotolerants. based on the crude enzymatic assay, the sc8 strain showed potential for bioprospecting as its protease activity was significantly higher than positive control and other strains at a lower temperature. optimal growth conditions of sc8 strain from this study will be useful for the development of large-scale production of cold-active protease in future. in the food industry, this cold active protease may act as the commercial meat tenderizers (papain and bromelain) as it is applied to the meat during cold storage and export journey. acknowledgement the research leading to these results received funding from yayasan penyelidikan antartika sultan mizan (2015) and international islamic university malaysia under grant number rigs 16-332-0496. the field survey and sampling were made possible with funding to j. smykla from the polish national science center within grant number nn305376438. references [1] turner j, anderson p, lachlan-cope t, colwell s, phillips t, kirchgaessner a, et al. (2009) record low surface air temperature at vostok station, antarctica. j geophys res atmos., 114(24). https://doi.org/10.1029/2009jd012104 [2] bornman jf, barnes pw, robson tm, robinson sa, jansen mak, ballare cl, et al. (2019) linkages between stratospheric ozone, uv radiation and climate change and their implications for terrestrial ecosystems. photochem photobiol sci., 18(3): 681-716. https://doi.org/10.1039/c8pp90061b [3] convey p, peck ls. (2019) antarctic environmental change and biological responses. sci adv., 5(11). https://doi.org/10.1126/sciadv.aaz0888 [4] faucher b, lacelle d, davila a, pollard w, fisher d, mckay cp. (2017) physicochemical and biological controls on carbon and nitrogen in permafrost from an ultraxerous environment, mcmurdo dry valleys of antarctica. j geophys res biogeosciences, 122(10): 36 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 2593-2604. https://doi.org/10.1002/2017jg004006 [5] pereira jl, pereira p, padeiro a, gonçalves f, amaro e, leppe m, et al. (2017) environmental hazard assessment of contaminated soils in antarctica: using a structured tier 1 approach to inform decision-making. sci total environ., 574: 443-454. https://doi.org/10.1016/j.scitotenv.2016.09.091 [6] pudasaini s, wilson j, ji m, van dorst j, snape i, palmer as, et al. (2017) microbial diversity of browning peninsula, eastern antarctica revealed using molecular and cultivation methods. front microbiol., 8(apr). https://doi.org/10.3389/fmicb.2017.00591 [7] ji m, van dorst j, bissett a, brown m v., palmer as, snape i, et al. (2016) microbial diversity at mitchell peninsula, eastern antarctica: a potential biodiversity “hotspot.” polar biol., 39(2): 237-249. https://doi.org/10.1007/s00300-015-1776-y [8] rong jc, liu y, yu s, xi l, chi ny, zhang qf. (2020) complete genome sequence of paenisporosarcina antarctica cgmcc 1.6503t, a marine psychrophilic bacterium isolated from antarctica. mar genomics, 49. https://doi.org/10.1016/j.margen.2019.05.005 [9] watanabe m, kojima h, fukui m. (2020) labilibaculum antarcticum sp. nov., a novel facultative anaerobic, psychrotorelant bacterium isolated from marine sediment of antarctica. antonie van leeuwenhoek, int j gen mol microbiol., 113(3): 349-355. https://doi.org/10.1007/s10482-019-01345-w [10] pavlov ms, lira f, martinez jl, olivares-pacheco j, marshall sh. (2020) pseudomonas fildesensis sp. nov., a psychrotolerant bacterium isolated from antarctic soil of king george island, south shetland islands. int j syst evol microbiol., 70(5): 3255-3263. https://doi.org/10.1099/ijsem.0.004165 [11] pereira jq, ambrosini a, passaglia lmp, brandelli a. (2017) a new cold-adapted serine peptidase from antarctic lysobacter sp. a03: insights about enzyme activity at low temperatures. int j biol macromol., 103: 854-862. https://doi.org/10.1016/j.ijbiomac.2017.05.142 [12] vullo d, de luca v, del prete s, carginale v, scozzafava a, osman sm, et al. (2016) sulfonamide inhibition studies of the γ-carbonic anhydrase from the antarctic bacterium colwellia psychrerythraea. bioorganic med chem lett., 26(4): 1253-1259. https://doi.org/10.1016/j.bmcl.2015.06.079 [13] sanchez ac, ravanal mc, andrews ba, asenjo ja. (2019) heterologous expression and biochemical characterization of a novel cold-active α-amylase from the antarctic bacteria pseudoalteromonas sp. 2-3. protein expr purif., 155: 78-85. https://doi.org/10.1016/j.pep.2018.11.009 [14] razzaq a, shamsi s, ali a, ali q, sajjad m, malik a, et al. (2019) microbial proteases applications. front bioeng biotechnol., 7(jun). https://doi.org/10.3389/fbioe.2019.00110 [15] singh r, mittal a, kumar m, mehta pk. (2016) microbial proteases in commercial applications. j pharm , chem biol sci., 4: 365-374. http://www.jpcbs.info/2016_4_3_06_rajendra.pdf [16] dos santos aguilar jg, sato hh. (2018) microbial proteases: production and application in obtaining protein hydrolysates. food research international, 103: 253-262. https://doi.org/10.1016/j.foodres.2017.10.044 [17] yu y, li hr, zeng yx, chen b. (2011) bacterial diversity and bioprospecting for coldactive hydrolytic enzymes from culturable bacteria associated with sediment from nella fjord, eastern antarctica. mar drugs, 9(2): 184-195. https://doi.org/10.3390/md9020184 [18] box gep, wilson kb. (1951) on the experimental attainment of optimum conditions. j r stat soc ser b., 13(1):1-38. https://doi.org/10.1007/978-1-4612-4380-9_23 [19] hamid nf, said fm. (2018) optimization of red pigment production by monascus purpureus ftc 5356 using response surface methodology. iium eng j., 19(1): 34-47. https://doi.org/10.31436/iiumej.v19i1.814 [20] latip maa, alias sa, smykla j, yusof f, mohamad man, nordin nfh. (2020) discovery of cold-active protease from psychrophilic bacteria isolated from antarctic region for bioprospecting. malays appl biol., 49: 55-60. https://doi.org/10.55230/mabjournal.v49i1.1654 [21] ram y, dellus-gur e, bibi m, karkare k, obolski u, feldman mw, et al. (2019) predicting microbial growth in a mixed culture from growth curve data. proc natl acad sci u s a. 37 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 https://doi.org/10.1073/pnas.1902217116 [22] garcía-cano i, rocha-mendoza d, ortega-anaya j, wang k, kosmerl e, jiménez-flores r. (2019) lactic acid bacteria isolated from dairy products as potential producers of lipolytic, proteolytic and antibacterial proteins. appl microbiol biotechnol., 103(13): 5243-5257. https://doi.org/10.1007/s00253-019-09844-6 [23] jimat dn, firdamohamed ib, azmi as, amid a. (2020) statistical analysis of growth conditions of newly isolate bacillus sp. producing l-asparaginase. iium eng j. https://doi.org/10.31436/iiumej.v21i2.1351 [24] sandle t. (2019) selection and application of culture media. biocontamination control pharm healthc., 103-123. http://dx.doi.org/10.1016/b978-0-12-814911-9.00007-9 [25] yadav an, verma p, kumar v, sangwan p, mishra s, panjiar n, et al. (2017) biodiversity of the genus penicillium in different habitats. new futur dev microb biotechnol bioeng penicillium syst prop appl., 3-18. https://doi.org/10.1016/b978-0-444-63501-3.00001-6 [26] cavicchioli r. (2016) on the concept of a psychrophile. isme j., 10(4): 793-795. https://doi.org/10.1038%2fismej.2015.160 [27] ramle z, abdul rahim r. (2016) psychrophilic lipase from arctic bacterium. trop life sci res., 27: 151-157. https://doi.org/10.21315%2ftlsr2016.27.3.21 [28] li d, liu s. (2018) water quality monitoring and management: basis, technology and case studies. 1st ed. water quality monitoring and management: basis, technology and case studies. acedamic press. 1-368. https://doi.org/10.1016/c2016-0-00573-9 [29] bowman js, deming jw. (2017) wind-driven distribution of bacteria in coastal antarctica: evidence from the ross sea region. polar biol., 40(1): 25-35. https://doi.org/10.1007/s00300-016-1921-2 [30] smykla j, drewnik m, szarek-gwiazda e, hii ys, knap w, emslie sd. (2015) variation in the characteristics and development of soils at edmonson point due to abiotic and biotic factors, northern victoria land, antarctica. catena., 132: 56-67. https://doi.org/10.1016/j.catena.2015.04.011 [31] lambrechts s, willems a, tahon g. (2019) uncovering the uncultivated majority in antarctic soils: toward a synergistic approach. front microbiol., 10(feb). https://doi.org/10.3389/fmicb.2019.00242 [32] siddiqui ks. (2017) defying the activity–stability trade-off in enzymes: taking advantage of entropy to enhance activity and thermostability. crit rev biotechnol., 37(3): 309-322. https://doi.org/10.3109/07388551.2016.1144045 [33] åqvist j, isaksen gv, brandsdal bo. (2017) computation of enzyme cold adaptation. nat rev chem., 1. https://doi.org/10.1038/s41570-017-0051 [34] panja as, maiti s, bandyopadhyay b. (2020) protein stability governed by its structural plasticity is inferred by physicochemical factors and salt bridges. sci rep., 10(1): 1822. https://doi.org/10.1038/s41598-020-58825-7 [35] latip maa, hamid aam, nordin nfh. (2019) microbial hydrolytic enzymes: in silico studies between polar and tropical regions. polar sci., 20. https://doi.org/10.1016/j.polar.2019.04.003 [36] damare s, raghukumar c, muraleedharan ud, raghukumar s. (2006) deep-sea fungi as a source of alkaline and cold-tolerant proteases. enzyme microb technol., 39(2): 172-181. https://doi.org/10.1016/j.enzmictec.2006.03.032 [37] wang qf, miao jl, hou yh, ding y, wang gd, li gy. (2005) purification and characterization of an extracellular cold-active serine protease from the psychrophilic bacterium colwellia sp. nj341. biotechnol lett., 27(16): 1195 -1198. https://doi.org/10.1007/s10529-005-0016-x [38] turkiewicz m, pazgier m, kalinowska h, bielecki s. (2003) a cold-adapted extracellular serine proteinase of the yeast leucosporidium antarcticum. extremophiles., 7(6): 435-442. https://doi.org/10.1007/s00792-003-0340-9 [39] margesin r, dieplinger h, hofmann j, sarg b, lindner h. (2005) a cold-active extracellular metalloprotease from pedobacter cryoconitis production and properties. res microbiol., 156(4): 499-505. https://doi.org/10.1016/j.resmic.2004.12.008 [40] gao r, zhou j, leng w, shi t, jin w, yuan l. (2020) screening of a planococcus 38 iium engineering journal, vol. 24, no. 1, 2023 latip et al. https://doi.org/10.31436/iiumej.v24i1.2447 bacterium producing a cold-adapted protease and its application in low-salt fish sauce fermentation. j food process preserv., 44(8). https://doi.org/10.1111/jfpp.14625 [41] saba i, qazi ph, rather sa, dar ra, qadri qa, ahmad n, et al. (2012) purification and characterization of a cold active alkaline protease from stenotrophomonas sp., isolated from kashmir, india. world j microbiol biotechnol., 28(3): 1071-1079. https://doi.org/10.1007/s11274-011-0905-1 [42] abou-taleb ka, galal gf. (2018) a comparative study between one-factor-at-a-time and minimum runs resolution-iv methods for enhancing the production of polysaccharide by stenotrophomonas daejeonensis and pseudomonas geniculate. ann agric sci., 63(2): 173180. https://doi.org/10.1016/j.aoas.2018.11.002 [43] nor nm, mohamed ms, loh tc, foo hl, rahim ra, tan js, et al. (2017) comparative analyses on medium optimization using one-factor-at-a-time, response surface methodology, and artificial neural network for lysine–methionine biosynthesis by pediococcus pentosaceus rf-1. biotechnol biotechnol equip., 31(5): 935-947. https://doi.org/10.1080/13102818.2017.1335177 [44] czitrom v. (1999) one-factor-at-a-time versus designed experiments. am stat., 53(2): 126131. https://doi.org/10.2307/2685731 [45] biswas g, kumari m, adhikari k, dutta s. (2017) application of response surface methodology for optimization of biosorption of fluoride from groundwater using shorea robusta flower petal. appl water sci., 7(8): 4673-4690. https://doi.org/10.1007/s13201-0170630-5 [46] ahmed sa, abdella maa, el-sherbiny gm, ibrahim am, el-shamy ar, atalla smm. (2019) application of one –factorat-a-time and statistical designs to enhance α-amylase production by a newly isolate bacillus subtilis strain-mk1. biocatal agric biotechnol., 22. https://doi.org/10.1016/j.bcab.2019.101397 [47] subara d, jaswir i, alkhatib mfr, noorbatcha ia. (2018) synthesis of fish gelatin nanoparticles and their application for the drug delivery based on response surface methodology. adv nat sci nanosci nanotechnol., 9(4). https://doi.org/10.1088/20436254/aae988 39 microsoft word 2_v17no2_compiled_v2_24nov16.docx iium engineering journal, vol. 17, no. 2, 2016 khan et al. 31 an efficient technique for retinal vessel segmentation and denoising using modified isodata and clahe khan bahadar khan*1, amir abdul khaliq 1, muhammad shahid2 and sheroz khan3 1department of electronic engineering, international islamic university, chairman office, sector h-10, islamabad 44000, pakistan. 2department of electrical engineering, capital university of science and technology, kahuta road, zone-v, islamabad 44000, pakistan. 3department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. *corresponding author: kb.khattak@gmail.com (received: 7th jan. 2016; accepted: 22nd aug. 2016; published on-line: 30th nov. 2016) abstract: retinal damage caused due to complications of diabetes is known as a diabetic retinopathy (dr). in this case, the vision is obscured due to damage of tiny retinal blood vessels. these tiny blood vessels may cause leakage that affect the vision and can lead to complete blindness. identification of these new retinal vessels and their structure is an essential for analysis of dr. automatic blood vessel segmentation plays a significant role to assist subsequent automatic methodologies that aid to such analysis. in literature, most authors have used computationally-hungry strong preprocessing steps followed by a simple thresholding and postprocessing steps. this paper proposed an arrangement of simple preprocessing steps that consist of contrast limited adaptive histogram equalization (clahe) for contrast enhancement and a difference image of green channel from its gaussian blur filtered image to remove local noise or geometrical objects. the proposed modified iterative self organizing data analysis technique (misodata) has been used for segmentation of vessel and non-vessel pixels based on global and local thresholding. finally, postprocessing steps have been applied using region properties (area, eccentricity) to eliminate the unwanted regions/segments, nonvessel pixels, and noise. a novel postprocessing steps are used to reject misclassified foreground pixels. the strategy has been tested on the openly accessible drive (digital retinal images for vessel extraction) and stare (structured analysis of the retina) databases. the average accuracy rates of 0.952 and 0.957 with average sensitivity rates 0.780 and 0.745 along with average specificity rates of 0.972 and 0.974 were obtained on drive and stare datasets, respectively. the performance of the proposed technique has been assessed comprehensively. the acquired accuracy, robustness, low complexity, and high efficiency make the method an efficient tool for an automatic retinal image analysis. the proposed technique perform well as compared to the existing strategies on the online available databases in term of accuracy, sensitivity, specificity, false positive rate, true positive rate, and area under receiver operating characteristic (roc) curve. abstrak: kerosakan retina yang disebabkan oleh komplikasi diabetes dikenali sebagai diabetic retinopathy (dr). dalam kes ini, penglihatan menjadi kabur disebabkan oleh kerosakan saluran darah kecil retina. saluran darah kecil boleh menyebabkan ketirisan yang menjejaskan penglihatan dan boleh mengakibatkan buta sepenuhnya. mengenal pasti saluran retina baru dan struktur mereka adalah penting iium engineering journal, vol. 17, no. 2, 2016 khan et al. 32 untuk dr analisis. segmentasi saluran darah secara automatik memainkan peranan penting untuk membantu kaedah automatik berikutnya dan ini akan membantu analisis tersebut. dalam literatur, kebanyakan orang telah menggunakan pengiraan langkah pra pemprosesan yang kuat diikuti dengan langkah ambang dan pos pemprosesan yang mudah. kami mencadangkan susunan langkah pra pemprosesan mudah yang terdiri daripada contrast limited adaptive histogram equalization (clahe) untuk mempertingkatkan kontras dan imej perbezaan saluran hijau daripada imej kabur gaussian yang ditapis untuk membuang bunyi tempatan atau objek geometri. modified iterative self organizing data analysis teknik (misodata) yang dicadangkan telah digunakan dalam membuat segmentasi piksel saluran dan bukan-saluran berdasarkan pengambangan global dan tempatan. akhir sekali, langkah pos pemprosesan telah digunakan dengan menggunakan ciri-ciri kawasan (kawasan, kesipian) untuk menghapuskan wilayah / segmen, piksel bukan saluran dan bunyi bising yang tidak diingini. kami telah menggunakan langkah pos pemprosesan baru untuk menolak piksel latar depan yang silap dikelaskan. strategi ini telah diuji pada pangkalan data terbuka yang boleh diakses iaitu drive (digital retinal images for vessel extraction) dan stare (structured analysis of the retina). kadar purata ketepatan 0.952 dan 0.957 dengan kadar purata sensitiviti 0.780 dan 0.745 bersama dengan kadar purata kekhususan 0.972 dan 0.974 telah diperolehi pada drive dan stare dataset, masing-masing. prestasi teknik yang dicadangkan itu telah dinilai secara menyeluruh. ketepatan yang diperolehi, kekukuhannya, kerumitan yang rendah dan kecekapan yang tinggi membuat kaedah ini alat yang berkesan untuk analisis imej retina automatik. teknik yang dicadangkan menunjukkan prestasi yang baik berbanding dengan strategi tersedia ada pada pangkalan data dalam talian terkini dari segi ketepatan, kepekaan, kekhususan, kadar positif palsu, kadar positif benar dan kawasan di bawah lengkungan ciri operasi penerima (roc). keywords: vessel segmentation; fundus imaging; denoising; drive; stare; diabetic retinopathy 1. introduction retinal blood vessel segmentation mainly focuses on the presence of the dr illness. retinal anomalies are commonly caused by dr and hypertensive retinopathy, which are the significant reasons for visual deficiency and impairment these days. to analyze retinal variation, fundus imaging is progressively used as a part of the screening process. the retinal vein elements like microaneurysms, scratching, and narrowing have been connected to the systemic sickness of retinopathy in its earliest stages [1]. visual deficiency usually caused by dr is irreversible even a recuperation procedure would not enable the patient to have earlier vision capacity. consequently, the early identification of dr on a retinal image will save the patient from having irreversible visual impairment. segmentation is considered one of the fundamental stages in an image processing. it divides a digital image into numerous locales to make it easy for investigation. analysis of the retinal veins can uncover early phases of cardiovascular ailment, hypertension, arteriosclerosis, diabetes, and stroke [2]. it alerts patients, enabling them to take anticipatory measures when the infection is in its initial stages. it is additionally used to recognize objects in an image of diverse nature. object shape, edges, and correlation are three principle factors that impact segmentation of an object in the image. object edges and object correlation is greatly influenced by noise or reproduction artifacts because they land on image attributes. moreover, they are methodology dependent parameters. the advancement of image segmentation techniques are influenced by the knowledge of object shape, object correlation, and object edges. segmentation methods attempt to identify iium engineering journal, vol. 17, no. 2, 2016 khan et al. 33 edges and correlated areas in the images and consolidate shape data to confine the subsequent state segmentation more precisely [3]. retinal images permit doctors to examine the retina and its inside segments, including the optic disk, vasculature, fovea, and so on [4]. retinal veins provide data that is very helpful in a few applications such as restorative analysis and sorting of cardiovascular and ophthalmological ailments. the vessel segmentation can be utilized to portray hypertensive retinopathy along with the estimation of vessel width, which is used to analyze hypertension [5]. symptoms of dr can be detected by changes in the vasculature distribution [4]. in addition, vessels are utilized to help laser surgeries [6] and can be used as landmark for image registration [7]. retinal vessel segmentation is necessary for all of these operations. in the typical scenario, trained experts do manual segmentation [2]. however, retinal blood vessel segmentation requires training and expertise to be manually segmented, which is also a tediously prolonged and exhausting task. it is usually acknowledged by medical experts that an automatic detection of vessels structure is the initial phase in the improvement of a computer-assisted indicative framework for ophthalmic problems. the performance can be examined by accuracy (acc), specificity (sp), sensitivity (sn) and roc curve on the distinctive databases like drive and stare. therefore, a retinal vessels segmentation approach that is accurate and presents shorter computation time is necessary for denoising images in order to recognize dr and other ophthalmologic illnesses. 2. related work the automatic discovery of retinal vessels structure is an essential in the improvement of automated framework for the scrutiny of vasculature distribution. a mechanism, which can be utilized to help with the conclusion of dr and ought to consequently recognize all retinal image elements is necessary. the retinal image elements are optic disk, blood vessels, fovea, and all irregularities in the retinal image, which can be microaneurysms, cotton-wool spots, edema, and hemorrhages [8]. automatic segmentation of retinal fundus images is considered one of the basic steps of vessel extraction from background. bad quality retinal images having some noise, variable width of vessels, and changes of brightness which make segmentation a challenging task. vessel structure in retinal fundus images can be extracted by numerous vessel detection techniques that have already been suggested in literature [8, 9]. these techniques can be comprehensively partitioned into supervised and unsupervised classifications. supervised strategies segregate between vessel and non-vessel pixels using pixel-based attribute vectors to train a classifier, while unsupervised techniques do not utilize classifiers but depend on thresholding filter responses to reduce false responses to online edges [10]. 2.1 supervised methods the requirement for this methodology is that an arrangement of important distinguishing features must be extracted for training from good quality images. for example, ricci and perfetti [11] utilized support vector machine (svm) to learn a feature vector extraction. becker et al. [12], presented supervised method to learn feature vector recognition utilizing gradient boosting framework. neural network and principal component analysis (pca) concepts were utilized for pixel classification and edge detection respectively by sinthanayothin et al. [13]. green plane was used for feature iium engineering journal, vol. 17, no. 2, 2016 khan et al. 34 vector extraction of each pixel and k-nearest neighbor (knn) was utilized to classify vessel pixels [14]. staal et al. [15], proposed a primitive-based supervised method to extract a feature vector for each pixel based on characteristics of the segments and the line components. the feature vectors were grouped utilizing a knn and successive forward feature selection techniques. soares et al. [16], used the pixel’s intensity to extract a feature vector and two-dimensional (2d) gabor wavelet transform was used to separate true positive and false positive pixels with the final segmentation by a gaussian mixture model (gmm) classifier. in [17], various concavity modeling approaches were used for blood vessel segmentation. bright lesions were handled by techniques utilizing differentiable concavity measures where dark scrapes were removed by line-shape concavity measures and random noise was managed by locally normalized concavity measures. these concavity measures were consolidated together as per their statistical distributions to distinguish vessel and non-vessel pixels. joshi et al. [18], presented an automated technique for detection and segregation of retinal vessel structure using a graph search method. 2.2 unsupervised methods in comparison, unsupervised techniques perform the segmentation of retinal vessels without utilizing trained information, or any classification methods. this class incorporates most segmentation methods in the literature. for instance, in [19], the authors proposed an active contour model to detect vessel borders and sustain vessel width consistency. zhang et al. [20], learned a multi-dimensional feature vector by morphological operation, pixel clustering by self organizing map (som), and classification of vessel and non-vessel pixels through otsu’s method. lupaşcu and tegolo [21], utilized som and a k-means clustering algorithm for training and division of map units. a hill-climbing strategy has been used for postprocessing of the segmented image. chaudhuri et al. [22], presented a 2d matched filter using a gaussian-shaped curve. they achieved very low average accuracy because of the low identification of retinal vessels. hoover et al. [23], used local and global vessel characteristics collectively by applying a thresholding and matched filter response (mfr) to segment the vessel system. in [24], second order derivative gaussian mfr has been used to find the centroid and vessel diameter, and an extended kalman filter for excellent predication of subsequent vessel regions. mendonca and campilho [25], used outputs of four differential filters with morphological operators for centerline detection, vessel features and morphological characteristics for filling vessel structures. zana and klein [26], employed cross-curvature evaluation and morphological filters together to segment vessel structure. however, their presented method was inadequate to segment thinner vessels. in [27], retinal blood vessel segmentation has been performed by a multiscale feature extraction and region growing algorithm. matinez-perez et al. [28] utilized first and second-spatial derivatives of the image intensity that give details of vessel structure to control the inherent issue of contrast variations in these images. this approach additionally empowers the analysis of vessels of variable lengths, widths and orientations. fraz et al. [29], used centerline detection techniques and morphological bit plane slicing for retinal vessel segmentation. bankhead et al. [30], utilized wavelets and edge location refinement method for retinal vessel segmentation. related works are summarized in table 1. iium engineering journal, vol. 17, no. 2, 2016 khan et al. 35 table 1: classification of retinal vessel segmentation techniques. method year proposed methodology performance parameters limitations ricci et al. [11] 2007 line operators and svm acc and auc high false positive rate and inadequate for noise removal. sinthanayothin et al. [13] 1999 pca and neural network sn and sp inadequate for geometrical object e.g. fovea removal. missed tiny blood vessels. niemeijer et al. [14] 2004 pixel classification based on knnclassifier acc and auc under-segmentation around the boundary of the optic disk. smaller vessels not detected properly. staal et al. [15] 2004 image ridges and knn-classifier acc and auc false detection of vessels at boundaries, optic disk and for pathological images. soares et al. [16] 2006 2d gabor wavelet transform and gmm classifier acc and auc incorrect recognition of noise and other artifacts. unable to detect some of the thinnest vessels. disregard useful information from shapes and structures present in the image. lam et al. [17] 2010 multiconcavity modeling acc and auc lesion detection problem. al-diri et al. [19] 2009 ribbon of twin active contour model sn and sp failed in edge identification and to accurately detect overlaps or closely parallel vessels. zhang et al. [20] 2015 morphological operation and som acc need to test on stare dataset and also must compute its sp and auc. lupaşcu et al. [21] 2010 som and k-means clustering sn, sp and acc greater time complexity. chaudhuri et al. [22] 1989 2d gaussian matched filter (mf) acc and auc false detection of edge on different retinal abnormal images. hoover et al. [23] 2000 threshold probing and mf sn, sp and acc improvement in the vessel detection rate required. mendonca et al. [25] 2006 detection of centerlines and morphological reconstruction acc and auc under-segmentation of several vessel regions. false detection of vessels. fractional, or complete, omission of thin vessel segments. zana and klein [26] 2001 mathematical morphology and curvature evaluation tpr, acc and auc it generates linked linear structures that are uncontaminated but not always connected to each other. tiny vessels of low contrast are incompletely identified. palomeraperez et al. [27] 2010 region growing technique and parallel multiscale implementation tpr, fpr and acc not suitable for high resolution images. martinez-perez et al. [28] 2007 multiscale feature extraction, two geometric properties and region growing tpr, fpr and acc incapable to remove geometrical objects e.g. hemorrhages, microaneurysms in mixture with the detection of blood vessels. fraz et al. [29] 2011 bit planes and centerline detection tpr, fpr, sp, acc and sn not appropriate for pathological and those retinal images where arterioles show clear light reflexes e.g. in images of younger applicants. bankhead et al. [30] 2012 wavelets and edge location refinement tpr, fpr and acc if the image contrast diminishes then proper zero-crossings may not be detected at all areas along the vessel. performance measures: sn– sensitivity, sp – specificity, acc – accuracy, auc – area under curve. fpr – false positive rate. tpr – true positive rate. iium engineering journal, vol. 17, no. 2, 2016 khan et al. 36 the work in this paper proposes a fast and precise unsupervised technique to identify and measure retinal vessels. the proposed method consists of clahe [31], modified isodata [32] and a novel postprocessing steps. clahe has been utilized to enhance the local contrast and prevent the uncorrelated areas in retinal image analysis. further, misodata technique has been applied to find the global threshold of the entire image which is compared with the individual local threshold of each segment in order to detect vessels. finally, postprocessing steps have been applied to obtain the resulting segmented image. the proposed method is demonstrated to be equipped for acquiring an enhanced state of accuracy and low estimation error both for low and high resolution images, as compared to other blood vessel segmentation techniques. 3. proposed technique retinal images are usually corrupted with noise due to illumination and contrast variation that make challenging the extraction of a vessel map. an efficient preprocessing method is required to fix this problem. this section illustrates distinctive preprocessing steps, thresholding techniques, and postprocessing steps to enhance and segment the retinal blood vessels. the flow diagram of the proposed technique is shown in fig. 1. fig. 1: flowchart of the proposed method.  input the rgb retinal image and extract the green channel of an input image.  image localized contrast enhancement through clahe.  take difference image of average filtered image and input image for removal of abnormalities/geometrical objects, e.g. optic disc, macula, and bigger structures. for an average filter, selected kernel size is more than vessel’s diameter size. this also makes the edges more prominent than the background.  segmentation based on the implementation of misodata.  execution of postprocessing using raster to vector transformation and then computation of area and eccentricity to scale down noise and non-vessel regions in order to obtain final binary retinal image. iium engineering journal, vol. 17, no. 2, 2016 khan et al. 37 3.1 contrast limited adaptive histogram equalization (clahe) in retinal images, it is difficult to differentiate between intensity variations of vessel and non-vessel segments. in order to enhance the algorithm result, intensity transformation is applied to increase the intensity gap between vessel and non-vessel pixels. contrast enhancement can be achieved in different ways e.g. histogram equalization (he) [33], adjustment, equalization, contrast stretching [33], and local adaptive histogram equalization (ahe) [34]. ahe is a well-known contrast enhancement strategy for medical and natural images proposed by pizer [34]. in its fundamental form, the histogram equalization of an image, each pixel is mapped on its surrounding pixels (its contextual region). this method is slow, and under particular conditions the enhanced image has unwanted components, as compared to its other counterparts. an advanced version of ahe known as clahe [31] is comparatively fast with better localized contrast results. clahe was initially designed for improvement of low contrast medical images [35]. clahe is implemented in the following way:  specify a square neighborhood (block) to estimate the histogram in the local block.  generate the transformation function by histogram equalization or specification and perform the gray level mapping for each pixel.  each time, the histogram can be updated without re-computing the histogram over all pixels in the new block.  move the center of the block to an adjacent pixel position and repeat the process. the discrete approximation of the transformation function t for histogram equalization [33] is given by: s = t(r ) = p r (1) for 0 ≤ k ≤ l − 1, p r = for j = 0, … … . . , l − 1 and n = ∑ n where n shows the number of pixels with gray levels r and n is the total number of pixels. l represents gray levels. clahe differs from normal ahe in constraining the contrast enhancement. clahe uses a user-defined value called the clip limit to constrain enhancement by clipping the histogram [31]. the clipping level specifies the noise level to be smoothened and contrast level to be enhanced. 3.2 modified iterative self organizing data analysis technique (misodata) before using misodata, a low pass filter is used for noise removal and computing the difference image. misodata is a thresholding method that automatically determines the optimal threshold value instead of imposing a manual threshold [32]. in general, misodata initially computes the global mean of an image that can be used as a global threshold (gt). secondly, using gt, all pixels were classified into two clusters called mean above threshold (matg) and mean below threshold (mbtg). in the third step, the new cluster mean vectors were computed based on all the pixels in each individual cluster. the second and third steps are repeated until the average mean in the third step becomes equal to global mean. besides calculating gt, the image is divided into square or rectangular local patches and each local patch is used to calculate local mean to set as a local threshold (lt). each patch is further classified into two clusters with a reference to a lt. using lt, all pixels iium engineering journal, vol. 17, no. 2, 2016 khan et al. 38 were classified into two levels having value greater than lt called mean above threshold (matl) and having value lower than lt called mean below threshold (mbtl). matl and mbtl have been computed based on all the pixels in each individual cluster. the iterative method is repeated until the local threshold became equal to the average mean threshold of both clusters. further, gt is compared with lt; in case lt>gt and has to be updated by lt=gt. if lt≪gt the lt=gt-threshold value is updated. in this way, misodata is implemented for classification of vessel and non-vessel pixels. further, the postprocessing technique has been applied to obtain a final segmented image. the block diagram for the presented misodata is shown in fig. 2. the proposed misodata visual and quantitative results have been compared with isodata [32], fuzzy c-means (fcm) also known as fuzzy isodata [40] and the kmeans clustering method [41]. figure 3 shows that the proposed misodata produced good visual results compared to fcm and k-means methods on the drive [36] dataset. the proposed misodata also extracts thin vessels along with the wide vessels. its quantitative results are tabulated in table 2, which clearly indicates that the proposed method shows superior performance to other methods. the drawback of basic isodata is that it fails sometimes to find an optimal threshold while fcm suffers from high computation complexity. the disadvantage of the k-means method is that the means of clusters are calculated once, then remain unchanged. the proposed misodata takes a little more computation time than the basic isodata algorithm because it has been applied once locally and then globally on the entire image. fig. 2: misodata block diagram. iium engineering journal, vol. 17, no. 2, 2016 khan et al. 39 fig. 3: visual results comparison of misodata with other clustering methods. (a) misodata segmented image. (b) isodata image. (c) fcm image. (d) k-means method image. table 2: performance comparison of misodata with other clustering methods. method drive acc sn sp auc isodata [32] 0.957 0.674 0.985 0.829 fcm [40] 0.913 0.751 0.935 0.843 k-means [41] 0.959 0.716 0.980 0.848 proposed misodata 0.952 0.780 0.972 0.876 3.3 postprocessing: region properties based non-vessels rejection the postprocessing consists of a number of distinct steps as shown in fig. 4. in the first step, the binary image produced by misodata has been labeled, each separate foreground pixel has been assigned specific number. the region properties, like eccentricity and area of each distinct patch have been calculated. the vessels patches are elongated and have a high area and eccentricity almost equal to one. based on these properties, the noisy parts are rejected. region properties are used to scale down the unwanted region, non-vessel pixels, and noise. the first stage in the raster-to-vector conversion process is usually an attempt to remove, or at least minimize the noise. if binarization and noise removal are successful, each line in the original drawing will generate an elongated region of black pixels in the binary image. the next step is to reduce each such region to a one-pixel wide string of pixel locations which is achieved by finding the center line of each region (skeletonisation). noise can appear in a binary image in several forms, e.g. separated pixels of the opposite sign in an object or background regions, often known as salt-and-pepper noise, small holes in objects and/or small spots on background areas, distinct lines merging and single lines splitting. skeletons can be achieved either by "thinning", an iterative process of removing black pixels until only a unit-width string remains, or via a "medial axis transform". thinning produces a "thinned" binary image in which object pixels lie upon the skeleton of the original object. the medial axis transform produces a "medial axis", the locus of the centers of a set of maximal discs laid over the object. this is equivalent to the locus of local maxima of some distance measure. visual results of retinal blood vessel segmentation with the major processing steps of the proposed method using the drive and the stare databases are shown in fig. 5 and fig. 6, respectively. iium engineering journal, vol. 17, no. 2, 2016 khan et al. 40 fig. 4: postprocessing raster-to-vector transformation steps. fig. 5: main processing steps of the proposed technique for retinal blood vessel segmentation. (a) rgb image from drive database. (b) extraction of green channel for later processing. (c) clahe used for contract enhancement. (d) low pass gaussian blur filter for noise removal. (e) difference image for background elimination. (f) masking to remove unwanted effects. (g) misodata for vessel and non-vessel pixels classification. (h) postprocessing steps for scaling down the unwanted regions, non-vessel pixels, noise, and removing erroneously detected segments. fig. 6: major processing steps proposed technique for retinal blood vessel segmentation. (a) rgb image from stare database (b) extraction of green channel for later processing (c) clahe used for contract enhancement (d) low pass gaussian blur filter for noise removal (e) difference image for background elimination (f) masking to remove unwanted effects (g) misodata for vessel and non-vessel pixels classification (h) postprocessing steps for scaling down the unwanted regions, non-vessel pixels, noise and removing erroneously detected segments. iium engineering journal, vol. 17, no. 2, 2016 khan et al. 41 4. experimental results and comparisons the efficiency of the presented framework has been assessed and compared with the latest techniques to evaluate its performance on two openly available the drive [36] and the stare [37] datasets. the stare and the drive datasets comprise 20 and 40 retinal images, respectively. both databases are isolated into two sets: a training set and a test set. in each dataset, the segmentation of the first observer has been utilized as a ground truth for assessment while the performance of the second observer has been used as a benchmark for comparison. these databases consist of manual segmentation of experts as a gold standard. based on these gold standards, the accuracy, sensitivity, and specificity of each method have been calculated. the performance measure for segmentation of retinal vessel structure is given in table 3. table 3: performance measures for segmentation of retinal vessel structure. metrics explanation tpr tp/vessel pixel count fpr fp/non-vessel pixel count sensitivity(sn) tpr or tp/(tp+fn) specificity(sp) 1-fpr or tn/(tn+fp) accuracy(acc) (tp+tn)/(tp+fp+tn+fn) auc sn+sp/2 tp, tn, fp and fn show the true positive (accurately detected vessel pixels), true negative (accurately detected background pixels), false positive (wrongly detected vessel pixels), and false negative (wrongly detected background pixels), respectively. the area under a receiver operating characteristic (roc) curve, also known as area under the curve (auc), has the ability to reflect the trade-offs between the sensitivity and specificity. note that an auc of 0.50 implies that the classification is equivalent to a pure random guess, and an auc of 1.0 implies that the classifier recognizes class examples perfectly. 4.1 accuracy the metrics calculated on the two public databases to analyze the efficiency of the algorithms are given in table 4. the parameters of the presented technique are set to deliver the highest possible accuracy. this can result decreased in a sensitivity to gain specificity in order to increase the overall accuracy. experimental results demonstrated that the proposed method is an efficient for segmentation of retinal blood vessels. the effectiveness of proposed method has been validated by comparison of the performance results with other existing methods on two openly available drive and stare datasets. the proposed method reaches a highest accuracy compared to other methods as shown in table 4, which presents the performance comparison on the drive and the stare datasets. the results of mendonça and campilho [25], martinez-perez et al. [28], palomera-perez et al. [27], zhang et al. [20], al-diri et al. [19], niemeijer et al. [14], lam et al. [17], bankhead et al. [30] and fraz et al. [29] are acquired from their original papers while soares et al. [16] and staal et al. [15] are obtained from their websites utilizing the segmented images. chaudhuri et al. [22] and zana and klein [26] techniques results were executed by niemeijer et al. [14]. the databases contain a second manual segmentation made by a human observer, which are also included in the comparison. the exploratory results on the drive and the stare dataset authenticate that the proposed technique is more efficient than the other mentioned frameworks. fig. 7 and fig. 8 show visual iium engineering journal, vol. 17, no. 2, 2016 khan et al. 42 inspection of proposed retinal vessels segmentation method using the drive and the stare databases, respectively. table 4: performance comparison for various methods. method type method drive stare acc sn sp acc sn sp unsupervised human observer 0.947 0.776 0.972 0.935 0.895 0.939 mendonça and campilho [25] 0.945 0.734 0.976 0.944 0.699 0.973 martinez-perez et al. [28] 0.934 0.725 0.965 0.941 0.751 0.955 palomera-perez et al. [27] 0.922 0.660 0.961 0.924 0.779 0.940 zhang et al. [20] 0.938 0.712 0.973 0.948 0.717 0.975 fraz et al. [29] 0.943 0.715 0.976 0.944 0.731 0.968 bankhead et al. [30] 0.937 0.703 0.971 0.932 0.758 0.950 chaudhuri et al. [22] 0.877 0.336 — — — — zana and klein [26] 0.938 0.697 — — — — al-diri et al. [19] — 0.728 0.955 — 0.752 0.968 proposed 0.952 0.780 0.972 0.957 0.745 0.974 supervised niemeijer et al. [14] 0.942 0.714 — — — — staal et al. [15] 0.944 0.719 0.977 0.952 0.697 0.981 soares et al. [16] 0.946 0.723 0.976 0.948 0.723 0.976 b.s.y. lam et al. [17] 0.947 — — 0.957 — — marin et al. [39] 0.945 0.706 0.980 0.952 0.694 0.981 “—” shows that this content was not available. fig. 7: visual results of vessel segmentation using the drive database. (a) rgb retinal input image (b) manual segmented image (c) proposed method final image. fig. 8: visual results of vessel segmentation using the stare database. (a) rgb retinal input image (b) manual segmented image (c) proposed method final image. one important factor of the proposed method is to suppress unwanted regions, nonvessel pixels and noise that will frequently show up in the anomalous retinal images iium engineering journal, vol. 17, no. 2, 2016 khan et al. 43 through postprocessing steps. in order to assess the performance of the proposed technique, in such pathological cases, the results are analyzed by various techniques on the normal and abnormal images in the drive and the stare databases shown in table 5. experimental results emphasized that for abnormal cases, the proposed technique achieves much better efficiency than chaudhuri et al. [22], mendonça and campilho [25], hoover et al. [23] and it performs slightly better than soares et al. [16]. fig. 9 and fig. 10 show visual results for abnormal retinal images of drive and stare databases, respectively. table 5: segmentation results comparison of the proposed method with various segmentation methods for normal versus abnormal cases image type method tpr fpr acc normal human observer 0.9646 0.0764 0.9283 chaudhuri et al. [22] 0.7335 0.0218 0.9486 mendonça and campilho [25] 0.7258 0.0209 0.9492 hoover et al. [23] 0.6766 0.0338 0.9324 soares et al. [16] 0.7554 0.0188 0.9542 proposed 0.8547 0.0191 0.974 abnormal human observer 0.8252 0.0456 0.9425 chaudhuri et al. [22] 0.5881 0.0384 0.9276 mendonca and campilho [25] 0.6733 0.0331 0.9388 hoover et al. [23] 0.6736 0.0528 0.9211 soares et al. [16] 0.6869 0.0318 0.9416 proposed 0.8510 0.0552 0.9451 fig. 9: visual segmentation results of an abnormal image of the drive database (a) rgb retinal input image (b) manual segmented image (c) proposed method final image. fig. 10: visual segmentation results of an abnormal image of the stare database. (a) rgb retinal input image (b) manual segmented image (c) proposed method final image. iium engineering journal, vol. 17, no. 2, 2016 khan et al. 44 the auc acquired from the segmentation results attained by the proposed technique is shown in table 6. it shows better auc results than the previously proposed techniques on the drive and the stare databases. table 6: performance comparison of auc with different methods method auc (drive) auc (stare) human observer 0.874 0.917 mendonça and campilho [25] 0.855 0.836 martinez-perez et al. [28] 0.845 0.853 palomera-perez et al. [27] 0.811 0.860 bankhead et al. [30] 0.837 0.854 fraz et al. [29] 0.846 0.850 zhao et al. [38] 0.861 0.881 al-diri et al. [19] 0.842 0.860 marin et al. [39] 0.843 0.838 staal et al. [15] 0.848 0.839 soares et al. [16] 0.849 0.849 proposed 0.876 0.861 5. conclusion precise detection of retinal vessels plays a significant role in the investigation strategy of retinopathy. some current techniques including supervised and unsupervised, can achieve good segmentation results for wide retinal vessels. however, for thin retinal vessels, these methodologies are unable to recognize them from the background and often lose some vessels connectivity. in this paper, a novel technique is presented for retinal vessel segmentation based on clahe and misodata. the former is used for contrast enhancement of an image, and the latter is used for retinal vessel detection using global and local thresholding. postprocessing steps are used to eliminate unconnected pixels. the proposed framework has been assessed utilizing multiple openly available databases with diverging image resolution. in each case, the proposed framework shows an increase both in sensitivity and accuracy to segment vessels compared to the results from different published papers. experimental results demonstrated that the presented system can segment both wide and thin vessels accurately, reaching the average accuracy of 95.21% and 95.69% on the drive and the stare databases, respectively. moreover, the proposed technique is unsupervised, which does not require any manual segmentation for training and also robust for both normal and abnormal images of the both datasets. references [1] gelman r, elena martinez-perez m, vanderveen dk, moskowitz a, fulton ab. (2005) diagnosis of plus disease in retinopathy of prematurity using retinal image multiscale analysis. investigative ophthalmology & visual science, 46(12): 4734-4738. [2] bernardes r, serranho p, lobo c. (2011) digital ocular fundus imaging: a review. ophthalmologica, 226(4): 161-181. [3] marius e, steger s, sakas g. (2012) regmentation: a new view of image segmentation and registration. j. radiation oncology informatics, 4(1): 1-23. iium engineering journal, vol. 17, no. 2, 2016 khan et al. 45 [4] mohammad saleh m, mahloojifar a. (2011) retinal image analysis using curvelet transform and multistructure elements morphology by reconstruction. ieee trans. biomed. eng., 58(5):1183-1192. [5] kanski jj, bowling b. (2012) synopsis of clinical ophthalmology. elsevier health sciences. [6] ying l, giovanni g, knighton rw, lujan bj, rosenfeld pj. (2011) registration of oct fundus images with color fundus photographs based on blood vessel ridges. optics express, 19(1):7-16. [7] zwiggelaar r, astley sm, boggis crm, taylor cj. (2004) linear structures in mammographic images: detection and classification. ieee trans. medical imaging, 23(9):1077-1086. [8] shabbir s, tariq a, akram mu. (2013). a comparison and evaluation of computerized methods for blood vessel enhancement and segmentation in retinal images. int. j. future comp. comm., 2(6):600-603. [9] muhammad moazam f, remagnino p, hoppe a, uyyanonvara b, rudnicka ar, owen cg, barman sa. (2012) blood vessel segmentation methodologies in retinal images–a survey. comp. meth. prog. biomedicine, 108(1): 407-433. [10] azzopardi g, strisciuglio n, vento m, petkov n. (2015) trainable cosfire filters for vessel delineation with application to retinal images. medical image analysis, 19(1):46-57. [11] ricci e, perfetti r. (2007) retinal blood vessel segmentation using line operators and support vector classification. ieee trans. medical imaging, 26(10):1357-1365. [12] becker c, rigamonti r, lepetit v, fua p. (2013) supervised feature learning for curvilinear structure segmentation. medical image computing and computer-assisted intervention– miccai 2013. springer berlin heidelberg, 526-533. [13] sinthanayothin c, boyce jf, cook hl, williamson th. (1999) automated localisation of the optic disc, fovea, and retinal blood vessels from digital colour fundus images. british j. ophthal., 83(8):902-910. [14] niemeijer m, staal j, van ginneken b, loog m, abramoff md. (2004) comparative study of retinal vessel segmentation methods on a new publicly available database. in medical imaging, 648-656. international society for optics and photonics. [15] staal j, abràmoff md, niemeijer m, viergever ma, van ginneken b. (2004) ridge-based vessel segmentation in color images of the retina. ieee trans. medical imaging, 23(4):501509. [16] soares jvb, leandro jjg, cesar jr rm, jelinek hf, cree mj. (2006) retinal vessel segmentation using the 2-d gabor wavelet and supervised classification. ieee trans. medical imaging, 25(9):1214-1222. [17] lam bsy, gao y, liew awc. (2010) general retinal vessel segmentation using regularization-based multiconcavity modeling. ieee trans. medical imaging, 29(7):13691381. [18] joshi vs, reinhardt jm, garvin mk, abramoff md. (2014) automated method for identification and artery-venous classification of vessel trees in retinal vessel networks. plos one, 9(2):e88061. [19] al-diri b, hunter a, steel d. (2009) an active contour model for segmenting and measuring retinal vessels. ieee trans. medical imaging, 28(9):1488-1497. [20] zhang j, cui y, jiang w, wang l. (2015) blood vessel segmentation of retinal images based on neural network. image and graphics. springer international publishing, 11-17. [21] lupaşcu ca, tegolo d. (2010) automatic unsupervised segmentation of retinal vessels using self-organizing maps and k-means clustering. computational intelligence methods for bioinformatics and biostatistics. springer berlin heidelberg, 263-274. [22] chaudhuri s, chatterjee s, katz n, nelson m, goldbaum m. (1989)"detection of blood vessels in retinal images using two-dimensional matched filters. ieee trans. medical imaging, 8(3):263-269. [23] hoover a, kouznetsova v, goldbaum m. (2000) locating blood vessels in retinal images by piecewise threshold probing of a matched filter response. ieee trans. medical imaging, 19(3):203-210. iium engineering journal, vol. 17, no. 2, 2016 khan et al. 46 [24] chutatape o, zheng l, krishnan sm. (1998) retinal blood vessel detection and tracking by matched gaussian and kalman filters. engineering in medicine and biology society, proceedings of the 20th annual international conference of the ieee. vol 6. [25] mendonca am, campilho a. (2006) segmentation of retinal blood vessels by combining the detection of centerlines and morphological reconstruction. ieee trans. medical imaging, 25(9):1200-1213. [26] zana f, klein jc. (2001) segmentation of vessel-like patterns using mathematical morphology and curvature evaluation. ieee trans. image processing, 10(7):1010-1019. [27] palomera-pérez ma, martinez-perez me, benítez-pérez h, ortega-arjona jl. (2010) parallel multiscale feature extraction and region growing: application in retinal blood vessel detection. ieee trans. inform. tech. biomed., 14(2):500-506. [28] martinez-perez me, hughes ad, thom sa, bharath aa, parker kh. (2007) segmentation of blood vessels from red-free and fluorescein retinal images. med. image analysis, 11(1):47-61. [29] fraz mm, barman sa, remagnino p, hoppe a, basit a, uyyanonvara b, rudnicka ar, owen cg. (2012) an approach to localize the retinal blood vessels using bit planes and centerline detection. comp. meth. prog. biomed., 108(2):600-616. [30] bankhead p, scholfield cn, mcgeown jg, curtis tm. (2012) fast retinal vessel detection and measurement using wavelets and edge location refinement. plos one, 7(3): e32435. [31] zuiderveld k. (1994) contrast limited adaptive histogram equalization. graphics gems iv. academic press professional, inc., san diego, ca, usa. 474-485. [32] ball gh, hall dj. (1965) isodata, a novel method of data analysis and pattern classification. stanford research inst., menlo park ca. [33] gonzalez rc, woods er. (2002) digital image processing. ed: prentice hall press, upper saddle river, new jersey. [34] pizer sm, amburn ep, austin jd, cromartie r, geselowitz a, greer t, romeny b, zimmerman jb, zuiderveld k. (1987) adaptive histogram equalization and its variations. comp. vis. graphics image proc., 39(3):355-368. [35] pisano ed, zong s, hemminger bm, deluca m, johnston re, muller k, braeuning mp, pizer sm. (1998) contrast limited adaptive histogram equalization image processing to improve the detection of simulated spiculations in dense mammograms. j. dig. imaging, 11(8):193-200. [36] staal j, abramoff md, niemeijer m, viergever ma, van ginneken b. (2004) drive public online database. [http://www.isi.uu.nl/research/databases/drive/]. [37] hoover and m. goldbaum. (2000) stare public online database. [http://www.ces.clemson.edu/∼ahoover/stare/]. [38] zhao y, liu y, wu x, harding sp, zheng y. (2015) retinal vessel segmentation: an efficient graph cut approach with retinex and local phase. plos one, 10(4): e0122332. [39] marín d, aquino a, gegúndez-arias me, bravo jm. (2011) a new supervised method for blood vessel segmentation in retinal images by using gray-level and moment invariantsbased features. ieee trans. med. imaging, 30(1):146-158. [40] bezdek jc. (1980) a convergence theorem for the fuzzy isodata clustering algorithms. ieee trans. pattern anal. machine intel., 1:1-8. [41] jain ak, dubes rc. (1988) algorithms for clustering data. prentice-hall, inc., englewood cliffs, new jersey. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 benoudjit et al. 11 pedot: pss–modified platinum microelectrodes for measurements in aqueous media: effect of polymer surface area on long-term anodic peak current stability abdelmohsen benoudjit, habibah farhana abdul guthoos, farah aida arris and wan wardatul amani wan salim department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. *corresponding author: asalim@iium.edu.my (received: 30 th aug. 2016; accepted: 17 th april 2017; published on-line: 1 st dec. 2017) abstract: contamination of drinking water by hazardous agents is becoming a serious global threat, so it is necessary to develop more efficient sensing technologies for applications in liquid media. the limited working lifetime of electrochemical biosensors, especially when measurements are made continuously in liquid media, remains an unsolved challenge. we studied the effect of pedot:pss surface area on platinum microelectrodes with respect to electrode ability to conduct reversible ion-to-electron transduction in liquid media. electropolymerization of 3,4ethylenedioxythiophene:poly(styrene sulfonate) edot:pss to poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (pedot:pss) was conducted on microplatinum electrodes 5 and 10 mm long using a galvanostatic mode. cyclic voltammetry was used to determine capacitive peak current; higher peak current indicates higher redox capacitance. field-emisison scanning-electron microscopy was used to study the surface morphology of the pedot:pss transucer layer after measurement in liquid media. the anodic capacitive peak currents did not differ significantly between the two electrodes at day one (~0.20 ma); however, peak current decreased by ~ 20% and ~ 80% at day six for 10and-5 mm electrode lengths, respectively. the results imply that pedot:pss surface area plays a role in transduction of pedot:pss in aqueous media. abstrak: air minuman yang dicemari agen merbahaya telah menjadi isu ancaman global yang serius, jadi aplikasi teknologi yang sesuai bagi mengesan bendasing dalam cecair adalah sangat diperlukan. biosensor elektrokimia mempunyai kekangan jangka hidup untuk beroperasi, terutama apabila bacaan diambil secara berterusan dalam medium cecair, masalah ini tinggal bermasalah dan masih belum diselesaikan. kami mengkaji kesan pedot:pss pada permukaan kawasan di atas mikro-elektrod, keupayaan elektrod untuk menggerakkan cas ion-kepada-elektron secara terbalik secara langsung dalam medium cecair. elektropolimer 3,4-ethylenedioxythiophene:poly(styrene sulfonate) edot:pss kepada poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (pedot:pss) telah dijalankan ke atas elektrod mikroplatinum 5 dan 10 mm panjang dengan menggunakan mod galvanostatik. kitaran voltametri telah digunakan untuk mendapatkan arus maksima kapasitan. arus maksimum bermakna ketinggian redox kapasitan. proses mikroskopi dapat mengesan elektron di kawasan-telah digunakan dalam kajian ini terhadap permukaan morfologi pedot:pss pada permukaan sensor iium engineering journal, vol. 18, no. 2, 2017 benoudjit et al. 12 selepas bacaan sukatan diambil dalam medium cecair. arus maksimum anod kapasitan tidak jauh berbeza antara kedua elektrod pada hari pertama (~0.20 ma); tetapi, arus maksimum telah berkurangan sebanyak ~ 20% dan ~ 80% pada hari ke enam bagi 10 dan 5 mm panjang elektrod, masing-masing. keputusan menunjukkan permukaan kawasan pedot:pss memainkan peranan dalam pergerakan arus pedot:pss dalam medium cecair. keywords: pedot:pss; electrochemical biosensor; anodic capacitive current; transducer; liquid media; microplatinum electrode 1. introduction the ability to evaluate food quality and freshness, as well as water quality, requires sensors that can operate in aqueous media. most sensors available in the market are not for long-time use in aqueous media, limiting their potential [1-3]. nowadays, the most common type of sensing technology for detection of biological agents is electrochemical biosensors, owing to their fast measurement, simple construction, low-cost fabrication, real-time measurement capability, and applicability to a wide range of sample types [4]. by definition, an electrochemical biosensor is a device for measuring the concentration of a biological analyte, with conversion of a biochemical signal to an electrical signal via an electrochemical transducer [5]. the transducer is often a conductive polymer with reversible ion-storage capacity. poly(3,4-ethylenedioxythiophene), abbreviated as pedot, is an organic conductive polymer derived from polythiophene. pedot can be deposited on biosensor electrodes by electropolymerization of the monomer (3,4-ethylenedioxythiophene (edot) in poly(styrene sulfonate) (pss) solution, forming the water-soluble pedot:pss [6]. many studies have reported application of pedot:pss in biosensor development; the pedot:pss composite possesses high electrical conductivity and biocompatibility, both important key characteristics in biosensor development [7]. a challenge that remains unsolved when pedot:pss is used as a transducer layer in electrochemical biosensors, is its limited working lifetime when electrical measurements are made in liquid media. pedot:pss is highly hydrophilic and unstable in liquid media because of the presence of the water-soluble pss chain [8], which has a tendency to degenerate in an aqueous medium; with time, it can be easily peeled off from the electrode surface, leading to a decrease in biosensor performance [9] and limiting pedot:pss application as the transducer layer in biosensors. considerable research has been performed to improve the longevity in liquid media of biosensors using pedot:pss. different techniques such as dip-coating and drop-casting have been used to deposit pedot:pss on the working-electrode surface; techniques of pedot:pss deposition can affect the quality of the transducer layer. a binder has been utilized in the deposition techniques in order to increase adhesion of pedot:pss to an electrode surface [9] [10]. to fabricate pedot:pss transducers that are stable with long lifetime in liquid media, good adhesion is required between the transducer and the electrode surface. in this preliminary work, we studied the effect of the pedot:pss surface area on anodic capacitive peak current. field-emission scanning-electron microscopy (fesem) was used to verify pedot:pss adhesion to the platinum electrode surface after electrode measurement in aqueous media. iium engineering journal, vol. 18, no. 2, 2017 benoudjit et al. 13 2. materials and methods 2.1 reagents and apparatus 3,4-ethylenedioxythiophene (edot), poly(sodium 4-styrene sulfonate) (napss) solution, and lithium perchlorate (liclo4) were purchased from sigma-aldrich, st. louis, mo, usa. potassium ferricyanide (k3fe(cn)6) and 0.1 m phosphate buffered saline (pbs), ph 7.4, were purchased from r&m chemicals, selangor, malaysia. distilled water was used throughout the experiments. electrochemical characterizations of pedot:pss as transducer material were performed using a three-electrode cell and pocketstat (ivium technologies, eindhoven, netherlands). 2.2 electropolymerization of pedot:pss on a platinum microelectrode (µpte) electropolymerization of edot monomer was performed under galvanostatic conditions (scan rate 100 µa/s, current 100 µa, and potential 400 mv) using a threeelectrode cell and pocketstat in an aqueous solution of 0.5 ml edot, 1 ml liclo4 (0.1 m), and 1 ml napss in 50 ml distilled water. the edot:pss solution was stirred for 24 hours before electropolymerization. two µptes, one 10-mm long and one 5-mm long, were used; the choice of lengths was determined by availability for purchase. 2.3 electrochemical characterization of µpte/pedot:pss cyclic voltammetry (cv) was performed in 0.1 m potassium ferricyanide (k3fe(cn)6) at a scan rate of 100 µv/s to evaluate the capacitive peak current of the pedot:pss transducer layer on a platinum microelectrode (µpte). 3. results and discussion 3.1 capacitive peak current of pedot:pss transducer in liquid media cv was performed in 0.1 m potassium ferrocyanide k₄[fe(cn)₆] solution to assess the capacitive peak current of pedot:pss on µptes (µpte/pedot:pss) 10 mm and 5 mm long for six consecutive days against a control (bare µpte). figures 1 and 2 show the cv curves at days one, two, three, and six and fig. 3 shows the values of anodic peak current from all days in comparison to the control. fig. 1: cv of 10-mm µpte/pedot:pss in 0.1 m k3fe(cn)6 solution at a scan rate of 100 mv/s over six days. fig. 2: cv of 5-mm µpte/pedot:pss in 0.1 m k3fe(cn)6 solution at a scan rate of 100 mv/s over six days. the anodic capacitive peak current for both coated µptes was ~ 0.2 ma during the first day of measurement (day one); however, after six days the anodic peak current of the 5-mm µpte had decreased by ~80% to 0.045 ma, while peak current for the 10-mm µpte iium engineering journal, vol. 18, no. 2, 2017 benoudjit et al. 14 had decreased by only 20% (from 0.195 ma to 0.143 ma), indicating that the 10-mm µpte/pedot:pss maintains redox activity, possibly as a result of the larger surface area that provides a stronger adhesion between pedot:pss and the µpte surface. fig. 3: oxidation peak current versus time for 10-mm and 5-mm platinum microelectrodes. 3.2 surface morphology of µpte/pedot:pss because the 10-mm electrode maintained anodic capacitive peak current with only a ~ 20% reduction, we utilized this electrode for chronoamperometry measurements in buffer solution; most electrochemical biosensors operate in this mode. we characterized the surface of the electrode using fesem to test the surface morphology of the electrodes after 24 hours of measurement in 0.1 m phosphate buffered saline (pbs). fig. 4: fesem images of pedot:pss before (a and b) and after (c and d) chronoamperometry measurement in 0.1 m pbs, ph 7.4, for 10-mm µpte (after 24 hours). iium engineering journal, vol. 18, no. 2, 2017 benoudjit et al. 15 figure 4 shows fesem images of pedot:pss before and after the chronoamperometry measurement. before measurement, the pedot:pss structure on the modified µpte was observed to be globular (fig. 4 (a-b)), suggesting an irregular amorphous shape, common to pedot material. after measurement, the pedot:pss structure lost the globular shape and became irregular as if ruptured as a result of prolonged measurement in liquid media (fig 4 (c-d)). however, more studies are required on pedot:pss morphology in liquid media. 4. conclusion pedot:pss was successfully deposited on a µpte via electropolymerization. electrodes with larger surface area maintained anodic peak current over a period of 6 days. fesem results imply that the structure of electropolymerized pedot could affect current measurement in liquid media. acknowledgment this work was funded by the malaysian ministry of higher education (mohe) under fundamental research grant scheme (frgs) (ref: frgs/2/2014/tk04/uiam/02/1). references [1] mello ld, kubota lt. (2002) review of the use of biosensors as analytical tools in the food and drink industries. food chemistry, 77(2):237-256. [2] perumal v, hashim u. (2014) advances in biosensors: principle, architecture and applications. journal of applied biomedicine, 12(1):1-15. [3] amini k, kraatz hb. (2015) recent developments in biosensor technologies for pathogen detection in water. jsm environ. sci. ecol, (3)(1):1-9. [4] velasco-garcia mn, mottram t. (2003). biosensor technology addressing agricultural problems. biosystems engineering, 84(1):1-12. [5] yogeswaran u, chen sm. (2008) a review on the electrochemical sensors and biosensors composed of nanowires as sensing material. sensors, 8(1):290-313. [6] yang x, kirsch j, olsen ev, fergus jw, simonian al. (2013) anti-fouling pedot: pss modification on glassy carbon electrodes for continuous monitoring of tricresyl phosphate. sensors and actuators b: chemical, (177): 659-667. [7] jiang q, liu c, song h, xu j, mo d, shi h, zhu z. (2014) free-standing pedot: pss film as electrode for the electrodeposition of bismuth telluride and its thermoelectric performance. int. j. electrochem. sci, (9):7540-7551. [8] salim ww, hermann ac, zietchek m a, pfluger je, park jh, ul haque a, porterfield dm. (2015, december) ion-selective electrode biochip for applications in a liquid environment. in international conference for innovation in biomedical engineering and life sciences, springer singapore, pp. 86-93. [9] zhang h, xu j, wen y, wang z, zhang j, ding w. (2015) conducting poly (3, 4ethylenedioxythiophene): poly (styrene-sulfonate) film electrode with superior long-term electrode stability in water and synergistically enhanced electrocatalytic ability for application in electrochemical sensors. synthetic metals, (204):39-47. [10] wang z, xu j, yao y, zhang l, wen y, song h, zhu d. (2014) facile preparation of highly water-stable and flexible pedot: pss organic/inorganic composite materials and their application in electrochemical sensors. sensors and actuators b: chemical, (196):357-369. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 al hazza et al. 189 a study on capabilities of different electrode materials during electrical discharge machining (edm) muataz hazza faizi al hazza*, ahsan ali khan, mohammad yeakub ali, siti fatihah hasim and mohd radzi che daud department of manufacturing and materials engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. *corresponding author: muataz@iium.edu.my (received: 18 th oct. 2016; accepted: 5 th feb. 2017; published on-line: 1 st dec. 2017) abstract: electrode material in the electro discharge machining (edm) process plays an important role in terms of material removal rate (mrr), electrode wear rate (ewr) and surface roughness (ra). the purpose of this research is to investigate the capability of different electrode materials: copper, aluminum, and graphite in edm of aisi 304 stainless steel as a work piece. the research focuses on three current settings: 2.5a, 4.5a, and 6.5a using kerosene as a dielectric fluid. the experiment was planned and analyzed using the full factorial of experimental design using response surface methodology (rsm). in this research, two outputs have been investigated: mrr and ewr. the results indicated that the responses increased with the increase in current. finally, the desirability function method has been used to determine the optimum values. the results show that maximum mrr and minimum ewr were achieved using a graphite electrode at current 6.5a. abstrak: bahan elektrod dalam proses pengeluaran elektron pada mesin edm berperanan penting dalam kadar pengeluaran bahan (mrr), kadar penggunaan ekektrod (ewr) dan kekasaran permukaan (ra). kajian ini bertujuan bagi menilai keupayaan pelbagai jenis bahan elektrod yang berlainan: tembaga, aluminium, dan grafit dalam edm pada aisi 304 keluli tahan karat sebagai bahan kajian. fokus kajian ini pada tiga takat arus: 2.5 a, 4.5 a dan 6.5 a menggunakan kerosin sebagai cecair dielektrik. eksperimen ini telah dirancang dan diuji menggunakan faktorial penuh pada binaan eksperimen menggunakan kaedah tindak balas pada permukaan (rsm). dalam kajian ini, dua keputusan telah diuji: mrr dan ewr. keputusan menunjukkan tindak balas bertambah dengan kenaikan arus. akhirnya kaedah fungsi keperluan telah digunakan untuk mencari nilai optimum. keputusan menunjukkan mrr maksimum dan ewr minimum telah dicapai menggunakan elektrod grafit pada arus 6.5 a. keywords: edm; electrode material; material removal rate; electrode wear rate; surface roughness 1. introduction electro-discharge machining (edm) is a thermoelectric process during which the heat energy of the spark produced between the electrodes is used to erode materials from the electrodes [1]. the performance of the edm process is measured by different outputs such as: material removal rate (mrr), electrode wear rate (ewr) and surface roughness (ra). many factors that control those outputs such as: peak current, polarity, pulse duration, http://scholar.google.com/scholar?q=edm+electro+discharge+machining&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=x&ved=0ahukewi895ji8f7oahwbo48khxbcb4yqgqmijtaa iium engineering journal, vol. 18, no. 2, 2017 al hazza et al. 190 power supply voltage, and many others. however, selection of the electrode materials is one of the more important aspects that require care in edm. this is because the improper selection of the electrode materials may cause poor machining characteristics. an improper electrode material may cause less mrr, leading to more machining time, leading to high ewr. many researchers have discussed and investigated the effect of current and electrode material and their effect on the mrr and ewr. however, machining characteristics change greatly when using different electrode materials due to the different erosion removal resistance [2]. lee and li compared three different electrode materials: graphite, copper-tungsten, and copper and their effect on mrr, ewr and surface roughness with different peak currents ranging from 12 a to 64 a [3]. they found that peak current was almost directly proportional to the mrr of these three electrodes; as peak current increased, the mrr also increased. among these three electrodes, graphite obtained better machining performance since it provided the highest mrr. graphite was followed by copper-tungsten, and lastly, copper. the study showed that low peak current provided a low electrode wear ratio for the graphite electrode but that the opposite was true for the copper electrode. at the highest peak current, the copper electrode showed the highest ewr, while the copper-tungsten electrode always gave the lowest electrode wear ratio at all ranges of peak current. other than that, analysis also showed a relationship between surface roughness and peak current. as peak current increased, surface roughness also increased for all electrode materials. singh et al. [4] studied four different electrode materials: copper, copper–tungsten, brass, and aluminum in the machining en-31 tool steel. the results showed that the copper and copper–tungsten had low wear rates. copper and aluminum showed high surface roughness when high current values were used. jahan et al. [5] investigated the fine-finish die-sinking micro-edm of tungsten carbide using different electrode materials namely, tungsten (w), copper tungsten (cuw), and silver tungsten (agw) electrodes. the results obtained showed that during the edm process, surface roughness becomes dependent mostly on the discharge voltage. the researchers further stated that during fine-finish micro-edm, the pulse energy supplied into the gap needs to be minimized. furthermore, electrical and thermal properties of the electrode material were founded to greatly affect the surface finish. it was found that the agw electrode provided a smooth surface with the lowest ra value among the three electrodes. for the mrr characteristic, the cuw electrode provided the highest value, followed by agw, especially at high gap voltage. in case of ewr, the w electrode was best, followed by cuw and agw, as it gave the lowest wear during edm. after reviewing all the performance parameters, the best electrode material for finish die-sinking microedm of tungsten carbide was selected to be agw. however, this research focused on using different tool electrode materials during the edm of aisi 304 stainless steel. this will include investigation of the effect of various electrode materials and peak currents on material removal rate (mrr) and electrode wear rate (ewr). 2. experimental procedure three different electrode materials have been tested: copper (cu), aluminum (al) and graphite (c) with three levels of current: 2.5 a, 4.5 a and 6.5 a. the dielectric fluid used was kerosene. the material removal rate (mrr) and electrode wear rate (ewr) have been iium engineering journal, vol. 18, no. 2, 2017 al hazza et al. 191 investigated. in this experiment, full factorial design has been used to conduct the experiment. nine (9) runs were conducted. table 1 concluded the maximum and minium boundaries of the experiment. the physical properties of the three different electrodes are concluded in table 2. table 3 concluded the setting of the machine during experiment. table 1: experimental design run electrode material current (a) 1 copper 2.5 2 aluminum 6.5 3 aluminum 2.5 4 copper 4.5 5 graphite 6.5 6 graphite 2.5 7 graphite 4.5 8 aluminum 4.5 9 copper 6.5 table 2: physical properties of electrode materials electrode material physical properties aluminum copper graphite electrical resistivity (ω.m) 2.65 × 10 -8 1.68 × 10 -8 3-60 × 10 -5 electrical conductivity (1/ω.m) 3.77 × 10 7 5.95 × 10 7 0.33-0.167 × 10 4 thermal conductivity 227 w/m.k 380.7 w/m.k 160 w/m.k melting point 660 o c 1083 o c 3550 o c specific heat 0.9 j/g o c 0.092 cal/g o c 0.17–0.2 cal/g o c specific gravity at 20 o c 2.73 g/cm 3 8.9 g/cm 3 1.75 g/cm 3 coefficient of thermal expansion 24 ×10 −6 o c −1 6.6 ×10 −6 o c −1 7.8 ×10 −6 o c −1 table 3: experimental settings experimental conditions value gap voltage 20 v pulse on time 10.0 μs pulse off time 6.0 μs spark gap 0.010 mm depth of cut 1.0 mm dielectric fluid kerosene electrode polarity negative work piece polarity positive 3. results the results of conducting nine experiments are concluded in table 4. mrr and ewr have been calculated using the following formulas: mrr (g/min) = ) )) (1) ewr (g/min) = ) )) (2) iium engineering journal, vol. 18, no. 2, 2017 al hazza et al. 192 where ) is the weight of the work piece before machining, ) weight of work piece after machining, ) is the weight of electrode before machining, ) is the weight of electrode after machining and is the machining time. table 4: results of full factorial experiment run electrode material current (a) mrr (g/min) ewr (g/min) 1 copper 2.5 0.0099 0.0006 2 aluminum 6.5 0.5109 0.0032 3 aluminum 2.5 0.0129 0.0009 4 copper 4.5 0.1259 0.0013 5 graphite 6.5 0.5957 0.0011 6 graphite 2.5 0.0565 0.0003 7 graphite 4.5 0.2608 0.0006 8 aluminum 4.5 0.1522 0.0023 9 copper 6.5 0.433 0.0025 the relationships between mrr and ewr with the current for each type of material have been plotted in fig. 1. the best ewr was achieved with a graphite electrode. however, the current negatively affects the ewr, whereas the effect of electrode material on mrr was unclear. finally, the mrr increased with the increase of current. fig. 1: relationships between mrr and ewr with the current and material. 3.1 3d profile the 3d profile for mrr and twe have been created using jmp software to lend a greater understanding of the effect of peak current and different electrode materials, as shown in fig. 2. iium engineering journal, vol. 18, no. 2, 2017 al hazza et al. 193 a) mrr b) ewr fig. 2: 3d surface profile. the results showed that higher mrr can be achived using a graphite electrode, followed by the performance of the aluminium electrode, with the copper electrode showing the lowest performance for the different current values. on the other hand, the least ewr was recorded for the graphite electrode, followed by the copper electrode and ending with the aluminium electrode for all current values. 3.2 statistical analysis the results were analyzed statistically using different presentation tools: regression plot, summary of fit, and comparison was made between actual and predicted values. figure 3 supported the results shown in the 3d profile, where the best material for both the higher removal rate and lower wear rate for the electrode was graphite. finally, the measured data and the predicted results have been plotted for both mrr and ewr, as shown in fig. 4. a) mmr b) ewr fig. 3: regression plot. a) mrr b) ewr fig. 4: actual and predicted plots. iium engineering journal, vol. 18, no. 2, 2017 al hazza et al. 194 the results showed high correlation, justified by calculating the summary fit measures that have been concluded in table 5. table 5: summary of fit mrr ewr r-square 0.957 0.989 r-square adj 0.886 0.970 table 5 shows that r² was close to one in all models and was very close to unity with the adjusted r², meaning that the models were reliable for predicting the different parameters. 4. desirability function the desirability function method has been implemented to achieve the maximum mrr and the minimum ewr. the results are presented in fig. 5. the figure shows that with 76% and using graphite material for electrode, the mrr will be 0.5739 g/min. the optimization results have been included in table 6. the best ratio of mrr to ewr can be achieved using a graphite electrode with 6.5 as a current with the ratio of 537.9 with higher desirability of 76%. fig. 5: optimization using a desirability function. table 6: optimization results current (a) mrr (g/min) ewr (g/min) ratio (mrr/ewr) desirability % graphite 6.5 0.573933 0.001067 537.8941 76% copper 6.5 0.40115 0.002417 165.9702 41% aluminum 6.5 0.474333 0.003283 144.4816 22% iium engineering journal, vol. 18, no. 2, 2017 al hazza et al. 195 5. concluding remarks the results of this study have been analysed and can be concluded by the following: i. for all different types of electrode material, increasing the current will increase both the mrr and ewr. in other words, increasing the current has a positive effect on mrr and a negative effect on ewr. therefore, the best measure was to take the ratio of mrr to ewr. ii. the desirability function, as one of the surface response methods, has been applied to determine the best cutting conditions. the results showed that by using the highest current of 6.5 a and the graphite electrode can give the best ratio of mrr to ewr of 534 with the desirability of 76%. iii. the mrr increased when the current increased. for this analysis, the graphite electrode gave the higher mrr (0.5957 g/min) compared to aluminum and copper electrodes. acknowledgement we would like to show our gratitude to the research management center (rmc), international islamic university malaysia (iium) for their support to conduct our research. we would like also to thank our colleagues in the department of manufacturing and materials engineering. references [1] kumar s, dave h k, desai kp. (2016). experimental investigation on performance of different tool movement strategies in edm process for boring operation. the international journal of advanced manufacturing technology, 87(5-8):1609-1620. [2] reynaerts d, hendrik vb. (1997) microstructuring of silicon by electro-discharge machining (edm)—part i: theory. sensors and actuators a: physical, 60(1):212-218. [3] lee sh, li xp. (2001) study of the effect of machining parameters on the machining characteristics in electrical discharge machining of tungsten carbide. j. materials proc. tech., 115(3):344-358. [4] singh s, maheshwari s, pandey pc. (2004). some investigations into the electric discharge machining of hardened tool steel using different electrode materials. j. materials proc. tech., 149(1):272-277. [5] jahan mp, wong ys, rahman m. (2009) a study on the fine-finish die-sinking micro-edm of tungsten carbide using different electrode materials. j. materials proc. tech., 209(8):3956-3967. microsoft word 233 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering dao et al. 53 modification of itu-r rain fade slope prediction model based on satellite data measured at high elevation angle hassan dao, md. rafiqul islam and khalid al-khateeb electrical and computer engineering department, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. rafiq@iium.edu.my abstract: rain fade slope is one of fade dynamics behaviour used by system engineers to design fade mitigation techniques (fmt) for space-earth microwave links. recent measurements found that fade slope prediction model proposed by itu-r is unable to predict fade slope distribution accurately in tropical regions. rain fade measurement was conducted in kuala lumpur (3.3� n, 101.7� e) where located in heavy rain zone by receiving signal at 10.982 ghz (ku-band) from measat3 (91.5� e) on 77.4� elevation angle. the measurement has been carried out for one year period. fade slope s parameter on itu-r prediction model has been investigated. new parameter is proposed for the fade slope prediction modeling based on measured data at high elevation angle, ku-band. abstrak: cerun hujan pudar adalah salah satu dinamik tingkah laku pudar yang digunakan oleh jurutera sistem untuk mereka bentuk teknik-teknik pengurangan pudar (fmt) bagi link gelombang mikro ruang bumi. ukuran baru-baru ini mendapati bahawa cerun pudar ramalan model yang dicadangkan oleh itu-r tidak mampu untuk meramalkan pengagihan cerun pudar tepat di kawasan tropika. pengukuran hujan pudar telah dijalankan di kuala lumpur (3.3� n, 101.7� e) yang terletak di kawasan hujan lebat dengan menerima isyarat pada 10,982 ghz (ku-band) dari measat3 (91.5� e) pada sudut ketinggian 77.4�. pengukuran telah dijalankan untuk tempoh satu tahun. parameter cerun pudar s pada model ramalan itu-r telah disiasat. parameter baru adalah dicadangkan untuk pemodelan cerun pudar ramalan berdasarkan data yang diukur pada sudut paras ketinggian, ku-band. keywords: fade slope; itu-r; fade mitigation techniques; sampling time interval 1. introduction in satellite communication on frequencies above 10 ghz, rain attenuation is great propagation phenomenon that influence large variations in received signal levels. rain attenuaton is inordinately degraded received signal. that is why many mitigating approachs have been developed to reduce fading outage of communication links. rain attenuation behaviours are extensively studied and measured but dynamic aspect of rain attenuation still has sparse study. knowledge on rain fade dynamics is noticeable important in the design of new satellite communication systems. adaptive power control (apc) and uplink power control (ulpc) are ones of rain countermeasure techniques relies on rain fade dynamics parameters by increasing transmitted power to compensate rain fading on propagation path. fade slope is one behaviour of fade dynamics iium engineering journal, vol. 12, no. 5, 2011: special issue characteristics that assesses tracking speed contributing factor to fade mitigation techniques (fmt) [1, 2] various researchers have studied and proposed parameters and prediction models for rain fade slope. most studies have based on temperate region measurements [1, 3 r p.1623 [8] has recommended a prediction model for fade slope base model [3, 4] measured at netherlands receiving signal from olympus satellite ( 26.78˚) on 12.5 30 ghz. the model was examined using data from other sites in the uk, france, belgium, italy, and the us [1]. however, some measurements [ have indicated the model is required to zones. this paper analyses rain fade slopes comparing between available model slope s parameters has also been focused and proposed on high elevation angle as a function of different fade levels 2. experimental setup experimental system has been monitored signal from measat 3 (geostationar e) at 10.982 ghz frequency (ku modulation provided 15 channels for malaysian direct broadcast satellite (dbs) pay television service (astro). the received signal level has been collected for 12 months perio table 1 have summarized experimental setup and system parameters, respectively at satellite communication lab, iium. fig. 1: experimental setup for measurement at ku satellite communications lab, iium. table ground station location beacon frequency satellite position polarization azimuth elevation angle antenna diameter nf of lnb g journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics 54 characteristics that assesses tracking speed contributing factor to fade mitigation various researchers have studied and proposed parameters and prediction models for rain fade slope. most studies have based on temperate region measurements [1, 3 r p.1623 [8] has recommended a prediction model for fade slope based on van de kamp model [3, 4] measured at netherlands receiving signal from olympus satellite ( 30 ghz. the model was examined using data from other sites in the uk, france, belgium, italy, and the us [1]. however, some measurements [9] in tropical zones have indicated the model is required to improve in order to correspond to different climate rain fade slopes characteristic on different sampling times and available model and measurement in kuala lumpur, malaysia. parameters has also been focused and proposed on high elevation angle as a different fade levels. experimental setup experimental system has been monitored signal from measat 3 (geostationar e) at 10.982 ghz frequency (ku-band), vertical polarization with qpsk modulation provided 15 channels for malaysian direct broadcast satellite (dbs) pay television service (astro). the received signal level has been collected for 12 months have summarized experimental setup and system parameters, respectively at te communication lab, iium. experimental setup for measurement at ku-band signal over earthsatellite communications lab, iium. table 1: system parameters of the link. ground station location 3.3°n, 101.7°e beacon frequency 10. 982 ghz (if = 1.232ghz ) satellite position 91.5° e (measat 3) vertical 253° elevation angle 77.4° antenna diameter 2.4 m 0.3 db 1 on science and ethics in engineering dao et al. characteristics that assesses tracking speed contributing factor to fade mitigation various researchers have studied and proposed parameters and prediction models for rain fade slope. most studies have based on temperate region measurements [1, 3-7]. itud on van de kamp model [3, 4] measured at netherlands receiving signal from olympus satellite (el = 30 ghz. the model was examined using data from other sites in the uk, 9] in tropical zones improve in order to correspond to different climate characteristic on different sampling times and measurement in kuala lumpur, malaysia. fade parameters has also been focused and proposed on high elevation angle as a experimental system has been monitored signal from measat 3 (geostationar band), vertical polarization with qpsk modulation provided 15 channels for malaysian direct broadcast satellite (dbs) pay television service (astro). the received signal level has been collected for 12 months . fig. 1 and have summarized experimental setup and system parameters, respectively at -space path at iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering dao et al. 55 signal from measat3 has been received by 2.4 m diameter of parabolic dish antenna with low noise block (lnb), 0.3 db noise figure. the signal is down converted to intermediate frequency (if) as l-band with local oscillator (lo) 975 mhz. the subsequent if is sent to spectrum analyzer setting post-detection bandwidth (video bandwidth) of 10 hz [10] to monitor carrier signal and remove spurious noise. consequent output signal from spectrum analyzer is logged and saved in databank by using software developed with sampling time interval of 1s. in addition, rainfall rate is also measured synchronously by 0.2mm-tipping bucket rain gauge every 10s time interval. 3. fade slope model proposed by itu-r itu-r has proposed statistical distribution model of fade slope developed by van de kamp [1, 11] that depends on cutoff frequency, attenuation and sampling time. the proposed prediction model of probability density function (pdf) is shown eq. 1, ( ) ( )( ) ( ) 1 22 / 1 2 | − + = sdbap ξς σξπσ ξ (1) where ξσ is the standard deviation of the conditional fade slope at a given attenuation level given by, db/s),( atffs b ∆=ζσ (2) where ( ) bbbb b tf tff /1 2 )2(/1 2 ),( ∆+ π =∆ (3) with b = 2.3, fb is the 3 db cutoff frequency of the low pass filter (hz), and s parameter is from experiment as derived above. 4. data pre-processing 4.1 clear sky reference level finding out zero db reference level from clear sky on measurement of satellite signal attenuation is a fundamental trouble requirement. defining clear sky reference level by hourly averaging after and before raining days [12]. raining events were determined on 10s interval time for tipping bucket type of rain gauge. the number of data points (second) during raining events used to generate fade slope for each attenuation values are shown in fig.3. it is obvious that the number of occurrences decreases with attenuation levels. fig. 3: number of time series (second) extracted from data measured from july 1, 2010 to june 30, 2011. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering dao et al. 56 4.2 rain attenuation and scintillation extraction attenuation time series during raining events are contaminated by fast fluctuations due to tropospheric scintillation. therefore, tropospheric scintillation is essentialy decimated prior to proceed next processes [13]. power spectral density (psd) is efficient technique in order to separate propagation due to scintillation and rain attenuation by specifying appropriate cutoff frequency (fc) [14, 15]. high pass filter (hpf) order 6 th of digital butterworth filter with cutoff frequency of 0.025 hz [16] obtained by the psd function and has been implemented to remove fast fluctuation due to scintillation. 5. data analysis and results fade slopes are calculated for each attenuation level thresholds after tropospheric scintillation has been decimated. each attenuation level (db), a is calculated when dbataa 5.0)(5.0 +≤<− , then fade slope is calculated by eq. (4) ( ) ( ) ( ) ( )sdb t tiatia t ∆ ∆−−∆+ = 2 δ (4) where ∆t is sampling time, 1s and i is sample number. 5.1 comparison between measured data and prediction model once fast fluctuation due to tropospheric scintillation has been decimated from the signal, fade slope has been calculated from eq. 4. the prediction model has been calculated by eq. 1 using fb 25 mhz obtained from the experiment, ∆t 1s and s = 0.01 (itu-r proposed). comparison of measurement and model has been depicted in fig. 4. fig. 4: pdf comparison between fitting of measured data (solid line) and itu-r (dash line) model for 1s sampling time. 5.2 investigation of standard deviation rain fade slope characteristic has been investigated to evaluate the parameters for itu-r [8] based on the measured data. principal parameters analysis was focused on standard deviation (σζ) with different attenuation thresholds. the measured standard deviation and the model have been presented as a function of attenuation thresholds in fig. 5 (a). measured σζ indicated that keeps increasing with attenuations from 0.0038 db/s and reaching maximum 0.018 db/s at 6db attenuation and subsequently reducing until 0.0079 iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering dao et al. 57 db/s at 10 db. standard deviation, σζ was estimated by itu-r prediction model indicated that σζ increased linearly with attenuation levels. (a) (b) fig. 5: (a)comparison of standard deviations between measured data (solid line) and predicted by itu-r prediction models (dash line), (b) the measured value of s as a function of attenuations between measurement (solid line) and zero offset fit (zof) (dash line). 5.3 proposed standard deviation itu-r prediction model has been proposed σζ which depends on fb, ∆t and parameter s. parameter s is a constant which depends on climate and elevation angle which affect to σζ of itu-r model. itu-r has proposed the constant averagely at 0.01 in europe and usa at elevation angle between 10�-60�. but there is no model proposed in tropical region and on high elevation angle. therefore, s is needed to derive in order to propose for the model on this region and high elevation angle. parameter s is obtained by eq. (5) using σζ from the experiment and has been presented by fig. 5(b). atff s b ),( ∆ = δ σ (5) thus, determination of empirical s is implemented by zero offset fit (zof) [2, 3, 4] yielded 0.0023 to propose in the model for this characteristics. 5.4 comparison with the model statistical distribution comparisons between measurement and model with different parameter s have been depicted in fig. 6(a) and 6(b) as a function of attenuations. figure 6 illustrates fade slope distribution comparison between measured data and the propoaed model. the models are drawn s parameters as applying zero offset fit (zof) method. pdf’s predicted by zof is closer fit with the measurement for attenuation between 1db6db. for attenuation higher than 6db, the model shows wider with attenuations while the measurement showd narrower with attenuations corresponding to standard deviations. table 2: descriptive pdf statistics comparison between measurement and models. attenuation (db) 1 3 6 8 10 mean measured 3.311 3.308 3.306 3.31 3.311 zof 3.357 3.311 3.31 3.309 3.307 sd measured 17.42 13.181 7.785 8.747 12.548 zof 25.123 13.626 9.345 7.921 6.929 skewness measured 6.403 5.24 2.859 3.19 4.702 zof 9.864 5.105 3.419 2.85 2.449 kurtosis measured 43.185 28.818 7.413 9.573 22.645 zof 105.662 26.963 11.22 7.316 4.996 iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering dao et al. 58 (a) (b) fig. 6: pdf comparison among measurement and model with different values of sparameters of (a)1db to 5db attenuations and (b) 6db to 10db attenuations levels. 6. conclusion rain fade was measured in kuala lumpur (3.3 0 n, 101.7 0 e) at 10.982 ghz (kuband) from measat3 (91.5 0 e) on 77.4 0 elevation angle. the measurement has been carried out for one year period. fade slope s parameter on itu-r prediction model has been investigated based on data processed with 1 sec integration time. the probability distribution functions proposed by itu-r with parameter s = 0.01 are much wider than the measurement for all attenuation levels. the value of s parameter is evaluated using implemention of zero offset fit (zof) with measured data. the new value of s = 0.0023 is proposed in the fade slope prediction model for high elevation angle, ku-band in tropical regions. acknowledgement the authors are very grateful to the research management centre (rmc), international islamic university malaysia (iium) for research grant supporting this project. references [1] l. castanet and m.v. de kamp, “modelling the dynamic properties of the propagation channel”, 5th management committee meeting of the cost 280 action, may 2003 [2] chambers, a.p., callaghan s.a. and otung, i.e., “analysis of rain fade slope for ka and vband satellite links in southern england”, ieee transac. on antenna and propagation, vol.54, no.5, may 2006. [3] m.j.l. van de kamp, “statistical analysis of rain fade slope”, ieee transac. on antenna and propagation, vol.51, no.8, august 2003 [4] m.m.j.l. van de kamp, “climatic radiowave propagation models for the design of satellite communication systems”, ph.d. thesis, eindhoven university of technology, eindhoven, the netherlands, isbn 90-386-1700-3, section 4, 1999. [5] e. matricciani, “rate of change of signal attenuation from sirio at 11.6 ghz”, electron. lett., vol.17, no.3 ,1981 [6] p.d. baxter, g.j.g. upton and d. eden, “revise method for calculation of rain-fade-slope”, electron. lett. vol. 37, no. 10, 2001 [7] stutzman w.l., pratt. t., safaai-jazi a., laster j., nelson b. and ajaz h. “results from the virginia tech propagation experiment using the olympus satellite 12, 20 and 30 ghz beacons”, ieee transac. on antenna and propagation, vol.43, no.1, january 1995. [8] itu-r p.1623, “prediction method of fade dynamics on earth-space paths”, itu, geneva, switzerland, 2003. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering dao et al. 59 [9] f.f. franklin, k. fujisaki, and m. tateiba, “fade dynamics on earth-space paths at kuband in fukuoka, japan fade-slope evaluation, comparison, and model”, ieee antenna and wireless propagation letters, vol. 5, 2006. [10] adhikari a. and maitara a., “studies on the inter-relation of ku-band scintillations and rain attenuation over an earth–space path on the basis of their static and dynamic spectral analysis”, journal of atmospheric and solar-terrestrial physics (jastp), volume 73, issue 4, november 2010. [11] h. dao, md. r. islam, k. al-khateeb, “fade dynamics review of microwave signals on earth-space paths at ku-band”, international conference on computer and communication engineering proceeding, may 2008. [12] y. maekawa, t. fujiwara, y. shibagaki, t. sato, m. yamamoto, h. hashiguchi, and s. fukao “effects of tropical rainfall to the ku-band satellite communications links at the equatorial atmosphere radar observatory”, journal of the meteorological society of japan, volume 84a, 2006. [13] mr islam, h. dao and ah zayuod, “rain fade slope analysis for terrestrial microwave link in malaysia”, 9 th malaysia international conference on communications (micc) proceeding, december 2009. [14] y. karasawa , t. matsudo, “characteristics of fading on low-elevation angle earth-space paths with concurrent rain attenuation and scintillation”, vol.39, no.5, may 1991. [15] i.e. otung, m.o. al-nuaimi, and b.g. evans, “extracting scintillations from satellite beacon propagation data”, ieee transac. on antenna & propagation, vol.46, no.10, october 1998. [16] h. dao, mr. islam, k. al-khateeb, “preliminary analysis of ku-band rain fade data for earth-to-satellite path measured in malaysia”, 10 th malaysia international conference on communications (micc) proceeding, october 2011 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 154 numerical analysis of tunnel led lighting maintenance factor mehmet sait cengiz1*, çiğdem cengiz2 1 dept. of technical vocational school, bitlis eren university, bitlis, turkey 2 faculty of arts and sciences, statistics department, bitlis eren university, bitlis, turkey *corresponding author: msaitcengiz@gmail.com (received: 9th oct 2018; accepted: 7th nov 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19i2.1007 abstract: it is necessary to periodically maintain lighting equipment in accordance with international standards. contamination of lamps caused by long-term use of lighting equipment will result in loss of luminous flux and optical losses. the decrease in lighting performance poses a visual difficulty for drivers and causes accidents. in this study, the total maintenance factor is numerically examined by considering the losses of diffuser and lens for led lamps used in tunnel lighting. the variation of luminaries performance with years considering maintenance factors as regards environmental conditions and features of the luminaries is evaluated to demonstrate the importance of tunnel lighting maintenance. moreover, to show the importance of led lamps maintenance factor, the variation of illumination levels of led lamps is analysed under different maintenance factors. it is observed that enhancing maintenance factor would contribute to energy efficiency. abstrak: penjagaan peralatan cahaya secara berkala mengikut piawai kebangsaan adalah amat penting. pencemaran lampu disebabkan penggunaan peralatan cahaya pada jangka panjang akan menyebabkan kehilangan kilauan kerdipan lampu dan optik. pengurangan pencahayaan ini menyebabkan kesukaran pandangan pada pemandu dan menyebabkan kemalangan jiwa. kajian ini mengkaji tentang jumlah faktor penjagaan secara numerik dengan mengambil kira pengurangan difuser dan kanta pada lampu led yang digunakan dalam terowong pencahayaan. faktor penjagaan pada perubahan kilauan berdasarkan tahun mengambil kira keadaan sekeliling dan ciri khas kilauan. tambahan, ini dinilai bagi menunjukkan kepentingan penjagaan terowong pencahayaan dan kepentingan faktor penjagaan lampu led. perubahan pada tahap terang pada lampu led dikaji dengan mengambil kira faktor penjagaan. peningkatan pada faktor penjagaan telah didapati dapat menjimatkan tenaga. key words: maintenance factor, led lamps, luminaries performance, numerical analysis, and tunnel lighting. 1. introduction luminaries and operating conditions are the most important parameters in lighting. environmental factors account for the loss in the efficiency of luminaries, as dirty luminaries have reduced luminous transmittance. in addition, operating time affects the efficiency of lamps. the performance of luminaries decrease over the time; thus, the performance of a lamp for a specified period of time can be specified. the performance of luminaries during a period of time may be improved by maintenance processes such as cleaning the glass of luminaire or replacing of the lamp [1-4]. moreover, renewal of all luminaries will also iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 155 improve performance. by considering the estimated performance loss at the system design phase, lighting systems would be able supply the minimum required lighting even at the end of the period when it exhibits the lowest performance [5]. fig. 1 illustrates the tolerance range associated with maintenance factor (mf) as regards performance loss. fig. 1. tolerance range associated with maintenance factor as regards performance loss [5]. maintenance factor is a parameter that specifies the performance to be supplied by a lighting system at the end of a certain period depending on the performance at the beginning of the period. maintenance factor is described as 80% for a system for which 20% of performance loss is estimated at the end of maintenance period. since mf is used as a multiplier in programs of lighting calculation, lighting levels reached by lighting calculations display the values at the end of a certain period [7-13]. maintenance factor varies with the technology level of luminaries. according to cie 154:2003, the mf of luminaries is formed by the product of multiple indicators of performance [6]. it depends on the protection degrees of the luminaries against contamination (ip65: completely dust prof, protect against water jets), sources of light used in luminaries and all effects that can cause decrease in illumination [6]. 2. lumi̇nous flux numerical calculation luminous flux is the proportion of flux blazing through a lamp that affects the optic. its unit is lumen, and it represents ability of radiation to stimulate a sense of radiance. furthermore, total luminous flux is described as the sum of luminous fluxes arising from a source and spreading over various parts of the space. the total luminous flux falling within a unit surface is defined as the illumination level of that surface, and it is represented by e. its unit is lux. the radiant power of a lux is equal to a candle light [5]. the illumination level of a point p and the geometrical representation of the illumination level of the point is illustrated in equation 1 and fig. 2, respectively. equation 3 demonstrates the relationship between maintenance factor and lighting level. 3 2 1 ( , ) .cos a p i i c e h      (1) iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 156 fig. 2. the tolerance range associated with maintenance factor as regards performance loss [5]. where, i (c,γ): is value of light intensity reaching from luminaire i to point p (cd), γ: is angle of gleam falling within point p by the vertical line, a: is the amount of luminaires contributing to point p, h: is ground clearance of luminaire photometric center (m) c: is plane angle. 3. maintenance factor for luminaires, maintenance factor is defined as the proportion of total light coming from a luminaire at the end of the maintenance period in relation to the total light of the luminaire during its primary use. following the standards associated with the use of mf in lighting, the specifications of lighting equipment in a lighting system are given considering environmental conditions and the maintenance factor calculated for a specified maintenance period cie 154:2003. according to cie 154:2003, lighting performance should not drop below the minimum levels specified in the standards. maintenance factor comprise lamp lumen maintenance factor (llmf), lamp survival factor (lsf), and luminaire maintenance factor (lmf). lamp lumen maintenance factor is the proportion of the luminous flux of a lamp at the end of a specified period in relation to the initial luminous flux. lamp survival factor is the percentage of lamp survival ratio for maintenance factor. luminaire maintenance factor (lmf) is the proportion of luminous flux lost at the end of described/specified period as a result of the structural features of luminaires as well as environmental factors. the lmf depends on the protection degree of luminaires against contamination (ip) and environmental pollution. it is specified by the designer according to the contamination condition of the environment during maintenance period or a relevant specification is consulted [5]. maintenance factor is calculated according to equation 2. mf llmf x lsf x lmf (2) 3 2 .cos . .i mf e h    (3) iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 157 4. tunel led lighting and maintenance factor relationship in this study, led lamp luminaires dually inserted 6 m high used in a tunnel are investigated. the mf for led lamp luminaires is the product of the three main factors described above. the mf of an led lamp luminaire with protection degree ip65 is numerically determined. fig. 3 illustrates a sample of tunnel led lighting with double suspensions [5]. fig. 3. a sample of tunnel led lighting with double suspensions. the time intervals for maintenance (by replacing led lenses and diffusers) should be specified by the environment pollution level in the site where lighting system will be installed for tunnel lighting. according to the principle of maintenance yearly followed and an environmental condition of high level of pollution, the luminaire maintenance factor (lmf) depending on the contamination of a luminaire with protection degree ip65 is specified as 0.91 in report cie 154 [6]. luminaire maintenance factor according to protection degree of luminaire and the category of environmental pollution is illustrated in table 1. table 1: luminaire maintenance factor according to protection degree of luminaire and the category of environmental pollution is [5] optical compartment ip rating pollution category exposure time [years] 1.0 1.5 2.0 2.5 3.0 ip2x high 0.53 0.48 0.45 0.43 0.42 medium 0.62 0.58 0.56 0.54 0.53 low 0.82 0.80 0.79 0.78 0.78 ip5x high 0.89 0.87 0.84 0.80 0.76 medium 0.90 0.88 0.86 0.84 0.82 low 0.92 0.91 0.90 0.89 0.88 ip6x high 0.91 0.90 0.88 0.85 0.83 medium 0.92 0.92 0.89 0.88 0.87 low 0.93 0.93 0.91 0.90 0.90 iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 158 4.1 llmf table 2 illustrates the llmf of an led lamp with a service life of 70000 hours. table 2: llmf of led lamp according to operating time in years years duration of study llmf% 1 8.766 0.980 2 17532 0.955 3 26.298 0.930 4 35.064 0.905 5 43.830 0.875 6 52.596 0.845 7 61.362 0.825 8 70.128 0.800 lenses are generally used to direct beams transmitted from led light sources towards the area to be lighted. unlike traditional reflector systems, the luminous transmittance of lenses decreases over time. time-dependent performance criteria of luminaries have been specified by iec 62722-2-1 and iec-62717. according to these criteria, confirmation tests of led modules and led luminaries were carried out considering 6000 hours maximum [14-16]. fig. 4 illustrates optical variance caused by use of led lens at uv/65°c for 6000 hours. fig. 4. optical variance caused by use of led lens at uv/65°c for 6000 hours. when determining mf in led luminaries in which lenses are used as a collimator, losses of 5% should be considered. in this study, it was assumed that lenses were used and that the luminous transmittance of the lenses would change by at least 5% over the considered time. table 3 illustrates the total llmf (%) of an led lamp exposed to optical effect. table 3: total llmf (%) of an led lamp exposed to optical effect. years duration of study llmf% optical effect % total llmf% 1 8.766 98.00 5 93.00 2 17532 95.50 5 90.50 3 26.298 93.00 5 88.00 4 35.064 90.50 5 85.50 5 43.830 87.50 5 82.50 6 52.596 84.50 5 79.50 7 61.362 82.50 5 77.50 8 70.128 80.00 5 75.00 iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 159 the decrease in luminous flux depending on the operating time of lamps was obtained from the catalogue of the producing company [17]. figure 5 presents the image as obtained from the catalogue. the figure displays the performance loss of led lamps, which lights the tunnel for 24 hours, depending on operating time. the decrease in luminous flux was determined as 7%, 9.5%, 12%, 14.5%, 17.5% and 20.5% at the end of operating times of 1, 2, 3, 4, 5 and 6 years, respectively. fig. 5 displays the decrease in luminous flux depending on the operating time of led lamps. fig. 5. decrease in luminous flux depending on the operating time of led lamps. 4.2 lsf in operation strategy, lsf = 1 is accepted in a case where each attenuated lamp is replaced as early as possible. however, since in general lamping applications, it is not possible to replace broken lamps in a short time, lamps are replaced periodically and collectively. all lamps are replaced in a period of attenuation by 10% in an area where 10% is accepted as the maximum ratio of the prescribed attenuation of lamps to replace lamps collectively. fig. 6 displays the line of lsf for led lamps. fig. 6. line of lsf for led lamps. table 4 illustrates the lsf (%) of led lamp according to operating time in years. iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 160 table 4: lsf (%) of led lamp according to operating time in years. years duration of study lsf% 1 8.766 98.75 2 17532 97.50 3 26.298 96.25 4 35.064 95.00 5 43.830 93.75 6 52.596 92.50 7 61.362 91.25 8 70.128 90.00 according to the lsf of the led lamp, 10% attenuation rate occurred after eight years. this demonstrates that it is not possible to use the lamp more than eight years. table 5 illustrates the mf and minimum luminance level required for tunnel lighting with led lamps. table 5: mf and minimum luminance level required for tunnel lighting with led lamps. years ip65high pollution lmf lsf total llmf mf (mf=lmf*lsf*llmf) e% 1 0,91 0,9875 93 0,8357 1,1966 2 0,91 0,975 90,5 0,803 1,2454 3 0,91 0,9625 88 0,7708 1,2974 4 0,91 0,95 85,5 0,7391 1,3529 5 0,91 0,9375 82,5 0,7038 1,4208 6 0,91 0,925 79,5 0,6692 1,4943 7 0,91 0,9125 77,5 0,6435 1,5539 8 0,91 0,9 75 0,6143 1,628 the led lamp investigated in this study has a service life of 70000 hours. this period corresponds to an operating time of about eight years. as seen in figure 4, the led lamp cannot be used when luminous flux decreases by 20%, that is, drops below 80%. the luminous flux of the led lamp would decrease by 20% after eight years (70000 hours) when led lens and diffuser effect are neglected. it is seen in table 2 that the llmf (%) of the led lamp is 80% in the eight year. the 5% loss is formed by time-dependent decrease in the luminous flux of the lenses used in directing led light. when this effect is considered in table 2, table 3 is reached. according to table 3, llmf is 80% in the sixth year. in other words, the led lamp cannot be used after six years because it is indicated in the producer’s catalogue that the led lamp should not be used if llmf decreases to below 80%. the operating time of the led lamp decreased from eight years to six years when the effect of optical lens was not considered. iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 161 4.3 tunnel lighting evaluation fig. 7. illustrates the optic performance change depending on operating for led luminaires. fig. 7. optic performance change depending on operating for led luminaires according to figure 7, • while mf decreases to 83.57% at the end of the first year, mf increases to 91% by replacing led lenses and diffusers • while mf decreases to 80.30% at the end of the second year, mf increases to 88% by replacing led lenses and diffusers. • while mf decreases to 77.08% at the end of the third year, mf increases to 83% by replacing led lenses and diffusers. • at the end of the sixth year, mf decreases to 66.92%. this indicates that all lamps should be replaced as cleaning the luminaire glasses is not sufficient. all lamps were changed since the decrease in illumination level cannot be tolerated as a result of the decrease in luminous flux at the end of the sixth mf year. according to these results, the following comments can be made: considering that the led lenses and diffusers for this lighting system will be replaced every six years and all the lamps will be replaced in the sixth year, to realize an illumination level of 100% at the end of the six-year period, an initial illumination level of additional 49.43% is required (1/0.6692 = 1.4943). the illumination level in interior zone of the tunnel is required to be 149.43 rather than 100 since the illumination level of the led lamps will decrease from 149.43% to 100% at the end of the six-year period. if the tolerance margin of 49.43% is not allowed, then iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 162 illumination deficiencies can cause accidents as they can adversely affect the visual condition in the tunnel. 5 conclusion it is seen in this study that an led lamp for tunnel lighting may have a service life lasting for 70000 hours. when examining the usage features of the led lamps used in the tunnel, it is seen that the lsf and llmf are 90% and 80% in the eighth year, respectively. moreover, 80% was reached at the end of the sixth year when optical led lens and diffuser effects are considered in the llmf. the conditions related to the use of led lamps in the tunnel were determined by llmf, which considers the lens and diffuser effects since the llmf decreased to below 80% at the beginning of the seventh year, the visual conditions in the tunnel will deteriorate at the seventh year, which may result to accidents. the mf at the end of the sixth year was calculated as 66.92% according to conditions. the total luminous flux (e%) is required to be higher by 49.43%, according to the lowest mf formed at the end of the year. efficiency will increase when mf is high. in addition, led lamps are not required to be replaced frequently and led lamps can be used for up to six years. references [1] cengiz, ms. mamiş ms. (2015) price-efficiency relationship for photovoltaic systems on a global basis, international j. photoenergy, (2015):1-12. [2] arı d, çıbuk m. ağgün, f. (2017) effect of relay-priority mechanism on multi-hop wireless sensor networks, bitlis eren university j. science and technology, 7(2):145–153, 2017. [3] cengiz ms, mamiş, ms, kaynaklı, m. (2017) the temperature-pressure-frequency relationship between electrical power generating in stirling engines, international j. engineering research and development, 9(2):59-64. [4] cengiz ms, mamiş ms, yurci y. (2018) providing electrical power increase by stimulating temperature difference at low temperatures in stirling motors, sigma j. engineering and natural sciences, 36(1):86-97. [5] cengiz ms, a simulation and design study for interior zone lumınance in tunnel lighting, light engineering (in press, may-jun 2019) [6] cie technical report, cie-154-2003. (2003) the maintenance of outdoor lighting systems. [7] çıbuk m, balık hh. (2010) a novel communication application model for biomedical networks, fırat univ. j. of enginering, 22 (1):95-109. [8] efe, s.b. (2016) effects of faults on power flow analysis for microgrids. 8th international ege energy syposium may 11-13, 2016. 971-976, afyonkarahisar. [9] efe sb, cebeci m. (2015) artificial neural network based power flow analysis for micro grids. bitlis eren university j. science and technology, 5(1):42-47. [10] cengiz ç, kaynaklı m, gencer g, eren m, yapıcı i, yildirim s, cengiz ms., selection criteria and economic analysis of leds, book of abstracts. imeset int. conf. mult. sci. eng. tech., october 27-29, 2017, bitlis, turkey. [11] eren, m., kaynaklı, m., yapıcı, i., gencer, g., yurci, y., cengiz, ç. numerical analysis of maintanance factor for tunnel and road in solid state lighting”, international conference on multidisciplinary, science, engineering and technology, october 27-29, 2017. bitlis. [12] yıldırım s, yapıcı i, atiç s, eren m, palta o, cengiz ç, cengiz ms., yurci y, numerical analysis of productivity and redemption periods in led illimunation. imeset book of abstracts, int. conf. mult. sci. eng. tech., 12-14 july 2017, baku. [13] cengiz ms, eren m, cengiz ç, yıldırım s, yapıcı i̇, yurci y, atiç s, palta o, numerical analysis of warming and warming problem in led lamps. imeset international conference baku book of abstracts, 12-14 july 2017. baku [14] iec 62717, (2014) led module for general lighting. performance requirements, 2014 iium engineering journal, vol. 19, no. 2, 2018 cengiz et al. 163 [15] iec 62722-2-1, (2014) luminare perforamnce part 1 general requirements, 2014 [16] iec 62722-1, (2014) luminaire performance–part 2-1 : particular requirements for led luminaries, 2014 [17] myled lighting-revision 2-2018, available:https://www.myledlightingguide.com/led-streetlight-40w-240w (07/01/2018) https://www.myledlightingguide.com/led-street-light-40w-240w https://www.myledlightingguide.com/led-street-light-40w-240w application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 kakde et al. 128 implementation of decoding architecture for ldpc code using a layered min-sum algorithm sandeep kakde 1* , atish khobragade 1 , shrikant ambatkar 1 and pranay nandanwar 1 1 department of electronics, faculty of engineering, yeshwantraochavan college of engineering, nagpur, india. *corresponding author: sandip.kakde@gmail.com (received: 25 th april 2016; accepted: 3 rd april 2017; published on-line: 1 st dec. 2017) abstract: ldpc codes provide remarkable error correction performance and therefore enlarge the design space for communication systems. this paper shows comparison of different digital modulation techniques and found that bpsk modulation technique is better than other modulation techniques in terms of bit error rate. it also gives error performance of ldpc decoder over awgn channel using min-sum algorithm. vlsi architecture is proposed which uses the value re-use property of minsum algorithm and gives a high throughput. the proposed work has been implemented and tested on xilinx virtex 5 fpga.the matlab result of ldpc decoder for low bit error rate gives a bit error rate in the range of 10 -1 to 10 -3.5 at snr=1 to 2 for 20 iterations. thus, it gives good bit error rate performance. the latency of the parallel design of the ldpc decoder has also decreased. it has attained a maximum frequency of 141.22 mhz and throughput of 2.02 gbps while consuming less area. abstrak: kod ldpc adalah sistem prestasi pembetulan ralat yang luar biasa dan dengan ini meluaskan peluang reka sistem komunikasi. kertas ini menyediakan perbandingan perbezaan pelbagai teknik digital modulasi dan didapati teknik modulasi bpsk adalah lebih baik daripada teknik modulasi lain dalam bentuk kadar ralat bit (bit error rate). ia juga memberi prestasi ralat ldpc penyahkod yang bagus berbanding saluran awgn menggunakan algoritma min-sum. struktur vlsi telah dicadangkan dengan mengguna semula nilai pakai dan menghasilkan nilai penghantaran yang tinggi. kerja cadangan ini telah dibina dan diuji mengguna xilinx virtex 5 fpga. keputusan matlab penyahkod ldpc bagi kadar ralat bit telah berhasil pada kadar 10 -1 to 10 -3.5 dan snr=1 kepada 2 dengan 20 kali iterasi. jadi ia berhasil memberikan prestasi kadar ralat bit yang bagus. latensi pada reka serentak ldpc penyahkod juga telah menurun. ia berhasil mencapai 141.22 mhz frekunsi maksimum dan penghantaran sebanyak 2.02 gbps pada luas kawasan yang sedikit. keywords: low-density parity-check (ldpc) codes; min-sum algorithm (msa); tdmp;offset min-sum algorithm (oms); bit error rate (ber); snr; awgn 1. introduction currently, low density parity check codes (ldpc) have gained major attention because of their performance near to the shannon limit and remarkable error correction capability. ldpc codes were invented by gallager in 1962 [1] and got more attention when they were rediscovered by mckay and neal in 1996 [2]. ldpc codes can achieve very low bit error rate (ber) for low signal to noise ratio (snr) applications [1]. ldpc codes has got several advantages such as low hardware complexity, inherit parallelism, no iium engineering journal, vol. 18, no. 2, 2017 kakde et al. 129 error floor at high snrs and high throughput potential. they have been used in several wireless standards such as ieee 802.16e, ieee 802.11n and dvb s-2 because of their excellent error correcting performance. a ldpc code is a linear block code which is defined by a sparse parity check matrix (h-matrix), as shown in fig 1. in matrix representation, consider a parity check matrix with n x m dimension. 1 1 1 0 0 0 0 0 0 0 0 1 1 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 h             fig. 1: example of parity check matrix. consider wr as weight of rows (i.e. number of 1‟s in each row) and wc as weight of columns (i.e. the number of 1‟s in each column). now for the matrix to be called a lowdensity matrix two conditions must be satisfied: wc<<n and wr<<m. they can be represented by a bipartite graph also called a tanner graph, shown in fig 2. a tanner graph contains two sets of nodes, bit nodes and check nodes. bit nodes represent the bits of a codeword and check nodes apply the parity-check constraints. between each bit node „i‟ and check node „j‟, there exists an edge only if h(i,j)=1. fig. 2: tanner graph. message passing algorithms, known as “sum-product” (sp) and “belief propagation” (bp) provide the standard decoding procedure, that iteratively exchange the message bits between the check nodes and the bit nodes along the edges of the tanner graph. based on the number of the processing units, there are various ways to implement the ldpc decoder. in general, they can be classified into three types: fully parallel architecture [3], serial architecture [4], and partial parallel architecture [5-7]. in serial architecture, one check node processor shares the computation of all the check nodes and thus it is very slow. in fully parallel architecture, every check node requires a check node processor for its operations which results in very large hardware, complex routing and is therefore less flexible. the ldpc decoder‟s implementation requires a balance between factors such as iium engineering journal, vol. 18, no. 2, 2017 kakde et al. 130 error correction performance, decoding throughput, and the hardware complexity. hence, partial parallel architecture is the best suited because multiple processing units are provided that allows proper trade-off between the hardware complexity and the decoding throughput. lambda min-sum algorithm based architectural issues, described and based on a serial-parallel-serial schedule based architecture is proposed in the paper [8]. chen and fossorier had given a performance comparison for different check updates [9,10]. in their research they showed that the offset min-sum decoding algorithm with 5-bit quantization could achieve the same ber performance as that of floating point sum-product and jacobian-based bcjr algorithm (named after its discoverers bahl, cocke, jelinik, and raviv) with less than 0.1 db penalty in snr). layered decoding can be done in two ways i.e. vertical layered decoding [11] and horizontal layered decoding [12, 13]. theoretically, both the methods are equivalent and prove that both can converge twice as fast as the belief propagation algorithm [14]. for min-sum algorithm, horizontal layered decoding is preferable and hence used in this paper. a different and multi rate block length high throughput architecture is proposed in the paper [15, 16]. 2. min-sum decoding algorithm assuming the codeword (a1,a2,a3,…,an) was sent over awgn channel and received as (b1,b2,b3,….,bn). a minimum sum algorithm can be summarized as follows:  variable nodes are first initialized with soft information bits, also called loglikelihood ratio (llrs) from channel. after the initialization, each bit node updates its corresponding check nodes with bits to check the message. (1) where qij is message from bit node v(i) to check node c(i).  check node update: check node messages are calculated using the q message received from the bit node as follows: ∏ | (2) where rij is the message from the check node c(i) to the bit node v(j). while calculating the for , check node processing needs to exclude v(j) therefore it is necessary to find two minima i.e. 1 st minimum (min1) and 2 nd minimum (min2). more precisely 'min ijq can be defined as { (3)  bit node update: bit nodes calculate variables to check messages, qij, using its old value and received rij message from all neighboring check nodes: ∑ (4) iium engineering journal, vol. 18, no. 2, 2017 kakde et al. 131 same as in case of check to bit messages, message from bit node v(i) to check node c(j) is calculated using all r message from neighboring check nodes except r message from check node c(j).  after bit node update is finished, for each bit the reliability value is calculated as in eq.(4) but with all r values received from neighboring check nodes as given in eq.(5) ∑ (5) from above equation ,the y vector is y = (y1, y2, y3,…,yn) fig. 3: flowchart of min-sum algorithm. bit values are calculated by { (6) now if h x z t = 0, then z is a valid code and the decoding process stops here, or else the decoding process continues until a valid code is obtained or until it reaches the maximum number of iterations count, resulting in the output of an error flag and proceeding for decoding of the next data frame. 3. decoder architecture and operation the architecture for the ldpc decoder is given in fig. 4. basically, the working of the decoder can be defined as two-state processing i.e. bit node processing and check node processing. the check node and the bit node processing are done in a time division multiplexed way. it takes m clock cycles to process a block row i.e. a layer. the check node processing unit (cnu) used here is a serial cnu. the working of the cnu can be explained from fig 5. incoming variable messages (q messages) are compared with the two up-to-date least minimum numbers stored in a partial state to generate the new partial state i.e. first minimum (m1), second minimum (m2), and iium engineering journal, vol. 18, no. 2, 2017 kakde et al. 132 the index of m1. the function of the min finder block is to find the first and the second minimum value. the offset block applies the offset correction and stores the values in the final state block. the final block contains three values m1, -m1, and +/-m2. the r-select block then assigns one of these 3 values to output r messages based on the r-sign value, which is obtained from xoring of the sign of r, and the index of m1. normally, bit node processing is done in 2‟s. complement arithmetic and the check node processing is done using signed magnitude arithmetic and therefore, here, 2‟s compliment is required, at the input of cnu, to perform sign conversion and at the output signed to 2‟s compliment. fig. 4: ldpc decoder architecture. fig. 5: flowchart of cnu block. the cnu array operates in pipelined mode on the partial states and the r messages of the adjacent block rows. the final state depends on the partial state, p and q messages are reliant on the final state. the final state of the previous block row is needed for passing the ldpc decoding message and this compact information for cnu is stored in the final state iium engineering journal, vol. 18, no. 2, 2017 kakde et al. 133 memory. partial state memory is required to store the partial states. the cnu array will initialize the partial state processing for succeeding block row as soon as the computation of the previous block row is over. the q messages that have been feed in the present block row depend on r messages of the current layer as well as the r messages belonging to different blocks of different layers, requiring the r selection process which can be obtained by the r-sel block. the r-sel block generates the r message for edges of a check node out of the three values stored in final state memory which is associated with the specific check node in a serial way. its working is the same as that of the r-select block in cnu. the flow chart of the cnu block is as shown in fig. 5. 4. matlab implementation results fig. 6: simulation result of ber versus snr (db) for different modulation techniques over awgn channel. firstly, simulation of bit error rate (ber) performance of various digital modulation techniques viz. qam, bpsk, qpsk and 8-psk over an awgn channel was shown, and demonstrated that the ber performance of bpsk is superior when compared to other digital modulation techniques, as shown in fig. 6. this is because in the bpsk modulation technique, only 1 bit per symbol is used for modulation and in case of qpsk it‟s 2 bits per symbol and for 8-psk it‟s 3 bits per symbol. as the number of bits per symbol is increased, the chances of getting an error in code also increases, hence the error rate increases. ber against snr performance of un-coded bpsk (theoretical and practical) and minsum algorithm over an awgn channel, as shown in fig. 7, is simulated in matlab software and found that min-sum algorithm shows exceptional ber against snr performance when compared with the un-coded bpsk. here, code length is 1000 and the maximum iterations is limited to 20. iium engineering journal, vol. 18, no. 2, 2017 kakde et al. 134 fig. 7: theoretical and practical ber versus snr performance of bpsk (un-coded) and using min-sum algorithm over awgn channel. (code length = 1000, code rate = 1/2, max iteration = 20) 5. verilog hdl implementation results table 1: device utilization summary for ldpc decoder (576-bits) ldpc decoder family:virtex5 target device: xc5vfx130t-2ff1738 features used available utilization no.of slice registers 1794 81920 2% no.of slice luts 1630 81920 1% no.of fully used lut-ff pairs 981 2443 40% no. of bufg/bufgctrls 1 32 3% table 2: comparison of the proposed ldpcdecoder with the state of the art implementations parameters [14] [15] [16] this work platform asic fpga fpga fpga tech./family 130 nm xilinx virtex-4 virtex-5 codelength 576~2304 648 1296 576 iterations 10, 15 5 15 10 luts -19332 36452 1630 throughput 133-928 mbps 127.36 mbps 1.1 gbps 2.02gbps iium engineering journal, vol. 18, no. 2, 2017 kakde et al. 135 throughput calculations throughput of the ldpc decoder is given by the formula where, fmax is the maximum operating frequency, nit is the number of decoding iterations, and θis the number of clock cycle required to complete one iteration. here the codelength is of 576 bits, from the synthesis result, the maximum operating frequency of decoder is 141.22 mhz, the number of decoding iterations required is 10, 4 clock cycles are required to complete one iteration, and throughput is 2.02 gbps. 6. conclusion this work provides the concept of implementing the ldpc decoder with a new check-node unit using a min-sum algorithm. the results show that the area of the proposed design is reduced from previous designs. the design is simulated in verilog hdl with xilinx 14.7 and in matlab for bit error rate performance. it can be concluded that the overall area needed for the design is less as compared to other design results of ldpc decoders. simulation has been carried out in matlab for different codelength and iterations assuming a binary phase shift-keying (bpsk) modulated signal transmitted over the awgn channel. the matlab result of the ldpc decoder for bit error rate gives a ber in the range of 10 -1 to 10 -3.5 at snr=1 to 2 for 20 iterations. therefore, it gives a good bit error rate performance. the latency of the parallel design of the ldpc decoder has also decreased. it has accomplished a 141.22 mhz maximum frequency anda throughput of 2.02 gbps while consuming less area (in terms of slice luts required) for the design. references [1] gallager r.(1962) low-density parity-check codes,” ire tans. inf. theory, 7:21-28. [2] mackay d, neal r. (1996) near shannon limit performance of low density parity check codes,” electron. lett., 32(18):1645-1646. [3] blanksby a, howland c. (2002) a 690-mw 1-gb/s 1024-b, rate-1/2 low-density paritycheck code decoder. ieee j. solid-state circuits, 37(3):404-412. [4] yeo e, pakzad p, nikolic b, anantharam v. (2001) vlsi architectures for iterative decoders in magnetic recording channels. ieee trans. magn., 37(2):748-755. [5] zhang t, parhi k. (2001) vlsi implementation-oriented (3,k)-regular low-density paritycheck codes. in proc. ieee workshop on signal process. syst. (sips), pp 25-36. [6] mansour m, shanbhag n. (2003) high-throughput ldpc decoders. ieee trans. very large scale integr. (vlsi) syst., 11(6):976-996. [7] wang z, cui z. (2007) low-complexity high-speed decoder design for quasi-cyclic ldpc codes. ieee trans. vlsi syst., 15(1):104-114. [8] guilloud eb, danger j. (2003) λ-min decoding algorithm of regular and irregular ldpc codes. in proc. 3rd int. symp. turbo codes and related topics, pp 451-454. [9] chen j, dholakia a, eleftheriou e, fossorier m, hu x-y. (2005) reduced-complexity decoding of ldpc codes,” ieee trans. commun., 53(8):1288-1299. [10] fossorier m, mihaljevic m, imai h. (1999) reduced complexity iterative decoding of lowdensity parity-check codes based on belief propagation. ieee trans. commun., 47(5):673680. iium engineering journal, vol. 18, no. 2, 2017 kakde et al. 136 [11] zhang j, fossorier m. (2005) shuffled iterative decoding. ieee trans. commun., 53(2):209-213. [12] gunnam kk, choi gs, yeary mb, atiquzzaman m. (2007) vlsi architectures for layered decoding for irregular ldpc codes of wimax, ieee international conference on communications, pp 4542-4547. [13] wu x, song y, cui l, jiang m, zhao c.(2010) adaptive-normalized min-sum algorithm. future computer and communication (icfcc), 2 nd international conference on, 2:661-663. [14] brack t, alles m, kienle f, when n.(2006) a synthesizable ip core for wimax 802.16e ldpc code decoding.in proc. ieee 17th int. symp.personal, indoor and mobile radio communications, pp 1–5. [15] itsara t, choomchuay s. (2012) a hardware design of ms/mms-based ldpc decoder. in electron devices and solid state circuit (edssc), 2012 ieee international conference on, pp 1-4. [16] predrag r, de baynast a, karkooti m, cavallaro jr. (2006) multi-rate high-throughput ldpc decoder: tradeoff analysis between decoding throughput and area. in personal, indoor and mobile radio communications, 2006 ieee 17th international symposium on, pp 1-5. [17] zhang j, fossorier m, gu d, zhang j. (2005) improved min-sum decoding of ldpc codes using 2-dimensional normalization," global telecommunications conference, globecom '05. ieee, pp1187-1192. [18] wei h, jianguo h, wu f. (2010) a modified min-sum algorithm for low-density paritycheck codes," wireless communications, networking and information security (wcnis), 2010 ieee international conference on, pp 449-451. [19] mahankal n, kakde s, khobragade a. (2016) ber evaluation of ldpc decoder with bpsk scheme in awgn fading channel, 9(40):397-404. [20] sun y, cavallaro jr. (2012) vlsi architecture for layered decoding of qc-ldpc codes with high circulant weight. ieee transactions on very large scale integration (vlsi) systems, pp 1063–8210. [21] kakde s, khobragade a. (2016) vlsi implementation of a rate decoder for structural ldpc channel codes. procedia computer science, 79:765-771. [22] kakde s, khobragade a. (2016) hdl implementation of an efficient partial parallel ldpc decoder using soft bit flip algorithm. international journal of control theory and applications, 9(20):75-80. [23] kakde s, khobragade a, ekbal husain md. (2016). fpga implementation of decoder architectures for high throughput irregular ldpc codes. indian journal of science and technology, 9(48):1-6. [24] scholl s, schläfer p, when n. (2016) saturated min-sum decoding: an “afterburner” for ldpc decoder hardware. in design, automation & test in europe conference & exhibition (date), pp 1219-1224. microsoft word paper v4-1-1.doc iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 1 enhanced coagulation efficiency of moringa oleifera seeds through selective oil extraction suleyman a. muyibi*, saad a. abbas**, megat johari m. m. noor**, fakrul razi ahmadun*** *department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak 53100 kuala lumpur malaysia. **department of civil engineering, faculty of engineering, universiti putra malaysia, serdang, selangor, malaysia. ***department of chemical and environmental engineering, faculty of engineering, universiti putra malaysia, serdang, selangor malaysia. email: suleyman@iiu.edu.my or engrmuyibi@yahoo.com abstract: in this laboratory based study, varying quantities of oil, corresponding to 20 % w/w, 25 % w/w and 30 % w/w kernel weight extracted from moringa oleifera seeds ( s1, s2, s3) respectively were applied in the coagulation of model turbid water (kaolin suspension) and turbid river water samples from river batang kali and river selangor in malaysia to determine the percentage oil removed which gave the best coagulation efficiency. for model turbid water (kaolin suspension) coagulation of low turbidity of 35 ntu, medium turbidity of 100 ntu and high turbidity of 300 ntu, sample s2 gave the best turbidity removal corresponding to 91.7%, 95.5% and 99% respectively. application of sample s2 to river batang kali with low initial turbidity of 32 ntu and high initial turbidity of 502 ntu gave a highest turbidity removal of 69% and 99% respectively. application to river selangor with medium initial turbidityof 87 ntu and high initial turbidity of 466 ntu gave a highest residual turbidity' of 94% and 98.9%, respectively. key words: moringa oleifera seed, selective oil extraction, coagulation, model turbid water (kaolin suspension), river water, turbidity removal. 1. introduction many researchers have reported on various uses of moringa oleifera seed extract as a primary coagulant in turbidity removal [1-3]. previous studies have focused mainly on the efficiency of moringa oleifera seed extract as a coagulant [4-6]. some researchers have focused on the physical factors affecting the use of moringa oleifera seeds in the coagulation of model turbid water as well as the active agents in the seed extract and mechanism of turbidity removal [7, 8].  corresponding author iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 2 other studies have focused on quality of water treated by coagulation using two forms of the seed (shelled and unshelled) as well as using water extract with model turbid water (kaolin suspension) as the water source[8, 9]. others have carried out investigations into the effect of extracting all the oil from moringa oleifera seed on its coagulation effectiveness using turbid river water as the raw water source [10]. in the present study, varying quantities of oil 20% w/w, 25% w/w and 30% w/w kernel weight was extracted from moringa oleifera seed. the cake remaining after oil extraction was dissolved in water and applied in coagulation of model turbid water (kaolin suspension) and turbid river water samples to determine the percentage of oil removed which gave the best coagulation efficiency. 2. materials and methods 2.1 model turbid water (kaolin suspension) samples five grams of kaolin, heavy grade (bdh chemicals) was added to 500 ml distilled water. 50 mg/l concentration of sodium carbonate solution was added to the kaolin suspension and the total volume was made up to one liter. the suspension was stirred slowly at 20 rpm for 30 minutes in a jar test apparatus for uniform dispersion and allowed to stand for 24 hours for hydration of the clay particles [1]. this stock solution was used in the preparation of water with turbidity varying from 25 to 400 ntu by serial dilution. turbidity was measured with hach turbidimeter (camlab model 2100 an). 2.2 river water samples river water samples were collected from the raw water inlet taps at two water treatment plants in selangor state, malaysia from river batang kali at batang kali and river selangor at rantau panjang lama. 2.3 moringa oleifera cake preparation dry moringa oleifera seeds used in the studies were obtained from gardeners in serdang, selangor, malaysia. the seed wings and coat were removed from selected dry good quality moringa oleifera seeds and the nuts ground to a fine powder using a food processor, national mj-85cn. the dry mill attachment of the food processor was used for the preparation of the water extraction of moringa oleifera powder after oil extraction. electro-thermal soxhlet apparatus was used to extract oil from the moringa oleifera seeds powder using hexane as solvent at a temperature of 70°c. trial runs were initially carried out to determine the number of cycles required to achieve the desired oil extracted. twenty percent by weight of seed was the lowest oil removable after one cycle of operation of the soxhlet apparatus while 30% w/w of seed was the maximum amount of oil removable from the seed samples used for the studies. samples of moringa oleifera seed powder cake corresponding to three levels of oil extracted viz. 20% w/w, 25% w/w and 30% w/w seed kernel weight respectively referred to as s1, s2, s3 in table 2 were used for the coagulation studies in two stages. the flow diagram for the seed preparation is shown in fig. 1. iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 3 table 1: characteristics of model turbid water (kaolin suspension) used in coagulation. parameter range of values turbidity(ntu) low 25 45 medium 50 100 high 150 400 ph 7.4 – 7.7 zeta potential (millivolt) 0.8 – 2.16 alkalinity( mg/l as caco3 ) 24 – 32 table 1: characteristics of model turbid water (kaolin suspension) used in coagulation parameter range of values turbidity(ntu) low 25 45 medium 50 100 high 150 400 ph 7.4 – 7.7 zeta potential (millivolt) 0.8 – 2.16 alkalinity( mg/l as caco3 ) 24 – 32 3. experimental procedures the coagulation studies were carried out in two stages. the first stage involved application of the three levels of water extracted solution corresponding to s1 s2, s3 respectively to coagulate low, medium, and high turbidity model turbid water (kaolin suspension). the characteristics of the model turbid water (kaolin suspension) and river water samples viz. turbidity measured with a turbidimeter hach model 21200p, zeta potential with zeta meter system 3.0+, ph with ph meter cyberscan 2000 and alkalinity using standard methods[11] are as presented in tables 1 and 2. the second stage of the investigation involved the application of the sample of moringa oleifera seed powder cake that achieved the best turbidity removal in coagulation of model turbid water (kaolin suspension) to the river water samples. iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 4 fig. 1: schematic of processing of moringa oleifera seeds used in coagulation studies. 3.1 coagulation of model turbid water: 500 ml of water samples for each level of turbidity was put in each of six 600 ml capacity beakers and placed under the jar test apparatus (jar tester cz 150). the apparatus was set at rapid mixing speed of 125 rpm for 4 minutes and slow mixing speed of 40 rpm for 25 minutes. varying dosages of s1 s2, s3 solution extracted in water was added to each beaker. a settling time of one hour was allowed after which the residual turbidity of the clarified water samples from each beaker was measured and recorded. 3.2 coagulation of river water samples from river batang kali and river selangor based on the results obtained from the first stage of the studies, the moringa oleifera seed powder cake that gave the best turbidity removal was used in the coagulation studies using the same operating physical parameters of rapid and slow mixing rates and times. for batang kali river samples two levels of turbidity used were 32 and 502 ntu respectively while for river selangor, 87 and 466 ntu were recorded respectively. seed preparation: remove wings, coat, shell, grind to fine powder extraction of oil using soxhlet distillation process residue cake: water extraction to be used as coagulant (s1, s2, s3 ) oil: dried and stored for other uses iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 5 4. results and discussion 4.1 raw water characteristics. model turbid water (kaolin suspension): table 1 shows the raw water characteristics of model turbid water. the ph varied from 7.4 to 7.7 with the alkalinity varying from 24 to 32 mg/l. the zeta potential varied from 0.8 to 2.16 millivolts. the raw water turbidity varied from 25 to 400 ntu. 4.2 surface water quality. table 2 shows the raw water characteristics of river water samples from river batang kali and river selangor respectively. the ph and total alkalinity for the two raw water samples were almost the same. the ph varied from 7 .4 to 8.0 implying slight alkalinity with alkalinity varying from 24 to 32 mg/l and zeta potential 0.90 to 1.40 millivolts for river batang kali water samples. for river selangor water samples, the ph varied from 7.1 to 7.3 implying almost neutral water with alkalinity varying from 30 to 34 mg/l and zeta potential of between 0.81 and 1.01 millivolts. the raw water turbidity for river batang kali varied from 32 to 502 ntu while that of river selangor varied from 87 to 321 ntu respectively. 4.3 coagulation of low turbidity model turbid water (kaolin suspension). figure 2 shows the results of coagulation studies on low turbidity model turbid water with initial turbidity of 35 ntu using s1, s2, s3 with dosage varying from 10 to 30 mg/l. it was observed that for the three seed preparations increasing dosage resulted in rapid decrease in residual turbidity up to 10 mg/l dosage when the residual turbidity started to increase gradually until the dosage reached 30 mg/l. the gradual increase was probably due to over dosage that led to restabilization of the destabilized suspended solids, which had agglomerated into flocs. more significantly it was observed that the best turbidity removal was that from s2 with residual turbidity of 2.9 ntu corresponding to 91.7% turbidity removal. 4.4 coagulation of medium turbidity model turbid water (kaolin suspension). figure 3 shows the results of coagulation studies on medium turbidity model turbid water with initial turbidity of 100 ntu using s1, s2, s3. for s3 with dosage varying from 50 to 100 mg/l, it was observed that from a rapid reduction in residual turbidity to 12 ntu at 50 mg/l., increasing dosage resulted in increasing residual turbidity' implying restabilization of destabilized flocs during the coagulation process. for s2 the residual turbidity was observed to decrease gradually to 7 ntu at 50 mg/l dosage and 4.5 ntu at 100 mg/l. similarly for s1 there was gradual decrease in residual turbidity with increasing dosage with a final lowest residual turbidity of 20 ntu at 100 mg/l. s2 again gave the best performance in turbidity removal corresponding to 95.5 % turbidity removal. iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 6 0 5 10 15 20 25 30 35 40 0 10 20 30 40 moringa oleifera dosage (mg/l) r es id ua l t ur bi di dt y( n tu ) s1 s2 s3 fig. 2: coagulation of model turbid water (kaolin suspension) with initial turbidity of 35 ntu using moringa oleifera seed extract 0 20 40 60 80 100 120 0 20 40 60 80 100 120 moringa oleifera dosage(mg/l) r es id ua l t ur bi di ty (n tu ) s1 s2 s3 fig. 3: coagulation of model turbid water (kaolin suspension) with initial turbidity of 100 ntu using moringa oleifera seed extract. iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 7 4.5 coagulation of high turbidity model turbid water (kaolin suspension). figure 4 shows the results of coagulation studies oil high turbidity model turbid water with initial turbidity of 300 ntu using moringa oleifera seed cake with s1, s2, s3 respectively. the moringa oleifera dosage applied was varied from 100 to 200 mg/l. for s3, the lowest level of residual turbidity of 9 ntu was recorded at a dosage of 100 mg/l after which there was a gradual increase of residual turbidity with increasing dosage. however for s2 and s1, residual turbidity continued to decrease with increasing dosage with lowest residual turbidity observed at 150 mg/1, of 6 ntu and 3 ntu respectively after which there was gradual increase in residual turbidity for all the three seed preparations until the test run was terminated. the gradual increase was probably due to over dosing which led to restabilization of tile destabilized suspended solids which had agglomerated into flocs. more significantly it was observed that the best turbidity removal was that from s2 with residual turbidity of 3 ntu corresponding to 99 % turbidity removal. 0 50 100 150 200 250 300 0 50 100 150 200 250 moringa oleifera dosage(mg/l) r es id ua l t ur bi di ty (n tu ) s1 s2 s3 fig. 4: coagulation of model turbid water (kaolin suspension) with initial turbidity of 300 ntu using moringa oleifera seed extract. 4.6 coagulation of water sample from rivers batang kali and selangor since sample s2 gave the best coagulation results with the model turbid water, it was selected for use in turbidity removal from the turbid river water samples. figure 5 shows the results of coagulation of water samples from river batang kali with initial turbidity of 32 ntu and 502 ntu respectively. for raw water sample with initial turbidity of 32 ntu, application of dosages of s2 from 10 to 30 mg/l caused initial decrease in residual turbidity to a lowest value of 10 ntu increasing to 27 ntu and finally decreasing to 21 ntu at 30 mg/l dosage. for water sample with initial turbidity of 502 ntu with dosages varying from 100 to 250 mg/l, the residual turbidity decreased sharply to 5 ntu at 150 mg/l dosage iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 8 after which there was an increase to 14 ntu at 200 mg/l followed by a gradual decrease again to a lowest value of 4 ntu at 250 mg/l dosage. results of coagulation of water samples from river selangor with initial turbidity of 87 and 466 ntu respectively are shown in fig. 6. for water sample with initial turbidity of 87 ntu, application of dosages of s2 varying from 50 to 200 mg/l, showed decreasing residual turbidity with increasing dosage to a lowest value of 5 ntu at 150 mg/l after which it increased again to 8 ntu at 200 mg/l. similar studies in which the raw water sample from river selangor with initial turbidity of 66 ntu gave residual turbidity of 6.3 ntu on treating with moringa oleifera seed extract with no oil extracted at 250 mg/l dosage while for 35 % w/w kernel weight oil extracted the residual turbidity was 6 ntu at 200 mg/l moringa oleifera dosage [ 10 ]. for water sample with initial turbidity of 466 ntu, there was rapid decrease in residual turbidity to a lowest value of 5 ntu at 250 mg/l dosage after which there was gradual increase (due to restabilization) in residual turbidity to 12 ntu at 300 mg/l dosage. in the present study in which 25 % w/w kernel weight oil was extracted ( s2 ), it was observed that not only was the residual turbidity achieved lower than in the previous studies [ 3, 5, 6, 7, 9] but also importantly the dosage at which this was achieved was much lower at 150 mg/l in contrast to 250 mg/l for no oil extracted and 200 mg/1, for 35 % kernel weight oil extracted. similarly for raw water samples with high initial turbidity of 321 ntu application of shelled blended moringa oleifera with no oil extracted gave a residual turbidity of 9.9 ntu (96.9 %) at the economic dosage of 250 mg/l whilst the shelled oil extracted moringa oleifera out performed it by achieving a residual turbidity of 6.6 ntu (97.9 % turbidity removal.) [ 10 ]. the present study achieved residual turbidity level of 7 ntu at 250 mg/l, dosage using 25 % kernel weight oil extracted( s2 ) which was better than that achieved in previous studies in which 35 % kernel weight oil was extracted [ 10 ].. 0 100 200 300 400 500 600 0 50 100 150 200 250 300 moringa oleifera dosage (mg/l) r es id ua l t u rb id it y( n tu ) initial turbidity : 32 ntu initial turbidity: 502 ntu fig. 5: coagulation of turbid water from river batang kali using moringa oleifera seed extract (s2). iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 9 0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 moringa oleifera dosage (mg/l) r es id u al tu rb id it y (n tu ) initial turbidity 87 ntu initial turbidity 466 ntu fig. 6: coagulation of turbid water from river selangor using moringa oleifera seed extract (s2). the present study involved the use of only jar tests in which only coagulation/flocculation and settling processes were employed. it is therefore recommended that investigations be carried out through pilot plant studies that will involve the application of all unit operations and processes employed in conventional water treatment of surface water for potable use. from the results of pilot plant studies, guidelines required for full-scale application of moringa oleifera as a primary coagulant for turbidity removal may be developed. 5. summary of findings/conclusions 1. for model turbid water (kaolin suspension) coagulation of low turbidity (35 ntu), medium turbidity (100 ntu) and high turbidity (300 ntu) using moringa oleifera seeds extract with 20% w/w, 25% w/w and 30% w/w (s1, s2, and s3 ) kernel weight of oil extracted respectively, 25 % oil extracted ( s2 ) gave the best turbidity removal. 2. application of moringa oleifera seeds extract with 25% w/w kernel weight oil extracted ( s2 ) to river batang kali with low initial turbidity (32 ntu) and high initial turbidity (502 ntu) gave a highest turbidity removal of 69 % and 99 % respectively. 3. application of moringa oleifera seed extract with 25 % kernel oil extracted( s2 ) to river selangor with medium initial turbidity (87 ntu) and high initial turbidity (466 ntu) gave a highest residual turbidity of 94 % and 98.9 % respectively. iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 10 4. turbidity removal was found to increase with increase in initial turbidity during coagulation of model turbid water (kaolin suspension) and river water samples. acknowledgements the malaysian ministry of science technology and environment (moste) kindly provided funding for the research through the "intensification of research in priority areas" (irpa) project no 09-02-04-00. references [1] s. a .muyibi and l. m. evison, “optimizing physical parameters affecting coagulation of turbid water with moringa oleifera seeds”. water. res. vol. 29, no. 12, 26892695.1995. [2] a. ndabigengesere,, k. s. narasiah, and b . g. talbot. “active agents and mechanisms of coagulation of turbid waters using moringa oleifera,” water res. (29), 703-7 10, 1995. [3] s. a. muyibi, “ moringa oleifera seeds in water treatment”. journal institution of engineers malaysia vol, 59, 3, 37 – 50, 1998 [4] j . p. sutherland, g. k . folkard, and w . d. grant,. “ moringa oleifera as a natural coagulant”. in pickford et al eds. . affordable water supply and sanitation, 20th wedc conference. proc. 297 – 299, 1994. [5] s. a. muyibi and c. a .okuofu,. , “coagulation of low turbidity surface waters with moringa oleifera seeds.” intern. journ. environmental studies, 1995, vol. 48, pp. 263273, 1995. [6] s. a. muyibi and l. m. evison (1995) “coagulation of turbid waters and softening hardwater with moringa oleifera seeds”. intern. journ. environmental studies 49, 247 – 259, 1995. [7] s. a. muyibi and l. m. evison, “coagulation of turbid water and softening of hard water with moringa oleifera seeds”. intern journ. environmental studies, 1996, vol. 49, pp 247-259, 1996. [8] a. ndabigengesere, k. b. narasiah, k. subraimanian “quality of water treated by coagulation using moringa oleifera seeds”. water res. vol. 32, no. 3, pp. 781-791, 1998 [9] s. a. muyibi, h. hazalizah, i, irmayanti, j. m. m. n. megat “coagulation of river water with moringa oleifera seeds and alum a comparative study”. journal institution of engineers malaysia vol.62 no, 2, 15-2 1, 2001. [10] s. a. muyibi, j. m. m. n, megat, h. n. lam, k . l. tan “effects of oil extraction from moringa oleifera seeds on coagulation of turbid water.” environmental studies vol 59(2) pp. 243 – 254, 2002. [11] american public health association (apha), american water works association (awwa) and water environment federation (wef) standard methods for the examination of water and waste-water.. 20th edition apha publication office, washington d.c. 1999 iium engineering journal, vol. 4, no. 1, 2003 s. a. muyibi et al. 11 biographies iium engineering journal vol 23 no 2 july 2022 iium engineering journal copyright notice consent to publish: the author(s) agree to publish their articles with iium press. declaration: the author(s) declare that the article has not been published before in any form and that it is not concurrently submitted to another publication, and also that it does not infringe on anyone's copyright. the author(s) holds the iium press and editors of the journal harmless against all copyright claims. transfer of copyright: the author(s) hereby agree to transfer the copyright of the article to iium press, which shall have the non-exclusive and unlimited right to publish the article in any form, including in electronic media. for the article with more than one author, the corresponding author confirms that he/she is authorized by his/her co-author(s) to grant this transfer of copyright. the iium engineering journal follows the open access policy. all articles published open access will be immediately and permanently free for everyone to read, download, copy and distribute for noncommercial purposes. iium engineering journal at https://journals.iium.edu.my/ejournal is licensed under a creative commons attribution-noncommercial 4.0 international license. iium engineering journal chief editor ahmad faris ismail, iium, malaysia technical editor sany izan ihsan, iium, malaysia executive editor ahm zahirul alam, iium, malaysia associate editor nor farahidah za’bah, iium, malaysia language editor lynn mason, malaysia copy editor hamzah mohd. salleh, iium, malaysia malay translator nurul arfah che mustapha, iium, malaysia editorial board members abdullah al-mamun, iium, malaysia abdumalik rakhimov, iium, malaysia aishah najiah bt. dahnel, iium, malaysia alya naili binti rozhan, iium, malaysia norsinnira bt. zainul azlan, iium, malaysia hanafy omar, saudi arabia hazleen anuar, iium, malaysia konstantin khanin, university of toronto, canada ma'an al-khatib, iium, malaysia meftah hrairi, iium, malaysia mohamed b. trabia, united states mohammad s. alam, texas a&m university-kingsville, united states mustafizur rahman, national university singapore, singapore ossama abdulkhalik, michigan technological university, united states mohamed hadi habaebi, iium, malaysia mohd. sultan ibrahim bin shaik dawood, iium, malaysia muhammad ibn ibrahimy, iium, malaysia nor fadhillah mohamed azmin, iium, malaysia waqar asrar, iium, malaysia aims & scope of iiumengineering journal the iium engineering journal, published biannually (january and july), is a carefully refereed international publication of international islamic university malaysia (iium). contributions of high technical merit within the span of engineering disciplines; covering the main areas of engineering: electrical and computer engineering; mechanical and manufacturing engineering; automation and mechatronics engineering; material and chemical engineering; environmental and civil engineering; biotechnology and bioengineering; engineering mathematics and physics; and computer science and information technology are considered for publication in this journal. contributions from other areas of engineering and applied science are also welcomed. the iium engineering journal publishes contributions under regular papers and invited review papers. it also welcomes contributions that address solutions to the specific challenges of the developing world, and address science and technology issues from an islamic and multidisciplinary perspective. referees’ network all papers submitted to iium engineering journal will be subjected to a rigorous reviewing process through a worldwide network of specialized and competent referees. each accepted paper should have at least two positive referees’ assessments. submission of a manuscript a manuscript should be submitted online to the iium-engineering journal website at http://journals.iium.edu.my/ejournal. further correspondence on the status of the paper could be done through the journal website. ii international advisory committee a. anwar, united states abdul latif bin ahmad, malaysia farzad ismail, usm, pulau pinang, malaysia hanafy omar, saudi arabia hany ammar, united states idris mohammed bugaje, nigeria k.b. ramachandran, india kunzu abdella, canada luis le moyne, isat, university of burgundy, france m mujtaba, united kingdom mohamed ai-rubei, ireland mohamed b trabia, united states syed kamrul islam, united states tibor czigany, budapest university of technology and economics, hungary yiu-wing mai, the university of sydney, australia. published by: iium press, international islamic university malaysia jalan gombak, 53100 kuala lumpur, malaysia phone (+603) 6421-5014, fax: (+603) 6421-6298 whilst every effort is made by the publisher and editorial board to see that no inaccurate or misleading data, opinion or statement appears in this journal, they wish to make it clear that the data and opinions appearing in the articles and advertisement herein are the responsibility of the contributor or advertiser concerned. accordingly, the publisher and the editorial committee accept no liability whatsoever for the consequence of any such inaccurate or misleading data, opinion or statement. iium engineering journal issn: 1511-788x e-issn: 2289-7860 iii iium engineering journal editorial chemical and biotechnology engineering 1713: effect of feed flowrates on the physical properties and antioxidant of mahkota dewa (phaleria macrocarpa) encapsulated powder ........................................................................................................... muhammad norzaman kathiman, siti kholijah abdul mudalip, jolius gimbun 1717: potential of low carbon nanotubes dosage on chromium removal from water .................................... nassereldeen ahmed kabbashi, firdaus abd-wahab, warqaa muhammed bahaaddin, lubna muhamed musa, nour hamid abdurahman and isam yasseen qudsieh 2234: physicochemical and functional properties of composite flours based on mocaf and tempeh flour for making cookies ........................................................................................................................................ dita kristanti and woro setiaboma civil and environmental engineering 2070: evaluation of ductility of reinforced concrete structures with shear walls having different thicknesses and different positions ............................................................................................................................ ri̇fat resatoglu and shahram jkhsi 2173: new approach to predict fecal coliform removal for stormwater biofilters application ....................... sai hin lai, chun hooi bu, ren jie chin, xiang ting goh and fang yenn teo 2367: granular subbase improvement with recycled concrete aggregates in tropical areas ............................. daniela l. vega a., josé eduardo salcedo fontalvo, richard jiménez triana, dulce maría palacios del barre and cesar fresneda saldarriaga electrical, computer and communications engineering 1763: secure slicing and allocation of resources of 5g networks in software-defined networking / network functions virtualization .......................................................................................................................... ali j. ramadhan 2168: the development of water pollution detector using conductivity and turbidity principles .................... nurulhasanah amir hamzah maju , hasmah mansor, teddy surya gunawan and robiah ahmad 2190: optimal distribution network reconfiguration using multi-objective cuckoo search algorithm ........ azrin saedi, mohd shahrin abu hanifah, hilmi hela ladin and siti hajar yusoff 2272: a new hardware architecture for high-performance parallel turbo decoder ....................................... sujatha elukuru, subhas chennapalli and giriprasad mahendra nanjappa 2385: fuzzy logic and pi controller for photovoltaic panel battery charging system ..................................... mazbahur rahman khan, s. m. a. motakabber, ahm zahirul alam and syed ahmad fawwaz wafa engineering mathematics and applied science 1697: a fuzzy system for evaluating trustworthiness of users in a social network ......................................... mohammad mahdi shafiei, hossein shirgahi, homayun motameni and behnam barzegar 2134: sarima-lstm combination for covid-19 case modeling ..................................................................... imam tahyudin, rizki wahyudi and hidetaka nambo 2164: forecasting of infection prevalence of helicobacter pylori (h. pylori) using regression analysis ........... komiljon usarov, anvarjon ahmedov, mustafa fatih abasiyanik and ku muhammad na’im ku khalif iv materials and manufacturing engineering 2182: mechanical and thermal conductive properties of natural and synthetic cellulose reinforced epoxy composites .............................................................................................................................................. omran a. shabeeb, dawood s. mahjoob, hamid m. mahan and muammel m. hanon 2196: characteristics of leachate upon hydrothermal treatment processing: case study of ampang district municipal solid waste leachate .............................................................................................................. hadi purwanto, siti salwa khamis, hamzah mohd salleh, alya naili rozhan, mohamed abd rahman and rashidi othman mechanical and aerospace engineering 2137: the effect of layer thickness on repeatability of 3d printed pla parts produced using openware 3d printer ..................................................................................................................................................... normariah che maideen, mohd ikmal hisham abdul rahim, salina budin, koay mei hyie and hamid yusoff 2143: characterization and sintering properties of hydroxyapatite bioceramics synthesized from clamshell biowaste ................................................................................................................................................. chui kim ng, kit yee sara lee, chin hong tan, singh ramesh, chen hunt ting, yea dat chuah, yong tan and ubenthiran sutharsini 2148: earlier denaturation of dna by using novel ternary hybrid nanoparticles ............................................ jalal mohammed zayan, akbar john, abdul khaliq rasheed, batoul alallam, mohammed khalid, ahmad faris ismail, bryan raveen nelson and hamzah salleh 2157: virtual prototype-based kinematic modeling and simulation of a multi-mode amphibious robot ........... mohammed rafeeq, siti fauziah toha, salmiah ahmad and mohd asyraf mohd razib microsoft word 167-588-1-rv completed.doc iium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 175 measurements of pressure distributions on a rotor blade using psp techniques ki-dong kim1 and ki-jung kwon2 1aircraft system engineering dept., university of science and technology (ust), daejeon, south korea. 2aerodynamics and structures dept., korea aerospace research institute (kari), daejeon, south korea. kjkwon@kari.re.kr abstract: surface pressure distributions on a rotating blade were measured by using pressure sensitive paint (psp) to understand aerodynamic characteristics of a rotor blade. the present study was conducted to investigate the psp techniques for measuring the pressure distributions on a rotor blade. in order to perform the experiment, the psp was required to response very fast due to rapid pressure fluctuations on a rotor blade. high energy excitation light source was also needed to acquire proper intensity images in a short excitation time. the techniques were based on a lifetime method. qualitative pressure distributions on an upper surface of small scale rotor in hovering condition were measured as a preliminary experiment prior to forward flight conditions in the kari low speed wind tunnel laboratory. from measured pressure distributions, striking pressure gradient was observed on an upper surface of rotor blade and the resulting pressure showed expected gradient depending on different collective pitch angles. abstrak: pengagihan tekanan permukaan ke atas berbilah putar disukat menggunakan cat sensitive tekanan (pressure sensitive paint (psp)) untuk memahami sifat-sifat aerodinamik suatu berbilah putar. kajian telah dijalankan untuk menyelidik teknik-teknik psp dengan mengukur agihan tekanan ke atas suatu berbilah putar. agar eksperimen dapat dijalankan dengan baik, psp harus bertindak cepat kerana tekanan naik turun dengan pantas ke atas berbilah putar. sumber cahaya ujaan tenaga tinggi diperlukan untuk mendapatkan imej keamatan wajar dalam jangka masa ujaan yang pendek. teknik-teknik tersebut terhasil daripada kajian semasa hayat. agihan tekanan kualitatif ke permukaan atas berskala kecil pemutar dalam keadaan mengapung diukur sebagai permulaan eksperimen, sebelum penerbangan kehadapan dalam makmal terowong angin laju rendah kari. daripada agihan tekanan yang disukat, kecerunan tekanan yang ketara diperolehi daripada permerhatian terhadap permukaan atas berbilah putar dan tekanan yang didapati menunjukkan tekanan kecerunan yang dijangka, bergantung kepada sudut himpunan anggul yang berbeza. keywords: pressure measurement; psp; rotor blade; single-shot; lifetime 1. introduction to know the accurate distribution of spatial pressure on a rotor blade has been a critical research topic of many researchers for the understanding of complex rotorcraft aerodynamics. it is known that aerodynamics and acoustics such as blade-vortex interactions (bvi) can be studied by observing the unsteady pressure distributions around a blade tip. as conventional pressure measurement techniques [1], pressure taps and piezoelectric sensors have been mounted on a blade surface to measure pressure iium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 176 fluctuations but they have a limitation on spatial resolution as well as high cost for sensor installation. pressure sensitive paint (psp) has been developed as an advanced measurement technique for measuring global surface pressure fields. the principle of psp is that the paint intensity are changed by concentration of oxygen on the model surface. figure 1 shows basic components of a psp system. the luminescent molecular probes are imbedded in a polymer binder form. on excitation by light of the proper wavelength, the luminescence which is quenched by oxygen is detected by a ccd camera. excitation led array 470 nm emission (>590 nm) detector ccd long-pass filter oxygen molecules luminescent probe model surface polymer binder ccd camera fig. 1: basic components of a psp system [18]. the relationship between the luminescent intensity from psp and oxygen concentration can be described by the stern-volmer relationship, ref ref p p tbta i i )()(  (1) where p is air-pressure, i is luminescent intensity and ref indicates reference conditions. a(t) and b(t) are calibration coefficients depending on temperature. psps are very sensitive about not only pressure but also temperature. the reference is used to eliminate the effects of non-uniform illumination and uneven paint coating. in case of wind tunnel test, the reference iref is taken when the air flow is off and i is taken during test condition. once the intensity ratio iref/i is known, and the pref is also known at the reference(windoff) condition, then the pressure at the test condition may be determined from eq. (1). since pressure sensitive paint was found in a laboratory, many researchers who work with wind tunnels have been spent their time to increase measurement accuracy and to find new ways to capture images for various experimental configurations. to compensate temperature effect dual luminophor which is called binary paint was developed [2]. this paint contains two different luminophors; pttfpl (platinum tetra porpholactone) and mgtfpp(magnesium tetra porphine). pttfpl is oxygen-sensitive and its image is used as pressure data. mgtfpp is, however, sensitive to temperature and used as a reference. the psps have different characteristics depending on luminophore-binder combinations. conventional polymer-based psps are not suitable for measuring surface pressure on a rotating blade due to response times as slow as seconds. therefore, fast response paint is needed for application to unsteady flows. in order to decrease response time of psp, porous pressure sensitive paint has been developed. fig. 2 shows the difference between iium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 177 porous psp and conventional polymer-based psp. a porous psp binder which improves the oxygen diffusion can allow oxygen molecules to easily interact with luminophores, so the psp quickly responds to changes in oxygen concentrations. comprehensive reviews of psp are published by bell et al. [3] and liu et al. [4-5]. a review of unsteady and fast response psp developments are described by gregory et al. [6-7] and asahi et al. [8]. fig. 2: comparison of porous psp and conventional psp [19]. there are two methods for acquiring psp data. one is an “intensity” technique, and the other is a “lifetime” technique [9-11]. in 1995, burns et al. [12] used psp for rotating compressor blade which was in steady condition. they adopted both intensity and lifetime methods to measure surface pressures. for unsteady pressures, lifetime method is necessary since intensity method gives us time averaged data only. the conventional lifetime method was qualitatively demonstrated by wong et al. [13], where outer the 15% of each blade was painted with psp. they used led lamps as light source. however, the led lamps are not eligible to obtain good images due to low light levels. kumar [14] demonstrated the surface pressure measurements on rotating surfaces with both steady and unsteady pressure using lifetime-based single-shot methods. it is significant that he used a pulsed nd:yag laser instead of led lamps as light source. the objective of a present study is to find best way for measuring the unsteady pressure on a rotating blade. one and half meter sized small scale rotor test stand was used in hovering condition as a preliminary experiment prior to a forward flight condition. the experiment was carried out using lifetime-based single-shot method [14] and compared led lamps with pulsed laser. 2. experimental the psp experiment was performed using small scale rotor test stand. the main body was a rc helicopter that is called hero -500. it had two blades and each blade length was 325 mm and its chord was about 33 mm. the total radius of the rotor was 375 mm including a hub. the airfoil was symmetrical and maximum section thickness was 13% of the chord length as shown in fig. 3. more specific rotor parameters are shown in table 1. iium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 178 fig. 3: airfoil section geometry. table1. rotor parameters. blade length (mm) 325 painted length (mm) 90 blade chord (mm) 33 rotor radius (mm) 375 rotational speed (rpm) 2050 tip speed (m/s) 80 the outer 27.7% of the blade was coated with a porous pressure sensitive paint (ppsp) and 10 markers for image alignment were located. this paint was developed by innovative scientific solutions inc, (issi). the porous paint was composed of three parts. part a was water based ceramics slurry. part b was acrylic polymer emulsion. part c was pt-based dye. because of the part a and b, it was commonly called polymer/ceramic psp (pc-psp). this psp binder was mixture of polymer and ceramic particles, so it needed to mix part a and part b as a metric before spraying the part c. the mixing ratio is that the volume of part b is 4% of the part a volume. the psp binder was coated using an airbrush tool, so that blade surface was uniformly covered with part a and b mixture. then, the coated blade should be dry in less than 30 minutes. after the blade surface was dry, part c which was pt-based dye sprayed over the under coated mixture. once the porous psp was coated and the painted model used for a few hours under the excitation light, the signal was diminished due to photobleaching. in this case, it could apply more overspray to enhance the fluorescence of the blade and increase the signal to its previous level. fig. 4: experimental set-up for a rotor blade pressure measurement. iium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 179 as a trigger signal for camera shutter and light source, a micro photo sensor was mounted under the rotor shaft. it could get a trigger signal where the rotor was in a certain azimuth angle. the trigger rate was a signal per revolution, so it could easily get the rotor rpm using micro photo sensor. also, the trigger signal was plan to use the external signal in pulse generator. the experimental setup for a rotor blade psp experiment is shown in fig. 4, which includes a light source, and a photo detector as well as a ccd camera with an optical band-pass filter placed in front of the lens. led lamps were also installed instead of pulsed laser as a light source. the images were obtained by monochrome charge coupled device (ccd) camera which was a pco.2000mod version. it has high resolution (2048 x 2048pixel) and low noise (down to 9e-rms). the camera can shot frequency up to 14.7 frames per second at full resolution, and minimum exposure time is 0.5 µs. to increase acquisition efficiency, the ccd chip was binned horizontally and vertically by 2. for capturing luminescence image in single-shot method, the camera was used in a double exposure mode. in the double exposure mode, the ccd sensor has trigger acknowledgment delay (0.2 µs) and intrinsic delay (5.3 µs). the timings are shown in fig. 5. the images were acquired from the ccd camera with camware software. fig. 5: timing diagram for the rotor blade experiment. before the psp experiment was performed using small scale rotor test stand, psp calibration chamber was used in order to determine the time intervals of gate-1 and gate-2. a small square coupon was painted with the porous psp as same as the blade to confirm the relationship between the luminescence intensity and pressure on it. the temperature was kept constant at 20ºc during the calibration and pressure was varied from 25 kpa to 250 kpa in 10 equal steps (25 kpa). once decide the gate-1 exposure time, the time of gate-2 was automatically decided in double exposure mode. therefore, the data was acquired by changing the time of gate-1 and the results are shown in fig. 6. the reference pressure was 125 kpa. a ratio of intensity (g2/g1)ref is a reference pressure value, and g2/g1 is a pressure sensitive one. the plot between (g2/g1)ref/(g2/g1) and p/pref represents stern-volmer relationship and the slope of the linear fit provides pressure sensitivity of the paint in twoiium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 180 gated lifetime measurement technique, which is well explained in the reference [14]. from these plots, the slope of lines increases as long as the gate-1 exposure time is increased. when the gate-1 exposure time was 15 µs, the pressure sensitivity of the paint was the best. however, the slope of line was not a linear, so it was difficult to apply the sternvolmer relationship. this non-linearity is due to low signal to noise ratio (snr). finally, the gate-1 exposure time was decided to equalize the gate-1 and gate-2 intensity ratios within 20% [20]. fig. 6: the pressure sensitivity of varied gate-1 exposure time. led lamps and pulsed nd:yag laser were attempted as a light source. at first, six led lamps were installed around the ccd camera. they provided uniform and stable illumination for pressure and temperature sensitive paint measurements. each led lamp had 400 nm wavelength and all lamps were synchronized with one trigger pulse from photo sensor. secondly, a pulsed nd:yag laser that had been used for piv measurement was used as an excitation source. the laser’s wavelength was 532 nm. using a laser as excitation source increased the signal-to-noise ratio (snr) because the psp response intensity is a function of both the pressure field and the illumination field. the laser was emitted with a q-switch delay of 180 µs from a flash lamp excitation and the ccd camera was set synchronous to the laser. for the control the each signal time, a quantum composer delay generator (model 9514) was used. after comparing the led lamps with pulsed laser, pulsed laser was selected for the experiment since the led lamps were found to have low intensity for excitation. the psp data was collected using lifetime-based single-shot method. the rotational speed of the rotor was rpm 2,050 as the test pressure condition, and reference pressure condition was rpm 300. the angle of attack for each blade could control simultaneously, so the psp data was obtained from three different angles of attack which were 5º, 8º, and 12º. the dark images also acquired during the experiment to apply the post-image processing. the black screens were installed around the model in order to block out all of the lights except laser light. atmospheric pressure was 100,860 pa and ambient temperature was 24ºc during the psp experiment. suppose that the forward flight direction was azimuth 180º. the camera shutter was open when the blade was located at 270º azimuth angle. for the single-shot lifetime technique, images were acquired using double exposure mode. the laser pulsed with a q-switch delay of 180 µs and it had intrinsic delay of around 0.8 µs. the ccd camera at double exposure mode had total iium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 181 initial delay of 5.5 µs and the lifetime of gate-1 was 3µs, so total gate-1 time was 178.3 µs. as it called single-shot, each image was collected by only one laser pulse light. after all images were acquired, the post-image processing was used by oms 3.0 software which was developed by issi and labview programs. 3. results and discussion by comparing six led lamps with pulsed nd:yag laser as excitation source, the image obtained from pulsed laser shows stronger intensity than led lamps. figure 7 shows the intensity of six led lamps and fig. 8 shows the intensity of the pulsed nd:yag laser. the intensity images were taken by applying the single-shot lifetime technique. as shown in fig. 7 and 8, the measured intensities using the pulsed laser are much higher than the intensities using six led lamps. the results are from different energy power. the power of each led lamp is about 2.7 w. if the six lamps are flashing for 3 µs, the power could be transferred to 48.6 µj. on the other hand, the pulsed nd:yag laser produces a 200 mj per pulse (8 ns). it is enough power to apply the single-shot life time technique. since the led lamps were found to have low intensity for excitation, pulsed nd:yag laser was selected as a light source fig. 7: the intensity of six led lamps. fig. 8: the intensity of pulsed nd:yag laser. the final result images were obtained after post-image processing procedure. figure 9 shows the measured surface pressure distributions on an upper surface of the rotor blade depending on the collective pitch angle. the temperature sensitivity of the porous paint was not considered even though the porous paint had temperature sensitivity. for this reason, the psp experiment was performed to qualitatively analyze the pressure distribution on the rotor blade, not quantitatively. as shown in the results, noticeable pressure gradient was acquired using single-shot lifetime technique with pulsed nd:yag laser. at the collective pitch angle of 5º condition, pressure distribution shows a high pressure region near the trailing edge and blade-tip area. at the 8º collective pitch angle condition, a lower pressure region exists near the leading edge of the blade and the pressure is increase in the chord wise direction toward the trailing edge. at the 12º collective pitch angle condition, pressure distribution on the blade is much lower than other angles. in this condition, the blades are expected to have a iium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 182 mixmum lift-force acting on the model. as expected, the pressure on an upper surface of the rotor blade is decrease while increasing the collective pitch angle fig. 9: the results of pressure distributions on a rotor blade. every image can find sharp high pressure distributions at the trailing edge. these sharp pressure distributions are made after post-image processing procedure that used test condition (wind-on) images and reference condition (wind-off) images. the test condition images were acquired when the rotating speed of the blade was rpm 2050 with a tip speed of around 80 m/s. in case of the test condition, the rotor blades slightly moved up due to the lift-force. on the other hand, the reference condition images were captured when the rotating speed of the blade was rpm 300. in case of the reference condition, the rotor blades could not move up because the lift-force was not enough to raise the blades. the height of installed ccd camera was fixed, so the acquired blade images’ sizes were different due to small change of the rotor blades’ height. these mismatched images made sharp high pressure distributions at the trailing edge. 4. counclusion this psp experiment was performed to verify a possibility of pressure distribution measurements on a rotor blade using psp. led lamps and pulsed nd:yag laser were attempted to compare measurement ability. the porous pressure sensitive paint was used for decrease the response time and the experiment was only demonstrated in hovering condition at the kari low speed wind tunnel laboratory. in case of hovering condition, the pressure on the upper surface rotor blade is steady state. the next step, however, is to measure unsteady pressure distribution for the forward flight condition to see as averaged pressure distributions with respect to blade azimuth angle. as discussed earlier, the high power light source is required to use the single-shot lifetime technique for get better images. iium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 183 although remarkable psp techniques were used with pulsed nd:yag laser for strong light source, several problems were also discovered through this psp experiment. at first, the porous psp was so sensitive to light source that the experiment could not be performed for a long time. for this reason, the useless light had to be blocked all the time to enhance luminescence time. second, the result images involve some error factors such as sharp high pressure region at the trailing edge. more accurate post-image processing is essential to reduce the error factors. therefore, image processing techniques will be also developed to decrease the psp uncertainty. finally, in order to measure quantitative pressure on a rotor blade with porous psp, the relationship among the luminescence intensity signal, air pressure, and temperature should be precisely controlled. references [1] f. x. caradonna, and c. tung, “experimental and analytical studies of a model helicopter rotor in hover” nasa-tm-81232 [2] g. e. khalil, c. costin, j. crafton, g. jones, s. grenoble, m. gouterman, j. b. callis, and l. r. dalton, “dual-luminopher pressure-sensitive paint i. ratio of reference to sensor giving a small temperature dependency”. sensor and actuators b: chemical, vol. 97, 2003, pp.1321. [3] j. h. bell, e. t. schairer, l. a. hand, and r. d. mehta, “surface pressure measurements using luminescent coatings”. annual review of fluid mechanics, vol. 33, 2001, pp.155-206. [4] t. liu, b. t. campbell, s. p. burns, j. p. sullivan, “temperature-and pressure-sensitive luminescent paints in aerodynamics,” applied mechanics reviews, vol. 50, no.4, pp.227246, 1997. [5] t. liu, j. p. sullivan, “pressure and temperature sensitive paints,” springer, new york, 2005. [6] j. w. gregory, “porous pressure-sensitive paint for measurement of unsteady pressures in turbomachinery” 42nd aiaa aerospace sciences meeting and exhibit, reno, nv, january, 2004, aiaa 2004-0294. [7] j. w. gergory, k. asai, m kameda, t. liu, and j.p. sullivan, “a review of pressuresensitive paint for high-speed and unsteady aerodynamics” proceedings of the insitiutitution of mechanical engineers, part g, journal of aerospace engineering, vol. 222, no.2, pp 249290. [8] k, asai, k. nakakita, m. kameda, k. teduka, “recent topics in fast-responding pressuresensitive paint technology at national aerospace laboratory” instrumentation in aerospace simulation facilities, 19th international congress on iciasf 2001, cleveland, oh, auguest, 2001, pp.25-36. [9] r. h. engler, and c. klein, “dlr psp system: intensity and lifetime measurements” instrumentation in aerospace simulation facilities, 17th international congress on iciasf 1997, pacific grove, ca, pp.46-56. [10] k. mitsuo, k. asai, a. rakahashi, and h. mizushima, “advanced lifetime psp imaging system for pressure and temperature field measurement” measurement science and technology, vol. 17, no. 6, june, 2006. pp.1282-1291. [11] a. n. watkins, j. d. jordan, b. d. leighty, j. l. ingram, and d.m. oglesby, “development of next generation lifetime psp imaging systems” instrumentation in aerospace simulation facilities, 20th international congress on iciasf ’03, august, 2003. pp. 372-382. [12] s. p. burns and j. p. sullivan, “the use of pressure sensitive paints on rotating machinery” instrumentation in aerospace simulation facilities, 16th iciasf’95 record, 18-21 july, 1995, pp. 32.1-32.14. iium engineering journal, special issue, mechanical engineering, 2011 kim and kwon 184 [13] o. d. wong, a. neal watkins, and joanne l. ingram, “pressure sensitive paint measurements on 15% scale rotor blades in hover” 35 th aiaa fluid dynamics conference and exhibit, san francisco, ca, june, 2005, aiaa 2005-5008. [14] p. kumar, “development of a single-shot lifetime psp measurement technique for rotating surfaces” m.s. thesis, the ohio state university, columbus, oh, 2010. [15] j. p. hubner, j. d. abbitt, b. f. carroll, “pressure measurements on rotating machinery using lifetime imaging of pressure sensitive paint” 32nd aiaa/asme/sae/asee joint propulsion conference and exhibit, lake buena vista, fl, 1-3 july, 1996, pp.1-9. [16] y. sakamura, t. suzuki, m. matsumoto, g. masuya, and y. ikeda, “optical measurements of high-frequency pressure fluctuations using a pressure-sensitive paint and cassegrain optics” journal of measurement science and technology, vol. 13, no.10, october, 2002. pp. 1591-1598. [17] m. kameda, t. tabei, k. nakakita, h. sakaue, k. asai, “imaging measurement of unsteady pressure fluctuation on a delta wing by an anodized aluminum psp” measurement science and technology, vol. 16, no12, 2005. [18] l. goss, g. jones, j. crafton, s. fonov, v. fonov, “temperature compensation for lifetime-based pressure sensitive paint systems” instrumentation in aerospace simulation facilities, 21st international congress on iciasf 2005, sendai, japan, pp.283-292 [19] h. sakaue, “porous pressure sensitive paints for aerodynamic applications” ms thesis, school of aeronautics and astronautics, purdue university, west lafayette, in, 1999. [20] t. j. juliano, p. kumar, d. peng, j. w. gregory, j. crafton, and s. fonov, “single-shot, lifetime-based pressure-sensitive paint for rotating blades” measurement science and technology, vol. 22, no.8, june, 2011. microsoft word 3-khateeb-54.doc iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 33 algorithm of face recognition by principal component analysis khalid a. s. al-khateeb and jaiz a. y. johari electrical and computer engineering department, faculty of engineering, international islamic university. malaysia (iium), jalan gombak, 53100, kuala lumpur, malaysia. e-mail: khalid@iiu.edu.my, jaiz@iiu.edu.my abstract: a face recognition algorithm based on principal component analysis (pca) has been developed and tested for computer vision applications. a database of about 400 facial images was used to test the algorithm. each image is represented by a matrix (112 x 92), the data base is divided into subsets, where each subset represents one of 10 different individuals. a 96% rate of successful detection and a 90% rate of successful recognition were obtained. several factors had to be standardized to provide a constrained environment in order to reduce error. the analysis is based on a set of eigenvectors that defines an eigen face (ef). the method proved to be simple and effective. the simplified algorithm and techniques expedited the process without seriously compromising the accuracy. 1. introduction the face is a natural biometrics, because it is a key component in the way humans remember and recognize each other. the subject of automatic face recognition systems is receiving considerable attention from a variety of interest. the effort has been encouraged by the ever increasing use of high tech-devices in a variety of applications. face recognition algorithms may in some respects out perform humans, particularly where a large database search is involved. most of the recently developed methods perform well under constrained conditions. however, the problem of live face recognition remains largely unsolved. face recognition techniques usually analyze the unique shape, pattern, and positioning of facial features. using computers for this purpose is a complex technology and largely software based. some of the problems associated with live real time recognition are complicated by the change of conditions, such as the position of the head and camouflage, which affect the performance of the recognition process considerably. therefore, to determine a specific face in a group image by computer becomes an extremely challenging problem, whereas the human eye with the built in faculties can detect a face at a glance. to overcome these difficulties and increase the accuracy, intelligent algorithms have to be developed, which can adapt to these changes. some of the more common techniques are based on neural networks, skin filter, template matching, and eigenvector analysis. the principal component analysis (pca) technique adopted in this work is based on eigenvectors. the technique was initially developed for the purpose of image compression and reconstruction [5,6]. this technique is suitable for both face and image recognition. the problem of face iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 34 detection, i.e. to find the location of every human face contained in an arbitrary still image, represents the first step in a fully automatic face recognition algorithm. it can then be used in an image database indexing or searching by content, for surveillance and human-computer interface systems. it also provides insight, on how to approach other pattern recognition problems. at the same time, it may be one of the challenging problems in the development of pattern recognition algorithms. the present work deals with four aspects of the problem namely, finding a face (input image), track the image in the database, recognizing the face and determining its identity. fig. 1: process of identifying an image. 2. principal component analysis (pca) the image is represented by a matrix of smaller images. the smaller images are derived from the full image in order to find the most significant eigenvectors of pixel-wise covariance matrix for a set of training images [1]. the value of a pixel can vary from 0 (black) to 256 (white) depending on its grayscale level. an algorithm capable of recognizing faces based on the principal component analysis or karhunen-loeve [6,7] transform is applied. it reduces the amount of processing. hence the task becomes more manageable. the computer treats a face image as matrix of several hundred by several hundred pixels. if the pixel matrix is turned into a vector, the picture will have a location vector in thousands of dimensional spaces. the small subsection of the multidimensional space is called the "face space." the eigenvectors create a new basis to represent the images as coordinates in a much smaller dimensional space. hence, images of the same person will be located nearer to one another in this space because of their similarity that gives close eigenvalues. fig. 2: formation of the face vector from the face image. iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 35 3. the eigenvalue problem the implementation of the face recognition algorithm for a grayscale image, and the software for the computing processes and the simulation of software interfaces were achieved by programming using matlab. the database images had to be standardized in terms of grayscale level, brightness and contrast in order to avoid large error. the theory behind the eigenface approach is derived from the mathematical definition of eigenvectors and the associated eigenvalues; if a is an n x n matrix, then a nonzero vector x in rn is an eigenvector of a, such that ax is a scalar multiplied by x, a x = x, (1) where,  is a scalar representing eigenvalues and x eigenvector of a the eigenvectors of a, and the corresponding eigenvalues, are the nonzero vector x that satisfy eq. (1) the eigenvectors corresponding to  are the nonzero vectors in the solution: (i a) xi = 0 i.e. the solution space or the eigenspace of a corresponding to . the recognition algorithm begins by collecting a large number of images in a database [6]. the system then creates a set of eigenfaces by combining all the facial images in the database and comparing commonalities and differences between groups of individual facial images. the eigenfaces developed by the system appear as two-dimensional sets of light and dark areas arranged in a particular pattern. then, the algorithm compares the inputs’ eigenface characteristics with those in the database and determines a "degree of fit" score for the target face. if the target face produces a high enough degree of fit score, it is recognized and accepted by the algorithm. in practice, any individual can be identified using a database of 1 to 100 eigenfaces. a variation of the eigenface approach is called eigenfeatures. the approach combines facial metrics, which involves measuring the distance between specific facial features, such as the eyes, nose, and mouth, with the eigenface approach. the distance between these points on an input live face as measured by the system are then compared to the sets of eigenfeatures stored in the database to determine whether the face is a match. 4. algorithm of the pca eigenvectors the principle component analysis (pca) method is based on statistical data analysis used in image coding to find a subset of principal directions in a data set of any statistical distribution [5-7]. an image can be represented as a point in an (m x n) dimensional image space, where each dimension is associated with one of the pixels in the image. the values in each dimension are the gray level of the pixels. the notion of direction of variance in a high dimensional space can be extracted from the covariance matrix. the eigenvectors of the covariance matrix define a space in which the dimensions are zero so that the matrix is diagonal. the m training images are iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 36 represented as points in m space. then, recognizing a face in a new test image would be to find its nearest neighbor in the image space. this approach however is rather slow. the size of image space may be very large and the images are likely to be clustered near one another, since they are all facial images. for image ii among a collection of m images, the average image of all the training images in i1, i2, …., im is defined as: 1 1 i i   m a ι m (2) the difference vector di, which shows how every image differs from the mean, can be calculated. i i d i a (3) the algorithm of covariance matrix c, of the data is thus defined as: 1 1 n m t n n  c d dm (4) c is very large, so this method is computationally intensive. however, there are relatively fast methods for finding the k largest eigenvector, which is all that is needed. the m' images; e1, e2, …, em', are called eigenfaces or eigenvectors [4,6]. these images define a basis set, so that each face image will be defined in terms of how similar it is to each of these basis images. for k = 1,…,m', a real-valued weight, wk can be computed, indicating the similarity between the input image i, and the kth eigenvector, ek. solving this eigenvector algorithm problem, any image i can be projected into eigenspace by wk, that is,  tk k w e i a (5) the algorithm of eigenvalues k, can be calculated as:  2 1 1 m t k nk n d    em (6) and defining the algorithm of eigenvector as: 1, if 0, otherwise t l k l k        e e (7) thus, any image i can be expended as a linear combination of ke and kw , where wk describes the contribution of each eigenvector. iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 37 1 1 m k k jm    i a w e (8) the accuracy of the eigenspace method as characterized by the performance of the eigenspace algorithm resulted in about 96% correct recognition. if a training set contains multiple images for each person, then the average point in eigenspace can be computed and the computed points represent each image of that person. the algorithm requires that all images of a 3d object such as a person's head or face from many different position, orientations and expression. the points in eigenspace corresponding to a different 3d view can then be combined by fitting a hyper surface to all the points, and storing this hyper surface in an eigenspace as a description of that person. then, classify a test image (input image) as a person corresponding to the hyper surface. the algorithm of reading and matching the eigenfaces examines a large number of pictures of faces are stored in a database. any facial image is built with different intensities of light. the lighting condition however must be controlled to be the same for all images. to identify a face, the algorithm compares its eigenface characteristics, which are encoded into a template, with those in the database, so as to select the face whose templates match the target most closely. to verify someone for example, a claim is first made for the person. this claim is in the form of a user id that can be represented as a 2d bar code, card, token or smart card. the user id claim is used to fetch the face template representing the true identity of the person (reference template), which is stored in a database. when the true face matches the known reference image in the database against the input image it produces a match score. for a match score greater than a preset threshold, the two faces are deemed to be for the same person. otherwise, they belong to another person. in the identification of an input image against a database and then all the match scores are sorted from the best score down to a percentage error is less than 4%. if the top score is above a matching threshold, then it is the best candidate to be identified the unknown person (input image). 5. creating and standardizing the image files in this algorithm, the input and database images represented as m x n matrix (112 x 92) pixels. the image is defined as a grayscale image in which case the data range is from 0 to 255. the image is formatted in tiff or giff file format. each image would have a pixel intensity arrangement of 2,637,824 possibilities. this gives a better accuracy, and the face recognition algorithm will be more reliable. the procedure begins by selecting only the face part from the original image. then, the brightness and contrast are standardized. the color photo is turned into a grayscale image. the size is changed to (112 x 92) pixels, and saved in tiff file format. some of the processing steps are illustrated in fig. 3 and fig. 4. the image information is standardized in terms of size and color intensity. the factors observed during the creation of the files are: 1) the distance between face and lens, and the light intensity are kept constant. this is especially important in creating images files for the same person. 2) each image is chosen to correspond to a different facial expression. this enhances the reliability of the system. 3) when converting the color image into a grayscale, the average intensity for each image in database must be specified. iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 38 the process of standardizing the brightness and the contrast is important because the conversion of the original color image into grayscale may introduce error, since the grayscale contains only 256 levels from black to white. 6. recognition algorithm the face recognition is the final stage of the process and is used for determining both the closest match for the identity of the person and the probability of that match. the algorithm compares the input image with every image in the database. the image in the database would have undergone similar process as the input images. fig. 3: steps of creating database and input image. fig. 4: standardizing the brightness and contrast. iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 39 fig. 5: process of crop and resize a singular eigenvalue will then be used to represent the input image. the eigenvalues will then be compared with the eigenvalues of the database images. a match is acquired only when the margin of error is less than 4 %. the algorithm of recognition is considered a failure if the error is greater than 4 %. furthermore, the number of eigenvalues can be as many as the total number of images in the database, which may cause a problem. this problem was solved by creating a new version of the set of eigenfaces represented by the eigenvalues. it is achieved by removing the images which conform least to the set. the result is reflected in enhancement of the recognition accuracy of the algorithm. of course, higher accuracy could still be expected with more accurate algorithm calculations rather than approximations. the improvement, however, will be at the cost of extra processing time. 7. testing and accuracy a number of testing procedures were adopted in order to find the optimum number of images for a person that gives highest recognition probability. several database sets were created, each comprising a different number of persons. the recognition percentage was standardized in each case, and the recognition is considered successful only when the match is above 96%. an example of the performed tests is shown in table 1. note that the images for each person were selected at random to test the algorithm accuracy. the highest accuracy obtained during the test was 90 %, when each individual was represented by five pictures. the lowest accuracy was 10 % when each individual was represented by 9 images. the problem when there are too many images representing the same person is that the eigenvalues will be closely spaced. hence, the eigenvalues images belonging to different persons may overlap. on the other hand, when the number is too small, the information will be insufficient to give acceptable recognition accuracy. in this case, five images seem a reasonable number, as shown in fig. 6. while the information is sufficient to represent an individual, the values are not too closely spaced as to cause confusion. a similar test was performed on images with different type of extension pcx and jpeg. for this test, two extra databases were built the content of each were images from different extensions. the pcx and jpeg images iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 40 were based on the original tiff images. the result of the test (fig. 7) shows the similarity between tiff and pcx in contrast with jpeg. table 1: test results of random image. number of images for each person person 1 2 3 4 5 6 7 8 9 s1 no no yes yes yes no yes yes yes s2 yes yes yes no yes yes no no no s3 no no yes yes yes yes no no no s4 no no yes yes yes yes no no no s5 yes yes no yes yes no no yes no s6 no no no no yes no yes no no s7 yes yes yes no yes no no no no s8 no yes yes yes yes yes yes yes no s9 yes no no no no yes no no no s10 no no yes yes yes no yes yes no 40 % 40 % 70 % 60 % 90 % 50 % 40 % 40 % 10 % recognition test 40% 40% 70% 60% 90% 50% 40% 40% 10% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 1 2 3 4 5 6 7 8 9 images per person s uc ce sf ul r ec og ni tio n iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 41 fig. 6: result of recognition versus no. of images representing one face. the pcx and tiff images have similar accuracy. the images do not encounter much loss of information during the exchange. as observed from fig. 7 jpeg suffers changes and encounters some losses during transformation. the jpeg is intended for compressing images that will be looked at by humans, where small errors do not cause a problem. these small errors (introduced by jpeg) may be a problem for images analyzed by machine, even if they are invisible to the eye. below is an example between the original images (tiff) which has undergone the jpeg transformation. slight changes can be recognized between the two images. the tiff image seems to have more details then the jpeg. when these two images are analyzed in terms of pixel values, some differences are noticed. the grayscale values go from 29 higher to –34 lower. this proves that the jpeg image undergoes a change during transformation. pcx tiff jpeg 74% 76% 78% 80% 82% 84% 86% 88% 90% 92% im ag e ty p e accuracy fig. 7: accuracy with the different extension. fig. 8: part of the face images used to create eigenspace. iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 42 the accuracy of the recognition system relies greatly upon how the eigenface algorithm is implemented. there are shortcuts and approximations that can save time and resources. however, this would be at the expense of accuracy. the eigenvalues and the covariance matrix are among the values that can be calculated in several ways. all the recognition algorithms are built on how these values are computed. the covariance matrix for example can be solved using the full algorithm computation method, which requires very large memory space. sometimes approximate values are sufficient, and these require less memory space and are much faster. the number of images in the database also plays an important role in determining the accuracy of the recognition, as discussed earlier. other factors affecting accuracy depend on differences in the design and structure of the system, since different programmers have their own ways of presenting the system. the algorithm of recognition by pca is reasonably fast and has several advantages such as, the raw intensity data are used directly for learning and recognition without a significant low-level or mid-level processing. the geometry and the reflectance of a face are not a requisite. the low-dimensional subspace representation suffices for data compression. the recognition process is rather simple and may be more efficient by comparison with other methods. on the other hand, the method has its limitation and drawbacks. theoretically, the constrained conditions are reasonably simple. experimentally, however, they may present serious limitations resulting in a number of disadvantages. for example, the method is sensitive to scale. therefore, a low-level preprocessing may still be necessary. the eigenface representation is faithful to the original images, in the least-square sense, but the recognition rate decreases under varying pose and illumination conditions. it has shown to be robust when dealing with facial expression and some disguise effects e.g glasses, but the tests were made with frontal view only. of course, the problem will be much more difficult for extreme changes pose, expression and disguise. the eigenface recognition method being “appearance-based” shares some drawbacks with other methods. first, it is difficult to update the database, because of the time-consuming learning for training images. second, the recognition is efficient only when the number of face classes is larger than the dimensions of the face space, otherwise the projection of an unknown image requires pixel by pixel multiplication of the input image by all eigenfaces, which is equivalent to or worse than template-matching. the current face recognition algorithm may work under constrained conditions. however, they nearly all fail under vastly varying conditions. in the future, recognition algorithms will need to recognize people in real-time and in much less constrained situations. improving the current algorithm may prove to be advantageous in real time recognition. it would first involve finding a face within an image, which in any real time situation a face can be seen from various angles at different distances from the camera. the recognition algorithm must be able to identify which part of the image captured is a face for later processing, and the normalization of illumination and other factors. 8. conclusions the algorithm of face recognition by principal component analysis (pca) is a rapidly developing area with many possible applications from crowd surveillance to improved iium engineering journal, vol. 3, no. 2, 2002 k. a. al-khateeb and j. johari 43 human-computer interaction. the goal of this work is to develop a recognition algorithm and investigate the issues involved in getting the algorithm to work. face recognition using eigenface algorithm by pca was evaluated with a number of images and shown to have a maximum recognition rate of 90%. the relationship between the recognition accuracy and type of image was investigated. it is found that the compressed image resulted in a slightly decreased performance. multiple techniques are available in obtaining values such as the covariance matrix and the eigenvalues. future work will continue be introduced to improve the existing algorithm. there are other aspects that can also improve the current algorithm such as real time recognition and the smart card implementation. face recognition by eigenfaces algorithm offers significant potential for commercial applications which makes it well suited for future development. references [1] khalid a. s. al-khateeb and jaiz a. y. johari, “implementation of eigen vectors in computer face recognition”, 8th babylon academic conference, babylon, iraq, 23rd april 2002. [2] h. anton and c. roses, "elementary linear algebra application version", john wiley and sons inc., u.s.a, 1994. [3] j.c. russ. “the image processing handbook, matlab”, second edition, crc press, boca raton, 1997. [4] m. turk and a. pentland "eigenfaces for recognition", journal of cognitive neuroscience vol.3, nov 1991 pp 71-86 [5] r. cappelli, d. maio and d. maltoni “multispace kl for pattern representation and classification”, ieee transactions and pattern analysis and machine intelligence vol.23, 2001 pp 977-996 [6] m. gross and h. luttermann, “combining principle analysis and neural networks for the recognition of human faces”, proceeding of pacific graphics, vol. 1, 176-192, 1993. [7] z. m. hafed and m.d. levine “face recognition using the discrete cosine transform” international journal of computer vision 43(3), pp 167-188, 2001. [8] b.j. oommen, k.s. loke “on the pattern recognition of noisy subsequence trees” ieee transactions and pattern analysis and machine intelligence, vol.23, pp 929-946, 2001. biography prof. khalid al-khateeb studied in the united kingdom and graduated at the royal college with an honors b.sc. degree in electronics in 1966, the master's degree in 1971 at salford university and the phd in 1975 at manchester university. his research interests include electronics, communications, computer applications and engineering education. his academic life stretches over decades, during which he worked at various universities in the uk, usa, iraq, algeria, jordan and malaysia. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 10, no. 2, 2009 alam et al. 69 tunable bandpass filter using rf mems switches a.h.m. zahirul alam*, md. rafiqul islam, sheroz khan, nik noor atikah nik mohd. salleh and noraini aziz wireless communication and signal processing research group, electrical and computer engineering department, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia *e-mail : zahirulalam@iium.edu.my abstract: a band pass tunable rf filter is proposed by using radio frequency (rf) microelectro mechanical systems (mems). the tunability is obtained by using capacitive mems switches that can be tuned within the bandwidth of 3.6 ghz to 4.4 ghz. the performance of the filter depends on geometry and location and types of the mems switches. optimization has been done to achieve tunability by using 3-d high frequency electromagnetic simulator (hfss). keywords: microelectro mechanical systems (mems), radio frequency (rf), bandpass filter, tunable filter 1. introduction modern wireless/satellite communication, radar, electronic warfare, and instrumentation, all demand tunable filters for flexible and adaptive operations over wide frequency range [1-3]. mechanically and magnetically tunable band pass filters, although widely employed and handle high power, provide just low to marginal tuning speed, and are bulky due to their macroscale tuning mechanism. electronically tuned filters, with compactness and quick tuning, are good candidates for highly integrated systems. however, due to losses and nonlinearity associated with p-n junctions and mos structures and the complexity in biasing, microwave control devices based on these mechanisms may lack of appeal to current wireless communication applications, and thus investigations into tunable filters based on diodes and transistors have barely reported. recently, rf mems tunable filters of various tuning topologies [4-7], with much lower insertion loss (il), nonlinearity and higher q factor than semiconductor based devices, have been demonstrated as an enabling technology for low cost and high performance integrated military or commercial rf systems. these surface micromachined devices have the advantages of simple (electrostatic) tuning with ultra-low tuning power consumption, large bandwidth and capability of monolithic integration with active circuit. existing designs suffer from passband attenuation mostly due to the architecture itself rather than conductor or dielectric loss. iium engineering journal, vol. 10, no. 2, 2009 alam et al. 70 reconfigurable band pass filters (bpfs) draw much attention in modern systems because of their diversity. reconfigurable bpfs with tunable bandwidth [8, 9], tunable center frequency [10], and switch ability [9] are reported. among these researches, pin diodes, piezoelectric transducers, and mems cantilever/bridge structures are used as the switch components. in this paper, rf mems switches have been proposed to design a reconfigurable interdigital band pass filter and describe the optimization procedure to obtain tunable bandwidth. 2. design and analysis interdigital bandpass filters are commonly used for microstrip implementation. the filter configuration consists of an array of n transverse electro magnetic (tem) -mode transmission line resonators, each of which has an electrical length of 90̊ at the midband frequency and is short-circuited at one end and open-circuited at the other with alternative orientation. the coupling is achieved by way of the fields fringing between adjacent resonators separated by spacing [11]. each line element serves as a resonator, except for the input and output line elements, which have an impedance-matching function . the input and output are also using tapped line which offer space and cost-saving advantages because the first and the last resonators are eliminated. these types of bandpass filters require use of grounding microstrip resonators which can be achieved via holes. the general structure for interdigital filter is shown in fig. 1. fig. 1: general structure for interdigital bandpass filter. in designing the interdigital bandpass filter, the specific frequency, stopband attenuation, attenuation response, and the number of the resonator must be calculated according to the following equations: passband )cos(cos)1log(10 '122 xm wnaa −+= (1) stopband )cos(cosh)1log(10 '122 xm wnaa −+= (2) where, 2ma is the ripple height, n is the order of the filter, ' xw is the bandwidth over which the attenuation has maximum ripple. the 2ma and ' xw can be calculated from the ripple magnitude by using the eqns. (3) and (4) as follows: )1log(10 2 += maripple (3) iium engineering journal, vol. 10, no. 2, 2009 alam et al. 71       − − = x x x f f f f ff f w 0 012 0' (4) where, f0 is the centre frequency, fx is the upper frequency, f2 –f1 is the frequency difference. from the eqn. 4, the number of the resonators in the design can be calculated in order to get the accurate pass band of the filter. according to the number of the resonators and the ripple magnitude, the values of gk can be found from the table of reference [12]. from this value, the loaded ql fgfql ∇= /10 and the normalized coupling coefficients, k between two resonators can be calculated by using the following equations: (5) )( 10 1, + + = nn nn ggf f k (6) the length of the resonators can be calculated by using this equation eff l ε λ 4 0= (7) by taking the value of 0.7 for w/h (width of the substrate over its height) and the substrate dielectric constant, rε the effective dielectric constant can be calculated in order to get the length of the resonators.               −+      + − + + = − 22/1 104.0 12 1 2 1 2 1 h w w hrr eff εε ε (8) the last parameter in designing the interdigital bandpass filter is the width of the input and output, w0. this parameter can be obtained from impedance zo 1/ ;25.0 8 ln 2 120 0 0 0 0 <      += hw h w w h z effεπ π from the following eqn. 9. (9) the schematic diagram of the interdigital filter is shown in fig. 2 drawn by using 3d electromagnetic simulator. the center frequency f0 = 4 ghz, and bandwidth = 0.8 ghz have been chosen for designing the filter. thefive resonators are assembled on the alumina substrate in the design. the alumina substrate is placed on the ground plane made of copper plate with 0.5 mm thickness. the filter requires use of grounding of the resonators. the grounding is placed at the side of one end of the resonator and connected to the ground plane via hole through the substrate. the microstrip line is used as the feeding technique. iium engineering journal, vol. 10, no. 2, 2009 alam et al. 72 fig. 2: the layout of inter digital band pass filter. figure 3 shows the inter-digital band pass filter response without the mems bridge/switches. the frequency response is obtained by using electromagnetic simulator hfss. 3.0 3.5 4.0 4.5 5.0 -80 -70 -60 -50 -40 -30 -20 -10 0 a tte nu at io n an d r et ur n lo ss , d b frequency, ghz s21 s11 fig. 3: simulated results of interdigital filter without mems switches. 2.1 one mems bridge parallel with the resonator the effect of one mems bridge placed above the middle resonator has been studied. the mems bridge consists of thin strip of metal (membrane) and insulator that is fixed at both ends. it is suspended above an electrode with spacing, forming a capacitor between these two conductors. the bridge is considered silicon nitride of dielectric constant εr = 6.8 with copper coating. the dimension of the bridge is 1.689 mm × 14 mm × 0.1 mm. the structure is shown in fig. 4. the insertion loss and return loss areshown in fig. 5. the result shows that the bandwidth is decreasing as the distance between the bridge and the resonator becomes closer. the upper frequency is nearly maintained while the lower frequency is changing. since air is separating the electrode and the switch, the up-state capacitance is small. by applying a voltage the upper membrane is deflected by the electrostatic force, and the membrane will snaps down to the opposite electrode. the spacing is also reduced and the capacitance is increased. electrostatic force between the top and bottom electrodes actuates the switch. the variation in capacitance will disturb the iium engineering journal, vol. 10, no. 2, 2009 alam et al. 73 frequency response of the filter. furthermore, the fringing fields capacitances of mems switches dependson the bridge dimensions and height. as a result the lower cutoff frequency decreases to lower value. the results are summarized in table 1. fig. 4: the layout of the filter with rf mems bridge placed above the middle resonator. 3.0 3.5 4.0 4.5 5.0 -40 -30 -20 -10 0 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 db s21 db frequency, ghz 1mm 2mm 3mm 4mm 5mm s11 fig. 5: simulated results of interdigital filter with single mems switch placed parallel to the center resonator. table 1: the result for the filter with five mems bridges parallel with the resonator. distance, d (mm) fl f (ghz) u f (ghz) c bandwidth (ghz) (ghz) 1 3.640 4.444 4.042 0.804 2 3.570 4.447 4.0085 0.877 3 3.544 4.455 3.9995 0.911 iium engineering journal, vol. 10, no. 2, 2009 alam et al. 74 4 3.520 4.454 3.987 0.934 5 3.505 4.467 3.986 0.962 2.2 two mems bridge parallel with the resonator the performance of the filter is analyzed by turning the switch on and off by placing two bridges parallel to the resonator places beside the centre resonator. it is observed from fig. 6 that there is not much in difference in bandwidth variation between the filter with placing only single mems bridge in parallel with the resonator. however, for two bridges, the bandwidth for the down-state is much wider than the single bridge. 3.0 3.5 4.0 4.5 5.0 -40 -30 -20 -10 0 -70 -60 -50 -40 -30 -20 -10 0 in se rti on l os s, d b frequency, ghz off on r et ur n lo ss , d b off on fig. 6: simulated results of interdigital filter with two mems switches placed parallel beside the center resonator. 2.3 one mems bridge perpendicular to the resonator the effect of mems bridge placed perpendicularly above the resonator has been studied. the bridge is made of silicon nitride with 0.889 mm ×24.885 mm ×0.1 mm with copper coating as shown in fig. 7. iium engineering journal, vol. 10, no. 2, 2009 alam et al. 75 fig. 7: the layout of the filter with rf mems bridge placed perpendicularly above the resonator. the performance of the filter is analyzed by turning the switch on and off. figure 8 shows the frequency response of the filter when the mems switch is down-state and upstate. from fig. 8, it can be observed that the bandwidth varies within the frequency range of 3.6 ghz to 4.4 ghz. in the off-state position, the bandwidth and center frequency has not been changed. on the other hand, when the mems bridge was moved down (on-state position), the gap was reduced and therefore the capacitance was increased and the bandwidth tends to degrade since the capacitive part of the resonators was changed. in this design, the lower frequency remains, while the upper frequency decreases when the switch is in the down-state. it is also observed that the lower frequency shifted to lower frequency region for the case of parallel bridge whereas the higher frequency shifted to high frequency for the case of perpendicular bridge. 3.0 3.5 4.0 4.5 5.0 -35 -30 -25 -20 -15 -10 -5 0 5 -70 -60 -50 -40 -30 -20 -10 0 in se rti on l os s, d b frequency, ghz off on r et ur n lo ss , d b off on fig. 8: simulated results of interdigital filter with mems switch placed perpendicular to the center resonator. 2.4 mems bridges parallel and covering all the resonators the filter was designed with mems bridges placed on the top of the each resonator, and all the mems bridges had the same width as the resonator. the layout of the filter is depicted in fig. 9. the performance of the filter is analyzed by varying the height of the resonators. iium engineering journal, vol. 10, no. 2, 2009 alam et al. 76 fig. 9 :the layout of the filter with rf mems bridges covered by all the resonators. the frequency response of the filter is shown in fig. 10 for different mems height. it is observed that the variation in bandwidth is independent of frequencywhen the height of the bridge varies. in this configuration, the bandwidth is dependent on the height of the bridge, as it is reducing the gap of the bridge. the resonators will result in increasing the capacitance of the bridge. therefore, increasing or decreasing the bridge capacitance enables the bandwidth to be tuned within the same pass band. table 2 depicted the center frequency and bandwidth for the filter. 3.0 3.5 4.0 4.5 5.0 -40 -30 -20 -10 0 -80 -60 -40 -20 0 db s21 db frequency, ghz 4mm 5mm 6mm 7mm s11 fig. 10: simulated results of interdigital filter with mems bridges covering all the resonators for various heights. table 2: the simulation results for one mems bridge placed parallel with the resonator. height of the bridge, (mm) fl f (ghz) u f (ghz) c bandwidth (ghz) (ghz) 4.0 3.76 4.36 4.06 0.6 5.0 3.72 4.38 4.05 0.66 6.0 3.68 4.4 4.04 0.72 7.0 3.62 4.4 4.01 0.78 figure 11(a) shows the equivalent circuit model of 5-wire interdigital filter. the couplings are restricted to be between adjacent lines, i.e. non-adjacent line couplings are assumed to be zero and also neglecting all the fringing capacitances. the equivalent circuit is going to modify by placing the mems bridge on the interdigital filter as shown in figs. 11(b)-11(d). if the mems bridge is placed on the center line the equivalent circuit is iium engineering journal, vol. 10, no. 2, 2009 alam et al. 77 shown in fig. 11(b) where cmems is series connected to the 3rd branch. if the mems bridge is placed along all the interdigital filter wire, mems capacitances are distributed iium engineering journal, vol. 10, no. 2, 2009 alam et al. 78 (a) (b) (c) (d) fig. 11: static equivalent capacitance model of proposed 5-wire interdigital filter (a) without mems, (b) mems bridge placed on centre line, (c) mems bridges placed across all the lines, and (d) mems bridges placed on each line. c1 c2 c3 c4 c5 c12 c23 c34 c45 cmems c1 c2 c3 c4 c5 c12 c23 c34 c45 cmems c1 c2 c3 c4 c5 c12 c23 c34 c45 cmems3 cmems4 cmems5 cmems2 cmems1 cmems12 cmems23 cmems34 cmems45 c1 c2 c3 c4 c5 c12 c23 c34 c45 cmems3 cmems4 cmems5 cmems2 cmems1 iium engineering journal, vol. 10, no. 2, 2009 alam et al. 79 throughout the coupling capacitance. all the branches are connected to the ground as shown in fig. 11(c), whereas mems capacitances are connected to all the branches without distributed in the coupling capacitance if mems bridges are placed parallel to the interdigital line as shown in fig. 11(d). the nodes connected to c1 and c2 acknowledgement are input and output nodes respectively. the variation of the mems capacitances results the variation of the frequency response of the bandpass filter. 3. conclusions the criteria of rf filters with a higher performance, smaller size, lighter weight, lower cost, low loss, and high selectivity can be achieved by using rf mems technology. the designing of the interdigital band pass filter has been presented with the analysis of the frequency responses of the filter. the use of capacitive rf mems switch in the application of interdigital band pass filter is investigated in this paper. the designs indicate that the application of capacitive rf mems switches in the tunable filter enables the filter to tune the bandwidth in the frequency range of 3.6 ghz to 4.4 ghz, which was the range for the filter design without mems switch. the tunability has made the filter suitable to be used in different types of application. the authors thank the ministry of higher educationfundamental research grant scheme, frgs grant ref: iium/504/res/g/14/3/05/frgs for funding this research through the international islamic university malaysia (iium). references [1] i.c. hunter, l. billonet, b. jarry, and p. guillon, “microwave filters—applications and technology”. ieee trans. microwave theory & tech. 50(3), pp.794-804, 2002. [2] j. uher, and j. r. hofer, “tunable microwave and milimeter-wave band pass filters”. ieee trans.microwave theory tech., 39(4), pp. 643-653, 1991. [3] g. l. matthaei, e. young, and e. jones, “microwave filters, impedancematching networks, and coupling structures”. norwood, ma: artech house, 1980 [4] g. m. rebeiz, “rf mems theory, design, and technology”. john wiely and sons, 2003. [5] k. entesari, and g. m. rebeiz, “a 12-18 ghz 3 pole rf mems tunable filter”. ieee trans. on microwave theory tech., 53 (8), pp. 2566-2571, 2005. [6] a. pothier, j. c. orlianges, and e. zheng “low loss 2-bit bandpass filters using mems dc contact switches”. ieee trans. on microwave theory tech. 53, pp. 354-360, 2005. [7] m. miao, j. bu, and l. zhao, “a bulk micromachined tunable microwave lowpass filter for 10-15ghz wireless/satellite communication”. proceedings of the 3rd ieee int. conf. on nano/micro engineered and molecular system, china, pp. 524528, 2008. iium engineering journal, vol. 10, no. 2, 2009 alam et al. 80 [8] c. rauscher, “reconfigurable band pass filter with a three-to-one switchable passband width”. ieee trans. microw. theory tech., vol. 52, no. 3, pp. 573–577, 2003. [9] w.h. tu, and k. chang, “piezoelectric transducer-controlled dual-mode switchable bandpass filter”. ieee microw. and wireless components lett, vol. 17, no. 3, pp. 199– 201, 2007. [10] k. entesari, k. obeidat, a.r. brown, and g. rebeiz, “a 25-75-mhz rf mems tunable filter”. ieee trans. microw. theory tech., vol. 55, no. 11, pp. 2399–2405, 2007. [11] j. s wong and m.j. lanchester, “microstrip filters for rf/microwave applications”. john wiley & sons inc, 2001. [12] a. das and s. d. das, “microwave engineering”. mcgraw hill international edition, 2001. tunable bandpass filter using rf mems switches 2.1 one mems bridge parallel with the resonator 2.2 two mems bridge parallel with the resonator 2.3 one mems bridge perpendicular to the resonator 2.4 mems bridges parallel and covering all the resonators acknowledgement references keywords : quantum cryptography, quantum key distribution, decoy state protocol, optical communications 2. experimental setup influence of polarization mode dispersion on the effect of cross-phase modulation in intensity modulation-direct detection wdm transmission system introduction system model theoretical analysis 3.1 modulation of the probe field results and discussion conclusion acknowledgement references towards a scalable scientific data grid model and services introduction related works the p2p data grid model the simulation study experiments and results conclusion and future work references anomalous electrodeposition of fe-ni alloy coating from simple and complex baths and its magnetic property microsoft word 164-564-1-rv completed revised.docx iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 162 sound transmission loss of a double-leaf solid-microperforated partition under normal incidence of acoustic loading a.y. ismail, a. putra and md. r. ayob faculty of mechanical engineering, university technical malaysia melaka (utem), hang tuah jaya, durian tunggal 76100 melaka, malaysia. its_ahmadyusuf@yahoo.com abstract: the micro-perforated panel (mpp) is recently well-known as an alternative ‘green‘ sound absorber replacing the conventional porous materials. constructed from a solid panel which provides a non-abrassive structure and also an optically attractive surface, there gives a feasibility to implement such a panel inside a vehicle cabin. this paper is the preliminary study to investigate the sound transmission loss (tl) of a solid panel coupled with a micro-perforated panel to form a doube-leaf partition which is already known as a lightweigth stucture for noise insulation in vehicles and buildings. the mathematical model for the tl subjected to normal incidence of acoustic excitation is derived. the results show that its performance substantially improves at the troublesome frequency of mass-air-mass resonance which occurs in the conventional double-leaf solid partition. this is important particularly for the noise source predominant at low frequencies. this can also be controlled by tuning the hole size and number as well as the air gap between the panels. abstrak: panel bertebuk mikro (micro-perforated panel (mpp)) kebelakangan ini dikenali sebagai alternatif penyerap bunyi yang mesra alam menggantikan bahan berliang lazim. dibina daripada satu panel padu yang memberikan satu struktur tak lelas dan juga satu permukaan yang menarik, ia memberikan kemungkinan penggunaan panel tersebut di dalam kabin kenderaan. tesis ini merupakan kajian permulaan dalam mengkaji hilang pancaran bunyi (sound transmission loss (tl)) oleh satu panel padu yang digandingkan dengan satu panel bertebuk mikro. kaedah ini menghasilkan satu sekatan lembar kembar yang sememangnya dikenali sebagai struktur ringan penebat bunyi di dalam kenderaan dan bangunan. model matematik diterbitkan untuk tl tersebut dengan menjalankan pengujaan akustik yang tuju normal. keputusan menunjukkan bahawa prestasi meningkat dengan ketara pada frekuensi yang susah semasa resonans jisim-udara-jisim berlaku di dalam sekatan padu lembar kembar lazim. ini penting terutamanya untuk sumber bunyi yang pradominan pada frekuensi rendah. ia juga boleh dikawal dengan menalakan saiz dan jumlah lubang serta luang udara di antara panel-panel tersebut. keywords: sound transmission loss; double-leaf; partition; micro-perforated panel 1. introduction low noise level inside a vehicle cabin, such as car, train and airplane is important to provide a ’comfort room’ for the passengers. hence the design of the structural car body such as the door, roof and cabin interior is made such that noise from engines, tires or wheel, brake and turbulence boundary layer is transmitted into the cabin with minimum amount. a well iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 163 known method for reducing the noise is by installing a partition panel. in general, the partition has a main function to reflect most of the noise and transmit the rest. this is caused by large changes of acoustic impedance in the transmission path created by the partition. a double-leaf partition is known as the lightweight structures in a vehicle such as car doors, train walls or aircraft fuselages. this double-panel is found to increase the transmission loss significantly compared with the single panel partition [1]. however, for noise source predominantly dominates at low frequencies, a double-partition gives a poor performance due to the socalled mass-air-mass resonance. the experimental results for sound transmission loss (tl) of single and double-leaf partitions can be seen in fig.1. this presents that the double-leaf gives the troublesome resonance frequency for noise insulation at around 100 hz. fig. 1: comparison of sound transmission loss between single and double-leaf partition [2]. several works have been done to improve the performance of the double-leaf partition including to overcome the problem at mass-air-mass resonance. this includes the introduction of a hemholtz resonator between the gap [2], by embedding long t-shaped resonators along the edge of the double panel partition [3], by placing loudspeaker and installing actuator between the gap to actively control the acoustic mode [4] and filling the absorbent material inside the gap [5]. the finding of a micro-perforated panel (mpp) by dah you maa in 1975 as sound absorber gives a new leap in the acoustical research. mpp is a perforated panel with millimetric size holes backed by air cavity and rigid surface. the holes diameter must be in the range between 0.05-1 mm and the perforation ratio is between 0.5-1.5% [6]. this finding has been attracting other researchers to employ this system as a ‘green sound absorber‘ in many applications [7]. since the mpp is made from a solid panel, it will provide a hygenic, optically attractive and non-abrasive structure. this therefore offers a feasibility to be also implemented in a vehicle cabin. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 164 many studies have been done to improve the performance of mpp in terms of its sound absorption including by coupling it into a double-leaf system [8], increasing the thickness to obtain better mechanical structure properties [9], modifying the hole shape [10] and partitioning the back cavity [11]. this paper is the preliminary study to investigate the performance of a solid plate coupled with a mpp in terms of its sound transmission loss (tl). the use of the mpp in this system is to provide a good sound absorption inside the cabin. on the other hand, the presence of the mpp is also expected to overcome the phenomenon of the mass-air-mass resonance for a double-leaf. the viscous force of the air flow inside the hole creates a friction force between the air and the inner wall of the holes. this becomes an additional damping which reduces the resonances of the system. for the rest of this paper, the system is referred as the solidmicroperforated partition (smpp) system. in the next section, the mathematical model of the tl for the smpp system is derived. 2. theory figure 2 shows a mechanical system of a smpp with uniform, unbounded and nonflexible panels having mass per unit area µ supported by viscous dampers r and elastic suspensions s impinging by normal incidence of sound wave. the incident and reflected sound pressure with frequency  at the solid (left) panel are given by jkx i eap  1 ~~ (1) jkx r ebp 1 ~~  (2) where ck / is the acoustic wave number and c is the speed of sound. the curl sign indicates complex number. using euler equation  dxdpjv //1~  at x = 0for eq. (1) and eq. (2), the particle velocity can be written as  11 ~~1~ bacv   (3) where  is the density of air. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 165 fig. 2: mechanical system of a double-solid-microperforated partition. since the left panel is solid, the particle velocity along the plate surface v~ is same with panel velocity pv ~ . eq. (3) can be rearranged as 11 ~~~ 1 bavz pf  (4) where cz f  is the impedance of the air and 1 ~ pv is the solid panel velocity. the acoustic pressure acting on the solid panel surface 1 ~p and 2 ~p at x = 0 and on the perforated panel surface at x = d are given by ri ppbap ~~~~~ 111  (5) 222 ~~~ bap  (6) jkdjkd ebeap 223 ~~~   (7) vz ftp  ~ (8) the mean particle velocity v in eq. (8) is obtained due to the presence of holes in the right panel. the particle velocity is no longer the same as the panel velocity, but it now includes the effect of the particle velocity inside the holes. according to takahashi and tanaka [12], this is given by   fp vvv ~1~ 2   (9) where fv ~ is the fluid velocity inside the holes, 2 ~ pv is the right panel velocity and  is the perforation ratio. the impedance of the holes ioroo zzz ,, ~~  is given by maa [6] where iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 166                          t dxx d tv z ooo o a ro 9 2 32 1 32 2/12 2, (10)                         t dx tjz ooio   3 8 32 91 ~ 2/12 , (11) with    2/1/2/ aoo vdx  for av is the air viscosity. the resistive or real part of the impedance roz , represents the viscous effect of air interaction with the panel surface in the hole and imaginary part ioz , ~ represents the acoustic reactance from the inertia of the air inside the holes. the following equation of the net force acting on the plate can be expressed as   pvzvvz fiopfro  ~~~~ ,, 2 (12) re-arrange eq. (12) and substitute to eq. (9) gives the mean particle velocity as a function of the pressure difference p z p vv p ~ ~ 2    (13) where  zz io ~/~1 , and /~~ ozz  . the equation of motion for the right panel due to the acoustic loading is given by     222 ~~1~ ~ , pfropp vvzpvz  (14) where the second term on the right hand side of eq. (14) is the viscous force inside the hole. re-arrange eq. (14) and using eq. (12) yields 2 ~ pvp  (15) where  is the modified panel impedance due to the perforations given by             z zz z iorop ~ ~ ~1 ,, 2 (16) where z z ro ~1 ,  . equation (7) can be expanded into     kdbajkdbap sin ~~ cos ~~~ 22223  kdvjzkdp pf sin ~cos~ 12  (17) the equation of motion of the left panel caused by the pressure difference acting on it is iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 167 21 ~~~~ 11 ppvz pp  (18) where  jsrjz p / ~ 1  is the impedance of the panel. again using euler equation for eq. (7) and substituting eq. (6) yields the pressure at x = 0+ (right side surface of the solid panel)   kdj vkdvz p pf sin cos~~ 1 2   (19) note that equivalent to eq. (3),  22 ~~~ 1 bavz pf  has been used in eq. (19). substituting eq. (19) to eq. (17) gives   kdj kdvvz p pf sin cos~~ 1 3   (20) the pressure difference at the perforated panel is tppp ~~ 3  (21) by substituting eq. (20) and eq. (8) into eq. (21) gives   kdj evvz p jkd pf sin ~ 1   (22) again substituting eq. (13) into eq. (22) and then to eq. (15) gives the ratio of the panel velocity          z e z kdj e v v jkd f jkd p p ~ sin ~ ~ 2 1  (23) from eq. (4) where ipa ~~ 1  and rpb ~~ 1  1 ~~~ pfir vzpp  (24) substituting eq. (5), eq. (19) and eq. (24) into eq. (18) yields the incident pressure           kdj vkdvz vzvzp pfpfppi sin cos~~~~ 2 1~ 1 111 (25) dividing by vcpt  ~ gives the ratio of the incident pressure and the transmitted pressure                                           kdj z z e z kdzj v v tp ip jkd f p p p sin~ ~ sin ~ ~ ~ 2 1 ~ ~ 1 2 1   (26) iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 168 by substituting the velocity ratio from eq. (23)                                                       kdj z z e z kdzj z e z kdj e p p jkd f p jkd f jkd t i sin~ ~ sin ~ ~ sin 2 1 ~ ~ 1   (27) the transmission coefficient  is given by the ratio of intensity, ./2 cp  from eq.(27) the yields 2 ~ ~ i t p p  (28) and the transmission loss is given by  log10tl  (29) 3. results and discussion figure 3 shows the theoretical results of the tl for the conventional solid double-panel (sdp) and smpp. the result for the single panel is also presented for comparison. the calculation is made for 1 mm thick steel plate with density 7800 kg/m3. the material properties of the mpp as the rear panel is the same, with hole diameter do = 0.1 mm, 50 mm air gap and perforation ratio 0.5%. it can be seen that at low frequencies below 100 hz, both results give identical values. fig. 3: sound transmission loss of single, double panel and smpp under normal incidence of acoustic loading (—sdp, – –smpp, – • –single panel). 10 1 10 2 10 3 10 4 0 20 40 60 80 100 120 frequency [hz] t ra ns m is si on l os s [d b ] iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 169 around 150 hz the common problem of ‘drop’ value for the conventional sdp occurs due to the system resonance. the double-leaf shows its superiority over the single panel across the frequency range except at the resonance. around this particular frequency, both the panels and air inside the cavity move in phase which is then known as ‘mass-air-mass’ resonance. the transmission loss is found to drop to almost 0 db which indicates a bad performance for a noise barrier especially for a noise dominating around this frequency. the dips around 3.5 and 7 khz are the cavity resonances which occur at the corresponding acoustic wavelength of nλ = 2d with n is any non-zero positive integer. for the smpp, a better performance is obtained around this troublesome resonance frequency. the air pressure passes through the hole creates a viscous shear stress due to friction between the air and the wall inside the holes. this friction force which has opposite direction to the motion of the panel gives additional damping to the cavity that reduces the coupling between the structural and the acoustic cavity modes. however, above this resonance, the tl from smpp is lower than that from the sdp. fig. 4: sound transmission loss of smpp with different hole diameter for 0.5% perforation ratio and 50 mm air gap under normal incidence of acoustic loading (—sdp, – – do = 0.1 mm, – • – do = 0.2 mm, ٠٠٠ do = 0.4 mm). figure 4 presents the results for smpp with different hole diameters and constant perforation ratio of 0.5% and gap distance 50 mm. this is plotted up to 1 khz to focus only around the resonance region. the sdp decreases the tl by roughly 15 db in average around the resonance. however, it can be seen that the use of a mpp for the rear panel improves the tl around the resonance. the improvement can be achieved by increasing the hole size, but in consequence, decreases the performance above the resonance. it can also be seen that doubling the diameter from 0.2 mm to 0.4 mm gives almost no effect on the tl at the resonance. 10 1 10 2 10 3 0 5 10 15 20 25 30 35 40 45 50 frequency [hz] t ra ns m is si on l os s [d b ] iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 170 figure 5 plots the results for constant hole diameter by varying the perforation ratios. the improvement of tl around the mass-air-mass resonance can also be seen by increasing the perforation ratio. the effect of the air gap is presented in fig. 6. it can be seen that the decrement of the air gap increases the resonance and at the same time also reduces the ‘drop value‘ significantly. the tl at the mass-air-mass resonance improves as the air gap is reduced. at high frequencies, the tl reduces as the gap increases. for clarity of analysis, the level of improvement or decrement of the tl can be represented by the insertion gain (ig) i.e. the ratio of the transmitted power after to before the introduction of micro-holes at the rear panel which is given by sdpsmpp sdp smpp tltllog10ig            (30) where tlsmpp is the transmission loss of the smpp and tlsdp is for the sdp. fig. 5: sound transmission loss of smpp with different perforation ratios for 0.1 mm hole diameter and 50 mm air gap under normal incidence of acoustic loading (—sdp, – – τ = 0.5%, – • – τ = 1%, ٠٠٠ τ = 1.5%). 10 1 10 2 10 3 0 5 10 15 20 25 30 35 40 45 50 frequency [hz] t ra ns m is si on l os s [d b ] iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 171 fig. 6: sound transmission loss of smpp with different air gaps for 0.1 mm hole diameter and 0.5% perforation ratio under normal incidence of acoustic loading (—sdp, – –d = 10 mm, – • –d = 20 mm, ٠٠٠d = 40 mm). figure 7 shows the ig for smpp with different diameters as in fig. 3. it can be seen that the improvement around the resonance is about 15-18 db. deterioration above the resonance can be seen to increase with frequency. fig. 7: insertion gain of smpp with different hole diameters for 0.5% perforation ratio and 50 mm air gap under normal incidence of acoustic loading ( – – do = 0.1 mm, – • – do = 0.2 mm, ٠٠٠ do = 0.4 mm). 10 1 10 2 10 3 0 5 10 15 20 25 30 35 40 45 50 frequency [hz] t ra ns m is si on l os s [d b ] 10 1 10 2 10 3 -20 -15 -10 -5 0 5 10 15 20 frequency [hz] in se rt io n g ai n [d b ] iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 172 figure 8 shows the ig for different perforation ratios. same with previous results, the improvement can be seen by 15-18 db at 150 hz. the ig for different air gaps are also presented in fig. 9. it can be seen that doubling the air gap reduces the tl at the resonance by roughly 4 db. however, as in figs. 7 and 8, the improvement is only around the mas-air-mass resonance. fig. 8: insertion gain of smpp with different perforation ratios for 0.1 mm hole diameter and 50 mm air gap under normal incidence of acoustic loading (– – τ = 0.5%, – • – τ = 1%, ٠٠٠ τ = 1.5%). fig. 9: insertion gain of smpp with different air gaps, for 0.1 mm hole diameter, 0.5% perforation ratio under normal incidence of acoustic loading (– –d = 10 mm, – • – d = 20 mm, ٠٠٠d = 40 mm). 10 1 10 2 10 3 -20 -15 -10 -5 0 5 10 15 20 frequency [hz] in se rt io n g ai n [d b ] 10 1 10 2 10 3 -20 -15 -10 -5 0 5 10 15 20 frequency [hz] in se rt io n g ai n [d b ] iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 173 4. conclusion preliminary study on the possibility to apply the mpp as the noise barrier in a double-leaf partition has been presented. in order to improve the poor performance at the resonance for transmission loss of the conventional double-leaf, the presence of micro-perforated holes in the rear panel is found to be effective. however, the improvement only happens at a very narrow frequency band around the mass-air-mass resonance. it is found that this improvement can be increased by increasing the hole size or the perforation ratio and by reducing the air gap. on the other hand, application of the mpp seems to sacrifice the performance at high frequencies. nevertheless, this is still beneficial especially for the noise source dominating at low frequencies. moreover, the model proposed assumes normal incidence of sound excitation. for more real application, which is diffuse field, the effect will be greater in terms of the frequency range. this will be investigated on the future work. acknowledgement this research is funded by the fundamental research grant scheme (frgs) of the ministry of higher education (mohe) malaysia at the university technical malaysia melaka. references [1] fahy, f., gardonio, p., sound and structural vibration : radiation, transmission and response. academic press, 2007. [2] mao, q., pietrzko, s., “control of sound transmission through double wall partition using optimally tuned hemholtz resonators” applied acoustics, 2005. [3] li, d., zhang, x., cheng, l., and yu, g., “effectiveness of t-shaped acoustic resonators in low frequency sound transmission control of a finite double-panel partition.” journal of sound and vibration, vol:329, pp. 4740-4755, 2010. [4] li and cheng, “mechanism of active control of sound transmission through a linked double wall system into an acoustic cavity,” applied acoustics, vol : 69, pp. 614-623, 2008. [5] alba, j., ramez, j., and snachez, v., “improvement of the prediction of transmission loss of double panel with cavity absorption by minimization techniques” journal of sound and vibration, vol:273, pp.793-804, 2004. [6] maa, d., “theory and design of microperforated panel sound absorbing construction (in chinese).” scientica sinica, vol:18, pp.55-71, 1975. [7] fuchs, h. v., zha, x., “micro-perforated structures as sound absorber – a review and outlook” acta acustica united with acustica, vol:92, pp.139-146, 2006. [8] sakagami, k., morimoto, m., and koike, w., ”a numerical study of double leaf microperforated panel absorber.” applied acoustics, vol:67, pp.609-619, 2006. [9] pfretzschner, j. and cobo, p., “microperfoated insertion units : an alternative strategy to design microperforated panels.” applied acoustics, vol:67, pp.62-73, 2006. [10] sakagami, k., morimoto, m., yairi, m., and minemure, a., “a pilot study on improving the absorptivity of a thick micoperforated panel absorber,” applied acoustics, vol:60, pp.179-182, 2008. [11] liu and herrin, “enhancing microperforated panel attenuation by partitioning the adjoining cavity,” applied acoustics, vol:71, pp.120-127. 2010. [12] takahashi, d., and tanaka, m., “flexural vibration of perforated plates and porous elastic materials under acoustic loading,” journal of the acoustical society of america, vol:112, pp.1456-1464, 2002. iium engineering journal, special issue, mechanical engineering, 2011 ismail et al. 174 nomenclature c sound speed in air m/s d gap distance m do hole diameter m j imaginary part k wavenumber rad/m p acoustic pressure n/m2 pressure difference n/m2 r damping coefficient per unit area ns/m s stifness per unit area n/m t panel thickness m tl transmission loss db va air viscosity kg/s.m particle velocity m/s panel velocity m/s z total acoustic impedance ns/m3 zo hole impedance ns/m3 zo,r real part of hole impedance ns/m3 zo,i imaginary part of hole impedance ns/m3 zf fluid impedance ns/m3 µ mass per unit area kg/m2 ω angular frequency rad/s ρ air density kg/s.m τ transmission coefficient p v~ pv ~ microsoft word vol 12_no1_2011_june.doc iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 53 design and fabrication of micronozzles k.h. cheah and j.k. chin department of chemical and environmental engineering, university of notitngham malaysia campus, jalan broga, 43500 semenyih, selangor darul ehsan, malaysia. e-mails: jit-kai.chin@nottingham.edu.my, cheah.keanhow@nottingham.edu.my abstract: micronozzle, a key component in micropropulsion system, has been designed and fabricated. quasi 1d inviscid theory was used in designing a series of conical micronozzles of different expander half-angles (10°-50°). aerospike micronozzle, a promising candidate to achieve high performance propulsion system, was designed with angelino method (or approximate method). both micronozzles were fabricated using soft lithography, an inexpensive and relatively simple technique comparing to well-established deep reactive ion etching (drie) technique, with polydimethylsiloxane (pdms) as structural material. micronozzles with two different nozzle throat width, 53.5 µm and 107 µm, were fabricated for comparison. microscopic inspections reveal 107µm is the more producible nozzle throat width with current equipments. the pdms-based micronozzle can be used as cold gas microthruster system for microand nanosatellites. abstrak: mikronozzle, satu komponen kunci dalam sistem pendorongan-mikro telah direkabentuk and dibina. teori quasi 1d inviscid telah digunakan dalam perekaan beberapa siri conical micronozzles dengan expander sudut-separa yang berbeza (10°50°). aerospike micronozzle, calon yang menjanjikan pencapaian prestasi tinggi untuk sistem dorongan telah direkabentuk dengan menggunakan angelino method (atau approximate method). kedua-dua micronozzles tersebut telah dibuat dengan menggunakan soft lithography, suatu teknik yang relatif murah and senang, dengan polydimethylsiloxane (pdms) sebagai bahan struktur. micronozzles dengan dua dimensi nozzle throat yang berbeza, 53.5µm and 107µm, telah dibuat untuk perbandingan. pemeriksaan mikroskopik mendedahkan bahawa 107µm adalah dimensi yang boleh dibuat dengan peralataan yang sedia ada. key words: micronozzles, micropropulsion, microfabrication, soft lithography 1. introduction microsatellites (<20 kg) have provided the space community a low cost platform in performing space education and demonstration of new technologies in the last decade. the launching cost reduces significantly due to their small size and volume. evolution of these satellites to perform actual scientific missions requires more pronouns manoeuvrability and fast response attitude control system for precise pointing and formation flying [1]. in order to fulfil the requirements of future missions, micropropulsion system with low thrust (µn to mn), system mass (<1 kg), volume (<1 cm3) and power (<1 w) is required [2]. iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 54 previous numerical studies show that performance of micronozzle, a key component in micropropulsion system, is strongly affected by viscous effect [3, 4]. a deep micronozzle is preferred to mitigate viscous loss due to merging of viscous boundary layers at end walls. aerospike micronozzle with virtual wall boundaries could further reduce viscous loss [5]. deep reactive ion etching (drie), a proven but complicated technique in fabrication of micronozzles, would cause photomask breakdown over time and reduced wall straightness as the depth increases [6]. moreover, the technique requires expensive equipments and tooling. in contrast, soft lithography, an inexpensive and relatively simple microstructures fabrication technique, enables fabrication of ultra-thick structure as thick as 1.5 mm with good vertical wall profile [7, 8]. in the present study, we first design two types of micronozzle, conical and aerospike, with the aim of improved efficiency through deep micronozzle approach. micronozzles are then fabricated using soft lithography with pdms as structural material. surface contour and geometry accuracy of fabricated micronozzles are examined under inverted light microscope and scanning electron microscope (sem). 2. design of micronozzles designing micronozzles requires some unique considerations. flow characteristics within micronozzles are different from their macro-scale counterparts. the flow is characterized by low reynolds number, re, where  vl re or `re a lm    (1) for a typical micronozzle operates at mass flow rate in the order of µ kg/s and characteristic length in µm scale, re is within the range of 101 to 103 suggesting the significance of viscous effect and laminar flow behaviour [9]. macro-nozzles experience small loss (less than 1% with occasionally up to 2%) of total energy due to viscous effect [10]. viscous boundary layer can occupy substantial portion of expander section causing a severe performance degradation in micronozzle. traditional nozzle design approach based on inviscid flow theory is quite satisfactory in designing macro-nozzle but it is not totally applicable when designing micronozzles. however, inclusion of viscous effect would complicate the governing equations. in light of the complication, conventional quasi 1d inviscid theory was used as first approximation in current design. important findings (e.g. larger micronozzle depth, shorter expander length etc.) from previous numerical studies on micronozzles were adapted into current design to mitigate viscous loss [3, 4]. fabrication constraints inherited from available equipments were considered and relevant design limits were applied during the design process. nozzle throat width, wt, was limited to not smaller than 50 µm. micronozzle depth was limited to 200 µm after compromising between performance degradation due to 3d viscous effect and allowable nozzle throat width [4]. the wt was magnified by a factor of two in order to evaluate the fabrication capability while the nozzle depth was reduced accordingly to maintain a constant area of nozzle throat. iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 55 2.1 conical micronozzles conical nozzles being the simplest nozzle shape are commonly used in micropropulsion system. conical micronozzle with optimum expander half-angle demonstrates very similar performance in comparing with bell-shaped micronozzle [12]. quasi 1d analysis [10] based on isentropic flow equations and rocket nozzle theory [13] were combined to evaluate for micronozzle design parameters such as micronozzle geometry and its internal flow characteristics. one of the most important parameters, nozzle expansion ratio, is formulated as 1 1 2 2 1 1 1 2 2 1 2                           k k e m k k e mta e a (2) the design parameters are summarized in table 1. conical micronozzles with expander half-angles, θ, ranging from 10º – 50º were designed. details of the design process can be found in authors’ previous work [11]. table 1: micronozzle design parameters. design input value design output value chamber pressure 280 kpa expansion ratio 9.8 chamber temperature 513 k nozzle throat width 53.5 µm (107 µm) nozzle depth 200 µm (100 µm) nozzle exit width 522.7 µm nozzle exit mach no. 3.65 mass flow rate 4.539 x 10-6 kg/s specific impulse 106.2878 s throat reynolds no. 1207 2.2 aerospike micronozzles aerospike nozzles were first investigated in early 1960s. the nozzle is characterized by no outer walls allowing exhaust gas to expand freely without constraining from walls. it is a promising candidate in achieving high performance propulsion system owing to this unique altitude compensation feature. current aerospike micronozzles were designed with angelino method (also known as approximate method) [14]. the method combines prandtl-mayer expansion theory and area-mach relation (equation 2) in determining spike geometry. figure 1 shows a typical 2d aerospike nozzle. iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 56 fig. 1: two dimensional aerospike nozzle [11]. characteristic lines cross the nozzle boundary at distance l from the lip, can be computed by   tt aall /1sin//  or m  (3) where α = µ(m) – ν(m). based on the same design parameters as conical micronozzles, length of the lines were calculated with equation (3) and converted into x and y coordinates. corresponding spike contour was plotted in fig. 2. fig. 2: spike contour calculated with angelino method. 3. fabrication of micronozzles 3.1 materials in this study, a 5 inch silicon wafer (shin-etsu (m) sdn. bhd.) was used as substrate. su-8 50 photoresist (pr) (microchem corp.) and propylene-glycol-methyl-ether-acetate iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 57 (pgmea) were used as coating material and developer respectively. the designs were drawn using autocad software and printed on a transparency film using a laser printer (epson t60) to generate a photomask. pdms (sylgard 184, dow corning) was used in replicating micronozzles from su-8 master. 3.2 methods the procedure of soft lithography is illustrated in fig. 3 and described in detail below. (a) spin coating (b) soft bake and exposure (c) post-exposure bake (d) pgmea development (e) pdms molding (f) pdms peel off (g) sealing fig. 3: schematic of soft lithography in fabricating micronozzles. a. master preparation prior to the process, silicon wafer was cleaned with standard rca cleaning procedure followed by a pre-baked at 200ºc for 5 minutes to remove any residual moisture on wafer surface [15]. about 5 ml of su-8 pr (1 ml per inch of wafer) was poured onto the wafer and slow spin at 500 rpm for about 20 seconds to spread pr evenly. this was followed by a fast spin at 1250 rpm for 30 seconds for a coating thickness of 100 µm. the spin coated wafer was then soft-baked at 65ºc for 50 minutes. soft-baking at lower temperature [16] would reduce stress-related crackings. baking and cooling process were carried out at a slow rate (5 ºc/min) to avoid thermal stress. for coating thickness of 200 µm, the steps were repeated for additional 100 µm. the polymerization of su-8 pr was assisted using self-customized uv-a radiation system (philip tl-k 40w/10r) which radiates highly concentrated radiation between 350 nm and 390 nm. post-exposure bake was carried out at 55ºc for 20 minutes with a ramping rate of 5 ºc/min. after 1 hour of relaxation time, the wafer was immersed into pgmea and agitated gently to dissolve the un-crosslink su-8 pr. developed wafer was silanized with 1,1,2,2 – tetrahydrooctyl-1-trichlorosilanem (uct, inc.) to facilitate mold release. the wafer with remaining patterns is known as su8 master. b. device fabrication pdms prepolymer was mixed thoroughly with its curing agent at 10:1 ratio by volume. the mixture was then placed into vacuum desiccators for degassing to remove iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 58 bubbles introduced during mixing process. degassed mixture was poured onto su-8 master and cured at 65ºc for 1 hour. pdms device was then peeled off from the master. c. device sealing fabricated pdms device was sealed using hydrophilic bond. a piece of pdms slide (cutting the leftover pdms from previous steps into desired shape) and pdms device was oxidized in freshly prepared strong oxidizing solution, a mixture of 98% h2so4 and 30% h2o2 at 1:1 ratio. the slide was dipped in the solution for 1 minute while the pdms device for 15 seconds. dipping for a longer time may damage the microstructures of the device. both pieces of pdms were rinsed with distilled water to remove residual acid and dried with compressed stream of air. the device was placed into contact with pdms slide and heated at 70ºc for 30 minutes. 4. results and discussion figure 4 shows selected images of micronozzles printed on transparency film (mask) and their replication on pdms. all images were investigated under inverted light microscope (olympus, ix 51) with magnification of 40x and bright field mode. in general, all printed features can be distinguished clearly as micronozzles. the printer is capable in printing the smallest nozzle throat width of 53.5 µm as nozzle throat was seen clearly and not filled by printer ink as shown in fig. 4. though, in comparison to wt=107 µm, the resolution is not satisfactory as micronozzle expander walls are not smooth in which some ripples were observed. images of pdms micronozzles are shown below of each mask pattern for comparison. for wt=53.5 µm and θ=10º, expander section of replicated micronozzle disintegrates from nozzle throat. the su-8 structural strength is weak at smaller wt, as shown in fig. 5(a), crack was observed at nozzle throat. it is believed that the crack further propagates during thermal heating. thermal stress is induced as a result of mismatch in thermal expansion coefficient of silicon and su-8, leading to the disintegration. for θ=17.5º and wt=53.5 µm, replicated nozzle loses its resolution, a narrow opening at nozzle throat which may retard or block the flow was observed. the resolution improves for wt=107 µm as no potential flow blockage was observed and wt was found close to that in mask. similar trend was observed for other expander angles. these results suggest wt=107 µm is the more producible nozzle throat width with current equipments. it is supported by sem images in fig. 5(b) and (c), both conical micronozzles with wt=107 µm show acceptable accuracy. current printing device is obviously lack of precision in printing full length spike geometry especially wt=53.5 µm. for wt=107 µm, geometry precision is acceptable up to 80% of total spike length. images of pdms aerospike micronozzle in fig. 4 further justify the producible nozzle throat width is 107 µm as blockage at nozzle throat was observed for wt=53.5 µm. current equipments unable to produce spike contour with a sharp spike tip. as shown in fig. 5(d), su-8 near the sharp tip was not completely removed during the development. as a consequence, the replicated spike tip for both wt are distorted as shown in fig. 4. iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 59 fig. 4: selected images of micronozzles (from left: conical 10º, conical 17.5º and aerospike) with different nozzle throat width (53.5 µm and 107 µm) observed under inverted light microscope. first row is printed patterns on transparency film; second row is the replicated patterns on pdms. (a) (b) (c) (d) fig. 5: sem (fei, quanta400f) images: (a) crack at nozzle throat, θ=10º, wt=53.5 µm; (b) conical micronozzle, θ=17.5º, wt=107 µm; (c) conical micronozzle, θ=40º, wt=107 µm; (d) aerospike micronozzle, wt=107 µm. (a) (b) (c) (d) fig. 6: size of (a) pdms conical micronozzle with θ=17.5º wt=107µm; (b) pdms aerospike micronozzle, wt=107 µm, compared with malaysian 10 sen coin (dia. ≈1.9 cm) and their sem images in (c) and (d) respectively. conical micronozzle aerospike micronozzle wt = 116.6µm wt = 133µm iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 60 figure 6 (a) and (b) show photographs of pdms micronozzles in comparison with a malaysian 10 sen coin (diameter ≈ 1.9 cm). figure 6 (c) and (d) are sem images of pdms conical (θ=17.5º and wt=107 µm) and aerospike (wt=107 µm) micronozzles. measurements show conical micronozzle has wt=116.6 µm while the aerospike micronozzle has wt=133.3 µm. further optimization on fabrication procedures is needed to improve wall smoothness and dimensional accuracy. higher resolution mask is required in fabrication of micronozzles of smaller wt. truncated aerospike micronozzle should be considered as alternative if better photomask still cannot eliminate the spike tip problem. 5. conclusion in this research, we demonstrated that micronozzles can be fabricated through soft lithography. the technique is inexpensive and relative simple compared to wellestablished drie technique. conical and aerospike micronozzles were designed and fabricated in two different nozzle throat widths for comparison purpose. microscopic inspections suggest 107 µm is the more producible dimension with current equipments. the potential application of pdms-based micronozzle is limited to cold gas microthruster system due to relatively low decomposition temperature of pdms. future research would focus on fabrication optimization and the use of alternative structural materials such as ceramic which can work under high temperature. acknowledgement the authors would like to acknowledge mosti escience fund for funding the research. references j. mueller, c. marrese, j. polk, e-u. yang, a. green, v. white, d. bame, i. chakraborty and s. vargo, “an overview of mems-based micropropulsion development at jpl.”, acta astronautica 52 (9-12): 881-895, 2003 r. osiander, m.a. g. darrin, and j.l. champion, “mems and microstructures in aerospace applications.”, crc press, us, 2006 w.f. louisos and d.l. hitt, “viscous effects on performance of two-dimensional supersonic linear micronozzles.”, journal of spacecraft and rockets, vol. 45, no. 4, 706715, 2008 w.f. louisos and d.l. hitt,“numerical studies of thrust production in 2d supersonic bell micronozzles.”, 44th aiaa/asme/sae/asee joint propulsion conference & exhibit, 2008 iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 61 a. zilic, d.l. hitt and a.a. alexeenko,“numerical simulations of supersonic flow in a linear aerospike micronozzle.”, 37th aiaa fluid dynamics conference & exhibit, 2007 r.l. bayt, a.a. ayon, and k.s. breuer, “a performance evaluation of mems-based micronozzles.”, 33rd aiaa/asme/sae/asee joint propulsion conf. & exhibit, 7-9 july, seattle, wa, 1997 y. xia, and g.m. whitesides, “soft lithography”, annual review of material science 28 (1): 153-184, 1998 c.h. lin, g.b. lee, b.w. chang, and g.l. chang, “a new fabrication process for ultra-thick microfluidic microstructures utilizing su-8 pr.”, jour. of micromech. and microeng.12 (5), pp. 590-597, 2002 louisos, w.f., alexeenko, a.a. hitt, d.l. and zilic, a. (2008) design considerations for supersonic micronozzles. international journal of manufacturing research 3, no. 1: 80113. g.p. sutton, and o. biblarz, “rocket propulsion elements.”, 7th edition, john wiley & sons inc, 2001 k.h. cheah, j.k. chin, and k.s. koh, “design and performance prediction of a 5mn han monopropellant microthruster”, int. conf. on mech. and aero. eng. 16-18 april, chengdu, china, 2010 w.f. louisos, and d.l. hitt, “numerical studies of thrust production in 2d supersonic bell micronozzles.”, 44th aiaa/asme/sae/asee joint propulsion conf. & exh., 21-23 july, hartford, ct, 2008 j.d. anderson, “modern compressible flow with historical perspective.” 3rd edition, new york: mcgraw-hill, 2003 g. angelino, “approximate method for plug nozzle design.”, aiaa journal, vol. 2 (10), 1834-1835, 1964 m. bachman, “rca-1 and rca-2 silicon wafer cleaning.”, inrf application note, 1999 t.a. anhoj, a.m. jorgensen, d.a. zauner, and j. hubner, “the effect of soft bake temperature on the polymerization of su-8 photoresist.” journal of micromechanics and microengineering, 16, 1819-1824, 2006 nomenclature re reynolds number ae nozzle exit area, m 2 at nozzle throat area, m2 ρ density, kg/m3 l characteristic length, m v flow velocity, m/s µ viscosity, kg/m2s m mass flow rate, kg/s a area, m2 iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 62 m mach number k ratio of specific heats α geometric angle with reference axis l length of characteristic segment, m λ l/lt, non-dimensional length for plane nozzle ε a/at, expansion ratio wt nozzle throat width θ expander half-angle b body force due to sediment particles ca cavitation number cd drag coefficient cµ anisotropic diffusion coefficient cs1, c s2, c 1ε, c 2ε rs coefficients dp particle diameter e erosion rate density fd drag force fcond cavitation condensation coefficient fvap cavitation vaporization coefficient g gravitational acceleration of the sediment particles k erosion model constant m particle mass n velocity exponent ps saturation pressure of water p fluid pressure pv vapour pressure rb bubble radius rep particle reynolds number iium engineering journal, vol. 12, no. 1, 2011 cheah et al. 63 rf cavitation rate under relaxation factor f fluid phase volume fractionݎ rnuc nuclei volume fraction p particulate phase volume fractionݎ uc fluid velocity up particle velocity u particle relative velocity vp particle impact velocity greek letters β particle mass loadings γ particle impact angle ρf fluid density ρp particle density ρs nucleation site density ρr density ratio σ stress tensor σε turbulence model constant σk turbulence model constant for the k-equation σt surface tension coefficient τp particle response time µ fluid dynamic viscosity ν fluid kinematic viscosity iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 87 iterative spatial sectoring: an extention of simpson’s rule for determining area of irregular closed shape abdulfattah a. aboaba1,2, shihab a. hameed1, othman o. khalifa1 and aisha h. abdalla1 1department of electrical & computer engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2computer engineering department, university of maiduguri, nigeria. abdulfattahaa@gmail.com; shihab@iium.edu.my; khalifa@iium.edu.my; aisha@iium.edu.my abstract: just as the method for determining the properties of shapes like triangles, parallelogram, cuboids, and geometric figures like circle, and spheres have standard formulae, the determination of a function f(x) in many dimensions have formulae or standard methods. complex 2d and 3d figures consisting of intricate merger of regular shapes have had their parameters determined through careful separation and determination of the properties of individual components that make up the figure. moreover, the case of irregular closed shapes mostly but not limited to 2d and 3d which abound in science and engineering have equally received attention resulting in lots of approximation methods evolved over time. the iterative spatial sectoring is a novel way of determining the area of 2d irregular closed shapes by expanding on the famous simpson’s method for finding the area of a function f(x) whose definite integral is either tedious or impossible by standard approaches. abstrak: seperti beberapa kaedah yang ada yang sering kali digunakan untuk menentukan sifat-sifat bentuk seperti segi tiga, segi empat selari, kuboid, dan rajah geometrik seperti bulatan, dan sfera; semuanya mempunyai formula-formula yang standard, penentuan fungsi f(x). bentuk kompleks dua dimensi, 2d dan tiga dimensi, 3d terdiri daripada penyatuan rumit bentuk-bentuk yang biasa dimana parameternya ditentukan melalui pengasingan yang cermat dan penentuan ciri-ciri komponen individu yang akhirnya membentukkannya. walaupun begitu, dalam hal bentuk tertutup yang tak nalar, ia bukan hanya terhad kepada bentuk 2d dan 3d yang banyak terdapat dalam bidang sains dan kejuruteraan. ia mendapat perhatian meluas dimana pelbagai kaedah penghampiran dihasilkan. pensektoran ruang berlelar merupakan cara baru yang digunakan untuk menentukan keluasan bentuk 2d tak nalar yang bertutup dengan mengembangkan kaedah simpson’s untuk mendapatkan keluasan dengan fungsi f(x) dimana kamirannya sama ada terlalu rumit ataupun di anggap mustahil mengikut cara biasa. keywords: function f(x); irregular shape; simpson’s method; definite integral; iterative spatial sectoring 1. introduction irregular 2d and 3d figures consisting of intricate merger of regular shapes have had their parameters determined through careful separation and determination of the properties of individual components that make up the figure [1-3]. moreover, the case of irregular iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 88 closed shapes mostly but not limited to 2d and 3d which abound in science and engineering like that of fig. 1 have equally received attention resulting in lots of approximation methods evolved over time. such methods include the graphical methods of calculating the area of irregular shaped lands usually employed by surveyors, civil and agricultural engineers, and also used in biometric measurements [4]. furthermore, the advent of computer programming brought the emergence of computer-based approximation methods like fractal analysis [5], monte carlo method, pixel-filling, wavelet, and so on. just as the method for determining the properties of shapes like triangles, parallelogram, cuboids, and geometric figures like circle, and spheres have standard formulae, the determination of a function f(x) in many dimensions have formulae or standard methods. one of such is the series expansion for function f(x) which does not fit into direct integration as in eqn. 1 or use of simpson’s rule where the use of series expansion becomes tedious, the like of which is in eqn. 2. again, we see that for finding areas under a curve which has a non-existence function/ impossible function/ difficult-toget function like the one in fig. 2, the method of finding area bounded by a curve in integral calculus application could be use with minimal error [6-9]. fig. 1: an example of irregular shape. = … (1) = √cos … (2) fig. 2: undefined function. iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 89 the iterative partial sectoring (ips) is an idea conceived to evolve yet another approximate method of finding the area of irregular closed shapes of the type in fig. 1 neither from the computer programming perspective nor by integrating an approximate function that describes the curve, but from the classical mathematics standpoint. hence, the ips methodology follows from approximate integral and integral application methods of solving area bounded by functions difficult to express mathematically or shapes whose function is either non-existent. we therefore reasoned that since the areas those complex curves could be evaluated using those approaches, the area of irregular closed shape could also be found by careful extension of those methods especially simpson’s rule. 2. understanding the simpson’s rule of approximate integration suppose we have a curve of the type in fig. 2, and assuming that its function f(x) is either non-existent or not solvable by any know integral approach, or tedious to expand by power series approach, the next logical approach in classical mathematics is the simpson’s rule. the rule says divide the area of interest into even number of spaces with equal spacing, that gives odd number of dividing lines and apply eqn. 3 to get an approximate area bounded by the curve. more so, the approximate area could be closer to reality b y further division of the region of interest into smaller areas as usually done in integral application. fig. 3: applying simpson’s rule. ≈ [( + ) + 4 + 2 ] … (3) fig. 4: analyzing simpson’s rule. iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 90 the simpson’s rule conceived by finding the area of the rectangle abcd bounded by two parallel but unequal length stripes ad and bc as shown in fig. 4. since the two parallel sides of a rectangle must be equal, thus find the area of abcd using the formula for rectangle will only give an approximate value whose error may be unacceptable. hence, the simpson’s formula of eqn. 3 is in effect finding the area of abcd twice such that each time one of the parallel sides (length) is used and the average of the two give a better approximation. that is: ≈ [( ∗ ) + ( ∗ )] 2 … (4) or ≈ … (5) fig. 5: analyzing figure based on integral application. when eqn. 5 is applied to all divisions under the curve it could be summed up as eqn. 3, and that greatly reduces the initial error margin as represented by aefb when length ad is used to something around half of that. furthermore, if we combine this with the idea of making s more and more smaller, when approaches zero as depicted in fig. 6, the error in our approximation also approaches zero. hence the area gotten at that stage becomes less of approximation but actual value. hence, the combination of the two methods to evolve a better result could named “iterative simpson’s method”. fig. 6: error reduction approach. when the problem is extended to irregular closed shape instead of just a curve, we foresee that the combination of these two concepts (“iterative simpson’s method”) and their reformulation in geometric terms will offer an intriguing result. iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 91 3. proof of concept l given that a function f(x) is a sin x represented diagrammatically in fig. 7 and inserted into a cartesian plane shown in fig. 8a and 8b, the area under this shape is found by integrating the function and inserting the limits. fig. 7: a sine function. fig. 8a: sine wave in cartesian plane on the x-axis. fig. 8b: sine wave in cartesian plane elevated. the solution to fig. 8a is the integration of f(x) and substituting the limit marked on the x-axis with a being the amplitude or magnitude of the wave on the y-axis, while the solution to fig. 8b is the same as that of fig. 8a but with the addition of area of the rectangle under the curve. that is, = = ( [ ] – [ ] ) + … (6) = = ( [ ] – [ ] ) + (4 − 1) + … (7) 0 1 2 3 4 5 0 1 2 3 4 5 iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 92 where a is the amplitude of the sine wave, b is the upward projection of the sine wave in fig. 4b, and c is the constant of integration. a good approximation of this result could be obtained by determining the area under the sine wave by combining the method of approximate integral and integral application. this is done by dividing the space under consideration into equally spaced subdivisions, and then, find the sum of the area of each of the subdivisions. that is the area of (a + b + c + d + e + f + g + h + i). given that each of the area of a to i as where is from 1 to 9 representing each of the subdivision, thence, y could be expressed as: ≈ … (8) this approximate solution could be improved upon by further reduction in the width (interspaces) between the red stripes as in figure 9thereby reducing the size of the rectangles formed. conversely, more accurate result could also be achieved by calculating the area of each rectangle twice using one the two lengths (vertical stripes) at a time and then find the average of the two areas. this is exactly what simpson [6-9] formularized as: ≈ [( + ) + 4 + 2 ] … (9) both approaches would be exploited as this work progresses. fig. 9: a section of the sine wave divided into smaller rectangles. 4. proof of concept ll furthermore, if the sine wave is made into a circle as in fig. 6a, the area bounded by the sine wave circle is the area of the inner grooves of the sine wave plus the area of the small circle enclosed by it. that is: = acos + + … (10) where a remains the magnitude of the sine wave, b is the area of the inner circle, and c is integration constant. iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 93 fig. 10a: sine wave made into circle (neatly wobbled irregular shape). fig. 10b: figure 10a separated into sine wave and inner circle. an approximate result could be obtained by dividing fig. 10b into smaller sectors and summing up the area of each of the smaller sectors. similar to what is done in integral applications, the error can be reduced to the barest minimum by making the sector further smaller. however, in taking this approach two questions need be answered that is, what is the angle of the intended sectors?, and what criterion would be used to obtain the reduction of the sectors into smaller ones?. the answer to these questions provides the basis for a quicker convergence of the solution to the problem, and more importantly adds value to this method above its predecessors – the simpson’s rule and the method of reducing the rectangle in integral application. it is observed that we can be close to the precise angle of the sector that will result in close approximation of the area bounded by the sine wave if we can determine the angular squeezeness of the wave. for instance, if we know how close the waves are to each other relative to the biggest expanse the wave as a whole, we could have determined its squeezeness and use the relationship to determine the sector angle, such that the ratio of the average area (determined by a circle drawn around the middle of the vertical compression of the wave such as circle b in fig. 10b) to that of the maximum expanse of the sine wave. in the absence of that we take ratio of circle a the maximum expanse of the sine wave to that of circle c the minimum space left inside it as it squeezes. iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 94 formula for determining sector angle based on the explanation above, we can determine sector angle by multiplying the ratio of a to c by 3600, then subtract 3600 from the product, and divide the magnitude by 10. round the answer to the nearest 100 for easy division. this is mathematically stated as: = (360°) − 360° 10 … (11) this will give sector angle relative to the squeezeness of the irregular shape, thus bringing the first sequence to be close enough to final solution such that with few iterations the solution will converge. 5. steps to solving real problem (a) construct a circle of known radius round the shape similar to a in fig. 10b as shown in fig. 11 (b) construct another circle within the shape similar to c in fig. 10b as shown in fig. 12 (c) find the ratio of a to c (d) do as in eqn. 11 (e) draw the sectors as in fig. 13 (f) mark the points of intersection of the radii with the irregular shape and measure its length (g) determine the area of each sector using eqn. 12 (h) calculate the approximate area of the irregular shape using eqn. 13 (i) reduce the size of the sectors (by halving if possible), and recalculate area of irregular shape using eqn. 14 (j) look for convergence of step (h) and (i) by finding the difference between and the modulus of the difference returns zero or something very close to zero. fig. 11: irregular shape encircled by its approximate largest expanse. fig. 12: the smallest possible circle inserted into the irregular shape. iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 95 fig. 13: irregular shape divided into sectors. ( ) = 360 . … (12) where is the angle derived from equation 11, and , represents the two radii of each sectors. ℎ ℎ ( ) = = = 360 . + 360 . ( ) … (13) ℎ ℎ ( ) = = ∑ = ∑ . + . … (14)( ) 6. conclusion a stepwise description of a iterative spatial sectoring is presented, it is a novel method for finding area of irregular closed spaces. the technique is based on idealistic understanding of methods of finding area under curves particularly the simpson’s rule combined with geometric way of finding area of a sector. the method is not computer based hence there is no need to compare it with computer based methods like fractal analysis, pixel filling, monte carlos and wavelet techniques. it also has the ability to accept error margin by setting |rtx – rtx+1| >= 0, instead of |rtx – rtx+1| = 0. finally there are on-going efforts to develop the software for implementing this method and advance it to a computer based technique. references [1] kreyszing erwin (1993). advanced engineering mathematics, john wiley & sons, new york [2] a.j.m. spencer, d.f. parker, d.s. berry, a.h. england, t.r. faulkner, w.a. green, j.t. holden, d. middleton and t.g. rogers (1983). engineering mathematics vol. 2, van nostrand reinhold com ltd, berkshine, new york [3] k.a. stroud (2007). advanced engineering mathematics, palgrave macmillan [4] http://biosystems.okstate.edu/home/ fharry/4112/500_information/ch%2011.docx [5] khan m. iftekharuddin (2005). techniques in fractal analysis and their applications in brain mr, in cornelius t. leondes (ed), medical imaging system technology – analysis and computational methods, world scientific publishing, singapore. [6] k.a. stroud (2007). engineering mathematics 6th ed, palgrave macmillan iium ej, vol. 12, no. 5, 2011 special issue on science and ethics in engineering. aboaba et al. 96 [7] a.j.m. spencer, d.f. parker, d.s. berry, a.h. england, t.r. faulkner, w.a. green, j.t. holden, d. middleton and t.g. rogers (1983). engineering mathematics vol. 1, van nostrand reinhold com ltd, berkshine, new york [8] john berry, & patrick wainwri (1991). foundation mathematics for engineers, macmillan press, houndmills [9] k. weltner et al. (1986). mathematics for engineers & scientist 2nd ed, stanley thornes, leckhampton application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 54 a novel method to estimate economic replacing time of transformer using monte carlo algorithm and ann mehdi zareian jahromi1, m.hossein mehrabanjahromi2, mohsen tajdinian3, mehdi allahbakhshi4 1, department of electrical engineering, amirkabir university of technology, no. 424, hafez avenue, tehran 1591634311, iran 2, department of electrical engineering,science and research branch, islamic azad university,tehran,iran. 3,4, school of electrical and computer engineering, shiraz university, shiraz, iran 1 m.jahromi@aut.ac.ir, 2 mh.mehraban@srbiau.ac.ir, 3 tajdinian.m@shirazu.ac.ir, 4 allahbakhshi@shirazu.ac.ir *corresponding author: mehdi zareian jahromi (m.jahromi@aut.ac.ir) (received: 9th feb 2017; accepted: 5th june 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19i2.793 abstract: a hybrid method for developing a more principled approach is presented to determine the life expectancy of transformers. the approach is constructed on an economic analysis of the transformers operational characteristics in combination with the technical issues incorporated in the decision process. in this method, firstly life time of transformer is estimated using a hybrid method based on monte carlo algorithm and artificial neural network. also pareto distribution function is applied to consider health history of transformer and uncertainty in dp behavior of transformer. in the next step, a method is proposed in order to estimate economic replacement time of transformer. this method is based on the well-known bathtub failure model, containing repairs and scheduled maintenance, in order to achieve at a more economically aim replacing decision. this aim is obtained in part by considering the uncertainty intrinsic in transformer failures and the corresponding discontinuations in power. in essence, this method organizes a decision support system for determination the life expectancy of a transformer. simulation results show the high accuracy and functionality of the proposed approach in estimating economic replacing time of the transformer. abstrak: kaedah hibrid bagi membangunkan cara yang lebih berprinsip telah dibentangkan bagi menganggarkan jangka hayat sesebuah transformer. kaedah ini telah dibuat dengan cara analisis secara ekonomi terhadap karakter operasi transformer melalui gabungan isu teknikal dan proses keputusan. melalui kaedah ini, perubahan masa hidup telah dianggarkan menggunakan kaedah hibrid berdasarkan algoritma monte carlo dan rangkaian saraf jadian. fungsi agihan pareto juga telah digunakan bagi mengambil kira sejarah kesihatan transformer dan ketidak pastian kelakuan dp pada transformer. langkah seterusnya adalah melalui anggaran ekonomi masa penukaran transformer ini. kaedah ini berdasarkan pada model kegagalan tab mandi yang terkenal, mengandungi jadual pembaikan dan penyelenggaraan, bagi mencapai sasaran keputusan tukaran yang lebih ekonomi. sasaran ini dicapai dengan menimbang kepentingan ketidakpastian pada kegagalan transformer dan tenaga yang ada. intipatinya, kaedah ini menyusun sistem iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 55 sokongan keputusan bagi mencapai jangka hayat transformer. hasil simulasi menunjukkan ketepatan yang tinggi dan kesesuaian cadangan kaedah ini dalam menganggarkan masa penukaran transformer secara ekonomi. key words: economic replacing time of transformer, monte carlo algorithm, neural network and pareto distribution. 1. introduction in general, the asset management of transformer is noticed to be one of the most important areas of management regarding power system equipment. assessing the assumed term when transformers will require to be changed, demonstrates a very significant asset management activity, particularly in consideration of the current aging status of the throughout power system network. the immense investment shown by power transformers and the significant duty they have in the power network are other factors that confirm the significance of the selection of suitable replacement times. since technical issues and economic factors are involved in aforementioned timing, management must be involved in decisions . several tests including tests for moisture content [1, 2]; oil gassing tendency [3, 4]; and partial discharge (pd) [5] can be carried out for obtaining data about a transformer technical performance. other tests, such as the polymerization degree (pd) and the retained tensile strength of the paper insulation, cannot be carried out because they need disposal to the insulating paper into the transformer. as a result, complete test results would prepare a generic evaluation of the circumstances of the transformer, but they would not concede any quantitative data regarding its life anticipation. obvious examples are transformers that have prepared years of service and as a result they are diagnosed to possess significant amounts of sludge in the oil. in the case of pd in oil-immersed transformers the pd intensity can change significantly with time, so that an enhanced pd intensity require not necessarily imply impendent failure, as a result, it is not possible to approximate their life expectancy in terms of pd intensity. thus, it is obvious that diagnostic tests supply effective information regarding the condition of transformers and can disclose problems, however, they do not yield the type of deterministic quantitative data regarding life expectancy that is needed for the future planning of power network. as the physical life of a transformer increases, the probability of its failure increases due to the aging of its components, and as a result it will be increased the costs of power interruptions and repairs of power transformers.. from economic point of view it is wisely to replace a transformer before it reaches to its physical end of life [6]. making decisions for transformers replacement in suitable time from economic point of view have appertained the operating and maintenance costs of the transformer[7-10]. however, the algorithm of economic replacement, as proposed in [7-10], have not used the realistic parameters for transformers. to be more precise, the impact of the failure rate of transformer on operating and maintenance costs has not been considered [11-13]. likewise, the economic replacement approaches presented in [7-10] do not consider the uncertainties intrinsic in rates of failure and repair. the asset annual unavailability, the cost of interruptions and repairs are the factors that are affected from the aforementioned uncertainties. the interruptions cost is itself not taken into account, and the annual present worth computed for the transformer is based on a depreciation method that iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 56 does not combined the different stages in the life of a transformer. a thermal model was suggested to determine the total transformer lifetime, the expected time to the end of the life of the transformer, and as a result, the suitable time for transformer replacement [14, 15]. however, any economic factors such as operating and maintenance costs have not been taken into account in aforementioned type of approach. moreover, these approaches also do not address the extra costs regarding interruptions [16, 17], and repairs [18] that is caused by the enhanced rate of failure when transformers are utilized in the course of their wearout stage. it can be noted that changing a transformer before its estimated thermal lifetime is sometimes more inexpensive than spending such high repair costs. the main purpose of the research study which it will be discussed in this paper is creating a reliable decision support system to determine from an economic aspect the appropriate time to replace power transformers, considering the consequences of all physical stresses that influence transformers. as mentioned,one of the most important issues to estimate transformer life time is study of aging insulating of transformer during operation lifecycle, because transformer insolation is not easily replaceable or repairable. on the other hand, aging insolation depends on amount of chemical furfural contained in transformer oil where estimation of furfural is very difficult and costly. therefore this study uses a heuristic method based on artificial neural network to estimate furfural contained in transformer oil. afterwards, this paper proposed a hybrid method based on pareto distribution and monte carlo search algorithm to estimate transformer end life. finally an economic idea is proposed to estimate economic replacement time of transformer. the procedure of process is described as detail in algorithm and implementation section. the new features of the proposed replacement method are as follows: 1) estimating of amount of furfural utilizing dga data and ann ; 2) determining of dp value of the transformer using ann output; 3) preparing health history using pareto distribution in order to take the uncertainty of actual behavior of dp value into account ; 4) applying monto carlo search algorithm to estimate end life of transformer; 5)applying new economical method based on the comparsion between aged and young transformer to determine the economic replacement time; the rest of this paper includes of four sections: section ii contains the background of the considerations of proposed algorithm for life-time estimation in power transformer, section iii presents the proposed approach and main concept of techno-economic utilized in this research, section iv demonstrates the results of the practical case study and section v provides the conclusions. 2. consideration of proposed algorithm and implementation as discussed in [16] the failure phenomenon of the transformer has a probabilistic nature which is assessed mainly by three parameters: design, aging, and external triggering events. as a result, end-of-life modeling intends to expand relationship between the aging iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 57 conditions and transformer inherent dielectric properties as well as transformer thermal life, represented as the service years for losing the mechanical strength of solid insulation under operational conditions [19]. fig. 1. the calculation procedure of economic replacement time of transformer. input data (transformer age, co2,bdv,co, acidity,loading data,..) estimation of furfural using ann estimation of ideal behavior of dp using eq.2 health history generation using pareto distribution end life estimation of transformer using monte carlo algorithm calculation of present worth value for old and new transformer at year n transformer annual cost (failure costs, maintenance costs and operating costs) calculation of euac for old and new transformer at each year economic replacement time of old transformer stage1:end life estimation of transformer euac new > euac old yes n=n+1 n=1 no stage2: estimation of economic replacement time iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 58 as mentioned, the aim of the proposed methos is estimating the end of normal life time and economic replacement time of transformer when it is considers health history of the transformer. fig .1 shows economic algorithm of transformer replacement time from the beginning to the end. the proposed method have two main stages. in the first stage of this algorithm, ann has been utilized for estimating the amount of furfural to determine the transformer dp value. also, after health history has been created using pareto distribution function, utilizingmonte carlo search algorithm end life of transformer can be estimated. in the second stage, an economic method has been proposed which compares economic valuation of aged transformer with young transformer to determine economic replacement time of old transformer. 3. data initioalization and fundamental of proposed techno-economic concept 3.1. estimation of furan content the impurities in the oil of transformer such as oxidation and water content are measured by breakdown voltage (bdv) . one of the significant sources of to enhance the water content in transformer oil is cellulose aging process. as a result, the oil bdv and furan content in the oil of transformer are correlated. also because of paper and oil degradation, water is generated in the transformer oil . the strength of dielectric is decreased as a result of creating high stressed areas in the insulating substance which catalyzes the aging process. thus, from paper insulation degradation point of view, water can advance and result in the insulation degradation .because of increasing hydrolysis of cellulose paper, acidity in transformer oil causes the degradation of paper insulation . the latter process eventually leads to generate glucose which transform to furanic combinations in transformer oil. utilizing disolved gas analisys, concentrations of co and co2 can be measured. one of the effective index to evaluvate of cellulose paper thermal degradation is the concentrations of co and co2 gases. as a result, co2/co ratio is utilized in utilities as a index for paper insulation degradation detection in transformers. it should be noted that both co and co2 are created in transformer oil as a result of the destruction of the transformer oil and not merely cellulose paper, which decreaes the reliability of these gases to evaluvate the solid insulation substance of the power transformer. in this paper, back propagation neural network is used to estimate furfural. back propagation networks are multi-layer networks with nonlinear transfer functions. back propagation networks are used to approximate a function, finding the relationship between inputs, and outputs and classification of inputs. also they usually have one or more hidden layers of neurons with a sigmoid transfer function and an output layer which mainly uses a linear function. fig. 2 shows a two-layer tansig/purelin network architecture which includes a hidden layer and an output layer with back propagation structure. this network can be used to approximate any function with a limited number of discontinuities [20]. iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 59 furan content x(1): acidity x(2): bdv x(3): co2 x(4) : co input layer hidden layer output layer fig. 2. the back propagation network structure with 4 input. in order to train the neural network, 2040 training patterns are used. 1734 patterns are used as training patterns and 306 patterns are used for testing the neural network, where acidity, break down voltage (bdv),co2 and co are used as inputs and the furfural is considered as the outputs of the neural network. 3.2. end life estimation of transformer as mentioned in previous section, transformer end life depend on aging insolating which is analyzed by the degree of polymerization (dp) according the following equation [21]: 0 2.5 log[ ] ( ) 0.005 f dp t   (1) therefore, the following equations can be written to estimate remaining life time of the transformer in the ideal case [21]:   2( ) ( ) ( ) ddp t k t dp t dt   (2) 0 0 0 ( ) ( ) 1 ( ) ( ) t t dp t dp t dp t k d     (3) ( ) exp( ) ( ) a g e k t a r t t   (4) where ( )t t is hot spot temperature of transformer which can be defined as follows: 2 ( ) ( ) ( ) ( ) a to t t t t t t t t   (5) where ( ) to t t is increasing oil temperature in the upper part of the transformer which is depended on load changes. also, (6) is used to consider effect of moisture and oxygen on aging insulating [22]: 2 2 [.5% ] 2 % normal life at h o normal life h o   (6) iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 60 where 2 h o is the amount of moisture in insulation system therefor (6) estimate transformer end life in ideal state. in the next step, pareto distribution is used to generate health history of transformer and model the uncertainty in ideal behavior of transformer lifetime. parameters of pareto probability distribution function which is used in this study are defined in appendix section. fig.3 shows ideal and non-ideal behavior of dp curve when pareto distribution is applied to ideal curve of dp. end life of transformer time (year) d g r e e o f p o la r iz a ti o n ideal behavior of dp curve actual behavior of dp curve end life year monte carlo algorithm fig. 3. estimation of end life of transformer considering actual behavior of dp curve. afterward, as can be seen in fig. 3, in order to consider the uncertainty of age searching on pareto distributed curve monte carlo algorithm is used to predict the failure probability of the transformer when dp curve of transformer intercept threshold dp of transformer at each step time of simulation. monte carlo which is used in this research have the following stages [23]: 1) compareing the history curve of dp with its ideal form to extract deviation of pareto distribution data at each time step of simulation. 2) fitting the extracted data on pareto distribution curve to estimate parameters of pareto function. 3) predicting the deviation of ideal dp curve in the future time by estimated pareto function. 4) finding the confluence of threshold dp and the area between ideal and deviated curve of dp using random search of monte carlo algorithm. 3.3. economic replacement time of transformer this section proposes a novel algorithm which considers all details to calculate economic replacement time of transformer because it is different from failure time of transformer. actually, economic value of transformer per year is obtained from calculation of operating costs of transformer in each year of operation. according to [24], economic valuation of transformer has five steps: iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 61 1) data collection 2) calculation of present worth value of transformer 3) transformer annual cost (failure costs, maintenance costs and operating costs) 4) calculation of euac 5) prioritizing transformers therefore, in order to calculate economic replacement time of transformer, firstly, economic valuation of old transformer and new transformer are calculated at each remaining years of their life time. afterward, the intersection of economic valuation curve of old transformer and new transformer is a suitable time for replacement of old transformer which is shown in fig. 4. in the other words, after this time, economic valuation of old transformer is less than new transformer. suitable time for economic replacement time of transformer time (year) e u a c o f tr a n sf o r m e r old transformer new transformer fig. 4. estimation of suitable time for economic replacement time of transformer. the most important step in proposed algorithm is calculation of present worth value transformer and calculation of annual cost of transformer. on the other hand bathtub curve is necessary to calculate annual cost of transformer [12, 13, 25]. also monte carlo algorithm is applied to model uncertainties of transformer such as unexpected output and repairing time [23]. all part of proposed algorithm are described as a detail in[24]. 4. case study in order to verify the performance of proposed method forty transformers that belong to distribution company have been utilized in the paper. the required training and testing data utilized in the ann model has been captured from maintenance records of transformers for transformers with voltage ratings of 420/36 kv, 245/11 kv and various ages. the mineral naphthenic oil is the type oil utilized in the investigated transformers. table 1 illustrates samples of the obtained data of oil testing which has been used in the research study. as can be seen in table 1, the results of the oil testing of the transformer provide a comprehensive range of transformer oil status. iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 62 table 1: samples of the oil data used in this study to predict furan content in transformer oil tr number co (ppm) co2 (ppm) tcg (ppm) tdcg (ppm) water contetnt (ppm) acidity (koh/g) bdv (kv) furan content (ppm) t1 393 4559 746 5323 39 0.54 28 17.96 t2 193 9128 322 9350 35 0.14 23 14.11 t9 298 2710 342 3052 21 0.19 54 4.23 t15 347 1816 361 2177 7.0 0.10 57 3.06 t16 229 1230 266 14.96 13.0 0.11 60.0 2.81 t26 374 2836 577 3413 12 0.03 89.9 1.57 t36 58 1775 129 19.04 14 0.04 58.0 0.04 t37 122 2386 190 3.26 10 0.04 78 0.38 t40 66 1147 78.0 1225 9.0 0.02 77 0.19 4.1. furfural estimation in this section, the ann which is explained in section 3.1, it is trained by the levenbergmarquardt training algorithm at 1000 epochs to estimate furfural of oil transformer. this study considers 60% of data for training, 20% for validation and 20 % for testing. as can be seen in fig. 5, after training the proposed network final mean square error for training, validation and test are less than 4 0.50 10   but the best validation performance is 5 1.3688 10   . after completing the training and testing procedure of ann, it is applied to the proposed approach. fig .5. mean squared error curve for training of proposed ann at each epoch. iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 63 finally, proposed ann predicts value of 0.20 for furfural for inputs values of below which is shown in table 1. after estimation of furfural, remaining life time of the transformer is estimated using monte carlo algorithm and pareto distribution function which will be discussed in the following section. 4.2. remaining life time in this section, remaining life time of transformer is estimated using eqs (1)-(6). fig. 6 shows ideal and actual behavior of dp curve. as can be seen in fig. 6, the actual behavior of dp curve of aging transformer is different form ideal curve form the first to the fifth year when the aging transformer has five years old. therefore distribution of deviation in dp will be extracted by comparing history curve and ideal curve of dp, which is shown in fig. 7. in the next step, according to fig. 8, the expected behavior of actual dp for the past years is predicted using pareto distribution function when threshold dp is 250. finally, monte carlo search algorithm finds the confluence of threshold dp and the area between ideal and actual curve of dp an d it predicts the transformer will be failed after 13.805 years which is shown in fig.9. fig6. comparison compare of ideal and actual behavior of dp. fig. 7. distribution of deviation in dp. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 400 450 500 550 600 650 time (year) d p v a lu e actual behavior ideal behavior -16 -14 -12 -10 -8 -6 -4 -2 0 2 0 1000 2000 3000 4000 5000 6000 deviation in dp n u m b e r o f o c c u rr e n c e s iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 64 fig.8. ideal and actual transformer history curve. fig. 9. failure probability across transformer lifetime. 4.3. economic replacement time in order to determine economic replacement time of transformer, economic valuation of old transformer and new transformer are calculated according to proposed approach which is shown in fig.1. fig. 10 shows economic valuation of old transformer and new transformer at each year of life time. as can be seen in fig. 10 economic valuation curve of old transformer intersects economic valuation curve of new transformer in the eleventh year therefore economic valuation of old transformer is less than new transformer after the eleventh year and this year is suitable time to economic replacement time of transformer although, two years remaining to end life of old transformer. 0 5 10 15 20 25 30 35 40 45 0 100 200 300 400 500 600 700 time (year) d p v a lu e actual behavior ideal behavior threshold 13.79 13.792 13.794 13.796 13.798 13.8 13.802 13.804 13.806 13.808 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 time (year) p ro b a b ili ty o f fa ilu re iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 65 fig.10. economic replacement time of old transformer. 5. conclusion a novel approach for estimating economic replacement time of transformer was proposed in this paper. for this purpose at the first step, ann was used to estimate furfural with high accuracy and low cost. after that, utilizing monte carlo algorithm end life of transformer was estimated when health history of transformer had been considered by pareto distribution at each year of operation. in next step, an economic approach was applied which considers all effective parameters of economic valuation of transformer to estimate economic replacement time of transformer. in this approach economic valuation of old transformer and new transformer are compared at each time of operation. finally, proposed method was tested on a sample transformer. simulation results show proposed method is a more practical and high precision method for estimating life time and economic replacement time of transformer since it considers all technical and economic factors of operation. references [1] abu-elanien, a. e. and m. salama (2010). "asset management techniques for transformers." electric power systems research 80(4): 456-464. [2] abu-elanien, a. e., m. salama and r. bartnikas (2011). "a techno-economic method for replacing transformers." power delivery, ieee transactions on 26(2): 817-829. [3] bartnikas, r. (1994). "engineering dielectrics volume iii electrical insulating liquids." [4] bowman, m. s. (1999). applied economic analysis for technologists, engineers, and managers, prentice hall. [5] brown, r. (2002). "electric power distribution reliability. 2002." north carolina, usa. [6] brown, r. e. (2008). electric power distribution reliability, crc press. 0 5 10 15 20 25 30 35 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 x 10 6 time (year) e u a c o f t ra n s fo rm e r ($ ) old transformer new transformer replacement time=11.45 (year) iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 66 [7] degarmo, e. p., w. g. sullivan and j. a. bontadelli (1979). engineering economy, macmillan new york. [8] ghunem, r. a., k. assaleh and a. h. el-hag (2012). "artificial neural networks with stepwise regression for predicting transformer oil furan content." dielectrics and electrical insulation, ieee transactions on 19(2): 414-420. [9] islam, s. m., p. r. jota and m. stace (1998). detection of oil-paper equilibrium moisture content in power transformers using hybrid intelligent interpretation of polarisation spectrums from recovery voltage measurements. electrical insulation, 1998. conference record of the 1998 ieee international symposium on, ieee. [10] jardini, j. a., h. p. schmidt, c. tahan, c. c. de oliveira and s. u. ahn (2000). "distribution transformer loss of life evaluation: a novel approach based on daily load profiles." power delivery, ieee transactions on 15(1): 361-366. [11] jirutitijaroen, p. and c. singh (2004). "the effect of transformer maintenance parameters on reliability and cost: a probabilistic model." electric power systems research 72(3): 213-224. [12] kachler, a. j. (2005). "aging of cellulose at transformer service temperatures. part 1: influence of type of oil and air on the degree of polymerization of pressboard, dissolved gases, and furanic compounds in oil." electrical insulation magazine, ieee 21(2): 15-21. [13] kurtz, m. (1984). handbook of engineering economics: guide for engineers, technicians, scientists, and managers, mcgraw-hill. [14] lelekakis, n., d. martin and j. wijaya (2012). "ageing rate of paper insulation used in power transformers part 2: oil/paper system with medium and high oxygen concentration." dielectrics and electrical insulation, ieee transactions on 19(6): 2009-2018. [15] li, w. (2013). reliability assessment of electric power systems using monte carlo methods, springer science & business media. [16] li, w., e. vaahedi and p. choudhury (2006). "power system equipment aging." power and energy magazine, ieee 4(3): 52-58. [17] modarres, m. (1992). what every engineer should know about reliability and risk analysis, crc press. [18] muthanna, k. t., a. sarkar, k. das and k. waldner (2006). "transformer insulation life assessment." power delivery, ieee transactions on 21(1): 150-156. [19] newnan, d. g., t. eschenbach and j. p. lavelle (2004). engineering economic analysis, oxford university press. [20] retterath, b., s. venkata and a. a. chowdhury (2005). "impact of time-varying failure rates on distribution reliability." international journal of electrical power & energy systems 27(9): 682-688. [21] sen, p., s. pansuwan, k. malmedal, o. martinoo, m. simoes and k. butler-purry (2011). "transformer overloading and assessment of loss-of-life for liquid-filled transformers." power systems engineering research center. iium engineering journal, vol. 19, no. 2, 2018 zareian jahromi et al. 67 [22] starr, t., b. dakin, p. mcmahon, p. harrold and c. densley (1979). engineering dielectrics volume i corona measurement and interpretation. engineering dielectrics volume i corona measurement and interpretation, astm international. [23] van bolhuis, j., e. gulski and j. smit (2002). "monitoring and diagnostic of transformer solid insulation." power delivery, ieee transactions on 17(2): 528-536. [24] wang, m., a. vandermaar and k. d. srivastava (2002). "review of condition assessment of power transformers in service." electrical insulation magazine, ieee 18(6): 12-25. [25] wouters, p. a., a. van schijndel and j. m. wetzer (2011). "remaining lifetime modeling of power transformers: individual assets and fleets." electrical insulation magazine, ieee 27(3): 45-51. microsoft word 0_vol_16_no_2_2015_special issue on energy_compiled.docx iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 79 performance evaluation of solar collectors using a solar simulator m. norhafana1, ahmad faris ismail1 and z.a.a. majid2 1department of mechanical engineering, faculty of engineering international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. 2faculty of allied health sciences, international islamic university malaysia, bandar indera makhota, 25200, kuantan, malaysia. norhafana@yahoo.com, faris@iium.edu.my, and zafriazran@yahoo.com (received: oct. 20, 2015; accepted: nov. 10, 2015; published on-line: nov. 30, 2015) abstract: solar water heating systems is one of the applications of solar energy. one of the components of a solar water heating system is a solar collector that consists of an absorber. the performance of the solar water heating system depends on the absorber in the solar collector. in countries with unsuitable weather conditions, the indoor testing of solar collectors with the use of a solar simulator is preferred. thus, this study is conducted to use a multilayered absorber in the solar collector of a solar water heating system as well as to evaluate the performance of the solar collector in terms of useful heat of the multilayered absorber using the multidirectional ability of a solar simulator at several values of solar radiation. it is operated at three variables of solar radiation of 400 w/m2, 550 w/m2 and 700 w/m2 and using three different positions of angles at 0º, 45º and 90º. the results show that the multilayer absorber in the solar collector is only able to best adapt at 45° of solar simulator with different values of radiation intensity. at this angle the maximum values of useful heat and temperature difference are achieved. abstrak: teknologi sistem pemanasan air suria merupakan salah satu aplikasi tenaga suria. penyerap merupakan satu daripada komponen sistem pemanasan air suria. prestasi sistem pemanasan air suria bergantung kepada penyerap pada pengumpul suria. di negara di mana cuacanya tidak sesuai, pengumpul suria ujian dalaman dengan penggunaan pensimulasi suria menjadi pilihan. oleh itu kajian ini dijalankan dengan menggunakan penyerap pelbagai lapisan dalam pengumpul suria pada sistem pemanasan air suria. kebolehan pengumpul suria juga dinilai menerusi tenaga haba yang terhasil dengan penggunaan penyerap pelbagai lapisan beserta keupayaan pelbagai haluan pensimulasi suria pada beberapa ukuran radiasi suria. pengumpul suria dengan penyerap pelbagai lapisan diuji dan dinilai dengan mengkaji haba yang boleh dimanfaatkan untuk menghasilkan air panas. ia dijalankan pada tiga pembolehubah radiasi suria iaitu pada 400 w/m2, 550 w/m2 dan 700 w/m2 pada tiga posisi sudut berbeza iaitu 0º, 45º dan 90º. keputusan menunjukkan kesan sistem pemanasan air suria sememangnya dijangka kerana pengumpul suria memainkan peranan utama apabila ia berupaya dilaraskan pada radiasi solar pelbagai haluan dengan intensiti pensimulasi suria yang berbeza. pengumpul suria pada pensimulasi suria berfungsi secara optimum pada 45º dengan nilai intensiti radiasi yang berbeza di mana haba berguna dan suhu yang berbeza diperolehi. keywords: solar water heating system; solar collector; multilayered absorber; solar simulator; solar radiation iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 80 7. introduction energy is one of important daily resources in all walks of life [1, 2]. there are many types of energy resources in this world and the most common one is electrical energy [3]. its importance is evident from the fact that if slight changes occur it can directly affect all human activities. this can be seen when there is only a change in the price of energy resources [4], it affects almost all human activities causing political and economic crises [3, 4] . this is due to the world’s energy supply based on diminishing fossil fuels[5]. this resource will begin to decrease starting in 2015 [6]. the impact of burning fossil fuels has also caused airspace to become increasingly polluted and cause global warming [7]. instead of using fossil fuel as energy sources, another alternative energy that can be used in decreasing the undesirable effects to the environment is solar energy [8]. solar energy is one of renewable energy that cannot be exhausted and is constantly renewed [9]. it is also considered to be economical, and environment friendly and due to its safety aspects it is worthwhile to be broadly applied and adopted by people. it can be harnessed either directly or indirectly deriving energy from the sunlight [10]. as there has been increase in demand as well as the higher cost of fossil fuels energy especially for domestic use, solar energy on the other hand, can overcome these problems especially in terms of water heating system applications [11]. in countries with unsuitable weather conditions, the indoor testing of solar collectors with the use of a solar simulator is preferred [12]. solar simulators are generally of two types which are; those that use a point source of radiation mounted well away from the collector and those with large area multiple lamps mounted close to the collector. for this experiment, it focuses more on this second type of solar simulator [6]. by using a solar simulator, the experiment cannot be equated with the actual conditions under daily solar radiation. this is due to the factor of the air temperature and daily solar radiation which are affected by relative humidity or mass of air and also movement of the air that causes heat loss more rapidly through convection. the error in efficiency measured by using a solar simulator as compared to the actual intensity of solar radiation is about 6%. this solar simulator delivers a high heating effect, which is due to the high wavelength of infrared radiation as compared to a halogen lamp [12]. the rise in temperature is directly proportional to the exposure time in the actual situation. however, to look at the changing nature of the solar collector to the intensity of solar radiation, the use of solar simulator is the best comparative method in which its radiation can be set up and which remains constant. 2. experimental setup this experiment is called a multidirectional solar simulator (mss) experiment. it uses the solar simulator instead of the intensity of the global solar radiation. it has been conducted by three variables of solar radiation that are at 400 w/m2, 550 w/m2 and 700 w/m2 at the different positions of angle which are at 0º, 45º and 90º (see figs. 1, 2 and 3 respectively). the objective of solar simulator experiment is to examine the useful heat of the multilayered absorber (fig. 4) in solar collector with multidirectional ability of solar simulator at several values of solar radiation. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 81 fig. 1: experiment setup with solar simulator at angle of 0°. fig. 2: experiment setup with solar simulator at angle of 45°. fig. 3: experiment setup with solar simulator at angle of 90°. fig. 4: multilayered absorber in solar collector. 2.1 experimental materials table 1 below shows the items or materials that are used in the long term experiment. these are solar water heating system, pyranometer, digital temperature sensor, container, container of mineral water, small bench and weighing scale. 2.2 experimental procedure the experiment begins with the following procedure. the solar simulator is positioned at of 0° based on figure 1 with average value of solar radiation 400 w/m2: iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 82 table 1: the experimental materials, their specifications and functions for mss experiment. item specification function total item used solar water heating system multilayered absorber (6 layers) of solar collector to produce hot water 1 solar simulator halogen lamp with 500 w/unit, 220-240v/unit to give the solar radiation by adjust the value of radiation 18 pyranometer apogee logan ut sp-110 to measure the intensity of the global radiation 1 digital temperature sensor k-type to record the temperature for each point 7 container 75g of container to collect hot water 1 container of mineral water 1.5 liter of container of mineral water container of mineral water as a water supply 1 weighing scale to weigh the mass of empty container or with water 1 small bench to support water channel in horizontal condition 1 1. mass of empty container, mc weighed by using weighing scale and the reading was recorded. 2. water is filled into the container of mineral water. water that has been used in this experiment is taken from the water supply. 3. then, water will be inserted into temporary water storage until the water level at the temporary water storage is at the maximum level and water channel will be positioned as in fig. 5. 4. the following initial data is recorded: a. ambient temperature (tat) b. water input temperature (t1) c. absorber temperature (t2) d. water output temperature (t3) (see figs. 6 and 7) e. outer cover temperature (tco) f. inner cover temperature (tci) g. air temperature at collector (tat) h. solar radiation (st) 5. after the initial reading being recorded, the solar water heating system has been exposed to the solar simulator within 600 s next reading recorded is at the next interval which is at 600 s. 6. when reaching the time at 600 s, the reading from ‘a’ until ‘h’ is recorded. 7. procedures 2 till 3 are repeated and the reading from ‘a’ until ‘h’ is recorded at 600 s intervals until the last reading at 3000 s. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 83 8. procedures 1 until 7 are then repeated with the solar simulator at the position of 45° and 90° (see figs. 2 and 3) respectively. 9. procedures 1 until 8 are then repeated with the average of solar radiation at 550 w/m2 and 700 w/m2. fig. 5: location of the clipped water channel. fig. 6: position of collecting water from inlet through absorber and outer pipe. fig. 7: position of collecting water from inlet through absorber and outer pipe (zoom in). 3. mathematical modelling 3.1 useful heat in this experiment, the important measurement calculated is useful heat from the solar water heating system. gravity energy is used since no external force such as pump is used in the investigation. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 84 figure 8: control volume. based on fig. 8, ̇ + ̇ = ̇ (1) ̇ = ̇ − ̇ (2) = ̇ − ̇ (3) let assume, = − (4) ̇ = (5) ̇ = ̇ = ̇ (6) = (7) = (8) the useful heat, q̇ = ̇ ( − ) (9) where mass of empty container [kg] mass of container + water [kg] mass of water [kg] ̇ mass flow rate of water [kg/s] ̇ mass flow rate input [kg/s] ̇ mass flow rate output [kg/s] ̇ rate of input heat transfer [j/s] ̇ rate of output heat transfer [j/s] ̇ useful heat [j/s] constant pressure specific heat of water [kj/kg°c] t total time to collect average water at outlet [s] iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 85 4. results and discussion in the solar simulator experiment, the useful heat, ̇ values have been compared using a solar simulator (not the real solar radiation), acting as the heat radiator, by determining the value of radiation intensity with 400 w/m2, 550 w/m2 and 700 w/m2 from the different angles. this experiment is conducted to prove the capability of the multilayer absorber to absorb heat from multidirectional angle at different values of radiation intensity. the usage of solar simulator in long term period has provided the infrared radiation that causes the air temperature of the solar collector higher compared to the intensity of real solar radiation. solar simulator with variation average value of radiation such as 400 w/m2, 550 w/m2 and 700 w/m2 are used for this experiment. the solar simulator angle is varied as 0°, 45° and 90° to examine the accumulation of heat through absorber. the time interval of 600s is used for each experiment. based on fig. 9 below, it shows the value of useful heat within interval of 600 s is the highest at angle of 45° followed by 90° and 0° which is the lowest value of useful heat. this also can be seen in fig. 10 and fig. 11 where the value of useful heat is the highest at the angle of 45° for 400 w/m2, 550 w/m2 and 700 w/m2 and the lowest is at the angle 0° (see fig. 1). in summary, at this angle of 45° (see fig. 2), the scattered intensity of the solar simulator is high and wide while the intensity of the solar simulator spread over the entire covering on each layer of the absorber. fig. 9: ̇ (j/s) versus time (s) at 400 w/m2. at the angle of 90° (see fig. 3), only the upper surface of the absorber could receive and absorb the high intensity of the solar simulator. the lower surface also will get the intensity of the solar simulator but its value is not as much as from the angle 45°. meanwhile, at the angle of 0°, the total of intensity of solar simulator and heat absorbed by the multilayered absorber is the lowest as only side part of the multilayered absorber is exposed to the total of intensity of solar simulator. other parts of the multilayered absorber, on the other hand get the lowest intensity of solar simulator which gives the lowest value of useful heat. the lowest surface area of the multilayered absorber that is exposed to the solar simulator radiation has given the big impact to the value of heat -100 -50 0 50 100 150 200 250 300 350 400 450 0 1000 2000 3000 4000 ܳ ̇radd (j/s) time (s) ܳ ̇radd vs time (400 w/m2) 45degree 90degree 0degree iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 86 absorbed by the solar simulator radiation and subsequently to the value of useful heat. the high intensity value of solar simulator also affects the value of useful heat because both of these parameter directly affect the heat absorption. this can be proven at the angle of 45° (see figs. 9, 10 and 11), in which the maximum value of useful heat at 400 w/m2, 550 w/m2 and 700 w/m2 are respectively at 384.88 j/s, 520.08 j/s and 696.34 j/s. high intensity of solar simulator gives the high value of useful heat. from these three graphs, it could be concluded that the highest value of useful heat is at the angle of 45° followed by 90° and 0° at 400 w/m2, 550 w/m2 and700 w/m2. it means the higher the intensity of solar simulator, the higher value of useful heat could be obtained. fig. 10: ̇ (j/s) versus time (s) at 550 w/m2. fig. 11: ̇ (j/s) versus time (s) at 700 w/m2. graphs in figs. 12, 13 and 14 clearly show that the useful heat versus temperature difference at 0° angle is the lowest value of useful heat. meanwhile, fig. 1 shows that the 0 100 200 300 400 500 600 0 500 1000 1500 2000 2500 3000 3500 ܳ ̇radd (j/s) time (s) ܳ ̇radd vs time (550 w/m2) 45degree 90degree 0degree 0 100 200 300 400 500 600 0 1000 2000 3000 4000 ܳ ̇radd (j/s) time (s) ܳ ̇radd vs time (550 w/m2) 45degree 90degree 0degree iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 87 light coming from the solar simulator is horizontally converging towards the absorber and solar collector. at this 0° angle, light can only be focused on the multilayered absorber closest to the solar simulator which is on the side layer. it means that only the side absorber layer can get the highest heat than the other opposite side and the following layer. subsequently, the heat collected by the absorber is little to be transferred to water and thus the temperature difference will be small as well as useful heat (see figs. 12, 13 and 14). this can be explained when there is high temperature difference then, the useful heat will also indicate a high value which is directly proportional. thus, it can be concluded that the temperature difference and the variety of solar simulator angles play a crucial role in this research in which they can be highlighted as benefactor for acquiring difference of useful heat values. fig. 12 : ̇ (j/s) versus δt (°c) at 400 w/m2. fig. 13 : ̇ (j/s) versus δt (°c) at 550 w/m2. -100 -50 0 50 100 150 200 250 300 350 400 450 -0.8 9.9 14.2 15.8 19.2 21.7 ܳ ̇radd (j/s) δt (°c) ܳ ̇ radd vs ∆ t (400 w/m2) 45degree 90degree 0degree 0 100 200 300 400 500 600 2.2 14.2 17.9 21.8 26 30.3 ܳ ̇radd (j/s) δt (°c) ܳ ̇ radd vs ∆ t (550 w/m2) 45degree 90degree 0degree iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 88 fig. 14: ̇ (j/s) versus δt (°c) at 700 w/m2. in addition, the area of absorber is leading to cause the highest of useful heat value. this situation can also be presented through the squares and multilayered absorber itself which it allows the intensity of the solar simulator focusing on the absorber layered by layered. thus, the collected heat transfer will be high and this can be concluded that there is a linear relation between the area of absorber and the useful heat. besides, it can be clearly shown in figs. 15, 16 and 17 that the temperature differences for the experiment with the angle of 45° is the highest at 400 w/m2, 550 w/m2 and 700 w/m2 followed by experiment with the angle of 90° and 0°. from figures 15, 16 and 17, the maximum value of temperature difference at 45° are 21.7°c, 30.3°c and 39.7°c respectively. the high temperature difference gives the consequence to the heat absorbed by multilayer absorber and it shows that the high ability and performance of the absorber in the solar collector of the solar water heating system. fig. 15: δt (°c) versus time (s) at 400 w/m2. 0 100 200 300 400 500 600 700 800 11.4 18.7 23.9 29.1 34.2 39.7 ܳ ̇radd (j/s) δt (°c) ܳ ̇ radd vs ∆ t (700 w/m2) 45degree 90degree 0degree -5 0 5 10 15 20 25 0 500 1000 1500 2000 2500 3000 3500 δt (°c) time (s) ∆ t vs time (400 w/m2) 45degree 90degree 0degree iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 89 fig. 16: δt (°c) versus time (s) at 550 w/m2. fig. 17: δt (°c) versus time (s) at 700 w/m2. the experiment using the solar simulator shows the differentiation and rise of high temperature caused by long wave radiation in the solar collector causing a greenhouse effect which raises the temperature of solar collector higher than the ambient air temperature. through the experiment using the solar simulator, it can be seen that the temperature is changing more than a real solar radiation. this is due to the solar simulator operation in the infrared wave range is higher compared to the real situation which is using solar radiation. from the experiment of solar simulation above, it can be concluded that the multilayer absorber in the solar collector is only able to best adapt at 45° of solar simulator with different values of radiation intensity compared to 90° and 0° angles as at this angle, the maximum values of useful heat is achieved and better impact to the solar water heating system. 0 5 10 15 20 25 30 35 0 500 1000 1500 2000 2500 3000 3500 δt (°c) time (s) ∆ t vs time (550 w/m2) 45degree 90degree 0degree 0 5 10 15 20 25 30 35 40 45 0 500 1000 1500 2000 2500 3000 3500 δt (°c) time (s) ∆ t vs time (700 w/m2) 45degree 90degree 0degree iium engineering journal, vol. 16, no. 2, 2015 special issue on energy norhafana et al. 90 6. conclusion as a conclusion, the multilayered absorber inside the solar collector of solar water heating system is proven to play its main role when it is able to adapt in multidirectional solar radiation with different intensity of solar simulator. it can be concluded that the multilayer absorber in the solar collector is only able to best adapt at 45° of solar simulator with different values of radiation intensity compared to 90° and 0° angles. at this angle, the maximum values of useful heat and the temperature difference are achieved resulting in a more efficient solar water heating system. acknowledgements the authors are thankful to the international islamic university malaysia and rad tec enterprise for providing laboratory facilities and financial assistance. references [1] s. mekhilef, r. saidur, and a. safari, “a review on solar energy use in industries,” renew. sustain. energy rev., vol. 15, no. 4, pp. 1777–1790, may 2011. [2] c.-d. ho, t.-c. chen, and c.-j. tsai, “experimental and theoretical studies of recyclic flatplate solar water heaters equipped with rectangle conduits,” renew. energy, vol. 35, no. 10, pp. 2279–2287, oct. 2010. [3] s. mekhilef, a. safari, w. e. s. mustaffa, r. saidur, r. omar, and m. a. a. younis, “solar energy in malaysia: current state and prospects,” renew. sustain. energy rev., vol. 16, no. 1, pp. 386–396, jan. 2012. [4] v. devabhaktuni, m. alam, s. shekara sreenadh reddy depuru, r. c. green, d. nims, and c. near, “solar energy: trends and enabling technologies,” renew. sustain. energy rev., vol. 19, pp. 555–564, mar. 2013. [5] s. kalogirou, solar energy engineering processes and systems. 2009. [6] zafri azran abdul majid, m. y. othman, m. h. ruslan, s. mat, b. ali, a. zaharim, and k. sopian, “multifunctional solar thermal collector for heat pump application,” pp. 342– 346, 2007. [7] s. sadhishkumar and t. balusamy, “performance improvement in solar water heating systems a review,” renew. sustain. energy rev., vol. 37, pp. 191–198, sep. 2014. [8] l. liu, z. wang, h. zhang, and y. xue, “solar energy development in china—a review,” renew. sustain. energy rev., vol. 14, no. 1, pp. 301–311, jan. 2010. [9] g. t. tucho, p. d. m. weesie, and s. nonhebel, “assessment of renewable energy resources potential for large scale and standalone applications in ethiopia,” renew. sustain. energy rev., vol. 40, pp. 422–431, dec. 2014. [10] y. g. yin, “design and application of solar water heater intelligent control system,” 2009 int. conf. energy environ. technol., pp. 580–583, 2009. [11] m. srinivas, “domestic solar hot water systems: developments, evaluations and essentials for ‘viability’ with a special reference to india,” renew. sustain. energy rev., vol. 15, no. 8, pp. 3850–3861, oct. 2011. [12] m. k. a. sharif, a. a. al-abidi, s. mat, k. sopian, m. h. ruslan, m. y. sulaiman, and m. a. m. rosli, “review of the application of phase change material for heating and domestic hot water systems,” renew. sustain. energy rev., vol. 42, pp. 557–568, feb. 2015. microsoft word 3_v17no2_compiled_v3_26nov16.docx iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 71 knn based classification of digital modulated signals asad hussain1, 2, sajjad ahmed ghauri*3, m. farhan sohail1, sheraz a. khan1and ijaz mansoor qureshi4 1national university of modern languages, islamabad 44000, pakistan. 2isra university, islamabad 44000, pakistan. 3international islamic university, islamabad 44000, pakistan. 4air university, islamabad 44000, pakistan. *corresponding author: sajjad.ghauri@iiu.edu.pk (received: 6t h mar. 2016; accepted: 20 jun. 2016; published on-line: 30th nov. 2016) abstract:demodulation process without knowledge of the modulation scheme requires automatic modulation classification (amc). when the receiver has limited information about the received signal, amc becomes an essential process. amc has an important place in many civil and military fields such as modern electronic warfare, interfering source recognition, frequency management, link adaptation, etc. in this paper, we explore the use of k-nearest neighbor (knn) for modulation classification with different distance measurement methods. five modulation schemes are used for classification purposes which are binary phase shift keying (bpsk), quadrature phase shift keying (qpsk), and quadrature amplitude modulation (qam) as both 16-qam and 64-qam. higher order cumulants (hoc) are used as an input feature set to the classifier. simulation results show that the proposed classification method provides better results for the considered modulation formats. abstrak:proses demodulation tanpa ilmu mengenai skim modulasi memerlukan klasifikasi modulation automatik (amc). apabila penerima mempunyai maklumat yang terhad mengenai signal yang diterima, maka amc menjadi proses yang penting. amc adalah penting didalam pelbagai bidang sivil dan ketenteraan seperti peperangan elektronik moden, gangguan di dalam pengiktirafan sumber, pengurusan kekerapan, penyesuaian pautan dan lain-lain. dalam kertas ini kami meneroka penggunaan jiran kterdekat (knn) bagi klasifikasi modulasi dengan kaedah pengukuran jarak yang berbeza. lima skim modulasi digunakan untuk tujuan mengklasifikasi adalah penguncian anjakan fasa biner (bpsk), penguncian anjakan fasa quadrature (qpsk), quadrature pemodulatan amplitud (qam), 16-qam dan 64-qam. cumulants paras tinggi (hoc) digunakan sebagai set ciri input yang ditetapkan untuk pengelas. hasil simulasi menunjukkan bahawa cadangan kaedah pengelasan memberi keputusan yang lebih baik untuk format modulasi yang dipertimbangkan. keywords:automatic modulation classification (amc); higher order cummulants (hoc);k-nearest neighbor (knn); qam and qpsk 1. introduction automatic modulation classification is a procedure performed at the receiver based on the received signal before demodulation when the modulation format is unknown to the receiver. it plays a key role in various tactical communication applications. it also finds applications in emerging wireless communication systems that employ interference cancelation techniques in order to demodulate and cancel the unknown interfering user’s iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 72 signal. in the interference application, the signal’s modulation format needs to be classified first. the solution to the problem of amc strongly relies on one of the two approaches i.e. the likelihood-based (lb) [1, 2] and the feature-based (fb) amc[3, 4]. the lb approach performs amc-based on the likelihood function of the received signal, by which modulation classification can be formulated as a multiple hypothesis test problem with multiple unknown modulation parameters [5]. the lb-based amc approach can theoretically reach the optimum solution in the gaussian condition, but at a cost of computational complexity. moreover, its performance is affected by model mismatch in the presence of carrier frequency offsets, phase errors, timing errors, and residual channel effects. in contrast, the fb approach is sub-optimal in performance but very feasible in real-time implementation. the fb-based amc approach mainly extracts reference features from the received signal and makes decisions from the calculated features based on the theoretical values for different modulation parameters. in brief, the fb approach benefits from lower computational complexity, with better efficiency and less sensitivity to possible model mismatches. in the fb approach, three features are often discussed in the literature: instantaneous information [6, 7], wavelet coefficients [8–10] and high-order statistics (hos) [11–15]. the instantaneous information may include the instantaneous amplitude, phase, or frequency of the incoming signal. these features are the most intuitive ones with less complex implementation. however, they are sensitive to additive noises and the residual channel effects. moreover, the extraction of instantaneous information relies on thresholds that are set in advance. the wavelet coefficients can be obtained through a haar wavelet transform by transforming the signal into its wavelet coefficients. modulation classification with wavelet coefficients has better resistance to the noise at the cost of higher complexity, compared with that with instantaneous information. hos is a more frequently adopted feature than the previous two, generally including the statistics of moments and cumulants [16–18]. in addition to classification of the modulation types, hos can distinguish modulation orders with high resistance to the additive white gaussian noise (awgn) as well. furthermore, the multipath channel effects can be easily modeled using the hos method [19–21]. most of the previous research work on amc has focused on the modulation classification techniques in awgn. actually, the correctness of modulation classification is seriously degraded subject to the multipath fading effect in wireless channels. the pioneer work by wu et al. [20] derived a relationship between the normalized channel coefficients and the normalized fourth-order cumulants. through their formulation, the classification of the transmitted modulated symbols can be obtained from the normalized fourth-order cumulants of the received signal. the blind channel estimation method using higher-order cumulants was then adopted in [22, 23] to improve the classification performance in cases of non-dispersive channels and one-dominant-path channels. in literature, a tree-structured modulation classification scheme [24, 25] based on three normalized fourth-order cumulants is also used for the same work. in this paper, hos was used for the modulation classification purpose; eleven eighthorder cumulants have been used throughout the research. the features are extracted for the noisy (awgn) signals. the modulation schemes used here are bpsk, qpsk, qam, 16qam, 64qam for a knn classifier with different distance measurement methods i.e. euclidean distance, correlation distance, minkowski distance, and mahalanobis distance. the rest of the paper is organized as follows: section 2 describes the system model and feature extraction. section 3 explains the classification methodology.section 4 gives iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 73 a comparative analysis of the knn classifier for five modulations using different distance methods under different snrs. conclusion and future work is presented in section 5. 2. signal model and feature extraction 2.1 signal model an awgn channel was used for these simulations. thus, the received signal is only impaired by additive white gaussian noise. figure 1 shows the system model. the generalized expression for signal received is given by [26]. ( ) = ( ) + ( ) (1) where ( )complex baseband is the envelope of the received signal, ( ) is the additive white gaussian noise and received signal ( ) is given by ( ) = ( ) ( ) ℎ( − + ) (2) where, ( ) is the input symbol sequence which is drawn from the set of m constellations of known symbols, not necessarily equi-probable. k is the amplitude of the signal, is the frequency offset constant, t is the symbol spacing, is the phase jitter which varies from symbol to symbol, ℎ(… )represents channel effects, and is the timing jitter. fig. 1: system model for modulation classification. 2.2 feature extraction cumulants are made up of moments which are used here as features. for the complex valued stationary random process r(n), cumulants of the 2nd, 4th, 6th and 8th order are as follows[27]: = [ ( )] = { ( ), ( )} (3) = [| ( )| ] = { ( ), ∗( )} (4) c40=m40-3m20 2=cum{y(n),y(n),y(n),y(n)} (5) c41=m40-3m20m21=cum{y(n),y(n),y(n),y*(n)} (6) c42=m42-|m20|2-2m21=cum y(n),y(n),y*(n),y*(n) (7) = − 15 + 30 = { ( ), ( ), ( ), ( ), ( ), ( )} (8) = − 5 − 10 + 30 (9) signal processing feature extraction classification rule bpsk qpsk qam 16qa 64qam iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 74 = { ( ), ( ), ( ), ( ), ( ), ∗( )} = − 6 − 8 − + 6 + 24 = { ( ), ( ), ( ), ( ), ∗( ), ∗( )} (10) = − 9 + 12 − 3 − 3 + 18 = { ( ), ( ), ( ), ∗( ), ∗( ), ∗( )} (11) = − 35 − 28 + 420 − 630 = { ( ), ( ), ( ), ( ), ( ), ( ), ( ), ( )} (12) = − 16 + | | − 18 − 72 − 24 = { ( ), ( ), ( ), ( ), ∗( ), ∗( ), ∗( ), ∗( )} (13) m stands for moments of received signal and it is given by m = e[y(k) y∗(k) ] (14) the above cumulants are used to classify the bpsk, qpsk, qam, 16qam and 64qam modulated signals in the presence of awgn noise. 3. knn classifier 3.1 introduction to knn classifier knn is a non parametric, slow adapting, and lazy algorithm in the sense that it does not make any assumptions on the underlying data distribution and requires more computations and memory. however, due to the non parametricness, knn is well suited to practical real world problems as much of the acquired data does not agree with assumptions made in theory for mathematical convenience. this resembles the philosphy of svm where non-support vectors can be omitted without sacrificing performance. knn works with a minimal training phase, however, testing is performed over the whole testing data which requires more memory for its storage. 3.2 knn classifiers the knn classifier is used to compare the accuracy of extracted features from different modulation schemes. the eleven features are the cumulants which have been extracted from the signal earlier. the method is quite simple. firstly,a few values are used as sample data for the knn classifier as there are eleven cumulants and therefore eleven dimensional spaces for knn. after this, some test values of these features are given to the knn classifier and knn calculates the distance of these samples from k neighbors' samples. the class having the maximum numbers of neighbors is considered to be the class of the test sample. 3.2.1 euclidean distance   ' 11 1 i t i st i s i i yxyxd    (15) where six the i th input is feature value and tiy is the test feature value. iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 75 3.2.2 correlation distance               11 1 ' '' ' 1 i t i t i t i t i s i s i s i s i t i t i s i s i yyyyxxxx yyxx d (16) where six is the ith input feature value and t iy is the test feature value and furthermore, s ix =  j sjxn 1 and siy =  j sjyn 1 3.2.3 mahalanobis distance        11 1 1 i i t i st i s i yxcyxd (17) where six is the i th input feature value and tiy is the test feature value and c is the covariance matrix. 3.2.4 minkowski distance p j p tjsj yxd    11 1 (18) where six the i th input is feature value and tiy is the test feature value. 4. simulation results the modulation classification using knn is evaluated in this section. firstly, the input data -extracted features from the received signal and desired output signalsare used to make the classifier model, after which different distance techniques are used to classify the input signals. the performance using different distance measurement techniques for knn under the influence of snr and number of samples are given in the tables. overall, 250 data samples were used at the training phase and 25 were used as test samples during the testing phase, in order to obtain the results shown in the table. the end result is an average of 10 iterations for each horizontal and vertical entryin the table. 4.1 knn with euclidean distance table 1 compares the performance of the knn classifier using euclidean distance for digital modulations which are bpsk, qpsk, qam, 16qam and 64qam with different number of samples.as can be seenin the table, the accuracy is enhanced with the increase of signal to noise ratio and number of samples.the performance accuracy for bpsk is 98.87 %. similarly,the performance accuracy table for qpsk demonstrates a classification accuracy of 99.73%. however, for the next modulation scheme, which is qam, the performance accuracy is 96.80% and for 16qam it is 99.70%.at last, the classification accuracy for 64qam is found to be 99.57%. iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 76 table 2: percentage classification accuracy using knn (euclidean distance) signal no of sample 0db 5db 10db bpsk 512 88.08 98.97 100 1024 98.49 99.98 100 2048 99.95 100 100 4096 100 100 100 qpsk 512 95.85 100 100 1024 99.97 100 100 2048 100 100 100 4096 100 100 100 qam 512 76 98 100 1024 90.64 99.96 100 2048 97.2 100 100 4096 99.88 100 100 16qam 512 97.87 99.41 99.73 1024 99.89 99.99 100 2048 100 100 100 4096 100 100 100 64qam 512 97.00 98.9 99.47 1024 99 99.98 99.72 2048 100 100 100 4096 100 100 100 table 2: percentage classification accuracy using knn (correlation distance) signal no of sample 0db 5db 10db bpsk 512 93.95 99.99 100 1024 99.8 100 100 2048 98.29 100 100 4096 99.95 100 100 qpsk 512 94.5 99.3 100 1024 94.58 99.68 100 2048 95.26 99.70 100 4096 96.35 99.79 100 qam 512 60.23 73.5 97 1024 71.92 82.19 97.99 2048 80.27 93.3 99.91 4096 87.05 93.57 100 16qam 512 80.33 90.3 93 1024 81.59 87.07 95.5 2048 83.24 92.45 96.73 4096 93.23 97.86 100 64qam 512 80.33 93.65 95 1024 87.94 94.98 96.39 2048 89.93 96.91 98.17 4096 90.43 97.83 100 4.2 knn with correlation distance table 2 compares the performance of the knn classifier using correlation distance for digital modulations which are bpsk, qpsk, qam, 16qam and 64qam with different number of samples.as can be seenin the table, the accuracy is enhanced with the iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 77 increase of signal to noise ratio and number of samples.the performance accuracy for bpsk is 98.33 %.similarly, the performance accuracy table demonstrates that the classification accuracy for qpsk is 67.53%. however, for the next modulation scheme, which is qam, the performance accuracy is 71.11% and the accuracy for 16qam is 41.29 %. at last, the classification accuracy for 64qam is found to be 41.17%. 4.3 knn with minkowski distance table 3 compares the performance of the knn classifier using minkowski distance for digital modulations which are bpsk, qpsk, qam, 16qam and 64qam with different numbers of samples.as can be seenin the table, the accuracy is enhanced with the increase of signal to noise ratio and number of samples.the performance accuracy for bpsk is 99.53 %.similarly, the performance accuracy table demonstrates that for qpsk, the classification accuracy is 99.95%. however, for the next modulation scheme, which is qam, the performance accuracy is 99.38% and for 16qam it is also 99.79%.at last, the classification accuracy for 64qam is found to be 99.63% which is same as qpsk, qam and 64qam. table 3: percentage classification accuracy using knn (minkowski distance) signal no of sample 0db 5db 10db bpsk 512 95.2 100 100 1024 99.23 100 100 2048 100 100 100 4096 100 100 100 qpsk 512 96.4 99.8 100 1024 99.98 100 100 2048 100 100 100 4096 100 100 100 qam 512 79.96 99.28 100 1024 90.62 99.93 100 2048 98.91 100 100 4096 99.92 100 100 16qam 512 98.63 99.48 99.53 1024 99.95 100 100 2048 100 100 100 4096 100 100 100 64qam 512 97.33 99.78 100 1024 99.95 99.96 100 2048 97.2 100 100 4096 99.88 100 100 4.4 knn with mahalanobis distance table 4 compares the performance of the knn classifier using mahalanobis distance for digital modulations which are bpsk, qpsk, qam, 16qam and 64qam with different numbers of samples. as can be seenin the table,the accuracy is enhanced with the increase of signal to noise ratio and number of samples.the performance accuracy for bpsk is 99.95 %. similarly, the performance accuracy table demonstrates that the classification accuracy is 99.97% for qpsk. however, for the next modulation scheme, which is qam, the performance accuracy is 99.97% and for 16qam it is also 99.91%. at last, the classification accuracy for 64qam is found to be 99.87%. iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 78 table 4: percentage classification accuracy using knn (mahalanobis distance) signal no of sample 0db 5db 10db bpsk 512 97.56 99.96 100 1024 99.80 100 100 2048 99.92 100 100 4096 100 100 100 qpsk 512 97.84 99.92 99.96 1024 99.92 100 100 2048 100 100 100 4096 100 100 100 qam 512 99.68 99.84 100 1024 99.76 99.84 100 2048 99.96 99.80 100 4096 100 100 100 16qam 512 98.63 99.92 100 1024 99.88 99.88 99.92 2048 99.80 99.92 99.96 4096 100 100 100 64qam 512 97.84 99.88 100 1024 99.88 99.88 99.88 2048 99.84 99.92 99.92 4096 99.80 99.92 99.88 4.5 average classification performance table 5 shows the overall performance accuracy of each modulated signal with different distance measurement method for the knn classifier. each column represents the distance measurement technique and rows show the modulation scheme which was used in this paper. the performance of knn with euclidean distance was excellent for almost every modulation technique used. a 98.87% performance accuracy was achieved in the case of bpsk, and for qpsk it was 99.73%. qam showed 96.80% performance accuracy, for 16qam it was 99.70%, and for 64qam performance accuracy was 99.57%. however, the correlation distance showed moderate results in comparison to other distance methods used. in the case of bpsk, a 99.33% accuracy was obtained.for 16qam,the accuracy was 90.94%.moreover, qpsk,qam, and 64 qam obtained 98.26%,86.41%, and 93.46% respectively.knn with minkowski distance gave excellent results in all means; which is evident from the above table. 64qam was classified with an accuracy of 99.63% and bpsk, qpsk, qam, and 16qam showedaccuracies of 99.53%, 99.95%, 99.38%, and 99.79% respectively. the mahalanobis distance with knn also showed very good results, 64qam had a low performance of 99.87%, while qpsk and qam had maximum performance with 99.97%. table 5: average classification performance accuracy for knn with used distance measurement approaches modulation type euclidean correlation minkowski mahalanobis bpsk 98.87 % 99.33% 99.53 %, 99.95 % qpsk 99.73% 98.26%. 99.95%. 99.97%. qam 96.80% 86.41% 99.38% 99.97% 16qam 99.70% 90.94% 99.79%. 99.91%. 64qam 99.57% 93.46%. 99.63% 99.87%. iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 79 4.6 comparison of classification accuracy with different distance methods this subsection presents the comparison of percentage of classification accuracy versus different snr values under different distance methods. due to limitations of space, graphs are presented in fig. 2 to fig. 6 for all 512 samples for the cases of bpsk, qpsk, qam, 16 qam and 64 qam modulation schemes. it can be clearly observed that the mahalanobis distance method produces higher classification accuracy percentage compared to euclidean, correlation, and minkowski distance methods for all modulation schemes under consideration. the correlation distance method is shown to have performed poorly compared to all other distance methods for all schemes other than bpsk. in the case of a bpsk modulation scheme,the correlation distance method out-performed the euclidean distance method. however, overall the correlation method is shown to be the least performing of all distance methods. fig. 2: classification accuracy of bpsk modulation scheme for 512 samples with different snr and distance methods. fig. 3: classification accuracy of qpsk modulation scheme for 512 samples with different snr and distance methods. iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 80 fig. 4: classification accuracy of qammodulation scheme for 512 samples with different snr and distance methods. fig. 5: classification accuracy of 16qammodulation scheme for 512 samples with different snr and distance methods. fig. 6: classification accuracy of 64qammodulation scheme for 512 samples with different snr and distance methods. iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 81 5. conclusion and future work in this paper, a classifier was proposed based on knn using different distance methods on the sample data, in which hoc was used to extract features from the received signal under influence of snr combined with an awgn channel. eleven eighth-order features were used for five different modulation schemes, namely bpsk, qpsk, qam, 16qam and 64qam to be classified. average performance accuracy was calculated with different snr and number of samples which showed that the mahalanobis distance method had a slight edge over the minkowski method in terms of accuracy. euclidean distance-based knn classifier fell behind the aforementioned two distance methods classifiers. correlation distance gave the least performance accuracy, making it unusable for classification. in future, normalized cumulants can be used for feature extraction and gp for the new sample data generation with knn as a fitness evaluator to improve the performance accuracy. different channels and different modulation schemescan be used for the same problem. references [1] ghauri sa, qureshi im, malik an, cheema ta. (2014) a novel modulation classification approach using gabor filter network. the scientific world journal, 2014:1-14. [2] xu j, su w, zhou m. (2011) likelihood-ratio approaches to automatic modulation classification. ieee trans. syst. man cybern. c, appl. rev., 41(4):455-469 [3] ghauri sa, qureshi im. (2015). m-pam signals classification using modified gabor filter network. mathematical problems in engineering. volume 2015:1-10 [4] ghauri sa, qureshi im, shah i, khan n. (2014) modulation classification using cyclostationary features on fading channels. res. j. app. sci. eng. tech., 7(24):5331-5339. [5] azzouz ee, nandi ak. (1998) algorithms for automatic modulation recognition of communication signals. ieee trans. commun., 46(4):431-436. [6] wang f, wang x. (2010) fast and robust modulation classification via kolmogorovsmirnov test. ieee trans. commun., 58(8):2324-2332. [7] ho kc, prokopiw w, chan yt. (2000) modulation identification of digital signals by the wavelet transform. iee proc. radar sonar navig., 147(4):169-176. [8] hong l, ho k. (1999) identification of digital modulation types using the wavelet transform. ieee military communications conf. proceedings:427-431 [9] zhao f, hu y, hao s. (2008) classification using wavelet packet decomposition and support vector machine for digital modulations. j. syst. eng. electron., 19(5):914-918. [10] li p, wang f, wang z.(2006) algorithm for modulation recognition based on high-order cumulants and subspace decomposition. in proceeding of icsp 2006,vienna (austria). [11] mirarab m, sobhani m. (2007) robust modulation classification for psk/qam/ask using higher-order cumulants. sixth int. conf. on information, communications and signal processing proceedings:1-4 [12] shen l, li s, song s, chen f. (2006) automatic modulation classification of mpsk signals using high order cumulants. eighth int. conf. on signal processing proceedings.1-4 [13] an n, li b, huang m. (2010) modulation classification of higher order mqam signals using mixed-order moments and fisher criterion. second int. conf. on computer and automation engineering proceedings:150-153 [14] shan z, xin z, ying w. (2010) improved modulation classification of mpsk signals based on high order cumulants. 2nd int. conf. on future computer and communication proceedings: 444-448 [15] swami a, sadler b. (2000) hierarchical digital modulation classification using cumulants. ieee trans. commun., 48(3):416-429. iium engineering journal, vol. 17, no. 2, 2016 hussain et al. 82 [16] han g, li j, chen c. (2003) a robust mdpsk modulation classifier based on cumulants. 17th int. conf. on advanced information networking and applications proceedings:265269. [17] pedzisz m, mansour a. (2005) automatic modulation recognition of mpsk signals using constellation rotation and its 4th order cumulant. digital signal process., 15(3):295-304. [18] yang l, ji z, xu x, dai x, xu p. (2007) modulation classification in multipath fading environments. fourth int. symp. on wireless communication systems proceedings, :171174. [19] wu hc, saquib m, yun z. (2008) novel automatic modulation classification using cumulant features for communications via multipath channels. ieee trans. wirel. commun., 7(8):3098-3105. [20] ramkumar b, bose t, radenkovic ms. (2010) robust multiuser automatic modulation classifier for multipath fading channels. ieee symp. on new frontiers in dynamic spectrum proceedings, 1-10. [21] orlic v, dukic m. (2009) algorithm for automatic modulation classification in multipath channel based on sixth-order cumulants. ninth int. conf. on telecommunication in modern satellite, cable and broadcasting services proceedings, 423-426. [22] orlic v, dukic ml. (2010) multipath channel estimation algorithm for automatic modulation classification using sixth-order cumulants. electron. lett., 1348-1349. [23] park c, kim d. (2006) a novel robust feature of modulation classification for reconfigurable software radio. ieee trans. consum. electron., 52(4):1193-1200. [24] nikias cl, petropuou a. (1993) higher-order spectral analysis. prentice hall, englewood cliffs nj. [25] stark h, woods jw. (2002) probability and random processes with applications to signal processing, 3rd ed. prentice hall, upper saddle river, nj [26] ghauri sa, qureshi im, aziz a, cheema ta. (2014) classification of digital modulated signals using linear discriminant analysis on faded channel. world app. sci. j., 29(10):1220-1227. [27] ghauri sa, qureshi im, malik an, cheema ta. (2014) automatic digital modulation classification technique using higher order cummulants on faded channels. j. basic. appl. sci. res., 4(3):1-12. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 1 adsorption of heavy metals and residual oil from palm oil mill effluent using a novel adsorbent of alginate and mangrove composite beads coated with chitosan in a packed bed column rana jaafar jawad*, mohd halim shah ismail and shamsul izhar siajam department of chemical and environmental engineering, faculty of engineering, universiti putra malaysia, 43400 upm serdang, selangor, malaysia. * corresponding author: ranajaafarjawad@yahoo.com (received: 14th sept 2016; accepted: 5th may 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.734 abstract: in this study, a novel adsorbent was prepared, namely alginate and mangrove composite beads coated with chitosan (amcbcc), and performed well to remove heavy metals and residual oil from palm oil mill effluent (pome) using continuous adsorption studies in a fixed bed column under different bed heights. thomas and yoon–nelson models were applied to predict the breakthrough curve and to compute the characteristic parameters such as maximum capacity and the time required for 50% of adsorbate breakthrough. it was found that the total removal percentage of iron ions, zinc ions, and residual oil were 26.75%, 76.74%, and 83% respectively at ph 3, and a bed height 27 cm. both models can well describe the breakthrough curve of heavy metals and residual oil. these results indicated that amcbcc can be used to remove heavy metals and residual oil from industrial wastewater. abstrak: kajian ini menyediakan tentang penjerap baharu iaitu alginat dan manik komposit bakau bersalut kitosan (amcbcc), berfungsi menyingkirkan logam berat dan sisa minyak daripada efluen kilang minyak sawit (pome) dengan sempurna, menggunakan kajian penjerapan berterusan dalam lapisan lajur tetap pada ketinggian berbeza. model thomas dan yoon-nelson telah digunakan bagi meramal lengkungan terbaik dan mengira parameter cirian seperti keupayaan maksimum dan tempoh diperlukan bagi 50% lengkungan terbaik penjerap. jumlah peratusan penyingkiran ion besi, ion zink, dan sisa minyak masing-masing sebanyak 26.75%, 76.74%, dan 83% pada ph 3, dan pada ketinggian lapisan 27 cm. kedua-dua model mampu menggambarkan lengkungan terbaik bagi logam berat dan sisa minyak dengan sempurna. dapatan ini menunjukkan amcbcc sesuai digunakan bagi menyingkirkan logam berat dan sisa minyak daripada air sisa industri. keywords: continuous adsorption; heavy metals; residual oil; palm oil mill effluent; adsorbent iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 2 1. introduction the palm oil industry is considered to be a major industry and a key contributor to economic prosperity in malaysia. a huge amount of effluent is discharged during the palm oil production process, which is known as palm oil mill effluent (pome). pome is a thick brown liquid owing to the presence of lignin, humic acid, lipids, fatty acids, and tannin [1]. it is hot with a temperature between 80 ᵒc and 90 ᵒc and acidic with a ph of 4.5–5 [2]. pome is oily wastewater mainly consisting of the following: water 95% 96%, total solid 4% 5%, and oil and grease 0.6% 0.7% [3]. the presence of residual oil in pome can pollute water sources and cause harmful effects to all aquatic creatures if it is discharged without treatment because pome has the ability to form an oily layer on the water surface. this reduces the light penetration into the water and subsequently has an adverse effect on photosynthesis. moreover, this oily layer decreases the transfer of oxygen from air to water, leading to a low level of dissolved oxygen in water. this creates a direct threat to marine living organisms, which in turn leads to adverse effects on humans through the food chain [4]. the residual oil content in untreated pome is is very high, at an average of 9065 mg/l [5], which exceeds the permissible limits issued by the department of environmental (doe) malaysia (50 mg/l). moreover, pome contains many heavy metals in critical levels such as iron and zinc. iron ions have the highest concentration and are found at a dangerous levels in pome with an average of 119.5 mg/l [6], which exceeds the permissible limits (5 mg/l) issued by doe malaysia. heavy metals are non-biodegradable, toxic, and bio-accumulate in aquatic living organisms. they can also be transferred to humans through the food chain, and can cause many diseases such as cancer [7-8]. untreated pome causes severe water and soil pollution. it changes the water to brown, stinky, and slimy, which may eliminate living marine organisms and also endanger the planet in the case of discharging pome on land [9-10]. although various methods have been used for the treatment of effluents containing heavy metals and residual oil, the adsorption process using natural adsorbents is a very encouraging method for pollutant removal [11]. a continuous adsorption process is very applicable to the batch adsorption process because a continuous process is cost-effective, feasible, requires less amount of adsorbent, and can be controlled [12]. limited studies have been conducted on the treatment of pome using natural materials as adsorbents by a continuous adsorption process. in this study, a novel type of adsorbent was prepared. it is known as alginate-mangrove composite beads coated with chitosan (amcbcc). the adsorbent is in the shape of beads, which is the best form of biopolymer adsorbent for the removal of pollutants in wastewater, and also to prevent column clogging problems [13]. in addition, it is easy to separate the beads from the wastewater after treatment and they can also be easily regenerated. mangrove bark is obtained from charcoal factories, alginate is a biopolymer obtained from the cell walls of brown algae, and chitosan is a copolymer obtained from chitin, which is produced from arthropods. these materials are natural and contain effective functional groups such as carboxylic, phenolic, and hydroxyl in mangrove bark, carboxylate and hydroxyl in alginate, and hydroxyl and amino in chitosan [14-16]. these functional groups are well known of their ability to remove pollutants from industrial wastewater [17]. the main purpose of the present research was to remove heavy metals and residual oil from actual pome using a new type of adsorbent (amcbcc) by continuous adsorption studies in a fixed bed column under different bed height. moreover, two kinetic models thomas and yoon-nelson were also conducted in this work. iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 3 2. materials and methods 2.1 materials a sample of pome was collected from a palm oil mill in seri ulu langat, malaysia. the sample was left to cool and kept in a cooling room at about 4 ᵒc. the characteristics of the sample are specified in table 1. mangrove bark was obtained from a charcoal factory in kuala sepetang, perak, malaysia, and chitosan with a medium molecular weight was obtained from a local factory in malaysia. the other chemicals (sodium alginate ~98.5%, acetic acid 99.8%, nitric acid 65%, calcium chloride 99.5%, hydrochloric acid 37%, sodium hydroxide 99%, and sulphuric acid ~95%) were purchased from r&m chemicals. hexane was supplied from h&m chemicals, and sodium sulfate anhydrous ~99% was supplied from bendosen chemicals. table 1: characteristics of raw pome sample characteristics values oil and grease 10843 mg/l cod 42240 mg/l fe 103.3 mg/l zn 7.5 mg/l ph 4.9 2.2 preparation of the adsorbent the mangrove bark was washed with distilled water, dried at room temperature, ground, and sieved using a 250-mesh sieve. it was then treated by 0.1 m naoh for 2 hours, as naoh is the best agent for improving the bark by increasing the active sites to obtain the maximum adsorption capacity [18]. moreover, this modification was conducted to increase the hydrophobicity of the mangrove bark to adsorb residual oil [11-19]. next, the bark was washed many times with distilled water until the ph of the solution became neutral. after that, the bark was filtered and dried in an oven at 60-63 ᵒc for 24 hrs. the treated bark was kept in a glass container for later use. the mixture of alginate and mangrove bark (am) was prepared by adding 5 g of sodium alginate into 200 ml of distilled water. the mixture was then stirred continuously until the alginate had completely dissolved. next, 2.5 g of the treated mangrove bark was added to the sodium alginate solution and mixed together until they became homogenous. a syringe pump device was used to form the alginate-mangrove composite beads (amcb) by dropping the alginate-mangrove mixture into a solution of 0.2 m cacl2. the beads were kept in the solution for 24 hrs before being washed with distilled water to remove the excess cacl2. they were then left to dry at room temperature and kept in a glass container for later use. to coat the beads, a chitosan solution was prepared by adding 7.5 g of chitosan powder to 250 ml of 0.2% acetic acid solution. the mixture was stirred continuously for 3 hrs at 4550 o c to obtain a viscous gel [20], then, the chitosan solution was inserted into an ultrasonic device for 10 mins, after which, the solution was left at room temperature for 24 hrs. 40 g iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 4 of amcb was immersed in 250 ml of chitosan solution and then stirred slowly at 45-50 ᵒc for one hour. next, the beads were removed from the chitosan solution and were immersed in 250 ml of 0.1 m naoh for one hour to neutralise the excess acetic acid [20]. finally, amcbcc was washed with distilled water until the ph of the solution became neutral. it was then left to dry at room temperature and kept in a glass container for further experimentation. 2.3 characterization studies fourier transform infrared spectroscopy (ftir) was used to determine the surface functional groups in the amcbcc, where the spectra were measured from 4000 to 600 cm1. the physical characteristics were checked for the beads to determine the weight and size of each bead. 2.4 column adsorption studies continuous studies for the removal of heavy metals and residual oil from pome were performed in a fixed bed column packed with amcbcc (fig. 1). the glass column was 40 cm long and 1.9 cm in diameter. the continuous studies were performed by studying the effects of bed height (9, 18, and 27 cm) at a constant ph obtained from the batch studies and at a constant flow rate of 3 ml/min, which was the lowest flow rate of this device. based on the previous studies, it was revealed that at the minimum flow rate, a shorter breakthrough curve can be found [12, 2122]. in order to do the experiment, the pome was acidified to ph 3 and put in the storage tank. the column was packed with amcbcc until it reached the required height, and then the flow rate was set 3 ml/min. the adjusted pome was then pumped through the fixed bed of amcbcc. at regular intervals, the sample of treated pome was collected and prepared to be analyzed to determine the heavy metals and residual oil. the experiments were performed for about 540 min. fig. 1 schematic diagram of adsorption column. 2.5 analytical techniques 2.5.1 determination of heavy metals the metals concentration in pome before and after treatment were determined using an inductively coupled plasma optical emission spectrometer (icp-oes). in order to iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 5 execute the test, the samples were filtered using filter paper and acidified by adding concentrated amount of hno3 to prevent the precipitation of heavy metals [13] 2.5.2 determination of residual oil the amount of residual oil in pome before and after the treatment was determined using the partition-gravimetric method, a standard recommended method for the examination of water and wastewater [23]. in this method, the sample of pome was first acidified with 1:1 h2so4 until the ph of the sample was equal or less than 2. the acidified sample was transferred to a separatory funnel, and 30 ml of hexane was added to the sample in the separatory funnel. the separatory funnel was capped and shaken 60 times for about 2 minutes while releasing the pressure from time to time. the layer was left to separate for 515 minutes. the lower layer was discarded. then, the top layer was drained slowly into filter paper containing 1g of anhydrous sodium sulphate placed in a funnel into a pre-weighted conical flask. the conical flask with the collected sample was then put in an oven at 70 ᵒc until it was completely dried. the conical flask was cooled in a desiccator for 30 minutes and weighted. the residual oil concentration was calculated using equation (1): residual oil (mg/l) = (𝑊2−𝑊1) 𝑉 × 106 (1) where: w1 and w2 are the initial and final weight of the conical flask, respectively (g), and v is the volume of the sample (ml). 2.6 mathematical equation of the fixed bed column in continuous studies the most important factor in the fixed bed column is the breakthrough curve, which is usually obtained from plotting a curve between [ 𝐶𝑡 𝐶𝑖 ] versus the contact time (t), where ci and ct are the inlet and outlet adsorbate concentration (mg/l) [12]. the total adsorbed adsorbate in the column (qtotal) is determined using equation (2): qtotal (mg) = 𝑄 𝐴 1000 (2) where: qtotal is the total metal ions or residue oil adsorbed quantity (mg). q is the volumetric flow rate (ml/min), and a is the area under the curve which is determined from plot of the adsorbed concentration (cad) versus time (t). a = ∫ 𝐶𝑎𝑑 𝑑𝑡 𝑡=𝑡 𝑡𝑜𝑡𝑎𝑙 𝑡=𝑡 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 where: cad is the adsorbed concentration (mg/l) obtained from (ci – ct). the equilibrium adsorbate uptake (qe.exp) is calculated using equation (3): qe.exp (mg/g) = 𝑞𝑡𝑜𝑡𝑎𝑙 𝑋 (3) where: x is the total dry weight of absorbent (amcbcc) in column (g) the total amount of metal ions or oil sent to the column (mtotal) is evaluated using equation (4): mtotal (mg) = 𝐶𝑖 𝑄 𝑡 𝑡𝑜𝑡𝑎𝑙 1000 (4) the unadsorbed concentration at equilibrium of metal ions or oil (ceq) is obtained by equation (5): ceq = 𝑀𝑡𝑜𝑡𝑎𝑙−𝑞 𝑡𝑜𝑡𝑎𝑙 𝑉 𝑒𝑓𝑓 × 1000 (5) iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 6 where: veff is the volume of effluent (ml) = q × t total the total removal percentage of metal ions or oil (y) is the ratio of the total capacity (qtotal) to the total amount of metal ions and oil sent to the column (mtotal) can be obtained from equation (6): y= 𝑞 𝑡𝑜𝑡𝑎𝑙 𝑀𝑡𝑜𝑡𝑎𝑙 × 100 (6) 2.7 modeling of the fixed bed column in this research, the description of the breakthrough behavior of iron ions, zinc ions and residual oil on the amcbcc and the characteristic parameters kth, qx, kyn, and ԏ were determined by two well-known models: the thomas model and the yoon-nelson model. 2.7.1 thomas model the thomas model is designed to determine the maximum capacity of adsorption, which is one of the most important factors for column design. this model is also used in the description of the breakthrough curve of the column [12-21]. the linearized form of the thomas equation is illustrated in equation (7): ln [ 𝐶𝑖 𝐶𝑡 – 1] = 𝐾 𝑇ℎ 𝑞𝑥 𝑚 𝑄 – kth ci t (7) where: ci and ct are the inlet and outlet adsorbate concentration respectively (mg/l), q is the volumetric flow rate (ml/min), t is the contact time (min), m is the mass of adsorbent (g), kth is thomas kinetic coefficient (ml/min.mg), qx is the maximum adsorption capacity (mg/g). with plot ln [ 𝐶𝑖 𝐶𝑡 – 1] versus t from the slope and the intercept, values of kth and qx are determined. 2.7.2 yoon-nelson model this model is developed based on the assumption of adsorption and breakthrough of adsorbate probability [12]. it is less complicated and needs fewer parameters than the other models; moreover, it is usually used to determine the time required for 50% of the adsorbate breakthrough (ԏ). the linearized form of yoon-nelson equation is illustrated in equation (8): ln 𝐶𝑡 𝐶𝑖−𝐶𝑡 = kyn t – kyn ԏ (8) where: kyn is the yoon-nelson rate of constant min -1, ԏ is the time required for 50% of adsorbate breakthrough min, and t is the contact time min. plot ln ct ci−ct versus t is to determine the slope and the intercept, and from the slope and the intercept, the values of kyn and ԏ are calculated. 3. results and discussion 3.1 characterization of amcbcc from fig. 2, it can be seen that the main peak was at the wave number of 3395.96 cm1, which refers to a hydroxyl group. this group was present in the mangrove bark, alginate, and chitosan [16, 24-25]. the wave number 1642.59 cm-1 refers to a carboxyl group, which was present in the alginate [26]. moreover, the wave numbers 1034.87 and 779.23 cm-1 iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 7 indicate the amine functional group, which can be considered as evidence of the coating by chitosan [27]. the physical characteristics of one bead are 0.0715 g weight, and 2.89 mm diameter. figure 3 shows image of the amcbcc bead. fig. 2: ftir spectrum of amcbcc. fig. 3: image of amcbcc. 3.2 effects of the bed height the breakthrough curve of iron ions, zinc ions, and residual oil at different bed height are illustrated in figs. 4, 5, and 6 respectively. it is shown in figs. 4, 5, and 6 that by increasing the bed heights from 9 cm to 27 cm, a slower breakthrough curve occurred and the adsorbent (amcbcc) needed a longer time to reach the exhaustion point (which was the point where the outlet concentration was equal to the inlet concentration). the explanation for this can be that increasing the adsorbent led to more available binding sites, more contact time, and more surface area [28]. on the contrary, decreasing the bed height led to a faster breakthrough curve and less time to reach the exhaustion point, and this trend had been reported in other research [29]. the mathematical characterization of the column parameters for iron ions, zinc ions, and residual oil can be seen in table 2. iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 8 fig. 4: effect of the height on the adsorption of iron ions. fig. 5: effect of the height on the adsorption of zinc ions. fig. 6: effect of the height on the adsorption of residual oil. table 2: mathematical characterization of column parameters of iron ions, zinc ions, and residual oil at constant flow rate q (3 ml/min) adsorbate bead height (cm) qtotal (mg) mtotal (mg) y% qe.exp (mg/g) ceq (mg/l) fe ci (103.3) mg/l 9 17.09 167.30 10.20 0.95 92.72 18 27.87 167.30 16.65 0.77 86.07 27 44.75 167.30 26.75 0.83 75.66 zn ci (7.5) mg/l 9 4.33 12.15 35.60 0.24 4.80 18 5.55 12.15 45.67 0.15 4.07 27 9.32 12.15 76.74 0.17 1.74 residual oil ci (1084.3) mg/l 9 1366.45 1756.57 77.78 75.90 240.80 18 1408.65 1756.57 80.20 39.13 214.76 27 1458.49 1756.57 83.00 27.00 183.99 iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 9 it can be noticed from table 2 that by increasing the bed height from 9 to 27 cm, the total removal percentage (y %) increased from (10.20 to 26.75) % of iron ions, (35.60 to 76.74) % of zinc ions, and from (77.78 to 83.00) % of residual oil. on the other hand, by increasing the bed height, the unadsorbed equilibrium concentration of iron ions, zinc ions and residual oil decreased from (92.72 to 75.66) mg/l, (4.80 to 1.74 ) mg/l, and (240.80 to 183.99) mg/l respectively. similar results were reported by a previous study [12]. 3.2 modeling of the fixed bed column 3.3.1 thomas model to obtain the parameters in the thomas model, a plot of ln [ 𝐶𝑖 𝐶𝑡 1] versus time is illustrated in figs. 7, 8, and 9 for iron ions, zinc ions, and residual oil respectively at different bed height, where the slope and the intercept of the linear equation were used to calculate the kth and qx respectively, which are presented in table 3. this model was applied to the range of 0.08< 𝐶𝑡 𝐶𝑖 < 0.97. fig. 7: thomas model of iron ions at different bed heights. fig. 8: thomas model of zinc ions at different bed heights. fig. 9: thomas model of residual oil at different bed heights. it is shown in table 3 that when the bed height was increased, the thomas kinetic coefficient (kth) decreased, and this was a normal trend, as mentioned in a previous research [30]. iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 10 table 3: mathematical characterization of thomas model of iron ions, zinc ions and residual oil at constant flow rate q (3 ml/min) adsorbate m (g) kth (ml/min.mg) qx (mg/g) qe.exp (mg/g) r2 fe ci (103.3) mg/l 18 0.040 3.06 0.95 0.9777 36 0.015 4.20 0.77 0.8874 54 0.011 2.86 0.83 0.8247 zn ci (7.5) mg/l 18 0.98 0.25 0.24 0.9011 36 0.94 0.18 0.15 0.9636 54 0.32 0.32 0.17 0.9677 oil & grease ci (1084.3) mg/l 18 5.26 × 10 -3 99.52 75.90 0.8877 36 5.99 × 10-3 54.15 39.13 0.8171 54 1.66 × 10-3 97.40 27.00 0.999 figures 10, 11, and 12 illustrated that the thomas model fitted better with zinc ions than with iron ions and residual oil, because the predicted values of zinc ions by the thomas model were more agreeable with experimental values than for iron ions and residual oil. the values of r2 from table 3 also showed that thomas models fitted better with zinc ions. lastly, in comparison between the experimental qe.exp and the thomas theoretical qx for iron ions and residue oil, it was clear that there was a prominent difference between them, and this was a normal trend that was mentioned in a previous research [31]. on the other hand the values of qe.exp and qx were in greater agreement for zinc ions. fig. 10: effect of bed height on iron ions removal predicted by thomas model. fig. 11: effect of bed height on zinc ions removal predicted by thomas model. fig. 12: effect of bed height on residual oil removal predicted by thomas model. iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 11 it is illustrated by table 4 that by increasing the bed heights from 9 cm to 27 cm, the time required to reach 50% adsorbate breakthrough (ԏ) increased from 174.92 min to 502.36 min, 196.60 min to 754.62 min, and from 550.70 min to 1617.94 min for iron ions, zinc ions, and residual oil, respectively. this trend had been reported in a previous study [32]. fig. 13: yoon-nelson model of iron ions at different bed heights. fig. 14: yoon-nelson model of zinc ions at different bed heights. fig. 15: yoon-nelson model of residual oil at different bed heights. table 4: mathematical characterization of yoon-nelson of iron ions, zinc ions, and residue oil at constant flow rate q (3 ml/min) adsorbate h (cm) kyn(1/min) ԏ (min) r2 fe ci (103.3) mg/l 9 0.0042 174.92 0.9776 18 0.0015 488.33 0.8874 27 0.0011 502.36 0.8214 zn ci (7.5) mg/l 9 0.0075 196.60 0.8933 18 0.0071 288.29 0.9642 27 0.0024 754.62 0.9678 residual oil ci (1084.3) mg/l 9 0.0057 550.70 0.8877 18 0.0065 598.01 0.8171 27 0.0018 1617.94 1 iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 12 figures 16, 17, and 18 illustrated that the yoon-nelson model fitted better with zinc ions than with iron ions and residual oil because the predicted values by the yoon-nelson model of zinc ions were more agreeable with experimental values than for iron ions and residual oil. moreover, the values of r2 from table 4 also showed that the yoon-nelson model fitted better for zinc ions. fig. 16: effect of bed height on iron ions removal predicted by yoonnelson model. fig. 17: effect of bed height on zinc ions removal predicted by yoon-nelson model. fig. 18: effect of bed height on residual oil removal predicted by yoon-nelson model. 4. conclusion in this work, the investigation of removal heavy metals and residual oil from pome was explored in a fixed bed column by a new type of adsorbent (amcbcc). the adsorbent was characterized by ftir to reveal the main functional groups in the beads. it was found that by increasing the bed heights from 9 cm to 27 cm, the adsorbent (amcbcc) needed a longer time to reach the exhausted point. moreover, by increasing the bed height, the removal percentage for iron ions, zinc ions and residual oil increased from 10.20 % to 26.75 %, 35.60 % to 76.74 %, and 77.78 % to 83.00 %, respectively. furthermore, the thomas model and the yoon-nelson model can both describe the adsorption of iron ions, zinc ions, and residual oil well, but the prediction data for both models are in greater agreement with the experimental data for zinc ions. lastly, this research suggested that alginate-mangrove composite beads coated by chitosan (amcbcc) are a promising adsorbent for the removal of heavy metals and residual oil from industrial wastewater. iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 13 acknowledgment the authors are grateful to universiti putra malaysia (upm) for the financial support under grant (gp-ips/2015/9453200). references [1] saeed mo, azizli k, isa mh, bashir mj. (2015) application of ccd in rsm to obtain optimize treatment of pome using fenton oxidation process. j. water process engineering, 8:e7-e16. [2] chan yj, tan wjr, how bs, lee jj, lau vy. (2015) fuzzy optimisation approach on the treatment of palm oil mill effluent (pome) via up-flow anaerobic sludge blanket–hollow centered packed bed (uasb–hcpb) reactor. j. water process engineering, 5:112-117. [3] azmi ns, yunos kfm. (2014) wastewater treatment of palm oil mill effluent (pome) by ultrafiltration membrane separation technique coupled with adsorption treatment as pretreatment. agriculture and agricultural science procedia, 2:257-264. [4] jameel at, muyubi sa, karim mia, alam mz. (2011) removal of oil and grease as emerging pollutants of concern (epc) in wastewater stream. iium engineering journal, 12(4):161-169. [5] bello m, nourouzi m, abdullah lc, choong ts, koay y, keshani s. (2013) pome is treated for removal of color from biologically treated pome in fixed bed column: applying wavelet neural network (wnn).journal of hazardous materials, 262:106-113. [6] wu ty, mohammad aw, jahim jm, anuar n. (2010) pollution control technologies for the treatment of palm oil mill effluent (pome) through end-of-pipe processes.journal of environmental management, 91(7):1467-1490. [7] bernard e, jimoh a. (2013) adsorption of pb, fe, cu and zn from industrial electroplating wastewater by orange peel activated carbon.international journal of engineering and applied sciences, 4(2):95-103. [8] ghaedi m, mosallanejad n. (2013) removal of heavy metal ions from polluted waters by using of low cost adsorbents: review.journal of chemical health risks, 3(1):7-22. [9] ohimain e, seiyaboh e, izah s, oghenegueke v, perewarebo t. (2012) some selected physico-chemical and heavy metal properties of palm oil mill effluents. greener journal of physical sciences, 2(4):131-137. [10] rupani pf, singh rp, ibrahim mh, esa n. (2010) review of current palm oil mill effluent (pome) treatment methods: vermicomposting as a sustainable practice. world applied sciences journal, 11(1):70-81. [11] ahmad a, bhatia s, ibrahim n, sumathi s. (2005) adsorption of residual oil from palm oil mill effluent using rubber powder. brazilian journal of chemical engineering, 22(3):371-379. [12] lim ap, aris az. (2014) continuous fixed-bed column study and adsorption modeling: removal of cadmium (ii) and lead (ii) ions in aqueous solution by dead calcareous skeletons. biochemical engineering journal, 87:50-61. [13] zhang m, zhang y, helleur r. (2015) selective adsorption of ag+ by ion-imprinted ocarboxymethyl chitosan beads grafted with thiourea–glutaraldehyde. chemical engineering journal, 264:56-65. [14] rozaini c, jain k, oo c, tan k, tan l, azraa a, tong k. (2010) optimization of nickel and copper ions removal by modified mangrove barks. int j chem eng appl, 1(1):84-89. [15] bée a, talbot d, abramson s, dupuis v. (2011) magnetic alginate beads for pb (ii) ions removal from wastewater. journal of colloid and interface science, 362(2):486-492. [16] igberase e, osifo p, ofomaja a. (2014) the adsorption of copper (ii) ions by polyaniline graft chitosan beads from aqueous solution: equilibrium, kinetic and desorption studies. journal of environmental chemical engineering, 2(1):362-369. [17] ahmad, sumathi, hameed. (2004) chitosan: a natural biopolymer for the adsorption of residue oil from oily wastewater.adsorption science & technology, 22(1):75-88. iium engineering journal, vol. 19, no. 1, 2018 jawad et al. 14 [18] argun me, dursun s.(2006) removal of heavy metal ions using chemically modified adsorbents. j. int. environ. appl. sci, 1(1-2): 27-40. [19] asadpour r, sapari nb, isa mh, orji ku. (2014) investigation of modified mangrove bark on the sorption of oil in water. applied mechanics & materials, 567:74-79. [20] popuri sr, vijaya y, boddu vm, abburi k. (2009) adsorptive removal of copper and nickel ions from water using chitosan coated pvc beads. bioresource technology, 100(1):194-199. [21] aksu z, gönen f. (2004) biosorption of phenol by immobilized activated sludge in a continuous packed bed: prediction of breakthrough curves.process biochemistry, 39(5):599613. [22] shavandi ma, haddadian z, ismail mhs, abdullah n. (2012) continuous metal and residual oil removal from palm oil mill effluent using natural zeolite-packed column. journal of the taiwan institute of chemical engineers, 43(6):934-941. [23] federation we, association aph. (2005) standard methods for the examination of water and wastewater.american public health association (apha), washington, dc, usa. [24] asadpour r, sapari nb, isa mh, orji ku. (2014) enhancing the hydrophobicity of mangrove bark by esterification for oil adsorption. water science & technology, 70(7):1220-1228. [25] kleinübing sj, da silva fgc, bertagnolli c, da silva mgc. (2011) heavy metal sorption by calcium alginate beads from sargassum filipendula. chemical engineering transactions, 24:1201-1206. [26] li x, kong x, shi s, zheng x, guo g, wei y, qian z. (2008) preparation of alginate coated chitosan microparticles for vaccine delivery. bmc biotechnology, 8(89): http://www.biomedcentral.com/1472-6750/8/89. [27] ahmad a, sumathi s, hameed b. (2005) adsorption of residue oil from palm oil mill effluent using powder and flake chitosan: equilibrium and kinetic studies.water research, 39(12):24832494. [28] sugashini s, begum s, meera k. (2012) column adsorption studies for the removal of cr (vi) ions by ethylamine modified chitosan carbonized rice husk composite beads with modelling and optimization. journal of chemistry, 2013: http://dx.doi.org/10.1155/2013/460971. [29] quek s, al-duri b. (2007) application of film-pore diffusion model for the adsorption of metal ions on coir in a fixed-bed column. chemical engineering and processing: process intensification, 46(5):477-485. [30] zhang j, xu s, zhang s, du z. (2008) preparation and characterization of tamarind gum/sodium alginate composite gel beads. iranian polymer journal, 17(12):899-906. [31] xu z, cai j-g, pan b-c.(2013) mathematically modeling fixed-bed adsorption in aqueous systems. journal of zhejiang university science a, 14(3):155-176. [32] han r, wang y, zhao x, wang y, xie f, cheng j, tang m. (2009) adsorption of methylene blue by phoenix tree leaf powder in a fixed-bed column: experiments and prediction of breakthrough curves. desalination, 245(1):284-297. microsoft word paper-v4-n2-2 new.doc iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 13 modeling of a reactive distillation column: methyl tertiary butyl ether (mtbe) simulation studies muhamad nazri murat, abdul rahman mohamed and subhash bhatia∗ school of chemical engineering, engineering campus, universiti sains malaysia, seri ampangan, 14300 nibong tebal, penang, malaysia email:chbhatia@eng.usm.my abstract: a process simulation stage-wise reactive distillation column model formulated from equilibrium stage theory was developed. the algorithm for solving mathematical model represented by sets of differential-algebraic equations was based on relaxation method. numerical integration scheme based on backward differentiation formula was selected for solving the stiffness of differential-algebraic equations. simulations were performed on a personal computer (pc pentium processor) through a developed computer program using fortran90 programming language. the proposed model was validated by comparing the simulated results with the published simulation results and with the pilot plant data from the literature. the model was capable of predicting high isobutene conversion for heterogeneous system, as desirable in industrial mtbe production process. the comparisons on temperature profiles, liquid composition profile and operating conditions of reactive distillation column also showed promising results. therefore the proposed model can be used as a tool for the development and simulation of reactive distillation column. key words: modeling, simulation, reactive distillation, relaxation method, equilibrium stage, heterogeneous, mtbe 1. introduction reactive distillation process has been given special attention in the past two decades because of its potential for process intensification for certain types of chemical reactions [1]. the most important benefit of reactive distillation technology is a reduction in capital investment, because two process steps can be carried out in the same device. such integration leads to lower costs in pumps, piping and instrumentation. for exothermic reaction, the reaction heat can be used for vaporisation of liquid. this leads to savings of energy costs by the reduction of reboiler duties. reactive distillation process is also advantageous when the reactor product is a mixture of species that can form several ∗ to whom the correspondence should be addressed iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 14 azeotropes with each other. reactive distillation conditions can allow the azeotropes to be “reacted away” through reaction [2, 3]. although the advantageous of reactive distillation process was known since 1920, even until 1980, the technology was only utilised for homogeneous esterification reaction and was under utilised in other areas [4]. developing reactive distillation column is a challenging task because of the complexities in column design, process synthesis and operability of reactive distillation processes resulting from the interaction of reaction and distillation [5]. with the aid of computer simulation, it was only recently been shown that difficult or unsolvable reaction-separation modeling problems are indeed solvable [6]. in more recent development, many reactive distillation processes such as esterification, hydration, alkylation have been utilised for reactions that rely on solid heterogeneous catalyst, often termed as catalytic distillation process. in the last two decades, research on heterogeneously catalysed reactive distillation has been extended to various industrial processes, including a well-known process for the production of octane booster methyl tert-butyl ether (mtbe), methyl acetate process and nylon 6,6 process [5, 7]. despite the recent advances by many researchers, it can be claimed that there is still no generally accepted design methods for reactive distillation. the main reason is the difficulty associated with reactive distillation processes and the parametric uncertainty of the model parameters [6]. with proper understanding of the thermodynamic and kinetic theories, several approaches and techniques have been proposed and claimed to be able to handle these difficult problems. most of reactive distillation mathematical models are originally derived from conventional distillation calculations, which are based on equilibrium stage model. the liquid and vapour phase are assumed to be in phase equilibrium, and the stage is associated with the mesh equations (material balance, equilibrium relationship, summation (constraint) equation, heat (energy) balance). relaxation method can be used as a solving tool for reactive distillation model with the mesh equations written in unsteady state form and thus utilising numerical integration to find the steady-state solution. this method is closely related to dynamic model; however, it is not often used because it was previously considered to be too demanding of computer time [2]. today, with the high performance personal computer (pc) available in the market at a very reasonable price, the issue of too much of processing time related to pc requirement for relaxation method is not a critical issue. one of the numerical integration schemes that have been implemented in reactive distillation is the linear multistep method based on backward differentiation formula [8]. as being known to author, so far, only the solution algorithm of chen et al. [5] used this integration method coupled with relaxation method for solving homogeneous reactive distillation problem. the following are the advantages of this method [5]: • it is robust for arbitrary initialisation, e.g. convergence is almost always guaranteed for steady state solution. • equilibrium stage models often have multiple steady state solutions, and the method greatly help the iteration to converge towards stable state, not to unstable state. iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 15 • model is very stiff especially when the system approaches equilibrium reactive limit and the method is chosen to maximise accuracy and stability in this limit. this paper demonstrates the applicability and reliability of relaxation method that can be extended to heterogeneous system of reactive distillation process. the numerical method scheme is based on backward differentiation formula linear multistep method for stiff system of equations [7]. the mtbe system is chosen for the verification of the proposed mathematical model. 2. modeling the model assumes adiabatic operation of the column and the reaction takes place in the liquid phase. each reactive stage is treated as a perfectly mixed continuous stirred tank reactor (cstr). the vapour and liquid leaving any stage are in phase equilibrium with negligible heat of mixing of liquid and vapour mixtures. the vapour hold-up is assumed to be negligible. the hydrodynamic effects are neglected in the present modeling work in order to simplify the modelling complexities. with reference to the column configuration given in figure 1, the model equations are presented in this section. they include mass and energy balances, vapour-liquid equilibrium (vle) model and summation (constraint) equation. the kinetic model is shown separately although it can be considered as part of the material balance. the overall material balance for equilibrium stage j: fj + lj–1 + vj+1 + δjrj = lj + vj (mol/s) (1) unsteady state component i material balance: hj t x ij d d , = (zj,ifj + xj–1,ilj–1 + yj+1,ivj+1) – (xj,ilj + yj,ivj) + δj ∑ = r r rjir rv 1 ,, )( (mol/s) (2) where j = 1, 2… n-1; i = 1, 2... c; r = 1, 2,..., r j is the stage number, i is the component number, r is the specific reaction number. the following definitions are useful in understanding and clarifying the derived material balance: • liquid hold-up on stage j, hj is defined as the molar quantity (or volumetric quantity) of liquid mixture that remains or held at certain level on stage j • ri is the total numbers of moles generated or disappear through reaction on stage j. • ri,r is the rate of reaction r on stage j (mol/s). parameter δj (0 or 1) refers to reaction occurrence on stage j. when reaction occurs on stage j, δj is set to unity but when there is no reaction; δj is set to zero value. iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 16 • symbols zj,i, xj,i, yj,i are component i mole fractions of feed flow fj (mol), liquid flow lj (mol), and vapour flow vj (mol) on stage j respectively. • the vr,i term is the stoichiometric coefficient of component i for reaction r. stage n-1 stage j hj, rj vj lj-1 vj+1 lj stage j +1 stage j -1 stage 1 lj+1 vn l1 vj-1 v1 stage 0 d = ld + vd l0 ld vd (v0) v1 vn ln-1 vn ln-1 stage n b = ln f1 fj-1 fj fj+1 fn-1 stage r1 reactive/catalytic distillation zone stage r2 fig. 1: schematic representation of a reactive distillation column iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 17 energy balance: ( ) ( ) ( )∑∑∑ = +++ = −−− = −+−+− c i l ij v ijijj c i l ij l ijijj c i l ij f ijijj hhyvhhxlhhzf 1 ,,1,11 1 ,,1,11 1 ,,, ( ) ( )∑∑ == −=∆− c i l ij v ijijj r r rj r rjjj hhxvrhw 1 ,,, 1 ,,δ (j/s), (3) where hl is the partial molar enthalpy of liquid (j/mol), hv is the partial molar enthalpy of vapour (j/mol), ∆hr is the heat of reaction (j/mol), and w is the weight of catalyst (kg). phase equilibrium: x p p y φ γ 0 = (4) the vapour phase is assumed to be ideal so that the entire fugacity coefficients φ for the system are equated to unity. the activity coefficients γ that characterise liquid phase nonideality are calculated from the uniquac method. the saturated vapour pressure po is calculated from the antoine equation and p is the total pressure. summation (constraint) equations: 0.1 1 , =∑ = c i ijx (liquid phase) (5) 0.1 1 , =∑ = c i ijy (vapour phase) (6) kinetic model: the principal reaction between methanol(meoh) and isobutene (ib) for mtbe synthesis is represented as: ch3oh + (ch3)2c=ch2 ⇔ (ch3)3coch3 (7) meoh ib mtbe the activity based rate model is:[9] iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 18         −= 2 meoh mtbe meoh ib ak a a a wqkrate eq f (mol/s) (8) where w is the weight of catalyst (kg) and q is the amount of acid groups on the resin per unit mass (4.9 equiv/kg). the forward rate constant, kf is given by [9, 11]       −×= t k f 11110 exp1067.3 12 mol/(s equiv) (9) the rate constant units are based on equiv of hydrogen ions present in the catalyst rather than weight of the catalyst. since hydrogen ions present in the catalyst are responsible for the catalytic reaction. the equilibrium constant keq is given by [9, 11] keq = 284 exp[f(t)] (10) and ( ) ( )+−+−+      +      −= 20 2 403 0 2 0 1 ln 11 )( ttatta t t a tt atf ( ) ( )40463035 ttatta −+− (11) where t0 = 298.15 k, a1 = -1.49277×103 k, a2 = -77.4002, a3 = 0.507563 k-1, a4 = 9.12739×10-4 k-2, a5 = 1.10649×10-6 k-3, a6 = -6.27996×10-10 k-4 [9, 11]. figure 2 shows the sequence of calculations and algorithm for solving reactive distillation simulation model. the following are the explanation of the steps involved [5, 10]: 1. specify all the specifications for a reactive distillation column to operate, and read all the constants and parameters related to the model equations 2. initialise liquid compositions xj,i for the column, or use the last converged simulation. 3. calculate vapour compositions yj,i and temperature tj on stage j through bubble point flash calculation. calculate liquid enthalpy and vapour enthalpy on stage j.calculate the liquid and vapour rates throughout the column. calculate all the mass balance derivatives, then calculate the residual from the average of the absolute value of all derivatives. check if the residual is less than the specified error tolerance (e.g. 1.0×10 -4 ). if yes, converged steady state solution is obtained, then go to next step. if no, predict next xj,i by calling the integration routine, then go to step 3. output the composition and temperature profiles of the column. iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 19 specify all column specifications and read all the required constants and parameters calculate all mass balance derivatives, and then calculate the residual initialise liquid composition throughout column output the temperature and composition profiles of the column calculate liquid and vapour flow rates throughout column calculate liquid and vapour enthalpy throughout column calculate vapour composition and temperature throughout column by bubble point calculation check the specified tolerance for residual, and are new temperature and composition profiles near the previous values? yes no call integration routine fig. 2: algorithms for solving reactive distillation simulation model. iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 20 3. simulation and results 3.1 simulation basis as a basis for simulations, it will be assumed that 197 mol/s (500 000 metric tons/year) mtbe is produced. total mass of catalyst is 6400 kg for 8 reactive stages (800 kg catalyst per reactive tray), which is located in the middle of the column from stage 3 to stage 10. the total numbers of stages are 17 (numbered top-down) with total condenser as stage 0 and partial reboiler as stage 16. the column pressure is 11 bar (10.87 atm.) and the reflux ratio is set to 7. the column has two feed streams: a methanol feed and a mixed butenes (isobutene and 1-butene) feed; a small stoichiometric excess of methanol is used. table 1 and figure 3 summarise simulation basis for heterogeneously catalysed mtbe synthesis [11]. catalytic reaction zone methanol feed: liquid at 320 k, 11 bar stage 10 flow rate: 206 mol/s butenes feed: vapor at 350 k, 11 bars stage 10 flow rate: 549 mol/s mole fraction isobutene = 0.356 1-butene = 0.644 total condenser partial reboiler bottom product distillate stage 0 stage 16 fig. 3: column configuration and feed specifications for mtbe synthesis 3.2 simulation assumptions the mtbe system will be assumed to consist of 4 components: (1) methanol, (2) isobutene, (3) mtbe and (4) 1-butene. the industrial mtbe process involves a minimum of 12 components with reactive components of methanol, isobutene and mtbe. the inert (c4 components) in mtbe system are quite similar to each other in physical and chemical properties, and thus assumed to be represented by 1-butene. the by products are very small in quantity and can be regarded as negligible [1]. iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 21 table 1 feed specifications, column configuration and operating conditions for mtbe synthesis quantity units methanol butenes feed mol/s 206 549 phase liquid vapour temperature k 320 350 pressure bar 11 11 feed stage 10 10 xmeoh 1.0 0.000 xib 0.0 0.356 xmtbe 0.0 0.000 x1-butene 0.0 0.644 number of stages, n 17 column pressure, p bar 11 catalyst weight, w kg 6400 (total) reflux ratio, r 7 bottom flow, b mol/s 197 3.3 simulation results and comparison table 2 shows the results comparison between the proposed model and with published simulation results [11]. as it can be seen from table 2, it is clear that the simulation results produced are quite close to the published simulation results [11]. this similarity verifies that the proposed model is capable of successfully simulating heterogeneously catalysed mtbe synthesis. it has been reported that a process utilising reactive distillation technology can boost the isobutene conversion up to 99% and higher [12], and possibly up to 99.99% isobutene conversion [13]. with agreement to the reported isobutene conversion, simulation results show an isobutene conversion of 99.5%, which is as desirable in real pilot plant reactive distillation column. figure 4 and 5 show the temperature and liquid composition profiles obtained from simulation. similar trend of temperature and composition profiles was reported[11] which is based on the uniquac model and redlich-kwong equations for the non-ideality in liquid and vapour phases respectively. in the present research, the simulation results presented are based on the same non-ideal liquid phase using uniquac model but with iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 22 the assumption of ideal vapour phase. the similarity in the simulation results indicate that the non-ideality in liquid phase is dominant, whereas the non-ideality of vapour phase does not significantly contribute to the differences in simulation results [10]. table 2: comparison of simulation results for operating conditions, feed and product flow compositions figure 6 shows the liquid phase activity coefficient profiles corresponding to the temperature and liquid composition profiles. it can be seen that quite large activity coefficients of methanol were obtained throughout the column. these large activity coefficients (as high as value of 11.6) express the highly non-ideal liquid behaviour of methanol in mtbe system. other components, however, behave almost ideally as individual activity coefficient shows values of nearly unity throughout the column. the highly non-ideal behaviour of methanol in liquid phase for mtbe system has been reported by the experimental work [9]. the calculation based on uniquac model has been reported to fit well the experimental data, by which the reaction kinetics has been formulated in activity basis [9]. nijhuis et al. (1993) proposed model quantity units top bottom top bottom xmeoh 0.04 0.00 0.032 0.000 xib 0.01 0.00 0.003 0.000 xmtbe 0.00 0.98 0.000 0.986 x1-butene 0.95 0.02 0.965 0.014 temperature, t k 348 424 348.8 423.8 product flow mol/s 366 197 363.7 197.0 heat duty, q mw 49.7 35.1 49.7 39.3 ib conversion mole % 98.5 99.5 mtbe purity mole % 98 98.6 reflux flow, l0 kmol/s 2.6 2.55 iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 23 temperature profile 340 350 360 370 380 390 400 410 420 430 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 stage number t em pe ra tu re (k ) fig. 4: temperature profile throughout column for mtbe synthesis composition profile 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 stage number l iq ui d m ol e fr ac tio n meoh ib fig. 5: composition profile throughout column for mtbe synthesis iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 24 activity coefficient profile 0 1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 stage number a ct iv ity c oe ff ic ie nt γ meoh ib mtbe 1-butene figure 6: activity coefficient profile throughout column for mtbe synthesis figure 7 shows the reaction rate profiles calculated from activity basis rate. in continuous reactive distillation operation, there are many factors influencing the reaction conversion. the main parameters influencing reaction rate namely the temperature, liquid composition and the activity coefficients are also subjected to changes due to distillation effect in the column. for a non-ideal system, the reaction rate kinetic is always expressed in activity basis for best fitting of the experimental data. therefore, it is very important to use reliable activity coefficient model since it is highly desirable to have correct activity coefficient values for the use in vapour-liquid equilibrium relationship as well as in activity based reaction rate kinetics. reaction rate profile 0 10 20 30 40 50 60 70 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 stage number r at e (m ol s -1 ) figure 7: reaction rate profile throughout column for mtbe synthesis iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 25 a proposed model for reactive distillation system cannot be considered a practical model until it is verified by the experimental or industrial operation data. the comparison with other researchers’ simulation works is only a base platform for model verification. in literature, there are very limited industrial data for reactive distillation system especially for mtbe system. recent research and simulation work [14] did include some of pilot plant data for mtbe system. all the data given are in weight (mass) basis, thus conversion to molar basis has to be made using relative molecular weight mr. table 3 shows the flows and liquid compositions of distillate and bottom product given in weight basis and corresponding calculated molar basis. table 4 shows the comparison of mtbe plant data [14] and simulation results from proposed model. from table 4, the overall comparison of reported mtbe plant data and simulation data show a reasonable agreement, but the simulation values for the c4 mole fraction in the product stream are not as close as to the reported plant data. this is because the typical industrial process for the mtbe production involves at least 12 components.[14] besides the reactive components, which are methanol, isobutene (isobutylene) and mtbe, the inert in c4 mixture and the by-products involve a minimum of 5 other components namely trans-2-butene, cis-2-butene, diisobutene, isobutane, 1-butane, tert butyl alcohol (tba) and propylene. table 3: flowrate and liquid composition of distillate and bottom product in mtbe plant [14] given data calculated component xi (wt. %) flowrate (kg/h) rel. mol. wt., mr flow rate (mol/s) xi (mole frac.) meoh 4.61 253.27 32.04 2.1957 0.0780 ib 0.24 13.19 56.11 0.0653 0.0023 mtbe 0 0 88.15 0.0000 0.0000 c4 95.15 5227.54 56.11 25.8794 0.9197 distillate 5494 28.1404 meoh 0.02 1.0857 32.04 0.0094 0.0005 ib 0 0 56.11 0.0000 0.0000 mtbe 98.64 5354.60 88.15 16.8734 0.9786 c4 1.34 72.74 56.11 0.3601 0.0209 bottom pdt. 5428.43 17.2429 iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 26 table 4: mtbe plant data [14] and simulation results comparison for mtbe synthesis distillate bottom product composition plant model plant model meoh 0.0780 0.1128 0.0005 0.0112 ib 0.0023 0.0000 0.0000 0.0000 mtbe 0.0000 0.0309 0.9786 0.9888 c4 0.9197 0.8563 0.0209 0.0000 operating parameters plant model % error distillate (mol/s) 28.14 26.06 7.39 bottom flow (mol/s) 17.24 17.24 (specified) top temp. (k) 336 343 2.08 bottom temp. (k) 417 417 0.00 reflux flow, l0 (mol/s) 14.13 13.03 7.78 ib conversion (%) 99.62 99.99 0.37 small amounts of water is also present in the hydrocarbon (c4 mixture) and in methanol feedstock but the reported data from product stream in the pilot plant [14] did not show any trace of water. this is because water is consumed in pre-reactor before it is fed into the reactive distillation column. although the inert in c4 mixture have very similar physical and chemical properties, the by-products formed have somewhat different properties. the main side reactions involved are the dimerisation of isobutene to diisobutene (2,4,4-trimethyl-1-pentene) and the hydration of isobutene to tert-butyl-alcohol (tba). the existence of the by-products is the main reason why the simulation results show some differences in the amount of c4 mixture. however, one advantage of mtbe reaction is that the by-products formed are very small in quantity [11] so that many researchers have assumed negligible sidereactions in mtbe synthesis. the hydration of isobutene to tba can be neglected since kinetic study shows that the reaction can only take place when excess of methanol is insufficient [14]. another reason that may contribute to the differences in simulation results is that the mtbe plant [14] uses structured catalyst packing, which has specific reaction efficiency and hydrodynamic conditions. modeling the catalyst reaction efficiency and hydrodynamic conditions of specific structure packing is a challenging task due to insufficient information and research on the structured packing itself [2, 14]. therefore the catalyst reaction efficiency and the hydrodynamic conditions are usually ignored especially in equilibrium stage modeling of reactive distillation column. iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 27 in the present simulation of mtbe synthesis, 1-butene (an inert component) has been assumed to be the representative of the entire inert components in c4 mixture including that of small quantity of by-products. this assumption is justified by the fact that the c4 mixture in the distillate stream in mtbe plant [14] contains the largest fraction of 1butene. all the inert in c4 mixture are light components, thus only small amount of inert will be recovered at the bottom of the column. 4. conclusion a steady state process simulation reactive distillation model was developed from unsteady state material balance equations based on equilibrium stage model. the model was verified and utilised for the simulation of heterogeneously catalysed mtbe synthesis. the proposed mathematical model describing reactive distillation process consists of mixed sets of ordinary differential equations (ode) and algebraic equations. the model equations were solved numerically using backward differentiation formula linear multistep method for stiff system of equations [8] based on relaxation method. the main advantage of the proposed solution strategies is that it is robust for arbitrary initialisation. convergence towards steady state is almost always guaranteed though it was considered slow when approaching the solution. the results obtained from the simulation of the proposed model have been shown to be capable of giving results as good as aspen plus simulation results [11] and mtbe plant data [14]. the simulation of mtbe synthesis shows the capability of the proposed model to give good prediction and thus capable of giving the insights of the performance of actual reactive distillation column. the temperature profiles, liquid composition profile and operating conditions of reactive distillation column showed promising results when compared to the published simulation results and the real mtbe plant data. therefore the proposed model can be used as a tool for the development and simulation of reactive distillation column. in addition, the optimisation of reactive distillation can also be carried out much easier and safer, with time efficient and reduced costs. acknowledgement the financial support by the ministry of science, technology & environment, malaysian govt. under long term irpa grant (project no. 03-02-05-0007) is gratefully acknowledged. references [1] t. pöpken, s. steinigeweng and j. gmehling, “synthesis and hydrolysis of methyl acetate by reactive distillation using structured catalytic packings: experimental and simulation,” ind. and eng. chemistry res., 40, 1566-1574, 2001. [2] r. taylor and r. krishna, “review: modelling reactive distillation,” chem. eng. science, 55, 5183-5229, 2000. iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 28 [3] a. tuchlenski, a. beckmann, d. reusch, r. düssel, u. wiedlich and r. janowsky, “reactive distillation – industrial applications, process design & scale-up,” chem. eng. science, 56, 387-394, 2001. [4] m.g. sneesby, m.o. tade, and t.n. smith, “steady-states transitions in the reactive distillation of mtbe,” computers and chem. eng., 22(7-8), 879-892, 1998. [5] f. chen, r.s. huss, m.f. malone and m.f. doherty, “simulation of kinetics effect in reactive distillation,” computers and chem. eng., 24, 2457-2472, 2000 [6] p.a. pilavachi, m. schenk, e. perez-cisneros and r. gani, “modeling and simulation of reactive distillation operations,” ind. and eng. chemistry res., 36, 3188-3197, 1997. [7] j. wang, x. ge, z. wang and y. jin, “development of a novel catalytic distillation column,” chem. eng. and processing, 41, 115-121, 2002. [8] c.w. gear, “numerical initial value problems in ordinary differential equations,” prentice hall inc., 1971. [9] a. rehfinger and u. hoffmann, “kinetics of methyl tertiary butyl ether liquid phase synthesis catalyzed by ion exchange resin-i. intrinsic rate expression in liquid phase activities,” chem. eng. science, 45(6), 1605-1617, 1990. [10] m.n. murat, “modeling and simulation of reactive distillation column for the production of methyl tertiary butyl ether (mtbe),” m.sc. thesis, universiti sains malaysia, 2002. [11] s.a. nijhuis, f.p.j.m. kerkhof and a.n.s. mak, “multiple steady states during reactive distillation of methyl tert-butyl ether,” ind. and eng. chemistry res., 32, 2767-2774, 1993. [12] j.l. degarmo, v.n. parulekar and v. pinjala, “consider reactive distillation,” chem. eng. progress, 88(3), 43-50, 1992. [13] g.g. podrebarac, f.t.t. ng and g.l. rempel, “more uses for catalytic distillation,” chemtech, 27(5), 37-45, 1997. [14] j. bao, b. gao, x. wu, m. yoshimoto, and k. nakao, “simulation of industrial catalyticdistillation process for production of methyl tert-butyl ether by developing user’s model on aspen plus platform,” chem. eng. j., 90(3), 253-266, 2002. notation a activity c total number of components fj feed flowrate of stage j mol/s hl partial molar enthalpy of liquid j/mol hv partial molar enthalpy of vapour j/mol ∆hr heat of reaction j/mol keq thermodynamic reaction equilibrium constant kf forward rate constant mol/(s equiv) lj liquid flowrate from stage j mol/s iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 29 mr relative molecular weight g/mol n total number of stages p pressure pa po saturated vapour pressure pa q ion exchange capacity equiv/kg rj total rate of generation of moles on stage j mol rj rate of reaction on stage j mol/s t temperature k t time s v stoichiometric coefficient vj vapour flow rate from stage j mol/s w weight of catalyst kg x liquid composition y vapour composition z feed composition 2.1.1. greek letters δj parameter for reaction occurrence on stage j (0 or 1) φ fugacity coefficient γ activity coefficient 2.1.2. subscript i component number j stage number r reaction number 2.1.3. superscript f feed l liquid r reaction(s) v vapour iium engineering journal, vol. 4, no. 2, 2003 m.n. murat et al. 30 biographies muhamad nazri murat received his b.sc. (hons) degree in chemical engineering from the university of manchester institute of science & technology (umist) in 1999. he obtained his m.sc. degree in 2002 from the school of chemical engineering, universiti sains malaysia. his research interests are in modeling and simulation, design and control aspect of reaction distillation column. dr. abdul rahman mohamed obtained his ph.d in chemical engineering from the university of new hampshire. his research interest is mainly in the environmental issues with emphasis in air pollution control. he is currently the dean and associate professor of the school of chemical engineering, unversiti sains malaysia. dr. abdul rahman has conducted and completed numerous funded research projects and has published more than 80 papers at various international and national conferences and journals. prof. subhash bhatia joined the school of chemical engineering, universiti sains malaysia in 1995. he was a full professor at the department of chemical engineering, indian institute of technology, kanpur (india). professor bhatia was a visiting faculty at the university of queensland, australia from 1988 – 1989 and 1994 – 1995. his research interests are zeolite catalysis, chemical reaction engineering and environmental catalysis. he has written a book on zeolite catalysis that was published by crc press, usa and has published more than 100 papers at national and international journals. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 biodegradation of mango seed starch films in soil nur’aishah ahmad shahrim*, norshahida sarifuddin, ahmad zahirani ahmad azhar and hafizah hanim mohd zaki department of manufacturing and materials engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia *corresponding author: nuraishahahmadshahrim@gmail.com (received: 21st september 2020; accepted: 13th october 2021; published on-line: 4th january 2022) abstract: the typical petroleum-based plastics have triggered environmental problems. for this purpose, biodegradable polymers such as starch are often used to manufacture biodegradable plastics. at present, the efforts are underway to extract starch as a promising biopolymer from mango seeds and subsequently to produce a biodegradable starch film to be used as plastic packaging. as such, in this work, glycerolplasticized mango starch films were prepared using a solution casting process, using different amounts of citric acid as a cross-linking agent. the blend ratio of starch to glycerol was set at 3:5 wt. each, while the amount of citric acid ranged from 0 to 10 wt.%. then, the casted films underwent 21 days of soil burial testing in the natural environment to determine their biodegradability behavior. the soil burial test is one of the common methods chosen to assess the biodegradability of polymers. the idea is that, by burying samples in the soil for a fixed time, samples are exposed to microorganisms (i.e. bacteria and fungi) present in the soil that serve as their food source. this is somehow likely to facilitate the process of deterioration. for this reason, the soil burial test can be regarded as an authentic approach to the process of deterioration in the natural environment. the films' susceptibility to biodegradation reactions was assessed within intervals of seven days through their physical appearance and weight loss. interestingly, it was found that the cross-linked starch films have been observed to degrade slower than the non-cross-linked starch films as burial time progressed. the declining percentages of weight loss, as well as the presence of microorganisms and eroded surface on the films observed by sem, explained the degradation behavior of the cross-linked starch films compared to the noncross-linked starch films. hence it is believed that cross-linked starch-glycerol films are biodegradable in soil, henceforth, the potential to be commercialized as a biodegradable packaging material soon. at the same time, this plastic packaging is expected to be recognized as a value-added product since the raw materials ergo mango seeds utilized to develop this product are from waste, therefore, environmentally friendly. abstrak: plastik yang berasaskan petroleum telah mencetuskan masalah persekitaran. untuk tujuan ini, polimer biodegradasi seperti kanji sering digunakan untuk membuat plastik yang boleh terurai. pada masa ini, usaha sedang dilakukan untuk mengekstrak pati sebagai biopolimer yang menjanjikan dari biji mangga dan kemudiannya menghasilkan filem pati yang terbiodegradasi untuk digunakan sebagai kemasan plastik. oleh yang demikian, dalam karya ini, filem pati mangga plastik-gliserol disusun menggunakan proses pemutus larutan, menggunakan jumlah asid sitrik yang berlainan sebagai agen penghubung silang. nisbah campuran pati dan gliserol ditetapkan pada 3:5 wt.% masingmasing, sementara jumlah asid sitrik berkisar antara 0 hingga 10 wt.% berat. kemudian, sampel plastik tersebut ditanam di dalam tanah selama 21 hari di persekitaran semula jadi untuk menentukan tingkah laku biodegradasinya. ujian penguburan tanah adalah salah 258 iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 satu kaedah biasa yang dipilih untuk menilai biodegradasi polimer. ideanya adalah bahawa, dengan menguburkan sampel di tanah untuk waktu yang tetap, sampel terdedah kepada mikroorganisma (iaitu bakteria dan jamur) yang terdapat di dalam tanah yang berfungsi sebagai sumber makanan mereka. ini mungkin memudahkan proses kemerosotan. atas sebab ini, ujian penguburan tanah dapat dianggap sebagai pendekatan yang sahih terhadap proses kemerosotan di persekitaran semula jadi. kerentanan filem terhadap reaksi biodegradasi dinilai dalam selang waktu tujuh hari melalui penampilan fizikal dan penurunan berat badan. menariknya, didapati bahawa filem-filem pati berangkai silang telah dilihat menurun lebih perlahan daripada filem-filem pati yang tidak bersilang ketika masa pengebumian berlangsung. peratusan penurunan berat badan yang menurun, serta kehadiran mikroorganisma dan permukaan yang terhakis pada filem yang diperhatikan oleh sem, menjelaskan tingkah laku degradasi filem pati berangkai silang berbanding dengan filem pati yang tidak bersilang. oleh itu, dipercayai bahawa filem kanji-gliserol berangkai silang dapat terbiodegradasi di dalam tanah, dan seterusnya, potensi untuk dikomersialkan sebagai bahan pembungkusan yang boleh terurai tidak lama lagi. pada masa yang sama, pembungkusan plastik ini diharapkan dapat diakui sebagai produk bernilai tambah kerana bahan mentah ergo mangga yang digunakan untuk mengembangkan produk ini adalah dari sisa, oleh itu, mesra alam. keywords: mango seed; starch; biodegradable polymer; soil burial 1. introduction over the past several years, due to the rise in environmental concerns, research has been focused on biodegradable materials in reducing the reliance on petroleum-based materials. for this purpose, a biopolymer has been widely developed as an alternative to conventional materials due to their attractive benefits such as biodegradability and sustainability towards the environment [1]. at present, the development of biodegradable materials based on polymers has been attempted in several approaches [2]. one of the approaches is to produce polymeric materials based on inherently biodegradable materials. this has been attracting rising interest in the utilization of starch as a biopolymer. consequently, the biodegradable constituent is predicted to be degraded rapidly by environmental factors such as biological activity, chemical conditions, moisture, heat, and light, initiating an overall deterioration of the polymeric matrix, which in turn boosts the disintegration of the whole material [2,3]. in this analysis, mango seeds were used to get native starch. mango (mangifera indica) belongs to the genus mangifera in the anacardiaceae family of flowering plants, is a common tropical fruit, and is widely grown practically. throughout the world's tropical and subtropical regions like malaysia, thailand, and india [4]. these types of fruits are usually consumed as fresh or processed into juices, and their seeds are discarded as waste. interestingly, these seeds are rich in starch and protein [5]. therefore, the seeds fit as a viable source of starch. because starch does not possess thermoplastic properties, polyols, such as glycerol, are often used as plasticizers to improve the workability and flexibility, as well as to overcome the brittleness of the native starch [6]. however, the usage of starch in developing biodegradable plastics may have several drawbacks. its hydrophilic characteristic may cause the synthesized materials to have a high-water sensitivity, poor moisture barrier properties, and high retrogradation over some time. hence, poly-carboxylic acids, such as citric acid, are introduced as cross-linking agents during the blending of thermoplastic starch to overcome the retrogradation phenomenon and improve its performance in numerous applications. citric acid is known as a natural organic acid, is nutritionally harmless compared with other substances, and consists of multi-carboxylic structures [7]. 259 iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 soil burial biodegradability behavior of starch incorporated with biopolymers such as starch grafted low-density polyethylene (ldpe) [8], corn starch with chitosan [9], and corn starch with polyvinyl alcohol (pvoh) [10] have been demonstrated. a similar approach by crosslinking cassava starch with citric acid has been reported its biodegradability properties through soil burial [7]. from these literatures, it can be concluded that starch-based films prepared from different sources of starch exhibited biodegradable behavior. however, study related to the biodegradability behavior of mango seed starch-based films is rarely reported. hence, in this research, the utilization of starch from mango seeds specifically obtained at the local market in malaysia have been processed to prepare the films. the extraction processes of the mango seeds included the separation between the kernel (outer) and cotyledon (inner), in which only the inner seeds were further processed and blended with glycerol and citric acid to fabricate films. this is to differentiate the findings obtained in this work with the mango kernel starch plasticized with glycerol and sorbitol that has been reported previously [11], which does not consider the biodegradation testing. the primary objective of this research was to develop a biodegradable starch-based film for packaging materials applications via solution casting method. prior to the main objective, a biodegradability analysis was conducted using a soil burial test to investigate the effect of cross-linking on the degradation rate of the glycerol-plasticized thermoplastic mango seed starch (gtps) films. it is expected that the non-cross-linked and cross-linked gtps films will experience weight loss during the soil burial test, proving that these films are biodegradable and sustain the environment after usage as packaging. 2. materials and methods 2.1 raw materials mango seeds had been collected from the local market as a source of starch. 85% pure glycerol was procured from merck sdn. bhd. (selangor, malaysia) and reagent-grade citric acid (≥99% purity) was procured from sigma-aldrich sdn. bhd. (selangor, malaysia). 2.2 extraction of mango seed starch via distillation method the starch from mango seed was extracted with minor modifications according to the procedure defined by noor et al. [5]. initially, 5 g of mango seed flour was introduced to 100 ml of distilled water at room temperature, with continuous stirring for 6 h. then, the slurry was filtered with a cloth bag (about 200 µm mesh), and the excess residues were rinsed three times with distilled water. the filtrate was immersed and precipitated at 4 °c overnight. finally, the starch obtained was filtered and dried in the oven for 24 h at 40 °c. the starch was crushed with a mortar and pestle, wrapped in a sealed plastic bag, and held at room temperature for further use. 2.3 preparation of starch-glycerol film cross-linked with citric acid starch-glycerol films that were cross-linked with citric acid were processed with some modifications using the solution casting method recommended by seligra et al. [7] and reddy & yang [8]. the starch-to-glycerol ratio was set at 3:5 (wt.%), while the citric acid content ranged from 0 wt.% to 10 wt.%. the total input mass was kept at 100 g. abbreviations of the material and corresponding sample compositions are presented in table 1. the blends were heated to 90 °c on a hot plate and kept with continuous stirring at 250 rpm during this temperature for 20 min. the formulations then were cooled to 65 °c and poured on an acrylic sheet. the cast films were allowed to dry in an oven at 40 °c and then peeled off plates after around 24 hours. the peeled films were preserved at 23 °c and 30% relative humidity in a desiccator before characterization. 260 iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 table 1: abbreviations and corresponding compositions of each sample material abbreviation weight proportion (g) starch glycerol citric acid distilled water gtps-ca0 g5 3.0 0.5 0 96.5 gtps-ca1 ca2 3.0 0.5 0.2 96.3 gtps-ca2 ca4 3.0 0.5 0.4 96.1 gtps-ca3 ca6 3.0 0.5 0.6 95.9 gtps-ca4 ca8 3.0 0.5 0.8 95.7 gtps-ca5 ca10 3.0 0.5 1.0 95.5 2.4 fourier-transformed infrared (ft-ir) spectroscopy ft-ir spectroscopy was used to examine the functional properties of non-cross-linked and cross-linked gtps films (spectrum 100, perkin elmer; usa). ft-ir spectra were recorded using an attenuated total reflection (atr) method to study the functional groups in starch. the analysis was performed in the 4000 cm−1 – 600 cm−1 range, with a resolution of 8 cm−1 and a scanning frequency of 32 per sample. 2.5 soil burial degradation degradation behavior of starch-based film incorporated with 5 wt.% glycerol crosslinked with 0, 2, 4, 6, 8, and 10 wt.% citric acids was carried out by soil burial test using procedures mentioned by azahari et al. [9] with slight modification. the soil will cover a grid from all the sides of the grid by cutting three samples of each film measuring between 20 mm and 20 mm. samples of every composition were then buried in separate pots of composted soil at a depth of 50 mm. the soil was then exposed to the natural weather and positioned in the open area. the weight loss of all samples was calculated at regular intervals of time (7 days) for the degradation rate of samples. the samples were carefully separated from the soil and washed away soil from the film with distilled water. the sample was left to dry, and the electronic mass balance was used to measure the weight of the dried sample. during the soil burial test, the weight loss of the sample was assessed according to eq. (1): 𝑊𝑒𝑖𝑔ℎ𝑡 𝑙𝑜𝑠𝑠 (%) = 𝑊𝑖 − 𝑊𝑑 𝑊𝑖 × 100 (1) where wi is the sample’s initial weight (g) and wd is the sample’s weight (g) after seven days. 2.6 scanning electron microscopy (sem) test the morphology of the film surfaces before and after the soil burial test were examined using a scanning electron microscope (jeol, jsm-it 100; japan), operated at an acceleration voltage of 7 kv. the samples were sputter-coated with palladium (sc7620 sputter coater, quorum technologies ltd, lewes, united kingdom). 3. results and discussion 3.1 functional properties figure 1 shows the ft-ir spectra of cross-linked mango seed starch-glycerol films. the observed peaks are the functional groups of starch, glycerol, and citric acid, with minor variations in intensity and band position. the following characteristic bands were visible in all spectra: 3270 – 3315 cm−1 corresponds to the stretching of the o-h group of starch, 261 iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 glycerol, and water, 2924 – 2928 cm−1 corresponds to the stretching of the c-h group due to the formation of intermolecular and intramolecular bonds between starch and glycerol hydroxyl groups, and 1611 – 1633 cm−1 corresponds to water related absorbance. fig. 1: ft-ir spectra of mango seed starch-glycerol cross-linked with citric acid concentrations of (a) 0, (b) 2, (c) 4, (d) 6, (e) 8, and (f) 10 wt.%. the addition of citric acid to the blend causes changes in the peaks. the hydroxyl grouprelated peak at 3270 – 3315 cm−1 was wider and less intense. this meant that there were more o-h in the blend that could easily vibrate, resulting in more o-h forming hydrogen bonds [7]. furthermore, the addition of citric acid to the gtps resulted in peaks shifting from 998.30 cm−1 to 1000.23 cm−1. this demonstrates that the interactions of citric acid's hydroxyl and carboxyl groups with c-o groups of c-o-c in starch are weaker than those of glycerol [6]. it is also observed that both non-cross-linked (fig. 1(a)) and cross-linked films (fig. 1(b) – 1(f)) have similar peaks, except for the additional peak in the cross-linked film at 1712 – 1713 cm−1. the c=o peak was attributed to the carboxyl and ester carbonyl bands, where there was chemical linkage from acid groups esters between citric acid and glycerol, as well as esters between starch and citric acid [7,12]. this suggests that crosslinking occurred in the starch-glycerol films. the addition of citric acid resulted in more intense peaks, implying that citric acid is more capable of disrupting starch chains' intermolecular and intramolecular hydrogen bonds [13,14]. (a) (b) (c) (d) (e) (f) (i) (a) (b) (c) (d) (e) (f) c=o stretching (aldehyde) c=o stretching (carbonyl) 262 iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 3.2 visual observation the pictorial view of the samples retrieved after being subjected to natural soil burial test for 21 days is presented in fig. 2. this denoted that the visual changes of samples can be used as the first indication of any surface degradation. from the figure, it was observed that the non-cross-linked films and cross-linked films at 2 wt.% to 10 wt.% citric acid contents started to experience deterioration in the first seven days. the deterioration of starch-based films in soil was governed by hydrolytic degradation, in which the excess water permeated through the soil and diffused into the samples, causing films to become soft and swelled. this could be described by the appearance of samples that seemed fragile and brittle and diminished in size. specifically, after being buried 21 days in soil, gtps-ca0 showed major deterioration compared to gtps-ca2. increasing citric acid content from 2 wt.% to 10 wt.%, making the cross-linked films more resistant to deterioration. at the same time, it was also noticed that there are white particles spotted on films, which are believed as micro-organisms on the surface of all samples. by some means, the deterioration of samples was boosted by the microbial attack, evidenced by sem images (fig. 3). moreover, the macro-organisms like fungus gnat larvae, the worm-like creatures that squirm their way around in soil and fungi to feed the decaying samples, hence boost up the degradation rate. these results imply that the films were degraded and decomposed in the soil environment, although the degradation rates were significantly varied among the starch-based films. fig. 2: macroscopic appearance of non-cross-linked and cross-linked mango seed starchglycerol films after being buried for 21 days. 3.3 morphological properties sem micrographs are shown in fig. 3(a) – 3(f) visualized the morphological changes of mango seed starch-glycerol-citric acid films after being subjected to a soil burial test for 7 days. the observation was done in short-term degradation due to the unfeasibility in observing the morphology of films after 21 days since there were only tiny pieces of films left when retrieved from the soil, shown previously. 263 iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 the morphology of starch-glycerol films with 0 wt.% citric acids displayed a significantly eroded surface with plentiful filamentous fungus, fungus colonization, and pores (fig. 3(a)). the addition of citric acid from 2 wt.% to 10 wt.% in starch and glycerol blend (fig. 3(b) – 3(f)) revealed the surface of the samples were colonized by microorganisms, however, with the existence of less filamentous fungus, fungus colonization, puffball spores, and pores. thus, it seems that starch-glycerol films with higher citric acid content degrade slowly, consequently had a lower percentage of weight loss (section 3.4). during the exposure of samples in soil within 7 days, the formation of numerous pores and microbial biofilm with many cells growing on the starch-based films appeared. the presence of pores on the deteriorated samples upon the biodegradation process is associated with the starch consumption by the microorganisms, lead to enhancement of microorganisms, water, and oxygen accessibility into the polymer matrix, and caused weight loss of samples. at the same time, the exposed films’ surface facilitates moisture permeation that fosters microbial attack on the starch and hydrolysis of the matrix component [15]. furthermore, the deterioration of starch-based films was also contributed by the fungal strains [16]. it is noted that the fungal species that existed in the film was identified as aspergillus sp. it is noticed in the form of the filamentous and unicellular arrangement was reproduced by spores. these micro-organisms are believed to exploit the starch film as a sole carbon source, causing degradation of films in the soil condition. a similar type of micro-organisms associated with polymer degradation in the soil was reported earlier [16] on cassava starch-based films. besides, the existence of filamentous fungus, spores, and fungus colonization on the film surface concurs with the fact that fungi are pervasive and very effective in influencing the film’s biodegradability behavior, especially in the soil condition. the observation is per the findings reported previously [17]. fig. 3: sem micrographs at 500× magnification of cross-linked mango seed starch films with various citric acid concentrations (a) 0, (b) 2, (c) 4, (d) 6, (e) 8, and (f) 10 wt.%. 3.4 weight loss the percent weight loss of mango seed starch-glycerol films cross-linked with different amounts of citric acid after being buried in soil for 21 days is illustrated in fig. 4. it was noticed that the percent weight loss of all samples progressed continuously over time. the result revealed that the non-cross-linked films (gtps-ca0) achieving the highest weight loss, thus denote the fastest rate of degradation compared to cross-linked films. the addition of citric acid to starch and glycerol blend resulted in a low percentage of weight 264 iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 loss. it was also remarked that the maximum weight losses were 91.76%, 91.41%, 90.32%, 87.93%, 86.44%, and 85.94% for gtps-ca0, gtps-ca2, gtps-ca4, gtps-ca6, gtps-ca8, and gtps-ca10, respectively after 21 days of soil burial. fig. 4: weight loss of non-cross-linked and cross-linked mango seed starch-glycerol films after buried in soil for 21 days. based on fig. 4, it was found that the weight loss observed after 21 days of soil burial was decreased with increasing citric acid content. within the burial time, the starch-glycerol films might absorb adequate water because of their hydrophilic characteristics, which facilitates microbial attack and hydrolysis of the matrix component. as a result, the hydrolytic depolymerization of starch chains to monomeric units occurs, and the probable deterioration of films is caused by microorganisms [18]. eventually, the formation of pores on the film surfaces as being viewed in sem micrographs (fig. 3) indicates the starch consumption by microorganisms. it is also important to note that the starch also might be attacked by micro-organisms as being visually observed (fig. 2), which might feed on the starch as a source of food, henceforth deteriorate the films. increasing citric acid content in starch and glycerol blend leads to a slower degradation rate because lesser microorganisms invade the films and weaker interaction of hydrogen bonds within the starch chains. however, the weight losses may underestimate because the soil and debris have adhered to the film surface. the weight loss of the cross-linked starch-glycerol films at 21 days of soil burial proved that they are biodegradable. this is in agreement with the findings reported [7] in cassava starch-glycerol cross-linked with citric acid, who observed that cross-linked films degrade slower in soil than non-cross-linked films. 4. conclusion from the present study, it is confirmed that the cross-linked mango seed starch-glycerol films are proved by the ft-ir spectra and its biodegradability by soil burial tests. the results obtained from the visual observation after exposure to soil burial test revealed that crosslinked starch films degrade slower which has been justified by the decreasing weight loss percentages as well as the presence of microorganisms and eroded surface on the films detected by sem. it is therefore hoped that the fabrication of mango seed starch-based films as biodegradable plastic packaging would soon minimize the environmental pollution mainly caused by typical petroleum-based plastics, specifically single-use plastics. having said that, the use of mango seeds as raw materials to produce biodegradable plastics will also offer a value-added material and reduce the production cost. overall, the extent of 0 10 20 30 40 50 60 70 80 90 100 0 7 14 21 w e ig h t l o s s ( % ) days g5 ca2 ca4 ca6 ca8 ca10 265 iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 starch-based film degradation following exposure to soil burial has been extensively inferred in this work. acknowledgement the authors wish to thank the international islamic university malaysia for the financial support (research initiative grant rigs16-072-0236 and fundamental research grant scheme frgs17-033-599). references [1] lu dr, xiao cm, xu sj. (2009). starch-based completely biodegradable polymer materials, 3(6):366–375. https://doi.org/10.3144/expresspolymlett.2009.46 [2] sutivisedsak n, cheng hn, dowd mk, selling gw, biswas a. (2012) evaluation of cotton byproducts as fillers for poly (lactic acid) and low-density polyethylene. industrial crops and products, 36(1):127–134. https://doi.org/10.1016/j.indcrop.2011.08.016 [3] orhan y, hrenović j, büyükgüngör h. (2004) biodegradation of plastic compost bags under controlled soil conditions. acta chimica slovenica, 51(3): 579–588. [4] hassan lg, muhammad ab, aliyu ru, idris zm, izuagie t, umar kj, sani na. (2013) extraction and characterisation of starches from four varieties of mangifera indica seeds. iosr journal of applied chemistry, 3(6):16–23. [5] noor f, rahman j, mahomud s, akter ms, talukder ai, ahmed m. (2014) physicochemical properties of flour and extraction of starch from jackfruit seed. international journal of nutrition and food sciences, 3(4): 347–354. https://doi.org/10.11648/j.ijnfs.20140304.27 [6] jiugao y, ning w, xiaofei m. (2005) the effects of citric acid on the properties of thermoplastic starch plasticized by glycerol. starch/ staerke, 57(10):494–504. https://doi.org/10.1002/star.200500423 [7] seligra pg, jaramillo cm, fama l, goyanes s. (2016) biodegradable and non-retrogradable eco-films based on starch-glycerol with citric acid as cross-linking agent. carbohydrate polymers, 138:66–74. https://doi.org/10.1016/j.carbpol.2015.11.041 [8] gautam n, kaur i. (2013) soil burial biodegradation studies of starch grafted polyethylene and identification of rhizobium meliloti therefrom. journal of environmental chemistry and ecotoxicology, 5(6):147–158. https://doi.org/10.5897/jece09.022 [9] coniwanti p, laila l, alfira mr (2014). pembuatan film plastik biodegredabel dari pati jagung dengan penambahan kitosan dan pemplastis gliserol. jurnal teknik kimia, 20(4):22– 30. [10] azahari na, othman n, ismail h. (2011) biodegradation studies of polyvinyl alcohol / corn starch blend films in solid and solution media, 22(2):15–31. [11] nawab a, alam f, haq ma, hasnain a. (2016) biodegradable film from mango kernel starch: effect of plasticizers on physical, barrier, and mechanical properties. starch stärke, 68 (9 10):919–928. https://doi.org/10.1002/star.201500349 [12] reddy n, yang y. (2010) citric acid cross-linking of starch films. food chemistry, 118(3):702–711. https://doi.org/10.1016/j.foodchem.2009.05.050 [13] shi r, zhang z, liu q, han y, zhang l, chen d, tian w. (2007) characterization of citric acid/glycerol co-plasticized thermoplastic starch prepared by melt blending. carbohydrate polymers, 69(4):748–755. https://doi.org/10.1016/j.carbpol.2007.02.010 [14] zuraida a, anuar h, yusof y. (2011) the study of biodegradable thermoplastics sago starch. key engineering materials, 471-472:397–402. https://doi.org/10.4028/www.scientific.net/kem.471-472.397 [15] sarifuddin n, ismail h, ahmad z. (2014) incorporation of kenaf core fibers into low-density polyethylene/thermoplastic sago starch blends exposed to natural weathering. molecular crystals and liquid crystals, 603(1):180–193. https://doi.org/10.1080/15421406.2014.976516 266 iium engineering journal, vol. 23, no. 1, 2022 ahmad shahrim et al. https://doi.org/10.31436/iiumej.v23i1.1620 [16] maran jp, sivakumar v, thirugnanasambandham k, sridhar r. (2014) degradation behavior of biocomposites based on cassava starch buried under indoor soil conditions. carbohydrate polymers, 101(1):20–28. https://doi.org/10.1016/j.carbpol.2013.08.080 [17] nuradibah ma, sam st, noriman nz, ragunathan s, ismail h. (2015) degradation assessment of natural weathering on low-density polyethylene/thermoplastic soya spent powder blends. aip conference proceedings, 1669:020040. https://doi.org/10.1063/1.4919178 [18] obasi hc, igwe io, madufor ic. (2013) effect of soil burial on tensile properties of polypropylene / plasticized cassava starch blends. advances in materials science and engineering, 2013:2–5. 267 microsoft word vol 4-1 pages 37-53.doc iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 37 comprehensive downtime prediction in nextgeneration internet w. f. al-khateeb, s. al-irhayim, k. a. al-khateeb department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, 53100 kuala lumpur, malaysia. e-mail: wajdi@iiu.edu.my abstract: the benchmark for the reliability quality of networks depends mainly on the accuracy and comprehensiveness of the reliability parameters. downtime prediction of a communication system is crucial for the quality of service (qos) offered to the end-user. markov model enables analytical calculation of average single figure cumulative downtime over one year. the single average approach, generally, does not adequately describe the wide range of service performance that is likely to be experienced in communications systems due to the random nature of the failure. therefore, it would be more appropriate to add downtime distribution obtained from network availability models to predict the expected cumulative downtime and other performance parameters among a large number of system populations. the distribution approach provides more comprehensive information about the behavior of the individual systems. laplacestieltjes transform enables analytical solutions for simple network architectures, i.e. the simplex system and the parallel system. this paper uses simulations to determine reliability parameters for complex architecture such as the multiprotocol label switching (mpls) backbone planned for next-generation internet. in addition to the single figure downtime, simulations provide other reliability parameters such as probability of zero downtime. the paper also considers the downtime distribution among a population of equally designed systems. key words: reliability, availability, downtime, multiprotocol label switching 1. introduction the internet is challenged to narrow down the significant quality and reliability gaps that still exist between the circuit-switched, voice-based telecom networks and the packetswitched, ip-based internet. qos, a mechanism that provides distinction of traffic type, which can be classified and administered differently through the network focuses on parameters that depend on application framework. typical parameters are: timeliness, accuracy and reliability. qos has become a key research area in the internet engineering task force (ietf). several rfcs [1], [2] and internet drafts [3], [4] are published proposing differing technologies on how to define and deal with reservation and differentiated services, in short “guaranties” needed by mission critical and real time services. but at the same time, iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 38 qos technology over the internet has not been comprehensively defined. numerous tools still require definition. no doubt these gaps will be filled one day, or at least, redefined given sufficient marketing and economic impetus beside a widespread acceptance among the users community. the focus of this paper, however, is on the platform needed by all those technologies in order to become acceptable by critical users of the telecommunications community, i.e. the availability of the backbone for the internet that is able to function in a similar way as the conventional telecom infrastructure known with its high reliability since the 60s of the 20th century. 1.1 internet reliability benchmarking in order to appreciate the role of high availability in next generation internet it is helpful to highlight the difference in the terminology before proceeding with any analysis. while “reliability” r(t) is the probability that a system will not fail during the time t, the availability a(t) of a system is the probability that the system is operating successfully at time t, or the ratio of time that the system is available to total time. it is common to express availability either in percentage, i.e. number of 9’s, or in downtime/year. although 99% availability may sound good, it is far from being that, because it still results in over three and half days of down time per year and therefore it is far from acceptable by the telecom industry which is used to availabilities in the range of 99.99% to 99.999% [5], or four to five nines. table 1 shows figures suggested by intel [6] to reflect possible availability benchmarking. table 1: typical suggested availability benchmarking 9’s availability downtime/yr examples 1 90.0% 36 day 12 hr personal clients 2 99.0% 87 hr 36 min entry-level businesses 3 99.9% 8 hr 46 min isps, mainstream business 4 99.99% 52 min 33 s data centers 5 99.999% 5 min 15 s carrier-grade telco, banking 6 99.9999% 31.5 seconds military defense system two notable reliability objectives are:  bell, 1964, telephone objective [5] of ‘no more than 2 hr downtime in 40 yr’ which converts into ‘no more than 3 min/yr’ while applying to voice communication. in terms of number of 9s it is between five and six 9s.  bellcore,1993, objective for end office switching system access to the ss7 common channel signaling (ccs) [7] is ‘two minutes per year’ that is equal to an access unavailability of about 3.8 x 10-6. this objective is also between five and six 9s. iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 39 1.2 mpls recovery schemes recovery in current ip based internet is based on instant re-computation of alternative path following a failure of an active path. time taken for such calculation exceeds the maximum delay allowed in mission critical and real time application. mpls based recovery on the other hand is based on rerouting the traffic to predefined backup paths. protected route backup route ingress egress backone with recovery end-to-end rero uting fast rerou ting dynamic rer outing fig. 1: mpls recovery schemes. a widespread topology used in connection with the mpls backbone consists of a main path, known as the “protected path” and a backup (or more) path(s). each path consists of a number of disjoint label-switch routers (lsr) and two common edge routers. the two edge routers which are shared by the two paths are the starting router, or the “ingress” and the end router, or the “egress”, (fig. 1). backup path around the ingress-egress is kept ready to carry the rerouted traffic following a failure in the main path. this arrangement resembles the 1+1 and 1:1 backup protection/switching in the infrastructures of conventional telecom backbones. this topology is effective in dealing with:  ingress-based protection/switching (pre-negotiated)  fast-rerouting restoration by a specific node detecting a failure in order to allow such topology to deal with dynamic routing, the protected and the backup paths are equipped with equal number of lsrs. the routers in the protected path are connected to their peers in the backup path through cross-links allowing for dynamic rerouting around a failed link. the behavior of the restoration mechanisms, i.e. end-to-end routing, fast rerouting, and dynamic routing are shown in fig. 1. assuming perfectly reliable nodes and links with a finite reliability p, a network model with protection for mpls backbone is shown in fig. 2. the links a through h may assume any failure and repair rates. fig. 2: triple bridge network e g f k h j a c b i d iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 40 the size of such network is determined by the number of the cross-links. due to the bridge structure of such complex network, it may be designated as n-tuple bridge. a network with one, two, three, or n cross-link(s) is called: single-bridge, double-bridge, triple-bridge, or n-tuple bridge. the scaling of the network structure, i.e. the number of the cross-links, is one of the criteria in evaluating the availability. 2. downtime objectives downtime objectives are intended to predict the amount of time that networks, either fully or partially, become unavailable, e.g. do not function to provide the intended service. these objectives are usually stated as a single number equal to the average unavailability among a population of systems designed to provide a given reliability/availability quality. due to the random nature of the failure in communications systems, generally nodes and links, a single average does not adequately describe the wide range of service performance that is likely to be experienced. therefore, it would be more appropriate to add downtime distribution obtained from network availability models to predict the expected cumulative downtime and other performance parameters. the downtime distribution provides a better way to respond to the query whether the range of a certain distribution is acceptable for the type of service being planned and hence allows consideration of tradeoffs between equipment failure rate and average restoration time in connection with the architecture of the system. 2.1 downtime prediction the markov’s model applied to a single component repairable system with two statesspace diagram results in the differential equations )()()( 10 ' 0 tptptp   (1.a) )()()( 10 ' 1 tptptp   (1.b) where p0 is the probability of being in state 0 or being operative, p1 is the probability being in state 1 or failed, λ and µ are the failure and repair rate both having exponential distribution. the solution [12] leads to tetpta )()(0)(                 (2.a) with a(t) is the availability and a is the steady state availability      )(0lim tpa t (2.b) hence for a simplex system without built-in redundancy (e.g., hot-standby) a can be rewritten in terms of mttf (mean time to fail) and mttr (mean time to repair) iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 41 mttrmttf mttf a   where mttf = 1/λ and mttr = 1/μ and the unavailability is     aa 1 (3) with a is being the unavailability, eq. 3 results from the state-space diagram for a single component repairable system. the expected cumulative steady-state system downtime can be expressed as e (cummulative downtime in a steady state period of length t) t      (4) using 525,600 minutes per year as a base, the downtime objective for a simplex unit is 525, 600 minutes per year      the unavailability of a complex system of two identical simplex units connected in parallel and operating in hot-standby mode is given by 2)(    a (5) equation 5 results from the state space diagram for a two components repairable system. for given mttf, the availability is solely influenced by mttr, which is set according to the criticality of the system. typical values of restoration rate that represent a cross section among systems that need to be treated with different degree of urgency are:  ccir uses mttr of 10 hrs which is a relatively a high number based on assumption of no technician on duty  u.s. department of defense may use figures as low as 20 min based on the assumption of the availability of technician and spare parts on sites  an average of 4 hr/failure is the basis to achieve an objective of two-minutes access downtime in connection with ss7 common channel signaling network (bellcore, 1993) for the particular case of the parallel a-link access to the ss7 common channel signaling, the downtime objective is 2( ) 525, 600 2 minutes per year       (6) iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 42 assuming an average restoration time mttr of 4 hours, corresponding to a repair rate of µ = 6/day, it follows that the downtime objective for the parallel system would be met at an mttf of 2047 hr/failure. 2.2 downtime distribution according to barlow [8] the exact distribution for the downtime of a simplex system having exponential failure rate with failure distribution f(t) = 1– e–at and exponential repair time with repair distribution g(t) = 1– e–bt (a and b are the failure and repair respectively). with above distributions and laplace-stieltjes transform the distribution (t,x) of a downtime x during an observed time “t” is given as          dyyxtabiyextab xtaext x by ))(2()(1)(),( 1 0 2/1 (7) where i1(x) is the bessel function of order 1 for the imaginary argument defined by:       0 1 !)1(! 12 )2/( )( j jj j x xi a simplex system with a cumulative average downtime objective of 17.5 hrs/yr and average restoration time of 4 hr/failure has selected distributions among the population of the systems as shown in table 2 [9]. table 2: downtime distribution of simplex system. expected cumulative down time 0 > 17.5 hr > 40 hr >53 hr percent of units in the population 1.2% 43.2% 5% 1% while the parameter of interest for the single system is the downtime distribution among a population of systems having same design objective, a parallel architecture will have an additional focus on the very small downtime objective associated with a large percentage of the population having zero downtime distribution over one year. the analytical solution of the downtime distribution for the parallel system is more complex. the numerical solution is not straight forward, however, upper and lower bounds on downtime distribution can be found that provide good estimation. the model for the parallel system assumes renewal process with negative exponential failure and restoration time distributions. the distributions are denoted by f(t) = 1– e–t/u and g(t) = 1– e–t/d where u is the expected time to unit failure and d is the expected unit restoration time. reciprocal of u and d are also defined as: iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 43 10010110 , 1 , 1   and d and u for a down time  and its distribution fd, the laplace-stieltjes transform of the steady state cumulative down time distribution over a time period of length t is given by [7] ] )()( )2()( [exp )()( )2()( )/(),(),( 2121 2 10 2 0 wwww www wwww ww tfdewf dt wt d            (8) where w1 and w2 are the solutions of 02)2( 10210 2   ww (9) exact solution of eq. 8 is not possible [7], however upper and lower bounds of the downtime distribution fd (t,α) are found to be good estimates of the downtime distribution associated with a small downtime objective such as the 2 minutes objective. in the following analysis only the upper bound is considered for being a more conservative estimate. the upper bound can be found for all 0 ≤ α ≤ t, )]}(1[2exp{)(),( 01   tkthtfd (10) where h(t) is given by eq. 13 and )(exp)1()exp()(1 21 twbtwbtk  (11) where 10 12 102     b ww w b  (12) while availability of spares is considered to be unlimited [7-9], the analysis in [11] considers the effect of limited spares on the downtime. this paper is a theoretical extension (with examples) of the barlow and proschan “mathematical theory of reliability” [8]. it discusses a methodology that addresses the success probability of enhanced mission time with selected repair actions and spare. spares have to be kept limited in complex practical systems because of cost and other considerations. this work studies the effect of spare availability on the availability of the system beside the failure and repair rates. eq. 7 is rewritten to include “sparing factor” in addition to other reliability parameters. 2.3 probability of zero downtime end office switching system access to the ss7 common channel signaling network is an example of systems designed to meet very small downtime objective, such as 2 minutes downtime over one year. this objective is small compared to a year of operating time and equals an ineffective attempt rate of 3.8 per million. as a consequence several years of observation time is required in order to obtain a reliable estimate of the average. another iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 44 consequence is that, within certain population the number of systems that experience zero downtime is expected to be very large. according to hamilton [7], the probability that a parallel system has zero downtime during a steady state period of length t is derived using the steady-state downtime distribution given by eq. 8. this probability is denoted as 1–h(t).     ww expexp)/ [1( h(t)-1  (13) where )12(1 )12)(1( 2 )/10(1 2 )/10( www ww a        (14) and w1 and w2 are the solutions of eq. 9. 3. simulation modeling as complexity of systems architecture grows beyond the simplex and the parallel model, simulation offers an alternative way for prediction system performance. backbones of next generation internet are among complex networks that need to be analyzed in term of availability and downtime distribution to provide comprehensive prediction extending beyond the single figure average downtime. however, as a first step the simulation model is required to be validated, i.e. to determine whether it is an accurate representation of the actual system being analyzed and to ensure the model’s faithfulness to simulate the real complex network being presented. in other words, crucial evidence is needed to support the model’s credibility. while simulations in this work focus on the reliability of mpls backbone, simulations in [10] are dealing with other performance issues. in this paper a simulator is proposed for mpls path restoration that can simulate the mechanism of the haskin scheme or the “fast restoration”, the makam scheme or the “end-to-end” restoration, and the dynamic scheme. it helps evaluating the reliability of the mpls restoration backbone as well as comparing the qos traffic with best effort traffic. performance evaluation criteria are: packet loss, reordering of packets and resource utilization. the paper covers the 1:1 protection topology and promises to evaluate the more complex 1:n topology. 3.1 model validation the validation procedure compares between the analytical results of the parallel architecture and the results obtained from its simulation model with respect to the following parameter: 1. the availability a of the system 2. the average expected downtime per year 3. the probability of zero downtime among a population of systems iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 45 the analytical solutions for the two first parameters follow from the solution of the markov differential eqs. 1.a and 1.b for the continuous process [9]. the solution for the third parameter is obtained by using the laplace-stieltjes transform, eq. 13. the simulator raptor is used for the purpose of the validation of the simple parallel architecture as well as for the subsequent simulations of the three complex network architectures of the n-tuple bridge type with the following considerations: 1. an effective system population of 10,000 has been assumed in the simulation processes. 2. the input data, i.e. mttf and mttr, for the validation process are based on the average downtime of two minutes per year. an assumed average restoration time of four hours, exponentially distributed, would result in a failure rate proportional to an mttf of 2047 hr, also exponentially distributed. results from simulation model are compared to the analytical results by assigning each block in the reliability block diagram (rbd) the assumed values of the mttr and mtbf of the analytical model. the validations are as follows: 3.1.1. validation of the availability. the analytical availability figure a1 based on exponential distributed mttr = 4 hrs and mtbf= 2047 hrs is a1 = 0.9999962. availability obtained from rbd model at 10 replications is a2 = 0.99999629 at a standard deviation σ = 0.00000179. the hypothesis test statistics is based on ns aa t / 12  with the rejection region | t | > t α/2 ; (n–1) where t 0.025 ; 9 = 2.262 t = (0.99999629 – 0.9999962)/(0.00000179 / √ 10) = 0.159 hence | t | = 0.159 is not greater than t0.025 ; 9 = 2.262 and not in the rejection region. therefore at α = 0.05 level of significance it can be concluded that there is no difference between the two results. 3.1.2. validation of the average downtime. the average downtime obtained from rbd is dt2 = 1.95 minutes at a standard deviation σ = 0.9406 is compared with the analytical average downtime over one year of dt1 = 2 minutes. | t | = |1.95 – 2|/ (0.946/√10) = 0.167 < t 0.025 ; 9 = 2.262 iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 46 similarly, it can be concluded that there is no difference between the analytical and simulation result at the assumed significance level. 3.1.3. validation of the probability of zero downtime. the analytical probability of zero downtime in the system population at system downtime objective of two minutes per year is p1 = 1–h1(1yr) = 98.35%. the respective figure obtained from the simulation of the parallel architecture is p2 = 1–h2(1yr) = 98.56. the standard deviation is σ = 0.435 t = (98.56 – 98.35)/(0.435/√10)= 1.525 < t 0.025 ; 9 = 2.262 similar acceptance is justified for the zero downtime probability. following the positive validation of the reliability parameters for the simple parallel architecture, simulations are carried out to analyze the behavior of complex architectures for internet based backbone. the chosen models represent mpls backbones with restoration and dynamic routing capabilities. the simulations are intended to analyze the backbone behavior between the two edge-routers of an mpls domain, i.e. the ingress and the egress by producing two type of availability information: 1. single figure availability objective figures: availability, downtime over one year, and probability of zero downtime over one year 2. availability distribution information: complementary cumulative downtime distribution 3.2 network architecture a scalable model is used to enable comparison between backbones of various sizes. assuming links of finite reliability p and perfectly reliable nodes, a network model with protection as in fig. 3 is set as a basis for the simulation analysis in this paper. the scaling elements are the parallel links 1.1, 1.2, …1.n+1 in the protected path and 2.1, 2.2, …., 2.n+1 in the backup path. the cross links are numbered 1, 2, …n, with n being the scaling parameter of the network. this model represents a complex bridge of n cross links referred to as n-tuple bridge. three variations are considered in the simulation processes, namely: single, triple, and 6-tuple bridge. fig. 3: n-tuple bridge network 1.2 2.1 2.2 2.3 1.3 n1 2 2. n+1 1.1 1. n+1 iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 47 4. simulation results parameters analyzed in the simulations are: the availability, the average downtime over one year, the probability of zero downtime over one year, and the downtime distributions. the results obtained from the simulations are then compared to the analytical results of the parallel model. 4.1 the availability availability figures of the simulated models show direct dependency on mttf and mttr of the links as well as the size of the models. simulations are based on equal rates for all links. for the parallel system, unit restoration rate is kept constant at 4 hr/failure while mttf rates are: 2047 hr, 1445 hr, and 1179 hr. these figures result in average downtime over one year of 2, 4, and 6 minutes respectively. fig. 4 shows the availability of the three models obtained from simulation processes over a population of 10,000 samples compared to the analytical availability figure of the parallel architecture. the links in the simulated models are configured with failure and restoration rates identical to those of the parallel system. availability changes between 0.9999962 and 0.9999886 in the parallel model as compared to between 0.999974 and 0.999917 in the 6-tuple model. fig. 4: effect of failure-rate and scaling on availability 4.2 average downtime in one year in the second simulation, the average cumulative downtime figures of the three complex models are compared to the steady state analytical cumulative downtime values of the simple parallel model (fig. 5). the comparisons show an increase in the cumulative downtime in two ways. first, due to the increased failure rate shown as increase of the downtime objective of the parallel model from two minutes to six minutes. second, due to architecture scaling from a single bridge to a triple bridge and finally to a 6-tuple bridge. the restoration rate is kept constant at 4 hours/failure during the simulation processes. the availability and cumulative downtime figures for the complex models are related to each other, as those from the analytical do, by: parallel single bridge triple bridge 6-tuple bridge 0.9999 0.99992 0.99994 0.99996 0.99998 1 2.0 3.0 4.0 5.0 6.0 downtime objective per year (mins) a va ila bi li iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 48  a)-(1 t)length of period statesteady ain downtime e(cumulativ e where a is the availability, e is the expected cumulative downtime, and t is the total observed time such as one year. the expected cumulative downtime over one year for the 6-tuple model from this relation is 13.6656 minutes compared to the simulated figure of 13.666 obtained from the simulation. the error between the two results is 0.003 %. fig. 5: effect of failure-rate and scaling on downtime. table 3: cumulative downtime/yr (minutes). parallel system single bridge triple bridge 6-tuple bridge 2 4.078 7.7 13.666 4 7.64 16.69 27.232 6 12.13 23.66 43.37 table 3 compares the simulation results of the cumulative downtime per year for the three complex models with the analytical results of the simple parallel system. the links of the analytical parallel model and the simulation models are configured with same failure and restoration rates. 4.3 probability of zero downtime the third group of simulations is intended to determine the expected number of systems among a population that will experience zero downtime over one year. since in the considered downtime objective of two to six minutes per year only little downtime may be observed, a very large number of population samples are needed to obtain reliable estimation. the simulation results are compared with the analytical results of the zero parallel single-bridge triple-bridge 6-tuple bridge 0 10 20 30 40 50 1 2 3 4 5 6 7 downtime objective of parallel system (mins) a ve ra ge d ow nt im e/ y ea r (m in ) average restoration time = 4 hrs iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 49 downtime probability of the simple parallel system. the analytical availability model developed in [7] shows that 98.35% of the system population will experience zero downtime over one year under an average downtime objective of two minutes. this figure will decrease to 96.73 % at an average downtime objective of 4 minutes and finally to 95.13 % at 6 minutes objective. the simulation model of the complex system closest to the parallel system, i.e. the single bridge system results in zero downtime probability figures of 97.05 %, 93.69 %, and 90.44 % respectively under identical failure and restoration rates as the parallel system. fig. 6 shows the behavior of the probability of zero downtime of the three complex models as compared to the analytical simple parallel model. table 4 summarizes the results of the simulation processes for the probability of zero downtime among system populations in the three complex simulation models as compared to the analytical parallel model. the links of the analytical parallel model and the simulation models are configured with same failure and restoration rates. table 4: probability of zero downtime. parallel system single bridge triple bridge 6-tuple bridge 98.35% 97.05% 93.68% 88.94% 2 mins 4.08 7.7 13.67 96.73% 93.69% 87.10% 79.14% 4 mins 7.64 16.69 27.23 95.13% 90.44% 82.01% 69.96% 6 mins 12.13 23.66 43.37 the columns in table 4 represent the three complex systems in addition to the parallel system while the rows include the probability figures of zero downtime for a given system (the upper entry in the row) associated with a given reliability objective (the lower entry in the same row). for example, the probability of zero downtime for the parallel system is 98.35 % at a reliability objective of two minutes, which decreases to 95.13 % at an objective of six minutes. similarly the probability of zero downtime for a 6-tuple bridge is 88.94 % at an objective of 13.67 minutes (a figure resulting from configuring the components of the 6-tuple bridge with same failure and repair rates as that of the parallel system for a two minutes objective), which decreases to 69.96 % at an objective of 43.37 minutes. iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 50 fig. 6: probability of zero downtime per year. 4.4 downtime probability distribution the fourth type of simulation processes is the most detailed one as it moves beyond the single figure average to provide more comprehensive details on the behavior of the units among the population that have been designed with equal downtime objective. the probability of zero downtime in one year provides a single figure information about the percentage of the systems that will experience no downtime. the average downtime provides information about the average downtime experienced by large number of system population. but neither tells us how do those units expected to experience equal average downtime will behave in detail. here again, simulation results will be compared to the analytical results of the simple parallel system. in the parallel system with two minutes downtime objective only 1.65 % are expected to fail over the duration of one year. but more than 60 % of those expected to fail over one year, or one percent of the entire population, will have a cumulative downtime of over one hour. furthermore, 0.6 % and 0.2 % of the entire population are expected to have a downtime of two hours and four hours respectively. similarly, it is obvious from the simulation results of the 6-tuple bridge at an objective downtime of 13.67 minutes per year, that 1 % of the population will have a downtime of over five hours. furthermore 1.58 %, 2.62 %, 4.18 %, and 6.72 % of the population will have cumulative downtime over one year of 4 , 3, 2, and one hour respectively. fig. 7 shows the complementary downtime distribution for the three complex models as compared to the analytical parallel architecture. links failure rates and restoration rates for all systems are configured identically with mttr = 4 hrs and mttf = 2047hrs correspondent to an average downtime objective of two minutes over one year for the parallel architecture. 6-tuple bridge triple bridge single bridge parallel 1 0 1 2 3 4 5 6 downtime objective per year (mins) 0.95 0.9 0.85 0.8 0.75 0.7 iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 51 fig. 7: complementary downtime distribution over one year. table 5 summarizes the downtime distribution behavior of the three models as compared to the analytical parallel architecture model. table 5: complementary downtime distribution. percent of population parallel system single bridge triple bridge 6-tuple bridge zero downtime 98.35% 97.05% 93.68% 88.94% % > 1 hr 1.00% 1.85% 4% 6.72% % > 2 hrs 0.62% 1.18% 2.43% 4.18% % > 3 hrs 0.38% 0.89% 1.45% 2.62% % > 4hrs 0.23% 0.56% 0.91% 1.58% downtime/yr 2 min 4.078 7.7 13.666 5. conclusions this paper presents a simulation based approach for comprehensive downtime prediction of networks backbone found in mpls based next-generation internet. available analytical models for comprehensive downtime prediction manage only simple network architectures of single component simplex system and simple backup (parallel) system. in this work a simulation model is used to analyze networks of complex structures with tendency to scale up. comprehensive downtime prediction adds more confidence to the reliability analysis of systems with random failure behavior as compared to the more common single figure average downtime prediction approach. 0.001 0.01 0.1 0 40 80 120 160 200 240 280 320 downtime threshold (mins) parallel single-bridge triple-bridge 6-tuple bridge mttr = 4 hrs mttf = 2047 hrs iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 52 average downtime approach predicts equal downtime to all systems members of wide population that are equally designed to deliver a specific downtime objective. the comprehensive downtime on the other hand provides information on the distribution of the expected downtime behavior across system population. hence, it enables us to determine the extreme cases as well as specific downtime behavior such as percentage of systems with zero downtime over one year, percentage within the designed downtime objective, or percentages exceeding specific limits. in summary, although the approach considered in this paper is aimed at the network infrastructure of next-generation internet, they are equally applicable to complex networks of similar structure. references [1] [rfc2212] s. shenker et al, “specification of guaranteed qos”, 1997. [2] [rfc2475] s. blake et al, “an architecture for differentiated services”, 1999. [3] p. ford and y. bernet, “integrated services-over-differentiated services”, ietf internet draft, 1998 [4] y. bernet et al, “a framework for differentiated services”, ietf internet draft, 1999. [5] h. malec, “communications reliability: a historical perspective,” ieee transaction on reliability, vol. 47, pp. 333-344, september 1998. [6] “economics of high availability for telecommunications systems”, an intel® primer, intel corporation, 2001. [7] c.m. hamilton, n.a. marlow, “analyzing telecommunications network availability performance using the downtime probability distribution.” globcom, december1991. [8] r.e. barlow, f. proschan, “mathematical theory of reliability.” new york: john wiley, 1965 [9] e.a. elsayed, “reliability engineering”, addison wesley longman, inc., 1996. [10] g. ahn and w. chun, “design and implementation of mpls network simulator supporting ldp and cr-ldp,” ieee international conference on networks (icon2000), singapore sept. 2000 [11] l.h. crow, “a method for achieving an enhanced mission capability”, 48th reliability and maintainability symposium, rams 2002, the international symposium on product quality & integrity, 2002. [12] r. billinton, and n.r allan, “reliability evaluation of engineering system”, plenum press, 1992. iium engineering journal, vol. 5, no. 1, 2004 w. f. al-khateeb et al. 53 biographies wajdi fawzi m. al-khateeb received his m.sc. degree from berlin university of technology, germany in 1968. he joined baghdad university of technology in 1968 and later persued in planning and consultancy engineering career in telecommunications industry from 1971 to 1993 with a focus on the reliability of telecommunications systems and disaster recovery. he joined iium as a lecture in 1995. his research interest include reliability of telecommunications systems and computer networks, networks simulation and modeling, traffic engineering and quality of service (qos) in computer networks and internet. sufyan al-irhayim is currently associate professor at the department of computer engineering, university of bahrain. he received his b.sc. degree from the university of mosul, iraq in 1977. he obtained his m.sc. in 1980 and his phd in 1985 from university of bradford, england. he joined university of mosul, iraq in 1987, iium in 1991, and university of bahrain, bahrain in 2004. his research interests include performance and reliability of ip networking, mobility and multicasting in computer networking, network security, and intelligent reactive compensator prof. khalid al-khateeb studied in the united kingdom and graduated at the royal college with an honors b.sc. degree in electronics in 1966, the master’s degree in 1971 at salford university and the phd in 1975 at manchester university. his research interest include electronics, communications, computer applications and engineering education. his academic life stretches over decades, during which he worked at various universities in the uk, usa, iraq, algeria, jordan and malaysia. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 a study of channel and delay-based scheduling algorithms for live video streaming in the fifth generation long term evolution-advanced network liza abdul latiff1, huda adibah mohd ramli2*, ani liza asnawi2 and nur haliza abdulwahab3 1razak faculty of technology and informatics, universiti teknologi malaysia, kuala lumpur, malaysia 2department of electrical and computer engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia 3faculty of engineering, universiti teknologi malaysia, johor bahru, malaysia malaysia *corresponding author: hadibahmr@iium.edu.my (received: 18th june 2021; accepted: 15th july 2021; published on-line: 4thjanuary 2022) abstract: this paper investigates the performance of a number of channel and delay-based scheduling algorithms for an efficient qos (quality of service) provision with more live video streaming users over the fifth generation long-term evolutionadvanced (5g lte-a) network. these algorithms were developed for use in legacy wireless networks and minor changes were made to enable these algorithms to perform packet scheduling in the downlink 5g lte-a. the efficacies of the exp and m-lwdf algorithms in maximizing the number of live video streaming users at the desired transmission reliability, minimizing the average network delay and maximizing network throughput, are shown via simulations. as the m-lwdf has a simpler mathematical equation as compared to the exp, it is more favoured for implementation in the complex downlink 5g lte-a. abstrak: kertas ini menyiasat prestasi sebilangan saluran dan algoritma penjadualan berdasarkan kelewatan untuk penyediaan qos (kualiti perkhidmatan) yang cekap dengan banyak pengguna video secara langsung melalui rangkaian generasi kelima long-term evolution advanced (5g lte-a). algoritma-algoritma yang disiasat di dalam kertas ini dicadangkan untuk digunakan dalam generasi rangkaian tanpa wayar yang lama dan sedikit perubahan dibuat untuk membolehkan algoritma ini menyokong penjadualan paket dalam downlink 5g lte-a. keberkesanan exp dan m-lwdf algoritma dalam memaksimumkan jumlah pengguna pada kebolehpercayaan transmisi yang diinginkan dari streaming video secara langsung, meminimumkan kelewatan rangkaian, dan memaksimumkan truput rangkaian ditunjukkan melalui simulasi. namun, dengan m-lwdf mempunyai formula matematik yang mudah dibandingkan dengan exp, ia lebih sesuai untuk digunakan dalam downlink 5g lte-a yang lebih kompleks. keywords: scheduling algorithms; 5g; orthogonal frequency division multiple access; quality of service; long term evolution-advanced (lte-a) 1. introduction fifth generation (5g) is the most current standard of wireless networks [1] deployed in malaysia. 5g was expected to provide satisfactory quality of service (qos) for a large 233 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 number of users [2] and be more resilient in terms of network flexibility and (re)configurations. to date, there is no formal definition for 5g radio access networks, but the majority of the studies extended the long-term evolution-advanced (lte-a) by embracing innovative features relevant to 5g (referred to as 5g lte-a). the 5g lte-a aggregates the available bandwidth (also known as component carriers (ccs)) to significantly increase data rates. moreover, another important 5g feature for meeting the desired qos for more mobile internet users is by packet scheduling. in each scheduling period, the packet scheduler in the downlink lte-a uses a scheduling algorithm to choose the packets of a user for transmission on each radio resource on each cc. the scheduling algorithms currently available in the extant literature are channelbased, delay-based, channel-and-delay-based or none of those. the decision whether to consider channel quality or packet delay or neither depends on the network performance to be maximized or the desired qos to be satisfied. for example, round robin (rr) [3] is neither a delay-based nor a channel-based scheduling algorithm that aims to fulfill the fairness requirement while maximum rate (max-rate) [3] is a well-known channel-based scheduling algorithm developed for maximizing throughput performance. on the other hand, the delay prioritized scheduling (dps) [4] is a delay-based scheduling algorithm. the dps does not account for the channel quality when selecting a user to receive its packets. the current trend in mobile internet usage shows an explosive request for live video streaming especially during this covid-19 era where most daily activities have migrated to the online domain. this video streaming traffic is delay-sensitive and demands for the provision of high transmission reliability (as described in the 3gpp specifications [5]) for a huge number of live mobile video users whilst ensuring the network performance is maximized. it was shown in [6,7] that channel and delay aware scheduling algorithms are the best candidates for meeting the desired qos of this delay-sensitive live video streaming traffic and are hence considered in this paper. an extensive number of channel and delay-based scheduling algorithms have been proposed for the legacy of wireless networks. quite a number of these channeland delaybased scheduling algorithms showed excellent performance in the wireless networks for which they were developed and there is a likelihood that these scheduling algorithms may perform well in the 5g lte-a. implementing these scheduling algorithms in the 5g ltea may require minor amendments because the 5g lte-a is a new wireless network and has different frameworks and features as compared to legacy wireless networks. therefore, the contribution of this paper is the study on the adaptations of the legacy channeland delay-based scheduling algorithms for use in the 5g lte-a network when streaming live video. 2. downlink 5g lte-a network model this paper considers the downlink 5g lte-a given that an enormous volume of mobile internet traffic is communicated in the downlink. orthogonal frequency division multiple access (ofdma) is the multiple access technique employed in the downlink 5g lte-a. this technique divides the wide bandwidth into multiple narrowband sub-carriers. the 5g lte-a modeled in this paper modifies the legacy 4g lte-a that performs packet scheduling at every 1 ms transmission time interval (tti). a total of 12 sub-carriers of 15 khz width each are used to carry the user packets. this group of sub-carriers (12 subcarriers) in the frequency domain and 1 ms tti (that contains 14 orthogonal division multiple access (ofdm) symbols) in the time domain is referred to as physical resource block (prb). 234 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 on the other hand, the downlink 5g lte-a, has a variable tti size (as illustrated in table 1). the packet scheduler may choose to perform scheduling every 0.14 ms tti for the case of delay-sensitive mobile internet traffic or every 4.0 ms tti for a more delayrelaxed mobile internet traffic. this paper considers modeling the 0.14 ms tti size as it aims to evaluate the scheduling algorithms for delay-sensitive live video streaming. the 0.14 ms tti size constitutes 2 orthogonal division multiple access (ofdma) symbols in the time domain and 12 sub-carriers in the frequency domain (see fig. 1) for each prb. at this tti size also, there will be a total of 8 prbs (as illustrated in table 1) that map to 192 resource elements (res) that will be used to carry user packets. additionally, to further increase the 5g lte-a performance as compared to the legacy wireless networks, the round trip time (rtt) of hybrid automatic repeat request (harq) is shortened from 8 ms to 4 ms [8]. table 1: tti and sub-band size [9]. tti size (ms) frequency domain scheduling block size (subband size) resource elements (res) per block size 0.14 8 prbs (1440 hz) 192 0.5 4 prbs (720 hz) 336 1.0 3 prbs (540 hz) 432 2.0 2 prbs (360 hz) 576 4.0 1 prb (180 hz) 576 fig. 1: prb time and frequency domain representation. 3. channel and delay-based scheduling algorithms this paper studies eight channeland delay-based scheduling algorithms for possible implementation in the downlink 5g lte-a when providing the desired qos of the delaysensitive live video streaming traffic. these algorithms are described in the following section. 3.1 modified-largest weighted delay first (m-lwdf) algorithm the m-lwdf [10] is a prominent scheduling algorithm proposed for a single-user wireless network. it should be noted that at each scheduling period, only one user is selected to receive its packets in this single-user wireless network. this is contrary to the downlink 5g lte-a that performs packet scheduling in both time and frequency domains (i.e., more than one user can receive its packets at each scheduling period). the m-lwdf 235 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 algorithm chooses the packets of a user that maximize eq. (1) at each scheduling period and transmits the chosen user packets on the entire bandwidth. 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑(𝒑𝒑) = 𝒂𝒂𝒑𝒑 ∗ 𝑾𝑾𝒑𝒑(𝒑𝒑) ∗ � 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑(𝒑𝒑) 𝑹𝑹𝒑𝒑(𝒑𝒑) � (1) 𝒂𝒂𝒑𝒑 = −� 𝒍𝒍𝒑𝒑𝒍𝒍 𝜹𝜹𝒑𝒑 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 � (2) 𝑹𝑹𝒑𝒑(𝒑𝒑) = �𝟏𝟏 − 𝟏𝟏 𝒑𝒑𝒄𝒄 �𝑹𝑹𝒑𝒑(𝒑𝒑 − 𝟏𝟏) + 𝑰𝑰𝒑𝒑(𝒑𝒑) ∗ 𝟏𝟏 𝒑𝒑𝒄𝒄 ∗ 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑(𝒑𝒑) (3) where priorityi(t) is the priority of the ith user at scheduling period t, ai is the desired qos of the ith user, δi is the packet loss ratio (plr) threshold of the ith user and pdti is the packet delay threshold of the ith user, wi(t) is the head-of-line (hol) packet delay of the ith user at scheduling period t, cqii(t) is the channel quality of the ith user at scheduling period t, ri(t) is the average throughput of the ith user at scheduling period t, tc is a constant and ii(t) is a function indicating whether the ith user is scheduled or not at scheduling period t. 3.2 exponential (exp) algorithm like the m-lwdf, the exp [11] was proposed for the single-user wireless network. the decision on which user packets to be transmitted at each scheduling period is made according to: 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑(𝒑𝒑) = 𝒂𝒂𝒑𝒑 ∗ 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑(𝒑𝒑) 𝑹𝑹𝒑𝒑(𝒑𝒑) 𝒆𝒆𝒆𝒆𝒑𝒑� 𝒂𝒂𝒑𝒑 ∗ 𝑾𝑾𝒑𝒑(𝒑𝒑) − 𝒂𝒂𝑾𝑾 𝟏𝟏 + √𝒂𝒂𝑾𝑾 � (4) 𝒂𝒂𝑾𝑾 = 𝟏𝟏 𝑵𝑵 �𝒂𝒂𝒑𝒑 ∗ 𝑾𝑾𝒑𝒑(𝒑𝒑) 𝒑𝒑=𝑵𝑵 𝒑𝒑=𝟏𝟏 (5) where priorityi(t) is the priority of the ith user at scheduling period t, ai is the desired qos of the ith user (as defined in eq. (2)), cqii(t) is the channel quality of the ith user at scheduling period t, ri(t) is the average throughput of the ith user at scheduling period t (see eq. (3)), wi(t) is the hol packet delay of the ith user at scheduling period t and n is the maximum number of available users. 3.3 channel-aware earliest deadline (c-aed) the provision of the desired qos for more users whilst maximizing network performance is the most challenging issue in the design of a packet scheduling algorithm. this is further complicated by the diverse qos requirement of mobile internet traffic as well as the nature of the time and frequency variation of mobile wireless channels. the caed [12] is another algorithm developed to address this complicated challenge in a single-user wireless network. decisions on which user to receive its packets at each scheduling period are made according to: 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑(𝒑𝒑) = 𝒂𝒂𝒑𝒑 ∗ 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑(𝒑𝒑) 𝑹𝑹𝒑𝒑(𝒑𝒑) � 𝑾𝑾𝒑𝒑(𝒑𝒑) 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 − 𝑾𝑾𝒑𝒑(𝒑𝒑) � (6) where priorityi(t) is the priority of the ith user at scheduling period t, ai is the desired qos of the ith user (as defined in eq. (2)), cqii(t) is the channel quality of the ith user at scheduling period t, ri(t) is the average throughput of the ith user at scheduling period t (see eq. (3)), wi(t) is the hol packet delay of the ith user at scheduling period t and pdti is the packet delay threshold of the ith user. 236 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 when compared with m-lwdf and exp that used the desired qos, channel quality, hol packet delay, and average throughput criteria in their priority equations, the c-aed includes additional criterion of the packet delay threshold in its priority calculation, with the goal of improvement in performance. 3.4 exponential based packet scheduling (ebps) algorithm the ebps [13] algorithm was developed for use in multi-user satellite downlink long term evolution (lte) networks. the satellite lte network aims to complement the limitations of terrestrial wireless networks by providing global coverage to users including in remote areas. this lte network contains only one cc, and similar to the 4g lte-a, packet scheduling in this wireless network is performed in every 1 ms tti. however, contrary to single-user wireless networks, the lte is a multi-user wireless network where more than one user can be scheduled in each tti due to the usage of ofdma as its multiple access technique. packet scheduling in this lte network is performed per prb and time basis and the ebps schedules packets of a user on each prb and at each tti according to eq. (7). 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) = 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) 𝑹𝑹𝒑𝒑(𝒑𝒑) 𝒆𝒆𝒆𝒆𝒑𝒑�� 𝒆𝒆 𝟎𝟎. 𝟗𝟗𝟗𝟗 ∗ 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 � ∗ � 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 − 𝑾𝑾𝒑𝒑(𝒑𝒑) 𝑾𝑾𝒑𝒑(𝒑𝒑) �� (7) where priorityi,j(t) is the priority of the ith user on jth rb at tti t, cqii,j(t) is the channel quality of the ith user on jth rb at tti t, ri(t) is the average throughput of the ith user at tti t (see eq. (3)), wi(t) is the hol packet delay of the ith user at tti t and pdti is the packet delay threshold of the ith user. it can be observed that when compared with m-lwdf, exp and c-aed, the algorithms developed for lte networks makes scheduling decision on each prb and at each tti. 3.5 joint user scheduling (jus) algorithm the jus [14] is another variation of ebps in which the algorithm was developed by the same authors for supporting the desired qos of delay-sensitive mobile internet traffic in the satellite lte network. at each tti and on each prb the scheduling decisions are carried out based on: 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) = 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) 𝑹𝑹𝒑𝒑(𝒑𝒑) 𝒆𝒆𝒆𝒆𝒑𝒑� 𝑾𝑾𝒑𝒑(𝒑𝒑) ∗ �𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) ∗ 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 − 𝟏𝟏� + 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 𝟐𝟐𝑾𝑾𝒑𝒑(𝒑𝒑) ∗ �𝟏𝟏 + 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) ∗ 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑� � (8) where priorityi,j(t) is the priority of the ith user on jth rb at tti t, cqii,j(t) is the channel quality of the ith user on jth rb at tti t, ri(t) is the average throughput of the ith user at tti t (see eq. (3)), wi(t) is the hol packet delay of the ith user at tti t and pdti is the packet delay threshold of the ith user. 3.6 exponential maximum-largest weighted delay first (exp-mlwdf) the exp-mlwdf [15] was developed for use in the lte for high mobility and dense area scenarios. the aim was to reduce congestion in lte wireless networks due to the high use of delay-sensitive mobile internet traffic such as video streaming and voice. it was shown via a series of computer simulations that the exp-mlwdf outperformed the m-lwdf algorithm in meeting the desired qos for more mobile users. this algorithm decides priority of each user according to: 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) = 𝒂𝒂𝒑𝒑 ∗ 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) 𝑹𝑹𝒑𝒑(𝒑𝒑) 𝒆𝒆𝒆𝒆𝒑𝒑� 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 − 𝑾𝑾𝒑𝒑(𝒑𝒑) � (9) 237 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 where priorityi,j(t) is the priority of the ith user on jth rb at tti t, ai is the desired qos of the ith user (as defined in eq. (2)), cqii,j(t) is the channel quality of the ith user on jth rb at tti t, ri(t) is the average throughput of the ith user at tti t (see eq. (3)), pdti is the packet delay threshold of the ith user and wi(t) is the hol packet delay of the ith user at tti t. 3.7 downlink scheduler based on deadlines (dsbd) similar to the previously discussed algorithms, the dsbd [16] was developed to efficiently utilize the limited lte radio resources and meeting the desired qos of delaysensitive mobile internet traffic for more users. this algorithm has the following equation: 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) = 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) 𝑹𝑹𝒑𝒑(𝒑𝒑) ∗ �𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 − 𝑾𝑾𝒑𝒑(𝒑𝒑)� (10) where priorityi,j(t) is the priority of the ith user on jth rb at tti t, cqii,j(t) is the channel quality of the ith user on jth rb at tti t, ri(t) is the average throughput of the ith user at tti t (see eq. (3)), pdti is the packet delay threshold of the ith user and wi(t) is the hol packet delay of the ith user at tti t. 3.8 efficient downlink packet scheduling (edps) the last algorithm considered in this paper is edps [17] where this algorithm combines the well-known earliest deadline first (edf) and proportional fair (pf) algorithms so as to support the transmission of delay-sensitive mobile internet packets via the downlink lte wireless network. it should be noted that the edf does not take channel quality into account whereas the pf does not consider packet delay in its algorithm. on each prb and at each scheduling period, the user with the highest priority of equation (11) will be selected to receive its packets. 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) = 𝒅𝒅𝒑𝒑 ∗ 𝑾𝑾𝒑𝒑(𝒑𝒑) 𝒍𝒍𝒑𝒑𝒍𝒍�𝟏𝟏 + 𝒃𝒃𝒑𝒑𝑾𝑾𝒑𝒑(𝒑𝒑) � + 𝒄𝒄𝒑𝒑 ∗ � 𝟏𝟏 𝑷𝑷𝑷𝑷𝑷𝑷𝒑𝒑 − 𝑾𝑾𝒑𝒑(𝒑𝒑) � ∗ 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) 𝑹𝑹𝒑𝒑(𝒑𝒑) (11) where priorityi,j(t) is the priority of the ith user on jth rb at tti t, cqii,j(t) is the channel quality of the ith user on jth rb at tti t, ri(t) is the average throughput of the ith user at tti t (see eq. (3)), wi(t) is the hol packet delay of the ith user at tti t and pdti is the packet delay threshold of the ith user. it was shown in [17] that when bi ,ci and di are set to 1, the edps achieved good scheduling performance. it can be observed in sub-section 3.3 through sub-section 3.8 that the conventional scheduling algorithms manipulated similar scheduling criteria but devised different priority metrics calculations in an attempt to maximize the number of users that received the desired qos of delay-sensitive mobile internet traffic. these algorithms showed good performance in the mobile network environments they were evaluated in. however, their performance in the downlink 5g lte-a may vary because the downlink 5g lte-a supports slightly distinguished frameworks and features as compared to the legacy wireless networks. as such, the contribution of this paper is to study the performance of these channel and delay-based scheduling algorithms in the downlink 5g lte-a where minor revisions were made to these algorithms to enable them to carry out packet scheduling in this wireless network. this includes the usage of variable tti size in which 0.14 ms tti size is assumed in this paper. this, therefore, requires packet scheduling to be performed in each 8 prbs. moreover, the average channel quality computed from all prbs for each cc will be considered for these algorithms instead of computing the channel quality across the 238 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 whole bandwidth for the m-lwdf, exp and c-aed and the channel quality on each prb for the rest. the example of average channel quality computation is represented in equation (12). 𝒄𝒄𝒄𝒄𝒑𝒑_𝒂𝒂𝒂𝒂𝒍𝒍𝒑𝒑(𝒑𝒑) = ∑ 𝒄𝒄𝒄𝒄𝒑𝒑𝒑𝒑,𝒋𝒋(𝒑𝒑) 𝒋𝒋=𝒎𝒎𝒂𝒂𝒆𝒆 _𝑹𝑹𝑹𝑹 𝒋𝒋=𝟏𝟏 𝒎𝒎𝒂𝒂𝒆𝒆 _𝑹𝑹𝑹𝑹 (12) where cqi_avgi(t) is the average channel quality of the ith user at tti t, cqii,j(t) is the channel quality of the ith user on jth rb at tti t and max_rb is the total number of available rbs. 4. simulation environments this paper adopted a simulation method [18-20] to evaluate the performance of the studied channel and delay-based scheduling algorithms as discussed in section 3. the downlink 5g lte-a network was modeled to comprise of only one base station. this base station used 43.01 db transmit power and operated at 2 ghz and 2.6 ghz ccs. each cc had 5 mhz bandwidth that mapped to a total of 50 prbs available to be used by the downlink users. cqi was reported by the downlink users in every 5 ms interval. these cqi reports reached the base station after 2 ms duration. erroneously received packets at the user end could be retransmitted 4 times and the rtt of harq process was constrained to 4 ms. this simulation software prioritized pending harq retransmission over new packets and new packets of users would only be transmitted if remaining prbs were available after retransmission of pending harq packets was completed. the simulation assumed live video streaming of 512 kbps average data rate as the delaysensitive mobile internet traffic. the delay threshold for the video users was capped at 80 ms and the qos provision of the video users was met when the transmission reliability was maintained above 99.99%. table 2 summarizes the assumptions used for simulation. table 2: a summary of simulation assumptions description assumption frequency spectrum 2 ghz and 2.6 ghz bandwidth 5 mhz number of available rbs 50 rbs (25 rbs each from each cc) base station transmit power 43.01 db cqi periodic cqi every 5 ms with 2 ms delay harq rtt 4 ms maximum number of harq retransmissions 4 times video delay packet threshold and the desired transmission reliability 80 ms and 99.99% transmission reliability, average network delay, and network throughput metrics, which are considered as common metrics for the video streaming qos provision, were used to evaluate the performance of each channel and delay-based scheduling algorithm. for example, the transmission reliability must be maintained above the 99.99% threshold to ensure that received video packets were not distorted during live streaming and hence guaranteed the desired qos received by the live video users. the transmission reliability, as well as other metrics, are defined next: 239 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 𝑷𝑷𝒑𝒑𝒂𝒂𝑻𝑻𝑻𝑻𝒎𝒎𝒑𝒑𝑻𝑻𝑻𝑻𝒑𝒑𝒑𝒑𝑻𝑻 𝒑𝒑𝒆𝒆𝒍𝒍𝒑𝒑𝒂𝒂𝒃𝒃𝒑𝒑𝒍𝒍𝒑𝒑𝒑𝒑𝒑𝒑 = 𝟏𝟏𝟎𝟎𝟎𝟎 − ∑ ∑ 𝒑𝒑_𝒅𝒅𝒑𝒑𝑻𝑻𝒄𝒄𝒂𝒂𝒑𝒑𝒅𝒅𝒑𝒑(𝒑𝒑) 𝒑𝒑=𝑷𝑷 𝒑𝒑=𝟏𝟏 𝒑𝒑=𝑵𝑵 𝒑𝒑=𝟏𝟏 ∑ ∑ 𝒑𝒑_𝒑𝒑𝒑𝒑𝒑𝒑𝒂𝒂𝒍𝒍𝒑𝒑(𝒑𝒑)𝒑𝒑=𝑷𝑷𝒑𝒑=𝟏𝟏 𝒑𝒑=𝑵𝑵 𝒑𝒑=𝟏𝟏 (13) 𝑨𝑨𝒂𝒂𝒆𝒆𝒑𝒑𝒂𝒂𝒍𝒍𝒆𝒆 𝑻𝑻𝒆𝒆𝒑𝒑𝒏𝒏𝒑𝒑𝒑𝒑𝒏𝒏 𝒅𝒅𝒆𝒆𝒍𝒍𝒂𝒂𝒑𝒑 = 𝟏𝟏 𝑷𝑷 � 𝟏𝟏 𝑵𝑵 �𝑾𝑾𝒑𝒑(𝒑𝒑) 𝒑𝒑=𝑵𝑵 𝒑𝒑=𝟏𝟏 𝒑𝒑=𝑷𝑷 𝒑𝒑=𝟏𝟏 (14) 𝑵𝑵𝒆𝒆𝒑𝒑𝒏𝒏𝒑𝒑𝒑𝒑𝒏𝒏 𝒑𝒑𝒕𝒕𝒑𝒑𝒑𝒑𝒕𝒕𝒍𝒍𝒕𝒕𝒑𝒑𝒕𝒕𝒑𝒑 = 𝟏𝟏 𝑷𝑷 � �𝒑𝒑_𝒑𝒑𝒆𝒆𝒄𝒄𝒆𝒆𝒑𝒑𝒂𝒂𝒆𝒆𝒅𝒅𝒑𝒑(𝒑𝒑) 𝒑𝒑=𝑷𝑷 𝒑𝒑=𝟏𝟏 𝒑𝒑=𝑵𝑵 𝒑𝒑=𝟏𝟏 (15) where p_discardi(t) is the size of discarded packets of the ith user at time t, p_totali(t) is the total size of packets of the ith user that arrive at the base station at time t, wi(t) is the hol packet delay of the ith user at time t, p_receivedi(t) is the size of correctly received packets at the ith user at time t, t is the maximum simulation time and n is the maximum number of users. 5. results and discussion the transmission reliability, average network delay, and network throughput performances of the channeland delay-based scheduling algorithms in the downlink 5g lte-a when streaming video are shown in fig. 2, fig. 3, and fig. 4, respectively. though all these scheduling algorithms consider the same scheduling criteria (i.e., channel quality, packet delay, etc.), the manipulation of these criteria into their respective mathematical equations map to a slight variation in performance. for example, if the qos provision of the live video users is to be satisfied, then the transmission reliability should be kept above 99.99%. it can be observed in fig. 2 and table 3 that the exp is superior to other channel and delay-based scheduling algorithms where it supports 16% more users compared to caed, dsbd and edps (i.e., exp supports 29 video users whereas the c-aed, dsbd, and edps support up to 25 users). furthermore, it can be observed in fig. 3 and fig. 4 that both exp and m-lwdf are capable of minimizing the average network delay as well as maximizing the network throughput. both exp and the m-lwdf prioritize the most urgent packets to avoid these packets from being discarded for delay violations and hence minimize the average network delay. the network throughput on the other hand is the most important metric for the network operator for profit maximization. therefore, the exp and m-lwdf are preferred as these algorithms provide higher network throughput as compared to the other evaluated scheduling algorithms. the achievement accomplished by exp and m-lwdf, as illustrated in table 3, is significant given that mobile users are streaming live video at an average rate of 512 kbps. the exp outperforms other scheduling algorithms because exp computes the average of the desired qos and the hol packet delay. this, however, incurs additional computational complexity because the extra step is needed in determining the priority of each user at each tti (the downlink 5g lte-a network is already complex and additional complexity in a scheduling algorithm is not preferred). the m-lwdf algorithm, on the other hand, has a simple mathematical equation and achieves slightly lower performance compared to the exp. it supports 12% more video users as compared to c-aed, dsbd and edps and is capable of minimizing average network delay whilst maximizing the network throughput (as demonstrated in fig. 3 and fig. 4). it also does not come with additional computational complexity as does exp. other variations of mathematical equations lead to worse performance as in c-aed, dsbd, and edps whereas more complex mathematical equations do not necessarily map to good video performance (see the ebps, jus, exp-mlwdf algorithms). 240 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 fig. 2: transmission reliability vs number of video users. fig. 3: average network delay vs number of video users. fig. 4: network throughput vs number of video users. 241 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 table 3: maximum number of users at desired video qos provision scheduling algorithms maximum number of users at desired live video qos provision m-lwdf 28 exp 29 c-aed 25 ebps 26 jus 27 exp-mlwdf 26 dsbd 25 edps 25 6. conclusion the enormous demand for video streaming traffic has accelerated the standardization of 5g wireless networks. packet scheduling is of paramount importance in the 5g wireless to efficiently utilize the scarce radio resources and provide satisfactory qos provisions of the diverse mobile internet traffic. this paper studies the performance of channeland delay-based scheduling algorithms in the downlink 5g lte-a wireless network when streaming live video. minor amendments were made to these algorithms because the frameworks and features of the downlink 5g lte-a are slightly different from legacy wireless networks. a series of computer simulations demonstrated that the exp outperforms other scheduling algorithms however, this algorithm incurs additional complexity for calculating the average of the desired qos and the hol packet delay at every tti. the m-lwdf seems the most eligible candidate because its performance is comparable to exp, and it does not come with an additional complexity cost. it supports 12% more users streaming video at 512 kbps average data rate, minimizing the average network delay and maximizing the network throughput. it can also be concluded, based on this study, that complex mathematical equations sometimes do not necessarily map to a good scheduling performance. what is most important is the exploitation of these scheduling criteria to effectively meet the desired qos for a huge number of users and maximizing the network performance. future works will investigate the performance of these algorithms in a multiple cell scenario, considering diverse mobile internet traffic. acknowledgement this work was fully funded by utm crg no. 08g12. references [1] nordin mam, ramli ham. (2020) performance analysis of 5g path loss models for rural macrocell environment. iium eng. j., 21(1): 85-99. [2] antonioli rp, fodor g, soldati p, maciel tf. (2021) decentralized joint beamforming, user scheduling, and qos management in 5g and beyond systems. ieee commun. stand. mag., 5(1):62-69. [3] dahlman e, parkvall s, skold j, beming p. (2007) 3g evolution: hspa and lte for mobile broadband. elsevier ltd. [4] sandrasegaran k, ramli ham, basukala r. (2010) delay-prioritized scheduling (dps) for real time traffic in 3gpp lte system, in ieee wireless communication and networking conference, pp. 1-5. [5] 3gpp (2019) technical specification group services and system aspects; system 242 iium engineering journal, vol. 23, no. 1, 2022 latif et al. https://doi.org/10.31436/iiumej.v23i1.2115 architecture for the 5g system (5gs); stage 2 (release 16). [6] ramli ham, basukala r, sandrasegaran k, patachaianand r. (2009) performance of well known packet scheduling algorithms in the downlink 3gpp lte system, in 2009 ieee 9th malaysia international conference on communications (micc), pp. 815-820. [7] ramli ham, isa fnm. (2016) improving real-time multimedia scheduling in practical mobile cellular channels, in ieee 6th international conference on intelligent and advanced systems (icias), pp. 1–6. [8] pocovi g, soret b, pedersen ki, amogensen p. (2017) mac layer enhancements for ultrareliable low-latency communications in cellular networks, in ieee international conference on communications workshops, pp. 1005–1010. [9] pedersen ki, niparko m, steiner j, oszmianski j, mudolo l, khosravirad sr. (2016) system level analysis of dynamic user-centric scheduling for a flexible 5g design, in ieee global communications conference, pp. 1–6. [10] mathewa, kumaran k, ramanan k, stolyar a, whiting p. (2001) providing quality of service over a shared wireless link. ieee commun., 39(2):150–154. [11] shakkotai s, stolyar a. (2000) a study of scheduling algorithms for a mixture of realand non-real-time data in hdr, bell labs tech memo. [12] elsayed kmf, khattab akf. (2006) channel-aware earliest deadline due fair scheduling for wireless multimedia networks. wirel. pers. commun., 38:233–252. [13] aiyetoro g, takawira f. (2017) an exponential based packet scheduling scheme for real time traffic in satellite lte networks, in ieee africon, pp. 215–220. [14] aiyetoro g, takawira f. (2018) joint user scheduling and prb mapping scheme in satellite lte networks, in 4th international wireless communications & mobile computing conference (iwcmc), pp. 24–29. [15] angri i, mahfoudi m, najid a, el bekkali m. (2018) exponential m-lwdf (exp-mlwdf) downlink scheduling algorithm evaluated in lte for high mobility and dense area scenario. int. j. electr. comput. eng., 8(3):1618–1627. [16] ashidani pj, guardieiro pr. (2013) downlink scheduler based on deadlines for lte networks, in international workshop on telecommunications (iwt), pp. 1–5. [17] liu b, tian h, xu l. (2013) an efficient downlink packet scheduling algorithm for real time traffics in lte systems, in ieee 10th consumer communications and networking conference (ccnc), pp. 364–369. [18] ramli ham, isa fnm, asnawi al, jusoh az, azman aw. (2019) urgency-aware scheduling algorithm for downlink cognitive long term evolution-advanced, in ieee 89th vehicular technology conference (vtc spring), pp. 1–5. [19] ramli ham, mansor mih. (2020) an enhanced packet scheduling algorithm for the downlink cognitive long term evolution-advanced. iium eng. j., 21(1):51-60. [20] ramli ham. (2020) a study on packet scheduling algorithms for healthcare contents over fifth generation (5g) mobile cellular network. int. j. electron. telecommun., 66(4):1–7. 243 1. introduction 2. downlink 5g lte-a network model 3. channel and delay-based scheduling algorithms 4. simulation environments 5. results and discussion 6. conclusion acknowledgement references application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 granular subbase improvement with recycled concrete aggregates in tropical areas daniela l. vega a.*, jose eduardo salcedo fontalvo, richard jimenez triana, dulce maria palacios del barre, cesar fresneda saldarriaga department of civil and environmental engineering, universidad de la costa, barranquilla, colombia. * corresponding author: dvega7@cuc.edu.co (received: 23rd march 2022; accepted: 24th may 2022; published online: 4th july 2022) abstract: use of recycled concrete aggregate (rca) for granular subbase (gsb) in the tropical area is evaluated in this work. among the materials widely studied as replacements in granular and surface layers is rca. its mechanical behavior in granular layers has mainly been evaluated with tests such as california bearing ratio (cbr). however, abrasion is also a determining property in the strength of these materials. in this study, the performance of natural aggregates (na) with replacement of rca was evaluated for use as gsb in a tropical area. even though several laboratory tests were performed, the focus of the article lies on the performance in the los angeles (la) abrasion test. two replacement percentages of coarse rca were considered: 10 and 15 % by weight of aggregates. the rca and na were characterized according to different laboratory tests: granulometry, absorption, atterberg limits test, plasticity, specific gravity, and la abrasion. in turn, all results were compared with colombian specifications for a typical gsb in the area. in addition, a simple life cycle assessment (lca) was included to evaluate the environmental impacts of the base and alternative scenarios. the results show that gsb with 10% rca present a higher abrasion resistance than the gsb with 15% rca. even better results are obtained with 10% rca than with natural gsb. specifically, average la abrasion test losses of 30.86, 29.80 and 32.07% were obtained for na, 10% rca and 15% rca, respectively. the lca results show an increase of 50% and 75% in energy consumption by comparing the base scenario with 10 and 15% rca replacement, respectively. this leads to an increase of 40 and 80% in carbon monoxide (co) emissions for 10 and 15% rca replacement respectively, and 100% in carbon dioxide (co2) emissions for both alternative scenarios. abstrak: penggunaan agregat konkrit kitar semula (rca) bagi subtapak butiran (gsb) bagi kawasan tropika telah dikaji dalam kajian ini. antara bahan yang banyak dikaji sebagai bahan ganti dalam butiran dan lapisan permukaan adalah rca. ciri-ciri mekanikal dalam lapisan butiran telah diuji, terutamanya dengan ujian seperti nisbah bearing california (cbr). walau bagaimanapun, pelelasan juga merupakan ciri penting dalam menentukan ketahanan material. kajian ini merupakan prestasi agregasi semulajadi (na) dengan ganti rca yang diuji bagi penggunaan gsb di kawasan tropika. walaupun pelbagai ujian makmal telah dijalankan, fokus artikel ini terletak pada prestasi ujian pelelasan los angeles (la). dua gantian bagi peratus rca kasar telah diambil kira: iaitu pada agregat berat 10% dan 15%. ciri-ciri rca dan na dikategori berdasarkan pelbagai ujian lab yang pelbagai: granulometri, penyerapan, ujian had atterberg, keplastikan, graviti tertentu dan pelelasan la. kemudian, kesemua dapatan kajian dibandingkan dengan ciri-ciri kolombia bagi ciri tipikal gsb di kawasan itu. tambahan, pentaksiran kitar hidup (lca) yang ringkas dimasukkan bagi menilai impak terhadap alam terhadap 59 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 penggunaanya pada pangkal bijirin dan pada senario alternatif. dapatan kajian menunjukkan gsb yang menggunakan rca 10% mempunyai rintangan lelasan tertinggi berbanding gsb dengan rca 15%. tambahan, dapatan kajian yang lebih baik didapati daripada rca 10% berbanding gsb semula jadi. terutama pada purata ujian lelasan la telah mengalami penyusutan sebanyak 30.86, 29.80 dan 32.07% bagi na, rca 10% dan rca 15%, masing-masing. dapatan lca menunjukkan peningkatan sebanyak 50% dan 75% pada penggunaan tenaga dengan perbandingan senario subtapak butiran dengan gantian rca 10% dan 15%, masing-masing. ini membawa kepada peningkatan sebanyak 40% dan 80% emisi karbon monoksida (co) bagi gantian rca 10% dan 15% masingmasing, dan emisi karbon dioksida (co2) 100% bagi kedua-dua senario alternatif. keywords: recycled concrete aggregate (rca); natural aggregates (na); granular subbase (gsb); los angeles (la) abrasion test; tropical area 1. introduction in recent years, the use of recycled concrete aggregate (rca) has been widely recognized worldwide, as it contributes to the preservation of the environment and has several economic and social benefits that make this alternative sustainable. in civil engineering projects, this material has been widely studied as a replacement for natural aggregates in asphalt mixtures [1]–[3], concrete mixtures [4]–[6] and as granular base improvement, just to mention a few [7]–[9]. rca is a material composed of virgin aggregates covered by a layer of cement mortar [8], these wastes are part of the composition of construction and demolition (c&d) waste. bonded cement mortar is related to different undesirable characteristics of rca behavior, such as higher absorption, lower durability, and lower mechanical behavior; compared to natural aggregates [3], [10]. however, as a replacement of the natural aggregates (na) in road structures in certain percentages, rca have shown a relatively good performance [10]. in general, studies show that rca replacements in pavement structure is an alternative to controlling c&d waste, since it reduces the consumption of natural aggregates and protects the environment [8], [11], [12]. its use on pavements has been categorized worldwide as a viable, cost-effective, and sustainability-friendly alternative [10], [13]. the stiff and durable structure of the rcas allows them to be used in the granular subbase (gsb) and granular base (gb) instead of conventionally used materials [9]. some studies have been carried out to evaluate and compare the properties of natural granular layers vs. granular layers with rca replacements. from the results reported in the literature regarding mechanical properties such as the california bearing ratio (cbr) and the la abrasion test, it has been determined that rcas are comparable to na [14], highlighting that lower strengths and higher abrasions are observed but they fulfill the standards for gsb. in terms of resilient modulus, it has been established that gb with rca show higher results than natural aggregates [14]. in addition, they found that rca had better mechanical properties than na but had higher permanent deformation. in general, rcas meet the desired criteria for granular layers, showing satisfactory performance in mechanical behavior [9], [15]. in addition, the environmental effects of the use of rca in road construction must be considered. it has been established that the use of rca as a replacement in highway structures reduces greenhouse gas emissions and energy use [10], [14]. the environmental savings that can be achieved with this alternative are mainly related to the production of the materials [14], [16]. a saving of about 16% in co2 generation has been established, when comparing the production of na versus a 70% na and 30% rca mix [17]. 60 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 on the other hand, another important variable in the environmental analysis of the use of rca in pavement structures is the transportation of the material [14], [18]. thus, when transportation is not included in the scope of the analysis, large environmental advantages are observed [19], [20]. however, when transportation of materials is considered, it can be concluded that there are savings in energy use only if the recycling facilities are close to the construction sites [10], [21]. in general, it has been established that, under certain replacement percentages and hauling distances, the use of rca in highway structures is an innovative and ecofriendly solution [10], [14], [17]. the influence of rca on properties such as cbr, resilient modulus, granulometry and others, has been extensively evaluated in the literature, but few studies have focused on abrasion [14], [22]. this resistance characteristic can be influenced by rca replacements, so it is studied in detail in this research. considering the evidence, the present research has been proposed to evaluate the improvement of a gsb with rca substitutions. two percentages of coarse rca replacement were considered: 10 and 15%. the rca and gsb were characterized according to different laboratory tests: granulometry, absorption, atterberg limits test, plasticity, specific gravity, and la abrasion test. the main comparison of the alternative scenarios versus the natural one was based on the resistance of the samples in the la abrasion test. in addition, environmental impacts were calculated by a lca, using the palate 2.0 tool. the analysis was carried out considering a base scenario of the construction of a pavement with a 100% natural gsb, and as alternative scenarios, substitutions of 10% and 15% in the same granular layer were evaluated. 2. methodology for the laboratory tests, samples of the granular materials (natural and recycled) were evaluated individually and then mixed with 10 and 15% replacements of coarse recycled concrete aggregate (rca). the recycled material was obtained from the demolition of a three-story house, located in the campo alegre neighborhood, barranquilla colombia. a portion of a concrete beam was extracted from the area, which was initially subjected to crushing processes in the laboratory. the crushing was carried out using a bico brarun jaw crusher (fig. 1) with a v-belt drive system, with a jaws capacity of 2¼ x 3" which allows a reduction of the material from 3/8 to 1/16”. to obtain smaller sizes, manual crushing was performed in the laboratory. physical and mechanical properties were evaluated on natural aggregates (na) and rca, as described below. in order to obtain results that can be comparable with other studies, american society for testing and materials (astm) standards were used for the development of the tests [23]–[27]. at the same time, these standards are the basis for many standards in different countries such as colombia. thus, having them as a basis can guarantee internationally comparable and representative results for the study area. in addition, all tests performed satisfy granular subbase (gsb) colombian standards [28]. specifically, the results were compared with the standards for a gsb with 37.5 mm (gsb38) as nominal maximum size. 61 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 fig. 1: laboratory scale jaw crusher used for the crushing of recycled material [29]. finally, each laboratory test was performed on at least three different samples of the material. it is important to mention that with the number of samples evaluated for each test, a clear trend in the results was observed. the tests carried out and their respective standards are mentioned in table 1. table 1: test, tested material and standard considered test tested material standard granulometry na, rca, 10 and 15% rca replacements astm d6913 [26] density, relative density and absorption rca astm c127 [24] atterberg limits and plasticity na and rca 10 and 15% rca replacements astm d4318 [25] specific gravity rca astm d854 [23] la abrasion na, rca, 10 and 15% rca replacements astm c131 [27] 3. results and discussion the section is divided into two parts: the first corresponds to the characterization of the samples of the granular subbase and recycled aggregates and the second part corresponds to the characterization of the granular subbase (gsb) mixed with coarse recycled concrete aggregate (rca) at 10 and 15% with respect to their dry mass. 3.1 characterization tests on natural and recycled aggregates (a) granulometry test the granulometry test was carried out including sieves from 1 1/2" to no. 200. fig. 2 presents the granulometry curve of the three samples evaluated for (a) natural aggregates (na) and (b) rca, including the limits established for gsb with 37.5 mm (gsb38) as nominal maximum size [28]. the natural aggregate complies with the granulometry parameter for gsb38 (dashed red and blue lines), showing a curve within the range established by the standard. considering the crushing method used for the rca, it was to be expected that its granulometry would not comply with the parameters established for gsb38. therefore, the rca should be blended with the necessary sizes so that its particle size complies with the range established by the standard [28] or it can be used as a partial replacement in granular 62 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 layers as analyzed in this work. in addition, fig. 3 shows the particle size distribution of one of the rca samples evaluated. (a) (b) fig. 2: granulometry curve of (a) na and (b) rca. fig. 3: particle size distribution of one of the rca samples evaluated. (b) density, relative density and absorption test considering that absorption is one of the properties that most affects the behavior of the rca and therefore of the mixtures where they are replaced [10]; density, relative density and absorption tests were carried out on the coarse fraction of the rca. 0 10 20 30 40 50 60 70 80 90 100 0.00.11.010.0 p er ce n ta g e p a ss in g ( % ) sieve size (mm) na granulometry curve sample 1 sample 2 sample 3 lower limit gsb38 upper limit gsb38 0 10 20 30 40 50 60 70 80 90 100 0.00.11.010.0 p er ce n ta g e p a ss in g ( % ) sieve size (mm) rca granulometry curve sample 1 sample 2 sample 3 lower limit gsb38 upper limit gsb38 63 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 table 2: density, relative density, and absorption results of coarse rca. a = mass of oven-dry test sample in air; b = mass of saturated-surface-dry test sample in air; c = apparent mass of saturated test sample in water specimen a [g] b [g] c [g] relative density (od) relative density (ssd) apparent relative density absorption [%] 𝑨 (𝑩 − 𝑪) 𝑩 (𝑩 − 𝑪) 𝑨 (𝑨 − 𝑪) [ (𝑩 − 𝑨) 𝑨 ] 𝒙𝟏𝟎𝟎 1 5072 5253 3035 2.29 2.37 2.49 3.57 2 5050 5251 3101 2.35 2.44 2.59 3.98 3 5010 5201 3089 2.37 2.46 2.61 3.81 the oven-dry (od), saturated-surface-dry (ssd), apparent relative density, and absorption results of the three samples evaluated are shown in table 2. these agree with those reported in the literature. where od is in the range of 2.20 to 2.40, ssd between 2.31 and 2.68, apparent between 2.42 and 2.70, and absorption between 1.43 and 8.05 for the coarse fraction of rca [14], [22], [30], [31]. (c) atterberg limits and plasticity test atterberg limits and plasticity index tests were performed on three samples of na and rca. the results show a non-plastic behavior for the na and slightly plastic for the rca. specifically, the rca results show a liquid limit (ll) of 33.54% and a plastic limit (pl) of 2.24% on average, complying with gsb38 standards [28]. (d) specific gravity test the specific gravity of three samples of fine rca were evaluated and the results show an average of 2.64. this agrees with the literature which shows a range of 2.14 to 2.65 for this property in fine rca [14]. (e) la abrasion test la abrasion tests were performed on three samples of na and rca. the results were compared as a measure of resistance and are shown in fig. 4. the figure shows the requirements for low (nt1), medium (nt2) and high (nt3) traffic levels for gsb38 [28], and both materials fulfill it. specifically, the limit for the different transit levels is a loss in abrasion of 50%. an average of 30.86 and 35.72% in abrasion loss were obtained for the na and rca, respectively. the results agree with those reported in the literature. it is stated that the rca has lower resistance in la abrasion test than the na [17], [22] and shows weight loss between 27.3 and 39.0% [14]. 3.2 characterization tests on gsb with rca replacements once the materials (natural and recycled) were characterized by the physical and mechanical properties tests described above, the evaluation of the alternative scenarios continued. the mechanical evaluation of the alternatives and their comparison with the base scenario was carried out based mainly on the results of the la abrasion test. properties such as granulometry and plasticity were also evaluated and compared according to gsb38 standards [28]. 64 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 fig. 4: la abrasion test results for na and rca. the alternative scenarios correspond to 10 and 15% coarse rca replacements. it should be noted that these percentages were determined considering the literature [14], [17], [22]. for both replacements, 10 and 15% coarse rca, three samples were evaluated for the granulometry test. as shown in fig. 5, the granulometry curve of both alternatives of rca replacement comply with gsb38 standards (dashed red and blue lines) [28]. a similarity in the granulometric curves was observed, as the size distributions remained similar, varying mainly in the percentage of rca substitution. (a) (b) fig. 5: granulometry curve of na with (a) 10% and (b) 15% coarse rca. for plasticity, no significant changes were observed due to the influence of the rca replacements. for both alternatives, slightly plastic behavior is found, with pl of around 2.5% on average. this satisfies the standards for gsb38, established as a maximum of 6% [28]. 36.37 36.44 34.37 31.06 30.92 30.61 0 10 20 30 40 50 60 sample 1 sample 2 sample 3 % a b r a s io n la abrasion test results for rca and na specimen rca specimen na nt1, nt2, nt3 maximun 0 10 20 30 40 50 60 70 80 90 100 0.00.11.010.0 p e rc e n ta g e p a ss in g ( % ) sieve size (mm) 10%rca granulometry curve sample 1 sample 2 sample 3 lower limit gsb38 upper limit gsb38 0 10 20 30 40 50 60 70 80 90 100 0.00.11.010.0 p e rc e n ta g e p a ss in g ( % ) sieve size (mm) 15%rca granulometry curve sample 1 sample 2 sample 3 lower limit gsb38 upper limit gsb38 65 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 comparing the results of the la abrasion test (fig. 6), it is observed that the 15% rca mixes show a weight loss 2.27% higher than the 10% rca mixes, on average. on average, values of 29.80 and 32.07% in abrasion loss were obtained for 10 and 15% rca replacement, respectively. in addition, the replacement of 15% rca decreases the la abrasion resistance when compared to the natural sample. whereas, with the 10% rca replacement, a small increase in this property is observed. fig. 6: la abrasion test results for 10% and 15% rca replacement. it is observed in fig. 6 that the highest value obtained for abrasion with 10% rca is 30.86% while the lowest value is 29.21%. when analyzing the 15% rca replacement, it is observed that the highest value is 32.32% compared to the minimum which is 31.75%. these values are very similar in the literature, which are less than 35% [14], [22]. however, both alternatives comply with the requirement for gsb38 [28] established as a maximum of 50% for the different levels of traffic (low: nt1, medium: nt2, high: nt3). subsequently, table 3 contains the average percentage results of la abrasion loss and differences found when comparing the results of the alternative scenarios versus the na. this indicates that, for replacements higher than 10% rca, the abrasion resistance of the granular layer decreases. wider replacement rates should be evaluated to determine an optimal replacement range. table 3: average percentage results of la abrasion loss and differences between na and alternative scenarios average results (%) difference (%) na 30.86 10%rca 29.80 1.06 15%rca 32.07 -1.21 finally, fig. 7 presents the ratio between la abrasion tests with 10% and 15% rca replacements with respect to the result obtained for na (i.e., la abrasion with replacement with rca/la abrasion with na). therefore, greater values than 1 represent negative influence; lower than 1 suggests a positive influence, and a value equal to 1 represents null influence. 30.86 29.33 29.21 31.75 32.32 32.15 0 10 20 30 40 50 60 sample 1 sample 2 sample 3 % a b r a s io n la abrasion test results for 10% and 15%rca replacement specimen 10% rca specimen 15% rca nt1, nt2, nt3 maximun 66 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 the results show that with a replacement of 10% rca, values lower than the reference value (1) are obtained, which are related to a reduction in the abrasion. on the other hand, a replacement with a 15% rca suggests values higher than 1, demonstrating an increase in abrasion. fig. 7: ratio la abrasion test results for 10% and 15% coarse rca replacement. analyzing the values presented in fig. 7, it is observed that for 10% rca a maximum ratio of 0.99 and a minimum of 0.95 was obtained, while for 15% rca the maximum value was 1.05 and the minimum was 1.02. this shows that there is a trend of decreasing abrasion when gsb is replaced with 10% rca. when analyzed with 15% rca replacement, an upward trend in abrasion loss is obtained. consequently, the abrasion values increase when 15% rca replacement is reached and decreases for 10% rca. thus, an optimum value can be found between the percentage of rca and the maximum decrease of abrasion as evidenced in the literature [14], [22]. 3.3 environmental results environmental impacts were calculated by a life cycle analysis (lca) using the palate 2.0 tool. it was carried out considering as a base scenario the construction of a pavement with a 100% natural gsb, and as alternative scenarios substitutions of 10% and 15% in the same granular layer were evaluated. in this study, the functional unit was defined as the construction of the gsb of a typical colombian road section: 1 km in length and 1 lane of 3.5 m wide. considering the typical conditions of the area and the regulations [28], the following design characteristics were established: (1) a traffic value of 5×106 equivalent single axle load (esal) of 80 kn; (2) cbr of 30%; (3) service life of 10 years; (4) a gsb modulus of 200 mpa. considering the above, 22 cm was considered as the gsb thickness. therefore, the construction of 770 m3 of gsb was evaluated for both the base and alternative scenarios. the palate 2.0 tool evaluates 12 environmental impacts, considering the stages of materials production, materials transportations and processes (equipment). it is important to highlight that in this study hauling distances were not considered, with the purpose of only considering the replacement of the rca as a variable. thus, the environmental impacts are related to materials production and processes (equipment). in addition, of the 12 impacts, the following impacts were considered: energy (mj), water consumption (kg), co2 (kg), particulate matter with a diameter of 10 microns or less pm10 (kg), and co (kg). the results presented in table 4 suggest that the use of rca as a replacement in gsb implies a significant increase in energy consumption and water consumption. this would 0.99 0.95 0.95 1.02 1.05 1.05 0.88 0.90 0.92 0.94 0.96 0.98 1.00 1.02 1.04 1.06 sample 1 sample 2 sample 3 % a b r a s io n ratio la abrasion test results for 10% and 15%rca replacement specimen 10% rca specimen 15% rca reference value 67 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 be related to the activities involved in the rca production process [10], [17]. in turn, this represents an increase in emissions of the different impacts evaluated. specifically, the lca results show an increase of 50% and 75% in energy consumption by comparing the base scenario with 10 and 15% rca replacement, respectively. this leads to an increase of 40 and 80% in co emissions for 10 and 15% rca replacement respectively, and 100% in co2 emissions for both alternative scenarios. in terms of pm10 emissions, a 50% increase was observed when comparing the base scenario with 15% rca replacement. table 4: environmental results of base and alternatives scenarios energy [mj] water consumption [kg] co2 [kg] pm10 [kg] co [kg] 100% na 13669 1 1000 2 5 10%rca 20504 1 2000 2 7 15%rca 23922 1 2000 3 9 the environmental results contrast with those reported in the literature. it has been established that the use of rca tends to represent a saving in emissions of different pollutants. savings of 16% in co2 generation are reported when comparing the production of na versus a mixture of 70% na and 30% rca [17]. in addition, significant savings in co emissions and energy consumption have also been found when evaluating the use of rca replacements in pavement structures [13]. however, when high percentages of rca (45% replacement) are analyzed, increases of 20% in co2 generation and 10% in emissions of particulate matter with a diameter of 2.5 microns or fewer of pm2.5 have been found [10]. also, increases in impacts such as climate change and eutrophication have been reported by including rca in concrete [21]. in general, environmental impacts are sensitive to the percentage of replacement and hauling distances of rca, so the use of rca does not necessarily imply environmental savings [10], [21]. thus, the environmental results are a function of the case study conditions and characteristics such as the functional unit evaluated. 4. conclusions the performance of natural aggregates with 10 and 15% replacement of coarse recycled concrete aggregate (rca) was evaluated for use as granular subbase (gsb) in colombia as a tropical area. initially, the physical and mechanical characterization of both materials (natural and recycled) was carried out considering granulometry, absorption, atterberg limits test, plasticity, specific gravity, and los angeles la abrasion test. at least three samples of each material were considered for each test. noting that with the number of samples evaluated for each test, a clear trend in the results was observed. then, results of natural aggregates (na) versus 10 and 15% rca replacement as alternative scenarios were evaluated and compared. the main comparison was based on the resistance of the samples in the la abrasion test. this is because abrasion is a determining property in the strength of these materials, however few studies have focused on its influence [14], [22]. therefore, the objective of the research is to evaluate how aggregate abrasion varies when a significant percentage of rca is added. 68 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 all results were compared with the gsb with 37.5 mm (gsb38) as nominal maximum size standards according to colombian regulations. this is because gsb38 is the typical gsb in the area. in addition, a simple life cycle assessment (lca) was included to evaluate the environmental impacts of the base and alternative scenarios. the lca was conducted considering materials production and processes (equipment) stages and including 5 environmental impacts: energy (mj), water consumption (kg), co2 (kg), particulate matter with a diameter of 10 microns or less pm10 (kg) and co (kg). based on the conditions and results of the study, the following can be concluded: • the granulometry of the na complies with gsb38 standards, while the rca shows a curve outside the range stipulated by the standard [28]. therefore, the rca would have to be mixed with other aggregates to achieve an acceptable granulometry curve. • the densities and absorption of the fine rca agree with those reported in the literature [14], [22], [30], [31]. with averages of 2.34, 2.42, 2.56 and 3.79% for od, ssd, apparent, and absorption, respectively. • the plasticity of the rca complies with gsb38 standards, showing an average result of 2.24%. for the na, a plastic limit (pl) showing non-plastic behavior was obtained. • the specific gravity of the fine rca agrees with the literature [14], showing an average value of 2.64. • the results of the la abrasion test comply with the standards for both materials. as expected, a higher loss is observed in the rca. specifically, an average weight loss of 30.86% was found for the na and 35.72% for the rca. • when evaluating the 10 and 15% rca replacements, the granulometry curves complied with gsb38 standards; the plasticity did not show major changes and complies with the requirement for this property in gsb38 too [28]. • the results of the la abrasion test show that gsb with 15% rca has higher losses than that with 10% rca. specifically, it is observed that the 15% rca mixes show a weight loss 2.27% higher than the 10% rca mixes, on average. • on average, values of 29.80 and 32.07% abrasion loss were obtained for 10 and 15% rca replacement, respectively. • the replacement of 15% rca decreases the la abrasion resistance compared to the natural sample. whereas, with 10% rca substitution, a small increase in this property is observed compared to the natural sample. • for replacements higher than 10% rca, the abrasion resistance of the granular layer decreases. wider replacement rates should be evaluated to determine an optimal replacement range. • the environmental results show that the use of rca as a replacement in gsb implies a significant increase in energy consumption and water consumption. in turn, this represents an increase in emissions of the different impacts evaluated. this would be related to the activities involved in the rca production process [10], [17]. • specifically, the lca results show an increase of 50% and 75% in energy consumption by comparing the base scenario with 10 and 15% rca replacement, respectively. this leads to an increase of 40 and 80% in co emissions for 10 and 15% rca replacement respectively, and 100% in co2 emissions for both alternative scenarios. 69 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 acknowledgement we are grateful to the universidad del norte for its support in processing the recycled concrete aggregate (rca) and to ingecost s.a. for supplying the natural aggregates (na) for the research. references [1] tahmoorian f, samali b, yeaman j, mirzababaei m. (2022) evaluation of volumetric performance of asphalt mixtures containing recycled construction aggregate (rca). international journal of pavement engineering, 23(7): 2191-2205. https://doi.org/10.1080/10298436.2020.1849686 [2] tahmoorian f, samali b. (2017) experimental and correlational study on the utilisation of rca as an alternative coarse aggregate in asphalt mixtures. australian journal of civil engineering, 15(2): 80-92. [3] daquan s, yang t, guoqiang s, qi p, fan y, xingyi z. (2018) performance evaluation of asphalt mixtures containing recycled concrete aggregates. international journal of pavement engineering, 19(5): 422-428. [4] ogbonna ac. (2018) laboratory evaluation of the characteristics of continuously reinforced concrete pavement incorporating recycled concrete aggregate. australian journal of civil engineering, 16(1): 38-45. [5] jindal a, ransinchung rn-gd, kumar p. (2017) study of pavement quality concrete mix incorporating beneficiated recycled concrete aggregates. road materials and pavement design, 18(5): 1159-1189. [6] cai x, wu k, huang w, yu j, yu h. (2021) application of recycled concrete aggregates and crushed bricks on permeable concrete road base. road materials and pavement design, 22(10): 2181-2196. [7] lopez-uceda a, ayuso j, jiménez jr, galvín ap, del rey i. (2020) feasibility study of roller compacted concrete with recycled aggregates as base layer for light-traffic roads. road materials and pavement design, 21(1): 276-288. [8] aghililotf m, palassi m, ramezanianpour am. (2021) mechanical and durability assessment of unconfined recycled concrete aggregates and natural aggregates used in road constructions. international journal of pavement engineering, 22(12): 1518-1530. [9] toka eb, olgun m. (2021) performance of granular road base and sub-base layers containing recycled concrete aggregate in different ratios. international journal of pavement engineering, 1-14. doi 10.1080/10298436.2021.1916819 [10] vega a dl, santos j, martinez-arguelles g. (2022) life cycle assessment of hot mix asphalt with recycled concrete aggregates for road pavements construction. international journal of pavement engineering, 23(4): 923-936. [11] martinez-arguelles g, coll md, pumarejo lgf, cotte ehs, rondon h, pacheco ca, ... & espinoza rgl. (2019) characterization of recycled concrete aggregate as potential replacement of natural aggregate in asphalt pavement. in iop conference series: materials science and engineering, 471(10): 102045. [12] vega a dl, gilberto ma, dos santos jm. (2019) life cycle assessment of warm mix asphalt with recycled concrete aggregate. in iop conference series: materials science and engineering, 603(5): 052016. [13] devaki h, shanmugapriya s. (2022) lca on construction and demolition waste management approaches: a review. materials today: proceedings. https://doi.org/10.1016/j.matpr.2022.03.286 [14] aytekin b, mardani-aghabaglou a. (2022) sustainable materials: a review of recycled concrete aggregate utilization as pavement material. transportation research record, 2676(3): 468-491. 70 iium engineering journal, vol. 23, no. 2, 2022 vega a. et al. https://doi.org/10.31436/iiumej.v23i2.2367 [15] kim j. (2022) influence of quality of recycled aggregates on the mechanical properties of recycled aggregate concretes: an overview. construction and building materials, 328: 127071. [16] colangelo f, forcina a, farina i, petrillo a. (2018) life cycle assessment (lca) of different kinds of concrete containing waste for sustainable construction. buildings, 8(5): 70. [17] martinez-arguelles g, acosta mp, dugarte m, fuentes l. (2019) life cycle assessment of natural and recycled concrete aggregate production for road pavements applications in the northern region of colombia: case study. transportation research record, 2673(5): 397406. [18] kadawo a, sadagopan m, during o, bolton k, nagy a. (2021) combination of lca and circularity index for assessment of environmental impact of recycled aggregate concrete. journal of sustainable cement-based materials, 1-12. https://doi.org/10.1080/21650373.2021.2004562 [19] nayana ay, kavitha s. (2017). evaluation of co2 emissions for green concrete with high volume slag, recycled aggregate, recycled water to build eco environment. int. j. civ. eng. technol, 8: 703-708. [20] kurda r, silvestre jd, de brito j. (2018) life cycle assessment of concrete made with high volume of recycled concrete aggregates and fly ash. resources, conservation and recycling, 139: 407-417. [21] yazdanbakhsh a, bank lc, baez t, wernick i. (2018) comparative lca of concrete with natural and recycled coarse aggregate in the new york city area. the international journal of life cycle assessment, 23(6): 1163-1173. [22] verian kp, ashraf w, cao y. (2018) properties of recycled concrete aggregate and their influence in new concrete production. resources, conservation and recycling, 133: 30-49. [23] bico braun international, manufacturers of mining and geological laboratory test equipment. [www.bicoinc.com]. [24] astm (2010). standard test methods for specific gravity of soil solids by water pycnometer d854. [25] astm (2012). standard test method for density, relative density (specific gravity), and absorption of coarse aggregate c127. [26] astm (2010). standard test methods for liquid limit, plastic limit, and plasticity index of soils d4318. [27] astm (2009). standard test methods for particle-size distribution (gradation) of soils using sieve analysis d6913. [28] astm (2010). standard test method for resistance to degradation of small-size coarse aggregate by abrasion and impact in the los angeles machine c131 [29] invias (2013). capítulo 3-afirmados, subbases y bases art. 300 disposiciones generales para la ejecución de afirmados, sub-bases y bases granulares y estabilizadas [30] kurda r, de brito j, silvestre jd. (2017) influence of recycled aggregates and high contents of fly ash on concrete fresh properties. cement and concrete composites, 84: 198-213. [31] pickel d, tighe s, west js. (2017) assessing benefits of pre-soaked recycled concrete aggregate on variably cured concrete. construction and building materials, 141: 245-252. 71 http://www.bicoinc.com/ application of digital cellular radio for mobile location estimation iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 design and implementation of twophase interleaved voltage source inverter for pv applications harika sridharan, seyezhai ramalingam department of electrical and electronics engineering, ssn college of engineering, chennai, india. *corresponding author: sriharkal@gmail.com (received: 10th march 2018; accepted: 29th june 2019; published on-line:2nd december 2019) abstract:the design of a voltage source inverter is challenging for pv-grid connected systems due to power quality issues. to improve the power quality,a two-phase interleaved voltage source inverter (ivsi) is proposed in this paper. ivsi phase shifts two voltage source inerters connected in parallel. the inverter topology is interfaced with a 40w pv panel employing a multiple maxima search (mms) mppt algorithm. this algorithm results in higher tracking efficiency compared to existing methods. modelling of the pv with mppt and the circuit configuration of the interleaved inverter is simulated in matlab/simulink. the switches in the ivsi is controlled by employing a unipolar pwm technique. the performance of the ivsi is investigated in terms of weighted total harmonic distortion (wthd), distortion factor (df), harmonic spread factor (hsf), and inductor current ripple and compared with classical vsi. from the analysis, it is inferred that the proposed inverter results in reduced total harmonic distortion(thd) and decreased inductor current ripple thereby producing a high-quality output. the hardware model of the two-phase ivsi is developed and interfaced with pv where gating pulses are generated in fpga. the simulation results are validated experimentally. abstrak: rekaan pembalik sumber voltan adalah mencabar pada sistem gabungan gridpv disebabkan isu kualiti tenaga. bagi memperbaharui kualiti tenaga, pembalik sumber voltan antara lembar dua-fasa (ivsi) telah dicadangkan dalam kajian ini. anjakan fasa ivsi pembalik sumber voltan dua-fasa telah dihubungkan secara selari. topologi pembalik telah diantaramukakan dengan 40w panel pv dengan mengunakan carian maksima berganda (mms) algoritma mppt. hasil algoritma menunjukkan lebih tinggi keberkesanan dibandingkan dengan kaedah sedia ada. pv model dengan mppt dan konfigurasi litar pembalik antaramuka telah disimulasi menggunakan matlab/simulink. suis dalam ivsi dikawal dengan menggunakan teknik pwm unipolar. dapatan kajian ke atas ivsi adalah berdasarkan berat pengherotan total harmoni (wthd), faktor pengherotan (df), faktor sebaran harmoni (hsf), getaran arus pembalik dan dibandingkan dengan kaedah klasik vsi. analisis menunjukkan kesimpulan dapatan kajian ke atas pembalik yang dicadangkan telah berkurang jumlah pengherotan harmoni (thd) dan getaran arus pembalik telah berkurang, oleh itu menghasilkan hasil akhir yang berkualiti tinggi. model perkakasan ivsi dua-fasa telah dibangunkan dan diantaramukakan dengan pv di mana signal pengegetan dihasilkan dalam fpga. dapatan hasil simulasi telah disahkan secara eksperimen. keywords:ivsi; total harmonic distortion(thd);ripple; mppt 127 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 1. introduction nowadays, renewable energy has been employed for various applications in order to meet the electricity demand and in particular, solar pv power generation is mostly used due to its eco-friendly nature and abundant availability [1]. the difficulty with this power generation is tracking peak power. to obtain maximum power from pv, various maximum power point algorithms have been investigated in the research work. [2]. the traditional mppt algorithms are perturb-and-observe (p&o), incremental conductance (inc), fractional open circuit voltage, fractional short circuit current, and current sweep. the p&o and inc suffer from the drawback that they lose the mpp tracking if the solar irradiation varies rapidly. existing fractional open circuit voltage and fractional short circuit current have the same drawback as their mpp tracking is not real, leaving the computation based on approximation. the sweep waveform of the pv array current is used in the case of the current sweep tracking method, which obtains mpp if the sweep is instantaneous but is difficult to apply in practical situations. thus the traditional algorithms fail to find global mpp under variable irradiation conditions [3]. thus, this research work proposes a mms algorithm that follows the direct search technique (dst) to track a maximum operating point that overcomes the cons of the traditional mppt algorithms. dst samples the sampling interval by assuming one point to be the center, dividing that intotwo intervals, and proceeding in the same way for the other intervals[4, 5]. in this way, an optimum operating point is obtained. with this mms algorithm, high tracking efficiency can be achieved even in a partially shaded condition. tracking efficiency of 97% is achieved with dst, based on the dividing rectangle algorithm. it is also possible to achieve a tracking efficiency of 99 % if this direct search algorithm is employed to get a globalpoint alongwith the traditional algorithm. thus, the mms mppt algorithm is implemented, as itis suited for pv [6, 7]. a voltage source inverter is the most commonly used interface circuit for pv [8] but it suffers from various issues like high thd and high inductor current ripple content. thus, this research work focuses on interleaving two voltage source inverters, known as the twophase interleaved voltage source inverter (ivsi) [9]. ivsi is defined as a parallel operation of two voltage source inverters with an interleaving angle (κ) that is chosen based on the equation given by, κ = (1) where, n = number of the inverter connected in parallel. the paper deals with twoinverters connected in parallel (n = 2). from equation (1), it is found that the interleaving angle is 180 degrees. the performance of the vsi depends upon the control strategy [10]. so, the proposed topology is investigated with different modulation strategies such as fundamental frequency switching, unipolar sine pwm, and space vector modulation. the performances of ivsi with different modulation strategies are compared and unipolar spwm was found to have low thd and reduced inductor current ripple [11]. thus, to improve the powerquality of the waveform, ivsi with unipolar spwm technique is studied in matlab/simulink. finally, a prototype model of the two-phase interleaved voltage source inverter is built and interfaced with a 40w solar panel. the schematic block diagram of the overall work is depicted in fig.1. the performance parameters computedfor comparisonare total harmonic distortion (thdv) and inductor current ripple. from the results, it is found that the two-phase ivsi has less thd and reduced inductor current ripple compared to traditional vsi. 128 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 fig.1: block diagram of the proposed work. 2. two-phase interleaved voltage source inverter the main feature of the two-stage ivsi is that it eliminates the zero voltage level, which is present in conventional voltage source inverters [12,13]. with the single-level inverter, the voltage levels are +vdc/3, 0, -vdc/3 but with a two-levelinverter, the voltage levels are +vdc/2 and -vdc/2. this shows that ivsi suits the pv application [14]. the circuit diagram of the proposed parallel connected voltage source inverter is shown in fig.2. fig.2: circuit diagram of the parallel connected voltage source inverter. figure 2 shows that the two voltage source inverters are parallel through the filter inductance and connected to the grid. the operation of the ivsi is elaborated into six periods, t1 to t6. the switching states are different for different intervals [15, 16]. during t1, the inductor voltage is zero if a single inverter is employed whereas, with two parallel connected inverters, the voltage across the inductor is vdc/2. similarly, during t2, if a single inverter is employed, the inductor voltage will be -vdc/3 whereas for interleaved inverter the voltage level will be vdc/2. thus, the zero voltage level is eliminated in the interleaving operation of the vsi. the circuit diagram of the interleaved vsi during t1 and t2 is depicted in fig.3. 3. modulation strategies the proposed two-stage ivsi is analyzed with different modulation strategies such as fundamental frequency switching, unipolar spwm, and space vector modulation [17]. the results of the different modulation strategies are compared in terms of current thd (total harmonic distortion) and inductor current ripple content [18]. from the comparison, the unipolar spwm is chosen since it has low thdi and reduced ripple content. then, the outputs of the interleaved inverter and conventional voltage source inverter are compared to prove that the proposed inverter topology has low thd, has low filter requirements, and operates at a high switching frequency. pv 129 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 (a) (b) fig.3: operation of the proposed inverter (a) during t1 and (b) during t2. the unipolar pwm requires one sinusoidal reference waveform and one triangular carrier waveform. the switches in the same leg are triggered in a complementary manner with one switch turned on and other switch turned off [19]. thus, only the gating pattern of the upper switch is considered. the three sinusoidal waveforms with 120-degree phase shift are compared with the triangular carrier waveform for vsi1 as depicted in fig. 4, whereas for vsi2 , the three reference sinusoidal waveform is compared with the 180 degree phase shifted carrier waveform. the pulse pattern for two-stage interleaved vsi is shown in fig.5. s1, s2, and s3 denote pulse output for vsi1 and s1',s2',and s3' denote pulse output for vsi2. fig.4: reference and carrier waveforms for unipolar pwm. fig.5: gating pattern of ivsi. a2 b2 c2 c1b1a1 a2 b2 c2 c1b1a1 130 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 4. simulation results the interleaved voltage source inverter has been simulated in matlab/simulink and the various pwm strategies have been implemented. the simulation model is depicted in fig.6 and the simulation parameters are shown in table. 1. the output voltage of the interleaved inverter is shown in fig.7. table 1: simulation parameters parameter values dc voltage(vdc ) 400 v inductor(l) 50mh modulation index (ma) 0.8 switching frequency 1050 hz interleaving angle 180 degree fig.6: simulink model of the proposed two-stage ivsi. fig. 7: output voltage of the parallel connected vsi. 131 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 table 2: comparison of different modulation strategies for the interleaved inverter modulation techniques thdi% ilr unipolar spwm 0.97 lia =0.82, l ib =0.82, l ic = 0.82 fundamental frequency switching 1.07 lia = 1.46, l ib = 1.38, l ic = 1.20 space vector pwm 2.92 lia = 2.59, l ib = 2.60, l ic = 2.59 table 3: comparison of interleaved inverter and conventional vsi modulation techniques thdi% ilr conventional single-stage voltage source inverter 2.33 l ia = 2.33, l ib = 2.33, l ic = 2.32 unipolar spwm 0.97 lia = 0.82, l ib = 0.82, l ic = 0.82 the comparison of the simulation results are depicted in table 2 and table3, showing that the two-stage ivsi with unipolar pwm has low thd and reduced ripple content compared to single-stage vsi. thus, the performance of the proposed topology with unipolar spwm is analysed for different modulation indexes. the performance parameters are total harmonic distortion(thd), weighted total harmonic distortion(wthd), distortion factor(df), and harmonic spread factor(hsf). 4.1 total harmonic distortion (thd) a deviation in the shape of an obtained waveform from its fundamental component is called total harmonic distortion, the expression for thd is thd = (2) where(v0)n = rms value of the harmonic component, (v0)1= rms value of the fundamental component. 4.2 weighted total harmonic distortion (wthd) evaluating the quality of pulse width modulation (pwm) inverter waveforms is commonly called a weighted total harmonic distortion (wthd). the frequency and the measured voltage harmonics are inversely proportional to each other. wthd = (3) 4.3 distortion factor (df) the distortion factor is a measure of the intensity of the deviations of the measured waveform from its fundamental waveform and the mathematical expression of the df is df = (4) 132 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 wherev1 = fundamental voltage, vn = total harmonics voltage, n = order of the harmonics. 4.4 harmonic spread factor(hsf) harmonic spread factor defines the noise generation level in the motor and measures the voltage spectrum quality of the inverters. hsf = (5) where hj= value of jth harmonic, h0 = average value of all n harmonics. fig. 8: performance analysis of the interleaved vsi. from fig. 8, it is proven that the total harmonic distortion(thd), weighted total harmonic distortion(wthd), distortion factor(df), and harmonic spread factor(hsf) are low at a modulation index of 0.8. hence, 0.8 is chosen as the modulation index for the proposed topology. 0 100 200 300 0 0.5 1 thdv thdv 0 0.2 0.4 0.6 0 0.5 1 thdi thdi 0 0.001 0.002 0.003 0.004 0.005 0.006 0 0.5 1 wthd wthd 0 0.000002 0.000004 0.000006 0.000008 0.00001 0.000012 0 0.5 1 df df 0 0.2 0.4 0.6 0.8 0 0.5 1 hsf hsf 133 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 5. interface of interleaved vsi with pv a pv panel is modeled in matlab/simulink. the parameters are obtained from the pv panel datasheet and the important electrical parameters need to be considered to get electrical characteristics of the pv panel for the open-circuit voltage and the short-circuit current [20]. practically, v-i and p-v characteristics are observed for a 40w solar panel as shown in fig.9. fig. 9: v-i and p-v characteristics of pv model for 40w panel. to track the maximum power from the pv, a mms mppt algorithm is used. the direct search technique based on the dividing rectangle strategy is clearly explained in fig.10. fig.10: dividing rule. figure 10 shows that v1 is taken as a sample and assumed as its centerpoint. when compared to v1 and v2, v3 has the maximum peak and it is further divided into three samples as v31, v3,and v32. by doing so, the mms mppt algorithm tracks the maximum power, even under the partially shaded condition, and reaches a high tracking efficiency of 97%. the results are compared with the traditional perturb-and-observe method. both mms and p&o algorithms are modelled in matlab/simulink and results are shown in fig. 11. from fig.11,tracking efficiency is calculated: with multiple maxima search mppt, tracking efficiency = = 92% 0 0.5 1 1.5 2 2.5 3 0 20 40 vi characteristics vi character istics 0 10 20 30 40 50 0 20 40 pv characteristics pv character istics 134 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 fig.11: actual power and tracked power. with perturb-and-observe, tracking efficiency = = 75% thus, it is proven that the multiple maxima search mppt has high tracking efficiency compared to a traditional algorithm. the overall circuit diagram of the proposed interleaved inverter interfaced with pv panel and output is shown in fig.12 and fig.13. fig.12: pv interfaced with ivsi. fig.13: output voltage (filtered output) of inverter interfaced with pv. 0 10 20 30 40 50 60 0 0.05 0.1 0.15 pando maxima actual power 135 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 6. hardware results the two-stage ivsi with unipolar spwm is implemented in hardware, which includes a gating circuit, pulse generation using fpga-spartan 3e, and design and development of a three phase two-stage interleaved voltage source inverter. the gating for the two-stage interleaved voltage source inverter is generated using xilinx spartan 3e fpga. the generated pulse is given to the switch (mosfet irf 840) using an optocoupler ic (tlp 350). the gating circuit is important for providing gate pulses to switches used in the inverter in order to isolate the low power control circuit and the high power inverter circuit. the pulse generated by fpga is given through the gating circuit. the logic for pulse generation of the proposed inverter is shown in figs.14 16. fig.14: sine wave generation. fig.15: triangular wave generation. (a) switch s1 (b) switch s2 fig.16: gating pulse for interleaved vsi. 136 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 figure 17 shows the prototype model of a two-stage interleaved voltage source inverter with gating circuit. the line-to-line voltage of the ivsi has a thd of 6.576% and its bar graph representation is shown in fig.18.the phase voltage of the interleaved vsi has a thd of 6.58% and its bar graph representation is shown in fig.19. fig.17: a prototype model of a two-stage ivsi. (a) (b) (c) (d) fig.18: (a) the output voltage of proposed inverter with filter (b) line-to-line voltage of interleaved voltage source inverter (c) line-to-line voltage thd (d) bar graph representation of voltage thd. 137 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 (a) (b) (c) fig.19: (a) phase voltage of interleaved voltage source inverter (b) phase voltage thd (c) bar graph representation of voltage thd. (a) (b) fig.20: (a) inductor current (b) inductor current ripple. 138 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 from fig.20, it is clear that the proposed interleaved vsi has a lower filter inductor current ripple of 10.747%. fig.21: two-stage vsi is interfaced with pv panel figures 18 20 prove that the proposed two-phase interleaved voltage source inverter has low thd and reduced inductor current ripple content compared to the conventional voltage source inverter. a prototype model of the interleaved inverter interfaced with pv is shown in fig.21.the comparison of simulation results and hardware results is listed in table 4. table 4: simulation andhardware results parameters simulation results hardware results thd (%) 4.1 6.58 inductor current ripple (%) 0.82 10.47 from table 4, it is found that the proposed two-phase interleaved vsi has reduced thd (6.58%) and lower inductor current ripple (10.47%). thus the simulation results are validated through a prototype model. 7. conclusion a two-stage interleaved vsi is studied and analyzed with different modulation strategies. the results of different modulation strategies are compared and it is concluded that the unipolar pwm has lower thd and reduced ripple content in comparison to the other techniques. then, the two-stage vsi and traditional vsi are analyzed and it is proven that the interleaved technique had better performance. a prototype model of the two-phase interleaved voltage source inverter is built and interfaced with pv through a charge controller. the simulation results are validated experimentally. hence, the proposed twophase interleaved voltage source inverter topology is an appropriate choice for a pv grid connected system. vsi 1 vsi 2 filter pv panel charge controller 139 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 acknowledgment authors thank the ssn institution for providing the financial support in carrying out this research work. references [1] kenneth j. sauer, thomas roessler, and clifford w. hansen. (2015) modelling the irradiance and temperature dependence of photovoltaic modules in pv syst. ieee journal of photovoltaic, 5(1):152-158. [2] t. esram, p.l. chapman. (2007) comparison of photovoltaic array maximum power point tracking techniques. ieee transactions on energy conversion, 22 (2): 439-449. [3] l. piegari, r. rizzo. (2010) adaptive perturb and observe algorithm for photovoltaic maximum power point tracking. iet renewable power generation, 4 (4): 317-328. [4] weidong xiao, fonkwe fongang edwin, giovanni spagnuolo, jurijatskevich. (2013) efficient approaches for modelling and simulating photovoltaic power systems. ieee journal of photovoltaics, 3 (1):500 508. [5] bader n. alajmi, khaled h. ahmed, stephen j. finney, and barry w. williams. (2013) a maximum power point tracking technique for partially shaded photovoltaic systems in microgrids. ieee transactions on industrial electronics, 60 (4): 1596 1606. [6] francesco adamo, filippo attivissimo, attilio di nisio, and maurizio spadavecchia. (2011) characterization and testing of a tool for photovoltaic panel modelling. ieee transactions on instrumentation and measurement, 60 (5): 1613 1622. [7] shibin qin, stanton t. cady, alejandro d. dominguez -garcia, and robert carl nikolai pilawa-podgurski. (2015) a distributed approach to maximum power point tracking for photovoltaic sub module differential power processing. ieee transactions on power electronics, 30 (4): 2778-2785. [8] feng yang, xu zhao, cong wang, zhifei sun. (2013) research on parallel interleaved inverters with discontinuous space-vector modulation. energy and power engineering, 5(4): 219-225. https://doi.org/ 10.4236/epe.2013.54b043 [9] abusara. mohammad a and sharkh. suleiman m. (2013) design and control of a gridconnected interleaved inverter. ieee transactions on power electronics, 28 (2), 748-764. [10] g. shen, d. xu, l. cao, and x. zhu. (2008) an improved control strategy for grid-connected voltage source inverters with an lcl filter. ieee transaction on power electronics,23 (4):1899–1906. [11] s.harika, dr.r.seyezhai. (2016) analysis of modulation strategies for two-stage interleaved voltage source inverter employed for pv applications. international journal of advanced research in basic engineering sciences and technology (ijarbest), 2 (11):1-12 [12] jonq-chin hwang, po-cheng chen and chuan-sheng liu. (2014) a novel single-phase interleaved bi-directional inverter for grid-connection control. ieee 23rd international symposium on industrial electronics (isie):375-379. https://doi.org/ 10.1109/isie.2014.6864642 [13] christian nemec, jörg roth-stielow. (2011) ripple current minimization of an interleavedswitched multi-phase pwm inverter for three-phase machine emulation. 14th european conference on power electronics and applications (epe):1-8. [14] abusara. m. a, jamil. m, sharkh. m.s. (2012) repetitive current control of an interleaved grid connected inverter. 3rd ieee international symposium on power electronics for distributed generation systems (pedg):558-563. https://doi.org/ 10.1109/pedg.2012.6254057 [15] miss. sangita r nandurkar, mrs. mini rajeev. (2012) design and simulation of three-phase inverter for grid-connected photovoltaic systems. proceedings of third biennial national conference, ncnte:80-83 [16] daniel glose and ralph kennel. (2016) continuous space vector modulation for symmetrical six-phase drives. ieee transactions on power electronics, 31 (5):3837 3848. 140 iium engineering journal, vol. 20, no. 2, 2019 harika and seyezhai https://doi.org/10.31436/iiumej.v20i2.1142 [17] siva prasad. j .s and narayanan. g. (2014) minimization of grid current distortion in parallel-connected converters through carrier interleaving. ieee transactions on industrial electronics, 61 (1), 76 91. [18] brenna. m, chiumeo.r, and gandolfi. c. (2011) harmonic analysis: comparison between different modulation strategies for three-phase inverter connecting distributed generation. ieee international conference on clean electric power(iccep):231-236. https://doi.org/ 10.1109/iccep.2011.6036261 [19] rixin lai, lei wang, juan sabate. (2011) a high-efficiency two-phase interleaved inverter for wide range output waveform generation. ieee energy conversion congress and exposition (ecce):4533-4537. https://doi.org/ 10.1109/ecce.2012.6342204 [20] marcelo gradellavillalva, jonas rafael gazoli, and ernesto ruppertfilho. (2009) comprehensive approach to modeling and simulation of photovoltaic arrays. ieee transactions on power electronics, 24 (5). 141 << /ascii85encodepages false /allowtransparency false /autopositionepsfiles false /autorotatepages /none /binding /left /calgrayprofile (gray gamma 2.2) /calrgbprofile (none) /calcmykprofile (none) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjobticket false /defaultrenderingintent /default /detectblends true /detectcurves 0.0000 /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedopentype false /parseiccprofilesincomments true /embedjoboptions true /dscreportinglevel 0 /emitdscwarnings false /endpage -1 /imagememory 1048576 /lockdistillerparams true /maxsubsetpct 100 /optimize false /opm 0 /parsedsccomments false /parsedsccommentsfordocinfo false /preservecopypage true /preservedicmykvalues true /preserveepsinfo false /preserveflatness true /preservehalftoneinfo true /preserveopicomments false /preserveoverprintsettings true /startpage 1 /subsetfonts false /transferfunctioninfo /remove /ucrandbginfo /preserve /useprologue false /colorsettingsfile () /alwaysembed [ true ] /neverembed [ true ] /antialiascolorimages false /cropcolorimages true /colorimageminresolution 200 /colorimageminresolutionpolicy /ok /downsamplecolorimages true /colorimagedownsampletype /bicubic /colorimageresolution 300 /colorimagedepth -1 /colorimagemindownsampledepth 1 /colorimagedownsamplethreshold 1.50000 /encodecolorimages true /colorimagefilter /dctencode /autofiltercolorimages false /colorimageautofilterstrategy /jpeg /coloracsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /colorimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000coloracsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000colorimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasgrayimages false /cropgrayimages true /grayimageminresolution 200 /grayimageminresolutionpolicy /ok /downsamplegrayimages true /grayimagedownsampletype /bicubic /grayimageresolution 300 /grayimagedepth -1 /grayimagemindownsampledepth 2 /grayimagedownsamplethreshold 1.50000 /encodegrayimages true /grayimagefilter /dctencode /autofiltergrayimages false /grayimageautofilterstrategy /jpeg /grayacsimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /grayimagedict << /qfactor 0.76 /hsamples [2 1 1 2] /vsamples [2 1 1 2] >> /jpeg2000grayacsimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /jpeg2000grayimagedict << /tilewidth 256 /tileheight 256 /quality 15 >> /antialiasmonoimages false /cropmonoimages true /monoimageminresolution 400 /monoimageminresolutionpolicy /ok /downsamplemonoimages true /monoimagedownsampletype /bicubic /monoimageresolution 600 /monoimagedepth -1 /monoimagedownsamplethreshold 1.50000 /encodemonoimages true /monoimagefilter /ccittfaxencode /monoimagedict << /k -1 >> /allowpsxobjects false /checkcompliance [ /none ] /pdfx1acheck false /pdfx3check false /pdfxcompliantpdfonly false /pdfxnotrimboxerror true /pdfxtrimboxtomediaboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxsetbleedboxtomediabox true /pdfxbleedboxtotrimboxoffset [ 0.00000 0.00000 0.00000 0.00000 ] /pdfxoutputintentprofile (none) /pdfxoutputconditionidentifier () /pdfxoutputcondition () /pdfxregistryname () /pdfxtrapped /false /createjdffile false /description << /ara <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> /bgr <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> /chs <feff4f7f75288fd94e9b8bbe5b9a521b5efa7684002000410064006f006200650020005000440046002065876863900275284e8e55464e1a65876863768467e5770b548c62535370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c676562535f00521b5efa768400200050004400460020658768633002> /cht <feff4f7f752890194e9b8a2d7f6e5efa7acb7684002000410064006f006200650020005000440046002065874ef69069752865bc666e901a554652d965874ef6768467e5770b548c52175370300260a853ef4ee54f7f75280020004100630072006f0062006100740020548c002000410064006f00620065002000520065006100640065007200200036002e003000204ee553ca66f49ad87248672c4f86958b555f5df25efa7acb76840020005000440046002065874ef63002> /cze <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> /dan <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> /deu <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> /esp <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> /eti <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> /fra <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> /gre <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> /heb <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> /hrv <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> /hun <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> /ita (utilizzare queste impostazioni per creare documenti adobe pdf adatti per visualizzare e stampare documenti aziendali in modo affidabile. i documenti pdf creati possono essere aperti con acrobat e adobe reader 6.0 e versioni successive.) /jpn <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> /kor <feffc7740020c124c815c7440020c0acc6a9d558c5ec0020be44c988b2c8c2a40020bb38c11cb97c0020c548c815c801c73cb85c0020bcf4ace00020c778c1c4d558b2940020b3700020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200036002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002e> /lth <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> /lvi <feff004c006900650074006f006a00690065007400200161006f00730020006900650073007400610074012b006a0075006d00750073002c0020006c0061006900200069007a0076006500690064006f00740075002000410064006f00620065002000500044004600200064006f006b0075006d0065006e007400750073002c0020006b006100730020007000690065006d01130072006f00740069002000640072006f01610061006900200075007a01460113006d0075006d006100200064006f006b0075006d0065006e0074007500200073006b00610074012b01610061006e0061006900200075006e0020006400720075006b010101610061006e00610069002e00200049007a0076006500690064006f0074006f0073002000500044004600200064006f006b0075006d0065006e00740075007300200076006100720020006100740076011300720074002c00200069007a006d0061006e0074006f006a006f0074002000700072006f006700720061006d006d00750020004100630072006f00620061007400200075006e002000410064006f00620065002000520065006100640065007200200036002e003000200076006100690020006a00610075006e0101006b0075002000760065007200730069006a0075002e> /nld (gebruik deze instellingen om adobe pdf-documenten te maken waarmee zakelijke documenten betrouwbaar kunnen worden weergegeven en afgedrukt. de gemaakte pdf-documenten kunnen worden geopend met acrobat en adobe reader 6.0 en hoger.) /nor <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> /pol <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> /ptb <feff005500740069006c0069007a006500200065007300730061007300200063006f006e00660069006700750072006100e700f50065007300200064006500200066006f0072006d00610020006100200063007200690061007200200064006f00630075006d0065006e0074006f0073002000410064006f00620065002000500044004600200061006400650071007500610064006f00730020007000610072006100200061002000760069007300750061006c0069007a006100e700e3006f002000650020006100200069006d0070007200650073007300e3006f00200063006f006e0066006900e1007600650069007300200064006500200064006f00630075006d0065006e0074006f007300200063006f006d0065007200630069006100690073002e0020004f007300200064006f00630075006d0065006e0074006f00730020005000440046002000630072006900610064006f007300200070006f00640065006d0020007300650072002000610062006500720074006f007300200063006f006d0020006f0020004100630072006f006200610074002000650020006f002000410064006f00620065002000520065006100640065007200200036002e0030002000650020007600650072007300f50065007300200070006f00730074006500720069006f007200650073002e> /rum <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> /rus <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> /sky <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> /slv <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> /suo <feff004b00e40079007400e40020006e00e40069007400e4002000610073006500740075006b007300690061002c0020006b0075006e0020006c0075006f0074002000410064006f0062006500200050004400460020002d0064006f006b0075006d0065006e007400740065006a0061002c0020006a006f0074006b006100200073006f0070006900760061007400200079007200690074007900730061007300690061006b00690072006a006f006a0065006e0020006c0075006f00740065007400740061007600610061006e0020006e00e400790074007400e4006d0069007300650065006e0020006a0061002000740075006c006f007300740061006d0069007300650065006e002e0020004c0075006f0064007500740020005000440046002d0064006f006b0075006d0065006e00740069007400200076006f0069006400610061006e0020006100760061007400610020004100630072006f0062006100740069006c006c00610020006a0061002000410064006f00620065002000520065006100640065007200200036002e0030003a006c006c00610020006a006100200075007500640065006d006d0069006c006c0061002e> /sve <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> /tur <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> /ukr <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> /enu (use these settings to create adobe pdf documents suitable for reliable viewing and printing of business documents. created pdf documents can be opened with acrobat and adobe reader 6.0 and later.) >> >> setdistillerparams << /hwresolution [600 600] /pagesize [595.440 841.680] >> setpagedevice microsoft word 3_v17no2_compiled_v3_26nov16.docx iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 47 performance evaluation of sdn controllers: floodlight and opendaylight shiva rowshanrad*, vajihe abdi and manijeh keshtgari department of computer and information technology, shiraz university of technology, shiraz, iran. *corresponding author: shiva.rrad@gmail.com (received: 27th jan. 2016; accepted: 25t h apr. 2016; published on-line: 30th nov. 2016) abstract: software defined networking (sdn) is a new network architecture. one of its components is the controller, which is the intelligent part of sdn. many controllers such as floodlight, opendaylight, maestro, nox, pox, and others have been released. the question is which controller can perform better in which situations. many works have been done to compare these controllers with respect to architecture, efficiency, and controllers’ features. in this paper, an evaluation based on some network qos parameters is done. two of the most popular controllers, floodlight and opendaylight are compared in terms of delay and loss in different topologies and network loads. this paper can help researchers to choose the best controller in different use cases such as clouds and multimedia. the results, with a 95% confidence interval, show that opendaylight outperforms floodlight in low loaded networks and also for tree topologies in midloaded networks in terms of latency. floodlight can outperform opendaylight in heavily loaded networks for tree topologies in terms of packet loss, and in linear topologies in terms of latency. there is no significant difference in performance of floodlight and opendaylight controllers in other cases. abstrak: software defined network (sdn) adalah seni bina rangkaian baru. salah satu komponennya adalah pengawal, yang merupakan bahagian pintar sdn. banyak pengawal seperti floodlight, open daylight, maestro, nox, pox dan lain-lain telah dikeluarkan. persoalannya ialah pengawal yang mana boleh berfungsi dengan lebih baik di dalam situasi yang mana. banyak kajian telah dibuat untuk membandingkan pengawal mengenai seni bina, kecekapan dan ciri-ciri pengawal. tetapi dalam kertas kerja ini, penilaian berdasarkan beberapa parameter rangkaian qos dilakukan. dua pengawal yang paling popular, floodlight dan opendaylight dibandingkan dari segi kelewatan dan kehilangan di dalam topologi dan muatan rangkaian yang berbeza. kertas kerja ini boleh membantu para penyelidik untuk memilih pengawal yang terbaik dalam kes penggunaan yang berbeza seperti awan dan multimedia. keputusan mempunyai 95% interval keyakinan menunjukkan bahawa prestasi opendaylight melebihi pencapaian floodlight dalam rangkaian muatan rendah dan juga untuk topologi pokok dalam rangkaian muatan pertengahan dari segi kependaman. floodlight boleh mengatasi prestasi opendaylight dalam rangkaian muatan berat untuk topologi pokok dari segi kehilangan paket dan dalam topologi linear dari segi kependaman. tidak ada perbezaan yang signifikan dalam prestasi pengawal floodlight dan opendaylight dalam kes-kes lain. keywords: floodlight; mininet; opendaylight; sdn iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 48 1. introduction the idea of programmable networks was introduced to meet the challenges that were faced by traditional networks and to facilitate network evolution. as a result, software defined networking (sdn) is a new paradigm that revolutionized traditional network architecture [1]. actually, sdn is a framework for automatically controlling large devices, services, topologies, traffic paths, policies, and apis in a network [1]. the main idea of sdn is related to the physical separation of two parts of the networks: the control plane and data plane. the control plane is separated from the data plane and is moved to a centralized server called the controller. this decoupling abstracts infrastructure from applications and causes flexibility, programmability, cost efficiency, and novel network architecture. in this case, the main role of a controller is to set up rules or make decisions for packets and the main role of data plane is to direct or forward packets based on the rules coming from controller. the controller is the intelligent part of network and the data plane is the slave to the controller’s orders. southbound and northbound interfaces are two other components in a software defined network. a southbound interface connects switches (data plane) to the controller and a northbound interface offers apis for network controlling and services [2]. one of the most famous implementations of the southbound interface is openflow [3] protocol. according to [3, 4] openflow is an open interface that is used to control the forwarding tables remotely in switches, routers, and access points. many controllers are developed based on openflow such as pox [5], nox [6], beacon [7], opendaylight [8], floodlight [9] and so many others. choosing the best controller can be problematic for network administrators and researchers. there are existing works to compare controllers in architectural and efficiency aspects such as scalability and availability, and also from the feature parameters viewpoint such as productivity, language, and interface and platform support. in this paper, two common controllers, floodlight and opendaylight, are compared to each other using mininet [10], an sdn emulator, in terms of qos parameters such as delay and loss. the comparison is done for different topologies and network loads. the results can help to choose the best controller for networks that have qos requirements, such as networks that carry multimedia traffic, or for other special use cases, such as datacenters and clouds. the rest of this paper is organized as follows: in section 2 related works are presented. section 3 introduces the controllers that are compared in this paper. there is also a short introduction to mininet and its supported topologies in this section. emulation and analysis are presented in section 4. the motivation for this, and future, works are discussed in section 5. finally, section 6 concludes the paper. 2. related works in recent years, many works have been done to compare sdn controllers, a review of some of which is presented in this section. in [11], four open-source openflow controllers including nox, beacon, maestro, and floodlight, were compared from architectural aspects, on a shared memory multi-core machine. four key performance bottlenecks are considered, including multi-core support, switch partitioning, packet batching, and task batching. architectural designs, including static switch partitioning and static batching are employed by beacon, nox-mt, and floodlight, while shared-queue and adaptivebatching are employed by maestro. the performance evaluation results show that static switch partitioning and packet batching designs are best for controllers in high throughput networks. packet batching and task batching designs are good for controllers with delaysensitive control plane applications. the results also show that sending control messages iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 49 out individually can improve the latency performance. based on these results, a controller was proposed whose performance was better than the compared controllers. in [12], five controllers named pox, ryu, trema, floodlight, and opendaylight are compared to each other. according to khondoker et al. [12], choosing a controller is a multi-criteria decision making (mcdm) problem because several properties of a controller are important for users. the authors chose an analytic hierarchy process (ahp) in management science because of pair-wise prioritization and an integrated consistency checking mechanism [12]. pox, ryu, trema, floodlight, and opendaylight were compared based on available interfaces, supporting of virtual switching, gui, supporting of rest api, productivity, being open source, having documentation, age, modularity, supporting language, platform, tls, openflow and openstack networking. the results show that ryu got the best value (0.287) in this priority vector. floodlight, opendaylight, trema, and pox got the next best results respectively. it is noticeable that the priority vector values of floodlight and opendaylight (0.275, 0.265) were very close to that of ryu. shalimov et al. [13] proposed a method to test and compare different open-source sdn/openflow controllers including nox, pox, beacon, floodlight, mul, maestro, and ryu. performance metrics including throughput and latency, scalability, reliability, and security were considered for comparison. the test of scalability and performance were done with cbench. reliability and security test were performed with hcprobe. in three experiments of finding average throughput with different number of threads, different number of switches, and different number of hosts, beacon achieved the maximum throughput. for the average response time of controllers with 105 hosts, mul, beacon and floodlight achieved minimum latency. in determining reliability between controllers, all except mul and maestro coped with the test load. for security measurements, five tests were performed including incorrect message length, invalid openflow version, incorrect openflow message type, malformed packet-in message, and malformed port status message. ryu best coped with these four cases across these five tests. al-somaidai and yahya [14] discussed five different versions of openflow switch standard including 1.0, 1.1, 1.2, 1.3 and 1.4, four different platforms for simulation and emulation of sdn including mininet, estinet, ns-3 and trema, seven types of controllers including nox, pox, floodlight, opendaylight, ryu, mul and beacon, and also different switch software and tools. they mentioned floodlight and opendaylight as the controllers with good documentation and flexibility. kaur et al. [15] used pox controller and mininet to emulate a sdn and verified the behavior of network applications in pox. also, the top five controllers including pox, ryu, trema, floodlight, and opendaylight were compared to each other with six features including language support, openflow support, being open-source, having a gui and rest api, and also platform support. govindraj et al. [16] stated that in the comparison of different switches, openflow based switching provides load balancing and reduces bandwidth wastage (due to use of the loop-free topology), so that this kind of switch has better utilization in data centers and enterprises. they also concluded that the usability of openflow can be increased. several other comprehensive sdn surveys [17-19] are available. iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 50 3. floodlight, opendaylight and mininet as presented in section 2, many works have been done to compare sdn controllers. among the controllers, floodlight and opendaylight were two controllers with closely similar results. also recently, these controllers were the focus of more research and papers than other controllers, especially in cloud computing, qos, and multimedia fields. the performance of these controllers were compared in terms of network qos parameters using mininet. in this section, floodlight and opendaylight are reviewed and also a short introduction to mininet is presented. 3.1 floodlight this controller is based on the beacon controller from stanford university and works with physical and virtual openflow switches. some of the features of this controller are as follows: apache-licensed, java-based (non-osgi), modular, event-driven, asynchronous application framework, thread-based, and using a synchronized lock. components of this controller are topology management, use for discovery of both openflow and nonopenflow endpoints (lldp), device management including mac and ip tracking, path computation, infrastructure for web access which is used for management, counter store used for openflow, bigdb (nosql, cassandra-based database) and quantum plug-in that causes interoperation with element agents supporting openflow. these components are loadable services; and floodlight provider is the core module that handles inputs and outputs receives from and sends to switches. this module also translates openflow messages into floodlight events. there are rest apis in controller for getting and setting the controller’s state, event notification systems, and passing emitted events by java event listeners. floodlight also has sample applications including learning switch, hub application and static flow pusher, firewall and load balancer [9]. 3.2 opendaylight in 2013, the opendaylight project consortium was formed as a linux foundation project. this controller creates a de facto northbound api standard so that different southbound protocols, like openflow, i2rs, and netconf can be programmed. some of the features of this controller are as follows: java-based (osgi), modular, pluggable and supporting of multiple southbound protocols. opendaylight supports the programming of a bidirectional rest and osgi framework that supports applications running in the same address space as the controller. internal and external requests for services will be mapped by a service abstraction layer to the appropriate southbound plugin and a basic service abstraction that higher-level services are built upon, will be provided; this feature depends on the capabilities of the plug-ins. topology abstraction and discovery, pce-p (and cspf), openflow, i2rs (as it evolves), and netconf are other built-in services within in opendaylight [8]. according to [8, 9, 12] a comparison of these two controllers is done and shown in table 1. 3.3 mininet mininet is a network emulator, which has been used by developers, teachers, and researchers to create virtual networks and sdn implementation. it was developed by the mininet team to run controllers, switches, and hosts in a virtual network on a single machine. the default topology in mininet consists of an openflow kernel switch connected to two hosts and an openflow controller. hosts on mininet are able to run underlying linux and file system commands [10]. for example, “ipref” parses bandwidth between a client and server and “topo” makes topologies with the python api for custom virtual networks. there are also three predefined common topologies in mininet which are iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 51 table 1: a comparison of floodlight and opendaylight [8, 9, 12] feature floodlight opendaylight developer big switch networks linux foundation supporters big switch networks cisco, hp, ibm , juniper, vmware, etc. written language java java supporting language java, python and any language supports rest api java rest api yes yes openstack networking (quantum) yes yes tls supporting yes yes open-source yes yes of version full support for 1.0 and 1.3, experimental support for openflow 1.1 and 1.2 1.0 , 1.3 user interface web, java web interfaces southbound (openflow), northbound (java, rest) southbound (openflow and other sb protocols), northbound (java rpc, rest) virtualization mininet, openvswitch mininet, openvswitch platform linux, mac, windows linux, windows active community yes yes age 4 years 3 years documentation good (documentations exist in official website or other developers sites) medium mailing list activity very high medium handling mixed noneopenflow and openflow networks yes yes installation very easy easy loop supporting topologies topologies and of islands (a) single topology (b) linear topology (c) tree topology fig. 1: three common topologies in mininet. presented in fig. 1: single, linear, and tree. a single topology has 1 controller, 1 switch, and a definable number of hosts. a linear topology has serial connections with definable number of switches and hosts. a tree topology consists of multiple topology levels with a definable number of levels (depth and fan-out). remote controllers also can be used in iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 52 mininet. therefore, a virtual network will be connecting to any remote controller in vm, local machine, or anywhere else. some other advantages of using mininet are system-level regression test supporting, complex topology testing and cli which is topology-aware and openflow-aware. developed code for an openflow controller, modified switch, or host on mininet, can move to a real system with minimal deployment. so a network design in mininet can usually move directly to hardware switches for line-rate packet forwarding [10]. 4. performance evaluation all network instances were installed and implemented on ubuntu 14.0.4 with 4 gb ram. native installation from source on ubuntu is considered for mininet installation. floodlight and opendaylight both supports openflow version 1.3. openvswitch 2.0.1 with link status of up to 10 mbps fdx is used as openflow switches. number of switches and hosts considered for each topology is shown in table 2. three different scenarios for each topology are considered. in the first scenario, no cross traffic was generated; while in the second scenario, nearly half of the bandwidth was cross traffic; and in third scenario, almost the whole bandwidth was filled with cross traffic. each scenario was repeated 10 times. to have a near-real experience, the production of some cross traffic was based on different rates of youtube video transmission for h264 [20] and skype video conferencing [21]. other cross traffic production was on a random basis to simulate any other traffic which can exist in a network. table 2: number of switches and hosts in single, linear and tree topology topology number of switch host single 1 8 linear 8 8 tree (depth=3 , fan-out=2) 7 8 the general network qos parameters are:  latency: also known as delay, is the amount of time that it takes for a packet to travel along the network from source to destination.  jitter: the variation of latency.  loss: the percentage of packets that failed to reach their destination. packet loss ratio is measured in percentage of total packets as in eq. (1). = ⁄ (1)  throughput: the ability of network to carry a volume of data over a unit of time [22]. throughput is related to network bandwidth (which is 10 mbps in all scenarios of this paper) and loss ratio. jitter can also be calculated using latency values. hence, the other two network qos parameters are considered for evaluating controllers. since, each scenario was repeated 10 times (less than 30), so the table should be used for confidence interval calculation. mean difference ( ̅) was calculated and then a 95% confidence interval (with a confidence level of α=0.05) of mean difference was determined by use of eq. (2), where (1 α/2) is 0.97 and the freedom degree (n – 1) is 9; iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 53 so based on the table, t[0.97, 9] should be used. if the ci range includes zero, it means that two controllers have the same performance [23]. ( ̅ − ∝ ; √⁄ , ̅+ [ ∝ ; ] √⁄ ) (2) tables 3 to 5 show the latency in each scenario. the exact comparison of these two controllers with 95% confidence intervals, are also shown in the last row of each table. in all topologies, latency of a specific flow between host 1 and host 8 is measured. there is no packet loss in first and second scenarios. table 3: latency with no cross traffic (low load network) single linear tree min (ms) floodlight 0.079 0.221 0.077 opendaylight 0.078 0.221 0.116 max (ms) floodlight 9.593 78.808 9.767 opendaylight 1.824 11.848 2.078 average (ms) floodlight 0.476 3.279 0.545 opendaylight 0.1 88 0.749 0.254 ci of averages difference (0.278, 0.298) (1.83, 3.22) (0.219, 0.363) table 4: latency with half of the bandwidth cross traffic (mid load network) single linear tree min (ms) floodlight 0.409 1.8 2.244 opendaylight 0.418 2.013 0.577 max (ms) floodlight 15.142 302.562 134.093 opendaylight 10.99 253.266 17.107 average (ms) floodlight 2.31 52.778 16.38 opendaylight 2.019 45.831 3.656 ci of averages difference (-0.393, 0.975) (-3.246, 17.139) (10.124, 15.32) table 5: latency with almost full bandwidth cross traffic (high load network) single linear tree min (ms) floodlight 1171.316 1143.583 1065.705 opendaylight 1165.575 1159.357 1205.207 max (ms) floodlight 1357.046 1488.846 1634.719 opendaylight 1450.293 1995.651 1235.842 average (ms) floodlight 1232.739 1306.647 1235.627 opendaylight 1213.287 1623.714 1212.662 ci of averages difference (-7.802, 46.706) (-409.314, -224.793) (-16.609, 62.539) according to table 3, maximum latencies in all three topologies belong to floodlight, but there is no significant difference between the results for minimum latency. maximum iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 54 latency in table 3 is related to the first packet received by switch which has no entry in its forwarding table for the flow. it is noticeable that maximum latency in floodlight is much more than opendaylight, it means that floodlight needs more time to find the route and send a decision for newly arriving flows. as the average latencies and their 95% confidence intervals in table 3 show, networks that use floodlight as their controller have more latency while the traffic is low. besides the actual function of each controller among a solitude network, floodlight and opendaylight must be responsible against a populated network. a traffic generator is used to generate large traffic (5 mbps for mid loaded network and about 10 mbps for high loaded network). unlike the fact that the maximum latency in table 3 is related to finding an action for the first packet by the floodlight and opendaylight controllers, the maximum latency measurement in table 4 and table 5 is about a time that network traffic is high. according to table 4, for mid loaded networks, in single and linear topologies, with 95% confidence intervals there is no difference in the latency results for floodlight and opendaylight and both act the same because their ci of average latencies difference, includes zero. in a more complicated topology (tree topology), the network with the opendaylight controller has less latency. for the heavily loaded network, according to table 5, there is no significant difference in single and tree topologies, while in linear topology, floodlight achieves less latency and acts faster. it is also noticeable that packet loss happened only in the heavy loaded network and there is no packet loss in low and mid load networks. the loss in heavy network happened at time when bandwidth was becoming full and caused congestion. the packet loss results are shown in table 6. table 6: average loss measurements in high load network single linear tree floodlight 41.6 41.3 34.4 opendaylight 15.8 32.4 47.2 ci of averages difference (15.659, 35.941) (-5.397, 23.197) (-25.349, -0.251) table 7: best controller in different situations latency loss (high load network) single low load opendaylight (2.5 times better) opendaylight (2.6 times better) mid load same heavy load same linear low load opendaylight (4.4 times better) same mid load same heavy load floodlight (1.2 times better) tree low load opendaylight (2.1 times better) floodlight (1.4 times better) mid load opendaylight (4.5 times better) heavy load same 5. motivation and future works recently sdn has attracted researchers’ attention as an emerging network architecture that can resolve today’s network issues in different cases such as multimedia iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 55 qos and cloud and datacenter management. many papers and research for different use cases has been done using different controllers, among them opendaylight and floodlight were the most popular controllers. despite this research, there is still a question of which controller can perform better in which situations or use cases. according to features listed in table 1 it is difficult to decide which controller is really better unless one exact feature, such as supporting non-openflow southbound interfaces, is needed. therefore, in this paper, these two controllers were compared in terms of network parameters like latency and loss. the comparison was done in three kinds of topology and different network loads. as table 7 shows, the results can be summarized as bellow: (a) opendaylight can perform better in networks with low load for any kinds of topology. (b) both controllers act the same while the network load is about 50% of actual bandwidth, except for the tree topology where opendaylight outperforms floodlight. (c) for networks with heavy traffic, opendaylight outperforms floodlight only in the single topology because of its better performance in terms of loss. (d) for networks with heavy traffic, floodlight can have a better performance than opendaylight for linear and tree topologies due to less latency and loss. (e) opendaylight is a better choice for single topologies with various network loads. (f) floodlight is a better choice for linear topologies with various network loads. (g) floodlight is a better choice for tree topologies with heavy network loads and traffic sensitive to loss, such as video and voice. (h) opendaylight is a better choice for tree topologies with various network loads except for traffic that is sensitive to loss. according to these results, one can choose the best controller based on the network’s features. for example, in data centers and clouds, tree topologies are used. according to (g) and (h) results which are about the performance of controllers in tree topology, opendaylight can be a better choice if a module/service for improving its performance in terms of loss being added to it. in another case, floodlight can be the best controller if a qos module for improving latency is added to it. for future work, the number of switches each controller can manage at the same time in different network loads will be tested. the future results, alongside this paper’s results and other features of the controllers, can help to make an optimized decision for choosing the best controller. 6. conclusion floodlight and opendaylight are two common controllers among sdn controllers. each of these two controllers is modular and could be programmed for new network services. they are both open-source with support java language. there are also some differences between floodlight and opendaylight. floodlight has a java-based user interface while opendaylight supports non-openflow control protocols and provides an abstraction layer, above south-bound protocols. there are works done to compare controllers in architectural and efficiency aspects such as scalability and availability and also from the feature point of view. in this paper, network latency and packet loss for floodlight and opendaylight are measured in single, linear and tree topologies, in various iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 56 traffic loads. the results with 95% confidence interval show that the controllers have a competitive behavior. there are situations where both controllers perform the same. there are situations where networks with opendaylight have better latency, such as in tree topology for a network with half of bandwidth traffic, while floodlight can outperform opendaylight in terms of packet loss in heavy loaded network in tree topology. comparing of these two controllers in more complicated topologies and with respect to the number of switches they can manage is considered for future work. references [1] azodolmolky s. (2013) software defined networking with openflow. packet publishing ltd, uk. [2] nadeau td, gray k. (2013) sdn: software defined networks. o'reilly media inc., usa. [3] pfaff b, lantz b, heller b. (2012) openflow switch specification version 1.3.0. open networking foundation, http://www-bcf.usc.edu/~minlanyu/teach/csci599fall12/papers/openflow-spec-v1.3.0.pdf (2012). accessed september 2015 [4] open networking foundation (2012) software-defined networking: the new norm for networks. onf white paper, https://www.opennetworking.org/images/stories/downloads/ sdn-resources/white-papers/wp-sdn-newnorm.pdf. accessed september 2015 [5] mccauley j. (2014) pox: a python-based openflow controller. pox. http://www.noxrepo.org/pox/about-pox, accessed: september 2015 [6] gude v, koponen t, pettit j, pfaff b, casado m, mckeown n, et al. (2008) nox: towards an operating system for networks. acm sigcomm comp. comm. rev., 38(3):105-110. [7] erickson d. (2013) the beacon openflow controller. proceedings of the second acm sigcomm workshop on hot topics in software defined networking, 13-18. [8] opendaylight: open source programmable networking platform (2015) opendaylight, a linux foundation collaborative project, http://www.opendaylight.org/software. accessed: september 2015. [9] floodlight is an open sdn controller. (2015) project floodlight. http://www.projectfloodlight.org/floodlight. accessed: september 2015. [10] mininet an instant virtual network on your laptop (or other pc) (2015). mininet team. http://mininet.org. accessed: september 2015. [11] shah sa, faiz j, farooq m, shafi a, mehdi sa. (2013) an architectural evaluation of sdn controllers. communications (icc) 2013 ieee international conference, 3504-3508. [12] khondoker r, zaalouk a, marx r, bayarou a. (2014) feature-based comparison and selection of software defined networking (sdn) controllers”, world congress on ieee on computer applications and information systems (wccais), 1-7 [13] shalimov a, zuikov d, zimarina d, pashkov v, smeliansky r. (2013) advanced study of sdn/openflow controllers. proceedings of the 9th central & eastern european software engineering conference, acm, 1-6. [14] al-somaidai mb, yahya e. (2014) survey of software components to emulate openflow protocol as an sdn implementation. am. j. software engin. appl., 3(6):74-82. [15] kaur s, singh j, ghumman ns. (2014) network programmability using pox controller. http://sbsstc.ac.in/icccs2014/papers/paper28.pdf. accessed: september 2015 [16] govindraj s, jayaraman a, khanna n, prakash kr. (2012). openflow, load balancing in enterprise networks using floodlight controller; university of colorado; http://morse.colorado.edu/~tlen5710/12s. accessed: september 2015 [17] kreutz d, ramos f, verissimo p, rothenberg ce, azodolmolky s, uhlig s. (2014) software-defined networking: a comprehensive survey. proceeding of the ieee, 103(1): 14-76 [18] mendonca m, nunes ba, nguyen x, obraczka k, turletti t. (2014) a survey of softwaredefined networking: past, present, and future of programmable networks. comm. surveys & tutorials, ieee, 16(3):1617-1634. iium engineering journal, vol. 17, no. 2, 2016 rowshanrad et al. 57 [19] lara a, kolasani a, ramamurthy b. (2014) network innovation using openflow: a survey. comm. surveys & tutorials, ieee, 16(1): 493-512. [20] youtube advanced encoding settings. (2013) available online: https://support.google.com/youtube/answer/1722171?hl=en, accessed: september 2015 [21] how much bandwidth does skype needs? (2015) available online: https://support.skype.com/en/faq/fa1417/how-much-bandwidth-does-skype-need, accessed: september 2015 [22] de gouveia f, magedanz t. (2002) quality of service in telecommunication network. telecommunication system and tchnologies, encyclopeida of life support systems(eolss). [23] jain r. (2008) the art of computer systems performance analysis. john wiley & sons, littleton, massachusetts. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 a hybrid of kansei engineering (ke) and analytical hierarchy process (ahp) to develop conceptual designs of portable oil spill skimmer rprakash ramanathan, lokman abdullah*, muhammad hafidz fazli md fauadi, muhammad syafiq syed mohamed and khairun najmi kamaludin faculty of manufacturing engineering, universiti teknikal malaysia melaka, 76100 durian tunggal, melaka, malaysia * corresponding author: lokman@utem.edu.my (received: 9th may 2022; accepted: 24th august 2022; published on-line: 4th january 2023) abstract: currently, there are huge demands on developing a design that fulfils the characteristics of performance, cost, safety, and aesthetics. however, the conceptual design stages in industrial products lack the involvement of user requirements as it is typically focused on the product's performance. consequently, specific criteria such as the product's ease of use, safety, and robustness cannot be compared and measured when designing industrial products. owing to this reason, this research proposes a new technique that integrates kansei engineering with analytical hierarchy process (ahp) to address the issue. the research objective is to investigate an oil spill skimmer's user and technical requirements by incorporating the kansei engineering method. the approach to carry out this research is to incorporate the kansei and the basic ahp methods. kansei engineering will suggest the required design elements that must be included to design and fabricate a portable oil spill skimmer. at the same time, the ahp method is used to select the best design based on the developed conceptual design. the effectiveness of the proposed method was verified by comparing it with other established methods, such as topsis (technique of order preference by similarity to ideal solution). moreover, sensitivity analysis was used to investigate the robustness of the ahp result. there are 5 conceptual designs in total, assessed in this research. the result showed that out of the 5 conceptual designs, design number 3 has the highest ranking (priority ranking = 0.2603). thus, the most suitable conceptual design for the portable oil spill skimmer to be fabricated is design 3. the finding also shows that the result from ahp was valid and robust. abstrak: pada masa kini, terdapat permintaan besar bagi membangunkan reka bentuk yang memenuhi ciri-ciri prestasi, kos, keselamatan dan estetika. walau bagaimanapun, industri kurang melibatkan keperluan pengguna pada peringkat reka bentuk konsep produk industri, kerana ia biasanya tertumpu pada prestasi produk. ini menyebabkan kriteria khusus seperti kemudahan menggunakan produk, keselamatan dan keteguhan produk tidak dapat dibandingkan dan diukur semasa mereka bentuk produk industri. disebabkan faktor berkenaan, kajian ini mencadangkan teknik baharu yang mengintegrasikan kejuruteraan kansei bersama proses hierarki analitik (ahp) bagi menangani isu tersebut. objektif kajian adalah bagi menyiasat keperluan pengguna dan keperluan teknikal menyaring tumpahan minyak dengan menggabungkan kaedah kejuruteraan kansei. pendekatan kajian ini adalah dengan menggabungkan kansei dan kaedah asas ahp. kejuruteraan kansei mencadangkan elemen reka bentuk yang diperlukan yang mesti disertakan bagi mereka bentuk dan menyaring tumpahan minyak mudah alih. pada masa sama, kaedah ahp iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 digunakan bagi memilih reka bentuk terbaik berdasarkan reka bentuk konsep yang dibangunkan. keberkesanan kaedah yang dicadangkan telah disahkan dengan membandingkannya dengan kaedah lain yang telah terbukti, seperti topsis (teknik aturan kehendak berdasarkan persamaan dengan solusi ideal). selain itu, analisis sensitiviti digunakan bagi mengkaji keteguhan keputusan ahp. terdapat 5 reka bentuk konseptual yang dinilai dalam kajian ini. dapatan kajian menunjukkan bahawa reka bentuk nombor 3 mempunyai keputusan tertinggi (keutamaan kedudukan = 0.2603) daripada 5 reka bentuk konseptual ini. oleh itu, reka bentuk konsep yang paling sesuai bagi saringan tumpahan minyak mudah alih yang akan dibina adalah reka bentuk 3. dapatan kajian juga menunjukkan bahawa hasil daripada ahp adalah sah dan kukuh. keywords: kansei engineering; analytical hierarchy process (ahp); product development process; oil spill skimmer 1. introduction industrial equipment sales often face tough challenges in maintaining their sales volume and customer loyalty since many manufacturers compete with one another for customers. therefore, manufacturers often spend their time and resources studying customers' purchasing behaviour and preferences, such as function, appearance, and usability. of all these requirements, visual appeal plays a vital role in influencing customer purchasing decisions. customer impressions are influenced by various elements, including the brand of the product, its purpose, look, and usefulness. however, the product look is the one that creates the most visual engagement to the client and product compared to other aspects [1]. the application of ahp has been utilised in the area of the machine tools industry and the textile industry consumer products, such as household appliances, are typically regarded as attractive and inexpensive, but industrial items, such as heavy machinery, should be of high quality but not necessarily attractive. any industrial product's development usually focuses on technical standards, including objectives and well-defined metrics such as speed, power, and many others that could be compared and tested. while meeting technical criteria is essential, it is not always enough for a product to succeed [2]. several elements are difficult to quantify yet influence machine design and selection. users' impressions of different machine tools have received minimal attention in terms of strategies for selecting, analysing, and comparing machine tools. thus, there is a need to incorporate both customer and technical requirements in the industrial product development process. a study done by marini investigated the use of ahp and analytical network process (anp) together with quality function deployment (qfd) in concept design and material selection for making better decisions to improve product success [3]. however, the involvement of customer requirements is still lacking when developing a design concept [4]. therefore, research was done to propose a method based on topsis and fuzzy ahp, which could be used in concept design evaluation [5]. renzi researched using ahp and anp together with other multi-criteria decision methods for design evaluation in the automotive industry, trying to transfer knowledge on decision-making methods to the industrial context [6]. moreover, rosli investigated a systematic product design model that assists decisionmakers or design engineers in improving current design through the idea generation method of theory of inventive problem solving (triz) and utilising the analytical hierarchy process (ahp) to perform the selection of best-generated idea [7]. iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 a study was conducted to show that the proposed (house of quality) hoq and fuzzyahp provided a novel alternative to existing methods to perform design concept evaluations in the early stages of product development, with the capability to accommodate uncertainties and vagueness using the optimum number of pairwise comparisons [8]. furthermore, a research was conducted by turan, proposing a rough number to be used by vikor and ahp methods to develop a systematic framework for the concept evaluation process [9]. nevertheless, the proposed best design concept might be biased toward designers' expectations rather than the customers' expectations. it is well known that previous researchers have investigated and reported on several modified ahp. to the best of the author's knowledge, however, the implementation of kansei engineering as a tool for optimisation paired with ahp in the development of industrial products such as oil spill skimmer is still inadequate and uncommon. furthermore, although several researchers have researched the fabrication of oil spill skimmers, there is no proof that ke and ahp were utilised in the design and fabrication process [10]–[15]. therefore, this study aims to employ kansei engineering to investigate the user and technical requirements to generate multiple conceptual designs for an oil spill skimmer, which will be analysed using analytical hierarchy process (ahp) to choose the ideal oil spill skimmer conceptual design. 2. methodology 2.1 research framework the development and selection of the best conceptual design for a portable oil spill skimmer are split into two sections in this study. first, kansei engineering is employed to build an overall design aspect of the oil spill skimmer in phase one. this methodology has five layers: kansei word selection, product sample collection, questionnaire distribution, reliability testing, data interpretation, and design idea creation. the ahp is then utilised in part 2 to determine the relative weight of each factor at each level to arrive at the overall product assessment system. this is done to determine which design idea produced by kansei engineering is the best. finally, to evaluate the robustness of the ahp, the results are compared and analysed using topsis and sensitivity analysis. 2.2 kansei engineering and reliability testing kansei engineering (ke) uses seven primary stages to categorise the customer's needs and technical requirements. kansei engineering type 1 is employed in this study. this method transforms a single product concept into a more complex concept, which is then developed to numerous levels and interpreted in terms of the physical characteristics of the product design. category categorisation is a breakdown strategy from a targeted concept of a new product to the corresponding subjective kansei to the objective design requirements. mazda's design of the miata, the world's most successful sports automobile, is a well-known example of this category application [16]. a previous research can be referred to identify the step-by-step procedure of kansei engineering methodology [17]. reliability testing aims to evaluate the reliability or internal consistency by utilising cronbach's alpha to measure the strength of the consistency. cronbach's alpha analysis determines whether the multiple-question likert scale survey is reliable. higher values of cronbach's alpha signify more reliability of the survey or questionnaire; it has a range of 0 to 1. the minimal number of questions and weak interconnection between objects result in a low alpha score in the reliability test. the alpha value achieved, for example, will be pretty iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 low due to a lack of correlation between the variables and items, resulting in the questionnaire being rejected and requiring modification. on the other hand, the items may be redundant if the alpha is too high since the questions are the same but in a different format. the formula of cronbach's alpha and the rule of thumb is shown below in eq. (1) [18]. 𝑎 = 𝑁.𝑐̄ v +(𝑁−1).c (1) where, n= the number of items c̄ = average covariance between items-pairs v̄ = average variance fig. 1: research framework. 2.3 analytical hierarchy process (ahp) in the next step, the research will focus on establishing the analytical hierarchy process (ahp) in determining the most proper rank of the design options. elements related to the goals, criteria, and relevant alternatives are synthesised from the kansei engineering method. table 1 shows the linguistic variables and the pairwise matrix value. iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 table 1: linguistic variables and values for pairwise matrix for basic ahp [19]. linguistic variables ahp scale important 9 very strongly important 7 strongly important 5 weakly important 3 equally important 1 intermediate 2,4,6,8 ahp technique is a process that consists of the following steps with the help of a few equations as narrated by [20]: step 1: first, decide what needs to be achieved, then narrow down the options. selecting criteria, a quantifiable aspect that aids in illustrating and specifying options, necessitates practical judgment. step 2: paired comparisons are needed in two segments as follows: 1. between criteria 2. between alternatives using each criterion. the matrices of pairwise comparisons are on a fundamental scale from 1 to 9. the application of ahp is based on expert judgment. one of the major advantages of ahp is that the analysis does not always require statistically significant sample size as reported by [21]. furthermore, it is obvious that conducting such huge numbers of real expert examinations requires too much effort, time, and financial resources. thus, an evaluation from a single qualified expert is adequate [22]. as the input data in ahp analysis are based on an expert’s perceived judgement, a single input from an expert is sufficient as a representative in the pairwise evaluation of ahp [23]. however, ahp may also be ineffective in research with a high sample size since "cold-called" experts are prone to give arbitrary responses, severely altering the consistency of the assessments [24]. data is gathered through questionnaires and interviews. the comparison matrix determines which criteria and sub-criteria are more critical than others. therefore, expert input is critical. an oil skimmer expert was selected as the respondent in this research. the respondent was chosen based on years of expertise and knowledge in the oil skimmer sector. the comparison matrix (n x n), where n is the number of criteria. step 3: let xij denote the order of preference of the ith factor compared to the jth factor. then eq. (2): xij = 1 𝑋𝑖𝑗 (2) step 4: a normalised pairwise comparison matrix is obtained by adopting the following procedure: 1. sum of every column. 2. divide all the numbers in the matrix respectively by the obtained column sum. 3. average the rows to obtain relative weights. step 5: calculate eigenvector, maximum eigenvalue, and consistency index (ci). refer to eq. (3). 𝐶𝐼 = 𝜆max− 𝑛 𝑛−1 (3) iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 here, λmax is the eigenvalue corresponding to the matrix of pairwise comparisons, and n is the number of criteria. consistency ratio (cr) is defined by referring to eq. (4): 𝐶𝑅 = 𝐶𝐼 𝑅𝐶𝐼 (4) where (rci) is a random consistency index. generally, a cr value of less than 0.1 is acceptable; otherwise, the pairwise comparisons should be altered to eliminate incoherence. the topsis and sensitivity analysis methods are used to validate the ahp results. first, the topsis analysis is used to confirm the ahp ranking result. the ahp and topsis parameters are the same, but the mathematical computations are different, allowing the topsis ranking result to confirm the ahp ranking result. in terms of sensitivity analysis, the ahp result is examined to determine the result's robustness in relation to the weighted criteria. when modifications in criterion weightage are applied, a complete sensitivity analysis is done to detect the variance in the behaviour of the ranking alternatives. 2.4 technique of order preference by similarity to ideal solution (topsis) topsis technique is a process that consists of the following steps with the help of equations [25]: step 1: form the decision matrix. refer to eq. (5). 𝐷𝑀 = 𝑥11 ⋯ 𝑥1𝑛 ⋮ ⋱ ⋮ 𝑥𝑚1 ⋯ 𝑥𝑚𝑛 (5) step 2: the normalised decision matrix is done. refer to eq. (6) 𝑁𝐷𝑀 = 𝑟𝑖𝑗 = 𝑥𝑖𝑗 √(𝛴𝑖=1 𝑚 𝑥𝑖𝑗 2 ) (6) step 3: the weighted normalised decision matrix refers to eq. (7) (skipped as the weightage is obtained from ahp). 𝑉 = 𝑣𝑖𝑗 = 𝑤𝑗.𝑟𝑖𝑗 (7) step 4: the positive and negative ideal solutions for each criterion refer to eq. (8) and eq. (9), respectively 𝑃𝐼𝑆 = 𝑉𝑗 + = 𝑀𝐴𝑋𝑖(𝑉𝑖𝑗) (8) 𝑁𝐼𝑆 = 𝑉𝑗 − = 𝑀𝐼𝑁𝑖(𝑉𝑖𝑗) (9) step 5: the geometry distance of each alternative from positive and negative ideal solution is calculated refer to eq. (10) and eq. (11), respectively. 𝑆𝑖 ∗ = √∑ (𝑉𝑖𝑗 𝑛 𝑗=1 − 𝑉𝑗 +)2 (10) 𝑆𝑖 ∗ = √∑ (𝑉𝑖𝑗 𝑛 𝑗=1 − 𝑉𝑗 −)2 (11) iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 2.5 sensitivity analysis validation is a crucial method to be incorporated into any type of research to identify the credibility and validation of results. the application can be widely seen in the domain of renewable energy [26], controller design [27], cnc machining process [28], decision making [29] and others. moreover, in engineering domains such as structural analysis and optimisation challenges, sensitivity analysis is used to analyse uncertainty. the goal of mcdm sensitivity analysis is to evaluate how changing the weights assigned to the criteria affects the ranking of the options. it also assures the robustness of the offered technique [29]. in addition, a sensitivity analysis is performed to confirm the final ranking recommendation. the sensitivity analysis results in several scenarios show that the best option could change depending on how the assessment criteria are weighted. 3. results and discussion 3.1 kansei engineering to conclude, the design aspects of the oil spill skimmer were identified using (pls) analysis, which could be referred from [17]. the technique and analysis provide the coefficient plot values, illustrating whether or not that design aspect is essential for designing a portable oil spill skimmer. certain design aspects have many high positive scores based on the table below. therefore, certain design factors will be prioritised when developing the oil spill skimmer. on the other hand, several design aspects negatively associate with the kansei terms. as a result, several design features will be neglected when developing the oil spill skimmer. these design components must be introduced into the design process and those that should be ignored while designing the portable oil spill skimmer (table 2). table 2: list of positive and negative design elements positive design elements negative design elements • compact body appearance • more than a pair of floating support • medium body size • external oil tank location • 41-100 kg weight • non-oleophilic skimmer material • medium-size oil tank • bulky body appearance • a pair of floating support aid • round body shape • outrigger floating support shape • vacuum type skimmer • square/rectangular body shape • small body size • oleophilic skimmer material • cylindrical body shape • water extraction below 10% • brush type skimmer • internal oil tank storage • less than 5 m/s speed 3.1.1 reliability testing the acquired data is subjected to reliability testing using a questionnaire to assess whether the data is trustworthy. as a result, cronbach's alpha is used to assess the data's dependability. cronbach's alpha is an internal consistency measurement that depicts the interaction of a group of items in collective data reliability, as represented by the coefficient figures. in contrast, homogeneity refers to one-dimensionality and falls under the reliability internal consistency component, which measures the phenomenon that provides stable and iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 consistent data collection. the questionnaire was conducted for 30 respondents in this research, calculated in eq. 1. the cronbach's alpha calculated using the spss programme (statistical package for social science) is 0.912, indicating that the questionnaire set has a excellent reliability coefficient, as shown in table 3 below. this result demonstrates that the questionnaires fit in, exhibiting the homogeneity of each question. however, originating from various parts demonstrates the dimensionality in measuring every response received, resulting in a more stable and complete analysis for this study. table 3: the cronbach's alpha value and reliability coefficient [30]. cronbach's alpha value reliability coefficient α > 0.9 excellent α > 0.8 good α > 0.7 acceptable α > 0.6 questionable α ≥ 0.5 poor 3.1.2 conceptual design the design concept of a portable oil spill skimmer is based on the results obtained from the kansei engineering analysis. figure 2 shows the conceptual designs of the portable oil spill skimmer. furthermore, the strengths and weaknesses of each design are elaborated in the ahp analysis, where it is compared using pairwise comparison with several sub-criteria. (a) (b) (c) (d) (e) fig. 2: developed conceptual design of portable oil spill skimmer: (a) design 1, (b) design 2, (c) design 3, (d) design 4, (e) design 5. 3.1.3 specifications of each design the specification of each design is shown in table 4. 3.2 analytical hierarchy process (ahp) the pairwise comparison matrix is created using the hierarchy model from fig. 3. the number in the pairwise matrix is decided by an expert such as oil and gas or osrr engineers. this is done to improve the result accuracy of the ahp. the pairwise comparison in this research has three stages: design alternatives, sub-criteria and overall analysis of the criteria, sub-criteria, and design alternatives analysis. finally, a matrix with regards to the plan will be determined. ahp is used to implement a hierarchy paradigm for structuring product principal decisions. figure 3 depicts a four-level hierarchy decision mechanism. iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 table 4: the specification of each conceptual design specification design 1 design 2 design 3 design 4 design 5 weight 5 – 40 kg 41 – 100 kg 5 – 40 kg 41 – 100 kg 41 – 100 kg speed less than 1 m/s less than 1 m/s less than 5 m/s less than 1 m/s less than 1 m/s oil tank capacity large large medium large medium oil suction capacity below 51 l/h below 51 l/h below 51 l/h below 51 l/h below 51 l/h self-propelling capacity no yes yes yes yes size big big medium medium large oil tank location external internal internal external internal water extracted with oil 20% 20% 10% 10% 20% body shape square/rectangular square/rectangular square/rectangular square/rectangular square/rectangular body appearance bulky bulky bulky compact compact portability carried by 2 person carried by more than 2 person carried by 2 person carried by more than 2 person carried by 2 person skimmer type brush brush roller roller brush material oleophilic oleophilic oleophilic oleophilic oleophilic floating support aid shape round cylindrical outrigger outrigger outrigger number of floating support aid 4 2 2 4 4 support aid type polyvinyl chloride (pvc) polyvinyl chloride (pvc) fibreglass pvc fibreglass iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 the criteria are labelled as follows: performance (p), safety (s), maintenance (m) and portability (p). the sub-criteria are labelled as follows: oil suction (os), manoeuvrability (ma), strong body frame (sbf), stability (sa), enclosed components (ec), easy to repair (er), easy to disassemble (ed), easy to relocate (etr) and lightweight (l). the stability of the design is evaluated according to the number of floating support (closely influenced by the shape of floating support) and floating support shapes (bow-ship shapes are recommended). furthermore, the oil suction is evaluated according to the types of skimmer material. this research does not consider the cost as main or sub-criteria since the criteria is not a concerning factor and also was inconsiderate in the previous research as well. the research in the oil and gas field that presents this scenario [31,32]. moreover, the product will be focusing on specific customers as it is characterised as high variety, low volume production. the basic characteristics of high variety, low volume is the manufacturing of one or few numbers of products designed and produced as per the requirement of customers within pre decided time, with a drawback of high cost of production [33]. thus, cost is not taken as one of the influencing factor as cost criteria will not affect the pairwise evaluation. fig. 3: a hierarchy model for the selection of design concept. the following table is the pairwise comparison matrix of the design alternatives in each sub-criterion. the table below shows the step-by-step process of the pairwise comparison matrix for the oil suction sub-criteria. this process is done through all the nine sub-criteria. note that the cr value needs to be less than 0.1. the expert decides the value inside the matrix. all the calculations were done following the steps explained in the methodology. table 4 shows the pairwise comparison matrix of each design in the oil suction sub-criteria. table 5: pairwise comparison matrix of each design in oil suction sub-criteria weight d1 d2 d3 d4 d5 d1 1 4 3 4 4 d2 0.25 1 2 3 3 d3 0.33 0.5 1 0.5 0.5 d4 0.25 0.33 2 1 1 d5 0.25 0.33 2 1 1 iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 next, the synthesised matrix and consistency testing were done in table 5. the same calculation applies to each of the sub-criteria. it is observed that the consistency ratio (cr) is below 0.1; thus, the pairwise comparison evaluation is accepted. all the sub-criteria are analysed as shown in tables 4 and 5. in the following analysis, the pairwise comparison of oil suction (os), manoeuvrability (ma), and strong body frame (sbf) was made to calculate which sub-criteria in the performance criteria has higher weightage. table 6 shows the pairwise comparison matrix of performance criteria. table 7 shows the process of averaging the normalised columns. first, the eigenvector was calculated by multiplying to obtain the new vector. as the consistency ratio (cr) value is less than 0.1, thus the pairwise comparison evaluation is accepted. table 6: synthesised matrix for the design alternatives wt d1 d2 d3 d4 d5 sum pv nv nv/pv ci ri cr d1 0.4800 0.6480 0.3000 0.4210 0.4210 2.271 0.4542 2.5483 5.6111 0.08 1.12 0.07 d2 0.1200 0.1620 0.2000 0.3150 0.3150 1.1137 0.2227 1.2163 5.4605 d3 0.1600 0.0810 0.1000 0.0520 0.0520 0.4463 0.0893 0.4689 5.2531 d4 0.1200 0.0540 0.2000 0.1050 0.1050 0.5846 0.1169 0.6002 5.1332 d5 0.1200 0.0540 0.2000 0.1050 0.1050 0.5846 0.1169 0.6002 5.1332 total 26.59 λ max 5.3182 table 7: pairwise comparison matrix of performance criteria wt os ma sbf os 1.0000 3.0000 5.0000 ma 0.3333 1.0000 2.0000 sbf 0.2000 0.5000 1.0000 table 8: synthesised matrix for the sub-criteria table 9: overall priority vector for the alternatives alternatives overall pv d1 0.3098 0.0587 0.0588 0.1347 d2 0.1800 0.1359 0.1367 0.0531 d3 0.2055 0.2375 0.4580 0.3928 d4 0.1451 0.2840 0.2474 0.1691 d5 0.1596 0.2840 0.0991 0.2503 table 9 reveals that design 3 (d3) has the most significant value (0.2603 or 26.03 per cent) among the various design concepts suitable for further development. design 4 (d4) is the second highest, with a value of 0.2356 (23.6 per cent), while design 1 (d1) is the lowest, wt os ma sbf pv nv nv/pv ci ri cr os 0.6522 0.6667 0.6250 0.6479 1.9485 3.0071 0.00 0.58 0.0032 ma 0.2174 0.2222 0.2500 0.2299 0.6902 3.0026 sbf 0.1304 0.1111 0.1250 0.1222 0.3667 3.0013 total 9.01 λ max 5.3182 iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 with a value of just 0.1323 per cent (13.23 per cent). as a result, d3 has been chosen as the preferred design idea, as it provides the most value among the five options. table 10: oil spill skimmer design concept ranking 3.3 technique for order preference by similarity to ideal solution (topsis) the topsis multi-criteria decision matrix is utilised in this paper to compare the ranking result with ahp for verification purposes. the step-by-step calculations are explained earlier in the paper. the weights of the criteria were obtained from ahp. the weightage of the criteria and sub-criteria was calculated to identify the global weight of each sub-criteria. the calculation example of the criteria and sub-criteria are as follows. table 11 shows the global weight of the priority vector obtained from ahp. table 11: global weight of the priority vector obtained from ahp criteria priority vector sub-criteria priority vector global weight performance 0.2776 (os) 0.6479 0.1799 (m) 0.2299 0.0638 (sbf) 0.1222 0.0339 safety 0.5635 (s) 0.7500 0.4226 (ec) 0.2500 0.1409 maintenance 0.1077 (er) 0.6667 0.0718 (ed) 0.3333 0.0359 portability 0.0512 (etr) 0.2500 0.0128 (l) 0.7500 0.0384 table 12 shows the pairwise comparison matrix of the topsis analysis showing the beneficial (b) and non-beneficial (nb) criteria. the value of the positive ideal solution (pis) is the highest, and the lowest value for the negative ideal solution (nis) is the beneficial (b) criteria. as for the non-beneficial (nb), it is contrariwise. table 12: pairwise comparison matrix the ranking is based on the ci score, with a more excellent value of ci indicating the best option among the five options (d1, d2, d3, d4, and d5). after calculating relative alternatives priority vector rank d1 0.1323 5 d2 0.1440 4 d3 0.2603 1 d4 0.2356 2 d5 0.2278 3 b b nb b nb b nb nb b os m sbf s ec etr etd er l d1 5 2 3 3 2 2 2 4 4 d2 3 3 2 3 4 3 3 2 2 d3 4 5 4 4 4 5 5 4 4 d4 3 4 3 4 4 4 4 4 4 d5 3 4 5 4 4 2 2 4 4 iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 closeness (ci), the value of ci is used to rank the candidates. because the d3 alternative has a better value than the other alternatives, it is rated first. d3 >d2 >d4 >d5 >d1 are the outcomes of all alternatives based on better scores, and their ordering preferences are shown in table 13. table 13: the ranking of the best design concept for oil spill skimmer alternatives si+ sici rank d1 0.1199 0.3024 0.7160 5 d2 0.0946 0.2524 0.7274 2 d3 0.1146 0.3078 0.7287 1 d4 0.1206 0.3113 0.7208 3 d5 0.1232 0.3154 0.7192 4 table 14 shows the ranking result from ahp and topsis. the analysis between ahp and topsis shows that design 3 is chosen as the best conceptual design for a portable oil spill skimmer. this result shows that the ranking from ahp is verified through the topsis analysis. table 14: the comparison ranking of ahp and topsis result alternatives ahp rank topsis rank d1 5 5 d2 4 2 d3 1 1 d4 2 3 d5 3 4 3.4 sensitivity analysis the weighting of the primary criteria significantly impacts the final priority alternatives. as a result, even slight adjustments in the weighting of the criteria might have a significant impact on the final ranking. furthermore, when extra criterion weights are applied, the ranking's stability must be reviewed because these weights are typically based on highly subjective viewpoints. consequently, sensitivity analysis was used to test the ahp finding's robustness. super decision software was used to conduct the sensitivity analysis. the performance graph depicts how the alternatives perform when the situation of all parameter’s changes. d1 red, d2 blue, d3 black, d4 green, and d5 yellow are the colours of the design choices. in figure 1, the first ranking changes from design idea 3 to design concept 1 when the performance priority vector increases by 65 per cent. figure 2 shows that when the priority is increased by 75%, design 4 gets the top position, followed by design 5 and design 1. in addition, when maintenance priority is increased by 70%, the ranking in design 2 to rank 3 and design 5 to rank 4 is shown in fig. 3. finally, there are ranking modifications for designs 2, 3, 4 and 5 for the portable criteria in fig. 4, at 15%, although design 3 remains at the top of the ranking. iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 (a) (b) (c) (d) fig. 4: the sensitivity analysis graph of the criteria; (a) performance, (b) safety, (c) maintenance, (d) portable. 4. conclusion extensive studies on product development trends and customer demands, as well as the study on design techniques and methodologies, are required for product design. designers should be able to see flaws in the design process, sum up the design experience regularly, and think about the meaning of the design from the perspectives of businesses, consumers, and social culture. the correct balance of perceptual inventiveness and rational assessment is required to develop exceptional design works. by combining kansei engineering and the analytical hierarchy process, this study extracts the approach of analysing an oil spill skimmer's user demand and technical specification at the early design stage and proposes a technique for assessing and choosing the most appropriate design concepts during the conceptual design stage. topsis and the sensitivity analysis approach were used to verify the ahp results. design 3 was the best design concept for a portable oil spill skimmer because it has the highest value (26% or 0.26). ahp can help design engineers analyse and choose the optimal design concept based on the criteria and sub-criteria for a decision. other forms of mcdm methods might be integrated with kansei engineering in the future as a recommendation since the findings would be valuable in determining whether other decision methods could be integrated to obtain more precise conclusions. in addition, the number of criteria and sub-criteria could be increased to produce more accurate result. iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 acknowledgment this paper and its research would not have been possible without the exceptional support from the utem short term grant no (pjp/2020/fkp/pp/s01775). furthermore, we are eternally grateful for the generous support from the center of research innovation management (crim) universiti teknikal malaysia melaka for the publication of this paper. references [1] gan y, ji y, jiang s, liu x, feng z, li y, liu y. (2021) integrating aesthetic and emotional preferences in social robot design: an affective design approach with kansei engineering and deep convolutional generative adversarial network. int j ind ergon. https://doi.org/10.1016/j.ergon.2021.103128 [2] mondragón s, company p, vergara m. (2005) semantic differential applied to the evaluation of machine tool design. int j ind ergon. https://doi.org/10.1016/j.ergon.2005.05.001. [3] marini cd, fatchurrohman n, azhari a, suraya s. (2016) product development using qfd, mcdm and the combination of these two methods. iop conference series: materials science and engineering. http://dx.doi.org/10.1088/1757-899x/114/1/012089. [4] azammi an, sapuan sm, ishak mr, sultan mt. (2018) conceptual design of automobile engine rubber mounting composite using triz-morphological chart-analytic network process technique. defence technology, 14(4): 268-277. https://doi.org/10.1016/j.dt.2018.05.009. [5] zhu gn, hu j, ren h. (2020) a fuzzy rough number-based ahp-topsis for design concept evaluation under uncertain environments. applied soft computing journal, 91: 106228. https://doi.org/10.1016/j.asoc.2020.106228. [6] renzi c, leali f, di angelo l. (2017) a review on decision-making methods in engineering design for the automotive industry. journal of engineering design, 28(2): 118-143. https://doi.org/10.1080/09544828.2016.1274720. [7] rosli mu, ariffin mka, sapuan sm, sulaiman s. (2013) integrating triz and ahp: a mpv’s utility compartment improvement design concepts. international journal of materials, mechanics and manufacturing, 1(1): 32-35. https://doi.org/10.7763/ijmmm.2013.v1.7. [8] turan fm, omar b. (2013) the integration of hoq and fuzzy-ahp for design concept evaluation. applied mechanics and materials, 315: 25-29. https://doi.org/10.4028/www.scientific.net/amm.315.25. [9] tiwari v, jain pk, tandon p. (2016) product design concept evaluation using rough sets and vikor method. advanced engineering informatics, 30(1): 16-25. https://doi.org/10.1016/j.aei.2015.11.005. [10] song j, lu y, luo j, huang s, wang l, xu w, parkin ip. (2015) barrel-shaped oil skimmer designed for collection of oil from spills. advanced materials interfaces, 2(15): 1-8. https://doi.org/10.1002/admi.201500350. [11] kumar sa, pawar sh, vishu a, yashodhan p, mayuresh p. (2020) design and fabrication of oil collector. international journal of progressive research in science and engineering, 1(3): 167-185. [12] patil p, shinde p, shetty a, lodha s, vaidya n. (2017) design and fabrication of oil skimmer. international research journal of engineering and technology, 4(5): 2282-2284. [13] rahman ma, manojkumar s, seenivasan m, sivaa gm, vignesh r. (2018) design and fabrication of oil skimmer. international research journal of engineering and technology, 6(4): 4-6. [14] siva s, praveen p. (2017) design and fabrication of belt type oil skimmer. international journal of engineering research & technology (ijert), 5(7): 1-5. [15] abidli a, huang y, cherukupally p, bilton am, park cb. (2020) novel separator skimmer for oil spill cleanup and oily wastewater treatment: from conceptual system design to the first pilot-scale prototype development. environ technol innov, 18: 100598. https://doi.org/10.1016/j.eti.2019.100598. iium engineering journal, vol. 24, no. 1, 2023 ramanathan et al. https://doi.org/10.31436/iiumej.v24i1.2426 [16] nagamachi m. (2008) perspectives and the new trend of kansei/affective engineering. the tqm journal, 20(4): 290-298. https://doi.org/10.1108/17542730810881285. [17] ramanathan r, abdullah l, mohamed ms. (2021) the utilisation of kansei engineering in designing conceptual design of oil spill skimmer. in symposium on intelligent manufacturing and mechatronics, 25: 434-447. https://doi.org/10.1007/978-981-16-8954-3_41. [18] ekolu so, quainoo h. (2019) reliability of assessments in engineering education using cronbach’s alpha, kr and split-half methods. journal of engineering education, 21(1): 24-29. [19] waris m, panigrahi s, mengal a, soomro mi, mirjat nh, ullah m, azlan zs, khan a. (2019) an application of analytic hierarchy process (ahp) for sustainable procurement of construction equipment: multicriteria-based decision framework for malaysia. journal of mathematical problem in engineering. https://doi.org/10.1155/2019/6391431. [20] sindhu s, nehra v, luthra s. (2017) investigation of feasibility study of solar farms deployment using hybrid ahp-topsis analysis: case study of india. renewable and sustainable energy reviews, (73): 496-511. https://doi.org/10.1016/j.rser.2017.01.135. [21] darko a, chan apc, ameyaw ee, owusu ek, pärn e, edwards dj. (2019) review of application of analytic hierarchy process (ahp) in construction. international journal of construction management, 19: 436-452. https://doi.org/10.1080/15623599.2018.1452098. [22] doloi h. (2008) application of ahp in improving construction productivity from a management perspective. construction management and economics, 26(8): 841-854. https://doi.org/10.1080/01446190802244789. [23] schot j, fischer k. (1993) introduction: the greening of the industrial firm, volume 3. island press; pp 3-33. [24] cheng ew, li h, ho dc. (2002) analytic hierarchy process (ahp):a defective tool when used improperly. measuring business excellence, 6(4): 33-37. https://doi.org/10.1108/13683040210451697. [25] jain v, sangaiah ak, sakhuja s, thoduka n, aggarwal r. (2018) supplier selection using fuzzy ahp and topsis: a case study in the indian automotive industry. neural computing applications, 29: 555-564. https://doi.org/10.1007/s00521-016-2533-z. [26] parameshwaran ma, sivaraj s, venkataram n. (2019) numerical simulation and experimental validation of planetary gearbox system design to govern constant generator speed in hydro power plant. in iop conference series: materials science and engineering, https://doi.org/10.1088/1757-899x/624/1/012008. [27] abdullah l, jamaludin z, chiew th, rafan na, mohamed ms. (2012) system identification of xy table ballscrew drive using parametric and non parametric frequency domain estimation via deterministic approach. procedia engineering, 41: 567-574. https://doi.org/10.1016/j.proeng.2012.07.213. [28] escudero gg, bo p, gonzález-barrio h, calleja-ochoa a, bartoň m, de lacalle lnl. (2022) 5-axis double-flank cnc machining of spiral bevel gears via custom-shaped tools—part ii: physical validations and experiments. international journal of advanced manufacturing technology, 119(3-4): 1647-1658. https://doi.org/10.1007/s00170-021-08166-0 [29] haddad m, sanders d. (2018) selection of discrete multiple criteria decision making methods in the presence of risk and uncertainty. operations research perspectives, 5: 357-370. https://doi.org/10.1016/j.orp.2018.10.003. [30] vaske jj, beaman j, sponarski cc. (2016) rethinking internal consistency in cronbach’s alpha. leisure science, 39: 163-173. https://doi.org/10.1080/01490400.2015.1127189. [31] dey pk. (2004) analytic hierarchy process helps evaluate project in indian oil pipelines industry. international journal of operations and production management, 24: 588-604. https://doi.org/10.1108/01443570410538122. [32] al-marri an, nechi s, ben-ayed o, charfeddine l. (2020) analysis of the performance of tam in oil and gas industry: factors and solutions for improvement. energy reports, 6: 2276– 2287. https://doi.org/10.1016/j.egyr.2020.08.012. [33] bandyopadhyay s. (2019) introduction to production and operations concept. production and operations analysis: traditional, latest, and smart views. 1st edition crc press; pp 1-8. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. air pollution index prediction using multiple neural networks zainal ahmad1*, nazira aniza rahim2, alireza bahadori3 and jie zhang4 1school of chemical engineering, engineering campus, universiti sains malaysia, 14300, nibong tebal, penang, malaysia. 2river basin research centre, national hydraulic research institute of malaysia, lot 5377, jalan putra permai, 43300 seri kembangan, selangor, malaysia. 3school of environment, science and engineering, southern cross university, lismore, new south wales, australia. 4school of chemical engineering and advanced materials, newcastle university, newcastle upon tyne ne1 7ru, united kingdom. *corresponding author: chzahmad@usm.my (received: 25th may 2016; accepted: 27th sept. 2016; published online: 30th may 2017) abstract: air quality monitoring and forecasting tools are necessary for the purpose of taking precautionary measures against air pollution, such as reducing the effect of a predicted air pollution peak on the surrounding population and ecosystem. in this study a single feed-forward artificial neural network (fann) is shown to be able to predict the air pollution index (api) with a mean squared error (mse) and coefficient determination, r 2 , of 0.1856 and 0.7950 respectively. however, due to the non-robust nature of single fann, a selective combination of multiple neural networks (mnn) is introduced using backward elimination and a forward selection method. the results show that both selective combination methods can improve the robustness and performance of the api prediction with the mse and r 2 of 0.1614 and 0.8210 respectively. this clearly shows that it is possible to reduce the number of networks combined in mnn for api prediction, without losses of any information in terms of the performance of the final api prediction model. abstrak: pemantauan dan ramalan kualiti udara adalah perlu bagi mengambil langkah berjaga-jaga terhadap pencemaran udara, seperti untuk meramalkan mengurangkan kesan puncak pencemaran udara terhadap penduduk sekitar dan ekosistem. dalam kajian ini rangkaian tiruan tunggal neural suap depan (fann) ditunjukkan masing-masing dapat meramalkan indek pencemaran udara (ipu) dengan purata ralat kuasa dua (mse) dan pekali penentuan, r 2 , daripada 0.1856 dan 0.7950. namun disebabkan oleh sifat tidak mantap fann tunggal, gabungan terpilih pelbagai rangkaian neural (mnn) diperkenalkan dengan menggunakan penghapusan ke belakang dan kaedah pemilihan ke hadapan. keputusan kajian menunjukkan bahawa kedua-dua kaedah gabungan terpilih boleh meningkatkan keteguhan dan prestasi ramalan api masing-masing dengan mse dan r2 daripada 0.1614 dan 0.8210. ini jelas menunjukkan bahawa ia adalah mungkin untuk mengurangkan bilangan rangkaian digabungkan dalam mnn untuk ramalan api, tanpa menjejaskan keupayaan mana-mana maklumat dari segi prestasi model ramalan akhir api. keywords: air pollution index;artificial neural networks; multiple neural networks; forward selection; backward elimination 1 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. 1. introduction air quality is monitored continuously and manually to detect any changes in the ambient air quality status that may cause harm to human health or the environment. the malaysian department of environment (doe) monitors the ambient air quality via a network of 51 monitoring stations across malaysia [1]. these monitoring stations are strategically located in residential, traffic, and industrial areas to detect any significant changes in the air quality which could be harmful to human health and the environment. the ambient air quality measurement in malaysia is described in terms of the air pollutant index (api), which is a simple way to describe and report the air quality instead of using the actual concentration of air pollutants. this api also reflects effects on human health, ranging from good to hazardous, and can be categorized according to its action criteria as specified in the national haze action plan malaysia. efficient methods for the assessment of air quality are needed in order to establish mechanisms for managing pollutant concentration and preventing illness in healthsensitive people. the criterion for good air quality varies with the kind of ecosystem and is established at different levels. several methodologies for the assessment and monitoring of air pollutants have been implemented by organizations such as the department of environment (doe) of malaysia which has developed indexes for air quality. in response to this concern, several studies on air quality prediction using artificial neural networks have been done [2, 3]. unlike other modelling techniques, artificial neural networks (ann) make no prior assumptions concerning the data distribution and require no mechanistic knowledge. ann is capable of modelling highly nonlinear relationships and can be trained to accurately generalize when presented with a new data set. an air quality prediction model based on neural networks had also been applied on a short-term and long-term basis. viotti et al [4] has applied this prediction model to predict the vehicular air pollutant levels in the city of perugia, italy, while sabri and tarek [5] have applied it in the region of annaba, algeria. however, the latter have combined a radial basis function (rbf) network and multiple layer perceptron (mlp) in their model to predict the air pollutant concentrations. in addition to the emission sources, meteorological factors (wind speed and direction, temperature, precipitation and boundary layer heights), can govern the variability of atmospheric pm10 [6, 7] as well. in fact, urban and industrialized areas tend to record their highest pm10 concentrations under stable meteorological conditions coupled with thermal inversions or during long range transport events [8, 9] while the lowest readings tend to occur during windy and rainy periods [10]. many researchers have studied the prediction of particulate matter concentration in the environment. perez et al. [11] and yan and jian [12] have focused their study on the prediction of the pm2.5 (particulate matter with a diameter smaller than 2.5 micrometers) concentration using an ann model. some of the researchers have developed an air quality prediction model based on neural networks with a multilayer perceptron structure. gardner and dorling [13] and perez and trier [14] have adopted this model to predict the no and no2 concentration based on meteorological data in central london and traffic junctions in santiago city in chile respectively. they have also concluded that the mlp has better performance compared to their previously developed regression models. feed-forward artificial neural networks (fann) have also been applied by sousa et al. [15] to predict hourly ozone concentration based on meteorological data while ul-saufie et al. [16] has applied it by combining with pca to predict pm10 concentration in negeri sembilan, malaysia. cigizoglu and kisi [17] have also applied fann. chelani et al. [18] have predicted so2 values at three sites in delhi, india, using neural networks and compared the results with 2 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. those of multivariate regression models. wind speed, wind direction index, relative humidity and temperature variables have been used as inputs for their developed recurrent neural network. even though there were successes in many applications of ann and considerably less restrictions on the environmental input data, large training data sets are usually required to improve the accuracy and minimize uncertainty in the output data, which up to now has been a significant disadvantage of these models. gardner and dorling [19] have reviewed the limitations and problems associated with the training of anns and emphasized that fundamental understanding of the basic theory is the key in developing anns. it is well known that a neural network can approximate any smooth nonlinear function between model inputs and outputs by selecting a suitable set of connecting weights and transfer functions [19]. therefore in this paper, selective combination of multiple neural networks (mnn) is introduced to improve the single feed-forward neural artificial network (fann) prediction for the api model as shown in fig. 1 [20]. this paper is organized as follows: section 2 presents the case study concerning the api sampling area and location in malaysia. the concept of single fann and mnn combination using fs and be method are presented in section 3. the results and discussions of the proposed mnn with selective combination are presented in section 4. finally, the last section concludes this paper. fig. 1: combining multiple neural networks. 2. case study: perak air pullution index monitoring stations, malaysia most air quality data are obtained from air quality monitoring stations directly or through remote sensing instruments. here, the air quality data from 4 monitoring stations around perak state were collected by the department of environment (doe), malaysia, which is stationed at ca0020, ca0041, ca0045 and ca0046, as illustrated in fig. 2. these continuous air quality monitoring (caqm)-type monitoring stations, are strategically located in residential, traffic, and industrial areas to detect any significant changes in the air quality that may be harmful to human health and the environment [1]. the air quality data was recorded for 4 years, from 2006 to 2009 for eight variables. for the api modelling, variables involved are the concentrations of the air pollutants and meteorological variables, and are divided into groups of input and output variables for the fann model. however for this study, 6 air pollutant inputs are selected for model 3 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. development as shown in table 1. a total of 1388 samples were used for the modelling and analysis in this study and the raw data for the modelling of year 2006 is shown in fig. 3. fig. 2: perak air monitoring stations [1]. table 1: air quality variables for api modelling input variables (average hourly) output variables  ozone, o3 (mg/l)  particulate matter with size less than 10 microns, pm10 (mg/l)  carbon monoxide, co (mg/l)  wind speed (km/hr)  air temperature (oc)  relative humidity (%) api 3. feed-forward artificial neural network model development in this case study, an hourly average of 1388 data samples were taken from malaysia’s department of environment database from year 2006 to year 2009. all the data was normalized to zero mean and unit standard deviation to cope with the different magnitudes in the input and output data. then, the input data were divided randomly using the matlabtm divideint command into three sets of data, namely 70% (972 samples) as training data, 15% (208 sample) as testing data, and 15% (208 samples) as unseen validation data. then the individual networks were trained using the levenberg-marquardt optimization algorithm with regularization and “early stopping”. the networks are single hidden layer feed-forward neural networks (fann). hidden layer neurons use the logarithmic sigmoid activation function whereas output layer neurons use the linear activation function. in this study, 20 networks with fixed identical structure were 4 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. fig. 3: raw data for input and output for fann model prediction for year 2006. (a) average wind speed, (b) average ambient temperature, (c) average relative humidity, (d) average co, (e) average pm10, (f) average o3, (g) api. developed from bootstrap re-samples of the original training and testing data. if the number of networks for combination is too small we might not get the optimum reduction of the mse in the combination. in re-sampling the training and testing data, a bootstrap resampling technique was applied where the training and testing data were first transformed into the discrete time functions, therefore re-sampling the discrete time data does not affect the input-output mapping of the models. the fann is developed based on the discrete time of the process as the prediction output at time (t), y(t), is predicted based on the process inputs at time t, u(t), as follows: )](),....,(),([)(ˆ 21 tututufty m  (1) 0 100 200 300 400 0 10 20 samples (a) a v e ra g e w in d s p e e d , k m /h r 0 100 200 300 400 0 50 100 samples (c) a v e ra g e r e la ti v e h u m id it y , % 0 100 200 300 400 24 26 28 30 samples (b) a v e ra g e a m b ie n t t e m p e ra tu re , c e ls iu s 0 100 200 300 400 0 0.5 1 1.5 samples (d) c o ,m g /l 0 100 200 300 400 0 50 100 150 samples (e) p m 1 0 , m g /l 0 100 200 300 400 0 0.01 0.02 0.03 samples (f) o 3 , m g /l 0 50 100 150 200 250 300 350 400 10 20 30 40 50 60 70 80 90 100 110 samples (g) a p i 5 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. where u(t) is the process input at time (t), y(t)is the predicted process output at time t, which is the api, and m is the number of the process inputs and for this case study is 6 as shown in table 1. then the forward selection (fs) and backward elimination (be) approach combined with simple averaging method was developed. the fs and be method was developed in our previous paper with the different application of the prediction [21]. generally, in fs, the individual networks are added one at a time to the aggregated network where when the network is combined or included in the aggregated network it will produces the greatest decrease in model prediction mse. this process starts with an empty aggregated model and the first network to be chosen in the aggregated network is the single network that has the least mse in training and testing data or what we call the best individual network. the second network added is the one, when combined with the first added network, produces the largest reduction in mse on the original training and testing data. this procedure is repeated until the mse on the training and testing data cannot be further reduced by adding more networks. on the other hand, in the be, the aggregated network begins with combining all the individual networks in the pool of networks and removes one network at a time until the mse on the training and testing data cannot be further reduced. the network deleted at each step is selected such that its deletion results in the largest reduction in the aggregated network mse on the training and testing data. the detailed procedures for the fs and be method can be found in [21]. the simple average method is used in combining the selected networks in both approaches as shown in eqn. (2) where, if all n networks are combined, the aggregated network output is:    n i i y n y 1 ˆ1ˆ (2) the performances of the actual and predicted models are based on the mse and coefficient determination, r2. the advantages of using the mse include its easy calculation and that it penalizes large errors in each observation. therefore the average sum square error in each sample observation is able to determine the quality of the prediction of the model. on the other hand, the r2 provides the inconsistency measure of the data reproduced or predicted and the fitness of the model to capture the actual process. the higher the values of r2, or closest to 1, and the smallest of the mse, or closest to zero, the better the model. 4. results and discussion the inputs of these network models are the hourly average of carbon monoxide, wind speed, air temperature, relative humidity, pm10 and o3 and their output is the api values as shown in eqn. (1). the single fann network with a single hidden layer was applied with the levenberg-marquardt training algorithm with a sigmoid activation function in the hidden layer and a linear activation function in the output layer. the structure of the single fann is represented by the number of nodes in each layer. the number of nodes in the input layer is 6, which represents the input variables, while the outer layer has only one node representing one model output variable. however, the fitted model was assured by the number of nodes in the hidden layer. therefore, the determination of the number of nodes in the hidden layer was carr ied out by calculating the mse for the combination of training and testing data. the number of nodes in the hidden layer was varied between 1 and 20 in order to find the “best” number of nodes for the model. figure 4 shows the performance of the model prediction 6 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. with different numbers of nodes in the hidden layer. the lowest mse value on the combination of the training and testing data was 0.1652, recorded by the model with 9 hidden nodes in the hidden layer. thus, the network with 9 hidden nodes was selected as the final model structure or network architecture, i.e. the topology of the network is 6-9-1. fig. 4: mse on the training and testing data with different numbers of hidden nodes. figure 5 shows the neural network model prediction performances on the training and testing data. in figure 4, the solid lines represent the scaled true values of api and the dotted lines represent the model predictions. it can be seen that the predicted values are very close to the actual values for both sets of data. the mse and the r2 for training and testing data are 0.1988, 0.1613 and 0.7962, 0.8257 respectively. figure 6 shows the model prediction performance on the unseen validation data from the single fann. in fig. 6, the scaled true values of api are represented by the solid line while the model predictions are represented by the dotted line. the single fann model clearly emulates the patterns of process accurately on the unseen validation data. the mse and the r2 values on the unseen validation data are 0.1856 and 0.7950 respectively. figure 6 clearly shows that the predicted and the actual values are close to each other. thus, it showed in the intricate model that the api process can be modelled and generalized quite well using single fann. however, even though single fann is shown to be able to predict the api quite accurately, single fann models sometimes lack robustness as shown in fig. 7a and 7b. single fanns sometimes suffer badly when applied to unseen data where some neural network might fail to deliver the correct result due to the network training converged to undesired local minima or over-fitting of noise in the actual data. in fig. 7a, one of the best single fanns in training and testing data was network number 14 but its 7 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. fig. 5: actual and predicted values for training and testing data. fig. 6: actual and predicted values on the unseen validation data from single fann. performance on the unseen data was not among the best. figure 7b shows that the best network on unseen validation data is network number 7, but its performance on the training and testing data is not among the best at all. there is no guarantee that the best model on the training and testing data will be the best on the unseen data. therefore the combination of multiple neural networks is proposed in this study with the aim of enhancing the neural network robustness on unseen data. 8 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. fig. 7: mse for single fann. (a) mse for training and testing data, (b) mse for validation data. fig. 8: mse for aggregated multiple neural networks on the unseen validation data for be and fs approaches. figure 8 shows the multiple neural network performance using selective combinations with be and fs methods. the performance of aggregated networks on training and testing data is consistent with the performance on the unseen validation data for both select ive 0 2 4 6 8 10 12 14 16 18 20 0.15 0.2 0.25 no. of networks (a) m s e t e s ti n g a n d t ra in in g d a ta 0 2 4 6 8 10 12 14 16 18 20 0.15 0.2 0.25 no. of networks (b) m s e v a li d a ti o n 9 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. combination methods. the reduction of mse in training and testing data for be and fs combinations are consistent with the reduction of mse in the unseen/validation data. it shows the robustness of the proposed modelling techniques as compared to the single fann where the best network performance in training and testing data will not guarantee the best performance in the unseen validation data. the numbers of networks for the final combination are reduced to 3 networks for both methods which show the minimum mse in training and testing data that also correspond to mse in validation data. the final result analysis is shown in table 2. in this particular case, the fs and be approaches led to the same individual networks being combined. even though the number of networks combined was quite small for both selective methods, the most important thing is that both combination approaches perform better than the single fann. table 2: statistical analysis of mnn performance on the unseen validation data number of networks combined mse r2 single fann 1 0.1856 0.7950 combined all mnn 20 0.1649 0.8170 fs aggregated mnn 3 (12,15,20) 0.1635 0.8200 be aggregated mnn 3 (12,15,20) 0.1635 0.8200 as for comparison, azid et al. [22, 23] did carry out api modelling for the southern region of malaysia with 2 different sets of data containing 202,050 and 232,505 observations respectively. in [22] the input was reduced to 10 from 12 possible inputs with the r2 and rmse of 0.724 and 7.562 for unseen validation data respectively. on the other hand, in [23], the input was reduced to 5 from a possible 8 with the r2 and rmse of 0.618 and 10.017 for unseen data respectively. therefore, the mnn did perform better than the [22] and [23] api modelling for malaysia as shown in table 2 with the r2 and rmse of 0.8200 and 0.160 for unseen validation data respectively. this performance was obtained with fewer sample data (1388 observations) as compared in [22] and [23]. 5. conclusion this study proposes single fann and multiple neural networks to model api based on the environmental monitoring data to get reliable and fast api predictions in order to mitigate the problems related to api. the single fann does model the api quite well with relatively small mse and high r2 values on the unseen data. however, in order to overcome the non-robust nature of single fann, multiple neural networks are proposed with two selective combination methods. both selective combination methods further improve the model prediction as compared to single fann and combining all networks. this clearly shows that it is possible to reduce the number of networks combined for the api prediction without losses in performance. acknowledgement the authors would like to acknowledge the support from the universiti sains malaysia (usm) and newcastle university, united kingdom, and special gratitude to department of environment (doe) malaysia for providing and giving permission to utilize their air quality data for this study. 10 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. references [1] asma. “air pollutant index (api),“ retrieved on july, 2012. available from http://www.doe.gov.my/portalv1/en/info-umum/english-air-pollutant-index-api/100 [2] akkoyunlu a, yetilmezsoy k, erturk f, oztemel e. (2010) a neural network-based approach for the prediction of urban so2 concentrations in the istanbul metropolitan area. international journal of environment and pollution, 40(4):301-315. [3] wang w, lu w, wang x , leung yt. (2003) prediction of maximum daily ozone level using combined neural network and statistical characteristics. environmental international, 29(5):555–562. [4] viotti p, liuti g, di genova p. (2002) atmospheric urban pollution: applications of an artificial neural network (ann) to the city of perugia. ecol modell., 148(1):27-46. [5] sabri g, tarek km. (2012) combination of artificial neural network models for air quality predictions for the region of annaba, algeria. int. j. environ. stud., 69(1):79-89. [6] amodio m, andriani e, cafagna i, caselli m, daresta be, de gennaro g, tutino m. (2010) a statistical investigation about sources of pm in south italy. atmos. res., 98:207218. [7] rodriguez s, querol x, alastuey a, kallos g, kakaliagou o. (2001) saharan dust contributions to pm10 and tsp levels in southern and eastern spain. atmos. environ., 35:2433-2447. [8] peyj, pérez n, querol x, alastuey a, cusack m, reche c. (2010) intense winter atmospheric pollution episodes affecting the western mediterranean. sci. total environ., 408(8):1951–1959. [9] pohjola ma, rantamäki m, kukkonen j, karppinen a, berge e. (2004) meteorological evaluation of a severe air pollution episode in helsinki on 27-29 december 1995. boreal environ. res., 9(1):75–87. [10] de gennaro g, trizio l, di gilio a, pey j, pérez n, cusack m, querol x. (2013) neural network model for the prediction of pm10 daily concentrations in two sites in the western mediterranean. sci. total environ., 463-464:875–883. [11] perez p, trier a, reyes j. (2000) prediction of pm2.5 concentrations several hours in advance using neural networks in santiago, chile. atmos. environ., 34:1189–-196. [12] yan ck, jian l.(2013) identification of significant factors for air pollution levels using a neural network based knowledge discovery system. neurocomputing, 99: 564-569. [13] gardner mw, dorling sr. (1998) artificial neural networks (the multilayer perceptron) a review of applications in the atmospheric sciences. atmos. environ., 32(14-15):2627-2636. [14] perez p, trier a. (2001) prediction of no and no2 concentrations near a street with heavy traffic in santiago, chile. atmos. environ., 35:1783-1789. [15] sousa s, martins f, alvimferraz m, pereira m. (2007) multiple linear regression and artificial neural networks based on principal components to predict ozone concentrations. environ. model softw., 22(1):97-103. [16] ul-saufie az, yahaya as, ramli na, rosaida n, hamid ha. (2013) future daily pm10 concentrations prediction by combining regression models and feedforward backpropagation models with principle component analysis (pca). atmos. environ., 77:621-630. [17] cigizoglu kh, kisi ö. (2006) methods to improve the neural network performance in suspended sediment estimation. j. hydrol., 317:221-238. [18] chelani ab, chalapati rc, phadke k, hasan m. (2002) prediction of sulfur dioxide concentration using artificial neural networks. environ. model softw., 17:161-168. [19] gardner mw, dorling sr. (1999) neural network modelling and prediction of hourly no and no concentrations in urban air in london. atmos. environ., 33:709-719. [20] zhang j. (1999) “developing robust non-linear models through bootstrap aggregated neural networks. neurocomputing, 25:93-113. [21] ahmad z, zhang j. (2009) selective combination of multiple neural networks for improving model prediction in nonlinear systems modelling through forward selection and backward elimination. neurocomputing, 72:1198-1204. 11 iium engineering journal, vol. 18, no. 1, 2017 ahmad et al. [22] azid a, juahir h, latif mt, mohd zain s, osman mr. (2003) feed-forward artificial neural network model for air pollutant index prediction in the southern region of peninsular malaysia. journal of environmental protection, 4:1-10. [23] azid a, juahir h, toriman me, kamarudin mka, mohd saudi as, ,che hasnam cn, abdul aziz na, zaman f, latif mt, mohamed zainuddin sf, osman mr, yamin m. (2014) prediction of the level of air pollution using principal component analysis and artificial neural network techniques: a case study in malaysia. water air soil pollut., 225:2063-2077. nomenclature ann artificial neural network api air pollution index be backward elimination co carbon monoxide mg/l fann feed-forward artificial neural network fs forward selection mlp multi-layer perceptron mnn multiple neural networks mse mean sum square error n number of networks combined no nitrogen monoxide mg/l no2 nitrogen oxide mg/l o3 ozone mg/l pca principle component analysis pm10 concentration of particulate matter with a size less than 10 microns mg/l pm2.5 concentration of particulate matter with a size less than 2.5 microns mg/l r2 coefficient determination g/mol x input data x̂ input data after resampling y output data ŷ network prediction output subscript i number of network 12 microsoft word 0_vol_16_no_2_2015_special issue on energy_compiled.docx iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 13 analysis and modeling of solar evaporator-collector zakaria mohd. amin1, m.n.a. hawlader2 and ye shaochun3 1school of chemistry, physics and mechanical engineering, queensland university of technology, australia. 2 department of mechanical engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. 3department of mechanical engineering, national university of singapore, 9 engineering drive 1, singapore 117576. zakaria.amin@qut.edu.au, mehawlader@iium.edu.my, and ye_shaochun@nmc.astar.edu.sg (received: august 10, 2015; accepted: october 30, 2015; published on-line: november 30, 2015) abstract: solar energy is considered a sustainable resource that poses little to no harmful effects on the environment. the performance of a solar system depends to a great extent on the collector used for the conversion of solar radiant energy to thermal energy. a solar evaporator-collector (sec) is basically an unglazed flat plate collector where refrigerants, such as r134a is used as the working fluid. as the operating temperature of the sec is very low, it utilizes both solar irradiation and ambient energy leading to a much higher efficiency than the conventional collectors. this capability of secs to utilize ambient energy also enables the system to operate at night. this type of collector can be locally made and is relatively much cheaper than the conventional collector. at the national university of singapore, the evaporator-collector was integrated to a heat pump and the performance was investigated for several thermal applications: (i) water heating, (ii) drying and (iii) desalination. a 2-dimensional transient mathematical model of this system was developed and validated b y experimental data. the present study provides a comprehensive study of performance. abstrak: tenaga suria merupakan sumber lestari yang tidak memudaratkan alam sekitar. keupayaan sistem ini bergantung sebahagian besarnya kepada kebolehan pengumpul untuk menukar tenaga suria kepada tenaga haba. pengumpul penyejat suria (sec) pada asasnya merupakan plat datar tanpa glasair di mana bahan penyejuk seperti r134a digunakan sebagai bendalir kerja. memandangkan suhu kendalian sec adalah amat rendah, ia boleh menggunakan penyinaran suria dan tenaga ambien agar memberikan efisiensi yang lebih tinggi daripada pengumpul konvensional. keupayaan sec dalam mempergunakan tenaga ambien membolehkan sistem ini beroperasi pada waktu malam. pengumpul merupakan keluaran tempatan dan ianya lebih murah berbanding pengumpul lazim. di universiti nasional singapura, pengumpul penyejatnya diintegrasikan pada pam haba dan prestasinya dikaji untuk beberapa aplikasi terma: (i) pemanasan air, (ii) pengeringan dan (iii) penyahgaraman. model matematik transien dua dimensi bagi sistem ini dikembang dan divalidasi berdasarkan data eksperimental. selidikan terkini memberikan kajian prestasi yang menyeluruh. keywords: heat pump; evaporator-collector. 1. introduction in view of the growing global energy needs and concern for environmental degradation, the possibility of running thermal systems using energy from the sun is iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 14 receiving considerable attention in recent years. solar energy is clean and is the most inexhaustible of all known energy sources. the low temperature thermal requirement of a heat pump makes it an excellent match for the use of solar energy. the combination of solar energy and heat pump system can bring about various thermal applications for domestic and industrial use, such as water heating, solar drying, space cooling, space heating, and refrigeration. unlike thermosyphon solar water heaters, solar heat pump systems offer the opportunity to upgrade low-grade energy resources from the surroundings as well as solar energy and makes use of it for domestic and industrial applications [1]. the concept of direct expansion solar-assisted heat pump (dx-sahp) was first proposed in an experimental study by sporn and ambrose [2]. they used double glazed collector which also act as evaporator for the heat pump with r-12 being the working fluid. they did not demonstrate the full potential of the concept due to a mismatched, oversized compressor. they also did experiments by removing the glazing and found that the removal did not affect the performance significantly. they found that removal of glazing or back insulation does not affect performance of two-phase flow solar collector significantly. the collector operating temperature in a solar-assisted heat pump system can be lower than the ambient temperature. in this case, an un-glazed solar evaporator collector is used. the simple structure of the un-glazed solar collector makes it an economical type of solar collector. however, its performance is highly dependent upon the environment, because its surface is exposed directly to the ambient. to improve the performance of unglazed solar collectors, a clear understanding of how the environment affects it is required. an uninsulated, bare two-phase collector is firstly used in franklin et al.’s [3] heat pump system. chaturvedi et al.[4, 5] found a variation of the evaporator temperature from 0°c to 10°c above the ambient temperature under favorable solar conditions. many authors [6-8] reported that for ambient temperatures above 25°c, the evaporator could be operated at an elevated temperature. hawlader et al.[1] performed analytical and experimental studies on a solar assisted heat pump using unglazed, flat plate solar collectors, known as an evaporator-collector, using a steady-state one-dimensional mathematical model. two-phase flow in collectors was first considered by sporn and embrose [2]. they used a double glazed collector which also act as evaporator for the heat pump with r-12 being the working fluid. they did not demonstrate the full potential of the concept due to a mismatched, oversized compressor. they also did experiments by removing the glazing and found that the removal did not affect the performance significantly. they found that removal of glazing or back insulation does not significantly affect performance of the twophase flow solar collector. literature on two-phase collectors report that two models of calculating pressure drop are most widely used. these are known as the martinelli nelson's method for separated flows and owen's homogeneous equilibrium model for misty or bubbly flow [9]. the homogeneous equilibrium model is the simplest method determining the pressure drop in two-phase flow and makes the basic assumption that the two-phases have the same velocity. by adopting an equilibrium, homogeneous, two-phase model as mentioned above, chaturvedi et al. [10] carried out preliminary theoretical performance studies concerning a solar-assisted heat pump that uses a bare collector as the evaporator. the analysis was iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 15 subject to limitation of a constant temperature evaporator with no superheating or sub cooling. it is the first time wherethe single phase flat plate collector theory was extended to the two-phase regime. the first comprehensive work about two-phase solar collector was carried out by soin et al. [6]. the collector efficiency was found to increase linearly with the liquid level. the researchers investigated the thermal performance of a thermosyphon collector containing boiling acetone and petroleum ether, and developed a modified form of the hottelwhillier-bliss equation (hwb)[11] to account for the fraction of liquid level in the collector with glazed. the steady-state thermal efficiency ηb containing a modified heatremoval factor fr, in the hwb equation, for a two-phase solar collector is firstly defined by al-tamimi and clark [7], accounting for the boiling and the sub-cooled portions of the collector. researchers conducted a detailed study of boiling fluid solar collector in 1984 [8], in which an analytical model was developed to investigate of sub cooling the fluid entering the collector and the level of fluid in the collector on the collector efficiency. the term z* was defined as reference to the fraction of the collector required to heat the fluid to its boiling temperature. mainly based on the results of al-tamini and clark's research, an ashrae 109-a test standard for two-phase solar collectors was established in 1984. this standard defined five sets of conditions for two-phase collector thermal efficiency [12]. ahmed et al. [13] developed and defined a new generalized heat removal factor, fs and a new overall thermal loss coefficient, ul for the two-phase flat-plate collector. further modification on ul was also done in 1989 [14]. first steady-state system simulations made with trnsys was done by freeman et al. [15]. the first thermodynamic model to analyze two-phase solar collector is developed by chaturvedi et al. [4]. the equilibrium homogeneous theory is used to model the two-phase flow in solar collectors. o’dell et al. developed a design method for heat pumps with refrigerant filled solar collectors [16]. the researchers obtained the heat gain at condenser and the cop as a function of evaporation temperature. numerical calculations of the collector efficiencies for a double-glazed two-phase flat-plate collector employing r-11 were carried out by kishore et al. [17]. they firstly express the collector efficiency as a function of the saturation temperature and liquid level by combining their experimental data. ramos et al.[18] also carried out theoretical investigation on two-phase collectors assuming laminar homogeneous flow and experimentally confirmed by them. mathur et al. [19] developed a method calculating boiling heat transfer coefficient in a two-phase thermosyphon loop. the first detailed model for boiling solar collector using trnsys was developed by price et al. [20] all the modeling or analysis mentioned above assume a homogeneous two-phase flow. the first theoretical model concerning non-homogenous for two-phase flow thermosyphon in the collector and condenser was carried out by yilmaz [21]. his results show that the homogenous model is not sufficient to describe the two-phase flow in the collector. variation of the properties of the working fluid and water with temperature are taken into account. considering the effect of long-wave radiation and wind speed, a modified form of the hottel-whillier-bliss solar collector efficiency function for unglazed solar collector characterization is investigated by morrison and gilliaert [22]. using the approach of element analyze of the steady one-dimensional two-phase energy conservation equations in finite, a mathematical model for natural circulation twophase solar collector with cover was developed by radhwan et al. [23]. torres reyes et al. conducted the first exergy analysis on a solar-assisted heat pump with two-phase collectoriium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 16 evaporator [24]. they theoretically analyzed and experimentally confirmed that 80% irreversibilities in sahp system occurs in collector-evaporator because a significant fraction of the total solar radiation absorbed is poorly employed. similar investigation and results were obtained by cervantes [25]. most of the researches before 1999 were for steady-state in two-phase flow. hussein firstly investigated theoretically and experimentally a two-phase closed thermosyphon flat plate solar collector under transient conditions [26]. he improved the modified the model in 2002 [27]. however no one has investigated the effect of the condensation phenomenon caused by high relative humidity (rh) on the surface of un-glazed solar collectors. the effect of the condensation phenomenon on the collector performance was investigated in this study. a transient two-dimensional mathematical model of the evaporator-collector has been developed to predict temperature distribution and useful energy gain. a series of experiments were performed under the meteorological conditions of singapore to validate the model. 2. system description a solar assisted heat pump system for air-conditioning, water heating and drying is shown in fig. 1. this system consists of five major components, namely the solar collector, evaporator, condenser (water cooled condenser and air cooled condenser), expansion valve, and compressor. refrigerant r-134a was used as the working fluid due to environmental and thermodynamic considerations [4]. in the present study, two evaporators connected in parallel can increase the system coefficient of performance (cop) significantly. one of the evaporators performs as a solar collector, absorbing heat from solar radiation and ambient air; while another evaporator absorbs heat from a room for cooling purposes. the energy from these two heat sources, plus the electrical energy supplied to the compressor, is used for water heating and air heating for drying purposes. fig. 1: schematic overview of solar assisted heat pump air-conditioner, water heater and dryer. the superheated refrigerant vapor leaving the compressor enters the water-cooled condenser and performs water heating. the refrigerant, a mixture of vapor and liquid, leaves the water-cooled condenser and enters an air-cooled condenser to ensure complete condensation of the refrigerant vapor. the hot air obtained from the air condenser is used for cloth drying purposes. once complete condensation of the refrigerant vapor has taken place, the refrigerant path splits into two: one goes to evaporator-collector to absorb solar energy and the other goes to air-conditioned space to absorb thermal energy from the room iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 17 to provide cooling. superheated refrigerant vapor from the two evaporators mix together and enters into the compressor for next cycle. two evaporator-collectors each with an area of 1.5 m2, made of 1mm copper plates were connected in series, as shown in fig. 2. a 9.52 mm diameter copper tube was soldered at the back of each absorber plate in a serpentine configuration (figure 2a). adequate insulations were provided at the back of the collector but no glass cover was used on the top surface, i.e. the unglazed collector (figure 2b). the collector surface was coated with a black paint with absorptivity of 90%. there is a bypass line from the exit of the first evaporator-collector to the exit of the second evaporator-collector, which remains closed or open depending on the solar irradiation. (a) (b) fig. 2: photograph of the un-glazed solar evaporator-collector. 3. evaporator-collector model a transient two-dimensional mathematical model of the evaporator-collector has been developed to predict temperature distribution and useful energy gain. fig 3: geometry and coordinate system of the unglazed solar evaporator collector. the function of an evaporator collector is to deliver the heat absorbed on the collector surface to the fluid in the tube. because the copper plate is thin and its onductivity is high, the temperature variation in the z-direction can be considered as negligible. however, the heat transfer in the y-direction, as shown in fig. 3, cannot be considered negligible because of the fact that the fluid temperature is not constant along the length of the tube. for this reason, the governing equation is derived to predict the performance of the evaporator collector by considering heat transfer in both x and y directions. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 18 fig. 4: energy balance in a control volume in the interior area of collector. an energy balance on the control volume is shown in fig. 4 gives: ( )x y u x x y y p t q q q q q c x y t             (1) the term ( )p t c x y t       represents the change of internal energy in the elemental control volume. the terms , and u x x y yq q q   are given by:  u uq q x y   ; 2 2x x x t q q k x y x        ; 2 2y y y t q q k x y y        substituting these three terms into equation (1) gives the partial differential equation: 2 2 2 2 pu cq t t t k x y k t            (2) where ( )u l l aq s q s u t t     this partial differential equation (2) requires one initial condition and four boundary conditions for its solution. the initial condition is 0, for all values of and aat t t t x y  3.1 the boundary at   0 and 0 2 w d y x     because the boundary at 0y  is exposed to the ambient, so  1 0, y l y aat y q u t t    x s xq x xq  y yq y yq  lq iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 19 where  1 0 and 0 2 w dy y x t t      fig. 5: energy balance on the control volume at y = 0. at 0y  , an energy balance on the control volume shown in fig. 5 gives: 1 2 ( ) 2 y x y u x x y p y ty q q q q q c x t             (3) the terms 2 y y q   are given by: 1 2 y y y t q k x y        substituting into equation (3):   2 1 1 1 12 2 2y y p yu l y a t t c tq u t t k x k y y y k t                (4) similarly, the other three partial differential equations for boundaries are derived. 3.2 the boundary at   and 0 2 w d y l x       2 2 2 2 22 2 2y y p yu l y a t t c tq u t t k x k y y y k t                3.3 the boundary at x = 0 and 0 < y < l 2 1 1 1 2 2 pu x x xcq t t t k y x x k t             3.4 the boundary at ( ) and 0 2 w d x y l      22 22 1 1 x f pu x x fi i b t t cq t t k d x k t k d h d c                  x s xq x xq  2 y yq 2 y y q   lq iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 20 where    2 1 2 and 0 0 and 0 and 0 2 2 ; ;w d w dy x xy l x x y l x y lt t t t t t            the four corner points are special conditions of the boundary conditions. the pde for them are derived by the same energy balance method as for the boundary conditions. 3.5 the overall heat transfer coefficient ul as shown in fig. 6 the plate on the tube has five parts of heat gain. fig. 6: the cross-section of plate and the tube. the energy released to the fluid is " , and '' '' '' '' '' ''[ ]u b r w m cq q q q q q     (5) where, " is decided by the flow condition inside the tube. '' ( ) 1 1 b f u fi i b t t q h d c          where              l hxj d k h fgdi i f fi 1re0082.0 2 the effect of condensation is built into the overall heat transfer coefficient, which can be separated into three parts: wind heat transfer coefficient ℎ , the radiation heat transfer coefficient ℎ and the condensation heat transfer coefficient ℎ l w r condu h h h   (6) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 21 where: 2.8 3w ah v  (7)     4 4 p sky r p p a t t h t t     (8) an empirical equation has been developed by swinbank in [8], which relates, tsky to ambient temperature, ta, as shown below: 4 1.50.0552sky at t (9) where, they are both in kelvin. for the condensation heat transfer coefficient ℎ , if tp is greater than tdew, condensation will not occur, then hcond = 0 if tp<tdew: 1 42 3 cos 1.13 ( ) w w fg cond a w p a p g k h h rh l t t            (10) lockhart-martinelli parameter xtt [10] is used for two-phase flow   0.5 0.1 0.91 l ltt v v x x                    (11) the two-phase heat transfer coefficient is 0.8632.44tp l tth h x  (12) 4. results and discussion results were obtained for both simulation and experimental data. meteorological data for a typical day in singapore is shown in fig. 7 and 8. singapore is located at a latitude of 1o22’n and longitude of 103o55’. there is hardly any seasonal variation of the meteorological conditions in singapore. the typical daily variations are shown in fig. 7 and fig. 8. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 22 fig. 7: variation of solar radiation and ambient temperature with time. fig. 8: variation of relative humidity and wind speed with time. as seen from fig. 7 and fig. 8, both solar radiation (global) and wind speed vary in an unpredictable manner with time. solar radiation is around 1000 w/m2 at noon. the ambient temperature reaches the highest point at around 2pm and relative humidity rises to as high as 86% in the morning and continuously decreases. the average and maximum wind speed are 3.0 and 4.1respectively, indicating that wind in singapore is not strong. in fig. 9, the measured and predicted useful energy gain, qu, by the unglazed solar evaporator-collector and solar irradiation are plotted against time. useful energy gain is a combination of energy gain from irradiation and the ambient. the contribution of these two parts is obtain by simulation analysis and presented in fig. 9. as seen from fig. 9, the energy from radiation qu_radiation is highly depended on the radiation level. in contrast to qu_radiation, energy absorbed from the ambient, qu_ambient, is relative constant. it decreased with the rise of radiation due to the fact that the temperature difference between ambient and collector dropped caused by the increase of plate surface temperature as a result of the rise of radiation. 23 24 25 26 27 28 29 30 31 32 0 100 200 300 400 500 600 700 800 900 1000 10:00 10:40 11:20 12:00 12:40 13:20 14:00 14:40 15:20 16:00 te m pe ra tu re , o c r ad ia ti on , w /m 2 time radiation ambient temperature 50% 55% 60% 65% 70% 75% 80% 85% 90% 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 10:00 11:00 12:00 13:00 14:00 15:00 16:00 re la ti ve h um id it y, % w in d sp ee d, m /s time wind speed relative humidity (rh) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 23 fig. 9: comparison of predicted and measured useful energy gain and solar radiation with time. it shows that predicted qu has a reasonably good agreement with experimental values in full mode operation. both of them varied in the range from 2.5 kw to 3.7 kw with the change of radiation. unlike the normal solar collector, the amplitude of the fluctuation of useful energy gain by this evaporator-collector is less than that of solar radiation. this can be attributed to the fact that it not only absorbs energy from radiation but also from ambient due to its low surface temperature, leading to a relatively steady useful energy gain. 4.1 comparison of 1-d and 2-d models in the current study, a two-dimensional (2-d) mathematical model of the evaporatorcollector has been developed. in this model, the plate heat transfer in both the x-direction (vertical to the tube) and y-direction (parallel to the tube) are taken into account. however, in the conventional one-dimensional (1-d) model, which is simpler than the 2-d mode, the heat transfer inside the plate in y-direction is neglected. the comparison of simulation results using both the 1-d and 2-d mathematical models of the evaporator-collector is presented in this section. results of different parameters are presented against solar radiation ranged from 100 w/m2 to 1000 w/m2. the other conditions are chosen as follows: ambient temperature = 30oc, refrigerant mass flow rate = 0.012 kg/s, wind speed = 3.5 m/sec, relative humidity = 70% and refrigerant condensed temperature = 35oc. before the comparison, the effect of radiation on the length of two-phase flow is presented in fig. 10. it should be noted that the total tube length is 30 m. simulation results of useful energy gain and collector efficiency from 1-d and 2-d model are plotted against solar radiation in fig. 11. as seen from the figure, simulation results using 1-d and 2-d mathematical model of the evaporator-collector are very close, especially in low radiation condition. the average difference is only 3% of the 2-d result. it can be explained by the fact that the heat transfer in y direction is almost 0 in two-phase flow region, caused by the constant refrigerant temperature in the two-phase region. 0 0.5 1 1.5 2 2.5 3 3.5 4 0 200 400 600 800 1000 1200 10:00 10:40 11:20 12:00 12:40 13:20 14:00 14:40 15:20 16:00 en er gy tr an fe r r at e, k w ra di at io n, w /m 2 time radiation qu_experiment qu_simulation qu_radiation qu_ambient iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 24 the difference between the 1-d and 2-d mathematical model results is mainly due the heat transfer inside the plate in y-direction, caused by the rapid change of refrigerant temperature in single-phase region. this is neglected in the 1-d model. therefore the difference between the results between the 1-d and 2-d model increases with the rise of radiation due to the rise of length of single-phase flow. as shown in fig. 11 difference, which is 4.3% of 2-d result, occurs at radiation i = 1000 w/m2 fig. 10: variation of length of two-phase flow with solar radiation. fig. 11: comparison of useful energy gain and collector efficiencies for 1-d simulation model and 2-d simulation model. 4.2 parametric study the condensed refrigerant after the expansion valve entered the unglazed evaporator collector in two-phase flow. the vapor quality is gradually increased to 1 and the flow becomes a super heated single-phase flow. the analysis against tube length in different 0 5 10 15 20 25 30 35 100 200 300 400 500 600 700 800 900 1000 le ng th o f t w oph as e flo w , m radiation, w/m2 length of 2φ flow(m=0.012kg/s) 0 500 1000 1500 2000 2500 3000 100 200 300 400 500 600 700 800 900 1000 u se fu l e ne rg y ga in , w radiation, w/m2 useful energy gain (1-d model) useful energy gain (2-d model) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 25 solar radiation conditions is presented in this section. the other conditions are chosen as follows: ambient temperature = 30oc, wind speed = 3.5 m/sec, relative humidity = 70%, mass flow rate = 0.012 kg/s and condensed temperature = 35oc. variation of vapor quality with tube length in different solar radiation is presented in fig. 12. fig. 12: variation of vapor quality with tube length in different solar radiation. the point at where vapor quality becomes 1 is the point of the end of the two-phase flow. as seen from the figure, the increasing rate of vapor quality in the tube is greatly affected by the level of radiation. it is observed that the higher the solar radiation, the shorter the length of two-phase flow. variation of heat transfer coefficient inside the tube with tube length in different solar radiation is presented in fig. 13. as can be observed in the figure, the heat transfer coefficient increase with the rise of vapor quality in two-phase flow and dramatically dropped in single-phase region. figure 14 shows the accumulated useful energy gain with tube length in different solar radiation. as shown in the figure, the increasing rate of useful energy gain dramatically dropped after the two-phase flow become single-phase, as a result of the fall of heat transfer coefficient inside the tube. it means the useful energy gain per unit length in two-phase region is much higher than that in single-phase region. for the total tube length, higher the solar radiation, higher is the total useful energy gain. it is also noted that the difference of useful energy gain between radiation at 600 w/m2 and 900 w/m2 is almost constant in the tube length for 20 m ~ 30 m. it can be attributed to the fact that both of them are in single-phase status in this region. it indicated that, the radiation effect on evaporator-collector performance of single phase flow is much less than that in two-phase flow. 0 0.2 0.4 0.6 0.8 1 1.2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 v ap or q ua lit y tube length, m vapour quality (i=300w/m2) vapour quality (i=600w/m2) vapour quality (i=900w/m2) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 26 fig. 13: variation of heat transfer co-efficient inside the tube with tube length and different solar radiation. fig. 14: variation of useful energy gain with tube length and different solar radiation. useful energy gain is the combination of energy gain from radiation and ambient. the energy gain from radiation and ambient with tube length in different solar radiation is presented in fig. 15. as shown in the figure, in the two-phase flow region, the solar radiation affects the collector useful energy gain mainly by affecting the useful energy gain from radiation. in the two-phase flow region, the higher the solar radiation, the higher is the qu_rad. however, the variation of useful energy gain from ambient, qu_amb, is almost same in two-phase flow for three radiation conditions. 0 1000 2000 3000 4000 5000 6000 7000 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 h ea t t ra ns fe r c oe ff , w /m 2. k tube length, m h.t.coeff (i=300w/m2) h.t.coeff (i=600w/m2) h.t.coeff (i=900w/m2) 0 500 1000 1500 2000 2500 3000 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 u se fu ll en er gy g ai n, w tube length, m useful energy gain (i=300w/m2) useful energy gain (i=600w/m2) useful energy gain (i=900w/m2) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 27 fig. 15: variation of energy gain from radiation and ambient with tube length in different solar radiation. the increasing rate of qu_rad drops slightly in single phase flow due to the drop of heat transfer coefficient inside the tube. in contrast, the increasing rate of useful energy gain from ambient dropped remarkably and even become negative in single phase flow. it is due to the rise of plate temperature caused by the increase of refrigerant temperature in single phase flow. figure 15 indicates that both qu_rad per unit length and qu_amb per unit length in two-phase region are higher than those in single phase region. variation of collector plate surface temperature with tube length for different solar radiation conditions is presented in fig. 16. fig.16: variation of collector plate surface temperature with tube length in different solar radiation. the plate surface in two-phase flow is not much different for the three radiation conditions. it is mainly determined and close to the refrigerant temperature, which is 0 500 1000 1500 2000 2500 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 u se fu ll en er gy g ai n, w tube length, m qu_rad (i=300w/m2) qu_rad (i=600w/m2) qu_rad (i=900w/m2) qu_amb (i=300w/m2) qu_amb (i=600w/m2) qu_amb (i=900w/m2) 0 10 20 30 40 50 60 70 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 te m pe ra tu re , o c tube length, m plate surface temperature (i=300w/m2) plate surface temperature (i=600w/m2) plate surface temperature (i=900w/m2) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 28 almost constant in two-phase flow. however, the plate surface temperature increases is caused by the increase of refrigerant temperature in single phase flow. the analysis against tube length indicated that the evaporator-collector performance in two-phase region and single phase region are quite different. hence it is important to identify the two-phase flow length in future studies. 5. conclusions an integrated solar heat pump system was designed and built to evaluate its performance under the meteorological conditions of singapore. the performance of a twophase unglazed solar evaporator-collector in a solar-assisted heat pump system is investigated. a transient two-dimensional mathematical model of the evaporator-collector has been developed to predict temperature distribution and useful energy gain. to validate the model, experiments were conducted under the meteorological conditions of singapore. it has been determined that the thermal performance of the two-phase unglazed solar evaporatorcollector is affected significantly by refrigerant mass flow rate, solar irradiation, collector area, ambient temperature and relative humidity. both experimental and analytical results show that for the two-phase unglazed solar evaporator-collector, instead of losing energy to the ambient, energy is gained by a significant amount due to low operating temperature of the collector. with this evaporator-collector, the system can be operated even in the absence of solar radiation at night. analytical results show that both the heat transfer coefficient and energy gain in twophase region of collector are much higher than those in the single phase (saturated vapor) region. the length of the two-phase region also increases while the refrigerant mass flow rate declines. this analysis shows that the two-phase unglazed solar evaporator-collector has good potential for application in the tropics. references [1] hawlader mna, chou sk, ullah mz. (2001) the performance of a solar assisted heat pump water heating system. applied thermal engineering, 21(10):1049-1065. [2] sporn p, ambrose er. (1995) the heat pump and solar energy, in world symposium on applied solar energy. phoenix, arizona, usa. [3] franklin jl, saaski ew, yamgiwa a. (1977) a high efficiency, direct expansion solar plane, in flat-plate solar collector conference. orlando, florida, usa. [4] chaturvedi sk, chiang yf, roberts as. (1982) analysis of two-phase flow collectors with applications to heat pumps. asme transaction journal of solar energy engineering, 104(4):358-365. [5] chaturvedi sk, mei vc. (1979) thermal performance of sahp system with combined collector/evaporator, in aiaa terrestrial energy systems conference. orlando, florida, usa. [6] soin rs, et al. (1979) performance of flat plate solar collector with fluid undergoing phase change. solar energy, 23(1):69-73. [7] al-tamimi ai, clark ja. (1983) thermal analysis of a solar collector containing a boiling fluid, in american solar energy society annual meeting. minneapolis, usa. [8] al-tamimi ai, clark ja. (1984) thermal performance of a solar collector containing a boiling fluid (r-11). ashrae transactions, 90:1b:681-693. [9] tong ls. (1965) boiling heat transfer and two-phase flow. john wiley and sons inc. new york. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy amin et al. 29 [10] chaturvedi sk, roberts as, mei vc. (1979) solar collector as heat pump evaporator, in 14th intersociety energy conversion engineering conference. boston, usa. american chemical society, proceedings 1, 99-104. [11] hottel h, whillier a. (1955) evaluation of flat-plate solar collector performance, in trans. conf. use of solar energy, 12 (3) (thermal processes) part 2. [12] spears rp, waldin vh. (1984) ashrae 109-a test standard for two-phase solar collectors. ashrae transcations, 90:697-706. [13] el-assy ay, clark ja. (1988) thermal analysis of a flat-plate collector in multiphase flows, including superheat. solar energy, 40(4):345-361. [14] el-assy ay, clark ja. (1989) thermal analysis of a flat-plate boiling collector having subcooled inlet and saturated exit states. solar energy, 42(2):121-132. [15] freeman tl, mitchell jw, audit te. (1979) performance of combined solar-heat pump systems. solar energy, 22(2):125-135. [16] o'dell mp, mitchell jw, beckman wa. (1984) design method and performance of heat pumps with refrigerant filled solar collectors. journal of solar energy engineering, 106(2):159-164. [17] kishore vvn, gandhi mr, rao ks. (1984) analysis of flat-plate collectors charged with phase-changing fluids. applied energy, 17(2):133-149. [18] ramos e, sen m, treviño c. (1985) a steady-state analysis for variable area oneand twophase thermosyphon loops. international journal of heat and mass transfer, 28(9):17111719. [19] mathur gd, mcdonald tw. (1986) simulation program for a two-phase thermosyphon loop heat exchanger. ashrae transcations, 92:473-485. [20] price hw, klein sa, beckman wa. (1986) analysis of boiling flat-plate collectors. journal solar energy engineering, 108(2):150-158. [21] yilmaz t. (1991) computer simulation of two-phase flow thermosyphon solar water heating system. energy conversion and management, 32(2):133-144. [22] morrison gl, gilliaert d. (1992) unglazed solar collector performance characteristics. journal of solar energy engineering, 114(3):194-200. [23] radhwan am, zaki gm. (1993) analysis of refrigerant-charged s olar collectors with phase change. heat recovery systems and chp, 13(5):429-439. [24] torres reyes e, picon nunez m, cervantes jg. (1998) exergy analysis and optimization of a solar-assisted heat pump. energy, 23(4):337-344. [25] cervantes jg, torres-reyes e. (2002) experiments on a solar-assisted heat pump and an exergy analysis of the system. applied thermal engineering, 22(12):1289-1297. [26] hussein hms, mohamad ma, el-asfouri as. (1999) transient investigation of a thermosyphon flat-plate solar collector. applied thermal engineering, 19(7):789-800. [27] hussein hms. (2002) transient investigation of a two-phase closed thermosyphon flat plate solar water heater. energy conversion and management, 43(18):2479-2492. iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 201 simulation of turbulent flow through tarbela dam tunnel 3 muhammad abid1, adam aslam noon1 and hafiz abdul wajid2 1 faculty of mechanical engineering, gik institute of engineering sciences and technology, topi, kpk, pakistan 2department of mathematics, comsats institute of information technology, lahore, pakistan e-mails: abid@giki.edu.pk, maangiki@yahoo.com, hadulwajid@yahoo.com abstract : tarbela dam is one of the largest earth filled dam in the world. the inflow of sediments in the tarbela reservoir has resulted in reduction in water storage capacity. during recent years, a reasonable increase of sediment particles in the tunnel has been observed. this is damaging to the tunnels, power generating units and is a severe threat to the plant equipment. to the authors knowledge, to-date no comprehensive simulation studies have been performed for flooding in the reservoir or turbulent flows in the tunnels. in this paper, turbulent flow in tunnel 3 of the tarbela dam is analyzed using reynolds stress model with and without considering the effect of sediments particle. results are presented for three different water heads in the reservoir i.e. considering summer, winter and average seasons and for one-way and two-way/full coupling for sediments particle tracking/deposition. the effect of cavitation erosion and damage to the tunnels due to erosion is investigated and results are compared with the experimental erosion results for similar geometries and are found to be in good agreement. sediments particulate analysis is also performed for the validation of the samples collected from wapda (water and power development authority). moreover, pressure, velocity and erosion rate results are discussed to get complete behavior of the turbulent flow of water in the tunnel. keywords: tunnel, turbulent flow, sediment particles, turbulent modeling, cavitations, erosion 12. introduction tarbela dam comprises of six tunnels, three of which are used for power generation and three for irrigation purposes. moreover there are four outlets of the tunnel used for power generation and four pressure relief valves. further details of this tunnel are given in table 1 [1,2]. during recent years, a reasonable increase of sediment particles in the tunnel has iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 202 been observed. this is damaging to the tunnels, power generating units and is a severe threat to the plant equipment. to the authors knowledge, to-date no comprehensive simulation studies have been performed for flooding in the reservoir or turbulent flows in the tunnels. in this paper, turbulent flow in tunnel 3 of the tarbela dam is analyzed using reynolds stress model with and without considering the effect of sediments particle. results are presented for three different water heads in the reservoir i.e. considering summer, winter and average seasons and for one-way and two-way/full coupling for sediments particle tracking/deposition. the effect of cavitation erosion and damage to the tunnels due to erosion is investigated and results are compared with the experimental erosion results for similar geometries and are found to be in good agreement. the studies performed in this paper are carried out on a large structure, the tunnel lengths and diameters are in meters. it makes this research work unique and different from previous studies cited as references in the paper. in addition, sediments particulate analysis is also performed for the validation of the samples collected from wapda (water and power development authority). moreover, pressure, velocity and erosion rate results are discussed to get complete behavior of the turbulent flow of water in the tunnel. in the related work, alamgir et al. [3] have investigated the particle deposition and suspension in a horizontal pipe flow. the deposition was studied as a function of particle diameter, density and velocity of fluid. the lighter particles were found to remain suspended with homogeneous distribution. the larger particles clearly showed deposition near the bottom of the wall. in our work the diameter of the flow passage is very large, the results show the dependance of velocity, pressure and erosion rate density on the passage diameter. xianghui et al. [4] presented a computational fluid dynamics (cfd)-based erosion prediction model and its application to oilfield geometries specifically elbows and plugged tee geometries. this comprehensive procedure consists of three major components: flow simulation, particle tracking, and erosion calculation. the analysis procedure is taken from this study but cavitation analysis procedure is different from this. gary [6] explains the lagrangian approach for particle tracking, authors have used the same approach in one way coupling but eularian approach is used for two way coupling. hari [7] explains the role of different forces when a solid particle passes through a fluid, but in our case the rotational force is ignored. table 1: details of tunnel 3 [1, 2]. parameter value length (m) 1394.98 inlet elevation (m) 360.43 inlet diameter (m) 13.72 outlet branch diameter (m) 7.32 outlet elevation (m) 337.11 high head (kpa) 1096.66 medium head (kpa) 723.65 low head (kpa) 344.46 average volume flow rate (m3/s) 1318.05 material of the steel liner high strength low alloy steel (a-441) steel liner thickness (cm) 5.4-6.35 quantity of turbines for power generation (nos) 4 capacity of each turbine (mw) for four turbines (mw) 432 1728 iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 203 13. theory 2.1 turbulent flow and particle tracking for flows with large, rapid, extra strains and flows with strong acceleration or retardation in the tunnel, we use second-moment closure model or reynolds stress model (rsm) as it can reproduce anisotropy of the flow in the turbulent boundary layer. coefficients of this model are given in table 2 [3]. table 2: rsm model constants [3]. cµ 0.09 σk 1.0 cs1 1.8 cs2 0.6 c1ε 1.44 c2ε 1.92 σε ------ for analysis of turbulent flow in the tunnel, we divide variables into time-averaged part and fluctuating part. governing equations of continuity and momentum for flow employed in cfx-11 are given in equations 1 and 2 respectively [4]. ( ). 0cu t ρ ρ ∂ + ∇ = ∂ uur (1) ( ) ( ) ( ). .c c c u u u b u u t ρ ρ ρ σ ∂ ′ ′+ ∇ ⊗ = + ∇ − ⊗ + ∂ uur uur uur ur (2) here, u u′ ′ρ ⊗ is the reynolds stress; and stress tensor σ is given by: ( )[ ]tc cp i u uµσ ρ ρ= − + ∇ + ∇ uur uur (3) for sediments particle deposition in turbulent flow, we use lagrangian particle transport and eulerian-eulerian multiphase approaches [5], using a rans framework. one-way and two-way/full coupling options are used depending upon the value of β, which is defined as the ratio of the particulate mass per unit volume flow to the fluid mass per unit volume flow and is given by; p p f f r r ρ β ρ = (4) iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 204 where, β = 0.2 is the threshold value [6]. one-way coupling is valid for volume concentration up to 14.86% and simply predicts particle paths during post-processing based on the flow field without affecting the flow field (i.e. particles are assumed not to interact with each other). in two way/full coupling particles exchange momentum with continuous phase, allowing the continuous flow to affect the particles and vice versa. generally, a small, rigid spherical particle entrained in the turbulent pipe flow encounters many forces [7], such as drag and lift forces, buoyancy force, rotation force and turbulence force etc and has the following general form (5) where, fx represents additional forces in the particle force balance that can be used under special circumstances. moreover, gx is the force of gravity. for present study we have ignored the force of gravity on the particle, it is important to note that for most cases the gravitational acceleration is taken zero. one can include the gravity force, but should define the magnitude and direction of the gravity vector. virtual mass force which is used to accelerate the fluid surrounding the particle is also ignored alongwith additional forces arise due to the pressure gradient in the fluid and due to rotation of the reference frame. later forces are important only when fluid is flowing in a rotating frame. another force which is not related for our model is produced because of temperature gradient effecting small particles suspended in a gas. this phenomenon is known as thermophoresis. for micro particles, the effects of brownian motion is optional and if required can be included in the additional force term. therefore, the governing particle equation of motion takes the following form: ( )p d c pdu f u u dt = − ur uur uur (6) where drag force per unit mass is expressed as: re1 24 p d d p f c τ = (7) with τp as the particle response time and is given by: 2 18 p p p dρ τ µ = (8) furthermore rep is the particle reynolds number based on the relative velocity between the particles and carrier phase given by ( ) re p p p d u u ν − = ur uur (9) iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 205 moreover cd is the drag coefficient and is used in cfx by the schiller naumann correlation. schiller naumann correlation is derived for flow of a single spherical particle and is valid in the dilute limit of small solid phase volume fractions for one-way coupling with a coefficient of 0.1. particle transport drag coefficient correlation is used in twoway/full coupling phenomena with a coefficient of 0.44 [8]. 2.2 erosion estimation and surface damage sediment erosion phenomenon is highly complicated and a wide range of factors contribute to erosion severity [9]. analysis is done using ansys cfx to determine the erosion rate under turbulent flow in the tunnel for different heads, and variation of particles concentration. in ansys cfx, only finnie and tabakoff erosion models are available. tabakoff model provides more scope for customization with its larger number of input parameters but presence of large number of coefficients in the model can become a source of errors in the numerical scheme [10]. we therefore use simplified erosion model of finnie with langrangian particle tracking and eulerian-eulerian multiphase approaches. we have used the following expression for erosion rate density: ( )2pe k v f γ= ⋅ ⋅ with (10) ( ) ( )21 cos 3 f γ γ= if γ > 18.26º (11) ( ) ( ) ( )2sin 2 3sinf γ γ γ= − if γ < 18.26º (12) in ansys cfx, implementation of overall erosion rate at each point on the surface is calculated by multiplying e with mass flow carried by the langrangian particle impacting the surface, and then summing for all particles. this ultimately leads to an erosion rate density variable. deformation wear occurs when repeated particle impacts at high impact angles and plastically deform surface layers of the material, eventually causing material loss through surface fragmentation. cutting wear occurs due to particle impacts at small angles, with a scratch or cut being formed on the surface if the shear strength of the material is exceeded. the other critical factor affecting wear is the particle impact velocity, with both cutting and deformation wear being proportional to impact velocity raised to a power n determined through physical tests. in general n varies between 2 and 3 depending on both the surface and particle materials. the value of k is set to 1 which has been determined experimentally [11]. the total erosion rate at a particular point on a surface is measured by summing the contributions due to the deformation and cutting mechanisms and depends on the properties of the material, with deformation wear being more significant for hard or brittle materials and cutting wear being more significant for softer or ductile materials. for standard commercial grade steels, as used in most of the bend surfaces, peak erosion rates iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 206 have been measured to occur at impact angles of 25-30° [12], indicating that cutting wear dominates. 2.3 cavitation erosion cavitation is a phenomenon of formation of vapor bubbles in low pressure regions and collapse in high pressure regions. high pressure is produced and metallic surfaces are subjected to high local stresses. it is a phenomenon which manifests itself in the pitting of the metallic surfaces of tunnel parts because of the formation of cavities. the most critical location is the s-bend at the middle of the tunnel where pressure falls well below the vapour pressure i.e; 750 pa in one way coupling and 450 pa in two way/full coupling. the tendency for a flow to cavitate is characterized by the pressure coefficient or cavitation number, given by [13]: ( ) 20.5 r v c p p ca u − = × ρ (13) 2.3.1 cavitation models different models have been proposed for cavitation phenomenon in literature, but here we consider the followings: the rayleigh-plesset equation provides the basis for the rate equation controlling vapour generation and condensation. the rayleigh-plesset equation describing the growth of a gas bubble from a liquid is given by: 22 2 2 1.5 vb bb f b f pd r dr r dt dt r σ + + =  ρ ρ  (14) the homogeneous model can be viewed as a limiting case of eulerian-eulerian multiphase flow in which the inter phase transfer rate is very large. this model is used in highly dispersed flows with one gas phase and the other dispersed liquid droplet phase. for the present study we use rayleigh plesset cavitation model which requires the model parameters given in table 3 [14]. table 3: rayleigh plesset cavitation model [14]. parameter value ps 4240 pa fcond 0.01 fvap 50 iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 207 ρr 1000 rnuc 5e-4 rf 0.25 rb 1 µm 3. modeling and analysis modeling of tunnel is done in pro-engineer software as per dimensions taken from [15] and is shown in fig. 1. tunnel model is then meshed in icem cfx with free mesh option using 1843803 tetrahedral elements as shown in fig. 2. fig. 1: tunnel model. fig. 2: tunnel mesh iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 208 meshed model is imported into ansys cfx for detailed analysis. the particles are assumed to be randomly distributed at the inlet. particles injected at the inlet are proportional to the mass flow rate of water flowing into the tunnel. the sediment particles volume fraction is only 0.007% at the high head during months of july till september, which increases to 6.1% at the minimum head level during march till june. these fractions fall in the case of one-way coupling. the samples collected and analyzed in february 2010 show that the concentration of sediment particle has increased to 19.6% which lies in the two-way/full coupling region as it crosses the threshold value of 14.86% [6]. the analysis reveals that the continuous flow changes to dispersed flow and flow field is now affected by the sediment particles, which is more critical for the damage caused by erosion. standard no-slip wall functions were applied at all solid surfaces for the fluid phase. furthermore, coefficient of restitution for the particles were taken as 0.9 for parallel flow direction and 1.0 for perpendicular flow direction. the effect of cavitation erosion is analyzed at the s-bend of tunnel of 200 m length. the velocity boundary conditions of 38.51 m/s and 32.09 m/s are specified at the inlet and outlet of the s-bend portion. during analysis, pressure relief valves are excluded in the geometry which might affect the water velocities and pressures at different locations of the tunnel. boundary and initial conditions applied are listed in table 4. zero pressure is specified at the tunnel outlet being exposed to the atmosphere. the list of other input parameters is given in table 5. table 4: boundary conditions and initial conditions. type head value high 1096.66 medium 723.65 boundary coditions (bcs) pressure (p) kpa low 344.46 low 0.563 medium 0.930 initial conditions (ics) velocity (v) ms-1 high 1.143 table 5: input parameters used in ansys cfx. sr # parameter details numerical numbers 1 mass flow rate sediment particles mass flow rate at high head 5.63 x 10-5 kg/s 2 erosion model finnie k = 1.0 and n = 2.0 3 wall roughness at the wall 0.2 mm 4 particles injection uniform injection at the tunnel inlet 6.1% particles for one-way coupling and more than 15% particles for full coupling 5 restitution coefficients parallel and perpendicular based on impact and rebound velocities 0.9 and 1.0 iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 209 schiller and naumann correlation for the evaluation of drag coefficient for one-way coupling 0.1 6 drag force particle transport drag coefficient for two-way coupling 0.44 7 numerical scheme specified blend factor 0 ~ 1 8 particle integration tracking distance and time 1394.98 m and 300 s navier–stokes equations for mass, momentum and fluid turbulence are solved with the commercial code cfx-11 using the finite volume technique. convection terms in momentum equations are discretized using a simple high resolution advection scheme. 3.1 mesh sensitivity analysis the purpose of mesh senstivity analysis is to determine the minimum grid resolution required to generate a solution that is independent of the grid used. starting with a coarse grid the number of cells was increased in the region of interest until the solution from each grid was unchanged for successive grid refinements. mesh sensitivity analysis was performed using the following methodology: 1. meshes of four different element sizes (2, 3, 5 and 7) were generated using ansys icem. 2. boundary conditions were applied to all these four meshes. 3. transient analysis was performed for all the four meshes. 4. final residuals were compared for differences in comparison for changes in mesh sizes. all the results were compared with a mesh size of 3 as the standard. we have evaluated the effect of further refining the mesh to a mesh size of 2 and also coarsening it to a mesh size of 5. the mesh senstivity statistics are tabulated in table 6. results of important variables such as velocity, pressure and erosion rate density were also taken at a particular point in the tunnel defined by the coordinates (793, 1, and -44) and are given in table 7. table 6: mesh senstivity statistics. mesh size number of elements 2 450,000 3 300,000 4 225,000 5 180,000 iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 210 table 7: variable values for tunnel 2 at four different mesh sizes. variables 2 3 5 7 velocity (v) ms-1 72.06 72.25 75.34 76.44 pressure (p) kpa 104.5 105 107 109 erosion rate density (e) x 10-5 kgs-1m-2 11.03 11.17 11.98 12.46 3.2 equation residual if the solution is “exact” then the residual is zero. exact means that each of the relevant finite volume equations is satisfied precisely. the “residual” of an equation identifies by how much the left-hand side of the equation differs from the right-hand side at any point in space i.e; ax-b = residual. the rms residual is obtained by taking all of the residuals throughout the domain, squaring them, taking the mean, and then taking the square root of the mean. the peak values of residues, final residues as summarized in table 8, convergence plots and important variables are compared for analysis performed on different mesh sizes for tarbela dam tunnels. table 8: final residuals. element mesh size equations 2 3 5 u-mom 7.89670e-03 3.22020e-02 7.49670e-02 v-mom 7.34670e-01 6.47095e-01 5.34670e-01 w-mom 3.16890e-02 5.17751e-02 6.16890e-02 uu-rs 1.98790e-02 2.94994e-01 1.98790e-01 vv-rs 3.46780e-01 2.94975e-01 1.46780e-01 ww-rs 4.12340e-01 2.94995e-01 3.12340e-01 uv-rs 2.87650e-02 1.06785e-02 2.37650e-02 uw-rs 8.94570e-04 5.14682e-03 7.94570e-04 vw-rs 5.23450e-02 3.96466e-02 1.23450e-02 e-diss.k 2.84340e+02 3.43782e+02 4.84340e+02 3.3 convergence plots turbulence, mass and momentum plots for the residuals are shown in fig. 3 and fig. 4. the mass and momentum plot of the mesh size of 2 shows smoother convergences as compared to the other mesh however none of the meshes have shown large peaks of the iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 211 residuals. this must be kept in mind that the mesh size of 2 takes far more computational power than the rest and still does not substantially improves the results. the turbulence plot of the mesh size of 2 again shows smoother convergences when compared to other meshes. this could be because of the finer mesh but the residual peak values do not justify the amount of computational time and power required for such fine mesh. fig. 3: turbulence convergence plot. fig. 4: mass and momentum convergence plot. 4. results and discussion the following sections are dedicated for complete analysis of results obtained using ansys cfx for velocity, pressure and erosion rate density for different coupling techniques and water heads. specific attention is paid to critical region such as s-bend. 4.1 one-way coupling at all heads with sediment particles iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 212 for one way coupling maximum velocities of water 28.89, 41.73 and 51.34 m/s are measured at low, medium and high head of water respectively at the s-bend. velocities are 7.23, 10.44 and 12.84 m/s at the inlet section. velocity increases to 21.67, 26.40 and 32.09 m/s when the water flow is fully developed at 150 m from the vertical section at low, medium and high water head respectively. velocity increases abruptly at the outlet branches due to reduction in their crossectional area. moreover, maximum pressures of water 346.70, 728.10 and 1103 kpa are measured at the inlet section where the velocity was minimum at low, medium and high water heads respectively. minimum pressures 1.75, 4.50 and 0.75 kpa are measured at the s-bend where the velocity has it highest value respectively at low, medium and high water heads. pressure decreases abruptly at the main branch and at the outlet branches due to increase in the velocity. furthermore, higher erosion rate densities 11.75 x10-5, 8.13x10-5, 7.13x10-5 kgs-1m-2 due to the sediment particles are measured at high, medium and low heads of water respectively at the inlet section are measured. the highest value of the erosion rate density is measured as 23.31x10-5 kgs-1m-2 at the s-bend. it changes abruptly at the main branch and at the outlet branches due to the higher impact velocity and impact angle at these locations. 4.2 effect of coupling at high head in one way coupling increase in sediment particles concentration does not effect the velocity, pressure and erosion rate density, but in two way/full coupling the velocity of water deccreases to about 5% and pressure of water increases to 1% at high head. the small change in velocity and pressure values is due to the fact that the diameter of the tunnel is too large to effect the flow field completely. but the erosion rate density of tunnel wall increases to about 35% because of the higher number of sediment particles striking the tunnel walls with higher impact velocity at high head. the results are shown in fig. 57 for one way coupling and fig. 8-10 for two way/full coupling. (a) (b) (c) (d) fig. 5: one way coupling with sediments: velocity profiles at high head at: (a) inlet, (b) straight portion, (c) s-bend, (d) outlet branches. iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 213 (a) (b) (c) (d) fig. 6: one way coupling with sediments: pressure profiles at high head at: (a) inlet, (b) straight portion, (c) s-bend, (d) outlet branches. (a) (b) (c) fig. 7: one way coupling with sediments: erosion rate density profiles at high head: (a) inlet, (b) s-bend, (c) outlet branches. (a) (b) (c) (d) fig. 8: two way/full coupling with sediments: velocity profiles at high head at: (a) inlet, (b) straight portion, (c) s-bend, (d) outlet branches. iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 214 (a) (b) (c) (d) fig. 9: two way/full coupling with sediments: pressure profiles at high head at: (a) inlet, (b) straight portion, (c) s-bend, (d) outlet branches. (a) (b) (c) fig. 10: two way/full coupling with sediments: erosion rate density profiles at high head: (a) inlet, (b) s-bend, (c) outlet branches. the velocity, pressure and erosion rate density values will be effected significantly when the sediment particles concentration reaches to the threshold value of 14.86% as the sediment delta is moving towards the tunnel. this shows that the coupling phenomena is a function of tunnel diameter. 4.3 effect of cavitation at high head at s-bend the cavitation phenomenon is observed at the s-bend for tunnel 3 due to the lower local pressure then the vapour pressure at this critical location. the local pressure at sbend is 3.57 kpa which is less than the vapour pressure of water i.e; 4.24 kpa as shown in fig. 11(a), therefore cavitation phenomena starts at this location. the water vapour volume fraction profile is shown in fig. 11(b). the highest fraction of 0.795 is found at the inner periphery of the curvature of the s-bend. the low pressure at this location generates the bubble formation, when these bubbles enter the higher pressure region, they explode. as a iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 215 result these bubble bursts causes the cavitaion erosion. the velocity profiles for water flow are discontinuous, i.e, water contents dominates the vapor contents at some portions and vice versa due to the mixing of water and water vapour phases (two phase flow) at s-bend as shown in fig. 12. (a) (b) fig. 11: cavitation at s-bend surface: (a) absolute pressure, (b) water vapour volume fraction. (a) (b) fig. 12: velocity profiles at s-bend for: (a) water, (b) water vapour. 4.4 effect of no sedimentation at high head negligible increase of less than 2% in velocity and pressure is observed for the sediments particle flow. this demonstrates that the flow field is uneffected in one way coupling. erosion in the tunnel for flow without the sediment particles is concluded due to the turbulent eddies [16] present at the walls of the tunnels at critical locations. iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 216 4.5 critical period for erosion at different heads the velocity and pressure are maximum at high head in the months of july, august and september which impedes the erosion rate and is the most critical period. the medium head remains for five months i.e. april, may, june, october and november, when the velocity and pressure are observed moderate. the low head remains for four months i.e. december, january, february and march when the water velocity and pressure are minimum. the results are summarized in table 9. hence high head is crucial for erosion damage. table 9: velocity, pressure and erosion rate density at all heads for tunnel 3. parameter head inlet section s-bend branch 1 branch 2 branch 3 branch 4 low 6.56 28.89 28.90 29.74 27.25 24.88 med 9.74 41.73 31.30 31.30 31.30 31.30 velocity (v) ms-1 high 12.94 51.34 38.51 38.51 38.51 38.51 low 438.7 4.70 149.4 149.4 149.4 149.4 med 728.10 4.50 294.10 149.4 149.4 149.4 pressure (p) kpa high 1103 0.75 664.70 22.63 22.63 22.63 low 3.23 7.13 6.23 6.23 6.23 7.14 med 3.93 8.23 6.23 6.23 6.23 7.14 erosion rate density (e)x10-5 kgs1m-2 high 4.34 11.32 7.34 7.34 7.34 9.83 4.6 sediments particles analysis including layers of sediment particles sediment particles are of three types including sand, silt and clay which are present in the reservoir bed of the tarbela dam in variable proportions in the form of layers. the bottom layer particles are known as bed flow particles and in this layer flow is such that the sediment particles remain attached to the surface of the river bed with only a slow translational movement. this type of particle flow is present in the reservoir bed, but as sediment delta is moving ahead, this type of flow can be observed at the tunnels surface in the future. due to the highest density of the sand particles, their concentration is the maximum in this layer. second layer of sediment particles is the one in which particles interact with each other in jumping fashion and so as known jumping particles. the translational as well as vibrational and rotational motions are present. this type of layer is mainly present in reservoir bed but it is also observed in tunnel to some extent. there is another layer in which particles are suspended in water, with extremely less interaction with the flow field and other particles. due to small concentration of sediment particles the flow is one way coupled. concentration of clay particles is maximum in this layer because of lowest density. the analysis for the composition, density, colour and size of the sediments particle is done using scanning electron microscope (sem) and particle analyzer as shown in fig. 13. results are presented in table 10 for comparison with data provided by wapda [17]. iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 217 the particles are found to be circular in shape with an average particle diameter of dp=74.13 µm and an average density of 1345 kg/m 3. a calibration study was first undertaken to ascertain the actual concentration (by volume and by mass) in tunnel. the sample preparation and analysis are shown in fig. 14 and results are given in table 11. (a) (b) (c) fig. 13: sem analysis of (a) sand, (b) silt, (c) clay. table 10: sediments particle analysis. particulate diameter, dp (µm) sediment particles sediments composition (jun-sep) 2008 density color wapda (1974) sample analysis in march 2010 sand 31.09 1535 dark grey 200 183 silt 53.34 1330 light grey 40 37 clay 15.58 1170 light brown 2 2.4 (a) (b) (c) (d) fig. 14: (a) sediments suspension, (b) heating, (c) evaporated form, (d) particulate form. iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 218 table 11: sediments particle concentration. mass basis 21% volume basis 25% 5. experimental validation 5.1 experimental set-up and procedure an experimental setup is developed to validate the numerical results discussed in section 5.2. the experimental setup is as shown in fig. 15. the pipe loop is constructed in the horizontal plane with a valve to allow flow to be diverted to another loop as necessary. a high power stirrer is installed to help distribute the sediments in the tank. pipe components are made of aisi 304l stainless steel with a nominal wall thickness of 3 mm. the geometric components like straight portion, bend-section and t-section are all analysed for their flow characteristics in this study. pipe sections are prepared for weighing by firstly thoroughly rinsing with water to remove any sediments and then cleaned with warm 5% citric acid to remove calcite deposits on internal surfaces. this was necessary to allow the change in mass of the pipe sections to be attributed solely to erosion. the pipes are then allowed to air dry, usually overnight, prior to weighing. the experiment is performed for continuous flow of sediments for 80 hours with sediments concentration of about 0.4% by volume and a velocity of 0.175 m/s. the reynolds number calculated is 2997 for this flow. the loops are then carefully dismantled for cleaning and weighing. 5.2 numerical solution of the experimental set-up pro-engineer wildfire 4.0 is used for the modeling of the components, i.e, straight portion, bend-section and t-section the ansys icem package is used for the meshing of the geometry. the number of elements used in the geometric components are 1500, 130 and 160 respectively. the analysis is done in ansys cfx as shown in fig. 15. table 12 shows the input parameters used in the software. specifications for different regions of tunnel 3 are summarized in table 13. the comparisons between the experimental and numerical results are tabulated in table 14. the results show an error of about 8% for erosion rate density. iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 219 (a) (b) (c) (d) fig. 15: (a) complete experimental set-up, (b) straight portion, (c) bend section, (d) tsection table 12: input parameters for the similar geometric components. parameter value radius of pipe/t/elbow 9.525 x 10-3 m cross-sectional area of pipe/t/elbow 2.850 x 10-4 m2 density of water 998 kg/m3 volume of water 0.10402 m3 mass of water 103.812 kg mass of sediments 0.4 kg table 13: specifications for different regions of tunnel 3. t-section straight portion bend section inlet outlets surface area (m2) 2.736x10-2 5.428x10-3 5.963x10-3 volumetric flow rate (m3/s) 5.00x10-5 5.0010-5 1.00 10-4 5.00x10-5 velocity (m/s) 0.175 0.175 0.350 0.175 mass flow rate of water (m3/s) 0.0499 0.0499 0.0998 0.0499 mass flow rate of sediments (m3/s) 1.923x10-4 1.923x 10-4 3.8454 10-4 1.92310-4 change in mass (g) 4.98 7.45 11.01 table 14: comparison between experimental and numerical result. straight portion bend section t-section erosion rate (kg/m2.s) 6.319x10-7 4.766x10-6 6.411x10-6 erosion rate from cfx (kg/m2.s) 6.909x10-7 4.960x10-6 6.638x10-6 % difference 8.50 3.90 3.40 iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 220 (a) (b) (c) fig. 15: erosion rate density profiles for the: (a) straight portion, (b) t-section, (c) bend-section. 6. conclusion a cfd-based velocity, pressure and erosion prediction procedure is presented, based on one way and two way/full coupling phenomena. we have found that erosion is high at high head because of higher impact velocity of the sediment particles during july, august and september. moreover, the results are shown for nine different locations of critical importance with and without sediment particles flowing through the tunnel where the velocities and pressures may vary causing the erosive damage. interestingly, the erosion rate density is found to be maximum at the s-bend due to the additive effect of the cavitation erosion. also, higher values of erosion are observed at the outlet branches due to several reasons like the higher velocity and impact angle and the production of turbulent eddies. furthermore, the cavitation phenomenon is observed at the s-bend due to the lower local pressure then the vapor pressure at this critical location. numerical simulations as well as experimental erosion tests are performed. comparisons show that the cfd-based erosion prediction procedure is able to reasonably predict the erosion profile and satisfactorily capture the trend of erosion with respect to the carrier velocity with a iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 221 maximum error of 8.5%. simulation results show that particle volume fraction increases rapidly as the sediment delta moving towards the tunnels. the particle concentration is found to be 21% by mass and 21% by volume. this increase in particle concentration is changing continuous flow to dispersed flow and is damaging the tunnel walls. the particulate analysis is shown to have a good agreement with the data provided by wapda (water and power development authority). the error in the average diameter of the particles found to be only 7.8%. acknowledgement the authors acknowledge pak-us project, wapda and uiuc usa in completing this study. the authors also acknowledge the support and working of mr ahmed danial, mr. talal mahmood, mr. abdul muqeet haider and mr. azeem sarwar in completing this extensive study. references [1] m. hanif, sediment concentration (ppm). annual reservoir sedimentation report, survey and hydrology department, tarbela dam project. pp. 5. 2009. [2] cunkui huang, s. chiovelli, p. minev, jingli luo and k. nandakumar. a comprehensive phenomenological model for erosion of materials in jet flow. powder technology, (187), 273-279, 20 november, 2008. [3] a. hossain, j. naser, k. macmanus, g. ryan. cfd investigation of particle deposition and distribution in a horizontal pipe. third international conference on cfd in the process industries. csiro, melbourne, australia. pp. 489-492.10-12, december 2006. [4] c. xianghui, s.m. brenton, a.s. siamack, application and experimental validation of a computational fluid dynamics (cfd)-based erosion prediction model in elbows and plugged tees, computers & fluids (33), 1251–1272. 2004. [5] s. dosanjh and j.a.c humphrey. the influence of turbulence on erosion by a particle laden fluid jet, wear (102), 309-330. 1985. [6] g. brown. use of cfd to predict and reduce erosion in industrial slurry piping system. fifth international conference on cfd in the process industries. csiro, melbourne, australia, pp. 13-15. december 2006. [7] h. prasad neopane. faculty of engineering science and technology, norwegian university of science and technology (ntnu) in partial fulfillment of the requirement of the degree of doctor of philosophy. trondheim, norway, march 2010. [8] drag models. ansys cfx solver theory guide, release 11.0. pp. 2. (19962006). iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 222 [9] l. bouhadji, three dimensional numerical simulation of turbulent flow over spillways, asl-aqflow inc., sidney, british columbia, canada. pp 1-7. 2003. [10] b. dobrowolski and j. wydrich. evaluation of numerical models for prediction of areas subjected to erosive. int. j. of applied mechanics and engineering (11), 735-749. 2006. [11] ansys cfx reference guide, release 11.0. pp. 1-4. (1996-2006). [12] b.r. munson, t.h. okiishi, fundamentals of fluid mechanics, 5th edition. isbn 9812-53-221-8. 2006. [13] erosion models. ansys cfx solver theory guide, release 11.0. pp. 12. (19962006). [14] jinyu jiao, zhengliang liu and ying zheng. evaluations and modifications on reynolds stress model in cyclone simulations, chem. eng. technol., (30), 15– 20, 2007. [15] tippets and abbett. civil engineering works. contract documents for construction. tarbela dam project. tams, international (6), p. 16. 1967. dam project. pp. 7-8. 2000. [16] p. j. zwart, a. g. gerber, and t. belamri. a two-phase flow model for predicting cavitation dynamics. icmf 2004 international conference on multiphase flow. yokohama, japan, may 30-june 3, 2004. paper no.152. [17] sediments composition. annual reservoir sedimentation report, survey and hydrology department, tarbela dam project. pp. 10-11. 2008. iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 223 nomenclature b body force due to sediment particles ca cavitation number c d drag coefficient cµ anisotropic diffusion coefficient cs1, c s2, c 1ε, c 2ε rs coefficients d p particle diameter e erosion rate density fd drag force fcond cavitation condensation coefficient fvap cavitation vaporization coefficient g gravitational acceleration of the sediment particles k erosion model constant m particle mass n velocity exponent ps saturation pressure of water p fluid pressure pv vapour pressure rb bubble radius rep particle reynolds number rf cavitation rate under relaxation factor �f fluid phase volume fraction rnuc nuclei volume fraction �p particulate phase volume fraction uc fluid velocity iium engineering journal, vol. 11, no. 2, 2010 muhammad abid et al. 224 up particle velocity u particle relative velocity vp particle impact velocity greek letters β particle mass loadings γ particle impact angle ρ f fluid density ρ p particle density ρs nucleation site density ρr density ratio σ stress tensor σε turbulence model constant σk turbulence model constant for the k-equation σt surface tension coefficient τp particle response time µ fluid dynamic viscosity ν fluid kinematic viscosity application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 use of tio2 as a reinforcement of cassava starch/pva composites on moisture-resistant properties of triboelectric nanogenerator (teng) film aris ansori1,2*, sudjito soeparman1, denny widhiyanuriyawan1 and teguh dwi widodo1 1 department of mechanical engineering, universitas brawijaya jl. mayjen haryono 167 malang 65145, east java, indonesia 2 department of mechanical engineering, universitas negeri surabaya, campus ketintang surabaya 60231, east java, indonesia * corresponding author: arisansori@unesa.ac.id (received: 30 july 2022; accepted: 3 february 2023; published on-line: 4 july 2023) abstract: high humidity environments can accelerate the transmission, neutralization, or dissipation of frictional charges on the frictional surface of solid-solid triboelectric nanogenerator films (tengs), which can reduce the output power. the moisture resistance properties of the teng triboelectric film are needed to overcome these problems. therefore, this study discusses the role of the tio2 nanofiller in cassava starch (cs) and polyvinyl alcohol (pva) nanocomposite matrix that can increase triboelectricity through the formation of hydrogen bonds and the provision of oxygen-free electrons. the research method was to incorporate different concentrations of tio2 nanoparticles (0%, 0.5%, 1%, 5%, 10% wt, and 15% wt) into the cs-pva nanocomposite matrix using the solvent casting method. the results showed an increase in surface polarity which was more triboelectric-positive due to the cs-pva hydroxyl group interacting with water molecules. increasing the concentration above 5% wt tio2 increases the density of the cs-pva nanocomposite film which can significantly reduce water vapor permeability (wvp) and increase water resistance. the teng performance of the cs-pva/tio2 nanocomposite film with a concentration of 15% wt tio2 under conditions of high humidity (rh, 95%) resulted in an output voltage of 2.5-fold (~70.5 v to ~180 v), and the output current increased 2.6-fold (~5.2 μa to ~13.7 μa). abstrak: persekitaran berkelembapan tinggi dapat mempercepatkan penghantaran, peneutralan, atau pelesapan cas geseran pada permukaan geseran filem nanopengeluaran triboelektrik pepejal (teng), di mana mengurangkan pengeluaran tenaga. sifat rintangan lembapan filem triboelektrik teng diperlukan bagi mengatasi masalah ini. oleh itu, kajian ini membincangkan peranan pengisi nano tio2 dalam matriks nanokomposit kanji ubi kayu (cs) dan polivinil alkohol (pva) yang dapat meningkatkan triboelektrik melalui pembentukan ikatan hidrogen dan bekalan elektron bebas oksigen. kaedah kajian ini adalah dengan menggabungkan kepekatan nanozarah tio2 berbeza (0%, 0.5%, 1%, 5%, 10%, dan 15%) ke dalam matriks nanokomposit cs-pva menggunakan kaedah tuangan pelarut. dapatan kajian menunjukkan peningkatan kekutuban permukaan yang lebih positif-triboelektrik adalah disebabkan oleh kumpulan hidroksil cs-pva yang berinteraksi dengan molekul air. pertambahan jisim kepekatan tio2 melebihi 5% meningkatkan ketumpatan filem nanokomposit cs-pva yang boleh mengurangkan kebolehtelapan wap air dan meningkatkan rintangan air dengan ketara. prestasi teng filem nanokomposit cs-pva/tio2 dengan jisim kepekatan tio2 15% dalam keadaan berkelembapan tinggi (rh, 95%) menghasilkan voltan keluaran sebanyak 2.5 kali ganda 269 mailto:arisansori@unesa.ac.id iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 (~70,5 v kepada ~ 180 v), dan arus keluaran meningkat 2.6 kali ganda (~ 5,2 μa kepada ~ 13,7 μa). keywords: nanocomposite films; tio2; cassava starch/pva; moisture resistant; triboelectric nanogenerators (teng) 1. introduction a triboelectric nanogenerator (teng) is a micro/nanoscale energy harvesting device that utilizes static electric charges or the triboelectric effect between two materials that have different electronegativities [1]. teng's working mechanism is a combination of contact electrification and electrostatic induction to convert mechanical energy that is abundant in the environment into electrical energy. the teng structure consists of two electrodes made of copper or aluminum, where electrode 1 is attached to the tribo-positive layer and electrode 2 is attached to the tribo-negative layer, the teng structure is presented in fig. 1a. there are four working modes of tengs, namely; contact mode, slide mode, single electrode mode, and freestanding mode [2,3]. the working modes of tengs are presented in fig. 1. fig. 1: the working modes of teng (a) contact electrification phenomena between different triboelectric materials, (b) the four working modes of teng. the schematic diagrams of working teng, are presented in fig. 2. the working teng mechanism that converts mechanical energy into electricity consists of four steps. in step i, the two layers of the triboelectric layer (tribo-positive layer and tribo-negative layer) are in contact with one another, where the contact of two surfaces of the triboelectric film layer has not resulted in charge (fig. 2a). in step ii, the application of mechanical energy to the tribo-positive layer 1 causes friction to occur, reduces the contact area between the tribopositive layer 1 and the tribo-negative layer 2, and causes a charge difference on the surface of the triboelectric film layer. then, electrons will flow from electrode 1 to electrode 2 through the outer circuit (resistor) to balance the surface charge on the two triboelectric layers until the contact of the two triboelectric layers is free (fig. 2b). in step iii, the sliding of the tribo-positive layer 1 optimally causes the contact of the two triboelectric layers to completely separate and there is a charge balance between the two triboelectric layers, so that there is no flow of electrons between electrode 1 and electrode 2 (fig. 2c). in step iv, the tribo-positive layer 1 moves and creates friction and surface contact again between the tribo-positive layer 1 and the tribo-negative layer 2 in the opposite contact direction in stage ii, this causes electrons to flow through an external circuit (resistor) from electrode 2 to 270 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 electrode 1 to balance the surface charges on the two triboelectric layers with opposite directions of electron flow (fig. 2d) until the two triboelectric layers return to full contact again at the stage i position. the sliding and closing of the triboelectric layers periodically generate an alternating current [4]. fig. 2: schematic diagrams working of teng. teng was first developed by wang et al. in 2013, the research was carried out utilizing the triboelectric effect of materials to harvest mechanical energy into electricity and showed high energy conversion efficiency. [5]. teng has become a promising energy conversion device to convert mechanical energy into electrical energy due to the capacity of triboelectric materials. teng can be a solution for new and sustainable energy harvesting, such as wind [5], ocean waves [6], human movement [7], rotational motion [811], flowing water [12], vibration [13], and other energy sources. in general, the teng device consists of two friction materials and electrodes at the top and bottom of the device wherein, physical contact between two friction materials with different levels of electronegativity can induce a triboelectric charge which can produce a potential decrease when separated by mechanical forces and increase the flow of electrons between the electrodes via an external circuit. the dominant factor that determines the performance of teng's output is the teng friction material, such as the use of nanocomposite friction materials on a nanoscale which has the advantages of mechanical strength, toughness, flexibility, transparency, dielectric, thermal, or electrical conductivity properties which show an effective and efficient teng performance improvement [6,7]. in the previous research report, the use of nanocomposite films showed an improved teng performance. one such nanocomposite material is polydimethylsiloxane (pdms), a silicon-based organic polymer compound (organosilicon). pdms nanocomposite films with tio2 deposition can cause changes in oxygen vacancies on the pdms surface which can contribute to electron exchange and trapping and have an impact on increasing teng output power [8]. poly (vinylidene fluoride) (pvdf) polymer with tio2 nps as filler can improve dielectric properties [9]. polydimethylsiloxane (pdms) with different tiox weight ratios as a function of dielectric constant control with 5% rutile tiox and 7% tiox anatase phase produces the highest teng output of ~180 v/8.2 μa and 211.6 v/8.7 μa [10]. tio2 nanoparticles 0.2% wt in portland cement increased the mechanical strength 1.3-fold and 3fold the power density of 265 mw/m2 than pure portland cement [11]. however, teng's output power may decrease due to high humidity environmental conditions. when the humidity is high, the water molecules in the air absorb on the surface of the friction film pair and form a conductive water film, which can increase the frictional interface conductivity and accelerate the frictional charge transfer or neutralize the charge on the next 271 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 contact. these conditions, will generate different frictional charges when the teng solidsolid films rub against each other [12]. several methods have been reported to solve the problem, such as; creating a hydrophobic or superhydrophobic film to reduce the adsorption of water molecules on the friction surface and loosen the texture of the structure to increase the permeability of the material [13,14]. for example, shen et al., using a hydrophobic polyvinylidene fluoride (pvdf) film, showed the performance of teng at 55% relative humidity with an output current of 28 μa, a voltage of 345 v, and a power density of 1.3 w/m2 [15]. lv et al. made a teng single electrode using a hydrophobic ionic liquid that showed high stability performance in various weather conditions (humidity up to 80%) [16]. zhou et al. used a teng with superhydrophobic pdms interlayer film that can maintain electrical output under initial conditions up to relative humidity of 80% [17]. however, modification of the hydrophobic surface when humidity is high cannot completely solve the problem of decreasing the output performance of solid-solid teng. in addition, the hydrophobic or superhydrophobic film process requires a complicated film-making process, and its manufacture is not easy to apply to some materials. currently, the use of biomaterials rich in hydroxyl groups has begun to be developed as a teng triboelectric film, several studies have shown that tengs output performance is very good by utilizing the ability to bind water molecules by forming hydrogen bonds. in addition, biomaterials are expected to replace synthetic polymers (pdms, pvdf, pet, and teflon) which still dominate the teng film. meanwhile, several applications of teng triboelectric films are made from biomaterials rich in hydroxyl groups, such as; pure potato starch exhibits high output performance of 60 mv to 300 mv per 4 cm2 area [18]. the triboelectric film of tapioca starch rich in hydroxyl groups can enhance the triboelectricity effect by improving water molecules on the friction film surface through hydrogen bonding [19,20]. potato starch biomaterials with 0.5% cacl2 showed an increase in triboelectric performance; the highest voltage output (1.2 v) was three times higher than that of pure starch [21]. in addition, the use of starch biomaterials has advantages, such as biocompatibility and biodegradability [18,19][21-23], abundant availability, easy processing, bring inexpensive, possessing hydroxyl groups, amorphous crystal structure, and rheological properties that can provide the required resistance for teng triboelectric film applications [24]. however, starch biomaterials still have problems in the application of teng triboelectric films, such as poor mechanical properties, ease of dissolving on prolonged contact with water, and poor tribological properties in high humidity environments and low moisture resistance when exposed to high humidity conditions as a friction film. therefore, to increase the functionality of starch biomaterials is to modify starch biomaterials into nanocomposite films. to the best of our knowledge, the use of tio2 nanoparticles as a starch biomaterial nanofiller with moisture resistance characteristics has not been reported. meanwhile, in this study, a type of nanocomposite film was made using a composite matrix of cassava starch (cs) and pva with tio2 nanofiller to increase moisture resistance. polyvinyl alcohol (pva), rich in hydroxyl groups with the addition of tio2, will cause intra/intermolecular interactions between tio2 nanoparticles and adjacent oh groups of pva through hydrogen bonds and form stable complex composites. pva compatibility increases with the addition of tio2 into the film due to the formation of c-o-ti. meanwhile, the starch/pva mixture changed the structure of the starch/pva composite film by forming c-h bond groups from alkyl groups in both starch and pva. after incorporating tio2 filler into the starch/pva mixture, c-o bonds will form at the macromolecular level, and intramolecular hydrogen bonds are formed between two neighboring oh groups on the 272 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 same side of the plane of the carbon chain. this allows for increased miscibility and compatibility between starch/pva and tio2 with the formation of hydrogen and c-o-ti bonds which can affect the characteristics of the nanocomposite film [25-27]. meanwhile, the basis for using tio2 nanofillers is that tio2 contains oxygen atoms that can be easily dispersed in a polar biopolymer matrix without surface modification. in addition, chemical bonds and electrostatic interactions between oxygen atoms on the metal oxide surface and functional groups in the polymer matrix make the nanoparticles disperse in the polymer matrix [28]. meanwhile, the special emphasis in this study is to investigate the effect of tio2 in the cs-pva polymer blend on the physicochemical, water resistance, and electrical properties of the nanocomposite films and the teng characterization of the cs-pva/tio2 nanocomposite films as positive friction surfaces and thin-film commercial polyimides as negative friction partners. we compared the results and analyzed the effect of tio2 on the moisture properties of the cs-pva nanocomposite films. the results of the measurement of the output voltage and current of teng cs-pva nanocomposite film without tio2 produced an output voltage and current of ~25.5 v and ~3.6 μa and with 0.5% wt tio2 output voltage of ~50 v and an output current of ~5,9 μa (relative humidity /rh, 15%). in this case, there was a significant increase in the effect from tio2 in the cs-pva polymer blend. the optimal increase of teng output voltage and current at a weight ratio of 15% wt tio2 at high humidity (rh, 95%) achieved a 2.5-fold increase in output voltage (~70.5 v to ~180 v), and an output current of 2.6-fold (~5.2 μa to ~13.7 μa). the addition of a weight ratio above 5% wt tio2 can reduce the water vapor permeability by 65%. therefore, these cs-pva/tio2 nanocomposite films have the potential for teng films under high humidity environmental conditions. 2. experimental methods 2.1 materials the starch used in the experiment was cassava starch produced by pt. budi starch & sweetener.tbk. in indonesia, polyvinyl alcohol (pva) with an average molecular weight of mw = 89,000–98,000, was procured from sigma aldrich. anatase tio2 nanoparticles with a particle size of 20 nm were purchased from sigma-aldrich, glycerol (99% purity, clear, colorless, and density: 1.261 g/cm3), aquades, and other chemicals naoh, hcl, and nacl were used to control humidity (rh, 15%, 55%, and 95%) from sigma-aldrich and merck. 2.2 fabrication of cassava starch (cs)-pva/tio2 nanocomposite films fig. 3: preparation of cs/pva-tio2 nanocomposite films by solvent casting method. 273 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 figure 3 describes the making of cassava starch (cs)/pva nanocomposite films with tio2 nanofiller using the solvent casting method. the step of making cassava starch (cs)/pva-tio2 nanocomposite films consists of six steps. in step 1, the constant weight ratio of the cs/pva mixture (70:30), cassava starch (4.2 g) was determined and dispersed with distilled water (50 ml) in borosilicate glass, and the addition of glycerol (3 g) served as a plasticizer. in step 2, the mixture of cs powder and glycerol was mechanically stirred for 5 minutes until a homogeneous solution was produced. in step 3, the mixture of cs powder and glycerol was stirred with a magnetic stirrer at 250 rpm at a temperature of 95 oc for 30 minutes to obtain a gelatinized starch suspension. meanwhile, a solution of 1.8 g pva with 40 ml of distilled water was prepared in the same way in another borosilicate glass, and a clear pva solution was produced. mixing of the two solutions (cs solution/pva solution) was carried out at room temperature with continued stirring with a magnetic stirrer (250 rpm, 95 oc) for 30 minutes. in step 4, the tio2 was incorporated into the cs/pva solution with different polymer weight ratios (0%, 0.5%, 1%, 5%, 10%, and 15% wt), and continuous stirring was carried out using a magnetic stirrer at 400 rpm, and temperature 95 oc for 30 minutes. in step 5, the production of nanocomposite films occurred, where the resulting cs/pva-tio2 viscous solution was poured into teflon molds (radius 50 mm) with the same volume of solution in each mold to produce relatively the same thickness of film samples; residual air was removed from the solution in a vacuum for 10 minutes using a vacuum machine. in step 6, the drying of the film was carried out in a hot air oven at 40 oc for 24 hours. the dry film was then carefully peeled off from the teflon mold and produced a film with an average thickness of 100 µm. the resulting nanocomposite films were kept in a zippered bag until tests were carried out to reduce water absorption according to the ramirez method [29]. 2.3 fabrication of cs-pva/tio2 nanocomposite film-based tengs figure 4 describes the structure of the teng mode rotary-disk freestanding (rdfteng). fig. 4: schematic of triboelectric nanogenerator based on cs-pva/tio2 nanocomposite film (a) structure of rotor and stator (b) teng component arrangement (c) freestanding electret rotary (fer) working mechanism (d) teng electrical circuit. 274 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 rotor structure parameters with the number of film segments (n) = 4, outer radius (r2) = 50 mm, inner radius (r1) = 5 mm, were made of commercial polyimide thin film (0.03 mm) as a tribo-negative film glued to an acrylic surface (radius = 50 mm). meanwhile, the stator structure parameters consisting of cs/pva-tio2 nanocomposite films were cut to form an equal-interval electrode model with the number of film segments (n) = 8, outer radius (r2) = 50 mm, inner radius (r1) = 5 mm, and the nanocomposite film thickness was 100 µm. next, the cut nanocomposite film was glued to the copper foil (electrode film a and b). where the tip of the copper foil electrode was slightly exaggerated to connect the external circuit with the help of a conducting wire so that electrons could flow into the external circuit. external mechanical energy used a dc electric motor that was connected to the teng rotor shaft in a freestanding rotational mode. meanwhile, the gap between the rotor and stator was controlled with a distance of 0.10 mm to keep the friction between the surface of the polyimide film and the cs/pva-tio2 nanocomposite film stable. the freestanding-electret rotary (fer) teng mode has four steps. in step i, electrode a is parallel to the polyamide electret film, and there is no electrostatic induction effect of rotating rotor. in step ii, the polyamide electret is parallel to the positions of electrodes a and b causing the charge at electrode a to be transferred to electrode b through an external load (resistor) and generating a current and voltage across the load resistor. in step iii, the polyamide electret is parallel to electrode b, and in step iv, the polyamide electret will go to electrode segment a and when parallel to electrode a and electrode b will generate current and voltage. a schematic of triboelectric nanogenerator based on cs-pva/tio2 nanocomposite film is presented in fig. 4. 2.4 physicochemical characterizations 2.4.1 chemical, crystalline structure and morphological characterization the functional groups of the nanocomposite films were analyzed using fourier transform infrared spectroscopy (ftir) with an irprestige-21 spectrophotometer (shimadzu, usa). ftir measurements were carried out at room temperature (25 ±10 c) in the wave number range of 600–4000 cm−1 with a resolution of 2 cm-1 and an average of more than 64 scans. the degree of crystallinity of the film samples was recorded using a panalytical xpert pro diffractometer with cu kα radiation at 40 kv and 40 ma, using a 20 mm ni filter. all sample films were scanned between 2θ = 50 to 69.990 at 50/min at a measurement temperature of 25 oc. morphological analysis of nanocomposite film by scanning electron microscope (fesem) fei quanta feg 650 to explore the effect of tio2 filler on the cell structure of the cs-pva polymer mixture. the dry film sample was sprayed with gold-palladium under vacuum conditions to increase its conductivity. the test was carried out at a voltage of 15xkv with a magnification of 500x. 2.4.2 water vapor permeability (wvp) the combination of fick's and henry's laws for the diffusion of vapors or gases through the film is used as the basis of the method for calculating wvp. the standard astm e96 test method (astm, 1993) was used to test the wvp of nanocomposite films [41]. in the initial step of the test, the film sample was cut into a circle with a radius of 1.75 cm and tightly mounted on the top surface of a special permeation cup containing cacl2 anhydrous. after weighing the initial weight, the cup was stored in a desiccator containing a saturated nacl solution with a constant relative humidity (rh) of 75% at 25 oc. the temperature in the desiccator was maintained at 25 oc throughout the experiment. permeation cup weights were recorded at 24-hour intervals until a constant weight gain was achieved. the amount of water vapor permeating through the film was calculated from the increase in cup weight 275 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 and plotted as a function of time. measurement of wvp (gm−1s−1 pa−1) was performed three times using eq. (1). 𝑊𝑉𝑃 = 𝑚. 𝑑 𝐴. 𝑡. ∆𝑝 ( 𝑔 𝑚. 𝑃𝑎 . 𝑠 ) (1) where m = increase in cell mass over a certain period, t = time, d = average film thickness, a = effective film area, and p = difference in water vapor pressure on both sides of the film. the wvp value of the nanocomposite films in this paper represents the effective permeability, which reflects the moisture barrier properties of the films under the humidity and temperature conditions used. 2.4.3 degradability tests the degradability test was carried out to analyze the resistance of the cs-pva/tio2 nanocomposite films in water. in the initial step of testing, the sample nanocomposite film was cut to a size of (2 x 3 cm), then the sample film was immersed in distilled water for a certain time until the sample film was destroyed. 2.5 electrical output measurement the performance test of the nanocomposite film on the teng unit was carried out in a closed cylindrical chamber with the same humidity control. the cylinder chamber was equipped with two inlets to circulate dry air and moist air, and one outlet was used to regulate air circulation in the cylinder to achieve the required relative humidity in the room accurately. the external mechanical energy of the rotor used a dc v = 24-volt, 0-500 rpm electric motor. measurement of output voltage and current used a digital oscilloscope (dsox6004a digital storage oscilloscope) with a load resistance of 100 mω, before the testing film was put in a closed box for 24 hours with adjusted humidity control (15%, 55 %, and 95%) with a saturated salt solution. 3. results and discussion 3.1 analysis of chemical, structural, and morphological of nanocomposite films structural analysis can be observed from the ftir spectrum of the material in the range of 4000-700 cm-1 are presented in fig. 5a, where the molecular bond spectra of the cs-pva polymer matrix and the change after incorporation of tio2 filler can be seen, which has several characteristic peaks reflecting the structure of the two biopolymers. the transmittance band of about 3285 cm-1 was determined from the stretching vibration of the hydroxyl group (–oh) in cs and pva polymers having a hydroxyl-rich average. the peak transmittance band of 1641.42 cm-1 indicates the formation of hydrogen bonds in pure starch due to the flexion of the –oh molecule and shows the hygroscopic nature of the starch polymer. characteristics of the bending of c-oh are in the 1205 cm-1 transmittance band. the peak at 770-1120 cm-1 is associated with the stretching of the c–o bond of the macromolecular portion, where an intramolecular hydrogen bond is formed between two adjacent oh groups that are on the same side of the plane of the c–c carbon chain of the c–o–c group of the unit glucose in starch [37]. pure pva showed hydroxyl and acetate groups, where the intermolecular and intramolecular hydrogen –oh bonds were shown in a wider band at 3296.35 cm-1. the structure of the alkaline group confirmed the peak in the transmission band 1480-1190 cm1 associated with the planar buckling vibrations of c–h and o–h in both cs and pva. the 276 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 presence of a carbonyl group (c=o) is indicated by the 1732 cm-1 transmission band and a hydrocarbon (alkane) group in pva is indicated by a peak at 1373.32 cm-1, as previously reported by abdullah [30]. meanwhile, the chemical interaction between cs-pva polymer molecules that causes changes in the characteristic spectral peaks of the composite, the c– oh hydrocarbon group is estimated to come from the c–o vibrations, which is confirmed by the peak of 1000-1250 cm-1. in addition, the vibration of the –oh group confirmed the absorption peak in the range of 3300-3000 cm-1. the formation of the c–h alkene functional group due to the mixing of starch-pva which was confirmed at a wavelength of 675-995 cm-1 and c–h alkane which was confirmed at a wavelength of 2850-2970 cm-1. fig. 5: physicochemical characterizations of cs-pva/tio2 nanocomposite films. (a) ftir spectra of cassava starch-pva/tio2, (b) xrd pattern of cassava starch film, (c) sem of cs-pva nanocomposite film. in addition, the c–h functional group of the aromatic ring was confirmed at the wavelength of 690-900 cm-1. the mixing of cs-pva polymer showed flexural vibrations of the hydrogen bonding of the –oh group at 1710.86 cm-1 and the c–o strain at 1050-1300 cm-1. the stronger interaction of cs-pva molecules is shown by intermolecular interactions through the formation of hydrogen bonds with water vapor molecules which can increase triboelectricity. at low concentrations (below 15% tio2 wt) in the cs-pva polymer mixture in the ftir spectrum, the vibration peaks did not show any additional peaks. this may be due to the overlapping bands of the cs-pva components. however, the 277 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 increase in tio2 concentration (above 1% tio2 wt) showed a slight shift in the peak positions of several bands in the range of 900-1100 cm-1. it is assumed that the absorption band at 1000 cm-1 is associated with the tio2 crystal domains hydrated into the cs-pva polymer matrix. in addition, the titanium ions of the tio2 particles can interact with the hydroxyl groups of cs-pva, which make the nanocomposite films highly compatible. figure 5b shows the xrd pattern of the sample film, the cassava starch film produced peaks at 2θ = 15.730, 16.510, 17.230, 19.690, 22.140, and 24.370 whereas, an important diffraction peak was located at 19.690, which indicates strong intermolecular and intramolecular hydrogen bonds and is indicative of a semi-crystalline structure. this is not much different from the signal of the 200 peaks of cassava starch reported by bergo et al. [31], and adamu et al. [32]. meanwhile, the cs-pva composite sample formulation produced peaks at 2θ = 13.110, 17.210, 19.760, and 24.540, which indicated a change in peak. these peaks can reveal that polymer cassava starch (cs) is dispersed in pva, which can change the characterization of the films [33,34]. the incorporation of tio2 filler into cspva with variations in tio2 concentration below 1% wt showed peak changes that were not easily visible at low concentrations. however, increasing the concentration above 1% by weight showed peaks at 2θ = 22.380, 27.600, and 54.430 in semicrystalline structure nanocomposite films and indicated the presence of titanium dioxide embedded in the cspva polymer. figure 5c shows the morphology of the polymer mixture of cassava starch (cs)-pva and the morphological changes of the nanocomposite films after the addition of tio2 can be observed from the material micrograph. the ability of starch granules to interact with various ceramic and mineral particles can hold these particles, which causes the added tio2 to adhere to the surface of the starch granules well. meanwhile, mixing cs-pva suspension with tio2 particles, during the gelatinization process, the tio2 particles remain attached to the surface of the starch granules and interact with the continuous phase macromolecules of water-soluble amylose and pva, this process most likely occurs through hydrogen bonding. the sem photos show morphologically the resulting film has a heterogeneous surface relief. the tio2 filler particles were evenly distributed within the polymer matrix. this can be seen from the sample of the film with a low concentration of tio2 (0.5% wt), the filler particles are still individual. this is in contrast with the addition of tio2 concentration of more than 1% wt indicating the association of filler particles in the composite. in addition, the presence of tio2 particles with a high ratio in the film can create a winding path that prolongs the transport of water vapor molecules. 3.2 water vapor permeability (wvp) water vapor permeability (wvp) was used as an indicator of the film’s ability to absorb water vapor. wvp values of nanocomposite films from the studied samples are presented in table 1. wvp values of cs-pva nanocomposite films with tio2 are lower than those without tio2. the wvp value was inversely correlated with the addition of tio2 concentration in the cs-pva mixture matrix. wvp value of sc-pva/tio2 nanocomposite films decreased with the addition of more than 1% wt tio2. this is due to the presence of hydroxyl groups in the cs-pv mixture making the water vapor molecules easy to diffuse. the addition of tio2 nanoparticles formed a denser nanocomposite film structure compared to the unfilled film. the presence of tio2 in the cs-pva matrix forms pathways in the polymer that prolong the transport of water vapor molecules. this result is not much different from the results of previous research reports, the effect of tio2 nanofiller in polymer films causes a decrease in moisture penetration of corn starch/pva-tio2 films, 278 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 [26], potato starch/lactucin-tio2 composite films [35], and potato starch/montmorillonitetio2 composite films [36]. table 1: physical properties of cs/pva-tio2 composites tio2 content % wt wvp value (×10-7 g/m h pa) 0 9.46±0.84 0.5 8.38±0.80 1 7.54±0.78 5 7.39±0.75 10 7.47±0.58 15 7.48±0.55 3.3 degradability testing the degree of damage film caused by water molecules was tested by immersing the nanocomposite film in distilled water (fig. 6a). fig. 6: (a) test method (b) water-resistance of cs-pva/tio2 nanocomposite films. the damage rate of cs-pva nanocomposite films with tio2 increased 3-fold compared to without tio2. figure 6b shows the water resistance of cs, cs-pva, and sc-pva/tio2 films, the resistance of cs films is the lowest compared to cs-pva and sc-pva/tio2 films. the durability of cs films is affected by the number of hydroxyl groups in the polymer molecules, where the hydroxyl groups bind to water molecules by forming hydrogen bonds. the increase in the number of hydroxyl groups in the cs-pva film can occur from the intramolecular interaction of the cs-pva polymer mixture, which can significantly increase the binding of water molecules. the use of reinforcement tio2 in the cs-pva composite increased the durability of the film in water for 315 minutes longer than the cs-pva film for 200 minutes. the most optimal increase was seen at a concentration of 15% wt tio2. the presence of tio2 in the cs-pva polymer mixture made the film denser which increased the absorption capacity of water molecules. in addition, the hydrophobic nature of tio2 can also slow down the absorption of water molecules on the film surface. 3.4 electrical teng the schematic diagram of the teng output test is shown in fig. 7. conditioning for humidity levels of 15%, 55%, and 95% were carried out by placing the teng in a closed cylindrical chamber. 279 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 fig. 7: teng performance measurements. the teng operating mode rotary freestanding (rf-teng). the stator comprises six sectors of a cs-pva/tio2 nanocomposite film connected to a copper foil electrode, the teng output circuit uses a rectifier diode to convert ac to dc, and a capacitor as electrical storage before being channeled to the led load. the rotor rotation speed was controlled stable (ω = 200 rad/s), and the load was 50 mω. teng output performance test with cspva triboelectric film without tio2 at a low humidity level (rh, 15%) resulted in an output voltage and current of ~25.5 v and ~3.6 μa, while the effect of adding 0.5% wt tio2 in the matrix of the cs-pva nanocomposite showed a 1.9-fold increase in output voltage from ~25.5 v to 50 v, and a 1.6-fold increase in output current from ~3.6 μa to ~5.9 μa. meanwhile, the addition of tio2 in the weight ratio (0% to 15% wt tio2) showed a linear increase in voltage and current, respectively, as shown in (fig. 8b-d). optimal output voltage and current were achieved at a concentration of 5%wt tio2 with a value of 117 v and 10.2 μa (fig. 8b). this increase in output voltage and current is due to an increase in the value of the dielectric constant due to the presence of tio2 nps in the cs-pva polymer mixture which can increase the triboelectric of the film. these results show similarities with some of the results of previous research reports, such as an increase in dielectric properties of poly (vinylidene fluoride) film with tio2 np deposition [9], dielectric constant changes linearly as a function of weight ratio of pdms embedded tiox np [10,37], tio2 doping on portland cement [11], natural rubber (nr)-tio2 [38]. in addition, the effect of differences in relative humidity factors (rh, 15%, 55%, and 95%) on the output performance of cs-pva/tio2 film-based teng at a weight ratio above 5% tio2 shows that the resulting voltage and current increase are directly correlated with increased humidity levels (fig. 8a-c.). the output performance of teng when the relative humidity condition increased from 15% to 55% (ratio of 15% weight of tio2) showed an increase in the output voltage of teng 1.8 -fold from ~70.5 v to ~130 v, and the output current increased by 1.1-fold from ~5.2 μa to ~5.6 μa. enhanced relative humidity of the cylinder chamber is carried out by continuously injecting wet air into the closed cylinder chamber to increase the humidity from 55% to 95% as shown in fig. 8b-c. under conditions of relatively high humidity (95%), teng can produce a 1.4-fold increase in teng output 280 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 voltage from ~130 v to ~180 v and a 2.4-fold increase in current from ~5.6 μa to ~13.7 μa. however, the increase in teng output voltage and current was lower at a tio2 weight ratio of less than 5%, about 1.1 times. meanwhile, the increase in teng's optimal output voltage and current when humidity is high (rh, 95%) with a concentration of 15% wt tio2 can reach 2.5-fold from ~70.5 v to ~180 v, and the current increases 2.6-fold from ~5.2 μa to ~13.7 μa. fig. 8: output voltage and current at film humidity level: a) humidity 15%, c) humidity 55%, and c) humidity 95%. the increase in teng output voltage and current is caused by the formation of hydrogen bonds between hydroxyl groups and water molecules (when humidity is high) on the surface of the cs-pva/tio2 nanocomposite film increasing the positive triboelectrification properties of the film. this is not much different from the research reported by wang et al. using starch polymers rich in hydroxyl groups with the formation of hydrogen bonds with water molecules when humidity is high can increase the output current of teng based on starch films [39], pva films rich in hydroxyl chains when humidity is high. high water molecules participate in triboelectric charging [40]. meanwhile, the effect of the presence of 15% wt tio2 concentration in the cs-pva nanocomposite film showed the most optimal increase at high humidity. the output voltage and current increased with a value to 1.9-fold voltage and 1.8-fold current due to the increase in the density of the nanocomposite film. the density of the film can increase the absorption 281 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 of water molecules when humidity is high. in addition, tio2 in the cs-pva matrix can form a winding path that can prolong the transport of water molecules, enhancing the triboelectric properties of the film. 4. conclusions this study presents a method for producing cassava starch (cs)/pva nanocomposite films using tio2 reinforcement. the effects of incorporation of tio2 on the structure and properties of the cs/pva composite were investigated. the ftir spectra indicate the response of hydroxyl groups in the cs/pva composite increased after inserting tio2 nanoparticles with the formation of hydrogen bonds and c-o-ti bonds. the interaction between ti ions and hydroxyl groups forms a complex composite mixture through intra/intermolecular hydrogen bonds. the xrd analysis reveals the tio2 concentration (> 1% wt) increased the crystallinity of the nanocomposite film with a semicrystalline structure and variations in crystal shape and uniform crystal size. the sem photo indicates the tio2 can be evenly distributed in the film surface of the cs/pva composite and resulting in a compatible nanocomposite film. the physical properties of the film increased significantly with the addition of tio2 (> 1% wt) with a decreased water vapor permeability (wvp) value 7.39±0.75 x 10-7 g/m h pa, and the degree of film damage in water decreased by 1.6-fold compared to cs/pva nanocomposite films without tio2 reinforcement. optimal performance of the cs-pva/tio2 nanocomposite film as a tribo-positive friction film for teng with a 5% wt tio2 concentration, while at high humidity (95% rh) with a 15% wt tio2 concentration, the output voltage and current of teng increased 1.9 -fold respectively and the current is 1.8-fold due to the formation of water molecule bonds with the hydroxyl chains, and the availability of free electrons in the film due to the presence of tio2 bonds in the cs-pva matrix. the findings of this study will promote starch-based nanocomposite films that have great potential for tribo-triboelectric nanogenerator (teng) film applications for high-humidity environmental conditions. acknowledgment this work was supported by the research and community service institute, universitas negeri surabaya (unesa), under the grant number b/37502/2021. references [1] dzhardimalieva gi, yadav bc, lifintseva tv, uflyand ie. (2021). polymer chemistry underpinning materials for triboelectric nanogenerators (tengs): recent trends. eur. polym. j, 142: 110-163. https://doi.org/10.1016/j.eurpolymj.2020.110163 [2] wang, j., wu, c., dai, y., zhao, z., wang, a., zhang, t., & wang, z. l. (2017). achieving ultrahigh triboelectric charge density for efficient energy harvesting. nature communications, 8(1), 1–7. https://doi.org/10.1038/s41467-017-00131-4 [3] xia k, fu j, xu z. (2020). multiple-frequency high-output triboelectric nanogenerator based on a water balloon for all-weather water wave energy harvesting. adv. energy mater, 10(28): 1-9. https://doi.org/10.1002/aenm.202000426 [4] yoon hj, ryu h, kim sw. (2018). sustainable powering triboelectric nanogenerators: approaches and the path towards efficient use. nano energy, 51(june): 270-285. https://doi.org/10.1016/j.nanoen.2018.06.075 282 https://doi.org/10.1016/j.nanoen.2018.06.075 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 [5] song, g., kim, y., yu, s., kim, m. o., park, s. h., cho, s. m., velusamy, d. b., cho, s. h., kim, k. l., kim, j., kim, e., & park, c. (2015). molecularly engineered surface triboelectric nanogenerator by self-assembled monolayers (mets). chemistry of materials, 27(13), 4749–4755. https://doi.org/10.1021/acs.chemmater.5b01507 [6] mallakpour s, jarang n. (2016). mechanical, thermal and optical properties of nanocomposite films prepared by solution mixing of poly(vinyl alcohol) with titania nanoparticles modified with citric acid and vitamin c. j. plast. film sheeting, 32(3): 293-316. https://doi.org/10.1177/8756087915597024 [7] khushboo, & azad, p. (2019). design and implementation of conductor-to-dielectric lateral sliding teng mode for low power electronics. in advances in intelligent systems and computing (vol. 698, issue may). springer singapore. https://doi.org/10.1007/978-981-131819-1_17 [8] park, h. w., huynh, n. d., kim, w., lee, c., nam, y., lee, s., chung, k. b., & choi, d. (2018). electron blocking layer-based interfacial design for highly-enhanced triboelectric nanogenerators. nano energy, 50, 9–15. https://doi.org/10.1016/j.nanoen.2018.05.024 [9] kum‐onsa, p., chanlek, n., manyam, j., thongbai, p., harnchana, v., phromviyo, n., & chindaprasirt, p. (2021). gold‐nanoparticle‐deposited tio2 nanorod/poly(vinylidene fluoride) composites with enhanced dielectric performance. polymers, 13(13), 1–14. https://doi.org/10.3390/polym13132064 [10] huynh nd, park h, chung k, choi d. (2018). effect on teng performance by phase control of tio x nanoparticles. compos. res, 31(6): 365-370. http://dx.doi.org/10.7234/composres.2018.31.6.365 [11] sintusiri j, harnchana v, amornkitbamrung v, wongsa a, chindaprasirt p. (2020). portland cement-tio2 triboelectric nanogenerator for robust large-scale mechanical energy harvesting and instantaneous motion sensor applications. nano energy, 74: 104802. https://doi.org/10.1016/j.nanoen.2020.104802 [12] nguyen v, yang r. (2013). effect of humidity and pressure on the triboelectric nanogenerator. nano energy, 2(5): 604-608. https://doi.org/10.1016/j.nanoen.2013.07.012 [13] zhang jh, hao x. (2020). enhancing output performances and output retention rates of triboelectric nanogenerators via a design of composite inner-layers with coupling effect and self-assembled outer-layers with superhydrophobicity. nano energy, 76: 105074. https://doi.org/10.1016/j.nanoen.2020.105074 [14] ahn, j., zhao, z. j., choi, j., jeong, y., hwang, s., ko, j., gu, j., jeon, s., park, j., kang, m., del orbe, d. v., cho, i., kang, h., bok, m., jeong, j. h., & park, i. (2021). morphologycontrollable wrinkled hierarchical structure and its application to superhydrophobic triboelectric nanogenerator. nano energy, 85(march), 105978. https://doi.org/10.1016/j.nanoen.2021.105978 [15] shen j, li z, yu j, ding b. (2017). humidity-resisting triboelectric nanogenerator for high performance biomechanical energy harvesting. nano energy, 40: 282-288. https://doi.org/10.1016/j.nanoen.2017.08.035 [16] lv, p., shi, l., fan, c., gao, y., yang, a., wang, x., ding, s., & rong, m. (2020). hydrophobic ionic liquid gel-based triboelectric nanogenerator: next generation of ultrastable, flexible, and transparent power sources for sustainable electronics. acs applied materials and interfaces, 12(13), 15012–15022. https://doi.org/10.1021/acsami.9b19767 [17] zhou, q., lee, k., kim, k. n., park, j. g., pan, j., bae, j., baik, j. m., & kim, t. (2019). high humidityand contamination-resistant triboelectric nanogenerator with superhydrophobic interface. nano energy, 57(december 2018), 903–910. https://doi.org/10.1016/j.nanoen.2018.12.091 [18] ccorahua r, cordero a, luyo c, quintana m, vela e. (2019). starch-cellulose-based triboelectric nanogenerator obtained by a low-cost cleanroom-free processing method. mrs adv, 4(23): 1315-1320. https://doi.org/10.1557/adv.2018.652 [19] wang n, zheng y, feng y, zhou f, wang d. (2020). biofilm material based triboelectric nanogenerator with high output performance in 95% humidity environment. nano energy, 77(may): 105088. https://doi.org/10.1016/j.nanoen.2020.105088 283 https://doi.org/10.1177/8756087915597024 http://dx.doi.org/10.7234/composres.2018.31.6.365 https://doi.org/10.1016/j.nanoen.2020.104802 https://doi.org/10.1016/j.nanoen.2013.07.012 https://doi.org/10.1016/j.nanoen.2020.105074 https://doi.org/10.1016/j.nanoen.2017.08.035 https://doi.org/10.1557/adv.2018.652 https://doi.org/10.1016/j.nanoen.2020.105088 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 [20] wang j, wu h, fu s, li g, shan c, he w, hu c. (2022). enhancement of output charge density of teng in high humidity by water molecules induced self-polarization effect on dielectric polymers. nano energy, 104(part b): 107916. https://doi.org/10.1016/j.nanoen.2022.107916 [21] ccorahua r, huaroto j, luyo c, quintana m, vela ea. (2019). enhanced-performance biotriboelectric nanogenerator based on starch polymer electrolyte obtained by a cleanroom-free processing method. nano energy, 59(march): 610-618. https://doi.org/10.1016/j.nanoen.2019.03.018 [22] shi, l., dong, s., xu, h., huang, s., ye, q., liu, s., wu, t., chen, j., zhang, s., li, s., wang, x., jin, h., kim, j. m., & luo, j. (2019). enhanced performance triboelectric nanogenerators based on solid polymer electrolytes with different concentrations of cations. nano energy, 64(august), 103960. https://doi.org/10.1016/j.nanoen.2019.103960 [23] zhu z, xia k, xu z, lou h, zhang h. (2018). starch paper-based triboelectric nanogenerator for human perspiration sensing. nanoscale res. lett, 13: 4-9. https://doi.org/10.1186/s11671-018-2786-9 [24] torres fg, troncoso op, torres c, díaz da, amaya e. (2011). biodegradability and mechanical properties of starch films from andean crops. int. j. biol. macromol, 48(4): 603606. https://doi.org/10.1016/j.ijbiomac.2011.01.026 [25] ben doudou b, vivet a, chen j, laachachi a, falher t, poilâne c. (2014). hybrid carbon nanotube silica/ polyvinyl alcohol nanocomposites films: preparation and characterisation,” j. polym. res, 21(4). https://doi.org/10.1007/s10965-014-0420-9 [26] kochkina ne, butikova oa. (2019). effect of fibrous tio2 filler on the structural, mechanical, barrier and optical characteristics of biodegradable maize starch/pva composite films. int. j. biol. macromol, 139: 431-439. https://doi.org/10.1016/j.ijbiomac.2019.07.213 [27] rajesh k, crasta v, rithin kumar nb, shetty g, rekha pd. (2019). structural, optical, mechanical and dielectric properties of titanium dioxide doped pva/pvp nanocomposite. j. polym. res, 26(4): 4-10. https://doi.org/10.1007/s10965-019-1762-0 [28] sarkar s, guibal e, quignard f, sengupta ak (2012). polymer-supported metals and metal oxide nanoparticles: synthesis, characterization, and applications. j. nanoparticle res, 14(2): 2-24. https://doi.org/10.1007/s11051-011-0715-2 [29] alvarez-ramirez j, vazquez-arenas j, garcía-hernández a, vernon-carter ej. (2019). improving the mechanical performance of green starch/glycerol/li + conductive films through cross-linking with ca2+. solid state ionics, 332(november): 1-9. https://doi.org/10.1016/j.ssi.2019.01.002 [30] abdullah am, aziz sb, saeed sr(2021). structural and electrical properties of polyvinyl alcohol (pva):methyl cellulose (mc) based solid polymer blend electrolytes inserted with sodium iodide (nai) salt. arab. j. chem, 14(11): 103388. https://doi.org/10.1016/j.arabjc.2021.103388 [31] bergo p, sobral pja, prison jm. (2011). effect of glycerol on physical properties of cassava starch films. j. food process. preserv, 34(2): 401-410. https://doi.org/10.1111/j.1745-4549.2008.00282.x [32] adamu ad, jikan ss, talip bha, badarulzaman na, yahaya s. (2017). effect of glycerol on the properties of tapioca starch film. mater. sci. forum, 888: 239-243. https://doi.org/10.4028/www.scientific.net/msf.888.239 [33] abral h, hartono a, hafizulhaq f, handayani d, sugiarti e, pradipta o. (2019). characterization of pva/cassava starch biocomposites fabricated with and without sonication using bacterial cellulose fiber loadings. carbohydr. polym, 206: 593-601. https://doi.org/10.1016/j.carbpol.2018.11.054 [34] surudžić, r., janković, a., bibić, n., vukašinović-sekulić, m., perić-grujić, a., miškovićstanković, v., park, s. j., & rhee, k. y. (2016). physico-chemical and mechanical properties and antibacterial activity of silver/poly(vinyl alcohol)/graphene nanocomposites obtained by electrochemical method. composites part b: engineering, 85, 102–112. https://doi.org/10.1016/j.compositesb.2015.09.029 284 https://doi.org/10.1016/j.nanoen.2022.107916 https://doi.org/10.1016/j.nanoen.2019.03.018 https://doi.org/10.1186/s11671-018-2786-9 https://doi.org/10.1007/s10965-014-0420-9 https://doi.org/10.1016/j.ijbiomac.2019.07.213 https://doi.org/10.1016/j.ssi.2019.01.002 https://doi.org/10.1016/j.arabjc.2021.103388 https://doi.org/10.4028/www.scientific.net/msf.888.239 https://doi.org/10.1016/j.carbpol.2018.11.054 iium engineering journal, vol. 24, no. 2, 2023 ansori et al. https://doi.org/10.31436/iiumej.v24i2.2554 [35] wang y, zhang h, zeng y,hossen md a, dai y, li s, liu y, qin w. (2022). development and characterization of potato starch/lactucin/nano-tio2 food packaging for sustained prevention of mealworms. food packag. shelf life, 33: 100-837. https://doi.org/10.1016/j.fpsl.2022.100837 [36] oleyaei sa, almasi h, ghanbarzadeh b, moayedi aa. (2016). synergistic reinforcing effect of tio2 and montmorillonite on potato starch nanocomposite films: thermal, mechanical and barrier properties. carbohydrate polymers, 152: 263-262. https://doi.org/10.1016/j.carbpol.2016.07.040 [37] park, h. w., huynh, n. d., kim, w., hwang, h. j., hong, h., choi, k. h., song, a., chung, k. b., & choi, d. (2018). effects of embedded tio2-x nanoparticles on triboelectric nanogenerator performance. micromachines, 9(8). https://doi.org/10.3390/mi9080407 [38] bunriw, w., harnchana, v., chanthad, c., & huynh, v. n. (2021). natural rubber-tio2 nanocomposite film for triboelectric nanogenerator application. polymers, 13(13), 1–12. https://doi.org/10.3390/polym13132213 [39] butyral, p., anti, e., agent, o., benas, j., huang, c., yan, z., liang, f., & li, p. (2022). nanofiber-based odor-free medical mask fabrication using polyvinyl butyral and eucalyptus anti odor agent. polymers 2022, 14: 4447. https://doi.org/10.3390/polym14204447 [40] wang, n., feng, y., zheng, y., zhang, l., feng, m., li, x., zhou, f., & wang, d. (2021). new hydrogen bonding enhanced polyvinyl alcohol based self-charged medical mask with superior charge retention and moisture resistance performances. advanced functional materials, 31(14), 1–14. https://doi.org/10.1002/adfm.202009172 [41] patil, s., bharimalla, a. k., mahapatra, a., dhakane-lad, j., arputharaj, a., kumar, m., raja, a. s. m., & kambli, n. (2021). effect of polymer blending on mechanical and barrier properties of starch-polyvinyl alcohol based biodegradable composite films. food bioscience, 44(pa), 101352. https://doi.org/10.1016/j.fbio.2021.101352 285 https://doi.org/10.1016/j.fpsl.2022.100837 https://www.sciencedirect.com/journal/carbohydrate-polymers https://doi.org/10.1016/j.carbpol.2016.07.040 https://doi.org/10.3390/polym14204447 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 effects of hive sizes and mesh materials on the productivity of propolis and honey produced by tetragonula laeviceps muhammad yusuf abduh1,2*, annisa shabrina1, andreas raden caman1, arsy elia pratiwi1 and muhammad ihsanu1 1 school of life sciences and technology, institut teknologi bandung, bandung, indonesia 2 university center of excellence for nutraceuticals, bioscience and biotechnology research center, institut teknologi bandung, bandung, indonesia * corresponding author: yusuf@sith.itb.ac.id (received: 4 january 2023; accepted: 2 june 2023; published on-line: 4 july 2023) abstract: propolis and honey are bioproducts produced by tetragonula laeviceps, a stingless bee species. both products have anti-inflammatory, antimicrobial, and antibacterial properties. modular tetragonula hives of different sizes were used in the cultivation of t. laeviceps to increase the productivity of propolis while maintaining the sustainability of the bee colonies. this study was carried out in jatinangor, west java, indonesia, with three size variations: small (21 × 18 × 14 cm), medium (26 × 22 ×17 cm), and large (30 × 26 × 17 cm). each hive was equipped with a mesh of a different material. the results obtained in this study showed that increasing the hive’s size increases the productivity of propolis. the highest productivity of propolis (2.53 ± 0.37 g/colony/week) was obtained when t. laeviceps was cultivated in large hives equipped with a nylon-based mesh. the highest productivity of honey (0.78 ± 0.18 g/colony/week) was obtained when t. laeviceps was cultivated in medium hives equipped with an aluminum-based mesh. the harvested propolis was extracted using a maceration method. total flavonoid and phenolic content of the propolis solution lies in the range of 1.77 ± 0.86 to 3.18 ± 1.43 mg qe/g propolis and 32.23 ± 14.09 to 112.13 ± 47.64 mg gae/g propolis, respectively. the harvested honey had a water content of 21.86%, with 72.86% reducing sugar, 192.86 μg/ml vitamin c, and 2613.41 μg/ml of antioxidant content. abstrak: propolis dan madu adalah produk bio yang dihasilkan oleh tetragonula laeviceps, spesies lebah kelulut. kedua-dua produk mempunyai ciri anti-radang, antimikrob dan antibakteria. sarang tetragonula modular dengan saiz yang berbeza digunakan dalam mengusahakan t. laeviceps bagi meningkatkan produktiviti propolis sambil mengekalkan kemampanan koloni lebah. kajian ini dijalankan di jatinangor, jawa barat, indonesia, dengan tiga variasi saiz: kecil (21 × 18 × 14 cm), sederhana (26 × 22 × 17 cm), dan besar (30 × 26 ×17 cm). setiap sarang dilengkapi dengan jaringan bahan yang berbeza. dapatan kajian yang diperolehi melalui kajian ini menunjukkan bahawa penambahan saiz sarang dapat meningkatkan produktiviti propolis. produktiviti tertinggi propolis (2.53 ± 0.37 g/koloni/minggu) diperoleh apabila t. laeviceps dibela dalam sarang besar yang dilengkapi dengan jaring berasaskan nilon. produktiviti madu tertinggi (0.78 ± 0.18 g/koloni/minggu) diperoleh apabila t. laeviceps diusahakan dalam sarang sederhana yang dilengkapi dengan jaring berasaskan aluminium. propolis yang dituai telah diekstrak menggunakan kaedah maserasi. jumlah kandungan flavonoid dan kandungan fenolik larutan propolis berada dalam julat 1.77 ± 0.86 hingga 3.18 ± 1.43 mg qe/g propolis dan 32.23 ± 14.09 hingga 112.13 ± 47.64 mg gae/g propolis, masing-masing. madu yang dituai mempunyai kandungan air 21.86%, dengan 72.86% penurunan gula, 192.86 μg/ml vitamin c, dan 2613.41 μg/ml kandungan antioksidan. 34 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 keywords: hive; honey; mesh, propolis; tetragonula laeviceps 1. introduction bees produce various beneficial products such as honey, pollen, propolis, beeswax, and bee bread. bees make propolis by mixing plant resin, which contains flavonoids, polyphenols, saponins, amino acids, and minerals, with wax and their saliva secretion [1]. propolis consumption can reduce inflammation, inhibit scar tissue contraction, promote wound healing, and enhance stamina and overall health. antibacterial and antifungal properties of propolis allow for its extensive use in the health and cosmetic industries [2]. moreover, bees also produce honey from flower nectars, which comprise flavonoids and other phenolic compounds, contributing to antimicrobial, antioxidant, anti-inflammation, and anticancer activities [3]. tetragonula laeviceps is a stingless bee species that produces propolis to seal cracks in their hive, to protect their hive from pests and diseases, and to build honey and pollen pots. t. laeviceps can produce propolis more abundantly compared to honeybees of genus apis with productivities of 3 kg/colony/year and 20–30 g/colony/year, respectively [4]. total flavonoid content in stingless bee propolis with quercetin equivalent (qe) reaches 4% (mg qe/g propolis extract), higher than apis bee with only 1.5% [5]. however, honey productivity of t. laeviceps is relatively small compared with its propolis only, around 6.5 kg/year/colony [6]. the physicochemical properties in t. laeviceps honey include a ph of 3.15–4.66, acidity of 5.9–109 meq/kg, anti-microbial activity of 0.9– 23 dn, 58–75.7 g/100 g of reducing sugar, 1.1–4.8 g/100g of sucrose, and water content (19.9–41.9 g/100 g) [7]. therefore, t. laeviceps is widely cultivated by stingless beekeepers for its propolis. there are several stingless beekeepers still beekeeping with bamboo, the bees’ natural hive. beekeeping with bamboo hives yields propolis at a rate of 2.36 g/colony/week [8]. however, the application of bamboo hives requires beekeepers to damage the hive during the harvesting process, which harms the colony and results in high contamination of pollen and honey in the propolis [9]. the hive design that is currently under development is a wooden box equipped with a mesh as a propolis trap. a modular tetragonula hive (motive) is a stingless beehive invention that combines a main wooden box and a perforated mesh to optimize the productivity of propolis [8,10,11]. the mesh in the hive contributes to an increase in propolis production compared to a simple wooden box without a mesh [8,10]. a motive can also sustain the colony and improve the quality of propolis harvested because they do not mix with non-propolis products [10]. motive beekeeping has been accomplished with motives the size of 21×14×18 cm which resulted in propolis productivity of 2–2.8 g/colony/week [8,10]. a motive is constructed of three main parts: the wooden box for the colony, a mesh holder comprised of two wooden frames above the wooden box, and the top cover that is legged to create a ventilation space above the mesh [8,10]. the mesh in the motive is a perforated material that serves as a place for the bees to attach propolis. the mesh requires properties such as rust resistance, acid resistance, odorless, and processability [12]. aluminum wire, nylon, and polyethylene are mesh materials that are widely used. nylon membranes have high ph, high-temperature resistance, and a small pore size distribution [13]. polyethylene membranes have a melting point of 115 °c and are flexible, whereas aluminum materials have high-temperatureand corrosion-resistant properties [14]. 35 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 in this study, t. laeviceps cultivation was carried out using motives with various hive sizes and mesh materials. according to abd-elmawgood et al. [15], the smaller hive results in a higher temperature inside the hive. internal conditions, such as temperature, will affect the condition and activity of the colony in the foraging process. in addition, the size of the hive, which is proportional to the mesh size, will affect the propolis production by the bees. therefore, this study was conducted to determine the size of motive and the mesh material that generates optimum productivity of propolis and honey. 2. materials and methods 2.1 preparations of colony twenty tetragonula laeviceps colonies were obtained from a breeder in kebumen, central java, indonesia, in september–november 2018. the t. laeviceps colonies were in bamboo hives and acclimatized at the cultivation site for one to two months. the motive was sterilized with ultraviolet (uv) light for 30 minutes. eighteen colonies were moved to the motive, and two colonies remained in the bamboo hive as control treatments. the colony inside the motive was re-acclimatized for two weeks. 2.2 variation of hive size and mesh type the motive used had three size variations: small (21 × 18 ×14 cm), medium (26 × 22 × 17 cm), and large (30 × 26 × 17 cm). each hive size had three variations of mesh materials: nylon, polyethylene, and aluminum wire placed between the wooden box and the cover. the pore size of the nylon mesh was 1 × 1 mm, while the pore size of the polyethylene and aluminum wire mesh was 2 × 2 mm. 2.3 harvesting of propolis and honey the beekeeping process of t. laeviceps was carried out for eight weeks at the wood laboratory, institut teknologi bandung, jatinangor campus, sumedang, west java. propolis was harvested every two weeks, while honey was harvested at the end of the cultivation period. the honey harvesting process was accomplished using a syringe and glass pipette. the mesh that was filled with propolis was weighed to determine the propolis weight. propolis productivity of t. laeviceps per week can then be determined by dividing the propolis weight by two (for the two-weeks period). the harvested honey was then measured for its weight and volume. honey productivity per week was determined by dividing the weight of the honey by eight (for the eight-weeks period). 2.4 extraction of propolis the propolis was extracted according to the method of machado et al. [16] with a slight modification. harvested propolis was separated from the mesh using liquid nitrogen. the ratio of propolis to ethanol was 1:15 (w/v). the extraction was carried out on a shaker incubator (ika ks 4000i control) with a rotational speed of 500 rpm and a temperature of 40 °c for one hour in a dark room. the extract was filtered with a glass funnel and filter paper whatman no. 2. the filtrate obtained was stored in a dark vial bottle. then, 0.5 ml of the propolis filtrate sample was transferred to evaporating dishes to evaporate the solvent using a hot plate at 40 °c. during this process, the evaporating dish was covered with aluminum foil to reduce air and light exposure. 36 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 2.5 determination of total flavonoid content total flavonoid content (tfc) was determined using a quercetin calibration curve, as described by machado et al. [16]. standard quercetin (0.05 g) was dissolved in 50 ml ethanol to obtain 1000 μg/ml of quercetin stock solution. the stock solution was then diluted to obtain quercetin solutions with concentrations of 100 μg/ml, 50 μg/ml, 25 μg/ml, 12.5 μg/ml, 6.25 μg/ml, and 0 μg/ml, for the blank solution. 2 ml of standard solution was mixed with 2 ml of 2% alcl3 solution and incubated for 30 minutes. next, the absorbance was measured at a wavelength of 415 nm with an ultraviolet-visible (uv-vis) spectrophotometer (shimadzu uv-1800). before analyzing the sample, propolis extract from the evaporation process was dissolved in 10 ml 80% methanol. the propolis-methanol solution was added to 2% alcl3, and the absorbance was measured. quercetin contents in the sample solution were considered as tfc in units of mg of quercetin equivalent per ml (mg qe/ml), determined by the following equation: tfcsample solution = ( 𝐴−0.0296 0.035 ) × 𝑁, (1) where a is the absorbance value of the sample, n is the dilution factor of the sample solution, and 0.0296 and 0.035 are the constant value and the coefficient of the quercetin calibration curve, respectively. meanwhile, the tfc in propolis extract was determined by the following equation: tfcpropolis extract (mg qe/g) = 𝑇𝐹𝐶 sample ( 𝑚𝑔 𝑚𝐿 )×𝑉solution (𝑚𝐿) 𝑚extract (𝑔) , (2) where vsolution (10 ml) is the total volume of propolis methanol extract solution, and mextract is the mass (g) of propolis extract (mass of remaining solids from the evaporation of propolis filtrate). 2.6 determination of total phenolic content the total phenolic content (tpc) of propolis was determined according to the folinciocalteu method, as explained by machado et al. [16]. a calibration curve was constructed by first dissolving 0.1 g of standard gallic acid in 10 ml ethanol and then diluting with 100 ml distilled water to obtain a stock solution with a concentration of 1000 µg/ml. the stock solution was diluted with distilled water to obtain standard solutions with concentrations of 750 μg/ml, 500 μg/ml, 250 μg/ml, 100 μg/ml, 50 μg/ml, and 0 μg/ml, for the blank solution. 0.5 ml of each standard solution was added to 2 ml of folin-ciocalteu reagent and 2.5 ml of 7.5% na2co3 solution. the mixture was then incubated for five minutes in a water bath at 50 °c. the absorbance of each standard solution was measured with a uvvis spectrophotometer at a wavelength of 765 nm. sample analysis was performed by dissolving evaporated propolis extract in 5 ml ethanol 80%. gallic acid contents in the sample solution were considered as tpc with a unit of mg of gallic acid equivalent per ml (mg gae/ml). tpc in the sample was determined with the following equation: tpcsample solutione (mg/ml) = ( 𝐴−0,1351 0,0111 ) × 𝑁 (3) where a is the absorbance value of the sample, n is the dilution factor of the sample solution, and 0.1351 and 0.0111 are the constant value and the coefficient of the gallic acid calibration curve, respectively. meanwhile, the tpc in the propolis extract was determined with eq. (2), with a vsolution of 5 ml. 37 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 2.7 characterization of honey honey characterization was carried out at sibaweh laboratories, bandung. the moisture content of the honey was measured according to indonesian national standard 013545-2004 (19sni, 2004) using a refractometer. reducing sugar content was determined with the luff-schoorl method according to the indonesian national standard 01-2892-1994 (20-sni, 1994). antioxidant activity was determined with the dpph (2,2-diphenyl-1picrylhydrazyl) activity method as suggested by sadeli et al. [17]. vitamin c content was measured using a titration method according to silva et al. [18]. 3. results and discussions 3.1 productivity of propolis produced by t. laeviceps t. laeviceps colonies that were cultivated in bamboo hives produced propolis at a rate of 0.67 ± 0.01 g/colony/week. the propolis productivity of the bees in small, medium, and large motives with nylon, polyethylene, and aluminum meshes ranged from 1.12–2.52 g/colony/week (table 1). t. laeviceps bees produce propolis to cover the holes in the hive for self-protection [19]. a motive is equipped with a perforated mesh to stimulate more propolis production by the bees. the productivity of propolis of the colonies in bamboo hives was lower than the colonies in the motives. this phenomenon is related to the difference in cavity size in the hives. bamboo hives have smaller cavity gaps, which extend vertically, resulting in less propolis produced and difficulty in harvesting. table 1: productivity of propolis and honey (g/colony/week) produced by t. laeviceps in various hive sizes and mesh materials hive sizes mesh materials propolis productivity [g/colony/week] honey productivity [g/colony/week] small nylon 1.24 ± 0.21a 0.09 ± 0.02 c polyethylene 1.12 ± 0.58a 0.08 ± 0.01c aluminum 1.12 ± 0.54a 0.02 ± 0.01c medium nylon 1.51 ± 0.63a,b 0.09 ± 0.07d polyethylene 1.60 ± 0.27a,b 0.12 ± 0.17d aluminum 1.81 ± 0.80a,b 0.78 ± 0.18d large nylon 2.52 ± 0.37b 0.12 ± 0.02c,d polyethylene 2.32 ± 0.39b 0.35 ± 0.35c,d aluminum 1.31 ± 0.50b 0.03 ± 0.01c,d *different letters indicate statistical differences (p-value < 0.05, duncan's test). the mesh sizes in this study were proportional to the motive size, such that the large motive has a larger mesh surface area than the small motive. thus, larger motive results in higher propolis productivity as the bees need to cover more areas. this phenomenon was shown through the propolis productivity in the large motives with nylon and polyethylene meshes, which were higher than that of the small and medium motive. however, the motive with an aluminum mesh did not show the same pattern. propolis productivity in the large motive with an aluminum mesh was lower than that of the medium motive. 38 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 propolis production by the bees was influenced by several factors, such as the colony condition during the beekeeping process [20]. in this study, the number of bees per colony varied with bee colonies. the large motives with nylon, polyethylene, and aluminum meshes had 859, 1120, and 937 bees, respectively. these population numbers were enough for the bees to cover the mesh with propolis, as shown by the highest productivity of propolis in the large motives. similarly, the medium motive with nylon and aluminum meshes also had enough populations with 774 and 1788 bees, respectively. interestingly, the medium motive with a polyethylene mesh only had 189 bees, but the colony could still meet the needs of propolis production to cover the mesh. this phenomenon is related to the task divisions of worker bees, which are determined based on anatomical and physical conditions, environmental stimuli, and age [21]. the bee colony was considered young, signified by the abundant brood cells and bee breads in the hive. thus, the high needs of the colony affected the activity of the forager bees in collecting resin [22]. in this study, the age of colony and number of bees per colony were not pre-determined prior to the study but were calculated after the harvesting process, which resulted in different numbers of bees in the colonies in each treatment. in the research conducted by agussalim et al. [23], the highest productivity of propolis was produced by the bees in a wooden box hive sized 35 × 20 × 17.5 cm with a value of 3.85 ± 3.66 g/colony/week. this value was higher than the colony from a wooden box hive sized 40 × 20 × 20 cm with a productivity rate of 2.30 ± 1.82 g/colony/week. these results were similar to this study, where the productivity of propolis in the motives with aluminum meshes was not linearly proportional to the size of the hive. this could be due to factors such as the number of worker bees, flight activities of the forager bees, and sources and availability of resins. table 1 shows that propolis productivity was more affected by hive size because propolis productivity differences were not significant in mesh material variation. the highest productivity of propolis was from the colonies in the large motive with a nylon mesh at 2.52 ± 0.37 g/colony/week. according to tsakgarakis et al. [24], propolis production is higher with smaller mesh pore size, which has a larger total surface area. pore sizes of the aluminum, nylon, and polyethylene meshes were 2 × 2 mm, 1 × 1 mm, and 2 × 2 mm, respectively. the small pore size of the nylon mesh results in more holes to cover but allows for easier propolis placement by the bees. 3.2 productivity of honey produced by t. laeviceps in addition to propolis, t. laeviceps bees produce honey at a rate of 0.02–0.78 g/colony/week. the honey tends to have a dark brown color with a distinctly sour taste. the results show that honey productivity is directly proportional to the size of motive with a polyethylene mesh, but not for the motive with nylon and aluminum meshes. according to bushal et al. [25], honey productivity is not affected by the size of the hive but is affected by the size of the colony, the number of populations in the colony, and the bees’ flight activity. honey production tends to increase when the population increases owing to the growing need for bees to forage, which results in more forager bees. based on the research conducted by salatnaya [26], honey productivity using a 25 × 15 × 15 cm wooden box hive was 0.02–0.19 g/colony/week, less than the honey productivity of small motives. in addition to the colony population, honey productivity is influenced by nectar flow, or the availability of nectar in the environment [27]. the bees will collect nectar in warm weather for supply during the rainy season. however, honey production for stingless bees, in general, is not as high as the apis honeybees owing to their smaller body sizes, which results in shorter flight distances [28]. the maximum flying distance of tetragonula 39 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 stingless bees is approximately 712 m [29]. however, its small body prevents the stingless bee from collecting nectar and pollen on small flowers [30]. several factors that can cause low honey production are the focus of worker bees on hive construction, waste disposal activity from the hive, and low productivity of the queen bee to produce worker bees [31]. in this study, honey productivity was directly proportional to propolis productivity in motives with polyethylene and aluminum meshes. this was because large amounts of honey can provide energy for the bees to forage other resources, such as pollen and resin. stingless bees, which are eusocial organisms, are interdependent to fulfil their needs and maintain hive conditions. these activities improved the sustainability of the colony, and the colony remained healthy and protected from pests and diseases. 3.3 total flavonoid and total phenolic content of propolis extract the harvested raw propolis was extracted. the resulting propolis extracts had a wide range of tfc and tpc. propolis from the bamboo hive had a tfc and tpc of 3.42 ± 1.15 mg qe/g and tpc 284.62 ± 39.46 mg of gae/g, respectively. the complete tfc and tpc of each motive size and mesh material are shown in table 2. the propolis extraction process will remove the inert materials and keep the polyphenol fraction [32]. the results of this study indicate that there is no correlation between hive size and propolis quality. the difference in propolis quality is caused by numerous factors, such as bee genetics (species), different sources of plant resins, and microclimates [26]. this is supported by the research of hakim & abduh [8] and abduh et al. [10], in which the colony of t. laeviceps in a motive sized 21 × 14 × 18 cm that was cultivated in the cileunyi wetan village had a tfc of 6.64–11.42 mg qe/g extract, whereas a motive in cibodas village had a tfc amounting to 14.8 mg qe/g extract. the extraction process of propolis also affects the dissolved flavonoids and phenolics content. the antioxidant content and activity of the propolis extract depend on the extraction method and the type of solvents used [33]. propolis extracted by the maceration method for three days resulted in tfc and tpc of 52.17 mg qe/g extract and 26.13 mg gae/g extract, respectively, whereas five days of maceration resulted in tfc and tpc of 68.04 mg qe/g extract and 46.68 mg qe/g extract, respectively [34]. these results indicate that the duration of the maceration process can affect the solubility and the yield of flavonoid and phenolic compounds associated with the mass transfer process of the compounds into the solvent. the solid-to-solvent ratio, temperature, and the maceration speed can also affect the tfc and tpc. tfc and tpc in the propolis from the bamboo hive were also measured with the result of 3.42 ± 1.15 mg qe/g extract and 284.62 ± 39.46 mg gae/g extract. tpcs in the propolis from motives were lower than tpc in the propolis from the bamboo hive. the position of propolis in the hive may play a role in the chemical composition of propolis. according to pratami et al. [35], propolis located inside the hive had a higher tfc and tpc compared with propolis located outside the hive, which was exposed to the external environment. propolis in the motives was more exposed to the external environment because of the ventilation space between the mesh and the top cover compared with propolis in the bamboo hive. therefore, the difference in propolis position in the hive may be a factor that caused differences in the tpc of the propolis. exposure to light, air, and high temperatures can change the structure of phenolic compounds affecting their degradation process [35]. moreover, the chemical composition of propolis is also influenced by the source of the plant resins. during the beekeeping process, the bees produce propolis from plant resins obtained near the beekeeping sites, such as mahogany (swietenia macrophylla), velvet apple 40 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 (diospyros blancoi), gmelina (gmelina arborea), guanacaste (enterolobium cyclocarpum), and kassod tree (senna siamea). the colors of propolis produced varied, light to dark brown, red, as well as greenish yellow. color differences in the propolis indicate that the chemical composition and the active compounds in each propolis might also be different [10]. table 2: total flavonoid and total phenolic content of propolis produced by t. laeviceps in various hive sizes and mesh materials hive sizes mesh materials total flavonoid content (tfc) [mg qe/g extract] total phenolic content (tpc) [mg gae/g extract] small nylon 3.18 ± 1.43a 112.13 ± 47.64b polyethylene 2.60 ± 1.66a 32.23 ± 14.09b aluminum 2.46 ± 1.21a 80.45 ± 53.93b medium nylon 1.95 ± 1.02a 39.10 ± 15.91b polyethylene 1.78 ± 1.02a 39.12 ± 23.35b aluminum 3.02 ± 1.50a 54.58 ± 26.76b large nylon 1.77 ± 0.86a 77.61 ± 34.61b polyethylene 2.84 ± 2.01a 52.44 ± 25.01b aluminum 2.84 ± 1.00a 71.41 ± 27.30b *different letters indicate statistical differences (p-value < 0.05, duncan's test). 3.4 characteristics of honey produced by t. laeviceps the honey harvested from t. laeviceps was measured for its moisture, reducing sugars, antioxidants, and vitamin c contents. table 3 shows that the moisture content, reducing sugars, and active antioxidants of t. laeviceps honey from motives were lower than in the honey from the bamboo hive. however, the vitamin c content of honey from the motives was higher than in honey from the bamboo hive. high moisture content can reduce the quality of honey because the presence of water can accelerate the rate of yeast growth so that fermentation occurs. the type of yeast that causes fermentation in honey is zygosaccharomyces [36]. the higher moisture content in the honey from the bamboo hive could be caused by the differences in the bamboo hive and motive structures. bamboo hives are narrower and have less ventilation space and, hence, higher humidity compared to the motives. honey is also hygroscopic, able to absorb water from the environment. therefore, the moisture content in honey could be influenced by environmental humidity [37]. according to souza et al. [7], the moisture content in apis bee honey is only 17%, lower than in honey from tetragonula bees, which is 24%. the difference is caused by the more open structure of honey storage pots in apis bees, so the rate of water evaporation in apis honey will be faster than in tetragonula honey. honey from the motives met the maximum moisture content requirement of 22% outlined by the indonesian national standard sni 01-3545-2004 [38]. yeast in honey will degrade sugars, such as glucose and fructose, into alcohol and co2. this will increase the reducing sugar content, which is the total amount of fructose and glucose in honey [37]. table 3 shows that the reducing sugars in honey from the bamboo hive was higher than in honey from the motives. this shows the correlation between moisture content and reducing sugar content in honey. bees from the meliponini family, such as t. laeviceps, generally have a reducing sugar content of 66% (w/w) with a sucrose content of 2.3% [9]. based on the standard quality of honey from the 41 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 indonesian national standard sni 01-3545-2004 [38], the minimum of total reducing sugar is 65%, and thus, honey from the bamboo hive and motives still meets this requirement. table 3: characteristics of honey produced by t. laeviceps parameters bamboo hive motive moisture content [%] 24.08 21.86 reducing sugar [%] 74.70 72.84 active antioxidant/ic50 [µg/ml] 3544.88 2613.41 vitamin c [µg/ml] 184.50 192.86 honey contains many antioxidant compounds such as catalase, glucose oxidase, peroxidase, and phenolic compounds. the active antioxidant of t. laeviceps honey from a bamboo hive is higher than in honey from a motive. however, both honeys have higher antioxidant content compared to honey researched by abduh et al. [10]. the antioxidant content of honey cultivated from this study in cibodas and cileunyi wetan, west java, were 1188.2 μg/ml and 1,341.88 μg/ml, respectively. the lower active antioxidant content in honey from this study could be caused by the location of cultivation, sources of nectar, and the age of honey. vitamin c (ascorbic acid) is one of the numerous compounds present in honey. the vitamin c content in honey from motives is higher than in honey from bamboo hives, which are 192.86 μg/ml and 184.5 μg/ml, respectively. different sources of nectar could cause the difference in vitamin c content [7]. therefore, both the content of vitamin c and antioxidants in honey is strongly influenced by the plant nectar sources around the cultivation site. 4. conclusion in brief, increasing the hive’s size increases the productivity of propolis. the highest productivity of propolis (2.53 ± 0.37 g/colony/week) was obtained when t. laeviceps was cultivated in large hives equipped with a nylon-based mesh. the highest productivity of honey (0.78 ± 0.18 g/colony/week) was obtained when t. laeviceps was cultivated in medium hives equipped with an aluminum-based mesh. the harvested propolis was extracted using a maceration method to determine the total flavonoid and phenolic content of the propolis which lies in the range of 1.77 ± 0.86 to 3.18 ± 1.43 mg qe/g propolis and 32.23 ± 14.09 to 112.13 ± 47.64 mg gae/g propolis, respectively. relevant properties of the harvested honey were also characterized and shown to meet the standard quality of honey. the result of this study provides an insight for larger scale cultivation of t. laeviceps to produce higher productivity of propolis from stingless bees. acknowledgment this work was financially supported by institut teknologi bandung (ppmi sith 2022). references [1] nakajima y, tsuruma k, shimazawa m, mishima s, hara h. (2009) comparison of bee products based on assays of antioxidant capacities. bmc complementary and alternative medicine, 9: 1-9. [2] silva cr, baltazar f, almeida ac. (2015) propolis: a complex natural product with a plethora 42 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 of biological activities that can be explored for drug development. evidence-based complementary and alternative medicine, 1-29. https://doi.org/10.1155/2015/206439 [3] rao p.v, krishnan kt, salleh n, gan sh. (2016) biological and therapeutic effects of honey produced by honey bees and stingless bees: a comparative review. revista brasileira de farmacognosia, 26: 657-664. [4] borror dj, triplehorn la, johnson nf. (1989) an introduction to the study of insects. 6th edition. saunders college publishing, philadelphia. [5] fadhilah r, rizkika k. (2015) laba lebah tanpa sengat, my trubus potential business. trubus swadaya, jakarta. [6] singh s, ketan v, saurabh s, jain n, tawale p. (2018) propolis market research report forecast to 2023. market research future. [7] souza ba, roubik dw, barth om, heard ta, enríquez e, carvalho ca, villas-bôas j, marchini l, locatelli j, persano-oddo l, almeida-muradian l, bogdanov s, vit p. (2006) composition of stingless bee honey: setting quality standards. interciencia, 31: 867-875. [8] hakim mn, abduh my. (2019) produksi propolis dari lebah tetragonula laeviceps menggunakan sarang motive yang dilengkapi dengan sistem instrumentasi. jurnal otomasi kontrol dan instrumentasi, 10: 133-148. [9] hilmi m, bradbear n, mejia d. (2011) beekeeping and sustainable livelihood, food and agriculture organization of the united nations, rome. [10] abduh my, adam a, fadhlullah m, putra re, manurung r. (2020) production of propolis and honey from tetragonula laeviceps cultivated in modular tetragonula hives. heliyon, 6: 1-8. [11] adam a, hakim mn, oktaviani l, inderaja bm, manurung, r, putra re, abduh my. (2020) techno-economic evaluation for integrated cultivation of coffee and stingless bees in west java, indonesia. biological and natural resources engineering journal, 3: 28-36. [12] budiaman, rahman a. (2006) uji efektivitas empat variasi propolis trap terhadap produksi propolis lebah madu apis mellifera l. jurnal perennial, 2: 1-4. [13] huang l, bui n, meyering mt, hamlin tj, mccutcheon j. (2013) novel hydrophilic nylon 6,6 microfiltration membrane supported thin film composite membranes for engineered osmosis. j. memb. sci., 437: 141-149. [14] surdia t, saito s. (1995) pengetahuan bahan teknik. pradnya paramita, jakarta, indonesia. [15] abd-elmawgood bh, al-rajhi ma, el-ashhab ao. (2015) effect of the internal size and thermal insulation of the hive on bee colonies strength and productivity. egyptian journal of agricultural research, 93: 185-195. [16] machado ba, silva rp, barreto gd, costa ss. silva df, brandao hn, rocha jlc, dellagostin oa, henriques jap, umsza-gues ma, padilha ff. (2016) chemical composition and biological activity of extracts obtained by supercritical extraction and ethanolic extraction of brown, green and red propolis derived from different geographic regions in brazil. plos one, 11: 1-26. [17] sadeli ra. (2016) uji aktivitas antioksidan dengan metode dpph (1,1-diphenyl-2picrylhydrazyl) ekstrak bromelain buah nanas (ananas comosus (l.) merr.). faculty of pharmacy, universitas sanata dharma, yogyakarta. [18] silva cr, simoni ja, collins ch, volpe pl. (1999) ascorbic acid as a standard for iodometric titrations: an analytical experiment for general chemistry. journal of chemical education, 76: 1421-1422. [19] sanpa s, popova m, bankova v, tunkasiri t, eitssayeam s, chantawannakul p. (2015) antibacterial compounds from propolis of tetragonula laeviceps and tetrigona melanoleuca (hymenoptera: apidae) from thailand. plos one, 10: 1-11. [20] bhusal s. thapa r. (2006) response of colony strength to honey production: regression and correlation analysis. journal of the institute of agriculture and animal science, 27: 133-137. [21] akratanakul, p. (1990) beekeeping in asia, food and agriculture organisation of the united nation, rome. [22] leonhardt sd, dworschak k, eltz t, bluthgen n. (2007) foraging loads of stingless bees and utilisation of stored nectar for pollen harvesting. apidologie, 38: 125-135. 43 iium engineering journal, vol. 24, no. 2, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i2.2709 [23] agussalim aa, umami n, erwan e. (2015) production of stingless bees (trigona sp.) propolis in various bee hives design. the 6th international seminar on tropical animal production, 2022 october 2015, universitas gadjah mada. [24] tsagkarakis ae, katsikogianni t, gardikis k, katsenios i, spanidi e, balotis gn. (2017) comparison of traps collecting propolis by honey bees. advances in entomology, 5: 68-74. [25] bushal sj, kafle l, thapa rb, shih cj. (2011) effect of colony strength on the performance of honeybees (apis mellifera) in nepal (hymenoptera:apidae). sociobiology, 58: 435-447. [26] salatnaya, h. (2012) produktivitas lebah trigona sp. sebagai penghasil propolis perkebunan pala monokultur dan polikultir di jawa barat, institut pertanian bogor, bogor. [27] jager aj, taylor gj, greeff p, lishman, aw. (2001) the effect of commercial propolis production on hive profitability. proceedings of the 37th international apicultural congress. [28] faheem m, aslam m, razaq m. (2004) pollination ecology with special to insects: a review, j. res. (sci), 15: 359-409. [29] smith, j. p., heard, t. a., beekman, m., gloag. r., 2016. flight range of the australian stingless bee tetragonula carbonaria (hymenoptera: apidae): flight range of the bee tetragonula carbonaria. austral entomology, 56: 1-4. [30] jalil am, kasmuri ar, hadi h. (2017) stingless bee honey, the natural wound healer: a review. skin pharmacology and physiology, 30: 66-75. [31] agussalim aa, umami n, budiasatra ig. (2017) the effect of daily activity stingless bees of trigona sp. on honey production. the 7th international seminar on tropical animal production, 12-14 september, universitas gadjah mada; pp. 223-227. [32] paviani lc, fiorito g, sacoda p, cabral fa. (2013) different solvents for extraction of brazilian green propolis: composition and extraction yield of phenolic compounds, iii iberoamerican conference on supercritical fluids. colombia. [33] narimane s, demircan e, salah a, ozcelik b, salah r. (2017) correlation between antioxidant activity and phenolic acids profile and content of algerian propolis: influence of solvent. pakistan journal pharmaceutical sciences, 30: 1417-1423. [34] zin nb, azemin a, rodi mm, mohd ks. (2018) chemical composition and antioxidant activity of stingless bee propolis from different extraction methods. international journal of engineering & technology, 7: 90-95. [35] pratami dk, mun'im a, sundowo a, sahlan m. 2018. phytochemical profile and antioxidant activity of propolis ethanolic extract from tetragonula bee. pharmacognosy journal, 10: 128135. [36] salas, pg, soto am, carretero am, gutierrez af. (2010) phenolic-compound-extraction systems for fruit and vegetable samples. molecules, 15: 8813-8826. [37] nanda pb, radiati le, rosyidi d. (2015) perbedaan kadar air, glukosa, dan fruktosa pada madu karet dan madu sonokeling, universitas brawijaya, malang. [38] standar nasional indonesia (sni). (2004) madu (sni 01-3545-2004). badan standardisasi nasional, jakarta. 44 microsoft word 71-591-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 43 implementation of semi-empirical models to enhance the accuracy of panel methods for drag prediction at supersonic speeds a. sh. mahdi al-obaidi senior lecturer, taylor's university, taylor's lakeside campus, no. 1 jalan taylor's, 47500 subang jaya, selangor de, malaysia. abdulkareem.mahdi@taylors.edu.my abstract: this paper introduces an attempt to enhance the accuracy of panel methods. a low-order panel method is selected and coupled with semi-empirical methods to enhance the accuracy of drag prediction of flying bodies at supersonic speeds. the semi-empirical methods are used to improve the accuracy of drag prediction by mathematical modelling of viscosity, base drag, and drag due to wing-body interference. both methods were implemented by a computer program and validated against experimental and analytical results. the comparisons show that a considerable improvement has been achieved for the selected panel method for prediction of drag coefficients. in general, accuracy within an average value of -4.4% was obtained for the enhanced panel method. such accuracy could be considered acceptable for the preliminary design stages of supersonic flying bodies such as projectiles and missiles. the developed computer program gives satisfactory results as long as the considered configurations are slender and the angles of attack are small (below stall angle). abstrak: kertas kerja ini memperkenalkan percubaan untuk mempertingkatkan ketepatan kaedah panel. kaedah panel tertib rendah telah dipilih dan digabungkan dengan kaedah separa empirik untuk mempertingkatkan ketepatan ramalan seret objek terbang pada kelajuan supersonik. kaedah semi empirikal yang digunakan untuk meningkatkan ketepatan jangkaan seret menggunakan model matematik bagi kelikatan, seretan dasar, dan seretan disebabkan oleh badan sayap interferens. kedua-dua kaedah dijalankan menggunakan program komputer dan disah berdasarkan keputusan uji kaji dan analisis. perbandingan keputusan menunjukkan peningkatan yang mendadak diperolehi melalui kaedah panel yang telah dipilih sebagai jangkaan pekali seret. secara umumnya, ketepatan yang melingkungi nilai purata sebanyak -4.4% telah diperolehi daripada kaedah peningkatan panel. keputusan sebegini boleh diterima untuk peringkat reka bentuk permulaan bagi objek terbang supersonik seperti projektil dan misil. program komputer yang direka memberikan keputusan yang memuaskan selagi konfigurasi yang dipilih adalah kecil dan sudut serangan adalah rendah (di bawah sudut tegun). key words: panel methods; semi-empirical methods; drag coefficient; supersonic speeds; wing-body configuration. iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 44 1. introduction the determination of aerodynamic characteristics of flight-vehicles has traditionally been relegated to the wind tunnel (experimental methods) or estimates from basic theory (theoretical methods). wind tunnel tests are costly, time consuming and require both constructions of a model and an adequate test facility. additionally, the lag time between the paper design and the wind tunnel results can be considerable. furthermore, any configuration change requires a change of the test model. the existing purely theoretical methods were initiated from the compressible form of the navier-stokes equations. considering the limits on the available computer power and the cost of calculations, one has to make a trade-off between the complexity of the mathematical model and the complexity of the geometric configuration that can be treated. this is illustrated in fig. 1 [1]. if the flow is assumed steady, irrotational, and inviscid then it is possible to introduce a velocity potential and the full navier-stokes equations reduce to the potential flow equation [2]. fig. 1: hierarchy of mathematical models [1]. during recent years, both computer power and numerical algorithm efficiency are simultaneously improved. as a consequence, numerical methods have been developed sufficiently to initiate some changes in traditional methods of aerodynamic design [3]. panel method, as one of numerical methods, has the advantage that the dimensionality is reduced (it only requires specification of the boundaries). the advantage of reducing the dimension of the problem gives a priority of special application in the early stages of design. however, they still have a reputation for being inaccurate or unreliable with respect to drag [4]. the latest codes being used currently are higher-order methods based, instead of the low-order method being used in the codes of the past. the application of numerical techniques allows the treatment of more realistic geometries of flight-vehicles. panel methods are traditionally based on assumption of potential flow. these methods usually follow the classical steps of potential flow numerical solutions; selection of singularity element, aerodynamic representation, discretization of geometry, calculation of the normal velocity at the control point, formation and solution of the boundary condition equations, and calculation of pressures, forces, and moments [5]. thus, the panel methods are iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 45 efficiently employed for the computation of lift and moments in an inviscid flow; they cannot capture the viscous effects. in a real fluid at supersonic speeds the total drag force is usually considered to be of three components; skin friction drag, wave drag, and base drag. of these components only the wave drag can be computed using panel methods. at low supersonic speeds for a body-alone configuration the skin friction drag and base drag about 60% of the total drag [6]. this indicates that panel methods (based on potential flow) can capture only 40% of the total drag of flight-vehicles at supersonic speeds. in the present work, a classical low-order panel method is selected and coupled with semi-empirical methods to improve the accuracy of drag prediction for flying slender bodies (such as missiles, projectiles, etc.) at supersonic speeds. briefly, the semi-empirical methods are used to model: (1) the effect of viscosity to calculate the skin friction drag, (2) the effect the base drag, and (3) the drag due to wing-body interference. 2. previous work there are many works to calculate the drag using semi-empirical methods. moore [7] combined several theoretical and empirical procedures to calculate lift, drag, and center of pressure on wing-body-tail configurations from mach 0 to about 3 and for angles of attack to about 15o. body and wing geometries could be quite general in that pointed or blunt nose bodies and sharp or blunt leading-edge wings could be assumed. comparison of this method with experiment for several configurations indicates that accuracies of ±10% could be obtained for force coefficients of most configurations. erickson [8] discussed in his report panel-method capabilities and limitations, basic concepts common to all panel-method codes, different choices that have been made in the implementation of these concepts into working computer programs, and various modelling techniques involving boundary conditions, jump properties, and trailing wakes. an approach for extending the method to nonlinear transonic flow was also presented. increasing the accuracy of numerical methods in predicting the drag by implementation of semi-empirical methods attracted many researchers. van dam [9] reviewed recent experiences in cfd-based drag prediction with an emphasis on flow solutions governed by the euler and reynolds-averaged navier–stokes equations. the review demonstrates that although significant progress has been made, cfd-based drag prediction still faces a number of hurdles that must be dealt with before it will become more widely accepted. coiro and nicolosi [10] developed a number of numerical and experimental tools devoted to aircraft design for low subsonic flows. these tools comprise numerical codes for analysis, design and simulation, and experimental tests performed in a wind tunnel particularly devoted to light aircraft design. voskuijl [11] used the analysis tool called vsaero [12], which implements a first order panel method, extended with several features such as an integral viscous boundary layer, prandtl-glauert correction for high mach numbers and a trefftz plane analysis to calculate the induced drag. iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 46 as clearly seen from this review the problem of drag prediction was attacked partially. the current paper attempts to predict all components of the drag by using both methods; numerical and semi-empirical. such a combined method becomes a very powerful tool especially when accurate drag prediction is required for non-conventional flight-vehicle configurations, such as space shuttle, multistage missiles, blended wing body aircraft, etc. 3. methods of analyses 3.1 panel methods panel-method-based computer programs are currently the workhorse codes for predicting the aerodynamics of complete configurations [8]. a representative flight-vehicle example that has been analyzed with panel method codes is shown in fig. 2. the equation that panel codes solve is the prandtl-glauert equation. fig. 2: aerodynamic representation used in panel method. for steady supersonic flow this equation is usually written as: 0)1( 2  zzyyxxm  (1) where m∞ is the free-stream mach number and  is the perturbation velocity potential [13]. eq. (1) is hyperbolic, with the x-derivative term behaving like time in the wave equation. a general solution to eq. (1) is given by heaslet et al. [14], based on volterra’s solution of the two-dimensional wave equation. this result was repeated by woodward and larsen [15] and gave, in integral form, the value of  at any point due to a small perturbation of the flow originating on a surface. the numerical method used by carmichael and woodward [16] replaced the actual wingbody combination by distributions of singularities, which satisfy the linearized equation of linear vortex distribution on tail panels constant source distribution on body panels x z y control point iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 47 supersonic flow, eq. (1), whose strengths are adjusted to satisfy the boundary conditions required by the geometry of the particular configuration. the wing warp and incidence are represented by distributions of vorticity corresponding to pressure differences across the wing. the wing thickness effect is given by sources and sinks located over the wing reference plane. the body thickness, camber, and incidence are simulated by line sources and doublets placed along the body reference axis. finally, the interference effects of the wing on the body are cancelled by a distribution of vorticity on the surface of the body. this numerical procedure has been programmed for automated computation for a great variety of configurations. thus many codes have been developed. kay et al. [17] provide a brief description of the codes aerodynamicists will most likely encounter. although such codes are routinely used to analyze very complicated geometries, they do so at the expense of ignoring much fluid physics. the prandtl-glauert equation is the simplest form of the fluid-flow equations that contain compressibility effects (i.e., the effect of mach number on fluid density). it is obtained from the more general navier-stokes equation by: (1) neglecting all the viscous and heat-transfer terms; (2) assuming that the flow is irrotational, thereby admitting the introduction of a velocity potential; and (3) discarding all nonlinear terms. this restricts the flow to be inviscid, irrotational, and linear. often, the flow is also assumed to be steady. physically, these restrictions mean that important flow behavior such as separation, skin-friction drag, base drag, and transonic shocks are not predicted with panel methods. items that are predicted include drag due-to-lift (often called induced drag for subsonic flow, and vortex drag for supersonic flow), and wave drag [8]. 3.2 semi-empirical methods the current paper uses a panel method in combination with semi-empirical methods to approximately account for additional fluid physics neglected by the prandtl-glauert equation. semi-empirical methods are used to model (1) the effect of viscosity to calculate the skin friction drag; (2) the effect the base drag; (3) the drag due to wing-body interference. 3.2.1 effect of viscosity the effect of viscosity can be partially modelled through the calculation of skin friction drag coefficient using a boundary layer solution. the skin friction drag coefficient cdfr of a wing-body configuration is the sum of the skin friction drag coefficient of the body (cdfr)b and the skin friction drag coefficient of the wing (cdfr)w     wdfrbdfrdfr ccc  (2) the general approach of calculating skin friction drag coefficient is by estimating the skin friction coefficient of a flat plate in an incompressible flow [18, 19], and then this coefficient is corrected according to the body wetted area and compressibility effect [20]. a) body skin friction drag coefficient, (cdfr)b iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 48 for fully-turbulent and compressible flow, the friction coefficient is given by       ref bwet bfbdfr s s cc  (3)   467.02 58.2 10 )21.01( )re(log455.0     m c b bf (4)    vlref bre (5) in the present work, the influence of surface roughness on the skin friction drag is neglegted. thus, the reynolds number based on body length (or wing mean aerodyanmic chord) and mach number is used for further calculations. the influence of surface roughness can be determined according to the methodology described in the usaf-datcom [21], whereby a so-called cut-off reynolds number is used to determine if surface roughness has an influence on the friction coefficient. the reynolds number based on a reference length and mach number is compared with the cut-off reynolds number and the smaller is used for further calculations. b) wing skin friction drag coefficient, (cdfr)w at supersonic speeds, the skin friction drag coefficient for wings is given in [22] by   ref wwet twfwdfr s s cc )( )(  (6) where (cf)w is the skin friction coefficient of wing, which is given by eq. (4) with reynolds number based on the wing mean aerodynamic chord cmac    vcmac wre (7) eq. (4) is applicable for ranges of reynolds number 2×106< re < 1010 and m∞ ≤ 4, as this is the limitation given by the prandtl-schlichting universal formula [18, 19]. t is the factor for the wing thickness effect. this factor takes into account that the actual wing is not a flat plate and is given by fig. 3 [23] as a function of the relative maximum thickness of the wing profile maxt macc t t maxmax  (8) iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 49 fig. 3: effect of profile thickness [23]. 3.2.2 base drag at supersonic speeds the base drag of the body, caused by a large negative pressure, results in a substantial increase in the body drag. the base drag coefficient of the body is related to the base pressure coefficient [23] bd pc b  (9) where pb is the base pressure coefficient for cylindrical base, determined from fig. 4 [23] as a function of mach number. fig. 4: base pressure coefficient [23]. iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 50 3.2.3 wing-body interference drag there exists an amount of drag, which arises from the wing-body interference. in this paper, this contribution is taken into consideration, where the change of drag force coefficient of the wing-body configuration for the body with cylindrical base is given by:   maxtcc wbwbd  (10) where cwb is the wing-body drag force parameter, which is obtained from fig. 5 [23] as a function of mach number. fig. 5: wing-body drag [23]. 3.3 enhancement of panel method as a case study a low-order panel method is selected. the computer code based in this method is popularly known as the nasa ames wingbody program. a complete description of the theory and programming details are contained in [15, 16, 24]. in the present work, this panel method, which is able to treat complete configurations, is coupled with the semiempirical methods (above outlined) to enhance the accuracy of drag prediction of flying bodies at supersonic speeds. both methods were implemented by a computer program and validated against experimental and analytical results. 3.3.1 effect of viscosity the methods described in subsections 3.2.1a and 3.2.1b are used to predict the skin friction drag for body and wing respectively. this method is programmed and added to the numerical computer program developed in the present work. 3.3.2 base drag the classical panel methods will not capture the effect of base drag. accordingly, the mathematical model described in subsection 3.2.2 is used to improve the results of drag computation via panel method. iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 51 3.3.3 wing-body interference drag the amount of drag due to interference between body and wing is also included in the computer program using the mathematical model of subsection 3.2.3. 4. results and discussion the only true test of validity, accuracy, and usefulness of a general computer program, is to compare it with experimental data. accordingly, the enhanced wingbody computer program has been validated against experimental results published in the literature and with data obtained by other theoretical methods. for this purpose, two configurations have been considered; body-alone and tail-body configurations. figure 6 shows the details of the dimensions of the selected configurations and the panel model representations used in the numerical program. figures. 7, 8, and 9 show the comparisons of the experimental data and the results of purely semi-empirical, numerical and modified panel methods. figure 7 shows a comparison of the pressure distribution for a body-alone configuration at mach number of 1.46 and attitudes of 0º and 180º, where a good agreement was found between the computation and experiment taken from [25], specifically at the nose region. (a) body-alone configuration. (b) tail-body configuration. fig. 6: the configurations and panel model representations considered for validation [7]. iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 52 fig. 7: pressure distribution on a body-alone configuration: comparison between experiment and theory (m∞=1.46,  = 5o). figure 8 shows zero-lift drag coefficient as a function of mach number and how it compares with experimental data taken from [7]. two points are worthy of note. first, this figure indicates the significant difference between the drag predictions by the original 'wingbody' and the modified program, where 'wingbody' predicts the drag coefficient within 50% error, while the modified program reduces this error to 2.3%. this is because the original 'wingbody' is based on a panel method neglects two important components of drag namely skin friction drag and base drag. the second point is that the numerical values of drag coefficient are the closest to the experimental ones, where the purely semi-empirical method used by [6] produces -11% average error for cd. thus, the modified numerical method provides better accuracy than the purely semi-empirical method. during the the preliminary design stage of flight-vehicle configurations such accuracy is usually accpeted. figure 9 compares the theoretical drag as a function of angle of attack for mach number 1.3. this figure shows that the agreement is within -50% (for the wingbody computer program [24]), -5% (for the purely semi-empirical method [6]), and -8% (modified wingbody program – present method). despite the fact shown on fig. 9 that the accuracy of the purely semi-empirical method is better than that of the modified numerical method, the results of the latter are much closer to the experimental compared with panel method. this shows again how efficiently the results have been improved using the modified numerical method. iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 53 fig. 8: zero-lift drag coefficient vs. mach number. a comparison between experiment and theory (= 0). fig. 9: drag coefficient vs. angle of attack. a comparison between experiment and theory (m∞=1.3). figure 9 also shows that the prediction of drag is more accurate at small angles of attack up to 8○. above this angle the accuracy is low which is due to not taking into account reynolds number effect on the body crossflow drag coefficient. in general, accuracy within average of -4.4% can be obtained for the enhanced numerical panel method. iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 54 5. conclusion the modified panel method in this work shows higher accuracy in prediction of drag force compared with the classical panel methods. including the effects of viscosity, base drag and wing-body interference greatly reduced the percentage error in prediction of drag as a function of mach number from 50% (classical panel method) to about 5% (modified panel method). however, the comparison of the drag force as a function of angle ot attack shows that the accuracy decreases with increasing angle of attack. the modified numerical metod is pereferbale over the purely semi-empirical methods especially if complex geometric configruations are treated. the proposed method, the numerical and semi-empirical methods give satisfactory results as long as the considered configurations are slender and the angles of attack are small (below stall angle). in general, the accuracy of the modified numerical program is good and adequate since it is within ±10%, which is acceptable for preliminary design stage of supersonic flying bodies such as projectiles and missiles. references [1] a. jameson, “the evolution of computational methods in aerodynamics.” journal of applied mechanics, 50(4b), 1052-1070, 1983. [2] d. r. chapman, “computational aerodynamics development and outlook”. aiaa journal, 17(12), 1293-1313, 1979. [3] c.r. o'neill, “determination of flight stability coefficient using a finite element cfd”. mechanical and aerospace engineering, oklahoma state university, stillwater, ok 74077, 2000. [4] j.s. letcher jr., “convergence of lift and drag predictions by a morino panel method (vsaero).” aiaa journal, 27(8), 1019-1020, 1989. [5] j., katz, and a. plotkin, “low-speed aerodynamics: from wing theory to panel methods.” mcgraw-hill book company, inc., new york, 1991. [6] a. sh. mahdi, “the influence of configuration design on the aerodynamics and stability of ssm at supersonic speeds.” ph.d. thesis. al-rasheed college of engineering and science, university of technology, baghdad, iraq, 2005. [7] f.g. moore,”static aerodynamics of missile configurations for mach 0 to 3.” journal of aircraft, 12(10), 797-806, 1979. [8] larry l. erickson, “panel methods an introduction.” nasa technical paper 2995, 1990. [9] van dam c. p. “recent experience with different methods of drag prediction.” progress in aerospace sciences, 35(8), 751-798, 1999. [10] d. p. coiro, and f. nicolosi, “design of low-speed aircraft by numerical and experimental techniques developed at dpa.” aircraft design, 4(1), 1-18, 2001. [11] mark voskuijl, gianfranco la rocca, frank dircken “controllability of blended wing body aircraft.” 26th international congress of the aeronautical sciences, 14-19 sep 2008, egan convention center, anchorage, alaska, usa., 2008 iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 55 [12] b. maskew, “vsaero a code for calculating the nonlinear aerodynamic characteristics of arbitrary configurations.” nasa cr-4023, 1987. [13] john j. bertin, and michael l. smith, “aerodynamics for engineers”, 3rd edition, prentice-hall international, inc., 1998. [14] m. a. heaslet, l. lomax, and a.l. jones, “volterra's solution of the wave equation as applied to three-dimensional supersonic airfoil problems.” naca report 889, 1947. [15] f. a. woodward, and j.w. larsen, “a method of optimizing camber surfaces for wing-body combinations at supersonic speeds. part i – theory and applications.” doc. d6-10741, pt. 1 the boeing co. nas2-2282, 1965. [16] ralph l. carmichael, and frank a. woodward, “an integrated approach to the analysis and design of wings and wing-body combinations in supersonic flow.” nasa tn d-3685, 1966. [17] j. kay, w. h. mason, w. durham, f. lutze, and a. benliel, “control authority issues in aircraft conceptual design: critical conditions, estimation methodology, spreadsheet assessment, trim and bibliography.” virginia polytechnique institute and state university, blacksburg, virginia 24061, 1996 [18] n. f. krasnov, “aerodynamics. part 2 (methods of aerodynamic calculations).” translated from the russian language by g. leib, mir publisher, moscow, 1985. [19] s. f. hoerner, “fluid-dynamic drag.” horner fluid dynamics, brick town n. j., 1965. [20] f. fankl, v. voishel “turbulent friction in the boundary layer of a flat plate in a twodimensional compressible flow at high speeds.” naca tech mem. 1053, 1943. [21] d. e. hoak, usaf stability and control datcom. flight control division, air force flight dynamics laboratory, rept. 0410, revised april 1972. [22] a. a. lebedev, and l. c. chernobrovken, “dynamika poleta bezpilotnich letatelnich aparatov. 'flight dynamics of pilotless of flight-vehicles'.” mashen ctroen, moscow, 1973. [23] s. jankovic, “aerodynamika projektila. 'aerodynamics of projectiles' masinski fakultet, univerziteta u beogradu, belgrade, 1979. [24] j. e. brown, a. s. kawaguchi, and e. larowe, “a method of optimizing camber surfaces for wing-body combinations at supersonic speeds. part i1 digital computer program description.” doc. d6-10741, pt. 11, the boeing co., nas2-2282, 1965. [25] h. fushs, and r. kapp, “prediction of dynamic derivatives”. dornier gmbh, abt. bf 20, postfach 1420, d-7990 friedrichshafen, frg, 1987. nomenclature cd drag coefficient dbc base drag coefficient dfrc skin friction drag coefficient doc skin friction drag coefficient  wbdc zero-lift drag coefficient cf wing-body interference drag coefficient cwb wing-body drag force parameter iium engineering journal, special issue, mechanical engineering, 2011 al-obaidi 56 cmac wing mean aerodynamic chord m lref reference length m m∞ free-stream mach number pb base pressure coefficient re reynolds number sref reference area m2 swet wetted area m2 maxt relative maximum thickness of the wing profile tmax maximum thickness of the wing profile m v∞ free-stream velocity m/s  angle of attack deg.  perturbation velocity potential  angle between velocity vector and x-axis deg. t factor for the wing thickness effect ∞ free-stream kinematic viscosity m2/s application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 khan et al. _______________________________________________________________________________________ 215 performance of electrical discharge machining (edm) with nickel added dielectric fluid ahsan ali khan1, muataz hazza faizi al hazza1*, a k m mohiuddin2, nurfatihah abdul fattah1 and mohd radzi che daud1 1 department of manufacturing and materials engineering, 2 department of mechanical engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. *corresponding author: muataz@iium.edu.my (received: 20th oct 2016; accepted: 15th nov 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.759 abstract: in this study, the effect of nickel powder mixed dielectric fluid on electrical discharge machining (edm) performance of mild steel has been carried out. peak current, tool/electrode diameter and concentration of powder are the process parameters. the process performance is measured in terms of material removal rate (mrr), tool wear rate (twr), and surface roughness (sr). the experiment has been designed using a full factorial in design of experiment (doe) software. the research outcome is to identify the important process parameters that maximize mrr and minimize twr and sr. the experiment has been carried out using 2 levels of current (3.5 a and 6.5 a), tool diameters (14 mm and 20 mm) and nickel powder concentrations (0 g/l and 6 g/l). the weight of the mild steel work piece and copper electrode are measured before and after each run. based on the results, current is the most significant parameter affecting mrr, twr, and sr. it was also found that with added nickel powder in the dielectric fluid, the tool life is longer and surface roughness of the work piece is improved. furthermore, it was shown that both mrr and twr increased with the increase in tool diameter. however, sr was improved as tool diameter increased but its effect was not very significant. abstrak: dalam kajian ini, mutu keberhasilan campuran serbuk nikel cecair dielektrik pada sisa mesin elektrik (edm) ke atas besi ringan telah dijalankan. arus tertinggi, alat/diameter elektrod dan ketumpatan serbuk adalah parameter kawalan. pencapaian proses diukur dari segi kadar penyingkiran bahan (mrr), kadar penggunaan alat (twr) dan kekasaran permukaan (sr). eksperimen ini direka bentuk dengan menggunakan perisian faktorial penuh dalam rekaan eksperimen (doe). hasil kajian ini adalah untuk mengidentifikasi kepentingan parameter kawalan yang mengoptimumkan mrr, meminimumkan twr dan sr. eksperimen ini dijalankan pada 2 peringkat arus elektrik (3.5 a dan 6.5 a), diameter alat (14 mm dan 20 mm) dan ketumpatan serbuk nikel (0 g/l and 6 g/l). berat bahan uji seperti besi ringan dan elektrod tembaga diukur pada sebelum dan selepas setiap ujian. berdasarkan keputusan, arus elektrik adalah faktor paling ketara yang mempengaruhi mrr, twr, dan kekasaran permukaan. turut didapati pada setiap pertambahan serbuk nikel ke dalam cecair dielektrik, jangka hayat alat turut bertambah dan kekasaran permukaan pada bahan uji turut bertambah baik. selain itu, kedua-dua mrr dan twr bertambah dengan setiap pertambahan diameter alat. sebaliknya, kekasaran permukaan bertambah baik dengan pertambahan diameter alat tetapi kesannya tidak ketara. keywords: edm; dielectric fluid iium engineering journal, vol. 19, no. 1, 2018 khan et al. _______________________________________________________________________________________ 216 1. introduction using a non-traditional method such as electro-discharge machining (edm) can solve the problems in the machining of high complexity shapes with higher accuracy and better surface finish. sandeep [1] described edm as one of the non-traditional machining processes where an electrical spark is generated by electrical energy and the thermal energy of the spark causes material removal. in edm, electric discharges occurring between two electrodes immersed in a dielectric fluid, cause metal to be removed from a work piece. webzell [2] mentioned that the history of edm techniques started in 1770, when english scientist joseph priestly noticed that electrical discharges, or sparks, have erosive effect. however, soviet scientists exploited the destructive properties of electrical discharges for constructive use and developed a controlled method of metal machining to machine metals by vaporizing material from the surface of the metal. furthermore, in the 1950s, lazarenko edm systems that used a resistance-capacitance type of power supply were widely used in edm machines, and later acted as models to enhance edm [3]. zhao et al. [4] mentioned that despite edm’s ability to produce high complexity shapes and to machine materials regardless of that material’s hardness, further applications are limited due to low machining efficiency and poor surface finish. thus, to improve the machining efficiency and surface finish, powder mixed electrical discharge machining (pmedm)) is a new process of material removal where powder is mixed into the dielectric fluid [4,5]. similarly, sharma et al. [6] indicated that powdermixed dielectric electric discharge machining (pmd-edm) is a new approach to improve the process’ capabilities. the gap distance and discharging rate also increased by adding powder into the dielectric fluid because the additive particles of powder mixed in the dielectric play significant roles in the discharge process. the conductive powder particles are energized by the high electric field and these conductive particles develop chains at different spots under the sparking area, thereby reducing the gap between electrode and work piece material. thus, because of this reduction effect, the gap voltage and insulating strength of the dielectric decreases and causes easy short circuiting. therefore, there is a discharge in the gap between the work piece and the electrode. due to electric density decreases; the suspended particles in the dielectric simultaneously broaden the plasma channel. hence, uniform distribution of the sparking takes place. abbas et al. [7] indicated that the edm process becomes more stable and enhances the material removal rate (mrr), machining efficiency, and surface quality when fine abrasive powder is mixed into the dielectric fluid. the dielectric performance is influenced by characteristics of the powder such as the type, size, and concentration [8]. jeswani [9] investigated the effect of the addition of 4 g of graphite powder to kerosene and stated that the material removal rate (mrr) was enhanced by 60% and electrode wear ratio was decreased by 15%. prihandana et al. [10] presented a new approach using ultrasonic vibration during the micro-edm processes that consisted of suspending micro mos2 powder in dielectric fluid. according to her, mrr was significantly increased and surface quality also improved using this new method. kansal et al. [11] enhanced the process parameters of powder mixed electrical discharge machining (pmedm) on tool steel using response surface methodology. according to them, using silicon powder mixed in the dielectric fluid of edm, mrr improved at maximum concentration rate of silicon powder. yan et al. [12] reported that using urea solution in distilled water, the mrr obtained had no significant difference compared to conventional water dielectrics and it was more suitable for the post edm process, for example as coating for the machined surface to induce iium engineering journal, vol. 19, no. 1, 2018 khan et al. _______________________________________________________________________________________ 217 better wear resistance. mrr increased in the dielectric when peak current was increased and mrr decreased with an increase in pulse duration. ojha et al. [13] studied the effect of a nickel micro powder mixed dielectric on edm performance measures on en-19 steel and proposed that the tendency of mrr to increase in any value of current and others factor is higher. the maximum mrr is obtained at high current and mrr increases with the increase in tool diameter owing to the increase in current. however, the mrr tends to decrease after a certain level of range of 12 mm due to inefficient flushing. also, with duty cycle and powder concentration, mrr tends to increase but the effect was not significant this study sought to investigate the effect of nickel powder mixed dielectric fluid on machining characteristics of mild steel. peak current, tool/electrode diameter, and concentration of powder were chosen as process parameters while material removal rate (mrr), tool wear rate (twr) and surface roughness (sr) were chosen as process performance indicators. 2. experimental procedure a pure copper electrode with a diameter of 15 mm and 20 mm was applied as a tool electrode. the type of work piece was mild steel. table 1 shows chemical composition of aisi 1018 mild steel. table 1: chemical composition of aisi 1018 mild steel element c fe mn p s content 0.14-.20% 98,81-99.26 % 0.60-0.90 % <0.040 % < 0.050 % nickel is the type of powder that was used for this experiment. kerosene was used as the dielectric fluid. to investigate the effect of the process parameters on pmedm performance, the design expert version 6.0.8 software was used. a full factorial experiment was conducted for three independent factors: current, powder concentration, and tool diameter, each with two levels to investigate their effect on material removal rate, tool wear rate, and surface roughness. the total number of experimental runs was 8, as shown in table 2. table 2: experiment design pattern current (a) powder concentration (g/l) tool diameter (mm) −−− 3.5 0 14 +−− 6.5 0 14 ++− 6.5 6 14 −++ 3.5 6 20 +++ 6.5 6 20 +−+ 6.5 0 20 −−+ 3.5 0 20 −+− 3.5 6 14 *note: (+) is the high level; (-) is the low level for each independent factor. iium engineering journal, vol. 19, no. 1, 2018 khan et al. _______________________________________________________________________________________ 218 the experiments were conducted using the edm die-sinking machine, mitsubishi ex22 model c11e fp60e. the machine was located at the tool and dies lab, ground floor of engineering building e0, faculty of engineering, international islamic university malaysia. 3. results material removal rate, tool wear rate, and surface roughness were measured and are displayed in table 3. table 3: mrr, twr, and ra pattern current (a) powder concentration (g/l) tool diameter (mm) mrr (g/min) twr (mg/min) ra (μm) − − − 3.5 0 14 0.0137 0.814 3.29 + − − 6.5 0 14 0.724 3.517 32.05 + + − 6.5 6 14 0.3112 1.669 28.06 − + + 3.5 6 20 0.0133 0.216 2.217 + + + 6.5 6 20 0.4082 2.055 21.463 + − + 6.5 0 20 0.4768 2.239 32.203 − − + 3.5 0 20 0.014 0.317 2.97 − + − 3.5 6 14 0.0144 0.053 2.993 4. statistical analysis regression analysis and analysis of variance (anova) are the most frequently applied statistical analyses in engineering research. the analysis of variance for the quadratic models was conducted. the results of the suggested models for a 5 % level of significance were implemented. table 4, 5, and 6 show the anova tables for the mrr, twr, and ra respectively. table 4: anova table for mrr source df sum of squares mean square f ratio model 4 0.46527562 0.116319 11.5595 error 3 0.03018787 0.010063 prob > f c. total 7 0.49546350 0.0362* table 5: anova table for twr source df sum of squares mean square f ratio model 4 9.1224735 2.28062 14.2283 error 3 0.4808624 0.16029 prob > f c. total 7 9.6033359 0.0272* iium engineering journal, vol. 19, no. 1, 2018 khan et al. _______________________________________________________________________________________ 219 table 6: anova table for ra source df sum of squares mean square f ratio model 4 1327.9161 331.979 76.6790 error 3 12.9884 4.329 prob > f c. total 7 1340.9045 0.0024* anova tables show that all the three models had significant effect with p values of 0.0362, 0.0272 and 0.0024 for mrr, twr, and ra respectively, as shown in tables 4, 5, and 6. for more detail, the sorted parameter estimates were created for the three responses as shown in tables 7, 8, and 9. tables 7: sorted parameter estimates for mrr term std error t ratio t ratio prob>|t| current (a)(3.5,6.5) 0.035466 6.28 0.0081* powder concentration(0,6) 0.035466 -1.99 0.1411 current (a)*powder concentration 0.035466 -1.41 0.2542 powder concentration*tool diameter (mm) 0.035466 0.92 0.4263 tables 8: sorted parameter estimates for twr term estimate t ratio t ratio prob>|t| current (a)(3.5,6.5) 0.949625 6.71 0.0068* powder concentration(0,6) -0.422125 -2.98 0.0585 powder concentration*tool diameter (mm) 0.230125 1.63 0.2025 current (a)*powder concentration -0.085875 -0.61 0.5869 tables 9: sorted parameters estimate for ra term estimate t ratio t ratio prob>|t| current (a)(3.5,6.5) 12.556375 17.07 0.0004* powder concentration(0,6) -2.204375 -3.00 0.0578 current (a)*powder concentration -1.478125 -2.01 0.1381 powder concentration*tool diameter (mm) -1.132625 -1.54 0.2213 sorted parameters estimate figures show that the most effective factor on the dependent responses is the current value. the current affected positively on the mrr. in contrast, the influence of increasing the current value leads to negative effect on both the twr and ra. finally the measures of fit were extracted from the software and concluded in table 10. both the results of the anova table and the summary of fit proved that the models can be used for predicting the mrr, twe, and ra. one of the main outputs for the research was the three mathematical models: mrr model, twr model and ra model. iium engineering journal, vol. 19, no. 1, 2018 khan et al. _______________________________________________________________________________________ 220 table 10: summary of fit mrr twr ra rsquare 0.939071 0.949928 0.990314 rsquare adj 0.857833 0.883164 0.977399 root mean square error 0.100313 0.400359 2.080737 mean of response 0.257238 1.420375 15.88763 observations (or sum wgts) 8 8 8 mrr model twr model ra model 4. optimization the three models have been optimized using a desirability function method in jmp software. figure 1 shows the desirability function for multi-objective optimization for three objectives: maximization of mrr, minimization of twr, and minimization of surface roughness. the results show that an mrr of 0.046 (g/min), twr of 3.6 (mg/min) and ra of 1.4 (µm) can be achieved with 68% of desirability with current of 3.5 (a), powder concentration of 6 (g/l) and tool diameter of 20 (mm). iium engineering journal, vol. 19, no. 1, 2018 khan et al. _______________________________________________________________________________________ 221 fig. 1: desirability function results. 5. concluding remarks nickel powder was suspended into the edm dielectric fluid to enhance the process output. three independent factors have been considered to measure the mrr, twr, and surface roughness. the results show the following: • increasing the current had a negative effect on both the twr and surface roughness. in contrast, the current increase had a positive effect on the mrr. • increasing the powder concentration positively affected the mrr while negatively affecting the twr and ra. • tool diameter had a negative effect on the mrr, while increasing the tool diameter reduced the twr. • the ratio of mrr to twr was calculated and the results show that the current had limited effect on the ratio. acknowledgement we would like to show our gratitude to the research management center, international islamic university malaysia for their support to conduct our research. we would like also to thank our colleagues in the department of manufacturing and materials engineering. references [1] sandeep k. (2013) current research trends in electrical discharge machining: a review. research journal of engineering sciences, 2(2):56-60. [2] webzell s. (2001) that first step into edm in machinery. united kingdom,uk: findlay publications ltd. [3] livshits al. (1960) introduction in electro-erosion machining of metals. department of scientific & industrial research, butterworth & co., london. iium engineering journal, vol. 19, no. 1, 2018 khan et al. _______________________________________________________________________________________ 222 [4] zhao ws, meng qg, wang zl. (2002) the application of research on pmedm in rough machining. journal of materials processing technology, 129:30-33. [5] kansal h, singh s, kumar p. (2003) state of the art concerning powder mixed edm. in proceedings of the international conference on emerging technology (icet-2003) kiit, bhubansewar, india. [6] sharma s, kumar a, beri n, kumar d. (2010) effect of aluminium powder addition in dielectric during electric discharge machining of hastelloy on machining performance using reverse polarity. international journal of advanced engineering technology, i(iii):13-24. [7] abbas nm, solomon dg, bahari mf. (2007) a review on current research trends in electrical discharge machining (edm). international journal of machine tools and manufacture, 47(7):1214-1228. [8] pecas p, henriques e. (2003). influence of silicon powder-mixed dielectric on conventional electrical discharge machining. international journal of machine tools and manufacture, 43(14):1465-1471. [9] jeswani ml. (1981) effects of the addition of graphite powder to kerosene used as the dielectric fluid in electrical discharge machining. wear. 70:133-139. [10] prihandana, g. s., mahardika, m., hamdi, m., wong, y. s., & mitsui, k. (2009). effect of micro-powder suspension and ultrasonic vibration of dielectric fluid in micro-edm processes—taguchi approach. international journal of machine tools and manufacture, 49(12-13), 1035-1041. [11] kansal hk, singh s, kumar p. (2005) parametric optimization of powder mixed electrical discharge machining by response surface methodology. journal of materials processing technology, 169(3):427-436. [12] yan bh, tsai hc, huang fy. (2005) the effect in edm of a dielectric of a urea solution in water on modifying the surface of titanium. international journal of machine tools and manufacture, 45(2):194-200. [13] ojha k, garg rk, singh kk. (2011) the effect of nickel micro powder suspended dielectric on edm performance measures of en-19 steel. journal of engineering and applied sciences, 6(1):27-37. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 application of driving behavior control system using artificial neural network to improve driving comfort by adjusting air-to-fuel ratio aris triwiyatno1*, suroto munahar2,3, m. munadi3 and joga dharma setiawan3 1 department of electronics engineering, diponegoro university, semarang, indonesia 2 department of automotive engineering, universitas muhammadiyah magelang, magelang, indonesia 3 department of mechanical engineering, diponegoro university, semarang, indonesia * corresponding author: aristriwiyatno@elektro.undip.ac.id (received: 7 march 2023; accepted: 22 may 2023; published on-line: 4 july 2023) abstract: energy-efficient engines were introduced due to limited amount of global energy and the need for engine power to carry vehicle loads. it was discovered that the power factor of these engines was essential in developing automotive technology with subsequent significant effect on driving comfort. moreover, it was possible to control the power and energy savings of vehicle engines by adjusting the air to fuel ratio (afr). therefore, this study focused on achieving afr values in the stoichiometric range of 14.7 in order to produce good emissions. the technology applied was observed to have some drawbacks, specifically in fulfilling engine power when the vehicle operates with a large load. this led to the development of a new method by designing an afr control system with due consideration for driving behavior using an artificial neural network (ann). the aim was to overcome the problem of meeting engine power and ensuring better efficiency. the driving behavior was classified into through categories including the sporty, standard, and eco schemes. the eco scheme was the smooth behavior of a driver during the movement of the vehicle in a busy urban area, the sporty scheme was the responsive driving behavior when the vehicle operates on the highway at speeds above 80 km/h, and the standard scheme was the behavior between the eco and sporty schemes. furthermore, the driving behavior in a sporty scheme required the addition of fuel to increase engine power while eco-scheme focused on reducing fuel to increase fuel economy. the findings showed that control system designed was able to improve driving comfort in terms of fuel economy during the eco scheme with an average afr value of 15.68. the system further reduced the value to 13.66 during the sporty scheme. furthermore, the afr under stoichiometry was discovered to have produced the maximum engine power. the system was expected to be incorporated into electric, gasfired and fuel cell vehicles in the future. abstrak: faktor kuasa enjin dan enjin cekap tenaga adalah penting dalam membangunkan teknologi automotif. mesin penjimat tenaga diperlukan kerana jumlah tenaga global yang terhad. manakala kuasa enjin digunakan bagi membawa muatan kenderaan. kedua-dua faktor ini sangat mempengaruhi keselesaan pemanduan. penjimatan kuasa dan tenaga dalam enjin kenderaan boleh dipenuhi dengan mengawal nisbah angin kepada minyak (afr). tumpuan kajian semasa adalah berorientasikan ke arah mencapai nilai afr dalam julat stoikiometri (14.7) atas sebab ingin mencapai pelepasan terbaik. namun begitu, teknologi ini mempunyai kelemahan terutama dalam 337 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 memenuhi kuasa enjin apabila kenderaan beroperasi dengan muatan besar. oleh itu, kajian ini adalah berkaitan kaedah baharu bagi mengatasi masalah memenuhi kuasa enjin dan mencapai enjin cekap tenaga dengan mereka bentuk sistem kawalan afr yang mempertimbangkan tingkah laku pemanduan menggunakan rangkaian neural buatan (ann). tingkah laku pemanduan direka bentuk kepada tiga skim: sporty, standard dan eko. skim eko adalah kelancaran tingkah laku pemandu apabila kenderaan bergerak di kawasan bandar yang sibuk. skim sporty ialah tingkah laku pemanduan responsif apabila kenderaan beroperasi di lebuh raya pada kelajuan melebihi 80 km/j, dan skema standard ialah tingkah laku antara skim eko dan sporty. tingkah laku pemanduan dalam skema sporty memerlukan penambahan bahan api bagi meningkatkan kuasa enjin. sementara itu, tingkah laku pemanduan dalam skim eko memerlukan pengurangan bahan api bagi meningkatkan penjimatan bahan api. hasil kajian menyatakan sistem kawalan yang direka mampu meningkatkan keselesaan pemanduan dari segi penjimatan bahan api apabila tingkah laku pemandu memasuki skim eko. afr dicapai pada nilai purata 15.68. apabila tingkah laku pemandu memasuki skim pemanduan sporty, sistem kawalan boleh mengurangkan afr dengan nilai purata 13.66. afr di bawah stoikiometri menghasilkan kuasa enjin maksimum. pada masa hadapan, sistem ini berpotensi untuk dibangunkan pada kenderaan elektrik, menggunakan gas dan sel bahan api. keywords: driving behavior; afr; ann; engine power; fuel saving 1. introduction vehicle comfort is a very important topic in the development of automotive technology and it can be increased through suspension control [1], steering system power transfer, engine power, and fuel economy. it is also significantly related to the aspects of engine power and fuel economy, and these two concepts have become international issues presently focused on by world researchers [2] due to the limited energy problem [3,4] and the very significant increase in global energy consumption. the current high increase in the number of vehicles using gasoline engines has made fuelsaving technology necessary. meanwhile, there is also the need to have the appropriate engine power to move the vehicle, especially when it is carrying a heavy load. it is important to note that vehicle comfort can be achieved from the engine power and fuel economy aspects by controlling the air to fuel ratio (afr) which is categorized into three including lean mixture with afr values above 14.7, ideal or stoichiometry ratio which is 14.7, and rich mixture with values below 14.7. the lean category usually produces low engine power with high fuel economy, the rich mixture is the opposite, and the stoichiometry category normally has optimal engine power and fuel economy. several studies have been conducted on afr using different variables such as the application of fuzzy logic which is artificial intelligence (ai) to set afr in a simulation [5]. it was discovered that the system was able to control the afr with inaccurate signals or data but it has not been applied to real conduction. another different study tried to add a variable turbo charge to increase the volumetric efficiency of the engine and changes were observed in the afr because the turbo charge added forced air into the engine based on the power generated by the exhaust gas pressure [6]. however, the research has not yet integrated an intelligent control system to modify the afr. some studies have also started focusing on afr stoichiometry control which was denoted by the achievement of lambda (λ) = 1 [7]. it is important to note that lambda (λ) is a comparative value between the actual afr and the stoichiometry of the theoretical afr. this method also has some problems which are making the vehicle users complain, especially due to the low engine power when the vehicle is operating on a steep or inclined surface or carrying a large load. 338 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 driving behavior has been empirically discovered to have a great influence on the fuel system (afr) dynamics but it was discovered that no study has focused on controlling afr through driving behavior. previous studies have only focused on using several variables such as the development of a car using systems in autonomous vehicles, application of a simulation scale connected vehicle driving strategy with intelligent model (cvds-idm), design of safety systems on vehicles, analysis of driving behavior, vision technology or graphical display, and the vehicle emissions dynamics when at a traffic light. driving behavior in car-following has also been studied with several variations such as autonomous vehicle dynamics, the use of cvds-idm, and a safe car-following behavior system. those related to the dynamics of the autonomous vehicle showed that the driver following a driverless autonomous vehicle was significantly affected psychologically [8]. moreover, cvds-idm was defined as a simulator tool to predict driving behavior in real time by providing a driver a stimulus with various variables, especially when driving behind another vehicle [9]. it was discovered that the cvds-idm was able to model the car-following mechanism through the method applied by the driver. another study also focused on safe driving behavior in order to develop a safety system based on the behavior of car-following drivers [10]. however, it was discovered that none of these three studies discuss the relationship between driving behavior and fuel consumption. further studies focused on driving behavior in relation to the safety systems design on vehicles such as the usage of cameras, vehicle theft prevention, and adaptive forward vehicle collision warning (fcw) systems [11] as well as the analysis of the driving behavior when the driver was sleepy [12]. the cameras were installed on the vehicle to record ongoing activities, hence it provides feedback for a sleepy driver in order to control the vehicle immediately and properly with the intention of reducing the occurrence of accidents. martinelli [13] also prevented vehicle theft by comparing driving behavior against a database. the research was initiated by learning and storing the driver's behavior in a control system and was later compared with the pattern through which an individual drive. the engine of the vehicle was programmed to stop when the driving behavior stored and observed are not similar to protect the vehicle from theft. another study by yuan [14] used an adaptive forward vehicle collision warning (fcw) to avoid collisions when the driver is driving abnormally. this was achieved by detecting the distance between the vehicle and the monocular. it is important to note that all these studies did not also consider the relationship between fuel usage systems and driving behavior. scholars also researched the improvement of driving safety through several variables which include analyzing the attitude and performance of drivers during sudden braking or steering operations and determining their safety rating [15]. another study also observed and assessed driver control and safe practices during the process of driving a vehicle using risky driving behavior as the research variable [16]. moreover, mafeni [17] and takashi bando [18] evaluated driving behavior errors with a focus on abnormal braking and vehicle speed operation when traveling at very high speeds. it was also observed that even though the studies have different objectives, none focused on energy consumption in evaluating driving behavior. subsequent research also focuses on driving behavior in autonomous and electric vehicles (evs). this was observed from the design of a lateral system control based on autonomous vehicles by hongbo [19] to trace the vehicle's turning angle accurately and provide a better steering control effect compared to conventional steering lateral control. moreover, ashkrof [20] developed evs control strategies to select travel routes and determine battery charging locations based on driving behavior. these studies do not also discuss variables related to energy use. 339 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 an automatic control system was introduced to recognize driving behavior by silver [21] and yansong [22] to alert drivers when they exceed safety limits. julian [23] also used vision sensors for the same purpose with the recognition results stored in a database and exclusively patented. these studies have interesting concepts but this could have been more exciting if the driving behavior recognition factor was used to control energy. unfortunately, it was not included. the other aspects studied in relation to driving behavior are traffic lights and graphical displays. this was observed in the analysis of emissions produced by vehicles at traffic lights, especially at road junctions, by stagios [24] through the observations made about the changes in vehicle emissions on the highway due to driving behavior. it was discovered that it is possible to reduce emissions by up to 26% when the driver behaves in certain conditions. however, this study only focused on changes in emissions without considering the energy consumption factor in behavioral changes. kohl [25] also showed that graphic displays, especially images/messages that frequently appear, have a significant influence on safe driving behavior. it was discovered that the frequent graphic display reduces the focus of drivers while driving and this is very dangerous for safety. this is considered very interesting but this study did not include the energy control influenced by driving behavior. this was followed by studies conducted on the relationship between energy consumption and driving behavior. xing [26] predicted future energy consumption by observing the behavior of the driver but the study does not lead to energy control. this simply implies several variables have been considered in studying driving behavior such as car-following systems, cvds-idm simulations, vehicle safety systems design, driving behavior analysis, vision technology or graphical display, and the vehicle emissions dynamics at traffic lights. it has also been discovered from previous studies that fuel energy control can be denoted by afr used to generate stoichiometry values, machine learning or artificial intelligence applications, and the use of turbochargers. however, research has not been conducted on using driving behavior to control fuel even though driving behavior has been empirically proven to have a significant influence on fuel consumption. therefore, this research was used to discuss the application of a driving behavior system to control fuel using an artificial neural network as a continuation of the previous study [26]. fig. 1: the concept of the designed control system. the control system developed based on the driving behavior using artificial neural network (ann) was successfully applied to real vehicles and presented in the following figure 1. it was designed to work on three inputs which include the steering speed sensor (a), braking speed sensor (b), and throttle valve opening speed sensor (c) as well as supporting components to assist its performance which include an engine to generate power to drive the vehicle (d) and engine control unit – ecu (e) designed with ann to recognize driving behavior in real time. the results obtained from the ann were used to control fuel consumption through the fuel pump (f) placed in the fuel tank (g) in order to deliver fuel to the injectors. it is important to 340 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 note that the speed of the fuel pump was controlled by the ecu with the ann applied to recognize driving behavior. 2. method 2.1 control system by driving behavior the behaviors of drivers are usually different when driving based on their needs, mood, and inclinations, and this greatly influences vehicle operation and fuel consumption. this led to the design of three schemes to control the vehicle which include eco-driving, standard or stoichiometry, and sporty behaviors. the eco-driving is the behavior associated with vehicles operating smoothly on busy urban roads [27] and allows the driver to operate the throttle valve opening, braking, and steering smoothly at a speed of approximately 40-60 km/hour. the sporty scheme is a responsive driving behavior that involves the vehicle operating on a toll road [28] and the driver is expected to generally drive responsively at a vehicle speed of more or less than 80 km/hour. meanwhile, the standard scheme is a driving behavior between the eco and sporty schemes. figure 2 shows the design of the control system developed in this study to regulate fuel using ann with due consideration for the driving behavior. the ann designed to be embedded in the control system is used to recognize driving behavior in real-time. moreover, the algorithm method applied in the ann was levenberg marquardt type learning (trainlm) while the learning performance was based on the mean squared error (mse) value using 300 nodes, one output layer, one hidden layer, and three inputs. fig. 2: ann system design embedded in the control system. the three ann inputs consist of signals generated by the throttle valve opening speed sensor (x1), steering speed sensor (x2), and braking speed sensor (x2). these three sensors produce a speed signal which in the next process becomes the average acceleration value (ma) which is processed using eqs. (1), (2), and (3). the ann (y) output is a driver behavior scheme to set the fuel pump. the types of layers used include logsig, tansig, and purelin models while the number of neural network learning used was 20,000 epochs with a learning success rate of 99.93%. furthermore, the neural network learning was conducted in the matlab simulink software and later embedded in the control system (microcontroller mega 2560). this study uses 3285 data for ann training. the training data used in this research is in the form of signal data generated by the throttle valve opening, steering, and braking sensors presented in fig. 3. this training data is obtained from measurements of real driving behavior characteristics. data from sensors is taken through data acquisition that has been processed beforehand using eqs. (1), (2), and (3). 341 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 fig. 3: data used for ann training. mapping driving behavior recognition with ann has 27 levels. the driving behavior scheme was designed using the three schemes presented in table 1. driving behavior recognition mapping consists of three schemes, including eco-driving (a), stoichiometry/normal driving (b), and sporty driving (c) schemes. determination of the driving behavior scheme serves to assess the characteristics of each driver. the detailed determination of the driving behavior scheme is presented in table 4. table 4 and it was discovered that it was designed on the operation of opening the throttle valve (x2), steering (x2), and braking (x3). the throttle valve opening operation has three low, medium, and high clusters for steering and braking operations. the findings of each cluster for throttle valve opening, steering and braking operations are presented in table 3. 2.2 equations used in control systems the throttle valve opening, steering, and braking sensors generated speed data which were later converted into an acceleration function embedded in the control system (microcontroller ni myrio). moreover, the average acceleration value (moving average ma) was applied to analyze the driver's behavior from opening the throttle valve, steering, and braking. this method was preferred due to its ability to reduce the value of erratic variations [29,30], thereby increasing its suitability to recognize the variations in the driving behavior. 2.2.1 acceleration function equation the speed data generated by the throttle valve, steering, and braking sensors were converted to the acceleration function presented in eq. (1). 𝑎𝑖 = (𝑣𝑖−𝑣(𝑖−1)) (𝑡𝑖−𝑡(𝑖−1)) (1) where: i = 1,2…180 𝑎𝑖 = acceleration value at the time i (mm/seconds 2). t = time of speed change in seconds. 𝑣𝑖 = speed value in period i (mm/seconds). 𝑣(𝑖−1)= speed value in period i -1 (mm/seconds). the next process after the speed has been changed into an acceleration function with eq. (1) was to determine the average acceleration value. 342 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 table 1: mapping driving behavior recognition with ann system no. schematic of driving behavior (y) driving operation type opening of the throttle valve (x1) steering (x2) braking (x3) 1. a 1 1 1 2. b 1 1 2 3. b 1 2 2 4. b 1 1 3 5. b 1 2 2 6. b 2 2 2 7. b 2 1 1 8. b 2 2 1 9. b 2 1 2 10. c 3 1 1 11. c 3 2 1 12. c 3 1 2 13. c 3 2 2 14. c 3 2 3 15. c 3 3 2 16. c 3 3 3 17. c 3 1 3 18. c 3 3 1 19. b 1 2 3 20. b 1 3 2 21. b 1 3 3 22. b 1 3 1 23. b 2 2 3 24. b 2 3 3 25. b 2 3 2 26. b 2 3 1 27. b 2 1 3 description: 1 = low, 2= moderate, 3 = high, a= eco driving scheme, b= stoichiometry/standard driving scheme, c= sporty driving scheme. 2.2.2 calculation of change in average acceleration the acceleration value obtained from eq. (1) was used to calculate the average value using the moving average (ma) method presented in eq. (2). 𝑀𝐴𝑖 = 𝑎𝑖+𝑎𝑖+1+𝑎𝑖+2 3 (2) where: i = 1, 2,…180 𝑀𝐴𝑖 = average acceleration (mm/seconds 2). 𝑎𝑖 = acceleration value in period i (mm/seconds 2). 𝑎𝑖+1 = acceleration value in period i+1 (mm/seconds 2) 𝑎𝑖+2 = acceleration value in period i+2 (mm/seconds 2). the ma value was successfully calculated using eq. (2) while the average was calculated again using eq. (3). it was discovered that the average ma had 178 constraints, 343 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 which were determined once every 15 minutes, and sent to the ecu to recognize driving behavior using the ann embedded in the control system (microcontroller mega 2560). 𝑀𝐴̅̅ ̅̅ ̅ = 𝑀𝐴1+𝑀𝐴2+⋯.𝑀𝐴178 178 (3) 2.2.3 control system testing set up developed the control system test was designed by mounting an afr sensor (1) on the exhaust gas line to detect the air and fuel mixture while a data acquisition microcontroller (2) was used to change the signal generated by the afr sensor and the engine speed sensor (4). moreover, the speed module (3) was employed to convert the pulse signal into a signal readable by the computer as indicated in fig. 2. it was also observed that the control system (8) developed has two components which include a ni myrio microcontroller (a) and a control module (b) with a mega 2560 microcontroller and an electronic circuit. the speed data generated every 5 seconds by the throttle valve opening, braking, and steering speed sensors were converted into an acceleration function in the ni myrio microcontroller (a). moreover, the process to change the speed function into an acceleration function is presented in eq. (1) after which the acceleration data obtained were averaged through eq. (2) using the moving average – ma method. the ma average results were also calculated using equation (3) every 15 minutes and sent to the ecu where an ai system with a neural network was used to perform clustering, analyze the different kinds of driving behavior, and send the cluster results to the speed controller module. the speed controller module was applied to control the fuel pump (2) to ensure the fuel is supplied to the engine according to the driving behavior. additionally, an ai system with a neural network is embedded in the mega 2560 microcontroller. the control system application setup is presented in fig. 4. fig. 4: driving behavior control system test setup. the installation of equipment to test the control system with driving behavior is presented in fig. 5. the afr sensor was used to measure the air and fuel mixture, the throttle valve speed sensor was mounted on one shaft with the throttle position sensor, while the braking speed sensor was fixed on the brake master shaft and actuated by the brake pedal. moreover, the steering speed sensor was placed on the side of the steering shaft using a v belt. it is important to note that there was direct documentation of the behavioral recognition test while the speed sensor was used to measure engine speed. while the specifications of the equipment used in the study are presented in table 2. 344 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 fig. 5: installation of afr sensor (1), throttle valve speed sensor (2), braking speed sensor (3), steering speed sensor (4), driving operation (5), and engine speed sensor (6). the installation of equipment to test the control system with driving behavior is presented in fig. 5. the afr sensor was used to measure the air and fuel mixture, the throttle valve speed sensor was mounted on one shaft with the throttle position sensor, while the braking speed sensor was fixed on the brake master shaft and actuated by the brake pedal. moreover, the steering speed sensor was placed on the side of the steering shaft using a v belt. it is important to note that there was direct documentation of the behavioral recognition test while the speed sensor was used to measure engine speed. while the specifications of the equipment used in the study are presented in table 2. table 2: specifications of the equipment used no. description specification a. steering speed sensor 12-volt direct current (dc) motor with gear ratio and dimensions of ∅ 30 × 60 mm. b. braking speed sensor. c. throttle valve speed sensor. d. engine. gasoline engine with injection type, which has a volume of 1500 cc. e. ecu with driving behavior control system using ann. ni myrio microcontroller and speed controller module equipped with atmega 2560 microcontroller. f. fuel pump 12-volt dc rotary type g. fuel tank capacity 44 liters h. test vehicle saloon-type vehicle with a capacity of 4 passengers 3. results and discussion 3.1 throttle valve opening sensor results the control system designed was applied directly to assess driving behaviors in order to determine the characteristics of drivers in real time based on three schemes which include the eco, stoichiometry/standard, and sporty schemes. each of these schemes was determined using the changes in acceleration generated by the throttle valve opening, steering, and 1 2 3 4 5 6 345 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 braking sensors as the input. moreover, the throttle valve opening signal was calculated through four stages which include the measurement of the throttle valve opening speed, change of the speed to acceleration, calculation of the moving average (ma) value, and determination of the average ma. the change in the throttle valve opening speed was monitored over three periods as indicated in fig. 6 with the first period found to be between 0 900 seconds, the second was 901-1800 seconds, and the third was 1,801 – 2,700 seconds. the findings showed that the speed change for these periods was 0–2.5, 0–2.6, and 0–4.6 mm/second respectively. it was observed that the third period tends to have a higher speed change rate and density level. fig. 6: change of throttle valve opening speed. fig. 7: change of throttle valve opening acceleration. the speed data presented in fig. 6 was converted into an acceleration function using eq. (1) and the results are presented in fig. 7 as a function of the change in acceleration. it was discovered that there was an acceleration value of 0 – 0.5 mm/seconds2 and a negative acceleration or deceleration value of 0-(-0.45 mm/seconds2) for 0 – 900 seconds. the findings also showed that the second period, 901 – 1,800 seconds, had 0 – 0.7 mm/seconds2 and 0-(-0.7 mm/seconds2) while the third period, 1,801 – 2,700 seconds, had 0 – 0.9 mm/seconds2 and 0-(-0.9 mm/seconds2) respectively. however, it is important to note that the third period had a higher density. the acceleration/deceleration values presented in fig. 7 were used in the next process to determine the average using the ma method in eq. (2). this was also followed by finding the average of the ma values using eq. (3) and the results are presented in fig. 8. it was discovered that the ma value for the 0 – 900 seconds period ranged from 0 – 0.14 mm/seconds2 and a negative acceleration (deceleration) value of 0-( -0.14 mm/seconds2). the results further showed that the 901 – 1,800 seconds period had 0 – 0.12 mm/seconds2 and 0-(-0.12 mm/seconds2) while 1,801 – 2,700 seconds period had 0 – 0.2 mm/seconds2 and 0-(-0.22 mm/seconds2) respectively. meanwhile, the average ma for 0 – 900 seconds was found to be 0.00 while 901 – 1,800 seconds had 0.002, and 1801 – 2700 seconds had 0.003. it is pertinent to restate that the average ma value was determined every 15 minutes and sent to the developed control system. it was discovered that the highest ma average value was recorded in the last period. 3.2 steering sensor results the changes observed in the steering speed of each driver are presented in fig. 9. it was discovered that the drivers possess quite diverse characteristics as observed with the 0 346 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 – 17 mm/second recorded for the 0 – 900 seconds period, 0 – 14 mm/seconds for the 901 – 1,800 seconds period, and 0 – 43 mm/seconds for the 1,801 – 2,700 seconds period which is the highest compared to the others. fig. 8: average ma value of driver throttle valve opening behavior. fig. 9: steering speed changes behavior. the change in driver acceleration presented in fig. 10 showed that the 0 900 seconds period had an acceleration value of 0 – 4 mm/seconds2 and a negative acceleration (deceleration) value of 0-(-4 mm/seconds2) while 901 – 1,800 seconds period had 0 – 4.1 mm/seconds2 and 0-(-4.1 mm/seconds2) and 1,801 – 2,700 seconds period had 0 – 5.8 mm/seconds2 and 0-(-3 mm/seconds2) respectively. it was observed that the driver tends to add more steering acceleration in the third period. the ma values recorded based on the changes in the driver's steering acceleration are presented in fig. 11. it was discovered that the 0 – 900 seconds period had an ma range between 0 1.3 mm/seconds2 and negative acceleration (deceleration) of 0-(-1.3 mm /seconds2) while the 901 – 1,800 seconds period had 0 – 1.1 mm/seconds2 and 0-(-1.1 mm/seconds2) and the 1,801 – 2,700 seconds period had 0 – 1.1 mm/seconds2 and 0-(-1.1 mm/seconds2) respectively. moreover, the average ma value in the 0 – 900 seconds period was found to be 0.0000, the 901 – 1,800 seconds period had 0.002, and the 1,801 – 2,700 seconds had 0.03 which is the highest. fig. 10: changes in steering acceleration behavior while driving. fig. 11: average ma value of driver steering behavior. 347 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 3.3 braking sensor results the changes in the driver's braking speed presented in fig. 12 showed that the value at the 0 – 900 seconds period was 0–2.9 mm/second, the 901 – 1,800 seconds period had 0-2.6 mm/second, and the 1,801 – 2,700 seconds had 0 – 4.5 mm/second. this implies the 0 – 900 seconds period has the greatest braking speed and lower density frequency compared to the others. the speed data presented in fig. 10 were converted into an acceleration function through eq. (1) to determine the changes in driver acceleration and the results are presented in fig. 13. it was discovered that the pattern acceleration for the drivers at the 0 – 900 seconds period was in the range of 0 – 0.4 mm/seconds2 and a negative acceleration (deceleration) value of 0-(-0.3 mm/seconds2) while the 901 – 1,800 seconds period had 0 – 0.7 mm/seconds2 and 0-(-0.6 mm/seconds2 and 1,801 – 2,700 seconds period had 0 – 0.8 mm/seconds2 and 0-(-0.8 mm/seconds2) respectively. fig. 12: braking speed on observed driving behavior. fig. 13: changes in the acceleration of the driver's braking behavior. the ma values associated with the changes in the driver's braking acceleration are presented in fig. 14. it was discovered that the 0 – 900 seconds period has a pattern where the ma values had the lowest frequency with values ranging between 0 – 0.15 mm/seconds2 and negative acceleration (deceleration) values 0-(0.13 mm/seconds2). the findings further showed that the 901 – 1,800 seconds period had 0 – 0.12 mm/seconds2 and 0-(-0.12 mm/seconds2) while the 1,801 – 2,700 seconds period had 0 – 2.1 mm/seconds2 and 0-(0.18 mm/seconds2). these ma values were later used to determine the average ma and the results showed that the value for the second driver was 0.0003 for the 0 – 900 seconds period, 0.0016 for the 901 – 1,800 seconds period, and 0.0021 for the 1,801 – 2,700 seconds period. this implies the 0 – 900 seconds period has the lowest average ma. 3.4 driving behavior recognition range the driving behavior control system was designed using several variables that cause a slight difference between the simulated conditions and the real control system. it was discovered from the control system that the real driving behavior has a negative value because of the deceleration process and this cannot be read by the microcontroller. therefore, a normalization system was needed through the inclusion of several different variables in the simulation scale and real control systems but the concept remains the same. normalization is a process of adding constants to signal conditioning so that the microcontroller can work according to its designation. the methods used to recognize the 348 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 driving behavior are listed in table 3 while the real decision-making process using the control system designed was based on the cluster system developed with the average ma value as indicated in table 4. fig. 14: average ma value of the driver's braking behavior. table 3: cluster average (ma̅̅ ̅̅ ̅) for the throttle valve, steering, and braking the average ma value generated by the sensor was analyzed to identify and recognize the driving behavior clusters using the ann that has been trained and embedded in the controller system as presented in table 3. it was discovered that the first period was in the eco scheme, the second period was in the stoichiometric scheme, and the third period was in the sporty scheme. table 4: recognition of the driver's steering behavior in the control system description low (mm/seconds2) middle (mm/seconds2) high (mm/seconds2) ma throttle valve acceleration (-0.001)-0.001 0.002 0.003 ma from steering (-0.02) 0.02 (-0.05) – (-0.03) & 0.03 0.05 (-0.08) – (-0.06) & 0.06 0.08 ma of braking acceleration (-0.0003)-0.0003 (-0.0009)–(-0.0006) & 0.0006 0.0009 (-0.005) – (-0.001) & 0.001 0.005 description first period (0-900s) second period (901-1,800s) third period (1801-2,700s) ma throttle valve acceleration low (0.000) middle (0.002) high (0.003) ma acceleration steering low (0.0088) low (0.0101) low (0.0021) ma braking acceleration low (0.0003) high (0.0016) high (0.0021) driving behavior scheme eco stoichiometry sporty 349 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 3.5 afr dynamics results the afr values were measured using the data previously acquired and validated through an afr meter and were subsequently applied to determine the influence of driving behavior on their variations based on the information in table 3. the first period is in the eco scheme, the second is in the stoichiometric scheme, and the third is in the sporty scheme. it is important to note that vehicles experience acceleration and deceleration when operating on the highway. acceleration is a condition associated with an increase in the speed of the vehicle by opening the throttle valve while deceleration involves reducing the vehicle's speed by closing the throttle valve. an increase in the vehicle speed by opening the throttle valve usually leads to a decrease in the afr value and vice versa. the dynamics of the afr value including the increase or decrease are presented in figure 15 for the models with and without the driving behavior control system. in the application of the driving behavior control system, the first period of driving behavior is known to have an afr value between 14.8 – 17.7 with an average of 15.87, while the second period is between 14 – 16.6 with an average of 14.84, and the third period had the value is between 11.5 – 16 and the average is 13.66. this shows that the driving behavior in the first period allowed maximum fuel economy compared to the second and third periods. meanwhile, the driving behavior in the third period led to the production of maximum power by the engine as indicated by the average afr value recorded. meanwhile, the dynamics of afr without applying a driving behavior control system have quite a high difference in average values. the average afr value without the developed control system is 14.78 for 2700 seconds. in the first period, the driver rarely decelerates, so the afr value has a lower fluctuation range value when compared to the second and third periods. the achievement of the highest fuel economy through the afr value above the stoichiometry of 14.7. this is in line with a previous study that predicted the potential development of technology to achieve a lean afr scale above the stoichiometry for commercialization purpose in order to have energy-efficient machines [31]. the research did not discuss the exact conditions to implement lean afr but this current study considered its application based on driving behavior. it was discovered that the afr above stoichiometry achieved in the first period, 0 – 900 seconds, led to smoother acceleration and this implies there is no need for large engine power. fig. 15: afr dynamics on observed driving behavior. 350 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 the afr values in the second period, 901 – 1,800 seconds, are classified to be in the stoichiometric range (14.7) and this is in line with the findings of a previous study that afr stoichiometry ensures the achievement of the most optimal value for power and fuel saving [7,32]. the research did not discuss the time and requirements to achieve maximum power saving but these are developed in this current study based on driving behavior. the driving behavior in the third period, 1,801 – 2,700 seconds, was observed to have led to the fulfillment of maximum power as indicated by the average afr stoichiometry value of 13.66. this agrees with the findings of a previous study that an afr under a stoichiometry value of 12–14 usually produces the greatest engine power [33]. the control system showed that the driving behavior required high engine power and this led to the addition of more fuel at an average afr value of 13.66. this shows that the control system was successfully developed with due consideration for the driving behavior. this was able to improve driving comfort in terms of fuel economy as indicated by the afr values above stoichiometry and fulfillment of the engine power requirements with values below stoichiometry. it was discovered that the fuel economy was satisfied in the first period when driving behavior is categorized as eco-scheme while the demand for the engine power was fulfilled in the third period when driving behavior is included in the sporty scheme. 4. conclusion the design of afr management with driving behavior control using ann has been successfully applied to actual vehicles. the designed control system can recognize driver behavior in real-time to control fuel and increase vehicle comfort. driving comfort is achieved by meeting the need for fuel economy when the driving behavior is included in the eco-driving scheme and aspects of fulfilling engine power when the driving behavior is included in the sporty scheme. when the driver enters the eco-driving scheme, the control system can control afr with an average value of 15.68 (entering the lean range). afr above stoichiometry can improve fuel economy. the eco scheme is achieved in the first period (0–900 seconds), where this decision is based on the ma value of throttle valve acceleration in the low category (0.0000 mm/second2), ma steering acceleration in the low category (0.0088 mm/second2) and braking acceleration ma in the category low (0.0003 mm/s2). when the driving behavior enters the sporty driving scheme, the control system can control afr with an average value of 13.66 (below stoichiometry). afr under stoichiometry produces maximum engine power. the sporty scheme is achieved in the third period (0–900 seconds), where this decision is based on the ma value of throttle valve acceleration in the high category (0.003 mm/second2), ma steering acceleration in the low category (0.0021 mm/second2) and braking acceleration ma in the high category (0.0021 mm/second2). this research is applied to vehicles with gasoline engines and has not considered the road angle. for this reason, future research can be applied to electric, gas-fueled, and fuel-cell vehicles, considering the road angle. acknowledgment the authors are grateful to the diponegoro university and the universitas muhammadiyah magelang for supporting this research. 351 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 references [1] burdzik r. (2022) a comprehensive diagnostic system for vehicle suspensions based on a neural classifier and wavelet resonance estimators. measurement, 200: 111602 https://doi.org/10.1016-/j.measurement.2022.111602. [2] uslu s, celik mb.(2020) performance and exhaust emission prediction of a si engine fueled with i amyl alcohol-gasoline blends : an ann coupled rsm based optimization. fuel, 265: 116922. https://doi.org/10.1016/j.fuel.2019.116922. [3] al-fattah sm. (2020) non-opec conventional oil : production decline, supply outlook and key implications. journal of petroleum science and engineering 189: 107049. https://doi.org-/10.1016/j.petrol.2020.1070. [4] kutlu o. (2020) global oil production declines in june 2020. energy. available: https://www.-aa.com.tr/en/energy/international-organization/global-oil-production-declinesin-june-2020-/29901. [5] wang y, fan y, wang d, liu y, qiu z, liu j. (2020) optimization of the areas of solar collectors and photovoltaic panels in liquid desiccant air-conditioning systems using solar energy in isolated low-latitude islands. energy, 198: 117324. https://doi.org/10.1016/j.energy.-2020.117324. [6] gagliardi g, mari d, tedesco f, casavola a. (2021) an air-to-fuel ratio estimation strategy for turbocharged spark-ignition engines based on sparse binary hego sensor measures and hybrid linear observers. control engineering practice, 107: 104694. doi:10.1016-/j.conengprac.2020.104694. [7] ahmed sfa. (2019) analyzing and predicting the relation between air – fuel ratio (afr), lambda (λ) and the exhaust emissions percentages and values of gasoline ‑ fueled vehicles using versatile and portable emissions measurement system tool. sn applied science, 1(11): 1-12. https://doi.org/10.1007/s42452-019-1392–5. [8] zhao x, wang z, xu z, wang y, li x, qu x. (2020) field experiments on longitudinal characteristics of human driver behavior following an autonomous vehicle. transportation research part c: emerging technologies, 114: 205-224. https://doi.org/10.1016-/j.trc.2020.02.018. [9] sharma a, zheng z, bhaskar a, haque m. (2019) modelling car-following behaviour of connected vehicles with a focus on driver compliance. transportation research part b, 126: 256-279. https://doi.org/10.1016/j.trb.2019.06.008. [10] fadhloun k, rakha h. (2020) novel vehicle dynamics and human behavior car-following model : model development and preliminary testing. international journal of transportation science and technology, 9: 14-28. https://doi.org/10.1016/j.ijtst.2019.05.004. [11] grove k, soccolich s, engström j, hanowski r. (2019) driver visual behavior while using adaptive cruise control on commercial motor vehicles. transportation research part f, 60: 343-352. https://doi.org/10.1016/j.trf.2018.10.013. [12] fung kc, dick tj.(2016) system and method for responding to driver behavior. https://patents.google.com/patent/us9440646b2. [13] martinelli f, mercaldo f, orlando a, nardone v, santone a, kumar a. (2020) human behavior characterization for driving style recognition in vehicle system. computers & electrical engineering, 83: 02504. https://doi.org/10.1016/j.compeleceng.2017. [14] yuan y, lu y, wang q. (2020) adaptive forward vehicle collision warning based on driving behavior. neurocomputing, 408: 64-71. https://doi.org/10.1016/j.neucom.2019.11.02. [15] raz o, fleishman h, mulchadsky i. (2008) system and method for vehicle driver behavior analysis and evaluation. https://patents.google.com/patent/us7389178b/en. [16] hong z, chen y, wu y. (2020) a driver behavior assessment and recommendation system for connected vehicles to prod prevention, 139: 105460. https://doi.org/10.1016/j.aap.2020.-105460. [17] mafeni j, majid s, mesgarpour m, torres m, figueredo gp, chapman p. (2020) evaluating the impact of heavy goods vehicle driver monitoring and coaching to reduce risky behaviour, accident analysis & prevention, 146: 105754. https://doi.org/10.1016/j.aap.2020.105754. 352 iium engineering journal, vol. 24, no. 2, 2023 triwiyatno et al. https://doi.org/10.31436/iiumej.v24i2.2781 [18] bando t. (2015) system for detecting abnormal driving behavior. https://patents.google.com-/patent/us9111400b2/en. [19] hongbo g, guotao x, hongzhe l, xinyu z. (2017) lateral control of autonomous vehicles based on learning driver behavior via cloud model. the journal of china universities of posts and telecommunications, 24(2): 10-17. http://dx.doi.org/10.1016/s1005-8885(17)601. [20] ashkrof p, homem g, correia da, van arem b. (2020) analysis of the effect of charging needs on battery electric vehicle drivers’ route choice behaviour : a case study in the netherlands. transportation research part d, 78: 102206. https://doi.org/10.1016/j.trd.2019.102206. [21] silver a, lewis l. (2015) automatic identification of a vehicle driver based on driving behavior. https://patents.google.com/patent/us9201932b2/en. [22] yansong r, o’gorman l, wood tl. (2019) driver behavior monitoring systems and methods for driver behavior monitoring. https://patents.google.com/patent/us9201932b2/en. [23] julian dj and agrawal a. (2017) driver behavior monitoring. https://patents.google.com/patent/us10460600b2/en. [24] stogios c, kasraian d, roorda mj, and hatzopoulou m. (2019) simulating impacts of automated driving behavior and traffic conditions on vehicle emissions. transportation research part d, 76: 176-192. https://doi.org/10.1016/j.trd.2019.09.020. [25] kohl j, gross a, henning m, baumgarten t. (2020) driver glance behavior towards displayed images on in-vehicle information systems under real driving conditions. transportation research part f: traffic psychology and behaviour, 70: 163-174. https://doi.org/10.1016/j.trf.2020.01.017. [26] xing y, lv c, cao d, lu c. (2020) energy oriented driving behavior analysis and personalized prediction of vehicle states with joint time series modeling. applied energy, 261: 114471. https://doi.org/10.1016/j.apenergy.2019.114. [27] vaezipour a, rakotonirainy a, haworth n. (2018) a simulator evaluation of in-vehicle human machine interfaces for eco-safe driving. transportation research part a: policy and practice, 118: 696-713. https://doi.org/10.1016/j.tra.2018.10.022. [28] reinolsmann n, alhajyaseen w, brijs t, pirdavani a, hussain q, brijs k. (2019) investigating the impact of dynamic merge control strategies on driving behavior on rural and urban expressways – a driving simulator study. transportation research part f: traffic psychology and behaviour, 65: 469-484. https://doi.org/10.1016/j.trf.2019.08.010. [29] kiat d, poh h, yee c, zhen r, markus c, ping t. (2021) internal quality control : moving average algorithms outperform westgard rules. clinical biochemistry, 98: 63–69. https://doi.org/10.1016/j.clinbiochem.2021.09.007. [30] maverick jb. (2022) advantages and disadvantages of the simple moving average (sma)?, investopedia. available: https://www.investopedia.com/ask/answers/013015/what-are-mainadvantages-and-disadvantages-using-simple-moving-average-sma.asp. [accessed: 05-may2022]. [31] zhu c, wang p, wang p, liu z, wang p, liu z. (2018) model prediction control of fuel-air ratio for lean-burn spark ignition gasoline. ifac-papersonline, 51(31): 640–645. https://doi.org/10.1016/j.ifacol.2018.10.150. [32] sardarmehni t, aghili aa, menhaj mb. (2019) fuzzy model predictive control of normalized air-to-fuel ratio in internal combustion engines. soft computing, 23(15): 61696182. https://doi.org/10.1007/s00500-018–3270, 2019. [33] martyr a and plint m. (2007) third edition engine testing theory and practice. elsevier ltd. 353 microsoft word 2_v17no2_compiled_v2_24nov16.docx iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 185 an intelligent neuro-fuzzy terminal sliding mode control method with application to atomic force microscope seied yasser nikoo, behrooz rezaie*, zahra rahmani and seied jalil sadati faculty of electrical and computer engineering, babol university of technology, shariati ave., babol, mazandaran, iran. *corresponding author: brezaie@nit.ac.ir (received: 9th jun. 2015; accepted: 19th aug. 2016; published on-line: 30th nov. 2016) abstract: in this paper, a neuro-fuzzy fast terminal sliding mode control method is proposed for controlling a class of nonlinear systems with bounded uncertainties and disturbances. in this method, a nonlinear terminal sliding surface is first designed. then, this sliding surface is considered as an input for an adaptive neuro-fuzzy inference system, which is the main controller. a proportional-integral-derivative controller is also used to assist the neuro-fuzzy controller in order to improve the performance of the system at the beginning stage of the control operation. in addition, a bee algorithm is used in this paper to update the weights of the neuro-fuzzy system as well as the parameters of the proportional-integral-derivative controller. the proposed control scheme is simulated for vibration control in a model of atomic force microscope system and the results are compared with conventional sliding mode controllers. the simulation results show that the chattering effect in the proposed controller is decreased in comparison with the sliding mode and the terminal sliding mode controllers. also, the method provides the advantages of fast convergence and low model dependency compared to the conventional methods. abstrak: dalam kertas ini, kaedah mod kawalan terminal jenis gelongsor cepat neuro-kabur adalah dicadangkan untuk mengawal sejenis kelas sistem tak linear dengan ketidaktentuan dan gangguan terbatas. dalam kaedah ini, permukaan terminal gelongsor yang tak linear adalah pertama direka. kemudian, permukaan gelongsor ini dianggap sebagai input bagi sistem inferens neuro-kabur penyesuaian yang merupakan pengawal utama. sebuah pengawal berkadar-penting derivatif juga digunakan untuk membantu pengawal neuro-kabur dalam usaha untuk memperbaiki prestasi sistem pada peringkat permulaan operasi kawalan. di samping itu, algoritma lebah digunakan dalam kertas kerja ini untuk mengemaskini wajaran sistem neuro-kabur serta parameter pengawal berkadar-penting derivatif. skim kawalan yang dicadangkan adalah simulasi untuk mengawal getaran dalam model sistem mikroskop daya atom dan keputusan dibandingkan dengan pengawal mod gelongsor konvensional. keputusan simulasi menunjukkan bahawa kesan chattering dalam pengawal yang dicadangkan itu menurun berbanding dengan mod gelongsor dan pengawal terminal mod gelongsor. selain itu, kaedah ini mempunyai kelebihan dari segi penumpuan cepat dan kebergantungan model rendah berbanding dengan kaedah konvensional. keywords: terminal sliding mode controller; adaptive neuro-fuzzy inference system; bee algorithm; atomic force microscope; nano manipulation iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 186 1. introduction nonlinear control methods have significantly developed in terms of theory and practice. important theoretical developments have been obtained in the fields of nonlinear robust control methods such as sliding mode control. the sliding mode controller (smc) has attracted the interests of many researchers due to its fast response and robustness against disturbance, noise, and uncertainty. the main reason for choosing this controller is its acceptable control performance in a wide range of operation conditions. also, two main challenges in control, namely stability and robustness, can be effectively solved using this method [1-3]. in conventional smc, the sliding surface is usually a linear surface that only guarantees the asymptotic stability. thus, error dynamics cannot converge to zero in finite time. by tuning the parameters of smc, faster error convergence can be achieved. however, this increases the control gain and thereby leads to a chattering phenomenon on the sliding surface that may damage the system [4]. terminal smc (tsmc) has been proposed in [5], for the first time, in order to solve the finite time asymptotic stability problem. in this method, a nonlinear sliding surface is used to obtain finite time asymptotic convergence. tsmc design includes two parts: choosing an appropriate sliding surface and choosing an appropriate control law that steers the system states of this sliding surface and makes them remain on it [5-7]. in order to have a good performance in smc-based controllers, obtaining and formulating the acceptable nonlinear dynamics of the system is very important. however, determining the nonlinear dynamics of the system is usually a very difficult task. in addition, one of the disadvantages of such controllers is their sensitivity to noise, when the control signal is close to zero. another important problem in smc-based methods is the chattering effect that leads to high frequency oscillations in the controller’s output and may damage mechanical components. to remove, or at least decrease, the chattering effects, various methods have been reported by many researchers [1, 8, 9]. artificial intelligence algorithms have been applied in smc-based methods to improve them. for example, neural networks, fuzzy logic systems and neuro-fuzzy systems have been combined with the sliding mode control method for controlling nonlinear systems with uncertainties. the fuzzy logic controller (flc) is one of the most important applicable systems, which can be utilized for uncertain nonlinear systems. it can convert the experimental science into the mathematical formulation. however, flc, by itself, cannot guarantee the stability condition and the acceptable performance [10]. some researchers have used fuzzy logic in smc to reduce the chattering effect in pure sliding mode control methods. their proposed controller is called a fuzzy smc (fsmc) [11-13]. fsmc is a smc that is combined with a fuzzy logic system to reduce or remove the high frequency oscillations. furthermore, it is utilized to compensate for the unknown dynamics of the model and also to tune the sliding surface slope. for example, sarailoo et al. have proposed a fuzzy-based smc [11]. moreover, wong et al. have combined a flc with smc and a pi controller to overcome the chattering effect [12]. a fuzzy system has been used in [13] to combine smc and a state feedback controller for reducing the chattering effect. some studies have also utilized fuzzy logic systems in tsmc [14-18]. in [14], an adaptive fuzzy system has been used in tsmc to reduce the chattering. adaptive tsmc using a fuzzy system has been developed in [15]. also, in [16], fuzzy tsmc has been proposed for fault-tolerant control. a combination of the state feedback controller and tsmc using a fuzzy system has also been investigated in [17]. many researchers have used the sliding mode control method in a fuzzy controller, called sliding mode fuzzy controller (smfc), to improve the stability of the system. iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 187 stability is the most important challenge in pure flc. the smfc method is a smc-based flc that is used for reducing fuzzy rules and improving closed-loop stability of the system. research in the field of smfc has been significantly performed as an applicable program. for example, this method has been used for robot control in [3, 8, 18, 19]. moreover, adaptive fuzzy methods have been applied in the smc for nonlinear systems in order to obtain accurate tracking and to remove the chattering effects [20, 21]. hwang et al. have proposed an adaptive fsmc based on type-2 fuzzy systems for nonlinear systems with uncertainties and external disturbances. in this method, the type-2 fuzzy controller has been utilized to obtain the linear feedback control law and an impulse controller has been used to compensate the error approximation between the control law and type-2 fuzzy controller [20]. benbrahim et al. have proposed an adaptive fsmc with a type-2 fuzzy controller for unknown nonlinear systems with uncertainties and external disturbances. in this method, two type-2 fuzzy logic systems have been applied for approximating the dynamics of the unknown system [21]. the main disadvantage of fsmc is the lack of systematic methods for designing the fuzzy rules and membership functions. adaptive fsmc can cope with this shortcoming. an adaptive neuro-fuzzy inference system (anfis) is an effective modeling method that provides the benefits of both a fuzzy inference system and neural networks [22]. anfis involves two types of tunable parameters, i.e., antecedent parameters and conclusion parameters. the training and parameter updating in anfis is mostly based on the gradient and computation of gradient at each stage, which is a complicated task. also, the chained rules that are used in this method may lead to local optimums. in the gradientbased method, the convergence of the parameters is slow and depends on the initial value of the parameters. also, finding the best learning gain is difficult. shoorehdeli has proposed different hybrid methods for training parameters in anfis [23-28]. in these hybrid methods, a particle swarm optimization (pso) algorithm with descending gradient [27], a recursive least square (rls) method [25], and extended kalman filter (ekl) [23] have all been used for training. in these studies, the pso algorithm has been used to train antecedent parameters, while the other methods have been used to train conclusion parameters. in a different study, shoorehdeli has used a forgetting factor recursive least square (ffrls) method to train conclusion parameters [26]. in this work, the stability of the algorithm has been investigated based on the lyapunov stability theory. moreover, shoorehdeli has applied a pso algorithm for the entire parameters of the neuro-fuzzy network [27]. chatterjee et al. have introduced an extended type of takagi-sugeno type neuro-fuzzy system for modeling robot manipulators in [28]. this type of neuro-fuzzy system has been trained by a pso algorithm. lin et al. have proposed a hybrid training algorithm based on fuzzy entropy clustering, modified pso, and recursive singular value decomposition method [29]. cus et al. [30] have proposed an approach that uses anfis to represent the manufacturer objective function and an ant colony optimization algorithm to obtain the optimal objective value. gunesekaran et al. [31] have integrated anfis with an artificial immune algorithm. training the neuro-fuzzy system is important for satisfactory operation of anfis and finding new algorithms for updating the weights of anfis is an open challenge. the conventional sliding mode control method has also combined with anfis in [3235]. these adaptive fsmc methods have the advantages of robustness and stability of the smc, the model-free feature of fuzzy systems, and the learning capability of anfis. in such hybrid configurations, the common sliding surface is a linear surface which only guarantees asymptotic stability. however, the error dynamic may not converge to zero in finite time. moreover, by tuning the parameters of smc, although fast convergence of the iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 188 error may be achieved, the control gain is then increased which results severe chattering on the sliding surface. these problems motivate the current research to improve the existing results. in the present paper, a combination of fast tsmc (ftsmc) and anfis are proposed to overcome the above mentioned problems. in the proposed scheme, both finite-time asymptotic convergence and chattering-free results can be achieved simultaneously. in fact, the nonlinear sliding surface is considered as the input of anfis. then an adaptive intelligent law is utilized to tune the weights in order to obtain the best weights with stable convergence property. to satisfy the lyapunov condition, an intelligent control law is applied for tuning the weights such that the most optimum value with a stable convergence property is achieved and thereby the lyapunov condition is satisfied. in this paper, a bee algorithm is used to determine the adaptive optimal control law. the bee algorithm is simple and fast in comparison with conventional descending gradient-based methods and can lead to satisfactory results. in the proposed scheme, a pid is also used in parallel with anfis to assist it by providing an additional control action. this pid controller is also tuned using the bee algorithm. by using this pid controller, the response of the anfis, in the beginning stages of control, will be improved. the advantage of the proposed controller, compared to the ftsmc, is its high robustness against uncertainties and undesirable disturbances. this robustness is due to the use of the terminal sliding surface as the input in the anfis structure. therefore, the network structure becomes simpler and the error converges to the sliding surface in less time. although the benefits of the fast terminal sliding surface are achieved, the chattering effect does not exist. moreover, improvement in the closed-loop stability and finite time asymptotic stability are the other advantages of the proposed controller with respect to the purely neuro-fuzzy controller. this method is applicable for the cases where the dynamic of a system is not available or the system is unknown. in this paper, the proposed control scheme is applied to an atomic force microscope (afm) system and the results are compared with conventional smcs. simulation results show the effectiveness and improved performance of the proposed controller. the paper is organized as follows. in section 2, the system description and control goals that are considered in this paper are explained. moreover, in this section, a mathematical model of the afm system is introduced as a case study to verify the theoretical results using simulations. in section 3, the fast terminal sliding mode control method is introduced and its stability for the considered class of nonlinear systems is proven. then, the neuro-fuzzy controller is introduced, after which the hybrid configuration of this network with tsmc is investigated. also, in this section, a bee intelligent algorithm is used instead of classical methods to tune the parameters of the proposed controller. in section 4, by applying the proposed method to the afm model, the simulation results are presented. finally, conclusion remarks are drawn in section 5. 2. problem formulation 2.1 system description in this paper, a neuro-fuzzy ftsmc (nfftsmc) is proposed for a class of nonlinear systems. consider a nonlinear dynamic system as follows: iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 189 1 1 for 1 -1 ( ) ( ) ( ) ( ) i i n d x i n dt d f f g u d t dt y x x x         x x x (1) where x(t)=[x1(t) x2(t) ... xn(t)]tϵrn is the state vector of the system, which is assumed to be measurable. ( ) and g(x) are nonlinear continuous functions and y is the output of the system. ∆ ( ) and ( ) represent uncertainty and bounded external disturbance respectively. also, uϵr denotes the control input of the system. moreover, it is assumed that the system (1) is controllable and g(x)≠0. 2.2 control objective the control objective is that the state vector of the above system, x(t), tracks the desired vector, xd(t)=[xd1(t) xd2(t) ... xdn(t)]t, which is known in [ , ∞). let the tracking error be: 1 1 2 2 1 2 ( ) ( ) ( ) [ ( ) ( ) ( ) ( ) ( ) ( )] [ ( ) ( ) ( )] d t d d n dn t n t t t x t x t x t x t x t x t e t e t e t        e x x   (2) to achieve the objective vector, a controller is designed such that tracking error satisfies the following equation: 0)()(lim)(lim   ttt dtt xxe (3) 2.3 afm system for nano manipulation model in this paper, after designing the controller for the system described by eq. (1), it is applied to a model of an afm system as a case study. the afm system is a well-known system that is widely used for nano manipulation in many industrial applications of nano technology. one of the goals in nano technology is to control material with high accuracy in nano dimensions in order to produce special materials and devices. thus, control of afm vibration behavior and construction of a micro-cantilever tip, which tracks a certain goal, is essential for particle manipulation in nano dimensions. the sharp tip of the afm is used for pressing, pulling, cutting, and indenting materials and surfaces. the afm includes a micro-cantilever, with a sharp tip at its end that is used for scanning the instance surface. figure 1 shows the structure used for this device. the afm cantilever is connected to a piezoelectric actuator with a photo detector. the photo diode provides a feedback signal for the controller by receiving a reflected laser beam to make the feedback from the cantilever deflection. the controller provides the input signal for the actuator based on the feedback signal received from the photo detector. the dynamics of the interaction of the micro-cantilever tip with the surface is proposed in [36, 37]. the main idea of the afm system is that the changes in vertical oscillation of the cantilever are measured when the vibrating tip scans the surface of the sample. the characteristics of the oscillation, such as frequency, amplitude, and phase, are recorded. in fact, while the sample is scanned using the vibrating tip, a feedback control loop adjusts the tip-sample separation to maintain the cantilever amplitude at a reference value [38]. iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 190 fig. 1: atomic force microscope (afm). in [39], the afm setup has been modeled as a mass-spring element in which the effect of the tip and the instant force has been obtained by molecular potential. this afm model can be considered as a special case of eq. (1) and is described using a nondimensionalized autonomous form as below: 1 2 22 1 2 1 1 2 ( , ) cos( ) ( )n n dx x dt dx x x h x f t u t dt y x              (4) where x1 and x2 are the position and speed of the cantilever tip and y is a measurement from the position of the cantilever tip while ωn is the natural frequency of the cantilever. ξ denotes the system damping, u(t) is the system control input and h is the interaction force between the surface and the cantilever tip. also, δ is a parameter for determining the distance between the instance and the equilibrium point from the cantilever tip in the absence of instance. finally, )cos( ~ tf  is the bounded external disturbance. a type of force that is usually used for modeling the interaction between a molecular pair is known as the lennard-jones potential [39] that is defined as follow: 1 2 2 8 1 1 1 max( ) ( ) ( , ) a a nomx xh x           (5) where a1 and a2 are constant parameters and δnom and δmax are the nominal value and the maximum value of δ respectively. this model demonstrates both attraction and repulsion intermolecular forces. parameter δ depends to the distance between the tip as a controller and the nano material and can be considered as an uncertainty in the model. 3. the proposed method 3.1 fast terminal sliding mode controller one of the main drawbacks of classical smc is that the control gain must be increased to compensate for the unknown dynamics of the system. moreover, this control method cannot guarantee the asymptotic convergence of the error. this means that the tracking error cannot converge to zero in finite time. to overcome this problem, the iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 191 ftsmc method is used instead of conventional smc. in this section, control of a class of nonlinear systems is introduced to track a desired trajectory based on ftsmc. consider a nonlinear system with uncertainty and disturbance in the form of eq. (1). the aim is that the state vector x(t) must track the objective vector xd(t). it is also assumed that |d(t)| ≤ δ1 and |f(x)| ≤ δ2 where δ1, δ2 > 0. the sliding surface is defined recursively as: 0 0 1 1 2 2 /0 1 0 0 0 0 /1 2 1 1 1 1 /2 1 2 2 2 2 n n q p q p q pn n n n n n ds s s s dt ds s s s dt ds s s s dt                       (6) where s0 = x1 xd1 and qi > pi , qi and pi are positive odd numbers and also αi ≥ 0 and βi ≥0, for i = 0, 1, ... , n-2 are the parameters of the sliding surface. for eq. (1), by considering the structure in eq. (6), if the control law u is designed as follow: 1 12 /1 11 1 0 ( ) ( ) ( ) ( ) ( )i i nn i n in q p d i i i i nn i n i n i d xd d u g x f x s s lsign s dt dt dt                         (7) where l > δ1+ δ2, then the states of the system (1) converges to the sliding surface, sn-1 = 0, in finite time, tn., then the tracking condition in eq. (3) can be satisfied. to prove this, consider the following lyapunov function: 2 1 1 2 n v s  its derivative is, 1 1 n n dsdv s dt dt   substitute eq. (7) into eq. (6), while considering the dynamics of eq. (1), we have: 2 2 3 3 2 2 2 /1 2 2 2 2 22 3 2 2 / /3 3 3 3 3 2 2 2 23 2 2 1 1 /0 1 1 ( ) ( ) ( ) ( ) ( ) ( ) n n n n n n i i q pn n n n n n q p q pn n n n n n n n n n n i n i q p i i i in n i n i i ds d s d d s s dt dt dt dt d s d d d d s s s s dt dt dt dt dt d s d d s s dt dt dt                                                        2 0 1 12 /1 1 1 0 1 ( ) ( ) ( ) ( ) ( ) i i n nn n i n in q pd i i i in n n i n i i n d xd x d d s s dt dt dt dt f d lsign s                              x x thus, we have: 1 1 1 2 1[ ( ) ( )] [ ( )] 0n n n dv f d x s l s l s dt            x iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 192 this shows that convergence to sn-1 = 0 will be satisfied in the following finite time [40]: )( )0( 21 1     l s t nn (8) ftsmc has attracted much attention because of its robustness against disturbance, noise, and uncertainty, and also due to its fast and finite-time convergence. however, ftsmc has some systematic drawbacks in real applications. some of these shortcomings are emerging chattering effect, the full-dependency of this method to the dynamic equations of the system and also the sensitivity of the method to noise when the input signal is very close to zero. therefore, in order to overcome these problems, a hybrid configuration of anfis and pid controller is used instead of the control law in eq. (7) to remove the chattering effect and also to remove the dependency of the controller to the accurate dynamic model of the system. 3.2 neuro-fuzzy fast terminal sliding mode control method in this section, the ftsmc method is extended by anfis in order to obtain an equivalent control through adaptation of the weights. accordingly, advantages of ftsmc and an adaptive controller design are combined into a neuro-fuzzy system. thus, a variable sliding surface is considered as the input of anfis and then the weights of the anfis are determined by an intelligent algorithm. 3.2.1 anfis structure both fuzzy logic and neural networks are model-free approximators that share their ability to deal with uncertainty and noise. fuzzy logic architecture can be converted to a neural network and vice versa. moreover, one can gain the benefits of both neural networks and fuzzy logic by combining these two methods. the network achieved by this method, similar to neural networks, possesses the capability of training and parameter adaptation. moreover, the obtained network has the ability inherent to fuzzy logic for interpreting in terms of linguistic variables. anfis is combination of neural network and fuzzy logic methods [22]. anfis network structure includes two parts. the first part involves an antecedent section, which is formed based on the if part of fuzzy rules. the second part involves the conclusion section, which is based on the then part of fuzzy rules. therefore, antecedent and conclusion parts are connected to each other as a network through fuzzy logic. these parts have some adjustable parameters that can be tuned, similar to weights in neural networks. the structure of anfis includes five layers as depicted in fig. 2. this figure illustrates one example of anfis structure that involves two inputs (x, y) and one output (z). there are four rules in the following form: if x is aj and y is bk then z=fi (for i=1,2,3,4 and j,k=1,2) where aj and bk are fuzzy sets with membership functions of ( ) ja x and ( ) kb x and fi is a linear function of x and y. iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 193 fig. 2 anfis structure with two inputs and one output the layers of the anfis are as follow:  layer 1: this layer is called the fuzzifier layer. this layer provides the membership functions (mfs) of each input. in this paper, triangular membership function is used as described in eq. (9). the parameters ai, bi, ci are the set of parameters that change the shape of the membership functions. parameters of this layer are called antecedent parameters. ( ) ( ; , , ) max(min( , ), 0), for 1, 2 ( ) ( ; , , ) max(min( , ), 0), for 1, 2 and 2 i i i i i i i j j i j j j j x a c x a i i i b a c a x a c x b j j j b a c a x trimf x a b c i x trimf x a b c i j i                   (9) the output of this layer can be written as: 2 1 1 ( ), for =1,2 ( ), for =3,4 i i i a i b o x i o x i      (10)  layer 2: this layer is called the rule layer. the rule layer indicates firing strength for each rule that is generated in fuzzifier layer. the output of this layer is: 2 ( ). ( ) 1, 2, 3, 4 and , 1, 2 j ki i a b o w x x i j k     (11)  layer 3: this layer is called the normalization layer. it normalizes the firing strength for each input. this normalization is the ratio of the i-th rule firing strength to the total firing strength as defined in eq. (12): 3 1 2 3 4 1, 2, 3, 4ii i w o w i w w w w       (12)  layer 4: this layer is called the defuzzifier layer. the output of each node in this layer is achieved by multiplying a polynomial with normalized firing strength and is calculated as below: 4 ( ) 1, 2, 3, 4i i i i i i io w f w m x n y l i     (13) the output of this layer is normalized. also, mi, ni and li in this layer denote the conclusion parameters.  layer 5: this layer is called the summation layer. this layer is obtained from the sum of all received signals. the overall output of anfis becomes: overall output 1, 2, 3, 4 i i i i i w f i i w i z w f i      (14) iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 194 3.2.2 neuro-fuzzy control scheme in this section, in order to remove the chattering effect, anfis is used for nonlinear mapping approximation between the terminal nonlinear sliding surface and the control output. the neuro-fuzzy network used in this paper has one input (sn-1) with five membership functions and one output (u) as depicted in fig. 3. fig. 3: anfis structure with single input and single output. five fuzzy rules are of the following form: if sn-1 is ai then u=mix +li (for i=1,...,5) where ai are fuzzy sets with membership functions of ( ) ia x with antecedent parameters of ai, bi and ci, and mi and li are conclusion parameters. the main problem in this neuro-fuzzy network is to tune the entire parameters of this algorithm to obtain the best value with stable convergence property. the training method i anfis is mostly based on the gradient. in the gradient method, due to its complicated calculation at each iteration, the convergence of the parameters is very slow and is dependent to the initial value of the parameters. also, the chained derivative rules used in this method may lead to local minimum and finding the best learning gain is very difficult. here, a method is proposed for updating all parameters that is simpler and faster than the descending gradient method. according to the lyapunov theorem, the nonlinear sliding surface of the terminal sliding must satisfy the condition sn-1ṡn-1 ≤ 0. to satisfy the lyapunov condition, an intelligent algorithm, namely the bee algorithm, is used for tuning the parameters such that the best value with the stable convergence property can be achieved. this algorithm determines the best weights wi, fi to obtain sn-1ṡn-1 ≤ 0. also, in the proposed method the initial value of the parameters and the learning rate is not required. the intelligent control scheme for controlling the system (1) is depicted in fig. 4. during this procedure, the best value of the antecedent and conclusion parameters of anfis are achieved through the bee algorithm. also, a nfftsmc has a poor performance in the beginning of the control operation, thus a pid controller is used to improve the control performance in this period and to have a total acceptable performance. after a short period of time, pid is replaced by nfftsmc controller and the output of pid controller (upid) is reduced to zero. iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 195 fig. 4: block diagram of the proposed nfftsmc system. according to fig. 4, total control input is as below: anfispidtotal uuu  (15) the bee algorithm is utilized to tune the coefficients of both the pid controller and the anfis antecedent and conclusion parameters. as a result, the bee algorithm will optimize all unknown parameters in utotal. 3.3 combining nfftsmc and bee algorithm one of the important challenges in anfis is its training and parameter updating. in this section, we propose a simple and fast method for updating the parameters of anfis. 3.3.1 bee algorithm the bee algorithm [41] is inspired from behavior of the honey bee in nature. in this algorithm, bees are divided into three categories: employed bees, onlooker bees, and scout bees. employed bees bring nectar from the explored source. these bees bring information such as distance, direction, and profitability of a location to the hive and share it with other bees. onlooker bees use a complex communication system. this system enables them to obtain information about the location and quality of nectar which is outside the hive. communication between the bees is performed by a dance called waggle dance that includes information about the quality, location, and position of the food source. scout bees search randomly for the food in the vicinity of the hive. these bees move from one location to another randomly. bees need high energy for flying. thus they try to find the shortest and the best path among swarms of flowers. in evolutionary algorithms, the main goal is the minimization of the objective function. this algorithm searches for the optimal points in the search space with inspiration from the bees’ dance. each point in the search space is considered as a food source. the scout bee randomly searches the space through a fitness function and by sampling from visited locations and ranking them in terms of quality. other bees search the best points ranked by fitness function. the bees of the algorithm promise the best solution and minimization of the cost function according to the measurement of the cost function. in the space dedicated to the solution interval defined as u={xrn; mini < xi < maxi; i=1, 2, ... , n} and a fitness function as f(x):u→r, each solution candidate is defined as a n-dimensional variable x=[x1, ... , xn]. table 1 shows the parameters in the bee algorithm. iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 196 table 1: parameters of bee algorithm parameter description ns number of scout bees ne number of elite sites nb number of best sites nre recruited bees for elite sites nrb recruited bees for remaining best sites ngh initial size of neighborhood the algorithm can be described as below [41]: a constant population of scout bees, ns, is selected. then, this population is randomly and uniformly spread throughout the solution space. each scout bee evaluates its position according to the fitness function, and then the algorithm enters into the main loop which includes four steps. at the end, the algorithm stops when the stopping criterion is met. ns is the visited site, and it is ranked according to the fitness information obtained by the scout bee. then, nb sites with best fitness (the measured minimums by the objective function) are chosen, for local exploration. this local exploration is performed by a class of other bees, called foragers, that steer to the vicinity of the site chosen by the scout bees. for each chosen location, the number of allocated foragers is defined as below: each scout bee that comes back from one of the best chosen sites, nb, performs a waggle dance that attracts foragers for a local search. for each ne first top-rated elite site that a scout bee visited, among nb best available sites, nre forager bees are sent to search in the neighborhood of these sites. then, for each nb-nre remaining sites, where nrb ≤ nre, forager bees are sent for searching in that vicinity. according to the above method, most of the bees are allocated for searching in sites with the highest fitness. thus, a local search is performed with more accuracy in the vicinity of elite sites that are hopefully sites of the search space for finding the optimal solution. the bees, employed by a scout bee, are located randomly with uniform distribution in the neighborhood of the specified site with high fitness. this flower patch is specified as an n-dimensional vector of sites to the center of the scout bee site. for each flower patch, the fitness of each visited site by an employed bee is evaluated. if the fitness of one of the employed bees is more than that of the scout bee, the selected bee is chosen as the new scout bee. in the end, the best bee (with maximum fitness) is achieved from each patch. in the global search process, ns-nb bees are spread randomly in the search space of the new flower patch. selection of scout bee in a random process is for exploring better sites by bee algorithm. at the end of each iteration, a new population of the bee colony is composed of two groups. the first group includes nb scout bees corresponding to the center (the best available solution) of each flower patch and denotes the local search. the second group includes ns-nb scout bees corresponding to solutions that are generated randomly and denotes the global exploration. the stopping criterion depends on the problem dimensions and can be a threshold considered for fitness such that if a site satisfies this condition, then it can be introduced as the optimal site. it can also be considered as a prescribed number of full cycles (for a certain number of algorithm iterations). figure 5 shows the flowchart of the bee algorithm. 3.3.2 training nfftsmc based on the bee algorithm the goal of designing nfftsmc is to obtain a control law, u, such that it can steer all the states of an uncertain nonlinear system (1) to the sliding surface s in finite time iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 197 fig. 5: flowchart of the bee algorithm. without chattering. to achieve this goal, a fast terminal sliding surface is first calculated, and then intelligent anfis is gained to obtain the control law u. the advantage of combining such methods is the appropriate chattering-free control action in the presence of bounded external disturbances and uncertainties. in the conventional anfis training methods, input-output data is usually required. however, in the proposed method, intelligent bee algorithm is used in on-line mode, and therefore, the best values of the anfis parameters are obtained, without any information about the system input and output. also, to help the anfis controller in the beginning of the control operation, a pid controller is utilized as depicted in fig. 4. as an initial time elapses, the control law of this controller converges to zero, as shown in fig. 6. fig. 6: control effort of the pid. 0 2 4 6 8 10 -40 -30 -20 -10 0 time (s) pi d c on tr ol in pu t iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 198 in this section, training and updating anfis and pid controllers, using a bee algorithm, is explained. anfis involves three antecedent parameters, ai, bi and ci and two conclusion parameters, mi and li for each fuzzy rule. thus, the total number of parameters is equal to the parameters associated with all fuzzy rules. in fig. 3, anfis includes five rules and each rule involves three antecedent parameters and two conclusion parameters. therefore, fifteen parameters are optimized in the antecedent part of anfis, and ten tunable parameters are adjusted in the conclusion part of anfis. on the other hand, there are three tunable parameters in a pid controller kp, ki and kd that must be obtained by bee algorithm. as a result, a bee algorithm is utilized in this paper to tune the antecedent and conclusion parameters in anfis and pid coefficients. thus, there are twenty eight tunable parameters in this controller that are determined by bee algorithm. 4. simulation results the proposed method is applied to the model of an afm described by eq. (4). the simulation results are performed in matlab/simulink. to obtain the nano manipulation goals, the cantilever tip of the afm must be able to strongly track a reference signal in the presence of uncertainties and disturbances. in this simulation, the unit step and periodic pulse inputs are considered as the reference signals. the pulse input oscillates between 0.8 and 1.2 with a period of 10 s. the parameters of the system described in eq. (4) are considered same as [42], i.e.: 1 ,2 ~ ,2.1 ,8.0 ,66.3 ,148.0 ,02.0 ,1 maxnom21  fen  (16) where δ is an uncertain parameter with a nominal value δnom and maximum value δmax (δnom < δ < δmax). first, conventional smc is applied to this model with uncertainty and disturbance. the results for the unit step and periodic pulse inputs are shown in fig. 7. it can be seen that chattering occurs for the control input signal. however, the output follows the inputs favorably. although the satisfactory results for this condition, as smc cannot guarantee a finite-time convergence, it is quite possible that for different conditions, a long time may be required for convergence. at the next step, the ftsmc method is used to solve the problem of finite time asymptotic stability. similarly, the ftsmc method is applied to this model with uncertainty and disturbance. the simulation results are illustrated in fig. 8. according to fig. 8, the output converges to the reference signals in less time in comparison with the smc method. also, ftsmc guarantees finite time asymptotic stability, but the control input signal still has chattering. in ftsmc, by appropriate selection of the sliding surface parameters, fast responses can be achieved. however, reducing the convergence time in this method may lead to chattering in the control signal, as can be observed in fig. 8. in order to remove the chattering effect, an anfis+pid control scheme is applied to this model with uncertainty and disturbance. the simulation results of pure anfis are illustrated in fig. 9. as can be seen from this figure, the results reveal less chattering compared with smc and tsmc, but the tracking performance is getting worse. in fact, without exact adjustment in the parameters of anfis, it may be difficult to achieve satisfactory tracking performance. moreover, the pure anfis cannot guarantee the stability condition and acceptable performance especially at the beginning of the operation [10]. it can be observed that the response performance of anfis is not desirable enough when the periodic pulse signal is applied as the reference input. therefore, the anfis iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 199 (a) (b) (c) (d) fig. 7: simulation results for conventional smc (a) tip position for step reference input (b) control input for step reference input (c) tip position for periodic pulse reference input (d) control input for periodic pulse reference input. (a) (b) (c) (d) fig. 8: simulation results for ftsmc (a) tip position for step reference input (b) control input for step reference input (c) tip position for periodic pulse reference input (d) control input for periodic pulse reference input. 0 2 4 6 8 10 0.5 1 1.5 2 2.5 3 time (s) ti p po si tio n (n m ) 0 2 4 6 8 10 -10 -5 0 5 10 15 20 time (s) co nt ro l i np ut (n n ) 0 5 10 15 20 25 30 0.5 1 1.5 2 2.5 3 time (s) tip p os it io n (n m ) 0 5 10 15 20 25 30 -40 -20 0 20 40 time (s) co nt ro l i np ut ( nn ) 0 2 4 6 8 10 0.5 1 1.5 2 2.5 3 time (s) ti p po si tio n (n m ) 0 2 4 6 8 10 -20 -10 0 10 20 time (s) co nt ro l i np ut (n n ) 0 5 10 15 20 25 30 0.5 1 1.5 2 2.5 3 time (s) ti p po si tio n (n m ) 0 5 10 15 20 25 30 -20 -10 0 10 20 time (s) co nt ro l i np ut (n n ) iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 200 (a) (b) (c) (d) fig. 9: simulation results for the anfis controller (a) tip position for step reference input (b) control input for step reference input (c) tip position for periodic pulse reference input (d) control input for periodic pulse reference input. controller by itself is not able to completely track sudden changes in the reference signal, and the system performance may be deteriorated. however, by exactly adjusting its parameters, a better performance can be attained. finally, the nfftsmc method is applied to overcome all shortcomings of the aforementioned methods. in fact, by combining these methods, finite time asymptotic stability, together with stability requirements and acceptable performance, can be obtained. also, the chattering effect is removed completely. moreover, due to the application of one input variable in the nfftsmc network, the number of fuzzy rules is less than other fuzzy-based method. also, fast convergence is obtained in comparison with previous methods. the simulation results of nfftsmc in fig. 10 verify these statements. it can be seen that the tip position tracks rapidly with the desired reference inputs and the proposed controller makes the effect of uncertainty and disturbance negligible. in addition, due to the use of anfis, it provides a chattering-free control action. the simulations reveal that the presented method has better tracking performance with negligible chattering in control action when compared with the other control methods. for comparison of all methods, the responses on unit step and periodic pulse reference signals are depicted in fig. 11. responses of all controllers are performed in the presence of the same uncertainty and disturbance as modeled in eq. (4). as can be seen from this figure, the value of overshoot for the anfis controller, due to its weak stabilty, is more than the other controller. it has been improved using the proposed nfftsmc. on the other hand, comparing the response time of the controllers, it can be stated that the proposed nfftsmc has a best response speed among the controllers. as expected, ftsmc converges more quickly than smc, but there is significant chattering in the control action (as shown in figs. 7 and 8). in the proposed nfftsmc, due to the use of 0 2 4 6 8 10 0.8 1 1.2 1.4 1.6 1.8 2 time (s) tip p os it io n (n m ) 0 2 4 6 8 10 -15 -10 -5 0 5 10 time (s) co nt ro l i np ut ( nn ) 0 5 10 15 20 25 30 0 0.5 1 1.5 2 time (s) ti p po si tio n (n m ) 0 5 10 15 20 25 30 -15 -10 -5 0 5 10 time (s) co nt ro l i np ut (n n ) iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 201 the bee algorithm for adjusting anfis parameters, the poor performance of anfis is improved while the control action is smoother than the other controllers. hence, the proposed method is obviously more efficient in comparison with the other control techniques, because of its acceptable control performance. (a) (b) (c) (d) fig. 10: simulation results for nfftsmc (a) tip position for step reference input (b) control input for step reference input (c) tip position for periodic pulse reference input (d) control input for periodic pulse reference input. (a) (b) fig. 11: comparison of the outputs of smc, ftsmc, anfis and nfftsmc (a) tip position for step reference input (b) tip position for periodic pulse reference input. 5. concluding remarks in this paper, a nfftsmc method has been proposed for a class of nonlinear systems to remove the chattering effect, to have finite-time asymptotic convergence, and to reduce fuzzy rules. in this method, an anfis network has been proposed to approximate between the terminal nonlinear sliding surface and the control law. a bee algorithm has been also used in this paper, which is fast and simple compared with the conventional descending 0 2 4 6 8 10 0.8 1 1.2 1.4 1.6 1.8 2 time (s) ti p po si tio n (n m ) 0 2 4 6 8 10 -20 -15 -10 -5 0 5 10 time (s) co nt ro l i np ut (n n ) 0 5 10 15 20 25 30 0.8 1 1.2 1.4 1.6 1.8 2 time (s) ti p po si tio n (n m ) 0 5 10 15 20 25 30 -20 -10 0 10 20 time (s) co nt ro l i np ut (n n ) 0 2 4 6 8 10 0.5 1 1.5 2 2.5 3 time (s) ti p po si ti on ( nm ) smc ftsmc anfis nfftsmc 0 5 10 15 20 25 30 0 0. 5 1 1. 5 2 2. 5 3 time (s) ti p po si ti on ( nm ) smc ftsmc anfis nfftsmc iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 202 gradient method. in fact, by using the intelligent bee algorithm, all weights of the neurofuzzy network have been optimized such that the stability condition, sn-1ṡn-1 ≤ 0, has been satisfied. the simulation results of the nfftsmc method, for an afm model, illustrate the effectiveness of the proposed control scheme and verify that the chattering effect has been totally removed in comparison with conventional smc and ftsmc. also, faster convergence has been observed with respect to other methods. in fact, by combining ftsmc with anfis, finite time asymptotically stability and acceptable performance have been achieved. moreover, due to application of one input variable in nfftsmc, the number of fuzzy rules is less than fuzzy-based methods. therefore, compared with the other conventional controllers, the proposed control method has advantages in the aspect of convergence time, chattering, implementation cost, response performance, and robustness. in this paper, the proposed controller has been applied to a mathematical model of afm using software simulations. future research will include experimental implementation of the proposed control method for a real application of the afm system. references [1] slotine jje, li w. (1991) applied nonlinear control. prentice-hall inc., new jersey. [2] utkin iv. (1992) sliding mode in control optimization. springer-verlag, new york. [3] iordanov n, surgenor bw, choi yh. (1997) experimental evaluation of the robustness of discrete sliding mode control versus linear quadratic control. ieee trans. control sys. tech., 5(2):254-260. [4] lee sh, park jb. (2007) terminal sliding mode control of nonlinear chaotic systems using self-recurrent wavelet neural network. proc. int. conf. control, automation and system, 1671-1676. [5] man z, paplinski ap, wu hr. (1994) a robust mimo terminal sliding mode control scheme for rigid robotic manipulators. ieee trans. autom. control, 39:2464-2469. [6] man z, yu xh. (1997) terminal sliding mode control of mimo linear systems. ieee trans circuits syst. i: fundam. theory appl., 44:1065-1070. [7] yu xh, man z. (1996) model reference adaptive control systems with terminal sliding modes. int. j. control, 64:1165-1176. [8] bartolini g, ferrara a, usani e. (1998) chattering avoidance by second-order sliding mode control. ieee trans. autom. control, 43(2):241-246. [9] levant a. (2007) principles of 2-sliding mode design. automatica, 43(4):576-586. [10] wang lx. (1993) stable adaptive fuzzy control of nonlinear systems. ieee trans. fuzzy syst., 1(2):146-154. [11] sarailoo m, rahmani z, rezaie b. (2012) fuzzy sliding mode control for hyper chaotic chen system. adv. electrical computer eng., 12:85-90. [12] wong lk, leung fhf, tam pks. (2001) a fuzzy sliding controller for nonlinear systems. ieee j. indust. electronics, 48(1):32-37. [13] khari s, rahmani z, rezaie b. (2016) designing fuzzy logic controller based on combination of terminal sliding mode and state feedback controllers for stabilizing chaotic behaviour in rod-type plasma torch system. trans. inst. meas. control, 38(2):150-164. [14] tao cw, taur ls, chan ml. (2004) adaptive fuzzy terminal sliding mode controller for linear systems with mismatched time varying uncertainties. ieee trans. syst. man. cybern., 34(1):255-262. [15] nekoukar v, erfanian a. (2011) adaptive fuzzy terminal sliding mode control for a class of mimo uncertain nonlinear systems. fuzzy sets syst., 179(1):34‐49. [16] xu ssd, liu yk. (2014) study of takagi‐sugeno fuzzy‐based terminal‐sliding mode fault‐ tolerant control. iet control theory appl., 8(9):667-674. [17] khari s, rahmani z, rezaie b. (2016) controlling chaos based on a novel intelligent integral terminal sliding mode control in a rod-type plasma torch. chinese phys. b, 25(5), 050201:1-12. iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 203 [18] lhee cg, park js, ahn hs, kim dh. (2001) sliding mode like fuzzy logic control with self-tuning the dead zone parameters. ieee trans fuzzy syst., 9(2):343-348. [19] zhang x, su h, chu j. (2003) adaptive sliding mode-like fuzzy logic control for high order nonlinear systems. proc. ieee conf. on intelligent control, 788-792. [20] hwang jh, kwak hj, park gt. (2011) adaptive interval type-2 fuzzy sliding mode control for unknown chaotic system. nonlinear dyn., 63:491-502. [21] benbrahim m, essounbouli n, hamzaoui a. (2013) adaptive type-2 fuzzy sliding mode controller for siso nonlinear systems subject to actuator faults. int. j. autom. computing, 10 (4):335-342. [22] jang js. (1993) anfis: adaptive-network-based fuzzy inference system. ieee trans. syst. man. cybern., 23(3):665-685. [23] shoorehdeli ma, teshnehlab m, sedigh ak. (2009) training anfis as an identifier with intelligent hybrid stable learning algorithm based on particle swarm optimization and extended kalman filter. fuzzy sets syst., 160:922-948. [24] shoorehdeli ma, teshnehlab m, sedigh ak. (2009) identification using anfis with intelligent hybrid stable learning algorithm approaches. neural computing appl., 18(2):157174. [25] shoorehdeli ma, teshnehlab m, sedigh ak. (2007) novel hybrid learning algorithms for tuning anfis parameters using adaptive weighted pso. proc. ieee conf. on fuzzy system, 1-6. [26] shoorehdeli ma, teshnehlab m, sedigh ak, khanesar ma. (2009) identification using anfis with intelligent hybrid stable learning algorithm approaches and stability analysis of training methods. appl. soft computing, 9(2):833-850. [27] ghomsheh vs, shoorehdeli ma, teshnehlab m. (2007) training anfis structure with modified pso algorithm. proc. mediterranean conf. on control and automation,1-6. [28] chatterjee a, watanabe k. (2006) an optimized takagi-sugeno type neuro-fuzzy system for modeling robot manipulators. neural computing appl., 15(1):55-61. [29] lin cj, hong sj. (2007) the design of neuro-fuzzy networks using particle swarm optimization and recursive singular value decomposition. neurocomputing, 71(1):297-310. [30] cus f, balic j, zuperl u. (2009) hybrid anfis-ants system based optimisation of turning parameters. j. achievements materials, 36(1):79-86. [31] gunasekaran m, ramaswami ks. (2011) a fusion model integrating anfis and artificial immune algorithm for forecasting indian stock market. j. appl. sci., 11:3028-3033. [32] masumpoor s, yaghobi h., khanesar ma. (2015) adaptive sliding-mode type-2 neurofuzzy control of an induction motor. exp. syst. appl., 42(19):6635-6647. [33] li q, zhang w, han g, yang y. (2014) adaptive neuro-fuzzy sliding mode control guidance law with impact angle constraint. iet control theory appl., 9(14):2115-2123. [34] cerman o, husek p. (2012). adaptive fuzzy sliding mode control for electro-hydraulic servo mechanism. exp. syst. appl., 39(11):10269-10277. [35] manceur m, essounbouli n, hamzaoui a. (2012) second-order sliding fuzzy interval type-2 control for an uncertain system with real application. ieee trans. fuzzy syst., 20(2):262275. [36] ashhab m, salapaka mv, dahleh m, mezic i. (1999) dynamical analysis and control of micro-cantilevers. automatica, 35:1663-1670. [37] basso m, bagni g. (2004) controller synthesis for stabilizing oscillations in tapping-mode atomic force microscopes. proc. ieee int. symp. computer aided control systems design, 372-377. [38] pishkenari hn, jalili n, meghdari a. (2006) acquisition of high-precision images for noncontact atomic force microscopy. mechatronics, 16(10):655-664 [39] basso m, giarre l. (2000) complex dynamics in harmonically excited lennard-jones oscillator: microcantilever-sample interaction in scanning probe microscopes. asme j. dyn. syst. meas. control, 122:240-245. [40] yu x, man z. (2002) fast terminal sliding-mode control design for nonlinear dynamical systems. ieee trans circ. syst., 49(2):261-264. iium engineering journal, vol. 17, no. 2, 2016 nikoo et al. 204 [41] pham dt, koc e, ghanbarzadeh a, otri s, rahim s, zaidi m. (2006) the bees algorithm a novel tool for complex optimisation problems. in intelligent production machines and systems. edited by pham dt, eldukhri ee, soroka aj. elsevier ltd, cardiff, uk, 454-459. [42] sadeghpour m, salarieh h, alasty a. (2013) controlling chaos in tapping mode atomic force microscopes using improved minimum entropy control. appl. math. modelling, 37(3):1599-1606. microsoft word 67-741-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 noh et al. 10 numerical investigation of chocked converging-diverging nozzles for thruster application m.h.m. noh , a.h.a. hamid, r. atan and h. rashid faculty of mechanical enineering, university technology mara (uitm), 45400 shah alam,selangor, malaysia. mhafiz_noh@yahoo.com ____________________________________________________________________ abstract:the need for low-thrust propulsion systems for small scale spacecraft is growing. low thrust characteristics generally lead to low reynolds number flows from propulsive devices that utilize converging-diverging nozzle. in the present work, seven choked converging-diverging nozzle flow characteristics operating at reynolds number of 46000 are numerically investigated using a commercial software fluent 6.1.22. computational work is carried out using axisymmetric flow spalart-allmaras model, twodimensional, axisymmetric, coupled solver and linearized using implicit scheme. the nozzles, which are intended to be used for thruster application, have a throat diameter of 11 mm and an area ratio of 4. all six nozzles are derived from a nozzle with divergence angle of 28°, where the divergence angle is reduced while maintaining the area ratio. the main objective of this work is to investigate the performance and flow characteristic of nozzles with different geometry. numerical findings show that there is thrust reduction observed as the divergence angle reduces from 28° to 10°, except for nozzle with divergence angles of 16° and 18°, where they produce thrusts higher than their derivative one. numerical result also reveals that the flow separation phenomenon occurs inside all nozzles, where normal shock forms inside nozzles with divergence angle of 20°, 14° and 10°, and this shock degrades the performance of the nozzle in term of the thrust produced. abstrak: keperluan sistem kuasa kipas tujahan rendah bagi pesawat angkasa berskala kecil makin meningkat. umumnya ciri-ciri tujahan rendah membawa kepada aliran nombor reynolds yang rendah dari alat dorongan yang menggunakan muncung tumpu-capah. buat masa ini, tujuh muncung cekik tumpu-capah beroperasi pada nombor reynolds 46000 telah dikaji menggunakan perisian komersil fluent 6.1.22. kerja pengiraan dijalankan dengan menggunakan model aliran simetri sepaksi spalart-allmaras, dua dimensi, simestri sepaksi, penyelesai terganding dan dilinearkan menggunakan skim tersirat. muncung tersebut, yang tujuannya adalah untuk digunakan dalam aplikasi penujah, mempunyai lubang berdiameter 11 mm dan bernisbah luas 4. kesemua enam muncung diterbitkan daripada satu muncung dengan sudut capahan 28°, dimana sudut capahan telah dikurangkan sementara nisbah keluasan dikekalkan. tujuan utama penyelidikan ini adalah untuk mengkaji prestasi dan ciri aliran muncung yang berbeza geometri. hasil kajian menunjukkan bahawa kuasa tujahan menurun apabila sudut capahan dikurangan dari 28° ke 10°, kecuali muncung bersudut capahan 16° dan 18°, yang menghasilkan kuasa tujahan lebih tinggi berbanding muncungmuncung terbitan yang lain. keputusan berangka juga menunjukkan bahawa fenomena pemisahan aliran berlaku di dalam kesemua muncung, dimana kejutan normal terjadi di dalam muncung dengan sudut capahan 20°, 14° dan 10°, dan kejutan ini mengurangkan prestasi muncung tersebut dari segi kuasa tujahan yang dihasilkan. ____________________________________________________________________ keywords: flow separation; normal shock wave; divergence angle; supersonic nozzle iium engineering journal, special issue, mechanical engineering, 2011 noh et al. 11 1. introduction aerospace propulsion system is a system in which the fundamental principle obeys newton’s laws, namely that force is proportional to rate of change of momentum, and that action and reaction are equal and opposite [1]. thrust chamber is one example of a system that works using these laws besides other systems i.e. turbojet and ramjet. thrust chamber is a system that provides thrust by expelling stored matter, called the propellant. this thrust can range from mega-newton to milli-newton. thrust chamber system can be main spacecraft propulsion i.e. rocket engine, auxiliary spacecraft propulsion, satellite launcher, missile launcher, assist-take-off engines for airplanes and even ejection of crew escape capsules. small thrusters are usually used as secondary spacecraft propulsion system in which some of the functions are attitude control, spin control, stage separation and station keeping. liquid propellant thrust chamber generally consists of injector, combustion chamber and convergent-divergent (c-d) nozzle or delaval nozzle. propellant is injected through an injector and burned in combustion chamber and produces hot gases. the gases move towards the nozzle throat at a subsonic flow. this process continues until there is enough pressure builds up to force a part of them out of a nozzle throat at supersonic velocity. a carefully designednozzle’s divergence part is vital as it will determine the overall efficiency of the thruster. the movement of gases through the nozzle results in the conversion of heat energy into kinetic energy, or energy of motion. figure 1 shows schematic diagram of typical liquid propellant thrust chamber with the three major zones within the combustion chamber. they are:  injection/atomization zone  rapid combustion zone  stream tube combustion zone fig. 1: schematic diagram of typical liquid propellant thrust chamber. the purpose of the thruster nozzle is to increase the acceleration of the gases as they leave the rocket and thereby maximizing the thrust.nozzle is basically characterized by the configuration, i.e. geometrical shapes of nozzle’s divergent portion (bell, conical or trumpet), the divergence angle and the area ratio (ratio of nozzle exit area to the throat area). selection of “correct” nozzle configuration is very important as it will improve the overall performance rapid combustion zone in je ct or atomization / mixing zone stream tube combustion zone acceleration/ supersonic flow combustion region with subsonic flow divergent angle divergent length iium engineering journal, special issue, mechanical engineering, 2011 noh et al. 12 of the thrust chamber.however, the best nozzle configuration depends on several factors and also fabrication capabilities and cost involved. 2. nozzle configuration and its association with overall performance pearson, landrum and hawk [2] have done numerical investigation on performance losses in small thrust chamber nozzles. they found that the viscous effect was the largest contributor to performance loss amongst two other losses mechanisms; chemical kinetics loss and divergence loss. this result further strengthens the research finding by grisnik and smith [3]. numerical results also showed that the viscous loss mechanism is the most sensitive to the nozzle downstream geometry variations, i.e. the divergence angle which largely determines the rate of expansion of the flow. the effect of viscous is reduced when the divergence angle is low and the flow was allowed to expand more gradually. to understand this, one must realize that viscous loss is contributed by two factors: viscous drag on the nozzle walls and flow blockage due to boundary layer growth. in the latter case, the high divergence angle produces thicker viscous boundary layer and smaller inviscid core flow which will “block” the stream. in the former case, a low divergence angle will reduce the nozzle's wetted surface. they reported that a specific impulse gain of 130 seconds was predicted by a numerical code when the divergence angle was reduced from the baseline value of 45° to20°. lowering the divergence angle also leads to another desirable effect: decrease in chemical kinetic loss [2]. it is also reported that this performance gain is offset slightly by the increase in divergence loss with decreasing divergence angle. it is because a large divergence angle allows the flow to expand quickly and hence more time for axial turning of the flow. the divergence losses are almost eliminated by increasing the diverging angle to 65° [2]. lengthening the nozzle is also an alternative, though this may increase the viscous loss since the nozzle’s wetted surface increase and there is also an increase in nozzle weight to a point that it is not practical for mission considerations. more recent research by ketsdever, clabough, gimelshein and alexeenko [4] have proved that shortening the nozzle resulted in higher axial flow velocities at the nozzle exit plane caused by asmaller impact of the viscous layer. they also found contradicting results where the viscous effect wasminimum at the largest divergence angle. numerical analysis showed that there was an increase in specific impulse when the divergence angle was doubled from 20° to 40°. this numerical data had proved the previous experimental results obtained by whalen [5], where it is found that 25° conical nozzle had slightly better efficiency, at lower reynolds number as compared to 20° conical nozzle. 3. flow separation phenomenon flow separation inside supersonic nozzle is almost impossible to be avoided for a fixed nozzle configuration. flow separates fully from the nozzle wall due to the presence of an oblique shock wave, which is also known as separation shock wave that originates from the nozzle wall and is directed towards the nozzle centerline. this separated shear layer flows as a free jet and it is termed as free shock separation (fss) since no reattachment occurs downstream of separation location [6]. by definition, oblique shock wave is a shock wave iium engineering journal, special issue, mechanical engineering, 2011 noh et al. 13 which is inclined to the flow direction inside the nozzle and it is formed from the nozzle wall due to the induced adverse pressure gradient [7]. reverse flow region exists at the downstream of the separation location in which the ambient air is being sucked into the nozzle due to the effect of the separated flow. another type of flow separation is restricted shock separation (rss) where the separated flow is then reflected towards the wall by the radial momentum of the separated jet which is directed towards the wall, forming a cap-shock pattern [8]. during real operation, there will be transition from fss structure to rss structure when the pressure ratio increases, as discussed by östlund [7] and nebbache and pilinski [9]. separated flow inside the nozzle is undesirable as transition of flow separation structure from fss to rss will produce side load to nozzle wall which may present life-limiting constraints on both the nozzle itself and other engine components [6, 7, 10 and 11]. furthermore, flow separation phenomena tend to reduce the nozzle efficiency, i.e. thrust produced [8]. in this study, seven different nozzles went through the performance testing and all nozzles were designed with the same configuration which is conical convergent-divergent and same throat diameter of 11 mm. the varied parameters are divergence angle and divergence length. 4. materials and methods the computational work was carried out to investigate the performance of seven different nozzles in term of flow characteristics. six nozzles are derived from a nozzle with divergence angle of 28°, where the divergence angle is reduced while maintaining the same area ratio. table 1summarizes the nozzles dimensions. the detail of fluid property is summarized in error! reference source not found.. table 1: tested nozzles dimensions. nozzle divergence angle (°) divergence length (mm) 1 28 22.1 2 24 25.9 3 20 31.2 4 18 34.7 5 16 39.1 6 14 44.8 7 10 62.9 all nozzles were modeled and meshed using gambit 2.1.6[14, 15], then, it is solved by fluent software [14, 15]. fluent software was chosen to solve the flow problem since several researchers had used this cfd software and found that the theoretical data provided gives a good agreement with experimental data [12, 13]. since the nozzles have a circular crosssection, it is reasonable to assume that the flow is axisymmetric. so the nozzles geometry was created in two-dimensional. fig.1 shows the typical geometry and grid distribution inside the iium engineering journal, special issue, mechanical engineering, 2011 noh et al. 14 nozzle. the grid density is higher in the divergent part of the nozzle and clustered at the nozzle exit to improve the resolution for capturing shocks. table 2: fluid properties. property units method value(s) density kg/m3 ideal-gas cp(specific heat) j/kg-k constant 1006.43 molecular weight kj/kmol constant 28.966 l-j characteristics length angstrom constant 3.711 l-j energy parameter k constant 78.6 thermal expansion coefficient 1/k constant 0 fig.1:grid distribution inside nozzle 1. for solving the problem, computational work was carried out using a two-dimensional, axisymmetric, coupled solver (which solves the governing equations of continuity, momentum, and energy simultaneously) and linearized using a implicit scheme to predict the performance of the thrust chamber nozzles. coupled solver was used since it is recommended when dealing with applications involving high speed compressible flows and the governing equations was linearized using implicit scheme since it will generally converge much faster than the explicit solver [14]. spalart-allmaras model was used as a turbulence model as it is designed specifically for aerospace applications involving wall-bounded flows and has been shown to give good results for boundary layers subjected to adverse pressure gradients [15]. furthermore, charmeau and anghaie [16] cited that this one-equation model has shown good accuracy in the analyses of converging-diverging nozzles. boundary conditions are imposed as follows: pressure and temperature at the nozzle inlet are set to be p = 500 kpa and t= 3400 k respectively to model the combustion pressure and temperature. the nozzle outlet pressure and temperature were set at 100 kpa and 2490 k respectively. the simulation was initially conducted with the initial guess values to be the ones at the inlet. iium engineering journal, special issue, mechanical engineering, 2011 noh et al. 15 5. results and discussion computed mach number contours for these nozzles are shown in fig. 2. the black circle on the figure indicates the position of the normal shock at the symmetry axis and the open circle indicates the position of the reflection of the internal shock at the symmetry axis. a) b) c) d) e) f) g) position of the normal shock at the symmetry axis position of the reflection of the internal shock at the symmetry axis fig. 2 :mach number contour, (a)nozzle 1, (b)nozzle 2, (c)nozzle 3, (d)nozzle 4, (e)nozzle 5, (f)nozzle 6, and (g)nozzle 7. it can be seen from fig. 2a and 3b that the normal shock wave (represented by the brown line) forms at the outside of the nozzle. a normal shock is a very thin region, perpendicular to the direction of a supersonic flow, through which the flow suddenly changes from supersonic to subsonic. this thin region is also known as mach disc. the position of the normal shock wave at the symmetry axis moves upstream as the divergence angle was reduced until it is located inside the nozzle, as shown in fig. 2c. at this point, the normal shock wave forms at the inside of the nozzle. further reduction in divergence angle was caused the reflected shock wave (represented by the green line) intersected with the separation shock wave (represented by the blue line) at the outside of the nozzle, and this was believed to be a reason why the normal shock wave is formed at the outside of the nozzle, as shown in fig. 2d and 3e. at the same time, the position of the normal shock wave at the symmetry axis moves upstream until it is located at the inside of the nozzle again, causing the normal shock wave to form at the inside of the nozzle, as shown in fig. 2f and 3g. iium engineering journal, special issue, mechanical engineering, 2011 noh et al. 16 numerical result also reveals that the thrust produced by the nozzle depends on the flow characteristics inside it. table 1 summarizes the expected thrust produced by all nozzles. table 1: expected thrust for all nozzles. nozzle thrust (n) nozzle divergence angle (o) thrust reduction (%), ∆thrust 1 45.08 28 0 2 37.13 24 17.6 3 31.69 20 29.7 4 49.60 18 10 5 50.81 16 12.7 6 32.52 14 27.9 7 31.01 10 31.2 based on this thrust data, it was observed that the nozzles where normal shock wave formed inside it had the lowest thrust produced, which is nozzle 3, nozzle 6 and nozzle 7 as compared to other nozzles. it is due to the fact that the flow at the exit plane of these nozzles is dominated by the subsonic core (fig.4). this subsonic core has led to a low average gas velocity at the exit plane and hence the thrust produced. the thrust data also shows that reducing the divergence angle from 28° to 24° while maintaining the area ratio reduces the thrust by 17.6 %. the thrust reduction is due to the increase in divergence loss with decreasing divergence angle. it is because a small divergence angle allows the flow to expand slowly and hence less time for axial turning of the flow. the thrust reduction is also due to the increment of nozzle’s wetted surface as a result of lower divergence angle, which may results in higher viscous loss. however, there is a contradicting result showed by nozzle 4 and nozzle 5. a slight increment in thrust, which is 2.4 %, was observed as the divergence angle reduced from 18° to 16°. this contradiction can be explained as follows: the viscous loss is reduced when the divergence angle is low since low divergence angle produces thinner viscous boundary layer and larger inviscid core flow which will increase the velocity of the outgoing stream. furthermore, lowering the divergence angle also tend to reduce the chemical kinetic loss [2]. it is also important to mention that nozzle 4 and nozzle 5 produce thrusts higher than their derivative one. referring to fig. 3, the location of flow separation at the nozzle wall move downstream as the divergence angle is reduced to 18° and the point of separation moves upstream further as the divergence angle is reduced to 16°. as a result, the volume of the reverse flow region decreases and the supersonic flow cross sectional area at the exit plane %100x thrust thrustthrust thrust control controlnozzle   iium engineering journal, special issue, mechanical engineering, 2011 noh et al. 17 becomes larger. this explains why nozzle 4 and nozzle 5 produce thrusts higher than their derivative one. furthermore, the location of normal shock wave depends on local pressure. the adverse pressure gradient creates the normal shock wave and the separation points plays an important role in determining the location of the normal shock wave. figure 3 :mach number contour of nozzle 6 fig.4:mach number contour of nozzle 6. 6. conclusions a total of seven nozzles with different divergence length and divergence angle were numerically investigated. one main conclusion is that formation of normal shock wave inside the nozzle reduces the thrust produced by the nozzle. the thrust reduction observed is as high as 36 %. results also reveal that reducing the nozzle’s divergence angle from 28° to 24° while maintaining the area ratio decreasesthe thrust produced by approximately 18 %. in contrast, reducing the nozzle’s divergence angle from 18° to 16° while maintaining the area ratio causes unnoticeable gain in thrust, which is less than 3 %. an analysis of flow characteristic inside all nozzles leads to a conclusion that separation of flow from nozzle wall cannot be eliminated by reducing the divergence angle while maintaining the area ratio. in addition, an increase in viscous loss reduces the strength of normal shock inside the nozzle. acknowledgement the authors would like to acknowledge and thank the almighty god, all colleagues that contributed either direct or indirectly to this research, to faculty of mechanical engineering, university technology of mara and all the members in this project especially mr. ahmad hussien abdul hamid. subsonic core 2.8 8 1.0 0 0.0 05 iium engineering journal, special issue, mechanical engineering, 2011 noh et al. 18 references [1] d. g. shepherd, aerospace propulsion (american elsevier publishing company, inc., 1972). [2] j. b. pearson, d. b. landrum, and c. w. hawk, “parametric study of solar thermal rocket nozzle performance,” nasa technical memorandum 111354, (1994). [3] s. p. grisnik and t. a. smith, “experimental study of low reynolds number nozzles,” nasa technical memorandum 89858, (1987). [4] a. d. ketsdever, m. t. clabough, s. f. gimelshein, and a. alexeenko, “experimental and numerical determination of micropropulsion device efficiencies at low reynolds numbers,” aiaa journal (43), 1-10 (2005). [5] m. v. whalen, “low reynolds number nozzle flow study,” nasa technical memorandum 100130, (1987). [6] s. b. verma, r. stark, and o. haidn, “relation between shock unsteadiness and the origin of side-loads inside a thrust optimized parabolic rocket nozzle,” journal of aerospace science and technology, 1-10 (2006). [7] j. östlund, “flow processes in rocket engine nozzles with focus on flow separation and sideloads,” royal institute of technology department of mechanics s-100 44 stockholm, sweden, tech. rep. (2002). [8] r. l. bayt, “analysis, fabrication and testing of a mems-based micropropulsion system,” ph.d. thesis, massachusetts institute of technology, (1999). [9] a. nebbache and c. pilinski, “pulsatory phenomenon in a thrust optimized contour nozzle,” journal of aerospace science and technology,295-308 (2006). [10] j. östlund, “supersonic flow separation with application to rocket engine nozzles,” royal institute of technology department of mechanics s-100 44 stockholm, sweden, tech. rep. (2004). [11] m. almqvist, “semi-empirical model for supersonic flow separation in rocket nozzles,” m.s. thesis, lulea university of technology, sweden, (2005). [12] a. raheem and v. babu, “numerical simulations of unsteady flows in solid rocket motors,” proceedings of 10th aiaa / ceas aero acoustics conference, aiaa 2004-2878, 1-15 (2004). [13] v. h. rapp, j. jacobsen, m. lawson, a. parker, and k. chen, “design, construction and testing of a desktop supersonic wind tunnel,” american journal of undergraduate research (4), 1-10 (2005). [14] fluent tutorial guide, modeling external compressible flow,fluent inc., (2003). [15] fluent user’s guide, modelling turbulence, fluent inc., (2003). [16] a. charmeau and s. anghaie, “a hybrid fine-coarse computational mesh simulation tool for space nuclear systems,” in proceedings of the space nuclear conference, (2005). microsoft word 66-190-1-rv completed.docx iium engineering journal, special issue, mechanical engineering, 2011 abdul hamid et al. 1 spray cone angle and air core diameter of hollow cone swirl rocket injector ahmad hussein abdul hamid, rahim atan, mohd hafiz mohd noh and helmi rashid faculty of mechanical engineering, university technology mara, 40450, shah alam, selangor, malaysia. hussein@salam.uitm.edu.my abstract:fuel injector for liquid rocket is a very critical component since that small difference in its design can dramatically affect the combustion efficiency. the primary function of the injector is to break the fuel up into very small droplets. the smaller droplets are necessary for fast quiet ignition and to establish a flame front close to the injector head, thus shorter combustion chamber is possible to be utilized. this paper presents an experimetal investigation of a mono-propellant hollow cone swirl injector. several injectors with different configuration were investigated under cold flow test, where water is used as simulation fluid. this investigation reveals that higher injection pressure leads to higher spray cone angle. the effect of injection pressure on spray cone angle is more prominent for injector with least number of tangential ports. furthermore, it was found that injector with the most number of tangential ports and with the smallest tangential port diameter produces the widest resulting spray. experimental data also tells that the diameter of an air core that forms inside the swirl chamber is largest for the injector with smallest tangential port diameter and least number of tangential ports. abstrak:injektor bahan api bagi roket cecair merupakan satu komponen yang amat kritikal memandangkan perbezaan kecil dalam reka bentuknya akan secara langsung mempengaruhi kecekapan pembakaran. fungsi utama injektor adalah untuk memecahkan bahan api kepada titisan yang amat kecil. titisan kecil penting untuk pembakaran pantas secara senyap dan untuk mewujudkan satu nyalaan di hadapan, berhampiran dengan kepala injektor, maka kebuk pembakaran yang lebih pendek berkemungkinan dapat digunakan. kertas kerja ini mebentangkan satu penyelidikan eksperimental sebuah injektor ekabahan dorong geronggang kon pusar. beberapa injektor dengan konfigurasi berbeza telah dikaji di bawah ujian aliran sejuk, di mana air digunakan sebagai bendalir simulasi. kajian ini mendedahkan bahawa suntikan bertekanan tinggi menghasilkan sudut semburan kon yang besar. kesan tekanan suntikan ke atas sudut semburan kon lebih ketara pada injektor yang mempunyai lubang tangen yang kurang tambahan pula, injektor yang mempunyai jumlah lubang tangen yang paling banyak dan lubang tangen berdiameter paling kecil menghasilkan semburan yang paling lebar. data eksperimental juga menunjukkan bahawa diameter teras udara terbesar terhasil di dalam kebuk pusar injektor yang mempunyai diameter lubang tangen terkecil dan jumlah lubang tangen yang paling kurang. keywords: swirl spray;air core diameter;spray cone angle; rocket injector iium engineering journal, special issue, mechanical engineering, 2011 abdul hamid et al. 2 1. introduction propellant injector is one of the most crucial part in liquid propellant rocket as it will determine the overall combustion efficiency and thrust produced. the main function of rocket injector is to atomize the fuel to a very fine droplets. it is known that one of the methods to improve combustion effiency of liquid fuel is to reduce the droplet size and hence to improve the quality of atomization [1]. the injector is the swirl type, where the propellant enters the swirl chamber at tangential component of velocity. there are several reasons of selecting a spray type fuel injector instead of a impinge type. first it will produce smaller fuel droplets that are readily vaporized and enhance mixing with the oxidizer, thus making the combustion process more efficient. the finely atomized liquid kerosene also expands the exposed surface which is necessary for easy ignition and to establish a flame front close to the injector face, thus a shorter combustion chamber is possible to be utilized. the larger droplets take longer time to burn and thus a longer combustion chamber is required, i.e. extra cost. comparative analysis of different types of injectors shows that swirl injectors have strong advantages over other types of injectors [2]. secondly, the fuel spray will provide liquid film cooling by means of excess fuel at the chamber inner wall. the excess fuel will form a thin layer of fluid over the wall and hence reduce the heat transfer to the gas-side wall of the combustion chamber. lastly, the spray type injector will produce high radial velocity component of propellant which will increase the resident time of fuel in the combustion chamber that allow more time for the propellant to mix and burn. since only fuel is introduced into combustion chamber through this injector, it is considered as a mono-propellant type injector. the advantage of a mono-propellant injector lies on its simple, compact design which allows placement of the oxidizer and fuel injectors nearby to provide better mixing [2]. the other type of jet-swirl injector is a dual-propellant swirl injector, where both fuel and oxidizer is premixed in the swirl chamber and it is not to be discussed in detail. in the injector, propellant is forced under high pressure to enter a swirl chamber through a set of tangential ports to create a high rotational velocity within the swirl chamber. hence, the atomizer is also called a swirl injector. the propellant then moves forward out of the orifice in the form of a tube. the tube becomes a cone shaped film of propellant as it emerges from the orifice, ultimately stretching to a point where it ruptures and throws off finely atomized and sufficiently diffused droplets for adequate mixing with the oxidizer. fig. 1 shows a schematic of the swirl injector geometry and also illustrates the spray pattern. due to tangential entry, an air-cored vortex flow of liquid takes place in the nozzle and the liquid comes out of the orifice in the form of hollow cone spray. it is noted that in the hollow cone spray, the concentration of droplets is at the outer edge with little or no fuel at the center. hollow cone spray injector has a wide application in spacecraft injector [3]. this paper summarizes injector testing effort that evaluated a swirl injector using water as the working fluid. the injector is intended to introduce the flow into the combustion chamber before impinge with oxidizer. in other words, the injector provides external mixing, which prevent the oxidizers from penetrating the fuel supply line through the entire parts of injector elements. iium engineering journal, special issue, mechanical engineering, 2011 abdul hamid et al. 3 fig. 1: schematic sectioning of hollow cone swirl injector. a number of injectors of geometrical shape as shown in fig. 1 with different physical dimensions were fabricated from perspex. the geometrical dimensions of the injectors tested are given in table 1. table 1 injector’s specification. injector number no. of tangential port, n tangential port diameter, dp (mm) swirl chamber diameter, ds (mm) orifice diameter, do (mm) 1 2 1 30 2 2 3 3 4 4 5 5 6 6 4 2 7 3 rv zv v swirl chamber air core orifice spray droplet tangential port  sd ad od iium engineering journal, special issue, mechanical engineering, 2011 abdul hamid et al. 4 2. literature review most of the works available in the literature in the area of liquid atomization intended to predict the characteristics of swirl injector towards a better fundamental understanding of liquid atomization phenomena.two important performance parameters are the spray cone angle and air core diameter that produced from the swirl injector. the size of the air core determines the effective flow area at the discharge orifice and thus controls the coefficient of discharge, which is one of the most important parameter of atomizer [4]. another important performance parameter is the spray cone angle that determine the coverage and dispersion of spray in the surrounding ambiance or combustion chamber. laryea and no [1] have studied the relationship between applied voltage and injection pressure on liquid breakup length and spray angle of charge-injected electrostatic pressure swirl nozzle. they reported that an increase in applied voltage and injection pressure increases the value of spray cone angle. recently, an experimental investigation on the breakup length and spray cone of swirl spray with different injection pressure had been done by hussein and atan [5]. they concluded that higher injection pressure leads to wider spray cone angle. however, at higher injection pressure, the injectors experience slight decreases in spray cone angle as the liquid film at the injector outlet contracted. earlier numerical investigation done by datta and som [4] have found that with the increase in the liquid flow rate at its lower range there occurs a sharp increase in spray cone angle but it become independent at the high range of flow rate (q > 1 ×105 m3 s−1). this result is in agreement with the work of halder, dash and som [3]. they observed that the spray cone angle remain almost constant with the reynolds number of the flow at inlet to the injector. 3. experimentation all injectors were cold-tested using water at room temperature to define the pressure drop and spray pattern characteristics. an experimental test rig was constructed to measure the spray cone angle and air core diameter for different injection pressure. a schematic diagram of the test rig is shown in fig. 2. compressed air was used to pressurize the water tank. the supply water pressure was controlled by a single ball valve and measured by bourdon type pressure gauge. the volume flow rate of the water was varied according to injection pressure. the injector nozzle is mounted downward on a vertical plane, so that the water spray is injected directly into a basin at the ambient condition. a cold flow injection test is an alternative to static firing test, where the original propellants are replaced by a simulated fluid which can be water or other liquids. it is a preliminary investigation of the swirl injector performance. the advantage of cold flow test is that the pure fluid atomization, jet break-up and jet stability of swirl injection can be identified and distinguished easily compared to more complex injection and chemical reaction of the firing test. figure 3 shows the typical photograph taken during cold flow test and the experimental setup. it is important to understand the characteristics of the resulting spray field as it has a significant impact on the combustion stability as well as the propulsion efficiency iium engineering journal, special issue, mechanical engineering, 2011 abdul hamid et al. 5 [6]. large-amplitude combustion oscillations lead to performance degradation, unacceptable noise levels, and structural damage. fig. 2: line diagram of the experimental setup. fig. 3: typical image of cold flow test. 4. results and discussion a fully developed spray was formed for all injectors at the highest tested injection pressure of 7 bar, as shown in fig. 4. the results of spray cone angle at different injection pressure and number of tangential ports is given in fig. 5. referring to the figure, it can be concluded that an increase in injection pressure increased the spray cone angle. it was also observed that the injector with the most number of tangential ports produced the widest spray for all injection pressure. this is because injector with more tangential port has the highest azimuthal velocity component which tends to widen the liquid film. however, for injector with 4 tangential ports, an additional tangential port does not increase the spray cone angle significantly for all tested ad iium engineering journal, special issue, mechanical engineering, 2011 abdul hamid et al. 6 pressure range. furthermore, it can be seen that at an injection pressure higher than 4 bar, the spray cone angle is almost uninfluenced by the injection pressure. injector 1 injector 2 injector 3 injector 4injector 5 injector 6 injector 7 fig. 4: typical photographs at injection pressure of 7 bar. the results of spray cone angle at different injection pressure and number of tangential ports is given in fig. 5. referring to the figure, it can be concluded that an increase in injection pressure increased the spray cone angle. it was also observed that the injector with the most number of tangential ports produced the widest spray for all injection pressure. this is because injector with more tangential port has the highest azimuthal velocity component which tends to widen the liquid film. however, for injector with 4 tangential ports, an additional tangential port does not increase the spray cone angle significantly for all tested pressure range. furthermore, it can be seen that at an injection pressure higher than 4 bar, the spray cone angle is almost uninfluenced by the injection pressure. fig. 5: effects of injection pressure and number of tangential ports on spray cone angle. it is also important to mention that there are no spray cone angle readings taken for injector with 2 and 3 tangential ports at lower range of injection pressure. it is because the sprays are not fully developed at low injection pressure. take injector 2 for example, at injection pressure of 1 bar, the spray is in distorted pencil form and the spray is in onion stage at injection pressure of 2 bar. at injection pressure of 3 bar, both injector 2 and injector 3 produces tulip stage spray (fig. 6). 0 10 20 30 40 50 60 1 2 3 4 5 6 7 injection pressure (bar) sp ra y c on e a ng le ( °) . 2 tangential ports 3 tangential ports 4 tangential ports 5 tangential ports 6 tangential ports iium engineering journal, special issue, mechanical engineering, 2011 abdul hamid et al. 7 injector 2 injector 3 1 bar 2 bar 3 bar 3 bar fig. 6: different stages of sprays. figure 7 shows the relationship between air core diameter, number of tangential ports and injection pressure. in general, air core diameter increased with an increase in injection pressure. this occurrence may be due to the increased azimuthal velocity of water stream exiting from the tangential ports with an increase of injection pressure, which subsequently increase the tendency for larger air core diameter. furthermore, greater number of tangential ports leads to larger air core diameter at injection pressure less than 4 bar. however, at injection pressure higher than 4 bar, injector with 3 tangential ports produces larger air core diameter as compared to the one with 4 tangential ports. the reason is that less number of tangential ports at higher injection pressure contributes to higher swirling strength of flow inside the injector and hence developing larger air core diameter. fig. 7: effects of injection pressure and number of tangential ports on air core diameter. the relationship between spray cone angle, tangential port diameter and injection pressure is presented in fig. 8. it can be seen that widest spray is produced by the injector with smallest tangential port for all injection pressure tested. this trend of variation can be attributed to the fact that the stream from the larger tangential ports increase the resistance offered by the injector to the swirling motion inside it and finally results in lower value of spray cone angle. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1 2 3 4 5 6 7 injection pressure (bar) a ir c or e d ia m et er ( m m ) . 3 tangential ports 4 tangential ports 5 tangential ports 6 tangential ports iium engineering journal, special issue, mechanical engineering, 2011 abdul hamid et al. 8 fig. 8: effects of injection pressure and diameter of tangential ports on spray cone angle. furthermore, a larger tangential port is accompanied by an increase in stream flow rate into the swirling chamber. that is why the diameter of air core developed is smallest inside the injector with largest tangential port (refer to fig. 9). it is also can be concluded that the air core diameter is almost uninfluenced by injection pressure for small tangential port. it should be noted that there is no air core diameter readings is recorded for 3 mm tangential port diameter at injection pressure lower than 4 bar due to very low swirling strength of flow inside the injector and thus causes the air core to vibrate. the uncertainty of measurements is high under this condition. fig. 9: effects of injection pressure and diameter of tangential ports on air core diameter. 5. conclusions a cold flow test was conducted to evaluate the performance of hollow cone swirl injectors which is to be applied as rocket injector. a total of 49 cold flow tests were completed with two injector parameters varied, which are number of tangential port and diameter of tangential port. injector performance was based upon spray cone angle and air core diameter as a function of injection pressure. it can be concluded that higher injection pressure leads to wider spray cone angle and larger air core diameter. furthermore, the effect of injection pressure on spray cone angle is more prominent for injector with least number of tangential ports. 0 10 20 30 40 50 60 1 2 3 4 5 6 7 injection pressure (bar) sp ra y c on e a ng le ( °) . 1 mm 2 mm 3 mm 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 1 2 3 4 5 6 7 injection pressure (bar) a ir c or e d ia m et er (m m ) . 1mm 2mm 3mm iium engineering journal, special issue, mechanical engineering, 2011 abdul hamid et al. 9 in overall, injector with the most number of tangential ports produces widest resulting spray and smallest air core diameter. it can also be concluded that injector with the smallest tangential port diameter produces the widest spray cone angle and largest air core diameter. acknowledgement the ministry of higher education (mohe) kindly provided funding for the research through the "fundamental research grant scheme" (frgs) project no 600-rmi/st/frgs 5/3/fst (125/2010). references [1] g. n. laryea and s.y. no, “spray angle and breakup length of charge-injected electrostatic pressure-swirl nozzle. journal of electrostatics, pp. 37–47, 2003. [2] y.i. khavkin, “theory and practice of swirl atomizers”. taylor & francis, new york, 2004. [3] m. r. halder, s. k. dash, and s. k. som, “a numerical and experimental investigation on the coefficients of discharge and the spray cone angle of a solid cone swirl nozzle”. experimental thermal and fluid science, vol. 28, pp. 297–305, 2004. [4] a. datta and s. k. som, “numerical prediction of air core diameter, coefficient of discharge and spray cone angle of a swirl spray nozzle”. international journal of heat and fluid flow, vol. 21, pp. 412-419, 2000. [5] a. hussein and r. atan, “spray characteristics of jet–swirl nozzles for thrust chamber injector”. aerospace science and technology, vol. 13, pp. 192–196, 2009. [6] m. r. soltani, k. ghorbanian, m. ashjaee and m. r. morad, “spray characteristics of a liquidliquid coaxial swirl atomizer at different mass flow rates”. journal of aerospace science and technology, pp. 592-604, 2005. nomenclature ds swirl chamber diameter mm da air core diameter mm do orifice diameter mm dp tangential port diameter mm n number of tangential port v velocity m/s ψ spray cone angle r in radial direction z in axial direction θ in azimuthal direction microsoft word pape-v4-2-3 new.doc iium engineering journal, vol. 4, no. 2, 2003 t. subramaniam et al. 31 comparison: simulation and experimental characterisation of an all-optical gainclamped erbium-doped fibre amplifier t. subramaniam, m. a. mahdi, p. poopalan, and h. ahmad photonics laboratory, department of physics, university of malaya 50603 kuala lumpur, malaysia. e-mail: sth_34@yahoo.com abstract: this paper presents the gc-edfa characteristics comparison between the simulated results (using edfa_design software) and experimental results. the comparisons reveal the usefulness of the software in simulating the behaviour of an alloptical gc-edfa system. comparisons are made for values obtained from the system operated at high laser power, in order to highlight the differences between the experimental and simulated values. the main objective for this comparison is to prove the capability of the software in simulating the gain-clamped system. therefore, the software can be used to test new configurations, aimed at improvising current gainclamped edfa performances. key words: optical, gain-clamping, erbium, fibre amplifier, simulation, experiment 1 introduction the all-optical gain-clamped erbium-doped fibre amplifier was first introduced in 1991 by m. zirngibl [1]. it is designed to solve the slow and undesirable gain fluctuations due to saturation effects in edfa that occurs when the edfa is used in networking and switch applications involving on/off-keyed packets or a multiplicity of wdm channels that are randomly turned on and off. the all-optical gain-clamped erbium-doped fibre amplifier is an erbium-doped fibre amplifier (edfa) designed with a cavity (either ring or fabry-perot type). this device generates laser by utilising the amplified spontaneous emission (ase) within the system in order to maintain the amplifier gain at a fixed value, independent of the input signal power. this feature also known as the gain linearization, is described by constantg p p in s out s == (1) this holds for any input signal power falling in a given dynamic range [2]. the gcedfa based on ring type cavities are more favourable, since the fabry-perot cavity is subject to; (a) spatial hole burning, causing inhomogeneous depletion of inversion in the laser medium and (b) strong mode competitions thus, is less stable [3]. an interesting ring-based gc-edfa configuration is the counter-propagating gc-edfa, which is proposed by kobayashi and muro [4]. it features elimination of laser from at the iium engineering journal, vol. 4, no. 2, 2003 t. subramaniam et al. 32 amplifier’s output. this set-up is configured in such a way that the circulation of the lasing signal is in the opposite direction of the input signals, thus preventing the laser from being emitted at the system’s output end. the design is shown below in fig. 1. fig. 1: counter-propagating gc-edfa configuration this paper presents for the first time, comparison between gc-edfa characteristic values based simulations using the edfa_design version 2.0 and actual experimental values. the edfa_design from optiwave corporation is one of the programs for basic edfa design and offers accurate algorithms for simulations. it is designed to model the physical parameters of the set-up easily [5]. earlier, this software was tested and evaluated for standard edfa performances in the laboratory. the software accurately predicts the gain, noise figure and gain spectrum profiles accurately. the accuracy is much higher in the high pump and low signal region, less than 3% discrepancy. following this success, the software was then used to simulate the gc-edfa system. the accuracy of these simulations is discussed below by comparing the simulation results with actual experimental values. comparisons are made for values very high laser power, with clamped gain value of about 12 db. the strong clamping effect will highlight any obvious discrepancies between the experimental and simulated values. 2 results and discussion the comparisons between the simulated results and the experimental results displayed below include the gain and noise figure performances, the gain spectrum and the amplifier output profile. these comparisons are made in an effort to validate the capability of the edfa_design software in simulating results for a gc-edfa system. as a result, this software can be further used to test new designs of the gain-clamped system aimed towards designing an optimized gc-edfa system. optimized gc-edfa should display sufficiently high clamped gain with high critical input power, low noise figure and does not exhibit laser at the output end. wdm opm attenuator tls ld wdm osa13m edf circulator tbf optical attenuator circulator iium engineering journal, vol. 4, no. 2, 2003 t. subramaniam et al. 33 a. gc-edfa gain -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 pump power (mw) g ai n (d b ) simulation experiment fig. 2: comparison between simulated and experimental gain versus pump power profile the comparison between the experimental and the simulated gain versus pump power profile is shown in fig. 2 for input signal power of 0 dbm. there are two obvious differences between the simulated and the experimental results. first, the pump power value indicating the onset of the laser is different. the experimental results indicate that the clamping effect was onset at around 9 mw, whereas the simulated results indicates that the clamping effect was onset at higher pump power around 14 mw. second, the simulated results are slightly higher than the actual experimental results. it is also important to note that the simulated values show ideal clamping effect with absolutely no gain variation in the clamped region whereas, the actual experimental values shows a slight increase as the pump power increases. the experimental clamped gain value is measured to be lower than the simulated clamped gain value by 2.2 db. this difference is reduced to 0.7 db at large input signal power showing a subtle gain increment of 1.5 db over the 13 mw to 109 mw pump power range. comparison between the experimental gain versus input signal profile and the simulated profile shown in fig. 3 also shows the non-idealistic behaviour of experimental gain. a difference of 0.7 db is observed for input signal power of –40 dbm and it increases as the input signal power increases. at 0 dbm, the difference between the experimental and the simulated gain reach up to 1.2 db. the actual experimental clamped gain values however, show a slight gain decrement of 0.5 db as the input signal power was increased from –40 dbm to 0 dbm. on the other hand, the simulated values show ideal clamping effect, where the gain is fixed at 13.3 db throughout the whole range of the input signal power of up to 0 dbm. iium engineering journal, vol. 4, no. 2, 2003 t. subramaniam et al. 34 fig. 3: comparison between simulated and experimental gain versus input signal power profile b. gc-edfa noise figure performance the similarity between the measured noise figure values as well as the simulated noise figure profiles against the pump power is shown in fig. 4. the noise figure differences observed between the experimental and simulated values does not show significant variation across the various pump power values. however, the experimental noise figure value of around 5.5 db is slightly lower than the simulated noise figure value, which is about 5.9 db. this is caused by the difference between the cavity loss in the simulation and the experimental set-up as mentioned earlier. figure 5 shows that the 0.4 db difference in the experimental and simulated noise figure value at input signal power of –40 dbm remains the same for input signal power of up to –15 dbm. the experimental noise figure for input signal power beyond –15 dbm shows an exponential growth, whereas the simulated noise figure remains constant throughout this region. the exponential noise figure growth in the experimental values occurs due to the source spontaneous emission from the signal source. the noise figure at 0 dbm reaches up to a maximum value of 9.2 db. the signal source in the simulation software is an ideal source, thus there is no source spontaneous source that can degrade to noise figure. the simulated noise figure values remains constant right up to -5 dbm input signal power. 0 2 4 6 8 10 12 14 16 18 20 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 input signal power (dbm) g ai n (d b ) simulation experiment iium engineering journal, vol. 4, no. 2, 2003 t. subramaniam et al. 35 0 1 2 3 4 5 6 7 8 9 10 0 10 20 30 40 50 60 70 80 90 100 110 120 pum p power (m w ) n oi se f ig ur e (d b ) experim ent sim ulation fig. 4: comparison between simulated and experimental noise figure versus pump power profile fig. 5: comparison between simulated and experimental values noise figure versus input signal power profile 0 2 4 6 8 10 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 input signal power (dbm) n oi se f ig ur e (d b ) simulation experiment iium engineering journal, vol. 4, no. 2, 2003 t. subramaniam et al. 36 c. gc-edfa gain spectrum fig. 6: comparison between simulated and experimental gain spectrum the gain spectrum of the experimental values as well as of the simulated values for input signal power of –40 dbm and pump power 109 mw is shown to be almost identical by fig. 6. although discrepancies between the experimental and the simulated values do exist, the differences observed is very small (less than 1 db) and it varies as the signal wavelength changes. the difference variation across the signal wavelength is small. d. gc-edfa output profile a wavelength (nm) experiment simulation fig. 7: comparison between simulated and experimental amplifier output 0 2 4 6 8 10 12 14 16 18 20 1520 1525 1530 1535 1540 1545 1550 1555 1560 1565 1570 wavelength (nm) g ai n (d b ) simulation experiment -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 1525 1530 1535 1540 1545 1550 1555 1560 1565 1570 1575 wavelength (nm) a se a t a m pl if ie r o ut pu t ( db m simulation iium engineering journal, vol. 4, no. 2, 2003 t. subramaniam et al. 37 the gc-edfa output profile measured and the gc-edfa output spectrum simulated at pump power of 109 mw shown in fig. 7 is almost identical. the 13 db difference between the simulated and the experimental ase levels is similar to the observations for standard edfa. this however, does not cause significant error in the measurement of the gc-edfa characteristic values. both the results show that the back-reflections in the system prevent total elimination of the laser at the output. the laser power level at the output is different, similar to the forward ase results. 3 conclusion the above comparisons show that the edfa_design software version 2.0 simulates the laser controlled counter-propagating gc-edfa system with high accuracy. this means that the software can be used to simulate various gc-edfa designs and to design an optimised gc-edfa system. simulations of the system gain as well as the noise figure values depict excellent consistency with experimental results. the only obvious discrepancy between the experimental and the simulated results is shown by the noise figure versus input signal power profile in the region of the large input signal power, which however, can be compensated by incorporating the influence of the signal to noise ratio (snr) degradation of the signal for the large signal power values. comparison of the experimental and simulated gain spectrum also depicts excellent consistency. the change in spectrum as compared to the standard edfa gain spectrum has also been simulated with high accuracy. 4 references [1] m. zirngibl, “gain control in erbium-doped fibre amplifiers by an all-optical feedback loop,” electron. lett., vol. 27, no. 7, pp. 560 – 561, march 1991. [2] e. desurvire, “erbium-doped fiber amplifiers: principles and applications,” john wiley & sons, canada, p. vi, preface, p. 421, chapter 5, p. 469, chapter 6, 1994. [3] d.r. hall, and p.e. jackson, “the physics and technology of laser resonator,” p. 62, chapter 4, 19. [4] m. kobayashi, and s. muro, “gain stabilisation in erbium doped fiber amplifier with optical feedback loop using circulators,” in tech. dig. oecc ’98, pp. 98 – 99, 1998. [5] m.m. kozak, r. caspary, and u.b. unrau, “computer aided edfa design, simulation and optimization,” proc. of 3rd int. conf. on transparent optical networks 2001, pp. 202 – 204, 2001. microsoft word 4-paper 49 asad.doc iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 45 wear behavior of woven roving aramid / epoxy composite under different conditions asad a. khalid department of mechanical engineering, faculty of engineering , international islamic university malaysia, jalan gombak, 53100 , malaysia email: asad@iiu.edu.my abstract: wear behavior studies of aramid woven roving /epoxy composite has been conducted. sliding the material against smooth steel counter face under dry and lubricated with oil conditions has been investigated. powder of silicon carbide has been mixed with the epoxy resin and tested also. the powder was mixed in a volumetric fraction of 10% with the epoxy resin. four laminates of six layers were fabricated by hand lay up method. a pin on disc apparatus has been fabricated to conduct the sliding wear tests on specimens of (4 mm  4 mm  12 mm) in size have been cut from the four laminates. the effect of sliding condition including dry, lubricated, dry with additives and lubricated with additives have been studied. wear rate tests have been conducted at different sliding speeds and loads. results show that the wear characteristics are influenced by the operating conditions and the construction of the composite material used. it was also found that the wear of aramid /epoxy composite onto the steel counter face were significantly reduced by using lubricant and additives but still took place. keywords: wear, composite materials, woven roving aramid, epoxy, additives, lubricant. 1. introduction the continuing growth in the scope of applications of fiber reinforced composites in various industries has provided considerable incentive for the study of tribological aspects of composite behavior. friction and wear resistance are not intrinsic material properties but are complex functions of a large number of external parameters (sliding velocity, normal load, environment, geometry, etc.) of the physical and mechanical properties of wearing and counterface materials. tribological studies on composite materials have focused attention on the effect of fiber type and orientation, load, matrix resin type, sliding speed, etc., on friction and wear behavior of composites [1-9]. otherwise, the studies of friction and wear have focused on polymeric composites (unidirectional reinforcing fibers). also, wear have been studied on fiber-reinforced composites of different matrix resins and fiber volume fraction sliding under dry conditions against a metallic counter face. wear behavior of glass woven roving/ modified phenolic composites has been studied by vishwanath et iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 46 al. [5]. theyconcluded that the volumetric wear rate increased non linearly with both the sliding velocity and normal load. aramid fibers have the lowest specific gravity and highest tensile strength to weight ratio but the lowest strength at high temperatures [10,11]. among the current reinforcing fibers, aramid fibers and as reinforcement, are being used in many marine and aerospace applications and helmets. where light-weight, high tensile strength, resistance to impact and better chemical and thermal stability is necessary. besides that, aramid fibers become more and more important as structural materials. thus, it is necessary to study and to improve its wear resistance. throughout this research, experimental wear tests have been carried out for woven roving aramid/epoxy composite. the volumetric wear rates were taken for dry, lubricated, dry with additive, and lubricated with additives specimens. wear equipment (pin on disc apparatus) was fabricated to study the effect of different sliding conditions at different speeds and different loads. 2. material properties 2.1 woven roving fiber and matrix specification laminates of aramid plain woven roving fabric shown in fig. 1, were supplied by ocf owens corning (usa). epoxy resin mixed with hardener in a volumetric ratio of 1:0.25 was used as a matrix material. the properties of the fiber and matrix used are shown in table 1. fig. 1: aramid fiber. iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 47 table 1 properties of fiber and its matrix. 2.2 composite laminates the epoxy resin type leco 811-164 , and hardener type leco 811-166 were used for this investigation. the aramid fiber volume fraction was 0.65. woven roving aramid fiber with epoxy resin plies of 300 mm x 300 mm were fabricated by hand lay-up of six layers of aramid woven roving fabrics cured at a room temperature of 32o c for 24 hours. the resin was filled with 10% in volume of particles of silicon carbide additive. specimens of rectangular cross-section of 4 mm x 4 mm, and 20 mm length were cut from the composite laminates and used for the wear tests. the reinforcements placed in parallel with respect to the sliding plane. samples of the fabricated specimens are shown in fig. 2. the initial weight of the specimens were in the range of 10 to 10.45 g. the properties of woven roving aramid/epoxy composite specimens are shown in table 2. fig. 2: sample of woven roving aramid/epoxy composite specimens. properties aramid fiber matrix (epoxy resin with hardener) density, ρ (g/ cm3) 1.45 g/cm3 1.14 g/ cm3 ultimate tensile strength, σu 3.8 gn/mm2 0.07 gn/ mm2 modulus of elasticity, e 131 gn/ mm2 7 gn/ mm2 iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 48 table 2: properties of fiber and its matrix. 3. experimental set up pin on disc apparatus as shown in figure 3, was designed and fabricated to carry out the sliding wear tests under dry and lubricated conditions. the schematic diagram of the pin on disc apparatus is shown in fig. 4. as shown, the specimen (1) is mounted on an adjustable holder (2). normal load on the specimen can be applied by placing dead weights (3) on the specimen holder (4). a horizontal holder (5) has the ability to extend and to move vertically on a vertical arm (6). a rubbing disc (7) is mounted on a shaft (8). the shaft is supported by two ball bearings. a v-belt (9) and two pulleys (10) were used to transfer the motion from an electric motor (11) to the shaft. the motor is connected to a speed controller to obtain different sliding velocities. a gear box (12) of speed ratio 1:10 is connected to the motor by a flexible coupling (13). for the purpose of lubricated wear tests, a lubricating system (14) is used. a steel table (15) is used to hold all the equipment of the wear testing. a range of sliding velocities could also be obtained by varying the radial location of the specimen on the rubbing disc. the sliding experiments were carried out at a speed varied from 0.5 m/s to 2 m/s and the applied normal load was in the range from 2.5 to 10 n. a ground finished cast iron disc of surface roughness in the range of 0.14 to 0.15 mm (cla) and hardness 180 hrb was used as a counter face. the composite wear rate was determined by measuring the mass loss of the specimen at a steady state condition after every test run interval. the average of three repeated tests was taken for each time interval. fabricated woven roving aramid/epoxy composite specimens have the crosssection 4 mm x 4 mm and length 25 mm. each specimen was slid 30 minutes on a mild steel disc and the average of three repeated tests was taken for each specimen tested. the volumetric wear rate for each composite specimen was calculated for the duration of 30 minutes. a lubricating oil (sae 30) was used during the lubricated wear tests. while the silicon carbide was used as an additive mixed with the matrix in a volumetric fraction of 10%. properties aramid/epoxy density, ρ (g/cm3) 1.44 ultimate tensile strength, σu (gn/m2) 1.38 modulus of elasticity, e11 , e22 (gn/m2) 88 poisson’s ratio, υ 0.34 iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 49 fig. 3: wear test rig. fig. 4: schematic diagram of pin on disc apparatus. 4. results results from this study include the effects of applied normal load, sliding velocity and wear test condition. besides that, scanning electron micrographs of some selected specimens were taken for a comparison purpose. iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 50 according to visconti [3], the wear rate could be calculated by the following equation: s m w v tr d = a , (1) where md is the mass loss (g), r is the density (g/m3), a is the apparent area of surface contact (m2), t is test time (s), and sv is the sliding velocity (m/s). wear losses were determined by the weight–loss method. the weight loss was measured by using an electron balance. for different normal loads and sliding velocities, data for the wear rate of the composite were obtained. for each test, three types of laminates were examined. an average data of three tests was taken. the test time was 30 minutes and the weight loss measurements were made at 10 minutes intervals by electron balance. the diameter of path was 180 mm. 4.1 sliding velocity figures 5 to 8 show the effect of sliding velocity on the wear rate of woven roving aramid/epoxy composite specimens at different loads. as shown from these figures, the wear rate increases with increasing sliding velocity and will be increased at higher loads. dry, lubricated, dry with additives and lubricated with additives have been tested. the lowest wear rate of 17.5 was found in a lubricated composite specimens with additives at a sliding velocity of 2 m/s and applied normal load of 10 n. 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 sliding velocity (m/s) w ea r r at e (1 0e -1 0) 1o a d=2 .5 n 1o a d=5 n 1o a d=7 .5 n 1o a d=10 n fig. 5: wear rate versus sliding velocity (dry sliding condition). iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 51 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 sliding velocity (m/s) w ea r r at e (1 0e -1 0) 1oad=2.5n 1oad=5n 1oad=7.5n 1oad=10n fig. 6: wear rate versus sliding velocity (dry with silicon carbide additive). 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 sliding velocity (m/s) w ea r r at e (1 0e -1 0) 1oad=2.5n 1oad=5n 1oad=7.5n 1oad=10n fig. 7: wear rate versus sliding velocity (lubricated sliding condition). iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 52 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 sliding velocity (m/s) w ea r r at e (1 0e -1 0) 1oad=2.5n 1oad=5n 1oad=7.5n 1oad=10n fig. 8: wear rate versus sliding velocity (lubricated with silicon carbide additive). 4.2 applied normal load the effects of applied load on the wear rate are shown figures 9 to 12. it was found that, with increasing applied load, the wear rate increases for all these tests. this is attributed to the increase of the fiber break and debonding with increasing the applied loads. 0 5 10 15 20 25 0 2 4 6 8 10 12 load (n) w ea r r at e (1 0e -1 0) sliding vel. = 0.5m/s sliding vel.= 1.0 m/s sliding vel. = 1.5m/s sliding vel.= 2.0m/s fig. 9: wear rate versus load (dry condition). iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 53 0 5 10 15 20 25 0 2 4 6 8 10 12 load (n) w ea r r at e (1 0e -1 0) sliding vel. = 0.5m/s sliding vel.= 1.0 m/s sliding vel. = 1.5m/s sliding vel.= 2.0m/s fig. 10: wear rate versus load (dry with additive). 0 5 10 15 20 25 0 2 4 6 8 10 12 load (n) w ea r r at e (1 0e -1 0) sl i d i ng v e l. = 0 . 5m/ s sl i d i ng v e l. = 1. 0 m/ s sl i d i ng v e l. = 1. 5 m/ s sl i d i ng v e l. = 2 . 0 m/ s fig. 11: wear versus load (lubricated condition). iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 54 0 5 10 15 20 25 0 2 4 6 8 10 12 load (n) w ea r r at e (1 0e -1 0) sliding vel. = 0.5m/s sliding vel.= 1.0 m/s sliding vel. = 1.5m/s sliding vel.= 2.0m/s fig. 12: wear rate versus load (lubricated with additive). 4.3 wear testing condition effect the effect of siding velocity on the wear rate at constant loads for dry, lubricated, dry with additives and lubricated with additives specimens are shown in fig. 13. the highest wear rate of 22 e-10 was found for the composite specimens lubricated with additives. figure 14 shows the effect of the applied normal load on wear rate at constant velocities for specimens of same types as the specimens of fig 13. 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 sliding velocity (m/s) w ea r r at e (1 0e -1 0) dry condition dry with additive lubricated condition lubricative with additive fig. 13: wear rate versus sliding velocity (at different conditions of sliding tests). iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 55 0 5 10 15 20 25 0 2 4 6 8 10 12 loads (n) w ea r r at e (1 0e -1 0) d r y c o nd it i o n d r y w it h ad d i t i ve lub ri c at e d c o nd i t i o n lub ri c at e d wi t h a d d i t iv e fig. 14: wear rate versus load (at different conditions of sliding tests). 4.4 scanning electron micrographs the microstructures for the worn surfaces of the woven roving aramid/epoxy composite specimens have been examined by using a scanning electron microscope (jeol jsm6500) with magnification of 70 times. the sem scanning electron micrographs of the worn surfaces of specimens tested at a sliding velocity of 1 m/s and applied load of 7.5 n are shown in fig.15. this figure includes four scanning electron micrographs of dry, lubricated, dry with additives and lubricated with additives specimens. another scanning electron micrograph was taken (fig. 16) for the sliding velocity of 2 m/s and applied normal load of 10 n. specimens of dry, lubricated, dry with additives and lubricated with additives were also used. it could be seen from these micrographs that the lowest debonding and delamination was found at the worn surfaces for the composite specimens with additives and lubricant. in general, the debonding and delamination occur on the worn surfaces at different levels. during sliding, the asperities present on the counterface surface produce lateral impacts on the exposed woven roving aramid fibers causing them to break. lubricants decrease the debonding on fibers. the increase in debonding causes more fractures in the fibers and it will be increased as the loads increase. this may be attributed to the inherent increase in the brittleness of the aramid/epoxy specimens. furthermore, the effect was higher in the dry and dry with additives conditions. iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 56 a. dry condition without additives. b. dry condition with additives. c. lubricated condition without additives. d. lubricated condition with additives. fig. 15: scanning electron micrographs for the worn surface of woven/roving/ epoxy composite specimens at sliding speed of 1 m/s and applied normal load of 7.5 n. a. dry condition without additives. b. dry condition with additives. c. lubricated condition without additives. d. lubricated condition with additives. fig. 16: scanning electron micrographs for the worn surface of woven roving/epoxy composite specimens at sliding speed of 2 m/s and applied normal load of 10 n. iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 57 5. discussion and conclusions the equipment was designed and fabricated to conduct the wear tests for the composite material used. tests were conducted carefully for all the specimens. the average of three tests was taken for each type of composite specimens. wear test graphs exerted from this investigation show the same trend when compared to other investigations (3) it was shown that the wear rate increased with increasing the applied load. while there is a difference in the overall wear rate for the tested conditions. the main conclusions which can be drawn from this investigation are: 1) with increasing applied normal load, the wear rate increases for all the tested specimens. the effect of applied load was found higher for the case of dry wear tests. 2) wear loss in lubricated tests for the same testing loads and speeds decreases and produces lower values of wear rates than other testing conditions. 3) silicon carbide additives decrease the wear rate for woven roving aramid/epoxy composites for both the dry and lubricated wear tests. 4) results show that the change of the applied normal load and sliding velocity has a nonlinear effect on the wear rate for the woven roving aramid composite. 5) scanning electron micrographs show that, debonding and delamination decreases for the specimens when using the lubricant with additives at the same applied normal loads and sliding velocities. acknowledgements the author would like to thank the research centre, international islamic university malaysia (iium) for providing financial support. thanks are due to mr fadli k. and hisham for preparing the specimens. special thanks are also due to the department of mechanical engineering, faculty of engineering, iium, for providing help for sem microscopic analysis in the materials and metallurgy lab. references [1] n. h. sung and n. p. suh, “effect of fiber orientation on friction and wear of fiber reinforced polymeric composites”, wear, vol. 53, pp. 129-141, 1980. [2] b. vishwanath, a. p. verma, c.v.s.k. rao, and r. k. gupta, “effect of different matrices on wear characteristics of glass woven roving polymer composites”, composites, vol. 24, no. 4, pp. 347-353, 1993. [3] i. c. visconti, a. langella and m. durante, “the wear behavior of composite materials with epoxy matrix fulled with hard powder” applied composite materials, vol. 8, pp. 179-189, 2001. [4] y. sirong, h. zhenming and c., kai, “dry sliding friction and wear behavior of short fiber reinforced zinc-based alloy composites”, wear, vol. 198 ,pp. 108-114, 1996. [5] b. vishwanath, a. p. verma, and v. s. k. rao, “friction and wear of glass woven roving modified phenol composite”, composites, vol.21, no. 6, pp. 531-536, 1990. iium engineering journal, vol. 3, no. 2, 2003 asad a. khalid 58 [6] n. s. el-tayeb and r. m. gadelrab, “friction and wear properties of e-glass fiber reinforced epoxy composites under different sliding contact conditions”, wear, vol. 192, pp. 112-117, 1996. [7] s. bahadur and v.k. polineni, “tribological studies of glass fabric-reinforced polyamide composites filled with cuo and ptfe”, wear, vol. 200, pp. 95-104, 1996. [8] m.d. dermudez g.m. nicolas., f.j. carrion, i.m. mateo., j.a. rodriguez, and e.j. herrera, dry and lubricated wear resistance of mechanically alloyed aluminumbase sintered composites, wear,vol. 248, pp. 178-186, 2001. [9] l. peiqing, x. qunji and l. weimin, 2000, tribological properties of ni3 al-cr7c3 composite coating under water lubrication”, tribology international, vol. 33, pp.469-47 [10] l.a. plato and m. j. michno, aramid fiber in advanced composite. springer – verlag. vol. 24, pp. 81-86, 1994. [11] matrinez m. a., navarro c., cortes r., redriguez j., 1993. friction and wear behavior of kevlar fabrics. journal of material science vol. 28, 1305-1311, 1993. biography dr. asad a. khalid is currently working as an assistant professor at the faculty of engineering, international islamic university malaysia. he obtained his b.sc. in 1986 and m.sc. in 1993, mechanical engineering department, faculty of engineering, basrah university, iraq. he received his ph.d. in 1999 from the department of mechanical engineering, faculty of engineering, university putra malaysia, upm, malaysia. his area of interest is stress analysis in composite materials. 20 25 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 olalere et al. 87 comparative study of pulsed microwave and hydrodistillation extraction of piperine oil from black pepper olusegun abayomi olalere * , hamid nour abdurahman, rosli mohd yunus, oluwaseun ruth alara and jayshree thraisingam faculty of chemical engineering & natural resources, universiti malaysia pahang, lebuhraya tun razak, 26300 gambang, pahang, malaysia. *corresponding author: abrahman@ump.edu.my (received: 17 th feb. 2017; accepted: 31 st oct. 2017; published on-line: 1 st dec. 2017) abstract: black pepper is a tropical crop with an extensive medicinal potential in ethnomedicine and nutraceutical applications. the pungent bioactive piperine is responsible for this functions which efficacy requires an efficient technologies for optimal extraction process. there is therefore a need to determine the best factor settings that optimize the relative efficiency of the system with minimal variability. in this study, the best factor settings was achieved using taguchi parametric l9-orthogonal methodology. the extraction parameters considered under this study were extraction time, microwave power, particle size and molar ratio. an optimal extraction condition was achieved at 90 min extraction time, 350 w microwave power, 0.105 mm particle size and 10 ml/g molar ratio. the signal-to-noise ratio (snr) otherwise known as response optimizer is an ideal metric in the determination of this optimum condition. the performance evaluation of reflux microwave extractor in relation to the hydrodistillation system placed the optimal efficiency and signal-to-noise ratio at 155.72% and 43.85, respectively. the higher optimal efficiency obtained indicated that the microwave reflux extraction is better and more efficient than the conventional hydrodistillation techniques. abstrak: lada hitam adalah tanaman tropika yang kaya dengan faedah perubatan terutamanya dalam perubatan alternatif dan bidang nutraseutikal. kehadiran piperina iaitu unsur kimia yang tergolong dalam kumpulan alkaloid menjadi penyumbang utama bagi kepedasan yang dihasilkan oleh rempah ini sekaligus berperanan besar dalam menjadikannya satu bahan yang memiliki nilai perubatan yang tinggi. keberkesanan fungsi lada hitam ini bergantung penuh pada teknologi pengekstrakan yang cekap bagi memastikan proses pengasingan yang optimal dapat dijana. sehubungan itu, penentuan faktor terbaik yang dapat mengoptimumkan keberkesanan relatif sistem pengekstrakan dengan pemboleh ubah dan ralat yang minimal perlu dikenal pasti. faktor terbaik didapati dengan menggunakan parameter l9 taguchi dalam rekaan ortagonal. dalam kajian ini, parameter pengekstrakan yang dikaji ialah masa pengekstrakan, kuasa radiasi, saiz zarah dan nisbah molar. pengekstrakan yang optimum tercapai pada minit ke-90 pengekstrakan, 350 w kuasa gelombang mikro serta pada saiz zarah 0.105 mm dan nisbah molar 10 ml/g. snr (signal to noise ratio) adalah metrik ideal yang diguna pakai untuk mendapatkan keadaan optimum tersebut. perbandingan dari segi keberkesanan kaedah pengekstrakan refluks menggunakan gelombang mikro dengan kaedah penyulingan hidro menunjukkan bahawa kaedah pengekstrakan refluks menggunakan gelombang mikro memiliki keberkesanan optimum pada 155.72% dan snr sebanyak 43.85. nilai keberkesanan optimal yang tinggi ini secara jelasnya membuktikan bahawa kaedah pengekstrakan refluks menggunakan gelombang mikro lebih efektif berbanding iium engineering journal, vol. 18, no. 2, 2017 olalere et al. 88 kaedah konvensional penyulingan hidro sekaligus menjadi indikator bagi pengekstrakan tanpa degradasi. keywords: black pepper; extraction; piperine; hydrodistillation; microwave extraction; taguchi optimization 1. introduction piper nigrum otherwise called black pepper is an important agricultural crop with economical, nutritional and health benefits. it is used as spices in the food industry, in traditional medicine as anti-rheumatic, in pharmaceuticals as an analgesic, essential balm production as an adiabatic substance, and also as tear gas components in policing [1–3]. there are however more than a thousand known species characterized by distinguishing pungency and flavoring properties [4]. black pepper is a climbing perennial plant, grown in many parts of india, brazil, indonesia, sri lanka, vietnam, and malaysia [5]. their flavoring and pungency properties is due to the presence of volatile and non-volatile oil containing an active compound called piperine [6]. other analogous active components in black pepper include piperettine, piperanine, piperyline-a, piperolein-b and pipericine. piperine is thereafter the active alkaloid reponsible for the pungent characteristics of black pepper. it hydrolyzes in aqueous alkali to forms a slightly pungent photosensitive isomer called piperidine. recent studies have shown the ability to boost the bioavailability of nutrients from other nutrients with an inhibitory capacity to cancer, inflammation, pain, and depression [8]. many studies had been conducted on the improvement and implementation of distinctive operating conditions for the extraction of piperine oil using different methods [9][10]. rafajlovska et al. [11] used solvent extraction method to extract piperine oil under distinctive conditions of extraction time, temperature and solvent type. nahak and sahu [12], isolated piperine from black pepper fruits with ethanol using the column chromatography method. the mass spectra obtained revealed the presence of a compound with a molecular weight 284.5 gmol -1 which confirmed the presence of piperine. raman and gaikar [13] investigated the use of microwave assisted technique to extract piperine oil from granular black pepper seeds. the extraction factors considered were the microwave power level, solvent type and solid loading. the results revealed that the selective extraction resulted in the production of high-quality piperine with 85% purity. in this study, the effects of microwave extraction parameters (irradiation time, microwave power level, feed particle size, and molar ratio) on the extraction yield and relative efficiency were investigated. the microwave reflux extraction works on the principle of ionic conduction and dipole rotation. due to their electromagnetic nature, microwaves possess electric and magnetic fields which are at right. the electric field generated inside the microwave induces an ionic current in the solution which triggers off the extraction process [14]. the relative efficiency of the microwave extraction technique was estimated based on their extraction yield in relation to that of the conventional hydrodistillation extraction method. 2. experimental 2.1 plant materials preparation the dried reticulated wrinkled brown surface black pepper was purchased from sarawak, malaysia. the seeds were then grinded and clarified into five different particle sizes (0.105 mm, 0.154 mm, 0.30 mm, 0.450 mm and 0.90 mm). iium engineering journal, vol. 18, no. 2, 2017 olalere et al. 89 2.2 extraction process 2.2.1 exhaustive hydrodistillation extraction an accurately weighed 5 g of the powdered black sample was loaded into round bottom reactor containing distilled water at 1:20 feed-to-water ratio [9]. the pepper feedstock was hydrodistilled step-wisely for 4 hr with the first extraction step-wisely carried out using 75 ml of distilled water for the first 2 hr and the second extraction process for another 90 min using 30 ml of water. with a 10 ml of water for the last 30 ml part of the extraction process in accordance with the method used by [15] 2.2.2 microwave reflux extraction an easy-controled automated microwave extraction system was employed for this study (milestone inc., north america). the auxiliary units attached to the system include magnetic stirrer, exhaust outlet, beam reflector, a reflux unit, and a magnetron of 2450 mhz with a nominal maximum power of 1000 w. a 5 g of the powdered dried sample at different particles sizes were loaded into the reactor containing a measure distilled water. three-level pulsed heating modes and this includwere used viz: 10 min of pre-heating mode (100 o c), irradiation mode (60 o c) and cooling for 10 min (30 o c). the application of pulsed heating reduces the variation imposed upon by noise factor (temperature) [16]. 2.3 determination of piperine yield moreover, an agilent gc-ms (5973n wilmington, de, usa) equipped with a c-18 capillary column of length 30 m, the internal diameter of 0.25 mm and film thickness 0.25 µm. this was used to determine the composition of the piperine in the piper nigrum sample at different parameter settings at an electron mode of 70 ev. the components of the spice oil extract were obtained using a computer controlled gc-ms system. the basis of their component identification was based on the retention indices and mass spectra matching in relation with the nist spectral libraries [17]. this was carried out by diluting the extract with an analytical standard grade acetone at a ratio 1:10.1 µl. this was then injected into the gc-ms for piperine detection and quantification. the actual percentage of piperine was calculated using the normalization techniques in relation to the quantity of the sample loading as shown in eq. (1). (1) 2.4 determination of relative efficiency the relative index is a performance evaluation tools used in determining the efficiency of one extraction technique over the other [14]. this is the ratio of yields from microwave reflux extraction (mre) to conventional hydrodistillation (hd). the ratio of the piperine yield in mre relative to hd was estimated for each experimental run in the design matrix. it is a dimensionless value which only reveals the proportion in which one extraction technique out-performed the other. the relative efficiency is therefore obtained by multiplying the relative index by 100 as shown in eq. (2). (2) iium engineering journal, vol. 18, no. 2, 2017 olalere et al. 90 2.5 determination of factor operating levels the extraction parameters under investigation were the irradiation time (a), microwave power level (b), feed particle size (c), and the molar ratio (d). three levels were selected from parameters variation as presented in table 1. table 1: extraction factors and levels extraction variables annotation/ units level 1 level 2 level 3 irradiation time a (min) 30 60 90 microwave power b (w) 300 350 400 feed particle size c (mm) 0.105 0.154 0.300 molar ratio d (ml/g) 6 8 10 2.6 optimized taguchi experimental design the taguchi experimental design is an orthogonal optimization array which offers flexibility in the choice of optimal product or process conditions, with a high performance and consistency in operation. this design takes into consideration that not all process parameters can be controlled in practical reality and these process parameters are called noise or uncontrollable factors [18]. from the experimental design matrix in table 2, the optimum extraction conditions for the black pepper relaxation were obtained at 90 min irradiation time (a), 350 w power level (b), 0.105 mm feed particle size (c) and 10 ml/g molar ratio (d). at the optimal level was attained at trial-8 with relative efficiency and signal-to-noise ratio of 155.72 % and 43.8469, respectively. according to olalere et al. [20], the optimal condition is the point with the largest snr (trial-8) as illustrated in fig. 1. table 2: design matrix and orthogonal test results for l9 (3^4) run a (min) b (w) c (mm) d (ml/g) responses snr py(w/w) ree (%) 1 30 300 0.105 6 1.39 105.69 40.48 2 30 350 0.154 8 0.70 52.83 34.46 3 30 400 0.300 10 0.72 54.16 34.67 4 60 300 0.154 10 1.19 90.35 39.12 5 60 350 0.300 6 1.11 84.10 38.50 6 60 400 0.105 8 0.87 65.64 36.34 7 90 300 0.300 8 0.59 44.32 32.93 8 90 350 0.105 10 2.056 155.72 43.85 9 90 400 0.154 6 0.77 58.00 35.27 a: irradiation time, b: microwave power, c: feed particle size, d: molar ratio, py: piperine yield, ree: relative extraction efficiency, snr: signal-noise ratio iium engineering journal, vol. 18, no. 2, 2017 olalere et al. 91 fig. 1: the graphical illustration of snr in relation to the ree. 3. results and discussion 3.1 analysis of response means the sample was hydrodistilled and validated under the same operating conditions and results indicated that the average mean of the piperine yield was 1.322 w/w, with relative standard deviation (rsd) of 0.92 % using water as the extracting agent. however, the optimal response characteristics mean was computed for each of the microwave extraction parameters using the larger-the-better quality characteristics [19]. from the results obtained from the analysis of mean (anom); the sample particle size played the most significant contribution. increasing the surface area of the pepper led to an improved efficiency (109.02%) as presented in table 3. however, irradiation time gave the least contribution to the piperine yield which suggested that the optimal efficiency can only be achieved at minimal microwave time [11]. table 3: average main effects a:irradiation time, b: microwave power, c: feed particle size, d: molar ratio, ree: mean relative efficiency from the characteristic means, the maximum efficiency was attained at the 3 rd level setting (90 min) with a relative extraction efficiency of 86.01% (fig. 2). this suggested that, as the irradiation time increased, the piperine yield increased. the higher optimal irradiation time could, therefore, be attributed to the higher molecular weight (285.34 g/mol) of piperine which involves longer time in breaking the forces of attraction holding their molecules together [21]. furthermore, the slope from main effect plots (fig. 2) gave a maximum response mean at power level-2 (350 w) indicating an improved yield with a mean response value 97.55%. also, the optimal response means for the feed particle size was estimated to be 109.2% at level-1 with a mesh size-140 (0.105 mm). optimum 0 0.5 1 1.5 2 2.5 0 50 100 150 200 0 1 2 3 4 5 6 7 8 9 s n r r e sp o n se ( r e e & p y ) % experimental trials ree (%) snr ree(%) a (min) b (w) c (mm) d (ml/g) level 1 70.89 80.12 109.02 82.60 level 2 80.03 97.55 67.06 54.26 level 3 86.01 59.27 60.86 100.08 delta difference 15.12 38.28 48.16 45.81 optimal ranking 4th 3rd 1st 2nd iium engineering journal, vol. 18, no. 2, 2017 olalere et al. 92 piperine yield was therefore obtained with a finely divided powdered pepper as compared with a more coarse size. this suggests that smaller particle size provides the good surface area with increase efficiency [22]. furthermore, the mean response efficiency of 82.60% was obtained at level-3, confirming that a higher molar ratio of 10 ml/g is required at optimum condition [23]. fig. 2: response graph illustrating variations of ree mean. 4. conclusion in the extraction of bioactive compounds from plant origin, the efficiency of the extraction procedure is often neglected. the relative efficiency is therefore the basis for measuring the productivity of an extraction method on an industrial scale. the determination of an optimal efficiency of microwave extractors could therefore be employed as performance index in the future scale up. this could be applied in the quantitative comparison between two or more extraction methods. this study compared the relative efficiency of microwave reflux with respect to the exhaustive hydrodistillation techniques. the effect of process parameters such as microwave power, irradiation time, feed particle size, molar ratio and signal-to-noise ratio characteristics were succinctly investigated. the performance evaluation of reflux microwave extractor in relation to the exhaustive hydrodistillation system gave an optimum efficiency of 155.72%. this indicated that the extract prepared using the microwave extractor presented a better extraction efficiency than the exhaustive hydrodistillation system. acknowledgements we acknowledge the financial contribution of research and innovation department universiti malaysia pahang (ump), malaysia through the grant pgrs-160320. references [1] viktorija m, liljana kg, tatjana r, rubin g. (2014) antioxidative effect of capsicum oleoresins compared with pure capsaicin. iosr j. pharm. 4:44-48. [2] nwokem c, agbaji e, kagbu j, ekanem e. (2010) determination of capsaicin content and pungency level of five different peppers grown in nigeria. ny sci j. 3:17-21. [3] adkins ld (2003) oleoresin capsicum: an analysis of the implementation of pepper spray into the law enforcement use of force continuum in a selected police department. electron. iium engineering journal, vol. 18, no. 2, 2017 olalere et al. 93 theses diss.86. http://dc.etsu.edu/etd/779. [4] vasavirama k, upender m. (2014) piperine: a valuable alkaloid from piper species. int. j. pharm. pharm. sci. 6:34–38. [5] ha ym, li wm, wang f. (2011) application of esr spectroscopy to identify and estimate original dose in irradiated cumin and white pepper, eur. food res. technol. 233:625-630. [6] meghwal m, tk g. (2012) nutritional constituent of black pepper as medicinal molecules: open access scienctific reports 1:129. [7] majeed, prakash l. (2000) the medicinal uses of pepper. international pepper news, 25:2331. [8] janakiraman k, manavalan r. (2008) studies on effect of piperine on oral bioavailability of ampicillin and norfloxacin. afr. j. tradit. complement. altern. med. 5:257-262. [9] olalere oa, abdurahman hn, yunus rm, alara or. (2017) multi-response optimization and neural network modeling for parameter precision in heat reflux extraction of spice oleoresins from two pepper cultivars (piper nigrum). j. king saud univ. sci. doi:10.1016/j.jksus.2017.09.010. [10] olalere oa, abdurahman hn, alara or, habeeb oa. (2017) parametric optimization of microwave reflux extraction of spice oleoresin from white pepper (piper nigrum). j. anal. sci. technol. 8:1-8. [11] rafajlovska v, slaveska-raicki r, klopcevska j, srbinoska m. (2011) extraction of oleoresin from pungent red paprika under different conditions, mass transf. chem. eng. process. 5:111–132. [12] nahak g, sahu rk. (2011) phytochemical evaluation and antioxidant activity of piper cubeba and piper nigrum, j. appl. pharm. sci. 1:153-157. [13] raman g, gaikar v. (2002) microwave-assisted extraction of piperine from piper nigrum, ind. eng. chem. res. 41:2521-2528. [14] mandal v, mohan y, hemalatha s (2008) microwave assisted extraction of curcumin by sample-solvent dual heating mechanism using taguchi l9 orthogonal design, j. pharm. biomed. anal. 46:322-327. [15] özek g, demirci f, özek t, tabanca n, wedge de, khan si, hüsnü k, bas c, duran a, hamzaoglu e. (2010) gas chromatographic – mass spectrometric analysis of volatiles obtained by four different techniques from salvia rosifolia sm and evaluation for biological activity,1217:741-748. [16] chan ch, lim jj, yusoff r, ngoh gc. (2015) a generalized energy-based kinetic model for microwave-assisted extraction of bioactive compounds from plants. sep. purif. technol. 143:152-160. [17] singh s, kapoor ips, singh g, schuff c, de lampasona mp, catalan can. (2013) chemistry, antioxidant and antimicrobial potentials of white pepper (piper nigrum l.) essential oil and oleoresins, proc. natl. acad. sci. india sect. b biol. sci. 83:357-366, [18] maghsoodloo s, ozdemir g, jordan v, huang ch. (2004) strengths and limitations of taguchi’s contributions to quality, manufacturing, and process engineering, j. manuf. syst.23: 73–126. [19] olalere oa, abdurahman nh, alara or. (2017) extraction, radical scavenging activities and physicochemical fingerprints of black pepper (piper nigrum) extract, j. food meas. charact.http://10.1007/s11694-017-9604-4. [20] olalere oa, abdurahman nh, alara or, habeeb oa. (2017) optimized microwave reflux extraction and antioxidant activities of piperine from black and white piper nigrum. chem. eng. res. bull.19:139-144. [21] zaveri m, khandhar a, patel s, patel a. (2010) chemistry and pharmacology of piper longum, int. j. pharm. sci. rev. res. 5:67-76. [22] kormin f, ahmed i, yunus rm, yusof za. (2010) the potential of modified microwave extraction system (mmes) to extract bioactive components from ferns. int. j. eng. technol. 10:7-21. [23] jokic s, velic d, bilic m, bucic-kojic a, planinic m, tomasa s. (2010) modelling of the process of solid-liquid extraction of total polyphenols from soybeans, czech j. food sci. 28:206-212. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 tursunov et al. 164 about the silicon sensitivity of the deep level with alternating pressure ikrom gulamovich tursunov1*, abdurahim abduraxmonovich okhunov2 and odiljon oxundadaevich mamatkarimov3 1 faculty of physics, national university of uzbekistan, 100174 tashkent, uzbekistan. 2 department of science in engineeringe, kulliyyah of engineering, international islamic university malaysia, po box 10, 50728, kuala lumpur, malaysia. 3 department of physics, namangan engineering and technology institute, 716030 namangan, uzbekistan. * corresponding author: ikromjon0804@gmail.com (received: 9th feb 2016; accepted: 4th april 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.794 abstract: this paper discusses the strain sensitivity of silicon with deep levels under variable pressure. it is shown that in the pressure swing in silicon with deep levels, there is a redistribution of the primary spatial inhomogeneities in the distribution of impurities so that the electron-hole relaxation after stress relief will occur in the new potential relief. abstrak: kajian ini membincangkan tentang sensitiviti kepekaan strain silikon pada pelbagai tahap dalam tekanan. keputusan menunjukkan terdapat ketidakharmonian agihan pada spasial utama dalam agihan kotoran dengan ayunan tekanan dalam silikon pada tahap dalam, supaya relaksasi lubang-elektron setelah pelepasan tekanan akan berlaku dalam pelepasan potensi baru. keywords: semiconductors; properties; dynamic and deep levels 1. introduction it is known [1-4] that semiconductors with deep levels are more sensitive to external influences. these properties of semiconductors are explained by the notion that the deep levels in semiconductors may be in a partially ionized state, even at room temperature. in addition, only in semiconductors with deep levels is there a dynamic tenzoprovodimost. until now, the dynamic strain conductivity was explained by a change in temperature at the pulse pressure. that is, it was assumed that the dynamic strain effect in semiconductors with deep levels was only seen by stimulated pulse pressure temperature. but, according to our experimental results, the dynamic strain effect is manifested not only by temperature but also by relaxation effects. strain sensitivity means in such samples may be due to the different components. in this regard, we studied the dynamic strain sensitivity in silicon samples with deep levels. we believe that when the pulse pressure is a common dynamic, strain sensitivity is determined by multiple components: the static, thermal, and dynamic. 2. experimental procedure to investigate the effects of contact strain sensitivity, si samples were prepared with varying degrees of compensation and conductivity type. samples of (si:au) compensated with gold have been obtained on the basis of single-crystal silicon brand sdp (silicon doped iium engineering journal, vol. 19, no. 2, 2018 tursunov et al. 165 with phosphorus) and sdp (silicon doped with boron) with resistivity ρ ~ 20-80 om·sm, these were grown by zhohralski method and the floating zone melting. for this study, crystals were made with a size of 3 6 3 3 mm  , with the directions of the crystallographic axes [100], [110], [111] along the edges of the large, crystallographic directions, determined by x–ray analysis. after si single crystal cutting, the samples were ground with diamond micro powders m–14 and m–4 by providing specific flatness lapping opposite edges up to (2-3) microns. in order to remove the crystals, the surface layer is impaired and degreased, and the samples were chemically etched in a solution of hf:hno3 = 3:5. the process of gold doping of silicon single crystals requires a diffusing layer deposited on a silicon surface by vacuum deposition on the installation vup-5. the diffusion furnace was used in a horizontal-type soul-4 in the temperature range of t=900÷1200 °с for two hours. the temperature in the furnace was controlled by thermocouple platinum –platinum– radii and maintained to within ±3 °с. the diffusion resulted in a high purity of au (99.999%). after diffusion annealing, removal of the surface layer on each side of the samples ground off layers 50–60 microns was performed using lapping, under conditions to preserve flatness of opposite faces, and then samples were subjected to chemical treatment. the electrical parameters of the samples (conductivity, concentration and mobility of charge carriers) were determined on the installation measurements of the hall effect. the samples were placed between the poles of a permanent magnet with a magnetic field of h = 3000, the magnetic field direction was changed by turning the magnet 180°. resistivity measurement sample was calculated according to the formula: u d b i l    where i – current through the sample, u –voltage between the potential contacts, b – width, d – thickness, l – length of the sample. the hall coefficient is calculated as follows: 3 8 10 x u d sm r j b кl         where the u hall electrical driving forces, b magnetic induction. the hall mobility was calculated by the formula: 2 x r sm v s          . electric parameters of investigated samples are presented in table 1. to control the temperature in the measurement, samples were attached to an alloyed copper thermocouple. to protect the electrical contacts of the samples were coated with epoxy resin. prepared in this way the samples were mounted on the holder and placed in a chamber in which a high hydrostatic pressure created. also, a heater has been installed on the holder for changing the temperature of the sample. table 1: electric parameters of investigated samples iium engineering journal, vol. 19, no. 2, 2018 tursunov et al. 166 № samples type conductivity specific resistance , оmsm concentration of charge carriers sm-3 charge carrier mobility sm2/v.s 1 si :au n 1.5102 3.961013 1219 2 si :au p 2.1102 3.151014 500 3 si :au n 2.88105 1.781010 1214 4 si :au n 4.7104 1.151010 1205 5 si :au n 2.98105 1.961010 1091 6 si :au p 5.8104 4.391011 254 7 si :au p 1.2105 1.821011 343 8 si :au n 3.2105 1.671010 1208 9 si :au n 1.95105 2.71010 1220 10 si :au n 2.2103 2.661012 1073 to control the temperature in the measurement samples was attached to the alloyed copper thermocouple. to protect the electrical contacts of the samples, they were coated with epoxy resin. prepared in this way the samples were mounted on the holder and placed in a chamber in which a high hydrostatic pressure was created. also, a heater has been installed on the holder for changing the temperature of the sample. to investigate strain properties of compensated samples under uniform hydrostatic compression, installation hydrostatic pressure is used as described in [5]. 3. the silicon sensitivity with deep-level pressure swing the total strain sensitivity can be represented as follows: ст д s s s  (1) where, ст s is the static part of the strain sensitivity, and дs is the dynamic part of strain sensitivity. the dynamic part of the strain sensitivity is also divided into two components. d t rels s s  (2) where, ts and rels are the temperature and relaxation of the strain sensitivity. in its general form, strain sensitivity components can be determined according to known relationships, in dimensionless form [6]. yo i e s i p   (3) where, i  is the current change at variable pressure, i  is the starting current, yo e  the young's modulus of the semiconductor crystal, and p  is the pressure pulse amplitude. iium engineering journal, vol. 19, no. 2, 2018 tursunov et al. 167 the kinetic dependence of the relative current change is shown in fig. 1. figure 2 illustrates the dependence of dynamic and thermal parts separately. from these figures, the individual components of the strain sensitivity can be identified. fig. 1: the relative change in current in pulsed hydrostatic pressure and increasing the temperature by an electric heater in the 3, 10si ni om sm   . fig. 2: the dynamic part of the relative change in the current passing through the sample 5, 10si ni om sm   . using the general strain sensitivity (3) and fig. 1, we find i i  for each component: relative to the total current change pressure 0 0 0 1m m i i ii i i i     swings and therefore, in this case, strain sensitivity becomes iium engineering journal, vol. 19, no. 2, 2018 tursunov et al. 168 0 1 yo m m i e s i p        (4) where the values of 0 mi i is taken from fig. 1. for the current temperature changes p e i i i ii i i ю ст t ст стt ст t              1 and strain sensitivity 1 yo t t cm i e s i p         (5) the change in the current for the dynamic part is 1 cm cm i i i i     and 1 yo cm i e s i p           (6) using formulas (2), (5), and (6) it is possible to find a general expression for the relaxation of the strain sensitivity 1 1 yo yo yo tt t cm cm cm i i iie e e s s s i p i p i p                              (7) with the help of formula (7) it is possible to calculate the contribution to the overall relaxation effects tensosensitivity compensated samples. so, using the above mentioned expression, it is possible to calculate all the components of the strain sensitivity. figure 3a shows the general tensosensitivity of the silicon with the impurities , ,si ni si mn si au represented by three curves, under static (1, 2, 3) and dynamic (1’, 2’, 3’) pressure, respectively. it can be seen that the static pressure is the biggest strain sensitivity in samples si ni . in the si mn samples, static strain sensitivity is lower. the silicon samples with gold impurities have little sensitivity to static pressure. in all the samples of silicon with deep levels, when resistivity increases, strain sensitivity increases. after overcompensation, with a further increase in the concentration of impurities, the resistivity starts to decrease and strain sensitivity reduced accordingly. from fig. 3, also shows the dynamic strain sensitivity of the samples in reverse order, since silicon samples doped with gold have the largest dynamic strain sensitivity and samples of si ni have smaller dynamic strain sensitivity. furthermore, in all the samples with deep impurity levels having a conductivity type p, the strain sensitivity is less than that of silicon samples with deep levels having n type conductivity. we calculated the individual components of the strain sensitivity for the above described samples. iium engineering journal, vol. 19, no. 2, 2018 tursunov et al. 169 fig. 3a: general strain sensitivity of the silicon with the impurities ni, mn, au where curves 1, 2, 3 are under static and dynamic (1’, 2’, 3’) pressure, respectively. fig. 3b: the temperature of the strain sensitivity of silicon samples with ni impurities (curve 3), mn (curve 2), au (curve 1). figure 3b shows the temperature gage component samples of , ,si ni si mn si au (curves 1, 2, 3, respectively). the figure shows that an increase in the degree of compensation, increasing the temperature and strain sensitivity component in the samples having a maximum degree of compensation (with a special resistance 510 om sm ), the maximum temperature gage of the component is reached. further, with increasing concentration, the type of conductivity of the sample and the temperature gage component decrease. st iium engineering journal, vol. 19, no. 2, 2018 tursunov et al. 170 fig. 3c: relaxation part of the strain sensitivity of silicon samples with impurities of the ni, mn, au (curve, 1, 2, 3, respectively). silicon samples with amphoteric impurities have almost no static and relaxation strain sensitivity components pressure swing. in these samples, only strain sensitivity associated with temperature effects were perceived. in the samples of si au si under the pulse pressure, there is a redistribution of the primary spatial homogeneities impurity distribution so that the electron-hole relaxation after removal of the stress will occur in the new potential relief. 4. conclusion silicon samples with acceptor impurities have large static and dynamic tensosensitivity that is smaller than silicon samples with donor and amphoteric impurities. silicon samples with amphoteric impurities have almost no static and relaxation components tensosensitivity pressure swing. in these samples, only tensosensitivity associated with temperature effects is observed. when the samples of si:au are under pulse pressure, there is a redistribution of the primary spatial in homogeneities impurity distribution so that the electron-hole relaxation, after removal of the stress, will occur in the new potential relief. acknowledgement the work is executed under grant f2-128 and ot–f2–75 by the committee for the coordination of the development of science and technology under the cabinet of ministers of the republic of uzbekistan, and also malaysian high education ministry frgs fund, project no. frgs13–074–0315. srelaxat ion iium engineering journal, vol. 19, no. 2, 2018 tursunov et al. 171 references [1] gulyamov g, gulyamov ag. (2015). tensosensitivity p-n-junction under illumination. physics and technology of semiconductor, 49(6):839–842. [2] sun y, thompson se, nishida t. (2007) physics of strain effects in semiconductors and metal-oxide-semiconductor field-effects transistors. journal of applied physics. 101:104503. [3] takei munehisa, kosemura daisuke, nagata kohki, akamatsu hiroaki, mayuzumi satoru, yamakawa shinya, wakabayashi hitoshi, ogura atsushi. (2010). channel strain analysis in high-performance damascene-gate p–metal–oxide-semiconductor field effect transistors using high-spatial resolution raman spectroscopy. journal of applied physics. 107(12):124507. [4] osadchuk vs, osudchuk av, bilokon nl, krivosheya aa. (2009). the effect of pressure on the parameters of semiconductor structures. automatics and information measuring equipment. 1:1–6. [5] abduraimov a, zaynabidinov sz, mamatkarimov oo, khimmatkulov o, khudaibergenov te. (1988). installing hydrostaticpressure pneumatic booster for research strain properties semiconductor materials. instruments and experimental techniques. 5:229-231. [6] polyakova aa. (1979) deformation of semiconductors and semiconductor devices. moscow, energy, 168. microsoft word paper v4-1-2.doc iium engineering journal, vol. 4, no. 1, 2003 i. s. said et al. 13 kinetics of selective catalytic reduction of nitric oxide over pt-cu-zsm5 catalyst ismail mohd saaid*, abdul rahman mohamed and subhash bhatia** * mechanical engineering program, universiti teknologi petronas, bandar sri iskandar, 31750 tronoh, perak, malaysia **school of chemical engineering, engineering campus, universiti sains malaysia, 14300 nibong tebal, seberang perai selatan, p. pinang, malaysia e-mail: chbhatia@eng.usm.my abstract: kinetics for the selective catalytic reduction (scr) of nitric oxide (no) using i-c4h10 as the reducing agent over pt-cu-zsm5 has been investigated in the temperature range of 200 c – 450 oc. langmuir-hinshelwood-hougen-watson model was proposed for kinetics of the reaction and reaction parameters were evaluated. the heat of adsorption of no was found to be considerably high, attributed to strong covalent bond between no gas molecules and metal active sites. using reaction parameters obtained from the experiment, the heterogeneous model could form a good correlation between experimental and simulated values of no reduction. key words: reaction kinetics, selective catalytic reduction, no reduction, bimetallic catalyst, h-zsm-5 zeolite. 1. introduction for the past decade, the intensive research on the methods for the decomposition of toxic and harmful species in the diesel exhaust gas have been reported [1]. the diesel engine is more economical and produces less concentration of hydrocarbons and carbon monoxide compare to other internal-combustion engines. however, the diesel exhaust emissions contain appreciable concentration of nox, and its removal become more stringent together with those of hydrocarbons and carbon monoxide under the international environment regulations. the reduction of nox emissions from diesel engines is done either by the modification of engine or reducing the emissions by addition of a reducing agent into the exhaust gas. selective catalytic reduction using a hydrocarbon as a reducing agent (hc-scr) has been widely proposed as one of the promising techniques to reduce the emission of nitric oxide (no) from diesel engine exhaust [1,2]. the technique eliminates the use of ammonia and its associated risk of storage commonly used in the selective catalytic reduction process at nitric acid or power plants. besides, the availability of unburned hydrocarbons in diesel exhaust can be utilised as a reducing agent. many types of catalysts especially those supported on zsm-5 zeolite such as cu-zsm5, co-zsm5, ni-zsm5 and fe-zsm5 have been proposed [2,3]. one of the major drawbacks is that these catalysts operate in a narrow temperature window for optimum reduction of no. recently we reported that platinum and copper co-loaded iium engineering journal, vol. 4, no. 1, 2003 i. s. said et al. 14 on zsm-5 zeolite could considerably widen the temperature window for optimum reduction of no [4]. in the present study reaction kinetics of the hc-scr process of no using i-butane as the reducing agent over pt-cu-zsm5 catalyst is reported. the reaction parameters were obtained from the proposed heterogeneous model based on langmuirhinshelwood-hougen-watson (lhhw) mechanism. the reaction parameters obtained were used to simulate the reduction of no in the packed bed reactor and compared with the experimental data obtained using the bimetallic pt-cu-zsm5 catalyst. 2. experimental samples of bimetallic catalysts, pt-cu-zsm5 were prepared by successive wet ion exchange process using 0.01 m copper nitrate and 0.0003 m chloroplatinic acid as chemical precursors for copper and platinum respectively [4]. the h-zsm5 zeolite support (si/al ratio 90) was supplied by süd chemie ag, munich. in essence, 10 g. of h-zsm5 zeolite and 100 ml. of respective metal solutions were used during wet ion exchange process. the wet ion exchange process was carried out in six 24-hour stages with vacuum filtration in between stages before drying overnight in static air at 110 c. the bimetallic catalyst samples were calcined in static air by increasing the temperature step-wise at 10 oc/min and held at 500 c for 1 hour. for comparison purposes, monometallic catalysts, pt-zsm5 and cu-zsm5 were also prepared using wet ion exchange process. samples were analysed in nitrogen adsorption isotherm (autosorb 1c) and electron dispersive x-ray technique (editor camscan) to examine their physical properties and chemical composition respectively as presented in table 1. the powder form of all samples was made into granular form by pressing under 35 tons, meshed into 250 355 m size before catalytic activity measurements. steady state catalytic activity measurements were carried out in a microcatalytic reactor (stainless steel tube 6 mm diameter and length 300 mm), horizontally placed in a mini tubular furnace (lindberg blue m). in-situ pre-treatment was carried out in flowing h2 (100 ml/min) at 450 oc for 4 hours for reduction of metal oxides to metal form. type k thermocouple connected to digital scanning thermometer (cole palmer model 92000-05) measured the catalyst bed temperature. mass flow control system (mks type 1179a controllers connected to mks type 247 4-channel control box) was used to prepare a feed gas mixture of 1000 ppm no, 1500 ppm i-c4h10, 3 % o2, and balanced by n2. online gas chromatograph (shimadzu 8a) equipped with porapak q column (80/100 mesh size) and molecular sieve 5a was used for analysis of gas (n2, o2, i-c4h10, n2o and co2) at the inlet and outlet of the reactor. enerac 2000e emission gas analyzer was used to measure online concentrations of no in ppm at the inlet and outlet stream. percentage of no reduction was calculated from the difference in the inlet and outlet concentration of no (cin and cout) as expressed in eq. (1). in out in c c % no reduction 100 (1) c        iium engineering journal, vol. 4, no. 1, 2003 i. s. said et al. 15 3. results and discussion 3.1. temperature window reaction. figure 1 shows temperature profiles of bimetallic catalysts as compared with monometallic pt-zsm5 and cu-zsm5 for the reduction of no. pt-zsm5 was clearly active in the low temperature region with maximum no reduction of 70 % at 250 oc. further increase in the temperature caused immediate drop in the no reduction, which became negligible above 500 oc. on the other hand, cu-zsm5 had negligible no reduction below 250 oc before a drastic increase to almost 100 % reduction at 350 oc. the no reduction remained relatively high even though there was a slight decline as temperatures were further increased. these results on cu-zsm5 and ptzsm5 agreed quite well with reported results [5,6,7]. temperature profiles of bimetallic catalysts (samples 1 and 2) showed synergistic effects of copper and platinum. in both samples, the range of temperature for optimum no reduction was expanded. pt-cu-zsm5 (i) offered the largest operating window than any other samples where more than 50 % no could be reduced over 250 c – 500 c region. regardless of the type of catalysts, their temperature profiles illustrated the general trend of catalytic activity for the reduction of no. the declining no reduction at high temperature was primarily attributed to excessive oxidation of hydrocarbon outside zeolite pores. besides, the relatively high temperature environment would possibly inhibit adsorption of intermediate species on the catalyst surface for the scr process. 3.2. mechanism and kinetic modeling the mechanism of catalytic reduction of no is quite complicated because it composed of multiple reaction steps and formation of various intermediate species [8,9]. it was reported that there were a number of active sites for each reaction step in the hc-scr of no [1]. there were sites for the oxidation of no to no2, sites for the coupling of nitrogen-containing molecules, sites for the activation of hydrocarbon and sites for the formation of carbon oxides [1]. moreover, the same site might be involved in more than one reaction step [1]. this was supported by a fouriertransformed-infrared study indicating that at least two active sites were involved in the no reduction process [9]. one site was associated with the al site of the zeolite support and the other site was attributed to metal cations such as cu2+ exchanged into the zeolite structure. for simplification of the reaction mechanism, it was assumed that the catalyst contained only one type of active site on which adsorption, surface reaction and desorption took place [1,9]. these adsorption, surface reaction and desorption steps are represented as follows. adsorption. o2 + 2 s  2o·s (2) no + s  no·s (3) c4h10 + s  c4h10·s (4) iium engineering journal, vol. 4, no. 1, 2003 i. s. said et al. 16 surface reaction. c4h10·s + 11o·s + 2no·s  n2·s + 4co2·s + 5h2o·s + 4s (5) desorption. n2·s  n2 + s (6) co2·s  co2 + s (7) h2o·s  h2o + s (8) these reaction steps could be generalized as eq. (9). 2no + c4h10 + 5.5 o2  n2 + 4co2 + 5h2o. (9) the surface reaction expressed by eq. (5) is where adsorbed molecules of i-butane, oxygen and nitrogen oxide react on the catalyst surface. oxygen concentration is much higher compared to no and i-butane, therefore the rate of reaction will be independent of oxygen concentration. assuming adsorptions of no and hydrocarbon control the reaction, the rate of reaction (-rno, mol/m3.s.gcat) based on lhhw [10,11] is expressed as: where, cno and cch are the concentrations of no (ppm) and i-c4h10 (ppm) respectively, k1 (m3/mol) and k2 (m3/mol) are the adsorption equilibrium constants for no and i-c4h10 respectively and ks (m3/mol.s.gcat.) is the apparent reaction rate constant. for estimating the rate of reaction from experiments, concentrations of no was measured at different space time in the temperature range of 250 c – 400 oc as shown in figure 2. the curves were fitted with suitable polynomials obtained from the microsoft excel program to represent the trend of the concentration profile. the second order polynomials presented in table 2 satisfactorily fitted the concentration profile at each temperature. nevertheless, a few data points were omitted from the polynomials and initial concentrations (cno)o were slightly different as per polynomial data fitting. the rate of reaction, (-rno), in eq. (10) was calculated from the differential of cno polynomial, (-dcno/d) divided by the weight of catalyst at respective space time (). based on the general reaction eq. (9), the concentration of hydrocarbon, cch, could be stochiometrically expressed in terms of cno as in eq. (11). both rates of reaction obtained from the experiment at each temperature and concentrations of no were used as inputs for a non-linear regression analysis to obtain estimated values of ks, k1 and k2 [11,12]. these values are summarized in table 3. it can be seen that the adsorption equilibrium constant for no (k1) is remarkably larger than that of i-c4h10 (k2). this further suggests that the adsorption of no could be rate controlling. it was also reported that the adsorption of the hydrocarbon (1600 ppm) and water vapor (2 %) did not appear in the denominator of the heterogeneous rate model using co-ferrierite catalyst [10]. the study indicated that the adsorption (-rno)´ = kk1k2 cnocch (1 + k1cno + k2 cch) (-rno)´ = kk1k2 cnocch (1 + k1cno + k2 cch) iium engineering journal, vol. 4, no. 1, 2003 i. s. said et al. 17 effect of either methane or water rapidly decreased at increasing reaction temperatures [10]. shen and kawi [13] found negligible effect of propylene adsorption on the catalytic reduction of no using pt-mcm-41 catalyst. the study suggested that most of the active sites of the catalyst were blocked by no species even at low temperatures of below 150 oc [13]. the activation energy of the reaction was estimated from the slope of the plot of apparent rate constant, ks against the reciprocal of reaction temperature, 1/t shown in figure 3. from the slope of the curve, the activation energy was found to be 58 1 kj/mol. this value of activation energy was also lower than reported values of 62 kj/mol (coox-alumina) [9], 92 kj/mol (co-ferrierites) [10], and 123 kj/mol (cuzsm5) [14] due to different types of catalysts. the bimetallic catalyst in the present study was active in the low temperature range of 250 c – 450 oc that favored catalytic reduction of no over oxidation of the hydrocarbon. the heat of adsorption was estimated from the slope of the plot of k1 against the reciprocal of temperature shown in figure 4. the apparent adsorption equilibrium constant is expressed as in eq. (12) [15]. ads 1 h a exp rt k        (12) where, a is the pre-exponential factor (es/r), (-hads) is the heat of adsorption, r is the gas constant (8.314 j/mol. k) and t is the temperature (k). the heat of adsorption was found to be –62kj/mol, a negative value since adsorption is an exothermic process. the heat adsorption value was considerably high due to possible covalent bonds between no gas molecules and metal active sites [16]. in fact, heat of adsorption of no on other transition metals such as ni and pd were as high as 105 – 130 kj/mol [16]. the heat of adsorption data in the catalytic reduction of no were not reported in the literature, therefore it was difficult to compare the value obtained in the present study from the reported value. it was suggested that the langmuirhinshelwood-hougen-watson (lhhw) rate expression was more suitable for catalyzed reactions. its denominator took into account the reduction in rate due to adsorption phenomena [15]. 3.3 simulation of rate law model for prediction of no reduction the proposed heterogeneous model in eq. (10) took into account the adsorption effects of no and hydrocarbon. it was of interest as well to evaluate the pore diffusion effect on the reaction rate because the catalyst was in the particle form. results from two experimental runs at 20,000 hr-1 with pt-cu-zsm5(i) catalyst conducted at two different particle sizes of 0.80-1.00 mm and 0.25-0.35 mm are shown in figure 5. it shows that both particle sizes gave almost same values of no reduction (i.e. maximum no reduction of about 80 % at 350 oc). this suggests that particle diffusional effect could be neglected in the kinetic model. the absence of mass transfer effects were also checked using weisz-parter criterion [11]. it was found that internal pore diffusion had negligible effect on the rate of reaction [17]. therefore, the rate model represented by eq. (10) is free from mass transfer effects and could be used for prediction of no reduction in a packed bed catalytic reactor. for simulation of fractional values of no reduction, integration was performed on the expression for contact time (, second) for a packed bed reactor, eq. (13) and is simplified as eq. (14). iium engineering journal, vol. 4, no. 1, 2003 i. s. said et al. 18   no(x ) no 0 no dx τ r r    (13) )14( x .759 1 lnk )x1(75.9 x .759 ln )x .759(c 1 c 5.6 τ nof 1 nof nof nofnono oo                       ss kk where, (xno)f represents the final fractional reduction of no. the integration was performed by eliminating the hydrocarbon adsorption effect as suggested by negligible k2 values. the value of  was calculated by using a series of different (xno)f values until it matched with that of the experimental values. the simulated values of no reduction, (xno)cal. were compared with experimental values, (xno)exp, as parity plots shown in figure 6. figure 6 clearly shows that simulated values do not deviate significantly from the experimental values. however, a few simulated values at 400 c and 450 oc were significantly higher than experimental values. it probably suggested a change in the reaction mechanism since the mean errors were in large interval (i.e. 21.6  18.5, 24.0  20.4 at 400 and 450 oc respectively) at 95 percent level of confidence [17]. 4. conclusions the kinetics parameters were evaluated based on reaction mechanism in the no reduction process involving hydrocarbon. a heterogeneous model was based on the langmuir-hinshelwood-hougen-watson (lhhw) reaction mechanism between no and hydrocarbon on the catalyst surface. the activation energy of 58.1 1 kj/mol reflected the low range of temperatures (250 c – 450 oc) for the optimum reduction of no. the reaction parameters for no reduction obtained from the model were used to predict the reduction of no over wide range of temperature (250 c – 450 oc) and gas hourly space velocity of 10,000 – 100,000 hr-1. the predicted values of no reduction from the model did correlate quite well with experimental values since the model took the adsorption effect of no into account in addition to concentrations of no and i-butane in the rate expression. it showed that the no adsorption had a major influence on the rate of reaction with 61.8  kj/mol of heat of adsorption reflecting strong interaction between no molecules and active metal species on the catalyst surface. the proposed model was tested and validated on the basis of experimental data and statistical analysis, which was applicable within a certain range of conditions studied experimentally. the proposed model should not be extrapolated beyond its range of study. acknowledgements the authors acknowledge the short term research grant provided by universiti sains malaysia, penang (fpp 2001/040) that has enabled the production of this article. references [1] m. shelef, “selective catalytic reduction of nox with n-free reductants”, chem. rev., vol. 95, pp. 209-225, 1995 iium engineering journal, vol. 4, no. 1, 2003 i. s. said et al. 19 [2] p.j ramirez, g. cortes, j.m.i. gomez, f. kapteijn, j.a. moulijn, and s.m.c. lecea, “reduction of no by propene over pt, pd, and rh-based zsm-5 under lean burn conditions”, react. kinet. catal. lett., vol. 69, no. 2, pp. 385-392, 2000. [3] i. m., saaid, a.r. mohamed, and s. bhatia, “comparative study of cuzsm5 and fe-zsm5 in the scr of nox with i-c4h10”, react. kinet. catal. lett., vol.75. no. 2 pp. 359-365, 2002. [4] i. m., saaid, a.r. mohamed, and s. bhatia, “activity and characterization of bimetallic zsm-5 for the selective catalytic reduction of nox”, journal of molecular catalysis a: chemical, vol. 189, pp. 241-250, 2002. [5] g. cortes, j.m.i. ramirez, j.p. gomez, f. kapteijn, j.a. moulijn and s.m.c. lecea, “effect of the support in de-nox hc-scr over transition metal catalysts”, react. kinet. catal. lett., vol. 70, no. 2, pp. 199-206, 2000. [6] g. cortes, j.m.i. gomez, a.l. solano, and s.m.c. lecea, “low temperature scr of nox with c3h6 under lean–burn conditions on activated carbonsupported platinum”, app. catal. b: env.,vol. 25, pp. 39-48, 2000. [7] c.e quincoces, a. kikot, e.i basaldella, and m.g. gonzalez, “effect of hydrothermal treatment on cu-zsm5 catalyst in the selective reduction of no”, ind. eng. chem. res., vol. 38, pp. 4236-4240, 1999. [8] p. carniti, a. gervasini, v. h. modica and n. ravasio, “selective catalytic reduction of no with ethylene over a series of copper catalysts on amorphous silicas” appl. catal. b: env., vol 28, pp. 175-185, 2000. [9] t. maunula, j. ahola and h. hamada, “reaction mechanism and kinetics of nox reduction by propene on coox/alumina catalysts in lean conditions”, appl. catal. b: env. vol. 26, pp. 173-192, 2000. [10] y. li and j.n. armor, “selective reduction of nox by methane on coferrierites”, journal of catalysis, vol. 150, no. 2, pp. 376-387, 1994. [11] h.s. fogler, elements of chemical reaction engineering, prentice hall, 3rd edn. new jersey, 1999. [12] w.h. press, b.d. flannery, s.a. teukolsky and w.t. vetteoling, numerical recipes, cambridge univ. press., cambridge, 1986. [13] s.c. shen and s. kawi, “kinetics studies of selective catalytic reduction of no by propylene on pt-mcm-41 catalyst”, catal. today. vol. 68, pp. 245-254, 2001. [14] v. tomasic, z. gomzi, and s. zrncevic, “catalytic reduction of nox over cuzsm5 catalyst”, appl. catal. b: env. vol. 18, no. 3-4, pp. 233-240, 1998. [15] c.n. satterfield, heterogeneous catalysis in industrial practice, 2nd edn., mc. graw hill inc., singapore,1993. [16] j.m.thomas, and w.j. thomas, principles and practice of heterogeneous catalysis, vch verlagsgesellschaft mbh, weinheim (germany), 1997. [17] i.m saaid, “develeopment of zeolite supported catalyst for the reduction of nox in diesel engine emissions”, ph.d thesis, p.pinang, univ. sains malaysia, 2002. biographies dr. ismail mohd saaid: he received b.sc in petroleum engineering from the university of missouri-rolla in 1993, msc. in environmental technology from the university of manchester institute of science and technology in 1998 and ph.d in chemical engineering from the universiti sains malaysia in 2003. prior to iium engineering journal, vol. 4, no. 1, 2003 i. s. said et al. 20 completing his msc he worked for bp oil malaysia, kuala lumpur. his current research interest includes environmental catalysis and petroleum reservoir engineering. at present he is lecturer in mechanical engineering program, universiti teknologi petronas, bandar sri iskandar, 31750 tronoh, perak, malaysia assoc. prof. dr. abdul rahman mohamad: he is the dean, school of chemical engineering, engineering campus, universiti sains malaysia. he received his b. sc in chemical engineering from university of southern california, los angeles in 1986. he obtained his m.sc and p.hd also in chemical engineering from the university of new hampshire, usa. his research areas are in catalysis and environmental engineering where he has published more than 70 papers in local and international journals and conferences. prof. subhash bhatia: he joined school of chemical engineering, universiti sains malaysia in 1995. he was a full professor at the department of chemical engineering, indian institute of technology, kanpur (india). prof. bhatia was a visiting faculty at the university of queensland, australia from 1988-89 and 19941995. his research interests are zeolite catalysis, chemical reaction engineering and environmental catalysis. he has written a book on zeolite catalysis that was published by crc press, usa and has published more than 80 papers in national and international journals. c 5.6 τ noo      s kk microsoft word vol 5-1 pages 55-64.doc iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 55 the effect of the operating conditions on the apparent viscosity of crude palm oil during oil clarification sulaiman al-zuhair*, mirghani i. ahmed‡ and yousif a. abakr‡ * school of engineering, taylor’s college, subang jaya, malaysia. ‡ department of mechanical engineering, international islamic university, malaysia. e-mail: mirghani@iiu.edu.my abstract: this paper discusses the apparent viscosity of crude palm oil, using rotary viscometer, under different boundary conditions. it was experimentally shown that the apparent viscosity of palm oil drops with increasing of the shear rate and the temperature. however, the effect of temperature on the viscosity tends to fade at temperatures beyond 80 oc. a correlation between the apparent viscosity of crude palm oil and the operating conditions was developed. this correlation can be used in design of crude palm oil settlers and in determining the optimum operating conditions. key words: crude palm oil, apparent viscosity, shear rate, modelling, separation 1. introduction the raw palm oil as pressed from the fruits is a product even cruder than the commercial crude palm oil. it contains a lot of fibres, dirt, water, soluble impurities and considerable amount of debris. the average composition (volume to volume) of the raw palm oil as received from the screw press is 40-75% oil, 10-40% water and 6-25% nonorganic solids [1]. the crude palm oil is left in a clarifier to allow for the separation of oil from water (together with most of the debris). water and its content of debris form immiscible liquids with the oil. the heavier water and debris settle to the bottom leaving the relatively clean and light oil on the top to be skimmed off later. previous studies found that a lot of oil is lost in the settler and most of the waste water is produced there. it is very important to determine the optimum design parameters of crude palm oil settler. the separation of clear oil droplets from crude palm oil mixture is treated as a coalescence process [2-4], with oil droplets rising upward. to determine the  corresponding author iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 56 optimum design parameters of crude palm oil settler, it is essential to determine the rising velocity of oil droplets in the aqueous phase. there are two main factors affecting the rising velocity, namely, density and viscosity [2]. the effect of the operating conditions, such as temperature and shear rate on the density is relatively small compared to their effect on viscosity [5-7]. hence, the density may be treated as a constant and the viscosity is considered the main operating condition influencing the separation process. regardless of the numerous research conducted previously, a reliable model to predict the effect of the independent operating conditions on the viscosity of crude palm oil is still lacking.this is due to the difficulty in studying crude palm oil, which behaves as a non-newtonian fluid [1], and also due to the composition complexity of the mixture itself (oil, water and debris). the fact is that, in all previous works to determine the design equations of crude palm oil settlers, the viscosity of crude palm oil mixture was always assumed, incorrectly, to be an additional variable, independent of temperature and shear rate [1, 6]. in this study, a correlation between viscosity and the independent operating conditions affecting it will be formulated (i.e., temperature and shear rate). this correlation will be employed into the design eqs. of crude palm oil settlers, and will be used to determine the optimum operation conditions. the proposed correlation will reflect the combined effects of both shear rate and temperature. 2. the mathematical model previous experimental work proved that crude palm oil is a non-newtonian fluid. the apparent viscosity was shown to change with shear rate applied. the power law, eq. (1), is widely used in the literature to express the effect of shear rate on the viscosity of nonnewtonian liquids at constant temperature [8-10], n-1 = k  (1) the apparent viscosity of crude palm oil was found to decrease with shear rate [1], this behaviour is called shear thinning, which is characterised by the value of the power index n being less than unity. on the other hand, temperature changes also affect the apparent viscosity of crude palm oil. like any other liquid, the apparent viscosity of crude palm oil is expected to reduce as temperature increases. this phenomenon is explained by the reduction of the intermolecular attractions with increasing temperature. in this work the effect of temperature on the apparent viscosity of non-newtonian liquids at constant shear rate is expressed using arrhenius expression [8],  e ave rta   (2) equations (1) and (2) describe the separate effects of either shear rate or temperature, however, it is desired to have an eq. that combines both effects (shear rate and temperature) in one model eq. that can be used in the design eq.s of crude palm oil settlers. mccabe et al [11] derived an expression that combines the effects of the shear rate and the temperature by combining eqs. 1 and 2, iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 57   1 av g e n r t a ok e          (3) the constants found in eq (3) can now be determined experimentally. 3. materials and method 3.1 materials screened crude palm oil samples were obtained from dengkil mill, malaysia, and diluted with 40% (vol/vol) water to simulate the mixture that enters the crude palm oil settler in the mill. 3.2 apparatus there are many methods to measure the apparent viscosity of non-newtonian fluids [11]. the apparatus used in this study is rotary viscometer (cannon 2020 lv, viscosity range 0.001 to 2000 pa sec, with accuracy of 1% ) in which a motor with variable speed drives a spindle immersing in the sample to be investigated with a spiral spring. the viscosity of the sample generates a resisting torque at the spindle, which can be measured with the aid of the torsion of the spiral spring and through a computer software. the shear stress can be calculated for different shear rates. the computer software is also used to calculate the apparent viscosity from the measured values of shear stress at various shear rates. a water jacket, with circulating temperature-controlled water, surrounds the sample pot to control the temperature. different shear rates were obtained by changing the size and the speed of the spindle. figure 1 shows the apparatus used. 3.3 methodology a sample of 25 ml volume was contained in the sample pot each time. the temperature of the sample was controlled by adjusting the temperature of the circulating water in the jacket. measurements were carried out for the changes of the apparent viscosity with shear rate at five different temperatures 40 oc, 50 oc, 60 oc, 70 oc and 80oc. 4. results and discussions the measured apparent viscosity at different temperatures and different shear rates are shown in fig. 2. it can be clearly seen that the crude palm oil mixture is a shear thinning fluid, as the viscosity decreases with the increase in shear rate. it can be also seen from fig. 2. that the apparent viscosity decreases with increasing the temperature, which is the case for all liquids, since the intermolecular attraction decreases with increasing temperature. iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 58 fig. 1: the rotary viscometer (cannon 2020 lv). the natural logarithmic of a was drawn against the natural logarithmic of  at five different temperatures and the results are shown in fig. 3. it can be clearly seen that the straight lines generated are almost parallel with identical slopes, which validates the proposed model. the values of n-1 at each temperature were determined from the slopes of the straight lines in fig. 3. the average value of n was then calculated as 0.4 with standard deviation of  0.036, which indicates a deviation of less that 10%. to determine the activation energy,  1ln na   was plotted against (1/t), and (eav/r), and ln(k) were determined from the slope and the intercept, respectively of the straight line generated (fig. 4) as predicted from eq (3). from the slope of the straight line in fig. 4., eav/r = 1511.6 1k  , and from the intercept, k = 3.5x10-3. the standard deviations of the results were low and in the range of 0.020 to 0.058, and presented in the error bars found in fig 4. iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 59 0.1 0.3 0.5 0.7 0.9 0 0.4 0.8 1.2 1.6 2 shear rate,  (sec-1) a pa re nt v is co si ty ,  a ( p a se c) 40oc 50oc 60oc 70oc 80oc fig. 2: the effect of temperature and shear rate on the apparent viscosity of crude palm oil. 40oc [y = -0.55x + 0.19] -1.8 -1.4 -1 -0.6 -0.2 -1.2 -0.7 -0.2 0.3 ln () ln (  a) 50oc [y = -0.56x 0.99] 60oc [y = -0.62x 1.19] 70oc [y = -0.62x 1.25] 80oc [y = -0.62x 1.38] fig. 3: the variation of ln(a)with ln() at different temperatures. iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 60 y = 1511.6x 5.6565 -1.5 -1.3 -1.1 -0.9 -0.7 0.0028 0.0029 0.003 0.0031 0.0032 0.0033 1/t (k-1) ln ( a/ n1 ) fig. 4: ln (an-1) versus 1/t the correlation between the apparent viscosity of crude palm oil and the operating conditions, including the shear rate and temperature is therefore, 3 0 61511 63 5 10 exp 0 02. . μ . γ . t         (4) fig. 5 shows the comparison between the experimental results and the proposed model curves that were based on eq (4), for three different temperatures (40, 60 and 80 oc). it can be noted that the model predicts fairly well the apparent viscosity at various shear rates for all three temperatures. the apparent viscosity correlation, eq. (4), can be introduced directly into any design eq. of crude palm oil settler, instead of keeping the viscosity as an additional variable and can be used to determine the optimum operating temperature. the rate of separation of crude palm oil increases as the viscosity decreases, hence, the temperature and the shear rate should be increased. the increase in temperature is always favourable for increasing the rate of oil separation, and crude palm oil settlers should be designed to operate under high temperatures, however, energy consumption and equipment materials costs should be considered. furthermore, it can be seen from fig. 6 that the effect of temperature on the viscosity tends to fade at temperatures beyond 80 oc, so increasing the temperature beyond this point, in addition to the energy consumption and material cost stresses, will not result in substantial decrease in the viscosity to justify this increase. on the other hand, iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 61 increasing the shear rate, although results in reducing the viscosity, enhances the dispersion of oil, but it is not advisable to increase it by agitation or by any other means. 0.1 0.3 0.5 0.7 0.9 0.3138 0.6276 0.9414 1.8828 shear rate,  (sec-1) a pa re nt v is co si ty , m a (p a se c) 40˚c 50˚c 60˚c 70˚c 80˚c fig. 5: comparison between experimental results and the proposed model curves showing the effect of agitation speed on the apparent viscosity at three different temperatures (40, 60 and 80 oc) figure 6 shows the combined effect of the shear rate and the temperature on the apparent viscousity of crude palm oil. this figure is a graphical presentation of eq. (4), where the effects of two parameters are both presented on the same graph. iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 62 fig. 6: the combined effects of temperature and shear rate on the apparent viscosity. 5. conclusion analytical and experimental studies of the behaviour of the crude palm oil in the palm oil settlers were conducted. a correlation between the apparent viscosity of crude palm oil and the operating conditions, has been determined. the results showed a good agreement between the experimental results and the estimated values of the obtained correlation. the new correlation reflects accurately the combined effects of both shear rate and temperature on the apparent viscosity of crude palm oil. this correlation can be employed into the design of crude palm oil settlers, and can be used also to determine the optimum operation conditions for palm oil settlers. references [1] k.h lim. and d.a.m whiting, the influence of non-newtonian behaviour of crude palm oil on the design of the clarification station equipment. the proceedings of the malaysian international symposium on palm oil proceedings and marketing, international developments in palm oil. malaysia, 1977. [2] e. barnea, and j. mizrahi, separation mechanism of liquid/liquid dispersion in deep layer gravity settler, part i, partii, part iii, and part iv. trans. inst. chem. eng., vol. 53, pp. 6192, 1975. iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 63 [3] s. hartland, and s.a.k. jeelani, choice of model for predicting the dispersion height in liquid-liquid gravity settlers from batch settling data. chem. eng. science, vol. 42, no. 8, pp. 1927-1938, 1978. [4] a. fasano, the dynamics of two-phase liquid dispersions: necessity of a new approach, milan journal of mathematics, vol. 70, no. 1, pp. 245-264, 2002. [5] b. marcia, s. günter, j.s. milan, o.a. elseoud, vegetable oils-based microemulsions: formation, properties, and application for "ex-situ" soil decontamination, colloid polym sci, vol. 280, pp. 973-983, 2002. [6] k.h. lim, theory and application of clarification in palm oil mills. harrisons and crosfield (m) sdn. bhd. malaysia 1982. [7] porim. data sheet for engineers. e. engineering news 1987. [8] n. aksel, a model for the bulk viscosity of a non-newtonian fluid, continuum mechanics and thermodynamics, vol. 7, no 3, pp. 333-339, 2002. [9] b.r. munson, d.f. young and t.h. okishi, fundamentals of fluid mechanics, third ed., john wiley & sons inc., new york. 1998. [10] g.b. wallis, one-dimensional two-phase flow, mcgraw-hill, new york. 1969. [11] w.l. mccabe, j.c. smith and p. harrott, unit operations of chemical engineering. 5th edition. mcgraw hill inc., new york. 1993. [12] n.a. park, t.f. irvine, an alternative method of simultaneously measuring viscosity and density of newtonian and power-law fluids using the falling needle viscometer. proc. of the xiiith international congress of rheology, cambridge, uk, vol. 3, pp. 140-142, 2002. nomenclature aα constant defined by eq. (2) (pa sec) eav activation energy (j mol-1) k constant defined by eq (1) ko constant defined by eq (3) n constant defined by eq (1) n the average value of the measured n r universal gas constant (j mol-1 k-1) t temperature (k) greek letters  shear rate (sec-1)  apparent viscosity (pa sec) iium engineering journal, vol. 5, no. 1, 2004 s. al-zuhair et al. 64 biographies sulaiman al-zuhair received his b.sc. in chemical engineering from jordan university of science and technology in 1996, m.sc. in chemical and environmental engineering from university putra malaysia in 1998, and ph.d. in biochemical engineering from university of malaya in 2003. at present, dr. al-zuhair works as a chemical engineering lecturer at taylor’s college, subang jaya, malaysia. mirghani i. ahmed was born in singa, sudan in 1956. he received his m.sc. and ph.d. in mechanical engineering from budapest technical university, hungary in 1987. he worked with the sudan university of science and technology as asst. prof. from 19871989. he worked with ibm – canada as research associate from 1989 1996. he is currently an associate professor at the department of mechanical engineering, international islamic university malaysia (iium). dr. ahmed’s primary research interests are renewable energy, thermal comfort problems, electronic component cooling, modeling and simulation, computational fluid dynamics applications and heat transfer. yousif a. abakr received his b.sc. and m.sc. in mechanical engineering from university of khartoum. he worked as a mechanical engineering lecturer at sudan university of science and technology, 1995 – 1997. currently, he is a ph.d. student at the international islamic university, malaysia. microsoft word 3_v17no2_compiled_v3_26nov16.docx iium engineering journal, vol. 17, no. 2, 2016 che mustapha et al. 21 efficient capacitance sensing for wireless health monitoring systems nurul arfah che mustapha*, a.h.m. zahirul alam, sheroz khan, and amelia wong azman department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. *corresponding author: n.c.2013@ieee.org (received: 5th jan. 2016; accepted: 26th mar. 2016; published on-line: 30th nov. 2016) abstract: this paper presents a low power capacitance to voltage converter (cvc) circuit using two differential amplifier circuits, two schottky rectifier diodes constructed in a symmetrical manner and combined with instrumentation amplifier circuits. the differential capacitance to voltage simulation work has been realized with inexpensive discrete components. energy from a combination of solar, vibration and heat sources is expected to charge the capacitance circuit. a constant dc voltage of 3 v has been used to power the cvc circuit in this work. simulation has shown that the converter circuit consumes 3.9 mw of total power, and operates at 40 khz using a 400 mv excitation signal. the circuit is able to detect changes of capacitance from 4 – 12.5 pf using a reference capacitance of 5 pf. a sensitivity of 0.132 mv for 1 ff capacitance change has been observed in the circuit. using discrete components with same component values as in previous work, this circuit has shown more sensitivity in capacitance detection with less power consumption. abstrak: kertas kerja ini membentangkan berkenaan litar penukar kapasitor voltan (cvc) berkuasa rendah dengan menggunakan dua litar penguat pembezaan, dua diod schottky, dibina secara simetri dan digabungkan dengan litar instrumen penguat. kerja simulasi litar pembezaan kapasitor voltan ini telah dibangunkan dengan menggunakan komponen diskrit murah. kombinasi tenaga dari solar, getaran dan haba digunakan untuk memberi sumber tenaga kepada litar kapasitor. voltan dc tetap sebanyak 3 v telah digunakan sebagai sumber tenaga cvc kerja ini. menerusi simulasi, didapati litar penukaran ini menjana 3.9 mw daripada jumlah tenaga, beroperasi pada kadar 40 khz dengan menggunakan 400 mv signal pemula. litar ini mampu mengesan penukaran kapasitan dari 4 – 12.5 pf menggunakan kapasitan rujukan 5 pf. tahap kepekaan pada 0.132 mv bagi tiap 1 ff perubahan kapasitan telah dikesan menggunakan litar ini. dengan menggunakan komponen diskrit dan nilai komponen yang sama seperti kerja sebelumnya, litar ini telah berhasil menunjukkan tahap kepekaan yang lebih sensitif dalam mengesan perubahan kepekaan dengan nilai penggunaan kuasa yang berkurangan. keywords: energy harvester; differential capacitance sensing; capacitance measurement system; health monitoring system 1. introduction recently, demand for wireless communications appliances has been on the rise. the wireless data communication approach, though not as reliable as the wired approach, is a preferable choice in many industrial applications where space and accessibility are not always guaranteed. designers of such appliances began searching for alternative ways to iium engineering journal, vol. 17, no. 2, 2016 che mustapha et al. 22 power their designs including opting for the use of the energy harvesting principle instead of the conventional wired or battery-powered methods. one of the appliances that will benefit the most from this research is smart wireless sensor technology. smart wireless sensors are part of an emerging sensor environment with essential features such as on-board micro-processors, sensing capabilities, wireless communication, battery-less power, and low-cost maintenance. previously, conventional wireless sensor nodes have utilized batteries as the main power supply. unfortunately, some of the known issues when using batteries occur during battery replacement, including interruption of services, loss of valuable time, tedious maintenance work, and additional operational costs during maintenance. therefore, it is favorable, even crucial, for smart sensor wireless systems to be equipped with self-generated power systems for a sustainable power supply. the self-generated power sources could come from any of the ambient sources that can be found in an industrial environment such as vibration, heat, water, human activity, and wind. 2. background and motivation capacitive measuring systems represent an important technology in transducer systems. the motivation behind using capacitive measuring system is that they provide easy and efficient conversion of changes in a parameter of interest into a wide range of capacitance changes, which are in turn changed into proportional voltage or frequency changes. the advantage here is that these conversions take place without functionality loss compared to other systems, such as inductive systems. using a source of vibrations and converting mechanical energy to electrical energy provides a promising solution for powering wireless sensor nodes. this method has been comprehensively researched in recent years. among the vibrations transducer methods used are piezoelectric, electromagnetic, and the capacitive-inductive or capacitive-electrostatic approach [1-4]. each method has its own advantages and disadvantages, but none can currently provide a solution with a sufficient power output [5, 6]. the selection of converting device is dependent on either capturing or measuring the available physical parameters such as displacement, velocity and acceleration. many wireless electronic devices such as tiny network wireless sensor nodes, wireless health monitoring systems, as well as consumer products such as smart phones have severely constrained power sources [1, 7]. the main challenge in the mentioned devices is largely with the effort to sustain a continuous and reliable power supply without the presence of batteries, which either require charging or replacement with a new battery altogether at the expense of cost and time. smart wireless powered sensors have been proven to be cost effective and an alternative solution to this problem when realized properly, particularly in electronic devices used in applications such as in structural health monitoring (shm) systems, monitoring forest fires, medical implants, ocean pollution spillages, etc. in this work, a capacitive sensor-based circuitry for wireless sensor devices is proposed using a hybrid energy harvesting technique, shown in fig. 1, where the energy generated is expected to be able to operate in the wireless frequency range with sufficient output power for the wireless sensor nodes. this work focuses on deriving energy from vibrations complemented by thermal energy. the method of generating energy is based on the wireless sensor network characteristic of lowering the response frequency, maximizing the bandwidth of frequency operation, lowering power consumption, and generating voltage. iium engineering journal, vol. 17, no. 2, 2016 che mustapha et al. 23 fig. 1: topology of the proposed capacitance sensing wireless sensor node. 3. state of the art it is important to reduce a device’s power requirement regardless of whether the power is from an energy harvester or from batteries. this is especially true with portable devices such as computing devices, medical implants, military equipment and wireless sensor networks. most of current research has focused on the microwatt to hundred milliwatt range of power output energy harvesters [4, 8]. the smaller the device size is, the smaller its power requirement becomes. when power requirements are at a minimum in modern devices, they are suited to harvesting energy from their environment from such sources as vibration, heat, and light. however, few research attempts have been made on medium range power output that would be especially suitable for mobile applications using energy harvester techniques [2]. efficiency of the power output of energy harvesters is significantly limited by the effectiveness of the energy converting transducers used for energy conversion. research in [9] has stated that power requirement must be scaled down to a size of less than 1 cm3 and the power consumption goal should be below 100 µw. it is necessary for the wireless sensor network to be operated in the range of at least 100 µw to 100 mw [10, 11]. portable electronic gadgets such as lightweight mobile smart phones, capacitive multi-touch screen tablet pcs, and all-in-one-computers, have been extensively developed over the past years [12, 13] while the focus on reducing the battery reliance of such devices has been gaining importance. such mechanisms are being researched in which energy is harvested from means such as vibration, solar, wind, heat, shoe power, water, and oceans. the difference between these techniques lies in the circuit design and the operation principle on which such energy conversion techniques are based. there are three common techniques used in harvesting energy from vibration, these are: capacitive/electrostatic, piezoelectric, and electromagnetic techniques. the capacitance inductive/electrostatic harvesting technique is more frequently considered over other techniques because of its ease of implementation in mems and cmos systems. in general, the design of energy harvesting device consists of three main components: a micro-generator, a voltage booster, and a storage element [1]. the fact that harvesting devices only produce a very small amount of energy to directly power electronic circuits can become a major drawback for circuit designers and researchers [2, 5]. some efficient and useful technique should be considered to gather and accumulate this energy or to store the converted electrical energy before the harvested energy can be used to power the wireless sensor devices. research in [14] has highlighted the importance of investigating environmental conditions before designing a harvester. energy profiles from two independent and available energy sources, thermal and solar, have been the focus. however, each harvester has provided a different electrical behavior with thermal supplying a level near 100 mv and solar supplying a few volts. in iium engineering journal, vol. 17, no. 2, 2016 che mustapha et al. 24 this case, both should supply the same level of energy in order to be combined into a single power supply. energy management is required for the combination of both solar cells and thermoelectric transducers to reach a high energy yield within a short start-up time, where an independent voltage booster of an available dc/dc converter can be applied to tackle the problem. extensive work has been reported [15-19] using the capacitance technique where this technique was suitable for use in wireless application and to source sensor nodes. one of the techniques used in mems technology is the capacitive principle. energy from the environment, such as from the vibration, is used to move a parallel plate spring mass system, which is capable of converting mechanical energy into electrical energy to source the capacitive technique. this capacitive principle requires the charging of the capacitor at all time to ensure the conversion technique. in order to maintain the conversion, these capacitors should be charged with a dedicated electronic switch. however, this technique requires additional complex circuitry and presents relatively high energy losses [15]. several researchers have highlighted the choice of material for the capacitor plate used. research in [16] has suggested using a soft polymer for the sensor device in order to replace battery dependency. a parylene-electrets generator material has also been reported in [17] where this mems-friendly material offers a very high surface charge density and has the characteristic of a high-aspect-ratio spring. consequently, it allows a low resonant frequency with large amplitude which is much desired in modern applications. however, this electrets technology can cause high costs due to the production and the poling of the dielectric electrets material [18, 19]. electrets have also been known for problems with long term stability [15]. in order to avoid the problem caused by the electrets, a different approach of charging the parallel-plate capacitor has been presented in [20], which makes use of two different materials in its work function. additional electronic circuitry and mems technology is, however, much simpler than the electrets technique. 4. proposed approach fig. 2: block diagram of the proposed capacitance sensing wireless sensor node. in this work, the capacitance sensor read-out circuit shown in [21] is used for the proposed sensing node architecture in fig. 2. the differences between the circuit used in iium engineering journal, vol. 17, no. 2, 2016 che mustapha et al. 25 [21] and this work are; (1) the pmos diode is replaced with a schottky diode, (2) the voltage divider is used to generate a single source supplied by the 3 v supply, generated from an energy harvester circuit to supply all reference signal sources, vref, (3) simulation as in fig. 3 is done using the pspice simulation tool, based on real components parameters obtained from its datasheet such that it can be easily constructed using commerciallyavailable discrete components, and (4) a lower frequency of 40 khz is used in this simulation. 5. methodology the cvc circuit shown in fig. 3 has five main blocks namely, the excitation source, the differential capacitance, the differential amplifiers, the rectifier circuit and the instrumentation amplifier circuit. the excitation amplitude set in this paper is based on [21]. it is chosen in the low range for amplitude (400 mv) and frequency (40 khz) for a later energy harvester’s application. both feedback, cf and reference capacitance, cr is set fixed at 5 pf. the capacitance detection, cx is varied to the nominal value cr to get accepted linear range, of the changes of capacitance to the output voltage. fig. 3: capacitance-to-voltage sensing circuit. fig. 4: voltage divider with unity gain buffer. in order to reduce the number of signal sources, a voltage divider is used to supply the reference voltage, vref at near half the level of the signal source, vs. figure 4 shows the voltage divider with feedback connected to an inverting input amplifier to act as a unity gain buffer amplifier or voltage follower. the circuit consists of a pair of resistors connected in series to make a potential divider which feeds the divided signal source to the non-inverting input of the op-amp. the output voltage of the buffer is connected to the inverting input. the differential between two potentials is applied to the buffer differential input whose output is fed as a reference voltage to the reference input of the iium engineering journal, vol. 17, no. 2, 2016 che mustapha et al. 26 instrumentation amplifier, the non-inverting input of the differential amplifier and rectifier. the unity gain buffer can control the potential difference and stop any unwanted current from appearing across the pair of resistors. according to thevenin’s law, vref is set as approximately half of vs using the same value of resistors in ra and rb         ba a sref rr r vv (1) fig. 5: differential amplifier circuit with feedback rf and cf. the feedback loop of the differential amplifier consists of the feedback capacitor, cf in parallel with the resistor, rf as in fig. 5. rf is added to reduce presence of small dc offset voltages at the input. the feedback value is chosen to be large enough in this work (rf = 10 mω) to overcome the sensitivity to noise problem that exists in the sensor circuit. for an ideal op-amp, the current flowing through the capacitor, dt dv c in is equal to the current flowing through the feedback loop,   fcf out zr v  the frequency domain analysis is obtained by expressing the impedance of the feedback components in the complex plane. the transfer function may be written as ff xf x f f c f in out crj crj cj cj r z z v v x       11 1 (2) from eq. (2) we can derive that vout is proportional to the changes of cx+∆c in eq. (3) in ff f x out v crj c cc v  1 1 1    (3) having the advantage of very low forward voltage drop and ultrafast switching properties, a schottky diode was chosen as a rectifier. in this work, we are using a 1n711 schottky diode. it is suitable for very low power and high frequency applications. it has a very low reverse leakage current of 200 na at maximum reverse voltage, vr = 50 v. according to [21], r and c are chosen to satisfy the range of τ = rc in fext-1 < τ < fs-1, where fext is the frequency at common terminal of cx and cr while fs is the frequency at cx. iium engineering journal, vol. 17, no. 2, 2016 che mustapha et al. 27 finally, the resistor gain rg at the instrumentation amplifier is chosen according to rg = 100 kω/(g-1) [22]. in this work, rg = 100 kω is selected to obtain a g = 2 gain from the analog device, ad623. all amplifiers used in this work are used as single supply amplifiers. 6. results this work has used the power generated from an energy harvester board as its voltage supply of 3 v to power a capacitance sensing circuit. figure 6 shows the output voltage for different capacitance value from 3.5 pf to 12.5 pf. the capacitance sensing circuit consists of two amplifiers and one instrumentation amplifier with two schottky rectifier diodes. an excitation supply signal of 400 mv is supplied to the common differential terminal to check for a low excitation frequency of 40 khz. results have shown a high level of linearity in the output voltage to capacitance variation as shown in fig. 7. for nominal 5 pf, the output voltage can be summarized as in eq. (4). 82832.013432.0  xout cv (4) the output voltage is proportional to the change of capacitance sensing cx in pf range. comparison of results is listed in table 1. fig. 6: voltage output for capacitance value variation at nominal 5 pf. fig. 7: high linearity performance of dc output circuit at nominal 5 pf. iium engineering journal, vol. 17, no. 2, 2016 che mustapha et al. 28 table 1: comparison of capacitance sensing work ref csense [pf] dc voltage [v] pdiss [mw] sensitivity [mv/ff] excitation signal, vext [21] 4.99 – 5.01 1.236 – 1.263 5.384 1.32 400 mv, 400 khz this work 4.00 – 12.5 1.392 – 2.516 3.900 0.132 400 mv, 40 khz 7. conclusion simulation results on the capacitance sensing circuit have shown that the proposed circuit is able to detect capacitance changes from 4 to 12.5 pf capacitance range using a 3 v signal supply. the detected voltage is from 1.4 to 2.5 v using 400 mv excitation sources with 40 khz frequency. the present results have shown that the circuit consumed 3.9 mw of power with a high level of linearity with r squared of 0.99929. similar linear results were also valid for other nominal capacitance values (e.g: 1 pf). the simulated circuit has shown a high degree of sensitivity of 0.132 mv/ff. in future, we hope to test the device for sending data wirelessly. elimination of the excitation source can be done by realizing an oscillator circuit at the front-end of the cvc circuit in the future. acknowledgement this work was funded by the exploratory research grant scheme (ergs13-0210054), ministry of higher education malaysia. references [1] kompis c, aliwell s. (2008) energy harvesting technologies to enable remote and wireless sensing. sensors and instrumentation ktn report, 1-72. [2] krupenkin t. (2011) method and apparatus for energy harvesting using microfluidics. us patent no. us007898096b1, 1-21 [3] wang l, yuan f. (2007) energy harvesting by magnetostrictive material (msm) for powering wireless sensors in shm. proc. spie sensors and smart structures technologies for civil, mechanical, and aerospace systems, 1 – 11, [4] beeby s, tudor m, white n. (2006) energy harvesting vibration sources for microsystems applications. measurement sci. tech., 17(12):r175-r195. [5] park g, rosing t, todd m, farrar c, hodgkiss w. (2008) energy harvesting for structural health monitoring sensor networks. j. infrastruct. syst., 14(1):64-79. [6] kloub h, hoffmann d, folkmer b, manoli y. (2009) a micro capacitive vibration energy harvester for low power electronics. powermems 2009, washington dc, usa, 165-168. [7] louisiana tech university (2010) shoe power generator, embedded in the sole of a shoe, harvest energy. science daily. retrieved march 24, 2012, from http://www.sciencedaily.com /releases/2010/04/100426113137.htm. [8] krupenkin t, taylor j. (2011) reverse electrowetting as a new approach to high-power energy harvesting. nature communications, 2(448):1-7. [9] cottone f. (2011) introduction to vibration energy harvesting [powerpoint slides]. retrieved from http://wwwnipslab.org/files/file/nips%20summer%20school%202011/cottone%20introducti on%20to%20vibration%20harvesting.pdf. [10] harrop p, das r. (2009) energy harvesting and storage for electronic device 2009-2019. idtechex report. iium engineering journal, vol. 17, no. 2, 2016 che mustapha et al. 29 [11] zhu d, beeby s, tudor j, white n, harris n. (2010) a novel miniature wind generator for wireless sensing applications. ieee sensors, 1-4. retrieved from http://eprints.soton.ac.uk/271682/. [12] sharma s. (2012) estyle buyers’ guide: your prescription to the right tablet. electronics for you, 44(2):88-92. [13] sharma s. (2012) embedded: touch screens what’s the latest? electronics for you, 44(2): 69-72. [14] viehweger c, baldauf m, keutel t, kanoun o. (2012) hybrid energy harvesting for autonomous sensors in building automation. proc. ieee int. instrum. measure. tech. conf. (i2mtc 2012), 610-613. [15] kuehne i, frey a, eckstein g, schmi u, seidel h. (2006) design and analysis of a capacitive vibration-to-electrical energy converter with built-in voltage. solid-state device research conference, 36:138-141. [16] stevens institute of technology miniature (2010) energy harvesting technology could power wireless electronics. science daily. retrieved march 22, 2012, from http://www.sciencedaily.com /releases/2010/07/100709131308.htm. [17] edamoto m, suzuki y, kasagi n, kashiwagi k, morizawa y, yokoyama t, seki t, oba m. (2009) low-resonant-frequency micro electret generator for energy harvesting application. proc. ieee int. conf. mems 2009, sorrento, 1059-1062. [18] sterken t, baert k, puers r, borghs g, mertens r. (2003) a new power mems component with variable capacitance. pan pacific microelectronic symposium 2003, 27-34. [19] arakawa j, suzuki y, kasagi n. (2004) micro seismic power generator using electret polymer film. fourth int. workshop on micro and nanotechnology for power generation and energy conversion applications, 187-190. [20] kuehne i. (2008) power mems a capacitive vibration-to-electrical energy converter with built-in voltage. sensors and actuators a: physical (142)1:263-269. doi:10.1016/j.sna.2007.02.036. [21] haider mr, mahfouz mr, islam sk, eliza sa, qu w, pritchard e. (2008) a low-power capacitance measurement circuit with high resolution and high degree of linearity., midwest symposium on circuits and systems, 261-264. [22] analog devices. (1997-2008) ad623: single-supply, rail-to-rail, low cost instrumentation amplifier. [online]. available: www.analog.com/media/en/technicaldocumentation/data-sheets/ad623.pdf [retrieved oct 22, 2015] application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 saedi et al. 15 investigation of bioflocculant as dewatering aid in sludge treatment mohammed saedi jami*, maizirwan mel, aysha ralliya mohd ariff, and qabas marwan abdulazeez department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. * corresponding author: saedi@iium.edu.my (received: 15th sept 2016; accepted: 5th may 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.735 abstract: sludge treatment is one of the most important and expensive steps in water and wastewater treatment plants. chemical conditioners such as polyaluminum chloride, aluminum sulfate, fenton’s reagent, gypsum, and polyacrylamide can produce byproducts that cause health and environmental problems. moringa oleifera (mo) seeds can be used as a natural alternative to chemical conditioners. the bioactive materials have to be extracted from mo seeds for better performance. in this study, the treatment methods of mo seeds were the bioactive extraction by nacl (1 m) and oil extraction by hexane solvent, as well as the untreated (crude) seeds powder. synthetic sludge samples were prepared using kaolin suspension (5% w/v). the most effective coagulant-form was determined based on the values of settling velocity (vs) and sludge volume index (svi). results showed that extraction by nacl gave the best results of 0.41 cm/min of settling velocity and 63.39 ml/g of svi. a svi value greater than 150 ml/g indicates poor settling qualities whereas the control sludge of the current study was 100 ml/g. the most effective coagulant-form was optimized with respect to three process conditions: mo seeds dosage, mixing speed, and contact time. the experiments were designed using 2 level factorialdesign by design-expert software. the optimum process conditions were seeds dosage of 3246 mg/l, mixing speed of 102 rpm, and mixing time of 29 min. mo seeds can be considered as a natural coagulant that can be used as main sludge conditioner. abstrak: rawatan kotoran mendapan adalah salah satu rawatan penting dan termahal dalam merawat air dan sisa kumbahan loji. perapi kimia seperti poli-aluminium klorida, aluminium sulfida, reagen fenton, gipsum, dan poli-akrilamida menghasilkan sisa, di mana memberi kesan kepada kesihatan dan alam sekitar. benih moringa oleifera (mo) boleh digunakan sebagai bahan ganti semula jadi kepada perapi kimia. bahan bio-aktif perlu diekstrak daripada benih mo bagi memberi kesan terbaik. dalam kajian ini, kaedah rawatan menggunakan benih mo adalah dari ekstrak bio-aktif nacl (1 m) dan ekstrak minyak dari bahan larut hexane, serta serbuk benih tidak dirawat (mentah). sampel sintetik kotoran mendapan disediakan dengan menggunakan ampaian kaolin (5% w/v). bentuk kogulan yang paling efektif didapati berdasarkan nilai halaju malar (vs) dan indeks ketumpatan kotoran mendapan (svi). keputusan menunjukkan ekstrak nacl memberi keputusan terbaik pada halaju malar 0.41 cm/min dan bacaan pada svi 63.39 ml/g. nilai svi lebih besar daripada 150 ml/g menunjukkan kualiti kadaran malar kurang baik berbanding 100 ml/g kajian kawalan semasa kotoran mendapan. bentuk kogulan yang paling efektif telah dioptimumkan pada tiga keadaan proses: dos benih mo, halaju campuran dan tempoh campuran. eksperimen dibentuk menggunakan 2 level factorialdesign daripada perisian design-expert. keadaan optimum proses adalah pada 3246 mg/l dos benih, 102 rpm halaju campuran, dan tempoh campuran selama 29 min. benih mo iium engineering journal, vol. 19, no. 1, 2018 saedi et al. 16 boleh di kategori sebagai kogulan semula jadi dan boleh digunakan sebagai perapi utama bagi kotoran mendapan. keywords: sludge treatment; moringa oleifera; dewatering; environmental friendly 1. introduction the major aim of wastewater treatment is to eliminate or minimize the dangerous effects on public health and the environment. various types of contaminants should be removed from wastewater, such as suspended solids, biodegradable matter (organic compounds), inorganic solids, nutrients, metals and pathogenic microorganisms. in order to remove these contaminants, wastewater treatment requires physical, chemical, and biological processes. the physical and chemical processes are usually used for potable water treatment while the biological process is mainly for wastewater treatment due to the high organic concentration [1]. sludge can be generated from settling tanks during primary, secondary and advanced treatment processes. these processes separate the suspended solids and colloidal materials from the liquid body and produce sludge at high solids content of 0.25 12% by weight [2]. with the high range of solid concentration, sludge management is considered to be one of the most difficult and expensive processes in wastewater treatment [3]. sludge should pass through many treatment stages before disposal, which may include thickening, anaerobic and aerobic digestion, and dewatering. thickening and dewatering processes reduce the content of water and increase solid concentration. the dewatering process occurs during use of mechanical systems such as belt filter presses, centrifuges or gravity drainage, and evaporation in sand drying beds. usually, mechanical dewatering equipment is expensive and consumes high amounts of energy [1]. dewatering by chemical conditioners is very efficient and it is used worldwide, but has negative impacts on human health and the environment associated with the formation of byproducts [4]. moringa oleifera (mo) seed is a natural polymer and a highly biodegradable coagulant that is affordable and environmentally friendly. the seeds have potential to be used as sludge conditioner for thickening and dewatering. these seeds were investigated for the removal of turbidity, heavy metal ions, color, and as disinfectant [5-8]. mo seeds with a cationic property are expected to be efficient in adsorbing the sludge particles and neutralizing the charge on their surface resulting in effective coagulation and elimination of the hazardous impacts on human health and the environment. 2. materials and methods 2.1 materials and equipment dry mo seeds were imported from genius herbs company, india. kaolin suspension was used as the synthetic sludge, which was bought from r&m chemicals sdn bhd. nacl from hmbg was used for bioactive material extraction. a kitchen blender was used for seed blending. soxhlet apparatus was used for oil extraction from mo seeds. jar test apparatus was used for process condition optimization. vacuum filtration with a buchner-funnel and whatman-filter-paper #3 were used to determine tss. a 500 ml graduated cylinder and stopwatch were used for the sludge volume index (svi). other laboratory equipment included a magnetic stirrer, a drying oven, and a weighing balance. iium engineering journal, vol. 19, no. 1, 2018 saedi et al. 17 2.2 methods 2.2.1 preparation of sludge sample sludge samples were prepared from kaolin suspension by adding 5 g of kaolin to 1 liter of distilled water in order to generate a sludge with 5% total solids (w/v). the sample was mixed at a speed of 200 rpm for about 10 min using jar test apparatus [9,10]. 2.2.2 preparation of different forms of mo seeds the shelled mo seeds were ground by kitchen blender and screened using a 212 µm sieve. three types of mo seeds were prepared as natural conditioners: crude mo seeds, defatted mo seeds, and mo extracted by nacl (1 m). all coagulant forms were used as an aqueous solution. the crude mo seed powder was used for coagulation without any treatment after mixing with distilled water. the second type was oil-extracted by hexane solvent using 10 g of mo seed powder with 200 ml of hexane. soxhlet extraction apparatus was used for oil extraction [6,9,11]. the first two types (crude and defatted mo seed powder) were mixed with distilled water by adding 10 g of powder into 1 liter distilled water, then, the mixture was rapidly mixed for 10 min to extract the bioactive materials. finally, the mixture was filtered using filter paper and the insoluble powder particles were removed. for salt extraction, 58.44 g of nacl was added to 1 liter of distilled water and mixed using jar test apparatus. the nacl solution was mixed with 10 g of crude mo seeds for 10 min. finally, the mixture was filtered using filter paper and the insoluble powder particles were removed [12]. 2.2.3 experimental procedures jar test apparatus was used for sludge conditioning using six beakers of 1 liter capacity. the selection of the most effective coagulant form was determined through the sludge volume index (svi) and settling velocity (vs). experiments were run at mo dosages of 2000, 4000, and 6000 mg/l. the most effective coagulant form was optimized under different process conditions. 2.3 design of experiment and statistical analysis 2.3.1 process conditions optimization the design of experiment (doe) was used to optimize the three process conditions: conditioner dosage, mixing speed and contact time, and the settling velocity (cm/min) was used as the response. the primary ranges were determined using one-factor-at-a-time (ofat) preliminary optimization. the experimental results were analyzed using designexpert software v10 (stat-ease inc.). the variables and their range of levels for the experimental design are listed in table 1. experimental design for process conditions optimization is listed in table 2. table 1: ranges of levels for experiment parameters parameters unit range of levels -1 0 +1 concentration of mo seeds mg/l 500 3250 6000 mixing speed rpm 50 100 150 contact time min 5 17.5 30 iium engineering journal, vol. 19, no. 1, 2018 saedi et al. 18 2.3.2 settling velocity (vs) measurement settling velocity (vs) was used to determine the most effective coagulant form together with svi. vs was also used as a response for process condition optimization. vs was measured using graduated beakers and a stopwatch and one reading was recorded each 1 min for 30 min. then, the settling rate was determined by plotting the vs values versus the time, and the slope of the curve represents the final settling velocity [10]. 2.3.3 sludge volume index (svi) measurement the sludge volume index (svi) is the volume of one gram of sludge after 30 min of settling. the svi was determined by placing the samples into cylinder beakers and measuring the settled sludge after 30 min [10]. the values of svi was determined using eqn. (1): svi = settled sludge volume (ml/l) x 1000 (mg/g) tss (mg/l) (1) 2.3.4 anova analysis the results were analyzed using analysis of variance (anova) approach and p-value. the significance of each coefficient was analyzed by comparing the obtained p-value with 0.05 (95% confidence level). the model is significant if p-value was less than 0.05 [13]. the optimum vs value was obtained using a regression model equation, and 2d and 3d plot analysis. 3. results and discussion 3.1 the most effective coagulant form settling rates were estimated from the slope of the straight-line portion of the plot interface height versus settling time. from the results obtained, vs for mo salt extract was the highest settling velocity of 0.41 cm/min at 4000 mg/l dosage, as shown in fig. 1. settling velocities for salt extraction were 0.37 and 0.366 cm/min for 2000 and 6000 mg/l, respectively. the defatted mo seeds showed lower settling velocities compared to the salt extract. the settling velocities were 0.35, 0.36, 0.34 cm/min for dosages of 2000, 4000, and 6000 mg/l, respectively. the lowest settling velocities were recorded using crude mo seeds. settling velocities of 0.33, 0.34, and 0.32 cm/min were recorded for dosages of 2000, 4000, and 6000 mg/l, respectively. the control sludge sample recorded a settling velocity of 0.32 cm/min. previous studies also reported the high efficiency of bioactive extraction using nacl. a study by okuda et al. showed that the bioactive extraction using salts improved the coagulation efficiency due to the increase in the dissociation of mo proteins, which then led to the increase of the protein solubility in the salt medium. the study also showed that there was no difference in the coagulation efficiency through the extraction of bioactive compounds using nacl, kno3, kcl, and nano3 [14]. the sludge volume index (svi) is an indicator for characterization of settled sludge. the lower svi value indicates better settling efficiency. the lowest svi value of 63.39 ml/g was obtained using mo salt extraction at 2000 mg/l, as shown in fig. 2. unexpectedly, the highest svi value of 143.34 ml/g was also for mo salt extraction at a 4000 mg/l dosage. the defatted mo seeds recorded the lowest svi value at a dosage of 4000 mg/l. an svi range of 50-150 ml/g indicates good sludge-sedimentation properties. the svi values iium engineering journal, vol. 19, no. 1, 2018 saedi et al. 19 higher than 150 ml/g indicate that the sludge sedimentation is poor and that there is the possibility of bulking problems [15]. however, the obtained svi values for all mo forms were in the normal range. fig. 1: different forms of mo seeds and their settling velocities at different dosages. fig. 2: different mo coagulant-forms and their svi values at different dosages. 3.2 optimization and statistical analysis the results of process condition optimization are listed in table 2. regression analysis was used to predict the optimal settling velocity using a third order factorial model. the predicted settling velocity was determined through regression model equation developed by design-expert software v10. from the experimental results, the highest settling velocity was 0.32 cm/min for experiment number 7 under process conditions of 3250 mg/l dosage, 17.5 minutes of contact time at 100 rpm of mixing speed. the 2d and 3d contour plots of the response surface are the graphical representation of the regression equation used to determine the optimum values of the variables within the ranges considered. the two plots were presented in fig. 3 and fig. 4. each contour curve represents an infinitive number of combinations of the two test variables. 0.3 0.32 0.34 0.36 0.38 0.4 0.42 0 1000 2000 3000 4000 5000 6000 s e tt li n g v e lo c it y ( c m /m in ) seed concentration (mg/l) crude mo seeds defatted mo seeds mo salt extraction by nacl 40 60 80 100 120 140 160 0 2000 4000 6000 s lu d g e v o lu m e i n d e x ( s v i) m l/ g mo dosage mg/l crude mo seeds defatted mo seeds mo salt extraction by nacl iium engineering journal, vol. 19, no. 1, 2018 saedi et al. 20 table 2: experimental design for process conditions optimization std run factor 1 a: concentration of seed (mg/l) factor 2 b: contact time (min) factor 3 c: mixing speed (rpm) response settling velocity (cm/min) predicted settling velocity (cm/min) 14 1 3250 17.5 150 0.31 0.31 12 2 3250 30 100 0.3 0.29 6 3 6000 5 150 0.19 0.20 15 4 3250 17.5 100 0.3 0.31 1 5 500 5 50 0.19 0.21 10 6 6000 17.5 100 0.2 0.22 20 7 3250 17.5 100 0.32 0.30 13 8 3250 17.5 50 0.28 0.31 17 9 3250 17.5 100 0.31 0.31 4 10 6000 30 50 0.28 0.28 9 11 500 17.5 100 0.23 0.22 18 12 3250 17.5 100 0.3 0.31 19 13 3250 17.5 100 0.3 0.31 5 14 500 5 150 0.25 0.25 2 15 6000 5 50 0.22 0.22 3 16 500 30 50 0.23 0.22 7 17 500 30 150 0.24 0.25 11 18 3250 5 100 0.3 0.28 8 19 6000 30 150 0.27 0.28 16 20 3250 17.5 100 0.3 0.31 fig. 3: the 2d contour plot of the interaction of dosage with contact time at mixing speed of 100 rpm. iium engineering journal, vol. 19, no. 1, 2018 saedi et al. 21 fig. 4: the 3d contour plot of the interaction of dosage with contact time at mixing speed of 100 rpm. figure 5 shows the regression value of actual and predicted settling velocity. using anova analysis, the model f-value of 11.65 implies the model is significant. there is only a 0.03% chance that an f-value this large could occur due to noise. values of "prob > f" lower than 0.05 indicate that the model terms are significant. due to noise, the "lack of fit f-value" of 7.88 implies the lack of fit is significant. there is only a 2.04% chance that a "lack of fit f-value" this large could occur. the "predicted r-squared" of 0.1695 is not as close to the "adj r-squared" of 0.8345. the final equation, in terms of the actual factors, is: settling velocity = 0.15646 +7.05342x10-5 a -9.69091x10-4 b +3.68182x10-4 c +4x10-7 ab -1x10-7 ac -6x10-6 bc -1.0278 x10-8 a2 +4.65455x10-5 b2 +9.09091x10-7 c2 (2) where a is the mo dosage, b is the contact time, and c is the mixing speed. fig. 5: regression value of actual and predicted settling velocity. iium engineering journal, vol. 19, no. 1, 2018 saedi et al. 22 table 3: regression value and standard deviation std. dev. 0.018 r-squared 0.9129 mean 0.27 adj r-squared 0.8345 c.v. % 6.63 pred r-squared 0.1695 press 0.030 adeq precision 10.045 from the optimization step, multiple solutions were obtained with a desirability of 1. the first five solutions were listed in table 4. table 4: optimization solutions no. dosage of mo seeds (mg/l) contact time (min) mixing speed (rpm) settling velocity (cm/min) desirability 1 3245.993 28.794 101.906 0.321 1.000 selected 2 3641.710 27.892 52.399 0.321 1.000 3 4148.779 29.743 149.907 0.321 1.000 4 3299.708 26.667 146.186 0.321 1.000 5 3474.074 29.444 125.185 0.325 1.000 4. conclusion different coagulant-forms derived from mo seeds were investigated as sludge conditioners. the mo coagulant extracted by nacl showed the highest settling velocity of 0.41cm/min and lowest svi of 63.39 ml/g, compared to the crude and defatted mo seeds. due to the soluble proteins of the mo seed, salt extraction can improve the coagulation efficiency through the salt-in mechanism. the coagulant derived from salt extraction was used in the optimization stage and the optimum process conditions were 3246 mg/l, 29 min, 102 rpm for dosage, contact time, and mixing speed, respectively, at an optimum vs of 0.321 cm/min. all the coagulant forms showed a significant improvement compared to the control sample. moringa oleifera can be used as a natural conditioner, and it has the opportunity to be used as a single coagulant or combined with chemical conditioners. acknowledgement this work was partially supported by international islamic university malaysia, (prgs 15011-0021) from ministry of higher education of malaysia. references [1] henderson jp, heinecke jw. (2003) waste water treatment and reuse in the mediterranean region. the handbook of environmental chemistry, d. barcelo and m. petrovic, eds springer, 3:201-214. [2] verlicchi p, zambello e. (2015) pharmaceuticals and personal care products in untreated and treated sewage sludge: occurrence and environmental risk in the case of application on soil a critical review. sci. total environ., 538:750-767. [3] abdul hamid sh, lananan f, khatoon h, jusoh a, endut a. (2016) a study of coagulating protein of moringa oleifera in microalgae bio-flocculation. int. biodeterior. biodegrad, 113:310-317. [4] leblanc rj, matthews p, richard rp. (2008) global atlas of excreta, wastewater sludge, and biosolids management: moving forward the sustainable and welcome uses of a global iium engineering journal, vol. 19, no. 1, 2018 saedi et al. 23 resource. [5] bichi mh. (2013) a review of the applications of moringa oleifera seeds extract in water treatment. civ. environ. res., 3(8):1-10. [6] abdulazeez qm, jami ms, alam mz. (2016) effective sludge dewatering using moringa oleifera seed extract combined with aluminium sulfate. j. eng. appl. sci., 11(1):372-381. [7] gold m, dayer p, faye mcas, clair g, seck a, niang s, morgenroth e, strande l. (2016) locally produced natural conditioners for dewatering of faecal sludge. environ. technol., 37(21):2802-2814. [8] kansal sk, kumari a. (2014) potential of m. oleifera for the treatment of water and wastewater. chem. rev., 114(9):4993-5010. [9] hussain j, jami ms, muyibi sa. (2012) enhancement of dewatering properties of kaolin suspension by using cationic polyacrylamide (pam-c) flocculant and surfactants. aust. j. basic appl. sci., 6(1):70-73. [10] abdulazeez qm, jami ms, alam mz, iwata m. (2015) analysis of the efficiency of sludge dewatering using moringa oleifera as natural phytocoagulant. int. j. res. chem. metall. civ. eng., 2(2):111-117. [11] ali en, muyibi sa, salleh hm, alam mz, salleh mrm. (2010) production of natural coagulant from moringa oleifera seed for application in treatment of low turbidity water. j. water resour. prot., 2(3):259-266. [12] muyibi sa, alfugara ams. (2003) treatment of surface water with moringa oleifera seed extract and aluma comparative study using a pilot scale water treatment plant. intern. j. environ. stud., 60(6):617-626. [13] yusoff mm, gordon mh, ezeh o, niranjan k. (2016) aqueous enzymatic extraction of moringa oleifera oil. food chem., 211:400-408. [14] okuda t, baes au, nishijima w, okada m. (1999) improvement of extraction method of coagulation active components from moringa oleifera seed. water resour., 33(15):33733378. [15] turovskiĭ is, mathai pk. (2006) wastewater sludge processing. new jersey: john wiley & sons, inc. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 series-series and series-parallel compensation topologies for dynamic wireless charging muhammad amirul asyraf roslan, nadia nazieha nanda* and siti hajar yusoff department of electrical and computer engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia * corresponding author: nnazieha.nanda@gmail.com (received: 16th october 2020; accepted: 2nd february 2021; published on-line: 4th july 2021) abstract: electric vehicles (ev) have gained worldwide attention since the implementation of a wireless power transfer (wpt) to charge their batteries. with wpt, it can be very convenient for ev to be charged dynamically. nevertheless, there are some issues in dynamic wpt, such as maintaining the power transfer efficiency. several factors that lead to these problems include disruption of the alignment and the optimum distance between the transmitter and receiver coils. it is thus contributing to the loss of power efficiency when charging the ev. not to mention, manufacturers build different specifications of ev charging station for different types of ev models in order to meet customer demands. an incompatible charging device will not utilize ev wireless charging to its maximum potential. hence, to improve the power output capability as well as stabilizing the maximum power transfer during the charging process, a compensation circuit is added to the system. this article focuses on comparing two available compensation circuits (series-series (ss) topology and series-parallel (sp) topology) under the application of dynamic wireless charging. the simulations are conducted using ni multisim based on the relationship of power transfer efficiency with resonance frequency, coefficient of coupling, and the load resistance. the wpt efficiency for sp-topology shows that it is sensitive to the change of resonance frequency and coupling coefficient, whereas ss-topology maintains good efficiency during the wpt process. nonetheless, ss-topology performance suffers efficiency loss when paired with a higher load, while sp-topology acts differently. this article will observe the best conditions on the selected compensation designs for better application in ev charging systems in a moving state. abstrak: kenderaan elektrik (ev) telah menarik perhatian dunia sejak pelaksanaan alih kuasa wayarles (wpt) bagi mengecas bateri. melalui wpt, ev lebih mudah kerana ia boleh dicas secara dinamik. namun, pengecasan dinamik wpt turut mengalami masalah, seperti mengimbang kecekapan pemindahan kuasa. beberapa faktor yang membawa kepada masalah ini adalah kerana terdapat gangguan penjajaran dan jarak optimum antara gegelung pemancar dan penerima. kerana ini, ia menyumbang kepada kehilangan kecekapan kuasa semasa mengecas ev. pengeluar juga membina spesifikasi stesen pengisian ev berlainan mengikut jenis model ev demi memenuhi permintaan pelanggan. namun, platform pengecas ev yang berbeza, tidak dapat mengecas ev secara wayarles dengan maksimum. oleh itu, bagi membaiki keupayaan jana kuasa serta menstabilkan pengeluaran kuasa maksimum semasa proses pengecasan, litar gantian ditambah ke dalam sistem. artikel ini memberi keutamaan pada dua litar gantian berbeza (topologi bersiri (ss) dan siri-selari (sp)) di bawah aplikasi pengecasan wayarles dinamik. simulasi dibuat menggunakan ni multisim mengikut kecekapan pemindahan kuasa dengan frekuensi resonan, pekali gandingan dan rintangan beban. kecekapan wpt bagi topologi-sp 199 mailto:nnazieha.nanda@gmail.com iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 menunjukkan ianya sensitif pada perubahan frekuensi resonan dan pekali gandingan. manakala topologi-ss kekal cekap semasa proses wpt. walau bagaimanapun, prestasi topologi-ss berkurangan ketika diganding dengan beban besar, begitu juga berbeza bagi topologi-sp. artikel ini akan mengkaji keadaan terbaik pada reka bentuk gantian terpilih bagi aplikasi ev dalam sistem pengecasan bergerak. keywords: electric vehicle (ev); wireless power transfer (wpt); dynamic charging compensation topology; capacitor arrangement 1. introduction the first electric vehicle (ev) introduction was more than 100 years ago. the invention started from a battery and gradually evolved to an electric motor. in the early 19th century, technology pioneers demonstrated a battery-powered conceptualization vehicle. a british inventor, robert anderson built the first-ever a simple electric carriage. in the 1890s, a chemist named william morrison successfully developed an electric car with a top speed of 14 miles per hour [1]. in the automotive industry, conventional vehicles can be manufactured easily and more affordably for consumers. still, they present some inconveniences such as being a bit noisy and emitting unpleasant pollutants from their exhaust systems. in comparison to a conventional vehicle, ev shows significant advantage in terms of noise, and environmental friendliness. not to mention that ev is a current solution for the concern of environmental pollution, and depletion of energy resources as well as the increased cost for petroleum [1,2]. ev uses electricity as its propulsion, so the main component to store the electricity is the lithium-ion battery. the lithium-ion battery has a shallow discharge rate; its implementation increases the energy stored as well as increasing the travel distances of an ev [3]. the application of wireless charging in ev brings more convenience to its consumer. the ability to charge without any contact reduces the hassle faced by consumers. it increases consumer’s safety, is spark-free, has fewer maintenance requirements, provides more reliability, and the charging method is not affected by its surroundings [4]. wpt uses the electromagnetism theory, where energy can be transferred using inductive coupling or capacitive coupling. for the capacitive coupling, the electric fields are used to transfer power between two plates. for inductive coupling, the energy is transmitted between the coils of the receiver and the transmitter via the magnetic field [5]. ampere’s law and faraday’s law are two principles behind the operation of inductive power transfer (ipt). figure 1 displays an illustration of the wpt system for ev. the main components that contribute to wireless power transfer are the transmitting coil and the receiving coil [6]. the power is transferred through the air from the coil at the charging pad to the coil installed in the ev. there are also other significant components for ev, which include both the transmitting side and the receiving side. at the transmitter, there is a voltage source, an ac/dc converter, a compensation circuit, and a transmitter coil. while at the receiver side, there is a receiver coil, a compensation circuit, ac/dc converter, and battery storage. the grid will supply power in terms of alternating current (ac). the ac/dc converter will convert it into dc and again convert it to ac as the concept needed to transfer wireless energy needs it to be ac current passing through the coils thus, the wpt phenomenon occurs. then, at the receiver side, the ac will be converted into dc so it can be stored into the battery bank [7,8]. 200 iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 through this implementation, ev can be charged in two states, either static or dynamic. static wireless charging (swc) is a charging process where the vehicle is idle such as when it is parked in a mall or garage. dynamic wireless charging (dwc) is a charging process that takes places while the vehicle is moving on the road. however, the combination of both swc and dwc is known as quasi-dynamic wireless charging (qwc) [9]. as the ev is in state of motion, the power transfer efficiency is varied due to the inconsistency of airgap distances as well as the misalignment between the transmitter coil and the receiver coil. this situation will cause a low magnetic flux density. it is known that flux density is directly proportional to induced current. low magnetic flux results in a loss of power efficiency due to of low magnetic flux density [10]. fig. 1: wpt main components in ev [8]. a compensation circuit can compensate for the power transfer loss. it ensures that the output power for the wpt is maintained at a fixed level across wide variations in coupling [5]. there are four basic compensation designs: series-series (ss) topology, series-parallel (sp) topology, parallel-series (ps) topology, and parallel-parallel (pp) topology. throughout this article, only two compensation circuits are chosen: series-series (ss) topology and series-parallel (sp) topology. ss-topology and sp-topology are more economically suitable for high power transmission [11]. these two topologies are further studied in finding which compensation designs performed well under dwc in terms of maximum power transfer capability and power transfer efficiency. the author of [10] used the approach of applying mutual coupling for a different set of compensation designs (ss-topology and sp-topology) to analyse which topology can work well during the charging of an ev battery at constant voltage and constant current. sstopology resulted in both situations of possible constant voltage or constant current, making it suitable for maintaining the charging process as the position of the primary system is changing with respect to the secondary system, such as an in-motion charging situation. same value of parameters was used in [13] research, where it focused on transferring the resonant frequency equally to the operating frequency of the power source. between sstopology and sp-topology, a larger transmission range can be achieved with the series design in the secondary side. parallel design, however, is capable of transferring higher output with a drastic load attached. in addition, the author in [15] carried out the test by setting up different compensation designs (ss-topology and sp-topology) using a mutual inductance model at resonance state. despite that, ss-topology exhibited 70% of maximum efficiency while sp-topology achieved 66%. 201 iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 2. analysis of ss-topology and sp-topology with the absence of the compensation circuit in the wpt system, the power transfer efficiency is inefficient compared to a circuit with compensation technology [12]. the inductance leakage in the wpt system causes low power efficiency. therefore, an additional capacitor is placed either in series or parallel at both the transmitter and receiver side to compensate for the leakage. the capacitive compensation not only solves the inductance leakage but also improves mutual coupling of the primary and secondary coils [13]. figures 2 and 3 show the schematic circuit diagrams for both ss-topology and sptopology. vi, c1 and l1 denote the supply voltage, primary capacitance, and primary inductance at the transmitter side of the circuit. c2, l2 and rl denote the secondary capacitance, secondary inductance, and the load resistance at the receiver side of the circuit. the m represents the mutual inductances in this circuit. for the ideal case, the r1 and r2 are neglected (r1 + r2 = 0) so that the circuit operates without the presence of disturbances. fig. 2: series-series topology [8]. fig. 3: series-parallel topology [8]. the model used for this article is an ev with a power consumption of 3.6 kw with 40 khz resonant frequency (ꞷo). the most common maximized output voltage is 168 v (vl) for the testing of a rechargeable battery in an ev [23]. therefore, the input voltage to recharge the ev’s battery is 240 v. as the output voltage and output power are already known (po equal to pin). the other parameters can be calculated, as shown below: the load resistance can be found using equation (1). a higher power delivery into the load with maximum power transfer capability and efficiency is improved by adding a compensation circuit at the secondary side, which is where the load is located [13]. 𝑅𝐿 = 𝑉𝐿 2 𝑃𝑜 (1) the root means square (rms) value for primary and secondary current can be found using equation (2) and (3). note that the output power (po) is equal to (pin) since the coil resistance is ignored. meanwhile, the rms value for the primary voltage is set to be 240 v. 𝐼1,𝑟𝑚𝑠 = 𝑃𝑖𝑛 𝑉𝐼,𝑟𝑚𝑠 (2) 𝐼2,𝑟𝑚𝑠 = 𝑉𝐿,𝑟𝑚𝑠 𝑅𝐿 (3) l2, m and l1 are calculated using the equation below. the quality factor, qs, and coupling coefficient, k, are set in the calculation as 4 and 0.2. the reason for the coupling coefficient to be 0.2 is that it can avoid the bifurcation issue. bifurcation is a phenomenon where there exists more than one angle frequency in resonance inductive power transfer. it happens due to an increase in the coupling coefficient to a certain value. therefore, the value of k should be addressed carefully to avoid a decrease in a voltage gain of the system [10]. it is noted 202 iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 that the coefficient of coupling is correlated with the distance between the coils. the inductance value will be affected if the value of the coupling coefficient is changed [14]. 𝐿2 = 𝑄𝑆𝑅𝐿 𝜔𝑜 (4) 𝑀 = 𝐼2,𝑟𝑚𝑠 𝑅𝐿 𝐼1,𝑟𝑚𝑠 𝜔𝑜 (5) 𝐿1 = 𝑀2 𝐿2𝑘 2 (6) ꞷo is the resonant frequency, which is equal to 2πf. a compensation circuit placed at the primary side can make the resonant frequency, ꞷo be transferred equally to the operating frequency of the power source [13,15]. using the value of the frequency, l1 and l2, primary capacitance, c1, and secondary capacitance, c2, can be known. equation (7) is used to find c1, whereas eq. (8) is used for c2. 𝑓1 = 1 2𝜋√𝐿1𝐶1 (7) 𝑓2 = 1 2𝜋√𝐿2𝐶2 (8) power calculation can be calculated at both the primary and secondary sides using eq. (9) below. p is the power of the primary/secondary side (w), v is the voltage at the primary/secondary side (v), and i is the current at the primary/secondary side (a). table 1 lists the required parameters for the simulations. 𝑃 = (𝑉)(𝐼) (9) table 1: parameters used in wireless power transfer component parameter vp primary voltage cp primary capacitance rp primary resistance lp primary inductance ls secondary inductance cs secondary capacitance rs secondary resistance rl load resistance q quality factor k coefficient of coupling both compensation designs are usually used in the high-power industry, including wpt. ss-topology and sp-topology provide a constant current and constant voltage during the charging process making them suitable to be applied to ev [10]. the arrangement of the capacitance inside the circuit determines the compensation design used. the series arrangement of the capacitor at the primary side (fig. 4a) makes it independent of the primary inductance as well as the load, making it suitable for dynamic applications. in contrast, the parallel arrangement of a capacitor is to increase the primary current of the 203 iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 circuit. at the secondary side, the series arrangement of capacitance (fig. 4a) is able to stabilize the voltage supply to the load, while the capacitance arrangement in parallel (fig. 4b) able to supply stable current to the load [10,15]. the compensation arrangement is not limited to only four arrangements, as already mentioned, but there is also a hybrid arrangement of capacitors and inductors [16]. the hybrid compensation circuits are lcc-lcc, lcl-lcl, lcc-p, lcl-p, s-clc, lcl-s, ccl-s and multi-lcc (fig. 5 in [17]). however, only ssand sp-topologies will be further discussed in this article. (a) (b) fig. 4: (a) series-series arrangement, (b) series-parallel arrangement [8]. despite that, it also depends on the type of load that is used in the system in order to maximize the capability of the compensation design applied to it. taking into consideration the ev to work with dwc, ss-topology can be seen as a better application towards charging the ev’s battery. the reason is that the coupling coefficient of the compensation design is less affected while the ev is in motion. also, ss-topology is capable of operating at both constant rates of voltage and current output which makes it more reliable to be implemented for the ev [10]. on the other hand, sp-topology compensation emits higher power output and efficiency with higher loads, making it appropriate to be applied in ev due to its problem in travel distance because of its small built battery capacity [13,15]. both ss and sp compensation designs display their advantages in implementation under dwc, but further analysis is required to find out which of the two compensations can perform under dynamic situations. 3. results and analysis ss-topology and sp-topology are constructed as in fig. 5 and fig. 6, in ni multisim software. the letter p or s is the notation for primary or secondary in the circuit diagrams. both compensation circuits were simulated under three variables. the variables that were manipulated were the resonant frequency, coefficient of coupling, and the resistance load. these variables are chosen based on dynamic situations that the ev may experience in the long run. under the ideal case, which there is zero resistance tolerance, ss-topology appeared to be better than sp-topology in terms of maximum output power and power transfer efficiency. the efficiency achieved by ss-topology was 99.94% while sp-topology struggled to transfer power wirelessly with 28.39% efficiency. 204 iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 fig. 5: ss-topology circuit diagram in ni multisim. fig. 6: sp-topology circuit diagram in ni multisim. table 2: calculated parameters for ni multisim simulations parameter value rl 7.84 ω lp 398 µh ls 124.78 µh m 44.57 µh cp 39.78 nf cs 126.87 nf k 0.2 qs 4 in order to analyse the performance between the two topologies, fig. 7, fig. 8, and fig. 9 show the relationship for each variable with power transfer efficiency. the coupling coefficient changes accordingly, based on the distance as well as the alignment between the coils [20]. the value range tested is between 0.01 and 0.2, in order to avoid the occurrence of the bifurcation issue. it is known that the coupling coefficient decreases with the increase of distance and vice-versa, as is the case with misalignment between the coils [21]. referring to fig. 7, from 0.06 (41.3 cm) to 0.2 (25.9 cm), ss-topology is able to transmit better power efficiency from the transmitter coils to the receiver coils. on the other hand, at the distance of 36.8 cm between the coils with 0.08 coupling coefficient, sp-topology reaches its maximum potential with 96.47% of efficiency. when it comes to tolerance to coupling coefficient, sp-topology appears to be less suitable based on its performance compared to ss-topology. ss-topology is capable of maintaining more than 90% efficiency with bigger air-gap fluctuation approximately ≈16 cm. fig. 7: ss and sp simulation for power efficiency, ƞ vs coupling coefficient, k. another simulation test conducted is the manipulation to the resonant frequency. based on fig. 8, both topologies show the fluctuation in power efficiency. the range of the 205 iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 resonant frequency for the simulation test is chosen between 30 khz and 50 khz because it is in the range of ev operational specifications for charging pad manufacturers. the frequency for inductive power transfer can range from 3 khz to 1 mhz [20]. in terms of maintaining power efficiency, both topologies are unable to consistently maintain power transfer as the frequency is altered. in spite of the inconsistency, ss-topology expresses better efficiency within the frequency range of 38 khz until 42 khz while sp-topology has its highest peak with 56.4% of power transfer efficiency when the resonant frequency is 41 khz. since the system is calculated and designed with a frequency value of 40 khz, the outcome for the maximum power efficiency is technically closer to the assigned value of the resonant frequency. sp-topology experienced more significant power loss compared to ss-topology in this study. hence, it can be observed that for any slight increase or decrease from the theoretical resonant frequency, the power efficiency will drop lower than the maximum power efficiency achieved. this proves that both topologies are sensitive when there is a deviation in resonant frequency [10]. the change in load resistance also affected the efficiency during the power transfer. load resistances represent the battery capacity in ev. bigger load signifies more power can be stored, thus requiring less charging time per day. figure 9 illustrates the results of power efficiency for both topologies under alteration of the load resistance value. in this simulation test, when both topologies were paired to a bigger load (100 ω), sp-topology operated better than ss-topology with regards to efficiency in wpt. contrarily, ss-topology attained 99.93% efficiency with a load value at 10 ω. fig. 8: ss and sp simulation for power efficiency, ƞ vs resonant frequency, ꞷo. based on the traits analysed for dwc, the relationship between efficiency with resonant frequency, coupling coefficient and load resistance, ss-topology and sp-topology each have their respective strengths in wireless charging. for optimum real application of ev, the coupling coefficient, k was kept at 0.2 to avoid any presence of more than one angle frequency during the resonance inductive power transfer. because both topologies’ efficiency easily affected by the resonant frequency, ꞷo=41 khz was set as ideal operational frequency at the transmitter side. the same parameter values in table 2 remain constant except for load resistance for each compensation design. series design at the receiver side resulted in lower voltage but higher current. parallel compensation at the secondary side made the voltage received to be high while the current received was low. under the condition of 3.6 kw model, ss-topology had a longer transmission distance with a load of rl=8.1 ω. as for sp-topology, the same output power was gained with rl=130 ω. table 3 represents the data simulated under those specifications with the expression of achieving 3.6 kw of power transmission. 206 iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 fig. 9: ss and sp simulation for power efficiency, ƞ vs load resistance, ω. table 3: compensation design 3.6 kw simulation paired with respective loads. series-series (ss) compensation design series-parallel (sp) compensation design resistance load, rl 8.1 130 primary voltage (rms) 240 v 240 v secondary voltage (rms) 171 v 683 v primary current (rms) 15.20 a 15.16 a secondary current (rms) 21.10 a 5.26 a power transmitted 3648 w 3640 w power received 3608 w 3592 w power efficiency, ƞ 98.9% 98.6% the main contribution is that both compensation designs have different features for wpt. ss-topology is fitted for small load systems, providing the compensation design of ss tolerance towards the change in frequency and airgap distance between coils. while sptopology is very relevant for large load systems. 4. conclusion the two topologies have been simulated based on dwc features when ev is technically in a state of motion. the relationship for power efficiency with resonant frequency, coupling coefficient and load resistances is tested to identify the best fitted compensation design for steady power transfer from the charging pad to the battery. from the simulation results acquired, both designs react differently for each variable. even using the same parameters, the maximum potential of dwc reflected on the load paired to the system. great efficiency was achieved as ss-topology used small loads, in contrast to sptopology which gained great efficiency with bigger loads. nevertheless, through comparing and analysing the simulation data, ss-topology appeared ideal to implement for dwc. despite the fact that it can only perform at utmost capability with small loads, it is important to highlight ss-topology’s potential to maintain it tolerance towards deviation in resonant frequency and coupling coefficient. for practical applications, the ability to transfer power at a consistent rate without major power loss is an important choice criterion when the vehicle is moving [22]. sp-topology paired greatly with bigger loads. however, it is suitable for longer travel distances but requires more charging time because of the bigger loads. sptopology seems more suitable for swc due to its sensitivity towards changes in coupling 207 iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 coefficient. not to mention, this article analysed the conditions for dwc which required an ev cruising while charging. for that reason, it touched on different application situations of two chosen compensation designs and elaborated on how to choose the ideal design suitable for practical applications. acknowledgement we would like to thank partial financial support by the international islamic university malaysia under the kulliyyah of engineering postgraduate tuition fee waiver scheme 2019 (tfw2019) and also this work was partially supported by the ministry of higher education malaysia under the fundamental research grant scheme (grant number frgs19-067-0675). references [1] vepachedu s. (2017) the history of the electric car. andhra journal of industrial news. 1427. [2] salah wa, alsayid b, albreem mam, abu zneid b, alkhasawneh m, al mofleh a, abu sneineh a, al aish aa. (2019) electric vehicle technology impacts on energy. international journal of power electronics and drive systems (ijpeds).10.1.10.11591/ijpeds.v10.i1.pp19. [3] ma s, jiang m, tao p, song c, wu j, wang j, deng t, shang w. (2018) temperature effect and thermal impact in lithium-ion batteries: a review. progress in natural science: materials international, 28(6): 653-666. doi: 10.1016/j.pnsc.2018.11.002 [4] lukic s, pantic z. (2013) cutting the cord: static and dynamic inductive wireless charging of electric vehicles. ieee electrification magazine, 1(1): 57-64. doi: 10.1109/mele.2013.2273228 [5] afridi k. (2018) wireless charging of electric vehicles. national academy of engineering. in frontiers of engineering: reports on leading-edge engineering from the 2017 symposium. washington, dc: the national academies press. doi: 10.17226/24906. [6] li s, mi cc. (2015) wireless power transfer for electric vehicle applications. ieee journal of emerging and selected topics in power electronics, 3(1): 4-17. doi:10.1109/jestpe.2014.2319453 [7] zaini sa, yusoff sa, abdullah aa, khan s, abd rahman f, nanda. nz. (2020) investigation of magnetic properties for different coil sizes of dynamic wireless charging pads for electric vehicles (ev). iium engineering journal, 21(1): 23-32. doi:10.31436/iiumej.v21i1.1108 [8] mi c, abdul masrur m. (2017) hybrid electric vehicles: principles and applications with practical perspectives. john wiley & sons. [9] ahmad a, alam ms, chabaan r. (2018) a comprehensive review of wireless charging technologies for electric vehicles. ieee transactions on transportation electrification, 4(1): 38-63. doi: 10.1109/tte.2017.2771619 [10] aditya k, williamson ss. (2014) comparative study of series-series and series-parallel compensation topologies for electric vehicle charging. ieee 23rd international symposium on industrial electronics (isie). doi: 10.1109/isie.2014.6864651 [11] shevchenko v, husev o, strzelecki r, pakhaliuk b, poliakov n, strzelecka n. (2019) compensation topologies in ipt systems: standards, requirements, classification, analysis, comparison and application. ieee access, 7, 120559-120580. doi: 10.1109/access.2019.2937891 [12] azambuja r, brusamarello vj, haffner s, porto rw. (2017) full four capacitor circuit compensation for inductive power transfer. conference record ieee instrumentation and measurement technology conference, 2-7. doi: 10.1109/i2mtc.2013.6555406. [13] chenggang f, jiancheng s, lingyan l, yameng w. (2017) practical considerations of seriesseries and series-parallel compensation topologies in wireless power transfer system 208 iium engineering journal, vol. 22, no. 2, 2021 roslan et al. https://doi.org/10.31436/iiumej.v22i2.1660 application. 2017 ieee pels workshop on emerging technologies: wireless power transfer (wow), id 41321671. doi: 10.1109/wow.2017.7959404 [14] rehman, m., baharudin, z., nallagownden, p., & islam, b. (2017). modeling and analysis of series-series and series-parallel combined topology for wireless power transfer using multiple coupling coefficients. ijcsns international journal of computer science and network security, vol.17 no.11, november 2017. [15] rituraj g, joy er, kushwaha bk, kumar p. (2014) analysis and comparison of series-series and series-parallel topology of contactless power transfer systems. tencon 2014-2014 ieee region 10 conference. doi: 10.1109/tencon.2014.7022440. [16] nanda, n. n., yusoff, s. h., toha, s. f., hasbullah, n. f., & roszaidie, a. s. a brief review: basic coil designs for inductive power transfer. indonesian journal of electrical engineering and computer science (ijeecs), vol. 20, no. 3, december 2020, pp. 17031716. doi: 0.11591/ijeecs.v20.i3.pp1703-1716. [17] abou houran m, yang x, chen w. (2018) magnetically coupled resonance wpt: review of compensation topologies, resonator structures with misalignment, and emi diagnostics. electronics, 11: 296. doi:10.3390/electronics7110296 [18] barman sd, reza aw, kumar n. (2014). efficiency maximization of resonant coupled wireless power transfer system via impedance matching based on coupling tuning. 3 rd international conference on computer engineering & mathematical sciences, langkawi, malaysia, november 2014. [19] el-shahat a, ayisire e, wu y, rahman m, nelms d. (2019). electric vehicles wireless power transfer state-of-the-art. energy procedia, 162: 24-37. doi: 10.1016/j.egypro.2019.04.004 [20] panchal c, stegen s, lu j. (2018) review of static and dynamic wireless electric vehicle charging system. engineering science and technology, an international journal, 21(5): 922937. doi: 10.1016/j.jestch.2018.06.015 [21] al-saadi m, al-gizi ag, al-chlaihawi s, al-omari ah. (2018). inductive power transfer for charging the electric vehicle batteries. electrotehnică, electronică, automatică, 66: 29-39. [22] carmeli ms, castclli-dezza f, mauri m, rossi m, dolata a, pedretti m, simonini i. (2018) analysis of a quasi-dynamic wireless power transfer system for ev batteries charging. 2018 international symposium on power electronics, electrical drives, automation and motion (speedam), 383-388. doi: 10.1109/speedam.2018.8445238 [23] aditya k. (2016) design and implementation of an inductive power transfer system for wireless charging of future electric transportation. phd thesis. electrical, computer and software engineering department, university of ontario institute of technology oshawa, ontario, canada. 209 microsoft word 2_v17no2_compiled_v2_24nov16.docx iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 83 cascade topologies for the asymmetric multilevel inverter by new module to achieve maximum number of levels emad samadaei, sayyed asghar gholamian*, abdolreza sheikholeslami and jafar adabi department of electrical and computer engineering, babol university of technology babol, iran. *corresponding auhtor: gholamian@nit.ac.ir (received: 16t h mar. 2016; accepted: 16th may. 2016; published on-line: 30th nov. 2016) abstract: multilevel inverters have been introduced as useful devices to connect between dc-ac systems. their high quality output and costs benefit a wide range of applications. asymmetric multilevel inverters are a type of multilevel inverter with an unequal dc link to create more voltage levels through fewer components. this paper presents new topologies of cascade multilevel inverters by a new module with reduced components. the base module produces 13 levels with two types of unequal dc sources and 10 switches. modular can be used to produce more and higher voltages levels. the designing of proposed multilevel inverter makes some preferable index with better quality than similar modular multilevel inverters, such as less semiconductors and dc sources, low switching frequency, creating of negative levels without any additional circuit, and module in cascade connections. also, two cascade topologies are presented in the modular connections of the proposed module to achieve high and significant number of levels. nearest level control (nlc) method as a switching technique is used in step changing levels for topologies to get more quality and lower harmonics. the presented module and cascade topologies are simulated by matlab/simulink and are implemented by the experimental prototype in laboratory to validate the performance of proposed topologies in which simulated and experimental results show a good performance. thd% (total harmonic distortion) of the module and cascade topology in experimental results calculated 4.94% and 2.05% respectively that satisfy harmonics standard (ieee519). abstrak: inverter pelbagai peringkat telah diperkenalkan sebagai peranti berguna untuk menyambung antara dc-ac sistem. sistem ini memberi output dan faedah kos berkualiti tinggi dan mempunyai pelbagai aplikasi. inverter pelbagai peringkat asimetrik adalah sejenis inverter pelbagai peringkat dengan pautan dc yang tidak sama rata untuk mewujudkan lebih banyak paras voltan menerusi lebih sedikit komponen. kertas kerja ini membentangkan topologi baru inverter pelbagai peringkat lata melalui modul baru dengan komponen yang dikurangkan. modul asas mengeluarkan 13 peringkat dari dua jenis sumber dc tidak sama rata dan 10 suis. modular boleh digunakan untuk mengeluarkan tahap voltan yang lebih banyak dan lebih tinggi. mereka bentuk inverter pelbagai peringkat yang dicadangkan menghasilkan beberapa indeks dengan kualiti yang lebih baik daripada inverter modular pelbagai peringkat yang serupa, saperti sumber semikonduktor dan dc yang lebih rendah, frekuensi pensuisan yang rendah, kejadian tahap negatif tanpa sebarang litar tambahan, dan modul dalam sambungan lata. juga, dua topologi lata ini dibentangkan dalam sambungan modular daripada modul yang dicadangkan untuk mencapai jumlah yang tinggi dan tahap yang ketara. kaedah tahap kawalan terdekat (nlc) sebagai teknik pensuisan digunakan dalam tahap langkah iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 84 berubah bagi topologi untuk mendapatkan harmonik yang lebih berkualiti dan lebih rendah. topologi modul dan lata yang dibentangkan disimulasikan oleh matlab/simulink dan telah dijalankan oleh eksperimen prototaip dalam makmal bagi mengesahkan prestasi topologi yang dicadangkan di mana hasil simulasi dan eksperimen menunjukkan prestasi yang baik. thd% daripada topologi modul dan lata dalam hasil eksperimen adalah 4.94% dan 2.05% masing-masing yang memenuhi harmonik standard (ieee 519). keywords: asymmetric; component; multilevel inverter; power electronics; nlc 1. introduction energy is a key concern to the world. in the 1970s, during the energy crisis, renewable energy and other supplies of dc power became possible alternative sources of energy to replace carbon-based fuels. recently, solar and wind sources have seen increased deployment because of their accessibility and non-polluting characteristics. power electronics and multilevel converters play a crucial role in improving these typically dc systems. multilevel converters have been one of the main subjects for dc systems research in the past decades because of their interesting features such as high quality output voltage, operation at high voltage/power levels, low stress on switches as switching frequency decreases, and rated voltage. also, multilevel converters have a very wide range of applications [1-6]: hvdc systems, photovoltaic and wind plants, active power filters, and electrical machine drives. multilevel converters are different arrangements of power electronic switches with dc links to create n-level waveforms on the output. fig. 1: n-levels waveform on multilevel inverter output (9-levels). fig. 2: inverters categories. figure 1 shows a sample waveform of multilevel output with 9 levels. generally, multilevel converters are divided into three types [7]: npc (diode clamped), fc (flying iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 85 capacitor), and cascade (cascade h-bridge). in 1981, the first multilevel converter introduced was of the npc type. it could be used for medium voltage levels [8]. by the early 1990s, fc was presented [9], and in 1996, chb was reintroduced [10]. figure 2 shows the various categories of converters. in fig. 2, there are two types in chb multilevel, specifically: symmetric (with equal dc link), and asymmetric (with non-equal dc link). the design of asymmetric multilevel inverters considers many parameters: the number of levels, semiconductors and dc links, the amplitude of thd (total harmonic distortion), the maximum voltage level, the creation of positive and negative levels, modular ability, and switch stress. researchers have presented different types of modular multilevel converter. in [11], two switches and one source create each level. these levels are added together to reach (n/2) levels. in the end, an auxiliary circuit (h-bridge) is used to create negative levels and n-levels are added. h-bridge switches tolerate higher voltage than other switches. in [12], the h-bridge is divided into sub-modules with two capacitors added for each dc source to find more levels without requiring more semiconductor devices. researchers have tried to reach more levels with fewer components. modules are designed based on optimal use of dc sources by reduced switches [13-15]. in addition, a modular ability is considered to find higher voltage in topologies [16, 17]. there are several parameters to design ideal multilevel inverters for various applications. some parameters are more important for some applications. for example, there is a high stress switch circuit on the end of h-bridges for high voltage applications. redesigning modules to divide the h-bridge into sub-modules leads to increases in the number of semiconductors and thus leads to higher construction cost. also, the total standing voltage (tsv) is raised on the module. using the maximum capacity for the dc link can be achieved by suitable arrangement of the switches in a suitable topology. this arrangement improves economic cost of implementation, switching frequency, tsv, the number of levels, and thd. this paper presents a new asymmetric multilevel module with new cascade connection topologies. the module can be used as two cascade method connections and it does not need any additional circuit to create negative levels. also, it makes 25 levels in the first method and 169 levels in the second method using only two modules. section 2 illustrates the proposed multilevel inverters including module description, switching patterns, and cascade connection in each of the two methods. nearest level control (nlc) method is introduced for switching modulation in section 3. simulation and experimental results of the proposed topologies are shown in sections 4 and 5. 2. proposed module the proposed topology is illustrated in two parts: module configuration and cascade connection topologies. 2.1 module configuration this subsection introduces a new asymmetric modular multilevel inverter featuring new component arrangements including 10 switches, 10 diodes, and 4 dc supplies with different voltage outputs (two 2vdc, two 1vdc). the arrangement of these components is very smart to produce 13 levels (6 positive levels, 6 negative levels, and a zero level) without any additional circuitry to create negative levels. additionally, negative levels are inherent to the model and it does not need an h-bridge converter. figure 3 depicts the proposed module. iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 86 s1 s2 s3 s4 s5 s6 s7 s8 2vdc 2vdc 1vdc 1vdc a b fig. 3: proposed multilevel inverter. of 10 switches, 4 switches work as two pair (s7, s8), which means the module has 6 unidirectional switches and 2 pairs of bidirectional switches. it helps to reduce switch drivers down to 8 drivers. 4 dc supplies are different amplitude to create different levels of output. also, equations for the number of components are written as follows: nlevels=12n+1 (1) nswitches=10n (2) ndiodes=10n (3) ndrivers=8n (4) ndc links=4n (5) total standing voltages (tsv)=20n × vdc (6) where n and n are the number of levels and module units, respectively. eqs. 2 to 6 can be rewritten as eqs.7 to 11 based on number of levels (nl): nswitches=5(nl-1)/6 (7) ndiodes=5(nl-1)/6 (8) ndrivers=4(nl-1)/6 (9) ndc links=(nl-1)/3 (10) total standing voltages (tsv)= 10(nl-1)/6 (11) table 1 describes the switching pattern and demonstrates that positive and negative levels have symmetrical paths to each other. s1 and s4 belong to positive levels and s2 and s3 belong to negative levels. also (s1, s2) and (s3, s4) cannot be on at the same time. three switches are on with some dc sources for each level pattern. switches s1, s6, and s7 and the upper left side and the lower right side in series from dc sources are used for +1vdc. switches s1, s7, and s8 with the upper left side of dc sources create +2vdc. adding the upper left side and the lower left side dc sources switches s1, s5 and s7 make +3vdc. two upper side of dc sources and switches s1, s4 and s6 generate +4vdc. two upper sides and the lower right side of dc sources and switches s1, s4 and s8 are considered for +5vdc. finally, all dc sources by switches s1, s4 and s5 are used to achieve +6vdc. similarly, the negative levels are available as symmetrically. iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 87 the module is designed for switches with low switching frequency. table 2 illustrates that the switching frequency of each switch per cycle is low. the output voltage waveform has 24 steps for each sinusoidal cycle. if system frequency is assumed to be 50 hz, there are four switches (s1, s2, s3 and s4) with a 50 hz in sinusoidal waveform and the maximum switching frequency is 400 hz for s8. this guarantees less switching losses and longer life. table 1: switching table of the proposed module levels s1 s2 s3 s4 s5 s6 s7 s8 the upper left side dc source (±2vdc) the upper right side dc source (±2vdc) the lower left side dc source (±1vdc) the lower right side dc source (±1vdc) p os it iv e l ev el 1vdc 1 0 0 0 0 1 1 0 √ √ 2vdc 1 0 0 0 0 0 1 1 √ 3vdc 1 0 0 0 1 0 1 0 √ √ 4vdc 1 0 0 1 0 1 0 0 √ √ 5vdc 1 0 0 1 0 0 0 1 √ √ √ 6vdc 1 0 0 1 1 0 0 0 √ √ √ √ n eg at iv e le ve l -1vdc 0 1 0 0 1 0 1 0 √ √ -2vdc 0 1 0 0 0 0 1 1 √ -3vdc 0 1 0 0 0 1 1 0 √ √ -4vdc 0 1 1 0 1 0 0 0 √ √ -5vdc 0 1 1 0 0 0 0 1 √ √ √ -6vdc 0 1 1 0 0 1 0 0 √ √ √ √ table 2: switching for each cycle and 50 hz sinusoidal waveform s8 s7 s6 s5 s4 s3 s2 s1 switch number 8 4 7 7 1 1 1 1 number of turning on for each switch in one cycle (13 level) 400 200 350 350 50 50 50 50 frequency of each switch in 50hz sinusoidal waveform table 3: comparison some modular multilevel inverter topology for 13 levels (for 13 levels) npc fc chb csmli [14] proposed module switches num. 24 24 24 14 10 diodes num. (+diode clamped) 24+20 24 24 14 10 dc links num. 6 6 6 6 4 drivers 24 24 24 14 8 )dctsv (x v 24 24 24 24 20 modular able complicate complicate simple simple simple some famous topologies are compared with the proposed module in table 3 to evaluate of number of components. table 3 illustrates the number of components for 13 levels specifically in npc, fc, chb and csmli. table 3 declares that the proposed module has the lowest number components of all topologies. the last column describes iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 88 how at least 4 switches, 4 diodes, 2 dc links, and 6 drivers are used in the proposed module fewer than other columns. also tsv is reduced down to 20vdc. 2.2 cascade connections the modularity of the cascade connections is another feature of the proposed inverter enabling the creation of more levels and the use of alternative switching paths. two cascade topologies are considered for the cascade connection to achieve greater performance. in the first cascade topology, each module (unit) has two 1vdc and two 2vdc dc links. units are joined in series to obtain the output voltage (see fig. 4). in this topology, multiple units can create the total output voltage. in other words, for two units, 6 levels are added on positive levels and 6 levels are added on negative levels (adding of 12 levels, totally). also, there are more switching state choices for each level which causes a high reliability. for example, there are 10 switching paths to produce total output voltage for vout=3vdc where vj is output voltage of unit j:(3v1+0v2), (2v1+1v2), (1v1+2v2), (0v1+3v2), (-1v1+4v2),(-2v1+5v2), (-3v1+6v2), (4v1-1v2), (5v1-2v2) and (6v1-3v2). a1 b1 a2 b2 s1 s2 s3 s4 s5 s6 s7 s8 2vdc 2vdc 1vdc 1vdc s1 s2 s3 s4 s5 s6 s7 s8 2vdc 2vdc 1vdc 1vdc a1 b1 a2 b2 s1 s2 s3 s4 s5 s6 s7 s8 2vdc 2vdc 1vdc 1vdc s1 s2 s3 s4 s5 s6 s7 s8 26vdc 26vdc 13vdc 13vdc fig. 4: the first proposed cascade topology (two unit). fig. 5: the second proposed cascade topology (two unit). in multi-unit cascade connections, there are many redundant switching states used to produce more levels and higher performance by using the second topology. for the second cascade topology, each module has a different amount of dc links in which the first unit has two 1vdc and two 2vdc dc links and the second unit has two 13vdc and two 26vdc dc links. these eight dc links can be connected together by different paths to generate more levels than the first cascade topology so that 169 levels can be achieved by the second topology. figure 5 illustrates the second proposed topology. dc links of each unit are calculated as follows (n=number of unit: 2, 3, 4, … and n): amplitude of lower dc links pair of unitn = 2 × (the maximum positive level of unitn-1) +1 amplitude of the upper dc links pair of each unitn = 2 × (amount of lower dc links of unitn) iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 89 table 4 demonstrates the switching pattern of the second cascade topology from level -84 to level +84. levels are created by unit1 and unit2. unit2 creates 0, ±13vdc, ±26vdc, ±39vdc, ±52vdc, ±65vdc, ±78vdc and unit1 creates 0, ±1vdc, ±2vdc, ±3vdc, ±4vdc, ±5vdc, ±6vdc for middle levels between levels of unit2. table 4: the switching pattern of the second cascade topology for levels: -84 to +84 levels dc sources switching pattern for unit2 from unit1 (*) from unit2 s1 s2 s3 s4 s5 s6 s7 s8 -84 to -72 (±2vdc±2vdc± vdc ±vdc) -26vdc -26vdc -13vdc -13vdc 0 1 1 0 0 1 0 0 -71 to -59 (±2vdc±2vdc± vdc ±vdc) -26vdc -26vdc -13vdc 0 1 1 0 0 0 0 1 -58 to -46 (±2vdc±2vdc± vdc ±vdc) -26vdc -26vdc 0 1 1 0 1 0 0 0 -45 to -33 (±2vdc±2vdc± vdc ±vdc) -26vdc -13vdc 0 1 0 0 0 1 1 0 -32 to -20 (±2vdc±2vdc± vdc ±vdc) -26vdc 0 1 0 0 0 0 1 1 -19 to -7 (±2vdc±2vdc± vdc ±vdc) -13vdc 1 0 1 0 0 0 0 1 -6 to +6 (±2vdc±2vdc± vdc ±vdc) 0vdc 1 0 1 0 1 0 0 0 +7 to +19 (±2vdc±2vdc± vdc ±vdc) +13vdc 0 1 0 1 0 0 0 1 +20 to +32 (±2vdc±2vdc± vdc ±vdc) +26vdc 1 0 0 0 0 0 1 1 +33 to +45 (±2vdc±2vdc± vdc ±vdc) +26vdc +13vdc 1 0 0 0 1 0 1 0 +46 to +58 (±2vdc±2vdc± vdc ±vdc) +26vdc +26vdc 1 0 0 1 0 1 0 0 +59 to +71 (±2vdc±2vdc± vdc ±vdc) +26vdc +26vdc +13vdc 1 0 0 1 0 0 0 1 +72 to +84 (±2vdc±2vdc± vdc ±vdc) +26vdc +26vdc+13vdc +13vdc 1 0 0 1 1 0 0 0 (*) switching pattern for unit1 is based on table 1 3. nearest level control (nlc) modulation method as a switching technique, the simplified nearest level control method is used in the proposed modular multilevel inverter [18]. the aim is to use the nlc method in inverter with a high number of levels which can reduce and simplify the calculation of the processor. figure 6 presents the nlc method pictorially. as shown in fig. 6a, the controller samples a point from reference voltage (vref) and then rounds it to the nearest of voltage level (van). each voltage level has a switching logic according to the switching lookup table to change switch status (fig. 6b). the sampling is repeated for each sample time (ts). a b fig. 6: nearest level control (a) waveform synthesis (b) control diagram. iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 90 4. simulation results the proposed multilevel inverter is simulated using matlab/simulink to examine the performance of the proposed module. figure 7 shows the output voltage of 13-levels for the proposed multilevel inverter with nlc switching technique. each level (vdc) is 50 volts. thd% is calculated 3.87% by fft analysis for waveform of fig. 7 which satisfied ieee519 (i.e max. of thd%: 8%). fig. 7: the waveform of output voltage for the proposed module (simulation). figures 8 and 9 depict the results of the first and the second cascade topologies with the nlc switching technique. they confirm the performance and modular abilities of proposed topologies as 25 levels with thd=1.99% for the first cascade topology and 169 levels with thd=0.11% for the second cascade topology. cascade topologies are known to offer good performance in creating waveforms similar to the sinusoidal waveform with low harmonics. fig. 8: the waveform of output voltage for the first cascade topology (25 levels) (simulation). fig. 9: the waveform of output voltage for the second cascade topology (169 levels) (simulation). 5. experimental results a sample prototype was built in the laboratory to validate the basic proposed module and modular connections with consideration of the limitations in laboratory facilities. each level is considered 50 volts; thus, there are two 50 volts and two 100 volts dc sources for modules. igbt 12n60a4, diode rhrp15120 are used in the laboratory model. microcontroller atmega16a creates a pulse for switches and hcpl3120 drives igbts (fig. 10). figure 11 shows the experimental setup in laboratory. the output of the one module (fig. 3) is a 50 hz sinusoidal waveform shown in fig. 12. also, fig. 13 depicts output voltage waveform for the first cascade topology (fig. 4) with 25 levels. experimental thd is 4.94% and 2.05% for 13 levels and 25 levels, respectively. as the comparison of fig. 12 and fig. 13a indicates, the voltage waveform with 25 levels is more similar to a sinusoidal waveform. also, fig. 13b and fig. 13c shows the voltage waveform iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 91 of each unit for the cascade topology. the cascade topology shows greater quality with higher waveform resolution and its peak to peak voltage (vp-p) reaches 1.2 kv against vp-p of 13 levels voltage waveform, which is 0.6 kv. consequently, the experimental test results based on module and cascade topologies show good performance to get more and higher levels by this creative topology. vin1 vin2 vout 1 vout 1 vout 2 vout 2 hcpl3120 bufferatm16 igbt/diode fig. 10: schematic of laboratory configuration. fig. 11: picture of experimental setup in laboratory. (a) (b) fig. 12: the output voltage of the proposed multilevel for the base module (a) and spectral analysis (b), 13-level (experimental test). (a) (b) (c) fig. 13: the output voltage for the first cascade topology in the proposed multilevel (two unit), 25-level (experimental test) (a) output voltage waveform in fig. 4 (b) for unit1 in fig. 4 (c) for unit2 in fig. 4. iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 92 6. conclusion nowadays, dc systems and dc sources are widespread. power quality is the most important quality of these systems for the connection of dc-ac systems. inverters are coupled with devices of dc-ac connections. this paper presented two new topologies of the multilevel inverter by a new proposed module. the proposed module creates 13 levels of voltage waveform through reduced components. it can be used in high voltage/power and using in dc systems (pv, fc, battery, dfig, and hvdc), because the module is able to easily be set in a cascade arrangement and offers low switching frequency for good design. two cascade topologies are presented for more voltage levels in which the first cascade topology generated 25 levels and the second method generated 169 levels using just two units. thus, it has a lower construction cost than similar topologies. it does not need any h-bridge circuit and harmonic filter at output. thd% obtained 3.87% and 4.94% in simulation and experimental results for the proposed module respectively, that satisfy harmonics standard (ieee519). also, thd% of the first cascade topology calculated 1.99% and 2.05% in simulation and experimental results by the fft analysis. the second topology has thd%=0.11% by 169 levels. references [1] feldman r, tomasini m, amankwah e, clare jc, wheeler pw, trainer dr, whitehouse rsa. (2013) a hybrid modular multilevel voltage source converter for hvdc power transmission. ieee trans. ind. appl., 49(4):1577-1588. [2] odavic m, biagini v, sumner m, zanchetta p, degano m. (2013) low carrier–fundamental frequency ratio pwm for multilevel active shunt power filters for aerospace applications. ieee trans. ind. appl., 49(1):159-167. [3] liu l, li h, hwang sh, kim jm. (2013) an energy-efficient motor drive with autonomous power regenerative control system based on cascaded multilevel inverters and segmented energy storage. ieee trans. ind. appl., 49(1):178-188. [4] liu y, ge b, abu-rub h, peng fz. (2014) an effective control method for quasi-z-source cascade multilevel inverter-based grid-tie single-phase photovoltaic power system. ieee trans. ind. informatics, 10(1):399-407. [5] mei j, xiao b, shen k, tolbert lm, zheng jy. (2013) modular multilevel inverter with new modulation method and its application to photovoltaic grid-connected generator. ieee trans. power electronics, 28(11):5063-5073. [6] rodriguez-rodriguez jr, moreno-goytia el, venegas-rebollar v. (2011) a transformerless, single dc-input, dc-ac 7-levels boost converter for pv applications. ieee north american power symposium (naps), august 2011,1-6. [7] rodriguez j, lai js, peng fz. (2002) multilevel inverters: a survey of topologies, controls, and applications. ieee trans. ind. electronics, 49(4):724-738. [8] nabae a, takahashi i, akagi h. (1981) a new neutral-point-clamped pwm inverter. ieee trans. ind. appl., ia-17(5):518-523. [9] meynard ta, foch h. (1992) multi-level choppers for high voltage applications. epe j., 2(1):45-50. [10] peng fz, lai js, mckeever jw, vancoevering j. (1996) a multilevel voltage-source inverter with separate dc sources for static var generation. ieee trans. ind. appl., 32(5):1130-1138. [11] babaei e, hosseini sh. (2009) new cascaded multilevel inverter topology with minimum number of switches. energy conversion and management, 50(11):2761-2767. [12] babaei e, kangarlu mf, sabahi m. (2014) extended multilevel converters: an attempt to reduce the number of independent dc voltage sources in cascaded multilevel converters. iet power electronics, 7(1):157-166. iium engineering journal, vol. 17, no. 2, 2016 samadaei et al. 93 [13] gupta kk, jain s. (2012) topology for multilevel inverters to attain maximum number of levels from given dc sources. iet power electronics, 5(4):435-446. [14] kangarlu mf, babaei e. (2013) cross-switched multilevel inverter: an innovative topology. iet power electronics, 6(4):642-651. [15] ounejjar y, al-haddad k, gregoire la. (2011) packed u cells multilevel converter topology: theoretical study and experimental validation. ieee trans. ind. electronics, 58(4):1294-1306. [16] alishah rs, nazarpour d, hosseini sh, sabahi m. (2014) new hybrid structure for multilevel inverter with fewer number of components for high-voltage levels. iet power electronics, 7(1):96-104. [17] kangarlu mf, babaei e. (2013) a generalized cascaded multilevel inverter using series connection of submultilevel inverters. ieee trans. power electronics, 28(2):625-636. [18] meshram pm, borghate vb. (2015) a simplified nearest level control (nlc) voltage balancing method for modular multilevel converter (mmc). ieee trans. power electronics, 30(1):450-462. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 performance analysis of predictive functional control for automobile adaptive cruise control system mohamed al-sideque zainuddin1,2, muhammad abdullah1*, salmiah ahmad1, mohd suhaimi uzair3 and zaid mujaiyid putra ahmad baidowi4 1 department of mechanical and aerospace engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia 2 department of automotive engineering technology, kolej kemahiran tinggi mara, masjid tanah, melaka, malaysia 3 testing & development, engine development, powertrain r&d, powertrain division, proton holdings berhad, shah alam, malaysia 4centre of foundation studies, universiti teknologi mara, cawangan selangor, kampus dengkil, 43800 dengkil, selangor, malaysia * corresponding author: mohd_abdl@iium.edu.my (received: 28th february 2022; accepted: 21st june 2022; published on-line: 4th january 2023) abstract: this paper presents the performance analysis of predictive functional control (pfc) for adaptive cruise control (acc) application. to cope with multiple driving objectives of modern acc systems such as passenger comfort, safe distancing, and fast time response, an advanced optimal controller such as model predictive control (mpc) is often used. nevertheless, mpc requires a high computation load due to its complex formulation and may overload the processing power of a microcontroller. thus, the prime objective of this work is to propose a pfc algorithm as an alternative controller, while providing a formal comparison between mpc and the traditional proportional integral (pi) controller. a standard kinematic model for vehicle longitudinal dynamics was modelled and used to derive the control law of pfc. since the open-loop dynamic of the derived transfer function is not stable, the second objective is to propose a pre-stabilized loop or cascade pfc structure for the system. a complete tuning procedure and analysis were presented. the simulation result shows that although mpc performance is the best for the acc application with root mean square error (rmse) of 1.4873, pfc has shown a promising response with rmse of 1.5501, which is better compared to the pi controller with rmse of 1.6219. all the imposed driving constraints such as maximum acceleration, maximum deceleration and safe distance were satisfied in the car following application. thus, the findings from this work can become a good initial motivation to further explore the capability of the pfc algorithm for future acc development. abstrak: kajian ini adalah berkenaan analisis prestasi kawalan fungsi ramalan (pfc) aplikasi kawalan mudah suai (acc). bagi memenuhi pelbagai keperluan objektif sistem pemanduan moden acc seperti keselesaan penumpang, penjarakan selamat dan tindak balas pantas, kawalan optimum terbaru seperti model kawalan ramalan (mpc) sering digunakan. walau bagaimanapun, mpc memerlukan beban pengiraan tinggi kerana rumusnya yang kompleks dan mungkin mengakibatkan beban berlebihan kuasa pemprosesan mikrokawalan. oleh itu, matlamat utama kajian ini adalah bagi mencadangkan algoritma pfc yang mempunyai pengiraan mudah sebagai kawalan alternatif, sementara menyediakan perbandingan formal antara mpc dan kawalan 213 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 tradisional berkadar keseluruhan (pi). oleh kerana model ini tidak stabil, objektif kedua adalah mencadangkan penggunaan struktur pfc berlapis bagi menstabilkan sistem terlebih dahulu sebelum algorithma kawalan digunakan atau dengan menggunakan struktur pfc secara berturut pada sistem. prosedur lengkap dan terperinci untuk analisis pfc dibentangkan. dapatan simulasi kajian menunjukkan walaupun prestasi mpc adalah baik bagi aplikasi acc dengan ralat punca min kuasa dua (rmse) bernilai 1.4873, namun pfc menunjukkan tindak balas baik dengan rmse bernilai 1.5501 berbanding kawalan pi yang mempunyai rmse sebanyak 1.6219. kesemua kekangan seperti pecutan dan nyahpecutan maksima, dan penjarakan selamat bertepatan dengan aplikasi kenderaan ini. dengan itu, penemuan ini adalah motivasi awal yang baik bagi meneroka lebih jauh keupayaan algoritma pfc bagi membangun acc pada masa hadapan. key words: predictive functional control; model predictive control; pid; adaptive cruise control 1. introduction adaptive cruise control (acc) is one of the basic features for an advanced driving assistant system (adas), where its function is to regulate the speed of a vehicle while retaining a safe following distance. compared to the conventional cruise control system, acc has two modes of operation: speed control and space control. with the advancement of sensor and microprocessor technologies, an energy efficient acc system which can satisfy multiple driving objectives such as passengers’ comfort, fuel efficiency, and safe distancing with acceptable time response are currently being developed. this type of acc system requires a more sophisticated control algorithm and structure as each of the driving objective functions needs to be optimized to get the optimum control action. it is also well noted that the vehicle longitudinal dynamics for full range operation is highly nonlinear and thus a hierarchal control structure is required where the upper-level system is controlled to provide a desired signal for the lower-level system to track [1]. at the same time the switching between space and speed control also needs to be considered to ensure the safety and comfort of the passenger. with a traditional pi controller, a special switching algorithm is used to ensure a smooth transition between the two modes to avoid jerking [2]. this operation can be done with the help of a look up table. nevertheless, the control performance is not robust since the decision making is solely based on the current measurement. to improve the robustness, a proper tuning strategy can be implemented, as demonstrated by [3]. however, the control structure has become more complicated and there is no systematic tuning approach for this type of modification leaving only trial and error or use of some optimal algorithm tuning scheme. several works also have proposed the use of fuzzy logic controller (flc) for an acc system. using a common logic rule, the switching strategy is developed based on the relative distance with the lead vehicle. the strategy is quite straightforward and implantable, yet as reported by [4], in the presence of unmeasured disturbance, the control performance will be deteriorated. indeed, there are several options to overcome these issues such as improving the accuracy of the fuzzy rule by using a different logic function or combining it with other advanced controllers [5]. however, there is no systematic rule that can be implemented as there are many parameters that need to be tuned and most of the modifications are system dependent. a predictive controller is another suitable option to control the upper level of an acc system. a representative kinematic mathematical model is used to predict the future 214 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 velocity and the input acceleration will be optimized to get the desired response while satisfying other driving constraints such as passenger’s comfort, fuel efficiency, and safe distancing. as reported in the literature, various authors have managed to prove that this algorithm can effectively control the vehicle speed in satisfying the multiple driving objectives either in simulation or real-time implementation [6-8]. the main reason behind this is the prediction capability where the controller can anticipate what will happen in the future and try to provide the best solution. hence, no special switching strategy is required and it can be replaced by a more systematic optimization problem. indeed, there are also several limitations such as a proper selection of the tuning parameters of prediction and control horizons based on certain applications. however, even with suitable parameters, the computation burden will still be heavy to implement in existing vehicle microprocessors. in a short sampling time i.e., 0.1 s, the algorithm needs to compute several heavy mathematical operations such as prediction, optimization, and constraints handling using a standard quadratic cost function. of course, there are several options to reduce the computation such as offline implementation [9] and changing the prediction structures using a special function [7,10], yet still the basic microprocessor in existing vehicles needs to be upgraded. this requirement will increase the cost and, in the future, full implementation of autonomous vehicles would further lead to a greater computation demands. due to the above reasons, this work intended to propose an alternative low computation predictive controller known as predictive functional control (pfc), which is novel in the acc application. in general, the algorithm principle is the same, but the optimization process is simplified without the use of the quadratic cost function. in return, the computation time can be reduced significantly [11]. the pfc algorithm has also been implemented in other engineering fields ranging from chemical, mechanical, and electrical industries [12,13]. however, there is a tradeoff in using pfc, where the optimality of the control solution will be reduced. this is a well-known tradeoff but for a single input single output (siso) application such as an acc system, it may become a good alternative strategy. besides, there are also a number of works that have improved the existing algorithm such as [14,15]. thus, the main objective of this work is to investigate and provide a formal performance comparison of pfc with mpc and a traditional pi controller to assess its capability in a vehicle following application. another important issue that needs to be highlighted is the application of pfc for marginally stable processes or type 1 processes where there will be an independent integrator in the transfer function’s denominator. since the input to the acc system is acceleration and the output is speed, if a step input is given, the output will not converge to a steady state value. thus, when a conventional pfc algorithm is implemented, the control solution will be ill-posed, where the prediction and actual control performance will differ [16]. to cope with this issue, a cascade pfc with feedback compensator will be used where the prediction structure is pre-stabilized before implementing the conventional algorithm [17]. a proper analysis on the tuning process will be discussed and denoted as one of the contributions of this works. 2. methodology 2.1 vehicle longitudinal dynamics modelling the mathematical model is the most important part of predictive control formulation. in general, the inputs to the system will be the pedal pressure from the throttle and brake, while the output of interest will be velocity. in a traditional cruise control system, the 215 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 braking effect is not considered, thus the standard kinetic vehicle longitudinal model can be used straight away to derive the control law of pfc as presented in [18]. however, the acc system needs braking input as well to keep the safe distancing with a lead vehicle. if a full kinetic modelling is used to derive the control law as in [18], the constraint implementation will be quite complicated especially if it is designed for full range dynamic operation where the nonlinearities will be very high due to the changing gear ratio and coefficient of friction between road and tire [2]. thus, a hierarchal control strategy is often proposed in the literature [5,6] as shown in fig. 1. fig. 1: hierarchical structure for vehicle longitudinal dynamics. in the hierarchal structure, the throttle and brake actuator correspond to powertrain and brake line dynamics respectively. as for the lower-level dynamic, it is responsible for the relationship between traction force 𝐹𝑡 and acceleration, 𝑎, by newton’s second law. the details of these models are available in many references including academic textbooks [2]. since the lower-level model is nonlinear in nature, the pfc controller will be derived based on the upper-level system that represents the kinematic dynamic between acceleration and velocity where the transfer function is given as: 𝑣(𝑠) = 1 𝑠(𝜏𝑠+1) 𝑎(𝑠) (1) the additional time constant 𝜏 in eq. (1) corresponds to the estimation of the first order lag of the lower-level controller [2]. in this case, it is expected that the car will track the velocity imperfectly and thus the nominal time constant 𝜏 is approximately equal to 0.5 s [2]. in this work, it is assumed that the lower-level controller can retain the nominal value in every operating speed, although in reality, it will be changed due to nonlinearities, especially for low-speed operation where the gear ratio is not constant. the investigation of the impact of nonlinearities on the overall control performance of an acc system and the possibility of using other robust control methods will denote future work. 2.2 cascade pfc prediction since the pfc algorithm works in the digital domain, the transfer function in eq. (1) needs to be discretized a with sampling time of 0.1 s [6]. from here on, a standard symbol for input 𝑢 will be used for acceleration 𝑎 and output 𝑦 for velocity 𝑣. the discrete transfer function can be represented as: 𝐺(𝑧) = 𝑦(𝑧) 𝑢(𝑧) = 0.009365𝑧 −1+0.008762𝑧−2 1−1.819𝑧−1+0.819𝑧−2 (2) another important part that needs to be considered is the nature of the transfer function in eq. (1) and eq. (2), where it is a type 1 system with independent integrator in the denominator. since the output response will not converge when given a bounded input, it needs to be pre-stabilized before deriving the control law. if not, it will lead to an illposed solution as reported in the literature [14]. there are two ways to overcome this issue [14,17], one is by splitting eq. (2) into two separate transfer functions that run in parallel, one using partial fractions and the other using a proportional gain, 𝐾, to stabilize the 216 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 system as shown in fig. 2. this work utilizes the second option since only a minor modification in the computed input is required when implementing the control law. fig. 2: proportional feedback loop for plant pre-stabilization. the inner loop 𝑇(𝑧) will be used as a prediction model instead of 𝐺(𝑧) as in eq. (2) to get a stable response and it is computed as: 𝑇(𝑧) = 𝑦(𝑧) 𝑥(𝑧) = 𝐺(𝑧)𝐾 1+𝐺(𝑧)𝐾 (3) where, 𝑥(𝑧) is the modified controlled input. a suitable value of proportional gain 𝐾 can be selected based on trial and error or by using a more systematic approach as presented in [17]. as in this work, the matlab pid tuner is utilized. using the function pidtune(sys,type), it provides the proportional value of 𝐾 = 1.147. according to the function description in matlab help desk, the given value is computed based on the balance performance between response time and robustness. a linear prediction structure based on the superimposed principle for transfer function in eq. (3) can be formed, and since the derivation is standard [23-26], only the final form is presented. the 𝑖-step ahead prediction at the k sampling is presented as: 𝑦(𝑘 + 𝑖|𝑘) = 𝐻𝑋 + 𝑃𝑋0 + 𝑄𝑌  + 𝑑 (4) the dimension of matrix 𝐻, 𝑃, and 𝑄 depends on the model parameters, and for a standard second order transfer function, the parameters 𝑋, 𝑋0 and 𝑌 are: 𝑋 = [ 𝑥(𝑘) 𝑥(𝑘 + 1) ⋮ 𝑥(𝑘 + 𝑖) ] , 𝑋0 = 𝑥(𝑘 − 1), 𝑌 = [ 𝑦(𝑘) 𝑦(𝑘 − 1) ] the term 𝑑 in eq. (4) corresponds the correction term to get an unbiased prediction using an independent model structure as shown in fig. 3. technically, it is the difference between the actual measured output form a plant 𝑦𝑝 and the calculated output 𝑦 from 𝑇(𝑧) in fig. 2. 𝑑 = 𝑦𝑝 − 𝑦 (5) fig. 3: independent model structure for pfc prediction. 2.3 cascade pfc control law 217 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 to compute the control input, the prediction in eq. (4) at n-step ahead is forced to coincide with a first order setpoint trajectory r, which is given as [11]: 𝑟(𝑘 + 𝑛|𝑘) = (1 − 𝜆𝑛)𝑅 + 𝜆𝑛𝑦𝑝(𝑘) (6) where r is the desired set point speed. in this stage, there are two tuning parameters that need to be specified. the first one is the coincidence horizon 𝑛, where the prediction in eq. (4) is forced to match with the target trajectory in eq. (6). the second one is 𝜆, which corresponds to the desired closed-loop time response (time taken to reach 95 % form the steady state value): 𝜆 = 𝑒−3𝑇𝑠/𝐶𝐿𝑇𝑅 (7) the term 𝑇𝑠 in eq. (7) denotes the sampling time. for a second order system, the selection of n has a general tuning guideline as presented in [17]. it should be selected between 40% and 80% of the response to avoid prediction mismatch. once all the tuning parameters have been selected, the general control law of pfc can be derived. using its standard assumption that the future modified control input will be constant i.e., 𝑥(𝑘) = 𝑥(𝑘 + 1) = ⋯ . 𝑥(𝑘 + 𝑛) [25], the n-th row of matrix 𝐻𝑛 will reduce to a single value in the form of: ℎ𝑛 = 𝐻𝑛 [ 1 1 ⋮ 1 ] (8) extracting the n-th prediction form each matrix and equating the predictions in eq. (4) and eq. (6) gives: ℎ𝑛 𝑥(𝑘) + 𝑃𝑛 𝑋0 + 𝑄𝑛𝑌  + 𝑑 = (1 − 𝜆 𝑛)𝑅 + 𝜆𝑛𝑦𝑝(𝑘) (9) the compensated input 𝑥 can be computed as: 𝑥(𝑘) = ℎ𝑛 −1[(1 − 𝜆𝑛)𝑅 + 𝜆𝑛𝑦𝑝(𝑘) − 𝑃𝑛 𝑋0 − 𝑄𝑛𝑌  − 𝑑] (10) it should be noted that since a cascade structure is used to pre-stabilized the response as explained in section 2.2. by referring to fig. 4, the actual input that will be sent to the plant is computed as: 𝑢(𝑘) = 𝐾[𝑥(𝑘) − 𝑦𝑝(𝑘)] (11) fig. 4: cascade pfc structure. 2.4 constraint handling for passenger comfort and safe distancing for the predictive controller framework, the conventional switching strategy from speed mode to space mode can be implemented by formulating a constraint control problem. fig. 5 shows the schematic diagram for vehicle following application and how the acc controller is implemented. 218 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 fig. 5: acc schematic diagram for vehicle following application. with the help of a distance sensor such as lidar, a relative distance 𝐷𝑟 or relative velocity 𝑣𝑟 with a lead vehicle can be measured. these two parameters can be used to regulate the acceleration to retain a safe following distance if necessary. a standard safe following distance equation as recommended in [2] is used, where: 𝐷𝑠𝑎𝑓𝑒 (𝑘) = 𝐷𝑑𝑒𝑓𝑎𝑢𝑙𝑡 + 𝑇𝑔𝑎𝑝𝑣(𝑘) (12) the default distance 𝐷𝑑𝑒𝑓𝑎𝑢𝑙𝑡 is set to 10 m, it means that if the velocity of vehicle is 0 m/s (both lead and ego vehicle are not moving or approaching a complete stop), the relative distance should not be less than 𝐷𝑑𝑒𝑓𝑎𝑢𝑙𝑡. the safe time gap 𝑇𝑔𝑎𝑝 between the vehicle is set to 1.4 s. based on eq. (12), the higher the velocity of a vehicle, the larger the safe distance needed to be maintained because it will take more time to slow down the car. based on the output velocity prediction in eq. (4), the future relative position between the car 𝐷𝑟 can be estimated by assuming the future velocity of the lead car is constant at the instantaneous sampling 𝐷𝑟 (𝑘 + 1) = [𝑣𝑙   −  𝑣(𝑘)]𝑇𝑠 + 𝐷𝑟 (𝑘) (13) using superposition, at each sampling time, the maximum velocity to keep the safe distance can be formed as: 𝑣𝑚𝑎𝑥 = (𝑣𝑙 𝑇𝑠 + 𝐷𝑟 (𝑘)– 𝐷𝑑𝑒𝑓𝑎𝑢𝑙𝑡 )/(𝑇𝑔𝑎𝑝 + 𝑇𝑠) (14) then a normal pfc output constraints formulation can be implemented by selecting a suitable validation horizon 𝑛𝑖 . the algorithm is given as below: algorithm (a). at each sample time: (1) compute the unconstrained compensated input 𝑥 as in eq. (10). (2) a simple ‘for’ loop is used to check the constraint violation while updating eq. (13) and eq. (14) (3) if 𝑣 > 𝑣𝑚𝑎𝑥 , then: 𝑥(𝑘) = 𝐻𝐿𝑖 −1[𝑣𝑚𝑎𝑥 (𝑖) − 𝑃𝑖 𝑈0 − 𝑄𝑖 𝑌  − 𝑑] (15) (4) else, the value of 𝑥 is retained. for taking care of passenger comfort and fuel efficiency, the input acceleration is constrained in between 𝑢𝑚𝑖𝑛= -3 to 𝑢𝑚𝑎𝑥 = 2 m/s 2. as discussed in many pfc papers [1617] a simple clipping strategy is enough to cater for input constraint such that if 𝑥 < 𝑦(𝑘) + 𝑢𝑚𝑖𝑛 /𝐾, then: 𝑥(𝑘) = 𝑦(𝑘) + 𝑢𝑚𝑖𝑛/𝐾 (16) similarly, if 𝑥 > 𝑦(𝑘) + 𝑢𝑚𝑎𝑥 /𝐾, then: 𝑥(𝑘) = 𝑦(𝑘) + 𝑢𝑚𝑎𝑥 /𝐾 (17) 219 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 3. simulation result 3.1 analysis of tuning parameter of pfc the first step in tuning the pfc is to select a suitable compensator gain to stabilize the open-loop behavior of the vehicle dynamics. since the open-loop transfer function is type 1 (with one integrator in the denominator), a single proportional gain is enough to stabilize the system. as discussed in section 2.2, an autotune pi controller in matlab is used to find an optimum proportional gain 𝐾 = 1.147 that will provide a balanced performance between response time and robustness [17]. figure 5 shows the open-loop response of the pre-stabilized system output 𝑦 against the desired output trajectory 𝑅 with cltr of 5s (𝜆 = 0.9418). fig. 5: pre-stabilized open-loop response compared to the desired trajectory. the objective of the pfc is to force the system to match the desired target trajectory at a specific coincidence horizon, 𝑛. in this stage, a proper coincidence horizon needs to be selected carefully. in general, a smaller coincidence horizon will provide more aggressive response and input, while higher coincidence horizon will be less aggressive and slow. the effect of coincidence horizon may be varied for different systems since the dynamics are different. several coincidence horizons are simulated to track a desired velocity of 5 m/s with 0.1 s sampling time, as shown in fig. 6. fig. 6: closed-loop response with varying coincidence horizon (n). it can be observed that a smaller horizon will lead to slower response and a larger value will lead to faster response than the desired one (black dashed line). based on the tuning guide proposed by [17], a suitable value should be selected between 40% and 80% rise of step response to its steady state value. in this case 𝑛=8 provides the closest response compared to the desired trajectory. a similar effect can be seen in the control 220 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 effort where large horizon will need larger over actuation compared to the smaller horizon value. nevertheless, all the control efforts violate the maximum allowable input acceleration, which is 2 m/s2. to satisfy the driving constraint, the algorithm (a) in section 2.4 is implemented. as expected, fig. 7 shows the response where the implied constraint is satisfied systematically, yet with a slower response in tracking the desired target trajectory. fig. 7: closed-loop response when input constraint is activated. fig. 8: closed-loop response for vehicle following application. 221 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 for the car following application, the output velocity also needs to be constrained to ensure that the safe following distance is always respected. with the prediction capability of pfc, it can anticipate the future relative distance and change the input accordingly. nevertheless, a suitable validation horizon (how far ahead the constraint is implemented) needs to be selected. figure 8 overlays different selections of validation horizons when following a lead vehicle with a constant velocity of 3 m/s and initial relative distance of 21 m. as can be observed, all three responses managed to prevent the relative distance from going lower than the safe following distance and respecting all the input constraints. nevertheless, there is a clear tradeoff in the selection of validation horizon, if it is too short (𝑛𝑖 =2 green solid line), an aggressive control effort is needed. nevertheless, if it is too large (𝑛𝑖 =18, red dash dotted line), the response may be too conservative, and the computation burden of the controller will increase as it needs to compute more mathematical operation. for this case, a validation of 𝑛𝑖 =8 (blue dotted line), which is equal to the coincidence horizon, is selected since it respects all the constraints with optimum control effort. this feature is very important to ensure the safety and comfort of the passengers. 3.2 performance comparison with pi and mpc to analyze the control performance of pfc, its closed-loop response is compared with two benchmark controllers: pi and mpc. the reason the pi controller is used instead of the pid is because it is a type 1 system. figure 9 shows the comparison of the input acceleration, output velocity and relative distance of the three controllers. the lead vehicle (black-dashed line) is assumed to operate with sinusoidal acceleration signal with amplitude of 0.35 m/s2 and frequency of 0.1 rad/s. the ego vehicle (the controlled vehicle) is set to track a desired velocity of 30 m/s while respecting the safe following distance. for predictive controllers (pfc and mpc), the safe following distance is treated as a constraint, while for pi controller, a simple switching strategy is used to change between speed and space mode. the gains are selected based on an auto tune function in matlab with p = 0.8, i = 0.001. at the same time, input acceleration is constrained between -3 m/s2 to 2 m/s2 for passenger comfort. as expected, it can be observed that from the result in fig. 9, mpc (green dasheddotted line) provides the most optimal response with less aggressive input acceleration followed by pfc (blue dotted line) and pi (red solid line). the difference in output velocity is not quite significant except that a large spike response is generated by the pi controller at 10 s when the ego car is trying to adjust its speed to match the leading vehicle. as for the safe distancing, both pfc and mpc managed to retain it, while pi needs to violate the safe distancing to satisfy input acceleration constraints at 60 s, 120 s and 180 s. besides the qualitative results, some quantitative values are shown in table 1 for each controller to numerically demonstrate their output velocity performance in terms of rise time τr, settling time τs and root mean square error (rmse). these quantitative values are measured over the duration of 40 s for tracking 30 m/s from rest and will be the performance indices of the controllers. it can be observed from fig. 9 and table 1 that the pi controller for the constrained closed-loop response requires longer settling times (199.5386 s) as compared to others although it has the fastest rise time (2.7213 s). another observation is that all the controllers do not produce an overshoot. however, the mpc and pfc provide the best fit response curve to the desired speed of 30 m/s with lower rmse of (1.5501) and (1.4873) respectively compared to pi controller rmse of (1.6219). 222 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 fig. 9: closed-loop performance comparison between pi, pfc, and mpc for vehicle following application. table 1: performance indices for all controllers. performance criteria pi pfc mpc rise time, τr 2.7213 2.7348 2.9551 settling time, τs 199.5386 199.5348 199.5295 rmse 1.6219 1.5501 1.4873 based on the analysis, it can be explained that the prediction capability is very important in an acc system to provide optimal response. by estimating a future behavior, a better control input can be generated while satisfying the constraints systematically. nevertheless, there is an obvious difference between pfc and mpc because the optimization algorithm is simplified to reduce the computation burden. however, it worth pointing out that pfc performance is better compared to pid. the main reason is because the pi computes the control action based on the current measurement rather than prediction. indeed, one may argue that if it is tuned properly or a suitable special switching strategy is used, a better performance can be obtained. nevertheless, it also should be noted that the tuning procedure is not as straightforward as expected since many trial-anderror procedures need to be implemented. 223 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 4. conclusion in summary, this paper describes a design that proposes the use of pfc in controlling the acc system of a vehicle. based on the simulation results, it is found that although the pfc performance with rmse of 1.4873 is not comparable with the more advanced mpc algorithm with rmse of 1.5501, it gives a better performance compared to the pi controller with rmse of 1.6219. besides, the pfc algorithm is also simple and straightforward to implement and requires less calculation compared to the mpc while retaining its predictive advantage compared to other traditional controllers. the tuning process is also intuitive, being based on the desired time constant and coincidence horizon selection. indeed, there is a lot of room for improvement and future work will provide a more systematic analysis of the computation requirement of both mpc and pfc controllers and their robustness properties. hence, it can be concluded that pfc can become a good alternative to mpc and pi by trading off some of the optimality properties for a lower computation burden. acknowledgement the authors would like to acknowledge the ministry of higher education, malaysia for funding this work under the fundamental research grant scheme frgs/1/2021/tk02/uiam/02/2 (frgs21-240-0849). the first author would like to acknowledge majlis amanah rakyat (mara) for his tuition fee waiver. references [1] jiang y, deng w, he r, yang s, wang s, bian n. (2017) hierarchical framework for adaptive cruise control with model predictive control method (no. 2017-01-1963). sae technical paper. [2] rajamani r. (2011) vehicle dynamics and control. springer science & business media. [3] haroon z, khan b, farid u, ali sm, mehmood ca. (2019). switching control paradigms for adaptive cruise control system with stop-and-go scenario. arabian journal for science and engineering, 44(3): 2103-2113. [4] alomari k, mendoza rc, sundermann s, goehring d, rojas r. (2020). fuzzy logic-based adaptive cruise control for autonomous model car. in robovis (pp. 121-130). [5] phan d, amani am, mola m, rezaei aa, fayyazi m, jalili m., ... khayyam h. (2021). cascade adaptive mpc with type 2 fuzzy system for safety and energy management in autonomous vehicles: a sustainable approach for future of transportation. sustainability, 13(18): 10113. [6] takahama t, akasaka d. (2018). model predictive control approach to design practical adaptive cruise control for traffic jam. international journal of automotive engineering, 9(3): 99-104. [7] li se, jia z, li k, cheng b. (2014). fast online computation of a model predictive controller and its application to fuel economy–oriented adaptive cruise control. ieee transactions on intelligent transportation systems, 16(3): 1199-1209. [8] guo l, ge p, sun d, qiao y. (2020). adaptive cruise control based on model predictive control with constraints softening. applied sciences, 10(5): 1635. [9] borek j, groelke b, earnhardt c, vermillion c. (2019, july). optimal control of heavy-duty trucks in urban environments through fused model predictive control and adaptive cruise control. in 2019 american control conference (acc) (pp. 4602-4607). ieee. [10] awad n, lasheen a, elnggar m, kamel a. (2022). model predictive control with fuzzy logic switching for path tracking of autonomous vehicles. isa transactions, 129: 193-205. [11] rossiter ja. (2018). a first course in predictive control. crc press. 224 iium engineering journal, vol. 24, no. 1, 2023 zainuddin et al. https://doi.org/10.31436/iiumej.v24i1.2341 [12] nasiri soloklo h. (2018). predictive functional control for tracking of core power variations in pressurized water reactor based on laguerre functions and reduced-order model. modares mechanical engineering, 18(1): 299-306. [13] li my, lu kd, dai yx, zeng gq. (2020). fractional-order predictive functional control of industrial processes with partial actuator failures. hindawi complexity, 2020: 1-25. [14] abdullah m, rossiter ja. (2018). input shaping predictive functional control for different types of challenging dynamics processes. processes, 6(8): 118. [15] abdullah m, rossiter ja, ghaffar afa. (2021). improved constraint handling approach for predictive functional control using an implied closed-loop prediction. iium engineering journal, 22(1): 323-338. [16] abdullah m, rossiter ja. (2021). using laguerre functions to improve the tuning and performance of predictive functional control. international journal of control, 94(1): 202214. [17] rossiter ja, aftab ms. (2021). a comparison of tuning methods for predictive functional control. processes, 9(7): 1140. [18] zainuddin mas, abdullah m, ahmad s, tofrowaih ka. (2022). performance comparison between predictive functional control and pid algorithms for automobile cruise control system. international journal of automotive and mechanical engineering, 19(1): 94609468. 225 microsoft word 2_v17no2_compiled_v2_24nov16.docx iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 59 a neural network based traffic-aware forwarding strategy in named data networking parisa bazmi and manijeh keshtgari department of computer and information technology, shiraz university of technology, shiraz, iran. bazmi.parisa@gmail.com; keshtgari@sutech.ac.ir (received: 29th jan. 2016; accepted: 3rd may. 2016; published on-line: 30th nov. 2016) abstract: named data networking (ndn) is a new internet architecture which has been proposed to eliminate tcp/ip internet architecture restrictions. this architecture is abstracting away the notions of both hosting and operation based on naming datagrams. however, one of the major challenges of ndn is supporting a qos-aware forwarding strategy so as to forward interest packets intelligently over multiple paths based on the current network condition. in this paper, neural network (nn) based traffic-aware forwarding strategy (nntf) is introduced in order to determine an optimal path for interest forwarding. nn is embedded in ndn routers to dynamically select the next hop based on the path overload probability achieved from the nn. this solution is characterized by load balancing and qos-awareness in terms of delay and packet drop via monitoring the available path and forwarding data on the traffic-aware shortest path. the performance of nntf is evaluated using ndnsim which is a ns-3 module that implements the ndn communication model. the simulation results show the efficiency of this scheme in terms of network qos improvement of 17.5% and 72% reduction in network delay and packet drop respectively. abstrak: data rangkaian bernama (ndn) adalah seni bina internet baru yang telah dicadangkan untuk menghapuskan sekatan seni bina internet tcp / ip. seni bina ini mengabstrakkan konsep hos dan dijalankan berdasarkan menamakan datagram. bagaimanapun salah satu cabaran utama ndn adalah menyokong strategi penghantar sedar qos supaya paket interest dikirim dengan bijak melalui beberapa laluan berdasarkan kepada keadaan rangkaian semasa. dalam kertas ini, neural network (nn) berdasarkan strategi penghantaran traffic-aware (nttf) diperkenalkan untuk menentukan laluan yang optimum untuk penghantar interest. nn tertanam dalam router ndn untuk memilih hop seterusnya secara dinamik berdasarkan kebarangkalian jalan beban dicapai dari nn. penyelesaian ini mempunyai ciri-ciri pengimbangan beban dan kesedaran qos dari segi kelewatan dan paket drop melalui pemantauan jalan yang ada dan penghantaran data di atas jalan traffic-aware yang tersingkat. prestasi nttf dinilai dengan menggunakan ndnsim yang merupakan modul ns-3 yang melaksanakan model komunikasi ndn. keputusan simulasi menunjukkan kecekapan skim ini dari segi peningkatan rangkaian qos adalah sebanyak 17.5% dan pengurangan kelewatan rangkaian dan drop paket adalah sebanyak 72%. keywords: named data networking; content-centric networking; forwarding strategy; neural network iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 60 1. introduction current internet architecture is based on a tcp/ip solution and has focused on pointto-point communication between two entities. today, the content from services dominates the marketplace and users care about content, while the internet is still working based on where the content is [1]. therefore, it is unable to serve these new applications and the increasing needs of companies and individuals [2]. a new architecture has been proposed originally in [1] to remove a tcp/ip internet architecture restriction which is the use of the naming datagram instead of ip addresses. content-centric networking (ccn), also called named data networking (ndn), is the latest proposed internet architecture based on naming datagrams. this architecture is abstracting away the notion of hosting [1]. in ndn, communication begins with the consumer. first, the consumer requests its desired content by sending an interest packet which contains its desired content name. the requested data is then transmitted to the consumer in the reverse path from interest packet receiver. the ndn router has three components: content store (cs), pending interest table (pit), and forwarding information base (fib). when an interest packet is received on the router’s interface, the cs (buffer memory which caches the data packets) is checked to find whether the received interest name is matched with any cs entry. if the name is matched, the cached data packet is sent back on the incoming interface. otherwise, it checks the pit table which keeps track of forwarded interest packets to find whether the desired interest has already been sent or not. if the interest has been sent, the interface of the router which interest packet was received through it is added to pit to transmit data packets in the reverse path. if the interest name is not matched with any pit or cs entry, the longest prefix match is done for interest packet routing in the fib table to decide which router’s interface to send an interest out to [1]. ndn’s loop-free data forwarding permits ndn routers to select its outgoing interface or interfaces adaptively from multiple choices. however, supporting intelligent forwarding strategy is one of the major challenges of ndn implementation [1, 3, 4]. on the other hand, ndn offers obvious advantages over tcp/ip, including adaptive forwarding provided by the state maintained in the router. since, in ndn, the router pit keeps track of interest packets and receiving data packets can be observed for each interest, routers can adaptively measure throughput, delivery performance, and packet loss. this ndn characteristic gives ndn routers an opportunity to forward packets intelligently and adaptively considering the current network status [5]. in this paper, this beneficial behavior of ndn is taken into account to design a new intelligent load-balancing forwarding strategy which is called neural network based traffic-aware forwarding strategy (nntf) for ndn. the neural network (nn) is designed to select the next hop dynamically, based on the current network status achieved from the feedback of data and interest packets. this solution is enacted by load balancing and qos-awareness via monitoring -not only available path resources but also the interest and data packets. the remainder of this paper is organized as follows. section 2 describes the related work on the ndn forwarding strategy. a detailed description of nnft is given in section 3. section 4 presents the performance evaluation of the proposed algorithm, and section 5 concludes the paper. iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 61 2. related works the original ndn forwarding strategy is flooding in which interest packets are broadcast on all possible router outgoing interfaces [1]. since the data packet is forwarded via the reverse path, the data packet, which was received sooner, is considered and the other received data packets from other interfaces are discarded. this strategy makes use of the fastest path, and as a result the path with the lowest delay due to the existence of a wide range of data and interest packets in the network, the performance of the network in terms of network delay, bandwidth consumption, and energy efficiency is reduced dramatically. the other possible strategy which can be used in ndn is to unicast interest packets to the best outgoing interface. however, this strategy is challengeable in finding the best outgoing interface dynamically and it is resilient against network failure. some probabilistic forwarding strategies are proposed to find the best next hop to transmit the interest packet [3, 4, 7]. the initial design of the ndn forwarding strategy is described in [5, 7]. using pit and two-way interest and data exchange gives the ndn forwarding strategy the opportunity to immediately detect network problems and decide on the outgoing interface using the current network condition. the interest nack packet is introduced in these papers to notify downstream nodes about a problem in a specific path. interface ranking is described in this paper based on the forwarding policy. possible outgoing interfaces for each name in fib are ranked based on the network policy and then an interest is sent to the interface with the highest rank. probability-based adaptive forwarding (paf) strategy is based on the ant colony algorithm optimization is presented in [3]. an ant colony is used to calculate the outgoing interface selection probability. it uses the feedback from data and interest packets to probe the performance of each interface in terms of delay. as a result, the selection probability is computed adaptively based on the network condition and optimizing a performance metric (delay). the load is balanced between interfaces of the router. a greedy ant colony forwarding (gacf) algorithm is proposed in [4] as an ndn forwarding strategy. it is a qos-aware forwarding strategy which uses the ant colony algorithm to optimize the possible paths and select the next hop probabilistically based on the current network state. using the ant colony algorithm in paf and gacf adds some complexity to ndn as distinguished interest packets are needed for probing only. in this paper, the best next-hop is investigated by implementing a preconfigured neural network (nn) in each router to decide which path should be selected to send the interest based on the current network condition. the preconfigured nn in the routers is very simple and does not need a separate interest packet for probing like ant colony does. 3. neural-network based traffic-aware forwarding strategy in this section, the use of nn is described to determine an optimal next-hop selection in ndn forwarding strategy. the forecasting algorithm using the neural network is embedded in each router to predict the load on its outgoing interfaces. in the ndn strategy layer, the router transmits interest packets on a traffic-aware shortest path. using a iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 62 predicting algorithm in ndn, forwarding strategy can play a pivotal role in guaranteeing qos and minimizing expected delay and loss in ndn. 3.1 neural network design the usage of nn as a tool for traffic prediction has been prevalent in the computer network due to its ability to learn complicated patterns [9-12]. nn can be used for nexthop selection in ndn forwarding strategy [6]. the summary of the designed nn and its design motivations are described in this section. in the designed nn network, packet drop is considered a warning that the load on the link is more than that link capacity. in other words, dropping packets occurs when the link is overloaded and the router’s queue has overflowed [13]. on the other hand, nn is a great way of packet drop prediction as it was used widely in tcp/ip networking [14, 15]. the designed nn predicts the probability of drop occurrence which is considered a link overload probability. the pre-trained multilayer perception (mlp) nn is implemented in each router and works in the router’s strategy layer to dynamically predict the overload probability based on the received feedback from that link and its training data. figure 1 illustrates the designed nn. as can be seen in fig. 1, a feed-forward, supervised two-layered neural network is designed using matlab software’s nn toolbox to predict overload probability on each link. a two-layer nn including one hidden layer and one output layer is selected based on the proposed theory in [16] that proved that one hidden-layer is enough to estimate any continuous function. fig. 1: designed nn diagram for the forwarding strategy. to reach the best nn design, different input parameters and different numbers of hidden layer neurons were evaluated. the mean square error (mse) is used to compare different models of nn implementation. the nn is run and repeated between 10 to 50 times for each value of a single parameter, while other parameters are kept constant and the nn is examined several times by means of this parameter so as to select the best nn design. as was discussed in [6], the mentioned input parameters include the factors which have an impact on the amount of load on the path in addition to the topology based parameters that influence congestion occurrence and link overload. different scenarios were implemented to obtain the best collection of input parameters. after few trials, between 10 to 50 times for each nn parameter, the neural network with 8 input neurons and 10 hidden layers with the sigmoid activation function and one neuron with a linear function in the output layer is selected to predict overload probability based on the analysis of mse and regression curve in the different designs. the 8 nn inputs comprise network topology input parameters and load parameters for each link as follows [6]: iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 63 1. number of incoming interest packets (byte) 2. number of outgoing interest packets (byte) 3. number of incoming data packets from the link (byte) 4. number of outgoing data packets on the link (byte) 5. link bandwidth 6. link delay (s) 7. current queue size (byte) 8. queue capacity (byte) the data from different network topologies with different loads is used as a training data in the designed nn. the nn dataset is divided into three sets including 70% for training, 15% for validation, and 15% for testing data, in order to evaluate the accuracy of the designed nn. figure 2 shows the errors for each set of data. the final mse (0.00004) is too small, which illustrates the correctness of nn design. additionally, there is no evidence of over-fitting by iteration 703. therefore, the nn evaluation results show the correct implementation of nn in addition to the accurate dependency between input and output parameters. table 1 gives the summary of the implemented nn algorithm. fig. 2: nn performance curve based on mse for training, test, and validation set. table 1: summary of the implemented nn algorithm parameter value number of records for nn training 2465625 dataset division (training, validation, testing) random learning algorithm scaled conjugate gradient performance criterion mse 3.2 interface ranking as described in [7], the available outgoing interfaces for each name in the fib entries, which is obtained from routing policy, are ranked to make forwarding strategy more convenient. this ranking is based on a forwarding policy that ndn considered for sending interest packets. in this paper, the traffic-aware shortest path in terms of delay is iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 64 used as a next-hop for sending interest packets. as a result, the path with the shortest propagation delay is assigned the highest interface rank. 3.3 forwarding strategy algorithm when a new interest is received in the router and it does not match any entry in the content store and pit, a new pit entry will be created. the new interest is then forwarded to the highest-ranked interface if nn overload prediction for this face is lower than 50%. otherwise, the next highest-ranked interface, whose overload prediction is less than 50%, is selected as a next-hop. in the situation where there is no available interface with an overload probability below 50%, the face with the smallest overload probability (lowest load) is opted for to forward the interest packet. the overload probability threshold (50%) was obtained and optimized from doing various simulations. the figure in which the performance of the network was higher is considered as a threshold to change the current working path. figure 3 illustrates nntf algorithm. in this algorithm, neuralnetwork_output (interface) is a method that implements trained nn for overload prediction of specified interface in the router. nntf is implemented in all routers’ strategy layer in order to select next-hop for sending interest. fig. 3: forwarding strategy algorithm. nntf works based on the information provided by the nn regarding the current network status. by fast rerouting, this scheme maintains load balancing and congestion avoidance. as a result, the overall performance of the network, including delay and packet loss, is improved. one of the other major features of this scheme is that it avoids instability by avoiding frequent vacillation of paths, unless it is predicted that the path is nearly overloaded. iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 65 4. evaluation of proposed algorithm due to the fast rerouting and load balancing based on nn output, the proposed forwarding strategy would improve the qos parameters and network performance. to evaluate the proposed forwarding strategy, a scenario is simulated in an open-source ndnsim [17] package, which implements the ndn protocol stack for the ns-3 simulator. the geant real topology [18] with 22 routers, 1 provider, and 20 consumers is implemented in ndnsim. geant is a real core network in europe. this topology has been used in various evaluations of the ndn network [6, 19-21]. table 2 gives information on the implemented scenario. table 2: network scenario parameter value topology geant with 22 router link capacity 1, 10 mbps number of consumers 20 number of producers 1 chunk size 1400 bytes interest size 32 byte cache size 0 consumer requested file size 12600 kbyte simulation time 100 s youtube traffic [22] is considered in this paper to evaluate the video qos improvement by implementing the proposed nn. video traffic with standard quality of 360 p, 1000 kbit/s transmission rate and 30 frames per second is simulated for this traffic. delay and packet drop are two common qos parameters in multimedia for evaluating network efficiency which are used in this paper. two scenarios, including the shortest path forwarding strategy and traffic-aware shortest path with nn implementation, are simulated to evaluate the efficiency of nntf. table 3 shows the delay comparison in 22 consumers between these two scenarios. the calculated delay is the time between transmitting an interest packet and receiving the desired data [23, 24] which consists of queuing, propagation, and transmission delay. by fast rerouting, based on the path overload probability, traffic-aware forwarding strategy forwards interest packets on the shortest and at the same time, not crowded path. as can be seen in table 3, the total network delay is reduced by 9%. it is obvious that under larger traffic load, this algorithm would act more effectively. to show this, some background traffic is added to the network to increase the probability of path overload. table 4 gives the results of this simulation. as shown in table 4, total network delay with nn prediction under larger traffic reduced by about 17.5 percent which is evidence of the efficiency of proposed algorithm. therefore, nntf works appropriately under heavy traffic, and it is an efficient forwarding strategy under heavy network load. to evaluate the network performance, the comparison of packet drops in the core routers of the network is calculated. figure 4 shows the packet drop rate in 10 routers of the network for both shortest path and nntf under heavy traffic. the details of the packet drop in all routers are presented in table 5. as can be seen in table 5, nntf reduces packet drop in network routers by 72.11% due to the fast rerouting that results in congestion avoidance and queue overflow prevention. iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 66 table 3: comparison of the delay (s) in network consumer between the normal shortest path algorithm and nntf mean delay in 100 s (s) consumers nntf shortest path 26.5963 27.9489 c1 4.091 4.53689 c2 26.471 28.6975 c3 7.67606 9.68352 c4 11.9117 12.7325 c5 25.1191 28.5499 c6 21.0264 26.8557 c7 27.28 29.6673 c8 28.706 28.7097 c9 28.289 28.2589 c10 6.534 6.86975 c11 22.768 24.2168 c12 23.8981 26.4765 c13 4.813 4.85138 c14 23.8017 27.4695 c15 14.599 14.6193 c16 20.8679 23.038 c17 22.8733 26.4403 c18 26.5185 27.069 c19 11.5951 16.8177 c20 19.26975 21.17545 overall network’s mean delay in 100 s 8.996% improvement percentage table 4: comparison of delay(s) in network consumer between the normal shortest path algorithm and nntf under heavy traffic mean delay in 100 s (s) consumers nntf shortest path 23.507802 28.70056 c1 6.042782 25.18629 c2 27.94695 29.58026 c3 27.43917 29.29922 c4 25.54593 30.27463 c5 27.02151 26.6662 c6 12.92972 22.54109 c7 27.93101 27.57811 c8 25.57313 30.16761 c9 27.93101 28.80371 c10 22.70501 28.99133 c11 24.00278 28.7824 c12 24.5023 26.6225 c13 22.43217 29.44756 c14 21.4878 27.15052 c15 21.59808 25.18447 c16 23.8936 26.47577 c17 23.27276 28.94153 c18 24.47638 29.50166 c19 14.81094 19.98871 c20 22.6872 27.49429 overall network’s mean delay in 100 s 17.4835% improvement percentage iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 67 fig. 4: the comparison between the shortest path and nntf of the packet drop rate of ten routers, in kbit. table 5: comparison of packet drop in the routers between the shortest path and nntf, in kbit. mean packet drop in 100 s (kbit) network routers nntf shortest path 384.97 2129.455 core1 0.16162 35.9596 core2 181.98 1059.879 core3 473.535 1752.646 core4 4.84849 45.1772 core5 0 0 core6 0 0 core7 0 0 core8 22.6263 173.8182 core9 13.0101 51.9596 core10 5.73737 87.91919 core11 440.081 1171.071 core12 10.5051 110.7879 core13 710.141 2034.909 core14 558.222 1884.606 core15 12.0404 92.92929 core16 224.647 794.3434 core17 519.758 1452.364 core18 6.62626 90.50505 core19 26.5859 204.9293 core20 337.212 927.8384 core21 187.271 671.4806 overall network’s mean packet drop (kbit) 72.11% improvement percentage nntf shortest path iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 68 5. conclusion ndn has been introduced as a new internet architecture in order to remove current internet architecture restrictions by using naming data rather than the host ip address. one of the main challenges of ndn is to provide an intelligent forwarding strategy in routers, as is addressed in this paper. here, nntf has proposed as a traffic-aware shortest path forwarding strategy that works based on nn prediction. a nn is designed and embedded in each ndn router to predict overload probability of each path, which is then used in the path selection for interest forwarding. the performance of nntf is evaluated by simulation using ndnsim, showing the efficiency of this scheme under heavy traffic by reducing 17.5% and 72% of network delay and packet drop respectively. references [1] jacobson v, smetters dk, thornton jd, plass mf, briggs nh, braynard rl. (2009) networking named content. acm proc. 5th inter. conf. emerging networking expts. tech., 1-12. [2] future content networks group. why do we need a content-centric future internet?” proposals towards content-centric internet architectures, european commission, information society and media. available at: http://www.future-internet.eu/. retrieved july, 2014. [3] qian h, ravindran r, wang gq, medhi d. (2013) probability-based adaptive forwarding strategy in named data networking. ifip/ieee international symposium on integrated network management, 1094-1101. [4] chengming li, wenjing liu, okamura k. (2013) a greedy ant colony forwarding algorithm for named data networking. proc. asia-pacific advanced network, 34:17-26. [5] yi c, afanasyev a, wang l, zhang b, zhang l. (2012) adaptive forwarding in named data networking. acm sigcomm comp. comm. rev., 42(3):62-67. [6] bazmi p, keshtgary m. (2014) a neural network based congestion control algorithm for content-centric networks. j. adv. comp. sci. tech., 3(2):214-220. [7] yi c, afanasyev a, moiseenko i, wang l, zhang b, zhang l. (2013) a case for stateful forwarding plane. comp. comm., 36(7):779-791. [8] floyd rw. (1962) algorithm 97: shortest path. communications of the acm, 5(6):345. [9] barabas m, boanea g, dobrota v. (2011) multipath routing management using neural networks-based traffic prediction. third int. conf. emerging network intelligence, 118-124. [10] rouhani m, tanhatalab mr, shokohi-rostami a. (2010) nonlinear neural network congestion control based on genetic algorithm for tcp/ip networks. ieee second int. conf. comp. intel. comm. syst. netw. (cicsyn),1-6. [11] cho hc, fadali ms, lee h. (2005) neural network control for tcp network congestion. ieee proc. american control conference, 3480-3485. [12] rovithakis g, houmkozlis cn. (2005) a neural network congestion control algorithm for the internet. ieee proc. inter. symp. intel. control, mediterranean conference on control and automation, 450-455. [13] jacobson v. (1988) congestion avoidance and control. acm sigcomm comp. comm. rev., 18(4):314-329. [14] mehrvar hr, soleymani mr. (2001) packet loss rate prediction using a universal indicator of traffic. ieee inter. conf. communications, 3:647-653. [15] barve yd. (2009) neural network approach to the prediction of percentage data packet loss for wireless sensor networks. ieee 41st southeastern symposium on system theory, 103106. [16] kurkova v. (1992) kolmogorov's theorem and multilayer neural networks. neural networks, 5:501-506. [17] afanasyev a, moiseenko i, zhang l. (2012) ndnsim: ndn simulator for ns-3. university of california, los angeles, tech. rep. iium engineering journal, vol. 17, no. 2, 2016 bazmi and keshtgari 69 [18] geant project website. available: http://www.geant.net. retrieved july, 2014. [19] tortelli m, grieco la, boggia g. (2013) performance assessment of routing strategies in named data networking. ieee icnp, 2013. [20] rossi d, rossini g. (2012) on sizing ccn content stores by exploiting topological information. infocom workshops, 280-285. [21] ciancaglini v, piro g, loti r, grieco la, liquori l. (2013) ccn-tv: a data-centric approach to real-time video services. 27th inter. conf. advanced information networking and applications workshops (waina), 982-989. [22] youtube sample rate:https://support.google.com/youtube/answer/1722171?hl=en.retrieved july, 2014 [23] almishari m, gasti p, nathan n, tsudik g. (2013) optimizing bi-directional low-latency communication in named data networking. acm sigcomm comp. comm. rev., 44(1):13-19. [24] jiang x, bi j. (2013) interest set mechanism to improve the transport of named data networking. acm sigcomm comp. comm. rev., 43(4):515-516. microsoft word 0_vol_16_no_2_2015_special issue on energy_compiled.docx iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 31 waste heat recovery in heat pump systems: solution to reduce global warming y. baradey, m.n.a. hawlader, ahmad faris ismail and meftah hrairi department of mechanical engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. yehyabaradei@yahoo.com, mehawlader@iium.edu.my, faris@iium.edu.my, and meftah@iium.edu.my (received: october 5, 2015; accepted: october 30, 2015; published on-line: november 30, 2015) abstract: energy conversion technologies, where waste heat recovery systems are included, have received significant attention in recent years due to reasons that include depletion of fossil fuel, increasing oil prices, changes in climatic conditions, and global warming. for low temperature applications, there are many sources of thermal waste heat, and several recovery systems and potential useful applications have been proposed by researchers [1-4]. in addition, many types of equipment are used to recover waste thermal energy from different systems at low, medium, and high temperature applications, such as heat exchangers, waste heat recovery boiler, thermo-electric generators, and recuperators. in this paper, the focus is on waste heat recovery from air conditioners, and an efficient application of these energy resources. integration of solar energy with heat pump technologies and major factors that affect the feasibility of heat recovery systems have been studied and reviewed as well. abstrak: teknologi penukaran tenaga, di mana sistem pemulihan haba buangan diambil kira, mula mendapat perhatian kebelakangan ini disebabkan oleh beberapa faktor. contohnya kurangnya tenaga fosil, peningkatan harga minyak, perubahan cuaca dan pemanasan global. pada aplikasi suhu rendah, terdapat banyak sumber haba buangan dan beberapa sistem pemulihan dan aplikasi berguna yang sesuai dicadangkan oleh pelbagai pengkaji dari seluruh dunia [1-4]. tambahan pula, berbagai alatan digunakan untuk memulihkan tenaga haba buangan daripada sistem yang berbeza kepada aplikasi suhu rendah, sederhana dan tinggi. alatan tersebut meliputi penukar haba, dandang pemulihan tenaga haba buangan, penjana elektrik-terma dan pemulih. kertas kerja ini memfokuskan kepada pemulihan tenaga haba buangan daripada penghawa dingin dan aplikasi yang efisien bagi sumber tenaga ini. turut dikaji juga, gabungan tenaga suria bersama teknologi pam haba dan faktor utama yang mempengaruhi kebolehlaksanaan sistem pemulihan tenaga haba. keywords: waste heat recovery; heat pump. 1. introduction generally, sustainability, safety, innovation, and energy conservation have recently become the most attractive and significant goals especially in modern societies. according to senda [1], energy conservation coupled with waste heat recovery has become an attractive topic for research in industrialized countries since the begining of the twenty first century. this started in the seventies due to the fact that oil is a finite energy source, iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 32 with significant increases in its price, and political conflicts associated with it. increasing the cost of fuel has a great effect on the running cost of fuel based systems. in vehicles, for instance, air conditioning systems adds up to 35% in extra cost [2]. hence reduction in air condition load by exploiting the waste heat from the engine will lead to significant reduction in the vehicle’s fuel consumption. in addition, huge increase in oil production and usage during the last century has caused climatic changes and problem such as global warming and ozone depletion. a comparison between the main cause of global warming, which is carbon dioxide gas emission, and energy consumption in australia has been made, as shown in figure1. from the figure it is observed that gas fired heat pumps consume energy double than that of electric heat pumps while the percentage of carbon dioxide emission is about half (0.42). however, due to the economic issues with regards to saving energy, waste heat recovery, has also become significantly more important. after signing the kyoto protocol on climate change in 1997, the world has been moving towards embracing renewable energy resources, particularly solar energy, wind energy, and biomass energy together with paying great attention on saving energy and waste heat recovery systems whr. fig. 1: comparison between energy consumption and co2 emission in australia. for example, the relationship between electric heat pump and co2 heat pump is 1:1 [3]. energy intensive industries have for many decades used waste heat recovery systems for either energy reuse or storage [1]. the wasted heat is transferred into an energy conversion system using different types of heat recovery equipment. the waste heat recovery concept requires efforts in preventing potential energy losses of any kind. it includes, for instance, designing and implementing useful and efficient systems to recover the wasted heat from air conditioning systems, thermal insulation to increase thermal system efficiencies, exploitation of heat losses from furnaces and vehicle engines, and repair of steam leaks in power plants. once the requirements are achieved, suitable strategies have to be made to stabilize shortterm energy saving and or/ energy recovery in systems using permanent solutions for implementation [4]. these permanent solutions are commonly termed heat recovery systems. 0 0.5 1 1.5 2 2.5 3 gas boiler gas fired heatpump electric heatpump relative energy consumption relative carbon dioxide emission 2.78 0.59 2.00 0.42 1.00 1.00 iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 33 different methods are used for recovering industrial waste heat. wasted heat can be either used in different processes for the same systems, such as wasted heat from a heat pump system exploited and used, by re-designing the pipe line for water heating within the same system, or can be re-used in same processes like using the hot exhaust gases from combustion to preheat combustion air in industrial boilers. table 1 reflects some resources of waste heat [5]. this paper focuses on recovery of dissipated heat from air conditioners (heat pump systems) and its potential useful applications. table 1: some of waste heat sources. waste heat sources combustion exhausts:  glass melting furnace  cement kiln  fume incinerator  aluminium reverberatory furnace  boiler process off gases:  steel electric arc furnace  aluminum reverberatory furnace cooling water from:  furnaces air compressors  internal combustion engines conductive, convective, and radiative losses from equipment:  hall-hèroult cells conductive, convective, and radiative losses from heated products:  hot cokes  blast furnace slags waste heat from air conditioners 1.1 recommended potential applications of waste heat different researchers recommended numerous potential applications of waste heat. the exhaust gas can be used in different applications depending on the level of its temperature. exhaust gas at a very high level is used to heat up the combustion air for boilers using preheaters, and for furnaces, gas turbines, and ovens by using recuperators. it is also used to preheat the boiling feed water using economizer when its temperature level is medium. when it is at a low temperature level it is used to heat water and feedstock. running absorption refrigeration systems for air conditioning is considered to be one type of waste heat potential application. waste heat from heat pump systems, which is the main focus in this paper, can be used for water heating and drying simultaneously. 1.2 factors influencing the feasibility of waste heat recovery the possibility of implementing an efficient and cost effective heat recovery system is affected by many factors. the evaluating process of the feasibility of waste heat recovery requires, at first, identifying the source of the heat and the steam which carries it. heat quantity or heat content, heat temperature or quality, chemical composition of the steam, and the minimum allowed temperature are the most common factors that affect the feasibility of the recovery system. the heat content is defined as the amount of energy that is carried by the steam and it is a function of temperature and mass flow rate of the steam, while the term quality indicates to its benefits. the temperature difference between the heat source and sink is a very important factor as the temperature of the heat source must iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 34 be higher than the temperature of the heat sink to enable the heat transfer process. this difference affects both the rate of heat transfer, and the efficiency of converting energy from one form to another. meanwhile, the temperature of the waste heat source affects the selection of material in the heat exchangers as well as the recovery systems because of some chemical reactions, such as corrosion and oxidation, which accelerate dramatically with increasing temperature. quality and quantity of the steam are not affected by the chemical composition of the steam as long as it does not include any fuel. but the composition effect is exclusively on the material selection, recovery process, and the thermal conductivity and heat capacity. minimum allowed temperature to prevent chemical reactions like corrosion depends on the sort of fuel used. for instance, minimum temperature for hot exhaust gases from natural gas is about 120oc , which differs from that for hot gases from coal or oil which is about 150oc. table 2 shows some typical waste heat temperatures from different sources at low, medium, and high level. table 2: typical temperatures of waste heat from different sources at low, medium, and high level. source of waste heat typical temperature (oc) aluminum refining furnace (high) 650-760 steel heating furnaces (high) 925-1050 open hearth furnace (high) 650-700 solid waste incinerators (high) 650-1000 glass melting furnaces (high) 10001550 steam boiler exhausts (medium) 230-480 reciprocating engine exhausts (medium) 315-600 drying and baking ovens (medium) 230 – 600 annealing furnace cooling systems (medium) 425 – 650 air conditioning and refrigeration (low) 32-88 air compressors (low) 27-50 cooling water from injection molding machines (low) 32-88 2. examples of waste heat recovery equipment used for low, medium and high temperature applications 2.1 heat exchangers (for low temperature applications) the heat exchanger is a device used in different fields to exchange heat from hot fluids (usually waster or gases) to cold fluids. various types of he are nowadays commercially available such as gasto-gas he, gas-to-liquid he, liquid-to-liquid he. for waste heat recovering systems from air conditioners, heat exchangers transfer heat from the hot refrigerant to the cold water tank, as shown in fig. 2. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 35 fig. 2: gas-to liquid heat exchanger for recovering waste heat from air conditioners. 2.2 recuperator (for medium & high temperatures) the recuperator is a device usually used to recover the waste heat from the exhaust gas in medium and high temperature applications, like melting furnaces, radiant tube burners, and soaking ovens. these devices can be based on convection and radiation heat transfer process. example of recuperator based radiation is shown in fig. 3, where the hot gas comes through the inner duct and heat transfers by radiation to the cold air in the outer shell [5]. fig. 3: schematic of recuperator based radiation sytem. hot air to process waste gas insulation and metal covering fuel gas cold air inlet iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 36 figure 4 shows an example of a recuperator-based convection heat transfer, where the hot wasted gas enters into tubes surrounded with cool fluid and the convection heat transfer process takes places resulting in producing heated fluid at high temperature. fig. 4: schematic of recuperator based convection system. 2.3 thermo-electric generator a huge amount of wasted heat is generated in thermal to electricity conversion systems. this wasted (energy) has relatively low temperature and energy density, so that it cannot be exploited to generate electricity using the conventional energy conversion cycles such as orc, and rankine. in this situation the direct conversion, without moving parts, of thermal energy to electrical energy may be the best alternative. the thermoelectric generator is a solid state device that converts thermal energy directly to electricity, and unlike the traditional heat engines it has no moving part and operates in a completely silent mode [6]. such devices can be used to recover the wasted heat from the low temperature sources, such as air conditioners, in order to generate electricity instead of throwing it away. physically, the principle of work of the thermoelectric generator is quite similar to that for solar cells, as shown in fig. 5. fig. 5: thermo-electric generator. cool fluid hot waste gas tubes for hot waste gas heated fluid cooled waste gas load current heat flow from the source iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 37 2.4 water heat recovery boiler the working principle of the water heat recovery boiler is similar to the normal water tube boiler, where the hot exhaust gases exchange heat with parallel tubes contain cold water. this leads to vaporize the water inside the tubes, and then it will be collected in the stream drum to be used for another application, as it is illustrated in fig. 6, which represents schematic of a water heat recovery boiler. fig. 6: schematic of waste heat recovery boiler. 3. heat pump (air conditioner) and heat recovery technologies the heat pump system is a vapor compression system consisting of four main components which are compressor, condenser, expansion device and an evaporator, as shown in fig. 7. figure 8 is the p-h (pressure-enthalpy) diagram of the conventional system [7]. these systems are designed in order to cool down the interior space by removing the heat from it and reject it into ambient air through the condenser. in the normal installation, heat rejection occurs directly to the ambient air, but recently many designations have been proposed by different researchers in order to recover the wasted heat to be used for different applications such as water heating, drying, and desalination, especially in buildings that run air-conditioners all day such as hotels and hospitals according to hawlader [8]. figure 9 represents as example of a heat pump system with heat recovery system used for water heating for domestic applications. cooled waste gas, out water tubes hot waste gas, in steam, out steam drum feed water, in iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 38 fig. 7: schematic of vapor compression air conditioning system. fig. 8: p-h diagram for conventional heat pump systems [7]. wasted heat is any source of rejected heat, which may include gas, solid, and liquid, can be partially or fully reused or recovered economically. practically, wasted heat from air conditioners or heat pumps is not only the heat that has to be removed from the environment, it also includes the heat added to the refrigerant from the compression process [9]. the prediction of the amount of wasted or dissipated heat from the air compressor condenser evaporator expansion valve press ure (psia) enthalpy condenser compressor evaporator expansion valve heat in heat out win iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 39 conditioners is a daunting task because the space load and the outside conditions vary from day to day during the season as well as the year. for example, the amount of wasted heat from a 20 ton air conditioner operating at full capacity may reach 24 tons of heat, while same units having same specifications may reject only 13 tons of heat or less at 30% capacity [9]. according to hawlader [10] in tropical countries such as malaysia, air conditioners are consuming more than half of the building energy, and every 1 kw of the consumed electricity by an air conditioner leads to about 4 kw of thermal energy at 85oc being thrown into the atmosphere, which contributes to global warming. normally, when the temperature of wasted heat is high, the recovery system will be more cost effective and of higher quality. many benefits could be achieved from recovering the wasted heat such as reducing the cost of the process by increasing the energy productivity, reduce the pollution, reduction in equipment size, and reduction in auxiliary energy consumption. fig. 9: example of heat pump system with heat recovery system for water heating. 4. solar assisted heat pump (sahp) technologies the solar assisted heat pump system is a conventional heat pump system where solar energy is the main heat source instead of/ besides the electrical energy, as shown in fig. 10. this system usually consists of a compressor, heat exchanger, evaporator (usually flat plat solar collector), and expansion valve [11]. many designs of sahp are nowadays available in the market which differ slightly or sometimes fundamentally from one another. the main differences are in the type and size of the heat source, heat storage system, and solar collector type. these systems usually use flat plate solar collectors with conventional refrigerants such as r134a. recently, many researchers are moving toward embracing and using co2 as refrigerant in sahp systems because of environmental issues such as ozone depletion, and global warming. besides that, co2 has thermodynamic properties which enable it to be competitive and most promising alternative of conventional refrigerants [12]. using co2 in sahp systems makes the system work under the transcritical thermodynamic cycle not the traditional vapor compression cycle. carbon dioxide heat pump systems will be detailed more in the next section. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 40 fig. 10: diagram of sahp system for water heating. 5. carbon dioxideas refrigerant in heat pump systems refrigerant, in such systems, is considered the blood of the system. it is very important to choose the proper refrigerant in sahp systems because the entire system will be affected by it [13]. according to maina and huan [14], the most important factors that must be taken into account in the selection of the refrigerant in the heat pump systems are safety, reliability, cost, heat transfer properties, performance, and environmental acceptability. carbone dioxide is inexpensive, readily available, odorless at low concentrations, compatible with materials, and not a corrosive refrigerant [14], non-toxic, and non-flammable [15]. the two most popular refrigerants used in the past are ammonia and carbon dioxide. ammonia was stopped being used by the industry because it is toxic and harmful. carbon dioxide was stopped because of the advent of the fluorocarbon chemicals, it requires extremely high pressure (more than 73.8 bar), so that the compressor outlet temperature is also very high (160oc), which will cause capacity and cop loss at high heat rejection temperature [16]. the only solution that was proposed to solve the capacity and cop loss issue was to utilize two-stage cycles. this was because the sealing technology was not high and advanced at that time. fluorocarbon chemicals are causing air, water, and land pollution. they also cause global warming and ozone depletion whereas natural refrigerant particularly co2 has zero global warming potential. due to that many researchers reconsidered the use of natural gas in particularly co2 as an alternative refrigerant because of its thermodynamic properties, non-toxicity, and non-flammability [15]. depending on the study that conducted by neksa in 2004, co2 (r744) is the most attractive refrigerant for heat pumps water heaters, hp for space conditioning, hp for dryers, and commercial refrigeration. according to stene [17], carbon dioxide heat pump water heater systems are the most attractive and promising technology for flats and apartments, nursing homes, hotels, sport centers, and hospitals. high pressure issue of co2 could be a demerit for it, but it is no longer a problem with the development of advanced sealing technology. therefore, high compressor outlet temperature is not a disadvantage, because it can provide hot water near to the boiling expansion valve water tank hot water cold water inlet compressor evacuated tube u-pipe solar collector/evaporator solar radiation iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 41 point (sometimes more than 90oc) and cooling near to 50oc [16]. this water could be used in different applications such as cooling space, drying, water heating, and desalination of seawater simultaneously if the system was properly designed. so that it would be more prudent to reconsider and reuse carbon dioxide as a promising alternative refrigerant in sahp systems. carbon dioxide driven sahp systems could provide hot water with temperature more than 90oc without any operational problems, as shown in fig. 11 which represents the temperature-entropy diagram (t-s) of the transcritical co2 cycle and shows the temperature of the co2 gas through the transcritical thermodynamic cycle [16]. laipradit et al. [18] simulated the performance of a carbon dioxide heat pump system for water heating. the systems consisted of compressor, gas cooler, expansion valve, and evaporator (finned tube cross flow heat exchanger type). the result of the computer simulation showed that the coefficient of performance (cop) was from 2 to 3 for 4 kw compressor, 10 kw gas cooler, and 6 kw evaporator. the water temperature was found to be 50 to 60c under these conditions. it is also concluded that the most suitable mass flow ratio water to refrigerant is 1.2 and 2.2 for producing hot water above 60c. fig. 11: t-s diagram of the co2 hp with whr system used for water heating applications [15]. 6. conclusion waste heat recovery technologies have been recently recommended and introduced by many researchers worldwide as a solution for energy conservation to reduce global warming and air pollution. the amount of waste heat from heat pump systems can be huge especially in tropical countries such as malaysia, where air conditioners are operated almost for the entire day as well as throughout the year. waste heat recovery technology from air conditioners to produce domestic hot water and drying could be an excellent solution if implemented in hospitals, hotels, halls, and apartments. refrigerants in such systems are considered the most important factor that affects the system efficiency. entropy, [kj/kg.k] t em pe ra tu re [ o c ] iium engineering journal, vol. 16, no. 2, 2015 special issue on energy baradey et al. 42 carbon dioxide driven heat pump systems have been tested worldwide, and recommended as the best alternative instead of traditional refrigerants because of its high volumetric capacity and, its ability to provide hot water close to the boiling point as well as efficient drying. references [1] senda fm. (2012) aspects of waste heat recovery and utilization (whr&u) in pebble bed modular. master of science thesis, the university of stellenbosch, south africa. [2] pathania a, mahto d. (2012) recovery of engine waste heat for reutilization in air conditioning system in an automobile: an investigation. global journal of researches in engineering, 12(1). [3] international energy agency heat pump program. (2012) heat pump and heat recovery technology.www.heatpumpcentre.org/en/aboutheatpumps/sidor/default.aspx [4] reay da. (1979) heat recovery systems, a directory of equipment and techniques. e. & f. n. spon: london. [5] us department of energy. (2008) heat recovery: technology and opportunities in us industry. [6] bitschi a. (2009) modelling of thermoelectric devices for electric power generation. doctor of sciences dissertation, swiss federal institute of technology zurich (eth zurich). [7] momin g, deshmukh sr, deshmukh mt, chavan pt, choudhari pp. (2014) cop enhancement of domestic refrigerator by recovering heat from the condenser. international journal of research in advent technology, 2(5):2321-9637. [8] hawlader, mna. (2013) utilization of solar energy and waste heat for water heating, drying and desalination of seawater. paper presented in (icmime2013), 1-3 november, 2013, ruet, rajshahi, bangladesh. [9] jarnagin re. (2008) heat recovery from air conditioning units. university of florida; florida cooperation extention service. fact sheet ees-26. retrived on 10 october 2015 from http://www.wec.ufl.edu/extension/gc/harmony/documents/eh126.pdf. [10] hawlader mna. (2014) water heating and drying using solar energy and waste heat from air conditioners. keynote paper presented in international symposium on green and sustainable technology isgst 2014, utar perak campus, malaysia, sept. 30oct.3. [11] islam mr, sumathy k. (2013) carbon dioxide driven solar-assisted heat pump water heating system: a theoretical analysis. int. res. j. env. sciences, 2(10):77-92. [12] austin bt, sumathy k. (2011) transcritical carbon dioxide heat pump systems: a review. renewable and sustainable energy reviews, 15:4013-4029. [13] zakaria ma (2010) a solar assisted heat pump system for desalination. phd thesis, national university of singapore, singapore. [14] maina p, huan z. (2013) effect of refrigerant charge in the output of co2 heat pump. african j. sci. tech. innov. dev., 5(4): 303-311 [15] neksa p. (2004) co2 as refrigerant for systems in transcritical operation principles and technology status. a paper presented in airah’s 2004 natural refrigerants conference, museum of sydney, july 28 – 2004. [16] sakar j. (2005) transcritical carbon dioxide heat pump for simultaneously cooling and heating. ph. d. thesis, indian institute of technology kharagpur, india. [17] stene j. (2008) high efficiency co2 heat pump water heater systems for residential and nonresidential buildings. retrieved on 20 october 2014 from http://www.r744.com/assets/link/r744com_co2-hpwh_2008.pdf [18] laipradit p, tiansuwan j, kiatsiriroat t, aye l. (2008) theoretical performance analysis of heat pump water heaters using carbon dioxide as refrigerant. int. j. energy research, 32:356-366. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 137 rpl load balancing in internet of things mohammad reza parsaei * , ahmad reza parnian, samaneh miri rostami and reza javidan iot laboratory, department of computer engineering and information technology, shiraz university of technology, shiraz, iran. *corresponding author: mr.parsaei@sutech.ac.ir (received: 20 th july 2016; accepted: 27 th march 2017; published on-line: 1 st dec. 2017) abstract: the wide address space provided by internet protocol version 6 (ipv6) lets anything be uniquely identified. consistency of the modified version of the ipv6 protocol stack with smart objects, facilitated the internet interconnection of smart object networks and introduced what is known as “internet of things”. a smart object is a small micro-electronic device that consists of a communication device, a small microprocessor, and a sensor or an actuator. a network made of such devices is called a low-power and lossy network. rpl routing protocol that is consistent to ipv6, is designed to be used in these kinds of networks. load balancing is not considered in the rpl design process. whenever rpl is used in large scale low-power and lossy networks, some nodes will suffer from congestion and this problem severely degrades network performance. in this paper, we consider solutions provided to tackle rpl load balancing problems. load balancing algorithms and protocols are evaluated through simulation. we evaluate ietf rpl implementation and lb-rpl method with contiki os java (cooja) simulator. they are assessed comprehensively through metrics such as packet delivery ratio, average end-to-end delay, and gateway throughput. lb-rpl improves rpl in terms of packet delivery ratio and throughput but increases average end-to-end delay. simulation results show that rpl load balancing needs extensive work to be performed. abstrak: ruang alamat yang luas yang disediakan oleh protokol internet versi 6 (ipv6) memberikan identiti yang unik bagi setiap objek untuk dikenal pasti, selaras dengan versi yang telah diubah oleh timbunan protokol ipv6 melalui objek pintar, ini membantu sambungan internet dalam rangkaian dan memperkenalkan perkara-perkara internet (internet of things). objek pintar adalah komponen mikro-elektronik yang kecil yang terdiri daripada peranti komunikasi, mikro-pemproses kecil dan sensor ataupun pemproses signal (actuator). rangkaian yang terdiri daripada komponen-komponen ini disebut rangkaian rendah ataupun kurang tenaga. protokol penghalaan rpl yang konsisten dengan ipv6, telah direka untuk digunakan dalam rangkaian ini. walau bagaimanapun, beban sama rata tidak dikira dalam rekaan proses rpl ini. apabila rpl digunakan dalam rangkaian sistem yang luas, kurang ataupun rendah tenaga, sebilangan nod akan terlibat dengan kesesakan dalam rangkaian dan masalah ini menyumbang kepada prestasi rangkaian akan terjejas teruk. kertas ini mengambil kira solusi yang disediakan untuk mengatasi masalah keseimbangan beban rpl. algorithma keseimbangan beban dan protokol telah dinilai melalui simulasi. kerja ini juga mengambil kira implementasi ke atas ietf rpl dan kaedah lb-rpl dengan mengunakan simulasi contiki os java (cooja). ianya dinilai secara menyeluruh dengan menggunakan matriks seperti nisbah paket dihantar (packet delivery ratio), purata kelewatan nod hujung-ke-hujung (average end-to-end delay), dan laluan masuk (gateway throughput). lb-rpl dapat menambah baik rpl dari segi nisbah paket yang dihantar dan laluan transmisi, tetapi menambahkan purata kelewatan transmisi data iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 138 hujung-ke-hujung nod. hasil simulasi menunjukkan beban keseimbangan rpl memerlukan kerja pembaikan yang banyak pada masa akan datang. keywords: internet of things (iot); low-power and lossy networks; rpl routing protocol; load balancing 1. introduction the digital revolution in the twenty-first century is more impressive than the past digital revolution. during the twentieth century, the world experienced two wonderful and important digital revolutions: first, computers found their way into homes and offices, and then the internet connected computers to each other, fundamentally changing the interaction between people and the digital world. now in the twenty-first-century revolution (smart objects), internet of things (iot) links the digital world to the physical world. industry forecasts the number of intelligent objects over the next ten years could be on the scale of billions. in the next decade, the world will see that iot will change human behaviour in regard to both the physical and digital world [1-4]. with the increasing development of microcontrollers and microelectronic technologies, smart objects have been introduced. a smart object is a small microelectronic device that includes a communication element (typically low-power rf), a small microprocessor, and a sensor or actuator. a large number of smart objects used in various applications establish networks of intelligent objects. these kinds of networks are called low-power and lossy networks due to the specific features of the smart objects. they use low-power communication radios with limited transmission rate. ieee 802.15.4 technology is the most common communication technology in such networks [5]. ipv6 protocol is selected as the best option for internet of things because it supports a very large address space. some efforts were done by ietf in order to define a standard for this [6, 7]. the 6lowpan group was formed to standardize the adaptation of ipv6 in ieee 802.15.4 based networks. they were ordered to determine how to transmit ipv6 packets on ieee 802.15.4 communication links and how to implement and configure ipv6-based sub-networks [8]. another group was established to standardize ipv6-based routing protocol independent of the communication link of equipment with limited resources [911]. in recent years, several routing protocols have been suggested for low-power and lossy networks. the best one is rpl, which was standardized by the ietf in 2012. rpl technology is used for a wide range of lln applications such as building automation, urban sensor networks [13], and smart grid communication [6]. 2. internet of things (iot) internet of things is the greatest challenge and opportunity for today's embedded ipbased devices such as sensors, home appliances, machinery, building automation equipment, and even toys. over the past decade, advances achieved in terms of microcontrollers, power, and microelectronics technology motivated industry to benefit ip-based smart devices (called smart objects) services on the internet. these services not only contain data created by humans but also data highly related to the physical world including sensor data, monitoring and control machines, and other types of physical items. this new field of internet provides applications that are crucially related to stability, efficiency, and safety. building automation, health, energy efficiency, smart grid communication, environmental monitoring are instances of such applications [1-3]. iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 139 exact estimation of iot dimensions is difficult. users don't affect its growth. due to a rapid increase in the number of embedded ip-based devices, it is assumed that soon the iot will outpace all other equipment on the internet in terms of size (number of nodes) and that its growth will continue to increase at a high rate. the greatest potential for future growth is low-power wireless networks and equipment that are not yet ip-based. 6lowpan technology was developed to realize internet of embedded devices. this will be achieved by simplifying ipv6 capabilities and header compression format and by taking the nature of wireless networks into account [14]. 3. low-power and lossy networks a typical smart object has several kilobytes of memory, a small microcontroller, and a limited power supply. smart objects can form sensor networks that potentially consist of hundreds of thousands of nodes. such networks are commonly known as low-power and lossy networks (lln). the name derives from serious energy restrictions and deployment of these networks in unpredictable environments. low-power and lossy networks equipment have limited resources such as the processor, memory, battery, and unstable radio communications. lln equipment pieces are connected to each other with a variety of communication links such as bluetooth, wifi, low power ieee 802.15.4, or plc (power line communications). using ieee 802.15.4 is significantly pervasive than other technologies [14]. lln networks can also be used for physical monitoring in various environmental conditions. some examples of these networks are environmental monitoring, home automation systems remote control, patient's vital signs monitoring, and intelligent building wireless lighting control. usual monitoring parameters are temperature, humidity, pressure, voltage in power lines, and vital signs. in these cases, the equipment pieces are sensors that consist of a microcontroller, transmitter, receiver, and power supply. sensors are very small in size. they are powered by batteries, solar cells, or electricity, so energy efficiency is essential. llns are applicable to low traffic networks. lln equipment uses short-range radio media, so it is prone to error bit. lossy communication is characteristic of llns. according to the vastness of lln topology, new routing protocols and mechanisms that compromise with their specific features must be served. lln lossy nature has a significant impact on the design of their routing protocols. since the link failures are frequent and usually transient, the routing protocol must not show a serious reaction to the network convergence because it is a temporary downtime. due to the mentioned reasons, finding the best path for data delivery is one of the challenging issues in llns, so an efficient routing mechanism should be used to find and keep track of the changes in the network path. the routing mechanism should consider both natures of llns i.e. resource constraints and the lossy media [15]. 4. adaptation layer 6lowpan the ietf 6lowpan working group [6lowpan] have been established to deal with problems in order to make possible usage of ipv6 in lln networks. special features of ipv6, such as simple header structure and hierarchical addressing scheme, make it ideal for use in 6lowpan-based lln networks. also, organizing a dedicated group of standards for such networks provides the minimum requirements for the implementation of ipv6 with a light 6lowpan stack that can be used for most limited-resource equipment. eventually, the specific characteristics of lln have been considered by designing a new version of neighbour discovery protocol for 6lowpan. so, 6lowpan is an efficient iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 140 development of ipv6 for lln networks that provides end-to-end ip-based communication in a wide range of embedded applications [1, 3]. in this paper, rpl routing protocol and its load balance problem are introduced. several suggested versions of rpl routing protocol designed to tackle load imbalance problem are also considered. lb-rpl is the most comprehensive among all the versions. rpl and lb-rpl are evaluated in a simulation scenario. section 5 introduces rpl and presents related works performed about rpl load balance. rpl and lb-rpl routing mechanisms are explained in section 6. section 7 presents simulation results and section 8 concludes the paper. 5. related works 5.1 rpl routing protocol ietf assigned a roll working group to determine the appropriate routing protocol for low-power and lossy networks according to the documented requirements with headings of routing requirements for home, building, industry and urban automation [1619]. major mentioned requirements in this documentation are as follows: • route tracking: information such as path quality, the number of nodes, and the replaced active route with its associated costs should be available to facilitate route discovery. the path quality is a relative metric determining priority of the chosen path from the source node to the destination node in comparison to other replaceable routes. the metric may be a function of the number of hops, signal strength, active routes or any other criteria. • route selection: reliable route selection and high quality communication link determination needs to be possible since the problem of joining nodes in the network initial setup is mitigated over time. • route cost: routing protocols must support path quality criteria. the criteria include signal strength, available bandwidth, number of hops, amount of available energy and communication error rate. • path flexibility: paths need to be flexible and should improve selection criteria (e.g. signal quality and the number of visited hops) during the converging time. • alternate routes: the network layer should determine and establish second and third alternate routes to be used in failure time. • constraint based routing: some nodes may lose their battery power faster than other nodes or some others may have a limited energy source. some nodes have a larger memory space, so they are able to save more neighbourhood information. some others have a powerful processor and hence they can collect data in more sophisticated ways. in such situations, routing protocol must also support constraint based routing. constraints such as the processor, memory size, battery level, etc. in other words, the routing protocol must be able to advertise the node’s capabilities. roll organized a detailed analysis on evaluating existing routing protocols, such as ospf [20], is-is [21] and olsr [22] over a set of applications broad enough to encompass common uses for llns. roll designed routing protocol for low power and lossy networks (rpl), since it found existing routing protocols, perform unsatisfactorily in their current form. rpl addresses the core requirements [16-19] of lln applications. iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 141 the roll provides an evaluation of existing routing protocols in table 1. the symbol "?" indicates that a specified result has not been received. table 1: an evaluation of existing routing protocols with lln criteria protocol table loss control link cost node cost ospf/is-is fail fail fail pass fail olsrv2 fail fail ? pass pass tbrpf fail pass fail pass ? rip pass fail pass ? fail aodv pass fail pass fail fail dymo[-low] pass fail pass ? fail dsr fail pass pass fail fail 5.2 rpl routing protocol in lln networks as far as possible, rpl routing protocol was designed in the modular form based on a large set of requirements listed in different documentation. rpl has been designed for lln networks that include resource-constrained equipment communicating through lossy wired and wireless communication links. many decisions taken in rpl design process are based on the specific characteristics of lln networks. the lossy nature of the lln links is not the only lln characteristic that affects rpl design process. as resources are restricted, control traffic should be reduced. in these networks, data traffic is usually limited and it is necessary to reduce control traffic as much as possible to save bandwidth and energy. 5.3 rpl routing method rpl is an ipv6 based routing protocol used in lln networks. this routing protocol makes a destination oriented directed acyclic graph (dodag) of network nodes. nodes organize vectors of dodag and communication links among nodes organize dodag edges. nodes forward received and generated data traffic to their parents in order to reach data to dodag root. lln border router (lbr) acts as dodag root and starts dodag construction process by broadcasting dodag information object (dio) messages. when other nodes receive dio messages for the first time, they join the dodag by selecting the dio sender as their parent and then broadcast dio messages. this process continues and nodes join the dodag. 5.4 load balancing in the rpl routing protocol design process, load balancing and congestion avoidance are not considered. the traffic passing through parent nodes and the size of their sub trees were not considered in the parent selection process. this causes an unbalanced tree. there have been extensive studies on rpl routing load balancing. some of them are in the following review. 5.4.1 imbalanced tree algorithm tripathi offered a greedy algorithm in order to solve load balancing problem. he calculated the load imbalance factor for each level of the routing. in this way, nodes that are prone to congestion are identified. this method aims to balance the routing tree and minimize the load imbalance factor. the algorithm selects a parent for a node from three nominated parents by itself. the root node executes the algorithm and tends to select iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 142 parents which minimizes load imbalance factor. this is done periodically, keeping the tree as balanced as possible during the network lifetime. this greedy algorithm aims to keep the load among same-level nodes balanced. the simulation results show that this algorithm significantly increases the average packet delivery ratio and network lifetime. the main algorithm characteristic is that it only needs a partial knowledge of the network [23]. the proposed algorithm by tripathi is only efficient for networks in which nodes generate the same amount of traffic. this method is completely centralized and is implemented by the root node. in addition, each period has significant delays. the difficulty of the balanced problem is np [24-26] and the complexity of the proposed algorithm is o (n 2 ). the proposed algorithm involves large computational complexity, so resources and time are highly consumed. the balanced tree construction is a complex mathematic problem. it needs a significant number of control messages. according to the specific conditions of low-power and lossy networks, especially poor communication links, the topology of these networks are completely dynamic and change constantly. balancing such topologies needs a lot of effort to be repeated frequently. 5.4.2 treeb algorithm kulkarni proposed a method for load balancing. in this method, dodag root knows the number of nodes in each subtree. each node that wants to join the dodag gets aware of the dodag's node count and joins a dodag with the lowest number of nodes [27]. in this method, nodes that want to join a dodag can be aware of the dodag size. this method has no effect on load balancing of each tree individually and just tries to keep the size of the trees the same. for example, this method can create trees with the same size and completely unbalanced. when there is only one root, this algorithm is completely ineffective and only increases overhead and slows tree creation process. 6. description and implementation of the lb-rpl and rpl protocols 6.1 rpl routing protocol rpl is an ipv6-based distance vector routing protocol utilized in lln. this routing protocol organizes a dodag of nodes in order to determine routing paths. it is possible to have multiple dodags when there are more than one lbr. rpl uses the dodag id to identify dodags. tree kinds of icmpv6 control messages are used in dodag construction and maintenance. dio is used in order to advertise dodag and route construction. dodag information solicitation (dis) is propagated by nodes that are eager to receive dios and finally, the destination advertisement object (dao) is transmitted from higher level nodes toward the dodag root in order to introduce routes toward them. rpl is a flexible routing protocol capable of serving in various application areas. objective function (of) is what enables rpl to be customizable according to different applications. of is defined through an equation containing metrics and constraints related to nodes and communication links. application requirements define constraints and metrics. rank is the computed value of of. every node has a rank and it is calculated using the of. when a node wants to calculate its rank, it first computes the of result and then adds it to its parent rank. so a node rank is the summation of its parent rank and the value provided by of. it is obvious that rank value increases from iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 143 root toward leaf nodes. rank is an indicator of the quality of the route that a node provides toward the root. in rpl, it is preferable to select a node that provides the lowest rank as parent. lbr starts the dodag construction process by broadcasting dio control packets. receiver nodes extract of and rank from dio and then compute their rank and select a dio sender as their parent. after joining the dodag, nodes can produce dio messages and propagate them in order to advertise the dodag. receiving dio, joining a dodag and advertising dodags continues until all nodes join the dodag. the dodag member nodes receive different dios. in this case, they extract information from the dio and calculate rank based on the received dio. if the dio advertiser node provides a better path than the current parent toward the root, it will be selected as the parent. if not, it will be held in a preferred parent set by the dio receiver node. each holds five best alternate neighbour nodes in its preferred parent set. 6.2 lb-rpl routing protocol liu proposed a lb-rpl routing protocol that detects load imbalance in a distributed and non-intrusive manner. it optimizes the data forwarding path by considering both workload distribution and link-layer communication qualities. in this method, each node delays dio message transmission based on the efficiency of its buffer. each node saves dio messages based on a priority of their received time and then sends its traffic data through a number of its parents which have sent dio messages earlier. lbr-rpl does not select a parent for a node as its primary parent, but it uses the workload differences. the data traffic is distributed among multiple parent nodes. this method modifies the dodag construction procedure by incorporating two techniques. the first one is workload imbalance detection and signaling, and the other is load balanced data forwarding [28]. each node delays dio message transmission according to its buffer utilization in order to inform others about its workload traffic. in fact, a node sets a timer based on the efficiency of its buffer in the previous period and transmits the dio message after the timer expiration. determining an appropriate value for the timer is crucial for detecting load imbalance. buffer capacity limitation significantly affects the data delivery ratio. therefore, buffer utilization is used to quantify a node’s workload. an appropriate value for the timer is set as following: ti = t0 * buffer utilization counter [28] (1) where t0 is a constant value and buffer utilization counter indicates efficiency of the buffer. after a node receives multiple copies of the dio message from different lower ranked nodes, it will form its parent set. the priority order of these parents is determined based on the time their dio messages have been received. a parent will have a higher priority if its dio has reached earlier than others. 6.3 lb-rpl algorithm unlike rpl that selects a single node as parent from parent set, lb-rpl uses the top k parent nodes as the next hop for data forwarding. the data packet transmission probability by node i to node j as the next hop is calculated through: iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 144     1 1 1 c ij ij k c ijj p f p     (2) where ij p is drop probability of the transmitted packet from node i to node j according to the node link state, and ij f is the probability of packet transmission from node i to node j. packets being ready for transmission by a node are distributed among k parent nodes according to their link states. moreover, when one of the parent nodes suffers from heavy workload in the current period, it will add more delay in the dio message transmission in the next round. a parent node will be out of the top k preferable next hop in its children’s parent table if it has a long delay due to heavy workload. this node will not be used as the next hop by its children for data forwarding, therefore workload imbalance can be alleviated. pseudo-codes of lb-rpl algorithm [28] are shown in fig. 1 and fig. 2. algorithm 1: sensor node initialization procedure 1: initialize parent set and buffer utilization counter 2: update the latest received version number 3: insert the dio message source into parent set according to the message arrival time 4: calculate its own rank value 5: set timer value ti 6: generate a dio message with its own rank number and the latest version number 7: when timer ti expires, broadcast a dio packet with current rank and version number fig. 1: node initialization procedure figure 3 is an example with k=2. a fraction of 63 63 64 p p p packets are sent to node 3 s and remaining packets are forwarded to 4 s . 6.4 evaluation of proposed approach in the lb-rpl method, the concept of objective function and rank are completely unused. rank is totally ineffective in parent selection and path criteria and restrictions are not considered, so the quality of the path provided by a parent node cannot be measurable. dio message arrival time can be result of collision, interference, lack of access to the channel and some other factors, so it is not necessarily due to a crowded buffer. moreover, if the dodag size is great, a considerable delay will be added to the network due to delaying dio message transmission. the purpose of load balancing is to make equal traffic for all nodes at the same level. since in this method traffic will be sent by k nodes, there will be idle nodes in each period and if there is high-volume traffic, all k nodes will be congested in each period. iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 145 algorithm 2: lb-rpl: load balanced rpl routing protocol 1: a sensor node listens to the radio channel 2: once a message m arrives, check the type of the message 3: if m is a dio message then 4: if new version of dio then 5: invoke sensor node initialization procedure 6: else 7: if current dio version then 8: if rank value carried in the message is less than current node’s rank then 9: insert the dio message source to parent set according to message arrival time 10: end if 11: else 12: discard this message 13: end if 14: end if 15: else 16: if m is a dao message then 17: process it according to rpl 18: else 19: if m is a data message then 20: if the data message comes from a child of current node then 21: increase workload counter 22: end if 23: forward this message by choosing the first two parent nodes from parent table, and selecting one as next hop with probability 24: end if 25: end if 26: end if fig. 2: lb-rpl load balanced routing protocol. fig. 3: message reception with time priority [28]. iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 146 7. simulation results in order to consider lb-rpl in an exact manner, this routing protocol is simulated by contiki cooja simulator. contiki was the first operating system that provided ip communication and is implemented in c programing language. the cooja simulator is a java-based sensor network simulator [29, 30]. in the simulation, a total number of 250 static nodes are randomly deployed in a 500 by 500 square meters area and one lbr is located at the top. simulation is run for 3 hours or 10800 seconds. in order to obtain more accurate results, nodes begin to send udp packets after 7 minutes of starting time. in the simulation scenario, all nodes send packets with a length of a hundred bytes to the root node. each node sends two packets with an interval of 30 seconds per minute. each node has a buffer which is enable to hold maximum 8 udp packets. in order to get more accurate results, the simulation scenario is repeated 5 times with different random seeds. we evaluated lb-rpl through packet delivery ratio, avg end-to-end delay and root node throughput. table 2 summarizes simulation parameters. table 2: simulation parameters parameter value simulation time 10800 seconds number of nodes 250 traffic type udp packet length 100 bytes area 500*500 m 2 simulator contiki cooja repetition 5 times buffer size 8 udp packets figure 4 illustrates packet delivery ratio versus simulation time. this figure proves that lb-rpl performs better than rpl in terms of packet delivery ratio with a 90% confidence. the simulated network consists of a great number of nodes and congestion occurrence is completely probable in such networks. rpl is not optimized for large scale networks and cannot balance network load in order to prevent performance reduction. this leads to noticeable packet loss. lb_rpl performs better in this case since this protocol distributes load and directs data traffic among multiple paths. therefore lb-rpl provides higher pdr. figure 5 illustrates avg end-to-end delay versus simulation time. rpl performs better than lb-rpl in terms of avg end-to-end delay and it is proven with 90% confidence. rpl makes routes based on the metrics and constraints formulated in of. the of used in rpl routing protocols is defined based on communication link quality. this results in better rank for nodes providing a route toward the root with lower time. rpl provides better avg end-to-end delay. in lb-rpl packets are distributed through the network, which results in longer paths. packets may travel many nodes and links that are not completely in an optimized path toward the root. as lb-rpl does not use of, it cannot formulate a delay in the routing process in order to decrease packets arrival time. iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 147 figure 6 depicts root node throughput versus time. it can be seen that lb-rpl performs better than rpl with 90% confidence. lb-rpl prevents from intermediate nodes buffer over-utilization and lets packets to reach to destination through alternate routes even though they are longer. this decreased packet loss since buffer overflow is prevented. rpl selects routes with better overall rank resulting in congestion in a part of network. fig. 4: packet delivery ratio comparing graph. fig. 5 average end to end delay comparing graph. fig. 6: throughput comparison graph. 0 10 20 30 40 50 p a c k e t d e li v e r y r a ti o ( % ) time (s) rpl lb-rpl 0 200 400 600 a v g e -t o -e d e la y ( m s) time (s) rpl lb-rpl 0 50 100 150 200 250 300 t h r o u g h p u t (p a c k e t p e r m in ) time (min) rpl lb-rpl iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 148 simulation result analysis was performed according to [31, 32]. initial data deletion was performed and the replication process through techniques presented in tables 3 to 5 present the simulation result report and confidence intervals. table 3: the mean performance of the approaches for packet delivery ratio method mean ci rpl 41.005 (39.052 , 42.958) lb-rpl 43.432 (41.272 , 45.592) table 4: the mean performance of the approaches for average end to end delay method mean ci rpl 372.532 (360.978 , 384.086) lb-rpl 398.484 (390.507 , 406.461) table 5: the mean performance of the approaches for throughput of root node method mean ci rpl 210.543 (204.403 , 216.683) lb-rpl 217.751 (212.196 223.306) 8. conclusion rpl routing protocol is the best choice for routing in low-power and lossy networks but load balancing is not considered in rpl routing protocol standardization process by ietf. as rpl routing protocol and llns are used in large scale networks, load balancing is an important issue to be considered. several methods have been proposed to alleviate the problem of load balancing. but they did not consider all aspects of rpl or some of them were not computationally efficient. lb-rpl is a new modification of rpl routing protocol, designed in order to tackle rpl load balance problems. this routing protocol distributes data traffic through the network and performs better than rpl in congestion prevention. in this paper, rpl and lb-rpl were evaluated in terms of packet delivery ratio, avg end-to-end delay and network throughput. lb-rpl performs better in terms of packet delivery ratio and network throughput. although lb-rpl prevents congestion, it is not the mature solution for rpl load balance problem cannot formulate application routing requirements and does not support advantages that ietf provided in rpl design process. a new version of rpl that saves ietf standardized design specifications and balances load especially in large scale networks is completely required. references [1] mazinani sm, chitizadeh j, yaghmaee mh, honary mt, tashtarian f. (2010) new clustering schemes for wireless sensor networks. iium engineering journal, 11(1):51-69. iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 149 [2] arshad a, khan s, alam az, ahmad fi, tasnim r. (2014) a study on health monitoring system: recent advancements. iium engineering journal, 15(2):87-99. [3] parsaei mr, parnian ar. (2015) ipv6 based routing in building automation network. in 2015 2nd international conference on knowledge-based engineering and innovation (kbei):1025-1031. doi: 10.1109/kbei.2015.7436185. [4] parnian ar, parsaei mr, javidan r, mohammadi r. (2017) smart objects presence facilitation in the internet of things. international journal of computer applications, 168(4):25-31. doi: 10.5120/ijca2017914345. [5] adams jt. (2006) an introduction to ieee std 802.15.4. ieee aerospace conference proceedings: 1-8. [6] deering s, hinden r. (1998) internet protocol, version 6 (ipv6) specification. [7] ismail y, sarif sm. (2012) availability of literature on engineering ethics in the internet. iium engineering journal, 12(5):219-229. [8] montenegro g, kushalnagar n, hui j, culler d. (2007) transmission of ipv6 packets over ieee 802.15.4 networks: rfc 4944. [9] parsaei mr, mohammadi r, javidan r. (2017) a new adaptive traffic engineering method for telesurgery using aco algorithm over software defined networks. european research in telemedicine/la recherche européenne en télémédecine, 6(3-4):172-179. doi: 10.1016/j.eurtel.2017.10.003. [10] parsaei mr, javidan r, fatemifar a, einavipour s. (2017) providing multimedia qos methods over software defined networks: a comprehensive review. international journal of computer applications, 168(9):1-4. doi: 10.5120/ijca2017914549. [11] rowshanrad s, parsaei mr, keshtgari m. (2016) implementing ndn using sdn: a review on methods and applications. iium engineering journal, 17(2):11-20. [12] parsaei mr, khalilian sh, javidan r. (2016) a comparative study on fault tolerance methods in ip networks versus software defined networks. international academic journal of science and engineering, 3(4):146-154. [13] taheri r, parsaei mr, javidan r. (2016) a new method for optimizing energy consumption in wireless sensor networks using enhanced leach protocol. journal of engineering and applied sciences, 100(3):576-581. [14] shelby z, bormann c. (2011) 6lowpan: the wireless embedded internet. the wireless embedded internet [book], 43. [15] ko j, terzis a, dawson-haggerty s, culler de, hui jw, levis p. (2011) connecting lowpower and lossy networks to the internet. ieee communications magazine, 49(4):96-101. [16] brandt a, porcu g. (2010) home automation routing requirements in low power and lossy networks. rfc 5826. [17] martocci j, vermeylen w, riou n, mil pd. (2010) building automation routing requirements in low power and lossy networks. ietf request for comments rfc 5867. [18] pister k, thubert p, dwars s, phinney t. (2009) industrial routing requirements in lowpower and lossy networks. rfc 5673. [19] dohler m, watteyne t., winter t, barthel d. (2009) routing requirements for urban lowpower and lossy networks. rfc 5548. [20] moy j. (1997) ospf version 2. [21] oran d. (1990) osi is-is intra-domain routing protocol. [22] clausen t, jacquet p. (2003) optimized link state routing protocol (olsr). rfc 3626. [23] tripathi j, de oliveira jc. (2013) quantifying load imbalance: a practical implementation for data collection in low power lossy networks. ieee 47th annual conference on information sciences and systems (ciss):1-6. [24] nabaei a, hamian m, parsaei mr, safdari r, samad-soltani t, zarrabi h, ghassemi a. (2016) topologies and performance of intelligent algorithms: a comprehensive review. artificial intelligence review: 1-25. doi: 10.1007/s10462-016-9517-3. [25] parsaei mr, javidan r, sobouti mj. (2016) optimization of fuzzy rules for online fraud detection with the use of developed genetic algorithm and fuzzy operators. asian journal of information technology, 15(11):1856-1864. https://doi.org/10.1109/kbei.2015.7436185 iium engineering journal, vol. 18, no. 2, 2017 parsaei et al. 150 [26] gao w, sarlak v, parsaei mr, ferdosi m. (2017) combination of fuzzy based on a metaheuristic algorithm to predict electricity price in an electricity markets. chemical engineering research and design: 1-13. doi: 10.1016/j.cherd.2017.09.021. [27] kulkarni p, gormus s, fan z. (2012) tree balancing in smart grid advanced metering infrastructure mesh networks. ieee international conference on green computing and communications (greencom):109-115. [28] liu x, guo j, bhatti g, orlik p, parsons k. (2013) load balanced routing for low power and lossy networks. ieee wireless communications and networking conference (wcnc):2238-2243. [29] dunkels a, gronvall b, voigt t. (2004) contiki-a lightweight and flexible operating system for tiny networked sensors. ieee 29th international conference on local computer networks: 455-462. [30] the contiki operating system. available: http://www.contiki-os.org/index.html. [31] parsaei mr, rostami sm, javidan r. (2016) a hybrid data mining approach for intrusion detection on imbalanced nsl-kdd dataset. international journal of advanced computer science and applications, 7(6):20-25. [32] parsaei mr, javidan r, kargar ns, nik hs. (2017) on the global stability of an epidemic model of computer viruses. theory in biosciences, 136(3-4):169-178. doi: 10.1007/s12064017-0253-2. iium engineering journal, vol. 16, no. 1, 2015 abid et al. 43 an experimental study on the relaxation of bolts muhammad abid1, muhammad shahid khalil2 and hafiz abdul wajid3,4 1interdisciplinary research centre, comsats institute of information technology, wah cantt, pakistan. 2department of mechanical engineering, university of engineering and technology, taxila, pakistan. 3department of mathematics, comsats institute of information technology, lahore, pakistan. 4department of electrical engineering, islamic university medina, kingdom of saudi arabia. drabid@ciitwah.edu.pk (received 1 january 2015; accepted 14 march 2015; published on line 29 may 2015) abstract: loss of pre-load with time, commonly known as ‘relaxation’ is an established phenomena. behaviour of a bolted joint depends upon the pre-load in the bolts in use, not the pre-load introduced by the mechanic. loss of pre-load is expected due to many factors such as embedment relaxation, gasket creep, elastic interactions, and vibration loosening or stress relaxation. in a gasketed joint, due to the gasket flexibility, relaxation in almost all bolts is always substantial during preliminary bolt tightening passes, as 80 to 100% loss is common hence resulting in a dynamic behaviour. it is observed that pre-load in a gasketed joint is controlled to a certain extent only in the final bolt-tightening passes. experimental study presented in this paper highlights the factors affecting the amount of bolt preload relaxation with time. important considerations are recommended to reduce bolt relaxation. both the short and long term relaxations are recorded and a ‘best fit’ model for relaxation behaviour is derived. abstrak: kehilangan prabeban berkadaran dengan masa, atau lebih di kenali sebagai ‘relaksasi’ adalah fenomena yang sememangnya wujud. sifat sambungan bolt bergantung kepada prabeban dalam bolt yang digunakan, bukannya prabeban yang dikenakan terhadapnya. kehilangan prabeban sememangnya dijangkakan; disebabkan oleh beberapa faktor seperti relaksasi pembenaman, rayapan gasket, saling tindak elastik dan kelonggaran getaran atau tegasan relaksasi. dalam sambungan bergasket, disebabkan oleh fleksibiliti gasket, relaksasi pada hampir semua bolt sering kali mapan sepanjang pengetatan awal laluan, di mana kekurangan sebanyak 80 ke 100% adalah perkara biasa; seterusnya menghasilkan sifat dinamik. prabeban pada sambungan gasket dikaji dan dikawal pada peringkat tertentu hanya semasa pengetatan akhir laluan sahaja. kajian bereksperimen mengetengahkan faktor-faktor penyebab kadar relaksasi prabeban berkadaran dengan masa. beberapa pertimbangan penting juga dicadangkan untuk mengurangkan relaksasi bolt. kedua-dua tempoh relaksasi pendek dan panjang telah direkodkan serta model sifat relaksasi yang paling sesuai diperolehi. keywords: preload; bolts; relaxation; experimental; joint; gasketed 1. introduction from a number of analytical and experimental studies of bolted flanged pipe joints, great importance is attributed to the bolting and assembly of the bolted joints due to iium engineering journal, vol. 16, no. 1, 2015 abid et al. 44 different bolt behaviour that can be observed [1-17]. in a gasketed joint, the presence of the gasket and rotation of flanges results in joint relaxation and improper preloading of the bolts. in addition to this, gasket crushing and flange yielding limits higher pre-load [1, 1534]. bolt quality and proper tooling has been proven to be important factors in getting proper pre-load in the joint [1]. in this study, pre-loads of 60%, 80% and more than 100% were applied to observe both short and long term relaxations. the bolts were also preloaded close to the ultimate tensile strength of the bolt material, to study its relaxation behaviour. this experimental study highlights important factors that affect amount of relaxation in bolts with time and presents important considerations that may be effective in reducing this occurrence. during this study, a bolt calibration unit developed for the measurement of force felt by the bolt was used. furthermore, both the short and long term relaxations are recorded and a ‘best fit’ model for relaxation behaviour is derived for different pre-loads. definitions of relaxation terms are given here for clarity: short term relaxation: most of the relaxation occurs shortly, after the joint has been assembled or at least soon after it has been put into service, due to the number of reasons, such as bolt bending, soft parts (gasket), improper tooling and torquing, bolt quality, nonparallelism of flange joint surfaces, geometric variance and so on. long term relaxation: it is generally due to the stress relaxation and vibration loosening. stress relaxation can be related to the creep, as this is substantial under high temperature applications. relaxation measurement: in practice different methods such as application of restarting or breakaway torque, bolt length measurement using ultrasonic extensometers are adopted. however none of these are observed perfect, as it is difficult to measure relaxation. 2. experimental setup and procedure a calibration unit consisting of an aluminium cylinder equipped with strain gauges arranged in a wheatstone full bridge circuit was used for bolt force measurement (fig. 1a). for better results in recording, an amplifier was also attached with the calibration unit. during the tests, m12 bolts as per iso-898 grade 8.8 and 10.9 were arranged [35]. nuts and washers of different thickness and geometry were used in different combinations with these bolts to observe pre-load loss effects. a detailed list of bolts, nuts and washers that were tested is given in table 1 and the material and strength of the bolts tested are given in table 2. one bolt from each set was placed in the calibration unit and was applied a given torque using a calibrated electronic torque wrench. bolts were pre-loaded up to a minimum of 60% (48 kn), 80% (65 kn) and more than 80% (78 kn and 81 kn) of their yield strength or proof load. pre-load was applied in increments of 10 kn. after each increment the torque reading from the calibrated electronic torque wrench was recorded. after application of the required pre-load, results for the pre-load drop/loss were recorded in the data logging system and were plotted using a pen plotter. in order to observe the effect of re-tightening on pre-load loss, tests were also carried out with bolts that were retightened after different time intervals. experimental set up, tools used, nuts, washers and bolts used are shown in fig. 1b, fig. 2a and 2b respectively. 3. data processing data recorded during the bolt relaxation was processed using the power and logarithmic function [1] to find the ‘best fit’ model. bolt relaxation for each bolt is calculated for the experimental time as well as for 15 seconds to 10 years. during the first iium engineering journal, vol. 16, no. 1, 2015 abid et al. 45 5 minutes a drop of only 1~3 percent was observed. for more than 1 day this value varied for different bolts. relaxation calculated for all the bolts was nearly the same for the first 24 hours whereas for longer periods it was found to be greater for the logarithmic function than for the power function. power function was found to be the ‘best fit’ model for the recorded data. results for the power function are summarized in table-3 for all the bolts tested. calculations of these correlation factors also include short term relaxation for the first 1 to 2 minutes as the torque wrench is taken off from the nut. however, neglecting the effect of this initial relaxation, a higher value of correlation factor will be obtained and the pre-load loss or relaxation will be very small, but cannot be neglected. (a) (b) fig. 1 (a) calibration unit, (b) experimental setup. table 1: details of bolts tested for pre-load applied and pre-load loss bolt no bolt used property class surface treatment as per code and marking applied preload (kn) re tightened 2 1st time 10.9 wax emulsion sa a4 316l 100m 66,52,78 yes 3 1st time 10.9 wax emulsion sa a4 316l 100m 66,52,78 no 4 1st time 10.9 wax emulsion sa a4 316l 100m 66,52,78 no 5,7 1st time 10.9 dry lubricant sa a4 316l 100m 78,81 no 6 1st time 10.9 dry lubricant sa a4 316l 100m 81 yes 6-ln 1st time 10.9 dry lubricant sa a4 316l 100m 81 no 9 1st time 8.8 bright zinc ml8.8 81 no 10-ln 2nd time 8.8 bright zinc ml8.8 60 yes 10-mk 2nd time 8.8 bright zinc & molykote ml8.8 60 yes 11 1st time 8.8 dry lubricant ml8.8 60 no 12 2nd time 8.8 dry lubricant ml8.8 60 yes 21 (9) 2nd time 8.8 bright zinc ml8.8 51 yes 22 (1) 2nd time 10.9 wax emulsion sa a4 316l 100m 46 no 27 (st) 2nd time 8.8 dry lubricant ml8.8 43 yes 28 (st) 2nd time 8.8 dry lubricant ml8.8 41 yes table 2: properties of the bolts tested bolt dia. (mm) property class stress area (mm2) min. yield strength (iso-898) proof load (kn) min. ut load (kn) pre-load recommended (kn) based on shank area (kn) m12 10.9 84.3 900 70.0 87.7 55.0 81.43 m12 8.8 84.3 640 48.9 67.4 39.0 57.91 iium engineering journal, vol. 16, no. 1, 2015 abid et al. 46 (a) (b) fig. 2 (a) bolts, nuts and washers used during tests, (b) tools (torque wrenches) used. table 3: preload loss with time for all bolts using best fit curve bolt no. time (min) correlation factor pre load a b x1 y y1 relaxation during ini. torque experimental time one day one year blt2 30.0 0.7654 >80 % 54.14 -0.15 0.62 58.27 65.59 11.15 23.35 66.67 blt2-r1 30.0 0.9278 >80 % 60.44 -0.16 0.64 64.86 65.07 0.33 14.13 63.55 blt2-r2 30.0 0.9262 >80 % 61.93 -0.15 0.66 65.95 66.20 0.38 13.50 62.24 blt3 30.0 0.9259 >80 % 49.18 -0.10 0.57 52.05 52.11 0.11 9.79 47.81 blt4 110.0 0.5793 >80 % 67.39 -0.19 0.67 72.65 74.90 3.00 18.38 70.58 blt6 70.0 0.7371 >80 % 66.37 -0.70 0.78 78.63 80.80 2.68 45.26 98.68 blt6-r1 30.0 0.8356 >80 % 70.91 -0.56 0.81 79.99 81.02 1.26 37.13 96.78 blt6-r2 15.0 0.8734 >80 % 73.84 -0.47 0.83 80.71 81.48 0.94 31.75 94.35 blt6-ln 120.0 0.6582 >80 % 75.56 -0.04 0.22 80.16 80.79 0.77 7.21 25.91 blt7 794.0 0.8190 >80 % 51.66 -0.09 0.24 58.41 59.16 1.27 14.26 47.34 blt9 65.0 0.8812 >80 % 74.16 -0.10 0.50 79.52 80.79 1.57 11.86 49.24 blt10-ln-r1 22.0 0.9374 >80 % 60.57 -0.71 0.99 61.22 61.49 0.44 39.39 98.49 blt10-mk 20.0 0.7771 >80 % 48.83 -0.08 0.06 60.94 61.58 1.04 21.10 50.63 blt10-mk-r1 60.0 0.8933 >80 % 55.83 -0.04 0.07 61.44 61.70 0.42 9.74 26.92 blt12 72.0 0.6205 >80 % 54.30 -0.30 0.80 58.14 59.24 1.87 23.05 84.28 blt12-r1 63.0 0.8679 >80 % 57.52 -0.22 0.85 59.66 59.85 0.32 15.91 73.46 blt21 44.0 0.7520 80% 48.37 -0.02 0.20 49.85 50.68 1.65 4.90 14.59 blt21-r1 40.0 0.9266 >80 % 48.13 -0.04 0.25 50.76 50.87 0.22 6.18 24.43 blt22 25.0 0.7622 60% 44.71 -0.17 0.28 55.82 42.26 -32.1 -1.36 62.08 blt27 20.0 0.7308 80% 34.45 -0.18 0.31 42.46 42.90 1.01 23.37 71.59 blt27-r1 10.0 0.7162 80% 36.41 -0.17 0.32 44.30 44.40 0.22 21.81 70.23 blt27-r2 10.0 0.5406 80% 40.45 -0.10 0.33 45.27 45.40 0.28 13.41 50.85 blt28t 40.0 0.7556 80% 38.68 -0.10 0.70 40.04 40.30 0.64 8.78 45.54 blt28t-r1 44.0 0.7898 80% 39.57 -0.03 0.76 39.95 40.00 0.12 2.96 19.16 blt28t-r2 36.0 0.8076 80% 39.59 -0.03 0.72 39.95 40.02 0.16 2.56 16.18 blt28r 35.0 0.8349 60% 29.34 -0.11 0.78 30.15 30.25 0.32 9.00 49.50 blt28r-r1 38.0 0.7941 60% 29.94 -0.02 0.83 30.04 31.00 3.09 4.54 13.72 4. results and discussion results for different bolts 2-7, 10 and 21 which are plotted in fig. 3 to fig. 8, and summarized in table 3 are discussed below. iium engineering journal, vol. 16, no. 1, 2015 abid et al. 47 (a) (b) (c) (d) fig. 3: loss of pre-load with time for bolt-2. (a) overall tightening, (b) first tight, (c) first re-tight, (d) second re-tight. (a) (b) (c) (d) fig. 4 loss of pre-load with time. (a) bolt-3, (b) bolt-4, (c) bolt-5, (d) bolt-7. 4.1 pre-load above 80% of the minimum yield strength of bolt material during these tests, the bolts were torqued above the recommended value of 80% of bolt yield [1-7]. pre-load applied is given in table 2. the purpose was to see its effect on the loss of pre-load. for all the bolts, during the first 1 to 2 minutes a rapid loss of pre-load was observed. this drop was different for different bolts. a variation in pre-load loss of 0.5 to 2 kn was noted which was about 1 to 3 percent of the initially applied torque. this is always expected from the bolt as the torque wrench or hydraulic tensioner is removed from the bolt. after 3 to 4 minutes, steady and continuous pre-load drop behaviour was recorded for all the bolts. all the bolts (blt1~blt12) were tested for the first time and results were recorded for different time intervals ranging from 10 minutes to 24 hours. results were used to obtain the best fit model via curve fitting. three models, namely the logarithmic, power and exponential models were tried. all were found to be very close to each other. the correlation factor for all the bolts was found ranging from 0.6205 to 0.9252. there were no visible difference in the results of bolts noted for different surface treatments and grades. iium engineering journal, vol. 16, no. 1, 2015 abid et al. 48 4.2 pre-load of 80% of the minimum yield strength of bolt material the bolts were pre-loaded to the recommended value of 80% of bolt yield [1-7]. preload applied is given in table 2. a very small drop of pre-load was observed for all the bolts during the first 1 to 2 minutes, which became very steady and nearly negligible. all the bolts (blt12~blt28) were tested for the second time and results were recorded for different time intervals ranging from 10 minutes to 24 hours. results were used to obtain the best fit model via curve fitting. three models, namely the logarithmic, power and exponential models were tried. all were found to be very close to each other. the correlation factor for all the bolts was found ranging from 0.7308 to 0.9. there were no visible difference in the results of bolts noted for different surface treatments and grades. 4.3 effect of lock nuts and lubricants this study was carried out to see the effect of lock-nut and lubricant on the loss of pre-load. bolt number 6 and 10 were tried with lock-nut for a pre-load of above 80%. it was noted during the test that the proper strength of the nyloc could not be utilised due to the bolt length. only two to three threads were utilised. however, the results recorded are presented in graphs for blt6-ln and blt-10n. a correlation factor of 0.6582 to 0.6652 was calculated. bolt blt10 was used with molykote lubricant for the pre-load of about 80% and a comparatively good correlation factor of 0.8359 was observed. 4.4 effect of re-tightening bolt relaxation during the first few seconds or minutes was observed to be rapid as the torque wrench is taken off the nut. however, rapidly it becomes very slow. this study was conducted during the actual situations for the first loading during proof testing and even after first tightening pre-load is reduced. the bolts were re-tightened after different intervals of time to see its effect on bolt relaxation. it was noted that re-tightening has a pronounced effect on the pre-load loss control as also highlighted by bickford and abid [1, 13]. some of the bolts were re-tightened twice after the first tightening. the correlation factor was noted to be higher and an initial pre-load drop was observed. for some of the bolts, results that were recorded were not found to be good. during re-tightening a smaller correlation factor was observed, e.g. for bolt blt27 and blt28r. this was due to a disturbance to the data logging system due to the use of some of the lab machines for routine maintenance. however, from the results plotted on a flat bed plotter and from the recorded results nearly the same behaviour was observed. 4.5 effect of tightening speed and number of passes during the present experimental study, the effect of bolt tightening speed was also found to be important in controlling pre-load loss. it was observed that the bolts that were tightened fast, may not have time to settle in during the tightening process. these may relax more after the tightening procedure. however, during the present study this effect was not recorded and is planned for future studies. in order to compensate for such factors, re-tightening of bolts is strongly recommended [1]. similarly, tightening of bolts in a series of passes to assemble the joint uniformly, rather than applying full torque on the first pass allows time for relaxation. for both of these reasons, progressive tightening is concluded a virtual necessity on large gasketed joints. 4.6 proper tooling and fastener dimensions at the start of experiments, no consideration was given to the tooling required for the bolts. however, it was found that some bolts are of metric dimensions and some were not. even for the same metric dimensions, nut and bolt heads of different dimensions were iium engineering journal, vol. 16, no. 1, 2015 abid et al. 49 observed e.g. for m12 bolt some were observed of 18-mm and some of 19-mm. different tools available in the lab i.e. conventional torque wrenches, open ring spanners, long handle spanner, electronic calibrated torque wrench were used to highlight the importance of proper tooling to get a required higher pre-load (fig. 2b). using conventional ring or open spanners it was found to be very difficult to tighten the bolts and using these tools the bolt head and nut hexagonal geometry were damaged. sometimes experiments were stopped because of the unavailability of the proper spanner due to the varying dimension of the bolt head or nut. it was also found that the bolts with the same marking have large variation in their quality, geometry, surface finish and other parameters. the bolts used in this study hadvery good quality with proper surface treatment. however torque variation is still observed in the recorded data. it is also observed that the quality of bolts can’t be guaranteed from unknown manufacturers or suppliers. hence only well known bolt manufacturers should be selected to ensure bolted joint performance for safe joint strength and sealing. (a) (b) (c) (d) fig. 5 loss of pre-load with time for bolt 6. (a) overall tightening, (b) first tight, (c) first re-tight, (d) second re-tight. (a) (b) (c) fig. 6 loss of pre-load with time for bolt 10 with molykot lubricant. (a) overall tightening, (b) first tight, (c) first re-tight. iium engineering journal, vol. 16, no. 1, 2015 abid et al. 50 (a) (b) (c) fig. 7: loss of pre-load with time for bolt 10 with locknut. (a) overall tightening, (b) first tight, (c) first re-tight. (a) (b) (c) (d) fig. 8 loss of pre-load with time for bolt 21. (a) overall tightening, (b) first tight, (c) first re-tight, (d) second re-tight. 5. conclusions and recommendations in light of the results and observations, the following conclusions and recommendations are made;  use of new, good quality and high strength bolts with original surface treatment, i.e. dry lubricant, proper bolt tightening speed by properly trained fitters, and with initial higher preload to compensate for the pre-load loss is recommended.  use of good quality locknuts and washers and proper tooling, preferably ring spanners instead of open spanners, are recommended.  re-tightening of the bolts after a few minutes to several hours and even after proof testing is very important.  to avoid embedment relaxation, it is recommended that bolts are used after undergoingseveral passes of loosening and tightening. embedment relaxation may be worse for new bolts. iium engineering journal, vol. 16, no. 1, 2015 abid et al. 51 more than one bolt tightening pass with proper bolt tightening sequence is recommended to achieve uniform preload bolts used in a joint. references [1] abid m. (2000) experimental and analytical studies of conventional (gasketed) and unconventional (non gasketed) flanged pipe joints (with special emphasis on the engineering of ‘joint strength’ and ‘sealing’. phd thesis, university of strathclyde, glasgow, uk. [2] webjörn j. (2000) the loss of bolt pre-load with time. document no. j0001.01 doc f46. [3] webjörn j. (1985) new look at bolted joint design. machine design, pp. 81-84. [4] webjörn j. (1985) the bolted joint – a series of problems. linköping studies in science and technology, dissertation no. 130, appendix a. [5] webjörn j. (1986) the development of compact flanges”. international symposium on fluid sealing (cetim), nantes, france, pp. 45-48. [6] webjörn j. (1990) discussion an alternative bolted joint for pipe-work. proc. instn. mechanical engineers, 204:139-140. [7] webjörn j. (“discussion-an alternative bolted joint for pipe-work”. proc. instn. mechanical engineers, 205:59-62. [8] almen jo. (1943) bolt failure as affected by tightening. machine design, pp. 133-134. [9] almen jo. (1994) tightening is vital factor in bolt endurance. machine design, pp. 158-162. [10] chesson ejr, munse wh. (1964) studies of the behaviour of high strength bolts and bolted joints. university of illinois college of engineering, engineering experiment station bulletin 469. [11] roehrich lr. (1967) torquing stresses in lubricated bolts. machine design, pp. 171-175. [12] bickford jh. (1981) an introduction to the design and behaviour of bolted joints,crc press. [13] bickford jh. (1983) that initial pre-load: what happens to it. mechanical engineering, pp. 5761. [14] haviland gs. (1983) designing with threaded fasteners. mechanical engineering, pp. 17-31. [15] abid m, nash dh. (2005) structural strength: gasketed versus non-gasketed flange joint under bolt up and operating condition. int. j. solids and structures, 217:1-14. [16] abid m. (2006) stress variation in flange of a gasketed flanged pipe joint during bolt up and operating conditions”. int. j. sci. tech. scientia iranica, 13(3):303-309. [17] abid m, nash dh, webjörn j. (2000) the stamina of non-gasketed flanges. fatigue 2000, cambridge, pp. 575-584. [18] abid m, nash dh. (2006) relaxation behaviour of a gasketed and non-gasketed bolted flanged pipe joint a comparative study. wseas transactions on applied and theoretical mechanics, 1(2):239-246. [19] abid m, hussain s. (2008) gasketed flange joint’s relaxation behaviour during assembly using spiral wound gasket. j. process mech. eng., proceedings of the imeche, part e, 222(2):123-134. [20] abid m, nash dh. (2006) bolt bending behaviour in a bolted flanged pipe joint: a comparative study”.asme pressure vessel and piping conference, hyatt regency vancouver, vancouver, british columbia, canada, july 23-27, pp. 1-9. [21] abid m, nash dh. (2006) joint relaxation behaviour of gasketed bolted flanged pipe joint during joint assembly. 2nd wseas international conference on applied and theoretical mechanics (mechanics'06) ttvenice, italy, november 20-22, pp. 319-325. [22] abid m, hussain s. (2007) bolted joint’s relaxation behavior: a fea study. failure of engineering materials and structures. fems, uet taxila, pakistan, 22-23 october, pp. 143-153. [23] abid m, hussain s. (2008) gasketed joint’s relaxation behavior during assembly using different gaskets: a comparative study. international conference on advanced design and manufacturing (icadam2008), 14-16 january, haiksou china. pp. 1-10. iium engineering journal, vol. 16, no. 1, 2015 abid et al. 52 [24] abid m. (2008) effect of bolt scatter on different sizes of gasketed bolted flange joints: a comparative fe study. 13th international conference on applied mechanics and mechanical engineering (amme-13), may 27-29, cairo, egypt, pp. 1-14. [25] kamran ak, abid m, chattha ja. (2009) gasketed bolted flange joint’s relaxation behavior under different bolt up strategy. proc. imeche, part e: j. process mechanical engineering, 223(4):259-263. [26] asme (2010) guidelines for pressure boundary bolted flange joint assembly. asme pcc1–2010. usa. [27] abid m, hussain s. (2010) gasketed flange joint’s relaxation behaviour during assembly. sadhana indian academy of sciences proceedings in engineering sciences, 35(1):3143. [28] abid m. (2010) behaviour of the gasketed flange joints of different sizes a parametric fea study. the technology world journal. ii(1):101-106. [29] abid m, shah ar. (2011) performance of a gasketed bolted flanged pipe joint under boltup, internal pressure and dynamic (harmonic and transient) axial loads. ned university journal of research, 2:62-69. [30] abid m, maqsood s, wajid ha. (2012) comparative modal analysis of gasketed and nongasketed bolted flanged pipe joints: fea approach. adv. mech. eng. pp. 1-8. doi:10.1155/2012/413583. 2012. [31] abid m, khan ym. (2013) the effect of bolt tightening methods and sequence on the performance of gasketed bolted flange joint assembly. structural engineering and mechanics, 46(6):843-852. [32] abid m, khan ka, chattha ja. (2013) performance testing of a gasketed bolted flange pipe joint under combined pressure and thermal loading. experimental techniques, pp. 1-3. [33] abid m. (2010) comparative performance study of gasketed and non-gasketed flange joints under combined internal pressure, axial and bending loading an experimental study. iium engineering journal, 11(2):179-200. [34] abid m, al-grafi mw, wajid ha. (2013) effect of bolt behaviour on the performance of a bolted joint”. world applied sciences journal, 26(1):89-96. [35] bs 3692 (1967) specifications for iso metric precision hexagonal bolts, screws and nut. nomenclature x independent variable y dependent variable m slope of line a,b constants ln with lock-nut (nyloc) mk with lubricant molykote 321r application of digital cellular radio for mobile location estimation iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 critical success factors for building information modelling (bim) implementation for power plant projects in malaysia mohd azrul aziz1, chee fui wong2*, nuzul azam haron3, aidi hizami ales3, raja ahmad azmeer raja ahmad effendi4 and ooi kuan tan2 1 tnb power generation sdn bhd, pjx hm shah tower, jalan persiaran barat, 46500, petaling jaya, selangor, malaysia 2 department of civil engineering, lee kong chien faculty of engineering and science, universiti tunku abdul rahman, 43000, kajang, selangor, malaysia 3 department of civil engineering, faculty of engineering, universiti putra malaysia, 43400, seri kembangan, selangor, malaysia; 4 department of industrial design, faculty of design and architectural, universiti putra malaysia, 43400, seri kembangan, selangor, malaysia *corresponding author: cfwong@utar.edu.my (received: 22nd june 2021; accepted: 17th october 2021; published on-line: 4thjanuary 2022) abstract: building information modelling (bim) has become increasingly important for the construction industry in malaysia. bim implementation process requires proper strategic planning and considerations from many aspects.malaysian government has realised the importance of bim as an emerging technology to transform the construction industry in malaysia,and thus has classified bim as one of the twelve main technology in cidb “construction 4.0 strategic plan 2021-2025”. bim implementation offer significant benefits to the power generation sector in malaysia thisstudy was conducted using the quantitaive research method in which questionnaires survey were distributed to the clients‘ representatives in the malaysian power sector. this study has identified the 13 critical success factors to be considered by clients for bim implementation in power plant projects in malaysia. the success factors were classified based on the four (4) main fields or factors namely management, people, process and technology. the study findings show that management support is the most important success factor for the power plant projects while other success factors such as people, process and technology were also identified and discussed. abstrak: model pembangunan maklumat (bim) merupakan sebuah konsep penting bagi industri pembinaan di malaysia. proses pelaksanaan bim memerlukan perancangan strategik dan pertimbangan wajar dari pelbagai aspek. kerajaan malaysia sedar akan kepentingan bim sebagai teknologi pemangkin dalam transformasi industri pembinaan malaysia di mana bim telah disenaraikan sebagai salah satu daripada 12 teknologi utama dalam cidb “plan strategik 4.0 pembangunan 2021-2025”. pelaksanaan bim memberi faedah ketara kepada sektor jana kuasa di malaysia. kajian ini dibuat menggunakan kaedah kuantitatif melalui kaji selidik ke atas wakil klien dalam sektor tenaga malaysia. kajian ini telah mengenal pasti 13 faktor kejayaan kritikal yang perlu dipertimbangkan oleh klien bagi menghasilkan projek loji jana kuasa di malaysia. faktor kejayan ini telah diklasifikasi berdasarkan 4 bidang utama seperti pengurusan, pekerja, proses dan teknologi. dapatan kajian menunjukkan bahawa sokongan daripada pihak pengurusan 34 mailto:cfwong@utar.edu.my iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 merupakan faktor utama bagi kejayaan sesebuah projek jana kuasa, di samping faktorfaktor lain seperti pekerja, proses dan teknologi juga telah dikenal pasti dan dibincangkan. keywords: building information modelling (bim); power plant project; bim implementation 1. introduction the construction industry is a vital part of the economy, environment, and society. the construction activities affect the quality of human life. other industries especially the economic related industries are connected to the construction industry since all industries require buildings or other built assets. in malaysia, construction industry contributed almost 5% to the national gross domestic product (gdp) and 9% to employment in 2016, with more than 100 other industries depended on construction for their growth [1]. based on recent report produced by bank negara malaysia [2], the construction sector registered slightly higher growth at 0.5% for the second (2nd) quarter of the year 2019 which contributed mainly by residential and special trade sub-sectors to become 4.9% of the national gdp. as reported by world economic forum 2016 [3], the construction industry is the largest raw material consumer globally with 50% of steel production and more than three billion tons of raw materials. the industry contributes 6% of total global gdp. therefore, any improvement in productivity as well as successful adoption of modern innovative will contribute major impact to the industry. electric energy produced by the power plants is very essential for economic growth and development of any country. among the major power plants standings on the globe are and the hydroelectric power plants and the thermal power plants which converts heat intro electric energy such as the conventional steam power plant, diesel power plant, gas turbine power plant, and nuclear power plant [4]. another source for electric energy comes from renewable energy which naturally reloaded by nature such as solar, wind, small hydropower, biomass, geothermal and tidal energy [5]. according to the bp statistical review of world energy (2019) [6], energy consumption grew at a rate of 2.9% in 2018, almost double its 10-year average of 1.5% per year, and the fastest since 2010. in relation to ir 4.0 and innovation, power plants that approach innovative digitalization strategy will gain significant competitive advantage as well as sustaining operational efficiency throughout the plant’s lifecycle [7]. in this perspective, building information modelling (bim) is specified as the key platform of digital technology to be adopted. based on the evaluation and estimation from industry experts on the case study of bim application at a gas turbine power plant; potential cost saving in design, engineering and construction is estimated at 10% to 20%, while in operation phase is estimated at 8% to 13% [8]. building information modelling (bim) is the key enabler for technology innovations in the construction industry. by adopting bim, project’s lifecycle costs can be reduced by almost 20% and bim can significantly improve completion time, quality, and safety [9]. instead of recording information in drawings, as conventional practice by the industry players, bim stores, maintains and exchanges information through comprehensive digital representations in the building information models. this methodology intensely improves the coordination of the design activities, the integration of simulations, the setup and control of the construction process, as well as the handover of building information for the operator or end user. furthermore, by reducing the manual data entry, difficulty and error-prone work can be avoided, thus increase the productivity and quality of the construction projects [10]. 35 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 bim as part of ict was recognized as vital in improving the construction industry in malaysia. however, the implementation process requires proper strategic planning and considerations from many aspects [11]. beside construction sector, bim implementation can benefit the power generation sector in malaysia. however, since there is no report and research related to the bim adoption in the power plant projects in malaysia, it is anticipated that bim was only applied during design and construction stage by the international contractors or consultants and does not benefit the local clients throughout the projects’ lifecycle. therefore, it is crucial to identify the current level of bim implementation in power plant projects in malaysia, the benefits that bim can offer to projects’ stakeholders especially the clients, and the success factors to be considered by the clients, this research focused on the clients’ perspective of malaysian conventional power plants which comprise the coal-fired power plants, gas turbine power plants, co-generation power plants, and hydroelectric power plants. additionally, the assessed power plant projects were constructed between year 2010 to 2019 throughout peninsular malaysia, sabah and sarawak, when bim implementation was relevant. this research is primarily interested in assessing the benefits that bim can offer throughout the lifecycle the power plant projects and factors to be considered for successful bim implementation in power plant projects in malaysia. 2. building information modelling for power plant projects in malaysia 2.1 power plants in malaysia based on data retrieved from malaysian energy commission in 2017, there were 61 existing power plants excluding 13 new power plant projects that were under construction or negotiation throughout malaysia [12,13]. this 2017 research only concentrated on the clients’ perspective of malaysian conventional power plants which comprise coal-fired power plants, gas turbine power plants, and hydroelectric power plants. the research excludes renewable energy power plants such as solar and wind power plants. therefore, focus then given to conventional power plant projects that has been constructed between year 2014 to 2025 in peninsular malaysia, sabah, and sarawak, as bim implementation is relevant throughout that duration. as shown in table 1 there are 23 projects that were completed, or still ongoing construction, or in negotiation phase within that duration. 2.2 bim implementation in the construction of electrical power plants there are two types of power plants in malaysia which are thermal power plants and hydroelectric plants. thermal power plants generate electricity from coal, natural gas, biomass and fuel oil, while hydropower plants transform water-heads into electric energy through water turbine [14]. according to survey by royal institute of chartered surveyor in 2013 [15], bim is suitable for larger and more complex buildings such as power plant, thus benefited in term of design consistency and visualization, cost estimations, clash detection, implementation of lean construction or improved stakeholder collaboration. basically, bim model is created by incorporating structures, equipment, instruments, piping and electrical facilities mainly for space management by the designers or contractors [16]. boston consulting group in 2016, reported that based on case study of bim application at a gas turbine power plant; potential cost saving in design, engineering and construction is estimated at 10% to 20% while in operation phase is estimated at 8% to 13% [17]. 36 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 table 1: list of power plant projects in malaysia from 2014 until 2025 [18]. year completed details type / fuel capacity (mw) status 2014 spr energy kimanis, sabah spr energy (m) sdn bhd gas 100 commissioned kimanis power, sabah kimanis power sdn bhd (kpsb) gas 300 commissioned 2015 tnb janamanjung (unit 4), manjung, perak tnb janamanjung sdn bhd coal 1,010 commissioned hulu terengganu hep, terengganu tnb hydro 250 commissioned 2016 ulu jerai hep, pahang tnb hydro 372 commissioned hulu terengganu (tembat), terengganu tnb hydro 15 commissioned tnb prai, prai penang tnb prai sdn bhd gas 1,071 commissioned tnb connaught bridge, klang, selangor tnb connaught bridge sdn bhd gas 375 commissioned tanjung bin energy, kukup, johor malakoff corporation berhad coal 1,000 commissioned 2017 pengerang co-gen pangerang, johor petronas gas 600 400 mw commissioned & 200 mw in construction tnb manjung five, manjung perak tnb manjung five sdn bhd coal 1,000 commissioned 2019 jimah east power, mukim jimah, negeri sembilan jimah east power sdn bhd coal 2,000 ongoing construction 2020 southern power generation, pasir gudang, johor southern power generation sdn bhd gas 1,440 ongoing construction upper padas, hep, sabah sesb hydro 192 negotiation phase 2021 erda energy, alor gajah, melaka erda energy sdn bhd gas 2,422 ongoing construction tanjung kidurong, bintulu, sarawak seb gas 842 ongoing construction tekai, hep jerantut, pahang tnb hydro 168 negotiation phase 2022 nenggiri hep, gua musang, kelantan tnb hydro 300 negotiation phase 2023 tadmax indah sdn bhd, pulau indah, selangor tadmax indah sdn bhd gas 1,200 negotiation phase lebir hep, gua musang, kelantan tnb hydro 274 negotiation phase 2024 thb power gurun, kedah thb power sdn bhd gas 1,200 negotiation phase telom, hep, kuala lipis, pahang tnb hydro 132 negotiation phase 2025 baleh, hep, sarawak seb hydro 1,285 ongoing construction total capacity (mw) 17,548 37 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 compared to normal building projects which usually use autodesk revit and autodesk naviswork for bim modelling, power plant projects require special bim software for power plant design and modelling. among the popular software in market for the plant design is e3d (aveva), pds and smart3d (intergraph), bentley plant wise and autodesk plant 3d. according to gerber & rice (2010), [16] the hydro powerplant project “hunan hydro & power design institute” which was developed by hanjiang yakou shipping hub was selected as the winner for the ‘going digital advancements in power generation’ category in year 2019. the bim model for this project was developed using bentley’s open buildings designer software that helped complete design works within 45 days and helped collaborative environment to eliminate errors and material shortages, thus reduced on-site change orders by 80%. overall, the bentley software helped the team to complete the task three months ahead of work schedule [19]. in malaysia, construction industry development board (cidb) has defined bim as modelling technology and associated set of processes to produce, communicate, analyse and use as digital information models throughout the construction project life cycle. bim is an intelligent three-dimension (3d) model-based process that gives the architecture, engineering, and construction professionals an insight and tools to plan more efficiently, design, construct and manage buildings and infrastructure [20]. malaysian government has realised the importance of bim as an emerging technology to transform the construction industry in malaysia where bim has been classified as one of the twelve main technologies in cidb “construction 4.0 strategic plan 2021-2025”. the construction industry transformation programme 2016 -2020 (citp 2016-2020) was introduced to transform the malaysian construction industry into one that is highly productive, sustainable and world-class by 2020. under cidb productivity strategic thrust, a key initiative is to roll out technological advantage across project life cycle by using advanced technologies such as bim. the citp 2016-2020 has outlined bim as an emerging technology that will improve the construction productivity. the ministry of works of malaysia through the public works department ‘s (jkr) strategic plan 2021-2025 has set the adoption of the mechanism to reach 50% by 2021 and 80% by 2025 [21]. the benefits that the power plant clients from the malaysian industry perspective during planning and design stages can gain from bim implementation are better understanding via model visualization in 3d, quicker approvals of project at early stages, upfront involvement of key stakeholders for earlier feedback, intelligent transfer of information between stakeholders, and improved efficiency for design production. meanwhile, during construction stage, the benefits would be improved coordination between client-consultantcontractor, improved communication between all stakeholders, reduce construction errors and waste, effective and accurate project time planning and sequencing, produce accurate quantity and cost estimate, and improved safety, quality and risk identification. 3. research method 3.1 project sampling and research method this research is conducted using quantitative methods with questionnaire survey distributed amongst the clients’ representatives in malaysian power sector. the clients’ engineers or technical representatives of the identified power plant projects were to answer closed ended questions in order to gain a thorough understanding on the bim implementation over malaysian power plant projects. 38 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 the respondents for this quantitative study are the four personnel that are involved in the bim implementation of twenty-three (23) projects, namely bim coordinator, civil engineer, mechanical engineer, and electrical or control & instrumentation (c&i) engineer. therefore, by multiplying with 23 projects, the total number of respondents, the client’s representative for bim implementation in the malaysian power plant projects perspective, is 92. subsequently by referring to formula as indicated below [22], a sample size of 42 was obtained at 90% confidence level which gives score, z of 1.65; sample proportion of 50%; and margin error of 10%. 𝑛 = 𝑁 × 𝑍2×𝑝(1−𝑝) 𝑒2 [𝑁−1+( 𝑍2×𝑝(1−𝑝) 𝑒2𝑁 )] = 92 × 1.652×0.5(1−0.5) 0.12 [92−1+( 1.652×0.5(1−0.5) 0.12×92 )] = 40 (1) where; n = population size, z = critical value of the normal distribution at the required confidence level, p = sample proportion, e = margin of error the study by roscoe [23], indicated that the appropriate sample size for a study must be ranged between 30 to 500. more than 30 respondents were deemed as the best population for sampling in this study context and followed the rules of thumb in determining the sample size [23] [24]. therefore, the sample size of 42 has met the requirement of sampling design and 1was adopted for the purpose of this study. questionnaire data were collected using various methods such as personal questionnaire, mail questionnaires, and electronic questionnaires. this method made the questionnaire easily accessible and made compiling data effortless [25]. the questions were generated from the literature review and distributed to the relevant personnel using online platforms such as email, whatsapp and linkedin. the four sections of the structured questionnaire consist of the respondent’s details, respondent’s background, benefits of bim, and success factors for bim implementation using content-based and close-ended questions. the questionnaire used was checked for validity and reliability before distribution. the quantitative data was then coded and analysed using descriptive statistics such as percentages and mean and standard deviation. statistical package for social sciences (spss version 23.0) were employed to aid in the coding, entry and analysis of the data obtained through questionnaires. the reliability analysis using cronbach’s alpha coefficient was conducted in this study to examine the validity of the data on the benefits of bim to clients and the pareto analysis was used to determine the critical success factors for bim implementation for power plants projects in malaysia. according to [26], reliability analysis refers to the stability and consistency of items in the study. additionally [27], stated that reliability is the extent to which results are consistent over time and representative of the total population of the study. in this study the reliability of all variables was examined by cronbach’s alpha score. the pareto analysis which was founded by vilfredo pareto in the late 1940s was adopted fort his research. pareto analysis is a formal technique useful with many possible courses of action are competing for attention. in essence, the problem-solver estimates the benefit delivered 115 by each action while it is common to refer to pareto as “80/20” rule under the assumption that in all situations, 20% of cause determine 80% of problems. 39 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 4. results and discussion 4.1 research respondents the aim of this research was to examine the benefits of building information modelling (bim) to power plant projects’ clients throughout the project lifecycle and to determine the critical success factors for bim implementation of power plants projects in malaysia. this research collected 42 questionnaires responses from the conventional power plant projects stakeholders that include the tenaga national berhad (tnb), sarawak energy berhad (seb), southern power generation (spg), sabah electricity sdn bhd (sesb), tnb prai sdn bhd, tnb manjung five sdn bhd, jimah east power sdn bhd (jep), petronas, kimanis power sdn bhd (kpsb), tnb janamanjung sdn. bhd. and tnb connaught bridge sdn. bhd. table 2 summarises the respondents' organisation. the respondents ‘designation and years of service in the organisation were tabulated in table 3 and table 4. table 5 shows the summary of the involvement of the respondents in power plant projects. the result indicates that majority of the respondents were involved in one or two power plant projects, 40.5% or 17 respondents were involved in only one project, 42.9% or 18 respondents were already involved in two power plant projects. additionally, five respondents (11.9%) were involved in three projects, and only two respondents (4.8%) were involved in all four types of power plant projects which are covered in this study, namely gas fired power plant, coalfired power plant, co-generation power plant and hydroelectric power plant. table 2: respondent’s organisation name of organisation n % tenaga nasional berhad 22 52.4 sarawak energy berhad 4 9.5 southern power generation 3 7.1 sabah electricity sdn bhd 2 4.8 tnb prai sdn bhd 2 4.8 tnb manjung five sdn bhd 2 4.8 jimah east power sdn bhd 2 4.8 petronas 2 4.8 kimanis power sdn bhd 1 2.4 tnb janamanjung sdn. bhd. 1 2.4 tnb connaught bridge sdn bhd 1 2.4 total 42 100 table 3: respondent’s designation designation n % engineer 16 38.1 senior engineer 15 35.7 manager 5 11.9 executive 4 9.5 senior manager 2 4.8 total 42 100 40 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 table 4: respondent’s year of organisation years in organisation n % 1-5 years 13 31.0 6-10 years 13 31.0 11-15 years 12 28.6 16-20 years 2 4.8 more than 20 years 2 4.8 total 42 100 table 5: respondent’s involvement in power plant project involvement of power plant project n % 1 type of power plant project only 17 40.5 2 type of power plant projects 18 42.9 3 type of power plant projects 5 11.9 all 4 type of power plant projects 2 4.8 total 42 100 4.2 reliability analysis table 6 indicates the reliability analysis of critical success factors for bim implementation along the lifecycle of power plants projects in malaysia. the value of cronbach’s alpha for management, people, process and technology were recorded at 0.946, 0.893, 0.914 and 0.948 respectively. all items of the reliability analysis were considered acceptable since the value is greater than 0.60 [24]. table 6: reliability analysis for critical success factors for bim implementation throughout the lifecycle of power plants projects in malaysia variables cronbach’s alpha management 0.946 people 0.893 process 0.914 technology 0.948 4.3 benefits of bim implementation bim practices have been very beneficial in achieving project success. the finding for this quantitative study was formulated using likert scale approach and the respondents were asked to rate what their opinion on the listed bim benefits based on their knowledge or experience in applying bim in their power plant projects. these responses were assessed through ranking based on average index (ai) values presented in table 7. 4.4 critical success factors for bim implementation the critical success factors for bim implementation were assessed through the questionnaires using likert scale approach. the respondent’s opinion on the listed critical success factors for bim implementation based on their knowledge or experience in applying bim in their power plants projects were assess and ranked using the average index (ai) values and presented in table 8. 41 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 table 7: benefits of bim implementation (overall) no benefits of bim ai standard deviation rank 1. construction stageimproved coordination between client-consultant-contractor 4.2432 0.95468 1 2. planning and design stagebetter understanding via model visualization in 3d 4.2432 0.89460 2 3. facility management stageallow for future updates of current asset information 4.1351 0.85512 3 4. facility management stageprovide a single source of information for project handover 4.1081 0.96563 4 5. construction stagereduce construction errors and waste 4.1081 01.10010 5 6. construction stageproduce accurate quantity and cost estimate 4.0541 0.94122 6 7. planning and design stageimproved efficiency for design production 4.0541 0.97028 7 8. planning and design stage-quicker approvals of project at early stages 4.0541 0.99850 8 9. construction stageimproved communication between all stakeholders 4.0541 1.02594 9 10. facility management stagebetter information for the whole lifecycle of asset management 4.0270 1.04047 10 11. planning and design stageintelligent transfer of information between stakeholders 4.0000 1.10554 11 12. facility management stageenhanced evaluation on maintenance approach of plant 3.9730 0.89711 12 13. construction stageeffective and accurate project time planning and sequencing 3.9730 1.21304 13 14. planning and design stageupfront involvement of key stakeholders for earlier feedback 3.9730 0.98563 14 15. construction stageimproved safety, quality and risk identification 3.8378 1.01416 15 table 8: critical success factors for bim implementation (overall) no critical success factors for bim implementation ai standard deviation rank 1 managementhigh commitment and continuous support 4.2703 0.87078 1 2 technologyrelevant software available for bim application 4.2162 0.88616 2 3 technologycentral repository system to house project information 4.1892 0.84452 3 4 processcomprehensive client’s requirements 4.1892 0.87679 4 5 peoplechange of mindset and awareness 4.1892 0.87679 5 6 peopleadequate education and trainings 4.1622 0.89795 6 7 managementclear business plan, vision and mission 4.1622 0.86646 7 8 technologystable and fast internet network system 4.1351 0.94757 8 9 technologyappropriate hardware i.e. high-end computers 4.1351 0.91779 9 10 processsystematic approach throughout project 4.0811 0.95389 10 11 peoplewell defined roles and responsibilities 4.0811 0.89376 11 12 technologyother tools and equipment i.e. drone for reality modeling 4.0000 0.97183 12 13 processagreed deliverables for asset lifecycle 4.0000 0.91287 13 42 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 the result shown in fig. 1 was employed to focus on the top portion of the critical success factors for bim implementation throughout the lifecycle of power plant projects in malaysia. from the pareto chart, 8 out of 13 factors of bim implementation were selected to be included in the concept map and “management – high commitment and continuous support” stated the highest percentage among the critical factor with 7.9% followed by “technologyrelevant software available for bim application” (7.9%), “-technology central repository system to house project information” (7.8%), “processcomprehensive client’s requirements” (7.8%), “peoplechange of mindset and awareness” (7.7%), “peopleadequate education and trainings” (7.7%), “managementclear business plan, vision and mission” (7.6%), and “technologystable and fast internet network system” that indicated 7.6%. fig. 1: pareto analysis of critical success factors for bim implementation throughout the lifecycle of power plant projects in malaysia. 5. conclusion this research has identified the benefits of building information modelling (bim) to power plant projects’ clients throughout the project lifecycle and has identified 13 critical success factors that need to be considered for bim implementation in malaysia. this research has identified the most important benefit of bim for power plant projects is the improved coordination between client, consultant and contractor during the construction stage. other benefits identified include better 3d visualisation during planning and design stage as well as smooth updates of asset information and single source handover project information during the facilities management stage. this research has also identified the most critical success factor for bim implementation of power plant projects in malaysia as the commitment and continuous management support. besides that, the power plants project stakeholders consider relevant software availability, central repository system, comprehensive client’s requirements and the change of mindset as the critical success factors for bim adoption for power plant projects in malaysia. 43 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 references [1] ipsos (2017) reference document & financial report: it’s time for simplicity. [2] bank negara malaysia (2019) outlook and policy in 2019. bank negara malaysia [3] world economic forum (2016) shaping the future of construction. a breakthrough in mindset and technology. [4] raja, a. k., & srivastava, a. p. (2006). power plant engineering. new age international. [5] ellabban o, haitham ar, blaabjerg f. (2014) renewable energy resources: status, prospects, and their enabling technology. renewable and sustainable energy reviews, 39: 748-764. doi: 10.1016/j.rser.2014.07.113 [6] bp (2019) bp statistical review of world energy [7] abb (2017) digitalization and power generation evolve, adapt, and thrive during the energy and fourth industrial revolutions, abb white paper. https://library.e.abb.com/public/5b1f31f8444f41a7922b200207e47177/digitalization%20and % 20power%20generation_wp.pdf [8] cidb (2008) malaysian construction industry outlook, presentation by business development, sector of cidb, in master builders journal (3rd quarter), 2008, 8-14. [9] cidb (2009) construction economic indicators. kuala lumpur: construction industry development board of malaysia [10] borrmann, a., könig, m., koch, c., & beetz, j. (2018). building information modeling: why? what? how? in building information modeling (pp. 1-24). springer, cham. [11] haron na, raja soh rpza, harun an. (2017) implementation of building information modelling (bim) in malaysia: a review. pertanika journal of science & technology, 25(3): 661-674. [12] energy commission (2017) energy malaysia, volume 12, energy commission, malaysia. [13] energy commission (2017) performance and statistical information on electricity supply industry in malaysia, energy commission. [14] shamsudin msn, rahman mn, wahid ma. (2016) power generation sources in malaysia: status and prospects for sustainable development. journal of advanced review on scientific research, 25(1): 11-28. [15] royal institution of chartered surveyors (2014) international bim implementation guide. https://www.rics.org/globalassets/rics-website/media/upholding-professionalstandards/sector-standards/construction/international-bim-implementation-guide-1st-editionrics.pdf [16] gerber bb, rice s. (2015) the perceived value of building information modeling in the u.s. building industry. journal of information technology in construction, 15: 185-201. [17] boston consulting group (2016) digital in engineering and construction. the transformative power of building information modeling. [18] energy commission (2018) malaysia_energy_statistics_handbook, energy commission, malaysia. http://www.sciencedirect.com/science/article/pii/s1364032114005656 [19] bentley (2019) bim projects in china using bentley’s open applications are setting a higher bar in manufacturing and power generation. bentley systems. https://www.bentley.com/en/about-us/news/2019/october/21/901-ai-bim-projects-china [20] cidb malaysia (2017) malaysia building information modeling report 2016. [21] cidb (2015) construction industry transformation programme 2016-2020: driving construction excellence together. cidb (isbn: 978-967-5317-96-5) [22] arya, r., antonisamy, b., & kumar, s. (2012). sample size estimation in prevalence studies. the indian journal of pediatrics, 79(11), 1482-1488. https://link.springer.com/article/10.1007/s12098-012-0763-3 [23] roscoe jt. (1975) fundamental research statistics for the behavioral sciences. (2nd edition). new york: holt, rinehart, and winston. [24] sekaran. (2003) research methods for business (4th edition). new york, usa: john wiley & sons, vol. 65. https://doi.org/10.1017/cbo9781107415324.004 [25] millar m, dillman da. (2012) encouraging survey response via smartphones. survey practice 5(3). https://doi.org/10.29115/sp-2012-0018 44 https://econpapers.repec.org/scripts/redir.pf?u=https%3a%2f%2fdoi.org%2f10.1016%252fj.rser.2014.07.113;h=repec:eee:rensus:v:39:y:2014:i:c:p:748-764 iium engineering journal, vol. 23, no. 1, 2022 aziz et al. https://doi.org/10.31436/iiumej.v23i1.2119 [26] sekaran u, bougie r. (2013) research methods for business: a skill-building approach (6th ed.). chichester, west sussex: john wiley & sons, inc. [27] joppe, m. (2000). the research process. retrieved february 2000. https://www.academia.edu/930161/the_research_process?pop_sutd=true 45 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 effect of the lignocellulolytic substrates and fermentation process parameters on mycocoagulant production for water treatment maroua fellah1, md zahangir alam1*, abdullah al mamun2, nasserldeen ahmed khabbashi1, nurul sakinah engliman1 and sonia hadj arab1 1 department of chemical engineering and sustainability, 2 department of civil engineering, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia * corresponding author: zahangir@iium.edu.my (received: 21st april 2022; accepted: 15th november 2022; published on-line: 4th january 2023) abstract: in the present research, a fungal strain was used to produce a myco-coagulant via solid-state bioconversion to reduce water turbidity. the production of myco-coagulant was achieved using several low-cost lignocellulolytic substrates, namely coco peat, sawdust, palm kernel cake, and rice bran as sources of carbon and nitrogen. this research involves the study of both the effect of lignocellulolytic substrates and the parameters involved in the fermentation process for myco-coagulant production. coco peat was chosen as a suitable lignocellulolytic substrate to serve as a carbon source for producing myco-coagulant, potentially reducing the turbidity by 84.6% from the kaolin suspension. sawdust, palm kernel cake, and rice bran showed 33.06%, 30.18, and 21.18 %, respectively. furthermore, a statistical approach to the plackett-burman design was conducted to evaluate the significant parameters that affect the production of myco-coagulant. eleven fermentation process parameters were selected: concentration of coco peat (24 %), incubation time (5-9 days), temperature (25-35 °c), ph (5-9), glucose (0-2 %), malt extract (1-2 %), yeast extract (0-2%), wheat flour (0-2 %), ammonium sulfate (0-1 %), inoculum size (1-3 %) and potassium dihydrogen phosphate (0-0.5 %). the selected variables were assessed through statistical analysis (main effects) based on their significance. based on the main effect of each variable on flocculation activity, three variables, namely glucose, malt extract, and ph influenced high levels. on the other hand, the remaining eight variables did not significantly affect the production of myco-coagulant. furthermore, a deeper study was conducted to further optimize the three effective variables involved in the fermentation process to evaluate these factors' influence on flocculation activity. abstrak: penyelidikan ini adalah berkenaan strain fungus yang digunakan bagi menghasilkan miko-koagulan melalui penukaran-bio berkeadaan pepejal bagi mengurangkan kekeruhan air. miko-koagulan dihasilkan dengan menggunakan beberapa substrat lignoselulolitik berkos rendah, iaitu habuk kelapa, habuk papan, hampas kelapa sawit, dan dedak padi sebagai sumber karbon dan nitrogen. penyelidikan ini mengkaji kesan substrat lignoselulolitik dan faktor-faktor yang terlibat dalam proses fermentasi bagi menghasilkan miko-koagulan. habuk kelapa dipilih sebagai substrat lignoselulolitik yang sesuai berfungsi sebagai sumber karbon dalam menghasilkan miko-koagulan, berpotensi mengurangkan kekeruhan sebanyak 84.6% daripada ampaian kaolin. sebaliknya, habuk papan, hampas kelapa sawit, dan dedak padi menunjukkan 33.06%, 30.18, dan 21.18 %, masing-masing. tambahan pula, pendekatan statistik ke atas reka bentuk plackett-burman telah dijalankan bagi menilai parameter penting yang mempengaruhi penghasilan miko-koagulan. sebelas 13 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 parameter proses penapaian telah dipilih: kepekatan habuk kelapa (24 %), masa pengeraman (5-9 hari), suhu (25-35 c), ph (5-9), glukosa (0-2 %), ekstrak malt (1-2), tepung gandum (02 %), ammonium sulfat (0-1%), saiz inokulum (1-3 %) dan kalium dihidrogen fosfat (0-0.5 %). pemboleh ubah yang dipilih dinilai melalui analisis statistik berdasarkan kepentingannya. berdasarkan kesan utama setiap pemboleh ubah terhadap aktiviti penggumpalan, tiga pemboleh ubah ini adalah glukosa, ekstrak malt, dan ph yang memberi kesan tertinggi. sebaliknya, lapan pemboleh ubah lain tidak mempengaruhi penghasilan miko-koagulan dengan ketara. tambahan lagi, kajian yang lebih mendalam telah dijalankan bagi membaiki tiga pemboleh ubah utama yang terlibat dalam proses fermentasi bagi menilai kesan yang mempengaruhi aktiviti penggumpalan. keywords: myco-coagulant, solid-state bioconversion, lignocellulolytic substrates, water treatment, turbidity removal, flocculation activity, pbd. 1 introduction high turbidity and suspended solids (ss) are significant problems that affect rivers due to wastewater discharge, terrain conditions, land cover, rainfall, soil type, agriculture, stirred bottom sediments, algal blooms, and other development activities. these problems indicate the essential need to protect the aquatic environment and life by diminishing the turbidity and residual levels in the rivers using both conventional and advanced technologies in water: from treatment such as sedimentation and filtration to more complex methods, including ultrafiltration, ozonation, and reverse osmosis, to process raw water sources before supplying it to consumers and to ensure that the treated water can meet the effluent discharge requirement before it is discharged to water bodies [1,2]. the coagulation-flocculation process is considered one of the most straightforward approaches to accelerate the removal of suspended impurities in water efficiently. even with advanced technologies, coagulation-flocculation remains one of the essential treatment processes for removing impurities (mainly suspended particles) in water treatment plants. this process requires adding components called coagulants/flocculants [3,4]. coagulants/flocculants are commonly applied in many industrial processes, such as potable water purification and wastewater treatment. generally, coagulants/flocculants are classified into three types: synthetic organic polymer flocculants like polyacrylamides, inorganic flocculants such as aluminium sulfate, iron sulfate, and iron chloride, and those that are naturally occurring, such as sodium alginate, chitosan, and microbial coagulants/flocculants [3,4]. due to flocculating efficiency, chemical coagulants-flocculants are widely used in conventional water treatment processes [5,6,7]. however, using chemical coagulants/flocculants in water treatment has been limited due to several disadvantages [8,9]. as reported in many studies, its usage can cause several environmental problems and human health concerns [10,11,12]. since the coagulants/flocculants play a significant role in the coagulation/flocculation process, developing highly efficient alternative coagulants/flocculants has always remained one of the most challenging research areas [13]. biocoagulants/flocculants have piqued the interest of many researchers due to their numerous advantages: biodegradability, nontoxic properties, and potential as an alternative for conventional coagulants/flocculants [11,14]. microbial coagulants/flocculants are extracellular biopolymers secreted by microorganisms such as bacteria, yeasts, fungi, and algae [2]. they contain mainly glycoproteins, polysaccharides, and proteins produced by microorganisms during active secretion [15]. however, the application of microbial coagulants/flocculants has been hindered by the 14 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 challenge of producing them on a large scale. currently, researchers produce microbial coagulants/flocculants by applying synthetic media which contain simple sugar (glucose, sucrose, lactose, fructose, maltose), alcohols, and organic acid as carbon sources through the liquid-state fermentation method. despite the potential applications of microbial coagulants/flocculants, the high production costs still limit their use. interestingly, new strategies to produce microbial coagulants/flocculants have been identified. the preference for ssf is more economically attractive due to the usage of low-cost materials such as agricultural and industrial byproducts via solid-state fermentation to produce bioactive compounds. ssf is of interest as an alternative to other conventional fermentation methods that are more costly and mainly chemically driven [16]. these bioprocessing technologies are devoted to developing cost-effective measures by utilizing inexpensive fermentation substrates to meet the current market demand for bioproducts [16], which may reduce production costs on industrial scales. thus, an appropriate, inexpensive, and abundant substitute for these substrates, such as byproducts and agricultural residues, should be utilized to replace the conventional substrates to solve this problem. solid-state fermentation may be better for producing a microbial coagulant/flocculant using filamentous fungi [17,18]. thus, this research will investigate a coagulant-produced fungus called myco-coagulant via solidstate fermentation using agricultural waste as a low-cost substrate. the present study aims to select the best lignocellulolytic substrates via a solid-state fermentation (ssf) process to produce an efficient myco-coagulant to reduce the turbidity of the water. it was also designed to study the impact of various fermentation process parameters, namely concentration of coco peat, incubation time, temperature, ph, glucose, malt extract, wheat flour, ammonium sulfate, inoculum size, and potassium dihydrogen phosphate (kh2po4) on the production of coagulants from a fungal strain using a placket-burman experimental design. 2 materials and methods 2.1 microorganisms the microorganism used in the present study was a fungal strain collected from a supermarket in kuala lumpur, malaysia. the fungal strain was maintained on potato dextrose agar (pda), stored in the chiller at 4º c, and kept at room temperature (30±2o c) for further use. 2.2 substrate collection and preparation in this study, different lignocellulolytic (lc) substrates, namely coco peat, sawdust, palm kernel cake, and rice bran, were collected from the international islamic university malaysia, kuala lumpur. the substrates were used as the supplementary media throughout this study, which were ground and milled into a fine powder using a domestic blender. the fine powders passed through a 50 mm-mesh sieve and were stored at room temperature for solid-state fermentation (ssf). these substrates may be seen as an inexpensive and abundant agricultural waste model, making the entire ssf process feasible and low-cost. 2.3 inoculum preparation (mycelium suspension) the mycelial suspension was prepared by fully grown plates of fungi cultures from the incubator after seven days of incubation. a wriggled l-shaped rod was gently scraped off each plate and washed carefully with 20 ml of sterilized distilled water. the suspended mycelial suspension was used as the main inoculum. 15 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 2.4 solid-state bioconversion (ssb) the solid-state bioconversion was conducted by moistening 3 g of each substrate, namely coco peat, sawdust, palm kernel cake, and rice bran, with 1 ml of fungal mycelial suspension and 7 ml of production media in a petri dish, which was sealed with a parafilm to avoid contamination with unwanted microbes. the medium consisted of 20 g of malt extract dissolved into 1000 ml of distilled water (2% w/v), and its initial ph was adjusted to 7 using 1 m naoh or 2 m hcl. the production medium was autoclaved at 120º c for 15 minutes. the inoculated plates were incubated at 30º c for seven days. the major activities involved in the research are shown in fig. 1. fig. 1. overall scheme of the major activity to produce myco-coagulant using solid-state fermentation. 2.5 surface morphology analysis scanning electron microscopy (sem) (sem-sipma-vp03-67, zeiss, and p-sigma, munich, germany) was used to observe the fungus's morphological surface and the mycelium formation in various lignocellulosic media. 2.6 extraction of myco-coagulant in this study, the extraction of the myco-coagulant from the biomass was conducted using an aqueous buffer solution at ph 7. after seven days of incubation, the fermented medium of ssf from each plate (2 g of the substrate) was mixed with 20 ml of aqueous buffered solution at ph 7. the mixture was kept in a shaker incubator for 1 hour at 250 rpm at 30º c. it was then filtered using muslin, followed by a whatman paper. the clear supernatant was collected as 16 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 the main myco-coagulant and used to determine their flocculating activity using the jar apparatus method. 2.7 determination of turbidity the turbidity meter (model 2100q: hach, loveland, usa) was switched on before the data recording, and a blank sample of 10 ml distilled water was poured into the turbidity vial. 10 ml of the supernatant from each untreated water sample was poured into the turbidity vial. the outer vial was cleaned and placed into the turbidity meter before the 'read' button was pressed to get the turbidity reading in ntu. finally, the average readings were calculated for record purposes. 2.8 jar test experiment the purpose of a jar test experiment was to observe the coagulation and flocculation processes of water treatment on the laboratory scale. the equipment needed in conducting jar tests was a flocculator unit (sw6, uk) that consisted of six paddle mixers to which respective beakers were placed and a control panel to adjust the stirring speed and time. four operating conditions of the jar test were set as the independent variables: the initial ph value, coagulant dosage of myco-coagulant, rapid mixing speed, and settlement time. after that, the required amount of myco-coagulant was added to synthetic turbid water and succeeded by rapid mixing to simulate the coagulation process. it was then followed by the slow mixing that demonstrated the flocculation process. then, the beakers containing treated wastewater were left aside for one hour to allow flocs sedimentation. after the flocs had settled, the supernatant of the treated wastewater was taken and analyzed for its final turbidity. 2.9 evaluation of flocculation activity via jar test the kaolin suspension was used to determine the flocculation activity of the mycocoagulant in its capacity to reduce the turbidity level. first, 0.7 g/l kaolin clay was suspended in 1500 ml of distilled water and ph 7 using 1m naoh or 2m hcl. initial turbidity was recorded at 480 ntu. 10 ml of the supernatant (myco-coagulant) was added to each jar containing 300 ml kaolin suspension. then, the jar was set up and operated at three stages: fast mixing at 250 rpm for 7 minutes, then 90 rpm for 22 minutes, and finally settling for one hour. next, the top layer of the water in each jar was collected with a micropipette, and the flocculation activity was calculated based on the percentage removal of turbidity. all the experiments were conducted in triplicate. the flocculating activity was calculated according to eq. (1). turbidity removal efficiency (%) = a−b a × 100 (1) where a is the initial turbidity of kaolin suspension directly after preparation (ntu) and b is the final turbidity of kaolin suspension after the settling period (ntu). a sartorius pb-10 ph meter was used to measure the ph value. the turbidity was measured by using a nephelometric turbidity unit (ntu) (standard method 2130 b) with a portable turbidimeter (2100q hach, usa). 2.10 screening of growth conditions using plackett-burman design statistical experimental design plays an essential role in developing fermentation bioprocesses by screening for the main factors of interest and then further optimizing these to improve industrial process performance. different nutritional and environmental variables were evaluated to determine the variables affecting flocculation activity by the production of the myco-coagulant. the plackett–burman statistical experimental design "design expert® 17 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 7.0.0" was used to identify the critical variables required to produce a myco-coagulant to reduce turbidity. the plackett-burman design (pbd) is an easy and fast method appropriate to screen multiple variables in a single experiment and is often used to evaluate the most significant variables affecting the culture requirements for fermentation and enzyme production. based on previous studies, several potential factors may affect the yield of the mycocoagulant. in this study, eleven factors were chosen. the eleven different independent variables are shown in table 1, including the physical/chemical parameters (temperature, incubation time, inoculum size, cocopeat concentration, ph), and nutrients (malt extract, glucose, wheat flour, yeast, ammonium sulfate (nh₄)₂so₄ and potassium dihydrogen phosphate (kh2po4)). each variable is represented at both high and low, denoted by (+) and (−). flocculation activity was used as the response variable. table 1: variables and their levels employed in plackett–burman design to screen culture conditions affecting myco-coagulant production by the fungus variables code low level (-) high level (+) temperature (ºc) a 25 35 incubation time (days) b 5 9 ph c 5 9 cocopeat concentration (g) d 2 4 malt extract e 1 2 ammonium sulfate (nh4)2 so4 (%) f 0 1 glucose (%) g 0 2 wheat flour (%) h 0 2 yeast extract (%) j 0 2 potassium dihydrogen phosphate kh2po4 (%) k 0 0.5 inoculum size (ml) l 1 3 3 results and discussion 3.1 estimation of biomass in solid-state fermentation the fungal mycelium penetrates deep into solid-state fermentation and remains attached to the solid substrate particles. as a result, it is difficult to separate the microorganisms from the solid particles. the present study used standard methods to estimate the biomass in solidstate fermentation [19,20,21]. 3.1.1 prescreening test for estimation of fungal growth estimating biomass is a critical step in a variety of microbial fermentation processes. in the present study, a prescreening test was performed to monitor and compare the growth rate of fungal strains on four distinct lignocellulosic substrates. as shown in fig. 2 on cocopeat substrates, the fungal strain grew swiftly and created intact homogenous and filamentous mycelium composite structures. in addition, sawdust showed slow growth during this time of incubation. on the other hand, the fungal strain grew on palm kernel cake and rice bran; you can barely see the growth. 18 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 coco peat saw dust palm kernel cake rice bran fig. 2. culture of fungus on different substrates after seven days of incubation (a) culture of fungus on cocopeat; (b) culture of fungus on sawdust; (c) culture of fungus on pkc; (d) culture of fungus on rice bran. 3.1.2 evaluation of fungal growth by scanning electron microscope (sem) a scanning electron microscope (sem) was used to observe the fungus's morphological surface and the mycelium formation in various lignocellulosic media. fig. 3 shows a significant variation in the density of the filamentous fibre of the fungus in various lignocellulosic media. on the other hand, the sem indicates no change in the morphological surface due to the use of the same strains. fig. 3 illustrates mycelium morphology observed in sem with randomly arranged and oriented filaments on cocopeat, sawdust, palm cake, and rice bran substrates, respectively. the mean hyphae filament diameter was 0.6 ± 0.66 μm. in contrast, the other substrates show a hyphal density of less than coco peat with a diameter of filaments with a mean of 0.7 μm, 0.9 μm, and 1 μm for sawdust, palm kernel cake, and rice bran, respectively. in general, there is no difference in the morphological structure, as shown in fig.3, which refers to using the same fungal strain. however, the density and size of filaments differed from one substrate to another. the variation of the branching density can be explained by the environmental conditions here, where various lignocellulosic media were used. fungal mycelial growth is aided by the substrate, which contains modest concentrations of carbohydrates, lipids, proteins, inorganic substances, and water [22]. therefore, the physical characteristics of the substrate may reveal differences in mycelium growth [23,24]. 19 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 fig. 3. scanning electron microscopy (sem) observations of fungal colonies on different substrates after seven days of incubation (a) culture of fungus on cocopeat; (b) culture of fungus on sawdust; (c) culture of fungus on pkc; (d) culture of fungus on rice bran magnification at x1000. 3.2 analysis of myco-coagulant activity microbial secondary metabolites are regarded as valuable products due to their large number of biological activities. the secondary metabolites are synthesized in a fermentation medium during the growth of the microbes [19]. in this research, the desirable secondary metabolite was a myco-coagulant secreted during fungus growth on different lignocellulosic media. fig. 4 shows the flocculation activity rate of the myco-coagulant using four lignocellulosic media. from the results, it can be clearly seen that coco peat recorded the highest flocculation rate at 84.59 % in removing suspended solids from kaolin suspension. on the other hand, the remaining lc substrates, namely sawdust, palm kernel cake, and rice bran, were recorded at 33.06 %, 23.91 %, and 21.18 %, respectively. based on the results, coco peat was chosen as the best media to serve as an lc substrate for the fungal strain and produced an efficient myco-coagulant. selecting an appropriate substrate suitable for fungal growth and the target of mycocoagulant synthesis is crucial in developing an efficient technology for myco-coagulant production. four substrates, namely coco peat, sawdust, palm kernel cake, and rice bran, were used in this study, which was collected from the biotechnology engineering laboratory of the international islamic university malaysia (iium). these solid substrates were considered to evaluate their ability to produce an efficient myco-coagulant to reduce the turbidity from water. 20 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 fig. 4. flocculation activity of the myco-coagulant in four different lignocellulosic media. the supernatants of the used fungus extracted from biomass were tested to determine the flocculation ability in terms of turbidity reduction from synthetic turbid water (kaolin suspension). the initial turbidity was recorded at 600 ± 30 ntu for kaolin suspension. the flocculation activity rate of the treated synthetic turbid water by the fungal supernatants extracted from the biomass showed a wide variation in flocculation activity all over the fourth biomass ranging from 18.7 % to 89.19 %. among the four fungal supernatants, the fungal supernatant extracted from coco peat from 623 to 96 ntu 84.59% showed the highest flocculation activity. on the other hand, sawdust, palm kernel cake, and rice bran showed 33.06%, 30.18, and 21.18 %, respectively. the myco-coagulant was evaluated to test its ability to remove turbidity by flocculating the particles' kaolin suspension using the jar apparatus. based on the results, the fungal strain has proven its ability to produce an efficient myco-coagulant via solid-state using cocopeat as a substrate in reducing turbidity. coco peat was the best supplement that offered the best carbon source in yielding a mycocoagulant, with the highest fa (84.59 %) obtained with kaolin clay suspension. therefore, the myco-coagulant extracted from coco peat that exhibited the best flocculating activity was chosen for further analysis, and the remaining substrates were eliminated from the remaining part of the study. as reported by luthfi et al. [25], aspergillus niger dwb showed a good flocculation activity rate of 60.5 % from oil palm empty fruit bunch (opefb) fiber. qi et al. [26] reported that alcaligenes faecalis subsp. phenolicus zy-16 showed a good removal efficiency (90.05%) of citrus peel wastes as substrates. 3.3. screening of process conditions for the ssf using pbd the effects of different nutritional components on myco-coagulant production using coco peat were studied to develop a medium that requires minimal nutritional supplementation for enhanced enzyme production. a plackett-burman design (pbd) was applied in this study to determine which variables significantly affected the flocculation activity by producing a mycocoagulant using solid-state fermentation. the pb design is a simple and fast method suitable for screening multiple variables in a single experiment and is often used to evaluate the most significant variables affecting fermentation and enzyme production culture requirements. the impacts of nutritional factors, including carbon and nitrogen sources and mineral salts, were studied using a pb design with 12 trials for 11 variables. as a first step, the corresponding responses in table 2 were carried out to identify the significant variables on myco-coagulant 21 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 production to reduce turbidity. pb experiments showed a wide variation in flocculation activity over all the different experiments, ranging from (18.7 to 89.19 %) presented in table 2, highlighting the importance of further media optimization to attain a high yield of the interesting product myco-coagulant with high flocculation activity. the effect of each nutrient component on flocculation activity is presented in fig. 5. the main effect was estimated based on the difference between the sum of responses obtained at each component's high level (+1) and the low level (−1). fig. 5 shows the main effect of each variable on the flocculation activity. concerning the main effect of each variable, the results showed that three variables from the eleven different independent variables, which were malt extract, glucose, and wheat flour, affected the high flocculation activity at a high level. the level of the carbon source in the growth medium is an essential factor in the production of the myco-coagulant. in the present study, the carbon source, glucose, and wheat flour showed a significantly high effect on the production of the myco-coagulant. previous studies reported that glucose positively affected the production of the myco-coagulant through liquid-state fermentation with lentinus squarrosulus strain 7-4-2 [27]. fig. 5. main effects of the nutritional components on flocculation activity moreover, [28] reported that b. agaradhaerens c9 was cultured in a medium containing glucose, and yeast produced a coagulant with a flocculating activity of 91.9 %. regarding the effect of ph a, similar results were reported by [15,29] which show the best initial ph of the medium was 6, which was in line with the best ph for bioflocculant production by a. niger. however, the remaining variables, temperature, coco peat concentration, cultivation time, kh2po4, ammonium sulfate, ph, and inoculum size, affected the flocculation activity at a low level. the nitrogen source malt extract and ammonium sulfate showed a significant effect on the production of myco-coagulant. the most significant parameter at a low level on the main impact was ph and aluminium sulfate, whereby maintaining the fermentation at acidic ph enhanced the flocculating activity of the metabolite produced. pu et al. [29] and nurul et al. [30] have reported that the flocculating activity was not affected by the inoculum size, which supported our finding. 22 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 table 2: plackett–burman experimental design and obtained responses variables temp. (ºc) cocopeat concentration (%) cultivation time (day) ph kh2po4 (%) malt extract (%) ammonium sulfate (%) yeast extract (%) glucos e (%) wheat flour (%) inoculum size (ml) flocculation activity (%) code run a b c d e f g h j k l 1 25 2.0 5 9.0 0.00 2.0 1.0 0.0 2.0 2.0 3.0 72.74 2 35 4.0 5 9.0 0.50 2.0 0.0 0.0 0.0 2.0 1.0 56.93 3 25 2.0 5 5.0 0.00 1.0 0.0 0.0 0.0 0.0 1.0 48.87 4 35 2.0 5 5.0 0.50 1.0 1.0 2.0 0.0 2.0 3.0 26.12 5 35 4.0 5 5.0 0.00 2.0 0.0 2.0 2.0 0.0 3.0 79.35 6 25 2.0 9 5.0 0.50 2.0 0.0 2.0 2.0 2.0 1.0 89.19 7 25 4.0 5 9.0 0.50 1.0 1.0 2.0 2.0 0.0 1.0 18.7 8 35 2.0 9 9.0 0.50 1.0 0.0 0.0 2.0 0.0 3.0 27.7 9 25 4.0 9 9.0 0.00 1.0 0.0 2.0 0.0 2.0 3.0 25.32 10 35 2.0 9 9.0 0.00 2.0 1.0 2.0 0.0 0.0 1.0 26.61 11 25 4.0 9 5.0 0.50 2.0 1.0 0.0 0.0 0.0 3.0 48.7 12 35 4.0 9 5.0 0.00 1.0 1.0 0.0 2.0 2.0 1.0 44.52 23 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 the use of coco peat as a low-cost nutrient composition was earlier not reported for the higher yield of myco-coagulant from fungal fermentation. based on this study, it was determined that the designed lignocellulosic substrate was economically significant in producing the desired myco-coagulant. to check the contribution of the selected factors affecting the flocculation activity of the produced myco-coagulant, pareto analysis was performed. analysis of the pareto chart in fig. 6 showed that malt extract, glucose, wheat flour, ph, and ammonium sulfate have the highest effect on flocculation activity. fig. 6. pareto chart illustrates the order and significance of the variables affecting flocculation activity using plackett-burman design (the blue color represents negative effects, and the orange color represent positive effects). plackett burman's design does not provide a complete idea about the exact amount of each variable as well as the interaction between the variables. thus, based on the calculations of the main effect and pareto chart, the plackett-burman design selected three parameters: malt extract, ph, and glucose as the most significant factors to produce a myco-coagulant with optimum flocculation activity. 4 conclusions since the cost of production of the myco-coagulant is among the challenges affecting its utilization, the results achieved in this study gave an insight into the utilization of different lignocellulosic substrates to produce an efficient myco-coagulant in reducing water turbidity as well as reduce the cost of experiments as we used abundant substrates. in this study, among the used lignocellulosic substrate, cocopeat was identified as a suitable substrate that serves as a carbon and nitrogen source to produce the myco-coagulant using solid-state fermentation, which can potentially reduce the turbidity by 84.6% from the kaolin suspension. on the other hand, sawdust, palm kernel cake, and rice bran showed 33.06, 30.18, and 21.18 %, respectively. coco peat, as an abundant raw material in malaysia, may be 24 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 utilized to meet this challenge and reduce the cost of production. the produced myco-coagulant may also contribute as a safe, low-cost, and environmentally friendly coagulant alternative to current chemical coagulants. the discovery of a safe and environmental-friendly microbial coagulant that possesses the ability for sustainable water treatment is in line with the global awareness towards creating a clean and healthy environment by using green technology employing solid-state fermentation. acknowledgements the authors would like to acknowledge the isdb grant no spi20-001-0001 for funding this research project. in addition, the authors would like to thank iium through the research management center (rmc) for financial management and monitoring of project progress and the biotechnology engineering department, iium for scientific equipment and facilities. references [1] ebeling jm, sibrell pl, ogden sr, summerfelt st. (2003). evaluation of chemical coagulationflocculation aids for the removal of suspended solids and phosphorus from intensive recirculating aquaculture effluent discharge. aquacultural engineering, 29(1-2): 23-42. [2] ang wl, mohammad aw. (2020). state of the art and sustainability of natural coagulants in water and wastewater treatment. journal of cleaner production, 262: 121267. [3] aljuboori ahr, idris a, abdullah n, mohamad r. (2013). production and characterization of a bioflocculant produced by aspergillus flavus. bioresource technology, 127: 489-493. [4] bernard knm, sylvere nk, patrice kg, joseph kg. (2019). coagulation and sedimentation of concentrated laterite suspensions: comparison of hydrolyzing salts in presence of grewia spp. biopolymer. journal of chemistry, 1-9. [5] ramavandi b. (2014). treatment of water turbidity and bacteria by using a coagulant extracted from plantago ovata. water resources and industry, 6: 36-50. [6] moran s. (2018) an applied guide to water and effluent treatment plant design. butterworthheinemann. [7] lapointe m, barbeau b. (2020). understanding the roles and characterizing the intrinsic properties of synthetic vs. natural polymers to improve clarification through interparticle bridging: a review. separation and purification technology, 231: 115893. [8] flaten tp. (2001). aluminium as a risk factor in alzheimer's disease, with emphasis on drinking water. brain research bulletin, 55(2): 187-196 [9] ward rj, mccrohan cr, white kn. (2006). influence of aqueous aluminium on the immune system of the freshwater crayfish pacifasticus leniusculus. aquatic toxicology, 77(2): 222-228. [10] mortula m, bard sm, walsh me, gagnon ga. (2009). aluminum toxicity and ecological risk assessment of dried alum residual into surface water disposal. canadian journal of civil engineering, 36(1): 127-136. [11] tomljenovic l. (2011). aluminum and alzheimer's disease: after a century of controversy, is there a plausible link? journal of alzheimer's disease, 23(4): 567-598 [12] kluczka j, zołotajkin m, ciba j, staroń m. (2017). assessment of aluminum bioavailability in alum sludge for agricultural utilization. environmental monitoring and assessment, 189(8): 1-8. [13] lee cs, robinson j, chong mf. (2014). a review on application of flocculants in wastewater treatment. process safety and environmental protection, 92(6): 489-508. [14] al-mutairi nz. (2006). coagulant toxicity and effectiveness in a slaughterhouse wastewater treatment plant. ecotoxicology and environmental safety, 65(1): 74-83. [15] aljuboori ahr, uemura y, osman nb, yusup s. (2014). production of a bioflocculant from aspergillus niger using palm oil mill effluent as carbon source. bioresource technology, 171: 66-70. [16] zulkeflee z, sánchez a. (2014). solid-state fermentation of soybean residues for bioflocculant production in a pilot-scale bioreactor system. water science and technology, 70(6): 1032-1039. 25 iium engineering journal, vol. 24, no. 1, 2023 maroua et al. https://doi.org/10.31436/iiumej.v24i1.2400 [17] hölker u, lenz j. (2005). solid-state fermentation—are there any biotechnological advantages? current opinion in microbiology, 8(3): 301-306. [18] gutarra mle, de godoy mg, silva jdn, guedes ia, lins u, castilho ldr, freire dmg. (2009). lipase production and penicillium simplicissimum morphology in solid-state and submerged fermentations. biotechnology journal: healthcare nutrition technology, 4(10): 1450-1459. [19] krishna c. (2005). solid-state fermentation system – an overview. critical reviews in biotechnology 25: 1-30. [20] pandey a, larroche c, soccol cr. (2008). general considerations about solid-state fermentation processes. in current developments in solid-state fermentation, springer, new york, ny. pp. 13-25. [21] yingyi d, lan w, hongzhang c. (2012). digital image analysis and fractal-based kinetic modelling for fungal biomass determination in solid-state fermentation. biochemical engineering journal, 67: 60-67. [22] krishna s. (2005). quantum dots-in-a-well infrared photodetectors. journal of physics d: applied physics, 38(13): 2142. [23] karimi s, mahboobi soofiani n, mahboubi a, taherzadeh mj. (2018). use of organic wastes and industrial byproducts to produce filamentous fungi with potential as aqua-feed ingredients. sustainability, 10(9): 3296. [24] ross, m. (2015). mechanical properties of sheets comprised of mycelium: a paper engineering perspective. honours theses. paper 68. university of north carolina, the usa. [25] luthfi wm, alias h, tay gs, lee ck. (2020). production and characterization of bioflocculant via solid state fermentation process using oil palm empty fruit bunch fibers as substrate. biocatalysis and agricultural biotechnology, 23: 101454. [26] qi x, zheng y, tang n, zhou j, sun s. (2020). bioconversion of citrus peel wastes into bioflocculants and their application in the removal of microcystins. science of the total environment, 715: 136885. [27] hamidah h. (2018). study on myco-coagulant from lentinus squarrosulus for water turbidity reduction. master's thesis. faculty of engineering, international islamic university malaysia. [28] liu w, hao y, jiang j, zhu a, zhu j, dong, z. (2016). production of a bioflocculant from pseudomonas veronii l918 using the hydrolyzate of peanut hull and its application in the treatment of ash-flushing wastewater generated from coal fired power plant. bioresource technology, 218: 318-325. [29] pu s, ma h, deng d, xue s, zhu r, zhou y, xiong x. (2018). isolation, identification, and characterization of an aspergillus niger bioflocculant-producing strain using potato starch wastewater as nutrilite and its application. plos one, 13(1): e0190236. [30] nurul-adela b, nasrin ab, loh sk. (2016). palm oil mill effluent as a low-cost substrate for bioflocculant production by bacillus marisflavi na8. bioresources and bioprocessing, 3(1): 18. 26 microsoft word 2_v17no2_compiled_v2_24nov16.docx iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 157 a new algorithm in nonlinear analysis of structures using particle swarm optimization iman mansouri*1, ali shahri2 and hassan zahedifar2 1department of civil engineering, birjand university of technology, p.o. box 97175-569, birjand, iran. 2department of civil engineering, shahid bahonar university of kerman, kerman, iran. *corresponding author: mansouri@birjandut.ac.ir (received: 8th sept. 2015; accepted: 15th jun. 2016; published on-line: 30th nov. 2016) abstract: solving systems of nonlinear equations is a difficult problem in numerical computation. probably the best known and most widely used algorithm to solve a system of nonlinear equations is the newton-raphson method. a significant shortcoming of this method becomes apparent when attempting to solve problems with limit points. once a fixed load is defined in the first step, there is no way to modify the load vector should a limit point occur within the increment. to overcome this defect, displacement control methods for passing limit points can be used. in the displacement control method, the load ratio in the first step of an increment is defined so that a particular key displacement component will change only by a prescribed amount. in this paper, the load ratio is obtained using a particle swarm optimization (pso) algorithm so that the complex behavior of structures can be followed, automatically. the design variable is load ratio, and its unbalanced force is also considered an objective function in the optimization process. numerical results are performed under geometrical nonlinear analysis, elastic post-buckling analysis and inelastic post-buckling analysis. the efficiency and accuracy of proposed method are demonstrated by solving numerical examples. abstrak: menyelesaikan sistem persamaan tak linear adalah masalah yang sukar dalam pengiraan numerik. mungkin algoritma yang paling terkenal dan paling banyak digunakan untuk menyelesaikan sistem persamaan tak linear adalah kaedah newtonraphson. satu kekurangan besar kaedah ini menjadi jelas apabila mencuba menyelesaikan masalah dengan titik had. setelah beban tetap ditakrifkan dalam langkah pertama, tidak ada cara untuk mengubahsuai vektor beban jika titik had berlaku dalam pertambahan. untuk mengatasi kecacatan ini, kaedah kawalan sesaran untuk melepasi titik had boleh digunakan. dalam kaedah kawalan sesaran, nisbah beban dalam langkah pertama peningkatan akan ditakrifkan supaya komponen sesaran utama tertentu akan berubah hanya dengan jumlah yang ditetapkan. dalam kertas ini, nisbah beban diperolehi dengan menggunakan algoritma pengoptimuman zarah swarm (pso) supaya tingkah laku yang kompleks daripada struktur boleh diikuti, secara automatik. pembolehubah reka bentuk adalah nisbah beban dan daya tidak seimbang yang juga dianggap sebagai fungsi objektif dalam proses pengoptimuman. keputusan numerik dilakukan di bawah analisis geometri tak linear, analisis pasca-lengkokan anjal dan analisis pasca-lengkokan tidak anjal. kecekapan dan ketepatan kaedah yang dicadangkan akan dibuktikan dengan menyelesaikan contoh numerik. keywords: nonlinear analysis; convergence acceleration; particle swarm optimization (pso) iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 158 1. introduction the structural problems with geometrically nonlinear features can often be analyzed by solving a system of nonlinear equations (algebraic or differential) to determine the path of nonlinear load-displacement. the literature on analysis of these problems is quite extensive and provides several approaches, most notably the incremental stiffness procedure [1], the perturbation method, the newton-raphson method and its modified variations, [1, 2], the initial value approach [3], and the self-correcting incremental procedure [1, 2], through all of which nonlinear equilibrium equations could be solved in an efficient manner. literature also provides several analytical approaches specifically developed for assessing the nonlinear behavior exhibited by structural members such as trusses; these include the approach suggested in a study by wempner [4], where complete sets of equilibrium paths of a number of mises trusses have been provided, the method of saffari et al. [5], who have used the newton-raphson iterative algorithm in conjunction with the flow path normal in nonlinear static analysis, and the method of saffari et al. [5], who have analyzed the nonlinear behavior of trusses via a modified normal flow algorithm. other notable works on this subject include but are not limited to the study by papadrakakis and gantes [6], where the optimization of geometrically nonlinear shallow trusses with stability-related constrains has been examined, the work of greco et al. [7], where space trusses has been analyzed by a new geometric nonlinear formulation based on nodal positions (instead of nodal displacements), and the article of papadrakakis [6], where trusses have undergone a second-order and large deflection analysis using the dynamic relaxation scheme. there has also been much progress as the result of the study conducted by huang and vahidi [8], where the snap-through buckling of two sample trusses has been analyzed by the elastic theory of prismatic bars, the article of kassimali and parsi-feraidoonian [9], which has been focused on nonlinear behavior of pre-stressed cable trusses, the work of bellini [10], where the snap-buckling problem has been solved via a novel mathematical model, the article of ramesh and krishnamoorthy [11], where the dynamic relaxation method has been used to analyze the inelastic post-buckling of trusses, and the work of thai and kim [12], where space truss structures with geometric and material nonlinearities have been analyzed for their inelastic large deflections. although solving a system of nonlinear equations could prove to be very difficult, literature has provided a number of methods for this purpose, nevertheless they do little in improving the computation time required by this procedure. the newton–raphson method, which attacks the problem via an iterative procedure of solving linear algebraic equations (corresponding to their non-linear counterparts), is perhaps one of the best techniques for solving nonlinear equations since it provides the quadratic convergence characteristics well suited for this application. there are a number of iterative methods specifically developed to improve the performance of the newton-raphson technique [13-15], but they often have questionable practicality mainly because they still follow an approach that requires the computation of second or higher derivatives, which can be very time-consuming and computationintensive. there are some techniques that can omit the second derivatives (hessian matrix) from this process [16, 17], and these are classified into two groups: one-step techniques, and two-step techniques [14]. two-step techniques, like the one used in this paper, are in fact the combinations of the newton-raphson method and another one-step method. this approach, constructed in conformity with predictor-corrector methods, and so taking most frequently newton's method in the first iteration, is used in this paper. the common iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 159 disadvantages of one-point methods, most notably their high computational intensity and their inadequate convergence, can be sidestepped using a series of very effective techniques known as multipoint iterative solvers [18]. rezaiee-pajand et al. [19, 20] the efficiencies and capabilities of residual load minimization, normal plane, updated normal plane, cylindrical arc length, work control, residual displacement minimization, generalized displacement control, and modified normal flow were evaluated. rezaieepajand and naserian [21] employed incremental–iterative methods for the base of iteration steps by setting each area to zero, and minimizing its perimeter separately. application of cubic spline on large deformation analysis of structures has been proposed by saffari et al. [22]. a dynamic relaxation (dr) method, suitable for nonlinear structural analysis, has been suggested by rezaiee-pajand and estitri [23]. the weakness of the newton-raphson method is that, in the course of computing structural response, having a solution point sufficiently close to the limit point will cause the method to exhibit significant divergence, possibly leading to significant errors in computation of failure loads. to deal with this problem, one can use a number of methods provided by literature, most important of which are classified as displacement control methods [24]. in the present study, to compensate for this inability of the newton-raphson method, a normal flow algorithm is used. the objective of this study is to assess the optimization of the structures that must undertake large deformations. a eulerian formulation is used to model the geometrically nonlinear structural behaviors and then a normal flow algorithm is used, which is a displacement-control iterative method to determine the point of equilibrium. finally, particle swarm optimization (pso) is used with the objective of effectively reducing the computational intensity of the analysis. 2. geometrical nonlinear analysis of space trusses the system equilibrium equations are generally defined as: }{)}({ pf  (1) where {f} is the resultant of the nodal internal loads and {p} is the external nodal force or load. according to equation expressing the member force deformation, {f} is a function of {δ} and is predominantly non-linear. equation 1, in its differential form, is expressed as: }{}]{[ p (2) in the above equation, {∆δ} is the increment of displacement, {δp} is the increment of load, and [τ] denotes the tangent stiffness matrix. 2.1 tangent stiffness matrix of the structural member the end displacements have an incremental relationship with end member forces, which is expressed by the following equation [5]:     vtf  (3) in the above equation, [t] is the tangent stiffness matrix of the member. the following formula provides a method to calculate this parameter: iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 160       gqbb l ae t t       (4) the structure of geometric matrix [g] is as follows [5]:                               )()( )()( )()( )()( )()( )()( 1 2222 2222 2222 2222 2222 2222 mlmnnlmlmnnl mnnllmmnnllm nllmnmnllmnm mlmnnlmlmnnl mnnllmmnnllm nllmnmnllmnm l g (5) 3. nonlinear solution algorithm 3.1 newton-raphson technique of several methods available to deal with non-linear problems, the newton-raphson technique is certainly one of the best and is generally the basis of other iterative algorithms developed to deal with this problem. while this section presents a brief introduction to this technique, the more detailed information regarding this subject can be found in [2]. this technique starts its first iteration with a procedure similar to the one followed in the linear incremental method, with the only difference being the calculation of member forces and their transformation into the global coordinates at the end of procedure. the next step of this technique is the calculation of imbalance between the external loads and the internal nodal forces. this procedure of iteration continues until it reaches a predefined termination condition, often based on a convergence criterion. 3.2 modified newton-raphson technique the difference between the normal newton-raphson technique and the modified newton-raphson technique is the frequency of reformation of the tangent stiffness, which will be repeated for every iteration of the normal technique, but will be done only once in the first iteration of the modified one. omitting the reformation process increases the number of iterations required to reach convergence, but reduces the computational intensity of each single iteration, leading to a shorter run time for the entire process. 4. normal flow algorithm this paper uses the normal flow algorithm, which is an effective approach for tracing the complete equilibrium path for this very same purpose. now, let i be the number of the steps, j be the number of the modifying iterations, and   j ip be the total load on the structure. in that case:    refjtotiji pp  (6) where j toti is the product of a total ratio and {pref} is a reference external load exerted via a series of load increments. figure 1 shows the schematic representation of this method. more detailed information regarding this method can be found in [5]. iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 161 fig. 1: schematic representation of the normal flow method. the following formulation is the general form of a nonlinear system of equilibrium equations: ),(),( 1111   ji j i j i j i j i fsj  (7) in this formulation, ),( 11  j i j ij  represents the jacobian matrix of order n×(n+1), and j is denotes the step size of newton–raphson technique. this step size can be calculated via eq. (8):                   ),(),( ),( 1111 11 j i j i j i j ij i j i ff j (8) the step size of newton–raphson technique for a normal flow algorithm can be determined by finding the minimum of an infinite number of solutions obtainable for eq. (9). the procedure stated below must be followed to find this minimum solution: first, the following equation should be used to calculate an initial solution {v}:         11   jirefjiji qpv  (9) where: j ii tj ii j ir tj iij i }{]}[{ }{]}[{      (10) in the above equation,   1 jiq denotes the vector of the unbalanced forces,   j ii represents the vector of tangential displacement at the point of convergence; and   j ir denotes the vector of unbalanced displacements such that, iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 162      ref j j i j i conv toti j i j i pfq              2 11 1 1  (11) where   j if denotes the vector representing the resultant of internal forces at the nodes. next, the following equation should be used to obtain the vector of unbalanced force:       11   ji j ir j i q (12) and finally, the following equation should be used to obtain the minimum solution of the norm:     jii i j ii t j i v v }{ }{}{      (13) this means that the process of calculating the unknown vectors {v} and   j ir by solving the system of equations should be repeated at each iteration. 5. particle swarm optimization (pso) this study uses the pso method to optimize its objective. authors of [25] have reported that the use of binary pso (bpso) for structural optimization has resulted in significant improvement in solutions. first proposed by eberhart et al. [26] in the 1990s, pso has been inspired by the social and group behavior of animals such as fish, insects, and birds. the mentioned authors were seeking to perform a socio-cognitive study on the group behavior of bird swarms and to achieve that purpose, they developed this amazingly effective optimization algorithm. this algorithm starts with a number of particles (or birds), which are spread randomly in the search space of the objective function (swarm of birds in a habitat). here, particles represent the potential solutions to the problem. at each iteration, all particles move around the search space based on the best positions (solutions) obtained at the previous iteration. this algorithm obtains this best solution by calculating the objective function and the fitness of all particles in the search space [26]. algorithm moves the position of particles based on the following equations: )(rc)(rc li ll i l i l i ll i xgbestxpbestvv   2211 1  (14) 11   li l i l i vxx (15) where, k is the number of iterations, k ix is the current position of i-th particle and k iv is the velocity of this particle; pi is the best position previously attained by the i-th particle (called pbest) and pg is the best position attained globally by all particles (called gbest); r1 and r2 are two uniform random sequences generated from interval [0, 1]; wk denotes the inertia weight that will be used to modify (reduce) the previous velocity of the preserved particle. according to shi and eberhart [25], the cognitive and social scaling parameters c1 and c2, should be selected such that c1 = c2 = 2.0, which consequently allows the product c1r1 or c2r2 to have a mean of 1. the minimum and maximum possible velocities are also incorporated into this design and are denoted by max iv and min iv (fig. 2). iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 163 fig. 2: flowchart of pso. this paper uses a modified euclidian criterion in the following form to express the displacement control:      j i tj i j i tj i }{]}[{ }{]}[{ (16) in the above relationship, ε is the defined error of calculation. in the updating scheme used in this paper, the number of performed iterations affects the load increment parameter. meanwhile, this algorithm uses the following formula to determine the sign of the determinant of the tangential stiffness matrix resulting from the previous step:          m dj i j i j j 1 (17) in the above formula, jd is the predefined number of iterations, jm is current count of performed iterations minus one, and γ is a constant. 6. numerical results in this section, the results of a computer program developed to implement the algorithm described in previous section are presented. the duration of calculation, or total runtime, can be obtained by entering the corresponding command into the program. this program is run on a 64–bit pc with a core™ i7-6700t processor, 8m cache, and uses similar parameters for all problem instances. these problem instances act as a measure to gauge the performance of the proposed method. here, the objective is to perform elastic iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 164 analysis, elastic post–buckling (epb) analysis, and inelastic post–buckling (ipb) analysis on typical truss structures using the proposed method, the conventional newton–raphson technique and other sub-stepping algorithms. in all tests, r = 0.4, x1 = 50 and x2 = 100, and the maximum error is defined as ε = 10-5 [12]. it should also be noted that all algorithms are tested with the smallest possible steps to ensure a uniform and accurate solution. 6.1 problem instance 1 the following geodesic dome truss has 156 members with identical cross-sections a = 6.5 cm2, and i = 1 cm4, and 61 nodes with outer ones attached by pin supports (ramesh and krishnamoorthy [11]). fig. 3: geodesic dome truss from problem instance 1 (all dimensions in cm) [11]. this dome is subjected to a point vertical load of p = 8 kn exerted on its center. here, the parameters of eq. (17) are 01.0 1 1  , λmax = 0.5, γ = 0.1, jd = 10, jmax = 100. the following equation expresses the height of each point of truss with respect to the x-y coordinates: 84.60)2.7( 222  zyx (18) this truss is built with a material with an elasticity modulus of e = 6895 kn/cm2 and yield strength of fy = 400 kn/cm2. figure 4 shows the load–displacement curves obtained as a result of elastic analysis, post–buckling (epb) analysis, and inelastic post–buckling (ipb) analysis conducted on this truss structure. fig. 4: load–displacement curves for the apex of a geodesic dome truss. -4 -3 -2 -1 0 1 2 3 4 5 0 2 4 6 8 10 vertical displacement at apex (cm) p (k n ) el a sti c anal ysi s epb anal ysi s ipb anal ysi s iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 165 the run times achieved in each mode of analysis by the proposed method and the conventional newton–raphson technique are shown in table 1. this result demonstrates the superiority of the proposed method in all modes of analysis. table 1: the runtime achieved for problem instance 1 (sec) flow algorithm pso method improvement% 106 71 33.02 6.2 problem instance 2 the semi-spherical truss shown in fig. 5 is composed of 168 elements with identical cross-sections with a = 50.431 cm2, and i = 52.94 cm4, and 73 nodes with total freedom degree of 147 [12]. in this problem, a vertical load p = 500 kn is applied on the apex of this truss. the pin supports defined at the outer nodes of the truss restrict the off-plane displacements. fig. 5: semi-spherical truss from problem instance 2 (all dimensions in cm) [12]. this truss is built with a material with elasticity modulus of e = 2.04×104 kn/cm2 and yield strength of fy = 25 kn/cm2. in this problem, the parameters of eq. (17) are 01.011  , 2max  , 5dj , 100max j , 1.0 . the load–displacement curves obtained via elastic analysis, post–buckling (epb) analysis, and inelastic post–buckling (ipb) analysis conducted on this truss are shown in fig. 6. the run times achieved in each mode of analysis by the proposed method and other tested technique are shown in table 2. these runtimes also show that the proposed method outperforms other algorithms and achieves the quickest convergence. iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 166 table 2: the runtime achieved for problem instance 2 (sec) flow algorithm pso method improvement% 99 77 22.22 fig. 6: load–displacement curves for node 2 of the semi-spherical truss. 6.3 problem instance 3 in this problem, a schewdeler’s truss is assessed with properties stated as ea = 640×103 kn, fy = 25 kn/cm2, i = 30.04 cm4 built in the form of 264 elements and 97 nodes. here, the outer nodes are again attached with pin supports [7]. fig. 7: dome truss from problem instance 3 (all dimensions in cm) [7]. this truss is subjected to a point load of p = 50 kn exerted at its apex. in this problem, the parameters of eq. (17) are 01.0 1 1  , 1max  , 1.0 , 2dj , 100max j . the load– displacement curves obtained through elastic analysis, post–buckling (epb) analysis, and -600 -400 -200 0 200 400 600 800 1000 -4 -3 -2 -1 0 1 2 3 vertical displacement at node 2 (mm) p (kn) el asti c anal ysi s epb anal ys i s ipb analys is iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 167 inelastic post–buckling (ipb) analysis performed on this truss are shown in fig. 8. the analyses conducted in three modes by the proposed method and other tested algorithms produced 12 sets of results. table 3 compares these techniques by examining their corresponding runtimes. as before, these runtimes demonstrate that the proposed method outperforms other algorisms and exhibits a clearly superior runtime. table 3: the runtime achieved for problem instance 3 (sec) flow algorithm pso method improvement% 104 83 20.19 fig. 8: load–displacement curve for the apex node of the truss. 7. conclusion the objective of this paper was to facilitate the process of complex structural analyses by developing a simple but equally accurate higher order predictor-corrector. the results obtained by this paper show that the runtime of nonlinear analysis can be reduced by about 20–30% through the use of a hybrid method composed of pso and newton-raphson algorithms. this paper developed its method based on two functions to accelerate the convergence and compared the obtained results with the results of a conventional newton–raphson technique. in the course of this study, authors developed a computer program to implement the proposed method and solve the systems of nonlinear equations in incremental forms through a numerical technique. several problem instances were solved by the proposed method and the results were compared with those of other algorithms. these comparisons demonstrated the ability of the proposed method to return equally accurate solutions through a lower number of iterations and a shorter runtime. references [1] crisfield ma, shi j. (1991) a review of solution procedures and path-following techniques in relation to the non-linear finite element analysis of structures. nonlinear computational mechanics: state of the art, 47-68. [2] crisfield ma. (1991) non-linear finite element analysis of solids and structures. 1991; vol. 1 -30 -20 -10 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 vertical displacement of center node (cm) p (k n ) el as ti c anal ys i s epb anal ysi s ipb anal ysi s iium engineering journal, vol. 17, no. 2, 2016 mansouri et al. 168 [3] bathe kj, cimento ap. (1980) some practical procedures for the solution of nonlinear finite element equations. computer methods in applied mechanics and engineering, 22:59-85. [4] wempner ga. (1971) discrete approximations related to nonlinear theories of solids. int j of solids and structures, 7:1581-1599. [5] saffari h, fadaee mj, tabatabaei r. (2008) nonlinear analysis of space trusses using modified normal flow algorithm. j of structural engineering,134:998-1005. [6] papadrakakis m, gantes cj. (1988) truncated newton methods for nonlinear finite element analysis. computers and structures, 30:705-714. [7] greco m, gesualdo far, venturini ws, coda hb. (2006) nonlinear positional formulation for space truss analysis. finite elements in analysis and design, 42:1079-1086. [8] huang nc, vahidi b. (1968) dynamic snap-through of an elastic imperfect simple shallow truss. zeitschrift für angewandte mathematik und physik zamp, 19:501-509. [9] kassimali a, parsi-feraidoonian h. (1987) strength of cable trusses under combined loads. j of structural engineering (us), 113:907-924. [10] bellini px. (1972) the concept of snap-buckling illustrated by a simple model. international j of non-linear mechanics, 7:643-650. [11] ramesh g, krishnamoorthy cs. (1994) inelastic post-buckling analysis of truss structures by dynamic relaxation method. int j for numerical methods in engineering, 37:3633-3657. [12] thai ht, kim se. (2009) large deflection inelastic analysis of space trusses using generalized displacement control method. j of constructional steel research, 65:1987-1994. [13] chun c. (2006) a new iterative method for solving nonlinear equations. applied mathematics and computation, 178:415-422. [14] petković ms, petković ld. (2007) a one parameter square root family of two-step rootfinders. applied mathematics and computation, 188:339-344. [15] petković ms, petković ld. (2010) families of optimal multipoint methods for solving nonlinear equations: a survey. applicable analysis and discrete mathematics, 4:1-22. [16] babajee dkr, dauhoo mz, darvishi mt, barati a. (2008) a note on the local convergence of iterative methods based on adomian decomposition method and 3-node quadrature rule. applied mathematics and computation, 200:452-8. [17] kassimali a, abbasnia r. (1991) large deformation analysis of elastic space frames. j of structural engineering (us), 117:2069-2087. [18] saffari h, mansouri i. (2011) non-linear analysis of structures using two-point method. int j of non-linear mechanics, 46:834-840. [19] rezaiee-pajand m, ghalishooyan m, salehi-ahmadabad m. (2013) comprehensive evaluation of structural geometrical nonlinear solution techniques part ii: comparing efficiencies of the methods. structural engineering and mechanics, 48:879-914. [20] rezaiee-pajand m, ghalishooyan m, salehi-ahmadabad m. (2013) comprehensive evaluation of structural geometrical nonlinear solution techniques part i: formulation and characteristics of the methods. structural engineering and mechanics, 48:849-878. [21] rezaiee-pajand m, naserian r. (2015) using residual areas for geometrically nonlinear structural analysis. ocean engineering, 105:327-335. [22] saffari h, shojaee s, rostami s, malekinejad m. (2014) application of cubic spline on large deformation analysis of structures. int j of steel structures, 14:165-72. [23] rezaiee-pajand m, estiri h. (2016) mixing dynamic relaxation method with load factor and displacement increments. computers and structures, 168:78-91. [24] riks e. (1979) an incremental approach to the solution of snapping and buckling problems. int j of solids and structures, 15:529-51. [25] shi y, eberhart rc. (1999) empirical study of particle swarm optimization . proceedings of the 1999 congress on evolutionary computation, cec 1999, 3, art. no. 785511, 1945-1950, doi: 10.1109/cec.1999.785511. [26] eberhart rc, shi y, kennedy j. (2001) swarm intelligence. morgan kaufmann, san francisco. microsoft word 236-931-3-ed completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abol hassan et al. 179 mammalian cell culture clarification: a case study using chimeric anti-cea monoclonal antibodies mohamed ali abol hassan 1 , abdul wahab mohammad 2 and badarulhisam abdul rahman 1 1 department of process science, innobiologics sdn bhd, nilai, negeri sembilan, malaysia. 2 department of chemical and process engineering, faculty of engineering and built environment, universiti kebangsaan malaysia, bangi, selangor, malaysia. wahabm@vlsi.eng.ukm.my abstract: the extracellular expression of monoclonal antibodies (mabs) in mammalian cell culture provides both opportunities and restrictions for the design of robust harvest and clarification operations. with advances in cell culture media and cell lines, it is now possible to achieve high titers of over 5 g/l for mabs. however, mammalian cells are sensitive to breakage due to shear stress that can result in release of proteases and other host cell proteins (hcps) which eventually affects product stability and purity. there is larger number of mabs undergoing clinical development and it has placed significant importance on platform technologies of process development. generally, centrifugation and microfiltration are the primary harvest techniques used in the industry and depth filtration is also used as a step operation on clarification. this study compares the unit operations; centrifugation, microfiltration and depth filtration for maximum recovery of monoclonal antibodies. the results have shown that the depth filtration as more suitable operation for mammalian cell culture clarification since it gives 96% recovery of mabs in comparison to centrifugation and microfiltration. abstrak: pengungkapan luar sel dari antibodi monoklon (monoclonal antibodies ((mabs) dalam kultur sel mamalia memberi ruang dan batasan terhadap reka bentuk penuaian yang cekap dan penerangan operasi. dengan kemajuan dalam media sel kultur dan cell lines (produk yang berupa sel kekal yang digunakan untuk tujuan kajian biologi), kini adalah berkemungkinan untuk memperolehi titer tinggi melebihi 5g/l untuk mabs [2]. walaupun begitu, sel mamalia sensitif terhadap retakan disebabkan tegasan ricih yang menyebabkan pengeluaran protease dan hos sel protein yang lain, (host cell proteins (hcps)) akhirnya mempengaruhi kestabilan dan keaslian produk. terdapat mabs dalam jumlah besar yang masih menjalani pembangunan klinikal dan sesungguhnya ini penting sebagai satu landasan teknologi dalam proses pembangunan. umumnya pengemparan dan mikropenurasan merupakan teknik asas tuaian dalam industri dan penurasan dalam juga digunakan sebagai satu pengendalian langkah dalam penjelasannya. kajian ini membandingkan operasi unit: pengemparan, mikropenurasan dan penurasan dalam untuk perolehan antibodi monoklon yang maksima. keputusan menunjukkan penurasan dalam adalah operasi yang lebih sesuai untuk penjelasan kultur sel mamalia kerana ia memberikan perolehan 96 % mabs berbandingkan dengan cara pengemparan dan mikropenurasan. keywords: monoclonal antibodies (mabs); centrifugation; microfiltration; depth filtration; host cell proteins (hcps) iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abol hassan et al. 180 1. introduction over the last decade, advances in recombinant protein technologies have overshadowed efforts in understanding the specific needs and problems of downstream processing (dsp). as a result the operational limitations of dsp, along with its costs, are now widely accepted as a major obstacle in the ability to rapidly develop and place commercially viable biotechnological products in the market place. in particular, the monoclonal antibodies (mabs) occupy an important niche within the biopharmaceutical industry [1]. currently, there are more than 27 monoclonal antibodies commercially approved and they are used to treat a wide range of clinical indications [3]. the wide range of mabs reflects their ability to target a number of cellular receptors and cytokines, either to block or to augment their function, to induce their destruction through antibodydependent cell cytotoxocity (adcc), or to activate the complement cascade [4]. among the monoclonal antibodies, the chimeric anti-carcinoembryonic antigen (cea) monoclonal antibody is useful for the immunocytochemical detection of colon cancer tissue [5]. in 1965, drs. gold and freedman from mcgill university were the first to describe the present tumor associated carcinoembryonic antigen (cea) in human colon cancer tissue extracts [6]. anti-cea could be measured in serum from patients with colorectal and other carcinomas using sensitive radioimmunoassay [7]. carcinoembryonic antigen has proven to be suitable target antigen for the detection of primary and metastatic colorectal and is currently being explored as a possible target for antibodymediated therapy [8]. generally, the cell culture process development and commercial production for monoclonal antibody can be divided into two major areas i.e. upstream and downstream. the upstream operations include cell line development, media optimization, and cell culture process optimization. the downstream operations comprises of cell harvest, antibody capture, viral inactivation, and polishing steps. harvest of biotechnological products from cell culture or fermentation process streams is often performed by a combination of several unit operations due to the gelatinous, compressible and of low density nature of cell culture. eventually, the drivers for the process design include maximizing product recovery, scalability, robustness and clarification of the process stream while operating in a physical and chemical environment where the product is stable. the harvest approach is dependent on the mode of expression of the target protein. for intracellular expression, the first step is cell concentration and followed by cell disruption to release the target protein into solution. after cell disruption, the cell debris is removed and protein solution is further clarified using filtration. on the other hand, the first step in harvest for the extracellular expression of target protein is to remove the cells via centrifugation or microfiltration or depth filtration. the density of the cell culture, shear sensitivity of the cells and stability of the product are all important cell line-specific characteristics that influence the harvest process design. relative to other types of cells (bacteria, yeasts, fungi and plants) used in expression of protein products, mammalian cells are favored because of the complexity and the large size of mabs, which comprise two heavy and two light chains joined together by covalent and noncovalent bonds to achieve the well-known y-shaped conformation. furthermore, mabs are glycoproteins whose glycan chains could play a significant role in their biological activity, and only mammalian cells produce the correct glycan chain structures [9]. mammalian cell culture systems such as chinese hamster overy (cho), sp 2/0 and nso cells express monoclonal antibodies extracellularly [10-11,12]. with advances in cell culture media and cell lines; it is now possible to achieve high titers and high cell densities iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abol hassan et al. 181 in fermentation systems. however, mammalian cells exhibit very low shear resistance which tends to easier cell breakage that leads to release of proteases and other host cell proteins into the broth. this can affect product stability and purity. cell culture media are fairly rich and can promote bacterial growth in the event of contamination. as a result, the hold times for both the production bioreactor after the termination of cell culture and for the harvest operations need to be limited. the large number of mabs undergoing clinical development has placed significant pressure on process development organizations to harmonize efforts through the adoption of platform technologies. this paper will focus on harvest of mammalian cells (nso) and the performance comparison of the above mentioned unit operations for clarifying cell broth in order to maximize the recovery of monoclonal antibodies. 2. methodology figure 1 illustrates the different approaches that were compared. option a involves a combination of centrifugation and depth filtration, option b consists of two depth filtration as primary and secondary and option c has a microfiltration step for clarification of the feed stream. 2.1 materials the fermentation broth was the nso cells with 5% fetal bovine serum (fbs) with the following profile: total viable cell density: 2.07 x 10 6 cells/ml with overall 75.85% and the target protein: chimeric anti-cea was expressed extracellularly (table 1 shows the culture specification). table 1: culture specifications during harvest. the high cell density monoclonal antibodies culture broth was produced at laboratory scale. the centrifuge used for the clarification work is sigma lab centrifuge 4k15 (type: tubular bowl centrifuge/solid wall centrifuge). two types of single use, disposable depth filter is carefully chosen among the other filters with the 1 st filter (millistak+hc mini capsule –dohc) carries retention range of 84 µ m / 1.5-0.6 µm as primary filter and 2 nd filter (millistak+hc mini capsule –b1hc) retention range of 0.7-0.3/ <0.1/0.1 µ m as secondary filter. both filters are made of cellulosic membrane with inorganic filter aid. flat cassette cellulose based membrane with pore size of 0.45 µ m and the surface area of 0.1 m 2 was obtained from sartorius stedim and used on kvick lab system, which is full featured with rotary lobe pump that can be used for shear-sensitive products, for microfiltration. turbidity 96 ntu mass of total protein 5735.9 mg mass of protease 0.859 mg mass of target product (chimeric anti-cea mabs) 16.2 mg iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abol hassan et al. 182 for the target protein analysis, enzyme linked immunosorbant assay (elisa) was performed using the pierce human igg, whole molecule (cat no: 31154, from thermo scientific) was used as standard antibody, anti-human igg : fc specific (cat no: i2136, from sigma-aldrich) as capture antibody, anti-human igg: γ-chain specific peroxidase conjugate (cat no: a6029, from sigma-aldrich) as secondary antibody and ultra tnb substrate (cat no: 010m1107, sigma-aldrich) for detection. the protease concentration and total protein present in the sample was quantified by colorimetric protease assay kit (pierce, u.s) and bca protein assay kit (pierce, u.s) respectively. 2.2 experimental methods the sample was centrifuged at ambient temperature with the relative centrifugal force (rcf) of 4000 x g for 10 minutes. after centrifugation, centrate was stored in the cold room (~4°c) prior to next process. during depth filtration, depth filters were first flushed with sufficient amount of buffer to thoroughly wet filter media and reduce the level of extractables. the centrate that was agitated and maintained at cold room (2-8°c) was then pumped using watson-marlow® peristaltic pump through the filters at constant flow rate of 200lmh. filtrate volume and differential pressure were recorded at different time intervals. similarly, the procedure was followed for both primary & secondary depth filtration. fig. 1: the outline for comparison of unit operations on harvest and clarification of mammalian cell culture [2]. iium engineering journal, vol. the apparatus used to perform the microfiltration experiment is presented schematically in fig. 2. a rotator lobe pump was used to circulate the fermentation broth and controls permeate flux. normalized clean w loading of feed material to the mf system. the targeted protein is stable in postproduction broth at room temperature. therefore, during mf process, the retentate was maintained at room temperature (2326°c) to reduce were set as feed pressure (pin) as 7 pressure (pr) maintained at zero. the target protein (chimeric anti (enzyme-linked immunosorbant assay). in elisa, used as standard. first, the 96 specific diluted in coating solution in the ratio of 1:1000 and incubated for overnight. after rinsing with 1 x 200 incubated for 2 hours followed by washing with 3 x 200 µ l washing buffer. a 100 µ l sample or standard solution was added to each well followed by adding secondary antibody anti-human igg: γ ratio of 1:2500 and incubated for 2 hours. then, the plate was washing buffer followed by addition of 100 µl tnb substrate and incubated for 15mins. lastly, the reaction was stopped by 2.5 colored absorbance was measured at a wavelength of 405 (biotek instruments, inc., winooski, vt). samples were diluted 100 to 12,000 diluent (0.01% tween 20 in 1x pbs) prior to assay depending on the antibody concentration. the shear sensitive mammalian cells release proteases during breakage of cells in any unit operations. the amount of protease present in the sample was determined using colorimetric protease assay kit and the total protein was quantified using bca protein assay kit (pierce, u.s). target protein concentration was determined for feed, centrate, permeate, retentate and filtrate pools were used to calculate protein recovery. was measured on the feed, centrate and filtrate samples using hach® portable turbidity meter in the unit of ntu. mass balances were performed using weights of all the feeds, centrates and filtrates. all the collection tanks were tared so that th volumes could be calculated for mass balance. fig. 2: basic flow path for cross flow filtration process g journal, vol. 12, no. 4, 2011: special issue on biotechnology abol hassan et al. 183 the apparatus used to perform the microfiltration experiment is presented 2. a rotator lobe pump was used to circulate the fermentation broth and controls permeate flux. normalized clean water permeability was tested prior to loading of feed material to the mf system. the targeted protein is stable in postproduction broth at room temperature. therefore, during mf process, the retentate was maintained at 26°c) to reduce fluid viscosity and maximize flux. the parameters were set as feed pressure (pin) as 7 psi, permeate pressure (pp) as 2 psi and retentate pressure (pr) maintained at zero. the target protein (chimeric anti-cea mabs) recovery was determined by elisa linked immunosorbant assay). in elisa, human igg, whole molecule standard. first, the 96-well plate were coated with 100 µl of anti-human igg : fc diluted in coating solution in the ratio of 1:1000 and incubated for overnight. µ l washing buffer, 200 µ l blocking buffer was added and incubated for 2 hours followed by washing with 3 x 200 µ l washing buffer. a 100 µ l sample or standard solution was added to each well followed by adding secondary human igg: γ-chain specific peroxidase conjugate diluted in 1xpbs in the ncubated for 2 hours. then, the plate was rinsed with 3 x 200 washing buffer followed by addition of 100 µ l tnb substrate and incubated for 15mins. stly, the reaction was stopped by 2.5 m sulfuric acid. the formation of golden yellow colored absorbance was measured at a wavelength of 405 nm via microplate reader biotek instruments, inc., winooski, vt). samples were diluted 100 to 12,000 uent (0.01% tween 20 in 1x pbs) prior to assay depending on the antibody the shear sensitive mammalian cells release proteases during breakage of cells in any unit operations. the amount of protease present in the sample was determined using colorimetric protease assay kit and the total protein was quantified using bca protein . target protein concentration was determined for feed, centrate, filtrate pools were used to calculate protein recovery. was measured on the feed, centrate and filtrate samples using hach® portable turbidity meter in the unit of ntu. mass balances were performed using weights of all the feeds, centrates and filtrates. all the collection tanks were tared so that the accurate mass and volumes could be calculated for mass balance. : basic flow path for cross flow filtration process abol hassan et al. the apparatus used to perform the microfiltration experiment is presented 2. a rotator lobe pump was used to circulate the fermentation broth ater permeability was tested prior to loading of feed material to the mf system. the targeted protein is stable in postproduction broth at room temperature. therefore, during mf process, the retentate was maintained at fluid viscosity and maximize flux. the parameters psi, permeate pressure (pp) as 2 psi and retentate cea mabs) recovery was determined by elisa human igg, whole molecule was human igg : fc diluted in coating solution in the ratio of 1:1000 and incubated for overnight. µ l washing buffer, 200 µ l blocking buffer was added and incubated for 2 hours followed by washing with 3 x 200 µ l washing buffer. a 100 µl sample or standard solution was added to each well followed by adding secondary diluted in 1xpbs in the rinsed with 3 x 200 µl washing buffer followed by addition of 100 µl tnb substrate and incubated for 15mins. ulfuric acid. the formation of golden yellownm via microplate reader biotek instruments, inc., winooski, vt). samples were diluted 100 to 12,000-fold with uent (0.01% tween 20 in 1x pbs) prior to assay depending on the antibody the shear sensitive mammalian cells release proteases during breakage of cells in any unit operations. the amount of protease present in the sample was determined using colorimetric protease assay kit and the total protein was quantified using bca protein . target protein concentration was determined for feed, centrate, filtrate pools were used to calculate protein recovery. turbidity was measured on the feed, centrate and filtrate samples using hach® portable turbidity meter in the unit of ntu. mass balances were performed using weights of all the feeds, e accurate mass and iium engineering journal, vol. 3. results and discussion the harvested volume was divided proportionally on centrifugation followed by depth filtration (option a), primary microfiltration on tangential flow filtration (tff 3.1 centrifugation this unit operation in option a used a sigma lab centrifuge 4k15 having universal swing, threaded bucket capable of 4x 50 divided into 40 ml per 50 ml transferred to a beaker and the pellets were discarded. the samples were taken before and after the operation for turbidity measurement, total protein determination, quantification of protease released and recovery of target protein (table 2 shows the results on option a). the volume recovered after the centrifugation followed by depth filtration was 97%. generally, the ratio of equivalent area (termed as sigma factor, centrifuge) and the flow rate through the chamber, q, is maintained on scale up process. however, keeping q/∑ ratio identical may still lead to underperformance at a larger scale. this lower efficiency is attributed to shear damage or hindered settling in centrifugation [13]. the shear happens during centrifugation damages cells & cell debris releases proteases which are highly evident in this study as option a shows 12.1 protease concentration and also generates submicron particles that were separated by depth filtration. shear sensitivity is main concern for mammalian cell it is main cause for release of proteases that could affect the stability of the target protein and host cell proteins (hcp) and fig. 3: filtration profile of millipo 3.2 depth filtration this option involved using a two depth filters from millipore (millistak+ hc mini capsule filters). first was the more open filter in primary tighter grade filter in secondary depth filtration. the pressure and filtrate flow rate readings were taken. in this no turbidity breakthrough was observed however pressure g journal, vol. 12, no. 4, 2011: special issue on biotechnology abol hassan et al. 184 results and discussion the harvested volume was divided proportionally on centrifugation followed by depth filtration (option a), primary and secondary depth filtration (option b) and microfiltration on tangential flow filtration (tff – option c). tion in option a used a sigma lab centrifuge 4k15 having universal swing, threaded bucket capable of 4x 50 ml falcon tubes. therefore, the sample was ml falcon tube. after centrifugation, the supernatant was r and the pellets were discarded. the samples were taken before and after the operation for turbidity measurement, total protein determination, quantification of protease released and recovery of target protein (table 2 shows the results on option a). volume recovered after the centrifugation followed by depth filtration was 97%. generally, the ratio of equivalent area (termed as sigma factor, ∑, in disk stack centrifuge) and the flow rate through the chamber, q, is maintained on scale up process. ratio identical may still lead to underperformance at a larger scale. this lower efficiency is attributed to shear damage or hindered settling in centrifugation . the shear happens during centrifugation damages cells & cell debris and e releases proteases which are highly evident in this study as option a shows 12.1 protease concentration and also generates submicron particles that were separated by depth filtration. shear sensitivity is main concern for mammalian cell culture clarification since it is main cause for release of proteases that could affect the stability of the target protein and dna, all of which can reduce product quality as well filtration profile of millipore depth filter carried out at flow rate of 200lmh (♦ pressure). this option involved using a two depth filters from millipore (millistak+ hc mini capsule filters). first was the more open filter in primary depth filtration followed by a tighter grade filter in secondary depth filtration. the pressure and filtrate flow rate readings were taken. in this no turbidity breakthrough was observed however pressure abol hassan et al. the harvested volume was divided proportionally on centrifugation followed by secondary depth filtration (option b) and tion in option a used a sigma lab centrifuge 4k15 having universal alcon tubes. therefore, the sample was alcon tube. after centrifugation, the supernatant was r and the pellets were discarded. the samples were taken before and after the operation for turbidity measurement, total protein determination, quantification of protease released and recovery of target protein (table 2 shows the results on option a). volume recovered after the centrifugation followed by depth filtration was 97%. ∑, in disk stack centrifuge) and the flow rate through the chamber, q, is maintained on scale up process. ratio identical may still lead to underperformance at a larger scale. this lower efficiency is attributed to shear damage or hindered settling in centrifugation and eventually releases proteases which are highly evident in this study as option a shows 12.1 µg/ml of protease concentration and also generates submicron particles that were separated by depth culture clarification since it is main cause for release of proteases that could affect the stability of the target protein dna, all of which can reduce product quality as well [2]. ied out at flow rate of 200lmh this option involved using a two depth filters from millipore (millistak+ hc mini depth filtration followed by a tighter grade filter in secondary depth filtration. the pressure and filtrate flow rate readings were taken. in this no turbidity breakthrough was observed however pressure iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abol hassan et al. 185 breakthrough is normally the basic limitation for constant flow depth filtration (fig. 3). in this constant flow filtration at 200lmh flux rate, the flow was steady and smoother with pressure increase only until 6 psi since maximum allowable differential pressure for minicapsule filter is 22 psi. the samples were taken before and after the operation for turbidity measurement, total protein determination, quantification of protease released and recovery of target protein (table 2 shows the results on option b). the volume recovered after the primary and secondary depth filtration about 94%. when the solids level is low, fine particles bind to the filter media due to electrostatic or other physicochemical interactions. once binding sites in the filter media are fully occupied, fine particles flow through in the filtrate, resulting in turbidity breakthrough. on the other hand, with high solids containing feed, pore, or flow channels within the filter media were progressively clogged with captured solids and the differential pressure across the filter gradually increases in response. in this case, mechanical sieving is the main capture mechanism since the characteristics (solids content, particle size distribution) of feedstock need to be considered while developing this application. table 2: results on all three different approaches on mammalian cell culture clarification. 3.3 microfiltration by tangential flow filtration (tff) in this application oriented study, the microfiltration technology is used to harvest the mammalian cells and cell debris from the fermentation broth. here, the broth was concentrated slightly to the permeate sieving the cells and debris on membrane and two diafiltration volumes (dv) of buffer were performed. target protein was washed into permeate tank and the cells were retained in the retentate tank. for the cross-flow mf, the membrane permeability is high since it has pore size of 0.45 µ m that nearly all the crossflow is converted to filtrate with very little tmp is applied. in this process, the 1.5 psi feed characteristics after centrifugation followed by depth filtration [option a] after primary & secondary depth filtration [option b] after microfiltration by tff [option c] initial volume (ml) 2800 1000 800 1000 turbidity measurement (ntu) 96 3 1 4 mass of total protein (mg) 5735.9 2306.7 886.18 1776.5 protease concentration (µg/ml) 0.31 12.1 2.8 4.1 product concentration (µg/ml) 5.79 4.104 5.955 5.730 iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abol hassan et al. 186 of transmembrane pressure (tmp) was applied during the operation. mostly process starts with very high initial flux and followed by dramatic flux decay due to high wall concentrations and high membrane fouling. generally in mf, the membrane resistance is negligible and the main resistance is from the cell cake & membrane fouling. it has been believed by researchers that mf of high cell density fermentation needs to be operated at conditions of high shear rate and low tmp. the high shear rate reduces the cell cake thickness and low tmp prevents over compressing of the cell cake. however, due to shear sensitive mammalian cells, lower recirculation rate was used during the study. the samples were taken before and after the operation for turbidity measurement, total protein determination, quantification of protease released and recovery of target protein after the operation (table 5 shows the result on option c). the volume recovered in permeate was about 85% with the protease release as 4.1 µg/ml and little amount of target protein was lost in the retentate. in this paper, the case study on comparison performance of clarification and recovery of chimeric anti-cea mabs from nso cells is presented using three different harvest approaches consisting of centrifugation, depth filtration and microfiltration. table 3 summarizes these results in terms of volume and final mass of target protein – chimeric anti-cea mabs recovery from nso cell culture. it is evident that all three approaches offer feasible methods for harvest and offer comparable product clarification & processing times except the vital product recovery. table: 3 summary of clarification performance by different unit operations. due to high shear occurred on mammalian cells during centrifugation, the option a has released 12.1 µg/ml of protease in comparison to the initial concentration of protease present in the sample 0.31 µg/ml. on the option c, the microfiltration gave lower stress to cells and it has released about 4.1 µg/ml. the primary and secondary depth filtration of option b had been a smooth operation with lowest release of protease as 2.8 µg/ml which leads to maximum recovery of target protein. 4. conclusion this study clearly concludes that nso cell culture clarification using primary & secondary depth filtration provides filtrate clarity of 1ntu on turbidity measurement, smooth and low stress on cells with the protease release of as 2.8 µg/ml in filtrate compare to other unit operation and lastly, this combination of depth filters with different retention ranges helps, to recover maximum of 96.5 percentage of chimeric mabs from nso cell centrifugation & depth filtration [option a] primary & secondary depth filtration [option b] microfiltration by tff [option c] protease release (µg/ml) 12.1 2.8 4.1 product recovery (%) 70.20 96.50 84.20 volume recovery (%) 97 93.75 85 iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abol hassan et al. 187 culture. however, the options of different clarification discussed in this paper differ significantly in the time required for development and optimization studies, scalability, cost of consumables, capital and other attributes of targeted product. thus, it is recommended that these considerations be taken into account while choosing the optimal harvest approach for an application. acknowledgments the authors would like to acknowledge staffs of innobiologics sdn bhd in the department of process science and quality control operations for contributing their help and guidance. special thanks to our technicians mr.zulhusni abd ghani and mr.muhammad ehsan for their help during experiments. references [1] reichert jm, rosensweig cj, faden lb, dewitz mc: monoclonal antibody successes in the clinic. nature biotechnology 2005, 23:1073-1078. [2] gottschalk u: process scale purification of antibodies, pp. 426. new jersey: john wiley & sons, inc; 2009. [3] an z: therapeutic monoclonal antibodies from bench to clinic. john wiley & sons, inc; new jersey 2009. [4] van dijk ma, van de winkel jgj: human antibodies as next generation therapeutics. current opinion in chemical biology 2001. 5:368-374 (2001). [5] morrison sl, johnson mj, herzenberg la, oi vt: chimeric human antibody molecules: mouse antigen-binding domains with human constant region domains. in proceedings of the national academy of sciences of the united states of america 81, 1984: 6851-6855. [6] gold p, freedman so: specific carcinoembryonic antigens of the human digestive system. journal of experimental medicine 1965, 122:467-481. [7] thomson dm, krupey j, freedman so, gold p: the radioimmunoassay of circulating carcinoembryonic antigen of the human digestive system. in proceedings of the national academy of sciences of the united states of america 64. 1969:161-167. [8] hammarstrom s: the carcinoembryonic antigen (cea) family: structures, suggested functions and expression in normal and malignant tissues. seminars in cancer biology; 1999:67-81. [9] jefferis r: glycosylation of recombinant antibody therapeutics. biotechnology progress 2005, 21:11-16. [10] chadd he, chamow sm: therapeutic antibody expression technology. current opinion in biotechnology 2001, 12:188-194. [11] chu l, robinson dk: industrial choices for protein production by large-scale cell culture. current opinion in biotechnology 2001, 12:180-187. [12] hu ws, piret jm: mammalian cell culture processes. current opinion in biotechnology 1992, 3:110-114. [13] russell e, wang a, rathore as: harvest of a therapeutic protein product from high cell density fermentation broths: principles and case study. in process scale bioseparations for the biopharmaceutical industry. edited by shukla aa, etzel mr, gadam s. pp. 575. boca raton: crc press, taylor & francis group; 2007. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 predicting trust in a social network based on structural similarities using a multi-layered perceptron neural network 1 amir hossein danesh1 and hossein shirgahi2* sogang university, seoul, south korea 2 computer engineering department, islamic azad university, jouybar branch, jouybar, iran * corresponding author: hossein.shirgahi@gmail.com (received: 9th september 2020; accepted: 14th october 2020; published on-line: 4th january 2021) abstract: although research on social networks is progressing rapidly, the positive and negative effects of this area should be evaluated. one of the problems is that social networks are very broad and anyone can have influence on them. this matter can cause the issue of people with different beliefs. therefore, determining the amount of trust to various resources on social networks, and especially resources for which there is no previous history on the web, is one of the main challenges in this field. in this paper, we present a method for predicting trust in a social network by structural similarities through the neural network. in this method, the web of trust data set is converted to a structural similarity data set based on the similarity of the trustors and trustees first. then, on the created data set, a part of the data set is considered as the training data and it is trained based on the multilayer perceptron neural network and then the trained neural network is tested based on the test data. in the proposed method, the mse value is less than 0.01, which has improved more than 0.02 compared to previous methods. based on the obtained results, the proposed method has provided acceptable accuracy. abstrak: walaupun kajian tentang rangkaian sosial adalah sangat pesat, kesan positif dan negatif dalam ruang lingkup ini perlu dinilai. masalah rangkaian sosial adalah sangat luas dan sesiapa sahaja boleh terpengaruh. perkara ini akan menyebabkan manusia dengan pelbagai isu kepercayaan. oleh itu, menentukan nilai kepercayaan melalui pelbagai sumber dalam rangkaian sosial, terutama sumber-sumber yang tidak mempunyai sejarah lepas dalam web, adalah salah satu cabaran dalam bidang ini. kajian ini membentangkan jangkaan kepercayaan dalam rangkaian sosial melalui persamaan struktur dengan menggunakan rangkaian neural. kaedah ini ditentukan dengan menukar set data web kepercayaan kepada struktur set data hampir sama berdasarkan kesamaan pemegang dan pemberi amanah. kemudian, sebilangan set data yang telah dibina ini dipertimbangkan sebagai data latihan dan ia dilatih berdasarkan rangkaian neural perseptron berbagai lapisan dan kemudian rangkaian neural yang terlatih ini diuji berdasarkan data ujian. dalam kaedah yang dicadangkan ini, nilai mse adalah kurang daripada 0.01, di mana telah diperbaiki kepada 0.02 lebih daripada kaedah-kaedah sebelum ini. berdasarkan dapatan kajian, didapati kaedah yang dicadangkan ini menunjukkan ketepatan yang boleh diterima. keywords: social network; trust; structural similarity; web of trust; neural network 103 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 1. introduction in recent years, topics such as social networks and semantic web have become the main topics of research in emerging social media. the philosophy of creating social networks is such as world wide web, in which everyone can produce information or use the information of others. so far, most of the researches that has been done in the field of semantic web and social network platform has been related to determine the standards of communication rules and facts such as xml, rdf, rdf diagram, owl, etc., which create the necessary basis for building a social network. it is clear we can't expect every user to know how reliable each resource is. also, due to the objective nature of the trust, the overall values of believability cannot be determined. it must be determined to what extent each source of information can be trusted. one solution is to keep all the information high quality and with no contradicted on social network. but due to the intensity and variety of resources, this is almost impossible. as a result, assuming the variety of information quality, an efficient solution must be provided that can be considered effective. the researchers of www found that a method to do this is using quality assertion in the link structure between pages [1]. such a function is also used in social networks. often in order to evaluate trust in social networks, web of trust is made based on users and their interactions and analysis of the above web of trust is done. the created web of trust may be used repeatedly to determine a user's trust to the other users. remember that unlike site ranking, the result of calculations on web of trust networks is not an accumulation of each user’s trust ability. instead, each user receives a set of his personal trusts that its amount is vary greatly from person to person. another challenge in this area is the type of assertion to the content of social networks, which can be logical or probable. if the user assertion is a logical type, each user can have agree or disagree assertion with each content. if all assertions are inconsistent about one content, that content can be believed with certainty and the assertions can be combined logically. otherwise, probabilistic calculations can be used. of course, the purpose is not to understand the reasons of the assertions. rather, due to the difficulty of establishing a degree of belief in an assertion that is explicitly stated by one or more resources on the social network, the goal is finding a solution for the above problem. the basic model is that a user's belief in an assertion should be a function of the trust to the source that provides it. if the user's belief in the source is clear, the user's belief in the person who determines the amount of trust for the source can be calculated. this is done in a variety of ways that is related to how people's beliefs are formed. if there are trusts from a to b scores at u amount and from b to c scores at v amount, then a will have a ratio of trust to c scores at t amount, which t is itself a function of u and v. this rule can be used to measure user trust in resources and also to answer the question of how much each user can trust sources that he or she does not know directly. this law is based on the hierarchical publication of trust. admissible methods of combining trusts that allow accurate and local calculation of derived trusts have limitations. these limitations in the composition of beliefs also cause to do only with the use of local information [2]. consider a system consisting of n users that have m assertions in overall. since each assertion is considered separately, we introduce the system in such a way that there seems to be only one assertion. beliefs: each user can affect his personal belief in assertion that ranges from 0 to 1. the high numerical value of this range indicates that the assertion is accurate and reliable. suppose bi represents the personal belief of the user i in the assertion. 104 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 if the user i does not have belief, we set bi to zero. the set of personal beliefs in the assertion is shown as a b-column vector. ijtthe high numerical value of ranges from 0 to 1.. it ijtas j can trust user iuser trusts: shows that user i trusts user j or they have the same interests. if the trust value is not do not have to be equal. jitand ijtto zero. note that ijtspecified, we set the set of personal trusts can be represented as a matrix t with n * n dimensions. ti represents the linear vector of the user i's personal trust to the other users [3]. integration: web of trust creates a structure in which we can calculate the level of belief of each user of the assertion. to distinguish it from the personal beliefs of the user (b), we call it integration beliefs. in this article, we do not deal with the details of users' beliefs and individual assertions on the content; rather, by using the web of trust and the specific values of trust in the data set, we predict the trust for nodes that do not have a direct edge. we perform predicting trust based on different structural similarities and their combinations using a multilayer perceptron neural network in social network. in previous research, a structural similarity method is usually used. as another innovation in this article, we used the similarity of both trustor and trustee to predict trust, but in previous methods, one of these two similarities is often used. 2. previous works review in general, there are two models of trust based on web of trust data set: the binary trust model with the probability distribution available in [4,5] and the multilevel trust model without the probability distribution [6]. most e-commerce websites, such as ebay, ali baba, amazon and yelp, have adopted a multi-level trust model. in some studies, the display of trust has been generalized in statistical distribution. in particular, reference [7] suggests a subjective logic to express distrust and to evaluate the trust probability distribution. but this method can only be used for the binary trust model. a variety of methods have been proposed to evaluate or trust propagation in different types of networks [8] and [9]. for example, in reference [9], a scoring system called eigen trust is created based on peers' historical functionality for peer to peer networks. however, this method is not directly applicable to assess the trust of social networks, because two people may have disparate opinions on a social network about the reliability of a person or party. according to reference [10], for each person, a global reputation on the network is evaluated from the view of valid nodes. a tidal trust algorithm was proposed in reference [6], that infer and speculate trust relations using continuous scale ranking. this method collects trust data from all reference paths according to the shortest path from one source to the destination. it then uses the weighted average method to calculate the total trust value. a trust inferential model called sunny is proposed in reference [4] to measure trust through possible sampling and to reduce the impact of longer-distance routes (usually for lowconfidence estimates). a flow-based trust assessment is proposed that considers the dependence of the path using network flows, and the trust models reduce or spread trust using expanding the flow associated with each node in the reference [5]. reference [11] uses a matrix to display direct trust relationships between users on a social network and uses the breadth-first search algorithm to enhance users trust. a binary decision chart based method [13] is proposed to evaluate the trust between the two parties, but it is only applicable for the binary trust model in the reference [12]. in this paper, the 105 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 relationship of trust between two directly connected parts is modeled using a multifaceted trust model with probability distribution. then, a probabilistic hybrid method based on multi-valued decision diagram (mdd)’s is presented to determine the probability distribution of different levels of trust between the two parties on the social network. the parties can be connected through multiple routes, including a direct link or several indirect links. dependence between different paths during the creation of the mdd model has been investigated. in reference [14], the tillit method is proposed, which is a pattern based on a combination of trust inference and user similarity. this similarity is based on the structure of the trust diagram and user’s trust behavior. this method is unlike other filter-based approaches that have used user rankings. the trust assessment is performed based on the reputation parameters of the recommendation according to the users’ profiles in the reference [3]. its purpose is to provide a fuzzy system for evaluating trust based on users’ profiles, examining the accuracy of the fuzzy system for evaluating trust, and examining the time complexity of the fuzzy system for evaluating trust in the semantic web. in this research, user profile data set based on semantic parameters has been used. for this purpose, they have considered their desired data set from cti depaul site, which includes a list of pages, user sessions, pages visited in each user session, and the time users visited the pages. mirroring trust is used to predict trust in reference [2], which estimates the amount of trust based on the degree of similarity between the trustor and the trustee. in this paper, the parameters degree, degree quality and local density in social networks have been used to determine similarity criteria and in order to calculate the similarity of each of these parameters, a fuzzy system is used. shirgahi et al. [1] gained the assessment of trust in the semantic web and social network by clustering the web of trust in their research first, after that they used distributed aggregation of indirect trust paths to predict trust for nodes that do not have direct trust. this method has an acceptable execution time. 3. multi-layered perceptron network past research shows that among the various methods of the neural network, the multilayer perceptron network (mlp) with the law of feed forward back propagation is one of the most widely used, basic, and at the same time simplest models of neural network available. also, mlp has been evaluated a suitable method in the field of estimating unknown parameters. the learning algorithm in these types of networks is a type of error correction algorithm, which is called error back propagation algorithm or back propagation briefly. these types of networks have an input layer, one or more hidden layers, and one output layer, and the information moves only in one direction, the direction of which is forward. in fact, the information starts from the input nodes and passes through the hidden layer (s) to the output nodes. so, there is no feedback. this means that the output of each layer only affects the next layer and does not change its own one (fig. 1). each network cell has a nonlinear function at the output and is derived for all inputs. the structure of the neural network used in this study is the back propagation neural network with two hidden layers and one output layer. also, the artificial neural network model is trained using the train set and different combinations of inputs are created. therefore, to achieve these goals, 60% of the data are used for training, 20% for testing and 20% for evaluation. 106 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 fig. 1: view of the two-layer artificial neural network back propagation. 4. proposed method in this section, the various criteria for structural similarity in the social network will be described first, then the structure of converting the social network data set to the structural similarity data set will be shown, and finally the structure of the proposed multi-layered perceptron neural network will be explained. 4.1 structural similarity criteria in social network in this article, to determine the structural similarity in the social network, we have used a series of structural similarities of the weighted directional graph and a series of structural parameters in the social network. before explaining the above criteria, we first describe the structure of web of trust. a web of trust is a weighted directional graph as fig. 1 and the values of the weights of the nodes and edges are in the range [0, 1]. the nodes in this part of the study are the trustors and trustees. the weight of each node determines the global reputation of each node which is determined by eq. 1. the weight of each edge u to v determines the value of direct trust obtained by direct interactions from u to v. (1) repi = { 0 nt = 0 ∑ 𝑇𝑗𝑖 j≠i,tji≠0 nt nt ≠ 0 in eq. 1, tji is the value of direct trust from j-node to i-node and nt is the total number of nodes that trust directly on i-node. 107 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 fig. 2: an example of a web of trust network. 4.2 graph structural similarities in this paper, 5 structural similarities based on edges are used. of course, the relationships of these similarities are weighed based on the amount of trust that exists between the nodes in the web of trust. since the numerator of deduction of all these equations of edges based structural similarity, are according to the intersection of two u and v nodes, we define the weighted intersection of nodes according to eq. 2. in eq. 2, v is a set of web of trust nodes and |tui − tvi| is the absolute value between tui and tvi . (2) |u ∩ v| = ∑ 1 − |tui − tvi| i∈v,tui≠0,tvi≠0 in this study, we weighted the structural similarities of cosine, dice, hdi, hpi, and jaccard. these similarities are calculated by eqs. (3) to (7), respectively. in these equations, |u ∩ v| is the weighted intersection of nodes u and v in accordance with eq. 2 and the repu and repv parameters are the reputation values of nodes u and v, respectively, based on eq. 1. simcosine(u, v) = |u∩v| √repu∗√repv (3) simdice(u, v) = 2∗|u∩v| repu+repv (4) simhdi(u, v) = |u∩v| max (repu , repv) (5) simhpi(u, v) = |u∩v| min (repu , repv) (6) simjaccard(u, v) = |u∩v| repu+repv−|u∩v| (7) 4.3 structural parameters in the social network in web of trust networks that are used to assess trust in social networks or semantic web, different parameters are considered to compare networks and the similarity of nodes . some of these parameters are semantic and are often used in semantic web, and others are structural parameters that are often considered in social networks to show similarities. in this part of the research, we describe some of the most important parameters of social networks that are used for the structural similarities of nodes. 108 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 out degree: the output degree parameter is used to determine how much a node exchanges information with other network nodes in a network. for discrete networks, the normal value of the out degree is obtained by dividing the number of output edges of a node by the maximum number of possible edges for that node (which can be the graph degree) . for example, if there are five nodes in a network and one source node connects with three of the other four nodes through an edge, the out degree of the source node is 0.75. in order to extend the out degree for weighted networks with weighted nodes, the values of these edges are weighted based on the importance of the nodes in the other heads leading to these edges .in this method, a node that is connected to other more important nodes has a higher out degree rather than a node that is connected to other nodes of the same size or less importance. in fact, in web of trust, not only the number of outgoing edges is important, but also the value of these edges and the reputation value of the destination nodes in the edges. because the value of the edges indicates the value of direct trust between the two nodes and the value (weight) of the destination nodes and the reputation value of the destination nodes. based on the explanations given in this study, we used eq. 1 to determine the out degree. (8)dout(i) = 1 1−repi ∑ repj × tij j≠i in eq. 8, in addition to the reputation of destination nodes and the direct trust from the source node to the destination node, the value of the source node reputation is also effective. in eq. 8, repi is the source node reputation, repj is the destination nodes reputation, tij is the value of the direct trust from i-node to j-node, and dout (i) is the out degree of i-node (source). since a node with a higher out degree can transmit more information to other nodes, so a node with a higher out degree can transmit faster or more appropriate information to other nodes compared with a node with a lower out degree. on the other hand, the out degree has no effect on the node that received the information. therefore, we cannot expect the out degree to be effective on the time required for a node to receive information. the degree of input in many researches in web of trust is also called degree of reputation. by combining weighted nodes, the in degree can be defined based on the eq. 9. (9) din(i) = 1 1−repi ∑ repj × tjij≠i in eq. 9, repi is the source node reputation, repj is the destination nodes reputation, tij is the value of the direct trust from j-node to i-node, and din (i) is the in degree of i-node (source). the input and output degrees are the same for symmetric networks, but these degrees are usually different in web of trust. in degree: the input degree parameter is used to determine how much a node receives information from other nodes. for discrete networks, the normalized value of the in degree is obtained by dividing the number of input edges of a node by the maximum number of possible edges for that node (which can be the degree of the graph). the advogato social network data set is a directed graph with 51332 edges and 47300 nodes. each record has 3 attributes, respectively the trustor user, the trustee user, and the value of trust. in this article, we have created a structural similarity data set using information about the edges and structural similarities of nodes. it has 51332 records, and each record is obtained based on the structural similarity analysis of each record in the advogato social network data set. 109 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 the structural similarity data set has 13 features for each ai record from the advogato social network data set. ai,1 is the number of a trustor node that trusts the trustee node ai,2 as much as ai, 3 in the i-th record of the data set. 4.4 converting web of trust data set to a structural similarity data set in this study, converting the web of trust data set to a structural similarity dataset is done based on graph structural similarity and structural parameters in the social web. first, look at fig. 3. the main problem is that the trustor p-node has no previous interaction with the trustee node q. the goal is to estimate the value of p to q based on the structural similarities between nodes p and q and other nodes. we can obtain the structural similarity of the q-node with all the trustee nodes with which the p-node has previously interacted (fig. 3a). based on this, the trust value can be predicted to determine the structural similarities of p-node with other nodes. in addition, we can obtain the structural similarity of p-node with all other trustor nodes that have previously interacted with q-node (fig. 3b) and predict the trust value on this basis. in this study, we used a combination of two structural similarities between trustors and trustees. also, the out degree of the p-node and the in degree of the trustee nodes have a large effect on the prediction of the trust. as a result, we consider both of these features. (a) (b) fig. 3. trustees similarities and trustors similarities in predicting trust a) trustors similarities, b) trustees similarities. the general structure of converting web of trust data set to a structural similarity data set is shown in fig. 4. in the social network data set, we have an an*3 matrix that n is the total number of edges and the three columns in a, respectively, are the number of trustor nodes, the number of trustee nodes, and the trust value corresponding to each trustor node to the trustee node. the structural similarity data set is a bn*13 matrix, which n is the total number of edges, columns 1 to 12 are the structural similarity features, and column 13 is the trust value of the corresponding record in matrix a. here's how to calculate the above 13 features: the first 5 features are obtained based on the structural similarity of ai,1 and ai,2 nodes in terms of the similarity of the trustees to them, respectively, according to the similarities of cosine, dice, hdi, hpi and jaccard and the sixth feature is obtained based on the normalized out degree of ai,1. the features 7 to 11 are obtained based on the structural similarity of ai,1 and ai,2 nodes in terms of the similarity of the trustors to them, respectively, according to the similarities of cosine, dice, hdi, hpi and jaccard. the twelfth attribute is based on the normalized value of ai,2 node’s in degree and the thirteenth attribute indicates the trust value, in other words ai,3 node. our goal of such a structural change has been to have a data set independence of the number of nodes, to have a trust value according to the different types of structural similarities between trustee and trustor nodes. 110 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 after creating the structural similarity data set, we randomly considered 70% of the data set as training data, 15% of the data as experimental data, and 15% of the data as validation data. you can see the general structure of the multilayer perceptron neural network in fig. 5. in this structural similarity data set, the first 12 features are considered as input and the last feature is considered as output. then, by teaching the above data set through the artificial neural network, the trust between structural similarity and trust value is obtained. finally, the trust value for nodes that do not have a direct edge in the web of trust data set is estimated based on the trained neural network. fig. 4: converting web of trust data set to a structural similarity data set. fig. 5: general structure of multilayer perceptron neural network in the proposed method. 5. simulations and tests the simulation of this article is done in matlab 2016. for this purpose, we used advogato web of trust data set, including a graph which characteristics are shown in table 1 [15]. this data set has 51332 records; each record contains 3 columns (attributes) that 111 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 represent the trustor node, trustee node and trust value, respectively. in this data set, the trust values are positive and have one of the values 0.6, 0.8 and 1, and there are no distrust values. clearly, if there is an edge between the two nodes, it shows that there has been a trusted interaction in the past. therefore, trust is inferred from trustee behaviors, in other words, if the trustee's performance is appropriate, the trustor will trust it. only if there is no direct edge between the two nodes, is it necessary to perform the trust prediction. in test operation, if there is a direct path between two nodes in web of trust, we also calculate the trust of the indirect path and compare the two values. table 1: advogato web of trust data set characteristics value characteristic 47300 number of nodes 51332 number of edges 0.0035 graph density 947 the most node degree 1 the least node degree 5.1 evaluation criteria in this paper, the following evaluation criteria are used to evaluate the performance of the proposed method : a) mean squared error (mse) and root mean squared error (rmse): the mean square error of a set with n data is a method of estimating the error value, which is actually the difference between the estimated values and what is estimated. 𝑴𝑺𝑬 = 𝟏 𝒏 ∑ (𝒙𝒊 − 𝒚𝒊 ) 𝟐𝒏 𝒊=𝟏 (10) 𝑹𝑴𝑺𝑬 = √ 𝟏 𝒏 ∑(𝒙𝒊 − 𝒚𝒊 ) 𝟐 𝒏 𝒊=𝟏 (11) where 𝐲𝐢 is the predicted value, 𝐱𝐢 is the measured value, 𝟏 𝒏 ∑ 𝒏𝒊=𝟏 has done averaging operation and 𝐱𝐢 calculates the value of square error of each data. b) scatter index (si): when the root mean square value is normalized to the measured average, it is sometimes referred to as the scatter index. 𝑴𝑺𝑬 = 𝟏 𝒏 ∑ (𝒙𝒊 − 𝒚𝒊 ) 𝟐𝒏 𝒊=𝟏 (12) c) coefficient of error (ce ): it provides information on the accuracy of estimates of each measurement where cex shows the average estimation and n is the number of people. 𝑪𝑬𝒙 = √𝑪𝑬𝟏 𝟐+𝑪𝑬𝟐 𝟐+⋯+𝑪𝑬𝒏 𝟐 𝒏 (13) d) correlation coefficient (r): this parameter expresses the power and direction of a linear correlation between two variables and its values are in the range -1 to 1. 1 indicates a oneto-one linearity and complete correlation, and -1 indicates a negative correlation. coefficient of determination (r2) describes the variance between two variables with a linear fit. 112 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 𝑅 = ∑ (𝑥𝑖− �̅� ) (𝑥𝑖− �̅� ) 𝑛 𝑖=1 √∑ (𝑥𝑖− �̅� ) 𝑛 𝑖=1 2 ∑ (𝑦𝑖− �̅� ) 𝑛 𝑖=1 2 (14) 𝑹𝟐 = [ ∑ (𝒙𝒊 − �̅� ) (𝒙𝒊 − �̅� ) 𝒏 𝒊=𝟏 √∑ (𝒙𝒊 − �̅� ) 𝒏 𝒊=𝟏 𝟐 ∑ (𝒚𝒊 − �̅� ) 𝒏 𝒊=𝟏 𝟐 ]𝟐 (15) 6. simulation results we use a multi-layered perseptron neural network for training, test and validation based on structural similarities and the levenberg training function. the maximum number of iterations is considered to be 1000 and the desired neural network is performed 10 times for 1 to 20 neurons in the hidden layer. we obtained the average results for each of the 1 to 20 neurons of hidden layer separately. you can see the implementation results in fig. 6 to fig. 11. figure 6 shows a comparison of the mse criterion with different number of neurons. the lowest mse is 0 with 3 neurons in training data, the lowest mse is 0.00000014 with 4 neurons in test data, and the lowest mse is 0.000012 with 1 neuron in validation data. figure 7 shows a comparison of the rmse criteria with different number of neurons. the lowest rmse is 0 with 3 neurons in training data, the lowest rmse is 0.00037 with 4 neurons in test data, and the lowest rmse is 0.0035 with 1 neuron in validation data. figure 8 shows a comparison of the ce criteria with different number of neurons. the maximum ce is 1 with 3 neurons in training data, the maximum ce is 0.99982 with 4 neurons in test data, and the maximum ce is 0.99959 with 1 neuron in validation data. figure 9 shows a comparison of the si criteria with different number of neurons. the lowest si is 0 with 3 neurons in training data, the lowest si is 0.04527 with 4 neurons in test data, and the lowest si is 0.42713 with 1 neuron in validation data. figure 10 shows a comparison of the r criteria with different number of neurons. the maximum r is 0.998225 with 3 neurons in training data, the maximum r is 0.98209 with 4 neurons in test data, and the maximum r is 0.97939 with 1 neuron in validation data. figure 11 shows a comparison of run time with different number of neurons, the minimum run time is 10.452 seconds with 3 neurons. figure 12 shows a comparison of the r criterion with 20 neurons. the r is 0.98225 in training data, the r is 0.98209 in test data, and the r is 0.97939 in validation data. in general, the criterion r is 0.97939. since the reference [14] researched in the field of predicting of trust on the advogato data set, so we compared the obtained results with the rmse criteria. you can see the comparison results in table 2. table 2: comparison of the proposed method with previous work method rmse mse structural similarity method with mlp 0.0035 0.000012 tillit [14] 0.1836 0.033708 113 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 fig. 6: comparison of mse criteria with a different number of neurons. fig. 7: comparison of rmse criteria with a different number of neurons. fig. 8: comparison of ce criteria with a different number of neurons. 114 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 fig. 9: comparison of si criteria with a different number of neurons. fig. 10: comparison of r criteria with a different number of neurons. fig. 11: comparison of execution time with a different number of neurons. 115 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 fig. 12: comparison of r criteria with 20 neurons in different states. 7. conclusions and suggestions in this research, after converting the web of trust data set into a structural similarity data set of trustors and trustees using a multilayer perceptron neural network, we trained the system. then we implemented the test and validation data on the trained network. the simulation results are reported as follows: for the validation data with 3 neurons in the hidden layer, the best mse was 0.000012 and the best rmse was 0.0035213. for the validation data with 1 neuron in the hidden layer, the most suitable ce was 0.99959 and the best si was 0.42713. the best r for validation data with 20 neurons in the hidden layer has been obtained 0.97939. the proposed method has achieved good accuracy based on the results and it can be useful for predicting trust on social networks. the proposed method is a centralized method, and on social networks with several hundred million users, predicting trust is a time consuming operation. our suggestion for future work is that if each user identifies a set of trusted users (possibly a small set) accurately, a distributed method can be used that offers a less expensive, faster, and more scalable method. in this case, although it may be somewhat less accurate, such an approach would be more effective on the semantic web and neural network. 116 iium engineering journal, vol. 22, no. 1, 2021 danesh et al. https://doi.org/10.31436/iiumej.v22i1.1622 references [1] shirgahi h, mohsenzadeh m, seyyed javadi hh. (2017) trust estimation of the semantic web using semantic web clustering. journal of experimental & theoretical artificial intelligence, 29(3): 537-556. [2] shirgahi h, mohsenzadeh m, seyyed javadi hh. (2018) a new method of trust mirroring estimation based on social networks parameters by fuzzy system. international journal of machine learning and cybernetics, 9(7): 1153-1168. [3] ashtari s, danesh m, shirgahi h. (2019) a novel user profile-based fuzzy approach for evaluating trust in semantic web. iium engineering journal, 20(1): 158-176. [4] kuter u, golbeck j. (2007) a new algorithm for trust inference in social networks using probabilistic con_dence models. in proc. aaai, vancouver, bc, canada, pp. 1377-1382. [5] jiang w, wu j, li f, wang g, zheng h. (2016) trust evaluation in online social networks using generalized network _ow. ieee trans. comput., 65(3): 952-963. [6] golbeck j. (2005) computing and applying trust inweb-based social networks. ph.d. dissertation, dept. comput. sci., univ. of maryland, college park, md, usa. [7] jøsang a, hayward r, pope s. (2006) trust network analysis with subjective logic. in proc. acsc, hobart, tas, australia. pp. 85-94. [8] wang g, jiang w, wu j, xiong z. (2014) fine-grained feature-based social in_uence evaluation in online social networks. ieee trans. parallel distrib. syst., 25(9): 2286-2296. [9] kamvar sd, schlosser mt, garcia-molina h. (2003) the eigentrust algorithm for reputation management in p2p networks. in proc. www, budapest, hungary, pp. 640-651 [10] levien r, aiken a. (1998) attack-resistant trust metrics for public key certification. in proc. usernix atc, san antono, tx, usa, pp. 229-242. [11] liu g, chen q, yang q, zhu b, wang h, wang w. (2017) opinionwalk: an ef_cient solution to massive trust assessment in online social networks. in proc. infocom, atlanta, ga, usa, pp. 1-9. [12] xing l, wang h, wang c, wang y. (2012) bdd based two party trust sensitivity analysis for social networks. int. j. secur. netw, 7(4): 242-251. [13] zaitseva e, levashenko v, kostolny j (2015) application of logical differential calculus and binary decision diagramin importance analysis. eksploat. niezawodn., 17(3): 379-388. [14] tavakolifard m, herrmann p, knapskog sj. (2009) inferring trust based on similarity with tillit. international federation for information processing, ifip aict 300, pp. 133-148. [15] http://www.trustlet.org/wiki/advogato_dataset 117 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 rhodopseudomonas palustris collagen-like recombinant protein purification using an aqueous two-phase system nursyahidatul azwa awang1, azura amid1* and zatul iffah arshad2 1 international institute for halal research and training (inhart), international islamic university of malaysia, jalan gombak, 53100 kuala lumpur, malaysia 2 faculty of chemical engineering and natural resources, universiti malaysia pahang, pekan, pahang, malaysia * corresponding author: azuraamid@iium.edu.my (received: 7th june 2022; accepted: 20th october 2022; published on-line: 4th january 2023) abstract: the potential use of recombinant collagen-like protein (recclp) extracted from bacteria as disease-free collagen has been studied over the past decade. however, the complexity of the downstream processing generates high demand for an efficient and low-cost purification method. aqueous two-phase system (atps) was adopted as a new approach to the recovery of biomolecules due to its simple, benign, and straightforward process. this study aimed to purify recombinant collagen-like protein from rhodopseudomonas palustris using atps formed by a polymer/salt system. recombinant collagen-like protein from r. palustris was partitioned in atps composed of polyethylene glycol (peg) and potassium phosphate and several factors that influence the protein partitioning such as volume ratio, system ph, the concentration of polymer and salt were studied. then, optimization of the selected atps conditions (peg and salt concentration) were performed using response surface methodology (rsm). results showed that the optimum conditions were found in atps with 24.80% (w/w) peg 2000 and 29.23% (w/w) potassium phosphate with recclp concentration of 3.23 ± 0.12 mg/ml with purification factor 7.48 ± 0.3. in comparison with the affinity chromatography method, atps was found to be low-cost, and time-saving with a higher protein recovery. hence, this study demonstrated the potential application of atps in the recovery of recombinant clps for large-scale downstream processing. abstrak: potensi penggunaan protein seperti kolagen rekombinan (recclp) yang diekstrak daripada bakteria sebagai kolagen bebas penyakit telah dikaji sejak sedekad yang lalu. walau bagaimanapun, kerumitan pemprosesan hiliran menjana permintaan yang tinggi untuk kaedah penulenan yang cekap dan berpatutan. sistem akueus dua fasa (atps) telah diterima pakai sebagai pendekatan baharu dalam pemulihan biomolekul kerana prosesnya yang mudah. tujuan utama kajian ini adalah untuk menyaring protein seperti kolagen rekombinan daripada rhodopseudomonas palustris menggunakan atps yang dibentuk oleh sistem polimer/garam. protein seperti kolagen rekombinan daripada r. palustris telah dibahagikan dalam atps yang terdiri daripada polietilena glikol (peg) dan kalium fosfat dan beberapa faktor yang mempengaruhi pembahagian protein seperti nisbah isipadu, ph sistem, kepekatan polimer dan garam telah dikaji. kemudian, keadaan atps terpilih (peg dan kepekatan garam) telah dioptimumkan menggunakan metodologi permukaan tindak balas (rsm). keputusan menunjukkan bahawa keadaan optimum dalam atps adalah 24.80% (b/b) peg 2000 dan 29.23 % (b/w) kalium fosfat dengan kepekatan recclp 3.23 ± 0.12 mg/ml dengan faktor penulenan 7.48 ± 0.3. berbanding dengan kaedah kromatografi afiniti, atps didapati menjimatkan kos dan 40 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 masa dengan pemulihan protein yang lebih tinggi. oleh itu, kajian ini menunjukkan potensi aplikasi atps dalam pemulihan clp rekombinan untuk pemprosesan hiliran berskala besar. keywords: recombinant collagen-like protein; r. palustri; aqueous two-phase system; purification; chromatography 1. introduction collagen is the main structural protein in the extracellular matrix of the animal kingdom comprised of specific amino acid compositions such as glycine (gly), proline (pro), and hydroxyproline that twisted together in the form of a triple-helix structure [1]. it strengthens the skin and benefits its elasticity and firmness besides helping in tissue and organ development. widespread applications of collagen in cosmetic, biomedical, and pharmaceutical industries make collagen a major industrial component [2]. furthermore, owing to its high biodegradability and biocompatibility thus making it is applicable as a biomaterial in the biomedical field [3]. apart from mammalian and marine collagen, scientists have discovered collagen-like proteins (clps) annotated in bacteria, viruses, and archaea that shared the similar (glyxaa-yaa)n repetitive amino acid sequences of mammalian collagen but different in terms of amino acid content and distribution [4]. clps in bacteria can form triple helix structures similar to mammalian collagens with high thermal stabilities (tm = 36.5-40 °c) despite the lack of hydroxyproline (hyp), which is important in the stabilization of protein structure and promote self-association [5]. furthermore, the result of calorimetric studies showed that high hyp content increases the enthalpic contribution thus providing stability to the proteins [6]. it has been reported that some of the clps work as a virulence factor to evade the immune system of higher animals and thus promote host cell invasion [7]. hence the availability of clps with similar features with mammalian collagen could benefit humans in establishing well-defined and novel collagen-based biomaterials [8,9]. furthermore, using recombinant technology, these clps can be produced in large quantities [10]. recombinant dna technology is one of the recent advances in biotechnology that involve the joining together of dna segments from different organisms and introduced into e. coli to produce a new genetic organism that is useful to science and industry [11]. this technology enables the production of disease-free products, uniform quality and abundance in quantity thus have been successfully exploited in various fields [12]. in recent years, downstream processing remains the major challenge in the production of recombinant protein. conventional methods like precipitation, filtration, and chromatography need multiple stages to produce highly purified protein. these multi-step purification processes lead to high process cost, time consumption, low yield, and difficulty in scale up is viewed as a significant disadvantaged [13,14]. according to warner and co-workers [15], nickel columns in affinity chromatography can give higher yield compared to other types of columns. these difficulties are avoided using an aqueous two-phase system (atps) method, a liquid-liquid extraction technique formed when two incompatible water-soluble phase components are mixed at appropriate conditions resulting in the formation of two phases at equilibrium [16]. atps is more preferable due to its simplicity, low cost, ease of scale-up, higher biocompatibility, and shorter processing time [17]. its high water content and low interfacial tensions provide the mild environment for sensitive biomolecules [18]. it has 41 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 been documented to be an effective method for protein purification such as bromelain [19], protease [20], collagenase [21], lipase [22], papain [23], pepsinogen [24] and interferon [12]. however, there is still a lack of studies regarding the purification of recclp using atps because of the complex process of protein partitioning that can be affected by many factors. the ph of the atps, concentration of salt, molecular weight, and concentration of polymers, are among the factors that can manipulate the distribution of protein molecules [12]. the potential factors that can affect the performance of atps such as volume ratio, ph, concentration of peg, and salt were studied and optimized. in addition, affinity chromatography method was conducted to compare the purification effect of atps. the purpose of this study is to provide a simple yet effective method of purifying the recombinant collagen-like protein from e. coli crude extract. to date, recombinant collagen-like protein has been purified using the chromatography method [25,26] and no study has been attempted for purification of recombinant collagen-like protein from e.coli using the atps method, which could be promising in clps research. 2. materials and method 2.1 materials polyethylene glycol with molecular weight of 2000 g/mol (peg 2000), dipotassium hydrogen phosphate (k2hpo4), and potassium dihydrogen phosphate (kh2po4) were purchased from merck-schuchardt (munich, germany). vegitone luria bertani agar and vegitone luria bertani broth were obtained from sigma-aldrich (st. louis, mo, usa) while enzyfluo collagen assay kit was procured from bioassay systems (hayward, usa). all chemicals used in this paper are analytical grade. 2.2 experimental setup 2.2.1 microorganism the recombinant plasmid pcoldii-clp-r. palustris was prepared by subcloning the sequence of clp-r. palustris from the source plasmid (puc57, genescipt, hong kong) to the target plasmid (pcoldii tkr-3322, takara, japan). the recombinant plasmid was then transformed into e. coli b strain (bl21de3) (new england biolabs, usa) competent cell using cold shock expression method [20]. ampicillin selection and colony pcr were performed to verify the successfully transformed pcoldii-clp into bl21 after overnight incubation at 37 °c on lb agar (unpublished data). 2.2.2 protein expression the positive clone of e. coli bl21de harboring collagen-like protein from r. palustris was cultured in 100 ml of m9 minimal medium at 37 °c, 250 rpm until od600 nm reached 0.8-1.0 in an incubator shaker (infors ht ecotron, switzerland). the recclp culture was then induced at 15 °c by adding 1 mm isopropyl ß-d-1 thiogalactopyranoside. after 24 hours, cultures were centrifuged in a refrigerated centrifuge (heraeus multifuge x1r refrigerated centrifuge, thermo scientific, usa), at 4696 xg for 10 minutes at 4 °c, to remove the debris and tissue. the crude extract was stored at -20°c until further processing. 2.2.3 cell lysis the cell pellets were resuspended in the lysis buffer (20 mm na2hpo4, 0.5 m nacl, ph 7.4) and sonicated at 40% amplitude, 10 seconds with 20 seconds interval between 42 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 each sonication for 10 times using an ultrasonicator (labsonic®p, sortarius, germany) to break open the cell, therefore releasing the recclp. subsequently, the culture was then centrifuged using eppendorf 580 4r refrigerated centrifuge (eppendorf, germany), at 12,000 rpm and 4 °c for 30 minutes to obtain a clear supernatant. the supernatant was considered as the soluble fraction whereas the pellet was known as the insoluble fraction. 2.2.4 aqueous two-phase system atps was prepared on fixed mass basis in a 2.0 ml microcentrifuge tube by mixing predetermined quantities of peg 2000, potassium phosphate buffer at ph 7.0 and 10% (w/w) of crude extract. distilled water was added to the system to give a total weight of 2 g. the mixture was vortexed to mix for 1 minute and then centrifuged at 1000 xg (heraeus multifuge x1r, thermo scientific, usa), and 25 °c for 10 minutes to speed up phase separation. after that, top and bottom phases were carefully collected for further analysis. the volume of the phases was then used to estimate the volume ratio (vr). it was noted that the most potent atps could not be determined by monitoring the total protein in the phases. thus, the total amount of recombinant collagen-like protein in both phases, partition coefficient (ke), as well as concentration of recclp, were quantified using fluorometric collagen assay kit. the binodal curves were referred elsewhere [28]. the strategy behind the selection of the experimental system is well described elsewhere [22]. according to arshad and amid [27], the tie-line length (tll) was estimated graphically by using volume ratio and it can be calculated using the equation as follows, 𝑇𝐿𝐿 = √[(∆𝑥2) + (∆𝑦2)] (1) where δx and δy indicate the difference between salt and peg concentration, respectively. 2.2.5 one-factor-at-a-time (ofat) ofat (one-factor-at-a-time) method was designed and applied for atps separation. the tested parameters involved in this study were volume ratio, ph, and concentration of peg and salt. the response was concentration of recombinant collagen-like protein and purification factor. data from experiments were expressed as mean ± standard error. analysis of variance (anova) was performed on the data and statistical significance was defined at p<0.05. 2.2.6 optimization response surface methodology (rsm) using design of expert 10.0.3 software (stateease inc., minneapolis mn, usa) was used for the optimization of atps conditions. a set of 11 experiments with two independent variables (concentration of polyethylene glycol and potassium phosphate) were coded using the face-centered central composite design with triplicate center point. the values of the center point were obtained based on previous atps separation by ofat. the recclp concentration and purification factor (pf) were chosen as the responses in each run. 2.2.7 affinity chromatography (fast-protein liquid chromatography) affinity chromatography was conducted using 1 ml histrap™ high performance chromatography column (ge healthcare, usa) prepacked with ni sepharose with an inner diameter of 7 mm connected to akta prime plus® (ge healthcare, usa). the collected supernatant after cell lysis was filter-sterilized using 0.45 µm pore filter. then, 2 ml of the solution was loaded into the packed column at a flow rate of 1 ml/min. the 43 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 unbound proteins were washed with binding buffer and the target protein was eluted using elution buffer (20 mm na2hpo4, 0.5 m nacl, 0.5 m imidazole, ph 7.4). collected fractions were analyzed by sds-page and fluorometric collagen assay. 2.2.8 quantification of recombinant collagen-like proteins (recclp) the concentration and total recclp in atps samples were measured using a commercially available collagen assay kit (bioassay systems, usa). briefly, collagen in the sample was enzymatically digested into peptides by mixing equal amounts of samples with digest enzyme and incubated at 37°c for 1 hour. then, dye reagent was added to react with the n-terminal glycine peptides in the solution, incubated at 37°c for 10 minutes, thus forming a fluorescent complex [26]. the sample was transferred to a 384black flat bottom microplate reader (corning, usa) and ready for fluorescence reading at λex/em 375/465 nm using a spark® multimode microplate reader (tecan, switzerland). in this study, bovine collagen type i was used as a standard for collagen assay. the fluorescent intensity, measured at λex/em 375/465 was directly proportional to the collagen concentration in the sample. 2.2.9 sodium dodecyl sulfate-polyacrylamide gel electrophoresis (sds-page) the protein sample from crude extract, top phase in atps and fplc fractions were analyzed using sds-page method. the samples were diluted to 1:1 ratio prior to loading into 12% resolving gel and 4% stacking gel. electrophoresis is run at 120 v, 400 ma for 60 min, the gels are stained using readyblue™ protein gel stain (sigma, usa) or silver staining method. 2.3 calculation the volume ratio is defined as, 𝑉𝑅 = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 𝑡𝑜𝑝 𝑝ℎ𝑎𝑠𝑒 𝑉𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 𝑏𝑜𝑡𝑡𝑜𝑚 𝑝ℎ𝑎𝑠𝑒 (2) the partition coefficient (ke) of the recclp was calculated as the ratio of total recclp in two phases, 𝐾𝐸 = 𝑇𝑜𝑡𝑎𝑙 𝑐𝑜𝑙𝑙𝑎𝑔𝑒𝑛 𝑖𝑛 𝑡𝑜𝑝 𝑝ℎ𝑎𝑠𝑒 𝑇𝑜𝑡𝑎𝑙 𝑐𝑜𝑙𝑙𝑎𝑔𝑒𝑛 𝑖𝑛 𝑏𝑜𝑡𝑡𝑜𝑚 𝑝ℎ𝑎𝑠𝑒 (3) the purification factor (pf) of the recclp was calculated according to the equation below, 𝑃𝐹 = 𝐶𝑜𝑙𝑙𝑎𝑔𝑒𝑛 𝑎𝑚𝑜𝑢𝑛𝑡 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 𝐶𝑜𝑙𝑙𝑎𝑔𝑒𝑛 𝑎𝑚𝑜𝑢𝑛𝑡 𝑖𝑛 𝑐𝑟𝑢𝑑𝑒 𝑙𝑦𝑠𝑎𝑡𝑒 (4) 3. results and discussion 3.1 selection of atps the result of system tie-line length (tll) and partition coefficient (ke) for atps samples composed of peg 2000/potassium phosphate with vr value of 1.0 are shown in table 1. the selection of binodal curves was decided according elsewhere [28]. to identify the best combination of atps, a quantitative fluorometric collagen assay was done to both top and bottom phases. the highest partition coefficient (ke) was achieved by the system with 26% (w/w) peg 2000 and 26% (w/w) potassium phosphate with tieline length (tll) of 54.78% (w/w), therefore proving that most of the protein of interest were favored in one phase which is peg-rich top phase. the concentration of salt in the 44 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 bottom phase increase as the tll increase and this may drive recclp towards the bottom phase as a consequence [12]. therefore, this combination of atps was chosen for further analysis. the bottom phase of atps with 26% (w/w) peg 2000 and 26 % (w/w) potassium phosphate showed a low concentration of recclp in the quantitative assay (unpublished data). therefore, in the further experiment, it was decided to conduct detection of recclp in the top-phase only. table 1: the tie-line length (tll) and partition coefficient (ke) of atps with vr of 1.0 % peg 2000 (w/w) % potassium phosphate (w/w) tll ke 25 25 50.51 1.33 26 26 54.78 4.03 27 27 60.26 1.55 28 28 64.42 1.28 3.2 screening of atps factors using ofat (one-factor-at-a-time) 3.2.1 effect of vr on recclp the impact of different volume ratios along the same tie-line of a system consisting of 26% (w/w) potassium phosphate and 26% (w/w) of peg 2000 at constant ph 7.0 was assessed and shown in table 2. five points indicate five different volume ratios (0.33, 0.8, 1.0, 1.57, 3.5) within the same tie-line. in defined atps, volume of top phase proportionally increases with the volume ratio resulting in more free volume available for the protein of interest to participate in the top phase. this situation caused a significant negative impact of free volume in the bottom phase [29]. on the other hand, an extremely low volume ratio may have limited free volume, thus limiting the partition of protein [12]. from the preceding result, either increasing or reducing the volume ratio did not cause any significant effect on recclp concentration in the top phase. as a rule of thumb, researchers who are using atps method for the first time are advised to use volume ratio equal to 1, making it convenient to measure the volume of each phase during partition experiments [27]. table 2: influence of different volume ratios on recclp in top-phase. the data are presented as means ± standard error, p<0.05 volume ratio recclp (mg/ml) purification factor (pf) 0.33 0.98 ± 0.004 2.77 ± 0.01 0.80 0.84 ± 0.003 5.78 ± 0.02 1.00 1.03 ± 0.006 8,84 ± 0.05 3.2.2 effect of peg 2000 % (w/w) on recclp the results of pf and concentration of recclp in different peg concentration were shown in table 3. a higher concentration of recclp with pf of 9.04 ± 0.25 was achieved in atps with 26% (w/w) peg2000. volume exclusion effect in top phase and salting-out effect in bottom phase are the crucial factors in partition behavior of biomolecules in the polymer-salt system [30]. those effects are responsible for reducing the available space in the top phase and thus obstruct the partition of biomolecules in the top phase. this hypothesis was concurrent with the behavior of recclp and pf when the peg concentration was decreased from 26% (w/w) to 29% (w/w). meanwhile, the trend with 45 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 peg concentration from 20% (w/w) to 26% (w/w) and from 29% (w/w) to 32% (w/w) was parallel with the theory stated that an increase of polymer concentration caused the movement of biomolecules to peg-rich phase due to the hydrophobic interactions between biomolecules and peg [31]. increasing peg concentration leads to the increase of top phase volume, resulting in the rising of free volume available for the protein of interest to participate in the top phase [29,32]. therefore, atps with 26% (w/w) of peg 2000 was further employed for the next factor. however, the best concentration of peg 2000 in the purification of recombinant recclp cannot be corroborated with any studies due to a lack of references regarding the application of atps in the partition of recclp. table 3: influence on the concentration of peg on recclp concentration and purification factor. the data are presented as means ± standard error, p<0.05 %peg 2000 (w/w) recclp (mg/ml) purification factor 20 0.944 ± 0.04 6.04 ± 0.27 23 1.08 ± 0.05 7.36 ± 0.33 26 1.18 ± 0.03 9.04 ± 0.25 29 0.95 ± 0.04 7.28 ± 0.33 32 1.10 ± 0.05 9.34 ± 0.39 3.2.3 effect of potassium phosphate % (w/w) on recclp in this part, the effect of different potassium phosphate concentrations from 20 to 32% (w/w) at ph 7.0 on the concentration of recclp was investigated and presented in table 4. as shown in table 4, the highest concentration of recclp was shown in atps with 29% (w/w) potassium phosphate, with 0.97 ± 0.006 mg/ml recclp and pf of 6.33 ± 0.04. the concentration of potassium phosphate % (w/w) is one of the factors which affect the partition behavior of the target protein. theoretically, ionic strength will increase as the salt concentration in the system increases, thus pushing the proteins to the top phase. besides, the ability of salt to capture water molecules will increase, hence moving biomolecules to the top phase [8,29]. however, a high concentration of salt also can lead to protein precipitation and denaturation thus reducing the amount of targeted protein in the phase [8,15]. this hypothesis supports the trend shown for concentration of recclp when the concentration of salt decrease from 29% (w/w) to 32% (w/w). meanwhile, due to the decreasing volume of top phase (20 to 32% (w/w)), pf decreased. when the free volume in the phase is preferred by protein of interest decreased, it will cause them to concentrate when the limits of protein solubility are exceeded [25]. thus, the protein content in that phase will decline. table 4: influence on the concentration of potassium phosphate on recclp concentration and purification factor. the data are presented as means ± standard error, p<0.05 % potassium phosphate (w/w) recclp (mg/ml) purification factor (pf) 20 0.78 ± 0.03 8.25 ± 0.28 23 0.93 ± 0.03 6.83 ± 0.22 26 0.92 ± 0.01 6.04 ± 0.06 29 0.97 ± 0.006 6.33 ± 0.04 32 0.95 ± 0.006 4.64 ± 0.03 46 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 3.2.4 effect of ph on recclp the effect of different ph values on the partitioning of recclp in atps was determined by varying the ph from 6.0-8.0 using different compositions of potassium phosphate salts (kh2po4 and k2hpo4), ± 0.5 accuracy of ph. system ph affects the partitioning of proteins by altering the charge and surface properties of the solute. the partitioning behavior of recclp is expected to be sensitive to the ph levels increased. this is due to the isoelectric point (pi) of the collagen (<7.0), which makes the protein become negatively charged and favors the peg-rich top phase. according to [33], the zwitterion along collagen molecules are negatively charged, making the entire collagen is negative. moreover, the pi glycine residues are 5.97 due to its acidic side chain, thus making the collagen-like protein carried a negative charge [34]. when the ph increases from 7.0 to 8.0, the protein of interest favored a partition in the bottom phase, which in turn decreased in protein concentration. besides that, at higher ph, more contaminants become negatively charged and tend to partition to the top phase [17]. the presence of contaminants in the top phase lowered the concentration of collagen-like protein. per the results shown in table 5, the system of ph 7.0 exhibited the highest values for the responses, 1.37 ± 0.13 mg/ml of recclp and pf of 6.44 ± 0.61. as a result, atps with ph 7.0 was chosen for further study. table 5: influence of ph on recclp concentration and purification factor. the data are presented as means ± standard error, p<0.05 % potassium phosphate (w/w) recclp (mg/ml) purification factor (pf) 6 0.76 ± 0.06 3.99 ± 0.32 7 1.37 ± 0.13 6.44 ± 0.61 8 1.22 ± 0.11 5.72 ± 0.51 3.3 optimization of atps experiment using design of expert (doe) response surface methodology with face-centered central composite design (fcccd) was applied to determine the optimum condition of the atps purification method. the effect of two factors known as concentration of peg 2000 and potassium phosphate on concentration of recclp was studied. the temperature of phase separation and ph of the system was kept constant at 25 °c and 7.0 respectively. the design matrix and the result of optimization were summarized in tables 6 and 7, respectively. for the successful development of atps purification method, the separation of recombinant collagen-like protein was optimized using a statistical experimental design involving the concentration of peg 2000 (a) and concentration of potassium phosphate (b) at ph 7.0. analysis of variance (anova) of a quadratic model for the responses were employed to determine the significant variable and their interaction with the response variable (tables 8-10). according to the analysis of variance, the f-value represents the accuracy of the model while the p-value indicates the interaction between the model terms. a significant model proved by the p-value that was less than 0.05 while a p-value greater than 0.10 is considered as an insignificant model. the coefficient of determination (r2) and adjusted r2 indicate the quality fit of the model equation [35]. it was found that the f-value of 7.65 and the p-value of 0.0217 (<0.05) indicate that the model is significant. furthermore, a non-significant value of 0.2674 for lack of fit showed that the quadratic model was valid for this study. the model coefficient of determination (r2) and adjusted r2 value was 0.8843 and 0.7687, respectively. both 47 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 values represent the correlation between actual and predicted data. r2 value obtained in this present study is acceptable as it exceeded 0.8 and the small difference between r2 and adjusted r2 is preferable and proved the good correlation for recclp partitioning. the model contains many insignificant terms proved by the huge difference between r2 and adjusted r2 [20,23]. in this experiment, r2 of 0.8843 indicates that the predicted model could explain 88.43 % of the variability in the response. as well, the adjusted r2, 0.7687 is also good to demonstrate a good correlation between actual and predicted data [20], [23]. from the three-dimensional plot in figs. 1 to 3, an increasing pattern showed when the concentration of peg and salt increase to the intermediate values and decline as the concentrations of peg and salt decrease. in summary, the maximum values of the response appeared near the center of the graph, indicating that the center point selected for this experiment is appropriate. the result from the software implied that optimized conditions for recclp partitioning occurred when the concentration of peg 2000 and potassium phosphate was set at 24.8% (w/w) and 29.23% (w/w) respectively with 3.026 mg/ml recclp. table 6: factors for face-centered central composite design (fcccd) study symbols factor range and levels -1 0 1 a concentration of peg 2000 % (w/w) 20 25 30 b concentration of potassium phosphate % (w/w) 25 28.5 32 table 7: design of experiment for optimisation of atps of recclp using fcccd % peg 2000 (w/w) % potassium phosphate (w/w) recclp concentration (mg/ml) 20 25 1.913 30 25 1.450 20 32 2.351 30 32 1.794 20 28.5 2.151 30 28.5 2.178 20 25 1.913 25 25 1.874 25 32 2.945 25 28.5 2.974 25 28.5 3.271 25 28.5 2.904 table 8: analysis of variance (anova) for the quadratic model for concentration of recombinant collagen-like protein sources sum of squares p-value prob>f model 3.10 0.0217 a-peg 2000 concentration 0.16 0.2142 b-salt concentration 0.57 0.0450 ab 2.209e-003 0.8754 a2 1.24 0.0113 b2 0.52 0.0519 lack of fit 0.33 0.2674 (not significant) r2 0.8843 adjusted r2 0.7687 48 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 fig. 1: three-dimensional surface plot of response surface analysis showing the effect of the interaction of concentration of peg 2000 and potassium phosphate on the recclp. table 9: analysis of variance (anova) for the quadratic model for fluorescence intensity of recombinant collagen-like protein sources sum of squares p-value prob>f model 1.610e+008 0.0238 a-peg 2000 concentration 8.587e+006 0.221 b-salt concentration 2.921e+007 0.050 ab 1.325e+005 0.869 a2 6.482e+007 0.012 b2 2.715e+007 0.056 lack of fit 1.798e+007 0.024 (not significant) r2 0.8798 adjusted r2 0.7596 fig. 2: three-dimensional surface plot of response surface analysis showing the effect of the interaction of concentration of peg 2000 and potassium phosphate on the fluorescence intensity. 49 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 table 10: analysis of variance (anova) for the quadratic model for purification factor of recombinant collagen-like protein sources sum of squares p-value prob>f model 17.96 0.0614 a-peg 2000 concentration 0.62 0.417 b-salt concentration 0.12 0.716 ab 0.033 0.847 a2 6.65 0.034 b2 5.96 0.041 lack of fit 3.44 0.1905 r2 0.8192 adjusted r2 0.6383 fig. 3: three-dimensional surface plot of response surface analysis showing the effect of the interaction of concentration of peg 2000 and potassium phosphate on the purification factor. the quadratic model for each response of fluorescence intensity, concentration of recclp and purification factor coefficient were predicted from equations as follows: fluorescence intensity (fl)= 25175.95 – 1196.33cpeg2000 + 2206.50cpp 182.00cpeg2000cpp -5058.37cpeg2000 2 – 327.87cpp 2 (5) concentration of recclp= 2.98 0.17cpeg2000 + 0.31cpp 0.023cpeg2000.cpp 0.70peg2000 2 0.45cpp 2 (6) purification factor (pf)= 7.71 + 0.32cpeg2000 + 0.14cpp + 0.091cpeg2000.cpp 1.62cpeg2000 2 1.53cpp 2 (7) atps with only one polymer in the presence of salt (polymer/salt) is the better choice with cheaper cost, ease of handling, and low viscosity [13,36]. a similar finding, conducted by de albuquerque wanderley and co-workers [21], showed that the best condition for purification of collagenase by atps is 15% (w/w) peg 3350 and 12.5% (w/w) phosphate salt. 3.4 validation of model validation of the model was conducted by carrying out three replicate experiments and the results were compared with the predicted results suggested by fcccd of rsm as tabulated in table 11. under the optimized condition which composed of at 24.8% (w/w) 50 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 peg 2000 and 29.23% (w/w) potassium phosphate at ph 7.0, the predicted recclp and pf were 3.026 mg/ml and 7.654 respectively. the experiments for validation of the predicted model resulting recclp of 3.233 ± 0.12 mg/ml. the minimal difference between predicted and experimental values proved rsm is a suitable tool for optimization of atps conditions for purification of recclp. table 11: validation of model. experiments were conducted in triplicate with data were presented as means ± standard error, p<0.05 model predicted experimental percentage error (%) concentration of recclp (mg/ml) 3.026 3.233 ± 0.12 6.9 purification factor 7.654 7.476 ± 0.29 2.3 model predicted experimental percentage error (%) 3.5 comparison of purification by atps and affinity chromatography as suggested by xu and co-workers [10], ph of 7.4 was used for binding buffer containing 20 mm of na2hpo4 and 0.5 m nacl. ni-nta resin with ph between 7.0 and 8.0 is preferable for most of the his-tagged proteins to prevent non-specific binding [37]. in this present study, the elution buffer containing 20 mm of na2hpo4, 0.5 m nacl and 0.5 m imidazole, ph 7.4 eluted the target protein from the column at fractions 17 to 19 (fig. 4.). affinity chromatography was performed under native conditions since the protein of interest is in soluble form [38]. based on the results, the sample at the peak of the chromatogram (fraction 18) was analyzed by collagen assay and sds-page and compared with purified recombinant recclp from atps purification method. the purification efficiency of recombinant collagen-like protein purified by atps and chromatography is summarized in table 12. both methods were performed directly after cell lysis stage. in the present study, ni sepharose chromatography (affinity) resulted in concentration of recclp of 2.036 mg/ml and with purification factor of 0.524. meanwhile, sample from atps with (24.8% w/w) of peg2000 and (29.20 % w/w) of potassium phosphate buffer at ph 7 recclp exhibited favorable result with 3.23 mg/ml and 7.48 purification factor. the yield is defined as the amount of purified total proteins divided by the initial amount of total protein (defined as 100%). table 12: purification efficiency of recombinant collagen-like protein by different purification methods. purification methods atps affinity chromatography fluorescence intensity 27069 18355 concentration of recclp (mg/ml) 3.233 2.036 purification factor 7.476 0.524 total protein (mg) 0.233 0.172 yield (100%) 19.74 17.28 purification methods atps affinity chromatography 51 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 based on economic analysis point of view as presented in table 13, atps exhibited shorter processing time with lower cost of operation compared to the chromatography method. due to expensive prepacked column with resin and chemicals used for 1h processing time, affinity chromatography is considered an expensive downstream purification method, thus making it unsustainable for bigger scale and long-term production. despite the high cost of operation, affinity chromatography is advantageous in terms of reusability. the chromatography resin can be re-used up to 100 times since the hydrophobic stationary phase is washable [39]. however, additional cost needs to be considered for the stripping and recharging chromatography columns [19]. in the case of atps, polymer and salt cannot be recycled as they were part of the final purified protein [19]. such economic analysis lays out a better understanding for future study, and atps method is proven to be cost-effective, time-saving with higher recovery that may be considered for the scale-up process. fig. 4: chromatogram of the purified samples from affinity chromatography of 2 ml loading volume of recombinant collagen-like protein lysates on ni-sepharose resin. binding buffer contain 20 mm of na2hpo4, 0. 5m nacl at ph 7.4. elution buffer contained 20 mm na2hpo4, 0.5 m nacl and 0.5 m imidazole, at ph 7.4. fractions (1 ml/tube) were collected at flow rate of 1 ml/min. table 13: direct comparison between chromatography and atps method for downstream processing of recombinant collagen-like protein purification methods atps affinity chromatography (fplc) processing time 30 minutes 1 hour cost prepacked column 228.36/5ml cost of chemicals (per kg) k2hpo4: usd 235.4 kh2po4: usd 163.98 peg 2000: usd 91.6 na2hpo4: usd 91.3 nacl: usd 128.02 imidazole: usd 543.88 cost of operation per system usd 490.86 usd 991.39 52 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 3.6 sds-page analysis of recombinant collagen-like protein the presence of recombinant collagen-like protein purified by atps with optimized conditions of was analyzed by sds-page electrophoresis under reducing conditions and compared with purified samples from the chromatography method. figure 5. shows the presence of a protein band with molecular weight of 36 kda for atps sample, indicating the recclp was successfully partitioned in the top phase. this was supported by the single band formed at the same size in samples from fplc fractions. however, several bands were observed between 45 kda and 60 kda and above 75 kda. this is explained by the fact that the bottom phase was unable to attract all of contaminants and unwanted proteins. fig. 5: sds-page analysis of purified sample of atps and affinity chromatography. lane m: standard protein marker. lane p: cell pellet. lane l: crude cell lysate. lane 1: fplc fraction (17). lane 2: fplc fraction (18). lane 3: fplc fraction (19). lane 4: atps top phase. note: for sdspage analysis, 20 µl of sample with sample buffer was loaded into a 12% resolving and 4% stacking gel. gel with fplc fractions was stained with readyblue™ protein gel stain and the gel with atps sample was stained with silver staining after electrophoresis at 120 v, 400 ma for 60 minutes. 4. conclusion the present study had demonstrated the potential application of atps in purification of recclp using peg2000/potassium phosphate system. the optimum conditions of atps comprised of 24.8% (w/w) peg 2000 and 29.20% (w/w) potassium phosphate at ph 7.0 which resulted in 27068 ± 900, 3.233 ± 0.12 mg/ml, 7.476 ± 0.29, for fluorescence intensity, concentration of recombinant collagen-like protein and purification factor, respectively. moreover, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (sds-page) confirmed the molecular weight of the recclp, which is 36 kda. this study clearly demonstrated atps was proven to be time-saving, cost-effective with higher recovery that may be considered for the scale-up process. the obtained results are pivotal for the design of a purification process and understanding the complex mechanisms controlling the phase behavior. besides, due to the lack of application of atps in purification of clps specifically from r. palustris, this present study can be used as a reference and deliver new information for future studies. acknowledgement special thanks are dedicated to ministry of higher education (mohe), malaysia for financial support under transdisciplinary research grant scheme [trgs/1/2018/uiam/01/1/1]. the authors are grateful to inhart laboratory for 53 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 providing laboratory equipment and the advanced institute of technology, upm for helping with the collagen assay experiment. references [1] yamazaki cm, kadoya y, hozumi k, okano-kosugi h, asada s, kitagawa k, nomizu m, koide t. (2010) biomaterials a collagen-mimetic triple helical supramolecule that evokes integrin-dependent cell responses. biomaterials., 31(7): 1925-1934. doi.org/10.1016/j.biomaterials.2009.10.014 [2] awang na, amid a, arshad zi. (2020) method for purification of collagen: a systematic review. asia pacific j. mol. biol. biotechnol., 28(3): 99-112. doi: 10.35118/apjmbb.2020.028.3.10. [3] lim y, ok y, hwang s, kwak j, and yoon s. (2019) marine collagen as a promising biomaterial for biomedical applications. mar. drugs, 17(467):1-32. [4] ilamaran m, janeena a, valappil s, ramudu kn, shanmugam g, and niraikulam a. (2019) biomaterials science a self-assembly and higher order structure biomaterial for cell proliferation. biomateriasl sci., doi: 10.1039/c9bm00186g. [5] gorres kl and raines rt. (2010) prolyl 4-hydroxylase. crit. rev. biochem. mol. biol., 45(2): 106-124. doi: 10.3109/10409231003627991. [6] privalov pl. (1982) stability of proteins. proteins which do not present a single cooperative system. adv. protein chem., 35: 1-104. [7] an b, kaplan dl, and brodsky b. (2014) engineered recombinant bacterial collagen as an alternative collagen-based biomaterial for tissue engineering, front. chem., 2: 1-5. doi: 10.3389/fchem.2014.00040. [8] pacak ca, mackay aa, and cowan db. (2014) an improved method for the preparation of type i collagen from skin. j. vis. exp., 83(e51011). doi: 10.3791/51011. [9] mohs a. (2007) mechanism of stabilization of a bacterial collagen triple helix in the absence of hydroxyproline. j. biol. chem., 282(41): 29757-29765. doi: 10.1074/jbc.m703991200. [10] xu c, yu z, inouye m, brodsky b, and mirochnitchenko o. (2014) bacterial collagen-like proteins that form triple-helical structures. j struct biol., 186(3): 451-461. doi: 10.1016/j.biotechadv.2011.08.021.secreted. [11] purandarey h. (2018) recombinant dna technology and its applications. int. j. medipharm res., 4(2): 98-98. doi: 10.5005/jp/books/10279_5. [12] khan s, ullah mw, siddique r, nabi g, manan s, yousaf m, hou h. (2016) role of recombinant dna technology to improve life. int. j. genomics., 2016: 1-14. doi: 10.1155/2016/2405954. [13] ratanapongleka k. (2013) recovery of biological products in aqueous two phase systems. int. j. chem. eng. appl., 1(2): 191-198. doi: 10.7763/ijcea.2010.v1.33. [14] andrews ba, nielsen s, and asenjo ja. (1996) partitioning and purification of monoclonal antibodies in aqueous two-phase systems. bioseparation. 6(5): 303-313. [15] warner lr, blasick cm, brown rj, and oxford jt. (2007) expression, purification, and refolding of recombinant collagen alpha1(xi) amino terminal domain splice variants. protein expr. purif., 52(2):403-409. doi: 10.1016/j.pep.2006.10.016. [16] alberto m. (2018) aqueous two-phase systems: properties, functions and advantages, may:1–14. doi: 10.13140/rg.2.2.20368.51209. [17] lin yk, ooi cw, tan js, show pl, ariff a, and ling tc. (2013) recovery of human interferon alpha-2b from recombinant escherichia coli using alcohol/salt-based aqueous two-phase systems. sep. purif. technol., 120: 362-366. doi: 10.1016/j.seppur.2013.09.038. [18] singh s and tavana h. (2018) collagen partition in polymeric aqueous two-phase systems for tissue engineering. front. chem, 6: 4-10. doi: 10.3389/fchem.2018.00379. [19] arshad zim, amid a, yusof f, sulaiman sz, mudalib ska, man rc, shaarani sm. (2017) perbandingan kaedah penulenan rekombinan bromelain daripada escherichia coli bl21-a1. malaysian j. anal. sci., 21(4): 958-971. doi: 10.17576/mjas-2017-2104-23. 54 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 [20] samad a and shukor a. (2017) protease purification from bacillus amyloliquefaciens b7 using aqueous two-phase system ( atps ). int. food res. j., 24: 292-297. [21] de albuquerque wanderley mc, wanderley duarte neto jm, campos albuquerque ww, de araújo viana marques d, de albuquerque lima c, da cruz silvério si, de lima filho jl, couto teixeira ja, porto alf. (2017) purification and characterization of a collagenase from penicillium sp. ucp 1286 by polyethylene glycol-phosphate aqueous two-phase system. protein expr. purif., 33: 8-14. doi: 10.1016/j.pep.2017.02.010. [22] ooi cw, tei bt, hii sl, ariff a, wu hs, lan jcw, juang rs, kamal smm, ling tc. (2009) direct purification of burkholderia pseudomallei lipase from fermentation broth using aqueous two-phase systems. biotechnol. bioprocess eng., 14(6): 811-818. doi: 10.1007/s12257-008-0306-y. [23] ling yq, nie hl, su sn, branford-white c, and zhu lm. (2010) optimization of affinity partitioning conditions of papain in aqueous two-phase system using response surface methodology. sep. purif. technol., 73: 343-348. doi: 10.1016/j.seppur.2010.04.020. [24] zhao l, budge sm, ghaly ae, brooks ms, and dave d. (2013) partition of pepsinogen from the stomach of red perch (sebastes marinus) by aqueous two phase systems: effects of peg molecular weight and concentration. enzym. eng., 2(1). doi: 10.4172/2329-6674.1000108. [25] lukomski s and mcnitt dh. (2020) expression and purification of collagen-like proteins of group a streptococcus in methods in molecular biology. 163-179. doi: 10.1007/978-1-0716-0467-0_12. [26] xu c, yu z, inouye m, brodsky b, and mirochnitchenko o. (2010) expanding the family of collagen proteins : recombinant bacterial collagens of varying composition form triple-helices of similar stability. biomacromolecules., 11: 348-356. [27] arshad zim and amid a. (2018). procedure to develop binodal curve and phase diagram for aqueous two-phase system. in multifaceted protocol in biotechnology. edited by a. amid, s. sulaiman, and d. n. jimat, eds. gateaway east, singapore: springer; pp. 75-85. [28] awang na, amid a, arshad zim. (2021) liquid-liquid equilibrium in aquesous two phase system (atps) and their application in purification of recombinant collagen-like protein from rhodopseudomonas palustris expressed in e.coli system. in proceedings of virtual international halal science conference ’21, july 2021, pp 127. [29] rito-palomares m, dale c, and lyddiatt a. (2014) aqueous two-phase fractionation of biological suspensions for protein recovery from bovine blood. biotechnol. tech., 12(9): 711-714. doi: 10.1023/a. [30] babu br, rastogi nk, and raghavarao ksms. (2008) liquid-liquid extraction of bromelain and polyphenol oxidase using aqueous two-phase system. chem. eng. process. process intensif., 47:83-89. doi: 10.1016/j.cep.2007.08.006. [31] gonzález-tello p, camacho f, and blázquez g. (1994) density and viscosity of concentrated aqueous solutions of polyethylene glycol. j. chem. eng. data., 39(3): 611614. doi: 10.1021/je00015a050. [32] benavides j and rito-palomares m. (2006) simplified two-stage method to b-phycoerythrin recovery from porphyridium cruentum. j. chromatogr. b anal. technol. biomed. life sci., 844: 39-44. doi: 10.1016/j.jchromb.2006.06.029. [33] thomas aw and kelly mw. (1922) the iso-electric point of collagen. j. am. chem. soc, 44(1): 195-201. doi: 10.1021/ja01422a025. [34] borsook h and macfadyen da. (1930) the effect of isoelectric amino acids on the ph+ of a phosphate buffer solution, j. gen. physiol., 13(5): 509-527. doi: 10.1085/jgp.13.5.509. [35] ma xx, fan dd, zhu ch, shang zf, and mi y. (2014) optimization of fermentation medium for collagen production of recombinant pichia pastoris during induction phase. j. chem. pharm. res., 6(7): 1802-1809. 55 iium engineering journal, vol. 24, no. 1, 2023 awang et al. https://doi.org/10.31436/iiumej.v24i1.2468 [36] awang na. (2022) purification of recombinant collagen-like protein from rhodopseudomonas palustris expressed in escherichia coli using aqueous two-phase system. master's thesis. international islamic university of malaysia, international institute for halal research and training. [37] zachariou m. (2008) affinity chromatography: methods and protocols. humana press. [38] bornhorst j.a. and falke jj. (2000) purification of proteins using polyhistidine affinity tags. methods enzymol., 326: 245-254. doi: 10.1038/jid.2014.371. [39] oscar a, veronica a, leobardo sc, and rito-palomares m. (2006) direct comparison between ion-exchange chromatography and aqueous two-phase processes for the partial purification of penicillin acylase produced by e . coli. j. chromatogr. b., 835: 77-83. doi: 10.1016/j.jchromb.2006.03.016. 56 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian a different approach in optimum design process using aco algorithm and fea validation of low-speed multi-phase ipmsms hamid reza gholinejad omran and sayyed asghar gholamian* department of electrical and computer engineering, babol noshirvani university of technology, babol, iran. *corresponding author: gholamian@nit.ac.ir (received: 28th mar. 2016; accepted: 27th sep. 2016; published online: 30th may 2017) abstract: magnet placement affects the performance of permanent magnet motors through changes to the magnetic flux density distribution. therefore, different magnet placements should be examined experimentally or by valid simulations. in this paper, an interior permanent magnet synchronous motor (ipmsm), called a spoke type, with specifications related to the propulsion of ships is designed and then optimized by ant colony optimization (aco) algorithm to increase the torque-to-volume ratio. the design procedure and its formulas are presented as simply as possible. based on these formulas, motor torque of about 16 knm in a volume of 0.87 m 3 was obtained. then, to verify the optimization results of the optimized motor, a two-dimensional finite element analysis (fea) is done. the error rate of the results was below 5%. also in this analysis, the core and the slot saturation were studied. abstrak: penempatan magnet memberi kesan kepada prestasi magnet motor kekal melalui perubahan kepada pengedaran ketumpatan fluks magnet. oleh itu, penempatan magnet yang berbeza perlu diperiksa secara eksperimen atau dengan simulasi sah. dalam kertas ini, motor segerak magnet kekal dalaman (ipmsm), yang dipanggil jenis spoke, dengan spesifikasi yang berkaitan dengan pendorongan kapal direka dan kemudian dioptimumkan oleh algoritma ant colony pengoptimuman (aco) untuk meningkatkan nisbah tork-kepada-isipadu. prosedur reka bentuk dan formula dikemukakan secara mudah. berdasarkan formula ini, tork motor kira-kira 16 knm dalam isipadu 0.87 m3 telah diperolehi. kemudian, untuk mengesahkan keputusan pengoptimuman motor yang optimum, satu analisis kaedah unsur finite dua dimensi (fea) telah dilakukan. keputusan menunjukkan kadar ralat adalah di bawah 5%. analisis ini juga membuat kajian mengenai teras dan tepu slot. keywords: interior permanent magnet synchronous motor; ant colony optimization; finite element analysis 1. introduction electric motors are one type of ship propulsion. their power depends on the ship weight and the number of ship propulsion sources. most of these motors work at low speeds and their operational voltage is between 400 volts and several kilovolts [1]. permanent magnet (pm) motors can be a choice for this application. pm motors present multiple benefits that have led to their use in many applications. increasing the phase number of these motors increases the fault tolerance and reliability but reduces the stator current (per phase) and harmonics in dc links compared to the conventional three-phase motors [2, 3, 4]. nowadays, advances that are obtained in the power electronics field have made it possible to implement more phases properly. therefore, in this paper, a multi133 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian phase pm motor will be investigated according to ship propulsion characteristics. a summary review of several related researches is given here. the advantages of a five-phase permanent-magnet motor are presented in [2]. the results show better performance of this motor than the three-phase pmsm and bldc counterparts. in [3], a five-phase halbach array permanent-magnet machine is optimized by genetic algorithm method to increase efficiency, acceleration, and output power. to achieve this goal, the analytical model of this motor based on motor geometrical and materials data is presented. in [5], using a new algorithm belonging to the class of controlled random search algorithms, a multi-objective optimization is done to decrease the weight and increase the efficiency of an interior permanent magnet synchronous motor. therefore, two motors with different speed and different output power have been optimized. one of them was single-layer buried magnet and the other one was doublelayer. in [6], ant colony optimization (aco) is used to optimize a magnet synchronous motor with surface permanent magnet topology. this algorithm has been applied to search for the optimum motor geometry. in this paper, error rate of 5% is considered to stop the algorithm. in [7], a systematic comparison of flat type, v-type, and spoke-type ipm machines is provided. to optimize the material cost, power losses, and the torque ripple of these motors, a combined multi-objective design optimization method employing design of experiments and differential evolution algorithms has been developed which is the most popular optimization method for electric machine design. in [8], after the initial design of a spoke type ipm for low voltage, the main purpose is using finite element analysis to improve its torque quality. so, in [8], a different number of segmented rotors and a changing mechanical air gap are used. according to these researches, this paper intends to provide a design procedure of a five-phase interior synchronous motor to be used as ship propulsion. the magnet placement in the rotor is at the wheel spokes and the optimal performance of this type compared to others is shown in a variety of researches [7-11]. in continuous operation, this motor will be optimized by an aco algorithm to reduce the size and increase the efficiency and torque. also, with the aim of achieving ship propulsion specifications, the optimization inputs will be considered in their acceptable ranges. then, based on optimal results, the motor will simulated based on fea and some cases such as copper losses, motor torque, air gap flux density, teeth and stator yoke saturation will studied to validate. 2. design procedure in motor design, determination of two types of initial parameters is essential. in fact, with the determination of these parameters, the design procedure will begin. the first types are determined by the motor application (according to customer requirements) such as the output power, the voltage, the applied frequency, and the rated speed, which are constant during the design procedure, whereas the second types are determined by the assumptions and experience of the designer and data sheets. the specific electrical loading, specific magnetic loading, excitation electromotive force (emf)-to-input voltage ratio, rotor length-to-diameter ratio, and in some cases the efficiency and the power factor are some of these parameters. first, the second types are assumed according to experience or data sheets and then, calculated at the end of each design cycle. the values will be compared and replaced with their previous values. if the percentage of the difference between the calculated values and the assumed values was acceptable, the design procedure will end and the results can be obtained. in the remainder of this section, and in the optimization section, the values of these parameters are given. 134 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian 2.1 dimensions of the motor motor dimensions contain rotor and stator dimensions. in this section, these dimensions are calculated by mathematical models of the motor. the dimensions of the magnets are discussed in the rotor section, because in the interior type, the size of magnet needed to provide output power, effects on the rotor yoke dimensions. the calculated dimensions are shown in fig. 1. fig. 1: dimensions of the motor. 2.1.1 rotor dimensions calculation in eqn. (1), diameter of the rotor is given by some of the initial parameters [1]. 3 4 4 2 f s av m w st s mpe i d b a k k n     (1) where ns is the motor speed in turns on second, is is the current per stator phase, m is the number of phases, p is the motor poles, and 𝐸f is the excitation emf. the value and the ranges of other parameters in this equation are listed in table 1. table 1: the value and the ranges of the initial parameters [1] parameters value and ranges specific magnetic loading 0.3 ≤ 𝐵𝑎𝑣 ≤ 0.8 specific electrical loading 10000 ≤ 𝐴𝑚 ≤ 55000 rotor length-to-diameter ratio 𝜋 𝑃⁄ ≤ 𝛼𝜏 ≤ 3𝜋 𝑃⁄ emf-to-input 0.6 ≤ 𝐸𝑓 /𝑉𝑖𝑛 ≤ 0.95 winding step coefficient (𝒌𝒘) 1 core lamination coefficient (𝒌𝒔𝒕) 0.95 the minimum value of the rotor yoke is calculated by the following equation, where in this equation [12, 13], 𝐵yr is the maximum saturated flux density in the rotor core. in this paper, it is considered to be 1.5 tesla. 135 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian 2 av yr yr st b d h b k   (2) the length of the magnet is equal to the length of the rotor (𝐿 = ατd), but its height (ℎm) and its thickness (𝑙m) must be calculated by analysing the specified magnetic equivalent circuit of this type, since they are long and complicated calculations, only the final equation is presented here [14]. equation (3) is obtained for the magnet height that has an acceptable answer for it (the positive one) [14], 2 2 2 2 2 2 5 5 5 4 4 4 s s s v out v out v out s s s m r av c r av c r r c s w s w sw c p d c p d c p d g w g w g w h lpb f h dg lpb f h dg lp b fh lp g                                          (3) and thus the magnet thickness is obtained by eqn. (4) [14]. 2 2 2 5 r s m av s r s m s l g b d w b ph g w                (4) in the above equations, pout is the motor output power that will be determined according to application. cv is a constant between 0.54 to 3.1 [1]. τs is the slot step and s is the slot number. ws is the width of the slot calculates from eqn. (6) [15]. µr is the relative magnetic permeability. f is applied frequency and hc is the magnet coercive force. the slot width is considered between two or three folds of the diameter of a conductor, experimentally. 2 ~ 3 4 / s s a w i j  (5)    74 10 / 0.6 ~ 0.8 m rg a d b p    (6) where 𝐽𝑎 is the current density in ampere per square meter with a range related to the cooling procedure of the motor and the type of insulation [1]. now, according to the height of the magnet and its top and bottom bridge thickness, the rotor yoke can be reformed. 2.1.2 stator dimensions calculation in this section, the slot and stator yoke dimensions are calculated under critical conditions. the critical conditions here mean the slot saturation threshold. under this condition, the stator dimensions are calculated slightly larger. similar to the eqn. (2), the minimum value of the stator yoke is calculated by eqn. (7), where in this equation, 𝐵ys is the maximum saturated flux density in the stator core, which is considered to be 1.5 tesla in this paper [12,13]. 2 av ys ys st b d h b k   (7) 136 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian the minimum tooth width is calculated according to maximum flux that can pass through one tooth as follows [12], av tb t b d w sb   (8) 𝐵t is the maximum saturated flux density in the teeth, which is also 1.5 tesla. the slot depth can be obtained by calculating the slot area in two ways (according to the crosssection of conductors placed in one slot and according to motor core geometry). by equalizing these two equations, a quadratic equation is obtained. then, slot depth can be calculated according to eqn. (9). this equation has an acceptable answer for the slot depth (the positive one).     2 2 2 2 2 2 2 2 2 teeth teethav av s s t t a d g h d g hb d b d s i h b b j                    (9) ℎ𝑡𝑒𝑒𝑡ℎ has been shown in fig. 1 and its value is about 1 to 2 mm. after determining the slot depth, 𝑤sb and 𝑤st , can be obtained by calculating the slot pitch in bottom and top of the slot and subtracting width of a tooth from them. these parameters are given in the following equations;  2 2sb s tbw d g h w s      (10)  2st tbw d g w s     (11) since the slot pitch is obtained by summing the width of top of the tooth and slot width, so it can be concluded that: st s w w  (12) 2.2 motor torque calculation this parameter is very important in propulsion applications where high torque at low speed is needed to move a very heavy vehicle. the interior permanent magnet motors are known as salient-pole motors. because of the changes in the effective air gap length and as a result, changes in the inductances. therefore, in addition to synchronous torque, these motors have reluctance torque, too. thus, interior permanent magnet motors can achieve higher torque than the surface mounted type [1, 14, 15]. the electromagnetic torque in electrical motors is [1, 14];   2 q f q dd q mp t i i xe i x f       (13) in this equation, 𝐼q and 𝐼d are the d-q-axis of the stator current and 𝑋q and 𝑋d are the d-q axis of synchronous reactances. achieving a torque value based on eqn. (13) seems too hard, because of difficulties in calculating its parameters. this paper proposes a simpler method to achieve the motor torque. the method is using the following equation [1]. 137 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian   4 in cu p p p t f   (14) where, 𝑃in is the input power and 𝑃cu is the copper losses. torque value calculated by eqn. (13) and eqn. (14) are equal to each other, but eqn. (14) is simpler. the copper losses are given in eqn. (15). this equation is reformed according to motor dimensions and considering the end-winding effect [16],      2 2 2 1 4 s s t ov q scu ph a h h p m n j l d d w y s s k i                                  (15) ρ is the conductors' resistivity and is equal to 1.68×10−8 for copper. the value and definition of some other parameters in the eqn. (15) are brought in table 2. table 2: the value and the ranges of eqn. (11) parameters [12] parameters value and ranges copper resistivity 𝜌 = 1.68×10−8 current density 3 ≤ 𝐽𝑎 ≤ 25 a practical value 1.6 ≤ 𝑘𝑜𝑣 ≤ 2 coil pitch 𝑦𝑞 = 𝐼𝑛𝑡(𝑆 𝑃⁄ ) 3. optimization method in this section, to achieve the main purpose of this article, an effective cost function is defined and optimization will be done based on an aco algorithm. the main purpose of this article is the torque-to-volume ratio increasing in the permanent magnet motors based on the equations that are provided in the previous section. the considered cost function in this paper is as follows; 1 c min max f tv v t   (16) where, 𝑉 is the motor volume (during optimization) and 𝑉min is the least possible volume in the solution space. similarly, 𝑇max is the maximum value of the motor torque. in the above equation, the influence of the specific magnetic loading, specific electrical loading, rotor length-to-diameter ratio and motor speed to increase the torque-to-volume ratio of the motor are considered. 3.1 aco algorithm this algorithm is based on aspects of the behavior of ants. as mentioned in introduction section, this algorithm has repeatedly been used in previous research, and all of these showed good performance. the pseudo-code of this algorithm is shown in table 3 and its flowchart is shown in fig. 2 [17]. 138 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian table 3: pseudo-code for ant colony [17] initialize parameter initialize pheromone trails create ants while stopping criteria is not reached do let all ants construct their solution update pheromone trails allow daemon action end while fig. 2: flowchart of the aco algorithm. based on aco, the transition rule quantifies the probability of an ant k, positioned at city i, traveling to city j, and given by:               2 2 2 2 . 1 / . 1 / k i j j k ij j j l ij i i j il i i t x x y y p t t x x y y                                ò (17) where, (xi,yi) and (xj,yj) are coordinates of the cities i and j respectively. 𝛼 and 𝛽 are weighting parameters for the pheromone and the distance between cities i and j. 𝜏ij(𝑡) is the pheromone in each arc. the evaporation process simulated by eqn. (18) applies an evaporation rate 𝛾 between 0 and 1 [17].      1 .1ij ijt t    (18) as 𝛾 value gets closer to 0, the pheromone importance increases. the pheromone quantity deposited in each arc can be expressed by the eqn. (19) [17], 139 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian    1 kij m k q t s t      (19) where, 𝑄 is a positive parameter and 𝑆k(𝑡) is the length of the tour constructed by ant k at interaction t. the value of algorithm parameters are: 𝛼 = 1, 𝛽 =3, 𝑄 = 100, 𝜌 = 0.4 and 𝜏0 = 0.000001. the optimization inputs such as specific magnetic loading, specific electrical loading, separation factor (rotor length-to-diameter ratio), and emf-to-input ratio are shown in table 1. these parameters vary in their ranges to achieve the optimum input. 3.2 optimum design of an ipmsm in this section, a five phase spoke type permanent magnet synchronous motor will be optimized to achieve the highest torque-to-volume ratio, based on equations and information that were given in the previous sections. initial parameters are: power; 160 kw, voltage; 1000 v, and frequency; 25 hz. also, motor speed has been considered as one of the optimization variables to find its optimum value between 200 to 800 rpm. at the first step of this section, two optimizations with a single objective function are done. these functions are the motor torque and the whole motor volume, which result in the maximum torque and the minimum volume. then, based on eqn. (16), the optimization with a multi-objective function is done. based on these optimizations, the maximum torque and the minimum volume value are achieved at 24044 nm and 0.4584 cubic meters respectively. optimum input and the results of the multi-objective function are shown in table 4. table 4: the optimization results parameters values unit parameters values unit 𝑽𝒐𝒍𝒖𝒎𝒆 0.8605 m3 𝜶𝝉 0.8702 𝑻orque 16200 nm 𝑬𝒇/𝑽𝒊𝒏 0.81 𝑷𝒄𝒖_𝒆𝒘 6954 w 𝑫 0.9444 m 𝑷𝒄𝒖 4123.3 w 𝑳 0.822 m 𝑩𝒂𝒗 0.5851 tesla 𝒉𝒚𝒓 0.119 m 𝑨𝒎 29456 a/m 𝒉𝒚𝒔 0.061 m the convergence curve of the aco algorithm is shown in fig. 3. in this figure, the curve tends to 0.5, because each of the parameters (torque and volume) in eqn. (16) are per-unit. the closer the curve to 0.5, the better the convergence. 4. simulation of an optimized motor before construction, fea is one of the ways of evaluating the proposed procedure, as its results are very close to experimental results. for this reason, the optimized motor will be simulated by ansys-maxwell® software which is based on fea. so far, this software 140 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian fig. 3: convergence curve of the aco. has been successfully used in previous research. some parameters derived from simulation, such as the motor torque, the copper losses and the air gap flux density will be compared with the optimization results to investigate the accuracy of the design procedure. also, the saturation in the teeth and stator yoke has been explained. this simulation is done on a 64-bit system that has 3 gigabytes of ram, and 2.53 ghz of cpu. the total number of mesh elements is 428588, the stop time is considered to be 80 milliseconds with 0.1 ms of step time. a view of the simulated motor is shown in fig. 4. also, table 5 represents the core type and the magnet characteristics used in simulation. fig. 4: 2-d and 3-d view of simulated motor. table 5: details of core and permanent magnet characteristics parameters details unit kind of core m19-24g mass density 7650 kg/m3 kc 0.0154809 w/m3 kh 6.92096e-005 w/m3 ke 0.000345255 w/m3 br 1.2 t hc -920000 a/m 141 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian 4.1 results of simulation as shown in fig. 5, the motor torque average value calculated by simulation is 15.5912 knm with 3.82% ripple. this value for torque ripple is acceptable and common in this type of motor, because of their particular structure [1, 4, 7, 8, 15]. the motor torque value calculated in optimization has less than 4% difference with the simulation result. compared to the error in the references [2, 3], this error is acceptable and represents the accuracy of the applied equations. there is 0.2% difference between the average value of flux density calculated by fea (0.58 tesla) and the optimization result. fig. 5: the curve of the motor torque. the motor performance, especially motor torque, will be improved as long as the air gap flux density distribution becomes better, because of its effects on whole design process. figure 6 shows the distribution of the air gap flux density in one pole pitch. ripple existence in this curve is due to stator slots. fig. 6: air gap flux density changes in one pole. as mentioned in section 2.2, motor torque can be achieved by calculating copper losses. since the effect of the end-winding is not taken into account in the twodimensional analysis, fig. 7 represents the copper losses without considering the effect of end-winding while in the eqn. (15) it is considered. but, it is possible to calculate copper losses without considering the end-winding effect to compare them more appropriately. 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 time [ms] 0.00 2.50 5.00 7.50 10.00 12.50 15.00 17.50 20.00 m o v in g 1 .t o rq u e [ k n e w to n m e te r] maxwell2ddesign2torque curve inf o avg pk2pk moving1.torque setup1 : transient 15.5912 0.5951 0.00 100.00 200.00 300.00 400.00 500.00 600.00 distance [mm] 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 m a g _ b [ m t e s la ] maxwell2ddesign2xy plot 1 curve inf o mag_b setup1 : transient time='10400000ns' 142 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian the copper losses calculated by aco is 4123.3 w which has a difference less than 4% with the fea result. fig. 7: the copper losses amount. investigation of the saturation gives designers an awareness of their design accuracy, so that if the flux density be higher than specified limit, it indicates that the calculated dimensions are less than what they should be. this comes into account as a defect in the design process. in fig. 8 and fig. 9, the amount of the flux density in the stator yoke and teeth are shown respectively. fig. 8: the flux density changes in the stator yoke. fig. 9: the flux density changes in the tooth. 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 time [ms] 3500.00 3750.00 4000.00 4250.00 4500.00 c o p p e r_ l o s s e s maxwell2ddesign2xy plot 1 curve inf o max avg copper_losses setup1 : transient 3987.8671 3967.9535 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 distance [mm] 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 m a g _ b [ te s la ] maxwell2ddesign2xy plot 3 curve inf o mag_b setup1 : transient time='10400000ns' 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 distance [mm] 0.63 0.83 1.02 1.23 1.43 1.63 m a g _ b [ te s la ] maxwell2ddesign2xy plot 2 curve inf o mag_b setup1 : transient time='10400000ns' 143 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian according to fig. 8 and fig. 9, it can be found that the saturation does not occur in the whole stator. it should be noted that in fig. 8, the maximum amount of the flux density is larger than the considered saturation density but is not significant and is acceptable in the design field. also, to illustrate a better view of the saturation issue, a magnetic flux density throughout the motor is shown in fig. 10. this figure confirms the validity of what was said about fig. 8 and fig. 9. table 6 represents a comparison between the optimization results and the simulation results in this paper. fig. 10: flux density distribution table 6: comparison of results parameters fea optimization error (%) rated torque (nm) 15591.2 16200 3.9 copper losses (w) 3968.6 4123.3 3.9 air gap flux density (t) ~0.59 0.5851 0.83 𝑬𝒇/𝑽𝒊𝒏 0.77 0.81 5.19 current density (a/mm 2 ) 3.01 3 0.033 5. conclusion in this paper, the optimum design procedure of a five-phase spoke type permanent magnet synchronous motor is presented. then the optimization is performed by an ant colony optimization (aco) algorithm with the aim of maximizing torque at the lowest volume to use as ship propulsion. finally, the finite element simulation is used for validating the results of the optimization. based on the results, the low percentage of errors show the validity and accuracy of the proposed design method. references [1] gieras jf. (2010) permanent magnet motor technology: design and applications. 3rd ed. usa: crc press. [2] parsa l, toliyat ha. (2005) five-phase permanent-magnet motor drives. ieee transactions on industry applications, 41(1):30-37. 144 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=28 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=28 iium engineering journal, vol. 18, no. 1, 2017 omran and gholamian [3] sadeghi s, parsa l. (2011) multiobjective design optimization of five-phase halbach array permanent-magnet machine. ieee transactions on magnetics, 47(6):1658-1666. [4] parsa l, goodarzi a, toliyat ha. (2005) five-phase interior permanent magnet motor for hybrid electric vehicle application. ieee vehicle power and propulsion conference, 631637. [5] parasiliti f, villani m, lucidi s, rinaldi f. (2012) finite-element-based multiobjective design optimization procedure of interior permanent magnet synchronous motors for wide constant-power region operation. ieee transactions on industrial electronics, 59(6):25032514. [6] tsampouris e, kakosimos p, kladas a. (2013) coupled computation of electric motor design and control parameters based on ant colonies speed trajectory optimization. ieee transactions on magnetics, 49(5):2177-2180. [7] zhang p, ionel dm, demerdash nao. (2013) morphing parametric modeling and design optimization of spoke and v-type permanent magnet machines by combined design of experiments and differential evolution algorithms. ieee energy conversion congress and exposition, 5056-5063. [8] demir y, ocak o, aydin m. (2013) design optimization and manufacturing of a spoke type interior permanent magnet synchronous motor for low voltage-high current servo applications. ieee international electric machines & drives conference, 9-14. [9] mi cc. (2006) analytical design of permanent-magnet traction-drive motors. ieee transactions on magnetics, 42(7):1861-1866. [10] jannot x, marchand c, vannier jc, gabsi m, saint-michel j, sadarnac d. (2011) multiphasic modeling of a high-speed interior permanent-magnet synchronous machine for a multiobjective optimal design. ieee transactions on energy conversion, 26(2):457-467. [11] gundugdu t, komurgoz g. (2010) design of permanent magnet machines with different rotor type. world academy of science, engineering & technology, 4:468-473. [12] bianchi n, bolognani s, frare p. (2006) design criteria for high-efficiency spm synchronous motors. ieee transactions on energy conversion, 21(2):396-404. [13] grauers a. (1996) design of direct-driven permanent magnet generator for wind turbines. chalmers university of technology. phd thesis. chalmers university of technology, göteborg, sweden. [14] seong taek l. (2009) development and analysis of interior permanent magnet synchronous motor with field excitation structure. phd thesis. university of tennessee, usa. [15] pyrhonen j, jokinen t, hrabovcov´a v. (2009) design of rotating electrical machines. 1st ed. great britain: cpi, 2009. [16] manninen a. (2012) evaluation of the effects of design choices on surface mounted permanent magnet machines using an analytical dimensioning tool. msc thesis. university school of electrical engineering, aalto, finland. [17] rodrigues monteiro ms. (2012) ant colony optimization algorithms to solve nonlinear network flow problems. phd thesis. university of porto, portugal, faculty of economics. 145 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=20 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=41 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=20 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=20 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=20 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=20 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=60 http://ieeexplore.ieee.org/xpl/recentissue.jsp?punumber=60 microsoft word pages-17-35.doc iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 17 gas permeation characteristics across nano-porous inorganic membranes m.r othman*, h. mukhtar and a.l. ahmad school of chemical engineering, engineering campus, university science malaysia, 14300 nibong tebal, p. pinang. program of chemical engineering, university technology petronas, 31750 tronoh, perak *e-mail: chroslee@eng.usm.my abstract: an overview of parameters affecting gas permeation in inorganic membranes is presented. these factors include membrane physical characteristics, operational parameters and gas molecular characteristics. the membrane physical characteristics include membrane materials and surface area, porosity, pore size and pore size distribution and membrane morphology. the operational parameters include feed flow rate and concentration, stage cut, temperature and pressure. the gas molecular characteristics include gas molecular weight, diameter, critical temperature, critical pressure, lennard-jones parameters and diffusion volumes. the current techniques of material characterization may require complementary method in describing microscopic heterogeneity of the porous ceramic media. the method to be incorporated in the future will be to apply a stochastic model and/or fractal dimension. keywords: inorganic membrane, surface adsorption, knudsen diffusion, micro-porous membrane, permeation, gas separation. 1. introduction the separation of mixtures of gases is a common and important unit operation in chemical industries especially natural gas processing plant. polymeric membranes have been used commercially for the separation of acid gases such as co2 and h2s from natural gas since 1979. however, polymeric membranes have several limitations attributable to low thermal and pressure resistant which hinder the use of such membranes for gas separation at high temperature. gas separation involving relatively high temperature and/or pressure needs inorganic material membranes because polymeric membranes are not suitable at high temperature due to its thermal stability and resistant. the use of inorganic membranes for separation application has gained popularity in academia as well as industries due to inherent stability in extreme operating conditions. apart from stability at high temperature and large pressure gradient, inorganic membranes are also known to be invulnerable to chemical attack from chemically active mixture and microbial degradation [1]. these favorable attributes have been identified to have brought about an increasingly improved acceptance level of inorganic membranes by industries. the fact that the service life of inorganic membranes is three to five times longer than their organic iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 18 adversaries has fostered and rekindled even more interest among researchers in enhancing the state of the art of the present inorganic material characterization [11]. inorganic membranes, commonly made from ceramic, sintered metal or metal oxide (al2o3, zro2, or tio2), zeolite, palladium metal, glass tubes and pyrolyzed carbon have been gaining attraction particularly for application in a laboratory scale experiment [11]. inorganic membranes can be tailored made to form a hybrid, asymmetric or composite membrane by means of sol-gel techniques or chemical vapor deposition [2]. due to the imposing efficacies as illustrated in many technical journals and reports, the use of inorganic membranes for air filtration or air cleaning from particulate matters has been made more prevalent today than in the past. they have been used in replacement of a conventional filter such as dead-end fabric for clean room applications. they also have made a successful entry into the market as in line gas filters in microelectronic packaging, food and pharmaceutical industries to remove fine particles from gas streams [2, 11, 20, 29]. a more promising application with which inorganic membranes have received considerable attention in a wide array of industrial operations is gas permeation. this is particularly important in fuel cell application in which h2 and o2 are use as feed gas and the membrane acts as solid electrolyte in order to generate electricity [3]. gas permeation involves feeding of gas mixture usually at a higher pressure or concentration into feed stream. lower molecular weight gas species is separated from higher molecular weight gas species by virtue of different rate of diffusion through the membrane. lower molecular weight species, having higher rate of diffusion will diffuse faster into a much lower pressure or concentration in the permeate stream of the membrane. the permeate stream, enriched with low molecular weight species is carried or driven by inert gas for further process or collection [4]. few instances of gas permeation applications using inorganic membrane include separation of co2 or h2 from methane and other hydrocarbons, adjustment of h2/co ratio in syngas, separation of air into nitrogen and oxygen, recovery of helium and methane from bio-gas. inorganic membranes also offer profound potential in applications for gas separation in a high temperature catalytic reaction and are potentially useful for the separation of trace contaminants such as ammonia, hydrogen sulfide and carbonyl sulfide from coal-gasifier fuel gases [5]. permeation of gas species in porous inorganic membrane of average pore size less than 2 nm is contributed primarily by two internal transport mechanisms. the first being, knudsen diffusion mechanism represented by the second term of eq. (1), is prevailed in most of the porous systems where collision frequency between molecules and the pore wall increases. mechanistically, the mean free path of the gas molecules before collision occurs is larger than the pore diameter of the membrane. the second mechanism is surface diffusion represented by the third term of eq. (1), contributed primarily by the affinity of gas molecules adsorbed and diffused along the pore wall. the contribution of surface diffusion, however, is claimed to be significant only in a process operated at low temperature and high pressure region [6,7,8]. minimal or insignificant effect was observed for high temperature process [9]. for a membrane having pore radius (rp) greater or equal iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 19 to the molecular radius of gas species i, (rgi), the gas permeation can be described mathematically by,                     fd m rtrrr rtz k ms gpp    ( 18 3 )(2 8 2 , where rp  rg (1) and the ideal selectivity or separation factor,  is defined as the ratio of the permeability of the more diffusive gas to the less diffusive gas. in a binary gas mixture, the observed separation factor can be obtained experimentally using,                x x y y 1 1  (2) where y and x represent the mole fractions of the gas component in downstream and upstream of the membrane, respectively. despite the usefulness and the advantages inorganic membranes have had to offer, they are not without drawbacks especially with respect to selectivity, and the dilemma associated with pore size reduction. extremely small pore size often reduces the permeability of the membrane [10], but high permeability is required for high flux of gas, whereas small pore size is desired for high degree of selectivity. in both cases, the success of separation process largely depends on many of the variables which range from the membrane’s physical-chemical characteristics, operational parameters of the process to gas molecular characteristics in which, the combined effect of the diffusive properties of the gas species and the characteristics medium works to cause the desired level of separation of the gas. various factors affecting permeation of gas across inorganic membranes have been recognized in many recent scientific publications [1-32]. they are however, very much eclectic in nature whose results, some of which, pose challenges to researchers who are making effort at arriving and standardizing research conclusion. the objective of this paper is to briefly overview the crucial factors that characterize nano-porous inorganic membrane from past and present literatures based on such factors as membrane physical characteristics, operational parameters and gas molecular characteristics. the performance of gas separation in a system comprising h2 in a binary gas mixture is provided in the discussion. anticipation on new methods of characterization of inorganic membranes in the future research setting is also included. 2. physical characteristics of membrane membranes formulated from different synthesis or techniques would result in membranes having different physical characteristics. nevertheless, the fundamental parameters of interest to researchers for further inference about their characterization are noted as follows: iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 20 2.1 membrane materials and surface area material selection and knowledge of physical adsorption of a gas for the selected material are particularly important for gas separation application using nano-porous inorganic membranes. selecting a material that exhibits higher adsorption of a gas relative to another gas using certain membrane material can be useful in separating the mixture of the two binary gas species. when gas molecules are adsorbed and mobile preferentially on the pore wall, they will diffuse along the pore wall in the direction of decreasing driving forces. if the pore wall of the membrane has an affinity for the gas molecules, a substantial amount of the molecules could be diffused in this manner. platinum and palladium, for instance, are known to exhibit preferential adsorption to hydrogen [4]. using these metal species in the membrane could help improve the selectivity of binary mixture of gas containing hydrogen component. pd impregnated membrane was used [11] and resulted in separation factor between 4 to 8 as illustrated in table 1 at relatively low pressure application (0.03-0.21 bar). in the absence of this metal, the separation was lower even at relatively higher operating pressures [11-15]. improvement in the selectivity can be realized if higher pressure is applied. this is due to the degree of the surface diffusion and adsorption contribution towards the permeability increase relies heavily on the pressure (for a given isotherm). the higher the pressure for a given isotherm, the more readily the gas molecules to be adsorbed and mobile along the pore surface of the membranes. the pressure-separation factor relationship will be articulated further in the ensuing topic. bet surface area, a physical characteristic of membranes, defines how much gas can be adsorbed or accommodated per gram of the material. higher surface area is preferred since it is the indication of the greater amount of gas that can be adsorbed onto the membrane’s pore surface. higher bet surface area commonly is correlated reciprocally with smaller average pore radii [16, 17]. the smaller the pore, the greater the separation factor. an infinite he/co2 separation factor (100 percent separation) could be obtained if membrane having pore radius less than 4 angstroms (410-10 m) or extremely small pores comparable to the size of gas molecules was used [18]. silica hollow fiber membrane, as illustrated in table 1, demonstrated the highest separation factor for h2/n2 mixture [13], and this is attributed to high bet surface area. for nano-porous inorganic membrane, the typical bet surface area is in the range between 200 to 400 m2/g [16]. bet surface area as much as 4000 m2/g was also observed for zeolitic materials [32]. 2.2 porosity, pore size and pore size distribution porosity is an important parameter that characterizes inorganic materials and differs them from dense membranes. the porosity values could be determined conveniently if micro pore volume and density of the membrane are known [19]. inorganic structures having high porosity value enable more gases to permeate through since porosity correlates proportionally with permeability. however, highly porous structures may not be able to achieve the desired selectivity of the gases. iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 21 table 1: comparison of hydrogen separation factor from different works. mixture (knudsen s.f) material and pore size (nm) preparation technique temp.(c) press.(bar) separation factor tio2 (4) multi-layer support [12] 27-29 1.19 4.8 h2/co2 al2o3 (4) pd impregnation [11] 104-445 0.03-0.21 4.0-8.0 (4.67) al2o3 (10-20) anodic alumina [11] -196-97 0.23-1.05 5.0 sio2 hollow fiber [13] 25-70 21 4.7-5.4 tio2 (4) multi-layer support [12] 27-29 1.19 2.71 h2/co al2o3 (4) multi-layer support [14] 20-300 1.3-17.4 1.2-2.2 (3.72) al2o3 (10-20) anodic alumina [11] -196-97 0.23-1.05 3.5 sio2 hollow fiber [13] 25-70 21 31-62 tio2 (4) multi-layer support [12] 27-29 1.19 2.02 h2/n2 al2o3 (4) pd impregnation [11] 104-445 0.03-0.21 4.0-10.0 (3.72) zeolite in situ synthesis [15] 20 1 3.06 sio2 hollow fiber [13] 25-70 21 125-163 h2/sf6 zeolite -zsm5 in situ synthesis [30] 27-29 1 51 al2o3 (200600) support [31] 27-29 1 1.12 h2/n-c4h10 hydroxysodalite zeolite (0.28) in situ synthesis [31] 27-29 1 >1000 iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 22 the choice of porosity values relies heavily on the desired selectivity and on the mechanical strength of the membranes that suit the process application. highly porous materials are usually associated with lower mechanical strength. vast number of researches advocated that the effective control over the level of porosity rests on proper selection of sintering temperature profile (to obtain firm coalescence between particles and particles with the support, and a well-determined membrane structure with good mechanical resistance) and binder composition during membrane synthesis. the overall porosity was found to decline with increase in temperature [1, 11, 20, 29]. this was due to the micro pore volume that decreased as a result of more of the micro pores evolved and coalesced with other micro pores (<2 nm) to form meso pores (2–50 nm) and macro pores (>50 nm) at higher temperature [16]. porous inorganic membranes are also frequently characterized in terms of their pore size and pore size distribution. when pore size is comparable to the size of the gas molecules, while other parameters remain constant, the gas permeability across the membrane, to some extent, follows the sequence of diameter of the gas molecules in a decreasing magnitude. normally, narrow pore size distribution is desired in inorganic membranes for gas separation since wider distribution encompasses unnecessarily large pores. this renders the membranes to be less effective in achieving the desired level of selectivity. 2.3 membrane morphology membrane morphology is another important parameter besides porosity that governs membrane’s characteristic. it is commonly performed through sem micrographs or tem imaging with certain level of magnification to identify nano-pore structures, in addition to textural details analysis of the top membrane layer. this is to examine the presence of defects forming such as cracks or pinholes and structural deformation. knowledge of the membrane morphology would be useful if surface modification process would necessitate the subsequent process in order to negate the undesirable defects from developing. fig. 1: sem micrographs of the surface of the sintered alumina membrane (sintered at 400°c) with with 500 magnification iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 23 in the textural analysis, a hill (observed as a white circle) or crater (observed as a black hole from the opposite side) may be discovered on the photo such as illustrated in figure 1. this should not be confused with pinholes or cracks, since despite its presence; the hill does not induce structural defection in the membrane. it is not uncommon to develop hills in membrane especially when the surface of the support material (usually petri-dish) contains dust or tiny grains that protrude from the dish surface. the uneven surface eventually contributes to the crater development. in normal procedures, the development of hills or craters is hindered by subsequently coating and firing of the membrane [20]. membrane samples are not only analyzed from the top and bottom but the crosssectional views as well. the analysis is performed to identify the continuity of the pores, the tortuous path of the membranes and perhaps their nominal lengths. the membrane thickness also could be examined in detail from the analysis such as illustrated in fig. 2. the answers to many conflicting results and eclectic remarks of membrane performance among researchers employing similar membrane materials and configuration in the past and present studies possibly lie within this analysis. fig. 2: sem micrographs of the cross-section of the sintered alumina membrane with 500 magnification. titania alumina perm selective skin iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 24 3. operational parameters 3.1 feed rate and concentration typically, by increasing the feed flow rate and concentration of gas mixtures will result in increase in the permeation of the gases. separation tends to increase as the concentration of lighter gas species in the feed stream is increased due to the more momentum that the lighter gas species gain from collision between its own molecules rather than the other components molecules [18]. however, the concentration effect on separation is less influential in comparison to the effects of feed pressure and temperature. unless the gas transport is promoted via adsorption mechanism by selecting a suitable material to enhance the degree of affinity of the gas towards the pore surface, the separation will be strictly confined to the knudsen separation demonstrated by knudsen diffusion mechanism such as shown in fig. 3 [12]. the figure demonstrates that separation tends to approach asymptotically to the respective knudsen separation factor of the binary gases at relatively high feed concentration. 0 1 2 3 4 5 6 7 10 20 30 40 50 60 70 80 90 h2 concentration in feed stream, % mol h 2 se pa ra tio n fa ct or ,  [y /( 1y )] ´[ (1 -x )/ x ] hydrogen nitrogen mixture hydrogen carbon monoxide mixture hydrogen carbon dioxide mixture h2/co2 knudsen separation factor h2/n2 and h2/co knudsen separation factor no separation fig. 3: hydrogen separation factor as a function of feed concentration at p =1.19106 g.cm-1.s-2 (t=301k, rp=2nm, /=0.385, avg0.22) [12]. figure 3 shows the effect of feed concentration on the separation of gas mixture across titania membrane at average pressure of 1.19106 g.cm-1.s-2, temperature 301k, average pore radius of 2 nm, stage cut  0.22 and the ratio of porosity to tortuous factor equivalent to 0.385. in separation of binary gas mixture, the gas with a lower molecular weight will adsorb faster than the gas with a higher molecular weight. in the study, the h2 gas adsorb faster than other gas component. as the h2 concentration was increased in the feed, the h2 concentration in the permeate stream also increased. the highest increase was for h2/co2 mixture followed by h2/co and h2/n2 mixtures. the dotted lines in the figure represent the knudsen or ideal separation factor, the ratio of the square root of the higher molecular weight gas to lower molecular weight gas. separation existed for all the mixtures but iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 25 apparently confined only to the knudsen separation demonstrated by knudsen diffusion mechanism. the hydrogen separation factor in h2/co2 gas mixture reached the knudsen separation factor asymptotically at high hydrogen concentration. similar trend was observed for h2/co and h2/n2 but to a magnitude lower than the respective ideal separation factor. the solid curves representing the experimental data for the respective mixtures in fig. 3 are calculated results employing complete mixing model. the curves follow second order exponential. 3.2 stage cut stage cut, defined as the ratio of the total permeate flow rate to the total feed flow rate, is one of the operational factors that remains to be crucial in the field of gas separation using inorganic membranes. in most instances, separation tends to increase with decrease in stage cut as illustrated in fig. 2 [12]. 0 1 2 3 4 5 6 7 0. 15 0.1 6 0. 17 0.1 8 0. 19 0. 20 0.2 1 0. 22 0. 23 0.2 4 0. 25 0. 26 0.2 7 0. 28 0.2 9 0. 30 0. 31 0.3 2 0. 33 0. 34 0.3 5 0. 36 stage cut, q [qp/qf] h 2 se pa ra tio n fa ct or , � hydrogen nitrogen mixture hydrogen carbon monoxide mixture hydrogen carbon dioxide mixture h2/co2 knudsen separation factor h2/n2 and h2/co knudsen separation factor no separation fig. 4: hydrogen separation factor as a function of stage cut atp =1.19106 g.cm-1.s-2 (50/50 mol ratio, t=301k, rp=2nm, /=0.385) [12]. figure 4 shows the hydrogen separation factor as a function of stage cut. the concentration in the inlet stream was maintained at 50 mol percent of hydrogen and 50 mol percent of the other component. the permeate flow rate varied in the range between 15 to 31 ml/min corresponding to the total feed flow rate increase from 50 to 200 ml/min, respectively. stage cut, , in the experiment was decreased by increasing the feed flow rate. as the feed flow rate was increased (and thereby  decreased), the separation factor increased and to a certain extend went beyond the boundary of knudsen separation factor. the influence of stage cut on the separation is governed by the molecular diffusion and driving force. at high feed flow rate (lower stage cut), the lighter permeating component from the mixture diffuses into the permeate stream faster due to the greater difference in concentration between feed and permeate stream. iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 26 3.3 pressure the influence of pressure on the permeation rate of the more diffusive gas has been widely acknowledged in the past and present work [1-32]. at relatively low pressure, separation is normally confined to knudsen separation contributed by knudsen diffusion mechanism [12, 21]. however, by increasing pressure substantially, separation of gases can exceed the boundary of knudsen separation factor, and at the onset, shift towards the desired level due to the presence of surface diffusion mechanism [12] as illustrated in fig. 5. essentially, the separation can be further increased if the preferential adsorption for particular gas is aided with proper material selection and this has been discussed under section 2.1 (membrane material and surface area). 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 1.19e+06 1.70e+06 3.08e+06 4.12e+06 5.15e+06 6.70e+06 average pressure, g.cm-1.s-2 � h 2 se pa ra tio n fa ct or ,  hydrogen nitrogen mixture hydrogen carbon monoxide mixture hydrogen carbon dioxide mixture h2/co2 knudsen separation factor h2/n2 and h2/co knudsen separation factor no separation fig. 5: hydrogen separation factor as a function of average pressure (50/50 mol ratio, t=301k, rp=2nm, /=0.385, avg 0.22) [12]. an experiment was conducted to investigate the influence of average pressure on the separation of gases [12], during which, the temperature was maintained at 301k, average pore radius of 2 nm, stage cut  0.22 and the ratio of porosity to tortuous factor equivalent to 0.385 were selected. the results of this work are shown in fig. 3. the figure shows that as average pressure was increased the separation factor increased beyond the knudsen separation factor for h2/co2 mixture and h2/co mixture to certain extend. for h2/n2 mixture, the observed separation factor reached approximately to knudsen separation factor at high average pressure. this demonstrates that at higher average pressure, hydrogen in h2/co2 mixture and h2/co to some extend no longer confined in the knudsen diffusion region. another mechanism started to prevail and apparently, that was the surface diffusion mechanism. essentially, the increase of separation factor at high pressure was dominated by the surface adsorption and the preferential adsorption for h2 by the membrane was actually higher than that of the other component gases, allowing more of h2 being adsorbed and mobile along the pore wall. iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 27 3.4 temperature other things remain equal, gas permeation has been known to vary inversely with the square root of temperature and that surface diffusion contributed minimally to gas permeation rate at a high temperature process. since adsorption mechanism is less promising at high temperature, the relative permeability reduction for component gas species should be significant enough in order to achieve higher separation of gases. this can be realized by making the pore size of membrane to be used in high temperature process even smaller or creating the tortuous path longer to prevent the less diffusive gas from permeating into the membrane readily [12]. fig. 6: separation factor of h2/n2 in commercial titania and modified titania (alumina +titania) membrane at low and high temperature respectively [21]. figure 6 illustrates separation factor for h2/n2 across titania and modified titania membrane at low and high temperature respectively [21]. the perm-selective skin coated on the membrane support (shown in figure 2) that had reduced pore size was effective in improving the separation of gas mixture containing h2 and n2 even at high operating temperature. the higher separation factor was obtained due to the perm-selective skin that was able to retain pores of smaller than four nm at higher operating temperature. the higher separation factor was also attributed to the fact that the surface flow of nitrogen diminished at a more distinct magnitude at higher temperature than that of hydrogen, yielding permeability ratio of h2/n2 (separation factor) at low temperature to be lower than at higher temperature. 4. gas molecular characteristics the distinctive characteristics of gas molecules play an important role in permeability of the gases across inorganic membranes [12, 21]. these molecular characteristics include iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 28 the gas molecular weight, diameter, critical temperature, critical pressure, molecular interaction (binding energy), lennard-jones parameters and diffusion volumes. defying the importance of these factors in gas separation application would limit the effectiveness of the membranes and their performance. examples of these characteristic values for selected gas species whose diameters are reported [13, 18] can be viewed from table 2. table 2: gas molecular properties. gas molecular diameter (å) tc (k) pc (atm) m (g/mol) lennard-jones parameters [18] [13]  (å) /k (k) h2 2.968 2.89 33.3 12.8 2.016 2.915 38 he 2.576 2.6 5.26 2.26 4.003 2.576 10.2 ch4 3.88 190.7 45.8 16.04 3.822 137 co 3.590 3.76 133 34.5 28.01 3.590 110 n2 3.681 3.64 126.2 33.5 28.02 3.681 91.5 o2 154.4 49.7 32.0 3.433 113 co2 3.996 3.3 304.2 72.9 44.01 3.996 190 the molecular interaction in the form of energy interaction between gas-gas molecules and gas-solid interface has been incorporated in a single dimensionless permeability equation [22]. lennard-jones parameters, when employed in an empirical formula [23] and diffusion volumes, used in the derived equation [24] could be a useful combination for analyzing gas viscosity at various temperatures and diffusivity estimation in the permeability studies. however, since gas viscosity has less effect on nano-porous membranes, more focus is dedicated towards the diffusivity of gases. permeability of gases across nano-porous inorganic membranes has been known to increase with increase in gas diffusivity. since h2 is much more diffusive than co2 in comparison to h2 and n2, and h2 and co, the former species retains in permeate stream much longer as demonstrated in fig. 5 [21] hence, higher concentration in the stream. 5. additional parameters all the various characteristic factors discussed earlier could be generalized to form a common ground for researchers in acquiring understanding of the microscopic nature and performance aspects of inorganic membranes. however, since accuracy and precision are becoming increasingly imperative, and the fact that the application of inorganic membranes is becoming more pervasive, there is a need to expand the knowledge of material characterization within the context discussed above. iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 29 0 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 h2 mol % in the feed h 2 m ol % in th e pe rm ea te s tr ea m hydrogen nitrogen mixture hydrogen carbon monoxide mixture hydrogen carbon dioxide mixture complete mixing model fig. 5: effect of feed concentration on permeation of hydrogen across titania membrane at p =1.19106 g.cm-1.s-2 (50/50 mol ratio, t=1073k, rp=2.5nm, /=0.385,  average  0.22) [21]. the current techniques of material characterization may not be adequate. this is further exacerbated by the fact that the micro-porous media may not be homogeneous. within the media there may exist variations in the gas velocities within a pore, between pores of slightly different sizes (diameter and length), and different tortuous paths that have slightly different lengths. an alternative method in describing this heterogeneity is to apply stochastic techniques. a stochastic model is an approach to use the stochastic functions such as arithmetic or geometric mean, standard deviation, variance, and correlation length to generate spatially correlated parameters. another alternatively innovative approach is to describe the heterogeneities utilizing fractal geometry. fractal geometry suggests that at the molecular size range, the surfaces of most materials are fractals. the fractal approach relies on the concept of self-similarity and is an alternative way to characterize complex geometries such as the surface area or pore structure of materials. the term “surface fractal” has been used to identify the fractal dimension, d. a higher d value suggests a greater wiggle and space filling surface and that the surface is extremely irregular. in the work of wei and wang [25], they investigated pore surface roughness change in composite al2o3–sio2 membranes by the analysis of surface fractal dimension. fractal features were analyzed from n2 adsorption–desorption measurements. it was found that surface fractal dimension increased with increase of sio2 content in composite membrane with different molar ratio of alumina to silica sintered at 600°c. the surface fractal dimension of membrane with 40 mol% silica content increased slightly at sintering temperature of 200 and 600°c but decreased at the temperature of 800°c. this was explained by the viscous mechanism and shrinkages/expands of mass fractal dimension of silica clusters at varying temperature huang et al. [26] reported a study on the pore microstructures in two viscous rayonbased activated carbon fiber samples by using nitrogen adsorption and extracted image of hrtem. one sample exhibited bet surface area of 640m2/g and another 1680m2/g. the iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 30 surface fractal dimensions, d of the samples were evaluated by using both nitrogen adsorption and tem image analysis [27-29]. in fractal geometry, a fractal dimension is used to explain the length scale or roughness of the flow paths measured in the laboratory. fractal geometry offers a model to explain distinct behavior or patterns at different length scale of irregular objects. data on this will be collated in the future publication. 6. conclusion fundamental parameters affecting gas permeation in nano-porous inorganic membranes are discussed. the solitary objective is in the emphasis of the crucial factors in membrane characterization concepts in general, from the past and present experience. these factors are grouped into three categories. the first category is the membrane physical characteristics, which include membrane materials and surface area, porosity, pore size and pore size distribution and membrane morphology. the second category is the operational parameters, which include feed flow rate and concentration, stage cut, temperature and pressure. the third category is the gas molecular characteristics, which include gas molecular weight, diameter, critical temperature, critical pressure, lennardjones parameters and diffusion volumes. supplementary characterization technique may be needed to gain deeper understanding about the heterogeneity of porous inorganic structures. alternatively, a method that has the potential to be incorporated in the future will be to apply a stochastic model and fractal dimension to explain distinct behavioral patterns of membrane architectures. acknowledgement this paper summarizes the results of work from research grant provided by usm and numbers of colleagues. the author also acknowledges contribution made by norzeeha mat rashid and nor faeqah idrus towards the completion of this article. references [1] lee, d., zheng, l., ogama, s.t., nin, s. and sarac, r.f. (2004). synthesis, characterization and gas permeation properties of a hydrogen permeable silica membrane supported on porous alumina. journal membrane of science, 231, 117-126. [2] bottino, a., capannelli, g., d’asti, v. and piaggio, p. (2001). preparation and properties of novel organic-inorganic porous membranes. separation and purification technology, 2223, 269-275. [3] boechetta, p.,chiavarotti, g., masi, r., sunseri, c. and di quarto, f. (2004). nanoporous alumina membranes filled with solid acid for thin film fuel cells at intermediate temperatures. short communication, electrochemistry communications, 16, 923-928. [4] howard, b.h., killmeyer, r.p., rothenberger, k.s., cugini, a.v., morreale, enick, r.m. and bustamante, f. (2004). hydrogen permeance of palladium-copper alloy membranes over a wide range of temperature and pressures. journal of membrane science, 241, 207218. iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 31 [5] venkataraman, v.k., rath, l.k. & stern, s.a. (1991). potential application of micro-porous inorganic membranes to the separation of industrial gas mixtures. key engineering materials, 62, 347-352 [6] zaman, j. and chakma, a. (1994). inorganic membrane reactors. journal of material science, 92, 1-28 [7] uhlhorn, r.j.r., keizer, k. & burggraaf, a.j. (1989). gas and surface diffusion in modified -alumina systems. journal of membrane science, 46, 225-241 [8] uhlhorn, r.j.r., huis int’l veld, m.h.b.j., keizer, k. & burggraaf, a.j. (1989). high permselectivities of microporous silica modified -alumina membrane. journal of material science, 8, 1135-1138 [9] van veen, h.m., tol, j.p.b.m., engelen, c.w.r. & veringa, h.j. (1991). high temperature gas separation with alumina membranes. key engineering materials, 62, 593-598 [10] kusakabe, k., yamaki, t., maeda, h. & morooka s. (1993). porous -alumina membrane modified with ultrafine zirconia particle prepared by reversed micelles method. american ceramic society, 38, 1-18 [11] hsieh h.p. (1996). inorganic membrane for separation and reaction. membrane science and technology series, 3. new york: elsevier publication. p. 28-71,242, 249-251 [12] othman, m.r., mukhtar, h. and ahmad, a.l. permeation of h2 across titania and modified titania membranes at low temperature region. 15th symposium of malaysian chemical engineers somche 2001. 11-12 september 2001, johor bharu. proceedings p. 121-126. [13] way, j.d. and roberts, d.l. (1992). hollow fiber inorganic membranes for gas separations. separation. science and technology, 27, 29-41 [14] wu, j.c.s, flowers, d.f. & liu, p.k.t. (1993). high temperature separation of binary gas mixtures using microporous ceramic membranes. journal of membrane science, 77, 85-98 [15] jia, m.d., peinemann, k. & behling, r. (1993). ceramic zeolite composite membranes: preparation, characterization, and gas permeation. journal of membrane science, 82, 15-26 [16] m.r. othman, h. mukhtar and a.l. ahmad. (2001). characteristics of unsupported alumina membrane prepared using sol-gel technique. asean journal on science and technology for development. vol. 18 no. 2 , 59-70 [17] a.f.m.leenaars, k.keizer, a.j.burggraaf. (1984).the preparation and characterization of alumina membranes with ultra-fine pores. journal of material science. 19, 1077-1088 [18] d.e fain and g.e roettger .(1993). coal gas cleaning and purification with inorganic membranes. journal of engineering for gas turbines and power. vol.115, 631-638 [19] de lange r.s.a., hekkink, j.h.a, keizer, k. & burggraaf, a.j. (1996). microstructural properties of non-supported microporous ceramic membrane top layers obtained by the sol gel process. journal of non-crystalline solids, 195, 203-221 [20] othman, m.r., mukhtar, h. review on development of ceramic membrane from sol-gel route: parameters affecting characteristics of the membrane. iium engineering journal, 2000, vol. 1, no. 2, p. 29-34. [21] ahmad, a.l. othman, m.r., and mukhtar, h. (2004). h2 separation from binary gas mixture using coated alumina-titania membrane by sol gel technique at high temperature region. international journal of hydrogen energy, 29, 817-828. iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 32 [22] shindo, y., hakuta, t., yashitome, h. & inoue, h. (1983). a dimensionless equation for gas diffusion in microporous media in knudsen’s regime. journal of chemical engineering japan, 16, 521-523 [23] bird r.b., stewart, w.e. & lightfoot, e.n. (2002). transport phenomena, 4th ed. new york: john wiley & son. 744-755 [24] geankoplis, c.j. (1993). transport process and unit operations, 3rd ed. p. 759-760. prentice hall [25] wei, qi and wang, d. (2003). pore surface fractal dimension of sol–gel-derived al2o3– sio2 membranes. materials letters, 57, 2015-2020. [26] huang zheng-hong, feiyu kang, wen lai huang, jun-bing yang, kai-ming liang, menglong cui, zhiying cheng. (2002). pore structure and fractal characteristics of activated carbons fibers characterized by using hrtem. journal of colloid and interface science, 249, 453-457. [27] carpinteri, a. and spagnoli, a. (2004). a fractal analysis of size effect on fatigue crack growth. international journal of fatigue, 26, 125-133. [28] wang, y. and xu, k.-w. (2004). characterization of surface morphology of copper tungsten thin films by surface fractal geometry and resistivity. thin solid films, 468, 310-315. [29] s.benfer, u.popp, h.richter, c.siewert, g.tomandl. (2001). development and characterization of ceramic nanofiltration membranes. separation and purification technology. 22-23, 231-237. [30] h. richter, i. voigt, g. fischer and p. puhlfürß (2003). preparation of zeolite membranes on the inner surface of ceramic tubes and capillaries. separation and purification technology, volume 32, issues 1-3, pages 133-138 . [31] xiaochun xu, yun bao, chunshan song, weishen yang, jie liu and liwu lin (2004) microwave-assisted hydrothermal synthesis of hydroxy-sodalite zeolite membrane. microporous and mesoporous materials, volume 75, issue 3, pages 173-181 [32] koichi matsuoka, yasushi yamagishi, toshiaki yamazaki, norihiko setoyama, akira tomita and takashi kyotani (2004). extremely high microporosity and sharp pore size distribution of a large surface area carbon prepared in the nanochannels of zeolite y. short communication. carbon. in press, corrected proof. nomenclature ds surface diffusion [m2.s-1]  equilibrium loading factor [mol.kg-1] k permeability [mol.s-1][m][m-2][kg-1.m.s2]  p average pressure in membrane pore [kg.m-1.s-2] m mass of molecule [kg.kgmol-1] r gas constant [kg.m2s-2.kgmol-1.k-1] rg radius of gas molecule [m] rp radius of membrane pore [m] iium engineering journal, vol. 5, no. 2, 2004 m.r othman et al. 33 t temperatue [k] z compressible factor [-] greek letters  tortuosity factor [-]  viscosity of gas [kg.m-1.s-1]  porosity [-] m density of membrane [kg.m-3] biographies mohd roslee othman currently is a lecturer, chairman of separation process and catalysis program and industrial training coordinator of school of chemical engineering, universiti sains malaysia (usm). he obtained his bachelor and master of science degree in petroleum engineering from university of missouri-rolla, usa in 1994 and 1997 respectively, before completing his ph.d. degree in chemical engineering from usm in 2002. his research areas include inorganic membrane development for gas separation, gas adsorption, permeability of fluid in porous media and reservoir study. hilmi mukhtar currently is a senior lecturer and the head of chemical engineering program, universiti teknologi petronas (utp). his research area is in membrane technology. abdul latif ahmad currently is a associate professor of chemical engineering, engineering campus, universiti sains malaysia (usm). he received his bsc., msc. and phd. in chemical engineering from wales, uk. his research area is in membrane technology. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 cytotoxicity effect of ionic liquidgraviola fruit (annona muricata) extract to human colon cancer (ht29) cell lines djabir daddiouaissa1,2*, azura amid2, nassereldeen ahmed kabbashi1, ahmed adam mohammed elnour1,2 and mohamad adika khairy bin mohd shaifudin epandy3 1 biotechnology engineering department, kulliyyah of engineering, 2 international institute for halal research and training (inhart), international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia 3 adikafirdaus resources, lot 24, jalan klebang selatan, 2/5 kampung tersusun, batu 6 klebang selatan, 31200 ipoh, perak, malaysia * corresponding author: daddiouaissa.djabir@live.iium.edu.my (received: 3rd november 2020; accepted: 31st march 2021; published on-line: 4th july 2021) abstract: the present study aimed to investigate the anti-proliferative effect of the ionic liquid-graviola fruit (il-gfe) extract on colon adenocarcinoma (ht29) cell lines and their kinetics behaviour to assess the graviola fruit potential as a therapeutic alternative in cancer treatment. the phytoconstituents content of il-gfe was identified using gc-tofms apparatus and measured its cytotoxicity on ht29 by tetrazolium bromide. then the cytokinetic behaviour of the treated ht29 cells with il-gfe was illustrated using the cells' growth curve. besides, the cell cycle phase perturbation for the treated ht29 was applied using a flow cytometry technique. qualitative identification of phytoconstituents of il-gfe showed that graviola fruit contains acetogenins, alkaloids, flavonoids, tannins and saponins compounds. il-gf extract displayed a cytotoxicity effect on ht29 cells with the ic50 value of 10.56 µg/ml, while taxol showed an ic50 value of 1.22 µg/ml. il-gfe also decreased the cell generation number from 3.93 to 2.96 generations compared to taxol-treated cells 2.01 generations. the microscope observation of the ht29 cells treated with the crude il-gfe displayed loss of density and cell detachment. the extract's growth inhibition was related to the cell cycle arrest at the g0/g1 phase. il-gfe inhibited colon adenocarcinoma ht29 cells' proliferation and affected their kinetic behaviour by lowering cell viability, inducing apoptosis, and arresting the cell cycle at the g0/g1 phase. abstrak: kajian ini bertujuan untuk mengkaji kesan anti-proliferatif ekstrak buah-ion graviola (il-gfe) pada garis sel adenokarsinoma kolon (ht29) dan tingkah laku kinetik mereka untuk menilai potensi buah graviola sebagai alternatif terapi untuk barah rawatan. kandungan fitokonstituen il-gfe dikenal pasti menggunakan alat gc-tofms dan mengukur sitotoksisitasnya pada ht29 oleh tetrazolium bromida. kemudian tingkah laku sitokinetik sel ht29 yang dirawat dengan il-gfe digambarkan menggunakan keluk pertumbuhan sel. selain itu, gangguan fasa kitaran sel untuk ht29 yang dirawat diaplikasikan menggunakan teknik sitometri aliran. pengenalpastian kualitatif fitokonstituen il-gfe menunjukkan bahawa buah graviola mengandungi asetogenin, alkaloid, flavonoid, tanin dan sebatian saponin. ekstrak il-gf memperlihatkan kesan sitotoksisiti pada sel ht29 dengan nilai ic50 10.56 µg/ml, sementara taxol menunjukkan nilai ic50 1.22 µg/ml. il-gfe juga menurunkan jumlah penjanaan sel dari 3.93 hingga 2.96 generasi berbanding sel yang dirawat taxol 2.01 generasi. pemerhatian mikroskop 50 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 sel ht29 yang dirawat dengan il-gfe kasar menunjukkan kehilangan ketumpatan dan detasmen sel. perencatan pertumbuhan ekstrak berkaitan dengan penangkapan kitaran sel pada fasa g0/g1. il-gfe menghalang percambahan sel ht29 adenokarsinoma kolon dan mempengaruhi tingkah laku kinetik mereka dengan menurunkan daya maju sel, mendorong apoptosis, dan menghentikan kitaran sel pada fasa g0/g1. keywords: colon cancer; cell cycle; flow cytometry; graviola (annona muricata); growth kinetics; gc-tofms; ionic liquids 1. introduction fruit consumption is hugely recommended to preserve the healthy life of a human being. annona muricata is known as graviola, also called soursop in english, due to its sour and delicious fruit [1]. graviola is predominately harvested in the tropical and subtropical regions of the world. nowadays, graviola fruit is vastly utilised to produce syrups, beverages and candies [2]. all graviola tree parts have ethnobotanically reported being used in alternative medicine, mainly the fruit that is obtained to reduce worms and parasites [3], treat fever and enhance mother's milk [4], as well as renal, liver infections [5], hypertension [6] and cancer treatment [7]. the frequent use of graviola in treating cancer may be related to its cytotoxic selectivity to cancer cells [4,8,9]. also, studies have reported that the toxicity of graviola to the cancer cells was more than healthy cells [10-12]. the potential anticancerous of the graviola fruit extract was reported to be related to the phytochemicals called annonaceous acetogenins that are thought to be cytotoxic against different cancer cell lines, as highlighted in our previous study [13]. recently, researchers are interested in the antitumor activity of acetogenins, as these are the main compounds isolated from the fruit [14]. the latest study confirmed that the il-gfe showed selectivity toward cancer cells by affecting only the breast adenocarcinoma (mcf-7) cell lines but not the normal (vero) cell lines, even with a high dose of 100 µg/ml [15]. this finding is in agreement with a study conducted by dai et al. [11]. hence, the graviola fruit can be a promising substitute or complementary supplement to reduce tumour cell proliferation generally. colon adenocarcinoma is a frequently high incident rate in both sexes, with an estimation of 101,420 new cases and 51,020 colon cancer (cc) deaths in the united states in 2019 [16]. therefore, it is hypothesised that the recent rapid declines in the colon cancer rate are due to the increased uptake of colonoscopy, which now is a useful screening test. common used protocols in cancer treatment such as radiotherapy, chemotherapy and surgical intervention cause various side effects such as nausea, fatigue, hair loss, vomiting and weak immune system [17]. hence, new approaches to treat cancer are highly recommended. lately, our research team has successfully extracted bioactive compounds from graviola fruit by ionic liquid-microwave-assisted extraction technique and showed a positive effect on breast cancer (mcf-7) cell line while it was safe toward normal vero cell line [15]. moreover, this extract did not cause any significant toxicity on the morphology of the treated zebrafish model [18]. ionic liquid-based microwave-assisted extraction (il-mae) method has been applied successfully to the efficient extraction of bioactive compounds from medicinal plants. this is related to the high extraction efficiency, shorter extraction time and the unique properties of ils which is proposed to be an environment-friendly technique in sample preparation. this may replace the well-known solvent used in extraction technique such as methanol (meoh) in which, its toxicity makes it undesirable for eco-friendly approaches [19]. it is expected that the il-mae method would be able to extract new bioactive compounds from 51 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 graviola fruit that are safe for human consumption to be used in cancer treatment. many outcomes achieved by using ionic liquid-based processes in the extraction and isolation of several bioactive compounds such as small natural compounds from biomass, lipids, proteins, amino acids and pharmaceuticals [20]. bogdanov [21] has reviewed the mechanism of ils action in the process of solid-liquid extraction from the plant, showing that the ils can attribute to the solvent-matrix interactions, which leads to the modification of permeability of the plant matrix. this is due to the disruption of the cell tissue and modifying the matrix permeability through the interaction of the h bonding with the carbohydrates from the cell walls. a previous study carried out by cláudio et al. [22] reported that aqueous solution of [c4mim]cl is the appropriate extractive solvent of caffeine from paullinia cupana seeds (guaraná) in which, at the optimum extraction conditions of (2.34 m [c4mim]cl, 70 °c, 30 min, s/l ratio 1:10) the extraction efficiency was enhanced by 50% compared with the one obtained by soxhlet extraction method using dichloromethane solvent. another study conducted by wang and co-workers. [23], reported that the 1-hexyl-3-methylimidazolium tetrafluoroborate [c6mim][bf4] water solution was used to extract lipophilic and hydrophilic metabolites from chrysanthemums and showed better extraction performance for the desired product than methanol. the ils extraction ability relies on their physicochemical characteristics, such as hydrophobicity, hydrogen bonding ability and viscosity, which may have promising applications in the extraction of the natural product from plant supplies [24]. thus, this research aimed to explore the phytochemical content and the potential anti-proliferative of the ionic liquid extract of graviola fruit (il-gfe) toward colon adenocarcinoma cell lines using mtt assay, cytokinetic behaviour and the flow cytometry technique. 2. materials and methods 2.1 chemicals and reagents all experimental chemicals utilised in this study were laboratory grade. the 1-butyl-3 methylimidazolium chloride [c4mim][cl] 96% solution was obtained from (alfa, usa). the n,o bis(trimethylsilyl)-trifluoroacetamide (bstfa) 99% was purchased from (sigmaaldrich, usa). media for cell growth include dulbecco's modified eagle's medium (dmem), fetal bovine serum (fbs) and penicillin/streptomycin were purchased from (gibco®, usa). for the anti-proliferative assay, the 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyl-tetrazolium bromide (mtt reagent) and the accutase solution (cell detachment) were obtained from (ict, usa). in addition, the rnase a / prepodium iodide kit of the cell cycle assay was purchased from (beckman coulter, usa). all these reagents were utilised to evaluate the anti-proliferative activity of il-gf extract on colon adenocarcinoma cell lines. 2.2 fruit sample preparation graviola fruit samples (db3) were chosen randomly from the farm of adikafirdaus (4.5921° n, 101.0901° e), perak state, malaysia. after that, the fruits were properly cleaned to eliminate all traces of insects and dust, removed the pericarp and seeds. the fruit pulp was then frozen at -20 °c for 72 hrs, then freeze-dried using a lyophiliser (christ alpha) based on the methodology of hoeing [25]. next, the dried sample was weighed and stored in falcon tubes at -20 °c for further analysis [26]. the fruit samples were stored in the herbarium with voucher number kaed/hbl/s1a047/2018/707 at the kulliyyah of architecture and environmental design, iium. the plant name was checked on www.theplantlist.org. 52 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 2.3 fruit sample extraction the dried graviola fruit sample was extracted as described in our previous study [15]. in brief, the dried sample was mixed at a ratio of [1:30] g/ml of 0.5 mol/l of [c4mim][cl] reagent. the extract suspension was heated under a microwave oven with irradiation power of 700 w for 3 min. then, the fruit extract (il-gfe) was cooled down to room temperature and then filtered using a 3 mm whatman filter paper. a back extraction to recover the ionic liquid was applied using phase separation with ethyl acetate at a ratio of 1:2 [27]. the extract was then lyophilised by freeze drier for 72 hrs. finally, the dried extract was stored at 4 °c chiller until further analysis [28,29]. 2.4 gc-tofms sample preparation and analysis the phytochemicals content of il-gfe was identified using gas chromatography (gc– tofms) analysis; the dry il-gf extract was silylated by using n,o bis(trimethylsilyl)trifluoroacetamide (bstfa) / acetonitrile (40:60; 1000 μl) and incubated at 60 °c for one hour. the sealed vials were vortexed at an interval of 1 min to achieve complete silylation. silyl derivatisation is a common process to raise the volatility and detectability of the chemical compound in gcms analysis [30]. in this research, gc-tofms analysis of the il-gfe used a 7890a agilent-technologies gc system formed by a 7693-mass spectrometer system detector (agilent technologies, usa). the method of muhamad et al. [31] was adopted with modification. the ms detector was run with an electron energy of 70 ev and a mass range of m/z 50–550. an hp-5 ms capillary column of (30 m × 0.25 mm, 0.25 µm film thickness) was utilised for separation. the gc oven temperature was set at 80 °c for 2 min, then raised to 240 °c at 5 °c/min and held for 5 min then finally increased to 300 °c at a rate of 3 °c/min and kept for 5 min. the temperature of the gc injector and ms transfer line was set at 225 °c and 300 °c, respectively. the sample was injected in the splitless mode at a ratio of 1:10. the carrier gas (helium) was utilised at a constant flow rate of 1.2 ml/min. consequently, essential compounds were identified by comparing their retention time and mass spectra with those of the standard and authentic compounds at the national institute of standard (nist) library. 2.5 cell culture in this study, the colon adenocarcinoma ht29 cell line (atcc no: htb-22™) was used as the experimental tumour cell. these cells were obtained from the american type collection culture and stored in liquid nitrogen until further utilisation. after thawing the frozen cells, they were inoculated into 25 cm2 t-flask with 5 ml of complete media, including dmem complemented with 10% fbs and 1% pen/strip. next, the culture cells were incubated at a 95% humidified incubator with 5% co2 at 37 °c. then, the cells were used for further experimental analysis when they reached approximately 80% confluence. 2.6 the mtt cell viability assay the viable cell number was quantified using the tetrazolium-based colourimetric (mtt assay). the confluent cells were detached from the bottom of the t-flask by adding 2 ml of accutase, and then the cell was counted using a haemocytometer. almost 5.0 x 104 cells were suspended in 100 µl of media and plated in each well of 96-well plate then incubated in a 5% co2 incubator for 24 hrs. after removing the media, 20 µl of serial dilutions (6.25400 µg/ml) of the il-gf extract in media free-fbs were added to the cells (triplicate wells per condition). the negative control received only dmso, and the positive control treated with taxol (0.39-6.25 µg/ml). the treated cells were incubated for 48 hrs, then added 20 µl of mtt reagent (5 mg/ml) into different wells. the incubation was then extended for another 3 hours then the media was carefully discarded. next, the solubilisation liquid 53 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 (dmso) (100 µl) was applied to each well to solubilise formazan then shake for 15 min at room temperature [32]. finally, the formazan absorbance was measured at 570 nm by a microplate reader. the percentage of viable/dead cells were calculated, and the ic50 of ilgf extract toward ht29 was determined using equation 1: 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝐶𝑒𝑙𝑙 𝑉𝑖𝑎𝑏𝑖𝑙𝑖𝑡𝑦 (%) = 𝐴𝑏𝑠 𝑜𝑓 𝑡𝑟𝑒𝑎𝑡𝑒𝑑 𝑐𝑒𝑙𝑙𝑠 𝐴𝑏𝑠 𝑜𝑓 𝑢𝑛𝑡𝑟𝑒𝑎𝑡𝑒𝑑 𝑐𝑒𝑙𝑙𝑠 𝑥 100 (1) 2.7 the 50% inhibitory concentration estimation the inhibitory effect of the il-gf extract on the colon cancer cell growth was shown as the inhibitory concentration that induced 50% inhibition of the cell population (ic50). this ic50 value was obtained graphically by plotting the percentage of viable cells against the associated different concentrations of the il-gf extract used. findings were presented as the mean ± one standard error (se), and statistically, the p ≤ 0.05 level was considered acceptable. 2.8 growth kinetics study the growth kinetics study was performed to establish a model that predicted the ilgfe effect on treated and non-treated colon adenocarcinoma ht29 cell lines and compared it to taxol-treated cells as a positive control. first, ht29 cells were counted and inoculated into 25 cm2 t-flask at 2.0 × 105 cells/ml and incubated for 24 hrs. there were three groups of flasks in this study (triplicate flasks per condition): untreated ht29, taxol-treated ht29 at the ic50 value of 1.22 µg/ml and ht29 treated with il-gf extract at the ic50 value of 10.56 µg/ml [33]. the treated cells in 20 flasks per group were counted every 8 hrs interval (from 0 to 144 hrs). after incubation, the media was discarded, and the cells received fresh media containing the samples, then incubated from 0 to 144 hrs. cell images were observed and recorded every 8 hours using a 10x magnification microscope. after that, cells were harvested from a monolayer and quantified using a trypan blue dye exclusion assay [34]. finally, the cell viability number was determined by using eq. 2: 𝐶 = 𝑛 𝑥 2 𝑥 104 (2) where n presents the average of the quantified cells, the number 104 is the conversion of volume 0.1 mm3 to 1 millilitre, and 2 is the dilution factor. the growth kinetics graph was plotted using the resulted data to calculate the number of cell generation, the specific growth rate and doubling time by using eqs. (3), (4) and (5). 𝑋 = 𝐿𝑜𝑔10𝑁 − 𝐿𝑜𝑔10𝑁0 𝐿𝑜𝑔102 (3) 𝐿𝑜𝑔10𝑁 = 𝐿𝑜𝑔10𝑁0 + 𝜇𝑡 (4) 𝑡𝑑 = 𝐿𝑜𝑔102 𝜇 = 0.301 𝜇 (5) where (x) is the number of cell generation; (n) is the number of cells at the end; (n0) is the primary number of cells; (µ) is the specific growth rate; (t) is the duration of treatment; (td) is the doubling time. 2.9 cell cycle assay the cell cycle phase perturbation in il-gf extract-treated ht29 was analysed in a timedependent manner using flow cytometry. first of all, approximately 5.0 x 104 of colon ht29 cell lines were inoculated into 25 cm2 t-flask and incubated for 24 hrs. after that, the media 54 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 was discarded and replaced with new media contains il-gf extract at the ic50 concentration value, then incubated progressively for 24, 48 and 72 hrs. after harvesting the cells with accutase, cells were thoroughly washed using 1x pbs and centrifuged at 1500 rpm for 5 min. the cells were fixed for one hour with 2 ml of 70% ethanol then centrifuged at 4000 rpm for 10 min at room temperature. then removed the supernatant and washed the cells with pbs. next, the treated cells were stained with 500 µl of 0.05 mg/ml of rnase a and 0.05 mg/ml of propidium iodide reagent in pbs [35]. the perturbation in cell cycle phases between the treated and untreated ht29 cells (10,000 events/group) was determined by the flow cytometry (cytoflex s, beckman coulter, usa). the cells in phases s and g2m were considered as proliferative cells and in the sub-g1 phase as apoptotic cells [36]. 2.10 statistical analysis the experiments of cell viability and cytokinetic growth were performed in triplicates, and the findings were displayed by the overall mean of three independent experiments ± standard deviation (sd). the statistical analysis of the data was carried out using graphpad prism software (version 7.00). one-way (anova) analysis of variance and tukey's test were applied using minitab software (version 17; pa, usa) to show the significant differences. the statistical analysis was considered acceptable when p ≤ 0.05. 3. results 3.1 gc-tofms analysis the phytochemical content of the il-gf extract was identified by using the gctofms instrument. the secondary metabolites detected in the extracts were validated by measuring the similarity of the pattern obtained from the gc-tofms reader with the existing database pattern. graviola fruit extract (gfe) constituents generally belong to the class of alkaloids, flavonoids, phenols, and acetogenins. according to many kinds of literature, these compounds have antidiabetic, anti-oxidant and anti-cancer activities [37]. the result of the gc-tofms analysis of il-gf extract was shown in table 1, where 55 compounds were identified as having greater than 70% similarity with the standard mass spectroscopy in the nist library. the major components identified by gc-tofms were d-psicofuranose, pentakis ether (13.53%), propyldecyl cyclopropane carboxylate (7.86%), tri-ruthenium dodecacarbonyl (7.86%), n-acetylimino dimethylsulfurane (7.86%), mannopyranose (7.74%), pyranone (7.74%), carbohydrazide (5.97%), nickel tetracarbonyl (5.57%), benzoic acid (5.46%), formic acid, ethenyl ester (4.45%) and propanetriol, 1acetate (3.68%). table 1 presents the complete list of bioactive components from the il-gf extract. 3.2 the ic50 of il-gf extract against ht29 cell lines after plotting the graph of viable cells (%) vs different doses of the sample (µg/ml), the estimation of the ic50 values for il-gf extract and taxol were 10.56 µg/ml (fig. 1) and 1.22 µg/ml (fig. 2), respectively. these findings confirmed that the il-gf extract has significantly inhibited the ht29 cell proliferation in a dose-dependent manner. 55 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 table 1: compounds present in the ionic liquid extract of graviola fruit identified by gc-tofms peak no area % compound name r. time (s) molecular weight g/mol 1 0.17 1-chloropropylene 180.232 76.01 3 0.15 butanedione, monooxime 182.125 101.05 4 0.55 nitrous acid, methyl ester 182.457 61.02 2 0.44 alpha-carotene 194.044 536.44 5 0.53 molybdenum carbonyl 205.697 662.12 6 0.80 propanediol, trimethylsilyl ether 206.062 148.09 7 1.70 pentanedione, 3-diazo 206.626 126.04 8 1.18 cyclopentane, 1-acetyl-1,2-epoxy 206.925 126.07 9 0.18 acetophenone, 4'-nitro-, thiosemicarbazone 208.585 238.05 10 0.69 propenoic acid, oxiranylmethyl ester 213.964 128.05 11 0.20 mercaptamine 220.039 77.03 12 0.13 nitroso-3-pyrroline 232.921 98.05 13 0.16 oxalic acid 256.061 90.00 14 0.92 acetic acid, (aminocarbonyl) 264.295 132.02 15 0.17 acronize 270.105 478.11 16 5.97 carbohydrazide 275.251 90.05 17 6.05 pyranone 275.45 144.04 18 4.45 formic acid, ethenyl ester 276.014 72.02 19 1.69 trifluoromethanesulfonic acid ethyl ester 276.313 177.99 20 0.44 ala-gly, trimethylsilyl ester 289.593 218.11 21 1.04 furanone, dihydro-4-hydroxy 290.755 102.03 22 0.18 β-phorbol 296.565 686.48 23 0.75 cyclobutane 344.44 56.06 24 0.15 butanoic acid, methyl ester 344.672 185.03 25 0.58 aminourea 345.9 75.04 26 0.23 cobalt, tetracarbonylsilyl 357.321 201.91 27 0.40 valeric acid hydrazide 363.994 116.10 28 0.19 oxotetrahydrofuran-2-carboxylic acid 365.256 130.03 29 0.30 à-d-glucopyranoside 390.853 331.16 30 3.68 propanetriol, 1-acetate 397.46 134.06 31 0.21 n-propyl fluoride 443.741 62.05 32 5.57 nickel tetracarbonyl 451.41 169.92 33 0.14 l-proline 456.755 187.31 34 7.86 propyldecyl cyclopropane carboxylate 493.375 268.24 35 7.86 tri-ruthenium dodecacarbonyl 494.172 641.65 36 7.86 n-acetylimino dimethylsulfurane 494.271 119.04 37 0.18 carbamic acid, ethylnitroso, ethyl ester 537.564 146.07 38 0.28 nitroethane 573.486 75.03 39 0.20 iron, hexacarbonyl 704.128 762.16 40 0.21 apigenin 8-c-glucoside 706.386 432.11 41 0.96 manganese, acetylpentacarbony 769.632 237.93 42 0.23 cyclobutanone 939.317 70.04 43 0.91 butanedioic acid 945.625 350.63 44 0.13 diethylene glycol, monotrimethylsilyl ether 996.853 178.10 45 0.20 trimethylene oxide 1012.82 58.04 46 0.53 silanol trimethyl, propanoate 1098.31 146.07 47 0.12 nitrohexane 1105.82 131.09 48 0.22 β-xylopyranose, tetrakis-tms 1334.63 438.21 49 13.54 d-psicofuranose, pentakis ether 1396.25 541.06 50 7.74 mannopyranose 1397.34 452.88 51 1.10 erythro-pentonic acid 1435.26 438.85 52 0.22 gluconic acid, ç-lactone 1435.46 421.71 53 0.11 quinazolin-2(3h)-thione 1974 392.16 54 0.19 difluoroacetylene 2278.77 62.00 55 0.74 aucubin, hexakis 2353.17 779.42 56 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 fig. 1: the percentage of cell viability of colon adenocarcinoma ht29 cells vs different concentrations of il-gf extract. fig. 2: the percentage of cell viability of colon adenocarcinoma ht29 cells vs different concentrations of taxol. 3.3 effect of il-gf extract on ht29 cell growth kinetics the growth kinetics graph of untreated ht29 cells (control), the il-gf extract-treated ht29 (10.56 µg/ml) and taxol-treated ht29 (1.22 µg/ml) were plotted and compared. the changes in the growth behaviour of the treated ht29 can be seen in (fig. 3). first, in the lag phase, the untreated and treated ht29 cells' growth was similar until 16 hrs of treatment. after that, a clear log phase was seen when the cells started to proliferate at 24 hrs. the il-gf extract-treated ht29 cells took 72 hrs to reach the peak, while the taxol treated ht29 cells showed less exponential phase and a smaller number of cells than control cells. fig. 3: growth profiles of untreated ht29 cells and the treated with il-gf extract (ic50=10.56 µg/ml) and taxol (ic50=1.22 µg/ml). from the growth curve, it can be seen that the untreated ht29 showed significant proliferation compared to the treated cells with il-gf extract and taxol. the cell number at the peak of the stationary phase for the treated ht29 cells with il-gf extract and taxol were only 15.6 x 105 ± 0.592 and 7.93 x 105 ± 0.411 cells/ml, respectively while the number reached 30.4 x 105 ± 0.753 for the control. based on the growth curve (fig. 3) and the fourth equation, cell growth at the log phase (fig. 4a), the death phase (fig. 4b), and the number of cell generations (table 2) were obtained for all treatments. 57 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 table 2: the number of cell generations (x), specific growth rate (μ) and duplication period (td) for ht29 control cells and the treated cells with il-gf extract and taxol *for all experiments, the initial number of cells (n0) was fixed at 2.0 x 105 cells/ml. different superscripts (a, b, c) display a significant difference (p ≤ 0.05). fig. 4: ht29 cells growth kinetic of the control and the treated cells with il-gf extract and taxol at a: exponential phase and b: death phase. the number of cell generation (x) was decreased from 3.93 generations in control to 2.96 generations in the il-gf extract-treated cells and 2.01 generations in the taxol-treated cells. this finding showed a significant difference when compared the number of cell generations between the control and different treatments. fig. 5: the ht29 cells photographs of a: control cells and b: treated cells with il-gf extract at a specified time point. cell growth maximum cells volume (n) (cells/ml) number of generations (x) specific growth rate µ (h-1) doubling time td (h) untreated ht29 cells 30.4 x 105 ± 0.753a 3.93 0.0134 22.46 il-gfe treated ht29 cells (ic50= 10.56 µg/ml) 15.6 x 105 ± 0.592b 2.96 0.0124 24.27 taxol treated ht29 cells (ic50= 1.22 µg/ml) 7.93 x 105 ± 0.411c 2.01 0.012 25.08 58 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 the typical photographs of the control cells and the treated ht29 with il-gf extract at 24, 72 and 120 hrs were shown in fig. 5. the density of cells was reduced in the il-gfe treated ht29 cells. that is probably because of the anti-proliferation effect of the il-gf extract against ht29 cell growth. the volume of cancer can be estimated in some types of tumours using the specific growth rate [38]. thus, the il-gf extract effect on the specific growth of ht29 cells was assessed by plotting the log number of cell viability versus treatment time, and the specific growth rate (µ) was taken from the regression slope. the growth rate of the treated ht29 cells with il-gf extract and taxol has significantly reduced by 0.0124 h-1 and 0.012 h-1, respectively compared to the control 0.0134 h-1. 3.4 cell cycle phase distribution the distribution of cell cycle phases in the treated ht29 with il-gf extract was analysed by flow cytometry combined with rnase a / propidium iodide. the flow cytometry result showed that in the treated ht29 cells with il-gf extract for 24, 48 and 72 hrs, the percentage of cells that were arrested at the g0/g1 phase has increased to 76.08% compared to the control 69.56% at 48 hrs then reduced. in contrast, the percentage of cells has declined in phases s and g2m compared to the control cells (fig. 6). fig. 6. distribution of cell cycle phases of the treated ht29 cells with the corresponding ic50 of il-gf extract in a time-dependent manner. furthermore, the treated ht29 cells showed an increase of cells arrested at the sub g0 phase in a time-increased treatment as compared with untreated ht29, considering the cells at the phase of sub-g0 as apoptotic cells [36]; there was an apparent increase of the apoptotic cells particularly after 48 hrs treatment. 4. discussion fruit and vegetables are related to a healthy life and reduce the risk of diseases. that is undoubtedly due to the different phytochemicals and secondary metabolites, including alkaloids, phenols, carotenoids, vitamins and flavonoids that are important in strengthening immunity [39]. many anti-cancer agents are used in cancer treatment, such as taxol, topotecan, cisplatin, etoposide and doxorubicin [35]. however, cancer patients suffer from the severe side effect of these drugs related to their capacity to damage healthy cells. hence, new anti-cancer drugs with fewer health risks are highly recommended to be investigated. the national cancer institute (usa) reported that any plant extracts showing an ic50 value under 20 µg/ml after a duration of incubation of 48 to 72 hrs are considered as a potent cytotoxic substance [40]. 59 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 different identified phytochemicals in this study have been found to possess various biological activities. it was reported a long time ago that the annonaceae family contained a considerable number of phytochemicals that exhibit anti-cancer activities such as acetogenins, alkaloids, terpenoids and flavonoids [41]. the claimed anti-cancer activity of several identified compounds have been reported, such as α-d-mannopyranose in cloves of allium sativum were showed cytotoxicity against breast cancer cells [42], tri-ruthenium dodecacarbonyl also was reported to have a highly selective anti-angiogenic against ovarian carcinoma a2780 cell lines [43,44]. silanol trimethyl, d-psicose pentakis, and butanedioic acid have been reported to contribute to drug delivery system, anti-proliferation, apoptosis and cell cycle arrest in different cancer cells lines [45-47]. another study reported that dihydro-dihydroxy-methyl-pyranone (ddmp) from onions had inhibited the growth of colon adenocarcinoma (hct116 and sw620) cells by inducing apoptotic cell death, modulation of tumour necrosis factor-α (tnf-α) and dna binding activity [48]. moreover, kameue et al. [49] reported that gluconic acid could induce apoptosis by stimulating butyrate production in the large intestine in a p53-independent manner and inhibiting cancer cell proliferation. these findings confirm the value of traditional use of the plant for medicinal purposes as well as pharmaceutical development. the use of graviola fruit in herbal medicine has been supported by the existence of these bioactive compounds with proven health benefits and hence an interest for further research on this plant. the anti-proliferative effect of the il-gf extract was evaluated on adherent colon adenocarcinoma ht29 cell line. the il-gf extract showed an anti-proliferative effect toward cancer cells as presented by mtt assay. many previous studies have reported the anti-cancer activity of graviola fruit toward many cancer cells, including human lung carcinoma a-549, breast adenocarcinoma mcf-7 cells, hepatoma hepg2 cell, prostate cancer pc-3 cells, and pancreatic tumour paca-2 cell lines with comparable outcomes to our research findings [14,15,50-52]. furthermore, the typical photographs of ht29 cells after treatment with il-gfe and the control at designated time points displayed cell density reduction after treatment. the increase of apoptotic cells can be indicated by the changes in the morphology and biochemical of the ht29 cells, including dna fragmentation and chromatin condensation, cell shrinkage and membrane blebbing [53]. moreover, a recent study conducted by daddiouaissa et al. [54] reported that after treating colon cancer ht29 cell line with il-gf extract, the pathway analysis of metabolomic profiles showed an alteration of different metabolic pathways such as aerobic glycolysis, amino acid metabolism, ketone bodies metabolism and urea cycle that contribute to cancer cells proliferation and energy metabolism. the growth kinetics model was investigated to estimate the inhibitory and cytotoxicity effects of il-gf extract on ht29 cell growth. a general model was developed for colon adenocarcinoma ht29 cells in response to the treatment of il-gf extract. generally, efficient therapies decrease the cells' proliferation rate (cytostatic effect) and increase the death rate of the cells (cytotoxic effect). many chemotherapy drugs disrupt the mechanism of cell division and dysregulate the cell cycle either through interfering or destroying dna synthesis [55]. this can be confirmed when the doubling time has expanded from 22.46 hrs in control to 24.27 hrs and 25.08 hrs for il-gf extract and taxol-treated ht29, respectively. the cytostatic effects can be observed at the log phase (fig. 4a), whereas cytotoxic effects were clearly demonstrated at the death phase (fig. 4b). although a biopsy sample is usually used to define the growth and spread of cancer growth and prescribe an effective therapy for it, the kinetics model in terms of simple 60 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 formulas may help predict the tumour size in a function of time. the first-order linear equation for the untreated colon adenocarcinoma ht29 cell growth was given as follows: 𝑙𝑜𝑔10𝑁 = 𝑙𝑜𝑔10𝑁0 + 0.0134𝑡 (6) after treating ht29 cell lines with il-gf extract, the equation of the first order linear presented as follows: 𝑙𝑜𝑔10𝑁 = 𝑙𝑜𝑔10𝑁0 + 0.0124𝑡 (7) moreover, after treating ht29 cell lines with taxol, the formula can be stated as follows: 𝑙𝑜𝑔10𝑁 = 𝑙𝑜𝑔10𝑁0 + 0.012𝑡 (8) however, if we neglect the tumour growth characteristics, the treatment's effectiveness can be estimated [38]. therefore, the final equation of the kinetic model in response to il-gf extract treatment was given as follows: 𝑙𝑜𝑔10nf = (𝑙𝑜𝑔10𝑁0 + 0.0134𝑡) − (𝑙𝑜𝑔10𝑁0 + 0.0124𝑡) (9) furthermore, the final equation of the kinetic model in response to taxol treatment was given as follows: 𝑙𝑜𝑔10nf = (𝑙𝑜𝑔10𝑁0 + 0.0134𝑡) − (𝑙𝑜𝑔10𝑁0 + 0.012𝑡) (10) where, (log10 nf) means the ultimate size of cancer after treatment, (log10 n0) means the primary size of a tumour and (t) means the treatment duration (tfinal – tinitial). with this model, it is possible to identify the presence and the size of the early-stage tumours (less than 1 cc). the interpolation and extrapolation of tumour volume can be predicted at any time points. cancer is classified as a cell cycle dysregulation disease. thus, an effective drug can block cancer cell division [56]. after treatment, the cell cycle distribution of the ht29 cells was investigated using the flow cytometry technique to see whether il-gf extract induced cell growth inhibition by cell cycle arrest. this study showed that il-gf extract arrested the cell cycle of the treated ht29 at the g1 phase of the growthstatic, explaining the anti-proliferative effect of il-gf extract. this confirmed the result of moghadamtousi and co-workers [57] when treated colon cancer hct-116 with ethyl acetate extract of a. muricata leaves. moreover, in our previous study, the flow cytometry result showed that il-gf extract had induced apoptosis in breast adenocarcinoma mcf-7 cell lines [15]. this was also validated by moghadamtousi et al. [57], and chamcheu et al. [58] after treating nonmelanoma skin cancer nmsc and colorectal cancer hct-116 and ht-29 with a. muricata leaves extract. on the other hand, torres et al. [59] reported the induction of necrosis in pancreatic cancer pc cells when treated with the graviola extract. this study concluded that graviola extracts inhibit cell metabolism through numerous signalling pathways, metastatic properties and arrests the cell cycle machinery in pancreatic cancer cells. many investigated studies of the phytochemicals contained in the leaves and fruits of graviola have extracted and identified a large number of secondary metabolites with a potential therapeutic such as anti-proliferative, apoptotic and cytotoxic towards many human cancer cells [57,60]. the synergistic effect of different metabolites in the graviola fruit extract such as acetogenins, flavonoids, terpenes, and alkaloids may be responsible for its anti-proliferative effect. thus, more investigations are still needed to detect the responsible active compounds for the anti-proliferation and inhibition effects of the graviola fruit. 61 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 5. conclusion the gc-tofms analysis of graviola fruit extracted using il-mae confirmed the existence of various chemical groups of compounds like acetogenins, terpenoids, alkaloids, fatty acids, sugars and lactones. il-gf extract presents anti-proliferative activity toward colon adenocarcinoma ht29 cell lines by inducing cell death through morphological changes, apoptosis, and the arrest of the cell cycle at the g0/g1 phase. this cytotoxicity showed selectivity toward the proliferation of colon cancer cells, indicating selective antitumor properties in il-gf extract against tumour cells. moreover, il-gf extract showed a great potentiality anticancerous when compared to the positive control, taxol. il-gf extract has inhibited the growth of ht29 cells by decreasing the number of cell generations and increasing duplication duration compared with untreated cells. these findings suggest that il-gf extract can be established as a new supplementary agent for preventing and curing colon cancer. additional research to explain the mechanism attached to the therapeutic effects and define the responsible bioactive compounds for the fruit extract's cytotoxicity. acknowledgements the authors are grateful to the international islamic university malaysia for offering a research grant (p-rigs18-065-0075) and laboratory facilities. references [1] patel ms, patel jk. (2016) a review on a miracle fruits of annona muricata. journal of pharmacognosy and phytochemistry, 5(1): 137-148. [2] ioannis p, anastasis s, andreas y. (2015) graviola: a systematic review on its anti-cancer properties. am. j. cancer prev, 3(6): 128-131. https://doi.org/10.12691/ajcp-3-6-5 [3] yajid ai, ab rahman hs, wong mpk, zain wzw. (2018) potential benefits of annona muricata in combating cancer: a review. the malaysian journal of medical sciences, 25(1): 5-15. https://dx.doi.org/10.21315%2fmjms2018.25.1.2 [4] badrie n, schauss ag. (2010) soursop (annona muricata l.): composition, nutritional value, medicinal uses, and toxicology. bioactive foods in promoting health, elsevier, pp. 621-643. https://doi.org/10.1016/b978-0-12-374628-3.00039-6 [5] coe fg. (2008) rama midwifery in eastern nicaragua. journal of ethnopharmacology, 117(1): 136-157. https://doi.org/10.1016/j.jep.2008.01.027 [6] samuel ajsj, kalusalingam a, chellappan dk, gopinath r, radhamani s, husain ha, muruganandham v, promwichit p. (2010) ethnomedical survey of plants used by the orang asli in kampung bawong, perak, west malaysia. journal of ethnobiology and ethnomedicine, 6(1): 1-6. https://doi.org/10.1186/1746-4269-6-5 [7] tisott g, molin d, colet c. (2013) the use of medicinal plants and herbal medicines for patients in chemotherapy in an oncology center of ijuı/rs. o mundo da saude, 39(3): 287298. [8] george vc, kumar d, rajkumar v, suresh p, kumar ra. (2012) quantitative assessment of the relative antineoplastic potential of the n-butanolic leaf extract of annona muricata linn. in normal and immortalised human cell lines. asian pacific journal of cancer prevention, 13(2): 699-704. https://doi.org/10.7314/apjcp.2012.13.2.699 [9] monigatti m, bussmann rw, weckerle cs. (2013) medicinal plant use in two andean communities located at different altitudes in the bolívar province, peru. journal of ethnopharmacology, 145(2): 450-464. https://doi.org/10.1016/j.jep.2012.10.066 [10] betancur-galvis la, saez j, granados h, salazar a, ossa j. (1999) antitumor and antiviral activity of colombian medicinal plant extracts. memórias do instituto oswaldo cruz, 94(4): 531-535. http://dx.doi.org/10.1590/s0074-02761999000400019 62 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 [11] dai y, hogan s, schmelz em, ju yh, canning c, zhou k. (2011) selective growth inhibition of human breast cancer cells by graviola fruit extract in vitro and in vivo involving downregulation of egfr expression. nutrition and cancer, 63(5): 795-801. https://doi.org/10.1080/01635581.2011.563027 [12] gavamukulya y, abou-elella f, wamunyokoli f, ael-shemy h. (2014) phytochemical screening, anti-oxidant activity and in vitro anti-cancer potential of ethanolic and water leaves extracts of annona muricata (graviola). asian pacific journal of tropical medicine, 7(13): s355-s363. https://doi.org/10.1016/s1995-7645(14)60258-3 [13] daddiouaissa d, amid a. (2018) anti-cancer activity of acetogenins from annona muricata fruit. international medical journal malaysia, 17(3): 103-112. https://doi.org/10.31436/imjm.v17i3.236 [14] sun s, liu j, sun x, zhu w, yang f, felczak l, dou qp, zhou k. (2017) novel annonaceous acetogenins from graviola (annona muricata) fruits with strong anti-proliferative activity. tetrahedron letters, 58(19): 1895-1899. https://doi.org/10.1016/j.tetlet.2017.04.016 [15] daddiouaissa d, amid a, kabbashi na, fuad fa, elnour am, epandy ma. (2019) antiproliferative activity of ionic liquid-graviola fruit extract against human breast cancer (mcf7) cell lines using flow cytometry techniques. journal of ethnopharmacology, 236: 466-473. https://doi.org/10.1016/j.jep.2019.03.003 [16] siegel rl, miller kd, jemal a. (2019) cancer statistics, 2019. ca: a cancer journal for clinicians 69(1), 7-34. https://doi.org/10.3322/caac.21551 [17] griffin a, butow p, coates a, childs a, ellis p, dunn s, tattersall m. (1996) on the receiving end v: patient perceptions of the side effects of cancer chemotherapy in 1993. annals of oncology, 7(2): 189-195. https://doi.org/10.1093/oxfordjournals.annonc.a010548 [18] daddiouaissa d, amid a, syahida a, elnour am. (2020) phytochemical analysis of ionic liquid-graviola (annona muricata) fruit extract and its acute toxicity on zebrafish early-life stages. asia pacific journal of molecular biology and biotechnology, 28(2): 113-124. https://doi.org/10.35118/apjmbb.2020.028.2.10 [19] koel m, kuhtinskaja m, vaher m. (2020) extraction of bioactive compounds from catharanthus roseus and vinca minor. separation and purification technology, 252: 117438. https://doi.org/10.1016/j.seppur.2020.117438 [20] ventura spm, e silva fa, quental mv, mondal d, freire mg, coutinho jap. (2017) ionicliquid-mediated extraction and separation processes for bioactive compounds: past, present, and future trends. chemical reviews, 117(10): 6984-7052. https://doi.org/10.1021/acs.chemrev.6b00550 [21] bogdanov mg. (2014) ionic liquids as alternative solvents for extraction of natural products, alternative solvents for natural products extraction, springer, pp 127-166. [22] cláudio afm, marques cf, boal-palheiros i, freire mg, coutinho ja. (2014) development of back-extraction and recyclability routes for ionic-liquid-based aqueous two-phase systems. green chemistry, 16(1): 259-268. https://doi.org/10.1039/c3gc41999a [23] wang t, wang q, li p, yang h. (2019) temperature-responsive ionic liquids to set up a method for the simultaneous extraction and in situ preconcentration of hydrophilic and lipophilic compounds from medicinal plant matrices. green chemistry, 21(15): 4133-4142. https://doi.org/10.1039/c9gc00995g [24] fan y, li w, zhang s, sun s, yang l. (2020) vitamin b3-based protic ionic liquids as green solvents for the isolation of astilbin from rhizoma smilacis glabrae. industrial crops and products, 152: 112563. https://doi.org/10.1016/j.indcrop.2020.112563 [25] hoenig m. (2001) preparation steps in environmental trace element analysis—facts and traps. talanta, 54(6): 1021-1038. https://doi.org/10.1016/s0039-9140(01)00329-0 [26] gyamfi k, sarfo d, nyarko b, akaho e, serfor-armah y, ampomah-amoako e. (2011) assessment of elemental content in the fruit of graviola plant, annona muricata, from some selected communities in ghana by instrumental neutron activation analysis. elixir food sci, 41: 5671-5675. 63 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 [27] rahman nrha, idris a, yunus na, mustaffa aa. (2019) optimisation of ionic liquid-based microwave extraction of flavonoid and phenolic acid from labisia pumila. aip conference proceedings (vol. 2124, no. 1, p. 020027), aip publishing llc. https://doi.org/10.1063/1.5117087 [28] bhan m, satija s, garg c, dureja h, garg m. (2017) a novel approach towards green extraction for glycyrrhitinic acid by ionic liquid based microwave assisted extraction and optimisation through response surface methodology. pharmacognosy journal, 9(6): 866-872. https://doi.org/10.5530/pj.2017.6.136 [29] zhang y, liu z, li y, chi r. (2014) optimisation of ionic liquid-based microwave-assisted extraction of isoflavones from radix puerariae by response surface methodology. separation and purification technology, 129: 71-79. https://doi.org/10.1016/j.seppur.2014.03.022 [30] jang z-h, chung h-c, ahn yg, kwon y-k, kim j-s, ryu j-h, kim c-h, hwang g-s. (2012) metabolic profiling of an alcoholic fatty liver in zebrafish (danio rerio). molecular biosystems, 8(7): 2001-2009. https://doi.org/10.1039/c2mb25073j [31] muhamad s, jamilah b, russly a, faridah a. (2017) in vitro antibacterial activities and composition of carica papaya cv. sekaki/hong kong peel extracts. international food research journal, 24(3): p976-984. [32] liu n, yang hl, wang p, lu yc, yang yj, wang l, lee sc. (2016) functional proteomic analysis revels that the ethanol extract of annona muricata l. induces liver cancer cell apoptosis through endoplasmic reticulum stress pathway. journal of ethnopharmacology, 189: 210-217. https://doi.org/10.1016/j.jep.2016.05.045 [33] chik ww, amid a, jamal p. (2010) purification and cytotoxicity assay of tomato (lycopersicon esculentum) leaves methanol extract as potential anti-cancer agent. journal of applied sciences, 10(24): 3283-3288. https://dx.doi.org/10.3923/jas.2010.3283.3288 [34] fouz n, amid a, hashim y. (2013) cytokinetic study of mcf-7 cells treated with commercial and recombinant bromelain. asian pacific journal of cancer prevention, 14(11): 6709-6714. https://doi.org/10.7314/apjcp.2013.14.11.6709 [35] magadi vp, ravi v, arpitha a. (2015) evaluation of cytotoxicity of aqueous extract of graviola leaves on squamous cell carcinoma cell-25 cell lines by 3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyltetrazolium bromide assay and determination of percentage of cell inhibition at g2m phase of cell cycle by flow cytometry: an in vitro study. contemporary clinical dentistry, 6(4): 529–533. https://dx.doi.org/10.4103%2f0976-237x.169863 [36] agu kc, okolie np, falodun a, engel-lutz n. (2018) in vitro anti-cancer assessments of annona muricata fractions and in vitro anti-oxidant profile of fractions and isolated acetogenin (15-acetyl guanacone). journal of cancer research and practice, 5(2): 53-66. https://doi.org/10.1016/j.jcrpr.2017.12.001 [37] suhendar u. (2018) geographical effect on the cytotoxic activity of annona muricata l. leaves extract against mcf7 cancer cell. fitofarmaka, 8(2): 12-19. [38] mehrara e, forssell-aronsson e, ahlman h, bernhardt p. (2007) specific growth rate versus doubling time for quantitative characterisation of tumor growth rate. cancer research, 67(8): 3970-3975. https://doi.org/10.1158/0008-5472.can-06-3822 [39] wang h, oo khor t, shu l, su z-y, fuentes f, lee j-h, tony kong a-n. (2012) plants vs. cancer: a review on natural phytochemicals in preventing and treating cancers and their druggability. anti-cancer agents in medicinal chemistry (formerly current medicinal chemistry-anti-cancer agents), 12(10): 1281-1305. https://doi.org/10.2174/187152012803833026 [40] boik j. (2001) natural compounds in cancer therapy (vol. 851). oregon medical press, 1st ed. [41] coria-tellez av, montalvo-gónzalez e, yahia em, obledo-vázquez en. (2018) annona muricata: a comprehensive review on its traditional medicinal uses, phytochemicals, pharmacological activities, mechanisms of action and toxicity. arabian journal of chemistry, 11(5): 662-691. https://doi.org/10.1016/j.arabjc.2016.01.004 64 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 [42] nazeer aa, veeraiyan s, vijaykumar sd. (2017) anti-cancer potency and sustained release of phytosomal diallyl disulfide containing methanolic allium sativum extract against breast cancer. international research journal of pharmacy, 8(8): 34-40. https://doi.org/10.7897/2230-8407.088141 [43] nazarov a, nosova yn, mikhalev o, kovaleva o, dyson p, milaeva e. (2016) antiproliferative activity of ruthenium and osmium clusters with phosphine ligands. russian chemical bulletin, 65(2): 546-549. https://doi.org/10.1007/s11172-016-1335-x [44] nowak-sliwinska p, zava o, van beijnum jr, groessl m, chisholm dm, ahmadi z, mcindoe js, griffioen aw. (2013) synthesis and characterisation of a new class of antiangiogenic agents based on ruthenium clusters. scientific reports, 3: 1485. https://doi.org/10.1038/srep01485 [45] belayachi l, aceves-luquero c, merghoub n, de mattos sf, amzazi s, villalonga p, bakri y. (2017) induction of cell cycle arrest and apoptosis by ormenis eriolepis a morrocan endemic plant in various human cancer cell lines. african journal of traditional, complementary and alternative medicines, 14(2): 356-373. https://doi.org/10.21010/ajtcam.v14i2.37 [46] cheng w, liang c, xu l, liu g, gao n, tao w, luo l, zuo y, wang x, zhang x. (2017) tpgs‐functionalized polydopamine‐modified mesoporous silica as drug nanocarriers for enhanced lung cancer chemotherapy against multidrug resistance. small, 13(29): 1-12. https://doi.org/10.1002/smll.201700623 [47] sui l, dong y, watanabe y, yamaguchi f, hatano n, tsukamoto i, izumori k, tokuda m. (2005) the inhibitory effect and possible mechanisms of d-allose on cancer cell proliferation. international journal of oncology, 27(4): 907-912. https://doi.org/10.3892/ijo.27.4.907 [48] ban jo, hwang ig, kim tm, hwang by, lee us, jeong h-s, yoon yw, kim dj, hong jt. (2007) anti-proliferate and pro-apoptotic effects of 2, 3-dihydro-3, 5-dihydroxy-6-methyl4h-pyranone through inactivation of nf-κb in human colon cancer cells. archives of pharmacal research, 30(11): 1455. https://doi.org/10.1007/bf02977371 [49] kameue c, tsukahara t, ushida k. (2006) alteration of gene expression in the colon of colorectal cancer model rat by dietary sodium gluconate. bioscience, biotechnology, and biochemistry, 70(3): 606-614. https://doi.org/10.1271/bbb.70.606 [50] consolacion y, geneveve s, ming-jaw d, chien-chang s. (2012) acetogenins from annona muricata. pharmacognosy journal, 4(32): 32-37. https://doi.org/10.5530/pj.2012.32.7 [51] sun s, liu j, kadouh h, sun x, zhou k. (2014) three new anti-proliferative annonaceous acetogenins with mono-tetrahydrofuran ring from graviola fruit (annona muricata). bioorganic & medicinal chemistry letters, 24(12): 2773-2776. https://doi.org/10.1016/j.bmcl.2014.03.099 [52] sun s, liu j, zhou n, zhu w, dou qp, zhou k. (2016) isolation of three new annonaceous acetogenins from graviola fruit (annona muricata) and their anti-proliferation on human prostate cancer cell pc-3. bioorganic & medicinal chemistry letters, 26(17): 4382-4385. https://doi.org/10.1016/j.bmcl.2015.06.038 [53] pieme ca, kumar sg, dongmo ms, moukette bm, boyoum ff, ngogang jy, saxena ak. (2014) anti-proliferative activity and induction of apoptosis by annona muricata (annonaceae) extract on human cancer cells. bmc complementary and alternative medicine, 14(1): 516. https://doi.org/10.1186/1472-6882-14-516 [54] daddiouaissa d, amid a, sani msa, elnour aa. (2021) evaluation of metabolomics behavior of human colon cancer ht29 cell lines treated with ionic liquid graviola fruit pulp extract. journal of ethnopharmacology, 270: 113813. https://doi.org/10.1016/j.jep.2021.113813 [55] o'reilly ms, boehm t, shing y, fukai n, vasios g, lane ws, flynn e, birkhead jr, olsen br, folkman j. (1997) endostatin: an endogenous inhibitor of angiogenesis and tumor growth. cell, 88(2): 277-285. https://doi.org/10.1016/s0092-8674(00)81848-6 65 iium engineering journal, vol. 22, no. 2, 2021 daddiouaissa et al. https://doi.org/10.31436/iiumej.v22i2.1687 [56] mantena sk, sharma sd, katiyar sk. (2006) berberine, a natural product, induces g1-phase cell cycle arrest and caspase-3-dependent apoptosis in human prostate carcinoma cells. molecular cancer therapeutics, 5(2): 296-308. https://doi.org/10.1158/1535-7163.mct-050448 [57] moghadamtousi sz, karimian h, rouhollahi e, paydar m, fadaeinasab m, kadir ha. (2014) annona muricata leaves induce g1 cell cycle arrest and apoptosis through mitochondriamediated pathway in human hct-116 and ht-29 colon cancer cells. journal of ethnopharmacology, 156: 277-289. https://doi.org/10.1016/j.jep.2014.08.011 [58] chamcheu j, rady i, chamcheu r-c, siddique a, bloch m, banang mbeumi s, babatunde a, uddin m, noubissi f, jurutka p. (2018) graviola (annona muricata) exerts antiproliferative, anti-clonogenic and pro-apoptotic effects in human non-melanoma skin cancer uw-bcc1 and a431 cells in vitro: involvement of hedgehog signaling. international journal of molecular sciences, 19(6): 1791. https://doi.org/10.3390/ijms19061791 [59] torres mp, rachagani s, purohit v, pandey p, joshi s, moore ed, johansson sl, singh pk, ganti ak, batra sk. (2012) graviola: a novel promising natural-derived drug that inhibits tumorigenicity and metastasis of pancreatic cancer cells in vitro and in vivo through altering cell metabolism. cancer letters, 323(1): 29-40. https://doi.org/10.1016/j.canlet.2012.03.031 [60] gajalakshmi s, vijayalakshmi s, devi rajeswari v. (2012) phytochemical and pharmacological properties of annona muricata: a review. international journal of pharmacy and pharmaceutical sciences, 4(2): 3-6. 66 microsoft word 247-858-1-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 mohiuddin 197 investigation of the swirl effect on engine using designed swirl adapter a.k.m. mohiuddin mechanical engineering department, kulliyyah of engineering, international islamic university malaysia (iium), jalan gombak, 53100, kuala lumpur, malaysia. mohiuddin@iium.edu.my abstract: swirl is the rotational flow of charge within the cylinder about its axis. the engine used in this investigation is a basic double overhead camshaft (dohc) which has a capacity of 1597 cc and installed with a total of 16 valves developed by malaysian car manufacturer proton. the swirl adapter is placed inside the intake port of the engine. the adapter angle is set to 30o to force the charge to bounce off the wall of the port to create swirl. the objective of this paper is to find the effect of swirl on the engine and to compare it with the normal turbulence mixing process. the swirl effect analysis is done by using the gt-suite which has a standard swirl flow embedded in the software. the effect is simulated on the gt-suite and it is found that the swirl affects the engine in reducing the fuel consumption and increasing the volumetric efficiency. the experimental result shows that the effect of swirl increases the power as well as torque in the idle and cruising speed conditions in comparison with normal turbulence. but it decreases rapidly in the acceleration speed. this happens due to the inability of the swirl adapter to generate swirl at higher wind flow velocity during the higher throttle opening condition. abstrak: pusar merupakan aliran putaran cas melingkungi silinder pada paksinya. enjin yang digunakan untuk penyelidikan ini merupakan enjin aci sesondol stas kembar (double overhead camshaft (dohc)) asas, yang mempunyai kapasiti 1597 cc. ia dipasangkan dengan 16 injap yang dibangunkan oleh pembuat kereta malaysia, proton. penyesuai pusar diletakkan di dalam masukan liang enjin. sudut penyesuai di tetapkan pada 30o untuk memaksa cas supaya melantun kepada dinding liang agar membentuk pusaran. tujuan tesis ini ditulis adalah untuk mendapatkan kesan pusar ke atas enjin dan membandingkannya dengan proses percampuran gelora normal. analisis kesan pusaran dilakukan dengan menggunakan gt-suite yang mempunyai aliran pusar yang telah dipiawaikan di dalam perisian tersebut. kesan tersebut disimulasikan menggunakan gt-suite dan didapati bahawa pusaran mengakibatkan penggunaan bahan api yang berkurangan dalam enjin dan juga meningkatkan kecekapan isi padu. keputusan eksperimental menunjukkan kesan pusaran meningkatkan kuasa, daya kilas dalam keadaan melahu dan laju jajap dibandingkan dengan keadaan golakan normal. walaupun begitu, ia berkurangan secara mendadak semasa pecutan kelajuan. ini berlaku disebabkan oleh ketakdayaan penyesuai pusar untuk menghasilkan pusaran pada aliran angin halaju semasa keadaan bukaan mendikit luas. keywords: swirl adapter; rotational flow; campro engine; volumetric efficiency; gtsuite; fuel consumption iium engineering journal, special issue, mechanical engineering, 2011 mohiuddin 198 1. introduction the main objective of this work is to investigate the effect of swirl on proton’s campro engine model 1.6 l. the campro engine is a basic double overhead camshaft (dohc) which has a capacity of 1597 cc and installed with a total of 16 valves. the bore and stroke dimensions of each cylinder are 76 mm and 88 mm respectively. it is claimed to produce 110 bhp (82 kw) @ 6500 rpm and 148 nm of torque [1]. extensive investigation of the swirl effect on campro engine is performed using gt-power – a solver of gt-suite. gt-suite is an integrated set of computer-aided engineering (cae) tools developed by gamma technologies, inc. to address engine and power train design [2]. these tools are contained in a single executable form which is essential to its use in "integrated simulations". gt-suite comprised of six solvers (gt-power, gt-drive, gt-vtrain, gt-cool, gt-fuel, and gt-crank), a model-building interface (gt-ise), a powerful post-processing package (gt-post), and a collection of supporting tools [3]. the solvers of gt suite are: 1. gt power – engine simulation for performance and acoustics analysis. 2. gt drive – vehicle performance and cycle analysis for fuel economy and emissions and driveline components dynamics. 3. gt valve train – valve train kinematics, dynamics and tribology, camshaft vibrations, cam design. 4. gt fuel – injection system pressure and flow dynamics, hydraulic system analysis. 5. gt cool – engine heat management and cooling system analysis. 6. gt crank – crankshaft dynamics and torsional vibrations, engine balance, block vibrations, mounts, bearing oil films 7. gt post – viewing the results of the simulation and customizing plots. gt-ise provides the user with the graphical user interface (gui) that is used to build models as well as the means to run all gt-suite applications. swirl is the rotational flow of charge within the cylinder about its axis [4]. swirl is usually defined as organized rotation of the charge about the cylinder axis. swirl is created by bringing the intake flow into the cylinder with an initial angular momentum. there are two general ways of producing swirl during the induction process. firstly, the flow is discharged into the cylinder tangentially towards the cylinder wall, where it is deflected sideways and downward in a swirling motion. in the other one, the swirl is largely generated within the inlet port: the flow is forced to rotate about the valve axis before it enters the cylinder. the directed port and the deflector wall port are two common ways of achieving this result. the directed port brings the flow toward the valve opening in the desired tangential direction. its passage is straight and due to the other cylinder head requirements restricts the flow area and it results in a relatively low discharge coefficient. the deflector wall port uses the port inner side wall to force the flow preferentially through the outer periphery of the valve opening, in a tangential direction. since only one wall is used to obtain a directional effect, the port areas are less restrictive. 2. engine simulation using gt-suite a gt-model is created to model the campro engine. the model data were referred from proton powertrain department database. however, some data were taken from default iium engineering journal, special issue, mechanical engineering, 2011 mohiuddin 199 value because of the insufficient information on the base engine. the engine model was first constructed using default values from the tutorial that is available in the gt suite. then, the data from the campro is put into the model. figure 1 shows the model of the campro in gt power. fig. 1: campro model in gt power. the design process of the engine is as follows:  the inlet and outlet boundary conditions are described by setting the endenvironment object  the intake and exhaust runner are created using pipe object.  the fstateinit template object is referred to the init object. it is the initial condition for the pipe object at the start of the simulation.  intake and exhaust ports are created using the pipe object. the created objects are cloned to create the other ports.  the cylinder is created using the engcylinder object. the cylinder geometry is set in the cylinder geometry object under the name of geom.  cylinder wall attributes are defined in the twal object under engcyltwall template.  cylinder heat transfer attributes are defined in the htr object under engcylheattr template. iium engineering journal, special issue, mechanical engineering, 2011 mohiuddin 200  cylinder combustion attributes are defined in the comb object under engcylcombsiwiebe template.  fuel injection attributes are defined in the si-inject object under injafseqconn template.  the cranktrain is created using the cranktrain object under the enginecranktrain template.  the friction attributes are defined. the friction object in the cranktrain main tab is named friction.  the parts are connected by creating links between each of them.  then the components are cloned to produce a 4 cylinder model.  after the model is built, the simulation is run.  gt-post is opened for result analysis. 3. swirl swirl is usually defined as organized rotation of the charge about the cylinder axis. swirl is created by bringing the intake flow into the cylinder with an initial angular momentum. while some decay in swirl due to friction occurs during the engine cycle, intake generated swirl usually persists through the compression, combustion, and expansion process. in engine design with bowl-in-piston combustion chambers, the rotation motion set up during intake is substantially modified during compression. swirl is used in diesels and some stratified-charge engine concepts to promote more rapid mixing between the inducted air charge and the injected fuel. swirl is also used to speed up the combustion process in spark-ignition engines. in two-stroke engines, it is used to improve scavenging. in some designs of pre-chamber engines, organized rotation about the pre-chamber axis is also called swirl. in the engine where swirl within the pre-combustion chamber is important, the flow into the pre-chamber during the compression process creates the rotating flow. 3.1 swirl measurement the nature of the swirling flow in an actual operating engine is extremely difficult to determine. accordingly, steady flow tests are often used to characterize the swirl. air is blown steadily through the inlet port and valve assembly in the cylinder head of an appropriately located equivalent cylinder. a common technique for characterizing the swirl within the cylinder is to use a light paddle wheel, pivoted on the cylinder centerline (with low friction bearings), mounted between 1 and 1.5 bore diameters down the cylinder. the paddle wheel diameter is close to the cylinder bore. the rotation rate of the paddle wheel is used as a measure of the air swirl. since this rotation rate depends on the location of the wheel and its design, and the details of the swirling flow, this technique is being superseded by the impulse swirl meter. a honeycomb flow straightener replaces the paddle wheel. it measures the total honeycomb exerted by the swirling flow. this torque equals the flux of angular momentum through the plane coinciding with the flow-straightener upstream face. for each of these approaches, a swirl coefficient is defined which essentially compares the flow’s angular momentum with its axial momentum. for the paddle wheel, the swirl coefficient cs is defined by iium engineering journal, special issue, mechanical engineering, 2011 mohiuddin 201   b c ps  where ωp is the paddle wheel angular velocity ( = 2πnp, where np is the rotational speed) and the bore b has been used as the characteristic dimension. the characteristic velocity, ν0, is derived from the pressure drop across the valve using an incompressible flow equation [5]: 2 1 0 0 (2          cppv or a compressible flow equation: 2 1 1 00 0 0 11 2                                        p pp v c where the subscripts 0 and c refer to upstream stagnation and cylinder values respectively. the difference between the equations is usually small. 3.2 swirl production there are actually two general ways of producing swirl during the induction process. firstly, the flow is discharged into the cylinder tangentially towards the cylinder wall, where it is deflected sideways and downward in a swirling motion. in the other one, the swirl is largely generated within the inlet port: the flow is forced to rotate about the valve axis before it enters the cylinder. the former type of motion is achieved by forcing the flow distribution around the circumference of the inlet valve to be non-uniform, so that the inlet flow has a substantial net angular momentum about the cylinder axis. the directed port and the deflector wall port are two common ways of achieving this result. the directed port brings the flow toward the valve opening in the desired tangential direction. its passage is straight, which due to other cylinder head requirements restricts the flow area and results in a relatively low discharge coefficient. the deflector wall port uses the inner side wall to force the flow preferentially through the outer periphery of the valve opening in a tangential direction. since only one wall is used to obtain a directional effect, the port areas are less restrictive [6]. flow rotation about the cylinder axis can also be generated by masking off or shrouding part of the peripheral inlet valve open area. a mask or shroud is often used on the valve in research engines as changes can readily be made. in production engines, the added cost and weight, problems of distortion, the need to prevent valve rotation, and reduced volumetric efficiency make masking the valve an unattractive approach. the more practical alternative of building a mask on the cylinder head around part of the inlet valve periphery is used in production of spark-ignition engines to generate swirl. it can easily be incorporated in the cylinder head casting process. 3.3 swirl adapter the swirl adapter is theoretically placed inside the intake port of the campro engine model. the adapter angle is set to 30o to force the charge to bounce off the wall of the port to create swirl. the ramp is design based on the inside surface area of the intake manifold. since iium engineering journal, special issue, mechanical engineering, 2011 mohiuddin 202 the inside of the campro intake port is oval and is considered as directed intake port, the charge should not have any problem to create swirling. the adapter was chosen due to its ability to plug in and out of the system. this will help in the future if there is any rendition intended to be done on the manifold or the adapter itself. the movement of the swirl adapter is locked by the surface of the cylinder head so that it does not go into the combustion chamber. the design of the adapter is shown in fig. 2 and the adapter placement is shown in fig. 3. fig. 2: swirl adapter. fig. 3: swirl adapter placement. swirl adapter placement iium engineering journal, special issue, mechanical engineering, 2011 mohiuddin 203 3.4 design and fabrication of swirl adapter in order to design the adapter a proper intake manifold is needed to estimate the angle of the ramp. the intake manifold is redesigned by using catia and the adapter is designed according to the inside surface of the intake manifold. the ramp is estimated to be 30o of the floor to allow it to deflect in accordance to the wall of the intake manifold. the fabrication of the swirl adapter is done by using a cnc milling machine coded by catia. catia generates a g-code with the design that had been done and the codes are used on the cnc milling machine. before applying the codes on to the machine a series of test must be done using dummy software on a separate computer. this is to ensure that the milling process runs smoothly without damaging the work piece or the tools. the simulation is thoroughly checked step by step to determine and predict its movement. 3. discussion and analysis the actual swirl adapters were placed inside the intake manifold and tested on the engine test bed using eddy current dynamometer. the data are obtained for both the swirl campro model and the normal campro model. figure 4 shows that the swirl is generated in the initial part of the engine speed. it starts off with 7.017 x 10-14 and gradually decreases. when the speed reaches 1500 rpm the swirl is completely gone since at higher speed the swirl process is not significant. while in fig. 5 as expected there is no swirl generation as the mixing process totally depended on normal turbulence only. fig. 4: swirl campro: swirl versus engine speed. iium engineering journal, special issue, mechanical engineering, 2011 mohiuddin 204 fig. 5: normal campro: swirl versus engine speed. the specific fuel consumption shows the effectiveness of an engine using the fuel supplied to produce work [7]. from the fig. 6 and 7, it can be deduced that the specific fuel consumption of the engine with swirl is lower than the normal campro model. the swirl effect shows that it has lower fuel consumption i.e., more fuel economy than the normal campro engine. even at higher rpm, the figures show that the swirl model saves more fuel than the normal model. fig. 6: swirl campro: indicated specific fuel consumption versus engine speed. iium engineering journal, special issue, mechanical engineering, 2011 mohiuddin 205 fig. 7: normal campro: indicated specific fuel consumption versus engine speed. 4. conclusion investigation of the swirl effect on campro engine is performed and the result is compared with the normal engine. the effect of swirl comparing to normal turbulence shows an increase in the power as well as torque during the idle and cruising speed while it decreases rapidly in the acceleration speed. this happens due to the inability of the swirl adapter to generate swirl at higher wind flow velocity during the higher throttle opening condition. the brake specific fuel consumption is considerably lower at the lower speed but increases above the normal aspirated graph as the speed goes above 3500 rpm. references [1] http://www.proton.com/innovation/rnd/campro.php, 2005. [2] gamma technologies, gt-suite, http://www.gtisoft.com, 2004. [3] gt-suite v6.1 user’s manual, gamma technologies, 2004. [4] heinz, h., advanced engine technology, arnold, (1995). [5] ohata, a., and ishida, y., “dynamic inlet pressure and volumetric efficiency of four cycle four cylinder engine” sae paper 820407, sae trans., vol. 91, (1982). [6] ganesan, v., internal combustion engines second edition. mc graw-hill., (2004). [7] kyung-h l, kisung k.(2001), “influence of initial combustion in si engine on following combustion stage and cycle-by-cycle variations in combustion process”. international journal of automotive technology microsoft word 4_vol17_no1_2016_(compiledversion_4).docx iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 63 probabilistic model of laser range finder for three dimensional grid cell in close range environment hafiz iman and nahrul khair alang md rashid department of mechatronics engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. hafiz.ghazman@gmail.com, and nahrul@iium.edu.my (received: 08 jul. 2015; accepted: 29 jul. 2015; published on-line: 30 apr. 2016) abstract: the probabilistic model of a laser scanner presents an important aspect for simultaneous localization and map-building (slam). however, the characteristic of the beam of the laser range finder under extreme incident angles approaching 900 has not been thoroughly investigated. this research paper reports the characteristic of the density of the range value coming from a laser range finder under close range circumstances where the laser is imposed with a high incident angle. the laser was placed in a controlled environment consisting of walls at a close range and 1000 iteration of scans was collected. the assumption of normal density of the metrical data collapses when the beam traverses across sharp edges in this environment. the data collected also shows multimodal density at instances where the range has discontinuity. the standard deviation of the laser range finder is reported to average at 10.54 mm, with 0.96 of accuracy. this significance suggests that under extreme incident angles, a laser range finder reading behaves differently compared to normal distribution. the use of this information is crucial for slam activity in enclosed environments such as inside piping grid or other cluttered environments. abstrak: model berkebarangkalian pengimbas laser membentangkan aspek penting untuk pemetaan dan penganggaran lokasi (slam). walau bagaimanapun, sifat pancaran laser pada sudut pantulan menghampiri 900 masih belum dikenalpasti dan tidak dikaji secara mendalam. oleh itu, kertas penyelidikan inibertujuan untuk melaporkan sifat taburan normal yang datang dari pengukur jarak laser di bawah keadaan jarak dekat di mana laser itu dikenakan dengan sudut insiden tinggi. pengimbas laser diletakkan di tempatterkawal yang terdiri daripada muka diding pada jarak yang dekat dan 1000 imbasan dikumpulkan. andaian ketumpatan normal data berhubung dengan jarak ukuran runtuh apabila pantulan laser merentasi sudut tajam dalam tempat terkawal. data yang dikumpul juga menunjukkan kepadatan pasca-modal pada keadaan di mana julat mempunyai ketakselanjaran. sisihan purata taraf pengukur jarak laser dilaporkan berpurata pada 10.54 mm di bawah ketepatan 0.96. penemuan menunjukkan bacaan pengimbas laser tidak mempunyai sifat taburan normal.pengetahuan ini wajar digunakan untuk slam di kawasan yang tertutup rapat seperti di dalam grid pempaipan dan persekitaran yang berselerak. keywords: hokuyo utm-30lx; kernel density estimation; probabilistic model 1. introduction simultaneous localization and mapping (slam) requires a robust sensor with known and tested measurement model. in regard to the theme of mapping an environment iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 64 probabilistically using continuous density, the model of a laser range finder is crucial for an esteem map. a laser range finder is an active range-bearing sensor that produces bearing information and range measurement collectively known as metrical data. while transmitting and receiving beam reflection, the light source of a laser range finder is reflected by a rightangled mirror or prism depending on the model of the laser scanner. the mirror is mounted on a built-in turntable and rotates about the z-axis. in fig. 1, the sequence of the rotation is shown to start at tinitial and move in a circular fashion to ݐ௙௜௡௔௟, known as planar sweeping. fig. 1: the sequence of a laser range finder, in the case of this paper the hokuyo utm-30lx, that has an active region of 2700, doing a planar sweep to gather continuous stream of metrical data. the beam propagation is perpendicular to the direction of the circular motion, and with continuous data acquisition, the beam will produce a metrical data as shown in fig. 2. figure 2 depicts three dimensional point clouds consisting of multiple layers of metrical data obtained from planar sweeping. the geometric information in point clouds are noise ridden and discontinuous which pose challenges to researchers. fig. 2: the metrical data, which is planar in nature, can be extended to spatial representation known as point clouds. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 65 without the model of the laser range finder, any slam solution would risk incorporating error in the measurement data. the need for the model proves more crucial since the sensor produces predominant noise in a confined-close-range environment due to bounce and beam width [1]. to remedy the uncertainty of the reading, the sensor should be modeled probabilistically [2]. however, attempts to quantify the parameter of a normal distribution for any laser range finder’s reading using density estimation method has yet to be introduced in the literature. furthermore, the gaussian modality of density of a laser range finder reading for close range confined space in a static environment has not been documented. density estimation is a statistical method to objectively select suitable pattern of random variables without the assumption that these variables belong to any distribution. this method eliminates any pre-assumption of distribution eliminating bias density. the method underlines a smoothing algorithm based on a certain bandwidth. although kernel density estimation regarded as trivial to some researchers, this paper will be attempting to use such method to investigate the density of the metrical data obtained by a laser range finder. the result of the density estimation method will also be used to determine if the modality of the metrical data can be represented by unimodal distribution under close range confined space. the efforts to prove that laser range finder readings follow gaussian density are crucial because the parameters from the density would give an insight, as an example, to an appropriate selection of a slam solution. with known value of probability parameter, the characteristic on the modality and accuracy of the sensor can be described succinctly [3]. the value can be used to optimize the slam solution and to indicate the type of filtering technique suitable for any adopted slam solution. the standard deviation of the sensor can also be used to pre-compute and approximate the gaussian of the sensor measurement without having to iterate the gaussian function each time a measurement is collected [4]. in this paper, kernel density estimation is used to compute the standard deviation of hokuyo utm-30lx under close range environment. figure 3 explains the process of obtaining the probability parameter from metrical data collected by the laser scanner. fig. 3: workflow for density estimation for a laser range finder called hokuyo utm-30lx. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 66 literature review guides the procedural aspect of this paper on how to obtain and gestate data from scanning sensor such as hokuyo utm-30lx. the literature review is followed by data collection using the scanner and feeding this data into kernel density estimation method. the underlying pattern present by the data via kernel density method would be used to validate the nature of the density obtained from metrical data collected by utm-30lx under confined close range space. the pattern, in a form of density, is also used to find the standard deviation of the laser scanner. upon conclusion of the most optimized value of standard deviation, the model grid cell of the sensor and the occlusion in close range space can be modeled. 2. related work ye and borenstein [5] outlined a method to characterize a laser scanner by imposing the scanner with various angles of reflection and collected multiple data series under such condition. fig. 4 shows the setup of their experiment, configured to impose varying angle of incident to one particular beam at a time. the laser scanner was mounted on a linear motion table where the distance of target and laser scanner could be varied, and the target surface was mounted on a rotatable stage for varying angle of eflection. the turn table is used to change the incident angle and a linear table was used to change the range between the target, placed on the turn table, and the scanner. fig. 4: the experimental setup for parametric investigation of lms 200 lidar by ye and borenstein [5]. ye and borenstein [5] assimilate their method by using sick lms-200. their method was reiterated by a number of researchers including kneip et al. [6] that uses hokuyo urg04lx 2d laser scanner. both lasers, sick lms-200 and hokuyo urg-04lx, are based on the principle of time of flight (tof) validating that the method used by ye and borenstein [5] is applicable for hokuyo urg-04lx. however, [6] extend the method by subjecting the laser scanner with different type of surface during scanning. their report concluded that the angle of reflection has marginal effect on the accuracy and of the sensor reading. they also concluded that the laser produces marginal error for different surfaces,. however, kneip et al. [6] suggest that hokuyo urg-04lx application should be confined to an environment that has minimal number of transparent or highly reflective surfaces. the lack of performance due to reflective and transparent surface is amplified, alwan et al. [7]. they reported that due to the nature of the source of a laser scanner, which is an amplified electromagnetic wave, light based lidar such as pbs 03jn, hokuyo utm-30lx, and sick lms-200 would register erroneous metrical data. this is because the reaction of light, iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 67 or lack thereof, to transparent surface would produce a bias maximum reading. also, the light beam would bounce at a wider beam width if a reflective surface is present which contributes to the bias reading. one aspect of map-building for autonomous robot is the selection of lidar or laser scanner. hokuyo laser scanners for example cater the need of autonomous robotics by producing a family of laser scanners that has a desirable weight to range ratio. figure 5 identifies laser scanners based on their weight and maximum range [8]. it is observed that two of the hokuyo laser scanner, urg-04lx and ubg 04lx, have a light weight feature but with maximum range of less than 10 meters. in spite of this shortcoming, the newest generation of hokuyo laser scanner, the utm-30lx, has a range of 30 m which weighs within 1 kg. the scanner is considerably light weight for a capacity of 30 m which rivals the more expensive laser scanner such as sick lms-200. it is evident that the ratio of maximum range to weight of utm-30lx is the highest among all laser scanners as seen in figure 5. this motivates the use of hokuyo utm-30lx in this research paper. fig. 5: mapping of various scanner models based on their weights and maximum range of scannings [8]. the characterization of the hokuyo laser scanner particularly utm-30lx, which will be used in this paper, has been limited. demski et al. [9] have produced results of their experiment based on ye and borenstein [5] method using hokuyo utm-30lx. demski et al. [9] suggested that the performance of hokuyo utm-30lx was under the standard deviation of 5 mm. their report acknowledged the drift of the laser scanner reading if the iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 68 scanning period was prolonged to two hours and more. the drift was also reported by pouliot et al. [10] who use the same hokuyo utm-30lx for their power line inspection robot called linescout. the standard deviation reported by pouliot et al. [10] was between 4.8 mm to 6.3 mm. the standard deviation of both demski et al. [9] and pouliot et al. [10] however, are assumed statistically without knowing the modality of the error’s probability. another work that characterize the error of hokuyo laser are by park et al. [11] who used ubg 04lx that follows the guidelines elucidated by ye and borenstein [5]. tretyakov and linden [12] evaluated the performance of utm-30lx together with other scanners namely, sick’s lms-291 and lms-iii, swiss ranger mesa sr-3100, and microsoft kinect under smoky condition. tretyakov and linden [12] validate the accuracy performance of the aforementioned scanners when introduced within a smoke laden room. the performance benchmark of the scanners is based on the absorbability of the transmission signal of all the scanners. the paper uses extinction coefficient to quantify the energy loss of the signal due to absorbability. all scanners performed well in smoky environment with mention of stellar performance by microsoft kinect and sick lms-291. thus far, all the literatures discussed have performed characterisation of laser scanners under ambient lighting. pomerleau et al. [8] raises the issue of laser scanner performance under direct sunlight and in highly reflective environment. much of the procedure was based on ye &borenstein[5] that uses three different laser scanners; sick lms-151, hokuyo urg-04lx and utm-30lx. the standard deviation of the sensor was reported to be 28 mm for urg-04lx, 18 mm for utm-30lx, and 12 mm for lms-151. these standard deviations are excerpts from a histogram method. the approach also assumes single modality of the entire scanner’s error. 3. grid cell of laser range finder in this paper, the probabilistic model of the hokuyo utm-30lx is hypothesized to be gaussian. the gaussian model will be used to compare the result of the kernel density estimation based on measurement collected. this paper will adopt a relaxed beam model, also known as ray tracing approach, based on the contingency that follows a close range confined space. the relaxed beam model is designed to reflect the assumptions that:  the environment is static, having no transparent or near transparent structure i.e glass  the geometric data of the environment are confined in a cube of width, depth, and length of less than 6000 mm  the sensor reading is independent of the absolute location of the sensor per se  the model of the sensor is prescribed before an actual grid map-building commence the beam model consists of four terms of probability functions: 1 2 3 41 2 3 4 1 1: , , 2 2: , , 3 3: , , 4 4: , , ( , , , )total z x m z x m z x m z x mf w w w w w f w f w f w f    (1) fn:z,x,m represent constituent conditional probability function regarding aspect of a laser model where, z, represents observation or measurement reading of an occlusion; x, represents the state of an autonomous robot; m, represents the map of the environment; wn, the weight of importance of the function term thrun [2]. since the model is based solely on the measurement of an occlusion, the function is simplified to, 1 2 3 4 1 1: 2 2: 3 3: 4 4:( , , , )total z z z zf w w w w w f w f w f w f    (2) iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 69 there are four terms in eqn.(2) each models a contingent in the measurement of a scanner. f1:z represent the accuracy and the repeatability of the sensor and the footprint of the beam of the sensor: 2 max 1: max 1 ( , , ) if z [0, ] ( ) 0 if z z n z z f z z       (3) where zmax is the maximum range of the scanner; µ, is the median; 2 , is the variance of the gaussian and, η, is the normalizing factor for the gaussian function n. f2:z represents the probability of the scanner when it reached its maximum reading:  max max 2: max if z [0,z ] ( ) 0 if z z z step z f z    (4) this occurs when there is no occlusion within the maximum range of the scanner. f3:z represents interference of the scanner with other scanners and surface reflection of the propagating beam with surface of any angle: the value is inverse of zmax so that the total area of density f3:z is unity. max max3: max 1 if [0,z ] ( ) 0 if z z z z zf z    (5) f4 represents the dynamic obstacle in the scanner active range which can be expressed as: max 4: max 1 if z [0,z ] ( ) 0 if z > z z z e f x      (6) λ, and, α, represent coefficients chosen to reflect the degree of importance of the decaying aspect of the function. decaying function is used to represent dynamic occlusion because the further the dynamic occlusion is from the scanner, the less probable that any object behind this dynamic occlusion have any effect on the measurement of the scanner. with all of the terms having a weight, wn, of unity, eqn.(1) can be depicted as shown in fig. 6. fig. 6: the beam tracing model represented by ftotal. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 70 however, since the relaxed beam model is of concern in this paper, eqn. (1) is rendered to, 1: 3:z zf f f  (7) figure 7 depicts the shape of the probabilistic model of the scanner measurement. fig. 7: comparison between the beam tracing model, ftotal, with the relaxed beam tracing model, f. with the model of the relaxed beam tracing established, the underlying density of the metrical range data can be compared. the kernel estimation method is used to validate the modality of the metrical data coming from laser range finder without any pre-assumption that the measurements would be gaussian. in this paper, the kernel density estimation method is done by minimizing the error between the underlying pattern and the random variables using box bandwidth as the kernel [13]. the method was derived from statistical method used to find optimal bin size for histogram for neuronal spike [14]. the method introduced in [13] and [14] are chosen because they do not assume any underlying pattern of the density of the reading. the absence of this assumption helps in investigating the actual distribution of the sensor reading under close range confined space because this method can eliminate any biased towards normal distribution if the readings are not gaussian. seven different locations in the controlled environment are sampled. these seven locations will be represented by range, or depth, of the laser reading. these random variables are used to estimate the underlining pattern of the laser error characteristic by using kernel density estimation as mentioned above. it should be noted again that this method does not assume the error of the laser reading to be gaussian to eliminate any bias towards normal distribution if the reading is multimodal or non-gaussian. the resulting density will be used to validate whether the scanner can be modeled based on the relaxed beam model. also, with the estimated density at hand, the most optimal standard deviation of the laser scanner can be found. the purpose of finding standard deviation for the scanner is to model the grid cell that represents occlusion and reading error based on the reading of the scanner. mentioned in the introduction of this paper was the importance of finding parameter of density of a sensor; to give insight to potential slam solution. grid cell, a model of occlusions in space, is a part of the solution to slam. the standard deviation is used to extend the grid cell to three dimensions which follows the premise introduced by pomerleau et al. [8]. pomerleau et al. [8] selected the bigger value of standard deviation between the range uncertainty reading and the beam width to parameterize their isotropic model of sensor error. pomerleau et al. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 71 [8] also introduce anisotropic model of the sensor bounded by these two parameters; the standard deviation of the depth along the beam propagation and the standard deviation of the beam width, forming an ellipsoid depicted in fig. 8. however, grid cell, in the form of cubes, used the knowledge of the sensor error parameter to model the sensor and the occlusion. by using a cube, the tessellation of the cubic grid cell will produce a continuous map. the dimension of the cube takes the value of 95% confidence of the scanner metrical range, 6*σ. figure 8 compares the structure of both the grid cell model of this paper and that of pomerleau et al. [8]. fig. 8: isotropic and anisotropic sensor models and the grid cell model adopted in this paper [8]. the method of tessellating the grid cell is beyond the scope of this paper but the grid cell would cluster the metrical data into voxel that has dimensions based on the value of the sensor’s standard deviation. figure 9 shows a sample of grid cell tessellation based on standard deviation of a scanner. 4. procedure protocol in this paper, close-range environment is defined by a pronounced incident angle imposed to the sensor and the abrupt changes in the range of occlusion. taking reference from few literatures such as the work of ye and borenstein [5], the experiment protocol consists of collecting range data in a controlled environment subjected to occlusions, in a form of walls, for 1000 iterations. with 1000 iterations, which produce 1000 scans, gaussian estimation can be performed on each angle increment of planar sweeping. the range of the planar sweeping is limited between -2.250 to 182.250. in fig. 10, the sensor is place at a close range of 40 mm from the wall. at a very small clearance of 40 mm, large incident angle is imposed to the scanner which has the propagating beam centers at 30 mm off from the outside chassis. the position of the laser between the two corners is asymmetrical. the distance between the laser and the first corner is 2770 mm and the distance between the laser and the second corner is 5670 mm. the iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 72 asymmetric nature of the laser scanning field divides the planar sweeping into two areas. while both areas have high angle of incident for scanning activity, the first half of the planar sweeping area has a relatively lower incident angle than the second half of the planar sweeping. fig. 9: an example of grid cells tessellation to produce continuous map optimized by recursive bayesian filtering method and bayes’ rule filtering method. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 73 as mentioned above, the laser scanner would collect metrical data called metrical range that scatters along the line of propagation of the beam as shown in fig. 11. since hokuyo utm-30lx has the maximum range of 30 m, the metrical range data would produce a faux range reading of 30 m if there is no occlusion within the 30 m range. fig. 10: depiction of the controlled environment and its configuration consist of two right-angled corners and the points for kernel density estimation sampling and the actual setup of the experiment activity. fig. 11 the metrical range scattering is due to occlusion or propagation beyond the range of 30 m where the scanner would register faux occlusion at 30 m. instead of using one single range reading, this method mimics the real time application of the laser scanner by collecting 1000 scans of the controlled environment. this set up is chosen to push the boundary of the sensors response time and to give a good method to address the repeatability of a measurement with respect to response time. with 1000 iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 74 iterations, the data that coincide with an expected value can be used to estimate the density of the reading. the kernel density estimation is performed on 7 different points in the controlled environment of the experiment (fig. 10). each of these points has 1000 sets of data and the data are fed into kernel density estimation operator to find the underlying pattern which then be used to validate the gaussian nature of the hokuyo utm-30lx reading. the estimated density are compared with an expected normal density based on the standard deviation of 10 mm [15]. 5. results 5.1. unimodal estimated density all of the 1000 scans of the walls are superimposed into one point cloud which depicts the scattering of the range measurement range about the expected value of the wall. these metrical ranges have precision interval depicted in fig. 12. the multiple isolated clusters noticeable in the left region of the metrical scatterings due to the 0.250 resolution of the planar sweep. the upper and lower boundary of the precision of the metrical range scatterings are calculated to show the overall precision of the metrical data collected. fig. 12: the scattering of metrical range after 1000 scans in which the median, upper and lower boundary of the metrical range precision are computed from the kernel density estimation. the standard deviation, median, and error for points 1 to 7 are calculated based on the density estimated from the kernel density estimation method. table 1 summarizes these values. the error column in table 1 is calculated based on the dimension of the wall seen in fig. 10 and the median value is obtained from the estimated density. table 1 gives insight of the highest error amongst the seven points of interest. this high error concludes that although the precision is high at point 5, the accuracy of the reading are low due to high incident angle between the beam and the plane at that point. it is also observed that the precision of the metrical range decreases at the second corner at point 6 because of sharp edge at the position coupled with high incident angle. as the result of these factors, the error at point 6 is high at 216 mm. the standard deviations of all points are less than 10 mm with the exception of point 6. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 75 table 1: standard deviation, median, and error for metrical range at points 1 to 7 point standard deviation, σ (mm) median, µ (mm) error (mm) 1 5.020 2770 0.00 2 8.50 2729 42 3 7.96 568 11.50 4 4.93 73 2.48 5 8.47 2316 20 6 26.080 5317 216 7 6.57 5666 3 all the estimated density in points 1 to 7 are compared with expected normal density based on standard deviation, σexpected=10 mm, about the actual range obtained from the dimensions of the experiment setup. the estimated density of points 1, 2, 3, 4, 7 are normal based on figs. 14, 15, 16, 17, 18, and 20 respectively. however, the density estimated at point 6 shows skewing to the left about the median 5454 mm. fig. 13: estimated density and normal density from point 1 with zero error. figure 13 shows a good example of a normal density with standard deviation smaller than the standard deviation of the expected normal density. the modality of the estimated density is unity and has no skewing. in fig. 14 the expected range is seen to be larger than the median of the estimated density. this does not affect the modality of the estimated density which is still unity with no local maxima. such result is of interest since at point 2 the scanner encounters with the first corner in the wall. however, no tail or multimodality is seen in the estimated density at point 2. the absence of density that could suggest multimodal density due to sharp edges might suggest that such anomaly only occurs at extreme incident angles. the only indication that a certain extreme feature encountered at point 2 from the metrical range data is the notable error. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 76 fig. 14: estimated density and normal density from point 2 with notable error of 42 mm. figure 15 presents the information of unimodality of the estimated density at point 3. the estimated density is normal and almost symmetrical but with a small overshoot in median value. figures 16, 17 and 18 present similar estimated densities at point 4, point 5, and point 7 respectively. fig. 15: estimated density and normal density from point 3 with error of 11.5 mm. fig. 16: estimated density and normal density from point 4 with 2.48 mm of error. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 77 fig. 17: estimated density and normal density from point 5 with 20 mm error. fig. 18: estimated density and normal density from point 7 with error of 3 mm. 5.2. multimodal density the presence of two local maxima is observed from the density estimation at point 6. the extreme angle change at the second corner causes the scattering of the metrical data to localize between two local maxima; 5454 mm and 5149 mm. the low number of scatterings at mode 5149 mm, however, has low probability. instead, the density at mode 5454 mm skewed to the left due to scattering at mode 5149 mm. the corners on both point 2 and point 6 are similar but with different incident angle. since the incident angle of the corner at point 6 is larger than that of point 2, the effect of sharp edges due to corners are seen to have more effect on the density at point 6 than the density at point 2. figure 19 shows the estimated density of metrical data at point 6. bimodal density is also observed for metrical data at angle sweep -2.250. figure 20 shows two regions of local maxima, with region 2 having a density about mode 2766 mm (refer to fig. 22), and region 1 having multimodal density (refer to fig. 21). the scattering of the range between these two regions suggest that the scanner encounters a large discontinuity of reading, explained only by two occlusion separated at a large depth. this observation contradicts any reports or assumption that there is no effect of intermediate value between two occlusions separated by large depth [6]. figure 23 explains the location of region 1 and region 2. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 78 fig. 19: estimated density and normal density from point 6 with 216 mm error. fig. 20: multiple modality at sweeping angle -2.250 are seen in region 1 and region 2, due to the presence of two occlusions separated by a large depth, with higher frequency in region 1. fig. 21: estimated density in region 1 with multimodal appearance of low probability. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 79 fig. 22: estimated density and expected density in region 2. fig. 23: location of region 1 and region 2 in the metrical range scattering. 5.3. standard deviation, error and accuracy the standard deviation of each incremental angle in the planar sweep is observed to change at 0.250 increments. the varying standard deviation is presented in fig. 24. figure 24 shows a high standard deviation in the discontinuity region at sweep angle -2.250. also a faint spike of standard deviation is observed when the beam propagation traverses across point 2 where the first corner is encountered. this spike is also seen when the beam propagation of the laser traverses across point 6 where second corner is situated. the average standard deviation is 10.54 mm. the standard deviation value of 10.54 is used to map the controlled environment using voxelized grid cell mapping method. the map is depicted in fig. 26 where each voxel was tessellated based on the value of the standard deviation. fig. 24: standard deviation for sweeping angle -2.250 to 182.250. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 80 two methods were used to find the error of each increment in the angle sweep. the naïve approach calculates the median based on the raw metrical data and compare the set of median values with the expected values. this results in a set of errors that is biased towards the maximum bound of the data reading. however, by using information from the estimated density, a more optimal set of error values can be calculated without any bias. figure 25 includes the set of errors obtained from the naïve approach. the remaining discussion on error in this section will reflect error data from the latter approach. fig. 25: accuracy and error from sweeping angle -2.250 to 182.250. the error on each angle sweep increment is observed to vary between 0 to 3039 mm. the large error margin is due to the nature of the environment that impose extreme angle of incident to the laser scanner. unlike the value of standard deviation, the errors are nominal at discontinuity region of the controlled environment. notwithstanding, high errors are seen at point 2 and point 6 where the beam propagation traverses into regions with corners. the accuracy of the laser range finder is high throughout the planar sweep but collapses when imposed with acute edges at high incident angles. the average accuracy of laser scanner under close-range confined environment is 0.96. table 2 summarizes the result obtained. table 2: summary on the behavior of the metrical data for hokuyo utm-30lx under various conditions in closed-range environment corners discontinuity high incident angle low incident angle standard deviation increase increase increase at high rate error high high nominal accuracy high low high density of metrical data multimodal unimodal multimodal iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 81 fig. 26: voxelized map of the control environment in the experiment protocol based on the value of standard deviation where (a) the map consist of tessellated grid cells with (b) length, width, and depth of each grid cells equal to 6*σ. 6. conclusions under a confined close range environment, the hokuyo utm-30lx shows a slightly different behavior. the standard deviation of the metrical data from the scanner increases while traversing through corners at incident angles approaching 900. standard deviation also increases at a very high rate when the laser encounters discontinuity. the average standard deviation is 10.54 mm. the error reading is higher when the scanning traverses across corners but nominal for region with discontinuous depth. the error is even more pronounced for corners at incident angles approaching 900. the average accuracy of the sensor is high at 0.96. this accuracy is only affected if the laser is introduced to corners or sharp edges at incident angles between 850and 900. the density of the metrical data throughout the planar sweeping is gaussian in majority. nevertheless, the normal density of the metrical data is affected when the scanning is imposed with discontinuity in depth. the collapse of the normal density is also seen when the scanning encounters corners at a high incident angle of 88.550 (first corner) to 89.290 (second corner). this information is crucial for the application of laser range finder in enclosed environments that introduce high incident angle such as slam for downstream pipes in oil and gas industry. the use of the method reported in this paper also optimized the value of the standard deviation of a laser scanner for use in any contingency in cluttered environment where extreme conditions such as close range scanning and high incident angles are likely to happen. acknowledgement special appreciation is addressed to dr.ing. wahju sediono who has given his full support througout this project. this research project is funded under ministry of science, technology & innovation under the escience scheme (sf11-003-0032). references [1] hebert m, krotkov e. (1991) 3-d measurements from imaging laser radars: how good are they? in intelligent robots and systems’ 91: intelligence for mechanical systems, proceedings iros’91. ieee/rsj international workshop, pp. 359-364. [2] thrun s. (2002) probabilistic robotics. commun. acm, 45(3):52-57. [3] silverman bw. (1986) density estimation for statistics and data analysis. pp. 1-2. [4] fernández-madrigal ja. (2012) simultaneous localization and mapping for mobile robots: introduction and methods. 1st edn., hershey, pa, usa. igi global. [5] ye c, borenstein j. (2002) characterization of a 2-d laser scanner for mobile robot obstacle negotiation. ieee int. conf. on robotics and automation (icra), pp. 2512-2518. iium engineering journal, vol. 17, no. 1, 2016 iman and md rashid 82 [6] kneip l, tache f, caprari g, siegwart r. (2009) characterization of the compact hokuyo urg-04lx 2d laser range scanner. ieee int. conf. on robotics and automation (icra): pp. 1447-1454. [7] alwan m, wagner mb, wasson g, sheth p. (2005) characterization of infrared range-finder pbs-03jn for 2-d mapping. ieee int. conf. on robotics and automation (icra), pp. 39363941. [8] pomerleau f, breitenmoser a, liu m, colas f, siegwart r. (2012) noise characterization of depth sensors for surface inspections. 2nd international conference in applied robotics for the power industry (carpi), pp. 16-21. [9] demski p, mikulski m, koteras r. (2013) characterization of hokuyo utm-30lx laser range finder for an autonomous mobile robot. in advanced technologies for intelligent systems of national border security. nawrat a, simek k, świerniak a., eds. springer berlin heidelberg, 143-153. [10] pouliot n, richard p, montambault s. (2012) linescout power line robot: characterization of a utm-30lx lidar system for obstacle detection. ieee/rsj international conference on intelligent robots and systems (iros), pp. 4327-4334. [11] park cs, kim d, you bj, oh sr. (2010) characterization of the hokuyo ubg-04lx-f01 2d laser rangefinder. 19th international symposium in robot and human interactive communication, pp. 385-390. [12] tretyakov v, linder t. (2011) range sensors evaluation under smoky conditions for robotics applications. ieee international symposium on safety, security, and rescue robotics (ssrr), pp. 215-220. [13] shimazaki h, shinomoto s. (2010) kernel bandwidth optimization in spike rate estimation. j. comput. neurosci., 29(1-2):171-182. [14] shimazaki h, shinomoto s. (2007) a method for selecting the bin size of a time histogram. neural comput., 19(6):1503-1527. [15] scanning range finder utm-30lx | photo sensor | products | hokuyo automatic co.,ltd.” [online]. available: https://www.hokuyoaut.jp/02sensor/07scanner/utm_30lx.html. [accessed: 21-aug-2014]. microsoft word vol 5-1 pages 1 -12.doc iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 1 antnet: a robust routing algorithm for data networks shariq haseeb*, khairul azami sidek*, ahmad faris ismail*, lai w.k. + & aw yit mei+ * faculty of engineering, international islamic university malaysia, 53100 kuala lumpur, malaysia. + mimos berhad, technology park malaysia, 57000 kuala lumpur, malaysia e-mail: faris@iiu.edu.my abstract: successful implementation and operation of a network largely depends on the routing algorithm in use. to date, several routing algorithms are in use but the problem with these algorithms is that they are either not adaptive or not robust enough, thus limiting the proper use of bandwidth. antnet is an innovative algorithm that may be used for data networks. it is a combination of both static and dynamic routing algorithms. in this algorithm, a group of mobile agents (compared to real ants) form paths between source and destination nodes. they explore the network continuously and exchange obtained information indirectly, in order to update the routing tables at different nodes. our version of antnet (hereinafter referred to as antnet2.0) has been improved to overcome the problems with other algorithms. this paper compares the performance of antnet2.0 against two other commercially popular algorithms, viz. link state routing algorithm and distant vector routing algorithm. the performance matrix used to compare the algorithms is based on average throughput, packet loss, packet drop and end-to-end delay. convergence time for this algorithm on a nation-wide telecommunications network will also be discussed. conclusions and areas of further work will also be presented in lucid manner, so that it may be transformed into real practice in the future. key words: mobile agents, swarm intelligence, networks and constant bit rate 1. introduction swarm intelligence is a novel solution to many constraint optimization problems such as the traveling sales person problem, quadratic assignment problem, job scheduling problem and the network routing problem. swarm intelligence is based on the behavior of insects that normally work in groups, such as ants and bees [1]. these insects cannot communicate with each other directly, so they have to use their surroundings as a means of interaction. they communicate by laying down a chemical called pheromone that can be sensed by other ants and thus attracting them towards it [2]. in nature, a traveling ant lays some pheromone (in varying quantities) on the ground, thus marking the path by a trail of this substance. while an isolated ant moves essentially iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 2 at random, an ant encountering a previously laid trail can detect it and decide with high probability to follow it, thus reinforcing the trail with its own pheromone. the collective behavior that emerges is a form of autocatalytic behavior, when there is a higher number of ants following a trail, the more attractive that trail becomes to the newer ants. the process is, thus, characterized by a positive feedback loop, where the probability with which an ant chooses a path increases with the number of ants that has previously chosen the same path. this ability of ants to collectively seek a better path can clearly be reflected in many constraint optimization problems, such as the network routing problem. in this problem, the constraints are the links and their capacities. the most efficient route is chosen, in order to achieve the best performance. the performance of a data network reflects the speed, reliability and capacity of the network, as overloaded networks may easily be disrupted by attacks. 2. ants and path selection process small insects like ants have only local knowledge. when a group of such insects interact with each other, they can exhibit a higher-level behaviour. this behaviour is most often called emergent behaviour. a group of insects like ants do not have a central controlling authority that steers the behaviour. all ants behave according to a few simple rules and by interacting with their environment. the resulting behaviour of the group of ants can be very complex [3]. the important aspect behind emergent behaviour is called stigmergy. stigmergy is a way for entities to communicate indirectly with each other through the environment. many social insects including ants use stigmergy. one of the abilities of a group of ants is to find the shortest route from their nest to a food source. ants only react to local stimuli from the environment and can change one or more of those local stimuli. this modification can be of two types. firstly, physical, in which behaviour of one ant influences the others to follow, i.e. an ant seen carrying food by other members of its colony, will influence these members also to carry food, hence resulting in a collective work being done. secondly, sign-based, in which one ant lays down a hormone trail as it moves resulting in the other ants to follow. the goal of sign-based stigmergy is to influence subsequent behaviour. ants are very good in using this second method [3]. ants can lay pheromone trails when going from the nest to the food source, from the food source to the nest or in both directions. when looking for food, ants follow the pheromone trails with about the same probability as the strength of the trail. they do not follow the trail with precisely the same probability, but with a certain amount of error also known as noise. the strength of the trail sensed by an ant depends on the original strength and the time elapsed since the trail was laid, since pheromones diffuse away over time. multiple ants can travel at the same route, so the resulting trail can consist of multiple trails laid by different ants at different times. the pheromone trail sensed by ants is, therefore, one that has been laid down by many ants, i.e. a composite trail [2]. iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 3 fig. 1: paths between nest and food. the four ants in a situation depicted in fig. 1 have a decision to make. ants a and b come out from the nest to the food source and the ants c and d come out from the food source to the nest. the ants in this example lay trails that influence the ants’ decisions in both directions. each ant has a choice between two routes from the nest to the food or vice versa. when no pheromone trails have been laid, the ants arriving at one of the branches have an equal probability of 0.5 of choosing either the left or the right route. ant b that travels from the nest to the food takes the left route. the ant following ant b, ant a, already senses a faint pheromone trail from the first ant. however, the influence of this faint pheromone trail is still small, because the ants use a sufficient amount of noise to make them explore new routes. this means that the probability of ant a choosing either the left or the right route is still close to 0.5. in this example, ant a chooses the right route. ants c and d that are travelling from the food to the nest take the same amount of steps. ant c chooses the left route and ant d chooses the right route. fig. 2: the ants have laid their pheromone trails. the two ants (b and d) that choose the shortest route have arrived at their destination as shown in fig. 2. the other two ants, ant a and c, are still travelling along the long route and are expected to arrive at their destination in due time. from fig. 2, it is clear that the shorter path between the nest and the food has a higher concentration pheromone at this particular instant. so, if new ants want to select a path either from the nest to food or the food to nest, there is a higher probability that they will be attracted to the shorter path because a stronger pheromone trail increases the chance of an ant choosing a route belonging to that trail. if this happens, they will further concentrate iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 4 the trail on the shorter path. the ants will be attracted towards the shortest paths, because of the following three reasons:  shorter routes will be completed earlier than longer routes and thus attract other ants to their source nodes first.  shorter routes involve fewer branches, so the number of ants will be larger than on longer routes with more branches.  ants travelling shorter routes will be younger when they arrive. this causes the pheromone trails to be stronger, because less of the pheromone trail has diffused away. when more and more ants start taking the shorter path, the concentration of pheromone on the shorter path becomes more concentrated. as a result, fewer and fewer ants take the longer path, until finally no more ants get attracted to the longer path. when this happens, the concentration of pheromone on the longer path tends to decrease, until finally, it completely disappears. 3. from natural to artificial system the behavior of ants represents a unique method of finding the shortest path between to locations. the setup of fig. 2 provides a solution to network routing problem too, however this system had to be modeled differently in order to represent a problem solving technique. m. dorigo[3] proposed the following modeling of the natural system that allowed network routing problems to be solved:  the ants were modeled as mobile agents or routing packets.  different locations on the ground were modeled at network nodes.  pheromones were modeled as probabilistic values. 4. the antnet routing algorithm there are two types of ants used in this algorithm, namely, forward ants and backward ants [5]. these ants can be compared to the ants leaving the nest for food and ants returning to nest from food, in the ant nest simulation explained earlier. the forward ants have the same priority as the normal data packets in a network. they accomplish their task by the help of a timer that measures the amount of time spent on a link. when forward ants reach their destination node, they become backward ants. these backward ants have a higher priority to travel the network. the reason for this is that they carry useful routing information that must be transferred to the routers immediately. thus, backward ants update the routing table of a node. iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 5 it is vital for these two ants to interact with each other in order to share information. this information sharing can only be done in an indirect way. live ants interact with each other by laying down pheromone trails on the ground. however, a network is not exactly like a path. it is a collection of nodes represented by routers and links are represented by wires as physical connections or wireless. the only place where digital pheromone can be laid down upon is the routers because the physical links have no memory of their own. figure 3 shows a typical content of a node in a network. it contains a routing table showing the digital pheromone (p11, p12, p13, …, pnn) concentration between different nodes and local traffic statistic table containing information about the interconnections of other links on the network. fig. 3: data structure of a node in the network [4,5]. 4.1. routing table construction the idea of emergent behaviour of natural ants can be used in telecommunication networks to build routing tables. telecommunication networks cannot sense the pheromone trails, but they can use probabilities. the routing tables will be called probability tables from this point onward. each node in the network has a probability table for every possible final destination. the tables have entries for each next (neighbour) node. the probabilities influence the agents’ selection of the next node in their journey to the destination node. the probability of the agents choosing a certain next node is the same as the probability in the probability table. the probability tables only contain local information and no global information on the best routes. each time an agent visits a node, the next step in the route of the agent is determined. this process is repeated until the agent reaches its destination. thus, the entire route from a source node to a destination node is not determined beforehand. the probability tables also contain information if a node is reachable or not. this information is contained in the last column of each table (fig. 4). if an agent detects that a node is unreachable, it will mark the entry for this destination node unreachable in the probability table of the agent’s source node. agents continue to be launched while old agents detect that a node is reachable again. the reachable node will then be marked reachable in the probability table of the agent’s source node. iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 6 table 1: an example of a probability table. first column of table 1 shows all the other nodes to which node 1 can send packets. the first row of the table shows the nodes to which node 1 is connected and ‘r’ represents the reachable status between node 1 and the destination nodes of column one, where ‘y’ stands for reachable and ‘n’ stands for not reachable, in column four. the probability values show the attractiveness of selecting the neighboring nodes. even though node six is not reachable, we noticed some probability values, which were assigned to the neighboring links before the path to node six was broken. 4.2. role of antnet as a load balancer in conventional algorithms, once a best route is selected, all the packets are routed along that route. this causes the link to become overloaded and thus decreasing it performance dramatically. in some cases, it might even cause the link to fail altogether resulting in 100% packet drop on that network. however, antnet has a mechanism for load balancing, where after selecting the best link, it sends its packets on it. it is different from the conventional algorithm in the sense that, as soon as a packet is released on the link, the sending node reduces the probability value in the routing table for the optimal link and increases the probability values of the other non-optimal links. if this process keeps on going, there will be a situation when the less desirable link will have a higher probability and thus making it the optimal route. when this happens, the next packet will now be routed on the new optimal path and this prevents the links from overloading. 4.3. performance metric we assume that all nodes can reach each other by some route through the network. there are two main performance criteria for network routing algorithms. the first one is effectiveness and the second one is efficiency. effectiveness means how good the algorithm is capable of doing its job, and efficiency means how well the resources are used. the parameters we used to test the algorithm can be classified as either effectiveness or efficiency metric as seen below. 4.3.1. effectiveness:  average throughput: a throughput value is the number of bytes sent in the network per second. this calculated value subtracts the dropped and lost bytes from the received bytes. node 1 2 4 r 2 0.95 0.05 y 3 0.67 0.33 y 4 0.05 0.95 y 5 0.83 0.17 y 6 0.73 0.27 n iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 7  packet drop: this value represents the number of packets dropped in the network.  packet loss: this value represents the number of packets lost on the network during transmission. 4.3.2. efficiency:  delay: delay value is calculated by subtracting the time at which a packet left the source node from the time at which it reaches the destination node. 4.4 experimental settings to test the antnet 2.0 algorithm, several test networks were made. in these test networks, number of nodes was increased from 5 until 50 with increments of 5 nodes at a time. the link capacity between nodes was set to 2 mb/sec and the default delay of each link was 10ms. each generated network was tested with two types of traffic, namely transfer control protocol (tcp) and constant bit rate (cbr). each simulation was run for 5 simulation seconds. in order to make comparisons, these settings were also used to simulate the other algorithms like distant vector (dv) and link state (ls). this setup is used because it provides variance to the network architecture and results in a more accurate result. as the number of nodes increases, the number of links connecting the nodes have to increase resulting to more paths available. an increase in the number of nodes also results in higher traffic, thus providing a solid platform for comparing the algorithms according to the following performance matrix: throughput, packet drops, packet loss and delay. 5. results results for tcp traffic sources are shown below: 0 50 100 150 200 250 0 5 10 15 20 25 30 35 40 45 50 no. of nodes th ro ug hp ut (k bp s) ls dv ant -200 0 200 400 600 800 0 5 10 15 20 25 30 35 40 45 50 no. of nodes n o. o f p ac ke ts d ro pp ed ls dv ant fig. 4: throughput vs. nodes. fig. 5: packet drop vs. nodes. iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 8 0 200 400 600 800 1000 0 5 10 15 20 25 30 35 40 45 50 no. of nodes n o. o f p ac ke ts ls dv ant 0 0.02 0.04 0.06 0.08 0.1 0.12 0 5 10 15 20 25 30 35 40 45 50 no. of nodes d el ay (s ) ls dv ant fig. 6: packet loss vs. nodes. fig. 7: delay vs. nodes. the above results were obtained by simulating the network topologies with a tcp source. tcp has variable bit rate and built-in flow control, as the new packets are only sent if acknowledgement packets for the sent packets have reached the source node. testing networks with tcp sources is justified because real world networks are normally based on variable bit rate conditions. from the graph shown in fig. 4, one can infer that the throughput produced by antnet 2.0 is better than that produced by ls and dv. figure 5 shows that antnet 2.0 has a lesser packet drop, as compared to ls and dv. it is visible from fig. 6 that antnet 2.0 has no packet loss while the other algorithms have a significant degree of packet loss. in a constraint optimization problem, one has to compromise on something in order to gain something. this is the case illustrated in fig. 7, where antnet produce more delay than other algorithms. results for cbr traffic sources are shown below: -20 0 20 40 60 80 100 0 5 10 15 20 25 30 35 40 45 50 no. of nodes th ro ug hp ut (k bp s) ls dv ant -5000 0 5000 10000 15000 20000 25000 30000 0 5 10 15 20 25 30 35 40 45 50 no. of nodes n o. o f p ac ke ts ls dv ant fig. 8: throughput vs. nodes fig. 9: packet drop vs. nodes iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 9 -5000 0 5000 10000 15000 20000 0 no. of nodes n o. o f p ac ke ts ls dv ant 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0 5 10 15 20 25 30 35 40 45 50 no. of nodes d el ay (s ) ls dv ant fig. 10: packet loss vs. nodes fig. 11: delay vs. nodes the results shown in figs. 10 and 11 were obtained by simulating the network topologies with a cbr source. cbr has constant bit rate and no flow control, as the new packets are sent and no acknowledgement packets are expected. testing networks with cbr sources is equivalent to doing an acid test of the network. it is justified because it shows the analyst how much data can be transferred, before the networks fails or is too overloaded to be used. from the graph shown in fig. 8, one can infer that the throughput produced by antnet 2.0 is much better than that produced by ls and dv. figure 9 shows that antnet 2.0 has much lesser packet drop, as compared to ls and dv. it is visible from fig. 10 that antnet 2.0 has no packet loss while the other algorithms have a high degree of packet loss. the result obtain in fig. 11 is extremely unique because antnet 2.0 should produce higher delay but for higher number of nodes, its delay is less than that of ls and dv. a simple explanation for this is that when we had higher number of sending nodes, the network became overloaded and since other two algorithms have no load balancing technique, they became too overloaded, which caused excessive delays. time to converge the previous section showed that antnet2.0 algorithm is more robust, scalable and reliable than the other two algorithms. however, another important factor that hinders the use any such algorithm in commercial networks is the convergence time factor. convergence time refers to the time that an algorithm takes so that all the nodes in the network have complete routing table. to test this phenomenon, we ran our algorithm on the simulated version of the jaring backbone network shown in fig. 12. the data to construct the replica of the network was provided to us by the jaring representatives. figure 13 only gives a rough idea of the topology, as more accurate information is classified and no third party is allowed to have access to it. iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 10 fig 12: jaring backbone network. in our experiment, the network of fig. 12 was routed repeatedly without changing any of the original conditions and the time to reach a convergence state was noted each time. when this network was routed for the first time, it took a lot of time to reach convergence, but it can be noticed from fig. 13 (values taken from table 2) that, as the network got routed more number of times, time to converge reduced exponentially. this was observed because the mobile agents produced in the first route, pass their information to the second batch of mobile agents generated in the second route. thus the newer agents have to traverse fewer areas of the network in order to construct the routing table. time to converge vs. batch of ants 0 1 2 3 4 5 1 2 3 4 5 6 7 8 9 10 batch ti m e (s ) fig 13: convergence times. iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 11 table 2: convergence times. batch time (s) 1 4 2 2.2 3 1.2 4 0.73 5 0.42 6 0.2351 7 0.1185 8 0.05935 9 0.029685 10 0.014844 6. conclusions and suggestions in conclusion, it is to be suggested that the antnet 2.0 algorithm performs better than the other algorithms in use today. however, it is to be noted that antnet 2.0 produces about 20 to 30 percent more delay than the other algorithms. this might deter the network engineers to implement the algorithm as it is today. future works in the area of reducing the delay may result in this algorithm being adopted widely by the private networks. references [1] m. dorigo, v.maniezzo, a. colorni. ‘the ant system: optmization by a colony of cooperating agents’. pp 1-13. vol. 26-part b. ieee transactions on systems, man, and cybernetics. 1996. [2] e. bonabeau, m. dorigo, and g. théraulaz, swarm intelligence: from natural to artificial systems, oxford university press, 1999. [3] m. dorigo, luca maria gambardella. ant colony system: a cooperative learning approach to the travelling salesman problem; ieee transactions of evolutionary computation, 1:5366(1), 1997. [4] networks and routing a survey; aronson. technical report 94-112, faculty of mathematics and computer science, delft university of technology, 1994. [5] g. di caro, m. dorigo. “antnet: distributed stigergetic control for communication networks”. artificial intelligence, 9, 317-365, 1998. [6] ruud schoonderwoerd. collective intelligence for network control; master thesis, faculty of mathematics and computer science, delft university of technology, 1996. [7] ruud schoonderwoerd, owen holland, janet bruten, leon rothkrantz. load balancing in telecommunication networks; adaptive behaviour, 5(2), 1997. iium engineering journal, vol. 5, no. 1, 2004 s. haseeb et al. 12 biographies shariq haseeb obtained his bachelor of engineering degree from international islamic university, malaysia. he is currently pursuing msc (computer and information engineering) in international islamic university, malaysia. his research interests are in swarm intelligence, mobileipv6, active networks and other computer network related areas. khairul azami sidek was born in melaka, malaysia in 1980. he received his b.sc. degree in computer and information engineering from the international islamic university malaysia in 2003. he is currently an assistant lecturer at the department of electrical and computer engineering at the international islamic university malaysia. his primary research interests are networking, software development, database management system and internet applications. ahmad faris ismail currently is a professor and the dean of faculty of engineering at international islamic university malaysia (iium). he obtained his bachelor of science in chemical engineering from university of houston in 1988 before completing his ph.d. from rice university, u.s.a. in 1993. his research areas include discrete modeling, energy systems, combustion, computational fluid dynamics, engineering mechanics, computer vision, and image processing. he has published more than 70 technical papers in these areas in international journals and conference proceedings. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 the effectiveness of 6t beamformer algorithm in smart antenna systems for convergence analysis sadiya thazeen* and mallikarjunaswamy srikantaswamy department of electronics and communication engineering, jss academy of technical education, bengaluru, india * corresponding author: thazeen.sadiya@gmail.com (received: 1 february 2023; accepted: 13 march 2023; published on-line: 4 july 2023) abstract: recently, the need for more capacity in wireless networks has motivated this current research towards the creation of standards and algorithms that selectively take advantage of space. the development of smart antenna arrays and related beamforming algorithms has received a lot of attention. cell planning is an important process in networking, which is used to ensure coverage and avoid interference. also, cell planning plays a vital role in the placement of base stations in a network. the communication between the base station (bs) and mobile station can happen either using a single antenna or an array of antenna elements. in the case of using a single antenna, if the electromagnetic (em) wave has low snr, then bs cannot decode the data and drops the signal. conversely, when an array is used, a signal with low snr also falls on the base station, and due to multiple delayed copies of the same signal, the data gets decoded successfully. with space division multiple access (sdma), the frequencies allotted for mobile communication are reused to provide channel access to multiple users at the same time preserving the allowable reuse distance in network architecture, thus increasing the channel capacity and facilitating multiple users separated by a distance at the same time with frequency reuse. the smart antenna system at the base station performs the transceiver function. the transmission phase uses the output from the reception i.e., the detected user direction radiates a beam towards the desired user for communication to narrow the beam. the proposed 6t beamformer method is a six-tap-based system with three taps having fixed step sizes and the other three having variable step sizes. with the execution of each tap or module, better convergence and quality of service are achieved. in the result analysis, the proposed method is compared with existing high-performing algorithms like lms, griffiths, and vsslms against mean square error (mse) to show that it converges faster at the 9th iteration which is better than others in all the probabilities. abstrak: dewasa ini, keperluan terhadap lebih kapasiti dalam rangkaian tanpa wayar menjadi motivasi kepada kajian terkini dalam membentu piawai dan algoritma yang menjimatkan ruang. pembangunan tata susun antena pintar dan algoritma pembentukan pancaran telah mendapat perhatian ramai. merancang sel adalah proses penting dalam jaringan, bagi memastikan liputan terhasil dan mengelak dari gangguan. juga, merancang sel memainkan peranan penting dalam menempatkan tapak stesen dalam rangkaian. komunikasi antara stesen pusat (bs) dan stesen bergerak dapat berlaku samada menggunakan antena tunggal atau elemen tata susunan antena. dalam kes antena tunggal, jika gelombang elektromagnetik (em) mempunyai snr rendah, bs tidak dapat menafsirkan kod data dan signal akan terabai. sebaliknya, apabila susun atur digunakan, signal dengan gelombang snr rendah akan terus ke stesen pusat dan disebabkan beberapa gelombang sama yang tertunda, data dapat ditafsir dengan sempurna. melalui capaian pelbagai pembahagi ruang (sdma), frekuensi yang ditimbulkan bagi komunikasi bergerak telah diguna balik bagi menyediakan kemasukan saluran kepada pelbagai 100 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 pengguna pada waktu sama memelihara jarak guna balik yang dibenarkan dalam binaan rangkaian, oleh itu menambah kapasiti saluran dan membantu gandaan pengguna yang dipisahkan oleh jarak dengan kekerapan guna balik pada masa sama. sistem antena pintar di stesen pusat pula menjalankan fungsi pemancar. fasa pemancaran ini menggunakan pengeluaran dari penerima iaitu, pengguna yang dikesan dari arah pancaran, akan memancarkan gelombang kepada pengguna yang memerlukan komunikasi, ini dapat mengecilkan jarak pancaran. kaedah yang dicadangkan ini menghasil pancaran 6t iaitu sistem berdasarkan-enam-tap di mana tiga tap mempunyai saiz langkah yang tetap dan tiga lagi mempunyai saiz langkah berubah. dengan pelaksanaan ini setiap tap atau modul mempunyai penumpuan yang lebih baik dan servis yang berkualiti terhasil. dapatan kajian menunjukkan, kaedah yang dicadangkan dapat dibandingkan dengan algoritma berprestasi tinggi sedia ada seperti lms, griffiths, dan vsslms berbanding min kuasa dua ralat (mse) bagi menunjukkan ia tertumpu lebih laju pada iterasi ke 9, iaitu lebih baik daripada ke semua kebarangkalian. keywords: beamforming; convergence analysis; mean square error; space division multiple access; weight computation 1. introduction communication systems involving 5g not only generate higher performance in convergence, capacity, and data rate but also reduce the latency, computational complexity, and cost. this research proposes a 2-stage suboptimal beamforming method to provide a solution to the problems encountered in the physical layer of the 5g system [1,2]. the role of adaptive algorithms in digital signal processing is pivotal. this study considers the application of the three existing high-performing adaptive algorithms in the quality of voiceover-ip with modifications in the step size, as step size contributes greatly to the convergence speed of the algorithms [3]. the grade of the antenna array will be better if the radiation is sent to the desired user [4]. the grade is directly dependent upon frequency or transmitter usage [5]. all the mobile users in the hexagonal cell will receive the signal with the same frequency at the same time but the angle of variation will distinguish the sources. the new arrays send the narrow beam toward actual mobile users to save an amount of energy [6]. the phase shifts are used to calculate the amount of energy reduced from the initial stage [7]. the concept of scheduler-based transmission will make the antenna array elements rest/constant at regular intervals and assign phase shifts to array elements to form the main beam [8]. the capacity for communication can be increased with the help of intelligent systems [9]. digital signal processing (dsp) is that crucial determining factor in advancing wireless communications technology and increasing the capacity of limited rf spectrum [10]. multiple techniques are used to decode the signal based on either summation of signals or by using maximum signal to noise ratio (snr) so that the signal formation is better at the receiving end [11]. during the reception phase, the electromagnetic (em) waves are obtained as the original signal and delayed versions of the original signal and are added up to get the main signal data. the maximum snr method will consider each signal, then find the snr and choose the signal which has the maximum snr [12]. the phase shifts are computed by taking the actual signal, noisy signal, and jammed signals to form the total signal. the total signal phase shifts are multiplied by the initial set of phase shifts to form the array output. in a legacy system, an array of dipole elements is arranged linearly. the energy wastage is greater whenever the radiation falls in other directions. to overcome that, the following contributions are made: 101 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 • the receiving phase's result or the user direction was detected and is used in the transmission phase to guide a beam in the direction of the intended user. • then, the 6t beamformer, a six-tap device used in the suggested technique, has three taps with fixed step sizes and the remaining three with variable step sizes. • better convergence is achieved with each tap or module that is executed in the result analysis. 2. literature review energy efficient multicasting via smart antennas in multipath environments has been proven by tong and ramanathan [13]. nodes can direct their transmission energy in the appropriate directions by utilizing an adaptive antenna array, which allows them to conserve energy. the fact that this work functions in rich scattering surroundings is a noteworthy aspect. the issue was framed as a non-linear issue. furthermore, it suggested two heuristics that are effective in computing. according to the numerical simulations, the two heuristics can significantly reduce power consumption when contrasted to the single antenna scenario. to fix the design problem and test the performance of the developed approaches, researchers likewise utilized simulation annealing. ali and hassan [14] used a microstrip antenna array to show a hybrid technique. this study contains the theoretical hybrid method, which integrates two methods to boost their effectiveness. this is accomplished by making use of two algorithms' strengths while avoiding their weaknesses. the least mean square and sample matrix inversion methods are those two techniques. the resonant frequency of the microstrip antenna, which operates between 1700 and 1950 mhz, is 1850 mhz. the influence of different parameters on minimal mean square error has been established by anjaneyulu et al. [15]. this evaluation considers the least mean square technique settings as well as antenna variables including step-size fluctuation and signal-tonoise variation. the major targets of all parameter changes are mean square error, null depth, convergence speed, and beamforming efficacy. the lms with suitable antenna input variables resulted in successfully displaying information at the location of the interferers and minimizing the error, as seen in all calculated values. mayyas and aboulnasr [16] presented the sensor which was placed at a distance, d, from each other. the weights are computed by making use of directivity, white noise, and interference ratio. once the phase shifts were computed using the previous version of phase shifts, step size, reference signal, and error signal, the trace of the autocorrelation was found. from the weights, the maximum value has been found and then normalized phase shifts are obtained. saqhib et al. [17]. describes the path establishment process in a wireless sensor network (wsn) for sending data packets and highlights how repeated participation in multiple paths can lead to reduced network lifetime. the paper seeks to provide recapitulation of wsn, the effects of lifetime ratio, and an energy-efficient routing protocol through numerical survey. mallaiah et al. [18] demonstrated the leaky lms algorithm, which was responsible for finding the phase shifts and then applying the components to create the beam. leaky lms was developed on top of the lms method with the variation in the computation of step size. the step size depends upon the eigenvalue and then the maximum value of eigen is found. the new phase shifts were calculated through earlier step size and phase shift. 102 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 beamforming by small-spacing microphone arrays through constrained lasso has been demonstrated by wang et al. [19]. the capon approach also determines the crosscorrelation between the bs signal and the real reference signal. toeplitz execution will be used on the phase shifts to discover new phase shifts. every component of the array was therefore subjected to the phase shifts to create the main beam. 3. system model consider a uniform linear array that has all dipole elements with each element separated from the other at an equal distance. fig. 1: uniform linear array elements. figure 1 shows radiating or antenna elements arranged linearly. na is the number of antenna elements separated by an equal distance d. the electromagnetic (em) wave along with the delayed versions falls on the array elements. the representation of the electromagnetic wave will create the delay vector having na* 1 with na as the number of elements. the disturbance can be suppressed with the help of multiple wavelengths. the delayed electromagnetic wave vector can be summarized as eq. (1) below, ( ) 1 1 a j sin( d ) j ( n ) sin( d ) e . em d . . e      − − −         =            (1) where, na is the number of array elements, and theta is the direction of impinging electromagnetic wave. the reference signal is generated for the mobile station which can be a sine or cosine reference signal with ns number of samples and is provided by the values as eq. (2) ( ) ( )r i cos pi i / ts=  (2) where, i = sample index ts = number of samples the reference signal would be better if the sampling is done using nyquist criteria in which the sampling period should have a certain minimum value. the sampling frequency should be greater or equal to the minimum value of 1 2/ * ts . the index will be varied between 0 i ns= = where ns is the maximum number of samples. 103 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 the array manifold vector is computed for the set of n users and the combination of direction vectors across interference user’s njammer directions 1 2 { , ,......................... } njammer    which is stated in eq. (3), 1 2 1 2 sin( )sin( ) sin( ) ( 1)sin( )( 1)sin( ) ( 1)sin( ) 1 1 .... 1 . . . nj a nja a jj j m j nj n j n e e e j e e e           −− − − −− − − −          =           (3) the jammer and noise signals are random and can be generated as nj number of samples. the electromagnetic wave received at the base station will have pure directional vector and reference signal combinations. the jammer signal, along with directional vectors across all the directions and noise signal, can be provided as eq. (4). 0 0 ( ) * , ( ) int signal v v o bsrs d rs js jm ns where d direction vector for an angle rs total reference signal in matrix format generated at the mobile station js total erference signal samples which are random in nature jm jammer sign    = + + = = = = al for all jammer directional vectors ns noise signal vector matrix= (4) the bsrs matrix along with the hermitian bsrs matrix can be multiplied to have an auto-correlation matrix which is represented in eq. (5) * , signal h bsrs signal signal signal h signal r bsrs bsrs where bsrs total recived signal at bs bsrs hermitian transpose of bsrs = = = (5) the error signal at the base station has been found through the combination of all electromagnetic waves as an array total which is referred to in eq. (6) ( ) ( ) ( ) ( ) ( ) h h th at n ps n bsrs n where ps n hermitian transpose of array phase shifts which are applied to individual phase shifters bsrs n bsrs for n sample = = = (6) 104 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 the error vector can be obtained using the difference among the reference signal which can be computed as eq. (7) ( ) ( ) ( )ev n bsrs n at n= − (7) each of the methods will have to compute the phase shifts in such a way that the error vector value has to be minimized while considering some of the existing algorithms, such as least mean square (lms) [16], which is the robust approach to computing the weights. then, the griffiths algorithm [20] extracts a particular signal among many signals’ incident at bs on the antenna array elements. finally, the variable step size griffiths method [21] is formed by combining lms along with the vsslms method to improve the performance. the step size is varied between 0 and the upper limit so that better and faster convergence can be achieved. the simulation results and their analysis are described in section 5. 4. proposed 6t beamformer algorithm figure 2 shows the functional block diagram of the smart antenna system at the bs where the antenna array picks up the signal from the user trying to access the communication channel to establish communication. the user direction is estimated using actual and delayed versions of the signal and the output is passed onto the beamforming block of the system where the advanced signal processing computes the weights for each iteration considering the output feedback and radiates a beam that is maintained sharp and noise-free to the best possible extent for the communication link to be of high quality. fig. 2: overall diagram for smart antenna system. the proposed 6t beamformer [22] is a six-tap phase shifts method with the combination of leaky least mean square (llms) and variable step size least mean square (vsslms). convergence is an important performance parameter wherein the convergence factor is the ith number of iterations at which the mean square error reaches zero. the performance of the algorithm is improved by lowering the iteration count and increasing the convergence factor. 105 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 fig. 3: six-tap phase shifts applier. figure 3 shows the arrangement of six tap phase shifts applier which can be divided into 7 different blocks. in the first block, the phase shifts are computed using a leaky least mean square (llms) method i.e. llms (1) to obtain kth phase shifts. a speed better module will provide the computation of weights in a better fashion which computes k+1 phase shifts and then it is continued to variable step size least mean square (vsslms-1) to compute k+3. it is followed by convergence betterment (cb) method which will compute k+4 phase shifts which will then be sent to llms (2) and vsslms (2) to have k+5, k+6. due to the execution of the modules, the convergence will be improved and then the error will be reduced to a lower value. 4.1 leaky least mean square this method is one of the versatile beamforming methods which makes use of phase shifts that are applied to specific antenna elements followed by the formation of an array factor. but lms faces certain disadvantages which are a) the rate at which convergence is achieved is quite low and b) drifting of weight causes more error. to overcome these disadvantages, the leaky factor is computed and used in the phase shifts (eq.(8-9)). the phase shifts of the leaky least mean square (llms) magnitude will be kept within bounded limits so that the drifting issue can be resolved. the step size for the llms module is computed as eq. (8) 2 ( ) * ( 1) * ( ) llms llms ss n ss n e n = + + (8) where,  = initial step magnitude between 0 to 1  = average square of the error signal the phase shifts vector used by llms can be defined as eq. (9) ( 1) [1 2* ( )] ( ) * ( ) ( )ps n ss n ps n e n bsrs n+ = − + (9) 4.2 speed betterment the convergence speed can be improved using speed betterment-based phase shift computation which will take into consideration cross-correlation, step size, and previous phase shifts, as stated in eq. (10). 106 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 1 ( 1) ( ) ([ 2 ] [ ( ) 2 ]) sb sb si xx si xs p n p n i bsrs p n bsrs  − + = + − − (10) the speed betterment phase shifts are computed using previous phase shifts, the base station received signal and then step size can be computed using eq. (11). 1 3 ( ) sb s b tr r  = (11) where s b r is the autocorrelation of base station received signal (bsrs) and ( ) s b tr r is the trace of autocorrelation matrix, which is obtained by performing the square root of the sum of square values of each principal element. 4.3 variable step size least mean square when the snr of the signals are varying, the constant value of step size is not helpful. the step size can be obtained using a fast and robust variation of the vsslms method by making use of the normalized sigmoid method. it overcomes the convergence by adjusting the step size value in an adaptive fashion which is used in the computation of phase shifts. the vsslms step size is varied to have better convergence which is expressed in eq. (12). ( 1) ( 1) 0 ( 1) 0 ( 1) s s upper s s upper s s ss n ss if ss n ss if ss n ss n otherwise + = +  = +  = + (12) where, s upper ss is the upper limit of step size. the upper limit size is computed by making use of the eigenvalue computation of autocorrelation which is stated in eq. (13). 2 m upper ev ss av + = (13) where, max ( ) m ev value of eigen values av array value of mean square error mse = = the phase shifts of the vsslms method can be computed using the following eq. (14). ( 1) ( ) ( ) * ( ) ( )ps n ps n ss n e n bsrs n+ = + …… (14) 4.4 convergence betterment this module helps in increasing the speed at which the error can be minimized by making use of a reference signal to the array output. the phase shifts are computed using the convergence betterment module by making use of the aitken process, which is referred to in eq. (15). 1 llms cb llms nu w l de = − (15) 107 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 where, 1 1vssgmk k k vssg k k k vssg nu m m w m n m w= + − 1 1 1 2 llmsmk k k llms k k k llms k llms de m m w m n m w n w = + − − + 1k k llms k k k l acs scs w acs ccs ccs= + + where, 2 k cb xx acs i r= − 2 k cb xs ccs r= . 5. simulation results in this section, simulation results of the proposed 6t beamformer are discussed in detail along with the comparison of the algorithm against the existing ones to mean square error which is also a measure of the converging speed of the algorithms. this paper considers a few existing high-performance algorithms such as least mean square (lms) [15], griffiths algorithm [19] and variable step size griffiths method [20] for comparison of mean square error. the radiation pattern, real phase shifts and imaginary phase shifts are simulated only for the proposed 6t beamformer as the comparison graph will have the results overlapped. the results are simulated by taking into consideration the probability of a number of jammers from one to many along with varying the number of antenna elements from few to many numbers. table 1 shows the probability-1 setup considering fewer array elements and one interference at 30 degrees. figures 4 and 5 display the real and imaginary phase shifts for the experimental setup considered. table 1: experimental setup for probability-1 few antenna elementssingle jammer values number of array elements 8 desired direction 45 interference count 1 interference directions 30 fig. 4: real array phase shifts. 1 2 3 4 5 6 7 8 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 sensor element index a rr a y p h a s e s h if ts m a g n it u te real array phase shifts-six tap 108 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 fig. 5: imaginary array phase shifts. figure 6 reveals the radiation array pattern for the setup as mentioned in probability-1 of 45 degrees. figure 7 shows a mean square error comparison plot for probability-1 where the proposed 6t beamformer algorithm successfully converges faster at run count or some iterations of 11 followed by vssg, with a run count of 45, griffiths along with lms with a run count of 70. hence the proposed 6t beamformer performs better than other methods for considering probability-1. table 2 shows the experimental setup considering a high number of antenna elements and a single interferer at 5 degrees with the desired source at 30 degrees for probability-2. fig. 6: radiation pattern for 6t beamformer at 45 degrees. table 2: experimental setup for probability-2 many antenna elementssingle jammer values number of array elements 100 desired direction 30 interference count 1 interference directions 5 1 2 3 4 5 6 7 8 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 sensor element index a rr a y p h a s e m a g n it u te imaginary array phase shifts-six tap 0.2 0.4 0.6 0.8 1 30 210 60 240 90 270 120 300 150 330 180 0 radition pattern six tap polar cordinates angle(deg) a rr a y f a c to r 109 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 fig. 7: comparative analysis of mse for probability-1. fig. 8: real phase shifts for probability-2. fig. 9: imaginary phase shifts for probability-2. figures 8 and 9 display the real and imaginary phase shifts for the experimental setup considered in probability-2 of 30 degrees. figure 10 represents the antenna radiation pattern with the main beam at the desired angle of 30 degrees and interferer given no signal strength. 10 20 30 40 50 60 70 80 90 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 run count m e a n s q u a re e rr o r comparision of algorithms w.r.t mse lms griffts vssg six-tap 0 20 40 60 80 100 120 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 sensor element index a rr a y p h a s e s h if ts m a g n it u te real array phase shifts-six tap 0 20 40 60 80 100 120 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 sensor element index a rr a y p h a s e m a g n it u te imaginary array phase shifts-six tap 110 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 fig. 10: radiation pattern for 6t beamformer at 30 degrees. fig. 11: comparative analysis of mse for probability-2. figure 11 shows the mean square error comparison graph for probability-2 where the 6t beamformer converges faster at just 10 iterations which means low mse followed by vssg converging in 34 iterations and griffiths, lms at 75 each. table 2 clearly shows that the 6t beamformer proves to perform better in the desired direction (30 degrees). table 3: experimental setup for probability-3 few antenna elementsmultiple jammer values number of array elements 8 desired direction 60 degrees interference count 3 interference directions [5 10 15] table 3 displays the experimental setup of lesser array elements considering multiple interferers. here, consider 3 interferers at 5, 10, and 15 degrees each. figures 12 and 13 exhibit real and imaginary phase shifts for the experimental setup considered in probability-3. these individual phase shifts are exploited to each element of the array for the formation of the main beam in the desired direction of 60 degrees with multiple 0.2 0.4 0.6 0.8 1 30 210 60 240 90 270 120 300 150 330 180 0 radition pattern six tap polar cordinates angle(deg) a rr a y f a c to r 10 20 30 40 50 60 70 80 90 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 run count m e a n s q u a re e rr o r comparision of algorithms w.r.t mse lms griffts vssg six-tap 111 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 interferers. figure 14 shows the radiation pattern for 6t beamformer forming a mean beam towards the desired user direction of 60 degrees while interferers are treated with nulls. fig. 12: real phase shifts for probability-3. fig. 13: imaginary phase shifts for probability-3. fig. 14: radiation pattern for 6t beamformer probability-3. 1 2 3 4 5 6 7 8 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 sensor element index a rr a y p h a s e s h if ts m a g n it u te real array phase shifts-six tap 1 2 3 4 5 6 7 8 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 sensor element index a rr a y p h a s e m a g n it u te imaginary array phase shifts-six tap 0.2 0.4 0.6 0.8 1 30 210 60 240 90 270 120 300 150 330 180 0 radition pattern six tap polar cordinates angle(deg) a rr a y f a c to r 112 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 fig. 15: comparative analysis of mse for probability-3 figure 15 shows the mean square error comparison graph for probability-3 where the 6t beamformer is seen converging faster, at just 10 iterations, giving low mse followed by vssg with a run count of 48, griffiths and lms converge at a run count of 80 and 78 respectively. hence, the novel 6t beamformer performs better than other methods for the considered probability-3. table 4 displays the experimental setup description wherein a large number of antenna elements and multiple interferers are considered as a probability at the base station. table 4: experimental setup for probability-4 many antenna elementsmultiple jammer values number of array elements 100 desired direction 15 degrees interference count 3 interference directions [45 50 55] fig. 16: real phase shifts for probability-4. 10 20 30 40 50 60 70 80 90 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 run count m e a n s q u a re e rr o r comparision of algorithms w.r.t mse lms griffts vssg six-tap 0 20 40 60 80 100 120 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 sensor element index a rr a y p h a s e s h if ts m a g n it u te real array phase shifts-six tap 113 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 fig. 17: imaginary phase shifts for probability-4. figures 16 and 17 reveal real and imaginary phase shifts for the experimental setup considered in probability-4. each phase shift is exploited to all sensor elements of the array for the formation of the main beam in the desired direction of 15 degrees with multiple interferers. fig. 18: radiation pattern for 6t beamformer probability-4. figure 18 exhibits the radiation pattern for the novel 6t beamformer algorithm which excellently forms a narrow main beam towards the desired user direction of 15 degrees. the algorithm works very well with more antenna elements. figure 19 shows the mean square error comparison graph for probability-4 where the 6t beamformer converges at just 9 iterations, implying lower mse, followed by vssg with a run count of 40, griffiths and lms converge at a run count of 70 and 62 respectively. hence, the novel 6t beamformer performs better than other methods for the considered probability-4. table 5 summarizes the point of convergence obtained from the simulation results. it can be seen that the proposed 6t beamformer converges faster than other algorithms with the least number of iterations implying low mean square error and high-speed performance of the algorithm. 0 20 40 60 80 100 120 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 sensor element index a rr a y p h a s e m a g n it u te imaginary array phase shifts-six tap 0.2 0.4 0.6 0.8 1 30 210 60 240 90 270 120 300 150 330 180 0 radition pattern six tap polar cordinates angle(deg) a rr a y f a c to r 114 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 fig. 19: comparative analysis of mse for probability-4. table 5: summarizing the convergence point of all the algorithms. array count jammer count lms griffiths vssg 6t beamformer 8 1 70 70 45 11 100 1 75 75 34 10 8 3 70 80 48 10 100 3 62 70 40 9 6. conclusion this research provides a novel beamforming method called 6t beamformer to improve the converging speed by reducing the mean square error. the novel algorithm makes use of both fixed and variable step size methods along with speediness betterment and convergence betterment feedback. the feedback of weights is shared between the modules to calculate the phase shifts that are exploited to specific parts to create the main beam for actual mobile users. lms, griffiths, and vssg are described in brief and these methods are then compared to the proposed six tap method which outperforms the existing ones for different scenarios of variation in array elements and jammer count. the convergence of six-tap is high compared to other methods. the proposed technique is contrasted with other, high-performing methods in the analysis of the results to demonstrate that it converges more quickly at the 9th iteration and performs better than others in all probabilities. this also implies reduced multipath fading. the algorithm is also efficient in interference rejection and overall increasing the capacity of the rf spectrum. in the future, this research will be further extended by analyzing novel methods with various performance metrics. references [1] kabaoğlu n. (2018) suboptimal frequency-selective transceiver design for multicarrier millimeter wave mimo systems. electrica, 18(1): 83-89. doi:10.5152/iujeee.2018.1813 [2] tokan nt. (2019) array antenna feeding network design for 5g mimo applications. electrica, 19(2): 120-127. doi: 10.26650/electrica.2019.19004 10 20 30 40 50 60 70 80 90 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 run count m e a n s q u a re e rr o r comparision of algorithms w.r.t mse lms griffts vssg six-tap 115 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 [3] hameed aa, ajlouni n, orman z, özyavaş a. (2020) investigating the effectiveness of adaptive step size lms algorithms for the use with voip applications. electrica, 20(2): 116123. doi: 10.5152/electrica.2020.19080 [4] li x, wang j, li z, li y, geng y, chen m, zhang z. (2022) leaky-wave antenna array with bilateral beamforming radiation pattern and capability of flexible beam switching. ieee trans. anntenas propag., 70(2): 1535-1540. doi: 10.1109/tap.2021.3111157 [5] ghaffar a, li xj, awan wa, hussain n. (2021) reconfigurable antenna: analysis and applications. in matin, ma (eds) wideband, multiband, and smart antenna systems. signals and communication technology. springer, cham:269-323. https://doi.org/10.1007/978-3-03074311-6_9. [6] kodgirwar vp, deosarkar sb, joshi kr. (2020) design of dual-band beam switching array for adaptive antenna applications using hybrid directional coupler and e-shape slot radiator. wireless personal communications, 113 :423-437. https://doi.org/10.1007/s11277-020-07207-3 [7] nawaz h, tekin i. (2020) ten switched‐beams with 2×2 series‐fed 2.4 ghz array antenna and a simple beam‐switching network. int. j. rf microwave comput. aided eng., 30(6): e22184. https://doi.org/10.1002/mmce.22184 [8] baba aa, hashmi rm, attygalle m, esselle kp, borg d. (2021) ultrawideband beam steering at mm-wave frequency with planar dielectric phase transformers. ieee trans. antennas propag., 70(3): 1719-1728. [9] simone m, fanti a, lodi mb, pisanu t, mazzarella g. (2021) an in-line coaxial-to-waveguide transition for q-band single-feed-per-beam antenna systems. appl. sci., 11(6): 2524. https://doi.org/10.3390/app11062524 [10] thazeen s, mallikarjunaswamy s, saqhib mn. (2022) septennial adaptive beamforming algorithm. in international conference on smart information systems and technologies (sist): 28-30 april 2022; nur-sultan, kazakhstan. pp 1-4. [11] cai z, zheng x. (2018) a private and efficient mechanism for data uploading in smartcyberphysical systems. ieee trans. network sci. eng., 7(2): 766-775. doi: 10.1109/tnse.2018.2830307 [12] dakulagi v, bakhar m. (2020) advances in smart antenna systems for wireless communication. wireless personal communications, 110(2): 931-957. [13] tong l, ramanathan p. (2004) energy efficient multicasting using smart antennas for wireless ad hoc networks in multipath environments. in ieee global telecommunications conference, globecom '04: 29 november 2004 03 december 2004; dallas, tx, usa. 6: 4109-4113. doi: 10.1109/glocom.2004.1379138 [14] ali wae, hassan ahg. (2014) a hybrid least mean square/sample matrix inversion algorithm using microstrip antenna array. in science and information conference: 27-29 august 2014; london, uk. pp 871-876. doi: 10.1109/sai.2014.6918288. [15] anjaneyulu p, rao pvds, sunehra d. (2021) effect of various parameters on minimum mean square error and adaptive antenna beamforming using lms algorithm. in 6th international conference for convergence in technology (i2ct): 02-04 april 2021; maharashtra, india. pp 15. doi: 10.1109/i2ct51068.2021.9418179. [16] mayyas k, aboulnasr t. (1997) leaky lms algorithm: mse analysis for gaussian data. ieee trans. signal process., 45(4):927-934. doi: 10.1109/78.564181. [17] saqhib mn, lakshmikanth s. (2020) performance anatomization of routing protocols in wireless sensor network. international journal of advanced trends in computer science and engineering, 9(4): 5691-5699. [18] mallaiah n, rao nvk, ramakrishna d. (2019) rls adaptive beamforming algorithm in terms of energy efficiency for smart antenna system. in ieee indian conference on antennas and propagation (incap): 19-22 december 2019; ahmedabad, india. pp 1-4. doi: 10.1109/incap47789.2019.9134501. [19] wang x, benesty j, chen j, cohen i. (2020) beamforming with small-spacing microphone arrays using constrained/generalized lasso. ieee signal process lett., 27: 356-360. doi: 10.1109/lsp.2020.2971790. 116 https://doi.org/10.1002/mmce.22184 https://doi.org/10.3390/app11062524 iium engineering journal, vol. 24, no. 2, 2023 thazeen and mallikarjunaswamy https://doi.org/10.31436/iiumej.v24i2.2730 [20] roopa s, narasimhan sv. (2021) improved stability performance of a feedback active noise control using a steiglitz-mcbride adaptive notch filter and robust secondary path identification based on variable step size griffiths lms algorithm. noise control engineering journal, 69(2): 136-145. https://doi.org/10.3397/1/376914 [21] shi l, zhao h, zeng x, yu y. (2019) variable step-size widely linear complex-valued nlms algorithm and its performance analysis. signal process., 165: 1-6. https://doi.org/10.1016/j.sigpro.2019.06.029 [22] tuladhar sr, buck jr. (2020) unit circle rectification of the minimum variance distortionless response beamformer. ieee j. oceanic eng., 45(2): 500-510. doi: 10.1109/joe.2018.2876584. 117 https://doi.org/10.3397/1/376914 https://doi.org/10.1016/j.sigpro.2019.06.029 microsoft word 3_v17no2_compiled_v3_26nov16.docx iium engineering journal, vol. 17, no. 2, 2016 djamolov 95 on the correctness of a nonlocal problem for the second order mixed type equation of the second kind in a rectangle sirozhiddin zuhriddinovich djamolov* the institute of mathematics at the national university of uzbekistan, 100125, tashkent, academgorodok, durmon yuli street, 29. *corresponding author: siroj@mail.ru (received: 15th apr. 2016; accepted: 1st jul. 2016; published on-line: 30th nov. 2016) abstract: in this work, the correctness of a nonlocal problem from the sobolev spaces is proven under some restrictions to the coefficients of the considered second order mixed type equation of the second kind. the proof is accomplished with multiple methods namely, "ε-regularization", priory estimates, and the galerkin method. abstrak: dalam karya ini, ketepatan satu masalah bukan setempat dari ruang sobolev telah dibuktikan di dalam beberapa sekatan kepada koefisien persamaan jenis bercampur perintah kedua daripada jenis yang kedua yang dipertimbangkan. buktinya dicapai dengan pelbagai kaedah iaitu, "ε-regularization", anggaran priori dan kaedah galerkin. keywords: second order mixed type equation of the second kind; sobolev space; galerkin and ε-regularization methods 1. introduction the basic concepts of the theory of differential equations in partial derivatives were formed in the study of classical problems of mathematical physics and are currently well understood. however, the current problems of natural sciences lead to the necessity of setting and qualitatively studying new tasks, which is a striking example of a class of nonlocal problems. as nonlocal problems we call such problems that determine relationships between the value of the solution or its derivatives at the boundary and interior points of a considered domain. in recent decades, nonlocal problems for partial differential equations are being actively studied by many mathematicians. among the first studies of non-local problems, we note a work by bitsadze and samarskii [4]. in this work, spatial and non-local problems for a certain class of elliptic equations were formulated and studied, which led to the study of non-self-adjoint spectral problems. subsequently, the problem formulated in [4], has been named a bitsadzesamarskii problem. the investigation of nonlocal problems is caused by both theoretical interest and practical necessity. this is due to the fact that the mathematical models of various physical, chemical, biological, and ecological processes are often problems in which, instead of the classical boundary conditions, definite connection values of the unknown function (or its derivatives) on and within the boundary are given. problems of this type may arise in the study of phenomena related to plasma physics, the spread of heat, the iium engineering journal, vol. 17, no. 2, 2016 djamolov 96 process of moisture transfer in capillary porous media issues, demographics, mathematical biology, and some technological processes. nonlocal problems also have practical value in solving the problems of solid mechanics. they allow to control the stress-strain state and these are similar to the control tasks [4, 8-12, 16, 17, 19]. for the first time, non-local problems in certain weight and negative spaces for equations of mixed type were investigated by functional methods in the works [1, 6, 8, 10, 11, 17]. 2. formulation of a problem in a rectangle (0,1) (0, )q t  we consider a second order differential equation ( , ) ( , ) ( , ) ( , ) (1) .tt xx tlu k x t u u x t u c x t u f x t     problem: to find a generalized solution of eq. (1) from the sobolev space 2 ( ) lw q , ( 2 l is integer), satisfying boundary conditions ( , 0) ( , ), (2 )u x u x t  (0, ) (1, ) 0, ( 3)u t u t  here 0const   . in the previous works [6, 7, 11, 17] the correctness of problem eqs. (1)-(3) in the case where ( , 0) ( , ) 0k x k x t  was proven under comparatively strong conditions to the coefficients of eq. (1). in the present work, we consider the case where, ( , 0) 0 ( , )k x k x t  . note that eq. (1) is the second kind of mixed type equation, since there is no restriction inside the domain q to the sign of the variable t of the function ( , )k x t [5]. first, we consider the case where 2l  . assuming the coefficients of eq. (1) are smooth enough and ( , ), ( , )x t c x t are periodic in function with respect to variable t . 3. uniqueness for problem theorem 1: let aforementioned conditions to the coefficients of eq. (1) are fulfilled, moreover let 1 22 0; 0t tk k c c           , where 2 ln t   , such that (1, )   . then for any function 2( , ) ( )f x t l q a generalized solution of problem eqs. (1)-(3) from the space 22 ( )w q is unique and the following inequality holds true 1 0 .u m f here (, )l and l are respectively regular scalar product and norm of the sobolev space 2 ( ) lw q , 2 l is an integer number and it is known that at 0l  , 02 2( ) ( )w q l q [2, 5, 13-15]. here, and further, by m we designate positive constants, the exact values of which are not of interest. iium engineering journal, vol. 17, no. 2, 2016 djamolov 97 proof: for any function 22 ( )u w q , one can easily get the following equality by using integration by parts:   2 2 2 2 2 2 0 1 0 0 2 exp( ) exp( )(2 ) ( ) (4) exp( ) 2 t t t x t q q t x t x q lu t u dxdt t k k u u c c u dxdt t ku u u u cu ds                                 where 0 1( cos( , ); cos( , ))t x       is a unit vector of the inner normal to the q . conditions of theorem 1 guarantee non-negativity of the integral over the domain q . let 2 2 ( )u w q satisfy boundary conditions eqs. (2)-(3), on condition that theorem 1, with respect to function ( , )k x t , must meet the condition of ( , 0) 0 ( , )k x k x t  . with respect to function ( , )c x t , the periodicity of variables t and 2 te  satisfy conditions eqs. (2)-(3), thereby leading to positivity of the following boundary integral.    2 2 2 2 2 20 1 0 0 0exp( ) 2 exp( )t x t x t x q q j t ku u u u c u ds t ku u cu ds                      1 1 2 2 2 2 1 0 0 2 [ ( , ) ( , 0)] ( , 0) [ 1] ( , 0)t tx t t x q u u ds k x t e k x u x dx e u x dx              1 2 2 0 0 [ ( , ) ( , 0)] ( , 0) 2 [ (0, ) (0, ) (1, ) (1, )] t t x t x tc x t e c x u x dx u t u t u t u t dt       … 1 1 2 2 0 0 [ ( , ) ( , 0)] ( , 0) [ ( , ) ( , 0)] ( , 0) 0 .tk x t k x u x dx c x t c x u x dx   … … omitting non-positive items from eq. (4) we get  2 2 22 exp( ) exp( ) (2 ) ( ) } . (5)t t t x t q q lu t u dxdt t k k u u c c u dxdt                applying young's inequality to eq. (5) [5, 13, 14] the following estimate is obtained 1 0 ,u m f„ from which the uniqueness of the solution of problem eqs. (1)-(3) follows. 4. existence for problem in order to prove the existence of the solution of problem in eqs. (1)-(3) in 22 ( )w q the "ε-regularization" method is used with the galerkin method [7, 13-15]. consider a nonlocal problem for a composite type equation ( , ) (6)l u u lu f x t t            0 ; 0,1, 2 (7) q qt tt t td u d u q     (0, ) ( ) 8) 1, 0 (u t u t   iium engineering journal, vol. 17, no. 2, 2016 djamolov 98 here , p p t p u d u t    0 , 0,1, 2,td u u p  2 2 2 2 u u u t x        is the laplace operator in a plane,  is a small positive number, and 0const   such that (1, )   . eq. (6) acts as an  -regularization of eq. (1) [5, 7, 13, 14]. the class of functions 2 2( , ) ( )u x t w q  , 2 ( )u l qt      are designated through v , satisfying conditions in eqs. (7), (8). definition: as the regular solution of problem in eqs. (6)-(8), function ( , )u x t v  satisfies eq. (6). theorem 2: let the following conditions holds true in q : 1 22 0; 0,t tk k c c           where 2 ln t   such that (1, )   . then for any function 2, ( )tf f l q , ( , 0) ( , )f x f x t  there exists a unique regular solution of problem in eqs. (6)-(8) and the following inequalities are true: 2 22 2 2 2 2 1 0 0 0 ) ( ) ;i u u u m f t t x            „ 2 2 2 2 2 0 0 0 ) .tii u u m f ft            „ proof: the proof of inequality i) will be done similarly to the proof of theorem 1, from which the uniqueness of the regular solution of problem in eqs. (6)-(8) follows. now, the second prior estimate is proven. let ( , )j x t are eigenfunctions of the following problem: 2 2 2 2 2 , 9) ( j j j j jt x              0 ; 0,1, ( 10)p pt j t jt t td d p    (0, ) (1, ) 0. (11)j jt t   due to the general theory of linear self-adjoint elliptic operators [2, 13, 15], it is known that all eigenfunctions of problem in eqs. (9)-(11) form a fundamental system in ( )c q , which is orthogonal in 2 ( )l q . solving problems in eqs. (9)-(11), is ( , ) cos sinj j jx t t x    , where 2 2 22 ; ; ; 0,1, 2,...j j j j j j j j t            using these sequences of functions, a solution of the auxiliary problem is constructed iium engineering journal, vol. 17, no. 2, 2016 djamolov 99 2 , (12) t j j je t           ( , 0) ( , ). (13)j jx x t  obviously, problem in eqs. (12)-(13) is uniquely solvable and its solution has the form 1 2 2 0 0 0 0 2 2 2 1 1 exp( ) exp( ) sin cos cos 2 1 2 1 sin sin cos 1 4 t t t t t j j j j j j j t j j j j j t d dt x e tdt e tdt e x t t                                           it is clear that the functions ( , ) ( )j x t c q  are linearly independent. really, if 1 0 m j j j c    for some set of sequences of functions 1 2, ,..., m   , then acting on this sum by the operator  results in 1 1 0, m m j j j j j j c c       from which follows that 0jc  for any 1,j m . note, from the construction of function ( , )j x t the following conditions to the functions ( , ) ( )j x t c q  follow: 0 , 0,1, 2 ( 4) 1q qt j t jt t qd d q     (0, ) (1, ) 0 (15)j jt t   now an approximate solution of eqs. (6)-(8) is searched for in the form 1 n n j j j w u c      , where coefficients jc ; 1,j m  are defined as solutions of the algebraic system. exp( ) exp( ) . (1 2 6) 2 n j j q q t t l u dxdt f dxdt         the unique solvability of the algebraic system in eq. (16) is proven. multiplying every equation of (16) by 2 jc and summarizing with respect to j from 1 to n , considering problem in eqs. (9)-(13) results in exp( ) exp( ) . (17) t t q q l w t w dxdt f t w dxdt      from which, by virtue of theorem 2, by integrating the identity in eq. (17) an approximate solution of problem in eqs. (6)-(8) is obtained that estimates i) i.e. 2 22 2 2 2 2 1 0 0 0 .u u u m f t t x                 this implies the solvability of eq. (16) [6, 8, 13, 14]. in particular, from the estimate i) we obtain a weak solution of problem in eqs. (6)-(8). iium engineering journal, vol. 17, no. 2, 2016 djamolov 100 now the second priory estimate ii) must be proven. thanks to eqs. (9)-(13), from the identity in eq. (16) comes 2 2 1 1 exp( ) exp( ) . (18) 2 2j jj jq q t t l w dxdt f dxdt                multiplying each equation of (18) by 22 j jc and summing j from 1 to n , taking eqs. (13),(14) into account from eq. (18), the following is derived 2 2 2 2 (19) 4 4 t ttt t tt t q q w w l we w w dxdt fe w w dxdt t t                              integrating eq. (19) according to the conditions of theorem 2 and the boundary conditions in eqs. (14)-(15), we obtain the following inequality   2 2 2 2 2 0 0 0 (2 ) (2 )tt t tt t tx xx q w m f f e k k w k k w w dxdt t                          3 2 2 2 0 1 1 ( ) 2 (20) t ttt tx xx tt tx t tx xt tt i iq q e k w w w ds e kw w w w w w ds j                where 1j is integral along the domain and ij , 2, 3i  are integral along the boundary. considering the condition of theorem 2, using young's inequality, results in: 2 2 2 2 1 0 exp( ) . (2 1)tt tx xx q w j m t w w w dxdt const t             based on boundary conditions in eqs. (14),(15) and the condition of theorem 2, 0, 1, 2. (22)ij i  c const does not depend on n , hence from eqs. (17)-(22) the second estimate for the approximate solution of eqs. (6)-(8) follows. an estimate of eq. (17) together with eq. (21) allows to pass to limit at n   and conclude that a subsequence  knu converges in view of the uniqueness (theorem 1) in 2 ( )l q together with a first-and second-order to the desired regular solution ( , )u x t of eqs. (6)-(8) possessing the properties stated in theorem 2 [6, 8, 10, 13, 14]. for ( , )u x t by virtue of eq. (21), the inequality holds true 2 2 2 2 2 0 0 0 (23)tu u m f ft            theorem 2 is thus proven. now using the method of "ε-regularization" the solvability of eqs. (1)-(3) is proven. theorem 3: let all conditions of theorem 2 be fulfilled. then the generalized solution of the problem from 22 ( )w q exists and is unique. iium engineering journal, vol. 17, no. 2, 2016 djamolov 101 proof: the uniqueness of the solution of problem in eqs. (1)-(3) from 22 ( )w q is proven in theorem 1. now the existence of a generalized solution of eqs. (1)-(3) from 22 ( )w q is proven. for this, consider eq. (6) in domain q with boundary conditions in eqs. (7), (8) at 0  . since all conditions of theorem 2 are fulfilled, then there exists a unique regular solution of problem eqs. (6)-(8) at 0  and for this solution estimates i), ii) are true. from here follows, under the known theorem of weak compactness, that from a set of functions  , 0u   it is possible to take a poorly converging sub-sequence of functions in v such that   i u u  at 0i  . it will be shown that limiting function ( , )u x t satisfies the equation lu f (1). in reality, as the sequence   i u converges poorly in 22 ( )w q and the sequence   3 3 , ( 0) i u t      is in regular intervals limited in 2 ( )l q , and the operator l linear it is had ( ) (24)i i i ii i u u lu f lu lu l u u t t                   from here, the following inequality will be performed 0 0 2 0 0 ( ) (25)i i i ii i u u lu f l u u m u u t t                  „ from (25) approaching a limit at 0i  we get the unique solution of eqs. (1)-(3). thus, theorem 3 is proven. 5. smoothness of the solution now, the more general case of 3l… must be proven. further, the coefficients of eq. (1) are assumed to be infinitely differentiable in a closed domain q . theorem 4: let the conditions of theorem 3 be fulfilled and let 2( ) 0t tmk k k       . then, for any function ( , )f x t such that 12 2( ), ( ) m m tf w q d f l q   , 0 m m t tt t t d f d f    , there exists a unique generalized solution to problem (1)-(3) from the space 22 ( ) mw q , where 0,1, 2, 3,...m  proof: from the smoothness of the solution to problem in eqs. (9)-(13), the following conditions for the approximate solution of eqs. (6)-(8) follow: 0 ( ); ; 0,1, 2, 3, 4,..., (0, ) (1, ) 0. n q q t tt t t w u c q d w d w q w t w t            iium engineering journal, vol. 17, no. 2, 2016 djamolov 102 considering the conditions of theorem 2 at 0  , nonlocal conditions at 0,t t t  and from the equality 2 2 2 2 0 0 0 ( , ) t t t t t t t t t t t t t e l u e u e lu e f x t t                                         then 0 ( , 0) ( , ) .ttt tttu x u x t const     hence, it follows that function ( , ) ( , )tv x t u x t  belongs to v and satisfies the following equation (26 ) tt t t t t p v l v k v f u c u f             from theorem 2, it follows that the set of functions  f is uniformly bounded in the space 2 ( )l q , i.e. 2 2 0 0 0t f m f f     further, from the conditions of theorem 3, one can easily see that operators ,( 0)p   satisfy the conditions of theorem 4. from here, based on estimates of i) and ii) for a function  v , the following analogical estimates are obtained   2 22 2 2 2 2 2 1 0 0 0 0 (27) tv v v m f ft t x                 2 2 2 2 2 1 0 0 (28)ttv v m f ft           function  u satisfies a parabolic equation with conditions in eqs. (2),(3) ( 1) , (29)t xx tt tu u u f u ku u cut                       here 2 ( )l q  . the set of functions   is uniformly bounded in 12 ( )w q i.e. 2 2 2 2 1 1 0 2 (3 0)ttm f f m f       based on priory estimates for parabolic equations [4,6] and inequality in eq. (30) , then 2 2 3 2 .u m f  similarly, one can prove that 2 2 2 , m m u m f   where 2, 3,...m  iium engineering journal, vol. 17, no. 2, 2016 djamolov 103 6. conclusion solvability of the problem considered can be formulated in the terms of smoothness of k (x, t) in the case where, ( , 0) 0 ( , )k x k x t  . in this the second kind of mixed type equation studied, since there is no restriction inside the domain. under the assumption that the coefficients of the equation are smooth enough and ( , ), ( , )x t c x t are periodic with respect to variable t . references [1] alimov na. (1983) on a nonlocal boundary value problem for a non-classical equation. the theory and methods for solving ill-posed problems and their applications. novosibirsk, 237-239. [2] berezinsky ym. (1965) expansion in eigenfunctions of selfadjoint operators. kyev. [3] berdyshev as. (1993) nonlocal boundary value problems for equations of mixed type in a deviation from the characteristics. differensial.uravn., 29(12):2118-2125. [4] bitsadze av, samarskii aa. (1969) on some simple generalizations of linear elliptic boundary value problems. dan sssr, 185(4):793-740. [5] vragov vn. (1983) boundary problems for non-classical equations of mathematical physics. novosibirsk, 216pp. [6] glazatov sn. (1985) nonlocal boundary problems for mixed type equations in a rectangle. siberian math. j., 26(6):162-164. [7] djamalov sz. (1989) on correctness of nonlocal boundary problems for many-dimensional mixed type equation. application of method of functional analysis to the non-classical equations of mathematical physics. novosibirsk, 63-70. [8] yogorov ie. (1995) on smoothness of a solution to a nonlocal boundary value problem for an operator-differential equation with variable time direction. mat. zametki yagu, 2(1):98104. [9] il'in va, moiseev yi. (2000) on the uniqueness of solution of mixed problem for wave equation with nonlocal boundary conditions. differens. uravn., ç6(5):656-661. [10] karatkoprakliev gd. (1987) nonlocal boundary problems for mixed type equations. differens. uravn., 23(1)78-84. [11] karatopraklieva mg. (1991) a nonlocal boundary-value problem for an equation of mixed type. differens. uravn., 27(1):68-79. [12] kalmenov ts. (1990) on the dirichlet problem and nonlocal boundary problems for wave equation. differens. uravn., 26(1):60-65. [13] kozhanov ai. (1990) boundary problems for equations of mathematical physics of odd order. novosibirsk, 132 pp. [14] kuzmin ag. (1990) non-classical mixed type equations and their applications to the gas dynamics. leningrad 271pp. [15] ladyjenskaya oa. (1973) boundary problems of mathematical physics. moscow 470 pp. [16] moiseev yi. (2001) on a solvability of a nonlocal boundary problem. differens. uravn., 37(11):1565-1567. [17] terekhov an. (1985) nonlocal boundary problems for equations of variable type. nonclassical equations of mathematical physics. novosibirsk, 148-158. [18] nakhushev am. (1982) on an approximate method for solving boundary value problems for differential equations and its application to the dynamics of soil moisture and groundwater. differens. uravn., 18(1):72-84. [19] beilin sa. (2006) on a mixed nonlocal problem for a wave equations. electronic j. diff. equations, 103:1-10. [20] berdyshev as, karimov et. (2006) some-non-local problems for the parabolic-hyperbolic type equation with non-characteristic line of changing type. central european j. math. (cejm), 4(2):183-193. iium engineering journal, vol. 17, no. 2, 2016 djamolov 104 [21] rassias jm, karimov et. (2010) boundary-value problems with initial non-local condition for parabolic equations with parameter. eur. j. pure appl. math. (ejpam), 3(6):948-957. microsoft word 242 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 189 rectification and revival of muslim world m. azram department of science, faculty of engineering, international islamic university malaysia, po box 10, kuala lumpur 50728, malaysia. azram50@hotmail.com abstract: the present doldrums position and state of decadence, internal differences, external aggression (geographical and ideological), lack of self-confidence and dependence, illiteracy, political instability, economic disaster, lack of knowledge and wisdom, back benchers in science and technology, education, medicine, trade and business, banking system and defensive incapability of muslim ummah prompted me to write this article. although most of the muslim nations got their independence because of their dedicated struggle and historic events and incidents but the old masters remained active for a remote control over the muslim ummah. their intellectuals and scholars, individually as well as collectively, have propagated and advised their leadership, the tactics and approaches by which muslim ummah can again be enslaved. writings of s.p. huntington and f. fukuyama are clear examples. they are actively gearing the international institutions so cleverly that muslim ummah does not even realize their ill motives and objectives. they brought their leadership in a confronting position with muslim ummah and hence threatening the world peace. this situation prompted us to look at our principal sources of inspiration, which are, the qur’an, sunnah of the prophet (saw), and examples of the “enlightened caliphs” and see if we could work out a seminal guidelines for our rectification and revival. we have gathered together some of these impressions; these are all tentative, nothing final about them, but these are here nonetheless. abstrak: kehadiran situasi kebelungguan dan keruntuhan, perbezaan dalaman, pencerobohan luar (geografi dan ideologi), kurang keyakinan diri dan pergantungan, buta huruf, ketidakstabilan politik, bencana ekonomi, kekurangan ilmu dan hikmah, ketinggalan dalam sains dan teknologi, pendidikan, perubatan, perdagangan dan perniagaan, sistem perbankan dan ketidakupayaan pertahanan umat islam mendorong saya untuk menulis artikel ini. walaupun kebanyakan negara-negara islam mendapat kemerdekaan mereka kerana perjuangan mereka yang berdedikasi dan peristiwa dan kejadian yang bersejarah tetapi sejarah orang lama yang kekal aktif untuk mengawal kedudukan umat islam. keintelektuallan mereka, secara individu dan secara berkumpulan, telah dikembangkan melalui nasihat kepimpinan mereka, taktik dan pendekatan yang muslim ummah sekali lagi boleh diperhambakan. karya sp huntington dan f. fukuyama adalah contoh yang jelas. mereka secara aktif menggerakkan institusi antarabangsa sehingga umat islam tidak menyedari motif tersirat dan objektif mereka. mereka telah membawa kepimpinan mereka dalam kedudukan yang dihadapi dengan umat islam dan dengan itu mengancam keamanan dunia. keadaan ini mendorong kita untuk melihat sumber-sumber inspirasi utama, iaitu al-quran, sunnah nabi (saw), dan contoh-contoh "khalifah pencerahan" dan lihat jika kita boleh merumuskan satu garis panduan pembetulan dan pemulihan. kami telah berkumpul bersama untuk mengawal perasaan, ini semua tentatif, walau bagaimanapun tiada apaapa jua yang muktamad tentang mereka. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 190 keywords: swt (subhana wa taala); pbuh (peace and blessings be upon him); ra (radiallahu anha/u) 1. introduction inner goodness and inner evil are always in conflict in all human beings. the same is also going on in a society. whichever element (goodness or evil) excels and dominates, one is attracted to the same in the society. consequently, one becomes either a party to allah )ب ا��� ( or a party to satan )ن �� )��ب ا� . the first group, i.e. messengers of allah, faithful, righteous, martyrs, saints, mystics, devoted people, calls human beings to the guidance of allah according to his command and will. they guide for selfpurification and taqwa, i.e. mysticism. regarding the same, imam ghazali has said that the inner intellect of islam is mysticism while the outer husk is jihad (for the cause of allah). in fact this group calls human beings to be the obedient servants of allah, who is the real creator and master. they call to establish equity and justice in society; to learn, to act and perform according to his command, will and guidance; to respect the rights of other human beings. they advise people to choose the path of goodness rather than evil; perform prayers; fast in the holy month of ramadan; pay zakat; love deeply the prophet (pbuh). they advise to take care of and protect human dignity, respect and honor; and participate in jihad (for the cause of allah). in fact they advise human beings to realize, to act and perform duties as real vicegerents of allah. they advise and teach the consequences of negligence, ignorance and laziness; motivate the people to realize the need of dedication and hard work. regarding this, one can read the qur’an (surah tawbah) and recall the tabuk expedition, wherein three highly placed dignified muslims failed to participate, remained clinging to their homes, and were slackers just because of laziness. they had participated in the battle of badr and uhud, but even then allah and his prophet (pbuh) disliked their act. muslim society was asked for a social boycott. in short, good deeds of their whole lives were at risk due to ignorance; not only that, their faith and belief was doubted and suspected. finally, after their begging for mercy and showing repentance for two months, allah revealed their forgiveness and they were accepted back in islamic society. from this, it is fair to conclude that if someone is negligent of a social or public responsibility or duty without any sharaie (lawful) excuse, his faith and belief will be suspected, doubted and deserve a social boycott by the islamic society. in contrast, unfortunately, the present situation of the muslim ummah is just the reverse. one can hardly find this kind of moral decline or degradation in any other society but still we complain that the muslim ummah is not given a place in the world order. the reality is that moral decadence is the root cause for this. one can recall the saying of the prophet (pbuh) that regarding mutual love, humanity and generosity, the muslim ummah is just like a single organism. if any part of it suffers, the whole body feels it (sahih albukhari). noble qur'an declares: surely this community of yours is one community (ummah), and i am your lord, therefore serve me. (q:21:92). you may think and judge the present standing and role of the muslim ummah. for understanding islam, scholars have divided the islamic rights, duties, and responsibilities into two categories, i.e., pure worship only for allah )ق ا����( and the rights of human beings )د ) ���ق ا��� . the pivotal place for the first one goes to prayer ( ا�ّ��ة( while for the second one it is zakat. prayer leads and brings us close to allah, while zakat keeps us linked with human beings. it is simply not possible to perform one and ignore the other, and still claim to be a muslim. regarding this, recall the sayings and actions of abu bakr siddique (ra). he declared jihad against those who refused to pay zakat and said that those who used to pay zakat during the time of prophet (saw) of iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 191 even a wooden nail fixed to camel’s nose, are liable to pay zakat, otherwise jihad will continue against them [6]. as long as the muslim ummah was strictly observing these two principles of islam, they were a power and their superiority, strength, solidarity and sovereignty were unquestionable. as soon as they turned their faces and started avoiding rather than sharing troubles of oppressed and deprived brethren, they were rolled back to the present insulting and disgraceful situation. on the other hand, if inner evil dominates, mankind joins the party of satan ن(�� )��ب ا� and consequently, degrade to an even worse state than brutes, resulting in a real loss, resolve on mischief, worship lust rather than allah, which is self destruction. they misguidedly assume their performance as extraordinary while the fact is that their deed’s foundation is nothing but a spider’s web. to allah, their deeds are of no value. it is stated in hadith qudsi that “continuous performance of good deeds results in enlightenment while consistent evil-doing results in maliciousness” and consequently, the evil-doers join the party of satan )ن �� )��ب ا� and lose the capability of performing good deeds. it is just like putting the goblet face down and expecting that rain will collect in it. as long as mankind and human society exist, good and evil, truth and falsehood will be at war. habeel and qabeel are not only two names but are also the names of two ideologies ( ��� ا��� ة�� ) and the fight between them is a perpetual fact. fortunate are those who join the party of allah )ب ا���( . presently, the muslim ummah is in a very disappointing situation. muslim ummah is in a state of decadence, internal differences, instability, external aggression both geographical and ideological, scattered, lack of selfconfidence and dependence, illiteracy, disaster at political and economic fronts, lack of knowledge and wisdom, back bencher in science and technology. on the other hand, non-muslims especially the capitalists are seriously busy and trying to establish and promote a new world order, a new form of capitalism. communism and capitalism were threats to each other but the fact is that communism was a byproduct of capitalism and was assumed to be a better system. in fact, both are unnatural; capitalism deprives the laborers while communism deprives people of belongings and wealth. failure is and will be the fate of both. the end of a better system cannot be a testimony to the merit and success of a bad system, which is wrongly assumed by capitalist countries. the dilemma is that the muslim ummah has failed to promote and establish a better alternative islamic system; therefore, capitalism is enjoying its monopoly. since capitalists are trying to establish and promote capitalism, they consider islam as a threat comparable to communism. consequently, cruelty and aggression on all fronts against muslims is a preplanned game. events in chechnya, bosnia, iraq, lebanon, somalia, algeria, kashmir, palestine, burma, philippines and afghanistan are clear examples. none of the muslim countries is self-sufficient in its defensive needs and unfortunately; they do not even realize this weakness. no wonder they are being mercilessly crushed all over the world. muslims ummah constitute fifty seven muslim nations with one-fifth of the world population, possess half of the world’s natural resources but have virtually failed to utilize these advantages. being on back benches in education, medicine, science and technology, trade and industries, no single country out of the fifty seven islamic countries or muslim ummah as a whole, can protect and defend their natural resources, or its geographical and ideological frontiers. the proposed world order is the last attempt to save and protect capitalism. capitalists are fearful that awakening of muslims may result in losing the natural resources of the muslim ummah especially the middle east. it is a fact that, wherever and whenever the leadership of islamic movements tried to upgrade the life standard of iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 192 the people, provided health and educational facilities, provided freedom of religious and apprehension, provided freedom of speech and writing, allah fearing governing activities, prepared to reoccupy their own resources from the aggressor, they were considered as a threat to their interest and are declared as terrorist, extremists, fundamentalists, uncivilized, fanatic, archaic, anachronistic, destructive and lawless to justify their elimination. unfortunately, in most of the islamic countries, their own leaders and rulers being planted by them perform this job. we have already said that as long as mankind remains, human history will be alive. the battle between good and evil, truth and falsehood is eternal. it will end only when there will be an end to humankind, otherwise this battle and clash will continue in some other forms. this is a most critical time for intellectuals, scholars, and leaders of muslim ummah. it is their moral obligation, duty and responsibility, to propagate the real spirit of islam to anti-islamists so that the wrongly propagated ideas can be defused. the solution of the world’s destruction especially that of the muslim world is concealed in the universal system of islam, which, we failed to promote and establish because we never adopted it at home. however, the following are some of the remedial basic principles, which we have gathered together from the qur’an, hadith, and writings of some muslim intellectuals. 2. equality and human rights the qur’an has essentially addressed mankind and is a revealed treatise on humanity respect and honor. human equality, brotherhood, freedom, reverence and greatness are in the charter of the qur’an, wherein, after the unity of allah (swt), the whole stress is on unity among mankind. after a profound study of the qur’an, it becomes evident that there is no single verse in the qur’an, which teaches us the art of slavery. the whole qur’an teaches the art of salvation. the qur’an guides and advises us to be a party of allah ) ب�� )ا� and his prophet (pbuh). it stresses that socio-economic justice is the basic ingredient to establish peace and harmony. the qur’an declares that humankind are the children of the same male (adam (ra)) and a female (eve (ra) (q: 49: 13)); hence, they are equal and are vicegerents of allah (swt), with the same basic rights. human life, property, selfrespect, and freedom ought to be respected. regarding human life, it is stated that killing (saving) of a single life is worth killing (saving) of the whole humanity. all human beings are equal before allah (swt). the bases of virtue and honor are only the dignified deeds and noble character, that is, righteousness and piety. blood, color, race, language, region or nationality may be a source of identification but not the source of distinction and glory. regarding the same, the qur’an says, “o mankind! lo! we have created you male and female, and have made you nations and tribes that ye may know one another. lo! the noblest of you, in the sight of allah, is the best in conduct. lo! allah is knower, aware” (q: 49: 13). similarly, “o mankind! be careful of your duty to your lord who created you from a single soul and from it created its mate and from them twain hath spread abroad a multitude of men and women. be careful of your duty toward allah in whom ye claim (yours rights) of one another, and toward the wombs (that bare you). lo! allah hath been a watcher over you” (q: 4: 1). allah-fearing, devotion, politeness and good deeds are the bases of dignity, respect and honor. in fact, all standards other than noble deeds are the causes of jealousy, enmity, rivalry, quarrel and disturbances. as an example; if personnel belongings are criterion, people will use fair and unfair means to collect them, which will eventually cause mischief, trouble and disturbance. if military skill is a criterion, bloodshed will be the fate, which is obvious in the present scenario. it is the iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 193 same with other criteria. rivalry and jealousy will never disturb if we have allah-fearing attitude, humility and devoutness. consequently, human life will be the cradle of peace and mankind can enjoy it. consider the address of the prophet (pbuh) at the farewell hajj, wherein in the light of qur’anic verse (q: 49: 13) he has said: “all mankind are from adam and eve, an arab has no superiority over a non-arab nor has a non-arab any superiority over an arab; also a white has no superiority over a black nor has a black any superiority over a white – except by piety and good deeds” [2]. this implies that color, race, language, and region carry no significance. good moral deeds will be the basis of prosperity. this was the last legacy of the last prophet (pbuh). this historic address is an abstract of the qur’an and a charter for equality. mankinds are fighting against each other. it seems that there is no end to racial and linguistic disturbances. the root cause of all grouping, fights, killings, and bloodshed is prejudice, which has been discarded in the above address. similarly, at the time of mecca victory [3], prophet (pbuh) said: “oh quraish! allah has eliminated the barbarous pride and genealogical glory. all men are from adam (ra) and adam (ra) was created from the dust”. afterwards he recited the same verse of surah al-hajurat (q: 49: 13). this indicates that, this verse of surah alhajurat is the basic principle of equality and the prophet’s address at the farewell hajj is the charter of humanity. unfortunately, muslims failed to consider it the basis in their own community. 3. freedom of religion and thought the qur’an says, there is no compulsion in din (way of life)( la ikra'a fi din). mao tse tung said that the communist revolution starts with the mouth of the gun, that is, compulsion is the only way of its establishment. today, it is very much clear that lenin and stalin had established communism at the cost of human bones and skeletons, that is, millions of people were killed. the establishment of capitalism is no more different. it started with the french revolution, wherein the basis was the bloodshed of millions of people. according to the qur’an, islamic revolution starts deeply from the heart wherein individuals are enlightened. compulsion or oppression may be a source of physical rule but cannot be the source of ruling the hearts and minds of people. force can conquer but cannot convert. morality and good deeds can only be expected with ambitious changes and this cannot be established by force. islamic approach is to appeal to the hearts of men, to awaken their sleeping nature, to stir their repressed inclination and desire towards progress and perfection, to return them to the presence of allah (swt), and to adopt such a method that would have convincing arguments and the sweetness of love and brotherhood. the moral values should be explained and clarified in a manner that the heart may be convinced that it is necessary to adopt these for attaining the good and righteous qualities. the qur’an says, “there is no compulsion in religion. the right direction is henceforth distinct from error. and he who rejecteth false deities and believeth in allah hath grasped a firm handhold which will never break. allah is hearer, knower” (q: 2: 256). similarly, “and if thy lord willed, all who were in the earth would have believed together. wouldst thou (muhammad) compel men until they are believers” (q: 10: 100). again, “say: o mankind! now hath the truth from your lord come unto you. so whosoever erreth only against it. and i am not a warder over you” (q: 10: 109). these verses of the qur’an clearly explain the concern of the prophet (pbuh) about human guidance. he said, “i have been sent only for the purpose of perfecting good morals’ (al-muta). it was almost impossible for him to see human killing and depravity. despite his inner grief, distraction and restlessness, he was not empowered to force any individual to enter islam. it is the will and wishes of humankind to believe in or to reject the guidance of allah. just as iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 194 equality is a matter of human honor, freedom in choosing religion, without any compulsion is a part of human respect and honor. islam expects that wisdom and intellect should be the source for the choice of religion. in contrast to the wrong interpretation by the non-believers, islam expanded by good conduct and moral rectitude. indonesia, malaysia and africa etc are clear examples. regarding self-respect and glory, it is advisable to be away from evil and seek blessing of allah. equality and freedom of belief and intellect are, as a result, the basic principles of the universal system of islam. disturbance in the society can be eliminated if humankind respects these principles. 4. establishment of justice establishment of justice has thoroughly been addressed in the qur’an. a majority of intellectuals say that the root cause of the downfall or rise of the nations is justice. many nations were empowered as a test to their ability for the establishment of justice. nations will not be judged on the day of judgment but nations are to be judged here and now, in and through history (q: 2: 213-214). if they establish a just socio-moral order in this world, allah (swt) will be with them and they have really grasped the trust worthiest handhold. if they establish cruelty and despotism rather than a just socio-moral order, allah (swt) lets them be ruined and replaced by some other nation. in fact, when they fail to live up to the expectations of the qur’an, they are pushed out of the commanding position and are buried in the dust of history, probably never to be heard of again. national morality and establishment of justice are the bases for survival of nations. islam says that the progress and survival of the nations, the nourishment and the development of their civilization and culture, and the consolidation of their power depend on morality. nations live till their morality lives. when their moral character decline they also decline. a famous saying of imam ibn taymiyah says, “allah guards the justice-loving government, even if it is the government of the infidels, and destroys the tyrannical government, even if it is the government of muslims”[5]. the establishment of justice is the basis in historic ups and downs. as mentioned in many places in the qur’an, the muslim ummah has been raised for the purpose of establishment of justice. qur’an says, “o ye who believe! be steadfast witnesses for allah in equity, and let not hatred of any people seduce you that ye deal not justly. deal justly, that is nearer to your duty. observe your duty to allah. lo! allah is informed of what ye do” (q: 5: 8). similarly, “ o ye who believe! be ye staunch in justice, witnesses for allah, even though it be against yourselves or (your) parents or (your) kindred, whether (the case be of) a rich man or a poor man, for allah is nearer unto both (then ye are). so follow not passion lest ye lapse (from truth) and if ye lapse or fall away, then lo! allah is ever informed of what ye do” (q: 4: 135). regarding justice, the qur’an stresses to the muslims to practice extraordinary caution and directs them not to distort, or debase justice because of wealth, power, or poverty. the basic principles of international relations must be straightforward. guarantor(s) must be of high moral character especially, allah-fearing attitude, attitude of accountability to allah (swt), and justice loving. the present situation is very much disappointing. as an example, consider the role of uno, wherein five nations are responsible to establish justice and peace at any cost. in practice, they only protect the interests (justified or unjustified) of their allies or those that are under their influence. only america and russia have used the “veto power” for almost a hundred times in favor of israel or other similar countries. the expectation of a just socio-moral order from such a uno is questionable. character is normally judged by the doings rather than sayings. performance and deeds are the actual reflection of professions. it will be more appropriate to determine the performances of the responsible people in the international security rather iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 195 than their sayings. it is interesting to note that 90% of the present ammunition is owned and manufactured by the nations responsible for international security and peace. peace is really not their concern because it will cause them a loss. it is just like leaving the wolf to watch the sheeps. according to the qur’an, there are three types of agonies. the first type includes the havoc of wind and rain as well as cruel and despotic rulers. the second type includes earth-quakes, famines or other catastrophes as well as cruelty to the poor. in the third type, men oppress men. presently, humanity is suffering from all three types of agonies. there must be repentance otherwise destruction will be the fate. time is really running short for rectification. the qur’an repeatedly reminds us to establish justice, because it brings us closer to taqwa (allah-fearing) and allah likes it. according to the qur’an, justice is the spirit of all deeds; those who excel in it are successful. the book (qur’an) that guides humanity for morality and justice should have been the source of peace and security. unfortunately, muslims themselves do not follow it, how can they invite others? 5. fulfilment of promises islam discourages the tendency of breaking both individual and social promises and crossing the limits. false promises are termed as symbol of disruption and cause of untold harm to society. relying on falsehood is unwise and brings a bad name. words become worthless unless appraised and enforced. regarding promises, the prophet (pbuh) considered the words coming out from the mouth as holy and the words that fell on ears as respectable. decency and manliness were his qualities and he never broke his promise. islamic history is full of cases where the prophet (pbuh) fulfilled his promise even in a very difficult situation. allah considers fulfilling of promises as one of the attributes of prophethood, “and make mention in the scripture of ishmael. lo! he was a keeper of his promise, and he was a messenger (of allah), a prophet. he enjoined upon his people worship and almsgiving, and was acceptable in sight of his lord”(q: 19: 54-55). nowadays, respect for and sanctity of promises especially the social promises are at stake. social promises are tied with the community, tribes and national interest. it is a common trend to break the promise and declare it as in conflict with the community, tribes or national interest. as an example: italy was allied to germany in the first world war. when it suspected that its interest was with the other side, italy joined with france and britain. in the second world war, when germany thought that it would be more appropriate to attack france through belgium, they broke all their promises to belgium. the same is the case with norway, denmark and holland. nato and cento promises to member countries are other examples. islam considers promises as sacred and discourages breaking them. if this principle of islam becomes part of international relations, this world can be a paradise for mankind. 6. islam and neutrality the qur’an says, “and if two parties of believers fall to fighting, then make peace between them. and if one party of them doeth wrong to the other, fight ye that which doeth wrong till it return unto the ordinance of allah; then, if it return, make peace between them justly, and act equitably. lo! allah loveth the equitable” (q: 49: 9). the prophet (saw) said: “help your brother irrespective of whether oppressor or being oppressed”. he was asked, how an oppressor could be helped; he replied, hold his hand from oppression.” (sahih bukhari, volume 3, hadith 624). the muslim ummah should have been supreme over muslim groups or nations. the essential conditions of course are iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 196 that there should be perfect fairness, justice, and respect for the highest principles. the muslim ummah as well as uno fails, because these essentials are absent. islam discourages neutrality. abu bakr siddique (raa) says, ‘ o people i heard allah’s messenger (saw) as saying, “verily when the people see the evil but make no effort to change it (to good), allah may inflict upon all of them his punishment” (ibn majah). this discouragement of being neutral is a principle to put a halt to disturbance and mutual quarrels among muslims but it can serve as a basic principle for relations between nations. the qur’an further says, “o ye who believe! profane not allah’s monuments nor the sacred month nor the offerings nor the garlands, nor those repairing to the sacred house, seeking the grace and pleasure of allah. but when ye have left the sacred territory, then go hunting (if ye will). and let not your hatred of a folk who (once) stopped your going to the inviolable place of worship seduce you to transgress; but help ye one another unto righteousness and pious duty. help not one another unto sin and transgression, but keep your duty to allah. lo! allah is severe in punishment.” (q: 5: 2). similarly, the qur’an (q: 7: 163) highlights the character of israel. they were prohibited from fishing on saturday. this resulted in three groups among them, the first insisted on fishing, the second, protested and tried to halt, and the third remained undecided. when punishment came, two groups suffered, including the neutral one, but not the one, who protested and tried to stop others. this clearly reflects that neutrality is meaningless in islam. it is advisable to be with the righteous. 7. unity and solidarity unity is strength. all philosophers, from plato to ibn khaldoon, commented that the national unity and solidarity (with justice) are the pivotal factors for the rise or fall of nations. mutual unity linked each sect of the society just as each part of the human body is linked. for national up lift, it is a must that the whole nation should think and act as a single individual. mutual recrimination, disturbance and disunity scattered the abilities and the strength. according to these philosophers, there could be many bases for national unity and solidarity, such as, race, tribe, language, color, region, objective, future dream, and a common enemy. more common things enjoin a better environment for unity. religion and the same purpose of life can be additional bases for unity but islam discards all other bases except the same religion. the muslim ummah can achieve a respectable future, if it follows just a single point in the sunnah of the prophet (pbuh). that single and crucial point is that the prophet (pbuh) left his tribe in mecca and assembled his companions in madina. there in madina, he assumed the managing of the religiopolitical affairs of city. here he could affect social reforms (such as imposing zakat for the betterment of the depressed classes of the society, to rescue the poor from the chronic debt, to improve the defense of the new-born city-state, allotting shares in the inheritance to women, regulating marriage and divorce, prohibiting usury and so forth) along with the promulgation of religio-moral and spiritual teachings of the qur’an (such as the exclusive worship of allah alone, a firm faith in eschatology, that is, the day of judgment and the life hereafter), then fight back with them till the victory of mecca. consequently, his own tribe became believers and followers. in the battle of badr, he begged allah (swt) for his blessing, help and victory of his companions against his own tribe. therein, his uncle, a son of abu bakr siddique (ra), a brother of ali (ra), the uncle of umar farooq (raa) and relatives of the companions were on one side representing his tribe and the prophet (pbuh) and his devoted companions were fighting against them. between the battle of badr and the victory of mecca, color, race, language, clan, region, and all factors, which constitute a tribe, were in mecca while his companions were residing in madina. may the muslim iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 197 world understand this single crucial point and put aside the mutual differences, concentrate on unity and solidarity! this will assure a respectable future for them; otherwise they will be mercilessly crushed all over the world and will be buried in the dust of history. 8. establishment of unity and solidarity establishment of justice, national unity and solidarity, and an effective defensive and strategic system are pivotal ingredients to assure future security. different sects of a nation can only be united if treated fairly (with justice) and given a chance to participate actively in the affairs of state. this will obviously strengthen national unity and provide inspiration and motivation to sacrifice property and even life, if needed, for national defense. end to justice is also an end to unity and solidarity. despotism and oppression are the root cause for national destruction. deprivation results in decline of sacrifices. hence, discrimination in state affairs divides a nation and gives rise to the feeling of hatred, resulting in national disunity. consequently, national resources will be utilized for destruction and disturbance rather than national construction, causing internal strife, which finally invites external aggression and ultimately foreign occupation. muslim ummah is really lacking to establish justice, which is the basis of morality and hence good deeds. the qur’an says, “o ye who believe! be ye staunch in justice, witnesses for allah, even though it be against yourselves or (your) parents or (your) kindred --(q: 4: 135). according to the qur’an, the objective of islam and hence the muslim ummah is to exhort to do good and forbid evil and continue this practice (jihad) till there is an end to oppression and evil. abu bakr siddique (ra) said: ‘o people i heard allah’s messenger (pbuh) as saying’, “verily when the people see the evil but make no effort to change it (to good), allah may inflict upon all of them his punishment” (ibn majah). establishment of a just socio-moral order must be the top priority. islam can only be established in the world if we muslims establish and really practice islam in our home and at the national level. to ensure unity and solidarity, the muslim world should immediately bring social justice in the daily life practices. mutual unity is a source of blessing to fight against evil. 9. knowledge and literacy the first revelation called upon the prophet (pbuh) and humanity to pursue education and acquire knowledge in accordance with the divine guidance of allah; “read and understand in the name of the lord and cherisher” (q: 96: 1). the qur’an says, “allah will raise up to honorable ranks (and degrees) those of you who believe and who have been granted knowledge (q: 58: 11). adam (ra) was raised to the highest rank among beings because of knowledge. the prophet (saw) “ ِ�ِ he attained the ;َ$َ&َ) اُ�ُ�&% ِ$َ#َ" height of eminence by his perfection; ; ِ�ِ he dispelled the darkness (of the ; َآَ َا�,+*% ِ$َ(َ" world) by his grace; ِ�ِ �َ/ِ 0ُ�ُ"ِ* 1ُ2َ3ُ�َ ; excellent were all his qualities; ; 9َ&8ُ� 7ََ&ْ�ِ َو4ِ�ِ ; pray for blessings on him and his descendants” (shaikh sa’di sheeraazi (ra)). he is asked in the qur’an to pray for an increase in knowledge ( )&7 :� "رّب زد . the prophet (pbuh) also said: “acquire knowledge from cradle to grave” (muttafaqun alaih). he further stated that the acquisition of knowledge is a duty imposed on every muslim (ibn maajeh vol. 1, section 17, hadith 224). it is inspiring to recall that the very first word that was revealed to him is iqra (read). human beings have many qualities which are latent or which they may wish to suppress or conceal to their own detriment. the prophet (pbuh) also said: “wisdom is the lost property of the muslim; he recovers it wherever he finds it” "(tirmizi). this is inspiring and indicates that there is no monopoly in matters of iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 198 knowledge. among children of adam (ra), those who excel in knowledge and wisdom, are the world leaders and hold the office of imam. knowledge and wisdom protect your ideological boundaries from evil. the muslim ummah, unfortunately, failed to excel in knowledge and wisdom. acquiring knowledge and understanding it (research) is left to the others, resulting a degradation in science and technology as well as in trade and business. the prophet (pbuh) said that knowledge is a foundation of islam. regarding this let us look at the prophet’s (pbuh) concern, attitude and priority. to educate muslim children up to reading level, he even asked the prisoners of badr, who were the nonbelievers of mecca, and considered this as their compensation. this reflects his concern about education and treatment of prisoners of war at a time when muslims were fighting for very survival. there is a difference in acquiring knowledge, understanding knowledge, and education targeting literacy. to increase the rate of literacy among muslims, the prophet (pbuh) utilized the services of even the non-believers of mecca, i.e., prisoners of badr. knowledge must be of truth and reality or of what the qur’an calls haqq. unfortunately, muslim ummah has confused knowledge with literacy. the dilemma is that we are utilizing our resources to increase the rate of literacy rather than acquiring knowledge, even then we fail in it. may allah (swt) bless us to fulfill our duties of acquiring and understanding knowledge, bring back our virtues and qualities, that is., competence, energy, initiative, seriousness, creativity, and wisdom, and enabling us for the world leadership (with justice) and to hold the office of imam. 10. mutual relationship a man who harasses his neighbor and makes him suffer any kind of damage is called cruel and stone-hearted by the religion. regarding this, the prophet (saw) said: “by god, he cannot be a momin; by god, he cannot be a momin; by god, he cannot be a momin (bukhari). he was asked; “who”? he answered; “ he from whose misdeeds his neighbor is not safe” (bukhari). in the present day scenario, arms race among the countries is the root cause for mutual tension among the regional powers. if we just follow the above hadith of the prophet (saw) as a basic principle for international relations, this world can be turned into a cradle of peace. the overriding objective of islam is to establish a just moral order and hence the peace. islam wishes an end to oppression resulting in a peaceful environment, wherein humankind can utilize their abilities and perform significantly for their betterment. the qur’an says, “then, even after that, your hearts were hardened and became as rocks, or worse than rocks, for hardness. for indeed there are rocks from out which rivers gush, and indeed there are rocks which split as under so that water floweth from them. and indeed there are rocks which fall down for the fear of allah (swt). allah (swt) is not unaware of what ye do” (q: 2: 74). hence, based on character and deeds, qur’an has divided humankind into four groups and compared them with rocks. the first kinds of rocks are the sources of rivers. a wide range of regions benefit from the water, nursing crops and gardens. humankind, animals and plants all benefit. (people belonging to the party of allah (swt) live a similar life). the second kinds of rocks are the source of springs and are beneficial to the surroundings. the third kinds of rocks are those, which do tremble with the fear of allah (swt) but yet have to be melted to become beneficial. the last kinds of the rocks are neither the source of rivers or springs nor have fear of allah (swt). these are just solid unkind stones, lying in rivers just to stop and divert the flow. present days muslims are just like this fourth type, neither beneficial to themselves nor to others but instead, are hurdles in the path of goodness and virtue. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 199 11. military and defensive capabilities while knowledge protects ideological boundaries, jihad protect the geographical and territorial frontiers, safeguards our lives, honor and dignity, besides the preservation of resources. military and defensive capabilities are to protect natural, mineral and financial resources as well as national sovereignty. the qur’an says that the standard of military and strategic preparations should be as if we are in an actual war. this will not only halt and discourage your enemies and the enemies of allah (swt) but they will not dare to attack a muslim state. abu bakr siddique (ra) observes in his inaugural address [4] that if a community begins to tolerate moral indecency and allows the spirit of jihad to cool down, it surrenders its right to exist on the face of the earth and qualifies instead for a safe burial. even today, muslim ummah might be aspiring for jihad but in the present scenario, military and strategic strength depends on advanced technology, which unfortunately, we left to the others. since muslims have allowed their spirit of jihad to cool and have adopted an apologetic attitude, they have placed themselves at the mercy of their enemies. innocent men, women and children are being killed in palestine, iraq, afghanistan, pakistan, kashmir, chechnya, bosnia, kosovo, and in so many other trouble spots, while we do not hear even ordinary murmurings in the muslim world. we are just helpless spectators of the brutal massacre of muslims. among fifty seven muslim states, none is in a position to defend itself. we have to wake up. defense will only be possible if the muslim ummah excel in science and technology especially computer and nuclear technology, and do not compromise on any issue regarding this. it is interesting to note that in early islamic days, iran and rome were considered to be world powers. the newborn islamic state of madina was lagging behind in military power, economy, education, science and technology, like us. their objective was clearly defined and pursued; hence, they succeeded in all fields. muslim ummah even today, if it concentrates on the moral and educational values, can achieve its target. allah changes history through ill-equipped but truth-loving people. the well known poet, thinker, and philosopher allama iqbal rightly said: “momin soldier, fight (jihad) even without sword”[9]. 12. allah-fearing leadership all expectations and dreams can become true if our leadership fear the supreme power rather than the superpower, that is., fear allah (swt) rather than non-believers. muslim ummah needs leadership, who fear allah (swt), are dedicated to serve humanity, consider the resources of the ummah as amanah (trust), and utilize these resources for the betterment and welfare of humanity, interested in lighting the lamp rather than blowing it off. they should strive for providing the basic necessities to the community rather than making their lives miserable. a famous event in the life of umar farooq (ra) is stated below in the hope that our leadership may get a lesson from it and consider this as a torch for their attitude. umar farooq (ra) [1] used to live a simple life and insisted also to his appointed governors to live simple lives, keep no guard at their doors and be accessible to people at all time. once, he was on a routine night watch going about the streets to see whether anyone needed help. he heard cries from a house. he ignored the cries, thinking that it may be unnecessary to interfere in family privacy. next night, he observed a similar situation from the same house. upon inquiry, the lady of the house informed him that the children were hungry. he asked the lady about the previous night. she replied that there was nothing to eat at home. yesterday i putted an empty pot on fire, just for their satisfaction and hope but today even this trick failed. umar farooq (ra), without iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 200 introducing himself, asked the lady about not asking the caliph for assistance. she replied; it should have been the moral and social responsibilities of the caliph to be watchful and aware about the needs of the poor; instead, we poor go to his door for begging. umar farooq (ra) argued how the caliph could know the needs of the poor and hungry among so many people. she replied; if the caliph is lacking these qualities, he must leave his office to give the chance to a better replacement. after hearing this, umar farooq (ra) trembled with fear of allah (swt) and then rushed to the public treasury and filled a bag to its maximum with food stuff. while he intended to comeback, the guard offered his services to carry to the destination. he replied; this is my own burden, let me lift this burden by myself. he offered the food to the lady. upon that, the lady responded and prayed for him by saying, “ o brother, may allah (swt) bless you and bless you to be our caliph rather than umar farooq (ra)”. at that stage, umar farooq (ra) introduced himself and requested the lady to pray for forgiveness for his negligence. only allah fearing leaders can assure, excel, and take the ummah out of the darkness of negligence and illiteracy. they can lead us to gain knowledge, wisdom, thoughtfulness, attitude of collective decision, justice and consequently, unity and solidarity. this will help us to fulfill our military and strategic needs so that oppression from enemies can be avoided. an allah-fearing leadership can only bring the nations and hence the ummah to a level to be called vicegerents. spreading goods, halting and stopping oppression can be considered as a moral obligation by only an allah-fearing leadership. 13. conclusion the qur’an says, “he it is who hath sent his messenger with the guidance and the religion of truth, that he may make conqueror of all religion, however much idolaters may be averse” [q: 61: 9]. the prophet (pbuh) and caliphs had faced more complex and difficult challenges but within decades, islam prevailed and for centuries the power of islam pre-dominated. presently, muslims are in the doldrums. non-believers have predicted the destiny, “if any religion has a chance of conquering england, nay europe within the next hundred years, that religion is islam” [7], similarly, “africa is a fair field for all religions, but the religion which the africans will accept, is a religion which best suits their needs; and that religion, every-one who has a right to speak on the subject says, is islam”. [8]. the promise of allah (swt) is true (wish this news does not lull us to sleep), the destiny is there, only dedication, motivation, strategic planning and exertion on our part, as an individual, as a community, and as an ummah, is the call of today. may allah bless us to serve for his cause (ameen). references [1] atiah, muhammad sabri. 1991. waqfah ma’a omar bin al-khatab, dar al-sharqih, cairo. [2] ibn kathir, ibi alfida’a. 1985. al-bidayah wa-al-nihayah, vol. 4, dar al-kutub al-ilmih, bayrut [3] ibn kathir, ibi alfida’a. 1985. al-bidayah wa-al-nihayah, vol. 5, dar al-kutub al-ilmih, bayrut [4] mohammad, ibn ahmad. 1997. al-khalifah al-rashidah, mu’assasat al-ma’arif, bayrut. [5] ibn taymiyah, ahmad ibn abd al-halim. 1976. al-amr bi-al-ma’ruf wa-al-nahyi’an almunkar, dar-al-kitab al-jadid, bayrut. [6] http://web.youngmuslims.ca/online_library/books/let_us_be_muslims/ch5top19.html [7] sir george bernard shaw. 'the genuine islam,' vol. 1, no. 8, 1936. [8] h. g. wells. the shape of things to come, the macmillan co (ny), 1933 iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 201 [9] http://www.memri.org/report/en/print3971.htm#_ednref1 iium engineering journal, vol. 19, no. 1, 2018 abid et al. 289 optimization of box type girder with and without industrial constraints muhammad abid1*, shahbaz mahmood khan2, and hafiz abdul wajid3,4 1interdisciplinary research center, comsats institute of information technology, wah cantt, pakistan. 2faculty of mechanical engineering, gik institute of engineering sciences and technology, topi, kpk, pakistan. 3department of mathematics, comsats institute of information technology, lahore, pakistan. 4department of electrical engineering, islamic university medina, kingdom of saudi arabia. *corresponding author: drabid@ciitwah.edu.pk (received: 26th may 2017; accepted: 30th dec 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.769 abstract: in this paper three dimensional nonlinear finite element analysis is performed for the optimization of an overhead crane box girder for capacity (50~120ton) and span (10 ~ 32 m) for safe bending stress and deflection with minimum mass and volume. a customized optimization code is developed using interpolative relations and correction factors to achieve optimized results with and without considering industrial constraints. a cutting and welding plan is developed to provide a standard operating procedure for the manufacturing of the box girder. bill of materials, box girder design dimensions, and cutting and welding lengths are recorded with considerable time saving. abstrak: kertas ini mengkaji tentang analisis tidak linear tiga dimensi unsur terhingga bagi mengoptimumkan kotak kren galang atas kepala bagi kapasiti (50 ~ 120 tan) dan pada kadar (10 ~ 32 m) bagi takat lentur selamat dan pesongan dengan jisim minimum dan isipadu. kod optimum penyesuaian telah direka mengguna pakai kaitan interpolatif dan faktor-faktor pembetulan bagi mencapai keputusan yang optimum, dengan dan tanpa mengambil kira kekangan industri. pelan pemotongan dan kimpalan telah dicipta bagi menyediakan prosedur operasi biasa bagi pembuatan kotak galang. rang undang-undang bahan, dimensi reka bentuk kotak galang, pemotongan dan panjang kimpalan telah direkodkan dengan penjimatan masa yang besar. keywords: box girder; optimization; industrial; bill of materials; cutting; welding; finite element analysis; industrial constraints 1. introduction overhead cranes are machines that are used to handle and transfer heavy loads from one place to another in shipping, automotive, logistics, and construction industries [1-2]. the use of cranes enhances efficiency, reliability, and productivity of processes by reducing the human effort and time for handling and moving heavy objects [3-4]. the cranes are regarded as critical material handling devices [5-15]. therefore, crane safety during operation is immensely important. asme ansi [16]; iso [17]; cmaa [18]; dintaschenbuch [19]; f.e.m. rules [20]; british standards [21]; and polish standards [22] are iium engineering journal, vol. 19, no. 1, 2018 abid et al. 290 organized to standardize and regulate the manufacturing and safe operation of these cranes. greiner's crane handbook [23] provides important information regarding crane design, manufacturing, and operation. otani et al. [24] described the vertical seismic response of a 150-ton box girder crane of 35m and concluded that a linear analysis was sufficient to find the reaction forces on the wheels even when the leap phenomenon had occurred in the overhead crane. alkin et al. [25] used shell and solid elements for the optimization of 32ton and 13 m span crane. farkas [26] studied the economy of the crane as a function of yield strength of the material used for the crane construction. niezgodzinski and kubiak [27] used experimental, analytical and numerical methods to study the effect of a local stability problem in box girder cranes and concluded that the addition of strips stiffens the web and reduces the chance of buckling. zuberi et al. [1] used non-linear generalized reduced gradient optimization code for the optimization of overhead crane box girders using available standards by cmaa and greiner's crane handbook. case studies were performed using 10-50 ton capacity and 22 m, 25.5 m, 27.5 m, and 30 m span cranes. the diaphragm spacing and proper thickness was concluded vital for mass minimization. imrak et al. [28] studied the linear and non-linear finite element behavior of a portal crane of 200×2 ton capacity and 100 m span. beam and shell elements were used during the modeling of the crane. blum and chodorowska [29] investigated the pre-stressing phenomenon in plate welded girders, mostly of the fillet welds. they concluded that the pre-stressed model is significantly stable and stiffened as compared to the non-pre-stressed model. abid et al. [30] optimized box girders of 150 ton and 32 m span to control buckling with proper quantity and positions of stiffeners. pinca et al. [31, 32] performed finite element analysis using shell elements for box girders and achieved a 21% theoretical mass reduction. gerdemeli et al. [33, 34] performed finite element analysis using ansys and abacus software for gantry cranes and concluded that simulation helps in the optimization of structures, increased reliability, durability, reduced cost, and manufacturing duration. gašić et al. [35] performed a dynamic analysis of cranes. zhang et al [36] presented finite element analysis of box girder beams for transport bridges. bećirović et al. [37] analyzed box girders of a 7 ton and 20 m span crane for cross-section optimization by changing its height-to-width ratio and the thicknesses of the plates and concluded a 38% mass reduction. gąska and pypno [38] studied static and dynamic stability of 20 ton cranes of various spans according to polish and english standards. lerga [2] proposed a design modification in existing designs of box girders of overhead cranes and concluded a 5.5% mass reduction. djelosevic et al. [39] studied the local stress parameters of box and trapezoidal girders and concluded that trapezoidal sections have lower localized stress influence as compared to the straight sections. capacity and span-wise optimization were performed by abid et al. [40, 41] and relations and optimization factors were developed for a capacity range of 50~120 ton and a span range of 10 m ~ 32 m. chauhan and bhatt [42] performed finite element analysis using three different steels (en-22, steel-20 and forged steel) for the hook for a 10 ton and 22 m span crane girder to study possible increase in its durability and minimum stresses were recorded for en-22. suratkar and shukla [43] performed finite element simulation of a 10 ton and 12 m span crane box girder using a five-point load model i.e. four points for the divided load and one point for the displaced centered load for the payload. it was concluded that the stresses produced were much less than the allowable stress values, thus proposed the optimization of the analyzed model. rabey [44] using a st-3-ps steel girder, performed an analysis with 1, 8, and 16 ton payloads and studied the behavior of the girder under collision. he proposed to implement standardized dynamic parameters for the collisions of bridge cranes and end stops. haniszewski [45] performed dynamic modeling of an overhead travelling crane and interaction of the dynamic geometric model with the finite element mode. an intricate geometric model was generated for a 5 ton and 20 m span crane for both iium engineering journal, vol. 19, no. 1, 2018 abid et al. 291 static and lanczos modal analysis. the static analysis was carried out for self-weight and applied load cases for loaded and unloaded cases. the loaded case was concluded critical under both the static and dynamic loading conditions. most of the available works have considered a single capacity or single span for optimization and take almost no consideration for industrial or manufacturing strategies. this paper discusses the results of automated optimization code developed using ansys parametric design language (apdl) and implemented for design optimization using developed correction factors without considering the industrial constraints. the box girder without industrial constraints (woic) is the one in which design variables such as hmax maximum height of the girder, rd web plate thickness factor, and ptflange plate thickness factors are modified independently as mentioned by abid et al. [40, 41]. later, using an automated optimization routine considering industrial constraints, optimized cutting lengths, welding lengths, edge preparation lengths, and manufacturing strategy is developed for reduced waste, mass, and efforts, after which the results are recorded. the box girder with industrial constraints (wic) is one in which hmax is constrained equal to the sizes available in the market. the width of the top plate is also constrained to one-third of hmax. two approaches for box girders with industrial constraints have been considered: (1) keeping all thicknesses the same i.e. tsp (thickness of side plate) = ttp (thickness of top plate) = tbp (thickness of bottom plate); (2) keeping web and flange thickness different. fig. 1: front view of box girder . (a) (b) (c) fig. 2: section view of box girder, (b) vertical stiffener, (c) horizontal stiffener iium engineering journal, vol. 19, no. 1, 2018 abid et al. 292 fig. 3: solid 186 element in ansys [47]. (a) (b) (c) (d) (e) fig. 4a-e: applied boundary conditions; (d) meshed model, (e) cut view of full geometry modeled with horizontal and vertical stiffeners. for the optimization of box girders of a capacity range of 50~120 ton and for a span of 10~32 m, a detailed 3d nonlinear finite element analysis is performed. initially, a 120 ton girder is optimized as the reference girder first by adding horizontal and vertical stiffeners to control torsion, buckling, and deflection within allowable limits [46]. later, this 1 elements f acel x y z iium engineering journal, vol. 19, no. 1, 2018 abid et al. 293 reference optimization is used for capacity-wise [40], span-wise [41] and combined optimizations in the present study. 2. box girder modeling; meshing, boundary conditions and material selection figure 1 shows the front view of a box girder with general parameters; figure 2a-c shows the sectioned view of the box girder, and vertical and horizontal stiffeners, respectively; figure 4a-c show applied boundary conditions (constraints, loading and reflective symmetry). figure 4d shows meshing of the half box girder model using solid186 elements; figure 4e shows a section view of the full geometry modeled with horizontal and vertical stiffeners. most of the researchers used shell elements dealing with finite element analysis of box girders [1, 27~45]. researchers have selected shell elements owing to fact that the box girder cranes are classified as thin walled structures [45]. the geometries they use is therefore simplified, neglecting features like rails and horizontal sections. use of solid elements is also found in the literature [3, 25, 30, 43], as these can be used for both thick and thin sections. due to the use of solid elements, only a single element type is required, therefore avoiding interfacing of element types. also, because the present study uses batch mode (by using apdl code), better control during parametric modeling is incurred. in the present study, solid186 (20 noded) element is used for discretization of the geometric model (fig. 3 and meshed model in fig. 4(d)). a half model was created due to the symmetry of the geometry. for meshing, the element edge length at this stage was set to 180 mm and at a later stage, during optimization, the edge length was selected by performing element sensitivity analysis to reduce error. because the optimization includes various sizes, the element edge length and the number of elements changes. for all optimized sizes, the element edge length was between 50 – 150 mm. a sample mesh sensitivity study is presented by authors in previous work [41]. ansys software [47] was used for finite element analysis. an ansys parametric design language (apdl) code was developed that was utilized to run the simulations in batch mode. the code, when entered in ansys, asks for two entities i.e. span and capacity. only these two inputs and the interpolative relations and correction factors determined in the present work are utilized to present the optimized parameters of the required size and capacity crane. the boundary conditions are as follows: (1) a single line load on the halfway of a rail equally divided on three nodes thus reducing stress singularity; (2) a loading impact factor of 1.25 is selected i.e. a 120 ton crane has a load of 120 * 1.25 = 150 ton and additionally its own weight. (3) a zero degree-of-freedom boundary condition is applied for all nodes on the support area (this is a purposely selected conservative approach); (4) symmetry condition at half length of girder; (5) gravitational acceleration to include the effects of self-weight are applied. structural materials for the construction of overhead crane girders i.e. rst-37-2 [25,30], st-42 [33], st-52-3 [34], structural steel [2], is: 2062, e 250b [42], structural steel s235 [45], and others are used. the most commonly available structural steel according to astm standard is a36 / a36m [46] and is an equivalent alternative of rst-37-2 according to din standard 17100. material a36 having elastic modulus = 200 gpa, yield strength = 250 gpa, ultimate tensile strength = 400~550 gpa, allowable stress = 160 mpa and density = 7.86×10-6 kg/mm3 is used for analysis in this study. although allowable deflection is a matter of professional judgment, the values of deflection must be between l/360 l/180 to iium engineering journal, vol. 19, no. 1, 2018 abid et al. 294 avoid visible sagging [50]. a box girder without proper stiffening will show lateral buckling (fig. 5). reference [30] utilized optimized positions and number of vertical and horizontal stiffening elements to reduce the deflection in the lateral direction, hence to avoid lateral buckling. the present study utilizes this approach to control lateral buckling. (a) (b) fig. 0: lateral bucking (uz plot in mm) at (a) support; (b) center. 3. optimization methodology without consideration of industrial constraints capacity-wise optimization optimizes box girders of different capacities of the same span and thus has capacity as the only input and is presented in [40]. span-wise optimization optimizes box girders of different spans and same capacity, thus has span as the only input and is presented in [41]. these studies use first order optimization using the ansys design optimization module with the overall mass and volume of the box girder as the objective parameter. the maximum number of iterations was set to 50. the maximum height (hmax) and web and flange thicknesses were design variables. other size parameters are related to these design variables. the maximum normal stress and normal deflections were the state variables. for capacity-wise optimization, this is repeated for 32 m box girders and different capacities between 50–120 tons. likewise, during span-wise optimization, design optimization is carried out with 100 ton girders with span between 10–32 m. the results of each are generalized in the form of interpolative relations. although, the authors first optimized capacity-wise and then span-wise, the reverse approach is considered equally valid. the capacity-wise and span-wise optimization methodologies are presented in fig. 6a and 6b, respectively. the interpolative relations developed during the capacity-wise and span-wise optimization are presented in relations (1~3) and (4~6), respectively. relations (1~3) are only valid for 32 m box girders of capacity range of 50~120 ton and relations (4~6) are only valid for 100 ton box girders of span range of 10~32 m. (hmax )c=(hmax )r-{[(hmax )r×(rc cc )/ 400 ] + hcf ×( rc – cc )} (1 ) (rd )c=(rd )r-[(rc-cc )/ 400 ] (2 ) mn mx x y z mn mx x y z -15.866 -13.962 -12.058 -10.154 -8.25 -6.346 -4.442 -2.539 -.634717 1.269 iium engineering journal, vol. 19, no. 1, 2018 abid et al. 295 (pt )c=(pt )r-[( rc-cc )/ 200 ] (3 ) (hmax )c=�(hmax )r {0.11 × [(hl )r – (hl )c ]}�+ 75 (4 ) (rd )c=�(rd)r+ {0.0000365 × [(hl )r(hl )c ]}�0.05 (5 ) (pt )c=�(pt )r-{ 0.00009375 × [(hl)r(hl )c]}�0.002 (6 ) where, rc is the capacity of the reference girder; cc is the capacity of the current girder; hcf is the height correction factor; (hl)r and (hl)c are half of the span length of reference and current girder respectively; and rd and pt are reduction factors. in order to develop relations for any given span and capacity, a generalized (apdl) code is developed based on the factors and relations developed during the span-wise and capacity-wise optimization routines and a generalized optimized code for combined capacity and span is developed and tested, with its results discussed in detail. the following relations are introduced for more useful dependencies: hmax = f(hmax1, hl) (7) rf = f(rf1, hl) (8) pt = f(pt1, hl) (9) where, hmax1, rf1 and pt1 are the maximum height, web thickness, and flange thickness optimization factors calculated during the capacity-wise optimization and hmax, rf and pt are the height and thickness factors calculated during span-wise relations. the aim is to define dependencies in such a way that the span-wise optimization relations are in terms of capacity-wise relations. thus, the optimization factors calculated in the capacity-wise calculations become inputs for the relations developed in the span-wise calculations. there are some correction or combination factors used to make these relations compatible with each other. finally, the capacity-wise relations act as the capacity control block and correction factors form correction block and finally the span-wise relations control the span related issues. (���� )� = 2600 − ((2600 × 0.0025 × (120 − ��)) + (120 − ��)) (10) (��)� = 0.727 − (0.0025 × (120 − ��)) (11) (��)� = 1.85 − (0.005 × (120 − ��)) (12) the span control block consists of the following modified span-wise interpolative relations: (���� ) = ((���� )� − (��� × (16000 − ��))) + ��� (13) (��) = (��)� + (0.0000365 × (16000 − ��))) − ��� (14) (��) = (��)� − (0.00009375 × (16000 − ��))) − ��� (15) iium engineering journal, vol. 19, no. 1, 2018 abid et al. 296 (a) (b) fig. 6: (a) capacity wise optimization (b) span wise optimization. iium engineering journal, vol. 19, no. 1, 2018 abid et al. 297 the capacity control block consists of the following modified capacity-wise interpolative relations: where spc is the maximum span control factor with a value of -125 and is only used for 32 m span box girders for any capacity; cmf is the height compensation factor for all spans; rdc is the side plate control factor that works for all spans in the range; prc is the top and bottom plate control factor; cc is the capacity of the giver sized girder; and hl is the half of the span. the general methodology for combined optimization is given in fig. 7. as a case study, correction factors for 50~120 ton capacity and different spans are summarized in table 1. table 1: correction factors for capacity 50~120 ton for different span ranges capacity (ton) span (m) correction factors 50~60 from to cmf rdc prc 30 32 0.180 0.050 0.002 24 26 0.115 0.050 0.002 10 12 0.100 0.050 0.002 60~80 30 32 0.175 0 0 22 26 0.115 0 0 10 16 0.097 0.050 0.002 80~100 30 32 0.175 0 0 24 28 0.115 0 0 10 12 0.102 0.050 0.002 100~120 30 32 0.175 0 0 24 26 0.115 0 0 10 12 0.114 0.100 0.002 as a case study, calculations are presented below using combined optimization strategy for a sample girder of 75 ton capacity and 26 m span box girder. 3.1 capacity control block using equations 10 through 12; the values of hmax, (rf)1 and (pt)1 are calculated to be 2262.5 mm, 0.6145, and 1.625 respectively. 3.2 correction block the correction factors are used from table 1 i.e. for 75 ton × 26 m, spc=0 (as the span is not equal to 32 m), cmf=0.143, rdc=0, and prc=0. 3.3 span control block from relations 13 through 15; as the span is 26 m, hl (half-length in mm) = 26/2*1000 = 13000 mm, hmax, rf, and pt are calculated as 1833.5 mm, 0.724, and 1.34375, respectively. therefore, the optimized 75 ton × 26 m girder will have the hmax = 1833.5 mm, rd = 0.724, pt = 1.34375. however, thickness of side and top plates can be calculated using equations 16 and 17 respectively, ��� = 16 × �� (16) iium engineering journal, vol. 19, no. 1, 2018 abid et al. 298 so, ��� = 16 × 0.724 = 11.584 �� and, ��� = ��� × �� (17) ��� = 11.584 × 1.34375 = 15.566 �� fig. 7: methodology for combined optimization. figure 8a presents a comparison of results of capacity-wise optimizations with 32 m span of girders with the results of the combined optimization methodology. figure 8b presents the comparison of span-wise optimization results of 100ton girders with the combined optimization methodology. as case study, results of combined optimization methodology for 120 ton, 80 ton, and 50 ton capacity and 10, 20, 30, and 32 m span box girders are summarized in table 2. (a) (b) fig. 8: (a) comparison of capacity-wise and combined results of 32 m span box girders, (b) comparison of span-wise and combined results of 100 ton capacity box girders. 16500 19000 21500 24000 26500 29000 31500 50 60 70 80 90 100 110 120 m as s (k g ) capacity (tons) 6750 11750 16750 21750 26750 14 16 18 20 22 24 26 28 30 32 m as s (k g ) span (m) iium engineering journal, vol. 19, no. 1, 2018 abid et al. 299 table 2: 50, 80, and 120 ton capacity girders after combined optimization capacity span hmax tsp ttp wtp hrl ths mbs usum uz mass ton m mm mm mm mm mm mm mpa mm mm kg 120 32 2525 12 22 878 70 8 154.1 39.4 6.1 30330 30 2400 13 22 834 66 7.5 156.4 35.1 5.3 27900 20 1850 16 21 643 51 6 154.4 18.9 3.0 14604 10 1313 17 14 457 36 3.5 154.8 6.5 1.6 3058 80 32 2160 11 19 751 60 6.75 155.9 44.2 6.0 23050 30 2125 11 18 739 59 6.75 154.4 39.0 5.5 20910 20 1670 14 16 580 46 5.25 151.5 19.5 2.9 11150 10 1178 16 10 410 33 3.75 150.2 6.4 1.4 3530 50 32 1950 9 14 678 54 6 154.4 46.5 6.3 16848 30 1895 9 13 659 53 6 156.5 42.3 5.8 15002 20 1445 12 12 502 40 4.5 155.5 21.7 2.9 8020 10 975 15 8 339 27 3 155.2 7.1 1.2 2640 4. optimization methodology considering industrial constraints the aim of the research is not only the optimization of the overhead crane box girders but also to optimize it in accordance with industrial constraints. the size of the plates for side, top, bottom, and vertical stiffeners; rail and horizontal stiffener sections calculated during the optimization were not realistic, being in fractions and mostly not corresponding to sizes available in the market. therefore, in order to make the optimized design more practical: standard libraries for the standard sections i.e. standard plates, rails, and horizontal stiffeners [48] as available in the market are added. the optimized parameters are modified according to the standard size libraries. finally, standard section libraries are added in the apdl code and optimized sections are achieved by selecting the closest available option for a given design variable that is used in the modeling and analysis instead of the ones calculated without considering industrial constraints. figure 9 compares the mass of 100 ton box girders before and after the addition of standard sizes. with the inclusion of standard sizes, the mass of the optimized box girders is increased and the maximum bending stresses are mostly found to have decreased due to the fact that a bigger or thicker section is always selected. hence, the over-design caused is unavoidable as the selection of the small or thin sizes mostly tends to cause under-design. however, in order to control mass and waste of material during cutting, and to reduce manufacturing cost: cutting and welding plans, modification of height and width of the plates is introduced and are discussed in the following sections. 4.1 height modification the design variables of the box girders optimized without industrial constraints are modified and re-optimized to design box girders with industrial constraints. the sizes of a36 structural steel plates, in terms of height and width, are according to state steel usa’s product catalogue [48], and are presented in table 3. it is observed that the difference between the heights is 304mm (1524-1219.2 = 304.8 mm) except the last size. therefore, if a constraint is added in such a way that the apdl code selects the closest, then the mass increases, which is not desired. another methodology is to sustain the heights of the plates calculated during the woic optimization and cutting and welding the plates together. this iium engineering journal, vol. 19, no. 1, 2018 abid et al. 300 causes an increase in the cost of manufacturing. this also causes an increase in deformations during welding, resulting in structural weakening. in order to overcome the above mentioned issues, the box girders are re-optimized for maximum height (hmax) equal to the ones that are available in the market. the first four sizes (1219.2 mm, 1524 mm, 1828.8 mm and 2133.6 mm), as mentioned in the table 3, were selected. as all parameters other than the height and thickness of plates depend upon the hmax optimization factor, therefore, the only design variables left after having hmax, is the thickness of the side, top, and bottom plates. thus, the optimization for height modification is done by changing the thicknesses of web and flange plates. the height of the plates is selected according to the hmax calculated in the previous optimizations and is divided into ranges as mentioned in table 4. fig. 9: mass comparison of 100 ton girder with and without industrial constraints. two approaches were used during this optimization:  keeping all thicknesses the same i.e. tsp = ttp = tbp. (approach 1).  keeping web thicknesses and flange thicknesses different from one another, but keeping the thickness of the top and bottom flange the same and left and right web plates the same. (approach 2). table 3: standard available heights and widths of plates table 4: ranges for height modification hmax (mm) hmax (mm) 850 ~ 1500 1219.2 1500 ~ 1755 1524.0 1755 ~ 2049 1828.8 2049 ~ 2650 2134.0 3500 5500 7500 9500 11500 10 12 14 16 18 m a ss ( k g ) span (m)with lib. without libs w (mm) h (mm) difference between heights (mm) 6000 1219.2 304 6000 1524.0 304 6000 1828.8 304 6000 2133.6 304 6000 2438.4 -- 6000 3048.0 -- iium engineering journal, vol. 19, no. 1, 2018 abid et al. 301 4.2 approach – 1 with same flange and web plate thickness the methodology is to select the thickness of all webs and flanges to be almost equal to the average of ttp and tsp calculated in the previous methodologies. hence, direct relationships are developed between the thicknesses of web or flange (as they are taken to be the same) with the capacity and span. these relations are different for different capacities and spans and are incorporated in the apdl code. as a case study, for 20 and 21 m span and 50~120 ton capacity cranes, the plate thicknesses are calculated as mentioned in table 5. the output stresses and deflections, thus produced, are within the allowable limits. table 5: height modification thickness for 20 m and 21 m span girders 4.3 width (wtp) modification the width of the box girder was calculated to be hmax/2.71 during previous optimizations. the ratio of hmax to wtp (width of top plate) or wbp (width of bottom plate) was set as 3 i.e. cutting it into three pieces, hence saving the loss in height of the plate. this also follows the bećirović et al. [37] recommendation that increasing the height to width ratio i.e. hmax/wtp, increases the static as well as dynamic stability of the box girders. 4.4 approach-2: with different flange and web thickness (dfw) using thicknesses initially calculated in the approach-1 and modifying the web and flange thicknesses so as to be ratios of approach-1 thicknesses. the study concluded that the web and flange plate thicknesses must be 0.9 times and 1.25 times of approach-1 thicknesses respectively. for example, if a thickness of 15 mm was concluded for a particular specification box girder, then the plate thicknesses used in approach-2 analysis will be 14 mm (i.e. 15×0.9 ≈ 14) for the side plates and 19mm (i.e. 15×1.25 ≈ 19) will be used for the top and bottom flanges. as an example the mass calculated for 85 ton capacity and 26 m span crane box girder using approach-2 was 19742 kg i.e. 1047 kg (5.04%) less than the mass of the girder according to approach-1. although the stresses and deflections are observed to be more than those observed for approach-1 but are still within the allowable limits. 5. comparison of woic and wic optimization results this section compares the optimization results in a case when no standard size for height was used (old method), to the case when standard heights were used. additionally, a comparison of cases where thicknesses of top/bottom and side plates were kept constant for approach-1 and not constant for approach-2 (diff-thick) were also used. finally, the case with width modification is also compared with the prior. the aim of this comparison is to analyze the feasibility of the later optimizations. the case study presented shows results of carne capacity 120 ton box girders of various spans. figure 10a-b show a comparison of span (m) capacity (ton) cpt (mm) 20 50~60 ((40+cc)/5) 60~95 ((60+6*cc)/30) 95~120 ((5*cc-125)/25) 21 50~55 18 55~85 ((6*cc-5)/25) 85~120 ((6*cc-20)/35) iium engineering journal, vol. 19, no. 1, 2018 abid et al. 302 mass, uz, and hmax results with and without considering industrial constraints. it is observed that as span increases, the difference between the old (woic) and new methodology (wic-sfw) increases. the mass of a 32 m span woic and wic optimized girder is 30060 kg and 36373 kg (~21% increase), respectively (fig. 10a). it concludes that the mass of the girders in wic increases as compared to the woic during an increase in span length and/or capacity. a similar trend is observed with wtp modification different thickness, but the difference is smaller in comparison to wic-sfw. abid et al. [30] have compared lateral buckling (uz) for different designs of the box girders and have concluded that lateral buckling control is better for wic compared to the woic. no notable difference in the bending deflections (uy) and shear buckling (ux). figure 10b compares hmax for the various case studies and shows that the height with wic is smaller compared to woic and width of the girders is directly related to hmax, thus, the volume (space) occupied by the wic is less than that of woic girders. the variety of plate sizes for manufacturing is greatly reduced as now the thickness of top and side plates is the same for the approach-1. although the mass of the girders is increased with wic methodology yet it is inconclusive to state that it is not cost effective, as cost effectiveness can only be known after knowing the cutting and welding as well as material costs for manufacturing and the already available inventory. therefore, approach-2 is proposed as the final design for the box girders. the cutting plan and welding methodologies are all based on this particular design. the features of the finalized design are summarized below;  the height of the girder web plate is selected as per ranges defined in the table 4.  the width of the flange plates (both top and bottom) is one-third of the maximum height of the girder web plate.  the ratio of thickness top/bottom flange to the web plates is 1.389.  all horizontal stiffeners and rail sections are selected according to the standard library. (a) (b) fig. 9: comparisons for 120 ton capacity with different spans; (a) mass, (b) hmax. iium engineering journal, vol. 19, no. 1, 2018 abid et al. 303 6. conclusions after detailed fea of box girders, the following conclusions are made;  optimization of an overhead crane box girder for capacity (50~120 ton) and span (10~32 m) is performed for safe bending stress and deflection with minimum mass and volume with and without consideration of industrial constraints using a customized developed optimization resulting in accuracy and automation.  the cutting and welding plan is optimized to reduce wastage and control manufacturing overheads.  the finite element model used solid186 elements because their use offers better control during parametric modeling. the shell elements on the other hand are not suitable for horizontal stiffener and rail sections as they cannot be treated as shells. also, after the inclusion of height modification in the height reduction in specific cases is made possible at the cost of thickness addition, thus, the error in shell element calculation is avoided.  the parametric optimization of the reference girder (120 ton × 32 m) concluded a 14.63% (or 5449 kg) mass reduction, 27.3% and 2.18% thickness reduction of web and flange plates respectively with respect to the existing box girder model. similar savings are observed in all the range of capacity and spans.  linear interpolated capacity-wise and span-wise relations were developed for the calculation of the design parameters (hmax, pt and rd) for the required capacity (50 ton~120 ton) and span (10 m ~ 32 m) of the box girder. before performing spanwise optimization, with the only input as span and fixed capacity (100 ton), mesh sensitivity analysis was carried out and an element edge length of 170 mm was concluded (for a 100 ton girder).  the combined optimization using combination/correction factors was performed in three steps (capacity, correction and span control block).  the optimized parameters concluded were modified according to the industrial constraints i.e. standard section libraries of plates and rolled sections available in the market. the addition of standard libraries increased the mass of the girder as the code selected an upper bound thickness.  the height of the girder (hmax), as calculated during the earlier optimizations, was modified keeping in mind the losses during the crane construction. hmax was concluded to be equal to the size of a given standard plate to avoid cutting along the height of the web. wtp was concluded to be 1/3 of the height of the girder (hmax). two optimization studies were performed to modify the height considering first web and flange thicknesses to be equal (approach-1), and secondly top/bottom plate thickness of 0.9 times and 1.25 times the thickness calculated in approach-1. all the optimization case studies performed were compared and it was concluded that the case studies with no height modifications had lower masses for greater spans (15 m ~ 32 m). the addition of mass due to height modification increases with the increase in both span and capacity. hence, the mass of the height modified cases for lower spans was observed to be less than the non-modified case studies. iium engineering journal, vol. 19, no. 1, 2018 abid et al. 304 references [1] zuberi rh, kai l, zhengxing z. (2008) design optimization of eot crane bridge. engopt 2008 international conference on engineering optimization. 01 05 june 2008; rio de janeiro, brazil. [2] lerga ji. (2011) modelling and simulation research on the metal structure of bridge cranes. m.sc. thesis, technical university sofia english language faculty of engineering, sofia. [3] satyanarayana, v.v., ghosh, d. p. and rao, j.s. (1980) dynamic response of the bridge girders of e.o.t. cranes due to dissimilar rail joints. mechanism and machine theory; 15, 385-395. [4] cranes [http://crawlercrane.net/solution/cranes/crane-introduction.html] [5] swuste, p. (2013) a normal accident with a tower crane? an accident analysis conducted by the dutch safety board. safety science; 57, 276–28. [6] zhang, c. and hammad, a. (2012) improving lifting motion planning and re-planning of cranes with consideration for safety and efficiency. advanced engineering informatics; 26, 396–410. [7] tam, v.w.y., and fung, i.w.h. (2011) tower crane safety in the construction industry: a hong kong study. safety science; 49, 208–215. [8] marquez, a.a., venturino, p. and otegui, j.l. (2014) common root causes in recent failures of cranes. engineering failure analysis; 39, 55–64. [9] ruud, s. and mikkelsen, å. (2008) risk-based rules for crane safety systems. reliability engineering and system safety; 93, 1369–1376. [10] navestad, t.o.(2008) safety understandings among crane operators and process operators on a norwegian offshore platform, safety science; 46, 520–534. [11] lei, z., taghaddos, h., hermann, u. and al-hussein, m. (2013) a methodology for mobile crane lift path checking in heavy industrial projects, automation in construction; 31, 41-53. [12] li, y. and liu, c. (2012) integrating field data and 3d simulation for tower crane activity monitoring and alarming. automation in construction. 27, 111–119. [13] rusiński, e. iluk, a., malcher, k., pietrusiak, d. (2013) failure analysis of an overhead traveling crane lifting system operating in a turbo generator hall. engineering failure analysis; 31, 90-100. [14] aneziris, o.n. (2008) towards risk assessment for crane activities. safety science; 46, 872884. [15] shepherd, g.w., kahler, r.j. and cross, j. (2000) crane fatalities – a taxonomic analysis. safety science; 36, 83-93. [16] american society of mechanical engineers, (2010) overhead and gantry cranes top running bridge, single or multiple girder, top running trolley hoist. asme b30.2-2005. three park avenue • new york, ny. [17] international organization for standardization (2005). cranes -design principles for loads and load combinations, part 4 jib cranes, iso 8686-4:2005; 1, 1-9. iso, geneva, switzerland. [18] the crane manufacturers association of america (2015). specification # 70, specifications for top running bridge & gantry type multiple girder electric overhead traveling cranes; 1-8. cmaa, usa. [19] anon (1995b), din: taschenbuch 185, fördertechnik 2, berlin: beuth-verlag. [20] fédération européenne de la manutention (1998) fem 1.001 rules for the design of hoisting appliances, 3rd edition, 8 booklets, 1-305. technos publicações ltda, brazil. [21] british standard institution (2012) code of practice for the safe use of cranes. inspection, maintenance and thorough examination. mobile cranes. 1-32, bsi, london, uk. (isbn: 978 0 580 78194 0) [22] polish standard. (1990) steel construction static calculations and design. polish standard pn-b-03200:1990, 1-48. standardization publishing house. poland. [23] greiner, h.g. (1967) crane handbook: design data and engineering information used in the manufacture and application of cranes. whiting corporation, harvey iii, usa, 3rd ed. 1206. iium engineering journal, vol. 19, no. 1, 2018 abid et al. 305 [24] otani, a. nagashima, k. and suzuki, j. (2002) vertical seismic response of overhead crane. nuclear engineering and design; 212, 211–220. [25] alkin, c., imrak, c.e. and kocabas, h. (2005) solid modeling and finite element analysis of an overhead crane bridge. acta polytechnica, czech technical university in prague; 45, 61-67. [26] farkas, j. (1986) economy of higher-strength steels in overhead travelling cranes with double-box girders. journal of construction steel research; 6, 285-301. [27] niezgodzin, t. and kubiak, t. (2005) the problem of stability of web sheets in box-girders of overhead cranes. thin-walled structures; 43, 1913-1925. [28] imrak, c.e., gerdemeli, i. and erdik, a. (2006) linear and nonlinear finite element modelling and stress analysis of portal cranes. proc. of 10th international research/expert conference, trends in the development of machinery and associated technology, barcelona-lloret de mar, spain, 793-796. [29] blum, a., and chodorowska, d. (2007) experimental analysis of prestressed thin-walled structures stability. thin-walled structures; 45, 834-839. [30] abid, m., akmal, m.h. and parvez, s. (2008) optimization of box girder of overhead crane," global design to gain a competitive edge: an holistic and collaborative design approach based on computational tools. 609-617. [31] pinca, c.b., tirian, g.o. and socalici, a.v. (2009) application of finite element method to an overhead crane bridge. wseas transactions on applied and theoretical mechanics; 2/4, 64-73. [32] pinca, c.b., tirian, g.o. socalici, a.v. and ardelean, e.d. (2009) dimensional optimization for the strength structure of a traveling crane. wseas transactions on applied and theoretical mechanics; 4/4, 147-156. [33] gerdemeli, s. kurt, h. and alkan, o. (2010) main girder beam design and finite element analysis of 2x160ton gantry crane. proc. 14th international research/expert conference. trends in the development of machinery and associated technology. mediterranean cruise. 565-568. [34] gerdemeli, s., kurt, h. and yildirim, m. (2010) calculations, modeling and analysis with finite element method of rubber tyred container stacking crane. 14th international research/expert conference. trends in the development of machinery and associated technology. mediterranean cruise. 545-548. [35] gašić, v., milovančević, m. and petković, z. (2010) fea implementation in moving load problem at bridge cranes. university of novi sad, faculty of technical sciences, adeko – association for design, elements and constructions, ceepus cii-rs-0304 / ceepus cii-pl0033, machine design; 25-30. [36] zhang, h., roches, r.d., yang, z. and liu, s. (2010) experimental and analytical studies on a streamlined steel box girder. journal of constructional steel research; 66, 906-914. [37] bećirović, d., vukojević, f. and hadžikadunić. (2011) optimization of double box girder overhead crane in function of cross section parameter of main girders. 15th international research/expert conference trends in the development of machinery and associated technology. prague, czech republic; 641-644. [38] gąska, d. and c. pypno, c. (2011). strength and elastic stability of cranes in aspect of new and old design standards. mechanika; 17/3, 226-231. [39] djelosevic, m., gajic, v., petrovic, d. and bizic, m. (2012). identification of local stress parameters influencing the optimum design of box girders. engineering structures; 40, 299316. [40] abid, m., khan, s.m. and shah, a.r. (2013) optimization of box type girder of overhead crane for different capacities with fixed span. 9th international conference on fracture and strength of solids, jeju, korea. 1-9. [41] abid, m. and khan, s.m. (2014) optimization of box type girder of overhead crane for different spans with fixed capacity. international conference on industrial engineering and operations management, bali, indonesia; 404-412. iium engineering journal, vol. 19, no. 1, 2018 abid et al. 306 [42] chauhan, n. and bhatt, p.m. (2012) improving the durability of the e.o.t. crane structure by finite element analysis, and optimize the hook material for improving its solidity. procedia engineering; 38, 837-842. [43] suratkar, v. s. (2013) 3d modelling and finite element analysis of eot crane. international journal of mechanical and production engineering; 1/2, 34-37. [44] rabey, v. the study of a stress-strain state of bridge cranes, metal constructions in the process of a collision with the end stops. faculty of mechanical engineering, astrakhan, fme transactions; 41, 195-201. [45] haniszewski, t. (2014) strength analysis of overhead traveling crane with use of finite element method. transport problems; 9/1, 19-26. [46] american society for testing and materials (1999) astm a36: standard specification for carbon structural steel. 46 cfr 160.035-3(b)(2), usa. [47] ansys. (2010) element reference manual. ansys inc. usa. [48] state steel supply company (2014) state steel product catalogue. rev. 7/03. usa. [49] ambrose, j. and tripeny, p. (2011) building structures, 3rd edition, isbn: 978-0-470-542606. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 samah et al. 94 fixed-bed adsorption of aqueous vanillin onto resin h103 rozaimi abu samah1*, norazwina zainol1, lai yee phang2 and suraini abd-aziz2 1 faculty of chemical and natural resources engineering, universiti malaysia pahang, lebuhraya tun razak, 26300 kuantan, pahang, malaysia. 2 department of bioprocess technology, faculty of biotechnology and biomolecular sciences, universiti putra malaysia, 43400 upm serdang, selangor, malaysia. *corresponding author: rozaimi@ump.edu.my (received: 7th feb. 2017; accepted: 14th oct. 2017; published on-line: 1st dec. 2017) abstract: the main objective of this work was to design and model a fixed-bed adsorption column for the adsorption of vanillin from aqueous solution. three parameters were evaluated for identifying the performance of vanillin adsorption in fixed-bed mode, which were bed height, vanillin initial concentration, and feed flow rate. the maximum adsorption capacity increased more than threefold to 314.96 mg vanillin/g resin when the bed height was increased from 5 to 15 cm. bohart-adams model and belter equation were used for designing a fixed-bed column and predicting the performance of the adsorption process. a high value of determination coefficient (r 2 ) of 0.9672 was obtained for the modelling of vanillin adsorption onto resin h103. abstrak: tujuan utama kajian ini adalah membentuk dan membina model penyerapan turus-padat bagi penyerapan vanilin daripada larutan akues. tiga parameter telah dikaji bagi menentukan prestasi penyerapan vanilin dalam mod turus padat, iaitu ketinggian padatan, kepekatan awal vanilin, dan kadar aliran suapan. peningkatan ketinggian padatan daripada 5 kepada 15 cm telah meningkatkan kapasiti penyerapan maksimum sebanyak lebih daripada tiga kali ganda kepada 314.96 mg vanilin/g resin. model persamaan bohart-adams dan belter telah digunakan untuk membentuk kolum turus padat dan prestasi proses penyerapan dijangakan menguna pakai persamaan ini. nilai pekali penentuan (r 2 ) yang tinggi pada 0.9672 telah diperoleh daripada model penyerapan vanilin menggunakan resin h103. keywords: adsorption; vanillin; fixed-bed; breakthrough curve 1. introduction a sweet odour characteristic is the main driver for vanillin’s use in food and beverage industries, as well as perfumes and cosmetics industries. vanillin (4-hydroxymethoxybenzaldehyde, c8h8o3, 152.15 g/mol) is produced by a traditional, tedious, and time-consuming process of curing vanilla pods from vanilla plants [1]. it can also be manufactured from several chemicals such as curcumin and eugenol, but the processes deal with high temperatures and pressures [2]. in addition, the waste products from the chemical reactions may impose problems on the environment [3]. moving forward, biotechnology offers ways of producing vanillin at ambient conditions by the action of microorganisms and/or enzymes on abundant sources of raw material such as biomass. iium engineering journal, vol. 18, no. 2, 2017 samah et al. 95 several components from biomass are identified as potential sources for the production of vanillin such as ferulic acid, vanillic acid, and lignin [4]. due to its phenolic and aldehyde functional groups in its molecular structure, vanillin can be toxic to the producing microorganisms. therefore, a proper separation technique is needed to intermittently remove the vanillin as it is being produced. membrane separation [5-7], extraction [8], and crystallisation [9] are among the possible separation techniques to recover vanillin directly from the production vessel. in addition, adsorption has gained a lot of interest among researchers to separate vanillin using several types of polymeric adsorbents such as sephabeads sp206, nka-2, s-8, and dm11 [10-17]. an anisolemodified hyper-cross-linked polystyrene hj-108 [15] and sepabeads sp700 [17] are among the recent reported polymeric resins to be used for vanillin adsorption in batch and fixed-bed modes. compared to the batch adsorption process, fixed-bed mode offers a greater insight into the adsorption behaviour. the adsorbent is packed in a column and solution is passed through the adsorbent bed. the packed column can be attached to an automatic delivery system or let gravity perform all the work. from the process, the most studied part is the breakthrough analysis. the solution is pumped through the packed column for continuous adsorption, until a point where the adsorbent is saturated with the target molecule. during the continuous feed, the concentration of target molecule is monitored in the effluent. a plot of the ratio of effluent to feed concentration (ct/c0) versus time (t) explains the behaviour of the adsorption process in fixed-bed mode, which is known as a breakthrough curve. a breakthrough point is where an acceptable amount of target molecule appears in the effluent that could be discarded (tb – breakthrough time, cb – breakthrough concentration). the breakthrough point value depends on any particular application. normally, the range is 1% to 10% of the feed concentration [18], but there are often cases where the acceptable limit is taken as 5% [19]. one of the advantages of utilising the fixed-bed mode is a large volume of the solution can be introduced to the adsorbent, but feeding the solution beyond the breakthrough point would result in loss of the target molecule. on the other hand, feeding a small volume of the solution would result in incomplete utilisation of the adsorbent’s capacity in the column [18]. this breakthrough analysis can determine the performance of a fixed-bed, and at the same time, a minimum number of experiments can be done so that the prediction of a larger scale fixed-bed adsorption could be done as well [20-23]. for all the advantages of the fixed-bed mode, this work was executed to evaluate the vanillin adsorption onto resin h103 in a fixed-bed mode. the use of resin h103 has been reported earlier for the adsorption of vanillin in batch mode [24]. 2. methodology 2.1 materials preparation resin h103 was purchased from shanghai sunny scientific collaboration co. (ltd). vanillin used in this work was purchased from acros organics (belgium). fixed-bed column adsorption studies were performed in tricon columns supplied by ge healthcare (i.d. 10 mm). the column was packed with resin h103 at certain heights. prior to packing, the resin was soaked in absolute methanol and subsequently filtered and washed with distilled water [25]. all experiments were performed at room temperature with an äktaexplorer 100 system (amersham pharmacia biotech). iium engineering journal, vol. 18, no. 2, 2017 samah et al. 96 2.2 scale-up analysis for vanillin adsorption the general methods were based on a previous work with slight modifications [26]. three bed heights were used in this work: 5, 10, and 15 cm. the initial flow rate used was 5 ml/min and the vanillin solution was prepared at 1,000 mg/l [12, 27]. the effluents from the column were collected at fixed time intervals of 6 min and analysed offline using a uv-visible spectrophotometer at 280 nm [28]. the breakthrough curve analysis was done by varying any one of the parameters. in this work, by fixing the bed height at 10 cm, two other parameters were varied, which were the flow rate (10 ml/min) and vanillin initial concentration (900 mg/l). subsequently, a breakthrough curve was plotted as the ratio of effluent vanillin concentration to vanillin initial concentration (ct/c0) versus time (t). 2.3 fixed-bed column design a bohart-adams model was used in the design of a fixed-bed vanillin adsorption column, as shown in eq. (1). 𝑙𝑛 ( 𝐶0 𝐶𝑏 − 1) = 𝑙𝑛 (𝑒𝑥𝑝 𝑘𝑁𝑍 𝑉 − 1) − 𝑘𝐶0𝑡 (1) where, c0 is the initial vanillin concentration (mg/l), cb is the breakthrough vanillin concentration (mg/l), k is the rate constant (g/mg·h), n is the adsorption capacity (mg/g), z is the bed height (cm), v is the linear velocity (cm/min), and t is the breakthrough time (min) [26, 29]. for the determination of adsorption capacity (n) and rate constant (k), the model was then linearised, as shown in eq. (2). 𝑡 = 𝑁𝑍 𝐶0𝑉 − 1 𝑘𝐶0 𝑙𝑛 ( 𝐶0 𝐶𝑏 − 1) (2) where, the slope (m) is 𝑁 𝐶0𝑉 , and the intercept (c) is − 1 𝑘𝐶0 𝑙𝑛 ( 𝐶0 𝐶𝑏 − 1). a plot of time versus bed height was used to determine the adsorption capacity and rate constant. at t = 0, eq. (2) was used to determine the minimum bed height of resin h103 to give an effluent concentration of cb, or critical bed height (z0), as shown in eq. (3). 𝑍0 = 𝑉 𝑘𝑁0 𝑙𝑛 ( 𝐶0 𝐶𝑏 − 1) (3) for designing a new fixed-bed adsorption column based on a different vanillin initial concentration, the slope and intercept parameters in the linearised plot were determined by the following relationships in equations (4) and (5) [26]. 𝑚2 = 𝑚1 𝐶1 𝐶2 (4) 𝑐2 = 𝑐1 ( 𝐶1 𝐶2 )[ ln(𝐶2 − 1) ln(𝐶1 − 1) ] (5) where m1 and m2 are the slope parameters for the original and new vanillin initial concentrations, respectively, and c1 and c2 are the original and new vanillin initial concentrations, respectively. iium engineering journal, vol. 18, no. 2, 2017 samah et al. 97 similarly, for designing a new fixed-bed adsorption column based on a different feed flow rates, the slope and intercept parameters in the linearised plot were determined by eq. (6) [26]. 𝑚2 = 𝑚1 𝑄1 𝑄2 (6) where q1 and q2 are the original and new feed flow rates, respectively. the intercept value change is assumed insignificant with respect to different feed flow rates [29]. 2.4 modelling of breakthrough curve the breakthrough curve for fixed-bed vanillin adsorption onto resin h103 was modelled based on a two-parameter model [30], as shown in eq. (7). 𝐶𝐸 𝐶𝐹 = 1 2 [1 + 𝑒𝑟𝑓 ( 𝑡 − 𝑡0 √2𝜎𝑡0 )] (7) where ce and cf are the vanillin concentrations in the effluent and feed, respectively, t0 is the time at which the vanillin concentration in the effluent is half in the feed (determined experimentally), erf(x) is the error function of x, and represents the standard deviation, a measure of the slope of the curve (determined experimentally). the experimental data were calculated using the above equation, and plotted on the same plot of ct/c0 versus time of the experimental data. the experiments were done with the bed height of 10 cm, volumetric flow rate of 5 ml/min, and initial vanillin concentration of 900 mg/l. coefficient of determination (r2) was determined to verify whether the model obtained was acceptable or not. 3. results and discussion 3.1 breakthrough curve analysis for fixed-bed adsorption three parameters are usually varied in fixed-bed adsorption, namely bed height, solute initial concentration, and feed flow rate. by varying these three factors, the behaviour of the adsorption in the fixed-bed column can be determined. in this work, only bed height was varied to determine the dynamic behaviour of vanillin adsorption onto resin h103 that was packed in a column. fig. 1: the effect of bed height on breakthrough curves for vanillin adsorption onto resin h103. iium engineering journal, vol. 18, no. 2, 2017 samah et al. 98 fig. 1 shows the effect of bed height on the breakthrough curves for vanillin adsorption onto resin h103. the breakthrough time decreased considerably with the increasing bed height. for 15-cm bed height, the exit concentration of vanillin increased very slowly at the beginning of the process, as compared to the other two bed heights. for 5-cm bed height, the vanillin was detected in the quite early stage of the feeding process. for a breakthrough point of 10%, the time taken in a 15-cm bed height was 150 min. it was reduced to 60 min for 10-cm bed height and roughly 12 min for 5-cm bed height. in the actual separation process using this mode, it would be beneficial to stop the feeding of the sample when the effluent reaches this breakthrough point, and the adsorbed solutes are eluted out from the column. after that, the adsorbent is normally regenerated for the next cycle of adsorption process, or the spent adsorbent is discarded [31]. the steepness of the curve determines the utilisation of the packed adsorbent. for a good and efficient fixed-bed, a very steep breakthrough curve would be observed, which means that most of the adsorbent capacity is utilised for the adsorption process [19]. in this work, the steepness of the curves obtained was considered as gradual, and this shows that the fixed-bed columns were of medium performance, as shown in table 1 that the fraction of total bed was only used up to 0.417. in a published work, polymeric adsorbent sephabeads sp206 gave a good utilisation of the adsorbent in a fixed-bed mode for the recovery of vanillin by obtaining steep breakthrough curves [12]. a similar trend was also reported on the effect of bed height in the adsorption of gallic acid onto activated carbon cloth and activated carbon i-60 [26]. table 1: the effect of bed height towards breakthrough capacity bed height (cm) amount of adsorbent (g) breakthrough time (min) breakthrough capacity (mg vanillin/g adsorbent) fraction used up to breakpoint maximum adsorption capacity (mg/g) 5 2.5 12 10.43 0.107 96.813 10 5.0 60 51.99 0.268 194.125 15 7.5 150 131.44 0.417 314.960 in a fixed-bed column of resin h103, an increase of its bed height caused the vanillin to have more time to be in equilibrium with the resin. this resulted into an increased time observed to detect vanillin in the effluent, hence the longer breakthrough time, as shown in table 1 [32, 33]. it may be because the increase in bed height gives more time for the solutes to have contact with the adsorbent, which results into higher removal capacity and lower solute concentration in the effluent. besides, at larger bed height, more effective surface area of adsorbent is available that offers more active sites for adsorption. for this work, when the bed height was increased threefold, the breakthrough capacity of the fixedbed adsorption increased more than tenfold from 10.43 to 131.44 mg vanillin/g adsorbent. the maximum adsorption capacity also increased approximately threefold. 3.2 designing fixed-bed column for vanillin adsorption a bohart-adams model was used on the assumption that the adsorption process is continuous where equilibrium is not attained instantaneously [34]. this model was used for designing a fixed-bed column, by varying any one of the parameters. the model explains the performance of a continuous column via eq. (1). the equation was rearranged to obtain a linearised plot of service time versus bed height, as shown in fig. 2. iium engineering journal, vol. 18, no. 2, 2017 samah et al. 99 fig. 2: bohart-adams model for different breakthrough points (bp) at different bed heights, constant flow rate (5 ml/min), and constant vanillin initial concentration (1,000 mg/l). under a constant condition of flow rate (5 ml/min) and vanillin initial concentration (1,000 mg/l), three different breakthrough points (20%, 30%, and 60%) were utilised for this model analysis. the slopes and intercepts of each linear line were used to obtain the dynamic adsorptive capacity and adsorption rate constant, as shown in table 2. table 2: bohart-adams model constants for the vanillin adsorption onto fixed-bed resin h103. breakpoint (%) bed height (cm) service time (min) slope, m (min/cm) adsorption capacity, n (mg/g) intercept, c (min) adsorption rate constant, k (g/mg·h) critical depth, z0 (cm) 20 5 12 19.2 116.41 −94 0.929 4.896 10 78 15 204 30 5 36 19.8 120.05 −74 0.721 3.737 10 102 15 234 60 5 92 28.6 173.40 −59.33 ~0 2.075 10 210 15 378 the adsorptive capacity increased according to the increment of the breakthrough point. this reflects the amount of vanillin adsorbed onto the resin. in the bohart-adams model, this value is used to predict the performance of the fixed-bed adsorption processes with different parameters. meanwhile, critical depth denotes a minimum height sufficient for the breakthrough concentration. critical depths (z0) of 4.9, 3.7, and 2.1 cm were obtained from the calculation and they were in agreement with the graphical determination shown in fig. 2 (by extrapolating the linear lines). values in table 2 were used in predicting the performance of the fixed-bed adsorption of vanillin onto resin h103 at different vanillin initial concentrations and feed flow rates. the method applied was based on eq. (1). for a new vanillin concentration, it was possible to predict the performance of the fixed-bed column using the slope and iium engineering journal, vol. 18, no. 2, 2017 samah et al. 100 intercept parameters in the linearised plot (fig. 2). the prediction of new slope (m2) and intercept (c2) were made using eqs. (4) and (5), respectively. table 3 lists the new slopes and intercepts and the predicted and observed times that occurred for fixed-bed adsorption with a new vanillin concentration of 900 mg/l. the predicted times for three different breakthrough points of 20%, 30%, and 60% were 110, 139, and 253 min, respectively. meanwhile, the observed times obtained through experiments were 108, 132, and 198 min, respectively. the times taken for each experimental breakthrough using 900 mg/l of vanillin feed concentration were also compared to the values of 1,000 mg/l of vanillin. it was proven that a lower feed concentration produced a longer breakthrough time because given the same amount of adsorbent resin, it took a longer time for the total adsorbent resin to be saturated with vanillin. table 3: predicted breakthrough times using a bohart-adams constant for new vanillin initial concentration (900 mg/l). flow rate and bed height were kept constant at 5 ml/min and 10 cm, respectively. breakthrough point (%) slope, m2 (min/cm) intercept, c2 (min) predicted time (min) observed time (min) observed time for 1,000 mg/l 20 21.33 -102.85 110 108 78 30 22 -80.97 139 132 102 60 31.78 -64.92 253 198 210 a small variation in the calculated and experimental values was observed in the fixedbed adsorption of gallic acid [26]. a duration of 1.25 h experimental breakthrough time at 10% breakthrough was obtained for the change of feed concentration from 50 to 100 mg/l of gallic acid, compared to 1.66 h of the predicted or calculated breakthrough time. in another work, 20 min was the observed breakthrough time at 20% breakthrough, compared to 22.3 min, when the inlet concentration of cr(vi) was reduced from 10 to 5 mg/l [35]. similar results were obtained for the adsorption of textile dye blue 86 using a carbon-alumina composite [33]. therefore, it can be concluded that the design parameters can be utilised to predict or design the column adsorption for other feed concentrations. table 4: predicted breakthrough times using bohart-adams constant for new flow rate (10 ml/min). vanillin initial concentration and bed height were kept constant at 1,000 mg/ml and 10 cm, respectively. breakthrough point (%) slope, m2 (min/cm) predicted time (min) observed time (min) observed time for 5 ml/min 20 9.6 50 66 204 30 9.9 75 84 234 60 14.3 155 144 378 table 4 lists the predicted and observed times that occurred for the new feed flow rate of 10 ml/min. the breakthrough points greatly reduced when the flow rate was doubled. when the flow rate was increased from 5 to 10 ml/min, it only took 66 min to reach the 20% breakthrough point, as compared to 204 min. it was also obvious that the differences between the predicted and observed times were small. it was observed that 66, 84, and 144 iium engineering journal, vol. 18, no. 2, 2017 samah et al. 101 min were the points of breakthrough for 20%, 30%, and 60%, respectively, while the calculated points were calculated to be 50, 75, and 155 min. the possible reason for the shorter breakthrough caused by increased feed flow rate might be due to the lesser contact time between vanillin and resin h103, or shorter residence time [33, 36]. similarly, in the adsorption of cr(vi), small differences were also observed, which were 7 min for 20% breakthrough, compared to the calculated time of 6 min [35]. this shows that bohart-adams model applied to the current data indicated good agreement between both calculated and experimental values. this analysis also enables the researchers to predict the performance of a given fixed-bed adsorption column without having to perform any further and extensive experiments for different process parameters [37]. the possible reason for the shorter breakthrough caused by increased feed flow rate might be due to the lesser contact time between vanillin and resin h103, or shorter residence time [33, 36]. another approach in predicting the breakthrough curve was made using a simple twoparameter model. figure 3 shows the comparison between the experimental data for a fixed-bed adsorption and the model using eq. (7). the experiment was performed using a bed height of 10 cm, flow rate of 5 ml/min, and new vanillin initial concentration of 900 mg/l. it was obvious that the simple two-parameter model could also predict the behaviour of vanillin adsorption onto resin h103 at different parameters, with a determination coefficient (r2) value of 0.9672. compared to the bohart-adams model, this approach is considered to be a simpler method because a minimum of one experiment is needed for the prediction of the fixed-bed adsorption behaviour. the standard deviation value () obtained from the modelling can be used for the determination of the changes in the breakthrough curve for a new fixed-bed adsorption column at different lengths and feed flow rates [30]. this approach was also tested and improved for the modelling of the adsorption of cadmium ions by marine algae [38], ascopyllum nodosum [39], and the adsorption of copper ions by polyvinyl formal-immobilised rhizopus arrhizus and native mucor miehei [40]. based on the model obtained, the saturation bed capacity, or maximum adsorption capacity, was determined to be 165.9 mg of vanillin/g of adsorbent for the bed height of 10 cm. fig. 3: mathematical modelling using belter equation. the experiments were done with a bed height (z) of 10 cm, volumetric flow rate (q) of 5 ml/min, and initial vanillin concentration (c0) of 900 mg/l. iium engineering journal, vol. 18, no. 2, 2017 samah et al. 102 4. conclusion the vanillin adsorption from aqueous solution in fixed-bed mode was successfully performed and modelled. fixed-bed mode can be utilised to predict the behaviour of the adsorption of vanillin onto resin h103. a bohart-adams model and a belter equation were used to perform scaling analysis of a fixed-bed adsorption. the dynamic adsorption capacities at 10% breakthrough point were experimentally determined to be 96.813, 194.125, and 314.960 mg of vanillin/g of adsorbent for different bed heights of 5, 10, and 15 cm, respectively. for comparison, the modelled maximum adsorption capacity for a 10cm bed height obtained was slightly different at the value of 165.9 mg of vanillin/g of adsorbent. acknowledgement the authors thank university research grant scheme, universiti putra malaysia, and academic training scheme for institutions of higher education (slai), malaysia, for financial supports throughout this research project references [1] reineccius g. (2005) flavoring materials, flavor chemistry and technology, second edition, crc press, florida, pp. 203-259. [2] dolfini je, glinka j, bosch ac. (1990) patent no. 4,927,805. washington: uspto. [3] vidal jp. (2008) vanillin, kirk-othmer food and feed technology, john wiley & sons, new jersey, pp. 526-538. [4] walton nj, narbad a, faulds c, williamson g. (2000) novel approaches to the biosynthesis of vanillin, current opinion in biotechnology, 11(5):490-496. [5] brazinha c, barbosa ds, crespo jg. (2011) sustainable recovery of pure natural vanillin from fermentation media in a single pervaporation step, green chemistry, 13(8): 2197-2203. [6] wu yt, feng m, ding ww, tang xy, zhong yh, xiao zy. (2008) preparation of vanillin by bioconversion in a silicon rubber membrane bioreactor, biochemical engineering journal, 41(2):193-197. [7] sciubba l, di gioia d, fava f, gostoli c. (2009) membrane-based solvent extraction of vanillin in hollow fiber contactors, desalination, 241(1):357-364. [8] de brito cardoso g, mourão t, pereira fm, freire mg, fricks at, soares cmf, lima ás. (2013) aqueous two-phase systems based on acetonitrile and carbohydrates and their application to the extraction of vanillin, separation and purification technology, 104:106113. [9] taber df, patel s, hambleton tm, winkel ee. (2007) vanillin synthesis from 4hydroxybenzaldehyde, journal of chemical education, 84(7):1158. [10] li r, jiang z, mao l, shen h. (1998) adsorbed resin phase spectrophotometric determination of vanillin or/and its derivatives, talanta, 47(5):1121-1127. [11] zhao lq, sun zh, zheng p, he jy. (2006) biotransformation of isoeugenol to vanillin by bacillus fusiformis cgmcc1347 with the addition of resin hd-8, process biochemistry, 41(7):1673-1676. [12] zabkova m, otero m, minceva m, zabka m, rodrigues ae. (2006) separation of synthetic vanillin at different ph onto polymeric adsorbent sephabeads sp206, chemical engineering and processing: process intensification, 45(7): 598-607. [13] hua d, ma c, song l, lin s, zhang z, deng z, xu p. (2007) enhanced vanillin production from ferulic acid using adsorbent resin, applied microbiology and biotechnology, 74(4):783-790. [14] wang z, chen k, li j, wang q, guo j. (2010) separation of vanillin and syringaldehyde from oxygen delignification spent liquor by macroporous resin adsorption, clean – soil, air, water, 38(11):1074-1079. iium engineering journal, vol. 18, no. 2, 2017 samah et al. 103 [15] jin x, huang j. (2012) adsorption of vanillin by an anisole-modified hyper-cross-linked polystyrene resin from aqueous solution: equilibrium, kinetics, and dynamics, advances in polymer technology, 32:1-10. [16] xiao gq, long lp, wang jl. (2012) synthesis of the water-compatible p-acetaminophen resin and its adsorption performances for vanillin in aqueous solution, chinese chemical letters, 23(1):123-126. [17] mota mif, pinto pcr, loureiro jm, rodrigues ae. (2016) adsorption of vanillin and syringaldehyde onto a macroporous polymeric resin, chemical engineering journal, 288:869-879. [18] ghosh r. (2006) principles of bioseparations engineering, world scientific, singapore. [19] geankoplis cj. (2003) transport processes and separation process principles (includes unit operations), fourth ed., prentice hall, new jersey. [20] krings u, berger r. (1995) porous polymers for fixed bed adsorption of aroma compounds in fermentation processes, biotechnology techniques, 9(1):19-24. [21] couteau d, mathaly p. (1998) fixed-bed purification of ferulic acid from sugar-beet pulp using activated carbon: optimization studies, bioresource technology, 64(1):17-25. [22] singh ts, pant kk. (2006) experimental and modelling studies on fixed bed adsorption of as(iii) ions from aqueous solution, separation and purification technology, 48(3):288-296. [23] adak a, bandyopadhyay m, pal a. (2006) fixed bed column study for the removal of crystal violet (c. i. basic violet 3) dye from aquatic environment by surfactant-modified alumina, dyes and pigments, 69(3):245-251. [24] samah ra, zainol n, yee pl, pawing cm, abd-aziz s. (2013) adsorption of vanillin using macroporous resin h103, adsorption science & technology, 31(7):599-610. [25] lee e-g, yoon s-h, das a, lee s-h, li c, kim j-y, choi m-s, oh d-k, kim s-w. (2009) directing vanillin production from ferulic acid by increased acetyl-coa consumption in recombinant escherichia coli, biotechnology and bioengineering, 102(1):200-208. [26] goyal m, dhawan r, bhagat m. (2010) adsorption of gallic acid from aqueous solution using fixed bed activated carbon columns, separation science and technology, 45(9):12651274. [27] zhang qf, jiang zt, gao hj, li r. (2008) recovery of vanillin from aqueous solutions using macroporous adsorption resins, european food research and technology, 226(3):377-383. [28] huesgen ag. (2011) analysis of natural and artificial vanilla preparations, agilent application note, pp. 1-12. [29] eckenfelder ww. (2000) industrial water pollution control, mcgraw-hill, new york. [30] belter pa, cussler el, hu ws. (1988) bioseparations: downstream processing for biotechnology, wiley, new york. [31] seader jd, henley ej, roper dk. (2010) separation process principles, john wiley & sons, new jersey. [32] chen n, zhang z, feng c, li m, chen r, sugiura n. (2011) investigations on the batch and fixed-bed column performance of fluoride adsorption by kanuma mud, desalination, 268(13):76-82. [33] dutta m, basu jk, faraz h, gautam n, kumar a. (2012) fixed bed column study of textile dye, direct blue 86 by using a composite adsorbent, archives of applied science research, 4(2):882-891. [34] bohart gs, adams eq. (1920) some aspects of the behavior of charcoal with respect to chlorine, journal of the american chemical society, 42(3):523-544. [35] kiran b, kaushik a. (2008) cyanobacterial biosorption of cr(vi): application of two parameter and bohart adams models for batch and column studies, chemical engineering journal, 144(3):391-399. [36] ko dck, porter jf, mckay g. (2000) optimised correlations for the fixed-bed adsorption of metal ions on bone char, chemical engineering science, 55(23):5819-5829. [37] chu kh, kim ey, feng x. (2011) batch kinetics of metal biosorption: application of the bohart-adams rate law, separation science and technology, 46(10):1591-1601. iium engineering journal, vol. 18, no. 2, 2017 samah et al. 104 [38] chu kh. (2004) improved fixed bed models for metal biosorption, chemical engineering journal, 97(2-3):233-239. [39] volesky b, prasetyo i. (1994) cadmium removal in a biosorption column, biotechnology and bioengineering, 43(11):1010-1015. [40] brady jm, tobin jm, roux j-c. (1999) continuous fixed bed biosorption of cu2+ ions: application of a simple two parameter mathematical model, journal of chemical technology & biotechnology, 74(1):71-77. iium engineering journal, vol. 16, no. 1, 2015 kumar and kumar 33 existence of solutions of fractional integrodifferential system with nonlocal conditions kamalendra kumar1 and rakesh kumar2 1department of mathematics, s r m s college of engineering and technology, bareilly-243001, india. 2department of mathematics, hindu college, moradabad-244001, india. kamlendra.14kumar@gmail.com; rakeshainil@gmail.com (received 6 may 2014; accepted 25 february 2015; published on line 29 may 2015) abstract:in the present paper we prove the existence and uniqueness of local solutions of a nonlocal cauchy problem for a class of fractional integrodifferential equation. the results are obtained by using the theory of resolvent operators, the fractional powers of operators, fixed point techniques, and the gelfand-shilov principle. abstrak:menerusi kertas kerja ini, kehadiran dan keunikan penyelesaian lokal terhadap permasalahan tak setempat cauchy untuk peringkat pecahan persamaan integrodifferential dibuktikan. keputusan diperolehi menggunakan teori operator leraian, operator kuasa pecahan, teknik titik tetap dan prinsip gelfand-shilov. keywords: fractional integrodifferential equation; nonlocal conditions; fractional powers; mild and classical solutions; resolvent operators 1. introduction the purpose of this paper is to prove the existence and uniqueness of local solutions for nonlocal fractional integrodifferential equations of the form: ( ) + ( ) ( ) = , ( ) + ℎ , , ( ), , , ( ) , (1.1) (0) + ( ) = , (1.2) in a banach space , where 0 < ≤ 1, ≥ 0. let = [0, ]. we assume that − ( ) is a closed linear operator defined on a dense domain ( ) in into such that ( ) is independent of . it is considered also that − ( ) generates an evolution operator in the banach space . let : × into , ℎ: × × × into , : × × into and : ( , ) → ( ) be given nonlinear operators. the differential equations involving fractional derivative in time have recently been proved to be valuable tools in the modeling of many phenomena in various fields of engineering, physics, economy and science. indeed, we can find numerous applications in viscoelasticity, electrochemistry, porous media, electromagnetic etc. (see [1-6]). they involve a wide area of applications by bringing into a broader paradigm concepts of physics and mathematics [7-9]. hence, fractional differential equations have become an object of extensive study during recent years as cited in [10-14] and references therein. iium engineering journal, vol. 16, no. 1, 2015 kumar and kumar 34 on the other hand, integrodifferential equations arise in many fields such as electronic, fluid dynamics, biological models and chemical kinetics. the equations of basic electric circuit analysis are well-known examples of these equations. hence, the study of integrodifferential equation is very important. fractional integrodifferential equations have been studied by many authors [8, 15-18]. fractional integro-differential equations arise in many fields of engineering such as optimal control problem and heat conduction of materials with memory, etc. the nonlocal condition, which is a generalization of the classical initial condition, was motivated by physical problems. the problem of existence of solutions of evolution equation with nonlocal conditions in banach space was first studied by byszewski [19]. as indicated in [19, 20] and the references therein, the nonlocal condition (0) + ( ) = can be applied in physics with better effect than the classical condition (0) = . in the present paper we have generalized the results given by pazy [21], balachandran and chandrasekaran [22] and debbouche [23]. the rest of this paper is organized as follows: in section 2, we give preliminary results and in section 3, we prove the results of existence and uniqueness of local solutions for the equations (1.1) − (1.2). 2. preliminaries in this section, we introduce some notations, definitions and results about fractional calculus and resolvent operators. following gelfand and shilov [24], we define the fractional integral of order > 0 as ( ) = 1 γ( ) ( − ) ( ) , and also, the fractional derivative of the function of order 0 < < 1 ta d  ( ) = ( ) ∫ ( )( − ) , where is an abstract continuous function on the interval [ , ] and γ( ) is the gamma function, see [25]. definition 2.1: by a solution of (1.1) − (1.2), we mean a function with values in such that: (1) is continuous function on and ( ) ∈ ( ), (2) exists and is continuous on (0, ), 0 < < 1, and satisfies (1.1) on (0, )and the nonlocal condition (1.2). definition 2.2: (see [26]) a resolvent operator for problem (1.1) − (1.2) is a bounded operator-valued function ( , ) ∈ ( ), 0 ≤ ≤ ≤ , having the following properties: (a) ( , ) is strongly continuous in and , ( , ) = , the identity operator on , 0 ≤ ≤ , and ‖ ( , )‖ ≤ ( ) for some constants and . (b) ( , ) ⊂ , ( , ) is strongly continuous in and on , and is the banach space formed from ( ), the domain − ( ), endowed with the graph norm. (c) for every ∈ , ( , ) is continuously differentiable in ∈ and iium engineering journal, vol. 16, no. 1, 2015 kumar and kumar 35 ( , ) = ( , ) ( ) . (d) for every ∈ , and ∈ , ( , ) is continuously differentiable in ∈ and ( , ) = − ( ) ( , ) , with ( , ) and ( , ) are strongly continuous on 0 ≤ ≤ ≤ . here, ( , ) can be deduced from the evolution operator of the generator − ( ). the resolvent operator is similar to the evolution operator for non-autonomous differential equations in banach space. it will not, however, be an evolution operator because it will not satisfy an evolution or semigroup property. because a number of results follow directly from the definition of resolvent operator. definition 2.3: a continuous solution : → is said to be a mild solution of problem (1.1) − (1.2) on if for all ∈ , it satisfies the following integral equation ( ) = ( , 0)[ − ( )] + 1 γ( ) ( − ) ( , ) , ( ) + ℎ , , ( ), , , ( ) . (2.1) we define the fractional power ( ) by ( ) = 1 γ( ) ( , ) , > 0. for 0 < ≤ 1, ( ) is a closed linear operator whose domain ( ) ⊃ ( ) is dense in . the closedness of implies that ( ), endowed with the graph norm of , ‖ ‖ ( ) = ‖ ‖ + ‖ ‖, ∈ ( ), is a banach space. since 0 ∈ ( ), is invertible. its graph norm |‖. ‖| is equivalent to the norm‖ ‖ = ‖ ‖. thus ( ) equipped with the norm ‖. ‖ is a banach space, which we denote by . 3. existence theorem to prove the main results we state the following lemma: lemma 3.1: (see [21, section 2.6]) let ( ) be the infinitesimal generator of a resolvent operator ( , ). we denote by [ ( )] the resolvent set of ( ). if 0 ∈ [ ( )], then (a) ( , ): → ( ) for every 0 ≤ ≤ ≤ and ≥ 0, (b) for every ∈ ( ), we have ( , ) ( ) = ( ) ( , ) , (c) the operator ( , ) is bounded and‖ ( , )‖ ≤ , ( − ) . theorem 1.1: assume that (a) − ( ) is the infinitesimal generator of a resolvent operator ( , ), 0 ≤ ≤ ≤ , in . (b) 0 ∈ [− ( )], the resolvent set. (c) for ≥ 0, the fractional power satisfies ‖ ( , )‖ ≤ , ( − ) for 0 ≤ ≤ ≤ , where , is a real constant. iium engineering journal, vol. 16, no. 1, 2015 kumar and kumar 36 (d) for an open subset of × , : → satisfies the condition, if for every ( , ) ∈ there is a neighborhood ⊂ and constants ≥ 0, 0 < ≤ 1, such that ‖ ( , ) − ( , )‖ ≤ | − | + ‖ − ‖ (3.1) for all ( , ) ∈ , = 1, 2. (e) for an open subset q of × × × , ℎ: → satisfies the condition, if for every ( , , , ) ∈ there is a neighborhood ⊂ and constants ≥ 0,0 < ≤ 1, such that ‖ℎ( , , , ) − ℎ( , , , )‖ ≤ | − | + | − | +‖ − ‖ +‖ − ‖ (3.2) for all ( , , , ) ∈ , = 1, 2. (f) for an open subset r of × × , : → satisfies the condition, if for every ( , , ) ∈ there is a neighborhood ⊂ and constants ≥ 0,0 < ≤ 1, such that ‖ ( , , ) − ( , , )‖ ≤ | − | + | − | +‖ − ‖ (3.3) for all ( , , ) ∈ , = 1, 2. (g) : → is continuous and there exists a number such that ‖ ( , 0)‖ < and ‖ ( ) − ( )‖ ≤ ‖ − ‖ (3.4) for all , ∈ . note that if ∈ , then ∈ . then the problem (1.1) – (1.2) has a unique local solution ∈ ([0, ): ) ∩ (0, ): . proof: choose ∗ > 0 and > 0 such that estimates (3.1) – (3.4) hold on the sets = {( , ): 0 ≤ ≤ ∗, ‖ − ‖ ≤ }, = {( , , , ): 0 ≤ , ≤ ∗, ‖ − ‖ ≤ , ‖ − ‖ ≤ }, and = {( , , ): 0 ≤ , ≤ ∗, ‖ − ‖ ≤ }, respectively. let = max ‖ ( , )‖ and = max , ∗ ℎ , , , ( , , ) set = sup ∈ ‖ ( )‖ and choose such that for 0 ≤ < , ‖ ( , 0) − ‖ ‖ ‖ + ≤ 2 , 0 ≤ < and 0 < < ∗, 2 , γ( )( − )( + + + + ) (3.5) let = (0, ]: be endowed with the supremum norm ‖ ‖ = sup ‖ ( )‖ , ∈ . iium engineering journal, vol. 16, no. 1, 2015 kumar and kumar 37 then be a banach space. define a map : → ( ) = ( , 0) [ − ( )] + 1 γ( ) ( − ) ( , ) , ( ) + 1 γ( ) ( − ) ( , ) ℎ , , ( ), , , ( ) . (3.6) obviously, (0) = [ − ( )]. let be the nonempty closed and bounded subset of defined by = { : ∈ , (0) = [ − ( )], ‖ ( ) − [ − ( )]‖ ≤ }. for ∈ , we have ‖ ( ) − [ − ( )]‖ ≤ ‖ ( , 0) − ‖‖ [ − ( )]‖ + 1 γ( ) ( − ) ‖ ( , )‖ , ( ) − ( , ) + 1 γ( ) ( − ) ‖ ( , )‖‖ ( , )‖ + 1 γ( ) ( − ) ‖ ( , )‖ ℎ , , ( ), , , ( ) − ℎ , , , ( , , ) + 1 γ( ) ( − ) ‖ ( , )‖ ℎ , , , ( , , ) ≤ 2 + , γ( ) ( − ) ( + ) + , γ( ) ( − ) { ( + ) } + , γ( ) ( − ) ≤ 2 + , γ( ) ( − ) [ + + + + ] ≤ 2 + 2 = . therefore, maps into itself. moreover, if , ∈ , then ‖ ( ) − ( )‖ ≤ ‖ ( , 0)‖‖ ( ) − ( )‖ + 1 γ( ) ( − ) ‖ ( , )‖ , ( ) − , ( ) + 1 γ( ) ( − ) ‖ ( , )‖ ℎ , , ( ), , , ( ) − ℎ , , ( ), , , ( ) iium engineering journal, vol. 16, no. 1, 2015 kumar and kumar 38 ≤ ‖ ( , 0)‖‖ − ‖ + 1 γ( ) , ( − ) ‖ − ‖ + 1 γ( ) , ( − ) [(‖ − ‖ + ‖ − ‖ ) ] ≤ ‖ ( , 0)‖‖ − ‖ + 1 γ( ) , ( − ) [ + (1 + ) ]‖ − ‖ ≤ 1 2 ‖ − ‖ + 1 2 ‖ − ‖ , which implies that‖ − ‖ ≤ ‖ − ‖ + ‖ − ‖ . by the contraction mapping theorem, mapping has a unique fixed point ∈ . this fixed point satisfies the integral equation ( ) = ( , 0) [ − ( )] + 1 γ( ) ( − ) ( , ) , ( ) + 1 γ( ) ( − ) ( , ) ℎ , , ( ), , , ( ) . (3.7) from (3.1), (3.2) and the continuity of it follow that → , ( ) and → ℎ , , ( ), , , ( ) are continuous on [0, ], and, hence, there exist constants and such that , ( ) ≤ (3.8) and ℎ , , ( ), , , ( ) ≤ (3.9) by using the same method as in [20, theorem 3.2], we can prove that ( ) is locally h ̈lder continuous on(0, ]. then there exist a constant such that for every > 0, we have ‖ ( ) − ( )‖ ≤ | − | , for all 0 ≤ ≤ , ≤ . the local h ̈lder continuity of → , ( ) follows from , ( ) − , ( ) ≤ | − | + ‖ ( ) − ( )‖ ≤ | − | + | − | for some > 0 and the local h ̈lder continuity of → ℎ , , ( ), , , ( ) follows from iium engineering journal, vol. 16, no. 1, 2015 kumar and kumar 39 ℎ , , ( ), , , ( ) − ℎ , , ( ), , , (ϕ) ≤ | − | + ‖ ( ) − ( )‖ + | − | + | − | + ‖ ( ) − ( )‖ ≤ | − | + | − | + | − | + | − | + | − | for some > 0. let be a solution of (3.7). consider the inhomogeneous initial value problem ( ) + ( ) ( ) = , ( ) + ℎ , , ( ), , , ( ) (3.10) (0) + ( ) = (3.11) this problem has a unique solution ∈ (0, ]: [21], which is given by ( ) = ( , 0)[ − ( )] + 1 γ( ) ( − ) ( , ) , ( ) + 1 γ( ) ( − ) ( , ) ℎ , , ( ), , , ( ) . (3.12) for > 0, each term of (3.12) belongs to ( ) and a fortiori in ( ). operating on both sides of (3.12) with we find that ( ) = ( , 0) [ − ( )] + 1 γ( ) ( − ) ( , ) , ( ) + 1 γ( ) ( − ) ( , ) ℎ , , ( ), , , ( ) . (3.13) from (3.7) the right hand side of (3.13) equals y(t) and therefore u(t) = a y(t) and by (3.12), u is a c (0, t]: x solution of (1.1) − (1.2). the uniqueness of u follows from the uniqueness of the solutions of (3.7) and (3.10) − (3.11). hence, the theorem is proved. 4. conclusion in this paper, the existence and uniqueness of mild and classical solutions for the nonlinear fractional integrodifferential equation with nonlocal condition are discussed. we applied the resolvant operators, the fractional powers of operaters, fixed point technique and gelfand-shilov principle to establish the existence results. the results presented in this paper may be useful in the field of engineering and physics. acknowledgement the authors wish to thank the referees for their valuable comments and suggestions. iium engineering journal, vol. 16, no. 1, 2015 kumar and kumar 40 references [1] mainardi f. (1997) fractional calculus: some basic problems in continuum and statistical mechanics, in fractals and fractional calculus in continuum mechanics, carpinteri a,mainardi f, eds.), springer-verlag, wien, pp. 291-348. [2] metzler f, schick w, kilan hg, nonnenmacher tf. (1995) relaxation in filled polymers: a fractional calculus approach. journal of chemical physics, 103:7180-7186. [3] diethelm k, freed ad. (1999) on the solution of nonlinear fractional order differential equations used in the modeling of viscoelasiticity, scientific computing in chemical engineering iicomputational fluid dynamics, reaction engineering and molecular properties (keil f, mackens w, voss h, werther j., eds) springer-verlag, heidelberg, pp. 217-224. [4] gaul l, klien p,kempfle s. (1991) damping description involving fractional operators. mechanical systems and signal processing, 5:81-88. [5] hilfer r. (2000) application of fractional calculus in physics, world scientific, singapore. [6] glocklewg, nonnenmacher tf. (1995) a fractional calculus approach of self-similar protein dynamics. biophysical journal, 68:46-53. [7] baleanu d, trujillo jj. (2010) a new method of finding the fractional euler-lagrange and hamilton equations within caputo fractional derivatives. commun. nonlinear sci. numer. simul., 15(5):1111-1115. [8] balachandran k, trujillo jj. (2010) the nonlocal cauchy problem for nonlinear fractional integro-differential equations in banach spaces. nonlinear analysis: theory, methods and applications, 72:4587-4593. [9] agrawal rp, lakshmikantham v, nieto jj. (2010) on the concept of solution for fractional differential equations with uncertainty. nonlinear anal., 72:2859-2862. [10] li f. (2010) mild solutions for fractional differential equations with nonlocal conditions. adv. difference equations, article id 287861, 9 pages. [11] mophou gm, guerekata gmn. (2009) mild solutions for semilinear fractional differential equations. electron. j. differential equations, 21:1-9. [12] el-borai mm. (2002) some probability densities and fundamental solutions of fractional evolutions equations. chaos, solutions and fractals, 14(3):433-440. [13] el-borai mm. (2005) on some fractional evolution equations with nonlocal conditions. int. j. pure appl. math.,24(3):405-413. [14] el-borai mm. (2004) semigroups and some nonlinear fractional differential equations. appl. math. comput.,149(3):823-831. [15] li f, guerekata gmn. (2010) existence and uniqueness of mild solution for fractional integro-differential equations. adv. difference equations, doi: 1155/2010/158789 (available on line). [16] ahmed hm. (2009) semilinear differential equations of fractional order with nonlocal conditions. int. j. of appl. math. mech., 5(3):69-74. [17] bragdi m, hazi m. (2010) existence and controllability result for an evolution fractional integro-differential system. int. j. contemp. math. sciences, 5(19):901-910. [18] el-borai mm, debbouche a. (2009) on some fractional integro-differential equations with analytic semigroups. int. j. contemp. math. sciences, 4(28):1361-1371. [19] byszewski l. (1991) theorems about the existence and uniqueness of solutions of a semilinear evolution nonlocal cauchy problem. j. math. anal. appl., 162:494-505. [20] deng k. (1993) exponential decay of solutions of semilinear parabolic equations with nonlocal conditions. j. math. anal. appl., 179:630-637. [21] pazy a. (1983) semigroups of linear operators and applications to partial differential equations, springer-verlag, new york, 1983. [22] balachandran k, chandrasekaran m. (1997) existence of solutions of nonlinear integrodifferential equation with nonlocal condition. journal of applied mathematics and statistics analysis, 10(3):279-288. [23] debbouche a. (2010) fractional evolution integro-differential systems with nonlocal conditions. advances in dynamical systems and applications,5:49-60. iium engineering journal, vol. 16, no. 1, 2015 kumar and kumar 41 [24] gelfand im, shilov ge. (1959) generalized functions. vol. 1, moscow, nauka. [25] debbouche a, el-borai mm. (2009) weak almost periodic and optimal mild solutions of fractional evolution equations. electron. j. differential equations, 46:1-8. [26] tidke hl, dhakne mb. (2011) existence of solutions and controllability of nonlinear mixed integrodifferential equation with nonlocal condition. applied mathematics e-notes, 11:1222. ams subject classification: 34g20, 34k05, 26a33, 35b65, 35a07. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 multicriteria decision making on supplier selection using soccer model integrated with analytical hierarchy process muataz al hazza1*, azura dapit2, islam faisal bourini3, zubaidah muataz2 and mohammad yeakub ali4 1 mechanical and industrial engineering, school of engineering, american university of ras al khaimah, road ras al khaimah, ras al khaimah, uae 2 department of manufacturing and materials engineering, international islamic university malaysia, jalan gombak, 53100 selangor, malaysia 3 dubai business school, university of dubai, dubai, uae 4 mechanical engineering programme area, faculty of engineering, universiti teknologi brunei, bandar seri begawan be1410, brunei darussalam * corresponding author: muataz.alhazza@aurak.ac.ae (received: 8 march 2023; accepted: 18 may 2023; published on-line: 4 july 2023) abstract: supplier evaluation and selection are key components in the supply chain because supplier performance directly affects the supply chain's efficiency. therefore, companies should think strategically when they need to select their suppliers. thus, selecting and evaluating new suppliers is essential in shaping the supply chain's smoothness and efficiency. selecting suppliers is a complex issue as it involves many factors and decisions to be considered and needs to be assessed with an auditing process. however, a supplier audit is an expensive way to evaluate supplier capability. this research aims to propose a supplier selection model for a corrugated carton manufacturing company. the soccer model, developed by steve rogers, was used as the supplier selection criteria. analytical hierarchy process (ahp) was used in the supplier selection. a face-to-face interview method was used in collecting data. the results show that the cost structure is the ultimate concern on supplier selection which bears 44.2% of the soccer model, followed by operational capability (23%), customer approach (13.5%), economic performance (8.3%), strategic direction (6.9%), and lastly research and development (4.1%). the percentages inform the company how much attention they need to pay when evaluating and selecting a new supplier. abstrak: penilaian dan pemilihan pembekal adalah kunci utama dalam rantaian bekalan kerana prestasi pembekal secara langsung melibatkan kecekapan rantaian bekalan. oleh itu, syarikat perlu memikirkan secara strategik apabila ingin memilih pembekal. dengan demikian, pemilihan dan penilaian pembekal baru adalah penting dalam pembentukan kelancaran rantaian bekalan dan kecekapan. pemilihan pembekal adalah isu kompleks kerana ianya melibatkan banyak faktor dan keputusan perlu difikirkan dan perlu dinilai bersama proses audit. namun, audit pembekal adalah mahal bagi menilai kemampuan pembekal. kajian ini mencadangkan model pemilihan pembekal bagi syarikat pembekal kotak karton. model soccer dicipta oleh steve rogers, telah digunakan sebagai kritia pemilihan pembekal. proses hirarki analitikal (ahp) digunakan dalam pemilihan pembekal. kaedah temuduga bersemuka digunakan dalam pengumpulan data. dapatan kajian menunjukkan struktur harga adalah kehendak utama dalam pemilihan pembekal iaitu 44.2% daripada model soccer, diikuti kemampuan operasi (23%), pendekatan pelanggan (13.5%), prestasi ekonomi (8.3%), misi strategik (6.9 %), dan 239 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 akhirnya penyelidikan dan pembangunan (4.1%). peratusan ini berguna untuk syarikat dalam memberi keutamaan dalam penilaian dan pemilihan pembekal baru. keywords: supplier selection; ahp; mcdm; soccer 1. introduction today, with a rapidly changing world and markets, companies face a vital challenge to stay competitive [1]. markets nowadays are witnessing major changes due to the global nature of trade and rapid technological development that leads to aggressive competition between manufacturers. this rapid technological advancement changed supply chain work and made it easier to communicate and faster to deliver goods. as a result, manufacturers have realized that suppliers’ performance is one of the main and important factors to survive in the market. capable suppliers are essential to ensure the supply chain runs smoothly and efficiently. thus, establishing a strong relationship and partnering with suppliers will result in a win-win situation where both parties would gain advantages through this relationship. however, supplier selection is complex as it should consider many factors [2]. researchers spend most of their time finding and determining the best supplier selection criteria, resulting in many approaches and checklist assessments [3]. each company may have different selection criteria as they have their own goals, needs, and industry types. selecting the best supplier is a complex and challenging procedure. therefore, choosing the best method has become one of the main success factors for manufacturers and thus, multicriteria decision-making methods (mcdm) will be useful and effective. 2. literature review mcdm methodology is a decision-support framework that can consider multiple inconsistent criteria [4]. it is a method in which different criteria are traded off to achieve the best alternative. it includes quantitative and qualitative factors, which are considered complex decision-making tools, making it the most widely used and favorable decision methodology in many fields [5]. different mcdm techniques employ different approaches. throughout their analysis research, velasquez and hester [6] identified eleven different mcdm. however, supplier selection is a complex critical problem that must trade off various conflicting criteria such as price, quality, and delivery time. these methods have been used and applied by different researchers in supplier selection such as multi-attribute utility theory [8], analytic hierarchy process (ahp) [7], fuzzy set theory [9], casebased reasoning [10], data envelopment analysis [11], goal programming [12], electre method [13], simple additive weighing [14], and fuzzy topsis technique [15]. other researchers prefer integrating two methods or techniques to have better and more effective decisions as an efficient approach [16-20]. many researchers [21-22] claim that merging ahp with one of the intelligent methods such as fuzzy set theory is favorable in decision making on the selection of suppliers due to high uncertainty in this decision-making process. however, each multicriteria technique has its advantages and disadvantages. thus, integrating several techniques is common in multicriteria decision-making to overcome deficiencies [6]. one of the most specific multicriteria frameworks in supplier selections is the soccer model [3]. the acronym represents the six main criteria, sstrategic direction, o operational capability, ccustomer approach, ccost structure, eeconomic performance and r-research & development. rogers, in his book [3], explained that the supplier assessment is needed to make sure that the supplier can handle the orders. 240 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 therefore, the soccer model is simply one of the most effective checklists when auditing suppliers. ho et al. [23] have reviewed the literature of the mcdm approaches for supplier selection in the international journals from 2000 to 2008. however, in this research, the integration between ahp as one of the effective tools in multicriteria methods with soccer model as one of the effective checklists in suppliers' selection auditing was implemented. 2.1 analytical hierarchical process thomas saaty introduced the analytical hierarchical process (ahp) in 1970 [24-25]. ahp is a structured method for dealing with complex decision-making. it aids the decisionmaker in setting priorities and making the best decision. it derives relative priorities on absolute scales (invariant under the identity transformation) from discrete and continuous paired comparisons in multilevel hierarchical structures [26]. ahp is a method that merges a decision's subjective and objective characteristics. the ahp considers a group of evaluation criteria and different options, among which the most effective decision will be created. first, the ahp generates a weight for every evaluation criterion according to the decision-makers pairwise comparisons of the factors. the higher weight, the more essential is the corresponding criterion. next, the ahp assigns a score to every possibility for a set criterion according to the decision maker's pairwise comparisons of the choices based on that criterion. the higher the score, the better the performance of choice concerning the considered criterion. finally, the ahp combines the criteria weights and the choices’ scores, determining a global score for every option and a consequent ranking. the global score for a given possibility is a weighted total of the scores it obtained concerning all the criteria. sipahi and timor [27] presented a comprehensive review of applications of ahp method and anp from 2005 to 2009. the paper additionally contains fuzzy ahp and fuzzy anp applications. ishizaka and labib [28] presented a theoretically-view of the ahp articles instead of classifying them by application areas. their paper mentioned problem modeling, pairwise comparisons, judgment scales, derivation techniques, consistency indices, incomplete matrix, synthesis of the weights, sensitivity analysis, and group decision problems. subramanian and ramanathan [29] reviewed and methodologically analyzed applications of ahp in operations management from 1990 to 2009. they classified 291 application research of ahp into operations strategy, process, and product style, designing and planning resources, project management, and managing the supply chain. ahp-primarily based techniques for supplier analysis were studied by bruno et al. [30]. their study underlined that the weak and strong points are rising from applying the ahp in a greater supply chain. 2.2 soccer model the soccer model was developed by rogers [3] to focus on the main factors in any supplier selection and what is needed for supplier analysis. the acronym represents the six main criteria, sstrategic direction, ooperational capability, ccustomer approach, c cost structure, eeconomic performance and r-research & development. each of the criteria has five sub-criteria, as shown in fig. 1. finally, after a sweeping review of the current literature in the area, it was identified that various investigators used diverse criteria and different methods. in this research, the integration between the soccer model developed by steve c. rogers and the analytical 241 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 hierarchy process (ahp) will add value to the area of knowledge and will reduce the risk of selecting an inappropriate supplier. ahp aids in developing a relative weighting and prioritizing the different criteria based on the organization's objectives. this integration considers the advantages of using a powerful qualitative method presented by the ahp method that focuses on the pairwise comparisons for every two main criteria and strengthens it by using a well-established framework that considers six main dimensions: strategic direction, operational capability, customer approach, cost structure, economic performance, and research & development. each of those dimensions has a sub-criteria that covers all the possible factors. fig. 1: supplier analysis factors [3]. 3. research methodology in this research, the integration between ahp with soccer framework was implemented. the advantage of using the ahp method is that it focuses on pairwise comparisons for every two main criteria. to enhance the output of using the ahp method and strengthens it by using a well-established detailed framework that considers six main dimensions: strategic direction, operational capability, customer approach, cost structure, economic performance, and research & development. each of those dimensions has a sub-criteria that covers all the possible factors. a sequential feedback loop is summarized in fig. 2. the main steps of the research can be concluded in the following steps: 1. analyze the suitability of using the soccer framework 2. integrate the framework with the ahp method 3. select the internal expertise in supplier selection for the company: quality assurance, customer service, and purchasing 4. design the interview framework: interview questions were designed to utilize the pairwise matrix. 5. creating the pairwise matrix based on the interview results. 6. test the consistency by avoiding bias due to the area of the expertise 7. develop a conceptual framework the consistency was determined using the followings steps [9,30]: 1. calculating the consistency index ci, using eq, (1), where n is the number of criteria in the comparison. ci =(max eigenvaluen)/(n-1) (1) 242 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 2. dividing its value by the random consistency index, which is stated by saaty depending on the value of n. the results are shown in table 14. 3. calculating the consistency ratio (cr) value using equation (2) where the value below 10% is considered consistent. cr=ci/ri<0.1~10% (2) where ci is the consistency index, cr is the consistency ratio, and ri is the random consistency index fig. 2: research methodology flow chart. 4. results supplier selection is a complex issue involving many factors and decisions due to the difficulties of trading off financial and performance evaluation. the data were gathered through interview sessions using the criteria based on the soccer model. the relative "priority" given to each element in the hierarchy is determined by comparing pairwise using the ahp method. the criteria ranking is decided through pairwise comparisons, and the preference scale ranking the hierarchy. an industrial company was selected to implement soccer and ahp. the representatives from three different departments: quality assurance, customer service, and purchasing, were interviewed through a comprehensive individual interview session designed in order to fit for pairwise comparison. the results were concluded based on the soccer model. the results were analyzed based on two steps: step 1: developing a decision matrix of the soccer model for the main factors for each interviewee. the results are shown in tables 1, 2, and 3. the results show an agreement on the cost structure with the higher priority of 0.45, 0.42, and 0.44 for the quality assurance, customer service, and purchasing departments. moreover, all the experts show agreement that the second essential criterion is the operational capability with the values of 0.27, 0.27, and 0,23. 243 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 table 1: decision matrix of soccer model by quality assurance strategic direction operational capability customer approach cost structure economic performance r&d priority vector strategic direction 1 1/7 1/4 1/8 3 3 0.060 operational capability 7 1 3 1/3 6 7 0.270 customer approach 4 1/3 1 1/5 5 6 0.150 cost structure 8 3 5 1 9 6 0.450 economic performance 1/3 1/6 1/5 1/9 1 1/3 0.030 r & d 1/3 1/7 1/6 1/6 3 1 0.040 ci = 0.1116, ri = 1.24, cr = 0.09 < 0.1 ok table 2: decision matrix of soccer model by customer services strategic direction operational capability customer approach cost structure economic performance r&d priority vector strategic direction 1 1/6 1/5 1/8 ½ 2 0.050 operational capability 6 1 3 1/2 4 5 0.270 customer approach 5 1/3 1 1/4 2 4 0.140 cost structure 8 2 4 1 5 8 0.420 economic performance 2 1/4 1/2 1/5 1 2 0.080 r & d ½ 1/5 1/4 1/8 1/2 1 0.040 ci = 0.0372, ri = 1.24, cr = 0.03 < 0.1 ok table 3: decision matrix of soccer model by purchasing strategic direction operational capability customer approach cost structure economic performance r&d priority vector strategic direction 1 1/5 1/3 1/6 1 3 0.070 operational capability 5 1 3 1/4 2 5 0.230 customer approach 3 1/3 1 1/3 2 3 0.140 cost structure 6 4 3 1 4 7 0.440 economic performance 1 1/2 1/2 1/4 1 2 0.090 r & d 1/3 1/5 1/3 1/7 1/2 1 0.040 ci = 0.0868, ri = 1.24, cr = 0.07 < 0.1 ok 244 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 step 2: developing a decision matrix of the soccer model for each interviewee for each sub criterion. tables 4, 5, 6, 7, 8, and 9 show the decision matrix for quality assurance. table 4: decision matrix of strategic direction by quality assurance strategic direction management approach business structure corporate strategy corporate governance management team priority vector management approach 1 1/5 1/3 5 1/6 0.070 business structure 5 1 4 7 1 0.360 corporate strategy 3 1/4 1 6 1/6 0.130 corporate governance 1/5 1/7 1/6 1 1/8 0.030 management team 6 1 6 8 1 0.410 ci = 0.0784, ri = 1.12, cr = 0.07 < 0.1 ok table 5: decision matrix of operational capability by quality assurance operational capability product quality human resource admin systems logistical capability information technology priority vector product quality 1 1/5 1/3 5 1/6 0.070 human resources 5 1 4 7 1 0.360 admin systems 3 1/4 1 6 1/6 0.130 logistical capability 1/5 1/7 1/6 1 1/8 0.030 information technology 6 1 6 8 1 0.410 ci = 0.1008, ri = 1.12, cr = 0.09 < 0.1 ok table 6: decision matrix of customer approach by quality assurance. customer approach key customers market position customer relations customer approach external relations priority vector key customers 1 9 1/2 2 6 0.330 market position 1/9 1 1/6 1/4 1/3 0.040 customer relation 2 6 1 1 5 0.340 customer approach 1/2 4 1 1 4 0.220 external relation 1/6 3 1/5 1/4 1 0.070 ci = 0.0784, ri = 1.12, cr = 0.07 < 0.1 ok. 245 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 table 7: decision matrix of cost structure by quality assurance cost structure wage base overhead costs supply base cost product cost delivery cost priority vector wage base 1 1/3 1/2 1/8 1/7 0.040 overhead costs 3 1 3 1/5 1/4 0.110 supply base cost 2 1/3 1 1/7 1/6 0.060 product cost 8 5 7 1 4 0.520 delivery cost 7 4 6 1/4 1 0.270 ci = 0.1008, ri = 1.12, cr = 0.09 < 0.1 ok table 8: decision matrix of economic performance by quality assurance economic performance profit level profit centers financial structure risk exposure cash flow priority vector profit level 1 1/2 1/6 1/3 1/4 0.050 profit centers 2 1 1/7 1/2 1/5 0.070 financial structure 6 7 1 4 3 0.500 risk exposure 3 2 1/4 1 1/2 0.140 cash flow 4 5 1/3 2 1 0.240 ci = 0.0336 ri = 1.12, cr = 0.03 < 0.1 ok. table 9: decision matrix of research & development by quality assurance research & development core competency research competency process scaleup project management intellectual property priority vector core competency 1 4 7 1/4 1/2 0.180 research competency 1/4 1 3 1/9 1/5 0.060 process scaleup 1/7 1/3 1 1/6 1/3 0.040 project management 4 9 6 1 2 0.470 intellectual property 2 5 3 1/2 1 0.240 ci = 0.0784, ri = 1.12, cr = 0.07 < 0.1 ok the results are concluded in table 10. the priority vector of strategic direction, operational capability, customer approach, cost structure, economic performance, and r & d were management team, product quality, customer relation, product cost, financial structure, and project management were 0.41,0.41, 0.43, 0.52, 0.50, and 0.74, respectively. the soccer model overall weight by the quality assurance is concluded in table 10. the quality assurance preferred cost structure (45%), followed by operational capability (27%), customer approach (15%), strategic direction (6%), research & development (4%), and economic performance (3%). 246 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 table 10: results of soccer model (quality assurance) factor item priority vector (%) sub-criteria weight according to main-criteria weight (%) strategic direction (6%) management approach 7.00 0.42 business structure 36.00 2.16 corporate strategy 13.00 0.78 corporate governance 3.00 0.18 management team 41.00 2.46 operational capability (27%) product quality 38.00 10.26 human resources 5.00 1.35 admin systems 25.00 6.75 logistical capability 26.00 7.02 information technology 6.00 1.62 customer approach (15%) key customers 33.00 4.95 market position 4.00 0.60 customer relations 34.00 5.10 customer approach 22.00 3.30 external relations 7.00 1.05 cost structure (45%) wage base 4.00 1.80 overhead costs 11.00 4.95 supply base cost 6.00 2.70 product cost 52.00 23.40 delivery cost 27.00 12.15 economic performance (3%) profit level 5.00 0.15 profit centres 7.00 0.21 financial structure 50.00 1.50 risk exposure 14.00 0.42 cash flow 24.00 0.72 research & development (4%) core competency 18.00 0.72 research competency 6.00 0.24 process scale-up 4.00 0.16 project management 47.00 1.88 intellectual property 24.00 0.96 the decision matrices for each main criteria for the customer service are shown in tables 11,12, 13, 14, 15, and 16. 247 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 table 11: decision matrix of strategic direction by customer service strategic direction management approach business structure corporate strategy corporate governance management team priority vector management approach 1 2 3 4 1/2 0.250 business structure 1/2 1 2 3 1/4 0.140 corporate strategy 1/3 1/2 1 2 1/5 0.090 corporate governance 1/4 1/3 1/2 1 1/6 0.060 management team 2 4 5 6 1 0.460 ci = 0.0112, ri = 1.12, cr = 0.01 < 0.1 ok table 12: decision matrix of operational capability by customer service operational capability product quality human resource admin systems logistical capability information technology priority vector product quality 1 8 6 4 3 0.500 human resources 1/8 1 1 1/5 1/4 0.050 admin systems 1/6 1 1 1/5 1/3 0.060 logistical capability 1/4 5 5 1 3 0.250 information technology 1/3 4 3 1/3 1 0.150 ci = 0.0896, ri = 1.12, cr = 0.08 < 0.1 ok table 13: decision matrix of customer approach by customer service customer approach key customers market position customer relations customer approach external relations priority vector key customers 1 4 1/3 1/5 4 0.140 market position 1/4 1 1/6 1/8 1/2 0.040 customer relation 3 6 1 1/3 4 0.250 customer approach 5 8 3 1 7 0.510 external relation 1/4 2 1/4 1/7 1 0.060 ci = 0.056, ri = 1.12, cr = 0.05 < 0.1 ok 248 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 table 14: decision matrix of cost structure by customer service cost structure wage base overhead costs supply base cost product cost delivery cost priority vector wage base 1 1/5 1/2 1/9 1/8 0.030 overhead costs 5 1 3 1/6 1/5 0.110 supply base cost 2 1/3 1 1/8 1/5 0.050 product cost 9 6 8 1 3 0.520 delivery cost 8 5 5 1/3 1 0.290 ci = 0.0784, ri = 1.12, cr = 0.07 < 0.1 ok table 15: decision matrix of economic performance by customer service economic performance profit level profit centers financial structure risk exposure cash flow priority vector profit level 1 1/2 1/7 1/4 1/5 0.040 profit centers 2 1 1/6 1/3 1/4 0.070 financial structure 7 6 1 5 4 0.520 risk exposure 4 3 1/5 1 1/3 0.130 cash flow 5 4 1/4 3 1 0.230 ci = 0.0784 ri = 1.12, cr = 0.07 < 0.1 ok table 16: decision matrix of research & development by customer service research & development core competency research competency process scaleup project management intellectual property priority vector core competency 1 2 4 1/6 1/5 0.100 research competency 1/2 1 2 1/7 1/4 0.070 process scaleup 1/4 1/2 1 1/8 1/5 0.040 project management 6 7 8 1 3 0.520 intellectual property 5 4 5 1/3 1 0.270 ci = 0.0672, ri = 1.12, cr = 0.06 < 0.1 ok. the results are concluded in table 17. the priority vector of strategic direction, operational capability, customer approach, cost structure, economic performance, and r & d were management team, product quality, customer relation, product cost, financial structure, and project management were 0.46, 0.50, 0.51, 0.52, 0.52, and 0.52, respectively. the quality assurance preferred cost structure (42%), followed by operational capability (27%), customer approach (14%), economic performance (8%), strategic direction (6%), and research & development (4%). 249 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 table 17: results of r1 based on soccer model (customer service) factor item priority vector (%) sub-criteria weight according to main-criteria weight (%) strategic direction (5%) management approach 25.00 1.25 business structure 14.00 0.70 corporate strategy 9.00 0.45 corporate governance 6.00 0.30 management team 46.00 2.30 operational capability (27%) product quality 50.00 13.50 human resources 5.00 1.35 admin systems 6.00 1.62 logistical capability 25.00 6.75 information technology 15.00 4.05 customer approach (14%) key customers 14.00 1.96 market position 4.00 0.56 customer relations 25.00 3.50 customer approach 51.00 7.14 external relations 6.00 0.84 cost structure (42%) wage base 3.00 1.26 overhead costs 11.00 4.62 supply base cost 5.00 2.10 product cost 52.00 24.84 delivery cost 29.00 12.18 economic performance (8%) profit level 4.00 0.32 profit centers 7.00 0.56 financial structure 52.00 4.16 risk exposure 13.00 1.04 cash flow 23.00 1.84 research & development (4%) core competency 10.00 0.4 research competency 7.00 0.28 process scale-up 4.00 0.16 project management 52.00 2.08 intellectual property 27.00 1.08 the results are concluded in table 24. the priority vector of strategic direction, operational capability, customer approach, cost structure, economic performance, and r&d were management team, product quality, customer relation, product cost, financial structure, and project management with 0.46, 0.51, 0.50, 0.52, 0.51, and 0.51, respectively. however, the unexpected outcome was that logistical capability ranked first with the priority vector of 0.517. the quality assurance preferred cost structure (44%), followed by operational capability (23%), customer approach (14%), economic performance (9%), strategic direction (7%), and research & development (4%). 250 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 5. supplier selection criteria framework the overall priority vector of the interviewees is concluded in table 25, which shows that the cost structure has the highest number by 0.442, which makes it 44.2% from the soccer model. the second highest was an operational capability with 23%, however, other factors of customer approach, economic performance, strategic direction, and r&d, had the remaining weightage of 13.5%, 8.3%, 6.9%, and 4.1, respectively. the decision matrix for each main criteria for the purchasing department representer are shown in tables 18, 19, 20, 21, 22, and 23. table 18: decision matrix of strategic direction by purchasing strategic direction management approach business structure corporate strategy corporate governance management team priority vector management approach 1 3 4 5 1/2 0.290 business structure 1/3 1 2 3 1/4 0.130 corporate strategy 1/4 1/2 1 1 1/6 0.070 corporate governance 1/5 1/3 1 1 1/6 0.060 management team 2 4 6 6 1 0.460 ci = 0.0224, ri = 1.12, cr = 0.02 < 0.1 ok table 19: decision matrix of operational capability by purchasing operational capability product quality human resource admin systems logistical capability information technology priority vector product quality 1 7 5 1/4 3 0.260 human resources 1/7 1 1/2 1/8 1/4 0.040 admin systems 1/5 2 1 1/6 1/3 0.060 logistical capability 4 8 6 1 4 0.510 information technology 1/3 4 3 1/4 1 0.130 ci = 0.0896, ri = 1.12, cr = 0.08 < 0.1 ok table 20: decision matrix of customer approach by purchasing customer approach key customers market position customer relations customer approach external relations priority vector key customers 1 5 1/3 2 4 0.240 market position 1/5 1 1/8 1/5 1/2 0.040 customer relation 3 8 1 4 6 0.500 customer approach 1/2 5 1/4 1 2 0.150 external relation 1/4 2 1/6 1/2 1 0.070 ci = 0.0336, ri = 1.12, cr = 0.03 < 0.1 ok 251 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 table 21: decision matrix of cost structure by purchasing cost structure wage base overhead costs supply base cost product cost delivery cost priority vector wage base 1 1/5 1/3 1/9 1/8 0.030 overhead costs 5 1 3 1/7 1/5 0.100 supply base cost 3 1/3 1 1/7 1/5 0.060 product cost 9 7 7 1 3 0.520 delivery cost 8 5 5 1/3 1 0.290 ci = 0.0896, ri = 1.12, cr = 0.08 < 0.1 ok table 22: decision matrix of economic performance by purchasing economic performance profit level profit centers financial structure risk exposure cash flow priority vector profit level 1 1/2 1/9 1/6 1/7 0.030 profit centers 2 1 1/7 1/5 1/6 0.050 financial structure 9 7 1 6 3 0.510 risk exposure 6 5 1/6 1 1/3 0.140 cash flow 7 6 1/3 3 1 0.270 ci = 0.0896ri = 1.12, cr = 0.08 < 0.1 ok. table 23: decision matrix of research & development by purchasing research & development core competency research competency process scaleup project management intellectual property priority vector core competency 1 3 5 1/5 1/3 0.130 research competency 1/3 1 2 1/7 1/4 0.060 process scaleup 1/5 1/2 1 1/8 1/7 0.040 project management 5 7 8 1 3 0.510 intellectual property 3 4 7 1/3 1 0.260 ci = 0.056, ri = 1.12, cr = 0.05 < 0.1 ok. table 24: results of r1 based on soccer model factor item priority vector (%) sub-criteria weight according to main-criteria weight (%) strategic direction (7%) management approach 29.00 2.03 business structure 13.00 0.91 corporate strategy 7.00 0.49 corporate governance 6.00 0.42 management team 46.00 3.22 operational capability (23%) product quality 26.00 5.98 human resources 4.00 0.92 admin systems 6.00 1.38 252 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 logistical capability 51.00 11.73 information technology 13.00 2.99 customer approach (14%) key customers 24.00 3.36 market position 4.00 0.56 customer relations 50.00 7.00 customer approach 15.00 2.10 external relations 7.00 0.98 cost structure (44%) wage base 3.00 1.32 overhead costs 10.00 4.40 supply base cost 6.00 2.64 product cost 52.00 22.88 delivery cost 29.00 12.76 economic performance (9%) profit level 3.00 0.27 profit centers 5.00 0.45 financial structure 51.00 4.59 risk exposure 14.00 1.26 cash flow 27.00 2.43 research & development (4%) core competency 13.00 0.52 research competency 6.00 0.24 process scale-up 4.00 0.16 project management 51.00 2.04 intellectual property 26.00 1.04 table 25: results of r1 based on soccer model factor item priority vector (%) sub-criteria weight according to main-criteria weight (%) strategic direction (6.9%) management approach 29.00 2.00 business structure 12.90 0.89 corporate strategy 6.70 0.46 corporate governance 6.00 0.41 management team 45.50 3.14 operational capability (23%) product quality 25.50 5.87 human resources 3.80 0.87 admin systems 6.00 1.38 logistical capability 51.70 11.89 information technology 12.90 2.97 customer approach (13.5%) key customers 23.50 3.17 market position 4.30 0.58 customer relations 50.30 6.79 253 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 customer approach 14.60 1.97 external relations 7.30 0.99 cost structure (44.2%) wage base 3.10 1.37 overhead costs 10.60 4.69 supply base cost 5.90 2.61 product cost 52.10 23.03 delivery cost 28.40 12.55 economic performance (8.3%) profit level 3.30 0.27 profit centres 4.90 0.41 financial structure 52.00 4.32 risk exposure 14.10 1.17 cash flow 25.80 2.14 research & development (4.1%) core competency 13.30 0.55 research competency 6.10 0.25 process scale-up 3.70 0.15 project management 51.30 2.10 intellectual property 25.60 1.05 finally, the overall weight supplier selection criteria were calculated. figure 3 shows the percentages of the soccer model supplier selection criteria. the results show that cost structures are the first criteria in supplier selection, with 44.2% of the total weight. however, out of this weight, 23% focused on product cost. these results are understandable, especially when analyzing the importance of criteria in small and medium companies. operational capability came next, with about 23% of the total weightage. however, it is unexpected that logistical capability ranked first with a priority vector of 0.517 with 11.89%. next in the ranks is the customer approach, with 13.5% of the overall weight. customer relations was the most focused on customer approach in supplier selection criteria, priority vector of 0.503. following this were the key customers (0.235), customer approach (0.146), external relation (0.073), and 55, and lastly market position (0.043). the market position showed a low percentage of 0.58% of overall weights due to filtering. thus, considering market position was the last thing they would consider. the economic performance stood in the second last place with 8.3% of overall weight. altogether, the interviewees agreed that financial structures (0.520) was the foremost factor to be considered. financial structure is the long-term and short-term company sources of capital composition. the suppliers manage their liabilities and equity to finance their operations. financial structures are significant if the company wants to have a long-term relationship with the suppliers to predict the supplier's performance in the future. a wellplanned financial structure means stability and will build trust in the company in the long run. finally, the overall weight showed that cost structure, operational capability, and customer approach with a total of 80.7% were the factors that contribute the most to supplier selection. 254 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 fig. 3: overall weight supplier selection criteria. 6. conclusions this paper has illustrated a case study for the supplier selection in manufacturing corrugated cartons company in malaysia. the research outputs can be concluded as the followings: 1. the soccer model is one of the most comprehensive models covering most essential supplier selection criteria. 2. integrating the ahp method and the soccer model gave a practical and valid framework. 3. consulting the company's internal expertise will make the framework better understood. 4. success in data gathering needs to recognize the bias due to specialty. 5. the results show that the consistency ratio (cr) is 10% or below to ensure data consistency. however, if the consistency ratio was more than 10%, the rating gathered during the in-depth interview would be revised using the recording as the reference. 6. the results show that the cost structure is the ultimate concern on supplier selection which bears 44.2% of the soccer model. followed by operational capability (23%), customer approach (13.5%), economic performance (8.3%), strategic direction (6.9%), and lastly research & development (4.1%). references [1] wahid z, daud mrc. (2020) study on productivity improvement of manual operations in soya sauce factory. iium engineering journal, 21(1): 202-211. [2] tsai ck, phumchusri n. (2021) fuzzy analytical hierarchy process for supplier selection: a case study in an electronic component manufacturer. engineering journal. 25(8): 73-86. [3] rogers sc. (2009) the supply-based advantage: how to link suppliers to your organization's corporate strategy. amacom div american mgmt assn. [4] shukor ja, omar mf, kasim mm, jamaludin mh, naim ma. (2018) assessment of composting technologies for organic waste management. int journal of technology. 9(8): 1579-1587. 255 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 [5] fagundes mvc, keler ác, teles eo, de melo sabv, freires fgm. (2021) multicriteria decision-making system for supplier selection considering risk: a computational fuzzy ahp-based approach: a computational fuzzy ahp-based approach. ieee latin america transactions, 19(9): 1564-1572. [6] velasquez m, hester pt. (2013) an analysis of multicriteria decision making methods. international journal of operations research, 10(2): 56-66. [7] al hazza mh, abdelwahed a, ali my, sidek aba. (2022) an integrated approach for supplier evaluation and selection using the delphi method and analytic hierarchy process (ahp): a new framework. int. j. technol, 13(1): 16-25. [8] shaik m, abdul-kader w. (2011) green supplier selection generic framework: a multi-attribute utility theory approach. international journal of sustainable engineering, 4(01): 37-56. [9] chen ct, lin ct, huang sf. (2006) a fuzzy approach for supplier evaluation and selection in supply chain management. international journal of production economics, 102(2): 289-301. [10] zhao k, yu x. (2011) a case based reasoning approach on supplier selection in petroleum enterprises. expert systems with applications, 38(6): 6839-6847. [11] sevkli m, lenny koh sc, zaim s, demirbag m, tatoglu e. (2007) an application of data envelopment analytic hierarchy process for supplier selection: a case study of beko in turkey. international journal of production research, 45(9): 1973-2003. [12] choudhary d, shankar r. (2014) a goal programming model for joint decision making of inventory lot-size, supplier selection and carrier selection. computers & industrial eng, 71: 19. [13] fahmi a, kahraman c, bilen ü. (2016) electre i method using hesitant linguistic term sets: an application to supplier selection. int j of computational intelligence systems, 9(1): 153-167. [14] kaur p, kumar s. (2013) an intuitionistic fuzzy simple additive weighting (ifsaw) method for selection of vendor. iosr journal of business and management, 15(2): 78-81. [15] zouggari a, benyoucef l. (2012) simulation based fuzzy topsis approach for group multicriteria supplier selection problem. engineering applications of artificial intelligence, 25(3): 507-519. [16] wan sp, xu gl, dong jy. (2017) supplier selection using anp and electre ii in interval 2-tuple linguistic environment. information sciences, 385: 9-38. [17] shaw k, shankar r, yadav ss, thakur l. (2012) supplier selection using fuzzy ahp and fuzzy multi-objective linear programming for developing low carbon supply chain. expert systems with applications, 39(9): 8182-8192. [18] kuo rj, lin yj. (2012) supplier selection using analytic network process and data envelopment analysis. international journal of production research, 50(11):2852-2863. [19] agrawal n, kant s. (2020) supplier selection using fuzzy-ahp: a case study. trends in manufacturing processes: select proceedings of icftmm 2018, 119-127. [20] ramanathan r, abdullah l, fauadi mhfm, mohamed mss, kamaludin kn. (2023) a hybrid of kansei engineering (ke) and analytical hierarchy process (ahp) to develop conceptual designs of portable oil spill skimmer. iium engineering journal, 24(1): 183-198 [21] bottani e, rizzi a. (2008) an adapted multicriteria approach to suppliers and products selection an application oriented to lead-time reduction. int j production economics, 111(2): 763-781. [22] ulutaş a. (2019) supplier selection by using a fuzzy integrated model for a textile company. engineering economics, 30(5): 579-590. [23] ho w, xu x, dey pk. (2010) multicriteria decision-making approaches for supplier evaluation and selection: a literature review. european journal of operational research, 202(1): 16-24. [24] golden bl, wasil ea, harker pt. (1989) the analytic hierarchy processes. applications and studies, berlin, heidelberg. [25] saaty tl. (2008) decision making with the analytic hierarchy process. international journal of services sciences, 1(1): 83-98. [26] ariff h, salit ms, ismail n, nukman y. (2008) use of analytical hierarchy process (ahp) for selecting the best design concept. jurnal teknologi, 49(1): 1-18. 256 iium engineering journal, vol. 24, no. 2, 2023 al hazza et al. https://doi.org/10.31436/iiumej.v24i2.2787 [27] sipahi s, timor m. (2010) the analytic hierarchy process and analytic network process: an overview of applications. management decision, 48(5): 775-808. [28] ishizaka a, labib a. (2011) review of the main developments in the analytic hierarchy process. expert systems with applications, 38(11):14336-14345. [29] subramanian n, ramanathan r. (2012) a review of applications of analytic hierarchy process in operations management. international journal of production economics, 138(2): 215-241. [30] bruno, esposito e, genovese a, passaro r. (2012) ahp-based approaches for supplier evaluation: problems and perspectives. journal of purchasing and supply management, 18(3): 159-172. 257 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 murad et al. 63 optimization of flocculation process by microbial coagulant for removal of turbidity in river water fatin nabilah murad, md. zahangir alam*, md. noor salleh and abdullah al-mamun bioenvironmental engineering research centre, department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 50728 kuala lumpur, malaysia. *corresponding author: zahangir@iium.edu.my (received: 15 th sept. 2016; accepted: 31 st oct. 2017; published on-line: 1 st dec. 2017) abstract: the existing process of coagulation and flocculation is using chemicals that known as the cationic coagulant such as alum, ferric sulfate, calcium oxide, and organic polymers. thus, this study focuses on optimizing of the flocculation process by microbial coagulant in river water. turbidity and suspended solids are the main constraints of river water quality in malaysia since they may reduce the dissolved oxygen in the water and affects the aquatic life. hence, a study is conducted to produce microbial coagulants isolated locally for river water treatment. the chosen microbe used as the bioflocculant producer is aspergillus niger. the parameters optimized in the flocculation process were ph, bioflocculant dosage and effluent concentration. the research was done in the jar test process and the process parameters for maximum turbidity removal was validated. the highest flocculating activity was obtained on day seven of cultivation in the supernatant. the optimum ph and bioflocculant dosage for an effective flocculation process were between 4-5 and 2-3 ml for 0.3 g/l of effluent concentration, respectively. the model was validated by using a river water sample from sungai pusu (pusu river) and the result showed that the model was acceptable to evaluate the bioflocculation process. abstrak: proses sedia ada pada pembekuan dan pemberbukuan adalah menguna pakai bahan kimia yang dikenali sebagai kationik kogulan seperti alum, sulfat ferum, kalsium oksida dan polimer organik. oleh itu, kajian ini memberi tumpuan kepada mengoptimumkan proses pembekuan daripada mikrob kogulan dalam air sungai. kekeruhan dan pepejal terampai adalah punca utama pada kualiti air sungai di malaysia kerana ia mungkin mengurangkan oksigen larut dalam air dan menjejaskan kehidupan akuatik. oleh itu, satu kajian telah dijalankan untuk menghasilkan mikrob kogulan terasing bagi merawat air sungai. pemilihan mikrob yang digunakan sebagai penghasil bio-pembekuan adalah aspergillus niger. parameter yang dioptimumkan dalam proses pembekuan ini adalah ph, sukatan bio-pembekuan dan sisa kepekatan. kajian telah dijalankan dalam proses ujian jar dan proses parameter untuk membuang kekeruhan secara maksimum telah disahkan. aktiviti pembekuan yang paling tinggi telah didapati pada hari ke-tujuh dalam supernatan. ph optimum dan sukatan bio-pembekuan untuk menghasilkan proses efektif pembekuan adalah antara 4-5 dan 2-3 ml bagi 0.3 g/l sisa kepekatan, masing-masing. model telah disahkan dengan menggunakan sampel air sungai dari sungai pusu dan keputusan menunjukkan model yang boleh diterima untuk penilaian proses bio-pemberbukuan. keywords: bioflocculant; river water; microbial iium engineering journal, vol. 18, no. 2, 2017 murad et al. 64 1. introduction one of the main constraints of river water quality in malaysia is turbidity that caused by suspended solids. currently, no technology has been established in managing the river basin. however, many purification processes are practiced for water and wastewater treatment using coagulation/flocculation processes. in water refinement, usually, there are a few processes that will be followed in order to remove impurities which involve screening, coagulation and flocculation, sedimentation, ph correction, filtration, disinfection and floridation [1]. there are many water treatment plants that have been established to clean the river water such as puncak niaga holdings berhad. most of puncak niaga’s treatment plants basically utilize conventional water treatment. unfortunately, these conventional water clarification treatment systems,at times, are unable to eliminate all those contaminants that polluted the river water, thereby, they might enter the distribution and supply network [2]. the existing process of coagulation and flocculation are using chemicals known as cationic coagulants such as alum, ferric sulfate, calcium oxide, and organic polymers [3]. chemical coagulation is usually accomplished by adding metallic salts like aluminum sulfate (alum) or ferric chloride. until now there are no organic materials as good as chemicals that can be used in coagulation and flocculation [4]. organic materials are safer than chemicals for water treatment and they are cheaper as well. basically, microbial coagulant which is sort of organic materials is relatively cheap, non-toxic, new efficient and would not make secondary pollution since the water treatment factor getting from the fermentation of microbiology and separation by biological procedure, which has biology resolvability and security [5].these chemicals are not safe for the environment as well as human health [6]. therefore microbial coagulants are necessary to overcome these limitations for water refinement towards maintaining river water quality. the distillation of river water by integration of coagulation and flocculation process is a good way of water treatment since its required simple equipment, convenient management and occupying small place [7]. although many researchers have been done to improve the flocculating activity of polysaccharides based or develop new-type bioflocculants [8], somehow, the results were not good enough for commercial applications due to high production cost [9]. basically, microorganisms that having good characteristics to be a bioflocculant and has been a worldwide researching focus is metabolites of microorganisms which comprise of polysaccharide, protein, nucleic acid and lipid [10]. the polysaccharides-based bioflocculants (psbs) having the most attention because of their tendency in disposing of various type of pollutants that involving heavy metal ion, dyeing pigment and other suspended impurities [11]. a bioflocculant candidate with a wide range of ph and high flocculating activity capability would be significant to replace the chemical flocculant. bioflocculant has been reported that it has the ability to remove organic and inorganic colloids by their flocculating activity. the effectiveness of natural coagulant to eliminate suspended solids, heavy metals, microorganisms and turbidity of different types of industrial wastewater effluents as well had been stated [12-14]. adebami and tayo [15] have been reported that fermentative conditions and nutritive compounds have an effect on bioflocculant production. besides that, bioflocculant production by microbial isolated from wastewater samples has been reported as a comparative effect of the medium composition. the present study was to achieve the optimization process for bioflocculation in a jar test for removal of turbidity of river water and to validate the process parameters for maximum turbidity removal. hence, the study was proposed to produce microbial coagulants for river water treatment. iium engineering journal, vol. 18, no. 2, 2017 murad et al. 65 2. materials and method 2.1 sample collection three liters of river water sample were collected from sungai pusu (pusu river), gombak, malaysia. the sample was stored in the container during the sample collection and then kept in the refrigerator at 4 o c. the time obf sampling the river water was done on november 2015 at evening right after rain during the rainy season in order to have the high concentration of colloidal in river water. the parameters involved in the river water analysis were turbidity, total suspended solids, chemical oxygen demand and ph. all the data presented were the average of duplicate. 2.2 bioflocculant production the strain, aspergillus niger was collected from a microbial stock in the environmental engineering laboratory, international islamic university malaysia which was isolated from river water sediment. the a.niger was subcultured in sterilized pda medium for 4-5 days. after 7 days, the inoculum was prepared by wash it with sterilized distilled water and incubate it on a rotary shaker for 1 day at 150 rpm. by using sterilized filter paper, the other substances were separated with the spores suspension. the fermentation of spores by using malt extract as the medium was carried out in 7 days with 150 rpm. for bioflocculant production the cultivation was carried out on nutrient broth (bile peptone broth, bpb) containing (g/l): glucose 20, urea 0.5, yeast extract 0.5, (nh4)2so4 0.2, k2hpo4 5.0, kh2po4 2.0, nacl 0.1 and mgso4.7h2o 0.2. the initial ph of the medium was adjusted to 6.0-7.0. the in the sterilized media (2-4 ml) and incubated on a rotary shaker at 150-200 rpm and 32±2 o c for 3 days. the biomass and supernatant were separated by filtration. biomass was dried using the oven at 105 o c. 2.3 determination of bioflocculant activity and turbidity according to kurane et al. [12], the mixture containing 9 ml kaolin clay suspension (5g/l, ph 7.0), 0.1 ml sample and 0.9 ml cacl2 solution (1%, ph 7.0) was stirred vigorously and left standing for 5 minutes. the samples were taken every 24 hours in order to measure for flocculating activity. the supernatant was measured for absorbance at 550 nm. a control was prepared by replacing the sample with distilled water. the flocculating activity has been done by following the equation shows below [6] flocculating activity = 1/ (a550) 1/ (a550)c (1) where, a550 = absorbance of the sample (a550)c = absorbance of control. all experiments were done following the standard jar test procedure [16]. 2.4 optimization of flocculation process the optimization of flocculation process was investigated by manipulating some parameters such as ph, and bioflocculant dosage and effluent concentration. the agitation and settlement time were fixed variables with value 150 rpm and 40 min and 30 min respectively. the ph range was 4-7, bioflocculant dosage of 2%v/v, 4%v/v and 6%v/v, and effluent concentration range was between 0.3 mg/l 0.5 mg/l. the design of experiment was prepared to know the number of the experiment should be conducted. the response surface method (rsm) was applied to identify the total experimental runs in the design of experiment. by using the design-expert 6.0.8 software, the design of experiment for the optimization of sedimentation process was face centered iium engineering journal, vol. 18, no. 2, 2017 murad et al. 66 composite design, level 3 [low (-1), medium (0), and high (+1)]. the 3 factors were ph, bioflocculant dosage and effluent concentration. the statistical analysis was conducted with anova, p-and t-test, regression coefficient (r 2 ), 2d and 3d surface plots. the optimum parameter was determined by using numerical solution in design expert software. 2.5 validation of the model the optimum values for manipulated variables such as ph, bioflocculant dosage and effluent concentration was applied to the river water sample in order to validate the values. 3. result and discussion the water quality of sungai pusu was investigated in order to determine total suspended solids (tss), turbidity, ph and chemical oxygen demand (cod). after the tss test was done, the sample was diluted to make sure the final concentration of 0.3 g/l from the initial concentration of 0.8 g/l. after dilution, the turbidity of the river water sample changed to 128 ntu. these two parameters were important to proceed with the validation of the model. besides that, the ph and cod of the sample water were 6.4 and 3.3 mg/l respectively. an experiment was conducted to investigate the highest day of production bioflocculant in terms of the presence of many exopolysaccharides. from the result obtained, it can be seen that, increased in the cultivation day resulted into an increased in cell growth and the related increase in bioflocculant production. the decrease in flocculating activity observed after 168 hours and could be referred to the presence of bioflocculant-degrading enzyme produced by the microorganisms [17]. as stated by manivasagen et al. [18], the supernatant was used throughout the research instead of the pallet. this is because the flocculant that produced by microorganisms was polysaccharides-based bioflocculant that was secreted as macromolecular substances. table 1: experiment parameters designed by design expert software with the response run ph bioflocculant dosage (ml) effluent conc. (g/l) turbidity (ntu) 1 7 6 0.5 170 2 5.5 4 0.4 106 3 7 4 0.4 93 4 4 6 0.5 4 5 5.5 4 0.4 106 6 5.5 2 0.4 90 7 5.5 4 0.5 223 8 5.5 4 0.4 106 9 7 2 0.5 87 10 5.5 4 0.3 101 11 7 2 0.3 6 12 4 6 0.3 98 13 4 2 0.5 119 14 4 2 0.3 27 15 5.5 4 0.4 106 16 7 6 0.3 168 17 5.5 6 0.4 136 18 5.5 4 0.4 106 19 5.5 4 0.4 106 20 4 4 0.4 86 iium engineering journal, vol. 18, no. 2, 2017 murad et al. 67 the model formulated by doe with the response of turbidity is as follows: (2) according to table 1 the lowest turbidity obtained was 4 ntu at ph 4, bioflocculant dosage of 6 ml at maximum concentration 0.5 g/l. in contrast, the highest reading of turbidity after the experiment was 223 ntu which was in ph 5.5, 4 ml of bioflocculant dosage and at the maximum effluent concentration as well. the lowest turbidity obtained lies into the class i of national water quality standard for malaysia which is 5 ntu was the maximum value [19]. the analysis demonstrated that the model was highly significant with a model f-value of 9.94 and prob>f less than 0.0006. in general, prob > f values of less than 0.05 indicate the model was significant, while values greater than 0.10 indicate the model terms were not significant. in this case, a, b, a 2 , ab, ac and bc were significants where a,b and c were ph, bioflocculant dosage and effluent concentration respectively. the values of coefficient of determination, r 2 and adjusted r 2 were in fair agreement 0.8995 and 0.8090 respectively and quite close to 1, which indicated a reasonable correlation between the experimental values and predicted values. table 2: analysis of variance (anova) of response surface quadratic model for the turbidity response of the sedimentation by bioflocculant source sum of squares df mean square f value prob.f model 170.17 9 18.91 9.94 0.0006 significant a 10.29 1 10.29 5.41 0.0424 b 14.87 1 14.87 7.82 0.0189 c 9.31 1 9.31 4.90 0.0513 a 2 13.14 1 13.14 6.91 0.0252 b 2 3.15 1 3.15 1.66 0.2270 c 2 1.97 1 1.97 1.04 0.3327 ab 42.45 1 42.45 22.32 0.0008 ac 10.45 1 10.45 5.49 0.0411 bc 52.09 1 52.09 27.39 0.0004 residual 19.26 10 1.90 lack of fit 19.13 5 3.83 150.21 <0.0001 insignificant pure error 0.000 5 0.000 r 2 = 0.8995 and adjusted r 2 = 0.8090 it can be summarized from the contour and 3-d plots as shown in fig. 1. the ph and bioflocculant dosage have the significant effect on the turbidity results that represent the sedimentation process was at optimum. the lowest of turbidity reading was at ph value 4, the interaction between ph and bioflocculant dosage was significance since the shape of response surface was curves. the interaction between the corresponding variables is significant as it can be indicated by an elliptical or saddle nature of the contour plots [20]. according to zainuddin [21], the ph influences the flocculating activity thus, affecting the sedimentation process. one of the ways of ph influences is by affecting the stability of suspended particles and floc formation [22]. usually, bioflocculant had a strong activity over a wide range of ph 3-11 [23]. as for bioflocculant produced by aspergillus niger, the optimum ph required to result in lowest turbidity was in the range 4-5. the black fungi iium engineering journal, vol. 18, no. 2, 2017 murad et al. 68 were capable to produce a bioflocculant that can work in acidic up to ph 4. on the other hand, the amount of bioflocculant dosage should be used accordingly because it also may affect the turbidity reading. the optimum bioflocculant dosage for effluent concentration 0.3 g/l in the finding was not more than 3 ml. as stated in the literature review, the common amount of bioflocculant dosage needed was 1 ml. ideally, a high dosage produces high viscosity which could prevent the settling of suspended particles by restabilization of particles. the high viscosity inhibits and blocks the adsorption site thereby reduce the flocculation process and floc formation. in contrast, a low dosage not favorable to make bridging flocculation mechanism of the bioflocculant to be effective [24]. the bridging flocculation takes place when bioflocculant extend from the particles‘ surface into the solution for a distance greater than the distance over which inter-particle repulsion acts and bioflocculant adsorb other particles to form flocs [25-26]. fig. 1: plot of contour and 3-d of interaction between ph and bioflocculant dosage. validation experiments are conducted in order to verify the obtained model’s predictability (table 3). three validation experiments were designed and conducted. they have classified into three which are minimum, medium and maximum. after that, validation model has been done according to model formulated by doe as shown in the eq. (2), the result of turbidity experimentally do not differ too much with the turbidity theoretically. hence, the model can be accepted as valid since it produces a parallel result between theoretical and experimental result. the error might come due to the inaccuracy during the preparation of the raw river water since it is difficult to achieve exact ph needed. but the all error is less than 10% and can be accepted. table 3: result of validation model by comparing the turbidity of theoretical with experimental ph bioflocculant dosage (ml) effluent concentration (g/l) turbidity (theoretically) turbidity (experimentally) minimum 5 2.9 0.3 25 27 medium 6 3.19 0.3 39.94 43 maximum 6.18 3.29 0.3 69.99 74 iium engineering journal, vol. 18, no. 2, 2017 murad et al. 69 4. conclusion the study shows that the aspergillus niger was capable of removing turbidity in the river water with optimum process conditions and could be one of the potential bioflocculant producers. by having optimization of certain parameters like ph and bioflocculant dosage, the bioflocculant can perform very well in reducing the turbidity of the river water. the optimal ph for the bioflocculant was between 4 and 5 while the bioflocculant dosage found was 3 ml for 0.3 g/l of effluent concentration. it is recommended to have a further study on characterization and evaluation as this bioflocculant has the potential to replace the use of chemical flocculant in water industries. acknowledgement the authors like to express their thanks to ministry of education (moe) for granting a fundamental research grant scheme (frgs), project no. frgs-14-109-0350 for the financial support. special thanks as well to the department of biotechnology engineering, faculty of engineering, international islamic university malaysia for providing the equipment, chemicals and instruments for this research. references [1] adlan ni, aziz a, hamidi a, hasan r. (2009) the effects of raw water turbidity in water treatment process at sg kampar treatment plant. universiti sains malaysia. [2] salleh m, zainudin z. (2011) portable water quality characteristics. [3] engelhardt bt, terry l. (2014) coagulation , flocculation and clarification of drinking water, application development manager: drinking water, 1-57. [4] awaleh mo, soubaneh yd. (2014) wastewater treatment in chemical industries: the concept and current technologies. hydrology: current research. [5] ramavandi, b. (2014) treatment of water turbidity and bacteria by using a coagulant extracted from plantagoovata. water resources and industry, 6:36-50. [6] tang j, qi s, li z, an q, xie m, yang b, wang y. (2014) production, purification and application of polysaccharide-based bioflocculant by paenibacillus mucilaginosus. carbohydrate polymers, 113:463-470. [7] lin jy, jian z. (2010) a study on the treatment of wastewater from reproduced papermaking using microbial flocculants by mycelia pellet. 4th international conference on bioinformatics and biomedical engineering. [8] aljuboori a, idris a, abdullah n, mohamad r. (2013) production and characterization of a bioflocculant produced by aspergillus flavus. bioresource technology, 127:489-493. [9] linsley rk, franzini jb, freyberg dl. (1992) water-resources engineering. new york: mcgraw-hill. [10] shih i, van y, yeh l, lin h, chang y. (2001) production of a biopolymer flocculant from bacillus licheniformis and its flocculation properties. bioresource technology, 78(3):267272. [11] deng s, yu g, ting y. (2005) production of a bioflocculant by aspergillus parasiticus and its application in dye removal. colloids and surfaces b: biointerfaces, 44(4):179-186. [12] kurane r, matsuyama h. (1994) production of a bioflocculant by mixed culture. bioscience, biotechnology and biochemistry, 58(9):1589-1594. [13] gao q, zhu x, mu j, zhang y, dong x. (2009) using ruditapesphilippinarum conglutination mud to produce bioflocculant and its applications in wastewater treatment. bioresource technology, 100(21):4996-5001. [14] lin j, zeng j. (2009) a study on the treatment of wastewater from reproduced papermaking using microbial flocculants by mycelia pellet. university ji’an, china: school of chemistry and chemical engineering; jinggangshan iium engineering journal, vol. 18, no. 2, 2017 murad et al. 70 [15] adebami g, adebayo-tayo bc. (2013). comparative effect of medium composition on bioflocculant production by microorganisms isolated from wastewater samples. report and opinion, 5(2):46-53. [16] water.me.vccs.edu. (2017). jar test procedure. [online] available at: http://water.me.vccs.edu/courses/env110/coagulation.htm [accessed 16 sep. 2017]. [17] li w, zhou w, zhang y, wang j, zhu x. (2008) flocculation behavior and mechanism of an exopolysaccharide from the deep-sea psychrophilic bacterium pseudoalteromonas sp. sm9913.bioresource technology, 99(15):6893-6899. [18] manivasagan p. (2015) production of polysaccharide-based bioflocculant for the synthesis of silver nanoparticles by streptomyces sp. international journal of biological macromolecules, 77:159-167. [19] department of environment (doe) (2005). interim national water quality standards (inwqs) for malaysia. http://www.doe.gov.my [20] panpae k, jaturonrusmee w, mingvanish w, nuntiwattanawong c, chunwiset s, santudrob k, triphanpitak s. (2008) minimization of sucrose losses in sugar industry by ph and temperature optimization. the malaysian journal of analytical sciences, 12(3):513-519. [21] zainudin z. (2010) benchmarking river water quality in malaysia. jurutera, 12-15. [22] nwodo u, green e, mabinya l, okaiyeto k, rumbold k, obi l, okoh a. (2014) bioflocculant production by a consortium of streptomyces and cellulomonas species and media optimization via surface response model. colloids and surfaces b: biointerfaces, 116:257-264. [23] okaiyeto k, nwodo uu, mabinya lv, okoh ai. (2013) characterization of a bioflocculant produced by a consortium of halomonas sp. okoh and micrococcus sp. leo. international journal of environmental research and public health, 10(10): 5097-5110. [24] zulkeflee z, aris a, shamsuddin z, yusoff m. (2012). cation dependence, ph tolerance, and dosage requirement of a bioflocculant produced by bacillus spp. upmb13: flocculation performance optimization through kaolin assays. the scientific world journal, 2012: 495659. [25] jebun n, al-mamun a, alam mz, raus ra. (2016) fungal flocculants to reduce turbidity of river water. arpn journal of engineering and applied sciences, 11(6):4094-4099. [26] tang w, song l, li d, qiao j, zhao t, & zhao h. (2014). production, characterization, and flocculation mechanism of cation independent, ph tolerant, and thermally stable bioflocculant from enterobacter sp. eth-2. plos one, 9(12):1-19. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. energy efficient auction-based dynamic spectrum access network abdulkarim a. oloyede1, lawal mohammad bello2 and david grace3 1department of telecommunication science, university of ilorin, ilorin, nigeria. 2department of electrical engineering, bayero university, kano, kano nigeria. 3communication and signal processing research group, university of york, york, united kingdom. *corresponding author: oloyede.aa@unilorin.edu.ng (received: 13th may 2016; accepted: 13th dec. 2016; published online: 30th may 2017) abstract: a framework aimed at increasing the much-needed revenue of wireless service providers is proposed. the model uses the price paid by the wireless users to control the amount of energy consumed and the admission process based on a dynamic spectrum access network. the scheme is based on a first price auction process with a reserve price, where price is used to allocate the radio spectrum for short term use. the proposed model allows for an opportunistic access to the spectrum white space in a manner that would protect the primary users in the system. the concept of green payment is used to penalize users who require high transmission power and subsidize those who require low transmission power. this work shows that with the proposed green payment in combination with the knowledge of the reserve price, the energy consumed and the delay in an auction based dynamic spectrum access network can be reduced. abstrak: satu rangka kerja yang bertujuan untuk meningkatkan hasil yang amat diperlukan daripada pembekal perkhidmatan wayarles dicadangkan. model ini menggunakan harga yang dibayar oleh pengguna tanpa wayar untuk mengawal jumlah tenaga yang digunakan dan proses kemasukan berdasarkan rangkaian akses spektrum dinamik. skim ini adalah berdasarkan kepada proses lelongan harga pertama dengan satu harga rizab, di mana harga yang digunakan untuk memperuntukkan spektrum radio untuk kegunaan jangka pendek. model yang dicadangkan membenarkan untuk akses yang oportunis kepada spektrum ruang putih dengan cara yang akan melindungi pengguna utama di dalam sistem. konsep pembayaran hijau digunakan untuk menghukum pengguna-pengguna yang memerlukan kuasa hantaran yang tinggi dan subsidi mereka yang memerlukan penghantaran kuasa yang rendah. kerja ini menunjukkan bahawa dengan bayaran hijau yang dicadangkan dalam kombinasi dengan pengetahuan daripada harga rizab dalam, tenaga yang digunakan dan kelewatan dalam rangkaian akses spektrum dinamik lelongan berdasarkan dapat dikurangkan. keywords: first price auction;green payment;cognitive radio;white space; dynamic spectrum access 1. introduction increase in the demand for the radio spectrum, and scarcity of the most precious bands for terrestrial mobile communication is one of the main reasons behind the introduction of the concept of dynamic spectrum access (dsa) [1, 2]. this is in addition to the inefficiencies associated with static spectrum allocation [3]. one of the inefficiencies of static spectrum allocation brought about the need for white spaces in the 73 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. radio spectrum to prevent interference from other users using the same channel in adjacent cells [4]. however, as the demand for the radio spectrum increases, there is a need to allow access to these white spaces. such white space includes the guard bands that are left unoccupied for technical reasons[5]. white spaces can also be a result of the recent switching off of transmitters that were previously allocated a band; such is the case with tv white space. tv white space is a result of the recent switching over from analogue to digital tv. this resulted in availability of bandwidth that was previously allocated (50 mhz -700 mhz in the uk) to tv around the globe [6]. dsa would enable wireless devices to access the radio spectrum in an opportunistic manner using the concept of cognitive radio. a cognitive radio is defined as a wireless network that can interact with and observe the wireless environment [7]. it also learns based on its interaction with the environment [8]. to allow for opportunistic access to the radio spectrum, there is a need to propose a scheme that would protect the primary users of the radio spectrum [9]. in addition to this, there is also a need to reduce the amount of energy consumed by wireless devices seeking access to the radio spectrum. reduction in the amount of energy consumed by wireless devices is important mainly due to the following three reasons. firstly, the spectrum is a shared resource which requires simultaneous access. accessing the same frequency band simultaneously, using a dsa scheme, could lead to more interference if not properly managed. secondly, the effects of energy consumption on carbon emissions into the human environment are leading to global warming. hence, there is an urgent need to reduce the amount of energy consumed in order to slow global warming. lastly, wireless devices are mostly battery powered. to increase the working time of the batteries, the energy consumed in transmitting and receiving information should be reduced. in addition to reduction in the energy consumed, there is a need to increase revenue from the use of the radio spectrum. revenue increase would allow wireless service providers (wsp) to expand their networks [10, 11]. expansion of the network is necessary as a result of the increase in the number of devices and applications seeking to use the radio spectrum [12]. therefore, there is a need to use the price paid for the radio spectrum to regulate short-term access to the radio spectrum while implementing dsa. the use of price has proven to be an efficient tool in the allocation of scarce resources like the radio spectrum [13]. in order to use pricing in a fair manner, an auction would be appropriate [14, 15]. an auction allows the highest bidder to be granted access to the use of the radio spectrum [16]. application of auctions to wireless communication was also studied in [17]. it proposed a low complexity auction framework to allow short-term access to the spectrum in near real-time. this paper proposes a model for an energy efficient wireless network for a future dsa network based on an uplink scenario in an infrastructure-based cognitive radio network. in the proposed model, the spectrum is allocated dynamically based on a first price sealed bid auction with a reserve price. the auction process is carried out before each transmitting period. a user seeking access to the radio spectrum submits a bid; a number of users equal to the number of available channels emerge as the winners to whom the radio spectrum is allocated. in the proposed model, the accepted bid for the winners must be above a set minimum price known as the reserve price. the concept of green payment (gp) is also used to encourage the efficient use of the spectrum white space and to penalize inappropriate behaviors. the gp is in the form of either a tax or subsidy. a user transmitting above the signal to noise ratio (snr) threshold from the receiver is taxed and a user whose snr is below the set threshold is subsidized. snr is used in this work since the users are grouped cell by cell. 74 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. in this paper, the users are divided into two groups: the low powered users (lpu) and the high powered users (hpu). the lpu require low transmit power while hpus require higher transmit power relative to the low powered transmitters. we model this type of user based on the proposed heterogonous nature of the future network as proposed in [18]. it is assumed that each user group has a target bit rate and to achieve the set bit rate, the users need a transmitting power level to sustain the signal to noise plus interference ratio (sinr) that is required, as suggested by shannon [19]. the auction process proposed in this work is an autonomous agent (proxy bidding) to allow for user participation without necessarily having a professional expertise in an auction process. we adopted the first price auction mechanism because of its simplicity and it requires less computatio n compared to the second price auction. the rest of this paper is as organized as follows. section 2 explains the system architecture. the simulation model is described in section 3. results and discussion are provided in section 4 followed by the conclusions in section 5. 2. system architecture we consider an infrastructure-based multi-channel wireless communication network in an uplink scenario where users transmit files via an access point (the base station). these users can be mobile phones, computers, laptops, or any other wireless device. the energy model and other components of the proposed model are as described below: 2.1 energy model off on 3 1 4 2 fig. 1: energy and system model as a two-state markov chain. the energy model used in this work is represented by a 2 state markov chain, as shown in fig. 1, and is similar to the energy model used in [20]. where the off state represents the energy consumed during the bidding process. the amount of energy consumed during the off state is considered small compared to the amount of energy consumed in the on state. therefore, we assume it to be negligible. the user would continue to be in such a state until the user is among the winning bidders and such a user moves from state 1 to 2. state 2 represents the transition to on, or transmitting state, and the user is assumed to have transmitted successfully provided the signal to noise plus interference ratio (snir) is above the minimum threshold as indicated in the parameter table presented in section 3. 2.2 the spectrum broker the spectrum broker is the central entity, who is fully aware of all the users present in each cell. the broker is also responsible for issuing a time bound spectrum access to all 75 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. users. the spectrum is assumed to be owned by the spectrum broker who determines which channel is free via the database. the aim of the broker is to auction off the spectrum to competing users based on their requirement. the spectrum broker can only assign a spectrum that is not in use by the primary users after probing the database. however, primary users are not considered in this work. the broker receives bids submitted by the users based on their valuation. the spectrum broker also calculates the reserve price, which is the minimum acceptable bid. 2.3 the users bid it is assumed that there are 𝑁 users in each of the cells in the system. 𝑁usa represents the users out of the 𝑁 users who require the use of the spectrum to transmit at time 𝑡. such a user submits a bid, 𝑏, to the spectrum broker during a bidding period, 𝑡. the bidding period is before the allocation period, 𝑇. the bids are formulated based on known principles of bid generation as shown in eqn. (1) 𝑏𝑖 (𝑃𝑟𝑖𝑐𝑒 𝑈𝑛𝑖𝑡) = (𝑁usa −𝑁ac )𝑉𝑖 𝑁ac + 𝑉min (1) for 𝑖 = 1,2,3 … … . 𝑁usa where subscript 𝑖 represents one of the 𝑁usa users, 𝑉𝑖 is the valuation of user 𝑖 based on the user’s budget and the belief of the user regarding the bids of others, a uniform continuous random distribution is assumed for the valuation of each of the users. this valuation is drawn from a known distribution with interval [𝑉𝑚𝑖𝑛 𝑉𝑚𝑎𝑥 ]. 𝑁usa is the number of users seeking access and 𝑁ac is the number of channels available. each of the users is assumed to have a fixed budget. we assume the same budget for all the users. in all the scenarios examined, a user cannot offer a bid above the specified budget and the available budget decreases after each payment. we assume that the users are rational, such that a losing bidder in the previous bidding round increases the bid submitted, using a known uniform random distribution 𝑓(𝑥) in the next auction round. users also decrease their bids after winning a bidding round, until a steady state is reached. this is similar to the proposed method in [21]. in some part of this work, we assume that the reserve price is known to all the users. this is known as the public knowledge of reserve price (pkrp). if a public knowledge of the reserve price is assumed, the users only generate a bid above the reserve price or rather not put in a bid. 2.4 the reserve price the reserve price increases with the traffic load because at high traffic load, the primary user incurs more interference from the secondary users and fewer channels are available. the reserve price, 𝑟, which is the minimum acceptable bid by the broker, is calculated as shown in eqn. (2) 𝑟𝑖 = 𝐶𝑟 𝐶𝑓 𝛾 𝑁ac (2) where 𝐶𝑓 is the congestion factor, 𝐶𝑟 is a factor used to specify the value of a particular frequency band and 𝛾 is is a constant which is determined by the broker depending on how much profit the broker intends to make. the congestion factor is the ratio of the number of users transmitting at time 𝑡 compared to the number of channels available. 𝐶𝑓 = 𝑁usa 𝑁ac (3) 76 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. the 𝐶𝑓 is same for all the users who want to transmit within the same period 𝑡. for easy analysis and simplicity, 𝛾 and 𝐶𝑟 are each assumed to be 1 in this work. 2.5 the green payments (gp) the concept of gp, which is in the form of either a tax or subsidy, is used. the gp is based on the inverse of the shannon truncated bound and previously proposed in [22]. thr={ 0 𝛼. 𝑆(𝑆𝑁𝐼𝑅) 𝑇ℎ𝑟𝑚𝑎𝑥 𝑆𝑁𝐼𝑅 < 𝑆𝑁𝐼𝑅𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑 𝑆𝑁𝐼𝑅𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑 < 𝑆𝑁𝐼𝑅 < 𝑆𝑁𝐼𝑅𝑚𝑎𝑥 𝑆𝑁𝐼𝑅 > 𝑆𝑁𝐼𝑅𝑚𝑎𝑥 𝛼. 𝑆(𝑆𝑁𝐼𝑅)=𝑙𝑜𝑔2(1 + 𝑆𝑁𝑅) (4) where 𝑇ℎ𝑟𝑚𝑎𝑥 is the throughput with a value of 4.5 𝑏𝑝𝑠/𝐻𝑧, 𝑆(𝑆𝑁𝐼𝑅) is the shannon bound and 𝛼 is the rate reduction factor with value of 0.65, 𝑆𝑁𝐼𝑅𝑚𝑎𝑥 is 21 𝑑𝐵 and 𝑆𝑁𝐼𝑅𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑 is 1.8 𝑑𝐵. the truncated shannon bound (tsb) is used to represent the transmission rates that can be achieved in practice given an adaptive modulation scheme in a real world scenario. this is dependent on the snir of the user. in order to use the gp to control the interference caused by the users requiring high snir in a fair manner, and to penalize or subsidize users based on the interference they contribute into the system, an equation related to the tsb is used to derive the gp equation. the reason for using this equation is due to the fact that the transmission rate is an important parameter in a wireless communication system. this is because the transmission rate is dependent on the snir and this is dependent on transmit power and interference. the derived gp equation is shown in eqn.(5) as formulated from the tsb: r(price unit) = { 21+ß𝜃 − 1 𝑔𝑟𝑒𝑒𝑛 𝑝𝑎𝑦𝑚𝑒𝑛𝑡 𝑠𝑢𝑏𝑠𝑖𝑑𝑦 21+ß𝜃 + 1 𝑔𝑟𝑒𝑒𝑛 𝑝𝑎𝑦𝑚𝑒𝑛𝑡 𝑡𝑎𝑥 (5) where ß is the gp factor derived later in this paper. the value of ß is chosen in such a way that the gp does not introduce too much tax/subsidy into the system leading to delay or reduction in the system throughput, hence the reason for it being called the gp factor. 𝜃 is the absolute value of the linear difference between the snr value of a user 𝑖 (ψ𝑖 ) and the value of the snr of a set threshold (ψ𝑗 ). 𝜃𝑖 = |ψ𝑖 − ψ𝑗 | for 𝑖=1, 2, 4…𝑁𝑈𝑆𝐴 (6) the set threshold is represented as (ψ𝑗 ). this is derived by first arranging the received snr of the 𝑁𝑈𝑆𝐴 users who are seeking access to the radio spectrum at time 𝑡 in an ascending order 𝛙𝑡 = [ψ1, ψ2, ψ3 … ψ𝑁𝑈𝑆𝐴 ] (7) then to determine which of the snr at time 𝑡 is the set threshold, eqn. (8) is used, where 𝑃𝑐 is the desired percentile as derived and explained in [22]. |𝑗| = ⌊ 𝑃𝑐 𝑁𝑈𝑆𝐴 100 + 1 2 ⌋ (8) equation (8) gives an absolute value (integer) known as the percentile rank. this shows that whatever the value of 𝑗, the 𝑗𝑡ℎ snr in eqn. (7) is the set threshold (ψ𝑗 ). the value of the percentile rank used has an effect on the total revenue needed to subsidize the 77 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. bids of the users as seen from eqn. (8). as 𝑃𝑐 increases, the percentile ranks also increases. the final bid of the user with the gp is as: 𝑏𝑖 𝑓 = (𝑁usa −𝑁ac )𝑉𝑖 𝑁ac + 𝑉min ± ɍ for 𝑖 = 1,2,3 … … . 𝑁usa . (9) where ɍ is the value of the gp. for the bids to be accepted by the spectrum broker the bid must be above the reserve price. 𝑏𝑖 𝑓 ≥ 𝑟𝑖 (10) 3. simulation model one spectrum broker and 𝑁 users are modelled in an uplink scenario where each user is transmitting at a fixed power level depending on the user group as specified in table 1. depending on the user's location, each user has an optimal power level. as explained earlier with the gp, the user is either taxed or subsidized depending on whether the user’s transmitting power falls below or above the set percentile level. it is assumed that a user cannot transmit in the off mode as explained in the energy model. a poisson distribution process with an arrival rate (𝜆) and inter-arrival rate described by an exponential distribution is assumed. each group transmits at a different bit rate depending on the snir level according to shannon bound giving in eqn. (4). table 1: the parameters used in the modeling parameters value cell radius 5 km interference threshold -40 db snir threshold 1.9 db users in a cell 100 noise floor -114 db/mhz number of cell 19 system bit rate 1 mbps 5 mbps target snr 4 db low powered users 15 db high powered users average file size 1 mbyte height of base station 15 m the broker does not know how much each user is willing to pay, hence the need for an auction. the value 𝐹(𝑣) that each bidder is willing to pay is known only to the bidder. it is also assumed that the value each bidder bids does not change even when the bidder knows the values other users are putting in as their bid. the rules of the auction require users to submit bids in discrete bids according to their private valuation (𝑏𝑖 , 𝑏𝑖 … 𝑏𝑁 ) for each round of bidding drawn from 𝐹(𝑣) which is strictly increasing for a losing bidder. this is because we assume rational bidders, such that a bidder who lost the previous round increases his bid in the next round and similarly a bidder who wins consecutive rounds decreases his bids in the next round until a steady state is reached. an auction round is carried out for each transmitting period. 78 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. following our model, suppose that a user 𝑖 transmitting at power 𝑝, submits a bid 𝑏𝑖 to the broker via the control channel. the bid is either taxed or subsidized by the broker. the path loss is dependent on the propagation model adopted, however, the winner ii model, as detailed in [23], was used in this work. this model was used because other theoretical models do not take obstruction and different terrain into account. the user is assumed to have transmitted successfully provided the snir is above the snir threshold and the final bid price is above the reserve prices. the system flow chart is as shown in fig. 2. traffic model ( schedule next arrival) start bid generation if power efficient green payment (tax subtracted) green payment (subsidy added) calculate reserve price increase price is bid above reserve price end assign channel yes no yes no yes no is snir above threshold fig. 2: system flow chart. 3. results and discussions we assume that a user derived the initial bid value from a uniform distribution between a value [3, 5]. the users increase their bids according to the rules of the sealed bid auction as explained earlier. figure 3 shows the average revenue for each traffic load. the revenue increases with traffic load because as the traffic load increases, the competition between the users to get access to the spectrum increases. as seen from the result, the pkrp lowers the revenue of the wsp compared to the gp when the reserve price is not known to the public. this is expected because when the users are aware of the reserve price, the reserve price will guide the user in fixing their bid as shown in eqn. (1). 79 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. the users' bids are distributed around the reserve price. however, without the public knowledge of the reserve price, the revenue of the wsp increases linearly until the system is approaching its capacity. this is because as the system approaches its capacity, the competition in the system increases therefore the users would only be able to win with a larger value of bid. the revenue with the gp also performs better after 3 erlangs as a result of the subsidy received by the low powered users. fig. 3: average revenue for different pricing scheme. at lower traffic load, the tax/subsidy would almost balance out but as seen from the figure, the revenue of the lpu also increases significantly at a traffic load above 3 erlang. this is because the lpu always gets a subsidy at that traffic load and very few highpowered users get through, making the revenue increase significantly. it is worth pointing out that as seen from the proposed model there is no need of subsidizing any user including the low-powered users at lower traffic loads. this is because the system can accommodate all users continently. the result also shows that apart from the reserve price, the gp also has an effect on the revenue. without the gp, the two user groups have an equal probability of winning and no tax or subsidy is applied, but the reserve price is still applied. figure 4(a) shows the average energy consumed for each of the user groups at different traffic loads. without gp, the average energy consumed by each of the user groups is significantly more than the scenario gp. this is because without the gp, both user groups are competing without any group having an advantage over the other and the hpu would be interfering with the lpu. the hpu are also admitted no matter their level of transmitting power. however, with the gp system, the lpu are given an advantage over the hpu because of the subsidy they receive and the only set of admitted hpu is those in the lower end. this is because the users would be admitted based on the received snr at the receiver as explained earlier. the public knowledge of the reserve price reduces the average energy consumed at traffic loads above 3 erlangs. this is because with the public knowledge of the reserve price, a user whose bid is below the reserve price 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0 1 2 3 4 5 6 7 8 (a) traffic load (erlang) a v e ra g e p ri c e p e r f il e s e n t (p ri c e u n it ) without gp with pkrp with gp 80 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. would choose not to transmit and since the reserve price increases with the traffic load more users would have their bids rejected without the knowledge of the reserve price. this is because the valuation of the user without the knowledge of the reserve price does not increase with traffic load until a bidder loses in a bidding round. this shows that our proposed energy model is energy efficient. figure 4(b) shows the average energy consumed without the gp, with the gp, and with public knowledge of the reserve price. the public knowledge of the reserve price performs better overall because of the same reason as explained in fig. 4(a). the knowledge of the reserve price also helps to further reduce the energy consumed because no energy is wasted as a result of the bid been rejected. predominantly, the most likely reason why a user is not admitted is if the sinr of the user is below the sinr threshold. the price feedback only has significant effect on the energy consumed by the highpowered users because, the probability of rejecting a bid as a result of being below the reserve price is more than that of the low powered users since their bid is subsidized, which increases their probability of winning. fig. 4: energy consumption for each user group and the overall system. figure 5(a) shows the delay against throughput for each of the user groups. delay is one of the major factors and it has tremendous impact on the application a wireless system can be put to use for, some applications are delay sensitive while others can cope with a bit of delay. without the gp, the hpu and the lpu experience more delay because the interference in the system is significant. the result also shows that users having the knowledge of the reserve price experience less delay because the users tend not to attempt to transmit when they feel their bid is below the reserve price but actually they should have attempted as the gp would have made their bid above the reserve price. this has 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0 2 4 6 8 10 (a) traffic load (erlang) a v e ra g e e n e rg y c o n s u m p ti o n ( w a tt h o u r p e r f il e ) 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0 2 4 6 8 10 12 14 (b) traffic load (erlang) with pkrp without gp with gp hpu without gp hpu with gp hpu with pkrp lpu without gp lpu with gp lpu with pkrp 81 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. more effect on the hpu compared to the lpu because they are the user group who get subsidized most of the time. it can be seen that our proposed model helps in increasing the revenue of the wsp, reduce the energy consumed and the delay experienced by the users. fig. 5: delay for each user group and for the overall system. 4. conclusion and future work this paper proposes an energy efficiency economic model for dynamic spectrum pricing in a multi-winner scenario using sealed bid auctions with a reserve price. we examined the scenario when the users do not have knowledge of the reserve price and the scenario when they do. it can be seen that our scheme with pkrp might lead to a reduction in the seller's revenue. pkrp also does not provide an incentive for sellers to bid their own true value because they have the knowledge of the reserve price. however, the scheme helps in preventing users who cannot afford to pay above the reserve price of putting in a bid. this helps in saving some energy as a result of putting in a bid and losing out after the auction process. our scheme shows that the user can use the gp to increase revenue, reduce energy consumed and delay experience. this is in addition to better throughput performance. the future work is expected to examine the impact of the proposed gp model on the primary users. references [1] sengupta s, chatterjee m. (2009) an economic framework for dynamic spectrum access and service pricing. ieee/acm transactions on networking, 17:1200-1213. [2] hossain e, niyato d, han z. (2009) dynamic spectrum access and management in cognitive radio networks, cambridge university press. [3] valenta v, marsalek r, baudoin g, villegas m, suarez m, robert f. (2010) survey on spectrum utilization in europe: measurements, analyses and observations, in cognitive radio 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0 0.2 0.4 0.6 0.8 (b) traffic load (erlang) without gp with gp with pkrp 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0 0.1 0.2 0.3 0.4 0.5 0.6 (a) traffic load (erlang) a ve ra ge d el ay p er f ile s en t (s ec ) hpu without gp hpu with gp hpu with pkrp lpu without gp lpu with gp lpu with pkrp 82 iium engineering journal, vol. 18, no. 1, 2017 oloyede et al. oriented wireless networks & communications (crowncom), 2010 proceedings of the fifth international conference, pp 1-5. [4] kash ia, murty r, parkes dc. (2014) enabling spectrum sharing in secondary market auctions. ieee transactions on mobile computing, 13:556-568. [5] nekovee m. (2009) quantifying the availability of tv white spaces for cognitive radio operation in the uk. ieee conference on communications workshops, pp 1-5. [6] akyildiz if, lee wy, vuran mc, mohanty s. (2008) a survey on spectrum management in cognitive radio networks. ieee communications magazine, 46:40-48. [7] haykin s. (2005) cognitive radio: brain-empowered wireless communications. ieee journal on selected areas in communications, 23:201-220. [8] mitola j. (1999) cognitive radio for flexible mobile multimedia communications, in mobile multimedia communications, 1999. (momuc '99) ieee international workshop, pp 3-10. [9] oloyede a, dainkeh a. (2015) energy efficient soft real-time spectrum auction in advances in wireless and optical communications (rtuwo), pp 113-118. [10] mölleryd bg, markendahl j, mäkitalo o. (2009) analysis of operator options to reduce the impact of the revenue gap caused by flat rate mobile broadband subscriptions, in 8th conf. on telecom, media & internet tele-economics. [11] jia j, zhang q, liu m. (2009) revenue generation for truthful spectrum auction in dynamic spectrum access, presented at the proceedings of the tenth acm international symposium on mobile ad hoc networking and computing, new orleans, la, usa, 2009. [12] sung hyun c, la rj. (2013) secondary spectrum trading auction-based framework for spectrum allocation and profit sharing. ieee/acm transactions on networking, 21:176189. [13] gizelis ca, vergados dd. (2011) a survey of pricing schemes in wireless networks. ieee communications surveys & tutorials, 13:126-145. [14] huang j, berry ra, honig ml. (2006) auction-based spectrum sharing. mobile netw. appl., 11:405-418. [15] fan r, zheng y, an j, jiang h, and li x. (2016) dynamic pricing over multiple rounds of spectrum leasing in cognitive radio. ieee transactions on vehicular technology, 65:1782-1789. [16] krishna v. (2010) auction theory: academic press usa. [17] gandhi s, buragohain c, cao l, zheng h, suri s. (2008) towards real-time dynamic spectrum auctions. computer networks, 52:879-897. [18] fitchard k. (2009) wireless 2025: a look at wireless in the year 2025. available: http://connectedplanetonline.com/wireless/news/wireless-future-year-2025-0409/ [19] burr b, papadogiannis a, jiang t. (2012) mimo truncated shannon bound for system level capacity evaluation of wireless networks in wireless communications and networking conference workshops (wcncw), pp 268-272. [20] oloyede a, grace d. (2016) energy efficient bid learning process in an auction based cognitive radio networks. bayero university journal of engineering and technology (bjet). [21] oloyede a, grace d. (2013) energy efficient soft real time spectrum auction for dynamic spectrum access. presented at the 20 th international conference on telecommunications casablanca. [22] oloyede a, grace d. (2016) energy efficient short term spectrum auction using the concept of green payments. wireless personal communications, pp 1-28. [23] kyösti p, meinilä j, hentilä l, zhao x, jämsä t, schneider c, et al. (2007). ist-4-027756 winner ii d1.1.2 v1.2 winner ii channel models. available: http://www.cept.org/files/1050/documents/winner2%20-%20final%20report.pdf 83 http://connectedplanetonline.com/wireless/news/wireless-future-year-2025-0409/ microsoft word 0_vol_16_no_2_2015_special issue on energy_compiled.docx iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 43 mathematical modelling and performance analysis of different solar air collectors m.a. karim and z.m. amin mechanical engineering discipline, science and technology faculty, queensland university of technology, australia. azharul.karim@qut.edu.au, and zakaria.amin@gut.edu.au (received: sept. 10, 2015; accepted: oct. 15, 2015; published on-line: nov. 30, 2015) abstract: the purpose of using solar air collectors is to raise the atmospheric air temperature to a temperature which can be used for various low and medium temperature applications. collector, absorber and airflow arrangement are the most important components in the solar air collector. the performance of the collector depends on its heat loss and the absorber area that is in contact with the airflow. this study involves the theoretical simulation of the effect of mass flow rate on the performance, for flat plate and v-groove collectors that are in single and double pass configurations. results show that the v-groove double pass air collector has the highest efficiency value of 56% at 0.06 kg/m s. the performance is greater than flat plate double pass collector, which has an efficiency of 54% under the same operating conditions. abstrak: tujuan menggunakan pengumpul udara solar adalah untuk meningkatkan suhu udara atmosfera kepada suhu yang boleh digunakan untuk pelbagai aplikasi suhu rendah dan sederhana. absorber pemungut dan susunan aliran udara adalah komponen yang paling penting pada pemungut udara solar. prestasi pengumpul bergantung kepada kehilangan haba dan kawasan penyerap yang melekat hubungan dengan aliran udara itu. kajian ini melibatkan simulasi teori kesan kadar aliran jisim kepada prestasi, untuk plat rata dan v-alur pengumpul yang dalam konfigurasi pas tunggal dan berganda. keputusan menunjukkan bahawa v-alur dua pengumpul udara pas mempunyai nilai kecekapan tertinggi sebanyak 56% pada 0.06 kg/m s. prestasi yang lebih besar dari plat rata pengumpul pas dua kali, yang mempunyai kecekapan 54% di bawah keadaan operasi yang sama. keywords: solar air collector; flat plate collector (fpc); v-groove collector; efficiency; single pass; double pass 1. introduction solar energy is a solution to the increasingly limited fossil fuel resources problem. the solar collector is one of the most important components of solar energy systems. the energy of the solar radiation is in this case converted to heat with the use of the solar panel [1]. solar air collectors have been used for several applications which include space heating, food drying, swimming pool heating, thermal industrial process and solar drying. attention has been given to the renewable energy sources due to several factors including environmental issues and limited resources of fossil fuel [2]. converting solar radiation into heat is one of the most common applications of solar energy [3]. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 44 the purpose of using solar air collectors is to raise the atmospheric air temperature to a higher temperature which can be used in different applications [4]. as the air passes through the solar collector, the heat that is gained by the sun’s radiation will be transferred to the air thereby raising its temperature. there are several designs of solar air collectors which are used in different applications. the designs are based on the required heat capacity. the efficiency of collectors in air heating is low due to low convective heat transfer coefficients between absorber and heat losses to the surrounding through the top cover [4]. in order to improve the performance of the collector, flow arrangement could be changed to reduce the heat loss and the absorber shape could be changed to a v-groove of finned shape to increase the absorbent area. this study was conducted to determine the efficiency of flat plate and v-groove solar collectors with different air flow arrangement by analysing the mathematical equations. there are many alternative designs for solar air collectors. a good design must be able to minimize heat losses from the collector in order to increase its operating efficiency. the three main features in the collector are the top cover, absorber, and coating [6]. top cover transmissivity (τ = fraction transmitted) which transmits the sunlight is made of glass or plastic. there could be some heat loss by radiation and convection to the ambient since the air is in contact with the glazed layer. the absorptivity (α = fraction absorbed) which is based on the absorber type, and the coating (ε = emittance) are the other main features. absorptivity varies with wavelength, which is very important when dealing with absorbed solar radiation and ambient temperature radiation on the same surface [6]. in addition to this, reflectivity ( = fraction reflected), is the parameter which refers to the amount of sunlight that is reflected by the glazed surface. the idea of the absorber is to convert the solar radiation to heat. the performance of the absorber also depends on the coating which is the surface that is facing the radiation [7]. dark colour paint or selective coating is used for the absorber as well as porous cloth material. this study looks at the mathematical equations of flat plate and v-groove solar air collectors with single and double pass mass flow to determine the thermal efficiency of each collector type. there are several factors that will affect the efficiency of the collector; therefore, these collectors will be tested under the same operating conditions. matlab software is used to run the simulations for these collectors. 2. collector types 2.1 flat plate collector (fpc) the flat plate collector (fpc) is one of the common solar collector designs. the system basically is a metal box that has a glass or plastic cover on the top and an absorber plate on the bottom. different materials can be used for the absorber plate such as copper, aluminium and steel. insulation is used in the back of the collector to minimise the heat losses. the insulation should be selected such that it does not melt, shrink or outgas at high temperatures of up to 200oc [7]. the fpc is usually used for applications with low or medium temperature range between ambient temperatures of 60 to 100oc [5]. the idea of the system is that the inlet air will heat up via the absorber plate when passing through it. the purpose of the absorber plate is to absorb the radiation from the sun. fpc collector designs have different airflow patterns including single pass which could be from the top or below or double pass flow. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 45 for the top flow case the air flow passes above the absorber plate as shown in fig. 1. the air flows between the glazed and the absorber plate. the efficiency in this case is low because the air is in contact with the glass cover which results to heat losses to the ambient air. fig. 1: top flow flat plate absorber [5]. the advantages of this type is that it has simple construction and cheap. however, it has only one surface that can transfer heat and has high heat losses. double-glazed glass can be used to reduce the heat losses but it also decreases the solar radiation. the configuration where the air flow passes below the absorber is commonly used in solar air collectors. as shown in fig. 2, a plate parallel to the absorber plate is provided for insulation. this increases the heat transfer surface area to the air stream. in the double pass flow case, the air flow passes on both sides of the absorber as can be seen in fig. 3. the advantage of this system is that it has double the effective heat transfer area which increases the heat transfer to the air [5]. this type of flow arrangement can also be applied to v-groove and finned collectors. fig. 2: bottom flow flat plate absorber [5]. fig. 3: double pass flow flat plate absorber [5]. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 46 2.2 v-groove collector since the heat transfer between the absorber plate and the flowing air is low on the flat plate collector, this configuration results in less air being heated. in order to improve the performance of the system, the v-groove plate was used as the absorber. in this type of collector, the solar radiation passes through the glass to the absorber, which in this case is a v-groove as shown in fig. 4. this type of collector can operate in single or double pass mass flow. according to the past research, a v-grooved absorber with double flow has 45% additional efficiency compared to that of the single mode [10]. fig. 4: v-groove collector [5]. 3. matlab simulation 3.1 flat plate collector (fpc) in order to simplify the collector modelling, the following assumptions were made. • the collectors are at steady state thermal performance. • the temperature drop through the glass cover, absorbing plate, and bottom plate are negligible. • the heat flow through the back insulation is one-dimensional, that is the direction perpendicular to the air flow. • the sky is assumed to be a blackbody for long-wavelength radiation at an equivalent sky temperature. • the front and back surfaces losses are the same as the ambient temperature. • dust and dirt on the collectors are considered negligible in its effect of shading of the collector absorbing plates. • the thermal inertia of collector components is neglected. • the operating temperatures of collector components and mean air temperatures in air channels are assumed to be uniform. • temperature of the air varies only in the flow direction. • the channels are free of air leakage. • the thermal losses through the collector backs are neglected. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 47 3.2 flat plate and v-groove collector single pass equations an iterative matrix method using matlab is used to calculate the temperatures. the temperatures will be assumed in the initial stage to determine the heat transfer coefficients and heat losses from the collector. the energy balance equations in the matrix form are used to calculate the new temperature of t , t , t , t and t . the values of these parameters will be obtained numerically with an iteration method. once the new temperatures are found, the equations given below can be used. the equations from [3] will be used to calculate the thermal performance using the matrix method. the thermal network for single pass air collector is illustrated in fig. 5 below: fig. 5: thermal network for the single cover solar air collector. the energy balance in the glass cover is: s + (h + h ) t − t = (h + h )(t − t ) (1) energy balance on the absorbing plate is: s = (h + h )(t − t ) + h t − t + h t − t (2) energy balance for the fluid: h t − t = q + h t − t (3) energy balance on the bottom plate h t − t + h t − t = u t − t (4) the solar radiation absorbed by the absorbing plate per unit area which is equal to the difference between the incident solar radiation and the optical loss, is calculated by: s = the convection heat transfer coefficient between the glass cover and the absorbing plate is: ℎ = ′ (b) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 48 h′ is the mean gap thickness between the cover and the absorbing h′ (m) is calculated by h′ = + 0.5 , where is the high of the v-groove absorber. for flat plate and v-groove collector, nusselt number for natural convection can be estimated by the following correlation: nu = 1 + 1.44 1 − ( . ) . 1 − + − 1 the equation above is valid for 0° ≤ θ ≤ 75°. ra is the rayleigh number, which is defined as: = radiation heat transfer coefficients between the glass cover and the absorbing plate and between the absorbing plate is represented as: ℎ = ( ) the overall top loss coefficient is: = ℎ + ℎ the convection heat transfer coefficient from the glass cover due to wind is ℎ = 5.7 + 3.8 . radiation heat transfer coefficient from the glass cover to sky referred to the ambient air temperature can be obtained as follows: ℎ = ( + )( + ) ( ) ( ) the sky temperature t is estimated by = 0.0552 . the incident solar radiation absorbed by the absorbing plate is s ≅ 0.97τ α i nusselt number for flat-plate collector can be obtained by the equation below: nu = 0.0158 re . also, the nusselt number for v-groove collector is estimated by the following correlation when < 2800 nu = 2.821 + 0.126re when 2800 ≤ ≤ 10 nu = 1.9 × 10 . + 225 when 10 ≤ ≤ 10 nu = 0.0302 . + 0.242 . where reynolds number for a flat plate absorber is: = iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 49 and reynolds number for a v-groove plate absorber is given by = hydraulic diameter of the airflow channel formed by the absorbing plate and the bottom plate is d (m). the hydraulic diameter for a flat plate absorber is given as = ′ ′ = . and the hydraulic diameter for a v-groove absorber is given as: = the radiation heat transfer coefficients between the glass cover and the bottom plate are predicted by: ℎ = ( ) the convection heat transfer coefficients for the fluid moving on the absorbing plate and on the bottom plate are calculated by: ℎ = the conductive heat transfer coefficient between the second pass fluid and the bottom plate is assumed to be equal, therefore, ℎ = ℎ the heat gain equation is given as: = − , where, = ̇ the conduction heat transfer coefficient across the insulation is estimated by: = δ finally, the collector efficiency can be determined by: = ( ) the data below are for t from 280 k to 470 k. the following empirical correlations can be used to estimate the air density: ρ = 3.9147 − 0.016082t + 2.9013 × 10 t − 1.9407 × 10 t thermal conductivity: k = (0.0015215 + 0.097459t − 3.3322 × 10 t ) × 10 and dynamic viscosity: µ = (1.6157 + 0.06523t − 3.0297 × 10 t ) × 10 also, β = (1/k) and c ≅ 1000 j/kg. k can be assumed. 3.3 flat plate and v-groove collector double pass equations and results the thermal network for double-pass solar air collector is illustrated in fig. 6. the equations from [8] will be used to calculate the thermal performance using the matrix method. energy balance equation for the top cover: + ℎ − + ℎ − = ( − ) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 50 energy balance equation for the fluid’s first pass: ℎ − = ℎ − + energy balance equation for the absorber plate: = ℎ − + ℎ − + ℎ − + ℎ ( − ) energy balance equation for the fluid’s second pass: ℎ − = ℎ − + energy balance equation for the bottom plate: ℎ − + ℎ − = ( − ) the amount of heat transferred in the first pass fluid and the second pass fluid are calculated as: = 2 ( − ) = 2 ( − ). fig. 6: thermal network of a double-pass solar air collector. 4. results and discussion the simulations were run at the same operating condition to identify the thermal efficiency of each collector. the simulations were done for the operating conditions listed below in table.1. figure 7 represents the variation of the efficiency and output temperature of the collector with the mass flow rate. for the outlet temperature, as the flow rate increases the air does not get much time to capture the solar heat. thus, the temperature has reverse relation with the flow rate which is also affirmed in fig. 7. for the case of efficiency, there is an initial increase with flow rate but after 0.02 kg/m2s, the efficiency is almost constant. these two curve trends are true for all the four collectors, as observed in fig. 7 and fig. 8. (b) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 51 table 1: initial parameters for simulation. parameter value unit parameter value unit 600 w/m2 0.94 - 30 degrees 0.9 - 1 m 0.94 - 2 m 0.06 - 0.05 m 0.95 - 0.025 m 0.84 - 0.035 kg/m2s 1 m/s 300 kelvins 5.67e-08 w/m2k4 300 kelvins 9.81 m/s2 0.025 w/mk 1 m/s fig. 7: performance analysis of v-groove double pass collector. figure 8 represents the variation of the outlet temperature for the four types of collectors. it is noticed that at higher flow rate the output temperature is almost similar for all the collectors. but for lower flow rate, the v-grove double pass collector clearly provides a better output with the maximum temperature of 385 kelvin. another observation from fig. 8 is that the double pass flat pate collector and single pass vgroove collector has similar thermal performance with mass flow rate. this indicates the better productivity through the v-groove corrugated absorber plate. 0 0.01 0.02 0.03 0.04 0.05 0.06 0.2 0.4 0.6 0.8 mass flow rate (kg/m2 s) e ff ic ie nc y % v-groove double pass collector mass flow rate vs efficiency efficiency 0 0.01 0.02 0.03 0.04 0.05 0.06 300 350 400 mass flow rate (kg/m2 s) te m p o ut p ut v-groove double pass collector mass flow rate vs temp out put temp out put iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 52 fig. 8: outlet temperature comparison for the four types of collectors. figure 9 represents the variation of the efficiency for the four types of collectors. the flat plate single pass flow collector has efficiency of 41%, flat plate double pass flow collector has efficiency of 55%, v-groove single pass flow collector has efficiency of 54% and v-groove double pass flow collector has efficiency of 56%. it is concluded from the results that v-groove double pass flow collector has the highest efficiency value due to the larger contacting area created by the v-groove absorber. in this case the air is in contact with the absorber from both sides. fig. 9: efficiency comparison for the four type of collector. the comparative relation of solar radiation and mass flow rate on thermal performance for v-groove double pass collector is represented in fig. 10 and fig. 11. in fig. 10, the radiation has a positive impact on output whereas flow rate has a negative impact on output. from fig. 10 it is further observed that flow rate dominates more on the 300 310 320 330 340 350 360 370 380 390 400 0 0.01 0.02 0.03 0.04 0.05 0.06 o ut p ut t em pe ra tu re mass flow rate v-groove sp v-groove-dp flat plate sp flat plate dp 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.055 0.06 0.065 ef fe ci ec y mass flow rate v-groove sp v-groove-dp flat plate sp flat plate dp iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 53 output temperature. as in fig. 10, slope for ‘output temperature vs. mass flow rate’ is steeper than ‘output temperature vs. radiation’. fig. 10: variation of output temperature with radiation and mass flow rate for vgroove collector. for case of efficiency as shown as fig. 11, the relation is not as straight forward as the radiation is embedded in the efficiency formula. figure 11 shows that there are some optimum points, and this may be further studied. fig. 11: variation of efficiency with radiation and mass flow rate for v-groove collector. 5. conclusion performance curves of flat plate and v-groove collectors with single and double pass have been obtained. these include the effects of mass flow rate and solar radiation on output temperature and efficiency of the solar collector. the results show that v-groove double pass collector has the highest efficiency. lastly, from the comparative study on the effects of flow rate and radiation, the thermal performance of the solar collector is found to be strongly dependent on the flow rate. 0 0.1 0.2 0.3 0.4 0.5 0.6400 600 800 1000 1200 0 200 400 mass flow rate radiation(w/m2) te m pe ra tu re o ut p ut -1200 -1000 -800 -600 -400 -200 0 200 400 0 0.1 0.2 0.3 0.4 0.5 0.6 400 500 600 700 800 900 1000 0 20 40 60 80 radiation(w/m2) mass flow rate f ff ec ie nc y( % ) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 54 references [1] karim ma, hawlader mna. (2004) development of solar air collectors for drying applications. energy conversion and management, 45:329-344. [2] tchinda r. (2009) a review of the mathematical models for predicting solar air heater systems. renewable and sustainable energy reviews, 13:1734-1759. [3] liu t, lin w, gao w, luo c, li m, zheng q, xia c. (2007) a parametric study on the thermal performance of a solar air collector with a v-groove absorber. international journal of green energy, 4(6): 601-622 [4] karim ma, hawlader mna. (2006) performance evaluation of v-groove solar air collector for drying applications. applied thermal engineering, 26:121-130. [5] tiwari gn, mishra rk. (2012) advanced renewable energy sources, cb4 0wf, rsc publishing thomas grahman house, cambridge, uk. [6] cengel y, boles m. (2005) thermodynamics: an engineering approach, 5th ed., mcgrawhill college, boston. [7] hastings sr, mørck o. (2000) solar air systems: a design handbook. colorado state university, usa. [8] ong ks. (1995) thermal performance of solar air heaters: mathematical model and solution procedure. solar energy, 55:93-109. [9] duffie ja, backman wa. (2006) solar engineering of thermal processes, 3rd ed., wiley, new york. [10] schumann tew. (1929) heat transfer: a liquid flowing through a porous prism. journal of the franklin institute, 208(3):405-416. nomenclature i solar insolation rate incident on the glass cover (w/m ) τ transmissivity of solar radiation of the glass cover α absorptivity of solar radiation of the absorbing plate s solar radiation absorbed by glass cover and absorber plate ( / ) q energy gain (w/m ) gap between v-groove absorber and glass cover ( ) height of v-groove ( ) sky temperature (k) mean temperature on the glass cover (k) mean temperature on the absorbing plate (k) mean air temperature (k) mean temperature on the bottom plate (k) ambient air temperature (k) inlet temperature (k) outlet temperature (k) q heat transferred to the air ( / ) c specific heat of air ( / ) ṁ air mass flow rate per unit area of collector iium engineering journal, vol. 16, no. 2, 2015 special issue on energy karim and amin 55 h thermal losses to the glass cover by natural convection ℎ thermal losses to the glass cover by thermal radiation ( / ) h thermal losses to the glass cover by the bottom plate by thermal radiation (w/m k) h convection heat transfer coefficient of fluid on the bottom plate (w/m k) h convection heat transfer coefficient from the glass cover due to wind (w/m k) h radiation heat transfer coefficient from the glass cover to sky (w/m k) u conduction heat transfer coefficient across the insulation (w/m k) h convection heat transfer coefficients for the fluid (w/m k) η efficiency v wind velocity of the ambient air (m/s) σ stefan-boltzmann constant (5.67 × 10 w/m k ) ε emissivity of thermal radiation of the glass cover ε emissivity of thermal radiation of the absorbing plate ε emissivity of thermal radiation of the bottom plate k thermal conductivity δ mean thickness of the insulation h mean gap thickness between the cover and the absorbing (m) nu nusselt number for the natural convection β thermal expansion coefficient µ dynamic viscosity of air (kg/m. s) g acceleration due to gravity (m/s ) d hydraulic diameter (m) w collector width (m) nu nusselt number for the convection of fluid re reynolds number for flat plate absorber ∅ tilt angle of the collector (degrees) k thermal conductivity of air (w/m. k) w width of the collector (m) l length of the collector (m) application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 ahmad fauzi et al. radiation performance of gan and inas/gaas quantum dot based devices subjected to neutron radiation dhiyauddin ahmad fauzi1*, nahrul khair alang md rashid2, muhammad rawi mohamed zin3 and nurul fadzlin hasbullah4* 1,4department of electrical and computer engineering, 2department of mechatronics engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 3materials technology group, malaysian nuclear agency, bangi, selangor, malaysia. *corresponding authors: 1dhiyauddin.fauzi@gmail.com, 4nfadzlinh@iium.edu.my (received: 18th mar. 2016; accepted: 4th dec. 2016; published online: 30th may 2017) abstract: in addition to their useful optoelectronics functions, gallium nitride (gan) and quantum dots (qds) based structures are also known for their radiation hardness properties. with increasing demand for such semiconductor material structures, it is important to investigate the differences in the reliability and radiation hardness properties of these two devices. for this purpose, three sets of gan light-emitting diodes (led) and inas/gaas dot-in-a well (dwell) samples were irradiated with thermal neutron of fluence ranging from 3×10 13 to 6×10 14 neutron/cm 2 in a puspati triga research reactor. the radiation performances for each device were evaluated based on the currentvoltage (i-v) and capacitance-voltage (c-v) electrical characterisation method. results suggested that the gan based sample was less susceptible to electrical changes due to the thermal neutron radiation effects compared to the qd based sample. abstrak: selain daripada kegunaanya sebagai bahan optoeletronik, struktur berasaskan galium nitrida (gan) dan kuantum dot (qd) juga dikenali atas sifatnya yang teguh daripada kesan radiasi. dengan permintaan yang kian meningkat, adalah amat penting bagi kedua-dua bahan ini diuji bagi melihat tahap prestasi dan keteguhannya terhadap kesan radiasi. bagi tujuan ini, tiga set sampel daripada diod pemancar cahaya (led) dan dot-dalam-takungan (dwell) di dedahkan kepada radiasi neutron haba dengan jumlah fluens dari 3×10 13 hingga ke 6×10 14 neutron/sm 2 di reaktor nuklear puspati triga. prestasi bagi setiap bahan ujikaji kemudian di uji dengan menggunakan kaedah arus elektrik-voltan (i-v) dan kapasitan-voltan (c-v). hasil daripada ujian berkenaan mencadangkan bahawa sampel dari gan kurang mengalami perubahan apabila didedahkan kepada radiasi neutron berbanding dengan sampel qd. keywords: gan; inas/gaas; quantum dots; neutron; electrical characteristics 1. introduction semiconductor based devices find many applications in harsh radiation environments such as space, for satellite optocouplers, and radiation physics laboratories, for particle detectors [1; 2]. serious damage due to the radiation effects such as increment in the leakage current [3; 4] and reduction in the charge collection efficiency [5] may occur in such devices if proper shielding is not well integrated. however, to some devices such as 101 iium engineering journal, vol. 18, no. 1, 2017 ahmad fauzi et al. sensors and radiation detectors, direct shielding may hinder the device‘s useful function which, at length, will result in precision and accuracy deterioration. to other devices, shielding could increase the payload of the system and consequently the cost of operation. for this reason, the reliability of these devices is greatly dependent on the material composition and material structure. the search for a radiation-hard semiconductor material and material structure has long been performed and the effort continues to progress along with the development of new semiconductor technology. to date, some of the materials and material structures deemed radiation-hard include; sic pn-junction, iii-v nitride-based heterostructure, inas/gaas quantum dot (qd) and ingaas quantum well (qw) [6-8]. for optoelectronics purposes, it was reported that gan and inas/gaas qd based diodes are less susceptible to radiation damage compared to other structures [9-11]. these two materials could hold the key for future free-space communication technology which highlights the importance of studying their reliability against the effects of radiation. this paper was written to evaluate the tolerance of two of the most radiation-hard material structures known in optoelectronics applications; the inas/gaas quantum dot-inwell (dwell) structure and the gan/sic double heterojunction light emitting diode (led) structure. all samples were subjected to thermal neutron radiation to assess their radiation hardness properties against the displacement damage. the investigations were carried out through two electrical characterisation methods; the current voltage (i-v) and capacitance-voltage (c-v) which yield information of the current density, series resistance, doping profile and the carrier removal rate of both samples. 2. experimental details 2.1 sample specifications for this study, two different types of diodes were used; commercial off-the shelf gan leds manufactured by vishay gmbh and mesa inas/gaas dwell diodes fabricated by the university of sheffield. the gan led samples were fabricated on sic grown by the metal-organic chemical vapour deposition (mocvd) technique with an approximate active area value of 0.09 cm2. further details on the gan led layers will not be disclosed due to the confidentiality policy of the manufacturer. the inas qds samples, on the other hand, were grown using stranski-krastanov (s-k) method where the qds were sandwiched between 2 nm thickness of in0.15ga0.85as and 6 nm thickness of in0.15ga0.85 as to develop a dwell structure. the active region consists of inas/gaas dwells separated by 50 nm gaas spacer layers. enclosing the active region are undoped 150 nm gaas/algaas waveguides with the n-type al0.4 ga0.6 as deposited on the lower cladding layers and the p-type on the upper layers. the growth process was completed with 300 nm p+-gaas ohmic contact. 2.2 neutron irradiation process all samples were exposed to thermal neutron radiation via pneumatic transfer system (pts) of the puspati triga mark ii research reactor at the malaysian nuclear agency. throughout the irradiation process, the power level of the reactor was kept at 750 kw with maximum thermal neutron flux rate peaked at 1×1012 neutron/cm2.s and the reactor core temperature maintained at an average of 300 oc. each set of samples contains three devices with nominally identical i-v and c-v characteristics, prepared in separate polyethylene vials. the qds and gan samples were exposed to two different thermal neutron fluence range; with 3×1013 to 9×1013 neutron/cm2 for the qds samples and 6×1013 102 iium engineering journal, vol. 18, no. 1, 2017 ahmad fauzi et al. to 6×1014 neutron/cm2 for the gan samples. the higher fluence range used on the gan samples is to produce new findings since the report on the lower fluence has been justified by li and subramanian [12] where there were no changes in the electrical characteristics observed. the electrical characterizations of all samples were conducted in the dark at room temperature (≈300 k) using keithley 42000 scs parameter analyzer connected to a probe station and 8101-4trx test fixture. measurements were consecutively repeated three times to achieve reproducibility on the obtained results. 3. results and discussion the reverse-bias and forward-bias current densities of the gan samples and qds samples plotted with respect to the voltage before and after neutron irradiation are shown in fig. 1 and fig. 2 respectively. voltage (v) -30 -20 -10 0 c u rr e n t d e n s it y ( a /c m 2 ) 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 non-radiated 6x10 14 n/cm 2 increasing neutron fluence fig. 1: reverse-bias and forward-bias i-v characteristics of gan samples before and after neutron irradiation of 6×1014 n/cm2. based on fig. 1 above, there are no significant changes observed neither in the forward bias nor in the reverse bias characteristics of the gan samples. similar trends were also observed in other tested models of gan/sic leds. increment in the leakage current however is observed for neutron fluence larger than 1×1015 neutron/cm2 which is in agreement with grant et al., lorenz et al. and qiu et al. [13-15]. some of the properties suggesting the radiation hardness of gan/sic based diode include; wide bandgap energy [11; 16], high thermal stability and self-annealing property [16; 17], as well as small thermal neutron capture cross section of the nitride [18]. additionally, due to the presence of sic (the polymer type is not disclosed by the manufacturer), it is believed that the bandgap of the heterostructure is altered to become much wider reducing the rate of generation-recombination of carriers [19]. a perfect fit of the forward-bias i-v characteristics with the ideal diode equation yield the value of the ideality factor, n of 3.5 and series resistance, rs of 0.5 ω. according to the sah-noyce-shockley (sns) analysis, as the value of n approaches 2, the dominant current in the device may largely be contributed by the generation-recombination process [20]. 103 iium engineering journal, vol. 18, no. 1, 2017 ahmad fauzi et al. however, since the ideality factor obtained in the gan sample is greater than 2, the sns analysis is therefore unaccountable for the current behavior. such behavior is reported to be either due to an excessive contact resistance between metal and the p-type layer of the sample or the deep-level trap-assisted tunneling mechanism [21]. figure 2 shows the i-v characteristics of the qds samples, indicating a significant increment in the reverse-bias leakage current densities of up to 2 orders of magnitude under the maximum neutron irradiation of 9×1013 n/cm2. the reverse-bias current densities are observed to increase proportionally with the increase in neutron fluence. a similar trend is also observed in the forward-bias i-v characteristics of the qds samples with maximum increment in the leakage current density of about 4.5 times. voltage (v) -30 -25 -20 -15 -10 -5 0 c u rr e n t d e n s it y ( a /c m 2 ) 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 non-radiated 3x10 13 n/cm 2 6x10 13 n/cm 2 9x10 13 n/cm 2 increasing neutron fluence fig. 2: reverse bias and forward bias i-v characteristics of qds samples before and after neutron irradiation of up to 9×1013 n/cm2. based on the fitting of the ideal diode equation on the forward bias i-v characteristics (illustrated in fig. 3), it is noted that the qds device ideality factor increases from 1.77 (before irradiation) to 1.86 (after being irradiated with 9×1013 neutron/cm2) while the measured series resistance increases from 0.02 ω to a maximum value of 0.05 ω. the parameters and results of the fittings are tabulated in table 1. increment in the leakage current densities is highly believed to be associated with the neutron induced trap-assisted generation-recombination (tagr) process [4; 22] which can be modelled as in [23]. these charge carrier traps or non-radiative recombination centers are known to be the result of the displacement damage effect which can be instigated by the incident neutron particles as well as recoil atoms through secondary events known as primary knock-onatoms (pkas) [4]. additionally, it is also believed that the formation of in situ traps due to growth defects may also assist in the propagation of further traps giving rise to the leakage current density values. 104 iium engineering journal, vol. 18, no. 1, 2017 ahmad fauzi et al. voltage (v) 0.0 0.2 0.4 0.6 0.8 1.0 c u rr e n t d e n s it y ( a /m 2 ) -30 -25 -20 -15 -10 -5 non-radiated n=1.77 rs=0.02 9x10 13 n/cm 2 n=1.86 rs=0.05 fig. 3: forward bias i-v fittings of the qd samples before and after neutron irradiation. table 1: fitting parameters of the qds forward bias i-v characteristics fluence (n/cm 2 ) n±0.01 rs±1m (ω) unirradiated 1.77 0.02 3×1013 1.81 0.03 6×1013 1.84 0.04 9×1013 1.86 0.05 neglecting the minimal effect of gamma radiation, the linear increment in the leakage current can be explained by the relation of the saturation current (a) with the neutron fluence, ϕn (n/cm 2) given by equation (1) [12]: 𝐼𝑜{𝜙𝑛} = 𝐼𝑜{0} + 𝑘𝜙𝑛 (1) where 𝐼𝑜{0} is the pre-exponential term before neutron irradiation, and k is the damage factor (acm2/n). the saturation current is further defined as io = q ni w σ υth n with q being the electron charge, ni the intrinsic concentration, w the width of depletion region, σ the electron and hole capture cross section, υth the electron’s thermal velocity, and nt the trap density. the damage factor for the 3, 6 and 9×10 13 neutron/cm2 irradiated samples are 3.52×10-22, 3.49×10-22 and 3.24×10-22 acm2/n respectively. based on these results, it is worthy to note that the damage incurred in the qd samples are reduced with increasing neutron fluence. this, to our knowledge, could be either a sign of a series resistance effect or the thermal annealing of defects initiated by the high temperature of the reactor core. with regard to the increment in the series resistance or the series resistance effect, review suggested that it may be caused by any of these three major reasons; thermal annealing effect [24], carrier removal through deep carrier trapping [4; 25] and neutron transmutation doping (ntd) effect [4]. the thermal annealing effect facilitates the curing of defects, hence causing the diode to behave like it is intrinsic. alternatively, the deep carrier trapping and ntd effects change the resistance by altering the carrier 105 iium engineering journal, vol. 18, no. 1, 2017 ahmad fauzi et al. concentration of the device. the carrier trapping reduces the concentration of carriers while the ntd changes the concentration type from p-type to n-type when the thermal neutron undergoes inelastic interaction with the lattice. to prove the existence of such effects after neutron irradiation, the samples are further characterized using a c-v characterisation technique. however, prior to the c-v characterisation of the samples, it is important to investigate the reverse bias leakage current mechanism to better understand the carrier transport of neutron irradiated qds. an attempt to fit the tagr model alone on the reverse-bias characteristics of the qd sample came to no avail. therefore, aside from the tagr process it is believed that there could be another mechanism that contributed to such i-v characteristics after the neutron irradiations. although some claimed that the extra contributing mechanism is due to tunnelling [9; 10; 22], our further analysis indicates that the viable mechanism in the high field region is due to the frenkelpoole mechanism [23] . voltage (v) -30 -25 -20 -15 -10 -5 0 c a p a c it a n c e ( f ) 2x10-12 3x10-12 4x10-12 5x10-12 6x10-12 7x10-12 8x10-12 9x10-12 10-11 non-radiated after 9x1013n/cm2 (a) width (m) 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 d o p in g c o n c e n tr a ti o n ( c m -3 ) 0.0 2.0e+15 4.0e+15 6.0e+15 8.0e+15 1.0e+16 1.2e+16 1.4e+16 1.6e+16 1.8e+16 2.0e+16 non-radiated after 9x1013n/cm2 (b) fig. 4: top (a): the c-v characteristics and bottom (b): the doping profile of the qd samples before and after neutron irradiation of 9×1013 n/cm2. 106 iium engineering journal, vol. 18, no. 1, 2017 ahmad fauzi et al. the room-temperature c-v measurements conducted for both gan and qd samples were done at a frequency of 1 mhz to eliminate the effect of built-in charge near the interface [26]. as expected, there are almost no changes observed in the c-v characteristics of the gan samples before and after neutron irradiation. instead, the qd samples show decrement in capacitance of about 6.4% as shown in fig. 4(a). the doping profile for the qd samples is derived based on the linear graded region as illustrated in fig. 4(b). based on the guide lines, it is observed that there is a reduction in the doping concentration of the qd sample after being exposed to thermal neutrons of up to 9×1013 n/cm2. it is understood that the observed trend is due the carrier removal effect which explains the increment in the value of the series resistance. based on other work, it is discovered that the cause of carrier removal is attributable to the ntd effect [23]. it has been suggested that among the key measures that can be taken to improve the susceptibility of the qd samples towards radiation damage include, increasing the number of qds stacks [27] and improving the growth condition [28]. 4. conclusion this paper presents the discussion of the radiation hardness of two different semiconductor material structures; gan/sic double heterojunction led and inas/gaas qds based diode against thermal neutron radiation of fluence ranging from 3×1013 to 6×1014 n/cm2. based on the i-v and c-v measurement analysis, the gan samples showed no significant changes to neutron fluence as high as 6×1014 n/cm2. conversely, the qd samples showed considerable increment both in the leakage current density and series resistance, even at a much lower fluence of 9×1013 n/cm2. we believe that the main reason causing the degeneration of the qd samples’ radiation hardness is the inherited defects incurred during the growth process. better growth of qds samples could be investigated in the near future to compare with current results. acknowledgement the authors would like to acknowledge the malaysian ministry of higher education for the research fund under frgs12-081-0230 grant. references [1] onoda s, mori h, okamoto t, hirao t, itoh h, okada s. (2001) investigation of radiatio n degradation of si and gaalas optical devices due to gamma-ray and electron irradiation. radiation physics and chemistry, 60(4-5):377-380. [2] bisello d, candelori a, giubilato p, kaminski a, litovchenko a, pantano d., et al. (2004) radiation hardness of semiconductor detectors for high energy physics applications. radiation physics and chemistry, 71(3-4):709-711. [3] poyai a, simoen e, claeys c, hayama k, kobayashi k, ohyama h. (2002) radiation effects on the current-voltage and capacitance-voltage characteristics of advanced p-n junction diodes surrounded by shallow trench isolation. nuclear instruments and methods in physics research, section b: beam interactions with materials and atoms, 186(1-4):409413. [4] claeys c, simoen e. (2002) basic radiation damage mechanisms in semiconductor materials and devices radiation effects in advanced semiconductor materials and devices (1st ed.), new york: springer, pp 9-52. [5] garcia lopez j, jimenez-ramos mc. (2014) charge collection efficiency degradation on si diodes irradiated with high energy protons. nuclear instruments and methods in physics research, section b: beam interactions with materials and atoms, 332:220-223. 107 iium engineering journal, vol. 18, no. 1, 2017 ahmad fauzi et al. [6] sciortino s, hartjes f, lagomarsino s, nava f, brianzi m, cindro v, et al. (2005) effect of heavy proton and neutron irradiations on epitaxial 4h-sic schottky diodes. nuclear instruments and methods in physics research, section a: accelerators, spectrometers, detectors and associated equipment, 552(1-2):138-145. [7] mansouri s, marie p, dufour c, nouet g, monnet i, lebius h. (2008) swift heavy ions effects in iii–v nitrides. nuclear instruments and methods in physics research, section b: beam interactions with materials and atoms, 266(12–13):2814-2818. [8] aierken a, guo q, huhtio t, sopanen m, he c, li yd, et al. (2013) optical properties of electron beam and γ-ray irradiated ingaas/gaas quantum well and quantum dot structures. radiation physics and chemistry, 83:42-47. [9] sobolev na. (2008) radiation effects in quantum dot structures. in m. henini (ed.), handbook of self assembled semiconductor nanostructures for novel devices in photonics and electronics, 1 st edn., elsevier, amsterdam, pp 392-447. [10] huang mb, zhu j, oktyabrsky s. (2003) enhanced radiation hardness of photoluminescence from inas quantum dots embedded in an alas/gaas superlattice structure. nuclear instruments and methods in physics research section b: beam interactions with materials and atoms, 211(4):505-511. [11] ionascut-nedelcescu a, carlone c, houdayer a, von bardeleben hj, cantin jl, raymond, s. (2002). radiation hardness of gallium nitride. ieee transactions on nuclear science, 49 i(6):2733-2738. [12] li c, subramanian s. (2003) neutron irradiation effects in gan-based blue leds. ieee transactions on nuclear science, 50(6i):1998-2002. [13] grant j, bates r, cunningham w, blue a, melone j, mcewan f, et al. (2007) gan as a radiation hard particle detector. nuclear instruments and methods in physics research, section a: accelerators, spectrometers, detectors and associated equipment, 576(1):60-65. [14] lorenz k, marques jg, franco n, alves e, peres m, correia mr, et al. (2008) defect studies on fast and thermal neutron irradiated gan. nuclear instruments and methods in physics research section b: beam interactions with materials and atoms, 266(12– 13):2780-2783. [15] qiu j, katz e, lin c.-h, cao l, brillson lj. (2013) the effect of thermal reactor neutron irradiation on semi-insulating gan. radiation effects and defects in solids, 168(11-2):924932. [16] pearton sj, deist r, ren f, liu l, polyakov ay, kim j. (2013) review of radiation damage in gan-based materials and devices. journal of vacuum science & technology a: vacuum, surfaces and films, 31(5):050801/1 050801/16. [17] kim h.-y, kim j, ren f, jang s. (2010) effect of neutron irradiation on electrical and optical properties of ingan/gan light-emitting diodes. journal of vacuum science & technology b: microelectronics and nanometer structures, 28(1):27-29. [18] atsumi k, inoue y, mimura h, aoki t, nakano t. (2014) neutron detection using boron gallium nitride semiconductor material. apl materials, 2(3):032106/1-032106/6 [19] johan bm. (2013) diffusion of fission products and radiation damage in sic. journal of physics d: applied physics, 46(47):3001-30052. [20] sze sm, ng kk. (2006) p-n junctions physics of semiconductor devices, john wiley & sons, inc., pp77-133. [21] antoranz p, miranda j m, sebastián j l, cámara m, fonseca v. (2005) high-frequency modeling of gan/sic blue light-emitting diodes. journal of applied physics, 97(9):096107096110. [22] schramm a, tukiainen a, pessa m, konetzni c, heyn c, hansen w. (2009). neutronirradiated schottky diodes with self-assembled inas quantum dots: optical and electrical properties. journal of applied physics, 105(10):104308/1-204308/6 [23] fauzi da, rashid nkam, zin mrm, hasbullah nf. (2015) neutron radiation effects on the electrical characteristics of inas/gaas quantum dot-in-a-well structures. ieee transactions on nuclear science, 62(6):3324-3329. [24] moscatelli f, scorzoni a, poggi a, nipoti r. (2007) annealing effects on leakage current and epilayer doping concentration of p+n junction 4h-sic diodes after very high neutron 108 iium engineering journal, vol. 18, no. 1, 2017 ahmad fauzi et al. irradiation. nuclear instruments and methods in physics research, section a: accelerators, spectrometers, detectors and associated equipment, 583(1):173-176. [25] messenger gc. (1992) a summary review of displacement damage from high energy radiation in silicon semiconductors and semiconductor devices. ieee transactions on nuclear science 39(3):468-473. [26] moloi sj, mcpherson m. (2013). capacitance–voltage behaviour of schottky diodes fabricated on p-type silicon for radiation-hard detectors. radiation physics and chemistry, 85:73-82. [27] ohshima t, sato s, morioka c, imaizumi m, sugaya t, niki s. (2010) change in the electrical performance of ingaas quantum dot solar cells due to irradiation. 35 th ieee photovoltaic specialists conference, 002594-002598. [28] hasbullah nf, jo shien n, hui-yun l, hopkinson m, david jpr, badcock tj, et al. (2009) dependence of the electroluminescence on the spacer layer growth temperature of multilayer quantum-dot laser structures. ieee journal of quantum electronics, 45(1):7985. 109 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 humayun et al. 151 a comparative analysis of the effect of temperature on band-gap energy of gallium nitride and its stability beyond room temperature using bose–einstein model and varshni’s model md abdullah al humayun 1, 2 , ahm zahirul alam 1* , sheroz khan 1 , mohamed fareq abdul malek 3 and mohd abdur rashid 4 1 department of electrical and computer engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2 department of electrical and electronic engineering, green university of bangladesh, dhaka -1207, bangladesh 3 faculty of engineering and information sciences, university of wollongong in dubai, dubai, united arab emirates. 4 department of electrical and electronic engineering, noakhali science & technology university, noakhali 3814, bangladesh. *corresponding author: zahirulalam@iium.edu.my (received: 28 th july 2016; accepted: 31 st may 2017; published on-line: 1 st dec. 2017) abstract: high temperature stability of the band-gap energy of the active layer material of a semiconductor device is one of the major challenges in the field of semiconductor optoelectronic device design. it is essential to ensure the stability in different band-gap energy-dependent characteristics of the semiconductor material used to fabricate these devices either directly or indirectly. different models have been widely used to analyze the band-gap energy-dependent characteristics at different temperatures. the most commonly used methods to analyze the temperature dependence of band-gap energy of semiconductor materials are: the passler model, the bose–einstein model, and varshni’s model. this paper is going to report the limitation of the bose–einstein model through a comparative analysis between the bose–einstein model and varshni’s model. the numerical analysis is carried out considering gan, as it is one of the most widely used semiconductor materials all over the world. from the numerical results it is ascertained that below the temperature of 95 k both the models show almost same characteristics. however, beyond 95 k varshni’s model shows weaker temperature dependence than that of the bose–einstein model. varshni’s model shows that the bandgap energy of gan at 300 k is found to be 3.43 ev, which establishes a good agreement with the theoretically calculated band-gap energy of gan for operation at room temperature. abstrak: kestabilan bahan peranti semikonduktor pada suhu tinggi di lapisan aktif jurang tenaga (band-gap) adalah salah satu cabaran penting dalam bidang reka bentuk peranti optoelektronik semikonduktor. faktor ini bergantung kepada bahan semikonduktor yang digunakan untuk proses fabrikasi peranti elektronik ini samada secara langsung atau tidak langsung, bagi memastikan kestabilan dalam pelbagai jurang lapisan tenaga. model yang berbeza telah digunakan secara meluas untuk mengkaji kebergantungan ciri jurang lapisan tenaga bahan semikonduktor pada suhu yang berbeza. kaedah yang paling biasa digunakan untuk menganalisa kebergantungan jurang lapisan iium engineering journal, vol. 18, no. 2, 2017 humayun et al. 152 tenaga bahan semikonduktor pada suhu adalah: model passler, model bose-einstein dan model varshni. sementara itu pada suhu melebihi 95 k, model varshni menunjukkan kebergantungan pada suhu adalah lemah berbanding model bose-einstein. model varshni menunjukkan bahawa jurang tenaga bagi gan pada suhu 300 k adalah 3.43 ev, di mana ia adalah tepat dan bersamaan dengan kiraan teori pada jurang lapisan tenaga gan untuk beroperasi pada suhu bilik. keywords: gan; bandgap energy; temperature; bose–einstein model;varshni’s model 1. introduction high temperature stability of the band-gap energy of semiconductor materials beyond room temperature is one of the most significant properties to be considered. it has been given the top-most priority in the field of semiconductor optoelectronic device design. ensuring the stability of band-gap energy above room temperature is an engrossing issue to researchers. they are continuously looking for the best ideas to overcome this challenge, as it is one of the most important parameters to determine the electrical and optical properties of semiconductor materials. since the transition to a direct band-gap energy in the monolayer form has important implications for photonics, optoelectronics, and sensing, this characteristic requires further investigation [1]. previously, a lot of methods have been applied to investigate the temperature dependence of the band-gap energy of semiconductor materials. those include: the two-oscillator model by passler, bose–einstein model, and varshni’s model [2-5]. these models are widely applied to analyze the effect of temperature on the band-gap energy of semiconductor materials for applications in optoelectronic devices like lasers, solar cells, and so on. furthermore group-iii nitride semiconductor materials have been identified as a group of materials having greater potential than other groups of existing semiconductor materials. therefore, these materials are widely used to fabricate optoelectronic semiconductor devices in the range between visible short-wavelength to the ultraviolet region [6, 7]. hence, a detailed numerical analysis on the temperature dependence from low to high temperature of bandgap energy of these materials is necessary for a promising design of such devices especially for high temperature applications. group iii–v nitride alloys are under extensive investigation in the field of semiconductor device design. these materials are widely used in order to design high performance semiconductor optoelectronic devices with lower temperature sensitivity. lower temperature sensitivity is the key point to ensure the stable operation of the device. hence, due to its scientific and technological importance, group iii nitride semiconductor materials have received extensive attention from the scientific community in this era of new technology in the fabrication of semiconductor optoelectronic devices with high temperature stability [8]. among the group iii nitrides, gan alloy is the most important material, because it has a wider range of band-gap energy in the ultraviolet spectral range at room temperature than other group iii nitrides. therefore, it is vital to recognize the effect of temperature on the properties of the band-gap energy of gan in order to calculate the band alignment for designing optoelectronic devices [9]. currently, gan is used widely to fabricate optoelectronic devices operating above room temperature. so, in this paper, we are going to focus on a comparative analysis of the effect of temperature on the band-gap energy of gan and its stability beyond room temperature using the well-known bose–einstein model and varshni’s model. iium engineering journal, vol. 18, no. 2, 2017 humayun et al. 153 2. energy band-gap and effective mass the energy band-gap of semiconductor materials is determined effectively by the temperature dependence of electron-phonon interactions due to the following reasons: (i) the band-gap reveals the bond energy, (ii) a rise in atmospheric temperature changes the chemical bonding as electrons are promoted to conduction band (cb) from valence band (vb). within the inherent temperature range, the direct effects of thermal band-to-band excitations are negligible. conversely, lattice phonons have relatively lower energies. furthermore, at normal temperature these lattice phonons are excited in huge quantities [10]. the temperature insensitive operation is therefore important not only for the stability of the semiconductor device operation but also for the chemical composition of the active layer material of the solid state optoelectronic device structure. otherwise, the device characteristics governed by the material property will also be changed. the analysis of temperature dependence of band-gap energy of semiconductor materials is essential in order to fabricate the semiconductor device. group-iii nitrides have a narrow band gap due to the non-parabolic configuration of the lowest cb of the semiconductor materials. the non-parabolic dispersion phenomena at the lowest cb of the group-iii nitrides occurs because of the k-p interaction transversely through the narrow gap between the cb and vbs, for narrow direct band-gap semiconductor materials like gan. the non-parabolic dispersion for the cb of gan is calculated by kane’s k-p model. neglecting the spin–orbit splitting, which is very much smaller than the band gap [11], the cb dispersion relationship is given by the following equation: √ (1) where, is the intrinsic band-gap energy of the semiconductor material and is an energy parameter related to the interaction momentum matrix element. electron effective mass can be calculated using the standard definition of the density of states, using the following formula: (k) = (2) now from eqs. (1) and (2) the following relationship is obtained. √ √ . (3) on the other hand, the free carrier effective mass on the fermi surface is given by the following equation: (4) where n is the carrier concentration, ωp is the plasma frequency, and = 6.7 is the optical dielectric constant. 3. temperature dependence of bandgap energy exact demonstration of temperature dependence of band-gap energy of a semiconductor material is one of the most vital problems in the field of semiconductor iium engineering journal, vol. 18, no. 2, 2017 humayun et al. 154 technology. at room temperature, a large scattering of the values of band-gap energies is also reported in the last decade [12]. in this research work, we are going to investigate the accuracy of varshni’s model over the bose–einstein model to analyze the temperature dependence of the band-gap energy of gan. gan has been chosen as the material for the analysis as it is the most widely used group-iii nitride semiconductor material to design semiconductor optoelectronic devices. in order to do so, a comparative analysis of these two models has been considered in this research work. the comparative analysis has been done through a numerical approach. 3.1 varshni’s model the effect of temperature on the band-gap energy of semiconductor materials is analyzed using varshni’s formula. varshni’s formula is given in the following expression [4]: (5) where is the band-gap energy of the semiconductor material at 0 k, t is the temperature in kelvin, and and are varshni’s fitting parameters. the varshni’s fitting parameters of semiconductor materials have been investigated comprehensively to analyze the temperature dependence of the band-gap energy in other nitride semiconductor materials [6]. so, by taking the first derivative of with respect to temperature, the following equation is obtained. = γ (6) here the (-ve) sign indicates that the band-gap energy of the semiconductor material decreases with the rise in temperature or vice versa. therefore, considering only the amplitude of the rate of change of band-gap energy of the semiconductor material with respect to temperature, the following equation is obtained. | | γ (7) 3.2 bose–einstein model the effect of temperature on band-gap energy is determined using the well known bose–einstein model [3]: . (8) where represents the strength of the exciton–phonon interaction and is mean phonon energy. now, taking the first derivative on both sides of eq. (8) with respect to temperature, the following equation is obtained. (9) here the (-ve) sign indicates that the band-gap energy of the semiconductor decreases with the rise in temperature or vice versa. therefore, considering only the amplitude of the iium engineering journal, vol. 18, no. 2, 2017 humayun et al. 155 rate of change of band-gap energy with respect to temperature, the following equation is obtained. | | (10) 4. results and discussion this section presents a detailed description of the numerical analysis of the effects of temperature on the band-gap energy of gan using the bose–einstein model and varshni’s model. the outcomes of the numerical analysis are presented graphically in fig. 1 and fig. 2 respectively. figure 1 has been plotted using eq. (5) and eq. (8) respectively. figure 2 has been plotted using eq. (7) and eq. (10) respectively. table 1: band gap and varshni parameters and of gan parameter gan eg(0)(ev) 3.507 γ (mev/k) 0.909 β 830 ab 111 300 k fig. 1: comparison of temperature dependency of band-gap energy of gan using the bose–einstein model and varshni’s model. as shown in fig. 1, the best fit is obtained for varshni’s model and the bose–einstein model with the values of eg(0) γ and β for gan, as in table 1. figure 1 presents the temperature dependence of the band-gap energy of gan. the red line and the blue line represent the temperature dependence of the band-gap energy of gan using the wellknown bose–einstein model and varshni’s model respectively. the band-gap energy of gan decreases non-uniformly with the uniform increase of temperature for both models used in our analysis. curves shown in fig. 1 give reliable values of the band-gap energy of 0 50 100 150 200 250 300 350 400 450 500 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 temperature (k) b a n d g a p o f g a n ( e v ) vershini's model bose einstein model iium engineering journal, vol. 18, no. 2, 2017 humayun et al. 156 gan. we are quite confident that the gan band-gap has the weaker temperature dependence using the bose–einstein model than that of varshni’s model below 95 o k, but above 95 k varshni’s model shows that the change of band-gap energy with respect to temperature is small as compared to that of the bose–einstein model. so, from the above discussion, it is clear for devices operating at higher temperatures that varshni’s model should be applied. another advantage of using the said model is the ease of calculation of the critical operating temperature. fig. 2: comparison of the rate of change of band-gap energy between the bose–einstein model and varshni’s model. figure 2 is plotted using eq. (7) and eq. (10). fig. 2 presents the effect of temperature on the rate of change of the band-gap energy of gan. the red line and the blue line represent the effect of temperature on the rate of change of the band-gap energy of gan using the well-known bose–einstein model and varshni’s model respectively. the rate of change of the band-gap energy of gan increased non-uniformly with the uniform increase of temperature for both models used in our analysis. it is revealed from fig. 2 that at room temperature (t=300 k), the rate of the change of the band-gap energy is only 0.3 mev/k using varshni’s model but the band-gap energy is about 2.4 mev/k using the bose– einstein model. from fig. 2, we can also conclude that the effect of the change of temperature on the band-gap energy of gan is almost linear in the case of varshni’s model. however, non-linear characteristics of temperature dependence are obtained using the bose–einstein model, which is another limitation of this model with respect to varshni’s model. here it is seen that the band-gap of gan changes dramatically in the range of 50 k to 160 k. 5. conclusion in conclusion, we have analyzed the temperature dependence of direct band-gap energy of gan using the bose–einstein model and varshni’s model in the temperature range between 0 k and 500 k. results show that using varshni’s model, the band-gap energy at 300 k was found to be 3.43 ev (fig. 1) which shows a good agreement with the band-gap of gan for operation at room temperature, as obtained by tangi and his research group [13]. in addition, fig. 1 shows the band-gap of gan was found to be around 3.3 ev 0 50 100 150 200 250 300 350 400 450 500 0 0.5 1 1.5 2 x 10 -3 temperature (k) r a te o f c h a n g e o f b a n d g a p o f g a n ( e v /k ) varshni's model bose-einstein model iium engineering journal, vol. 18, no. 2, 2017 humayun et al. 157 using the bose–einstein model, which is far below the recognized value of the band-gap energy of gan. the temperature independence and large value of the broadening parameter might be related to the wide range of effective mass. hence, the material property will be changed, which will also affect the device characteristics. we can conclude that the stability of the band-gap energy is essential to ensure the stability of the cb dispersion and the effective mass of the material. finally, we can say that varshni’s model is more reliable than the bose–einstein model in the temperature range above 95 k. acknowledgement the post-doctorate fellowship for the first author by the international islamic university malaysia is gratefully acknowledged. references [1] wang qh, kalantar-zadeh k, kis a, coleman jn, strano ms. (2012) electronics and optoelectronics of two-dimensional transition metal dichalcogenides. nature nanotechnology, 7(11):699-712. [2] passler r. (2001) dispersion-related assessments of temperature dependences for the fundamental band gap of hexagonal gan. j. applied physics, 90(8):3956-3964. [3] walukiewicz w, li sx, wu j, yu km, ager jw, haller ee, lu h, schaff wj. (2004) optical properties and electronic structure of inn and in-rich group iii-nitride alloys. j. crystal growth, 269:119–127. [4] cui k, fathololoumi s, kibria mg, botton ga, mi z. (2012) molecular beam epitaxial growth and characterization of catalyst-free inn/inxga1-xn core/shell nanowire heterostructures on si (111) substrates, nanotechnology, 23(8):085205. [5] sarswat pk, free ml. (2012) a study of energy band gap versus temperature for cu2znsns4 thin films. physica b: condensed matter, 407(1):108-111. [6] humayun ma, rashid ma, malek f, hussain an. (2012) effect of lattice constant on bandgap energy and optimization and stabilization of high-temperature inxga1−xn quantum-dot lasers. j. russian laser research,33(4):387-394. [7] rashid ma, yusuf a, humayun ma, al-khateeb aknm, tamaki s. (2013) stability analysis of solar cell characteristics above room temperature using indium nitride based quantum dot. american j. applied sciences,10(11):1345-1350. [8] hossain mm, humayun ma, hasan mt, bhuiyan ag, hashimoto a, yamamoto a. (2012) proposal of high performance 1.55 µm quantum dot heterostructure laser using inn. ieice transactions on electronics, 95(2):255-261. [9] gupta l, rath s, abbi sc, jain fc. (2003) temperature dependence of the fundamental band gap parameters in cadmium-rich znxcd1-xse using photoluminescence spectroscopy. pramana j. physics, 61(4):729–737. [10] o’donnell kp, chen x. (1991) temperature dependence of semiconductor band gaps. appl. phys. lett., 58(25):2924-2926. [11] wu j, walukiewicz w. (2003) band gaps of inn and group iii nitride alloys. super-lattices and microstructures, 34:63-75. [12] manjon fj, hernandez-fenollosa ma, mari b, li sf, poweleit cd, bell a, menendez j, cardona m. (2004) effect of n isotopic mass on the photoluminescence and cathodoluminescence spectra of gallium nitride. the european physical journal b, 40:453458. [13] tangi m, mishra p, ng tk, hedhili mn, janjua b, alias ms, anjum dh, tseng cc, shi y, joyce hj, li lj. (2016) determination of band offsets at gan/single-layer mos2 heterojunction. applied physics letters, 109(3):032104. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 168 on the control of heat conduction fayziev yusuf ergashevich national university of uzbekistan, 700174, students town, tashkent, uzbekistan. corresponding author: fayziev.yusuf@mail.ru (received: 9th feb 2017; accepted: 15th march 2018; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.796 abstract: mathematical models of thermo control processes in a rectangular plate are considered. in the model under consideration, the temperature inside a plate is controlled by heat exchange through one boundary while the other three are insulated. the control parameter is a function that satisfies certain integral equations. sufficient conditions for achieving the given projection of the temperature at a fixed point on the plate and given average temperature are studied. abstrak: model matematik bagi proses kawalan suhu dalam bekas segi empat tepat telah dipilih. melalui model ini, suhu bekas dikawal dengan menukar haba melalui salah satu sisi bekas, manakala tiga sisi lain telah ditebat. parameter kawalan ini ialah fungsi, di mana ia sesuai dengan persamaan sesetengah integral. keadaan sesuai bagi mencapai suhu tetap bekas seperti cadangan dan suhu purata yang diberikan turut dikaji. keywords: non-homogeneous heat equation; control of heat conduction; boundary conditions; initial conditions 1. introduction many physical processes and engineering problems are described by heat/diffusion equations and the study of the properties of the solutions is important. methods of the solutions of various boundary value problems and problems with the initial conditions can be found in [1]. for the first time, a detailed explanation of the problems of control of the system with distributed parameters, described by partial differential equations were given in [2]. in recent years, interest in the study of a system with distributed parameters has increased significantly. in works [3-5] by il’in and moiseev, the questions of boundary control by the various systems described by a wave equation are studied. notable works [6, 7], studied problems related to the process of control associated with the equations of parabolic type, particularly the heat transfer process. equation (1), in the homogeneous case, describes the problem of heat control studied by alimov in [8-12]. the problem for the non-homogeneous equation (1), in the case of heat transfer, is a rod studied in [13]. 2. formulation of problems consider the non-homogeneous heat equation iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 169 2 ( ) ( , , )t xx yyu a u u f x y t   , 1 20 , 0x l y l    , 0t  (1) with the boundary conditions 1 2 (0, , ) ( ), ( , , ) 0, ( , 0, ) 0, ( , , ) 0, (0) 0, | ( ) | u y t t u l y t u x t u x l t t m            0t  (2) and initial conditions ( , , 0) ( , )u x y x y , 1 2 0 , 0x l y l    , (3) where φ(x,y) – a given function and m – a positive number. it is known that the boundary condition (2) means µ(t) heat entry from the x = 0 side of the rectangle and zero temperature kept in other sides. in the present paper we study following problems: problem 1: let b > 0 be given number. it is required to find such a temperature µ(t) that problems (1) – (3) has a solution satisfying following integral relation (fig. 1): 1 2 0 0 ( , , ) l l u x y t dydx b (4) fig. 1: total heat. problem 2: let b > 0 be a given number. find a temperature µ(t) such that the problem (1) – (3) has a solution that at time t at inside point ( , ) o o a x y satisfies the condition (fig. 2): ( , , ) o o u x y t b (5) 1 2 0 0 ( , , ) l l u x y t dydx b l 1 l 2 0 x y h e a t iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 170 fig. 2: the temperature at point ( , ) o o x y . problem 3: now we consider equation (1) with the initial condition (3) and the boundary conditions as follows 1 2 (0, , ) 0, ( , , ) ( ), ( , 0, ) 0, ( , , ) 0, (0) 0, | ( ) | u y t u l y t t u x t u x l t t m            t ≥ 0 (6) let b > 0 be a given number. find a temperature µ(t) such that problems (1), (3), (6) have a solution that satisfies (4). note, that boundary condition (6) means that heat flow µ(t) is coming from the boundary x = l1 other boundaries kept with zero temperature. 3. the solution of problem 1 in this section we solve problem 1. theorem 1: let b > 0 be given number. at the time t a solution of the problem (1) – (3) satisfying the condition (4) if for the function µ(t) following equality is true: 0 ( , ) ( ) ( ) t k t d g t     (7) where 2 2 ( ) ( )21 2 4 2 2 1 1 1 ( 1) 1 ( 1)4 ( , ) ( ) nm n m a t nm n m l l k t a e n m                       (8) ( , , ) o o u x y t b l 1 l 2 0 x y h e a t xo yo iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 171 2 ( )1 2 2 1 1 1 ( 1) 1 ( 1) ˆ( ) ( ) nm n m a t nm nm n m l l g t b f t c e nm                       (9) 1 2 2 ( ) 1 2 1 20 0 0 4ˆ ( ) ( , , ) sin sin nm l lt a nm n m f t f e d d d l l l l             (10) 1 2 1 2 1 20 0 4 ( , ) sin sin l l nm n m c d d l l l l           (11) 2 2 1 2 nm n m l l                 (12) proof: solution of the problem (1) – (3) can be represented as following series: 2 ( ) 1 1 ( , , ) ( , , ) ( ) sin sin ,nm a t nm nm n m n m u x y t u x y t f t c e x y               (13) where 1 2 1 2 ( ) 0 ( , , ) 0 0, l x t if y l lu x y t if y y l          1 2 2 2 1 1 2 10 0 0 4 ( ) ( , , ) ( ) sin sin nm l lt a nm n m l f t f e d d d l l l                         (14) 1 n n l    , 2 m m l    and nmc is defined by (11). according the theorem a solution should satisfy condition (4) which means 1 2 1 2 1 10 0 0 0 ( , , ) ( ) l l l l l x b u x y t dydx t dydx l       1 2 2 ( ) 1 10 0 ( ) sin sin .nm l l a t nm nm n m n m f t c e x ydydx              in the second term, we change the order of integration and summation after evaluation to get 2 ( )1 2 1 2 2 1 1 1 ( 1) 1 ( 1) ( ) ( ) 2 nm n m a t nm nm n m l l l l b t f t c e n m                  . then from (14) and (10) obtain iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 172 2 ( )1 2 1 2 2 1 1 1 ( 1) 1 ( 1) ˆ( ) ( ) 2 nm n m a t nm nm n m l l l l b t f t c e nm                        1 2 2 ( ) ( )1 2 1 1 10 0 0 4 ( ) sin sinnm l lt a t n m n m x l e x ydydxd l                          1 ( 1) 1 ( 1) n m nm           . due to µ(0) = 0 the last integrals can be evaluated as follows 2 2 2 ( ) ( ) ( )2 0 0 ( ) ( ) ( ) ( ) ,nm nm nm t t a a t a nm e d t e a e d                 2 2 0 sin 1 ( 1) l m m l ydy m         , 1 1 1 10 sin l n x l l xdx l n      . thus, we have 2 ( )1 2 1 2 2 1 1 1 ( 1) 1 ( 1) ˆ( ) ( ) 2 nm n m a t nm nm n m l l l l b t f t c e nm                        2 2 ( ) ( )21 2 4 2 2 1 1 0 1 ( 1) 1 ( 1)4 ( ) ( ) ( ) nm n mt a t nm n m l l t a e d n m                                . write the last equation in a form 2 ( )1 2 1 2 2 1 1 1 ( 1) 1 ( 1) ˆ( ) ( ) 2 nm n m a t nm nm n m l l l l b t f t c e nm                        1 2 4 2 2 1 1 4 8 ( ) (2 1) (2 1)i j l l t i j            2 2 ( ) ( )21 2 4 2 2 1 10 1 ( 1) 1 ( 1)4 ( ) ( ) .nm n mt a t nm n m l l a e d n m                                after evaluation of the series in third term and taking into account following notations 2 2 ( ) ( )21 2 4 2 2 1 1 1 ( 1) 1 ( 1)4 ( , ) ( ) nm n m a t nm n m l l k t a e n m                       , iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 173 2 ( )1 2 2 1 1 1 ( 1) 1 ( 1) ˆ( ) ( ) .nm n m a t nm nm n m l l g t f t c e nm                     to obtain 2 2 1 2 1 2 4 0 32 ( ) ( ) ( , ) ( ) ( ) 2 8 8 t l l l l b t t k t d g t                . thus we obtain the following integral equation 0 ( , ) ( ) ( ) t k t d b g t      . if we denote ( ) ( )g t b g t  then 0 ( , ) ( ) ( ). t k t d g t     theorem 1 is proven. 4. the solution of problem 2 in this section we study problem 2. theorem 2: let b > 0 a given number. at time t a solution of the problem (1) – (3) satisfies the condition (5) if function µ(t) satisfies following integral equation 0 ( , , , ) ( ) ( ), t o o k x y t d g t     (15) where 2 ( ) ( )2 2 1 1 1 ( 1)4 ( , , , ) ( ) sin sin ,nm m a t o o nm n o m o n m k x y t a e x y nm                        2 ( ) 1 1 ˆ( ) ( ) sin sinnm a t nm nm n o m o n m g t b f t c e x y                . proof: it is known that a solution of problems (1) – (3) has the form of (13). let this solution satisfies condition (5). then obtain the following equality 1 1 ( , , ) ( )o o o l x b u x y t t l      2 ( ) 1 1 ( ) sin sinnm a t nm nm n o m o n m f t c e x y              . using equality (14) obtain following iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 174 2 ( )1 1 11 ˆ( ) ( ) sin sinnm a to nm nm n o m o n m l x b t f t c e x y l                   1 2 2 ( ) ( )1 1 11 2 10 0 0 4 ( ) sin sinnm l lt a t n m n m l e d d d l l l                             2 ( ) sin sin .nm a t n o m o e x y       as it was done in the previous problem, by evaluation of the integrals, we obtain following equality 1 1 ( ) ( , , )o o o l x b t g x y t l      2 ( ) ( )2 2 1 1 0 1 ( 1)4 ( ) ( ) ( ) sin sinnm m t a t nm n o m o n m t a e d x y nm                               where 2 ( ) 1 1 ˆ( , , ) ( ) sin sinnm a t o o nm nm n o m o n m g x y t f t c e x y               . from this we get 1 1 ( ) ( , , )o o o l x b t g x y t l      1 2 2 1 1 (2 1) sin 2sin 4 ( ) 2 1 o o n k x n y k l l t n k                               2 ( ) ( )2 2 1 10 1 ( 1)4 ( ) ( ) sin sinnm mt a t nm n o m o n m a e x y d nm                                 . by evaluation of the series in the third term and using following notation 2 ( ) ( )2 2 1 1 1 ( 1)4 ( , , , ) ( ) sin sinnm m a t o o nm n o m o n m k x y t a e x y nm                        obtain 1 1 1 1 0 0 ( ) ( ) ( , , , ) ( ) ( , , ) ( , , , ) ( ) ( , , ). t o o o o o o t o o o o l x l x b t t k x y t d g x y t l l k x y t d g x y t                      iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 175 if we denote ( ) ( , , ) o o g t b g x y t  , the obtained integral is equation (15). theorem 2 is proven. 5. the solution of problem 3 in this section we find the solution of problem 3. theorem 3: let b > 0 be a given number. at a time t, the problem (1), (3), (6) has a solution that satisfies (4) if µ(t) a solution of the following integral equation 0 ( , ) ( ) ( ) t k t d g t     (16) where 2 2 1 ( ) ( )21 2 4 2 2 1 1 ( 1) 1 ( 1) 1 ( 1)4 ( , ) ( ) nm n n m a t nm n m l l k t a e n m                         , 2 ( )1 2 2 1 1 1 ( 1) 1 ( 1) ˆ( ) ( ) nm n m a t nm nm n m l l g t b f t c e nm                       , 1 2 2 ( ) 1 2 1 20 0 0 4ˆ ( ) ( , , ) sin sin nm l lt a nm n m f t f e d d d l l l l             , 1 2 1 2 1 20 0 4 ( , ) sin sin l l nm n m c d d l l l l            , 2 2 1 2 nm n m l l                 . proof: we know that a solution of the problem (1), (3), (6) as follows 2 ( ) 1 1 ( , , ) ( , , ) ( ) sin sinnm a t nm nm n m n m u x y t u x y t f t c e x y               (17) where 2 1 2 ( ) 0 ( , , ) 0 0 x t if y l lu x y t if y and y l          , 1 2 2 2 1 2 10 0 0 4 ( ) ( , , ) ( ) sin sin .nm l lt a nm n m f t f e d d d l l l                         (18) according to the conditions of theorem 3, a solution (17) must satisfy (4) which means iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 176 1 2 1 2 10 0 0 0 ( , , ) ( ) l l l l x b u x y t dydx t dydx l     1 2 2 ( ) 1 10 0 ( ) sin sinnm l l a t nm nm n m n m f t c e x ydydx              . in the second term, change the order of summation and integration after evaluation of the integrals to obtain the following 2 ( )1 2 1 2 2 1 1 1 ( 1) 1 ( 1) ( ) ( ) 2 nm n m a t nm nm n m l l l l b t f t c e n m                  . from (18) and (8), obtain 2 ( )1 2 1 2 2 1 1 1 ( 1) 1 ( 1) ˆ( ) ( ) 2 nm n m a t nm nm n m l l l l b t f t c e nm                        1 2 2 ( ) ( ) 2 1 1 10 0 0 4 ( ) sin sinnm l lt a t n m n m x e x ydydxd l                          1 ( 1) 1 ( 1) n m nm           . taking into account 2 2 2 ( ) ( ) ( )2 0 0 ( ) ( ) ( ) ( )nm nm nm t t a a t a nm e d t e a e d                 , 2 2 0 sin 1 ( 1) l m m l ydy m         , 1 11 10 sin ( 1) . l n n x l xdx l n      from the last equality, by introducing the notation 2 ( )1 2 2 1 1 1 ( 1) 1 ( 1) ˆ( ) ( ) nm n m a t nm nm n m l l g t f t c e nm                     . obtain the following equation 1 2 ( ) ( ) 2 l l b t g t   2 1 1 2 4 2 2 1 1 ( 1) 1 ( 1) 1 ( 1)4 ( ) n n m n m l l t n m                    2 2 1 ( ) ( )21 2 4 2 2 1 10 ( 1) 1 ( 1) 1 ( 1)4 ( ) ( ) .nm n n mt a t nm n m l l a e d n m                                  by evaluation of the series in the third term and by denoting iium engineering journal, vol. 19, no. 1, 2018 yu.e.fayziev 177 2 2 1 ( ) ( )21 2 4 2 2 1 1 ( 1) 1 ( 1) 1 ( 1)4 ( , ) ( ) nm n n m a t nm n m l l k t a e n m                         obtain 0 ( , ) ( ) ( ) t k t d b g t      . if we denote g(t) = b–g(t) then we obtain integral equation (16). the theorem is proven. 6. conclusion the results of this study have been analyzed and it can be concluded that both a fixed average amount of heat and a fixed heat at a given internal point of the rectangular plate can be controlled from the one of the boundaries. in this paper, a control function must be a solution of the integral equations found in this study. references [1] tikhonov an, samarsky aa. (1966) equations of mathematical physics. nauka, moscow (in russian) [2] lions jl. (1968) contrôle optimal de systèmes gouvernés par des équations aux dérivées partielles. dunod gauthier-villars, paris [3] il’in va. (2000) differential equations. 36:1670-1686 [4] il’in va, moiseev ei. (2005) progress math. scien., 60(6):89-114. (in russian). [5] il’in va, moiseev ei. (2006) doc. acad. scien. russian. 411(6):736-740. (in russian). [6] fattorini ho. (2002) time and norm optimal control for linear parabolic equations: necessary and sufficient conditions. in: control and estimation of distributed parameter systems. international series of numerical mathematics, 143:151-168. birkhäuser, basel [7] barbu v, rascanu a, tessitore g. (2003) carleman estimates and controllability of linear stochastic heat equations. appl. math. optim., 47(2):97-120. [8] alimov sho. (2005) on a control problem associated with the heat exchange process, uz. маth. jur. 4:13-21, (in russian). [9] alimov sho. (2008) on a control problem associated with the heat exchange process. doc. acad. scien. russian, 421(5):583-585, (in russian). [10] alimov sho, albeverio s. (2008) on a time-optimal control problem associated with the heat exchange process, appl. math. optim. 57: 58-68. [11] alimov sho. (2010) on a control problem associated with the heat transfer process, eurasian mathematical journal, 1(2):1730. [12] alimov sho. (2011) on the null-controllability of the heat exchange process, eurasian mathematical journal, 2(3):519. [13] fayziev yue, khalilova n. (2016) on a control problem associated with the heat transfer process, вестник нууз, 2/1:49-54, (in russian). microsoft word vol11_no1_final iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 124 role of discrete nature of chip formation and natural vibrations of system components in chatter formation during metal cutting a. k. m. nurulamin*, i. h. jaafar, a. u. patwari and w. w. d. zubaire department of manufacturing and materials engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia, *e-mail: akamin@iiu.edu.my abstract : in the present work a review of the existing theories of chatter formation has been conducted and the weaknesses of the most widely accepted ‘regenerative chatter theory’ in explaining various phenomena related to chatter formation have been identified. an attempt has been made in this work to determine the common causes of chatter formation in different metal cutting operations, namely, turning, thread cutting and end milling conducted on plain carbon steel aisi 1040. experimental investigations have been conducted during the above types of machining processes to identify the marks of instability and chatter on the formed chips. it has been identified that in all the three machining operations the chips formed show a common type of discreteness in the form of secondary saw teeth, which appear at the free edge of the chip. mechanism of formation of these teeth has been studied and the frequencies of their formation have been determined for different cutting conditions. apart from the secondary saw teeth primary saw teeth have also been identified at the main section of the chip and their frequencies were also determined. at the same time the natural vibrations of the main system components have been identified and the acceleration amplitudes at the prominent natural frequencies during actual machining were recoded using a dedicated vibration monitoring system. the frequencies of secondary chip serration and the natural frequencies of the system components were plotted against cutting speed. acceleration amplitudes at the prominent natural frequencies were also plotted separately against cutting force. based on comparison and analysis of these two frequency and amplitude graphs it was concluded that chatter (vibration with relatively high amplitude) appears in the system when the frequency of secondary saw teeth approaches values equal to half or integer multiple of a prominent natural frequency of the system resulting in resonance. in the case of thread cutting and turning the main vibrating component was identified as the tool holder and in the case of end milling the main vibrating components were the tool holder and the spindle. severe vibration/chatter was found to appear during end milling when the tool and the spindle simultaneously entered into resonance. this occurred when the chip serration frequency got close to the spindle’s natural frequency, which was approximately twice the value of the natural frequency of the tool holder in the conducted experiments. keywords: chip formation instability, secondary saw teeth, natural frequencies, resonance and chatter. iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 125 6. introduction chatter is defined the self-excited violent relative dynamic motion between the cutting tool and work piece. it is an undesirable but sometimes unavoidable phenomenon in metal cutting. it has adverse effects on the product quality, operation cost, machining accuracy, output and machine-tool life. it is also responsible for reducing output. the main characteristic of machine tool chatter is its self-induced nature, not caused by external periodic forces. although chatter has been extensively investigated in the past 40 years, the root cause of chatter still remains debatable. taylor suggested that element chip formation is responsible for chatter [1], but this proposition was not acceptable since element chip formation occurs at extremely low cutting speed where chatter is seldom observed. kuznetsov considered that the periodic effect of built-up-edge (bue) formation can excite vibration [2]. kudinov [3] and shteinberg [4] also considered that the vibration caused by the unstable and periodically broken bue is responsible for chatter. however, again no serious chatter is observed in the cutting speed range with bue formation and chatter generally exists at relatively higher cutting speeds where bue is absent. doi [5], doi and kato [6], and later kato [7] stated that chatter was established primarily due to a phase lag of the cutting force with respect to the fluctuation of chip thickness. nevertheless, smith [8] and later smith and tobias [9] suggested on the findings of doi and kato that, the force phase lag was primarily related to the low frequency of vibration. it was found by them that as the vibration frequency increased, the phase difference decreased, and at higher frequencies the force fluctuations even preceded the fluctuation of the chip thickness. doi and kato [6] proposed the regenerative chatter theory, according to which vibration marks on the work piece left from the previous cuts is responsible for chatter in the subsequent cuts. the latter has found overall acceptance in the metal cutting research community and is often referred to in numerous models developed to simulate the chatter phenomenon. according to the regenerative theory, chatter arises in the system as result of the waviness left from the previous cut which the tool follows in the subsequent cut. appearance of chatter and stable cutting are thought to be the result of offsetting and coincidence of phase of the previous and the current waviness. however, based on experimental results, amin [10-12] concluded that waviness on the cutting/job surface is not the cause of chatter, rather it’s after effect. he also observed that chatter occurred at nearly constant frequencies, close to the natural frequencies of prominent system components over a range of cutting speed for a given set of cutting conditions, which can not be explained by the regenerative chatter theory. apart from that initial tests conducted on helical turning i.e. thread cutting, show that there is gradual amplification of vibrations which occur at constant frequencies, close to the natural frequency of the spindle and the tool holder similar to the case of turning, though there is no previous waviness which the tool is following. regenerative chatter theory again has no explanation for the amplification of vibration amplitudes in this particular cutting operation. amin observed a type of serrated teeth at the free edge of the chip found that when the frequency of formation of these chips coincided with the natural frequency of a system component, chatter appeared during the cutting operation as a result of resonance. similar results were found by israd [13] during room temperature end milling and also by amin and abdelgadir [14, 15] during preheated end milling operations of mild steel and stainless steels. it is therefore essential to know whether the formative mechanisms of chatter during end milling, turning and thread cutting are similar in these three diversified processes involving interrupted and continuous cutting. in the first two of the above iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 126 processes the tool follows the traces of the previous chatter marks, but in the last operation the tools cuts though fresh material without following the traces of chatter marks of the previous cut. commonness of the mechanism would prove beyond doubt that chatter appears in the system not due to the ‘regenerative’ effect (following chatters marks left from the previous cut) but due to some other mechanism, may be due to the resonance effect, as proposed by amin. studies conducted by altintas and others [16-19] contributed to understanding of chatter in end milling operations. altintas developed the chatter dynamic models. mann et al [20] also studied on the stability and chatter frequency characteristics. for determining the type of instability of the periodic motion of this nonlinear, non-homogeneous, nonautonomous, delay-differential system, numerical schemes with an analytical basis are required. in their work, [21, 22] insperger and stépán have improved the semidiscretization method to examine the stability of periodic solutions of systems with two time delays. long and balachandran [23] worked with systems with variable time delay. the present work has the following objectives: 1. to verify the presence of secondary saw teeth at the free side(s) of the chip during turning, thread cutting and end milling and to determine the frequency their formative cycle. 2. to determine the role of the secondary chip serration frequency in chatter formation in the three proposed machining processes. 3. to study the frequency-amplitude characteristics of vibration/chatter under variable cutting and system parameters to investigate whether there is any common mechanism of chatter formation in these three different machining processes. 2. experimental setup and methodology 2.1 experimental setup the main thrust of the experiments was on the study of chips and monitoring of vibrations during different types of machining operations, involving different machine tools and fixture systems. for studying the chips, scanning electron microscope (sem), optical microscope and a digital camera were used. for monitoring the vibration a specially designed data acquisition system was used. datalog dasylab 5.6 was used for signal analysis and processing. the main software modules used are the amplitude-time display (time domain), the fft display (frequency domain). frequency range of interest was 0 – 10,000 hz. the fast fourier transform, or the fft, was used for changing the signals from the time to the frequency domain using the power density spectrum. turning and threading operations were conducted on lathe machine of model harrison m600. the schematic illustration of the experimental setup used in turning and threading operations is shown in fig. 1a. sandvik made inserts of code number: cnmg 12 04 08 wm were fitted onto a tool holder of code number: pclnr 2525m12 were used for both these operations. three different overhang values of the tool holder: 40, 50 and 60 mm, were used to introduce a variation in the elastic system parameters. investigations for all the three machining operations were conducted on carbon steels aisi 1040. cutting iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 127 parameters used for turning were: cutting speed = 50 – 350 m/min, at an interval of 50 m/min, depth of cut = 2 mm and feed = 0.1 mm/rot. during thread cutting/helical turning the compound rest was inclined to ensure equal side and auxiliary cutting edge angles. the tool holder was clamed with an overhang value of 50 mm. cutting speeds were in the range 2.5 – 18 m/min, at an interval of approximately 2 m/min and depth of cut was 1.0 mm. the feed (pitch) value was maintained above 2.5 mm so that the tool did not follow the previous cut. fig. 1b presents the schematic illustration of the experimental setup used in the end milling operation. end milling tests were conducted on vertical machining center modeled zps 1060. all the cutting operations involved the use of an end mill cutter (sandvik coromill r390). the overhanging length of the tool holder was 63 mm and the diameter 20 mm. the number of inserts used at a time was varied between 1, 2, or 3. (a) (b) fig. 1: schematic diagrams of the experimental setup used in: (a) plain and helical turning and (b) end milling. the inserts chosen were sandvik coromat pm 4040 tin coated carbide. study was also conducted on chips generated during end milling using circular inserts under preheated and non preheated conditions to investigate the chip behaviour under those extreme cutting conditions. the workpiece material used in the experiment was medium carbon steel aisi 1040. depths of cut were 1 and 2 mm and feed rate 0.2 mm/tooth. 2.2 experimental procedures 2.2.1 free vibration free vibration analysis of the relevant components of the machine-tool-job-fixture system was conducted for both lathe and milling machines. a forced excitation is given to the system using a plastic mallet. the free vibration data were sensed by an accelerometer attached to the element opposite to the point of impact. the free vibration response is observed in the frequency domain. peak amplitudes denoted resonance of the system’s natural frequencies. iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 128 2.2.2 chip analysis in order to have a close look at the chip to identify the presence of the primary and the secondary saw teeth and any other type of instability that might be present in the outer view of the chip, the latter was viewed under a scanning electron microscope (sem). the frequency of the secondary saw teeth formation, fc, was calculated knowing the length of the portion of the chip in the sem picture, l, the coefficient of chip shrinkage, k, cutting speed, v m/min and the number of secondary saw teeth, n, observed on the sem picture; using the following formula: fc )(60 1000 lk nv  [hz] (1) 3. results and discussion 3.1 free vibration samples of free vibration analysis of the relevant components of the machine-tool-jobfixture system for both lathe and milling machines are shown in fig. 2 (a) for lathe tool and fig. 2 (b) for vmc tool-chuck system. the natural frequencies of the lathe machine system are listed in table 1 and those for the vmc in table 2. (a) (b) fig. 2: samples of fft plot of the natural frequencies for the system components: (a) for the tool and chuck system of vmc and (b) the tool holder of 60 mm overhang in lathe. table 1: natural frequency of the lathe machine system. system component tool holder with overhang, mm carriage w/p ss w/p -aisi 1040 spindle 40 50 60 approximate natural frequency, (hz) 2705 2475 2250 1760 158 150 870 hz 500 1000 1500 2000 2500 3000 3500 4000 4500 500 0.000150 0.000125 0.000100 0.000075 0.000050 0.000025 0.000000 iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 129 table 2: natural frequency of the different components of the vertical machining center (vmc). system component chuck, hz tool holder, hz tool (63 mm overhang), hz spindle, hz approximate natural frequency, (hz) 795 2000 2540 4700 3.2 analysis of chips produced during turning a sample of sem view of the chip formed during turning is shown in fig. 3. the presence of the secondary saw teeth at one side of the chip can be observed from the figure. apart from the secondary saw teeth deformation of grain (as indicated in the figure) at frequency higher compared to the secondary tooth serration frequency, can also be observed in the same figure. from fig. 3, the following observations were made on instability of chip formation during turning: 1. chip formation is unstable because of the formation of secondary saw/saw teeth which are regularly spaced and located at free edge of the chip (at the edge opposite to the location of the tool nose). 2. apart from these relatively larger saw teeth, marks of grain shear running across the whole width of the chip are also observed. these are also termed as primary saw teeth. a certain number of these minute sheared grains combine to form a large secondary saw tooth. 3. cracks are observed at the boundary between two adjacent secondary saw teeth. (a) (b) fig. 3: sample of the sem view of the top surface of chips formed during turning of plain carbon steel aisi 1040 at cutting speed of 350 m/min, at depth of cut of 2 mm and feed rate of 0.1 mm/rev: (a) at 50x, and (b) at 150x for section a. tool overhang value = 60 mm. iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 130 3.3 analysis of chip produced during thread cutting experiments on thread cutting were conducted to verify the presence of secondary saw teeth in the chip and their influence on system vibration and chatter. samples of the sem top views of the chips are shown in fig. 4. following observations are made from the views of chips formed during helical turning/thread cutting similar to the one shown in fig. 4: 1. saw teeth are observed along both the (lengthwise) edges of the chip. in this operation cutting is performed by both the cutting edges of the tool and hence there are two free edges of the chip along which secondary saw teeth are formed. 2. the appearance and the mechanism of formation of these secondary saw teeth are similar to those formed during outer turning operation, as illustrated in fig. 4. but since these elements are formed at very low speeds, at which the material undergoes more of strain hardening and less of temperature softening or annealing, cracks appear not only at the boundary lines of the secondary saw teeth but also at the shear boundaries of individual grain (fig. 4 a, b). 3. the number of saw teeth per unit length of chip is found to increase with cutting speed (fig. 4 a, b). 3.4 analysis of chips produced in end milling the chips formed during end milling using rectangular and circular inserts were mainly investigated and it has been found that in the case of circular inserts chip formation presents extreme case of secondary and primary chip serration especially at certain specific cutting conditions. typical sem pictures and micro-sections of chips formed under various conditions were also studied. some sample pictures are shown in fig. 5, 6. fig. 4: samples of the sem top views of the chips produced during helical turning cutting of a shaft of carbon steel aisi 1040 at depth of cut of 1 mm and feed rate of 10 mm/rev at cutting speeds: (a) v = 2.5 m/min and (b) v = 10.9 m/min. iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 131 fig. 5: sem top views of the chip formed during end milling using prismatic inserts: (a) top views at different magnifications, and (b) enlarged top sectional view of a saw tooth. fig. 6: views of chip formed during end milling with circular inserts: (a-c) at 50 m/min applying workpiece preheating, (d) at speed of 250 m/min room temperature cutting, (b) enlarged view of saw elements of (a), (c) micro section of the chip along line i-i shown in (a). cutting conditions: feed rate = 0.1 mm/tooth and depth of cut = 1 mm. iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 132 the following observations are made from fig. 5, 6: chips formed in end milling using prismatic inserts are continuous with the presence of secondary saw teeth. the saw teeth are formed along the free edge of the chip at almost equal spacing. the top sectional view (fig. 5 b) of a saw element shows the presence of directional flow of the deformed material. chips formed in end milling using circular inserts are very much saw in nature with the presence of secondary saw teeth running along the entire width of the chip. several sheared grains are found to combine into a relatively larger secondary saw element at the free edge of the chip (fig. 6 a, c, d). in some cases the chips get segregated into needle shaped elements loosely joined together at one of the edges (fig. 6a,b,d), especially during preheated end milling using circular inserts and also at higher cutting speeds during room temperature machining (fig. 7d). this phenomenon indicates the tendency of the chip to get separated into discrete elements along the boundary lines between two neighboring secondary saw teeth. hence it may be also concluded from here that secondary saw teeth formation is the outcome of the inherent discreteness of the chip formation process. cross sectional view of the chip (fig. 6c) reveal that the mechanism of formation of saw teeth is similar to that in turning, in which each chip element undergoes alternate phases of compression and shear. it can be concluded from the above analyses of chips that the mechanisms of chip formation in turning, thread cutting and end milling are very similar with minor differences. in all these cases, the chip formation process is accompanied with inherent instabilities and the tendency to form primary and secondary saw teeth. several primary saw teeth combine to form a secondary serrated tooth ultimately may lead to the formation of discrete elements. the secondary saw teeth lead to the formation of discrete chip elements or loosely bound segmented chips under severe cutting deformation conditions as in the case of end milling conducted with circular inserts. 3.5 relationship between the frequency of secondary saw teeth and vibration /chatter in turning and thread cutting in this section the frequencies of secondary saw teeth were compared with the chatter frequency and amplitude at different cutting speeds to identify the relationship among these parameters. for recording the vibration data, a single sensor was mounted at the lower surface of the tool holder, as mentioned earlier. fft output in power spectrum were analyzed and the highest acceleration amplitude peaks and the corresponding excited frequencies at every cutting condition were recorded for both the operations. typical fft output in power spectrum for plain turning is shown in fig. 7 and that for thread cutting in fig. 8. it can be observed from these two figures and table 1 that the most significant vibrations in the cases of turning and thread cutting correspond to the vibrations of the tool holder near its natural frequency. the observed acceleration amplitudes at the excited frequencies from these fft diagrams are plotted against cutting speed for turning in fig. 9a and for thread cutting in fig. 10a. to analyze the relationship between chip instability iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 133 and excitation of chatter, the primary and secondary chip serration frequencies vs. cutting speed relationships are plotted for turning in fig. 9b and for thread cutting in fig. 10b. the following observations are made from the above figures: the main vibration mode in the cases of turning and thread cutting are almost identical. the most significant vibrations in these cases correspond to the vibrations of the tool holder near its natural frequency (fig. 7, 8 and table 1). however, the magnitudes of the peak acceleration amplitude in the case of thread cutting are much lower (approximately 100 times) compared to those in turning. this is because of the very low cutting speeds employed in thread cutting (17.3 m/min) as compared to turning (350 m/min). hz 0.000 2498.779 4997.559 7496.338 9995 y/t chart 0 v*wb 0.0250 0.0225 0.0200 0.0175 0.0150 0.0125 0.0100 0.0075 0.0050 0.0025 0.0000 2465.82 hz 3833.01 hz hz 0.000 2498.779 4997.559 7496.338 9995 y/t chart 0 v*wb 0.000200 0.000175 0.000150 0.000125 0.000100 0.000075 0.000050 0.000025 0.000000 2407.23 hz fig. 7 (left): fft power spectrum for turning at cutting speed of 350 m/min, depth of cut of 2 mm and feed rate of 0.1 mm/rot. too holder overhang = 50 mm fig. 8 (right): fft power spectrum for thread cutting at cutting speed of 17.3 m/min, depth of cut of 1 mm and feed rate of 2.5 mm/rot. tool holder overhang = 50 mm. the frequency of secondary and/or primary saw teeth formation increases almost linearly with cutting speed, but close to the natural frequency of the tool holder (or at approximately half of it, in the case of thread cutting) the rise in the frequency is either slowed down (fig. 9b) remains constant (10b). the overhang value (the natural frequency) of the tool holder has some influence on the primary chip serration frequency during turning due to mutual interaction, but the three curves are quite close (fig. 9b). looking at the arrangement of the frequency of chip serration and the actual vibration frequency vs. cutting speed curves (fig. 9b) and the amplitude vs. cutting speed plots (fig. 9a) for turning, it is observed that the amplitude sharply increases when the chip frequency curve approach the corresponding natural frequency curve (at approximately 100 m/min). in the case of thread cutting the primary and secondary chip serration frequencies are much lower than the tool holder’s natural frequency. that is one of the reasons for low acceleration amplitude of the tool holder. however the amplitude is found to sharply increase as the main chip segmentation frequency (freq 1), appearing at the chip edges (fig. 4a-b), approaches the natural frequency of the workpiece, which is around 150 hz (table 2), and the second chip segmentation frequency (freq 2), appearing at the middle iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 134 section of the chip (fig. 4a-b), is approximately half of the natural frequency of the tool holder (starting from 10.9 m/min). over the cutting speed range from 10.9 to 17.3 m/min the two chip frequencies are found to be constant, while the acceleration amplitude of the natural frequency mode of the tool holder increase sharply (fig. 10 a, b), similar to what was observed by amin earlier [11]. therefore, it can be concluded from the above observations that, the mechanisms of chatter formation in turning and in thread cutting are identical. however, chatter appears in the system during turning when the chip serration frequency approaches the natural frequency of the tool holder but in thread cutting when the frequency is half of the natural frequency of the same component. fig. 9: the frequency vs. cutting speed curves (a) and vibration acceleration amplitude vs. cutting speed relationships (b) for carbon steel aisi 1040 during turning plotted for three overhang values of the tool. feed rate and depth of cut were 0.1 mm/rot and 2 mm respectively. fig. 10: the frequency vs. cutting speed curves (a) and vibration acceleration amplitude vs. cutting speed relationships (b) for thread cutting plotted for tool overhang value of 50 mm. pitch = 6.5 mm (mbs7x) and depth of cut: 1 mm. work material: carbon steel aisi 1040. 3.6 relationship between secondary/primary saw teeth frequency and vibration/chatter frequency in end milling the vibrations were recorded during machining using the data acquisition system in the time domain and the then the fast fourier transformation was performed. a sample of iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 135 fft power spectrum is shown in fig. 11, which indicates that there are mainly two excited frequency ranges in which high acceleration amplitudes are recorded. the frequency ranges are: 2500-2700 hz and 4000-4700 hz, which are close to the natural frequencies of the tool and the spindle respectively (table 2). there is also some amplification in the frequency ranges of 400-600 and 2000-2400 hz, but the acceleration amplitudes at these two frequency ranges are one order lower compared to that in the first two ranges. figure 12 shows the changes in the frequency of secondary saw teeth formation (fig. 5, 6) with cutting speed. the method of calculation of the saw teeth frequency was discussed in the methodology section. chip serration frequency vs. cutting speed curves for 20 mm dia tool of 63 mm overhang with 1, 2 and 3 inserts 0 1000 2000 3000 4000 5000 6000 100 150 200 250 300 350 400 450 500 cutting speed, m/min f re q u e n c y , h z 1 insert 2 inserts 3 inserts fig. 11 (left): fft power spectrum for end milling of steel aisi 1040 at the cutting speed 200 m/min (2 mm depth of cut, 0.1 mm/tooth feed, 3 insert). tool diameter = 20 mm and overhang = 63 mm. fig. 12 (right): frequency vs. cutting speed curves for 1, 2 and 3 inserts for end milling (doc = 1 mm, feed = 0.1 mm/tooth. fig. 13: bar charts of acceleration amplitude vs. cutting speed: (a) for tool vibration (2500-2700 hz) and (b) for spindle vibrations; for 1, 2 and 3 inserts for end milling of steel aisi 1040. (doc = 1 mm, feed = 0.1 mm/tooth, tool diameter = 20 mm and overhang = 63 mm) after careful comparison of the frequency vs. cutting speed curves (fig. 12) with the two amplitude vs. cutting relationships (fig. 13 a-b); the following observations were made: hz 500 1000 1500 2000 2500 3000 3500 4000 4500 500 0.0008 0.0007 0.0006 0.0005 0.0004 0.0003 0.0002 0.0001 0.0000 iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 136 when the frequencies of secondary serrated teeth approach the natural frequency of the tool (2540 hz) or that of the spindle (4700 hz), there is a tendency of flattening of the frequency vs. cutting speed curves (fig. 12) over a range of cutting speed, similar to that in turning and thread cutting, as discussed in the previous section (fig. 9b, 10b). in the frequency range of the tool (fig. 12), acceleration amplitudes are found to increase as the chip serration frequency get close to and crosses the natural frequency level of the tool in the cutting speed range of 100–250 m/min (fig. 13a). in the spindle’s natural frequency range no severe vibrations are observed up to the cutting speed of 250 m/min because the chip frequency in this cutting speed range is much below the natural frequency range of the spindle (fig. 12, 13b), but the amplitude starts to increase from 300 m/min when the chip frequency approaches the natural frequency of the spindle for all the insert combinations. the double insert tool is found to be very stable in the entire cutting speed range with respect to the spindle vibrations except at the speed of 300 m/min. the peak for single insert tool is at 500 m/min and that for the double insert tool is at 450 m/min. 4. conclusion the following conclusions have been drawn from the work: 1. the chips produced during turning and end milling, exhibit regularly spaced secondary saw teeth along the free edge of the chip. in the case of thread cutting these secondary saw teeth appear along both the edges of the chip. the primary and the secondary saw teeth have definite formative cycles and their frequencies increase with the cutting speed. 2. apart from the discreteness of the chip formation process, the machine tool workpiece-fixture system has various natural frequencies, some of which play prominent role in chatter formation. it has been found that the natural frequency of the tool holder plays a prominent role in generating vibration and chatter during turning and thread cutting. in end milling, there are two components responsible for chatter; they are the tool and the spindle. however, the spindle has been identified as the main “weak component”, since high amplitudes of vibration of the entire machine occurs when this component starts vibrating with high amplitude at frequencies close to its natural frequency. 3. it has been also found that chatter or vibration with high amplitude appears in the system during turning, thread cutting and end milling when the frequency of chip formation instability becomes approximately half (as in thread cutting), equal to or integer multiple of the prominent natural frequency (ies) of the system component(s) (as in turning and end milling). hence there is a common mechanism of formation of chatter in these different machining processes. chatter arises in the system as a result of resonance caused by the interaction of secondary (primary) saw teeth frequency and the natural frequencies of the prominent system components. 4. the prominent system component responsible for chatter in lathe operations is the tool holder in the practically applied cutting speed range and in end milling the two the two prominent system components are the tool (at relatively lower cutting speeds) and of the spindle (at relatively higher speeds). in end milling the most severe chatter is iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 137 attributed to the spindle, especially when simultaneous chatter of the spindle and the tool are excited. 5. the phenomenon of chatter in the absence of chatter marks from earlier cut in the case of thread cutting that ‘regenerative effect’ is not the cause of chatter. acknowledgements the authors would like to acknowledge the financial support received from the ministry of higher education, malaysia in conducting this research work and the research management centre iium for overall management of the projects. support of the undergraduate and graduate students and lab technicians in the work are also recorded with deep appreciation. references [1] taylor f w, the art of metal cutting, usa, (1922). [2] kuznetsov v d, fizika rezania trenia metallov e kristalov, moscow, nayka, (1977) p 310. [3] kudinov v a, dynamics of machine tools moscow: publication of machine building, 1965, p 358. [4] shteinberg i c, removal of chatter appearing during the metal cutting process on lathe machine, moscow: publication of machine building, (1976). [5] doi s, on the chatter vibrations of lathe tools, memoirs of the department of mechanical engineering, nagoya university, 5, (1953) p 179. [6] doi s and kato s, chatter vibrations of lathe tools, trans. amer. soc. mech. eng., 78, (1953) p 1073. [7] kato s, theoretical research on chatter vibration of lathe tools, memoirs of the department of mechanical engineering, nagoya university, (1958) p 117. [8] smith j d, the dynamic cutting of metals, ph.d. thesis, university of cambridge, (1962). [9] smith j d, tobias s a, the dynamic cutting of metals, int. j. machine tool design and res., 1, (1961) p 283. [10] amin a k m n, investigation of the laws governing the formation of chatter during metal cutting processes and their influence on tool wear, ph.d. thesis, georgian polytechnic institute, georgia, (1982) p 276. [11] amin a k m n, investigation of the mechanism of chatter formation during the metal cutting process, mech. eng. res. bulletin, 6/1, (1983) pp 11-18. [12] amin a k m n, influence of the characteristics of machine-tool-fixture-work (mtfw) system on chatter, journal of the institute of engineers bangladesh, 13/4, (1985) pp 9-16. [13] israd h j, investigations in machine tool chatter in an end milling operation on a vertical machining center, m.sc. thesis, international islamic university of malaysia, malaysia, (2002) p 156. [14] amin a k m n, abdelgadir m m, the effect of preheating of work material on chatter during end milling of medium carbon steel performed on a vertical machining center (vmc), asme journal of manufacturing science and iium engineering journal, vol. 11, no. 1, 2010 nurul amin et al. 138 engineering, transactions of the asme, usa, vol. 125, nov. (2003) pp 667-680. [15] amin a k m n, abdelgadir m, the effect of preheating of work material on chatter of vmc and machinability of work materials, proceedings of the second world engineering congress, kuching, malaysia, (2002) pp 215-220. [16] altintas y and e. budak. analytical prediction of chatter stability in milling – part 1: application of the general formulation to common milling systems. journal of dynamic systems, measurement and control, transactions of the asme, 120:2330, 1998. [17] altintas, y & budak, e. (1995), analytical prediction of stability lobes in milling. ann. cirp 44, 357-362. [18] altintas, y. and budak, e. (1995). “analytical prediction of stability lobes in milling,” [19] altintas, y., (1999), analytical prediction of stability lobes in ball end milling, trans. asme, vol. 121, pp. 586-592. [20] mann b.p., t. insperger, p.v. bayly and g. stépán, 2003, stability of up-milling and down-milling. part 2. experimental verification, i.j. mt m 43, pp. 35–40. [21] insperger, t. and stépán, g. (2001). “semi-discretization of delayed dynamical systems,” proceedings of detc ’ 01 asme 2001 design engineering technical conference and computers and information in engineering conference pittsburgh, pa, [22] insperger, t., and stépán, g. (2002). “semi-discretization method for delayed systems,” international journal of numerical methods in engineering, vol. 55, pp. 503–518. [23] long, x.h., and balachandran, b. (2004). “milling model with variable time delay,” proceedings of imece 2004 asme international mechanical engineering congress. microsoft word paper v4-n1--3new.doc iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 21 review of wavelet theory and its application toimage data compression othman omran khalifa electrical & computer department, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia fax: +603 2056 4853, email: khalifa@iiu.edu.my abstract: the fast development of computing multimedia has led to the demand of using digital images. the manipulation, storage and transmission of these images in their raw form is very expensive, it significantly slows the transmission and makes storage costly. in this paper, a brief review of wavelet transform theory is given using filters as examples to show the related multiresolution analysis. advantages over fourier transform is investigated and several results are derived. the pyramid algorithm is also presented and some features of wavelets in image data compression are given. a modified version of lind boze and gray (lbg) algorithm using partial search partial distortion (pspd) is presented for coding the wavelet coefficients to speed up the codebook generation and the search required for nearest neighbour codevector of input image. the proposed scheme can save 70 80 % of the vector quantization (vq) encoding time as compared to fully search vq and reduced arithmetic complexity with less sacrificing performance. key words: image compression, wavelets transform, vector qquantization. 1. introduction wavelet transform [1-3] has emerged as a powerful mathematical tool in many areas of science and engineering specifically for data compression [4,5]. the wavelet transform was first introduced in the context of a mathematical transform in 1984 by a. grosman and j. morlet. although haar constructed the first wavelet system in 1910. daubechies brought a big breakthrough in 1988 [6], her work immediately stimulated a rapid development in the theory and applications of wavelet analysis. in 1989, mallat presented the theory of multiresolution [3], with this technique; the wavelet system can be constructed with desired properties. wavelets has provided a promising vehicle for image processing applications, because of its flexibility in representing images and its ability to take into account human visual system characteristic. it is mainly used to decorrelate the image data, so the resulting coefficients can be efficiently coded. it also has good energy compaction capabilities, which results in a high compression ratio. it can be viewed as a special case of multi-rate filter bank with dyadic tree decomposition. wavelets were developed independently in the fields of mathematics, physics, electrical engineering and seismic-geology. interchanges between these fields during the iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 22 last ten years have led to many wavelet applications, such as image compression, denoising, human vision, radar, and the list could be continue. also, it is being used in many areas of science and engineering such as: signal processing, fractal analysis [7][8], numerical analysis [9], statistics [10], and astronomy [11]. recently, wavelets were determined to be the best way to compress a huge library of fingerprints [12]. the advantages of using the discrete wavelet transform (dwt) over the discrete cosine transform (dct) lies in the fact that the dwt projects high details of image components onto shorter basis function, with higher resolution, where lower detail components are projected onto larger basis functions, which corresponds to narrower subbands [8,13,14]. in addition, the wavelet transform compression provides a superior image quality at a low bit rate, since it is free from blocking effects. also, it has a link with digital filters and can handle non-stationary signals. however, there are still significant amounts of redundancies within the subbands. the goal of most wavelet researchers is to create a set of basis functions and transforms that will give an informative, efficient, and useful description of a function or signal. if the signal is represented as a function of time, wavelets provide efficient localisation in both time and frequency [3,15]. since the wavelet basis functions have short support for high frequencies and long support for low frequencies, smooth area of an image may be represented with very few bits. it is known that most of the energy is concentrated in low frequency information, and for the remaining high frequency components of the image, most energy is spatially concentrated around edges. high frequency details are added where they are needed. indeed, before the introduction of wavelets, a number of closely related coding works have been extensively studied in the image coding community, including pyramid coding [16], where the coarse version is derived from the original image by filtering. from this coarse version, the original image can be predicted and the prediction error can be calculated. if the prediction error is small it can be well compressed. the process can be iterated on the coarse version. a perfect reconstruction can be achieved if the compression of difference signals is lossless by simply predicting the original image and adding back the predicted image and the difference, the compression rate depends on how well the original image can be predicted from the filtered and down sampled image. they split up the input image into frequency bands and then code each subband using coder bit rate method to the statistics of the band. initial efforts in using wavelet transform in compression research concentrated on the hope of more efficient compaction of energy into a few number of low frequencies. this generated some wavelet based coding algorithms [7,17] which were designed to exploit the energy compaction properties of the wavelet transform by applying scalar or vector quantizers for the statistical of each frequency band of wavelet coefficients. 2. wavelet transform history advent the basic idea of applying a wavelet transform for image compression is that of successive approximation of an input image signal at reduced resolution together with the added detail signal at that resolution. this wavelet representation provides a iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 23 multiresolution and multi-frequency expression of nonstationary images with localisation in both time and frequency domain. it is a tool which breaks up data into different frequency components or subbands and then studies each component with a resolution that matched to its scale. there is continuous wavelet transform (cwt) and discrete wavelet transform (dwt). definition: 2.1 the continuous wavelet transform (cwt) of a function 2( ) ( )f x l r with respect to 2( ) ( )x l r  is / 2( )( , ) | | ( ) ( ( ))jcwt f a b a f x a x b dx     (1) where, , , , 0a b r a  and j is a resolution number. definition 2.2 the discreet wavelet transform (dwt) of a function 2( ) ( )f x l r with respect to 2( ) ( )x l r  is / 2 0 0 0( ( , )) | | ( ) ( ) j jdwt f j k a f x a x kb dx     (2) where, 0 0 0, , , 0, ,a b r a j k z   for the discrete wavelet transform 0 0a and b are usually set to 2 and 1. in such case, the dwt becomes: / 2( ( , )) 2 ( ) (2 )j jdwt f j k f x x k dx     (3) 3. wavelet analysis and comparison with fourier transform a wave is usually defined, as an oscillating function of time, such as a sinusoid. fourier analysis expands signal or functions in terms of sinusoids, which has proven to be extremely valuable. wavelets are mathematical functions that cut up data into different frequency components. it has advantages over traditional fourier methods in analysing physical situations where the signal contains discontinuities and sharp spikes. by comparing wavelets with sine waves, which are the basis of fourier analysis, sinusoids do not have limited duration that is, they extend from minus to plus infinity. and where sinusoids are smooth and predictable, wavelets tends to be irregular and asymmetric. in 1907 joseph fourier showed that any 2 periodic function could be expressed in terms of its complex exponential, which enables breaking up a signal into sine waves of various frequencies. for stationary signal, the fourier transform can be defined as: iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 24 ( ) ( ) j tx x t e dt      (4) similarly, wavelet analysis is the breaking up a signal into shifted and scaled versions of the original wavelet as follows: 1/ 2 , ( ) ( )a b t b t a a     (5) where is a and b are scale and shift parameters respectively. in fourier transform domain, we completely lose information about the localisation of the features of an image, quantisation error on one coefficient can affect the quality of the entire picture. the wavelet representation explicitly contains position information: the index a of wavelet ,a b indicates by how much the mother wavelet needs to be shifted to obtain one of the basis functions. the size of the region affected depends on how well the mother wavelet is localised. also, all wavelets tend to zero at infinity, which is already better than the fourier basis function. furthermore, wavelets can be made to tend to zero as fast as possible. figure 1 shows the original signal, fig. 2 shows the reconstructed signal via the fourier transform while fig. 3 shows the reconstructed signal using wavelet transform. in a fourier analysis a single point in the fourier domain contains information from everywhere in the image. it specifies the amount or strength of that particular spatial frequency that exist in the image. in the image domain, the existence of a strong high frequency component means that there are edges in the image, it shows how their orientation relates to the orientation of the spatial frequency, but the frequency domain result does not tell us where they exist in the image. in fact one could not even know if the edge information is constrained to one particular area of the image or if it is dispersed over the entire image as a texture pattern. technically, it says that the fourier basis functions have infinite support. practically, this fact has important ramifications. in other words, image compression using the fourier transform is independent of the image context. this is in many cases a disadvantage. often what is needed in image compression is a scheme that retains details where required and compresses non-significant areas of the image. wavelets, on the other hand, have compact or finite support and it enables different parts of the image to be represented at different resolution. fourier transform has been successful in a wide range of applications, however, it is suitable only if the signal consists of a few stationary components. also, the amplitude spectrum does not provide any idea of how the frequency components evolve with time. this drawback can be overcome by applying a time window on the data and then taking the fourier transform. this is known as short-time fourier transform (stft), which can be calculated as iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 25 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 . 7 0 . 8 0 . 9 1 1 0 . 5 0 0 . 5 1 1 . 5 i n p u t s i g n a l fig. 1: input signal (one dimension example). 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -1 -0.5 0 0.5 1 1.5 fig. 2: fourier approximation 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -1.5 -1 -0.5 0 0.5 1 1.5 fig. 3: wavelet approximation. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 26 *( , ) ( ) ( ) j txstft b x t g t b e dt       (6) where ( )x t is the input signal and the window ( )g t b is a time-localised function is shifted over the time axis to calculate the transform at several time locations b. one of the commonly used is the gaussian time window with a corresponding gaussian frequency window. this transform is called the gabor transform. the stft has two major drawbacks. first, both the time and frequency windows are fixed. hence, stft cannot adapt to the signal statistics. a short time window will be able to detect the high frequency components, but will provide poor response to low frequency components and vice versa. secondly, it is desirable to have a window function that has some decay in the time domain as well as in the frequency domain. wavelet transform overcomes both of these drawbacks. it can be viewed as dilated and translated versions of the mother wavelet ( )t . the arguments a and b denote scale and location parameters respectively. dilation corresponds to the change of frequencies and translation refers to localisation of time or position. the tiling of the time-frequency plane for both stft and wt is shown in fig. 4. it is noted that the time and frequency windows are fixed for stft, once the width of the window ( , )w t t is chosen, this tiling is fixed. however, it would be desirable to study the slowly varying properties of the signal (low frequencies) over a longer time span and vice versa for high frequencies. but this is provided by employing dwt as analysing functions. for higher scale, the time window narrows and for lower scale, it widens. this type adaptation is very useful in most practical situations. since, the high frequency components are normally short lived and hence need a narrow time window to improve the time resolution. on the other hand, low frequency components change slowly over time, thus requiring a wider time window to detect the slow changes. time frequen cy frequen time (a) (b) fig. 4: time-frequency plane showing resolution cells a) stft, b) wt iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 27 4. the discrete wavelet transform the application of wavelet transform in signal and image compression has attracted a great deal of attention. it is known that it generates a multiresolution representation of an image. there are several subimages or subbands that might be encoded more perfectly than the original image. the wavelet transform technique breaks the image information into various frequency bands and encodes each subband using suitable coding system. consequently, different coding approaches or different bit rates could be assigned to every subimage. the separate coding of different subbands provides some desirable features. first, by allocating the available bits for encoding among the subbands and using an appropriate quantizer for each of them, the encoding process can be tailored to the statistics of each subband. second, spectral shaping of the quantisation noise is possible. this feature can be used to take advantage of the noise perception of the human auditory system for speech or the human visual for images. third, the subband decomposition of the signal or image leads naturally to multiresolution decomposition. this is useful for progressive transmission of images in which an increasingly higher resolution and quality image can be reconstructed by the decoder. to get high compression ratio, one can not code the whole information of an image. only the significant information of an object is needed to reconstruct the image with less distortion or degradation. a more sophisticated wavelet can also provide more energy compaction than haar wavelet. daubechies et al [18] has shown that a wavelet ability measure is to provide compaction by the number of vanishing moments it possesses. more vanishing moments imply more compaction in smooth regions. the haar wavelet has only one vanishing moment. therefore, it does not possess a very strong compaction ability. daubechies has generated a family of wavelets parameterised by the number n of vanishing moments [18]. this family has 2n non-zero coefficients. these wavelets have problems because of the asymmetry that it introduces which result in subjective displeasing distortions when errors are introduced into the decomposition coefficients. she also designed another family of wavelets called the coiflet. it has vanishing moments for both the wavelets and the scale function. these filters are very close to symmetric where this wavelet is increased filters length: for l vanishing moments, the filters have 3l non-zero coefficients. fig. 5 and fig. 6 show the l =12, 8 coiflet and daubechies coefficients respectively. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 28 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 . 5 1 0 . 5 0 0 . 5 1 fig. 5: coiflet coefficients, l=12 (a) scaling function (bold line) (b) wavelet (dash line). 0 1 2 3 4 5 6 7 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 fig. 6: daubechies coefficients, l=8 (a) scaling function (bold line), (b) wavelet (dash line). iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 29 5. design of wavelet filters this section describes the design procedure for two popular wavelets, namely daubechies and coiflet family. a comparative study to determine the role of different characteristics of the wavelet filters e.g. regularity, perfect reconstruction linear phase, filter length, and coding gain, to the performance of wavelet compression proposals can be found in [23]. the choice of filter bank in wavelet compression is an important issue that can affect image fidelity as well as system design. the efficiency of any wavelet transform coder essentially depends on the energy compaction by the dwt. there is considerable flexibility in designing the filter bank where the transforms can be implemented. during the appropriate design the following characteristics are desirable:  perfect reconstruction or the ability to exactly obtain the original input.  orthonormal or biorthogonal bases.  reasonable spatial and frequency resolution. the two-channel filter bank has four filters involved: two are analysis filters and two are synthesis filters. the system is said to be a biorthogonal filterbank if ( ) ( )j ir e e e i   for all  . this implies perfect reconstruction, i.e., ˆ( ) ( )x n x n . the coder is orthonormal or paraunitary if ( )je e  is unitary for all  . in this case biorthogonality is achieved by setting ( ) ( )j jr e e e  . the dwt can be easily implemented using finite impulse response filter banks [17,19,20]. two-dimensional (2-d) of dwt can be obtained by a separable decomposition in the horizontal and vertical directions [3,21]. a pair of appropriately designed quadrature mirror filters (qmfs) can efficiently implement the forward and inverse wavelet transforms. therefore, it can be viewed as a form of subband coding. the quadrature mirror filter (qmf) pair consists of a low pass filter ( ( ))g g h n , and ( ( ))h h h n , n z , where h n( ) , g n( ) are daubeche’s 6-tap filter. the impulse response h , and g are mirror images, and related by: 1 1( 1) n n ng h    (8) the impulse response of the forward and inverse transform qmfs denoted ( , )   h g and ( , )h g respectively are related by: g gn n   h hn n   each pair consists of a lowpass filter (h) and a highpass filter (g) which divide or split the input signal/image into two components. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 30 the choice of filter bank in wavelet compression is an important issue that affects image quality as well as system design. figure 7 illustrates a single 2-d forward wavelet transform of an image, which is implemented by two separate 1-d transforms. the image ),( yxf is first filtered along the x-dimension, then down sampled by 2, then filtered along y-dimension and down sampled by 2, resulting in four subimage ),(11 yxf  , ),(21 yxf  , ),(31 yxf  and ),(41 yxf  . the resulting are the main signal ),(11 yxf  which is the low frequencies band and three detail signals. the process is repeated on the low band to generate the next level of the decomposition. down sample by 2 along x down sample by 2 along x h n( ) g n( ) down sample by 2 along y h n( ) down sample by 2 along y g n( ) down sample by 2 along y h n( ) down sample by 2 along y g n( ) f x y( , ) original image f x y1 1 ( , ) f x y1 2 ( , ) f x y1 3 ( , ) f x y1 4 ( , ) figure (7) block diagram of 2-d forward wavelet transform 6. wavelet representation there are many types of wavelets with different associated representations in the context of image compression or coding. we consider only separable 2-d wavelets, which are implemented by corresponding 1-d wavelets and scaling functions. in this paper, the biorthogonal wavelet has been used because of the linear phase and compactness properties. most of the wavelet applications are in image coding and image processing [3,22,23]. however, the pyramid wavelet transform that is going to use is not suitable for compression of texture-dominant images due to its significant middle frequency components. this can be demonstrated if the first wavelet (pyramid) is taken of that image, it can note the energy compaction is not concentrated in ll subband as the natural images as shown in table 1. in fact there are many types of wavelet such as full wavelet decomposition where the decomposition is applied to all frequency channels, but this scheme does not achieve good energy compaction since it sacrifices some spatial localisation properties. another flexible structure of wavelet decomposition is to apply the two-scale decomposition only to channels that contain a significant amount of information and further decomposition could achieve a better energy compaction. this kind of transform is called wavelet packet (wp) transform. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 31 table (1) energy weight for the four subbands of a number of still test images after first-level wavelet decomposition. subban d natural images medical images lena boat camera goldhill chest ( ct) head (mr) ll 94.03 % 94.27% 92.92% 91.40% 99.22% 91.82% lh 2.58 % 2.50 % 3.11 % 3.12 % 0.31 % 3.92 % hl 1.95 % 2.23 % 2.52 % 3.50 % 0.32 % 3.28 % hh 1.44 % 1.00 % 1.45 % 1.98 % 0.15 % 0.98 % 6.1 orthogonal wavelets it is the family of wavelets that generate orthonormal bases of. 2 ( )nl r the most important to image compression are compactly supported orthogonal wavelets. in dwt, compactly supported wavelets correspond to finite impulse response (fir) filters. but has a major disadvantage, which is their asymmetry. this property translates into nonlinear phase in the associated fir filters that may cause artifacts at the borders of the wavelet subbands. this can be avoided by using linear phase wavelet filters. defining jw as the orthogonal complement of vj in vj 1 , i.e., jj vw  and 1 jjj vvw (9) jw can be seen as the amount of detail added when going from resolution jv to the larger resolution 1jv . if we want both symmetry and compact support in wavelets, we are led to biorthogonal wavelets, it is more a general class of wavelet transforms. 6.2 biorthogonal wavelets it has been mostly used for their symmetry, it is characterised by two wavelets, the analysis wavelet )(t , and the synthesis one )(t [24]. this is can be represented as follows: , ,( ) ( )m n m n m n x t c t        (10) where iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 32 , , ( ) ( )m n m nc t x t dt     (11) and / 2 , ( ) 2 (2 ) m m m n t t n     (12) / 2 , ( ) 2 (2 ) m m m n t t n     (13) however, the , ( )m n t are orthogonal to , ( )m n t , this means: , , , ,( ) , ( )m n m n m k n lt t     7. multiresolution wavelet analysis this section briefly discusses the theory of multiresolution analysis (mra). the wavelet decomposition of any function 2( ) ( )nf x   is implemented using a family of functions generated by dilating and translating a single wavelet function :    . the function ( )x is called the mother wavelet and the function 1 2 , ( ) 2 (2 ) j j n x x n   from an orthonormal basis for 2 ( ) , ( )x is often obtained from a companion ( )x and is known as the scaling function through the following equations: 0( ) 2 ( ) (2 ) k x h k x k   (15) and 1( ) 2 ( ) (2 ) k x h k x k   (16) where 0{ ( )}h k and 1{ ( )}h k are pair of discrete quadrature mirror filters (lowpass and highpass) for orthogonal system of the form: 1 1 0( ) ( 1) ( 1) kh k h k    (17) wavelet transforms can be understood more easily through the concept of multiresolution signal representation [19]. 8. pyramids algorithm it is image transforms where multiple copies of an image at different resolutions are formed. it consists of an image at the bottom of the pyramid that is the highest or limiting resolution together with copies at lower and lower resolution. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 33 there are many types of pyramids such as, low pass pyramid, a band pass pyramid and a wavelet pyramid. a low pass pyramid consists of the finest resolution image, followed by a half resolution version, followed by a quarter, and so on., where each version is formed from the previous one by an averaging process. the top of the image is a single pixel that is the average of the entire image. in a band pass pyramid the top of the pyramid is a single pixel as well, and every other level contains detail imagery required to generate an image at a desired resolution level from the previous one. the third type of image pyramid is the most frequently used. this is the wavelet transform and it can be thought of as a type of bandpass pyramid which stores separate detail images for horizontal, vertical and diagonal. 9. wavelets features for image compression this is a summary of some features of image compression using wavelets. 1. wavelet transform has a good energy compact, it is preserved across the transform, i.e. the sum of squares of the wavelet coefficients is equal the sum of squares of the original image. 2. wavelets can provide a good compression [4, 19], it can perform better than jpeg, both in terms of snr and image quality. thus show no blocking effect unlike jpeg. 3. the entire image is transformed and compressed as a single data object using wavelet transforms, rather than block by block. this allows for uniform distribution of compression error across the entire image and at all scales. 4. the wavelet transform methods have been shown to provide integrity at higher compression rates than other methods where integrity of data is important e.g., medical images and fingerprints, etc. 5. multiresolution properties allow for progressive transmission and zooming, without extra storage. 6. it is a fast performance operation, in addition to symmetry: both the forward and inverse transform have the same complexity, in both compression and decompression phases. 7. many image operations such as noise reduction and image scaling can be performed on wavelet transformed images. resultant wavelet multiresolutions are scaled subbands. coarse approximation scaled from the original image and the others are detail coefficients where there are a statistical dependence across scale in these coefficients. efficient encoding is to exploit such dependence. this is how the art wavelet transforms compression is achieved. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 34 10. modified lbg algorithm using partial search partial distortion in basic vector quantization (vq), a full search technique is used, where the euclidean distance measure is calculated for the entire code vector in the codebook. it results in complexity in computation and time consummation. these are the most serious problems facing vq. in this paper, the lbg algorithm is modified to make it more efficient in speeding up codebook generation and encoding phase. the improvement is based on the fact that two equal-sized image blocks cannot be closely matched unless their local means and variance are closely matched. in the proposed modification a significant feature, the combination of variance 2 and mean m is used to reject a large number of code vectors from the search consideration without calculating their distortion distance from the training vectors. then, the partial search is used to find the closed or best match code vectors from the remaining possible match of the codebook. the algorithm is described as follows: step (1). initialization. let n =length of training vectors, n =codebook size, k =vector dimension, 0c =initial codebook, 1d =initial average distortion. step (2). compute the variance 2 and mean m values of each code vector in the codebook to find 2 h m   , and sort the codebook in ascending order according to the increase of h . step (3). calculate the minimum distortion partition. all training vectors are grouped into clusters is using the minimum distortion rules as follows: (a). compute xh for the input vector x (e.g. 2 x x x h m   ). (b). find the best match of xh from the sorted codebook in step (2). (c). define the partial codebook, the upper and lower bound from the sorted codebook with a window size w from the best match vector. (d). find the best match code vector of the input vector from the partial codebook by calculating the distortion of each codevector and selecting the minimum distortion. ( e ). repeat ( a ) to ( d ) for all training vector. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 35 step (4). calculate the average distortion iterationd for this iteration as follows: 1 0 1 min ( , ) iteration n iteration iy c i d d x y n      step (5). if 1( ) /iteration iteration iterationd d d    , stop with codebook, otherwise go to step (6). step (6). compute the centroid of each cluster and then go to step (1) for next iteration. 11. simulation results experiments are performed on standard 256x256 greyscale lena, cameraman, boat and goldhill images to test the proposed algorithms at several bit rates. the daubechies filters are used in the experiments with 4-level wavelet decomposition. the lowest band is coded separately from the remaining bands. the results of this algorithm on the above test images are presented. all the images have a mixture of large smooth regions and long oscillatory patterns. in order to evaluate the performance of the algorithm, it is compared to the direct vq and the standard jpeg. the performance of the algorithm is reported in fig. 8, fig. 9 and fig. 10. figure 8 shows the peak signal to noise ratio (psnr) versus compression ratio for the test images using this algorithm. figure 9 shows reconstructed ‘cameraman’ test image with different compression ratios and psnr in decibel. as it may be seen, no blocking effect can be noticed and the image quality is acceptable. the images out side the training have less psnr of approximately 1-1.5 db. 1 0 2 0 3 0 4 0 5 0 6 0 7 0 2 4 2 6 2 8 3 0 3 2 3 4 3 6 3 8 4 0 c o m p r e s s i o n r a t io ps n r ( db ) c a m e r a l e n a b o a t fig. 8: compression ratio vs. psnr of the proposed algorithm upon some of the test images. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 36 fig. 9: simulation results using wavelet transform. (a) original test image (top left). (b) compression ratio 12:1, psnr=32.85 (top right). (c) compression ratio 31.6:1, psnr=26.78 (bottom left). (d) compression ratio 64.25:1, psnr=23.99 (bottom right). compression ratio 10 20 30 40 50 60 70 15 20 25 30 35 40 45 ps n r (d b ) jpeg wt fig. 10: psnr comparison between jpeg and proposed wavelet technique for cameraman test image. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 37 12. comparison with other coders the measure criterion for comparison was psnr, which can be calculated directly from the original and reconstructed data. figure 10 shows a comparison of jpeg and the proposed wavelet codec for the test image cameraman and with a size 256x256. in terms of statistical error, wavelet codec gives higher signal to noise ratio in two of the examples, lena and cameraman. although all images contained noise introduced by the digitisation process, the wavelet codec effectively removed this noise whilst jpeg spent valuable bits sending this data. as a conclusion, wavelet codec provides a very efficient implementation in terms of execution time, quality and compression ratio. to summarise, the proposed codec perform satisfactory compared to the industrial standard jpeg algorithm as shown in fig. 11 and much better than vector quantisation technique. these results show that the algorithm provides a highly competitive solution to the problem of image data compression fig. 11: simulation results using standard jpeg. (a) original test image (top left). (b) compression ratio 8:1, psnr=33.19 db (top right). (c) compression ratio 32:1, psnr=24.3 db (bottom left). (d) compression ratio 64:1, psnr=16.9 db (bottom right). 13. conclusion & recommendation for further work the quality of reconstructed images within the training set yielded a compression ratio of 60 50 and a psnr was 36 -32 db, with greatly reduced computation and iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 38 execution time needed for codebook design and encoding phase. it reduces the computation complexity to o(kf) arithmetic operations instead of o(kn) in full search, where n is the number of codevectors, k is the vector dimension, and f is the window width, (where f << n). the proposed scheme can save 70 80% of the vq encoding time compared to full search vq. to increase the efficiency, fast algorithm for wavelet transform has to be incorporated. developing fast hardware architecture for wavelet transform and vector quantization is an area to be future investigated. references [1] [1]. rioul, o. and vetterli, m., ‘wavelet and signal processing’, ieee sp magazine, october 1991, pp. 14 – 37. [2] [2]. rioul o. and duhamel p., ‘fast algorithms for discrete and continuous wavelet trnasforms’, ieee trans. on information theory, vol. 38, no. 2, march 1992, pp. 569586. [3] [3]. s. g. mallat, a theory for multiresolution signal decomposition: the wavelet representation,ieee trans. on pattern analysis and machine intelligence, vol. 11, no. 7, pp. 674 – 693, july 1989. [4] [4]. devore r. a., jawrth b. and lucie b. j., ‘image compression through wavelet transform’, ieee trans. on information theory, 38, 1991, pp. 719-746. [5] [5]. kim y. h. and modestino j. w., ‘adaptive entropy coded subband coding of images’, ieee trans. on image processing, vol. 1, january 1992, pp. 31-48. [6] [6]. daubechies, the wavelet transform, time-frequency localization and signal analysis, ieee trans. on information theory, vol. 36, no. 5, pp. 961-1004, september 1990. [7] [7]. wong, s., zaremba, g. d. and huary. hk, ‘radiologic image compression a review’, ieee proc., vol. 83, 1995, pp. 194 – 219. [8] [8]. woods j. w. and o’neil s., ‘subband coding of images’, ieee trans. acoustics, speech, and signal processing, vol. 34, 10, october 1986, pp. 1278-1288. [9] [9]. beylkin g., coifman r., and rokhlin v., ‘ fast wavelet transforms and numerical algorithms i’, comm. pure and applied math., vol. 54, pp. 141-183, 1991. [10] [10]. donoho d. l., ‘ nonlinear wavelet methods for recovery of signals, densities and spectra from indirect and noisy data’, technical report, derpartment of statistics, stanford university, stanford ca, 1994. [11] [11]. starck j., bijaoui a., lopez b., and perrier c., ‘image reconstruction by the wavelet transform applied to aperture synthesis’, astronom. and astrophys., february 1994. [12] [12]. hopper t. and preston f., ‘compression of gray-scale fingerprint images’, in proc. dcc’92, 1992 data compression conf., snowbird, utah, march 1992, pp. 309-318. [13] [13]. woods j. w., ‘subband image coding’, kluwer academic, 1991. [14] [14]. z. xiong, k. ramchandran and m. t. orchard, space-frequency quantization for wavelet image coding, ieee trans. on image processing, vol. 6, no. 5, pp. 677-693, 1997. [15] [15]. s. g. mallat, multifrequency channel decompositions of images and wavelet models, ieee trans. acoust., speech, signal processing, vol. 37, no. 12, dec. 1989, pp. 2091-2110. iium engineering journal, vol. 4, no. 1, 2003 o. o. khalifa 39 [16] [16]. burt p. j. and adelson e. h., ‘the laplacian pyramid as a compact image code’, ieee trans. on communication, vol. 31, 1983, pp. 532-540. [17] [17]. j. d. villasenor, b. belzer and j. liao, wavelet filter evaluation for image compression, ieee trans. on image processing, august 1995. [18] [18]. daubechies i., ‘ten lectures on wavelets’, society for industrial and applied mathematics, philadelphia, 1992. [19] [19]. m. antonini , m. barlaud and i. daubechies., image coding using wavelet transform, ieee trans. on image processing vol.1, no.2, pp. 205 – 220, april 1992. [20] [20]. vitterli m. and hereley c., ‘wavelets and filter banks: theory and design’, ieee trans. on signal processing, vol. 40, 1992, pp. 2207-2232. [21] [21]. wannamaker r. a., ‘fractal wavelet compression of audio signals’, journal of audio engineering society, vol. 45, nos. 7-8, 1997, pp. 540-553. [22] [22].hilton h., jawerth b., and sengupta a., ‘compressing still and moving images with wavelets’, multimedia systems, vol. 2, no. 3, 1994. [23] [23]. .khalifa o. o. and dlay s. s., ‘wavelets for image data compression using bit allocation with scalar quantization’, s.f., isie’97, guimaraes, portugal, july 7-11, 1997, pp.77-81. [24] [24]. o. o. khalifa and s. s. dlay, medical image lossless compression for transmission of cross-limited bandwidth channels, spie, medical imaging, san diego, usa, pp. 342346, february 1999. biography othman omran khalifa received his bachelor’s degree in electronic engineering from the garyounis university, libya in 1986. he obtained his master degree in electronics science engineering and phd in digital image processing from newcastle university, uk in 1996 and 2000 respectively. he worked in industrial for eight years and he is currently an assistant professor at the department of electrical and computer engineering, international islamic university malaysia. his area of research interest is information theory and coding, digital image / video communication, coding and compression, wavelets, fractal and pattern recognition. microsoft word 258 completed iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 213 over expression of voltage dependent anion channel 2 (vdac2) in muscles of electrically stunned chickens norshahida abu samah 1 , azura amid 1,2 and faridah yusof 1 1 bioprocess and molecular engineering research unit, department of biotechnology engineering, 2 international institute for halal research and training (inhart), international islamic university malaysia, p.o. box 10, 50728 kuala lumpur, malaysia. azuraamid@iium.edu.my abstract: water bath stunning is a common practice in commercial slaughterhouses. such treatment is economic and in line with animal welfare practice. however, the conditions applied for the stunning process may vary from a slaughterhouse to another slaughterhouse. such a loose regulation on the stunning procedure has opened up doors for food adulteration such as over dose stunning. in this study, a simple and reliable approach using proteomics have been developed to study the effect of different currents and voltages in stunning on the protein expression of the chickens. protein profiles of the chickens were constructed in order to detect any differences in protein expression and modifications. the different voltage studied were 10 v, 40 v and 70 v while the values for current studied were 0.25 a, 0.5 a, and 0.75 a. after the proteomics analyses using 2d platinum imagemaster 6.0 and matrix-assisted laser desorption ionizationtime of flight (maldi tof) spectrometry identification, voltage dependent anion channel 2 (vdac2) was identified to be over expressed in the muscle sample of over stunned chicken. the over expression of vdac2 was confirmed at the transcriptional level of rna expression. real time pcr showed that all over stunned samples contained higher mrna expression level for vdac2 genes. the mrna level of vdac2 was upregulated by 59.87 fold change when normalized with housekeeping gene. in conclusion, vdac2 could serve as potential biomarkers for identification of electrically stimulated chickens. the existence of these biomarkers will help to monitor the slaughtering and stunning process in the future. it will revolutionize the food authentication field and give a new breathe to the meat industry. abstrak: kaedah “waterbath stunning” merupakan amalan biasa di pusat-pusat penyembelihan. kaedah ini adalah ekonomik dan selari dengan amalan kebajikan haiwan. walaubagaimanapun, syarat-syarat yang digunakan untuk proses kejutan tersebut mungkin berbeza antara sebuah pusat sembelihan dengan pusat sembelihan yang lain. sebarang peraturan yang longgar semasa proses kejutan tersebut membuka ruang kepada adulterasi makanan seperti lebihan dos kejutan elektrik. dalam kajian ini, satu pendekatan yang mudah dan boleh dipercayai menggunakan proteomik telah dibangunkan untuk mengkaji kesan arus dan voltan yang berbeza dalam proses kejutan elektrik terhadap ekspresi protin di dalam ayam. profil protein ayam telah dibuat untuk mengesan sebarang perbezaan terhadap ekspresi dan modifikasi protin. nilai voltan berbeza yang dikaji ialah 10 v, 40 v dan 70 v manakala nilai arus yang dikaji 0.25 a, 0.5 a, dan 0.75 a. selepas analisis proteomik menggunakan platinum 2d imagemaster 6.0 dan matrix-assisted laser desorption ionization-time of flight (maldi tof) spectrometry identification, voltage dependent anion channel 2 (vdac2) dikenal pasti terlebih ekspres di dalam sampel otot ayam yang terlebih dos kejutan elektrik. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 214 lebihan ekspresi vdac2 disahkan di peringkat transkripsi ekspresi rna. real time pcr menunjukkan bahawa kesemua sampel yang terlebih dos kejutan mengandungi tahap ekspresi mrna yang lebih tinggi di dalam gen vdac2. tahap mrna vdac2 dikawal oleh 59.87 perubahan kali ganda apabila dinormalkan dengan gen housekeeping. kesimpulannya, vdac2 boleh bertindak sebagai penanda biologi yang berpotensi untuk mengenal pasti ayam yang dirangsang elektrik. kewujudan penanda biologi ini akan membantu memantau proses penyembelihan dan kejutan pada masa akan datang. ia akan merevolusikan bidang pengesahan makanan dan memberi nafas baru kepada industri daging. keywords: stunning; slaughtering; proteomics; voltage dependent anion channel 2; chicken muscle 1. introduction stunning renders animals insensible during slaughtering procedures. electrical stunning is accomplished by passing a sufficient amount of electrical current through the brain of birds for a given amount of time. electrical stunning methods used in the past include electrified knives [1], electrified contact grids or plates and a v-shaped stunner but the most common is the water bath stunner. the electrical current passes the body from the head, which is in contact with the water in the bath, to the feet, which is in contact with a conveyor line. water bath stunning is applied to relax neck muscles and contract wing muscles for easy fixation of the head for automatic killers, prevent excessive struggling and wing flapping during bleed out, facilitate rapid bleeding and relax or loosen feathers [2]. the efficiency of electrical stunning depends on the control of parameters such as voltage, amperage, current frequency and immersion time. main adverse effects associated with high current or voltage stunning are wing hemorrhages, red skin conditions including red wing tips and pygostyles, poor plucking, broken bones and blood blemishes or blood coagulates in breast muscle [3]. proteomics is a widely used tool in biomarker identification especially in disease development and cancer studies. a biomarker is a substance found in the blood, urine, cerebrospinal fluid, or tissues and is often detected in higher than normal amounts in samples with certain disease or condition [4] . for many diseases, such as cancer, protein function is altered in the context of key signaling pathways that regulate critical cellular functions including proliferation, apoptosis, differentiation, survival, immunity, metabolism, invasion, and metastasis [5]. validation of a biomarker requires the analysis of thousands of samples to ensure that the potential biomarker is indeed related to a disease state and is not simply a function of the variability within the samples due to differences in diet, genetic background, lifestyle, and so on [6, 7]. even though biomarker discovery has been mostly focused on prognosis and diagnosis of a disease, this approach is also suitable for other applications such as biomarkers for food adulteration. in addition to contaminated meats and incorrect labeling, such adulterations include over dose stunning during slaughtering process. voltage dependent anion channel (vdac) has several isoforms which are vdac-1, vdac-2 and vdac-3. this protein is a major component of the outer mitochondrial membrane, and highly conserved large conductance anion channel involved in fluxes of ions and metabolites across the outer mitochondrial membrane [8]. vdac provides the main trans-membrane transport of ions, atp and other metabolites through the outer mitochondrial membrane. vdac shows both ion selectivity and voltage dependence [9]. in open state, anions are favored over cations, but the selectivity is relatively weak. both iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 215 positive and negative membrane potentials close vdac. the voltage effect is symmetrical, and half maximal closure occurs at about 50 mv [10]. vdac closure very effectively blocks movement of organic anions, including respiratory substrates, creatine phosphate, atp, adp, and pi [11]. vdac closure also help to explain inhibition of metabolite movement during anoxia and the persistent suppression of mitochondrial function in cytopathic hypoxia during septic shock and multiple organ failure [12-14]. 2. material and methods 2.1 experimental design female broiler chickens aged 35 days and weighing approximately 1.5 kg were collected from a farm in kuang, selangor, malaysia, electrically stunned, and slaughtered. the two parameters studied for stunning were current and voltage with three levels each: 0.25 a, 0.5 a and 0.75 a for the current and 10 v, 40 v and 70 v for the voltage. the treatments for stunning were designed using a three-level full factorial design (design expert software version 6.0.8) and compared to the control, which was the non-stunned sample (0 a, 0 v). two biological replicates were studied with three replicates of gels for each sample. a water stunner was designed to supply different sets of current and voltage. a glass aquarium was equipped with a copper plate sized 56.5 cm x 28.5 cm x 28.5 cm. the positive terminal of the circuit was immersed in the copper plate of the aquarium while the negative terminal was attached to the shackle used to hang the chicken’s leg. each chicken was stunned for duration of 5 seconds. 2.2 sample preparation muscle was sampled from thigh and homogenized in 10 volumes of phosphate buffer (250 mm of po4 + buffer, ph 7.5, 0.01 % triton x-100). the homogenate was centrifuged at 4ºc, 10 000 x g for 15 minutes and the supernatant was retained and stored at -80ºc until needed. the protein content of each sample was assayed using bradford assay [15]. 2.3 two-dimensional gel electrophoresis (2-d ge) ten microgram (10 µ g) of sample was added to the sample buffer (7 m urea, 2 m thiourea, 4 % chaps, 3 mg/ml dtt, 0.5 % pharmalyte) resulting in a total volume of 170 µl. after that, 170 µl of rehydration buffer (7 m urea, 2 m thiourea, 4 % chaps, trace amount of bromophenol blue, 3 mg/ml dtt, 0.5 % pharmalyte) was added and the mixture was left at room temperature for 30 minutes. isoelectric focusing was conducted on ipgphor 3 according to the manufacturer’s protocol (ge healthcare). the temperature was kept constant at 20ºc and the current was maintained at 50 µa per strip. after ief, a second separation step (sds-page) was performed on a vertical setup of 12.5 % polyacrylamide gel. the strips were reduced with 100 mg of dtt dissolved in 10 ml of equilibration buffer (6 m urea, 50 mm tris-hcl, 30 % glycerol, 2 % sds) and alkylated with 250 mg of iodoacetamide in equilibration buffer with a trace amount of bromophenol blue. the ipg strip was sealed in place using 0.5 % agarose solution dissolved by heat in electrophoresis buffer (250 mm tris, 1920 mm glycine, 1 % sds). after electrophoresis, the gel was stained with silver nitrate solution for visualization. the gels were scanned by using imagescanner iii labscan 6.0 software (ge healthcare). the scanner was set at 300 dpi, transparent mode with green filter. 2.4 proteomic analysis of imagemaster platinum 6.0 iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 216 protein spots were detected and analyzed using imagemaster 2d platinum 6.0 software (ge healthcare). after proteomics software analysis, the spots of interest were identified. the sample was run again on the same conditions and stained with coomassie brilliant blue instead of silver staining as silver staining is incompatible with mass spectrometry analysis. after staining with coomassie brilliant blue, the spot of interest were manually excised and subjected to maldi-tof mass spectrometry analysis. the excised spot from the gel was digested with trypsin and subjected to zip tip purification. 2.5 maldi tof mass spectrometry analysis after ziptip treatment, the spot was analyzed by maldi tof/tof mass spectrometer (applied biosystems). both ms and ms/ms spectra were recorded in the combination mode. in ms spectrum, 1800 shots were accumulated and 4500 shots were accumulated for each ms/ms spectrum. protein was identified from their accumulated ms and ms/ms spectra by manual searching using a locally implemented mascot server and compared to swissprot and ncbi database. 2.6 validation of proteomics result by real time pcr in order to confirm the identified candidate protein through proteomics analysis, a validation was conducted on the transcriptional level of rna. rneasy lipid tissue mini kit (qiagen) was used for the extraction of total rna. after the extraction of total rna, the complementary dna was synthesized by using superscript iii cellsdirect cdna synthesis system (invitrogen). the single-stranded cdna concentration was measured and stored at -20ºc for further pcr amplification. the complete sequence for the candidate gene was obtained from ncbi database. primers of the potential biomarker as well as the housekeeping gene were designed using primer3 free software (hhtp://frodo.wi.mit.edu/primer3/). real time pcr was conducted using sybr green as the detection method with dissociation curve analysis. the results were analyzed using mxpro software (stratagene). the sybr green ct values from triplicate experiments were calculated to find an average ct value for each sample. these average values were then used to calculate the ratio using a formula from pfaffl [16]. for each experiment, 18s rrna gene was used as the reference gene, and the non-stunned chicken muscle cdna was the control sample. 3. results it was observed that in 0.75 a, 70 v stunned chicken (fig. 1), protein l was over expressed and it was completely not detected in the 0 a, 0 v non stunned samples (fig. 2). therefore, protein l could be considered as protein where expression was influenced by the electrical treatment introduced during stunning process. in fig. 3, for instance, gel number 97584 is the reference gel for 0.75 a, 70 v stunned chicken and displayed on the y axis while gel number 97567 which is plotted on the x axis represents the non-stunned chicken. the number of matched spot displayed when gel number 97584 is plotted against gel number 97567 is 214 with data correlation of 0.907. a correlation near to 1 indicates that the two gels were highly correlated. therefore, any new spot emerged from gel number 97584 is considered as a true biomarker. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 217 fig. 1: protein profile of 0.75 a, 70 v stunned chicken muscle. the red crossed signs represent the detected protein spots. l1, l2 and l3 represent landmarks for gels alignment and matching. protein l was identified as protein spot that was only detected in 0.75 a, 70 v stunned sample. fig. 2: protein profile of 0 a, 0 v non stunned chicken muscle. the red crossed signs represent the detected protein spots. l4 and l5 represent landmarks for gels alignment and matching. fig. 3: scatter plot for muscle sample. the y axis represents 0.75 a, 70 v stunned sample while x axis represents 0 a, 0 v non stunned sample. correlation near to 1 indicates that the two gels are highly correlated and free from staining variations. l iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 218 figure 4 shows the interaction graph of protein l. the graph was generated from the design expert software via 3-level full factorial design. it was shown that the protein intensity is increasing as the amount of voltage increase when the current was maintained at 0.75 a. in contrast, the amount of protein intensity is decreasing as the amount of voltage increased when the current is set at low value (0.25 a). therefore, the protein intensity was observed to be greatly influenced by the amount of current introduced during the stunning process. in table 1, it was observed that current (b), interaction of voltage and current (ab) and current 2 (b 2 ) had significant influence on the release of protein l with p-value of 0.0048, 0.0336 and 0.0219 respectively at 95 % confidence level. there were only 0.48 %, 3.36 % and 2.19 % that the variable terms f-value could occur due to noise. the lack of fit of 0.5610 is insignificant relative to pure error, and it is desirable because the model is expected to fit (table 1). fig. 4: interaction graph for protein l intensity to the stunning parameters. the interaction graph plots protein intensity versus voltage (v). red plot represents current at 0.75 a while black plot represents 0.25 a. table 1: analysis of variance for protein l intensity. a represents voltage while b represents current and ab represents the interaction between voltage and current. protein prob > f model a b ab a 2 b 2 lack of fit l 0.0109 0.5000 0.0048 0.0336 0.5495 0.0219 0.5610 after proteomics analysis, protein l was identified as voltage dependent anion channel 2 (vdac2) via maldi tof mass spectrometry (table 2). after maldi tof identification, the expression levels were further confirmed at the transcriptional level by real time pcr. the vdac2 gene has been up-regulated by 59.87 fold change in 0.75 a, 70 v stunned sample compared to the 0 a, 0 v non stunned chicken muscle (table 3). gene up-regulation on the vdac2 gene confirmed the findings from maldi-tof analysis, thus, suggesting the protein as promising biomarker in identification of electrically stimulated chicken meat. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 219 table 2: identification of protein l by maldi-tof spectrometry. protein l was identified as voltage dependent anion channel 2 (vdac2). spot id protein name accession no protein mw protein score protein score c.i % total ion score total ion confirmed c.i % l voltagedependent anion channel 2 gil46048903 30293.3 460 100 394 100 table 3: real time pcr validation of vdac2 at transcriptional level. spot id protein name gene name ct value sample ct value control ct value difference a value fold increment l vdac2 vdac2 22.74 ± 0.24 24.18 ± 0.24 1.44 -3.237 59.87 4. discussion vdac2 levels were up-regulated under iron deprivation in k562 (human erythromyeloblastoid leukemia) cells by high resolution 2d electrophoresis and confirmed via western blot analysis [17]. iron deprivation is known to stimulate hypoxia and hypoxia induces membrane lipid peroxidation [18]. stark studied that membrane lipid peroxidation results in the activation of vdac-mediated transport [19]. vdac is also useful in regulating some enzymes that involved in redox status control, such as, copper and zinc containing superoxide dismutase [20]. cheng et al., studied that vdac2 coevolved to regulate cell death and vdac2 has a distinctive physiological role in vivo as a specific inhibitor of bak (b-cell leukemia/lymphoma 2 homologous antagonist/killer)dependent mitochondrial apoptosis [21]. chandra et al., suggested that an increase in vdac2 complex formation in stimulated hct116 (colonic epithelial) cells might be considered as a prosurvival mechanism activated by apoptotic stimuli [22]. in other studies conducted by turko and murad, [23] mostyn et al., [24] and mccabe [25], vdac has been associated with type 2 diabetes mellitus. in addition, vdac accumulation has been associated with dystrophic neurites of β-amyloids plaques in alzheimer’s disease [26]. yuqi et al., concluded that an increased expression of mitochondrial vdac and subcellular co-localization of vdac/bax increases mitochondrial permeability and apoptosis [27]. the increased of vdac expression highlight the potential importance of mitochondrial genes in the etiology of hypertension. vdac seems to act as a brake on mitochondrial metabolism. in other instances, dynamic regulation of vdac conductance by glucose-metabolizing enzymes may control insulin secretion in pancreatic beta cells and aerobic glycolysis in cancer cells. however, excessive vdac closure may also promote apoptosis, cytopathic hypoxia, fatty liver disease and other pathophysiological changes. vdac acts as a governator that establishes iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 220 set points for global mitochondrial activity that change in response to cellular needs and metabolic stresses. it was observed that direct current of 600 µ a and monophasic current of 2.5 to 3.0 ma with pulse duration of 300 microseconds and 100 hz stimulate the expression of wound healing protein, vascular endothelial growth factor (vegf) in male sprague-dawley rats [28]. on the seventh days after surgical incision, it was observed that the skin vegf expression was significantly elevated in the direct current group. electrical stimulation with 4 ma rectangular pulses of 0.5 ms duration at 2 hz lasting for 1 hour would be a potential treatment for preventing atrophy of denervated skeletal muscles [29]. although electrical stimulation alone is effective to prevent muscle atrophy, the combination of electrical stimulation and isometric contractions was observed to have further effect [30]. electrical stimulation of cultured cartilage explants was discovered to result in significant increases in proteoglycan and collagen production and a highly significant upregulation of aggrecan and type ii collagen mrna expression [31]. these findings support the contention that delivery of a specific, defined electrical field to articular cartilage could result in matrix preservation and wound healing. meanwhile, a delivery of high current and voltage will cause an over expression of hypoxia associated mitochondrial protein such as voltage-dependent anion channel 2. 5. conclusion we found voltage-dependent anion channel 2 (vdac2) to be elevated in the samples of muscles of chickens stunned at 0.75 a, 70 v. this protein is completely absent in the samples from non-stunned (0 a, 0 v) chickens. when confirmed at the transcriptional level, the gene coding for vdac2 exhibited up-regulation of 59.87 fold in samples from chickens stunned with 0.75 a, 70 v. therefore, vdac2 could be potentially developed as a biomarker for identification of over stunned chicken in the market. 6. acknowledgements we would like to thank the mohe of malaysia for funding the research through research grant frgs 02-07-43 and the ministry of science, technology and innovation (mosti) for providing an nsf scholarship for norshahida abu samah throughout her msc program. references [1] h.j. reynolds, “recent developments in poultry processing”, american poultry journal, vol. 74 (4), pp. 17-21, 1943. [2] j.a. dickens, and a.d. shackelford, “feather-releasing forces related to stunning of chickens, and its effect on the quality of the meat”, fleischwirtschaft, vol. 68, pp. 14161420, 1988. [3] n.g gregory, “from stunning and slaughter”, in processing of poultry, edited by g.c. mead, london, elsevier sci publishers ltd, 1989. [4] j.s. macneil, “better biomarkers for the diagnostics labyrinth”, genome technol, pp. 2433, 2004. [5] k.r. calvo, l.a. liotta, and e.f. petricoin, “clinical proteomics: from biomarker discovery and cell signaling profiles to individualized personal therapy”, bioscience reports, vol. 25, pp. 107-125, 2005. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 221 [6] s.p. gygi, g.l. corthals, y. zhang, y. rochon, and r. aeberson, “evaluation of twodimensional gel electrophoresis based proteome analysis technology”, pnas, vol. 97 (17), pp. 9390-9395, 2000. [7] t. rabilloud, “detecting proteins: separated by 2-d gel electrophoresis”, anal chem, vol. 72 (1), pp. 48a-55a, 2000. [8] m.a. baker, d.j. lane, j.d. ly, v. de pinto, and a. lawen, “vdac1 is a transplasma membrane nadh-ferricyanide reductase”, j biol chem, vol. 279, pp. 4811-4819, 2004. [9] v.a. menzel, m.c. cassara, r. benz, v. de pinto, a. messina, v. cunsolo, r. saletti, k.d. hinsch, and e. hinsch, “molecular and functional characterization of vdac2 purified from mammal spermatozoa”, bioscience reports, vol. 29, pp. 351-362, 2009. [10] j.j. lemasters, and e. holmuhamedov, “voltage-dependent anion channel (vdac) as mitochondrial governator – thinking outside the box”, biochimica et biophysica acta, vol. 1762, pp. 181-190, 2006. [11] t.k. rostovtseva, a. komarov, s.m. bezrukov, and m. colombini, “vdac channels differentiate between natural metabolites and synthetic molecules”, j membr biol, vol. 187, pp.147-156, 2002. [12] e.d. crouser, “mitochondrial dysfunction in septic shock and multiple organ dysfunction syndrome”, mitochondrion, vol. 4, pp. 729-741, 2004. [13] m.p. fink, “bench-to-bedside review: cytopathic hypoxia”, crit care, vol. 6, pp. 491-499, 2002. [14] m.p. fink, “research: advances in cell biology relevant to critical illness”, curr opin crit care, vol. 10, pp. 279-291, 2004. [15] m.m. bradford, “a rapid and sensitive method for the quantification of microgram quantities of protein utilizing the principle of protein-dye binding”, anal biochem, vol. 72, pp. 248-254, 1976. [16] m.w. pfaffl, “a new mathematical model for relative quantification in real-time pcr”, nucleic acids research, vol. 29 (9), pp. 2002-2007, 2001. [17] k. valis, j. neubauerova, p. man, p. pompach, j. vohradsky, and j. kovar, “vdac2 and aldolase a identified as membrane proteins of k562 cells with increased expression under iron deprivation”, mol cell biochem, vol. 311, pp. 225-231, 2008. [18] c. behn, o.f. araneda, a.j. llanos, g. celedon, and g. gonzalez, “hypoxia-related lipid peroxidation: evidences, implications and approaches”, respir physiol neurobiol, vol. 158, pp. 143-150, 2007. [19] g. stark, “functional consequences of oxidative membrane damage”, j membr biol, vol. 205, pp. 1-16, 2005. [20] m. budzinska, h. galganska, m. wojtkowska, o. stobienia, and h. kmita, “effects of vdac isoforms on cuzn-superoxide dismutase activity in the intermembrane space of saccharomyces cerevisiae mitochondria”, biochem biophys res commun, vol. 357, pp. 1065-1070, 2007. [21] e.h.y. cheng, t.v. sheiko, j.k. fisher, w.j. craigen, and s.j. korsmeyer, “vdac2 inhibits bak activation and mitochondrial apoptosis”, science, vol. 301, pp. 513-517, 2003. [22] d. chandra, g. choy, p.t. daniel, and d.g. tang, “bax-dependent regulation of bak by voltage-dependent anion channel 2”, the journal of biological chemistry, vol. 280 (19), pp. 19051-19061, 2005. [23] i.v. turko, and f. murad, “quantitative protein profiling in heart mitochondria from diabetic rats”, j biol chem, vol. 278, pp. 35844-35849, 2003. [24] a. mostyn, s. pearce, t. stephenson, and m.e. symonds, “hormonal and nutritional regulation of adipose tissue mitochondrial development and function in the newborn”. exp clin endocrinol diabetes, vol. 112, pp. 2-9, 2004. [25] e.r. mccabe, “microcompartmentation of energy metabolism at the outer mitochondrial membrane: role in diabetes mellitus and other diseases”, j bioenerg biomembr, vol. 26, pp. 317-325, 1994. [26] i. ferrer, “altered mitochondria, energy metabolism, voltage-dependent anion channel, and lipid rafts converge to exhaust neurons in alzheimer’s disease”, j bioenerg biomembr, vol. 41, pp. 425-431, 2009. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology abu samah et al. 222 [27] l. yuqi, g. lei, l. yang, l. zongbin, x. hua, w. lin, c. rui, l. mohan, w. yi, g. minxin, and w. shiwen, “voltage-dependent anion channel (vdac) is involved in apoptosis of cell lines carrying the mitochondrial dna mutation”, bmc medical genetics, vol. 10, p. 114, 2009. [28] m.r. asadi, g. torkaman, and m. hedayati, “effect of sensory and motor electrical stimulation in vascular endothelial growth factor expression of muscle and skin in fullthickness wound”. journal of rehabilitation research & development, vol. 48 (3), pp. 195202, 2011. [29] t. arakawa, a. katada, h. shigyo, k. kishibe, m. adachi, s. nonaka, and y. harabuchi, “electrical stimulation prevents apoptosis in denervated skeletal muscle”, neurorehabilitation, vol. 27 (2), pp. 147-154, 2010. [30] n. fujita, s. murakami, t. arakawa, a. miki, h. fujino, “the combined effect of electrical stimulation and resistance isometric contraction on muscle atrophy in rat tibialis anterior muscle”, bosn j basic med sci, vol. 11 (2), pp. 74-79, 2011. [31] c.t. brighton, w. wang, and c.c. clark, “the effect of electrical fields on gene and protein expression in human osteoarthritic cartilage explants”, j bone joint surg am, vol. 90 (4), pp. 833-848, 2008. nomenclature 2d : two dimensional maldi tof : matrix assisted laser desorption ionization time of flight page : polyacrylamide gel electrophoresis application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 16 philosophy of modern bioengineering ibrahim ahmed shogar 1* and suzanah abdul rahman 2 1 department of computational and theoretical science, faculty of science, 2 department of biomedical sciences, facuty of allied health sciences, international islamic university malaysia, kuantan campus, pahang, malaysia. *corresponding author: shogar@iium.edu.my (received: 25 th aug. 2016; accepted: 5 th may 2015; published on-line: 31 st dec. 2017) abstract: this article investigates the philosophical foundations of modern bioengineering to articulate its rational framework. engineering, as an ultimate mechanism to transform knowledge into practice, is essential for both physical and biological sciences. it reduces data, concepts, and designs to pictorial forms. integration of engineering with newly emerging biosciences, has presented a unique opportunity to overcome major challenges to environmental ecology and human health. to harness the potential of modern bioengineering and establish a sustainable foundation for green technology, scientists and engineers should be acquainted with the normative questions of science and technology. besides acquiring the general principles of scientific research and identification of the intrinsic goals of the endeavor, philosophy of bioengineering exposes scientists to both the descriptive „how‟ questions of the physical world as well as the normative „why‟ questions of values. such an interdisciplinary approach is essential, not only for inspiration to acquire the genuine knowledge, but also to expose the scientists and bioengineers to their ethical and social responsibilities. introducing the conceptual framework of bioengineering, this paper has investigated the three major philosophies that have been dominating the basic presuppositions of the scientific research method in the modern history of science, namely: (i) the mechanical approach of physical sciences, (ii) the functional (goal-guided) approach of biological processes, and (iii) the integrated approach. the paper also has conducted an analytical study on various branches of the emerging discipline of bioscience. it has concluded that adopting the interdisciplinary approach is essential to harness potentials of bioengineering and to establish foundations of green technology based on moral values. to materialize such a noble goal, both epistemological and normative knowledge must be acquired in bioengineering research and education. the former is essential for invention and innovation; while the latter exposes bioengineers to their ethical and moral commitments. abstrak: artikel ini mengkaji tentang falsafah asas bidang biokejuruteraan moden bagi menjelaskan rangka kerja rasional. bidang kejuruteraan adalah mekanisma muktamad untuk mengubah ilmu kepada aplikasi, penting bagi kedua-dua sains fizikal dan sains biologi. ia mengurangkan data, konsep dan rekaan kepada bentuk bergambar. integrasi kejuruteraan bersama kemunculan biosains baharu, telah memberi peluang yang unik untuk mengatasi cabaran utama yang dihadapi oleh ekologi persekitatan dan kesihatan manusia. bagi memanfaatkan potensi biokejuruteraan moden dan membina asas kukuh pada teknologi hijau, saintis dan jurutera sepatutnya mengetahui soalan normatif tentang sains dan teknologi. selain mendapatkan prinsip umum kajian saintifik dan mengenal pasti matlamat intrisik bagi usaha ini. falsafah biokejuruteraan mendedahkan saintis kepada dua deskriptif soalan ‘bagaimana‟ pada dunia fizikal serta soalan normatif ‘mengapa‟ pada nilai-nilai. kepentingan kaedah interdisiplinari ini iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 17 bukan sahaja memberi inspirasi bagi menambah ilmu yang tulen, malah mendedahkan kepada saintis dan bio-jurutera kepada tanggungjawab etika dan sosial. melalui pendedahan konsep struktur biokejuruteraan, kertas ini telah mengkaji tiga falsafah penting yang mendominasi pengetahuan asas kaedah kajian saintifik dalam sejarah moden sains, seperti berikut: (i) kaedah mekanikal sains fizikal, (ii) pendekatan berfungsi (berpandukan-matlamat) proses biologi, dan (iii) pendekatan bersepadu. kertas ini juga telah menjalankan kajian analitikal terhadap pelbagai cabang kemunculan disiplin biosains. sebagai rumusan, pendekatan multidisiplin adalah sangat penting diamalkan untuk manfaat potensi biokejuruteraan dan membina asas teknologi hijau berdasarkan nilai moral. bagi merialisasi matlamat mulia ini, kedua-dua ilmu epistemologikal dan normatif mesti di pelajari dalam penyelidikan biokejuruteraan dan pelajaran. ilmu epistemologikal penting bagi ciptaan dan inovasi, sementara ilmu normatif mendedahkan bio-jurutera kepada komitmen etika dan moral. keywords: philosophy; bioengineering; integrated approach; systems biology; goal-directed process; causal explanation; ethics 1. introduction in its ambitious plan for a bioengineering research programme in the 21 st century, harvard university emphasizes that there is enormous potential for transformation of bioengineering into a discipline directed toward synthesis of technologies that have profound impact on human well-being and the future of the planet earth. the plan further explains that bioengineering is an exciting, deeply interdisciplinary, intellectual area that naturally integrates physical, life sciences, and information sciences to understand complicated biological systems. it is the basic point of intellectual integration for engineering, medicine, molecular biology, chemistry, synthetic biology, bio-energy, systems biology, stem cell research and biological computation 1 . the interdisciplinary approach that integrates engineering with biological and physical sciences is becoming the central issue of the modern philosophy of science. it presents a unique opportunity for scientific enterprise to develop methods to enhance human health and protect the natural environment. harnessing such opportunities to tackle challenges posted by ecological crises represents the great advantage of bioengineering science, which promotes the integrated approach. for this purpose, scientists, engineers, philosophers and theologians need a constructive team collaboration to sustain natural recourses and bring better chances for life on planet earth. integration of the two traditional methods of scientific explanation is one of the major objectives of philosophy of bioengineering. the causal and teleological explanations are the dominating philosophies of scientific inquiry in the modern history of science2. modern philosophy of science presupposes that processes of the physical world are mechanical and deterministic in nature, while biological processes are functional and purposive (goal-guided). thus, the causal explanation is mainly concerned with the physical world, while the teleological explanation deals with the goal-directed processes of biological and behavioral organisms. the key difference between the two modes of 1 see details at https://hms.harvard.edu/sites/default/files/assets/about_us/off_dean/files/bioengineer.pdf 2 the teleological explanation in fact finds its roots and origins in ancient greek philosophy, therefore it should be understood in two contexts: (i) in the context of classical philosophy that interprets the entire phenomena of the world based on purpose and function; and (ii) in the context of modern philosophy that applies the concept on biological and purposive processes / actions of organisms or systems. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 18 explanation lies in the circumstance under which cause and effect are related to each other. in goal-guided processes of biology, the future (the goal) plays a major role to determine the present act, while in causal explanation of the physical processes the past explains the present and determines the future act [13, 20]. the major characteristic of biological systems is that they are brought about by interactions of their parts but these parts in isolation display no similar characteristics of their components! in other words, it is hard to predict the behavior of biological processes from knowledge of their individual parts [17]. this profound difference between the physical and biological worlds has critical impacts on their methods of investigation and understanding. biological systems are too complex to be explained fully by the method of physical sciences, which has been remarkably successful in developing approaches to understand and control the physical world3. mathematical modeling and computer simulations play a crucial role to understand the internal nature and dynamics of biological processes to arrive at predictions about their structural development and the effect of their interactions with the environment [17]. in contrast to the classical philosophies, the integrated approach presumes no essential difference between motivational explanation in biology and causal explanation in physics. physical and biological processes, according to the integrated method, can be approached either by the causal explanation, as emphasized by carl g. hempel and paul oppenheim [13], or through application of teleological method on physical sciences, as perfectly presented by producing goal-directed systems, such as plastic missiles. the scientific advancements in the first half of the twentieth century, especially during world war ii, brought to scientists‟ attention the practical value of teleological explanation to develop goal-guided systems to communicate and control biological as well as physical systems. this transdisciplinary approach has become known as „cybernetics‟. one of the fundamental works on this method is the work of eminent mathematician norbert wiener, entitled “cybernetics”, published in 19484. it is evidently clear that biological processes constitute the basic part of the integrated approach of contemporary philosophy of science. articulation of the philosophical foundations of bioscience, understanding its rational framework, the formulation of its principles, and developing the relevant approaches to understand the complex systems of life is, therefore, becoming the major objective of the modern philosophy of science. these are the basic themes that this paper aims to highlight. through reflection on philosophical foundations of bioengineering, this paper aims at articulating fundamentals of the integrated approach. it also investigates the ethical concerns of bioengineering research and practice. the basic content of paper is divided into three major parts, including the conceptual framework, the philosophical foundations of bioengineering, and ethical concerns of bioengineering where the islamic perspective on the negative impacts of bioresearch will be presented. conclusions and findings of the paper are found in the final section. 3 in their preface, the authors of “systems biology: a textbook” remark that „life is probably the most complex phenomenon in the universe‟. this statement, and other researcher‟s view on biology, emphasize that there are more practical questions to be answered by systems biologists, such as what is life, and why do we age and die? 4 the full title of the book is “cybernetics or control and communication in the animal and the machine. it is obvious that prof. wiener has clarified the term “cybernetics” by the other part of the title. however, it can be defined as a transdisciplinary approach for exploring regulatory systems, their structures, constraints, and possibilities. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 19 2. the conceptual framework of bioengineering the term „science‟ in modern philosophy of science, is used in three interconnected contexts: first, science as a systematic method of inquiry which aims at understanding the natural and human phenomena; second, science as an accumulative body of acquired knowledge 5 ; and third, science as an application of knowledge. „bioengineering’ is the interdisciplinary approach that related to the third meaning. it can be defined as the application of method of physical sciences and mathematical principles to understand the complex systems of life for practical purposes. bioengineering encompasses various sciences which integrate engineering and life science and its applications, such as biomedical engineering, bioinformatics, and systems biology. in contrast to the conventional concept of „biology‟, biosciences are mainly practical. in education, engineering largely aims at developing skills and abilities of conceptualization and calculation, whereas biology education develops the descriptive and connective abilities [15]. the common objective of biosciences, however, is to understand the complex systems of life for practical ends. a comparative and analytical study on bioengineering reveals that it works in collaboration with other fields, especially with systems biology and bioinformatics. the set of bioscience can be divided, based on their final objectives, into two major groups 6 : the first group constitutes an effective method of analyzing to understand the complex systems of life, while the other group concerns with application of the cumulative knowledge. the first group aims to produce knowledge through collection and analytical study of data; while the other group aims at transforming the existing knowledge into practice. for example, bioinformatics and systems biology are concerned with building databases, analysis, and the molding of complexities of the biological phenomenon for proper understanding of the phenomena. bioengineering and biomedical engineering, on the other hand, are concerned with application of knowledge to produce technologies and to develop methods that promote human well-being and sustain the environmental health. 2.1 the analytic approaches we are using the term „analytic‟ to describe biosciences concerned with collection, analyzing and modeling of biological data for practical ends. the term should not indicate that these sciences are less practical than „applied‟ sciences; rather it emphasizes that such sciences are effective methods or useful tools to create databases for understanding the complex systems of life. among many types of biosciences, bioinformatics and systems biology might be regarded as key elements of analytical approaches that are capable of providing relevant methods which enable bioengineers to build systematic databases and access various forms of biological systems for explanation and understanding. both depend on mathematics and computer science as major tools for analysis, designing and modeling. 5 with regard to the cumulative body of knowledge, scientific inquiry, according to arthur a. noyes, has two distinctive objectives: first, science aims at making the comprehension of the existing knowledge that already acquired by mankind as easy as possible; second, it aims to add to the total sum of human knowledge by the discovery of previously unknown phenomena. [noyes, arthur a., (1902). the general principles of physical science. (henry holt and company, new york), p3-4.] 6 it should be noted that these classifications are procedural to facilitate the study for better understanding; there are no real boundaries between biosciences, they overlap each other, especially in their research method. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 20 2.1.1 bioinformatics bioinformatics is an interdisciplinary science that develops methods and software tools for understanding biological data. it is the basic approach of bioscience research that is concerned with building databases and analysis. the simple view of bioinformatics science is the process of collection, storage, and analysis of biological information. as an interdisciplinary approach, bioinformatics integrates computer science with statistics, mathematics, and engineering to analyze and interpret biological data. alongside the data handling, bioinformatics deals with a wide range of data that starts from simple analytical approaches that are routinely conducted by molecular biologists to find the related gene and protein sequence, through an expended mode of specialized tools for data analysis, to sophisticated statistical methods for high-throughput data analysis [12, 18]. systems biology projects mainly rely on bioinformatics techniques and infrastructure to conduct their data analysis. annotation of genome sequences might be regarded as one of the most basic application of bioinformatics methods. according to many biologists, such as clair and alistair, the bioinformatics field is moving from focus on functions of single genes to consider wider relationships between genes as they operate together in pathways and networks. in other words, bioinformatics is increasingly considering the questions of molecular systems biology; therefore, the question may arise about the real contribution of bioinformatics to the new emerging science of systems biology. the practical cases show that bioinformatics can serve systems biology in many ways, but two of the most basic forms are that: first, bioinformatics provides methods to obtain systems information from the vast amount of available databases that constitute the basic infrastructure for analysis and generating new data. second, in the context of data handling, bioinformatics is regarded as an important method which concerned with designing the appropriate standards and databases for proper archiving[12]. 2.1.2 systems biology what is systems biology, how does it work, and why is it important? such questions are important to understand the emerging approach to interpret the biological phenomenon that encompasses various methods of explanation. biological systems like organisms, cells, or biomolecules are highly organized in their structure and function. biologists have developed different approaches to explain and understand such systems. systems biology, however, might be regarded as one of the most effective and promising approaches to understand the complex systems and mysterious behaviors of biological phenomena. it integrates various methods to develop a qualitative and quantitative understanding, such as experiment and modeling on one hand and mathematical and computational analysis on the other. these characteristics qualify systems biology as an effective method to understand the complexity of life. by studying the structure and physiology of living systems in detail, researchers from different disciplines have discovered how the mystery of life arises from the structure and functional organization of cells and from the continuous refinement by mutation and selection[17]. there are, however, still many critical questions that biologists need to deal with, such as the problem of aging and death. authors of “systems biology: a textbook” believe that systems biology is the key to answer many questions of biology. they explain that systems biology is the combined study of biological systems which aims at: (i) investigating the components of cellular networks and their interactions; (ii) applying experimental high-throughput and whole-genome techniques; and (iii) integrating computational method with experimental efforts[17]. klipp and her colleagues have summarized the major factors behind the flourishing of systems biology. they emphasize iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 21 that the systemic approach in biology is not new, but it recently gained new thrust due to the emergence of powerful experimental and computational methods. it is based on the accumulation of an increasingly detailed biological knowledge, on the emergence of new experimental techniques in genomics and proteomics, tradition of mathematical modeling of biological processes, the exponentially growing computer power, as prerequisite for databases and the calculation of large systems, and on the internet as the central medium for a quick and comprehensive exchange of information [17]. a systemic approach to life sciences research is necessary for better qualitative and quantitative understanding of the functioning of biological systems in health and pathological conditions. the ultimate goal of systems biology is to understand the structure and function of physiological and patho-physiological systems, to develop fruitful approaches in biotechnology. for example, knowledge gained from systems biology can open up the way for disease control, prevention and treatment. systems biology has great benefits since a thorough understanding of complex biological processes will allow tackling of many real problems, especially in relation to health sciences. in providing solutions to such practical problems, systems biology is regarded as the key approach towards understanding secrets of life for practical purposes in the twenty first century[18]. 2.2 the applied approaches the process of engineering, in any product, is usually composed of three parts: analysis, synthesis, and design. analysis is the study of systems in order to understand their function. synthesis is the practical building of the systems under analysis. both steps contribute to the end goal of engineering, which lies in the final design of the product. the useful approaches of bioscience are that which have a practical value in transforming the theoretical knowledge into technologies and practical methods. bioengineering and biomedical engineering are the two most practical aspects of bioscience. both aim at employing biological knowledge for practical purposes, such as producing and using artificial tools to enhance human health, and using organisms and biological processes in industry. some researchers view these two effective approaches of bioscience as the same, in the sense that biomedical engineering is a specific form of bioengineering that concerns itself with medical and health sciences. however, others treat these two sciences as different disciplines. they emphasize that, while bioengineering is concerned with developing tools and technologies, biomedical engineering aims at practical application of those technologies for health care purposes 7 . 2.2.1 bioengineering according to arthur johnson, bioengineering does not imply a particular application or industry. in this sense it differs from biomedical engineering, environmental engineering, or agricultural engineering, each of which applies knowledge about biology to particular application areas. the term „bioengineering‟ 8 or biological engineering is used for the interdisciplinary approach that integrates physical sciences with life sciences in the crucible of mathematical principles for practical purposes. technically, it can be defined as „the application of scientific and mathematical principles to understand and 7 summary of these views is found with mark r. riley (2007) in his “introducing journal of bioengineering” at https://jbioleng.biomedcentral.com/articles/10.1186/1754-1611-1-1#cr5 8 the word „bioengineering‟ is comprised from the prefix „bio‟ which denotes things related to life, and „engineering‟ which stands for the application of mathematical principles to optimize nature for human needs, such as making designs, processes, and systems. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 22 employ life systems for practical ends‟. according to the national institute of health (nih) 9 , "bioengineering integrates physical, chemical, mathematical sciences and engineering principles for the study of biology, medicine, behavior, or health” 10 . it advances fundamental concepts, creates knowledge for the molecular to the organ systems levels, and develops innovative biologics, materials, processes, implants, devices, and informatics approaches for the prevention, diagnosis, and treatment of disease, for patient rehabilitation, and for improving health" [5]. encyclopedia britannica defines „bioengineering‟ as `the application of engineering knowledge to fields of medicine and biology'. the above definitions are obviously focused on biomedical engineering, which is a central subject of bioengineering, but the broader meaning of biological engineering stretches beyond the medical area to address the full spectrum of the life sciences, including applications to agricultural, environmental, and ecological systems that utilize engineering approaches and rationale to deal with biological problems. the major application areas of bioengineering, according to encyclopedia britannica, include medical engineering, agriculture engineering, bionics, biochemical engineering, human factors engineering and bioenvironmental engineering. bioengineering, as an applied science, has become the major method to transform the knowledge of life science into practice. as elaborated by the harvard university bioengineering plan, a large number of the basic mechanisms have been discovered and the essential mystery of life has been stripped away within the last few years in the history of molecular biology. for instance, biomedical engineering has yielded revolutionary advances, including new imaging modalities, prosthetic devices, dialysis, and drug delivery systems, and it is poised to tackle the increasingly complex and sophisticated problems of everyday life 11 . indeed, the practical value of bioengineering in modern scientific platform has convinced professors of engineering to call for an integrated curriculum for engineering professions. they are suggesting that the three basic sciences that have been traditionally studied by engineering students, i.e. physics, chemistry, and mathematics, be integrated with biology. they stress that all engineers, regardless of their specializations, must be exposed in their undergraduate years to the biological sciences. professor johnson emphasizes that engineers of the future must be true synthesizers instead of just designers [15]. 2.2.2 biomedical engineering using scientific principles to solve the practical problems of life is the key characteristic of bioengineering [23]. biomedical engineering is the major application field of bioengineering; therefore, they are interchangeably used in many cases. since technology has such a dramatic impact on medical care, engineering professionals have become intimately involved in many medical ventures. as a result, the discipline of biomedical engineering has emerged as an integrating medium for two dynamic professions, medicine and engineering, and has assisted in the struggle against illness and 9 see their website and following link: http://www.sci.utah.edu/~macleod/bioen/bme-definition.shtml 10 riley, mark r. (2007) introducing journal of bioengineering: https://jbioleng.biomedcentral.com/articles/10.1186/1754-1611-1-1#cr5 11 engineering biology for the 21st century a plan for bioengineering at harvard (https://hms.harvard.edu/sites/default/files/assets/about_us/off_dean/files/bioengineer.pdf) iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 23 disease by providing tools, such as biosensors, biomaterials, image processing, and artificial intelligence, that can be utilized for research, diagnosis, and treatment by health care professionals. thus, biomedical engineers serve as relatively new members of the health care delivery team that seeks new solutions for the difficult problems confronting modern society [3]. there are various definitions for biomedical engineering. the institute of biological engineering defines bioengineering as `the biology-based engineering discipline that integrates life sciences with engineering in the advancement and application of fundamental concepts of biological systems from molecular to ecosystem levels [5]. it also defined as „application of the knowledge gained by a cross-fertilization of engineering and the biological sciences so that both will be fully utilized for the benefit of man‟ [22]. others defined biomedical engineering as „the application of engineering disciplines, technology, principles, and design concepts to medicine and biology‟ [9]. all these attempts emphasize that biomedical engineering integrates „engineering‟ with „medicine‟ and bridges the gap between them. as noted by fazel-reza, creating such a bridge requires deep understanding and major cross-disciplinary efforts by engineers, researchers, and physicians at health institutions, research centers, and industry sectors. the ultimate objective of all biomedical engineering fields, in research and education, is to improve the quality of life and reduce the impact of disease on individuals, and to provide an appropriate infrastructure to promote and enhance the interaction of biomedical engineering researchers. generally, biomedical engineering includes several disciplines, such as bioinstrumentation, biostatistics, biotransformation, biomaterial, biomechanics, biosignal, biosystem, clinical, tissue, rehabilitation and cellular engineering [9]. the field of biomedical engineering, however, is ever expanding as new engineering applications in the medical field emerge. all fields of biomedical engineering science aim at creating an overall improvement in health care, in terms of diagnosis, treatment and prevention, through the application of physical science methodology [22]. although the medical science has a long history, the technologically based health care system, however, has provided a wide range of capabilities for health care, such as effective diagnostic technologies and highly therapeutic methods for treatments. 3. the philosophical foundations of modern bioengineering the philosophical foundations of bioengineering are defined by its two components, biology and engineering, which imply the application of engineering methods to biological systems. philosophy of biology, generally, deals with the theoretical questions of life science. this includes the theoretical problems of biology, in its traditional sense, and problems of the emerging approaches of biosciences such as systems biology (sb), evolutionary systems biology (esb), and bioengineering. philosophers of science believe that there are some distinctions between the natural laws that govern the physical processes and that which govern life systems. according rudolf carnap, physical laws are mechanistic, in the sense that they can be generalized by observation; while biological patterns are theoretical, in the sense that they may not be generalized by simple observations [4] 12 . the method of physical sciences has been remarkably successful in developing approaches to understand and control the physical world. however, despite the 12 we use the term „theoretical‟ in the same sense of rudolf carnap‟s use as explained in the section of philosophy of physical sciences, bellow. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 24 substantial efforts that have been made, the mechanistic approach of physical sciences seems to be unsuccessful at answering many critical questions of the life sciences. the study of the philosophical foundations of the emerging biosciences, such as sb, esb, and bioengineering, is therefore essential to formulate their rational framework. this would enable to deal with the theoretical, ethical, and methodological problems of biosciences and to create new opportunities for understanding biological processes for practical purposes. 3.1 the philosophy of physical sciences the general philosophy of science investigates foundations, methods, and application of sciences. it is mainly concerned with the theoretical, ethical, and methodological questions of science that lead to perfection of scientific inquiry. this includes problems of scientific research method, clarification of concepts, classifications, reliability of theories, and the ultimate goal of scientific endeavor. physical sciences are disciplines that are concerned with the study of inanimate natural objects including physics, chemistry, astronomy, and other related subjects [21]. life science or biology is the counter part of the physical sciences. the method of bioengineering science tries to integrate biological and physical sciences through application of the method of physical sciences to deal with life sciences for practical purposes. in other words, bioengineering is the application of knowledge produced by the method of physical sciences on life sciences. philosophy of physical sciences is well investigated by the eminent figures of modern philosophy of science, such as alfred north whitehead (d.1947), rudolf caranp (d. 1970), c. d. broad (d. 1971), and karl r. popper (d. 1994). rudolf carnap has made special focus on philosophy of physical sciences, through many of his renowned works, such as “introduction to philosophy of science” and “philosophical foundations of physics”. with regard to understanding physical world, he identifies two modes of natural laws: the empirical laws, and the theoretical laws. empirical laws, according to carnap, are laws that can be confirmed directly by empirical observations 13 . they contain processes either directly observable by the senses or measurable by relatively simple techniques. sometimes such laws are called empirical generalizations, as a reminder that they have been obtained by generalizing results found by observations and measurements (inductive method). they include not only simple qualitative laws, such as, "all metal are good for electricity conduct" but also quantitative laws that arise from simple measurements. the laws relating to pressure, volume, and temperature of gases are of this type [4]. the theoretical laws, according to carnap, also called abstract or hypothetical laws, are laws that cannot be measured in simple and direct ways, such as laws that govern the behaviors of entities such as molecules, atoms, electrons, protons, electromagnetic fields, and others 14 . carnap shifts the attention that a theoretical law is not to be distinguished from an empirical law by the fact that it is not well established, but by the fact that it contains terms of a different kind. the terms of a theoretical law do not refer to 13 carnap shifts the attention here that philosophers and scientists have quite different ways of using the terms „observable‟ and „non-observable‟. to a philosopher, „observable‟ has a very narrow meaning. it applies to such properties as „blue‟, „hard‟, „hot‟. these are properties directly perceived by the senses. to the physicist, the word „observable‟ has a much broader meaning; it includes any quantitative magnitude that can be measured in a relatively simple and direct way. for example, a philosopher would not consider a temperature of 80 degrees centigrade, or a weight of 93 pounds, as observable because there is no direct sensory perception of such magnitudes. to a physicist, both are observables because they can be measured in an extremely simple way. see: rudolph carnap (1966). philosophical foundations of physics. 14 as exampled by carnap, i think these are the laws which are suitably applicable to study and understand the complex systems of biology. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 25 observables even when the physicist's wide meaning for what can be observed is adopted. if there is a static field of large dimensions, which does not vary from point to point, physicists call it an observable field because it can be measured with a simple apparatus. but if the field changes from point to point in very small distances, or varies very quickly in time, perhaps changing billions of times each second, then it cannot be directly measured by simple techniques. physicists would not call such a field observable [4]. theoretical laws are concerned with non-observables of the physical world, and very often they are called micro or macro processes. carnap uses the term „theoretical law‟ in a wider sense to include all laws that contain non-observables, regardless of whether they are micro-concepts or macro-concepts [4]. 3.2 philosophy of biology the available literature on philosophy of science shows that modern philosophy is more focused on physical sciences. in other words, many fields of life science are still fresh for philosophical exploration. this might be due to the historical fact that the physical sciences were developed first, but it also emphasizes the fact that the philosophy of biology is increasingly shifting attention of philosophers of science. 3.2.1 the subject matter of biological philosophy philosophy of biology is generally concerned with methodological, theoretical, and ethical questions of life sciences. this includes the traditional questions of biology, such as the origin of life or the diversity and source of change in living creatures; beside the critical questions posted by the emerging branches of biotechnology and bioengineering, such as systems biology and evolutionary systems biology. some authors suggest that philosophers of modern biology have been engaged with three major themes: firstly, they are arguing about the position of biology in relation to physical sciences: is it regarded as an autonomous science or not? secondly, they are discussing evolutionary biology that studies how living systems came to be; and finally, philosophers of biology are arguing about biological functions and causal explanation [10]. exceptional to the philosophical questions that are posed by the evolution theory in the nineteenth century, modern philosophy of science hardly explored the nature, method, and the functional issues of life sciences. beside the traditional questions pertaining to evolution of living creatures, the modern philosophy of biology should focused on molecular and experimental biology. as observed by many authors, this philosophical trend is necessary largely due to the rise of genetics and molecular biology 15 . 3.2.2 biology of being and becoming for the purposes of this article, the biological sciences can be divided, based on their method of explanation, into two basic parts: first, biology in its traditional sense that concerns with the study of living organisms to understand their morphology, physiology, and anatomy; and second, the newly emerging trends of bioscience, which aim at understanding the complex systems of life for practical purposes. this type is mainly concerned with particular forms of biological changes that seem to have a directional component or goal-guided functions. understanding the directional change behavior of biological systems may lead to the prediction of their future. this is clearly informed by principles of modern genetic engineering. 15 ingo brigandt. philosophy of biology. draft of a contribution to the continuum companion to the philosophy of science, edited by steven french and juha saatsi. continuum press, london. p 2 iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 26 the major difference between the two modes of biology is that the first one is biology of being, in sense that we study systems to understand their constructions and functions; while the second is biology of becoming which aims to predict the future of biological systems based on understanding their behavior as governed by theoretical laws of nature [10]. in this article, we use the term biosciences to indicate the latter type, which includes new approaches, such as stems biology, evolution systems biology, and bioengineering. 3.3 philosophy of evolutionary biology the theory of biological evolution is central in modern biology. it is the philosophical foundation which provides the scientific explanation why there are so many different kinds of organisms on the planet earth, and gives an account of their similarities and differences. according to its proponents, evolution is the process that explains how today‟s organisms have descended from their ancient ancestors. it explains living creatures in terms of their morphological, physiological, and genetic development. this theory was developed profoundly, as a comprehensive philosophical approach to understand living organisms, by charles darwin in his eminent work “on the origin of species”, in 1859. in this book darwin answers the two fundamental questions on living organisms: (i) the question about the origin of life and the cause of change in living creatures; and (ii) the question about source of diversity and fascinating characteristics of living creatures. both questions are philosophical in nature. darwin, in this theory, emphasizes that the various forms of life on earth gradually evolved from the simplest kinds of organisms by means of natural selection. he further explains that the evolution and adaptations of organisms are the outcome of a process that causes, over time, the gradual accumulation of features beneficial to organisms, whenever these features increase the organisms‟ chances for survival and reproduction [6]. the basis of natural selection, according to this theory, lies in three facts: first, the characteristic of heredity which means that an individual organism plant or animal produces offspring after its own image. second, the offspring does not completely run after the image of the parent, but may differ from it in ways also subject to heredity. the third element of darwinian evolution is that the overreach pattern of spontaneous variation is trimmed by difference in the viability of different variation, most of which, tend to diminish the probability of continued racial existence, although some, perhaps very few, tend to increase it [25]. 3.3.1 the mechanism of evolution and change each of the following four processes is regarded as a mechanism of evolutionary change: i. mutation: the changing in the structure of a gene caused by the alteration in dna, which results in variation in the subsequent generations. for example, it could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. ii. migration: movement of populations, groups or individuals from one region to another. in genetic, migration causes movement of genes from one population into another (gene flow). iii. genetic drift: change in type of genes in a population due to random reproduction, that leads a gene to get popular qualities or may lead to the total disappearance (sterilization). when an organism which has genes causing a specific genetic trait reproduced with another which does not have similar gene iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 27 characteristics, the resulting genes may get better qualities or they totally disappear. it is variation in the relative frequency of genotypes, in a small population, that may lead to the disappearance of particular genes as individuals die or do not reproduce. for example, imagine that in one generation, two brown beetles happened to have four offspring that survived to reproduce. several green beetles were killed when someone stepped on them and had no offspring. the next generation would have a few more brown beetles than the previous generation. these changes from generation to generation are known as genetic drift[6]. iv. natural selection: the process through which the organisms will be adapted to their environment to get better chances for survival and reproduction. it is the process by which the organism with favorable traits enables them to adopt themselves to specific environmental pressure, such as climate changes or competition for food or mates, to survive and reproduce rather than others of their kind, thus ensuring the perpetuation of those favorable traits in succeeding generations. charles darwin believed that the natural selection is the main factor that brings about evolution[6] 16 . the most controversial part of the theory of evolution is its basic assumption that the process of evolution and adaptation of organisms is purely internal (natural), without any involvement of external being or supernatural power. 3.3.2 criticism of evolution theory the evolution theory became controversial and created various conflicting views among biologists, as well as among the other intellectuals. the proponents of the theory emphasize that nothing in biology makes sense except in the light of evolutionv[8]. they further explain that the acceptance of evolution meant the world could no longer be considered merely as seat of activity of physical laws but had to incorporate history and, more importantly, the observed changes in the living world in the course of time [19]. the opponents of the theory, on the other hand, hold that despite the excellent capabilities of evolution theory to expose mankind to the understanding of living creatures, the major problem of the theory however lies in its basic assumption that proposes an explanation that removes the role of any external force in the evolution process. this assumption, as held by many intellectuals, does not answer many important questions about the perfect structural orders and systematic functions of living creatures. this account is known as „design argument‟, which has been held since the early history of religious thought by theologians to prove the existence of god (the intelligent mind) as sole creator and designer of life systems 17 . the common ground of the evolutionists and creationists, however, is that both agree that the evolution theory was a great leap towards the proper understanding of living organisms in the history of biological science. however, the evolution theory has nothing 16 see a good presentation on evolution theory by ernst mayr (2002) in his eminent work “what evolution is”, published by phoenix, london-uk, forward by jared m. diamond. 17 theologians are keen with the design argument to prove existence of god rationally. one of the earliest who emphasized this argument was ibn rush (d. 1198), in his book “faslul al-maqal”, but the best who argued for this account was william paley (1743-1805) who made a systemic presentation in his eminent work, entitled “natural theology” in which he aimed to prove god, not nature or chance, was the source of evolution, change, and diversity of living creatures. i think paley‟s discourse in this book inspired, in one way or another, darwin‟s account in the sense that it shifted his attention to the mechanistic approach instead of teleological explanation that was dominant. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 28 to do with the question of the efficient cause of an organism, which has been the major concern of teleological approach. the evolution theory, as articulated by darwin, constitutes the philosophical foundations of modern biology, but a biology which is descriptive rather than predictive, a biology that asserts that an understanding of the living world will come from descriptions of the history of organisms, in particular their genetic history, and from a catalogue of the molecules of which organisms are composed. this is what differentiates the philosophies of evolutionary biology and systems biology. the former studies how living systems came to be, whereas systems biology studies how living systems are or how it should be. it is the biology of being versus the biology of becoming, and this is the profound difference. the aim of systems biology is to understand how functional properties and behavior of living organisms are brought about by the interactions of their constituents [10]. 3.4 philosophy of systems biology the emergence of systems biology as a new field has necessitated construction of its philosophical foundations. systems biology, in fact, is regarded as one of the most promising and pragmatic approaches to life science. it needs, therefore, a considerable effort to develop its own philosophical foundations. the available literature is focused on fundamentals 18 , principles 19 , functions, and applications of systems biology 20 . there are only a few works to address the question of philosophy in systems biology. one of the most comprehensive works on this topic, among others, is “systems biology philosophical foundations”, which edited by fred c. boogerd, frank j. bruggeman, jan-hendrik s. hofmeyr, and hans v. westerhoff (first edition 2007) 21 . the authors of the book believe that systems biology is the culmination of biology. in the first section under title: towards philosophical foundations of systems biology, the authors explain that the aim of systems biology. it is to understand how functional properties and behavior of living organisms are brought about by the interactions of their constituents. they emphasize that the contemporary systems biology is a vigorous and expanding discipline, in many ways a successor to molecular biology and genomics on the one hand and mathematical biology and biophysics on the other. the interdisciplinary nature of systems biology was also emphasized by the authors: “it is perhaps unprecedented in its combination of biology with a great many other sciences, from physics to ecology, mathematics to medicine and linguistics to chemistry” [10]. the major difference between molecular biology and systems biology was clearly identified by the authors. they hold that the aim of molecular biology is to characterize the molecular constituents of living organisms. it measures the properties of each component and, in the case of molecular cell biology, its localization in the living cell. although its methods and results are breathtaking and highly important, they are straightforward and do not require any philosophy that extends the philosophical foundations of physics. by contrast, systems biology is concerned with the relationship 18 see for example: foundations of systems biology / edited by hiroaki kitano (2001) and also: what is stems biology? / by rainer breitling (2010) 19 see for example: tracing organizing principles: learning from the history of systems biology / by sara green and olaf wolkenhauer. 20 one of the useful works in application of systems biology is a book entitled “understanding and exploiting systems biology in biomedicine and bioprocesses” edited by manuel canovas, jose l. iborra, and aruro manjon (2006). the major themes of the book are: systems biology, fundamentals and tools systems biology applications, biomedicine, systems biology applications, and bioprocesses. 21 beside others, i think, fred c. boogerd and his colleagues, maureen a. o‟malley and sara green (who earned her phd in this field), have done their best to develop and promote the philosophy of this newly emerging science. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 29 between molecules and cells. it is concerned with how the functional properties in the molecules emerge from the particular organization of and interactions between its molecular processes. systems biology uses models to describe particular cells and generalizes over various cell types and organisms to arrive at new theories of cells as molecular systems [10]. the importance of philosophical foundations of systems biology was highlighted by the authors as well, emphasizing that “because systems biology may well become main stream biology and medicine in the coming years, and because practicing systems biologists are often hindered by paradigm battles with molecular biologists, we found it important that this issue be discussed intensely and openly by experts in fields ranging from molecular and systems biology to the philosophy of science” [10]. the book was reviewed by jonathan f. davies and maureen a. o‟malley, who credited the book by the following words: “systems biology: philosophical foundations‟ is an insightful and timely book that fuses scientific and philosophical insights in a highly effective and mostly accessible manner. numerous books address scientific aspects of the emerging and expansive field of systems biology but this is the first to deal specifically with its underlying philosophical issues. a key aim of this book is to bring the philosophy of biology into a new mode of biological thinking and expand the limited range of biological research it has tended to address. this is an aim very likely to be realized as systems biology becomes increasingly a topic of reflection for philosophers of biology” [7]. 4. the ethical concerns of bioengineering the pragmatic nature of bioengineering science may qualify it to be the science of the new millennium, especially in relation to the enhancement of human health and preservation of environment ecosystems. to harness potentials of bioengineering, however, the ethical concerns must be observed. in fact, there are critical ethico-legal questions posed by advanced bioengineering research and its applications, especially in biomedical engineering. beside the classical ethical problems, the modern biomedical engineering has produced more serious ethical questions across its various stages, in research as well as application. the ethical issues of bioengineering are currently studied in various fields, such as bioethics, biomedical ethics and engineering ethics. from a holistic perspective, however, the basic structure of ethical enterprise can be divided, for the purpose of this article, into three major groups: (i) issues of clinical ethics, (ii) research ethics, and (iii) bioethics. clinical research ethics is mainly concerned with ethical matters related to living organisms used for medical research purposes, especially human elements. this could be extended to all medical professions and practices. therefore, clinical ethics requires both personal ethics, such as honesty and sincerity, as well as protocols which assigned strictly by the medical professions, which must be observed regardless of personal religious background. such protocols are necessary to guarantee the objective of good medical practices. research ethics are related to personal ethics, which is essential for proper knowledge production and scientific progress. research ethics is mainly concerned with three basic types of deviation in proper research conduct: fabrication, falsification, and plagiarism (ffp), besides other types which belong to none of these three. “bioethics” is the major concern of bioengineering philosophy, due to its critical consequences on life, human health and environment. the term “bioethics” is used for all ethical concerns related to the new technologies of life sciences (bioengineering), either in iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 30 medical field, such as genetic and tissue engineering (biomedical ethics), or related to biotechnology as general, such as genetic modification and cloning. issues of biomedical ethics can be divided into two basic types: (i) classical issues, such as organ transplantation, abortion, and euthanasia; and (ii) issues of advanced bioengineering technology, such as stem cell, genetic modification, reproduction technology, biomedical imaging, and neural engineering [2]. 4.1 ethics of the advanced bioengineering ethics of advanced bioengineering includes all forms of advanced biotechnology research and practices, such as genetic modification, tissue engineering, biomaterials and prostheses, and ethics of biomedical imaging. in fact the scientific progress in both fields of physical and biological sciences has posed complicated ethical problems. therefore, „ethics‟ has become a common theme for various fields of scientific research. the eminent mathematician norbert wiener, the father of „cybernetics‟ whose theories assisted in producing the goal-guided missiles during the world war ii, has expressed his deep concern about the social and ethical implications of scientific progress. he especially emphasizes the importance of observing the ethical concerns in advanced technologies. in his eminent work “god and golem” wiener observes that: “knowledge is inextricably intertwined with communication, power with control, and the evaluation of human purposes ethics and the whole normative side of religion”. wiener emphasizes in his book “the human use of the human being, 1989”, that (we are swimming upstream against a great torrent of disorganization, which tends to reduce everything to the heat death of equilibrium and sameness described in the second law of thermodynamics). he further explains (what maxwell, bolzmann and gibbs meant by this heat death in physics has a counterpart in the ethics of kierkegaard, who pointed out that we live in a chaotic moral universe). in his discussion of ethical concerns on modern technology, wiener observes consequences of advanced technologies on environmental ecology, human health, and social life. through integration of advanced technologies with moral values, wiener was attempting to articulate foundations of a meaningful life. for that purpose, his eminent works “the human use of human being” and “god and golem” were produced, where he discussed ethical issues at length. 4.2 ethics of bioengineering from an islamic perspective for proper development of human life, man needs two elements: first, natural resources to maintain life and to fulfill the material needs of an individual and society, and second, knowledge of the principles of individual and social behavior to fulfill himself and to maintain justice and tranquility in human life. the latter type constitutes foundations of law, ethics and moral values. islam, as a final mode of divine revelation, has addressed and provided both of these elements in full measure 22 . the islamic code of ethics, therefore, is capable of managing all human affairs, in everyday life, in social interactions, scientific research, as well as in personal affairs. with regard to scientific research and application, there is no specific code of ethics for this sort of human activity but there are general principles to guide the steps. these principles were compiled and summarized by early muslim scholars in five major objectives of islamic law, known as maqasid alshariah, which consisted of: (i) preservation of religious freedom, (ii) preservation of human life, (iii) preservation of mind, (iv) preservation of human progeny, and (v) 22 with few modifications, the statement was adopted from a revised version of an article written by khurshid ahmad, entitled “islam: basic principles and characteristics”, published by islamic publications ltd., lahore. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 31 preservation of property. the contemporary muslim scholars regarded preservation of nature as the sixth objective. the entire philosophy of the islamic legal system aims at promoting these principles and protecting human interests (maslah). beside commandments of god, these principles provide all the necessary guidelines to determine what is permissible and what is impermissible (halal and haram) in islam. for example, the principle of preservation of human life aims to promote human dignity and to maintain a meaningful life, therefore it forbids all acts and activities which expose human dignity for humiliation or cause death, such as using human subjects for research purposes without free and informed consent. moreover, the principle of progeny preservation aims to sustain human reproduction, based on principle of human dignity. accordingly, it will consider some reproduction methods of modern bioengineering as impermissible. for instance, by application of the above two principles, it can be decided that reproduction of what is named as “motherlessbabies” or “fatherless-babies” is impermissible in islam [1]. there are enormous works and countless religious rulings (fatwa) issued within the last few decades to deal with the major ethical problems of advanced bioengineering technology. in many cases there was inconsistency between the various rulings on the same issue. lack of standard criterion for judgment might be the major source of diversity among muslim scholars‟ views on many issues of bioengineering ethics. the rigid observation of above principles of islamic law “maqasid al-shariah”, therefore, would provide an objective standard of judgment for various forms of human activities, especially in bioengineering technology. 5. conclusion according to the traditional philosophy of science, natural processes, i.e. physical and chemical, are understood based on causal explanation. meanwhile the biological (goalguided) processes and conscious acts of human being are understood based on teleological explanation. the major difference between the two methods lies in the relationship between the cause and effect. in biological processes, the future determines the present, while in physical processes the past determines the future. however, the distinction between physical and biological processes, according to the integrated approach, is unnecessary. theories, such as goal-directed control or information feedback control, are developed by the „cybernetics‟ research method to emphasize the integrated approach. indeed, the new integrated method of scientific inquiry has made remarkable implications on both physical and biological sciences. one of the major impacts on biological research was the tremendous progress in bioengineering science within the last few decades. the advancement in bioengineering has brought the science of biology, in classical sense, to its turning point. biology now is ready only to deal with the method of physical sciences, creating firm engagement with mathematics, engineering and computer sciences, to serve the practical needs of mankind on earth. this new approach in biological research clearly emphasizes the quantitative method that enables scientists to predict biological processes, leading to new means to control them. to harness potentials of modern bioengineering, it is necessary to acquire both the practical and theoretical knowledge of bioengineering. as emphasized by prof. johnson, bioengineers should have the conceptual and philosophical framework of biological science which is essential for fundamentals of bioengineering. this entails that the ideal bioengineers should be capable of incorporating the ethical, aesthetic, and environmental aspects into the processes and products. they should also be capable of thinking analogically and comprehensively, in iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 32 the sense that they will be able to transfer knowledge from a system that is familiar to that unfamiliar. generally, the study of the philosophy of science initiates the interdisciplinary approach, provides deep insights, develops analytical skills, and opens new horizons for scientific research. for actualization of such a motivating proposal, the authors of this article emphasize the following three requirements: first, engineering students, regardless of their area of specialization, should be exposed to the biological sciences, especially to the systems biology approach. second, all science and engineering students should be aware of the philosophical foundations of modern science. this point may need to be emphasized by offering courses on the philosophy of science as core subjects to all. third, bioengineering research must be integrated with ethics and moral values to produce green technologies that are free from any potential harm to the environment or to human health. acknowledgement authors of this article acknowledge all cited works and their authors for valuable thoughts benefited; especially those whose texts and conclusions were directly cited. we especially acknowledge norbert wiener, sawhney, g.s., and arthur t. johnson who inspired the basic idea of the paper. we acknowledge rudolf coranp who benefited this work by his classifications on method of physical sciences. the authors also acknowledge klipp, e. et al. and joel l. cuello; fred c. boogerd, et al., frederick b. marcus, and others for insights benefited from their remarkable works. our thanks are due to everybody who contributed in the production of this work and those who have provided assistance in making it a reality. fred c. boogerd, frank j. bruggeman, jan-hendrik s. hofmeyr, and hans v. westerhoff, eds amsterdam: elsevier, 2007 references [1] atighetchi d. (2007) islamic bioethics: problems and perspectives. springer, the netherlands. [2] brey p. (2009) biomedical engineering ethics. eds. berg-olsen j, pedersen s, hendricks v. [3] bronzino j. (2005) biomedical engineering: a historical perspective. enderle / introduction to biomedical engineering 2nd ed. [4] carnap r. (1966) an introduction to philosophy of science. basic books inc. [5] cuello jl. (2006) the descent of biological engineering. printed in great britain int. j. engng ed. vol. 22, no. 1 [6] darwin cr. (1859) on the origins of species by means of natural selection. appleton and company, new york. [7] davies aom, maureen aom. (2007) book review: toward a philosophy of systems biology. biological theory 2(4) 2007, 420–434. _c 2008 konrad lorenz institute for evolution and cognition research. [8] dobzhansky t. (1973) nothing in biology makes sense except in the light of evolution. published in the american biology teacher, vol. 35, no.3, pp. 125-129. [9] fazel-rezai, reza. ed. (2011). biomedical engineering – from theory to applications. published by intech. janeza trdine 9, 51000 rijeka, croatia. [10] fred c. boogerd, frank j. bruggeman, jan-hendrik s. hofmeyr, and hans v. westerhoff, (eds, 2007) systems biology philosophical foundations (elsevier, oxford, uk. [11] garson j. (2016). a critical overview of biological functions. springer. [12] grierson, clair (eds, 2008) practical system biology. taylor & francis, london and new york. iium engineering journal, vol. 18, no. 2, 2017 shogar and abdul rahman 33 [13] hempel cg, oppenheim p. (1948) studies in the logic of explanation. philosophy of science, 15(2):135-175. [14] iltis as. (2016) expertise, ethics expertise, and clinical ethics consultation: achieving terminological clarity. journal of medicine and philosophy, 41:416-433. [15] johnson at. (1995) philosophical foundations of bioengineering. journal of engineering education. volume 84, issue 4, pages 311–318. [16] kitcher p, salmon wc. (eds. 1989) scientific explanation, volume xiii of minnesota studies in the philosophy of science, university of minnesota. [17] klipp e, wolfram liebermeister, christoph, and ralf herwiq (2009) systems biology: a textbook. willy –vch verlag gmbh & co. kgaa, weinheim. [18] marcus fb. (2008) bioinformatics and systems biology (springerverlag berlin heidelberg. [19] mayr e. (2002) what evolution is. phoenix, london-uk, forward of jared m. diamond. [20] nagel e. (1977) goal-directed process of biology. the journal of philosophy, 74(5):261279. [21] noyes aa. (1902) the general principles of physical science. henry holt and company, new york. [22] sawhney gs. (2007) fundamentals of biomedical engineering. new age international (p) ltd., publishers. [23] tao, bernald y., douglas k. and martin r. okos (2006) the evolution of biological engineering. int. j. engng ed.vol. 22, no. 1, pp. 45-52. [24] wiener n. (1989) the human use of human being: cybernetics and society. free association books, london. [25] wiener n. (1963) god and golem, inc. (the m.i.t. press, cambridgemassachusetts. [26] wiener n. (1985) cybernetics: or control and communication in the animal and the machine. the m.i.t. press, cambridgemassachusetts. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 online news classification using machine learning techniques jeelani ahmed*and muqeem ahmed department of computer science and information technology, maulana azad national urdu university, hyderabad, india * corresponding author: jeelani.jk@gmail.com (received: 18th october 2020; accepted: 31st march 2021; published on-line: 4th july 2021) abstract: a massive rise in web-based online content today pushes businesses to implement new approaches and resources that might support better navigation, processing, and handling of high-dimensional data. over the internet, 90% of the data is unstructured, and there are several approaches through which this data can translate into useful, structured data—classification is one such approach. classification of knowledge into a good collection of groups is significant and necessary. as the number of machinereadable documents proliferates, automatic text classification is badly needed to classify these documents. unlabeled documents are categorized into predefined classes of labeled documents using text labeling, a supervised learning technique. this paper reviewed some existing approaches for classifying online news articles and discusses a framework for the automatic classification of online news articles. for achieving high accuracy, different classifiers were tried. our experimental method achieved 93% accuracy using a bayesian classifier and present in terms of confusion metrics. abstrak: peningkatan tinggi pada masa kini pada maklumat dalam talian berasaskan web menyebabkan kaedah baru dalam bisnes telah diguna pakai dan sumber sokongan seperti navigasi, proses, dan pengurusan data berdimensi-tinggi adalah perlu. 90% data di internet adalah data tidak berstruktur, dan terdapat pelbagai kaedah data ini dapat diterjemahkan kepada data berguna, lebih berstruktur — iaitu melalui kaedah klasifikasi. klasifikasi ilmu kepada koleksi kumpulan baik adalah penting dan perlu. seperti mana mesin-boleh baca dokumen berkembang pesat, teks klasifikasi automatik juga sangat diperlukan bagi mengklasifikasi dokumen-dokumen ini. dokumen yang tidak dilabel dikategori sebagai pengelasan pratakrif dokumen berlabel melalui teks label, iaitu teknik pembelajaran berpenyelia. kajian ini mengkaji semula pendekatan sedia ada bagi artikel berita dalam talian dan membincangkan rangka kerja bagi pengelasan automatik artikel berita dalam talian. bagi menghasilkan ketepatan yang tinggi, kami menggunakan pelbagai alat klasifikasi. kaedah eksperimen ini mempunyai ketepatan 93% menggunakan pengelas bayesian dan data dibentangkan berdasarkan matriks kekeliruan. keywords: text classification; naïve bayes; support vector machine; news articles 1. introduction today, the overwhelming volume of digital content is expanding and growing constantly. automatic text classification into existing categories is considered a primary method to process and manage this enormous amount of data. this kind of textual data is generated from various sources and is available in conference materials, editorials, digital/electronic documents, web pages, emails, publications, and journals. many people use these online sources for day-to-day 210 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 information access instead of being limited to printed material such as newspapers, magazines, and books. the entrance to such information has become more comfortable; however, the organization of knowledge is difficult, making it challenging to manage. organizing this kind of digital data is considered a critical method to effectively classify this digital information. text classification has a vital role in text retrieval, information abstraction and summarization, and question-answering. usually, the data available on the web used for classification are diverse, from various sources like broadcast or printed news, bulletin boards, newsgroups, advertisements, and movie reviews. because of their varied nature, like being multi-sourced and having different vocabularies, different formats, and different writing styles for documents, automatic text classification is essential [1]. due to the enormous amount of text that is stored in the electronic format, it is necessary to understand and examine such data and extract similar details, which may be useful when making decisions [2-4]. when a document is classified under an already defined category this action is termed text classification (fig. 1). a document can be single labeled or multi-labeled, depending upon the classes. a document is termed as a single label when it is allocated to a single class and is named multi-label if the document assigns it to multiple classes [5]. fig. 1: text classification process. text classification comprises feature selection, document representation, applying the algorithm, and performance assessment. because of the sudden growth of online transactions and the colossal accessibility of text documents, it is essential to retrieve vital data from documents using classification. today, organizing and managing text information is considered a crucial practice [6]. neural networks [8], support vector machines [7], k-nearest neighbor [9], and naïve bayesian [10] classification are algorithms that may be used for constructing classification methods. one area where we encounter a considerable amount of daily text is online news articles. due to information technology developments, persons are worried about their busy lifestyle and thus they desire to only read news articles of their interests [11]. it is a big task to mine pertinent news concerning an individual's interest because much of the news articles are enlightening but could be less significant. an individual's lure can be contingent on many factors such as the news location and the type of news articles [12]. here, we classify the news articles rendering to the type/category of the news articles. for example, imagine an individual who prefers to read news related to politics. since the web is a sea full of news articles, it would be challenging for a particular person to read only articles related to politics. 211 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 in this work, to customize the news articles for a specific category, we have applied machine-learning techniques. the category may be politics, crime, sports, entertainment, or world news. we trained and tested the classification model using the huff post data set, which contains around 75k news articles. after training and testing, we applied this model for the news articles taken from different live news websites such as the hindu, the print, indian express, and the quint. 2. background 2.1 naive bayes (nb) this algorithm is used as the classifier for the news articles. it is a prevalent method of classification when dealing with multi-class classification. it works based on the probabilistic technique first proposed by lewis [13] and drives its roots from the bayes theorem. this algorithm can run very efficiently with a large dataset. for text classification problems, naïve bayes is used as a standard because it has a fast run time as compared to other classifiers. naïve bayes is also used to solve problems like spam detection. due to its simplicity, it outpaces many advanced classification techniques. 2.2 k-nearest neighbors (knn) the problems of regression and classification domain can be solved using this supervised machine learning algorithm [9]. knn works by calculating the space between a query and all the instances (k) nearer to the question and then selects the majority recurrent label. it is comprehensible and applied very quickly. it slows down its performance when there is an upsurge in the data sample. it stores all the training data, due to which it is a somewhat costly algorithm. it requires high memory storage as compare to other methods. knn is used in many areas, such as in politics; it can classify a voter into various classes like 'will not vote,' 'will vote,' or 'will vote to aap party’. 2.3 support vector machine (svm) svm is a supervised machine-learning algorithm [7]. svm works when provided training data along with associated labels. once the training is over, if supplied a data set, the model assigns a label to it. the support vector machine works well when dealing with linear classification problems. for classification, it makes a hyper-plane by choosing the maximum distance between adjacent data points. it is both a flexible and powerful technique of machine learning that is used for regression and classification. when dealing with high dimensional space, svm works well and offers excellent accuracy, and it requires very little memory for processing. 2.4 logistic regression (lr) it is the best regression analysis to be conducted where the dependent variable is binary. as for all studies of regression, logistic regression is a statistical process. it describes data and describes the relationship between one conditional dependent variable and one or more interval, ordinal, nominal, or ratio-level independent variables. 3. related work with the rapid increase in demand for managing substantial text databases, text classification is a popular and dynamic research field of data mining. it becomes necessary and essential to competently handle the textual data to search and access any document quickly due to the enormous growth of digital textual information [14,15]. 212 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 text classification uses unique rules to grant classes from a category of already specified classes to unlabeled text documents. text classification typically operates manually, but because the classification rules are generated manually, such a procedure is time-consuming and costly. therefore, machine learning is another methodology that uses automatic rule creation to classify documents [16]. the numerous classifiers are: support vector machines [7], neural networks [8], bayesian classification [10], nearest neighbor (knn) [9], association based classification [17-19], term graph model [20,21] and decision tree (dt) [22,23], etc. many authors use the mentioned machine learning techniques; the table below was formulated after a brief study of these techniques. table 1: related work in the field of text classification by various authors references & year datasets algorithm / technique used conclusion/note [24] (2014) reuter-21578 knn algorithm the accuracy of the knn is maximum compared to term graph and naïve bayes. its time complexity is maximum as compared to others is the only drawback. [25] (2014) sohu laboratory corpus svm-knn algorithm by making recommendations and improving the classifying probability, the svm-knn algorithm will improve the classifier's efficiency. this algorithm increases the low amount of processing difficulty. moreover, svm is efficient and fast for classification. [26] (2015) single-label news corpus svm, tf-idf for the classification of indonesian news posts, the authors used algorithm adoption and problem transformation methods. the authors develop a combination technique for the automatic classifying of the news articles and achieve better results with an f-measure is 85.13%. [27] (2015) reuters21578 hyper rectangular keyword extraction the authors proposed vital extraction based on the document categorization hyper rectangular method. this method generates excellent and accurate results when compared to traditional classification approaches. [28] (2015) czech news articles linear svc, sgd, pa, nb the authors proposed a method for enhancing the classification accuracy of multi-document classification. the baseline classifier naïve bayes performed better than other classifiers. [29] (2016) various news websites naïve bayes (nb) various news webpages were classified using structure attributes and url content. the naïve bayes algorithm showrd better results compared to existing approaches when implemented on the same dataset. [30] (2016) news articles of emotional topics nb, c45, dt, svm vectors, winnow, balanced winnow, and max entropy the authors experimented with hierarchical classification with the purpose of sentiment analysis of news articles. svm and tf-idf were used with six and four classification algorithms respectively and achieved better results. [31] (2016) stock new of china softmax training algorithm, weighted sort algorithm, and selection algorithm for making investment decisions, authors classified stock news by proposing a novel algorithm. the authors achieved better accuracy and availability with this method compared with a general algorithm. 213 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 references & year datasets algorithm / technique used conclusion/note [32] (2016) online news articles neural network classifier the performance of the ann using feature reduction performed better as compared to the essential ann and gave better results for the classifications. the training process was prolonged. [7] (2017) various news websites articles naïve bayes, svm, random forest the performance of the svm was at the bottom when compared with naïve bayes and random forest. also, svm took much training time. [33] (2017) korean news articles knn, nb, svm, and logistic regression (lr) the author performed two studies using four classifiers. study 1, which had the data with less complexity, achieved a higher level of accuracy. study 2, which had the data with more high complexity, may have harmed the classification results. [34][2017] reuters.com news articles and gold standard dataset svm, sdg, lr the authors used various classification algorithms to classify text articles to detect opinion, spam, and fake news. classifiers achieved good results with an increase in the features. [35] (2017) yahoo news us edition keyword matching, newsmap the work developed a semi-supervised classifier for the classification of geographical news. the overall classification accuracy was 0.80, which was relatively low when compared to other traditional classifiers. [36] (2018) nlpcc2014, rev1-v2 attention gru birnn centered on the process of neural network interest, the authors proposed a bi-directional recurrent neural network algorithm that performed classification on two datasets and achieved a high accuracy of 83.9 compared to other classifiers. [37] (2018) br news dataset us news dataset anova, svm the work performed classification on two news datasets and proved noticeable differences between reliable and unreliable news sources. [38] (2018) indonesian news articles latent dirichlet allocation (lda) classification results of indonesian news articles represented using a word cloud, which allowed easy understanding of each category's results and trends; however, more explanation was needed in terms of classification. [39] (2018) china news svm, cnn, maxent the authors applied three algorithms in two schemes for the classification of chinese news articles. svm performed better than the other two, but a detailed explanation of the experiment is needed. [40] (2019) news articles and tweets word2vec convolutional neural networks the algorithm used is classified tweets and news articles into related and unrelated words. word2vec enhanced performance by learning the semantic relations between words. [41] (2019) arabic news articles from websites svm, nb, dt, rf, lr the work classified arabic news articles collected from various news websites. svm performed better than all other classifiers and achieved an accuracy of 87%. [42] (2019) indonesian news articles convolutional neural networks, recurrent neural networks the work performed a systematic classification of risk document to get the financial risk information in real-time. authors achieved better classification results using extensive data. however, manual labeling of new data was a tedious process. 214 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 references & year datasets algorithm / technique used conclusion/note [43] (2019) thai pbs, khaosod, and dailynews svm, decision tree, deep learning the authors discussed the performance of various classifiers using thai news as a dataset. deep learning outperformed the svm and decision tree. [44] (2019) bbc datasets, five groups of 20newsgroup svm, naïve bayes, bi-lstm, lstm, cnn this work used five classifiers for the classification of two chinese news datasets. they also pointed out the difference between ml and dl classification that ml was a time-consuming classification process that required preprocessing and feature extraction. in contrast, dl did not require cleaning activities. however, using ml, they obtained efficient and reliable results and the best accuracy. [45] (2020) society channel of sina c4.5 decision tree algorithm the authors proposed a classification approach for emotions in news articles. they classified emotions into fear, joy, and sadness. this method achieved a high accuracy of 87.83% and compared it with the svm classifier. [46] (2020) uzbek daryo online news svm, dt, rf, lr, multinomial naive bayes the authors used six algorithms for news article classification in uzbek languages. the approach achieved the highest accuracy of 86.88%. [47] (2020) tigrigna news dataset svm, dt, lr, rf, knn, etc. the authors constructed the tigrigna news dataset and have experimented with eight various classifiers. svm outperformed other classification algorithms. moreover, it achieved the highest accuracy. we reviewed several papers; table 1 contains some recent papers. several scholars studied and categorized texts in various languages, such as korean [33] and chinese [39]. there were still several works available covering arabic language classification [41], shedding light on academic articles based on the usage of classical classifications of supervised machine learning, like svm [34,37], knn [24,25], decision tree [45], and naïve bayes [7,29]. although other authors focused on classification through neural networks [32] and deep learning [42], the overall output was higher. finally, it is evident that the classification algorithm’s performance in every language was significantly impaired by the consistency of the data source, as the unnecessary and repetitive characteristics of the data undermined the precision and output of the classifier. 4. research design and implementation based on the above literature, we proposed a framework to perform text classification of english news articles obtained from various indian news websites. for ease of understanding, we divide the proposed framework into three main modules: data extraction, data preprocessing, and classifier module as illustrated in fig. 2. first, the dataset is cleaned using data preprocessing. then, we divide the dataset into train and test parts. train data hold 70%, and test data hold 30% of the dataset. the next module trains the classifier to predict the class labels for the collected news articles and assign a category label in the next step. thereby performance evaluation of the classifier is carried out using some performance metric. the next section contains a detailed explanation of each module. 215 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 fig. 2: news article classification process. 4.1 data extraction the process starts with a data collection module, in which news articles from seven different news websites are crawled, as shown in fig. 2. firstly, tweets of various news twitter handles are crawled from twitter using tweepy. various news articles were extracted from crawled tweet urls. further, news article web pages from each news website are extracted by visiting each url. in the module, the data extraction module downloads tweets and news articles from seven news websites. we have also used a dataset that contains around 75k news headlines with its content and category from the year 2012 to 2018 taken from huff post. these news articles contain eight categories: entertainment, crime, politics, business, world news, sports, media, and technology. the percentage of each class of news articles is shown in fig. 3. fig. 3: percentage of each news article category. crime 5% entertainment 21% world news 3% politics 44% business 10% media 6% tech 4% sports 7% news articles category 216 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 the dataset that was used is shown in fig. 4. it contains the first ten lines of the dataset, which have eight categories of news articles in csv format, as shown below. fig. 4: description of the dataset. 4.2 data preprocessing the data preprocessing module performs the cleaning of the dataset, which is considered to be an important task to achieve good results. firstly, we perform the tokenization of articles; the module changes a group of characters to groups of strings with some recognizable meaning. next, by using the python nltk package, we remove stop words such as 'what' and 'the' as these are the words that have minimal prominence and occur commonly. 4.2.1 label encoding we used the labelencoder class from the scikit-learn library in python to transform categorical text data into model comprehensible numerical data. from the scikit-learn library, we use labelencoder class to encode the first column, then fit and transform the data of that column. then, the new encoded data replaced the existing text data. after running the labelencoder piece of code, we get the following table. table 2: label encoding for different news category category name category code crime 0 entertainment 1 world news 2 politics 3 sports 4 business 5 media 6 tech 7 217 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 4.2.2 train-test split our work includes a single labeled classification of the news articles collected from seven different news websites. for training and testing purposes, we divided our dataset into 70% for training and 30% for testing. the training data set consisted of 52635 labeled news articles and the testing set consisted 22558 of news articles. in training data, we have used the 10 fold cross-validation, fitted the final model to it, and then evaluated with the unclassified data and obtained evaluation metrics that showed as little bias as possible. 4.3 training the classifier the training set and the set of labels corresponding to it are the input data for the classifier. the labels we used along with training set are: 'crime', 'entertainment', 'world news', 'politics', 'sports', 'business', 'media', and 'tech'. based on the pre-decided category tag, processed news articles were numerically labeled. because the classifier input consists of two vectors, it was essential to vectorize news articles and the labels. they functioned as an input to the classifier after the vectorization of these two entities. 4.4 testing the classifier the classifier model was tested on the testing data once the classifier was trained with the trained data. the classifier predicted the category of the corresponding news articles. an example of the news article's 'business' category from the testing set is presented in fig. 5. naive bayes classifier performed better, with 93% accuracy. furthermore, our model is sure that the above 'business' article would belong to the same category. fig. 5: news article classified as business category. 4.5 performance metrics we made use of scikit-learn to implement all the classification algorithms. the performance measurements for classifiers were studied to represent the act imbalances on conventional measuring instruments like accuracy, recall, and precision. these metrics use knowledge about the classes currently and projected classes from classification tasks. the following confusion matrix may reflect all possible scenarios of the findings. 218 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 table 3: confusion matrix predicted actual positive negative positive true positive (tp) false negative (fn) negative false positive (fp) true negative (tn) when an instance belongs to a class, it is considered a positive case, and when an instance does not belong to a specific class, it is considered a negative case. an instance is called true positive (tp) when it belongs to the positive case and is appropriately labeled as such. the false negatives (fn) are such cases that are incorrectly classified as negative cases when they belong to the positive cases. the false positives (fp) are such cases that are incorrectly classified as positive when they belong to the negative cases. the instances belonging to the negative case are correctly classified as such. these are called the true negatives (tn). below we highlight some of the performance metrics based on the confusion matrix. 4.5.1 accuracy accuracy is the number of all right predictions the classifier has made divided by the overall data collection [48]. the accuracy mathematically expressed as 𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = 𝑇𝑟𝑢𝑒 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒 + 𝑇𝑟𝑢𝑒 𝑁𝑒𝑔𝑎𝑡𝑖𝑣𝑒 (𝑇𝑟𝑢𝑒 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒 + 𝐹𝑎𝑙𝑠𝑒 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒 + 𝑇𝑟𝑢𝑒 𝑁𝑒𝑔𝑎𝑡𝑖𝑣𝑒 + 𝐹𝑎𝑙𝑠𝑒 𝑁𝑒𝑔𝑎𝑡𝑖𝑣𝑒) (1) the error rate (err) is the sum of all incorrect forecasts separated by the dataset's total number. the highest error rate is 0.0, while 1.0 is the worst. the error mathematically expressed as 𝐸𝑟𝑟𝑜𝑟 𝑅𝑎𝑡𝑒 = 1 − 𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 (2) 4.5.2. precision the number of articles that are properly identified (true positive) by the number of articles that the classifier estimates corresponds to a specific group (true positive and false positive). the precision [48] in mathematical form is 𝑃𝑟𝑒𝑐𝑖𝑠𝑖𝑜𝑛 = 𝑇𝑟𝑢𝑒 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒 (𝑇𝑟𝑢𝑒 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒 + 𝐹𝑎𝑙𝑠𝑒 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒) (3) 4.5.3. recall the ratio of positive articles correctly predicted to all articles in the actual class is termed a recall [49]. the recall is mathematically expressed as 𝑅𝑒𝑐𝑎𝑙𝑙 = 𝑇𝑟𝑢𝑒 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒 (𝑇𝑟𝑢𝑒 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒 + 𝐹𝑎𝑙𝑠𝑒 𝑃𝑜𝑠𝑖𝑡𝑖𝑣𝑒) (4) a good recall implies that much of the positive cases (tp+fn) are rated as positive (tp). this situation is likely to result in more fp measurements and lower average precision. a poor recall implies we have a significant fn volume (should have been positive but categorized as negative). this ensures that we have greater confidence that this will be a positive case if we find a positive scenario. on imbalanced classification, when scholars use machine learning techniques, accuracy is not accurate. in imbalanced conditions, higher accuracy can be obtained since all data is predicted as the majority class. hence, the f1 score and the receiver operating characteristic (roc) curve are accepted as fair measurements by the machine learning community. the tradeoff between false positive and true positive is indicated by the roc 219 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 curve. when the false positives get overlooked, and the emphasis is distorted, it would probably reflect precision only for the true positives. on the other hand, if the real positives get overlooked, and the emphasis is distorted for false positives, the ratings would most definitely represent the recall. the classifier's efficiency is reflected by the area under the curve (auc). 4.5.4 f1-score the harmonic mean of precision and recall is the f1 score. if we combine precision and recall, then it will become the f1 score [50]. the optimal and worst values for f1 score are 1 and 0, respectively. it is efficient to use one value for measurement instead of using two precision and recall values as it combines both. f1 score is presented as 𝐹1 𝑠𝑐𝑜𝑟𝑒 = 2 ∗ 𝑅𝑒𝑐𝑎𝑙𝑙 ∗ 𝑃𝑟𝑒𝑐𝑖𝑠𝑖𝑜𝑛 (𝑅𝑒𝑐𝑎𝑙𝑙 + 𝑃𝑟𝑒𝑐𝑖𝑠𝑖𝑜𝑛) (5) 5. experimental results and performance analysis for every classification algorithm checked on our dataset, table 4 displays the assessment of comparative results of svm, lr, knn, and naive bayes algorithms using multiple news websites in terms of all mentioned performance metrics. accuracy and f1 score are nearly similar. figure 6 illustrates the analysis of all four algorithms in graphical form. table 4: result table fig. 6: comparing all four classifiers. in all four classifiers, the naive bayes classifier performed better than others with 93.0% accuracy. moreover, the worst result was displayed by the knn classifier at 72.0%. the best (nb) and worst (knn) classifier's confusion matrices are shown in fig. 7 and fig. 8. figure 9 shows classifier output by imbalanced ratios. when training data for minority groups is sparse compared to other algorithms, naive bayes worked better than the other classifier accuracy precision recall f1 score naive bayes 0.93 0.93 0.93 0.9 lr 0.81 0.75 0.79 0.81 svm 0.76 0.76 0.76 0.75 knn 0.72 0.64 0.52 0.72 220 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 classifiers. it touched a 0.5 f1 score while the imbalance was 11%, whereas others reached 22% of the imbalance with the similar f1 score. nonetheless, the efficiency of the classifier will not improve after imbalanced levels dropped to 44%, whereas some algorithms eventually demonstrated better results after more class imbalance training data were produced. overall, the lowest result was obtained by the knn classifier. to attain an average f1 score above 0.7, it took an imbalance level of 66 percent, while the majority of the classifiers achieved an average f1 score above 0.7 at a 44 percent disparity rate. in the most imbalanced conditions, naive bayes worked the best. fig. 7: confusion matrix for the naive bayes classifier. fig. 8: confusion matrix for the knn classifier. 221 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 fig. 9: performance of classifiers naive bayes performs best while knn performs worst. 6. conclusion in this research, for online news posts, we implemented a single-class text classifier system. we presented a sample dataset containing approximately 75k news articles sliced from seven various websites with their tags. we defined the dataset's collection, cleaning, and construction phases. we analyzed our dataset by adding four distinct classifiers. we used naïve bayes and several other classification algorithms for classification and performed a comparison of different classifiers’ outcomes from seven various sites on the same dataset, and the findings confirm that naïve bayes showed better performance than most classifiers; when working with various news datasets, it offers sufficient classification accuracy. this study has many possible extensions. our future aim is to discover and implement a classification methodology in various regional languages. acknowledgement the authors send their humble gratitude to the university for providing all the facilities during this research. references [1] jindal r, malhotra r, jain a. (2015) techniques for text classification: literature review and current trends. webology, 12(2): article 139. https://www.webology.org/2015/v12n2/a139.pdf [2] turney p. (2002) thumbs up or thumbs down? semantic orientation applied to unsupervised classification of reviews. computing research repository, 417-424. doi:10.3115/1073083.1073153. [3] wilson t, wiebe j, hoffmann p. (2009) recognizing contextual polarity: an exploration of features for phrase-level sentiment analysis. computational linguistics, 35(3): 399433. doi:10.1162/coli.08-012-r1-06-90 [4] quan c, ren f. (2009) construction of a blog emotion corpus for chinese emotional expression analysis. in proceedings of the 2009 conference on empirical methods in natural language processing, 3: 1446-1454. [5] wang ty, chiang hm. (2011) solving multi-label text categorization problem using support vector machine approach with membership function. neurocomputing, 74(17): 3682-3689. https://doi.org/10.1016/j.neucom.2011.07.001 222 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 [6] harrag f, el-qawasmah e, al-salman ams. (2010) comparing dimension reduction techniques for arabic text classification using bpnn algorithm. in proceedings of the 2010 first international conference on integrated intelligent computing, bangalore, india, 2010, pp 6-11. https://doi.org/10.1109/iciic.2010.23 [7] sapankevych n, sankar r. (2009) time series prediction using support vector machines: a survey. ieee computational intelligence magazine, 4(2): 24-38. https://10.1109/mci.2009.932254. [8] zhihang chen, chengwen ni, murphey, yl. (2006) neural network approaches for text document categorization. in proceedings of the ieee international joint conference on neural network proceedings, pp.1054–1060. https://doi.org/10.1109/ijcnn.2006.246805 [9] zhang x, bicheng li, xianzhu sun. (2010) a k-nearest neighbor text classification algorithm based on fuzzy integral. in proceedings of the sixth international conference on natural computation, pp 2228–2231. https://doi.org/10.1109/icnc.2010.5584406 [10] martinez-arroyo m, & sucar le. (2006) learning an optimal naive bayes classifier. in proceedings of the 18th international conference on pattern recognition (icpr’06), pp 748–752. https://doi.org/10.1109/icpr.2006.748 [11] pendharkar b, ambekar p, godbole p, joshi s, abhyankar s. (2007) topic categorization of rss news feeds. group, 4, 1. [12] rao v, sachdev j. (2017) a machine learning approach to classify news articles based on location. in proceedings of the international conference on intelligent sustainable systems (iciss), pp 863-867. https://doi.org/10.1109/iss1.2017.8389300 [13] lewis dd. (1998) naive (bayes) at forty: the independence assumption in information retrieval. in european conference on machine learning, 4-15). springer, berlin, heidelberg [14] chen n, blostein d. (2006) a survey of document image classification: problem statement, classifier architecture and performance evaluation. international journal of document analysis and recognition (ijdar), 10(1): 1-16. https://doi.org/10.1007/s10032-006-0020-2 [15] gupta v, lehal gs. (2009) a survey of text mining techniques and applications. journal of emerging technologies in web intelligence, 1(1): 60-76. https://doi.org/10.4304/jetwi.1.1.60-76 [16] manning cd, raghavan p, schutze h. (2008) introduction to information retrieval? cambridge university press, pp 405-416. [17] li w, han j, pei j. (2001) cmar: accurate and efficient classification based on multiple class-association rules. in proceedings of the 2001 ieee international conference on data mining, san jose, ca, usa, 2001, pp. 369-376. doi: 10.1109/icdm.2001.989541. [18] yin x, han j. (2003) cpar: classification based on predictive association rules. in proceedings of the 2003 siam international conference on data mining, pp 331-335. [19] berzal f, cubero j, marín n, sánchez d, serrano j, vila a. (2005) association rule evaluation for classification purposes. actas del iii taller nacional de mineria de datos y aprendizaje, pp 135-144. [20] jiang c, coenen f, sanderson r, zito m. (2010) text classification using graph miningbased feature extraction. in research and development in intelligent systems xxvi, springer, london, pp 21-34. [21] huynh d, tran d, ma w, sharma d. (2011) a new term ranking method based on relation extraction and graph model for text classification. in proceedings of the thirty-fourth australasian computer science conference, 113: 145-152. [22] han j, kamber m. (2001) data mining concepts and techniques, morgan kaufmann publishers. san francisco, ca, pp 335-391. [23] chen j, huang h, tian s, qu y. (2009) feature selection for text classification with naïve bayes. expert systems with applications, 36(3):5432-5435. https://doi.org/10.1016/j.eswa.2008.06.054 [24] bijalwan v, kumar, v, kumari p, pascual j. (2014) knn based machine learning approach for text and document mining. international journal of database theory and application, 7(1):61-70. https://doi.org/10.14257/ijdta.2014.7.1.06 223 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 [25] lin y, wang j. (2014) research on text classification based on svm-knn. in proceedings of the ieee 5th international conference on software engineering and service science, beijing, china, pp 842-844. https://doi.org/10.1109/icsess.2014.6933697. [26] rahmawati d, khodra ml. (2015) automatic multi-label classification for indonesian news articles. in proceedings of the 2nd international conference on advanced informatics: concepts, theory and applications (icaicta), chonburi, thailand, 2015, pp 1-6. https://doi.org/10.1109/icaicta.2015.7335382. [27] hassaine a, mecheter s, jaoua a. (2015) text categorization using hyper rectangular keyword extraction: application to news articles classification. in proceedings of the international conference on relational and algebraic methods in computer science, pp 312-325. https://doi.org/10.1007/978-3-319-24704-5_19 [28] lehečka j, švec j. (2015) improving multi-label document classification of czech news articles. in proceedings of the international conference on text, speech, and dialogue, pp 307-315. [29] arya c, dwivedi sk. (2016) news web page classification using url content and structure attributes. in proceedings of the 2nd international conference on next generation computing technologies (ngct), dehradun, india, 2016, pp. 317-322, https://doi.org/10.1109/ngct.2016.787743. [30] li j, fong, s, zhuang, y, khoury, r. (2015) hierarchical classification in text mining for sentiment analysis of online news. soft computing, 20(9), 3411-3420. https://doi.org/10.1007/s00500-015-1812-4 [31] weng, w., liu, y., wang, s., & lei, k. (2016) a multiclass classification model for stock news based on structured data. in proceedings of the sixth international conference on information science and technology (icist), dalian, china, pp 72-78. https://doi.org/10.1109/icist.2016.7483388. [32] kaur s, khiva nk (2016). online news classification using deep learning technique. international research journal of engineering and technology, 3(10): 558-563. [33] suh y, yu j, mo j, song l. (2017) a comparison of oversampling methods on imbalanced topic classification of korean news articles. journal of cognitive science, 18(4): 391-437. [34] ahmed h, traore i, saad s. (2017) detecting opinion spams and fake news using text classification. security and privacy, 1(1), e9. https://doi.org/10.1002/spy2.9 [35] watanabe k. (2017) newsmap. digital journalism, 6(3): 294-309. https://doi.org/10.1080/21670811.2017.1293487 [36] du c, huang l. (2018) text classification research with attention-based recurrent neural networks. international journal of computers communications & control, 13(1): 50-64. https://doi.org/10.15837/ijccc.2018.1.3142 [37] gruppi m, horne bd, adali s. (2018) an exploration of unreliable news classification in brazil and the us. arxiv preprint arxiv:1806.02875. [38] kusumaningrum r, adhy s. (2018). wcloudviz: word cloud visualization of indonesian news articles classification based on latent dirichlet allocation. telkomnika, 16(4): 1752-1759. [39] cecchini d, na l. (2018) in proceedings of the 2018 ieee international conference on big data and smart computing (bigcomp), shanghai, china, pp 681-684. https://doi.org/10.1109/bigcomp.2018.00125. [40] jang b, kim i, kim jw. (2019) word2vec convolutional neural networks for classification of news articles and tweets. plos one, 14(8): e0220976. https://doi.org/10.1371/journal.pone.0220976 [41] qadi la, rifai he, obaid s, elnagar a. (2019) arabic text classification of news articles using classical supervised classifiers. in proceedings of the 2nd international conference on new trends in computing sciences (ictcs), amman, jordan, pp 1-6. https://doi.org/10.1109/ictcs.2019.8923073. [42] gumilang m, purwarianti a, nurdinasari f. (2019) systemic risk document classification on indonesian news articles using deep learning and active learning. in proceedings of the international conference on electrical engineering and informatics (iceei), bandung, indonesia, pp 46-51. https://doi.org/10.1109/iceei47359.2019.8988829 224 iium engineering journal, vol. 22, no. 2, 2021 ahmed and ahmed https://doi.org/10.31436/iiumej.v22i2.1662 [43] noppakaow a, uchida o. (2019) examinations on the performance of classification models for thai news articles. in proceedings of the 2019 11th international conference on information technology and electrical engineering (icitee), pattaya, thailand, 2019, pp. 1-4 https://doi.org/10.1109/iciteed.2019.8929959 [44] huang cm, jiang yj. (2019) an empirical study on the classification of chinese news articles by machine learning and deep learning techniques. in proceedings of the international conference on machine learning and cybernetics (icmlc), kobe, japan, pp 1-6. https://doi.org/10.1109/icmlc48188.2019.8949309 [45] winster sg, kumar mn. (2020) automatic classification of emotions in news articles through ensemble decision tree classification techniques. journal of ambient intelligence and humanized computing, 1–12. https://doi.org/10.1007/s12652-020-02373-5 [46] rabbimov im, kobilov ss. (2020) multi-class text classification of uzbek news articles using machine learning. journal of physics: conference series, 1546(1): 012-097. [47] fesseha a, xiong s, emiru ed, dahou a. (2020) text classification of news articles using machine learning on low-resourced language: tigrigna. in proceedings of the 3rd international conference on artificial intelligence and big data (icaibd), chengdu, china, pp 34-38. https://doi.org/10.1109/icaibd49809.2020.9137443. [48] sharma a, mishra pk. (2020) state-of-the-art in performance metric and future direction for data science algorithm. journal of scientific research, 64(2): 221-238. [49] saura jr. (2020) using data sciences in digital marketing: framework, methods, and performance metrics. journal of innovation & knowledge, 6(2): 92-102. https://doi.org/10.1016/j.jik.2020.08.001 [50] pereira l, nunes n. (2020) an empirical exploration of performance metrics for event detection algorithms. non-intrusive load monitoring. sustainable cities and society, 62: 102399. https://doi.org/10.1016/j.scs.2020.102399 225 microsoft word fathaddin et al 31-38.doc iium engineering journal, vol. 12, no. 1, 2011 fathaddin et al. 31 surfactant-polymer flooding performance in heterogeneous two-layered porous media m.t. fathaddin1, asri nugrahanti1, putri n. buang2 and k.a. elraeis2 1department of petroleum engineering, universitas trisakti, indonesia 2department of geoscience and petroleum engineering, universiti teknologi petronas, malaysia abstract: in this paper, simulation study was conducted to investigate the effect of spatial heterogeneity of multiple porosity fields on oil recovery, residual oil and microemulsion saturation. the generated porosity fields were applied into utchem for simulating surfactant-polymer flooding in heterogeneous two-layered porous media. from the analysis, surfactant-polymer flooding was more sensitive than water flooding to the spatial distribution of multiple porosity fields. residual oil saturation in upper and lower layers after water and polymer flooding was about the same with the reservoir heterogeneity. on the other hand, residual oil saturation in the two layers after surfactant-polymer flooding became more unequal as surfactant concentration increased. surfactant-polymer flooding had higher oil recovery than water and polymer flooding within the range studied. the variation of oil recovery due to the reservoir heterogeneity was under 9.2%. abstrak: dalam makalah ini, kajian simulasi dijalankan untuk mengetahui kesan heterogeniti spasial berbagai-bagai medan porositi pada perolehan minyak, ketepuan minyak baki dan mikroemulsi. medan-medan porositi yang dijana digunakan ke dalam utchem untuk mensimulasi pembanjiran surfaktan-polimer di dalam media berpori berlapis-dua heterogen. dari analisis, pembanjiran surfaktan-polimer lebih peka daripada pembanjiran air pada taburan spasial berbagai-bagai medan porositi. ketepuan minyak baki di lapisan atas dan bawah selepas pembanjiran air dan polimer adalah hampir sama pada heterogeniti reserbor tersebut. di sisi lain, ketepuan minyak baki dalam kedua lapisan selepas pembanjiran surfaktan-polimer menjadi lebih tak sama ketika kepekatan surfaktan ditingkatkan. pembanjiran surfaktan-polimer mempunyai perolehan minyak yang lebih tinggi daripada pembanjiran air dan polimer dalam julat yang diteliti. perbezaan perolehan minyak akibat heterogeniti reserbor di bawah 9.2%. key words: heterogeneity, porosity, surfactant-polymer flooding, recovery factor 1. introduction the surfactant-polymer flooding is aimed to enhance oil recovery (eor). the surfactant-polymer is injected into the reservoir as a finite slug. the slug is then pushed towards the producer by a water drive. several interactions between surfactant and reservoir fluids occur due to the injection such as microemulsion phase creation, adsorption, wettability alteration, and interfacial tension (ift) reduction [1, 2]. the iium engineering journal, vol. 12, no. 1, 2011 fathaddin et al. 32 surfactant helps in recovering the oil through oil solubilization and oil mobilization [3]. the former is the result of the microemulsion phase creation and adsorption, while the latter is the result of the wettability alteration and ift reduction. the polymer solution has an elevated viscosity, which is useful to reduce the water mobility. further water mobility reduction is caused by polymer retention and adsorption [4]. the reduction in water mobility improves the displacement conditions for increasing oil recovery. the displacement conditions which are improved cover viscous fingering reduction, fractional flow improvement, and the increase of area and vertical sweep efficiency [5, 6]. additional recovery the after secondary recovery depends upon three factors: oil in place at the start of the flooding, reservoir sweep efficiency, and microscopic displacement efficiency. reservoir sweep efficiency is the key factor in determining the final residual oil of water flooding within an economic limit [7]. the sweep efficiency is dependent upon the reservoir heterogeneity that affecting the flood front, breakthrough, and flow pattern of the injecting fluid. the effects of reservoir heterogeneity in surfactant-polymer flooding have been reported. dakhlia [8] investigated the effect of spatial heterogeneity of multiple permeability fields. it was found that water-flooding was less sensitive than surfactant flooding to the spatial distribution of heterogeneity. shiyi et al. [9] studied the effects of vertical heterogeneity of multilayered reservoir models on chemical combination flooding. it was found that both water and chemical flooding deteriorated along with the increase of reservoir heterogeneity. however, comparing with water flooding, the eor extent of chemical flooding increased with reservoir heterogeneity under its certain scope. zhang et al. [10] performed stochastical analysis to measure the effect of soil spatial variability and heterogeneity on the recovery of denser-than-water non-aqueous phase liquids (dnapl) by injecting a surfactant solution. it was found that the average dnapl recovery decreased exponentially with increasing soil heterogeneity, characterized by the standard deviation of the log of permeability. in this paper the effects of spatial heterogeneity of multiple porosity fields on surfactant-polymer, polymer flooding, and water flooding were studied. for this purpose, heterogeneous two-layered reservoir models were generated. permeability of the two layers was set to be equal in order to focus on porosity parameter effect. the porosity values followed a normal distribution, while its spatial structure was described by a variogram. 2. method 2.1 simulation model utchem is a three-dimensional, three-phase, compositional chemical flood simulator. the simulator was originally developed by pope and nelson [11]. the numerical model used for the surfactant-polymer flooding simulation is an extension of the model used in the simulator. the simulator takes into account the saturation of water, oil, and microemulsion. in this study, utchem was applied to investigate the effect of spatial distribution of heterogeneity on oil recovery, oil and microemulsion saturation. iium engineering journal, vol. 12, no. 1, 2011 fathaddin et al. 33 2.2 simulation setup the parameters of surfactant-polymer flooding simulation were taken from dakhlia [8] and are listed in table 1. for each case, a quarter five-spot was initialized with initial water saturation. one injection well was located near the south-west corner of the x-y plane, with x and y coordinates of 25 ft and 25 ft. one production well was located near the north-east corner with x and y coordinates of 475 ft and 475 ft. all the wells are vertical, completed in the z direction and connected to all layers. the boundaries were modeled as closed reservoir rock. table 1: data used in the simulation. property value the dimension of the porous media [ft x ft x ft] 500 x 500 x 60 grid size 10 x 10 x 2 horizontal permeability [md] 50 vertical permeability [md] 5 initial water saturation 0.3 average porosity 0.2 water viscosity [cp] 0.75 oil viscosity [cp] 8 specific weight of water [psi/ft] 0.433 specific weight of oil [psi/ft] 0.388 surfactant concentration in solution, cs [%] 0, 1.25, 2.5, 5 polymer concentration in solution, cp [%] 0.1 the simulations of surfactant-polymer flooding were carried out using 0.25 pore volume (pv) of surfactant-polymer solution and followed by 1 pv of chase water. after that, all of the simulations with the same reservoirs were repeated for water flooding. in each simulation of water flooding, 1.25 pv water was injected. the results of surfactantpolymer flooding and water flooding simulations were then compared and analyzed. 2.3 random fields of rock porosity the variogram is a measure of dissimilarity between two points in space separated by a distance h [12]. the variogram is a geostatistical tool for modeling spatial variability [13]. matheron [14] proposed a method of moments approach to approximate the variogram [15]:    )( 1 2)]()([ )( 1 )(2 hn i ii huzuzhn h (1) where  is the variogram; h is the separation vector; n(h) is the number of pairs of data separated by vector h; u is location and z of random variable of a rock property. iium engineering journal, vol. 12, no. 1, 2011 fathaddin et al. 34 the mean of porosity was set equal to the porosity of the homogeneous rock (0.20). four values of standard deviation of porosity (0.25, 0.5, 0.75, and 1.0) were selected to generate random fields of the rock porosity. the correlation lengths in the x and y directions were the same as grid block size of 50 m. for each simulation, two layers of random porosity fields were generated for x and y directions independently. porosity fields in the z direction was then calculated according to the anisotropy ratios. for the same set of values of mean, variance, and correlation lengths, different porosity fields were generated by setting different seed values for the random number generator in the program. for each simulation, a generated porosity field was incorporated into utchem to simulate surfactant-polymer or water flooding in a heterogeneous porous medium. 3. results and discussion for each of the four values of standard deviation of porosity, 10 randomly porosity fields were generated. each of the random porosity fields was incorporated with utchem for simulations of surfactant flooding in heterogeneous two-layered porous media. the simulated results were then used to analyze the effects of reservoir rock variability on the distribution and recovery of oil and microemulsion saturations. figure 1 shows oil saturation ratio between the first and the second layers after injecting 1.25 pore volumes (pv) of surfactant-polymer solution and chase water. the figure indicates that the residual oil saturation ratio for surfactant-polymer flooding (cs > 0%) fluctuate more than water flooding (cs = 0%, cp = 0%) to the spatial distribution of multiple porosity fields. further results presented in fig. 1 indicate that residual oil saturation ratio of polymer flooding (cs = 0%, cp = 10%) was closer to one than that of water flooding. while the residual oil saturation ratios of surfactant-polymer flooding were farther to one than that of water flooding. this means that the amount of oil swept became more unequal between the two layers. it indicated that polymer flooding has good vertical sweep efficiency, while surfactant-polymer flooding has worse vertical sweep efficiency than water flooding. 0.8 0.85 0.9 0.95 1 1.05 1.1 0 0.2 0.4 0.6 0.8 1 dev. std. of porosity o il s at ur at io n r at io cs=0%,cp=0% cs=0%,cp=10% cs=1.25%,cp=10% cs=2.5%,cp=10% cs=5%,cp=10% fig. 1: residual oil saturation ratio between the first and the second layers. iium engineering journal, vol. 12, no. 1, 2011 fathaddin et al. 35 figure 2 shows residual oil saturation after injecting 1.25 pv of surfactant-polymer solution and chase water. fig. 2 indicates that there was no significant change on the residual oil saturation as deviation standard of porosity increased. the fluctuation of the residual oil saturation was affected by the restriction on lateral direction due to more variation of pore size as the porosity deviation standard increased. the restriction in lateral direction made the injecting fluid to cross between the layers to find the most favorable path. another result presented in fig. 2 indicates that the residual oil saturation reduced as higher surfactant concentration applied. the average residual oil saturation for surfactant concentrations of 0%, 1.25%, 2.5%, and 5% was 0.362  0.005, 0.298  0.015, and 0.204  0.026, and 0.079  0.010, respectively. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.2 0.4 0.6 0.8 1 dev. std. of porosity o il s at ur at io n cs=0%,cp=0% cs=0%,cp=10% cs=1.25%,cp=10% cs=2.5%,cp=10% cs=5%,cp=10% fig. 2: average residual oil saturation after injecting 1.25 pv. the surfactant injected was a surface-active agent which had hydrophilic and hydrophobic parts. the parts solubilized oil and water to form emulsion. fig. 3 shows the correlation between standard deviation of porosity and microemulsion saturation. as expected, higher microemulsion saturation was formed as higher surfactant concentration was used. the microemulsion saturation affected the residual oil saturation since the microemulsion phase contained water, surfactant and oil. therefore the effect of surfactant concentration and standard deviation of porosity on the microemulsion saturation had reverse pattern to the residual oil saturation (fig. 2 and 3). in the presence of water saturation, higher microemulsion saturation occupied the layer with lower oil saturation and vice versa. the average microemulsion saturations for surfactant concentration of 1.25%, 2.5%, and 5% were 0.317  0.032, 0.416  0.014, and 0.547  0.004, respectively. figure 4 shows oil recovery for various deviation standards of porosity and surfactant concentrations. the figure indicates that the oil recovery by surfactant-polymer flooding (cs > 0%) was more sensitive than water flooding to the spatial distribution of multiple porosity fields. the recovery of oil tends to slightly fluctuate as the porosity deviation standard increases. the maximum alteration of oil recovery compared with the homogeneous porous media for surfactant concentrations of 0%, 1.25%, 2.5%, and 5% was 3.6%, 9.2%, 5.3%, and 5.5%, respectively. oil recovery was directly correlated with iium engineering journal, vol. 12, no. 1, 2011 fathaddin et al. 36 the microemulsion saturation and the residual oil saturation. meanwhile, the saturations were affected by flow path which was resulted in the heterogeneity of porous media. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.2 0.4 0.6 0.8 1 dev. std. of porosity m ic ro em ul si on s at ur at io n cs=1.25%,cp=10% cs=2.5%,cp=10% cs=5%,cp=10% fig. 3: microemulsion saturation after injecting 1.25 pv. additional results presented in fig. 4 indicate that, the oil recovery increases as the surfactant concentration increases. the average oil recovery for surfactant concentrations of 0%, 1.25%, 2.5%, and 5% was 0.482  0.008, 0.567  0.022, 0.650  0.013, and 0.714  0.017, respectively. this phenomenon indicated that surfactant-polymer flooding improved sweep efficiency in lateral direction. figures 2 to 4 show that although oil saturation in porous media was suppressed by applying higher surfactant concentration, but more oil left in the porous media in form of emulsion at 1.25 pore volume injection. therefore, more water injection or a polymer slug drive was required to sweep out more emulsion. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.2 0.4 0.6 0.8 1 dev. std. of porosity o il r ec ov er y cs=0%,cp=0% cs=0%,cp=10% cs=1.25%,cp=10% cs=2.5%,cp=10% cs=5%,cp=10% fig. 4: average oil recovery after injecting 1.25 pv. iium engineering journal, vol. 12, no. 1, 2011 fathaddin et al. 37 4. conclusion based on the simulation results and analyses shown above, the following conclusions are made: 1. the effect of spatial heterogeneity of multiple porosity fields on surfactant-polymer flooding was higher than that on water flooding and polymer flooding. 2. surfactant-polymer flooding results in more unbalance residual saturation in the two layers than water flooding and polymer flooding. this indicated that the vertical sweep efficiency of surfactant-polymer flooding was worse than water flooding and polymer flooding. 3. although the effect of spatial heterogeneity of multiple porosity fields on the oil recovery of surfactant-polymer flooding was higher than that on water flooding and polymer flooding, the surfactant improved the oil recovery of polymer flooding and water flooding by increasing lateral sweep efficiency. the variation of recovery factor of surfactant-polymer flooding due to the reservoir heterogeneity was under 9.2%. references [1] a. seethepalli, b. adibhatla, k. k. mohanty, “wettability alteration during surfactant flooding of carbonate reservoirs”. spe 89423, the spe/doe fourteenth symposium on improved oil recovery, pp. 1-10, 2004. [2] d. zhang, surfactant-enhanced oil recovery process for a fractured, oil-wet carbonate reservoir, ph.d. thesis, rice university, houston, u.s.a., 2005. [3] n.f. najafabadi, modeling chemical eor processes using impec and fully implicit reservoir simulators, ph.d. thesis, the university of texas at austin, 2009. [4] w. littmann, polymer flooding, elsevier science publishing company inc., new york, 1988. [5] s. naji, field scale simulation of chemical flooding, ph.d. thesis, the university of texas at austin, 1989. [6] g. brook, , investigation of non-thermal enhanced oil recovery techniques for heavy oil production, master thesis, university of calgary, 1999. [7] c. zheng, b. l. gall, t. r. french, r.s. bryant, “modeling and simulation of polymerenhanced oil production,” systems and information technology review journal, vol. 6, 2, pp. 55-67, 1998. [8] h. dakhlia, a simulation of polymer flooding and surfactant flooding using horizontal wells, ph.d. thesis, the university of texas at austin, 1995. [9] y. shiyi, y. hua, s. kuiyou, y. puhua, “effects of important factors on alkali/surfactant/polymer flooding”, spe 50916, the 1998 spe international conference and exhibition, pp. 357-374, 1998. [10] r. zhang, a. l. wood, c. g. enfield, s. w. jeong, “stochastical analysis of surfactantenhanced remediation of denser-than-water nonaqueous phase liquid (dnapl)– contaminated soils,” j. environ. qual., vol. 32, pp. 957-965, 2003. iium engineering journal, vol. 12, no. 1, 2011 fathaddin et al. 38 [11] g. a. pope and r. c. nelson, “a chemical flooding compositional simulator,” spe journal 6725, vol. 18, 5, pp. 339-354, 1978. [12] t. elkateb, r. chalaturnyk, p. k. robertson, “simplified geostatistical analysis of earthquake induced ground response at the wildlife site, california, u.s.a,” can. geothech. j., vol. 40, pp. 16-35, 2003. [13] i. sahni, wavelet analysis of multiple history-matched reservoir models, a report, stanford university, 2003. [14] g. matheron, les variables regionaliseés et leur estimation, masson, paris, 1965. [15] s. h. derakhshan, a decision support system for variogram calculation, ms thesis, university of alberta, 2007. microsoft word 211-703-2-rv completed-corrected iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 99 molecular cloning and production of recombinant phytase from bacillus subtilis asuia243 in pichia pastoris nor soleha mohd dali 1 , tamrin nuge 1 , mohd. hafidz mahamad maifiah 1 , faridah yusof 1 , anis shobirin meor hussin 2 , abd-elaziem farouk 3 and hamzah mohd. salleh 1 1 bioprocess and molecular engineering research unit, department of biotechnology engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2 department of food technology, faculty of science and food technology, 43400, university putra malaysia, serdang, selangor, malaysia. 3 department of biotechnology, faculty of science, taif university, 21974 taif, al-hawiayah, p. o. box. 888, saudi arabia. hamzah@iium.edu.my abstract: phytase gene obtained from bacillus subtilis asuia243 was cloned into a medium vector and transformed into e. coli. restriction enzyme digestion was conducted to get blunt-ended phytase gene and ligated into the pichia expression vector, ppiczαa. the recombinant vector, ppiczαa-243hpp was then linearized with pmei and transformed into p. pastoris strain x33. screening for multi copy gene number of transformants was done by re-plating the selected colonies on increasing concentration of zeocin. one positive clone, x243hpp#2 was then grown in bmgy media as the starting culture, followed by induction in bmmy media for protein expression study. the supernatant was then analysed by sds-page and western blot method to check the protein expression. abstrak: gen fitase yang didapati daripada bacillus subtilis asuia243 diklonkan sebagai vektor perantara dan berubah menjadi e. coli. sekatan pencernaan enzim dijalankan untuk mendapatkan gen fitase berhujung tumpul dan diligatkan dengan vektor ekspresi pichia, ppiczαa. vektor rekombinan, ppiczαa-243hpp kemudian dilinearkan dengan pmei dan berubah menjadi p. pastoris strain x33. penyaringan untuk nombor gen berbilang salinan yang menjalani transformasi genetik dijalankan dengan menyalur semula koloni terpilih dengan penambahan kepekatan zeocin. satu klon positif, x243hpp#2 kemudian dibiarkan hidup dalam perantara bmgy sebagai kultur permulaan, diikuti dengan aruhan dalam perantara bmmy untuk kajian penglahiran protein. supernatan kemudian dikaji dengan sds-page dan kaedah sap western untuk menyemak penglahiran protein. keywords: phytase; bacillus subtilis; pichia pastoris; gene cloning 1. introduction phytase (myo-inositolhexakiphosphate phosphohydrolase) catalyzes the hydrolysis of phytic acid (the principle storage form of phosphorus in legumes, cereals, oil seeds and nuts) to myo-inositol and inorganic phosphate. phytic acid is a polyanionic chelating agent that forms complexes with several divalent cations of major nutritional importance such as ca 2+ , mg 2+ , zn 2+ , cu 2+ , fe 2+ , and mn 2+ [1]. therefore, the catalytic activity of phytase on iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 100 phytic acid leads to the loss of ability of phytic acid to chelate metal ions. the animal feeds contain phytic acid which cannot be digested by monogastric animals because they have no or low level of phytase activity in their digestive tracks [2]. inorganic phosphate is frequently added to their feed to facilitate optimal growth for these animals which leads to stimulation of algal blooms and euthrophication of surface water due to the high content of phytate and inorganic phosphate in the excretion of the animals [3]. thus, supplementation of animal feeds with phytase increases the bioavailability of phosphorus and reduces the phosphorus pollution in the environment. thus, the benefits of phytase are two-fold: saving the expensive and non-renewable inorganic phosphorus resource by reducing the need for its inclusion in animal diets and protecting the environment from pollution of excessive manure phosphorus runoff [4]. recent research has shown that microbial sources are more promising for the production of phytases on a commercial level [5]. most of the scientific work has been done on those originating from filamentous fungi such as aspergillus niger [6,7], rhizopus oligosporus [8] and cladosporium species [9]. other than these species, phytase from other microbes such as escherichia coli [10], pseudomonas species [11], klebsiella species [12] and bacillus species [13] were also identified. therefore in this research, a local wild type bacillus subtilis strain asuia243 has been chosen as the source for phytase gene and the gene was cloned in an expression vector with strong promoter, ppiczαa. the recombinant vector was then transformed in the methylotrophic yeast, pichia pastoris strain x33 for enzyme production. p. pastoris has been chosen as the production host because of the ability to produce the heterologous protein extracellularly, therefore eliminating the method for cell lysis, and the expressed proteins are generally hyperglycosylated [8]. 2. materials and methods 2.1 strains, plasmids and media the wild type bacillus subtilis asuia243 strain was obtained from a previous study [14]. the ppiczαa vector, pcr ® -blunt ii-topo ® vector, pichia pastoris strain x33 and one shot ® top10 competent cell were purchased from invitrogen, usa. low salt luriabertani (lb) broth and agar were purchased from becton, dickinson and company, usa. yeast extract, peptone, dextrose and agar for ypds, bmgy and bmmy media were purchased from merck, germany. glycerol and methanol were purchased from merck, germany. sorbitol was purchased from mp biomedicals, france. yeast nitrogen base (ynb) for bmgy and bmmy media was purchased from laboratorios conda, spain. 2.2 isolation of phytase gene the plasmid dna was isolated from the wild-type b. subtilis asuia243 by using qiaprep ® spin miniprep kit (qiagen). the phytase gene was then amplified by polymerase chain reaction (pcr). the oligonucleotide primers were designed based on the b. subtilis subsp. subtilis str. 168 complete genome obtained from ncbi database (genbank accession no. np_389861.1) the primer sequences are the following: bsnf5pp (forward): 5’-ggtaccatgaaggttccaaaaacaatgctg-3’ bsnr6pp (reverse) : 5’-tctagatagccgtcagaacggtct-3’ the underlined sequences in forward and reverse primers represent restriction enzyme site for kpni and xbai, respectively. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 101 the reaction mixture contained 10 µ l of 5x phusion hf buffer (finnzyme), 1 µ l of each primer, 5 µl of plasmid dna, 1 µ l of 10 mm dntps, and 0.5 µ l of pfu dna polymerase (finnzyme). pcr was conducted at a condition of 98 o c for 2 minutes, 30 cycles of 98 o c for 10 seconds, 55 o c for 10 seconds, and 72 o c for 10 seconds, followed by 72 o c for 10 minutes, and hold at 4 o c. gel electrophoresis was done on the pcr products by using 0.8% agarose gel followed by gel purification using gel extraction kit (qiagen). 2.3 cloning into ppiczαa vector and transformation into p. pastoris the purified pcr products were cloned into pcr ® -blunt ii-topo ® as medium vector and transformed into competent one shot ® top10 e. coli according to the manufacturer’s instructions. the transformants were plated out onto lb medium containing 50 µ g/ml kanamycin and incubated overnight at 37 o c. next, single colonies were selected and grown at 250 rpm overnight at 37 o c in 10 ml lb broth containing 50 µ g/ml kanamycin. the plasmids were extracted by using qiaprep ® spin miniprep kit (qiagen) and digested with kpni and xbai at 37 o c for 2.5 hours. the digestion product, 243hpp was purified by using gel extraction kit (qiagen). the purified products were then ligated with expression vector, ppiczαa that has been already been digested with the same restriction enzymes. the ligation was conducted at 16 o c for 16 hours. ligation product was then transformed into one shot ® top10 e. coli and plated on low salt lb medium containing 25 µ g/ml zeocin (invivogen, usa). the plates were incubated at 37 o c overnight. single colonies were selected and grown in low salt lb broth containing 25 µ g/ml zeocin at 37 o c, 250 rpm overnight. the plasmids ppiczαa-243hpp were extracted by using qiaprep ® spin miniprep kit (qiagen) and digested with kpni and xbai to confirm for positive clones. one positive clone, ppiczαa243hpp#1 was chosen for sequencing analysis. the recombinant plasmid ppiczαa-243hpp#1 was linearized with pmei at 37 o c for 2.5 hours and transformed into the pichia pastoris strain x33 (mut + ) by chemical transformation according to the manufacturer’s instructions. the cells were cultured on ypds media (1 % yeast extract, 2 % peptone, 2 % dextrose, 2 % agar, 1 m sorbitol) containing 100 µ g/ml zeocin at 30 o c for 3 days. 2.4 screening for multiple copy of gene the positive colonies were plated again on ypds agar containing different concentration of zeocin: 100 µg/ml, 500 µg/ml and 1000 µg/ml to screen for the clone with multiple gene copy number. the resistant colony at 1000 µ g/ml was selected and transferred to other fresh agar plates. colony pcr was conducted for a few selected colonies to determine the stable integration of the gene inside the host. 2.5 expression of recombinant phytase gene in p. pastoris one clone from the multiple gene copy number screening was grown in a 250 ml shake flask containing 25 ml of bmgy media (1 % yeast extract, 2 % peptone, 1.34 % ynb, 4x10 -5 % biotin, 1% glycerol, 100 mm potassium phosphate ph 6.0) at 30 o c and shaken at 250 rpm until the od600nm reached 2.0-6.0 (about 26-30 hours). cells were harvested by centrifugation at 5000 x g at 4 o c for 5 minutes. the cells were resuspended to an od600nm of 1.0 in 100 ml bmmy (1% yeast extract, 2% peptone, 1.34% ynb, 4x10 5 % biotin, 0.5% methanol, 100mm potassium phosphate ph 6.0) at 30 o c for 4 days followed by induction with 0.5% methanol for every 24 hours. samples (1 ml) were taken iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 102 at 24-hour intervals to analyse the protein expression. all these methods followed the manufacturer’s instructions (invitrogen, 2002). 2.6 analysis of expressed recombinant protein protein expression was analysed on 12% sds polyacrylamide gel [15]. two sets of gels were prepared where one set was subjected to coomasie blue staining and the other set was subjected to western blot analysis. samples (20 µ l) were loaded into each well of the gel. for western blot analysis, proteins separated by sds-page was transferred onto nitrocellulose membrane, blocked and incubated overnight with the primary antibody (1:5000). afterwards, the membrane was washed with buffer and incubated with the polyclonal goat anti rabbit igg-alkaline phosphatase conjugate used as the secondary antibody for another six hours. the membrane was incubate in a combination of nbt and bcip (bio-rad laboratories, usa) for colour development. 3. results and discussion 3.1 cloning and transformation into p. pastoris host the b. subtilis asuia243 phytase gene was successfully amplified by using the designed primers, bnsf5pp and bsnr6pp. the primers were designed in such that the nterminal of the gene was in frame with the α-factor signal sequence and the c-terminal of the gene contained no stop codon to include the c-myc epitope and 6x-his tag. from the gel electrophoresis (fig. 1), the bands were located at approximately 1,149bp which is the size of b. subtilis phytase gene according to the original dna template obtained from the ncbi website. fig. 1: gel electrophoresis of b. subtilis asuia243 phytase gene by using bsnf5pp and bsnr6pp primers. the bands are located at approximately 1,149bp. the phytase gene 243hpp was successfully ligated into the expression vector ppiczαa and transformed into the one shot ® top10 e. coli in order to get many copies of the recombinant plasmid. re-screening was done to ensure that the clones were not false positives that caused by nonspecific binding. according to dale and von schantz (2002) [16], the re-screening of recombinant colonies is a common practice to pick a recombinant colony that is free from contaminating neighbours. the true positive colonies, ppiczαa-243hpp were then grown in low salt lb broth, plasmids were extracted and sent for sequencing (fig. 2). iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 103 fig. 2: sequencing result of ppiczαa-243hpp shows that the phytase gene is in frame with the α-factor signal sequence (italic and green highlighted), c-myc epitope (blue highlighted) and the 6x-his tag (yellow highlighted). the positive recombinant plasmids were linearized with pmei before being transformed into the p. pastoris x33 competent cell. the linear vector dnas can generate stable transformants of p. pastoris via homologous recombination between sequences shared by the vector and host genome [17]. by linearizing the recombinant vector at the unique site located in his4 region, mut+ recombinants were generated [18]. about 38 colonies were selected for multiple gene copy screening, and among these 38 colonies, only 12 colonies contained multiple copy of gene while others were not grown on the 1000µ g/ml zeocin plate. colony-pcr was performed on seven of the 12 colonies to determine stable integration of the gene inside the host genome (fig. 3). one positive clone, x243hpp#2 was selected for shake-flask expression. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 104 fig. 3: gel electrophoresis of colony-pcr. number #1, #2, #17, #22, #23, #25 and #26 are the positive colonies from high copy selection. vector only is the host with ppiczαa only; +ve is the extracted recombinant plasmid with inserted gene; extract vector is the extracted ppiczαa; -ve is the mixture of pcr reagent with primers only. the result shows that all clones except #26 have stable integrated gene. the upper bands are located at appr. 2200bp while the lower bands are the inserted genes with parent plasmid pcr products (1149bp + 588bp = 1737bp). for the vector only, the result shows two bands, the upper one is the aox1 gene (2200bp) and the lower one is the parent plasmid pcr product (588bp). for +ve, the band indicates the positive result for the gene of interest (1737bp). 3.2 expression of recombinant phytase in p. pastoris as shown in fig. 4, there is no expected band appeared on the sds-page gel after 4 days of induction. the predicted size of phytase x243hpp#2 is about 45.02 kda (including the c-myc epitope and 6x-his tag). similarly, no bands were detected on the membrane for western blot analysis (data now shown). this indicates that no protein was expressed during the induction. however, from the colony-pcr result, we can see that the gene was indeed integrated in the host genome and the dna sequencing result confirmed that the phytase gene is in frame with the α-factor signal sequence, c-myc epitope and the 6x-his tag. these results showed that the phytase gene has correctly been inserted into the yeast genome. since there was no expressed protein detected on the sds-page gel and nitrocellulose membrane, there might be a few reasons that would explain this problem. there are many cases of protein expression failure but only fews were reported. burt et al. [19] explained three main reasons for the lack of expression of biologically active proteins in heterologous system. host cell lacking components for translation of recombinant protein, the heterologous protein being prone to proteolysis as it emerges from translation, and incomplete or improper folding of heterologous protein can be some of the reasons that lead to the failure of protein expression in heterologous system. sreekrishna et al. [20] listed two possible factors which influence protein expression in pichia systems; untranslated regions in recombinant mrna, and transcriptional and translational blocks. since the phytase gene was correctly inserted into the yeast genome, there is also a possibility of excessive transcription. gasser et al. [21] reported in their work that excessive transcription may cause cellular stress, such that the production rate of polypeptides can be rapid and interfere with correct protein folding. only properly folded and assembled proteins can be exported within the yeast cell, modified and and iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 105 transported to the extracellular space [22]. misfolded or aggregated proteins in the cell will be degraded inside the cell [23]. accumulation of unfolded or misfolded proteins in the cell can also suppresses transcription of the secretory target protein [24]. fig. 4: sds-page result for induction of phytase x243hpp#2. x33: untransformed host cell; v: p. pastoris x33 transformed with ppiczαa vector only; c: multiple gene copy clone (x243hpp#2); un: clone that was grown in media without methanol inducer; m: protein low range standard marker. there is no expected band appeared on the gel for all four days of induction. there are many possibilities that can lead to the failure of protein expression in pichia pastoris. although only few have been reported, these can be the possible reasons for the problem in this work. further investigation needs to be conducted. the process conditions and media compositions during the induction time can be other possible reasons for the failure of protein expression and these two conditions should be optimized. romanos (1995) [25] reported that a critical factor that has long been recognized to affect induction efficiency is aeration of p. pastoris culture because in shake-flask inductions, iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 106 the tendency of cultures, especially mut + strains, to become oxygen-limited is quite high. besides that, changing the codons in the foreign gene that those of codons more frequently used by the yeast significantly improves the levels of expression of those foreign genes [26]. the a+t ratio of a foreign gene can be changed to one more similiar to the p. pastoris genome to improve expression [27]. changing the expression vector to other alternative vectors is also possible to improve the protein expression. the ppiczαa vector contains aox1 promoter which requires methanol as an inducer. when methanol is oxidized by the alcohol oxidase, the accumulation of the oxidized products, formaldehyde and hydrogen peroxide, can lead to toxicity for the host cell itself, which also can be one of the factors for protein expression failure [28, 29]. therefore, changing to other alternative expression vector for protein secretion such as pgapzα can be a better solution for this problem. this vector has the glyceraldehyde-3-phosphate (gap) promoter which does not require methanol for induction, and it is not necessary to shift cultures from one carbon source to another, making strain growth and protein expression more convenient and straightforward [30]. 4. conclusion despite of the problem occurred, p. pastoris has become one of the favourite expression systems for the production of various proteins of interest. it is well known that p. pastoris secretes very little native protein, providing an advantageous means to recover foreign secreted protein from the supernatant. other advantages of using p. pastoris expression system are ease of fermentation to high cell density, genetic stability and scale up without loss of yield [31], molecular genetic manipulations are simple and protocols are available, can be grown in a simple mineral salts medium [32], high eukaryotic protein modifications such as glycosylation, disulfide-bond formation and proteolytic processing [33]. in this research, the failure of protein expression can be further investigated. it is suggested that the process conditions and media compositions should be optimized to improve the cell growth and protein expression, since the phytase gene was integrated stably in the host genome. the same clone can be used for the optimization or the gene can be re-transformed into a new competent cell. since there are many reports of successful production of heterologous phytase from various sources using p. pastoris expression system, it is possible that our phytase can also be expressed using this expression system after further investigations are conducted. acknowledgement this research work is funded by biotech research project from the ministry of science, technology and innovation (mosti) malaysia, (grant project no. 07-01-08-eib011). the authors also thanked dr. farah diba abu bakar for valuable discussions. references [1] harland, b. f., oberleas, d. phytic acid complex in feed ingredients. in: m. b. coelho, e. t. kornegay, (eds) phytase in animal nutrition and waste management. 2 nd rev edn. basf, mexico, 1999, 69-76. [2] schroder, b., brever, g., rodehutscord, m. mechanisms of intestinal phosphorus absorption and availability of dietary phosphorus in pigs. dtsch tieraerztl wochenschr., 1996, 103: 209-214. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 107 [3] oh, b. c., choi, w. c., park, s., kim, y. o., oh, t. k. biochemical properties and substrate specificities of alkaline and histidine acid phytases. appl microbiol biotechnol., 2004, 63, 362-372. [4] xin g. l. and porres, j. m. phytase enzymology, applications, and biotechnology. biotechnology letters, 2003, 25: 1787-1794. [5] pandey, a., szakacs, g., soccol, c. r., rodriguez-leon, j. a., soccol, v. t. production, purification and properties of microbial phytases. bioresource technology., 2001, 77, 203214. [6] ngo, t. x., mai, t. h., vu, n. t. cloning and over expression of an aspergillus niger xp phytase gene (phya) in pichia pastoris. world academy of science, engineering and technology, 2009, 56, 750-753. [7] soni, s. k., and khire, j. m. production and partial characterization of two types of phytase from aspergillus niger ncim 563 under submerged fermentation conditions.” world j. microbiol. biotechnol., 2007, 23, 1585-1593. [8] casey, a., walsh, g. identification and characterization of a phytase of potential commercial interest. j. biotechnol., 2004, 110, 313-322. [9] quan, c. s., tian, w. j., fan, s. d., kikuchi, y. i. purification and properties of a lowmolecular-weight phytase from cladosporium sp. fp-i.” j. biosc. bioeng., 2004, 97, 260266. [10] greiner, r., konietzny, u., jany, k. d. purification and characterization of two phytases from escherichia coli. arch. biochem. biophys., 1993, 303, 117-113. [11] cho, j. s., lee, c. w., kang, s. h., lee, j. c., bok, j. d., moon, y. s., lee, h. g., kim, s. c., choi, y. j. purification and characterization of a phytase from pseudomonas syringae mok1. curr. microbiol., 2003, 47, 290-294. [12] sajidan, a., farouk, a., greiner, r., jungblut, p., mueller, e. c., borriss, r. molecular and physiological characterization of a 3-phytase from soil bacterium klebsiella sp. asr1.” appl. microbiol. biotechnol., 2004, 65: 110-118. [13] kerovuo, j., lauraues, m., nurminen, p., kalkkinen, n., apajalahti, j. isolation, characterization, molecular gene cloning, and sequencing of a novel phytase from bacillus subtilis. appl. environ. microbiol., 1998, 64, 2079-2085. [14] anis shobirin m. h., farouk, a., greiner, r. potential phytate-degrading enzyme producing bacteria isolated from malaysian maize plantation. african j. biol., 2009, vol. 8, no. 15, 3540-3546. [15] laemmli, u. k. cleavage of structural proteins during the assembly of the head of bacteriphage t4. nature, 1970, 227, 680-685. [16] dale, j. w., and von schantz, m. from gene to genomes: concepts and applications of dna technology. john wiley & sons ltd., new york, 2002. [17] higgins, d. r. and cregg, j. m. pichia protocols. humana press, new jersey. vol.10, 1998. [18] zou, l., wang, h., pan, x., tian, g., xie, z., wu, q., chen, h., xie, t., and yang, z. expression, purification and characterization of a phyam-phycs fusion phytase. journal of zhejiang university science b, 2008, vol. 9, no. 7, 536-545. [19] burt, t. r., edavettal, s. c., hall, j. p. and mattern, m. r. sumo fusion technology for difficult-to-express proteins. protein expr. purif., 2005, vol. 43, no. 1, 1-19. [20] sreekrishna, k., brankamp, r. g., kropp, k. e. strategies for optimal synthesis and secretion of heterologous proteins in the methylotrophic yeast pichia pastoris. gene, 1997, vol. 190, no. 1, 55-62. [21] gasser, b., maurer, m., gach, j., kunert, r., and mattanovich, d. engineering of pichia pastoris for improved production of antibody fragments.” biotechnol. bioeng., 2006, 94, 353-361. [22] klausner, r. architectural editing: determining the fate of newly synthesized membrane proteins. new biol., 1989, 1, 3-8. [23] yoshida, h. er stress and diseases. febs journal, 2007, 274, 630-658. [24] schroder, m. and kaufman, r. j. the mammalian unfolded protein response. annu. rev. biochem., 2005, 74, 739-789. iium engineering journal, vol. 12, no. 4, 2011: special issue on biotechnology mohd dali et al. 108 [25] romanos, m. a. advances in the use of pichia pastoris for high-level gene expression. current opinion in biotechnology, 1995, 6, 527-533. [26] gurkan, c. and ellar, d. j. expression of the bacillus thuringiensis cy t2aa1 toxin in pichia pastoris using a synthetic gene construct.” biotechnol. appl. biochem., 2003, 38, 25-33. [27] cregg, j. m. distinctions between pichia pastoris and other expression system. in methods in molecular biology: pichia protocols (ed) cregg, j. m., humana press, new jersey, p110, 2007. [28] couderc, r. and baratti, j. oxidation of methanol by the yeast, pichia pastoris, purification and properties of the alcohol oxidase. agric. biol. chem., 1980, 44, 2279-2289. [29] van der klei, i. j., bystrykh, l. v., harder, w. alcohol oxidase from hasenula polymorpha cbs4732. methods enzymol., 1990, 188, 420-427. [30] li, p., anumanthan, a., gao, x., ilangovan, k., suzara, v. v., düzgüneş, n., renugopalakrishnan, v. expression of recombinant protein in pichia pastoris. appl. biochem. biotechnol., 2007, 142, 105-124. [31] tuite, m. f., clare, j. j., romanos, m. a. expressing cloned genes in the yeasts saccharomyces cerevisiae and pichia pastoris.” in protein expression: a practical approach (eds) higgins, s. j. and hames, b. d., oxford university press, new york, 1999. [32] jahic, m., veide, a., charoenrat, t., teeri, t., enfors, s. process technology for production and recovery of heterologous proteins in pichia pastoris. biotechnol. prog., 2006, 22, 14651473. [33] cregg, j. m., cereghino, l., shi, j., higgins, d. r. recombinant protein expression in pichia pastoris. mol. biotechnol., 2000, 16, 23-52. microsoft word 250 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ashari and nordin 105 theoretical modeling and simulation of phase–locked loop (pll) for clock data recovery (cdr) z. m. ashari and a.n. nordin electrical and computer engineering department, kulliyyah of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. zainab_ashari@yahoo.com abstract: modern communication and computer systems require rapid (gbps), efficient and large bandwidth data transfers. agressive scaling of digital integrated systems allow buses and communication controller circuits to be integrated with the microprocessor on the same chip. the peripheral component interconnect express (pcie) protocol handles all communcation between the central processing unit (cpu) and hardware devices. pcie buses require efficient clock data recovery circuits (cdr) to recover clock signals embedded in data during transmission. this paper describes the theoretical modeling and simulation of a phase-locked loop (pll) used in a cdr circuit. a simple pll architecture for a 5 ghz cdr circuit is proposed and elaborated in this work. simulations were carried out using a hardware description language, verilogams. the effect of jitter on the proposed design is also simulated and evaluated in this work. it was found that the proposed design is robust against both input and vco jitter. abstrak: sistem komunikasi dan komputer moden memerlukan pemindahan data yang cekap (gbps), dan bandwidth yang besar. pengecilan agresif menggunakan teknik sistem digital bersepadu membenarkan bas dan litar pengawal komunikasi disatukan dengan mikroprocessor dalam cip yang sama. protokol persisian komponen sambung tara ekspres (pcie) mengendalikan semua komunikasi antara unit pemprosesan pusat (cpu) dan peranti perkakasan. bas pcie memerlukan litar jam pemulihan data (cdr) yang cekap untuk mendapatkan kembali isyarat jam yang tertanam dalam data semasa transmisi. karya ini menerangkan teori pemodelan dan simulasi gelung fasa terkunci (pll) untuk cdr. rekabentuk 5 ghz pll yang mudah telah dicadangkan dalm kertas kerja ini. simulasi telah dijalankan menggunakan perisian verilog-ams. simulasi mengunnakan kesan ketar dalam reka bentuk yang dicadangkan telah dinilai. reka bentuk yang dicadangkan terbukti teguh mengatasi ganguan ketar di input dan vco. key words: phase-locked loop (pll); jitter; phase detector; low-pass filter; voltagecontrolled oscillator 1. introduction aggressive scaling in accordance with moore’s law has allowed miniaturization of both the processor and its communication controller circuits. submicron transistors result in cpus with ghz clock speeds. high speed data transfer rates (gbps) between peripheral components and the central processing unit (cpu) is important to avoid bottlenecks in modern computer systems. the peripheral component interconnect express (pcie) protocol handles all communications between the hardware devices and the cpu. during transmission, clocks are often embedded in the data to allow efficient synchronization between the iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ashari and nordin 106 transmitter and receiver modules. as such, the clock data recovery (cdr) circuit is an important component in a pcie system. this scheme is vulnerable to jitter, clock skews and channel latency. the quality of the clock is difficult to optimize with increased bandwidth demands and high speed transfer rates. different clock architectures can be used for synthesis, distribution and recovery of i/o clocks. to cater for high-speed data links different techniques can be used namely: clock multiplication, forwarded clock recovery, embedded clock recovery, per-pin deskew, jitter filtering and duty-cycle error correction [1]. the first generation of i/o interconnects known as pcie 1.0, had initial speeds of 2.5 gbps. the next generation, pcie 2.0 is based on pcie 1.0 principles, but it supports speeds of 5gbps. the ability of the cdr circuit to influence pcie’s performance during gbps data transmission makes its design critical. there are different cdr circuit top such as delay-locked loop (dll) and phase-locked loop (pll). the dll is a feedback system, similar to pll but the dll tracks the phase of a reference signal [2]. the dll circuit is a simple, robust and stable clock generator [1]. unlike a pll, dll do not filter input reference jitter. pll is generally known as a negative-feedback system with forward gain term and feedback term. it purposely used to synchronize the output frequency by an oscillator with the reference signal [3] and works as a demodulator [4]. in other words, it generates a signal with less phase difference. plls based are often implemented in designing cdr because they offer filtering to the phase or frequency signal. with transfer rate of 5 gbps, pll approached are preferably chosen in [5] and [6]. theoretical modeling and simulation of high performance of cdr based on the pll transfer functions is demonstrated in this work. modeling of analog mixed-signal architecture for dedicated cdr circuit using verilog-ams hdl is proposed. six important sections are presented in this paper. the system architecture of pll is described in section2. section 3 illustrates building blocks and transfer function of proposed cdr circuit. jitter in pll, simulation and results, discussion, and conclusion are analyzed in section 4, 5 and 6. 2. proposed cdr architecture the pll comprises of a phase detector (pd), a low-pass filter, voltage controlled oscillator (vco) and a feedback divider, as illustrated in fig. 1. this pll is designed to generate high output frequency of 5 ghz from a low frequency input of 50 mhz. the input source is derived from the embedded clock in the data stream. this pll then compares this input at the pd with the reference clock generated from the divider circuit. the phase difference between the reference clock and the input source feeds the loop filter. the loop filter produces a dc voltage that controls the vco. the vco generates a high frequency output (ghz) which is also the recovered clock. in the proceeding analysis, each block was using its transfer function. 2.1 phase detector (pd) phase detector (pd) is the first block in pll architecture. it is used to compare the phases of the incoming data with the phase of the clock generated by the divider circuit [7]. the phase detector determines the performance of a cdr circuit. the best phase detector basically should accomplish three essential functions which are data transition detection, phase difference detection and have low spur noise [8]. phase difference between the input phase and the output phase as well as the phase difference between the input voltage and the output voltage are also of concern. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ashari and nordin 107 fig. 1: circuit design of proposed pll. in locked condition, the phase difference between the output phase, φout and the input phase, φin should be small and constant. it makes the output angular frequency, ωout equal to angular frequency of the input, ωin. the output voltage of the pd, vpd is proportional to the phase difference of both inputs. the value of vpd can be calculated according to the equation (1) below: ( ) φφφ ∆=−= pdinoutpdpd kkv (1) where kpd is a pd gain and ∆φ is a phase error between two inputs. the kpd also can be determined based on the slope of vpd and ∆φ. the width of the output pulses at pd varies if the phase difference of the two inputs is also varied. in order to reduce the phase error in a pll system, kpd and kvco must be large. 2.2 rlc low-pass filter the following block in the pll system after a phase detector is a loop filter. a low pass filter is applied as a loop filter to pass lower frequency output of the phase detector and suppress the higher frequency jitters. in most cdr circuit designs, a simple rlc low pass filter with one pole and one zero is frequently used [8, 9]. the transient response of a stable low-pass filter depends on the magnitude of the pole and zero. the number of poles and zeroes in low pass filter verify the type of pll system. fig. 2: low-pass filter circuit. fljx l π2= (2) iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ashari and nordin 108 fcj x c π2 1 = (3) ( ) 22 rxxz cl +−= (4) in pll applications, loop filters of second order and higher are can be applied to offer better noise filtering. figure 5 shows rlc low pass filter circuit. the circuit design and numerical values of rlc low pass filter is verified according to the following equations (2) to (4). the inductor’s impedance, xl, capacitor’s impedance, xc, and total impedance of the loop filter circuit, z were determined. the function of low pass filter is to diminish jitter, which is generated at the input of pd. jitter exists as the input data stream experiences pulses or ripples. the rlc low pass filter transfer function is identified as shown below from (5) to (9). equation (5) shows a second order transfer function of rlc low pass filter. the equation (6) is the same as the equation (5) except that the denominator has been organized with a1 =1/lc and a2 = r/l so highlight that the denominator is a quadratic equation. the actual factoring processes for the gain is based on denominator in (6) with values of s are given by s1 and s2. the quadratic equation is used to determine the value of s1 and s2 as illustrated in equation (7) and (8). the two poles are complex and the resulting transfer function of g(s) = 0.4672+5.02x10 -11 j was obtained based on (9) and the calculated r, l, c values are shown in fig. 2. ( ) lcslrs lc sg 1 1 2 ++ = (5) ( ) 12 2 1 asas a sg ++ = (6) 2 4 1 2 22 1 aaa s −+ −= (7) 2 4 1 2 22 2 aaa s −− −= (8) ( )       −      − = 21 21 11 1 s s s s slcs sg (9) 2.3 vco another important part of the pll is the vco. the major function of vco is to create an oscillating signal proportional to the applied control voltage [10]. according to [11], the value of vvco depends on the dc component of vcont which extracted from vpd via low-pass filter. there are two unknown quantities, which need to be calculated for the vco to function properly, namely phase error, φerr and vcont (controlled voltage). the vcont iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ashari and nordin 109 will be equal to vout as the input and output frequencies are equal to ωout. thus, the vco and pd characteristics required to make it reliable are derived as (10) to (13): contvcoinout vk+= ωω (10) ϕ err = v cont k pd = ω out − ω in k pd k vco (11) ( ) s k sg vco vco = (12) based on (10), output frequency of the vco, ωout is depends on ωin (input frequency signal), kvco (vco gain) and the dc output of the loop filter, vcont. vcont in (11) can also be used to describe the difference between input and output frequency signal. when vcont is divided over the vco gain, φerr is obtained. the transfer function of the vco block is demonstrated in (12) which consist of kvco. two important characteristics are recognized after the loop returns to lock. all parameters such as the voltage due to the phase difference, vpd, and vco frequency remain constant except for total input and output phases. otherwise, vcont from the output low pass filter can be utilized in analyzing pll system [11]. 3. simulations of jitter in pll the existence of jitter is normally happens during the transmission and receive process. this phenomenon is indirectly effects overall system performance in pll. the transmission signal or data will experience noise and distortion especially for large bandwidth data. as a result, transfer rate and speed of a pll system decreased. small changes in period during transmission and receive process affects the excess phase and the total phase of the waveform. in other words, excess phase and total phase varies as the the waveform becomes unstable. jitter can be categorized according to its speed as fast jitter or slow jitter. slow jitter occurs whenever frequency of a signal varies slowly from one period to the other whereas fast jitter is due to changes in period. trend of jitter in pll can be modelled as an input to the pd, typically known as the input excess phase (φin) and as a random component (φvco) at the vco. generally, jitter is generated in pd and finally produced at the vco output. in fact, it can also be purposely injected at pd and vco circuit to test the ability of a system in withstanding distortion signals as demonstrated in fig. 3 and fig. 6. the smash dolphin integration verilog-ams tools have been used for all the simulation presented in this section. all the results in are based on the effect of injected jitter in input pd and vco. 3.1 jitter at input pd cdr’s circuit performance in sensing and recovering distortion signal at the input is tested in this section. figure 3 shows that jitter is added at the input of pd. the distortion signal is superimposed on the 50 mhz input and passes through the pd, loop filter, vco and divider. the resulting output 5 ghz waveform (φout ) is not affected by the jitter at input φ in > 0 as verified in fig. 5. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ashari and nordin 110 fig. 3: effect of pd jitter. fig. 4: input signal of 50 mhz with jitter. fig. 5: output waveform of proposed pll 5 ghz (φout ). 3.2 jitter at vco in this part, jitter is injected at the vco block, (φ vco ) and no jitter is applied at the input pd, φout = 0. at pd, two 50 mhz input signals are compared as shown in fig. 7 and fig. 8. a clean output signal of 5 ghz is generated after passing through pd, loop filter and vco. the distortion signal shown in fig. 9 is an input to the vco. the vco shows robust noise characteristics as the output of the pll produces a clean signal as shown in fig. 10. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ashari and nordin 111 fig. 6: effect of vco jitter. fig. 7: input signal of 50 mhz without jitter. fig. 8: feedback waveform of the divider. fig. 9: waveform signal of jitter, (φvco ). iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ashari and nordin 112 fig. 10: output waveform of proposed pll 5 ghz (φout ). 4. discussion this work proposes a design of a 5 ghz cdr pll circuit comprising of an rlc loop filter, pd, vco and divider circuit connected in feedback. the pd compares the clock embedded in the data stream with a reference clock. its output is sent to an rlc circuit. the rlc low-pass filter is used to ensure the cdr’s stability by filtering high frequency noise. the rlc is connected to a vco, which can generate a stable high frequency sinusoidal signal based on the dc voltage output from the rlc. the divider block divides the output frequency produced by the vco by a factor of n in order to be equal to the input frequency signal of 50 mhz. the effects of jitter are illustrated using simulation results. jitter, (φin ) is purposely injected at the input pd to test cdr circuit performance as shown in fig. 3. based on the resulting waveform in fig. 5, the proposed pll model can generate a clean high frequency output a hundred times larger than the distortion input frequency of 50 mhz. the presence of jitter at vco, (φvco) was also implemented as shown in fig. 6. the vco is able to tolerate distortions generated from the jitter as illustrated in fig. 10. this means that the proposed pll circuit is capable of handling ghz data and removing jitter at input pd and vco as illustrated in fig. 5 and fig. 10. 5. conclusion a simple model of pll architecture has been demonstrated and transfer function of several important parts is described. the proposed design composed of pd, rlc low–pass filter, vco, feedback divider and a resistor was used to realize a stable system. in this pll, a high frequency sinusoidal signal of 5 ghz is generated with 50 mhz input signal. a simple pll system tolerant to jitter was successfully modelled by running several configurations with different jitter inputs. it was shown through simulations using verilog ams that the pll model is robust and suitable for cdr applications in the ghz frequency range. acknowledgement this work is funded by the ministry of science and technology’s (mosti) techno fund grant tf0409d100. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ashari and nordin 113 references [1] b. casper and f. o'mahony, "clocking analysis, implementation and measurement techniques for high-speed data links a tutorial," ieee transactions on circuits, vol. 56, pp. 17-39, 2009. [2] j. moreira and h. wekmann, an engineer's guide to automated testing of high-speed interfaces. norwood, ma: artech house, 2010. [3] j. encinas, phase locked loops: chapman & hall, 1993. [4] m. saber, y. jitsumatsu, and m. t. a. khan, "design and implementation of low power digital phase-locked loop," presented at information theory and its applications (isita), 2010 international symposium on. [5] s. kim, d. lee, y.-s. park, y. moon, and d. shim, "a dual pfd phase rotating multi-phase pll for 5 gbps pci express gen2 multi-lane serial link receiver in 0.13um cmos," presented at vlsi circuits, 2007 ieee smposium on, 2007. [6] t. k. -siang, m. s. sulaiman, m. reaz, c. hean-teik, and m. sachdev, "a fully-integrated 5 gbit/s cmos clock and data recovery circuit," analog integrated circuits signals process (2007), pp. 101-109, 2007. [7] b. razavi, "a 10-gb/s cmos clock and data recovery circuit with a half-rate linear phase detector," ieee journal of solid-state circuits, vol. 36, pp. 761-768, 2001. [8] t.k.siang, m.s.sulaiman, c.h.teik, and m.sachdev, "design of high-speed clock and data recovery circuits," pp. 15-23, 2007. [9] t.oura, y.hiraku, t. suzuki, and h.asai, "modeling and simulation of phase-locked loop with verilog-a description for top-down design," presented at circuits and systems, 2004. proceedings. the 2004 ieee asia-pacific conference on 2004. [10] j.meyer, "modeling phase-locked loops using verilog," presented at 39th annual precise time and time interval (ptti) meeting, 2007. [11] b. razavi, design of analog cmos integratedircuits. los angeles: mcgraw-hill 2001. iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 solar thermal process parameters forecasting for evacuated tube collectors (etc) based on rnn-lstm muhammad ali akbar1, ahmad jazlan1, muhammad mahbubur rashid1*, hasan firdaus mohd zaki1, muhammad naveed akhter2 and abd halim embong1 1 department of mechatronics engineering, kulliyyah of engineering, international islamic university malaysia, kuala lumpur, malaysia. 2 department of electrical engineering, rachna college of engineering and technology gujranwala 52250 (a constituent college of university of engineering and technology lahore), pakistan * corresponding author: mahbub@iium.edu.my (received: 28th march 2022; accepted: 22nd august 2022; published on-line: 4th january 2023) abstract: solar heat for industrial process (ship) systems are a clean source of alternative and renewable energy for industrial processes. a typical ship system consists of a solar panel connected with a thermal storage system along with necessary piping. predictive maintenance and condition monitoring of these ship systems are essential to prevent system downtime and ensure a steady supply of heated water for a particular industrial process. this paper proposes the use of recurrent neural networkbased predictive models to forecast solar thermal process parameters. data of five process parameters namely solar irradiance, solar collector inlet & outlet temperature, and flux calorimeter readings at two points were collected throughout a four-month period. two variants of rnn, including lstm and gated recurrent units, were explored and the performance for this forecasting task was compared. the results show that root mean square errors (rmse) between the actual and predicted values were 0.4346 (solar irradiance), 61.51 (heat meter 1), 23.85 (heat meter 2), inlet temperature (0.432) and outlet temperature (0.805) respectively. these results open up possibilities for employing a deep learning based forecasting method in the application of ship systems. abstrak: penggunaan sumber bersih seperti tenaga solar dalam proses industri (ship) adalah satu kaedah alternatif untuk menhasilkan tenaga yang boleh diperbaharui bagi mengurangkan kesan gas rumah hijau yang terhasil dari proses industri. sistem ship biasanya mengandungi panel solar dan sistem penyimpanan haba yang berhubung melalui paip yang sesuai. penyelengaraan secara berkala diperlukan bagi memastikan sistem ini sentiasa membekalkan tenaga solar pada kadar bersesuaian dan bekalan tenaga solar yang terhasil berterusan dan tidak menjejaskan sistem pemanasan air bagi sesuatu proses industri. kajian ini mencadangkan penggunaan model ramalan rangkaian neural berulang bagi meramal parameter proses pemanasan solar. kelima-lima parameter proses iaitu – iradiasi solar, suhu saluran keluar & masuk pengumpul solar dan bacaan kalorimeter fluks pada dua tempat diambil sepanjang empat bulan (dari julai 2021 sehingga oktober 2021). dapatan menunjukkan dua varian rnn termasuk lstm dan unit berulang dapat dibanding prestasinya bagi tugas ramalan ini. dapatan kajian menunjukkan ralat punca min kuasa dua (rmse) antara bacaan sebenar dan ramalan adalah masing-masing 0.4346 (iradiasi solar), 61.51 (meter terma 1), 23.85 (meter 256 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 terma 2), suhu salur masuk (0.432) and suhu salur keluar (0.805). ini membuka peluang kajian mendalam berdasarkan kaedah ramalan dalam aplikasi sistem ship. keywords: evacuated tube collectors; solar irradiance; flux calorimeter; recurrent neural networks; long short term memory 1. introduction more than 80% of energy generation in today’s world is sourced from non-renewable energy resources such as coal, natural gas, and oil [1-3]. the reduction of fossil fuel resources worldwide combined with increased environmental concerns have resulted in a higher demand for renewable and cleaner energy such as solar, wind, hydroelectric, biofuels, piezoelectric and rf energy. oleochemical industries commonly utilize natural gas (ng) for generating low, medium, and high temperature heating, which is required as part of the overall oleochemical process flow. however, ng-based heating is known to increase undesirable greenhouse gas emissions [4]. in malaysia, solar energy is viewed as a viable, sustainable energy source due to the sunlight availability throughout the year, which is attributed to the tropical climate. therefore, historically, solar energy has been widely utilized for both residential and commercial water heating applications. evacuated tube collectors (etc) and flat plate collectors (nc-fpc) are the two most commonly used solar collectors for low to medium temperature industrial and residential water heating applications. these solar collectors are connected to thermal storage systems to allow energy to accumulate. therefore, when solar irradiation is at its highest during the day, it enables energy to continue to be delivered. on the other hand, solar irradiation is at its lowest or utterly unavailable during rainy weather or at night, therefore, no energy can be delivered. thermal storage systems consist of various heating equipment such as pumps, heat exchangers, electrical boilers, and gas boilers. a typical complete solar heat for industrial process (ship) system, at its simplest, consists of a control system, water circulation pump with power supply, hot & cold water storage tanks, piping, monitoring systems and a heat exchanger. to ensure the long-term performance of the overall system and minimize downtime, condition monitoring as well as predictive maintenance of this heating equipment are essential. the ability to forecast, identify, and locate when and where a fault may occur in one part of this equipment and its sub-processes will save maintenance costs and prevent long-term damages to the overall system. machine learning based models describing an industrial process are useful for applications such as anomaly detection, fault diagnosis and forecasting future system characteristics. the remaining useful life (rul) of equipment such as pumps, valves, compressors and batteries refers to the time interval before the equipment experiences failure [5-7]. knowledge about the rul of an equipment is crucial for maintenance engineering practices and engineering system reliability analysis in a plant. rul can be forecast using suitable machine learning models. previous studies have demonstrated the applicability of machine learning models for the analysis of rotating mechanical equipment using sound and vibration measurements, encoder data and temperature measurements [8]. machine learning models are highly datadriven and therefore require high-quality data of a particular process to generate meaningful results. effective measurement and data preprocessing methods are essential. recurrent neural networks (rnn) are a category of artificial neural networks (ann) that work well with time-series data in various applications such as speech recognition and language translation. rnn are the basis for widely used tools worldwide, 257 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 namely google translate and siri by apple [9]. similarly to convolutional and feedforward neural networks, rnn also use training data for learning. the difference is that rnn utilize information from prior inputs to affect current inputs and outputs. traditional convolutional and feedforward neural networks also have a disadvantage since inputs and outputs are assumed to be independent of each other. long short term memory (lstm) rnn is a modified version of the standard rnn with promising performance. lstm rnn has successfully been applied in biomedical signal classification, radar target classification, keyword detection, text generation, and video classification [10-15]. this paper presents the design and development of an evacuated tube solar heat for industrial process (ship) system to generate the thermal energy required in an oleochemical plant. this plant manufactures fatty acids, glycerin, and soap noodles that are the base material for many types of industrial processes such as the manufacturing of household and toilet detergents. a long short-term memory recurrent neural network (lstm-rnn) was used to forecast solar irradiance, solar collector inlet/outlet temperature, and flux calorimeter readings collected throughout a four (4) month period starting from july 2021 and ending in october 2021. existing studies on forecasting of such parameters were carried out only on smaller-scale experimental prototypes. in contrast, in this study, forecasting was carried out for the first time on a larger scale industrial-grade evacuated tube collector solar thermal system installed in malaysia. forecasting of these parameters is essential for the estimation of throughput and of future return of investments (roi). 2. preliminaries 2.1 overview of installed ship system and data collection experimental work and data collection were carried out at an oleochemical process plant based in malaysia. the solar heat for industrial process (ship) at this factory was implemented using a total of 75 evacuated tube collector solar panels (linuo ritter model cpc 1518). each of these 75 solar panels consisted of 18 evacuated tubes. in this factory, solar energy heating was utilized as an energy-efficient replacement for existing legacy gas boilers. evacuated tube solar collectors have a useful life ranging between 20-25 years. therefore, they are a viable option for achieving a long-term return of investment (roi) [16-18]. this ship system was installed at 01°28°57° latitude and 103°54°25° longitude coordinates. this location was selected to avoid the impact of shading effects which would cause a significant reduction of the solar panel efficiency [19-23]. reviews on various factors affecting solar energy performance and machine learning methods applied in the context of solar energy have been described in previous studies [24-26]. the solar panels were positioned on the roof directly above the boiler at an inclined angle of 10°, as shown in fig. 1 and fig. 2. this 10° inclined angle selection was based on the manufacturer’s recommendation to maximize the solar energy that can be generated from the solar panels. the cumulative surface area of these 75 solar panels was 225 m2. the total elevation of the solar panels relative to sea level was 16.35 meters. solar irradiance was measured using a solar pyranometer radiation sensor (rika rk 200-03) which was installed at the roof top close to the etc. five process parameters namely solar irradiance, solar collector inlet/outlet temperatures, and flux calorimeter readings from two points were recorded throughout a 4-month period starting from july 2021 until october 2021. 258 https://www.environmental-expert.com/products/brand-linuo-ritter iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 solar irradiance and solar collector inlet and outlet temperature were collected daily starting from 8:00 am until 7:00 pm with a sampling rate of 15 minutes. flux calorimeter readings were collected hourly every day from 8:00 am until 7:00 pm. the data collected for each process parameter can be represented as a single time series with time steps corresponding to either 15 minutes or 1 hour accordingly. this data was then used in an lstm network for the prediction of future process data. fig. 1: array of evacuated tube collectors (front view). fig. 2: array of evacuated tube collectors (side view with 10 degree inclination). 2.2 process flow and its description fig. 3: overall process flow diagram for ship system. the overall process flow diagram of the evacuated tube solar heat for industrial process (ship) system which was implemented at a malaysian oleochemical process factory is shown in fig. 3. the blue arrows indicate the flow pipes, whereas the red arrows indicate the return pipes with heated water. the process starts by supplying cold water to the coldwater tank, which can store a maximum volume of 20 m3 of water (cold water injection). a pump (pump 1) will then control the flow of water from the outlet of the cold storage tank to the inlet of the heat exchanger. the flow rate of the water being transferred from the cold storage tank to the heat exchanger is fixed at 5.5 m3/hour. a second pump (pump 2) will control the flow of water circulation from the first outlet of the heat exchanger to the array of evacuated tube collectors, generating hot water, which will be delivered to the hot water tank through the heat exchanger. a flux calorimeter (heat meter 1) is used to monitor the thermal energy of the hot water circulating from the array of evacuated tube collectors back into the heat 259 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 exchanger. this flux calorimeter is equipped with a flow meter and two temperature sensors at both the flow and return pipes. the flux calorimeter device calculates the temperature difference between the flow and return pipes. this temperature difference is multiplied by the volume of the water measured by the flow meter and the hot water’s thermal coefficient resulting in the final readings in kilo-watt hour (kwh). the flow rate of the water circulating from the first output of the heat exchanger to the array of evacuated tube collectors and back to the heat exchanger is fixed at 5.5 m3/hour. the hot water from the heat exchanger is then allowed to flow into a hot water storage tank, which can store a maximum volume of 20 m3 of water. industrial grade ultrasonic long body sensors are placed at the top of the hot water storage tanks for liquid level monitoring. these industrial-grade ultrasonic sensors can work in harsh environments and are unaffected by moisture, debris, or heat. a second flux calorimeter (heat meter 2) is used to monitor the thermal energy of the hot water which is circulating from the heat exchanger into the hot water storage tank. finally, a third pump (pump 3) will be used to deliver the water from the hot water storage tank to the oleochemical industrial process. in this process, the input parameters are the solar irradiance and etc inlet temperature. the intermediate parameters are the readings from heat meter 1 & 2. the output parameter is the etc outlet temperature. in this paper, all these 5 parameters will be forecast using an lstm regression network. the data presented in table 1 shows that the value of solar irradiance continuously fluctuates between 50 w/m2 and 95 w/m2. this fluctuation is expected since solar irradiance commonly peaks during midday before gradually declining in the evening. furthermore, the collector inlet temperature fluctuates between 26 and 65 degrees celsius, as reflected in table 2. the first flux calorimeter (heat meter 1) readings have a higher fluctuation range (between 0 kwh and 360 kwh). whereas the second flux calorimeter (heat meter 2) readings vary between 0-125 kwh, as reflected in tables 1 and 2. finally, the solar collector outlet temperature which represents the temperature of the water heated by the solar irradiation fluctuates between 25 and 70 degrees celsius, as reflected in table 3. this heated water will then be delivered for use at a particular oleochemical processing stage. table 1: minimum, maximum, and mean values for solar irradiance and flux calorimeter (heat meter 1) readings month solar irradiance (w/m2) heat meter 1 (kwh) min max mean min max mean july 54.80 83.70 68.20 2.60 302.80 139.30 august 50.80 86.70 70.10 0.04 283.00 150.40 september 54.80 93.70 72.50 0.03 300.10 144.50 october 53.80 94.60 74.50 0.57 366.70 171.60 table 2: minimum, maximum, and mean values for flux calorimeter (heat meter 2) and solar inlet temperature readings month heat meter 2 (kwh) solar inlet temperature (celsius) min max mean min max mean july 0.10 98.60 43.80 26.00 65.70 38.00 august 0.05 114.20 38.50 26.00 55.00 37.00 september 0.03 116.40 47.80 27.00 48.00 34.40 october 0.06 124.90 45.20 27.00 48.00 35.00 260 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 table 3: minimum, maximum, and mean values for solar inlet temperature readings month solar outlet temperature (celsius) min max mean july 24.90 70.00 40.30 august 26.00 68.70 39.00 september 25.80 63.50 37.80 october 26.80 65.70 38.40 3. methodology 3.1 lstm-rnn based forecasting this section describes the forecasting of time series data collected from the solar heat for industrial process (ship) system by using long short-term memory networks (lstm). future time steps of a time series sequence can be forecast by training a sequence-to-sequence lstm network such that the outputs to the network are the input sequence shifted ahead by one time step. at a particular time step of the input sequence, the lstm network learns to forecast the values at the following time step. the time series data of solar irradiance, flux calorimeters (heat meters 1 & 2), solar collector inlet & outlet temperature were each partitioned into training and test data. in each case the first 90% of the time series data sequence was used as the training data and the remaining 10% of the time series data sequence was used as the testing data. standardization/normalization of the training data was performed in order to achieve a better fit and convergence of the lstm rnn training. firstly, the mean of the training data is calculated using eq.(1) as follows: n x = (1) where  is the mean of the training data, x is the summation of all the elements in the training data and n is the total number of elements in the training data. secondly, the standard deviation of the training data is calculated using eq.(2) as follows: n x i − = 2 )(   (2) where  is the standard deviation of the training data and i x is each element in the training data. the normalization of the training data, ix can then be found using eq.(3) as follows:  − = i i x x (3) forecasting the values of future time steps in a sequence of data is then done as follows. two vectors that consist of data extracted from the training data are defined as: predictors = ]...,,[ 1,3,21 −+++ niiii xxxxx responses = ]...,,[ ,4,321 niiii xxxxx ++++ the responses are simply the values of the training data shifted by one time step. the predictors are the training data, excluding the final time step. at a particular time step ix , the lstm network will learn to forecast the value of the following time step 1+ix . the 261 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 same process will be repeated where at the time step 1+ix , the lstm network will learn to forecast the value of the following time step 2+ix . the final forecast will be done at the time step 1−nx where the lstm network will learn to forecast the value at the final time step nx and therefore the training will be completed. the lstm layer was specified to have 200 hidden units. the adam optimization, a widely used extension of the stochastic gradient descent optimization was utilized for training the lstm regression network. the lstm regression network is used due to its high computational efficiency, smaller memory requirements and feasibility for large scale time series forecasting applications. the training was fixed at 250 epochs. the gradient threshold was set to 1 to prevent the gradients from exploding. the initial learning rate was specified to be 0.005 and this learning rate is dropped after 125 epochs by multiplication by a factor of 0.2. the matlab deep learning toolbox is equipped with the ‘predictandupdatestate’ function to execute this step-by-step prediction when used together with a ‘for’ loop. 4. results the lstm networks were then used to forecast solar irradiance, flux calorimeter (heat meter 1 & 2) readings, solar collector inlet, and outlet temperatures. the lstm forecasting was implemented on a hp 15-bw075ax laptop model with an amd a129720p radeon r7 processor and 4gb of ram. the root mean square error (rmse) values between the true and predicted values were calculated using eq. (4) and tabulated in table 4. the actual and forecast values of solar irradiance, flux calorimeter (heat meter 1 & 2) readings, solar collector inlet and outlet temperatures using test data are shown in fig. 4, 5, 6, 7, and 8. solar irradiance, collector inlet and outlet temperature could be forecast well with a low value of rmse, which is less than 1. flux calorimeter readings could be forecast as well by using an lstm network. however, the rmse values obtained were significantly higher since flux calorimeter readings could only be captured hourly. in contrast, solar irradiance, collector inlet and outlet temperature are captured every 15 minutes resulting in more training data to be available for the lstm network. this result confirms that one of the constraints of forecasting is the sampling rate used by the sensors. if increased accuracy of the forecasting is desired, the sampling rate of the sensors should be increased. for comparison, these simulations were repeated using equivalent gated recurrent units (gru) instead of lstm. it was found that lower rmse values can be achieved using lstm compared to gru. n actualpredicted rmse n i  = − = 1 2 )( (4) in fig. 4, the solar irradiance predicted values almost overlap the observed values, resulting in a lower rmse value (0.43457). the lowest errors were for the samples that were within 1800 to 3000. the largest errors were for the samples with the range 600 to 1700. the largest errors were attributed to the fluctuation in solar irradiance which occurred between samples 600 to 1700 as shown in fig. 4. the lower errors for samples in the range 1800 to 3000 were attributed to the steady decline in solar irradiance at this period as shown in fig. 4. in fig. 5, the predicted collector outlet temperature values almost overlap the observed values, resulting in a lower rmse value (0.80517). the error is relatively low throughout the samples except for the presence of an outlier at sample 1050. at this point, 262 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 fig. 4: actual and forecast values of solar irradiance with root mean square error. fig. 5: actual and forecast values of collector outlet temperature with root mean square error. fig. 6: actual and forecast values of collector inlet temperature with root mean square error. there was a sudden rise in the collector outlet temperature and the lstm model was not able to forecast this sudden rise in the collector outlet temperature accurately as compared to the rest of the samples in this time series data. similarly in fig. 6, the predicted collector inlet temperature also overlaps the observed value curves, resulting in a lower 263 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 rmse value (0.43164). although the overall error is relatively low, there is an outlier that also occurs at sample 1050 such that the lstm model could not forecast the sudden rise in collector inlet temperature. the sudden change in the collector inlet and outlet temperature was due to the tripping of pumps that regulate the fluid circulation. the rmse values for forecasting heat meter 1 and 2 were recorded as 61.5091 & 23.8541 respectively and found to be higher than other parameters (solar irradiance, outlet & inlet temperatures). the main reason is that these energy meter readings are being logged hourly, therefore fewer samples of data are available for training the lstm model resulting in a higher rmse value. it can be observed from fig. 7 that the error is higher for samples in the range from 20-70 but lower in other ranges. in the range from 20-70 the lstm model had both underestimated and overestimated the readings for heat meter 1. the higher error at this range is attributed to the fluctuations in the heat meter 1 as well as the limitation in the number of samples of data available. fig.8 shows the actual and forecast values for heat meter 2. a lower rmse value was obtained for the forecasting of heat meter 2 values compared to heat meter 1. this lower rmse value was due to less fluctuations occurring since the heat meter 2 readings steadily rise and decline in a predictable cyclic manner. heat meter 2 readings represent the final delivery of the water to the hot water tank and, therefore less fluctuations. fig. 7: actual and forecast values of the first flux calorimeter readings (heat meter 1) with root mean square error. fig. 8: actual and forecast values of the second flux calorimeter readings (heat meter 2) with root mean square error. 264 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 the results presented in fig. 4, 5, 6, 7, and 8 are summarized in table 4. overall results prove that lstm is a suitable forecasting method to be applied at the backend of data logging systems for displaying forecast values and preliminary analysis. in particular, the forecast for heat meter 2 is beneficial for capacity planning of the factory to plan and meet the day ahead energy demand for their day-to-day operations. table 4: total number of data samples, training time and rmse of lstm network implementation 5. conclusion in this study, a solar heat for industrial process (ship) system was designed and commissioned for implementation at a malaysian oleochemical factory. five process parameters were recorded throughout a 4-month period namely solar irradiance, solar collector inlet/ outlet temperature and flux calorimeter readings. in order to incorporate predictive maintenance, condition monitoring, assisting with planning, and commissioning existing renewable and non-renewable resources, two methods were used to forecast future values of these parameters namely lstm and gru. it was found that rmse values obtained by applying lstm were lower when compared to using gated recurrent units (gru). the results of this study reveal that lstm can be integrated into the backend of existing data logging systems used in process industries in order develop websites that display forecasts of both engineering related parameters and also return of investments (roi). acknowledgement the authors would like to thank the malaysian ministry of higher education for the funding received for this project under the fundamental research grant scheme grant no: frgs19-057-0665. furthermore, the authors would like to thank the iot sata sdn. bhd, the participating factory, and all supporting agencies for providing the technical data and support to carry out this research. supplementary materials the codes for performing the forecasting and also the datasets used in this study are publicly available at the following github repository: https://github.com/ahmadjazlan/lstm-solar-parameter-forecasting references [1] apergis n, payne je. (2012) renewable and non-renewable energy consumption-growth nexus: evidence from a panel error correction model, energy economics, 34(3): 733-738. parameter (s) total data samples training time (minutes) rmse (lstm) rmse (gru) solar irradiance (w/m2) 35337 410 0.43 0.85 heat meter 1 (kwh) 1354 30 61.51 72.34 heat meter 2 (kwh) 1354 28 23.85 35.76 inlet temperature (celsius) 35340 430 0.43 0.78 outlet temperature (celsius) 35340 415 0.80 1.53 265 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 [2] can tansel tugcu, ilhan ozturk and alper aslan. (2012) renewable and non-renewable energy consumption and economic growth relationship revisited: evidence from g7 countries, energy economics, 34(6): 1942-1950. [3] guney t. (2019) renewable energy, non-renewable energy and sustainable development, international journal of sustainable development & world ecology, 26(5): 389-397. [4] kim d, kim kt., park yk. (2020) a comparative study on the reduction effect in greenhouse gas emissions between the combined heat and power plant and boiler. sustainability, 12(12): 5144-5155. [5] yaguo l, naipeng l, liang, ningbo l, tao y and jing l. (2018) machinery health prognostics: a systematic review from data acquisition to rul prediction, mechanical systems and signal processing. 104: 799-834. [6] zhang y, xiong r, he h, and pecht mg. (2018) long short-term memory recurrent neural network for remaining useful life prediction of lithium-ion batteries. ieee transactions on vehicular technology, 67(7): 5695-5705. [7] zhao r, ruqiang y, jinjiang w, and kezhi m. (2017) learning to monitor machine health with convolutional bi-directional lstm networks, sensors, 17(2): 273-290 [8] haedong j, seungtae p, sunhee w and seungchul l. (2016). rotating machinery diagnostics using deep learning on orbit plot images, procedia manufacturing, 5: 1107-1118. [9] wu y. et al. (2016) google’s neural machine translation system: bridging the gap between human and machine translation. preprint at https://arxiv.org/abs/1609.08144. [10] park k, kim j and lee j. (2019) visual field prediction using recurrent neural network. sci rep 9: 8385-8397. [11] yuan l. (2017). recurrent neural networks for classifying relations in clinical notes, journal of biomedical informatics, 72: 85-95. [12] lyu c, chen b, ren y and ji d. (2017) long short-term memory rnn for biomedical named entity recognition. bmc bioinformatics, 18(1): 462-473. [13] zhang f, hu c, yin q, li w, li h-c and hong w. (2017) multi-aspect-aware bidirectional lstm networks for synthetic aperture radar target recognition. ieee access, 5: 26880-26891. [14] chen c and dai j. (2021) mitigating backdoor attacks in lstm-based text classification systems by backdoor keyword identification. neurocomputing, 452: 253-262. [15] ogawa t, sasaka y, maeda k and haseyama m. (2018). favorite video classification based on multimodal bidirectional lstm, ieee access, 6: 61401-61409. [16] lan h, gou z and cheng b. (2020) regional difference of residential solar panel diffusion in queensland, australia, energy sources, part b: economics, planning, and policy, 15(1): 1325. [17] tsuchiya y, swai ta, goto f. (2020) energy payback time analysis and return on investment of off-grid photovoltaic systems in rural areas of tanzania, sustainable energy technologies and assessments, 42(2020):100887-100894. [18] ozcan o, ersoz f. (2019) project and cost-based evaluation of solar energy performance in three different geographical regions of turkey: investment analysis application, engineering science and technology, an international journal, 22(4): 1098-1106. [19] gupta ak, maity t, anandakumar h, chauhan yk. (2021) an electromagnetic strategy to improve the performance of pv panel under partial shading, computers & electrical engineering, 90: 106896-106908. [20] mert bd, ekinci f and demirdelen t. (2019) effect of partial shading conditions on off-grid solar pv/hydrogen production in high solar energy index regions, international journal of hydrogen energy, 44(51): 27713-27725. [21] niazi k, khan ha, and amir f. (2018) hot-spot reduction and shade loss minimization in crystalline-silicon solar panels. journal of renewable and sustainable energy 10(3):033506-1 033506-8 [22] torres jpn, nashih sk, fernandes caf and leite jc. (2018) the effect of shading on photovoltaic solar panels. energy systems 9: 195-208. 266 https://arxiv.org/abs/1609.08144 https://aip.scitation.org/author/niazi,+kamran https://aip.scitation.org/author/khan,+hassan+abbas https://aip.scitation.org/author/amir,+faisal iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 [23] wang d, qi t, liu y, wang y, fan j, wang y and du h. (2020) a method for evaluating both shading and power generation effects of rooftop solar pv panels for different climate zones of china, solar energy, 205: 432-445. [24] akhter mn, mekhilef s, mokhlis h and shah nm. review on forecasting of photovoltaic power generation based on machine learning and metaheuristic techniques, iet renewable power generation 13(7): 1009-1023 [25] akhter mn, mekhilef s, mokhlis h, olatomiwa l and muhammad ma. (2020) performance assessment of three grid-connected photovoltaic systems with combined capacity of 6.575 kwp in malaysia. journal of cleaner production, 277: 123242. [26] akhter mn, mekhilef s, mokhlis h, ali r , usama m , muhammad ma. (2022) a hybrid deep learning method for an hour ahead power output forecasting of three different photovoltaic systems, applied energy, 307: 118185 267 iium engineering journal, vol. 24, no. 1, 2023 akbar et al. https://doi.org/10.31436/iiumej.v24i1.2374 appendix fig. 9: flowchart for matlab programming. no yes time series data inputs (solar irradiance, flux calorimeters (heat meter 1 & 2), solar collector inlet & outlet temperature) partition the data into training and testing data sets (90% for training, 10 % for testing. standardization/normalization of training & test data prepare predictors and responses from training data train lstm networks. predict the following based on the current value and update the network state final prediction made? unstandardized predictions and end program 268 microsoft word 3_v17no2_compiled_v3_26nov16.docx iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 117 innovations in micro/nano patterning using tool-based methods md tanjilul islam and mustafizur rahman* department of mechanical engineering, faculty of engineering, national university of singapore, singapore. *mpemusta@nus.edu.sg (received: 26t h feb. 2016; accepted: 1st jul. 2016; published on-line: 30th nov. 2016) abstract: in recent years, the trend in miniaturization of products has been pervasive in areas such as information technology, biotechnology, and the environmental and medical industries. micro/nano patterning is the key supporting technology that has to be developed to meet the challenges posed by product miniaturization requirements and the industrial realization of nanotechnology. micro/nano patterning techniques can be based on energy beams or solid cutting tools (tool-based micro-machining). tool-based micro/nano patterning is a relatively new area; however, over the last two decades, owing to the predominant trend in the miniaturization of products, micro/nano patterning using tool-based techniques has become a key supportive technology. the energy beambased patterning process (electron-beam lithography) has some limitations due to poor control of 3d structures, low material removal rate, and low aspect ratio. moreover, these processes require special facilities, and the maximum achievable thickness is relatively small. some of these limitations can be overcome by a tool-based approach using ultra-precision machine tools and solid tools as cutting elements to produce the micro-features with well-controlled shape and tolerances. these micro/nano machiningbased patterning techniques have been achieved through a paradigm shift in the ideas and processes of conventional machining. in this paper, an attempt has been made to present the recent innovations in tool-based micro/nano patterning processes. abstrak: pada tahun kebelakangan ini, trend dalam pengecilan saiz produk telah menguasai pelbagai bidang seperti teknologi maklumat, bioteknologi dan industri alam sekitar dan perubatan. pencorakan mikro/nano merupakan teknologi sokongan utama yang perlu dibangunkan bagi menghadapi cabaran keperluan pengecilan produk dan kesedaran industri nanoteknologi. teknik pencorakan mikro/nano boleh dilakukan dengan teknik yang berasaskan rasuk tenaga atau alat pemotong yang kukuh (pemesinan mikro berasaskan alat). pencorakan mikro/nano berasaskan alat adalah perkara yang agak baru; namun dalam tempoh dua dekad kebelakangan ini, oleh kerana trend pengecilan produk semakin berpengaruh, pencorakan mikro/nano menggunakan teknik berasaskan alat telah menjadi satu teknologi sokongan yang utama. proses pencorakan berasaskan rasuk tenaga (rasuk-elektron litografi) mempunyai beberapa batasan kerana kawalan lemah terhadap struktur 3d, kadar pembuangan bahan adalah rendah dan nisbah aspek adalah rendah. selain itu, proses ini memerlukan kemudahan khas, dan ketebalan maksimum yang boleh dicapai adalah agak kecil. sebahagian daripada kelemahan kaedah ini boleh diatasi dengan pendekatan berasaskan-alat, menggunakan alat mesin ultra-precision dan peralatan yang padu sebagai elemen pemotong bagi menghasilkan ciri mikro yang mempunyai bentuk dikawal dengan baik serta had yang boleh diterima. teknik pencorakan mikro/nano berasaskan pemesinan telah dicapai melalui satu anjakan paradigma dalam idea dan proses pemesinan konvensional. dalam kertas ini, suatu percubaan telah dibuat untuk mengemukakan inovasi terkini dalam proses pencorakan mikro/nano berasaskan alat. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 118 keywords: patterning; micro-machining; nano-machining; ultra precision machining; combined machining; hybrid machining 1. introduction owing to recent trends in the miniaturization of products in areas such as information technology, biotechnology, and the environmental, medical and optics industries, the micro/nano patterning process using tool-based micro/nano machining is becoming a key supportive technology. micro/nano patterning using tool-based micro/nano machining includes precision machining processes such as turning, milling, and electrical discharge machining. in most of these processes, material removal is done at the micron level; however, material removal at the submicron level is also achievable using a precision diamond-tool-based machining process. the key advantages of patterning using such a process are that almost every material, including metals, plastics, and semiconductors, can be machined with no limitation for high aspect ratio. on the other hand, microstructures produced by photolithography have the limitations of low aspect ratio and quasi-3d structure [1, 2]. it is possible to fabricate high-aspect-ratio components with submicron structure by the lithographie galvanoformung und abformung (liga) process (german – a combination of lithography, electroplating, and molding) using the synchrotron radiation process and focused ion beam (fib) machining process. however, present laboratoryscale and industrial fabrication techniques using liga require special and extremely expensive facilities like a synchrotron system and the machining of expensive masks that have hindered the quick and economical fabrication of micro parts. furthermore, such processes offer an extremely low dimensional range, and often they are not required for a particular application. the major drawback of the tool-based process is the limitation on machinable sizes; however, this limitation can be overcome in some cases through a hybridized/compound machining process. for example, a combination of conventional turning and nonconventional electrical discharge machining can be used to produce micro hole patterns. thanks to such innovations in recent years, micro patterning using micro machining has become widely accepted for various applications. moreover, in recent years, thanks to the advance in diamond-tool-based machining, for example fts diamond turning, high precision-level patterning has been achieved. consequently, it is possible to manufacture high-precision master tooling for many high-precision roll-to-roll manufacturing processes. if semiconductors and optical devices can be fabricated by rollto-roll manufacturing on large substrates, then many devices could be fabricated at a fraction of the cost of the traditional manufacturing process. all of these advances in micro/nano patterning processes have been achieved as a result of revolutionary innovations in machine tools. in this paper, an attempt has been made to present the recent advances in the machine tools and the machining processes for micro/nano patterning using a tool-based approach. 2. development of state-of-the-art machine tools micro/nano patterning with a tool-based micro/nano machining process has become increasingly popular because of a growing demand for industrial products, with an increased number of functions, and with reduced dimensions, higher dimensional accuracy, and better surface finish. in order to achieve such micro/nano patterning using a machining process, it is necessary to realize a thermally stable machine tool structure. shinno et al. presented an actual design concept of a thermally and dynamically stable machine tool structure [3]. the stable machine tool structure shown in fig. 1 is achieved if iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 119 the following attributes are present: (1) desirable structural design of a machine tool for microand nanometer-scale processing, (2) isolation of the error sources, (3) minimization of the error sources, and (4) control of the error sources. key design factors to be considered include independent metrology frame, symmetric machine structure, heat flow control, minimization of abbe offset, perfect noncontact structure, and active vibration control [3]. fig. 1: concept of stable mechanical tool structure for micro and nanometer-scale processing [3]. in order to rationally meet such processing requirements, micro/nano machining tools capable of producing micro/nano patterning have been produced by the leading machine tool manufacturers and by advanced research institutes around the world. machine tools for micro/nano patterning could be divided into two types. the first type is used for microlevel components, such as high-aspect-ratio micro components. commonly used machine tools in this area include micro-edm, micro turning, micro drilling, and micro milling. the second type is machine tools and processes capable of performing nano finished patterning, and could be defined as those tools which generate surfaces suitable for optical functions. however, this definition does not limit the machine from being used to make surfaces and features intended for mechanical functions. 2.1 machine tools for micro patterning among conventional and nonconventional micro machining techniques, micro-edm is the process most commonly used for patterning. in this area, the leading machine tool manufacturers are sarix, smal tec, mikrotools, and takashima. figure 2 shows a microedm machine from sarix, and a micro-edm and nano grinding machine from small tec. fig. 2: sarixmikro edm machine (left); small tec micro-edm and nano grinding machine (right) [4, 5]. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 120 the key problem of micro patterning using machine tools is that often a single machining process cannot fulfill all the requirements because of the limitations of that process. most machine tools capable of nonconventional machining are not designed to perform conventional machining processes. in recent years, therefore, research institutions and machine tool manufacturers have focused on the development of compound/hybrid machine tools capable of performing two or more manufacturing processes in one single setup/platform. rahman et al. reported that, to achieve effective implementation of compound and hybrid micromachining techniques, four important areas need to be addressed, as shown in fig. 3 [6]. fig. 3: the technologies required for successful development of compound and hybrid micromachining processes [6]. fig. 4: integrated multi-process machine tool from mikrotools (left); multiple function machine from takashima (right) [6, 7]. therefore, the first and most important requirement for the development of the compound and hybrid machining processes is the development of a multipurpose machine tool or the integration of facilities for performing two or more manufacturing processes in one single setup and platform. leading machine tool manufacturers and research institutions have developed machine tools suitable for compound/hybrid machining. the world’s first integrated multi-process machine tool for micro machining has been developed at the national university of singapore (machine model: dt – 110). multiple types of micro machining, e.g. micro turning, micro milling, micro-edm, and microecm, can be carried out on the same machine (fig. 4). this highly flexible machine ensures high rigidity for precision machining. the special features of the developed machine include: (a) miniature machine design, (b) low noise and low heat generation, (c) iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 121 high resolution with full feedback (resolution of 0.02 µm and accuracy of +/-1.0 µm), and (d) the ability to handle multiple processes, such as µ-edm, µ-ecm, µ-milling, µturning and µ-drilling. this technology is patented and licensed to mikrotools pte ltd, a spin-off company of the national university of singapore. fig. 5: micro-edm with on-machine-tool fabrication and on-machine-tool inspection steps in mikrotools dt – 110 machine [8]. 2.2 machine tools for nano patterning nano-level patterning is usually achieved using diamond as a tool to generate precision surfaces on a nanometer scale. in this area, diamond turning has been widely accepted by the industry for more than three decades. diamond turning machines are often equipped with fast tool servo (fts) for its advantages in surface finish and precision level. current turnkey machines have a resolution of up to below 1 nm. however, only a few suppliers in the world can produce such machine tools. the two major market shareholders are ametek precitech and moore nanotechnology systems, both located in keene, new hampshire. at present, these two companies produce two-axis diamond turning machines for simpler applications like contact lens making, as well as multi-axis machines for much more complex applications such as functional free-form surface generation [9]. as with the development of multi-axis machines, an ultra-precision vertical axis has enabled the process of patterning using a diamond micro milling technique. with the further development of more advanced linear motors, hydrostatic slide guides, high resolution grate scales, and high-performance cnc motion control systems, the accuracy and performance of diamond turning will be continuously improved for more complex applications. figure 6 shows two multi-axis machines, built by ametek precitech and moore [10, 11]. fig. 6: examples of multi-axis diamond turning machines: nanoform 700 ultra (left) [10], and nanotech 350fg (right) [11]. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 122 over the years, a lot of development has taken place in the machine tool industry for ultra-precision machining whereby the resolution of machine movement has reached subnanometer scale. however, the challenge of making an affordable ultra-precision machine tool has not been adequately addressed, and no significant research has been carried out in this area. a project was initiated to design, develop and fabricate a highly affordable ultraprecision machine tool at the national university of singapore [12], and a high-speed and low-cost desktop ultra-precision lathe has been reported. this was achieved by incorporating a fast/fine tool servo (fts) system on a precision machine that is to be designed and fabricated using mainstream components at low cost. the machine components and elements are arranged as shown in fig. 7. the arrangement features a high-speed aerostatic work spindle of 15,000 rpm in a t-base 2-axis system mounted on a granite base. a piezoelectric actuator which can actuate forward and backward in very high resolution is used to drive the fts system in the z-axis direction. fig. 7: fts-high speed diamond turning machine (upl –series) [12]. 3. machining process for micro patterning an innovative patterning process is the key supportive technology that has to be developed to meet the challenges posed by the requirements of product miniaturization. in conventional micro-machining operations such as milling, turning, and drilling, machining forces influence the accuracy of the finished micro parts. however, researchers have tried to mitigate this issue by implementing simple engineering solutions. usually, if a manufacturing engineer is asked to fabricate a micro shaft that is 50 µm in diameter and 10 mm in length, the engineer will argue that it is impossible. the usual reason why such a narrow shaft cannot be machined is the insufficient stiffness of the product, which will deflect because of the cutting force, because the engineer will think only of a turning process from the free end of the blank up to the desired length by longitudinal turning, and in this process these dimensions cannot be achieved. however, aziz et al. showed that engineers tend to forget that the problems of both deflection and cutting force can be solved by applying fundamental engineering knowledge. as shown in eq. (1) and eq. (2), they can control the deflection by calculating the step size, which will ensure that even a 50 µm shaft will be able to withstand the deflection without yielding. if step turning is carried out as shown in fig. 8a (path b instead of path a), then the machining of a narrow shaft can be performed easily. machined shafts are shown in fig. 8b [13]. air bearing spindle workpiece diamond tool granite slab fine tool servo piezoelectric stack position sensing detector shroud laser diode position adjustment stage protected plate collet x-a xis z-axis iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 123 deflection, ߜ = ி௟ య ଷாூ = ଺ସி௟ య ଷగாௗర (1) bending stress, ߪ = ଷଶி௟ గௗయ (2) fig. 8: (a) two possible ways to do turning; (b) micro shafts of diameter 50 microns; (c) bending of micro shafts in conventional turning below 50 microns [13]. although step cutting force could be applied to control the deflection in a certain range, in conventional machining a fully straight shaft below 50µm diameter is difficult to achieve (fig. 8c). because of this limit on machinable sizes, conventional micro machining is not suitable for high-aspect-ratio micro patterning. on the other hand, nonconventional machining processes such as micro-edm and micro-ecm have become available over the last two decades as methods for manufacturing microparts and micro patterns. key benefits are the absence of cutting force, and flexibility for machining irrespective of the material’s hardness. through optimization of the process parameters, high-aspect-ratio micro patterning can be achieved using these nonconventional micromachining processes. for example, khalid et al. performed processing of a carbon nanotube forest configuration of a high-aspect-ratio 3d micro-structure. high-frequency pulses were developed to process the nanotube to target shapes in a forest [14]. the optimal dispensation level was established in air with 30 v voltage and 60 ma current for a 10 µm discharge gap. a 5 µm feature in forests with an aspect ratio of 20 has been reported at minimized discharge energy and gap. fig. 9: multi-level micro channel structures patterned in a cnt forest using micro-edm [14]. although stand-alone (single function) machine tools are used as major means to fabricate micro products, in many cases a single micro-machining process cannot fulfill all of the requirements of product miniaturization because of the limitations of that process. the major limitations are in relation to machinable sizes, accuracy, and surface roughness. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 124 however, some limitations on machinable sizes can be overcome through hybridized/compound machining processes. there is no exact definition for a hybrid machining process. from time to time a number of definitions have been proposed by researchers. in 2014, the collaborative working group on hybrid processes of the college international pour la recherche en productique, or international academy for production engineering (cirp), put forward the following definition: hybrid machining processes are based on the simultaneous and controlled interaction of machining mechanisms and/or energy sources/tools having a significant effect on the process performance. the wording “simultaneous and controlled interaction” means that the processes/energy sources should interact more or less in the same processing zone and at the same time [15]. in this paper, on the basis of this definition, combined/ hybrid micro-machining processes are classified as  compound micro-machining processes for patterning  hybrid micro-machining processes for patterning. this section provides a comprehensive review on the recent state-of-the-art innovations in tool-based combined/hybrid micromachining processes. other patterning processes such as coating, laser micro machining, lithography, molding, etching, and assembly of films and substrates are non-tool-based approaches and are therefore not covered in this paper. 3.1 compound micromachining process for patterning as presented earlier, a compound micro-machining process is a combination of two different machining processes in a single set-up applied one after another. this compound micro/nano machining can only be achieved through a paradigm shift in the ideas and processes of conventional machining. in recent years many attempts have been made in the compound micromachining area to combine conventional material-removal processes, such as turning and milling, with non-conventional machining processes like edm, edg, and ecm to fabricate micro parts with high dimensional accuracy. 3.1.1 micro-edm and micro turning micro turning has the capability to produce three-dimensional (3d) structures on microscale. the major drawback of the micro turning process is the limit of machinable sizes and the fact that the cutting forces influence machining accuracy. it is very difficult to achieve a straight shaft below 50 mm in diameter, and in many cases the tool either breaks or starts to wobble, owing to excessive radial cutting force on the micro shaft. therefore, a compound process has been reported by asad et al. [16] where the commercial cutting tool is modified using the micro-edm process to reduce the force component responsible for breaking of the shaft. this compound process is the combination of micro-edm and micro turning in a single setup. first, a commercially available polycrystalline diamond (pcd) tool is modified by the micro-edg process to reduce the nose radius of the cutting tool, thus minimizing the force component that causes shaft deflection during micro turning. commercially available pcd inserts, designed for a light finishing cut, have a relatively large tool nose radius (e.g. 100 µm). this tool nose resolves the cutting force on the shaft into two components, namely fx and fy, as can be seen in fig. 10a. the fy component of the cutting force does the actual cutting, while the fx component causes deflection of the micro shaft. a commercially available pcd insert is modified using the micro-edg process to achieve a very sharp cutting edge, so as to reduce the fx component of the cutting force significantly. this modification of the cutting tool makes it possible to iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 125 achieve a straight shaft of much smaller diameter. the compound process combining micro-edg and micro turning is presented schematically in fig. 10b. a dual-cutter setup is arranged for micro turning, one with a round nose for initial turning up to 100 µm, then a sharp tool for a final cut up to 20 µm. after the micro turning process, the fabricated microelectrodes are used in machining of small and higher-aspect-ratio micro holes by micro-edm on the same machine (fig. 10c). therefore, this compound process is in fact a combination of three steps: modifying the cutting tool using micro-edg, fabricating micro shafts using micro turning, and applying fabricated shafts in micro-edm drilling. figure 11 illustrates the concept of the micro-turning–micro-edm compound machining process. an electrode of required dimension is first fabricated by micro turning prior to micro fig. 10: (a) modification of a conventional cutting tool using the micro-edg (variant of micro-edm) process; (b) a schematic representing the compound process combining modification of a cutting tool by micro-edm and turning of a micro shaft by a modified tool tip; (c) compound process of fabricating a microelectrode using micro turning and applying a fabricated microelectrode in the micro-edm drilling [16]. fig. 11: (a) a 19-mm graphite electrode of 0.5 mm length fabricated by a micro-edg– micro-turning compound process; (b) micro holes (up to 6.5 µm hole in 50 µm plate) fabricated with the microelectrode obtained by the micro-turning–micro-edm drilling compound process [6]. edm. using this compound process, clamping error can be avoided, and deflection of the electrode can be minimized; consequently, the accuracy of machining can be improved. the fabricated microelectrode and machined micro holes pattern using the microelectrode are presented in fig. 11a and fig. 11b, respectively. 3.1.2 micro-edm and micro grinding the fabrication of a miniaturized (sub-100 µm) grinding tool for difficult-to-cut materials like pcd and tungsten carbide (wc) is necessary for the machining of micro iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 126 channels with an improved surface finish. the micro-edm process is found to be capable of machining any difficult-to-cut materials down to the desired dimension. therefore, a compound process is being developed [16] to solve the issues by combining the microedm process with the micro grinding process. in this compound machining process, a pcd tool is fabricated on a machine in a desired shape using the block micro-edg process. the pcd tool contains randomly distributed protrusions of diamond particles with dimensions around 1 µm that serve as the cutting edges for micromachining on glass. when the dimension of the pcd tool is reduced to the required dimension of the grinding tool by the micro-edg process, the binder materials (usually nickel or wc) are removed because they are conductive, thus protruding the diamond particles, which are nonconductive. pcd with a cobalt binder, which can be shaped with micro-edg, is emerging as a tool material for micro grinding of hard and brittle materials. the cobalt binder provides an electrically conductive network that can be removed with edm. the diamond cutting edges are exposed as the discharges erode away the cobalt binder. figure 12 shows the different steps of the micro-edm–micro-grinding compound process with a machining example in bk-7 glass. as can be seen from fig. 12c and fig. 12d, the fabricated slot has a very fine and smooth surface, which is comparable to the surface obtained from ductile mode cutting of glass in macro scale. fig. 12: (a) a schematic diagram showing the block micro-edg process (a variant of micro-edm); (b) a pcd tool before the micro-edg process; (c) fabrication of a micro grinding tool with the micro-edg process; (d) micro channels on glass machined by the micro grinding process with a fabricated pcd tool; and (e) surface finish of the microchannel in glass [16]. fig. 13: (a) a pcd scratch tool produced with the wedg process; (b) a scratch in ule glass produced with the tool shown in (a); (c) a cylindrical 50 mm pcd tool used to cut pockets in ule glass; and (d) a slot ground in ule glass using the tool shown in (c)[17]. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 127 3.1.3 coated edm and wire edm ferraris et al. have demonstrated a process for manufacturing a high-aspect-ratio micro punching die pattern using a coated-edm and wire-edm combined process [18]. initially, micro holes were drilled using a coated electrode. commercial wc tubes, having a diameter of 130 -4/-6 µm and inner hole between 40 and µm were employed as tool electrodes to perform experiments with internal flushing. a parylene c coating was applied on the electrode via chemical vapor deposition. as compared to standard wc tools, parylene-c-coated tools showed better performance in terms of aspect ratio and low tool wear. it is reported that micro holes of about 0.18 mm in diameter and 10 mm in depth (ar 60) are achievable with 30-mm-long tools within 30 min [18]. this highaspect-ratio micro drilling strategy is finally combined with micro wire edm for fabricating a pattern on a micro punching die, as in fig. 14. fig. 14: optical image of a pattern for micro punching (right) fabricated via micro wire edm from a high-precision micro deep hole (left) drilled using a parylene-c-insulated tool electrode [18]. fig. 15: edm surface (left); improved surface after combined milling (right) [19]. 3.1.4 sequential micro-edm and micro-ecm a sequential micro-edm and micro-ecm process is the combination of micro-edm and -ecm processes in a single set-up. the objective is to improve the surface finish generated by the micro-edm, using micro-ecm as a secondary process. usually, a surface machined by micro-edm is relatively rough due to the micro craters and micro cracks produced by micro discharge. zeng et al. reported on a milling process for a 3d micro structure combining micro-edm and micro-ecm. micro-edm shaping and microecm finishing processes were carried out in sequence on the same machine with the same electrode but with a different dielectric medium. the surface roughness of 0.707 µm ra resulting from edm is lowered to 0.143 µm ra by applying micro-ecm finishing [19]. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 128 figure 15 shows the pattern produced by the micro-edm and micro-ecm combined process. for the 3d microstructure pattern, the combined process showed higher accuracy than that achieved merely by micro-ecm milling. 3.1.5 x-ray lithography, electroplating and moulding (liga) and micro-edm micro-edm has many advantages in terms of precision, surface quality, and complex 3d shape formation. however, micro-edm has not achieved widespread use in product manufacturing, primarily because of its productivity drawbacks. for instance, to produce arrays of micro holes, a single electrode is used to machine one hole at a time. moreover, if the number of holes is very high, the electrode may need to be changed in the middle of the machining process. to resolve this issue a compound micro-machining process has been developed by takahata et al., which combines micro-edm and liga. in this combined process, the liga process fabricates arrays of microelectrodes, and then those electrodes are used for the machining of a microstructure with a high-aspect-ratio holes pattern [20]. fig. 16: (a) a 20 ×20 array of liga-fabricated copper electrodes; (b) through-holes batch-machined in 50 mm thick stainless steel by the micro-edm process using the array of electrodes shown in (a) [20]. 3.2 hybrid micro-machining process for patterning as presented earlier, hybrid machining processes are based on the simultaneous and controlled interaction of machining mechanisms and/or energy sources/tools having a significant effect on the process performance [15]. here the wording “simultaneous and controlled interaction” means that at least one machining process is superimposed with input from other types of machining process/energy source. in summary, the processes/energy sources should interact more or less in the same processing zone and at the same time. 3.2.1 simultaneous edm and ecm process (sedcm) with the ceaseless demand towards smaller, thinner and lighter products, many innovations have been made in micromachining for micro and nano applications. among these processes, micro-edm and micro-ecm have the advantage of negligible cutting force due to the non-contact nature of the processes. notwithstanding this advantage, each process has some undesirable effects which limit its capability. by appropriate combination of these two processes, their adverse effects could be significantly mitigated. however, micro-edm operates in non-conductive dielectric fluid whereas micro-ecm employs conductive electrolyte. because of these divergent requirements, micro-edm and micro-ecm are usually used sequentially. this requires the repetitive change of machine iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 129 tool or machining fluid, which hinders the practical use of micro-edm and microecm for micromachining. hence, to overcome the aforementioned issues, a process combining micro-edm and micro-ecm has been reported by nguyen et al. to achieve improved performance on both surface finish and dimensional accuracy [21]. this hybrid machining process is named simultaneous micro-edm and micro-ecm (sedcm). to resolve the machining fluid issue, low resistivity deionized water was used, which has characteristics of both conductive fluid and a dielectric fluid. in addition, short voltage pulses were also applied to localize the material dissolution zone for higher precision. by examining the effect of different pulse parameters, it was found that pulse-on time is the main factor affecting the effectiveness of localization or suppression of material dissolution. the material removal phenomenon of micro-edm in low-resistivity deionized water was then investigated. it was observed that there is a conversion from mere micro-edm to hybrid micro-edm/ecm (sedcm) when the federate is reduced. for predicting suitable machining conditions for sedcm milling, an analytical model was proposed and developed which can indicate critical conditions for transitions of microedm/sedcm/micro-ecm milling in low-resistivity deionized water [21]. fig. 17: simultaneous edm and ecm (sedcm) process carried out in each cycle (edm during on-time and ecm during off-time) to improve the surface finish to mirror finish (machine model: dt – 110) [21]. sedcm was applied to milling to fabricate intricate 3d micro-shapes with enhanced surface finish and dimensional accuracy. micro shapes with surface roughness as low as 22 nm ra have been obtained as shown in fig. 17. 3.2.2 micro-electrochemical discharge machining micro–ecdm is a combination of electrochemical (ec) reaction and electrodischarge (ed) action. ecdm has been investigated by many researchers using different materials [22-26]. figure 18 shows a 3d pattern produced by ecdm process in pyrex glass. fig. 18: examples of 3d microstructure pattern in pyrex glass [27]. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 130 in the ecdm process as a result of the electrochemical action there is a generation of positively charged ionic gas bubbles, e.g. hydrogen (h2). as the dc power voltage is applied between the tool (or cathode) and the anode there is a breakdown of the insulating layer of the gas bubbles, resulting in material removal due to melting and vaporization of the work piece material. fig. 19: material removal mechanism of ecdm process (left) [28]; schematic of ecdm process (right) [29]. 3.2.3 assisted machining process in recent years, some assisted hybrid machining processes for patterning applications have been reported. in assistive hybrid types of machining process, the major machining process is superimposed with input from other types of energy such as ultrasonic vibration, laser, and magnetic, fluid. two major assistive machining processes are vibration-assisted and heat-assisted. researchers have used vibration-assisted machining for patenting in both conventional and nonconventional machining processes. in a conventional vibration-assisted process, reduction in average chippings and better groove shape are reported [30-32]. figure 20 shows an example of the improvement of surface pattern with the aid of elliptical vibration-assisted cutting. besides vibration-assisted machining, laser-assisted machining is receiving attention from researchers [33]. in the laser-assisted process, due to thermal softening at elevated temperature, high-strength materials which are otherwise difficult to machine are often easy to machine. fig. 20: comparisons of pyramid patterns machined by conventional cutting (left) and elliptical-vibration cutting (right) (work piece material: inconel 600) [30]. 4. machining process for nano finished patterning the nano finished patterning process is used for producing surfaces suitable for optical functions, by the manufacturing of a master mould for a roll-to-roll manufacturing process. previously, for optical-level surface generation, the most common process was iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 131 single-point diamond turning. in recent years, with the advances in machine tools, some advanced processes have been developed for nano finished patterning. 4.1 free-form diamond turning the traditional single-point diamond turning process is limited to producing mirror finish on a rotationally symmetrical surface. however, by using fast-tool-servo technology it is possible to produce a pattern whose rotational centre is not coincident with the centre of the part. researchers have also reported other machining techniques, such as an automated guilloche machining technique for non-rotationally-symmetrical patterns [34]. early fast tool servos were limited in the amount of off axis displacement that was possible. recent innovations such as long-stroke fast-tool-servo technology enable offaxis displacement up to 1 mm at 100 hz bw and 6 mm at 20 hz bw [35]. fig. 21: fts diamond-turned faceted mirrors (left); fts diamond turned finished freeform micro-lens array mould insert containing 1,219 single spherical lenslets (right) [36, 37]. non-rotationally-symmetrical applications often require displacement of more than a few mm. this problem can be tackled through innovated slow-slide servo technology, where the main linear slides of the machine can be controlled with precision of the main spindle rotation. keong et al. have proposed a method to extend the limited stroke length of fts without modifying an existing fts system by generating a layered tool trajectory [38]. 4.2 diamond micro milling development of an ultra-precision vertical axis has enabled machining of optical surfaces using micro milling. complex micro lens array patterns, gratings, and optical moulds can be manufactured in this process [35]. fig. 22: micro-lens array pattern generated by diamond micro milling of each lens individually [37]. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 132 fig. 23: machined micro-array lens with a pyramid shape on the surface sample using a rotating cutting tool controlled by an electromagnetic actuator [39]. kim et al. proposed a new rotating spindle system with a rotating cutting tool controlled by an electromagnetic actuator. a pid controller was adopted to make the system stable, and adaptive feed forward cancellation is used to compensate effectively for the run-out of the spindle system during machining. the machining results show that this compensation improves the pattern accuracy [39]. 4.3 diamond turning for master tooling ultra-precision diamond turning is the foundation for generating the master tooling for many roll-to-roll embossing processes. however, the roll-to-roll processing process for many applications is still in the development stage. if semiconductors and optical devices can be fabricated in this way on large substrates then many devices could be fabricated at a fraction of the cost of the traditional manufacturing process. in recent years, therefore, a few new machining processes for the preparation of master tooling for roll-to-roll embossing have been reported by researchers. 4.3.1 direct patterning of a radial fresnel lens on a roller mould the conventional fts diamond turning process is not capable of machining steep circular grooves on the roller, because of the fixed tool–work piece relative position and limited degrees of freedom. a radial fresnel lens comprises a series of central symmetric steep circular grooves. therefore, direct diamond turning of radial fresnel lens structures on a roller mould was considered unfeasible, due to their fixed tool–work piece relative position and limited degrees of freedom. figure 24 schematically describes the inability of the ultra-precision diamond turning approach to generate radial fresnel lens structures on a roller. the dark shaded zone represents the portion where the work material cannot be removed owing to the steep circular groove profiles and the fixed cutting angle. fig. 24: inability of the ultra-precision diamond turning method to machine a radial fresnel lens on a roller [40]. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 133 a novel process named synchronized tool and roller (str) diamond machining has been reported by huang et al. to solve the problem illustrated above which is currently faced by the industry [40]. a four-axis synchronized tool work piece interactive motion is designed to realize precise machining of the radial fresnel lens microstructures containing steep circular grooves on the outer cylindrical surface. the potential of the str diamond machining process has been demonstrated by direct machining of a radial fresnel lens structure with 10 mm diameter and 8.25 nm surface roughness on a roller mould in 8 h, which satisfies the industry’s requirement of high-precision optical roller moulds. fig. 25: 4-axis integrated tool-work piece motion [40]. 4.3.2 engraving/patterning for roll-to-roll gravure printing roll-to-roll gravure printing has received great attention in recent years owing to its superior performance compared with the conventional silicon-based semiconductor industry. currently available roller gravures have a large gravure width (usually 25µm). so it is often difficult to scale down the printed line width, which is crucial for the film’s circuit density, resolution and transparency. zhang et al. proposed a novel method called diamond micro engraving to reduce the ink volume transfer read during the machining process. a v-shaped sharp diamond tool, two linear axes and one rotary axis of ultraprecision machine was used to miniaturize the line width to 7 µm [41]. fig.26: gravure roller with a specified pattern for metal mesh printing [41]. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 134 fig. 27: scaling down of printed line width using gravure rollers machined by dme [41]. the researchers demonstrated the performance of the dme-machined roller moulds. by replacing the laser-engraved roller with the gravure rollers machined by dme, the line width of printed metal mesh film, which works as a kind of transparent conductive film used in touch screen modules, was reduced from 47 µm to 19 µm, and its transmittance for visible light was increased from 65.2% to 80.4% [41]. 5. conclusion in this paper, a short review on recent innovations in tool-based micro/nano patterning has been provided. tool-based micro-and nanometer-scale processing is one of the core technologies for patterning applications. with the development of machine tools and machining processes, more tool-based patterning processes are finding applications in the areas previously dominated by lithography-based processes. future machine tools for micro-and nanometer-scale processing require a machining capability of sub-nanometerorder resolution to find patterning applications in areas that are currently dominated by lithography-based processes. references [1] okuyama h, takada h. (1998) micromachining with sr and fel. nuclear instruments and methods in physics research section b: beam interactions with materials and atoms, 144(1-4):58-65. [2] rajurkar kp, yu zy. (2000) 3d micro-edm using cad/cam. cirp annals manufacturing technology, 49(1):127-130. [3] shinno h, (2014) 11.02 machine tools for microand nano-meter scale processing, in comprehensive materials processing, yilbas, ed., elsevier, oxford, 15-26. [4] sarix the best micro edm technology [http://www.sarix.com/] [5] smal tec [http://www.smaltec.com/] [6] rahman m, asad a.b.m.a, masaki t, saleh t, wong y s, senthil kumar a (2010) a multiprocess machine tool for compound micromachining. int. j. machine tools and manufacture, 50(4):344-356. [7] takashima. [http://www.takashima.co.jp/en/index_e.html] [8] mikrotools, [http://mikrotools.com/] [9] zhang xq, woon ks, rahman m. (2014) 11.09 diamond turning, in comprehensive materials processing, yilbas, ed., elsevier, oxford, 201-220. [10] precitech nanoform 700 ultra, [http://www.precitech.com/products/nanoform700ultra/nanoform_700_ultra.html] [11] moorenanotech 350fg [http://www.nanotechsys.com/machines] iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 135 [12] rahman m, asad a.b.m.a, masaki t, saleh t, wong y s, senthil kumar a. (2010) compound micro/nano machining – a tool-based innovative and integrated approach, in key engineering materials. trans tech publ. [13] azizur rahman m, rahman m, senthil kumar a, lim h s. (2005) cnc microturning: an application to miniaturization. int. j. of machine tools and manufacture, 45(6):631-639. [14] khalid w, ali mohamed s m, dahmardeh m, choi y, yaghoobi p,nojeh a,takahata k (2010) high-aspect-ratio, free-form patterning of carbon nanotube forests using micro electro discharge machining. diamond and related materials, 19(11):1405-1410. [15] lauwers b, klocke f,klink a,tekkaya a e,neugebauer r, mcintosh d (2014) hybrid process in manufacturing. cirp annals manufacturing technology, 63(2):561-583. [16] asad abma, masaki t, rahman m, lim h s, wong y s (2007) tool-based micromachining. j. materials processing technology, 192-193:204-211. [17] morgan, cj, vallance rr, marsh er. (2006) micro-machining and micro-grinding with tools fabricated by micro electro-discharge machining. int. j. nanomanufacturing, 1(2):242258. [18] ferraris e, castiglioni v, ceyssens f, annoni m, lauwers b, reynaerts d. (2013) edm drilling of ultra-high aspect ratio micro holes with insulated tools. cirp annals manufacturing technology, 62(1):191-194. [19] zeng z, wang y, wang z, shan d, he x. (2012) a study of micro-edm and micro-ecm combined milling for 3d metallic micro-structures. precision engineering, 36(3):500-509. [20] takahata ki, gianchandani yb. (2002) batch mode micro-electro-discharge machining. j. microelectromechanical systems, 11(2):102-110. [21] nguyen md, rahman m, wong ys. (2012) simultaneous micro-edm and micro-ecm in low-resistivity deionized water. int. j. machine tools and manufacture, 54–55:55-65. [22] wüthrich r, hof la. (2006) the gas film in spark assisted chemical engraving (sace) a key element for micro-machining applications. int. j. machine tools and manufacture, 46(7-8):828-835. [23] sarkar br, doloi b, bhattacharyya b. (2006) parametric analysis on electrochemical discharge machining of silicon nitride ceramics. int. j. adv. manuf. tech., 28(9-10):873881. [24] cao xd, kim bh, chu cn. (2009) micro-structuring of glass with features less than 100 µm by electrochemical discharge machining. precision engineering, 33(4):459-465. [25] cheng c-p, wu k-l, mai c-c, yang c-k, hsu y-s, yan b-h (2010) study of gas film quality in electrochemical discharge machining. int. j. machine tools and manufacture, 50(8):689-697. [26] yang c-k, cheng c-p, mai c-c, cheng w a, hung j-c, yan b-h. (2010) effect of surface roughness of tool electrode materials in ecdm performance. int. j. machine tools and manufacture, 50(12):1088-1096. [27] zheng zp, cheng wh, huang fy, yan bh. (2007) 3d microstructuring of pyrex glass using the electrochemical discharge machining process. j. micromechanics and microengineering, 17(5):960-966. [28] bhattacharyya b, doloi bn, sorkhel sk. (1999) experimental investigations into electrochemical discharge machining (ecdm) of non-conductive ceramic materials. j. mater. processing tech., 95(1-3):145-154. [29] chavoshi sz, luo x. (2015) hybrid micro-machining processes: a review. precision engineering, 41:1-23. [30] kim g, loh b. (2011) direct machining of micro patterns on nickel alloy and mold steel by vibration assisted cutting. int. j. prec. engin. manuf., 12(4):583-588. [31] kim g, loh b. (2013) cutting force variation with respect to tilt angle of trajectory in elliptical vibration v grooving. int. j. prec. engin. manuf., 14(10):1861-1864. [32] ammouri a, hamade r. (2012) bueva: a bi-directional ultrasonic elliptical vibration actuator for micromachining. int. j. adv. manuf. tech., 58(9-12):991-1001. [33] sun s, brandt m, dargusch ms. (2010) thermally enhanced machining of hard-to-machine materials a review. int. j. machine tools and manufacture, 50(8):663-680. iium engineering journal, vol. 17, no. 2, 2016 islam and rahman 136 [34] neo dwk, kumar as, rahman m. (2015) an automated guilloche machining technique for the fabrication of polygonal fresnel lens array. precision engineering, 41:55-62. [35] luttrell de. (2010) innovations in ultra-precision machine tools: design and applications. japan society of precision engineering, japan, 2-2:1-4. [36] scheiding s, yi allen y, gebhardt a, li l, risse s, eberhardt r, tünnermann a (2011) freeform manufacturing of a microoptical lens array on a steep curved substrate by use of a voice coil fast tool servo. optics express, 19(24):23938-23951. [37] infrared [http://www.iiviinfrared.com/index.html] [38] keong nw, kumar as, rahman m. (2012) a novel method for layered tool path generation in the fast tool servo diamond turning of non-circular microstructural surfaces. proceedings of the institution of mechanical engineers, part b: j. engineering manufacture, doi: 10.1177 [39] kim j, lee s-k. (2006) micro-patterning technique using a rotating cutting tool controlled by an electromagnetic actuator. int. j. machine tools and manufacture, 101:52-64. [40] huang r, zhang x, rahman m, kumar a s, liu k (2015) ultra-precision machining of radial fresnel lens on roller moulds. cirp annals manufacturing technology, 64(1):121124. [41] zhang x, liu k, sunappan v ,shan x (2015) diamond micro engraving of gravure roller mould for roll-to-roll printing of fine line electronics. j. mater. processing tech., 225:337346. microsoft word 240 completed iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 179 epistemology an islamic perspective m. azram department of science, faculty of engineering international islamic university malaysia po box 10, kuala lumpur 50728, malaysia. azram50@hotmail.com abstract: since man is the vicegerent of god in this world. and in order to enable him to fulfill his responsibilities (of his vicegerency), god has endowed man with the potentials of creative & conceptual knowledge. it becomes incumbent upon him to mould knowledge in the framework provided by islam. thus all types of knowledge whether it is natural science, social science or even pure science, should be understood with the aim to establish an islamic system. in this paper we will discuss the background of epistemology, different areas of epistemology-like source, types (revealed and derived), elements in islam, principles (unity of allah, unity of creation,and unity of thoughts) and limitations. abstrak: manusia merupakan khalifah allah di muka bumi ini. agar manusia dapat menjalankan tugasnnya (sebagai khalifah), allah telah memperkenankan manusia dengan kebolehan berkreatif dan berfikir. manusia diwajibkan keatasnya untuk mempergunakan ilmu seperti yang dirangkakan dalam agama islam. dengan itu, segala jenis ilmu sama ada sains semula jadi, sains sosial atau pun sains tulen, perlu difahami dengan tujuan membentuk sistem islam. kertas ini mengkaji latar belakang epistemologi, pelbagai sumber ilmu yang berbeza, jenis (yang didedahkan dan diterbitkan), elemen dalam islam, prinsip (keesaan allah, keesaan kewujudan dan keharmonian pemikiran) dan batasannya. 1. introduction epistemology, (which comes from the greek word episteme) inquires into the nature of knowledge and justification of belief. indeed, many writers prefer to use the label “the theory of knowledge”, “epistemology, however has an advantage of being a philosophical term of art, whereas the theory of knowledge could also apply to the investigators of sociologists of knowledge and historians of ideas”, for example [1]. 'knowledge' falls short of expressing all the aspects of 'ilm. knowledge in the western world means information about something, divine or corporeal, while 'ilm is an all-embracing term covering theory, action and education [2]. naquib al attas had once made a very interesting observation. he noted that, “all wisdom is knowledge but all knowledge is not wisdom.” sometimes what we assume knowledge to be, is in real only the contemplation of man. the more this contemplation becomes consolidated with facts, the more it comes near to truth, wisdom. therefore wisdom can be considered the final stage of man’s contemplation, which could be according to qur’an, either, ‘ilm al – yaqin’ (q:120:5), ‘ain al yaqin’(q:120:7), or ‘haqqul yaqin’ (q:69:51). hence the difference between wisdom and knowledge could be considered as the progress of human thought’. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 180 the commencement of human thought is ‘raib’ (fantasy), (q:9:25), and the end is yaqin (certainty) (q:120:5&7). the beginning of this journey is aided by ‘ta’wil’ (interpretation). however, it should be done by those who have a firm ground in matters of knowledge; those, who are considered the people of understanding. in this paper therefore, the different areas of epistemology like the source, types, and principles of knowledge will be discussed, to get a brief idea of the philosophical topic. 2. source of knowledge the islamic conception of the sources of knowledge differs from the conception of materialistic atheists; which makes existence their only source and cannot conceive of a methodology of knowledge except that by which the realities of the physical universe became known. it also differs from the other religious metaphysical conceptions. the pivotal difference between islamic concept and these other systems is that the latter establishes proofs from the observable universe for its claim that there is a second source of knowledge, i.e. revelation, while the materialists deny this reality, which is indicated by the source of knowledge they acknowledge, which places them in contradiction; the proponents of other religious metaphysical conceptions believe in sources for which they possess no trace of proof for their authenticity. the divine revelation has always been considered as the ultimate source of knowledge but it was never the sole. muslim thinkers from the past consistently tried to acquire detailed knowledge about how to derive the rules and concepts of the qur’an, but they developed these only on the basis of common sense instead of a unifying methodology [3]. the only approach to qur’an should be after the priors are fulfilled: 1) the first requirement for understanding the qur'an is to understand the arabic language. 2) the second requirement is what we call "tafseerun-nassi bin-nass." nass is a statement. statement in the qur'an must be interpreted, after we know the general arabic meaning, by going to the qur'an itself. because the qur'an as they say in arabic, "yufassiru ba'duhu ba'dan” itself explains the qur'an. 3) the third requirement for a proper understanding of the qur'aan is the sayings, the commentaries, the explanations of the prophet sunnah, and after him, his companions. 4) if there is consensus, ijmaa', that has to be taken to be the meaning of the ayah or the hadeeth of the prophet (pbuh). there is also what is called qiyas. qiyas is not a means of obtaining facts directly from the qur'an but it is a way of knowing the ruling, the "hukm", of something which is not mentioned specifically in the qur'an. qiyas as the word analogy explains: we read in the qur'an and the hadeeth that the ruling on a is b. now, we find something x which is similar to a. so we say that the ruling on this x is also b, because of the similarity between the two. 5) a very important requirement is sincerity. any person, even if he is not a muslim, he can master the language, he can read and learn by heart the ahaadeeth of the prophet, or the verses from the qur'an, he can know the superficial meaning of these verses, but allah will give the real meaning, the meaning that influences a person's life and gives him hidaayah, guidance, only to someone who is sincere. iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 181 therefore, the main sources of knowledge in islam have to be the qur‘an and the sunnah of the prophet (pbuh). for acquired knowledge also has to have the basis from these main sources of knowledge. 3. type of knowledge there are two main types of knowledge accepted by many islamic scholars: revealed knowledge and derived knowledge. 3.1 revealed knowledge the first type of knowledge, also known as al-wahy, can be further broken into two more types; the instinctive knowledge and the knowledge revealed to us through the prophet (pbuh). divine revelation explicates to us two very important concepts, ‘fikr’ (reflection) and dhikr (contemplation/remembering). fikr is the quest for knowledge through the ayat (signs) of allah (swt) while dhikr is a recollection of previously given knowledge. it is fikr that is rational and attempts to ‘reach’ god, i.e. the final stages of ilm al yaqin and ain al yaqin. however dhikr, does not and cannot ‘reach’ god through rational methods. therefore when we do dhikr, instead of really remembering god, we actually praise him! in other words, we are not really recollecting the previous knowledge {example, the covenant that man took with allah (swt)}. rather allah simply admonishes us to praise him as remembering him through the only means humans have, rationality, is not possible. thus in fikr, we try to ‘reach’ god while in dhikr we tend to praise him rather than trying to ‘reach’. it is the co-relationship between these two concepts that give us the final notion of knowledge in islam. “verily in the creation of the heavens and the earth, and the alternation of night and day there are indeed signs for men of understanding; men who remember allah, standing, sitting, and lying down on their sides, and contemplate the creation of the heavens and the earth (with the thought) "our lord! not for nothing have you created (all) this. glory to you! give us salvation from the suffering of the fire" (q:3:190-191). the qur’an reminds us that we have to remember allah all the time and thus do dhikr, while fikr has already helps man to look for the signs of allah. "it is he who brought you forth from the wombs of your mother you did not know a thing, and he gave you hearing, sight, and mind in order that you may give thanks"(q:16:78). from this verse we can see that a baby is born without any knowledge, and it is the mercy of allah to bestow him with fitrah. even the prophet (pbuh) said in a hadeeth, “every child is born with a pristine nature (fitrah); then his parents make him a jew or a christian or a magician.” 3.2 derived knowledge the second type of knowledge is acquired knowledge. this type of knowledge is also from allah but humans are supposed to use islamic methodology and the faculties given by allah to acquire this knowledge. through their senses, research and deep thinking, can iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 182 they conceptualize, acquire, comprehend and search this type of knowledge. again, the sincerity in the search is an important prior. there are two types of knowledge in the qur’an. they are: a) ilm (knowledge) which belongs to god wherein there is no question of ‘zan’ (conjecture) (q:4:157). b) ilm (knowledge) which progresses from raib to yaqin. 4. elements of knowledge in islam the topic of discussion here is the elements of knowledge in islam. a question that could spout in one’s mind would be, “are the elements of knowledge in islam essentially different from other disciplines of knowledge?” many scholars have answered this question according to their own specific perceptions. we have scholars like ibn rushd (or averroes) most prominently, followed by ibn sina (or avicenna) and also al farabi. these scholars adamantly believed that scientific thought and the qur’anic revelation were essentially synonymous due to many inherent common qualities like reason. this concept of reason itself had emanated from aristotle and these scholars desperately attempted to reconcile both reason and revelation. it could perhaps be better understood in the word of sarton: “the whole history of medieval thought, in almost every part of the world, is dominated by a continuous and desperate endeavor to reconcile the facts of rational experience with some system of knowledge (revelation) considered a priori as perfect and unimpeachable.”[4] however we have many muslim scholars who had taken the bold step of moving against this strong wind of modern thought. the first and foremost is ghazali. ghazali was the first among the contemporary scholars of his time to be skeptical of the infallibility of sense perception and therefore rested his philosophy on principles that were intuitively certain [5]. he freed himself of ‘taqlid’ (acceptance without proof) and rejected the authority of human teachers. according to him, “to attain to knowledge of the realities of things it is indispensable to ascertain what knowledge means”[6]. thus he began to place science, philosophy and reason in position inferior to religion and theology, an approach which was happily accepted by the scholastics. he then managed to create such a culture, that medieval philosophy almost completely transformed itself to what gazalli had propounded though ibn rushd still persistently adhered to his belief and even wrote a critique on al ghazali, ‘tahafut al-tahafut’(incoherence of incoherence). another scholar in the later times was muhammad iqbal, who agreed to ghazalli’s notion and rejected the philosophy of ibn rushd. he says: “ghazali’s chief opponent, ibn rushd who defended greek philosophy against the rebels, was led through aristotle to what is known as the doctrine of immortality of active intellect, a doctrine which once wielded enormous influence on the intellectual life of france and italy, but which to my mind, is entirely opposed to the view that the qur’an takes of the value of destiny of the human ego. this ibn rushd lost sight of a great and faithful idea in islam and unwatingly helped the growth of what enervating philosophy of life obscure man’s vision of himself, his god and his world.[7]” iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 183 we have seen the views of some of the scholars of islam on the theory of knowledge in islam. comprehending what the term ‘knowledge’ means in islam, and understanding the ‘theory of knowledge in islam’, we can now proceed to the final part of this article, the principles that make up the theology of islam. 5. basic principles of knowledge 5.1 unity of allah (tawhid) this is the first and foremost principle. this principle states that allah (swt) is the only creator of everything and that he is absolutely one, and that everything is separate and different from him as a creator. it is therefore the duty of a muslim to give allah (swt) his due recognition, love and obedience. hence it becomes incumbent upon a muslim to have allah (swt) constantly present in one’s consciousness. thus the qur’an says that true muslims are those who: …who celebrate the praises of allah, standing, sitting, and lying down on their sides and contemplate the (wonders of) creation in the heavens and the earth, (with the thought) “our lord! not for naught has thou created (all) this glory to thee! give us salvation from the penalty of fire. (q:3:191) it is necessary therefore to accept the authority of allah (swt). in cases where this authority is not conceded, the following problems result that make man incapable of searching knowledge and understanding knowledge: a) lack of faith: this puts a veil in front of our eyes and we become incapable of understanding the message of the qur’an as we do not believe in allah (swt): “say: consider what is in the heavens and the earth; and signs and warners do not avail people who would not believe.” (q:10:101) b) blind imitation: this puts blinkers on their eyes and they begin to see the path which has been shown to them by parents and the people in power. “and they shall say: o our lord! surely we obeyed our leaders and our great men, so they led us astray from the path.” (q:33:67) c) superstitions: when we believe that allah (swt) is the sole creator of everything and thus begin to follow his commands, we are saved from baseless superstitions. “and they have no knowledge of it; they do not follow anything but conjecture (zan), and sure conjecture does not avail against the truth at all.” (q:53:28) 5.2 unity of creation when we believe that there in the concept of unity of god, then quite logically we should also believe that there should be unity in his creation. khalil has noted this point very well and explains: “it is self-evident that the qur’anic and scientific data should coincide and correspond (in the general sense and outside the realm of relativities and variables), and it is obvious that there should be no contradictions or barriers between them.” iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 184 natural or pure science is basically the study of the creation of god. khalil has succinctly expounded the relationship of science with quran. he says that there are basically four main categories. the first is about the philosophy of science and the theory of knowledge. the second category facilitates us with the methodology of discovering scientific facts. the third informs us of the laws that apply in the various fields of science, i.e. the creation (natural or pure science) while the fourth admonishes us that those laws that have been discovered through experimental methodology should be applied by a muslim as a vicegerent of allah (swt) to create a just society. he calls this field, the applied sciences. according to him therefore, we should use these scientific laws created by allah (swt) for creating a civilization where people comply with the commandments of allah (swt) and therefore are able to live in a just and peaceful society. i would like to discuss here the notion of causality as it is linked directly to the concept of unity of creation. to put it succinctly, this concept states that everything has a cause. there are two basic fundamentals attached to this principle: a) the principle of determinism – every cause has an effect and that without a cause it is impossible to have an effect. b) the principle of uniformity of nature: similar causes ensue similar effects. there is an assumption that has been going on for a very long time. according to many scientists there are certain laws that are governing our physical universe. the principle of causality gives meaning to the application of any law used to explain natural phenomenon. there are many instances in the qur’an that speak about this too: “then should they wait for aught except the way of the former people? for you shall not find any alternation in the course of allah.” (q:3:43) another verse that is in consonance to the concept of causality is: “the nature made by allah in which he has made men; there is no altering of allah’s creation” (q:30:30) however some asharite scholars like al-ghazali and al-razi, believe that adhering to this concept would imply that allah (swt) is dependent on the causality factor. there are again other scholars who have accepted this concept of causality like faruqi. he observes that: “the causal and finalistic interconnections of the objects of creation are the substance of the subservience, which would be futile and meaningless without them. if man could not depend upon causes to bring about their effects or the means not to be good for the ends, he would quickly lose interest in creation and give up any attempt to transform it into the ought – patterns revealed by allah (swt)[8]”. contemplating at both views critically, the notion of faruqi is more feasible. this is because the causality concept itself can be considered a creation of allah (swt). there is a reason behind every creation of allah (swt). here we could assume that allah (swt) has created this causality factor to act as a stimulant to man so that he can work to achieve means. golshani has explicated this concept very well: “…what is commonly called a cause is implying an intermediary or preparing cause, rather than the efficient cause” the role of intermediary means i to prepare the ground for the creation of everything, but he creates everything through definite intermediary and preparing causes, and these are themselves created by allah (swt)”[9]. 5.3 unity of thought (revelation and reason) iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 185 we had seen above that when the source of science and qur’an are the same, they cannot logically contradict each other. the same is veracious for revelation and reason. revelation is by allah (swt) and reason, just like causality, is created by allah (swt) to act a stimulant for man. al ghazali had also subscribed to this comprehension when he spoke of the ‘division in knowledge’. according to him, in the categorization of knowledge, shari (which depends ultimately on revelation) and aqli (which depends on reason), are not really in themselves distinct. in his words, “…most shari knowledge is aqli to him who know it and most aqli knowledge is shari to him who understands it [10]. it is quite evident that revelation and reason share inherent qualities. however it would be incorrect to say that both are exactly the same. this is because reason is just based on the zahir (what can be seen). however the qur’an is replete with verses that speak about the many physical phenomena that man is unable to see: “but nay! i swear by that which you see, and that which you do not see”. (q:69:38-39) “he created the heavens without pillars as you see the…”(q:31:10) this is where the drawbacks of reason commence. it is unable to see and therefore perceive many physical phenomena. in other words, reason on its own is based on incomplete empirical data. thus the conclusions it makes on its own cannot be guaranteed to be correct. thus, faruqi rightly concludes that: “reason will be well balanced only when it submits to the guidance of revelation as to the ultimate aim of existence” [11]. to put it succinctly, we acknowledge the limitation of human mind. therefore we do not only want to make use of the human invention system, trial and error. 5.4 unity of man allah (swt) had created adam (ra) and taught him the “name of things”. then allah (swt) ordered all the angel to prostrate before adam (ra) when they could not say the name of things which he had taught to adam (ra). an interesting point that qadir notes here is that the angels were asked to prostrate to adam (ra) due to the superiority adam’s wisdom and not his piety. it is obvious that in terms of piety, the angel eclipsed adam. however, allah (swt) still commanded them to prostrate before adam due to his superiority of knowledge [12]. this not only reveals the importance of knowledge, but also the great responsibility. man has been placed in this world as a vicegerent of allah (swt). therefore it becomes his duty to make use of this knowledge as one of the means to achieve his ends, both physical and spiritual. khalil has therefore rightly observed that: “muslims cannot carry out their functions as vicegerents, or obtain sufficient guarantees and assistance to enable them to achieve their objectives of perpetual progress unless they use scientific research methods and methodologies to discover the laws of the world, nature, and the cosmic system.” it would be futile to speak on this unless a very prominent scholar of islam, faruqi’s integrated view on man, knowledge and his purpose of life are not comprehended: “islam’s view of man. allah (swt) has appointed him to achieve two objectives. first, humans should transform creation into divine patterns, i.e., to rearrange its materials so as to make them fully and beneficially serve human needs, which are materials( food, shelter, comfort, procreation) as well as moral intellectual, and esthetic. second, in the very act of transforming creation, humans need to give substance to ethical values by choosing to enter iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 186 into those acts of transformation in an ethical way, i.e., in a way that fulfills the requirements of devotion to allah (swt) and justice to mankind”[13]. 6. limitations of human knowledge even though seeking knowledge is considered on of the basic steps towards understanding allah, humans are incapable of perceiving some knowledge which is unseen or cannot be perceived with our limited senses. as allah states in the qur‘an: “i swear by what you see and what you do not see…”(q:69:38-39) “glory be to him who created pairs of all things, of what the earth grows, and of their kind and of what they do not know…”(q:36:36) the faith in the limitation of human knowledge and the unseen is an incentive for us not to stop our mind at the sensory stage and never think that we have discovered everything [14]. the quest of knowledge is endless for a muslim, and he must be sincere. he must just not fall out of the unique methodology of acquiring knowledge or understanding the divine scriptures; the holy qur‘an. 7. conclusion in islam 'ilm is not confined to the acquisition of knowledge only, but also embraces socio-political and moral aspects. knowledge is not mere information; it requires the believers to act upon their beliefs and commit themselves to the goals which islam aims at attaining. in brief, the theory of knowledge in the islamic perspective is not just epistemology. it combines knowledge, insight, and social action as its ingredients. the main sources of knowledge for muslims will eternally be qur‘an and the sunnah. if we hold on to these two sources of knowledge, we will not fall prey to any unislamic activity. understanding the different types of knowledge and the principles behind the theory of knowledge will remain the basis of islamic philosophy. thus before going through any type of knowledge we must begin with unity of allah that leads us quite logically to the unity of his creation. the unity of allah and his creation form the fundamentals for the basis of thought that should be in islam. this is called the unity of thought. all these principles provide the aim and purpose of life for man-vicegerency (khilafa). this is the principle of unity of man. since man is the khalifa, it becomes incumbent upon him to mould knowledge in the framework provided by islam. thus all types of knowledge whether it is natural science, social science or even pure science, should be understood with the aim to establish an islamic system. the understanding of these sciences is done with the help of the principle expounded above that form the basis of the theory of knowledge in islam. references [1] e. cooper, david, epistemology the classic readings, university of durham, (usa,1999), p. 1 [2] akhtar, dr. sayyid wahid, al-tawhid the islamic concept of knowledge, vol xiii no.3, (dubai ,2001) iium engineering journal, vol. 12, no. 5, 2011: special issue on science and ethics in engineering azram 187 [3] safi, louai, the foundation of knowledge: a comparative study in islamic and western methods of inquiry, selangor darul ehsan, malaysia, international islamic university and international institute of islamic thought, malaysia, 1996, pp. 180-182 [4] g. sarton, inroduction to the history of science, 3 vols, (new york, 1997). [5] w. montgomery watt, the faith and practice of alghazali (london, allen and unwin, 1953), p. 12 [6] w.r.w. gardener, al ghazali , (madras : christian literature society for india, 1919) p. 33. [7] iqbal, muhammad, the reconstruction of islamic religious thought in islam, (lahore: sh. muhammad ashraf, 1982) pp. 149-150 [8] ismail r. al faruqi, islamization of knowledge : general principles and work plan (herndon, va : iiit, 1987), p. 39 [9] mehdi golshani, “philosophy of science from the qur’anic perspective”, towrds islamization of disciplines. iiit, washington d.c, 1989 pp. 73-92 [10] al ghazali, al risalah al laduniyyah, 2 nd editin, (cairo: matba’ah as sadah, 1342, a.h.) p. 32 [11] ismail r. al faruqi, islamization of knowledge : general principles and work plan (herndon, va : iiit, 1987), p. 52 [12] qadir, c. a., philosophy and science in the islamic world, usa, 1988, croom helm, p. 6 [13] ismail r. al faruqi, islamization of knowledge : general principles and work plan (herndon, va : iiit, 1987), p. 44 [14] mehdi golshani, “philosophy of cience from the qur’anic perspective”, towrds islamization of disciplines. iiit, washington d.c, 1989 p. 84 microsoft word problems in biotechnology research-1.doc iium engineering journal, vol. 3, no. 1, 2002 p. jamal and h. salleh 35 problems in biotechnology research parveen jamal and hamzah m. salleh kulliyyah of engineering, iium, malaysia jparveen@iiu.edu.my; hamzah@iiu.edu.my abstract: to meet the challenges posed by the growing population of the world, biotechnology research is being pursued in all countries. in the area of medicine remarkable success has been achieved. it is believed that in future this trend will continue. in the area food also scientists and technocrats have shown considerable success, but in this area they have not received appreciation because of many objections. the paper discusses issues pertaining to biotechnology researches, because if these issues are not thoroughly discussed and problems are not hammered out, biotechnology researches will go on but will fail to serve the humanity. key words: biodiversity, biotechnology, cloning, germ cell, genetic materials, biosafety. 1. prelude with the increase of population of the world, food demand is also increasing. this phenomenon will continue. in times to come, contrary to developed countries, the food demand in developing countries will escalate, because in developed countries, the population will stabilize and developing countries’ population will keep on growing at 3 to 4 per cent per annum. this phenomenon will demand building more and more settlements and related infrastructures and facilities to ensure comfortable living. for this, we will have to sacrifice our agricultural lands and forests to the sustainable extent. the increased population will demand a healthy environment, health promotion facilities both prevention and cure. if these demands are not met amicably, the world will confront with a disastrous situation and the developing countries will be immensely hit from the afflictions and sufferance. only biotechnology scientists can avert this type of situation and they are making their best efforts. all states, including developing countries like malaysia, have increased their biotechnology budget allocations, and they are providing all kinds of facilities to their scientists to spearhead as fast as possible. it seems that after the information and communication technology, including the computer engineering, the era that is knocking at the door of the k-economy is the biotechnology engineering, especially its area of gene manipulation and bio-pharmaceuticals. but the biotechnology engineering is suffering from various problems and challenges legal, social, religious and ethical, economic, and scientific. the purpose of writing this paper is to highlight some of those problems and to make modest attempts to find possible pragmatic solutions to them. 2. lack of international cooperation developed countries are resourceful and technologically advance. because of these, they are playing a leading role in the area of research and development pertaining to biotechnology. international cooperation in this area is not significant at all. developed countries do not subscribe to the idea of transparency in the area of biotechnology. the reason that seems to be conspicuous is economic; compassion has no influence on them. these countries want to cash their research. the episode of supply of medicine for curing aids in some african countries proves this. the problem has aggravated from the fact that most of the researches are in the private sector, and companies as business organizations have a predominant profit motive. this is evident from the fact that some american companies earned billions of dollars from their researches in the area of medicine and vaccines. they did not fairly share their income with the developing countries from where they collected the relevant genetic materials. their attitude can change only when governments interfere. but why will governments interfere? that stage is yet to come. it is better if researches are conducted as a joint venture between scientists of developed and developing countries work together in certain specified areas. this is possible in both the ways, arranged between private sectors and between government owned institutions, like public laboratories, research institutions and universities. it will be better if collaborations are done through respective governments. there is a recent example of this kind. indian scientists in collaboration with some american scientists have developed a vaccine for prevention of infection from hiv. they have significant breakthrough in developing the vaccine. test has successfully been conducted on mice, and before it is tested on humans, as a second step, tests on monkeys are in progress. this practice will certainly have a greater degree of transparency, and if liberally applied, will immensely serve the humanity. another recent significant research is invention of vaccine for parkinson disease by a group of scientists in new zealand. the author feels that profit motive iium engineering journal, vol. 3, no. 1, 2002 p. jamal and h. salleh 36 should be there, because this will encourage scientists to venture in the area of biotechnology. but the element of compassion should totally be thrashed out. so as to bring them together, cooperation between developed and developing countries become crucial. for this, initiatives will have to be taken by developed countries. 3. sharing benefits this has been pointed out above that private sector companies in the west and other developed countries have successfully conducted most of the biotechnology researches and they are reluctant in sharing benefits of the researches with the countries from where they collected genetic materials. the convention on biodiversity (cbd) provides for collection of genetic materials on the informed consent basis under a specified procedure. it also provides, on this basis, to share profits accruing from biotechnology researches. for implementing this provision, states have to make law. if a plant or animal is found in a region, all countries of the region should have similar legislations and should cooperate in preventing smuggling of that plant or animal or its body parts. the object of the law should not be to defeat the research, but to facilitate it. in this context, the attitude of private companies in the west has to be changed. the whole process will work equitably only when flexibility on both the sides is observed. it will be better for those companies to establish laboratories in developing countries where genetic materials exist. these laboratories should conduct researches, should manufacture end products, and should market them from the developing and under developed countries. respective developing countries should share the copyright, and there should be joint patenting of products. if this is practiced, developing countries will have confidence, there will be equitable distribution of profits, and the area of biotechnology research will flourish fast. 4. training of biotechnology scientists this is also a cooperation area that is highly demanded. although sincere efforts in developing countries in the area of biotechnology research are being made, scientists in theses countries are handicapped for two reasons: lack of enough financial resources, lack of sophisticated equipments and lack of truly competent scientists and technocrats. many developing and less developed countries cannot afford the cost of necessary equipments; and many others can afford the financial burden, but due to lack of enough trained human resources, cannot pursue research and development activities. they can get them only on the basis of liberal transfer of technology. but unfortunately the process of transfer of technology is utterly slow. developed countries want to sell technology; they do not want to provide for free. for this, they find a pretext and say that technology is mainly in private sector and they do not want to interfere. likewise, due to lack of experts in the area, the training of the younger generation scientists is awfully slow. the situation can improve only when developed countries show enough political will and meaningfully facilitate both the aspects. the cbd mentions about it in the area of conservation of the biological diversity of the world, which is the basic foundation and genetic materials for biotechnological researches, the conference of parties (cop) has not been able to come up with a meaningful breakthrough. the author is of the opinion that the monopolistic approach of the west will create a situation, in the long run, when the third world population will either be a burden on developed countries or will virtually become slave of the west. developing countries should also do their best to provide impetus to biotechnology researches. for this, they should strive hard to develop international cooperation, to woo their scientists working outside their countries, to attract foreign scientists, to provide incentives to those who are working in this area, to encourage local scientists and technocrats, to provide scholarships to excel in this area. it is not impossible. most of the developing countries, including malaysia, have potential and capability to do all these and they are doing. south-south cooperation can also help to some extent. 5. biosafety this is one of the pertinent problems related to biotechnology. if a biotechnology research is not safe to man and other living organism, as the case may be, the research will become a curse rather than a boon. because of this reason, biosafety has become a priority issue. it is notable here that the african country zambia has opted to starve rather than accepting genetically modified corn for their people. it has asked the world food programme (wef) to take away the gm corn supplied to them, half of that is already in warehouses. whereas, malawi, lesotho, mozambique and zimbabwe have decided to accept milled grains rather than intact corn. the restrictive measures adopted by african countries have posed a social problem. will it be advisable for them to try and see the effect of the gm corn? on the contrary, will it be appropriate to let the starving people die of hunger? it is argued by the relief providers that in the united states alone millions of tonnes of gm corn, tomatoes and other gm food are consumed annually. but the ngos based in europe have never been favorable to gm food. they always speak against such food. that has generated a lot of doubts in the minds of people and governments around the world. in fact, people are scared of such food now. these ngos argue that each state should take its own decision. united states has angrily condemned the zambian decision and the attitude of the ngos. this has given rise to a controversy. the us agriculture secretary and andrew natsoin of the us agency for international development have branded the act of ngos as misinformation and disgraceful. while reacting against such comments, geert ritsema, a campaigner of gm iium engineering journal, vol. 3, no. 1, 2002 p. jamal and h. salleh 37 issues for friends of earth europe, said it was unfair and untrue to target green groups this way. once the united nations got embroiled in the debate when one of its officials, jean ziegler declared gm food dangerous to the human organs. contrary to this, gro harlem brundtland, director general of the who holds the view that gm food can safely be eaten. here a question arises: why the african courtiers are so scared of genetically modified food? the answer seems to be simple. those who have developed such food have not come up with the guarantee of its safety. had the safety tests been meaningful, transparent and positive, there would not have been such hue and cry. the burden of testing the safety of genetically modified food primarily lies on those who have developed them. it is their ethical as well as moral duty. this should be indisputably be made a legal duty as well. prominent among the genetically modified food are: corn, soybean, tomato and cottonseeds (for oil). producers want to market them and products containing them without guaranteeing their safety aspects. the task of biosafety tests is not difficult. producers can conduct it, and it can be done by other agencies (for example, ngos) having competent scientists as well. but while doing this, vested interests and politics should be kept away. for example, a company wants to market its genetically modified mustard oilseed in india. when indian scientists and farmers created hue and cry, the government postponed its ingress in the country. likewise, attempts are being made to foster bt cotton in the indian market. it is claimed that in the bt cotton has a kind of toxin its own that kills harmful insects. but the company, which has developed this, does not have satisfactory answer about the following related aspects: what will happen if insects develop immunity? will the oil extracted from their seeds be safe for eating? another related aspect is maintaining purity of indigenous varieties. pollens of genetically modified varieties will contaminate the local ones. there is a simple answer to this objection: maintain a buffer around the genetically modified varieties. but this is possible only when there are big farmers venturing in a big chunk of land. what about the places where farmers have small landholdings? in countries like india and for that matter other developing countries, there are smallholdings; the idea of keeping buffer around genetically modified verities cannot be practiced effectively. under the biosafety protocol, which has been made under the cbd, requires from the member states to adopt certain measures that ensures safety of human health and conservation of the environment as such. thus, measures have to be taken for ensuring the safety of invented living modified organisms (lmos). the protocol authorizes states to adopt restrictive measures about transboundary movements of such lmos. in spite of this international law, private companies for their vested interests are striving hard to avoid the treaty norms of the protocol. unless this attitude is changed, the protocol or any other development of law in that direction will not yield the desired result. in view of the above paragraphs, it is suggested that the biosafety issue should be given priority. efforts should be made to develop food varieties that are satisfactorily safe. profit motive should not dominate the safet y issue. if we produce a lot, but if that lot cannot be used, that lot will be of no use. because of this reason, some scientists prefer developing superior species of plants and animals by way of cross-fertilization and grafting. the authors feel that this area of research should not be neglected. but it cannot be the sole area of research. we will have to resort to the gene manipulation technology to enhance the development of superior species of plants and animals mentioned above. 6. patenting of lmos and gm food according to the patent law prevalent in almost all countries, innovations can be patented. this protection has been provided for inventors so that they could enjoy the fruits, in terms of money, of their inventions. in view of the process of globalization and preventing the inventions internationally, the agreement on trade-related intellectual property rights (trips) was signed in 1992 at the time of the rio conference. now, every lmo can be patented and thus protected from duplication and other kind of unlicensed use. with the result of this development, big biotechnology companies are protected. they have the monopoly of their inventions. other persons can even use them only on their permission. it is for this reason that such patenting is considered as non-friendly to developing countries and poor peasants of those countries. we know the basmati rice episode. patenting of this variety of rice by an american company was an attempt to deprive poor peasants of india and pakistan who had been growing this rice from the time immemorial and ultimately to deprive these two countries from exporting this kind of rice. due to largescale protests in two countries, it was ultimatel y decided by the competent authority in the united states of america that only invented variety of rice could be patented; the varieties that already exist cannot be patented. this gave a shy of relief to indian farmers. a similar problem arose when some companies in europe patented pesticides made from neem trees. indian and pakistani farmers were already using a natural pesticide prepared from various parts of neem tree. this was a gross violation of their customary right and a misuse of the patent law. only after a long representation by these countries and interest groups it was held that the patenting was legally wrong. the story of termination seeds is annoying. termination seeds will make farmers totally dependent on the companies that have invented them, because from the crop farmers cannot get new seeds. every growing season they will have to buy seeds from the respective companies or from their dealers. this will provide clear chance to biotechnology companies to economically exploit poor farmers. another great loss iium engineering journal, vol. 3, no. 1, 2002 p. jamal and h. salleh 38 will be the vanishing of indigenous varieties. if in future, for biotechnology research purposes local seeds are required, they would not be available. this will be a great handicap to the field of biotechnology engineering. the situation will be something like what was experienced in cambodia. here the farmers selected one or two of the local rice varieties. with the result of that, all other varieties vanished. it was a big handicap for scientists for conducting research on improving upon the existing indigenous rice species and inventing entirely new species. fortunately those vanished rice varieties were there in the international rice gene bank in the philippines. scientists took genetic materials from the gene bank and conducted their research. 7. protection to the environment new lmos have some qualities in them. one of these is to survive in adverse weather conditions. if such lmos are not used with strict precautionary measure, there will be all chances that other varieties will be overwhelmed by the new variety. this may happen in both, plants and animals. it is, therefore, suggested that before introducing such varieties into the environment, their impacts on other similar and other species should be thoroughly assessed. otherwise the new variety will survive and other varieties will vanish. likewise, when a new variety is to be introduced, it should be ensured that other similar varieties would also survive side by side. this phenomenon has in happened in south africa. here a variety of tree was brought into the country for plantation purposes. the weather of the country so suited to the imported plant variety that it overwhelmed the local diversity in the same kind of trees. so as to protect them, the whole lot of the imported variety had to be destroyed. likewise, in the united states, scientists of the university of south carolina on the basis of a research conducted by them have revealed that on many occasions gm crops crossed their boundaries and cross-pollinated the normal plants to create ‘super weeds’ that are resistant to insect attack and could spread rapidly. this shows that the growing gm crops might be sheer destruction of the environment if not properly controlled and thoroughly assessed. 8. right to information and biotechnology because of lack of transparency in scientific safety findings, people are scared of genetically modified food (gm food). they assert their right to information and want to know about what they are eating. some want to know it for religious reasons. muslims also want to know it, because if impure genetic materials have been used for developing lmos, they will not be halal (permitted) for muslims. some countries have enacted law for declaring input of genetically modified stuff in food. so every product must disclose this fact. some other countries, like malaysia, are in the process of making such law. it is, therefore, suggested that engineers and technocrats should do an intensive scientific investigations about the lmos, and findings should be repeated. there should be transparency in the whole process so that people could develop confidence in the edibles prepared from them or using them as one of the ingredients. all countries should make law to protect the right to information of their people. 9. genetic engineering and human cloning in the light of shariah and ethics some ulama (experts of muslim theology), who are actually in minority, hold the opinion that gene manipulation is interference in the domain of allah. thus, such acts are prohibited in islam. on the other hand, some right-minded ulama, who really want to take care of the growing human mass, are of the opinion that use of this technology is a must, provided the injunction of quran and sunnah (traditions of the prophet) are not violated. in view of this, it is necessary to investigate into the original sources in islam and commentaries written on them. genetic engineering has attracted lengthy discussions amongst islamic scholars around the world. the issues pertaining to this branch of science have generated interests among scientists and religious scholars equally. in islam the biotechnology processes are questioned on the basis of the quranic ayah, “verily of thy servants i shall most certainly take my due share, and shall lead them astray and fill them with vain desires. and i shall command them so that they cut off the years of cattle (in idolatrous sacrifice), and i shall command them and they will change god’s creation.” (4:119). however, there is no consensus on the issue of total ban on genetic engineering. the author feels that genetic engineering is knowledge. this knowledge will not be acceptable unless it is not in conformity with quran and sunnah. it is submitted that beneficial aspects (in the form of safe and environment friendly biotechnology) are in no way against them. rather, it has a predominant element of maslaha (public interest) in it, because demands fostering such biotechnological researches in muslim countries are pressing now. contrary to this, all kinds of cloning, human and animal, should be considered as interference in the domain of allah (swt), as allah has made a natural system of reproduction and the act of cloning is against that system. cloning amounts to denial of allah’s wisdom. in 1998, in kuwait a seminar was held on “genetics, genetic engineering, the human genes, and genetic treatment – an islamic perspective” in line with the authors’ view on biotechnology and cloning the following principles were approved. 1. any tampering with man’s basic constituents would be in violation of man’s god given dignity (al-quran, 17:70). 2. islam is a religion of knowledge and science, which imposes no restrictions on constructive scientific iium engineering journal, vol. 3, no. 1, 2002 p. jamal and h. salleh 39 research. thus, islam supports genetic engineering. 3. nobody’s genes should be subject of research without evaluating its pros and cons. 4. no research on human genes or application of any such research should take precedence over the shariah and the respect of human rights, basic liberties and human dignity of any individual or group of individuals. 5. the reading of human gene by mapping out the full genome is part of man’s endeavor to understand him and appreciate god’s power of creation. it is important for medical point of view also. 6. genetic engineering may be used in the prevention, treatment or alleviation of diseases. genetic engineering should not use germ cells (for example, stem cells of a premature fetus). 7. genetic engineering should not be used for any sinister or offensive purposes, or crossing the genes boundaries between various species in order to produce hybrids or merely for sport or scientific curiosity. 8. genetic engineering must not be used for changing the human structure. 9. poor should also benefic from scientific researches.10. islam does not object to the use of genetic engineering in the fields of agriculture and livestock, without ignoring, however, those voices that have recently warned of possible harmful long-term effects on man, animals, crop or the environment. the declaration supported genetic fingerprinting, genetic counseling, and genetic diagnosis because they are in the interest of man. the conference recommended for promotion of genetic research in muslim countries financially supported by governments and other financial institutions. among the views highlighted above and agreed by the participants of the kuwait conference, cloning and use of germ cells (also known as stem cells) obtained from premature human fetuses are highly objectionable. thus all kinds of cloning and germ cell based researches should be prohibited. this may be noted that use of germ cells encourages for abortion of premature fetuses for small economic interest. there are rackets involved in this immoral and unreligious act. they are targeting developing and underdeveloped countries. their main job is to collect such foetuses and to smuggle them to developed countries. in bangladesh, some of these have been rounded up. but the process is continued even though the use of germ cells for biotechnological researches has been made illegal in many countries. legally, although there is very little to stop scientists from cloning, in the united states, in january 2002, the national academy of sciences recommended a ban on human cloning. in pursuance to that, some of the american states, including california, michigan and louisiana, have enacted laws declaring human cloning as a banned activity. however, according to the existing law, germ cells collected only before 9th august 2001 can be used for the approved kind of research. so is the case in germany. countries have taken prohibitory measures because they consider it unethical and it may have unwarranted scientific, social and economic consequences. for example, recently, scientists are doing research to create human mouse hybrid by infusing stem cells into an early mouse embryo when it is still a small ball of cells called ‘blastocyst’. this way, the hybrid mouse will have tissues with human cells also (this is known as ‘pluripotentiality’). this will help for conducting research to protect human being from some hereditary diseases. but some scientists are of the opinion that this might yield dangerous results if human cells radically change the mouse or if the mouse producing human sperms meets another mouse having human eggs. it is, therefore, suggested that muslim scientists should keep themselves away from these. if they do so, there will not be any setback to the ongoing biotechnology research because other options are available. so far as cloning is concerned, in addition to the reason mentioned above against it that it is interference in the domain of allah, it might be against the biodiversity also. for example, if a giant species is created, that species will overwhelm the existing species and a time will come when the situation will be no less than total disaster of the biodiversity of the environment. another important aspect that needs to be controlled by all means is production, stockpiling and use of biological weapons. this is also against the islamic teaching of environment and the islamic law of war because it would affect innocent people. it is necessary, therefore, to destroy the existing stocks of these weapons and to abandon all kinds of research in progress we have noted above that every biotechnological breakthrough will not be acceptable in islam. genetic materials used in the research must be obtained from halal objects by halal means. thus, if genetic materials are taken from a pig or any other living object that muslims cannot eat are prohibited to be used for genetic research. vaccines are the significant biotechnology researches. but if the genetic material has been taken form a pig in order to manufacture any vaccine, the vaccine will be haram (prohibited) for muslims. recently, fatawa committees of some countries, including malaysia, have declared the ‘monomune vaccine’, which is used to preventing meningococcal meningitis, as haram because it contains amino acids (proteins) derived from pigs, or from cows and duck not slaughtered in the islamic way. this has been done because alternative to this vaccine by the name of ‘mencivax’ is available. ‘monomune vaccine’ will be allowed to muslims only when it is guaranteed that the protein used for manufacturing the vaccine was from a cow or a duck properly slaughtered. if no alternative is available and human mass cannot survive without that, the opinion might be different. activities that are considered to be prohibited in islam are also considered as socially deviant activities. all socially deviant activities are immoral. activities that are immoral in the area of human activities are considered as unethical also. thus, activities that are considered as socially deviant in the area of biotechnology are unethical to biotechnology scientists. in islam, quran and sunnah basically govern human conducts, human relations and human behaviors. iium engineering journal, vol. 3, no. 1, 2002 p. jamal and h. salleh 40 these, thus, have to be compatible with the two basic sources of the islamic shariah. any social practice that opposes them is ultra vires and has to be prohibited, and its practice has to be dealt with severely. 10. conclusions and suggestions biotechnology, in fact, is the need of the day. if intensive and speedy research in this area is not done, the growing population might create a chaotic situation that might then be difficult to solve. to meet the challenge, all countries, including muslim countries, are making efforts in this area according to their ability. but developing countries due to limited number of trained scientists and technocrats, insufficient resources, and lackadaisical attitude of developed countries in the area of transfer of technology and financial resources are lagging behind. in developed countries, the area of biotechnology is generally in the private sector. because of this, profit motive has overwhelmed the humanitarian and other considerations. this attitude is depriving many from their rights to have a safe environment and healthy food. it is, therefore, suggested that the biosafety aspect of biotechnology research is in no way less important than the research itself. it will be appropriate to double the efforts developing better quality of plant and animal species through cross breading and grafting. biotechnology should be given a cautious approach so that some thing harmful is not introduced into the environment or brought for consumption. before commercializing any product, thorough investigations from the point of view of safety should be done. somewhere biotechnology has entered into the arena of immorality. scientists and technocrats there are keen to come out by any means any kind of research. this way, they have gained name but have failed to serve the humanity. termination seeds, bt cotton and the like are the examples. this tendency should be abandoned. likewise, malpractices of doing research on germ cells obtained from premature foetuses should be stopped. it will be in the fitness of the thing if biotechnology scientists, technocrats and others involved in biotechnology researches and marketing of their outcomes are given periodical religious orientation. recently, a scientist in the united states has claimed to have a conducted successful birth of a cloned baby girl, some others, according to an italian scientist, are on the way to take birth in the month of january. if this is proven to be true, this will be a perversion of science and socially and morally an outrageous and deviant behavior. it is thoughtless to justify cloning on the myth that life on the earth was created through cloning by extraterrestrials. presently, there is very little in the law to stop scientists from human cloning. if immediate restrictive efforts, at global level, are not made, the situation might be grave. therefore, the authors are of the opinion that all kinds of cloning, including human cloning, should be banned with immediate effect. islam does not prohibit biotechnology research. rather, the principle of maslaha encourages muslim scientists to play a leading role in this area. if they take the lead, many evils that exist now will certainly vanish and humanity will receive the real reward of biotechnology researches. in muslim countries, therefore, biotechnology research should be made a priority area and for fostering it all kinds of incentives should be provided. references [1] a. h. ansari and parveen jamal, “the convention on biological diversity: a critical appraisal with special reference to malaysia”, indian journal of international law, vol. 40, pp. 137-145, 2000. [2] t. dobson, “ the loss of biodiversity: an international environmental policy perspective”, north carolina journal of international law and commercial regulations, vol. 17, pp. 34-49, 1992. [3] s. h. bragdon, “national sovereignty and global environmental responsibility”, vol. 33, p. 382, 1992. [4] w. m. flavares, “ecosystems economics and ethics: protecting biological diversity at home and abroad”, southern california law review, vol. 65, pp. 204 263, 1998. [5] a. h. ansari, “scientific aspects of the convention on biological diversity: perspectives and challenges”, in proceedings of the international symposium on future issues of research in science and technology, tokyo institute of technology, pp. 184-89, 1997. [6] j. r. kloppenburg and d. c. cleinman, “seeds of controversy: national poverty v. common heritage”, in jack r. cloppenburg (ed.) seeds of sovereignty , pp. 173-192, cambridge, uk 1988. [7] m. s. swaminathan, “biotechnology and a better common present: a synthesis”, in i. p. getubig, v. l. chopra and m. s. swaminathan (eds.), biotechnology for asian agriculture, pp. 95-116, asia and pacific development centre, kuala lumpur, 1991. [8] p. h. yue, “altering genes in food crops”, new straits times, 24 november 1998. [9] d. a. ramirez, “biosafety: an area of concern”, pp. 201-208, in biotechnology for asian agriculture (supra). [10] suman sahai, “how do we protect our resources”, economic and political weekly, 6 july 1996. [11] a. j. wells, “patenting new life forms: an ecological perspective”, european intellectual property review, vol 3. pp. 111-132, 1994. [12] youssef ibrahim, “new soya bean alarms europeans”, new sunday times, 17 november 1996. [13] a. h. ansari, readings in environmental law, pp. 170-186, subhashit ankan, india, 1995. [14] g. s. nijar, “biodiversity in malaysia: prospects and problems”, in the state of environment in malaysia, pp. 209-216, cap, malaysia, 1997. [15] joseph edwin, “will and way in biodiversity”, new straits times, 20 september 1995. [16] a. h. ansari, “contemporary issues in international trade law and environmental law”, proceedings of iium engineering journal, vol. 3, no. 1, 2002 p. jamal and h. salleh 41 international conference on law and commerce, jointly organized by iium and victoria university, pp. 121-139, clj, malaysia, 2002. [17] a. h. ansari and parveen jamal, “towards an islamic jurisprudence of environment: an expository study”, religion and law review, vol. 23, pp. 34-49, 2002. [18] proceedings of the seminar organized by the fiqh academy, jeddah and the islamic education, science and culture organization, kuwait, kuwait 13-15 october 1998. reproduced at: www.islamset.com. [19] richard ingham, “gm food row clouds famine relief”, new straits times, december 3, 2002. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 solid state fermentation of turmeric rhizomes with aspergillus sp. to improve yield and composition of extracted turmeric oil muhammad yusuf abduh1*, asri ifani rahmawati1,2, tinta komariyah1,3, and yohanes theda1,4 1 school of life sciences and technology, institut teknologi bandung, jl ganesha no. 10 bandung 40132, indonesia 2 pt partner impian milenial, soho pancoran f16, south jakarta 12810, indonesia 3 research center for vaccine and drug, national research and innovation agency, jl raya jakarta – bogor km. 46, cibinong, bogor 16911, indonesia 4 pt cultiva tunas niaga, setrasari plaza b11, sukagalih, sukajadi, bandung 40164, indonesia *corresponding author: yusuf@sith.itb.ac.id (received: 26th september 2020; accepted: 30th november 2022; published on-line: 4th january 2023) abstract: this research aimed to determine the role of aspergillus awamori, aspergillus niger, and aspergillus oryzae in degrading starch on turmeric rhizome substrate to increase the yield of turmeric oil. the substrate in the form of turmeric rhizome was given additional yeast extract of 10% weight per volume to meet the nutritional needs of fungal growth. the fungal concentration used in inoculation was 5x107 cells/ml. the solid-state fermentation process was carried out in dark conditions (~0 w), temperatures of 25–28 ºc, 99% humidity, and aeration (3.5 l/min). turmeric oil was extracted using a steam distillation method for three hours, with the substrate moisture content of 68–71% and a substrate– water ratio of 1:5. the biodegradation process was conducted for 11 days. the starch content and turmeric oil yield was determined during the fermentation particularly on days 7, 9, and 11. the results showed that the biodegradation process of starch in solid-state fermentation succeeded in increasing the yield of turmeric oil. aspergillus awamori showed the most desirable starch degradation activity by 62.5% to 2.9% wet weight on the 11th day of fermentation. aspergillus oryzae had the most positive effect, nearly doubling the turmeric oil yield to 3.17% dry weight after 11th day of fermentation. the main constituents of turmeric oil are β-turmerone, α-turmerone, and ar-turmerone. abstrak: penelitian ini bertujuan bagi mengkaji peranan aspergillus awamori, aspergillus niger, dan aspergillus oryzae dalam mendegradasikan kanji pada substrat rizom kunyit bagi meningkatkan hasil minyak kunyit. substrat dalam bentuk rizom kunyit telah diberi tambahan ekstrak yis 10% mengikut berat setiap isipadu bagi memenuhi keperluan nutrisi pertumbuhan kulat. kepekatan kulat yang digunakan dalam inokulasi adalah 5x107 sel/ml. proses penapaian berkeadaan pepejal telah dijalankan dalam keadaan gelap (~0 w), suhu 25–28 ºc, kelembapan 99%, dan pengudaraan (3.5 l/min). minyak kunyit diasingkan menggunakan kaedah penyulingan wap selama tiga jam, dengan kandungan lembapan substrat 68-71% dan nisbah substrat-air 1:5. proses biodegradasi dijalankan selama 11 hari. kandungan kanji dan hasil minyak kunyit ditentukan semasa penapaian terutamanya pada hari ke-7, 9, dan 11. hasil kajian menunjukkan bahawa proses biodegradasi kanji dalam penapaian berkeadaan pepejal berjaya meningkatkan hasil minyak kunyit. aspergillus awamori menunjukkan aktiviti degradasi kanji yang paling diingini iaitu sebanyak 62.5% hingga 2.9% berat basah pada hari ke-11 penapaian. aspergillus oryzae mempunyai kesan yang paling positif, iaitu hampir dua kali ganda hasil minyak kunyit kepada 3.17% berat 1 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 kering selepas hari ke-11 penapaian. konstituen utama minyak kunyit ialah β-turmerone, αturmerone, dan ar-turmerone. key words: aspergillus sp., biodelignification, starch, turmeric rhizome, turmeric oil 1. introduction turmeric (curcuma longa l.) is an herbaceous plant that has been widely used as a condiment and in medicine in asia since ancient times [1]. the main part of the turmeric plant is the rhizome which contains various types of compounds including curcuminoid compounds, turmeric oil, and oleoresin [1]. it has been reported that the rhizome contains 56% essential oil [2] that is commonly used in food, cosmetics, and pharmaceutical applications due to its anticancer, anti-inflammatory, antibacterial, antifungal, and antitumor effects [3-4]. turmeric is widely cultivated in indonesia with a total cultivation area of 7,481 ha being reported in 2018 [5]. nevertheless, valorization of the rhizomes to produce turmeric oil is still considered to be very limited. based on the data of the indonesian central bureau of statistics, large-scale turmeric oil processing is still in the development stage since 2018. in 2020, a production plant for producing turmeric oil was built in pacitan, east java, indonesia, with a production capacity of 2.4 tons/year, relatively small as compared to a total rhizome production of approximately 193,000 tons/year [5]. this is due to the difficulty of isolating turmeric oil during the distillation process, which results in low oil recovery of approximately 0.46% [6-7]. turmeric oil in the rhizome is located in secretory cells surrounded by starch granular parenchymal tissue, which can inhibit the extraction of turmeric oil. various studies addressing the turmeric oil extraction process have been carried out. one example is a pretreatment using enzymes to degrade polysaccharide compounds on cell walls so that oil yield can increase by 70% [8]. the enzymes are expensive and, therefore, in the large-scale production of turmeric oil, are considered to cause a significant increase in production costs [9]. microorganisms, especially fungi, can be an alternative solution to increase the yield of turmeric oil while still saving production costs. fungi can produce various types of extracellular enzymes that can degrade polysaccharide and consequently increase oil yield without using commercial enzymes [10]. fungi are used because they have complete enzymatic devices, filamentous bodies that can penetrate the substrate, and accumulated ability [11]. fungi from genus aspergillus, such as aspergillus niger, aspergillus oryzae, and aspergillus awamori, are capable of being starch-degrading agents in turmeric because they are able to produce polysaccharide-breaking hydrolytic enzymes, such as amylase enzymes [12-16]. these three specific types of fungi were selected because they could survive the antimicrobial compounds of turmeric [4]. therefore, this study was conducted to determine the species of aspergillus and fermentation time that can degrade starch efficiently and produce a relatively high yield (≥ 2.5%) of turmeric oil. an average yield of 2.5% is considered satisfactory for commercial productions [17]. 2. materials and methods 2.1. preparations of turmeric rhizomes the turmeric rhizomes used in this study were harvested at the age of 8 months from cimasuk, tanjung sari, sumedang regency, west java, indonesia. they were then washed 2 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 and sliced to a thickness of ± 0.1 cm. after that, all rhizomes were stored at room temperature (25-28 ºc) and relative humidity (50-70%). 2.2. cultivation of aspergillus sp. inocolum stocks of aspergillus niger, aspergillus oryzae, and aspergillus awamori were obtained from the microbiology laboratory, school of life sciences and technology, institut teknologi bandung. each species of fungi was cultivated in a semisolid potato dextrose agar (pda) medium with a concentration of 39 g/l [15]. the pda medium was sterilized using an autoclave (121 ºc, 1.5 atm). the fungi were cultivated for 4 days in a test tube at room temperature until the active fungi spores covered the entire surface of the medium. 2.3. preparation of aspergillus sp. inocolum the 4-day old aspergillus sp. cultures were harvested with harvesting solution (0.85% nacl + tween80 0.1%) to obtain a 600 ml inoculum solution with a concentration of 5x107 spores/ml [16, 18]. measurement of the spore concentration was conducted using a hemocytometer under a microscope. the cell chamber of the hemocytometer was filled with a 1 ml aliquot of the spore solution. appropriate dilutions of the aliquot were done when there were too many spores to count by eyes. the resulting number from cell counting was then multiplied by the dilution factor. 2.4. solid-state fermentation of turmeric rhizome with aspergillus sp. the fermentation process was carried out under aseptic conditions. the inoculum solution and yeast extract solution were mixed with the sterilized turmeric rhizome in the following proportions: 1 ml inoculum solution, 1 ml yeast extract solution, and 10 g turmeric rhizome [18]. the fermentation process took place in a fermenter tray (50 × 30 ×15 cm) with perforation to remove excess liquid. the fermenter tray was sealed with plastic wrap and black color plastic, so that fermentation could take place at a light intensity of ~0 w [16]. aeration was given every 2 days for 5 minutes, at a rate of 3.5 l/min. samples were stirred every 2 days. the fermentation process was carried out by varying the incubation time of 7, 9, and 11 days. 2.5. extraction of turmeric oil using a steam-distillation method fermented turmeric rhizome was dried using an oven at 50 ºc for 24–26 hours to reach a moisture content of 68–71% [19]. moisture content was measured using a mettler toledo infrared moisture content analyzer. turmeric oil was extracted using a steam distillation method with a ratio of 100 g substrate to 500 ml of distilled water for 3 hours [20-23]. distillates were collected in a 500 ml separating funnel, and the oil and hydrosol were separated. the obtained turmeric oil yield was calculated using eq. (1): 𝑌𝑖𝑒𝑙𝑑 (%𝑤𝑑) = 𝑚𝑚 (𝑔) 𝑤𝑑(𝑔) × 100 (1) where mm is the mass of oil in grams, and wd is the dry weight of the substrate in grams. the value of wd can be calculated using eq. (2): 𝑤𝑑(𝑔) = (1 − 𝑚𝑜𝑖𝑠𝑡𝑢𝑟𝑒 𝑐𝑜𝑛𝑡𝑒𝑛𝑡) × 𝑚(𝑔) (2) where moisture content is in percent, and m is the substrate mass in grams at the initial moisture content (~90%). 2.6. determination of turmeric rhizome starch content the starch content was determined using a luff schoorl method (sni 01-2891-1992). the preparation of the luff schoorl reagent was carried out by mixing the following: 143.8 g 3 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 of anhydrous na2co3 in 300 ml of distilled water, 50 g of citric acid in 50 ml of distilled water, and 25 g of cuso4.5h2o in 100 ml of distilled water. the solution was stirred until homogeneous. next, 3% hcl (200 ml) was added to 5 g of fermented turmeric rhizome. the mixture was boiled using a reflux extractor for 3 hours and then cooled down, and the ph was adjusted to 7.0 using a 30% naoh solution. the solution was diluted to a volume of 500 ml and filtered. 10 ml of this filtrate was mixed with 25 ml of the luff schoorl reagent and 15 ml of distilled water and then boiled for 10 minutes using an upright cooler. 15 ml of ki 20% and 25 ml of 25% h2so4 were slowly added. the final solution was titrated with na2s2o3 (0.1 n), and its volume increase was measured. starch solution 0.5% weight– volume (w/v) was used as an indicator. the calculation of starch content was carried out using eq. (3), where w1 is the sample mass of turmeric rhizome (mg), w is glucose (mg) contained for every milliliter of na2s2o3 used, fp is a dilution factor, and the value 0.9 is a glucose conversion factor for starch. the value of w was determined using the sugar conversion table according to sni. starch content (%) = 0.9𝑤1 (𝑚𝑔)𝑓𝑝 𝑤 (𝑚𝑔) × 100% (3) 2.7. characterization of turmeric oil the oil characteristics were determined particularly color, refractive index, and density. the color of turmeric oil was observed subjectively by eye. the refractive index value of turmeric oil was tested using a refractometer. the density was determined by measuring the volume v of oil (ml) using a measuring cup and oil mass m (g) on the analytic balance and calculated using eq. (4). density = 𝑚𝑡𝑢𝑟𝑚𝑒𝑟𝑖𝑐 𝑜𝑖𝑙 (𝑔) 𝑉𝑡𝑢𝑟𝑚𝑒𝑟𝑖𝑐 𝑜𝑖𝑙 (𝑚𝐿) (4) 2.8. determination of composition using a gas chromatography-mass spectrometry the composition of turmeric oil was analyzed using a gas chromatography–mass spectrometry (gc–ms) device. the initial temperature was set at 60 ºc, then raised to 280 ºc at a rate of 8 ºc/min. the samples were injected in split mode with a split ratio of 200. the rate of the column was set to 1.31 ml/min with a linear speed of 41.7 m/s. the analysis was carried out at the instrumental chemistry laboratory, universitas pendidikan indonesia, bandung, indonesia. 3. results and discussions 3.1. effects of moisture content on turmeric oil yield the effects of moisture content on the yield of turmeric oil are shown in fig. 1. a dry weight base was used for this study so that the values of different moisture content could be compared. the results indicate that the yield of turmeric oil increases with decreasing moisture content of the material before decreasing after reaching an optimum moisture content. a lower moisture content requires longer drying time and consequently more turmeric oil is susceptible to evaporation during the drying process. the turmeric oil yield with 87.9% moisture content was 1.27% dry weight (dw). lower moisture content in the range of 74–78% resulted in more turmeric oil. specifically, the yield of turmeric oil at 77.9% moisture content was 1.70% dw, and at 74.3% moisture content, it was 1.69% dw. the optimum moisture content was at 69.2% (obtained after drying for 24 hours) which resulted in a yield of 1.89% dw. 4 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 fig. 1. effects of moisture content on turmeric oil yield. the drying process was carried out using an oven at 50 ºc. the selection of the drying method considered two important parameters that affected the extraction of essential oils, namely drying time, and temperature [24]. the higher the temperature in the drying process, the lower the yield of essential oil due to evaporation. according to hamrouni-sellami et al. [25], the drying process at a temperature of 50 ºc can produce a high amount of volatile oils, while temperature above 50 ºc will reduce their yield. for medicinal plants, high temperatures (>50 ºc) may cause a drastic decrease in their essential oil yield. an increase in temperature by 20 ºc can cause the loss of essential oils up to 92.3% [25]. this is because high temperatures can damage the biological structure of oil glands and epithelium cells in medicinal plants and reduce the permeability of plasma membranes [25]. the effect of drying time on the yield of essential oils is related to the rate of evaporation of essential oils, which is greater with the length of the drying time. for example, the process of drying tymus subsp. doenensis leaves uses the shade drying method, which causes the reduction of essential oils to increase. the yield of essential oils by drying treatment using an oven at 50 ºc amounted to 1.46%, while the yield by shade drying was only 0.91%. this is due to the long drying time that caused the loss of essential oils as they diffused into the air [24]. the moisture content measured in this study ranged from 66–87% (fig. 1). a moisture content of 69.24% resulted in the optimal yield of turmeric oil of 1.89%. after reaching the optimum yield at 69% moisture content, the oil yield decreased as the moisture content was reduced. the dried rhizome to 66.96% moisture content resulted in a yield of only 0.54% dw due to the length of drying time, which caused longer evaporation of turmeric oil. the high yield of turmeric oil obtained at 69% moisture content or 24 hours drying (1.89% dw) is in accordance with the literature, which states that drying for 24 hours will result in the extraction yield of essential oils from rhizome plants in the range of 1.6–2.2% [26]. hence, a moisture content range of 68–71% was used in this study. 3.2. effects of fermentation time on starch content of biodegraded rhizomes and turmeric oil the test results on the content of turmeric rhizome starch fermented by the fungus aspergillus sp. are shown in fig. 2. the content of the control rhizome starch (day 0 of fermentation) was measured to be 7.8% wet weight (ww). the starch content in fermented rhizomes by all three species showed the same tendency. the content of rhizome starch 2 4 66 68 70 72 74 76 78 80 82 84 86 88 900 0.3 0.8 1.3 1.8 0.5 1.0 1.5 2.0 y ie ld ( % w d ) moisture content (%) 5 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 continued to decrease along with the length of fermentation time. in the fermentation process using the aspergillus niger, starch content decreased in the range of 14.7–30.6% ww to 6.6% ww on the 7th day, 5.8% ww on the 9th day, and 5.4% ww on the 11th day. meanwhile, the decrease of starch content in the fermentation by aspergillus oryzae was 11.8–59.3% ww to 6.9% ww on the 7th day, 4.2% ww on the 9th day, and 3.2% ww on the 11th day. fermentation using aspergillus awamori showed a better starch degradation activity. aspergillus awamori successfully reduced starch in the range of 31.8–70.6% with the starch content to decrease to 5.4% ww on the 7th day, 3.1% ww on the 9th day, and 2.9% ww on the 11th day. fig. 2. effects of fermentation on rhizome starch content. the profile of turmeric oil obtained in this study is shown in fig. 3. turmeric oil yield for the control sample (day 0 of fermentation) was 1.06% dw. the fermentation process of each fungal species yielded an increase in turmeric oil with the increasing fermentation time. the aspergillus oryzae showed a significant increase in the yield of turmeric oil compared to the other two fungal species. the 7th day fermentation resulted in the acquisition of turmeric oil by 2.17% dw and continued to increase to 2.60% dw on the 9th day and 3.17% dw on the 11th day. the fermentation process using aspergillus awamori produced turmeric oil of 2.38% dw on the 7th day, 2.50% dw on the 9th day, and 2.62% dw on the 11th day. meanwhile, fermentation using aspergillus niger had the lowest yield of 1.44% dw on the 7th day, 1.82% dw on the 9th day, and 1.92% dw on the 11th day. according to the study by de castro [27], the amylase hydrolytic enzyme group stabilizes after 4 days of fermentation and reaches a maximum point after 6 days. the test results of the control rhizome starch content (fig. 2) of 7.8% ww were similar to the research of kusbiantoro and purwaningrum [28], which obtained the value of turmeric rhizome starch content of 8% ww. a decrease in the starch content occurs with the ongoing fermentation process, owing to the growth and metabolic activity of the fungus aspergillus sp. hydrolytic enzymes, especially amylase, are enzymes that correlate closely with growth [26]. aspergillus spp. secrete enzymes as an effort to extract nutrients that support colony growth and regulation of metabolism [29]. the secretion of hydrolytic enzymes in the process of metabolic fungi results in the cutting of the glycosidic bonds of starch compounds on the cell wall, causing the breakdown of complex compounds into simpler ones, namely glucose, and a decrease in starch content [29-30]. it is known from the research of reyes et al. [31] that the fermentation time of 3 days is sufficient to degrade starch granules in the material. 6 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 the previous study used pure starch whereas this study used turmeric rhizome as the substrate, which is a complex medium. in complex media, fungi consume simple sugars at the initial time to support their growth before finally degrading starch complexes. therefore, they take longer to degrade than pure starch substrates [32]. fig. 3. effect of fermentation on turmeric oil yield. in this study, the growth of fungal hyphae was not seen until it reached the 2nd day. aeration to the system was given after the emergence of hyphae, which was evenly distributed on the 2nd day of fermentation to allow the fungal hyphae to grow around the entire surface of the turmeric rhizome in the fermenter tray. more evenly distributed fungal growth was observed qualitatively on the 3rd to 9th day. after the 9th day, there was no mycelium growth observed owing to the absence of any remaining organic matter in the turmeric rhizome that aspergillus could take as nutrition. in addition, the metabolic activity of the fungus allowed a decrease in ph on the substrate, so that the growing environment was no longer suitable for fungi [33]. in other words, fungal growth had entered a decreasing phase in which metabolic activity did not degrade starch [33]. the results of the starch content revealed that the aspergillus awamori fungus showed the greatest reduction in starch content relative to the other two species, as shown in fig. 2. this was predicted to occur because of the differences in the enzyme activity of the three species. the amylase enzyme activities measured in solid-state fermentation systems by aspergillus niger, aspergillus oryzae, and aspergillus awamori were 467.8, 500, and 589.7 iu/g, respectively [34-35]. greater enzyme activity in aspergillus awamori causes the fungus to degrade more starch [36]. aspergillus awamori can degrade starch in the range of 31.8– 70.6%, with a maximum decrease occurring on the ninth day of 62.5%. this data is in accordance with the results of research by umsza-guez et al. [37], which states that aspergillus awamori fungi can degrade up to 64% in a span of six days in solid-state fermentation systems. the increase in turmeric oil yield was caused by the decreased presence of starch in the rhizome cell wall that had been degraded. the aspergillus fungal metabolism results in secretory cells in the parenchyma tissue, that had been initially protected, to become more open. changes in the structure around the secretory cells allow the turmeric oil to be more easily extracted [29, 38]. the results of fermented turmeric oil measurements in fig. 3 show that the fermentation with aspergillus oryzae produced the largest yield of turmeric oil. even though the degradation of starch produced by aspergillus oryzae was lower than aspergillus awamori, the yield of oil produced was higher. during fungal metabolism, other hydrolytic 7 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 enzymes are involved that can degrade complex compounds other than starch on cell walls, such as endo-1, 4-β-glucosidase, or β-glucosidase, which act as catalysts in degrading cellulose [39]. 3.3. characteristics and composition of turmeric oil the physical-chemical characteristics of turmeric oil obtained in this study are shown in table 1. turmeric oil from fermented rhizome was yellow in color with a density of 0.89 g/ml. the measured refractive index of turmeric oil was 1.45. the results are in accordance with the results of a previous study by naibaho [40] and comply to the national standard in indonesia. the composition of turmeric oil is shown in table 2. this study found 30 components of constituent compounds of turmeric oil that comprise monoterpenoids and sesquiterpenoids. the main compounds found were ar-turmerone, α-turmerone, and βturmerone. in general, the solid-state fermentation process caused some components of minor compounds not to be detected in turmeric oil. fermentation by different aspergillus sp. resulted in varied amounts of components of the main compounds in turmeric oil. table 1: physical-chemical characteristics of turmeric oil characteristics this study sni reference [40] color yellow yellow orange density (g/ml) 0.89 ± 0,02 0.82-0.92 0.92 refractive index 1.45 ± 0.07 1.46-1.47 1.47 the main compounds of fermented turmeric oil are ar-turmerone, 10.4%, α-turmerone, 16.2%, and β-turmerone, 33.8%. in the fermentation using aspergillus awamori, there was a decrease in the ar-turmerone compound but an increase in α-turmerone and β-turmerone compounds. the ar-turmerone compound was measured in the range of 1.6–9.4%. the αturmerone compound was measured in the range of 14.5–18.1%. the β-turmerone compound was measured in a larger range, 41.9–48.5%. the fermentation process using aspergillus niger showed the same tendency. the ar-turmerone compound decreased to 0.98–9.88%. the α-turmerone and β-turmerone compounds were measured in the range of 11.59–15.29% and 20.97–45.36%, respectively. aspergillus oryzae had a different influence on the content of the main compounds of turmeric oil. the fermented turmeric rhizome using aspergillus oryzae did not have any detrimental effect on the content of the main compounds. fermentation using aspergillus oryzae increased ar-turmerone, α-turmerone, and β-turmerone compounds to the ranges of 10.09–13.50%, 14.47–16.38%, and 26.07–37.52%, respectively. turmeric oil from the biodegraded rhizomes of the three species generally had a relatively similar compound-content profile. β-turmerone was the highest concentration, followed by α-turmerone, then ar-turmerone. aspergillus niger and aspergillus awamori had relatively the same effect on changes in turmeric oil compound concentrations: decreasing the concentration of ar-turmerone on the seventh day, before an increase due to the transformation of α-turmerone and β-turmerone. however, the treatment using aspergillus oryzae produced turmeric oil with decreases in ar-turmerone. 8 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 table 2: composition of turmeric oil for fermented rhizome with aspergillus sp. an: a. niger, ao: a. oryzae, aa: a. awamori the concentration of each of the three main compounds in turmeric oil, as a result of the biodegradation of the three aspergillus spp., increased and decreased on different fermentation days. the increase in the content of the antioxidant compounds can be due to starch degradation and other structural polymers that made antioxidant compounds more accessible during distillation [45]. however, in all samples with 11 days of fermentation time, there was no increase in the content of α-turmerone and β-turmerone compounds, owing to lower starch content, compared to the other timeframes. with a higher concentration of ar-turmerone, a decrease in the content of α-turmerone and β-turmerone was found. α-turmerone and β-turmerone are unstable compounds that will turn into a more stable aromatic form (ar-turmerone) with continuous exposure to air. the content of ar-turmerone compounds decreased in turmeric oil by biodegradation treatment of the three aspergillus spp., a genus that can carry out biotransformation of ar-turmerone to a more oxidized form [46]. this decrease was discovered on days 7 and 11 for aspergillus niger and aspergillus oryzae and day 9 for aspergillus awamori. previous studies reported that the largest compound in turmeric oil was ar-turmerone, followed by α-turmerone and βturmerone in relatively equal amounts [3, 41]. such results are slightly different with the findings obtained in this study and may be caused by several factors, such as geographical origins, microclimate conditions, soil content, and the differences of turmeric root age [4147]. 4. conclusion the treatment of biodegradation in turmeric rhizomes using fungi from the genus aspergillus can reduce starch content in turmeric rhizomes, thereby increasing the yield of turmeric oil. aspergillus awamori reduced starch content more than the other two species, compounds percentage of compounds (%) fermentation day-7 fermentation day-9 fermentation day-11 ref. an ao aa an ao aa an ao aa [3,4147] α-turmerone 15.3 16.4 14.6 15.1 15.1 16.8 11.6 14.5 18.1 13-32 β-turmerone 45.4 37.5 48.5 34.1 36.2 41.8 21.0 26.1 46.2 7.1-18 ar-turmerone 1.0 13.5 1.6 9.9 10.2 9.4 6.3 10.9 2.8 17-31.7 1-phellandrene 0.8 0.5 0.6 1.7 0.8 1.5 0.6 0.4 1.0 0.1-1 α-terpinolene 0.2 0.2 0.4 0.2 0.3 0.2 0.3 0.1 trans-caryophyllene 0.8 0.8 0.8 0.8 1.1 0.6 0.6 0.4 0.6 2.2-3 zingiberene 2.5 1.3 2.1 2.8 1.9 3.5 1.7 1.7 2.1 0.2-11.8 α-bisabolene 0.6 0.6 0.3 0.4 0.2 β-bisabolene 0.8 0.3 0.7 0.7 0.6 0.5 0.5 0.4 0.5 0.7-3 βsesquiphellandrene 2.5 1.4 2.2 2.4 1.9 1.9 1.7 1.6 1.8 5.6-8.8 (-)-caryophyllene oxide 1.0 0.5 β-myrcene 0.3 δ-3-carene 0.3 α-terpinene 1.4 1,8-cineole 0.2 0.1 0.9-2.6 γ-terpinene 0.1 ar-curcumene 2.5 1.8 1,8 2.2 1.4 1.3 1.4-4.5 γ-curcumene 0.1 α-santalol 0.3 0.3 0.5 3.7 0.2 1.2 0.6 β-santalol (-)-α-pinene 0.2 α-patchoulene 0.4 (+)-α-atlantone 1.3 2.3 4.7 β-himachalene 0.1 farnesol 0.1 0.1 9 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 reaching 2.9% ww. aspergillus oryzae resulted in the highest turmeric oil yield compared to the other two species of 3.2% dw after 11 days of fermentation. of the three aspergillus spp., the greatest decrease in starch content and increase in the oil yield occurred on the 9th day. incubation of turmeric rhizomes by aspergillus reduced the content of ar-turmerone but increased the content of α-turmerone and β-turmerone compounds, which could be transformed into ar-turmerone. the use of aspergillus oryzae as a biological agent for the biodegradation process showed the most positive influence on the extraction of turmeric oil compared to the other two species, with the maximum increase in oil yield and decrease in starch content on the 11th day. references [1] lertsutthiwong p, rojsitthisak p. (2011) chitosan-alginate nanocapsules for encapsulation of turmeric oil. pharmazie, 66:911-915. [2] chopra d, simon d. (2000) the chopra centre handbook: natural prescriptions for perfect health. india, rider. [3] awasthi p, dixit s. (2009) chemical composition of curcuma longa leaves and rhizome oil from plants of northern india. journal of young pharmacists, 1(4):312. [4] parveen z, nawaz s, siddique s, shahzad k. (2013) composition and antimicrobial activity of the essential oil from leaves of curcuma longa l. kasur variety. indian j. pharma sci., 75(1):117-122. [5] statistika tanaman biofarmaka indonesia. available: https://www.bps.go.id/publication/2019/10/07/65ba24004819d2bbb96bdf63/statistik-tanamanbiofarmaka-indonesia-2018.html [6] diederich m, noworyta k. (2012) natural compounds as inducers of cell death. usa, springer science and business media. [7] manzan accm, toniolo fs, bredow e, povh np. (2003) extraction of essential oil and pigments from curcuma longa [l] by steam distillation and extraction with volatile solvents. journal of agricultural and food chemistry, 51(23):6802-6807. [8] kurmudle n, bankar sb, kagliwal ld, singhal rs. (2013) enzyme-assisted extraction for enhanced yields of turmeric oleoresin and its constituents. food bioscience, 3:36-41. [9] klein-marcuschamer d, oleskowicz-popiel p, simmons ba, blanch hw. (2011) the challenge of enzyme cost in the production of lignocellulosic biofuels. biotechnology and bioengineering, 1-5. [10] el-gendi h, saleh ak, badierah r, redwan em, el-maradny ya, el-fakharany em. (2022) a comprehensive insight into fungal enzymes: structure, classification, and their role in mankind’s challenges. j fungi (basel), 8(1):23-33. [11] hakala tk. (2007) characterization of the lignin-modifying enzymes of the selective white-rot fungus. phd thesis, university of helsinki, helsinki. [12] andersen mr, giese m, de vries rp, nielsen j. (2012) mapping the polysaccharide degradation potential of aspergillus niger. bmc genomics, 13(1):313-319. [13] varga j, frisvad jc, samson ra. (2009) a reappraisal of fungi producing aflatoxin. world mycotoxin journal, 2:263-277. [14] de vries rp, visser j. (2001) aspergillus enzymes involved in degradation of plant cell wall polysaccharides. microbiology and molecular biology reviews, 65(4):497-552. [15] abduh my, zuliansyah w, aprina l, arazella n. (2019) effect of pectin biodegradation with aspergillus niger on total flavonoid content of citrus limon l. j biodjati, 4(2):194-203. [16] abduh my, nababan e, ginting f, juliati j, nugrahapraja, h. (2020) biodegradation of lemon peels using aspergillus sp. to improve yield and composition of extracted lemon oil. iium engineering journal, 21(2):55-66. [17] national horticulture board. avalable: https://nhb.gov.in/model-projectreports/horticulture%20crops/patchouli/patchouli1.htm [18] zambare v. (2010) solid state fermentation of aspergillus oryzae for glucoamylase production on agro residues. international journal of life sciences, 4:16-25. 10 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 [19] diaz-maroto mc, perez-coello ms, gonzalez vma, cabezudo md. (2003) influence of drying on the flavor quality of spearmint (mentha spicata l.) journal of agricultural and food chemistry, 51:1265-1269. [20] manzan accm, toniolo fs, bredow e, povh np. (2003) extraction of essential oil and pigments from curcuma longa [l.] by steam distillation and extraction with volatile solvents. journal of agricultural and food chemistry, 51:6802-6807. [21] inderaja bm, pradhita o, hanifa r, manurung r, abduh my. (2018) factors affecting biomass growth and production of essential oil from leaf and flower oil salvia leucantha cav. journal of essential oil bearing plants, 21(4):1021-1029. [22] ahmad hn, raba he, fadilla i, fajar a, manurung r, abduh my. (2018) determination of yield and chemical composition of eucalyptus oil from different species and locations in indonesia. biological and natural resources engineering journal, 1(1):36-49. [23] abduh my, ibrahim in, atika u, manurung r, suheryadi d. (2020) influence of water stress and plant age on the yield and chemical composition of essential oil from cymbopogon winterianus jowitt. biotropia, 27(1):80-87. [24] rahimmalek m, goli sah. (2013) evaluation of six drying treatments with respect to essential oil yield, composition and color characteristics of tymys daenensis subsp. daenensis, celak leaves. industrial crops and products, 42:613-619. [25] hamrouni-sellami i, wannes wa, bettaieb i, berrima s, chahed t, marzouk b, limam f. (2011) drying sage (salvia officinalis l.) plants and its effects on content, chemical composition, and radical scavenging activity of the essential oil. food and bioprocess technology, 5(8):2978-2989. [26] sourestani mm, malekzadeh m, tava a. (2014). influence of drying, storage, and distillation times on essential oil yield and composition of anise hyssop [agastache foeniculum (pursh.) kuntze. journal of essential oil research, 26:177-184. [27] de castro am, carvalho df, freire dmg, castilho lr. (2010) economic analysis of the production of amylases and other hydrolases by aspergillus awamori in solid-state fermentation of babassu cake. enzyme research, 1-9. [28] kusbiantoro d, purwaningrum y. (2018) pemanfaatan kandungan metabolit sekunder pada tanaman kunyit dalam mendukung peningkatan pendapatan masyarakat. jurnal kultivasi, 17(1):544-549. [29] de soulza pm, magalhaes po. (2010) application on microbial α-amylase in industry-a review. brazillian journal of microbiology, 41(4):850-861. [30] nangin d, sutrisno a. (2015) enzim amilase pemecah pati mentah dari mikroba: kajian pustaka. jurnal pangan dan agroindustri, 3(3):1032-1039. [31] reyes i, cruz-sosa f, hernandez-jaimes c, venon-carter ej, alvarez-ramirez j. (2017) effect of solid-state fermentation (aspergillus oryzae var. oryzae) on the physcochemical properties of corn starch. starch, 69:1-10. [32] standbury pf, whitaker a, hall sj. (2003) principles of fermentation technology. oxford, butterworth-heinemann. [33] doughari jh, santos baq, ntwampe sko. (2016) application of aspergillus awamori grown on citrus peel supplemented growth medium for cyanide bioremediation. nigerian journal of microbiology, 30(1):3221-3224. [34] zambare v. (2010) solid state fermentation of aspergillus oryzae for glucoamylase production on agro residues. international journal of life sciences, 4:16-25. [35] farid maf, shata hmah. (2011) amylase production from aspergillus oryzae ls1 by solidstate fermentation and its use for the hydrolysis of wheat flour. iranian journal of biotechnology, 9(4):267-274. [36] kalaiarasi k, parvatham r. (2015) optimization of process parameters for α-amylase production under solid-state fermentation by aspergillus awamori mtcc 9997. journal of scientific & industrial research, 74:286-289. [37] umsza-guez ma, diaz ab, de ory i, blandino a, gomes e, carlo i. (2011) xylanase production by aspergillus awamori under solid state fermentation conditions on tomato pomace. brazilian journal of microbiology, 42(4):1585-1597. 11 iium engineering journal, vol. 24, no. 1, 2023 abduh et al. https://doi.org/10.31436/iiumej.v24i1.1629 [38] kurmudle n, bankar sb, kagliwal ld, singhal rs. (2013) enzyme-assisted extraction for enhanced yields of turmeric oleoresin and its constituents. food bioscience, 3:36-41. [39] yamane y, fujita j, izuwa s, fukuchi k, shimizu r, hiyoshi a, fukuda h, mikami s. (2002) properties of cellulose-degrading enzymes from aspergillus oryzae and their contribution to material utilization and alcohol yield in sake mesh fermentation. journal of bioscience and bioengineering, 93(5):479-484. [40] naibaho ra. (2018) karakterisasi simplisia, isolasi dan analisis komponen minyak atsiri dari rimpang dan daun kunyit (curcuma domestica val.) kering secara gc-ms. [41] huong ntm, cuc ntk, dung tk, ha tl, cuong pv. (2013) chemical composition and antifungal activity of vietnamese turmeric aromatic products obtained from curcuma longa (zingiberaceae) by different methods. food science, engineering, and technology, 60:539-545. [42] chane-ming j, vera r, chalchat jc, cabassu p. (2002) chemical composition of essential oils from rhizomes, leaves and flowers of curcuma longa l. from reunion island. journal of essential oil research, 14(4):249-251. [43] naz s, ilyas s, parveen z, javed s. (2010) chemical analysis of essential oils from turmeric (curcuma longa) rhizome through gc-ms. asian journal of chemistry, 22(4):3153-3160. [44] chowdhury ju, nandi nc, bhuiyan mni, mobarok mh. (2008) essential oil constituents of the rhizomes of two types of curcuma longa of bangladesh. bangladesh. [45] hur sj, lee sy, kim yc, choi i, kim gb. (2014) effect of fermentation on the antioxidant activity in plant-based foods. food chemistry, 160:346-356. [46] fujiwara m, marumoto s, yagi n, miyazawa m. (2010) biotransformation of turmerones by aspergillus niger. journal of natural products, 74(1):86-89. [47] baser khc, buchbauer g. (2015) handbook of essential oils: science, technology, and applications. crc press. 12 microsoft word 243 completed iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ghazali et al. 97 automated characterization of single-photon avalanche photodiode aina mardhiyah m. ghazali 1 , audun nystad bugge 2 , sebastien sauge 3 and vadim makarov 2 1 department of science in engineering, faculty of engineering, international islamic university malaysia, p.o box 10, 50728 kuala lumpur, malaysia. 2 department of electronics and telecommunications, norwegian university of science and technology, no-7491 trondheim, norway. 3 school of information and communication technology, royal institute of technology (kth), electrum 229, se-16440, kista, sweden. ainamardhiyah71@gmail.com abstract: we report an automated characterization of a single-photon detector based on commercial silicon avalanche photodiode (perkinelmer c30902sh). the photodiode is characterized by i-v curves at different illumination levels (darkness, 10 pw and 10 µ w), dark count rate and photon detection efficiency at different bias voltages. the automated characterization routine is implemented in c++ running on a linux computer. abstrak: kami melaporkan pencirian pengesan foton tunggal secara automatik berdasarkan kepada diod foto runtuhan silikon (silicon avalanche photodiode) (perkinelmer c30902sh) komersial. pencirian diod foto adalah berdasarkan kepada plot arus-voltan (i-v) pada tahap pencahayaan yang berbeza (kelam tanpa cahaya, 10pw, dan 10µ w), kadar bacaan latar belakang, kecekapan pengesanan foton pada voltan picuan yang berbeza. pengaturcaraan c++ digunakan di dalam rutin pencirian automatik melalui komputer dengan sistem pengendalian linux. keywords: avalanche photodiode (apd); single photon detector; photon counting; experiment automation 1. introduction single-photon detectors (spds) are widely used for measuring extremely low light intensities. they have found diverse applications in laser ranging [1], astronomy [2], fluorescence detection [3], quantum optics, quantum information and quantum key distribution [4]. nowadays, technologies for spds include photomultipliers, avalanche photodiodes (apds), frequency up-conversion, visible-light photon counters, and several types of superconducting devices [5]. however, in real applications, apds are often the most practical choice due to several advantages as compared to other photodetectors: small size, ruggedness, reliability, low sensitivity to magnetic fields and external disturbance in general, as well as lower cost [6, 7]. in order to detect single photons, the apd is operated in geiger mode, and is also known as a single-photon avalanche diode (spad) [7]. in this mode the apd is biased above its breakdown voltage vbr. single-photon sensitivity is achieved by exploiting the internal signal amplification, called avalanches, due to the process of impact ionization. in the geiger mode, the electron-hole generation becomes self-sustaining, and one can register a macroscopic current flow due to a single incident photon. currently, silicon iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ghazali et al. 98 apds are the most common choice for single-photon detection in the visible to nearinfrared range up to ~1000 nm [4, 7]. there are several characteristics associated with the spad that need to be assessed prior to its use, for example its spectral range, dark count rate, dead time, photon detection efficiency, and timing jitter [7]. often, characterization of many apd samples at different temperatures is required. repeated characterization of the same sample may be useful in reliability studies and tests of apd’s resilience against external factors, such as radiation and laser damage. in all these cases, a manual characterization would be impractical, and might also be less consistent. in this paper, we report a fully automated characterization of the i-v curves, dark count rate and photon detection efficiency of a perkinelmer c30902sh commercial silicon avalanche photodiode. a custom testing setup has been built, and characterization programmed in c++ on a linux platform. 2. experimental setup when the apd is reverse-biased above the breakdown voltage, an absorbed photon will trigger an avalanche event consisting of thousands of carriers. the current continues to flow until the avalanche is quenched by lowering the bias voltage to vbr or below. in our single-photon detector, we use a simple and robust passively-quenched scheme (fig. 1) [11–13]. the circuit consists of a high-voltage supply, 390 kω bias resistor, and a highspeed comparator for sensing the avalanche current. the avalanche current is initially sustained by charge stored in apd stray capacitance, however the voltage at the apd quickly drops and the avalanche self-quenches in about 1 ns. then the capacitance is slowly charged via the bias resistor, and the detector recovers its sensitivity in ~1 µs. the apd is cooled with a thermo-electric cooler to a fixed temperature of –25 °c, in order to reduce its dark count rate [8]. fig. 1: passively-quenched detector circuit. figure 2 depicts a schematic diagram of the characterization setup. signametrics smu 2055 multimeters were used to measure the bias voltage, average current flowing through the apd, and apd temperature. a stanford research systems sr620 universal time interval counter was used to measure the frequency of photon counts registered at the detector. we used two signal lasers: one jdsu 54-00213 and one sanyo dl-8141-002, both powered by a highland technology p400 signal generator. the lasers were coupled via single-mode optical fibers and 10/90 coupling ratio optical fiber coupler into one attenuated arm to the spad, and another arm to the power meter. the laser power was measured by a newport 1830-c power meter using a newport 818-sl-l photodetector head. an oz optics da100 programmable attenuator was used to attenuate the laser light illumination to the desired intensity at the spad. the attenuation was calculated based on the power measured by the power meter and the manually determined splitting ratios of the coupler including fixed attenuation. all instruments were connected to the computer 60 mv 100 ω detector output vbias 10 kω 390 kω apd hermetical housing + = = _ iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ghazali et al. 99 using rs-232 interface, except the smu 2055 multimeters which were connected via usb interface. fig. 2: apd characterization setup. sufficient blackout measures were implemented to leave the apd in complete darkness when both lasers were unpowered. in order to run complete characterization of spad as a function of bias voltage automatically, we should be able to a. control the power level of lasers and measure the power; b. set the bias voltage of the spad; c. measure the photon count rate registered by the detector; b ia s v o lt a g e ( v ) d io d e c u rr e n t t e m p e ra tu re ( v ) s ig n a l o u tp u t to comparator/ signal out apd circuit optical setup apd newport 818sl 90/10 10/90 fixed attenuator variable attenuator da100 808 nm 830 nm 0 – 10 v high voltage supply usb usb rs-232 rs-232 rs-232 rs-232 computer pulse generator p400 power meter newport 1830-c pulse counter sr620 3 multimeters smu 2055 nidaq usb 6215 signal laser sanyo signal laser jdsu v v 390 kω 10 kω 100 ω gnd iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ghazali et al. 100 d. measure the bias voltage applied; e. measure the average current through the spad. we implement the automated characterization routine using the object-oriented c++ programming language in a linux environment. for data analysis, shell scripts and the open source numerical computation language/interpreter octave were used. 3. spad characterization parameters in order to detect single photons, the spad must be operated in geiger mode, i.e., it is biased above the breakdown voltage. overbias voltage is defined as ����� � ��� � ��� , (1) where vbias is the bias voltage applied. while operating in geiger mode in darkness, spurious avalanches in the spad produce random pulses at a frequency known as the dark count rate (dc). these counts arise due to thermal carrier generation, band-to-band tunneling, and afterpulses (emission of trapped carriers from deep trap levels) [7, 12]. as vbias is increased, there is a sharp increase in the photodiode current, i if the spad is under suitable illumination. a sharp bend in the i-v curve roughly coincides with vbr. the intensity of the incident light must be strong enough that it triggers many avalanches when the bias voltage increases past vbr, yet weak enough to not cause a significant amplified photocurrent below vbr. alternatively, vbr can be determined from threshold voltage vth. threshold voltage is defined as the voltage at which photon counts start to appear at the detector output. vth is higher than vbr by a fixed offset that depends on the comparator threshold setting, as the avalanche pulse must be of certain amplitude to be detected by the comparator. in our detector, this offset is 3.3 v (vbr for calculating this offset value was determined manually by observing on an oscilloscope at which bias voltage small analog avalanche pulses begin to appear at the comparator input). the photon detection efficiency (de) is defined as the probability of detecting a photon incident on the detector. it depends on the diode’s quantum efficiency and the probability for an electron-hole pair to trigger an avalanche [10]. the detection efficiency can be obtained through two distinct methods: by a calibrated light source [5] and by the correlated photon method [14]. we implemented the former. in this work the spad was illuminated with thousands photons per second at 830 nm. de can be calculated as de � �� � dc�/�, �2� where c is the measured photon count rate, � � ��/�� is the calibrated incoming photon rate, p is the continuous-wave (c.w.) optical power focused in the middle spot of the spad photosensitive area, λ is the laser wavelength, h is the planck constant and c is the speed of light. in our experiment, we restricted p to 10 fw which corresponds to 41750 photons/s, in order to avoid having to take into account detector saturation effects [8]. in most photon-counting applications, a high value of de is advantageous, however as we’ll see later there is a tradeoff with increased dc. iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ghazali et al. 101 4. measurement methods and algorithms the entire spad characterization specified above is run from a c++ program on a computer. each instrument was assigned with its own namespace which contained a class definition, and functions declaration for the instrument to be working accordingly. a main function was created to run the entire characterization program. for each measurement, one function was created to set the instruments as per measurement requirements. for all measurements, the maximum overbias voltage was limited to 50 v (corresponding vbias known from a rough manual measurement), to avoid damage to the spad. the counting time was 10 s, except at vover = 15 v it was set to 100 s to reduce statistical uncertainty in data. 4.1 i-v curves the initial step in the automated characterization of the spad was to measure the breakdown voltage, vbr from the i-v curve. the algorithm was as follows. as different bias voltages, vbias were applied across the spad, the potential drop over the 10 kω resistor v10k was measured by a smu 2055 multimeter (see fig. 2). then, the current i through the spad was calculated as � � ���� /10 kω. �3� next, the voltage across the apd vapd could be determined as � !" � ��� � �#$%$&', �4� where �#$%$&' � �)*�* +, and )*�* + = 390 kω (bias resistor) + 10 kω + 100 ω = 400100 ω. a plot of i versus vapd was then created using these equations. all calculations and plots were done in octave software. i-v curves were obtained for three different illumination levels; zero, weak and medium illumination power. the purpose of the low power illumination was to detect the sharp increase in current which occurs at vbr. the purpose of the medium illumination power was to observe avalanche multiplication below vbr and diode quantum efficiency at low values of vbias (when no multiplication occurs). the measurements were achieved using the following parameters. a. zero illumination: both lasers were off. b. weak illumination: the apd was illuminated at 10 pw c.w. power at 830 nm. c. medium illumination: the apd was illuminated at 10 µw c.w. power at 808 nm. 4.2 threshold voltage threshold voltage vth was obtained by measuring the dark count rate and the photon count rate (at 41750 photons/s) as a function of vbias, using the sr620 counter. vth determination was divided into two parts: binary search, and linear search with 0.1 v increment. binary search is needed because of the large range of possible vbias. first, the search starts as a linear search in ±0.5 v range around a manually pre-calibrated value of vth. at this point, if no counts were detected, or if counts were found at the lower bound of the linear search, the algorithm escapes to a binary search. the binary search will be conducted in the range between vth and the maximum vbias if the linear search produced no counts. it will be conducted in the range between 0 v and the initial vth if counts were registered at the lower bound of the linear search. the binary search seeks vth by iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ghazali et al. 102 repeatedly splitting the search range into half, until the range becomes smaller than 1 v. then, a linear search will be executed over the remaining voltage range. unexpected conditions such as always zero counts or always non-zero counts over the full range of bias voltages are recognized by the program, and will be registered in the log file. the program is designed such that it will not crash or hang due to such conditions. 4.3 dark count rate and photon detection efficiency once vbr is determined, the dark and photon count rates are measured as a function of overbias voltage, at vover = 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45 v. the data is then used to calculate de via eq. 2. 5. results figure. 3 depicts the plots of i versus vapd at three different illumination levels. at 10 pw illumination, the sharp bend indicating vbr ≈ 166.6 v is clearly visible {fig. 3(b)}. from fig. 3(c), we calculate the quantum efficiency of 82 % at low bias voltage, when the apd has no internal gain. fig. 3: i-v curves at (a) no illumination, (b) weak illumination (10 pw), and (c) medium illumination (10 µw). the results of dark count rate and photon count rate measurements are shown in fig. 4. the value of vth ≈ 170 v can be readily observed from both curves. dc increases 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 c u r r e n t (µ a ) apd reverse bias (v) a) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 0 50 100 150 200 0 50 100 150 200 0 50 100 150 200 c u r r e n t (µ a ) apd reverse bias (v) weak light (10 pw) no light b) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 c u r r e n t (µ a ) apd reverse bias (v) medium light (10 µ w)c) iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ghazali et al. 103 with overvoltage. de also increases, until it peaks at vover ≈ 30 v. the following decrease of the count rate is due to self-sustaining avalanches, which is a known characteristic of the passively-quenched scheme [8]. based on the data of fig. 4 and eq. 2, de is calculated, (fig. 5). the highest photon count efficiency is ≈ 55% at vover ≈ 30 v. fig. 4: detector count rate vs. bias voltage at (a) no illumination (dark count rate), and (b) 10 fw c.w. illumination (41750 photons/s). fig. 5: photon detection efficiency vs. bias voltage. 6. conclusion we demonstrated automated characterization of a spad. using the developed algorithms, implemented in c++ and octave on linux platform, we were able to measure i-v curves, automatically determine breakdown voltage, measures dark count rate and photon detection efficiency. the developed characterization platform can be easily adapted and extended for different experimental needs. 0 5000 10000 15000 20000 25000 150 160 170 180 190 200 210 220 c o u n ts p e r se c o n d c o u n ts p e r se c o n d 0 500 1000 1500 2000 2500 3000 3500 150 160 170 180 190 200 210 220 bias voltage (v) bias voltage (v) 41750 photons per second (10 fw continous wave) dark countsa) b) 0 10 20 30 40 50 60 160 170 180 190 200 210 p h o to n d e te c ti o n e ff ic ie n c y ( % ) bias voltage (v) iium engineering journal, vol. 12, no. 5, 2011: special issue -1 on science and ethics in engineering ghazali et al. 104 acknowledgements we thank raihan othman and johannes skaar for group leadership, qin liu and lars lydersen for help with programming, christian kurtsiefer for providing the detector electronics design. this work was supported by the research council of norway (grant no. 180439/v30). a.m.m.g. acknowledges travel support from the international shari’ah research academy for islamic finance (isra). s.s. acknowledges support from the ecoc’2004 foundation and the research council of sweden (vr, grant no. 621-20074647). references [1] i. prochàzka, k. hamal, and b. sopko, “photodiode based detector package for centimeter satellite laser ranging”, proc. 7 th int. workshop laser ranging instrumentation, c. veillet, oca-cerga grasse, 1990, ed., matera, italy, oct. 2–8, 1989, pp. 219–221. [2] n. s. nightingale, “a new silicon avalanche photodiode photon counting detector module for astronomy”, exp. astron. 1, 407–422 (1991). [3] s. cova, a. longoni, a. andreoni, and r. cubeddu, “ a semiconductor detector for measuring ultra-weak fluorescene decays with 70 ps fwhm resolution”, ieee j. quantum el., qe-19, 630–634 (1983). [4] n. gisin, g. ribordy, w. tittel, h. zbinden, “quantum cryptography”, rev. mod. phys. 74, 145–195 (2002). [5] r. h. hadfield, “single-photon detectors for optical quantum information applications”, nat. photonics 3, 696–705 (2009). [6] zappa et al., “an integrated active-quenching circuit for single-photon avalanche diodes”, ieee trans. instrum. and measurements 49, 6, 1167–1175 (2000). [7] s. cova, m. ghioni, a. lotito, i. rech, and f. zappa, “evolution and prospects for singlephoton avalanche diodes and quenching circuits”, j. mod. opt. 51, 1267–1288 (2004). [8] y.-s kim, y.-c. jeong, s. sauge, v. makarov, and y.-h. kim, “ultra-low noise singlephoton detector based on si avalanche photodiode”, rev. sci. instrum. 82, 093110 (2011). [9] f. zappa et al., “integrated array of avalanche photodiode for single-photon counting”, ieee european solid-state device research conference (essderc), 600–603 (1997). [10] c. niclass, m. sergio, and e. charbon, “a single photon avalanche diode array fabricated in deep-submicron cmos technology”, in proc. date, 1–6 (2006). [11] r. h. haitz, “model for the electrical behavior of a microplasma,” j. appl. phys. 35, 1370– 1376 (1964). [12] r. h. haitz, “mechanisms contributing to the noise pulse rate of avalanche diodes,” j. appl. phys. 36, 3123–3131 (1965). [13] s. cova, m. ghioni, a. lacaita, c. samori, and f. zappa, “avalanche photodiodes and quenching circuits for single-photon detection,” appl. opt. 35, 1956–1976 (1996). [14] d. n. klyshko, “use of two-photon light for absolute calibration of photoelectric detectors,” sov. j. quantum electron. 10, 1112–1117 (1980). iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 53 large eddy simulation for transesterification of waste vegetable oil a. k.m. mohiuddin and nabeel a. adeyemi department of mechanical engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. mohiuddin@iium.edu.my (received 15 march 2015; accepted 26 march 2015; published on line 29 may 2015) abstract:this paper provides detailed information involved in the numerical simulation of transesterification of waste vegetable oil (wvo). the main objective of this work is to perform a mixing study based on large eddy simulation particle image velocimetry (les-piv) which is resolved in the turbulent scale. reynolds stress model (rsm) was subsequently used to validate the result using a multiple reference frame (mrf) approach for the impeller-vessel geometry. experimental fame yield and liquid velocities were found to be dependent on stirrer speeds, impeller bottom distance and bulk flow pattern. thermodynamic properties of the reaction components were incorporated as user defined function (udf) for the mixing models. fame yield was predicted in terms of species concentration and compared fairly well with experimental condition for 1-l and 2-l str, where yield from the numerical model varied by about 18 and 23 % for 1-l and 2-l str respectively. the characteristic time scales were used to show the relevant mixing scale to describe the process. abstrak: kertas kerja ini memberikan informasi terperinci dalam pentransesteran simulasi berangka sisa minyak sayuran (wvo). matlamat utama penyelidikan ini adalah untuk menjalankan kajian bauran berdasarkan kepada velosimetri imej partikel simulasi pusaran besar (les-piv) yang terlerai pada skala turbulen. model stress reynolds (rsm) kemudiannya digunakan bagi mengesahkan keputusan menggunakan kaedah kerangka rujukan berbilang (mrf) untuk geometri bekas-pendesak. keputusan eksperimental fame dan halaju bendalir didapati bergantung kepada kelajuan pengacau, jarak dasar pendesak dan corak aliran pukal. ciri-ciri termodinamik komponen reaksi digunakan sebagai fungsi mentakrif pengguna (udf) untuk model bauran. hasil fame dijangkakan dalam terma konsentrasi spesis dan dibandingkan dengan adilnya dengan kondisi eksperimental untuk str bagi 1-l dan 2-l, dimana hasil daripada model berangka didapati berbeza di antara 18 dan 23% untuk str bagi 1-l dan 2-l. untuk menggambarkan proses, skala berciri masa digunakan bagi menunjukkan kaitan hubungan skala bauran. keywords: transesterification; cfd; waste vegetable oil; str; impellers 1. introduction the main objective of this paper is to use computational fluid dynamics (cfd) modeling approach to integrate reaction measurements and computational modeling in a multi-scale framework. the cfd model of the wco transesterification is proposed to be used in the development process condition with few experimental data regarding transesterification of wvo. iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 54 the production of biodiesel in str takes place in the turbulent range. understanding the mixing regime for process improvement is quite important. literatures on biodiesel production mostly report radial impellers to achieve mixing during oil transesterification [1]. at a stoichiometric molar ratio of 3:1 (alcohol to oil), the conversion of oil to biodiesel takes place in the presence of a homogenous catalyst where the reaction is understood to be either the formation of two intermediates before forming the final product [2] or the formation of only one intermediate subsequent to formation of the final product [3]. formations of undesirable products are often mitigated by increasing rate of reaction with excess alcohol [4]. however, studies on effects of impellers are few. different mixing impellers produce certain different effects in multi-component reactions [5]. where it is necessary to promote yield of a single component without unnecessary side products, mixing velocities is selected to produce the right mixing-scale and a mass transfer rate. flow varies significantly both in magnitude and direction within the str and difficult to experimentally quantify. where the flow in str have been quantified and compared reasonably with a numerical model [6], the added complexity due to reaction gives rise to uncertainties which are not addressed in kinetic reaction models. dynamic modeling couples the physical phenomena (reaction and flow) using numerical methods to study flows and reactions. it provides a broader insight into the equipment designs and compares performance of the reactors under different operating conditions [7]. in principle, numerical solutions of flows, in confined space, with appropriate boundary and initial conditions are used to study mixing processes and their solutions are applicable over a wide range of conditions that are rather expensive to obtain experimentally. 2. wvo transesterification parameterization transesterification was carried out in a 2-l stirred tank reactor (str) (fig. 1). the str dimensions are listed table 1. the naoh catalyst (1-1.5 ± 0.02 % oil wt) was dissolved in methanol (140 ml). the oil-to-alcohol stoichiometric ratio was kept at 1:6 and the excess methanol was used to drive the reaction forward and prevent auto-catalysis. the reaction conditions with regards to the molar ratio of oil to alcohol and catalyst amount was according to the optimized value [8] used for fryer grease. all mixing was carried out for 60 min with a variable speed motor, automatic timer and temperature controller. products samples were rinsed with hot water (90°c) and dried for 6 hr. fig. 1 2-l laboratory str. iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 55 table 1: description of tank an impeller geometry with dimensions tank height, h (mm) 200 tank diameter, t (mm) 130 mixed flow impeller, impeller diameter, d (mm) impeller blade height (mm) impeller blade length (mm) no of blades blade angle to the shaft (downward/axial flow) 55 d/4 d/1.5 3 50 impeller bottom distance (ibc), c t/4 t/5 t/6.5 2.1 evaluation of free fatty acid (ffa) in wco for the evaluation of the ffa in wco sample, 50 ml isopropyl alcohol was prepared and added to 1 g of wco sample in the presence of 1 g of phenolphthalein. the solution was titrated against 0.1 m koh until color change was noticed in the solution. this was done in triplicates and the average ffa was calculated by eq. (1). (1) 2.2 taguchi method design of experiment the experiment was based on the taguchi orthogonal array (oa) l9 method [9]. three variables (temperature, speed and ibc) at 3 levels were used to design the experiment (table 2) in minitab 14. the taguchi method based on oa reduces variance for the experiments by optimizing setting of control parameters. to identify the effect of temperature, impeller speed, and ibc on yield, the signal to noise ratio (s/n) of the taguchi method (which are log functions of desired output) was used for data analysis and prediction of optimum parameters. table 2: taguchi design variables variables levels 1 2 3 temperature, t (°c) 60 65 70 impeller speed, s (rpm) 600 650 700 impeller bottom clearance, ibc (mm) 20 25 30 the s/n is defined as (2) where, n is the number of observations in the sub-sample and y is the data observations in the subset. the s/n is used to calculate the performance statistics values and contribution ratios of each parameter. thus the combination of design of experiments with optimization of control parameters to obtain the best results is achieved in the taguchi method. oa provides a set of well balanced (minimum) experiments. without the taguchi method, 16 experimental runs would have been needed to investigate the effect of each of the three 25.6 0.0864 naoh volume % difference in ffa sample weight      2 1 1 10 log bigger ys n n                iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 56 parameters instead of the 9 used. with the main effect analyses, possible combination of optimum parameters is predicted. these were further analyzed to determine the interactive effect of the three parameters. 2.3 standards and sample preparation for t, dg, mg and glycerol analysis gc-ms analysis of biodiesel according to astm d6584 was used to verify the g, mg, dg, t, and total glycerin content in wco and fame sample. experimental samples were analyzed on a db 23 agilent 6890 gc system with a split/splitless inlet and a column of 60 m × 0.25 mm id × 0.15 μm [10]. five gc calibration standards were prepared by mixing aliquots of the individual stock standards in proportions specified by the astm method. after mixing, 100 μl of the derivatization agent, n-methyl-n(trimethylsilyl) trifluoroacetamide (mstfa) was added to each calibration standard. after 20 min, 8 ml of reagent grade n-heptane was added to each calibration standard. these final reaction mixtures were directly injected into the gas chromatograph. 2.4 sample preparation for fatty acid analysis wco samples were analyzed by weighing 100 mg sample in a 20 ml test tube (with screw cap) and dissolved in 10 ml of hexane. 100 μl of 2 n koh in methanol (11.2 g in 100 ml) was added and vortex for 30 seconds. the supernatant was then transferred into a 2 ml auto sampler vial for gc analysis. 2.5 gc-ms analysis of t, dg, mg and glycerol fame yield was obtained by eq.3 during the reactions at time interval of 5, 10, 15, 30, 45 and 60 min. t, dg, mg and glycerol content in the fame samples were estimated using the relative retention times from the gc reading [10]. the retention time of the first internal standard, 1,2,4-butanetriol was used to identify and quantify free glycerin (g) while that of the second internal standard, tricaprin was used to identify and quantify the mgs, dgs, and ts in from the monoolein, diolein, and triolein calibration functions respectively. total glycerin (tg) was obtained using eq.4. (3) where, mfame = mass of ester, mwfame = molecular mass of ester, mwoil = molecular weight of oil and moil = mass of oil (4) 2.6 analyses of biodiesel properties the ignition quality tester (iqt) was used to measure the cetane number. kinematic viscosity and density were measured by using a kvs 702 tensiometer according to astm d445; pour point according to astm d97 by using a cloud and pour point analyzer (isl cpp 97-2); flash point by using a pensky-martens flash point tester (petrotest pma 4) based on astm d93; moisture content was determined by the karl fisher method; and oxidative stability by metrohm 743 rancimat according to en 14115 method and glyceride content was measured according to the method described above. all tests were carried out at the malaysian palm oil board, kajang, selangor, malaysia. 2.7 single phase two dimensional (2-d) particle image velocimetry in order to model the reaction, the hydrodynamic parameter such as velocity of impeller, turbulent kinetic energy and dissipation rate are needed. these were later ( %) 100 3 fame oil oil fame m yield mol m mw mw     tg g 0.255m 0.146d 0.103t    iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 57 compared with numerical results obtained from the cfd model and estimated from flow measurement of two mixing impellers using piv technique. 2-d velocity data of the liquid flow filed in a geometrically similar cylindrical acrylic flat-bottomed tank (fig. 2a) was set up as (i) unbaffled and (ii) baffled (fitted with 4 vertical baffles equally spaced radially at 90) tank were used along with a dantec piv equipment at high spatial resolution, which allowed the estimation of spatial velocity gradients and ε. the laser light sheet thickness was approximately 2 mm (0.15% of tank diameter) and aligned parallel to the z axis, 30 mm from the shaft center, just at the tip of the impeller. when the laser sheet is focused at the cente of the vessel, reflections from the impeller/shaft surface cast a shadow over the half of the piv in the images as a result of the reflective steel surfaces. the camera was focused on a 150 × 120 mm2 area which covered the whole impeller stream region and nearly to the tank wall in the horizontal. for piv measurement the set up parameters are listed in table 3. the vessel is filled with water ( =1000 kgm3, = 10-6 m2/s). (a) (b) fig. 2 (a) cylindrical acrylic flat-bottomed tank (b) mixed flow impeller. table 3: piv recording parameters for flow in str flow geometry : parallel to light sheet and plate max in-plane velocity : umax≈ 1.2m/s field of view : 150 × 120mm2 observation distance : z0 ≈ 0.6m recording method : dual frame/single exposure recording medium : full frame interline transfer ccd illumination : nd:yag laser 120mj/pulse pulse delay : δt = 263μs seeding material : psp (dp ≈ 20 μm), =1030 kg/m3 2.8 flow measurement the piv readings were performed on the plane x-y and y-z to the impeller shaft. to define the flow conditions in the 2 l batch str, cylindrical acrylic tank (3 mm thick) was placed in a square tank with water to observe distortions in the piv.   field of iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 58 fig. 3 plane of piv measurement (a) z-x plane (b) z-y plane. measurements were taken at impeller speeds of 600, 650 and 700 rpm. in the turbulent flow regime, the instantaneous velocity of the fluid at any point is impossible to predict, hence a statistical approache is used to calculate mean and root mean square (rms) velocities provided the flow is steady on average (constant flow rate). for each set of 2-d measurements, 600 pairs of pictures were taken at a frequency of 4 hz and the measurements were repeated a number of times to establish reproducibility. basically, a pair of images is divided into smaller regions (interrogation windows). the crosscorrelation between these image sub-regions measures the optic flow (displacement or velocity of the objects) within the image pair. two consecutive images were crosscorrelated to give the velocity field with a total of 39 × 31 velocity vectors for the entire plane. the time separation between two exposures was estimated using eq.5 (5) where s is scale factor, n is interrogation area, d is pixels pitch, and v is velocity (estimated). in our case n=64 pix, d = 6.7 μm where the time used in the experiment should be less than the calculated t. the maximum desired particle displacement, dmax, between pulses was ensured to be one quarter of the interrogation length, liv, where maximum separation was then given as a function of the magnification of the image, m and the maximum velocity, utip, within the system ௠௔௫ܦ = ଴.ଶହ௅಺ೇெ ௎೟೔೛ (6) where m is image magnification in μm/ pixel. interrogation area (ia) of 64 × 64 pixels was used for the first pass and 32 × 32 pixels were adopted for the second pass at 50% overlap between ia, and the final resolution of the velocity measurements was 32 × 32 pixels. post-processing of the piv data for an interrogation area of 32 × 32 and 64 × 64 pixels were compared to determine the best size. mean velocity using 64 × 64 was seen to be closer to the theoretical value compared to results using 32 × 32 as shown in fig. 4. in order to obtain good quality results, the vectors obtained from the piv were processed by removing the outer rows of vectors. spurious vectors around the image edges occur due to high pixel sensitivity in that region. also vectors which have a velocity greater than 1.5 times the tip velocity were taken to be spurious.    t s 0.25n 2 d / vmax vmin   iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 59 fig. 4 static piv calibration. impeller rotation is clockwise as viewed from above and origin of the coordinate system used is the base of the center of the vessel with and being the mean and root-mean-square (rms) velocities in the axial (z, directed upwards), radial (r, directed outward from the shaft) and tangential ( , directed out of the plane) directions respectively. the tip velocity (vtip) and reynolds number (re) are estimated for the impeller according to eq.7 and eq.8 and data from table 1. (7) (8) and average volume dissipation rate in str, is (9) and (10) where power, p is the impeller power needed for the mixing, m is the number of blades and t is the torque. considering that eddies present in the flow must be accounted for, spatial resolution (δ) must be similar to the kolmogorov length scale ( ), where the mean kolmogorov length scale is estimated as: (11) in previous studies, spatial resolution has also been shown to strongly affect the value of dissipation [11]. spatial resolution is required to be similar to when studying turbulence in order to take into account the smallest turbulent scales in piv measurement [12]. in order to capture the turbulence scale, the piv resolution (spatial resolution) must be similar to the kolmogorov length scale. to resolve the seeding particle relaxation time , eq.12 is a convenient measure for the tendency of particles to attain velocity equilibrium with the fluid. this eq.13 is compared with eq.12 such that time due to u ,u ,uz r  , ,z ru u u    d ntipv    2re /n d   p v    p 2 nmt   (1/ 4) 3v           p iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 60 diameter of the largest particle is smaller than time associate with the kolmogorov time scale, eq.9 is computed from the overall mean dissipation rate at the rotation speed of the impeller [12]. (12) (13) (14) (15) (16) (17) (18) using the analogy of les, a large eddy piv method is used for estimation of the dissipation rate [13]. here, the biggest eddies in high reynolds number turbulent flows absorb energy from the mean flow, and transport it to smaller eddies. the large eddies are highly anisotropic, and strongly flow-dependent whereas the smallest eddies involved in tke dissipation tend to be flow-independent. this is why the spatial resolution of piv exceeds the smallest eddy sizes if dissipation rate is to be measured. hence the les analogy can resolve both velocity field (analogous to solving the ns equations), and model the unresolved scales using an interrogation cell size that is naturally the spatial filter. going by the les analogy, an inertial sub-range exists between the integral and kolmogorov scales. it is assumed that for dynamic-equilibrium that the flux of tke through the inertial sub-range is equal to the dissipation rate. to estimate this, only length scales within the inertial sub-range are required and it is not necessary to resolve the velocity field down to the kolmogorov scale. for the mixed flow impeller, the mass flow rate, q (m3 /s) through the impeller is taken as mass flow out of the impeller both at the side and the bottom. radial mass flow rate, q (m3 /s), was calculated by (19) over a radial distance equal to the radius of the impeller and integrated at the height, z, of the impeller. pumping number and power number are estimated using eq.20 and eq.21 respectively. (20) and p   2 p p p 18 d v     1/ 2 v         q 3 q n = nd b c b bn w dfl a b d t                0 3 2 ir z qr v rdr n nd    0 3 2 rr z qs v rdr n nd      i ii i p a r   2 1 q 2 . z r rz r u dz  2 1 32 / z q z n ru nd  iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 61 (21) to characterise the performance of impellers, non-dimensional power number of np (eq.21) is calculated. impeller speed 600, 650 and 700 rpm corresponds to re = 3.16 × 104, 3.43 × 104, and 3.69 × 104 with μ=0.789e-3 ns/m2 at 25c for water. 2.9 pre-processing of computational domain in the pre-processing stage, the tank and impeller were drawn in a cad environment and imported into gambit as a para-solid file for the meshing process. this ensured that the profile of the vessel is preserved when exported into gambit. even though other options like stp, iges or stl file format can be used to transfer the geometry into neutral format, loss of geometry is often experienced. edges that needed to be reconnected in gambit when iges format is used require time consuming refinement for the grid process. although gambit is not user friendly, as a pre-processor tool for geometry modeling, generated mesh is transferable to fluent without loss of features. 2.10 meshing the computational grid was divided into three parts; vessel, rotation part and impeller geometry. a hybrid mesh over the full three dimensional domain was adopted. the multiple reference frame (mrf) approach was selected for handling the stationary and the rotating walls in a fully-predictive way (fig. 5 and fig. 6). the vertical size of the rotating reference frame was 60 mm in diameter and 55 mm in height. the solution convergence was monitored as the residual of the variable approaches to 10−7. mesh resolution was obtained with 3 mesh sizing using gambit. the full vessel was modeled as the result of the shape of the impeller where blade overlaps into the other sector of the next blade. table 4 shows the mesh employed in this study. unstructured hexahedral cells ensured the edge of the geometry were not lost during geometry translation. skewness of all the meshes was below 0.81 as required for ansys fluent. (a) (b) fig. 5 (a) plane cut (b) 3-d unbaffled str with mixed-flow impeller using the mrf. 3 5 2 p nn n d     iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 62 (a) (b) fig. 6 (a) plane cut (b) 3-d baffled str with mixed-flow impeller using mrf. table 4: total cell number in baffled and unbaffled vessel for mixed flow impeller with multiple reference frame (mrf) baffle vessel unbaffled vessel mrf tank mrf tank mesh 1 64437 98353 88043 69591 mesh 2 187601 98353 82973 214985 mesh 3 110396 407917 85912 321827 mesh 4 187601 645504 761130 10171 mesh 5 560013 1225747 934194 90345 the mrf boundary was located at r/r = 0.46. the vessel wall was specified as stationary in the moving zone. for the mrf approach, no averaging was carried out while exchanging the information between the rotating and stationary zone in a fully-predictive way. the distance between the impeller blades and baffles were assumed to be sufficient so that the flow around the impeller is unaffected by the rest of the tank using the mrf. wall functions were used to specify wall boundary conditions. the top surface of the liquid pool was assumed to be flat and was modeled as zero normal velocity with zeroshear. the tank wall, shaft and impeller had a no-slip boundary condition. the torque from the numerical simulation is plotted against the different grid numbers (fig. 7) as a preliminary validation of the mesh size. from the grid dependency study, calculated torque from the numerical simulation was varied by 41% for mesh 1 (162790 cells), 23% for mesh 3 (518313 cells), 21% for mesh 4 (833105 cells) and 24% for mesh 5 (1785760 cells) from the experimental torque estimated as an average value of 0.01 nm. fig. 7 optimization check using five different mesh sizes. m iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 63 the difference between the torque estimation of 800,000 cells and the experimental value was considered to be within an allowable estimate and thus was used for this study. further increment in cell numbers did not improve calculated torque. 2.11 convergence monitoring scaled residuals were monitored to ascertain convergence until the values of residuals were reduced to three to five orders of magnitude. the momentum, lift and drag were also monitored thru the impeller surface. the integral of static pressure on the faces of the impeller blade was also included. 2.12 cfd mixing model the mixing model presented here follows the work of baldgya [6] using a closure modeling approach of transport equations. the average reaction rate is calculated based on a model of the local mixture structure accounting for concentration fluctuations on different scales [14]. vicum et al. [15] employed a multi-scale model, where a mean and fluctuating concentration of scalar tracer captured the different scales [16]. to consider the macro-mixing, the concentration of a scalar trace f from a mixture fracture is taken as (22) where dm is the molecular diffusivity and dt the turbulent diffusivity. to consider the micro-mixing, the variance of the mean of a tracer concentration and local concentration of f is decomposed to . the model of the decomposed variance represents the inertial-convective, viscous convective and viscous diffusive mechanism. the time scale for the changes in variance due to the inertialconvective is thus defined as . similarly dissipation of and production of is and . this way the model accounts for mixing at all the scale. a probability density function , approximated by a beta function is assumed for the mixture fraction. putting in terms of and f gives; (23) and are local concentration of the wco and fame. the concentration of fame is thus solved by a mass balance approach (24) dr j m t j j j f f p f u d d t x x x                    r   2 2 s f f   2 2 2 1 2 3, ,   2 1 / s  2 2 2 3 2 2 / e  2 3 / g  ( )f ( )f 2i 1 2 2 2 0 ( ) ( ) ( )r k cacb k ca f cc f f df     ( )ac f ( )cc f 2j m t j j j cc cc p cc u d d r t x x x                     r iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 64 however, the function describes the mixture fraction and can be used to determine , and f simultaneously [15]. for further details see baldyga and bourne [6] and baldyga et al. [16]. to solve conservation equations for chemical species, the conservation equations take the form of eq.16. the mass and transport equations have been studied with various approaches. in this work reynolds averaging approach is adopted, where the velocity and concentration of the transport equation are decomposed into a fluctuating and average concentration and velocity components: (25) (26) (27) eq.24 and eq.25 inserted into eq.23 yields (28) the terms and give an infinite set of moments because they must be resolved for each set of the species involved in the reaction. ordinarily, these terms could be ignored but the reactions are at the sub-grid level and these are the terms that explain the phenomenon at this level. first and second [17] order closure models have been used to close the equation. second order models yield higher order unclosed terms when a relatively larger number of equations have to be solved. when the species are perfectly mixed, the fluctuation term will approach to zero. however, the magnussen model, developed for combustion is used to incorporate the effect of the reaction rate on the fluctuation and average component implemented in the fluent solver as: (29) two mixing rates from the reactants and products that depend on the local turbulence kinetic energy and dissipation rate are computed as (30) (31) 0 , , a b c b c a b bulk c bulk c c c c c c c c       ( )ac f ( )cc f ', jc u  ,j jc u 2 12 j j j i a b i i c c c u d k c c t x x          j j jc c c  j j ju u u      2 ' ' ' ' 12 j j j i j j a b a b i i i c c c u d u c k c c c c t x x x              ' ' j ju c ' ' a bc c ', _ 1 1 exp j k f k k n nn n a k i k i k i k j i k i j j j e r m a t c k m c rt                              1 r m i k i k i k i k r m r m a m          2 , ' ' ' r p m i k i k i n j k j j m r m ab m            iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 65 the approach accounts for the high turbulence mixing. since this study is turbulence oriented, the yield in the str is determined by the degree of turbulence, power requirement, pumping capacity of the impeller and recirculation time through the strs. hence, the accuracy of the simulation is evaluated by comparing simulated results with available field measurements. a variety of turbulence models, convection schemes as well as different grid resolutions were employed and the models performance assessed. the major challenge was in the coupling of the reaction model, which contained unresolved component. 2.13 cfd process parameter the density for the wco and fame alcohol is estimated as 848.8 – 907.9 kg/m3 and 857 – 885 kg/m3 respectively, which has been verified experimentally. according to kay’s rule [18], thermo-physical properties of fame are estimated from their methyl ester composition. using the linear regression of the molecular weight of fame to specific heat [19], the specific heat for the fame and wco can be obtained as; (32) specific heat for t, dg was calculated as (33) where is the ideal gas specific heat capacity from the joback group contribution method and obtained as. (34) are parameters obtained based on contribution of methyl, alkyl, ester groups present in methyl ester. better estimation has been reported with modified rowlinson correlation with constantinou and gani acentric factor correlation, [19]. r is the universal gas constant. specific heat for mg and glycerol is provided by the expression in eq.35 and eq.36 respectively [20]; (35) (36) the viscosity of fame as a function of molecular weight and number of bonds is expressed as; (37) 21 06( ) 0.0009( ) 1.9291pc e m m     0 1/3 1 1 1.45 .45 / (1 ) 0.25 [17.11 25.2(1 ) 1.742(1 )] p p r r r r c c t t t r t             0 pc 0 2 3 37.93 0.210 0.000391 2.06 7 p j j j j j j j j c n a n b t n c t n d e t                                        , , and a b c d     2955.54 1703.1 4.1768pc t t   78, 468 480.714pc t  ( ) 12.503 2.496. ( ) 0.178i iln in m n     iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 66 where m is the molecular weight and n is the number of double bond [21]. with the strong dependency of viscosity on temperature [20], dynamic viscosity for t and mg is expressed as eq.38and eq.39, respectively; (38) (39) glycerol viscosity is taken as 3.5-5 mm2/s according to en14214 standard. the thermal conductivity, which is linearly dependent on temperature, is expressed as eq.40 and eq.41 for mg and glycerol respectively (40) (41) 2.14 time scaling the time-scale of reaction are defined in eq.42, eq.43 and eq.44 for, macro, micro and meso-mixing respectively; (42) where is the pumping volume around the impeller. this is obtained as the integral of the area over the impeller using with a three-dimensional cfd model. is a constant value. eq.48 accounts for the diffusivity at the feed point of mixing. however, the feed point was not included in this case study as the naoh/alcohol fraction was assumed to be part of the mixture. (43) the micro-scale mixing is reported to be driven by viscous-convective deformation [6], which has a time characteristic expressed as eq.44. (44) the molecular diffusion that produces micro-mixing at this level where the eddies, r is larger the kolmogorov mixing is accounted for by eq.45. (45) v is the kinematic viscosity, dm is the turbulent diffusivity and 218584exp 136.48 18.61ln 2596500t t t         1731.2 exp 11.67 t        0.22919 0.00019t   0.258 0.0001134t   c feed v q   3 1 impcq c nd 1c feed d t q ud   1/ 2 1 17.24e v e           1 17050 0.030g e sc           m v sc d  iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 67 the combination of all the above time scales is almost impossible to be included in a single model. the multi-scale time-scale model was used to identify the relevant mechanism to be considered in modeling a bimolecular reaction [14]. it was concluded that a time-scale based on micro-mixing did not affect the yield prediction; hence it was safely ignored. although, that study was a parallel reaction involving bimolecular species with feed point, our current study is limited to the single step transesterification without consideration of a feed point. thus, time scale due to feed addition time has is neglected. the comparison of the time scale forms the basis of characterization and subsequent cfd modeling of the reaction with focuses on the micro and macro-mixing effect. the characteristic time for the reaction is taken as eq. (46), with mixing time-scales calculated as average values. (46) the present cfd mode employs the cell-centered finite-volume method that allows use of computational elements with arbitrary polyhedral shape method [22]. the convective terms were solved by second order accurate upwind scheme and the diffusion terms as second order accurate central-differencing scheme. the velocity-pressure coupling was achieved using the simplec type segregated algorithm for instructed, nonuniform mesh [23]. simulation of the full 3-d geometry of the str was implemented in ansys fluent. for the cases conducted, convergence was set at 0.5  10-5 for the mass residual. these calculations required 42-76 hours of cpu time using a 3 ghz intel processor and 4gb ram. 3. discussion and analysis 3.1 piv: mixed flow impeller figure 8a and 8b show the piv result for the mixed axial flow in unbaffled and baffled vessel. the maximum radial velocity, ur/utip is 0.1 and 0.38 in unbaffled and baffled vessel respectively. the flow feature in the unbaffled vessel presents a streamline away from the impeller face with a distinct up-pumping flow field. in the baffled vessel, the mixed flow feature was however more obvious with the recirculation loop/ vortexes appearing near the wall at the baffle. axial flow was also observed to be parallel to the shaft, towards the center of the tank. the velocity due to the impeller at the bottom of the tank did not change even with increase in impeller distance (not shown). consequently, it is assumed that corresponding energy will not vary significantly with the change in impeller distance from the bottom of the vessel. it was also noticed that axial and radial flow were combined with this impeller. this flow is similar to impellers with strong primary and secondary flow [24]. in this piv study, this feature was noticed to mask velocity disparity in the unbaffled tank (fig. 8a). due to the combined axial and radial flow for the baffled vessel, near the baffle and shaft respectively (fig. 8b), the result was referenced against the data for the axial impeller. it showed consistent similarity to flow generated by an axial impeller [24]. 1 2 1 ( )ri ik c c    iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 68 (a) (b) fig. 8 piv velocity magnitude at impeller speed of 600 rpm in (a) unbaffled and (b) baffled vessel. 3.2 les analogy using les analogy the dissipation rate was determined from the tke balance [13]. the les analogy accounts for flow and resolves turbulence at the smallest scales using a sub-grids scale model. the spatial distributions of ε (0.4n3d2) from this method are shown. the single phase flow generated by the mixed flow impeller is an str. fig. 9 dissipation rate using tke from pseudo-isotropic assumption, assuming 2-d piv ensemble-averaged measurements at 600 rpm. fig. 10 field of view for mixed flow impeller. 5 10 15 20 25 30 35 40 5 10 15 20 25 30 35 40 0.5 1 1.5 2 2.5 3 fov iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 69 in order to determine whether the magnitude of the estimated dissipation rate were reliable, the power dissipated in the field of view (fov) was compared to the total power input by the impeller. power no. for the axial impeller is substituted for the power no. of mixed flow impeller [25]. power input, was calculated to be 0.4983 w. the power dissipated in the field of view, simplified for 2-d application was obtained by double integration of the area over the field of view; (47) the power dissipated in this field of view is calculated as 0.5344 kw. was 0.04. the ratio of the two parameters is generally agreed to be < 1 [26]. however, when the dissipation is known to be non-homogenous, variation could be significant. for comparison purposes, the dimensional analysis and les estimation methods yielded ratios of 0.04 and 0.05 respectively. based on the average dissipation rate from the power input (ε) (table 5) the kolmogorov length scale was found to be 31.88 μm at 600 rpm which corresponds to ~35 piv resolution. this should have been ~2 in order to capture 90 % of the dissipation rate [27]. however, this requirement for research is difficult to resolve, probably due to the high solidity ratio and high magnitude in the discharge stream. the ε estimated here was subsequently used for the cfd simulation for the mixed flow. 3.3 experimental validation to validate the experimental result, power drawn for the impeller was calculated from current consumed during stirring [28]. similarly, the power was used to estimate the torque required to rotate the impeller. the impeller power number, compared reasonably with the theoretical (table 5) between 600 to 700 rpm (i.e. 10 – 11.7 rps). table 5: hydrodynamic properties of mixed flow impeller n (rps) d (m) rel x 10 3 power (kw) ε (w/kg3) η (μm) tk (μs) 10 0.055 3.03 0.34 0.44 0.96 31.88 5.16 mixed 10.8 0.055 3.27 0.32 0.46 1.22 30.09 4.10 flow 11.7 0.055 3.57 0.34 0.44 1.55 28.33 3.23 no technical information was available for the mixed-flow impeller used. thus the reynolds mixing number was read from a power curve. this approach was similarly used to arrive at the reynolds number, npc for the axial impeller [29]. the power obtained from the electric current measured during unloads and loading at 100-700 rpm is shown in fig. 11, corresponding to a specific power (p/v) of 82.07 w/m3 for the mixed flow impeller respectively. the net volumetric power being higher in the mixed flow impeller increases the amount of material transported through the vessel. power consumption increased steadily with speed for both impellers until 400 rpm. at speed higher than 400 rpm (i.e. turbulent region), this change becomes less significant [30]. inp 2 2 1 1 2 z r fov z r p rdrdz    fovp /fov inp p /fov inp p /fov inp p pn t pn c pn t pn c iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 70 fig. 11 power drawn measurements for mixed impeller between 100-700 rpm in baffled and unbaffled vessels. 4. numerical simulation the numerical simulation carried out in 3-d using the standard к-ε, sst (к-ω) and rsm turbulent models is presented. the semi-implicit method for pressure-linked equations (simple) algorithm for velocity-pressure coupling and second-order upwind discretization scheme was adopted in obtaining the mean velocity at mass residuals 0.510–5. this strategy did not produce satisfactory result by the models for the baffled vessel. sahu et al. [31] had earlier reported that simulation at large grid size could not converge easily using the simple algorithm. however, the problem was subsequently solved by initiating the model as a lamina flow using the first-order scheme and simplec algorithm to obtain convergence. this was the only algorithm that led to convergence for the baffled vessel. similarly, none of the models used in this work were successfully solved with the simple algorithm using unstructured mesh. several authors [32-34] had noted that discretization scheme had no effect on predicted mean velocity in unbaffled tanks. however, the turbulence prediction is seriously affected. 4.1 comparison of piv-cfd velocity data the comparison of the values of the velocity components by the к-ε, sst (к-ω) and rsm and piv data over the field view at x/r = 0.3 (bottom) and 0.46 (top) in an r-z plane are shown in figs. 12–14 for the mixed flow impeller in baffled vessel. for the baffled vessel, normalized mean velocity was better predicted by the rsm between r = -0.02 to 0.02 m at x/r = 0.38. the highest error between piv data and rsm occurred near the baffled zone with difference of about 60 %. it was observed that a higher deviation occur on the opposite side of the vessel. meanwhile, the к-ε and sst (к-ω) model grossly under-predicted the mean velocity at x/r = 0.3 between r = -0.06 m and vessel center. at x/r = 0.46, maximum difference was 102 % and 82.5 % for the к-ε and sst (кω) model respectively at r = -0.06 m to the center of the vessel. in fig. 15, the normalized axial velocity as a function of the radial position showed that the region occupied the impeller had the highest difference for the к-ε and sst (к-ω) models. at x/r = 0.46, the difference observed between the piv and rsm model over the axial region at x/r = 0.46 was lower compared to the к-ε and sst (к-ω) model. under-prediction of the axial velocity similar to that for the mean was recorded at x/r = 0.38 for the к-ε and sst (кω). 100 200 300 400 500 600 700 154 156 158 160 162 164 166 168 170 172 speed, rpm p o w er (w at ts ) mixed flow-baffled mixed flow-unbaffled iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 71 fig. 12 normalized mean velocity at x/r = 0.3 and 0.46 for piv and cfd turbulent model at 600 rpm for baffled vessel using mixed flow impeller. fig. 13 normalized axial velocity at x/r = 0.3 and 0.46 for piv and cfd turbulent model at 600 rpm for baffled vessel using mixed flow impeller. -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0 0.5 1 1.5 vessel radius, r(m) n or m al is ed m ea n ve l (u /u tip ) top, x/r = 0.46 rsm rke sst piv -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0 0.5 1 vessel radius, r(m) n or m al is ed m ea n ve l (u /u tip ) bottom, x/r = 0.38 rsm rke sst piv -0.06 -0.04 -0.02 0 0.02 0.04 0.06 -1 0 1 vessel radius, r(m)n or m al is ed a xi al v el , u z/u tip x/r = 0.46 rsm rke sst piv -0.06 -0.04 -0.02 0 0.02 0.04 0.06 -2 -1 0 1 vessel radius, r(m)n or m al is ed a xi al v el , u z/u tip x/r = 0.3 rsm rke sst piv iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 72 fig. 14 normalized radial velocity at x/r = 0.3 and 0.46 for piv and cfd turbulent model at 600 rpm for baffled vessel using mixed flow impeller. the normalized radial velocity at x/r = 0.46 was also observed to be better predicted between the baffle and impeller tip with difference value of 17-72 % for the rsm and up to 200 % for the к-ε and sst (к-ω) models. at x/r = 0.3, the rsm performed better over the radial distance measured (fig. 17). flow away from the impeller, towards the tank surface is generally poorer for the к-ε model as demonstrated so far. however, the area closer to the baffles is well represented by all the models at distances closer to the liquid surface. even though the rsm gave a better overall results, values close to the mid of the vessel did not tally with experimental result. by this analysis, the rsm model produced a more realistic outcome. the sst (к-ω) have been reported to give reasonable results where other models are known to fail severely [31]. similarly, the mean axial and radial velocity component in the unbaffled vessel (figs. 15 – 17) revealed better prediction at x/r = 0.3 with the rsm when compared with the piv data. except where a very poor result was obtained for the radial component at x/r = 0.46 (fig. 17), all other region had errors less than 35-50%. again, the к-ε model gave greater error (under 120 %). overall, the rsm gave reasonable velocity values except at the impeller region, which has the rotating reference frame. the simulation could probably be further improved by using a finer grid around the mrf. further refinement of the grid in the mrf did not improve the results. this is kept as one of the challenge faced during this study. furthermore, the κ-ε model seems to be an inappropriate model especially with baffled vessel. the magnitude of the difference in velocity component in the unbaffled vessel varied similarly to that of the baffled vessel as explained above for the axial and mean velocity. for the radial velocity component, the κ-ε model had the least difference in magnitude compared to the rsm and sst (κ-ω) models. earlier, the radial component was not successfully resolved at locations below and above the impeller in the baffled vessel (fig. 6). however, the radial velocity in the unbaffled vessel (fig. 5) span of the plane measured. -0.06 -0.04 -0.02 0 0.02 0.04 0.06 -1 0 1 vessel radius, r(m) n or m al is ed ra di al v el (u r/u tip ) x/r = 0.46 rsm rke sst piv -0.06 -0.04 -0.02 0 0.02 0.04 0.06 -0.5 0 0.5 1 vessel radius, r(m) n or m al is ed ra di al v el (u r/u tip ) x/r = 0.3 rsm rke sst piv iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 73 fig. 15 normalized mean velocity at x/r = 0.3 and 0.46 for piv and cfd turbulent model at 600 rpm for unbaffled vessel using mixed flow impeller. fig. 16 normalized axial velocity at x/r = 0.3 and 0.46 for piv and cfd turbulent model at 600 rpm for unbaffled vessel using mixed flow impeller. fig. 17 normalized radial velocity at x/r = 0.3 and 0.46 for piv and cfd turbulent model at 600 rpm for unbaffled vessel using mixed flow impeller. -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0 0.5 1 vessel radius, r(m) n or m al is ed m ea n ve l (u /u tip ) x/r = 0.46 rke rsm sst piv -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0 0.5 1 1.5 vessel radius, r(m) n or m al is ed m ea n ve l (u /u tip ) x/r = 0.3 rke rsm sst piv -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 -0.4 -0.2 0 0.2 0.4 vessel radius, r(m) n or m al is ed a xi al v el (u z/u tip ) x/r = 0.46 rsm rke sst piv -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 -0.4 -0.2 0 0.2 0.4 vessel radius, r(m) n or m al is ed a xi al v el (u z/u tip ) x/r = 0.3 rsm rke sst piv -0.06 -0.04 -0.02 0 0.02 0.04 0.06 -0.4 -0.2 0 0.2 0.4 vessel radius, r(m) n or m al is ed ra di al v el (u r/u tip ) x/r = 0.46 rke rsm sst piv -0.06 -0.04 -0.02 0 0.02 0.04 0.06 -0.05 0 0.05 0.1 0.15 vessel radius, r(m) n or m al is ed ra di al v el (u r/u tip ) x/r = 0.3 rke rsm sst piv iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 74 table 6: magnitude of difference between cfd and piv result over vessel radius, r = -0.06 m to 0.065 m for baffled vessel mean velocity r = -0.06 m to 0 m r = 0 m to 0.06 m κ-ε 7-107.1 17.6-70.6 x/r = 0.38 sst (κ-ω) 5.5-210 33-63.5 rsm 3 60.1 0-51 κ-ε 17.2 102.5 4 200 x/r = 0.46 sst (κ-ω) 10.8 – 82.5 30 – 110 rsm 12.4 127 1.2 – 95.1 axial velocity κ-ε 18-226 ~ x/r = 0.38 sst (κ-ω) 1.1-37.1 ~ rsm 100-112 ~ κ-ε 60-110 ~ x/r = 0.46 sst (κ-ω) 1.7-101.1 ~ rsm 1-23 ~ radial velocity κ-ε 36-144 3.8-146 x/r = 0.38 sst (κ-ω) 10-125 50-93 rsm 1-17 17-72 κ-ε 91.5-181.1 99-200 x/r = 0.46 sst (κ-ω) 2.1-94.9 1-200 rsm 6-76 5-181 table 7: magnitude of difference between cfd and piv result over vessel radius, r = -0.06 m to 0.065 m for unbaffled vessel mean velocity κ-ε 11-97 x/r = 0.38 (sst) (κ-ω) 46-131 73-99 rsm 0-25 κ-ε 46-200 98-200 x/r = 0.46 sst (κ-ω) 25-1000 65-600 rsm 16-250 61-700 axial velocity κ-ε 385-100 57-309 x/r = 0.38 sst (κ-ω) 156-2000 10-350 rsm 115-135 13-350 κ-ε 79-140 ~ x/r = 0.46 sst (κ-ω) 56-475 ~ rsm 8-990 ~ radial velocity κ-ε 34-87 36-99 x/r = 0.38 sst (κ-ω) 65-155 ~ rsm 12-97 27-169 κ-ε ~ ~ x/r = 0.46 sst (κ-ω) ~ ~ rsm ~ ~ iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 75 tables 6 and 7 summarize the magnitude of difference between mean, radial and axial velocity in cfd models and piv in str (vessel radius, r = 0.06 m to 0.065 m) for baffled and unbaffled vessel. in summary, the rsm resolves the mean and axial component better than the κ-ε and sst (κ-ω) models away from the wall and below the impeller until the tip of the impeller region r = -0.025 m. the significance is that the mean/ axial component of the velocity can be estimated accurately going by the comparison with piv particularly below the impeller. from the estimated values which coincide with piv data, it could also be assumed that the model has been verified. however, as the assumptions behind the models are time-average based, a model including the fluctuating component would improve the results considerably. 4.2 comparison of the mass flow rate, torque, flow number and power number the comparison of the power number (np), pumping number (nq) and mass flow rate (qr) is shown in table 8. since the flow field by the mixed flow impeller was taken as that produced by the axial impeller, the nq value was expected to fall within the range of 0.68 – 0.86 [35]. the к-ε model did not predict the nq adequately, with a value of 0.19. while the κ-ω (sst) and rsm gave 0.53 and 0.58 respectively. np was obtained within the expected range of 0.9 – 1.62 with both κ-ω (sst) and rsm at 0.99 and 1.44 respectively. np for the mixed flow impeller was over-estimated by the κ-ε model in both vessels. table 8: comparison of the mass flow rate, torque, flow number and power number by κ-ε, sst (κ-ω) and rsm models at 600 rpm axial (m3/s) radial (m3/s) qr (m3/s) torque (n.m) nq np (cfd) κ-ε 0.45 -0.13 0.32 0.031 0.19 3.75 mixed flow sst (κ-ω) 0.75 0.13 0.89 0.015 0.53 1.84 (unbaffled) rsm 1.00 -0.036 0.97 0.008 0.58 1.00 κ-ε 0.27 -0.0064 0.26 0.0658 0.16 8.23 mixed flow sst (κ-ω) 1.00 -0.17 0.81 0.0079 0.49 0.99 (baffled) rsm 0.98 0.40 1.10 0.012 0.72 1.40 4.3 time scale of mixing the actual experiment was conducted by adding methanol and naoh into the str containing the wco. the reaction in the 2-l was extended to 60 min. the mixing time was taken as the concentration of the local species of interest instead of inert tracer due to difficulty in measurement; hence the species of interest were directly measured. the mixture model assumed that all the species were contained in the str at the commencement of mix. this eliminates the need to consider the effect of meso-mixing in the time scale. the mixing-time scales are compared in table 9. table 9: time-scales of the mixing wco transesterification in batch str macro-mixing time micro-mixing time circulation time engulfment molecular diffusion n(rpm) (s) (s) (s) 600 0.401 0.603 1.705 1-l 650 0.370 0.550 1.421 700 0.343 0.492 1.137 c e g iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 76 the value of being lesser than and . as explained by vicum et al. [15], when >> 1 molecular diffusion are negligible and micro-mixing is by diffusion especially when sc are large in the range of thousand. were this analysis based solely on comparison of and , this would have led to the conclusion that macro-mixing control the reaction as is smaller than and . this observation suggests that model may neglect micro-mixing, however in order to capture the dynamics of the process all the scales needs to be consider. 4.4 simulation reaction and computational details user-defined function (udf) and user defined scalar (uds) were written in c language for ansys fluent to define the thermo-physical and chemical properties of wco, fame and the individual glycerides derived from eqs. 38–47. based on these considerations, the batch transesterification in str was modeled using the rsm model. at first and independent flow field was calculated without inclusion of the energy or transportation of the species. this is only calculated once, to obtain the distributions of the average velocity, the average kinetic energy, κ, and the average rate of the energy dissipation, ε. occasioned by the difficulty in obtaining convergence with multiple reaction steps the fame – wco was made the focus of this analysis. the cfd simulation at 600 and 60 c was carried out for 360 time steps. each time step represented 5 sec of the physical period for a total simulation of 30 min. fame yield in terms of mass fraction from the cfd simulation result were extracted for a total of 10 intervals. two monitoring points were used to take record the concentration of fame during the simulation and compared with experimental data. these two points were kept close below the impeller. convergence of the solution was enabled by patching an initial concentration for the methanol, wco and fame to the fluid domain at an initial concentration of 31% and 16% of the triglyceride. as in the previous experiments, the fame yield takes an exponential form (eq.48): (48) fig. 18 1-l experimental and simulation result of fame yield at 600 rpm, 60c in 1-l str. c e g/e g  g c e c e g 2 2( ) ( ) 1 2 max 2 1 1 k t k tk exp k exp fame x k k         0 5 10 15 20 25 30 0 20 40 60 80 100 120 140 time (min) fa m e c on c. (d m ol /d m 3 ) exp 60°c, 600 rpm eddy dissipation model finite rate model iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 77 a significant agreement between the model and experiment is shown in the 1-l and 2-l cases. experimental yield data range from xfame =0.56 in the 1-l str to xfame = 0.52 in the 2-l str on the average. the conversion, xfame in both cases were > 0.5, indicating that kinetic does not play a role in the mixing and confirming the indication of mixing effectiveness. similarly, the finite rate model, which also employs the arrhenius rate in place of the ε/κ ratio as well, under predicts the fame in both unbaffled str. the yield trend was similar showing that the exponential form of yield can be used to model transesterification. the results shown is limited to fame using the mass fraction from the cfd simulation and compared with the experimental results in figs. 18–19. fig. 19 2-l experimental result of fame yield at 600 rpm, 60c in 2-l str. 5. conclusion a model for the transesterification of wco in an str is presented using a mixed flow impeller. in this work, the hydrodyamic parameter from a single-phase flow field based on the turbulence model was obtained in the rotating reference frame. the process parameters and proporties of wco and fame from experiemental work and published literature have been sourced for two mixing models based on (i) kinetic-controlled flow and (ii) turbulence-governed reaction have been compared. the time scale of the reaction showed the kinetics-independence of the reaction, while a reasonable estimate of fame yield for the 1-l and 2-l reaction was given by the turbulence based model. it should be pointed out that the validation of the stirred flow is based on the rsm model. the 3-d model demonstrates the capabilty to obtain near-experimental result within the set limit, indicating that it is a fully reliable cfd model, not far away for transesterification of wco. references [1] stamenkovic o, lazic m, todorovic z, veljkovic v, skala d. (2007) the effect of agitation intensity on alkali-catalyzed methanolysis of sunflower oil. bioresource technology, 98(14):2688-2699. [2] meher l, dharmagadda v, naik s. (2006) optimization of alkali-catalyzed transesterification of pongamia pinnata oil for production of biodiesel. bioresource technology, 97(12):1392-1397. [3] freedman b, butterfield r, pryde e. (1986) transesterification kinetics of soybean oil. j. am. oil chemists' soc., 63(10):1375-1380. [4] wahlen b, barney b, seefeldt l. (2008) synthesis of biodiesel from mixed feedstocks and longer chain alcohols using an acid-catalyzed method. energy & fuels, 22(6):4223-4228. 0 10 20 30 40 50 60 0 20 40 60 80 100 120 140 160 180 time(min) fa m e c on c. ( d m ol /d m 3 ) exp 60°c, 600 rpm eddy dissipation model finite rate model iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 78 [5] yang y, yoon rh, telionis dp, weber a, foreman d. (2009) flow property measurements of stirred-tank flow across three reynolds number decades. asme conference proceedings, 329-336. [6] baldyga j, bourne j r. (1999) turbulent mixing and chemical reactions. wiley, new york. [7] tu j, yeoh gh, liu c. (2008) computational fluid dynamics: a practical approach. butterworth heinemann. [8] issariyakul t, kulkarni mg, dalai ak, bakhshi nn. (2007) production of biodiesel from waste fryer grease using mixed methanol/ethanol system. fuel processing technology, 88(5):429-436. [9] rao rs, kumar cg, prakasham rs, hobbs pj. (2008) the taguchi methodology as a statistical tool for biotechnological applications: a critical appraisal. biotechnology j., 3(4):510-523. [10] mccurry jd, wang cx. (2007) analysis of glycerin and glycerides in biodiesel (b100) using astm d6584 and en14105. application-hpi/petrochemicals/polymers. [11] baldi s, yianneskis m. (2004) on the quantification of energy dissipation in the impeller stream of a stirred vessel from fluctuating velocity gradient measurements. chemical engineering science, 59(13):2659-2671. [12] delafosse a, collignon ml, crine m, toye d. (2011) estimation of the turbulent kinetic energy dissipation rate from 2d-piv measurements in a vessel stirred by an axial mixel ttp impeller. chemical engineering science, 66(8):1728-1737. [13] sheng, j., meng, h., fox, r. (2000) a large eddy piv method for turbulence dissipation rate estimation. chemical engineering science, 55(20):4423-4434. [14] baldyga j, bourne jr. (1990) the effect of micromixing on parallel reactions. chemical engineering science, 45(4):907-916. [15] vicum l, ottiger s, mazzotti m, makowski l, bałdyga j. (2004) multi-scale modeling of a reactive mixing process in a semibatch stirred tank. chemical engineering science, 59(89):1767-1781. [16] baldyga j, henczka m, makowski l. (2001) effects of mixing on parallel chemical reactions in a continuous-flow stirred-tank reactor. chemical engineering research and design, 79(8):895-900. [17] fox ro. (2003) computational models for turbulent reacting flows. cambridge univ. press. [18] kay wb. (1936) density of hydrocarbon gases and vapors. industrial and engineering chemistry research, 28:1014-1019. [19] anand k, sharma rp, mehta ps. (2011) a comprehensive approach for estimating thermophysical properties of biodiesel fuels. applied thermal engineering, 31:235-242. [20] wang wc, natelson rh, stikeleather lf, roberts wl. (2012) cfd simulation of transient satge of continuous countercurrent hydrolysis of canola oil. computers and chemical engineering, 43:108-119. [21] ramírez-verduzco lf, rodríguez-rodríguez je, jaramillo-jacob adr. (2012) predicting cetane number, kinematic viscosity, density and higher heating value of biodiesel from its fatty acid methyl ester composition. fuel, 91(1):102-111. [22] rhee sh, joshi s. (2005) computational validation for flow around a marine propeller using unstructured mesh based navier-stokes solver. jsme international journal series b, 48(3):562-570. [23] versteeg hk, malalasekera w. (2007) an introduction to computational fluid dynamics: the finite volume method. prentice hall. [24] aubin j, mavros p, fletcher d, bertrand j, xuereb c. (2001) effect of axial agitator configuration (up-pumping, down-pumping, reverse rotation) on flow patterns generated in stirred vessels. chemical engineering research and design, 79:845-856. [25] aubin j, le sauze n, bertrand j, fletcher df, xuereb c. (2004) piv measurements of flow in an aerated tank stirred by a down-and an up-pumping axial flow impeller. experimental thermal and fluid science, 28(5):447-456. [26] unadkat h. (2009) investigation of turbulence modulation in solid-liquid suspensions using fpiv and micromixing experiments. loughborough university, london, loughborough. iium engineering journal, vol. 16, no. 1, 2015 mohiuddin and adeyemi 79 [27] saarenrinne p, piirto m, eloranta h. (2001) experiences of turbulence measurement with piv. measurement science and technology, 30(1):27-35. [28] ascanio g, castro b, galindo e. (2004) measurement of power consumption in stirred vessels a review. chemical engineering research and design, 82(9):1282-1290. [29] coroneo m, montante g, paglianti a, magelli f. (2010) cfd prediction of fluid flow and mixing in stirred tanks: numerical issues about the rans simulations. computers & chemical engineering, 100(4):277-299. [30] mununga l, hourigan k, thompson m. (2003) numerical study of the effect of blade size on pumping effectiveness of a paddle impeller in an unbaffled mixing vessel. third international conference on cfd in the minerals and process industries csiro, melbourne, australia. [31] sahu a, kumar p, joshi j. (1998) simulation of flow in stirred vessel with axial flow impeller: zonal modeling and optimization of parameters. industrial & engineering chemistry research, 37(6):2116-2130. [32] aubin j, fletcher df, xuereb c. (2004) modeling turbulent flow in stirred tanks with cfd: the influence of the modeling approach, turbulence model and numerical scheme. experimental thermal and fluid science, 28(5):431-445. [33] brucato a, ciofalo m, grisafi f, tocco r. (2000) on the simulation of stirred tank reactors via computational fluid dynamics. chemical engineering science, 55(2):291-302. [34] deglon da, meyer cj. (2006) cfd modelling of stirred tanks: numerical considerations. minerals engineering, 19:1059-1068. [35] chapple d, kresta sm, wall a, afacan a. (2002) the effect of impeller and tank geometry on power number for a pitched blade turbine. chemical engineering research and design, 80(4):364-372. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. a brief account of river rehabilitation experiences md nuruzzaman1, abdullah al-mamun2* and md noor salleh1 1bioenvironmental engineering research centre, department of biotechnology engineering 2department of civil engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. *corresponding author: mamun@iium.edu.my (received: 5th oct. 2015; accepted: 4th dec. 2016; published online: 30th may 2017) abstract: rivers are vital water resources which are being altered due to urbanization and industrialization, causing threats to the environment. as a result, rehabilitation of polluted rivers has gained great importance during the last century in many countries of the world. literature on river rehabilitation projects has been reviewed in this paper, highlighting the experiences gathered in the developed nations of the world; such as the usa, the uk, japan, etc. rehabilitation issues of the rivers crossing borders have also been discussed in this paper. key lessons from different experiences in different regions have been extracted and a comparison has been made. summarised statistics on different experiences also have been presented. finally, some guidelines have been provided based on various experiences, which should be helpful for developed and developing nations while making their river rehabilitation efforts. abstrak: sungai adalah sumber air yang penting dan ia sedang diubah kerana perbandaran dan perindustrian menyebabkan ancaman besar kepada alam sekitar. kerana itu, pemulihan sungai yang tercemar telah mendapat kepentingan yang besar kepada banyak negara di dunia sejak abad yang lalu sebagai literatur mengenai projek-projek pemulihan sungai telah dikaji memberi tumpuan kepada bahagian yang membangun di dunia seperti amerika syarikat, united kingdom, jepun dan lain-lain. isu-isu pemulihan sungai merentasi sempadan juga telah dibincangkan dalam kertas ini. pengajaran penting dari pengalaman yang berbeza di rantau yang berbeza telah diekstrak dan perbandingan telah dilakukan. statistik mengenai pengalaman yang berbeza juga telah dibentangkan. akhirnya, beberapa garis panduan telah disediakan berdasarkan pengalaman yang berbeza, yang sepatutnya menjadi berguna untuk negara-negara maju dan membangun membuat usaha pemulihan sungai. keywords: aquatic; ecosystem; experiences; rehabilitation; river 1. introduction the rehabilitation of stream ecosystems is a comparatively young multidisciplinary field, and the literature on aquatic rehabilitation is fragmented even if a huge number of papers is available [1]. the term restoration here refers to the return to a totally recovered natural ecosystem [2]. on the other hand, rehabilitation refers to a similar return toward natural conditions but where some elements of the original ecosystem are not recovered [2]. according to several authors [3-5], restoring components of an ecosystem is defined as 27 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. rehabilitation. it has been stated that reviving an ecosystem to its’ undisturbed natural state is termed as restoration and includes activities like enhancement, improvement, mitigation and creation of habitats, and other situations [6]. these activities are more precisely defined as rehabilitation when they do not restore an ecosystem in full scale [7]. among the ecosystems in a jeopardized condition, the condition of rivers and wetlands is the worst [810]. the diversity of a river’s ecology, the presence of habitats, and a river’s potential for recreational purposes depend largely on the quality of the water. fluvial and ecological processes occurring in the river stream sustain habitats including animal and plant life [11]. rivers serve human beings by supplying water, mitigating floods, and receiving waste water and these activities have led to the biological death of many rivers in the world, thus attracting the attention of scientists [12]. a sustainable ecosystem, especially for fresh water systems, has become a challenge for the environmental legislators, activists, scientists and professionals. the demand for water is soaring as the rapidly increasing human population around the world competes with measures to protect stream ecosystems and ecological benefits [13]. urban streams are important to the society as source of water supply, disposal of wastewater, and flood mitigation [14, 15]. on the other hand, the urban rivers are being polluted by various anthropogenic activities causing ecological damages. restoring these rivers is a huge challenge to the governments, especially for developing countries. due to availability of sufficient knowledge on the impacts of river pollution on human life and ecology, concerned authorities are forming legislation to stop further degradation of streams and taking initiatives to recover natural river ecosystems [16]. according to malakoff and palmer et al. [17, 18], nearly 30 billion usd have been spent on more than 30,000 projects to rehabilitate rivers in the usa alone. restoring rivers has become a vital and increasingly important activity in europe as well as in north america to benefit humans as well as stream habitats [18, 19]. in such river improvement programs, rehabilitation of habitats has become a major concern [6]. a large proportion of these projects target the rehabilitation of fisheries resources; in particular cases, huge amounts of funds are spent solely on a single species or a group of species [20]. it has been observed that large scale projects to rehabilitate streams are often far more successful than small scale projects even if large initiatives consume much time to achieve predefined objectives [21]. the objective of this paper is to illustrate the issues faced by scientists, stakeholders and other relevant bodies in river rehabilitation programs in some parts of the world. the paper does not cover the experiences of the whole world; rather, it focuses on developed countries like the usa, the uk, japan, etc. as river rehabilitation works have been conducted mostly in the developed world. although the rivers in developing countries are also polluted, rehabilitation efforts are rare, mainly due to lack of fund. although the information are mainly gathered from the developed countries, the challenges experienced in those countries could deliver important lessons for the other countries who have yet to launch such programs. however, more detailed investigation should be done in developing countries to predict possible difficulties that are not faced by developed countries. 2. background many japanese rivers suffered from rapid urbanization, regulation of flow, loss of habitat, and appearance of huge amounts of exotic plants [22, 23]. the 136 km long tama river in japan underwent geomorphic transformation from a large braided river to a single thread channel due to the hamura weir, a massive excavation of gravel, and a drastic decline of sediment supply [22-24]. extending the width of the channel and increasing 28 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. sedimentation supply were necessary to rehabilitate the river. downstream of the hamura weir, gravel was artificially added to increase the sediment supply. widening of the channel was done at two sites. although there are no scientific evaluations performed yet, there are certain signs of recovery. lakes are considered an integral part of river systems. lakes are also polluted by human activities which cause environmental degradation. the kasumigaura lake in japan turned into a dead lake within a mere 30 years. emergent plants decreased by half and submerged plants were very few in number in 2000 while the transparency depth decreased drastically. excavated bottom sediments were used in the rehabilitation project of the lake. locally extinct plants were recovered using natural seed banks [22]. helfield et al. [25] picked out the pite river in sweden to check the effects of river rehabilitation on riparian biodiversity in secondary channels. they stated that the regained stream could not revive flood adapted plants; this is probably due to the short time elapsed since rehabilitation. however, previous studies illustrated quick responses to similar programs in single channel tributaries, but they have shown how rehabilitation results may differ depending upon climatic, ecologic, and hydrologic factors, demonstrating the necessity of site-specific rehabilitation measures. bond and lake [26] discussed several issues which have direct influence on the success of a stream habitat rehabilitation project. impediments to colonization, temporal shifts in habitat use, introduction of new species, massive processes, and inaccurate scales of rehabilitation are the items explained by them. the initial goal was to alert ecologists as well as other stakeholders, but they have also thrown light on scopes created by habitat rehabilitation. the interaction between flow and form of the lower missouri river was performed by modeling four different combinations of modern and historical flow and forms [27]. they concluded that rehabilitation programs that tend towards the historical condition have the potential to increase topographic diversity and sensitivity of the availability of the habitat to flow regime. palmer et al. [28] insist that there is a paucity of documentation of river rehabilitation projects and as a consequence, crucial information that may trigger the success of such programs is unpublished. therefore, they have written an article providing an overview, reflecting on lessons learned that are critical to implement these projects. they further state that investing a tiny fraction of the funds allocated for river rehabilitation projects to keep records on factors conducive to success will immensely benefit such types of projects. koehn [29] gave an overview on fish habitat rehabilitation in the murray-darling basin focusing on present and past management issues, attitude of people and stakeholders, support from the local people, and trends in rehabilitation activities. he suggested several points, categorizing them into management, science, and community. enhancing interplay between policy makers and scientists and focusing on ecosystem outcomes were two of his vital suggestions under managerial issues. he added that scientific knowledge should be disseminated properly to the local practitioners and that the community should be stakeholders in rehabilitation projects. in many european countries, including switzerland, reducing flood risks through ecological rehabilitation has been implemented. though urban river revival programs are gambled by major risks and challenges, they can enhance societal life standards and be appreciated by all people [22]. table 1 presents focal points of rehabilitation works with their objectives, scopes, and methods. most of the river rehabilitation works mainly focus on water and riparian zone [30]. however, based on scope, objective, and other relevant issues, rehabilitation works are also done on aesthetics, habitats, and flood mitigation. 29 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. 3. lessons learned proper and effective methods cannot be devised without sufficient information on river rehabilitation and lack thereof hinders a perfect guidance [31-33]. thus, in this section of the article, experiences gathered from river rehabilitation programs from different parts of the world are briefly summarized. table 1: rehabilitation works and their objectives, scopes, and methods rehabilitation target objective scope methods water to achieve standard water quality instream habitats, recreation, water consumption etc. 1. removing point source pollution 2. altering land use of catchment aesthetics to facilitate recreational facilities recreation, commercialization 1. reinstating natural flow and channel shape 2. manipulating sediment and vegetation instream habitats to save fisheries, flora, fauna, and rare species saving ecosystems, food consumption 1. cleaning up contaminant sources. 2. returning natural productivity riparian zone to maintain natural course of a stream and stabilize bank recreation, ecosystem, urban areas 1. revegetation 2. maintaining urban riparian zone flood mitigation to protect property and lives human settlement 1. increasing pool volume 2. floodplain reconnection 3.1 the usa experience the rehabilitation efforts in the usa are generally launched with a view to improving riparian zones, ameliorating water quality, improving stream habitats, stabilizing banks, etc. few projects are analyzed deeply, and very few of them are audited for ecological achievement [34]. it is truly essential to accurately judge how much the rivers benefit from rehabilitation efforts and the authorities need to gather proper information regarding the potency of their strategies. however, a huge program, the national river restoration science synthesis (nrrss), has been launched by the usa incorporating freshwater scientists and their river rehabilitation experiences [34] to find common elements leading to river rehabilitation success as well as to compensate for a lack of information in ecological sciences that should be investigated for more fruitful rehabilitation activities [18]. according to the us national research council [5], in the twentieth century, the mighty missouri river was altered by the construction of dams, reservoirs, and navigation channels for commercial purposes, all to produce many social benefits. unfortunately the toll for this was paid by the loss of habitats and extinction of many fish species [5]. however in the usa, questions relating social and economic factors are likely to come to the forefront while taking any river rehabilitation action e.g. what will be the effect on local economies due to floodplain land acquisition or recovery of ecosystems. in these situations, us nrc [5] suggests that the policy makers must include the social and economic effects due to any action taken along with the scientific factors. the interaction among scientific and nonscientific factors is observed in the missouri river sediment management program. 30 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. it is a daunting task for decision makers to remain within the boundaries set by the scientists, local communities, and stakeholders. however, to use the scientific knowledge efficiently, it is a requisite for all parties to admit different aspects of science and policy and consider the lack of information about the river’s natural system. lack of information may occur due to the absence of any monitoring or evaluation phase of the river rehabilitation programs. many authors have described monitoring as part of a learning cycle and also have suggested adaptive management [18, 19, 35]. in the usa, evaluation or monitoring were done only on 10% of the projects in the national database [36]. alexander and allan [37] mentioned that record keeping activities should be standardized and findings disseminated properly to ensure that the projects are economical and rehabilitation effectiveness is maximized. reeves et al. [38] expressed their opinion that response to a rehabilitation program, often requires monitoring of the said river for not less than 10 years. 3.2 the uk experience river rehabilitation in the uk started in the late 1980s to ensure a strong foundation for improved river management in the future [39]. however, analysis made by wharton and gilvear reported that river rehabilitation projects inside the uk are piecemeal and need to be approached as part of a catchment-wide strategy. they also predicted that this initiative can cause multiple benefits to the ecological status of a river, including flood risk minimization [39]. they also emphasized on combined stream and land management. bannister et al. [40] stated that 35 projects in the uk were identified as catchment scale based projects but none of them was a truly integrated catchment scale river rehabilitation. they concluded that catchment scale river restoration must be incorporated into these schemes to achieve higher ecological success and to address flooding problems. it was their recommendation that literature review should be extended beyond the uk and a detailed database be prepared containing critical information to appropriately use necessary tools. 3.3 japanese experience nakamura gave an overview and perspective of river rehabilitation projects in japan [22]. he also summarized the drawbacks as well as the key factors to successfully complete these initiatives in different situations. his observations are illustrated here, learned from experiences of rehabilitation efforts taken in japan. in the usa, along with europe, most river reinstatement projects are supported by financially and technically well-off organizations like wwf, iucn, tnc etc., whereas in japan, such initiatives are mainly launched by small ngos [22]. however, these organizations have the potential to trigger large projects by connecting local people with the river authorities, and scientists as well, even if they have financial and technical limitations. the largest lake rehabilitation project in japan for lake kasumigaura was initiated by a local ngo called “asaza project”. another local ngo initiated the nationwide “nature oriented river works” program in 1990 in japan [22]. these examples in japan are models for developing countries because the ngos are comparatively small in size and few in numbers. in japan, resurrecting rivers is toilsome work because of its catchment characteristics, floodplain, dynamic stream, and sediment regime [22]. the reinstatement of the tama river confirms that there is no conflicting issue between the protection of property and people and the betterment of ecosystems. 3.4 spanish experience the european research project forecaster (facilitating the application of output from research and case studies on ecological responses to hydro-morphological degradation and rehabilitation) was formulated between 2008 and 2010 with a view to assessing research outcomes from various parts of the world and reviewing case studies on 31 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. the hydromorphological deterioration and placing hydromorphology in river rehabilitation schemes [16]. del tánago et al. analyzed case studies of sixty spanish river rehabilitation programs and concluded that there is a propensity to building river structures overlooking improvement of river processes like floodplain management, flow regime, etc. [16]. in mediterranean areas, insufficient water quantity and inferior water quality exacerbates the rivalry for water resources hindering rural development [41, 42]. there is enough data on rehabilitation theory and practice from humid-temperate regions [43], whereas there is a huge lack of information from mediterranean areas where water is scarce and many restraints reduce river rehabilitation possibilities. in spain, difficulties for administrative staff to apply river rehabilitation guidelines have been identified. many of the identified difficulties were due to lack of experience as well as lack of environmental background [16]. they also mentioned that training is very essential in this case and involvement of scientific community and stakeholders will be extremely worthy. they continued that the measures taken (vegetation in the riparian zone, fish migration, elimination of weirs, etc.) to revive spanish rivers are not meeting the demand for better ecological status. in addition, spanish rivers are strictly regulated without determining flow regulation effects. however, distribution of proper in-stream limiting other consumptive water uses seems to be fruitful, symbolizing a major issue in mediterranean countries for river rehabilitation projects where river management must necessarily be combined with human and environmental needs. mora´n-tejeda et al. [44] argue that the strain may rise due to climate alteration as well as urban population growth. 3.5 danish experience the danish “wet meadow” program demonstrated that the objectives or goals of a river reinstatement program are to be definite and explicitly described while the outcomes expectation should be justified [45]. in this project a pre-drainage was revived in reclaimed meadows to heighten denitrification. only a little fraction of the total budget of 70 million euros for the project was spent for construction, whereas 80% of the allocated fund was spent to compensate farmers and other purposes. a vital measure in danish projects is the enhanced migration facility for salmonids [45]. fish passages give little room to fishes for a successful migration [46] whereas replacing weir or dam with a riffle paves the way for fish to fish migrate easily [34]. again, there is a huge difference between successful migration and successful recolonization. salmonid population can be sustained depending upon the availability and quality of breeding region habitats. the upstream reaches should also be revived where the breeding areas of the fish are destroyed by ochre and sand [34]. 3.6 australian experience similar to other countries, many australian streams are also polluted and millions of dollars are allocated every year to stop the aggression and revive rivers [45]. based on the experiences of the usa, spain, and other developed countries, few australian river rehabilitation projects are well judged before the initiation of the projects [45]. the cooperative research center for freshwater ecology (crcfe) has been established, aiming to provide crucial information to maximize practical rehabilitation efforts [47]. the precise objective of the research is to interpret various ecological processes helping to regain polluted rivers and disturbed stream ecosystems [45]. 3.7 malaysian experience pollution of malaysian rivers is due to the effect of rapid urbanization and expansion of agriculture. malaysian rivers have become overstressed and have been pushed to their limits to provide life sustaining resources [48]. it is noted that out of 91 monitored rivers in 32 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. malaysia, only three were very polluted in 1987. whereas in the year 2002, out of 120 rivers monitored, 22 were found to be very polluted. the klang river in malaysia underwent seven years of clean-up programs and demonstrated encouraging results, yet some aspects of the project were frustrating like solid waste disposal into the river [48]. the study conducted by chan et al. illustrated that river rehabilitation programs in malaysia can only be successful with a joint venture of government, local people and ngos [48]. a case study conducted by chun et al. revealed that most people in malaysia are willing to participate in river conservation programs [49]. however, more effective initiatives are necessary to see big changes in the river ecology. 3.8 trans-boundary rivers 3.8.1 danube river the mighty danube river extends from germany to the black sea reaching nearly 3000 km in length. it underwent extreme alteration due to massive scale hydro-engineering projects for hydropower production in the second half of 20th century [50]. even if the floodplain rehabilitation of danube involved multidisciplinary planning by ecologists, engineers, hydrologists, and nature conservationists, it was considered a learning step for future improvement. hydrological connectivity between the danube and its floodplain was considered one of the most vital steps in the rehabilitation program [51]. according to [52], rehabilitating its hydrological connectivity will maintain a higher productivity. among several project goals, improvement of water quality is in dire need of international coordination and commitment. however, it was concluded that regaining the high diversity of danube flood plain can be fully understood by reconstituting the fluvial dynamics and connectivity gradients instead of rehabilitating individual species or group [51]. 3.8.2 rhine river the rhine river is comparatively smaller in length than that of the danube which stretched 1300 km over switzerland, austria, germany, france, luxembourg, belgium, and the netherlands [53]. regulation and normalization of main and tributary channels caused habitat reduction and other impacts in this river [54]. it was found that connectivity and redevelopment of secondary channels were necessary to rehabilitate the river [54]. on the other hand, the disappearance of salmon from the rhine in the mid-20th century due to promotion of navigation and hydropower on the rhine by the netherlands showed that one-sided activities without any collaborative approach are a threat to trans-boundary river rehabilitation [53]. vaate [55] mentioned several reasons for improved water quality in the rhine in the late 1970s, among which international agreements and implementation of environmental protection laws were two vital reasons. 3.8.3 meuse river the 870 km long meuse river belonging to france, belgium, luxembourg, germany and the netherlands, [53] suffered from extreme river engineering and industrial waste water disposal like other european rivers [55]. countries sharing the meuse river basin united in 1994, forming the international commission on protection of the meuse river (icpm). the meuse action program was launched in 1997 focusing mainly on water quality improvement. unfortunately, icpm did not set any specific target for pollution minimization and improvement of the ecology [55]. 3.8.4 hirmand hamoon wetland iran and afghanistan share a wetland named hamoon that receives water from the hirmand (helmend) river; a very important and unique freshwater source to both countries 33 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. [56]. the implementation of the project, launched by the afghanistan government to expand agriculture under their river jurisdiction during the mid-20th century led to the degradation of the wetland [56]. however, in 1973, the hirmand (helmend) water treaty was signed between the two sides through which lawful steps were taken to rehabilitate the wetland. furthermore, international organizations like unep and funding agencies such as gef came forward to help revive the wetland [56]. despite iranian the noteworthy investment of huge sums of money and technical support to rehabilitate the wetland, the results could be far better if cooperation from afghanistan were available [56]. 3.8.5 jordan river the jordan river, which is shared by jordan, syria, lebanon, israel, and palestine, is suffering from a scarcity of water and other degradations due to excessive exploitation and regulation of water [57]. over exploitation, pollution, and lack of regional management turned this mighty river in to a trickle [58]. israel and jordan signed a peace treaty promising that they will work together to rehabilitate the river [58, 59] and friends of the earth middle east (fome) was founded in that same year [58]. however, neither government has taken any concrete step to revive the freshwater until now [58, 59]. palestinians are restricted from the right to extract water from the jordan river by israel while fome believes that transboundary collaboration is the only hope of reviving the river to its’ pre-disturbed state [58]. the key lessons learned from different countries as well as cross-border rivers are summarized in table 2. table 2: summary of key lessons learned country/river/wetland key lessons usa  tracing out common elements of successful river rehabilitation programs  considering social and economic factors  monitoring of rehabilitated rivers and disseminating the findings uk  need catchment scale river rehabilitation  managing stream and land together  preparation of detailed database japan  role of small ngos to trigger large scale rehabilitation projects spain  difficulties among administrative staffs due to lack of experience and environmental background  arrangement of proper training denmark  definite objectives of rehabilitation programs and justified outcome expectations australia  proper judgment before initiation of any rehabilitation project malaysia  need joint venture of government, local people and ngos  willingness of malaysian people to participate in conservation programs danube river  international co-ordination and commitment rhine river  one sided activitiesa threat to river rehabilitation  international agreement and implementation of environmental laws meuse river  fixing specific target for pollution reduction and improvement of ecology hirman-hamoon wetland  equal contribution of both sides sharing the water and land  help from international organization jordan river  concrete action from all countries involving the river  equal opportunity for all sharing countries 34 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. 3.9 comparison of different experiences table 3 presents the similarities and differences between rehabilitation experiences, based on the experiences of the different countries mentioned above. different countries undergo different experiences on a same issue. for instance, rehabilitation efforts in developed countries like the usa and uk are mainly funded by large organizations whereas, despite japan being a developed country, small ngos played vital role in rehabilitation efforts. differences are also observed in other issues like public opinion, catchment scale rehabilitation effort, upstream reach rehabilitation, ecological emphasis, international co-operation, and rehabilitation objectives in different countries. on the other hand, in connection with documentation of rehabilitation works, monitoring, the necessity for prior investigation, and unilateral activities, most of the countries underwent similar experiences. table 3: comparison of different rehabilitation experiences comparison experience type differences funding by large organizations by small ngos public opinion crucial trivial catchment study performed excluded upstream reach rehabilitation considered ignored ecological study emphasized disregarded international co-operation existing lacking rehabilitation objectives specific vague similarities documentation not enough monitoring lacking prior investigation very important unilateral activities a threat the experiences mentioned above, and compared in the table, have been selected based on fundamental requirements for any project and special requirements for river rehabilitation work. for instance, funding and public opinion are basic driving factors for any kind of project. on the other hand, study of the catchment of the river under consideration, is a special requirement for a river rehabilitation project. furthermore, for local rivers, international co-operation is not always essential, whereas for trans-boundary rivers, international co-operation becomes very crucial. 4. statistics on river rehabilitation experiences figure 1 demonstrates monitoring of river rehabilitation projects in several parts of the usa. bernhardt (2005) suggested that in the us, projects having higher budget are more likely to be monitored [60] due to availability of adequate fund for the monitoring activities and data archiving. though the tendency of a project being monitored can be observed in some areas, a significant or very strong relationship cannot be concluded from such information (fig. 1). berhardt et al. [36] reports that on average, 10% of the projects are monitored in the usa. detail statistics in most of the other countries are not available. 35 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. fig. 1: monitored projects in the usa [60]. from fig. 2, it is evident that within 1970 and 1990, the number of river rehabilitation projects recorded and documented was almost nil. even though, after 1990, there was a rise in number, many projects have gone unrecorded and they affected the succeeding projects due to lack of information. the same goes for newspaper and scientific articles. however, the number of newspaper and scientific articles is not anywhere near to the number of recorded projects. bernhardt et al. interviewed 317 river rehabilitation project managers in the usa and compared the data with the nrss top projects [61]. part of that data is shown in table 4. the issue of interest here is public involvement, which is where almost half of a community (49%) was engaged with ongoing river rehabilitation projects in the usa. chun et al. also reported the willingness of the malaysian people in river rehabilitation programs in their respective areas [49]. however, the precise data is not available for malaysia. another aspect is the number of sponsors or funders, which is on average 3.6 funders for each project. 0 5 10 15 20 25 30 35 40 45 50 0 1 2 3 4 5 6 7 8 9 10 11 12 m o n it o re d p ro je c t (% ) p ro je c t c o st ( m il li o n u s d ) project cost/1000 km % monitoring indicated 36 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. fig. 2: national river restoration science synthesis (nrss) record of river rehabilitation projects in the usa [36]. table 4: interview statistics for 317 us river rehabilitation projects particular value expenditure range $140–$116 million expenditure (median) $150,000 rehabilitation length (median) 914 m average number of sponsors 3.6 average number of partners/agencies/entities 7.1 public participation (%) 49 figure 3 illustrates guidelines for future river rehabilitation work. as the tasks shown in the horizontal boxes are done with the action shown in the vertical boxes, a river rehabilitation program is expected to shift to the right of the horizontal axes. the outcomes of each action during different stages of rehabilitation are given in the horizontal axis, which starts at failure and ends at ultimate success. 0 10 20 30 40 50 60 70 0 1000 2000 3000 4000 5000 6000 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 n e w sp a p e r & s c ie n ti fi c a rt ic le s r e c o rd e d p ro je c ts year recorded projects newspaper articles scientific articles 37 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. fig. 3: guideline chart for future river rehabilitation based on different experiences. 5. conclusions this paper summarizes the experiences gathered in river rehabilitation programs in the developed countries and also for some trans-boundary rivers. the lessons learned from those countries are not just local, rather these experiences will serve vital information for river rehabilitation programs in the developing countries as well. this paper contributes to the knowledge of river rehabilitation experiences by enabling the readers to compare issues faced in the past. the comparison of different experiences can be regarded as a birds eye view for stakeholders, which will help them to take proper decisions. therefore, this paper is of great importance for the legislators, stakeholders, funders, engineers, and managers involved in such kind of projects. some guidelines have also been provided based on the past experiences recorded in the literature. 38 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. references [1] buijse ad, coops h, staras m, jans l, van geest g, grift r, ibelings bw, oosterberg w, roozen fc. (2002) restoration strategies for river floodplains along large lowland rivers in europe. freshwater biology. 47(4):889-907. [2] rutherfurd id, marsh n, jerie k. (2000) a rehabilitation manual for australian streams. vol. 1.: land and water resources research and development corporation and cooperative research centre for catchment hydrology canberra, australia. [3] rhoads bl, wilson d, urban m, herricks ee. (1999) interaction between scientists and nonscientists in community-based watershed management: emergence of the concept of stream naturalization. environmental management, 24(3):297-308. [4] sparks re. (1995) need for ecosystem management of large rivers and their floodplains. bioscience, 45(3):168-182. [5] staff iom. and staff, nrc. (2002) the missouri river ecosystem: exploring the prospects for recovery. national academies press. [6] roni p, beechie tj, bilby re, leonetti fe, pollock mm, pess gr. (2002) a review of stream restoration techniques and a hierarchical strategy for prioritizing restoration in pacific northwest watersheds. north american journal of fisheries management, 22(1):1-20. [7] stanford ja, ward j, liss wj, frissell ca, williams rn, lichatowich ja, coutant, cc. (1996) a general protocol for restoration of regulated rivers. us department of energy publications: 43. [8] brinson mm. malvárez ai. (2002) temperate freshwater wetlands: types, status, and threats. environmental conservation, 29(2):115-133. [9] malmqvist b, rundle s. (2002) threats to the running water ecosystems of the world. environmental conservation, 29(2):134-153. [10] tockner k, stanford ja. (2002) riverine flood plains: present state and future trends. environmental conservation, 29(3):308-330. [11] peters ne, meybeck m. (2000) water quality degradation effects on freshwater availability: impacts of human activities. water international, 25(2):185-193. [12] paul mj. meyer jl. (2001) streams in the urban landscape. annual review of ecology and systematics: 333-365. [13] assessment me, ecosystems and human well-being. vol. 200. 2003: washington, dc: island press. [14] morley sa, karr jr. (2002) assessing and restoring the health of urban streams in the puget sound basin. conservation biology, 16(6):1498-1509. [15] walsh cj. (2000) urban impacts on the ecology of receiving waters: a framework for assessment, conservation and restoration. hydrobiologia, 431(2):107-114. [16] del tánago mg, de jalón dg, román m. (2012) river restoration in spain: theoretical and practical approach in the context of the european water framework directive. environmental management, 50(1):123-139. [17] malakoff d. (2004) the river doctor. science, 305: 937. [18] palmer m, bernhardt e, allan j, lake p, alexander g, brooks s, carr j, clayton s, dahm c, follstad shah j. (2005) standards for ecologically successful river restoration. journal of applied ecology, 42(2):208-217. [19] downs pw, kondolf gm. (2002) post-project appraisals in adaptive management of river channel restoration. environmental management, 29(4):477-496. [20] roni p, hanson k, beechie t. (2008) global review of the physical and biological effectiveness of stream habitat rehabilitation techniques. north american journal of fisheries management, 28(3):856-890. [21] lake p. (2001) on the maturing of restoration: linking ecological research and restoration. ecological management & restoration, 2(2):110-115. [22] nakamura k. (2008) river restoration efforts in japan: overview and perspective. public works research institute, japan. http:// www. pwri. go. jp/ eng/ activity/ pdf/ reports/ k. nakamura. 80601. 39 http://​ http://www.​ iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. [23] shimatani y. (2003) restoration of river channel morphology at the nagata area in the tama river. ecology and civil engineering, 5(2):233-240. [24] minagawa t, shimatani y. (1999) study of indices for river restoration on braided river. environmental systems research, 27:237-246. [25] helfield jm, engström j, michel jt, nilsson c, jansson r. (2012) effects of river restoration on riparian biodiversity in secondary channels of the pite river, sweden. environmental management, 49(1):130-141. [26] bond n, lake p. (2003) local habitat restoration in streams: constraints on the effectiveness of restoration for stream biota. ecological management & restoration, 4(3):193-198. [27] jacobson rb, galat dl. (2006) flow and form in rehabilitation of large-river ecosystems: an example from the lower missouri river. geomorphology, 77(3):249-269. [28] palmer m, allan jd, meyer j, bernhardt es. (2007) river restoration in the twenty‐first century: data and experiential knowledge to inform future efforts. restoration ecology, 15(3):472-481. [29] koehn, j. (2004) rehabilitation of fish habitats in the murray-darling basin–where have we been and where are we going. in native fish habitat rehabilitation and management in the murray-darling basin: statement, rrecommendations and supporting papers. proceedings of a workshop held in albury, 2004. [30] wohl e, angermeier pl, bledsoe b, kondolf gm, macdonnell l, merritt dm, palmer ma, poff nl, tarboton d. (2005) river restoration. water resources research, 41(10). [31] chapman pm. (2000) the sediment quality triad: then, now and tomorrow. international journal of environment and pollution, 13(1-6):351-356. [32] frissell ca, nawa rk. (1992) incidence and causes of physical failure of artificial habitat structures in streams of western oregon and washington. north american journal of fisheries management, 12(1):182-197. [33] reeves g, hall j, roelofs t, hickman t, baker c. (1991) rehabilitating and modifying stream habitats. [34] madsen j. (1995) impacts of disturbance on migratory waterfowl. ibis. 137(s1): s67-s74. [35] jungwirth m, muhar s, schmutz s. (2002) re‐establishing and assessing ecological integrity in riverine landscapes. freshwater biology, 47(4):867-887. [36] bernhardt e, palmer m, allan j, alexander g, brooks s, carr j, dahm c, follstad-shah j, galat d, gloss s. (2005) restoration of us rivers: a national synthesis. science, 308:636637. [37] alexander gg, allan jd. (2006) stream restoration in the upper midwest, usa. restoration ecology, 14(4):595-604. [38] reeves g, hohler d, hansen b, everest f, sedell j, hickman t, shively d. (1997) fish habitat restoration in the pacific northwest: fish creek of oregon. watershed restoration: principles and practices, pp 335-359. [39] wharton g, gilvear dj. (2007) river restoration in the uk: meeting the dual needs of the european union water framework directive and flood defence? international journal of river basin management, 5(2):143-154. [40] bannister n, mant j, janes m. (2005) a review of catchment scale river restoration projects in the uk. the river restoration centre, report–december. [41] grantham te, merenlender am, resh vh. (2010) climatic influences and anthropogenic stressors: an integrated framework for streamflow management in mediterranean‐climate california, usa. freshwater biology, 55(s1):188-204. [42] hooke j. (2006) human impacts on fluvial systems in the mediterranean region. geomorphology, 79(3):311-335. [43] feld ck, birk s, bradley dc, hering d, kail j, marzin a, melcher a, nemitz d, pedersen ml, pletterbauer f. (2011) from natural to degraded rivers and back again: a test of restoration ecology theory and practice. advances in ecological research. 44:119-209. [44] morán-tejeda e, ceballos-barbancho a, llorente-pinto jm. (2010) hydrological response of mediterranean headwaters to climate oscillations and land-cover changes: the mountains of duero river basin (central spain). global and planetary change, 72(1):39-49. 40 iium engineering journal, vol. 18, no. 1, 2017 nuruzzaman et al. [45] madsen b, boon p, lake p, bunn s, dahm c, langford t, zalewski m. (2006) ecological principles and stream restoration. internationale vereinigung fur theoretische und angewandte limnologie verhandlungen, 29(4):2045-2050. [46] aarestrup k, koed a. (2003) survival of migrating sea trout (salmo trutta) and atlantic salmon (salmo salar) smolts negotiating weirs in small danish rivers. ecology of freshwater fish, 12(3):169-176. [47] cottingham p, thoms m, quinn g. (2002) scientific panels and their use in environmental flow assessment in australia. australian journal of water resources, 5(1):103-111. [48] chan nw, abdullah al, ibrahim al, ghazali s. (2003) river pollution and restoration towards sustainable water resources management in malaysia. [49] chun mh, sulaiman wna, samah maa. (2012) a case study on public participation for the conservation of a tropical urban river. polish journal of environmental studies, 21(4):821829. [50] schiemer f, baumgartner c, tockner k. (1999) restoration of floodplain rivers: the'danube restoration project'. regulated rivers: research & management, 15(1):231-244. [51] tockner k, schiemer f, ward j. (1998) conservation by restoration: the management concept for a river-floodplain system on the danube river in austria. aquatic conservation: marine and freshwater ecosystems, 8(1):71-86. [52] hein t, baranyi c, herndl gj, wanek w, schiemer f. (2003) allochthonous and autochthonous particulate organic matter in floodplains of the river danube: the importance of hydrological connectivity. freshwater biology, 48(2):220-232. [53] huisman p, de jong j, wieriks k. (2000) transboundary cooperation in shared river basins: experiences from the rhine, meuse and north sea. water policy, 2(1):83-97. [54] van den brink f, van der velde g, buijse a, klink a. (1996) biodiversity in the lower rhine and meuse river-floodplains: its significance for ecological river management. netherland journal of aquatic ecology, 30(2-3):129-149. [55] vaate a. (2003) degradation and recovery of the freshwater fauna in the lower sections of the rivers rhine and meuse. 2003: [sn]. isbn 90-5808-844-8. [56] najafi a, vatanfada j. (2011) environmental challenges in trans-boundary waters, case study: hamoon hirmand wetland (iran and afghanistan). international journal of water resources and arid environments, 1(1):16-24. [57] venot j-p, molle f, courcier r. (2008) dealing with closed basins: the case of the lower jordan river basin. water resources development, 24(2):247-263. [58] mehyar m, al khateeb n, bromberg g, koch-ya’ari e. (2014) transboundary cooperation in the lower jordan river basin. water and post-conflict peacebuilding. [59] gafny s, talozi s, al sheikh b. (2010) towards a living jordan river. [60] bernhardt e. (2005) national river restoration science synthesis (nrrss) statistics page for all node areas. us geological survey. available: nrrss. nbii. gov.(december 2005). [61] bernhardt es, sudduth eb, palmer ma, allan jd, meyer jl, alexander g, follastad‐shah j, hassett b, jenkinson r, lave,r. (2007) restoring rivers one reach at a time: results from a survey of us river restoration practitioners. restoration ecology, 15(3):482-493. 41 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. kinetic, isotherm and equilibrium study of adsorption of hydrogen sulfide from wastewater using modified eggshells omar abed habeeb1, ramesh kanthasamy1*, gomaa abdelgawad mohammed ali2,3, rosli bin mohd. yunus1 and olusegun abayomi olalere1 1 faculty of chemical & natural resources engineering, 2 faculty of industrial sciences & technology, universiti malaysia pahang, 26300 gambang, pahang, malaysia. 3 chemistry department, faculty of science, al–azhar university, assiut, 71524, egypt. *corresponding author: ramesh@ump.edu.my (received: 22nd june 2016; accepted: 14th nov. 2016; published online: 30th may 2017) abstract: the studies of adsorption equilibrium isotherms and the kinetics of hydrogen sulfide–water systems on calcite–based adsorbents prepared from eggshells were undertaken. the effects of operating variables, such as contact time and initial concentration, on the adsorption capacity of hydrogen sulfide are investigated. the modified eggshells are characterized using different analytical approaches such as scanning electron microscopy (sem) and fourier transform infrared (ftir). the batch mode adsorption process is performed at optimum removal conditions: dosage of 1 g/l, ph level of ph 6, agitation speed of 150 rpm, and contact time of 14 h for adsorbing hydrogen sulfide with an initial concentration of 100–500 mg/l. in the current study, the langmuir, freundlich, temkin, and dubinin models are used to predict the adsorption isotherms. our equilibrium data for hydrogen sulfide adsorption agrees well with those of the langmuir equation. the maximum monolayer adsorption capacity is 150.07 mg/g. moreover, the kinetics of h2s adsorption using the modified calcite of eggshells follows a pseudo–second–order model. from the current work, it has been found that the calcite eggshells are a suitable adsorbent for h2s containing wastewater. most importantly, chicken eggshells are waste products that are vastly available; hence, they could serve as a practical means for h2s adsorption. abstrak: kajian keseimbangan isoterma penjerapan dan kinetik sistem air– hidrogen sulfida terhadap penjerap berasaskan calcite yang disediakan daripada kulit telur telah dijalankan. kesan pembolehubah operasi seperti masa jerapan dan kepekatan awal pada kapasiti penjerapan hidrogen sulfida disiasat. kulit telur yang telah diubahsuai dianalisa menggunakan cara analisis yang berbeza seperti scanning electron microscopy (sem) dan fourier transform infrared (ftir). proses penjerapan untuk mod batch dilakukan pada keadaan penyingkiran optimum: dos 1 g/l, tahap ph ph 6, kelajuan pergolakan 150 rpm dan masa jerapan 14 jam untuk menjerap hidrogen sulfida dengan kepekatan awal 100–500 mg/l. dalam kajian semasa, model langmuir, freundlich, temkin dan dubinin digunakan untuk meramalkan isoterma penjerapan. data keseimbangan yang diperoleh untuk penjerapan hidrogen sulfida mengikut baik persamaan langmuir. kapasiti maksimum penjerapan monolayer adalah 150.07 mg/g. selain itu, kinetik penjerapan h2s menggunakan kalsit kulit telur yang diubah suai didapati mengikut model pseudo–tertib kedua. dari kerja semasa, ia telah mendapati bahawa calcite daripada kulit telur adalah penjerap sesuai untuk h2s yang mengandungi air sisa. perkara yang paling penting, kulit 13 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. telur ayam boleh didapati secara meluas; oleh itu, ia boleh dijalankan secara praktikal sebagai medium untuk penjerapan h2s. keywords: adsorbents; hydrogen sulfide; chicken eggshells; kinetic; isotherm 1. introduction hydrogen sulfide (h2s) is an exceptionally deadly and damaging substance that is broadly delivered as a by–product in many industries. h2s can bring about wellbeing issues, for example, coma, irritation of eyes, and respiratory system irritation. excess exposure to h2s might cause both chronic and acute ramifications [1, 2]. a concentration of h2s equivalent to 500 – 1000 ppm or more, can threaten human life and lead to imminent impairment on the human physique [3]. therefore, the occupational safety and health administration (osha) has regulated the exposure limit to 20 ppm for the general industry. moreover, the neural system and major organs, such as the liver and the kidneys, are the main target of h2s [4, 5]. on the other hand, another risk associated with h2s in the natural environment is the threat of acid rain, which is precipitated through its oxidation into water– soluble sulfuric acid (4–6 g/l) [6]. in a solution, h2s exists in three forms, i.e. h2s, bisulfide (hs-) and sulfide (s2-) [7]. moreover, h2s safety problems posed by its highly flammable nature as well as economic problems arising from corrosion of metals (even in the low level of h2s) [8]. in addition, h2s is a corrosive medium for wastewater pipelines [9]. another negative impact is that h2s is one of the main poisons for many industry catalysts. in addition, it is a destructive gas to pipelines and equipment [10]. on a very frequent basis, adsorption is employed in wastewater treatment to remove toxic materials from industrial effluents [11]. wastewater (e.g. from petroleum refinery plants) contains a huge amount of organic and inorganic toxic materials, such as h2s. most of the waste water from petroleum refineries is treated using chemical substances to remove toxic pollutants such h2s. these chemicals consist of strong oxidants such as peroxide (h2o2), sodium hypochlorite (naocl), and sodium hydroxide (naoh) [12]. the shortcoming of hydrogen peroxide, sodium/calcium hypochlorite and ferrous/ferric salts on dissociation of h2s in wastewater have been investigated by abdullah [12] who notes that strong oxidants would increase the risk of many serious health problems. for instance, there are ~3300 accidents per annum caused by naocl solutions in britain. in addition, the national fire protection agency (nfpa) has declared that solutions containing more than 40% naocl by weight are considered as hazardous oxidizers. moreover, naocl is an expensive chemical substance and a concentration of 40 g/l is required to remove the dissolved h2s (at 20 mg/l concentration) in wastewater [12]. from that, chemical scrubbing in packed towers is costly [13]. oxidation reactions are generally corrosive and the mixing of an acid cleaner with a naocl bleach generates chlorine gas. also, the mixtures of other cleaning agents and organic matter would lead to a gaseous reaction causing acute lung injury. occupational safety and health administration (osha) has also warned that long term exposure to naocl would cause serious health problems. owing to the shortcomings of chemical adsorbents, the use of non–conventional adsorbents consisting of agricultural wastes has recently been proposed. fine rubber particle media (frpm) has limited porosity and hence its surface area is inadequate to support the pure physical adsorption of h2s with the carbonated steel slag [14, 15]. on the other hand, the use of crushed oyster shell as adsorbent has been examined by asaoka et al. [16]. the removal of mn and h2s from palm oil mill effluent (pome) using activated 14 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. carbon was studied [17, 18]. in the current work, it has been found that eggshells, consisting of 94%–97% calcium carbonate, can be regarded as a practical adsorbent because it is easily available and cost–effective. huge amounts of eggshells are produced as a by–product because hen's eggs are one of most common traditional food articles and are utilized universally. eggshells occupy ~11% of the total weight of an egg [19, 20] and they are normally thrown away without any pre– treatment [21], which leads to environmental pollution such as odor. recently eggshells have been found to contain a high amount of minerals and amino acids [21], and exhibit interesting characteristics such as high porosity, good antibacterial or anti–inflammatory behavior [20], and excellent adsorbent properties [22]. eggshells membranes have been applied in areas such as therapeutic, nutraceutical, metallurgy, and bioremediation areas [20]. in addition, eggshells have been used to remove heavy metals (21–160 mg/g) [23], phenolic compounds (0.052–0.143 dm3/mg) [24], dyes (113.6 mg/g) [22] and pesticides (0.964 mmol/g) [25]. from the mentioned adsorption capacities, it is clear that eggshell– derived materials have a high ability to absorb the different materials with high efficiency. in addition, due to properties such as high amounts of minerals and amino acids [21]; high porosity, antibacterial or anti–inflammatory characteristics [20], and excellent adsorbent properties [22], researchers have shifted their focus onto natural porous materials in the last couple of years. various researches have been conducted to evaluate the adsorption ability of eggshell as a low cost adsorbent, in artificial wastewater with mono– or multi–components. researchers have demonstrated the effectiveness of this adsorbent in the removal of heavy metals [23] this study aims to evaluate the adsorption capacity of calcite eggshells while removing the dissolved h2s in wastewater (from petroleum industry). in addition, a suitable kinetic and equilibrium isotherm model was identified in order to describe the current adsorption process employed using eggshells. 2. materials and methods 2.1 preparation of the adsorbent the eggshells were collected from poultry dump sites and they were immediately washed with deionized water to remove impurities. to dissolve the residual shells, the inner membrane was dismantled from the main eggshells and soaked in an acetic acid solution (70%) for two days, then washed with deionized water to reduce the acidity level up to a neutral ph. the eggshells were then blended, permeated through a set of sieves to 0.25, 0.3 and 0.5 mm, and finally dried at 105 °c in a hot air oven for eight hours. the eggshells were then calcinated at a temperature of 900 °c for 2 h soaking time, which was carried out at a constant heating rate of 10 °c/min with nitrogen (n2) flow rate of 30 cm 3/min. the pyrolysis treatments were conducted in a horizontal furnace. 2.2 physical and chemical characterization measurements the porous texture and morphology were examined by scanning electron microscope (sem). the porous properties of the resulting eggshell particles were investigated by measurement of the nitrogen adsorption–desorption isotherm. the sem runs at 20 kv accelerating potential on a hitachi s–3400n. in order to measure the ph of surface adsorbent, a sample consisting of 0.4 g of dry carbon powder was added into 20 ml of water. the suspension was stirred overnight to reach equilibrium and subsequently the ph of the suspension was measured. fourier transform infrared (ftir) was used to examine the 15 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. functional groups (responsible for h2s adsorption) on the surfaces of modified and unmodified samples. 2.3 preparation of hydrogen sulfide solution in this work, the synthesis of wastewater was prepared using the standard laboratory reaction process between hydrochloric acid (hcl) and ferrous sulfide (fes) in a kipp generator to produce h2s, which was then allowed to dissolve in distilled water according to the following reaction: fes (s) + 2hcl (aq) → fecl2 (aq) + h2s (g) (1) 2.4 batch equilibrium studies the adsorption behaviors of unmodified eggshell particles were determined by examining the rate of removal of h2s dissolved in an aqueous solution. the pollutant concentration was initially measured. all the experiments were performed using a batch process. the adsorption was carried out under a fume hood due to the toxicity of h2s. a sample of 0.1g of calcite of eggshells was used. the solution ph was fixed to ~7.0 (neutral), and the solution was shaken at 150 rpm at 30 °c for 14 hours to determine the adsorption capacity. a spectrophotometer (hach dr2800) was used to measure the residual solution after filtered the suspensions. eq. (2) was used to calculate the adsorption capacity of the pollutants [26, 27]. 𝑞𝑒 = ( 𝐶0−𝐶𝑒)𝑉 𝑚 (2) where v is the solution volume (l), m is the mass of the adsorbent (g), co and ce are the initial and final concentrations of the pollutant, respectively, and qe is adsorption capacity (mg/g). in order to ensure the repeatability of the experimental result, all adsorption experiments were repeated for three times and it was found that the maximum deviation was within 5%. subsequently, the equilibrium data were fitted using isotherm models. 2.5 adsorption isotherm models in the current study, the correlation between the adsorbent and the adsorbate at equilibrium is described using four well–known isotherm models, namely langmuir, freundlich, temkin and dubinin–radushkevich models [28]. the parameters such as isotherm constants, sum of squared error (sse), and fitting (r2) were subsequently determined. 2.5.1 langmuir isotherm langmuir isotherm assumes that adsorption takes place at a specific surface which contains a finite number of adsorption sites. this process is commonly known as homogeneous adsorption, whereby constant enthalpy and sorption activation energy are extracted from each molecule [29, 30]. the linear form of langmuir’s isotherm model can be expressed as: 𝐶𝑒 𝑞𝑒 = 1 𝑄0 𝑏 + ( 1 𝑄0 ) 𝐶𝑒 (3) where ce is the equilibrium concentration of the adsorbate (h2s) (mg/l), qo and b are langmuir constants, and qe is the amount of adsorbate adsorbed per unit mass of adsorbent (mg/g). the main characteristics of the langmuir isotherm can be expressed in terms of the dimensionless equilibrium parameter (rl), which is defined by: 16 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. 𝑅𝐿 = 1 1+𝑏𝐶0 (4) where c0 the initial concentration of h2s (mg/l) and b is the langmuir constant. according to [30], the value of rl indicates the shape of the isotherm to be either unfavorable (rl > 1), favorable (0 < rl < 1), linear (rl = 1) or irreversible (rl = 0). 2.5.2 freundlich isotherm the freundlich isotherm assumes heterogeneous surface energies and it becomes more heterogeneous as the value of the slope approaches zero [31]. the slope ranges between 0 and 1 and it is used to measure the adsorption intensity or surface heterogeneity. the slope (1/n) value of >1 indicates cooperative adsorption [32]. the correlation coefficient (r2) indicates the fitting error. equation (5) gives the linear freundlich model: log 𝑞𝑒 = log 𝐾𝐹 + ( 1 𝑛⁄ ) log 𝐶𝑒 (5) where 𝑞𝑒 is the adsorption capacity at equilibrium (mg/g), 𝐶𝑒 is the equilibrium concentration of the adsorbate (h2s) and 𝐾𝐹 and n are freundlich constants. 2.5.3 temkin isotherm model temkin isotherm assumes indirect interactions between the adsorbent and the adsorbate molecules on adsorption isotherms. the heat of adsorption of all the molecules in the layer would decrease linearly (instead of logarithmically) due to the interactions [33, 34]. the temkin isotherm is examined using eq. (6): 𝑞𝑒 = 𝑅𝑇 𝑏 𝑙𝑛𝐴𝑇 + ( 𝑅𝑇 𝑏𝑇 ) 𝑙𝑛𝐶𝑒 (6) where rt/b = b, r is the gas constant (8.314 j/mol k) and t is the absolute temperature in k, and b is related to the heat of adsorption (j/mol). 2.5.4 dubinin–radushkevich isotherm dubinin and radushkevich isotherm model is generally applied to express the adsorption mechanism on the heterogeneous surface. based on the potential theory [35]. 𝑙𝑛𝑞𝑒 = 𝑙𝑛𝑞𝑑 − 𝐾𝑎𝑑 𝜀 2 (7) where ε can be correlated as: 𝜀 = 𝑅𝑇𝑙𝑛 [1 + 1 𝐶𝑒 ] (8) here, qd is the adsorption capacity (mg/g). 2.6 kinetic studies adsorption kinetics models can be used to simulate the uptake of h2s by adsorbents. in order to investigate the adsorption kinetics of h2s onto the adsorbents, two well–known kinetic models, i.e. the pseudo–first–order and the pseudo–second–order models, are implemented. 2.6.1 pseudo–first–order kinetic model the rate constant of adsorption is determined from the pseudo–first–order eq. given by langergren and svenska [27, 36]: ln( 𝑞𝑒 − 𝑞𝑡 ) = ln 𝑞𝑒 − 𝑘1 𝑡, (9) 17 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. where qe and qt are the amounts of dissolved h2s (mg/g) at equilibrium and at time t(h), respectively, and k1 is the rate constant of adsorption (h−1). k1 is calculated from the linear plot of eq. (9). 2.6.2 pseudo–second–order kinetic model a pseudo–second–order eq. based on equilibrium adsorption [34, 37] is expressed as: 𝑡 𝑞𝑡 = 1 𝑘2𝑞𝑒 2 + 1 𝑞2 𝑡 (10) where k2 (g/mg h) is the rate constant of second–order adsorption. 2.6.3 validity of kinetic model besides r2, the sum of squared error (sse, %) is calculated for all kinetic models. the adsorption kinetics of h2s of eggshells calcinations are tested at different initial concentrations. in general, sse is expressed as: 𝑆𝑆𝐸(%) = √ ∑(𝑞𝑒,𝑒𝑥𝑝−𝑞𝑒,𝑐𝑎𝑙) 2 𝑁 (11) where n is the number of data points. qexp and qcal (mg/g) are the experimental and calculated adsorption capacities, respectively. the numerical fitting is good if r2 is ~1.0 and sse is ~ 0.0. 3. results and discussion 3.1 textural characterization of prepared adsorbent the pyrolysis treatment of eggshells has a significant role to enhance the porosity and oxygenated functional group. during thermal treatment, the calcium carbonate (caco3), converted to cao and co2, is emitted as a by–product that might enhance the efficiency of the adsorbent toward h2s [38] as described by eq. (12). scanning electron microscopy (sem) and ftir were used to characterize the modified and raw eggshells. the results obtained from sem are shown in fig. 1(a) and 1(b). fig. 1: sem images of raw (a) and calcite (b) eggshells. figure 1(a) shows that raw eggshells exhibit low porosity, while enhanced porosity is observed for modified (calcinated) eggshells as illustrated in fig. 1(b). from the eggshell calcination process, the (o2) and (c) components have been reduced. the acidic medium and the high concentration of h+ have increased the number of positively charged caoh2+. 18 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. equation (13) shows the dissociation of calcium oxide in water to form calcium hydroxide on the surface of the adsorbent. equation (14) shows the reaction of h2s with calcium hydroxide. the oh– from ca(oh)2 reacts with h2s to form ca(hs)2, which is then converted to elemental sulfur (see eq. (15). caco3 → cao + co2 (12) cao + h2o → ca(oh)2 (13) ca(oh)2 +h2s → ca (hs)2 + 2h2o (14) ca(hs)2 +o2 → ca(oh)2 + 2s (15) the ftir method has been widely used to characterize the surface oxygenated groups of different oxides on the adsorbent surface. the ftir structure of calcite eggshells exhibits an angular pattern of fracture as seen in fig. 2. the bands of the modified adsorbent are located at 712, 882, 1080 and 1400 cm-1, which corresponds to the presence of symmetric stretching υ1 mode of carbonate, out–of–plane bending (υ2 mode) vibrations of carbonate, υ1 and υ3 mode of crystalline vaterite (caco3) phase. decreasing the intensity of the former bands after calcination indicates to the conversion of calcium carbonate into calcium oxide. in addition the band at 3640 cm-1 is due to o–h of adsorbed water. same observations noticed in studies done by others [39–41]. fig. 2: ftir of the calcite and raw materials of eggshells. 3.2 effect of contact time and initial h2s concentration on adsorption equilibrium a series of contact time experiments for the h2s adsorption process have been carried out at a temperature of 30 °c for different initial concentrations (100–500 mg/l) and the results are shown in fig. 3. for cases of lower initial concentration (100–200 mg/l), a relatively short equilibrium time of ~6 hours is needed. however, cases of higher initial concentrations (300–500 mg/l) require a longer time (~9 hours) to reach equilibrium. the adsorption rate was initially high but it reached equilibrium after a sufficiently long period. this phenomenon occurs due to the abundance of vacant surface sites available for adsorption during the initial stage. after a long period of time, the remaining vacant surface sites are difficult to be occupied due to repulsive forces between the solute molecules on the solid and bulk phases. therefore, the initial stage plays an important role during the adsorption process. at the equilibrium point, the amount of h2s desorbing from the 19 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. adsorbent is in a state of dynamic equilibrium with the amount of h2s being adsorbed on the adsorbent. choo [42] has reported that higher initial concentration could enhance the adsorption capacity, which is contradictory to that observed by xiao [43]. fig. 3: the variation of adsorption capacity at various initial h2s concentrations. 3.3 adsorption isotherms the langmuir, freundlich, temkin and dubinin–radushkevich isotherm models were applied to determine the suitable adsorption isotherm model for this process [44–47]. the isotherm models can also be used to demonstrate how the adsorption molecules are distributed between the solid phase and the liquid phase and to estimate the equilibrium time. the langmuir adsorption isotherm equilibrium model for the adsorption process of h2s onto calcite eggshells is shown in fig. 4. the fitting error can be judged by examining the r2 value. the straight line with a slope of 1/qo is obtained from the plot ce/qe vs. ce is shown in fig. 4. from eq. (2), the langmuir constants b and qo and are calculated and the values are reported in table 1. the r2 value of 0.9907 shows that the current adsorption data correlates well with the langmuir isotherm model. meanwhile, the value of rl is 0.0503, showing that the langmuir isotherm is favorable. fig. 4: langmuir adsorption isotherm of h2s onto eggshells adsorbent. 20 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. table 1: langmuir, freundlich, temkin and dubinin–radushkevich isotherm model parameters and correlation coefficients for adsorption of h2s on the prepared adsorbent. isotherm models concentration (mg/l) parameters r2 langmuir 500 q0 (mg/g) b (l/mg) 0.9907 0.9825 150.07 0.0377 freundlich 500 kf (mg/g(l/mg)1/n 1/n 0.21515 0.2033 0.9723 temkin 500 a (l/g) bt 1.886 115.5 0.8483 dubinin– radushkevich 500 qd (mg/g) kad 129.009 3.206×10-5 the numerical fitting using the freundlich isotherm model is shown in fig. 5. from the linear plot, the slope (1/n) is recorded at 0.2033. the fitting error is higher (r2 = 0.9825) as compared to that of the langmuir model. accordingly, the freundlich constants such as kf and n are calculated from eq. (8) and those values are listed in table 1. for the temkin isotherm model, qe is plotted against ln(ce) to obtain a straight line as shown in fig. 6. the fitting error is higher than those of the langmuir and freundlich models. finally, the dubinin–radushkevich isotherm model (see fig. 7) reports the smallest r2 value (0.8483). fig. 5: freundlich adsorption isotherm of h2s onto eggshells adsorbent. fig. 6: temkin adsorption isotherm of h2s onto eggshells adsorbent. 3.5 adsorption kinetics for the pseudo–first–order kinetic model shown in fig. 8, the results of r2 and k1 values are shown in table 2. the r2 values are low and the experimental qe values are not in good agreement with those calculated from the pseudo–first–order kinetic model. this indicates that the pseudo–first–order equation may not be effective to describe the current adsorption process. 21 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. fig. 7: dubinin–radushkevich adsorption isotherm of h2s onto eggshells adsorbent. fig. 8: pseudo–first–order kinetics for adsorption of h2s onto eggshells adsorbent. table 2: pseudo–first–order, pseudo–second–order, intra–particle diffusion kinetic model and correlation coefficient for adsorption of h2s onto eggshells adsorbent. initial h2s concentration (mg/l) qe,exp (mg/g) pseudo–first–order kinetic model pseudo–second–order kinetic model qe,cal (mg/g) k1 (1/ h) r2 sse (%) qe,cal (mg/g) k1 (1/ h) r2 sse (%) 100 80 59 7.4285 0.876 7.4 105 4.574 0.997 8.8 200 110 147.7 10.464 0.775 13.3 148 3.297 0.926 13.4 300 128 220 9.6785 0.744 32.52 153.3 4.940 0.991 9 400 130 298.4 8.3928 0.750 59.53 148.7 0.015 0.947 6.6 500 145 380 6.3571 0.704 83.08 157 0.012 0.998 4.2 however, when the pseudo–second–order kinetic model was used (fig. 9), the correlation coefficients were greater than 0.926, showing that the adsorption of h2s on calcite eggshells could be best described by the second–order kinetic model. 22 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. fig. 9: pseudo–second–order kinetics for adsorption of h2s onto eggshells adsorbent. 4. conclusions in the current work, eggshells have been analyzed and characterized to determine their physical and chemical properties. the eggshells have been used for adsorption of h2s dissolved in the synthetic wastewater. adsorption of h2s with an initial concentration of 100–500 mg/l has been examined with batch mode adsorption process. the optimum removal conditions were: 1 g/l, 6, 150 rpm and 14 h for dosage, ph, agitation speed and contact time. it has been found that the current adsorption behavior comes closer to the monolayer langmuir isotherm model with r2 values of 0.9907. with the kinetic data adapted to a pseudo second–order model gave r2 value of 0.998 for the higher contaminant, the maximum adsorption capacity was found to be 150.07 mg/g. in general, the current work has witnessed the effectiveness of calcite eggshells for the removal of h2s from wastewater over a wide range of initial concentrations. acknowledgement the authors would like to thank the faculty of chemical and natural resources engineering, universiti malaysia pahang, for the laboratory facilities provided to carry out this research. references [1] lambert tw, goodwin vm, stefani d, strosher l. (2006) hydrogen sulfide (h2s) and sour gas effects on the eye. a historical perspective. sci. total environ., 367(1):1–22. [2] atsdr, “minimal risk levels (mrls) for hazardous substances. agency for toxic substances and disease registry.url: http://www.atsdr.cdc.gov/mrls/,” 2008. [3] epa, “toxicological review of hydrogen sulfide. url: www.epa.gov/iris,” 2003. [4] guidotti tl. (1994) occupational exposure to hydrogen sulfide in the sour gas industry: some unresolved issues. int. arch. occup. environ. health, 66(3):153–160. [5] hendrickson rg, chang a, hamilton rj. (2004) co‐worker fatalities from hydrogen sulfide. am. j. ind. med., 45(4):346–350. [6] heinonen a. (2012) adsorption of hydrogen sulfide by modified cellulose nano/microcrystals. [7] silva pr, ponte ha, ponte mjjs, kaminari nms. (2011) development of a new electrochemical methodology at carbon steel/na2s system for corrosion monitoring in oil refineries. j. appl. electrochem., 41(3):317–320. 23 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. [8] ozekmekci m, salkic g, fellah mf. (2015) use of zeolites for the removal of h2s: a minireview. fuel process. technol., 139:49–60. [9] us environmental protection agency. (1991) hydrogen sulphide corrosion in wastewater collection and treatment system. in us environmental protection agency, , p. technical report, 430/09-91-010. [10] chen q, wang j, liu x, li z, qiao w, long d, ling l. (2011) structure-dependent catalytic oxidation of h2s over na2co3 impregnated carbon aerogels. microporous mesoporous mater., 142(2–3):641–648. [11] derylo-marczewska a. (1993) analysis of the adsorption equilibrium for the system dilute aqueous solution of dissociating organic substance-activated carbon. langmuir, 9(9):2344– 2350. [12] tomar m, abdullah tha. (1994) evaluation of chemicals to control the generation of malodorous hydrogen sulfide in waste water. water res. 28(12):2545–2552. [13] couvert a, sanchez c, laplanche a, renner c. (2008) scrubbing intensification for sulphur and ammonia compounds removal. chemosphere, 70(8):1510–1517. [14] wang n, park j, ellis tg. (2013) the mechanism of hydrogen sulfide adsorption on fine rubber particle media (frpm). j. hazard. mater., 260:921–928. [15] asaoka s, okamura h, morisawa r, murakami h, fukushi k, okajima t, katayama m, inada y, yogi c, ohta t. (2013) removal of hydrogen sulfide using carbonated steel slag. chem. eng. j., 228:843–849. [16] asaoka s, yamamoto t, kondo s, hayakawa s. (2009) removal of hydrogen sulfide using crushed oyster shell from pore water to remediate organically enriched coastal marine sediments. bioresour. technol., 100(18):4127–4132. [17] amosa mk. (2015) process optimization of mn and h2s removals from pome using an enhanced empty fruit bunch (efb)-based adsorbent produced by pyrolysis. environ. nanotechnology, monit. manag., 4:93–106. [18] amosa mk, jami ms, alkhatib mfr, jimat dn, muyibi sa. (2014) comparative and optimization studies of adsorptive strengths of activated carbons produced from steamand co2-activation for bpome treatment. adv. environ. biol., 8(3):603–612. [19] stadelman wj. (2000) eggs and egg products. in: francis, f.j. (ed.) encyclopedia of food science and technology, second ed.. john wiley sons, new york, p. 593–599. [20] pundir cs, bhambi m, chauhan ns. (2009) chemical activation of egg shell membrane for covalent immobilization of enzymes and its evaluation as inert support in urinary oxalate determination. talanta, 77(5):1688–1693. [21] tsai wt, yang jm, lai cw, cheng yh, lin cc, yeh cw. (2006) characterization and adsorption properties of eggshells and eggshell membrane.. bioresour. technol., 97(3):488– 93. [22] tsai w-t, hsien k-j, hsu h-c, lin c-m, lin k-y, chiu c-h. (2008) utilization of ground eggshell waste as an adsorbent for the removal of dyes from aqueous solution. bioresour. technol., 99(6):1623–1629. [23] chojnacka k. (2005) biosorption of cr (iii) ions by eggshells. j. hazard. mater., 121(1):167– 173. [24] koumanova b, peeva p, allen sj, gallagher ka, healy mg. (2002) biosorption from aqueous solutions by eggshell membranes and rhizopus oryzae: equilibrium and kinetic studies. j. chem. technol. biotechnol., 77(5):539–545. [25] elwakeel kz, yousif am. (2010) adsorption of malathion on thermally treated egg shell material 2. materials and methods. water sci. technol., 61(4):53–65. [26] mohammad ys, igboro sb, giwa a, okuofu ca. (2014) modeling and optimization for production of rice husk activated carbon and adsorption of phenol. j. eng. 2014: http://dx.doi.org/10.1155/2014/278075. [27] agarwal s, sadegh h, monajjemi m, hamdy as, ali gam, memar aoh, shahryarighoshekandi r, tyagi i, gupta vk. (2016) efficient removal of toxic bromothymol blue and methylene blue from wastewater by polyvinyl alcohol. j. mol. liq., 218:191-197. [28] allen sj, mckay g, porter jf. (2004) adsorption isotherm models for basic dye adsorption by peat in single and binary component systems. j. colloid interface sci., 280(2):322–333. 24 iium engineering journal, vol. 18, no. 1, 2017 habeeb et al. [29] weber tw, chakravorti rk. (1974) pore and solid diffusion models for fixed‐bed adsorbers. aiche j., 20(2):228–238. [30] bello os, adeogun ia, ajaelu jc, fehintola eo. (2008) adsorption of methylene blue onto activated carbon derived from periwinkle shells: kinetics and equilibrium studies. chem. ecol., 24(4):285–295. [31] weber wj, physicochemical processes for water quality control. wiley interscience, 1972. [32] haghseresht f, lu gq. (1998) adsorption characteristics of phenolic compounds onto coalreject-derived adsorbents. energy & fuels, 12(6):1100–1107. [33] hosseini m, mertens sfl, ghorbani m, arshadi mr. (2003) asymmetrical schiff bases as inhibitors of mild steel corrosion in sulphuric acid media. mater. chem. phys., 78(3):800– 808. [34] abdel ghafar hh, ali gam, fouad oa, makhlouf sa. (2015) enhancement of adsorption efficiency of methylene blue on co3o4/sio2 nanocomposite. desalin. water treat., 53:29802989. [35] günay a, arslankaya e, tosun i. (2007) lead removal from aqueous solution by natural and pretreated clinoptilolite: adsorption equilibrium and kinetics. j. hazard. mater., 146(1):362– 371. [36] lagergren s, zur theorie der sogenannten absorption gelöster stoffe. pa norstedt & söner, 1898. [37] ho y-s, mckay g. (1998) sorption of dye from aqueous solution by peat. chem. eng. j., 70(2):115–124. [38] sanosh kp, chu m-c, balakrishnan a, kim tn, cho s-j. (2009) utilization of biowaste eggshells to synthesize nanocrystalline hydroxyapatite powders. mater. lett., 63(24):2100– 2102. [39] amosa mk, jami ms, alkhatib mfr. (2016) electrostatic biosorption of cod, mn and h2s on efb-based activated carbon produced through steam pyrolysis: an analysis based on surface chemistry, equilibria and kinetics. waste and biomass valorization, 7(1):109–124. [40] alkhatib mf, muyibi sa, amode jo. (2011) optimization of activated carbon production from empty fruit bunch fibers in one-step steam pyrolysis for cadmium removal from aqueous solution. environmentalist, 31(4):349–357. [41] guo h, sun p, qin z, shan l, zhang g, cui s, liang y. (2014) sodium lignosulfonate induced vaterite calcium carbonate with multilayered structure. eur. j. inorg. chem., 2014(6):1001– 1009. [42] choo hs, lau lc, mohamed a, lee kt. (2013) hydrogen sulfide adsorption by alkaline impregnated coconut shell activated carbon. j. eng. sci. technol., 8(6):741–753. [43] xiao y, wang s, wu d, yuan q. (2008) catalytic oxidation of hydrogen sulfide over unmodified and impregnated activated carbon. sep. purif. technol., 59(3):326–332. [44] habeeb oa, ramesh k, ali gam, yunus rm, thanusha tk, olalere oa. (2016) modeling and optimization for h2s adsorption from wastewater using coconut shell based activated carbon, aust. j. basic appl. sci. 10(17):136-147. [45] sadegh h, ali gam, gupta vk, makhlouf ash, shahryari-ghoshekandi r, nadagouda mn, sillanpää m, megiel e. (2017) the role of nanomaterials as effective adsorbents and their applications in wastewater treatment, j. nanostruct. chem. 7(1):1-14. [46] gupta vk, agarwal s, sadegh h, ali gam, bharti ak, hamdy as. (2017) facile route synthesis of novel graphene oxide-β-cyclodextrin nanocomposite and its application as adsorbent for removal of toxic bisphenol a from the aqueous phase, j. mol. liq. http://doi.org/10.1016/j.molliq.2017.04.113. [47] amosa mk. (2016) sorption of water alkalinity and hardness from high strength wastewater on bifunctional activated carbon: process optimization, kinetics and equilibrium studies, environ. technol., doi: 10.1080/09593330.2016.1139631. 25 microsoft word vol 5-1-pages 13-24.doc iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 13 the effect of catalyst support on the decomposition of methane to hydrogen and carbon sharif hussein sharif zein and abdul rahman mohamed* school of chemical engineering, engineering campus, universiti sains malaysia, seri ampangan, 14300 nibong tebal, s.p.s, pulau pinang, malaysia *e-mail: chrahman@eng.usm.my abstract: decomposition of methane into carbon and hydrogen over cu/ni supported catalysts was investigated. the catalytic activities and the lifetimes of the catalysts were studied. cu/ni supported on tio2 showed high activity and long lifetime for the reaction. transmission electron microscopy (tem) studies revealed the relationship between the catalyst activity and the formation of the filamentous carbon over the catalyst after methane decomposition. while different types of filamentous carbon formed on the various cu/ni supported catalysts, an attractive carbon nanotubes was observed in the cu/ni supported on tio2. key words: methane decomposition, carbon nanotube, cu/ni supported catalysts. 1. introduction all conventional options of hydrogen production from natural gas, mainly methane e.g., steam reforming, partial oxidation, and autothermal reforming, involve co2 production at some point in the technological chain of the process. another approach is to decompose methane into hydrogen and carbon. it is a technologically simple one-step process without energy and material intensive gas separation stages and shows the potential to be a co2-free hydrogen production process [1]. although the decomposition of methane over metal-oxide transition metal catalysts produces high initial hydrogen concentration, their activity rapidly drops because of the surface deposition of carbon. however, the generally accepted mechanism of the growth of carbon nanotube proved that this kind of carbon deposition occurs without encapsulating of the metal surfaces, hence, maintaining the catalyst activity for a period of a time. thus, efficient catalyst for methane decomposition could be developed when the condition of filamentous carbon growth are provided. cu/ni is known as one of the active catalysts in methane decomposition [2-5]. when active metal species are deposited on different supports, it is generally accepted that the catalytic performance of metal species depends on the types of supports. this can be attributed to the change of the structure or electronic state of the metal species due to the iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 14 interaction with the supports [6]. it is also reported that methane decomposition depend on type of support and this might be the case with which carbon migration occurred from metal support [7]. therefore, it is worth examining the best support and its combination of the active component in order to design a catalyst having a high catalytic performance for the decomposition of methane. the objective of this study is to identify the effect of cu/ni supported on mgo, al2o3, tio2, and sio2 towards methane decomposition to hydrogen and carbon. 2. experimental the catalysts used in this study were 15 mol%cuo/20mol%nio catalyst supported on mgo, al2o3, tio2, and sio2. the catalysts were prepared using impregnation method. the experiments were carried out at atmospheric pressure in a stainless steel fixed bed reactor system. a schematic diagram of the reactor system is shown in fig. 1. the reactor was fabricated from a stainless steel tube (o.d. 12.7 mm, i.d. 10.92 mm and 600 mm length). a thermocouple of type k in an inconel tube, with 3 mm diameter and 600 mm long was used to measure the temperature of the catalyst bed in the reactor. the catalyst layer was situated in the centre of the reactor. the free space before and after the catalyst layer was filled with quartz particles (rdh) in order to minimize the reactor dead volume. furnace used was a single zone (model carbolite vst 11) with temperature controller and was supplied by carbolite, u.k. a pressure gauge (ashcroft, usa) located just above the reactor was used to read the inlet pressure. methane (supplied by malaysian oxygen sdn. bhd.) with 99.999% purity and argon (supplied by sitt tatt industrial gasses sdn bhd.) with 99.999% purity were mixed before entering the reactor. argon was used as a diluent gas as nitrogen might react with the hydrogen at high temperatures. flow of methane was regulated using a mass flow controller (mks) and argon flow was regulated by brooks mass flow controller (model 5850e). outlet gas flow was monitored by a gas flow meter (alexander wright dm3 b). the product gases were analyzed using an on-line gas chromatograph (gc) (hewlettpackard series 6890, usa). the gc was controlled on-line using hp chemstation rev. a. 06.01. [403] software. porapaq n and molecular sieve 5å (1/8” diameter, 6 feet long length) stainless steel columns, situated in a series with the porapaq n column located in front were used. the porapaq n column was used to separate carbon dioxide, ethane, ethylene and propylene and the molecular sieve 5 å column for hydrogen, oxygen, carbon monoxide, nitrogen and methane. since higher hydrocarbons and carbon dioxide can ruin the molecular sieve 5 å column, two valves operated at 333 k were used to control the outlet gas from the porapaq n column to the detectors while avoiding passing through the molecular sieve 5 å. valve 1 functioned as sampling mechanism and valve 2 to control the flow of the product through the molecular sieve 5 å column. when one of the valve is turned off, it indicates that the gas is allowed to flow through the molecular sieve 5 å column. the gas chromatograph injector temperature was set at 313 k. the initial and the final temperature of the oven were set at 313 and 473 k, respectively. a heating rate of 5 k/min was used. the detector temperature was kept at 473 k. pure argon gas (99.999%) was used as a carrier gas. the total analysis time was 25 minutes for each injection. standard gas was injected into the gas chromatograph and the area of each of the component in the standard gas was determined. the standard gas mixture was supplied by iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 15 boc gases, uk. chromatogram of hydrocarbons such as methane, ethylene, ethane, and propylene were obtained using a flame ionization detector (fid) whereas hydrogen, oxygen, carbon monoxide and carbon dioxide were detected using thermal conductivity detector (tcd). pore size and surface area measurements of the different samples were determined via nitrogen adsorption/desorption isotherms at liquid nitrogen temperature (77 k) using an automated gas sorption system, (autosorb i, quantochrome corporation, usa). all samples were degassed at a temperature of 573 k for 3 hours prior to the measurements. computer programs (micropore version 2.46) allowed for rapid numerical results for the surface area and pore texture from adsorption-desorption isotherm. x-ray diffraction refined by reitfield method was used to characterize the catalyst structure. roomtemperature xrd was conducted on a siemen d-5000 diffractometer, using cuk radiation, and a graphite secondary beam monochromator. specimen was prepared by packing sample powder in a glass holder. intensity was measured by step scanning in the 2 range between 10 – 90, with a step of 0.02 and a measuring time of 2 second per point. the diffraction lines of the xrd pattern were used to identify the formation of solid solution by comparing the 2 values of the materials with those of phase from the powder diffraction files. spent catalysts, covered with carbon were analyzed using a transmission electron microscope (philips tem cm12). in preparation for tem experiments, a few samples of the spent catalyst were dispersed in distilled water, and then a drop was deposited on a coated copper grid. the conversion of methane and the yield of hydrogen are defined as follows: 100 inputmethaneofmole reactedmethaneofmole (%)conversion  (1) 010 2inputmethaneofmole producedhydrogenofmole (%)yield *    (2) 24 2hcch   3. results and discussion thermal decomposition of methane converts methane to hydrogen and solid carbon at high temperatures. it is believed that methyl radicals polymerize to form cyclic and aromatic precursors to graphitic soot particles. however, the form of carbon produced by catalytic decomposition of methane depends on the catalyst used and the reaction parameters. table 1 shows the physical properties of the fresh cu/ni supported on tio2, sio2, mgo, and al2o3, respectively. the surface area of the cu/ni on al2o3, cu/ni on mgo, cu/ni on sio2, and cu/ni on tio2 was 14.27, 11.27, 5.28, and 4.79 m2/g, respectively. the total pore volume shows the same trend as in the surface area and with the value of 0.009, 0.008, 0.004, and 0.003 cc/g for the cu/ni on al2o3, cu/ni on mgo, cu/ni on sio2, and cu/ni on tio2, respectively. the cu/ni on mgo had the largest pore diameter iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 16 (~27 å), while cu/ni on al2o3 and cu/ni on tio2 had average pore diameter (~ 26 å). the cu/ni on sio2 had the smallest average pore diameter (~ 24 å). this might be the change of the structure of the catalyst due to the support. reactor catalyst bed furnace gas trap gas flow vent gas chromatograp recorder methane argon gas mixing reactor system on line system analysis mass flow meters mixer thermocouple meter gas chromatograph data gas mixing system reactor system on line system analysis pre-heater fig. 1: schematic diagram of the reactor system. table 1: the physical properties of the fresh cu/ni supported on different supports. catalyst surface area (m2 /g) total pore volume (vp) (cc/g) average pore diameter (å) cu/ni on mgo 11.27 0.008 26.99 cu/ni on al2o3 14.27 0.009 25.73 cu/ni on tio2 4.79 0.003 26.07 cu/ni on sio2 5.28 0.004 23.81 table 2 shows the performance of cu/ni catalyst supported onto tio2, al2o3, mgo, and sio2 supports for methane dissociation to hydrogen and carbon at 998 k and gas hourly space velocity (ghsv) of 2700 h-1. generally, methane decomposition proceeded over all the catalysts upon contact with the catalysts. the ratio of methane conversion and hydrogen formation was found to be in a ratio of 1:2. in fact, hydrogen was the only gas detected after five minutes on stream. the initial methane decomposition obtained within the first 5 minutes of reaction decreased in the order sio2  al2o3  tio2  mgo support. iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 17 these data should be relatively free of deactivation effects due to blocking of active sites by the decomposition products. after 60 minutes on stream, the order of activity changed to tio2  sio2  mgo support and pressure build up was observed on al2o3 support. at 120 minutes on stream, the tio2 system maintained its activity and the mgo decreased from 16% to 8% while pressure build up in the sio2 supported catalyst system. table 2: the effect of the catalyst support on hydrogen production via catalytic decomposition of methane at 998 k (ghsv = 2700 h-1). catalyst conversion (%) & h2 yield (%) conversion (%) & h2 yield (%) conversion (%) & h2 yield (%) 5 min 60 min 120 min cu/ni on mgo 52 16 8 cu/ni on al2o3 73 nd nd cu/ni on tio2 65 61 62 cu/ni on sio2 74 49 nd nd = not determined. when the inlet pressure exceeds 1 atm. the methane decomposition over cu/ni supported onto tio2, al2o3, mgo, and sio2 supports was significant, as can be seen from table 2. this can be explained in terms of the relative magnitudes of the rate of methane decomposition and the rate of migration of the deposit from the metal to the support. it is assumed that the rate of methane decomposition decreases with increasing coverage while the rate of migration of the deposit from the metal to the support increases with coverage. initially, the observed rate is determined by the rate of methane decomposition since all metal sites are vacant. however, as coverage of the active metal by carbonaceous deposit increases, the rate of migration of the deposit from the metal to the support is increased whereas the methane decomposition rate is decreased. when monolayer coverage is achieved, the observed rate is controlled by the rate of migration of the carbonaceous deposit from the metal to the support [8]. when the rate of migration at monolayer coverage is lower than the initial rate of decomposition and as coverage of metal increases, the rate controlling step changes from decomposition of methane to migration of the deposit from the metal to the support. accordingly, as the carbonaceous species migrate from the metal to the support, metal sites are regenerated and further reaction can occur. hence, the mobility of the carbonaceous deposit from the metal to the support must be an important factor. thus, in the parameters studied, it was concluded that the carbonaceous deposit migrates onto support more readily for tio2  sio2  mgo  al2o3 support and the cumulative methane decomposition is therefore greater for cu/ni supported on tio2  sio2  mgo  al2o3 support. iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 18 the x-ray diffraction (xrd) profiles of the cu/ni loaded on different supports are shown in fig. 2 (a) – (d). as shown in fig. 2 (a) and (b), the cu/ni on tio2 support and cu/ni on mgo support contained 20 mol%nio, but large nio particle was not observed on their xrd profiles, which indicated nio on these two catalysts was highly dispersed. it is well known that mgo and nio could form a solid solution due to very good mutual solubility between mgo and nio. this can be brought out by the results of xrd determination of the catalyst precursor nio-mgo, in which does not have difference in comparison with that of the pure mgo and nio phase but the crystal cell of this newly formed phase is between those of nio and mgo, perhaps implying the formation of nixmg1-xo formation solid solution [9]. since the cu/ni on tio2 support was more active than cu/ni on mgo support, in this case the ni+2 ions in the nio-mgo system may be highly dispersed and evenly distributed in the lattice of mgo due to the mutual solubility between nio and mgo, so that the ni-component in the nixmg1-xo would be inactive in methane decomposition in the studied process. the nio characteristic peaks (2 =37.4, 43.4 and 63.1) were not observed. the characteristic peaks of nio are obvious in the xrd spectrum of cu/ni on sio2 support catalyst which indicates that the ni is comparatively inconsistently loaded on this support and its surface becomes rough (fig. 2 (c)). this phenomenon is probably caused by sintering of the catalyst and is also responsible for the loss in catalytic activity. the xrd pattern of cu/ni on sio2 support revealed peaks at 2 =37.3, 43.3 and 62.9 indicated large crystal of nio particles were formed [10]. the cu/ni on al2o3 support catalyst was found to be the least crystalline as shown in fig. 2 (d). this might caused interaction between cu/ni and the al2o3 support. as a result, the catalyst was not stable during reaction. fig. 2: the xrd pattern of the fresh catalyst containing cu/ni supported on (a) tio2, (b) mgo, (c) sio2, and (d) al2o3. table 3 shows the physical properties of used cu/ni catalysts supported on tio2, sio2, mgo, and al2o3. carbon formation affected the physical properties of the catalysts. the (a) (b) (c) (d) iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 19 surface area of the cu/ni supported on al2o3, mgo, sio2, and tio2 was 24.38, 25.86, 22.10, and 38.23 m2/g, respectively. the total pore volume was 0.015, 0.017, 0.014, and 0.025 cc/g for and the cu/ni supported on al2o3, mgo, sio2, and tio2, respectively. the average pore diameter for the cu/ni on mgo, cu/ni on al2o3, and cu/ni on tio2 gave ~ 26 å. the cu/ni on sio2 had the smallest average pore diameter (~ 25 å). table 3: the physical properties of the used cu/ni catalysts supported on different supports. these catalysts were used in the methane decomposition reaction at 998 k and ghsv of 2700h-1. carbon samples obtained on cu/ni catalysts loaded into various supports were further studied using tem. the result obtained elucidated that introduction of the support influence the carbon morphology remarkably. the tem micrograph of carbon synthesized on cu/ni on mgo support is shown in fig. 3. it looks like small tubes connected to each other. figure 4 shows the tem images of the carbon synthesized on cu/ni on al2o3 support. a major part of the carbon looks like short and broken small tubes and are free of metal particles, and only empty ends of tubes are seen in the micrographs. on the other hand, the tem image of cu/ni on sio2 support shows that the carbon nanotube looks like not developed fully yet and also the presence of black spots which might be the sintered nio particle (fig. 5) although it has a catalyst particle at the tip of the carbon. the carbon formed using cu/ni on tio2 support catalyst (fig. 6) was the best among the supported catalysts. it shows well developed long carbon nanotubes with a catalyst particle located at the tip of the carbon and clear image of the pore where reactants and the products can flow. data presented above demonstrate that long-lived catalysts could be developed when the conditions of filamentous carbon growth are provided. thus, the catalytic activity depended strongly the kind of support. a mechanistic interpretation for the growth of carbon on the catalyst was proposed [11, 12]. the result in fig. 5 support the proposed mechanism for the growth of carbon nanotube on the catalyst. methane decomposes on the front surface of certain active sites of the cu/ni/tio2 based catalyst and the carbon formed diffuses through the metal and precipitates at the rear surface. the driving force which pushed the carbon diffusion was suggested to originate from the concentration gradient of dissolved carbon between the two interfaces i.e. the metal-gas interface to the metal-nanocarbon interface. catalyst surface area (m2 /g) total pore volume (vp) (cc/g) average pore diameter (å) cu/ni on mgo 25.86 0.017 26.12 cu/ni on al2o3 24.38 0.015 25.89 cu/ni on tio2 38.23 0.025 25.76 cu/ni on sio2 22.01 0.014 25.12 iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 20 fig. 3: the transmission electron microscope image of the nanotube produced on cu/ni supported on mgo at 998 k and ghsv of 2700 h-1. fig. 4: the transmission electron microscope image of the nanotube produced on cu/ni supported on al2o3 at 998 k and ghsv of 2700 h-1. iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 21 fig. 5: the transmission electron microscope image of the nanotube produced on cu/ni supported on sio2 at 998 k and ghsv of 2700 h-1. fig. 6: the transmission electron microscope image of the nanotube produced on cu/ni supported on tio2 at 998 k and ghsv of 2700 h-1. catalyst particle carbon nanotube iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 22 4. conclusion hydrogen production is of great significance on seeking a better way to use natural gas resources. catalytic decomposition of methane to hydrogen and carbon is a technologically simple single step process without energy and material intensive gas separation stages. it produces only hydrogen and solid carbon. it was found that the catalyst activity in the methane decomposition depended on the filamentous carbon formed. the best catalyst obtained was cu/ni supported on tio2. tio2 was found to be an effective support for the catalytic decomposition of methane into hydrogen and carbon, giving high activity, attractive carbon nanotube as well as the longest catalyst lifetime. acknowledgment the authors acknowledge the financial support provided by ministry of education, malaysia and universiti sains malaysia under fundamental research grant scheme (project: a/c no: 6070014). list of abbreviations fid flame ionisation detector gc gas chromatograph ghsv gas hourly space velocity pb pressure build up. when the inlet pressure exceeds 1 atm tcd thermal conductivity detector tem transmission electron microscope vp total pore volume xrd x-ray diffraction references [1] n.z. muradov, “co2-free production of hydrogen by catalytic pyrolysis of hydrocarbon fuel”, energy fuels, vol. 12, no. 1, jan. 1998. [2] v.v. chesnokov, v.i. zaikovskii, r.a. buyanov, v.v. molchanov, l.m. plyasova, “morphology of carbon from methane on nickel-containing catalysts”, catalysis today, vol. 24, no. 3, pp. 265-267, june 1995. [3] l.b. avdeeva, o.v. goncharova, d.i. kochubey, v.i. zaikovskii, l.m. plyasova, b.n. novgrodov, and sh.k. shaikhutdinov, “coprecipitated ni-alumina and ni-cu-alumina iium engineering journal, vol. 5, no. 1, 2004 s. h. sharif zein and a. r. mohamed 23 catalysts of methane decomposition and carbon deposition. ii. evolution of the catalysts in reaction”. applied catalysis a: general, vol. 141, no. 1-2, pp. 117-129, 4 july 1996. [4] v.b. fenelonov, a.yu. derevyankin, l.g. okkel, l.b. avdeeva, v.i. zaikovskii, e.m. moroz, a.n. zalanov, n.a. rudina, v.a. likholobov, “structure and texture of filamentous carbons produced by methane decomposition on ni and ni-cu catalysts”. carbon, vol. 35, no. 8, pp. 1129-1140, april 1997. [5] v.n. parmon, g.g. kuvshinov, v.a. sadykov, and v.a. sobyanin, “new catalysts and catalytic processes to produce hydrogen and syngas from natural gas and other light hydrocarbons”. in proceedings of the 5th international natural gas conversion symposium, giardini naxos – taormina, italy, sept. 20-25, 1998. a. parmaliana, d. sanfilippo, f. frusteri, a. vaccani, and f. arena, eds., pp. 677-684, amestardam, holand, 1998. [6] s. takenaka, h. ogihara, i. yamanka, and k. otsuka, “decomposition of methane over supported-ni catalysts: effects of the supports on the catalytic life time”. applied catalysis a: general, vol. 217, no. 1-2, pp. 101-110, sept. 2001. [7] f. solymosi, a. erdoheyli, , j. cserenyi and a. felegi, “decomposition of ch4 over supported pd catalysts”. journal of catalysis, vol. 147, no. 1, pp. 272-278, may 1994. [8] g. boskovic and k.j. smith, “methane homologation and reactivity of carbon species on supported co catalysts”. catalysis today, vol. 37, no. 1, pp. 25-32, july 1997. [9] p. chen, h.-b. zhang, g. –d. lin, q. hong and k.r. tsai, “growth of carbon nanotubes by catalytic decomposition of ch4 or co on a ni-mgo catalyst”. carbon, vol. 35, no. 10-11, pp. 1495-1501, april 1997. [10] x. zhang, j. liu, y. jing, and y. xie, “support effects on the catalytic behavior of nio/al2o3 for oxidative dehydrogenation of ethane to ethylene”. applied catalysis a: general, vol. 240, no. 1-2, pp. 143-150, feb. 2003. [11] t. zhang, and m.d. amiridis, “hydrogen production via the direct cracking of methane over silica-supported nickel catalysts”. applied catalysis a: general, vol. 167, no. 2, pp. 161172, feb. 1998. [12] m.a. ermakova, d.yu. ermakov, a.l. chuvilin, and g.g. kuvshinov, “decomposition of methane over iron catalysts at the range of moderate temperatures: the influence of structure of the catalytic systems and the reaction conditions on the yield of carbon and morphology of carbon filaments”. journal of catalysis, vol. 201, no. 2, pp 183-197, july 2001. biographies abdul rahman mohamed is an associate professor and the dean of the school of chemical engineering, universiti sains malaysia. he got his ph.d. from university of new hampshire, usa in the area of chemical reaction engineering. his research interest is in the area of chemical reaction engineering and air pollution control. sharif hussein sharif zein is a lecturer in the school of chemical engineering, universiti sains malaysia. he got his ph.d. from universiti sains malaysia in the area of reaction engineering and catalysis. his research interest is in the field of reaction engineering and catalysis, natural gas processing and catalyst development. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 bello et al. 71 challenges in textile wastewater and current palliative methods: an overview ibrahim adebayo bello 1 , nassereldeen ahmed kabbashi 1 *, md. zahangir alam 1 , ma’an fahmi alkhatib 1 , fatin nabilah murad 1 and issam yassin qudsieh 2 1 department of biotechnology engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2 chemical engineering department, college of engineering,nanotechnology research unit (ntru) jazan university p.o.box 706, jazan 45142 saudi arabia *corresponding author: naserldin@iium.edu.my (received: 15 th sept. 2017; accepted: 20 th sept. 2017; published on-line: 1 st dec. 2017) abstract: effluents from dye and textile industries are highly contaminated and toxic to the environment. high concentrations of non-biodegradable compounds contribute to increases in biochemical oxygen demand (bod) and chemical oxygen demand (cod) of the wastewater bodies. dyes found in wastewater from textile industries are carcinogenic, mutagenic, or teratogenic. biological processes involving certain bacteria, fungi, activated carbon, and carbon nanotubes (cnts) are promising methods for treating the wastewater. these methods are either inefficient or ineffective. these complexities necessitate a search for new approaches that will offset all the shortcomings of the present solutions to the challenges faced by textile wastewater management. this article reviews the past and recent methods used in the treatment of textile dye wastewater and future opportunities for efficient treatment of textile wastewaters. abstrak: sisa daripada pewarna dan industri tekstil telah mengakibatkan pencemaran yang teruk dan pembuangan toksid kepada alam sekitar. kepekatan tinggi pada kompaun bukan bio-kitar semula menyumbang kepada peningkatan permintaan bio-kimia oksigen (bod) dan permintaan kimia oksigen (cod) pada sisa air buangan. pewarna yang dijumpai daripada industri kain adalah karsinogenik, mutagenik atau teratogenik. proses biologi melibatkan sesetengah bakteria, kulat, karbon diaktifkan dan karbon nanotiub (cnts) merupakan kaedah-kaedah yang dijanjikan untuk merawat sisa air. kaedahkaedah ini samada tidak efisien ataupun tidak efektif. ia memerlukan pencarian kepada pendekatan baru yang akan menghilangkan semua kekurangan pada solusi terkini kepada cabaran-cabaran yang dihadapi dalam pengurusan air sisa buangan kain. artikel ini akan mengulas kaedah-kaedah terdahulu dan terkini yang telah digunakan dalam pengurusan air sisa buangan pewarna kain dan peluang akan datang bagi mendapatkan pengurusan yang cekap pada air buangan sisa tekstil. keywords: wastewater; dye; fungi; carbon nanotubes iium engineering journal, vol. 18, no. 2, 2017 bello et al. 72 1. introduction effluents (dye wastewaters) discharged from textile and dyestuff industries, as a result of the dye materials, are highly colored and contain a high level of nonbiodegradable compounds, soaring up its biochemical and chemical oxygen demand [1]. the release of colored wastewater into the environment signifies a hazardous effect for aquatic life. effluents from dye industries usually contain a high amount of chemicals that are known to be highly toxic, teratogenic and equally carcinogenic to the plant and animal community. due to the complex molecular structure of the dyes [2], they have proven very difficult to treat by conventional biological and physico–chemical processes. dye wastewater effluent, therefore, needs to be well treated (dye removal) before being released safely into the environment. its impact on water bodies, and particularly on the growing public, is highly devastating. therefore, there is a very urgent need for dye wastewaters to be treated. due to their color, they significantly affect the activities of photosynthesis in aquatic life, bringing about turbidity and reduced light penetration. moreover, due to the presence of aromatics, metals, chlorides, etc. in these effluents, aquatic plants and animals may become toxic and unsafe for human consumption. usually having synthetic origins and complex aromatic molecular structures, dye components are hardly degradable and their concentration (of as low as 1.0 mg/l) could contaminate water, making it unfit for drinking and other domestic usage [3]. the main objective of this article is not only to create awareness on the current trend of dye wastewater treatment but also to recommend the application of the latest treatment methods to solve the problem. 2. past, present and future opportunities in the past, so many methods have been employed in the removal of dye from industrial effluents. the various methods that have been employed can be broadly categorized into three: physical, chemical, and biological methods. these methods include removal of debris, filtration, flocculation, precipitation, adsorption, ion exchange membrane, electro chemical technologies, sedimentation and then use of processes such as the activated sludge process wherein microbes are introduced into wastewater to remove biodegradable material, that may then be followed by some chemical additions for the best treatment. however, literature studies have shown that these technologies are not without some major setbacks such as low efficiency, high cost, and a non-environmentally-friendly nature, amongst others [4]. the methods have been extensively reviewed [5] and due to the complex molecular structure of dyes, it has proven very difficult to treat by the conventional biological and physico-chemical processes [2]. recently, several researchers have shown that biosorption (adsorption) can be a better substitute to the physicochemical, microbial and or enzymatic biodegradation methods. among treatment technologies, adsorption has been shown to be the most promising option for the removal of nonbiodegradable organics from aqueous effluents. so many adsorbent materials, such as activated carbon, cotton, velvet, sponge, clay, and carbon nanotubes (cnts), are in existence. cnts have gained a high popularity due to their large specific surface area and nano structure, outstanding thermal and chemical stability, excellent adsorption efficiency, environmental friendly nature and high flux membranes, high reactivity, porosity, surface functional groups, binding strength, high affinity between sites and the particular pollutant of interest, high adsorptive capacities etc. from various research conducted, cnts have been excellent in the treatment of heavy-metal-contaminated aqueous solutions [7]. they are, however, very expensive [8] and they have some disadvantages when used in high concentration for removal of pollutants. iium engineering journal, vol. 18, no. 2, 2017 bello et al. 73 apart from cnts, other adsorbents have also been used in textile dye removal. recently, a number of studies have focused on low-cost adsorbent that is capable of degrading and adsorbing dyes from wastewater. a material could be assumed to be low cost if it is abundant in nature, inexpensive, requires little processing, and is effective in the treatment process [9]. low-cost adsorbents could be obtained from any agriculture and industrial by-products, natural materials, and biosorbents that contain high surface area and porosity [10]. adsorption of dyes onto low-cost adsorbents is largely dependent on dye properties such as molecular structure and type, number and position of substituent in the dye molecule [11], source of raw materials used, preparation and treatment conditions such as pyrolysis temperature and activation time, surface chemistry, surface charge, pore structure and surface area of the adsorbent [12]. nowadays, the adsorbents mostly investigated for different effluent treatment are dead plants and animal residues, known as biomass, which includes charcoals, activated carbons, activated sludge, compost, and various plants. 2.1 activated sludge the most widely used adsorbent is activated sludge. important factors affecting the optimum adsorption of color with activated sludge are its quality and concentration, the hardness of the water and the duration of the treatment. research by [13] investigated the application of activated sludge for the removal of water-soluble acid and reactive dyes and water insoluble disperse dyes. they found that the concentration of sludge, water-hardness and time for optimum removal of color were 3 g/l, 80 mg/l, ca 2+ and 1–2 days, respectively. although activated sludge is suitable for removal of various textile dyes, it alone cannot satisfy modern day’s tight consent limits. 2.2 clays clay is one of the biosorbents that can be used in the treatment of dye wastewater. clay minerals are important inorganic components in soil. their sorption capabilities come from the high surface area and exchange capacities. the negative charge on the structure of clay minerals gives clay the capability to be modified by the surfactant. different types of clays and diatomaceous earth, including activated bleaching earth, montmorillonite, bauxite, alumina pillared clays, mesoporous alumina, aluminum phosphates and bentonitic or kaolinitic clays were investigated for wastewater treatment [14]. their use encourages flocculation of organic impurities. the feasibility of using peat and lignite as adsorbents for the removal of basic dyes was studied by [15]. a two resistance model based on external mass transfer and pore diffusion was developed to predict the performance of agitated-batch adsorbers, but the validity of the model was not tested against a real industrial effluent. 2.3 activated carbon activated carbon is the most widely used for the removal of a variety of organics from water [16], but the disadvantage associated with it is the high regeneration cost and the generation of carbon fines, due to the brittle nature of the carbon used for the removal of organic species. carbon nanotubes are also quite expensive (the higher the quality, the greater the cost), non-selective, and ineffective against dispersing and vat dyes. one of the main disadvantages of activated carbon is also fouling by natural organic matter (nom) [17]. it competes with other organic pollutants for adsorption sites and prevents them from entering the micro-pores by blocking them. they also showed the possibilities of using activated carbon fiber (acf) as an alternative to granular activated carbon and claimed it to be less affected by the presence of nom. the use of alternative cheaper carbonaceous iium engineering journal, vol. 18, no. 2, 2017 bello et al. 74 adsorbents, including coconut husk charcoal and pyrolyzed bagasse char was also investigated for decolorization and reduction of cod and found to be as efficient as activated carbon [18]. this has thus simulated research into specialty absorbents using synthetic resins that may facilitate a cheap and effective chemical regeneration process. the last three decades have witnessed an extensive study of biomass being a perfect replacement for activated carbon. microbial decolorization is now given much attention for textile dye wastewater treatment because of its cost-effectiveness [19]. different researches have been conducted to see the effects of microbes on the adsorption of various pollutants ranging from heavy metals to organic materials. such research works have demonstrated the capacity of various microbial biomass (bacteria yeast, fungi, and algae) and agricultural waste materials to adsorb or accumulate dyes [20]. among the various types of biomass, the fungal biomass has proven to be particularly suitable [21]. aspergillus niger has been experimented and found to be important in the biodegradation of toxic chemicals, treatment of waste beet molasses, olive mill waste, and bioconversion of wastewater sludge. a waste fungal biomass containing killed cells of a. niger has been efficiently utilized for the removal of toxic metal ions such as nickel, calcium, iron and chromium from aqueous solution. fungi have advantages over bacteria because fungi are able to degrade more complex substances and a variety of substrates. the advantages of fungal treatment are cost-effectiveness, environmental-friendly, toxic compound removal, and sludge reduction [22]. table 1 shows the adsorption capacities for some microorganisms and materials and from the table, it is shown that dead macro fungi, rhizopus nigricans (fungi) and jute fiber carbon (jfc) all have very high adsorption capacities. table 1: adsorption capacities for some natural materials dye material used adsorbent capacity (mg/g) working isotherm references reactive dye ry-145; rb-b sorel’s cement ry-145 d 107.67 rb-b d 103.14 langmuir isotherm [23] congo red australian kaolin more than 85% colour removal langmuir isotherm; pseudofirstorder kinetic model [24] mb(basic dye) dead macro fungi 232.73 langmuir isotherm [25] reactive dye reactive black 8; brown 9; green 19; blue 38 rhizopus nigricans 90–96% adsorption of the selected dyes langmuir and freundlich isotherm [26] mb glass wool 2.24 langmuir and freundlich isotherms [27] iium engineering journal, vol. 18, no. 2, 2017 bello et al. 75 mb the brown alga cystoseira barbatula 38.61 langmuir isotherm; pseudosecondorder kinetic model [28] reactive red jute fiber carbon (jfc) 200 langmuir isotherm; pseudosecondorder kinetic model [29] the main reasons why biosorption remains the best method for dye removal from industrial effluents are its high selectivity and efficiency, good removal from large volumes, and the potential cost effectiveness. the majority of the physico-chemical technological processes such as ion-exchange, dilution, coagulation and flocculation, adsorption, chemical precipitation, oxidation, reverse osmosis and ultra-filtration are presently employed for color removal from the aquatic media. however, due to high cost, formation of hazardous by-products, intensive energy requirements and inefficient reusability of adsorbents, limitations have been encountered during the application of these techniques [30]. various classifications of fungi exist. microscopic fungi include yeasts with spherical budding cells and molds with elongated filamentous hyphae in mycelia. the molds are filamentous fungi, such as pencillium, aspergillus, etc. the body or vegetative structure of a fungus is called thallus (pl., thalli), which varies in complexity and size from a single cell microscopic yeast to multicellular molds. a single filament is called a hypha. hyphae usually grow together, collectively to form mycelium. most fungi are sturdy organisms and can generally tolerate more levels of pollutants and contaminants than bacteria. bioremediation capabilities of fungi in the tropical forest may not be as effective as those in the temperate regions. many genera, either in living or dead form, of fungi have been employed for the removal of dye in aqueous solutions, as shown in table 1. the use of microorganisms in dye treatment such as the use of bacteria to degrade azo dyes started in the 1970s with reports of bacillus subtilis, followed by aeromonas hydrophila, and bacillus cereus [31]. the use of fungi as adsorbents in wastewater treatment is known as bioadsorption or biosorption. use of bioadsorbent in the adsorption process can reduce dye concentration to parts-per-billion (ppb) levels. bio-adsorption is a novel, cheap, and effective process [32]. different types of dyes have also been used in the textile industries. dyes can be defined as soluble colored substances that can be applied mainly to textile materials from a water solution. dye molecules comprise two main components: chromophores and auxochromes. chromophores are known as a group of atoms principally responsible for the colour of the dye. the most important chromophores are the azo (–ndn–), carbonyl (cdo), methine (–chd), and nitro (–no2) groups. auxochromes are useful in providing an essential “enhancement” of the colour [33]. common auxochrome groups (include hydroxyl (oh) and amino (nr2) groups) normally increase the intensity of the colour and shift the absorption to longer wavelengths of light [33, 34]. synthetic dyes are solely recalcitrant organic compounds that are extensively used in various branches of textile industries [35], pulp and paper industries [36], leather tanning iium engineering journal, vol. 18, no. 2, 2017 bello et al. 76 industries [37], food industries [38], agricultural research [39], hair colorings [40], lightharvesting arrays [41], etc. however, nowadays, scientists have started looking into genetic manipulations of microorganisms to aid the production of biological agents whose efficiency will be more than the existing ones and also with an option of using purified enzymes for decolorization [42]. according to the literature, fungal decolorization has great potential to be further developed as a solution to the dye wastewater treatment problem in the near future [42]. 3. conclusion the review shows that different methods have been employed in treating wastewater. however, the methods are either ineffective or inefficient. the ineffectiveness of the previous methods of dye wastewater treatment, therefore necessitates the search for new approaches that would help to offset all the short comings of the past and present methods. based on the characteristics of cnts and fungal biomass presented, it will be interesting to develop a biosorbent where a matrix of carbon nanotubes immobilizes a biomass, such a biosorbent would be able to combine the powerful adsorptive abilities found in both for a very effective dye wastewater treatment. 4. recommendation although, its application in the removal of textile dyes is yet to be ascertained, cnts have been investigated as the best adsorbent for industrial pollutants even from dilute solutions [6]. fungal biomass has also proved to be particularly suitable for the adsorption processes [11]. therefore, a low-cost immobilization technique using cnts and fungal biomass could be an effective alternative to overcome the current problems, with an added advantage of helping to remove very low concentration pollutants. this will bring about the development of a novel biosorbent as cnts immobilized fungal biomass (cntib) to treat low concentration of dyes in the textile industry. references [1] moreira, s., milagres, a., mussatto, s. (2014) reactive dyes and textile effluent decolorization by a mediator system of salt-tolerant laccase from peniophora cinerea. separation and purification technology, (135):183-189. [2] fu, y., viraraghavan, t. (2002) removal of congo red from an aqueous solution by fungus aspergillus niger. advances in environmental research, 7(1):239-247. [3] malik, a. (2004) metal bioremediation through growing cells. environment international, 30(2):261-278. [4] ismail, a., loganathan, m. (2012) effect of bioadsorbents in removal of colour and toxicity of textile and leather dyes. journal of ecobiotechnology, 4(1). [5] robinson, t., mcmullan, g., marchant, r., nigam, p. (2001) remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative. bioresource technology, 77(3):247-255. [6] chen, c., wang, x., nagatsu, m. (2009) europium adsorption on multiwall carbon nanotube/iron oxide magnetic composite in the presence of polyacrylic acid. environmental science & technology, 43(7):2362-2367. [7] stafiej, a., pyrzynska, k. (2007) adsorption of heavy metal ions with carbon nanotubes. separation and purification technology, 58(1):49-52 [8] baughman, r., zakhidov, a., heer, w. de. (2002) carbon nanotubes--the route toward applications. science, 297(5582):787-792. iium engineering journal, vol. 18, no. 2, 2017 bello et al. 77 [9] bailey s, olin t, bricka r, adrian d. (1999) a review of potentially low-cost sorbents for heavy metals. water research, 33(11):2469–2479. [10] crini g. (2006) non-conventional low-cost adsorbents for dye removal: a review. bioresource technology, 97(9):1061–1085. [11] freeman, h. (1996) environmental chemistry of dyes and pigments. john wiley & sons. [12] rafatullah, m., sulaiman, o. (2010). adsorption of methylene blue on low-cost adsorbents: a review. journal of hazardous materials, 177(1):70–80. [13] pagga, u., taeger, k. (1994) development of a method for adsorption of dyestuffs on activated sludge. water research, 28(5):1051–1057. [14] danis, t., albanis, t., petrakis, d., pomonis, p. (1998) removal of chlorinated phenols from aqueous solutions by adsorption on alumina pillared clays and mesoporous alumina aluminum phosphates. water research, 32(2):295–302. [15] allen, s., murray, m., brown, p., flynn, o. (1994) peat as an adsorbent for dyestuffs and metals in wastewater. resources, conservation and recycling, 11(1–4):25–39. [16] gomez, v., larrechi, m., callao, m. (2007) kinetic and adsorption study of acid dye removal using activated carbon. chemosphere, 69(7):1151–1158. [17] hopman r, hoek j, paassen jv. (1998) impact of nom presence on pesticide removal by adsorption: problems and solutions. water supply, 16(12):497–501. [18] demirbas, a. (2009) agricultural based activated carbons for the removal of dyes from aqueous solutions: a review. journal of hazardous materials, 167(1):1–9. [19] stolz, a. (2001) basic and applied aspects in the microbial degradation of azo dyes. applied microbiology and biotechnology, 56(1):69-80 [20] crini, g. (2006) non-conventional low-cost adsorbents for dye removal: a review. bioresource technology, 97(9):1061–1085. [21] prigione, v., tigini, v., pezzella, c., anastasi, a., sannia, g. (2008) decolourisation and detoxification of textile effluents by fungal biosorption. water research, 42(12):2911-2920. [22] more, t., yan, s., tyagi, r., surampalli, r. (2010) potential use of filamentous fungi for wastewater sludge treatment. bioresource technology, 101(20):7691-7700. [23] aelterman, p., freguia, s., keller, j., verstraete, w., rabaey, k. (2008). the anode potential regulates bacterial activity in microbial fuel cells. applied microbiology and biotechnology, 78(3):409–418. [24] zou, y., pisciotta, j., baskakov, i. (2010) nanostructured polypyrrole-coated anode for sunpowered microbial fuel cells. bioelectrochemistry, 79(1):50–56. [25] wang, x., feng, y., ren, n., wang, h., lee, h. (2009) accelerated start-up of twochambered microbial fuel cells: effect of anodic positive poised potential. electrochimica acta, 54(3):1109–1114. [26] huang, l., cheng, s., hassett, d., gu, t. (2012) wastewater treatment with concomitant bioenergy production using microbial fuel cells. advances in water treatment and pollution prevention. springer netherlands. [27] mottaghitalab, v., spinks, g., wallace, g. (2005) the influence of carbon nanotubes on mechanical and electrical properties of polyaniline fibers. synthetic metals, 152(1):77–80. [28] caparkaya, d., cavas, l. (2008) biosorption of methylene blue by a brown alga cystoseira barbatula kützing. acta chimica slovenica, 55:547–553. [29] senthilkumaar, s., kalaamani, p. (2006) adsorption of dissolved reactive red dye from aqueous phase onto activated carbon prepared from agricultural waste. bioresource technology, 97(14):1618–1625. [30] arıca, m., bayramoğlu, g. (2005) cr (vi) biosorption from aqueous solutions using free and immobilized biomass of lentinussajor-caju: preparation and kinetic characterization. colloids and surfaces a: physicochemical and engineering aspects, 253(1):203–211. [31] anjaneyulu, y., chary, n., raj, d. (2005) decolourization of industrial effluents– available methods and emerging technologies–a review. reviews in environmental science and bio/technology, 4(4):245–273. [32] sharma, s., sanghi, r., mudhoo, a. (2012) green practices to save our precious “water resource.” in advances in water treatment and pollution prevention. springer netherlands. [33] christie, r. (2014). colour chemistry. royal society of chemistry. iium engineering journal, vol. 18, no. 2, 2017 bello et al. 78 [34] raghavacharya, c. (1997) colour removal from industrial effluents: a comparative review of available technologies. chemical engineering world, 32(7):53–54. [35] firmino, p., & silva, m. da. (2010) colour removal of dyes from synthetic and real textile wastewaters in one-and two-stage anaerobic systems. bioresource technology, 101(20): 7773–7779. [36] jain, c., kumar, a., & izazy, m. (2009) color removal from paper mill effluent through adsorption technology. environmental monitoring and assessment, 149(1– 4):343–348. [37] kabdaşli, i., tünay, o., & orhon, d. (1999) wastewater control and management in a leather tanning district. water science and technology, 40(1):261–267. [38] bhat, r., mathur, p. (1998) changing scenario of food colours in india. current science, 74(3):198–202. [39] cook, s., linden, d. (1997) use of rhodamine wt to facilitate dilution and analysis of atrazine samples in short-term transport studies. journal of environmental quality, 26(5): 1438–1440. [40] scarpi, c., ninci, f., centini, m., & anselmi, c. (1998) high-performance liquid chromatography determination of direct and temporary dyes in natural hair colourings. journal of chromatography a, 796(2):319–325. [41] wagner, r., lindsey, j. (1996) boron-dipyrromethene dyes for incorporation in synthetic multi-pigment light-harvesting arrays. pure and applied chemistry, 68(7):1373–1380. [42] kaushik, p., malik, a. (2009) fungal dye decolourization: recent advances and future potential. environment international, 35(1):127–141. microsoft word 5-harurn 48.doc iium engineering journal, vol. 3, no. 2, 2002 s. w. harun et al. 59 letter to the editor growth characteristics of fiber bragg gratings fabricated in high germania boron co-doped fiber s. w. harun, p. poopalan and h. ahmad department of physics, faculty of science, university of malaya, 50603, kuala lumpur. e-mail: wadi72@yahoo.com abstract: this paper reports and provides an explanation for the growth characteristics of fibre bragg gratings (fbgs) fabricated in high germania boron co-doped optical fiber by using a continuous wave (cw) doubled frequency argon ion laser as an uv light source. the grating reflectivity and bragg wavelength shift as a function of exposure time are measured. the index modulation time is observed to have a good fit to a power law of the form n = ctb (t is the time, c and b are constants), whereas the exponent b of 0.3 is obtained for the fbgs. the uv laser light also causes a shift of the resonant wavelength with fabrication time. the fastest wavelength shift is shown to be 0.53 nm after 524 seconds exposure. keywords: fiber bragg grating, argon ion laser, phase mask method, growth characteristics. 1. introduction fiber bragg gratings have a wide range of applications in optical communication, in optical sensors or in laser areas [1-2]. they are commonly fabricated in germanosilicate fiber by exposure to pulsed or cw uv light in the wavelength band of 240 to 260 nm. the existence of a germanium defect absorption band near 240 nm suggests that index changes caused by uv light result from one-photon absorption by germanium-related defect [3]. one of the techniques commonly used to inscribe bragg gratings in the core of optical fibers utilizes a phase mask to spatially modulate and diffract the uv beam to form an interference pattern. the interference pattern induces a refractive index modulation in the core of the photosensitive fiber which is placed directly behind the phase mask. the phase mask technique is gaining recognition interferometric and point by point writing due to its simplicity and reduced mechanical sensitivity. in this paper, the growth characteristic of fbg’s inscribed with a 244 nm cw frequency doubled argon ion laser in high germania boron co-doped optical fiber is investigated. iium engineering journal, vol. 3, no. 2, 2002 s. w. harun et al. 60 letter to the editor 2. experiment and discussion in the experiments, fbg’s with a bragg wavelength of 1553.3 nm were written in high germania boron co-doped optical fiber by the contact printing method. the fiber was exposed to a 244 nm cw uv laser with a ex-shutter power of 80 mw through a phase mask. a broadband light source from a fiber amplifier and an optical spectrum analyzer (osa) were used to monitor transmission spectra of fbg’s during uv inscription. the growths of the reflectivity of the fbgs with time are plotted in fig. 1. it can be seen that the reflectivity grew rapidly during the first few minutes before slowly reaching the maximum value. fig. 1: the fbgs reflectivity as a function of exposure time. the reflectivity growth with time is fit using equation (2) , which is explained in the text. the growth in reflectivity is explained in terms of an effect called “photosensitivity” which enables an index grating to be written. the photosensitivity of the optical fiber is due to a defect formation inside the ge-doped core of silica fiber [4]. the presence of ge atoms leads to formation of oxygen-deficient bonds (such as si-ge, si-si, and gege), which acts as defects in the silica matrix. the most common defect is the so-called gee' defect. it forms a defect band with an energy gap of about 5 ev (energy required to break the bond). single photon absorption of 244 nm radiation from a frequency doubled argon ion laser breaks this defect bonds, and the released electrons are trapped at hole-defect sites to form color centers such as ge(1) and ge(2). resulting changes in the absorption spectrum are accompanied by a corresponding index change through the kramers-kronig relation [5]. since index changes occur only in the regions of fiber core where the uv light is absorbed, a periodic intensity pattern is transformed into an index grating. 0 20 40 60 80 100 120 0 200 400 600 800 1000 1200 1400 1600 1800 exposure times (s) r ef le ct iv ity (% ) fb g 1 fb g 2 fb g 3 fb g 4 fb g 1 f it fb g 2 f it fb g 3 f it fb g 4 f it iium engineering journal, vol. 3, no. 2, 2002 s. w. harun et al. 61 letter to the editor gilbert et. al. [3] explained a simple model of grating growth arising from the depletion of a homogeneously broadened defect population by one-photon absorption. that model predicts an exponential growth of the index to a maximum value corresponding to the complete depletion of the defects. the dependence of n on the time and intensity is given by n = nmax [1-exp(-ait)] (1) where nmax is the index change that would be produced if the defect population were fully depleted, t is the uv exposure time, i is the intensity of the uv light, a = /h, and  is absorption cross section and h is the energy of a 244 nm photon. this equation assumes that the grating is in the early stages of growth. for exposure times long enough to saturate the index change, however, the reflectance is expected to reach a maximum and then decrease to zero as the defects in the low intensity regions are depleted. however, it is observed that the dependence of index modulation on time and intensity does not agree with the predictions of the model. the reflectivity r of the fabricated fbg is given by [4] r = tanh2 [(ln)/], (2) where  is the fraction of the single mode intensity contained in the core, l is the grating length and is the bragg wavelength. the solid curves in fig. 1 are obtained by fitting n to a power law of the form n = ctb, and inserting this dependence into eq. 2. the fit given by the power law is very good, whereas the exponent b is evaluated as 0.3 for the fbgs. the power law dependence of n is produced by an inhomogeneous broadening of the defect population. although the phase mask limits the wavelength that can be reflected in the fiber, however, there are effects of the uv laser light that causes a shift of the resonance wavelength with fabrication time. fig. 2 shows the change of bragg reflection wavelength with fabrication time, which increases in tandem with bragg reflection strength for the fabricated fbgs. the fbg 1 shows the fastest wavelength shift. its wavelength is shifted roughly by 0.53 nm after 524 seconds exposure. we assume that the shift is mainly due to a variation of the core index of the optical fiber averaged over the irradiated region that arise from the un-modulated component of the uv induced index change. another mechanism that could explain a grating wavelength shift is the possibility of residual curvature of the uv laser wavefront impinging on the phase mask which causes a slight increase of the grating period from one edge of the grating to the other. this causes the grating wavelength to shift as the grating grows with line. because the intensity and the visibility of the interference pattern decrease when the interference order increases [6], a possible saturation and/or threshold of the writing may lead not only to an asymmetry and to a broadening of the spectral shape but also to a positive shift in the resonance wavelength of the grating as the fabrication time is increased. iium engineering journal, vol. 3, no. 2, 2002 s. w. harun et al. 62 letter to the editor 0 0.1 0.2 0.3 0.4 0.5 0.6 0 200 400 600 800 1000 1200 1400 1600 1800 exposure tim e s (s ) w av e le ng th s hi ft ( nm ) fbg 1 fbg 2 fbg 3 fbg 4 fig. 2: bragg wavelength shift with time. there are many factors influencing the wavelength shift and therefore was not fit with theoretical calculation. 3. conclusions this work has shown that high reflectivity fbg can be produced with the frequency doubled argon ion laser that is considerably less expensive than the pulsed uv systems. an exponent b of 0.3 for the dependence of index modulation on time (n = ctb) is obtained and the index modulation is produced by an inhomogeneous broadening of the defect population. the positive shift in bragg resonant wavelength is observed as the fabrication time is increased. acknowledgement one of the authors (s. w. harun) acknowledges the support of a national science fellowship (nsf), moste. references [1] w. w. morey, g. a. ball and g. meltz, “photo induced bragg gratings in optical fibers“, opt. photon. news, pp. 8-14, feb. 1994. [2] p. st. j. russel, j. archambault and l. reekie, “fiber gratings”, physics world, pp. 41-46, oct. 1993. [3] h. patrick and s. l. gilbert, “growth of bragg gratings produced by continuous-wave ultraviolet light in optical fiber”; opt. lett., 18(18), pp. 1484, 1993. [4] g. meltz and w. w. morey, “bragg grating formation and germanosilicate fiber photosensitivity”, spie proc., 1516, pp. 185-199, 1991. iium engineering journal, vol. 3, no. 2, 2002 s. w. harun et al. 63 letter to the editor [5] t. e. tsai, d. l. griscom, e. j. fribele and j. w. fleming, “radiation induced defect centers in high purity geo2 glass”, j. appl. phys., 62, pp. 2262-2268, 1987. [6] m. douay, s. canon, s. legoubin, e. fertein, p. bernage, p. niay and j. f. bayon, “formation of bragg grating in germanium doped optical fibers using prism interferometer,” 2nd , international conference grenoble, 1991. biographies sulaiman wadi harun finished his b. eng. in electrical and electronic system engineering from nagaoka university of technology, japan in 1996. currently he is a m.sc. student in the department of physics, university of malaya. prabakaran poopalan finished his b.sc. and m.sc from the university of malaya in 1994 and 1996, respectively. currently he is a ph.d student in the department of physics, university of malaya. harith ahmad is a professor in the physics department, faculty of science, university of malaya. he was awarded the ph.d from the university of wales (u.k) in laser technology in 1983. he has been involved in research related to laser for the past 18 years. he has a considerable publications in both local and international journals. microsoft word 4_vol17_no1_2016_(compiledversion_4).docx iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 115 chaos control and synchronization using synergetic controller with fractional and linear extended manifold morteza pourmehdi, abolfazl ranjbar noei*, and jalil sadati department of electrical & computer engineering, babol university of technology, babol, iran. morteza.pourmehdi1366@gmail.com; *a.ranjbar@nit.ac.ir; and j.sadati@nit.ac.ir (received: 02 jun. 2015; accepted: 20 sept. 2015; published on-line: 30 apr. 2016) abstract: in this manuscript, for the first time, a fractional-order manifold in a synergetic approach using a fractional order controller is introduced. furtheremore, in the synergetic theory a macro variable is expended into a linear combination of state variables. an aim is to increase the convergence rate as well as time response of the whole closed loop system. quality of the proposed controller is investigated to control and synchronize a nonlinear chaotic coullet system in comparison with an integer order manifold synergetic controller. the stability of the proposed controller is proven using the lyapunov method. in this regard stabilizing control effort is yielded. simulation result confirm convergence of states towards zero. this is achieved through a control effort with fewer oscillations and lower amplitude of signls which confirm feasibility of the control effort in practice. abstrak: manuskrip ini memperkenalkan, buat kali pertama, manifold pecahan pesanan dalam pendekatan sinergi yang menggunakan pengawal pecahan pesanan. dalam teori sinergi pembolehubah makro diperluaskan menjadi satu kombinasi linear pembolehubah keadaan. tujuannya adalah untuk meningkatkan kadar penumpuan serta masa tindak balas keseluruhan sistem lingkaran tertutup. kualiti pengawal yang dicadangkan dikaji dari segi mengawal dan menyelaras sistem coullet tak linear berbanding dengan pengawal sinergi pesanan integer manifold. kestabilan pengawal yang dicadangkan terbukti dengan penggunaan kaedah lyapunov. keadaan ini menghasilkan kawalan yang stabil. simulasi menghasilkan penumpuan keadaan ke arah sifar. ini dicapai melalui usaha kawalan yang mempunyai kurang pengayunan dan amplitud isyarat lebih rendah dan ini mengesahkan bahawa usaha kawalan dalam amalan boleh dilaksanakan. keywords: synergetic control theory; fractional order system; synchronization; nonlinear chaotic coullet system; chaos control 1. introduction synergetic control theory is primarily reported by russian researchers [1]. in essence, a synergetic controller is of an analytical topic with high flexibility in defining dynamical manifold. fractional order controllers are shown providing quality and robust performance in the presence of uncertainties and disturbances for nonlinear systems [2]. during the design procedure, undesired dynamics can be eliminated by introducing dynamical constraints, defined in a manifold. in this regard specifications of desired performance can be applied to the system according to this manifold. elimination of undesired dynamics and reduction of the system’s order are some issues of desired control specifications. the aim of the synergetic controller is to force states of the system to reach and remain on a manifold iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 116 through macro variables. these variables are selected according to the control goals. when system reaches to the desired manifold, its behavior is usually controlled by a first order differential equation. innovatively a combination of fractional controller and the synergetic controller is used to improve the tuning process and the convergence of states. although synergetic controller is recently proposed, several applications are successfully reported in different fields of engineering. this controller is successfully applied in nonlinear power electronic and industrial processes. nonlinear power system stabilizers [3],power converters for pulse current charging [4], dc-dc boost converters [5] and control of chaotic oscillation in power systems [6] are such of these applications. fractional calculus by over 300 years’ history is a generalization of integer order derivative and integral into a real order one. in recent decades, applications of fractional calculus in modeling and control are widely reported. several works such as [7-16] deals with fractional calculus. fractional order dynamics are involved in deferent systems such as viscoelasticity materials, electrochemical processes, electrical machines and etc. it is shown in many fields of science and engineering that the fractional operators can provide more accurate modeling[17,18]. during modeling of physical systems which exhibit hereditary, diffusion and viscoelasticity properties [19-22], heat transfer [23], [24], [25], [12] and fractional pid [26] controllers can be mentioned as such examples of applying fractional order controllers in different field. recently [27] incorporates a combination of synergetic controller with fuzzy theory. in this manuscript, fractional derivative in the caputo sense [15] will be utilized. the current research proposes an idea to combine both synergetic controller and fractional operators to control a fractional order chaotic system. this proposed approach shows improving time response and the convergence rate. the rest of the paper is organized as follows: in section 2, basics of synergetic theory are introduced. section 3 briefly describes the caputo fractional calculus. synergetic controller with fractional order and together with combined linear extension of the manifold is proposed for the first time in section 4. the stability of the control system is analyzed in this section. section 5 investigates with quality of the proposed method through a chaos control of a fractional order system. synchronization is made possible in section 6 using the proposed fractional-order synergetic structure. finally, section 7 closes the work by a conclusion. 2. basics of synergetic theory synergetic method generates a control effort through defining a macro variable introducing required dynamic as a manifold. assume that the system is represented in the following nonlinear state space equations: (1) ̇ = ( , , ) where denotes vector of the state variable, u refers to the vector of the control input, defines the time variable and finally ( , , ) indicates a nonlinear relation between states and input. synergetic design uses macro variable ψ( ) in either linear or nonlinear function of the state variable such as: (2) = ( ) iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 117 appropriate control law drives states towards and stays on manifold of ( ) = 0. the designer may choose macro variable according to the control specifications and requirements [28]. macro variables are usually considered as a liner combination of the state variables. number of macro variables may be defined as much as the control input channels (multi input). a dynamical equation of manifold may be defined as follows [2]: (3) ̇ + = 0, > 0 where denotes the design parameter. this eventually adjusts rate of the convergence of the states in the manifold (2). equation (3) immediately yields: (4) ( ) = , ≥ 0 the convergence of ( ) towards the manifold ( ) = 0 is guaranteed with any bounded initial condition where here the rate of convergence will be tuned by appropriate choice of the design parameter . roll of parameter can be found using the following chain rule of eqn.(4): (5) ̇ = = ̇ substituting equation eqn.(5) into eqn.(3), involving the system eqn.(1) achieves: (6) t (x, u, t) + = 0 finally, an appropriate control law will be achieved using eqn.(6) considering other specifications. each manifold imposes a new constraint to the system which decreases the order of the system. 3. the caputo fractional derivative in fractional calculus several methods of grünwald–letnikov, riemann–liouville and caputo are commonly used. in this manuscript, the caputo fractional derivative [15] is used. benefits of the caputo technique are studied in [29-32]. this is because initial conditions in the caputo are of an integer order which is physically realizable. in the riemann–liouville definition the initial condition is of a fractional order that is less realizable in practice as well as increases the complexity [15]. the caputo fractional derivative is defined as follows: (7) ( ) = 1 γ( − ) ( )( ) ( − ) where γ(. ) is the euler gamma function. for − 1 < < , initial condition of the fractional order differential equation is the same as the integer order one [15]. a unified formula for fractional order integral of ( ) i.e. ( ), with ∈ (0,1) in sense of the caputo in the time interval [0,t] is defined as follows [15]: (8) ( ) = 1 γ( ) ( − ) ( ) iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 118 likewise ( ), − 1 < < is a caputo fractional order derivative of as defines as follows [15]: (9) ( ( )) = ( ) − ( )( ) ! ( − ) for = 0, = 0 and 0 ≤ < 1 [15] it is shown that he following relation is yielded: (10) ( ( )) = ( ) − (0) furthermore, the following relations are also held for the caputo method [15]: (11) ( ( )) = ( ), ( = 0,1,2, … ; − 1 < < ) meanwhile: (12) ( ( )) = ( ( )) = ( ) ( )(0) = 0 , ∈ ℕ , = , + 1, … , ( = 0,1,2, … ; − 1 < < ) in the following, the above fractional calculus is combined with the synergetic control theory to obtain appropriate control law. 4. methodology: analytical investigation of the stability of fractional-order manifold synergetic controller in this section, the synergetic controller in eqn.(2) to eqn.(6) gains a fractional manifold. the combination gives advantages of both the synergetic theory and the fractional calculus. the latter provides more flexibility and degree of freedom to design the fractional controller. when a higher integer order is needed a small size fractional controller provides better results [17, 33-35].the idea is also developed to consider a linear combination of state variables. in this regard, a fractional order form of the synergetic manifold of eqn.(3) is proposed as follows: (13) ( ) + ( ) = 0, > 0 where is a real number in the interval ∈ (0, 1). in the following, performance of the proposed controller is compared with conventional synergetic controller of integer order manifold when fractional order chaotic coullet system [36] is controlled. chaotic systems are found very sensitive to initial conditions. this means two identical systems but with a minor deviation in their initial conditions may produce a completely different result. hence, it is difficult predict the behavior of these systems. the term chaos arises from a deterministic dynamic with nearly stochastic (almost unpredictable) behavior. the chaos effect and control is a more challenging topic. therefore the following section addressess control of chaotic coullet dynamic. 4.1 stabilizing the chaos the coullet system is used in a synchronization approach, which is as follows: iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 119 (14) = = = + + + parameters of the coullet system are chosen as a = 0.8, b = -1.1, c = -0.45, d = -1 and = 0.95 together with the state initial conditions: x (0) = −0.8, x (0) = 1.2 and x (0) = 0.2. state response of the system (4.2) to initial conditions is simulated in 50 seconds where depicted in fig. 1 for − . fourth plot in fig. 1 represents a phase portrait of the system. fig. 1: states (x1-x3) responses of together with a phase portrait (fourth). as can be seen from the first three graphs in fig. 1, state x1-x3 are of chaotic (neither periodic nor converging). the fourth plot also confirms states fail to converge to any point. to deeply verify the chaos, an fft of x1 is assessed and plotted in fig. 2, using power gui facility in the matlabtm simulink. as can be seen from fig. 2, all of the frequency components occur in the frequency spectrum. this is in confirmation that the signal is not pure oscillatory. this is main characteristics of chaos (similar to frequency characteristics of noise) where all frequencies can be seen in the chaos [5-6, 37-38]. although this is for x1, similar results are achieved for x2 and x3. in order to control the chaos, a control effort ( )is applied to the third equation of eqn.(4.2): (15) = = = + + + + 0 20 40 60 -1 -0.5 0 0.5 1 1.5 time (s) a m pl itu de x1 state 0 10 20 30 40 50 -1 -0.5 0 0.5 1 1.5 time (s) a m pl itu de x2 state 0 20 40 60 -1 -0.5 0 0.5 1 time (s) a m pl itu de x3 state -2 0 2 -2 0 2 -1 0 1 x1x2 x3 iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 120 fig. 2: time (the above) and frequency (bottom) response of state x1 of the coullet system. the control takes places using the synergetic technique. the duty is to provide zero convergence of the state variables. the macro variable is defined as follows [2]: (16) = + + in order to make more degree of freedom, arbitrary gains of , and are innovatively added to the macro variable in eqn. (16). this generalization expands the macro as in the following: (17) = + + it will be shown that the proposed macro in eqn. (17) increases the performance. the required control effort can be obtained when the conventional manifold in eqn. (16) i.e. ψ = x + x + x = 0 is substituted into eqn. (13), which is as follows: (18) = − 1 ( ) + ( ) + ( + + + ) + ( ) + ( ) + ( ) likewise, anew control law is derived for the proposed manifold in eqn. (17) using the following fractional dynamical equation of macro variables: (19) ( ) + ( ) = 0, > 0 substitution of eqn. (19) into eqn. (13) yields: (20) ( ) + ( ) + ( ) + ( ) + ( ) + ( ) = 0 0 10 20 30 40 50 -0.5 0 0.5 1 selected signal: 50 cycles. fft window (in red): 1 cycles time (s) 0 10 20 30 40 50 0 10 20 30 40 50 60 frequency (hz) fundamental (1hz) = 0.3419 , thd= 78.96% m ag ( % o f f un da m en ta l) iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 121 where ( ) is -order derivative of state variable in the caputo sense as: (21) ( ) = = / by substituting dynamical equation eqn. (15) into eqn. (20), the following equation is obtained: (22) ( ) + ( ) + ( + + + + ) + ( ) + ( ) + ( ) = 0 the control input u is finally extracted form (22) which is as follows (23) = − 1 ( ) + ( ) + ( + + + ) + ( ) + ( ) + ( ) the stability of the proposed controller will be analyzed through the following theorem: theorem: consider the coullet fractional order system in eqn. (15). if the control law in eqn. (23) is applied, system states asymptotically converge to zero. proof: the lyapunov function is candidate as in the following: (24) = 1 2 (ψ( )) ≥ 0 the conventional derivative yields: (25) v̇ = (ψ( ))( )ψ( ) = ψ( )ψ( ) a fractional form of the macro-variable i.e. ψ( ), is achieved as follows: (26) ( ) = ( ) + ( ) + ( ) = ( ) + ( ) + ( + + + + ) replacement the control effort ( ) from eqn. (23) into eqn. (26) provides: (27) ( ) = ( ) + ( ) + ( + + + − 1 ( ) + ( ) + ( + + + ) + ( ) + ( ) + ( ) = − 1 ( ) + ( ) + ( ) = − 1 ( ) substituting ψ( ) = − ψ( )from eqn. (27) into eqn. (25) achieves: iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 122 (28) v̇ = − 1 ( ) ( ) = − 1 ( ( ) ) ≤ 0 inequality eqn. (28) guarantees strictly decreasing nature of the lyapunov function in eqn. (22). this confirms that the control input eqn. (21) is a stabilizing control effort for system eqn. (15). 5. results: application of the proposed synergetic controller to control a chaos a simulation is carried out for the fractional order coullet system gaining both the manifold in eqn. (16) [2] and the proposed manifold in eqn. (17). time responses of three states are shown in fig. 3, fig. 4 and fig. 5 when initial conditions are assumed as (0) = −0.8, (0) = 1.2, (0) = 0.2 and t = 0.1 whilst gains are chosen = 3, = 5 and = 1 using eqn. (3) to eqn. (6). from fig. 3 it can be seen that by considering extra gains into eqn. (16) the macro variable in eqn. (17) causes reduction in the overshoot. meanwhile better performance with respect to the conventional macro variable in eqn. (17) is also achieved. however, errors in two methods approach zero. the time behavior of the second state variable in fig. 4 is similar to the first state variable as in fig. 3. in contrast to those two state variables, the third state variable in fig. 5 provides more negative peak with respect to that of the conventional macro in eqn. (16). however, the proposed macro in eqn. (17) provides a faster convergence rate (with the price of more negative peak). this necessitates to tune those gains in an optimal way rather than simple selection of = 3, = 5 and = 1. fortunately, this probable draw back requires no more attention to provide the control effort which is depicted in fig. 6 which makes the lack of negative peak negligible. fig. 3: time response of state variable x in fractional order coullet system with conventional macro eqn. (16) as = + + = 0 and the proposed macro eqn. (17) as = + + = 0. fig. 4: time response of state variable x in fractional order coullet system with conventional macro eqn. (16) as = + + = 0 and the proposed macro eqn. (17) as = + + = 0. 0 5 10 15 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 time(s) x 1 the proposed method method in [2] 0 5 10 15 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 time(s) x 2 the proposed method method in [2] iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 123 fig. 5: time response of state variable x in fractional order coullet system with conventional macro eqn. (16) as = + + = 0 and the proposed macro eqn. (17) as = + + = 0. fig. 6: the required control input for using the conventional macro in eqn. (16) as = + + = 0 and the proposed macro eqn. (17) as = + + = 0. 6. synergetic synchronization of fractional-order coullet system basically, chaos synchronization means forcing two systems work in a same way in a master-slave structure. the designed nonlinear control system obtains signals from the master to control the slave dynamics. block diagram of the master and slave synchronization using the synergetic controller is shown in fig. 7. fig. 7: block diagram of the master and slave synchronization using the synergetic controller. the goal is to synchronize a fractional-order coullet system assuming the master as in eqn. (29) to be followed by the slave as in eqn. (5.2) using the proposed synergetic controller eqn. (23). (29) = = = + + + supposing (0) = −0.8, (0) = 1.2 and (0) = 0.2 where the makes the system chaotic. the slave dynamics is similarly shown by: 0 5 10 15 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 time(s) x 3 the proposed method method in [2] 0 5 10 15 -6 -5 -4 -3 -2 -1 0 1 time(s) co nt ro l e ff or t the proposed method method in [2] iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 124 (30) = = = + + + + initial conditions of the slave are assumed different as (0) = 1, (0) = −1.2 and (0) = −0.4. the error is defined as discrepancy of the corresponding states, i.e. = − for i = 1,2,3. deducing the master dynamic from the slave leads to: (31) = = = + + + + the same procedure as in eqn. (19) to eqn. (23) using the proposed linear gains leads to generate the following control effort: (32) = − 1 ( ) + ( ) + ( + + + ) + ( ) + ( ) + ( ) a proper selection of control parameters ki, i.e. k1 = 3, k2 = 5.75 and k3 = 1 provides lim → = 0. outcomes of the synchronization are shown in fig. 108, fig. 9 and fig. 10. the proof is similar to that of in eqn. (24) to eqn. (28). this immediately means that output of the slave asymptotically follows the master state i.e. = . this confirms that the synchronization between master and slave is made possible. fig. 8: synchronization of states and together with the = − . fig. 9: synchronization of states and together with the = − . fig. 10: synchronization of states and together with the = − . 0 5 10 15 20 -4 -2 0 2 time(s) x 1 ,y 1 x 1 y 1 0 5 10 15 20 -4 -2 0 2 time(s) e 1 =x 1y 1 0 5 10 15 20 -2 0 2 time(s) x 2 ,y 2 x 2 y 2 0 5 10 15 20 0 1 2 3 time(s) e 2 =x 2y 2 0 5 10 15 20 -2 -1 0 1 time(s) x3 ,y 3 x3 y3 0 5 10 15 20 -2 -1 0 time(s) e rr or = x3 -y 3 iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 125 7. discussion and conclusion in this paper, a new controller is proposed by considering a fractional derivative in linear weighted combination of state variables in the synergetic controller. the degree of freedom is also increased by adding control coefficients , , and to the designed synergetic manifold. by tuning parameters , and frequency of oscillations is decreased when convergence is finally achieved. the stability of the proposed configuration is proven using the lyapunov theory. the achievement confirms performance of the proposed structure. the parameters , and are determined by a trial and error process, while they can be determined using intelligent algorithm such as pso (particle swarm optimization) or other algorithms to obtain better results. references [1] kolesnikov a, et al. (2000) modern applied control theory: synergetic approach in control theory. trtu, moscow, taganrog. [2] djennoune s, bettayeb m. (2013) optimal synergetic control for fractional-order systems. automatica, 49(7):2243-2249. [3] jiang z. (2009) design of a nonlinear power system stabilizer using synergetic control theory. electric power sys. res., 79(6):855-862. [4] jiang z, dougal ra. (2004) synergetic control of power converters for pulse current charging of advanced batteries from a fuel cell power source. ieee trans. power electronic, 19(4):1140-1150. [5] santi e, et al. (2003) synergetic control for dc-dc boost converter: implementation options.ieeetrans.ind.app., 39(6):1803-1813. http://dx.doi.org/10.1109/tia.2003.818967 [6] ni j, et al. (2014) variable speed synergetic control for chaotic oscillation in power system. nonlinear dynamics, 78(1):681-690. [7] delavari h, lanusse p, sabatier j. (2013) fractional order controller design for a flexible link manipulator robot. asian j. control, 15(3):783-795. [8] el-khazali r. (2013) fractional-order controller design. computers & mathematics with applications, 66(5):639-646. [9] faieghi mr, delavari h, baleanu d. (2012) control of an uncertain fractional-order liu system via fuzzy fractional-order sliding mode control. j. vib. control, 18(9), 1366-1374. [10] kilbas aaa, srivastava hm, trujillo jj. (2006) theory and applications of fractional differential equations, vol. 204, elsevier science limited. [11] magin rl. (2006) fractional calculus in bioengineering. begell house, rodding. [12] mainardi f. (1997) fractional calculus. springer. [13] monje, ca, et al. (2010) fractional-order systems and controls: fundamentals and applications. springer. [14] odibat z, momani s. (2006) application of variational iteration method to nonlinear differential equations of fractional order. int. j. nonlinear sci. num. simulation, 7(1):27-34. [15] podlubny i. (1998) fractional differential equations: an introduction to fractional derivatives, fractional differential equations, to methods of their solution and some of their applications. vol. 198. academic press. [16] sabatier j, agrawal op, machado jt. (2007) advances in fractional calculus. springer. [17] luo y, et al. (2010) tuning fractional order proportional integral controllers for fractional order systems. j. process control, 20(7):823-831. [18] meng l, wang df, han p. (2012) identification of fractional order system using particle swarm optimization. ieee international conference on machine learning and cybernetics (icmlc). [19] saxena r, mathai a, haubold h. (2004) unified fractional kinetic equation and a fractional diffusion equation. astrophysics and space science, 290(3-4):299-310. [20] bagley rl, torvik p. (1983) a theoretical basis for the application of fractional calculus to viscoelasticity. j. rheology, 27(3):201-210. iium engineering journal, vol. 17, no. 1, 2016 pourmehdi et al. 126 [21] di paola m, zingales m. (2012) exact mechanical models of fractional hereditary materials. j. rheology, 56(5):983-1004. [22] hilfer r, et al. (2000) applications of fractional calculus in physics. vol. 128. world scientific. [23] poinot t, trigeassou j. (2004) identification of fractional systems using an output-error technique. nonlinear dynamics, 38,133-154. [24] cois o, oustaloup a, battaglia e. (2000) non-integer model from modal decomposition for time domain system identification. 12th ifac symposium on system identification, santa barbara, ca, usa. [25] sabatier j, et al. (2002) crone control: principles and extension to time-variant plants with asymptotically constant coefficients. nonlinear dynamics, 29(1-4):363-385. [26] podlubny i. (1999) fractional-order systems and pi/sup/spl lambda//d/sup/spl mu//controllers. ieee trans. autom. control, 44(1):208-214. [27] nechadi e, et al. (2012) type-2 fuzzy based adaptive synergetic power system control. electric power sys. res., 88:9-15. [28] santi e, et al. (2004) synergetic control for power electronics applications: a comparison with the sliding mode approach. j. circ. sys. comp., 13(4):737-760. [29] caputo m. (1969) elasticita´ e dissipazione. zanichelli. bologna. [30] caputo m. (1989) the rheology of an anelastic medium studied by means of the observation of the splitting of its eigenfrequencies. j. acoustical soc. america, 86(5):1984-1987. [31] el-sayed am. (1995) fractional order evolution equations. j. fract. calc, 7:89-100. [32] el-sayed am, ibrahim a. (1995) multivalued fractional differential equations. app. math. comp., 68(1):15-25. [33] vinagre b, et al. (2002) using fractional order adjustment rules and fractional order reference models in model-reference adaptive control. nonlinear dynamics, 29(1-4):269-279. [34] xue d, zhao c, chen y. (2006) fractional order pid control of a dc-motor with elastic shaft: a case study. proceedings of american control conference. [35] jesus is, machado jt. (2008) fractional control of heat diffusion systems. nonlinear dynamics, 54(3):263-282. [36] arneodo a, coullet p, tresser c. (1981) possible new strange attractors with spiral structure. comm. math. phys., 79(4):573-579. [37] liu y, chen l. (2013) chaos in attitude dynamics of spacecraft. springer. [38] petržela j, kolka z, hanus s. (2011) simple chaotic oscillator: from mathematical model to practical experiment. models and applications of chaos theory in modern sciences, p. 317. microsoft word paper-v4-1-4.doc iium engineering journal, vol. 4, no. 1, 2003 s. w. harun and h. ahmed letter to the editor 41 performance enhancement in l-band edfa through dual stage technique s. w. harun and h. ahmad department of physics, faculty of science, university malaya, 50603 kuala lumpur e-mail: wadi72@yahoo.com abstract: an experiment on gain enhancement in the long wavelength band erbium doped fiber amplifier (l-band edfa) is demonstrated. it uses a dual stage technique with dual forward pumping scheme. compared to a conventional single stage amplifier, the small signal gain for 1580nm signal can be improved by 5.5db without paying much noise figure penalty. the corresponding noise figure penalty was 0.3db due to the insertion loss of the optical isolator. the optimum pump power ratio for the first pump is experimentally determined to be 33%. the maximum gain improvement of 8.3db was obtained at a signal wavelength of 1568nm while signal and total pump powers were fixed at -30dbm and 92mw, respectively. the employment of dual stage amplifier system seems to play an important role in the development of practical l-band edfa from the perspective of economical usage of pump power. key words: erbium doped fibre; optical amplifier; l-band edfa; dual stage edfa; amplified spontaneous emission 1. introduction ultra-wideband erbium-doped fiber amplifier (edfa) now represents one of the promising future network elements, for the ever-increasing high capacity wavelength division multiplexed (wdm) system application [1]. among many attempts suggested so far, the silica based edfas in parallel configuration (c-band: 1530 ~ 1560nm plus l-band: 1570 ~ 1610nm) [2-3] have been considered to be the most immediate viable candidate for real system applications, due to the maturity of the supporting technologies. there has been a lack of research effort on l-band edfa compared to c-band edfa. the l-band require longer erbium-doped fiber (edf) lengths to obtain the same gain as a conventional band (c-band) edfa due to its operating wavelengths are very far from the emission peak of silica-based edf at 1531nm. therefore, many researches for l-band focused on the efficiency improvement, to relax the need for higher pump power compared to c-band edfa. iium engineering journal, vol. 4, no. 1, 2003 s. w. harun and h. ahmed letter to the editor 42 one of the approaches to power conversion efficiency in l-band edfa is to recycle a unwanted backward ase as a secondary pump source to pump an under-pumped edf section [4]. other approaches are c-band injection seeding [5] and using a double pass technique [6]. in this letter, two stages l-band edfa is proposed to improve the gain using optical isolator to split the edf into two segments. in this amplifier, both segments are pumped separately using forward pumping scheme and the optical isolator is inserted between the first and second stages to eliminate any backward propagating amplified spontaneous emission (ase). 2. experimental set up the experimental set up is shown in fig. 1. figure 1(a) shows a single stage amplifier configuration. figure 1(b) shows a configuration of the proposed dual stages l-band edfa, in which an optical isolator splits the edf 1 into two segments of edf 2 and edf 3. edf with an erbium the peak absorption of 5.6db/m at the 1531nm was used for both configurations. edf 1 was 50m long and it was split into 20m for edf 2 and 30m for edf 3. edf 1, edf 2 and edf 3 are pumped by 980nm laser diode at 92mw, 35mw and 57mw, respectively using forward pumping scheme. the gain and noise figure for the proposed two stages amplifier are measured using optical spectrum analyzer (osa) and are compared with the single stage amplifier. (a) (b) fig. 1: configuration of the l-band edfa (a) single stage (b) dual stage wsc 1 wsc 2 tls osa 980nm pump 1 edf 1 wsc 1 tls osa 980nm pump 1 980nm pump 2 edf 2 edf 3 isolator iium engineering journal, vol. 4, no. 1, 2003 s. w. harun and h. ahmed letter to the editor 43 3. result and discussion figure 2 depicts the ase spectra of both single stage and dual stage amplifiers with a total pump power of 92mw where the thin line represents the ase spectrum of the proposed dual stages amplifier. as seen, the spectrum of the proposed amplifier is much higher than the single stage amplifier, represented by the thick line. by splitting the pumping to two positions along the edf length as a dual stage amplifier, the ase level is increased due to large forward ase from first stage that has not been depleted by backward ase of second stage. the power level of this ase spectrum is not very high due to insufficient pump powers to generate the ase. this can be solved by deploying 1480nm laser diodes that provide better power conversion efficiencies and consequently higher ase powers. the pump power of the first stage is fixed at 35mw that is 33% of the total pump power because this is the optimum value as shown in fig. 3. fig. 3 also shows the gain and noise figure as a function of the power ratio of pump 1. the maximum gain is obtained at 33% before decreasing slowly until the ratio reached 85%. on the other hand the noise figure shows a constant value of 3.2db at pump 1 ratios of 28% to 85%. fig. 2: ase spectra of the l-band edfa while the total pump power is fixed at 92mw. for dual stage amplifier, pump 1 and pump 2 are fixed at 35mw and 57mw, respectively. the gain and noise figure characteristics of the 1580nm signal against input signal power were measured by varying the input signal power from –40 to 0dbm for both cases as shown in fig. 4. a gain enhancement of about 5.5db is obtained at small signal levels for the dual stage amplifier compared to single stage amplifier. this is attributed to the dual forward pumping scheme that increased the forward ase level and thus the amount of energy available for transfer from short to long wavelength also increases. the first stage amplifier works as a pre-amplifier with a relatively high inversion, while the second stage acts as a power amplifier with high pump efficiency. the saturation power of the single and dual stage amplifiers are obtained at –12dbm and –14dbm, respectively. on the other hand, the noise figure of the proposed dual stage amplifier is slightly higher by 0.3db compared to the single stage amplifier for all input signal powers. this noise figure degradation is caused by the inserted component loss. the optical isolator is used to separate the edf into two -80 -70 -60 -50 -40 -30 -20 -10 0 1530 1550 1570 1590 1610 1630 wavelength (nm) a s e p ow er (d b m ) dual stage single stage iium engineering journal, vol. 4, no. 1, 2003 s. w. harun and h. ahmed letter to the editor 44 sections to prevent the backward ase from entering the first stage section and degrades the noise figure terribly. fig. 3: gain (closed) and noise figure (clear) as a function of power ratio of pump 1. fig. 4: gain (closed) and noise figure (clear) as a function of input signal power. fig. 5 shows the gain and noise figure spectra for an input signal power of –30dbm and total pump power of 92mw. as seen, the gain of the dual stage amplifier is higher compared to the single stage amplifier especially at shorter wavelengths. this improvement is obtained by amplifying and employing the forward ase from the first stage to the second stage. the first 10~15 meters of the forward-pumped edf 0 5 10 15 20 25 0 20 40 60 80 100 pum p ratio pi/(p1+p2) (%) g ai n (d b ) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 n oi se fi gu re (d b ) gain nf 0 5 10 15 20 25 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 input signal power (dbm) g ai n (d b ) 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 n oi se fi gu re (d b ) s ingle s tage dual stage iium engineering journal, vol. 4, no. 1, 2003 s. w. harun and h. ahmed letter to the editor 45 experiences a very high pump power with correspondingly high population inversion rates in the c-band in both the forward and backward directions. however, insertion of the isolator blocks the backward ase from the second stage, which has a higher pump power allocation. suppression of this high power backward ase, enables builtup of forward ase in the first stage since there is no other mechanism to deplete the inversion. this results in a very high power forward ase which can be used to transfer from the higher energy c-bands to the lower energy l-band wavelengths. it also can be seen in fig. 5 that the maximum gain enhancement value of 8.3db is obtained in the dual stage amplifier compared with the conventional single stage amplifier at wavelengths of 1568nm. the corresponding noise figure penalty is 0.5db. the noise figure penalties were obtained especially at longer wavelengths due to the same reason as explained above. fig. 5: gain (closed) and noise figure (clear) as a function of input signal wavelength. 4. conclusions an l-band edfa with improved gain characteristic, which uses dual forward pumping scheme, has been proposed and demonstrated. the amplifier has improved the small signal gain for 1580nm signal by 5.5db at the expense of 0.3db noise figure penalty compared to a conventional single stage amplifier. the noise figure penalty is due to the insertion loss of the optical isolator. the optimum pump power ratio for the first pump is experimentally determined to be 33%. a maximum gain improvement of 8.3db was obtained at a signal wavelength of 1568nm while signal and total pump powers were fixed at -30dbm and 92mw, respectively. these results show that the employment of dual stage amplifier system will play an important role in the development of practical l-band edfa from the perspective of economical usage of pump power. iium engineering journal, vol. 4, no. 1, 2003 s. w. harun and h. ahmed letter to the editor 46 acknowledgements one of the authors (s. w. harun) acknowledges the support of a national science fellowship (nsf), moste. references [1] a. k. srivastave, “wide bandwidth high capacity systems,” opt. fiber comm. conf. 1999, and the international conf. on integrated optics and opt. fiber comm. ofc/iooc '99. technical digest, pp. 59-60, 1999. [2] m. yamada, h. ono, t. kanamori, s. sudo and y. ohishi, “broadband and gainflattened amplifier composed of a 1.55m-band and a 1.58m-band er3+-doped fiber amplifier in a parallel configuration,” electron. lett., 33, 710-711, 1997. [3] y. sun, j. w. sulhoff, a. k. srivastava, j. l. zyskind, t. a. strasser, j. r. pedrazzani, c. wolf, j. zhou, j. b. judkins, r. p. espindola and a. m. vengsarkar, “80nm ultrawideband erbium-doped silica fiber amplifier,” electron. lett., vol. 33, pp. 1965-1967, 1997. [4] j. lee, u.-c, ryu, s. j. ahn, and n. park, “enhancement of power conversion efficiency for a l-band edfa with a secondary pumping effect in the unpumped edf section,” ieee photon. technol. lett., 11, 42-44, 1999. [5] m. a. mahdi, f. r. mohamd adikan, p. poopalan, s. selvakennedy, w. y. chan and h. ahmad, “long wavelength edfa enhancement through 1550nm band signal injection,” opt. comm., 176, pp. 125-129, 2000.. [6] s. w. harun, p. poopalan and h. ahmad, “gain enhancement in l-band edfa through double pass technique,” ieee photon. technol. lett, 14, pp. 296-298, 2002. biography sulaiman wadi harun received his b. eng in electrical and electronic system engineering from nagaoka university of technology, japan in 1996. currently he is studying for his ph.d. in department of physics, university of malaya. harith ahmad is a professor at physic department, faculty of science, university of malaya. he obtained his ph.d from university of wales (u.k) in laser technology in 1983 and has been involved in laser related research the past 18 years. he has numerous research papers published both local and international journals. c 5.6 τ noo      s kk 273 iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 77 numerical study of laminar forced convection of water/al2o3 nanofluid in an annulus with constant wall temperature a. kashani, d. jalali-vahid and s. hussainpour department of mechanical engineering, sahand university of technology, tabriz, iran. 1 amin_k101@yahoo.com; 2 davoodjalali@sut.ac.ir; 3 hossainpour@sut.ac.ir abstract: in this paper, laminar forced convection of a nanofluid consisting of water and al2o3 in a horizontal annulus has been studied numerically. a two-phase mixture model has been used to investigate thermal behaviors of the nanofluid over constant temperature thermal boundary condition and with different volume concentration of nanoparticles. comparisons with previously published both experimental and analytical works on flow behavior in horizontal annulus show good agreements between the results as volume fraction is zero. in general, convective heat transfer coefficient increases with nanoparticle concentration. abstrak: kertaskerja ini mengkaji secara numerik olakan paksa bendalir lamina yang menganduangi air dan al2o3 didalam anulus mendatar. model campuran dua fasa digunakan bagi mengkaji tingkah laku haba bendalir nano pada keadaan suhu malar dengan kepekatan nanopartikel berbeza. perbandingan dengan karya eksperimen dan analitikal yang telah diterbitkan menunjukkan bahawa kelakuan aliran didalm anulus mendatar adalah baik apabila pecahan isipadu adalah sifar. pada amnya, pekali pemindahan haba olakan meningkat dengan kepekatan nanopartikel. keywords: nanofluid; volume concentration; heat transfer enhancement; laminar flow convection; annulus. 1. introduction energy has been rated as the single most important issue currently facing humanity. fundamentally, energy conversion and transportation occur at atomic or molecular levels, nanoscience and nanotechnology are expected to play a significant role in revitalizing the traditional energy industries and stimulating the emerging renewable energy industries. among all the forms of energy we are using today, over 70% are produced in or through the form of heat. in many industrial systems, heat must be transferred either to input energy into a system or to remove the energy produced in a system. considering the rapid increase in energy demand worldwide, intensifying heat transfer process and reducing energy loss due to ineffective use have become increasingly important tasks. for achieving this important task, fluids in conversion and transportation of energy have important roles. using of them have paid attention widely but for importing thermal characteristics of fluids, shoud be used new technology and produce nanofluid and replace it with common fluids [1]. nanofluids are dilute suspensions of functionalized nanoparticles smaller than 100 nm, which belong a new type of functional composite materials developed about a decade ago with the specific aim of increasing the thermal conductivity of heat transfer fluids, which have now evolved into a promising nanotechnological area [1]. iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 78 in less than several years since the seminal work by choi concerning the concept of nanofluids, interest in this area has grown rapidly. however, investigators are having difficulty in understanding the anomalous behavior of nanofluids in regard to thermal conductivity and convection heat transfer coefficient [2]. these difficulties show the lack of agreement between results obtained in different laboratories, the often poor characterization of the suspensions, and the lack of theoretical understanding of the mechanisms responsible for the observed changes in properties [3]. now we consider some of the researches in this field. among common materials, in many energy conversion systems, only specific materials are used in the production of nanofluids having high thermal conductivity and other properties like cost, easy production etc. from these common materials, engine oil, ethylene glycol and water have the lowest thermal conductivity. on the other hand materials such as copper, aluminum and others have high thermal conductivity. this was the main idea of producing nanofluids by using base fluids like water, oil and nanoparticles of copper, aluminum or their oxides like cuo, al2o3. in an article from pawel keblinski, jeffery a.eastman, david g.calill some of researches have been collected [3]. masuda el al. [4] reported a 30% increase in the thermal conductivity of water with the addition of 4.3 vol. % al2o3 nanoparticles. xuan and li [5] measured the turbulent friction factor of water-based nanofluids containing cu nanoparticles in a volume fraction range of 1.0 – 2.0. interestingly, they found that the friction factor for the nanofluids is approximately the same as that of water. wang et al. [6] measured the viscosity of al2o3 – water nanofluids and showed that nanofluids have lower viscosities when the particles are more dispersed. they also found an increase of about 30 % in viscosity at 3 vol. % al2o3, compared with that of water alone. also numerical works have paid attention beside experimental researches in recent years. for example, maiga et al. [7] studied heat transfer enhancement by using nanofluids in forced convection flows. in this paper, the problem of laminar forced convection flow of nanofluids has been thoroughly investigated for two particular geometrical configurations, namely a uniformly heated tube and a system of parallel, coaxial and heated disks. numerical results, as obtained for water al2o3 and ethylene glycol al2o3 mixtures, have clearly shown that the inclusion of nanoparticles into the base fluids has been produced a considerable augmentation of the heat transfer coefficient that clearly increase with an increase of the particle concentration. xuan et al. [8] used an experimental system for investigation of convective heat transfer and flow features of nanofluids in a tube. both the convective heat transfer coefficient and friction factor of the sample nanofluids for the turbulent flow are measured, respectively. the sample nanofluids are prepared by mixing the nano structured cu particles below 100 nm diameter and deionized water. nanofluids possess 0.3, 0.5, 0.8, 1.0, 1.2, 1.5,2 % volume fractions of cu nanoparticles. the reynolds number, re, varies between the range 10.000 ~ 25.000. in comparison with water, nusselt number of nanofluids with 2 vol. % cu nanoparticles is 60% greater. lee et al. investigated the same issue [9]. fully developed laminar mixed convection of a nanofluid consists of water and al2o3 in horizontal and inclined tubes has been studied numerically by akbari et al. [10]. it is shown that the nanoparticles concentration does not have significant effects on the hydrodynamics parameters. heat transfer coefficient increases by 15% at 4 vol. % al2o3. iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 79 lee et al. [11] researched effective viscosities and thermal conductivities of aqueous nanofluids containing low volume concentrations of al2o3 nanoparticles. the measured viscosities of the al2o3 – water nanofluids show a nonlinear relation with the concentration even in the low volume concentration (0.01 % 0.3 %) range, while the einstein viscosity model clearly predicts a linear relation, and exceed the einstein model predictions. in contrast of viscosity, the measured thermal conductivities of the dilute al2o3 – water nanofluids increase nearly linearly with the concentration, agree well with the predicted values by the jong and choi model [11], and are consistent in their overall trend with previous data at higher concentrations. kyo sik hwang et al. have measured the pressure drop and convective heat transfer coefficient of water based al2o3 nanofluids flowing through a uniformly heated circular tube in the fully developed laminar flow regime [12]. the experimental results show that nanofluid friction factor shows good agreement with analytic prediction from the equation of darcy for single – phase flow. however the convective heat transfer coefficient of the nanofluids increases by up to 8% at a concentration of 0.3 vol. % compared with that of pure water. behzadmehr et al. [13] did a numerical study of laminar mixed convection of a nanofluid in a horizontal tube by using two – phase mixture model. the nanofluid consists of water and al2o3. comparisons with previously published experimental and numerical works on mixed convection in horizontal tubes show good agreements between the results. it is shown that at the fully developed region the nanoparticle concentration does not have significant effects on the hydrodynamics parameters. however its effects on the thermal parameters are important. concentration of the nanoparticles is higher at the bottom and also at the near wall region. ho et al. [14] did numerical simulation of natural convection of nanofluid in a square enclosure. the rayleigh number was varied between, ra= 10 3 – 10 6 and the volumetric fraction of alumina nanoparticles between, ф=0 – 4%. joseph et al. [15] studied heat transfer enhancement with the use of nanofluids in radial flow cooling systems considering temperaturedependent properties. water / al2o3 nanofluid with a volume fraction of nanoparticles as low as 4% can produce a 25% increase in the average wall heat transfer coefficient when compared to the base fluid alone. heris et al. [16] used nanofluids containing cuo and al2o3 oxide nanoparticles in water as base fluid in different concentrations and investigated the laminar flow convective heat transfer through circular tube with constant wall temperature boundary condition. at low volume concentration the heat transfer coefficient is close to single phase result but with increasing volume concentration higher heat transfer enhancement for al2o3 /water can be observed. behzadmehr et al. [17] studied effect of nanoparticles mean diameter on mixed convection heat transfer of a nanofluid in a horizontal tube. nanoparticles distribution at the tube cross section shows that the non–uniformity of the particles distribution augments when using larger nanoparticles and / or considering relatively high value of the grashof numbers. annulus appears in many industrial heat exchangers. therefore, many investigations have been done on the heat transfer mechanisms of an annulus. among them srivastara et al. [18] experimentally investigated the effect of an unheated length and the annulus ratio on the variations in heat transfer coefficient in the early entrance region of an annulus. iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 80 they showed that the effect of the shape of unheated section only becomes significant within x/d =2. however, thereafter the results correspond to the fully developed condition. lu and wang [19] experimentally studied the convective heat transfer of water flow in a narrow annulus. they showed that the thermal characteristics of fluid flow in an annulus are different from those in circular tubes. transition from laminar to turbulent occurs at the lower reynolds number compared to the one for circular tubes. gupta and grag [20] numerically studied flow in the hydrodynamic entrance region of an annular tube by using an implicit finite difference. they found that for a very small annulus ratio the results depart significantly from those for a circular pipe. el – shaarawiy et al. [21] solved numerically the transient laminar forced convection in the entrance region of an annuls. for different initial thermal condition, they found that generally the responses associated with heating the outer boundary are more pronounced associated with heating the inner boundary are. izadi et al. [22] investigated numerically laminar forced convection of a nanofluid of al2o3 and water in an annulus. it is shown that the dimensionless axial velocity profile does not significantly change with the nanoparticle volume fraction. but, the temperature profiles are affected by the nanoparticle concentration. also they showed that by increasing the heat fluxes ratio (outer to inner), the effect of one wall heat flux on the nu of another wall increases via its effects on the bulk temperature. as seen in these and similar works, heat transfer mechanisms in annulus could be very complex and this geometry is very common in many industrial installation. therefore, the present work aims to investigate some behaviors of nanofluid flow into such a geometrical configuration. also our study follows the research of izadi et al. [22] and by using of their computational codes some studies have been done. in this work, the effects of constant temperature thermal boundary condition on walls of annulus on thermodynamics properties of a laminar forced convection have been studied and hydrodynamics parameters do not change in comparing with studies of izadi et al. [22]. 2. mathematical model laminar forced convection of a nanofluid consisting of water and al2o3 in horizontal concentric annulus with constant temperature at walls has been studied by developing a computational code. the effective viscosity and effective thermal conductivity of the fluid are varied with the temperature while the other properties are assumed to be constant. dissipation and pressure work are neglected. with this assumption the dimensional conservation equation for steady state condition are as follows: continuity equation: ( ) 0. =∇ meff vρ (1) momentum equation: ( ) ( )meffmmeff vpvv ∇∇+−∇=∇ µρ .. (2) energy equation: ( ) ( )ttcv effmeff ∇∇=∇ µρ .. (3) the physical properties of the above equation are: iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 81 effective density: pfeff φρρφρ +−= )1( (4) chon et al. [23] correlation which considers the brownian motion and nanoparticles mean diameter has been used for calculation the effective thermal conductivity 2321.19955.0 7476.03690.0 7460.0 repr7.641 ××                 ×+= f s p f f eff k k d d k k φ (5) where pr and re in eq. (5) are defined as, ff αρ µ =pr (6) bf cf l tb 2 3 re πµ ρ = (7) bfl is the mean free path of water, cb is boltzman constant (1.3807×10 -23 j/k) and µ is calculated by the following equation: 5-2.414ea 247,b 140,c ,10 ===×= −ct b aµ (8) masoumi [24] correlation which considers the brownian motion of nanoparticles, nanoparticles mean diameter and effect of temperature variation has been used for calculation of the effective nanofluid viscosity: appbfeff µµµ += (9) where bfµ and appµ are respectively base fluid viscosity and apparent viscosity. apparent viscosity is defined by the following equation: c dv pbp app δ ρ µ 72 2 = (10) the constant c depends on base fluid viscosity, diameter of nanoparticles and some constants. δ depends on diameter and volume fraction of nanoparticles. bv is brownian velocity that depends on temperature, diameter and density of nanoparticles. iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 82 fig. 1: (a) schematic of the considered problem, (b) grid distributions. 2.1 boundary condition this set of nonlinear elliptical governing equations has been solved subject to following boundary conditions: at the inlet annulus (x=0): 0mrimx tt and 0v ,vv === (11) at the walls ( io rr ,rr == ) 0vv mrmx == , i = constant and o = constant (12) at the annulus outlet (x=l): the diffusion flux in the direction normal to the exit plane is assumed to be zero for all variables except temperature that discrete fully developed energy equation is composed at outlet. an overall mass flux balance is also applied to correct velocities in outlet which are used for pressure correction. 2.2 numerical method this set of coupled non-linear partial differential equations was discretized with the finite volume method. for the convective term a first order upwind method is used while the simple algorithm was introduced for the velocity-pressure coupling. cells of grid are non-uniform in two directions of axisymmetric geometry. it is finer near the wall and annulus entrance because the variables gradient is higher than other positions. 2.3 grid test and results validation several grid size have been tested to ensure that variation of grid numbers have no effect on the results. the selected grids consist of 15 and 200 cells, respectively in the radial and axial directions. figure 2 compares the experimental results of frictional pressure drop at various reynolds numbers [25] with the predicted results. while fig. 3 compares the fully developed nu profile with the corresponding analytical results for the state of constant heat flux thermal boundary condition [26]. good agreements between the results are seen. iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 83 10 100 1000 0.1 1 10 fr ic ti o n a l p r e ss u r e d r o p (f p ) re present work experimental data [ lu&wang ] fig. 2: comparison of frictional pressure drops in horizontal annulus with experimental data [25]. fig. 3: comparison of nuo in fully developed region of horizontal annulus with analytical calculation [27]. 3. results and discussion numerical simulation of forced convection of a nanofluid flow has been performed over reynolds number, 900 and nanoparticle mean diameter, 25 nm. wall temperatures were imposed at kit 302) = , kot 298) = on inner and outer walls and the temperature of the inlet nanofluid is constant at 300 k. hydrodynamics parameters such as velocities and friction coefficient at walls were like izadi et al. [22] studies. figure 4 shows heat flux behavior at inner wall. it is observed that heat flux decreases at the entrance region then increase in the length of the annulus. it is thought increasing in nanoparticle concentration increases heat flux. figure 5 shows the inner wall convective heat transfer coefficient at re=900. it is seen that at such conditions the convective heat transfer coefficient reduces at the entrance region and goes to its minimum value then increases along the annulus. 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 6 6.5 7 7.5 q " i /q " o n u o present work kays & crawford & weigand present work kays & crawford & weigand r i /r o =0.714 r i /r o =0.8 iium engineering journal, vol. 14, fig. 4: axial evolution of heat flux at the inner wall (w/m fig. 5: axial evolution figures 6 and 7 show the outer wall heat flux and convective heat transfer coefficient along the annulus for re=900 respectively. the result is similar to the one obtained for the inner wall. figures 8, 9, 10, 11 show the temperature distribution in the annulus for thermal boundary condition of the problem for nanoparticles volume concentration of 0.0, 0.05, 0.08, and 0.1 (in these figures z=x). 1120 1140 1160 1180 1200 1220 1240 1260 0 q i( w / m 2 ) ф=0.05 ф=0.08 ф=0.1 re=900 dp=25nm 590 600 610 620 630 640 650 660 670 0 h i( w / m 2 k ) ф=0.05 ф=0.08 ф=0.1 re=900 dp=25nm g journal, vol. 14, no. 1, 2013 84 evolution of heat flux at the inner wall (w/m 2 ). of convective heat transfer coefficient at the inner wall (w/m 2 k). 6 and 7 show the outer wall heat flux and convective heat transfer coefficient along the annulus for re=900 respectively. the result is similar to the one obtained for the 8, 9, 10, 11 show the temperature distribution in the annulus for thermal boundary condition of the problem for nanoparticles volume concentration of 0.0, 0.05, 0.08, and 0.1 (in these figures z=x). 0 0.2 0.4 0.6 0.8 1 x/l 0.2 0.4 0.6 0.8 x/l kashani et al. of convective heat transfer coefficient at the inner wall 6 and 7 show the outer wall heat flux and convective heat transfer coefficient along the annulus for re=900 respectively. the result is similar to the one obtained for the 8, 9, 10, 11 show the temperature distribution in the annulus for thermal boundary condition of the problem for nanoparticles volume concentration of 0.0, 1.2 1 iium engineering journal, vol. 14, fig. 6: axial evolutio fig. 7: axial evolution -1270 -1250 -1230 -1210 -1190 -1170 -1150 -1130 0 q o (w / m 2 ) ф=0.05 ф=0.08 ф=0.1 -680 -670 -660 -650 -640 -630 -620 -610 -600 0 h o (w / m 2 k ) ф=0.05 ф=0.08 ф=0.1 g journal, vol. 14, no. 1, 2013 85 evolution of heat flux at the outer wall (w/m 2 ). of convective heat transfer coefficient at the outer wall (w/m 2 k). 0 0.2 0.4 0.6 0.8 1 x/l 0.2 0.4 0.6 0.8 1 x/l kashani et al. of convective heat transfer coefficient at the outer wall 1.2 1.2 iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 86 (a) (b) fig. 8: (a) temperature distribution in the annulus (ф=0.0), (b) the zoomed form of the inner wall zone in (a). iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 87 (a) (b) fig. 9: (a) temperature distribution in the annulus (ф=0.05), (b) the magnified form of the inner wall zone in (a). iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 88 (a) (b) fig. 10: (a) temperature distribution in the annulus (ф=0.08), (b) the magnified form of the inner wall zone in (a). iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 89 (a) (b) fig. 11: (a) temperature distribution in the annulus (ф=0.1), (b) the magnified form of the inner wall zone in (a). iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 90 4. conclusion numerical study of laminar forced convection of a nanofluid consists of water and al2o3 in horizontal concentric annulus with constant temperature at walls have been studied by developing a computational code. two-phase model has been used for investigation of nanoparticles’ (spherical shapes) volume concentration effects with above mentioned thermal boundary conditions, especially convective heat transfer coefficient. it is shown that increasing the nanoparticle volume concentration increases the convective heat transfer coefficient and also we observe that in the length of the annulus the heat flux and the convective heat transfer coefficient decreases in the entrance and then increases. because of the aforementioned reasons, it can be said that in the length of the annulus there are sediments of nanoparticles that increase the heat transfer. and with increasing nanoparticles’ volume concentration the effects of this phenomenon will be significant. these results have well accordance with experimental data. for example nusselt number of al2o3-water nanofluid with the characteristics that have been written is brought here (fig. 12). fig. 12: the local nusselt number (nusselt number, nu = ��� � and knudsen number, kn =λ/dh) [28]. then there is a good accordance between nusselt number (fig. 12) and heat transfer coefficients (figs. 5 and7) of the wall in the entrance section of annulus. on the other hand there is a linear relation between hi and ho with qi and qo respectively. as a result numerical data are verifying with experimental data. references [1] donogsheng wen, guiping lin, saied vafaei, kai zhong. “review of nano for heat transfer applications.” chinese society of particulogy and institute of process engineering, chinese academy of sciences, 2009. [2] stephen u.s. choi, nanofluid technology: current status and future research, energy technology division, argonne national laboratory, argonne, [3] pawel keblinski, jeffrey a. eastman, and david g.cahill, “nanofluids for thermal transport, materials today,” 8.36 (2005). [4] h. masuda, a. ebata, k. teramae, n. hishinuma, “alteration of thermal conductivity and viscosity of liquid by dispersing ultra-fine particles.” netsu bussei, 7.33 (1993): 227. iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 91 [5] xuan , y., and li, q., “investigation on convective heat transfer and flow features of nanofluid.” journal heat transfer, 125 (2003): 151-55. [6] wang , x., xu, x., and choi, s.u.s., “thermal conductivity of nanoparticle-fluid mixture.” journal of thermo physics and heat transfer , 13 (1999): 474. [7] sidi el becaye maiga, samy joseph palm, cong tam nguyen, gilles roy, nicolas galanis., “heat transfer enhancement by using nanofluids in forced convection flows.” international. journal. of heat and fluid flow, 26 (2005): 530-46. [8] y. m. xuan, q. li, “investigation on convection heat transfer and flow features of nanofluids.” journal of. heat transfer. 125 (2003): 151-55. [9] li q, xuan y. “convective heat transfer and flow characteristics of cu-water nanofluid.” science in china (series e) 45.4 (2002): 408. [10] m. akbari, a. behzadmehr, f. shahraki., “fully developed mixed convection in horizontal and inclined tubes with uniform heat flux using nanofluid.” international . journal. of heat and fluid flow 29 (2008) 545-56. [11] jihwan lee , kyo sik hwang, seok pil jang , byeong ho lee , jun ho kim, stephen u. s. choi, chul jin choi, “effective viscosities and thermal conductivities of aqueous nanofluids containing low volume concentrations of al2o3 nanoparticles.” international. journal. of heat and mass transfer 51 (2008) 2651-56. [12] kyo sik hwang, seok pil jang, stephen u. s. choi, “flow and convective heat transfer characteristics of water-based al2o3 nanofluids in fully developed laminar flow regime.” international . journal. of heat and mass transfer 52 (2009): 193-99. [13] s. mirmasoumi, a. behzadmehr, “numerical study of laminar mixed convection of a nanofhild in a horizontal tube using two-phase mixture model.” applied thermal engineering 28 (208) 717-27. [14] c.j. ho, m. w. chen, z. w. li, “numerical simulation of natural convection of nanofluid in a square enclosure: effects due to uncertainties of viscosity and thermal conductivity.” international. journal. of heat and mass transfer 51(2008) 4506-16. [15] samy joseph palm, gilles roy, cong tam nguyen., “heat transfer enhancement with the use of nanofluids in radial flow cooling systems considering temperature-dependent properties.” applied thermal engineering 26 (206) 2209-18. [16] s. zeinali heris, s. gh. eternad, m. nasr esfahany., “experimental investigation of oxide nanoflids laminar flow convective heat transfer.” international. communications in heat and mass transfer 33(2006) 529-35. [17] s. mirmasoumi, a. behzadmehr, “effect of nanoparticles mean diameter on mixed convection heat transfer of a namofluid in a horizontal tube.” international. journal. of heat and fluid flow 29 (2008) 557-66. [18] n.c. srivastava, f. bakhtar, f.k. bannister, “an investigation into thermal boundary layer growth in the entrance region of an annulus.” international. journal. heat mass transfer. 14 (1973) 49-59. [19] g. lu, j. wang, experimental investigation on heat transfer characteristics of water flow in a narrow annulus, applied. thermal.engineering.28 (2008) 8-13. [20] s.c. gupta, v.k.garg, “developing flow in a concentric annulus.” computer.methamatics.applied.mechanical 28 (1981) 27-35. [21] m.a.i.el-shaarawiy, m.k. alkam,”transient forced convection in the entrance region of concentric annuli.” international. journal. heat mass transfer. 35 (1992)3335-44. [22] m. izadi, a. behzadmehr, d. jalali-vahid, “numerical study of developing laminar forced convection of a nanofluid in an annulus.” international journal of thermal sciences 48 (2009) 2119-129. [23] c.h. chon, k.d. kihm, s.p. lee, s.u.s. choi, “empirical correlation finding the role of temperature and particle size for nanofluid (al2o3) thermal conductivity enhancement.” applied. physics. letters. 87 (2005) 1–3. iium engineering journal, vol. 14, no. 1, 2013 kashani et al. 92 [24] masoumi n. sohrabi, n., behzadmehr, a.,” a new model for calculating the effective viscosity of nanofluid.” journal of physics 42 (2009). [25] guangyao lu, ć jing wang, “experimental investigation on flow characteristics in a narrow annulus.” heat mass transfer 44 (2008):495–499. [26] w.kays, m.crawford, b.weigand, “convective heat and mass transfer,.” mcgraw-hill international edition (2004). [27] s.u.s. choi, “enhancing thermal conductivity of fluid with nanoparticles, developments and applications of non-newtonian flow.” (1995) 99–105. [28] akbarinia, morteza abdolzadeh, r. laur,”critical investigation of heat transfer enhancement using nanofluids in micro channels with slip and non slip flow regims.” applied thermal engineering journal, (2010). nomenclature bc boltzman constant (j/k) kn knudsen number c specific heat (j/kg k) x axial direction cf area average friction coefficient (= ζiai+ ζoao /ai + ao /( ρv0 2 /2)) greek letter dp nanoparticle diameter(nm) φ volume fraction df molecular diameter of base fluid(nm) µ dynamic viscosity(ns/m 2 ) dh hydraulic diameter(m) ρ density(kg/m 3 ) fp friction coefficient λ mean free path(m) hi inner wall convective heat transfer coefficient (w/m 2 k) subscripts ho outer wall convective heat transfer coefficient (w/m 2 k) app appearance k thermal conductivity (w/m k) eff effective lbf mean free path of base fluid (m) f base fluid ni inner wall nusselt number i inlet no outer wall nusselt number m mixture p pressure (pa) mr mixture in radial direction pr prandtl number mx mixture in axial direction qw uniform heat flux (w/m 2 ) o outlet r radius(m) p particle re reynolds number s solid t temperature (k) w wall v velocity (m/s) wi inner wall nu nusselt number wo outer wall microsoft word vol 6-2p2v2-press.doc iium engineering journal, vol. 6, no. 2, 2005 s. parasuraman et al. 13 behaviour based mobile robot navigation technique using ai system: experimental investigation on active media pioneer robot s. parasuraman1, v. ganapathy 2, bijan shirinzadeh3 1, 2monash university malaysia, bandar sunway, malaysia 3monash university, clayton, victoria, australia, s.parasuraman@eng.monash.edu.my abstract: a key issue in the research of an autonomous robot is the design and development of the navigation technique that enables the robot to navigate in a real world environment. in this research, the issues investigated and methodologies established include (a) designing of the individual behavior and behavior rule selection using alpha level fuzzy logic system (b) designing of the controller, which maps the sensors input to the motor output through model based fuzzy logic inference system and (c) formulation of the decision-making process by using alpha-level fuzzy logic system. the proposed method is applied to active media pioneer robot and the results are discussed and compared with most accepted methods. this approach provides a formal methodology for representing and implementing the human expert heuristic knowledge and perception-based action in mobile robot navigation. in this approach, the operational strategies of the human expert driver are transferred via fuzzy logic to the robot navigation in the form of a set of simple conditional statements composed of linguistic variables. keywards: mobile robot, behavior based control, fuzzy logic, alpha level fuzzy logic, obstacle avoidance behavior and goal seek behavior 1. introduction the real world environment during mobile robot navigation has the following problems: a) knowledge of the environment is partial, uncertain, imprecise and approximate, b) the environment is vast and dynamic and the obstacles can move, appear or disappear and c) due to the quality of the ground, sensors data received are not completely reliable. the issues (a) and (b) affect the behavior rule selection and (c) affects the sensors input space to match the complex environment into robot’s output. in the past, several works relating to robot navigation have been done which describe mathematical models and fuzzy logic systems for behavior selection, but the limitations are the insufficient knowledge based perception of the environment and absence of decision-making capability similar to human driver. a variety of behavior-based control schemes have been inspired by the success of brooks work [1]. arkin [2] has described the use of reactive behaviors called schemas. in this method, potential field is used to define the output of each schema. then all the outputs are combined by weighted summation. similar techniques for defining reactive control behaviors are used by gat [3], anderson and donath [4] and tianmio and bo [5]. the adaptation of the action selection problem given in [6] is constrained to a particular mathematical model. p. althauas et al., [7] have described a scheme for behavior coordination that is based on a non-linear dynamical system approach. coordinations among behaviors are modeled by iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 14 means of an additional competitive dynamics that controls the weights of behaviors. this method also encounters the problem of multiple behavior conflicts between the outputs of different concurrent behaviors. coordination mechanism suggested in [8] and [9] is called a temporal sequencing, in which the system is partitioned into discrete operating states and enumerates the perceptual trigger, which causes transitions between those states. examples of cooperative mechanisms are the potential-field method [10], vector summation used in [11], blending of fuzzy behaviors [12], the dynamic system approach [13] and voting mechanism [14]. the authors of [6] to [14] describe the mobile robot navigation techniques using mathematical models for behavior selection and they do not deal with the natural way of describing the behavior rules and behavior selection during behavior conflicts. behavior arbitration scheme introduced by saffiotti et al., [15] used fuzzy logic system, which allows one behavior at a time to be active. another technique [16] focuses on combining the input of each behavior using predetermined weighting factors. this leads to direct conflict in execution when multiple behaviors give contradictory commands. to deal with these limitations, another strategy called fusion methodology is employed in which each behavior is allowed to provide the final output based on the situational context, [15] and [17]. tunstel et al., [17] have used a similar method of [15], in that, adaptive hierarchies of multiple fuzzy behaviors are combined and the output is actuated based on the degree of applicability. in this approach, certain behaviors are allowed to influence the overall behaviors based on the current situation and goal. in order to perform realistic tasks of a mobile robot in a complex surrounding, it must select ‘the most appropriate’ or ‘the most relevant’ next action at a particular moment, when facing a particular problem. in this paper, behavior rule selection or decision-making procedure incorporating alphalevel fuzzy logic system is discussed and used for selecting an appropriate action during mobile robot navigation. in the proposed approach, the control model is also presented incorporating the alpha level fuzzy logic system. in the present approach, the operational strategies of the human expert driver are transferred via fuzzy logic to the robot navigation in the form of optimized behavior rules and resolved the conflicts similar to human way of decision making capabilities. the technique presented in this paper is validated by conducting simulation and real world experiments using active media pioneer robot. 2. theoretical work 2.1 behavior rules conflict and alpha-level thresholds when the context data of the environment are matched with the condition parts of the logic rules in a rule base of the robot navigation system, it may be possible that more than one rule is fired. the set of rules fired in this manner is termed as the conflicts set. then, a method of conflict resolution must be invoked to select the rule that would be fired. conflict resolution in the control of behavior-based robot is the control decision process, which should be taken as a result of the firing among several similar kinds of fuzzy behavior rules. in the present mobile robot system, control of a robot is shared between a set of perception based action units, called behaviors. these behaviors are obstacle avoidance, seek goal, wall follow, terrain etc. behavior rule selection in robot navigation is the way that an agent selects the most appropriate or the most relevant next action to take in a particular moment, when facing a particular problem. based on environment context data, each behavior produces an action to control the robot with respect to a particular objective such as avoid obstacle, goal seek etc. when sensory data matches several behavior rules (condition part of the rules), then more than one behavior rule is fired at a time. as a result of multiple rule firing, behavior rules iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 15 conflict each other. in order to resolve these conflicts, an alpha level fuzzy inference system is introduced and this establishes the minimum truth threshold for a particular behavior rule that needs to be fired at a time. as and example “if s1 is small and s2 is small then the output is alpha threshold value”. the truth of the fuzzy proposition ‘s1 is small’ is less than [0.3], this rule will not fire due to the set level of alpha limit. thus an alpha threshold is an important control in the execution of fuzzy rules. behaviors within the environment are well defined by a set of control parameters through fuzzy sets and fuzzy membership values. 2.2 structure of controller with alpha threshold level the overall structure of the pid controller interfaced with the fuzzy inference system (fis) with alpha threshold level is shown in fig. 1 and the block diagram shows that the mobile robot (each wheel drives a separate motor) is controlled by a pid controller and the controller is executed in an interrupt routine of the main processor. the motor controller is used in two control modes: speed and position modes. figure 1 schematically shows the location of alpha threshold level in the fuzzy control system. the alpha threshold stored in the system control block (xsysalfacut) is the primary threshold value in the fuzzy system and is initiated to zero when the fuzzy model is connected to the control system (mdlconnecttofms). this value is automatically used by the fuzzy conditional proposition (fzycondproposition) and fuzzy unconditional proposition (fzyuncondproposition) to decide whether or not the predicate is true. when fuzzy sets and fuzzy variables are initialised, their alpha thresholds are inherited from the current output value of system control block (xsysalfacut). the alpha cut stored with fuzzy set descriptor block (fdb) is used to control the truth membership array resulting from the fuzzy set operators. this value inherited from the threshold associated with the variable (vdbalfacut) is used to adjust the solution prior to defuzzification [18]. the alpha level fuzzy logic methodology is established mathematically, analysed and discussed in the reference [18]. fig 1. control model of a mobile robot with fuzzy inference system (fis). iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 16 3. experimental work 3.1 modeling the control parameters the robot behaviors tested by using the present method comprise of obstacle avoidance, seek goal and wandering behaviors. all these behaviors are developed for active media pioneer robot, which is shown in fig. 2. active media pioneer robot uses the front sonar arrays with eight transducers that provide object detection around obstacles (fig. 2(a)). the sonar positions in all arrays are fixed one on each side, and six facing outwards at 20-degree intervals as shown in fig. 2(a). these sensors report the distances between the robot and the closest obstacle in each of the eight sectors (0-7). each obstacle distance is represented by the three linguistic input fuzzy sets {small, medium, big} and two output fuzzy sets which are speed and turn angle. the input and output fuzzy sets are as shown in the fig. 3 (a) and (b). (a) (b) (c) fig. 2: active media pioneer robot (a) sensors position (b) sensors region (c) actual robot. input parameters, which provide the context data of the environments, are the front sensors (s3 and s4) data are shown in fig. 2(b). these data are converted into three fuzzy sets namely small, medium and big. the small fuzzy set is further sub-divided into alpha level fuzzy set as shown in fig. 3 (a). similarly the output data is converted into five number of fuzzy sets namely medium positive (mp), small positive (sp), zero (z), small negative (sn) and medium negative (mn). the output fuzzy sets are further sub-divided into alpha level sets as shown in fig. 3 (b). 0 1 2 3 4 5 0 0 .2 0 .4 0 .6 0 .8 1 x 1 d eg re e of m em be rs hi p a s 3 m e d iu m b igs m a l l a s 2a s 1 a s 4 -50 -4 0 -3 0 -20 -1 0 0 10 20 3 0 40 5 0 0 0 .2 0 .4 0 .6 0 .8 1 u d eg re e o f m em be rs h ip mn z ero mpspsn s to p a z1 alphau1 as n 1 as n 2 a s n3 a sn 4 a z 2 a z 3 a sp 1 a s p2 a s p3 a sp 4 fig. 3 (a). input fuzzy set with alpha intervals. (b). fuzzy output set with alpha intervals. behaviors rules are established using the alpha level intervals of input and output fuzzy sets based on the environment perceived by sensors s3 and s4. iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 17 3.2 behavior selection figure 4 shows the fis for behavior rule selection based on the alpha threshold level set in the input and output fuzzy sets. figure 5 shows an example of rule firing based on the proposed methodology. fig. 4:. fis for behavior selection. 0 1 2 3 4 5 0 1 2 3 4 5 -30 -20 -10 0 10 20 30 s1s2 tu r n a n g le fig. 5: rule firing during navigation. 3.3 avoidobstacle behavior this behavior is to allow the robot to avoid collision with obstacles while it maintains its navigation. it is a combination of three simple behaviors namely move, turn and stop. the decision of each behavior depends on the behavior rules, which are established based on proposed methodology. examples of some of the rules are shown below: 110. if (x2 is not as3) and (x3 is alpha3) and (x4 is alpha2) and (x5 is not alpha1) then (u is alpha_u1)(v is low) (0) 111. if (x2 is not as3) and (x3 is alpha1) and (x4 is alpha2) and (x5 is not alpha1) then (u is az1)(v is low) (0) 112. if (x2 is not as3) and (x3 is alpha1) and (x4 is alpha_3) and (x5 is not alpha1) then (u is az1)(v is low) (0) 113. if (x2 is not as3) and (x3 is alpha3) and (x4 is alpha1) and (x5 is not alpha1) then (u is alpha_u1)(v is low) (0) iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 18 114. if (x2 is not as3) and (x3 is alpha3) and (x4 is alpha2) and (x5 is not alpha1) then (u is alpha_u1)(v is low) (0) 115. if (x2 is not as3) and (x3 is alpha3) and (x4 is alpha_3) and (x5 is not alpha1) then (u is az1)(v is low) (0) 116. if (x2 is not as3) and (x3 is alpha2) and (x4 is alpha1) and (x5 is not alpha1) then (u is alpha_u1)(v is low) (0) 117. if (x2 is not as3) and (x3 is alpha2) and (x4 is alpha2) and (x5 is not alpha1) then (u is alpha_u1)(v is low) (0) 3.4 goal-attract a set of fuzzy logic navigation rules that drive the robot from a known initial position to a user-specified goal position are presented as shown below: if δ is goal far-left, then ω is large-neg if δ is goal medium-left, then ω is medium-neg if δ is goal-left, then ω is small-neg if δ is goal head-on, then ω is zero if δ is goal right, then ω is small-pos if δ is goal medium-right, then ω is medium-pos if δ is goal farright, then ω is large-pos where δ is the goal direction and ω is the turn angle of the robot. in these cases, the robot initially performs an in-place rotation towards the goal to nullify the heading error. once the robot is aligned with the goal direction, then it proceeds towards the goal position on a straight path. 3.5 control model control model e (u) is established and cited in the reference [18] and also shown below )]u(c,)u(min[)u(e  . 1(a) where )][()( )....,....,(max 21 nii xxxxrc eu   and )]'nx.... ' ix,...... ' 2x, ' 1x(ir[(maxe)u(   . 1(b) where )u(cand)u(  are the outputs.the parameters in the equation 1 (a) and 1(b) are as defined in the reference [18]. 4. results and discussion the control model e(u) is applied to the mobile robot, and simulation and real world experiments are conducted. based on the environmental context, the output is selected between )u(cand)u(  . the results are analysed and compared with the most accepted methods. 4.1 simulation simulation is conducted at two different situations, which are discussed in this section and the simulation results are shown in figs. 6 to 13. the simulation environment is built with maps, which represent obstacles, home position of robot and the robot with sonar sensors. robot and sensors are designed based on the real parameters of active media iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 19 pioneer robot. the maps, which are designed for navigation are unstructured and contain various objects with unsymmetrical shapes and sizes and placed in different locations. there are 14 sensors and each sensor array delivers the echo corresponding to the maximum distance of 5000 mm, if there is no object in front of the sensor. fig. 6: robot navigate towards goal while avoiding obstacle in the situation of environmental conflicts. the experimental results shown in fig.s 6(a-d) are the simulation results of active media pioneer robot. the results show the robot path from the initial position to the target position with various obstacles. the robot behavior rules in these positions in the present situation are conflicting because of multiple rules activation at the same time. in fig. 6(a), the robot is facing two obstacles, which are located at a distance of 0.6 meter and 1.0 meter respectively from the robot. these obstacles are located in the vicinity of the one fuzzy set, which is called small. in these situations, behavior rules conflict arises because more than one rules are active. this is due to more than one obstacle present in the small fuzzy set. in this situation, the alpha level fuzzy logic rules are active for navigation with minimum proximity to the obstacles. figure 6(b) shows the movement of the robot that is based on two different value of the alpha level. in all situations, the robot decides its path based on the min value of the output membership functions )u(cor)u(  . based on these control outputs, robot navigates in an optimum path and reaching the goal position, which are shown in fig. 6(c) and fig. 6(d). the simulation results are evaluated as follows. figure 7 shows the plot of sensors data s3 and s4 of the robot for a period of 300 sec. plot illustrated in fig. 8 is the turn angle plotted against distance traveled over a period of time 300 sec. in all these situations multiple obstacles are presented close to the robot. in these situations the simulation clearly indicates that the robot is turned and navigated without any behavior rule conflicts. from the graph it is observed that the robot navigates with a minimum deviation from each of the obstacle according to the alpha intervals. this shows that the proposed approach provides better conflict resolution when compared to fuzzy behavior coordination approach used in the literature. the experimental results that are shown in fig. 9 (a-d) are for the other situations, where more obstacles are placed. the results are analysed and plotted as shown in fig. 1013. iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 20 0 500 1000 1500 2000 2500 3000 3500 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 t im e x 1 0sec se ns or s re ad in gs 0 5 0 0 1 0 00 1 5 00 2 0 00 2 5 00 3 0 00 3 5 00 s3 s4 -25 -20 -15 -10 -5 0 5 10 15 20 time x10 sec t ur n an gl e 0 2 4 6 8 10 di st nc e ta rv al le d turn angle distance fig 7: sensors readings over a period of time 300 sec fig. 8: turn angle against travel distance over a period of time 300 sec. fig 9: robot navigates towards goal while avoiding obstacles in the situation of multiple behavior conflicts. 0 500 1000 1500 2000 2500 3000 3500 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 time x10 sec se ns or s re ad in g -25 -20 -15 -10 -5 0 5 10 15 20 25 tu rn a ng le s4 turn angle 0 5 0 0 10 0 0 15 0 0 20 0 0 25 0 0 30 0 0 35 0 0 time x 10 sec 2 5 2 0 15 10 5 0 5 10 15 2 0 2 5 s 3 turn ang le fig 10: sensors readings over a period of time 300 sec. fig. 11: turn angle against travel distance over a period of time 300 sec. the experiments conducted from the present study, it is concluded that, based on the multiple obstacles present close to the robot, the output turn angles are automatically computed based on the alpha intervals and robot navigates with minimum deviation from obstacles. iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 21 0 10 20 30 40 50 60 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 time x10 [sec] d is ta nc e tr av el le d -25 -20 -15 -10 -5 0 5 10 15 20 25 t ur n an gl e distance turn angle -500 0 500 1000 1500 2000 2500 3000 3500 1 6 11 16 21 26 time x 10 [ sec] -30 -20 -10 0 10 20 30 40 50 60 s3 s4 dist ance turn angle fig 12: turn angle and distance traveled. fig 13: sensors data verses turn angle and distance. 4.2 real world experiments the behavior rules obtained from the proposed methodology are tested in a real world environment using active media pioneer robot. figure 14 shows various positions of the robot while encountering obstacles during navigation. plot illustrated in fig. 15 is the robot travel time plotted against sensors reading and turn angle over a time period of 300 sec. in this plot, it is observed that the robot’s positions at 9th and 22nd sec, sensors s3 and s4 encounter obstacles each at a distance of 1000 mm from the robot. the distances from both sensors are inferenced as a small fuzzy set. in this situation alpha level fuzzy threshold is active and the system decides the behavior rule selection. this is illustrated in the graph shown in fig. 16. this figure illustrates the relationship between the obstacle positions from robot obtained by sensors s2 to s5 and the turn angle for a continuous run of 300 sec. from the real world experiments conducted using the present methodology, it is observed that the sensors’ (s2 to s5) data have been used and these data decide the robot turn angle based on fuzzy alpha level intervals, when the robot faces an obstacle. fig. 14: (a), (b), (c) and (d): active media pioneer robot encountering walls and obstacles during navigation. iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 22 in the proposed methodology, input and output fuzzy sets are set to minimum ranges using alpha level fuzzy system so that the robots’ turn angle deviations are minimum with respect to the obstacles positions in the environment. in the most accepted methods in the past, these values are set with larger intervals and as a result the angle of deviations from obstacles are quite large. influence of s3 and s4 0 500 1000 1500 2000 2500 3000 3500 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 time x10 [sec] se ns or s re ad in g [m m ] -30 -20 -10 0 10 20 30 a ng le [d eg ] s3 s4 angle fig.15: plot of robot travelling time against output responses of the front sensors (s3s4) and turn angle of robot 0 500 1000 1500 2000 2500 3000 3500 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 time in s ec se ns or s re ad in g in m m -25 -20 -15 -10 -5 0 5 10 15 20 25 r ob ot p os iti on in d eg s2 s3 s4 s5 posit ion fig. 16: plot of robot travelling time against output responses of sensors (s2-s5) and turn angle of robot. 5. . comparisons arkin’s [2] motor schemas method is model based and the data perceptions are not dealt with the natural way of solving complex environment. the proposed methodology deals with a natural way of resolving behavior conflicts through alpha level fuzzy logic system. potential field methods [10] are constructed with a map-like internal representation of the world, while the proposed methodology of alpha level fuzzy logic system does not need such a map. iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 23 the robot navigation based on pid controller and fuzzy logic system [22] is compared with the proposed alpha fuzzy logic approach and the results are analysed using the plot shown in fig. 17. in previous work given in [22], the pid and fuzzy logic approaches used larger intervals of inputs and as a result the robot deviated much from obstacles through a wider angle during navigation. this affects the behavior selection, when more obstacles are present closely in the environment. in the proposed alpha level fuzzy logic, inputs and output levels are set with alpha level threshold limits and as a result the robot navigates with close proximity to obstacles with minimum deviation especially when the obstacles are present closely. in fig. 17, the proposed alpha level fuzzy system shows that the robot deviates with minimum angle from obstacles compared to the other two approaches used in the ref [22]. -60 -40 -20 0 20 40 60 80 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 time in sec (1000 ms) r ob ot p os iti on in d eg fuzzy pid alpha fuzzy fig 17. comparison of results using pid, fuzzy and alpha fuzzy control system. the robot navigation based on kalman filtering [23] and [24] requires mathematical models for the system estimation and measuring instruments and the filter called data processing algorithm is a black box containing an electrical network, which processes the inputs and produce outputs. in the proposed method, the most useful measurement data are integrated and mapped onto the system model itself. the model used in the proposed method for the decision making is an integral part of the control process. in the proposed method, the fuzzy algorithm makes a decision by considering several different types of situations at the same time resulting in a more human like decision. genetic algorithm [25] performs randomized global search of an environment whereas the proposed alpha level fuzzy system uses continuous search. the present methodology is based on classical reasoning and transparent modeling approaches that are invariably based on boolean logic, which is simple to implement for optimization of robot bath navigation. 6. conclusion a new deterministic approach to resolve the behavior conflicts in the complex situation during mobile robot navigation is developed and validated with real world experiments. the behavior rules containing the alpha intervals of input and output spaces are adapted iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 24 with-ease and the robot is found to navigate with minimum deviation when encountered with obstacles. the experimental results clearly indicate the mapping of inputs to outputs with optimum path in every control cycle of robot navigation. this approach involves the natural way of dealing with the environments using simple linguistic logic rules without using any mathematical model. the knowledge base of each behavior rule is easy to comprehend, because it captures the behavior rules in a linguistic form by simple intuitive alpha threshold interval based rule statements. references [1] r.a. brooks, "a robust layered control system for a mobile robot," ieee journal of robotics and automation, vol. ra-2, no.1, pp 14-23. year? [2] r.c. arkin, "motor schema based navigation for a mobile robot: an approach to programming by behavior," proceedings of the ieee intl. conference on robotics and automation, 1987, pg 264-271. [3] e.gat, "on the role of stored internal state in the control of autonomous mobile robots," ai magazine, pp. 64-73, spring 1993. [4] l.t. anderson and max donath, "animal behavior as a paradigm for developing robot autonomy," robotics and autonomous systems, vol. 6, 1990, pages 145-168. [5] w.t and zhang bo, "time-varying (sic) potential field based 'perception-action' behaviors of mobile robot," in proceedings of the 1992 ieee international conference on robotics and automation, may, 1992, nice, france [6] p.maes, “how to do the right things”. ne 43-836, ai-laboratory, mit, ma 02139, usa, 1989. [7] p. althaus, h. christiansen, and f.hoffmann. using the dynamical system approach to navigate in realistic real-world environments. in proceedings of the ieee/rsj international conference on intelligent robotics and systems, page 1023-1029, 2001. [8] d.c mackenzie, r.c arkin, and j.m. cameron, “specification and execution of multiagent mission,” college of computing, georgia institute of technology, atlanta, georgia, usa. 1995. [9] r.c arkin, “integrating behavioral, perceptual, and world knowledge in reactive navigation,” robotics and autonomous systems 6, pp. 105-122, june 1990. [10] o.khatip, real–time obstacle avoidance for manipulators and mobile robots”, the international journals of robotics research 5(1), pp. 90-98,1986. [11] r.c.arkin, “towards the unification of navigational planning and reactive control,” aaai press, 1995. [12] a.saffotti, k.konolige, and e.h ruspini,” a multi-valued logic approach to integrating planning and control,” artificial intelligence, march 1995. [13] e.w. large, h.i. christensen, and r.bajcsy, “scaling the dynamic approach to path planning and control: competition among behavioral constrain,” international journal of robotics research, 1997. [14] j.k rosenblatt, “damn: a distribute architecture for mobile navigation,” in aaai press, march 1995. [15] a. saffiotti, “fuzzy logic in autonomous robotics: behavior coordination,” in proc. 6th int. conf. fuzzy systems, barcelona, spain 1997, vol.1, pp. 573-578. iium engineering journal, vol. 6, no. 2, 2005 s.parasuraman et al. 25 [16] e. gat, r. desai, r. ivlev, j. loch, and d.p. miller, “behavior control exploration of planetary surfaces,” ieee. trans. robot. automat., vol. 10, aug 1994. [17] e. tunnstel, t.lippincott, and m.jamshidi, “behavior hierarchy for autonomous mobile robots: fuzzy behavior modulation and evolution,” in. j. intell. automat. soft compute., vol 3, no. 1, pp 37-49, 1997. [18] s.parasuraman, v.ganapathy, bijan shirinzadeh, “behavior based mobile robot navigation by ai techniques: behavior selection and resolving behavior conflicts using alpha level fuzzy inference system” proceeding of the icgst international conference on automation, robotics and autonomous system, aras2005, egypt. p1130533120. [19] liu xin; vadakkepat, p.; tong heng lee; xiao peng; pang ki kim. “comparison of khepera robot navigation by evolutionary neural networks and pain-based algorithm evolutionary computation”, 2002. cec '02. proceedings of the 2002 congress on volume 2, 12-17 may 2002 page(s): 1994 – 1999. [20] petru rusu, thom e.whalen, aurel cornell and hans j.w spoelder "behavior based neuro-fuzzy controller for mobile robot navigation ieee transaction on instrumentation and measurement", vol. 52, no. 4, august 2003. [21] botelho, s.s.c. do valle simoes, e.; uebel, l.f.; barone, d. “high speed neural control for robot navigation” systems, man, and cybernetics, 1996. ieee international conference on volume 3, 14-17 oct. 1996 page(s):1956 1959 vol.3. [22] jong-soo kim, seong-joo kim and hong-tae jeon “intelligent trace algorithm of mobile robot using fuzzy logic” college of engineering chung ang university, seoul, 156-756, korea. [23] simon d: kalman filtering, embedded.com, viewed on dec. 10, 2001. http://www.embedded.com/showarticle.jhtml?article id=9900168 (2001). [24] welch, g., bishop, g.: an introduction to the kalman filter, acm siggraph 2001, course 8, available at http://www.cs.unc.edu/_welch/kalman (2001). [25] john h. holland, adaptation in natural and artificial systems, mit press, cambridge, ma, 1992 . application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 sharma et al. 47 study of different treatment methods on chicken feather biomass swati sharma 1* , arun gupta 2 , syed m. saufi 1 , chua yeo gek kee 1 pradeep kumar podder 1 , malini subramaniam 1 and jayshree thuraisingam 1 1 faculty of chemical and natural resources engineering, 2 centre for biocomposite and innovative materials, universiti malaysia pahang, lebuhraya tun razak, 26300 gambang, pahang, malaysia. *corresponding author: sspandit.89@gmail.com (received: 18 th feb. 2017; accepted: 26 th sept. 2017; published on-line: 1 st dec. 2017) abstract: chicken feathers (cfs) make up to 10 % of total chicken dry mass and they have many potential industrial applications. cfs contain protein fibers called keratin, which is an insoluble protein. primary sanitization phases are complex because of the presence of many blood-borne microbes, pathogens, and parasites in raw biomass. the extraction process of keratins from the unprocessed feathers is also a challenging task. prior to the extraction, the cleaning/sanitization of feathers is a very necessary step. thus, the present work was conducted to optimize an efficient surfactant for the cleaning process of the cfs using ionic and non-ionic surfactants. the experiment was conducted by the washing of feathers with double distilled water (ddh2o), detergents, ether, and lastly with boiling water. the washed feathers were treated with surfactants (sodium dodecyl sulfate (sds), cetrimonium bromide (ctab) and polyethylene glycol (peg)) and the effect of each surfactant was analyzed by a microbiological test that indicates the extent of the presence of different bacteria on the treated feathers. sem, edx, ftir were used to study the morphology and composition of untreated and treated cfs. sem showed no detectable fiber damage after treatment. cetrimonium bromide (ctab) (t3) was one of the best surfactants recommended for the treatment of cfs among all the surfactants used. the present study described the best treatment method for the cfs. abstrak: bulu ayam (cf) terdiri daripada 10 % daripada total jisim bulu ayam kering dan terdapat pelbagai potensi aplikasi dalam industri. cf mengandungi gentian protein dinamakan sebagai keratin, iaitu merupakan protein tidak larut. sanitasi primer adalah kompleks kerana kehadiran banyak mikrob bawaan dalam darah, patogen dan parasit dalam biojisim mentah. proses pengekstrakan keratin daripada bulu yang masih belum diproses juga adalah tugas yang mencabar. proses ekstrak pengeringan/sanitasi bulu juga adalah langkah yang sangat diperlukan. oleh itu, kajian ini dijalankan untuk mengoptimumkan kadar surfaktan yang berkesan untuk proses pembersihan pada cf dengan menggunakan surfaktan ionik dan bukan ionik. eksperimen ini dijalankan dengan membasuh bulu dengan air suling double (ddh2o), bahan pencuci, eter dan akhir sekali dengan air mendidih. bulu yang telah dibasuh dirawat dengan surfaktan (natrium dodecyl sulfate (sds), cetrimonium bromide (ctab) and polyethylene glycol (peg)) dan kesan terhadap setiap surfaktan dianalisa dengan ujian mikrobiologi. kehadiran bakteria pada bulu yang telah dirawat telah didedahkan melalui ujian mikrobiologi ini. sem, edx, ftir telah digunakan untuk mengkaji morfologi dan komposisi cf yang tidak dirawat dan dirawat. sem menunjukkan tiada kerosakan serat dikesan selepas rawatan. cetrimonium bromide (ctab) (t3) adalah salah satu surfaktan terbaik yang iium engineering journal, vol. 18, no. 2, 2017 sharma et al. 48 disyorkan untuk rawatan cf berbanding surfaktan lain. kajian ini menjelaskan kaedah rawatan terbaik bagi cf. keywords: feathers; surfactants; ftir; sanitization 1. introduction feathers are one of the byproducts of poultry farming. chicken feathers (cfs) are the waste biomass of the poultry industry with more than 4×10 6 tons generated per year worldwide [1]. generally, cfs are turned into low value feedstock [2] or sent into landfills [3]. when fresh feathers are removed from the chicken, they can contain waxy, fatty substances and some blood-borne pathogens that can cause various human health hazards. it is very important to sanitize/cleanse the cfs before their use in the laboratory. cfs are comprised of protein fibers named keratin; which is also one of the main components of wool. cfs consist of 91% keratin macromolecules with an average molecular weight of 10-20 kda [4, 5]. the keratin is an insoluble protein commonly found in avian and mammalian species, in their beaks, claws, hooves, horns, hairs, nails, wool, and feathers [6-8]. the keratin consists of an α-helix and β-sheet conformation [9]. cfs have potential applications in biopolymers, regeneration, fabrication, bioplastics and tissue engineering [10-13]. they are abundant, biodegradable, and have guaranteed supply, which makes them an interesting choice for research. besides this, the adequate cleaning and sanitizing of cfs before their use as laboratory material is a crucial task. feathers can be a habitat for some microorganisms such as escherichia spp., salmonella, and pseudomonas spp. as the freshly plucked feathers are prone to the bloodborne pathogens, their sanitization/cleaning can be performed with different surfactants and organic solvents, as reported previously [14-16]. it is important to study the effect of the treatments on the morphology and composition of keratin proteins. feather-borne parasites and microorganisms can be neutralized by physical and chemical means [17]. surfactants are comprised of hydrophobic and hydrophilic chemical groups in their chemical structures and they are efficient to remove the insoluble, waxy, and fatty dirt particles [18]. surfactants have been proven to exhibit decontamination ability but their antibacterial effects are largely undocumented with few sources [19]. two types of hydrocarbon contaminants generally bind to feathers; one having a low boiling point and the other has a higher boiling point. the latter is difficult to remove due to its strong binding. high concentrations of the surfactant are generally used to remove large amount of contaminants [16]. these also have wide applications in removing oily particles in soft water, in contrast to hard water that adversely affects the cleaning performance. the aim of this study is to screen for the best surfactant for the sanitization/decontamination of the cfs and effects of treatments of surfactants on the morphology and chemistry of feathers were explored. the method includes the washing of the cfs with detergent and ether after receiving them from the slaughterhouse. different surfactant treatments were given to the cfs. then, microbial testing, visual observation, scanning electron microscope energy dispersive x-ray spectroscopy (sem-edx), fourier transform infrared (ft-ir) spectroscopy, thermo gravimetric analysis (tga) were used to characterize the treated and untreated cfs. 2. materials fresh chicken feathers from slaughtered adult chickens with a length of 2-25 cm were supplied by a chicken processing plant at jaya gading, kuantan, malaysia. sodium iium engineering journal, vol. 18, no. 2, 2017 sharma et al. 49 dodecyl sulfate (sds) and cetrimonium bromide (ctab) were purchased from fisher scientific uk ltd, bishop, united kingdom. polyethylene glycol (peg) was acquired from merck schuchardt ohg, germany. all other chemicals used were provided by sigma-aldrich (m) sdn. bhd. kuala lumpur, malaysia. milli-q water was used to make solutions and for washing. all chemicals were used without any further processing after receipt. 3. methods different treatment methods were used to decontaminate the cfs. purchased feathers were first rinsed with water at 60 o c. after washing, these were incubated in detergent for 2 h and again rinsed at 60 o c. after that, the feathers were degreased using petroleum ether for 12 h, and then washed with distilled water and conditioned at 20 o c, 65 % rh for 24 h. after their first cleaning, the feathers were further treated with different surfactants. each treatment step was run for 3 h. cleaned defatted cfs were then chopped into small pieces and dried in sunlight for 48 h and stored at 4 o c for further usage. after purification, microbial testing was done in triplicate and results were compared. the methods of purification were investigated with three classes of the surfactant: sds (an anionic surfactant), peg (non-ionic surfactant), and ctab (cationic surfactant). aqueous solutions (1 g/l) of sds, peg, and ctab were formed separately in beakers and 10 g of feathers having a ratio of 100:1 was added to each and named as t2, t3 and t4 respectively, whereas the name for the unwashed feathers was t0 and, the sample after first washing was named t1. the combination was mixed using a magnetic stirrer at 40 o c for 3 h under vigorous stirring at 300 rpm. 3.1 microbiological testing the total aerobic microbial count for different treatment preparations was studied via the standard plate count method (spc). the spc was performed by the detection of e coli, staphylococcus aureus, salmonella spp., pseudomonas aeruginosa in the central laboratory at universiti malaysia pahang, gambang, malaysia. the samples were inoculated on the selective media for different microbes. the microbial number was calculated as colony forming units per gram (cfu/g). 4. characterization 4.1 morphological studies the effect of the surfactants on the cfs morphology was analyzed using digital photography, which showed a great advantage from treatment. the cfs were further investigated by sem analysis. edx in the sem was used to do the elemental analysis of treated cfs. it was performed using a hitachi tm3030plus. 4.2 fourier transform infrared spectroscopy (ft-ir) chemical characterization of treated and untreated cfs was done using ft-ir spectroscopy to detect the presence of amide groups or protein [20]. nicolet is5 from thermo scientific ft-ir was used for chemical characterization of treated and untreated cfs in between the 4000 cm -1 and 700 cm -1 wave number range. 4.3 thermo gravimetric analysis (tga) thermo gravimetric measurements of untreated and treated cfs were performed using tga analyzer q 500 under nitrogen atmosphere, in a temperature range between 10 iium engineering journal, vol. 18, no. 2, 2017 sharma et al. 50 o c and 900 o c at a ramping time of 10 o c/min. the samples were vacuum dried at 40 o c. samples with a mass of 3 mg were put in an aluminum crucible and the data obtained was analyzed. 5. results and discussion 5.1 microbiological testing the unwashed feathers (t0) have highest total aerobic microbial count (8.0×10 5 cfu/g) followed by washed (t1) with an aerobic microbial count of 1.8×10 5 whereas ctab treatment (t3) displayed lowest count (3.4×10 3 cfu/g) among other treatments. this is supported by previous studies which showed that the use of ctab as a surfactant was effective to reduce the microbial count [21]. as per the guidelines of australian food and drug administration for the spc microbiological examination (december 2001), if the cfu number is <10 4 , then the quality is satisfactory and if <10 5 , then it is marginal and lastly if ≥10 5 , then it is unsatisfactory and not acceptable. surfactants act as a decontaminants because they have two main functions such as surface activity and an intrinsic disinfecting/bactericidal function [19]. the strong detergent property of the surfactant is inversely proportional to the value of the surface tension and critical micelle concentration (cmc) [22], which means low value of surface tension and cmc will give the strong detergent properties. the values for surface tension and cmc is as follows ctab (49.6 mn/m and 0.99 × 10 -3 mol/l) < sds (50.2 mn/m and 0.44 × 10 -3 mol/l) < peg (75.9 mn/m and 0.78 × 10 -3 mol/l) [22, 23]. the reduction in the total microbial count among all surfactants was in the same trend as was observed in case of surface tension and cmc values. it was concluded that detergent mostly help in the removal of bacteria. table 1 shows the values of the total microbial count with each surfactant. the lower count indicates the strong bactericidal competence. table 1: total microbial count of treated and untreated chicken feathers sample no. surfactants /samples total microbial count [cfu/g] 1 unwashed (t0) 8.0×10 5 2 washed (t1) 1.8×10 5 3 sds (t2) 1.1×10 3 4 ctab (t3) 3.4×10 2 5 peg (t4) 1.6×10 3 there was no detection of e. coli after all treatments, which showed that all surfactants were efficient to abolish e. coli which is in agreement with the research stated by pourjavaheri et al. regarding the presence of e. coli. there was a visible growth of pseudomonas spp. and staphylococcus aureus, thus they were detected after t0, t1, t2, t3 and t4. the treatment with surfactants were efficient in the removal of bacteria like s. aureus and pseudomonas spp. as previously reported [21]. there was a detection of salmonella spp. in t0, t1 and t2 but it was not found in t3 and t4. among the three surfactants, two showed efficiency to destroy a gram of negative bacteria; which was unexpected as they are less efficient to destroy the salmonella spp. [24]. sds was unable to do the same for salmonella spp. it may be due to insufficient concentration of the surfactant, although it was higher than suggested in the previous studies [25]. iium engineering journal, vol. 18, no. 2, 2017 sharma et al. 51 consequently, the best purification surfactant, t3, was selected for further study in this project. 5.2 morphological analysis the outcome of each treatment method on the chicken feather morphology was studied via the naked eye and using a camera. the results showed the presence of all major components of the feather and can be differentiated in treated feathers. further, morphological analysis was done using scanning electron microscopy and energy dispersive x-ray spectroscopy (sem-edx) as shown in fig. 1. fig. 1: sem-edx derived from the chicken feathers (a) unwashed (t0); (b) washed (t1); (c) treated via sds (t2) (d) treated via ctab (t3) (e) treated via peg (t4). chicken feathers treated via t2, t3, t4 showed over erection and lack of woolly part as compared to t0 and t1 treatments along the feather structure. the major elements found in all the treatments after elimination of c were: o, na, al, s, ca and cu. the weight iium engineering journal, vol. 18, no. 2, 2017 sharma et al. 52 proportion (% w/w) associated with s were 37.10, 36.24, 27.97, 37.18, 28.59 and na 0.09, 0.58, 0.36, 0.29, 0.00 in the feathers with treatments t1, t2, t3, t4 respectively. there was no detectable fiber damage in the treated feathers. the results showed that there were minimum changes in the feather structure in treatment t3 followed by t4 when compared to t0 and t1. thus, in this study, it was shown that t3 was the best surfactant among others and there was no deposition of surfactant in treatment t3 but some were seen on the t2 and t4 feathers. the deposition of surfactants on feathers can cause mild skin irritation on human skin upon contact [18]. 5.3 fourier transform infrared spectroscopy (ft-ir) in order to understand the chemical structure of treated and untreated chicken feathers, ft-ir spectra was used, (fig. 2). after comparison of five samples, it was found that the characteristic peaks are similar with each other and are comparable with other studies [26]. on the other hand, the surfactants have little effect on the chemical structure of protein and all the treatments showed transmission bands to the peptide bonds (-conh) and are known as amide a, amide i, amide ii, amide iii [10, 27, 28]. the transmission band region between 3500 cm -1 to 3200 cm -1 is attributed to stretching vibration of -o-h and -n-h (amide a) [29]. the transmission bands appeared in the range between 3000 cm -1 and 2800 cm -1 were related to symmetrical ch3 stretching vibration [30, 31]. the strong transmission band is attributed to c=o stretching (amide i), which occurs in the range of 1700 cm -1 to1600 cm -1 [20, 27]. the transmission band (amide ii) in the range of 1580 cm -1 to 1480 cm -1 is for n-h bending and c-h stretching [31]. the weak band between 1300 cm -1 and 1220 cm -1 is associated with amide iii, which is derived from c-n stretching and n-h bending [32, 33, 34] and with some contribution from c=o bending and c-c stretching vibration [28, 35, 36]. the transmission band between 750 cm -1 and 600 cm -1 is related to n-h out-of-plane bending [29, 37]. fig. 2: ft-ir spectra of treated and untreated chicken feathers. the transmission vibration around 1700 cm -1 is attributed to c=o group of fatty acid ester found in animal skins [38]. the c-o stretching vibration associated with ester linkage, attributed at 1200 cm -1 to 1270 cm -1 , was not detected. no transmission band at 3500 2800 2100 1400 700 60 80 100 t ra n s m it ta n c e ( % ) wavelength (cm -1 ) t0 t1 t2 t3 t4 -conh bond amide i amide ii amide iii iium engineering journal, vol. 18, no. 2, 2017 sharma et al. 53 1700 cm -1 was detected after the treatments, which confirms the action of surfactants in removing fatty materials from chicken feathers (fig. 2). overall, it was shown that there are no effects on the chemical composition of feathers after treatment with surfactants. 5.4 thermo gravimetric analysis (tga) thermal stability of the untreated and treated feather material was conducted by tga. as shown in fig. 3, all the untreated and treated samples have the same profiles present in a similar pattern with two stages of decomposition, which showed that the thermal stability of all samples were at par. some percentage of weight loss occurred before 100 °c, which is due to the evaporation of water, including free water and bounded water. all samples were stable until 200°c. after that point, a steep weight loss occurred until 400 °c. this loss was allied with the helix denaturation, skeletal degradation and destruction of peptide bridge chain linkage [39-41]. with this, there was decomposition of some volatile compounds such as hcn, h2s, co2 and h2o [42]. this indicated that the treatment of feathers had no effect on their thermal stability. after pyrolysis a total weight loss of ~70 % was observed. fig. 3: tga of untreated and treated chicken feathers. 6. conclusion chicken feathers with treated ctab (t3) exhibited the lowest bacterial counts as compared to other treatment preparations. this treatment removed salmonella also. treated feathers had the same morphology in optical evaluation. there was no detectable fiber damage in the treated feathers and the least changes in the feather structure in treatment t3. there was the elimination of fatty esters from the feathers confirmed with ft-ir. therefore, t3 was selected as the best surfactant, among other tested surfactants, for the decontamination and preparation of chicken feathers for other applications. acknowledgement the authors greatly acknowledge the financial support from universiti malaysia pahang for providing the doctoral scholarship scheme. authors also want to say thanks to the central lab and carif universiti malaysia pahang for their support of his part of the work. 0 200 400 600 800 1000 0 20 40 60 80 100 w e ig h t (% ) temperature (°c) t0 t1 t2 t3 t4 iium engineering journal, vol. 18, no. 2, 2017 sharma et al. 54 references [1] amieva ej-c, velasco-santos c, martínez-hernández a, rivera-armenta j, mendozamartínez a, castaño v. (2015) composites from chicken feathers quill and recycled polypropylene. journal of composite materials, 49(3): 275-283. [2] bertsch a, coello n. (2005) a biotechnological process for treatment and recycling poultry feathers as a feed ingredient. bioresource technology, 96(15):1703-1708. [3] shi b, shannon tg, pelky e. (2010) novel use of waste keratin and cotton linter fibers for prototype tissue papers and their evaluation. bioresources, 5(3):1425-1435. [4] rad zp, tavanai h, moradi a. (2012) production of feather keratin nanopowder through electrospraying. journal of aerosol science, 51:49-56. [5] wang y-x, cao x-j. (2012) extracting keratin from chicken feathers by using a hydrophobic ionic liquid. process biochemistry, 47(5):896-899. [6] martinez-hernandez al, velasco-santos c, de icaza m, castano vm. (2005) microstructural characterisation of keratin fibres from chicken feathers. international journal of environment and pollution, 23(2):162-178 [7] wallenberger ft, weston no. (2004) natural fibers, plastics and composites. materials source book kluwer academic publishers, norwell. [8] coward-kelly g, agbogbo fk, holtzapple mt. (2006) lime treatment of keratinous materials for the generation of highly digestible animal feed: 1. chicken feathers bioresourse technology, 97:1337-1343. [9] sharma s, gupta a. (2016) sustainable management of keratin waste biomass: applications and future perspectives. brazilian archives of biology and technology, 59. [10] xu h, cai s, xu l, yang y. (2014) water-stable three-dimensional ultrafine fibrous scaffolds from keratin for cartilage tissue engineering. langmuir, 30(28):8461-8470. [11] li j, li y, li l, mak af, ko f, qin l. (2009) fabrication and degradation of poly (l-lactic acid) scaffolds with wool keratin. composites part b: engineering, 40(7):664-667. [12] khosa ma, ullah a (2014) in-situ modification, regeneration, and application of keratin biopolymer for arsenic removal. journal of hazardous materials 278:360-371. [13] kar p, misra m (2004) use of keratin fiber for separation of heavy metals from water. journal of chemical technology and biotechnology 79(11):1313-1319. [14] griffith ba. (2002) feather processing method and product pct patent, wo/0238853 a2. [15] gassner g, schmidt w, line mj, thoms c, waters rm. (1998) fiber and fiber products produced from feathers. us patent, 5,705,030. [16] bryndza he, lumlberg b. (1995) methodolgy for determining surfactant efficacy in removal of petrochemicals from feathers. [17] rai sk, konwarh r, mukherjee ak. (2009) purification, characterization and biotechnological application of an alkaline β-keratinase produced by bacillus subtilis rm-01 in solid-state fermentation using chicken-feather as substrate. biochemical engineering journal, 45(3):218-225. [18] effendy i, maibach hi. (1995) surfactants and experimental irritant contact dermatitis. contact dermatitis, 33(4):217-225. [19] davis j. (1960) methods for the evaluation of the antibacterial activity of surface active compounds: technical aspects of the problem. journal of applied bacteriology, 23(2):318344. [20] mohanty ak, misra m, drzal lt (2005) natural fibers, biopolymers, and biocomposites. crc press, [21] pourjavaheri f, mohaddes f, bramwell p, sherkat f, shanks ra. (2015) purification of avian biological material to refined keratin fibres. rsc advances, 5(86):69899-69906. [22] mandavi r, sar s, rathore n. (2008) critical micelle concentration of surfactant, mixed– surfactant and polymer by different method at room temperature and its importance. orient journal of chemistry, 24:559-564. [23] xu q, wang l, xing f. (2011) synthesis and properties of dissymmetric gemini surfactants. journal of surfactants and detergents, 14(1):85-90. iium engineering journal, vol. 18, no. 2, 2017 sharma et al. 55 [24] pérez l, garcia mt, ribosa i, vinardell mp, manresa a, infante mr (2002) biological properties of arginine‐ based gemini cationic surfactants. environmental toxicology and chemistry, 21(6):1279-1285. [25] naidu a. (2000) natural food antimicrobial systems. crc press. [26] ma b, qiao x, hou x, yang y. (2016) pure keratin membrane and fibers from chicken feather. international journal of biological macromolecules, 89:614-621. [27] aluigi a, zoccola m, vineis c, tonin c, ferrero f, canetti m (2007) study on the structure and properties of wool keratin regenerated from formic acid. international journal of biological macromolecules, 41(3):266-273. [28] idris a, vijayaraghavan r, rana ua, fredericks d, patti a, macfarlane d. (2013) dissolution of feather keratin in ionic liquids. green chemistry, 15(2):525-534. [29] pavia dl, lampman gm, kriz gs, vyvyan ja. (2008) introduction to spectroscopy. cengage learning. [30] edwards h, hunt d, sibley m. (1998) ft-raman spectroscopic study of keratotic materials: horn, hoof and tortoiseshell. spectrochimica acta part a: molecular and biomolecular spectroscopy, 54(5):745-757. [31] eslahi n, dadashian f, nejad nh. (2013) an investigation on keratin extraction from wool and feather waste by enzymatic hydrolysis. preparative biochemistry and biotechnology, 43(7):624-648. [32] vasconcelos a, freddi g, cavaco-paulo a. (2008) biodegradable materials based on silk fibroin and keratin. biomacromolecules, 9(4):1299-1305. [33] wojciechowska e, włochowicz a, wesełucha-birczyńska a. (1999) application of fouriertransform infrared and raman spectroscopy to study degradation of the wool fiber keratin. journal of molecular structure, 511:307-318. [34] sharma s, gupta a, chik smsbt, kee cyg, poddar pk. (2017b) dissolution and characterization of biofunctional keratin particles extracted from chicken feathers, in: iop conference series material science engineering, vol 1, iop publishing, 012013. [35] zhang j, li y, li j, zhao z, liu x, li z, han y, hu j, chen a. (2013) isolation and characterization of biofunctional keratin particles extracted from wool wastes. powder technology, 246:356-362. [36] sharma s, gupta a, chik smsbt, kee cyg, poddar pk, thuraisingam j, subramaniam m. (2016) extraction and characterization of keratin from chicken feather waste biomass: a study. national conference for postgraduate research universiti malaysia pahang, pekan. pp. 693-699. [37] kamarudin nb, sharma s, gupta a, kee cg, chik smsbt, gupta r. (2017) statistical investigation of extraction parameters of keratin from chicken feather using design-expert. 3 biotech, 7(2):127. [38] al-itry r, lamnawar k, maazouz a. (2012) improvement of thermal stability, rheological and mechanical properties of pla, pbat and their blends by reactive extrusion with functionalized epoxy. polymer degradation and stability, 97(10):1898-1914. [39] subramaniam m, gupta a, sharma s, abdullah n. enhanced degradation properties of polypropylene integrated with of fe and co-stearates and its synthetic application doi:10.1002/app.46028 (in press) [40] ullah a, wu j. (2013) feather fiber based thermoplastics: effects of different plasticizers on material properties. macromolecular materials and engineering, 298(2):153-162. [41] sharma s, gupta a, chik smsbt, kee cg, mistry b, kim dh, sharma g. (2017a) characterization of keratin microparticles from feather biomass with potent antioxidant and anticancer activities. international journal of biological macromolecules, 104:189-196. [42] popescu c, augustin p. (1999) effect of chlorination treatment on the thermogravimetric behaviour of wool fibres. journal of thermal analysis and calorimetry, 57(2):509-515. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 multi-objective optimization of snake robot in serpentine locomotion marwan badran, md raisuddin khan*, siti fauziah toha and zulkifli zainal abidin department of mechatronics engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia *corresponding author: raisuddin@iium.edu.my (received: 8th november 2020; accepted: 14th february 2021; published on-line: 4th july 2021) abstract: this paper presents multi-objective optimization for a snake robot with serpentine locomotion. genetic algorithm (ga) is used to achieve two objectives: minimizing the total travelling time and minimizing the total energy consumption. the effect of initial values of winding angle and acceleration on energy consumption and average speed is depicted. the simulation results show a periodic pattern of the joint torques when the robot maintains a serpenoid curve during travel. moreover, a paretooptimal front was generated for optimal solutions of both of the objectives, while the weighted sum method was used for selecting the best solution. finally, the simulation results were verified experimentally on an eight-link snake robot considering the limitations of the servomotors used in the experiment. the experimental results with the winding angle of 30° was found as the optimum winding angle that can achieve both objectives of minimizing the energy consumption and the travelling time. abstrak: kajian ini berkenaan pelbagai-objektif optimum bagi robot ular dengan gerakan serpentin. algoritma genetik (ga) diguna bagi mencapai dua objektif ini iaitu mengurangkan jumlah masa gerakan dan guna tenaga. gambaran kesan awal nilai sudut belitan dan pecutan pada guna tenaga dan purata kelajuan dihasilkan. dapatan simulasi menunjukkan corak berkala tork sendi yang tetap terhasil semasa robot ini berkeadaan lengkung serpenoid ketika bergerak. tambahan, pareto-optimal berdepan terhasil bagi solusi optimum pada kedua-dua objektif, sementara kaedah berat campuran digunakan bagi menentukan solusi terbaik. akhirnya, dapatan simulasi disahkan secara eksperimen pada robot ular lapan-bahagian dengan menimbangkan kekurangan servomotor yang digunakan dalam eksperimen. dapatan eksperimen menunjukkan sudut belitan 30° adalah sudut belitan optimum bagi kedua-dua objektif iaitu mengurangkan tenaga dan masa gerakan. keywords: snake robot; serpentine locomotion; genetic algorithm; multi-objective optimization; pareto optimality 1. introduction snake robots are robotic mechanisms inspired by the motion of biological snakes. snake robots were studied during the last five decades, although the early work on real snakes was conducted by the zoologist, gray [1]. the first snake robot was developed by hirose in 1972 [2]. a considerable number of research projects on snake robots focused on their design and modelling; thus, various models of snake-like robots were proposed in the literature [3-7]. on the other hand, several studies focused on the control of the snake 364 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 robot locomotion [8,9], while others focused on applications for snake robots such as pipe inspection [10], and rescue tasks [11,12]. the pioneer model of a snake robot was presented by hirose in his book [3], where he presented a thorough study of the locomotion patterns of the natural snake and formulated what he called a serpenoid curve, which closely mimics the locomotion of living snakes. hirose used a snake robot with passive wheels in his experiments to achieve normal friction much higher than tangential friction, which was an essential principle in snake movement. on contrary, saito et al. [4] designed a wheel-less snake robot with direct contact to the ground. the snake has the potential of adapting to the environment at the cost of increased power consumption. saito developed his model based on hirose’s principle and obtained equations of motion for a multi-link snake robot travelling with serpentine locomotion. their model, which was based on the directional friction coefficients, had the feature of decoupling the inertial locomotion from the internal shape motion. another detailed work on snake robot was introduced in [13]. they presented a systematic complete description of a snake robot in travelling wave locomotion based on the snake robot model introduced by hirose. the effects of the initial winding angle and friction coefficient on the joint input torques were also discussed. simulation and experiment in that study were carried out using locomotion along a vertical plane. however, this type of locomotion usually needs two periods of serpenoid curve to guarantee two supporting points in contact with the ground to keep the snake robot balanced. unlike traditional robots, snake robots are unique in terms of their shape variant, degree of freedom, and locomotion types. hence, a snake robot has a controllable shape that can achieve a specific locomotion that helps the snake to follow a certain path in a certain direction. more precisely, the snake robot’s amplitude (which is controlled by the initial winding angle) and the number of cycles can be controlled so that the shape and the size of the snake robot are both variable. besides, the acceleration of the snake robot plays a role that affects the travelling speed and energy consumption, and that leads to the need for optimization of locomotion parameters. therefore, optimization was another area of interest in the research on snake robots, as noticed in [14]. the authors in this study introduced the snake robot model in such a way that optimization could be used to find the optimal parameters for power and speed efficiency. in their study, they used pareto optimality to obtain the optimal values of snake parameters. for example, they found that one period of the serpenoid curve could achieve the optimal power efficiency. similar work was proposed in [15] for the locomotion efficiency of snake robots. optimization was also used by [16], who proposed a path planning technique based on a serpenoid curve and real time dual genetic algorithm to control the snake-like robot. they used multi-objective optimization to find the shortest path and the minimum curvature deviation, as well as decrease the influence of motion error. another study in [17] used genetic algorithm (ga) to find the optimal central pattern generator (cpg) parameters in terms of moving speed of a snake robot considering the effect of friction coefficients. the study included the design of a fuzzy tuner for cpg-network parameters during robot motion to achieve maximum speed. genetic algorithm (ga) was also used to optimize the control parameters of a snake robot in [18]. the proposed pi/backstepping control in that study aimed to reduce the tracking error and control energy in snake robot motion. the focus of this paper is on multi-objective optimization of a snake robot’s parameters to enhance its efficiency in terms of travelling speed and energy consumption. this study considers the serpentine locomotion of the snake robot while travelling along a straight line. 365 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 2. system description in this section, a brief description is introduced for the snake robot model used in this study including the dynamics of the snake robot. furthermore, the parameters that play role in achieving the objective functions are also discussed. 2.1 model of snake robot the model of snake robot used in this study is the one introduced in [3]. in that model, the serpenoid curve is used to control the body shape of the snake robot during travel in serpentine locomotion. the serpenoid curve can be achieved by the curvature function as follows: 𝜌(𝑠) = −2𝜋𝛼 𝐿 𝑠𝑖𝑛 ( 2𝜋 𝐿 𝑠) (1) where 𝐿 is the length of the snake body, 𝛼 is the initial winding angle of the curve, and 𝑠 is the body length along the body curve, as shown in fig. 1. fig. 1: snake robot scheme with serpenoid curve. here, all the links are assumed to have the same length 𝐿𝑢. hence, by integration of the curvature function in eq. (1), the approximate values of relative angle 𝜃𝑖(𝑠) can be derived as follows 𝜃𝑖 (𝑠) = ∫ 𝜌(𝑢)𝑑𝑢 𝑠+𝑖𝐿𝑢 𝑠+(𝑖−1)𝐿𝑢 = −2𝛼 𝑠𝑖𝑛 ( 𝜋 𝑛 ) . 𝑠𝑖𝑛 ( 2𝜋𝑠 𝐿 + 2𝜋𝑖 𝑛 − 𝜋 𝑛 ) (2) consequently, angular velocity �̇�𝑖 (𝑠) and angular acceleration �̈�𝑖(𝑠) can be obtained as follows: �̇�𝑖 (𝑠) = − 4𝜋𝛼 𝐿 . 𝑠𝑖𝑛 ( 𝜋 𝑛 ) . 𝑐𝑜𝑠 ( 2𝜋𝑠 𝐿 + 2𝜋𝑖 𝑛 − 𝜋 𝑛 ) �̇� (3) �̈�𝑖 (𝑠) = − 4𝜋𝛼 𝐿 . 𝑠𝑖𝑛 ( 𝜋 𝑛 ) . 𝑐𝑜𝑠 ( 2𝜋𝑠 𝐿 + 2𝜋𝑖 𝑛 − 𝜋 𝑛 ) �̈� + 8𝜋 2𝛼 𝐿2 . 𝑠𝑖𝑛 ( 𝜋 𝑛 ) . 𝑠𝑖𝑛 ( 2𝜋𝑠 𝐿 + 2𝜋𝑖 𝑛 − 𝜋 𝑛 ) �̇�2 (4) where 𝑖 = 1,2, … , 𝑛 − 1 serpenoid curve 𝛼 𝑠 𝜙1(𝑠) 𝜃𝑖−1(𝑠) 𝜙𝑖 (𝑠) 𝐿𝑢 𝑖+1 link model 𝑥 𝑦 366 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 𝑛 = number of links 𝐿𝑢 = length of single link �̇� is the velocity along the body curve �̈� is the acceleration along the body curve given as �̈� = { 𝑎 0 ≤ 𝑡 < 𝑅 0 𝑅 ≤ 𝑡 < 𝑇 − 𝑅 −𝑎 𝑇 − 𝑅 ≤ 𝑡 < 𝑇 (5) where, 𝑎 is the initial acceleration, 𝑅 is the acceleration/deceleration time and 𝑇 is the total travelling time. since �̈� is given, �̇� and 𝑠 can be found by finding the first integral and second integral of �̈�, respectively. based on the above equations, 𝜃𝑖(𝑠) can be varied to control the body shape and travelling speed of the snake robot. 2.2 dynamics of the snake robot as mentioned above, the locomotion of the snake robot relies on the difference between tangential friction and normal friction. thus, the dynamics of the snake robot describes the relationship between the joint torques, frictional force and the robot locomotion as illustrated in fig. 2. fig. 2: scheme of forces acting on link i. to represent the environment dynamics, coulomb friction is used so that the direction of motion is taken in consideration in terms of the sign of the velocity. hence, tangential friction force (𝐹𝑇) and normal friction force (𝐹𝑁) for link 𝑖 can be calculated as follows: 𝐹𝑖𝑇 = 𝜇𝑡 . sgn(𝑣𝑖𝑇 ). 𝑚𝑔 (6) 𝐹𝑖𝑁 = 𝜇𝑛. sgn(𝑣𝑖𝑁). 𝑚𝑔 (7) where 𝜇𝑡 and 𝜇𝑛 are tangential and normal friction coefficients of link 𝑖, while 𝑣𝑖𝑇 and 𝑣𝑖𝑁 are tangential and normal velocity at the center of gravity of link 𝑖. the latter two velocities can be calculated as follows: 𝑣𝑖𝑇 = �̇�𝑖𝐺 cos 𝜙𝑖 + �̇�𝑖𝐺 sin 𝜙𝑖 (8) 𝑣𝑖𝑁 = �̇�𝑖𝐺 sin 𝜙𝑖 + �̇�𝑖𝐺 cos 𝜙𝑖 (9) 367 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 where �̇� and �̇� are the velocity components at the centre of gravity of link 𝑖. using eqs. (6) and (7), the 𝑥 and 𝑦 components of the friction force are expressed as: 𝐹𝑖𝑥 = 𝐹𝑖𝑇 . cos 𝜙𝑖 − 𝐹𝑖𝑁 . sin 𝜙𝑖 (10) 𝐹𝑖𝑦 = 𝐹𝑖𝑇. sin 𝜙𝑖 − 𝐹𝑖𝑁 . cos 𝜙𝑖 (11) referring to fig. 2 and by applying newton’s second law of motion, the motion for the link 𝑖 with respect to the link 𝑖+1 can be described as follows 𝑓𝑖𝑥 − 𝑓𝑖+1𝑥 + 𝐹𝑖𝑥 = 𝑚�̈�𝑖𝐺 (12) 𝑓𝑖𝑦 − 𝑓𝑖+1𝑦 + 𝐹𝑖𝑦 = 𝑚�̈�𝑖𝐺 (13) 𝜏𝑖 − 𝜏𝑖+1 + (𝑓𝑖𝑥 + 𝑓𝑖+1𝑥 + 𝐹𝑖𝑥 ) 𝐿𝑢 sin 𝜙𝑖 2⁄ − (𝑓𝑖𝑦 + 𝑓𝑖+1𝑦 + 𝐹𝑖𝑦) 𝐿𝑢 cos 𝜙𝑖 2⁄ = 𝐼𝑖�̈�𝑖 (14) however, joint 1 and joint 𝑛+1 represent the tail and the head of the snake robot where no actuators are attached. therefore, torque and force at both ends will be zeros as expressed in the following two equations: 𝑓1𝑥 = 𝑓1𝑦 = 𝑓𝑛+1𝑥 = 𝑓𝑛+1𝑦 = 0 (15) 𝜏1 = 𝜏𝑛+1 = 0 (16) by taking summation of both sides of the recursive formulas eqs. (12) and (13) and then satisfying the conditions in eqs. (15) and (16), the force equations eqs. (17) and (18) of link 𝑖 are obtained. 𝑓𝑖𝑥 = ∑ 𝑚�̈�𝑗𝐺 𝑛 𝑗=𝑖 − ∑ 𝐹𝑗𝑥 𝑛 𝑗=𝑖 (17) 𝑓𝑖𝑦 = ∑ 𝑚�̈�𝑗𝐺 𝑛 𝑗=𝑖 − ∑ 𝐹𝑗𝑦 𝑛 𝑗=𝑖 (18) substituting eq. (17) and (18) in the torque eq. (14), we get: 𝜏𝑖 − 𝜏𝑖+1 + (2 ∑ 𝑚�̈�𝑗𝐺 𝑛 𝑗=𝑖 − 2 ∑ 𝐹𝑗𝑥 𝑛 𝑗=𝑖 − 𝑚�̈�𝑖𝐺 + 𝐹𝑖𝑥 ) 𝐿𝑢 sin 𝜙𝑖 2⁄ − (2 ∑ 𝑚�̈�𝑗𝐺 𝑛 𝑗=𝑖 − 2 ∑ 𝐹𝑗𝑦 𝑛 𝑗 =𝑖 − 𝑚�̈�𝑖𝐺 + 𝐹𝑖𝑦 ) 𝐿𝑢 cos 𝜙𝑖 2⁄ = 𝐼𝑖�̈�𝑖 (19) consequently, summation of both sides of eq. (19) gives: ∑ {(2 ∑ 𝑚�̈�𝑗𝐺 𝑛 𝑗 =𝑖 − 2 ∑ 𝐹𝑗𝑥 𝑛 𝑗 =𝑖 − 𝑚�̈�𝑖𝐺 + 𝐹𝑖𝑥 ) 𝐿𝑢 sin 𝜙𝑖 2⁄ 𝑛 𝑖=1 − (2 ∑ 𝑚�̈�𝑗𝐺 𝑛 𝑗=𝑖 − 2 ∑ 𝐹𝑗𝑦 𝑛 𝑗 =𝑖 − 𝑚�̈�𝑖𝐺 + 𝐹𝑖𝑦 ) 𝐿𝑢 cos 𝜙𝑖 2⁄ } = ∑ 𝐼𝑖�̈�𝑖 𝑛 𝑖=1 (20) by solving eq. (20) we obtain the only unknown variable (�̈�1) which is the rotation acceleration of the first joint. however, from kinematics of link 𝑖 at the center of gravity we have: 368 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 �̈�𝑖𝐺 = �̈�𝑖 − 𝐿𝑢 2 cos 𝜙𝑖�̇�𝑖 − 𝐿𝑢 2 sin 𝜙𝑖 �̈�𝑖 (21) �̈�𝑖𝐺 = �̈�𝑖 − 𝐿𝑢 2 sin 𝜙𝑖 �̇�𝑖 + 𝐿𝑢 2 cos 𝜙𝑖�̈�𝑖 (22) hence, substituting eqs. (21) and (22) in eqs. (17) and (18) gives: 𝑛�̈�1 − ∑ [∑(𝐿𝑢 cos 𝜙�̇�𝑘 2 + 𝐿𝑢 sin 𝜙𝑘 �̈�𝑘 ) + 𝐿𝑢 2 cos 𝜙𝑖 �̇�𝑖 + 𝐿𝑢 2 sin 𝜙𝑖 �̈�𝑖 𝑖−1 𝑘=1 ] 𝑛 𝑖=1 = ∑ 𝐹𝑖𝑥 /𝑚 𝑛+1 𝑖=1 (23) 𝑛�̈�1 − ∑ [∑(𝐿𝑢 sin 𝜙�̇�𝑘 2 − 𝐿𝑢 cos 𝜙𝑘 �̈�𝑘 ) + 𝐿𝑢 2 sin 𝜙𝑖�̇�𝑖 − 𝐿𝑢 2 cos 𝜙𝑖 �̈�𝑖 𝑖−1 𝑘=1 ] 𝑛 𝑖=1 = ∑ 𝐹𝑖𝑦 /𝑚 𝑛+1 𝑖=1 (24) substituting (�̈�1) obtained from eq. (20) into eqs. (23) and (24), we get the linear acceleration of the first link (�̈�1) and (�̈�1). moreover, substituting the obtained variables from eqs. (20), (23) and (24) into eq. (19), all the joints’ torques required to generate the robot motion are obtained. consequently, the power consumption of each joint can be calculated as 𝑃𝑖 = |𝜏𝑖 �̇�𝑖 | (25) hence, total energy consumption of all joints for the travelling time, t can be calculated as 𝐸𝑇 = ∑ ∫ |𝜏𝑖 �̇�𝑖| 𝑇 0 𝑑𝑡 𝑛 𝑖=1 (26) since time segment used in this case is discrete, trapezoidal numerical integration can be used to find an approximation of the total energy consumption. 2.3 energy consumption and average speed as mentioned earlier in this paper, the target of this study is to achieve the maximum average speed (or minimum travelling time) of the snake robot using minimum energy consumption. for this purpose, we need to study the factors that may affect the average speed and the energy consumption of the snake robot. namely, we focus on the winding angle and the acceleration of the snake robot, as illustrated in the following subsections. 2.3.1 effect of winding angle on energy consumption and average speed in order to study the effect of acceleration and winding angle of the snake robot on energy consumption and average speed of the forward motion, several simulations were performed. in these simulations, the snake robot travelled forward using serpentine locomotion for a distance of 3 meters. in the next step, winding angle was varied within the range 0.3 to 1.5 radians, while the acceleration was kept constant at 0.1 m/s2. the results of this simulation are shown in fig. 3. as seen in fig. 3, increasing the winding angle of the snake robot has an undesired effect on both energy consumption and average speed. in other words, if the winding angle is increased, the average speed of the snake robot is decreased, and the energy consumption is increased. since the objective is to minimize the energy consumption as well as the travelling time of the snake robot, it is obviously clear that selecting a minimum winding angle would achieve both objectives. the detailed results of this simulation are listed in table 1. 369 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 fig. 3: effect of winding angle on energy consumption and average speed. table 1: effect of winding angle on energy consumption and average speed winding angle travelling time (s) average speed (m/s) energy consumption (j) radian (°) 0.3 17.2 06.70 0.45 0.70 0.4 22.9 06.80 0.44 0.96 0.5 28.6 06.90 0.43 1.22 0.6 34.4 07.10 0.42 1.50 0.7 40.1 07.30 0.41 1.86 0.8 45.8 07.70 0.39 2.41 0.9 51.6 08.00 0.38 2.88 0.1 05.7 08.30 0.36 3.52 1.1 63.0 08.90 0.34 4.34 1.2 68.8 09.40 0.32 5.15 1.3 74.5 10.20 0.30 6.17 1.4 80.2 11.10 0.27 7.35 1.5 85.9 12.20 0.25 8.76 as illustrated in table 1, while the winding angle is gradually increased from 0.3 to 1.5 radians, the travelling time of the snake robot is also increased. accordingly, the average speed (travelled distance divided by travelling time) is decreased. table 1 shows that applying minimum winding angle (0.3 radian) can achieve maximum average speed (0.45 m/s) and minimum energy consumption (0.70 j). on the contrary, applying maximum winding angle (1.5 radian) leads to undesired minimum average speed (0.25 m/s) and undesired maximum energy consumption (8.76 j). 2.3.2 effect of acceleration on energy consumption and average speed to study the effect of acceleration along the body of the snake robot on energy consumption and average speed, simulation tests were carried out using different values of 0.2 1.2 2.2 3.2 4.2 5.2 6.2 7.2 8.2 9.2 0.3 0.5 0.7 0.9 1.1 1.3 1.5 0.2 0.25 0.3 0.35 0.4 0.45 0.5 e n e rg y c o n su m p ti o n ( j) winding angle (radian) a v e ra g e s p e e d ( m /s ) average speed energy consumption 370 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 acceleration ranging between 0.1 and 1.3 m/s2, while the winding angle was kept constant at 𝜋/3 radian. simulation results are shown in fig. 4. fig. 4: effect of acceleration on energy consumption and average speed. figure 4 demonstrates that the acceleration along the body of the snake robot has a contradictory effect on average speed and energy consumption. hence, increasing the acceleration will increase average speed, and that matches the first objective. on the other hand, increasing the acceleration will increase energy consumption of the snake robot, which mismatches the second objective. therefore, there is no single value of acceleration that can achieve both objectives. for more details, table 2 illustrates the effect of the initial acceleration of the snake robot on average speed and energy consumption. for example, applying the maximum acceleration (1.3 m/s2) achieves the maximum average speed (1.60 m/s), however, that leads to undesired maximum energy consumption (5.32 j). while applying the minimum acceleration (0.1 m/s2) achieves the minimum energy consumption (1.61 j), but leads to undesired minimum average speed (0.42 m/s). table 2: effect of acceleration on energy consumption and average speed acceleration (m/s2) travelling time (s) average speed (m/s) energy consumption (j) 0.1 7.2 0.42 1.61 0.2 4.9 0.63 1.83 0.3 4.0 0.77 1.96 0.4 3.5 0.89 2.40 0.5 3.1 0.99 2.55 0.6 2.8 1.08 2.65 0.7 2.6 1.17 2.85 0.8 2.5 1.27 3.93 0.9 2.3 1.33 3.88 0.1 2.2 1.41 4.27 1.1 2.1 1.48 4.97 1.2 2.0 1.54 4.94 1.3 1.9 1.60 5.32 in conclusion, both objective functions (minimizing of energy consumption and maximizing of average speed) are dependent on winding angle and acceleration of the 0.20 1.20 2.20 3.20 4.20 5.20 6.20 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 0 0.2 0.4 0.6 0.8 1 1.2 1.4 e n e rg y c o n su m p st io n ( j) a ve ra g e s p e e d ( m /s ) acceleration (m/s2) average speed energy consumption 371 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 snake robot. consequently, the latter two parameters need to be optimized in order to achieve the mentioned objective functions. once the optimization parameters are defined, the simulation setup can be started as described in the following section. 3. simulation setup multi-objective optimization described in the previous section was implemented using the gamultiobj function in matlab that applies a genetic algorithm to find paretooptimal front of multiple objective functions. pareto-optimal front contains optimal solutions that fit the objective functions. the general form of the gamultiobj function is expressed as follows: [x, fval] = gamultiobj (fitnessfcn, nvars, a, b, , , lb, ub, options) where x: is a matrix of all solutions of the design variables (winding angle and acceleration) fval: is a matrix of all values of objective functions defined in fitnessfcn (average speed and energy consumption) a fundamental step in optimization techniques is that initial values need to be set before moving forward in the optimization process. the initial values of the function’s parameters that have been used in this study are described in table 3. table 3: initial values for parameters of gamultiobj function parameter value description fitnessfcn multiobjfcn fitness function nvars 2 number of design variables lb [𝜋/6, 0.1] lower bounds ub [𝜋/3, 2.0] upper bounds populationsize 50 number of individuals generations 15 total number of generations the fitness function in this simulation uses the snake locomotion model as described in section 2. the fitness function has two parameters as input: winding angle and acceleration, the values of which are generated by the genetic algorithm. on the other hand, the fitness function returns the values of the two parameters: energy consumption and average speed, which will be used by genetic algorithm to determine the fitness value of the input variables. moreover, the other variables related to snake robot are initialized in the fitness function as described in table 4. table 4: initial values for snake robot variables variable value description n 8 number of links l 1 length of snake body (m) m 0.1 mass of single link (kg) i 0.0001 moment of inertia (kg m2) mu_t 0.07 tangential friction coefficient mu_n 0.7 normal friction coefficient 372 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 the travelling distance was set to 3 meters, which is enough to get more than one full cycle of the snake shape. meanwhile, the speed of the snake �̇� along the serpenoid curve is determined by rise time r as described in �̈� function in eq. (5). arbitrarily, the value of r is set to 5 seconds. the process of multi-objective optimization is illustrated in the flowchart shown in fig. 5. fig. 5: flowchart of multi-objective optimization process. 4. simulation results at first, the fitness function was simulated using settings in section iii. the fitness function uses kinematics and dynamics of the snake robot to achieve the serpentine locomotion. the results show a variety of input torques of the snake robot joints as seen in fig. 6. fig. 6: input torque for snake robot joints. the pattern of the joints’ torques shows a periodic shape because the snake is following a repeated sinusoidal path. however, it can be noticed that the middle joint objective function 𝑋1 (winding angle) 𝑋2 (acceleration) 𝑉𝑎𝑙2 (average speed) 𝑉𝑎𝑙1 (energy consumption) -0.25 -0.15 -0.05 0.05 0.15 0.25 0 1 2 3 4 5 6 7 8 9 10 11 t o r q u e ( n .m ) time (s) joint 3 joint 5 joint 7 373 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 (joint 5) has the highest torque compared to the other joints. consequently, the torque is lower when joints are farther from the centre of the snake robot (joints 3 and 7), which makes sense, as each joint is affected by the forces of the preceding and succeeding links. several simulations were carried out using gamultiobj tool in order to optimize the winding angle and acceleration parameters. therefore, different values of these two parameters were used for multi-objective optimization. on the other hand, population size was selected as follows: 20, 30, 40 and 50, along with different values of the number of generations and pareto fraction. the travelling distance was selected as 3 meters. eventually, the configuration that showed the least gaps between solution points was selected, which was as follows: populationsize: 50, generations: 15, pareto fraction: 0.7. using the previous configuration, simulation was repeated for three trials giving the optimal solutions using pareto-optimal front as shown in fig. 7. fig. 7: pareto-optimal front using (populationsize = 50, generations = 15). despite using the same parameters in the three trials, the possible solutions are different from one trial to another as seen in fig. 7. that is referred to the algorithm of the optimization technique, which uses random numbers for the initialization process. nevertheless, by looking at the pareto-optimal front in fig. 7, all the possible solutions of the three trials lie within the same precision, which denotes the stability of the optimization process. the three trials have almost the same range of solutions that is located between 1.3 and 6.8 joules for energy consumption, and between 1.5 and 6.2 seconds for travelling time. it is also noticed that concentration of solutions decreases as travelling time increases. the solutions in the pareto-optimal front are used to determine the relative angles for each joint of the snake robot to achieve the objective functions. table 5 shows the relative joints’ angles based on the optimized parameters. by looking at table 5, it is noticed that all values of winding angle (𝛼) are approaching π/6 which is the minimum value within the angle bounds as initialized in gamultiobj function. these values match with winding angle curve behaviour in fig. 3. on the other side, values of acceleration have wider range that almost covers the whole range of acceleration (0.1 to 2.0) as initialized in the gamultiobj function. however, all pareto optimal solutions in table 5 are slightly different from each other, which denotes the fact that all solutions can be accepted with a little difference in fitting the objective functions 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 travelling time (s) e n e rg y c o n s u m p ti o n ( j ) 1 s t trial 2 n d trial 3 r d trial 374 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 table 5: relative joints’ angles for optimized parameters pareto-optimal front pareto solution winding angle (°) acceleration (m/s2) joints’ angles (°) 𝜽𝟏 𝜽𝟐 𝜽𝟑 𝜽𝟒 𝜽𝟓 𝜽𝟔 𝜽𝟕 1 31.0 0.22 -09.2 -22.0 -21.8 -8.9 09.2 22.0 21.8 2 31.0 0.62 -09.5 -22.1 -21.7 -8.6 09.5 22.1 21.7 3 31.0 1.80 -10.3 -22.4 -21.4 -7.8 10.3 22.4 21.4 4 31.0 1.57 -10.1 -22.3 -21.5 -8.0 10.1 22.4 21.5 5 31.1 0.51 -09.5 -22.1 -21.8 -8.7 09.5 22.1 21.8 6 31.1 1.12 -09.9 -22.3 -21.7 -8.3 09.9 22.3 21.7 7 31.2 0.72 -09.6 -22.2 -21.8 -8.6 09.6 22.2 21.8 8 31.2 0.93 -09.8 -22.3 -21.8 -8.5 09.8 22.3 21.8 9 31.3 0.57 -09.6 -22.3 -21.9 -8.8 09.6 22.3 21.9 10 31.3 0.83 -09.7 -22.3 -21.9 -8.6 09.7 22.3 21.9 11 31.3 1.27 -10.0 -22.5 -21.7 -8.3 10.0 22.5 21.7 12 31.3 0.31 -09.4 -22.2 -22.0 -8.9 09.4 22.2 22.0 13 31.3 1.87 -10.5 -22.6 -21.6 -7.8 10.5 22.6 21.6 14 31.3 1.61 -10.3 -22.6 -21.6 -8.0 10.3 22.6 21.6 15 31.3 1.41 -10.1 -22.5 -21.7 -8.2 10.1 22.5 21.7 16 31.3 0.78 -09.7 -22.4 -21.9 -8.6 09.7 22.4 21.9 17 31.3 1.78 -10.4 -22.6 -21.6 -7.9 10.4 22.6 21.6 18 31.4 0.95 -09.9 -22.5 -21.9 -8.5 09.9 22.5 21.9 19 31.5 1.26 -10.1 -22.6 -21.9 -8.3 10.1 22.6 21.9 20 31.5 1.13 -10.0 -22.6 -22.0 -8.4 10.0 22.6 22.0 21 31.6 1.03 -10.0 -22.6 -22.0 -8.5 10.0 22.6 22.0 22 31.6 0.16 -09.4 -22.4 -22.3 -9.1 09.4 22.4 22.3 23 31.8 1.84 -10.6 -23.0 -21.9 -8.0 10.6 23.0 21.9 24 31.8 1.93 -10.7 -23.0 -21.9 -7.9 10.7 23.0 21.9 25 31.8 0.15 -09.4 -22.5 -22.5 -9.2 09.4 22.6 22.5 4.1 selection of the best solution after obtaining the pareto optimal solutions, which can be considered as equally accepted solutions, only one solution is needed to achieve the objective functions. for such a case, several methods are available and can be used to select a single solution from all pareto optimal solutions. one of these methods the weighted sum method (also called utility function), which is one of the simplest and most meaningful methods for solving multi-objective optimization problems [19]. moreover, the weighted sum method is more suitable for a convex pareto frontier (which is the case in this study). in this method, a weighting factor (𝑤𝑖 ) is given for each of the objective functions (𝑓𝑖) based on its importance compared to the other objective functions. then a total or overall utility function 𝑈 can be defined as follows [20]: 𝑈 = ∑ 𝑤𝑖 𝑓𝑖 (𝑋) 𝑘 𝑖=1 (27) where 𝑤𝑖 is the weighting factor 𝑘 is the number of objective functions 𝑋 is a vector of design variables. 375 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 the solution can be found by maximizing (or minimizing) the total utility 𝑈 based on the objective function. the result of this method is a single value, but it may denote more than one solution when they have the same utility value. let us say there are two objective functions: 𝑓1 and 𝑓2, then there should be two preselected weighting factors: 𝑤1 and 𝑤2. the weights used in this method usually satisfy the normalization condition: ∑ 𝑤𝑖 = 1 𝑘 𝑖=1 (28) using the solution set of trial 1 in fig. 7, the weighted sum method was applied several times using various weights for each of the objective functions. however, all values of the objective functions need to be normalized (between 0 and 1) to eliminate the effect of the big difference among values of different units. hence, the following formula was used for normalization purposes: 𝑥𝑛𝑜𝑟𝑚 = 𝑥 − 𝑥𝑚𝑖𝑛 𝑥𝑚𝑎𝑥 − 𝑥𝑚𝑖𝑛 (29) each time the weighted sum method was applied, only one solution was selected out of all solutions in the pareto curve. the results of using different combination of weights are shown in table 6, where 𝑓1 and 𝑓2 represent the objective functions, while 𝑤1 and 𝑤2 represent their weights. as mentioned earlier, the weighted sum method needs a predefined weight for each of the objective functions. these weights are user-defined parameters, and vary from one case to another. therefore, table 6 has various values to include a wide range of weights for each objective function to show the effect of this variety on the selection of the best answer. the last two columns in table 6 clearly show that the values match with the behaviour shown on the curves in fig. 3 and fig. 4. for example, when high priority is given to minimize energy consumption, as in the first case in table 6, the minimum energy consumption is achieved (1.323 j) with the cost of minimum average speed (0.119 m/s). on the other hand, when high priority is given to maximize the average speed, as in the last case in table 6, the maximum average speed is achieved (2.039 m/s) with the cost of maximum energy consumption (6.784 j). nevertheless, in some of the cases, different pairs of weights may lead to the same result, like cases 6 and 7 in the same table. for more clarification, fig. 8 illustrates the optimization results, including all possible solutions, the pareto-optimal front, and the best solution (using 𝑤1= 0.4 and 𝑤2= 0.6). table 6: applying weighted sum method using variant weights for objectives functions 𝒘𝟏 𝒘𝟐 𝒘𝟏𝒇𝟏 𝒘𝟐𝒇𝟐 ∑ 𝒘𝒊𝒇𝒊 𝟐 𝒊=𝟏 𝜶 (radian) acceleration (m/s2) avg. speed (m/s) energy cons. (j) 0.10 0.90 0.100 0.000 0.100 0.541 0.119 0.481 1.323 0.20 0.80 0.147 0.034 0.181 0.541 0.393 0.894 1.552 0.34 0.66 0.236 0.041 0.277 0.545 0.449 0.956 1.662 0.40 0.60 0.188 0.110 0.298 0.541 0.848 1.309 2.326 0.54 0.46 0.158 0.167 0.325 0.543 1.244 1.584 2.326 0.60 0.40 0.051 0.246 0.297 0.541 1.785 1.907 4.679 0.70 0.30 0.059 0.184 0.244 0.541 1.785 1.907 4.679 0.82 0.18 0.054 0.126 0.180 0.541 1.823 1.937 5.131 0.90 0.10 0.000 0.100 0.100 0.551 1.975 2.039 6.784 376 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 fig. 8: pareto-optimal front showing dominated points. 4.2 validation of the obtained results in order to validate the obtained results of multi-objective optimization, arbitrarily variant values of winding angle and acceleration were tested and compared with the optimized parameters. the tested values were selected from the same range of winding angle (𝜋/6 to 𝜋/3) and acceleration (0.1 to 2.0) as initialized in gamultiobj function. the comparison of results is shown in table 7. table 7: comparison of selected and optimized parameters winding angle acceleration (m/s2) average speed (m/s) energy cons. (j) remarks radian (°) 1.047 60.0 0.100 0.349 03.978 not optimized 1.047 60.0 0.500 0.860 07.907 not optimized 1.047 60.0 1.100 1.285 17.501 not optimized 1.047 60.0 1.400 1.440 19.691 not optimized 0.785 45.0 0.200 0.599 02.743 not optimized 0.785 45.0 0.700 1.118 04.749 not optimized 0.785 45.0 1.000 1.345 07.136 not optimized 0.785 45.0 1.500 1.659 11.385 not optimized 0.628 36.0 0.300 0.770 01.962 not optimized 0.628 36.0 0.600 1.085 02.653 not optimized 0.628 36.0 0.120 0.473 01.644 not optimized 0.542 31.1 0.314 0.797 01.511 optimized 0.541 31.0 0.848 1.309 02.326 optimized 0.541 31.0 1.272 1.611 03.549 optimized 0.543 31.1 1.427 1.709 03.909 optimized 0.541 31.0 1.823 1.937 05.131 optimized the results in table 7 clearly show that using any combination of values for winding angle and acceleration other than the values obtained by pareto-optimal front do not achieve better results in terms of fitting the objective functions. therefore, these results show the validity of using multi-objective optimization technique for snake robot locomotion. 1.5 2 2.5 3 3.5 4 4.5 5 1 2 3 4 5 6 7 travelling time (s) e n e rg y c o n s u m p ti o n ( j ) all solutions pareto-front solutions best solution (w 1 =0.4) 377 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 5. experimental results to verify the simulation results, several experiments were conducted to check the effect of changing the related factors on power consumption, namely, acceleration, winding angle and surface friction. 5.1 effect of acceleration on energy consumption acceleration here means the change of speed in the forward motion of the snake robot along the serpentine path after it starts moving. consequently, this acceleration will determine the forward speed of the snake robot, which is theoretically assumed to be constant. however, direct control of acceleration is not an easy job; instead, controlling the rotation speed of the servomotors is much easier. accordingly, the effect of the acceleration on power consumption can be simply found by varying the rotational speed of the servomotors and getting the final reading of energy consumption. to conduct the experiment, the value of the winding angle needs to be fixed, while the rotation speed of the servomotor needs to be changed within a specific range. for more analysis, the experiment was repeated several times using a range of winding angle from 20° to 45° with a 5-step increment, while the range of the servomotor rotation speed was varied for each winding angle between the rotation speed code ‘30’ which represents 0.77 rad/s, and the rotation speed code ‘60’ which represents 1.43 rad/s. in this experiment, the snake robot was run 42 times for 6-meter travel. meanwhile, the winding angle and rotation speed were varied for each experiment. digital wattmeter was used to measure the total energy consumption for each travel of the snake robot. the results are illustrated in fig. 9. fig. 9: travelling time for 6-meter distance. figure 9 illustrates the relationship between the servomotor rotation speed and the travelling time of the snake robot. the experiments were conducted using different values of servomotor rotation speed, starting from rotation speed code ‘30’ (0.77 rad/s) until rotation speed code ‘60’ (1.43 rad/s) with a 5-step increment. meanwhile, the winding angle was varied from 20o to 45o with a 5-step increment also. as seen in the above figure, all the curves demonstrate a similar trend, which shows that the travelling time is inversely proportional to the servomotor rotation speed. in other words, increasing the servomotor rotation speed can decrease the travelling time of the snake robot. it is also noticed that the travelling time increased when the winding angle was above 30° as the body of snake 10 15 20 25 30 35 40 45 50 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 t ra v e lli n g t im e ( s) servomotor rotation speed (rad/s) winding angle 20 ° 25 ° 30 ° 378 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 robot became more twisted. therefore, the objective of decreasing the travelling time of the snake robot when it is used for exploration task can be achieved by simply increasing the rotation speed of the servomotors. the speed range used in these experiments considered the limitations of the servomotors. therefore, the minimum rotation speed selected was 0.77 rad/s, since the speed below this value is relatively slow, while the maximum speed was 1.43 rad/s, as controlling the snake robot became difficult beyond that speed. 5.2 effect of winding angle on energy consumption the following experiment aims to find the relationship between the winding angle of a snake robot and the energy consumption after travelling a specific distance. this experiment was actually a part of the previous experiment, where the actual time needed by the snake robot to travel for 3 meters and 6 meters was measured and recorded. as mentioned in the previous experiment, the range of winding angle was 20° to 45° while the range of servomotor rotation speed was from 0.77 rad/s to 1.43 rad/s. in this experiment, the acceleration of the snake robot or, in other words, the servomotor rotation speed was kept constant (e.g. 1.43 rad/s) while the winding angle was varied within a range of 30° to 60°. later on, the experiment was repeated using different values of winding angles while the servomotor rotational speed was kept constant. in this case, increasing the winding angle will obviously increase the undulation of the snake robot and consequently reduce its length (along the body axis) as shown in fig. 10, which demonstrates snapshots of a snake robot with three different winding angles. 𝛼 = 20° 𝛼 = 30° 𝛼 = 45° fig. 10: undulation of the snake robot with different winding angles. based on the above figure, increasing the undulation of the snake robot increases the travelling distance (because of the body shrinking), thus, the snake robot will take a longer time to reach its destination. the energy consumptions were measured starting from the beginning of each travel until the end of each travel of the snake robot using a digital wattmeter. the results of these experiments for 3 meters and 6 meters travelling distances are presented in tables 8 and 9, and plotted in figs. 11 and 12 respectively. 379 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 table 8: energy consumption for 3-meter distance (wh) winding angle (°) servomotor rotation speed (rad/s) 0.77 0.79 0.87 0.98 1.12 1.26 1.43 20 72 72 86 65 65 65 58 25 72 72 65 65 65 72 58 30 79 79 72 72 72 58 65 35 79 79 86 72 72 72 65 40 86 94 94 94 79 79 72 45 101 101 94 94 101 94 86 table 9: energy consumption for 6-meter distance (wh) winding angle (°) servomotor rotation speed (rad/s) 0.77 0.79 0.87 0.98 1.12 1.26 1.43 20 137 122 115 122 115 108 108 25 137 122 122 122 122 115 108 30 130 122 115 122 115 115 101 35 137 144 137 130 130 130 115 40 158 166 158 151 144 144 137 45 173 166 166 166 173 158 144 fig. 11: energy consumption for 3-meter distance. fig. 12: energy consumption for 6-meter distance. 40 50 60 70 80 90 100 110 120 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 e n e rg y co n su m p ti o n ( w h ) servomotor rotation speed (rad/s) winding angle 20° 25° 30° 35° 40° 45° 80 100 120 140 160 180 200 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 e n e rg y co n su m p ti o n ( w h ) servomotor rotation speed (rad/s) winding angle 20° 25° 30° 35° 40° 45° 380 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 the experiments were conducted using different values of servomotor rotation speed, starting from rotation speed code ‘30’ (0.77 rad/s) until rotation speed code ‘60’ (1.43 rad/s) with a 5-step increment. meanwhile, the winding angle was varied from 20o to 45o with a 5-step increment. the curves in both the figures demonstrated a general trend showing that energy consumption is inversely proportional to the servomotor rotation speed. however, that is not the case in some ranges such as in the range between the rotation speed of 0.87 rad/s and 1.12 rad/s for the winding angles 25° and 30°. furthermore, it can be noticed from figs. 11 and 12 that doubling the travelling distance did not necessarily double the energy consumption. instead, the energy consumption for the 6 meters travelling distance increased in the range of 1.3 to 2 times the energy consumption of the 3 meters travelling distance for different winding angles and servomotor speeds. on the other hand, the direct proportional relationship between the winding angle and the energy consumption can be seen clearly in both figures, which means that increasing the winding angle increases the energy consumption. however, the curve of 30° winding angle demonstrates an exception as it shows less energy consumption than the 25° curve, and even less than the 20° curve in some points. it can be deduced from the above analysis that minimizing energy consumption can be achieved by selecting a low value of winding angle. however, the practical experiment proved that the optimal winding angle is not necessarily the one with minimum value as seen in fig. 11, where the 30° curve shows the minimum energy consumption despite it not being the minimum winding angle. therefore, from an optimization perspective, selection of the winding angle of 30° could achieve the minimum energy consumption in serpentine locomotion of the snake robot. 6. comparison of simulation and experimental results a comparison is conducted between simulation results as shown in fig. 13 and experimental results shown in fig. 12, with respect to energy consumption and travelling speed of the snake robot. in both simulation and experiment, the snake robot was tested for travelling for a specific distance using different values of winding angle and rotation speed at each time. the trend of energy consumption is divided into three regions as shown in fig. 13. in the first region (region 1) and the last region (region 3), the energy consumption is directly proportional to acceleration, while the middle region (region 2) demonstrates an inversely proportional relationship. by comparing both figures, it can be seen that energy consumption in fig. 12 is inversely proportional to servomotor rotation speed, which matches the trend of the middle region (marked with a red rectangle) in fig. 13, where the energy consumption is inversely proportional to acceleration. although the x-axes are not the same in both figures, they both lead to the average speed of the snake robot. it can be concluded from the above figures that the rotation speed of the servomotors used in this experiment is limited. therefore, the experimental energy consumption shown in fig. 12 cannot demonstrate the trend of region 3 of the simulation results as seen in fig. 13. 381 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 fig. 13: energy consumption in simulation results. moreover, simulation results show that for achieving the objectives of minimizing travelling time and energy consumption the minimum winding angle and fastest rotation speed should be selected. on the other hand, the experimental results demonstrated different behaviour when servomotor rotation speed was set above 1.2 rad/s as seen in fig. 9. in the mentioned figures, winding angles 25° and 30° showed less travelling time than the winding angle 20°. moreover, the experimental results in fig. 12 show that the minimum energy consumption can be achieved using the winding angle of 30°. finally, it was experimentally found that the winding angle of 30° is the optimum winding angle that can achieve the objectives of minimizing the energy consumption and the travelling time when the snake robot travels in serpentine locomotion. 7. conclusion in this paper, a multi-objective optimization for snake robot locomotion is presented. the model of the snake robot is introduced including the dynamic effects of the environment including friction. the equations listed in this paper describe the model of the snake robot travelling in serpentine locomotion besides necessary calculation of energy consumption and average speed of the snake robot. simulation results show that acceleration has a contradictory effect on average speed and energy consumption, while the initial value of winding angle affects both energy consumption and average speed analogously. matlab gamultiobj function was used to achieve two objectives: minimizing the total travelling time and minimizing the total energy consumption by obtaining the pareto-optimal front. the comparison of selected and optimized parameters shows the validity of using a multi-objective optimization technique for snake robot locomotion to achieve both objectives. on the other hand, the experimental results conformed with the simulation results regarding the effect of acceleration on energy consumption except for the winding angles of 25°and 30°, which demonstrated less energy consumption than the winding angle of 20° when the servomotor rotation speed was above 1.2 rad/s. furthermore, the experimental results showed that the winding angle 30° was the optimum winding angle that can achieve both objectives of minimizing the energy consumption and the travelling time. 0 2 4 6 8 10 12 14 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 e n e rg y co n su m p ti o n ( jo u le ) acceleration (m/s2)      region 1 region 2 region 3 382 iium engineering journal, vol. 22, no. 2, 2021 badran et al. https://doi.org/10.31436/iiumej.v22i2.1691 acknowledgement the authors profoundly acknowledge the ministry of higher education (mohe), malaysia for funding this research through the fundamental research grant scheme (grant no. frgs130720313). references [1] gray j. (1946) the mechanism of locomotion in snakes. journal of experimental biology, 23(2): 101-120. [2] hirose s, mori m. (2004) biologically inspired snake-like robots. robotics and biomimetics, 2004. robio 2004. ieee international conference on (pp. 1-7). ieee. [3] hirose s. (1993) biologically inspired robots: snake-like locomotors and manipulators, vol. 1093. oxford: oxford university press. [4] saito m, fukaya m, iwasaki t. (2002) modeling, analysis, and synthesis of serpentine locomotion with a multilink robotic snake. ieee control systems magazine, 22(1): 64-81. [5] chen l, ma s, wang y, li b, duan d. (2007) design and modelling of a snake robot in traveling wave locomotion. mechanism and machine theory, 42(12): 1632-1642. [6] chernousko fl. (2005) modelling of snake-like locomotion. applied mathematics and computation, 164(2): 415-434. [7] ariizumi r, matsuno f. (2017) dynamic analysis of three snake robot gaits. ieee transactions on robotics, 33(5): 1075-1087. [8] sanfilippo f, azpiazu j, marafioti g, transeth aa, stavdahl ø, liljebäck p. (2017) perception-driven obstacle-aided locomotion for snake robots: the state of the art, challenges and possibilities. applied sciences, 7(4): 336. [9] wang z, gao q, zhao h. (2017) cpg-inspired locomotion control for a snake robot basing on nonlinear oscillators. journal of intelligent & robotic systems, 85(2): 209-227. [10] trebuňa f, virgala i, pástor m, lipták t, miková ľ. (2016) an inspection of pipe by snake robot. international journal of advanced robotic systems, september-october, 1-12. [11] bando y, suhara h, tanaka m, kamegawa t, itoyama k, yoshii k, ... & okuno hg. (2016) sound-based online localization for an in-pipe snake robot. in 2016 ieee international symposium on safety, security, and rescue robotics (ssrr) (pp. 207-213). ieee. [12] whitman j, zevallos n, travers m, choset h. (2018) snake robot urban search after the 2017 mexico city earthquake. 2018 ieee international symposium on safety, security, and rescue robotics (ssrr) (pp. 1-6). ieee. [13] chen l, ma s, wang y, li b, duan d. (2007) design and modelling of a snake robot in traveling wave locomotion. mechanism and machine theory, 42(12): 1632-1642. [14] saito m, fukaya m, iwasaki t. (2002) modeling, analysis, and synthesis of serpentine locomotion with a multilink robotic snake. ieee control systems magazine, 22(1): 64-81. [15] kelasidi e, jesmani m, pettersen ky, gravdahl jt. (2018) locomotion efficiency optimization of biologically inspired snake robots. applied sciences, 8(1): 80. [16] liu j, wang y, ii b, ma s. (2004) path planning of a snake-like robot based on serpenoid curve and genetic algorithms. in intelligent control and automation, 2004. wcica 2004. fifth world congress on (6: 4860-4864). ieee. [17] hasanzadeh s, tootoonchi aa. (2008) adaptive optimal locomotion of snake robot based on cpg-network using fuzzy logic tuner. in robotics, automation and mechatronics, 2008 ieee conference on (pp. 187-192). ieee. [18] jafari m, shahmansoorian a. (2014). pi/backstepping control of snake robot optimized by genetic algorithm. in electrical and computer engineering (ccece), 2014 ieee 27th canadian conference on (pp. 1-6). ieee. [19] rao ss, rao ss. (2009) engineering optimization: theory and practice. john wiley & sons. [20] marler rt, arora js. (2010). the weighted sum method for multi-objective optimization: new insights. structural and multidisciplinary optimization, 41(6): 853-862. 383 application of digital cellular radio for mobile location estimation iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 87 influence of polarization mode dispersion on the effect of cross-phase modulation in intensity modulation-direct detection wdm transmission system m. s. islam1* and s. p. majumder2 1institute of information and communication technology 2department of electrical and electronic engineering bangladesh university of engineering and technology, dhaka-1000, bangladesh. * 1. introduction e-mail: mdsaifulislam@iict.buet.ac.bd abstract: cross-phase modulation (xpm) changes the state-of-polarization (sop) of the channels through nonlinear polarization rotation and induces nonlinear time dependent phase shift for polarization components that leads to amplitude modulation of the propagating waves in a wavelength division multiplexing (wdm) system. due to the presence of birefringence, the angle between the sop changes randomly and as a result polarization mode dispersion (pmd) causes xpm modulation amplitude fluctuation random in the perturbed channel. in this paper we analytically determine the probability density function of the random angle between the sop of pump and probe, and evaluate the impact of polarization mode dispersion on xpm in terms of bit error rate, channel spacing etc for a two channel intensity modulation-direct detection wdm system at 10 gb/s. it is found that the xpm induced crosstalk is polarization independent for channel spacing greater than 3 nm or pmd coefficient larger than 2 ps/√km. we also investigate the dependence of sop variance on pmd coefficient and channel spacing. keywords: polarization mode dispersion, cross-phase modulation, state of polarization, birefringence, bit error rate. cross-phase modulation (xpm) is a nonlinear phenomena occurring in optical fibers when two or more optical fields are transmitted through a fiber simultaneously. it has an important impact on the performance of high-speed wavelength division multiplexing (wdm) in optical fiber communication systems [1]. in the last few years, many research works have been carried out on the interaction among fiber nonlinearity, polarization variation and polarization mode dispersion (pmd) [2-8]. physically, pmd has its origin in the birefringence that is present in any optical fiber. just like signal distortion due to chromatic dispersion and nonlinearity accumulate along the length of the communication link, so does the polarization and pmd. polarization fluctuations and pmd become increasingly important as the per-channel data rates have increased and now arguably the most important of the polarization effects. lin and agrawal [4], developed a vector theory of xpm in optical fiber and used to investigate the effect of pmd on xpm crosstalk in a wdm system in terms of amplitude of the probe fluctuation induced by a co-propagating pump channel and found that pmd reduces the difference in the average crosstalk level iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 88 between cases of copolarized and orthogonally polarized channels. zhang et al. [5], experimentally reported that self-phase modulation (spm) can suppress pmd penalty and xpm-induced polarization scattering can reduce the pmd impairment in single channel and dense wdm transmission system respectively. here, we focus for simplicity on the pump-probe configuration and neglect pulse broadening induced by group velocity dispersion (gvd), but includes the group velocity mismatch between the pump and probe owing to their different wavelength. we use jones-matrix formalism for pumpor probe field evolution and stokes-vector formalism for sop of pump and probe change on the poincare sphere. pmd-induced fluctuation is the relative orientation between the pump and probe sop which causes the xpm modulation amplitude to be random. in this paper we analytically determined the probability density function (pdf) of the random angle ( )zθ between the pump and probe sop fluctuation that produce intensity dependent pulse distortion on a propagating signal. using the pdf we analyzed the impact of pmd on xpm in terms of average bit error rate (ber) for an intensity modulation-direct detection (im-dd) wdm system at a bit rate of 10 gb/s. we also find the variance of the sop between pump and probe with respect to fiber link and channel spacing. to our knowledge the influence of pmd on xpm in terms of ber is yet to be reported. 2. system model the block diagram of a pump-probe configuration wdm system with edfa in cascade used for theoretical analysis is shown in fig. 1. the pump and probe are multiplexed by wdm mux and the composite signal is transmitted through a standard single mode fiber (smf). to describe the effect of pmd on xpm, we assume that the pump, 1a act as channel 1, which modulates the transmitted ( 1f ) data from the laser diode at wavelength, 1λ and the probe, 2a act as channel 2, which is a low-power continuous wave (cw) at wavelength, 2λ . the in-line edfa’s are used in cascade to compensate the fiber losses. finally, the composite signal is demultiplexed at wdm demux and from the modulated carrier; 2λ original signal 1f is recovered through imdd method. fig. 1: block diagram of a 2-channel wdm system with edfa in cascade. iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 89 3. theoretical analysis 3.1 modulation of the probe field the probe is assumed to be weak enough that the spm, xpm and intrachannel pmd induced by it can be neglected. although these effects broadens pulse in each channel, they barely affect the interchannel xpm interaction because the channel spacing typically is much larger than channel bandwidth and the evolution of sop of the channels is mainly governed by the birefringence. the xpm induces a time dependent phase shift as well as nonlinear polarization rotation on the probe channel that cause the xpm induced modulation amplitude to be random. the cw probe field is modulated by the pump field by the combination of xpm and pmd. to study the temporal modulation of cw probe field as a consequence of pump field, let us linearize the probe field 2a by assuming unperturbed, 20a and perturbed, 21a probe fields respectively. with these simplifications, we can write the following equations for pump and probe field evolutions as [4], 11 111 aa aaa 01 1 2 2 21 1 22 pi i z ε− α − τ∂ ∂β − τ∂ ∂ δβ−= ∂ ∂ (1) 2020 20 ab.σa a ω− α −= ∂ ∂ 22 2 i z (2) [ ])(3 22 00 2 22 2 22 zcosθsp ii z + ε +α− τ∂ ∂β −= ∂ ∂ 2120 21202120 aa aaaa (3) where, 11 aa=0p and 2020 aas =0 are the pump and unperturbed probe power; 0 ˆ pp 11 aσa= and 0ˆ saσa 2020=s are the unit vector representing the sop of the pump and unperturbed probe on the poincare sphere; )( 12 ω−ω=ω is the channel spacing, 11 98 γ=ε and 22 98 γ=ε are the effective nonlinear parameters, )(ˆˆ)( zspz .=θ is the random angle between the pump and probe sop, )( 12111 β−β=δβ is the group velocity mismatch between the two channels and )( 12 zt β−=τ is the reduced temporal variable. from (1) we see that the pump polarization p̂ remain fixed in the rotating frame. however, pmd changes the relative orientation between the pump and probe stokes vectors at a rate dictated by the magnitude of channel spacing and relative birefringence ( bω ). the total optical power of the probe field is given by, [ ] 002120202022 δssaaaaaa +≡++≈ .. cc (4) where 0δs is the modulation amplitude, which is a measure of the xpm induced crosstalk. pmd randomly changes the angle between p̂ and (z)ŝ along the fiber and thus probe field modulation amplitude becomes a random quantity. solving equation (3) iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 90 analytically and introducing the normalized modulation amplitude as, )(),( ~ )( ~ 00 lslsx ωδ=ωδ ; we obtain, [ ] dzdzzzθcoszz l z l x       βω+ωε−=ωδ ∫∫ 11222 0 2 )(2 1 sin)(3),( ~ )()( ~ 0p (5) where a tilde denotes the fourier transform and ),( ~ ωz0p is the fourier spectrum of the pump power at a distance z inside the fiber and 22β is the gvd coefficient of the pump. 3.2 pdf of )(zθ , sop and crosstalk variance since the pump polarization p̂ remains constant and the random variation of (z)ŝ (unit vector of sop of the probe) will be responsible for the randomness of )(zθ . thus to find the pdf of the angle )(zθ between pump and probe, we assume that it is driven by the white noise process and can be written as, )(ˆ zs dz d = θ (6) where, 0)(ˆ =zs (7) )()(ˆ)(ˆ 12 2 21 zzzszs −δη= (8) where 31 22ω==η pd dl ; 12 ω−ω=ω is the channel spacing and pd is the pmd parameter. this model captures all the essentials of the more realistic case in which both the angle )(zθ and birefringence vary randomly. from equation (8) a diffusion equation for the probability distribution of )(zθ or simply θ can be obtained [9], 2 2 2 2 1 θ∂ ∂ η= ∂ ∂ p z p (9) where ),( zp θ is π2 periodic in θ and )(),0( 0θ−θδ=zp . 0θ is the value of θ at 0=z , 0θ is the relative angle between the pump and probe sops at the input end of the fiber. by solving the equation (9) we get the pdf )(zθ and expressed as, )(cos) 2 1 exp( 1 2 1 ),( 0 22 1 θ−θη− π + π =θ ∑ ∞ = mzmzp m (10) the sop of the pump and probe depends on the power and bit pattern of the pump. the sop fluctuates with time because of its doubly in nature. in the absence of residual birefringence, randomness comes only from the bit pattern. the sop of pump and probe variance can be obtained by taking the inverse fourier transform of equation (8) along the fiber link length l, iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 91 { }       −δηωω π = =σ ∫ ∫∫∫ ∫∫ ∞ ∞ ∞ ∞ − l l ll sop zzdzdzdd zszsfdzdz 0 0 21 2 21 _ 2 _ 12 21 1 0 2 0 1 2 )( 4 1 )(ˆ)(ˆ (11) to find the ),( ~ ωz0p , we assume that the effects of dispersion and nonlinearities do not significantly change the pulse shape of the pump channel along the fiber and analytically solving(1), we then obtain, [ ]       δβω+α−ω=ω ∫ z dzzizz 0 1111100 )()(exp),0( ~ ),( ~ pp (12) substituting this expression in (5), we obtain the following analytic result for the xpminduced crosstalk, [ ] dzzfzcosθ l x )()(3),0( ~ )( ~ 0 ∫ +ω=ωδ 0p (13) where the function )(zf takes into account loss and dispersion variation along the fiber link and is given by, [ ] dzdzzdzzizzzf l z z       βω       δβω+α−ε−= ∫∫ 11222 0 111112 )(2 1 sin)()(exp)()( (14) the crosstalk level changes with time depending on the bit pattern in the pump channel. thus, )(τδ x fluctuates with time and the crosstalk variance, also called xpm-induced interference can given by, [ ]       ω−ω ωδωδωω π = ττδ≡σ ∫∫ ∫ ∞ ∞− ∞ ∞− − 2 )( )( ~ )( ~ 4 1 )( 1 21 2 * 1212 2 2 22 t incsdd d t xx t t xm (15) where, t is the time interval of measurement. usually the measurement time t is small compared with the fluctuation time of pmd and birefringence fluctuations remain frozen during measurement. 3.3 bit error rate (ber) expression the output noise contributed by the photodetector quantum shot noise, the receiver thermal noise, the interferometric noise due to input intensity fluctuation. the different spectral densities of the noises are: iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 92 bwieprfs sdpd 22)( == (16) l thth r bwkt ifs 4 )( 2 == (17) )]()([5.0)( 222 fxfsprfs xsdpdi δ − −= (18) where )( fs x and − x represent the psd and the mean value of x(t) respectively and δ(f) is a delta function in frequency. denoting the total noise power spectral density by, )()()()( fsfsfsfs pdithpdn ++= (19) the total noise power (noise variance) at the receiver output can be obtained as, dffhfs rnn 22 )()(∫ ∞ ∞− =σ (20) where, )( fh r is the transfer function of a gaussian low-pass filter in the receiver of 3-db bandwidth equal to 0.75 b. the signal to crosstalk noise ratio (scnr) can be written as, 22 2 0 )( nm d srscnr σ+σ = (21) where 2mσ crosstalk variance due to pmd, dr is the responsivity and 0s is the probe power and 0sri ds = . thus, 2 0 2 2 0 )( )( nm siangleforscnr σ+θσ =θ (22) for a given value of 0θ , the conditional ber can be expressed as         θ =θ 2 )( 5.0)( 00 angleforscnr erfcber (23) because of environmental changes (i.e., temperature, pressure, vibration, stress, twisting etc.), pmd fluctuates randomly. generally, the impact of pmd fluctuations as well as the variation of angle, )(zθ between the pump and probe sop typically occurs on a time scale of milliseconds. thus the average ber is given by, θθθ= ∫ π π− dzpberber ),()( 0 (24) iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 93 4. results and discussion following the analytical approach, we investigate the influence of pmd on xpm of the pump-probe configuration of im-dd wdm system at a bit rate of 10 gb/s. the pdf of the random polarization angle between pump and probe is evaluated at various length of single mode fiber and shown in fig. 2. from the figure, it is found that for particular channel spacing the pdf is a delta function at 0=z and becomes flat as the link length increases. it is observed that for any lightwave system of fiber length much larger than the diffusion length ( =eh 280 m 1.5 km), pdf become gaussian like distribution. fig. 2: plots of pdf of )(zθ at different length of fiber link. figure 3 shows the variance of pump and probe polarization sop versus fiber link length for different pmd coefficient. it is noticed that as the pmd coefficient increases, the variance of sop also increases linearly. thus the fibers which have higher values of pmd (usually older fiber) will subject to larger amount of amplitude modulation fluctuation. fig. 3: plots of variance of sop against fiber link length for different pmd parameters. iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 94 the average ber versus pump power is plotted in fig. 4. it is observed that interaction of pmd and xpm increases as the channel spacing decreases for a specific pump power and system suffers a large amount of ber. the significant dependence of xpm effect on ber as a function of channel spacing comes from the fact that the pmd diffusion length is inversely proportional to the square of the channel spacing. however, at increased pump power the ber increases and when pump power is about 16 dbm the ber curves makes a floor at 10-1 irrespective of channel spacing. fig. 4: plots of average ber against pump power for different channel spacing. the plots of average ber versus probe power is shown in fig.5. it is seen that at high pump and probe power the ber performance of the fiber link deteriorates sharply. this happens due to the strong interaction of pmd and xpm on each other channel. for example, when the pump power is -15 dbm, we can achieve a ber of 10-9 for a 6.25 dbm probe power. keeping the probe power same, it is found that at 25 dbm pump power the ber drops to a value of 10-1 only. this happens due to the higher modulation amplitude fluctuation as a result of high pump power. fig. 5: plots of average ber vs probe power for different pump power. iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 95 figure 6 depicts the variance of sop as a function of channel spacing for different length. for smaller channel spacing and short length of fiber link the variance is very negligible. as the link length increases and so does the channel spacing, the variances increases exponentially for larger values of channel spacing. fig. 6: plots of variance of sop against channel spacing ( λ∆ ) for different link length. 5. conclusion an analytical approach is used to investigate the effect of pmd and xpm interaction in a two channel pump-probe configuration wdm system using smf. we determine the probability distribution function of the random sop angle between the pump and probe in an im-dd wdm system, which causes the xpm induced modulation amplitude to be random. the strength of the xpm effect is strongly influenced by the evolution of lightpolarization of the wdm carriers. our results show that the xpm induced crosstalk becomes polarization independent when channel spacing is large ( i.e., λ∆ > 3 nm) or when the fiber has a relatively large value of pmd coefficient (i.e., kmpsd p /2> ) . thus at relatively high pump the combination of nonlinearity and pmd can limit the performance of a dense wdm fiber link significantly. acknowledgement this research work has been carried out as a part of ph.d thesis work in the department of electrical and electrical engineering (eee) of bangladesh university of engineering and technology (buet), dhaka, bangladesh. iium engineering journal, vol. 10, no. 2, 2009 islam and majumder 96 references [1] p. i. killey, h. j. thiele, v. mikhailove and p. bayvel, “prediction of transmission penalties due to cross-phase modulation in wdm systems using simplified technique’, ieee photon. technol. lett., vol.12, no.7, 804 806, 2007. [2] n. hanik “influence of polarization mode dispersion on the effect of cross-talk modulation in optical wdm transmission”, proc. of the 6th international conference on transparent optical networks (icton’04), vol.1, 90-194, 2004. [3] a. bononi, a. vanocci, a. orlandini, e. corbel, s. lanne and s. bigo, “degree of polarization degradation due to cross-phase modulation and its impact on polarization mode dispersion”, j. lightwave technol., vol. 21, no.9, 1903-1913, 2003. [4] q. lin and g. p. agrawal, “effects of polarization mode dispersion on cross-phase modulation in dispersion managed wavelength-division-multiplexed systems”, j. lightwave technol., vol. 22, no. 4, 977-987, 2004. [5] g. zhang, j. t. stango, x. zhang and c. xie, “impact of fiber nonlinearity on pmd penalty in dwdm transmission systems,” ieee photon. technol. lett., vol.17, no. 2, 501-503, 2005. [6] c. r. menyuk and b. s. mark, “interaction of polarization mode dispersion and nonlinearity in optical fiber transmission systems”, j. lightwave technol., vol. 24, no.7, 2806-2826, 2006. [7] r. khosravani, y. xie, l. -s. yan, a. e. willner and c. r. menyuk, “bit pattern dependent polarization rotation in the first-order pmd-compensated wdm systems”, optics communications, 191-196, 2005. [8] l. moller, y. su, g. raybon, s. chandrasekar and l. l. buhl, “penalty interference of nonlinear intra-channel effect and pmd in ultra-high speed tdm systems”, electron lett., vol.38, no.6, 281-283, 2002. [9] p. k. a wai and c. r. menyuk, “polarization mode dispersion, decorrelation and diffusion in optical fibers with randomly varying birefringence,” j. lightwave technol., vol.14, no.2, 148-157, 1996. tunable bandpass filter using rf mems switches 2.1 one mems bridge parallel with the resonator 2.2 two mems bridge parallel with the resonator 2.3 one mems bridge perpendicular to the resonator 2.4 mems bridges parallel and covering all the resonators acknowledgement references keywords : quantum cryptography, quantum key distribution, decoy state protocol, optical communications 2. experimental setup influence of polarization mode dispersion on the effect of cross-phase modulation in intensity modulation-direct detection wdm transmission system introduction system model theoretical analysis 3.1 modulation of the probe field results and discussion conclusion acknowledgement references towards a scalable scientific data grid model and services introduction related works the p2p data grid model the simulation study experiments and results conclusion and future work references anomalous electrodeposition of fe-ni alloy coating from simple and complex baths and its magnetic property microsoft word 4_vol17_no1_2016_(compiledversion_4).docx iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 83 a review on lower appendicular musculoskeletal system of human body m. akhtaruzzaman*, a. a. shafie, and m. r. khan department of mechatronics engineering, faculty of engineering, international islamic university malaysia, 53100 kuala lumpur, malaysia. *akhter900@gmail.com, aashafie@iium.edu.my, and raisuddin@iium.edu.my (received: 20 jul. 2015; accepted: 24 dec. 2015; published on-line: 30 apr. 2016) abstract: rehabilitation engineering plays an important role in designing various autonomous robots to provide better therapeutic exercise to disabled patients. hence it is necessary to study human musculoskeletal system and also needs to be presented in scientific manner in order to describe and analyze the biomechanics of human body motion. this review focuses on lower appendicular musculoskeletal structure of human body to represent joints and links architectures; to identify muscle attachments and functions; and to illustrate muscle groups which are responsible for a particular joint movement. firstly, human lower skeletal structure, linking systems, joint mechanisms, and their functions are described with a conceptual representation of joint architecture of human skeleton. this section also represents joints and limbs by comparing with mechanical systems. characteristics of ligaments and their functions to construct skeletal joints are also discussed briefly in this part. secondly, the study focuses on muscular system of human lower limbs where muscle structure, functions, roles in moving endoskeleton structure, and supporting mechanisms are presented ellaborately. thirdly, muscle groups are tabulated based on functions that provide mobility to different joints of lower limbs. finally, for a particular movement action of lower extremity, muscles are also grouped and tabulated to have a better understanding on functions of individual muscle. basically the study presents an overview of the structure of human lower limbs by characterizing and classifying skeletal and muscular systems. abstrak: kejuruteraan pemulihan memainkan peranan yang penting dalam mereka bentuk pelbagai robot autonomi untuk menyediakan latihan terapeutik yang lebih baik untuk melumpuhkan pesakit. jadi, ia adalah perlu untuk mengkaji sistem otot manusia dan perlu disampaikan secara saintifik untuk menerangkan, dan menganalisis biomekanik gerakan tubuh manusia. kajian ini memberi tumpuan kepada struktur otot appendicular bawah badan manusia untuk mewakili sendi dan menghubungkan seni bina; mengenal pasti lampiran otot dan fungsi; dan menggambarkan kumpulan otot yang bertanggungjawab untuk pergerakan sendi tertentu. pertama, struktur rangka yang lebih rendah manusia, sistem yang menghubungkan, mekanisme sendi dan fungsi mereka adalah seperti yang dinyatakan dengan perwakilan konsep seni bina bersama rangka. seksyen ini juga mewakili sendi dan anggota badan dengan membandingkan dengan sistem mekanikal. ciri-ciri daripada ligamen dan fungsi mereka untuk membina sendi tulang juga dibincangkan secara ringkas di bahagian ini. kedua, kajian memberi tumpuan kepada sistem otot anggota badan manusia yang lebih rendah. struktur otot, fungsi, peranan dalam menggerakkan struktur rangka dalam, dan menyokong mekanisme yang dibentangkan di dalam bahagian ini. ketiga, kumpulan otot adalah jadual berdasarkan fungsi yang menyediakan mobiliti kepada sendi yang berbeza anggota badan yang lebih rendah. akhir sekali, untuk tindakan gerakan tertentu hujung yang lebih rendah, otot juga dikumpulkan dan dijadualkan untuk mempunyai pemahaman yang lebih baik mengenai fungsi otot iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 84 individu. pada asasnya kajian mewakili gambaran keseluruhan struktur anggota bawah manusia dengan mencirikan dan mengelaskan sistem rangka dan otot. keywords: musculoskeletal system; human lower limbs; muscle groups; joint motion; biomechatronics; rehabilitation. 1. introduction stroke is one of the major causes for morbidity and disability, both in the developed and developing countries [1]. it is a common neurological disorder that causes post-stroke depression among survivors. many survivors suffer from physical and psychological disabilities. one study presents that 66% of 80 stroke patients were in post-stroke depression where 51% were in mild, 11% were in moderate and 4% were in severe condition [2]. about 15 million people globally suffer from stroke where 5 million people die and 5 million become permanently disabled [3, 4]. neurological impairment of post-stroke patient often conducts to hemiparesis (partial paralysis of one side of body). hemiparesis can lead to profoundly impaired functional performance of daily activities such as running, walking, standing, speaking, and eating. it is observed that, at 6 months of post-stroke, about 50% of survivors get hemiplegia, 30% are unable to walk and 26% become dependent for their daily activities [5]. nowadays robot assisted therapy is increasingly attractive in stroke rehabilitation both for upper and lower limbs of human body [6, 7]. robotic systems unfold a wide range of opportunities to study on functional adaptation of various limbs of post-stroke patients [8 10]. robotic tools also provide opportunity to observe and measure improvements of functionality of a particular muscle as well as limbs [11-14]. robot assisted therapy for lower limbs shows successful improvements in functional limitations of stroke patients with reduction of motor impairments [5, 15]. basically, robotic skeletal arm provides external force to perform limb motions of lower extremity so that muscle and joint system mobility remains active. this therapeutic exercise also improves the nervous system of human lower limbs. the activity can be represented in a block diagram as presented in fig. 1. fig. 1: block diagram of musculoskeletal system activity process versus rehabilitation. it is very important to keep in mind that simply movement (passive exercise) of impaired limbs do not provide maximum recovery level for a stroke patient. recognition of cortical functionalities, feedback control, and learning of motors are also involved in intense use of impaired limbs. studies on the response of complex biological systems, in terms of its mechanics and electronics, is the focus of biomechatronics engineering. therefore, understanding musculoskeletal structure of biological systems especially the human body iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 85 becomes very important in biomechatronics engineering research. in this review, only musculoskeletal structure of human lower extremity is studied to present endoskeletal joint structures, muscle attachments, muscle groups, and muscle functionalities of a particular movement of lower limbs. studies on biomechanics and biomechatronics of musculoskeletal system provides better understanding of joint movements, trajectories, joint functions, and dynamic properties of biological systems [16]. appropriate design of various mechanical and robotic systems such as artificial joint, orthotic devices, medical therapeutic devices, robot assisted system, exoskeleton etc. are also required for a proper analysis and understanding of musculoskeletal systems [17] and functions of biological systems so that any secondary injury can be avoided. 2. skeletal system of human lower limbs the human musculoskeletal system has a primary responsibility to interact with physical environment to produce normal movement. balancing body and normal locomotion, especially walking, are ensured by proper functioning musculoskeletal structure of the lower limbs of human body. the lower limbs also support superior parts of a body such as neck, head, and torso. basically, human body is the accumulation of a number of independent systems. holding structure and balancing body movements are controlled by nervous system, vascular system, skeletal system, muscular system, ligaments, and tendons [18]. for the purpose of lower limbs rehabilitation, it is important to understand the functions of lower torso of human body as well as functions of independent systems of musculoskeletal structure. study on functions of lower extremity not only focuses on a single joint movement, but also refers to the structure and behavior of limbs, pelvis, and trunk [18]. figure 2 presents structure of human endoskeletal system. fig. 2: anterior and posterior view of human endoskeletal structure focusing on the lower extremity of the system [22]. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 86 human body musculoskeletal structure is formed based on endoskeleton of human body that consists of rigid bones. skeletal system not only provides structural support but also ensures protection, functions as levers, works as storage (of minerals and fats), and helps in blood cell formation [18]. lower extremity of human skeletal system consists of pelvic girdle segment, thigh (proximal segment), shank (distal segment/lower leg), and foot. connection portions of segments are called joints. most of the joints of lower limbs are synovial joints (joint so articulated as to move freely) with cavities that contain synovial fluid [18,19]. all of these joints are almost frictionless (fr ≈ 0) comparing to any other systems in the world and are also highly efficient shock absorbers [19]. hip, knee, and ankle are the largest articulated joints of lower extremity of human endoskeleton. these joints are holding segments (bones) in place through a system of cartilage, tendons, and ligaments [18-20]. figure 3 shows a conceptual architecture of the joints of human musculo-skeletal system. fig. 3: basic and conceptual architecture of joint in human musculoskeletal system. 2.1. pelvis girdle between torso and lower limbs, pelvic girdle plays an important role as a crucial linking system that acts as a fulcrum in between actions of upper and lower extremities [18,19]. movement of one leg is counter balanced by other leg through the anatomical structure of pelvic. hip joint mechanism of musculoskeletal system is structurally supported by the pelvic girdle [20,21]. pelvis is formed by three bones; ilium, ischium, and pubic symphysis [21,22] as shown in fig. 4(a). pubic symphysis is a kind of cartilaginous joint. this type of joint has slight movement capability which separates articulating surface of contingent bones [22]. this type of joint exists between bodies of vertebrae and also in structure of ribcage. slight movement capability of joint allows pelvic girdle work as a suspension system while walking, running, and jumping especially on uneven surface. (a) (b) fig. 4: pelvic girdle and hip (coxal) joint structure [22], (a) skeleton of pelvis, and (b) hip joint structure (synovial joint). iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 87 2.2. hip joint (coxal joint) joint that is formed at the meeting point of femur head and hip’s acetabulum socket is a perfect example of ball and socket joint as presented in fig. 4(b). this is a type of synovial joint (diarthrotic joint) that allows triaxial movement of lower limbs. synovial joints are the most mobile comparing to all other joints in human skeleton [22]. triaxial movement of lower limbs can be characterized as flexion, extension, abduction, adduction, medial rotation, lateral rotation, and circumduction. figure 5 shows the ligaments of pelvis and hip structure of human endoskeleton. (a) (b) fig. 5: ligaments of pelvis and hip of human skeletal system [23], (a) anterior view of pelvis and hip, (b) posterior view of pelvis and hip. 2.3. knee joint (tibiofemoral joint) lower portion of femur and upper side of tibia (shin bone) are connected together with multiple ligaments at knee joint. there is a small bone at the anterior portion of knee joint which is called as patella. these three bones form the synovial joint (diarthrotic joint) for knee which is an example of a hinge joint with ellipsoidal shape allowing roll and glide movement capability [18,19,22]. patella has sliding movement capability on femoral groove as it is connected with tibia through patella tendon at the bottom side and with quadriceps muscles through quadriceps tendon on the upper side [23]. articular cartilage at the surface of opposing bones provides principal interface of articulation [25]. multiple ligaments at knee ensure stability of the joint [24]. furthermore, lateral and medial meniscus (have loose peripheral attachment to the joint capsule) of knee joint provide extra structural support. studies show that meniscus has about 50% of intrinsic elastic modulus and 10% to 16% of permeability of articular cartilage [19]. so, compressive viscoelastic creep behavior of meniscus is regulated, to a great extent, by interstitial fluid that flows through tissue during compression. two characteristics, low compressive stiffness and low permeability, of menisci prove that the system is able to function as a robust and efficient shock absorber. most of the mechanical shocks are generated at knee joint and absorbed by meniscus. total mass of menisci is much greater than articular cartilage-bearing load across knee joint (femoromeniscotibial articulation) [19]. deformable characteristic of menisci with low compressive, shear stiffness, and permeability ensures well distribution of load at knee joint. tibiofemoral joint (knee joint) allows one degree of freedom (dof) of movement which can be characterized as flexion and extension [22]. knee joint also allows a slight medial and lateral rotation which characterize the joint as biaxial (2 dof) [18]. figure 6 presents knee joint motions and example of hinge joint resembling tibiofemoral joint. ligaments involved to stable tibiofemoral joint are presented in fig. 7. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 88 (a) (b) fig. 6: tibiofemoral joint (knee joint) structure and movements [22], (a) lateral view of tibiofemoral joint representing roll and glide of tibiofemoral joint while flexion and extension, (b) convex-concave surface of a hinge joint that follows the convex-concave rule to determine direction of glide and roll movement. (a) (b) fig. 7: ligaments of tibiofemoral joint [23], (a) anterior and (b) posterior view of right knee joint. 2.4. leg (syndesmosis) leg of human skeleton is formed with two bones, tibia and fibula. these two bones are also firmly attached by interosseus membrane and ligaments. this is fibrous type joint called syndesmosis [22]. this type of joint is more stable as bones are connected tightly together and there is a little (or no) movement at this joint. figure 8 shows skeletal architecture of lower leg and fig. 9 presents syndesmosis (fibrous joint) between tibia and fibula. (a) (b) fig. 8: skeletal structure of human leg, ankle, and foot [26], (a) anterior, and (b) posterior view. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 89 fig. 9: syndesmosis (fibrous joint) of leg formed by ligaments and interosseous membrane [22]. 2.5. ankle joint (talocrural articulation) connection point between lower leg and foot is called ankle joint which also works like a hinge joint. medial malleolus and lateral malleolus of ankle joint are formed by inferior portion of two bones, tibia and fibula, of leg. both malleolus of ankle is connected and attached to main ankle-foot tarsal bone called talus. ankle joint is uniaxial and has only one dof. mobility of ankle joint is characterized as planter flexion and dorsiflexion [18,26]. these movement capabilities of ankle hinge joint drive body forward or backward on sagittal plane. foot is one of the most mobile structures having complex joint mechanisms that supports body to absorb shock of ground contact force and adapt with various surfaces [26]. complex multi joint structure has in total of seven tarsal bones which ensure triaxial movement (3 dof) of a foot. as a result, foot movements are also characterized as inversion and eversion. these tarsal bones are attached to each other such as, talas with calcaneus (heel bone), talas with navicular, calcaneus with cuboid, calcaneus with navicular, navicular with three cuneiforms (medial, internal and lateral), navicular with cuboid, and cuneiform bones with each other. calcaneus bone of tarsal group supports almost 50% of total body weight [18,26]. skeletal structure of a foot is presented in fig. 10. tarso-metatarsal joint comprises four tarsal bones (three cuneiforms and cuboid) connected to five metatarsal bones of toes as shown in fig. 10. first three metatarsal bones are connected with three cuneiform bones accordingly. fourth metatarsal is connected with both lateral cuneiform and cuboid bones. finally, lateral metatarsal is solely connected to cuboid tarsal [18,26]. first and second metatarsals support about 25% of total body weight. rest of the body weight (about 25%) is absorbed by 3rd, 4th, and 5th metatarsals [18]. figure 11 to 14 show ligament structure of a foot skeleton. phalanges of five toes are contacted with five metatarsal bones where each of the phalanges, from 2nd to 5th has three bones (proximal phalanx, middle phalanx, and distal phalanx) and 1st one has two bones, proximal phalanx and distal phalanx, as presented in fig. 10. phalange joints are also considered as hinge joints having 1 dof and movements are characterized as flexion and extension. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 90 (a) (b) fig. 10: skeletal structure of right foot [26]. (a) lateral view, and (b) medial view. fig. 11: ligaments of right foot (lateral view) [26]. fig. 12: ligaments of right foot (medial view) [26]. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 91 fig. 13: ligaments of right foot (posterior view) [26]. fig. 14: ligaments of right foot (inferior view) [26]. 3. muscular system of human lower limbs skeletal muscle plays an important role in protecting endoskeleton against injury, producing joint movements and locomotion. skeletal muscle forms about 40% to 45% of total body weight [21]. rudimentary structural element of skeletal muscle is muscle fiber, a single cell, which is apparently very long but usually shorter than individual muscle [21]. each fiber is surrounded by endomysium layer and fibers are bundled together called fascicles. fascicles are surrounded by perimysium and finally multiple perimysium are layered by epimysium which is tough enough, friction less, and anchors muscle fibers to tendons at both ends of a muscle. other end of each tendon is attached with endoskeleton. a muscle could be attached with bones through one or more joints [18,21,27]. figure 15 and 16 present conceptual architecture and anatomy of skeletal muscle respectively. (a) (b) fig. 15: conceptual architecture and connectivity of skeletal muscle, (a) tendon and bone connectivity concept, and (b) cross sectional architecture concept. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 92 fig. 16: basic anatomy of skeletal muscle [27]. primary uses of skeletal muscles of lower extremity are leverage and locomotion by exerting a pull on bones. during both dynamic activities and static posture, skeletal muscle plays a significant role to stabilize skeletal segments and joint structures [18]. skeletal muscles, such as abdominal muscle, protect underlying structure and organs of human body. other two important activities of skeletal muscles are, producing body heat (thermogenesis), and vascular pumping. about 75% of total energy generated by muscle tissue is heat which keeps the body warm [27]. on the other hand, contraction of skeletal muscle helps to propel fluids of lymphatic vessels and veins having comparatively low pressure than arteries. basically, skeletal muscle congregates properties of extensibility (stretching without sustaining damage), elasticity (ability to return to its original shape), excitability (ability to response to a stimulus by generating electrical signals), conductivity (ability to propagate electrical signals), and contractility (ability to produce force by shorten or thicken), which ensures unique ability of skeletal muscles. endoskeleton is a multi-joint system of rigid bones acting as levers and with the muscle system it produces internal forces to move it. this mechanism is comparable with a composite system of levers [27] where joints act as axes of levers. common resistances (external opposite force) of muscle force are gravity and friction. there are three types of levers in human musculoskeletal system, (a) first-class lever, (b) second-class lever, and (c) third-class lever [27,28]. in a first-class lever axis is in between the force and the resistance, can be represented as force-axis-resistance (far). this type of lever mechanism is used in skeletal structure for balancing. a second-class lever is forceresistance-axis (fra) type where resistance is in the middle of force and axis. this type of lever mechanism is found at ankle joint when a human being try to stand on the tips of their feet. second-class lever is very powerful in terms of motion range and speed. finally, third-class lever mechanism has force in between resistance and axis, reflecting resistanceforce-axis (rfa) type. this is the most common type of lever found in human musculoskeletal structure. knee joint movements are managed by this type of lever mechanism. muscles of lower extremity can be grouped depending on various criteria such as, (a) corresponding segments [18], (b) actions or movements [23], (c) innervation [23], (d) corresponding joints [29] etc. figure 17 and 18 show muscles of the lower musculoskeletal system of a human body. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 93 fig. 17: muscles of human body lower extremity (anterior view) [27]. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 94 fig. 18: muscles of human body lower extremity (posterior view) [27]. muscles acting on various joints of the lower extremity of a human body are grouped and characterized based on their functions of particular joint movements, as presented in table 1, table 2, and table 3. muscles are also characterized based on their attachments, origins (o) and insertions (i), with corresponding bones, and their innervation system. in terms of robotic therapy systems, these significant characteristics are very important to understand the complex system of humanoid lower extremity. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 95 table 1: muscles acting on lower extremity hip joint [23,30-32] muscles (hip joint) group innervation attachments functions psoas (major and minor) iliopsoas femoral nerve; l2, l3, l4. o: transverse processes, lateral bodies, and corresponding intevertberal disks of tl2, l1 l5. i: lesser trochanter of femur. flx., lr.(asst.) iliacus o: iliac fossa and ala of sacrum. i: lesser trochanter of femur. rectus femoris quadriceps o: anterior inferior iliac spine (aiis). i: tibial tuberosity via patellar tendon. flx., ab.(asst.) sartorius anterior femoral femoral nerve; l2, l3. o: anterior superior iliac spine (asis). i: medial shaft of tibia via pes anserine tendon. flx., ab.(asst.), lr pectineus adductor femoral and obturator nerves; l2, l3, l4. o: superior ramus of pubis. i: pectineal line of femur. flx., add. adductor brevis obturator nerve; l2, l3, l4. o: outer surface of inferior ramus of pubis. i: pectineal line and proximal part of medial lip of linea aspera of femur. add., flx., lr.(asst) adductor longus o: between pubic crest and symphysis. i: middle one-third of medial lip of linea aspera of femur. add., flx., mr.(asst.) adductor magnus tibial division of sciatic nerve; l2, l3, l4. o: inferior ramus of pubis, ramus of ischium, and ischial tuberosity. i: medial lip of linea aspera of femur, medial supracondylar line, and adductor tubercle. ext.(asst.), add., flx.(asst), mr gracilis obturator nerve; l2, l3, l4. o: inferior ramus of pubis. i: medial shaft of tibia via pes anserine tendon. add., mr.(asst.) gluteus maximus gluteal inferior gluteal nerve; l5, s1, s2. o: posterior iliac crest, sacrum, and sacrotuberous ligament. i: greater trochanter of femur, gluteal tuberosity, and lateral tibial condyle via iliotibial band. ext., lr., ab. (upper fibers), add. (lower fibers) gluteus medius superior gluteal nerve; l4, l5, s1. o: external surface of ilium between anterior and posterior gluteal lines. i: lateral surface of greater trochanter of femur. ab., asst: (mr., flx., ext., lr.) gluteus minimus o: external surface of ilium between anterior and inferior gluteal lines. i: anterior border of greater trochanter of femur. ab., mr., flx.(asst) tensor fasciae latae o: anterolateral lip of iliac crest. i: lateral condyle of tibia via iliotibial band. flx.(asst.), ab.(asst.), mr piriformis lateral rotator sacral plexus; s1, s2. o: anterior surface of sacrum. i: superior border of greater trochanter of femur. ab.(asst.), lr. superior gemellus sacral plexus; l5, s1. o: external surface of ischium. i: medial surface of greater trochanter of femur. ab. (asst), lr.(asst.) inferior gemellus o: proximal part of ischial tuberosity. i: medial surface of greater trochanter of femur. obturator internus sacral plexus; l5, s1, s2. o: inferior surface of obturator membrane of ischium. i: medial surface of greater trochanter of femur. ab., lr. obturator externus obturator nerve; l5, s1. o: pubis and ischium, superior and inferior rami. i: trochanteric fossa of femur. lr. quadratus femoris sacral plexus; l4 s2. o: lateral part of ischial tuberosity. i: between greater and lesser trochanters of femur. biceps femoris posterior femoral (hamstring) sciatic nerve; l5, s1 s3. o: long head: ischial tuberosity, short head: lateral lip of linea aspera. i: head of fibula. ext., lr.(asst.) semimembranosus tibial division of sciatic nerve; l5, s1, s2. o: ischial tuberosity. i: posteromedial portion of medial tibial condyle. ext., mr.(asst.) semitendinosus o: ischial tuberosity. i: medial tibial shaft via pes anserine tendon. *o: origin. *i: insertion. *flx.: flexion. *ext.: extension. *ab.: abduction. *add.: adduction. *mr: medial rotation. *lr: lateral rotation. *asst.: assisting muscle. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 96 table 2: muscles acting on lower extremity knee joint [23,30-32] muscles (knee joint) group innervation attachments functions rectus femoris quadriceps femoral nerve; l2 – l4. o: anterior inferior iliac spine (aiis). i: tibial tuberosity via patellar tendon. ext. vastus lateralis o: greater trochanter of femur, gluteal tuberosity, and proximal, lateral lip of linea aspera. i: tibial tuberosity via patellar tendon. vastus medialis o: intertrochanteric line and medial lip of linea aspera of femur. i: tibial tuberosity via patellar tendon. vastus intermedius o: proximal two-thirds of anterior shaft of femur. i: tibial tuberosity via patellar tendon. sartorius anterior femoral femoral nerve; l2 – l3. o: anterior superior iliac spine (asis). i: medial shaft of tibia via pes anserine tendon. flx. (asst.), mr. (pronation) biceps femoris posterior femoral (hamstring) tibial division (long head) and common peroneal division (short head) of sciatic nerve; l5, s1 – s3. o: long head: ischial tuberosity; short head: lateral lip of linea aspera. i: head of fibula. flx., lr. (supinaiton) semimembranosus tibial division of sciatic nerve; l5 – s2. o: ischial tuberosity. i: posteromedial portion of medial tibial condyle. flx., mr. (pronation) semitendinosus o: ischial tuberosity. i: medial tibial shaft via pes anserine tendon. popliteus lateral rotator tibial nerve; l4 – s3. o: lateral femoral condyle. i: proximal posterior surface of tibia. flx. (asst), mr. (pronation) gracilis adductor obturator nerve; l2 – l4. o: inferior ramus of pubis. i: medial shaft of tibia via pes anserine tendon. gastrocnemius triceps surae tibial nerve; s1 – s2. o: medial head: posterior surface of medial femoral condyle; lateral head: posterior surface of lateral femoral condyle. i: posterior surface of calcaneus via achilles tendon. flx. (asst.) plantaris o: distal part of lateral supracondylar line of femur. i: posterior surface of calcaneus via achilles tendon. flx. (asst) *o: origin. *i: insertion. *flx.: flexion. *ext.: extension. *ab.: abduction. *add.: adduction. *mr: medial rotation. *lr: lateral rotation. *asst.: assisting muscle. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 97 table 3: muscles acting on lower extremity ankle joint [26,30-32] muscles (ankle joint) group innervation attachments functions tibialis anterior extrinsic deep peroneal nerve; l4 – l5. o: lateral condyle and proximal half of tibia and interosseous membrane. i: plantar surface of medial cuneiform and base of first metatarsal. ank. df., ft. inv. extensor digitorum longus deep peroneal nerve; l4 – l5. o: lateral tibial condyle, proximal ant erior fibula, and interosseous membrane. i: middle and distal phalanges of digits 2-5, by four tendons to dorsal surfaces. ank. df., toe 2-5 plf., ft. ev. extensor hallucis longus deep peroneal nerve; l4 – l5. o: middle of anterior surface of fibula and membrane. i: base of first distal phalanx, dorsal side. ank. df., big toe plf., ft. add. (inv.) peroneus longus superficial peroneal nerve; ia – 52. o: head and lateral t wo-thirds of fibula. i: lateral sides of first metatarsal and medial cuneiform. ank. plf., ft. ab., ft. ev. peroneus bravis superficial peroneal nerve; l5 – s2. o: distal two-thirds of lateral surface of fibula. i: tuberosity on base of fifth metatarsal. ank. plf., ft. ev. peroneus tertius deep peroneal nerve; l4 – l5. o: distal one-third of anterior surface of fibula and interosseous membrane. i: dorsal surface of base of fifth metatarsal. ank. df., ft. ev. gastrocnemius extrinsic & triceps surae tibial nerve; s1 – s2. o: medial head: posterior surface of medial femoral condyle; lateral head: posterior surface of lateral femoral condyle. i: posterior surface of calcaneus via achilles tendon. ank. plf. soleus o: soleal line and posterior surface of tibia and posterior head and proximal surface of fibula. i: posterior surface of calcaneus via achilles tendon. plantaris tibial nerve; s1 – s2 o: distal part of lateral supracondylar line of femur . i: posterior surface of calcaneus via achilles tendon. ank. plf. (asst.) tibialis posterior intrinsic tibial nerve; l4 – l5 o: lateral, posterior tibia, proximal twothirds of medial fibula, and interosseous membrane. i: navicular tuberosity, cuneiforms l-3, cuboid, and bases of metatarsals 2-4. ank. plf. (asst), ft. inv. flexor digitorum longus tibial nerve; s2 – s3 o: middle of posterior surface of tibia. i: base of distal phalanges of digits 2-5,by four tendons to plantar surfaces. toe 2-5 df., ank. plf. (asst), ft. inv. (asst.) flexor hallucis longus tibial nerve; s2 – s3 o: distal posterior surface of fibula and interosseous membrane. i: base of first distal phalanx, plantar surface. big toe df., ank. plf. (asst), ft. ad., ft. inv. (asst.) *o: origin. *i: insertion. *ank..: ankle. *df.: dirsiflexion. *plf..: plantarflexion. *add.: adduction. *ab.: abduction. *inv.: inversion. *ev.: eversion. *ft.: foot. *asst.: assisting muscle. movements of joints occur along any of three section planes of human body, sagittal plane (lateral plane), frontal plane (coronal plane), and transverse plane (axial plane) [28,33]. each of these three planes has corresponding axis around which a particular iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 98 movement occurs. movements, flexion and extension (front-back) occur on sagittal plane along frontal axis, abduction and adduction (side-side) occur on frontal plane along sagittal axis, and rotational movements, lateral rotation and medial rotation, occur on transverse plane along longitudinal axis. muscles that are involved in particular movements of limbs can be grouped together to identify and monitor performances of affected muscles during rehabilitation or therapy. muscle groups are presented in table 4, table 5, and table 6, according to the movements of the lower extremity of a human body. table 4: hip joint movements and muscle groups [23,32] hip movements muscle groups abductor 1. sartorius 2. tensor fascia latae 3. piriformis 4. giuteus maximus (upper fibers) 5. gluteus medius 6. gluteus minimus 7. gemellus superior 8. gemellus inferior 9. obturator internus adductor 1. pectineus 2. adductor brevis 3. adductor longus 4. gracilis 5. adductor magnus 6. gluteus maximus (lower fibers) extensor 1. adductor magnus (posterior fibers) 2. gluteus maximus 3. gluteus medius (posterior fibers) 4. biceps femoris (long head) 5. semimembranosus 6. semitendinosus flexor 1. psoas 2. iliacus 3. sartorius 4. tensor fascia latae 5. rectus femoris 6. pectineus 7. adductor brevis 8. adductor longus 9. adductor magnus (anterior fibers) 10. gluteus medius (anterior fibers) 11. gluteus minimus lateral rotator 1. psoas 2. iliacus 3. sartorius 4. adductor brevis 5. gluteus maximus 6. gluteus medius (posterior fibers) 7. piriformis 8. gemellus superior 9. gemellus inferior 10. obturator internus 11. obturator extemus 12. quadratus femoris 13. biceps femoris (long head) medial rotator 1. tensor fascia latae 2. gluteus medius (anterior fibers) 3. gluteus minimus 4. semimembranosus 5. semitendinosus iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 99 table 5: knee joint movements and muscle groups [23,32] knee movements muscle groups extensor 1. rectus femoris 2. vastus lateralis 3. vastus intermedius 4. vastus medialis flexor 1. sartorius 2. gracilis 3. biceps femoris 4. semimembranosus 5. semitendinosus 6. plantaris 7. popliteus 8. gastrocnemius lateral rotator 1. biceps femoris medial rotator 1. gracilis 2. sartorius 3. semimembranosus 4. semitendinosus 5. popliteus table 6: ankle and foot movements and muscle groups [26,32] foot movements muscle groups dorsiflexor (flexor) 1. tibialis anterior 2. extensor digitorum longus 3. extensor hallucis longus 4. peroneus tertius plantar flexor (extensor) 1. gastrocnemius 2. soleus 3. plantaris 4. peroneus longus 5. peroneus brevis 6. tibialis posterior 7. flexor digitorum longus 8. flexor hallucis longus foot invertor 1. tibialis anterior 2. extensor hallucis longus 3. tibialis posterior 4. flexor digitorum longus 5. flexor hallucis longus foot evertor 1. extensor digitorum longus 2. peroneus longus 3. peroneus brevis 4. peroneus tertius toe extensor (plantar flx.) 1. extensor digitorum longus (2-5) 2. extensor hallucis longus (1) toe flexor (dorsiflx.) 1. flexor digitorum longus 2. (2-5) 3. flexor hallucis longus (1) iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 100 intrafusal fiber is a special muscle fiber of muscle spindle which is surrounded by a coil of sensory nerve endings, ‘gamma motor neuron’ and ‘afferent fibers’. muscle spindles are special nerves distributed in muscles and tendons that monitor stimuli regarding changes of position, movement, and magnitude of stretch of muscle tissues [27]. if any external force is applied, ‘extrafusal fibers’ of muscle spindle acknowledge ‘alpha motor neuron’ to adjust length of muscles in order to protect muscle fiber from damage. this reaction is known as myotatic reflex. on the other hand, tension of muscle spindle is adapted by ‘gamma motor neurons’ to manage length monitoring function [27,34]. in terms of therapy, it is important to consider that a fast or strong force or stretch that cross a certain limit may cause potential damage of tissues [27,34]. force-velocity relationship of muscle shows inverse characteristics as increment of external force will decrease motion velocity [35,36]. so, it is important to consider and analyze these biological functions and reactions in designing robot assisted rehabilitation systems. 4. conclusion the main focus of lower limbs rehabilitation is to maintain normal mobility of lower extremity joints by providing external force in harmony to ensure repetitive and persistent movement actions within the range of musculoskeletal motion. therefore, the lower extremity maintains its normal functions instead of muscles being shrunk and will improve muscle performance as well as the nervous system. as an automated rehabilitation system should provide better facility to do exercise without any risk of accident or secondary injury, it is very important to study human musculoskeletal structure. considering this point, the review presents a basic overview on musculoskeletal structure of human lower limbs by characterizing and classifying skeletal and muscular system based on various types of functionalities, movements, and joint architecture. acknowledgement the authors would like to express their gratitude to the ministry of education (moe), malaysia for funding the project through the fundamental research grant scheme (frgs). references [1] venketasubramanian n. (1998) the epidemiology of stroke in asean countries – a review. neurol j. southeast asia, 3:9-14. [2] glamcevski mt, tan ct. (2000) prevalence of post-stroke depression, a malaysian study. neurol j. southeast asia, 5:51-53. [3] tan ks, tan ct, churilov l, mackay m, donnan ga. (2010) ischaemic stroke in young adults: a comparative study between malaysia and australia. neurology asia, 15(1):19. [4] nazifah sn, azmi ik, hamidon bb, looi i, zariah aa, hanip mr. (2012) national stroke registry (nsr): terengganu and seberang jaya experience. med. j. malaysia, 67(3):302 304. [5] johnson mj. (2006) recent trends in robot-assisted therapy environments to improve real-life functional performance after stroke. j. neuroengin. rehab., 3(29):1-6. [6] hesse s, mehrholz j, werner c. (2008) robot-assisted upper and lower limb rehabilitation after stroke: walking and arm/hand function. medicine, dtsch arztebl int., 105(18):330 336. [7] akhtaruzzaman m, shafie aa, khan mr. electro-goniometric system; an instrumentation to capture knee movements for forward walking. the 10th asian control conference 2015 (ascc 2015), may 31 2015-june 3 2015, kota kinabalu, malaysia, pp. 1-4. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 101 [8] hidler j, nichols d, pelliccio m, brady k. (2005) advances in the understanding and treatment of stroke impairment using robotic devices. topics in stroke rehabilitation, thomas land publishers, inc., 12(2):22-35. [9] capó-lugo ce, mullens ch, brown da. (2012) maximum walking speeds obtained using treadmill and overground robot system in persons with post-stroke hemiplegia. j. neuroeng. rehab., 9(1):1-14. [10] akhtaruzzaman m, shafie aa, khan mr. gait analysis: systems, technologies, and importance. journal of mechanics in medicine and biology, world scientific publishing company, 16(7), accepted on dec. 20, 2015. [11] sartori m, lloyd dg, reggiani m, pagello e. (2009) a stiff tendon neuromusculoskeletal model of the knee. ieee workshop on advanced robotics and its social impacts, tokyo, japan, november 23-25, pp. 132-138. [12] sartori m, lloyd dg, reggiani m, pagello e. (2010) fast operation of anatomical and stiff tendon neuromuscular models in emg-driven modeling. ieee int. conf. on robotics and automation (icra), pp. 2228-2234. [13] akhtaruzzaman m, shafie aa, khan mr. (2016) automated threshold detection for object segmentation in colour image. arpn journal of engineering and applied sciences, asian research publishing network (arpn), vol. 11, no. 6, pp. 4100-4104. [14] akhtaruzzaman m, shafie aa, khan mr. (2016) representation of human gait trajectory through temporospatial image modelling. arpn journal of engineering and applied sciences, asian research publishing network (arpn), vol. 11, no. 6, pp. 4105-4110. [15] sartori m, reggiani m, lloyd dg, pagello e. (2011) a neuromusculoskeletal model of the human lower limb: towards emg-driven actuation of multiple joints in powered orthoses. ieee int. conf. rehabilitation robotics, eth zurich science city, switzerland, june 29 july 1, pp. 706-714 [16] oatis ca. (2009) kinesiology: the mechanics & pathomechanics of human movement, second edition. wolters kluwer health/lippincott, williams & wilkins. [17] pennestrı` e, stefanelli r, valentini pp, vita l. (2007) virtual musculo-skeletal model for the biomechanical analysis of the upper limb. j. biomechanics, 40:1350-1361. [18] reid crd. (2009) occupational lower extremity risk assessment modeling. ph.d. thesis, university of central florida, orlando, florida, usa. [19] arnoczky sp, mcdevitt ca. (2000) the meniscus: structure, function, repair, and replacement. orthopaedic basic science: biology and biomechanics of the musculoskeletal system, 2nd edition. editors: joseph a. buckwalter, thomas a. einhorn, sheldon r. simon. american academy of orthopaedic surgeons, pp. 532-545. [20] woo sly, an kn, frank cb, livesay ga, ma cb, zeminski j, wayne js, myers bs. (2000) anatomy, biology, and biomechanics of tendon and ligament. orthopaedic basic science: biology and biomechanics of the musculoskeletal system, 2nd edition. editors: joseph a. buckwalter, thomas a. einhorn, sheldon r. simon. american academy of orthopaedic surgeons, pp. 582616. [21] garrett we, and best tm. (2000) anatomy, physiology, and mechanics of skeletal muscle. orthopaedic basic science: biology and biomechanics of the musculoskeletal system, 2nd edition. editors: joseph a. buckwalter, thomas a. einhorn, sheldon r. simon. american academy of orthopaedic surgeons, pp. 684-716. [22] cael c. (2010) functional anatomy: musculoskeletal anatomy, kinesiology, and palpation for manual therapists, chapter 2, osteology and arthrology. wolters kluwer health/lippincott, williams & wilkins, pp. 26-48. [23] cael c. (2010) functional anatomy: musculoskeletal anatomy, kinesiology, and palpation for manual therapists, chapter 8, pelvis, thigh and knee. wolters kluwer health/lippincott, williams & wilkins, pp. 307-369. [24] jung hj, fisher m b, woo sly. (2009) review: role of biomechanics in the understanding of normal, injured, and healing ligaments and tendons. sports medicine, arthroscopy, rehabilitation, therapy & technology, 1(9):1-17. iium engineering journal, vol. 17, no. 1, 2016 akhtaruzzaman et al. 102 [25] recklies ad, poole ar, banerjee s, bogoch e, batista jd, evans ch, firestein gs, frank cb, karp dr, mort js, marks no, varga j, berg wvd, zhang y. (2010) pathophysiologic aspects of inflammation in diarthrodial joints. orthopaedic basic science: biology and biomechanics of the musculoskeletal system, 2nd edition. editors: joseph a. buckwalter, thomas a. einhorn, sheldon r. simon. american academy of orthopaedic surgeons, pp. 489-530. [26] cael c. (2010) functional anatomy: musculoskeletal anatomy, kinesiology, and palpation for manual therapists, chapter 9: leg, ankle, and foot. wolters kluwer health/lippincott, williams & wilkins, pp. 371-421. [27] cael c. (2010) functional anatomy: musculoskeletal anatomy, kinesiology, and palpation for manual therapists, chapter 3: myology. wolters kluwer health/lippincott, williams & wilkins, pp. 49-73. [28] neumann da. (2010) kinesiology of the musculoskeletal system: foundations for rehabilitation, second edition. mosby, elsevier. [29] seeley rr, stephens td, tate p. (2004) anatomy and physiology (6th edition), chapter 10: muscular system gross anatomy. mcgraw-hill science engineering, pp. 313-362. [30] martini f, timmons m, tallitsch r. (2005) human anatomy (5th edition), chapter 11: the muscular system, the appendicular musculature. benjamin cummings, pp. 284-326. [31] thibodeau ga, patton kt. (2007) anatomy and physiology (6th edition), unit ii, support and movement, chapter 10: anatomy of the muscular system. mosby elsevier, pp. 347-393. [32] hamill j, knutzen km. (2009) biomechanical basis of human movement (3rd edition), section ii: functional anatomy, chapter 6: functional anatomy of the lower extremity. wolters kluwer health/lippincott, williams & wilkins, pp. 187-257. [33] akhtaruzzaman m, shafie aa. (2011) an attempt to develop a biped intelligent machine bim-uia. 4th international conference on mechatronics (icom’11), 17-19 may, kuala lumpur, malaysia. [34] hamill j, knutzen km. (2009) biomechanical basis of human movement (3rd edition), section i: functions of human movement, chapter 4: neurological considerations for movement. wolters kluwer health/lippincott, williams & wilkins, pp. 105-135. [35] visser jj, hoogkamer je, bobbert mf, huijing pa. (1990) length and moment arm of human leg muscles as a function of knee and hip-joint angles. eur. j. app. phys., 61:453460. [36] dzahir mam, yamamoto s. (2014) recent trends in lower-limb robotic rehabilitation orthosis: control scheme and strategy for pneumatic muscle actuated gait trainers. robotics, 3:120-148. doi:10.3390/robotics3020120. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 104 the effects of cable characteristics on maximum overvoltage in combined overhead/cable lines protected by surge arresters reza alizadeh* and mohammad mirzaie department of electrical and computer engineering, babol noshirvani university of technology, shariati ave, babol, iran. *corresponding author: reza.alizadeh14@gmail.com (received: 7th aug 2016; accepted: 7th feb 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.707 abstract: this paper presents the calculation of maximum lightning overvoltage for a transmission system consisting of overhead lines in combination with an underground power cable. for this purpose, a 132 kv overhead transmission line combined with an underground cable is considered. this combined line has been protected by surge arresters. emtp-rv and matlab software are used to conduct the modeling, simulation and calculation works. lightning strikes on the tower top and results in large over-voltages appearing along overhead lines and cable. underground cable characteristics have significant effects on maximum lightning over-voltages. therefore, the three characteristics considered for these effects are: (i) cable length; (ii) cable core resistivity, (iii) cable sheath resistivity. tower footing resistance effect is also included in the computer simulation. abstrak: kajian ini berkenaan tentang pengiraan takat maksimum voltan kilat berlebihan bagi sistem transmisi melibatkan kabel atas kepala termasuk kabel tenaga bawah tanah. bagi tujuan ini, talian kabel penghantaran atas kepala 132 kv termasuk kabel bawah tanah telah diambil kira. kombinasi kabel ini dilindungi dengan penahan lonjakan voltan tenaga. perisian emtp-rv dan matlab telah digunakan untuk membuat model, simulasi dan kerja-kerja pengiraan. panahan petir di atas puncak bangunan merupakan penyebab utama voltan berlebihan muncul bersama talian atas kepala dan kabel. ciri-ciri kabel bawah tanah merupakan faktor penyumbang utama ke atas voltan berlebihan daripada kilat. oleh itu, tiga kes telah diambil kira sebagai penyumbang voltan berlebihan: (i) panjang kabel; (ii) rintangan teras kabel, (iii) rintangan sarung kabel. kesan rintangan tapak bangunan turut diambil kira dalam simulasi komputer. keywords: combined line; overvoltage; surge arrester; cable; lightning 1. introduction overhead lines are important parts of power networks. they transfer electrical energy from the point of generation to the place of consumption. the coexistence of overhead and cable lines in the so called "combined" lines raises several questions regarding their behavior both in steady state and in transient. in recent years, with the expansion of the power system and increasing demand for power, cable lines and combined overhead iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 105 transmission lines with underground power cables have been used. cable lines offer the possibility of a reduced environmental impact; for this reason they are often accepted by public opinion instead of new overhead lines. nowadays, cross-linked polyethylene cables (xlpe) are the most common cable types in underground cable systems and power transmission networks. a fault in the cable system can lead to an outage of equipment from electric networks [1] because the insulation of underground insulated cables is not self-restoring such as air insulated transmission lines where the basic insulation level (bil) may decrease as a result of aging. furthermore, repairing damaged cable lines takes several days or even weeks [2]. therefore, protection of cables in combined transmission lines is very important. there is a very obvious difference in the risk and magnitude of any lightning impulse in an underground cable compared to that on an overhead line. power cables are designed according to the required transient impulse and power frequency voltage withstand levels. transient faults are typically caused by lightning activity, and they have a very short duration. thus, lightning overvoltages must be taken into account in the insulation system designing process because it can be a major cause for underground cable failure [3-4]. this problem has recently been analyzed by a cigre wg (b1.05) [5]. as noted above, lightning impulse voltage is the main parameter in the design of insulation that is defined in an ieee standard as 1.2⁄50 µs impulse voltage [6]. when a lightning strike hits a conductor line or the inside of an overhead line in a transmission network, two travelling waves are set up and spread quickly. once the wave, which travels to the underground cable, meets the arrester, both reflected and refracted waves are initiated. over time, gradually decreased electrical resistance of the cable insulation and low amplitude overvoltage can lead to cable insulation failure [7]. cable line length has a significant effect on the amount of maximum overvoltage along a cable. therefore, surge arresters can be used to decrease faults and overvoltage in cable lines [8]. surge arresters have high impedance against normal voltage and have low impedance against transient voltages, thereby transferring those electric waves to the ground. reference [9] attempts to assess the reliability of three common substation configurations. at first, maximum voltages on equipment are calculated in different lightning strike locations through simulation in emtp-rv. then the impact of the surge arrester placement on substations reliability indices is calculated. reference [3] describes the maximum over voltage in a cable protected by surge arresters at both ends due to a continuous reflected voltage wave between cable ends that had occurred within the cable but not in the terminals. in this case, the shorter the length of cable, the higher the maximum overvoltage will be. hence, cable line length has an important role in insulation coordination [10-11]. reference [12] presents an improved approach where the jmarti line model is utilized to obtain voltages and currents at the line ends used to calculate the internal points using an off-line time step. the analysis of maximum overvoltages inside an underground cable due to lightning strokes is presented in [8] based on lattice diagrams. however, according to this reference, proper attenuation constants are not accounted for, yielding approximate positions where the maximum voltage occurs. a frequency–domain (fd) approach has been presented to calculate the maximum overvoltage along an underground cable due to lightning [13]. it is considered that the underground cable is protected by surge arresters at both ends. in this proposed method, the cable is spatially subdivided and direct fd algebraic relations are used to calculate the voltage at each subdivision. in this reference, surge arresters are piece-wise represented in the fd and resolved based on the superposition principle. flashovers are also assessed and resolved in the fd using the superposition principle. reference [14] deals with frequency-dependent surge arrester models and transmission line models utilized for insulation coordination studies. in this iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 106 paper, various frequency-dependent surge arrester models and transmission line models have been compared. simulations of lightning transients in the analyzed power system have been performed and presented for various surge arrester and overhead line models. also, influence of models application during calculations on simulation results has been analyzed. in this paper, maximum overvoltage along the cable is calculated by adding the peak value of the voltage wave in the forward direction and the peak value of the voltage wave in the backward direction. this sum is greater than the voltage at the remote end when the two maxima do not appear simultaneously. this paper is aimed at determining the effect of cable and tower characteristics on maximum lightning overvoltage in combined overhead/cable lines, which is explained in different sections. these characteristics are cable length, cable core resistivity, cable sheath resistivity and tower footing resistance. 2. theory of determine the maximum overvoltage figure 1 shows an overview of the under studied system and cable status. the lengths of the overhead lines on both sides of the cable are to be assumed infinite and the cable is also protected by surge arresters at both ends. the aim is to calculate the maximum overvoltage along the cable caused by lightning strikes on the overhead line. a bcable guard wire overhead line lightning stroke guard wire overhead line x=0 x=l cable length zl zlzc fig. 1: combined transmission line. the voltage at any point x along the cable is calculated by the sum of a forward voltage (+) and a backward voltage (-) propagating wave [3]. 𝑉𝑉(𝑥𝑥, 𝑡𝑡) = 𝑉𝑉+(𝑥𝑥, 𝑡𝑡) + 𝑉𝑉−(𝑥𝑥, 𝑡𝑡) (1) where the forward voltage wave (𝑉𝑉+) is generated at the exposed end (x=0) and the backward wave (𝑉𝑉−) generated at the remote end (x= l) [3]. 𝑖𝑖𝑎𝑎𝑎𝑎𝑎𝑎(𝑡𝑡) = 2×𝑉𝑉+(𝐿𝐿,𝑡𝑡) 𝑍𝑍𝐶𝐶 − 𝑉𝑉 (𝐿𝐿,𝑡𝑡) 𝑍𝑍𝐶𝐶 + 𝑉𝑉 (𝐿𝐿,𝑡𝑡) 𝑍𝑍𝐿𝐿 (2) where 𝑍𝑍𝐶𝐶 and 𝑍𝑍𝐿𝐿 are the characteristic impedance of the cable and overhead line, respectively. these characteristic impedances are determined by emtp-rv. then, according to equations 1 and 2, forward and backward waves are calculated by the following equations: 𝑉𝑉+(𝐿𝐿, 𝑡𝑡) = � 𝑍𝑍𝐶𝐶 2 �𝑖𝑖𝑎𝑎𝑎𝑎𝑎𝑎(𝑡𝑡) + � 𝑍𝑍𝐶𝐶+𝑍𝑍𝐿𝐿 2𝑍𝑍𝐿𝐿 �𝑉𝑉(𝐿𝐿, 𝑡𝑡) (3) iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 107 𝑉𝑉−(𝐿𝐿, 𝑡𝑡) = 𝑉𝑉(𝐿𝐿, 𝑡𝑡) − 𝑉𝑉+(𝐿𝐿, 𝑡𝑡) (4) generally, the flowchart of calculating maximum overvoltage along a cable has been found in fig. 2. determine forward and backward waves at end b of cable by using equations 1 and 2 and matlab program. determine maximum overvoltage by adding peak value of the forward and backward voltage waves at end b of cable. compare obtained maximum over voltage with voltage at both cable ends. use emtp-rv for calculating surge arrester current and voltage at end b of cable. fig. 2: flowchart for determining maximum overvoltage along the cable. 3. description of the network configuration and model in this paper, a three phase combined transmission line (consists of overhead lines and cable lines) is selected to determine the maximum lightning overvoltage at one phase of the network. this system is simulated in emtp-rv software. in this system, voltage and frequency are 132 kv and 50 hz, respectively. overhead line length at both ends of the cable is infinite; and span lengths of overhead line are assumed to be 200 m cables per phase, protected by surge arresters at both ends. figure 3 shows the basic configuration for one phase. 30ω 30ω 30ω 30ω 1 2 µ h12µh 1ω 1ω 12µh 450ω 450ω 200m 200m 200m 200m lightning stroke cable vflash=600 kv fig. 3: system basic configuration. the steel towers are usually represented as a single conductor distributed parameter line terminated by a resistance representing the tower footing impedance [15]. it has been known that the footing impedance tends to be capacitive in the case of a high resistivity iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 108 earth, and inductive in low-resistivity earth. it can be resistive, inductive, and capacitive depending on the season and the weather. therefore, footing impedance is modeled by resistance [16]. a constant parameter (cp) model is used to simulate the towers. tower surge impedance and wave velocity, as the principal parameters of the cp line, are considered to be 200 ω and 3 × 108 𝑚𝑚 𝑠𝑠⁄ , respectively. the footing resistance is considered 30 ω. the lightning surge is modeled by a current and a parallel resistance (cigre model). this resistance value is assumed to be 400 ω, which was derived by bewley [16]. in this paper, lightning current is considered to be 200 ka with 1µs front time and 300 µs time to half value strikes the tower top in the second tower. this causes a back-flashover in the struck tower. a flashover is assumed to take place at the second tower, when the magnitude of the voltage between the phase conductor and the tower exceeds 600 kv. note that no flashover occurs in the right part of the line; and ground wires are neglected in that part of the line. also, in this paper, a frequency-dependent model (fd model) is used for overhead lines. in this model, resistance and inductance of the transmission line are considered as an fd model determined by skin and ground effects. line capacitance is assumed constant and a non-zero parallel conductance included in this model. table 1 and table 2 show technical specifications of transmission line consisting of conductors and guard wires and table 4 shows input data for conductor and guard wires. table 1: technical specifications of conductors conductor number phase horizontal distance (m) vertical distance (m) 1 1 -4.15 23.2 2 2 -4.15 19.2 3 3 -4.15 15.2 4 4 4.15 23.2 5 5 4.15 19.2 6 6 4.15 15.2 table 2: technical specifications of guard wires guard wire number horizontal distance (m) vertical distance (m) 1 -4.15 26.5 2 4.15 26.5 the studied cable is xlpe, single core with 630 mm2 cross section. figure 4 indicates diagrammatic representation of the cylindrical cable in emtp-rv. table 3 presents the input data of the cable in emtp-rv. six single-core cables deployed in a triangle, like in fig. 5 are located underground. this type of configuration is common between conductors, because of the reduction of the magnetic coupling effect and it is preferable to bury it flat. table 5 shows the amount of peculiarity phases. horizontal axis (x) is parallel with the ground and vertical axis (y) is perpendicular to the ground. the origin of the coordinates iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 109 is the intersection of the vertical axis that passes from center of the cable 1 to the ground surface. in this paper, ground resistivity is considered 100 ω. table 3: technical data for cable cable layers outer radius [m] resistivity [ohm-m] relative permittivity relative permeability conductor 0.01525 1.946e-8 1 internal insulation 0.03725 3.052 1 sheath 0.038087 1.678e-8 1 external insulation 0.043087 3.125 1 conductor radius , r1 [m] internal insulation radius , r2 [m] sheath radius , r3 [m] outer insulation radius , r4 [m] fig. 4: diagrammatic representation of underground cable in emtp-rv. table 4: technical data for the conductor and guard wire characteristics input data conductor name moose/olive number of conductors 6 conductors radius [m] 0.013 dc resistance of the conductor [ohm/km] 0.1 vertical height at midspan for conductors [m] 5 guard wire name opal number of guard wires 2 guard wire radius [m] 0.00653 dc resistance of the guard wire [ohm/m] 2.9 vertical height at midspan for guard wires [m] 5 iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 110 the voltage reference is 132 × �2 3⁄ = 107.8 kv, which equals to 1 p.u. a protective level and per unit reference voltage and inductance of the surge arrester are considered to be 395 kv and 12 µh, respectively. the common grounding resistance for the cable screen, the arrester, and the adjacent tower is 1 ω. the surge arrester v-i characteristic is given in table 6. cable 1 cable 2 cable 3 cable 4 cable 5 cable 6 y x fig. 5: cable configuration. table 5: amount of peculiarities phases axis cable 1 cable 2 cable 3 cable 4 cable 5 cable 6 horizontal axis [m] 0 0.11 0.22 0.33 0.44 0.55 vertical axis [m] 1.1985 1.0075 1.1985 1.0075 1.1985 1.0075 table 6: surge arrester current-voltage characteristic current [a] voltage [kv] 1.0000e-4 172.02 9.9996e-4 194.52 9.9981e-3 206.65 1.0002e-1 218.82 9.9991e-1 234.59 2.5000e+2 308.67 1.0000e+3 331.03 4.9998e+3 369.53 1.0000e+4 395.00 2.0000e+4 435.99 iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 111 4. emtp simulation results and analysis this section reports the results of the emtp-rv simulation of the modeled system. we will focus on some of cable characteristics such as cable length, cable core, and sheath resistivity, as well as tower footing resistance. the simulation results have been analyzed and discussed in following sections. 4.1 effect of cable length on maximum overvoltage figure 6 shows forward and backward waves at the end b of the cable when the cable length is 1 km. according to fig. 6 and equation 2, maximum overvoltage along the cable is 359.5+205=564.5 kv that is equal to the sum of the maximum incoming wave and the maximum reflected wave at the remote end. as mentioned above and according to fig. 7, maximum overvoltage for a 10 km cable length is also equal to 292.9+181.2=474.1 kv. for a 40 km cable, according to fig. 8, maximum overvoltage is equal to 245.8+173.5=419.3 kv. these results show that maximum overvoltage strongly depends on cable length. in these figures, the sum of the incoming wave and reflected wave is the main voltage. fig. 6: forward and backward voltage waves at end b of cable (1 km cable). therefore, maximum overvoltage for different lengths is calculated in the range of 500 m to 65 km in order to investigate the effect of cable length. figure 9 shows variations of the maximum overvoltage in the end of the cable line by increasing the length of the cable line. according to fig. 9, maximum overvoltage decreases from 570 kv to 387.9 kv, when cable line length increases from 500 m to 65 km, due to the cable attenuation effects. also, by increasing the cable length, maximum overvoltage gets closer to the surge arresters’ protective level. therefore, according to the above results, maximum overvoltage decreases when cable line length increases. hence, optimum cable line length should be considered when designing and coordinating the cable insulation because unsuitable iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 112 design can lead to cable insulation failure and network outage. according to simulation results, a lightning strike on top of the second tower in this paper, if cable length more than 31 km, cannot be dangerous for the cable and the cable doesn’t need a surge arrester at both ends because maximum voltage along the cable is less than the bil of the cable. fig. 7: forward and backward voltage waves at end b of cable (10 km cable). fig. 8: forward and backward voltage waves at end b of cable (40 km cable). iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 113 fig. 9: maximum overvoltage along the cable as function of cable length. fig. 10: maximum overvoltage as function of resistivity of the cable core (1 km, 10 km and 40 km cable). 4.3 effect of resistivity of the cable sheath on maximum overvoltage figure 11 compares maximum overvoltage along the cable with three different values of sheath resistivity for different cable lengths (1 km, 10 km and 40 km). as seen from the simulation results, maximum overvoltage decreases when sheath resistivity for each length of the cable increases. for example, for every 10 km length of the cable, maximum overvoltage along the cable for sheath resistivity 2.8×10−9 ω-m, 1.678×10−8 ω-m, and 2.1×10−6 ω-m are 481.9 kv, 474.1 kv, and 405.7 kv, respectively. 4.4 effect of tower footing resistance on maximum overvoltage one of the transmission line parts that can have a significant effect on maximum overvoltage is the tower. during a back flashover, the major part of the strike current flow is transferred toward the ground via the guard wires and towers. the tower footing iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 114 resistance effect on maximum overvoltage is caused by back flashover. therefore, maximum overvoltage along the cables can be reduced by using a suitable tower footing resistance. figure 12 shows maximum overvoltage for three different values of tower footing resistance for three different cable lengths (1 km, 10 km and 40 km). according to this figure, for each length of the cable, maximum overvoltage increases when tower footing resistance increases. results also show that maximum overvoltage decreases when cable length increases under certain tower footing resistance values. for example, for every 10 km length of the cable, maximum overvoltage along the cable for each tower footing resistance of 10 ω, 30 ω, and 90 ω is 398.7 kv, 474.1 kv, and 514 kv, respectively. fig. 11: maximum overvoltage as function of resistivity of the cable sheath (1 km, 10 km and 40 km cable). fig. 12: maximum overvoltage as function of tower footing resistance (1 km, 10 km and 40 km cable). iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 115 5. conclusion this paper investigates the impact of cable and tower characteristics on maximum lightning overvoltage along a cable in a combined transmission line. results show that maximum overvoltage along the cable decreases by increasing the length of the cable line. therefore, increasing cable line length can be a way of protecting cable lines against transient overvoltages. generally, maximum overvoltage along the cable decreases when cable core resistivity and cable sheath resistivity increases. also, this maximum overvoltage increases by increasing tower footing resistance. in this paper, simulations show that by increasing the cable length, surge arresters are no longer required because maximum overvoltage gets closer to the surge arresters’ protective level when the cable length increases and maximum voltage along the cable is less than the bil of the cable, so the cable can tolerate the overvoltage. with regard to the obtained results, choosing a suitable type of cable and optimum cable line length can be considered effective factors on cable insulation failure, because the maximum overvoltage strictly affects the insulation coordination. references [1] transpower report. (2005) comparison of reliability of a 400 kv underground cable with an overhead lines for a 200 km long circuit. [2] transpower report. (2005) effect of short cable sections on reliability of a 400 kv overhead line. [3] henriksen mt, gustavsen b, balog g, baur u. (2005) maximum lightning overvoltage along a cable protected by surge arresters. ieee transactions on power delivery, 20(2):859-866. [4] sadeh j, damchi y. (2010) maximum lightning overvoltage location and reliability indices in power system with combined transmission line. in transmission and distribution conference and exposition: latin america (t&d-la), 2010 ieee/pes, pp. 212-217, ieee. [5] balog g. (2005) transient voltages affecting long cables. report of cigre wg b1-05, technical brochure no. 269 from cigre. [6] ieee std c62.82.1-2010 (revision of ieee std 1313.1-1996) ieee standard for insulation coordination--definitions, principles and rules. [7] zhou lm, boggs sa. (2002) effect of shielded distribution cables on lightning-induced overvoltages in a distribution system. ieee trans, on power delivery, 17(2):569-574. [8] martinez ja, gonzalez-molina f. (2000) surge protection of underground distribution cables. ieee transactions on power delivery, 15(2):756-763. [9] hosseini sa, mirzaie m, barforoshi t. (2015) impact of surge arrester number and placement on reliability and lightning overvoltage level in high voltage substations. international journal of electrical power & energy systems, 65:146-158. [10] marzinotto m. (2007) relationship between statistical distributions of impinging and stressing overvoltages in power cable lines. ieee lausanne power tech, pp. 1911-1916. [11] marzinotto m, mazzetti c, schiaffino p. (2005) statistical approach to the insulation coordination of medium and high voltage cable lines. ieee power tech. [12] marti l, dommel hw. (1997) calculation of voltage profiles along transmission lines. ieee trans, power del, 12(2): 993-998. [13] miguel c, ramirez a. (2014) frequency-domain computation of maximum lightning overvoltage along a cable protected by surge arresters. north american power symposium (naps), ieee. [14] oramus p, florkowski m. (2014) simulations of lightning overvoltages in hv electric power system for various surge arresters and transmission lines models. przegląd elektrotechniczny, 90(10):137-140. iium engineering journal, vol. 19, no. 1, 2018 alizadeh and mirzaie 116 [15] ieee modeling and analysis of system transients working group. (1996) modeling guidelines for fast transient. ieee trans, power del, 11(1): 493-506. [16] ametani a, kawamura t. (2005) a method of a lightning surge analysis recommended in japan using emtp. ieee trans, power del, 20(2, pt. 1):867-875. 1. introduction 2. theory of determine the maximum overvoltage 3. description of the network configuration and model 4. emtp simulation results and analysis references application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 117 development of wireless power transfer system using resonance principle with security features chandrasekharan nataraj 1* , sheroz khan 2 , mohamed hadi habaebi 2 , asan gani abdul muthalif 3 and ravi lakshmanan 1 1 school of engineering, asia pacific university, 57000, kuala lumpur, malaysia. 2 department of electrical and computer engineering, 3 department of mechatronics engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. *corresponding author: chander@apu.edu.my (received: 17 th march 2016; accepted: 13 th nov. 2017; published on-line: 1 st dec. 2017) abstract: this research describes a resonance principle based low power wireless power transfer (wpt) system. the reflective impedance model is derived to evaluate the resonance coupling between coils. additionally, a cockroft-walton voltage boosting circuit is incorporated to boost up the received voltage to the appropriate level, instead of using traditional conditioning circuits. the prototype model, operating at 130 khz, is demonstrated experimentally and analysed graphically to validate the performance of the designed circuit. for an overall span of 100 mm coil separation distance, a maximum efficiency of 60% with no load and 36% with loaded system, is observed at a distance of 55 mm with approximate (e.g., manual) axial orientation of coils. it can be supported widely for portable electronic products and biomedical devices. as an added contribution, the wpt circuit was enabled by a password security feature using an arduino microcontroller. abstrak: kajian ini menerangkan sistem tanpa wayar (wireless) berkuasa rendah berasaskan prinsip resonans pemindahan kuasa (power transfer (wpt)). model pantulan rintangan telah dihuraikan bagi menilai resonans antara dua gegelung litar. selain itu, litar peningkatan voltan cockroft walton turut digunakan untuk meningkatkan input voltan pada tahap sesuai, tanpa mengguna pakai litar tradisional. prototaip model pada operasi 130 khz, telah diuji secara eksperimen dan dianalisa secara grafik untuk menilai prestasi litar yang dicipta. bagi span keseluruhan 100 mm jarak pemisahan gegelung, kecekapan maksimum 60% tanpa beban dan 36% dengan beban sistem telah diperhatikan pada jarak 55 mm berdasarkan anggaran (secara manual) pada orientasi paksi gegelung. kajian ini sesuai digunakan secara meluas pada produk mobil elektronik dan peranti bioperubatan. sebagai sumbangan tambahan, litar wpt telah diaktifkan dengan ciri keselamatan kata laluan mengguna pakai sistem pengawal mikro arduino. keywords: wireless power transfer; resonant frequency; refelective impedance; microcontroller 1. introduction wireless power transfer (wpt) consists of energy transfer from any appropriate source to an energy consuming device without the use of wires or conducting material. wireless power transmission has received special attention recently for the iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 118 implementation of low-cost and low-power batteryless operated sensors. the development of portable devices in the digital world has increased the demand of battery-less gadgets. devices are usually powered through cables, or any other conductive material, from wall outlets or other power sources such as battery cells. these existing methods may not be feasible choices in certain applications while battery use eventually requires replacement of exhausted batteries. batteryless technology is a favourable method for powering electronic gadgets without the use of wires or cables. wpt technology is emerging as an essential companion to the handheld portable products of the very near future. wpt is realized through an electric field called a capacitive coupling or a magnetic field inductive coupling. the magnetic field coupling based wireless power transfer was historically conceptualized in 1891 by nikolas tesla [1]. however, its practical application has only recently appeared to satisfy the needs of emerging field applications and the devices of the portable digital world. the inductively coupled resonance wpt has numerous benefits, such as being simple in construction, omnidirectional, non-radiative, effective for midrange power transfer, and losing minimum power [2]. in theory, inductive and capacitive coupling modes are popular methods to transfer power wirelessly. the capacitive coupling has many limitations and could be used for very limited applications as compared to the inductive coupling [3]. the inductive coupling technique has been used in many low power applications [4]. there are three modes that are commonly used for wpt, such as inductive coupling for short range, resonant coupling for mid-range, and electromagnetic coupling for long range [5]. the coils are resonated at a resonant frequency, maximizing power transfer to devices at locations by few centimeters away. as per the application requirement, the geometry of the inductor coils can be diverse and the shapes can also vary, from circular, to rectangular or square [6, 7]. the use of the resonant technique in wpt to charge the devices at close proximity is a low cost feasible technique [8, 9]. at resonance, two coupled circuits will oscillate at a particular frequency referred to as resonance frequency through an impedance matching technique [10]. a resonant based wpt system integrated with the digital controller can make up an innovative approach. earlier studies focused on addressing the primary objective of increasing power efficiency through shortening coil separation distance [11]. existing systems do not contain any provisions to control the power transfer between transmitter and receiver coils. in real time applications, a wpt system without control units will supply power to the remotely connected load at times when power transfer is not needed [12]. these kind of systems are not sustainable and lead to the unnecessary power wastage and increases the demand for increased power supply. this can be avoided when any kind of controlling mechanism is provided in the transmitter circuit for controlled transfer of power between source and load coils. the usage of microcontrollers is a well-known technique to facilitate the controlling prospects. the system, comprising of both a wpt and a digital controller, is referred to as an integrated system. this integrated system also serves many purposes including cost reduction, improved protection, and centralised monitoring [13]. hence, a password-based digital controller was combined with wpt, making it a more attractive technique for biometric authentication embedded with distinctive biological features [14]. this paper is organized as follows: section ii describes the theory of reflective impedance involved in the wpt. the complete design details of wpt with password iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 119 protection are explored in section iii. consequently, the findings of the experiments and its validations are presented in section iv. finally, the conclusion is drawn in section v. 2. circuit theory based wpt model using reflective impedance figure 1 depicts the electrical equivalent circuit for the wpt system and it can be represented in matrix form by assuming voltages and currents in r.m.s values,                        01 1 2 1 s l s lcll scss v i i c/ljrmj mjc/ljr (1) fig. 1: electrical equivalent circuit. the source and load coil inductances and resistances are represented as scl , lcl , s cr and lcr . the value of sr , lr , 1c and 2c represents source resistance, load resistance, and loading capacitors of source and load circuits, respectively. when two coils placed in the critical coupling mode, the coupling factor k can be represented as, . qq k ls 1  (2) where ss sc s r l q   and ll lc l r l q   are the q factors of source and load coils. under nonmutual induction, oscillating angular frequencies of source and load coil are defined as, 1 1 clsc s  and 21 1 cllc l  . (3) capacitors 1c and 2c are added to each side and tuned appropriately. both coils will oscillate at an angular resonance frequency cl/ coil1 . then, maximum power transfer takes place from source to load coil in the critical coupling mode. at the resonant condition, conventional figure of merit (u) of the complete circuit is written as, ls qqku  (4) iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 120 hence, intensity of magnetic field established in the source coil shall be improved by the value of the q factors. these values are very appropriate to significantly increase the efficiency and maximum achievable efficiency can be represented as,  2211 u u opt   (5) rather than this conventional method, circuit theory (ct) based analysis is more appealing because of characteristics of straightforward mutual inductance calculation [9]. figure 2 illustrates the simplified reflected impedance model for the electric equivalent circuit of wpt shown in fig. 1. let us consider refr , sz and scm are representing the reflected impedance from load to source loop, source side total impedance, and mutual inductance, respectively. under resonance state, the impedance reflected from load to source coil is referred as reflective impedance. fig. 2: simplified reflective impedance model. llc sl ref rr m z    22 (6)       llcsscslllc sl rrrrmrr m    22 22 (7)    222 222 llcsscsl lssl l rrrrm rvm p    (8) equations (7) and (8) represent the conditions for maximizing the power transfer efficiency and hence power received at the load with respect to slm and lr . with the above equations, and transfer power related with reflected impedance can be drawn easily. ssc lcsl m ax rr rm    22 (9) lc ssc sl lmax r rr m p     22 (10) iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 121 equations (9) and (10) represent the optimized equations for achieving maximum efficiency and power. figure 3(a) shows the measurement of the coupling factor as a function of coil separation distance, with an applied input voltage of 5 v. the system is tested with three different coil sizes of 20 mm, 25 mm, and 30 mm. it is observed that the coupling factor (k) achieves almost unity for the 30 mm sized coil for less than 10 cm of coil separation distance while it achieves a 0.2 coupling factor when the coil separation distance reaches 70 cm. in general, the inference made is that the coupling factor (k) decreases as the coil separation distance is increased. similarly, fig. 3(b) shows the measurement of output voltage as a function of coupling factor. the output voltage is measured by varying the coupling factor from 0.1 to 1 in both simulation and experimental analysis. the coupling factor is calculated through the formula s l q q k  , where sq and lq are the quality factor of source and load coils respectively. hence, the coupling factor is inversely proportional to the distance of coil separation between source and load coils. in other words, increasing the separation distance reduces the coupling factor, and vice versa. (a) (b) fig. 3: (a) measurement of coupling factor as a function of coil separation distance with different coil sizes (b) simulated and experimental measurement of output voltage as a function of coupling factor for no load and load conditions. subsequently, it can be observed that the output voltage gradually increases as coupling factor is increased, for both the simulated and measured results. however, the simulated output voltage increases rapidly, reaching a maximum of 4.5 v at the resonant coupling factor k=0.95, while the measured output voltage produces 3 v only for the same resonant coupling factor under no load condition. this is due to several factors such as the component tolerance levels, accuracy of winding of coupled coils, quality factor of coils and, most importantly, the accuracy of coil orientation, all of which add an element of uncertainty to the obtained results. furthermore, the simulated output voltage increases gradually, reaching a maximum peak of 4 v at resonant coupling factor k=0.95, while the measured output voltage produces 2 v only at the same resonant coupling factor under loaded condition. thus, only 60% and 40% of the output voltage has been achieved experimentally as compared to simulation, both under no load and loaded conditions. this is due to fact that the experimental results exhibit uncertainties in the measurements as compared to the simulation results. 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 10 20 30 40 50 60 70 coupling factor [k] c o il s e p a ra ti o n d is ta n c e [ c m ] system with 30mm coil size system with 25mm coil size system with 20mm coil size 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 coupling factor [k] o u tp u t v o lt a g e [ v ] simulated in no load simulated in loaded measured in no load measured in loaded iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 122 however, this could be further improved through the use of more reliable components with less tolerance levels and using motorized setting for accurate coil orientation. furthermore, it is observed that the optimum peak voltage of 2.25 v and 1.25 v occurs at the resonant condition with a coupling factor of 0.6 under no load and loaded condition. this is equivalent to 25 cm of separation distance for a 30 mm sized coil. hence, it can be concluded that the system with the coupled inductive coils provides an optimum power transfer efficiency under the resonance coupled condition. 3. design of wpt system with passsword protection fig. 4: hardware block diagram of a wireless power system with password security. a simple and cost-effective integrated wireless power transfer system embedded with password authentication features is shown in fig. 4. the whole system is resonated at a frequency of 130 khz and a separate password security digital module is developed to control the frequency of generator circuit. the password protection system provides a degree of user control, in which only an authorised user can activate the system. upon entry of the password, the transmitter module is activated and the transmitter coils get coupled to receiver coil at resonance. in resonance mode, both transmitter and receiver circuits are tuned into a common frequency, thus maximizing power transfer. the voltage across the receiver coil is rectified as dc and will be used as a appropriate power for the target ic as load. the ic 555-based square wave generator in fig. 4 is designed and operated at resonant frequency. the dc input supply is converted into ac pulses to excite the transmitter coil for generating the required magnetic field. the receiver coil, under the influence of the magnetic field, then induces a voltage, and is hence able to deliver ac voltage across it, making power ready to be harvested. the harvested voltage is passed to the conditioning circuit and rectifier, converting it back to dc voltage for use by the load circuit. the hardware circuit of the frequency generator shown in fig. 5 comprises of a 555 timer, mosfet switch and two npn transistors. as mentioned earlier, the square wave iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 123 output generated from 555 timer is applied to the mosfet switch for conditioning and stabilizing purposes. it means that the stable alternating pulses are generated to trigger on and off npn transistors thus exciting the transmitter coil in a pre-determined sequential manner. the purpose of two transistors is to provide the good driving capability for developing appropriate voltage across the transmitter tank circuit. pin.3 of the ic 555 provides the functionality of an external trigger. fig. 5: resonant frequency generator circuit. in order to enable the successful power transfer, the coil inductance deciding the performance of the system, is determined using wheeler’s formula [15]: (11) where, l = self-inductance in µh; a = inner radius of coil in meter; b = outer radius of coil in meter; l = length of coil in meter; and n = total number of turns. the inductance of the coil inductor is calculated with the parameters listed in table 1 is, table 1: coil parameters in the coil designs. self-inductance ( µh) inner radius (m) outer radius (m) length (m) 15.177 0.031 0.035 0.006 in addition, a special cockroft-walton (cw) voltage boosting converter is adopted in this design to convert harvested ac voltage across the receiver coil into desired dc voltage, by boosting the received output voltage. this circuit is constructed using voltage multipliers along with conditioning capacitors and uni-directional diodes as of fig. 6. )(1096 6.31 22 abla na l   .177.15 )066.007.0(10)005.0(9)066.0(6 )11()066.0(6.31 22 hl    iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 124 fig. 6: simulation diagram and the measurements of cockroft walton voltage boosting circuit. an experimental setup of an arduino microcontroller-based wpt system integrated with password security functionality is shown in fig. 7. the resonant frequency for the transmitter module is authenticated by a password security system using the arduino processor. the trigger control signal generated by the microcontroller is connected to pin.3 of the ic 555 timer-based oscillator circuit. the oscillator will generate the resonant frequency when the password is entered through the keypad. then, the power is harvested by the receiver coil under resonant coupling mode through the microcontroller which initiates the control signal to trigger up the transmitter module and thereby achieve wireless power transfer. in this work, a new feature of authentication technique based on a microcontroller is adopted. the developed system has a significant feature of password protection integrated with the wireless power transfer system. fig. 7: experimental setup of password security based wpt system. iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 125 4. results and discussion the developed lab test bed wpt system is evaluated and analysed using two experimental set-ups. both experiments are conducted using the coil of diameter of 7 cm with 0.5 initial air gap by applying a 5 v input voltage. the efficiency of the designed system in terms of voltage is measured using two parameters: coil separation distance in axial and radial orientations. it is experimented through the setup of two same sized stationary coils oriented in parallel planes to each other. fig. 8: measurement of output voltage with respect to coil separation distance. the first test is carried out to measure the output voltage with respect to the coil separation distance. the transmitter coil is fixed and receiver coil is moved axially apart over a span of 100 mm. the measurement of output voltage at the receiver end as a function of distance is conducted using a meter ruler placed horizontally along the axis of the coils and then the receiver coil is moved in 10 mm steps axially. initially when the coil separation is kept at its minimum (10 mm), the system is able to harvest the maximum voltage of 4.5 v under loaded condtion and 4.8 v under no load conditions. subsequently, the harvested voltage across the load gets decreased gradually as the coil separation distance increases for every 10 mm of incremental step. furthermore, it can be observed from results in fig. 8 that the output voltage with load decreases at a faster rate compared to the output voltage at no load condition for the same coil separation distance. this test is performed by keeping the fixed value of resonant frequency at 130 khz. the optimum coil separation distance is observed to be between 50 60 mm over a span of 100 mm. the output voltage obtained, at this optimum coil separation distance, is 3.1 v and 1.8 v with an efficiency of 62%, and 36% at the receiver, under no load and loaded conditions respectively as shown in fig. 8. max. efficiency (loaded condition) = (1.8 / 5)×100 = 36%. max. efficiency (no load condition) = (3.1 / 5)×100 = 62%. the second experiment is conducted to estimate the power transfer efficiency in terms of voltage ratio under the non-orientated configuration. here, the coils are not aligned properly as the load coil is placed radially above the source coil with the constant radial 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 distance [mm] o u tp u t v o lt a g e [ v ] no load condition loaded condition iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 126 distance of 10 mm and applied input voltage of 5 v. initially, the coils are fixed with the phase angle of 90 degrees, which produces the zero distance between the coils. subsequently, the receiver coil is moved apart from the source coil in the z-direction with a maximum distance of 70 mm to measure for effective power transmission. this measurement of output voltage is performed under load and no-load conditions as shown in fig. 9. fig. 9: measurement of voltage ratio with respect to the distance in axial direction. it is observed that the voltage ratio is almost zero until a distance of 20-25 mm, which means that the receiver coil is out of phase with the source coil so that no voltage is harvested at the receiver end. subsequently, the receiver coil is moved axially, which will reduce the phase angle indirectly and hence output voltage is harvested at the receiver end. from the plots shown in fig. 10, it is observed that the maximum output voltage is achieved at an intersection distance in the range of 50-60 mm and then gradually decreases as the coil is parted from the source coil, i.e., non-oriented coil configuration. 5. conclusion a newly integrated, password embedded security protection system for wpt application is presented. the design utilizes an arduino microcontroller for password security implementation. the controller controls the resonant switching frequency of the transmitter coil for effective flux linkage and power transfer between coupled coils. in order to analyze the coupling strength between coils for improving efficiency, two distinct efficiency measurements, as a function of coil separation distance with two coil configurations, are performed experimentally. the wireless power system controlled by digital controller is the unique feature of this work. the performance of the constructed integrated system is effectively demonstrated through the prototype built. the experimental results confirm the effectiveness and good performance of the design, achieving maximum efficiency of 62% in an ideal case at a distance of 55 mm. the results are in line with those of [16] where power declines beyond critical value of coupling coefficient. 0 10 20 30 40 50 60 70 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 intersection distance [mm] v o lt a g e r a ti o ,[ v l /v s ] recorded max.eff.with res.freq 130 khz no load-60% & loaded-36% no load condition voltage ratio loaded condition voltage ratio iium engineering journal, vol. 18, no. 2, 2017 nataraj et al. 127 references [1] tesla n. (1914) u.s. patent 1. 119,732. [2] brown wc. (1984) history of power transmission by radio waves. ieee transactions on microwave theory and techniques. mtt-32(9):1230-1242. [3] arshad a, khan s, zahirul alam ahm, tasnim r, gunawan ts, ahmad r, nataraj c. (2016) an activity monitoring system for senior citizens living independently using capacitive sensing technique. ieee international instrumentation and measurement technology conference (i2mtc 2016) proceedings, 449–454. [4] nataraj c, khan s, habaebi mh, abdul muthalif ag, arshad a. (2016) resonant coils analysis for inductively coupled wireless power transfer applications. ieee international instrumentation and measurement technology conference (i2mtc 2016), 109-114. [5] angrisani l, alessandro gd, arco md. (2015) an experimental energy set-up for wireless battery recharging. ieee international instrumentation and measurement technology conference (i2mtc 2015) proceeding, 1699-1704. [6] khan im, khan s, khalifa oo. (2012) transfer of power to low power implanted biomedical devices: coil design considerations. proceedings of i2mtc 2012, graz, austria. [7] torla l, haider s, shobaki m, abdul muthalif ag, khan s, azman a, mustafah y. (2013). low voltage dc power supply with spike-blocking features. i2mtc2013, minneapolis, 6-9 may 2013. [8] sample ap, meyer a, and smith jr. (2010) analysis, experimental results, and range adaption of magnetically coupled resonators for wireless power transfer. ieee transactions on industrial electronics, 58(2):544-554. [9] jabbar h, jeong ys. (2010) wirelessly charging mobile devices from ambient rf sources. consumer electronics (icce), 2010 digest of technical papers international conference, 455-456. [10] nataraj c, khan s, habaebi mh, abdul muthalif ag. (2016) hybrid of conical and spiral approach for wireless power transfer. ieee student conference on research and development (scored 2016), kuala lumpur, malaysia. [11] sandrolini l, reggiani u, puccetti g, and neau y. (2013) equivalent circuit characterization of resonant magnetic coupling for wireless transmission of electrical energy. international journal of circuit theory appl., 41:753-771. [12] nataraj c, khan s, eniola ff, selvaperumal sk. (2017) design of simple dc-to-dc wireless power transfer via inductive coupling. international conference on advances in electrical, electronics, information, communication and bio-informatics (aeeicb17), chennai, india. [13] xun l, ng wm, lee ck, hui syr. (2008) optimal operation of contactless transformers with resonance in secondary circuits. proceedings of the twenty-third annual ieee applied power electronics conference and exposition (apec 2008), austin, tx, usa, 645-650. [14] bright ja, lee wj. (1998) integrated monitoring, protection, and control systems for industrial and commercial power systems. ieee computer applications in power, 24-30. [15] wheeler ha. (1928) simple inductance formulas for radio coils. proceedings of the institute of radio engineer, 16:1398-1400. [16] seo d-w, lee j-h, lee h-s. (2016) optimal coupling to achieve maximum output power in a wpt system. ieee transactions on power electronics, 31(6):3994-3998. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 238 recycling and disposal of lithium batteries: an economical and environmental approach ataur rahman 1* , rafia afroz 2 and mohd safrin 1 1 department of mechanical engineering, faculty of engineering, 2 department of economics, faculty of economics and management sciences, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. *corresponding author: arat@iium.edu.my (received: 28 th nov. 2016; accepted: 30 th oct. 2017; published on-line: 1 st dec. 2017) abstract: the adoption of lithium-ion battery technology for electric vehicles/hybrid electric vehicles (ev/hev) has recently received attention worldwide. the price of cobalt (co) and lithium (li) has increased due to the production of ev/hev. a used lithium battery is a valuable source of active metals (co, li, and al) and the optimal way of extracting these metals from this waste is still studied. the focus of this paper is to recover active metals using the hydrometallurgical method on a laboratory scale with a 48.8 wh battery to reveal economic and environmental benefits. calcination of extracted active metals as pre-thermal treatment has been conducted at 700°c to remove the organic compounds from the surface of active metals. the experiment has been conducted and the result shows that the recovery of active metals (cathode) is 41% of the cell cathode and 8.5% of the cell anode materials, which represent 48.8% and 23.4% of the cathode and anode cell material price, respectively. by recycling about 47.34% of the battery active metals, emissions can be reduced by 47.61% for battery metal production and 60.7% for disposal transportation of the used battery. the total emission can be reduced by about 52.85% by recycling the active metals in used batteries. abstrak: adaptasi teknologi bateri litium-ion ke dalam kenderaan elektrik/ kenderaan elektrik hibrid (ev/hev) telah memdapat perhatian seluruh dunia baru-baru ini. harga kobalt (co) dan litium telah bertambah hasil daripada ev/hev. perggunaan bateri litium adalah sumber berharga kepada logam-logam aktif (co, li dan al) dan cara terbaik untuk mengekstrak logam-logam ini daripada sisa ini masih dipelajari. fokus kertas ini adalah untuk mendapatkan logam aktif dengan menggunakan kaedah hidrometalurgikal dalam skala makmal dengan bateri 48.8 wh untuk mendedahkan faedah ekonomi dan alam sekitar. proses penulenan pada logam aktif yang diekstrak sebagai rawatan pre-haba telah dijalankan pada suhu 700 o c untuk membuang kompoun organik daripada permukaan logam aktif. eksperimen telah dijalankan dan keputusan menunjukkan logam aktif didapati pada (katod) adalah 41% daripada sel katod dan anod adalah 8.5% daripada bahan sel anod, di mana 48.8% dan 23.4% daripada sel katod dan harga bahan sel anod, masing-masing. dengan kitar semula logam aktif bateri sebanyak 47.43%, pelepasan boleh dikurangkan sebanyak 47.61% bagi penghasilan logam bateri dan 60.7% bagi pengangkutan pelupusan bateri terpakai. pelepasan total boleh dikawal sebanyak 52.85% dengan mengitar semula logam aktif pada pengeluaran bateri. keywords: li-ion battery; electro-chemistry; calcination; recycling;economics and environmental values iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 239 1. introduction demand for electric vehicles (evs) is growing around the world fairly rapidly. the ev/hev sales share will represent at least 50% of light-duty vehicle sales worldwide by 2050. the aim of evs/hvs is to contribute greenhouse-gas emission reductions and deliver substantial benefits in terms of improved oil security, reduced urban area pollution, and noise. the actual penetration of evs has been seen as a key factor in material demand because these vehicles require larger batteries [1]. lithium-ion batteries play a major role in powering electric vehicles by meeting their torque and speed demands. however, there is a threat regarding the availability of the lithium needed for battery production. this threat has shifted focus towards ensuring a continuous supply of materials needed for the green revolution through reuse and recycling. the dominant chemistry used in electronics batteries of active metals like ni, co., and al for lca battery, li, fe and phosphate (p) for lfp and li, manganese (m) and sulfate (s) for lms battery electrochemistry, as shown in table 1. the battery contains a weight percentage (wt%) of lithium carbonate that is less expensive compared to cobalt (co) or nickel (ni). the average lithium cost associated with li-ion battery production is less than 3% of the production cost while the battery metal production cost is about 200% higher than the battery metal‟s recycle cost [2]. intrinsic value for the li-ion recycling business currently comes from valuable metals such as co and ni that are more highly priced than li. table 1: battery materials system /electrodes lca lfp lms graphite graphite ms tio cathode lini0.8co0.15al0.05o2 lifepo4 limn2o4 limn2o4 anode graphite graphite graphite li4ti5o12 note: nca: nickel, cobalt and aluminum; lfp: lithium iron phosphate; lmo: lithium manganese oxide; lms: lithium manganese salt general motor‟s claim that “one million tons of lithium is enough to produce 395 million chevrolet volts each with the power capacity of 16 kwh and battery electrochemistry chemistry lifepo4”, i.e. 158 g of lithium metal required per kwh battery and hence the lithium needs are in the range of 113-246 g per kwh lithium-ion battery development. in addition, the theoretical charge density of lithium metal from fundamental electrochemistry is 3.8 ah/g, representing 1 g of lithium, could supply 3.8 a of electric current for 1 hour [3]. recycled lithium is as much as five times the cost of lithium produced from the least costly brine-based process [4,5]. however, with the increasing number of evs entering the market in the future, and with a significant supply crunch, recycling is expected to be an important factor for consideration in effective material supply for battery production. metal compositions of li-ion batteries are mainly al, cu, co, fe, and li, as shown in table 2. the anode typically consists of cu foil covered by a fine layer of carbon while the cathode contains al, co, and li metals. it is particularly interesting to focus research on the recycling of cathodes as the active material. such components represent 41%, by weight, of the cell components or 48.8% of the cell price. the price of al, cu, ni, co and li per kilogram are usd1.58, usd5.3, usd10.57, usd27.5 and usd9.5, respectively [1]. iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 240 research has been reviewed to identify an economical and easy recycling process [6, 7]. several methods could be preferred to recycle used li-ion batteries for metal recovery; hydrometallurgical-based and pyro-metallurgical-based processes are the most predominant. as the pyro-metallurgical process is expensive and consumes too much energy, most of the previous literature prefers the hydrometallurgical process for metal recovery. in this study, the recovery of al, co, fe, and li metals from the cathode of the used li-ion battery is focused using hydrometallurgical processes [8]. the steps are associated with the hydrometallurgical processes: physical separation of the battery (dismantling), manual separation of anode and cathode, acid leaching for the cathode, and crystallization testing for recovery of the co metal. the global ev market will represent more than 7% of the light-duty vehicle market by 2020 and 70% of evs are powered by li-ion batteries. the green revolution, through reuse and recycling of batteries, has become a crucial topic in the automotive industry ensuring the availability of lithium needed for battery production. recycling of used lithium batteries is the primary focuses of this work to extract active valuable metals such as cobalt (co) and lithium (li). table 2: composition of lithium battery [6] components amount (wt%) cathode, anode, and electrode 40  1.5% plastic case 22  1 steel case 11  1.5 copper foil 9  0.5 aluminum foil 6.5  0.5 electrolyte 5  1.5 solvent 5.5  1 electrical board and circuit 1.5 0.5 2. materials and methods recycling batteries is beneficial to the environment. it keeps them out of landfill, where heavy metals may leak into ground when the battery casing corrodes, causing soil and water pollution. the composition of an li-ion battery is shown in table 2. 2.1 recycling and disposal the author [9] has developed a „hydrometallurgy‟ process (fig. 1) by modifying the hydrometallurgy process to recover the licoo2 battery metals. mechanical pre-treatment (calcination) and physical separation are applied to recover the battery materials such as plastic, metal casings, co, li, cu, al, and fe [7]. in the hydrometallurgical process, lithium batteries are first dismantled to separate plastic and iron scraps from the active electrode materials by physical separation using crushing, sieving, and magnetic separation. the leaching method involves a model to separate the battery electrodes by dissolving them into an aqueous solution hcl, and h2so4 with and without h2o2. the used licoo2 battery of 48.8 wh capacity and 302 g weight has been used in this study to recover the metals. mechanical treatment, breaking apart plastic and cells, and some physical separations have been performed by means of gravity and magnetism. crushed plastics from shells can be separated by flotation. using magnetism the steel parts of the containers are separated. iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 241 fig. 1: lithium battery recycling model (a) metallurgy process, (b) precipation process by using na2co3 solution, (c) solvent extraction process by cyanex 272 agent, (d) electrolysis process by using current density 200-250 a/m 2 , (e) crystalization process. 2.2 leaching process leaching is a liquid-solid operation. two phases are intimately in contact; the anode of the battery is diffused from the electrolyte to the liquid phase, which causes a separation of the components originally in the solid. the rate of mass transfer of the cathode can be estimated by, (1) where, is the mass rate of cathode materials dissolved into the solution, a is the surface area of chop particles of cathode in m 2 , km is the mass transfer coefficient of cathode into the acid solution in m/s, scm(s) is the saturation solubility of the battery active materials (li, co, al) in the aqueous solution (hcl and h2so4 with and without h2o2) in kg∙mol/m 3 , and ca is the concentration of the aqueous soluble compounds of cathode materials at time t sec in kg∙mol/m 3 . the rate of accumulation of li in the solution is equal to the dissolving beaker: dc a s li s( ) -c ac a i( ) c a f( ) ò = k m v a dt ti t f ò (2) if the dissolving time (t) of the cathode material into the solution between time, t= ti to tf and concentration, ca = ca(i) to ca(f), by integrating eq. (2), the saturation solubility of li can be modelled as, iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 242 s cm s( ) = c a f( ) -c a i( )( )+e kmadt v (3) with dt = t f -t i( ). where, scm(s) is the rate of cathode material accumulation in the solution kg∙mol/m 3 . the 3 m of hcl solution has been prepared by mixing 75 ml of hcl with 300 ml of distilled water based on reported work [8]. the cathode of the battery was cut into small pieces of 2g each and put into acid solution and stirred with a magnetic stirrer for 1 hr. the temperature of the solution was varied to identify the changes in leaching rate. the leaching test was performed at room temperature of 30 o c and by varying the temperature in the range of 60 o c 80 o c with the inorganic acid solutions of hcl and h2so4 with and without h2o2. the effect of h2o2 on the percentage of metal obtained from the leaching process was studied. from observation, the presence of h2o2 as the reducing agent of h2so4 makes a „piranha‟ solution (h2so5) and separates lithium and co metal. 2.3 physical separation the composition of the licoo2 battery after physical separation is presented in table 3. the peeled cobalt lithium oxide from aluminum foil is gained by the vacuum pyrolysis process, which is leached with inorganic acids such hydrochloric acid (hcl), and sulfuric acid (h2so4). hydrochloric acid can leach co and li more efficiently and economically. by adding h2o2 with h2so4, the co and li leaching efficiencies have been increased. the optimal volume percentage of h2o2 is in the range of 1-10% and can be used in the leaching process [8, 9]. in this study, 2 vol% of h2o2 with 4 m h2so4 were used. after leaching, the leaching solution and insoluble residue were separated by filtration for the precipitation, solvent extraction, and electrolysis processes to recover co and crystallization test to identify the intensity of cu, li, coso4 using the established x-ray diffraction (xrd) method. table 3: battery (48.8 wh licoo2) materials composition components amount (%) cathode, anode, and electrode 46.2 plastic case 18.63 steel case 10.56 copper barrel 7.5 aluminum foil 1.8 electrical board and circuit 2.75 others 12.56 2.4 precipitation the chemical precipitation method has been conducted for recovering co and li. the precipitation of the leaching processes was collected to recover li. the ammonium oxalate [(nh4)2c2o4] 2 m was used with the precipitate for further precipitation of co. the precipitation was then collected and treated with na2co3 to recover li and co. the li was recovered about 82% with the co impurities about 0.90%. the result can be supported by the findings [10-12]. while the co was extracted to 84%. 2.5 solvent extraction solvent extractant cyanex 272 (a dialkyl phosphine acid extractant) was used to iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 243 recover cobalt after leaching with h2so4 without h2o2 based on the study with h2o2 [13,14]. the co was recovered 81.78% by using of 1.5 m cyanex 272 with the organics/aqueous ratio and 85.42% by using of 1.5 m cyanex 272 with the organics/aqueous ratio (o/a) of 1.6. by using 0.5 m of cyanex 272 with the o/a of 1, the 99% of the rest co (14.58%) was recovered. 2.6 electrolysis the authors [14] have used the electrolysis process for ni recovery from a leaching solution using h2so4 with an h2o2 after-solvent extraction of co with cyanex 272. nickel electrowinning was performed at 250 a/m 2 current density at 50 o c, ph 3–3.2, with an electrolyte having about 50 g/l ni and 20 g/l h3bo3, produces a good aspect ni deposit with a current efficiency of 87% and a specific energy consumption of 2.96 kwh/kg [15]. in this study, we have used the electrolysis process to recover co from a leaching solution using h2so4 with h2o2 after solvent extraction of co with cyanex 272. the co electrowinning extraction was conducted with the current density of 240 a/m 2 at temperature 60 o c. the pure co was extracted about 92.01%. fig. 2: procedure of cathode separation. 2.7 crystallization test a crystallization test was conducted to separate the cathode and the intensity of the cathode was identified using an x-ray diffraction test. a crystallization model (fig. 2) has been developed from this study to analyze the cobalt sulphate (coso4) electrolyte. the pure solution from the acid leaching process has been reheated with temperature in the range of 100-150 o c for 3-4 hours to obtain high pure coso4. the coso4 was washed with acetone and filtered. the coso4 was left dried and weighed and processed the sample for metal detection and analyzed by x-ray diffraction (xrd). the atomic plane of ! ! ! ! ! ! wash the coso4 with acetone filter!to! obtain! salt! powder! wight!the!salt! powder!coso4! reheat the coso4 solution obtained from acid leaching test !at 100-150c by using x-ray diffraction (xrd) analysis coso4 coso4 dry salt iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 244 coso4 causes an incident beam of x-rays to interfere with one another. the phenomenon is called x-ray diffraction (xrd). it is a rapid analytical technique used for phase identification of a crystalline material. 2.8 emission estimation transportation is essential for battery collection prior to recycling or disposal in a landfill. when fuel is burned in an engine combustion chamber, most of the carbon is eventually oxidized to co2 and emitted to the atmosphere. the emission of co2 can be improved drastically if the battery is processed for recycling rather than disposal. the emission of carbon can be estimated using equation [16]: c emission =m c  ´ (fc) oxidized (4) with mc =qfuel ´ sfcc(coeff ) and qfuel =vfuel ´hvfuel where, mc is the mass of carbon content in fuel in kg, sfcc(coeff) is the coefficient of carbon content in fuel in kg/j, qfuel is the fuel combustion energy in j, vfuel is the volume of fuel in l, hvfuel is the heating value of fuel in j/l. equation (4) can be rewritten: c emission =v fuel  ´hv fuel ´ sf cc(coeff ) ´ (fc) oxidized (5) where, (fc)oxidized is the fraction of carbon oxidized in percentage. co 2 emission( ) =c emission ´ co 2 (m.w) c m.w( ) (6) where, m.w represents molecular weight and cemission is the amount of carbon emission in kg. equation (6) can be re-written by using eqs. (5) and (6): co 2 emission( ) =v fuel  ´hv fuel ´ sf cc(coeff ) ´ (fc) oxidized  ´ co 2 (m.w) c m.w( ) (7) where, vfuel is the volume of fuel in liters. the amount of fuel (volume) can be estimated directly from the vehicle mobile source. 3. results and discussion the separation of co metal by leaching with 4 m of hcl and h2so4 with and without h2o2 has been studied for the temperature of 60-80°c and is presented in table 5. the leaching rate of co metal extraction has increased 45% for the leaching with hcl and increased 21% for changing temperature from 60 to 70 o c and decreased 6% due to the removal of the impurities from the surface of co metal. the leaching rate of co metal extraction has increased 7% for changing temperature from 60 to 70 o c and decreased 2.5% for changing temperature from 70 to 80 o c. overall, the co leaching rate was lower than the leaching rate for the acid hcl and h2so4 without h2o2. this could be the decomposition of h2o2 resulting in the evolution of oxygen onto the co. the conclusion can be supported by the research work of the authors [18]. furthermore, the weight of co extraction by using hcl and h2so4 without h2o2 is more than by using h2so4 with h2o2. this is due to the formation of caro acid (h2so5). caro acid has an acidic property and a higher oxidizing potential, which has the high potentiality to remove impurities and residue from the surface of co. the conclusion can be supported by the authors„ published research work [17-18]. based on the results exhibited in table 5, it is concluded that the leaching rate of the co by hcl is more than the h2so4 without h2o2 and h2so4 with iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 245 h2o2 because of the boiling temperature in the range of 60-80 o c. in this case, the h2so4 with and without h2o2 are stronger than the hcl. fewer impurities remained on the surface of the co when it was leached by h2so4, with and without h2o2. table 4: leaching of the co for temperature of 30 o c acid solution concentration (m) leaching rate (%) hcl 1 37.5 2 47.6 3 55.7 4 60.5 h2so4 1 48.6 2 71.8 3 85.3 4 99.0 h2so4 with 2% vol. of h2o2 1 40.2 2 67.8 3 78.9 4 83.0 table 5: temperature effect on acidic leaching process acid solution temp. ( o c) weight of co (g) leaching rate (%) initial final difference 4 m hcl 60 2.00 1.10 0.90 55.0 70 2.00 1.43 0.57 71.5 80 2.00 1.58 0.42 79.0 h2so4 60 2.00 0.98 1.02 49.0 70 2.00 1.4 0.60 70.0 80 2.00 1.45 0.55 64.0 h2so4 with 2% vol. of h2o2 60 2.00 0.74 1.26 37.0 70 2.00 0.88 1.12 44.0 80 2.00 0.83 1.17 41.5 table 6: metal extraction metal extracted purity of metal extracted (%) precipitation solvent extraction with h2so4 electrolysis (electro-winning) (nh4)2c2o4 na2co3 with h2o2 without h2o2 lithium (%) 82 cobalt (%) 84 85.42 81.78 92.01 table 6 shows the lithium and cobalt extraction from the leached solution by three different processes with the leached solution, which was made with 4 m h2so4 + 2% h2o2. the electrowinning process is a promising process of the hydrometallurgy family of techniques. table 7 shows the composition of the powder of li-ion battery, which was found from the recycling of a 48.8 wh battery (weight 302.7 g). the amount of cobalt (co) 9.11% (27.85 g) in the battery mass (or 13.8% the total amount of anode, cathode and iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 246 electrolyte mass) is greater than the other anode and cathode materials. the amount of total recycled active metals (co, li, cu and al) is 29.78%. table 7: battery‟s metal obtained after recycling components weight (g) amount (wt%) plastic 56.27 18.63 steel (battery pack cover) 12.56 3.98 lithium 8.58 4.03 anode and cathode extracted 24.82% cobalt 27.85 13.08 aluminum 7.45 2.46 copper 15.84 5.25 electrical board and circuit 8.32 2.75 others (including electrolyte) 55.14 18.25 table 8 shows the metal obtained from recycling for the equivalent of a 1000 wh battery. the economic value of co obtained from the 48.8 wh battery is usd 0.77 while for the 1000 wh battery it is approximately usd 15.7. the economic values of the recycled licoo2 battery of a 48.8 wh is usd 0.91 while for the 1000 wh battery, it is approximately usd 20.29. if an electric vehicle is equipped with a licoo2 battery with a capacity of 33 kwh (standard power pack for an electric car), the recycled value of anode and cathode materials is usd 669.57; where the value of co is usd 528.00. for 100 ev batteries, each with 33 kwh of electrochemistry licoo2, the recycled values of co is only usd 52800.00. fig. 3 shows that the cleavage faces of the anode, cathode, and crystalline electrolyte appear to reflect x-ray beams at certain angles of incidence (theta, θ). results show the cleavage faces 111, 200, 220, 222, 311, and 511 for the atoms of an anode, cathode, and electrolyte. the shape of the incident beam or counts depends on the focal projection of the filament onto and from the anode material. cu (atomic number 29) is suitable for most diffraction examinations and is the most widely used anode material. co (atomic number 27) is often used with ferrous samples, fe (atomic number 26) fluorescence radiation would cause interference and cannot be eliminated by other measures. li (atomic number 3) is the lightest metal and the least dense solid element. table 8: economic values of recycled cathode and anode materials materials materials extracted (g) international price (usd/kg) values of extracted materials (usd) 48.8 wh 1000 wh 48.8 wh 1000 wh lithium 8.58 175.82 9.5 0.082 3.41 cobalt 27.85 570.65 27.5 0.77 15.7 aluminum 7.45 152.65 1.58 0.012 0.24 copper 15.84 324.56 5.3 0.046 0.94 total price of extracted materials of battery (usd) 0.91 20.29 iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 247 (a) cathode (li) (b) anode (cu) crystal (coso4) fig. 3: x-ray analysis for licoo2 battery. fig. 4: overall cost breakdown of battery production [18]. 3.1 economic benefit of recycling recycling of automotive batteries has economic benefit. recycling means saving natural resources and energy, generating income, and reducing imports. in addition, the biological activities of co are largely confined to its role in the vitamin b12 series of coenzymes and the cu presents in a variety of proteins and enzymes, including cytochrome oxides, an enzyme in respiratory chains [19]. therefore, battery recycling is a much better option than disposal in landfills. the recycling cost can be limited by the steps involved in the metallurgical process. stewardship ontario program pays usd1.24 per kg of batteries for recycling, compensating recyclers usd1,240. the estimated cost to detection of diffractedx-rays by a diffractometer photon counter detector amplifier c circle of diffractometer recording focalization circle bragg brentano focus geometry, cullity figure : bragg’s-bretano focus geometry : detection of diffracted x-ray by a diffractometer. 54 other acid solutions. leaching process at temperature of 80 o c using 4m hcl solution will be selected as its leaching rate was the highest (79%). 4.5 xrd analysis fig. 45 x-ray patterns of the metal obtained after leaching process after conducting the leaching process, the metal obtained was dried before being analyzed using x-ray diffraction (xrd). the dried sample was tested in order to characterize the metal content. the peak of the graph showed the metal available from the sample. based on fig. 4-5, the metal obtained from leaching process mostly lithium metal. it can be concluded that the leaching process separates lithium metal from other metal which available at the cathode. data can be obtained from appendix a. li li li 0 20 40 60 80 100 120 140 0 10 20 30 40 50 60 70 c o u n ts / s 2 theta xrd analysis for cathode peak figure : x-ray analysis for cathode. (200 (220) (111) li(311) li (331) (2 theta) (theta) text intensity iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 248 recycle batteries is about usd2,000 per ton, while the cost for the hydrometallurgical process is about usd1,500 per ton [20]. fig. 5: reproduce energy for battery production [2]. table 9: battery pack for ev and its baseline cost [24]. battery parameter baseline electric vehicle range, km 50 number of battery pack 1 number of cells per pack 52 battery system total energy, kwh 8.7 cell capacity, ah 43 module (2s2p) capacity, ah 86 battery system capacity, ah 86 battery nominal voltage, v (ocv at 50% soc) 100 cost for baseline battery with total price to oem: usd 2528 the recycled metal is usd 20.03/kwh, which will reduce the material cost. electrode cost is usd 140 per kwh battery. it is calculated that the recycled metal can save 14% of the total cost of active metal per kwh battery. if an ev battery power pack equivalent to 33 kwh is recycled, its production cost can be reduced usd 660 by using the recycled materials. figure 4 shows the breakdown of unit costs for baseline battery with total price to oem of usd 2,528. the total battery cost to the oem, including pack integration components but excluding thermal management external to the pack usd 2,923 [21-22]. figure 5 shows that the metal production for the battery is 3 times more than the battery production while it is 300 times more than the recycling process. by recycling, the cathode and anode are obtained by 41% and 8.5% by weight of the cell components respectively, which is usd 20.03/kwh of the battery. table 9 shows the capacity of a 8.7 kwh battery for the short travelling range of an electric vehicle (about 50 km), which has been developed and tested [22]. the total cost of 52 table 42 data from the leaching process with different temperature acid solution temperature ( o c) initial weight (g) final weight (g) 𝚫m (g) leaching rate (%) 4m hcl 60 2.0 1.10 0.90 55.0 70 2.0 1.43 0.57 71.5 80 2.0 1.58 0.42 79.0 4m h2so4 60 2.0 0.98 1.02 49.0 70 2.0 1.40 0.60 70.0 80 2.0 1.28 0.72 64.0 4m h2so4 + 2 vol% h2o2 60 2.0 0.74 1.26 37.0 70 2.0 0.88 1.12 44.0 80 2.0 0.83 1.17 41.5 4.4.1 sample calculations to calculate the leaching rate for different temperature, the same equation to be used as follows: leaching rate; xb=    x  100% sample calculations: initial weight of cathode used = 2.0 g weight of the filter paper = 0.56 g weight of metal after filtration + weight of filter paper = 2.14 g final weight = (2.14-0.56) = 1.58 g leaching rate = (1.58) / (2.0) x 100% = 79% 30 40 50 60 70 80 90 55 iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 249 the battery was usd 2528. the battery lifespan was considered as 5 years based on the oem. the recycled materials value for 8.7 kwh batteries is 14% of the active cost and 8% of the battery oem baseline price. the battery electrodes values are estimated as 0.49 × usd 2528 or usd 1238 and the recycled material values as usd 20.03×8.7 or usd 174.26. table 10: emission on battery metal production and transportation note: wo-rc = without recycling; wi-rc = with recycling assumption (i) *fuel consumption of a pick-up van with 500 kg payload = 0.121 liter/km. (ii) source of energy = diesel (iii) standard battery capacity for an ev= 33 kwh (iv) 33 kwh battery mass = 264 kg (v) co2 emission = 2.2 kg/liter (vi) distance:  ev battery exchanging workshop to landfill = 20 km  battery exchanging workshop to recycling plant = 0 km  recycling plant to landfill = 8 km it is also estimated that the if the battery capacity of 34 kwh for an ev with a range of 117 km (aeo recommended), the recycled material values of the battery materials (cathodes and anodes) would be usd 681. if the 100,000 evs each of battery capacity 34 kwh will be under recycled (i.e, 3400,000 kwh battery), the material would save 833.77 g/kwh battery and its values would be usd68102 which is very much profitable for a small scale company. the recycled values of the material of batteries 41 % and 48.8% price of the cathode and anode are 8.5% and 23.4% price of the anode. it shows that by recycling the electrodes of the battery, consisting mainly of cobalt, nickel, and lithium, will save up to 48.8% of new battery manufacturing cost. this indicates that in a lithiumion battery recycled component values can be higher and would encourage people to set up recycling plants to recycle large-scale batteries. this not only contributes economically but also environmentally. ! metal production description energy required emission (co2) (g) (mcal/kwh) gasoline (litre) 1 kwh 33 kwh metal production wo-rc (need 100% materials) 290 0.042 92.4 3049 wi-rc (reduces 47.43% metals production) 153.7 0.022 48.4 1597.2 transportation *transportation (used battery) fuel consumption for each 33 kwh battery pack (litre) emission (co2) (g) wo-rc 0.26 572 wi-rc 0.05 110 iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 250 3.2 environmental benefit of recycling the battery powered ev is increasing significantly to improve the environment for living planets. furthermore, batteries in the modern day world have become universal. they make available energy for a wide range of products that are used across all sections of economic activity, from households to large industrial enterprises. they also provide backup power for activities that involve an uninterruptible power supply (ups). the battery is categorized as hazardous waste at the end of its life as it can damage human health or the environment [23]. furthermore, mining and processing ores (e.g., sox emissions from smelting of sulfide ores, such as those that yield copper, nickel, and cobalt) creates significant negative environmental impacts. these are avoided if the materials can be recycled [24]. if usable materials used batteries can be recovered, excessive battery materials production cost can be avoided, which could be 200% more than the battery production, as shown in fig. 5. it should be mentioned that the higher input on the material production causes more co2 emission than the battery production as the motorized system uses for the material production, which is powered by the ic engine or electrical motor. table 10 shows the amount of emission (co2) on battery metal production and transportation. table 6 shows that the valuable anode and cathode metals can be recycled by 24.82% while total metal recycled, including plastic and steel, is 47.43%. the result indicates that the metal production decreases by about 47.43%, which reduces the energy consumption. fig. 5 shows the energy required for metal production is 290 mcal per kwh of licoo2 battery. it is considered that the energy required also decreases by 47.43%, which causes the co2 reduction by 47.61%. furthermore, if the battery is disposed of in a landfill some distance away from the recycling center, the emission of co2 will be increased, as the co2 emission is directly proportional with the engine fuel consumption. the emission of co2 is estimated at about 2.2 kg per liter of diesel using eq. (9). a diesel pick-up van (engine capacity of 2.4 liter) is considered for transportation, which reduces fuel by 1 liter for every 8 km. the van is considered to go to & from the disposal point. it is estimated that the co2 reduction from transportation with recycling is 80.7% lower than that of without recycling. total emission (co2) can be controlled by recycling is about 52.85%. 7. concluding remarks the cobalt and lithium recovery from used lithium batteries is discussed in this work. the hydrometallurgical method is used for the extraction of materials from the waste. calcination was chosen for thermal pretreatment of co, li, and cu black masses from the used portable lithium batteries. calcination was conducted at 700 o c for 60 minutes to remove the organic impurities before leaching process. the leaching process has been conducted mainly with different concentrations, mainly of acid h2so4 , with and without an h2o2 reducing agent at varying temperature 60 o c 80 o c. the electrolysis process can be considered as it could achieve the cobalt compound of very high purity from lithium battery since it does not introduce other substances and avoid impurities. this process has the disadvantage of consuming too much electricity and the safety. the recovery of the cathode (li, co and al) is 41% of cell cathode and anode (cu) is 8.5% of the cell anode materials, which are 48.8% and 23.4% of the cathode and anode cell material price, respectively. this could be considered as the motivation and encouragement to recycle large-scale used batteries. iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 251 based on the recycled metals, it is found that the emission reduced by 47.61% for metal production of battery and 80.7% for transportation of used battery disposal. in overall, emission for the metal production and transportation can be controlled by 52.85% if the battery active materials will be recycled and used in battery production. acknowledgement the authors are grateful to the ministry of higher education, malaysia and research management center, international islamic university malaysia for financing this project by myra grant. references [1] codeff data research on lithium within the reduse project partners countries, (2011). http://www.reduse.org/en/blog/lithium-extraction-chilean-north. [2] habashi f. (1997). principle of extractive metallurgy. vol. iv: lithium. wiley-vch, weinheim, 1997. [3] william t. (2010) how much lithium does a liion ev battery really need?meridian international research francehttp://www.meridian-int-res.com/ [4] linda g. (2009). lithium ion battery recycling issues, linda gaines, argonne national laboratory. retrieved date: 21/5/09. [5] lain mj. (2001) recycling of lithium ion cells and batteries. j power sources, 97-98:736-738. [6] li j, zha or, he x. (2009) preparation of licoo2 cathode materials from spent lithium-ion batteries, ionics, springer berlin, 15(1):111-113. [7] rahman a, rafia a. (2017) lithium battery recycling management and policy. international journal of energy technology and policy, 13(3):278-291. [8] ferreira da, prados lm, mansur mb. (2009) hydrometallurgical separation of aluminium, cobalt, copper and lithium from spent li-ion batteries. j power sources 187:238-246. [9] alexandre c, beata p. (2013). a brief review on hydrometallurgical technologies for recycling spent lithium-ion batteries. j chem technol biotechnol 88:1191-1199. [10] paulino jf, busnardo ng, afonco jc. (2008) recovery of valuable elements from spent lithium batteries. journal of hazardous materials, 150:843-849. [11] nan j, han d, zuo x. (2005) recovery of metal values from spent lithium-ion batteries with chemical deposition and solvent extraction. journal of power sources, 152:278–284. [12] xia zd, xie xq, shi yw, lei yp, guo f. (2008) recycling cobalt from spent lithium ion battery. mater. sci., 2(3):281-285. [13] kang j, senanayake g, sohn j, shin sm.(2010) recovery of cobalt sulfate from spent lithium ion batteries by reductive leaching and solvent extraction with cyanex 272. hydrometallurgy, 100:168171. [14] lupi c, pasquali m. (2003) electrolytic nickel recovery from lithium-ion batteries. minerals engineering, 16:537–542. [15] xu j, thomas hr, francis rw, lum k, wang j, liang b, (2008) a review of processes and technologies for the recycling of lithium-ion secondary batteries. j. power sources, 177:512-527. [16] rahman a, fadhilah r, rafia a, mohiuddin akm, hawlader mna. (2015) power generation from waste of ic engines. renewable and sustainable energy reviews, 51:382-395. [17] adebayo ao, ipinmoroti ko, ajayi oo. (2003). dissolution kinetics of chalcopyrite with hydrogen peroxide in sulfuric acid medium. chemical and biochemical engineering quarterly, 17(3):213-218. [18] ferella fi, michelis d, veglio f (2011). process for the recycling of alkaline and zinc-carbon spent batteries. journal of power sources, 183(2):805-811. [19] olubambi pa, borode jo, sdlovu s. (2006). sulfuric acid leaching of zinc and copper from nigerian complex sulfide ore in the presence of hydrogen peroxide. the journal of the southern african institute of mining and metalurgy, 106:765-770. [20] raymond c. (2005). physical chemistry for the bioscience, university science book, sausalito california (www.uscibooks.com), retrieved date: august 2016. [21] rahman a, farhan s, ahmed h, hawlader, mna, (2014). development of evaporative battery cooling system for evs/hevs. international journal of electric and hybrid vehicle system, inderscience, 8(2):233-240. http://www.reduse.org/en/blog/lithium-extraction-chilean-north http://www.meridian-int-res.com/ http://irep.iium.edu.my/52452/ http://www.uscibooks.com/ iium engineering journal, vol. 18, no. 2, 2017 rahman et al. 252 [22] rahman a, helmi a, hawlader, mna. (2017) two-phase evaporative cooling battery thermal management system for electric vehicle. international journal of automotive technology, 18 (3):72882. [23] rahman a, afroz r, alam z. (2014) development of electric vehicle: public perception and attitude, the malaysian approach. world review of intermodal transportation research, 5(2):149-167. [24] dunn j, gaines l, sullivan mq. (2012). the impact of recycling on cradle to gate energy consumption and green gas emissions of automobile lithium-ion batteries. environ. sci. technol. 46:12704-12710. microsoft word 0_vol_16_no_2_2015_special issue on energy_compiled.docx iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 57 nano-battery technology for ev-hev panel: a pioneering study ataur rahman, m. rashid, a.k.m. mohiuddin and m.n.a. hawlader department of mechanical engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. arat@iium.edu.my; mahbub@iium.edu.my; mohiuddin@iium.edu.my; and mehawlader@iium.edu.my (received: nov. 2,2015; accepted: nov. 10, 2015; published on-line: nov. 30, 2015) abstract: global trends toward co2 reduction and resource efficiency have significantly increased the importance of lightweight materials for automobile original equipment manufacturers (oem). co2 reduction is a fundamental driver for a more lightweight automobile. the introduction of electrical vehicles (evs) is one initiative towards this end. however evs are currently facing several weaknesses: limited driving range, battery pack heaviness, lack of safety and thermal control, high cost, and overall limited efficiency. this study presents a panel-style nano-battery technology built into an ev with cuo filler solid polymer electrolyte (spe) sandwiched by carbon fiber (cf) and lithium (li) plate. in addition to this, an aluminum laminated polypropylene film is used as the electromagnetic compatibility (emc) shield. the proposed battery body panel of the ev would reduce the car weight by about 20%, with a charge and discharge capacity of 1.5 kwh (10% of car total power requirement), and provide the heat insulation for the car which would save about 10% power consumption of the air conditioning system. therefore, the ev would be benefited by 30% in terms of energy reduction by using the proposed body. furthermore, the proposed body is considered environmental-friendly since it is recyclable for use in a new product. however, the main limiting factors of the spe are its thermal behavior and moderate ionic conductivity at low temperatures. the spe temperature is maintained by controlling the battery panel charging/discharge rate. it is expected that the proposed panel-style nano-battery use in an ev would save up to 6.00 kwh in battery energy, equivalent to 2.81 liters of petrol and prevent 3.081 kg of co2 emission for a travel distance of 100 km. abstrak: trend global ke arah pengurangan co2 dan kecekapan sumber telah meningkat dengan ketara pentingnya bahan-bahan ringan bagi pengeluar peralatan asal kereta (oem). pengurangan co2 adalah pemacu asas untuk kereta yang lebih ringan. pengenalan ev adalah satu inisiatif ke arah ini bagaimanapun ev sedang menghadapi beberapa kelemahan: sasar terhad, bateri pek berat, kekurangan keselamatan dan kawalan haba, kos yang tinggi, dan kecekapan keseluruhan yang terhad. kajian ini membentangkan gaya panel teknologi nano bateri dibina ke dalam ev dengan elektrolit pengisi cuo polimer pepejal (spe) diapit oleh fiber karbon (cf) dan plat lithium (li). di samping itu, aluminium berlapis filem polipropilena menggunakan sebagai keserasian elektromagnet (emc) perisai. dicadangkan panel badan bateri ev akan mengurangkan berat badan kereta dengan kira-kira 20%, dengan kapasiti caj dan pelepasan 1.5 kwh (10% daripada kereta jumlah keperluan kuasa), dan menyediakan penebat haba untuk kereta yang akan menjimatkan kira-kira 10 % penggunaan kuasa sistem penghawa dingin. oleh itu, ev itu akan mendapat manfaat sebanyak 30% dari segi pengurangan tenaga dengan menggunakan badan yang dicadangkan. tambahan pula, badan yang dicadangkan dianggap mesra alam kerana ia boleh dikitar semula untuk digunakan dalam iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 58 produk baru. walau bagaimanapun, faktor utama yang menghadkan spe adalah tingkah laku haba dan kekonduksian ionik sederhana pada suhu rendah. suhu spe dikekalkan dengan mengawal panel bateri kadar caj / pelepasan. ia dijangka bahawa dicadangkan gaya panel penggunaan nano bateri dalam kereta ev akan menjimatkan sehingga 6.00 kwh tenaga bateri, bersamaan dengan 2.81 liter petrol dan mencegah 3,081 kg pelepasan co2 untuk jarak perjalanan 100 km. keywords: epoxy resin; carbon fiber; lithium thin plate; energy generation; solid electrolyte battery 1. introduction the cost of fuel consumption and emission of automobiles have always been a problem for users and the environment. the use of lightweight materials is significantly growing in the automotive industry due to its vehicle traction power reduction and improvement of greenhouse gas (ghg) emission. lightweight materials offer weight reduction potential at a higher cost – carbon fiber (cf) has the highest weight reduction potential which is 50-60% lighter than steel as shown in table 1. the industrialization of cf may yield a cost decrease up to 70%, thereby making it a significantly more attractive alternative. for example, the average emissions of all models sold by an oem in one year needs to drop co2 per kg from 140 g in 2012 to 75 g in 2025 and beyond [1]. the energy source of electric vehicle (ev) is bulky due to the weight of battery pack. this paper presents an innovative potential solution to the problem by developing a new ev body, which is able to reduce the weight of the vehicle and act as a storage of energy, thereby decreasing co2 emission [2]. the ev body consists of cf that acts as an anode, cuo filler er as the solid electrolyte, and a lithium thin plate as the cathode. researchers [3] have demonstrated the load bearing capacity and electrochemical characteristics of a structural battery built with carbon nano-fiber-reinforced active material composites. the cf electrochemical characteristics have been studied [4-8] and literature reports that electrochemical potential of cf against li is less than 0.5 v throughout the state-of-charge (soc). specific charge capacity is found to be 372 ma h/g, which is larger than common cathode materials such as licoo2, limn2o4, and lifepo4 [9-11]. table 1: weight reduction potential [1]. lightweight material material replaced mass reduction (%) magnesium steel, cast iron 60 75 carbon fiber composites steel 50 60 aluminum matrix composites steel, cast iron 40 60 aluminum steel, cast iron 40 60 titanium steel 40 55 glass fiber composites steel 25 35 advanced high strength steel mild steel 15 25 high steel strength mild steel 10 15 epoxy resin (er) is a polymer widely used in a variety of applications such as structural composites, electronics, adhesives and coatings. the cured resins have many useful properties, such as excellent combination of stiffness, strength, chemical resistance, iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 59 insulating properties, electric mobility with filler materials, and environmental stability. however, such epoxy resins tend to be rather inherently brittle in nature with poor crack resistance. numerous attempts have been carried out to improve its performance, especially in terms of the thermal conductivity of er [12-15]. a very high micro-filler loading, normally 60 vol% or even higher, is needed to satisfy percolation thresholds and to obtain a high thermal conductivity to form continuous heat conducting chains. however, conductive metal fillers (al2o3, cuo, graphite) and er can give a better conductivity due to their higher electrical characteristics and chemical stability [3].the author [3] also reported that by adding 15wt% of cuo filler and 20 wt% plasticizer at ambient temperature can increase the dielectric properties of solid polymer electrolyte. a hybrid filler comprised of carbon nano materials has been studied [16] and reported that a remarkable thermal conductivity of 5 w/mk can be achieved with an extremely high concentration of nano fillers of cuo of about 50 wt.%. 2. materials and methods 2.1 mathematical modeling the description of the mathematical models for the estimation of anode, and electrolyte electric and thermal conductivity, panel-style battery structure, development of cf specimens and cuo filler solid polymer electrolyte (spf) is the core discussion of this section. the electrical conductivity is the major concern of this paper’s discussion. different wt% of filler materials are synthesized with epoxy resin (er) to enhance its electron mobility or ionic conductivity and thermal conductivity. the electrical conductivity of spe can be estimated by using the equation:  c  4  dc d 2 cos2        vp f    x  (1) where,ߪ௖ is the conductivity of the composite, f is the conductivity of the fibers, dc the diameter of the circle contact, d is the diameter of the fiber, l is the average fiber length, x represents a factor depending on the contact number of fibers, and θ is the fiber orientation angle. the dielectric strength of the cuo filler er electrolyte indicates the potentiality of the spe for charge storage and release. the breakdown voltage (considered as cut off voltage, vcut-off (kv) of the spe and the dielectric strength, e (kv/mm) can be calculated as, e = vcut-off / t , where, t is the thickness of the sample in millimeters. although the vcutt-off is not expected from the spe as it will be in continuous charging and discharging mode by the vehicle regenerative braking system (rgb) power. the voltage of the proposed ev body (nano-battery) can be estimated by considering it as a capacitor: vd  c 2 2c c  vc  (2) where, vd is the developed voltage from ev body in volts, vc is the charging voltage of the cuo filler er in volts, and c is capacitance in farads. vd will be zero if the solid polymer electrolyte state-of-discharge (sod) reaches 85% of the state-of-charge (soc). the capacitance of the proposed body can be estimated as, soc of c c a d iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 60 with where, εc , ɛf, and ɛm is the dielectric constant of composite (cf), filler (cuo) and matrix (er), a is area of plates in m2, and d is the distance between plate in m. instantaneous charging current (ic) of battery can be estimated as, ic  sod   of c  s vd ( )  (3) where, is is the instantaneous charging current of the capacitor in ampere, cs is the instantaneous capacitance, vd(s) is the instantaneous discharge voltage developed by the car body in time ts. is will be more if the there is no gap between the (i) cuo filler polymer electrolyte and the carbon fiber (anode electrode), and the (ii) cuo filler polymer electrolyte and the lithium thin plate (cathode electrode). in this case, there will be an increase in the movement of electrons and the current flow. electric conductivity of cuo filler er has been measured after sandwiching with cf and li-plate. the discharge current of the body is kept in the range of 20-35 a to avoid the heating effect, which might melt the er film. total heat generated (qgen) inside a battery due to the electron mobility qjoule can be expressed by using the equation [17]: (4) with i bat p t t p t t lncdt t c s bat i   the proposed body would be able to reduce the car weight by about 20%, charge and discharge capacity of 1.5 kwh (10% of car total power requirement), and provide the heat insulation for the car which would be able to save about 10% power consumption of the air conditioning system. therefore, the ev would be benefited by 30% in terms of energy by using the proposed body. the insulating heat of the proposed body can be estimated based on the equation: q  k1 a1 x1 t t1  k2 a2 x2 t1 t2  k3 a3 x3 t2 tic        dt 0 t  (5) where, k1, k2, and k3 are the coefficient of heat conductivity of cf, electrolyte and li-plate respectively, x1, x2, x3 are the thickness of cf, electrolyte and li-plate respectively, a1, a2, and a3 are the area of cf, electrolyte and li-plate respectively, t is the environmental temperature, t1 is the temperature of cf, t2 is the temperature of solid electrolyte and tic is the temperature inside the cabin oc. at ev starting time, the inside cabin temperature is always in the range of 18-20oc. 2.2 development of panel type nano-battery the structural battery has been developed by using cf as the anode, cuo filler er as the electrolyte and lithium thin plate as the cathode, as shown in fig. 1. the carbon fiber (cf) plate was developed using araldite cy231 epoxy resin with an anhydride hardener aradur hy925. a mold was used, built with two copper alloy plates, with a spacer distance of 200µm. the nano-particle cuo filler er solidified electrolyte specimens was   fm fm mc    .12 ...2   iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 61 fabricated by mixing of 0.1 wt%, 0.3 wt%, 0.5 wt%, 1 wt%, 3 wt% and 5 wt% of cuo with liquid er. the mixtures were casted into the mold and post cured for 24 hours at 140oc. fig. 1: panel type nano-battery technology. aluminium laminated polypropylene film has been used with the proposed body panel to prevent emc effect on the passenger cabin. the allowable temperature of the body panel was controlled to be in the range of 20-30oc both in charging and discharging mode, by using a resistor-capacitor circuit. figure 1 shows the panel type nano-battery where the charging and discharging rate can be controlled by an electronic power management system [18]. fabrication of the composite cf plate was achieved using the vacuum bagging method. the hand lay-up technique considered constructing the cf through integration of resin and reinforcement (fiber) components. special care was taken to fabricate the cf to avoid the surface pockets, uneven surface, and pinholes. a few specimens of carbon fiber with different thicknesses and plies have been fabricated for the strength and conductivity testing. four layers of carbon fiber sheet with 10.0 cm length and 10.0 cm height has been fabricated. the epoxy resin and the hardener were mixed together with a ratio of 2:1. the presence of air was detected if the maximum level of vacuum could not be achieved (-28ʺhg). a description of the sample is presented in table 2. the solid polymer electrolyte (spe) was made with a casting technique by using acetonitrile, polyethylene oxide (peo), copper oxide (cuo) and ethylene carbonate. the polyethylene oxide acts as a host matrix, acetonitrile as a dissolver, copper oxide as the filler and ethylene carbonate as the plasticizer. the polyethylene oxide was dissolved into acetonitrile. the cuo was mixed with polyethylene to toughen the surface and enhance the ionic conductivity of spe. the spe nanoscale specimens was made with : (i) cuo filler of 15 %wt and ethylene carbonate of 20 %wt, (ii) cuo filler of 10 %wt and ethylene carbonate of 30 %wt, (iii) cuo filler of 5 %wt and ethylene carbonate of 35 %wt. the mixture of cuo and ethylene carbonate was stirred for 24 hours to arrive at a homogeneous solution at room temperature and was stored in a dry place. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 62 table 2: description of the specimens. 1st specimen 2nd specimen 3rd specimen 4th specimen 5th specimen 6th specimen number of plies: 3 layers 3 layers 3 layers 6 layers 3 layers 3 layers size: 200 mm × 50 mm 200 mm × 50 mm 200 mm × 50 mm 200 mm × 50 mm 200 mm × 50 mm 200 mm × 50 mm nominal thickness: 1.17 mm 1.24 mm 1.18 mm 2.29 mm 2.35 mm 2.39 mm mass: 12.85 g 13.59 g 12.5 g 24.51 g 26.72 g 26.9 g 3. results experimental studies of the composite panel structure of ev built with a cuo filler er sandwiched by cf and li plate has carried out for the: (i) tensile and impact testing of cf, (ii) microscopic testing of cuo filler er, (iii) thermal and electric conductivity of spe, (iv) ionization characteristics of li thin plate and (v) electric charge storing and releasing capacity of composites structural panel. table 3: strength of carbon fiber. number of woven plies specimen no. nominal thickness (mm) maximum force (n) maximum stress (n/mm2) 3 1 1.17 3789.6 101.06 2 1.24 5271.3 140.57 3 1.18 5801.1 114.69 6 4 2.29 17369.2 458.7 5 2.35 17445.0 465.2 6 2.39 17507.2 466.86 9 7 2.90 29928.8 798.1 8 2.85 27988.1 787.29 9 2.81 29969.9 780.20 3.1 tensile and impact testing the cf tensile strength test was carried out based on astm d30392 with nine specimens by using a universal testing machine mts model 744, with a hydraulic grip and mts 632 12c-20 extensometer at a constant speed of 2.0 mm/min at room temperature. table 3 shows the strength of the carbon fiber (cf). the maximum force indicated in the table is the allowable force for the specimen. if the force increases more than the allowable force, the specimen fails. figures 2 and 3 show the supporting force by the specimen before failure. the maximum force and elongation (fig. 2) before failure are 5.8×103n and 3 mm, 16.25×103n at elongation of 3.9 mm, 29.5×103n at 4.9 mm for the woven number of plies 3, 6, and 9 respectively. while, the maximum stress (fig. 4) at the failure mode is recorded as 114.69 kn/m2, 458.7 kn/m2 and 780.2 kn/m2 respectively. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 63 (a) (b) (c) fig. 2: tensile test for force vs displacement, (a) specimen #1 (woven plies 3), (b) specimen #4 (woven plies 6), (c) specimen # 7 (woven plies 9). (a) (b) (c) fig. 3: tensile test for stress vs strain, (a) specimen #1 (woven plies 3), (b) specimen #4 (woven plies 6), (c) specimen # 7 (woven plies 9). impact testing of the cf for a plate thickness of 2.29 mm was conducted using an impactor as shown in fig. 4. figure 4(a) shows that the plate can absorb a maximum zforce (load) of 1.22 kn in 2.2 s and can absorb maximum energy of 5 j in 8 s. the failure of the plate occurs after 2.2 s even increasing the load. figure 4(b) shows that the plate can absorb a maximum of 7.25 j at 8s when the impact energy applied is 10 j. based on the result it is concluded that the cf plate of thickness 2.29 mm is not suitable for the car even for the roof. (a) 5 j iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 64 (b) 10 j fig. 4: impact testing of cf for specimen 1 of thickness 2.29 mm with (a) 5 j, (b) 10 j. 3.2 microstructure test of spe scanning electron microscopic (sem) analysis was conducted to observe the surface morphology in terms of distribution of copper oxide particles in the matrix, resin copper interface, and thermal and ionic conductivity by using jeol, jsm 6100. the sample of spe was coated by jpc-1600 auto fine coating machine with copper to avoid charge build-up, so that the interface of cuo and er and deformation behavior could be clearly identified. the composites were filled with mps-treated nanoparticles cuo at a 10 wt.% loading. the high magnification image in fig. 5 shows the air gaps between the polymer and the nanoparticle cuo. the agglomerated cluster indicates non-uniform distribution of cuo within the polymer matrix causing a weak interaction between the cuo and er polymeric matrix (i.e., a poor bond in the nanoparticle filled er-cuo composites). therefore, the cuo filler er has lower tensile strength and smaller electron mobility. 3.3 electric conductivity of spe solid polymer electrolyte (spe) has many advantages such as high ionic conductivity, high specific energy, solvent-free condition, wide electrochemical stability windows, lightweight and ease of processing. the dielectric properties of fillers and thermal treatment are major determinants for the ionic conductivity enhancement of solid electrolyte. the fillers affect the dipole orientation of the matrix host (i.e, epoxy resin) by their ability to align dipole moments, whereas the thermal history determines the flexibility of the polymer chains for ion migration. the dielectric strength of spe has been measured after sandwiching by cf and li foil. a sample of size 200x20 mm2 was placed between the electrodes and the ac voltage at 50 hz supply increased. table 4-6 shows the effectiveness of cuo electric conductivity, power discharging and charging capacity. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 65 (a) (b) (c) (d) fig. 5: sem micrograph of (a) 5 wt% (b) 10 wt% (c) 15 wt% (d) 20 wt% of copper oxide in er-cuo solution. table 4: electric conductivity of different wt% cuo filler er. composition of cuo (%wt) thickness of specimen (mm) electric conductivity (103) temperature difference (δt), oc 3 6 9 12 5 3.44 0.002 0.007 0.166 0.226 10 2.86 0.008 0.011 0.207 0.226 15 3.87 0.042 0.087 0.118 0.245 20 3.83 0.011 0.012 0.125 0.105 table 5: power discharging capacity of different cuo %wt. composition of cuo (%wt) minimum resistance maximum resistance current (a) voltage (v) current (a) voltage (v) 5 0.25 1.10 2.51 2.10 10 0.40 1.22 2.6 2.34 15 0.66 1.26 2.9 2.45 20 0.33 1.47 3.01 2.70 note: experimental result has been recorded for the composite specimen size (200mm x 50mm). iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 66 table 6: power saving of the car. compositi on of cuo (%wt) vehicle weight saving (kg) power saving (kw) fuel consumpti on (kg/s) power produced (kw) power saving * (kw) ap (m2) av (m2) 5 21 1.43 5.46 × 10-3 5.28 0.792 3.55 10 20 1.36 5.58 × 10-3 6.08 0.912 3.18 15 18 1.22 5.46 × 10-3 7.105 1.065 4.03 20 17 1.15 5.47 × 10-3 5.78 0.867 4.36 figures 6-7 show the power discharge capacity of the panel type nano-battery for different weight percentages (%wt) of cuo as the filler of the er. figure 6 shows that for cuo of weight percentage of 15%, the electric conductivity increases almost linearly with increasing temperature. figure 7(a) shows that cuo 15 %wt has higher discharging capacity than others. figure 7(b) shows that the nano-battery charging voltage (voltage gain) is maximum for a sample with 15 % wt of cuo. therefore, cuo as a filler material for the er can be optimized at 15 %wt filler for the er in panel style nano-battery. this conclusion agrees with the results in [19]. fig. 6: electric conductivity vs temperature difference. (a) current produce. (b) voltage gain. fig. 7: power discharged and charged by the composite body. 0! 0.05! 0.1! 0.15! 0.2! 0.25! 0.3! δt=0! δt=3! δt=6! δt=9! δt=12! el ec . rc "c on du c. vi ty ,"σ "(1 0^ 3) " temperature"different,"δt,k" 5%!cuo! 10%!cuo! 15%!cuo! 20%cuo! 0 5 10 15 20 25 30 5% 5% 10% 15% 20% cu rr en t p ro du ce (m a ) composition of %wt cuo reading 1 reading 2 0 1 2 3 4 5% 5% 10% 15% 20%v ol ta ge p ro du ce (m v ) composition %wt of cuo reading 1 reading2 iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 67 table 7: fuel consumption and emission. vehicle weight (kg) power consumption co2 reduction per 100km travelling (g) co2 for the using of proposed composite body (%) steel composite steel composite steel composite 1033 827 52 36.4 87.55 70.23 19.71 4. conclusion an ev roof built with a composite of cuo (15% wt) filler er sandwiched by cf and li-plate can save power of up to 1.22 kw due to reduction in weight, and saving cooling power from heat insulating as shown in table 7. the proposed new battery technology could be considered as a suitable technology for vehicle due to its storing and releasing 3.5kw power (energy equivalent to 2.81 liters of petrol) and prevent 6.00 kg of co2 emission for every 100 km distance travelled. acknowledgement this study has been conducted to meet one of the objectives of the project “development of green transportation system”. the authors are grateful to the malaysian ministry of education (moe) for financing this project. the authors would like to thank the technicians of international islamic university malaysia (iium) for helping to conduct this study. references [1] cheah lw. (2010) cars on a diet: the material and energy impacts of passenger vehicle weight reduction in the u.s. ph.d. dissertation, massachusetts institute of technology, cambridge, ma. [2] gacitua w, ballerini a, zhang, j. (2005) polymer nanocomposites: synthetic and natural fillers a review. maderascienc. y tecnol., 7:159-178. [3] liu p, sherman e, jacobsen a. (2009) design and fabrication of multifunctional structural batteries. j of power sources, 189:646-650. [4] tanaka, t. (2005) dielectric nano-composites with insulating properties. ieee transactions on dielectrics and electrical insulation, 12(5): 914928. [5] amaral fa, dalmolin c, canobre sc, nerilso b, rocha frc, biaggio sr. (2007) electrochemical and physical properties of poly based gel electrolytes for lithium ion batteries. j. power sources, 164(1):378-7753. [6] li z., su,g, wang x, gao d..(2005) micro-porous p based polymer electrolyte filled with cuo nanoparticles. solid state ionics, 176(23-24):1903-1908. [7] manual sa. nahm ks, kumar t, kulandainathan m, ravi g, wilson j. (2002) thermal, electrical and mechanical properties of plasticized polymer electrolytes based on peo/p blends. electrochimi acta, 48(2):205-209. [8] thomas jp, qidwai ma. (2004) mechanical design and performance of composite multifunctional materials. acta materialia, 52:2155-2164. [9] hossain s, kim yk, saleh y, loutfy, r (2006) overcharge studies of carbon fiber composite-based lithium-ion cells. j power sources, 161:640-647. [10] flandrois s, simon b. (1999) carbon materials for lithium-ion rechargeable batteries. carbon, 37:165-180. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy rahman et al. 68 [11] imanishi n, kashiwagi h, ichikawa t, et al. (1993) charge discharge characteristics of meso phase-pitch-based carbon fibers for lithium cells. journal of the electrochemical society 140:315-320 [12] han z, fina a. (2011) thermal conductivity of carbon nanotubes and their polymer nano composites: a review. prog. polym. sci, 36(7):914–44. [13] yang f, zhao x, xiao p. (2010) thermal conductivities of ysz/al2o3 composites. j eur ceram soc., 30(15):3111-3116. [14] shi z, radwan m, kirihara s, miyamoto y, jin z. (2009) enhanced thermal conductivity of polymer composites filled with three-dimensional brush like aln nano whiskers. appl phys lett, 95,224104. [15] cui w, du f, zhao j, zhang w, et al. (2010) improving thermal conductivity while retaining high electrical resistivity of epoxy composites by incorporating silica-coated multiwalled carbon nanotubes. carbon, 49(2):495-500. [16] li tl, hsu slc. (2010) enhanced thermal conductivity of polyimide films via a hybrid of microand nano-sized boron nitride. j phys chem b, vol.114(20): 6825–6833. [17] rahman a, farhan s, ahmed h, hawlader, mna. (2014) fuzzy controlled evaporative battery cooling system for evs/hevs. international journal of electric and hybrid vehicle system. inderscience, 8(2):233-240. [18] rahman a, hossain a, zahirul alam ahm, mahbubur r. (2012) fuzzy knowledge-based model for prediction of traction force of an electric golf car. journal of terramechanics, 49(1):13-25. [19] south jt, carter rh, snyder jf, et al. (2005) multifunctional power-generating and energystoring structural composites for us army applications. materials research society symposium proceedings, 851:139-150. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 biodegradation of fats, oil and grease using microorganisms isolated from palm oil mill effluent ma'an fahmi rashid al khatib*, fadi alqedra and md. zahangir alam biotechnology engineering research center (berc), department of chemical engineering and sustainability, kulliyyah of engineering, international islamic university malaysia, kuala lumpur, malaysia * corresponding author: maan@iium.edu.my (received: 30 august 2022; accepted: 19 january 2023; published on-line: 4 july 2023) abstract: the biodegradation of fat, oil, and grease (fog) is important in water pollution control and wastewater management. in this study, the viability of fogdegrading microorganisms on palm oil biodegradation was assessed. seven strains capable of degrading fog were isolated from palm oil mill effluent (pome). the potential bacterial strains were selected based on tween-80-degrading ability. micrococcus lylae strain dsm 20315 showed the highest growth compared to the other strains. hence, it was selected for fog degradation test. the biodegradability was performed as a function of ph (6, 7, 8), initial oil concentration (1, 3, 5% v/v), and inoculum concentration (2, 6, 10% v/v). optimization of these parameters of palm oil degradation was studied using 2-level factorial design. the maximum oil degradation was 68%, obtained at ph 6, initial oil concentration 1 % v/v, and bacterial inoculum concentration of 10 % v/v. the lowest oil degradation obtained was 22%. the initial oil concentration followed by bacterial inoculum concentration enhanced the removal efficiency of fog, but the ph level did not significantly promote the degradation rate. as a result, the optimum process conditions for maximizing oil degradation were at ph 6, initial oil concentration 1 %v/v, and bacterial inoculum concentration of 10 %v/v. abstrak: biodegradasi lemak, minyak, dan gris (fog) adalah penting dalam kawalan pencemaran air dan rawatan air buangan. kajian ini adalah berkenaan kebolehhidupan organisma pengurai-fog dalam biodegradasi minyak kelapa sawit. tujuh strain berkeupayaan mendegradasi fog diasingkan daripada cairan buangan minyak kelapa sawit (pome). strain bakteria yang berpotensi telah dipilih berdasarkan keupayaan degradasi-geladak-80. strain mikrokokus lilae dsm 20315 menunjukkan pertumbuhan tertinggi berbanding strain lain. oleh itu, ia dipilih bagi ujian degradasi fog. keupayaan biodegradasi telah dihasilkan berdasarkan fungsi ph (6, 7, 8) ketumpatan awal minyak (1, 3, 5% v/v) dan ketumpatan inokulum (2, 6, 10% v/v). parameter optimum degradasi minyak kelapa sawit dikaji menggunakan reka bentuk faktorial 2-tahap. nilai maksimum degradasi minyak adalah sebanyak 68%, terhasil pada ph 6, berketumpatan awal 1% v/v, dan ketumpatan inokulum bakteria 10% v/v. degradasi minyak terendah pula adalah sebanyak 22%. ketumpatan awal minyak diikuti ketumpatan bakteria inokulum meningkatkan kecekapan penyingkiran fog, tetapi level ph tidak ketara dalam membantu kadar degradasi. sebagai kesimpulan, keadaan optimum bagi degradasi minyak maksimum adalah pada ph 6, ketumpatan awal minyak 1% v/v dan ketumpatan bakteria inokulum sebanyak 10% v/v. keywords: fog; degradation; pome; oil; optimization; wastewater 1 iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 1. introduction wastewater with high fat, oil, and grease (fog) concentrations is attracting more attention because of population growth and industrialization. fog accumulation in sewer systems has a negative impact on both health and the environment, thus effective strategies for controlling fog deposition are critical. triglycerides, or triglycerides linked to glycerol molecules, are the building blocks of fat, oil, and grease. the physical properties of fat, oil, and grease vary depending on the type of fatty acids that comprise the triglycerides and their physical state. fog is produced by the dairy industry, slaughterhouses, food processing plants, and other industries that process fatty substances, in addition to private residences [1]. when wastewater carrying fat, oil, and grease flow in sewer pipes, fog will deposit in the pipes by forming layers of lipid-rich materials [2]. sewer blockage causes over 25,000 flooding events in the united kingdom each year. fog is thought to account for more than half of all sanitary sewer overflows (ssos) [3]. the american environmental agency (epa) estimates that between 10,350 and 36,000 sanitary sewer spills occur in the united states each year, with fog accounting for approximately 47% of the total. furthermore, indah water konsortium (iwk), the wastewater municipality in malaysia, reported that up to 45% of ssos may be caused by fog [4]. due to their prevalence in sewer systems (such as pipelines, pump stations, wet wells, etc.) and subsequent wastewater treatment facilities, fog deposits have an impact on health and the environment. they often result in sanitary sewer overflows (ssos) by reducing sewer diameter or totally blocking the pipelines. the ensuing sewage discharge increases water contamination and pathogen exposure. fog can also attract vermin such as rats, and sloughed deposits can clog pumping stations and sewage treatment plants [5]. to implement effective control measures, it is necessary to have a complete understanding of the properties and impacts of fog. approaches to controlling fog can be categorized as physical, chemical, or biological. long chain fatty acids are introduced to wastewater during the chemical hydrolysis of fog, which may limit microbial activity and disrupt the wide variety of microorganisms present [6], resulting in a decline in wastewater treatment efficacy and recurrent production of intolerable odors. physical methods use fog's reduced density in comparison to water. grease traps (also known as grease interceptors) are one of the most frequently used physical-based fog removal devices used prior to entering wastewater systems. when fog-containing wastewater enters a grease trap, lower density fog floats to the surface, allowing virtually fog-free water to exit the grease trap and enter the sewer system. the fog that has floated to the surface will be manually removed. tilted plates (tp) are a modified grease trap. tp are parallel gravity separators that offer a large surface area while taking up less than 10% of the volume of a typical grease trap [7]. during dissolved air foliation, micro-bubbles bind to fog particles, allowing them to float to the water's surface and be swiftly removed. to clear the accumulating fog layers, physical approaches require human intervention. the increased demand for human resources raises the expense of fog cleaning and the maintenance of related facilities, which already cost millions of dollars per year. furthermore, these techniques are ineffective at reducing fog, which can eventually limit the oxygen transfer rate, compromising biological treatment [8]. additionally, it was shown that microbial activity in grease traps generated large amounts of long-chain fatty acids, which, when released into sewer systems, aid in the production of fog deposits [9]. biological fog treatment is gaining traction due to its ability to treat fog at the source and prevent it from entering sewer systems. fog is biologically treated by bacteria capable 2 iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 of secreting enzymes that speed up the hydrolysis process or by direct use of enzymes such as lipases and commercial additives. isolating such bacterial strains and determining the optimal parameters and overall process. teixeira et al. isolated bacteria from activated sludge and wastewater effluent to biodegrade triolein and oleic acid [10]. aeromonas sp. and staphylococcus cohnii were shown to be the best degraders. however, in a 7-day assessment of fog content, the elimination of oleic acid and/or triolein was 37.9% and 19.1%, respectively. phong et al. identified bacteria from wastewater collected from restaurants and canteens containing vegetable oil [11]. because of its strong lipid degradation ability, acinetobacteria soli strain al3 was selected as a potential for fog biodegradation. similarly, strains belonging to the genera acinetobacter, bacillus, and pseudomonas demonstrated the ability to efficiently degrade fog [12]. the fog removal efficiency of pseudomonas sp. strain d2d3 were 94.5% and 94.4% for olive oil and animal fat, respectively, whereas sunflower oil had the lowest percentage at 62% [2]. it is beneficial to isolate the bacteria from a medium that is rich in fog and where the microorganisms have had time to acclimate to ensure a high degree of biodegradation. raw palm oil mill effluent (pome) contains high concentrations of organic substances, including oil and grease, which lead to elevated levels of cod and bod. pome treatment in open oxidation ponds will eventually reduce these amounts significantly [13]. this suggests that pome would accommodate and sustain bacteria capable of metabolizing palm oil during the natural decomposition process in the ponds. many studies have demonstrated the potential of isolating lipolytic bacteria from pome [14]. some strains, however, were unable to use palm oil directly as a carbon source. as a result, the isolation and screening procedures were modified to select bacterial strains capable of using palm oil as a carbon source. pome is a preferred source for isolating lipid-degrading bacteria due to its nature and potential. the objective of this study is to isolate bacteria from palm oil mill effluent and screen them for lipolytic activity on tween 20. the high-performing bacteria will then be used to biodegrade cooking palm oil, which is a popular oil with a fatty acid composition similar to that of fog. the selected bacteria's growth conditions will then be optimized. 2. materials and methods 2.1 screening and isolation of lipolytic bacteria pome that was serially diluted from 101 to 107 was used to isolate bacterial strains. a sample of each dilution was plated on lb agar and incubated overnight at 37 °c [15]. to obtain the pure strains, the colonies that formed on the agar plates were sub-cultured on new agar plates. more than 20 pure strains were obtained. the lipase activity was seen using kanmani et al.'s agar plate assay [16]. tween 20 (sigma-aldrich) was utilized as a substrate since it is suitable for the simple and rapid detection of microbial lipolytic activity on an agar plate. the pure colonies were streaked on tween 20 agar plates. lipase producers have a zone of white-like precipitate surrounding the lipase-active colony. the first 7 strains that appeared on agar were selected for further screening. 2.2 characterization of the isolated strains individual bacteria isolates were identified beforehand using classical tests such as cell shape, gram staining, and colony morphology on solid nutrient media. first base laboratories sdn. bhd., malaysia, performed the genetic identification of isolates by determining the nucleotide sequence of the 16s rrna gene. 3 iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 2.3 growth profile of the isolated strains the lipolytic strains were added to a 250 ml erlenmeyer flask containing 1 ml of palm oil as a carbon source and 100 ml of minimal salt medium (msm) media. the author of [15] describes how to make an inoculum in lb broth medium. the inoculum was added to 100 ml of msm containing 2.5 g/l nacl, 4.74 g/l k2hpo4, 0.56 g/l kh2po4, 0.5 g/l mgso4.7h2o, 0.1 g/l cacl.6h2o, and 0.5 g/l nh4no3 in dh2o. the media (100 ml) were poured into a 250 ml erlenmeyer flask and autoclaved for 15 minutes at 121 °c. all samples were inoculated with a starter culture (1% v/v) produced in lb medium (od600=1.0) [15]. before inoculation, the starter culture was centrifuged (13,000 rpm, 10 minutes, 4°c) and rinsed a couple of times in a physiological salt solution to avoid the transfer of lb organic compounds into fresh media. bacteria were omitted from the control samples. all the samples underwent a two-week incubation period in a rotary shaker (150 rpm, 25 °c). on a uv-visible spectrophotometer every 6 hours, the growth was measured at absorbance of 600 nm [17]. 2.4 optimization of fog-degradation biodegradation of palm oil was performed to determine the highest concentration of palm oil that could be degraded using bacterial strains in 250 ml erlenmeyer flasks that were stoppered with cotton wool to promote oxic conditions. each flask held 100 ml of msm, supplemented with a predetermined oil concentration, inoculum concertation, and ph level. 1n naoh or hcl were used to adjust the ph. before inoculation, samples were autoclaved. the experiment lasted two weeks at 37 °c and 150 rpm. experiments with bacterial samples and controls were carried out in duplicate. using design expert 6.0.8 software, biodegradation optimization runs were designed applying 2-level factorial design (2lfd) with one replicate and three center points. the optimized parameters were the ph of the msm medium (a), the concentration of oil (b), and the inoculum concentration (c). these variables were assessed at 3 different levels: ph (6, 7, 8), oil concentration (1, 3, 5% v/v), and inoculum concentration (2, 6 and 10% v/v). the software developed a matrix containing 11 experiments. under predetermined conditions, oil degradation was carried out as designed. following the incubation period, the oil was degraded using gravimetric methods. the software was used to enter and analyze these data. anova (standard analysis of variance) and a contour plot were produced. the partition gravimetric technique was implemented to estimate the medium's residual oil content [18] the residual oil content was strained numerous times with 5 ml of hexane such that there was no oil layer in the aqueous phase and the solvent phase was clear. in a water bath at 70°c, the mixed solvent extract was completely evaporated, and the amount of residual oil was calculated to determine the percent decrease [3]. 3. results and discussion 3.1 growth profile of the isolated strains to construct an efficient oil-containing wastewater treatment system, oil-degrading microorganisms were isolated from pome. a sample of palm oil mill effluent was serially diluted and screened. in the initial screening, twenty pome isolates were obtained. the oildegrading ability of the selected strains was then tested using tween 20 agar medium. seven strains that displayed the highest precipitate formation around the colonies in tween 20 agar plates were selected for subsequent fog biodegradation experiments. the growth profiles of the seven strains were screened using optical density, and the strain with the highest cell 4 iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 growth rate was investigated for oil degradation optimization. figure 1 depicts the growth curve for the selected seven. strain x3 demonstrated the highest growth, hence it was selected for further investigation. 3.2 characterization of isolated bacteria based on gram staining of the isolated strains, table 1 indicates that two strains belong to gram negative category, while the other five strains belong to gram positive bacteria. table 2 shows the phenotypical characteristics of the seven isolates when grown on lb agar. fig. 1: the growth curve for the seven selected strains. table 1: identification of the isolated strains sample gram staining identification of the strains (x1, x2,x3) gram positive micrococcus lylae strain dsm 20315 x4 gram positive corynebacterium aurimucosum strain h2456 x5 gram negative lysinibacillus boronitolerans strain 10a x6 gram positive staphylococcus hominis subsp. novobiosepticus strain gtc 1228 x7 gram negative bacillus drentensis strain lmg 21831 table 2: phenotypical characteristics of the seven isolates when grown on lb agar isolate (x1, x2, x3) x4 x5 x6 x7 form of colony irregular circular circular circular circular elevation convex convex flat flat flat margin entire entire entire entire entire pigmentation yellow white red white red texture rough smooth smooth smooth smooth optical properties opaque opaque opaque opaque opaque appearance dull shiny shiny shiny shiny strain x3, which showed the highest degradation capability, was identified using morphological tests and 16s rna sequence analysis (fig. 2). strain x3 was gram-positive bacteria capable of producing lipase. the 16s ribosomal rna (16s rrna) gene was sequenced and the generated sequences were analyzed using blast to reveal that x3 belongs to the genus micrococcus. the 16s rrna (500bp) sequence analysis of strain x3 revealed a significant similarity (more than 99%) to that of the genus micrococcus. based on these traits and its 16s rrna sequence, strain x3 was identified as micrococcus lylae strain dsm 20315. x 1 x 2 x 3 x 4 x 5 x 6 x 7 5 iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 fig. 2: phylogenetic tree of x3 strain. in the present study, micrococcus lylae strain dsm 20315 was shown to have lipolytic activity. to the knowledge of the researchers, this study was the first time micrococcus lylae strain dsm 20315 was used as a potential lipid-degrading strain. this supports the hypothesis that pome is a potential source for oil-degrading bacteria [5]. table 3: two lfd experimental design setup and response run no. a ph b oil conc. % (v/v) c inoculum conc. % (v/v) response oil biodegradation % std exp’l pred. 1 7.0 3.0 6.0 35.3 44.9 6.79 2 8.0 5.0 10.0 25.4 22.8 1.84 3 8.0 1.0 2.0 58 55.4 1.84 4 6.0 5.0 2.0 38.6 36.0 1.84 5 7.0 3.0 6.0 33 44.9 8.41 6 8.0 1.0 10.0 53 55.6 1.84 7 7.0 3.0 6.0 37 44.9 5.59 8 6.0 1.0 10.0 68 65.4 1.84 9 6.0 5.0 10.0 29.2 31.8 1.84 10 8.0 5.0 2.0 37 39.6 1.84 11 6.0 1.0 2.0 50 52.6 1.84 3.3 statistical optimization of fog-degradation the highest biodegradation achieved following the experimental design setup (table 3) was 68% at ph 6, 1% (v/v) oil concentration, and 10% (v/v) inoculum concentration (run no. 8). lipid-degrading bacteria such as bacillus thermoleovorans ihi-91 was found to be able to degrade palmitic acid, steric acid, lanoline, olive oil, sunflower seed oil, soya oil, and fish oil as sole carbon source [19]. [2] isolated and identified pseudomonas sp. strain d2d3 that is capable of degrading fat, oil, and grease. they also found that the degradation rate ranged from (62.0% -94.5%) based on the substrate. [20] investigated the lipolytic activity of raoultella planticola bacterial strain and found its efficiency to degrade a mixture of lipids substances with maximum degradation level of 91.9% for oleic acid. anova for the 2lfd model (table 4) revealed an f-value of 11.84, indicating that the model is significant and that there is only a 3.4% likelihood that such a big f-value could occur due to noise. model terms are significant when "prob > f" is less than 0.05. in this case, b (oil concentration) and bc are significant model terms. values larger than 0.10 6 iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 suggest that the model terms are not significant. generally, large magnitudes of t and f, as well as smaller p-values, indicate that the associated coefficient terms are significant. r2 indicates how much of the observed response's variability may be attributed to the experimental factors and their interactions. r2 is a measure of how well a model can predict a response, and the closer it is to 1, the stronger the correlation between experimental and predicted values are. a ratio larger than 4 is preferred when measuring the signal to noise ratio with adequate precision. with a ratio of 10.975, it is clear that there are sufficient signals and models to help one move about the design space. lack of fit > 0.05 is insignificant, and because the lack of fit test reflects how well the model fits the experimental data, this model could be used to make predictions. the final equation terms of coded factors are: oil biodegradation = +44.9 -1.55 * a -12.35 * b – 1.00 * c +0.2 * a * b – 3.15 * a * c -4.25 * b * c (1) the equation can be used to make predictions about the outcomes, for given amounts of each of the factors. it can also be used to ascertain the relative influence of factors by comparing the factor coefficient. table 4: anova of oil biodegradation source sum of squares df mean square f-value p-value prob >f model 1471.6 6 245.2667 11.839 0.034 significant a-ph 19.22 1 19.22 0.928 0.407 b-oil conc. 1220.18 1 1220.18 58.896 0.005 c-inoculum conc. 8 1 8 0.386 0.578 ab 0.32 1 0.32 0.015 0.909 ac 79.38 1 79.38 3.832 0.145 bc 144.5 1 144.5 6.975 0.078 pure error 8.0726 2 4.0363 lack of fit 54.08 1 54.08 13.398 0.067 not significant figure 3 shows the predicted versus actual plot values. the data points are evenly distributed across the 45° line, indicating agreement between the actual data and that produced by the model. fig. 3: predicted versus actual plot of oil biodegradation percentage. 7 iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 fig. 4: 3d response surface showing the effects of (a) ph and oil concentration (b) ph and inoculum concentration and (c) oil concentration and inoculum concentration on oil degradation. the 3d response surface plots are a graphical approach to expressing the regression equation. they illustrate how the variables interact and are used to identify the optimal value of each factor for a suitable response. the plots for the interactions between ph and oil concentration (a-b), ph and inoculum concentration (a-c), and oil concentration and inoculum concentration (a-c) are shown in fig. 4 a, b, and c, respectively (b-c). figure 4a shows a decrease in oil biodegradation with an increase in oil concentration while ph did not show any effect. figure 4b depicts the interaction between ph and inoculum concentration. increased ph resulted in a slight increase in oil biodegradation, whereas increased inoculum concentration resulted in an increase in oil biodegradation at lower ph. in fig. 4c, the interaction between oil concentration and inoculum concentration shows that oil degradation is highest when the oil concentration is lowest, and the inoculum concentration is highest. this is consistent with what is stated by [21]. increased bacterial enzyme accessibility to substrate will result in improvement of the hydrolysis reaction rate. (a) (b) (c) 8 iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 this study revealed that while microbial concentration does not have significant effect as a single factor (table 4) its interaction with oil concentration has a significant effect on the amount of degraded oil. microbial concentration is important as it provides more bacterial cells and thus more enzyme secretion to degrade the oil and therefore increase the rate of degradation [22]. by applying the 2-level factorial design of oil degradation, a maximum oil degradation was obtained at a ph of 6, oil conc. 1% (v/v), and 10% (v/v) of bacterial inoculum. 4. conclusions seven microorganisms isolated from pome were studied for the degradation of fog. micrococcus lylae strain dsm 20315 was identified as the largest growing microorganism through morphological tests and 16s rrna sequence analysis. this strain was used to optimize the degradation process. the optimum condition that achieved the highest biodegradation was at ph 6, oil concentration 1% (v/v), and 10 % (v/v). the results revealed that microorganisms isolated from pome are capable of biodegrading fog, which could be attributed to the two wastes' similar properties. acknowledgment this study was partially funded by the international foundation for science (ifs), stockholm, sweden and thankful to the department of chemical engineering and sustainability at international islamic university malaysia. references [1] brooksbank am, latchford jw, mudge sm. (2007) degradation and modification of fats, oils and grease by commercial microbial supplements. world journal of microbiology and biotechnology 23 (7): 977-985. doi: 10.1007/s11274-006-9323-1. [2] shon hk, tian d, kwon dy, jim cs, lee tj, chung wj. (2002) degradation of fat, oil, and grease (fogs) by lipase-producing bacterium pseudomonas sp. strain d2d3. journal of microbiology and biotechnology, 12(4): 583-591. [3] williams jb, clarkson c, mant c, drinkwater a, may e. (2012) fat, oil and grease deposits in sewers: characterisation of deposits and formation mechanisms. water research, 46(19): 6319–6328. doi: 10.1016/j.watres.2012.09.002. [4] husain iaf, alkhatib mf, jammi ms, mirghani mes, zainudin z, hoda s. (2014) problems, control, and treatment of fat, oil, and grease (fog): a review. journal of oleo science, 63(8): 747-752. doi: 10.5650/jos.ess13182. [5] del mundo dmn, sutheerawattananonda m. (2017) influence of fat and oil type on the yield, physico-chemical properties, and microstructure of fat, oil, and grease (fog) deposits. water research, 124: 308-319. doi: 10.1016/j.watres.2017.07.047. [6] ma j, zhao qb, laurens llm, et al. (2015) mechanism, kinetics and microbiology of inhibition caused by long-chain fatty acids in anaerobic digestion of algal biomass. biotechnology for biofuels, 8(1): 1-12. doi: 10.1186/s13068-015-0322-z. [7] willey r. (2001) fats, oils, and greases: the minimization and treatment of wastewaters generated from oil refining and margarine production. ecotoxicology and environmental safety, 50 (2): 127–133. doi: 10.1006/eesa.2001.2081. [8] abomohra aef, elsayed m, esakkimuthu s, sheekh me. (2020) potential of fat, oil and grease (fog) for biodiesel production: a critical review on the recent progress and future perspectives. progress in energy and combustion science, 81: 100868. doi: 10.1016/j.pecs.2020.100868. 9 https://pubmed.ncbi.nlm.nih.gov/?term=drinkwater+a&cauthor_id=23039918 https://pubmed.ncbi.nlm.nih.gov/?term=may+e&cauthor_id=23039918 iium engineering journal, vol. 24, no. 2, 2023 khatib et al. https://doi.org/10.31436/iiumej.v24i2.2590 [9] he x, de los reyes fl, ducoste jj. (2017) a critical review of fat, oil, and grease (fog) in sewer collection systems: challenges and control. critical reviews in environmental science and technology, 47(13): 1191-1217. doi: 10.1080/10643389.2017.1382282. [10] teixeira pd, silva vs, tenreiro r. (2020) inegrated selection and identification of bacteria from polluted sites for biodegradation of lipids. international microbiology, 23(3): 367-380. doi: 10.1007/s10123-019-00109-w. [11] hong nt, duyen nt, diep cn. (2014) isolation and characterization of lipid-degrading bacteria in wastewater of food processing plants and restaurants in can tho city, vietnam. american journal of life sciences, 2(6): 382-388. doi: 10.11648/j.ajls.20140206.18. [12] bhumibhamon o, koprasertsak a, funthong s. (2002) biotreatment of high fat and oil wastewater by lipase producing microorganisms. kasetsart j(natsci), 36: 261-267. [13] alias z, tan ikp. (2005) isolation of palm oil-utilising, polyhydroxyalkanoate (pha)producing bacteria by an enrichment technique. bioresource technology, 96(11): 1229-1234. doi: 10.1016/j.biortech.2004.10.012. [14] affandi ie, suratman nh, abdullah s, ahmad wa, zakaria za. (2014) degradation of oil and grease from high-strength industrial effluents using locally isolated aerobic biosurfactantproducing bacteria. international biodeterioration & biodegradation, 95: 33-40. doi: 10.1016/j.ibiod.2014.04.009. [15] kis á, laczi k, zsíros s, rákhely g, perei, k. (2015) biodegradation of animal fats and vegetable oils by rhodococcus erythropolis pr4. international biodeterioration and biodegradation, 105: 114-119. doi: 10.1016/j.ibiod.2015.08.015. [16] kanmani p, kumaresan k, aravind j. (2015) utilization of coconut oil mill waste as a substrate for optimized lipase production, oil biodegradation and enzyme purification studies in staphylococcus pasteuri. electronic journal of biotechnology, 18(1): 20-28. doi: 10.1016/j.ejbt.2014.11.003. [17] iqbal sa, rehman a. (2015) characterization of lipase from bacillus subtilis i-4 and its potential use in oil contaminated wastewater. brazilian archives of biology and technology 58(5): 789-797. doi: 10.1590/s1516-89132015050318. [18] latha r, kalaivani r. (2012) bacterial degradation of crude oil by gravimetric analysis. analysis 3(5): 2789-2795. [19] markossian s, becker p, märkl h, antranikian g. (2000) isolation and characterization of lipid-degrading bacillus thermoleovorans ihi-91 from an icelandic hot spring. extremophiles : life under extreme conditions 4 (6): 365–371. doi: 10.1007/s007920070006. [20] sugimori d, watanabe m, utsue t. (2013) isolation and lipid degradation profile of raoultella planticola strain 232-2 capable of efficiently catabolizing edible oils under acidic conditions. applied microbiology and biotechnology 97(2): 871-880. doi: 10.1007/s00253-012-3982-7. [21] tzirita m, papanikolaou s, chatzifragkou a, quilty b. (2018) waste fat biodegradation and biomodification by yarrowia lipolytica and a bacterial consortium composed of bacillus spp. and pseudomonas putida. engineering in life sciences 18(12): 932-942. doi: 10.1002/elsc.201800067. [22] campbell mk, farrell so (2016) biochemistry. cengage learning. 10 https://www.researchgate.net/profile/gabor-rakhely microsoft word 2-96 page 23-40.doc iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 23 biotransformation of domestic wastewater treatment plant sludge by two-stage integrated processes -lsb & ssb md. zahangir alam1,2*, a. h. molla2,3, a. fakhru’l-razi2 1bioenviromental engineering research unit (beru), department of biotechnology engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur. 2department of chemical and environmental engineering, faculty of engineering, university putra malaysia, 43400 upm serdang, selangor, malaysia. 3department of crop botany, bangabandhu sheikh. mujibur rahman agricultural university, salna, gazipur 1706, bangladesh. e-mail: zahangir@iiu.edu.my abstract: the study of biotransformation of domestic wastewater treatment plant (dwtp) sludge was conducted in laboratory-scale by two-stage integrated process i.e. liquid state bioconversion (lsb) and solid state bioconversion (ssb) processes. the liquid wastewater sludge [4% w/w of total suspended solids (tss)] was treated by mixed filamentous fungi penicillium corylophilum and aspergillus niger, isolated, screened and mixed cultured in terms of their higher biodegradation potential to wastewater sludge. the biosolids was increased to about 10% w/w. conversely, the soluble [i.e. total dissolve solid (tds)] and insoluble substances (tss) in treated supernatant were decreased effectively in the lsb process. in the developed lsb process, 93.8 g kg-1of biosolids were enriched with fungal biomass protein and nutrients (npk), and 98.8% of tss, 98.2% of tds, 97.3% of turbidity, 80.2% of soluble protein, 98.8% of reducing sugar and 92.7% of chemical oxygen demand (cod) in treated sludge supernatant were removed after 8 days of treatment. specific resistance to filtration (1.39x1012 m/kg) was decreased tremendously by the microbial treatment of dwtp sludge after 6 days of fermentation. the treated biosolids in dwtp sludge was considered as pretreated resource materials for composting and converted into compost by ssb process. the ssb process was evaluated for composting by monitoring the microbial growth and its subsequent roles in biodegradation in composting bin (cb). the process was conducted using two mixed fungal cultures, trichoderma harzianum with phanerochaete chrysosporium 2094 and (t/p) and t. harzianum and mucor hiemalis (t/m); and two bulking materials, sawdust (sd) and rice straw (rs). the most encouraging results of microbial growth and subsequent solid state bioconversion were exhibited in the rs than the sd. significant decrease of the c/n ratio and germination index (gi) were attained as well as the higher value of glucosamine was exhibited in compost; which clearly implied that the increased bioconversion occurred in the treated process. comparatively, superior composts were produced by t/p at 50-60 days of ssb. significantly lower heavy metals (pb, cd, cr, ni, cu and zn) were recorded in chemical analysis of the end products (composts) after ssb, in comparison to the usa’s recognized limits for application in municipal solid waste (msw). iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 24 keywords: liquid state bioconversion, solid state bioconversion, domestic wastewater sludge, filamentous fungi, biosolids and compost. 1. introduction the treatment and disposal of domestic wastewater sludge, which are mainly of organic origin, pose one of the most serious challenges all over the world. proper operation, maintenance and appropriate technology are essential for future waste management strategies to overcome these challenges by efficient utilization of sludge disposal. bioconversion i.e, biological-based treatment of wastewater sludge is probably the only way that could lead to sustainability and environmental friendly, and seems to be an immediate solution to these problems. although there exist many alternatives for sludge treatment and disposal such as landfill, incineration, physical-chemical process, physicochemical process, adsorption, membrane process. none of them are environmental friendly or non-hazardous, every one is disseminating some sort of contaminants to the environment as well as ground water [1, 2]. in recent years, interest has twisted to the methods/processes based on resource recovery approach known as recycling and utilization of organic materials from sludge. the concept of organic matter recovery by applying biological-based treatment is becoming more popular to be applied for various purposes. composting as a resource recovery is becoming a more acceptable alternative for sludge treatment due to its potential use for land application as biofertilizer and soil conditioner [3]. bio-transformation of domestic wastewater treatment plant sludge by liquid state and solid state bioconversion (lsb & ssb) is being proposed to solve these problems. considering the existing treatment processes, the employment of fungal treatment using lsb & ssb is a new approach for the biodegradation, bioseparation, biosolids accumulation, biotransformation or bioremediation of soluble and insoluble organic and/or inorganic substances of dwtp sludge which exhibits the benefit of being non-hazardous and environmental-friendly for all living beings [4, 5]. the processes were developed with sterilized and semi-sterilized conditions in the laboratory. in lsb process, the filamentous fungi isolated from wastewater and dwtp sludge [6] entrap the solid particles in higher strength of sludge (4% w/w of tss) during their growth and enhance the biosolids accumulation, bioseparation and biodegradation of treated supernatant [7, 8]. in lsb treatment, sludge particles are compacted by filamentous mycelia that modify the prose structure of the treated sludge and enhance its filterability and dewaterability [9]. after liquid state bioconversion of the dwtp sludge, the separated fungal biomass containing biosolids generated during the treatment of sludge that was used as composting materials for rapid and effective composting by solid state bioconversion (ssb) process [5]. it contains large content of organic matters, macroand micro-nutrients and existing high potential microbes for quick bioconversion. the treated supernatant can be disposed without any further treatment as it meets the standard values of discharge [10]. solid state bioconversion, a biological based process, is well known as a novel low cost promising bioremediation technique [11]. the ssb has been traditionally practiced in composting of agricultural wastes for mushroom cultivation and production of organic iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 25 acids. the process often brings about an improved quality of substrate and enhances the nutritional quality of products [12]. furthermore, the process offers faster degradation of the substrate due to more homogeneous distribution of excreted enzymes by filamentous fungi [13]. the treatment of wastewater sludge by lsb and ssb has not been widely investigated. therefore, the present study was undertaken to evaluate the two-stage integrated process for biotransformation, biosolids accumulation and bioseperation of dwtp sludge into a value added product (compost). 2. material and methods 2.1 microbial strains for lsb and ssb processes the fungal strains of aspergillus niger scahma103 (imi385267) and penicillium corylophilum wwzp1003 (imi385277) were evaluated for lsb process based on performances of a series of experiments of isolation/identification [6], screening [14] and compatible mixed cultures [15]. the a. niger and p. corylophilum strains were isolated from sludge cake and wastewater, respectively and optimized on the basis of potential performance for the treatment of dwtp sludge using lsb process. two mixed fungal cultures, trichoderma harzianum with phanerochaete chrysosporium 2094 and trichoderma harzianum with mucor hiemalis were used for ssb process. among these three strains, t. harzianum and m. hiemalis were isolated from local relevant sources [16] while the last one was collected from lab stock. these strains were found as compatible in mixed culture [17] and adapted to higher percentage of dwtp sludge-rich growing media [18]. the cultures were maintained on 3.9% w/v of potato dextrose agar (pda, oxoid) slants, subcultured once in a month and stored at 40c. 2.2 collection and preparation of dwtp sludge and bulking materials for lsb, the dwtp sludge of 1-2% w/w of tss (ph 6.7) was collected from an aeration tank in indah water konsortium (iwk)’s domestic wastewater treatment plant, kuala lumpur, malaysia. the sludge concentration of 4% w/w of tss was prepared by removing of the excess free water with the solid/water mass balance. the final ph recorded in the concentrated sludge (4% w/w) was 6.5. the sludge medium (4% w/w of tss) supplemented with co-substrate of 2% w/w of wheat flour (wf, optimized cheap carbon source) was used throughout the study. the moisture was recorded around 90% w/w of the biosolids for composting in the ssb process. the sawdust was collected from a local sawmill and a rice straw from malaysian agricultural research and development institute (mardi). sawdust was cured for three days followed by sieving with 2.38 mm and the rice straw was cut into 3-4 cm followed by milling in bar mill to reduce its size to 0.5 cm to 3 cm. the biosolids (for ssb) were also cured for several days at ambient temperature to reduce moisture content of 90% w/w to 55% w/w. the final moisture content recorded was 18.00% and 7.04% for the sawdust (sd) and the rice straw (rs), respectively. iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 26 2.3 experimental procedures for the lsb process the optimized inoculum and bioconversion process were used to develop the sludge treatment technique in a batch fermenter. the optimized carbon source (c) of wheat flour as co-substrate and the process conditions were used as in alam et al. [19]. to evaluate the microbially treated biosolids as pretreatment resource materials for rapid and effective composting in developed conditions, a 6-liter capacity biostatct compact laboratoryscale fermenter (b. braun biotech international) with a 5-liter working volume was used. the fermenter was a vertical glass cylinder with the height/diameter ratio of 2.2:1. the fermenter and all its parts were sterilized to be used along with the substrate at 1.5 barg and 1210c for 45 min. filtered air was supplied into the substrate in the fermenter just below the impeller by an air compressor. the initial ph of the substrate was adjusted to 5.5 but it was not controlled thereafter. temperature, agitation and aeration rate were maintained automatically bya microprocessor controller in the fermenter. an experiment was carried out in the fermenter containing 3 kg sludge of 4% w/w of tss content supplemented by 2% w/w of co-substrate (wheat flour). the treatment was started by inoculating 2% v/w of spore suspension of mixed inoculum of a. niger and p. corylophilum (1:1 ratio of individual) for 10 days (sampling of every two days interval). the concentration of mixed inoculum of a. niger and p. corylophilum used were 2104 and 1.25104 spores/ml respectively. inoculum preparation (spore suspension) was done according to the method of alam et al. [15]. 2.4 experimental procedures for the ssb process the ssb process was conducted to evaluate the feasibility of the ssb process of dwtp sludge by considering the performance of microbial growth and its subsequence affect on biodegradation. a study was conducted with three inocula and two bulking agents. the experiment was carried out in a plastic composting bin [h 35 cm, d (upper) 32 cm and d (bottom) 25 cm] at semi sterile condition. three inoculations, two bulking agents, and a total of six treatments were conducted to evaluate the composting process with seven harvests 0, 5, 15, 30, 45, 60 and 75 days after inoculation. the mixed inoculum of 6% (v/w) of spore/mycelial suspension (1:1 ratio of each in mixed inoculum) was used to inoculate the substrate. equal volumes of mycelial suspension of p. chrysosporium 2094 were mixed with their compatible partner. the inocula were prepared according to the procedure of molla [5]. the concentration of inoculum was 3.28x103 and 2.99x103 spores/ml for t. harzianum and m. hiemalis, respectively. two bulking materials, sawdust and rice straw, were used individually with fungal treated biosolids for the ssb process. mixed biosolids (55% moisture, 32.6% c and 3.6% n) with sawdust (18% moisture, 44% c and 0.1% n) for preparation of biosolids-sawdust substrate using in the ratio 1:1. similar ratio was also followed to mix biosolids with rice straw (7.04% moisture, 49.4% c and 0.44 % n) for biosolids-rice straw substrate. a 3 g of kh2po4, 0.3 g of mgso4 and 0.3 g of cacl2 were used as available nutrients dose per kg of substrate for the initial activation of inoculated fungi. the amount (1.9 g for biosolidsawdust and 1.5 g for biosolid-rice straw per 100 g of substrate) of available carbon source, wf as co-substrate was determined to maintain the c/n ratio 30:1. in both substrates, 65% moisture was adjusted as optimum for effective operation of the ssb process. in composting bin, 6 kg of biosolids-saw dust and 3 kg of biosolids-rice straw iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 27 substrates were used. the ph and final moisture content were adjusted for the substrate after autoclaving at 1210c for 50 min. the substrates were inoculated with 6% mixed spores/mycelial suspension. the composting bins were in a shade house for 75 days at ambient temperature (28±20c). at every harvest, a stick was used for mixing the substrate in a composting bin. 2.5 chemical analysis and parameters studied the dry biosolids (sludge cake) was collected by filtering the fermentation broth (treated sludge) and dried at 1050c for 48 h. the supernatant was used for analysis after centrifuging the fermented broth at 3000 rpm for 30 min. the standard methods [20] were followed for analyzing ts, tss, and cod. the optical density (od) of the supernatant was measured at 660nm against distilled water in an uv spectrophotometer (uvikon 933) that was considered as turbidity. soluble protein was determined according to lowry method [21]. total dissolved solids (tds) was determined by using ec (electrical conductivity)/tds meter (hanna instruments, hi 9835) according to manual instructions of hanna instruments. reducing sugar was measured according to the method of dns [22]. total organic carbon (toc) was measured according to the method of navarro et al. [23]. total nitrogen was determined by micro-kjeldahl method [24]. heavy metals determination was followed by aqua regia extraction method [25]. the sample preparation and calculation for specific resistance to filtration (srf) test was determined according to carman [26]. the compost material after harvesting was used for chemical and physical analysis. the analysis was done by using dry compost and its water extract. the sample was dried (at 1050 c for 24 h) in an oven for dry basis calculation. the water extract was collected by adding distilled water to substrate (10:1 v/w) followed by a three hour shaking at 180 rpm in orbital shaker at room temperature. finally the filtrate was collected after filtration through whatman no. 1 filter paper. the toc, total nitrogen and heavy metals of dry compost were determined as same method as in the lsb process. glucosamine and germination index were measured from water extract to evaluate the performance of fungal growth & multiplication, and the level of maturity of compost through biodegradation by ssb, respectively. glucosamine was determined according to zheng and shetty [27]. germination index was measured by using seeds of brasicca napus based on the procedure of zucconi et al. [28]. 2.6 statistical analysis. the experiment was conducted using a completely randomized design with three replicates. the data were analyzed by f factor after anova, and comparisons means were done separately using the statistical package mstat-c [29]. the standard deviation was presented in respective tables. iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 28 3. results and discussion 3.1 liquid state bioconversion process 3.1.1. biosolids accumulation, biodegradation and bioseparation of dwtp sludge. the production of dry biosolids (dbs) enriched with the protein, nutrients and trace elements in treated dwtp sludge using mixed fungal inocula of a. niger and p. corylophilum is presented in table 1. the results shown in table 1 shows that the maximum composting materials (biosolids) production of 93.8 g kg-1 was recorded from its initial concentration of 40 g kg-1 of liquid sludge after 8 days of fungal treatment. the production rate was slightly declined during final days of treatment (10 days). it might be due to the nature of growth curve of treated microbes in death phase. the dwtp biosolids increased with fungal treatment was used as pretreated resource materials for rapid and effective composting by solid state bioconversion (ssb) process [5]. the fungal treated biosolids improved with nutrients (npk) and trace elements that could make as the richer composting material compared to other composting materials (sewage sludge, municipal solid wastes, paper sludge, etc) are shown in table 2. the reports on increasing sludge cake/biosolids in different waste materials of its bioconversion using fungi have been cited by several researchers [8, 30, 31]. table 1: bisolids accumulation, protein enrichment, macroand micro-elements and c/n ratio in fungal treated biosolids as pretreatment material for composting with different fermentation period. biosolids, proteins, nutrients and trace elements treatment period day 0 day 2 day 4 day 6 day 8 day 10 abiosolids (g kg-1) bprotein (g kg-1) c/n n (g kg-1) p (g kg-1) k (g kg-1) fe (g kg-1) ca (mg kg-1) mn (mg kg-1) na (mg kg-1) cu (mg kg-1) zn (mg kg-1) pb (mg kg-1) 40.02.10 16.71.10 7.30 48.30.22 19.90.49 0.80.01 09.30.40 01.40.02 49010.4 2007.50 73.02.50 30252.5 32.05.20 59.02.07 19.90.93 7.10 53.00.82 26.71.20 01.50.05 08.90.24 01.40.03 39030.7 660110. 62.07.10 30041.2 28.01.10 74.72.50 24.10.60 6.90 59.40.44 26.70.92 01.50.10 08.20.11 01.20.02 30012.20 43040.80 61.05.00 30072.10 28.01.50 85.63.20 28.30.38 6.90 60.80.11 28.61.10 01.40.01 09.00.03 01.60.03 42025.50 56020.40 70.03.40 30061.40 29.04.10 93.82.70 30.20.73 7.00 61.40.09 30.10.42 01.630.00 09.90.07 01.70.17 54010.00 45010.90 92.04.40 31032.50 43.02.20 92.22.10 30.11.23 7.10 62.30.85 31.50.65 01.50.10 09.30.07 02.10.02 48020.10 44040.00 87.010.1 30522.00 36.02.50 iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 29 aaccumulated biosolids by lsb was determined in g kg-1 of liquid dwtp sludge (4% w/w of tss), bprotein enrichment was determined in g kg-1 of dry biosolids. all heavy metals analysis were done in dry wet basis. the protein was also enriched with fungal biomass during microbial treatment of dwtp sludge. enriched protein in biosolids containing fungal biomass is shown in table1. increasing trend of protein in biosolids followed similar trend of biosolids production, as it was determined from biosolids. a maximum of 30 g of protein was determined in per kg of dry biosolids of treated sludge after 8 days of treatment. extensive researches have been done in food and animal husbandry industry for protein enrichment [12], where as very little works were conducted to convert the waste materials into valueadded product with enrichment of protein by microbial treatment [8]. chemical characterization of compost is generally based on two criteria, agronomic value and heavy metal contents. with regards to the agronomic value, the availability of major elements such as n, p, k and trace elements e.g. cu, zn, mn, fe, ni, ca, and na must be evaluated [32]. the nutrient values (n, p, k) were determined in dwtp sludge to evaluate the quality of composting materials. the microbial effect on nutrient enrichment is shown in table 1. the results shown in this study reveal that initial values of nutrients were increased up to final days of fungal treatment. in untreated sludge (control), n, p, and k were recorded with 48.27, 19.87 and 0.82 g kg-1, which were increased to 62.34, 31.47 and 1.49 g kg-1 of dry biosolids, respectively after 10 days of fungal treated sludge. the increased protein in sludge cake has been examined by several authors [8]. the total crude protein is positively correlated with total nitrogen content and fungal biomass, the total n may increase due to enrichment of fungal biomass in biosolids. the increases in total n have been observed in many other composting processes [33]. table 2: properties of different composting materials compared to treated biosolids of dwtp sludge. parameters composting raw materials (wastes) atreated biosolids by lsb bseawge sludge cmsw ddps c (%) 43.4 44.5 18.6 40 n (%) 6.2 9.7 1.1 0.3 c/n 7.0 4.6 16.8 135.6 p (%) 3.0 2.3 0.9 0.1 k (mg kg-1) 1530  5200 1.3 ca (mg kg-1) 2005  6800 12300 mn (mg kg-1) 540 278 486.3  na (mg kg-1) 450  207 1013 cu (mg kg-1) 92 726 10.3 123 zn (mg kg-1) 310 4038 110 35 dwtp – domestic wastewater treatment plant; mswmunicipal solid waste; dps de-inking paper sludge; lsb – liquid state bioconversion, amicrobially treated biosolids after 8-10 days of iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 30 dwtp sludge treatment; chemical analysis were done in dry basis , bfang et al. [49]; csoumaré et al. [32]; dcharest and beauchamp [50]. total heavy metals recorded in biosolids after microbial treatment of dwtp sludge with different fermentation time is shown in table 1. the initial value of ca in biosolids without treatment recorded was 1.4 mg kg-1 and it was increased to 2.1 mg kg-1 after 10 days of fungal treatment. the maximum increase of the trace elements ca and na were 43% and 115% respectively, compared to its initial values (0 days, control) in microbially treated biosolids. however, the obtained data are not followed any uniform trends in terms of fermentation period (table 1), while in most cases, trace elements were slightly increased in fungal treated sludge. biosolids were enriched with fungal biomass, which has higher biosoption capacity for metals, and might adsorb metals from treated supernatant and perhaps it increased the metals content [34, 35]. moreover, it was also slightly decreased with different fermentation time. compared to the different waste composting materials such as municipal solid waste (msw), citrus waste, sewage sludge and manure, the mineral content in microbially treated biosolids as pretreated material for composting was lower [32, 36, 37]. in composting process, the c/n ratio is a very important factor for compost maturity. as the product biosolids as well as pretreated materials were converted into compost, the c/n ratio in biosolids was recorded after lsb of dwtp sludge (table 1). the c/n ratio can be increased to > 25 from the recorded value of about 7 by the adjustment of carbon contained bulking substances for composting by ssb process. the biodegradation of the dwtp sludge supernatant during microbial growth recorded was very important because the supernatant was disposed directly to the environment as it meets the standard values of discharge [10]. the total suspended solids (tss), the total dissolved solids (tds), reducing sugar as substrate utilization, soluble protein as nitrogen content, optical density at 660 nm as turbidity, and the chemical oxygen demand (cod) were determined in treated supernatant to evaluate the lsb process for the treatment of the dwtp sludge. the results indicated that the filamentous fungi significantly (p>0.05) influenced on reduction of tss, tds, reducing sugar (rs), soluble protein (sp), optical density (od) and cod in supernatant of treated sludge and enhanced the lsb process (table 3). the higher reduction rate was recorded at day 6-8 of the lsb treatment period and no significant difference was observed thereafter. the filamentous fungi entrapped the suspended solid particles in the sludge and enhanced the tss reduction process significantly [8, 30]. during treatment, the fungal strains utilized the dissolved substances as food and energy sources in sludge and enhanced the reduction of tds, sp, and rs of treated sludge [8] in the treatment, the fungal cultures utilized the soluble suspended matters resulting in higher reduction of turbidity. the cod was an important factor to evaluate the organic content of the dwtp sludge. the results suggested that cod removal was highly accelerated by the microbial treatment of the sludge. fungal growth and its secondary metabolites helped to reduce the soluble and insoluble organic substances in sludge effectively [8]. cod removal of waste materials by fungal treatment have been studied by many authors and they found that cod were reduced by mixed culture of aspergillus niger, penicillium corylophilum; aspergillus awamori and trichoderma reesei; and single culture of penicillium spp., aspergillus oryzae and rhizopus oligosporus in domestic wastewater [7], olive mill wastewaters [31], and starch processing wastewater [30] with a considerable values (60-90%). iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 31 table 3: biodegradation and bioseparation of dwtp sludge by the mixed culture of a. niger and p. corylophilum. treatment period (day) increased biodegradability in supernatant and filterability of treated biosolids g l-1 optical density (660 nm) for turbidity specific resistance to filtration (r1012, m/kg) cod rs tds sp tss 0 1.280.03 12.90.16 5.50.01 0.330.01 8.100.21 0.850.01 85.452.10 2 0.960.02 9.20.18 3.70.11 0.250.01 5.860.20 0.710.00 65.212.08 4 0.660.05 6.30.29 1.60.17 0.190.02 3.100.17 0.110.02 42.370.18 6 0.220.03 3.80.24 0.20.18 0.090.01 0.500.16 0.050.01 1.390.12 8 0.150.01 1.40.19 0.10.01 0.070.01 0.090.00 0.020.02 1.580.22 10 0.090.01 0.40.01 0.10.05 0.070.09 0.100.01 0.030.01 1.650.11 cod chemical oxygen demand; rs reducing sugar; tds total dissolved solid; sp soluble protein; tss total suspended solid. specific resistance to filtration (srf) was determined to assess the dewaterability/filterability of the treated sludge. the filterability of treated sludge was significantly influenced by the fungal treatment as compared to untreated sample (table 3). the filamentous fungi entrapped the solid particles of dwtp sludge and compressed sludge solids by filamentous mycelia, which modified the porosity structure of sludge cake, and accelerated the filtration process [9]. fakhru’l-razi et al. [8] has studied the filterability test of higher solids content of domestic wastewater sludge in shake flask using aspergillus and penicillium to evaluate its potentiality for bioconversion of wastewater sludge and has produced effective results. 3.2 solis state bioconversion process c/n ratio. the toc and total kjeldahl nitrogen (tkn) ratio (c/n ratio) decreased gradually in all situations over time of bioconversion periods (table 4). in all cases, the treatments of mixed fungal culture influenced in decreasing (significantly at p 0.05 by lsd) the c/n ratio than the control treatment. the obtained results of two different mixed cultures were roughly similar and insignificant in the solid state bioconversion of dwtp sludge. comparatively sharp decreasing value was exhibited up to the period of 45 days mostly in all cases. the minimum 12.1 and 12.6 of the c/n ratio were recorded for rs in compost by t/p and t/m, respectively after final days of treatment. in the case of the sd, the lowest c/n ratio were 16.0 and 16.7 which were achieved by t/p and t/m, respectively in the process after the same period of treatment. the c/n ratio is an index traditionally used to evaluate the maturation of compost; the value cannot be used as an absolute indicator of compost maturation [3]. a c/n ratio < 20 iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 32 could be considered a satisfactory maturation level of compost [37] but a ratio ≤ 15 is more preferable [23]. in the present study, the obtained results in cb implied the excellent maturation of compost. fang et al. [3] recorded the final range of c/n ratio of 17-19 over 100 days composting of sewage sludge, which was 25 initially in pile composting that did not have any microbial treatments. in 70 days composting program of soybean leaves, the final range of c/n ratio 18-22 was achieved, when the initial ratio was 30 [38]. mathur et al. [39] cited of c/n ratio in the topic of ‘determination of compost biomaturity’ that the ideal c/n ratio of mature compost is 10, as in humus, hardly ever achieved by composting. in spite of this difficulty, they also remarked that the c/n ratio up to 20 is acceptable for composts as long as they are biostable or mature. the c/n ratio does generally decrease, except for an occasional increase due to loss of ammonia from some systems and reaches more or less a more stable level. therefore, the c/n ratio is a potential indicator of compost maturity but it cannot be used as a sole indicator of biomaturity for all types of composts [39]. germination index. germination index (gi %) decreased gradually and attained to minimum at 30 days in both bulking materials (table 5). the minimum value of gi for sd was 52.8 and 55.0% by t/m and t/p, respectively. conversely, it was 33.4 and 39.6% for rs by t/p and t/m, respectively. in all situations, the values of gi increased to about 90% and above. at final harvest, the gi in sd was ≥100% in both mixed cultures. at last harvest, the highest level of gi was 99.0 and 122.2% were observed using bulking material of sd. on the other hand, for bulking material rs, the maximum 92.3% was recorded at last harvest (table 5). brassica napus seeds were used for gi, the profile of it clearly presented that the trend of gi started from around 100%, then it gradually declined to 35-40% (most of the cases) at 30 days of ssb treatment of mixed fungal cultures and next it was increased around 100% and above at 60 to 75 days. the gi (using brasicca napus seeds) was the most sensitive parameter to evaluate the toxicity and degree of maturity status of compost [40]. the dropping of gi value in profile around 30 days of treatment might be the reason to the release of high concentration of ammonia and low molecular weight organic acids [3]. excess of free ammonia is well known toxic organic chemical for seed germination and seedling growth. the gi level increased significantly (p<0.05) (122.2 & 119.5% in sd by t/p & t/m, respectively; 89.2 & 92.3% in rs by t/p & t/m, respectively) at 75 day, perhaps the relief of phytotoxins especially the ammonia volatilization and reduction of unstable organic acids. higher phytotoxins, sources of unstable organic substances caused severe injuries of root systems [41]. immature compost retarded plant growth due to nitrogen starvation, phytotoxicity of nh3 and some organic acids [39]. the gi of 50% has been used as an indication of phytotoxin-free compost [40]. but in another report, when the gi value exceeded 80%, then the sludge compost was considered as mature [42]. glucosamine in water extract of compost. glucosamine, an essential component in chitin of mycelial cell wall, is water-soluble sugar and stable component. it can be considered as a good parameter for indirect estimation of the nature of mycelial growth in solid substrate [43]. in another report, roche et al. [44] found positive correlation between biomass and glucosamine content of fungi in solid state fermentation. in solid state fermentation of cranberry processing, higher mixed fungal mycelial growth was examined by estimation of glucosamine content [27]. iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 33 table 4: the changes of c/n ratio during solid state bioconversion of domestic wastewater sludge using two mixed cultures. treatment c/n ratio day 0 day 5 day 15 day 30 day 45 day 60 day 75 sd rs sd rs sd rs sd rs sd rs sd rs sd rs control 29.97 29.80 28.34 27.50 24.32 23.25 23.00 23.11 22.76 18.88 22.80 17.79 21.32 17.25 t/p 29.97 29.80 24.88 23.67 21.35 18.86 24.04 15.79 18.59 13.91 16.49 12.63 15.98 12.14 t/m 29.97 29.80 25.90 24.60 21.04 18.37 19.76 14.58 18.42 13.68 16.83 12.90 16.65 12.58 lsd (5%) 0.24 0.35 1.02 1.00 0.82 0.26 0.70 0.70 0.59 1.04 0.32 0.75 sd – sawdust; rs – rice straw; t/p – trichoderma harzianum with phanerochaete chrysosporium; t/m – t. harzianum with mucor hiemalistable 5: the changes of germination index (gi) during solid state bioconversion of domestic wastewater sludge. treatment germination index (%), control 100 day 0 day 5 day 15 day 30 day 45 day 60 day 75 sd rs sd rs sd rs sd rs sd rs sd rs sd rs control 117.6 103.2 99.9 84.8 110.8 85.6 91.0 71.0 107.2 105.3 103.2 91.6 98.3 79.5 t/p 117.6 103.2 93.6 71.4 72.7 65.1 55.0 33.4 80.7 72.2 121.17 85.2 122.2 89.2 t/m 117.6 103.2 89.5 61.3 79.9 71.6 52.8 39.6 82.7 65.7 112.9 89.8 119.5 92.3 lsd (5%) 8.5 16.1 8.1 12.8 3.4 4.1 8.6 7.7 16.2 14.2 10.0 8.9 sd – sawdust; rs – rice straw; t/p – trichoderma harzianum with phanerochaete chrysosporium; t/m – t. harzianum with mucor hiemalis comparatively, higher results were achieved for rs than the sd (table 6). it implied the higher growth of fungal mycelium occurred for rs. the results showed significantly higher trend of glucosamine profiles by fungal treatments than the control in all situations. but enhanced results were observed for rs by fungal treatments. relatively poor results for sd implied the poor adaptation and growth of fungi might be due to the hard cell wall of wood than the rice straw. in cranberry processing under solid state culture, zheng and shetty [27] also explained the significant growth of fungi trichoderma and penicillium species by estimation of glucosamine and suggested as a good indicator of fungal biomass estimation in heterogeneous substrates. iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 34 table 6: glucosamine during solid state bioconversion of dwtp sludge using two mixed cultures and bulking materials. treatment glucosamine, (%) day 0 day 5 day 15 day 30 day 45 day 60 day 75 sd rs sd rs sd rs sd rs sd rs sd rs sd rs control 0.079 0.114 0.115 0.142 0.268 0.239 0.302 0.285 0.354 0.343 0.318 0.274 0.285 0.287 t/p 0.079 0.114 0.229 0.584 0.309 0.411 0.463 0.756 0.422 0.649 0.428 0.623 0.392 0.557 t/m 0.079 0.114 0.238 0.487 0.336 0.435 0.453 0.786 0.431 0.622 0.439 0.608 0.369 0.576 lsd 5% 0.018 0.040 0.024 0.032 0.030 0.042 0.028 0.046 0.022 0.050 0.026 0.120 sd – sawdust; rs – rice straw; t/p – trichoderma harzianum with phanerochaete chrysosporium; t/m – t. harzianum with mucor hiemalis. 3.3 heavy metals and nutrients in compost of biosolids produced by ssb technique. the heavy metals status of compost produced by ssb of the dwtp sludge was not so changed by microbial treatment (table 7). the analyzed record of heavy metals (in dry basis) in compost was lower than that of sludge (table 4) due to dilution effect (i.e. composting is the mixture of equal half w/w of sludge and bulking materials). all heavy metals in table 7 were about half or 50% of the amount present in sludge except mn for rs. the reasons might be that the present study was carried out using sludge to bulking materials ratio of 1:1 (w/w). therefore, analysis of heavy metals from compost would be half than the sole sludge. higher mn in compost of rs might be the reason of bulking agent rice straw. remediation of heavy metals is the limitation of bioconversion/bioremediation program, which was reported by boopathy [45]. the acting microbes could assimilate some of the metals. but in chemicals analysis, which was not reflected because the metals absorbed by microbes were also contributing in results table 7. heavy metals status of compost after 75 days of solid state bioconversion of iwk dwtp sludge using mixed fungal culture t. harzianum with p. chrysosporium 2094 (t/p) and t. harzianum with m. hiemalis (t/m). treatment pb ni cu mn cd zn sd rs sd rs sd rs sd rs sd rs sd rs mg kg-1 control 33.00 37.53 9.47 11.20 63.07 75.47 30.34 168.3 1.83 1.93 1120.0 1193.4 t/p 33.73 36.27 8.73 10.53 63.53 75.53 34.93 165.67 1.99 2.24 1130.0 1200.0 t/m 32.67 31.87 9.07 10.27 58.47 74.53 35.53 163.80 1.75 2.02 1073.4 1160.0 lsd 5% 1.77 1.06 5.22 11.81 0.21 61.04 sd – sawdust; rs – rice straw; t/p – trichoderma harzianum with phanerochaete chrysosporium; t/m – t. harzianum with mucor hiemalis, chemical analysis for heavy metals estimation was done in dry basis. iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 35 it was not possible to separate out the acting microbes from compost before chemical analysis. the heavy metals were significantly changed between composts of rs (i.e, crs) and sd (i.e, csd) due to influence of bulking materials (table 7). the higher amount was achieved in rice straw. furthermore, the amounts of heavy metals present in composts (crs and csd) are quite low than the standard limits of several countries except for chromium (cr) and zinc (zn) in some cases (table 8). on an average the amount of heavy metals present in composts (crs and csd) are 30 times lower compare to the level that have recommended to be applied for crop production by usa in compost of msw [46]. indah water konsortium (iwk) is dealing with only urban sewage sludge and free from industrial wastewater. therefore, it contains comparatively lower amount of heavy metals. ishak et al. [47] reported that significant higher amount of cd and zn was disseminated in soil after direct application of the iwk wastewater sludge for corn cultivation. contamination of cu, cr, and cd are mainly concerned with industrial wastewater but zn and pb are mainly from domestic wastewater [48]. it might be the reason of higher amount of zn in iwk sludge (table 8). table 8: nutritional status of composts from iwk dwtp sludge. standard limits of heavy metals of msw composts in some countries [46, 51] and typical level in soil [52]. parameters composta usa ec australia china typical value in soil crs csd moisture (%) 69.87 66.88 25-35 25-35 ph 5.27 5.15 7.0-8.5 6.5-8.5 5.0 c/n ratio 12.11 15.60 11 ec (ds m-1) 1.49 0.35 bd (kg m-3) 1099.22 953.26 1300 n (%) 3.10 2.87 0.6 0.5-1.5 ≥ 0.5 0.4 p (%) 0.84 0.62 0.5 0.4-0.8 ≥ 0.3 0.05-0.2 k (%) 3.13 0.25 0.3 0.3-1.0 ≥ 1.0 0.04-3.0 ca (%) 0.10 0.05 0.7-50 mg (%) 0.21 0.05 0.06-6.0 pb (mg kg-1) 36.27 33.73 300 750 200-900 ≥ 100 2-100 ni (mg kg-1) 10.53 8.73 420 50 30-200 cd (mg kg-1) 2.24 1.99 39 5 1-6 ≥ 3 0.01-7.0 cr (mg kg-1) 508.33 450.0 1200 150 50-300 ≥ 300 5-3000 cu (mg kg-1) 75.53 63.53 1500 300 1000 2-100 mn (mg kg-1) 165.67 34.93 500-1200 100-4000 zn (mg kg-1) 1200.0 1130.0 2800 1000 300-1500 10-300 na (mg kg-1) 436.50 1364.5 400-30000 fe (mg kg-1) 9200 8066 acrs: compost -rice straw, csd: compost -sawdust. both prepared with mixed fungi t. harzianum and p. chrysosporium 2094 inoculation by ssb process. all nutrients were analyzed as dry basis. iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 36 moreover, in the present study, the end product (compost) of ssb of dwtp sludge achieved the suitable characteristics of stable matured composts in compared to others in relatively shortest period of time (table 9). the composting duration may significantly reduce if the process is operated in mechanized control condition. it contains more or less all nutrients (table 8). it can supplement the trace elements to the soil in sufficient amount for better plant growth. the compost of crs possessed higher nutrients levels than the csd i.e. all major nutrients are higher in crs than the csd (table 8). table 9: comparative study of composts of iwk dwtp sludge by ssb process with others*. compost quality characteristics siegfried agro and asiagreena nutri plusb compost (negro et al., 1999)c crs csd dry substance (% ds) 40-60 55 62 47.66 46.95 ph value 7-8 5.3 5.27 5.15 ec (ds/m) 0.5-1.5 2.98 1.49 0.35 organic matter (% om) 16-29 75 31.67 37.37 nitrogen (%) 0.6-1.3 0.9 3.0 1.48 1.38 phosphorous (%) 0.15-0.62 0.88 0.40 0.29 potassium (%) 0.37-1.49 0.57 1.49 0.12 calcium (%) 2.48-9.94 1.3 0.005 0.05 0.02 magnesium (%) 0.4-1.6 0.45 0.10 0.02 toc (%) 39 17.93 21.53 c/n ratio 12-18 13 12.11 15.60 bulk density (kg m-3) 1099.22 953.26 germination index (%) 80-94 >50 90 122 weight loss (%) 18.29 7.57 duration (days) 56-70 >365 50-60 50-60 odor status free odor free odor free out look good good n (%) supplement in crop production 50% 50% weed status free free free *all chemical analysis was done as wet basis. both composts (crs: compost of biosolids with rice straw and csd: compost of biosolids with sawdust) were produced in solid state bioconversion using filamentous mixed fungal culture t. harzianum with p. chrysosporium 2094. asiegfried agro ltd from switzerland and asiagreen environmental sdn bhd in malaysia are commercially producing composts in joined venture and recommended the optimal level of characteristics of matured quality compost. b nutri plus is compost produced commercially by edmonton composting facility, canada from municipal solid waste and sewage biosolids. ccompost produced from sewage sludge with sorghum bagasse, the chemical analyzed was done in dry basis iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 37 4. conclusion in the present study, lsb process increased the biosolids accumulation, moreover it enhanced nutrients and dewaterability, and minimized soluble and insoluble organic/inorganic substances in supernatant. the results also revealed that the ssb process efficiently and effectively converted the treated biosolids from lsb into compost and retained high nutrient values compared to other composts. the integrated processes of lsb and ssb may show a complete solution of higher concentration of wastewater sludge (4% w/w) to value added products (compost) by enhancing the biosolids accumulation, bioseparation and biodegradation. this study may enhance the planning of sludge management strategies using this integrated processes in future research, solutions and applications. acknowledgement the authors are grateful to the department of chemical and environmental engineering, universiti putra malaysia (upm) for their kind support and iwk for their research grant as well as providing the sludge sample during this study. references [1] o. lorain, p. thiebaud, e. badorc, y. aurelli, “potential of freezing in wastewater treatment: soluble pollutant applications”, water res. vol. 35(2), pp. 541-547. 2001 [2] m. oudeh, m. khan, j. scullion, “plant accumulation of potentially toxic elements in sewage sludge as affected by soil organic matter level and mycorrhizal fungi”, environ. poll, vol. 116, pp. 293-300, 2002. [3] m. fang, j. w. c. wong, g. x. li, m. h. wong, “changes in biological parameters during co-composting of sewage sludge and coal ash residues”, bioresource technol, vol. 64, pp. 55-61, 1998. [4] m. z. alam, a. fakhru'l-razi, a. h. molla, p. k. roychoudhury, “treatment of wastewater sludge by liquid state bioconversion process”, j. environ. sci. health, vol. a36 (7), pp. 1237-1243, 2001. [5] a. h. molla, “solid state bioconversion of domestic wastewater treatment plant sludge into compost by screened filamentous fungi”, ph. d. thesis. faculty of engineering, universiti putra malaysia (upm), malaysia, 2002. [6] a. fakhru'l-razi, m. z. alam, a. idris, s. abd-aziz, a. h. molla, “filamentous fungi in indah water konsortium (iwk) sewage treatment plant for biological treatment of domestic wastewater sludge”. j. environ. sci. health, vol. a37 (3), pp. 309-320, 2002. [7] m. z. alam, a. fakhru'l-razi, “enhanced settleability and dewaterability of fungal treated domestic wastewater sludge by liquid state bioconversion process”, water res. vol. 37, pp. 1118-1124, 2003. [8] a. fakhru’l-razi, m. z. alam, a. idris, s. abd-aziz, a. h. molla, “domestic wastewater biosolids accumulation by liquid state bioconversion process for rapid composting”, j. environ. sci. health, vol. a37 (8), pp. 1533-1543, 2002. iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 38 [9] m. z. alam, a. fakhru'l-razi, “biosolids accumulation and biodegradation of domestic wastewater treatment plant sludge by developed liquid state bioconversion process using a batch fermenter”, water res. vol. 37, pp. 3569-3578. 2003. [10] ilbs (international law book services), “laws of malaysia. in environmental quality act 1974 (act 127) & subsidiary legislation”, international law book services (ilbs), kuala lumpur, malaysia, pp.121, 1999. [11] r. p. tengerdy, “solid state fermentation of lignocelluloses. in solid substrate cultivation”, eds. h. w. doelle, d. a. mitchell, and c. e. rolz, pp. 269-282, elservier science ltd., london, 1992. [12] x.yang, h. chen, h. gao, z. li, “bioconversion of corn straw by coupling ensiling and solid-state fermentation”, bioresource technol. vol. 78, pp. 227-280, 2001. [13] m. raimbault, “general and microbiological aspects of solid substrate fermentation”, electronic j. biotechnol. vol. 1(3), pp. 1-15, 1998. [14] m. z. alam, a. fakhru'l-razi, a. h. molla, “evaluation of fungal potentiality for bioconversion of domestic wastewater sludge”, j. environ. sci, vol. 16, 132-137, 2004. [15] m. z. alam, a. fakhru’l-razi, s. abd-aziz, , abul h. molla, “optimization of compatible mixed cultures for liquid state bioconversion of municipal wastewater sludge”, water, air and soil pollution, vol. 149, pp. 113-126, 2003b. [16] a.h. molla, a. fakhru’l-razi, s. abd-aziz, m.m. hanafi, p.k. roychoudhury, m.z.alam, “a potential resource for bioconversion of domestic wastewater sludge”, bioresource technol, vol. 85(3), pp. 263-272, 2002. [17] a.h. molla, a. fakhru’l-razi, s. abd-aziz, m.m. hanafi, m.z. alam, “in-vitro compatibility evaluation of fungal mixed culture for bioconversion of domestic wastewater sludge”, world j. microbiol. biotechnol, vol. 17(9), pp. 849-856, 2001. [18] a.h. molla, a. fakhru’l-razi, m.m. hanafi, s. abd.-aziz, m.z. alam, “potential non-phytopathogenic filamentous fungi for bioconversion of domestic wastewater sludge”, j. environ. sci. health a vol. 37(8), pp. 1495-1507, 2002. [19] m. z. alam, a. fakhru'l-razi, a. h. molla, “optimization of liquid state bioconversion process for microbial treatment of domestic wastewater sludge”, j. environ. eng. sci. vol. 2, pp. 299-306, 2003. [20] apha, “standard methods for the examination of water and wastewater”, 17th edition, american public health association, washington, dc. 1989. [21] o.h. lowry, n.j. rosebrough, a.l. farr, r. j. randall, “protein measurement with the folin phenol reagent”, j. biol. chem. vol. 193, pp. 265-275, 1951. [22] g.l. miller, “use of dinitrosalicylic acid reagent for determination of reducing sugar”, anal. chem, vol. 31, pp. 426-428, 1959. [23] a.f. navarro, j. cegarra, a. roig, d. garcia, “relationships between organic matter and carbon contents of organic wastes”, bioresource technol. vol. 44, pp. 203-207, 1993. [24] j. m. bremner, “determination of nitrogen in soil by the kjeldahl method”, j. agric. sci, vol. 55, pp. 11-31, 1960. [25] a. cottonie, g. velghe, m. verloo, l. kiekens, “analytical methods for plants and soils”, laboratory of analytical and agrochemistry, state univ., ghent-belgium, pp. 29, 1979. [26] p. c. carman, “fundamental principals of industrial filtration (a critical review of present knowledge)”, trans. insts. chemical engineers. vol. 16, pp. 168, 1977. iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 39 [27] z. zheng, k. shetty, “cranberry processing waste for solid state fungal inoculant production”, process biochem, vol. 33(3), pp. 323-329, 1998. [28] f. zucconi, m. forte, a. monaco, m. de bertoldi, “biological evaluation of compost maturity”, biocycle, vol. (7&8), pp. 27-29, 1981a [29] mst (michigan state university), “user’s guide to msat-c”, michigan state university, east lasing, mi, 1989. [30] b. jin, j. van leeuwen, q. yu, b. patel, “screening and selection of microfungi for microbial biomass protein production and water reclamation from starch processing wastewater”, j. chem. technol. biotechnol, vol. 74, pp. 106-110, 1999. [31] a. robles, r. lucas, g. alvarez de cienfuegos, a. galvez, “biomass production and detoxification of wastewaters from the olive oil industry by strains of penicillium isolated from wastewater disposal ponds”, bioresource technol, vol. 74, pp. 217-221, 2000. [32] m. soumaré, a. demeyer, f.m.g. tack, m.g. verloo, “chemical characteristics of malian and belgian solid waste composts”, bioresource technol, vol. 81, pp. 97-101, 2002. [33] j.j. thambirajah, m.d. zulkali, m.a. hashim, “microbiological and biochemical changes during the composting of oil palm empty-fruit bunches-effect of nitrogen supplementation on the substrate”, bioresource technol. vol. 52 (2), pp. 133-144, 1995. [34] e. valdman, l. erijman, f.l.p. pessoa, s.g.f. leite, “continuous biosorption of cu and zn by immobilized waste biomass sargassum sp.”, process biochem. vol. 36, pp. 869-873, 2001. [35] m. s. price, j. j. classen, g. a. payne, “aspergillus niger absorbs copper and zinc from swine wastewater”, bioresource technol, vol. 77, pp. 41-49, 2001. [36] g. wen, j.p. winert, r.p. voroney, t.e. bates, “potassium availability with application of sewage sludge, and sludge and manure compost in the field experiments”, nutr. cyc. agroecosys. vol. 47, pp. 233-241, 1997. [37] i. van heerden, c. cronjé, s. h. swart, j. m. kotzé, “microbial chemical and physical aspects of citrus waste composting”, bioresource technol, vol. 81, pp. 71-76, 2002. [38] j.w.c. wong, k.f. mak, n.w. chan, a. lam, m fang, l.x. zhou, q.t. wu, x. d. liao, “co-composting of soybean residues and leaves in hong kong”, bioresource technol, vol. 76, pp. 99-106, 2001. [39] s.p. mathur, g. owen, h. dinel, m schnitzer, “determination of compost biomaturity. i. literature review”, biol. agril. hort, vol. 10, pp. 65-85, 1993. [40] f. zucconi, a. monaco, m. forte, “phytotoxins during the stabilization of organic matter. composting of agricultural and other wastes”, ed. j. k. r. gasser, pp 7385. elsevier applied science publishers, 1984. [41] f. zucconi, a pera, m. fote, “evaluation toxicity of immature compost. biocycle”, vol. (3 & 4), pp. 54-57, 1981b. [42] h. xu, “studies on aerated static pile on sewage composting. m. sc. dissertation”, research center for eco-environmental sciences, chinese academy of sciences, beijing, 1999. [43] c. desgranges, c. vergoignan, m. georges, a. durand, “biomass estimation in solid-state fermentation. i. manual biochemical methods”, appl. microbiol. biotechnol, vol. 35, pp. 200-205, 1991. iium engineering journal, vol. 6, no. 1, 2005 m z alam et al. 40 [44] n. roche, a. venague, c. desgranges, a. durand, “use of chitin measurement to estimate fungal biomass in solid state fermentation”, biotechnol. advan, vol. 11, pp. 677-683. 1993. [45] r. boopathy, “factors limiting bioremediation technologies”, bioresource technol, vol. 74, pp. 63-67, 2000. [46] y.-s. wei, y.-b. fan, m.-j. wang, j.-s. wang, “composting and compost application in china”, resource, conservat. recycl, vol. 30, pp. 277-300, 2000. [47] c.f. ishak, r.a. bakar, h.m. saud, t.l. abdullah, “application of sewage sludge from indah water treatment plants”, agro-search, vol. 6(1), pp. 14-19, 1999. [48] l. kuai, f. doulami, w. verstraete, “sludge treatment and reuse as soil conditioner for small rural communities”, bioresource technol. 73, 213-219. 2000. [49] m. fang, j. w. c. wong, k. k. ma, m. h. wong, “co-composting of sewage sludge and coal fly ash: nutrient transformations”, bioresource technol, vol. 67, pp. 19-24, 1999. [50] m. -h. charest, c. j. beauchamp, “composting of de-inking paper sludge with poultry manure at three nitrogen levels using mechanical turning: behaviour of physicochemical parameters”, bioresource technol, vol. 81, pp. 7-17, 2002. [51] x.t. he, t. j. logan, s. j. traina, “physical and chemical characteristics of selected u. s. municipal solid waste composts”, j. environ. qual, vol. 24, pp. 543-552, 1995. [52] d. c. adriano, a. l. page, a. a. elseewi, a. c. chang, i. straughan, “utilization and disposal of fly ash and other coal residues in terrestrial ecosystem: a review”. journal of environmental quality, vol 9, pp. 333-334, 1980. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 ali et al. 34 electrochemical characterization of polylactic acid-block-poly (2vinylpyridine)/gold nanoparticle composites for glucose biosensor development fathilah ali, jiajia long and wan wardatul amani wan salim department of biotechnology engineering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. *corresponding author: fathilah@iium.edu.my (received: 4 th sept. 2017; accepted: 17 th july 2017; published on-line: 1 st dec. 2017) abstract: nanocomposites that consist of diblock copolymer (bcp) and gold nanoparticles (aunps) can be applied as a matrix to immobilize enzymes or other molecules, based on the well-defined core/shell nanostructures of these composites. in this research, polylactic acid-block-poly(2-vinylpyridine) (pla-b-p2vp)/hydrogen tetrachloroaurate(iii) hydrate (haucl4.3h2o) composites were hybridized and then reduced in dichloromethane (dcm) solution. the hybridizations between gold precursors and the p2vp domain were prepared with different ratios of gold to p2vp block (1:1, 1:5, 1:10, 5:1, 10:1) by taking advantage of the association between the longpair nitrogen of the pyridine group of p2vp. the reduction of the au 3+ /pla-b-p2vp composite was accomplished by hydrazine solution in order to get gold nanoparticle/pla-b-p2vp composites, which was visually confirmed by a direct color change from bright yellow to purple. in this work, ultraviolet–visible (uv-vis) spectroscopy and fourier transform infrared spectroscopy (ftir) were used to confirm the association between gold precursors and pyridine groups as well as the synthesis of gold nanoparticles. the composite which labeled as r3 (au 3+ : p2vp = 10:1) showed the highest peak current based on the cyclic voltammetry (cv) measurement. furthermore, graphene oxide (go) was added into r3 to prepare bcp/aunps/go composite and reduced to bcp/aunps/rgo through electrochemical reduction. the resulting bcp/aunps/rgo showed high potential to be used in amperometric biosensor. abstrak: nanokomposit yang terdiri daripada diblok kopolimer (bcp) dan nanopartikel emas (aunps) boleh digunakan sebagai matrik untuk memegun enzim atau molekul lain berdasarkan struktur asas nano komposit. dalam kajian ini, polilaktik asidblok-poli(2-vinylpyridine) (pla-b-p2vp)/hidrogen tetrachloroaurate (iii) hidrat (haucl4.3h2o) komposit telah dihibrid dan kemudian direduksi dalam larutan diklorometana (dcm). proses hibridasi antara prekursor emas dan domain p2vp dilakukan dengan nisbah yang berbeza; emas kepada blok p2vp (1:1, 1:5, 1:10, 5:1, 10:1) dengan mengambil peluang daripada gabungan antara kumpulan nitrogen dan kumpulan p2vp piridina. reduksi komposit au 3+ / pla-b-p2vp dapat dihasilkan dengan larutan hidrazin bagi mendapatkan komposit nanopartikel emas/pla-b-p2vp, ini disahkan dengan perubahan warna daripada kuning kepada ungu. dalam kajian ini, kehadiran-ultraungu spektroskopi (uv-vis) dan perubahan fourier inframerah (ftir) telah digunakan untuk mengesahkan hubungan antara prekursor emas dan kumpulan piridina serta sintesis emas nanopartikel. komposit yang dilabelkan sebagai r3 (au 3+ : p2vp = 10:1) menunjukkan puncak tertinggi arus berdasarkan nilai kitaran voltammetri iium engineering journal, vol. 18, no. 2, 2017 ali et al. 35 (cv). tambahan, graphene oksida (go) telah ditambah ke dalam r3 untuk menyediakan komposit bcp/aunps/go dan menukarkan kepada bcp/aunps/rgo melalui teknik penurunan elektrokimia. keputusan komposit bcp/aunps/rgo menunjukkan potensi yang tinggi untuk digunakan dalam biosensor amperometrik. keywords: block copolymer; gold nanoparticles; poly(2-vinylpyridine); polylactic acid; cyclic voltammetry 1. introduction a glucose biosensor, consisting of a recognition element and a transducer, is the basic technology to monitor glucose levels, particularly those of diabetic patients [1]. it is widely acknowledged that nanomaterial-modified electrodes of an enzymatic biosensor play an important part in improving the sensitivity and stability of analyte detection. among candidate nanomaterials, gold nanoparticles (aunps) have gained considerable attention based on their excellent conductivity and catalytic properties. aunps have many advantages to electrochemical sensors, including their ability to provide biocompatibility and efficient loading sites for immobilizing enzymes and further improving electron transfer between the active site and electrode [2]. certain properties of polymers, including stability, ease of synthesis, excellent tailorability, and good processability, also attracted many researchers’ attention [3]. block copolymers (bcps) made of blocks of different polymerized monomers linked by covalent bonds at their ends likewise attracted interest based on their structure, size, and chemical composition. self-assembly of bcps can generate nanostructured particles with tunable internal structures, shapes, and surface properties, which provide potential application in particle-based technology [4]. furthermore, it is well acknowledged that incorporating nanoparticles into a polymer matrix can have a significant influence in the properties of the binding matrix, including mechanical strength, conductivity, permeability and catalytic activities [5]. graphene attracted a lot of attention due to its’ one-atom-thick planar sheet of sp 2 bonded carbon atoms that are densely arranged into a 2d honeycomb-structure with superior electrical conductivity, excellent chemical stability and high surface to volume ratio [6]. different reduction strategies were used to reduce go into rgo, such as thermal annealing, chemical reagent reduction and electrochemical reduction [7]. electrochemical reduction is a method that shows promise for the reduction of go which depends on the electrochemical removal of oxygen functional groups. in this research, polylactic acid-block-poly(2-vinylpyridine) (pla-b-p2vp) was used for hybridization with au 3+ by taking advantages of the association between the long-pair nitrogen of the pyridine and various metal irons [8]. the synthesis of gold nanoparticles was accomplished through reduction of bcp/au 3+ by using hydrazine hydrates as reducing reagent. the optimum ratio of pla-b-p2vp/aunps composites was chosen based on cv results. graphene oxide (go) was added in to the optimum ratio composite to prepare bcp/aunps/go composite and reduced to bcp/aunps/rgo through electrochemical reduction. the electrochemical properties of bcp/aunps/rgo was characterized through cv measurements. 2. experimental 2.1 reagents and apparatus polylactic acid-block-poly(2-vinylpyridine) (pla-b-p2vp) with molecular weight (mw) 38 400 g mol -1 and fpla = 0.36 was used in this work. gold(iii) chloride trihydrate iium engineering journal, vol. 18, no. 2, 2017 ali et al. 36 (≥99.9% trace metals basis, haucl4•3h2o), hydrazine solution (35 wt% in h2o, n2h4•h2o) and dichloromethane (ch2cl2, anhydrous, ≥99.8%) were all purchased from sigma-aldrich. potassium ferricyanide (k3fe(cn)6) was purchased from r&m chemicals, selangor, malaysia. graphene oxide (go) sheets were purchased from abalonyx, oslo, norway. ultra-highly concentrated single-layer graphene oxide (uhc go), 6.2 mg/ml, was purchased from graphene-supermarket.com (usa). all electrochemical experiments to characterize bcp/aunp composites were performed using a conventional three-electrode cell and a pocketstat (ivium technologies, eindhoven, netherlands) as potentiostat/galvanostat/impedance analyzer at 25 °c. a modified glassy carbon electrode (gce, inner diameter of 3.0 mm) was used as the working electrode (we), platinum (pt) was used as the counter electrode (ce), and silver/silver chloride (ag/agcl) in 3.0 m saturated sodium chloride (nacl) was used as the reference electrode (re). all electrodes were purchased from als co., ltd., tokyo, japan. prior to surface modifications, the gce was polished with diamond (0.1 µm) and alumina slurry (0.05 µm) purchased from als co., ltd., tokyo, japan, ultrasonicated in ethanol for 1 minute and then deionized (di) water for 1 min, and dried in a desiccator for 30 min before use. uv–vis spectroscopy measurements (350 – 650 nm) were performed using uviline 9400 (secoman, france) at room temperature with a 10 mm optical length quartz cuvette. the fourier transform infrared spectroscopy (ftir) investigations were carried out with the nicolet is50 ft-ir spectrometer (thermo scientific, usa). 2.2 hybridization of bcp and gold precursors (au 3+ ) five wt% of diblock copolymer (pla-b-p2vp) solution was prepared in dichloromethane (dcm) solution and stirred for 14 hours, followed by the hybridization between gold precursors and the p2vp block using different ratios of gold to p2vp block (labeled from h1 to h5 respectively representing au 3+ : p2vp ratios from 1:1, 1:5, 1:10, 5:1, and 10:1 hybridization samples). the hybridization samples (h1, h2, h3, h4, h5) and control (bcp in dcm) were characterized via ftir for investigation of association between the long-pair nitrogen of the p2vp pyridine group and au 3+ . 2.3 synthesis of gold nanoparticles the synthesis of aunps was accomplished through reduction by hydrazine hydrate solution which labelled to ratios of au:p2vp as r1 (1:1), r2 (5:1), r3 (10:1), r4 (1:5), r5 (1:10), corresponding to the hybridization samples. uv-vis spectroscopy was applied to characterize the synthesis of aunps in pla-b-p2vp/aunp composites. 2.4 electrochemical characterization of pla-b-p2vp/aunps composites cyclic voltammetry (cv) was performed to evaluate the electron-transfer capabilities of the modified layer based on the oxidation peak current. 0.05 m potassium ferricyanide (k3fe(cn)6) solution was used as redox solution and 50 mv/s as the scan rate. 2.5 the preparation and electrochemical reduction of pla-b-p2vp/aunps/go composite graphene oxide (go) was added into the optimum ratio composite with the ratio of 1:1 in order to prepare bcp/aunps/go composite and reduced to bcp/aunps/rgo through 30 cv cycles of electrochemical reduction in 0.01 m pbs (ph 5). 2.6 electrochemical characterization of pla-b-p2vp/aunps/rgo composites cyclic voltammetry (cv) was performed to evaluate the electron-transfer capabilities of the modified layer based on the oxidation peak current of bcp/aunps/rgo composite iium engineering journal, vol. 18, no. 2, 2017 ali et al. 37 in 0.05 m potassium ferricyanide (k3fe(cn)6) solution was used as redox solution and 50 mv/s as the scan rate. 3. results and discussion figure 1 showed the ftir spectrum of the hybridization samples (h1, h2, h3, h4, h5) and control sample (bcp only). the two peaks around 1434 and 1474 cm -1 are the c=c stretching in the rings of the pyridine groups of the p2vp block. the peak around 1755 cm -1 was the c=o stretching of the pla block [9]. another peak from 1580 to 1600 cm -1 was related to c=n stretching of the pyridine group. based on the reference, a blue shift of the c=n stretching was related to the association of the gold ions with the longpair nitrogen in the p2vp block [8]. wavenumber (cm -1 ) 130014001500160017001800 % t ra n s m it ta n c e control h5 (1:10) h4 (1:5) h3 (10:1) h2 (5:1) h1 (1:1) fig. 1: ftir spectrum of control and hybridized samples. in addition, a blue shift was suggested as a characteristic normally attributed to the association of the gold precursors with the long-pair nitrogen in a p2vp block as the association caused an increase of binding energy associated with in-plane c=n stretching. table 1 also showed a small blue shift in c=n stretching between the peak of the control sample and those of the hybridization samples; the wavenumber of c=n stretching in h1 was shifted 1.93 cm -1 compared to the control. the degree of the blue shift can be applied to determine the association degree between the metal precursors and the pyridine groups of a p2vp block [8]. table 1: wavenumber of the c=n stretching of pyridine groups in ap2vp block samples wavenumber (cm -1 ) control 1592.94 h1 1591.01 h2 1591.97 h3 1591.97 h4 1591.97 h5 1591.29 iium engineering journal, vol. 18, no. 2, 2017 ali et al. 38 the successful synthesis of gold nanoparticles through hydrazine reduction of haucl4•3h2o was proved via uv-vis spectra over the wavelength range of 350 to 650 nm. the characteristic plasmon resonance absorption band for aunps occurred between 500 and 600 nm in the visible region of the electromagnetic spectrum, which confirmed the formation of nanoparticles in the composites [10]. figure 2 showed that all the reduction samples of the bcp/aunps (r1, r2, r3, r4, and r5) exhibited the characteristic peak of gold nanoparticles. the absorbance showed the concentration gradient of gold nanoparticles as r3>r2>r1>r4>r5, furthermore, table 2 showed the peak of gold nanoparticle absorbance in different composites. as particle size increases, the wavelength of surface plasmon resonance (spr) related to absorption shifted to longer wavelengths; based on this, the size of gold nanoparticles in different samples can be identified. r1 > r3 > r2 > r4=r5 [10]. wavelength (nm) 450 500 550 600 650 a b s o rb a n c e 0.0 0.5 1.0 1.5 2.0 2.5 3.0 r1 r2 r3 r4 r5 fig. 2: uv-vis absorbance of gold nanoparticles in reduction samples (r1, r2, r3, r4, r5). table 2: surface plasmon resonance (spr) peak of gold nanoparticles via uv-vis spectroscopy samples wavenumber (cm -1 ) r1 543 r2 534 r3 536 r4 527 r5 527 the electrochemical properties of the bcp/aunps composites were identified through cyclic voltammetry. figure 3 showed that peak currents for bare gce and gce modified with control (only bcp) and different ratios of bcp/aunps nanocomposites. the peak current of different nanomaterials modified gce are lower than that for a bare gce (270.27±6.60 µa) owing to the non-conductive property of the bcp. iium engineering journal, vol. 18, no. 2, 2017 ali et al. 39 voltage v vs ag/agcl -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 c u rr e n t (m a ) -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 bare gce bcp modified gce r1 (1:1) r2 (5:1) r3 (10:1) r4 (1:5) r5 (1:10) fig. 3: cvs of bare gce, control (only bcp), and gces modified with different ratios of bcp/aunps nanocomposites (r1, r2, r3, r4, r5) in 0.05 m k3fe(cn)6 solution at a scan rate of 50 mv/s. voltage v vs ag/agcl -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 c u rr e n t (m a ) -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0.00 0.05 control r1 (1:1) r2 (5:1) r3 (10:1) r4 (1:5) r5 (1:10) fig. 4: cvs of bcp-modified gces including control and different ratios of bcp/aunps nanocomposites modified gce) in 0.05 m k3fe(cn)6 solution at a scan rate of 50 mv/s. however, fig. 4 showed the peak current among bcp-modified gces (control: 0 µa), r1 (34.58 ± 0.078 µa), r2 (59.23 ± 0.518 µa), r3 (86.62 ± 8.30 µa), r4 (34.14 ± 0.023 µa), r5 (30.27 ± 0.980 µa), confirming that the higher peak current was attributable to the higher content of aunps in these composites. the morphological study of the optimum r3 composite was through transmission electron microscopy (tem). figure 5 showed tem image of r3. tem study of gold nanoparticles in bcp confirmed that the particles are almost spherical in shape with an average size ranging from 10-50 nm. iium engineering journal, vol. 18, no. 2, 2017 ali et al. 40 fig. 5: tem images of r3 (au 3+ : p2vp = 10:1), (a) low magnification of 0.5 µm, (b) high magnification of 100 nm. in order to improve the conductivity and electron transfer rate of the optimum composite (r3), graphene oxide (go) was added into the r3 to prepare bcp/aunps/go composite and reduced to bcp/aunps/rgo through different cycles of electrochemical reduction. the resulting bcp/aunps/rgo composite was electrochemically reduced by performing different continuous potential cycling (10, 20, 30, 40, 50, 60) in the potential range 0 to 1.5 v in pbs (ph 5). after each 10 cycling reduction, the p4vp/aunps/rgo composite was characterized through cv. figure 6 showed the cv curves after every 10 cycles. voltage v vs ag/agcl -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 c u rr e n t (n a ) -1.5 -1.0 -0.5 0.0 0.5 1.0 bare 10 cycles 20 cycles 30 cycles 40 cycles 50 cycles 60 cycles eletrochemical reduction cycles fig. 6 cvs of bare and bcp/aunps/rgo after different cycling of electrochemical reduction in 0.05 m k3fe(cn)6 solution at a scan rate of 50 mv/s. as shown in fig. 6, the peak currents of all the bcp/aunps/rgo modified gce were higher than bare gce due to the high conductivity of rgo. during different cycling of electrochemical reduction, 40 cycles showed the highest peak current (894.187 na) compared to 10 cycles (256.054 na), 20 cycles (704.551 na), 30 cycles (842.356 na), 50 cycles (892.187 na) and 60 cycles (855.962 na). these results also indicated that bcp/aunps/rgo after 40 cycling of electrochemical reduction have high potential for application in amperometric biosensors. a b iium engineering journal, vol. 18, no. 2, 2017 ali et al. 41 4. conclusion in this research, we studied the preparation of different ratios for hybridization (bcp/au 3+ ) and reduction of bcp/aunp composites and r3 shown the potential application in glucose biosensor for enzyme immobilization through the preliminary cyclic voltammetry performance study. additionally, graphene oxide (go) was added in to r3 to prepare bcp/aunps/go composite and reduced to bcp/aunps/rgo through different cycling of electrochemical reduction. the resulting bcp/aunps/rgo after 40 cycles of reduction show high potential to be used in amperometric biosensors based on the cv measurements. acknowledgement this work is funded by malaysian ministry of higher education (mohe) under fundamental research grant scheme (frgs) (ref: frgs14-105-0346) and research acculturation grant scheme (rags) (ref: rags14-038-0101). references [1] sivanesan a, john sa. (2009) gold nanoparticles modified electrodes for biosensors. in nanostructured materials for electrochemical biosensors, pp 97-128. [2] putzbach w, ronkainen nj. (2013) immobilization techniques in the fabrication of nanomaterial-based electrochemical biosensors. sensors, 13(4): 811-4840. [3] wang x, uchiyama s. (2013) polymers for biosensors construction. in state of the art in biosensors – general aspects, pp 67-86. [4] smart t, lomas h, massignani m, flores-merino mv, perez lr, battaglia g. (2008) block copolymer nanostructures. nano today, 3(3):38-46. [5] chiu jj, kim bj, kramer ej, pine dj. (2005) control of nanoparticle location in block copolymers. j. am. chem. soc., 127(14):5036-5037. [6] pumera m. (2011) graphene in biosensing. mater. today, 14(7): 308-315. [7] pei s, cheng hm. (2012) the reduction of graphene oxide. carbon., 50(9): 3210-3228. [8] lin t, li cl, ho rm, ho jc. (2010) association strength of metal ions with poly (4vinylpyridine) in inorganic/poly (4-vinylpyridine)-b-poly (ε-caprolactone) hybrids. macromolecules, 43(7):3383-3391. [9] yuen cwm, ku ska, choi psr, kan cw, tsang sy. (2005) determining functional groups of commercially available ink-jet printing reactive dyes using infrared spectroscopy. rjta, 9(2): 26-38. [10] johan mr, chong lc, hamizi na. (2012) preparation and stabilization of monodisperse colloidal gold by reduction with monosodium glutamate and poly (methyl methacrylate). int. j. electrochem. sci., 7:4567-4573. microsoft word vol 12_no1_2011_june.doc iium engineering journal, vol. 12, no. 1, 2011 khan et al. 79 design and implementation of potentiometer-based nonlinear transducer emulator sheroz khan, jamaludin omar, sk khairul hasan, aliza aini binti md ralib, ma li ya, atika arshad, hanum syahida hussin, norhanis aida mohd nor, ahm zahirul alam and md rafiqul islam electrical and computer engineering department, faculty of engineering, international islamic university malaysia (iium), jalan gombak, 53100, kuala lumpur, malaysia. e-mail: sheroz@iium.edu.my abstract : transducers are normally with nonlinear responses over the entire of a physical parameter they are meant to measure. a potentiometer can be regarded as a linear differential resistive transducer for measuring linear (or angular) movement. in this work, an analog is suggested to make a potentiometer catwalk in order to emulate an actual transducer with its nonlinear response represented as a concatenation of linear segments with known slopes. each segment of a given slope is implemented by a potentiometer to emulate the variation of input ranging over a given input section of the input. ultimately we get as many circuits as the number of segments the nonlinear response is made of. next, an input circuit is used to decide on a range the input is falling into for making use of appropriate potentiometer circuit with the help of a digital selection circuit. the circuit is simulated using multisim to verify that variations in the input voltage give rise to an output voltage that emulates very closely the envisaged nonlinear response. the utility of this work lies in emulating purpose-built real world transducers. abstrak: transduser merupakan respon yang tidak linear bagi keseluruhan parameter fizikal yang perlu diukur. meter pembolehubah atau ‘potensiometer‘ boleh dikaitkan/dianggap sebagai transduser pembezaan linear resistif untuk mengukur linear (atau sudut) gerakan. sistem analog yang terhasil adalah tidak linear. dalam kajian, potensiometer ini dapat menghasilkan respon linear yang hampir sama dengan transduser sebenar. dengan ini, respon yang tidak linear dapat dibahagikan kepada rangkaian cerun-cerun segmen yang linear. setiap cerun segmen dapat digunakan oleh potensiometer untuk meniru variasi julat input ke atas setiap input segmen. akhirnya, kita dapat menghasilkan sebanyak mungkin litar bagi tiap-tiap respon segmen tidak linear yang terhasil. kemudian, litar input ini dapat digunakan untuk menentukan julat input yang terhasil. julat ini dapat digunakan oleh litar potensiometer yang bersesuaian dengan bantuan sistem pemilihan litar digital. litar ini disimulasikan dengan menggunakan perisian multisim untuk menyemak perubahan pada voltan input yang kemudiannya menghasilkan kenaikan kepada voltan output yang dipercayai dapat meniru dengan tepat respon yang tidak linear. kajian ini berguna bagi tujuan pembinaan transduser sebenar. key words: emulator transducers, nonlinear transducers, potentiometer, differential, transducers, quantization errors iium engineering journal, vol. 12, no. 1, 2011 khan et al. 80 1. introduction analog to digital conversion has always been associated with some adjustments that could lead to losing some of the information that could be termed as affordable quantization errors in quite a number of applications. however, in some other applications it would not be in the interest of the signal concerned that one is able to obtain as much a digital equivalent of the signal as is possible as losing some content would not be considered a concern one can come to terms as acceptable. the data losing concern becomes quite significant when it comes to reading data from sensors with nonlinear responses, however the fast development in both wired and wireless communication has been heralding an improvement of analog to digital conversion and even concerns of nonlinear errors are addressed so properly leading to final research products are achieving high level of accuracy conversion. adcs which are serving as bridging platforms in between real world signals and a digital processor system are the fundamental elements in all measurements and circuits applied. generally sensor will produce analog output and adc is needed for its conversion to produce smart sensor. analog to digital conversion has becoming so important a device that it comes in besides stand alone, as integrated in some processors designed and meant for measurement and monitoring system. this is because that today’s modern systems are digital that are programmed for automation finely tuned and better equipped for enhanced features. however, all conventional adc work on linear fashion, and produce a digital code in direct proportional to the length of the section of the analog input signal that is sampled to be digitized. no matter how much accurate and quick adcs are, they are associated with the errors inherited from the very basic mechanism in which they are designed to function. the errors are quantization error, offset errors and nonlinearity errors. quantization error is due to the finite resolution present in all adc conversion mechanism, and is an inherited in all types of adc [1]. an analog input voltage falling between two adjacent output codes will result inaccurate output code that does not become a true replica of the given analog signal, something termed as quantization that one is unable to avoid. offset error is the difference between the ideal lsb transitions to the actual transition point. for nonlinearity errors, all adcs suffer from non-linearity errors resulting in their output to deviate from a linear function of their input. on top of these errors there is another source of error that is stemming out from the transducers from which is the analog to be digitized is obtained. this error may not sound significant in applications where the control system is operating over a limited range of the input parameter or even in system which such error falls well within the level that is acceptable in most application. however in some critical applications even a small error of the level of a single degree of celsius temperature change such as in the cases of industrial boilers may not be an affordable quantity. researchers have presented the solution of the nonlinearity issues. the solution for linearization technique can be categorized into three: nonlinear analog signal conditioning circuits, correction based on digital signal processing and correction based on nonlinear analog to digital ad converters [2, 3]. iium engineering journal, vol. 12, no. 1, 2011 khan et al. 81 the work is analysed using mathematical linear equations for the segments of which the nonlinear response is made. using excel data sheet, it is then shown to be a close fit of the whole response curve. having decided on the number of analog circuits, the excel sheet response is then verified by implemented the complete circuit by using multisim. the excel sheet response and that from mulitisim closely relate, showing that the mathematical derivations of excel sheet are hardware implement able. 2. mathematical analysis and excel implementation 2.1 figure1 shows an actual airflow transducer characteristic response characteristic for a supply pressure varying between 0 and 15 p.s.i. (103.42 kpa) using equation (1) below pbavvolts  (1) 2.2 where a= 0.788, and b= 1.084 [2]. the 0-15psi pressure is linearly represented by 0-5 v potentiometer reading. fig. 1: actual and segmented nonlinear characteristics curve. the curve of fig. 1 is sectioned into four such that the output voltage is assumed to be varying linearly with input parameter over its respective ranges as given in table 1. iium engineering journal, vol. 12, no. 1, 2011 khan et al. 82 using excel the mismatch of the linear segments with their respective actual segments is also shown in the form of errors. an actual response curve is sectioned into four segments such that one can easily define the four segments by the following four equations by identifying their slopes and y-intercepts as given in table 2. table 1: theoretical selection of segments. input-bytes pressure (psi) volts 0 0.00000 0.78800 96 1.40762 2.07409 320 4.69208 3.13608 640 9.38416 4.10868 1024 15.00000 4.98631 table 2: input-ranges with slopes and y-intercept. 3. circuit implementation the main system hardware components of the proposed design consist of: (a) range selection circuit, (b) channel selection circuit, (c) digital logic switching circuit, and (d) linear conversion circuit. 3.1 range selection circuit the range selection circuit consists of four comparators named as u12a, u11a, u10a, and u9a using lm339m as shown in fig. 2. the input voltage is applied to the positive inputs of comparators while the voltages coming from a resistive chain are applied to the negative terminals as the lower limits of respective ranges. seg. no voltage range slope-m y-intercept 1 0-0.5 v 1.315 0 2 0.5-2.0 v 0.63 0.319 3 2.0-3.0 v 0.4 0.6 4 3.0-5.0 v 0.252 1 iium engineering journal, vol. 12, no. 1, 2011 khan et al. 83 fig. 2: range selection circuit. an input voltage from the potentiometer, e.g., in the 0.5-2.0v range, will obviously produce a logic ‘1’ at the output of comparator u11a, thus making the channel selection circuit to extend the input voltage with its appropriate reference value (in this case 0.319v) and slope (0.5634) to the output stage in such a way such that the last stage (presumably adc) of the circuit makes the input keep ranging almost linearly. 3.2 channel selection circuit the channel selection circuit is designed based on boolean logic principles given in table 3, consists of four input and gates and three inverters as shown in fig. 3. the design is such that a logic ‘1’ at the output of an and gate will shows all logic ‘1’ at the output of comparators up to that stage. assuming that switch j8 is turned on, the output of the and (gate 2) will be high at logic ‘1’ and one of the input of the and (gate 1) will be inverted and its output will be made to stay at logic ‘0’, that is to say switch j9 is turned off. the same condition applies for other switches. u 9a u1 0a u1 1a u1 2a v 6 key= 4 r 13 3 r 17 2 r 18 1 9 v 2 9 v iium engineering journal, vol. 12, no. 1, 2011 khan et al. 84 table 3: truth table for channel selection circuit. fig. 3: linear conversion circuit. u12a, u11a, u10a and u9a are comparators, assuming the highlighted are inverted forms of their variables, and j9, j8, j7, j6 are switches with boolean functions given by: j9 = u12a u11a u10a u9a j8 = j9’.u11a u10a u9a j7 = j9’.j8’.u10a u9a j6 = j9’.j8’.j7’.u9a vt u12a u11a u10a u9a j9 j8 j7 j6 0 ≤ vt ≤ 0.5 v 1 0 0 0 1 0 0 0 0.5 ≤ vt ≤ 2 v 1 1 0 0 0 1 0 0 2. ≤ vt ≤ 3 v 1 1 1 0 0 0 1 0 3 ≤ vt ≤ 5 v 1 1 1 1 0 0 0 1 channel 4 channel 3 channel 2 channel 1 u6b u4b u1b r4 r13 r3 r17 r2 r18 v1 9 v v 9 v u9a u10a u11a u12a 9v r6 1k? key=b u3a u2a u5a u7 7 r1 r7 r8 0 r9 iium engineering journal, vol. 12, no. 1, 2011 khan et al. 85 at one time, only one switch is turned on indicated by a blinking led shown in fig. 3, thus choosing only one range for extension on to the next stage made of linear conversion circuits. accordingly, the adc at its intended output stage is thus facilitated to keep functioning linearly, minimizing the nonlinearity errors thus eliminating causes of the read-in signal to be obscured. this way the equivalent digital code of a sample is tuned up/down considerably closer to its actual value. the same basic principle applies to the other remaining three input voltage ranges already mentioned. 3.3 linear conversion circuit the linear conversion circuit of fig. 3 is utilizing two-stages of operational amplifiers, the first stage is to set the slope for the segment under consideration while the second stage is meant to provide the straight line equations with a proper yintercept, thus implementing the straight linear equation. the input stage after having chosen the range of 0.5-2v passes on the input to the boolean logic to select the onward channel. the boolean logic on the basis of the input closes switch j8, the third form the bottom switch, and hence the input is put through block two among the output stages. the respective output stage provides the adc (if any) with an input that is varying linearly over its range lying between the lower infliction and the upper infliction points. 3.4 whole circuit design and description figure 5 shows a complete circuit for a virtual transducer, which is a combination of range selection circuit, channel selection circuit, linear conversion circuit before the signal is finally applied to an adc or microcontroller with built-in a/d. 4. simulation result and discussion simulation of circuit shown in fig. 4 is performed using multisim where input is derived from a potentiometer varying over the ranges identified in table 2. data collected tabulated and plotted in fig. 5 shows a very close resemblance to that shown in fig.1. 5. conclusion with reference to the principles of piecewise linear approach, a schematic circuit has been developed. the circuit helps translate a potentiometer (also called a linear transducer) to emulate an actual transducer of interest. the circuit was designed utilizing an emulator that provides output characteristics similar to that of an actual transducer. the emulator was used to replace the need of an actual transducer that was unavailable due to shortage of funds. although, the various design principles have already been individually reported in other literature reviews, the iium engineering journal, vol. 12, no. 1, 2011 khan et al. 86 collective aspect of the applications has never been reported. a boolean based digital logic circuit is used to integrate all stages such that when the input voltage ranges and crosses over the inflection points, the circuit behaves linearly with a new slope and yintercept for the transducer. when the input voltage is made to vary over the entire input range, ultimately, it provides a concatenation of the straight line-segments. the implementation is straightforward and easy to be realized with discrete components besides being considered for chip integration. the simulated output response curve matches very closely to that which has been proposed and analyzed as shown in fig. 6. the piece-wise linear approach is implemented using excel for seeing the nonlinear response curve as made of four segments fitting closely to the curve in fig. 1, which also shows the errors incurred (referred to as mathematical analysis). increasing errors are observed when the transducer is operated at points where the pwl segments do not fit with the actual curve. in our multisim simulation, the actual curve is sectionalized into four segments manually through a pencil and ruler for known slopes and y-intercepts as shown in table 2. this data is used for deciding on the values of elements given in fig. 2, 3, and 5. after repetitive runs over the entire range, the output data were obtained. the comparative analysis of fig. 5 and fig. 1 is provided in fig. 6. the comparative analysis has clearly verified the variations in the input voltage which give rise to an output voltage that emulates very closely the envisaged nonlinear response. the utility of this work lies in emulating purpose-built real world transducers. iium engineering journal, vol. 12, no. 1, 2011 khan et al. 87 fig. 4: complete nonlinearity correction circuit diagram. u9a lm 339m 54 3 2 12 u10a lm 339m 54 3 2 12 u11a lm 339m 54 3 2 12 u12a lm 339m 54 3 2 12 pos 9v r6 1kω key=b 50% neg neg neg neg pos pos pos pos u3a u2a u5a u7a 15 pos15 107 8 r1 1ω 0 r7 100ω 0 r8 100ω 0 r9 100ω 0 led4 15 led1 9 led2 22 led3 23 u6b u4b u1b 11 20 16 13 0 j4 1mv 0mv j1 1mv 0mv j2 1mv 0mv j3 1mv 0mv sw1 sw2 sw3 sw4 pos r4 850ω r13 50ω r3 200ω r17 700ω r2 300ω r18 600ω 000 v1 9 v v2 9 v neg pos 26 u14 3288rt 1 2 54 3 r23 400ω r24 1kω u15 3288rt 1 2 54 3 r25 1kω r26 1kω r27 1kω v3 0.6 v neg pos neg pos 12 0 5 14 0 0 2 u16 3288rt 1 2 54 3 r28 574.6ω r29 1kω u17 3288rt 1 2 54 3 r30 1kω r31 1kω r32 1kω v5 0.319 v neg pos neg pos 34 0 33 35 0 0 32 u18 3288rt 1 2 54 3 r33 1.315kω r34 1kω u19 3288rt 1 2 54 3 r35 1kω r36 1kω r37 1kω v6 0 v neg 48 neg pos 46 0 45 47 0 0 44 u83288rt 1 2 54 3 r5 252.4ω r10 1kω u13 3288rt 1 2 54 3 r11 1kω r12 1kω r14 1kω v4 1 v 24 2421 18 0 17 19 0 0 4 pos pos pos pos j5 1mv 0mv 25 j6 1mv 0mv 28 sw4 j7 1mv 0mv sw3 j8 1mv 0mv 30 29 sw1 0 6 1 3 sw2 0ut4 out3 out2 out1 ground 38 v: 1.60 v v: 2.50 v iium engineering journal, vol. 12, no. 1, 2011 khan et al. 88 s im u la te d v e rs u s a n a ly s is 0 1000 2000 3000 4000 5000 -176 24 224 424 624 824 1024 in p u t v o lta g e (m v ) o u tp u t v o lt ag e (m v ) fig. 5: simulation plot of the complete circuit of fig. 4. fig. 6: comparison of simulation results with analysis outputs. iium engineering journal, vol. 12, no. 1, 2011 khan et al. 89 references [1] nicholas gray “abc of adcs analog to digital converter basics”, november 24, 2003. [2] j. m. dias pereira, "octavian postolache, p. m. b. silva girão, “a digitally programmable a/d converter for smart sensors applications” ieee transactions on instrumentation. meas. vol.56, no. 1, february 2007. [3] giovanni bucci, marco faccio, and carmine landi, “new adc with piecewise linear characteristic : case study implementation of a smart humidity sensor”, ieee trans. instrum. meas., vol. 49, no. 6, december 2000. [4] s. kaliyugavaradan, p. sankaran, and v. g. k. murti, “a new compensation scheme for thermistor and its implementation for response linearization over a wide temperature range”, ieee trans. instrum. meas., vol. 42, no. 5, pp. 952–956, oct. 1993. [5] m. yamada, t. takebayashi, s. i. notoyama, and k. watanabe, “a switched capacitor interface for capacitive pressure sensor”, ieee trans. instrum. meas., vol. 41, pp. 81–86, feb. 1992. [6] c. marven and g. ewers, “a simple approach to digital signal processing”, new york: wiley-interscience, 1996. microsoft word 4_vol17_no1_2016_(compiledversion_4).docx iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 29 a qualitative analysis of biomass flow sensing behavior using capacitive technique rumana tasnim1, sheroz khan2, musse mohamud2 and atika arshad2 1department of mechatronics engineering, world university of bangladesh, bangladesh 2department of electrical and computer engineering, international islamic university malaysia, malaysia 1rumanatasnim415@gmail.com, sheroz@iium.edu.my, mussemoh@yahoo.com, and atikaarshad@hotmail.com (received: 17 may. 2013; accepted: 23 apr. 2015; published on-line: 30 apr. 2016) abstract: flowsensing technology from today’s application perspective has gained significant research interest over the past few years. among the existing sensing techniques, electrostatic and capacitive sensing techniques have proven promising although cable capacitance and stray capacitance cause inaccuracy while measuring very small capacitances. the existing measurement circuit model is complicated and has flawed electrode arrangement. by sensing very small capacitive variation, the developed capacitive technique has proven capable of reducing the stray and residual capacitance effect by using an interface sensing circuit based on circular and semicircular shaped electrode and modified capacitive bridge. the proposed interface circuit is simulated via pspice for realizing the small capacitive variation with permittivity variation. hardware implementation is carried out using a flow sensing set up that senses two kinds of biomass flow variation as a change of dielectric permittivity under room conditions. the output voltage has been reproduced as a representative of the flow. moreover, a comprehensive investigation into experimental data shows an agreeable level of consistency with the simulation results. abstrak: dari perspektif pemakaian semasateknologi penderiaan aliran menimbulkan faedah penyelidikan yang ketara sejak beberapa tahun kebelakangan ini.antara teknik penderiaan semasa teknik penderiaan elektrostatik dan kapasitif terbukti berkesan walaupun kemuatan kabel dan kemuatan sesat menyebabkan ketidaktepatan serta mengukur kapasitans yang sangat kecil.model litar pengukuran sedia ada adalah rumit dan mempunyai susunan elektrod yang cacat.dengan mengesan perubahan kapasitif sangat kecil, teknik kapasitif yang dibina ini telah terbukti mampu mengurangkan kesan kemuatan sesat dan sisa melalui penggunaan litar antara muka penderiaan berdasarkan elektrod yang berbentuk bulat dan separuh bulat dan kapasitif sambunganyang diubahsuai.litar antara muka yang dicadangkan adalah simulasi menggunakan pspiceyang mampu mendapatkankan perubahan kapasitif kecil dengan perubahan ketelusan.pembinaan perkakasan menggunakan kaedah penderiaan aliran yang mengesan perubahan aliran dua jenis biomass sebagai perubahan ketelusan dielektrik dalam keadaan bilik.voltan keluaran telah dihasilkan semula untuk menunjukkan aliran. siasatan menyeluruh pada data eksperimen menunjukkan tahap yang konsisten dengan hasil simulasi. keywords: electrodes; sensing; capacitance; electrostatic; piping; measurement iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 30 1. introduction suitable instrumentations for on-line monitoring and measurement in gas-solid twophase flow has proven to be an exigent task for scientists and researchers at universities and institutes. the term ‘gas-solid flow’ signifies dilute or dense phase flow with a very little concentration of solids. for conducting such flow measurement generally velocity and volumetric concentration of the flow particles are needed to be measuredsolids are foundas powder and grain being carried in air that has various applications in industries namelychemical, pharmaceutical, food processing. also, while flowing agricultural particles (e.g., grains, wheat, corn) [1] as well as transporting pulverized coal in fuel lines of thermal power stations. electrostatic and capacitive methods [2-3] are the most reliable electrical sensing techniqus for solid flow measurement techniques. high sensitivity and cost effectiveness of capacitance sensing make the measurementof concentration and velocity of solid particles the most effective sensing solutions. some research works have been done onnovel electrode design and such designs were tested as versatile hardware platform for suiting in industrial sector [4]. in order to convert capacitance-to-digital (cdc), few capacitance measurement schemes [5-6] were implemented in integrated circuit (ic). a promising capacitive sensing technique [7] based on stainless steel source grid sensing electrodes to increase high and homogeneous capacitance sensitivity over the pipe cross section was developed by some researchers for measuring pulverized fuel concentration in a laboratory scale pneumatic conveying system along with the calibration facility. holler et al., [8] projected a sensing principle based on a multi-electrode structure (eleven ring shaped) in order to increases the sensitivity to dielectric permittivity variations. however, proper characterization of flow particles was not done in this technique which results in providing inaccurate information about flow. recently some authors [9], presented flow velocity measuring electrostatic sensing technique using circular and arc-shaped sensor arrays. online continuous measurement of “mean” and “local” characteristics of blended biomass flow is done. from the reviewed papers it is apparent that different electrode structure design and optimization along with pipeline, complicated capacitance measurement circuits have been developed previously. although not much research has been undertaken on the perception of biomass sensing behaviour in term of signal detected from the measurement circuit which influences the measurement procedure of concentration and velocity of biomass particles. furthermore, biomass transportation by air is unpredictable owing to the particles’ complicated physical characteristics. it results in insufficient industrial biomass process; so the prospective of biomass as renewable energy source is still unrealized. this paper aims to analyze on biomass flow sensing behaviour by making use of a cost effective and simple measurement interface circuit (that reduces stray and residual capacitance) along with two designed semi-circular and circular shaped capacitive electrodes. 2. system architecture to conduct real-time flow measurement, a capacitance sensing techniqueis developed.the capacitive sensor is constructed with a pair of conductive sensing electrodes with the placement of dielectric material in between them. the parameter which determines capacitance change in the developed capacitive sensor are the flow of biomass materials. the excitation voltage combined with measurement circuits can transform capacitance variations into a voltage. the block diagram of this research work is illustrated in fig. 1. the system structure which consists of a sensing segment and a processing part is shown in fig. 2. the experimental set up and two types of electrodesis are shown in fig. 3(a) and (b) respectively. iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 31 fig. 1: block diagram of a capacitive sensing technique. fig. 2: integrated sensing and processing unit of system. (a) (b) fig. 3: (a)experimnetal set-up, and (b) circular and semicircular electrode. the biomass is pneumatically sucked by an industrial suction pump located at the far end through the pipe, on which five pairs of electrodes are mounted. a biomass collector measurement pipe section interface circuit suction pump semi circular electrode circular electrode iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 32 bag is placed at the other end.the test pipe section is of 1000 mm with an upward flow direction and made of polyvinyl chlorides. the inside and outside diameter of the pipe is 25mm and 27mm respectively. the biomass test materials are wheat and fodder (agricultural grain). ground grain (wheat) is replicated as fine biomass base. an inexpensive solely noncontact circular (e.g., ca, cb; made of mild steel) and semi-circular (e.g., sa. sb, sc; made of galvanized steel) capacitive electrodes make one arm of the bridge circuit. the electrode’s width is chosen as w =12 mm, electrode separation d= 3 mm, the ratio of capacitive sensor electrode width (w) to electrode separation (d) is 4:1, the number of electrodes, k =10 and radius of the pipe r =12.5 mm. the measurement interface circuit (in processing part in fig.2) is an inexpensive operational amplifier based capacitance bridge circuit [10]. this measurement circuit detects very small capacitance variation because of the change in biomass flow medium. the flow pipe is inserted as a lone arm of the bridge, while the upper arms are made up of fixed and variable capacitances. an identical potential is sustained at the output nodal points of bridge circuit which reduces the effect of the stray capacitance between the output leads of bridge network. the lower bridge arms are made up of resistors to keep point b at a virtual ground to improve the flow stability by variable capacitance arm, cx. the middle op-amp offers adjustable sensitivity to overall output and the third op-amp stops the load from having any effect on the measurement. the interface circuit is analysed through the mathematical derivation of proportional relationship between output voltage and capacitance changes [derived in eqn 5]. the bridge circuit is balanced (no flow) only when cr1= cr2. from fig.2, the current through 1i is given by ; current through is ; current through is ; is using kirchhoff’s law, (1) hence (2) again substituting the values we will get, ⇛ jvc ω + v r + v r = 0 ⇛ v r = −jvc ω − v r ⇛ v r = −jv (c + ∆c)ω − v r ⇛ v r = −jvc ωr − jv∆cω − v r ⇛ v r = −jvω[c r + ∆c] − v r ab jvc 2i ad jvcx 3i 1 1 v bc r  4i 1 2 1 2 1 ; f f v v cd i r r   1 3 0i i  1 1 0 v jvc r    1 1v jvc r  2 4 0fi i i   iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 33 ⇛ v r = −jvω[cr + ∆c] − v r ⇛ v r = −jvωcr − jvω∆c + jvωcr r ⇛ v r = −jvω∆c r ⇛ ⇛ v = −jωr r v∆c (3) employing a single node voltage equation at the inverting terminal of the buffer which acts as an inverting amplifier, we get; i + i = i (4) as the voltage at v = 0, v = 0 as differential input voltage is zero, v = v = 0 so, i = and i = ideally the equivalent input resistance is infinite resulting i = i = 0 from equation (4) we can write, i + i = 0 ⇛ v r + v r = 0 ⇛ v r = − v r ⇛ v = − r r × v since v = −jωr r v∆c so, v = jωr r r r v∆c the output voltage of the circuit , v = v(c − c ) (5) 3. results and discussion the processing circuit was simulated initially using pspice. the simulation is supported by experimental validation, clearly showing how this work has been successful in sensing two type of biomass materials. the simulation and experimental validation of the results on the instrumentation part of this work are detailed below. 2 0( )f xv j r v c c   iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 34 in balanced condition, the values chosen are, c=10pf, co=10pf, r1= 1kω (standard resistance), r2=1kω, r3= 10 ω. when the circuit will be balanced, then cr1=cr2. the sensitivity factor; rf1=100kω, rf2= 100kω. figure 4(a) and 4(b) shows the simulation circuit for balanced condition and the simulation output. fig. 4(a): simulation circuit for balanced condition. fig. 4(b): simulation results for balanced condition. when the circuit goes unbalanced; cx=20pf, c=10pf, r1= 1k, (standard resistance), r2=4.7k, r3= 10. cr1 is not equal to cr2, sensitivity factor; rf1=100 k, rf2= 100k (which can be changed for bridge sensitivity). figure 5 shows simulation result for unbalanced condition. the simulation approach was later supported by experimental validation for achieving desired research objectives. the experimental steps along with results are discussed below. air flow is produced by turning on a suction pump, withan air velocity which is kept fixed. an excitation voltage (10v ac) with a stabilized frequency of 10 hz is applied to excite the bridge network. a lcr meter measures the capacitance changes. the experimental setup is first tested when the bridge is balanced under no-flow conditions only to be unbalanced with biomass flow. the circuit is first tested by flowing light weight fodder biomass which has 500µm diameter and moves faster than wheat (100 µm). figure 6(a)6(b) shows fodder flow sensing behaviour (voltage outputs and capacitance graphs) at 1000g/min over 60 seconds involving 10 seconds step. electrodes’ location made a significant impact on the sensing phenomenon. semi-circular electrode sc fitted near to the container has obtained the highest output voltage (8.5-9.3v) along with maximum capacitance (90.5-91.6pf). horizontally positioned sb electrodes exhibited lowest and v u3 opamp + out r 3 10 v v freq = 10 vampl = 5 voff = 0 c 10pf c o 10pf rf 1 100k v1 opamp + ou t r1 1k 0 0 u 2 opamp + ou t 0 r2 1k rf o 100k 0 iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 35 relatively less fluctuated capacitance values (65.6-68pf) which depicted an almost stable graph. in case of galvanized iron semi-circular electrode; sa mounted on the vertical pipe section near to the suction pump showed fluctuated voltage whereas the capacitance sensed by this electrode depicted a stable graph with no noticeable fluctuation. fig. 5: pspice simulation result for unbalanced condition (with cx=30pf). (a) (b) fig. 6: (a) voltage output, (b) capacitance as a function of fodderflow (1000g/min). the circular electrodes showed ups and downs in a minimal variation. both horizontally positioned sb and cb showed matching behaviour in measured voltages where after a certain period graphs declined. also the galvanized iron electrodes are proved to be iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 36 more sensitive due to the better conductivity than the other ones. fine particle wheat (100µm) is replicated as a ground grain fine particle. figure 7(a)-(b) illustrated voltage and capacitance variation as a function of wheat flow (600g/min). fig. 7(a): voltage output as a function of wheat flow. fig. 7(b):capacitance as a function of wheat flow range. the variation of wheat materials flow range has been sensed well by circular electrodes while semicircular electrodes have shown steady response. similar kind of behaviours is observed also in case of wheat material. from the analysis of experimental and simulated voltages, the semi-circular electrodes show better sensitivity. to analyze the conformity between simulated and experimental results, simulation has been carried out using pspice for the capacitances obtained from the experimental results, first under balanced conditions and then under unbalanced condition, the product cr1 being unequal to the product cr2, led to an output voltage. a set of simulation results are obtained for the experimentally obtained results for fodder flow sensed by sa ( table 1). table 1: experimental and simulated output voltages ascended (sensed by sa) capacitance(pf) experimental voltage simulation voltage 77.6 8.75 8.4 80 8.8 8.5 80.1 8.85 8.54 80.2 8.9 8.5 80.3 8.9 8.6 80.4 9 8.6 iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 37 fig. 8(a): simulation output for 77.6 pf capacitance. fig. 8 (b): experimental and simulation voltage for fodder flow across sa. figure 8(a) depicts the simulation results distinctively for a specific capacitance of 77.6 pf. the tabulated experimentally obtained capacitance values and simulated results are plotted in figure 8(b) to validate conformity between the results. figure 8(b) shows that, simulation and experimental results are consistent in terms of output voltage variation, with minimal discrepancy towards higher capacitance changes. with larger capacitance changes the output voltages starts showing nonlinear response. likewise another set of simulation results are obtained for experimental values which is depicted in table 2 and plotted in fig. 9. figure 9 illustrates the simulation and experimental results which show identical pattern of variation having similar slope, but the simulation show better sensitivity than the experimental. table 2: experimental and simulated output voltages ascended (sensed by ca) capacitance(pf) voltage (experimental) voltage (simulation) 87.8 8.8 9.4 88 8.9 9.5 88.1 8.9 9.5 88.2 9 9.5 89.3 9 9.6 91.1 9 9.9 iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 38 fig. 9: experimental and simulation voltage for fodder biomass flow sensed by ca. figure 9 also suggests, with the increase of capacitance values, the simulation and output voltage starts to show nonlinear response. from the above results it is apparent that, semicircular electrodes showed better sensitivity in output voltages. once again similar set of simulation results is achieved for the experimentally obtained capacitances using other electrodes and also in case of fine particle wheat. the results obtained show almost similar patterns with a small variation in the output voltage range. in case of fodder, simulation and experimental consistency has been proven to be relatively more linear for semicircular electrode rather than circular ones. the capacitive measurement of biomass (fodder and wheat) concentration obtains solid phase concentration by measuring the capacitance of capacitive sensor based on the established relationship between solid phase concentration and measurement capacitance (c ). = ( − ′ ∈ )/ ′(∈ −∈ ) (6) where, =biomass (solid phase) concentration, =biomass (solid phase) density ∈ =biomass (solid phase) permittivity ∈ =air (gas phase) permittivityb is addressed by structure and dimension of capacitance sensor plates (c ) =measurement capacitance(c ) from equation (5), v r r = −jωvr r (c − c ) ⇛ jωvr r c = jωvr r c − v r r ⇛ c = jωvr r c − v r r jωvr r ⇛ c = c − v r r jωvr r and from equation (6), iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 39 ρ = ρ (c − k′ ∈ )/k′(∈ −∈ ) ⇛ ρ=ρ c − − k′ ∈ /k′(∈ −∈ ) (7) so, biomass concentration is derived with respect to measured capacitance and voltage output in equation (7). this has established a correspondence relationship between biomass concentrations with biomass and air phase density, dielectric permittivity of test biomass materials as well the physical characteristics and structure of the capacitive electrode. the experimental results have shown likewise behaviour. 4. conclusion the experimental and simulation results obtained for a particular flow regime in the case of distinctive biomass materials has been observed, where the output voltage has become the representative of flow, as a measure of small capacitance change (in pf) which proves the mathematical derivation. for real time biomass flow sensing as well as measurement, the outcome of this research work has proven to be successful by setting up a prototype experimental setup.the general observations on the overall results have shown significant effects on electrodes’ shapes, location of electrodes on the piping system, biomass material type and its’ individual characteristics.the proposed sensing unit will be connected with data processing unit from where the plant operators will be able to pass on useful data for improving flow control system performance. the novelty of this research lies in the use of cost effective operational amplifier based capacitive sensing circuit along with two specifically designed measuring electrodes for analyzing biomass flow sensing behaviour. as a whole, this work investigates and analyzes biomass flow sensing behaviour in order to open up a branch of research for practical implementation. references [1] heping cui & john r. grace (2006). “pneumatic conveying of biomass particles: a review”, china particuology, vol. 4, no.3-4, pp.183-188. [2] yan, y. (1995). “flow rate measurement of bulk solids in pneumatic pipelines: problems and solutions”. bulk solids handling, vol. 6, no. 3, pp. 447–56. [3] yan, y. (1996). “mass flow measurement of bulk solids in pneumatic pipelines”. measurement science and technology, vol. 7, no.12, pp.1687–706. [4] hrach, d., & fuchs, a. (2008). “investigation of field electrode geometries in capacitive flow measurement”. ieee sensors 2008, pp. 17–20. [5] brasseur, g., brandstatter, b., & zangl, h. (2003). “state of the art of robust capacitive sensors”. ieee transactions on instrumentation and measurement, vol. 52, no.4, pp. 12611265. [6] bretterklieber, t., zangl, h., hrach, d., holler, g., hammerschmidt, d., & motz, m. (2008). “versatile programmable integrated interface for robust capacitive sensors”. elektrotechnik and information stechnik, vol. 125, no.4, pp.123-128. [7] hu, h.l., xu, t.m., hui, s. e., & zhou, q.l. (2006). “a novel capacitive system for the concentration measurement of pneumatically conveyed pulverized fuel at power stations”. flow measurement and instrumentation, vol. 17, pp.87-92. [8] holler, g., fuchs, a., & hrach, d. (2008). “flow velocity determination in cryogenic media by means of capacitive sensing”. sensing technology icst 2008, pp. 472–476. [9] xiangchen qian & yong yan. (2012). “flow measurement of biomass and blended biomass fuels in pneumatic conveying pipelines using electrostatic sensor-arrays”.ieee transactions on instrumentation and measurement, vol. 61, no.5, pp. 13431352. iium engineering journal, vol. 17, no. 1, 2016 tasnim et al. 40 [10] bera, s.c., & mandal, h., (2012). “a flow measurement technique using a noncontact capacitance-type orifice transducer for a conducting liquid”. ieee transactions on instrumentation and measurement, vol. 61, no. 9, pp.25-53 microsoft word 87-pages 35-51-1.doc iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 35 esterification of palmitic acid with methanol in the presence of macroporous ion exchange resin as catalyst amelia qarina yaakob and subhash bhatia* school of chemical engineering, universiti sains malaysia, engineering campus, 14300 nibong tebal, penang malaysia *email: chbhatia@eng.usm.my abstract: the esterification of palmitic acid with methanol was studied in a batch reactor using macro porous ion exchange resin amberlyst 15 as a catalyst. methyl palmitate was produced from the reaction between palmitic acid and methanol in the presence of catalyst. the effects of processing parameters, molar ratio of alcohol to acid m, (4-10), catalyst loading (0-10 g cat/liter), water inhibition (0-2 mol/liter), agitator speed (200800 rpm) and reaction temperature (343-373k) were studied. the experimental kinetic data were correlated using homogenous as well as heterogeneous models (based on single as well as dual site mechanisms). the activation energy of the reaction was 11.552 kj/mol for forward reaction whilst 5.464 kj/mol for backward reaction. the experimental data fitted well with the simulated data obtained from the kinetic models. keywords: palmitic acid, methanol, esterification, ion exchange resin, kinetics. 1. introduction african oil palm, elaeis guineensis, is one of the most important plants in malaysia. it produces palm oil and palm kernel oil, which are widely used in food and oleo chemical industries for the production of fatty acids and cosmetics. malaysia is the world's largest producer and exporters of these oils, accounting for approximately 10% of the world's oil and fat production. about 100,000 metric tons of the natural fatty acids are consumed in the preparation of various fatty acid esters. the simple esters with lower chain alcohols (methyl-, ethyl-, npropyl-, isopropyland butyl esters) are used as emollients in cosmetics and other personal care products and lubricants. organic esters are most frequently used as plasticizers, solvents, perfumery and flavor chemicals. esters of fatty acids with more complex alcohols, such as sorbitol, ethylene glycol, diethylene glycol and polyethylene glycol are consumed in foods, personal care, paper, water treatment, metal working fluids, rolling oils and synthetic lubricants. methyl palmitate is one type of methyl esters and being used in industry such as for biodiesel, solvents for paint, adhesives, cosmetics and toilet soap. iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 36 esterification is the reaction of free fatty acids with alkyl alcohol to form fatty acid esters and water as shown in the following chemical reaction: r-cooh + r’-oh  r-coo-r’ + h2o (1) it is an endothermic reaction [1]. this process is usually carried out in the presence of acid catalysts such as h2so4, h3po4 and sulfonic acid. to shift the equilibrium of the esterification towards the desired alkyl ester, one of the reactant, usually the alcohol is fed in excess and product water is continuously removed respectively during the reaction. generally water is eliminated chemically, physically, or by pervaporation [2]. in the present work, the kinetics of the heterogeneous esterification of palmitic acid with methanol is studied in a batch reactor using amberlyst 15 (cation exchange resin) as a catalyst. methyl palmitate is produced from palmitic acid and methanol via catalytic esterification represented as: ch3 (ch2)14cooh + ch3oh  ch3 (ch2)14cooch3 + h2o (2) palmitic acid methanol methyl palmitate water the use of a solid ion exchange resin as catalyst has a number of advantages [3]. these are i. the catalyst can be easily removed from the reaction products by decantation or filtration. ii. continuous operation in columns is possible. iii. the purity of the products is higher since side reactions can be completely eliminated or are less significant. iv. it is possible to isolate the reaction intermediates v. ion exchange resin can discriminate between small and large molecules. there are many solid catalysts reported in the literature for esterification reactions [46]. cation exchange resin is the most commonly used solid acid catalyst in organic reactions [5]. ion exchange resins have been used in esterification [7] and hydrolysis of methyl acetate in a catalytic distillation column [8]. the objective of the present study is to find the applicability of the cation exchange macro porous resin as catalyst for the fatty acid esterification and to study the effects of important processing parameters for esterification process. the kinetics of esterification of palmitic acid with methanol in the liquid phase using cation exchange macro porous resin amberlyst 15 is studied. the reaction rates are evaluated using homogeneous and heterogeneous models and experimental data are compared with the simulated data. iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 37 2. materials and method 2.1 materials 2.1.1. palmitic acid palmitic acid was obtained from acidchem international sdn.bhd. penang, malaysia. the purity of palmitic acid used in the experiments was 98.9%. 2.1.2. catalyst amberlyst 15 was purchased from acros organics new jersey, usa. the properties of amberlyst 15 are presented in table 1. table 1: typical physical and chemical properties of amberlyst 15 catalyst properties amberlyst 15 physical form ionic form concentration of acid sites (meq h+/(g.cat)) moisture content (mass%) particle size (mm) porosity (ml/g) average pore diameter (nm) surface area (m2/g) maximum temperature (0c) crosslinking density (%dvb) opaque, spherical bead h+ 4.9 53 0.35-1.20 0.30 25.0 45 120 20 3. catalyst preparation the fresh resin was washed with deionized water and kept at 348k in a vacuum oven before used in an experimental run. 3.1 experimental setup a 4-neck pyrex flask of 500 ml capacity was used as the reactor. the volume of the mixture used for each reaction was 300 ml.the condenser was connected to the central opening; the two side openings were used to measure the reaction temperature using a thermocouple (k type) and to withdraw the samples during the reaction respectively. one opening was used for feeding alcohol. an oil bath with digital temperature controller was used to supply heat to the system. silicon oil was used in the bath since it can be heated up to high temperature (up to 300 iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 38 ºc). the oil bath was equipped with a heater, a thermocouple to indicate the temperature in the bath, a temperature controller and a circulator. the circulator was used to circulate the oil continuously and to keep the temperature in the bath uniform. the temperature was controlled with the accuracy of ±1 ºc. a magnetic stirring plate was placed right at the bottom of the oil bath to stir the reaction mixture continuously. a glass coil condenser was used to cool and condense back the reaction mixture vapors during the reaction. the reaction temperature was varied from 70 ºc to 100 ºc, well above the boiling point of methanol (64.7 ºc). the average boiling point of the reaction mixture was 65 ºc to 70 ºc depending on the molar ratio of reactants used. a thermocouple and a temperature controller were used to monitor the reaction temperature. 3.2 procedure the esterification of palmitic acid with methanol was carried out in a batch reactor system. the data were obtained to study the kinetics of the reaction and to evaluate the kinetic parameters of the esterification process. a pre-mixed method was opted in order to study the behavior of the heterogeneous catalyst. blank experiment was carried out in the batch reactor without catalyst to check any conversion during esterification. the palmitic acid and catalyst were mixed in the flask of the reactor. pre-heated alcohol (50 ºc) was added once the desired temperature was reached. this time was considered as the beginning of the experiment. it took about 30 minute to get steady state temperature. the reactant temperature was maintained constant (±0.1 ºc). two ml sample of the reaction mixture was drawn from the flask every 20 minutes interval using a sampling tube and were immediately cooled to 0 ºc in order to stop the reaction. the sample was titrated to determine the amount of fatty acid that remained unreacted. 4. results and discussion 4.1 process studies 4.1.1. effect of important processing variables experiments were conducted by various processing variables such as reaction temperature, alcohol to acid ratio, catalyst loading, speed of agitation and the presence of water. table 2 shows the variation of these variables with its range. (a) effect of reaction temperature in order to investigate the effect of temperature, the reaction temperature was adjusted from 343 to 373 k. the esterification process was carried out at the methanol to palmitic acid molar ratio of 4 (m=4) and the catalyst loading of 5 g cat/liter. iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 39 table 2: range of processing variables over esterification of palmitic acid with methanol using amberlyst 15. processing parameters range temperature 343 to 373 k methanol/palmitic acid 4 to 10 catalyst loading 0 to 10 g cat/liter water inhibition 0 to 2 mol/liter agitation speed 200 to 700 rpm figure 1 shows the effect of reaction temperature on the conversion of palmitic acid to methyl palmitate. since the esterification of fatty acid with alcohol is an endothermic reaction, therefore with the increase of temperature, the conversion of fatty acid increased [9]. similar trends were reported in the literature [1, 10]. it can be seen from the figure that the effect of temperature on the rate of methyl palmitate production is significant. the reaction rate increased sharply with increasing temperature. the reaction temperature was limited to 373k due to thermal stability of ion-exchange resin. 0 0.1 0.2 0.3 0.4 0.5 0.6 0 50 100 150 200 time (min) co nv er si on 343 k 348 k 353 k 358 k 363 k 373 k fig. 1: effect of temperature on the conversion of palmitic acid to methyl palmitate rate at the operating conditions of m=4 and catalyst loading of 5 g cat/liter. iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 40 (b) effect of molar ratio methanol was taken in far excess over palmitic acid to shift the equilibrium towards the formation of ester. this method was chosen because it was not easy to remove water, since the boiling point of methanol (64.5 ºc) was much lower than the boiling point of water (100 ºc). the molar ratio of palmitic acid to methanol used was 1:4, 1:6, 1:8 and 1:10. the process was carried out at constant temperature of 343 k and catalyst loading of 5 g cat/liter. figure 2 shows the effect of molar ratio on the conversion of palmitic acid to methyl palmitate. it is clear from the figure that the higher reaction rates and higher equilibrium conversion were achieved when the alcohol was in excess. the concentration of methanol influenced the reaction rate and conversion. as the molar ratio of methanol to palmitic acid increased, the conversion of palmitic acid increased due to excess concentration of methanol. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0 50 100 150 200 time (min) co nv er si on pa:meoh of 1:4 pa:meoh of 1:6 pa:meoh of 1:8 pa:meoh of 1:10 fig. 2: effect of molar ratio on the conversion of palmitic acid to methyl palmitate at temperature 343 k and catalyst loading of 5 gcat/liter. (c) effect of catalyst loading figure 3 shows the effect of catalyst loading (0-10 g cat/liter) on the conversion of palmitic acid at a temperature of 343 k and methanol to palmitic acid molar ratio of 4. figure shows that with the increase of catalyst loading from 2 g cat/liter to 5 g cat/liter, the rate of reaction was increased. it was also found that at 10 g cat/liter catalyst loading, the conversion rate of palmitic acid to methyl palmitate was almost similar to that obtained at 5 g cat/liter catalyst loading. this was because at 10 gcat/liter, the reactor was no more operated as a liquid phase batch reactor but rather as a slurry phase reactor. in slurry reactor, both the external and internal mass transfer resistance could be present. these iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 41 resistances affected the conversion and therefore the conversion did not increase with the increase of catalyst loading to 10 g cat/liter. this type of solid acid catalyzed esterification is a typical solid-liquid slurry reaction at higher loading of catalyst. (d) effect of agitation speed the experiments were carried out at different speeds, varied from 200 to 700 rpm. it is important to obtain intrinsic kinetics that the experiments were conducted under vigorous stirring to avoid mass transfer effects especially film diffusion. the experiments were conducted at m=4, reaction temperature of 343 k and catalyst loading 5g cat/liter. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0 50 100 150 200 time (min) co nv er si on no catalyst 2 g-cat/litre 5 g-cat/litre 10 g-cat/litre fig. 3: effect of catalyst loading on the conversion of palmitic acid to methyl palmitate at temperature 343 k and m=4. figure 4 shows that the conversion of palmitic acid was unaffected by the agitation speed in the range of 400-800 rpm but between 200 and 400 rpm, the speed affected the conversion rate of palmitic acid. at higher stirrer speeds, there was no noticeable effect on conversion indicating that diffusion was not the controlling mechanism in the rate of reaction. this was inline with the findings of chakrabarti and sharma [5] where they reported that the external diffusion doesn’t generally control the overall rate in ion exchange resin catalyzed process unless the viscosity of the reactant mixture is very high or the speed of agitation is very low. iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 42 (e) effect of water inhibition the effect of water inhibition on the conversion of palmitic acid was studied by varying the volume of water in the range of 0.3 to 2 mol/liter of total reactant mixture. the reaction temperature of 343k, methanol to palmitic acid molar ratio of 4 and catalyst loading of 5g cat/liter were kept constant in all runs. the effect of water inhibition in the feed on the esterification of palmitic acid is shown in figure 5. as the water concentration in the feed was increased, the conversion dropped. it was due to the reversibility of the reaction where some of the methyl palmitate was hydrolyzed to palmitic acid. similar effect of water inhibition was reported for carboxylic acids esterification studies [1]. water molecules can occupy the active sites of ion exchange resin, amberlyst 15, therefore the conversion dropped due to a decrease in active sites available for the reaction. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0 20 40 60 80 100 120 140 160 180 200 time (min) co nv er si on 200 rpm 400 rpm 600 rpm 800 rpm fig. 4: effect of agitation on the conversion of palmitic acid to methyl palmitate at temperature 343 k, m=4 and catalyst loading of 5 g cat/liter. iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 43 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0 20 40 60 80 100 120 140 160 180 200 tim e (m in) co n ve rs io n wit ho ut wat er wit h 0.3 mo l/litre water wit h 2 mo l/ litre water wit h 3 mo l/ litre water fig. 5 effect of water inhibition in the feed on the conversion of palmitic acid to methyl palmitate at temperature 343 k, m=4 and catalyst loading of 5 g cat/liter. 4.1.2. ion exchange resin reusability the reusability of ion exchange resin was also studied in order to check the deactivation of the catalyst during reaction. the reusability test was conducted at temperature 343 k, methanol to palmitic acid molar ratio of 4 and catalyst loading of 5g cat/liter. the reused resin was washed with deionized water and kept in the oven overnight at 348 k to remove the moisture completely. figure 6 shows the conversion of palmitic acid with fresh and the reused catalysts. no sign of deactivation was observed for the used catalyst, so the resin could be used repeatedly after suitable treatment. however, fresh resin was used for each run to ensure the consistency of experimental conditions. iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 44 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0 20 40 60 80 100 120 140 160 180 200 time(min) co nv er si on fresh resin 1st reuse 2nd reuse fig. 6: catalyst reusability test at temperature 343 k, m=4 and catalyst loading of 5 gcat/litre. 5. kinetics and modelling the kinetic parameters for the esterification of palmitic acid were determined using homogeneous and heterogeneous models. the kinetics was used for the prediction of conversion over a wide range of reaction conditions. the esterification between fatty acid (a) and alcohol (b) was treated as an elementary second order reversible reaction and is represented as: a + b  e + w (3) homogeneous and heterogeneous models were used for comparison of kinetic parameters obtained in the present study. 5.1 homogeneous reaction kinetics when both external and internal mass transfer resistances are absent, the kinetics of the reaction can be expressed using power law model [10]. the conversion of fatty acid ester was determined by titration during the reaction at different interval of time in a batch reactor. equation (4) expresses the rate equation of the elementary second order reversible reaction for batch system [11].   tc a a a m 1 a m 1 x 2a a m 1 x2a a m 1 in ao1 1 2 2 2 a12 a 12 k                            . (4) iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 45 the palmitic acid conversion at different reaction temperature is summarized in table 3. the experiments were conducted at different temperature by keeping the molar ratio of reactants (m=4) and catalyst loading (5 g cat/liter) constant. the conversion value obtained at the end of 3 hours from the start of the reaction is taken as the equilibrium value. table 3: conversion of palmitic acid at different reaction temperatures temperature (k) conversion (xa) 343 0.404 348 0.436 353 0.467 358 0.508 363 0.534 373 0.551 figure 7 shows the plot of the left hand side term of the equation (4) against reaction time, t. all the experimental data were found to be in excellent agreement with eq. (4). the forward rate constant k1 at various temperatures (343-373 k) was determined from the slope of straight line of fig. 7. the backward reaction rate constant, k2 was obtained from eq. (5). keq = 2 1 k k (5) table 4 presents the values of rate constants k1 and k2 at different temperatures. the activation energy of the forward reaction was estimated as 11.552 kj/mol whereas the activation energy for backward reaction was 5.464 kj/mol. the relationship of rate constants in terms of activation energy and pre-exponential factor is given by eq.(6) and eq. (7), respectively. k1 = 3258 exp       t 1389.5 (6) k2 = 3167 exp       t 657.29 (7) iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 46 0 100 200 300 400 500 600 700 0 50 100 150 200 time (min) ln [{ (1 + m + a2 -2 a1 x a )(1 + m -a 2)} /{ (1 + m -a 2+ 2a 1x a )( 1+ m + a2 )}] 343 k 348 k 353 k 358 k 363 k 373 fig. 7: second order reaction model plot for calculation of forward rate constant k, at m = 4 and catalyst loading = 5 g cat/liter. figure 8 shows plot of experimental rates (rexp)' versus calculated rates (rcalc)'obtained from the rate equation. the calculated and experimentally measured values of rates for all run of the experiments were in good agreement. r2 = 0.954 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 (rcalc)' x 106m ol/litre .gcat.s (r ex p) ' x 1 06 m o l/l itr e .g ca t.s fig. 8: plot for experimental (rexp)' and calculated reaction rates (rcalc)' at m=4, catalyst loading = 5 g cat/liter using power law model equation. iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 47 5.2 heterogeneous reaction kinetics since the reaction involves more than one phase; catalyst is a solid and the reactants and products are in liquid form, the reaction is treated as heterogeneous catalytic reaction. heterogeneous model analysis and results can be compared with the homogeneous model results. the heterogeneous rate of reaction is defined as: ( ) concentration of methyl palmitate (mol/liter) (weight of catalyst (g) x time (s)) 'exp r = (8) table 5 summarizes the rate of reaction, (rexp)' obtained after 3 hours from the start of the reaction. the langmuir hinshelwood hougen watson (lhhw) equation for surface reaction control for esterification of palmitic acid with methanol is given by eq. (9) [1]:                                         2 weaaoaaobaaoa s 2 aaowe aa 2 aoba k k x c x m c k x 1 c k 1 k x c k k x m x 1 c k k ssexp k ' r ' r (9) table 5: experimental rate of reaction (rexp)' in heterogeneous system temperature (k) experimental reaction rates -(rexp)́ ́ ', x 106 mol/liter.gcat.s 343 1.44 348 1.85 353 2.36 358 2.87 363 3.34 373 3.61 the value of ks, ks, ka, kb, ke, and kw were determined using non linear least square method [12, 13] by minimizing the sum of squared differences of the experimental reaction rate and calculated reaction rate from eq. (10) [12].    1 -p n ))'()'(( 2exp2 rr s cal (10) iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 48 where n is a number of experimental data (=22) and p is a number of parameters to be determined (=5) the values of ks, ks, ka, kb, ke and kw were determined by polymath software [13] and are summarized in table 6 and table 7, respectively. the pre-exponential factor, surface reaction constant and adsorption enthalpies are summarized in table 8. the activation energy calculated from the heterogeneous model was 59.87 kj/mol and was higher than the activation energy obtained from the homogeneous model. the adsorption enthalpies were negative because the adsorption is an exothermic process. table 6: surface reaction rate constant, ks and equilibrium constants, ks at different temperatures temperature (k) surface reaction rate constant, ks (g cat/liter.mol.s) surface equilibrium constant, ks 343 0.437 1.944 348 0.576 1.972 353 0.654 2.000 358 0.876 2.029 363 1.756 2.057 373 1.954 2.114 table 7: adsorption equilibrium constant at different reaction temperatures obtained for model eq. (9) temperature (k) adsorption equilibrium constant (liter/mol) ka kb ke kw 343 5.71 x 10-2 5.46 x 10-1 6.03 x 10-1 6.03 x 10-1 348 4.33 x 10-2 9.65 x 10-2 5.71 x 10-2 5.51 x 10-2 353 7.87 x 10-3 3.54 x 10-2 7.54 x 10-3 2.35 x 10-2 358 5.23 x 10-3 7.43 x 10-3 1.98 x 10-3 8.11 x 10-3 363 2.87 x 10-4 5.32 x 10-3 5.41 x 10-4 3.75 x 10-3 373 5.21 x 10-5 6.87 x 10-4 1.23 x 10-4 5.51 x 10-4 iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 49 figure 9 shows the plot of experimental rates exp( )'r versus calculated rates ( )'calcr . there was an excellent agreement between the calculated and experimentally measured values of rates for all the experiments. r2 = 0.9823 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 (rcalc)' x 10 6 mol/litre.gcat.s (r ex p) ' x 10 6 m ol /li tr e. gc at .s fig. 9: plot for experimental and calculated reaction rates at m=4, catalyst loading = 5 g-cat/liter using lhhw model equation. 6. conclusions the esterification of palmitic acid with methanol in the presence of macro porous ion exchange resin as catalyst was performed. the reaction rate increased with an increase in reaction temperature (343-373k), increase in the molar ratio of palmitic acid to methanol (4-10) and with an increase of catalyst loading (0-10 g/liter). the reaction rates were unaffected by the agitation speed in the range of 400-800 rpm but between 200-400 rpm the speed affected the conversion of palmitic acid showing the presence of film diffusion. the conversion of palmitic acid was dropped in the presence of water (0-2 mol/liter) due to inhibition of water. amberlyst 15 was found to be an effective catalyst for the reaction between palmitic acid and methanol. although sulfuric acid is cheaper than resin as a catalyst, but resin can be recycled and suitable for esterification process due to various advantages over the homogeneous catalyst. the lhhw heterogeneous model could be applied for representing esterification kinetics for the formation of methyl palmitate. these models are useful in the rational design of reactors for the production of ester in oleochemical industries in malaysia. iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 50 nomenclature a fatty acid a1 (i – keq-1) a2 [(m+ 1)2 4a1m]1/2 b alcohol c ester cao initial concentration of fatty acid (mol l-1) ca concentration of fatty acid (mol/liter) at any time, t d water keq equilibrium rate constant=k1/k2 ka, kb, ke and kw adsorption equilibrium constant of fatty acid, alcohol, fatty acid ester and water respectively (liter/mol.g cat.s) ks equilibrium surface reaction rate constant for esterification reaction (liter/mol) ks surface reaction rate constant (liter/mol.gcat.s) k1 forward reaction second order rate constant (l mol-1 h-1) k2 backward reaction second order rate constant (l mol-1 h-1) m cbo/cao = molar ratio n number of experimental data p number of parameters to be determined r gas law constant (8.314 kj/mol. k) (-rs)' rate of surface reaction in terms of palmitic acid consumption (mol/liter. gcat.s) (rexp)' experimental rate of reaction, mol/litre.gcat.s (rcal)' calculated rate of reaction, mol/litre.gcat.s t temperature, k xa 1 (ca/cao) , dimensionless σ2 variance references [1] s.h. fogler, “elements of chemical engineering, 3rd edn.” prentice hall, new jersey (usa), 1999. [2] s. goto, t. tagawa and a. yusoff, “kinetics of the esterification of palmitic acid with isobutyl alcohol.” international journal of chemical kinetics, 23, pp. 17-26, 1991. [3] o. levenspiel, “chemical reaction engineering, 3rd edn.” wiley-interscience publication, new york, 2002. [4] r.h. perry and d. green, “perry’s chemical engineer’s handbook, 6th edn,” mcgraw hill, new york (usa). iium engineering journal, vol. 5, no. 2, 2004 a. q. yaakob and s bhatia. 51 [5] c. vieville, z. moulooungui and a. gaset, “esterification of oleic acid by methanol catalyzed by p-toluenesulfonic acid and the cation-exchange resins k2411 and k1481 in supercritical carbon dioxide.” ind. eng. chem. res. 32, pp. 2065-2068, 1993. [6] a. chakrabarti and m.m. sharma, “cation ion exchange resin as catalyst.” react. polym., 20, pp. 1-45, 1993. [7] y. fuchigami, “hydrolysis of methyl acetate in distillation column packed with reactive packing of ion exchange resin.” j. chem. eng. japan, 23, pp. 354-358, 1990. [8] j. savkovic-stevanovic, m. misic-vukovic, g. boncic-caricic, b. trisovic and s. jezdic, “reactive distillation with ion exchanger.” sep. sci. technol., 27, pp. 613630, 1992. [9] k. tanabbe, m. misono, y. ono, and h. hattori, “new solid acids and bases.” kodansha ltd., tokyo and elsevier science publishers b.v., amsterdam, 1989. [10] m. thomas, sir john, “solid acid catalysts.” sci. am., 266(4), pp. 112-118, 1992. [11] r. roy, and s. bhatia, “kinetics of esterification of benzyl alcohol with acetic acid catalyzed by cation-exchange resin (amberlyst 15).” j. chem. tech. bioteknol., 37, pp. 110, 1987. [12] h.j. bart, j. reidetschager, k. schatka, and a. lehmann, “kinetics of esterification of levulinic acid with n-butanol by homogenenous catalysis.” ind. eng. chem. res., 33, pp. 21-25, 1994. [13] g.f. froment, and k.b. bischoff, “chemical reaction analysis and design, 2nd ed.” johnwiley and sons, new york, 1979. [14] u.r. unnithan, and k.k. tiwari, “kinetics of esterification of oleic acid and mixtures of fatty acids with methanol using sulfuric acid and p-toluene sulfonic acid as catalyst.” indian journal of technology, 25, pp. 477-479, 1987. biographies amelia qarina yaakob obtained her b. sc. degree in chemical engineering from university science malaysia in 2004. she is currently working with jabatan penerbangan awam in putrajaya as a technical engineer. prof. subhash bhatia joined the school of chemical engineering, university science malaysia, engineering campus, in 1995. he was full professor in the department of chemical engineering, indian institute of technology, kanpur (india). prof. bhatia was a visiting professor at the university of queensland, australia from 1998-1989 and 1994-1995. his research interests are zeolite catalysis, chemical reaction engineering and environmental catalysis. he has written a book on zeolite catalysis that was published by crc press, usa and has published more than 150 papers in national and international refereed journals. 423 iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 163 blanket representation and expedient of disinfecting water using pulsing electromagnetic field ibragimova ozoda and khalikov abdulhak tashkent institute of railway engineering 1001676, tashkent, uzbekistan. icenter@tashiit.uz abstract: the paper deals with comparative analysis of existing expedients and devices of disinfecting water, spots ways of the solution and a new method of water purification using electromagnetic field applied in a crosswise direction. using the parameter description and theory, the paper draws a model of the installation and conduct a finite element analysis. finally, the article offers a few additional applications of the pulse electromagnetic device for disinfecting and treating water. abstrak: dalam operasi, analisis perbandingan dijalankan bagi menentukan kesesuaian yang sedia ada dan alatan untuk menyahjangkit air. dengan mengaplikasikan medan magnet lintang, penyelesaian masalah dikenal pasti dengan meningkatkan kemagnetan terhadap medan elektromagnet ke atas air. keywords: water disinfection; electromagnetic field; cross magnetic field. 1. introduction in uzbekistan there are many existing and newly constructed railways passing over the deserted and semidesertic regions. in this connection there is a problem of the population potable water. the railway transportation also is the consumer of water, in particular water is used in many productions, such as cooling of compressors of diesel engines, of diesel locomotives and other inventory, reception a pair, refueling of carriages, rheostat tests of diesel locomotives, etc. hence, it needs preparation of technical water for a locomotive facility and other services. in this connection special interest represents a question of disinfecting and water treating [1]. the expedient of processing of fluids and the yields including processing of water by a pulsing electromagnetic field with a pulse length 10 -5 10 -7 of micro seconds and an instantaneous power of a pulse 50 1000 mwt [2]. deficiencies of this expedient are a low degree of disinfecting of water, small productivity, major specific rates of flux of the electric power. the second analog, the close by technical opportunities is the expedient of disinfecting of water the electromagnetic pulse, based on processing of water by an electromagnetic field with induction 7-8 tl, frequency of following of pulses 10 15 hz, a pulse length 10-15 ms and power consumption 4.0 4.5 kwt. a deficiency of this expedient is difficulty of arrival of necessary meanings of induction of a magnetic field and major power consumptions. iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 164 in operation expedients of sewage treatment with high concentration of organic pollutant a method of methane fermentation and plasma discharges which device is very much the composite surveyed. the existing methods of sewage treatment by an electromagnetic field using a special generator working in a frequency span from 10 up to 20 khz [3] is not very effective and the device is very complex. in operation the technology of water-preparation in rural areas with use complex electrical and a magnetic action on underground potable water is surveyed. installation for electro pulsing magnetic processing will consist of the generator of electromagnetic pulses and a working body [4]. the generator of electromagnetic pulses includes three functional parts in the composition: a charger, the energy storage unit and the discharge device. in impulse generator the charging and discharge devices function on a various time interval and feebly interact among themselves. however, to the present time, concrete recommendations to the choice of generators and to a substantiation of the parameters, with reference to systems of disinfection of potable water is missing. most close technical solution to disinfecting water is using the electromagnetic pulse, is by an electromagnetic field with induction of 7-8 mtl, frequency of pulses in the range of 10-15 hz, with pulse length of 10-15 ms and with a pulse current amplitude of 200-300 a. however, a deficiency of the given expedient being a small influence the electromagnetic field on molecules of water when lines of flux of a field are guided along fluxion of water, instead of their being perpendicular to fluxion of water in the form of a low degree of disinfection of water. the device includes a housing, inside which there is a high-voltage electrode, isolated from the housing with the help of the bush sets [8]. the high-voltage electrode is executed as the volumetric lattice which is anchored on shunt. the high-voltage electrode is located between the earthed electrodes which are executed as volumetric lattices and are connected to a housing. in a top hamper of the device for water delivery which acts as a collector with distributive punch sets. on the switching centre the branch pipe bringing stripped water is connected to a target branch pipe ejector, through which in the stripped water moves. below the electrode system the running nozzle which acts as riffle is located. the branch pipe draining out the processed water is placed in a bottom of a housing and is connected to the intermediate capacity. below the branch pipe below the hurdle nozzles on a housing is intended for tap unreacted ozone to an air mix sets. the branch pipe is connected to the pump to ensures delivery from the intermediate capacity. the application of free air in the device is carried out through a branch pipe. the given work has the high-voltage electrode located between earthed electrodes and hurdle a nozzle for dissolution of ozone on water that creates complexity in a design and difficulties in its operation. use of a high pressure demands creation of additional systems of protection and the raised qualification of the attendants of the device. the device will consist of a reactor for processing water and electrode system [5]. the reactor will consist of the case in which top part the unit of creation of a water-gas mix of the electrode system located under unit producing the water-gas mix and unit of tap of a water-gas mix is placed under the electrode system. the unit producing the water-gas mix includes aerator, ejector, branch pipes of a supply of water and tap of air and gases, the aerator being connected to a fan. the unit of tap of a water-gas mix includes the chamber response on which output in ejector and a iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 165 target branch pipe is established. the generator of high-voltage pulses is connected to the electrode system. lacks of the given methods are complexity of the device, a low resource of work of isolation of electrode systems and electrodes, application of high-voltage pulses of equal 1000 pulses/seconds, application of filters with special road-gravel loading for clarification of water. the task in view is to solve the problem that would provide lower the influence of electromagnetic field on processable water by applying cross magnetic field in which power lines are directed perpendicularly to a liquid, and also by applying vertical electric field created by a core. under the action of a magnetic field, additional pressure which entails increase in distance between molecules of water is created. bubbles are formed inside the water by high density of the microbes. when the pulse pressure is terminated the bubble bursts due to change of pressure leading to dstruction of the microbes. for branch of pure water separated from the impurity due to the application of vertical electric field under which ions of oxygen in the water are formed which creates a helical trajectory, twisting around a core, and all the impurities settle at the bottom of a pipe. since the speed of an electromagnetic wave in water is 5 x10 5 m/s, that is exceeds many times the speed of a liquid which is 1.5 2 m/s, there is a repeated clearing process. with this characteristic of the system it provides the required kolli an index and necessary number of microbes in gramme to a molecule of water. time of clearing does not depend on the geometrical sizes of a pipe and speed of movement of a liquid. the method of disinfecting water by a pulse electromagnetic field, created by inductance, and also a vertical electric field, is developed with the cross power lines directed perpendicularly to a current of water. inductance is outside the dielectric pipe, the core is inside (in the middle of) a dielectric pipe. the device (fig. 1) for disinfecting represents the solenoid with the general length, lс =2 m, reeled up on top of a nonmetallic pipe (for isolation from water) with diameter, d = 159 mm and is placed inside a metal pipe for prevention from external damages. the solenoid should provide an induction within the limits of 7-10 mt. water, passing through the solenoid with speed v = 1m/s, serves as a natural heat-conducting path for him. thus, passing through the solenoid in length lc = 2m, water is processed during time т, equal т return = lc / v = 2s. the solenoid is fed from the transformer which includ a network of alternating current by a pressure of 220 v through a thyristor. the thyristor itself manages the pulse generator, since thyristor and the transformer represent the pulse generator. for management of the pulse generator pulses frequency of 10 15 hz and10 15 ms duration are required. for this purpose the power supply having the one-vibrator, a divider of frequency and the amplifier of capacity of rectangular pulses is required. there are no data, allowing to define parameters of the device and working body in view of productivity of a source of water and his initial contamination. at the same time presence of such clear advantages of the electromagnetic device as an opportunity of concentration and distribution of significant energy at small capacities of devices with a control system, compactness, reliability and controllability process, predetermine their use for disinfecting water with wide areas of his application. it is found that existing devices and ways of disinfecting water by the pulse electromagnetic field, the waters based on processing by an electromagnetic field with set iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 166 forth above parameters have rather low efficiency, have small influence of an electromagnetic field on molecules of water as power lines of a field are directed along flow of a liquid, instead of directing them perpendicular to the flow, that gives a low degree of disinfection of water. fig. 1: a function chart of the device for disinfecting water. 2. design equations 2.1 parameter description the comparative analysis of existing ways and devices of disinfecting of water allows the determination of ways selecting the optimal application of electromagnetic field on processable water. it is found that the application of a cross magnetic field in which power lines are directed perpendicularly to the direction of the flow of a liquid, and also the effect of a vertical electric field created by a core, taking place inside and in the middle of a dielectric pipe gives the best results in terms of the efficiency of purification of water. the latter is found to be a recommended device [6-7] with control systems with uniform spatial electromagnetic field is presented in fig. 2. improvement of technical and operational characteristics are required for higher efficiency and opportunities in practical application of the device. proceeding from this, the dissertator puts the following problem: to raise the area of possible application with the improved power parameters and reliability.this problem is solved by improvement of designs of devices of control systems with uniform spatial electromagnetic field. the pulse generator will consist of the following functional blocks: the one-vibrator, a divider of frequency, the amplifier of capacity, a power unit thyristor, and the agreeing transformer. installation is fixed on the mobile device, i.e. can work at any place. iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 167 for reduction of losses contacts are executed as trunks, long wires pass in pipes for exception of influence of an electromagnetic field on them. for cancellation of the influence of electromagnetic field on the operator the coil of inductance are closed by an aluminum foil. the degree of disinfecting of water is adjusted by the frequency of pulses, developed the generator of pulses. fig. 2: the schematic image of a design and blocks of the device of disinfecting water using uniform spatial electromagnetic field. in installation for disinfecting water it is possible to allocate 4 power-intensive elements: the power transformer, coils of inductance (the dry transformer), control system and a core which are connected by the closest image with each other. the power transformer has system of two coils inductance, included among them selves in parallel, opposite and is consecutive with them a core. from a control system the pulse which opens thyristor moves and through coils of inductance the current 120 a. cheers a pipe water with a speed of 0.2-0.4 m/s proceeds. coils of inductance create a cross electromagnetic field. on the part of a field force which creates additional pressure. under the action of this pressure the distance between molecules of water increases, the area in which microbes and microorganisms are to be collected is formed. then water gets in the vertical electric field created by a core. the electric field slams area, microbes perish and also the water supplied with ions of oxygen, is wound on this core, and larger particles settle downwards and are thrown out through a branch pipe located under a corner at 45 0 to to the basic pipe. intensity of clearing can be changed by changing the frequency of pulses, and by change the diameter of apertures in a pipe. for this purpose the input and the output of a pipe are supplied with the adapters, allowing to changing entrance and target diameters of a pipe. 2.2 the parameter theory iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 168 the theory of a uniform spatial field allows to look through the questions of an effective decontamination, a demineralization and water treating, and also to study agencies of electrical, magnetic fields and electromagnetic waves on the physical, chemical and biological processes occurring in fluids. in the arbitrary section of a pipe with the current fluid which centre of gravity is at height h from a zero level of readout, the following parity (bernoulli's theorem) should be carried out: consthgp =++ 2 2 ρυ ρ (1) where р an ambient pressure; υ velocity of movement through the given section; ρ density of a fluid. from the power point of view pressure is the operation made by superposed forces above individual volume of a fluid: 2 2 ρυ ρ += hgw (2) for two arbitrary sections of a fluid stream the law of conservation energy for the current fluid is observed: 22 2 2 22 2 1 11 ρυ ρ ρυ ρ ++=++ hgphgp (3) water, being in the made space (a non-conducting pipe), and tests pressure on the part of a uniform spatial field which is defined by the force coming per unit of an exterior surface [8]: 2 2 00 20 2 0000 h dx x hxhjdf µ τ τ µµ ττ = − ∫=∫= , (4) where f the force working on the part of a uniform spatial field; н a field force; j conduction currents; τ length of a lamina. on the other hand: 22 2 0 8 a i f π µ = (5) where а radius of a pipe. however, maxwell and representation about pressure of a field seems to be too formal to us to present an origin of such pressure, as interaction of a uniform spatial field and a current of propellant charges more ease and more evident. the molecule of water has the major dipole moment (рw=6,1•10 -30 calorie • . meters), owing to what on the distances having the order of distance between molecules in fluids (r=1 0 а=10 -10 meters), around of her there is the strong electric field agrees: iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 169 d e 21 ϕϕ − = (6) where: b r p e 6 104 1036106 4 20 930 2 0 ≈ ⋅⋅ ⋅⋅⋅⋅ ≈≈ − − π π πε ϕ . (7) it is the parent of an electrical dissociation. hence, the uniform spatial field reinforces process of dissociation in water, and orbital electrons of two atoms of hydrogen and one atom of oxygen of water establish around of themselves the strong no uniform electric field that gives in division of water and connections contained in her into devices. if the fluid goes with velocity υ across lines of flux of a field with induction в, in volume of a fluid the elf of induction is aimed: lb⋅⋅=υε , (8) where l length of a section of a fluid in a pipe. resistance of a section of a fluid: l i r ⋅ = γ , (9) where γ a specific conductance of a fluid. induced current in a fluid: 2 ind. lb r i ⋅⋅⋅== υγ ε (10) on a lenz rule the induced current interacts with a field so that incipient force of interaction interferes with travel of water. thus, except for usual hydrodynamic forces, in a fluid work also electromagnetic forces. induction density of a field of induced currents: lb l i hb υγµ µ µ 0 ind0 ind0ind ≈ ⋅ ≈⋅= (11) the force working on the part of a magnetic field: 32 lbf a υγ= (12) this force can be compared to a friction force: υη ⋅⋅= lf тр , (13) where, η a coefficient of viscosity of a fluid. force of resistance of pressure: 22 pressure. lpf ⋅⋅≈ υ (14) the attitude of force of the ampere to force of resistance of pressure term as measure stuart: υρ γ ⋅ ⋅⋅ == lb r f n a 2 (15) iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 170 comparison of force of the ampere (12) with force of resistance of pressure (14) gives us measure hartman: η γ bl f f м тр а == (16) if the fluid flows on a pipe across a uniform spatial field at small numbers hartman or stuart the field feebly influences character of fluxion, and the attractive resistance originates in basic because of viscosity of a fluid. at major numbers hartman or stuart viscosity of a fluid draws off on the second plan, the attractive resistance originates in basic because of interaction of a fluid with a uniform spatial field. therefore water is saturated subzero with the charged ions of oxygen that is she is pure. positive charges of hydrogen are pernicious for an alive organism. let us consider model of installation at insert of a field. fig. 3, а) shows the inside view of a solenoid set and в) shows a cross-sectional view the set. it is known, that water has diamagnetic properties (coefficient of its magnetic conductivity µ =0,999991), and at interaction with a magnetic field from him is pushed out. in result there should be a force, breaking a stream. as the number of molecules of water in each unit volume is the orthographic pure of braking forces will represent a straight line. thus, inside the solenoid and directly ahead of it in a stream there is a section of compression where pressure of a fluid is higher, and velocity of movement is less, than in other stream. but, due to bulk strength of a fluid, its {her} stream is indissoluble, and immediately behind a section of compression the section of a tension where pressure is less should be formed, and velocity is higher, than in a main stream (a point "with" on fig. 3). origination under a field action of a pressure gradient can cause effect of cavitations in water [9]. studying interaction of a field and fluid stream is of interest at different alternatives of a direction of a field (perpendicularly to a stream and in bridge to it opposite and it agrees), his different form (a field constant, pulsing, rotaries, the homogeneous and the no uniform), at the single or no single action of a field on water, etc. fig. 3: model of the installation. iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 171 3. finite element analysis on the basis of the enunciated theory it is possible to make the following deductions: (1) the uniform spatial field allows to decontaminating and strip water (2) pulsing electrical and magnetic fields allow to saturating water with ions of oxygen (3) the spatial field allows to deleting heavy metals from water (4) with the help of pulsing electromagnetic fields it is possible a carry reagent less disinfection of water, to annihilate viruses, a carry sterilization of milk and juices, to heat up a fluid for the account, increases of an internal energy to create non-polluting devices with high efficiency (5) use of a uniform spatial field in development of technology and technological means for decontamination and water treating allows to sparing considerably power and material resources in deserted and semi-desertic requirements of the republic of uzbekistan. the device of clearing and disinfecting of water can be applied in structure of a technological complex for the following applications: • on clearing industrial drains of metal works, including drains of galvanic manufactures, dairy and fat-and-oil combines, meat-packing plants, confectioner's shops and paper-mills; • on water treating from the dissolved mineral oil, to increase of an overall performance of clearing constructions of the oil refining enterprises; • on regeneration of cooling liquids; • on clearing wash over waters, for removals of adjournment in capacities from under mineral oil; • on clearing mine waters; on clearing passing wash over and bedded waters at extraction of gas and oil. • executive element of devices of a winding excitation 4. conclusion our offers on the following additional application of the pulse electromagnetic device for disinfecting and treating water: • processing silt clearing constructions. • clearing drains of any impurity. • recycling the polluted waters, its return in agricultural revolution. • minimization of salinity soil. • desalination, desalination, disinfecting of waste waters. • the organization of a watering place of animals from salted well qualitative water. • recycling harmful impurity of waste components. references [1] amirov s.f., ibragimova o.a. “device of disinfecting, to desalinate and heatings of water by a pulse electromagnetic field”, the international magazine, chemical technology. the control and management. tashkent, 2012. no. 1. pp. 12-15. [2] aynakulov e.b., lifan m. “the way of disinfecting of water”. ampere-second. iap 0281. bi no. 5. 31.10. 2005. pp. 62-63. [3] us 005304302a. patent number: 5,304,302, apr. 19, 1994.( no author and title of article) iium engineering journal, vol. 14, no. 2, 2013 ozoda and abdulhak 172 [4] radjаpov а., ibragimov м., berdishev a.s., “technology of water-preparation in rural settlements with use of in a complex electric and magnetic influence”. innovational technologies in management, formation, the industries. a part 2 аcтintex-2007, astrakhan, pp. 231-233. [5] patent ru no. 2136600 published 1999.09.10. .( no author and title of article) [6] ibragimova o.a. “research of questions of stability and definition of stocks of stability of the devices, the developed control systems with a winding of excitation by a uniform superficial electromagnetic field’. a scientific seminar of young scientists, actual problems of innovational technologies on a railway transportation. iium engineering journal 14.2 (2011): 142-143. [7] ibragimova o.a. classification , “the comparative analysis of power electromagnetic pulse systems and the theory of a uniform spatial field is considered”. seventh world conference on intelligent system for industrial automation-wcis-2012, b-quadrat verlag. -tachkent , (2012) :163-177. [8] kolesnikov i.k., halikov a.a., karimov r.k., “electromagnetic field and waves”. tashkent. new century generation, (2008): 218 microsoft word vol11_no1_final iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 1 using uml scenarios in b2b systems a. jakimi, a. sabraoui, e. badidi, a. salah and m. el koutbi e.n.s.i.a.s, laboratory si2m, university mohammed v-souissi, b.p. 713 rabat, morocco elkoutbi@ensias.ma abstract: scenarios has become a popular technique for requirements elicitation and specification building. since scenarios capture only partial descriptions of the system behavior, an approach for scenario composition and/or integration is needed to produce more complete specifications. the unified modeling language (uml), which has become a standard notation for object-oriented modeling, provides a suitable framework for scenario acquisition using use case diagrams and sequence or collaboration diagrams. in this paper, we suggest an algorithmic and tool support for composing and integrating scenarios that are represented in form of sequence diagrams. we suggest four operators (;: sequential operator, ||: concurrent operator, ?: conditional operator and * :iteration operator) to compose a set of scenarios that describe a use case of a given system. in this paper, we suggest also to apply the scenario approach to b2b systems (business to business). we propose to develop b2b systems as a three activities process deriving formal specifications and code skeletons from uml scenarios. activities of this proposed process are generally automatic and are supported by a set of developed algorithms and tools. keywords : scenario engineering, scenario composition, scenario integration, model transformation, uml. 1. introduction over the past years, scenarios have received significant attention and have been used for different purposes such as understanding requirements, human computer interaction analysis, specification generation, and object-oriented analysis and design. notably, they have been identified as a promising technique for requirements engineering. scenarios have been evolved according to several aspects, and their interpretation seems to depend on the context of use and the way in which they were acquired or generated. in a survey, rolland [1] proposed a framework for the classification of scenarios according to four aspects: the form, contents, the goal and the cycle of development. the form view deals with the expression mode of a scenario. are scenarios formally or informally described, in a static, animated or interactive form? the contents view concerns the kind of knowledge which is expressed in a scenario. scenarios can, for instance, focus on the description of the system functionality or they can describe a broader view in which the functionality is embedded into a larger business process with various stakeholders and resources bound to it. the purpose view is used to capture the role that a scenario is iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 2 aiming to play in the requirements engineering process. describing the functionality of a system, exploring design alternatives or explaining drawbacks or inefficiencies of a system are examples of roles that can be assigned to a scenario. the lifecycle view considers scenarios as artefacts existing and evolving in time through the execution of operations during the requirements engineering process. creation, refinement or deletion are examples of such operations. the uml is an expressive language that can be used for problem conceptualization, software system specification as well as implementation. it covers a wide range of issues from use cases and scenarios to state behaviour and operation declarations. scenarios describe partial views of the system. to obtain a global view, we need to define an approach to merge or to compose these partial views. we aim, in this paper, to provide an automatic support for this operation of scenarios composition. there are several related works in this field but most of them have addressed this operation using formal techniques (like statecharts, petri nets, z schemas, etc.). in this paper, we suggest to compose scenarios that describe a given system in a natural way based directly on sequence diagrams. section 2 of this paper gives a brief overview of the uml diagrams relevant for our work. section 3 describes in detail the algorithm of merging several scenarios (of a given use case) in form of sequence diagrams into a global sequence diagram corresponding to the behaviour of that use case. section 4 discusses the scenario approach applied to b2b systems. finally, section 5 provides some concluding remarks and points out to future work. 2. scenarios in uml oo analysis and design methods offer a good framework for scenarios. in our work, we have adopted the unified modeling language, which is a unified notation for oo analysis and design. scenarios and use cases have been used interchangeably in several works meaning partial descriptions. uml [2] distinguishes between theses terms and gives them a more precise definition. a use case is a generic description of an entire transaction involving several objects of the system. a use case diagram is more concerned with the interaction between the system and actors (objects outside the system that interact directly with it). it presents a collection of use cases and their corresponding external actors. a scenario shows a particular series of interactions among objects in a single execution of a use case of a system (execution instance of a use case). a scenario is defined as an instance of a given use case. scenarios can be viewed in two different ways through sequence diagrams (sequenceds) or collaboration diagrams (collds). both types of diagrams rely on the same underlying semantics. conversion from one to the other is possible. 2.1 use case diagram the usecased [3] in uml is concerned with the interaction between the system and external actors. one use case can call upon the services of another use case using some relations (include, extends, etc). an example of the include relation is given in fig. 2. this iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 3 relation is represented by a directed dotted line and the label <<include>>. the direction of an include relation does not imply any order of execution. figure 1 gives an example of usecased. service2 service4 service1 service3 <<include>> <<extend>> <<use>> user fig. 1: example of use case diagram. 2.2 sequence diagram in this work, we chose to use sequence diagrams (sequenceds) because of their wide use in different domains. a sequenced shows interactions among a set of objects in temporal order, which is good for understanding timing and interaction issues. it depicts the objects by their lifelines and shows the messages they exchange in time sequence. however, it does not capture the associations among the objects. a sequenced has two dimensions: the vertical dimension represents time, and the horizontal dimension represents the objects. messages are shown as horizontal solid arrows from the lifeline of the object sender to the lifeline of the object receiver. a message may be guarded by a condition, annotated by iteration or concurrency information, and/or constrained by an expression. each message can be labeled by a sequence number representing the nested procedural calling sequence throughout the scenario, and the message signature. sequence numbers contain a list of sequence elements separated by dots. each sequence element consists of a number of parts, such as:  a compulsory number showing the sequential position of the message, and  a letter indicating a concurrent thread (see messages (m3, m4 and m5), and  an iteration indicator * (see message m2) indicating that several messages of the same form are sent sequentially to a single target or concurrently to a set of targets. in b2b systems, several information systems isi interacts between then to realize a scenario. in fig. 2, objects are prefixed by the name of isi where they evolve. 2.3 constraints in sequence diagram to ease elicitation of non-functional requirements, some new constraints have been defined. in this work, we focus more on time and security requirements that are very important for b2b systems. iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 4 fig. 2: example of a sequenced. 2.3.1 time constraints to model real-time constraints in early stages of development, we defined eight additional constraints [4] which can be are summarized in table 1. the four first constraints are applied to a single message, while the remaining time constraints concern two or more messages. this range of time constraints gives a good modelling framework for several communication and distributed real-time systems. table 1: real-time constraints associated to messages in a sequenced. constraint significance m{at(a)} the message m will occur at the time a m{after(a)} the message m will occur after the time a m{before(b)} the message m will occur before the time b m{between(a,b)} the message m will occur at the time a, and will takes at most b-a seconds m1{starts(m2)} the messages m1 and m2 start at the same time m1{ends(m2)} the messages m1 and m2 finish at the same time m1{equals(m2)} the messages m1 and m2 start and finish at the same time m1{meets(m2)} m1 starts before the end of m2 1:m1 2*:m2 2 1a:m3 2.1b.1:m4 2.1b.2:m5 2.2:m6 is1.o1 is2.o2 is1.o4 is2.o3 iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 5 2.3.2 security constraints today, security has become a major issue for information systems (e-business, e-trade, etc.). it will be convenient to be able to define and represent these constraints in the step of requirement engineering. we were interested to the major security aspects: authenticity and confidentiality. authenticity means the proof of identity and confidentiality relates to the privacy of information. using uml, when a message is sent from a source to a target object, it can carry some information (message parameters). we aim to express that the exchange is private using some encryption algorithms (rsa, aes, 3des, etc). this can be specified as a parameter of the constraint. the two constraints defined to model security aspects are given below: table 2: security constraints. constraint signification m{auth} the message m must be signed by the sender object to proof its identity to the receiver object. m{crypt(algo)} the message content (message parameters) must be encrypted using the algorithm (algo). these defined constraints are very useful for the purpose of code generation [5, 6] from uml models. 3. composition uml scenarios uml scenarios are considered as partial descriptions. to obtain a global description of a given service of the system or the description of the whole system, an operation of integration or composition is needed. the operation of integration will be described in section 4.3. the difficulty of scenarios composition comes in the fact that the scenarios are being described independently one to another. figure 3 gives an overview of the merging algorithm based on scenarios represented in the form of sequence diagrams. scénario résultant scénario 1 scénario 2 algorithme de algorithme de compositioncomposition fig. 3: composing uml scenarios. in this paper, we consider four operators (;: sequential operator, ||: concurrent operator, * :iteration operator and if-else operator) to compose a set of scenarios that describe a use case of a given system. our developed algorithms can automatically produce a global sequenced representing any way of composing scenarios. for example, we can compose three scenarios s1, s2 and s3 to obtain the resulting scenario sr. sr = (s1 ; s2 || s3) *[5], means to compose s1 and s2 sequentially, the obtained scenario will be composed concurrently composition algorithm resulting scenario scenario 1 scenario 2 iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 6 with s3, then the obtained scenario will be iterated five times. given a set of scenarios, our algorithms can produce any composing form of the given scenarios. we can also visualize the scenarios at different levels of detail: is level where objects of an is are hidden behind it, object level which is the detailed level, or any set of objects. the abstraction/refinement operator has been developed for this purpose. 3.1 the sequential operator this operator is the simplest one to implement. the interactions between objects (or actor and objects) of two sequenceds are ordered in such a way that the interactions of first sequenced (sd1) will occur before those of the second sequenced (sd2). to compose sequentially two sequenceds, they need to have at least one common object. the principle of composing two scenarios using this operator is described as follows:  put initially the resulting sequenced sdf equal to the first sequenced sd1.  calculate the maximum sequence numbers (maxns) in sd1.  add this number (maxns) to all sequence numbers in the second sequenced sd2 before merging them in sdf.  add to sdf objects that only belong to sd2. an example of composing sequentially two scenarios sd1 and sd2 is shown in fig. 4. (a) (b) (c) fig. 4 : (a) sequenced sd1, (b) sequenced sd2 and (c) resulting sequenced sdf = sd1 ; sd2. 3.2 the alternative operator this operator acts as the sequential operator. all messages in the second scenario sc2 (if cond sc1 else sc2) will be prefixed by the condition cond. iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 7 3.3 the concurrency operator this operator allows us to define a competition between scenarios. this kind of composition can be used to describe the independence or the interleaving between two sequences of interaction. two cases have to be considered. the first case, when the two scenarios have some common objects. the second case relates to two scenarios having different objects acting for separate sub systems. in this approach, we were interested by the first case which is more complex to implement than the second. we need to review sequence numbers of the two sequenceds that will be merged by the concurrent operator (||) :  update all sequence numbers of sd1 by adding a letter, that is not yet used in sd1 or sd2, representing a new thread of execution.  update all sequence numbers of sd2 by adding a letter, that is not yet used in sd1 or sd2, representing the second thread of execution.  compose sequentially the updated sequenceds sd1 and sd2. figure 5 shows an example of a concurrent composition of two scenarios in form of sequenceds. (a) (b) (c) fig. 5: (a) sequenced sd1, (b) sequenced sd2 and (c) resulting sequenced sdr = sd1 || sd2. 3.4 the iteration operator this operator gives the possibility to iterate a given scenario many times. the condition that guards the iteration must be indicated *[cond-iteration] as we do it in an iterative message in a sequenced. sdr = sd1*[3] means that the scenario sd1 will be executed three times. the condition of the iteration must be propagated globally to all messages of the scenario sd1. suppose that sd1 contains two sequential messages m1 and m2. we note that sd1 = (1:m1 ; 2:m2). if we propagate the iterative condition directly to all iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 8 messages of the scenario sd1, we will obtain the resulting scenario sdr that is equal to (*[3]1:m1 ; *[3]2:m2). this means that the message m1 will be iterated three times then the message m2 will do the same. this is naturally different of what we want sdr = *[3](1:m1 ; 2:m2). to solve this problem, we have considered that the scenario sd1 is represented by one abstract message m sent by the first object of the scenario to itself and all concrete messages will be viewed as are refinement of this message m. thus, sd1 can be seen as equal to one message sd1 = 1:m and this message is refined with 1.1:m1 and 1.2:m2 (1:m = 1.1:m1; 1.2:m2). the resulting scenario sdr can be seen as equal to *[3] m which is equal to *[3](1.1:m1; 1.2:m2). 3.5 the abstraction/refinement operator this operator offers the possibility to visualize a scenario at different levels of detail. figure 6 shows an example where all objects of the is2 is hidden. (a) (b) fig. 6: (a) detailed view, (b) corresponding abstract view where objects of is2 were hidden. 3.6 tool support to implement the four operators described above, we have used the eclipse environment, the togetherj plug-in for uml modeling and the application programming interface (api) jdom for xml manipulation. figure 6 gives a picture of how these tools have been used in this work. eclipse has been chosen because of its modular integrated environment of development (ide). many modules (plug-ins) are provided by eclipse and it is very easy to add others developed either by the eclipse community or by software companies. we used the plug-in for uml diagrams (from together) which makes it possible for us to create use case and sequence diagrams. moreover, our composition algorithm can be used with any plug-in of uml diagrams as shown in fig. 7. scenarios are first acquired throw the uml diagram plug-in, and then there are transformed in form xml files. these xml files serve as input to our developed composition operators that produce a merged xml file related to the resulting composed 1:m1 2*:m2 2.1a:m3 2.1b.1:m4 2.1b.2:m5 2.2:m6 is1.o1 is2 is1.o4 1:m1 2*:m2 2.1a:m3 2.1b.1:m4 2.1b.2:m5 2.2:m6 is1.o1 is2.o2 is1.o4 is2.o3 iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 9 scenario. this xml file can also be imported via the uml diagram plug-in for purposes of visualization and annotation. fig. 7: tool support for scenario composition. 4. the scenario approach in b2b systems in this section, we give an overview of the iterative process that derives a formal specification for the system from use cases and scenarios. figure 8 presents the sequence of activities involved in the proposed process. s e q u e n c e d s u s e c a s e d s p e c i f i c a t i o n b u i l d i n g c o d e g e n e r a t i o n s y s t e m p r o t o t y p e r e a l w o r l d s c e n a r i o a c q u i s i t i o n p r o t o t y p e e v a l u a t i o n c p n v e r i f i c a t i o n i n t e g r a t e d c p n s fig. 8: activities of the proposed process. iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 10 in the scenario acquisition activity, the analyst elaborates the usecased, and for each use case, he or she elaborates several sequenceds corresponding to the scenarios of the use case at hand. the analyst then uses some composition operators as defined in section 3.1 to capture interaction at different levels: use cases, scenarios and messages. the specification building activity consists on deriving cpns from the acquired usecased and sequenceds and compose them to obtain a global cpn with three levels of hierarchy. the composed cpns serve as input to both cpn verification and system prototype generation activities. during prototype evaluation, the generated prototype is executed and evaluated by the end user. in the cpn verification activity, existing algorithms can be used to check behavioral properties. in the following subsections, we will focus on the two first activities this process: scenario acquisition and specification building. 4.1 scenario acquisition in this activity, the analyst elaborates the usecased capturing the system functionalities, and for each use case, he or she acquires the corresponding scenarios in form of sequenceds. scenarios of a given use case are classified by type and ordered by frequency of use. we have considered two types of scenarios: normal scenarios, which are executed in normal situations, and scenarios of exception executed in case of errors and abnormal situations. to obtain a global description of a given service (use case) of the system or the description of the whole system, an operation of integration or composition between use cases and/or between scenarios is needed. the operation of integration looks like a generalization, where the analyst tries to identify and abstract some common parts in the system behaviour. composition constructs new behaviors from existing ones. this operation (composition) can be applied to different interaction objects like use cases, scenarios or messages. the difficulty of composition comes from the fact that interaction objects (use cases or scenarios specially) are being described independently one to each others. 4.2 specification building this activity consists on deriving hierarchical cpns from both the acquired and composed use cases and all of the sequenceds. the obtained cpn will have three levels of hierarchy: the first level captures use cases interactions, the second level describes scenario interactions of the same use case and the third level shows interactions between messages within a given scenario. each use case (a transition in the cpn above) is expended in a cpn handling relations between its scenarios. suppose that service2 is described by three scenarios sc1, sc2 and sc3 composed as follow: (sc1; sc2) || sc3. the service2 will be expended as shown in fig. 9. iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 11 fig. 9: cpn corresponding to scenario interactions. the third level concerns scenarios. we first derive the cpn structure, the cpn semantic is added by the help of the analyst. the cpn structure is automatically obtained from the graph of messages (fig. 6b) in the scenario by adding places between each pair (fig. 10a) of sequential messages. m1 m3 m4 m6 m2 m5 m 1 m 2 m 3 m 4 m 5 m 6 (c ) (a) (b) fig. 10: cpn second level of hierarchy (corresponding to message interactions). for the cpn semantic, the analyst can build an associated table of object states from the scenario by following the exchange of messages from top to bottom and by identifying the changes in object states. 4.3 scenario integration in this activity, we aim to merge all cpns corresponding to the scenarios of a use case uci, in order to produce an integrated cpn modeling the behavior of the use case. our algorithm is based on a preliminary version presented in [7]. it takes an incremental approach to integration. given two scenarios with corresponding cpns cpn1 and cpn2, sc1 begin_service2 sc2 sc3 end-service2 iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 12 the algorithm merges all places in cpn1 and cpn2 having the same names. the merged places will have as color the union of the colors of the two scenarios. then, the algorithm looks for transitions having the same input and output places in the two scenarios and merges them with an or between their guard conditions. in the following, we describe the algorithm in pseudocode, using the “dot”-notation known from object-oriented languages. integrating two scenarios whose cpns have the colors [sc1] and [sc2], respectively, will produce a cpn with the list [sc1,sc2] as color. the operation of merging follows the steps described below: integrate(uc_cpn,sc_cpn) uc_cpn.addplaces(sc_cpn) // adds in uc_cpn places of sc_cpn that do not exist in uc_cpn for each t in sc_cpn.getlistoftransitions() t' = uc_cpn.lookfortrans(t) // t' is a transition of uc_cpn with t=t' and t=t' if (t' does not exist) uc_cpn.addtrans(t) endif end uc_cpn.addedges(sc_cpn) // adds to uc_cpn edges of sc_cpn that do not exist in uc_cpn uc_cpn.mergecolors(sc_cpn) // calculates the new color of the integrated cpn (uc_cpn) uc_cpn.putcolorsonplaces(sc_cpn) // all places of the net will have the merged color uc_cpn.putguardontransitions(sc_cpn) // common transitions will be guarded by the merged color, // the others will be guarded by their original colors uc_cpn.putvariablesonedges(sc_cpn) // put on edges variables or token expressions end merge the resulting specifications derived from scenarios can be verified using exiting tools. we can check scenario specifications before and after integration to detect easily scenarios that cause incoherence in the integrated specification. we used the designcpn [6]. to check and the simulation of the resulting hierarchical cpn. 5. conclusions in this work, we have presented a new approach that produces automatically a global description or specification of a given service of the system or the whole system. the developed algorithms permit to derive the behavior of a use case by simply composing the scenarios describing it. four operators for composing scenarios have been implemented: sequential, conditional, iterative and concurrent. one of the most prominent features of our approach is that it supports many kinds of scenarios (sequential, iterative and concurrent), whereas most of the other approaches can handle only sequential scenarios. most of the related approaches are semi-automatic whereas our approach is fully automatic and offers either algorithmic or tool support. we presented the use of the scenario approach in b2b systems. we have discussed the need of a unified model of interaction that gives a unique syntax to express interactions at different levels: use cases, scenarios and messages. five scenario operators have been implemented: sequential, conditional, iterative, concurrent and abstraction/refinement. iium engineering journal, vol. 11, no. 1, 2010 jakimi et al. 13 as future work, we prospect to study the possibility of code generation from scenarios in from of sequenceds which will be a good plug-in to add. we plan to generate code from uml diagrams that describe dynamic and non-functional aspects of a system while remaining platform independent. references [1] c. rolland, c. ben achour, c. cauvet, j. ralyté, a. sutcliffe, n.a.m. maiden, m. jarke, p. haumer, k. pohl, e. dubois and p. heymans. “a proposal for a scenario classification framework”. the requirements engineering journal, volume 3, number 1, 1998. [2] omg: object management omg. unified modeling language specification version 2.0: infrastructure. technical report ptc/03-09-15, omg, 2003. [3] jacobson i. use cases—yesterday, today, and tomorrow. software syst. model. 2004, 3 210– 220. [4] bennani m., elkoutbi m., and nafil k.; modelling real-time aspects using uml scenarios proceedings of the 3rd international conference on software methodologies, tools and techniques, pp. 200-213, leipzig, germany, september 2004. [5] m. elkoutbi, and r.k. keller. “ user interface prototyping based on uml scenarios and high-level petri nets,” application and theory of petri nets 2000 (proc. of 21st intl. conf. on atpn), aarhus, denmark, june 2000. springer. lncs 1825, pp. 166-186. [6] m. elkoutbi, khriss i., r.k. keller. “automated prototyping of user interfaces based on uml scenarios”. the automated software engineering journal, 13, 5-40, 2006. [7] design cpn: version 4, meta software corp. <http://www.daimi.aau.dk/designcpn>. microsoft word vol11_no1_final iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 51 new clustering schemes for wireless sensor networks s.m. mazinani1, 2 , j. chitizadeh2, m.h. yaghmaee3, m. t. honary2, f. tashtarian4 1dept. of electrical and computer engineering, imam reza university, mashhad, iran 2dept. of electrical engineering, ferdowsi university, mashhad, iran 3dept. of computer engineering, ferdowsi university, mashhad, iran 4dept. of information technology, islamic azad university, mashhad, iran {smajidmazinani,mh_yaghmaee, tashtarian, m.tolou,}@gmail.com chitizad@um.ac.ir abstract : in this paper, two clustering algorithms are proposed. in the first one, we investigate a clustering protocol for single hop wireless sensor networks that employs a competitive scheme for cluster head selection. the proposed algorithm is named eecsm that is a modified version to the well known protocol eecs where some of the nodes become volunteers to be cluster heads with an equal probability. in the competition phase in contrast to eecs using a fixed competition range for any volunteer node, we assign a variable competition range to it that is related to its distance to base station. the volunteer nodes compete in their competition ranges and every one with more residual energy would become cluster head. in the second one, we develop a clustering protocol for single hop wireless sensor networks. in the proposed algorithm some of the nodes become volunteers to be cluster heads. we develop a time based competitive clustering algorithm that the advertising time is based on the volunteer node’s residual energy. we assign to every volunteer node a competition range that may be fixed or variable as a function of distance to bs. the volunteer nodes compete in their competition ranges and every one with more energy would become cluster head. in both proposed algorithms, our objective is to balance the energy consumption of the cluster heads all over the network. simulation results show the more balanced energy consumption and longer lifetime. keywords: wireless sensor networks, clustering, residual energy, balanced energy, single hop. 1. introduction the sensor network is a collection of small-size, low-power, low-cost sensor nodes that have some computation, communication, storage and even movement capabilities. these nodes can operate unattended, sensing the environment, generating data, processing data, and providing the data to users. with these features, sensor networks have been adopted in many pervasive computation and communication scenarios such as remote surveillance, habitat monitoring, and so on [1, 2]. iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 52 the deployment of wireless sensor networks in many application areas, e.g., aggregation services, requires self-organization of the network nodes into clusters. in these cases, sensors in different regions of the field can collaborate to aggregate the information they gathered. for instance, in habitat monitoring applications the sink may require the average of temperature; in military applications the existence or not of high levels of radiation may be the target information that is being sought. it is evident that by organizing the sensor nodes in groups i.e., clusters of nodes, we can reap significant network performance gains. clustering not only allows aggregation, but limits data transmission primarily within the cluster, thereby reducing both the network traffic and the contention for the channel. in this case, the gathered data from each node is processed locally and aggregated in a central coordinator referred to as a clusterhead (ch) and the redundant data (if any) is omitted to provide more accurate reports about the local region being monitored. in addition, data aggregation reduces the communication overhead in the network, leading to significant energy savings. node clustering is an efficient network organization in order to support data aggregation and it improves network lifetime [3]. direct transmission (single hop) and hop-by-hop (multi hop) transmission are two basic communication patterns in wireless networks. it was noticed that in the case of single hop communication the furthest sensors tend to deplete their energy budget faster than other sensors. in other words in direct transmission where packets are directly transmitted to the sink without any relay, the nodes located farther away from the sink have higher energy burden due to long range communication, and these nodes may die out first. to achieve balanced energy consumption, an elegant solution is to do make the clusters’ size related to the energy consumption of the cluster heads. thus smaller clusters are needed in the further distances from the bs in order to save more energy for the cluster heads. the main contribution in this paper is to gain energy balancing through clustering in such single hop networks. with this motivation, we propose a clustering protocol as the first proposed algorithm that employs level’s total energy and their distances to bs to form clusters. we point to a competitive algorithm proposed in [4] named eecs, for selecting chs among many other tentatively selected nodes. in the proposed algorithm that we name it eecs-m (modified eecs) some of the nodes become volunteers to be ch in the network. then they start broadcasting a competition message in their pre-assigned competition range is (in contrast to eecs using a fixed competition range) a function of distance to bs. every other volunteer node in its competitive range would quit the competition, if they have less energy. cluster architecture simplifies topology management and reduces the number of sensor nodes contending for the channel access. however, a ch drains its energy more quickly than ordinary nodes due to the more computational and operational activities. thus, a ch election algorithm must be distributed, energy-efficient, and load balanced [3]. with this motivation, we also propose a clustering algorithm as the second one in this paper that employs node’s residual energy for chs’ selection and their distance to bs to form clusters. we point to eecs as a competitive algorithm for selecting chs among many other tentatively selected nodes. a variable competition range, which is derived from a iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 53 recursive formula, is chosen which is proportional to the cluster’s size. as it is shown later, these unequal clusters make the load to distribute evenly on the whole network and results in more nodes’ longevity. in the second proposed algorithm, the whole network’s lifetime is the time until the first node in the network runs out of energy. in fact in the second proposed algorithm, we developed a competitive clustering algorithm that uses a time based advertising procedure. initially some of the nodes become volunteers to be ch in the network. then they start advertising in the network using a timing schedule that is a function of energy. every node that has more residual energy would start advertising sooner. each node is also assigned a competitive range that may be fixed or variable as a function of distance to bs. every other volunteer node in its competitive range would stop advertising, if they have less energy. otherwise they will wait for their turn for advertising. the remainder of this paper is outlined as follows: in section 2, we present related work on some previous well-known clustering schemes proposed in the literature. in section 3 a common model for wsns is introduced and network’s operation stages including cluster selection/formation phase and data gathering/reporting phase are described for both algorithms. section 4 focuses on the proposed algorithms in details. simulation results are also included in section 5. 2. related work lots of methods and researches are dealing with energy efficient issues and to prolong the lifetime of the wireless sensor networks and in the past few years, many clustering algorithms have been proposed for ad hoc and sensor networks aiming to improve the energy efficiency. leach [5] is an application-specific clustering protocol that utilizes random selection and frequent rotation of chs for distribution of the total load into all nodes. the clustering process involves only one iteration, after which a node decides whether to become a ch or not and nodes take turns in carrying the ch’s role. the data communication in leach is based on single-hop communication model. the author also proposed two variants of leach, which are referred to as leach-c (leachcentralized), and leach-f (leach with fixed clusters). aros [6] is a new version of leach which uses asymmetric communication with a semi-centralized clustering algorithm. the author demonstrated that aros improves communication energy efficiency when the network size increases. heed [7] selects chs through o(1) time iteration according to a hybrid of nodes’ residual energy and another parameter such as node proximity to its neighbors or node degree. the author in [4] presented eecs, which is a novel approach to distribute the chs uniformly across the network through a localized single hop communication with little overhead. a competitive algorithm is suggested for chs selection phase and a fixed competition range is specified to each volunteer node. a weighted cost function is also introduced to manage the number of cluster members. every node, which finds a more powerful node in its competition set, will give up the competition immediately and broadcast its quit acknowledgment message. any node that finds itself more powerful than the others in its competition radius will introduce itself as a ch and broadcast its iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 54 advertisement message. the message complexity in this algorithm makes trouble in the dense networks for having too many nodes competing for being ch. a similar approach is performed in [8] where the authors applied a variable competition radius to the tentative nodes. an energy balancing criterion for every ch is used to derive a recursive equation for its competition range based on the nodes distance to the bs. in [9], several energy-efficient communication protocols have been proposed based on power control and load balancing, aiming at even distribution of the residual energy of the sensors and thus prolonging network lifetime. dagher, et. al. [10] presented a theory for maximizing the lifetime of multihop wsn. an optimal centralized solution was presented in the form of an iteration algorithm. in [11], a taxonomy and general classification of published clustering schemes was presented. the authors surveyed different clustering algorithms for wsns. in [12], an investigation about cluster size and the number of cluster heads in the region was achieved when all the devices in a wsn are deployed randomly. in this paper, since we are not to design an efficient mac layer, an ideal simple mac layer is recommended that is collision-free and uses a tdma schedule for nodes’ data communication. our goal is to balance the energy consumption in the whole network in such a way that network’s lifetime is increased. 3. system model to illustrate the impact of the physical limits of sensor networks on the design of our algorithms we briefly discuss related wireless network model, which highly depends on the application. we consider a network with characteristics as below:  the sensor nodes are homogenous and they are uniformly distributed in a square field.  the sink and the sensor nodes are assumed to be static once deployed.  the sink node or base station (bs) is sited outside of the square field.  all sensor nodes are able to set their power transmission according to the distance to the destination.  sensor nodes are assigned a unique id and they are fully synchronized via a synchronization beacon broadcasted from the bs at the beginning of every round. a. network’s operation and data gathering model for most data gathering applications, the sensors usually operate in a low-duty-cycle mode. the interval between one duty cycle to the next may be several minutes, hours even days. this characteristic motivates the utilization of periodical sleeping to conserve energy. each ch acts as a local coordinator of data transmission in the cluster. it sets up a tdma schedules for all the cluster’s nodes to ensure that there is no collisions among data messages. this schedule also allows the radio component of relative nodes to be turned off at all the times except during their transmit time [5]. the data reporting process, which sometimes is called “steady state phase”, is divided into rounds. in each round, any non-ch nodes in a cluster send their raw data obtained from sensing environment directly iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 55 to their respective chs. the nodes are also supposed to embed their residual energy information in the same packet. this information would be useful to compute the average network’s energy in the bs. the chs nodes are responsible for coordinating the members in their clusters and communicate with the sink node on behalf of their clusters and via a single hop communication. in addition, chs aggregates the received data from its members with its own gathered data to compress the amount of data, which is to be sent to the bs. the data aggregation increases the performance of the network in terms of communication cost. however, the optimality of performing data aggregation is beyond the scope of this paper. at the end of each round, the clustering phase will restart and the new chs are selected for the next round. b. energy consumption model in single hop networks in our model, we assume that each sensor can intelligently choose the transmission power based on the link distance. this is true in typical sensor node implementations. a simple model is described in [5] where each node dissipates energy to run the radio electronics and power amplifier in transmitter side. the power attenuation is a function of the distance between transmitter and receiver. there is a cross over distance that can be simply used to model the propagation loss. thus, to transmit a l-bit message to a distance d, the radio expends: 2 4 ( ) elect freespace crossover tx elect multipath crossover le l d d d e d le l d d d           (1) where the eelect is the energy required for running the electronic circuits. εfreespace and εmultipath are two parameters which depend on the noise figure and the required snr for proper signal detection at the receiver. it can also be written in a more general from as: ( )t xe d p q d   (2) where p and q are constants related to node energy dissipation to run the radio electronics and power amplifier in transmitter and α is the path loss factor. besides, there are two more sources of energy consumption of the chs. each ch consumes energy for receiving data from adjacent nodes or cluster members and fuses it into a single packet that is outlined by: rf e le c t b f e m l e e  (3) where in both equations, m is the number of cluster’s members and ebf is the computed energy for beam forming data aggregation [5]. iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 56 4. the proposed algorithms in this paper, we propose two clustering algorithms which result in more balanced energy consumption and longer lifetime. 4.1 details of first algorithm (eecs-m) as discussed previously, any detected event must be reported to the bs in the form of data packets. in some applications such as fire detection, the event must be reported as soon as possible and too much latency is unacceptable. the recommended communication model for such networks is single hop communication. nevertheless, further nodes consume more energy for data reporting. a. determining the length of levels figure 1 depicts a simple network which is divided into three radial levels with the bs at the center. the clusters located in the further levels seem to be smaller than the closer clusters. thanks to having more distance to the bs, the ch needs to spend more power to send its own packet. having smaller cluster formed with less number of members, the ch can save most of its energy for data communication to the bs. on the other hand, since the closer ch nodes do not consume a large amount of energy for data communication to the bs, they are able to form larger clusters to cover more area and support more number of members. fig. 1: radial regions (levels) with the bs at the center. the contribution is to gain energy balancing for each individual level. the total energy consumption of the ith level is the sum of the consumed energies of every single cluster in that level. considering k number of clusters in a level, the total level’s energy is: iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 57 i l e v e l c l u s t e re k e  (4) where ecluster (the total energy consumed in each cluster) is composed of the total energy consumed by the member nodes and the energy consumed by the ch itself as follows: c l u s t e r c h c me e e  (5) where ech and ecm are the ch's energy consumption and cluster members' energy consumption respectively. the ch receives all the packets from the members and fuses it into a single packet and forwards to the bs. considering ρ as the nodes density and a circular region for the cluster with the coverage radius crl, the energy consumed by the ch is as follows: 2 4. . .( )c h rf tob se c r l e p qd    (6) where dtobs is the total distance from the ch to the bs. if the network's width is named y and the distance of the bs to the closest edge of the network is called r0 (see fig. 2), we have: 0t o b sd y r c r l   (7) the cluster members' energy consumption can be derived as bellow: 2 2. . .( )c m to c he c r l p qd   (8) generally speaking the expectation of nodes' distance to the ch must be applied in eq. (8). in [5] it is derived as follows: 2 2 2 2 3 0 0 4 [ ] ( ) ( , ) .2 . 4 t o c h c r l e d x y x y d x d y r d d r c r l              (9) where in the last step it is assumed that the node's density, ρ, is independent of the physical positions. inserting eq. (6) and eq. (8) into eq. (5) and the result into eq. (4), the total energy consumption of the ith level is: iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 58 2 4 _ . . . ( .2 . ) 4 ( ) rf ii i level tx tx tobs i e crl crl e k e e d                      (10) where k is the number of clusters in that level: 2 2 . . . i i c r l y k c r l  (11) also dtobs_i is derived as follows: 1 _ 0 1 2 i tob s i j i j d y r c r l c r l       (12) in this equation there are two unknowns, eilevel and crli. the energy balancing criterion in this article is the equality of levels' total energy consumption. since the furthest nodes from the bs are supposed to die faster, we compute the minimum of the first level’s total energy consumption and equal this to the other levels’. by this way we get rid of the unknown eilevel. at this time considering i=1 in eq. (10) we get an equation for the first level's total energy consumption as a function of crl1. having this equation minimized, the derivation with respect to crl must be vanished. it is easy to show that eq. (10) has minimum and the derivation has a single acceptable result in the feasible range for the last level. fig. 2: clusters grow up by enclosing the bs. using the obtained result, the minimum of the first level’s total energy consumption can be reached and it is considered equal to the other level’s total energy consumption. therefore according to eq. (10) eilevel is known and only the crli, is unknown which can iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 59 be computed easily for other levels. in fig. 2, it is obvious that the clusters grow up by enclosing to the bs. b. competitive clustering algorithm this section describes the chs’ selection and cluster formation phase. in this stage we refer to [4] for the competition phase among those tentatively selected nodes. in this clustering scheme, the tentative nodes compete for being final chs. these nodes become tentative with an equal probability t and they broadcast a competitive message in their competition radius which is assumed to be fixed in eecs. this message contains the node’s id, its residual energy and its competitive range, rcompetition. if there is any other tentative node in this radius it would hear this message. any node that finds itself more powerful than the others in its competition radius will introduce itself as a ch and broadcast its advertisement message. the main difference of the proposed algorithm and eecs is in the competition radius which was considered to be fixed in eecs. in this algorithm we consider that every tentative node competes in its respective level’s crl. as we can see the competition range of each level increases as the region’s distance from the bs decreases. this means the smaller clusters with fewer nodes joining them is expected to be formed in far distances to bs. 4.2 details of second algorithm this section describes the chs’ selection and cluster formation phase. in our purposed clustering scheme, we assumed that the nodes, whose residual energies are more than the average network’s energy, are more proper to become a ch at each round. for this purpose, we need to take the advantage of the hello message that is broadcasted from the bs at the beginning of every round for nodes synchronization. this hello message contains the average network’s energy that is computed in the bs. remember that we assumed that every node is supposed to send its residual energy to its respective ch, and ch is supposed to embed the average cluster’s energy in the header of the aggregated data packet and forward it to the bs. the next step is the competition stage where the tentative nodes compete for final chs. in the previous proposed algorithm, eecs, the nodes has to broadcast a competitive message in their competition radius and if there is any other tentative node in this radius would hear this message. any node that finds itself more powerful than the others in its competition radius will introduce itself as a ch and broadcast its advertisement message. the message complexity in this algorithm makes trouble in the dense networks for having too many nodes competing and negotiating too many packets for being ch. we omitted the negotiation in the competition phase and replaced it with a timing schedule for advertising nodes. in this algorithm each tentative node will broadcast its advertisement message across the network based on a timing schedule as bellow: 0. initial residual advertisem ent initial e e t t e         (13) iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 60 where einitial and eresidual are the initial and residual energy of the volunteer node respectively and t0, is the maximum waiting time for advertisement and is a predefined parameter. it is obvious that the node with more residual energy will advertise itself sooner. in the advertising packet the node’s id, its residual energy and competitive range, rcompetition are embedded. suppose that si is a tentative node that is a volunteer to become a ch. the goal is to remove any tentative node sj (j≠i) that is in si’s competition set and its energy is less than si’s residual energy. if sj hears the advertisement and it determines that it has less residual energy than si, it stops waiting for advertising itself and quits the competition immediately and goes to sleep mode like other ordinary nodes. otherwise it waits for its turn to advertise and starts advertising if there is no any heard advertising message. the low message complexity in this approach is obvious since no extra negotiation is needed between the competing nodes. in the simulation section we will demonstrate the effectiveness of using timing schedule on the network’s lifetime. in the first step we consider a fixed competition range just like eecs. then we refer to [8] on deriving a competitive range as a function of distance to bs for a divided network into equal-length radial levels with the bs at the center as the following:  222 1 id i i kr r      (14) where according to [8] ri is the competition range of the ch in the i th level. the parameter α and di are the region increment and the region distance to the bs respectively and the parameter k is a constant dependent to the network’s primarily settings. by this equation, the competition range of each ch is derived based on its distance to the bs and the obtained competition range for the previous level. as we can see the competition range of each level decreases as the region’s distance from the bs increases. this means the smaller clusters with fewer nodes joining them is expected to be formed in far distances to bs. therefore, less energy for receiving data is consumed and ch can save majority of its energy for data transmission to the bs. we evaluated the network’s efficiency in the sense of lifetime using a variable competition range and a timing schedule together. the results are brought with details in the next section. 5. simulation and results the performance of proposed algorithms is evaluated via matlab. a. eecs-m evaluation in this section, eecs-m is evaluated. the simulated network has the characteristics described in section 2. other simulation parameters are listed in table. 1. the simulations are performed in fair situations and the results are compared with the eecs algorithm. iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 61 in fig. 3 the network's lifetime is depicted in two scenarios in the sense of the number of alive nodes. the eecs-m shows longer lifetime with respect to eecs. more fairness in load distribution is obtained in our proposed algorithm by using this variable competition range (variable cluster sizes) for each level. iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 62 table 1: simulation parameters parameter value network size 300×300 m2 bs location 150,500 m number of sensors 400 (scenario1) 800 (scenario2) initial energy 0.5 j eelec 50 nj/bit εfs 10 pj/bit/m 2 εmp 0.0013 pj/bit/m 4 ebf 5 nj/bit/singnal data packet size 4000 bits control packet size 32 bits d0 87 m t 0.2 0 100 200 300 400 500 600 0 50 100 150 200 250 300 350 400 round n u m b e r o f a liv e s e n s o rs eecs-m eecs 0 100 200 300 400 500 600 0 100 200 300 400 500 600 700 800 round n u m b e r o f a liv e s e n s o rs eecs-m eecs (a) (b) fig. 3: number of alive nodes. (a) scenario1 (400 nodes), (b) scenario2 (800 nodes). measuring the total network’ energy consumption is useful to compare the three cases for the whole lifetime (fig. 4). the lower steep in the figure shows more fairness in energy distribution. it implies that the nodes consume their energy much slower than other case. eecs-m shows more efficient energy consumption than eecs in the both scenarios. this is due to using unequal clusters based on their distances to the bs. another useful parameter for efficiency evaluation is the total number of data packets received at the bs. it is assumed that each ch forwards a single packet to the bs at each round of network's lifetime. then one may guess this parameter is only related to the number of clusters formed in the network. however, the total number of packets received at the bs is also related to the nodes average lifetime. iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 63 0 100 200 300 400 500 600 0 50 100 150 200 250 round t o ta l n e tw o rk 's e n e rg y eecs-m eecs 0 100 200 300 400 500 600 0 50 100 150 200 250 300 350 400 450 round t o ta l n e tw o rk 's e n e rg y eecs-m eecs (a) (b) fig. 4: total network's energy. (a) scenario1 (400 nodes), (b) scenario2 (800 nodes). if there are too many clusters formed in the network without considering their distance to the bs, the energy of the ch nodes would drain so quickly. even if they can forward many packets to the bs, they will not last long enough to do so. fig. 5 illustrates the total number of data packets received in each round of network lifetime. it is obviously clear that the proposed clustering algorithm delivers more data packets in both scenarios. 0 100 200 300 400 500 600 0 1 2 3 4 5 6 x 10 6 round n u m b e r o f d a ta p a c k e ts r e c e iv e d a t b a s e s ta ti o n eecs-m eecs 0 100 200 300 400 500 600 0 2 4 6 8 10 12 x 10 6 round n u m b e r o f d a ta p a c k e ts r e c e iv e d a t th e b a s e s ta ti o n eecs-m eecs (a) (b) fig. 5: total number of data packets received at the bs. (a) scenario1 (400 nodes), (b) scenario2 (800 nodes). useful numerical results are brought in table. 2. the number of levels formed using eq. (12) is three levels for 400 nodes and four levels for 800 nodes. in both cases the fnd (first node's death) in eecs-m is sooner than eecs. however the lnd (last node's death) is quite longer in eecs-m with respect to eecs. the tnsp (total number of sent packets to the bs) values are interestingly larger in both cases for eecs-m that is5.1 million packets against 1.8 million in scenario 1 and so on. iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 64 table 2: numerical results. eecs-m eecs eecs-m eecs #nodes 400 400 800 800 # levels 3 1 4 1 crl4 133.35 54.65 112.13 crl3 71.81 54.06 crl2 70.23 51.82 crl1 49.70 39.49 fnd 5 51 9 42 lnd 453 367 570 427 tnsp 5.1e+6 1.8e+6 1.04e+7 2.5e+6 b. the second algorithm evaluation in this section, the second algorithm is evaluated. the simulated network has the characteristics described in section 2. other simulation parameters are listed in table. 3. in the figures, vcr stands for “variable competition range” and ts stands for “timing schedule”. we simulated the network for two different cases. in the first step we apply the variable competition range derived via the recursive equation as (14) with the r0 equal to 25 on the proposed algorithm eecs. then we employ the timing schedule and the variable competition range together. in both cases we evaluated the networks lifetime in the sense on first/last node death. the results are depicted in fig. 6 compared with eecs with no timing schedule and a fixed competition range. we also employed the cost function described in eecs choosing the more proper chs for each non-ch node in all the cases. in fig. 6 it is obvious that the timing schedule improves the efficiency in the sense of lifetime. the eecs algorithm uses a competition phase at the beginning of each round. the number of packets that has to be negotiated in this phase is quite high. thus the nodes lose their energy at the beginning of each round. applying the variable competition range results in an improvement in the lifetime. however this is not the case. employing the time schedule and the variable competition range together in the algorithm shows a better improvement in network’s lifetime. this is due to the better energy balancing and more fairness in load distribution by using this variable competition range. nevertheless the timing schedule makes better energy efficiency in the setup phase of the algorithm. in fig. 7 and fig. 8 the same result is illustrated with the focus on the time of the first and last iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 65 node’s death in the three algorithms respectively. the improvement in the lifetime is more visible in these figures. table 3: simulation parameters. parameter value network size 100*100 m bs location 50,200 m number of sensors 400 initial energy 0.5 j eelec 50 nj/bit εfs 10 pj/bit/m 2 εmp 0.0013 pj/bit/m 4 eda 5 nj/bit/singnal data packet size 4000 bits d0 87 m t0 0.008 s r0 25 0 200 400 600 800 1000 1200 0 50 100 150 200 250 300 350 400 rounds n u m b e r o f a liv e n o d e s eecs eecs + vcr eecs + vcr + ts 900 920 940 960 980 1000 1020 350 360 370 380 390 400 410 rounds f ir s t n o d e 's d e a th eecs eecs + vcr eecs + vcr + ts fig. 6: number of alive nodes. fig.7: network lifetime. first node’s death time iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 66 900 950 1000 1050 0 10 20 30 40 50 rounds l a s t n o d e 's d e a th eecs eecs + vcr eecs + vcr + ts fig. 8: network lifetime. last node’s death time. measuring the total network’ energy consumption is useful to compare the three cases for the whole lifetime (fig. 9). the lower steep in the figure shows more fairness in energy distribution and longer lifetime. in this figure the competitive algorithm with timing and variable competition range shows a lower steep in decreasing the total energy of the network. it implies that the nodes consume their energy much slower than two other cases. considerable amount of energy is consumed in eecs for competition setup phase. 0 200 400 600 800 1000 1200 0 50 100 150 200 rounds n e tw o rk 's t o ta l e n e rg y eecs eecs + vcr eecs + vcr + ts fig. 9: network energy consumption. in the next step, the network is simulated for 100 independent distributions of sensor nodes. the simulation is done in fair situations for our model employing a variable/fixed competition range on the eecs algorithm and also using the timing schedule and the variable range together. a fixed competition range ropt=25 that depends on the optimum number of clusters in the network is proposed for eecs. figure 10 illustrates the result of network’s lifetime comparison in the sense of first nodes death for 100 independent simulations. it is clear that 1.5% is achieved in applying a variable competition range on iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 67 eecs. however the improvement in lifetime becomes 10% in using the timing schedule and the variable competition range together in the proposed algorithm. 0 10 20 30 40 50 60 70 80 90 100 900 910 920 930 940 950 960 970 980 eecs eecs & vcr ts & vcr fig. 10: network’s lifetime (first node’s death) in 100 different simulations. 6. conclusion in this paper, we reviewed the energy balancing technique in wireless sensor networks via clustering. energy consumption of each ch in such a single hop network depends on its distance to bs and the number of cluster members. in the first proposed algorithm, we provide an extension of a well-known clustering protocol that uses a competitive algorithm to form clusters. in contrast to eecs, eecs-m used unequal competition ranges of tentative ch nodes, which are derive as a functions of node’s distance to bs. in the proposed algorithm we initially found the optimum length for the first (furthest) level in the network. the reason was that these nodes are supposed to die sooner than any other nodes closer to the bs. then assuming equal energy consumption for every subsequent level, we found the optimum length of that level and also the number of clusters. the main difference between eecs-m and eecs is that eecs uses a fixed competitive range for tentative nodes. however, eecs-m employs the levels' total energy consumption to find the competition ranges. the proposed algorithm eecs-m prolongs the network lifetime due to more energy efficiency obtained from using the unequal clusters. the acceptable results such as longer lifetime and larger amount of received data packets in the whole network lifetime prove the effectiveness of this proposed algorithm in the sense of energy efficiency. in the second proposed algorithm, we again provide an extension of eecs and our previous proposed algorithm in [8] that uses a competitive algorithm for determining competition range. in contrast to eecs, our model used unequal competition ranges of tentative ch nodes, which are recursively functions of node’s distance to bs. this selection forms unequal cluster size in the whole network. every ch node that is far away from the bs would form a smaller cluster with fewer members and can save most of its energy for data transmission. in the second proposed algorithm, timing schedule based advertising instead of the negotiation between the volunteer nodes is applied. this schedule was a function of nodes energy. the node with more residual energy would iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 68 advertise itself sooner. any node that heard the advertisement and it determined that it had had less residual energy would stop waiting for advertising itself and it would quit the competition. otherwise it would wait for its turn to advertise and it started advertising if there have not been any heard advertising messages. we simulated the network for the ordinary algorithm eecs and our proposed timing based algorithm with/without a fixed competition range. in the first step we applied the timing schedule on the proposed algorithm eecs with the fixed competition range. then we employed the variable competition range derived via the recursive equation as eq. (14). in both cases we evaluated the networks lifetime in the sense on first/last node death. employing the time schedule and the variable competition range together in the algorithm shows a better improvement in network’s lifetime. this is due to the better energy balancing and more fairness in load distribution and low energy drainage in the setup phase for competition negotiation. besides the competitive algorithm with timing and variable competition range shows a lower steep in decreasing the total energy of the network. it implies that the nodes consume their energy much slower than two other cases since considerable amount of energy is consumed in eecs for competition setup phase. references [1] f. ye, h. luo, j. cheng, s. lu, and l. zhang, “a two-tier data dissemination model for large-scale wireless sensor networks”, acm international conference on mobile computing and networking (mobicom’02), pp. 148–159, september 2002. [2] g. wang, g. cao, t. la porta, and w. zhang, “sensor relocation in mobile sensor networks”, ieee infocom, march 2005. [3] o. younis, m. krunz and s. ramasubramanian, “node clustering in wireless sensor networks: recent developments and deployment challenges”, ieee transactions on networking, vol. 20, issue. 3, pp.20-25, 2006. [4] m. ye, c. f. li, g. h. chen, and j. wu, “eecs: an energy efficient clustering scheme in wireless sensor networks”, in proceedings of ieee int’l performance computing and communications conference (ipccc), pp. 535-540, 2005. [5] w. heinzelman, “application-specific protocol architectures for wireless networks”, ph.d. dissertation, mass. inst. technol., cambridge, 2000. [6] j. neander, e. hansen, m. nolin, m. bjorkman, “asymmetric multihop communication in large sensor networks”, 1st international symposium on wireless pervasive computing, pp. 1 – 7, 16-18 jan. 2006 [7] o. younis and s. fahmy, “heed: a hybrid, energy-efficient, distributed clustering approach for ad hoc sensor networks”, ieee transactions on mobile computing, vol. 3, no. 4, pp. 366 – 379, oct.-dec 2004. [8] m. tolou honary and j. chitizadeh, “lifetime prolonging of wireless sensor networks via a recursive clustering algorithm”, proc. of third ieee international conference in central asia on internet the next generation of mobile, wireless and optical communications networks, ici 2007, tashkent. [9] y. wang, h. wu, r. nelavelli, and n. f. tzeng, “balance based energy-efficient communication protocols for wireless sensor networks”, in proceedings of the international workshop on wireless ad hoc and sensor networks (wwasn2006), 2006. iium engineering journal, vol. 11, no. 1, 2010 mazinani et al. 69 [10] j. c. dagher, m. w. marcellin, and m. a. neifeld, a theory for maximizing the lifetime of sensor networks, ieee trans, on communications, vol. 55, pp. 323-332, feb. 2007. [11] a. a. abbasi, m. younis, “a survey on clustering algorithms for wireless sensor networks”, elsevier on computer communication, vol. 30, pp.2826-2841, june 2007. [12] c. sevgi, a. kocyigit, “on determining cluster size of randomly deployed heterogeneous wsns”, ieee communications letter, vol. 12, no. 4, april. 2008. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 a robust framework for driver fatigue detection from eeg signals using enhancement of modified z-score and multiple machine learning architectures rafiuddin abdubrani1*, mahfuzah mustafa1 and zarith liyana zahari1,2 1 faculty of electrical and electronics engineering technology, universiti malaysia pahang, pekan 26600, pahang, malaysia 2 electronic section, universiti kuala lumpur british malaysia institute, gombak 53100, selangor, malaysia * corresponding author: rafi128@yahoo.com (received: 21 march 2023; accepted: 8 may 2023; published on-line: 4 july 2023) abstract: physiological signals, such as electroencephalogram (eeg), are used to observe a driver’s brain activities. a portable eeg system provides several advantages, including ease of operation, cost-effectiveness, portability, and few physical restrictions. however, it can be challenging to analyse eeg signals as they often contain various artefacts, including muscle activities, eye blinking, and unwanted noises. this study utilised an independent component analysis (ica) approach to eliminate such unwanted signals from the unprocessed eeg data of 12 young, physically fit male participants between the ages of 19 and 24 who took part in a driving simulation. furthermore, driver fatigue state detection was carried out using multichannel eeg signals obtained from o1, o2, fp1, fp2, p3, p4, f3, and f4. an enhanced modified z-score was utilised with features extracted from a time-frequency domain continuous wavelet transform (cwt) to elevate the reliability of driver fatigue classification. the proposed methodology offers several advantages. first, multichannel eeg analysis improves the accuracy of sleep stage detection, which is vital for accurate driver fatigue detection. second, an enhanced modified z-score in feature extraction is more robust than conventional z-score techniques, making it more effective for removing outlier values and improving classification accuracy. third, the proposed approach for detecting driver fatigue employs multiple machine learning classifiers, such as convolutional neural networks (cnns), recurrent neural networks (rnns), artificial neural networks (anns) that utilise long shortterm memory (lstm), and also machine learning techniques like support vector machines (svm). the evaluation of five classifiers was performed through 5-fold crossvalidation. the outcomes indicate that the suggested framework attains exceptional precision in identifying driver fatigue, with an average accuracy rate of 96.07%. among the classifiers, the ann classifier achieved the most significant precision of 99.65%, and the svm classifier ranked second with an accuracy of 97.89%. based on the results of the receiver operating characteristic (roc) and area under the curve (auc) analysis, it was observed that all the classifiers had an outstanding performance, with an average auc value of 0.95. this study’s contribution lies in presenting a comprehensive and effective framework that can accurately detect driver fatigue from eeg signals. abstrak: isyarat fisiologi, seperti elektroencefalogram (eeg), digunakan bagi memerhati aktiviti otak pemandu. sistem eeg mudah alih menyediakan beberapa kelebihan, termasuk kemudahan operasi, keberkesanan kos, mudah alih dan sedikit sekatan fizikal. namun, isyarat eeg mungkin sukar dianalisis kerana ia sering 354 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 mengandungi pelbagai artifak, termasuk aktiviti otot, mata berkedip dan bunyi yang tidak diingini. kajian ini menggunakan pendekatan analisis komponen bebas (ica) bagi membuang isyarat tidak diperlukan daripada data eeg yang belum diproses daripada 12 peserta lelaki muda, cergas fizikal berumur 19 hingga 24 tahun yang mengambil bahagian dalam simulasi pemanduan. tambahan, pengesanan keadaan lesu pemandu telah dijalankan menggunakan isyarat eeg berbilang saluran yang diperoleh dari o1, o2, fp1, fp2, p3, p4, f3, dan f4. penambah baik skor z digunakan dengan ciri diekstrak daripada transformasi wavelet berterusan (cwt) domain frekuensi masa bagi meningkatkan kebolehpercayaan klasifikasi keletihan pemandu. metodologi yang dicadangkan menawarkan beberapa kelebihan. pertama, analisis eeg berbilang saluran meningkatkan ketepatan pengesanan peringkat tidur, penting bagi pengesanan keletihan pemandu secara tepat. kedua, penambah baik skor z dalam pengekstrak ciri adalah lebih teguh daripada teknik skor z konvensional, menjadikannya lebih berkesan bagi membuang unsur luaran dan meningkatkan ketepatan pengelasan. ketiga, pendekatan yang dicadangkan bagi mengesan keletihan pemandu menggunakan pelbagai pengelas pembelajaran mesin, seperti rangkaian neural konvolusi (cnn), rangkaian neural berulang (rnn), rangkaian neural buatan (ann) yang menggunakan memori jangka pendek panjang (lstm), dan juga teknik pembelajaran mesin seperti mesin vektor sokongan (svm). penilaian lima pengelas dilakukan melalui pengesahan silang 5 kali ganda. dapatan kajian menunjukkan cadangan rangka kerja ini mencapai ketepatan yang luar biasa dalam mengenal pasti keletihan pemandu, dengan kadar ketepatan purata 96.07%. antara kesemua pengelas, pengelas ann mencapai ketepatan paling ketara sebanyak 99.65%, dan pengelas svm menduduki tempat kedua dengan ketepatan 97.89%. berdasarkan keputusan analisis ciri operasi penerima (roc) dan kawasan di bawah lengkung (auc), didapati semua pengelas mempunyai prestasi cemerlang, dengan purata nilai auc 0.95. sumbangan kajian ini adalah terletak pada rangka kerja yang komprehensif dan berkesan mengesan keletihan pemandu secara tepat melalui isyarat eeg. keywords: driver fatigue; electroencephalogram (eeg); z-score; deep learning 1. introduction according to statistics from the world health organization, roughly 127,000 individuals lose their lives in traffic accidents yearly, with nearly one-third of those casualties being teenagers and young adults [1]. fatigue driving contributes to fatalities in road accidents, contributing to more than ten thousand deaths in a conservative estimate. recently, some autonomous vehicles have proposed a warning system to prevent road accidents due to driver fatigue. the system would prompt drivers to take a break from prolonged driving by sounding an alarm in the vehicle, notifying the driver to stop driving and grab a coffee break. physiological signals such as electroencephalograms (eeg) are used to observe a driver’s brain activities. a portable eeg system provides several advantages over other electroencephalography systems, including ease of operation, cost-effectiveness, portability, and few physical restrictions [2]. the presence of artefacts in eeg signals, such as muscle activity, eye blinking, and unwanted noise, can pose a significant challenge for analysis. therefore, the current paper proposes using an independent component analysis (ica) technique to eliminate such noise from the raw eeg signal. numerous studies have suggested that an essential component of precise sleep stage detection is the analysis of multichannel eegs [3]. consequently, the present study considers multichannel eeg signals obtained from o1, o2, fp1, fp2, p3, p4, f3, and f4 for detecting driver fatigue states. 355 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 the features from a time-frequency domain, continuous wavelet transform (cwt) with enhanced modified z-score improved the accuracy of driver fatigue classification. it is important to choose the best features to get better results. the morlet mother wavelet is a common practice in conventional cwt techniques due to its computational efficiency, surpassing other methods. this is because the morlet wavelet involves fewer computations, most of which are performed through the fast fourier transform, requiring less code [4]. in the field of data analysis and quality control, the identification of outliers is a crucial step in ensuring the accuracy and validity of statistical analyses. the z-score is a widely used method for detecting outliers in datasets, but it is susceptible to extreme values and is not considered robust in the presence of such outliers. the modified z-score was introduced to address this issue, which is less sensitive to outliers and has become a popular method for outlier detection in various applications. in recent years, the modified z-score has also been applied to feature extraction in machine learning and signal processing, where removing outlier values is crucial for accurate and robust analysis. this paper presents an enhancement of the modified z-score method for feature extraction in signal processing, specifically in driver fatigue detection using eeg signals. our proposed method has several strengths. first, using multichannel eeg analysis improves the accuracy of sleep stage detection, which is vital for accurate driver fatigue detection. second, our use of enhanced modified z-score in feature extraction is more robust than conventional z-score techniques, making it more effective for removing outlier values and improving classification accuracy. third, our approach utilises various machine learning classifiers, providing a comprehensive and accurate method for driver fatigue detection. this paper presents a methodology for the precise identification of distinct levels of driver drowsiness by utilising diverse machine learning classifiers, including convolutional neural networks (cnns), recurrent neural networks (rnns), artificial neural networks (anns) that incorporate long short-term memory (lstm), and machine learning approaches like support vector machines (svm). a modified z-score technique to enhance the statistical feature of the classification was also introduced, which significantly improved the accuracy of the proposed method. to evaluate the effectiveness of this approach, a 5fold cross-validation strategy was employed to distinguish between driver fatigue and normal states. 2. related works outlier detection is critical in various fields, including environmental monitoring, geology, epidemiology, and data mining. the modified z-score is a frequently employed technique for detecting outliers, which considers the weighted mean of adjacent data points to estimate the anticipated value of each point. aggarwal et al. proposed a modified z-score method for detecting spatial outliers in datasets with spatial autocorrelation [5]. the technique improves the accuracy and robustness of the z-score test using a trimmed mean instead of the usual arithmetic mean. the study evaluated the method on simulated and realworld datasets and showed promising results in detecting spatial outliers. although the modified z-score method proposed by aggarwal et al. effectively detects spatial outliers with spatial autocorrelation, it may not perform well in datasets without spatial autocorrelation. additionally, using a trimmed mean instead of the arithmetic mean may result in the loss of valuable information from the dataset. 356 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 sandbhor et al. investigated the importance of detecting outliers in data mining and their effect on the quality and output of prediction models [6]. the study’s primary objective was to determine the most effective approach for detecting outliers in neural networks (nn) to forecast real estate values. the authors assessed several univariate outlier detection methods, such as tukey’s standard deviation (sd), median, z-score, median absolute deviation (mad), and modified z-score, on a set of 3,094 instances of property sales data. based on the findings, it can be concluded that for this particular problem, the median technique proved to be the most efficient approach for detecting outliers. although sandbhor et al. found that the median technique was the most efficient approach for detecting outliers in neural networks for real estate value prediction, it is important to note that this conclusion may not necessarily apply to other types of datasets or outlier detection techniques. moreover, the study only evaluated univariate outlier detection methods and did not consider multivariate techniques, which may be more effective in certain applications. leite et al. conducted a study to evaluate the effectiveness of the modified z-score as an indicator for identifying changes in entropy-based features to detect faults in bearings [7]. the research involved using 12 entropy-based features across the time, frequency, and time-frequency domains, in addition to three different entropy measures, namely shannon entropy, renyi entropy, and jensen-renyi divergence. the proposed technique was applied to process two real-bearing datasets obtained from experiments conducted until the point of failure. furthermore, three bearings with different defects were examined to verify the performance of the entropy-based features. the results demonstrated that the modified zscore is a robust method for detecting changes in entropy-based features, highlighting its potential for early detection of anomalies in the vibration signals of bearings. this finding suggests that the proposed technique can be effectively utilised for fault diagnosis in bearings. however, it is important to note that the study only evaluated the effectiveness of the modified z-score method on two real-bearing datasets obtained from experiments conducted until the point of failure and three bearings with different defects. although outlier detection is a powerful tool for identifying unique data points, several limitations must be considered. for instance, in some cases, there may not be a clear definition of what constitutes an outlier, making it challenging to determine which data points to flag. moreover, outlier detection methods may produce false positives or negatives, leading to incorrect conclusions and recommendations. furthermore, choosing the appropriate outlier detection method for a specific dataset or problem can be complex, and there is no one-size-fits-all solution. additionally, while outlier detection can identify anomalous data points, it may not always address the underlying cause of the outlier or provide a solution to the problem. therefore, to get the most out of outlier detection, careful consideration of the goals and context of the analysis is essential. it is also important to use outlier detection in conjunction with other analytical tools and techniques to gain a more comprehensive understanding of the data and to develop effective solutions that address the root cause of any identified anomalies. several techniques have been suggested to identify the underlying mechanisms of fatigue in eeg signals. among them, one method entails computing distinct types of entropies as feature sets based on a solitary channel [8]. quintero-rincon has presented a straightforward and efficient method for identifying driver fatigue in real-time systems using a single-channel eeg signal [9]. the algorithm selects the most significant channel and extracts four feature parameters to detect fatigue using an ensemble bagged decision trees classifier. by utilising data obtained from the jiangxi university of technology database, the proposed approach achieves an accuracy of 92.7% with a 1.8-second time delay. however, it is important to note that the study evaluated the method on a specific 357 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 dataset, and further research may be needed to determine its effectiveness on other datasets and under different conditions. additionally, the time delay of 1.8 seconds may not be practical for real-time monitoring in some situations, and it is important to consider the potential impact on driver safety if there is a delay in detecting fatigue. in another study, jing et al. aimed to detect driving fatigue in low-voltage and hypoxia plateau environments using subjective and objective monitoring methods [10]. eeg signals from real-time driving tests were subjected to nonlinear and linear analyses to assess the signal trend during awake, critical, and fatigue states. the (α+θ)/β and (α+β)/θ energy features were identified as potential markers of driving fatigue in these environments, providing a basis for the development of a driving fatigue warning system. however, the study was limited to field driving fatigue tests in a specific environment, and further research is needed to validate the findings in other environments and driving conditions. additionally, zhang et al. proposed an innovative approach known as clustering on brain networks (cbns) to improve the performance of driver fatigue detection [11]. the cbns approach employs a clustering algorithm to identify spatial nodes with unique connectivity features from electroencephalogram (eeg) data. the wavelet entropy features obtained from these nodes are then transformed into spatiotemporal images and examined using an image edge detection technique to differentiate between various stages of fatigue. this method reduces signal interference and detects fatigue before the onset of subjective feelings, making it a potentially useful tool for early warning and accident prevention. the research demonstrated the limitations of using eeg indicators in time and frequency domains for reliable detection of driver fatigue due to the challenge of signal mixing and limited sample size, lacking comparison with existing methods and validation in real-world driving scenarios. then, the previous researcher proposed an intelligent system for automated driver fatigue detection utilising eeg signals [12]. this system comprises a feature generation network that utilises texture descriptors and a hybrid feature selection method to enhance detection accuracy. the proposed framework achieved an impressive classification accuracy of 97.29% for detecting fatigue using eeg signals, highlighting its potential for efficient driver fatigue detection. however, the proposed framework used traditional machine learning algorithms, which may limit its ability to adapt to complex and dynamic driving environments. the proposed research introduces a novel approach for efficiently detecting driver fatigue using eeg signals [13]. the method employs a new channel selection algorithm based on correlation coefficients, an ensemble classifier using random subspace k-nearest neighbours (k-nn), and power spectral density (psd) for feature extraction. the approach achieved an impressive accuracy of 99.99% for identifying driver fatigue using eeg signals in a 0.5-second time window. the proposed method demonstrates strong performance and can effectively detect eeg-based driver fatigue. however, due to its high computational complexity, a k-nn-based ensemble classifier may not be suitable for real-time applications. hwang et al. proposed a subject-independent eeg-based driver fatigue state classification model in another study that addresses individual performance gaps [14]. the authors utilised an adversarial training approach to induce the misclassification of subject labels in the classification model. additionally, they incorporated an inter-subject feature distance minimization (ifdm) technique to minimise performance discrepancies between individuals. their method enabled training on eeg datasets with limited, subject labels and was evaluated on the seed-vig dataset, resulting in superior accuracy and decreased individual performance variability when classifying drowsiness. however, one of the major drawbacks is that eeg signals contain large differences between individuals, making it challenging to build a unified model that can perform well for all individuals. 358 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 the studies reviewed propose various methods for detecting driver fatigue using eeg signals, ranging from single-channel feature extraction to more complex machine learning models. one common approach involves using power spectral density and various entropy measures as feature sets, while others utilise clustering algorithms and image edge detection to distinguish different stages of fatigue. several studies also address individual performance gaps and subject variability by employing adversarial training strategies and component-specific batch normalisation. these studies demonstrate the potential of eegbased driver fatigue detection for early warning and accident prevention, achieving high accuracies and providing new possibilities for extracting more information from complex eeg data. however, the methods vary in computational complexity, the number of channels required, and the level of subject independence achieved, suggesting that further research is needed to identify the most efficient and effective approach for practical applications. wilapiprasitporn et al. proposed a deep learning approach that combines cnn and rnn to identify individuals using affective eeg data [15]. their study used the database for emotion analysis using physiological signals (deap) dataset and showed that the proposed method outperforms an svm baseline system with a correct recognition rate (crr) of up to 99.90-100%. recent research suggests that cnn-gru models outperform cnn-lstm models in identifying individuals using eeg data from the brain’s frontal region, and they are effective at countering the impact of affective states. however, the proposed method relies on eeg signals, which may require specialised equipment and data collection and analysis expertise. qin et al. proposed a deep learning model that combines cnn and lstm to extract vein features from raw images for finger-vein biometrics [16]. the proposed model uses supervised encoding to eliminate binary vein texture, resulting in significantly improved verification accuracy when evaluated on a publicly available fingervein database. however, deep learning models are prone to overfitting, learning the training data too well and failing to generalise to new data. techniques such as regularisation and dropout can help prevent overfitting. mondal et al. developed a multitask learning framework using a cnn and a bidirectional long short-term memory (bi-lstm) model to analyse surgical workflows from video data [17]. their framework included a joint distribution loss function for concurrent tool usage during phase identification. the proposed method demonstrated excellent tool and phase identification performance compared to previous approaches when evaluated on the cholec80 dataset. however, the limitation of this study was that it was only evaluated on a single dataset, and it is unclear how well the proposed approach would generalise to other surgical datasets. hu et al. proposed the deep complex convolution recurrent network (dccrn), a network architecture that can handle both cnn and rnn structures and replicate complex-valued operations [18]. in the interspeech 2020 deep noise suppression (dns) challenge, dccrn outperformed previous networks based on objective and subjective metrics and obtained the top rank for the real-time track and the second rank for the non-real-time track based on mean opinion score (mos). the proposed dccrn network with 3.7m parameters proved highly effective in this task. however, the study focused on speech enhancement in clean environments and did not consider noisy or reverberant conditions common in real-world scenarios. researchers proposed a machine learning model that utilised cnn, u-net architecture, rnn, and lstm architecture to create structural topology configurations that fulfilled minimum compliance and deformation criteria under various load conditions and volume fraction limitations. the model was trained using randomly generated finite element simulation data and a strategy to remove elements during training. the model outperformed traditional methods regarding time, cost, and practicality when applied to two-dimensional 359 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 and three-dimensional cantilever-beam structural topology designs. this data-driven approach can speed up preliminary structural design procedures [19]. however, the study’s limitations include the need for training data and the lack of validation on real-world applications. later, other researchers focused on improving solar radiation estimation models in agriculture meteorology due to limited data availability and low data quality [20]. several neural network models (svm, extreme learning machine, cnn, and lstm) were developed and tested in southern spain using different input variable configurations. performance was analysed using various statistical indices. one limitation of this study is that it only focused on using temperature and relative humidity as input variables for solar radiation estimation. other climatic variables that can affect solar radiation, such as atmospheric pressure, cloud cover, and wind speed, which were not included in this study. incorporating these variables could potentially improve the accuracy of solar radiation estimation. the previous works discussed different deep learning approaches for various applications, including affective eeg-based person identification, finger-vein biometrics, surgical workflow analysis, speech enhancement, and structural topology design. the proposed models showed significant accuracy, efficiency, and applicability improvements over previous methods. different deep learning architectures, such as cnns, rnns, and lstm, extracted features from raw data, such as eeg signals, video data, and simulation data. the models were evaluated on different datasets and achieved state-of-the-art results regarding recognition rate, mean average precision, and mean opinion score. additionally, deep learning models were used to improve solar radiation estimation models in agriculture meteorology. in conclusion, an outlier detection is a valuable tool for identifying anomalies in data. however, its limitations must be carefully considered, such as the lack of a clear definition for what constitutes an outlier, the possibility of false positives or false negatives, and the challenge of choosing the appropriate method for a specific dataset or problem. eeg-based driver fatigue detection has shown great potential for early warning and accident prevention using various deep learning methods, achieving high accuracies and extracting more information from complex eeg data. moreover, deep learning has significantly improved accuracy, efficiency, and applicability for various applications, such as affective eeg-based person identification, finger-vein biometrics, surgical workflow analysis, speech enhancement, and structural topology design. further research is needed to identify the most efficient and effective approach for practical applications in outlier detection and deep learning. 3. methodology the research design is structured into four major components, data acquisition, preprocessing, classifiers, and evaluation metrics, as illustrated in fig. 1. the successful implementation of independent component analysis (ica) was critical in enhancing frequency resolution and achieving improved energy conservation results in the proposed study. to eliminate unwanted noises and artefacts, such as muscle movements and eye blinks, ica was employed as a pre-processing step for eeg signals. additionally, ica was utilised to obtain eeg amplitude and correctly position the signal in the appropriate coordinate system for further analysis. the resulting clean eeg signals were then divided into alpha, delta, and theta sub-bands. 360 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 fig. 1: the framework of enhancement of modified z-score. this study [21] employed continuous wavelet transform (cwt) as the preferred technique for time-frequency domain analysis in the feature extraction stage. the morlet wavelet was chosen as the mother wavelet, a combination of a complex sinusoid and a gaussian envelope with a time scale of t and exhibited an inverse relationship between scale and frequency, leading to an increase in frequency as the scale decreased. the researchers then enhanced statistical features using the modified z-score in the feature extraction process to improve the accuracy of the classification process. in the final step, the classification process involved using cnn, rnn, and ann, including lstm, and machine learning methods like svm using a 5-fold cross-validation strategy to distinguish between fatigue and normal states. 3.1 data acquisition the dataset used in this study was obtained from a previous researcher’s online database [22]. the dataset consisted of eeg recordings from 12 healthy male participants (19-24) who completed a driving simulator task for up to 2 hours. eeg data from eight specific channels (o1, o2, fp1, fp2, p3, p4, f3, and f4) were selected from a neuroscan device that had 30 electrodes and operated at a sampling rate of 1000 hz. the study was divided into two phases: a 5-minute normal and a 5-minute fatigued state. fatigue was self-reported by the participants after 40-100 minutes of driving. the zy-31d driving simulator, which features a wide-screen display consisting of three 24-inch screens, was utilised in the study. the driving environment was created using a peking ziguangjiye program zg-601, resulting in a low traffic density scenario. this study’s driver fatigue detection system focused on eeg channel o1, which exhibited the highest correlation among the selected channels. electrodes o1, o2, and fp1 were chosen based on their correlation with fatigue and drowsiness. combining fp1 and fp2 achieved an accuracy of 85% in classifying fatigue driving, which was higher than using fp1 alone (79%) or fp2 alone (68%) [23]. the eeg electrode f4 was chosen for analysis due to its high performance in the classification process. in addition, electrode p4 positively impacted drowsiness and poor driving performance. other electrodes, such as o2, fp2, f3, and p3, were also included for further research. previous studies have used ten eeg channels, including fp1, fp2, f3, and f4, to obtain the best results [24]. according to the study, the electrodes fp1 and p3 were the most effective for driver fatigue detection. interestingly, these electrodes have also been successful in eeg emotion recognition in previous studies. 3.2 pre-processing the purpose of using matlab software is to create programs. raw eeg signals typically contain interference and noise that must be removed before processing. in order to accomplish this, the independent component analysis (ica) method was employed during the pre-processing stage. this method can eliminate unwanted noises and artefacts and 361 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 separate source signals from observed signals, all without prior knowledge of the mixture. the ica mixture model can be represented as a vector matrix. 𝑥 = 𝐴𝑠 (1) matrix a represents the mixing matrix or the linear combination of independent components that contribute to the observed mixed signals in eeg data. each row in matrix a corresponds to a unique independent component, and the columns represent different time points. on the other hand, the observed mixed signals are represented by the rows in matrix s. each row in s corresponds to a specific time point in the eeg data, and the columns represent different electrodes or sensors used to measure the electrical activity in the brain. in essence, matrix a and matrix s represent two views of the same eeg data. matrix a provides information about the underlying independent components contributing to the observed signals, while matrix s includes information about the observed signals at each electrode or sensor. to reduce redundant data in a dataset, a feature extraction technique known as continuous wavelet transform (cwt) creates a time-frequency distribution. in order to identify signs of fatigue, the signal was partitioned into distinct sub-bands, namely alpha (813 hz), delta (0.5-4 hz), and theta (4-8 hz), that are recognised as significant in this regard. the cwt is a highly effective method for these tasks because it has superior computing performance, provided that enough wavelets of analytics are used. the cwt can be defined as: 𝐶𝑊𝑇{ℎ(𝑥)} = 𝑆𝐶𝑊𝑇 (𝑥, 𝜔) = ∫ ℎ(𝜀)𝜓 ∗ ((𝜀 − 𝑥)𝜔)𝑑𝜀 ∞ −∞ (2) the output obtained from this method is a spatially dependent spectral decomposition that exhibits the spectral response for both spatial frequency (ω) and spatial area (x). the cwt output is typically represented as a two-dimensional plot, where the x-axis represents time or position, and the y-axis represents frequency or scale. the plot shows the wavelet coefficients as a function of time and frequency, with higher coefficients indicating more robust signal content at that time and frequency. this plot is often referred to as a spectrogram or a scalogram. the mother wavelet, denoted as ψ, plays a crucial role in the cwt process. it determines the shape and frequency characteristics of the wavelet used in the transformation and serves as the basis for analysing signals in various fields such as engineering, physics, and finance. the choice of the mother wavelet can significantly impact the results of the cwt analysis, as different wavelets are better suited for different types of signals or applications. in addition, the selection of the mother wavelet can also affect the computational efficiency and accuracy of the cwt algorithm. a wide range of mother wavelets are available, each with its unique advantages and disadvantages, and researchers continue to develop new wavelets with improved performance in various applications. as such, the study of mother wavelets remains an active and important area of research in signal processing. in the context of eeg analysis, cwt can be used to analyse the spectral content of neural activity at different spatial locations on the scalp. by applying cwt to eeg data from multiple electrodes, researchers can generate a map of the spectral response for different spatial frequencies and locations, providing insights into the spatial distribution of neural activity at different frequency scales. the paper proposes using a modified z-score to enhance statistical features in the classification process. unlike the traditional z-score, which can be unreliable in the presence 362 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 of outliers, the modified z-score uses the median and median absolute deviation (mad) instead of the mean and standard deviation to detect outliers in a dataset. the modified zscore is less affected by extreme values and is particularly useful for datasets with nonnormal distributions or with extreme values. the formula for calculating the modified zscore is: 𝑀𝑜𝑑𝑖𝑓𝑖𝑒𝑑 𝑧 − 𝑠𝑐𝑜𝑟𝑒 = 𝑘 ∗ (𝑋𝑖 − 𝑀𝑒𝑑𝑖𝑎𝑛)/𝑀𝐴𝐷 (3) where k is the constants, xi is the observation, the median is the median of the dataset, and mad is the median absolute deviation. the constant, k, was modified from 0.6745 to 0.33725 to account for the larger input data spread, making the modified z-score comparable to the z-score for normally distributed data. the larger spread of input data can be accounted for by lowering the value of k. when the value of k is reduced, the range of acceptable data points also decreases. this means that the modified z-score becomes less sensitive to outliers or extreme values, which may be more likely to occur in data with a larger spread. by decreasing the value of k, the modified z-score can be more comparable to the zscore for normally distributed data. this can help ensure the analysis is accurate and reliable, particularly when working with large or complex data sets. then, further improvement of the modified z-scored data is multiplied by a binary mask, which assigns a value of 1 to rows that correspond to the fatigue data and a value of -1 to the rows that correspond to the non-fatigue data. this allows the non-fatigue and fatigue data to be easily separated based on their modified z-scores, with the fatigue data having positive values and the non-fatigue data having negative values. the modified z-score is a statistical technique commonly used to identify dataset outliers. it is more robust than other outlier detection methods because it is less sensitive to extreme values. this is particularly important in data analysis and quality control applications, where outliers can significantly impact the overall analysis or conclusions drawn from the data. the modified z-score is considered a more reliable approach to identifying outliers because it uses the median absolute deviation (mad), a robust measure of variability not affected by extreme values. in contrast, traditional z-score methods use the sample standard deviation, which can be heavily influenced by extreme values and may not accurately represent the variability of the dataset. therefore, the modified z-score is often preferred over other outlier detection methods in situations where robustness and reliability are critical, such as analysing eeg signals for driver fatigue detection. the modified z-score is a powerful tool that enables researchers and analysts to identify and handle outliers more reliably and consistently. using a robust measure of variability not influenced by extreme values, the modified z-score can accurately detect and flag outliers in a dataset. this, in turn, allows analysts to handle outliers more effectively, either by excluding them from the analysis or by applying appropriate statistical techniques to account for them. as a result, using a modified z-score can lead to more accurate and reliable statistical analysis and better-informed decision-making. in addition, the ability to detect outliers reliably and consistently is particularly important in fields where the impact of outliers can be significant, such as in eeg signal analysis for driver fatigue detection. using the modified z-score, researchers and analysts can ensure that their analyses are robust and reliable and that conclusions drawn from the data are based on accurate and representative information. 3.3 classifiers on the other hand, rnns, including lstm, are better suited for sequential data, such as time series data, and have been used for fatigue detection based on physiological signals, 363 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 such as eeg and ecg. these signals provide valuable insights into the driver’s physiological state and can help detect the onset of fatigue before the driver becomes visibly drowsy or sleepy. additionally, anns and svms have been used for fatigue detection based on physiological and behavioural data, such as steering wheel movements, vehicle speed, and lane deviations. overall, the use of machine learning and deep learning methods for fatigue detection shows great promise for improving road safety. these automated systems can provide real-time feedback to drivers and alert them when they are at risk of falling asleep at the wheel, thereby preventing accidents and saving lives. sequential data, like time-series data, is best processed by rnns because they can identify the temporal dependencies between consecutive frames of video or physiological signals. this is particularly important in detecting driver fatigue. meanwhile, ann is a versatile type of neural network that can be utilised for various tasks, such as classification. our study divided the dataset into two subsets for the ann classifier, 80% for training and 20% for testing. ann is often used as a baseline for comparing with other deep-learning models and is an appropriate starting point for developing a fatigue detection system [25]. when dealing with datasets with fewer features, svm is a popular machine learning algorithm that can be used for classification and regression analysis [11]. lastly, lstm is an rnn architecture that solves the problem of vanishing gradients in traditional rnns by enabling the neurons to give feedback on their output as inputs to the next neuron, allowing rnns to identify sequential dependencies between different time steps in a time series. driver fatigue is a significant issue on the road that can lead to accidents and fatalities. automated systems that detect and classify driver fatigue in real time are a potential solution to this problem. deep learning methods like cnn, rnn, and lstm and machine learning methods like ann and svm have shown promise in fatigue detection [26]. these classification algorithms were implemented using python for its ease of use and flexibility. these classifiers were selected based on their suitability for analysing eeg signals and their proven success in related classification tasks. precisely, cnns effectively extract relevant features from multichannel eeg signals, rnns and lstms are well-suited for handling sequential eeg data, and svms are known for their ability to handle high-dimensional data and perform well with limited sample sizes. anns are versatile and widely used types of classifiers that can be applied to a range of data types. we used multiple classifiers to compare their performances on the eeg dataset and evaluate their suitability for driver fatigue classification. 3.4 evaluation metrics we aimed to evaluate the fatigue detection system’s effectiveness using standard metrics typically employed to gauge classifier performance. classification models in machine learning are commonly evaluated using metrics such as accuracy, sensitivity, and specificity. accuracy indicates the model’s ability to classify instances correctly and is calculated by determining the percentage of correctly classified cases. sensitivity evaluates the true positive rate by determining the percentage of actual positives correctly identified by the model. conversely, specificity measures the true negative rate by determining the proportion of real negatives correctly identified by the model. when false positives or negatives may have profound implications, combining sensitivity and specificity can provide a more comprehensive evaluation of the model’s performance. in evaluating the performance of our fatigue detection system, we utilised receiver operating characteristic (roc) curves and area under the curve (auc) in addition to standard metrics. roc curves plot true and false positive rates at varying classification thresholds, providing a comprehensive evaluation of the classifier’s performance, mainly 364 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 when the costs of false positives and negatives are distinct. meanwhile, the auc yields a single value summarising the classifier’s overall performance, with a score of 1 denoting perfect classification and 0.5 indicating random classification. by incorporating these metrics, the system’s performance could be effectively evaluated and areas for improvement identified. in order to increase the reliability of these findings, a 5-fold cross-validation approach was employed. this process randomly partitions the dataset into five equally sized subsets, with four subsets utilised for training and one subset reserved for testing. this procedure was repeated five times, with each subgroup used once as a test set, to ensure each fold received equal representation. each fold’s evaluation metrics were calculated, including accuracy, sensitivity, specificity, roc curves, and auc, to assess the classifier’s performance. by computing these metrics for each fold, the classifier’s performance was evaluated more accurately across the entire dataset. finally, the evaluation metrics were averaged over the five folds for a final classifier performance estimate. to compare the performance of various classifiers, the wilcoxon signed-rank test was utilised; this non-parametric statistical test compares paired data sets to determine if there is a significant difference between them. the aim was to compare the performance of different classifiers on the same dataset, considering a statistically significant difference if the p-value was less than 0.05, using a significance level of 0.05. the wilcoxon signed-rank test was combined with a cross-validation strategy to obtain unbiased and dependable results, allowing the evaluation and comparison of different classifiers’ performance objectively. 4. results and discussion this study analysed the patterns of brainwave activity in a group of participants using electroencephalography (eeg). specifically, the focus was on the alpha (8-13 hz), delta (0.5-4 hz), and theta (4-8 hz) frequency bands, which have been linked to different cognitive and emotional processes. the data were analysed using statistical and visualisation techniques, including box and scatter plots. the results revealed the presence of outliers in the data, which are data points that fall far outside the expected range and can significantly impact the overall pattern of results. these outliers were particularly evident in the alpha and delta frequency bands, with fewer outliers observed in the theta band. outliers are data points that fall far outside the expected range and can significantly impact the overall pattern of results when analysing a data set. one approach to identifying outliers is to use z-scores or modified z-scores, which are measures of how many standard deviations a given data point is away from the mean of the dataset. by plotting these scores visually, it is possible to detect outliers in a dataset and evaluate their impact on the overall data pattern. this method allows the identification of the magnitude of the outliers and assesses their potential influence on the analysis. figures 2 and 3 illustrate the distribution of data points, where the blue dots correspond to data points that fall within the expected range, and the red dots represent data points that fall outside the expected range and are considered outliers. in addition to the potential impact of outliers on statistical analyses, it is important to note that outliers can also affect the interpretation and generalisation of research findings. outliers can lead to overestimation or underestimation of effect sizes, which can have significant implications for the practical significance of research results. thus, appropriate identification and treatment of outliers 365 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 are essential to ensure research findings’ integrity and applicability to the broader population or context of interest. fig. 2: identification of outliers in z-score data. fig. 3: identification of outliers in modified z-score data. in fig. 4, the proposed method enhancing modified z-scores was influential in ensuring that all data points fell within the expected range, indicating that it successfully addressed the issue of outliers and improved the overall data quality. the method effectively managed and adjusted the data points to achieve the desired outcome without reducing any data classified as outliers during the process. this study evaluated the performance of five popular machine learning models, rnn, cnn, ann, svm, and lstm, to determine the most effective classification task. 366 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 fig. 4: identification of outliers in the enhancement of modified z-score data. the z-score is a method of standardisation that involves subtracting the mean from the data and dividing it by the standard deviation. however, datasets that include outliers, such as driver fatigue detection, may not be well-suited for this method. the mzs process uses the median and median absolute deviation instead of the mean and standard deviation to standardise the data. the mzs is more robust to outliers and has been used in several studies for driver fatigue detection. in this study, we further enhanced the mzs, the so-called enhancement of modified z-score (emzs), by applying a scaling factor to adjust the sensitivity and specificity of the classifier. this enhancement resulted in the highest accuracy among the five classifiers tested: rnn, cnn, ann, svm, and lstm. table 1: classification results using z-score, modified z-score (mzs), and enhancement of modified z-score (emzs) classifier accuracy (%) sensitivity (%) specificity (%) z-score mzs emzs z-score mzs emzs z-score mzs emzs rnn 61.69 61.16 93.85 0.00 0.00 84.20 100.00 100.00 100.00 cnn 63.16 64.74 97.19 n/a n/a 95.68 63.16 66.21 100.00 ann 63.09 64.15 99.65 88.04 84.17 99.48 23.02 32.85 100.00 svm 61.69 61.16 97.89 0.00 0.00 96.62 100.00 100.00 100.00 lstm 63.16 64.91 93.86 n/a n/a 100.00 63.16 64.91 91.36 based on the results in table 1, the ann performed the best among the five classifiers tested. the ann demonstrated higher accuracy and specificity than the other classifiers, with values of 99.65% and 100.00%, respectively. however, its sensitivity value of 99.48% was slightly lower than that of different classifiers. nonetheless, the results indicate that the ann was still proficient at detecting driver fatigue. this result outperformed the accuracy of 96% and sensitivity of 94% reported by a previous researcher in the field [27]. therefore, our study demonstrates the effectiveness of the proposed approach for accurate driver fatigue detection. the sensitivity of the classifier cnn and lstm were not applicable (n/a) in this study due to the absence of negative instances in the test set. as a result, the denominator of the sensitivity calculation was zero, and the sensitivity value was undefined. 367 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 however, the high precision and specificity values achieved by the classifier suggest that it effectively identifies positive instances. implementing the enhanced, modified z-score approach resulted in an accuracy improvement of over 30.00% compared to the traditional modified z-score method. the svm accuracy result, 97.89%, indicates high accuracy compared to the previous researcher, who used the same machine learning with eight electrode channels [13]. according to the results, the proposed enhanced, modified z-score method was found to be more efficient than the traditional modified z-score approach in identifying driver fatigue from eeg signals. the accuracy of the improved process was significantly better than the conventional method, as indicated by the study’s findings. the proposed approach effectively minimises false positives and negatives, which is critical for detecting driver fatigue with high precision. notably, the accuracy results obtained through the proposed method were competitive with the findings of similar studies that used eeg signals for driver fatigue detection. furthermore, the proposed framework’s multi-classifier approach could be used to improve the detection of other physiological signals related to driver fatigue, such as eye movements and heart rate variability. roc curves were utilised to plot and evaluate the performance of each classifier to establish the ideal threshold for classification. the results indicated that the cnn and ann classifiers exhibited the highest true positive and lowest false positive rates, suggesting they could accurately distinguish between normal and fatigued states. additionally, the svm classifier displayed a high true positive rate and a low false positive rate, indicating its effectiveness in classifying driver fatigue. fig. 5: performance evaluation of rnn using roc curve. in contrast, the lstm and rnn classifiers had slightly lower true positive rates and higher false positive rates than the other classifiers. this suggests that they were less effective in accurately classifying driver fatigue. despite these limitations, the lstm and rnn classifiers still represent promising approaches to detecting driver fatigue and should be further investigated to determine if their performance can be improved. the findings suggest that the cnn and ann classifiers and the svm classifier have significant potential for accurately detecting driver fatigue from eeg signals. these results have important implications for reducing the risks associated with drowsy driving and improving overall road safety. 368 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 fig. 6: performance evaluation of cnn using roc curve. fig. 7: performance evaluation of ann using roc curve. fig. 8: performance evaluation of svm using roc curve. 369 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 the study’s findings indicate that the enhanced modified z-score approach proposed, combined with multiple classifiers, was exceedingly influential in detecting driver fatigue from eeg signals with high accuracy. in particular, the ann classifier outperformed the other classifiers, exhibiting the highest accuracy and specificity. on the other hand, the cnn and lstm classifiers achieved perfect classification with the highest area under the curve (auc) values. the ann classifier is particularly well-suited for detecting driver fatigue from eeg signals due to its capacity to learn complex nonlinear relationships between input and output variables, flexibility in handling vast amounts of data, and ability to adapt to changing input patterns over time. therefore, the ann classifier represents a promising approach to accurately detecting driver fatigue and mitigating the risks associated with drowsy driving. ann classifier has several benefits but has limitations, such as the need for high-quality input data, significant training data, and customisation to specific contexts. despite these challenges, the ann classifier remains a promising approach for accurately detecting driver fatigue. fig. 9: performance evaluation of lstm using roc curve. artificial neural networks (anns) are inspired by the structure and function of the human brain, consisting of interconnected nodes that process information and transmit signals. by adjusting the weights between nodes based on training data, anns can learn to identify complex patterns and make highly accurate predictions. in the case of detecting driver fatigue from eeg signals, anns can analyse the intricate patterns of brainwave activity associated with fatigue and accurately distinguish them from normal brainwave patterns. the proposed approach has exhibited significant improvements in accuracy as compared to the traditional modified z-score method, which is an important development in the field of driver fatigue detection. moreover, the multi-classifier approach has shown potential in detecting other physiological signals related to driver fatigue, thereby enhancing the overall reliability of driver fatigue detection systems. these findings could have farreaching implications in ensuring road safety by enabling the development of more accurate and reliable driver fatigue detection systems. 5. conclusion in conclusion, the proposed framework for driver fatigue detection using enhancement of modified z-score and multiple machine learning architectures was highly influential in accurately detecting driver fatigue from eeg signals. our study demonstrated that the 370 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 framework achieved high accuracy for all classifiers, with the ann achieving the highest accuracy of 99.65%. the svm and cnn also achieved high accuracy, with 97.89% and 97.19%, respectively. although the rnn and lstm achieved slightly lower accuracy, they still achieved over 90.00% accuracy. our study’s contribution lies in presenting a comprehensive and effective framework that can accurately detect driver fatigue from eeg signals, surpassing the performance of previous approaches. furthermore, the proposed framework can potentially be applied to practical driver fatigue detection systems, improving driving safety and reducing the number of road accidents caused by driver fatigue. future research could build on this framework by investigating its performance in real-world settings and exploring ways to improve its sensitivity to subtle changes in eeg signals. references [1] gao z, wang x, yang y, mu c, cai q, dang w, zuo s. (2019) eeg-based spatio-temporal convolutional neural network for driver fatigue evaluation. ieee transactions on neural networks and learning systems, 30(9): 2755-2763. https://doi.org/10.1109/tnnls.2018.2886414 [2] mehreen a, anwar sm, haseeb m, majid m, ullah mo. (2019) a hybrid scheme for drowsiness detection using wearable sensors. ieee sensors journal, 19(13): 5119-5126. https://doi.org/10.1109/jsen.2019.2904222 [3] hasan mj, shon d, im k, choi hk, yoo ds, kim jm. (2020) sleep state classification using power spectral density and residual neural network with multichannel eeg signals. applied sciences (switzerland), 10(21): 1-13. https://doi.org/10.3390/app10217639 [4] cohen mx. (2019) a better way to define and describe morlet wavelets for time-frequency analysis. neuroimage, 199: 81-86. https://doi.org/10.1016/j.neuroimage.2019.05.048 [5] aggarwal v, gupta v, singh p, sharma k, sharma n. (2019) detection of spatial outlier by using improved z-score test. in 2019 3rd international conference on trends in electronics and informatics (icoei) (pp. 788-790). tirunelveli, india. doi: 10.1109/icoei.2019.8862582. [6] sandbhor s, chaphalkar nb. (2019) impact of outlier detection on neural networks based property value prediction. in: satapathy, s., bhateja, v., somanah, r., yang, xs., senkerik, r. (eds) information systems design and intelligent applications. advances in intelligent systems and computing, vol 862. springer, singapore. https://doi.org/10.1007/978-981-133329-3_45 [7] leite gnp, araújo am, rosas pac, stosic t, stosic b. (2019) entropy measures for early detection of bearing faults. physica a: statistical mechanics and its applications, 514: 458472. https://doi.org/10.1016/j.physa.2018.09.052 [8] hosseini m-p, hosseini a, ahi k. (2021) a review on machine learning for eeg signal processing in bioengineering. ieee reviews in biomedical engineering, 14: 204-218. https://doi.org/10.1109/rbme.2020.2969915 [9] quintero-rincon a, fontecha me, d’giano c. (2019) driver fatigue eeg signals detection by using robust univariate analysis. retrieved from http://arxiv.org/abs/1912.13351 [10] jing d, liu d, zhang s, guo z. (2020) fatigue driving detection method based on eeg analysis in low-voltage and hypoxia plateau environment. international journal of transportation science and technology, 9(4): 366-376. https://doi.org/10.1016/j.ijtst.2020.03.008 [11] zhang c, sun l, cong f, kujala t, ristaniemi t, parviainen t. (2020) optimal imaging of multichannel eeg features based on a novel clustering technique for driver fatigue detection. biomedical signal processing and control, 62: 102103. https://doi.org/10.1016/j.bspc.2020.102103 [12] tuncer t, dogan s, ertam f, subasi a. (2021) a dynamic center and multi threshold point based stable feature extraction network for driver fatigue detection utilising eeg signals. cognitive neurodynamics, 15(2): 223-237. https://doi.org/10.1007/s11571-020-09601-w 371 https://doi.org/10.1109/tnnls.2018.2886414 https://doi.org/10.1109/jsen.2019.2904222 https://doi.org/10.3390/app10217639 https://doi.org/10.1016/j.neuroimage.2019.05.048 https://doi.org/10.1016/j.ijtst.2020.03.008 https://doi.org/10.1016/j.bspc.2020.102103 iium engineering journal, vol. 24, no. 2, 2023 abdubrani et al. https://doi.org/10.31436/iiumej.v24i2.2799 [13] rashid m, mustafa m, sulaiman n, abdullah nrh, samad r. (2021) random subspace knn based ensemble classifier for driver fatigue detection utilising selected eeg channels. traitement du signal, 38(5): 1259-1270. https://doi.org/10.18280/ts.380501 [14] hwang s, park s, kim d, lee j, byun h. (2021) mitigating inter-subject brain signal variability for eeg-based driver fatigue state classification. icassp 2021 2021 ieee international conference on acoustics, speech and signal processing (icassp), 990-994. https://doi.org/10.1109/icassp39728.2021.9414613 [15] wilaiprasitporn t, ditthapron a, matchaparn k, tongbuasirilai t, banluesombatkul n, chuangsuwanich e. (2020) affective eeg-based person identification using the deep learning approach. ieee transactions on cognitive and developmental systems, 12(3): 486496. https://doi.org/10.1109/tcds.2019.2924648 [16] qin h, wang p. (2019) finger-vein verification based on lstm recurrent neural networks. applied sciences (switzerland), 9(8): 1-18. https://doi.org/10.3390/app9081687 [17] mondal ss, sathish r, sheet d. (2019) multitask learning of temporal connectionism in convolutional networks using a joint distribution loss function to simultaneously identify tools and phase in surgical videos. 1–15. retrieved from http://arxiv.org/abs/1905.08315 [18] hu y, liu y, lv s, xing m, zhang s, fu y, … xie l. (2020). dccrn: deep complex convolution recurrent network for phase-aware speech enhancement. proceedings of the annual conference of the international speech communication association, interspeech, 2020-octob, 2472-2476. https://doi.org/10.21437/interspeech.2020-2537 [19] qiu c, du s, yang j. (2021) a deep learning approach for efficient topology optimisation based on the element removal strategy. materials and design, 212: 110179. https://doi.org/10.1016/j.matdes.2021.110179 [20] bellido-jiménez ja, estévez j, garcía-marín ap. (2021) assessing neural network approaches for solar radiation estimates using limited climatic data in the mediterranean sea. 19. https://doi.org/10.3390/ecas2020-08116 [21] abdubrani r, mustafa m, zahari zl. (2023) enhancement of morlet mother wavelet in time– frequency domain in electroencephalogram (eeg) signals for driver fatigue classification . in: , et al. advances in intelligent manufacturing and mechatronics. lecture notes in electrical engineering, vol 988. springer, singapore. https://doi.org/10.1007/978-981-19-8703-8_13 [22] kamti mk, iqbal r. (2022) evolution of driver fatigue detection techniques – a review from 2007 to 2021. transportation research record, 2676(12): 485-507. https://doi.org/10.1177/03611981221096118 [23] luo h, qiu t, liu c, huang p. (2019) research on fatigue driving detection using forehead eeg based on adaptive multi-scale entropy. biomedical signal processing and control, 51: 5058. https://doi.org/10.1016/j.bspc.2019.02.005 [24] islam mr, ahmad m. (2019) wavelet analysis based classification of emotion from eeg signal. 2nd international conference on electrical, computer and communication engineering, ecce 2019, 1-6. https://doi.org/10.1109/ecace.2019.8679156 [25] xie y, oniga s. (2020) a view of processing methods and classification algorithm for eeg signal. carpathian journal of electronic and computer engineering, 13(1): 23-29. https://doi.org/10.2478/cjece-2020-0004 [26] sarkar a, singh a, chakraborty r. (2022) a deep learning-based comparative study to track mental depression from eeg data. neuroscience informatics, 2(4): 100039. https://doi.org/10.1016/j.neuri.2022.100039 [27] parekh v, shah d, shah m. (2020) fatigue detection using artificial intelligence framework. augment hum res 5: 5. https://doi.org/10.1007/s41133-019-0023-4 372 https://doi.org/10.1109/icassp39728.2021.9414613 https://doi.org/10.1109/tcds.2019.2924648 http://arxiv.org/abs/1905.08315 https://doi.org/10.1016/j.matdes.2021.110179 https://doi.org/10.1109/ecace.2019.8679156 microsoft word book review1.doc iium engineering journal, vol. 3, no 1, 2002 h. malik 43 book review: materials science and engineering -an introduction by william d. callister sixth edition, wiley international, 2003. for a number of decades, materials science and engineering an introduction, has been an essential and trusted source of literature, as an introduction to materials science and engineering. now revised and updated the sixth edition is now available. this latest edition blends important traditional materials engineering subjects coupled with modern technologies, techniques and practices. the book’s 820 pages contains information divided into chapters on introduction, atomic structure and inter-atomic bonding, structure of crystalline solids, imperfection in solids, diffusion, mechanical properties of metals, dislocation and strengthening mechanisms, failure, phase diagrams, phase transformations in metals, application and processing of metal alloys, structure and properties of ceramics, application and processing of ceramics, polymer structures, characterization application and processing of polymers, composites, corrosion and degradation of materials, electrical properties, thermal properties, magnetic properties, optical properties, economic environmental and social issues in materials science and engineering. the first chapter provides a useful introduction to the student in terms of history, the importance of the subject, development of advanced materials and future trends. many of the chapters that follow deal, with the fundamental aspects of materials engineering on the atomic, microscopic and macroscopic scale. the concept of electronic structure and the various types of bonding in solids is covered, along with the specification of planes and directions within the perfect crystal. in reality however crystals are not perfect so their defects are explained through the presence of vacancies and dislocations. these ideas are further developed and employed to explain the mechanical behavior of metals, how dislocations are involved in particular slip systems in given lattice types and the benefit of dislocations and grain boundaries in helping to increase the strengthen of metals and alloys. a macroscopic/microscopic examination is given on how to recognize ductile and brittle fracture and fracture due to fatigue. adequately covered by the author is the value of understanding and interpreting a phase diagram with reference to the cooling of alloys under equilibrium conditions, the development of the microstructure and the determination of phase composition and amount of each phase. coupled to this quenching and cooling in an isothermal environment is mentioned and how it leads to the formation of matensitic, bainitic and pearlitic microstructures, as well as the industrial cold working and annealing of ferrous and non ferrous alloys. the hardening of material is detailed through diffusion and the applications of fick’s laws. the information given on polymers considers the structure of polymer molecules, polymerization, mechanical behavior, fabrication and their processing. this leads well into the next section which looks at the way in which different materials previously studied can be combined to form composites such as metal matrix composite, polymer matrix composites, ceramic matrix composites, carbon carbon composites and hybrid composites. with the basic foundations now developed the next chapters talk about the degradation of the materials analyzed and their electrical, magnetic, optical and thermal properties. the degradation mainly involves the fundamental aspects of corrosion theory, the various types of corrosion, passivity, protection methods and high temperature oxidation.. electrical properties are considered in terms of bonding and how materials such as silicon and germanium can be doped to make n and p type semiconductors. electronic structure is again used to explain the magnetic aspects of material behavior. although the book possesses many examples as well as questions with answers, the sixth also includes a free cd-rom, which plays a prominent role in appreciating, understanding and visualizing various concepts towards the understanding of material behavior. although the book is packed with all the important diagrams and features the cd gives the reader the opportunity not only to browse the text but also to have a fair degree of computer interaction with the subject. interactive play allows the student to grasp the main ideas related to directions and planes in a crystals, edge and screw dislocations, motion of dislocations, practical construction of stress/strain diagrams, phase diagrams, diffusion, geometry of polymers and structure of ceramics. the cd in addition to the book contains a myriad of data related to crystals, metals and alloys. detailed solutions to selected problems are also provided in the cd. the design of the questions is extremely good as it requires the student to collect information needed to answer the question and analysis of diagrams. hassan malik dept of mechanical engineering faculty of engineering, iium hassanmalik@iiu.edu.my microsoft word vol 6-2p3v2-press.doc iium engineering journal, vol. 6, no. 2, 2005 k. rahman and s. j. m. idrus 27 an at89c52 microcontroller based high resolution pwm controller for 3-phase voltage source inverters k. m. rahman and s. j. m. idrus department of mechatronics engineering faculty of engineering, international islamic university malaysia, p.o. box 10, 50728, malaysia kazi@iiu.edu.my, junita@iiu.edu.my abstract: a novel technique for generating real time high resolution pulse width modulated patterns for a three phase voltage source inverter is presented in this paper. an at89c52 microcontroller computes the pwm pulse widths on carrier cycle basis based on the input frequency. the microcontroller send the pulse width information for the three phases to a memory minimized rom lookup table, which is scanned by a binary counter to generate the real time pwm patterns. the on board timer of at89c52 is utilized to generate programmed clock for the scanning binary counter. the overall design is hardware minimized and compact that makes it feasible for low cost high performance ac drive applications. the proposed pwm controller supports variable frequency variable voltage operation for wide range and hence is ideally suited for industrial drives requiring wide speed variations. keywords: pulse width modulation, microcontroller application, voltage source inverter, variable speed ac drives. 1. introduction three phase voltage source inverters are controlled by pulse width modulation (pwm) techniques. the prime goal of a pwm technique is to minimize the harmonics in the phase voltage and phase current spectrum. different pwm strategies are available in the literature for controlling three phase inverters using per phase modulation such as regular sampled pwm (rspwm) or voltage space vector (svpwm) technique. both rspwm [1-4] and svpwm [5-6] have well defined switching equations for computing pwm pulse widths and are usually implemented using timers and a microprocessor. the svpwm needs more computations than the rspwm, however, svpwm have linear over modulation capability. harmonic elimination pwm (hepwm) is another technique that computes switching points strategically eliminating some selective harmonics and is the most computation intensive pwm technique that cannot be implemented directly in real time. switching patterns close to hepwm are obtainable using regular sampled harmonic elimination pwm (rshepwm), where, the leading edge of a pwm switching pulse for any phase is calculated from the sine modulating reference and the trailing edge is computed from a shifted sine reference [7-8]. considering harmonic behaviour, the rspwm is the most efficient pwm technique for feed forward inverter control iium engineering journal, vol. 6, no. 2, 2005 k. rahman and s. j. m. idrus 28 applications. the rspwm is one of the mostly used pwm techniques and have a number of derivatives. the symmetric time averaged rspwm [9] is very efficient in respect of both performance and speed. the performance of a pwm scheme depends on how the pwm control patterns are calculated and also on the implementation strategy. even the most efficient pwm technique may offer worst performance if the resolution of the pwm pattern is not maintained properly. this happens because of the limitations of the digital hardware through which the pwm strategy is implemented in real time. 2. pulse width calculations the pwm pulse widths are to be calculated such that the inverter output has the lowest order harmonic near the carrier switching frequency. amongst the various pwm strategies, the regular sampled pwm is found to give better output at lesser computation complexity. 2.1 regular sampled pwm the modulating signal is a sinusoid at the inverter fundamental frequency (f). the modulating signal is sampled at regular intervals at the carrier frequency (fs). the number of samples in a fundamental period is nmax given by, f fn smax (1) the three phase modulating signals are, )3/4sin( )3/2sin( )sin(       tvv tvv tvv mc mb ma (2) fig. 1: pulse width calculations for two-level pwm, the area under the modulating signal for nth carrier period is equated to be same as the area of the two-level pwm pulse. for the nth pwm pulse, the area of the two-level pwm pulse should be equal to the shaded area under the modulating signal as illustrated in fig. 1, +vs/2 0 -vs/2 nts twa(n) ts va = vm sin(t) iium engineering journal, vol. 6, no. 2, 2005 k. rahman and s. j. m. idrus 29   ssmwasswas ttnvntt v nt v  )sin()( 2 )( 2  (3) solving (3), the pwm pulse width is given by,        )sin( 2 1 2 )( s s ms wa tnv vt nt  (4)  )sin(1 2 )( s s wa tnm t nt  (5) where, m is the index of modulation, m = 2vm/vs. equation (5) gives the pwm pulse width for phase a. for phases b and c, the pwm pulse widths are,  )3/2sin(1 2 )(   s s wb tnm t nt (6)  )3/4sin(1 2 )(   s s wc tnm t nt (7) adding (5), (6) and (7) results, 2 3 )()()( swcwbwa t ntntnt  (8) from (8), the pwm pulse width for phase c can be obtained as,  )()( 2 3 )( ntnt t nt wbwa s wc  (9) 2.2 pwm pulse width in sampled domain for generating real time pwm waveforms for the three phase inverter using a digital hardware, the pwm pulse widths are transformed into sampled domain. considering kmax samples in a carrier period ts, the sampling time ts is given by, maxk tt ss  (10) if ka(n), kb(n), and kc(n) are the numbers of ‘high’ samples for the phases a, b, and c respectively in sampled domain, their magnitudes are given by, )sin( 22 )( )( maxmax s s wa a tnm kk t nt nk    (11) )3/2sin( 22 )( )( maxmax     s s wb b tnm kk t nt nk (12)  )()( 2 3)( )( max nknk k t nt nk ba s wc c   (13) 3. implementation scheme the pwm implementation scheme is shown in fig. 2. the core processor is an at89c52 microcontroller, where, the desired frequency/speed is set by an analogue potentiometer. an 8-bit adc (adc0804) converts the frequency/speed setting into digital binary code that is given as input to port 2 of at89c52. iium engineering journal, vol. 6, no. 2, 2005 k. rahman and s. j. m. idrus 30 fig. 2. an at89c52 microcontroller based scheme for three-phase pwm pattern generation using three rom lookup tables and a scan counter. the microcontroller calculates the scan clock frequency and sets the corresponding rcap2l and rcap2h values for the onboard timer 2. the timer 2 of at89c52 is configured in clock generator mode that gives the programmed clock output at p1.1. the scan counter is clocked from p1.1 and the ripple carry out from the scan counter is made to interrupt the microcontroller after every 256 counts that correspond to the total number samples in a carrier period. the pwm waveform pattern samples are sent to rom lookup tables through port p0. the pwm patterns for three phases are sent through the same port p0 using multiplexing and latch principle. for each phase there is a set of latch and rom lookup table, so that they can generate the pwm patterns independently. 3.1 frequency setting the fundamental frequency of the pwm output patterns are dependent on the microcontroller clock frequency (fcpu), counter clock frequency (fclk) and the number of carrier pulses per fundamental cycle (nmax). since the counter clock (fclk) is derived from the microcontroller clock frequency (fcpu) by a divide by counter (timer 2 of the microcontroller), the output frequency (f) is given by 256 1 max clkf n f  (14) at89c52 8-bit binary counterclock latch 1 latch 3 latch 2 8 select 1 p1.0 p0 select 2 select 3 interrupt g 1 g4 g 3 g 6 g 5 g 2 scan pulse width pulse width scan pulse width scan ripple carry output p1.2 p1.3 p1.4 p1.5 8 8-bit adc +5v pot frequency p2 rom enable p1.6 +5v start/stop p1.7 r iium engineering journal, vol. 6, no. 2, 2005 k. rahman and s. j. m. idrus 31 divn65536 1 4   cpuclk f f (15) combining (1) and (2), the divn value is given by max1024 65536divn fn f cpu (16)        256 divn rcap2h floor (17) rcap2h-divn rcap2l  (18) 3.2 integer arithmetic models for pwm patterns the microcontroller does not have floating point computation support. hence, it can not compute sine functions directly. rather, it has to be calculated using tailor series expansion method that require huge computation time. to reduce the computation complexity, (11) and (12) are simplified having only integer manipulations. )( 2 2 )( 22/2 )( 2 )sin( 22 )( max max max max maxmaxmaxmax ns k mk ns k k mk nms k tn k m k nk a tag aasa          (19) where, )sin( 2 )( max sa tn k ns  and 2 maxkmm tag  . for phase b, )( 2 2 )( max max ns k mk nk b tag b  (20) where, )3/2sin( 2 )( max   sb tn k ns and 2 maxkmm tag  . the values of sa(n) and sb(n) are computed off line, rounded to integer numbers and stored in lookup table inside the program code of the at89c52. the mtag value is chosen from the adc output that is always an integer. hence, the computations of ka(n), kb(n) using (19) and (20) involves only integer arithmetic that can be done efficiently with at89c52 in real time. 3.3 real time pwm pattern generation pwm patterns having 256 different duties are stored in the pwm roms as a lookup table. the microcontroller computes the pwm patterns on carrier cycle basis and the real time pwm patterns are generated in the rom data bus using the following algorithm: algorithm for pwm pattern generation step 1. set p1.5 = 1 to disable the pwm roms. step 2. initialize n = 1. step 3. read p2 and set ftag = p2. step 4. choose nmax and fclock, set rcap2l and rcap2h. step 5. compute ka(n), kb(n) and kc(n). step 6. set p0 = ka(n) and p1.2 = 0 (ka(n) data to latch 1). iium engineering journal, vol. 6, no. 2, 2005 k. rahman and s. j. m. idrus 32 step 7. set p0 = kb(n) and p1.3 = 0 (kb(n) data to latch 2). step 8. set p0 = kc(n) and p1.4 = 0 (kc(n) data to latch 3). step 9. wait for interrupt at p1.6 and goto step 10 if interrupt occurs, otherwise loop to step 10. enable the data roms by setting p1.5 = 0. step 11. read the shut down status at p1.7. step 12. if p1.7 = 0, disable the data roms (set p1.5 = 1) and goto step 16, else goto step . step 13. increment n, n = n+1. step 14. if n>nmax, set n = 1. step 15. goto step 3. step 16. halt operation. 3.4 performance simulation the performances of the proposed pwm scheme are studied through simulation with a three phase voltage source inverter. the inverter is shown in fig. 3 and drives a star connected inductive load with insulated neutral. the switching functions for phases a, b and c are sa, sb and sc respectively. the switching function and associated transistor status are shown in table 1. each switching function has two level statuses; either +1 or 1, where, +1 drives the top transistor and -1 drives the bottom transistor of a leg of the inverter. fig. 3: three phase voltage source inverter connected to star connected r-l load with insulated neutral (sa, sb and sc are two level switching functions having magnitudes +1 and -1, for driving the associate top and bottom transistors in a leg). the pwm switching patterns for three phases and inverter output phase voltages are shown in fig. 4 for supply voltage vs = 600v (1 pu), modulation index m = 1 at f = 50 hz, and carrier frequency fs = 1.2 khz. the corresponding fourier frequency spectrum of the pwm switching function (sa) and line to neutral (phase) voltage van are shown in fig. 5. the noticeable point is that although the fundamental frequency amplitude in sa is 1 pu (equal to m), the fundamental phase voltage output is 0.5 pu, that confirms the analysis described earlier. the inverter output currents (three phases) and fourier frequency spectrum are shown in fig. 6 for an r-l load of 10 ohms at 0.8 pf lagging. due to low vcn vbn van n a c b q5 q2 q3 q6 q1 q4 ic ib ia + vs r l r l r l sa sb sc iium engineering journal, vol. 6, no. 2, 2005 k. rahman and s. j. m. idrus 33 pass action in the output current, the harmonics die out in the current spectrum (fig. 6) although they are noticeable in the phase voltage spectrum (fig. 5). table 1: switching functions and transistor operating status for the three phase voltage source inverter. switching function switching status transistor status sa (leg a) +1 q1 = on q4 = off -1 q1 = off q4 = on sb (leg b) +1 q3 = on q6 = off -1 q3 = off q6 = on sc (leg c) +1 q5 = on q2 = off -1 q5 = off q2 = on 0 0.005 0.01 0.015 0.02 -1 0 1 time (s) s a (p u) 0 0.005 0.01 0.015 0.02 -1 0 1 time (s) s b (p u) 0 0.005 0.01 0.015 0.02 -1 0 1 time (s) s c (p u) 0 0.005 0.01 0.015 0.02 -1 0 1 time (s) v a (p u) 0 0.005 0.01 0.015 0.02 -1 0 1 time (s) v b (p u) 0 0.005 0.01 0.015 0.02 -1 0 1 time (s) v c ( pu ) fig. 4: pwm switching patterns at f = 50 hz, fs = 1.2 khz, m = 1 for the three phase legs of the inverter and the phase voltages for star connected load with insulated neutral. iium engineering journal, vol. 6, no. 2, 2005 k. rahman and s. j. m. idrus 34 0 10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1 (a) frequency (xf) s a (p u) 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 frequency (xf) v a ( pu ) (b) fig. 5: voltage spectrum of (a) switching function sa and (b) the corresponding phase voltage va for the three phase inverter. 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 -20 0 20 time (s) c ur re nt (a ) (a) 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 frequency (xf) m ag ni tu de i a (a ) (b) fig. 6: inverter output currents (three phases, a, b and c) and fourier frequency spectrum at f = 50 hz, m = 1, fs = 1.2 khz, vs = 600v, z = 10 ohm at 0.8 pf lagging. iium engineering journal, vol. 6, no. 2, 2005 k. rahman and s. j. m. idrus 35 4. conclusions a simplified technique of implementing regular sampled sine pwm is presented. the simplification involves integer arithmetic only that can be implemented with a low cost microcontroller at moderate speed. the simulation results show no deterioration in performance, although computations are all transformed from floating point into integer arithmetic. the hardware implementation scheme is compact, employing a memory minimized real time pwm pattern generator having less burden on the microcontroller. due to low cost and high performance operating characteristics, the proposed pwm scheme is suitable for household, commercial and industrial applications for efficient control of voltage source inverters. references [1] k. m. rahman and m. quamruzzaman, “a new hybrid pwm scheme for voltage source inverters,” in proc. icece 2002, dhaka, bangladesh, pp. 332-335, 26-28 december 2002. [2] s. r. bowes, “novel real-time harmonic minimized pwm control for drives and static power converters,” ieee trans. power electron., vol. 9, no. 3, pp. 256-262, may 1994. [3] s. r. bowes, “advanced regular sampled pwm control techniques for drives and static power converters,” ieee trans. ind. electron., vol. 42, no. 4, pp. 367-373, august 1995. [4] s. r. bowes, “regular sampled harmonic elimination pwm control of inverter drives,” ieee trans. power electron., vol. 10, no. 5, pp. 521-531, september 1995. [5] k. m. rahman, “pc controlled look-up table based pwm scheme for voltage source inverters and ac drives,” in proc. iccit 99, dhaka, bangladesh, pp. 84-88, 3-5 december 1999. [6] k. m. rahman, “pc based regular sampled pulse width modulator for inverters and drives,” in proc. iccit 99, dhaka, bangladesh, pp. 89-93, 3-5 december 1999. [7] k. m. rahman, “analysis and implementation of pc based space vector pwm controller for vsi inverters and ac drives,” in proc. iccit 2000, dhaka, bangladesh, pp. 49-54, 25-26 january 2001. [8] k. m. rahman, k. m. z. shams and a. h. m. z. alam, “fpga implementation of space vector pwm controller for three phase voltage source inverters,” in proc. iccit 2001, dhaka, bangladesh, pp. 154159, 28-29 december 2001. [9] s. r. bowes and s. s. grewal, “novel space-vector harmonic elimination inverter control,” ieee trans. ind. applicat., vol. 36, no. 2, pp. 549-557, march 2000. [10] y. s. lai and s. r. bowes, “a new suboptimal pulse-width modulation technique for per-phase modulation and space vector modulation,” ieee trans. energy convert., vol. 12, no. 4, pp. 310-316, december 1997. iium engineering journal, vol. 16, no. 1, 2015 hossain and kurny 1 studies on the effect of artificial ageing hardness on tensile properties and impact strength of al-6si-0.5mg-2ni alloy abulhossain and abu syedwais kurny department of materials and metallurgical engineering, bangladesh university of engineering and technology, dhaka-1000, bangladesh. ah_buetmmesgfl@live.com (received 5 april 2014; accepted 25 february 2015; published on line 29 may 2015) abstract:the effect of different scheduled artificial ageing hardness on the tensile and impact properties of al -6si-0.5mg-2ni alloy was studied. the solution treated al-6si-0.5mg-2ni alloy was aged isochronally for 1 hour at temperatures up to 300oc. the precipitation stages during ageing were monitored by hardness measurements. tensile and impact properties were determined by standard tests. during artificial ageing, the yield and ultimate tensile strength were found to increase with ageing hardness; the maximum being attained at peak hardness. ductility and impact toughness of the alloy, on the other hand decreased with ageing hardness, reaching the minimum at the highest hardness. the strength of al 6si-0.5mg-2ni alloy was best at highest hardness but exhibits poor ductility and impact strength. abstrak:kajian dijalankan bagi menyelidik kesan penjadualan yang berbeza terhadap kekerasan penuaan buatan ke atas sifat tegangan dan impak aloi al -6si0.5mg-2ni. larutan melalui tempoh yang penuaan sama digunakan bagi merawat aloi al-6si-0.5mg-2ni selama 1 jam pada suhu sehingga 300oc.peringkat pemendakan sepanjang tempoh penuaan dipantau dengan ukuran kekerasan. sifat tegangan dan impak ditentukan berdasarkan ujian piawai. sepanjang tempoh penuaan buatan, hasil kekuatan tegangan dan kekuatan tegangan muktamad didapati bertambah dengan kekerasan penuaan; di mana ia paling maksima ketika ia berada di puncak kekerasannya. kemuluran dan impak ketahanan aloi, sebaliknya berkurangan dengan kekerasan penuaan, di mana ia berada pada tahap minima ketika ia paling keras. kekuatan aloi al-6si-0.5mg-2ni berada pada tahap terbaik pada kekerasan paling tinggi tetapi kemuluran dan impak kekuatannya kekal lemah. keywords: al-6si-0.5mg-2ni alloy; ageing; hardness; tensile properties; impact strength 1. introduction age hardened al allo ys are widely used in engineering applications due to the considerable improvements in their yield strength and hardness by controlled thermo mechanical treatments [1]. al-si based multi-component foundry alloys provide several advantageous characteristics such as good castability, high corrosion and wear resistance, as well as high thermal conductivity and adequate strength at elevated temperatures [2]. for al–si–mg alloys, age hardening is caused by the precipitation of β" and/or β' phases (precursor of mg2si phases) [3, 4]. al-mg-si iium engineering journal, vol. 16, no. 1, 2015 hossain and kurny 2 alloys have been widely used in transportation systems owing to their fair strength, weldability and corrosion resistance. the precipitation sequence of solution-treated al-mg-si ternary alloys during artificial aging can be reported to be: α supersaturated solid solution (sss) → gp-i zones → metastable needle-like β″precipitates (or called gp-ii zones; formed through the transformation of gp-i as nuclei) → metastable rod-like (or lath-like) β′ precipitates → stable β phase [2]. the use of al-si-mg allo ys, in particular for the automotive industry, is attractive due to its lightweight and reasonable strength after ageing treatment [6]. the accelerated need for weight reduction, however, leads to higher mechanical and thermal loading of these aluminum castings in future vehicles, requiring improved al-si foundry alloys concerning strength at elevated temperatures [1 -3, 5]. when a heat-treatable a356 aluminum alloy undergoes precipitation hardening (age-hardening), fine precipitants will dissolve completely in a saturated matrix to achieve high strength in the material [6]. when the supersaturated solid solution undergoes aging treatment; a large amount of small and uniformly distributed precipitants will appear thus the mechanical properties of the material can be improved. uniform and delicate mg2si precipitants can be obtained in the matrix of a heat-treatable al-si-mg casting part with t6 treatment (involves solution treatment, quenching and artificial aging), leading to improvements in its tensile strength, elongation and toughness [3, 7]. for the development of new al-si-mg-ni foundry alloy with superior elevatedtemperature strength a detailed physical understanding of the role of each particular alloying element concerning its ability to improve the high-temperature properties is required. in the past ni was identified to significantly enhance the high-temperature performance of al-si foundry alloys, though just to a certain level, depending on the fraction of eutectic phase in the alloy. ni stabilizes the contiguity of the eutectic network by increasing the volume fraction of rigid phases(si + al3ni) in the eutectic [8-10]. heat treatment (ht) is a commonly used technique to enhance the mechanical properties of the respective allo ys, such as strength (ht: t6) or ductility (ht: t4, t7). however, during a solution treatment the eutectic si spheroidizes and its aspect ratio decreases, which results in a loss of the contiguity of the eutectic platelets [8, 11]. the aim of this paper is to evaluate the effects of ageing hardness on the tensile properties and charpy impact strength of al-6si-0.5mg-2ni alloy with applications in automotive engineering. 2. materials and methods 2.1 materials aluminum a356 alloy, contained in a clay-graphite crucible, was melted in a gas-fired pot furnace. nickel, in the form of chips, was initially charged into the bottom of the crucible. magnesium (99.7% purity) in the form of ribbon and packed in an al-foil was added to the melt. the final temperature of the melt was maintained at 900±15oc. before casting, the melt was degassed with solid hexachloroethane (c2h6) and homogenized by stirring at 700oc. casting was done in a metal mould measuring 15mm x 150mm x 300mm and preheated to 200oc. the alloy wasanalyzed by wet chemical and spectrochemical methods simultaneously. iium engineering journal, vol. 16, no. 1, 2015 hossain and kurny 3 2.2 heat treatment the cast samples were ground to remove the oxide layer from the surface and were homogenised for 24 hr at 500oc. samples for hardness, tension and charpy impact tests were prepared from the homogenised plates according to an astm standard. then the test samples were solution treated at 540oc for 120 min and quenched in ice-salt-water solution. the solutionized samples were isochronally aged upto 400oc for 1 hr to find out the proper precipitation hardening behaviour of the alloy. the tensile and charpy impact samples were isochronally aged upto 300oc for 1hr. 2.3 tests the hardness tests were carried out in a rockwell hardness testing machine in f scale. the averages of seven consistent test results were accepted as the hardness test values for the corresponding samples. tensile testing was carried out in an instron testing machine at a strain rate of 10-3s-1 for the alloy and the impact tests were carried out in a charpy impact machine. the averages of three consistent test results were accepted as the tensile and impact value for the corresponding sample. 3. results and discussion 3.1 effect of thermal ageing treatment on hardness the hardness values of the aged al-6si-0.5mg-2ni alloy increased with ageing temperatures up to 225oc (92.6 hrf).its hardness was observed to decrease sharply for temperatures in the range of 225-400oc. this shows that the al-si-mg alloy has a peak ageing temperature of 225oc (figure 1). the reasons for this may be due to the fact that a decrease in the hardness is associated with an increase in the inter-particle spacing between precipitates, which makes dislocation bowing much easier. the increase in hardness beyond an underaged condition is more pronounced with the increase of ageing temperature and the hardness decreased significantly beyond ageing of 250oc. fig. 1 variation of hardness of al-6si-0.5mg-2ni alloy at different ageing temperatures. iium engineering journal, vol. 16, no. 1, 2015 hossain and kurny 4 3.2 effect of thermal ageing hardness on ultimate tensile strength figure 2 shows the ultimate tensile strength of the al-6si-0.5mg-2ni alloy at different thermal ageing hardness. the hardness is the results of solutionizing, underageing, peakageing and overageing operations. the plot of the ultimate tensile strength against the thermal ageing hardness reveals a significant improvement of the strength at peakaged condition. both tensile and yield strength show similar trends as can be clearly seen in figure 2 and figure3. the high ageing temperature (overaged) performance of al-6si-0.5mg-2ni alloy seems to be considerably reduced when exposed to over ageing thermal treatment. fig. 2 ultimate tensile strength as a function of ageing hardness of al-6si-0.5mg-2ni alloy. fig. 3 yield strength as a function of thermal ageing hardness of the al-6si-0.5mg-2ni alloy. iium engineering journal, vol. 16, no. 1, 2015 hossain and kurny 5 3.3 effect of thermal ageing hardness on yield strength figure 3 illustrates the influence of thermal ageing treatment on the yield strength of al-6si-0.5mg-2ni alloy depending on their ageing hardness. obviously, in this case overageing treatment has a negative effect on yield strength. although a linear increase of strength with increasing thermal ageing hardness is observed from underaged to peakaged condition. the yield strength of the overageing treated alloy starts at a significantly lower value and approaches the as-quenched alloy with decreasing ageing hardness(due to overage treatment). 3.4 effect of thermal ageing hardness on ductility the effect of ageing hardness on ductility of al-6si-0.5mg-2ni alloy is shown in fig. 4.the ductility of solutionized al-si-mg-ni alloy was maximum but its hardness was found to be lower. the alloy shows maximum strength at peak hardness but maintain poor ductility. beyond the peak ageing i.e. at overaged condition the ductility increases with hardness decreases for the alloy. fig. 4 ductility as a function of thermal ageing hardness of the al-6si-0.5mg-2ni alloy. 3.5 effect of thermal ageing hardness on impact strength figure 5 shows the charpy impact strength (absorbed energy) during fracture as a function of thermal treated hardness. heat treatment, especially solution treatment and ageing (under, peak and over ageing), significantly influenced the capacity of impact strength. in the as-quenched condition, the alloy has lower hardness and lower impact strength. the capacity of impact strength was found to be lower at underaged hardness. the decrease in absorbed energy is due to brittleness caused by precipitation of intermediate phases. the maximum decrease in absorbed energy was observed in the peakaged hardness. the impact energy increases significantly from peakaged to overaged hardness due to microstructure softening at overageing iium engineering journal, vol. 16, no. 1, 2015 hossain and kurny 6 fig. 5 impact strength as a function of rockwell hardness of the al-6si-0.5mg-2ni alloy in the solution treated, underaged, peakaged and over aged conditions. 4. conclusion the tensile and impact strength of al-6si-0.5mg-2ni heat treated alloy as a function of ageing hardness was reported. the al-si-mg-ni alloy showed improved strength at higher ageing hardness in the peakaged condition but maintain poor ductility. maximum hardness and tensile strength was found for the cases when ageing the alloy at ~225oc for 1 hr. overageing reduced the hardness and tensile strength but maintained improve impact strength. references [1] nakanishi t, yamagata e, yoneda k, nagashima t, kawasaki i, yoshida t, mori h, kobayashi t. (2000) strength and fracture of aluminum alloys. mater. sci. eng. a, 286:333341. [2] stadler f, antrekowitsch h, fragner w, kaufmann h, uggowitzer pj.(2012) the influence of solution treatment on the high temperature strength of al-si foundry alloys with ni. metals 2012 edited by carlos e., suarez tms. [3] shivkumar s, keller c, apelian d. (1990) ageing behavior in cast al–si–mg alloys. afs trans., 98:905–911. [4] kashyap kt, murali s, raman ks, smurthyks. (1993) overview casting and heat treatment variables of al–7si–mg alloy. mater sci., 9:189–203. [5] liyg, yang y, wu yy, wangly, liu xf. (2010) quantitative comparison of three nicontaining phases to the elevated-temperature properties of al-si piston alloys. mater. sci. and eng. a, 527: 132-7137. [6] apelian d, shivkumar s, sigworthg. (1989) fundamental aspects of heat treatment of cast al-si-mg alloys. am. foundry soc. trans., 97:727-742. [7] shueiwan juang h, shyh-ming w. (2008) study on mechanical properties of a356 alloys enhanced with preformed thixotrophic structure. j. of marine sci. tech., 16(4):271-274. [8] asgharz, requenag, kubel f. (2010) the role of ni and fe aluminides on the elevated temperature strength of an al-12si alloy. mater. sci. and eng. a, 527:5691-5698. [9] stadler f, antrekowitsch h, fragner w, kaufmann h, uggowitzerpj. (2011) theeffect of ni on the high-temperature strength of al-si cast alloys. mater. sci. forum, 690:274-277. iium engineering journal, vol. 16, no. 1, 2015 hossain and kurny 7 [10] stadler f, antrekowitsch h, fragner w, kaufmann h, peter j, uggowitzer (2012) effect of main alloying elements on the strength of al-si cast alloys at elevated temperatures. int. j. of cast metals res., 25(4):215-224. [11] lasagnif, lasagnia, markse, holzapfelc, mücklichf, degischerhp. (2007) threedimensional characterization of 'as-cast' and solution-treated al-12si(sr) alloys by highresolution fib tomography. acta mater., 55:3875-3882. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 islam et al. 79 bioelectrochemical behavior of wild type bacillus cereus in dual chamber microbial fuel cell mohammed amirul islam 1 , chee wai woon 1 , baranitharan ethiraj 2 , abu yousuf 3 , huei ruey ong 1 and md maksudur rahman khan 1* 1 faculty of chemical engineering & natural resources, universiti malaysia pahang, lebuhraya tun razak, 26300 gambang, pahang, malaysia. 2 department of biotechnology, bannari amman institute of technology, sathyamangalam, erode district, india. 3 faculty of engineering technology, universiti malaysia pahang, lebuhraya tun razak, 26300 gambang, pahang, malaysia. *corresponding author: mrkhancep@yahoo.com (received: 27 th feb. 2017; accepted: 30 th oct. 2017; published on-line: 1 st dec. 2017) abstract: a microbial fuel cell (mfc) is a bioelectrochemical system that uses living microbes as biocatalyst to oxidize organic substrates as well as release electrons that can be harvested in an external circuit to produce electrical energy. in this study, a proteolytic biocatalyst, bacillus cereus, has been employed for the first time in a microbial fuel cell (mfc). the wild type pure culture was isolated from municipal wastewater and identified using biolog gen iii analysis. the mfcs were fueled with palm oil mill effluent (pome) and attained a maximum power density of about 3.88 w/m 3 . the electrochemical behavior of the mfc was evaluated using a polarization curve, electrochemical impedance spectroscopy (eis), and cyclic voltammetery (cv) analysis. the cv and eis results suggest that the predominant electron transfer occurred through the electron shuttle mechanism. the electron shuttle mediators excreted by b. cereus significantly reduced the anode charge transfer resistance (52.95%). the fesem result shows that b. cereus has the capability to form an effective biofilm on the anode electrode surface. these results revealed the electrocatalytic potentiality of b. cereus, making it a promising candidate to be used in mfcs. therefore, this biocatalyst can be used to generate electricity through wastewater valorization. abstrak: sel bahan api mikrob (mfc) adalah sistem bioelektrokimia yang menggunakan mikrob hidup sebagai bio pemangkin untuk mengoksida substrat organik bagi menghasilkan tenaga elektrik dengan membebaskan elektron mengunakan litar tertentu. kajian ini telah menggunakan bio pemangkin proteolitik bacillus cereus buat pertama kali dalam sel bahan api mikrob (mfc). kultur asli jenis liar telah diasingkan daripada sisa air kumbahan dan dikenal pasti dengan menggunakan analisis biolog gen iii. mfc ini telah diberi bahan bakar bersama efluen kilang minyak sawit (pome) dan didapati ketumpatan kuasa maksimum adalah sebanyak 3.88 w/m 3 . tindak balas elektrokimia mfc ini dinilai menggunakan analisis lengkung polarisasi, elektrokimia impedan spektroskopi (eis) dan kitaran voltammetri (cv). keputusan cv dan eis menunjukkan dominasi pemindahan elektron telah berlaku menerusi mekanisme pemindahan elektron. pengantara pemindahan elektron ini yang terhasil daripada b. cereus telah menurunkan rintangan pemindahan cas anod dengan ketara (52.95%). hasil fesem menunjukkan bahawa b. cereus mempunyai keupayaan membentuk biofilem yang berkesan pada permukaan elektrod anod. keputusan ini menunjukkan potensi iium engineering journal, vol. 18, no. 2, 2017 islam et al. 80 elektrokatalitik b. cereus sebagai calon terbaik dalam mfc. ini kerana bio pemangkin ini boleh digunakan untuk menjana tenaga elektrik melalui volarisasi air kumbahan. keywords: microbial fuel cell; bacillus cereus; biofilm; palm oil mill effluent; cyclic voltammetry; electron transfer mechanism 1. introduction the microbial fuel cell (mfc) is an important type of bioenergy source for the future because it can use a wide variety of substrates, including soluble or dissolved complex organic wastes and various types of artificial or real wastewater [1]. in mfcs, the use of pure cultures may not be suitable due to high costs and its inefficiency to utilize the complex substrates; therefore, it is not efficient for practical operation such as treatment of industrial effluents. on the other hand, mixed cultures from natural sources such as soil, wastewater, and anaerobic sludge (as) have been widely used as inoculum in mfcs since they are more readily obtainable in large quantities, more tolerant to environmental fluctuations, and more accommodating to a variety of substrates [2, 3]. however, as could not achieve a significant performance because of the presence of non-electrogenic bacteria (i.e., methanogenic bacteria and denitrifying bacteria) in mixed cultures that consume organic substrates without generating electricity [4]. therefore, this problem can be solved using wild type pure culture bacteria that can utilize a wide variety of substrates as inoculum in mfcs. in the past decade, a number of new strains of bacteria have been reported to be capable of generating electrical current through mfcs. although many new strains have been identified, only a few strains are capable of producing significant power using complex wastewater as a substrate [5, 6]. one of them is bacillus cereus. it is a grampositive, soil-native bacteria, widespread in different habitats around the world. some studies showed that gram-positive bacteria especially bacillus spp. increased current generation through the redox shuttles in mfc [7, 8]. besides that, it has the capability to degrade toxic waste compounds and efficiently utilize them as a carbon sources [9, 10]. these degrading skills shown by b. cereus could be improved if it grows in adverse environmental conditions [11, 12]. therefore, bacillus cereus can be considered as a potential biocatalysts to be used in mfc for simultaneous power generation and wastewater treatment. bacteria are, so far, known to transfer electrons to anode surfaces via two mechanisms. the first is a biofilm mechanism, where exoelectrogens form a biofilm on the anode surface. some microorganisms can even produce nanowires carrying electrons from the cell to anode surface. the second is the electron-shuttle mechanism, where the microorganism itself can produce and use low molecular weight compounds, soluble mediators (e.g. phenazine, quinones) that eliminate the need for direct contact between the cell, and electron acceptors [13]. the understanding of electron shuttles in these electrongenerating processes is emergent to effectively harvest the electricity from mfcs. a pure exoelectrogen strain is required for studying the mechanism of electricity production in mfc. currently, quite a number of pure exoelectrogens are demonstrated to have electrochemical activity, such as geobacter and shewane1la [14]. however, only a few strains were capable of producing electron shuttles, such as pyocyanin by pseudomonas aeruginosa and riboflavin by s. oneidensis mr-1 [15]. the purpose of this study is to investigate the electrochemical activity as well as electron transfer mechanism of wild type b. cereus in microbial fuel cells. the iium engineering journal, vol. 18, no. 2, 2017 islam et al. 81 electrochemical activity was evaluated using the polarization measurement, biofilm formation capability, electrochemical impedance spectroscopy and cyclic voltammetry analysis. 2. materials and methods 2.1 source of microorganism and sample collection palm oil mill effluent (pome) samples were obtained from a local palm oil mill industry located in pahang, malaysia. municipal wastewater was collected in a sterilized bottle from a drainage discharge point in kuantan, pahang, malaysia. all samples were stored at 4 o c to minimize the degradation of samples by indigenous microbial activities, thus preserving the quality of the samples. 2.2 isolation of microorganism the source of microorganisms was municipal wastewater. enrichment of the cultures was carried out by preparing an overnight culture in lb broth (10% v/v) incubated at 35 o c with shaking at 150 rpm. the overnight culture (10% v/v) was used as primary inoculum in the anode compartment. after 13 days of mfc batch operation, the anode was taken out and placed in 0.1 m phosphate buffer and shaken vigorously to detach bacteria that grew as biofilm on the anode. the side of the anode was also carefully scraped and resuspended in phosphate buffer. the bacterial suspension was serially diluted and the pure culture bacteria were obtained using the spread plate technique. the predominant colony was identified using biolog gen iii, specifically b. cereus. 2.3 mfc configuration the dual chamber mfc was fabricated with a plexiglas cube with a dimension of 5 cm x 5 cm x 5 cm (shanghai, sunny scientific, china) and a total working volume of 25 ml. a carbon brush was used as an electrode in all experiments. nafion 117 membrane was used to separate the anode and cathode compartments of mfc (dupont co., usa). prior to use, the nafion membrane was pretreated using diluted h2so4 for 1 hour followed by washing with di (de-ionized) water several times. after the whole mfc set up was tightened up with screws, the anode compartment was filled with sterilized 50% pome (20ml) and subsequently the pure culture bacteria (1ml) were inoculated into it while the cathode chamber was filled with kmno4 solution. the anode chamber was purged with n2 for 30 min and then tightly closed to maintain the anaerobic condition. the whole experiment was conducted in batch mode. the anode and cathode electrodes were connected using titanium wires with a rheostat (crotech drb-9, uk) to form a circuit. 2.4 fesem analysis field emission scanning electron microscopy (fesem) was used to observe the microorganisms grown on the electrode material. a small portion of the electrodes was cut off for fesem observation. the electrode sample was immediately immersed in 3% glutaraldehyde and 0.1 m phosphate buffer solution and then dehydrated with increasing ethanol concentration (30–100%) [16]. thereafter, samples were freeze dried and sputter coated with a thin layer of platinum under vacuum to neutralize the charging effects prior to scanning in the fesem. the morphology was observed under a scanning electron microscope (hitachi, japan, model: 3400n) with an acceleration voltage of 5 kv during the scanning. iium engineering journal, vol. 18, no. 2, 2017 islam et al. 82 2.5 measurement and analyses the voltage (v) and current (i) across an external resistor (1 kx) in the mfc circuit was monitored using a digital multimeter with data logger (fluke 289 true rms multimeter, usa) connected to a computer through a usb cable adapter. to obtain polarization data, the external resistance was varied from 50 to 20,000 x. power density normalized by surface area (pa, w/m 3 ) was measured and calculated using the following equations. pa = ui (1) pv = rvi 2 /v (2) where v is the volume of the mfc (m 3 ), u is the voltage of the cell (v) and rv is the external resistance (ω), and i is the current (a). 2.6 eis and cv analysis electrochemical impedance spectroscopy (eis) was carried out using an electrochemical workstation (autolab 2273, par, usa). a conventional threeelectrode system was employed with the anode as the working electrode, the cathode as the counter electrode, and an ag/agcl reference electrode that was placed as close as possible to anode electrode [17]. the impedance data were fitted to the equivalent electrical circuit to obtain key parameters such as the electrochemical charge transfer resistance for the anode. the nyquist plots of the impedance spectra were analyzed using nova 1.9 (nova software). the cv was run at a scan rate of 30 mv/s with a scan range of -1.0 to +1.0 v versus ag/agl and the voltammogram was compared for different days in identical configuration and operational conditions. 3. results and discussions 3.1 performance of mfc the performance of mfc fed with 50% of pome (cod=18,260 mg/l) and inoculated with 1 ml of liquid culture was investigated. the mfc performance was recorded for 13 days, as shown in fig 1. fig. 1: maximum power densities of the mfc versus time. fig. 2: polarization curves of the mfc on the 3 rd and 11 th day using b. cereus. iium engineering journal, vol. 18, no. 2, 2017 islam et al. 83 the performance of the mfc gradually increased until 7 days of operation and reached maximum power density of 3.52 mw/m 3 . after 7 days of operation, it showed that stable power generation was achieved for a few days. maximum performance of 3,88 mw/m 3 achieved on the 11 th day and started decreasing after 11 days of operation. our previous study [12] showed that b. cereus possesses electrogenic properties and could form an effective biofilm. moreover, usually gram-positive bacteria develop viable biofilm compared to gram negative bacteria and that could also be a reason for achieving a higher performance in mfc3 [7]. however, the drastic decrease in power generation could be due to the excessive bacterial colonization on the anode surface, which might have limited the substrate access to the inner layer of the biofilm [18]. hence, it reduced the number of viable cells in the inner layer which in turn declined the power generation. the polarization curve for the 3 rd day and 11 th day has been shown in fig. 2. as can be seen from the fig. 2, the power generation on 11 th day was around 3 times higher than the 3 rd day. the higher performance on 11 th day was attributed to the formation of an effective biofilm on the anode surface that resulted in higher kinetics of the bio-electrochemical reaction on the surface of the mfc anode [19]. 3.2 biofilm analysis the formation of a biofilm is vital for the mfc because it significantly influences the electron transfer through the extracellular polymeric substances [20]. fesem analysis was done to visualize the biofilm on the anode electrode surface before and after operation (on the 3 rd and 11 th days) of the mfc, and the results have been presented in fig. 3a and 3b. on day 3, as shown in fig 3a, less bacterial colonization was scattered around the electrode and loosely associated microbial clumps were observed in some locations on the electrode surface. however, on day 11, it can be seen that the significant bacterial cells, that colonized the electrode surface and formed the mature biofilm, are embedded in a self-produced matrix of extracellular polymeric substance (eps) (fig. 3b). hence maximum performance was achieved by the mfc. read et al. [7] reported that a biofilm is a crucial component of the mfc that allows considerable conversion capacity and opportunities for extracellular electron transfer. moreover, the cells attached on the electrode surface need less of a diffusion path for the transport of electrons from the microbes to the electrode [21]. the results suggest that an effective biofilm, comprising of higher active microorganisms might have produced more redox compounds that enhanced the electron transfer efficiency as well as the performance of the mfc. fig. 3: fesem images on anode carbon brush in the mfc fed with pome as substrate, (a) day 3 and (b) day 11. iium engineering journal, vol. 18, no. 2, 2017 islam et al. 84 3.3 electrochemical impedance analysis nyquist plots for the anode configuration on different days of operation are shown in fig. 4. the measurement of eis spectra for the anode demonstrates the key information of resistance created by electrode and bacterial metabolism. the impedance at the high frequency region is attributed to the ohmic resistance and the diameter of the semicircle represents the polarization resistance (or charge transfer resistance), which is affected by the kinetics of electrode reactions [22]. the charge transfer resistance (rct) values using b. cereus on the 3 rd and 11 th day were found to be 89.7 ω, and 42.37 ω, respectively. the higher rct using b. cereus (89.7ω) on the 3 rd day might be due to the absence of mature biofilm on electrode surface (fig. 3a). however, on the 11 th day, the rct was reduced by 52.95% (42.37 ω) indicating that the b. cereus formed an effective biofilm on the anode. thus, it decreased the anode activation losses by enhancing the kinetics of the bioelectrochemical reactions [19]. these results revealed that the effective biofilm is necessary to facilitate the anodic electron transfer as well as power generation in the mfcs. fig. 4: nyquist plots of b. cereus on the 3 rd and 11 th day of operations. fig. 5: cyclic voltammetry curves of b. cereus on the 3 rd day and 11 th day of operations. 3.4 cyclic voltammetry analysis cv analysis has been extensively used to evaluate the bioelectrocatalytic activity of anodic biofilms and to determine the electron transfer mechanisms [23]. the cv was conducted before inoculation and after inoculation on day 3 and 11, as shown in fig 5. marked variations of catalytic behavior between the 3 rd and 11 th day are clearly observed by cv analysis, as shown in fig. 5. the observation that the maximum current reached up to 0.23 a on day 11, which is about 2 times higher than that of 3 rd day (0.01 a), might be due to the excretion of large amounts of electron shuttle compounds in the anode [24]. moreover, a reversible cv peak apparently demonstrates the redox transformation of electro chemically active species [21]. the abundance of electron shuttle compounds decreased the charge transfer resistance in the mfc by around 52%. the catalytic measurements demonstrated that the presence of a recyclable electrochemical active compounds produced by b. cereus would have mainly contributed to the electricity generation in the mfc [12]. moreover, the electrochemical activity of b. cereus behaved distinctly different during different stages, suggesting that suspension cells were growing or adhering onto the anode to form a biofilm in the mfc [25]. however, further study is 0 80 160 240 320 400 0 80 160 240 320 400 (b ) -z " (o h m ) z' (ohm) day 3 day 11 iium engineering journal, vol. 18, no. 2, 2017 islam et al. 85 needed in order to identify the redox compound produced by b. cereus. 4. conclusion the outcome of this study suggests that b. cereus is an efficient microorganism to be used as inoculum in an mfc. b. cereus showed significant power production of about 3.9 w/m 3 using pome as substrate. the reversible cv peak confirmed that b. cereus produced electron shuttle compounds that enhanced the electron transfer efficiency. the anode charge transfer resistance decreased by 52%, indicating that the presence of an efficient biofilm formation. the visualization of the biofilm by fesem further confirms the formation of effective biofilm after 10 days of operation. further developments can be made by mixing different kinds of microorganisms with b. cereus in order to possibly improve the power generation of the mfc. acknowledgements this work was supported by the university malaysia pahang, malaysia (rdu 140322 and grs 150371). references [1] pant d, van bogaert g, diels l, vanbroekhoven k. (2010) a review of the substrates used in microbial fuel cells (mfcs) for sustainable energy production. bioresource technology, 101:1533-1543. [2] ismail zz, jaeel aj. (2013) sustainable power generation in continuous flow microbial fuel cell treating actual wastewater: influence of biocatalyst type on electricity production. the scientific world journal, 2013:13515-13522. [3] islam ma, khan mr, yousuf a, wai wc, cheng ck. (2016) electricity generation form pretreated palm oil mill effluent using klebsiella variicola as an inoculum in microbial fuel cell. 4th international conference on the development in the in renewable energy technology (icdret): ieee; p.1-4. [4] logan be, regan jm. (2006) microbial fuel cells-challenges and applications. environmental science & technology,40:5172-5180. [5] majumder d, maity jp, tseng m-j, nimje vr, chen h-r, chen c-c, et al. (2014) electricity generation and wastewater treatment of oil refinery in microbial fuel cells using pseudomonas putida. international journal of molecular sciences,15:16772-16786. [6] li n, liu l, yang f. (2014) power generation enhanced by a polyaniline–phytic acid modified filter electrode integrating microbial fuel cell with membrane bioreactor. separation and purification technology,132:213-217. [7] read st, dutta p, bond pl, keller j, rabaey k. (2010) initial development and structure of biofilms on microbial fuel cell anodes. bmc microbiology,10:1-10. [8] nimje vr, chen c-y, chen c-c, jean j-s, reddy as, fan c-w, et al. (2009) stable and high energy generation by a strain of bacillus subtilis in a microbial fuel cell. journal of power sources,190:258-263. [9] vélez-lee ae, cordova-lozano f, bandala er, sanchez-salas jl. (2015) cloning and expression of vgb gene in bacillus cereus, improve phenol and p-nitrophenol biodegradation. physics and chemistry of the earth,91:38-45. [10] islam ma, chee ww, baranitharan e, abu y, chin kc, khan mr. (2016) evaluation of electricity generation and wastewater treatment from palm oil mill effluent using single and dual chamber microbial fuel cell. [11] banerjee a, ghoshal ak. (2010) phenol degradation by bacillus cereus: pathway and kinetic modeling. bioresource technology,101:5501-5507. iium engineering journal, vol. 18, no. 2, 2017 islam et al. 86 [12] islam ma, ethiraj b, cheng ck, yousuf a, khan mmr. (2017) electrogenic and antimethanogenic properties of bacillus cereus for enhanced power generation in anaerobic sludge driven microbial fuel cell. energy & fuels, 31(6):613-6139. [13] deng l, li f, zhou s, huang d, ni j. (2010) a study of electron-shuttle mechanism in klebsiella pneumoniae based-microbial fuel cells. chinese science bulletin,55:99-104. [14] wrighton kc, agbo p, warnecke f, weber ka, brodie el, desantis tz, et al. (2008) a novel ecological role of the firmicutes identified in thermophilic microbial fuel cells. the isme journal,2:1146-1156. [15] marsili e, baron db, shikhare id, coursolle d, gralnick ja, bond dr. (2008) shewanella secretes flavins that mediate extracellular electron transfer. proceedings of the national academy of sciences,105:3968-3973. [16] nandy a, kumar v, kundu pp. (2013) utilization of proteinaceous materials for power generation in a mediatorless microbial fuel cell by a new electrogenic bacteria lysinibacillus sphaericus va5. enzyme and microbial technology,53:339-344. [17] baranitharan e, khan mr, yousuf a, teo wfa, tan gya, cheng ck. (2015) enhanced power generation using controlled inoculum from palm oil mill effluent fed microbial fuel cell. fuel,143:72-79. [18] islam ma, rahman m, yousuf a, cheng ck, woon cw. (2016) performance of klebsiella oxytoca to generate electricity from pome in microbial fuel cell. matec web of conferences: edp sciences, 38:1-6. [19] ramasamy rp, ren z, mench mm, regan jm. (2008) impact of initial biofilm growth on the anode impedance of microbial fuel cells. biotechnology and bioengineering,101:101108. [20] marsili e, rollefson jb, baron db, hozalski rm, bond dr. (2008) microbial biofilm voltammetry: direct electrochemical characterization of catalytic electrode-attached biofilms. applied and environmental microbiology,74:7329-7337. [21] islam ma, woon cw, ethiraj b, cheng ck, yousuf a, khan mmr. (2017) correlation of power generation with time-course biofilm architecture using klebsiella variicola in dual chamber microbial fuel cell. international journal of hydrogen energy, 41(41):2593325941. [22] he z, mansfeld f. (2009) exploring the use of electrochemical impedance spectroscopy (eis) in microbial fuel cell studies. energy & environmental science,2:215-219. [23] samsudeen n, radhakrishnan t, matheswaran m. (2015) bioelectricity production from microbial fuel cell using mixed bacterial culture isolated from distillery wastewater. bioresource technology,195:242-247. [24] islam ma, woon cw, ethiraj b, cheng ck, yousuf a, khan mmr. (2016) ultrasound driven biofilm removal for stable power generation in microbial fuel cell. energy & fuels, 38(1):968-976. [25] islam ma, karim a, woon cw, ethiraj b, cheng ck, yousuf a, et al. (2017) augmentation of air cathode microbial fuel cell performance using wild type klebsiella variicola. rsc advances,7:4798-4805. 477 iium engineering journal, vol. 15, no. 1, 2014 altaf et al. 61 review of passive drag reduction techniques for bluff road vehicles alaman altaf, ashraf a. omar and waqar asrar departmentof mechanical engineering, faculty of engineering, international islamic university malaysia, po box 10, 50728, kuala lumpur, malaysia. aao@iium.edu.my abstract: this paper presents a review of the techniques used to reduce aerodynamic drag over bluff bodies such as cylinders, spheres, 2d bodies with blunt backs and their application to commercial road vehicles. the recent research carried out on the drag reduction is presented and categorised. a new classification of the techniques is introduced and major contributions under them are shown in this paper. moreover, it can be concluded that there is not much work done with realistic 3d bluff bodies, especially using passive methods. abstrak: kertas kerja ini membentangkan kaji selidik semula teknik yang digunakan untuk mengurangkan seret aerodinamik ke atas jasad tubir seperti silinder, sfera, jasad 2d dengan belakang tumpul dan aplikasinya terhadap kenderaan jalan raya komersial. pengurangan seretan dibentangkan dan dikategorikan dengan kajian terkini. klasifikasi teknik terkini diperkenalkan dan sumbangan utamanya diperbentangkan. secara kesimpulannya terdapat banyak tugasan yang tidak yang dapat dijalankan dengan menggunakan jasad tubir 3d sebenar, terutamanya dengan penggunaan kaedah pasif. keywords: drag reduction; bluff body; passive drag reduction; active drag reduction 1. introduction drag reduction is of paramount importance in the transportation field. a major part of the fuel in commercial (aerial/ground/marine) vehicles is spent on overcoming aerodynamic drag one of the main contributors to overall drag. with the recent recession, increase in global warming and rapid depletion of fossil fuels, researchers are now looking into means to minimize the fuel consumption and reduce emissions; such as to move towards greener technologies. heavy vehicles due to their large frontal area and bluff shapes are aerodynamically inefficient and take up to 65% of fuel to overcome drag. as mentioned by hsu and davis [1], it is estimated that with a drag reduction of about 40%, 10,000 usd/year/vehicle can be saved. however redesigning these vehicles altogether is an impractical solution especially in developing countries which are already burdened with their poor economy. following newton’s 3 rd law of motion, when a solid body moves through a fluid, the fluid exerts an equal and opposite reaction force on the body; a component of which tries to resist the motion. this force called drag is expressed in the following equation: iium engineering journal, vol. 15, no. 1, 2014 altaf et al. 62 acvd d 2 2 1 ∞ = ρ (1) where d is on the drag, � is the density of the fluid, �� is the free stream velocity, �� is the non-dimensional drag coefficient and a is the reference area. the commonly used reference areas are: frontal area (in case of stubby, bluff bodies e.g. buildings, trucks), planform area (in case of thin, flat shapes e.g. wings) and wetted area (e.g. ships, barges). the total drag on a body is the summation of skin friction drag and pressure drag. from the equation above it is seen that drag basically depends on flow conditions and the geometry of the body. for streamlined bodies, changing the flow conditions (reynolds number, re) can effectively reduce drag to some extent. however in case of bluff bodies with sharp corners, change in re has no effect on drag, thus the need to modify or manage the flow around a body arises in order to reduce drag [2]. drag reduction techniques are mainly divided into two categories: passive, which involves no energy expenditure and active, which requires energy and involves a control system. different techniques offered so far include: blowing, suction, base cavities, ventilated cavities, vortex generators, afterbody modification, splitter plates, boat tailing, injecting additives/droplets or fibers, large eddy breakup devices. these techniques basically try to modify the flow around the body, prevent separation, reduce wake, mass transfer into the boundary layer. over the past two decades with the increasing developments in science and technology, using active flow control methods has become increasingly feasible. with very efficient micro and nano scale sensors and actuators, having a feedback control system has become easier and simpler. but such systems are not economically cost effective. and in the times where the concerns for global warming, depleting natural resources and greener technologies is rising every day, it is logical that the future control strategies should focus on passive techniques. the merits of these approaches are that they require no energy expenditure, no input from the user and are cheaper than active techniques. many attempts have been made to summarize the work done in the field of drag reduction, but very little (if not none) is done to review only passive drag reduction methods. 2. literature review this section provides the review on the work done in passive drag reduction. the main approaches using passive methods to reduce drag have been broadly categorized into three groups as shown in fig.1 and are discussed below. 2.1 retrofits muhammed-kassim and fillippone [3] conducted a numerical study of fuel saving potential of various drag reducing retrofits. they found that vehicle parameters alone do not affect total drag; operational parameters have a large effect as well. it was found that using aerodynamics devices is optimal when these vehicles travel at high speeds on long haul driving cycles as weight does not have any direct effect on drag. driving through urban areas utilizes most fuel for acceleration and deceleration. these factors are important because every part of a truck contributes, iium engineering journal, vol. 15, no. 1, 2014 altaf et al. 63 positively or negatively, to the total drag of the truck. commonly used retrofits are given in the following subsections. fig.1: classification of passive drag reducing techniques. 2.1.1 flaps/deflectors lee and ko [4] studied flow field behind a perforated gurney-type flaps and concluded that perforated flaps are better than solid ones to reduce drag and wake width and unsteadiness. however study was done on flaps alone, without any actual 3d body. fouree et al. [5] in their experimental study using deflector on a generic car model found that drag reduction of up to 9% was obtained depending upon the deflector angle (fig. 2). beaudoin and aider [6] did the experimental study on a 3-d bluff body called ahmed body, a commonly used 3d bluff body for benchmarking purposes, using flaps at all the edges on the two rear surfaces and found that the most efficient configuration was the two flaps on side edges of rear slant. depending on various configurations, the drag could be reduced by 25% and lift by 107%. ha et al. [7] carried out experimental and computational study of drag reducing capability of a rear downward flap on a pickup truck. they found that the cd was reduced with the increasing flap length. they deduced that the flap displaced the flow attachment enabling more downwash, hence reducing the reverse flow in the wake. with the increase in downward angle, there was an increase in drag reduction. they proposed that this happens because the cabin back pressure increases with the increase in downward angle, which reduces the drag co-efficient. however the performance doesn’t stay constant with increasing flap length and downward angle. it was suggested that the rear downward flap needs to be designed which would have an optimum downward angle. while studying the use of back-flaps on a full-sized truck, muhammed-kassim and fillippone [3] found a reduction of 4-5% of total drag. this is one of the few studies conducted on a full-sized truck; however, it did not address the shape or design of the flap, or optimization of the dimensions for maximum drag reduction. iium engineering journal, vol. 15, no. 1, 2014 altaf et al. 64 fig. 2: description of the deflector: overview (a) and definition of deflection angle θ (b). figure taken from fouree et al. [5]. 2.1.2 splitter plates gilieron and kourta [8] did wind tunnel testing on ahmed body using splitter plates at the front/rear at different skew angles. drag reduction of 12% was achieved with splitter plates placed downstream and 27%-47% with plates positioned upstream. drag reduction was achieved by eliminating longitudinal vortices, reducing wake cross section and minimizing pressure loss. the effect of vortex interaction when plates are present at both front and rear was not studied. park et al. [9] investigated the total drag reducing efficiency of outer layer vertical plates and achieved drag reduction of 9.6% without considering the increased wetted surface area. the height and spacing between the plates were optimized and found to be most efficient when the plates were nearest and shortest. the height of the plates was found to be the most prominent parameter. plates with height more than the boundary layer thickness caused drag to increase rather decrease. however, many aspects such as loading on blades, vibration and downstream effect need to be studied before this can be applied to real engineering problems. 2.1.3 boat tails lancer et al. [10] studied the effectiveness of boat tailing on a tractor/trailer at nasa research centre wind tunnel. it was concluded that the modified flow due to the boat tails increased the pressure over the base area, hence reducing the aerodynamic drag. khalinghi et al. [11] extended the work done by lancer and his team by doing the computational and experimental study on bodies with and without the drag reducing device. the computational fluid dynamics (cfd) simulations were done using both steady and unsteady reynolds-averaged navier-stokes (rans) approach. hot wire anemometry and particle imagine velocimetry (piv) were used to understand the wake flow better. it was found that the drag coefficient reduced by 6% for steady and 18% for unsteady cfd simulations; as compared to 20% experimentally measured value. they concluded that unsteady rans is more valid and useful in studying wake flows. 2.1.4 fences modi et al. [12] did wind tunnel and full scale road tests to see the effect of ‘fences’ (boundary layer control method) on drag reduction. wind tunnel testing done on a 1/6 th scale model at subcritical re showed drag reduction of 31.4% while the road tests showed the drag reduction of only 16.6%. the discrepancies in results iium engineering journal, vol. 15, no. 1, 2014 altaf et al. 65 were attributed to the much idealized circumstances in wind tunnel as compared to the roads; the wind tunnel model was not exactly same as the full scale model; the scaling of fence and their orientation for full scale trucks were not accurate; and that the number of fences used on the wind tunnel model and the full scale trucks were not same. also it was found that the effectiveness of the ‘fences’ reduced at speeds lower than 30 km/h. the optimization in terms of location of fences was left as future work. 2.2 control surfaces bruneau et al. [13–15] presented a new passive flow control method using a porous layer. in their paper they explained the solid-porous-fluid physical models used;the setup of the boundary conditions for such flow; integration of darcy equations with navier stokes equations and a penalization method applied. numerical simulations were done to understand the passive flow control capability of porous layer at high reynolds number and it was found to reduce vortex induced vibrations. based on the location of porous layer on an ahmed body, it was found that drag coefficient could be reduced by 40%. however the drag reduction was not very significant in case of ahmed body with a rear window. bruneau et al. [16] found that using a porous layer on the roof of the body modifies the shear forces reducing the drag by 22%. the porous layer induces the kelvin helmotz instabilities which change the size of vortices on the top of the body hence reducing the drag. however their study was performed only on 2d body and concluded that the more detail understanding of vortex dynamics is required to be able to modify it substantially. 2.2.1 riblets chen et al. [17] did a numerical study to see the effect of bionic riblets on drag reduction of revolution body. it was found that the drag could be reduced by almost 9%. the basic reason of drag reduction was found to be reduction in skin friction drag due to control and correction of boundary layer. sirovich and karlson [18] showed that by having ‘vee’ shaped protrusions, drag can be reduced by almost 10%. however, studying various protrusion heights, ‘vee’ angles and their effects was left as future work. parker and sayers[19]found that symmetric v groove riblets on a flat plate perform better at reducing drag than unsymmetrical u groves. these grooves suppress the streamwise vortices, turbulent mixing and hence turbulent shear stress. gruneberger and hage [20, 21] found that triangular riblets with trapezoidal grooves aligned parallel to flow reduce drag upto 7.6% by effectively increasing wetted area. 2.2.2 vents and strips falchi et al. [22] studied the effect of passive ventilation on flow control. it was found that 7-8% drag reduction was achieved for clean vented and 20% drag reduction with strips. however no direct pressure measurements were done, so the results could be under/overestimated. suryanarayana and prabhu [23] found that drag can be reduced by 65% in a vented sphere. 2.2.3 streaks pujals et al. [24, 25] studied the suppression of separation behind an ahmed body by large scale coherent streaks forced on the roof. the streaks were formed using small cylinders upstream slanted rear end. drag reduction of about 10% was obtained. however, the minimum streak amplitude necessary for separation was not found. iium engineering journal, vol. 15, no. 1, 2014 altaf et al. 66 2.2.4 dimples mode [26] did a numerical study of dimples on a surface of a flat plate to understand the physics involved and effect of the dimples on drag reduction. it was found that the presence of the dimples cause the flow to accelerate, producing a favorable pressure gradient which prevents the bl separation and hence reduces the wake. 2.2.5 tabs park et al. [27] proposed a new passive control method to reduce form drag over 2-d blunt bodies. they found that by attaching small tabs on the trailing edge of a body, flow characteristics in wake changes, leading to the drag reduction. both experimental and computational studies were done to comprehend the efficiency in reducing drag. parametric studies were done by varying spacing, height and width of tabs at three different reynolds numbers. it was found that the tabs reduce the strength of the vortices in the wake, leading to increase in base pressure (decreased drag). norman and mckeon [28] studied effect on a stud (tab) on an otherwise smooth sphere using piv (fig. 3). it was found that in subcritical regime, with an isolated roughness added, the flow separation was delayed further downstream. the stud seems to increase the reynolds stresses which leads to decrease in the shear layer instabilities and hence the narrower wake. however in supercritical regime, it seems that the stud causes premature separation and hence an increase in drag. the researchers also studied the effect of the size of stud (tab). though only cylindrical tabs were used, the effect of other geometries was left as future work. fig. 3: the stationary stud locally delays separation on the subcritical regime, likely leading to the production of weak counter-rotating vortices. figure taken from norman and mckeon [28]. 2.3 modifying / optimizing existing designs park et al. [29] investigated flow over the backward facing step. it was found that the 51% reduction of reattachment length was achieved using rectangular tabs located at the edge of the step. the tabs caused the span wise modulation of streamwise velocity profile. hsu and davis [1]found that by adding humps on the top, bottom and/or sides of trailer along with boat-tail flaps (as shown in fig. 4) can reduce drag by about 50.9%. but the method isn’t feasible for real automobiles. jing et al. [30] did a comparative study of commercial truck with a dome on top and iium engineering journal, vol. 15, no. 1, 2014 altaf et al. 67 deflector at the rear, using cfd and wind tunnel testing. they concluded that drag could be reduced by about 10%. strachan et al. [31] studied wake flow of ahmed body with overhead supporting struts and both with and without moving ground. the results obtained were compared to two previous studies done. they found that the overhead supporting struts reduced the strength of the trailing counter rotating vortices, which in turn lead to the separation of flow earlier than the critical back angle. it was also concluded that the moving ground had little to no effect on the overall results. they also found that there were small vortices developing near the ground (behind the model) which were not reported by any previous researches; most probably due to the interference of the struts used to mount the model. however they could not provide any accurate measurement of the distance the vortices propagate. fig. 4: hump and curved boat-tail flaps geometry. figure taken from hsu and davis [1]. 3. conclusion from the literature provided in the previous section it is seen that passive drag reduction is a fast growing field. a lot of work has been done on this topic and researchers all over the world continue adding to the knowledge. in this review, existing passive flow control methods were classified into three categories: retrofits, control surfaces and design modifications (shown in fig. 1) and the work done under each category was presented and discussed. as mentioned earlier, control methods are either active or passive. due to the simplicity, cost effectiveness and easier implementations, passive techniques are gaining popularity. though as compared to the active flow management, this field still seems to be in infancy. much of the work done previously in this field is on 1d and 2d bodies. however it is only when a reliability of a method is proven in 1d or 2d, that it can be developed to more complex geometries. the flow around a 3d body is much more complex and requires much deeper understanding. retrofits, amongst the three categories presented, is widely used and studied on 3d bodies. splitter plates, flaps and deflectors are already employed on various commercial vehicles. following the same trend it won’t be long before other methods would be proven to be useful on 3d bodies. more studies should be done to apprehend the flow around 3d bodies and to obtain an effective drag reduction. iium engineering journal, vol. 15, no. 1, 2014 altaf et al. 68 references [1] hsu, f.-h., davis, r. l. “drag reduction of tractor-trailers using optimized add-on devices.” journal. fluids engineering, 132(8), 084504. doi:10.1115/1.4001587 [2] hucho, w.-h. ed. “aerodynamics of road vehicles”, 4th ed. society of automotive engineers. [3] mohamed-kassim, z., filippone, a”fuel savings on a heavy vehicle via aerodynamic drag reduction.” transportation research part d vol. 15. pp 275-285. (2010). [4] lee, t., ko, l. s. “piv investigation of flowfield behind perforated gurney-type flaps.” experiments in fluids 46(6) 1005-19, 2009. [5] fourrié, g., keirsbulck, l., labraga, l., gilliéron, p. “bluff-body drag reduction using a deflector.” experiments in. fluids, (2011), 50 (2): 385-395. [6] beaudoin, j.-f., aider, j.-l. “drag and lift reduction of a 3d bluff body using vortex generators, “experiments in fluids, (201) 48, 771-789. [7] ha, j., jeong, s., obayashi, s. “drag reduction of a pickup truck by a rear downward flap.” international. journal. automotive. technology, (2011) 12.3:369-74. [8] gilliéron, p., kourta, a. “aerodynamic drag reduction by vertical splitter plates.” experiments in fluids, 48(1), 1–16. doi :10.1007/s00348-009-0705-7, . [9] park, h., an, n. h., hutchins, n., choi, k.-s., chun, h. h., lee, i. “experimental investigation on the drag reducing efficiency of the outer-layer vertical blades“journal. mar. science. technology, 16(4), 390–401. doi:10.1007/s00773-011-0135-0 [10] lancer, w. r., ross, j., kaufman, a. e. “aerodynamic performance of a drag reduction device on a full-scale tractor/trailer.” aerospace technology conference and exposition sae technical paper, 1991. [11] khalingi, b., zhang, s., koromilas, c., balkanyi, s. r., bernal, l. p., iaccarino, g., moin, p. “experimental and computational study of unsteady wake flow behind a bluff body with drag reducing device.” sae trans., 110.6(2001):1209-222. [12] modi, v. j., hill, s. s., yokomizo, t“drag reduction of trucks through boundary-layer control“j. wind eng. ind. aerodyn., 54.55(1995):583-94. [13] bruneau, c h., mortazavi, i., gilliéron, p.”flow regularisation and drag reduction around blunt bodies using porous devices.” iutam symposium on flow control and mems springer netherlands. 2008. [14] bruneau, c. h., gilliéron, p., mortazavi, i. “passive control around the two dimensional square back ahmed body using porous devices” journal fluids engineering, 130.6(2008):611. [15] bruneau, c. h., mortazavi, i. “numerical modelling and passive flow control using porous media. “computers and fluids, 37.5(2008):488-98. [16] bruneau, c. h., depeyras, d., mortazavi, i. “active and passive flow control around simplified ground vehicles.” journal of fluid mechanics, 5.1(2012):89-93. [17] zhang, c., wang, j., shang, y“numerical simulation on drag reduction of revolution body through bionic riblet surface. “science. china technology. sci 53.11(2010):2954-959 [18] sirovich, l., karlsson, s. “turbulent drag reduction by passive mechanisms”. nature, 388(1997):753-55. [19] parker k., sayers, a. t. “the effect of longitudinal microstriations and their profiles on the drag of flat plates”. proc. inst. mech. eng. part c journal. mechanical. engineering. science, 213.8(1999):775-85. [20] grüneberger r., hage, w. “drag characteristics of longitudinal and transverse riblets at low dimensionless spacings.” experiments. fluids, 50.2(2010):363-73. [21] falchi, m., provenzano, g., pietrogiacomi, d., romano, g. p“experimental and numerical investigation of flow control on bluff bodies by passive ventilation.” experiments in fluids, 41.1(2006):21-33. [22] suryanarayana g. k., prabhu, a. “effect of natural ventilation on the boundary layer separation and near-wake vortex shedding characteristics of a sphere.” experiments in fluids, 29.6(2000):582-91. iium engineering journal, vol. 15, no. 1, 2014 altaf et al. 69 [23] pujals, g., depardon, s., cossu, c. drag reduction of a 3d bluff body using coherent streamwise streaks. experiments in fluids, 49.5(2010):1085-94. [24] pujals, g., cossu, c., depardon, s. forcing large-scale coherent streaks in a zero-pressuregradient turbulent boundary layer. journal.ofturbulence, 11(2010):25. doi:10.1080/ 14685248.2010.494607 [25] mode, j. m. simulation of the flow over a flat dimpled plate. arizona state university. msc thesis. (2010). [26] park, h., lee, d., jeon, w.-p., hahn, s., kim, j., kim, j., choi, j., choi, h. drag reduction in flow over a two-dimensional bluff body with a blunt trailing edge using a new passive device. journal of fluid mechanics, 563(2006):389, doi:10.1017/s0022112006001364. [27] norman, a. k., mckeon, b. j. unsteady force measurements in sphere flow from subcritical to supercritical reynolds numbers. experiments.in fluids 51.5(2011):1439-53. [28] park, h., jeon, w.-p. choi, h. and yoo, j. y. mixing enhancement behind a backwardfacing step using tabs. physics.of fluids, 19.10(2007):103-05. [29] jing, c., yun-zhu, w., deng-feng, w., wei-gang, x., gui-jin, wresearch on aerodynamic drag reduction of heavy commercial vehicle. 2nd international conference on computer engineering and technology, 5(2010):194. [30] strachan, r. k., knowles, k., lawson, n. j. the vortex structure behind an ahmed reference model in the presence of a moving ground plane. experiments in fluids, 42.5(2007):659-669. nomenclature 1d one dimensional 2d two dimensional 3d three dimensional dr drag reduction re reynolds number piv particle image velocimetry cfd computational fluid dynamics rans reynolds averaged navier stokes application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 43 wide range modulation indexes featuring carrier-based pwm stepped waveform for half-bridge modular multilevel converters majdee tohtayong1*, sheroz khan2, mashkuri yaacob2, siti hajar yusoff2, nur shahida midi2 and musse muhamud ahmed3 1 department of electrical engineering, faculty of engineering, princess of naradhiwas university, 99, khokkhian, muang, narathiwat 96000, thailand. 2 department of electrical and computer engineering, kulliyah of engineering, international islamic university malaysia, po box 10, 50728 kuala lumpur, malaysia. 3 department of electrical and electronic engineering, faculty of engineering, universiti malaysia sarawak, kota samarahan, 94300 sarawak, malaysia. * corresponding author: powerelectronics911@hotmail.com (received: 12th dec 2016; accepted: 5th june 2018; published on-line: 1st dec 2018) https://doi.org/10.31436/iiumej.v19.i2.788 abstract: this paper presents simulation results of the influence of wide range modulation index values ( am ) in carrier-based pwm strategy for application in generating the stepped waveform. the waveform is tested for application in single-phase half-bridge modular multilevel converters (mmcs) topology. the results presented in this paper include a variation of the fundamental component (50 hz) in the voltage output. it also studies total harmonic distortion of the output voltage (thdv) and the output current (thdi) when the modulation index is changed over the linear-modulation region, 0 < am < 1. it also explores the effect of a modulation index greater than 1. moreover, different output voltage shapes, as a consequence of varied am on mmcs, are also illustrated for showing the effect of varying the value of am on sub-module of mmcs. abstrak: penulisan ini berkenan simulasi pengaruh pelbagai nilai indeks modulasi ( am ) dalam strategi pwm berasaskan aplikasi dalam menghasilkan bentuk gelombang yang bertingkat. bentuk gelombang ini diuji untuk aplikasi dalam topologi mmcs. penilaian dan hasil dari artikle ini termasuk variasi komponen asas (50 hz) dalam voltan keluar. ia juga meneliti jumlah penyelarasan harmonik voltan keluar (thdv) dan arus keluaran (thdi) apabila indeks modulasi ditukar dalam rantau modulasi linear, 0 < am <1. ia juga meneroka kesan indeks modulasi lebih daripada 1. selain itu, bentuk voltan keluar yang berbeza sebagai akibat dari pelbagai am pada mmcs juga digambarkan untuk menunjukkan kesan berbeza-beza nilai am pada sub-modul mmcs. keywords: pwm; converter; stepped waveform; mmc; thd iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 44 1. introduction power converters are generally used in renewable electrical energy sources’ applications of the photovoltaic source or micro-hydropower [1–4]. the circuit is simple and low cost, but it needs a connection in series (or parallel) of a large number of photovoltaic panels to meet high voltage load (or grid system) demands [5]. in the case of solar, unusual environmental condition factors such as shadows from clouds, trees, buildings, dust, moisture, the temperature will cause voltage instability. on the contrary, dc-to-dc converters are proven helpful in maintaining voltage stability. hence, dcto-dc converters are beneficial in the case that the voltage between the primary sources of photovoltaic panels and dc-link (or the dc load) remain unstable. such inverters need be with maximum power point tracking (mppt) features [6,7] for optimizing the amount of electrical energy harvested from the photovoltaic array to dc-link (common coupling point of micro-grid) or the dc load [8]. on the other hand, conversion from available dc-to-ac makes an important step for grid-connectivity in distributed generation (dg) [9]. current areas of research interest include strategic planning of electricity consumption for forecasting futuristic supply demands or suggesting areas or regions of high demand for electric supply investment. in dc-to-ac conversion, control of the modular structure of panels and devices makes the core part. this is to generate smooth output waveforms through operation of switches employed in dc-to-ac converters. however, no matter how smooth the switches operate, there remain associated harmonics as a result of level transitions. in general, each type of dc-to-ac converter topology has a unique pattern of switching operation related to the converter and its topologies such as diode-clamped inverter topology, flying capacitor inverter topology, and modular multilevel inverter topology [10,11]. furthermore, various novel structures of mmcs are proposed to overcome this challenge, such as reducing the mmcs components or the number of power switches [12,13]. the output voltage demand of ac-load can be adjusted by dc-to-dc converters on each module of the mmcs, but in this work, we will report on varying the modulation index in carrier-based pwm strategy on mmcs to produce an output closer to the fundamental component. thd of the output voltage and output current show significant change due to modulation index variation. the carrier-based pwm strategy is flexible and easier in adjusting its value of modulation index such that the switching signals are to generate the desirable value of modulation index over a wider range without complex calculation methods such as shepwm strategy [14]. the modulation index is varied by the mmcs simulation in order to find the lowest value of thd and the changing pattern of the fundamental component. the structure and switching pattern of half-bridge modular multilevel converters are given in section 2. it shows a single sub-module operation, and also an example of mmcs module rearrangement as a single-phase 7-level half-bridge mmc. the effect of modulation index values on the carrier-based pwm strategy is introduced in section 3. section 4 shows the simulation result of a single-phase half-bridge mmc using six sub-module converters for releasing the maximum 7-level stepped waveform. wherewithal, the output terminal of the mmc is connected to an ac load consisting of a single-phase induction motor. the conclusive output of this work is presented in conclusions as section 5 in the end. iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 45 2. half-bridge modular multilevel converter half-bridge modular multilevel converters (half-bridge mmcs) are developed with features such as new configurations, modeling, control schemes, and modulation strategies for applications in medium or high voltage systems [15]. other features of mmcs in focus include topology, easily implementable modular structures, highly responsive speed, harmonics mitigation, increased output power or loss reduction as a result of the improved switching frequency. for an instant, low frequency on switching in mmcs is needed to reduce switching losses and likewise enhance the overall energy efficiency of the power converter [16]. mccs are being employed in hvdc transmission systems, in medium voltage drives (mvds), in power quality systems, and in the distributed battery energy storage system (bess). mmcs are one of the famous inverter topologies used in renewable energy applications due to the fact that they can connect to several separate dc sources. the cascaded half-bridge module converters and the cascaded full-bridge module converters are two common types of mmc topology. vdc sw1 sw2 s1 s2 vo n s2 s1 +vdc 0 2π 4π t 2π 4π t 2π 4π t vo (a) (b) fig. 1: (a) a module of the half-bridge converter and (b) its operation waveforms. a half-bridge converter (hbc) is what can be used for producing complicated modular structures of inverter topologies. hbc includes two series switches and a dc source, whereas va and n are connected to the load at the output terminals and its operation waveform is as shown in fig. 1. here, the circuit can generate two voltage levels of the dc source, +vdc, and zero volts. in principle, switch sw1 is turned on and switch sw2 is turned off to obtain +vdc. on the other hand, switch sw1 is turned off and switch sw2 is turned on to obtain zero volts. however, the output of a half-bridge converter, though alternating, is far from being ac voltage. therefore, a pair of cascaded half-bridge modules is connected to generate ac output voltage in association with a lowpass filter. in addition, for grid-connected applications, the filter design is regularly a challenge to meet the grid and distribution codes [17]. the output voltage level can be increased by configuring a number of hb-mmcs appropriately. an m-level inverter can be connected by m-1 mccs; for example, to obtain a seven-level output voltage, six modules are needed. figure 2(a) illustrates a single-phase half-bridge mmc for generating seven levels of output voltage. the circuit includes six modules with separated dc sources for each module. with this topology, there are three upper side modules for releasing positive output voltage at va, and three lower side modules for releasing negative output voltage at vb. however, both output voltage va and vb share the common neutral point of n. in addition, every single module of a single-phase half-bridge module converter generates iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 46 different waveforms compared to other modules. moreover, each upper and lower side module is working in a complementary fashion for producing a half period cycle of the output. for instance, swa1, swa2, swa3, swa4, swa5, and swa6 are operated for generating the output waveform on the first half period. the switches swb1, swb2, swb3, swb4, swb5, and swb6 are operated for generating the output waveform on the second half period. its operation waveform is illustrated in fig. 2(b). vdc vdc vdc vdc vdc vdc swa1 swa2 swa3 swa4 swa5 swa6 swb6 swb5 swb4 swb3 swb2 swb1 sb6 sb5 sb4 sb3 sb2 sb1 sa1 sa2 sa3 sa4 sa5 sa6 va vb n +vdc +2vdc +3vdc -3vdc -2vdc -vdc 0 2π 4π 2π 4π 2π 4π 2π 4π 2π 4π 2π 4π 2π 4π 2π 4π 2π 4π t t t t t t t t t sa5 sa6 sa3 sa4 sa1 sa2 sb5 sb6 sb3 sb4 sb1 sb2 +vdc +2vdc +3vdc 0 +vdc +2vdc +3vdc 0 vab van vbn (a) (b) fig. 2: (a) a single-phase 7-level half-bridge mmcs and (b) its operation waveforms. 3. carrier-based pwm stepped waveform numerous pwm techniques are proposed for controlling mmcs [18], producing staircase output voltage very closely approximating a sine waveform with minimized total harmonics distortion (thd). one of many pwm techniques for modular multilevel converter operation is known as carrier-based pwm strategy. carrier-based pwm technique for mmc topology is the most popular and easy to implement in generating pwm signals for mmc topologies. here, a simple sinusoidal reference waveform is compared with multi-triangular carrier signals to produce pwm signals. iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 47 vtri1 vtri2 vtri3 vtri4 vtri5 vtri6 vref. sa1 sa2 sa3 sa4 sa5 sa6 sb1 sb2 sb3 sb4 sb5 sb6 fig. 3: an analogue circuit for carrier-based pwm simulation. carrier-based pwm strategy using an analog circuit is as shown in fig. 3 above. it consists of six sub-modules of hbc for producing the 7 levels of the stepped output waveform. furthermore, the simple sinusoidal reference waveform has amplitude, ma , and frequency, mf , and it is placed in the middle of the carrier signal group and a number of triangular carrier signals are equal to m-1, where m is the number of output levels, with the same amplitude, c a , and also the same frequency, cf . the parameters of amplitude modulation index, am , and the frequency modulation, f m , are defined by eq. (1) and eq. (2). c m a am a m   )1( (1) m f c f f m  (2) 4. simulation and discussion the simulation of mmcs uses the analog circuit, as shown in fig. 3, to generate signals by carrier-based pwm technique and mmcs, as shown in fig. 2(a), as a power circuit with an ac load which is an equivalent circuit of a single-phase induction motor with rs = 34 ω ohm, rr =15.2 ω, ll =300 mh and lm =1.06 h, as shown in fig. 4. in addition, the modulation index, am , is varied over a wide range of 0 to 4 at frequency modulation, f m , of 50. vbva rs ll rr lm fig. 4: the equivalent circuit of a single-phase induction motor as a load. iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 48 (a) (a) (b) (b) (c) (c) (d) (d) (e) (e) fig. 5: (a) multicarrier-based pwm signals at am = 0.25, (b) the output voltage waveform, (c) voltage harmonic spectrum, the output current waveform, and (e) current harmonic spectrum. fig. 6: (a) multicarrier-based pwm signals at am = 0.55, (b) the output voltage waveform, (c) voltage harmonic spectrum, the output current waveform, and (e) current harmonic spectrum. 1 1.01 1.02 1.03 1.04 time (s) 0 -1 -2 -3 -4 1 2 3 4 vsin_ref vtri1 vtri2 vtri3 vtri4 vtri5 vtri6 1 1.01 1.02 1.03 1.04 time (s) 0 -1 -2 -3 -4 1 2 3 4 vsin_ref vtri1 vtri2 vtri3 vtri4 vtri5 vtri6 1 1.01 1.02 1.03 1.04 time (s) 0 -200 -400 200 400 vmaininv 1 1.01 1.02 1.03 1.04 time (s) 0 -200 -400 200 400 vmaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 100 200 300 400 vmaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 100 200 300 400 vmaininv 1 1.01 1.02 1.03 1.04 time (s) 0 -2 -4 2 4 imaininv 1 1.01 1.02 1.03 1.04 time (s) 0 -2 -4 2 4 imaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 1 2 3 4 imaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 1 2 3 4 imaininv iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 49 (a) (a) (b) (b) (c) (c) (d) (d) (e) (e) fig. 7: (a) multicarrier-based pwm signals at am = 0.85, (b) the output voltage waveform, (c) voltage harmonic spectrum, the output current waveform, and (e) current harmonic spectrum. fig. 8: (a) multicarrier-based pwm signals at am = 1.00, (b) the output voltage waveform, (c) voltage harmonic spectrum, the output current waveform, and (e) current harmonic spectrum. 1 1.01 1.02 1.03 1.04 time (s) 0 -1 -2 -3 -4 1 2 3 4 vsin_ref vtri1 vtri2 vtri3 vtri4 vtri5 vtri6 1 1.01 1.02 1.03 1.04 time (s) 0 -1 -2 -3 -4 1 2 3 4 vsin_ref vtri1 vtri2 vtri3 vtri4 vtri5 vtri6 1 1.01 1.02 1.03 1.04 time (s) 0 -200 -400 200 400 vmaininv 1 1.01 1.02 1.03 1.04 time (s) 0 -200 -400 200 400 vmaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 100 200 300 400 vmaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 100 200 300 400 vmaininv 1 1.01 1.02 1.03 1.04 time (s) 0 -2 -4 2 4 imaininv 1 1.01 1.02 1.03 1.04 time (s) 0 -2 -4 2 4 imaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 1 2 3 4 imaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 1 2 3 4 imaininv iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 50 (a) (a) (b) (b) (c) (c) (d) (d) (e) (e) fig. 9: (a) multicarrier-based pwm signals at am = 1.25, (b) the output voltage waveform, (c) voltage harmonic spectrum, the output current waveform, and (e) current harmonic spectrum. fig. 10: (a) multicarrier-based pwm signals at am = 3.55, (b) the output voltage waveform, (c) voltage harmonic spectrum, the output current waveform, and (e) current harmonic spectrum. 1 1.01 1.02 1.03 1.04 time (s) 0 -1 -2 -3 -4 1 2 3 4 vsin_ref vtri1 vtri2 vtri3 vtri4 vtri5 vtri6 1 1.01 1.02 1.03 1.04 time (s) 0 -6 -12 -18 -24 6 12 18 24 vsin_ref vtri1 vtri2 vtri3 vtri4 vtri5 vtri6 1 1.01 1.02 1.03 1.04 time (s) 0 -200 -400 200 400 vmaininv 1 1.01 1.02 1.03 1.04 time (s) 0 -200 -400 200 400 vmaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 100 200 300 400 vmaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 100 200 300 400 vmaininv 1 1.01 1.02 1.03 1.04 time (s) 0 -2 -4 2 4 imaininv 1 1.01 1.02 1.03 1.04 time (s) 0 -2 -4 2 4 imaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 1 2 3 4 imaininv 0 500 1000 1500 2000 2500 frequency (hz) 0 1 2 3 4 imaininv iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 51 the simulation results of carrier-based pwm strategy operation, output voltage waveforms and their harmonic spectrums, and output current waveforms and their harmonic spectrums are given in fig. 5, fig. 6, fig. 7, fig. 8, fig. 9, and fig. 10. the output waveforms of fig. 5, fig. 6, fig. 7, and fig. 8 are obtained over the linearmodulation region; however, fig. 9 and fig. 10 results are for a modulation index in the over-modulation region. moreover, all results show a modulation index-reliant behaviour. for instance, fig. 5 shows results of 3-level output voltage over a range of 0 < am < 0.33 while modulation reliance results over a range of 0.33 < am < 0.66 are given in fig. 6. a 7-level output voltage for am > 0.66 is shown in fig. 7. the results thus have shown modulation indexes as a function of featured inverters’ levels. it can be noted that sub-modules are always working normally even if the modulation index is varied over a wide range. experimentally, this may cause imbalance switching-heat sharing that may lead to inflicting damages on the mmc’s circuit. (a) (b) fig. 11: (a) fundamental component and (b) %thd of the output voltage. (a) (b) fig. 12: (a) fundamental component and (b) %thd of the output current. iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 52 the plot of the wide-range modulation index versus the fundamental component of the output voltage (vf), and the output current (if) are illustrated in fig. 11(a) and fig. 12(a), respectively. consequently, vf and if linearly increase as am is varied over the linear-modulation region until it increases, even if modulation, am , continues into the over-modulation region, though non-linear with a slightly reducing slope. figure 11(b) and fig. 12(b) show the wide-range modulation index versus the total harmonic distortion of the output voltage (thdv) and the output current (thdi) respectively. the lowest thdv is 12.55% for a modulation index of am = 1.1 and thdi is 0.33% for a modulation index of am = 1. besides, thdi is below 3% while the mmc is operated under the linear-modulation region, but it dramatically grows when am increases beyond into the over-modulation region and it rises up over 5% while am is more than 1.44. 5. conclusions this paper has presented simulation results of multi-level inverters made from halfbridge converters (hbcs) with a modulation index, am , ranging in values from 0 to 4. the carrier-based pwm strategy for generating a stepped waveform is implemented using single-phase half-bridge modular multilevel converter topology. the fundamental component and the total harmonic distortion of the output voltage are presented as results. the regions of the wide range modulation variation are identified as 0-0.33, 0.33-0.66, and above 0.66. the linear-modulation region shows linearity for the fundamental frequency component and low thdi. that means that the larger modulation indexes give larger magnitude of the fundamental frequency component. however, the linearity is lost in the case of over-modulation, that is, for a modulation index of more than 1.0, with regards to changes in fundamental component but quite high thdi. hence, thdv (thd=12.55%) and thdi (thdi=0.33%) show the lowest thd simulation results. the minimum thd values for current and voltage both appear at the boundary (modulation index of 1.0) of linear and nonlinear regions, featuring the effect of modulation index more clearly. references [1] blaabjerg f, yang y, ma k, wang x. (2015) power electronics the key technology for renewable energy system integration. in proceedings of international conference on renewable energy research and applications: 22 november 2015; pp 1618-1626. [2] choi um, lee kb, blaabjerg f. (2012) power electronics for renewable energy systems: wind turbine and photovoltaic systems. in proceedings of international conference on renewable energy research and applications: 11 november 2012; pp 1-8. [3] liang x. (2017) emerging power quality challenges due to integration of renewable energy sources. ieee transactions on industry applications, 53(2):855-866. [4] karimov ks, abid m, al-grafi mw, islomov si, karimova nh. (2013) the economics of micro hydro power plants. iium engineering journal, 14(2):173-181. [5] kjaer sb, pedersen jk, blaabjerg f. (2005) a review of single-phase grid-connected inverters for photovoltaic modules. ieee transactions on industry applications, 41(5):1292-1306. [6] shi y, li r, xue y, li h. (2016) high-frequency-link-based grid-tied pv system with small dc-link capacitor and low-frequency ripple-free maximum power point tracking. ieee transaction power electronics, 31(1):328-339. iium engineering journal, vol. 19, no. 2, 2018 tohtayong et al. 53 [7] alajmi bn, ahmed kh, adam gp, finney sj, williams bw. (2011) modular multilevel inverter with maximum power point tracking for grid connected photovoltaic application. in proceedings of 2011 ieee international symposium on industrial electronics: 27 june 2011; pp 2057-2062. [8] koutroulis e, blaabjerg f. (2011) design optimization of grid-connected pv inverters. in proceedings of twenty-sixth annual ieee applied power electronics conference and exposition: 6 march 2011; pp 691-698. [9] mahzarnia m, sheikholeslami a, adabi j. (2013) a voltage stabilizer for a microgrid system with two types of distributed generation resources. iium engineering journal, 14(2):191-205. [10] tohtayong m, khan s, yusoff sh, yaacob m, ahmed mm, motakabber sm, aboadla eh. (2016) stepped waveform generation for multilevel inverter topology applications. in proceedings of international conference on computer and communications engineering: 26 july 2016; pp 219-224. [11] samadaei e, gholamian sa, sheikholeslami a, adabi j. (2016) cascade topologies for the asymmetric multilevel inverter by new module to achieve maximum number of levels. iium engineering journal, 17(2):83-93. [12] babaei e, laali s, bayat z. (2015) a single-phase cascaded multilevel inverter based on a new basic unit with reduced number of power switches. ieee transactions on industrial electronics, 62(2):922-929. [13] masaoud a, ping hw, mekhilef s, taallah as. (2014) new three-phase multilevel inverter with reduced number of power electronic components. ieee transactions on power electronics, 29(11):6018-6029. [14] buccella c, cecati c, cimoroni mg, razi k. (2014) analytical method for pattern generation in five-level cascaded h-bridge inverter using selective harmonic elimination. ieee transactions on industrial electronics, 61(11):5811-5819. [15] perez ma, bernet s, rodriguez j, kouro s, lizana r. (2014) circuit topologies, modelling, control schemes and applications of modular multilevel converters. ieee transactions on power electronics, 30(1):4-17. [16] edpuganti a, rathore ak. (2015) optimal low-switching frequency pulse width modulation of medium voltage seven-level cascade-5/3h inverter. ieee transactions on power electronics, 30(1):496-503. [17] zabaleta m, burguete e, madariaga d, zubimendi i, zubiaga m, larrazabal i. (2016) lcl grid filter design of a multimegawatt medium-voltage converter for offshore wind turbine using shepwm modulation. ieee transactions on power electronics, 31(3):1993-2001. [18] varghese lj, keziselvavijila c, raglend ij. (2016) a survey of modulation techniques for a series connected voltage source inverters. international journal of advanced engineering technology, 7(2):571-581. microsoft word vol 5-1-page 25-35.doc iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 25 conventional treatment of surface water using moringa oleifera seeds extract as a primary coagulant suleyman a. muyibi+*, ahmed hissein m birima ‡, thamer a. mohammed‡, megat johari m. m. noor‡ + department of biotechnology engineering, faculty of engineering, international islamic university malaysia, 53100 kuala lumpur, malaysia. ‡ department of civil engineering, faculty of engineering universiti putra malaysia, 43400 serdang, selangor, malaysia. *e-mail: suleyman@iiu.edu.my abstract: the present study involved the use of a model pilot scale water treatment plant to treat turbid surface water from a stream using processed moringa oleifera seed with 25 % w/w oil extracted as primary coagulant. the water treatment plant was made up of four unit operations: coagulation, flocculation, sedimentation, and filtration (rapid sand filter). test runs were carried out for three hours per run over a three-month period with turbidities ranging from 18 to 261 ntu. the turbidity, ph, and alkalinity as well as the filter head loss were measured every 30 minutes during the experimental runs. average turbidity removal of up to 96 % at an effective doses of 20 and 30 mg/l of oil extracted m. oleifera for low (< 50 ntu) and moderate turbidity (< 100 ntu) water respectively was observed doses 50 – 80 mg/l for high turbidity (> 100 ntu) water. m. oleifera seed extract was found to have no significant effect on ph or alkalinity of the water. the residual turbidities measured during most of the test runs satisfied the malaysian guideline for drinking water supplies. key words: moringa oleifera, primary coagulant, coagulation, pilot plant, filtration. 1. introduction many coagulants are widely used in conventional water-treatment process for turbidity removal during potable water production. these coagulants may be classified as inorganic, synthetic organic polymer, and natural polymer. these coagulants are used for various purposes depending on the chemical characteristics of the water to be treated. aluminium salts are by far the most widely used coagulant in water and wastewater treatment. however, recent studies have pointed out several serious drawbacks in using alum salts [13] such as alzheimer’s disease and similar health related problems associated with residual alum in treated waters, beside production of large sludge volumes. there is also the problem of reaction of alum with natural alkalinity present in water leading to reduction of ph and a low efficiency in coagulation of cold waters [2]. ongoing studies to produce more effective aluminium coagulants, such as polyaluminum chloride (pac), iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 26 have not corrected all the drawbacks mentioned above [2]. ferric salts and synthetic polymers have also been used as coagulants but with limited success because of similar disadvantages manifested in the use of aluminium salts. in addition to these problems, chemicals used for water treatment in developing countries constitute a high percentage of annual running expenditure of water treatment companies. the costs of these chemicals have also been increasing at an alarming rate because local manufacturing companies cannot cope with the demand for these chemicals in other industrial applications. therefore, the shortfall has to be imported with scarce convertible foreign currency. these problems force many water treatment companies to resort to under-dosing of chemicals so as to meet the increasing water demand. the result is the supply of poor quality water, especially during the rainy season, when suspended solids concentration and other pollutants in surface water are very high [3, 4]. on the other hand, naturally occurring coagulants are usually presumed safe for human health. some studies on natural coagulants have been carried out and various natural coagulants have been produced or extracted from microorganisms, animals, or plants [5]. moringa oleifera (family moringaceae) is a tropical plant known to contain coagulating/flocculating compounds in the seeds. many researchers have used m. oleifera seed as a primary coagulant, for water treatment [1-4, 6, 7]. many studies [1, 2, 6, 8, 9-12] have been carried out on the performance of m. oleifera seeds as a primary coagulant, coagulant aid and as conjunctive with alum. m. oleifera showed a high coagulation activity for the high turbidity water. the coagulation activity was low for low turbidity water. results of only three pilot scale studies [9 – 11] using m. oleifera seeds extract as a primary coagulant in turbid surface water treatment worldwide have been documented. the main objective of the present study was to investigate the use of a model pilot scale water treatment plant to evaluate the efficiency of m. oleifera seeds with 25 % w/w seed oil extracted in the treatment of turbid surface water from a stream. in previous studies by others [9-11], m. oleifera seed used was not processed to remove some of the oil content. it has, however, been found that processing of the seed to remove the oil improved the coagulation efficiency of the seeds [12, 13]. based on results from a related study, in which selected oil removals were observed to give enhanced coagulation properties to the m. oleifera seed extract with the best results achieved from 25 % w/w oil extracted [13], 25% w/w oil was extracted from m. oleifera seed kernel. 2. experimental 2.1 materials and methods 3.1.1. pilot plant design and fabrication a pilot water treatment plant was designed and built to a distorted scale of 1/40 horizontal and 1/15 vertical. the model treatment plant schematic is shown in figure 1. it was located near a small stream at the hydraulic laboratory in the department of civil engineering faculty of engineering at universiti putra malaysia in serdang, selangor iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 27 state of malaysia. raw water was pumped into the overhead tank of the pilot plant. the plant was designed and constructed as a compact system that could be moved easily. fig. 1: schematic of pilot scale water treatment plant. 3.1.2. pilot plant details. figure 1 shows the schematic diagram of the pilot plant. the pilot plant consisted of a raw water inlet pipe connected to a small centrifugal pump, raw water tank (1) equipped with an automatic flow level controller and flow meter. it has a coagulant dosing tank (5) equipped with variable speed masterflex pump (cole-palmer instruments, usa) which was connected to the coagulation and flocculation units (2, 3) equipped with ika rw variable speed digital mixers (ika works, malaysia). a settling unit equipped with inclined plates (3) and connected to rapid gravity sand filter equipped with a manometer (4), and treated water tank (6). 2.2 water sample the raw water used in this study was pumped from the stream located near the hydraulics laboratory. the raw water quality parameters measured during the 18 5 cm 2 3 5 21 5 cm 14 5 cm 1 4 6 backwash pump raw water pump 1. raw water tank with automatic flow rate controller and flow meter 2. coagulation tank 3. flocculation / settling tank with inclined plates 4. rapid gravity filter with underdrain and manometer 5. coagulant dosing tanks with dosing pumps 6. treated water tank with backwash pump iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 28 experimental runs were; ph 7.1 to 7.5; alkalinity 0.78 to 2.8 mg/l as caco3; and turbidity 18 to 261 ntu. 2.3 preparation of m. oleifera seed suspension dry m. oleifera seeds used in the study were obtained from trees around sri serdang area of selangor state, malaysia. the seed wings and coat were removed and the seed kernel dried in the oven at 50 oc for 24 hours. the seeds were ground using a domestic food blender. oil was extracted from the ground seed using a soxhlet apparatus and hexane as the solvent. only 25 % w/w oil was extracted from the seed kernel because in a previous related study, it was observed that extraction of 25 % w/w oil from m. oleifera seed powder gave the best performance when applied to coagulation of turbid water [13]. five grams of oil extracted seeds (remaining cake) powder was blended at high speed for two minutes in a variable speed domestic food processor (national mjc85n) with 200 ml of distilled water added. the resulting suspension was filtered through a clean muslin cloth in a beaker and the filtrate made up to a final volume of 500 ml to yield a stock solution of approximately 10000 mg/l. 2.4 equipment a jar test apparatus (jar tester cz 150) was used to obtain the optimum m. oleifera coagulant dose for each experimental run. a portable turbidimeter (hach model 2100p) was used to measure the turbidity. filter head loss development was measured using a manometer (armfield instruments, uk) with plastic small bore tubing mounted on a wooden board connected to different levels in the rapid gravity filter. 2.5 experimental methods the experimental program followed in this study consisted of two parts. firstly, a sample of raw water was collected from the overhead tank and jar tests carried out to determine the effective dose for each experimental run. the stock solution of m. oleifera required for the 3-hour experimental run was prepared according to the effective dose obtained from the jar tests. the flow rate was set and the dosing pump calibrated to the required flow rate. during each run water samples were taken every 30 minutes from the overhead tank (initial sample), settling tank and from the treated water. turbidity, ph, and alkalinity were measured for both raw water and treated water from the filter outlet according to standard guidelines and procedures [14]. the filter head losses at different levels in the manometer tubing were also measured and recorded every 30 minutes. 3. results and discussion 3.1 turbidity removal 3.1.1. low turbidity (< 50 ntu) figure 2 shows the average results of 3 runs of 9 hours duration when the surface water turbidity was low varying from 18.0 – 28.0 ntu. the residual turbidity varied from 4.5 to iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 29 5.2 ntu which was well within the malaysian minimum guideline for drinking water supplies. it is pertinent to note that m. oleifera performed very well as a primary coagulant in the removal of turbidity from water with low initial turbidity in contrast to the results obtained from previous studies [4, 2, 9, 10] which all concluded that since the bioactive constituents in m. oleifera seed extract is a low molecular weight short chain polyelectrolyte, it would be inefficient in the removal of turbidity from water with low initial turbidity. a possible reason which may be postulated for this observation is the method of preparation of m. oleifera used which involved extraction of oil of up to 25% of kernel weight (83% oil removal) from the powdered seed kernel before using the residual cake as primary coagulant. all previous studies in which m. oleifera seed extract was used as primary coagulant, no oil was extracted from the seed kernel before application. 0.0 5.0 10.0 15.0 20.0 25.0 30.0 0 3 6 9 run time (hrs) t ur bi di ty ,n t u inlet turbidity filter outlet malays ian limit fig. 2: turbidity of inlet and filtered outlet at a dose of 30 mg/l using 25 % w/w oil extracted m. oleifera seed (initial turbidity of water 18 to 28 ntu) 3.1.2. moderate turbidity (50  turbidity 100 ntu) figure 3 presents the average results for moderate turbidity that varied from 65 to 90 ntu. the effective dosage of m. oleifera used was 30 mg/l. the turbidity dropped from 77.8 ntu to 5.6 ntu after filtration at the beginning of the experiment and reduced gradually to 4.5 ntu, satisfying the malaysian guideline for drinking water supplies. the overall turbidity removal after filtration varied from 91.9 % 94.9 %. the gradual improvement in turbidity removal within the experiment run may have been due to the improvement in flow conditions in the filter bed because the filter was operated for 12 hours without backwashing during the initial commissioning before the experimental runs commenced. during this period, flocs and other sediments were deposited through the sand media due to the effects of particle transport and attachment mechanisms. the deposited micro and macro particles reduced the effective pore area of the sand media, thus forming a deep bed deposit, which improved the quality of the filtered water. iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 30 1 10 100 0.5 1.0 1.5 2.0 2.5 3.0 3.5 run time (hrs) t ur bi di ty ,n t u inlet turbidity filter outlet m alay sian standard fig. 3: turbidity of inlet and filtered outlet at a dose of 30 mg/l using 25 % w/w oil extracted m. oleifera seed (initial turbidity of water 65 to 90 ntu). 3.1.3. high turbidity (≥ 100ntu) figure 4 represents the average results for high turbidity varying from 100 to 260 ntu. the effective dosage of m. oleifera used varied from 50 mg/l to 70 mg/l. the turbidity removal after coagulation and settling was found to improve with an increase in initial turbidity of raw water and time of filter run. for example, for water with an initial turbidity of 100 ntu, the residual turbidity recorded was 7 ntu corresponding to a removal 93 %. after two hours the initial raw water turbidity increased to 134 ntu, while the residual turbidity reduced to 5.5 ntu corresponding to 96 % removal. this observation may be explained in terms of the increase in suspended particles available with an increase in initial turbidity. this increase created more sites for adsorption and inter-particle bridge formation resulting in an increase in particle collision frequency and agglomeration rate leading to decrease in residual turbidity [4]. as much as 98 % of the solids were removed and the turbidity of the filtered water was between 4.5 and 7 ntu. 3.1.4. ph variation figure 4 indicates the relationship between the ph of raw water and treated water for average results from four experimental runs. the ph of raw water varied from 7.23 to 7.84 (average of 7.43 and standard deviation of 0.144). in general the ph of the treated water was slightly lower than the ph of the raw water. in a laboratory based study in which alum and m. oleifera, shelled and non-shelled seed were used as coagulants, the ph value was found to be constant in the case of m. oleifera while it decreased from 7.6 to 4.2 with addition of alum [2]. this implied that further chemical addition was necessary in order to correct the ph of the treated water to values between 6.5 and 9 to meet the malaysian standard. the effect of m. oleifera on the ph of iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 31 the water was insignificant and no ph adjustment for the water was required after treatment. this is a major advantage when m. oleifera is used for coagulation. 1 10 100 1000 0.5 1.5 2.5 3.5 4.5 run time (hrs) t ur bi di ty ,n t u inlet turbidity filter outlet malays ian standard fig. 4: turbidity of inlet and filtered outlet at a dose of 50 to 70 mg/l 25 % w/w oil extracted m. oleifera seed (initial turbidity of water 100 to 260 ntu). 3.1.5. alkalinity variation figure 5 shows the composite results of variation of alkalinity of both raw and treated water as a function of time for three experimental runs. the alkalinity of the raw water ranged between 1.5 and 2.2 mg/l caco3. it was observed that the alkalinity of the treated water was generally equal to that of the raw water. in very few instances the alkalinity of treated water was slightly less than that of the raw water with a maximum variation of 0.2 mg/l caco3. 7.25 7.30 7.35 7.40 7.45 7.50 0.5 1.5 2.5 3.5 run time (hrs) ph raw water treated water fig. 5: ph of inlet and filtered outlet at a dosage of 30 mg/l 25 % w/w oil extracted m. oleifera seed. iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 32 the low alkalinity of the raw water as well as the treated water could initiate corrosion problems in the distribution networks. it is common practice in water treatment to add alkalinity in the form of bicarbonate or lime to increase the alkalinity. with m. oleifera, it may therefore be necessary to add lime or soda ash to alleviate the possible occurrence of such a problem. 0 0.5 1 1.5 2 2.5 3 0.5 1.5 2.5 3.5 run time (hrs) a lk al in ity ,m g/ l as c ac o 3 raw water treated water fig. 6: alkalinity of inlet and filtered outlet at a dose of 30 mg/l 25 % w/w oil extracted m. oleifera seed. 3.1.6. head loss development development of head loss at four different depths, 10, 20, 30, and 40 cm from the sand surface are shown in figure 7. the figure shows the average head loss development for five runs carried out after back washing. the raw water turbidity varied between moderate and high with an average of 162 ntu. the variation of head loss with time was recorded from the third run after back washing as the results of the second run after backwashing were not available because of malfunctioning of the manometers. it was observed that the head loss at 40 cm after 60 minutes was 6.3 cm, which increased gradually with time up to 24 cm after 6 trials (18 hrs). it then dropped to 15.7 cm. breakthrough occurred after 19 hours of operation and the turbidity of the filtered water increased from 4.5 ntu to 9.7 ntu. the experimental runs were then terminated and the filter was backwashed. 0 5 10 15 20 25 0 1 2 3 4 5 6 7 8 9 10 11 12 13 run time (hrs) h ea d lo ss (c m ) manometer 10 manometer 20 manometer 30 manometer 40 fig.7: variation of filter head loss at inlet and filtered outlet. iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 33 3.2 filter head loss and residual turbidity the relationship between the filter head loss and residual turbidity is presented in figure 8, which represents a composite of three experiments. the average initial turbidities of low, medium and high turbidity were 18.5, 82.8 and 142 ntu respectively. it was observed that the residual turbidity decreased with increase in the head loss. the highest turbidity removal was at residual turbidity of 4.5 ntu, which was obtained for raw water with high turbidity and medium turbidity. the corresponding head loss was 9.6 and 11.9 cm respectively. 0 1 2 3 4 5 6 7 8 9 10 1 1.5 2 2.5 3 run time (hrs) r es id ua l t ur bi di ty ,n t u 5 6 7 8 9 10 11 12 13 14 15 fi lte r h ea d lo ss , c m r.turb. for low. turb. r. turb. for medium r. turb. for high turb. low turb. head loss medium turb. headloss high turb. head loss fig. 8: filter head loss and residual turbidity variation. 3.3 summary of findings 1 effective doses of 20 and 30 mg/l of m. oleifera for low (< 50 ntu) moderate turbidity (< 100 ntu) and 50 – 80 mg/l for high turbidity (> 100 ntu) feed water respectively removed an average 96 % of the initial turbidity of the raw water. 2 the effective dose of m. oleifera used for the test runs was obtained from the jar test results. for low turbidity it was 20 mg/l, moderate turbidity 30 mg/l and for the high turbidity the dosage varied from 50 to 80 mg/l depending on the initial turbidity. 3 analysis of the water treated in the pilot plant showed that m. oleifera did not significantly affect the ph or alkalinity after treatment. 4 the maximum filter head loss, after which the breakthrough occurred, was 24 cm at the depth of 40 cm. the corresponding operation time was 18 hours. 5 the residual turbidities measured during most of the test runs satisfied the malaysian guideline for drinking water supplies. iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 34 acknowledgement the authors are grateful to the malaysian ministry of science, technology and innovation for funding the research under the irpa grant no. 09-02-04-0089 program cycle 2 and 3, 1998. references [1] a. ndabigengesere, k.s. narasiah, and b.g. talbot, “active agent and mechanism of coagulation of turbid waters using moringa oleifera”, water research, vol. 2, pp. 703-710, 1995. [2] a. ndabigengesere, k.s. narasiah, “quality of water treated by coagulation using moringa oleifera seeds”, water research, vol. 32, no. 3, pp. 781-791, 1998. [3] s.a. muyibi, “moringa oleifera seed extract in water treatment”, journal-institution of engineering, malaysia, vol. 59, no. 3, pp. 37 – 50, 1998. [4] s.a. muyibi. and l.m. evison, “optimizing physical parameters affecting coagulation of turbid water with moringa oleifera seeds”, water research, vol. 29, no. 12, pp. 2689-2695, 1995. [5] t, okuda, a.u. baes, w. nishijima, m. okada, “coagulation mechanism of salt solution extracted active component in moringa oleifera”, water research, vol. 35, no. 3, pp. 830834, 2001. [6] s.a. muyibi and c.a. okuofu, “coagulation of low turbidity surface waters with moringa oleifera seeds”, international journal of environmental studies, vol. 48, pp. 263-273, 1995. [7] s.a. muyibi and c.a. okuofu, “softening hard waters with moringa oleifera seed extracts”, international journal of environmental studies, vol. 50, pp. 247-257, 1996. [8] s.a. muyibi. and l.m. evison, “coagulation of turbid water and softening of hard water with moringa oleifera seeds”, international journal of environmental studies, vol. 49, pp. 247-259, 1996. [9] f. kasser, c. werner, and o. nahayo, “rural water treatment using moringa oleifera seeds as coagulant”, natural resources development, 33, 33-47, institute for scientific cooperation, tubingen, germany, 1990. [10] j.p. sutherland, g.k. folkard, and w.d. grant, “development of robust water treatment incorporating natural coagulants”, field study report, environmental engineering group, department of engineering, university of leicester, uk, 1992. [11] g.l. mcconnachie g.k. folkard, m.a. mtawali, and j.p. sutherland, “field trials of appropriate hydraulic flocculation process”, water research, vol. 33, no. 6, pp. 1425-1434., 1999. [12] s.a. muyibi, j.m.m.n. megat., h.l. lam, k.l. tan, “effects of oil extraction from moringa oleifera seeds on coagulation of turbid water”, international journal of environmental studies, vol. 59, no. 2, pp. 243-254, 2002. [13] s.a. muyibi, s.a. abbas, j.m.m.n. megat, a. fakhrul-razi “enhanced coagulation efficiency of moringa oleifera seeds through selective oil extraction”. iium journal of engineering(in press 2003). iium engineering journal, vol. 5, no. 1, 2004 s. a. muyibi et al. 35 [14] american public health association (apha), american water works association (awwa) and water environment federation (wef) standard methods for the examination of water and waste-water, 20th edition apha publication office, washington d.c., 1999. biographies dr. suleyman aremu muyibi was born in 1950 in osogbo, osun state nigeria. he earned his bs in engineering from the university of central florida, usa in 1979, meng from the university of benin, nigeria in 1987 and phd in environmental engineering from the university of newcastle upon tyne, uk in 1995. he also earned a diploma in islamic studies (dis) from the international islamic university malaysia in 2001. he is a member of the nigerian society of engineers (nse), a registered civil engineer (coren, nigeria), and a member of the malaysian national committee on irrigation and drainage (mancid), and group leader of the environmental biotechnology engineering research group (eberg) at the international islamic university malaysia. he is currently an associate professor in the department of biotechnology engineering, faculty of engineering, international islamic university malaysia. his area of research interest include environmental biotechnology, water supply and treatment, wastewater treatment, water pollution control, development of bioactive materials for use in water and waste treatment and environmental hydraulics. he has authored and co-authored more than 50 publications in journals, conferences, technical reports, and a textbook. ahmed hissein m birima bs (libya), msc (upm). ahmad is currently a phd candidate in water engineering at the department of civil engineering, faculty of engineering, universiti putra malaysia. dr. thamer ahmad mohammed bsc. (mosul), msc. (baghdad), phd (upm). dr. thamer is currently an associate professor in the department of civil engineering, universiti putra malaysia. his research interest includes surface and groundwater modelling with environmental considerations and environmental hydraulics. dr. thamer has authored and co-authored more than 20 publications in journals, conferences and technical reports. ir. megat johari m. m. noor b.sc. (hons), m.sc. (loughborough), p.eng. m.i.e.m., m.i.f.s., miwa, mmancid. ir. megat is an associate professor in the department of civil engineering, universiti putra malaysia. his areas of research interest include design and development of membrane bioreactor for treating high strength municipal wastewater, m. oleifera seeds extracts as a coagulant and coagulant aid in water treatment, the use of natural coagulants for water treatment, tertiary treatment of industrial and domestic wastewater using microfiltration, soil stabilization, and sludge treatment for safe disposal and recoveries. ir. megat has authored and co-authored more than 50 publications in journals, conferences and technical reports. microsoft word papre v4-n2-1 new.doc iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 1 influence of temperature and pressure on dispersion properties of nonlinear single mode optical fibers mostafa h. ali*, ahmed e. elsamahy†, maher a. farhoud†, taymour a. hamdalla† *faculty of engineering, alexandria university †faculty of science, alexandria university e-mail: mosaly @ aast.edu abstract: near field distribution, propagation constant and dispersion characteristics of nonlinear single-mode optical fibers have been investigated. shooting-method technique is used and implemented into a computer code for both profiles of stepindex and graded-index fibers. an error function is defined to estimate the discrepancy between the expected electric-field radial derivative at the core-cladding interface and that obtained by numerically integrating the wave equation through the use of runge-kutta method. all of the above calculations done under the ocean depth in which the depth will affect the refractive index that have a direct effect on all the optical fiber parameters. key words: nonlinear refractive index, normalized propagation constant, mode delay factor, material dispersion, waveguide dispersion. 1. introduction the attractiveness of the lightwave communications is the ability of the silica-optical fibers to carry large amount of information over long repeaterless spans. to utilize the available bandwidth, numerous channels at different wavelengths can be multiplexed on the same fiber and higher transmitter powers are required to increase system margins. all these attempts to fully utilize the capabilities of silica fibers will ultimately be limited by nonlinear interactions between the information-bearing light waves and the transmission medium. these optical nonlinearities can lead to interference, distortion and excess attenuation of the optical signals, resulting in the systems degradation [1]. refractive index as a function of the pressure is very important for all the fiber parameters like the electric field, the normalized propagation constant and all dispersion types. so, it plays a vital role in the optical fiber communication system in particular for the undersea submarine optical fiber cables which are used to transmit optical signals from one continent to another. up to now, most of the researches are focused on the waveguide structure mentioned above. boardman and egan [4] developed a general dispersion equation for nonlinear optical waveguides of the second kind with a kerrtype nonlinearity. this equation has been used in the investigation of guided iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 2 characteristics for a saturable case.[3] the dispersion equation has been modified to exclude possible spurious modes by dividing the two types of dispersion equations. the results are considered to be exact when compared with results obtained numerically in the present work. yuan performed calculations above the sea level without taking into account the influence of pressure and temperature on the refractive index for planner waveguide [5]. throughout this paper, the second-order differential equation for nonlinear optical fibers has been solved by the runge-kutta numerical integration and the secant method, using the concept of the shooting method. all effects of the various fiber parameters on the modal field distribution, the propagation constant and the dispersion characteristics have been studied for both step and graded index fibers. calculations were done after taking into account the refractive index as a function of pressure and temperature. 2. basic model and analysis the nonlinear refractive index of the fiber, n, can be represented as a sum of two terms: n = no + nii i, (1) where no is the ordinary refractive index associated with the material, nii is the intensity dependent refractive index and i is the optical intensity. equations used for determining the exact value for no due to pressure dependence have the form: 2 2 2 2 2( , ) b d n p a c e λ λ λ λ λ = + + (2) where λ is the wavelength, -6 -8 2 -6 -8 2 -2 -8 -10 2 -6 -8 2 1.29552 9.86385 10 0.544763 10 0.809872 42.0899 10 -1.71823 10 1..07945 10 0.56693 10 0.894313 10 0.917151 38.7911 10 -1.13552 10 100 a p p b p p c p p d p p e = + × + × = + × × = × × + × = + × × = , (3) and p is the pressure in mn/m2. the effect of temperature on the refractive index can also be calculated from: 23 2 2 2 1 ( ) ( , ) 1 ( ) i o i i a t n t t λ λ λ λ= = + − ∑ (4) where 1 2 3 1 2 3 ( ) 0.6961663 , ( ) 0.4079426 , ( ) 0.8974749 ( ) 0.0684043 , ( ) 0.1162414 , ( ) 9.896161 t t t t t t a t a t a t t t t α α α λ β λ β λ β = × = × = × = × = × = × (5) -40.93721 2.0857 10 , ot t t t t α β= + × × = (6) iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 3 in which to = 27 °c and t is the ambient temperature. the pressure and temperature can be calculated as a term of the ocean depth (d in km) from the relation: -1 2 -3 3 2 2 2 2 3 4 5 9.91 0.23744 10 0.19232 10 10 km 27.7 0.62671 10 0.53838 10 0.20674 10 3.5994 0.23156 p d d d d t d d d d d = × + × ≤ = × × + × × × × + × × (7) the controlling differential equations for the radial field component in both core and cladding are respectively written as [5]: 22 2 2 2 2 1 1 1( ) 0 2 c ed e de v b f r e dr r dr a n α  + + =    (8) 2 2 2 2 1 0 d e de v be dr r dr a + = , (9) where a is the core radius, b is the normalized propagation constant, v is the normalized frequency, αc is the nonlinearity term and f(r) is an assumed function that defines whether the fiber under consideration is step or graded index. for step index f(r) = 0 and for graded index f(r) = (r/a)2. so, using the shooting method, two initial guesses, β1 and β2 for the propagation constant are used. the core differential equation is integrated step-by-step using the fourth order rungekutta method. the electric field and its derivatives are calculated each step till reaching the core-cladding interface. a certain problem appeared in the numerical integration process due to the cylindrical geometry. an approximation must be used to overcome this problem. the gaussian approximation has been used to estimate both the electric field and its derivative at the radial coordinate as an initial condition. the used gaussian function has the form: e= eo exp (-r2/ωo2), (10) where eo is the axial value of the electric field and ωo is the spot size of the fundamental mode. both e and de/dr obtained from gaussian approximation are used as initial values in the numerical integration process. performing the integration, a matching condition may be represented as the formula in: 1 ( )1 ( )o k wde w e dr a k w = , (11) where k1(w) is the modified bessel function of first order and w2 = a2(n12k2 β2) with k the wave number and β is the propagation constant. an error function is used to evaluate the mismatch between the predicted result of the first derivative of the electric field and that obtained by the numerical integration. this error function is defined as: iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 4 1 ( ) ( )o k wa de err e w dr k w = , (12) the error function is estimated twice, once for each of the two initial guesses for βe using the secant method. the two obtained error values are used to estimate a correction term for a new guess of the effective index, βnew, through the formula: 2 1 2 2( ) ( 12)new err err err β β β β= , (13) where err1 and err2 are corresponding error values obtained. these new guesses together with one of the initial guesses, will give smaller error. also, a second iteration process is necessary. to obtain the first derivative of the normalized propagation constant b, eq.(8) is differentiated with respect to v and to obtain the second derivative of b with respect to v, the wave equation differentiated twice, by obtaining the exact value for b, db/ dv and also d2b/ dv2, we can easily calculate the power normalized electric field, propagation constant and the dispersion properties. 3. results 3.1 power normalized electric field we discuss the effect of the depth, d, on the normalized electric field in fig. 1. the normalized electric field is represented by the following equation: 2 n o n e a e p π η = , (14) where n2 is the cladding refractive index, ηo is the impedance of free space and p is the input power. changing the depth d from 0 to 5 km, we found an obvious change on the values of the normalized electric field. in fig. 2, the change of core radius at 3 km depth, increasing the core radius (which increases the v-number in a direct manner) gives an obvious increase in the model field distribution. this is achieved by taking the power equal to 1-mw. the effect of the depth appears also for the core radius of 4 and 5 µm by a shift up. the values of the normalized electric field behind the core appear closer to the sea level. far from the core center and closer to the clad, there will be a wider change in the modal field at 3 km rather than that at the sea level. 3.2 normalized propagation constant for the step index fibers the variation of the normalized propagation constant as a function of the normalized frequency for both linear and nonlinear operation at 3 km depth (n2 = 1.44) is shown in fig. 3. it is shown that as the core radius or its refractive index is increased, the effect of nonlinearity begins to increase and then the nonlinearity effect slowly loses its strength. increasing the core refractive index, that behavior is a normal behavior because of the increase of the refractive index due to the depth increase. for graded index fibers, similar to the case of step index fibers, the normalized iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 5 propagation constant for a certain v-value under nonlinear operation is dependent on the overall v-value and also its constituent parameters. figure 4 represents the normalized propagation constant as a function of the normalized frequency, and the dotted curve represents the propagation constant at 3 km depth. 0 1 2 3 4 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 a = 3 µm n2 = 1.444 λ = 1.55 µm d = 0 km d = 5 km t he p ow er n or m al iz ed e le ct ric f ie ld radial coordinate, r in µm fig. 1: the effect of the ocean depth from 0 to 5 km on the model field distribution along the core radial coordinate 0 1 2 3 4 5 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 d = 3 km n2 = 1.444 λ = 1.55 µm = 3 µm = 4 µm a = 5 µm t he p ow er n or m al iz ed e le ct er ic f ie ld radial coordinate, r in µm fig. 2: the effect of variation of the core radius on the model electric along the core radial coordinates iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 6 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.0 0.2 0.4 0.6 0.8 si d = 0 km d = 3 km n or m al iz ed p ro pa ga tio n c on st an t, b normalzied frequency, v fig. 3: the variation of the propagation constant with the normalized frequency at 0 and 3 km depths for the step index fibers 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 gi d = 0 km d = 3 km n or m al iz ed p ro pa ga tio n c on st an t, b normalized frequency fig. 4: the variation of the normalized propagation constant with normalized frequency at 0 and 3 km depths for the graded index fibers iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 7 3.3 mode delay factor the mode delay factor, d, is a universal dispersion parameter which plays a major role in the theory of single mode fibers. it is defined through the formula: ( )d vb db d v b dv dv = = + . (15) the mode delay factor affects the group delay of the guided mode fibers as it described the change in-group delay caused by the changes in power distribution between the fiber core and cladding. the variation of the mode delay factor for the step index fibers as a function of the normalized frequency is illustrated in fig. 5 under both cases above the sea level and at 3 km depth. it is clear from the graph that the effect of the ocean depth leads to the refractive index increase that gives an increase in the normalized propagation constant and also its derivative with respect to v ended with the increase in the mode delay factor. calculations in this part will be done in two different ways: one of them uses the dependence of the refractive index on the pressure only which is represented in the graph by the solid line, and second uses the dependence of the refractive index on both the pressure and temperature represented by the dashed line. the dependence of the mode delay factor on the normalized frequency for the graded index fibers is illustrated in fig. 6 for a depth change from 0 to 3 km taking into account both cases mentioned above for the pressure and temperature dependence. v number is increased by increasing the radius or the refractive index of the fiber core, d(v) begins to increase slowly at the small values of v, then increases till reaching a certain value of v, the d(v) values begin to be nearly constant. this behavior could be explained physically by considering the relation between the mode delay factor and the sharing of the optical power between the core and cladding. as either the core radius or the refractive index is increased from small values, the percentage of the power confined in the core region starts to rise up quickly and the normalized propagation constant does in consequence. 3.4 waveguide dispersion coefficient the third parameter, which governs the dispersion behavior of the optical fiber, is the waveguide dispersion coefficient, which is defined as: ( )2 2 2 d vb db db g v v dv dv dv  = = +    . (16) for step index fibers, the variation of the normalized waveguide parameter, as a function of the normalized frequency is shown in fig. 7. for larger values of v, the values of the waveguide coefficient begin to be much closer for both cases. it is noted that, for the single mode operation, where the normalized frequency is less than 2.404, the waveguide dispersion is always positive which means that the waveguide dispersion parameter is always negative. figure 8 represents the relation between the waveguide parameter and the v-number for the graded index fibers. calculations are performed two times as mentioned in the step index discussion. one can deduce from the two figures that, for any v value, the step index has a greater value of the waveguide parameter than the graded index under any chosen depth. iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 8 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 p = 100 kw si d = 0 km d = 3 km m od e d el ay f ac to r, d normalized frequency, v fig. 5: the effect of the ocean depth from 0 to 3 km on the mode delay factor as a function of normalized frequency for the step index fibers, the dashed line is due to the dependence of the refractive index on pressure and temperature, the solid one is due to the pressure dependence only 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 p = 100 kw gi d = 3 km d = 0 km m od e d el ay f ac to r, d normalized frequency, v fig. 6: the effect of the ocean depth from 0 to 3 km on the mode delay factor as a function of normalized frequency for the graded index fibers, the dashed line is due to the dependence of the refractive index on pressure and temperature, the solid one is due to the pressure dependence only. iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 9 1 2 3 4 5 0.0 0.2 0.4 0.6 0.8 1.0 1.2 d = 3 km d = 0 km p = 100 kw gi n or m al zi ed w av eg ui de c oe ffi ci en t, g normalized frequency, v fig. 7: the effect of the ocean depth from 0 to 3 km on the normalized waveguide coefficient as a function of normalized frequency for the step index fibers, the dashed line is due to the dependence of the refractive index on pressure and temperature, the solid one is due to the pressure dependence only 0 1 2 3 4 0.0 0.5 1.0 1.5 p = 100 kw si d = 3 km d = 0 km n or m al iz ed w av eg ui de c oe ffi ci en t, g normalized frequency, v fig. 8: the effect of the ocean depth from 0 to 3 km on the normalized waveguide coefficient as a function of normalized frequency for the graded index fibers, the dashed line is due to the dependence of the refractive index on pressure and temperature, the solid one is due to the pressure dependence only iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 10 3.5 material dispersion material dispersion results from the variation of the velocity of light in a medium, and hence, its refractive index, with the optical wavelength, and is given by: 2 2dm = c d n d λ λ       where n is the refractive index of the core or cladding. 0.8 1.0 1.2 1.4 1.6 -120 -100 -80 -60 -40 -20 0 20 40 m at er ia l d is pe rs io n, ( ps /n m /k m ) wavelength, λ in µm fig. 9: the variation of the material dispersion as a function of the wavelength at 3 km depth (dashed line) and above the sea level (solid line) 3.6 waveguide dispersion the waveguide dispersion coefficient, g, estimated before is used now to estimate the waveguide dispersion parameter dw as: 2 1 2 2 ( ) ( )w n n d vb d v c dvλ = , (18) the waveguide dispersion is illustrated as a function of the wavelength in fig. 10 for two chosen depths, 0 and 3 km. from fig. 10, the waveguide dispersion above the sea level has a greater shift up than at 3 km depth. this shift will decrease with the increasing of the wavelength. the same behavior for the step and graded index fibers is expected because of the same change in the waveguide dispersion parameter which is the only parameter affecting the waveguide dispersion. iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 11 0.8 1.0 1.2 1.4 1.6 -20 -10 0 10 20 30 40 si gi w av eg ui de d is pe rs io n, d w wavelength, λ in µm fig. 10: effect of the ocean depth (from 0 to 3 km) on the waveguide dispersion parameters as a function of the wavelength for the step index (si) and graded index (gi) fibers 4. conclusion below sealevel the refractive index increases, and this increase will affect all the parameters related to performance of the optical fiber including the power normalized electric field, propagation constant and especially the dispersion parameter. also, calculations done above sealevel show that the effect of the refractive index increase due to temperature and pressure cannot be neglected. in the nonlinear operation (in the core of the optical fiber), the characteristic curves of the normalized propagation constant, the mode delay factor, and the normalized waveguide dispersion coefficient are found to depend on the way by which the value of v is varied, the injected power, kerr nonlinearity coefficient. rerefences: [1] d.c. agrawal, fiber optics communication, second edition, inc, new york, 1993. [2] h.k. chiang, r.p. kenan, and c.j. summers, "spurious roots in nonlinear waveguide calculations and a new format for nonlinear waveguide dispersion equations." ieee. j. quantum electron, vol. 28, pp. 1756-1760, 1992. [2] s.j. al-bader and h.a. jamid, "guided waves in nonlinear saturable self-focusing thin films." ieee j. quantum electron, vol. qe-23, no. 11, pp. 1947-1955, 1987. iium engineering journal, vol. 4, no. 2, 2003 m. h. ali et al. 12 [3] a.d. boardman and p. egan. "optically nonlinear waves in thin films." ieee j. quantum electron, vol. qe-22, no. 2, pp. 319-324, 1986. [4] l.p. yuan, “a numerical technique for the determination of the j. propagation characteristics of nonlinear planar optical waveguide,” ieee quantum electron, vol. 30 p. 134, 1994. [5] a.m. abdel naser, "high speed submarine optical fiber communication system: pressure and temperature," iium engineering journal, vol. 1, no. 1, pp. 42-55, 2000. [6] g. ghosh and h. yajima, "pressure-dependent sellmeier coefficients and material dispersion for silica fiber glass", j. lightwave technol, vol. 16, no. 11, pp. 2002-2005, 1998. [7] r. h. stolen, “nonlinearity in fiber transmission”, ieee journal, vol. 68, p. 1232, 1980. [8] j.m. senior, “ptical fiber communication,” second edition, prentice-hall, 1992. biographies mostafa h. ali was born in alexandria, egypt. he received his b.sc. from the alexandria university in 1976, and the m.sc. from the same university in 1982. he is currently a professor at the department of mathematics and physics, faculty of engineering, alexandria university. ahmed e. elsamahy was born in alexandria, egypt. he received his b.sc. from the alexandria university in 1966 , and the m.sc. from the same university at 1971. he is currently a professor at the department of physics, faculty of science, alexandria university. taymour a. hamdalla was born in alexandria, egypt. he received his b.sc. from the alexandria university in 1997, and the m.sc. from the same university in 2002, he is currently an assistant lecturer at the department of physics, faculty of science, alexandria university. microsoft word 0_vol_16_no_2_2015_special issue on energy_compiled.docx iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 1 on the experimental study of composite dessicants for energy efficient air dehumidification k.j. chua and m.r. islam department of mechanical engineering, engineering science programme, national university of singapore, 9 engineering drive 1, singapore 117576. mpeckje@nus.edu.sg, and espmri@nus.edu.sg (received: august 3, 2015; accepted: october 30, 2015; published on-line: november 30, 2015) abstract: this paper presents the development and performance characterization of new composite desiccants. the main compositions for the composite desiccants include silica gel, lithium chloride, calcium chloride and bentonite. different percentage compositions of these four components were tested to determine the optimal material composition for improving moisture removal capacity under varying inlet air temperature and humidity, and amount of moisture released under different regenerative temperature. for the first time, four-layered composite desiccants were developed and tested experimentally to determine their moisture removal capacity and moisture regeneration capacity at temperature of about 60oc under inlet air conditions similar to singapore’s tropical climate. the performances of these composite desiccants were benchmarked with the performance of pure silica gel the most commonly used desiccant in the market today. it was observed experimentally, that employing a fourlayered composite desiccant, comprising silica-gel (sio2), bentonite, lithium chloride (licl), and calcium chloride (cacl2), has enabled greater moisture removal capacity for varying inlet air temperature and humidity ranging from 25 to 35oc and 55 to 95% relative humidity (rh). the percentage improvements, in contrast to pure silica gel, are 14 to 22.5%, and 10 to 26.3% for varying inlet air temperature and varying inlet rh, respectively. abstrak: kertas kerja ini membentangkan perkembangan dan prestasi pencirian desiccants komposit baru. komposisi utama bagi desiccants komposit termasuk gel silika, litium klorida, kalsium klorida dan bentonit. peratusan komposisi yang berbeza daripada empat komponen telah diuji untuk menentukan komposisi bahan yang optimum untuk meningkatkan penyingkiran kapasiti kelembapan di bawah pelbagai suhu masuk udara dan kelembapan, dan jumlah kelembapan dikeluarkan di bawah suhu regeneratif yang berbeza. buat kali pertama, desiccants komposit empat lapis telah dibangunkan dan diuji secara eksperimen untuk menentukan penyingkiran kelembapan kapasiti dan kelembapan kapasiti penjanaan semula mereka pada suhu kira-kira 60oc di bawah keadaan udara masuk sama dengan iklim tropika di singapura. persembahan ini desiccants komposit ditanda aras dengan prestasi gel silika tulen bahan pengering yang paling biasa digunakan dalam pasaran hari ini. diperhatikan, uji kaji, yang menggunakan bahan pengering komposit empat lapisan yang terdiri daripada silika gel (sio2), bentonit, lithium chloride (licl), dan kalsium klorida (cacl2), telah membolehkan lebih besar penyingkiran kapasiti kelembapan bagi mengubah suhu udara masuk dan kelembapan antara 25 hingga 35oc dan 55 hingga 95% kelembapan relatif (rh). peningkatan peratusan, berbeza dengan gel silika tulen, 14 ke 22.5%, dan 10 hingga 26.3% bagi mengubah masuk suhu udara dan berbeza-beza masuk rh, masing-masing. keywords: experiments; composite desiccant; dehumidification; energy efficiency iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 2 1. introduction there is a need to control the temperature and relative humidity (rh) in the indoor environment of buildings to achieve a specified range of human thermal comfort. air that is too dry will cause human discomfort ranging from dry skin to respiratory irritation. according to american society of heating, refrigeration and air conditioning engineers (ashrae), air with relative humidity of less than 30% will cause such discomfort [1]. it is also of great importance to control the temperature and relative humidity in certain industries such as the food, medical, and electronic industries. the controlled humidity condition helps to slow down the growth of bacteria and reduces the spread of viral infections through air [2]. in singapore, the use of air-conditioning has become a norm in practically every building. in fact, about 50% of a building’s energy consumption is attributed to air-conditioning alone [3]. with the rising price in electricity and the depletion of fossil fuels, it is therefore, necessary to increase the efficiency of airconditioners to reduce the energy consumption for the consumers. many research works have been conducted on the different types of desiccant available for the dehumidification process. these desiccants could be broadly categorised into liquid and solid states. each has its own strengths and shortcomings. liquid desiccants are widely deployed in their utilization due to their ability to incur lower pressure drop and to regenerate at lower temperature [4,5]. however, liquid desiccants are also known to be toxic and corrosive in nature which renders them to be unsuitable for airconditioning applications. also, liquid desiccants are also found to have carryover effects [4]. some examples of liquid desiccants are lithium chloride, lithium bromide and calcium chloride. solid desiccants are more compact and most importantly, there is less tendency for them to corrode and provide carryover effects [6]. solid desiccants are, in general, dependent on its porous form, surface area, surface energy and crystalline structure to adsorb moisture from the air [7,8]. examples of solid desiccants include silica gels, zeolites, activated carbon and activated clay such as bentonite. the most commonly used desiccants in the market today for air-conditioning application is silica gel due to their great pro surface area and good moisture adsorption capacity [9]. since solid desiccants and liquid desiccants have their advantages and disadvantages, it is suggested that combining both by mixing them chemically or physically will help to overcome the individual shortcomings of each type. for instance, combination of silica gels with lithium chloride will help to reduce the effect of toxicity and to reduce the regeneration temperature achieving the intermediate characteristic [10]. many research works have been carried out in this field where these desiccants are referred to as composite desiccants. commonly used solid desiccants such as silica gel, activated carbon and molecular sieves such as zeolites were conducted in several experiments [8,11,12]. silica gel has high moisture adsorption capacity and low regenerative temperature of 120oc. it is also established that adsorption capacity of silica gel generally decreases with the rise in temperature [8]. activated carbon and alumina required a higher regeneration temperature of 250oc for a less adsorption capacity as compared to silica gel. molecular sieves such as zeolites are found to have the largest amount in moisture adsorption capacity due to its large pore size and highly polar surface [13]. however, the deterring factor for using it as desiccant is the high regenerative temperature of 350°c that it requires. composite desiccants made by impregnating hygroscopic substance in the pores of solid adsorbents have been found to be effective in increasing the moisture adsorption iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 3 capacity of the adsorbents and they are called selective water sorbents [14]. one example is the combination of activated carbon with inorganic salts such as lithium chloride and calcium chloride [15]. for the same amount of lithium chloride content and calcium chloride content added to the activated carbon, the former has a better moisture adsorption performance [15]. at the same condition of 84% relative humidity, activated carbon impregnated with lithium chloride can adsorb moisture as much as 194% of its mass as compared to the one with calcium chloride where its moisture adsorption is 170% of its mass. many experiments have also been conducted for composite desiccants consisting of calcium chloride being contained in the pores of silica gel [16-18]. the moisture adsorption capacity of this composite desiccant is better than that of silica gel. it is also established that the deciding factor in the improvement of the sorption capacity is the percentage of calcium chloride content in the mixture. combinations of silica gel and lithium chloride have also been experimented [10,19,20]. similar to calcium chloride, the lithium chloride content in the composite desiccants plays a huge role in the moisture adsorption capacity. it is also a well-known that lithium chloride is corrosive in nature and this halts the progress of lithium chloride as a liquid desiccant. however, by impregnating it in silica gel, its corrosive effect is kept to the minimum and the combined desiccant also benefits in terms of moisture regeneration. another type of composite desiccant that is of great commercial interest is the lowcost composite desiccant. since clay is cheap in price and can adsorb moisture moderately, by combining it with the hygroscopic substance, its moisture removal capacity will also be improved. research has also been done and it is found to have reasonable performances [21,22]. for small-scale application, where moisture removal is not prominent, this desiccant is good enough for application. however, it is observed that after going through cycles of sorption and desorption process, cracks are created on the surface of the desiccant while the overall structure remains intact. its regeneration temperature is found to be less than 100oc and low-grade waste heat can be utilized to regenerate it. it is clear from the mentioned literature that the primary focus is on the dehumidification and regeneration capacity of either basic adsorbents such as silica gel and zeolites and basic adsorbents-halides. to date, very limited research work has been done on comparing different composite desiccants under the same operating condition. in this article, the combination of four layered composite desiccants will be explored to determine the highest moisture removal capacity at varying temperatures and rh and also the highest regenerative moisture capacity under different temperature environments. the four types of desiccating materials are silica gel, bentonite, lithium chloride and calcium chloride. 2. materials and methods 2.1 experimental setup a laboratory small-scale experimental setup, shown in fig. 1, was used to test the performance of the composite desiccants. the setup, comprised of a polypropylene air tunnel with low thermal conductivity, was used to host different composite desiccants and to let the process air pass through the desiccant. the process air was drawn in by using a suction pump. thermo/hygrometer sensors and velocity sensor were mounted on the setup as shown in the schematic diagram in fig. 1 to measure the condition of the air before and after passing through the desiccant. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 4 the process air to be directed to the desiccant was first conditioned in the metal box condition chamber (depicted in fig. 2b) while allowing the air to flow through the bypass section. with the help of a system controller and a humidifier, the temperature and rh of the incoming air were judiciously controlled. after achieving the target air temperature and relative humidity, the valves were switched to let the process air to flow through the desiccant in place. the air flow continued until the tested composite desiccant reached its saturation state. fig. 1: schematic diagram of small-scale system. fig. 2: (a) a pictorial view of the actual small-scale system setup; (b) a condition chamber with system controller; (c) a humidifier to regulate the humidity of the inlet air to the experimental setup. (a) (b) (c) iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 5 to switch the process to the regeneration mode (moisture desorption), there was a need to condition the air again in the metal box which increases the air temperature to the required regenerative level. the flow of air was again directed through the bypass section. after the target temperature was achieved, the air was passed through the desiccant to allow it to release the moisture it adsorbed. sigma-aldrich supplied the desiccants used in the experiments. in the set-up, the temperature and relative humidity of the process and outlet air are measured by using a series of accurate and digital thermo/hygrometers. the sensor model used to measure temperature and humidity is kimo th200. the upper limit of the measurable temperature is 120oc, the lower limit is -20oc and the precision of the temperature sensor is within ±3%. the relative humidity monitored with the sensor ranges from 0% to 100% rh and its precision is within ±5%. the measuring points are located far from the air fan so as to minimize interference to the measurements. a kimo ctv100 air velocity transmitter is employed to measure the air flow rate, and its precision is 3%. a konics series ss-3010 measures the pressure difference of the wheel with an accuracy of ±3pa. for regeneration experiments, samples are weighed using a digital weighing scale (ohaus explorer, model e1d120). a dry-heat oven (memmert gmbh+co.kg, model 200) is employed to obtain the bone-dry weights of saturated desiccants over seven hours at 80°c, 100°c and 120°c. the desiccants were regularly taken out at 30 minutes interval and their weights are determined. the inlet process air used for the experiments was selected to match singapore’s outdoor climate that varies from 25oc to 31.20c in temperature and relative humidity of 60% to as high as 95% [42]. efforts to minimize leakage were considered by using rubber or silicone sealants and flanges on areas where leak was likely to occur such as the joints for both the small-scale and large-scale system. table 1 below shows the geometric parameters of the experimental setup. table 2 shows the operating air conditions employed for the present dehumidification study. table 1: geometrical parameters of the laboratory experimental setup. geometric parameters values thickness of desiccant placed in holder, lsmall (m) 0.035 radius of desiccant holder, rsmall (m) 0.025 volume of desiccant holder, v (m3) 6.87*10-5 table 2: operating air flow parameters for experiments. operating parameters baseline value parametric variations temperature of process air, tair (oc) 25 25 30 relative humidity of process air, rh (%) 50 50 95 process air velocity, v (m/s) 1 1 3. results and discussion the performances of the composite desiccants were tested under conditions similar to singapore’s climatic condition that is high in temperature and relative humidity. research on composite desiccants generally involve two-layered materials that consist of a host matrix with open pores such as silica gel, and a hygroscopic substance such as lithium iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 6 chloride. however in this study, a four-layered composite desiccant was explored and tested. similar to other studies on composite desiccants, moisture adsorption capacity and regeneration capacity were calculated to compare the performances of the various composite desiccants. in addition to this, pressure drop across the desiccants were also measured and compared as one of the performance indicator of the composite desiccants. the factors of choosing the most promising composite desiccants are in the following order of importance: moisture adsorption capacity, regeneration capacity at relatively low temperature (600oc), and pressure losses across the desiccants. only the better performing desiccants were used for further testing and are discussed in this report. the performance of composite desiccants will be referenced with the performance of the silica gel, since this is the most widely used commercial desiccant for dehumidifying operations. 3.1 performance of composite desiccants table 3 presents the overview of the performances of the different composite desiccants when they were exposed to air with temperature of 30oc and relative humidity of 80% which is the average climatic condition in singapore. based on this table, better performing composite desiccants were judiciously selected to undergo further tests under varying temperature and relative humidity conditions. table 3: adsorption capabilities and pressure difference of the desiccants at temperature of 300c and rh of 80%. % composition by mass saturation time (min) % capacity of mass of h2o adsorbed drop in rh from 80% moisture removal capacity (g/ kg of dry air) average pressure difference (pa) sio2 licl cacl2 bentonite activated carbon 100% 0% 0% 0% 0% 18.5 28.50% 42.67% 8.168 353.60 95.1% 4.9% 0% 0% 0% 11.6 29.70% 49.37% 8.583 384.70 91.1% 8.9% 0% 0% 0% 15.0 33.40% 51.45% 9.808 389.67 93.8% 0% 6.2% 0% 0% 16.5 29.40% 50.40% 7.824 348.17 91.3% 0% 8.7% 0% 0% 17.7 30.51% 50.78% 8.840 368.20 92.75% 3.625% 3.625% 0% 0% 17.0 30.34% 50.24% 9.125 381.52 66.92% 6.72% 6.72% 19.64% 0% 23 32.49% 41.56% 7.780 258.29 64.85% 6.85% 6.85% 21.53% 0% 23.5 32.50% 50.67% 8.709 257.00 60.44% 6.33% 6.33% 26.90% 0% 26.0 30.50% 39.21% 7.491 245.00 58.22% 5.77% 5.77% 30.24% 0% 20.0 27.71% 35.67% 6.759 195.00 0% 23% 0% 0% 77% 27.5 67.29% 41.84% 8.076 124.67 0% 0% 23% 0% 77% 25.0 44.38% 29.57% 6.170 121.17 based on the experimental results, the maximum composition of a hygroscopic substance that can be impregnated into the pores of silica gel is approximately 10% of its mass. from table 3, regarding moisture removal capacity, the desiccant made from sio2 91.1% + licl 8.9% is the best choice. however, it is noted that this desiccant incurred the highest pressure difference across the composite desiccant that translates to greater energy required to draw the air through the desiccant. it is also observed that composite desiccants involving bentonite reach saturation point at a longer period. in addition, the presence of more bentonite in the mixture generally lowers the pressure drop across the desiccants. this implies that less energy is required to draw the air across the desiccants. the addition of bentonite further promotes iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 7 hygroscopic characteristic in the composite desiccants. therefore, looking at the requirement for desiccant drying as a whole, the desiccant mixture comprising sio2 64.85% + licl 6.85% + cacl2 6.85% + bentonite 21.53% seems to be the better choice at temperature of 300oc and relative humidity of 80%. it has a relatively high moisture removal capacity and an average pressure difference that is relatively low (27% lower than silica gel) primary due to presence of bentonite that binds the mixture together. its performance under the varying temperature and relative humidity, and its regenerative capability is presented in the ensuing sections. it can also be noted from table 3 above that composite desiccants involving activated carbon have very high moisture removal capacity by mass. essentially, these can hold more hydrophilic salt on the surface. base on the experiments, the maximum composition of hydrophilic salt that activated carbon can contain is about 23% of its mass as compared to silica gel that contains 9% of its mass. the low pressure drop across the activated carbon composite desiccant is also very attractive. however, regarding the absolute amount of moisture that is removed by activated-carbon embedded composite desiccants, the quantity is rather low. since the packing density of activated carbon composite desiccant in the holder is rather small. therefore, despite the high moisture removal capacity by mass, the physical mass of water vapour that it adsorbed is lower than other composite desiccants. 3.1.1. moisture removal capacity against temperature in fig. 3(a), it is observed that the addition of licl/cacl2 helps to increase the moisture removal capacity when the inlet air temperature is varied. the effect of licl increases the moisture removal capacity of the composite desiccants by about 20% compared to cacl2 which increases the moisture removal capacity by about 10%. it is apparent in fig. 3(b) that the addition of bentonite to the composite desiccants reduces their moisture removal capacity. the graphs indicate that even with the presence of both licl and cacl2, the moisture removing performance of the composite desiccants compared to pure silica gel does not differ much. it is observed that the best performing desiccants is sio2 64.85% + bentonite 21.53% + licl 6.81% + cacl2 6.81%. when compared to silica gel, the moisture removal capacity improved by about 10%. also, from fig. 3(c), it is apparent that under humid outdoor air conditions, the best moisture removal capacity is sio2 91% + licl 9% followed by sio2 64.85% + bentonite 21.53% + licl 6.81% + cacl2 6.81%. the improvement in moisture removal capacity spans 14% to 22.5% when benchmarked with silica gel. in summary, the graphs displayed in fig. 3(a) to (c) show that the moisture removal capacity of different composite desiccants with varying temperature keeping the rh constant at 80%. in general, the moisture removal capacity of composite desiccants increases with temperature at constant rh. 3.1.2. moisture removal capacity against relative humidity in fig. 4(a), it is observed that the addition of licl helps to promote the moisture removal capacity of the composite desiccants by about 20% at rh greater than 70%. the addition of cacl2 does not appear to have a major impact on the performance of the desiccant under varying rh conditions. in fact, at rh lower than 70%, the performance of pure silica gel is observed to be better. from fig. 4(b), it is observed that the addition of bentonite to the composite desiccants helps to bind the desiccants together but it reduces the moisture removal capacity of the desiccants. as shown from the graph, even with the presence of both licl iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 8 and caclଶ, there is not much difference in its performance when compared to pure silica gel for rh above 70%. (a) (b) (c) fig. 3: (a) moisture removal capacity of two-layered composite desiccants compared to silica gel at varying temperature; (b) moisture removal capacity of four-layered composite desiccants compared to silica gel at varying temperature; and (c) moisture removal capacity of best composite desiccants as compared to silica gel at varying temperature. figure 4(c) shows that the composite desiccants with the best moisture removal capacity for simulated inlet air conditions similar to singapore’s external weather is sio2 91% + licl 9% followed by sio2 91.3% + cacl2 8.7%, and sio2 64.85% + bentonite 21.53% + licl 6.81% + cacl2 6.81%. under varying rh conditions, the improvement in moisture removal capacity spans 10% to 26.3% when benchmarked with silica gel. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 9 (a) (b) (c) fig. 4: (a) moisture removal capacity of two-layered composite desiccants compared to silica gel at varying rh; (b) moisture removal capacity of four-layered composite desiccants compared to silica gel at varying rh; and (c) moisture removal capacity of best composite desiccants as compared to silica gel at varying rh. in summary, the graphs portrayed in fig. 4(a) to (c) show the moisture removal capacity of different composite desiccants at varying rh from 55% to 90% at constant temperature at 30oc. for all the composite desiccants studied, the moisture removal capacity increases with rh. 3.1.3. regeneration at varying temperatures it is observed in fig. 5(a) that the addition of hygroscopic substance such as licl and cacl2 lowers the regeneration capacity of composite desiccants. this is attributed to the chemical bond formed by water molecules with the hydrophilic salt that potentially retards the diffusion of moisture flow during the regenerative process. it is apparent from fig. 5(b) that desiccants incorporated with bentonite generally have a greater effect from changing regeneration temperature. as illustrated by the graphs, the regenerative capability of silica gel at 900oc marginally improved when compared to iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 10 the one at 700oc. comparatively, for other composite desiccants, the improvement of the regenerative capability from 700oc to 900oc is quite significant. from the graphs shown in fig. 5(a) and 5(b), it can be inferred that the higher the regeneration temperature, the higher the moisture released from the desiccants. it is also clear that at low regeneration temperatures spanning 60 – 650oc, the difference in the moisture released from the desiccants is not significant. (a) (b) fig. 5: (a) regenerative capability of two-layered composite desiccants as compare to silica gel; and (b) regenerative capability of four-layered composite desiccants as compare to silica gel. 4. concluding remarks in this paper, we have demonstrated that in contrast to silica gel, improved performance of composite desiccants in terms of greater moisture removal capacity as well as better moisture regenerative ability. for the first time, four-layered composite desiccants, comprising of different mass contents of silica gel, lithium chloride, calcium chloride and bentonite, have been developed and studied. in general, each component has contributed in making composite desiccants perform relatively better compared to silica gel lithium chloride. the best performing moisture adsorbing four-layered desiccant is sio2 64.85% + bentonite 21.53% + licl 6.81% + cacl2 6.81% by mass. this composite desiccant was evaluated to have similar moisture removal capacity to a silica gel-lithium chloride combination. furthermore, its regeneration capacity at a lower temperature of 60oc was found to be close to pure silica gel and silica gel-lithium chloride. in the pressure drop across this composite desiccant was determined to be 27% and 34% lower than that of pure silica gel and silica gel-lithium chloride, respectively. acknowledgement the authors gratefully acknowledges the kind support of agency for science, technology and research (a*star) and ministry of national development (mnd) through their green building joint grant (no: 112 176 0023) funding for this research and the effort of mr. vincent marthawan jonghong in conducting the experiments presented in this work. iium engineering journal, vol. 16, no. 2, 2015 special issue on energy chua and islam 11 references [1] american society of heating, refrigerating and air-conditioning engineers, thermal environmental conditions for human occupancy, atlanta, 2004. [2] arundel, sterling e, bigging j, sterling t. (1986) indirect health effects of relative humidity in indoor environment. environmental health perspectives, 65:351-361. [3] air-con system efficiency primer: a summary. (2011). [online]. available: http://app.nccs.gov.sg/data/resources/docs/techprimers/aircon%20primer.pdf?aspxautode tectcookiesupport=1. [accessed 23 february 2013]. [4] daou k, wang r, xia z. (2006) desiccant cooling air conditioning: a review. renewable and sustainable energy reviews, 10:55-77. [5] katejanekarn t, kumar s. (2008) performance of a solar-regenerated liquid desiccant ventilation pre-conditioning system. energy and buildings, 40:1252–1267. [6] techajunta s, chirarattananon s, exell r. (1999) experiments in solar simulator on solid desiccant regeneration and air dehumidification for air conditioning in a tropical humid climate. renewable energy, 17:549-568. [7] li x, li z, xia q and xi h. (2007) effects of pore sizes of porous silica gels on desorption activation energy of water vapour. applied thermal engineering, 27:869-876. [8] demir h, mobedi m, ulku s. (2011) microcalorimetric investigation of water vapor adsorption on silica gel. j therm anal calorim, 105:375-382. [9] chang k, wang h, chung t. (2004) effect of regeneration conditions on the adsorption dehumidification process in packed silica gel beds. applied thermal engineering, 24:735742. [10] jia c, dai y, wu j, wang r. (2007) use of compound desiccant to develop high performance. international journal of refrigeration, 30:345-353. [11] ng k, chua h, chung c, loke c, kashiwagi t, akisawa a, saha b. (2001) experimental investigation of silica gel-water adsorption isotherm characteristics. applied thermal engineering, 21:1632-1642. [12] özdinç mc, yildirim m. (2004) energy and exergy analyses of an experimental open-cycle desiccant cooling system. applied thermal engineering, 24:919-932. [13] proverbio e, restuccia g, russo f, bonaccorsi l, freni a. (2006) zeolite coated copper foams for heat pumping applications, microporous and mesoporous materials, 91:7-14. [14] aristov y, restuccia g, cacciola g, parmon v. (2002) a family of new working materials for solid sorption air conditioning systems. applied thermal engineering, 22:191-204. [15] smith, dm, lucky, ea, natividad, v. (2000) desiccant composition. usa patent 6559096. [16] zhang x, sumathy k, dai y, wang r. (2006) dynamic hygroscopic effect of the composite material used in desiccant rotary wheel. solar energy, 80:1058-1061. [17] zhang x, qiu l. (2007) moisture transport and adsorption on silica gel–calcium chloride composite adsorbents. energy conversion and management, 48:320-326. [18] mandegari m, pahlavanzadeh h. (2009) introduction of a new definition for effectiveness of desiccant wheels. energy, 34:797-803. [19] jia c. (2011) study on adsorption mechanism and dehumidification property of composite desiccant. advanced materials research, 150-151:912-916. [20] gordeeva l, grekova a, krieger t, aristov. (2009) adsorption properties of composite materials (licl + libr)/silica. microporous and mesoporous materials, 12:262-267. [21] thoruwa t, johnstone c, grant a, smith j. (2000) novel, low cost cacl2 based desiccants for solar crop drying applications. renewable energy, 19:513-520. [22] tretiak c, ben abdallah n. (2009) sorption and desorption characteristics of a packed bed of clay–cacl2 desiccant particles. solar energy, 83:1861-1870. 438 iium engineering journal, vol. 14, no. 2, 2013 rakhimov 183 on calculation of multiple eigenvalues of the linear operator-function by reduction pseudo-perturbation methods d. g. rakhimov national university of uzbekistan, vuzgorodok, tashkent, 700174, uzbekistan. davranaka@yandex.com abstract: this article examines the theory of bifurcations, which applies to the problem of retaining of the approximately given multiple eigenvalues and their generalized eigenvectors. this approach allows the reduction of algebraic multiplicity of eigenvalue for one and transfers the problem to the similar one but with simple eigenvalue. the method of the false perturbation is used to construct iterative processes. abstrak:dalam artikel ini, kaedah teori bifurkasi diaplikasikan terhadap masalah untuk mengekalkan penghampiran pelbagai nilai eigen dan vektor eigen yang teritlak. kaedah ini membenarkan pengurangan kegandaan aljabar nilai eigen kepada satu dan memindahkan permasalahan kepada yang hampir serupa tetapi dengan nilai eigen yang lebih mudah. pengkaedahan usikan palsu digunakan untuk proses pelelaran. keywords: bifurcation theory methods; multiple eigenvalues; root number; reduction pseudo-perturbation method 1. introduction many of engineering tasks connected with free fluctuations are reduced to eigenvalue problems so that many of them aren't solved analytically but resort to the approached methods. the problem of retaining of the approximately given eigenvalue and its generalized eigenvectors has been considered in the articles [1-3]. the authors used method of the false perturbations which was introduced by gavurin [4]. according to this method the operator of the false perturbation builds in a way that the known approximations of the eigenvalue and generalized eigenvectors become the exact ones but for the perturbed operator-function. using the method of the theory of bifurcation [5], the iteration processes are then built in order to find the exact values of the eigenvalues and generalized eigenvectors of initial operator-function. the most general operator of the false perturbations was built in [3]. in its formula the generalized eigenvectors of the direct operator-function and their adjoints were used in a symmetrical way. this operator was applied to several problems of mathematical physics [6, 7]. the method of the finite-dimensional regularization [8] allows the reduction of geometric multiple of the eigenvalue to a unit (in this case operator-function has many linearly independent eigenvectors without generalized jordan chains' elements). here, using the results and methods developed in [8], it will be shown that algebraic multiplicity of the eigenvalue also could be reduced to a unit. the terminology and notations of [5] are used. iium engineering journal, vol. 14, no. 2, 2013 rakhimov 184 2. problem setting let 1e and 2e be banach spaces, ,)(: 2010 eadea →⊃ 2111 )(: eadea →⊃ are the densely defined closed linear operators, where )()( 10 adad ⊂ and 1a subordinate to 0 a (i.e. 122 01 eee xxaxa +≤ on )( 0 ad ) or )()( 01 adad ⊂ and 0 a subordinate to 1 a (i.e. 122 10 eee xxaxa +≤ on )( 1ad ) . we consider eigenvalue problem ( ) 0 10 =− xtaa . (2.1) let unknown eigenvalue λ be the fredholm point of the linear operator-function 10 taa − with ( ) },,,{ 110 nspanaan ϕϕλ κ=− ( ) },,{ 1*1*0 nspanaan ψψλ κ=− . then corresponding −1a and − * 1 a jordan chains [5] are defined by formulas: ( ) ,)1( 1 )( 10 − =− s i s i ataa ϕϕ ( ) ,)1(* 1 )(* 1 * 0 − =− s i s i ataa ψψ i ps ,2= , ni ,1= , (2.2) 0,det )1()( 1 ≠= j p i iak ψϕ , 0det ≠= ijll , )()1( 1 , l k jp iij ial ψϕ −+= , nki ,1)( = , )(,2)( ki pplj = . according to [9] elements )()( , l k j i ψϕ , )(,2)( ki pplj = , nki ,1)( = of the −1a and −* 1 a jordan chains, could be chosen in such a way that they satisfy following biorthogonality conditions: jlik l k j i δδγϕ =)()( , , jlik l k j i z δδψ =)()( , , )(,2)( ki pplj = (2.3) )1(* 1 )( lp k l k ka −+ = ψγ , )1( 1 )( jp i j i iaz −+ = ϕ , nki ,1)( = . we assume that ,λ , )( 0 s i ϕ )( 0 s i ψ are sufficiently good approximations to an unknowns eigenvalue λ and elements of jordan chains: εϕϕ ≤− )( 0 )( s i s i , εψψ ≤− )( 0 )( s i s i , εϕϕ ≤− )( 0 )( s i s i . we suppose that numbers 0k and 0l (which are approximations of k and l from the formula (2.2)) are close to 1. next lemma was proved in [3]. lemma. going over linear combinations, can be defined as the systems { } ,, 1, )( kpn lk l k = γ )1(* 1 )( lp k l k ka −+ = ψγ , { } ,, 1, )( kpn lk l k z = )1( 1 )( lp k l k kaz −+ = ϕ (2.4) that satisfies the following biorthogonality conditions: jlik l k j i δδγϕ =)( 0 )( 0 , , jlik l k j i z δδψ =)( 0 )( 0 , , )(,2)( ki pplj = . (2.5) now we want to apply methods developed in [8] to the problem of retaining of the approximately given multiple eigenvalues and their generalized eigenvectors. iium engineering journal, vol. 14, no. 2, 2013 rakhimov 185 3. reduction pseudoperturbation methods let us introduce an operator-function ( ) ( ) ∑∑∑ = = −+ = −+ ⋅+⋅+−≡ n i p k kp i k i p k kpk i izztaata 2 1 )1( 0 )( 0 2 )1( 10 )( 1010 ,, 1 1 γγ (3.1) which we call regularisation of the operator function 10 taa − . theorem 3.1 unknown eigenvalue λ is the simple eigenvalue of the operator-function (3.1). moreover, the eigenvector and the defect functional of ( )ta are defined by formulas ∑∑∑∑ − == == +++= 1 1 )( 11 2 2 )( 1 1 )( 1 1 1~ p s s s n i p s s iis n i ii p ccc i ϕϕϕϕϕ , ∑∑∑ == = ++= n i ii n i p s s iis dd i 2 1 1 2 )( 1 ~ ψψψψ (3.2) proof: if the formulas (3.2) hold then ( ) ( ) ( ) ( ) +++== ∑∑∑ − == = 1 1 )( 11 2 2 )()( 1 1 1~0 p s s s n i p s s iis p acacaa i ϕλϕλϕλϕλ ++++ ∑∑∑∑∑ − = = −+ = = −+ = −+ 1 2 2 )1( 10 )( 10 )( 11 1 2 )1( 10 )( 101 2 )1( 10 )( 10 )( 1 1 1 1 1 1 1 11 ,,, p s p k kpks s n i p s sps ii p s spsp zczcz γϕγϕγϕ ++++ ∑∑∑∑∑∑∑∑ = = = −+ = = −+ = = = −+ n i n s p k kp s k s s ii n i p k kp i k i p n i p s p k kpks iis s s i i i zczzc 1 2 1 )1( 0 )( 0 )( 1 2 1 )1( 0 )( 0 )( 1 2 2 2 )1( 10 )( 10 )( ,,, 1 1 1 γϕγϕγϕ ,,, 2 2 2 2 )1( 0 )( 0 )( 2 1 2 2 )1( 0 )( 0 )( 11 1 ∑∑∑∑∑∑∑ = = = = −+ = − = = −+ ++ n l n i p s p k kp l k l s iis n i p s p k kp i k i s s i l l i i zczc γϕγϕ ( ) +++== ∑∑∑ ∑∑ = = −+ = = −+ = − n i p s ssp i n i p s ssp p s s iis zdzada i 2 2 )( 101 )1( 101 1 2 )( 101 )1( 10 2 )1(* 1 1 1 1 1 ,, ~ *0 γψγψψψλ ∑∑∑∑∑ = = −+ = = = −+ +++ n i p k k i kp i n i p s p k sk i sp is i i i zzd 2 1 )( 01 )1( 0 2 2 2 )( 10 )()1( 10 ,, 1 1 γψγψ .,, 2 2 1 )( 0 )1( 101 2 1 1 2 )( 0 )()1( 0 1 1∑∑∑∑∑∑∑ = = = −+ = = = = −+ ++ n i p j p k k ii kp j n i p k n j p s k i s j kp ijs ii j i zdzd γψγψ applying the functional )( 0 µ νψ to the first equality and elements )( 0 µ νϕ to the second one, we obtain the system of the linear algebraic equations to find the unknown coefficients ;,, 11 nnp cc κ :,, 12 nnp dd κ , 1)( 1 i ak j jij exa =∑ − = 1)(,2 −= aki ; (3.3) ,' 1)( 1 i ak j jij eyb =∑ − = 1)(,2 −= aki , (3.4) iium engineering journal, vol. 14, no. 2, 2013 rakhimov 186 where n ppak ++= λ 1 )( is a root number of the operator-function ( )ta , jj cx 1 = , 1,1 1 −= pj , 1,21 ++ = jjp cx , 1,0 2 −= pj , 1,11 ++++ = − jkjpp cx kλ , 1,0 −= k pj , nk ,2= , )( 1011 , l i a γϕ= , )( 10 )( 1 )1( 10 )2( 1 ,, 11 lklpkp ik za γϕψ += −+−+ , 1,2 1 −= pk , )( 10, , 11 l ippl i a γϕ= −++λ , )( 10 )()1( 10 )1( 1, ,, 11 11 lk i lpkp kppl za i γϕψ += −+−++++ −λ , 1,2 1 −= pk , 1,1 1 −= pl , ni ,2= , =+++ − 1,11 lpp sa λ )1( 01 , + = l s γϕ , =+++ − klpp sa ,11 λ )( 0 )( 1 )1( 0 )2( 1 ,,1 l s klp s kp sz γϕψ +−+−+ , 1,2 1 −= pk , = −− +++++ 1111 , is pplpp a λλ )( 0 , l si γϕ= , =++++++ −− kpplpp isa 1111 , λλ )( 0 )1()1( 0 )1( ,, l s k i lp s kp i siz γϕψ +−+−+ + , 1,1 −= i pk , ni ,2= , 1,1 1 −= +spl , ns ,2= ; 1,1 += jj dy , 1,1 1 −= pj , 1,11 ++++ =− jkjpp dy kλ , 1,1 −= k pj , nk ,2= , )( 1 )1( 01, 1 11 , plp slpp s s b γϕ −++++ =−λ , =+++ − klpp sb ,11 λ )( 1 )()1( 1 )1( 0 ,, 1 kl s kplp s zs ψγϕ +−+−+ , 1,1 −= s pk , i l spplpp zb is ψ,)( 0, 1111 = −− +++++ λλ , =++++++ −− kpplpp isb 1111 , λλ )1()( 0 )1()1( 0 ,, +−+−+ + k i l s kp i lp s zis ψγϕ , 1,1 −= i pk , ni ,2= , 1,1 1 −= +spl , ns ,2= ; [ ],,, )(10)(1)1(10)2(1 11 ipipi ze γϕψ +−= −+ 1,1 1 −= pi , [ ],,, )( 20 )( 1 )1( 20 )2( 1 12 1 ipip ip ze γϕψ +−= −++ , 1,1 2 −= pi , [ ],,, )( 0 )( 1 )1( 20 )2( 1 12 11 i s pip ipp ze s γϕψ +−= −++++ −λ , 1,1 −= spi , ns ,2= ; 1 )( 10 ,' ψi i ze = , 1,1 1 −= pi , 1 )( 0 ,' 11 ψi sipp ze s −=+++ −λ , 1,0 −= spi , ns ,2= . it is not difficult to show that ( )εoaii += 1 , ( )εoa ii +=+ 11, , ( )εoaij = , 1, +≠ iij , 1)(,1, −= akji , ( )εob ii += 1 , ( )εob ii +=+ 1,1 , 2,1 1 −= pi , ( )εob pp += 111 , ( )εob ii +=+ 11, , ( )εob ii = for 1, +≠ iij , and for all other cases. consequently, ( )εoais += 1det , ( )εob is += 1det , i.e. systems (3.3) and (3.4) have unique solutions. because of )(1,, )2( 10 )2( 1 )1( 10 )( 11 11 1 εψγϕ oze pp p +=+= − − , and )(εoei = , for all 1 1 −≠ pi , we obtain )(εoc i = , 11 −≠ pi and )(111 εoc p +−=− . therefore, )1( 10 )( 100 11~ −−= pp ϕϕϕ and 100 ~ ψψ = should be taken as initial approximations for ϕ and ψ . the solution of the equation ( ) 0~,~ 00 =ψϕta , is taken as the initial approximation for eigenvalue λ , i.e. 001 000 0 ~,~ 1 ~ , ~ ψϕ ψϕ λ a a + = . choosing 10 * 1 0 0 1~ ψγ a k = and 01 0 0 ~1~ ϕa k z = , we find that 1~,~ 00 =γϕ , 1 ~,~ 00 =ψz , because 0 ~ , ~ , ~ , ~ , ~ 0 )( 1010 )1( 1010 )( 1010010 111 ≠=−== − ψϕψϕψϕψϕ ppp aaaak . we define pseudoperturbed operator using formulas ( ) ( ) 0000000 ~~*,~~, zaxaxxd ψλϕλγ += , ( ) ( ) 00000 * 0 ~*,~~,~ ψλγϕλ ayzyaxd += . iium engineering journal, vol. 14, no. 2, 2013 rakhimov 187 then, ( ) 0000 ~~ ϕλϕ ad = , ( ) 000 * 0 ~ * ~ ψλψ ad = , i.e. ( )( ) { }000 ~ϕλ =− dan , ( )( ) { } 0 * 00 ~ * ψλ =− dan . using the schmidt's regularization [5] the equation ( ) 0=xta could be reduced to the system: ( ) ( )( )[ ]     = −+γ+= − .~, , ~ 0 0 1 000 γξ ϕλξ x atadix (3.5) where, ( )[ ] 1 00000 ~~., − +−=γ zda γλ . if we substitute x in the second equation (3.5) with the value found from the first, we construct the equation: ( ) ( ) ( )( )[ ] ,0~,~1 00 1 000 =−+γ+−≡ − γϕλataditf (3.6) which is called "bifurcation equation". the exact eigenvalue λ is a simple root of bifurcation equation. let ( )ρλ ; 0 s be the ball of radius ρ centred at 0 λ . theorem 3.2 if initial approximations is the sufficiently good, then there is the ball ( )rs ;0λ , where , 2 411 ρη ≤ −− = h h r ( ) ( ) 4 1 ' 0 1 0 ≤= − λλ flfh , ( ) ( )0 1 0 ' λλη ff − = , in which equation (3.6) has unique solution λ=t . the iterations defined by the newton's modified method, given below, ( )[ ] ( ) mmm ff λλλλ 1 01 ' − + −= , κ,2,1,0=m , (3.7) will converge toward this solution. proof: firstly we verify the conditions of the theorem 3.2 [10, p.446]: 1) ( ) [ ] ( );~,~~,~1~,~1 00000000 1 000 doddif =−+−=γ+−= − λψϕγϕγϕλ ( ) ( ) 010 dcf ≤λ ; 2) ( ) [ ] [ ] −=γ+γγ+= −− 00100 1 0010 1 000 ~,~~,~' ψϕγϕλ adiadif λλ +γ−=+γ− 00000000000 ~,~2~,~2 ψϕψϕ ddkdd , ( ) ( ) 0200 ' dckf −≥λ , ( ) ( )[ ] 1 020 1 00 ' −− −≤= dckfm λ ; 3) ( ) ( ) ( )( )( ) 2112121121 "'' ttltttttftftf −⋅≤−−+=− θ , where ( )tfl gt "sup ∈ = . iium engineering journal, vol. 14, no. 2, 2013 rakhimov 188 if initial approximations are sufficiently good, we can choose ε such that 4 1 10 ≤lcm . then, according to theorem 3.2 [10, p.446]-where, there is unique solution of the equation (3.6) in the ball ( )rs ;0λ , where ρη ≤ −− = h h r 2 411 . the iterations calculated by formula (3.7) converge toward this solution. it should be noted that on every step of iterative process it is necessary to solve only one equation: ( )[ ] 000 ~~~, zxza m =⋅+ γλ . theorem 3.3 the elements of gjs { } ipn ji j i , 1,1, )( = ϕ , { } ipn ji j i , 1,1, )( = ψ are the solutions of the following recurrent systems: 0 1 0010 , i n s ss zxzaa =      ⋅+− ∑ = γλ , 0 1 00 * 1 * 0 , i n s ss yzaa γγλ =      ⋅+− ∑ = , 0,11, 1 0010 , iijij n s ss zxaxzaa +=      ⋅+− − = ∑ γλ , ,1 iix ϕ= )( j iji x ϕ= , 0,1 * 1 1 00 * 1 * 0 , iijji n s ss yayzaa γγλ +=      ⋅+− − = ∑ , ,1 iiy ψ= )( j iji y ψ= , i pj ,2= , ni ,1= . proof. we want to apply method of false perturbations to initial equations (2.1) and (2.2). in order to do this we are using pseudo perturbed operator 0d suggested by loginov [8]: ∑∑∑∑ ∑∑ = == = = = +      −= n i p j j i j i n i p j n k p s s k s k j i j i j i ii k zxzxxd 1 1 )( 0 )( 0 1 1 1 1 )( 0 )( 0 )( 0 )( 0 )( 00 ,,, τψσσγ , ∑∑∑∑ ∑∑ = == = = = +−= n i p j j i j i n i p j j i n k p s s k s k j i j i ii k yzyzxd 1 1 )( 0 )( 0 1 1 )( 0 1 1 )( 0 )( 0 )( 0 )( 0 * 0 ,,, τγψσσ , which, according to theorem 1 [3], has the following properties: )( 0 )( 00 j i j i d σϕ = , )( 0 )( 0 * 0 j i j i d τψ = . then ( ) { }n ii daan 10010 = =−− ϕλ , ( ) { }n ii daan 10 * 0 * 0 * 0 = =−− ψλ . the equation ( ) 0 10 =− xaa λ is reduced to the system [ ]      == γ+= ∑ = − ,,1,, , 0 1 0 1 00 nsx dix ss n s ss γξ ϕξ where 1 1 000100 , − =       ⋅+−−=γ ∑ n s ss zdaa γλ -is the bounded linear operator which exists according to the e. schmidt's lemma [5]. then iium engineering journal, vol. 14, no. 2, 2013 rakhimov 189 [ ] ,, 1 00 1 00∑ = − γ+= n s kssk di γϕξξ nk ,,2,1 κ= . because the initial equation has exactly n linearly independent solutions, the last system also has n linearly independent solutions. it means that the rank of the matrix of the coefficients of this system is equal to zero and therefore it is possible to assume [ ] 0 1 00 ii di ϕϕ − γ+= . similarly (2.2) could be reduced to the system [ ] [ ]      == γγ++γ+= − − = − ∑ .,1,, , 0 110 1 00 1 0 1 00 nkx xadidix kssk s n k ksks γξ ϕξ substituting s x in the second part of the system with the value found from the first one we can simplify the system: [ ] [ ] 0110 1 00 1 00 1 00 ,, ks n l klslsk xadidi γγϕξξ − − = − γγ++γ+= ∑ . because it was mentioned earlier that the rank of the matrix of this system equals 0 for each s , we can assume that [ ] [ ] ksksk xadidix ,110 1 000 1 00 − −− γγ++γ+= ϕ , nk ,1= , 1>s . similarly, applying the same arguments to equations ( ) 0* 1 * 0 =− yaa λ and ( ) 1 * 1 * 1 * 0 −=− ss yayaa λ we come to recurrent equations: [ ] 0 1* 0 * 0 kk di ψψ − γ+= , [ ] [ ] ksksk yadidiy ,1 * 1 * 0 1* 0 * 00 1* 0 * 0 − −− γγ++γ+= ψ , nk ,1= , 1>s . example: in order to illustrate these results, we consider the eigenvalue problem 0" =+ uu λ , ( ) 00 =u , ( ) ( )1'' 0 uxu = in the space ( ) ( )[ ] [ ]1;01,,0 1 00 2 cxxc ∩∪ . detailed study of this problem could be found in [11]. if 122 122 0 ++ +− = ms ms x and 2 1 0 +<< sm , the exact value of eigenvalue is 0 µµµ == sm ( here 0 m 1 2 x m + = π µ , ( ) 0 s 1 12 x s + + = π µ ). this is the eigenvalue of multiplicity 2 and the corresponding eigenvector and jordan chain elements are x 0 )1( sin µϕ = , xx 0 0 )2( cos 2 1 µ µ ϕ −= , iium engineering journal, vol. 14, no. 2, 2013 rakhimov 190       ≤≤ − ≤≤ = ,1,cos 1 8 ,0,0 002 0 0 0 )1( xxx x xx µ µψ ( )        ≤≤ − − − ≤≤ + − = .1,sin 1 14 ,0,sin 1 4 002 0 00 0)2( xxx x x xxx x µ µ ψ as initial approximations of functions )1(ϕ , )1(~ψ and elements of jordan's )2(ϕ , )2(~ψ , have been taken the initial segments of their taylor series with 25 terms. all calculation experiments were carried out using program maple 11. under 1== sm , 5 1 0 =x , 6850275,61 4 25 2 == π λ : 8321723,61 0 =λ ; 6728554,611 =λ ; 6850467,612 =λ ; 6850275,613 =λ ; 6850275,61 4 =λ . references [1] b.v. loginov, d.g. rakhimov, “on pseudoperturbation method in the presence of generalized jordan chains.” differential equations and it is applications, ed. m.s. salakhitdinov, fan, tashken, (1979): 113-25. [2] b.v. loginov, d.g. rakhimov, n.a. sidorov,”development of m. k. gavurin's pseudoperturbation method.” fields institute communications, 25 (2000):367-81., [3] b.v. loginov, o.v.makeeva, a.v. tsiganov, “retaining approximately givens jordan chains of the linear operator-functions of the spectral parameter on the base of the perturbation theory.” ulyanovsk state pedag.university, interunivesity collection of the science works "functional analysis", 38(2003):52-62. [4] m.k. gavurin , “on pseudoperturbation method for eigenvalues determination.” journal .computer. mathematics. physics., russian, 1.5(1961):751-70. [5] m.m.vainberg, v.a.trenogin, “branching theory of nonlinear equations.”, nauka, moskow, (1969)., , 1974. [6] b.v. loginov, o.v.makeeva, “pseudoperturbed iteration methods generalized eigenvalue problems.” romai journal, 1(2008):149-68. [7] b.v. loginov, o.v.makeeva, “the pseudoperturbation method in generalized eigenvalue problems.” doklady mathematics,. 77.2 (2009): 194-97. [8] d.g. rakhimov,”on calculation of multiple fredholm's points of discrete spectra of the linear operator-functions by pseudoperturbation methods.” trudy srednevolzskogo matematicheskogo obshchestva, 12.3(2010):106-12. [9] b.v.loginov, yu.b.rusak, “generalized jordan structure in the branching theory.” in right and inverseproblems for partial differential equations, ed. m.s.salakhitdinov. fan, tashkent,( 1978)” 133-148 [10] l.a.lyusternik, v.i. sobolev, “elements of functional analysis.” nauka, (1964). [11] o.v. makeeva, “pseudoperturbation method in generalized eigenvalue problems.”] kandidat dissertation, ulyanovsk, 2007. russian microsoft word most-pages 53-63.doc iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 53 erbium doped fiber amplifier performance using differenthost materials in the band 1450-1650 nm: a comparative study yahya m. zakaryia1, moustafa h. aly2*, osama mahran3, ahmed e. elsamahy3 1faculty of engineering, university of alexandria, alexandria, egypt 2 faculty of engineering, arab academy for science & technology, alexandria, egypt 3faculty of science, university of alexandria, alexandria, egypt e-mail: mosaly@aast.edu abstract: a numerical investigation of the performance characteristics of erbium doped fiber amplifier using different host materials is presented. the emission and absorption curves of each of these hosts are fitted to guassian fitting parameters. a software program is then implemented to calculate the gain coefficient, gain spectrum and the equivalent input noise factors in forward and reverse directions. the hosts under consideration are: almino-germanosilicate, bismuth, linbo3, tellurite, sodium niobium phosphate, oxyfluoride silicate, al2o3 and fluoride phosphate glasses. the corresponding gain covers the 1450-1650 nm wavelength range. 1. introduction as an optical signal propagates through a fiber, its power dissipates as a result of absorption and scattering [1]. optical signals have to be regenerated for longer distance propagation. electronic repeaters are commonly used to restore the signal. such repeaters limit the progress in optical communication systems due to their relatively slower electronic speed that hinders the transmission rates of the system. two decades ago, attention has been diverted toward optical amplifiers because of their advantages over electronic repeaters [2-5]. optical amplification may be attained by either semiconductor optical amplifiers or fiber amplifiers. the erbium doped fiber amplifier receive more attention because its emission coincides with the 1.55 m window, corresponding to minimum attenuation in silica fibers. the most important parameters of optical amplifiers are their gain spectrum and noise properties. it is important that the maximum gain be centered at the wavelength of interest. the almino-germanosilicate glass exhibits high gain, high saturation output power, polarization independent gain and no crosstalk [6]. while the host, bismuth glass, exhibits broadened and flattened gain spectra of (edfa), low noise figure and low insertion loss [7]. the host, linbo3 glass, is considered as one of the most popular dielectric materials in optoelectronics for remarkable electro-optical, acousto-optical and nonlinear properties [8]. the tellurite based fiber amplifiers and lasers, which can be used for the l-band operation, are capable of providing large and broad stimulated emission cross section because of their high refractive indices at the iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 54 communication band, and are attractive host materials for broadband applications [9]. the host, sodium niobium phosphate glass shows good quality optical waveguides by the ionexchange technique [10]. the oxyfluoride silicate can be used for potential broadband optical amplifier in the wavelength–division–multiplexing (wdm) network system [11]. the use of the host al2o3 results in a high mode intensity in the waveguides and allows for a small bending radius and thus compact waveguide devices [12]. fluoride phosphate glasses are interesting gain materials for lasers and amplifiers in the eye-safe region around 1.5 µm for applications in telecommunication systems, medicine and meteorology [13]. 2. theory 2.1 rate equation in three level systems the rate equations corresponding to the specific case of confined er-doping are [6]:    q dz dq apep )(  , (1) okekkakek k pp dz dp  2)(    , (2) where q is the normalized pump power, pk is the normalized sum of the signal power and the noise power introduced by the amplified spontaneous emission (ase) at a signal wavelength k, the positive sign refers to the forward direction while the negative sign refers to the reverse direction and pok is the equivalent input noise power normalized to the saturation power at k. the emission and absorption coefficients are γe, γa and the letters p and k correspond to the pump and the signal, respectively. for the three-level pumping scheme, the emission and absorption coefficients are defined as [14]: 1 ( ) 1 ; 0 1 ( ) k j j j j ap p ep j j j p p q q p p                       , (3)          j jj j jj j k k kek ppqq ppqq )(1 )( 1 )(     , (4) iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 55          j jj j jj j k kak ppqq pp )(1 )( 1 1    , (5) where papop   , (6) and kakok   , (7) where αp is the pump and αk is the signal absorption coefficients, гp,k the overlap factors of the pump and signal at λpk, the wavelength of pump and signal and ρo is the dopant density. 2.2 amplifier gain introducing the emission and absorption coefficients to the power rate equations, one can get: )}]log()( 1 {exp[        o l ol p kp p k ol q q qqpp     , (8) where op and  lp are the normalized input and output signal powers, ηp and ηk are the ratio of the emission to the absorption cross section for the pump and the signal, respectively. from eq.(8), the amplifier gain, g, can be obtained as: )}]log()( 1 {exp[          o l ol p pk p k o l q q qq p p g     . (9) from the definition of the absorption coefficient, p, and using an amplifier of length l, one can get the relation between the input and output pump powers, qo and ql, as:           l o plo q q lqq log . (10) equation (9) is now used with eq.(10) to get: )exp( laqq gol   , (11) where ag is the gain-dependant pump absorption coefficient, given by: iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 56                     l g a kp pk k p pg      log 11 1 (12) the input pump power oq is then expressed as a function of the amplifier gain g, by eliminating lq from eqs.(11) and (12) as:   kp k po ql q lq   1exp1   , (13) with             l g q kk p k   log 1 1 1 . (14) the output pump power lq is then rewritten: ))1(exp( kpol qlqq    (15) for forward pumping case, lq is always smaller than  oq and hence qk must be smaller than one. equation (14) gives the following condition for the peak gain as:            lg k p pk    1 exp , (16) which sets the upper limit for the gain, gmax, through which the amplifier length, l, can be determined. through the amplifier gain, one can get the normalized input and output signal powers as:   nppgp okokl )2( , (17) and   nppgp oklko )2( , (18) where n  and n  are the ase photon numbers in forward and backward directions, respectively, which are given by:                                             l p pk l p k lo p k p k k qqqqin          1 )log(exp),( 1 )( , (19) iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 57                                             o p pk o p k lo p k p k k qqqqin          1 )log(exp),( 1 )( , (20) with                 o l ps q q l p pk p k lo dx x qqi      1 exp , . (21) 2.3 equivalent input noise factor in terms of the gain and the ase noise photon numbers, the equivalent input noise factors for the forward and backward pumping schemes, eqn , and the optical noise figures,  of , are defined by [14]:     g n n kkeq      , (22)   g n f ko      21 )( . (23) using eqs. (19)-(21), the equivalent noise factors and the optical noise figures can be written in the forms:                                       o p pk o p k lo p k p k keq qqqqin          1 )log(exp, 1 )( (24) g nf keqko 1 )(2)(    (25) 3. results the experimental emission and absorption cross sections of the different hosts [3-16] are fitted to gaussian curves and the parameters are used in calculations of the gain coefficient, gain spectrum and the equivalent input noise factors in forward and reverse directions. one considers an edfa pumped at λp= 980 nm, at which the edfa operates as a three-level laser system, with the ratio of emission to absorption cross section of pump ηp= 0. figure 1 plots the gain coefficient around the 1.5 µm for a typical er3+-doped aluminogermanosilicate glass fiber amplifier for different values of the relative inversion d, by iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 58 incremental steps of 0.2. it is clear that for d = -1, all ions are in the ground state and the medium is absorbing at all signal wavelengths, as the gain coefficient is negative. as the value of d increases, however, a spectral region near the long wavelength side of the transition is characterized by a positive gain coefficient. -10 -8 -6 -4 -2 0 2 4 6 8 10 1420 1480 1540 1600 1660 wavelength, l, nm g ai n co ef fic ie nt , g, m 1 d=+1 d=-1 fig.1: signal gain coefficient of erbium doped alumino-germanosilicate glass. the gain coefficient for the hosts, bismuth glass, linbo3 glass, tellurite, sodium niobium phosphate glass, oxyfluoride silicate, al2o3 and fluoride phosphate glass fiber amplifier, is calculated in the same manner. the edfa gain spectrum g(λ) corresponding to the hosts, alumino-germanosilicate glass, bismuth glass, linbo3 glass and tellurite is shown in fig.2, while that of the sodium niobium phosphate glass, oxyfluoride silicate, al2o3 and fluoride phosphate glass hosts is shown in fig.3. figure 4 displays the dependence of the equivalent noise figure on both signal gain and signal wavelength for the forward pumping for the alumino-germanosilicate glass at different values of the maximum gain. it is noted that, as the gain increases the equivalent input noise figure becomes nearly independent of signal wavelength and for the case of complete population inversion it reaches unity. such a regime can be achieved with a pump wavelength of 980 nm, for which the edfa operates as a three-level system, as mentioned before. iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 59 0 5 10 15 20 25 30 35 1500 1550 1600 1650 wavelength, l, nm g ai n sp ec tr um , g , db aluminogermanosilicate host bi-glass host linbo3 host tellurite glass host qo=51.8 mw 0 5 10 15 20 25 30 35 40 45 1450 1500 1550 1600 1650 wavelength, l, nm g ai n sp ec tr um , g , db sodium noibium host oxyf louride silicate host al2o3 host fluoride phosphate host qo=51.8 mw fig. 2: gain spectrum plotted at qo=51.8 mw. fig. 3: gain spectrum plotted at qo=51.8 mw. g(peak)db 4 8 12 16 20 24 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1490 1510 1530 1550 1570 wavelength, , nm e qu iv al en t no is e fig ur e, n eq (+ ) fig.4.forward equivalent noise figure for the erbium doped alumino-germanosilicate iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 60 figures 5 and 6 display the dependence of the equivalent noise figure on both input normalized pump power and signal wavelength for the forward pumping, for the eight mentioned hosts, at the maximum gain of each host. 0.6 0.8 1 1.2 1.4 1.6 1.8 2 1500 1550 1600 1650 wavelength, l, nm e qu iv al en t no is e fig ur e, n eq (+ ) aluminogermano silicate bismuth linbo3 tellurite 24 db gmax=23 db 25.3 db 20.09 db 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 1500 1550 1600 1650 wavelength, l, nm e qu iv al en t no is e fig ur e, n eq (+ ) sodium niobium phosphate oxyf luoride silicate al2o3 glass fluoride phosphate glass gmax=12.95 db 38.99 db 33.37 db 29.1 db fig. 5: forward equivalent noise figure for the erbium doped in aluminogermanosilicate, bismuth, linbo3 and tellurite glasses, respectively. fig. 6: forward equivalent noise figure for the erbium doped in, sodium niobium phosphate, oxyfluoride silicate, al2o3 and fluoride phosphate glasses, respectively. the optical noise figure for the almino-germanosilicate glass fiber amplifier is plotted in figs. 7, at different values of the signal gain g, having its maximum value around 1530 nm. the optical noise figure for the almino-germanosilicate, bismuth, linbo3, tellurite, sodium niobium phosphate, oxyfluoride silicate, al2o3 and fluoride phosphate glass fiber amplifiers is plotted in figs. 8 and 9 at the maximum gain of each host. figures 7 and 8 indicate that for the highest gains, the optical noise figure reaches a lower limit of 3 db and is very nearly wavelength independent. for the un-pumped fiber (qo= 0), the optical noise figure is the reciprocal of the fiber transmission. as the fiber is pumped with an increasing input power, corresponding to increasing gains and overall fiber inversion, the optical noise figure is seen to decrease for forward propagation direction. iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 61 g(peak)db 4 8 12 16 20 24 1.0 2.0 3.0 4.0 5.0 1520 1540 1560 wavelength, ,nm o pt ic al n oi se f ig ur e, f o (+ ) fig.7: forward optical noise figure for the erbium doped alumino germanosilicate glass. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 1500 1560 1620 wavelength, l, nm o pt ic al n oi se f ig ur e, f o( + ) aluminogermano silicate bismuth glass linbo3 glass tellurite glass gmax=20.09 db 23 db 25.3 db 24 db 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 1500 1520 1540 1560 wavelength, , nm o pt ic al n oi se f ig ur e, f o( + ) sodium niobium phosphate oxyf luoride silicate al2o3 glass fluoride phosphate glass 33.37 db gmax=38.9 db 12.95 db 29.1 db fig .8: forward optical noise figure for the erbium doped in, alumino-germanosilicate, bismuth, linbo3 and tellurite glasses, respectively.erbium doped with the hosts, alumino germanosilicate glass, bismuth glass, linbo3 glass and tellurite respectively. fig. 9: forward optical noise figure for the erbium doped in, sodium niobium phosphate, oxyfluoride silicate, al2o3 and fluoride phosphate glasses, respectively. iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 62 4. conclusion a numerical investigation of the performance characteristics of erbium-doped in the host materials, almino-germanosilicate, bismuth, linbo3, tellurite, sodium niobium phosphate, oxyfluoride silicate, al2o3 and fluoride phosphate glass fiber amplifiers. one summarize the features of the amplifier with different hosts in table 1, where g is the amplifier gain,  is the 3 db broadening of the gain, fo, is the noise figure calculated at the maximum gain, gmax, and o is the central frequency which corresponds to the maximum gain. the amplifier gain using these different hosts covers the wavelength range 1450-1650 nm. from table 1, it is clear that the erbium-doped oxyfluoride silicate fiber amplifier exhibits a maximum gain of 39 db at the central wavelength of 1540 nm and minimum noise figure ≤1db, but the broadening in the gain curve is just 21 nm. one can also see that the erbium doped alumino-germanosilicate fiber amplifier exhibits a more broadening in the gain curve (= 40 nm), which allows amplifying the signal at a large range of wavelengths, which is the case in wdm systems. the case of erbium doped sodium niobium phosphate glass fiber amplifier exhibits a less gain (=12.9 db) than other hosts and large noise figure (=4 db) in comparison with the other hosts, and the broadening (δλ=20 nm) is considerably small. table 1 features of the edfa with different hosts. host o (nm) gmax (db) fo(db)  (nm) alumino-germanosilicate 1540 24 1.5 40 bismuth 1550 23 3 30 linbo3 1553 25.3 2.2 15 tellurite 1530 20 4 28 sodium niobium phosphate 1540 12.9 2 20 oxyfluoride silicate 1540 39 1 21 al2o3 1530 33.37 3.5 22 fluoride phosphate 1530 29 0.1 23 iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 63 references [1] william l. barnes, richard i. laming , eleanor j. tarbox, and p. r. morkel, "absorption and emission cross section of er3+ doped silica fibers," ieee j. quantum electron., vol. 27, pp1004-1010, 1997. [2] m. v. d. vermelho, ulf peschel. and j. stewart aitchison, "simple and accurate procedure for modeling erbium-doped waveguide amplifiers with high concentration," j. lightwave technol., vol. 18, pp 401-408, 2000. [3] piotr myslinki, dung nguyen and jacek chrostowski, "effects of concentration on the performance of eribum-doped fiber amplifiers," j. lightwave technol., vol. 15, pp112-120, 1997. [4] paul wysocki and vincent mazurczyk, "polarization dependent gain in erbium-doped fiber amplifiers: computer model and approximate formulas," j. lightwave technol., vol. 14, pp 572-583, 1996. [5] emmanuel desurvire and jay r. simpson, "amplification of spontaneous emission in erbium-doped single-mode fibers," j. lightwave technol., vol. 7, pp 835-845, 1989. [6] e. desurvire, j. l. zyskind and j. r. simpson, "spectral gain hole-burning at 1.53 µm in erbium-doped fiber amplifiers," ieee photonics technol. lett. vol. 2, pp 246-248, 1990. [7] jianhu yang, shixun dai, yuefen zhou, lei wen, lili hu and zhonghong jiang, "spectroscopic properties and thermal stability of erbium-doped bismuth-based glass for optical amplifier," j. appl. physics, vol. 93, pp 977-983, 2003. [8] c.h. huang, l. mccaughan and d. m. gill, "evaluation of absorption and emission cross sections of er-doped linbo3, for application to integrated optic amplifiers," j. lightwave technol., vol. 12, pp. 803-809, 1994. [9] x. peng, f. song, s. jiang, n. peyghambarian, makoto kuwata-gonokami and lei xu, "fiber-taper-coupled l-band er3+-doped tellurite glass microshere laser," appl. phys. lett., vol. 82, pp. 1497-1499, 2003. [10] g.c. righini, s. pelli, m. fossi, m. brenci, a.a. lipovskii, e.v. kolobkova, a. speghini and m. bettinelli, "characterization of er-doped sodium-niobium phosphate glasses," proceedings of spie, vol. 4282, pp. 210-215, 2001. [11] shiqing xu, zhongmin yang, shixun dai, jianhu yang, lili hu and zhonghong jiang, "spectral properties and thermal stability of er3+-doped oxyfluoride silicate glasses for broadband optical amplifier," j. alloys and compounds, vol. 4, pp. 142-148, 2003. [12] gerlas n.van den hoven, jan a. van der elsken, albert polman, cor van dam, koos w. m. van uffelen and meint k. smit, "absorption and emission cross section of er3+ in al2o3 waveguides", appl. opt. , vol. 36, pp. 3338-3341, 1997. [13] j.f. philipps, t. töpfer, h. ebendorff-heidepriem and d. ehrt, r. sauerbrey, "spectroscopic and lasing properties of er3+: yb3+-doped fluoride phosphate glasses," appl. phys. b 72, pp.399–405 (2001). [14] e. desurvire, erbium doped fiber amplifiers: principles and applications, new york: wiley, 1994. [15] martin achtenhagen, robert james beeson, feng pan, bruce nyman and amos hardy,"gain and noise in ytterbium-sensitized erbium-doped fiber amplifiers: measurements and simulations," j. lightwave technol., vol. 19, pp 1521-1526, (2001). iium engineering journal, vol. 5, no. 2, 2004 y. m. zakaryia et al. 64 [16] federico caccavale, francesco segato and ibrahim mansour, "a numerical study of erbium doped active linbo3 waveguides by the beam propagation method," j. lightwave technol., vol. 15, pp 2294-2300, 1997. biographies yahya mounir zakaria was born in 1963 in alexandria, egypt. he obtained his b.sc. in nuclear engineering, and m.sc. in engineering physics from faculty of engineering alexandria university in 1986 and 1989, respectively. he obtained his ph.d. in 1996 from mcmaster university, canada. currently, he is assistant professor at the engineering physics department, faculty of engineering, university of alexandria, alexandria, egypt. moustahfa hussein aly born in 1953 in alexandria, b.sc. electrical engineering 1976, m.sc. 1983 and ph.d. 1987, all from faculty of engineering, alexandria university. currently, he is a professor of communications, college of engineering and technology, arab academy for science & technology & maritime transport, alexandria, egypt ahmed azz el-arab el-samay was born 1944 in alexandria, egypt. he obtained his b.sc. and m.sc. in physics from faculty of science, alexandria university in 1966 and 1971, respectively.. he obtained his ph.d. in 1976 from moscow university, russia. currently, he is a professor, at the physics department, faculty of science, university of alexandria, alexandria, egypt ossama s. mahran was born in 1970 in alexandria, egypt. he obtained his b.sc., m.sc., ph.d. in physics from faculty of science, alexandria university in 1992, 1999 and 2004, respectively. his current position is assistant professor at the department of physics, faculty of science, university of alexandria, alexandria, egypt. 493 iium engineering journal, vol. 15, no. 2, 2014 abid et al. 59 sealing performance of gasketed flange joints – a parametric study muhammad abid 1 , kamran ahmed khan 1 , javed ahmad chatta 1 and hafiz abdul wajid 2 1 faculty of mechanical engineering, gik institute of engineering sciences and technology, topi, pakistan. 2 department of mathematics, comsats institute of information technology, lahore, pakistan. abid@giki.edu.pk, chattha@giki.edu.pk, hawajid@ciitlahore.edu.pk abstract: this paper aims at finding the leak rate through ansi class#150 flange joints using compressed asbestos sheet gasket under combined structural and thermal transient loading conditions. the solution is obtained using two different leak rate models and two different bolt up values. the gasket compressive strain based model employs strains that are determined using finite element analysis. the other model is based on the porous media theory in which gasket is considered as a porous media. leak rates determined using these leak rate models are compared for different tightness classes and discussed. abstrak: kajian bertujuan mencari kadar bocor menerusi sambungan bebibir kelas ansi#150 menggunakan gasket kepingan asbestos termampat di bawah kondisi bebanan gabungan struktur dan terma fana. solusinya diperolehi dengan menggunakan dua model kadar bocor yang berbeza dan dua nilai atas bolt yang berlainan. model terikan berasaskan pemampat gasket menggunakan terikan yang ditentukan dengan analisis unsur terhingga. model yang lainnya berasaskan teori bahantara berongga di mana gasket digunakan sebagai medium. kadar bocor ditentukan dengan menggunakan model kadar bocor, yang kemudiannya dibandingkan pada kelas keketatan yang berbeza dan keputusannya dibincangkan. keywords: bolted flange; gasket; leak rate; finite element analysis; tightness class compressive strains; porous media 1. introduction conventional gasketed-flanged pipe joints are widely used in process industries for connecting pipes to pipes, and pipes to equipments. for bolted flange joints, two main concerns are joint strength and sealing capability. present available design methods and codes address only the structural strength of the flange joint under internal pressure and do not consider the sealing capability of the joints under transient thermal loading. when gasketed-bolted connections are used in mechanical structures such as pipe flange connections, covers of pressure vessels in chemical plants, and the cylinder head in combustion engines, they are usually under thermal conditions. in the available published work, thermal behavior of the pipe flange joints is discussed under steady state loading with or without internal pressure [1-5] and under transient loading condition without internal pressure [6, 7]. iium engineering journal, vol. 15, no. 2, 2014 abid et al. 60 in this study, sealing behavior of different sizes of gasketed-bolted flanges joint under combined internal pressure and thermal transient loading is determined using finite element analysis and two available analytical leak rate models. 2. finite element modeling ansi 150# flange sizes of 0.5, 1, 2, 3, 4, 10, 14, 18 and 24 inches are first analyzed numerically using ansys® software under combined internal pressure and transient properties. neglecting the holes in the flange and the local effect of individual bolts around the flange, it is assumed that the system can be modeled as an axisymmetric structure. this may be thought of in the form of a continuous bolt ring with the bolt force applied at each bolt location. this provides a bolt force that is uniformly distributed along the circumference [8]. the resulting two dimensional flange joint models is shown in fig. 1. structural element (plane 82) is used for the structural stress analysis of the flange joint. thermal element (plane77) that is compatible with plane82 element is used to determine temperature distribution. two-dimensional ‘node-to-surface’ conta172 contact elements, in combination with targe169 target elements are used to simulate contact distribution between flange face and gasket surface, the top of the flange, and the bottom of the bolt head. friction is assumed negligible between surfaces, since the forces normal to the contact surfaces would be far greater than the shear force. thermal and mechanical properties of flange and pipe, bolt, and gasket are taken from ref. [9]. fig. 1: fe model and applied boundary conditions. 2.1 thermal boundary conditions the initial thermal condition at time t = 0 seconds is a temperature of t = 20 o c (ambient). for time t>0, convective boundary conditions with internal temperature of iium engineering journal, vol. 15, no. 2, 2014 abid et al. 61 100°c with a convective heat transfer coefficient of 150 w/m 2 / o c is applied at the pipe inner surface of the pipe, flange, and gasket. an ambient temperature of 20°c with a convective heat transfer coefficient of 20 w/m 2 / o c is applied at the outer surface of pipe, flange, and gasket as shown in fig. 1. the analysis is performed for 1500 seconds. 2.2 structural boundary conditions the flange is free to move in either the axial or radial direction, resulting in flange rotation. a symmetry condition is applied to the lower portion of the gasket. the bolt is constrained in the radial direction. the target torque depends on the flange size as specified by the process industry [10] and the gasket manufacturer [11] as shown in table 1. the associated asme code [12] does not specify a magnitude of preload for the bolts, referring only to a minimum seating stress that relates to the gasket style and composition. a certain displacement is applied at the bottom of the bolt to obtain a pre-stress condition. after pre-stress application, an internal pressure of 1.8 mpa (18 bar) [10] is applied at the inner diameter of the flange and the gasket. loading due to the head (end cap) is directly applied as nodal forces at the end of the pipe [8]. table 1: target torque values. sr # flange size (in) gasket id (mm) gasket od (mm) target torque (n-m) gasket manufacturer target bolt stress (mpa) target torque (n-m) industry target bolt stress (mpa) 1 0.5 14.2 34.9 34.3 106.7 35 108.8 2 1 26.9 50.8 34.3 106.7 50 108.8 3 2 55.6 92.1 67.6 107.5 130 206.7 4 3 81.0 127.0 67.6 107.5 130 206.7 5 4 106.4 157.2 67.6 107.5 130 206.7 6 10 268.2 323.8 188.4 109.2 300 173.9 7 14 349.3 412.7 281.8 109.5 500 194.2 8 18 449.3 533.4 398.4 108.7 705 192.3 9 24 603.3 692.1 555.7 110.5 985 195.9 3. leakage analysis 3.1 leak rate model based on gasketed compressive strains (lr-1) leak from a flange joint is observed during operating conditions when there is insufficient contact stress on the gasket due to insufficient bolt load. in order to estimate the leak rate, a mathematical model based on the compressive strain of a gasket is proposed in ref. [13], as it provides a simplified test procedure eliminating the complex loading-unloading sequence on the gasket. the proposed gasket strain formulation also incorporates thermal loading on flange joint to estimate the leak rate. experimentally, leak rates through flange joints is observed to be directly proportional to the internal pressure and inversaly proportional to the gasket strains. the following equations 1 and 2 were derived from the experimental test data of compressed asbestos (cas) gasket [13]. n n n n n nn n pabh n n l − −−         −      − = 11 1 2πλ (1) iium engineering journal, vol. 15, no. 2, 2014 abid et al. 62 where, and β is the shape factor which is defined as n n n n n abh − −−         −= 11 β (2) p = internal pressure (mpa); ε = compressive gasket strain; h = gasket height (mm); b= gasket outside diameter (mm); a = gasket inside diameter (mm); β = shape factor; c, n and α are constants that are dependent on the gasket type. for the non-asbestos compressed fiber sheet gasket, the values of c, n and α are 0.474, 1.35 and -57.8 respectively [13]. the main input in this model is the gasket strain ‘ε’ that is calculated from finite element analysis. this leak rate model is used for both gases and liquids. a detailed flow chart for the leak rate determination based on gasket compressive strain is shown in fig. 2. fig. 2: analysis flow chart using gasket compressive strains leak rate model (lr-1). 3.2 leak rate model based on porous media theory (lr-2) the leak prediction is also carried out using porous media theory by integrating navier-stokes equations with first order slip flow boundary conditions [14]. equation 3 is applicable to a wide variety of gasket materials in which gasket permeability is the main factor to determine leak rate. analysis approach numerical analytical structural thermal coupled filed leak rate model leak rate results εαλ ⋅⋅= ec iium engineering journal, vol. 15, no. 2, 2014 abid et al. 63 2 2 * 0 1 ln sfi v o rm g g i tk p p l rr t r π µ − = (3) here, lrm = mass flow rate (kg/sec); t = gasket thickness (m); kv = gasket intrinsic permeability (m 2 ); po = ambient pressure (mpa); p* = ration of the inlet over outlet pressures; µg = dynamic viscosity (pa s -1 ); rg= specific ideal gas constant (j kg -1 k -1 ); t= temperature (k); ro, ri = outer and inner radius of gasket. leak rate prediction for liquids by authors in ref. [14] validates the hypothesis of using gasket permeability from a reference gas test. 4. results and discussion 4.1 leak rate model based on gasketed compressive strains (lr-1) leak rate is determined from the flange joints using both gases and liquids. for liquids, crude oils of densities 915 and 973 kg/m 3 respectively are used. for gases, helium and nitrogen with densities of 0.1786 and 1.251 kg/m 3 respectively are used. klingersil®c4400 sheet gasket is used for crude oil, helium, and nitrogen. the leak rates were calculated by taking an initial contact area and effective contact area of the gasket (fig. 3). figures 4 to 7 show that leak rates for the effective contact area are less than the initial contact area of the flange joint. figures 4 and 5, show variation in the leak rates for each size of the flange joint. the leak rate of nitrogen is observed to be more than that of helium for the same target torques as specified in ref. [10]. a maximum leak of 3.86 and 7.98 mg/sec is observed in the flange size of 4 inches for the target torques specified by the industry and gasket manufacturer respectively. the difference between the leak rates is due to the torques recommended which is higher in the industry specification case. this results in a higher generation of compressive gasket strain and lower leak rate. the leak rates of flange joints with sizes of 4, 6, and 8 inches are above the tightness class t3 [15] but the leak rates tend to decrease with the increase in flange size approaching the t3 regime. however, for the gasket manufacturer torque values, the leak rates of flange sizes from 2 to 24 inches are observed to be more than the t3 tightness class and lie in the t2.5 class for nitrogen gas. the leak rate of helium lies in the t3 class for both the target torque values. for crude oil, only the 0.5 and 1 inch flange sizes lie in the t2 class for both the recommended target torques, and the leak rate for the remaining flange sizes remains in the t1 class. this shows that the target torque values are recommended for the t1 class. to improve the leak rate, the target torque should be adjusted to meet the higher tightness class requirements. (a) (b) fig. 3: (a) initial contact area, (b) effective contact area. iium engineering journal, vol. 15, no. 2, 2014 abid et al. 64 fig. 4: leak rate of gases using torques recommended by industry (ica= initial contact area, eca= effective contact area), he = helium, n2 = nitrogen. fig. 5: leak rate of gases using torques recommended by gasket manufacturer (ica= initial contact area, eca= effective contact area): he = helium, n2 = nitrogen. 0.00e+00 5.00e-06 1.00e-05 1.50e-05 2.00e-05 2.50e-05 3.00e-05 3.50e-05 4.00e-05 4.50e-05 0.5in 1in 2in 3in 4in 10in 14in 18in 24in l e a k r a te ( m g /s e c ) flange size he ica he eca n2 ica n2 eca t3 0.00e+00 1.00e-05 2.00e-05 3.00e-05 4.00e-05 5.00e-05 6.00e-05 7.00e-05 8.00e-05 9.00e-05 0.5in 1in 2in 3in 4in 10in 14in 18in 24in l e a k r a te ( m g /s e c ) flange size he ica he eca n2 ica n2 eca t3 iium engineering journal, vol. 15, no. 2, 2014 abid et al. 65 fig. 6: leak rate of crude oil using torques recommended by industry (ica= initial contact area, eca= effective contact area). fig. 7: leak rate of crude oil using torques recommended by gasket manufacturer (ica= initial contact area, eca= effective contact area). 4.2 leak rate model based on porous media theory (lr-2) using the porous media theory, high leak rates are observed for gases compared to the gasket compressive strains theory for the same gasket and boundary conditions (fig. 8). for helium gas, all flange sizes qualified for the t2 tightness class except for the flange size of 4 inches which lies in the t1 class for target torques recommended by the gasket 0.00e+00 5.00e-03 1.00e-02 1.50e-02 2.00e-02 2.50e-02 3.00e-02 3.50e-02 0.5in 1in 2in 3in 4in 10in 14in 18in 24in l e a k r a te ( m g /s e c ) flange size d1 ica d1 eca d2 ica d2 eca t2 d1= 915 kg/m3 d2= 973 kg/m3 0.00e+00 1.00e-02 2.00e-02 3.00e-02 4.00e-02 5.00e-02 6.00e-02 7.00e-02 0.5in 1in 2in 3in 4in 10in 14in 18in 24in l e a k r a te ( m g /s e c ) flange size d1 ica d1 eca d2 ica d2 eca t2 iium engineering journal, vol. 15, no. 2, 2014 abid et al. 66 manufacturer. for nitrogen gas, only flange sizes of 0.5, 1 and 2 inches qualify for t2 class and remaining all flange sizes lie on tightness class t1 for both the target torques. it is obvious that the higher leak rate is obtained for the gasket manufacturer’s recommended target torque as compared to the industry recommended torques. for the industry recommended target torque, the maximum leak rate of 8.19e-01 mg/sec is observed. for the gasket manufacturer’s recommended target torque, the leak rate is observed to be 2.78 mg/sec for the flange size of 4 inches. it is concluded that this is due to the higher value of the industry recommended target torque compared to the gasket manufacturer recommended setting. fig. 8: leak rate of gases using torques recommended by industry and gasket manufacturer. he = helium, n2 = nitrogen. 5. conclusions for ansi class#150 flanges, different leak rates are calculated for different flange sizes. the maximum leak rate was found for the flange joint size of 4 inches using both leak rate models. the compressive strain based model predicts a higher leak rate compared to the porous media bases leak rate model. compressive strain based model is applicable to liquids and gases but the gasket type is limited to a compressed asbestos sheet. the porous media based model that should be applicable to any type of gasket has been validated for gases only. for liquids, the model is yet to be checked and validated. for gas (nitrogen), the maximum leak rate is observed for the 4 inch flange size, which is 7.98e-8 kg/sec for lr-1 and 2.78e-06 kg/sec for lr-2 using the gasket manufacturer’s recommended target torque. for the case of crude oil, the leak rate was reduced by 50% when industry recommended target torque is applied. for the same target torque, flange sizes meet t2 tightness class requirement for liquids. however for the case of gases, flange sizes meet t3 tightness class requirement due to the difference in their densities. industry recommended target torque is concluded to be better than the gasket manufacturer‘s target torques due to higher gasket stress and low leak rates. 2.00e-03 5.02e-01 1.00e+00 1.50e+00 2.00e+00 2.50e+00 3.00e+00 0.5 in 1 in 2in 3 in 4 in 10 in 14 in 18 in 24 in l e a k r a te ( m g /s e c ) flange size he he (gasket manf) n2 n2 (gasket manf) t1 t 2 iium engineering journal, vol. 15, no. 2, 2014 abid et al. 67 acknowledgement the development of this work has been supported by the higher education commission (hec), pakistan. references [1] abid m, ullah b. (2007) three-dimensional nonlinear finite element of gasketed flange joint under combined internal pressure and variable temperatures. j. of engineering mechanics 133(2):22-229. [2] kumano h, sawa t, hirose h. (1994) mechanical behavior or bolted joint under steady heat conduction, asme j. pressure vessel technology 115(2):142-146. [3] bouzid ah, nechache a, brown w. (2002) the effect of steady state thermal loading on the deflections of a flanged joint with a cover plate. asme pressure vessel and piping conference, vancouver, british columbia, canada, august 5-9, 433:153-162. [4] brown w, derenne m, bouzid ah. (2000) determination of the steady state operating temperature of pressure vessel flange components: part-1analytic methods. asme pressure vessel and piping conference, seattle, washington, july 23-27, 405:5-104. [5] sawa t, takagi y, tatsuoka t. (2005) thermal stress analysis and evaluation of sealing performance in pipe flange connections with spiral wound gaskets under elevated temperature and internal pressure. asme pressure vessel and piping conference. 105-113. [6] sawa t, hirose t, kumano h. (1993) behavior of pipe flange connection in transient temperature field. asme j. pressure vessel technology 115:142-146. [7] brown w, derenne m, bouzid ah. (2002) determination of gasket stress levels during thermal transient. asme pressure vessel and piping conference, vancouver, british columbia, canada, august 5-9, 433:21-28. [8] nash dh, spence j, tooth as, abid m, power dj. (2000) a parametric study of metal-tometal full face taper-hub flanges, int. j. pres. ves. & piping 77:791-797. [9] abid m, chattha ja, khan ka. (2007) finite element analysis of a gasketed joint under combined internal pressure and thermal transient loading. asme pressure vessel and piping conference, san antonio, texas, usa, july 22-26, p1-7. [10] es/090 rev: 1. design and engineering practices (deps), dep 31.38.01.15.gen (piping class exploration and production). 1998. [11] http://www.klinger.co.uk [12] section viii, asme boiler and pressure vessel code, design considerations for bolted flange connections, appendix-2, asme, ny, usa. 1986. [13] kobayashi t, nishida t, suzuki m, yamanaka y. (2000) leak tightness evaluation of gaskets based on compressive strain. asme pressure vessel and piping conference, seattle, washington, july 23-27, (405):23-27. [14] jolly p, marchand l. (2009) leak predictions for static gasket based on the porous media theory. j. pr. vessel tech., trans of the asme. (131):021203:1-6. [15] bickford jh. (1998) gaskets and gasketed joints. marcel dekker inc. isbn 0-8247-9877-5. iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 19 obtaining hysteresis loops at low frequency for characterization of materials to be used in biomedical applications atika arshad, rumana tasnim, sheroz khan and ahm zahirul alam electrical and computer engineering department, international islamic university malaysia, jalan gombak, 53100, kuala lumpur, malaysia. atikaarshad@hotmail.com (received 19 may 2013; accepted 12 march 2015; published on line 29 may 2015) abstract:the promising development of magnetic sensors in the biomedical field demands an appropriate level of understanding of the magnetic properties of the materials used in their fabrication. to date some types of magnetic materials are encountered where their magnetic properties, characterization techniques and magnetization behavior are yet to be explored more suitably in light of their applications. this work studies the characterization of such materials by using a cost effective and simple circuit consisting of inductive transducer and an op-amp as a voltage integrator. in this approach the circuit was simulated using pspice and experiments have been conducted to achieve the desired results. the simulation and experimental results are obtained for three test materials namely iron, steel and plastic. the novelty lies in applying the simple circuit for material testing and characterization via obtaining simulation results and validating these results through experiment. the magnetic properties in low external magnetic field are studied with materials under test. the magnetization effect of a magneto-inductive sensor is detected in the low frequency range for different magnetic core materials. the results have showed changes in magnetization behavior of magnetic materials due to the variation of permeability and magnetism. the resulting hysteresis loops appear to have different shapes for different materials. the magnetic hysteresis loop found for an iron core demonstrated a bigger coercive force and larger reversals of magnetism than those of a steel core, thus obtaining its magnetic saturation at a larger magnetic field strength. the shape of the hysteresis loop itself is found to be varying upon the nature of the material in use. the resulting magnetization behaviors of the materials show their possible applicability for use in sensing devices. the key concern of this work is found upon selecting the appropriate magnetic materials at the desired frequency of operation for magneto resistive applications, magneto-resistive sensors and for an extensive range of biomedical sensor application. abstrak: kemajuan penderia bermagnet yang menggalakkan dalam bidang bioperubatan memerlukan peringkat pemahaman yang tertentu bagi memahami ciri-ciri bermagnet bahan yang digunakan dalam fabrikasi. kini, hanya terdapat beberapa jenis bahan bermagnet yang ditemui; di mana sifat-sifat bermagnet, teknik pencirian dan kelakuan pemagnetan masih belum dikaji agar sesuai di gunakan untuk aplikasi yang sepatutnya. analisa ini mengkaji ciri-ciri bahan dengan menggunakan litar yang mudah dan berkesanan kos yang terdiri daripada aruhan pentransduksi dan op-amp sebagai integrasi voltan. litar disimulasi menggunakan pspice dan eksperimen dijalankan untuk mendapatkan keputusan yang diingini. keputusan simulasi dan eksperimen iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 20 diperolehi dengan menggunakan bahan uji besi, keluli dan plastik. menariknya, litar yang mudah digunakan untuk kajian bahan dan penciriannya diperolehi menggunakan keputusan simulasi dan keputusan tersebut disahkan dengan eksperimen. sifat-sifat bermagnet pada medan magnet luaran rendah dikaji dengan bahan-bahan uji kaji. kesan pemagnetan daripada penderia induktif-magneto dikesan dalam linkungan frekuensi yang rendah untuk bahan teras magnet yang berbeza. keputusan menunjukkan sifat pemagnetan bahan magnet disebabkan oleh perbezaan kemagnetan dan kebolehtelapan. keputusan gelung histerisis didapati menghasilkan bentuk yang berbeza untuk bahan yang berbeza. gelung histerisis magnetik yang terdapat pada teras besi memberikan daya paksa dan kemagnetan berbalik yang lebih besar berbanding dengan teras keluli; jesteru memberikan magnetik tepu pada kekuatan medan magnet yang lebih besar. bentuk gelung histerisis juga berbeza bergantung kepada keadaan bahan yang digunakan. sifat pemagnetan yang terhasil menunjukkan berkebolehgunaan bahan-bahan tersebut sebagai alat penderia. matlamat utama pengkajian ini adalah untuk memilih bahan magnetik yang sesuai pada frekuensi yang diinginkan untuk tujuan aplikasi rintangan megneto, penderia rintangan–magneto dan aplikasi skop penderia bioperubatan yang ekstensif. keywords: hysteresis loop; characterization; magnetization 1. introduction understanding the properties of magnetic materials is very important for their applications in device fabrication used in parameter sensing and knowing the function of electronic devices. an added reason for this understanding also comes from the particular fact that magnetic materials over the last twenty years have changed dramatically both in terms of their applications and in the amount of their use. traditionally, magnetic materials have found applications in mechanical systems making use of heavy current circuits, but in recent years, new and improved materials with magnetic properties have been developed for use in consumer electronics such as gadgets, toys and handheld electronic devices available in the market, leading to finding applications never imaginable a few years ago. the development of various sensors has opened up several possibilities for significant improvements in the advancement of bio-implantable devices or medical equipment. hence many problems regarding the magnetic properties of magnetic materials need to be examined from the elementary point of view. to select a magnetic material necessitates complete familiarity with the material’s magnetic properties. this warrants a renewed attention and research interest required for proper investigation on characterization of magnetic materials. magnetic materials can be used in fields such as magnetic sensing circuitry for cell separation, immunoassays, magnetic resonance imaging (mri), drug and gene delivery, minimally invasive surgery, radionuclide therapy, hyperthermia, and artificial muscle application. among the physical properties that make magnetic materials appropriate for biomedical applications is that these materials can be manipulated by an external magnetic field, which is useful in hyperthermia applications. however, not all magnetic materials have similar magnetic properties. characterization is vital in order to put emphasis on the appropriate applicability of magnetic materials. this research is an attempt at characterizing magnetic materials through analyzing the magnetization behavior in low frequencies for biomedical applications. the idea of using various sensors in magnetic field system applications was first put forward by mokwa [1] and ben et al. [2]. this also allowed the possibility of simple device fabrication. a work reported by [3] demonstrates the use of magnetic materials for a biomedical application. the delivery of drugs using nano-particles (as shown in fig. 1) iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 21 is carried out by encapsulating the magnetic material to ensure its biocompatibity, then by means of an applied magnetic field, the magnetic nanoparticles can then have the possibility of being led towards a specific target in the human body. the applied magnetic field has to be very low. suitable materials used in this case are those with high magnetization at the operation temperature (magnetic iron oxide). thus the relative amount of this material and its material properties should be taken into consideration. fig. 1 therapeutic strategy using magnetic nano-particles [3]. in [4], the author designed a tongue drive system for enabling a person with severe disabilities. it predicts the users’ intentions by wirelessly tracking the movements of a permanent magnetic tracer that are secured on their tongues using an array of magnetic sensors (see fig. 2). comprehensive research work [5-8] has shown increasing interest on numerous magnetic materials used in biomedical applications. fig. 2 block diagram of tongue-computer interface system, based on wireless magnetoinductive sensor [4]. iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 22 this work applies an inductive transducer to investigate magnetic and non-magnetic materials under low frequency. the aim of the proposed work is to identify the material to be used as the inductive sensory system, eventually identifying materials for sensors fabrication. the materials are distinguished by achieving unique hysteresis loops. the procedure adopted is in the form of a suitably selected circuit. simulation results are obtained using pspice. the simulation work is also validated via experiments. this work will be able to characterize magnetic and non-magnetic materials for biomedical applications, which require low frequencies 2. introduction to magnetic hysteresis for characterization of materials one of the key features of magnetic fields is that they are not affected by the presence of any external element such as (soil, water, or air). this effect enhances the material suitability to be used as sensors [9]. a magnetic sensor carries out the measurement of physical properties (such as pressure, temperature, and flow), as well as the detection of any type of change that occurs in magnetic field. thus the understanding of the characteristic properties of magnetic core materials will enable the readers to know the response of the sensors. in general, these magnetic materials are classified into two types: soft and hard magnetic materials. soft magnetic materials can be easily magnetized and demagnetized while the hard magnetic materials cannot be demagnetized so easily, since they retain their magnetism. usually ferromagnetic materials are magnetized easily; in strong magnetic fields the magnetization approaches a certain limit called saturation. with sudden application of a field and its removal, magnetization does not return to its original value this is denoted as hysteresis. for a ferromagnetic core material, the hysteresis loop is plotted between the magnetizing intensity, h, on the horizontal axis and the magnetic flux density, b, on the vertical axis. in order to trace the shape of the hysteretic loop for magnetic materials, many experiments have been conducted. an instance demonstrating the hysteretic behavior is shown in fig. 3. fig. 3 hysteresis loop of magnetic material [10]. the shape of the b-h curve is different for different core materials. also, the rate of change in the magnetic field affects the b-h curve shape. in accordance with the field strength, flux density keeps increasing until it arrives at a specific value where it stops increasing and becomes almost constant since the field strength keeps on raising to the iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 23 amount of flux density that can be produced by the core. flux density increases in proportion to the field strength until it reaches a certain value where it cannot increase anymore and becomes almost level and constant as the field strength continues to increase due to a certain limit to the amount of flux density that can be generated by the core. any further increase will have no effect on the value of b, and the point on the graph where the flux density reaches its limit is referred as magnetic saturation, which is also identified as saturation of the core. by changing the direction of the magnetizing current constantly through the coil from a positive direction to a negative direction, the magnetic hysteresis loop of the ferromagnetic core can be produced [10]. the appropriate selection and processing of magnetic core materials determines the magnetic performance level. some researchers have applied techniques which have been developed to analyze the magnetic hysteresis loop and magnetization process (the properties of the magnetic materials which might affect the sensors responses). 3. hysteresis loops circuit model the hysteresis loop setup for characterization of materials is designed by using the diagram illustrated in fig. 4. the setup is an integration of two parts; the coil setup and the op-amp integrator. the coil setup is a magneto-inductive coupling circuit consisting of primary and secondary windings, which allows wireless transfer of signals across narrow gaps. the internal distance between the coils has an effect on the strength of signal transmission. the op-amp integrator circuit in the diagram (as in fig. 4) is connected to the secondary circuit of the coil, thus the output of the transformer coil becomes the input of the op-amp, and hence the output voltage waveform of the op-amp responds to the changes in the input voltage waveform. the integrator amplifier acts as a storage element, which produces a voltage output that is proportional to the integral of its input voltage with respect to time. fig. 4 hysteresis circuit setup for characterization of materials. in fig. 4, primary coil (n1) and secondary coil (n2) are the magnetization coils of the test samples and turn of the measuring coil. an ac sinusoidal signal is injected into the excitation winding / primary coil, which induces a magnetic field h in the test sample. iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 24 r1is the resistor which limits the current flow to the test sample primary coil loop while r2 is the shunt resistor. the value of current ip (current in the primary loop) is obtained by measuring the voltage drop across the shunt resistor. hence, the value of applied magnetic field h is directly proportional to the current and this is represented by the following formula: 122 / nlhrriu px  hence, 1nh i l  (1) the applied magnetic field in the excitation coil / primary coil gives rise to an induced voltage e2 across the secondary coil. the relation between the induced voltage e2 and magnetic induction intensity b is given by: dtadbne /22  hence, an b 2   (2) where, h = magnetic field strength in [a/m] b = flux density [t] n1= total number of turns in the primary coil n2 = total number of turns in the secondary coil. l = length of the test material [m] i = magnetizing current [a]  = magnetic flux [wb] a= cross sectional area of the sample magnetic material [m2] the operational amplifier is connected to the secondary winding that is used as a voltage integrator. the capacitors c1 and c2 were selected as 1 µf and 100 nf respectively. the output of the operational amplifier is derived as:     t y t sy crabndte cr u dtv cr uv 0 1322 13 013 0 / 1 1 (3) where the value of frc 2/1 . by using eq.3 and eq.1, the value of b and h can be obtained respectively. thus, uy and ux are said to be proportional to b and h, which are the horizontal and vertical inputs. the physical dimension of coils in the circuit, the distance between the two coils and the permeability of the cores, the number of turns in each coil [11] etc. are related to the mutual inductance. the mutual inductance between two coils, l1 and l2, can be written in term of the inductance of each coil and the coupling coefficient, k. the formula is written as: iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 25 1 2 m k l l  (4) 2n a l l  (5) where n is the number of turns per unit length of the coil of length l, a is the crosssectional area of core, and µ is the permeability of the core. thus, hbr /0   hm -1 (6) 4. results analysis and discussion this work demonstrates the use of a simple circuit for material testing and characterization via obtaining simulation results and validating these results through experiments. the proposed circuit model was simulated using pspice and experiments were conducted to achieve the desired results. the simulation and experimental results are obtained for three test materials namely iron, steel and plastic. 4.1 simulation analysis to obtain b-h loops in pspice simulation the effect of changing core materials is modelled through selecting relevant values of the coupling coefficient representing core materials of iron, steel and plastic. the relationship between k and µ is such that, k is inversely proportional to the square root of the product of self-inductance, that is 21 llk  , and the inductance, 2n a l l  is influenced by the permeability of the material. henceforth, it can be said that the change in the material’s permeability is represented by the change in the coupling coefficient factor. the coupling coefficient determines the strength of magnetic coupling between two coils. the coupling coefficient is considered to be maximum (k=1) when the total flux in one coil links with the other. the coupled coils are then referred as tightly or perfectly coupled coils. in that case, the mutual inductance between the two coils also reaches maximum with the maximum value of k. moreover, when the two coils are at greater distance in space; the value of k is very small. in this case the two coils are said to be loosely coupled. the value of k varies in the range of 0 to 1. k is a non-negative fraction and has a maximum value of unity. for an iron core coupled coil, the value of k is approximately 0.99 whereas for air core and paramagnetic material the value of k ranges from 0.1 to 0.7. the circuit in fig. 4 was simulated using the pspice software using the component values provided by table 1, the simulation results are illustrated as follows. table 1: component values of the circuit model component values v1 25 v v2 +15 v v3 -15 v r1 68 ω r2 1 ω r3 1 kω r4 10m ω c1 1 µf c2 100 nf iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 26 fig. 5 input signal of the primary coil. . fig. 6 output signal at the secondary coil. figure 5 shows the input signal, which is the supplied ac current to the primary coil, and the voltage in the secondary windings is illustrated in fig. 6; both curves are almost true sin waves. the secondary waveform shows some distortion. this is due to core being saturated. the results demonstrated by fig. 7 (a) to (c) show b-h curves obtained when the coupling coefficient value is varied for k=0.99, k=0.6, and for k=0.3, representing the three test materials. the exact coupling coefficient for each material being tested is not known, however the values of k is chosen according to the range the materials fall under. figure 7a presents the b-h curve when the coupling coefficient value was set to 0.99 since the iron core is said to have a coupling coefficient of k=0.99. hence it can be said that a soft magnetic core material is simulated. the plot shows low hysteresis loss, indicated by a narrow or ‘flat’ b-h loop, owing to the theatrical concept of b-h plots of a soft magnetic core material. the maximum saturation point attained is (373.17 m, 1.54), iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 27 and minimum saturation point attained is (-343.6 m, -1.54). for k=1 it is considered to be tightly coupled [12] whereas an iron-core is also known to be a tightly coupled coil. fig. 7 (a) hysteresis loop for k=0.99. fig. 7 (b) hysteresis loop for k=0.6. iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 28 fig. 7 (c) hysteresis loop for k=0.3. figure 7b shows the b-h curve when the coupling coefficient value was set to 0.6. the maximum and minimum saturation values of magnetism obtained are (661.9 m, 1.56) and (-621.16 m, -1.56) respectively. a fairly high hysteresis loss is seen. for a coupling coefficient, ranging between k=0.4 to 0.7 is considered to be loosely coupled [12]. hence the b-h loop curve seems to be broader than the loop compared for k=0.99. in fig. 7(c), the b-h loop for k=0.3 possesses a high value of energy product, thus a high hysteresis loss. this loss can be indicated by the saturation value. maximum saturation value is (914.1 m, 1.56) and the minimum saturation value is (-868.13 m, -1.56). for air core coupled circuits the coupling coefficient is usually denoted for k < 0.4 [12]. 4.2 experimental analysis to obtain b-h loops the resulting simulation details are then supported by the laboratory implementation of the circuit in which the core element is made of the actual materials of iron, steel and plastic. the results thus produced are consisting of several sets of b-h curves obtained by using the selected material samples. the pictorial view of the circuit setup is illustrated in fig. 8. the equipment used for the experimental setup are; function generator, oscilloscope, voltmeters and cored coils. the results are displayed on the oscilloscope. the oscilloscope was set to work in xy mode to produce the hysteresis loop across the transformer, channel 1 probe (x-axis) of the oscilloscope was set at r2, which measured the voltage across r2 and channel 2 probe (y-axis) was set at the output of the op-amp (v0). the experiment was conducted on three samples; cores of iron, steel and plastic. table 1 gives the component values used in the construction of the circuit model and table 2 provides the specification of the coils. iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 29 fig. 8 pictorial view of the circuit setup for material testing. table 2: specification of coils number of turns primary coil 22 secondary coil 25 material of wire: copper thickness of wire: 0.19 mm length (mm): 160 diameter (mm): 30 experimentally the processing for the measurements of flux density, b and field strength, h signals are obtained for different core materials as shown in fig. 9. b increases in proportional to h, until it reaches a certain value where it cannot increase further. the increasing strength is the magnetization process and the decreasing portion is the demagnetization process. fig. 9(a) hysteresis loop obtained using iron-core. iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 30 fig. 9 (b) hysteresis loop obtained using steel-core. fig. 9 (c) hysteresis loop obtained using plastic-core. figure 9a demonstrates the hysteresis loop of iron-core with the maximum saturation value of (1.6, 2.4). due to iron being a soft magnetic material, a relatively narrow hysteresis loop is obtained, justifying the simulated result obtained in fig. 7a. figure 9b illustrates the hysteresis loop of a steel-core material. the shape of the steel core also shows the loop to be “flat” or narrow owing to the fact that being a soft magnetic material, its hysteresis loop obtained should be “flat”. the maximum saturation value noted is (1.8, 2.4). the steel core resulted in a smaller coercive force than iron, which is one of the properties of soft magnetic materials. the magnetic saturation is also attained faster with a steel core, compared to an iron core. the set of magnetic hysteresis loop obtained for the iron core showed a larger coercive force, thus attaining its magnetic saturation at a higher magnetic field strength. moreover the shape of the hysteresis loop depends upon the nature of the iron or steel used, and iron showed considerably large amounts of reversals of magnetism. the various magnetization behaviors of the materials determine their potential applicability for sensing devices. figure 9c presents the hysteresis loop obtained experimentally using a plastic-core. plastic is a non-magnetic material, thus there was no effect on the magnetic field. plastic core is regarded as a free space, as they have very low values of permeability. thus plastic is used as a reference core material. the elliptical shape obtained by air-core shows a very good resemblance to the simulated results shown in fig. 7c. theoretically/simulated iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 31 results indicate that for an air-core a wide loop should be obtained. here the maximum saturated valued of x-y is (1.3, 2.5). the simulated results (fig. 7) showed a good level of resemblance of the experimental result (fig. 9) obtained, thus justifying the experimental result of the hysteresis loop obtained. 5. conclusion and future work magnetic materials, which are essentially used in magnetic sensors, require proper characterization. the characterization of magnetic materials has led towards the use of magnetic biomedical devices along with electromagnetic equipment. the appropriate characterization of magnetic material should be made for the proper choice of materials in specific applications, which is indeed a challenge to any user. this work showed that the widely available simulation tool of pspice can reveal the magnetic properties of the materials which are relevant to the experimental study. the change in a material’s permeability is represented by the change in the coupling coefficient factor, k. k is inversely proportional to the square root of the product of self-inductance of the coil, that is 21 llk  ,and the inductance is influenced by the permeability of the material. with an increase in the value of k the hysterisis loop becomes bigger as well. however, for a soft magnetic material the hysteresis loop graph should be “flat”. the simulation output shows low hysteresis loss, indicated by narrow or ‘flat’ b-h loop, owing to the theatrical concept of b-h plots for a soft magnetic core material. the coupling coefficient value is varied for k=0.99, k=0.6, and for k=0.3. the change in the materials’ permeability is represented by the change in the coupling coefficient factor. k is inversely proportional to the square root of the product of self-inductance, and the inductance is influenced by the permeability of the material. the resulting simulation details are then supported by the laboratory implementation of the circuit in which the core element is made of the actual materials of iron, steel and plastic. with this technique of characterization, the hysteresis model can be implemented easily without using any statistical functions that lead to suitable applications of magnetic materials in biomedical sectors. the novelty lies in applying a simple magnetic sensing circuit for material testing and characterization via obtaining simulation results and validating these results through experiments. to further improve the work, ring shaped core materials can be implemented instead of using hollow solenoid tubes . ring shaped cores will provide a continuous magnetic path length. furthermore, when conducting magnetic analyses it is important to determine the magnetic mineralogy, grainsize, and concentration of the various magnetic components within a sample, hence this can be considered in future work. references [1] mokwa w. (2007) medical implants based on microsystems. meas. sci. technol., 18:r47– r57. [2] ben hmida g, ekuakille al, kachouri a, ghariani h, trotta a. (2009) extracting electric power from human body for supplying neural recording system. int. j. on smart and intelligent systems, 2(2):229-245. [3] gupta ak, gupta m. (2005) synthesis and surface engineering of iron oxide nanoparticles for biomedical applications. biomaterials, 26:3995-4021. [4] huo x, wang j, ghovanloo m. (2008). a magneto-inductive sensor based wireless tonguecomputer interface. ieee trans. on neural sys. rehab. eng., 16(5):497-504. iium engineering journal, vol. 16, no. 1, 2015 arshad et al. 32 [5] safarik i, safarikova m. (2002) magnetic nanoparticles and biosciences. monatshefte fur chemie, 133(6):737-759. [6] shinkai m. (2002). functional magnetic materials for medical applications. j. of bioscience bioeng., 94: 606–613. [7] bahadur d, giri j. (2003) biomaterials and magnetism. sadhana, 28:639-656. [8] pankhurst qa, connolly j, jones sk, dobson j. (2003) applications of magnetic nanoparticlesin biomedicine. j. of physics d: applied physics, 36:167-181. [9] markham a, niki t, stephen a, david w. (2010) revealing the hidden lives of underground animals using magneto-inductive tracking. proceedings of the 8th acm conference on embedded networked sensor systems, 281-294. [10] o’handley, rc. (2000) modern magnetic materials principles and application, wileyinterscience. [11] james wn, susan ar. (2004)electric circuit, 7th edition, prentice hall. [12] sadiku mno, alexander ck. (2009) fundamentals of electric circuits,4th edition. mcgraw hill. microsoft word 3-65 page 41-54.doc iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 41 natural convection heat transfer in concentric horizontal annuli containing a saturated porous media ahmed f. alfahaid*1, r.y. sakr1 and m. i. ahmed2 1department of mechanical technology, riyadh college of technology, saudi arabia. p.o. box 91471 riyadh 11633, saudi arabia *alfahaid@gotevot.edu.sa 2department of mechanical engineering, international islamic university malaysia. abstract: natural convection in horizontal annular porous media has become a subject receiving increasing attention due to its practical importance in the problem of insulators, such as ducting system in high temperature gas-cooled reactors, heating systems, thermal energy storage systems, under ground cable systems, etc. this paper presents a numerical study for steady state thermal convection in a fully saturated porous media bounded by two horizontal concentric cylinders, the cylinders are impermeable to fluid motion and maintained at different, uniform temperatures. the solution scheme is based on two-dimensional model, which is governed by darcy-oberbeck-boussinesq equations. the finite element method using galerkin technique is developed and employed to solve the present problem. a numerical simulation is carried out to examine the parametric effects of rayleigh number and radius ratio on the role played by natural convection heat transfer in the porous annuli. the numerical results obtained from the present model were compared with the available published results and good agreement is observed. the average nusselt number at the heating surface of the inner cylinder is correlated to rayleigh number and radius ratio. keywords: natural convection, numerical investigation, saturated porous media, finite element method, concentric horizontal annuli. 1. introduction natural convection in horizontal porous annuli has a wide variety of practical applications such as the insulation of aircraft cabin or horizontal pipes, cryogenics, the storage of thermal energy, and the underground cable systems. lui et al. [1] studied experimentally the natural convection in a horizontal annulus for a fluid layer and showed a multicellular regime for a relatively small radius ratio, (r = 1.15). later, bishop and carley [2] provided photographs showing oscillatory flow regime. grigull and hauf [3] used a mach-zehnder interferometer and visualized different convective regimes including one where three-dimensional effects were present in the upper part of the layer. using purturbation method, mack and bishop [4] solved the steady two-dimensional equations and although the analysis is valid only for small rayleigh numbers, the results revealed the iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 42 existence of secondary flows in the upper and lower parts of the layer for very small prandtle numbers. kuehn and goldstein [5] have conducted an experimental study, which included flow visualization and heat transfer measurements. the analogous problem of the thermal convection in eccentric annulus containing viscous fluid (non-porous medium) has attracted some attention in recent literature. yao [6] developed a purturbation solution for slightly eccentric cylinders, using two-parameter expression in terms of eccentricity and rayleigh number. for this purpose, yao [6] used a special coordinates transformation in which the inner circle was transformed into pole. more recently, prusa and yao [7] constructed a finite difference method simulation using yao’s [6] transformed coordinates. projahn, et al. [8] and by cho et al. [9] provided numerical simulations of viscous fluid in an eccentric annulus. the former applied nonorthogonal body fitted curvilinear coordinates, while the later used bi-cylindrical coordinate. the experimental work of fant et al. [10] showed that at fairly high rayleigh numbers, thermal instability for air appears as steady counter rotating cells near the top of the annulus. perhaps their most interesting result is that the same flow exhibits hysteresis behavior for small gap widths. as prandtle number tends to zero, unsteady hydrodynamic instability was demonstrated at high grashof numbers in the middle of the annulus. cheddadi et al. [11] solved the same equations using the artificial compressibility method to obtain the pressure field. the tangential velocity component was measured using laser doppler anemometry in air-filled annular space. experimental and numerical values agree well; hysteresis behavior was also reported. few results for porous layer are present. caltagirone [12] visualized the thermal field using the christiansen effect and observed a fluctuating three-dimensional regime in the upper part of the layer even though the lower part remained strictly two-dimensional. both a perturbation method and finite difference technique were used to solve two-dimensional boussinesq equations. burns and tien [13] examined the variations of the overall heat transfer coefficients with the external heat transfer coefficient and radius ratio by steadystate two-dimensional analyses with the finite difference method and purturbation method. it was indicated that a maximum value of overall heat transfer coefficient existed depending upon the radius ratio. using finite difference method, echigo et al. (14) also obtained two-dimensional steady state numerical results taking into account the radiation effect. bau [15], in recent works, took eccentricity into consideration and demonstrated that heat transfer in the annulus could be optimized by a proper choice of eccentricity. as mentioned above although several works have been done on the problem, most of them were restricted to one flow pattern, the unicellular one, except for the case of narrow annulus. however, the experimental measurements of caltagirone [12] show, the flow pattern is unlike and not as simple as unicellular one and mainly because of this, the overall heat transfer rates predicted numerically disagree in a margin with those experimental data. rao el al. [16] investigated analytically with the galerkin method steady and transient analyses of natural convection in horizontal porous annulus heated from the inner surface. they obtained three families of convergent solutions appearing one after the other with increasing modified rayleigh number corresponding to different initial conditions. their predictions were limited to modified rayleigh number up to 300. they also determined numerically the bifurcation point, which coincide very well with that from the iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 43 experimental observations of caltagirone [12]. mota and saatdjian [17] solved twodimensional boussinesq equations using finite difference scheme with an adi method and successive under relaxation to a very fine grid. they showed that for very small radius ratio and on increasing the rayleigh number, the steady state regime changes from two to four to six to eight cells without exhibiting a hystresis loop. for radius ratio above 1.7 approximately, closed hystersis loops between ranges containing 2 or 4 cells are obtained. mota and saatdjian [18] used an accurate finite difference code to solve two-dimensional darcy-boussinesq equations for eccentric, horizontal annulus filled with a saturated porous medium. they showed that reducing the radius ratio or increasing the eccentricity has the same impact on the geometry in the top part of the layer where the convective effects are more pronounced. 2. mathematical formulation the problem considered here is a porous layer bounded between two horizontal concentric cylinders of radii ri and ro as shown in fig. (1). the two cylinder walls are assumed to be impermeable. the surfaces of the two cylinders are assumed to be maintained at a constant temperatures ti and to respectively with ti to. the governing equations for steady state natural convection with oberbeck-boussinesq approximation, darcy flow are given as follows: 0 u v x y ¶ ¶ + = ¶ ¶ (1) = 0 f p u x k m¶ + ¶ (2a) g = 0 f f p v y k m r ¶ + ¶ (2b) 2 2 2 2 e f f t t k t t u v x y c x yr æ ö¶ ¶ ¶ ¶ ÷ç+ = + ÷ç ÷÷ç¶ ¶ ¶ ¶è ø (3) r 1 ( )f f rt tr r bé ù= -ë û (4) by taking the curl of eq. (2) and using eq. (4), we obtain the following equations: 2 r = g f f k t x ¶ y r b m ¶ ñ (5) 2 f f e c t t 0 y x y t k x r ¶y ¶ ¶y ¶ ¶ ¶ ¶ ¶ é ù ê úñ = ê úë û (6) where, iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 44 = , = u v y x ¶y ¶y ¶ ¶ (7) non-dimensionalizing the variables as defined below; o i i i t -t x y , x , y = t r rot q = = = ; where = , e f f k c y a a r y the governing equations reduce to the following: 0 = yx xy 2                 (8) x ra = *2    (9) where, ra* = ra . da, ra* is the modified rayleigh number and is given by: feioiffr f * k/r)tk(t c gra  ra; is rayleigh number and given by: fe 3 ioiffr f k/r)t(t c gra  and da; is darcy number and given by 2 ir/k da  2.1 boundary conditions the problem is assumed to be symmetric about the vertical axis, and as a result, only one half of the flow domain will be considered in this analysis. the boundary conditions are handled as follows: aplane of symmetry: 0 x , 0 =     (10a) binner cylinder surface 1.0 , 0 =  (10b) couter cylinder surface 0 , 0 =  (10c) 2.2 heat transfer the local nusselt number at the inner and outer cylinders surfaces can be calculated from the following equations respectively: iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 45 nk rh nu 1yxe ii i 22           (11a) nk rh nu ryxe oo o 22           (11b) where n: represent the direction normal to the cylinders surfaces. the steady state average nusselt numbers at the inner or outer cylinders surfaces are assumed to be equal ( onu = inu = nu) and given by:      0 ii d )(nu 1 nu (12a)      0 oo d )(nu 1 nu (12b) 3. numerical solution the solutions of eqs. (8) and (9) subject to the boundary conditions specified by eq. (10) is obtained numerically by using the galerkin based finite element method [19, 20]. the objective of the finite element is to reduce the system of governing equations into a discretized set of algebric equations. the procedure begins with the division of the continuum region of interest into a number of simply shaped regions called elements. the grid used in the present calculation is illustrated in fig. (1). the element type which used here is linear triangular element. fig. 1: physical geometry and sample grid of the present problem. x y r ro  iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 46 the approximate expressions of temperature and stream function in an element are given by polynomials in terms of the nodal values and interploation functions. the interpolation functions are derived from the assumption of linear variation of temperature and stream function through the element and are given by the following equation:    3 1m mm e n = (13a)    3 1m mm e n = (13b) where nm is the usual interpolation function and is defined by: nm= 1 2a (am + bm x + cmy) (14) where a is the element area and 23321 yxyxa  321 yyb  (15) 231 xxc  the other components are given by cyclic permutation of the subscripts in the order 1,2 and 3. if the approximation given by eq. (13) is substituted in the governing eqs.(8-9), and the global errors are minimized using the above interpolation functions nm as weighting functions, and after performing the weighted inegration over the domain g and the application of green’s theorem, the present model can be written in the equivalent forms: [k1] {} = {f1} (16a) [k2] {} = {f2} (16b) where; e 1 tte 1 1 dg ][ [n] ][ [n] dg ) ][ . ][][ . ][ (][               e e xy tt g e e y n x n y n y n x n x n k e         ett e 1e 1 dy n ]n[ x n ]n[}f{ e               e tt g e 1e 2 dg )y ]n[ . y ]n[ x ]n[ . x ]n[ (]k[ e                         e e g eett e e ee dg x n rad y n n x n nf 1 t 1 2 ][ [n] ][][}{      iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 47 and, e = total number of elements, g= bounded domain,  = domain boundary, y , x yx       equations (8) and (9) result in two sets of linear equations which have been solved by gauss elemination method. the resulting two sets of equations have been solved iteratively through a computer code written here in fortran langauge. the iterative procedure was terminated when the following relative convergence criterion was satisfied:      1i i1i 10-4 (17) where i denote the iteration number performed. 4. model validation the code was validated by solving the convection problem of two concentric horizontal cylinders for which solutions are available. the obtained results compared with the available published data. table 1 shows the average nusselt number for different previous researchers. a good agreement is found between the present work and the other researchers. table 1: comparison of the average nusselt number for natural convection for convective flow between two concentric cylinders with radius ratio of 2. caltagirone [12] rao et al. [16] bau [21] facas [22] facas & farouk [23] present code grid size 49x49 10x10 30x44 50x50 25x25 10x18 ra=50 1.328 1.341 1.335 1.342 1.362 1.317 ra=100 1.829 1.861 1.844 1.835 1.902 1.865 iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 48 5. results and discussion a parametric study of five different radius ratios namely 1.2, 1.4, 1.6, 1.8 and 2 is carried out. in fig. 2, the variation of the average nusselt number (nu) with the rayleigh number (ra) for a radius ratio r of 1.2 is illustrated. it is noticed from this figure that, for a very small ra the dominant mode is the pure conduction. as the ra increases the nu decreases until ra reaches 400. above this value, as ra increases the nu increases too. also, the figure shows a break point at ra about 800, which may indicate different flow characteristics, as stated by [16-17]. the variation of nu with ra for r=1.4 is illustrated in fig. 3. a slight decrease of nu is noticed at very low ra<100, then as ra increases the nu increases. a break point at about ra=140 is also noticed. the variation of the nu with ra for r=1.8 is depicted in fig. 4. it is noticed from the figure that as ra increases the nu increases. also, two breaking points are noticed at ra=200 and 400 respectively. this may be due to change in flow characteristics at these conditions. figure 5 illustrates the variation of nu with ra for r=2. the variation of nu with r for different ra is shown in fig. 6. it can be concluded that for small ra (i.e. ra ≤ 10), where the conduction is the dominant mode of heat transfer, the increase of the insulation thickness (r) leads to decrease of nu (i.e the decrease of heat loss). as ra increases (where the natural convection becomes the dominant mode) the useful insulation radius ratio (r) becomes smaller. the heat transfer and flow characteristics in the porous layer for r = 2 and 1.6 for ra = 120 are illustrated in figs. 7 and 8 respectively. the natural convection is dominant in the top portion of the figure while the conduction is dominant at the bottom. 500 500 1000 1000 1500 1500 ra 4.7 4.7 4.8 4.8 4.9 4.9 5 5 5.1 5.1 5.2 5.2 5.3 5.3 5.4 5.4 5.5 5.5 5.6 5.6 5.7 5.7 5.8 5.8 n u 500 500 1000 1000 1500 1500 ra 2.5 2.5 3 3 3.5 3.5 4 4 4.5 4.5 5 5 n u fig. 2: variation of nu and ra for r = 1.2. fig. 3: variation of nu and ra for r = 1.4. iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 49 200 200 400 400 600 600 800 800 ra 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 4 4 n u 100 100 200 200 300 300 400 400 ra 1.2 1.2 1.4 1.4 1.6 1.6 1.8 1.8 2 2 2.2 2.2 2.4 2.4 2.6 2.6 2.8 2.8 n u fig. 4: variation of nu and ra for r = 1.8. fig. 5: variation of nu and ra for r = 2. 1.2 1.2 1.4 1.4 1.6 1.6 1.8 1.8 2 2 radius ratio r 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 4 4 4.5 4.5 n u ra = 10 ra = 80 ra = 160 ra = 400 fig. 6: variation of nu with the radius ratios for different ra. the heat transfer and flow characteristics in the porous layer for r=1.2 and ra=120 are illustrated in fig. 9. due to the small thickness of the porous layer, the conduction mode is dominant mode of heat transfer in the whole layer. figure 10 shows the comparison between the predicted and correlated average nusselt number. iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 50 fig. 7: temperature filled () and stream function () contours for r = 2 and ra =120. t 0.9375 0.875 0.8125 0.75 0.6875 0.625 0.5625 0.5 0.4375 0.375 0.3125 0.25 0.1875 0.125 0.0625 -37.9131 -32. 858 -10.1102 -2.52754 fig. 8: temperature filled () and stream function () contours for r = 1.6 and ra =120. t 0.9375 0.875 0.8125 0.75 0.6875 0.625 0.5625 0.5 0.4375 0.375 0.3125 0.25 0.1875 0.125 0.0625 iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 51 t 0.9375 0.875 0.8125 0.75 0.6875 0.625 0.5625 0.5 0.4375 0.375 0.3125 0.25 0.1875 0.125 0.0625 -2.77668 1.85 112 -0.185112 fig. 9: temperature filled () and stream function () contours for r = 1.2 and ra =120. 1 1 2 2 3 3 ra0.2018 r-1.47 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 4 4 4.5 4.5 5 5 5.5 5.5 6 6 a ve ra ge n u nu (predicted) nu (correlated) fig. 10: the comparison between the predicted and correlated average nusselt number nu. 6. conclusions the numerical solution of natural convection in a porous medium bounded by two horizontal isothermal cylinders is obtained. the solution of five different radius ratios namely 1.2, 1,4, 1,6, 1.8 and 2.0 are presented. also, the present code is validated through the comparison of its results with those available in the literature. iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 52 for a small insulation thickness, the dominant heat transfer mode is the conduction regardless of ra. the useful maximum insulation thickness decrease as ra increases. from the data obtained, the average nusselt number is correlated with rayleigh number and radius ratio as:-nu = 1.82 ra0.2018 . r-1.4713 with 6.7 % sum of square errors. references: [1] c.y. liu, w. k. muller, and f. landis, “natural convection heat transfer in long horizontal cylindrical anuuli”, int. devl. heat transfer, vol. 5, pp. 976-984, 1961. [2] e. h. bishop, and c.t. carley, “photographic studies of natural convection between concentric cylin ders”, proc. of heat transfer & fluid mechanics institute, stanford univ., pp. 63-78, 1966. [3] u. grigull, and w. hauf, “natural convection in horizontal annuli,” proc. 3 rd int. heat transfer conf., vol. 2, 1966, pp. 182-195. [4] l.r. mack, and e.h. bishop, “natural convection between concentric cylinders for low rayleigh numbers,” quart. j. mech. appl. math., vol. 21, pp. 223-241, 1968. [5] t.h kuehn, and r.j. goldstien, “an experimental and theoritical study of natural convection in the annulus between concentric cylinders,” j. fluid mechanics, vol. 74, pp. 695-719, 1976. [6] l.s. yao, “analysis of heat transfer in slightly eccentric annuli,” asme j. of heat transfer, vol. 102, 1980, pp. 279-284. [7] j. prusa, and l.s. yao, “natural convection heat transfer between eccentric cylinders,” asme j. of heat transfer, vol. 105, 1983, pp. 108-116. [8] u. projahn, h. rieger, and h. bear “numerical convection between concentric and eccentric cylinders,” numerical heat transfer, vol. 4, pp. 131-146. [9] c.h. cho, k.s. chung, and k.h. park, “numerical simulation of natural convection in concentric and eccentric cylindrical annuli,” asme j. of heat transfer, vol. 104, 1982, pp. 624-630. [10] d.b. fant, a. rothmayer, and j. prusa, 1989, “natural convective flow instability between horizontal concentric cylinders”, numerical methods in laminar and turbulent flow, pineridge press, swansea, u.k., vol. 6, part 2, pp. 1047-1065. [11] a. cheddadi, j.p. caltagirone, and a. motjtabi, 1989, “an experimental and numerical study of natural convection in horizontal cylindrical annuli”, numerical methods in laminar and turbulent flow, pineridge press, swansea, u.k., vol. 6, part 2, pp. 1047-1065 [12] j.p. caltagirone, 1976, “thermo-convective instability in porous medium bounded by two concentric horizontal cylinders,” j. of fluid mechanics, vol. 76, pp. 337-362. [13] p.j. burns, and c.l. tien, “natural convection in porous media bounded by concentric spheres and horizontal cylinders,” int. j. of heat mass transfer, vol. 22, pp. 929-939. [14] r. echigo, s. hasegawa, s. tottori, h. shimonure, and y. okamoto, 1978, “an analysis on the radiation and free convective heat transfer in horizontal annulus with permeable insulators,” proc. 6 the international heat transfer conf., vol. 3, pp. 385-390. [15] h.h. bau, 1984, “low rayleigh number thermal convection in saturated porous medium bounded by two horizontal eccentric cylinders,” asme j. of heat transfer, vol. 106, 1984, pp. 166-175. iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 53 [16] y.f. rao, k. fukuda, and , s. hasegawa “steady and transient analysis of natural convection in a horizontal porous annulus with galerkin method,” asme j. of heat transfer, vol. 109, 1987, pp. 919-927. [17] j.p.b. mota, and f. sattdjian, “natural convection in porous horizontal cylindrical annulus,” asme j. of heat transfer, vol. 116, 1994, pp. 621-626. [18] j.p.b. mota, and f. sattdjian, “on the reduction of natural convection heat transfer in horizontal eccentric annuli containing saturated porous media,” int. j. num. methods heat fluid flow, 7 (4), pp. 401-416, 1997. [19] s. s. rao, the finite element methods in engineering, pergamon press, 1982. [20] d.w. pepper, and j.c. heinrich, the finite element methodbasic concepts and applications, hemisphere publishing corporation, 1992. [21] h.h. bau, “thermal convection in a horizontal, eccentric annulus containing a saturated porous mediuman extended purturbation expansion”, int. j. heat mass transfer, vol. 27, pp. 2277-2287, 1984. [22] g.n. facas, “natural convection from a buried pipe with external baffles”, numerical heat transfer, part a, 27:595-609, 1995. [23] g.n facas, and b. farouk, “transient and steady state natural convection in a porous medium between two concentric cylinders”, asme j. heat transfer, vol. 105, pp. 660663, 1983. nomenclature c specific heat of fluid at constant pressure da darcy number; 2ir/k da  g gravity acceleration g bounded domain h heat transfer coefficient ke effective thermal conductivity of the porous medium k permeability nu nusselt number n normal direction r radius ratio, ro/ri ri inner cylinder radius ro outer cylinder radius ra rayleigh number; fe 3 ioiffr f k/r)t(t c gra  t temperature u velocity component in x – direction v velocity component in y – direction x,y cartesian coordinates x,y dimensionless cartesian coordinates greeks  thermal diffusivity of the porous medium  thermal expansion coefficient of the fluid  circumferential angle  domain boundary iium engineering journal, vol. 6, no. 1, 2005 a. f. alfahaid et al. 54  dimensionless temperature; (t-to)/(ti-to)  dynamic viscosity  density of fluid  kinematic viscosity  stream function  dimensionless stream function; / subscripts e effective f fluid i. inner o outer r reference x,y cartesian components superscripts e element level i iteration number t transpose  average application of digital cellular radio for mobile location estimation iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 105 recovery of the biological active compounds of musa sp. through microwave assisted extraction farhan mohd said * and tan kai quan faculty of chemical and natural resources engineering, universiti malaysia pahang, lebuhraya tun razak, 26300 gambang, pahang, malaysia. *corresponding author: farhan@ump.edu.my (received: 20 th feb. 2017; accepted: 31 st oct. 2017; published on-line: 1 st dec. 2017) abstract: this study set out to investigate the recovery of the biological active compounds of musa sp. through microwave-assisted extraction (mae) system. the aim of this paper is to critically analyze the effects of temperature, microwave power, irradiation time, and solid to liquid ratio on antioxidant activity and phenolic compounds. the extraction was conducted on the unripe peel, unripe pulp, ripe peel, and ripe pulp of musa sp. the extraction process was carried out by utilizing distilled water as an extracting agent. the antioxidant activity and phenolic compounds for unripe and ripe musa sp were observed to be extracted best at 70 o c, microwave power range of 500 w – 800 w, and 90 s irradiation time at 3:60 solid to liquid ratio. overall, antioxidant and phenolic compounds were found to be significantly higher in the following order: unripe peel, ripe peel, unripe pulp, and ripe pulp. abstrak: kajian ini adalah untuk mengkaji kedapatan sebatian aktif biologi dari musa sp. mengguna sistem ekstrak mikrogelombang (mae). objektif kajian ini adalah untuk menganalisa dengan kritikal kesan suhu, kuasa gelombang mikro, tempoh sinaran gelombang dan nisbah pepejal kepada cecair terhadap aktiviti antioksida dan sebatian fenolik. pengekstrakan dilakukan pada kulit yang belum matang, pulpa yang belum matang, kulit masak dan pulpa masak musa sp. proses pengekstrakan dilakukan dengan menggunakan air suling sebagai agen pengekstrak. aktiviti antioksidan dan sebatian fenolik bagi musa sp. yang masak dan tidak masak adalah paling baik diekstrak pada suhu 70 o c, kuasa gelombang mikro antara 500 w – 800 w, tempoh iradiasi selama 90 saat pada nisbah 3:60 pepejal kepada cecair. keseluruhannya, sebatian antioksidan dan fenolik adalah lebih tinggi pada turutan berikut: kulit yang belum matang, kulit masak, pulpa yang belum matang dan pulpa masak. keywords: antioxidant; phenolic; microwave assisted extraction; musa sp.; toxicity free solvent 1. introduction generally, musa sp. is known as banana, and it is one of the most consumed worldwide fruits [1] and has also been classified as one of the antioxidative foods [2]. results showed that musa sp. pulp and peel contain various antioxidants such as vitamins, β-carotene as well as phenolic compounds such as catechin, epicatechin, lignin and tannins, including anthocyanins [3-5]. in addition, musa sp. is also remarkably rich with minerals such as potassium and phosphorus [4, 6]. the peels possess higher phenolic compounds and antioxidant properties [3, 7] along with mineral contents compared to musa sp. pulps. [8]. iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 106 antioxidants can be found either in plant materials or supplements (synthetic). there are zero side effects that have been reported on the use of natural antioxidants from plants, whereas synthetic antioxidants were found to have a genotoxic effect [9]. in addition, natural antioxidant agents have grabbed serious attention due to their ability to scavenge free radicals [10]. there is crucial interest on free radicals due to the development of a number of disorders, including cancer, neurodegeneration, and inflammation [11]. the presence of antioxidants such as phenolics and flavonoids in plants may provide protection against a number of diseases, in which the mortality from degenerative disorders has inversely led to the ingestion of natural antioxidants [12]. hence, its application on foods allows rancidity to be minimized as well as retard the formation of toxic oxidation products, which helps maintain the nutritional quality and increase food shelf life [13]. natural antioxidants are in high demand, especially to be applied in nutraceuticals, biopharmaceuticals, and food additive pertinent to consumer preferences. in recent years, apart from an antioxidant, phenolic compounds have also received much attention as a result of their potential ability and beneficial implications in human health [14]. several studies have identified the extraction of antioxidants and phenolic compounds. direct extraction using solvents is the most common technique employed to obtain extracts with high antioxidant activity. an extraction process is intended to achieve the maximum yield of substances and the highest quality of targeted compounds [15]. the solvent extraction has been widely used to extract bioactive components from the plants [16]. the standard solvents for extracting antioxidant include methanol, ethanol, and acetone, which are used either separately or in combination with an aqueous solution [5, 17-19]. for the past 10 to 15 years, the interest in mae has significantly increased in regards of their advantages which include its ability to reduce the extraction time, solvent volume, and improve extraction yield [20-23] in comparison to the traditional extraction techniques (e.g. soxhlet extraction and hot water extraction (hwe)). it is important to note that conventional extraction methods have been associated with high solvent requirements, longer extraction times and a higher risk of degradation of heat sensitive constituents. in addition, mae is a green technology and considered as a potential alternative to the conventional solid-liquid extraction of bioactive compounds from plant matrices [24]. furthermore, mae is a process that uses microwave energy and solvents to extract the targeted compounds from the matrices. microwave energy acts as a non-ionising radiation that causes rotation of the dipoles. the extremely high temperature at the restricted area of mae was found to cause selective migration of target compounds from material to the surroundings at a higher rapid rate. mae performs similar or better recoveries compared to the conventional extraction method. in mae, the solvent and sample are contained in sealed extraction vessels under controlled temperature and pressure conditions. the closed vessels allow the temperature of the solvent to increase above its boiling point, which then shortens the extraction time and subsequently increases extraction efficiency. the efficiency of mae depends on several variables which may not be suitable for all plant materials as a result of different nature of the existing bioactive phytochemicals [22, 25]. it has been observed that up to this date, there is no report on the use of a toxicity-free solvent in mae on the maturity pulp and peel of musa sp. therefore, the specific objective of the study was to determine the effect of mae method using distilled water as a toxicity free solvent in extracting antioxidant and phenolic compounds of ripe and unripe musa sp. pulp and peel. iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 107 2. materials and method 2.1 chemicals methanol, 2,2-diphenyl-1-picrylhydrazyl (dpph), gallic acid (ga), folin-ciocalteu reagent, sodium bicarbonate was obtained from sigma-aldrich. 2.2 sample material and preparation the musa sp. was obtained from a local supermarket at kuantan, pahang, malaysia. an approximate of 2 kg unripe (green) and ripe musa sp. (yellow) were washed and separated into pulps and peels, which was then sliced into a thickness of 2 mm. musa sp. sliced sample was dried overnight at 60 o c using an oven prior to the extraction [26]. meanwhile, fresh musa sp. sample was prepared freshly. 2.3 microwave-assisted extraction (mae) the extractions of antioxidant activity and total phenolic content were performed using mae (brand ethos e touch control, milestone corporation, monroe, ct). a total of 30 g fresh and dried pulp musa sp. was investigated at different extraction temperature (40 o c to 70 o c). other parameters such as microwave power, distilled water, and irradiation time were fixed at 800 w, 600 ml, and 60 s, respectively. a series of the experiment was conducted by manipulating other parameters which include microwave power (100 w to 800 w), irradiation time (30 s to 90 s), and solid to liquid ratio (1:60 to 3:60). the temperature was fixed at 70 o c. fresh musa sp. was examined during the experiment. on top of that, fresh musa sp. was divided into 4 types throughout the process, namely unripe peel, unripe pulp, ripe peel, and ripe pulp. all samples were performed in triplicate. 2.4 antioxidant activity using free radical (dpph) this method requires 0.2 nm solution of 2,2-diphenyl-1-picrylhydrazyl (dpph) in methanol to be prepared. next, 0.5 ml of the extract was added to 3 ml of methanol, followed by 0.3 ml of dpph added in methanol. the mixture was known as the sample extract. the blank sample contains 3.3 ml of methanol and 0.5 ml of extract, while control sample contains 3.5 ml of methanol and 0.3 ml of dpph in methanol. the mixture was shaken immediately and left standing at room temperature. this experiment was conducted in the dark. the mixture was then measured in a uv-vis of absorbance at 517 nm after 30 min [27]. the antioxidant activity was measured by taking into account the inhibition of free radical (%) as shown in eq. (1). samples were analyzed in triplicate and average values were calculated. %100 a aa (dpph)(%) radical free of inhibition o o    (1) ao refers to the absorbance of dpph solution without a sample, while a represents the absorbance of the test sample mixed with dpph solution. 2.5 total phenolics content determination the concentration of total phenolic compounds was determined using the folin– ciocalteu total phenol procedure with certain modifications as described by spanos and wrolstad [28]. gallic acid (ga) standard solutions were prepared at 0.0 to 0.5 mg/ml. the extracts (0.1 ml) and the ga standards (0.1 ml) were transferred into 15 ml test tubes. 3.0 ml of 0.2 n folin–ciocalteu reagent were added to each test tube and mixed using a vortex iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 108 mixer. after 1 minute, 2.0 ml of 9.0% (w/v) sodium carbonate (na2co3) in water were added and mixed. the absorbance at 765 nm was determined using a uv-vis spectrophotometer (hitachi u-1800) after being left for 2 h at room temperature [29]. all samples were determined in triplicate. total phenolic content (tpc) was expressed as mg ga per g fresh weight (fw) musa sp. 3. results and discussion 3.1 effect of fresh and dried pulp on the temperature of % scavenging activity the purpose of preliminary studies is to determine the antioxidant activity of fresh and dried pulp musa sp. at different temperatures. other parameters such as the ratio of solid to liquid, microwave power, and irradiation time were also fixed. the antioxidant activity was determined using methanol solution of dpph reagent. the result showed that freshly prepared dpph solution fades the deep purple color when antioxidant molecules extinguish dpph free radicals and change them into a colorless or bleached product, thus resulting the absorbance to be reduced at 517 nm band [30]. as can be seen in figure 1, the antioxidant activity is expressed in terms of percentage of inhibition of free radical (%). according to the same figure, both fresh and dried pulps show the highest antioxidant activity when the temperature is set at 70 o c. the antioxidant activity concentration shows major increment when the microwave temperature is increased from 40 o c to 70 o c. at 70 o c, the antioxidant activity of fresh pulp is 45% higher compared to the dried pulps represented by 58% and 40%, respectively. the dehydration of the samples caused a decrease of the antioxidant to about 50% on average. the difference of antioxidant activity might be caused by the process of drying performed on the dried pulp, which resulted in the breakdown of some of the antioxidant compound and denatured at high temperature (> 70 o c) or evaporated during the drying process. these results match those observed in earlier studies where antioxidants are heat sensitive, whereby prolong heat treatment may cause irreversible chemical changes to the antioxidant contents [31-33]. fig. 1: antioxidant activity of fresh and dried pulp musa sp at different temperatures. 3.2 effect of microwave power on antioxidant activity and total phenolic content the effect of microwave power was investigated on the antioxidant activity and total phenolic compounds of pulp and peel of ripe and unripe musa sp. results obtained for each element are illustrated in fig. 2 and fig. 3, respectively. generally, the power applied in mae was found to be significantly affecting the antioxidant activity of ripe and unripe musa sp., pulp and peel (fig. 2). as shown in fig. 2, the trend of antioxidant activities of ripe and unripe pulp and peel musa sp. is dissimilar. meanwhile, the antioxidant activity iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 109 observed on ripe pulp is significantly higher at 500 w with 82% inhibition of free radical. the result is different for 800 w and 100 w, where the inhibition of free radicals is 52.1% and 52.4%, respectively (fig. 2a). on the other hand, for the ripe peel, no significant difference of antioxidant activity is observed for both microwave power 500 w or 800 w (fig. 2a). fig. 2: antioxidant activity of ripe pulp and peel (a) and unripe pulp and peel (b) at a different microwave power of mae. temperature, irradiation time and solid to liquid ratio were fixed at 70 o c, 60 s and 3:60, respectively. on the other hand, the antioxidant activities were increased with the escalation of mae power from 100 w to 800 w, for both the unripe pulp and peel. according to the results, the extract obtained from the peel contains higher antioxidant activity compared to the pulp, especially for the unripe musa sp (fig. 2b). this result is consistent with fatemah et al. suggestion [34]. the increase of the microwave power of mae resulted in higher antioxidant activity, whereby the inhibition of free radical is 65% and 91% on unripe pulp and peel at 800 w, respectively (fig. 2b). the increased in the antioxidant activity was due to the increase of microwave power in mae. this may be associated with the direct effects of microwave energy on biomolecules through ionic conduction and dipole rotation. the microwave energy tends to cause the power to be dissipated inside the solvent and plant material, which later generates molecular movement and heating. as a result, the cell walls may be ruptured, which enhances the extraction of antioxidant activity [35-37]. in addition, more electromagnetic energy was transferred to the extraction system, which also improved the extraction efficiency when the microwave power is increased from 100 w to 800 w. however, this phenomenon was not the case for ripe musa sp. (fig. 2a) that obtained higher antioxidant on the pulp. this might be caused by other compounds other than phenolics and flavonoids that were also involved in inhibiting the dpph radicals. compounds such as ascorbic acid, β-carotene, α-carotene, and (a) (b) iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 110 different xanthophylls [7, 38] were detected in musa sp. and may influence the antioxidant activity of the extracts. fig. 3: total phenolic content of ripe pulp and peel (a) and unripe pulp and peel (b) at a different microwave power of mae. temperature, irradiation time and solid to liquid ratio were fixed at 70 o c, 60 s and 3:60, respectively. figure 3 shows the total phenolic content of ripe and unripe musa sp., pulp, and peel. microwave power of mae is observed to significantly affect the total phenolic content of ripe and unripe musa sp. moreover, a similar trend is observed for the ripe and unripe peel, whereby a higher total phenolic content is obtained at 500 w but no further increments are detected at 800 w, with 268 ± 13.4 mg ga/ 100 g fw and 389 ± 19.5 mg ga/ 100 g fw, respectively. by contrast, the total phenolic content of the pulp is found to be the highest at 800 w microwave power, for ripe and unripe (figure 3). the dissimilarity of the trend might be the result of the complexity of the pulp matrix structure, where in mae, the microwave power that contains irradiation energy enhances the penetration of the solvent into the pulp matrix. the electromagnetic field offers a rapid transfer of energy to the solvent and solid matrix through molecular interaction, thus allowing the components to be extracted [39]. unlike the peel, the total phenolic content can be extracted at low power (500 w), which is believed to be the result of the less complex structure of the peel. phenolic compounds are essential to fruit constituents because they exhibit antioxidant activity by inactivating lipid free radicals or preventing decomposition of hydroperoxides into free radicals [40]. the findings show that the total phenolic content in the extracts was inversely correlated with the antioxidant activity, especially for the unripe musa sp. (fig. 3b and fig. 2b), which further shows that the mae conditions that obtain high antioxidant activity are not selective for phenolic content. (a) (b) iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 111 3.3 effect of irradiation time on antioxidant activity and total phenolic content the yield of antioxidant activity and the total phenolic content were investigated on the pulp and peel of ripe and unripe musa sp. figures 4 and 5 demonstrate the antioxidant activity and the total phenolic content of pulp and peel of ripe and unripe musa sp., respectively. fig. 4: antioxidant activity of ripe pulp and peel (a) and unripe pulp and peel (b) at different extraction time of mae. temperature, microwave power and solid to liquid ratio were fixed at 70 o c, 800 w and 3:60, respectively. in general, the longer the extraction time; hence, the greater the recovery of the antioxidant activity. the ripe pulp is represented by the trend shown in fig. 4a. the antioxidant activity was high at a longer extraction time (90 s), where the inhibition of free radical was observed to increase from 32% to 88%, at 30 s to 90 s extraction time. however, prolonging the extraction time did not improve the antioxidant activity for an unripe peel (fig. 4b). this phenomenon might be the result of the breakdown of antioxidant compounds in the less complex matrix structure of unripe peel. longer extraction time coupled with higher microwave power might increase the temperature of the solvent, thus causing the cell wall of the peel to be ruptured [20]. in addition, longer exposure of the sample to the solvent and microwave irradiation may stimulate extraction of other components (such as polysaccharides and proteins) of the musa sp., which then relatively reduced the antioxidant activity in extracts [41-42]. as a result, extending the irradiation time with a higher microwave power may lead to thermal degradation of the phenols [29]. (a) (b) iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 112 fig. 5: total phenolic content of ripe pulp and peel (a) and unripe pulp and peel (b) at different extraction time of mae. temperature, microwave power and solid to liquid ratio were fixed at 70 o c, 800 w and 3:60, respectively. figure 5 shows the total phenolic content of ripe and unripe musa sp., pulp and peel at different extraction times. the figure reveals similar trend for ripe and unripe musa sp., where the total phenolic content increased with the increase of the extraction time. from the figure, phenolic content was found to be significantly higher in unripe musa sp. in contrast to ripe musa sp., where the total phenolic contents were 477 ± 23.9 mg ga/ 100 g fw and 247 ± 12.4 mg ga/ 100 g fw, respectively. this finding is in agreement with fatemah et al. (2012), where the total phenolic content was generally higher in the unripe than in ripe, whereas the peel contains higher total phenolic content than the pulp [34]. the variation in total phenolic content among different plant materials might be indicated by several factors such as natural chemical composition, maturity at harvest, soil state, and conditions of post-harvest storage [43]. 3.4 effect of solid to liquid ratio on antioxidant activity and total phenolic content another factor that significantly affected the amount of the antioxidant and total phenols is solid to liquid ratio. the effect of solid to liquid ratio in mae was identified based on the yield of antioxidant activity as well as the total phenolic content of pulp and peel of ripe and unripe musa sp. figures 6 and 7 show the antioxidant activity and the total phenolic content of pulp and peel of ripe and unripe musa sp., respectively. the solid to liquid ratio of 2:60 of ripe musa sp. resulted in higher antioxidant activity with the free radical inhibition of 82% when compared to the other ratios (ratio 1:60 and 3:60) (fig. 6a). hence, this further explains that the volume of solvent extraction was enough to swell the ripe musa at the solid to liquid ratio of 2:60, which caused the cell of (a) (b) iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 113 ripe musa to directly absorb the microwave energy. as a result, the cell was ruptured, and the antioxidant was consequently released to the surrounding [44]. in contrast, the antioxidant activity was increased with the increase of solid to liquid ratio in the unripe musa sp. (fig. 6b). fig. 6: antioxidant activity of ripe pulp and peel (a) and unripe pulp and peel (b) at different solid to liquid ratio in mae. temperature, irradiation time and microwave power were fixed at 70 o c, 60 s and 800 w, respectively. on the other hand, the total phenolic content of ripe and unripe musa sp. was significantly increased with the increase of solid to liquid ratio (fig. 7). the total phenolic content was increased from 200 ± 10 mg ga/ 100 g fw to 287 ± 14.4 mg ga/ 100 g fw, at solid to liquid ratio of 1:60 and 3:60 (unripe pulp), respectively. the experimental data suggested that the presence of an excessive amount of the solvent at the ratio of 1:60 (solid to liquid) may absorb more energy, and the material will reduce the microwave absorption. therefore, the outcome leads to less efficient extraction and lower phenolic content in the musa sp. extract [45]. therefore, it is very crucial to find the best solvent mixture ratio in order to get higher extraction yield. an optimised sample to liquid ratio could pinpoint the importance of extracting the target compounds or extracts. 4. conclusion the results of this study indicate that musa sp. has a great potential to be utilized as a natural antioxidant and phenolic compound sources. higher antioxidant and total phenolic content were obtained from the peel in comparison to the pulp of musa sp. the results also suggested that antioxidant and total phenolic content of musa sp. extracted using mae (a) (b) iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 114 fig. 7: total phenolic content of ripe pulp and peel (a) and unripe pulp and peel (b) at different solid to liquid ratio in mae. temperature, irradiation time and microwave power were fixed at 70 o c, 60 s and 800 w, respectively. with toxicity free solvent (distilled water) set in better extraction compared to the conventional extraction coupled with methanol as obtained by shaida et al. [26]. the total phenolic content in this study (similar species to shaida et al. [26]) was 87.3 mg ga/ 100 g fw, whereas the total phenolic content with methanol was found as 0.03 mg ga/ 100 g fw for ripe pulp. hence, this experiment demonstrated that musa sp. extracted using mae with solvent-free toxicity is a better extraction method for natural antioxidant and phenolic content. consequently, temperature, microwave power, irradiation time, and solid to liquid ratio play a huge role in affecting the efficiency of the mae. acknowledgement this work was funded by research grant granted by universiti malaysia pahang research grant no. rdu 150317. references [1] meechaona r, sengpracha w, banditpuritat j, kawaree r, phutdhawong w. (2007) fatty acid content and antioxidant activity of thai bananas. maejo intern. journ. sci. technol., 1:222-228. [2] kanazawa k, sakakibara h. (2000) high content of dopamine, a strong antioxidant in cavendish banana. journ. agricul. food chem., 48:844-848. [3] someya s, yoshiki y, okubo k. (2002) antioxidant compounds from bananas (musa cavendish). food chem., 79:351-354. (a) (b) iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 115 [4] wall mm. (2006) ascorbic acid, vitamin a, and mineral composition of banana (musa sp.) and papaya (carica papaya) cultivars grown in hawaii. journ. food composition and analysis, 19:434–445. [5] lim yy, lim tt, tee jj. (2007) antioxidant properties of several tropical fruits: a comparative study. food chem., 103:1003-1008. [6] hardisson a, rubio c, baez a, martin m, alvarez r, diaz e. (2001) mineral compositions of the banana (musa acuminata) from the island of tenerife. food chem., 73:153-161. [7] kondo s, kittikorn m, kanlayanarat s. (2005) preharvest antioxidant activities of tropical fruit and the effect of low temperature storage on antioxidants and jasmonates. postharvest biology and technol., 36:309-318. [8] emaga th, andrianaivo rh, wathelet b, paquot m. (2007) effects of the stage of maturation and varieties on the chemical composition of banana and plantain peels. food chem., 103:590-600. [9] chen c, pearson ma, gray ij. (1992) effects of synthetic antioxidants (bha, bht and pg) on the mutagenicity of iq-like compounds. food chem., 43:177-183. [10] saeed n, khan mr, shabbir m. (2012) antioxidant activity, total phenolic and total flavonoid contents of whole plant extracts torilis leptophylla l., bmc complement. altern. med., 12:221. [11] ferguson lr. (2010) chronic inflammation and mutagenesis. mutat. res. fund. mol., 690:3-11. [12] gulcin i. (2012) antioxidant activity of food constituents: an overview. arch. toxicol., 86:345-391. [13] jadhav sj, nimbalkar ss, kulkarni ad, madhavi dl. (1996) lipid oxidation in biological and food systems,” in: madhavi, d.l., deshpande, s.s., and salunkhe, d.k. (eds.), food antioxidants. dekker press, new york, pp. 5-63. [14] ross ja, kasum cm. (2002) dietary flavonoids: bioavailability, metabolic effects, and safety. annu. rev. nutr., 22:19-34. [15] spigno g, tramelli l, faveri dmd. (2007) effects of extraction time, temperature and solvent on concentration and antioxidant activity of grape marc phenolics. journ. food engin., 81:200-208. [16] musa kh, abdullah a, jusoh k, subramaniam v. (2011) antioxidant activity of pink-flesh guava (psidium guajava l.): effect of extraction techniques and solvents. food analytical methods, 4(1): 100-107. [17] alothman m, bhat r, karim aa. (2009) antioxidant capacity and phenolic content of selected tropical fruits from malaysia, extracted with different solvents. food chem., 115:785-788. [18] saravanan k, aradhya sm. (2011) polyphenols of pseudostem of different banana cultivars and their antioxidant activities. journ. agriculture and food chem., 59(8):3613-3623. [19] ma yq, chen jc, liu dh, ye xq. (2009) simultaneous extraction of phenolic compounds of citrus peel extracts: effect of ultrasound. ultrasonics sonochemistry, 16:57-62. [20] dhobi m, mandal v, hemalatha s. (2009) optimization of microwave assisted extraction of bioactive flavonolignan–silybinin. journ. chem. metrl., 3(1): 13–23. [21] salerno l, modica mn, pittala v, romeo g, siracusa ma, giacomo cd, sorrenti v, acquaviva r. (2014) antioxidant activity and phenolic content of microwave-assisted solanum melongena extracts. the sci. world journ., 2014(11): 1-6. [22] dahmoune f, nayak b, moussi k, remini h, madani k. (2015) optimization of microwave-assisted extraction of polyphenolsfrom myrtus communis l. leaves. food chem., 166:585-595. [23] routray w, orsat v. (2012) microwave-assisted extraction of flavonoids: a review. food bioprocess technol., 5:409-424. [24] li h, deng z, wu t, liu r, loewen s, tsao r. (2012) microwave-assisted extraction of phenolics with maximal antioxidant activities in tomatoes. food chem., 130:928–936. [25] bhuyan dj, vuong qv, chalmers ac, altena iav, bowyer mc, scarlett sj. (2015) microwave-assisted extraction of eucalyptus robusta leaf for the optimal yield of total phenolic compounds. ind. crops prod., 69:290-299. iium engineering journal, vol. 18, no. 2, 2017 mohd said and quan 116 [26] shaida fs, nor amy, ibrahim me, eng ms, azliana abs, supriatno, kheng lo. (2011) correlation between total phenolic and mineral contents with antioxidant activity of eight malaysian bananas (musa sp.). journ. food composition and analysis, 24:1-10. [27] junlong w, ji z, xiaofang w, baotang z, yiqian w, jian y. (2009) a comparison study on microwave-assisted extraction of artemisia sphaerocephala polysaccharides with conventional method: molecule structure and antioxidant activities evaluation. intern. journ. biological macromolecules, 45:483-492. [28] spanos ga, wrolstad re. (1990) influence of processing and storage on the phenolic composition of thompson seedless grape juice. journ. agricultural and food chem., 38:1565-1571. [29] ballard ts, mallikarjunan p, zhou k, o’keefe s. (2010) microwave-assisted extraction of phenolic antioxidant compounds from peanut skins. food chem., 120(4):1185-1192. [30] amarowicz r, pegg br, rahimi-moghaddam p, bar b, weil ja. (2003) free-radical scavenging capacity and antioxidant activity of selected plant species from the canadian prairies. food chem., 84:551-562. [31] lin tm, durance td, scaman ch. (1998) characterization of vacuum microwave, air and freeze dried carrot slices. food res. intern., 31(2):111-117. [32] meza eim, yanez ja, davies nm, rasco b, younce f, remsberg cm. (2008) improving nutritional value of dried blueberries (vaccinium corymbosum l.) combining microwavevacuum, hot-air drying and freeze drying technologies. intern. journ. of food engin., 4(6):16. [33] reblova z. (2012) effect of temperature on the antioxidant activity of phenolic acids. czech j. food sci., 30(2): 171-177. [34] fatemeh sr, saifullah r, abbas fma, azhar me. (2012) total phenolics, flavonoids and antioxidant activity of banana pulp and peel flours: influence of variety and stage of ripeness. intern. food res. journ., 19(3):1041-1046. [35] karabegovic it, stojicevic ss, velickovic dt, nikolic nc, lazic ml. (2013) optimization of microwave-assisted extraction and characterization of phenolic compounds in cherry laurel (prunus laurocerasus) leaves. sep. purif. technol., 120:429-436. [36] milutinovic m, radovanovic n, stojanovic mr, marinkovic ss, dimitrijevic s, brankovic sd. (2014) microwave-assisted extraction for the recovery of antioxidants from waste equisetum arvense. ind. crop. prod., 61:388-397. [37] pavlovic md, buntic av, marinkovic sss, brankovic sid. (2013) ethanol influenced fast microwave-assisted extraction for natural antioxidants obtaining from spent filter coffee. sep. purif. technol., 118:503-510. [38] subagio a, morita n, sawada s. (1996) carotenoids and their fatty-acid esters in banana peel,” journ. nutritional sci. and vitaminology, 42(6):553-566. [39] yan mm, liu w, fu yj, zu yg, chen cy, luo m. (2010) optimisation of the microwaveassisted extraction process for four main astragalosides in radix astragali. food chem., 119:1663-1670. [40] maisuthisakul p, suttajit m, pongsawatmanit r. (2007) assessment of phenolic content and free radical-scavenging capacity of some thai indigenous plants. food chem., 100:14091418. [41] nagarajaiah sb, prakash j. (2011) chemical composition and antioxidant potential of peels from three varieties of banana. as. j. food ag-ind., 4(1):31-46. [42] swamy gj, muthukumarappan k. (2017) optimization of continuous and intermittent microwave extraction of pectin from banana peels. food chemistry, 220:108-114. [43] huang d, ou b, prior rl. (2005) the chemistry behind antioxidant capacity assay,” journ. agricultural and food chem., 53: 1841-1856. [44] guo zk, jin qh, fan gq, duan yp, qin c, wen mj. (2001) microwave assisted extraction of effective constituents from a chinese herbal medicine. analytica chimica acta, 436:4147. [45] maran jp, sivakumar v, thirugnanasambandham k, sridhar r. (2013) optimization of microwave assisted extraction of pectin from orange peel. carbohydrate polym., 97:703709. 409 iium engineering journal, vol. 14, no. 2, 2013 tawfik et al. 133 disease detection from field spectrometer data o. h. tawfik 1 , h. z. mohd shafri 1 and a. a. mohammed 2 1 department of civil engineering, faculty of engineering, university putra malaysia upm, 43400 serdang, selangor, malaysia, 2 department of civil and structural engineering, faculty of engineering and built environment, national university of malaysia ukm, 43600 bangi, selangor darul ehsan, malaysia. aliukm@yahoo.com abstract: oil palm plants have been planted in a large scale of areas. however, ganoderma disease has been recognized and diagnosed in the oil palm plants that has infected almost a half of the oil palm plants in malaysia. to deal with this problem, the use of vegetation indices analysis on hyper spectral field data, this paper examines the ability of spectral data in identifying the stages of ganoderma disease. the favourable result will be helpful to control the spreading of the diseases. by using vegetation indices, the oil palm plants could be classified into three categories, namely: 1 (t1 healthy), 2 (t2 semi healthy) and 3 (t3 severe damage). the results show that the best vegetation index is the modified red edge simple ratio (msr705) among the vegetation indices to identify the oil palm health stages. moreover, it has been observed that the index of narrowband greenness vis has been exhibited an acceptable outcome in differentiating between the oil palm plant stage 1 (t1 healthy) and stage 2 (t2 semi healthy). abstrak: tanaman kelapa sawit ditanam secara meluas. penyakit ganoderma dikenali dan didiagnosikan menjangkiti hampir separuh tanaman kelapa sawit di malaysia. untuk mengawal penyakit ini daripada merebak, analisis indeks tanaman dijalankan ke atas data kawasan spektrum melampau di mana keupayaan data ini diuji dalam membezakan peringkat-peringkat penyakit ganoderma terhadap tanaman kelapa sawit. dengan menggunakan indeks tanaman, kelapa sawit dapat diklasifikasikan kepada 1 (t1 sihat), 2 (t2 separa sihat) dan 3 (t3 rosak); kelas tanaman dengan tepat. keputusan menunjukkan indeks tanaman terbaik sebagai modified red edge simple ratio (msr705) yang merupakan indeks tanaman dalam membezakan peringkat kesihatan kelapa sawit. adalah didapati pengubahsuaian terhadap indeks modified red edge simple ratio (msr705) yang juga indeks jalur sempit hijau vi telah memberikan keputusan yang munasabah dalam membezakan peringkat tanaman kelapa sawit peringkat 1 (t1 sihat) dan peringkat 2 (t2 separa sihat). keywords: oil palm; vegetation indices; spectrometer; msr; ganoderma. 1. introduction approximately, 70 percent of the earth’s land surface is covered with vegetation [1]. furthermore, vegetation provides a basic foundation for all living beings and it is one of the most important components of the ecosystem [1, 2]. dealing with disease problem in oil palm plantation involves a variety of curative measures in which disease detection and mapping play a central role. hyperspectral iium engineering journal, vol. 14, no. 2, 2013 tawfik et al. 134 remote sensing data offer a better chance of disease detection [3]. vegetation indices are widely used for the estimation of crop and vegetation variables by using visible and near infrared regions (nir) of the electromagnetic spectrum. healthy plant typically displays very low reflectance and transmittance in visible region and very high reflectance and transmittance in nir [3]. sixteen vegetation indices and four modifications were tested on hyper spectral field data. thus the presence of stresses in oil palm trees will be associated with the chlorophyll absorption in reflectance and the normalized pigment chlorophyll vegetation indexes which will be showing a loss of chlorophyll pigment compared to healthy oil palm plants [3]. basal stem rot in oil palm is caused by ganoderma boninense and it is the most severe fungal disease of oil palm in malaysia. it has the ability to infect oil palms from as young as 12-24 months [4] to over 24 years after field planting [5]. high incidences of this disease have been reported in oil palms planted on coastal soil and peat [6-8]. the incidence of ganoderma inland soils was relatively low and confined to waterlogged area [6]. ganoderma is a white rot fungus. the organism causes economic loss of oil palm (op) in various regions around the world including southeast asia [9], where the current author has had considerable experience of the crop disease. the basic premise of this review is that it is important for the control of ganoderma disease to consider it specifically as a white rot fungus. this can be integrated with other approaches [10, 11]. the term white-rot is derived from the fungus degrading specifically the lignin component of wood while leaving white cellulose exposed. typically the fungus may attack already weakened oil palm plants as ganoderma seldom seriously infects undamaged trees. a classic example is ganoderma adspersum, which causes [12]. 2. materials and methods the data that have been used in this study is taken by the apogee spectroradiometer (300 1000 nm) with spectral resolution of 0.5 nm. these data were offered from nursery managed by malaysian palm oil board (mpob), bangi on november 2007. the measurement taken from 1 healthy and 2 unhealthy oil palms leaves, and classified as t1 (healthy), t2 (light symptom) and t3 (severe symptom). each wavelength in the data has 24 samples. sixteen vegetation indices were applied for 24 samples at three stages to extract the results of vegetation indices to know if the results are within the green vegetation range or not and also to find out which index can exhibit the best way to differentiate between the oil palm disease stages. figure 1 shows the overall flow of the steps that had been implemented in this study [6, 8, 12]. 2.1 determine the best vegetation vegetation indices (vis) are combinations of surface reflectance at two or more wavelengths designed to highlight a particular property of vegetation [13, 14]. they are derived using the reflectance properties of vegetation described in plant foliage. each of the vis is designed to accentuate a particular vegetation property. sixteen equations were applied for 24 samples at three stages to extract the results of vegetation indices to know if the results are within the green vegetation range or not and also to find out generally, this study is comprised of two important parts. the first determined the best vegetation index iium engineering journal, vol. 14, no. 2, 2013 tawfik et al. 135 fig. 1: flowchart of methodology. and the second was modified the best vegetation index [15, 11, 16]. the matlab software package ver.6.5 was used to determine the results of the vegetation indices broadband greenness (4 indices) [12, 17, 14, 15]: ntr red ntr red p p ndv i p p − = + (1) ntr red p sr p = (2) iium engineering journal, vol. 14, no. 2, 2013 tawfik et al. 136 2.5 6 7.5 1 ntr red ntr red blub p p ev i p p  − =   + − +  (3) (2 ) (2 ) ntr red blub ntr red blub p p p a rv i p p p − − = + − (4) which index can exhibit the best way to differentiate between the oil palm disease stages. the indices are grouped into categories that calculate similar properties. the categories and indices are narrowband greenness (6 indices) [10, 16, 18]: 750 705 705 750 705r p p ndv i p p − = + (5) 750 460 705 705 460 p p msr p p − = + (6) 750 705 705 705 705 460 2 p p mndv i p p p − = + − (7) 740 720 1 p v og p = (8) 740 747 715 726 2 p p v og p p − = + (9) 734 747 715 720 3 p p v og p p − = + (10) light use efficiency (2 indices) [19-21]: 910 460 553 460 4 p p modification p p − = + (11) 800 460 800 680 p p sipi p p − = + (12) leaf pigments (4 indices) [22, 23]: 510 550 1 1 1cri p p     = −        (13) 510 100 1 1 2cri p p     = −        (14) iium engineering journal, vol. 14, no. 2, 2013 tawfik et al. 137 550 100 1 1 1a r i p p     = −        (15) 800 550 100 1 1 2ari p p p      = −           (16) the broadband greenness equations represent the surface reflectance in an image band with a center wavelength as follows: pnir = 800 nm, pred = 680 nm and pblue = 450 nm. 2.2 modified best vegetation index the best vegetation index can only differentiate between t1 (healthy plant) and t3 (severe damage) and cannot differentiate between t1 (healthy plant) and t2 (semi healthy). so to make this index able to differentiate between t1 (healthy plant) and t2 (semi healthy) a modification on this index is needed. using the default best index to differentiate between t1 (healthy plant) and t2 (semi healthy) is not detectable and it is difficult to specify the right stage for the plant. by randomly selecting a different wavelengths and substituting in the default best index, it can be shown that a four modified best indices can be obtained. these four indices can differentiate clearly between t1 (healthy plant) and t2 (semi healthy) that’s mean that simply we can distinguish between the plant stages. the four obtained modified best indices are [23]: 910 460 690 460 1 p p modification p p − = + (17) 738 460 554 460 2 p p modification p p − = + (18) 910 460 554 460 3 p p modification p p − = + (19) 910 460 553 460 4 p p modification p p − = + (20) 3. results and discussion the modified red edge simple ratio (msr705) index provides the best result than the other indices. the modified red edge simple ratio (msr705) index results and the average of each stage of this index are obtained for 24-samples. table 1 contains the obtained results of (msr705). figures 2, 3 and 4 show the (msr705) index range of each stage. figures 5 and 6 show the graphs of (msr705) range of the three stages with the 24-samples and their averages. the common range for green vegetation is 2 to 8. iium engineering journal, vol. 14, no. 2, 2013 tawfik et al. 138 table 1: results of (msr705) index for the 24 samples and their average at each stage. msr705 t1 t2 t3 1.9289 1.9542 1.6241 2.2812 2.1408 2.0042 1.8115 1.8775 2.1952 1.8115 1.9241 2.3484 1.8115 2.3953 2.132 2.333 2.3014 2.1979 1.9777 2.3463 1.7486 2.1524 2.0096 1.8433 1.964 2.0096 1.4375 1.8322 1.9871 1.9948 2.0387 2.0841 1.9395 2.4495 2.0074 2.1526 2.4867 2.1664 1.6989 2.0708 1.9931 1.611 1.8841 1.8922 1.6973 1.9262 2.0325 1.5515 2.3315 1.9102 1.5636 1.9963 1.9185 1.5636 1.9963 1.8371 1.8672 2.1426 2.1424 1.6576 2.1426 2.1137 1.5725 2.1426 1.9396 1.8166 2.1279 2.1267 1.7602 1.6596 1.772 1.6241 average average average 2.0541 2.0367 1.8168 fig. 2: the (msr705) index results of t1. in d e x r a n g e values of msr equation iium engineering journal, vol. 14, no. 2, 2013 fig. 3: the (msr fig. 4: the (msr fig. 5: the (msr705 in d e x r a n g e 0 0.5 1 1.5 2 2.5 3 1 3 5 in d e x r a n g e t1 healthy plant g journal, vol. 14, no. 2, 2013 139 fig. 3: the (msr705) index results of t2. fig. 4: the (msr705) index results of t3. 705) index results of 24 samples of t1, t2 and t3. values of msr equation 7 9 11 13 15 17 19 21 23 t1 healthy plant t2 semi healthy t3 severe damage tawfik et al. ) index results of 24 samples of t1, t2 and t3. iium engineering journal, vol. 14, no. 2, 2013 tawfik et al. 140 fig. 6: the average of 24 results of the (msr705) index of t1, t2 and t3. by using the jeffries-matusita (jm) distance method, it has been found that the msr705 index is the best index to differentiate between t1 (healthy plant) and t3 (severe damage), by providing the maximum distance 0.9900167 and the percentage 70.015 % between t1 and t3 shown in table 2. by using the jeffries-matusita (jm) distance method, it has been found that the modification 1 index is the best index to differentiate between t1 (healthy plant) and t2 (semi healthy), by providing the maximum distance and the highest percentage which was 70.715 % from among the four modification indices shown in table 3. table 2: the jeffries-matusita (jm) distance calculation for msr705. t1 t3 sun 49.2993 43.6022 average 2.0541375 1.816758333 avt1-avt3 0.237379167 sum(t1+t2) 92.9015 djm 0.990167233 % 70.015 table 3: the jeffries-matusita (jm) distance calculation of all modification indices. modification 1 modification 2 modification 3 modification 4 t1 t2 t1 t2 t1 t2 t1 t2 sum 123.2413 119.8307 123.0741 120.4596 121.9408 119.6175 124.6445 122.067 average 5.135054 4.992946 5.128088 5.01915 5.080867 4.984063 5.193521 5.086125 sum(t1+t2) 243.072 243.5337 241.5583 246.7115 avt1-avt2 0.142108 0.108938 0.096804 0.107396 djm 1.000069992 1.000040997 1.000032825 1.000038976 % 70.715 70.713 70.712 70.713 iium engineering journal, vol. 14, no. 2, 2013 fig. 7: the (vog1) index results of 24 samples of t1. fig. 8: the (vog1) index results of 24 samples of t2. fig. 9: the g journal, vol. 14, no. 2, 2013 141 fig. 7: the (vog1) index results of 24 samples of t1. fig. 8: the (vog1) index results of 24 samples of t2. fig. 9: the (vog1) index results of 24 samples of t3. tawfik et al. iium engineering journal, vol. 14, no. 2, 2013 tawfik et al. 142 4. conclusion according to the results it was realized that the modified red edge simple ratio (msr705) index of narrowband greenness vis has been exhibited an acceptable results as well as it can differentiate between the oil palm plant stage 1 (t1 healthy) and stage 3 (t3 severe damage) using the default equation index because of the healthy plant has a high amount of chlorophyll than severe damage plant. also the modification equation of modified red edge simple ratio (msr705) index of narrowband greenness vis was applied on stage 1 (t1 healthy) and stage 2 (t2 semi healthy) and exhibited an acceptable results as well as it can differentiate between them. references [1] apan, a., held, a. phinn, s. and markley, j.,: formulation and assessment of narrowband vegetation indices from eo-1 hyperion imagery for discriminating sugarcane disease. proceedings of the spatial sciences conference, sep. 22nd-27th, 2003, canberra. (2003):113. [2] jensen, j.r,. remote sensing of the environment: an earth resource perspective. prentice hall series in geographic information science, usa, chap.1 and 10,. (2000):1-28, 333-377. [3] kumar, l., schmidt, k., dury, s. and skidmor, a.,: imaging spectrometriy and vegetation science. in: imaging spectrometry: basic principles and prospective applications, van der meer, f.d. and de jong, s.m. (eds.), kluwer academic publishers, dordrecht.(2001): 11155. [4] shafri, h.z.m. and nasrulhapiza hamdan, hyperspectral imagery for mapping diseaseinfection in oil palm plantation using vegetation indices and red edge techniques. am. j. applied sci., ." american journal of applied sciences 6.6(2009): 1031-35. [5] singh, g. singh, gurmit, a. darus, and j. sukaimi. “ ganoderma-the scourge of oil palm in the coastal area.” in: ariffin, d. and s. jalani (eds.). proc. ganoderma workshop, 11 september 1990, palm oil research institute of malaysia, bangi, selangor, malaysia,. (1990): 7-35. proceedings of ganoderma workshop, bangi, selangor, malaysia, 11 september 1990.. palm oil research institute of malaysia, 1991. [6] thompson, a.,. stem-rot of the oil palm in malaya. bulletin straits settlement and fms., science series, 6:23. us government printing office, 1931. [7] laudien, r., bareth, g. and doluschitz, r., 2003: “analysis of hyperspectral field data for detection of sugar beet diseases. in: information technology for a better agri-food sector, environment and rural living.” proceedings 4th conference of the european federation for information technology in agriculture, food and environment, harnos, z., herdon, , m. and wiwczaroski, t.b. (eds.), debrecen, budapest, hungary, i (2003) 375-81. [8] blackburn ga. “hyperspectral remote sensing of plant pigments.” j exp bot, 2007, 58:844867.." journal of experimental botany 58.4 (2007): 844-67. [9] gitelson, a.a., m.n. merzlyak, and o.b. chivkunova, 2001. “optical properties and nondestructive estimation of anthocyanin content in plant leaves.” photochemistry and photobiology 71:38-45..74.1 (2001): 38-45. [10] kaufman, y.j. yoram j and d. didier tanre, 1996. “strategy for direct and indirect methods for correcting the aerosol effect on remote sensing: from avhrr to eosmodis.” remote sensing of environment 55:65-79. 55.1 (1996): 65-79. [11] kumar, l., schmidt, k., dury, s. and skidmor, a., 2001: “imaging spectrometriy andvegetation science. in: imaging spectrometry: basic principles and prospective applications. van der meer, f.d. and de jong, s.m. (eds.), kluwer academic publishers, dordrecht,, (2001) 111-155. [12] ariffin, d., a.s. idris, 2003. “progress and research on ganoderma basal stem rot of oil palm.” in: mohd basri, w., k. w. chan, d. mohd tayeb and s. sundram (eds.). proc. iium engineering journal, vol. 14, no. 2, 2013 tawfik et al. 143 “seminer on elevating national oil palm productivity and recent progress in the management of peat and ganoderma. bangi, selangor, malaysia, (2003): 167-205. [13] rouse, j.w., r.h. haas, j.a. schell, and d.w. deering, 1973. “monitoring vegetation systems in the great plains with erts.” third erts symposium, nasa sp-351 i: 309317. nasa special publication 351 (1974): 309. [14] sellers, p.j., 1985. “canopy reflectance, photosynthesis and transpiration.” international journal of remote sensing 6:1335-1372. 6.8 (1985): 1335-1372. [15] huete, a.r., h. liu, k. batchily, and w. van leeuwen, 1997. “a comparison of vegetation indices over a global set of tm images for eos-modis.” remote sensing of environment 59(3):440-451.59.3 (1997): 440-451. [16] sims, d a. and gamon (2002). “relationships between leaf pigment content and spectral reflectance across a wide range of species, leaf structures and development stages.” remote sensing of environment 81 (2-3): 337-354. 81.2 (2002): 337-54. [17] tucker, c.j., 1979. “red and photographic infrared linear combinations for monitoring vegetation.” remote sensing of the environment 8:127-150. 8.2 (1979): 127-50. [18] datt, b., 1999. “a new reflectance index for remote sensing of chlorophyll content in higher plants: tests using eucalyptus leaves.” journal of plant physiology 154 (1999):30-36. [19] vogelmann, j.e., b.n. rock, and d.m. moss, 1993. “red edge spectral measurements from sugar maple leaves.” international journal of remote sensing 14 (1993):1563-575. [20] gamon, j.a., j. penuelas, and c.b. field, 1992. “a narrow-waveband spectral index that tracks diurnal changes in photosynthetic efficiency.” remote sensing of environment 41(1992):35-44. [21] gitelson, a.a., gritz, y. and merzylak, m.n. (2003). “relationships between leaf chlorophyll content and spectral reflectance and algorithms for nondestructive chlorophyll assessment in higher plant leaves.” journal of plant physiology, 160(2003): 271–82. [22] penuelas, j., f. baret, and i. filella, 1995. “semi-empirical indices to assess carotenoids/chlorophyll-a ratio from leaf spectral reflectance.” photosynthetica 31(1995): 221-30. [23] gitelson, a.a., y. zur, o.b. chivkunova, and m.n. merzlyak, 2002. “assessing carotenoid content in plant leaves with reflectance spectroscopy.” photochemistry and photobiology 75 (2002):272-281. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 enhancement of mppt module for partial shading photovoltaic system under uniform irradiance conditions hameed ali mohammed1, rosmiwati mohd-mokhtar1* and hazem ibrahim ali2 1 school of electrical and electronic engineering, university sains malaysia, nibong tebal, pulau pinang, malaysia 2 control and systems engineering department, university of technology-iraq, baghdad, iraq * corresponding author: eerosmiwati@usm.my (received: 17 february 2023; accepted: 15 april 2023; published online: 4 july 2023) abstract: maximum power point tracking (mppt) algorithms play a critical role in maximizing the output power of solar panels. different mppt techniques are evaluated based on several criteria, such as tracking speed, simplicity, and accuracy with changes in solar irradiance and ambient temperature. under partial shading conditions (pscs), conventional techniques fail to track global maximum power points (gmpp). this paper aims to present an automatic and accurate method to fix the complexity of determining the accurate lookup table data in an automatic and fast process under uniform irradiance conditions (uics) and pscs. the proposed method runs the photovoltaic (pv) module with all potential irradiance and temperature. it automatically calculates the perfect voltage reference (vref) for all potential pv system cases. the vref is collected in an array, sent into a two-dimensional lookup table, and used for controlling the boost converter. simulation results verify the effectiveness of the proposed method. in addition, a comparison was also made with the conventional perturb and observe (p&o) method. under uics, the proposed method takes less time than the conventional p&o algorithm to reach the mpp. the time difference between them is ∆t = 0.133 sec and ∆t = 0.04 sec for the first scanning process at t = 0 sec and sudden change irradiance at t = 1.5 sec, respectively. as for pscs, the proposed method reached the gmpp during pattern 104 (first peak) without any power loss, while the p&o mppt was able to track the gmpp but with power losses of 2729.97 watts. abstrak: algoritma penjejakan titik kuasa maksimum (mppt) memainkan peranan penting dalam memaksimumkan kuasa keluaran panel solar. teknik mppt yang berbeza dinilai berdasarkan beberapa kriteria seperti kelajuan pengesanan, kesederhanaan, dan ketepatan dengan perubahan dalam sinaran suria dan suhu ambien. di bawah keadaan teduhan separa (psc), teknik konvensional gagal menjejak titik kuasa maksimum global (gmpp). kajian ini bertujuan bagi membentangkan kaedah automatik dan tepat bagi membetulkan kesusahan dalam menentukan carian data berjadual secara tepat, automatik dan pantas di bawah keadaan sinaran seragam (uic) dan psc. kaedah yang dicadangkan menjalankan modul fotovoltaik (pv) dengan semua potensi sinaran dan suhu dan mengira rujukan voltan sempurna (vref) secara automatik bagi semua kes yang berpotensi dalam sebarang jenis sistem pv. vref dikumpul dalam tata susunan, dihantar ke dalam jadual carian dua dimensi, dan digunakan bagi mengawal penukar rangsangan. keputusan simulasi mengesahkan keberkesanan kaedah yang dicadangkan. perbandingan juga dibuat dengan kaedah konvensional perhati dan ganggu (p&o). di bawah uic, kaedah yang dicadangkan mengambil masa yang lebih singkat berbanding algoritma konvensional p&o bagi mencapai mpp. perbezaan masa antara keduanya adalah masing-masing, ∆t = 117 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 0.133 saat dan ∆t = 0.04 saat bagi proses pengimbasan pertama iaitu pada t = 0 saat dan sinaran perubahan mendadak pada t = 1.5 saat. bagi psc, kaedah yang dicadangkan mencapai gmpp semasa corak 104 (puncak pertama) tanpa kehilangan kuasa manakala mppt p&o dapat mengesan gmpp tetapi dengan pengurangan kuasa sebanyak 2729.97 watt. keywords: photovoltaic; global maximum power point; maximum power point tracking; lookup table method; partial shading condition 1. introduction the mppt is a critical technique for getting maximum power from a pv panel system. the electrical energy is obtained directly from a group of connected pv cells. solar irradiance and ambient temperature conditions affect the amount of extracted power from the pv module. the mppt technique aims to dynamically obtain the maximum power by forcing the pv panel to work at an efficient voltage operating point (vmpp) [1,2]. the mppt technique can be classified into two methods, under uics and pscs. in the uics case, classical mppt techniques include constant perturb and observe (p&o), incremental conductance (inc), open-circuit voltage (ocv), short circuit current (scc), lookup table, and hill-climbing (hc) methods [3]. the nonlinearity of the p-v curve for the pv system means it only has one optimum operating point called the maximum power point (mpp). the location of this point on the p-v curve significantly depends on atmospheric conditions, such as irradiance and ambient temperature. during pscs, the p-v curve will have several local maximum power points (lmpps) and only one global maximum power point (gmpp) [4,5]. the aforementioned techniques are sometimes combined with other methods to find the gmpp. conventional mppt techniques suffer from three major drawbacks; 1) rapid oscillations around the mpp even at the steady-state response, 2) the inability to effectively track during sudden changes in irradiance, and 3) the inability to identify the gmpp during pscs because they may be busy in one of the lmpps. this situation creates a complicated process to find the system’s gmpp [6,7]. research has been done in the literature to overcome the drawbacks of conventional mppt techniques. a two-phased tracking method was presented to improve the tracking behavior of the conventional incremental conductance mppt [8]. the method improved the performance of the conventional inc mppt, but it was still unable to track the gmpp during pscs. research by basoglu used the concept of the ocv method to first estimate the locations of gmpp by assuming that the maximum power point was located at 0.85 and 0.8 of opencircuit voltage, respectively [9]. then, the p&o mppt algorithm was used to track the maximum point. the method has a good tracking performance, but it is ineffective when the peaks are not always in ascending order toward the gmpp. an optimization method called artificial bee colony (abc) was presented in [10]. the drawbacks of this algorithm are slow tracking, and even though the technique can track under pscs with high tracking speed, the efficiency declines when the shading patterns are changed immediately. also, the general drawbacks of the method were the implementation complexity, and the high financial cost. the method presented in [11] estimated the mpp by calculating the i-v curve’s maximum power point voltage (vmpp). regrettably, the method resulted in lower output power than the p&o technique. also, the method was unable to find the gmpp under pscs. in [12], adaptive neuro-fuzzy inference system (anfis) mppt techniques were trained for the non-linear characteristic of the pv system. these algorithms had a high 118 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 accuracy under rapid changes in irradiance conditions. however, they had a high complexity in selecting the output target data and could not be implemented quickly. authors in [13] and [14] used the lookup table technique and compared it with p&o mppt. this technique’s problem was the complexity of calculating the lookup table data, especially under pscs. moreover, the lookup table data must be increased to get highly accurate tracking and cover all operating points, thus increasing the calculation difficulties. to solve the complexity problem, the authors in [15] and [16] combined p&o mppt and lookup table mppt. the method recorded the irradiance and duty cycle values from the p&o mppt and sent the data into a table to use the next time. the method could not enhance the performance of p&o mppt because it used the same duty cycle used in the p&o method, which limited this method with the p&o algorithm limitation. for designing lookup table systems, the researchers faced a big problem with determining the table data accurately. the design process needed a large amount of accurate data to ensure accurate results. moreover, mppt based on the lookup table method was inefficient under pscs. this paper proposes an automatic and accurate method to solve the problem of the calculation complexity associated with the lookup table method and makes it capable of tracking the gmpp and working efficiently under pscs. this method can calculate and track the mpp for any pv system under uics and pscs and builds a complete data array that contains pmpp and corresponding voltage vmpp for all potential cases in just a few minutes. 2. solar array mathematical model the single-diode pv array equivalent circuit is shown in fig. 1. the current source (iph) represents the cell photocurrent connected in parallel with a diode. ns is the number of series cells, np is the number of parallel cells, rsh and rs are the shunt and series resistances of the cell, respectively [15,16]. the current source (iph) is described by [17] 𝐼𝑝ℎ = 𝐼𝑠𝑐 + 𝐾𝑖 (𝑇 − 298) ∙ 𝐺 1000⁄ (1) fig. 1: equivalent circuit of solar array [17]. where isc is the short-circuit current (a), ki is the short-circuit current of the cell at 25 °c and 1000 w/m2, t is the operating temperature (k), and g is the solar irradiation (w/m2). the reverse saturation current (irs) is 𝐼𝑟𝑠 = 𝐼𝑠𝑐 [𝑒𝑥𝑝(𝑞 ∙ 𝑉𝑂𝐶 𝑁𝑆 ∙ 𝑘 ∙ 𝑛 ∙ 𝑇⁄ ) − 1]⁄ (2) 119 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 where q is the electron charge (1.6 × 10−19), voc is the open-circuit voltage (v), n is the ideality factor of the diode, and k is the boltzmann’s constant (1.3805×10−23 j/k). the saturation current (i0) is given by 𝐼0 = 𝐼𝑟𝑠(𝑇 𝑇𝑟⁄ ) 3𝑒𝑥𝑝[(𝑞 ∙ 𝐸𝑔0 𝑛 ∙ 𝑘⁄ )(1 𝑇𝑟 − 1 𝑇⁄⁄ )] (3) where tr is the nominal temperature (298 k), eg0 is the bandgap energy of the semiconductor (1.1 ev). the pv module output current (i) is [15] 𝐼 = 𝐼𝑝ℎ 𝑁𝑃 − 𝐼0𝑁𝑆 [𝑒𝑥𝑝 (((𝑉 𝑁⁄ )𝑠 + (𝐼 ∙ 𝑅𝑆 𝑁𝑃⁄ ) 𝑛 ∙ 𝑣𝑡⁄ )) − 1] − 𝐼𝑠ℎ (4) with 𝑣𝑡 = 𝑘 ∙ 𝑇 𝑞⁄ (5) 𝐼𝑠ℎ = (𝑉(𝑁𝑃 𝑁𝑆⁄ ) + 𝐼 ∙ 𝑅𝑠) 𝑅𝑠ℎ⁄ (6) where vt is the diode thermal voltage (v), and ish is the current through the shunt resistance. this paper uses era solar espmc-215 pv model as a reference module. the pv model parameters are given in table 1. table 1: parameters of espmc-215 pv module name symbol value maximum power pmpp 213.15 w voltage at the maximum power point vmpp 29.00 v current at the maximum power point impp 7.350 a open circuit voltage voc 36.30 v short circuit current isc 7.840 a number of cells connected in series ns 10 number of cells connected in parallel np 40 3. proposed method the p&o mppt algorithm is the most well-known technique because of its ease of design and implementation. from the flowchart shown in fig. 2, notice that the p&o mppt determinations compare the change in pv power, ∆p, and change in pv voltage, ∆v, for two points, k and k-1, on a p-v curve to identify the maximum power point. the main disadvantages of this technique are inability to deal with rapid weather changes, high oscillations around the mpp, the slow response, and failure to track gmpp under psc [18], [19]. to avoid the disadvantages of the p&o mppt method and solve the complexity problem associated with the lookup table method and make it work efficiently under pscs, an automatic and accurate method is proposed in this paper. in the first step, the method starts to ask the user to enter the specifications of the solar array, the maximum and minimum limits of solar radiation (gmax and gmin), and the maximum and minimum limits of the ambient temperature (tmax and tmin) respectively, as well as the number of connected cells in series (ns) and parallel (np). the flowchart in fig. 3 shows the whole tracking process of the proposed method. 120 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 then, it runs the pv module and measures the pv voltage (vpv) and current (ipv) and calculates the pv power (ppv). from the vpv and ppv that have been calculated, it generates the pv curves for all operating point cases (for all potential irradiance and temperatures). it calculates the mpp for each operating point case. after calculating mpps, it automatically calculates the corresponding voltage for every mpp without manual calculation and considers it a reference voltage (vref). after finishing all offline testing cases, it collects all the calculated reference voltages in an array and sends them with input vectors (irradiance and temperature) into a lookup table. the lookup table makes the vref array more flexible because it uses this array to map input values to output values, allowing the system to estimate the missing data. the system has been divided into three groups of pv modules connected in series to simulate the pscs. group 1 is set as no shading pv array, while groups 2 and 3 are shading pv arrays with 20 shading patterns for each. the details are explained in the next section. fig. 2: flowchart of p&o algorithm. the proposed method is evaluated for 400 patterns (20x20) and calculates the gmpp for each pattern. it calculates the mpp irrespective of the number of peaks on the pv curve, which allows this method to work effectively under pscs. this capability is considered one of the most vital points of the proposed method. in this paper, a boost converter is designed and used as a power driver between the pv array and the load to adjust the solar module voltage to extract the maximum power from the pv array at the converter input side. the system uses the vref generated from the proposed mppt method and compares it with the actual vpv to generate an error signal. the proportional integral (pi) controller has been designed to manage the error signal and generate the duty ratio to control the boost converter. on the other hand, the parameters of the boost converter, as given in table 2, have been calculated carefully to achieve minimum fluctuation around the mpp. figure 4 shows the overall system, pv array, mpp method, boost converter, and pi controller. 121 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 table 2: parameters of a boost converter name symbol value input capacitor cin 3227 µf inductor l 1.45 mh output capacitor cout 1000 µf output resistance rout 20 ω fig. 3: the flowchart of the proposed algorithm. fig. 4: the overall system with pi controller. 122 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 3.1 pv system modeling under uics and pscs under uics, the proposed method tests 400 patterns; 20 for changing solar irradiance (from 50 to 1000 w/m2 by step change of 50 w/m2) x 20 for changing cell temperature (from 5 to 55 °c by step change of 5 °c). it runs the pv module for each pattern, measures the (vpv, ipv, and ppv) and generates the pv curve for all these patterns, as shown in fig. 5. this method obtained the mpp for each pattern from the pv curves generated during the previous step, then calculates the corresponding reference voltage and sends it into an array. figure 6 shows a 3-dimensional view of the array data, which contains a different irradiance, g and temperature, t as an input vector, and reference voltage (vref) as the output array. fig. 5: the p-v curves for changing solar irradiance (50 to 1000 w/m2) and temperature (5 to 55 °c). fig. 6: the 3-dimensional view for irradiance (g), temperature (t), and reference voltage (vref) under uics. fig. 7: partially shaded pv array (a) three pv partial shading groups connected in series, (b) different shading patterns for two pv arrays. under pscs, a pv module is shaded if three or more cells receive lower than the normal irradiance level [8,20]. figure 7(a) shows the three groups of the pv module connected in series with 20 levels of different shading conditions for groups 2 and 3. under the partial 123 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 shading test, group 1 is set as no shading pv array with 160 modules ((4–series) x (40parallel)) and groups 2 and 3 are shading pv arrays with 120 modules ((3–series) x (40parallel)) for each. figure 7(b) shows the different shading patterns (irradiance changed from 1000 to 50 w/m2 for group 2 and group 3). the proposed algorithm was evaluated on 400 patterns (20x20), and the global maximum power point was calculated for each. the p–v curves test obtained using the proposed method for a pv array with 400 modules (10×40) at a different shading pattern (one normal group and two shaded groups) is shown in fig. 8. these curves are used to calculate the gmpp. from fig. 8, notice that each pv-curve has one gmpp and one or more lmpp. it can also be seen that the only case in which the p-v curves contain one mpp is when all groups (groups 1, 2, and 3) receive the same amount of irradiance. from the obtained mpp, the proposed method calculates the voltage corresponding to the mpp for each pattern and considers it as a reference voltage (vref). to evaluate the system, we assumed that the system works under three different patterns; 1) pattern 104 (g1=1000, g2=100 and g3=300 w/m2), 2) pattern 302 (g1=1000, g2=100 and g3=800 w/m2) and 3) pattern 320 (g1=1000, g2=1000, and g3=800 w/m2) where g1, g2, and g3 are the amount of solar radiation falling on the groups (1, 2, and 3), respectively. these three patterns were chosen because each one gives a gmpp in a different location from the others. fig. 9 shows a 3-dimensional view of different shading conditions for groups 2 and 3, irradiance, and reference voltage for the pscs test. fig. 8: pv curves testing of patterns 1 to 400 under pscs. fig. 9: the 3-dimensional view for irradiance and reference voltage under pscs. 4. results and discussion simulation analysis was conducted using matlab / simulink and m-file code to verify the efficacy of the proposed method. this section analyses the proposed method’s performance under uniform irradiance and partial shading conditions. 124 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 4.1 uniform irradiance sudden change figure 10 compares the dynamic response of the pv array output power (ppv) based on the proposed and p&o methods under five-scenario uniform irradiance sudden changes (step increase on the left side and step decrease on the right side). then, a comparison is made with the calculated mpps as a reference signal calculated directly from the p-v curves. fig. 10 shows that each mppt technique (proposed and p&o) tracked the mpp for each step change. however, the proposed method reached the mpp with a faster speed response, greater accuracy, and lower steady-state fluctuations around the mpp compared with p&o mppt at the same sudden changes in irradiance. the simulation results shown in fig. 10 prove that the proposed method’s effectiveness has been superior to the conventional p&o mppt algorithm in terms of accuracy, tracking speed, and the fluctuations around the mpp. the reason is that it directly determines the optimum value of vref, taking it from the lookup table, which makes the proposed method very fast and accurate in reaching the mpp without a need to scan the voltage range on the p-v curve. also, selecting one value of the vref caused the elimination of all fluctuations around the mpp. fig. 10: comparison of the output power of p&o and proposed mppt techniques with the reference signal under sudden changes of irradiation. figure 11 shows the zoomed view of the output power during the first scanning process (t = 0 to 0.15 sec) and the sudden change in irradiance at t = 1.5 sec. from fig. 11(a) and (b), the proposed method takes less time to reach the mpp than the conventional p&o algorithm. the time difference between them is ∆t = 0.133 sec and ∆t = 0.04 sec for the first scanning process at t = 0 sec and sudden change irradiance at t = 1.5 sec, respectively. this problem can be solved for the p&o algorithm by increasing the vref step size (∆vref). unfortunately, that would cause another problem, a more significant fluctuation around the mpp. as shown in fig. 11, the proposed method reached the mpp with no power loss, while the p&o mppt causes power losses (∆p ≈ 51800 51000 = 800 watts) and (∆p ≈ 71817 68070 = 3737 watts) for (a) and (b), respectively. as mentioned before, the proposed method does not need a scanning process, making it very fast to reach the mpp. in the first scanning process shown in fig. 11(a), the conventional p&o mppt algorithm took a very long time to reach the mpp because it depends on the initial vref (in this case, vref initial equal to 250 volts), while the vmpp equal to 293 volts at 600 w/m2. another problem is that the p&o mppt has very high fluctuations around the mpp compared to the proposed method, which has no fluctuations around the mpp. the fluctuations problem can be solved by decreasing the ∆vref. however, decreasing the ∆vref would slow down the output response. also, it is evident from fig. 11(b) that the maximum overshot due to sudden change in irradiance is very small in the output power based on the proposed method. at the same time, it is higher for the conventional p&o 125 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 mppt algorithm. the fluctuation and slow-down situations associated with the conventional algorithms cause additional power losses in the pv systems. these problems cannot be solved because both situations are related, so one needs to find an acceptable case between them. fig. 11: zoomed view of fig. 10(a) due to the first scanning process (at t = 0 to 0.15 sec), (b) due to the sudden irradiance changes at (t = 1.5 sec). 4.2 load changes this analysis is meant to verify the proposed method under hard conditions. the output resistance (rout) of the boost converter is changed from 5 ω to 20 ω at (t = 0.3 sec) and then returned to 5 ω at (t = 0.6 sec) as shown in fig. 12. it can be seen from fig. 12 that the proposed method is superior by maintaining the dynamic response without fluctuations after the rout has been changed. further, when the load resistance disturbance occurred at t = 0.3 sec, the power losses reached approximately (∆𝑃 ≈ 85180 – 82600 = 2580 watts) using the conventional p&o mptt algorithm compared to the proposed method. at the same time, the p&o mppt generates high fluctuations around the mpp at the steady-state response. also, when the rout return to 5 ω at t = 0.6 sec, the p&o mppt takes about 0.11 sec to reduce the fluctuations and return the dynamic response to the first situation with power losses (∆p ≈ 85180 – 84200 = 980 watts). the reason p&o mppt was affected by changing the rout is that the input resistance has been affected, which caused offsetting of the position of the operating point on the pv curve. fig. 12: comparison of the output power of p&o and proposed mppt techniques under load changes. 126 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 4.3 partial shading conditions this analysis aims to verify the proposed method’s ability to track gmpp under psc. three shading patterns have been generated where three pv module groups have been connected in series to simulate the partial shading conditions. the three patterns have three different shapes based on the location of the gmpp on the p-v curve, where each one has one gmpp. the gmpp for pattern 104 (point a) is located at the first peak, making it easy to track if the voltage range scan starts from zero, while for pattern 302 and pattern 320, the gmpps are located at the second (point b) and third (point c) peak, respectively, which needs a unique tracking technique. figure 13 shows the three different partial shading p–v curves for 1) pattern 104 (g1=1000, g2=100 and g3=300 w/m2), 2) pattern 302 (g1=1000, g2=100 and g3=800 w/m2) and 3) pattern 320 (g1=1000, g2=1000 and g3=800 w/m2). it is observed that each p-v curve has 3 peaks, and the mppt algorithm needs to scan all these peaks to decide which one represents the gmpp. figure 13 shows the p-v curves of the sudden change scenario, assuming that a series of partial shading had just happened, which shifts the operating points from pattern 104 to pattern 302 to pattern 320 under pscs at t = 1 and 1.5 sec, respectively. when partial shading scenarios occur, the p-v curves give multi lmps and single gmpp for each pattern, where the goal here is to track the gmpp, which is point (a, b and c) in the shortest possible time. fig. 13: three different partial shading p–v curves for patterns 104, 302 and 320. figure 14 shows the pv output power response of the proposed method compared with the conventional p&o mppt algorithm under pscs, where the scenarios shown in fig. 13 have been used. as seen in fig. 14, both proposed, and conventional p&o mppt has reached the gmpp at the first pattern (point a) at the first zone on the p-v curve. the p&o mppt algorithm reached the gmpp because it is located in the first zone, making it easy to track based on the initial scanning voltage, which has been set in zone one. even though the conventional mppt algorithm tracked the gmpp, it took more time with very high fluctuations, while the proposed method reached the gmpp faster with fewer fluctuations around the gmpp (∆𝑡 ≈ 8 msec). at t = 1 sec, the operational point jumped from pattern 104 to pattern 302, which means that the gmpp has been moved to zone two on the p-v curve, point b. at this operational point, the conventional p&o mppt algorithm could not track the gmpp because it is located on the second peak on the pv curve, while the start scanning point located within peak one depends on the first gmpp (point a). the conventional p&o mppt algorithm will remain stuck in zone one when the scanning point crosses point a. the p&o mppt algorithm would return due to low power indication. at this period, the p&o mppt algorithm failed to track the gmpp, while the proposed method tracked the gmpp 127 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 accurately as fast as possible. the same process occurred when the operational point jumped to pattern 320. fig. 14: comparison of the output power of p&o and proposed mppt techniques with the reference signal under pscs with three different patterns. in contrast, the proposed method reached the gmpps of all three patterns in the shortest time without any fluctuations around the gmpp. the conventional mppt algorithms fail to track the gmpps under pscs because they cannot jump from one zone to another on the pv curve. at the same time, the proposed method was not affected by changing the operational point, which gives enough flexibility to move on the p-v curve. figure 15 shows the zoomed view of fig. 14 for the three different patterns during the time intervals (0.1 to 0.16 sec), (1.1 to 1.25 sec), and (1.75 to 1.85 sec) for patterns 104, 302, and 320, respectively. it shows how the proposed method and the p&o mppt algorithm tracked the gmpp when partial shading occurs. as shown in fig. 15(a), the proposed method reached the gmpp during pattern 104 without any power loss, compared to the reference power signal, while the p&o mppt tracked the gmpp but with power losses (∆p = 33475.42 30745.45 = 2729.97 watts). also, the fluctuation around the gmpp is very high compared to the proposed method. the p&o mppt algorithm can track the gmpp at this period because gmpp is located within the first peak. in the patterns 302 and 320 shown in fig. 15(b) and fig. 15(c), respectively, the p&o mppt failed to track the gmpps (50765.41 and 74069.11 watts) and instead tracked the first lmpp = 33493 watts for patterns 302 and second lmpp = 61499 watts for patterns 320, and missed tracking the gmpp because it did not locate in the second peak (pattern 302), or third peak (pattern 320). the overall simulation results substantiate that the proposed method’s effectiveness has been superior to the conventional p&o mppt algorithm in terms of accuracy, tracking speed, fluctuations around the mpp, and tracking the gmpp under pscs. fig. 15: zoomed view of fig. 14 (a) due to pattern 104, (b) due to pattern 302, (c) due to pattern 320. 128 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 5. conclusion this paper proposed an automatic and accurate method for tracking the mpp for any pv system under uics and pscs. it has fixed the complexity of determining the accurate lookup table data in an automatic and fast process under uics and pscs. the proposed method has been running the pv module with all potential irradiance and ambient temperatures to get the pv curve and then calculating the corresponding vmpp automatically for each case. then, the calculated array voltage was set as the pv array reference operating voltage [vref]. five scenarios of sudden irradiance changes under uics and three-pattern scenarios under pscs were done to verify the proposed method. compared with the conventional p&o mppt technique, the proposed method harvests higher power from the pv system because it has a fast-tracking response, robust stability, and fewer fluctuations around the mpp. from the study, the lookup table data generated automatically using the proposed method worked ideally compared to conventional data collection methods. this method gives the lookup table control system the ability to track the gmpp under pscs, which solves the weakness point associated with this kind of control system. a future recommendation to validate this method under all potential challenges is to test it with more extended string pv modules. this method will be the subsequent research investigation to be considered. acknowledgment this research work is supported by the ministry of higher education malaysia for fundamental research grant scheme with project code: frgs/1/2019/tk04/usm/02/12. references [1] heelan my, al-qrimli fam. (2020) design and simulation of neuro-fuzzy-based mppt controller for pv power system. proceedings of the int. conf. on electrical, communication, and computer engineering (icecce 2020), 12-13 june 2020, istanbul, turkey, pp. 1-6. doi: 10.1109/icecce49384.2020.9179287. [2] zhang x, gamage d, wang b, ukil a. (2021) hybrid maximum power point tracking method based on iterative learning control and perturb & observe method. ieee trans. on sustainable energy, 12(1): 659-670. doi: 10.1109/tste.2020.3015255. [3] ostadrahimi a, mahmoud y. (2021) novel spline-mppt technique for photovoltaic systems under uniform irradiance and partial shading conditions. ieee trans. on sustainable energy, 12(1): 524-532. doi: 10.1109/tste.2020.3009054. [4] xu s, gao y, zhou g, mao g. (2021) a global maximum power point tracking algorithm for photovoltaic systems under partially shaded conditions using modified maximum power trapezium method. ieee trans. on industrial electronics, 68(1): 370-380. doi: 10.1109/tie.2020.2965498. [5] kumar n, hussain i, singh b, panigrahi bk. (2018) framework of maximum power extraction from solar pv panel using self-predictive perturb and observe algorithm. ieee trans. on sustainable energy, 9(2): 895-903. doi: 10.1109/tste.2017.2764266. [6] bhattacharyya s, kumar dsp, samanta s, mishra s. (2021) steady output and fast tracking mppt (soft-mppt) for p&o and inc algorithms. ieee trans. on sustainable energy, 12(1): 293-302. doi: 10.1109/tste.2020.2991768. [7] ahmed rm, zakzouk ne, abdelkader mi, abdelsalam ak. (2021) modified partial-shadingtolerant multi-input-single-output photovoltaic string converter. ieee access, 9: 3066330676. doi: 10.1109/access.2021.3058695. [8] hsieh g, hsieh h, tsai c, wang c. (2013) photovoltaic power-increment-aided incremental conductance mppt with two-phased tracking. ieee trans. on power electronics, 28(6): 2895-2911. doi: 10.1109/tpel.2012.2227279. 129 iium engineering journal, vol. 24, no. 2, 2023 mohammed et al. https://doi.org/10.31436/iiumej.v24i2.2752 [9] basoglu me. (2019) module level global maximum power point tracking strategy. proceedings of the 2019 4th int. conf. on power electronics and their applications (icpea), 25-27 sept 2019, elazig, turkey, pp. 1-5. doi: 10.1109/icpea1.2019.8911173. [10] gonzalez-castano, restrepo c, kouro s, rodriguez j. (2021) mppt algorithm based on artificial bee colony for pv system. ieee access, 9: 43121-43133. doi: 10.1109/access.2021.3066281. [11] zadeh mjz, fathi sh. (2017) a new approach for photovoltaic arrays modeling and maximum power point estimation in real operating conditions. ieee trans. on industrial electronics, 64(12): 9334-9343. doi: 10.1109/tie.2017.2711571. [12] reddy d, ramasamy s. (2019) an artificial intelligent mppt controller based three level sepic topology for 1.2kw solar pv system. proceedings of the 2019 innovations in power and advanced computing technology (i-pact), 22-23 mar 2019, vellore, india, pp. 1-6. doi: 10.1109/i-pact44901.2019.8960135. [13] chandran a, mathew bk. (2020) comparative analysis of p&o and fuzzy logic controller based mppt in a solar cell. proceedings of the 2020 third int. conf. on smart systems and inventive technology (icssit), 20-22 aug 2020, tirunelveli, india, pp. 622-626. doi: 10.1109/icssit48917.2020.9214187. [14] udayalakshmi jk, sheik ms. (2018) comparative study of perturb & observe and lookup table maximum power point tracking techniques using matlab/simulink. proceedings of the 2018 int. conf. on current trends towards converging technologies (icctct), 1-3 mar 2018, coimbatore, india, pp. 1-5. doi: 10.1109/icctct.2018.8550835. [15] rolevski m, zecevic z. (2020) mppt controller based on the neural network model of the photovoltaic panel. proceedings of the 24th int. conf. on information technology (it), 18-22 fen 2020, zabljak, montenegro, pp. 1-4. doi: 10.1109/it48810.2020.9070299. [16] bouazza f, mohamed m, bouziane b, abdelhak d. (2019) photovoltaic generator modeling based on lookup table approach and implementation on stm32f407 board of the perturb & observe algorithm based mppt. proceedings of the 2018 int. conf. on applied smart systems (icass), 24-25 nov 2018, medea, algeria, pp. 1-7. doi: 10.1109/icass.2018.8652000. [17] ngo s, chiu c. (2020) simulation implementation of mppt design under partial shading effect of pv panels. proceedings of the 2020 int. conf. on system science and engineering (icsse), 31 aug – 3 sept 2020, kagawa, japan, pp. 1-6. doi: 10.1109/icsse50014.2020.9219306. [18] alhussain hma, yasin n. (2020) modeling and simulation of solar pv module for comparison of two mppt algorithms (p&o & inc) in matlab/simulink. indonesian journal of electrical engineering and computer science, 18(2): 666-677. doi: 10.11591/ijeecs.v18.i2.pp666-677. [19] moreira hs, gomes dos reis mv, de araujo ls, perpetuo e oliveira t, villalva mg. (2017) an experimental comparative study of perturb and observe and incremental conductance mppt techniques for two-stage photovoltaic inverter. proceedings of the 2017 brazilian power electronics conference (cobep), 19-22 nov 2017, juiz de fora, brazil, pp. 1-6. doi: 10.1109/cobep.2017.8257370. [20] ghasemi ma, foroushani hm, parniani m. (2016) partial shading detection and smooth maximum power point tracking of pv arrays under psc. ieee trans. on power electronics, 31(9): 6281-6292. doi: 10.1109/tpel.2015.2504515. 130 microsoft word 4_vol17_no1_2016_(compiledversion_4).docx iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 103 extraction and quantitative determination of ascorbic acid from banana peel musa acuminata ‘kepok’ khairul anwar mohamad said, zainad radzi, ibrahim yakub, and mohamed afizal mohamed amin department of chemical engineering and energy sustainability, faculty of engineering, universiti malaysia sarawak, 94300, kota samarahan, sarawak, malaysia. 1 mskanwar@feng.unimas.my, 2 zainabradzi@gmail.com, 3 yibrahim@feng.unimas.my, 4mamafizal@feng.unimas.my (received: 14 aug. 2015; accepted: 03 dec. 2015; published on-line: 30 apr. 2016) abstract: this paper discusses the extraction of an antioxidant compound, which is ascorbic acid or vitamin c, from a banana peel using an ultrasound-assisted extraction (uae) method. the type of banana used was musa acuminata also known as “pisangkepok” in malaysia. the investigation includes the effect of solvent/solid ratio (4.5, 5 g and 10 ml/g), sonication time (15, 30 and 45 mins) and temperature variation (30 , 45 and 60oc ) on the extraction of ascorbic acid compounds from the banana peel to determine the best or optimum condition of the operation. out of all extract samples analyzed by redox titration method using iodine solution, it was found that the highest yield was 0.04939 ± 0.00080 mg that resulted from an extraction at 30oc for 15 mins with 5 ml/g solvent-to-solute ratio. abstrak: kertas kajian ini membincangkan kaedah mengekstrak antioksida khususnya asid askorbik atau vitamin c daripada kulit pisang melalui teknik ultrasonik (uae). jenis pisang yang dipilih sebagai bahan kajian ialah musa acuminata, sejenis pisang yang digunakan dalam masakan. ia juga dikenali sebagai pisang kepok di malaysia. kajian kali ini mengetengahkan tindakbalas nisbah pelarut/pepejal (4.5, 5 g dan 10 ml/g), masa proses ultrasonik (15, 30 and 45 min) dan perubahan suhu (30, 45 and 60oc) ke atas kadar ekstrak asid askorbik daripada kulit pisang bagi menentukan tindakbalas optimum didalam proses ini. selepas analisis dibuat melalui kaedah titrasiredoks, didapati bahawa hasil yang tertinggi dari segi kadar ekstrak asid askorbik adalah 0.04939 ± 0.00080 mg pada catatan suhu 30oc untuk 15 minit dengan pelarut/ bahan larut 5 ml/g. keywords: musa acuminata; ultrasound-assisted extraction; vitamin c; redox titration 1. introduction banana is one of the main crops in the world that has significance to humans for its nutrition and mineral contents. it must have been one of the first known tropical crops since there are records of it being in cultivation 4000 years ago [1]. according to [2], edible bananas originated from melesia, a biogeographical region consisting of the primary centre including malaysia, indonesia, philippines and new guinea as well as the secondary centre which is india. as far as banana is concerned, there are two type of wild banana originally from south east asia: musa acuminata colla (aa) and musa balbisiana colla (bb) where the iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 104 difference between both types is mainly the cultivation method [3]. musa acuminata is categorized as highly polymorphous where the growth is in clumps while musa balbisiana colla (bb) usually grows as a plant with a massive trunk [4]. bananas are divided into three categories; desert banana, plantain and cooking banana [4]. desert banana is usually associated with musa acuminata from triploid character for example aaa whereas plantain and cooking banana originated from a hybrid of musa acuminata and musa balbisiana. hybrid banana also has triploid character from aa x bb which brings plantain character to musa aab while cooking banana is known as musa abb [5]. the main difference between dessert banana and plantain or cooking banana is pulp/flesh. plantain/cooking banana requires cooking before consumption and its pulp has more starch and less sugar. the only similarity between them is that plantain and cooking banana look very similar to unripe desert banana although it (plantain/cooking banana) usually has larger size [6]. every part of a banana plant has its own usage from a good source of nutrients to religious ceremonies. in africa and asia, banana fruit is a source of starch staple food and dessert bananas are also a main cash crop in many developed and developing countries [7]. their contribution to human health is due to its great medicinal value. banana fruit is claimed to prevent anemia, regulate blood pressure, prevent constipation, cure heartburns and prevent stroke [8]. even the leaves are used as food wrappings and plates for their pleasant smell [9]. several studies have found that banana pulp and peel contain various high value nutritional use in pharmaceutical industries for instances vitamins (a, b, c and e), ߚcarotene and phenolic compounds such as gallocatechin [10], dopamine [11], lignin and tannins [12] and phytosterols and triterpenes such as cycloeucalenol and cycloartenol [13]. ascorbic acid also known as vitamin c is an organic compound with physical appearance of white solid while sometime has yellowish color for impure samples. ascorbic acid is important to living beings where animals are able to self-synthesise it from glucose while human beings fulfill ascorbic acid needs from nutritional supplement or fruit [14]. several methods have been developed and utilized to quantify ascorbic acid. among them is the classic method known as volumetric method which required titration of an oxidant solution to ascorbic acid [15]. there are a variety of oxidant solution such as potassium iodate [16] and bromate [17]. another method is by utilizing spectrophotometer to determine oxidation of ascorbic acid to dehydroascorbic acid where the absorbance spectrum is set at 450 nm. this method requires a reducing agent such as cu(ii)-neocuproine complex which later is reduced to cu(i)-bis(neocuproine) when mixed with ascorbic acid [18]. apart of using cu(ii)-neocuproine complex, there are other methods that utilize the spectrophotometrical determination but use different compounds, for instance iodine [19] and chemiluminescence [20]. due to the consumer demand for products from natural sources, the economic impact of plant-based extracts especially for food, nutraceuticals, cosmetics, flavors or fragrances, and pharmaceutical industry has developed in the last few years. extraction technology like ultrasonic-assisted extraction and many other methods are usually used to fulfill the demands. conventional method such as boiling or hot water extraction has been utilized before any other extraction methods exist in order to extract antioxidants, unfortunately hot water extraction method has several disadvantages mainly antioxidant degradation due to high temperature and oxidation as well as the long extraction period [21]. in recent years, the emergence of new extraction processes for instance microwave assisted extraction [22– 24], ultrasonic assisted extraction [21,25–27] and supercritical fluid extraction [28–30] has helped to reduce the extraction period and at the same time reduce degradation rate of antioxidant. among these, ultrasonic assisted extraction has three qualities that other iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 105 methods lack which are easier procedure, inexpensive and this process can also be conducted with no external heat i.e. at troom temperature [31]. ultrasound can be defined as a sound wave with frequency higher than 18 khz. a lot of studies have been done on the application of both high and low power ultrasound [32]. the different intensity of powers has different usage in various fields. low power ultrasound are mainly applied in medical ultrasonography while high power ultrasound have numerous uses such as ultrasonic welding, degassing of solutions, defect detection and sonochemistry [32]. an important phenomenon associated with power ultrasound is called cavitation bubbles. when liquids are sonicated at high ultrasound intensities, the sound waves that propagate into the liquid media causes alternating high-pressure (compression) and low pressure (rarefaction) cycles, where rates are dependent on the frequency [33]. the bubbles are produced during rarefaction cycle of the wave when the liquid structure are broken resulting in the formation of tiny voids which collapse in the compression cycle [34]. in early application of ultrasonic techniques, ultrasonic cleaning bath has been introduced into metallurgy and chemical laboratories in the 1960’s and considering how soiled glassware was being cleaned and immiscible organic solvents dispersed in aqueous detergent, it was not surprising that it is being used by chemists to enhance chemical reactivity [34]. until today, sonochemistry has been an ongoing investigation for over 50 years [35]. some of the reports on the extraction of banana products using hot water extraction methods have been published. these state that the optimum condition for hot water extraction methods for extracting banana juice were 95oc for 120 mins [36] while others also choose to proceed with this methods for a duration of 120 mins [37]. ascorbic acid is a highly sensitive material subjected to a number of processing conditions and is also a thermolabile substance [38]. furthermore, in order to understand ascorbic acid degradation; it follows two mechanism pathways aerobic or anaerobic which are related closely to processing conditions [38,39]. in this study, a temperature range from 30oc until 60oc are chosen for extraction in order to reduce ascorbic acid degradation resulting from heat. subsequent, solid to solvent ratio is also an important parameter related to extraction and by knowing the optimized ratio could help reduce wastage of solvent and reduced bulk process. for instances, ratio of 1:10 in extraction of piperine from piper longum was considered the optimum because at a higher ratio, only small increment of yield was observed [40]. with this knowledge, solid to solvent ratio of (4.5, 5 g and 10 ml/g) have been used. finally, extraction time is usually based on the process cost. the best process must be operated with minimal energy and shorter time at each extraction cycle. based on several studies, it can be concluded that acceptable time for extraction of antioxidant ranges from 3 to 45 minutes where optimum time usually falls within 30 to 40 minutes [40–44]. with this in mind, extraction times of (15, 30 and 45 mins) have been used. therefore, considering the promising application of this method to extract ascorbic acid, there is a great potential for using ultrasonic assisted extraction method to extract ascorbic acid from banana pulp. the aim of this study is to test feasibility of extracting ascorbic acid using ultrasonic cleaning bath, to investigate effects of different parameters towards extraction of ascorbic acid and finally to determine optimum extraction conditions using ultrasonic cleaning bath. 2. methodology 2.1 materials banana from species musa acuminata ‘kepok’ were obtained from the kota samarahan market in the state of sarawak, malaysia. the maturity of bananas was observed visually iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 106 which can be described as follows; the bananas were fully ripe and have yellow skin. besides, methanol 99.8% (sigma-aldrich), iodine 99.9% anhydrous (sigma-aldrich), potassium iodide anhydrous (acs reagent) used was of analytical grade while vitamin c was obtained from abbot laboratories, usa. 2.2 sample preparation initially, all bananas were washed with municipal tap water to remove soil or dust. then cleaned bananas were peeled and the peels were collected for sampling. the peels were freeze-dried using freezone® 4.5 liter freeze dry systems (labconco, usa) which was set to run automatically at a pressure and temperature of 7 bar and -30oc respectively before sliced into smaller pieces using ika a11 basic analytical mill (sigma-aldrich) to a fine powder form. 2.3 extraction of antioxidant the ultrasonic-assisted extraction of ascorbic acid from dried banana peels were executed in an ultrasonic bath (s900h, elmasonic elma schmidbauer gmbh, germany) at a constant power of 2000 w and ultrasonic frequency of 37 khz. the extraction was conducted with different solvent-to-solute ratio, temperature and sonication time. the solvent used was 60% methanol. it must be noted that single electron transfer and hydrogen atom transfer are affected by the type and polarity of the solvent used to extract ascorbic acid from the banana peel [45]. fine banana powders (110 g) were used for these experiments. the experiments were conducted with a solvent/solid ratio of 4.5 ml/g, 5 ml/g and 10 ml/g. the samples in the beaker were then transferred to a 250 ml sample bottles and were placed in the ultrasonic bath to be extracted at different experimental conditions. sonication time of extraction was varied at 15, 30 and 45 mins while the temperature at 30oc, 45oc and 60oc. extraction temperature was controlled by a built-in function of ultrasonic bath. after that, the crude extracts were filtered using whatman filter papers before the extracts were heated until a significant amount of methanol solvent evaporated which was collected to estimate the oil yield. the extracts were then titrated with iodine to determine the ascorbic acid or vitamin c content. 2.4 quantification of ascorbic acid a 500 mg vitamin c tablet was used for the construction of the standard curve. the single tablet was dissolved in 200 ml distilled water where 1 ml aliquot was taken using a pipette out of the sample solution and transferred into a 250 ml conical flask. one milliliter of starch indicator solution was added and the flask was filled to 200 ml with distilled water. the sample was titrated with 0.005 mol/l iodine solution. the endpoint of the titration was identified as the first permanent trace of a dark blue-black colour due to the starchiodine complex. it was repeated with further aliquots of sample solution until concordant results were obtained. titration was repeated three times and the average value was taken. sample (1 ml) was diluted in a 250 ml conical flask with distilled water filling to 200 ml. then, 50 ml aliquot of the solution was taken for titration and mixed with 1 ml starch solution and diluted again with distilled water to 200 ml. the sample was again titrated with 0.005 mol/l iodine solution. the end point of the titration was identified as the first permanent trace of a dark blue-black colour due to the starch-iodine complex. the titration was repeated three times with the same amount of aliquots of sample solution until concordant results were obtained and the average volume of iodine used was calculated. iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 107 3. results and discussion 3.1 effect of sonication time on vitamin c yield figure 1 shows the effect of sonication time; 15, 30 and 45 mins, solvent/solid ratio; 4.5 ml/g, 5 ml/g, 10 ml/g, and extraction temperature: 30°c on the extraction yield of vitamin c from banana peel. the methanol concentration: used throughout this experiment is kept at a constant concentration which is 60%. at 30°c, the yield decreases as the time is extended from 15 to 30 mins. this may happen because longer sonication time can affect the extraction results since the extra sonication can degrade the quality of extracts [31]. the increase of yield occurred as the time increased to 45 mins. at 15 mins, 0.04939 ± 0.00080 mg of yield were obtained from extracts which is the highest yield throughout the experiment whereas at 30 mins and 45 mins, 0.03046 ± 0.00138 mg and 0.03416 ± 0.00080 mg were obtained respectively. both are lower than the yield at 15 mins by 61.68% and 69.16% correspondingly. in conjunction with sudden rise of extraction yield at 15 mins for 4.5 ml/g solvent-solid ratio, there are few other researchers experience of the same occurrence when utilizing ultrasonic method. all agree that optimum extraction time falls between 15 to 20 mins and further period of ultrasonication will result with a decrease of extraction yield [46–48]. there are two phases of extraction process which can also be indicated by extraction time: the first phase involve dissolution of soluble on the surface of sample followed by the second phases that focus on mass transfer from within the sample either through osmosis or diffusion [49]. based on this two phases, it is believed that 4.5 ml/g solvent-solid ratio has lowest saturation of ascorbic acid which enable two phases of extraction whereas other configuration suffer from high saturation of ascorbic acid which prevents high mass transfer rate and after 20 mins has passed, apparent ascorbic acid degradation has started to occur which in the end results in a decrease of extraction yield. fig. 1: effect of ultrasonication time; 15, 30 and 45 mins, solvent/solid ratio; 4.5 ml/g, 5 ml/g, 10 ml/g, and extraction temperature: 30°c on the extraction yield of vitamin c from banana peel. methanol concentration: 60%. at 30°c (fig. 1) and solvent/solid ratio of 4.5 ml/g and 5 ml/g both indicate that the yield levitates as the time is extended from 15 to 30 mins. however, the increase is immediately diminished when sonication time is extended to 45 mins. this is also true for the yield obtained at 45°c (fig. 2) and solvent/solid ratio of 10 ml/g. at 60°c (fig. 3), all three ratios shows the same pattern with the same temperature changes. in the view of time usage, it is not recommended to exceed 30 mins. sonication time plays an important part in this extraction too. as discussed earlier, longer sonication time causes less ascorbic acid yield because the cavitation depletes as the 0 0.01 0.02 0.03 0.04 0.05 0.06 0 10 20 30 40 50 a sc or bi c a ci d (m g) sonication time (min) 4.5ml/g 5ml/g 10ml/g iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 108 sonication time increases. the optimum time found in this study indicates the lowest time experimented. lesser time for extraction is feasible and practical for this extraction to be done at an industrial scale. figure 2 shows the yield of ascorbic acid trend for extraction temperature 45oc and solvent to solid ratio of 4.5 to 10 ml/g, in general the results show an increment of all parameter setting until 30 minute which show sudden drop for 10 ml/g solvent-solid ratio from 0.042 mg to 0.026 mg whereas other configuration experience equilibrium trend. rapid decrease of extraction yield for 10ml/g solvent-solid ratio was caused by saturation of ascorbic acid [47,50]. the same occurrence has been observed with ultrasonic assisted extraction of phenolic compound from sugarcane where the extraction yield diminishes after 30 mins and increasing for a period of 10 mins within time frame of 20 to 30 mins [51]. another possibility that might cause yield losses at 10 ml/g was oxidation of ascorbic acid. it was believed that longer extraction period has exposed more oxygen to the extract and therefore incite oxidation process [52]. in a different occasion, extraction of piperine from piper longum show equilibrium yield after 18 mins of extraction with yield fluctuating within 4 to 5 mg/g [40]. this findings was found to agree with the current yield in fig. 2 for 4.5 and 5 ml/g solvent-solid ratio which show small increase of yield in span of 15 to 45 mins of extraction. at 5 ml/g solventsolid ratio, the lowest point was 0.044 for 15 mins and peak at 0.045 ml/g at the end of the extraction process. otherwise, 4.5 ml/g solvent-solid ratio show 0.009 mg increase between 15 to 30 mins of extraction time and settle at 0.031 at 45 mins of extraction. each point of yield for 4.5 ml/g solvent-solid ratio are 0.019, 0.028 and 0.031 mg corresponding to 15, 30 and 45 mins of extraction. fig. 2: effect of ultrasonication time; 15, 30 and 45 mins, solvent/solid ratio; 4.5 ml/g, 5 ml/g, 10 ml/g, and extraction temperature: 45°c on the extraction yield of vitamin c from banana peel. methanol concentration: 60%. figure 3 shows the effect of extraction period against ascorbic acid yield at 4.5, 5 and 10 ml/g solvent-solid ratio and 60oc. at this configuration, solvent-solid ratio of 10 ml/g reach equilibrium in term of ascorbic acid yield after 30 mins of extraction where the yield fluctuates within interval of 0.043 to 0.045 mg. otherwise, 5 ml/g solvent-solid ratio has reached a constant yield at 0.027 mg after 15 mins of extraction while 4.5 ml/g experiences a sudden drop of ascorbic acid yield after 30 mins from 0.026 mg to 0.020 mg. solute equilibrium in this work was a constant yield of ascorbic acid can only be achieved by principles of saturation. according to the literature [53], saturation was achieved when amount of solvent has restricted any further process to extract the remaining solute from samples. according to mass transfer principles, higher diffusion can be achieved when there was high driving force which solely relate to concentration gradient. higher concentration gradient can only be achieved when quantity of solvent is higher than sample weight [53,54]. 0 0.02 0.04 0.06 0 10 20 30 40 50a sc or bi c a ci d (m g) sonication time (min) 4.5ml/g 5ml/g 10ml/g iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 109 as far as the 10 ml/g solvent-solid ratio is concerned, this configuration has the highest solvent volume per gram of samples and its yield was consistent to mass transfer principles that state the increase of yield with the increase of solvent quantity. fig. 3: effect of ultrasonication time; 15, 30 and 45 mins, solvent/solid ratio; 4.5 ml/g, 5 ml/g, 10 ml/g, and extraction temperature: 60°c on the extraction yield of vitamin c from banana peel. methanol concentration: 60%. 3.2 effect of temperature on vitamin c yield figure 4 shows the effect of temperature on the extraction yield of vitamin c from banana peel. using solvent/solid ratio of 4.5 ml/g and sonication time of 15 mins, the extraction yield of vitamin c decreases as temperature was increased from 30°c to 60°c. the temperature was manually changed by the built-in functions of the ultrasonic bath.the basis of choosing 4.5 ml/g solvent-solid ratio over other parameter was based on amount of yield where the highest yield recorded was 0.049 mg at 4.5 ml/g, 30oc and 15 mins of extraction. fig. 4: effect of temperature on vitamic c yield at 4.5 ml/g of solvent/solid ratio. the highest yield was obtained at 30°c with the value of 0.04939 ± 0.00080 mg which was 60.7% higher than yield at 45°c. at 30°c, the mass transfer has improved due to the increasing solubility of vitamin c and the decreasing viscosity of the solvent. the yield at 45°c is 60.75% less than the yield at 30oc while at 60°c, it is lower by 64.49%. this may be caused by the degradation of vitamin c at elevated temperature where the ultrasonic probe causes an increase in the bulk temperature [55]. 0 0.02 0.04 0.06 0 10 20 30 40 50 a sc or bi c a ci d (m g) sonication time (min) 4.5ml/g 5ml/g 10ml/g 0.00000 0.01000 0.02000 0.03000 0.04000 0.05000 0.06000 30 45 60 v it am in c (m g) temperature condition (°c) 4.5ml/g iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 110 when the amplitude is higher, the temperature increases faster and it can go beyond the desired temperature in a short period of time. the most apparent effects that can occur are the degradation of compounds tested, and the volatilization of low volatile analytes. in addition, the increase of temperature changes the physical characteristics of the liquid media in such a way that it affects the ultrasonic transmission with no cavitation achieved, which is a phenomenon known as decoupling [56,57]. as temperature is a very important parameter, it must be controlled but it is not easy to achieve the desired value. this has also been observed for ultrasonic assisted extraction of salvia officinalis where the result obtained show that it is crucial to accurately control the extraction temperature when ultrasound is used for it constantly generates heat [58]. on the other hand, lower heat supply in addition to the heat generated by ultrasound calls for a lesser energy use in the industry which could attract more interest on its investment [58]. 3.3 effect of solvent-to-solid ratio on vitamin c yield figure 5 displays the effect of solvent/solid ratio on the extraction yield of vitamin c from banana peel. the experiment was carried out with a constant methanol concentration of 60%, extraction temperature of 30°c and sonication time of 30 mins. the yield shows an increasing trend as the solvent/solid ratio increases. at 4.5 ml/g of solvent/solid ratio, the extraction yielded 0.03046 ± 0.00138 mg of vitamin c and a slight increase to 0.03093 ± 0.00524 mg can be seen as the ratio was increased to 5 ml/g. it increased further to 0.03185 ± 0.00635 mg at 10 ml/g of solvent/solid ratio. a larger solvent volume can dissolve targeted components more efficiently and therefore resulted in an enhancement of the extraction yield. the observation therefore obeys the mass transfer principle, where the driving force during the mass transfer was the concentration gradient between the solid and bulk liquid in which was escalated with a higher solvent/solid ratio usage [59,60]. at 60°c, the vitamin c yields also exhibited increasing value when the solvent/solid ratio was increased. from fig. 5, it can be seen that extracts obtained by using 4.5 ml/g contained 0.02677 ± 0.00212 mg vitamin c and had10.76% more that was 0.03000 ±0.00890 mg at 5 ml/g ratio. the highest yield obtained was when 10 ml/g solvent was used that resulted with 0.04477 ± 0.01525 mg vitamin c. this shows that the extraction yields more compounds with more solvent used. ultrasound-extraction at 30°c yielded higher ascorbic acid at any solvent/solid ratio in comparison to the extraction at 60°c. for instance at 4.5 ml/g solvent, the difference between the yield values of ascorbic acid at 30°c and 60°c were 12.12% and 2.99% at 5 ml/g. this substantiated the findings discussed in section 3.2 that the decrease in vitamin c was caused by thermal effects as it is a sensitive molecule that is altered at temperature above 60°c. the presence of ultrasound had caused the temperature to increase beyond the targeted temperature, so lower heating supply is needed for a particular extraction temperature. the phenomenon where decreasing acoustic cavitation bubbles created by the ultrasound had also caused the yield to decrease at 60°c. therefore, even though the yield increased with increasing solvent-to-solid ratio, the yield had a slight decrease when the temperature was increased. iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 111 fig. 5: comparison between yields at 30°c and 60°c, solvent to solid ratio of 4.5, 5 and 10 ml/g and sonication time of 30 mins. 4. conclusion the results obtained from this study indicate the feasibility of extraction of vitamin c from banana peel using ultrasonic assisted extraction method. based on all extract samples analyzed by redox titration method, it was found that the highest yield was 0.04939 ± 0.00080 mg obtained at the temperature 30°c, sonication time of 15 mins and solvent/solid ratio of 5 ml/g amongst other conditions. of the three parameters chosen, it was found that temperature and sonication period have significant effect on the extraction yield of ascorbic acid from banana peel. the main idea of utilizing ultrasonic assisted extraction is to provide mechanical disruption to the cell structure without effect of heat. ultrasonic extraction is providing cavitation effect towards the banana peel samples causing it to release the extract or contents. long extraction period followed by temperature more than 30oc will increase the possibility of oxidation of ascorbic acid and degradation of ascorbic acid due to heat. therefore, it is important to choose efficient extraction condition i.e. extraction temperature, time period and ratio of solvent to solid in order to maintain and preserve extraction yield. acknowledgement the author gratefully acknowledges universiti malaysia sarawak and ministry of education malaysia for technical and financial support through research acculturation grant scheme (rags) no: e14099/f02/69/943/2012(44). references [1] allen bm. (1975) common malaysian fruits, longman malaysia sdn. bhd., selangor. [2] n.w. simmonds, k. shepherd (1955), the taxonomy and origins of the cultivated bananas., j. linn. soc. london, bot. 55:302–312. [3] shian te, abdullah a, musa kh, maskat my, ghani ma. (2012) antioxidant properties of three banana cultivars (musa acuminata “berangan”,’mas' and “raja”) extracts. sains malaysiana, 41:319-324. [4] aurore g, parfait b, fahrasmane l. (2009) bananas, raw materials for making processed food products. trends food sci. technol. 20:78-91. [5] hassan nmm. (2004) banana r & d in malaysia: update and highlights, in: v.d.b.i.& 0 0.01 0.02 0.03 0.04 0.05 4.5 5 10 a sc or bi c ac id (m g) solvent-solid ratio (ml/g) 30 60 iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 112 m.m.a.g. molina a. b., eusebio j.e., roa v.n. (eds.), adv. banan. plantain r d asia pacific, vol. 12, inibap, jakarta. [6] happi emaga t, andrianaivo rh, wathelet b, tchango jt, paquot m. (2007) effects of the stage of maturation and varieties on the chemical composition of banana and plantain peels. food chem., 103:590-600. [7] abdullah fc, yap lv, mohammad wali y, sundaraj hs, khamis s. (2011) peeling the scientific facts of banana. international islamic academy for life sciences & biotechnology, universiti selangor., shah alam, selangor. pg 9-24. [8] ahnwange b, ugye t, nyiaatagher td. (2009) chemical composition of musa sapientum (banana) peels. electron. j. environ. agric. food chem., 8:437-442. [9] orhan i. (2001) biological activities of musa species. j. fac.farm., 30:39-50. [10] someya s, yoshiki y, okubo k. (2002) antioxidant compounds from bananas (musa cavendish). food chem., 79:351-354. [11] kanazawa k, sakakibara h. (2000) high content of dopamine, a strong antioxidant, in cavendish banana. j. agric. food chem., 48:844-848. [12] lim yy, lim tt, tee jj. (2007) antioxidant properties of several tropical fruits: a comparative study. food chem., 103:1003-1008. [13] knapp ff, nicholas hj. (1969) the sterols and triterpenes of banana peel. phytochemistry, 8:207-214. [14] sebastian m, padayatty j, sun h, wang y, riordan hd, hewitt sm, katz a, wesley ra, levine m. (2004) implications for oral and intravenous use, annals of internal medicine 140:533–537. [15] fadhel d. (2012) spectrophotometric determination of ascorbic acid in aqueous solutions. jnus. org., 15:88-94. [16] pisoschi am, pop a, serban ai, fafaneata c. (2014) electrochemical methods for ascorbic acid determination, electrochim. acta., 121:443-460. [17] ensafi a, rezaei b, movahedinia h. (2002) kinetic-spectrophotometric determination of ascorbic acid by inhibition of the hydrochloric acid-bromate reaction. spectrochim. acta. a. mol. biomol. spectrosc., 58:2589-94. [18] güçlü k, sözgen k, tütem e, özyürek m, apak r. (2005) spectrophotometric determination of ascorbic acid using copper(ii)-neocuproine reagent in beverages and pharmaceuticals. talanta, 65:1226-32. [19] noroozifar m, khorasani-motlagh m. (2003) solid-phase iodine as an oxidant in flow injection analysis: determination of ascorbic acid in pharmaceuticals and foods by background correction. talanta, 61:173-9. [20] dong yp, gao tt, chu xf, chen j, wang cm. (2014) flow injection-chemiluminescence determination of ascorbic acid based on luminol–ferricyanide–gold nanoparticles system, j. lumin., 154:350-355. [21] zhang g, he l, m.(2011) optimized ultrasonic-assisted extraction of flavonoids from prunella vulgaris l. and evaluation of antioxidant activities in vitro. innovative food science and emerging technologies 12:18–25. [22] pan y, wang k, huang s, wang h, mu x, he c, et al. (2008) antioxidant activity of microwave-assisted extract of longan (dimocarpus longan lour.) peel. food chem.,106:1264-1270. [23] hayat k, zhang x, farooq u, abbas s, xia s, jia c, et al. (2010) effect of microwave treatment on phenolic content and antioxidant activity of citrus mandarin pomace. food chem.,123:423-429. [24] qu x, fu y, luo m, zhao c, zu y. (2013) acidic ph based microwave-assisted aqueous extraction of seed oil from yellow horn (xanthoceras sorbifolia bunge.), industrial crops and products, 43:420–426. [25] yang b, zhao m, shi j, yang n, jiang y. (2008) effect of ultrasonic treatment on the recovery and dpph radical scavenging activity of polysaccharides from longan fruit pericarp. food chem., 106:685-690. [26] aybastıer ö, işık e, şahin s, demir c. (2013) optimization of ultrasonic-assisted extraction of antioxidant compounds from blackberry leaves using response surface methodology. ind. iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 113 crops prod., 44:558-565. [27] ramandi nf, ghassempour a, najafi nm, ghasemi e. (2012) optimization of ultrasonic assisted extraction of fatty acids from borago officinalis l. flower by central composite design. arabian journal of chemistry. [28] huang w, li z, niu h, li d, zhang j. (2008) optimization of operating parameters for supercritical carbon dioxide extraction of lycopene by response surface methodology. j. food eng., 89:298-302. [29] passos cp, silva rm, da silva fa, coimbra ma, silva cm. (2010) supercritical fluid extraction of grape seed (vitis vinifera l.) oil: effect of the operating conditions upon oil composition and antioxidant capacity. chem. eng. j., 160:634-640. [30] mazzutti s, ferreira srs, riehl cas, smania a, smania fa, martínez j. (2012) supercritical fluid extraction of agaricus brasiliensis: antioxidant and antimicrobial activities. j. supercrit. fluids, 70:48-56. [31] wang l, weller cl. (2006) recent advances in extraction of nutraceuticals from plants. trends food sci. technol., 17:300-312. [32] kwiatkowska b, bennett j, akunna j, walker gm, bremner dh. (2011) stimulation of bioprocesses by ultrasound. biotechnol. adv., 29:768-780. [33] suslick ks, othmer k. (1998) encyclopedia of chemical technology, 4th edn., j. wiley & sons, new york. [34] mason t, lorimer jp. (1998) sonochemistry, theory, applications and uses of ultrasound in chemistry. ellis harwood limited, chichester west sussex. [35] lee wc, yusof s, hamid nsa, baharin bs. (2006) optimizing conditions for hot water extraction of banana juice using response surface methodology (rsm). j. food eng., 75:473479. [36] gonzález-montelongo r, gloria lobo m, gonzález m. (2010) antioxidant activity in banana peel extracts: testing extraction conditions and related bioactive compounds. food chem., 119:1030-1039. [37] valdramidis v, cullen p. (2010) quantitative modelling approaches for ascorbic acid degradation and non-enzymatic browning of orange juice during ultrasound processing. journal of food engineering, 96:449–454. [38] blasco r, esteve mj, frígola a, rodrigo m. (2004) ascorbic acid degradation kinetics in mushrooms in a high-temperature short-time process controlled by a thermoresistometer, lwt. food sci. technol., 37:171-175. [39] vieira mc, teixeira aa, silva clm. (2000) mathematical modeling of the thermal degradation kinetics of vitamin c in cupuacu (theobroma grandiflorum) nectar. j. food eng., 43:1-7. [40] rathod ss, rathod vk. (2014) extraction of piperine from piper longum using ultrasound. ind. crops prod., 58:259-264. [41] tian y, xu z, zheng b, martin lo y. (2013) optimization of ultrasonic-assisted extraction of pomegranate (punica granatum l.) seed oil. ultrason. sonochem., 20:202-208. [42] zhang h, yang x, zhao l, wang y. (2009) ultrasonic-assisted extraction of epimedin c from fresh leaves of epimedium and extraction mechanism. innovative food science and emerging technologies, 10:54–60. [43] teng h, choi yh. (2014) optimization of ultrasonic-assisted extraction of bioactive alkaloid compounds from rhizoma coptidis (coptis chinensis franch.) using response surface methodology. food chem., 142:299-305. [44] shirsath sr, sonawane sh, gogate pr. (2012) intensification of extraction of natural products using ultrasonic irradiations a review of current status. chem. eng. process. process intensif., 53:10-23. [45] becker em, nissen lr, skibsted lh. (2004) antioxidant evaluation protocols: food quality or health effects. eur. food res. technol., 6:561-571. [46] liu j, zheng s, fan q, yuan j, yang s. (2015) optimisation of high-pressure ultrasonicassisted extraction and antioxidant capacity of polysaccharides from the rhizome of ligusticum chuanxiong. int. j. biol. macromol., 76:80-85. [47] pongmalai p, devahastin s, chiewchan n, soponronnarit s. (2015) enhancement of iium engineering journal, vol. 17, no. 1, 2016 mohamad said et al. 114 microwave-assisted extraction of bioactive compounds from cabbage outer leaves via the application of ultrasonic pretreatment. sep. purif. technol., 144:37-45. [48] prakash maran j, manikandan s, thirugnanasambandham k, vigna nivetha c, dinesh r. (2013) box-behnken design based statistical modeling for ultrasound-assisted extraction of corn silk polysaccharide. carbohydr. polym., 92:604-611. [49] şahin s, şamli r. (2013) optimization of olive leaf extract obtained by ultrasound-assisted extraction with response surface methodology. ultrason. sonochem., 20:595-602. [50] liu x, mu t, sun h, zhang m, chen j. (2013) optimisation of aqueous two-phase extraction of anthocyanins from purple sweet potatoes by response surface methodology. food chem., 141:3034-3041. [51] feng s, luo z, tao b, chen c. (2015) ultrasonic-assisted extraction and purification of phenolic compounds from sugarcane (saccharum officinarum l.) rinds, lwt. food sci. technol., 60:970-976. [52] naczk m, shahidi f. (2004) extraction and analysis of phenolics in food. j. chromatogr. a., 1054:95-111. [53] elksibi i, haddar w, ben ticha m, gharbi r, mhenni mf. (2014) development and optimisation of a non conventional extraction process of natural dye from olive solid waste using response surface methodology (rsm). food chem., 161:345-352. [54] ho chl, cacace je, mazza g. (2008) mass transfer during pressurized low polarity water extraction of lignans from flaxseed meal. j. food eng., 89:64-71. [55] h.m. santos, c. lodeiro, j.-l. capelo-martínez (2009), the power of ultrasound, ultrasound in chemistry: analytical applications. pp. 1–16. [56] mason tj. (1992) practical sonochemistry: users guide to applications in chemistry and chemical engineering. ellis horwood ltd, new york. [57] mason tj. (2000) sonochemistry. oxford chemistry primers, oxford, uk. [58] salisova m, toma s, mason tj. (1997) comparison of conventional and ultrasonically assisted extractions of pharmaceutically active compounds from salvia officinalis. ultrasonics sonochemistry, 4:131-134. [59] zhang q, zhang z, yue x, fan x, li t, chen s. (2009) response surface optimization of ultrasound-assisted oil extraction from autoclaved almond powder. food chemistry, 116: 513518. [60] herodez ss, hadolin m, skerget m, knez z. (2003) solvent extraction study of antioxidants from balm (melissa officinalis l.) leaves. food chemistry, 80:275-282. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 behaviors of thermoelastic properties in ni-ti-based shape memory alloys, processed by metal forming techniques tarsila tenório luna da silva1*, fillipe virgolino2, niédson silva3, carlos oliveira4, carlos araújo5, oscar olimpio de araujo filho4 and cezar gonzalez4 1 departamento de engenharia mecânica (dem), universidade federal da bahia (ufba), salvador, brazil 2 departamento de engenharia mecânica (demec), universidade de pernambuco (upe), recife, brazil 3 departamento de engenharia mecânica (demec), instituto federal de pernambuco (ifpe), caruaru, brazil 4 departamento de engenharia mecânica (demec), universidade federal de pernambuco (ufpe), recife, brazil 5 departamento de engenharia mecânica (demec), universidade federal de campina grande (ufcg), campina grande, brazil * corresponding author: tarsila.silva@ufpe.br (received: 14 may 2022; accepted: 23 march 2023; published on-line: 4 july 2023) abstract: in this work, the thermoelastic properties of ni-ti shape memory alloys (sma) processed by conventional rolling and equal channel angular extrusion (ecae) were investigated. smas have two phases: austenite (at high temperature) and martensite (at low temperature). the samples were compared under five different thermal and processing conditions: homogenized, rolled, rolled-annealed, extruded, and extrudedannealed. the homogenized sample served as a reference. the samples were analyzed by differential scanning calorimetry (dsc) to determine the thermoelastic transformation temperatures. images were taken using scanning electronic microscopy (sem) in conjunction with energy dispersive spectroscopy (eds). the dynamic area was completed for two tests: under constant load bending (simulation of the memory effect to determine the reversible thermoelastic strain) and dynamic mechanical analysis (dma). the results showed that the plastic forming processes alter the properties, especially for samples exposed to the ecae, which can block the martensitic phase. however, r-phase (a rhombohedral phase), that can appear at low temperatures before the martensitic phase, emerges totally when the extruded sample suffers annealing. the images of sem, confirmed by eds, show that any type of forming process and the presence of precipitates have a significant influence on the behavior of the elastic property. it was found that extrusion has a greater effect on the restoring properties of the alloys than rolling. this analysis is of great importance for the use of sma in applications requiring high mechanical strength combined with the functional properties of shape recovery through martensitic phase transformations. abstrak: kajian ini adalah berkaitan sifat-sifat bentuk aloi ingatan (sma) termoelastik ni-ti yang diproses melalui penggelek konvensional dan penyemperitan sudut saluran sama (ecae). sma mempunyai dua peringkat: austenit (pada suhu tinggi) dan martensit (pada suhu rendah). sampel dibandingkan pada lima tahap kepanasan dan proses iaitu: percampuran, penggulungan, penggulungan-rataan, perataan dan penyemperitan-rataan. sampel campuran yang dihomogenkan dijadikan sebagai sampel rujukan. sampel dianalisis dengan pengimbas kalorimetri pembezaan (dsc) bagi menentukan suhu 209 mailto:tarsila.silva@ufpe.br iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 transformasi termoelastik. imej diambil menggunakan pengimbas mikroskop elektronik (sem) bersama spektroskopi penyebaran tenaga (eds). kawasan dinamik diuji dengan dua ujian: di bawah lenturan beban malar (simulasi kesan memori bagi menentukan terikan termoelastik boleh balik) dan analisis mekanik dinamik (dma). dapatan kajian menunjukkan bahawa proses pembentukan plastik telah mengubah sifat, terutama pada sampel yang terdedah kepada penyemperitan sudut saluran sama ecae, yang boleh menyekat fasa martensit. walau bagaimanapun, fasa-r (fasa rombohedral) yang boleh muncul pada suhu rendah sebelum fasa martensitik, muncul sepenuhnya apabila sampel tersemperit mengalami penyepuhlindapan (penyemperitan-rataan). imej pengimbasan mikroskop elektron, seperti yang dibuktikan dengan spektroskopi penyebaran tenaga (eds), menunjukkan bahawa apa-apa jenis proses pembentukan dan kehadiran mendakan mempunyai pengaruh kuat terhadap sifat elastik. dapatan kajian juga mendapati bahawa penyemperitan mempunyai kesan yang lebih besar terhadap sifat pemulihan aloi berbanding proses penggulungan. analisis ini sangat penting bagi penggunaan bentuk aloi ingatan (sma) dalam aplikasi yang memerlukan kekuatan mekanikal yang tinggi bersama sifat pemulihan bentuk melalui transformasi fasa martensit. key words: equal channel angular extrusion; shape memory alloy; ni-ti alloys 1. introduction shape memory alloys (sma) are active materials that can restore plastic deformations through suitable thermal conditioning. the phenomenon of shape memory effect (sme) is closely related to martensitic phase transformations, which are crystallographically reversible [1]. figure 1 summarizes the shape memory effect when comparing an ordinary plastic deformation, a superelastic deformation and a shape memory deformation. fig. 1: comparison between the diagram "stress x strain" in 3 forms: ordinary plastic deformation, superelastic deformation and deformation with shape memory [2] apud [3]. smas have two phases: austenite (at high temperature) and martensite (at low temperature). the phase transformation temperatures are austenite onset (as), austenite end (af), martensite onset (ms), martensite end (mf) and martensite transformation temperature by deformation (md). figure 1 shows that superelastic and shape memory deformations can be as high as 8%. the smas can also deform with a temperature difference [2]. the fabrication of ni-ti family smas is of great importance because slight variations in chemical composition can change the critical temperatures of martensitic transformation to about 100 °c [2]. therefore, plasma is efficiently used for the manufacturing process as it leads to negligible losses due to oxidation during melting [4]. ni-ti based smas are widely used due to their wide range of technological applications, ranging from aerospace and biomedical to petrochemical and other industries [5,6]. 210 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 the sma can be considered an electric drive if the sme is activated by the application of current pulses (joule effect). on the other hand, if the sme is activated directly by controlled temperature changes, they are considered thermal actuators. when these alloys are subjected to plastic deformation processes, they exhibit increased mechanical strength due to their hardening (significant increase in the density of crystalline defects) and reduced grain size after deformation and heat treatment. this change in mechanical properties leads to changes in the thermoelastic properties of sma (critical transformation temperatures, transformation enthalpies, thermoelastic deformation, thermal hysteresis and others), which are essential characteristics for the use of these materials in technological applications [7,8]. equal channel angular extrusion (ecae) or equal channel angular pressing (ecap) is a metal-forming process recently developed by segal et al. [9]. the process promotes the passage of material between two successive channels that intersect, forming angles between 90° and 120° and causing plastic deformation. these channels have identical geometric dimensions so that material does not change its dimensions after processing. in this process, the material undergoes several plastic deformations that cause high critical shear stress without changing the cross-section of the sample. some studies show that the deformation phenomena during the ecae process are independent of the sample size [6]. several technological applications of these processed materials are already idealized, especially for parts that need to have a high mechanical strength obtained by plastic deformation processes without changing their dimensions during processing. sun et al. [10] examined the properties and hardening behavior of ecae-processed mg-al binary alloys. as a result, the dynamic compressive test shows a significant strength increase attributed to the precipitates and the strength improvement from grain size refinement (hall-petch effect). yang et al. [11] processed ni-ti-nb smas by ecap. niti-nb is a wide hysteresis shape memory alloy with great application potential in aerospace. the ecap process decreased grain size (or the increase of grain boundary content), and the transformation hysteresis temperature and recovery stress of the ni-ti-nb alloy increased simultaneously. ni-ti shape memory alloys are widely used for medical components, as they can accommodate large strains in their superelastic state. to further improve the mechanical properties of ni-ti, grain refinement by severe plastic deformation is applied to generate an ultrafine-grained microstructure with increased strength. leitner et al. [12] performed experiments in ultrafine-grained ni-ti, processed by ecap, and comprehensive fracture and fatigue crack growth experiments to assess its damage tolerance, which is essential for safely using this material in medical applications. other methods of plastic forming were studied. jiang et al. [13] studied the mechanically induced martensite in ni-ti-fe alloys, with shape memory effect, manifesting the suggested in the deformation plane, concluding that the plastic deformation necessary to produce the product of the dislocations plays an essential role in the formation of mechanically induced martensitic transformation, unlike stress-induced martensite where control of dislocations only occurs after deformation. zhang et al. [14] subjected ni-tibased superelastic alloys to severe cold rolling and observed that stress-induced martensite reorientation (b19' phase) dominates the reaction. liang et al. [15] described the martensitic strain states of cold-rolled ti50.8at%ni alloys for different thickness reduction levels. silva [16] rolled two ni-ti wires with a shape memory effect. both wires showed important characteristics and high performance, such as good responses to several cold rolling, low thermal hysteresis, reasonable dimensional control, nanostructure, and excellent properties mechanics. it can be used in highly complex engineering applications requiring precision in actuation and control. 211 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 this study aims to obtain a ni-ti alloy with an sme and subject these materials to mechanical forming processes by conventional rolling and ecae. in the work, the properties of ni-ti sma were analyzed using dsc analysis, sem-eds and a constant bending load test. the latter test simulates the shape memory effect and the thermoelastic properties are determined from the curves obtained. 2. materials and methods a sma of the equiatomic composition of ni-50at.%ti, corresponding to ni-45wt.%ti, was obtained by the plasma skull-push pull (pspp) process with a controlled atmosphere melting chamber. a plasma flame of a tungsten electrode melts the metallic material. plasma energy is enough for melting most metallic alloys cleanly and efficiently. the furnace chamber receives high pressure by vacuum in its mold cavity, continuously filling the mold in a push-pull sequence. the machine has a mode control that determines time and temperature according to the alloy [17,18]. it was found that to ensure good homogeneity of the sma, the melting process should be repeated five times. heat treatments were made in a jung muffle furnace, model lf4212, followed by cooling in water. the ingot was homogenized for 120 min in a muffle furnace at 900 °c, followed by quenching in water at room temperature (~25 °c). the ingot was cut on a precision cutter with a diamond disk to produce samples as prismatic bars for metal forming processes: conventional mechanical rolling process and ecae. the sample used in the rolling process has 5 × 1.5 mm². hot rolling was performed on a conventional rolling machine. after each step, the sample was heated in a muffle furnace at 900 °c for 1 min. the sample was deformed from 1.5 mm to 0.5 mm, with a final deformation rate of 66.7% (20 steps with 0.05 mm for each step). for the angular extrusion, the sample was a bar with a 5 × 5 mm2 square cross-section. the die for the angular extrusion process has an angle of 130° between internal channels. angular extrusion was performed on a universal mechanical testing machine (emic), controlled to operate in a compression test mode with 0.5 mm·min-1 speed at room temperature (~25 °c). this work obtained samples after homogenization (using a sample without plastic deformation as a reference), mechanical rolling, and ecae. the samples obtained for each plastic deformation process were subjected to annealing at 450 °c for 15 min and cooled in water at room temperature for stress relief. table 1 presents the nomenclature and procedures applied to each of the samples analyzed in this study. table 1: nomenclature and procedures of the ni-ti samples sample processes applied h homogenized at 900 °c for 120 min rl rolled ra rolled and annealed at 450 °c for 15 min e extruded ea extruded and annealed at 450 °c for 15 min the calorimetric properties (temperatures and enthalpies of austenitic, martensitic, and rhombohedral phase transformations and their thermal hysteresis) were performed by a mettler ta3000 dsc. the dsc technique is very effective for determining the record of phase transformation temperatures in lmf. the advantage of this technique is the possibility of measuring the energy involved in the process based on measuring the area of 212 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 the endothermic peak in heating and the exothermic peak in cooling. even so, the transformation enthalpies, thermal hysteresis (difference between the transformation peak temperatures), and phase transformation temperatures (as, af, ms, mf measured by crossing the tangents at the peaks) are measured. this technique also allows obtaining graphs, in which it is possible to analyze whether the phase transformation occurs in one or two steps [19,20]. the dsc heating chamber was filled with nitrogen gas to prevent the oxidation of the material. the samples were analyzed over a temperature range of -60 °c to 120 °c, with a heating/cooling rate of 10 °c/min. the dma experiment consisted of applying an oscillating force to a sample in uniaxial tension mode and investigating the response of the material to this applied load. the equipment allows working between 25 °c and 500 °c in bending, tensile and uniaxial cantilever (curved at one end and free at the other) modes [21,22]. in this work, dma tests were performed on equipment installed in an anti-vibration bed to avoid interference during data acquisition. the experiment was conducted in single cantilever mode, following standard parameters: frequency of 1 hz, a heating rate of 2 °c/min and a vibration amplitude of 5 × 10-3 mm [23]. the sma ni-ti slides used had a useful length and width of approximately 17 and 5 mm, respectively. prior to all tests, the samples were cooled to temperatures of about -30 °c to collect data on the reverse martensitic transformation upon heating. as with the dsc tests, the transformation temperatures obtained from the dma curves were determined using the tangent crossing method. conventional metallographic procedures (grinding and polishing with diamond paste) were performed and kroll reagent (2 ml hf, 4 ml hno3, and 100 ml h2o) was used for etching. the microstructures of the samples were recorded with a hitachi tm3000 sem. together with the sem-eds tests are carried out to semi-quantitatively check the chemical composition of the sample. a special apparatus was developed to determine the thermoelastic properties of sma under constant bending load (cantilever test). the load is applied to the sample through a pulley system. a programmable silicon oil bath is used to perform heating and cooling cycles between -10 °c and 100 °c. during cooling, the plate (sample) is deformed, and when heated, the sample regains its original shape. a linear variable displacement transducer (lvdt) and a thermocouple measure the deformation and temperature, respectively [24]. in this work, the samples were individually tested under a constant bending load of 80 mpa and thermally cycled 20 times between 20 °c and 100 °c with a rate of 10 °c.min-1 during heating and 3 °c.min-1 for cooling. the samples have prismatic bar geometry with dimensions of 20 × 5 × 0.5 mm³. figure 2 shows representative thermoelastic deformation versus temperature curves obtained from data collected in the thermomechanical tests under constant load. there are two cycles, in which thermoelastic properties are determined. the martensitic transformation temperatures (austenite and martensite phases) can be found across the tangent line technique. thermoelastic deformations (εt) and previous plastic strain (x) are found in the ordinate axes as indicated in fig. 2. the thermal hysteresis (ht = a50 m50) can be also calculated [25]. 213 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 fig. 2: representative thermoelastic deformation versus temperature curves obtained during a typical test of thermomechanical cycles in simple bending mode. the investigated parameters are pointed out in this figure [25]. “reproduced with permission from gonzalez, c.h. and de araújo, c.j, study of martensitic stabilization under stress in cu–al–be shape memory alloy single crystal; published by materials science and engineering, 2004”. 3. results and discussions 3.1 calorimetric curves (dsc) figures 3-6 show calorimetric curves for the samples submitted to the five conditions: homogenized (h), rolled (rl), rolled and annealed (ra), and extruded (e), respectively. figure 3 was used as the reference sample. in the case of the rolled sample (rl) (fig. 4), the start temperature of the r-phase remains practically unchanged from to ms temperature of the homogenized (h) sample (fig. 3). the curve of the rolled sample (fig. 4) indicates that the plastic deformation process causes a decrease in ms temperature during cooling and as temperature is also reduced. in principle, it can be assumed that the initial inflection during cooling is due to the presence of the rhombohedral phase (r-phase) [1]. the plastic deformation process increases the linear defects density (dislocations) that may hinder or even inhibit direct (austenite => martensite) and reverses (martensite => austenite) martensitic transformations. fig. 3: calorimetric curves with martensitic transformations of the ni-ti alloy homogenized (h). fig. 4: calorimetric curves with martensitic transformations of the ni-ti alloy rolled (rl). 214 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 fig. 5: calorimetric curves with martensitic transformations of the ni-ti alloy rolled and annealed (ra). fig. 6: calorimetric curves with martensitic transformations of the ni-ti alloy extruded (e). in the rolled and annealed (ra) sample (fig. 5), it was observed that the calorimetric curve and its data are like the reference sample (fig. 3), so this treatment eliminates the effects of the mechanical rolling process in this alloy. the extruded (e) sample’s (fig. 6) dsc shows the peaks of the r-phase (rhombohedral) and monoclinic martensite phase (b19'), with lower temperatures of rs and ms than in the roller (rl) sample (fig. 4). this clearly shows that the angular extrusion process introduces crystalline defects much larger than rolled process, however, it produces no reduction in the geometric dimensions of the sample. table 2 summarizes the main results obtained through the dsc test, the temperatures of the martensitic transformations, including the r-phase, the heating and cooling enthalpies, and the thermal hysteresis reaction. table 2: martensitic transformations, enthalpies, and hysteresis of the ni-ti alloy samples sample as [°c] af [°c] ∆hheating [j/g] rs [°c] rf [°c] ms [°c] mf [°c] ∆hcooling [j/g] ht [°c] h 51.2 63.5 10.3 31.2 19.6 10.9 32.3 rl 44.0 60.1 13.4 33.8 20.4 20.4 2.5 14.7 39.7 ra 48.1 62.9 15.0 34.6 19.8 13.4 28.3 e 8.5 29.3 17.2 21.6 -7.1 -7.1 -42.8 18.2 36.4 ea 26.8 42.4 17.0 31.3 14.0 -15.4 -35.5 16.0 57.8 in fig. 7 the calorimetric curve of the extruded and annealed sample (ea) shows a complete separation between the peaks of the r-phase and the martensitic phase, with a larger temperature interval between peaks. this heat treatment was able to restore the rs temperature of the r-phase, in this way, it was effective to eliminate (or minimize) the effects of the angular extrusion process in this crystal structure. for the martensitic phase, this treatment has become ineffective or even complicates the process to initiate the transformation. 215 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 fig. 7: calorimetric curves with martensitic transformations of the ni-ti alloy extruded and annealed (ea). 3.2 thermomechanical test figures 8-12 show the thermomechanical cycling curves of the ni-ti samples in the bending tests under constant load. table 3 summarizes the results obtained in these tests. fig. 8: thermomechanical cycling curves of the ni-ti alloy homogenized (h). fig. 9: thermomechanical cycling curves of the ni-ti alloy rolled (rl). 216 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 fig. 10: thermomechanical cycling curves of the ni-ti alloy rolled and annealed (ra). fig. 11: thermomechanical cycling curves of the ni-ti alloy extruded and annealed (ea). fig. 12: thermomechanical cycling curves of the ni-ti alloy in the extruded (e) condition. table 3: results of the thermomechanical cycling curves of the ni-ti samples in fig. 8, the homogenized (h) sample had the maximum reversible thermoelastic deformation. in the calorimetric tests, the critical temperatures of phase transformation of the rolled and annealed (ra) sample (fig. 10) returned to effectively the same temperatures sample as [°c] af [°c] rs [°c] rf= ms [°c] mf [°c] εt [mm] h 44.9 49.8 26.5 15.1 4.50 rl 53.2 74.6 33.2 12.6 0.86 ra 42.9 50.2 30.9 15.1 2.21 e 0.09 ea 33.2 50.8 41.7 29.1 -2.6 0.74 217 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 obtained for the reference sample (h), as seen in table 2, which also shows the enthalpies of transformation. however, this treatment was not enough to restore the reversible thermoelastic deformation obtained in the reference sample, since the maximum value obtained for the annealed sample was lower than the reference sample (h). from the results of thermoelastic tests, this treatment appears to have not been able to eliminate all the effects of the rolling process. the extruded (e) sample (fig. 11) practically did not show any thermoelastic deformation. this was probably due to the limitation of the thermal bath, which has a minimum temperature of -10°c, but in these cases (fig. 12) it is also possible that the energy provided by the system was not enough to complete the entire transformation due to the blocking provided by the large increase in dislocation density. when external stress is applied to a shape memory alloy it promotes the increase of the critical transformation temperatures. the load applied was not enough for these temperatures to increase sufficiently to be detected by the device. the extruded and annealed (ea) sample (fig. 12) showed a low recovery deformation, indicating a high degree of hardening when compared with the reference sample (h). the heat treatment and training process seriously affects the internal friction behavior in ti-ni alloys. these events have an importance on the reconfiguration of ti-ni alloy defects, inducing modification that might change the material properties such as memory effect, damping capacity, strength, hardness, and others [26-28]. 3.3 dma analysis figure 13 shows the damping curves, during heating, provided by the dynamic tests. it can be noticed that the decrease in the energy absorption capacity of the shaped samples, especially in the sample that was submitted to the ecae, sample (e). the mechanical rolling process generates elongated grains according to the deformation direction [29,30]. these elongated grains are in a preferential direction and the result of this is the improvement of the damping capacity for rl and ra samples. the random grains obtained in sample e induce more stress field dislocation blocking the phase transformation. the large damping capacity of the ea sample is due to heat treatment who is efficient to liberate blocking regions and dislocations. fig. 13: dma analysis. temperature versus damping capacity in the conditions: homogenized (h), rolled (rl), rolled and annealed (ra), extruded (e), and extruded and annealed (ea). 218 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 according to the literature, ni-ti-based alloys have a high damping capacity during phase transformation and in the martensitic phase, whereas their austenitic phase shows a much lower energy dissipation [31]. the high damping capacity of the martensite phase is related to the hysteretic movement of interfaces (martensite variant interface and twin boundaries) [32,33]. it is established that the global internal friction is also controlled by dislocations and their interactions with other lattice defects. the high damping capacity of ti-ni alloys comes from the movement of several twin boundaries. the accommodation of twin boundaries under external stress is believed to be responsible for high damping capacity [34]. 3.4 micrography analysis (sem) figures 14-15 show micrographs of the samples. figure 14a exhibits the microstructure of the homogenized sample and consists of equiaxial and heterogeneous grains with segregation as found in jiang’s et al. [35] work. furthermore, as they exhibit a eutectic structure around grain boundaries, it was verified the regions with the highest percentage of ni due to the exclusion of this element during solidification, confirmed by eds [24]. figure 14b and 14c show the rolled (rl) and the rolled and annealed (ra) samples. the arrows indicate this preferential orientation of the grains, which became more evident after the annealing heat treatment was carried out (fig. 14c). literature also suggests that with rolled process some particles of ti2ni and others might be found in the grain boundaries provoking a second transformation in the grain boundaries and it is also related to r-phase transformation [36,37]. fig. 14: sem micrographs of samples: (a) homogenized (h), (b) rolled (rl) and (c) rolled and annealed (ra). figure 15 shows the microstructure for extruded (e) and extruded and annealed (ea) samples. in the images, it is possible to see the reduced grain compared with the homogenized (h) sample and particles provided by the high-stress state made by the mechanical process. these samples were subjected to severe shear deformations during the forming process, which can be confirmed by the reduction of transformation temperatures, damping capacity, and thermoelastic deformation. from the images, despite not having a 219 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 morphology with preferential orientation, it is possible to visualize the contours and decrease the grain sizes of the homogenized (h) sample. there is the presence of particles between the grains, which suggests that they are precipitated from the state of tension caused by ecae. unlike samples annealed after conventional rolling, the micrographs of rolled and extruded (fig. 15b) samples show that the latter process produces grains without preferential orientation. probably, the configuration of the stress fields generated by the increased dislocation density must be highly disoriented. these facts seem to be responsible for the greatest loss of thermoelastic properties in the extruded samples. fig. 15: sem micrographs of samples: a) extruded (e) and b) extruded and annealed (ea). 3.5 energy dispersive spectroscopy (eds) figure 16 shows the analyzed regions of the sample as cast, where the percentage of elements in the alloy matrix (a), inside the grain (b), and in the region of its contour (c) was verified. fig. 16. eds’ analyzed regions: alloy matrix (a), inside the grain (b), and in the region of its contour (c). figures 17, 18, and 19 showed results of each region introduced in fig. 16. the percentage in weight is close to the nominal of the alloy, considering it to be a semiquantitative analysis with a certain margin of error (around 5%). in turn, it was revealed the presence of a high percentage of nickel in the region along the grain boundaries, a probable result of the precipitation of this element during the solidification of the ni-ti alloys [38]. 220 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 fig. 17: eds of area a showed in fig. 16. fig. 18: eds of area b showed in fig. 16. fig. 19: eds of area c showed in fig. 16. an eds analysis for the equiatomic alloy showed a higher amount of ni in the grain boundary region. although the percentage of ti is still lower, there is an increase in the detection of this element compared to the homogenized (h) sample, which suggests the presence of precipitates related to the mechanical conformation, ti2ni. 4. conclusion plastic forming processes by mechanical rolling and angular extrusion promoted increased mechanical resistance of samples due to the reduction of the grain size caused by shear stress during plastic deformation and introducing defects in the crystalline structure. mechanical rolling and angular extrusion increased the mechanical resistance of samples by reducing the grain size and introducing defects in the crystalline structure. these processes have significantly affected the thermoelastic behavior of the shape memory alloy. although one cannot compare directly (quantitatively) the influence of the two processes on the properties of shape memory alloys, it became evident that the process of angular extrusion seems to be much more effective in hardening the samples. the results of the calorimetry curves when compared with data curves under constant load tests are complementary. the critical phase transformation temperatures of the samples were reduced by plastic deformation processes since there is a higher need for energy to perform the transformations. the micrographs of rolled and extruded samples show that the latter process produces grains without preferential orientation. probably, the configuration of the stress fields 221 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 generated by the increased dislocation density must be highly disoriented. these facts seem to be responsible for the greatest loss of thermoelastic properties in the extruded samples. in the technological applications of the sma, it is important to take into consideration the fact that the increased mechanical strength is achieved at the expense of reduced transformation temperatures and of the thermoelastic properties of the shape memory effect and may be recovered partly by heat treatment. the extrusion-forming process proved to be more severe than the rolling process to the shape-recovery properties presented by the alloys. this analysis is of great importance in the use of lmf in applications that require high mechanical strength combined with the functional properties of shape recovery provided by martensitic phase transformations. acknowledgement this work was supported by the conselho nacional de desenvolvimento científico e tecnológico (cnpq); coordenação de aperfeiçoamento de pessoal de nível superior (capes) and the fundação de amparo à ciência e tecnologia do estado de pernambuco (facepe). references [1] otsuka k, wayman cm. (1998) shape memory materials. cambridge, cambridge university press. [2] qader in, kök m, dagdelen f, abdullah ss. (2020) the effect of different parameters on shape memory alloys. sakarya university journal of science, 24(5): 881-902. doi: 10.16984/saufenbilder.733645 [3] desroches r, mccormick j, delemont m. (2004) cyclic properties of superelastic shape memory alloy wires and bars. journal of structural engineering, 130(1): 38-46. doi:10.1061/(asce)0733-9445(2004)130:1(38) [4] antunes as, tosetti jpv, otubo j. (2013) high shape recovery ni–ti sma wire produced from electron beam melted ingot. journal of alloys and compounds, 577(1): 265-267. doi:10.1016/j.jallcom.2012.03.043 [5] de araújo cj, gomes aac, silva ja, cavalcanti ajt, reis rpb, gonzalez ch. (2009) fabrication of shape memory alloys using the plasma skull push-pull process. journal of materials processing technology, 209(7): 3657-3664. doi:10.1016/j.jmatprotec.2008.08.025 [6] silva nj. (2018) estudo de ligas com memória de forma ni-ti processadas por laminação e extrusão angular. phd thesis. universidade federal de pernambuco, centro de tecnologia e geociências. [7] silva kca. (2014) estudo de ligas com memória de forma ni-ti processadas por laminação e extrusão angular. phd thesis. universidade federal de pernambuco, centro de tecnologia e geociências. [8] figueiredo am, modenesi p, buono v. (2009) low-cycle fatigue life of superelastic niti wires. international journal of fatigue, 31(4): 751-758. doi:10.1016/j.ijfatigue.2008.03.014 [9] segal vm. (1995) materials processing by simple shear. materials science and engineering: a, 197(2):157-164. doi:10.1016/0921-5093(95)09705-8 [10] sun x, wu dy, kang m, ramesh kt, kecskes lj. (2023) properties and hardening behavior of equal channel angular extrusion processed mg-al binary alloys. materials characterization, 195: 112514. doi:10.1016/j.matchar.2022.112514 [11] yang z, li h, zhang y, liu x, gu q, liu x. (2022) ecap based regulation mechanism of shape memory properties of nitinb alloys. journal of alloys and compounds, 897: 163184. doi:10.1016/j.jallcom.2021.163184 222 http://dx.doi.org/10.16984/saufenbilder.733645 https://doi.org/10.1016/j.jmatprotec.2008.08.025 https://doi.org/10.1016/j.ijfatigue.2008.03.014 https://doi.org/10.1016/0921-5093(95)09705-8 https://doi.org/10.1016/j.matchar.2022.112514 https://doi.org/10.1016/j.jallcom.2021.163184 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 [12] leitner t, sabirov i, pippan r, hohenwarter a. (2017) the effect of severe grain refinement on the damage tolerance of a superelastic niti shape memory alloy. journal of the mechanical behavior of biomedical materials, 71:337-348. doi:10.1016/j.jmbbm.2017.03.020 [13] jiang sy, yu jb, zhang yq, xing xd. (2020) mechanically-induced martensite transformation of nitife shape memory alloy subjected to plane strain compression. trans. nonferrous met. soc. china, 30: 1325-1334. doi:10.1016/s1003-6326(20)65299-2 [14] zhang j, chen t, li w, bednarcik j, dippel ac. (2020) high temperature superelasticity realized in equiatomic ti-ni conventional shape memory alloy by severe cold rolling. materials and design, 193: 1008875. doi:10.1016/j.matdes.2020.108875 [15] liang q, zhao s, liang c, zhao t, wang d, ding x, li s, wang y, zheng y, ren x, mills m, wang y. (2022) strain states and unique properties in cold-rolled tini shape memory alloys. acta materialia, 231: 117890, 2022. doi:10.1016/j.actamat.2022.117890 [16] silva ttl. (2022) comportamento termoelástico de fios de ni-ti com efeito memória de forma processados por laminação a frio. phd thesis. universidade federal de pernambuco, centro de tecnologia e geociências. [17] silva ttl, virgolino fss, oliveira can, de araújo cj, gonzalez ch. (2021) fabricação de uma liga equiatômica de tini com efeito memória de forma pelo método plasma skul-push pull. revista engenharia e tecnologia, 13(4): 270-280. retrieved from https://revistas.uepg.br/index.php/ret/article/view/19659 [18] simões jb. (2017) fabricação de componentes miniaturizados de ligas com memória de forma niti usando fundição de precisão. joão pessoa, ideia. [19] virgolino fss. (2017) comportamento em fadiga termomecânica de fios de liga com memória de forma ni-ti-cu. dissertation. universidade federal de pernambuco, centro de tecnologia e geociência. [20] aghamiri sms, ahmadabadin mn, shahmir h, naghdi f, raygan s. (2013) study of thermomechanical treatment on mechanical-induced phase transformation of niti and tinicu wires. journal of the mechanical behavior of biomedical materials, 21: 32-36. doi:10.1016/j.jmbbm.2013.01.014 [21] karaca he, kaya i, tobe h, basaran b, nagasako m, kainuma r, chumlyakov s. (2013) shape memory behavior of high strength ni54ti46 alloys. materials science & engineering, 580: 66-70. doi:10.1016/j.msea.2013.04.102 [22] khaleghi f, allafi jk, chianeh va, noori s. (2013) effect of short-time annealing treatment on the superelastic behavior of cold drawn ni-rich niti shape memory wires. journal of alloys and compounds, 554: 32-38. doi:10.1016/j.jallcom.2012.11.183 [23] van humbeeck j. (2003) damping capacity of thermoelastic martensite in shape memory alloys. journal of alloys and compounds, 335(1-2): 58-64. doi:10.1016/s0925-8388(03)00268-8 [24] oliveira can, gonzalez ch, de araújo cj, araujo filho oo, urtiga filho sul. (2010) thermoelastic properties on cu-zn-al shape memory springs. materials research, 13(2): 219-223. doi:10.1590/s1516-14392010000200016 [25] gonzalez ch, de araújo cj, quadros nf, guénin g, morin m. (2004) study of martensitic stabilization under stress in cu–al–be shape memory alloy single crystal. materials science and engineering, 378(1-2): 253-256. doi:10.1016/j.msea.2003.11.069 [26] yoshida i, ono t, asai m. (2000) internal friction of ti-ni alloys. journal of alloys and compounds, 310(1-2):339-343. doi:10.1016/s0925-8388(00)00957-9 [27] yoshida i, monma d, iino k, ono t, otsuka k, asai m. (2004) internal friction of ti-ni-cu ternary shape memory alloys, mat sci. engineering structures, 370(1-2): 444-448. doi:10.1016/j.msea.2003.05.003 [28] genlian fan yz, otsuka k, ren x. (2006) ultrahigh damping in r-phase state of ti-ni-fe alloy. applied physics letters, 89:3. doi:10.1063/1.2363173 [29] ma y, du z, cui x, cheng j, liu g, gong t. et al. (2018) effect of cold rolling process on microstructure and mechanical properties of high strength β titanium alloy thin sheets. progress in natural science: materials international, 28(6): 711-717. doi:10.1016/j.pnsc.2018.10.004 223 https://doi.org/10.1016/j.jmbbm.2017.03.020 https://doi.org/10.1016/s1003-6326(20)65299-2 https://doi.org/10.1016/j.matdes.2020.108875 https://doi.org/10.1016/j.actamat.2022.117890 https://doi.org/10.1016/j.jmbbm.2013.01.014 https://doi.org/10.1016/j.msea.2013.04.102 https://doi.org/10.1016/j.jallcom.2012.11.183 https://doi.org/10.1016/s0925-8388(03)00268-8 https://doi.org/10.1590/s1516-14392010000200016 https://doi.org/10.1016/j.msea.2003.11.069 https://doi.org/10.1016/s0925-8388(00)00957-9 https://doi.org/10.1016/j.msea.2003.05.003 https://doi.org/10.1063/1.2363173 https://doi.org/10.1016/j.pnsc.2018.10.004 iium engineering journal, vol. 24, no. 2, 2023 silva et al. https://doi.org/10.31436/iiumej.v24i2.2442 [30] sadeghpour s, abbasi sm, morakabati m, karjalainen lp, porter da. (2018) effect of cold rolling and subsequent annealing on grain refinement of a beta titanium alloy showing stressinduced martensitic transformation. materials science and engineering: a, 731: 465-478. doi:10.1016/j.msea.2018.06.050 [31] lu xl, cai w, zhao lc. (2003) damping behavior of a ti44ni47nb9 shape memory alloy. journal of materials science letters, 22: 1243-1245. doi:10.1023/a:1025445832316 [32] van humbeeck j, liu y (2000). the high damping capacity of shape memory alloys. springer-verlag. https://doi.org/10.1007/978-3-642-59768-8_4 [33] oliveira can, gonzalez ch, araujo filho oo, silva nj, guimaraes pb, mendonza en et al. (2015) thermomechanical analysis on ti-ni shape memory helical springs under cyclic tensile loads. mat. res., 18(2): 17-24. doi:10.1590/1516-1439.334514 [34] wu sk, lin hc. (2003) damping characteristics of tini binary and ternary shape memory alloys. journal of alloys and compounds, 355(1-2): 72-78. doi:10.1016/s0925-8388(03)00279-2 [35] jiang sy, zhang yq. (2012) microstructure evolution and deformation behavior of as-cast ni-ti shape memory alloy under compression. transactions of nonferrous metals society of china, 22(1): 90-96. doi:10.1016/s1003-6326(11)61145-x [36] bhagyaraj j, ramaiah kv, saikrishna cn, bhaumik sk, gouthama. (2013) behavior and effect of ti2ni phase during processing of ni-ti shape memory alloy wire from cast ingot. journal of alloys and compounds, 581: 344-351. doi:10.1016/j.jallcom.2013.07.046 [37] duerig tw, bhattacharya k. (2015) the influence of the r-phase on the superelastic behavior of niti. shape memory and superelasticity, 1: 153-161. doi:10.1007/s40830-015-0013-4 [38] chen y, jiang hc, liu sw, rong lj, zhao xq. (2009) damping capacity of tini-based shape memory alloys. journal of alloys and compounds, 482(1-2): 151-154. doi:10.1016/j.jallcom.2009.03.148 224 https://doi.org/10.1016/j.msea.2018.06.050 https://www.researchgate.net/deref/http%3a%2f%2fdx.doi.org%2f10.1023%2fa%3a1025445832316 https://doi.org/10.1007/978-3-642-59768-8_4 https://doi.org/10.1590/1516-1439.334514 https://doi.org/10.1016/s0925-8388(03)00279-2 https://doi.org/10.1016/s1003-6326(11)61145-x https://doi.org/10.1016/j.jallcom.2013.07.046 https://doi.org/10.1007/s40830-015-0013-4 https://doi.org/10.1016/j.jallcom.2009.03.148 microsoft word 68-666-3-ed completed.docx iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 19 numerical simulation and analysis of coanda effect circulation control for wind-turbine application considerations h.djojodihardjo1, m.f.abdulhamid2, s. basri2, f. i. romli2 and d. l. a. abdul majid2 1universitas al-azhar indonesia, jakarta, indonesia 2department of aerospace engineering, faculty of engineering, university putra malaysia (upm), 43400 upm serdang, selangor darul ehsan, malaysia. harijono@djojodihardjo.com abstract: in the efforts to investigate the performance of coanda jet in enhancing lift of an airfoil, a numerical study is carried out. tangential jets that take advantage of coanda effect to closely follow the contours of the body are considered to be simple and particularly effective in that they can entrain a large mass of surrounding air. this can lead to increased circulation in the case of airfoils, or drag reduction (or drag increase if desired) in the case of bluff bodies such as an aircraft fuselage. critical review and analysis is also carried out for the application of coanda jet to optimize the aerodynamic performance of wind turbine, using the results of the numerical study and taking advantage of recent efforts to introduce coanda effect as a novel circulation control technique. for this purpose a simple twodimensional cfd modeling is utilized to reveal the key elements that could exhibit the desired performance criteria, in particular the lift enhancement and drag reduction, or a combination of both. three dimensional configurations will be synthesized using certain acceptable assumptions, to compare such results with existing experimental data. hence in this work the problem is idealized as basic airflow over a two-dimensional airfoil in subsonic flow; by the use of cfd technique, parametric study is carried out to arrive at plausible design considerations and to assess the practicability of coanda jet in wind turbine design. parametric study carried out shows the effectiveness of coanda-jet in producing enhanced lift, which can contribute to increased torque in wind turbine application and increased axial thrust for propeller application. the numerical study also shows that appropriate trailing edge rounding off and tailoring the coanda-jet thickness and momentum coefficient can produce enhanced lift to drag ratio. abstrak:dalam usaha untuk mengkaji prestasi coanda jet bagi mempertingkatkan daya angkat suatu aerofil, kajian berangka telah dijalankan. tangen jet yang mengambil manfaat efek coanda mengikut kontur permukaan dianggap mudah dan berkesankerana ia dapat mengiring satu jisim besar udara sekeliling. ini mendorong kepada penambahan edaran udara dalam kes aerofil, atau penurunan seret (juga penambahan seret jika diingini) dalam kes jasad tubir seperti fiuslaj pesawat.ulasan kritikal dan analisis telah dijalankan bagi aplikasi coanda jet untuk mengoptimumkan prestasi aerodinamik turbin angin, menggunakan keputusan kajian berangka dan mengambil manfaat usahamemperkenalkan penggunaan efek coanda sebagai satu teknik pengawalan edaran udara. untuk tujuan ini, permodelan dua dimensi cfd telah digunakan untuk mendedahkan punca utama elemen yang dapat mededahkan kriteria prestasi yang diingini, khususnya peningkatan daya angkat iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 20 dan penurunan seret, ataupun kombinasi kedua-duanya.konfigurasi tiga dimensi akan disintesis menggunakan beberapa andaian yang boleh diterima, untuk membandingkan keputusan tersebut dengan data eksperimental yang sedia ada.permasalahan dalam kajian ini diunggulkan sebagai aliran udara asas subsonik di atas aerofil dua dimensi; dengan menggunakan teknik cfd, kajian berparameter dijalankan untuk mendapat reka bentuk yang munasabah, dan mengkaji kebolehlaksanaan coanda jet dalam reka bentuk turbin angin.kajian berparameter menunjukkan keberkesanan coanda-jet dalam menghasilkan peningkatan daya angkat, justeru menyumbangkan kepada peningkatan daya kilas dalam aplikasi turbin angin, dan juga penambahan tujah paksi dalam aplikasi bebaling.kajian berangka ini juga menunjukkan pembundaran pinggir mengekor, pemilihan ketebalan coanda-jet dan pekali momentum yang sesuai, akanmenghasilkan peningkatan nisbah daya angkat terhadap seretan. keywords: aerodynamics, wind-energy, computational fluid dynamics, numerical method 1. introduction the interest in the use of flow control for enhanced aerodynamic performance has grown, in particular the use of jets (continuous, synthetic, pulsed, etc.) [1-14]. it is widely documented that these active control concepts can dramatically alter the behavior of aerodynamic components such as airfoils, wings, and bodies. in this conjunction, and with the progress of cfd, the use of coanda effect to enhance lift has attracted renewed interest [2-5, 8-12, 17-19]. tangential jets that take advantage of coanda effect to closely follow the contours of the body are considered to be simple and particularly effective in that they can entrain a large mass of surrounding air. this can lead to increased circulation in the case of airfoils, or drag reduction (or drag increase if desired) in the case of bluff bodies such as an aircraft fuselage. figure 1 (a) illustrates the utilization of coanda jet for enhancing lift in a proposed aircraft [2,15], while fig. 1 (b) illustrates the concept of coanda-effect jet tangential blowing over trailing edge surface for lift enhancement [3]. in the design of a novel wind-turbines, in particular for large windturbines in land-based or off-shore wind-farms for significant renewable energy contribution, in which the reynolds number may reach 5 x 106 or above [20, 21], using the latest aerospace engineering technology, including aerodynamics, new light-weight materials, and efficient energy extraction technology, highly efficient aerodynamic surface came as a key issue. recent efforts in the last decade have also indicated that coanda effect has been given new and considerable considerations for circulation control technique [16-19]. taking advantage of these recent results, the present work will look into the effort to optimize aerodynamic performance of wind turbines and to critically review the use of coanda effect. the progress of high speed computers exemplified by the availability of new generations of notebooks has made possible the use of first-principles-based computational approaches for the aerodynamic modeling of wind turbine blades, to name an example. as pointed out by sankar [8, 16-17], since these approaches are based on the laws of conservation of mass, momentum, and energy, they can capture much of the physics in great detail. these approaches are particularly helpful at high wind speeds, where appreciable regions of separation are present and the flow is unsteady. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 21 in the design of circulation control technique, one may note the progress of stallcontrolled and pitch controlled turbine rotor technology for dealing with power production at low and high wind conditions, as pointed out by tangler et al. [20]. of interest is the deployment of wind turbines at larger range of sites not limited to a relatively small number of sites where favorable conditions exist. at the other extreme, precautions should be taken when the wind speeds become very high, when the rotor invariably stalls and experiences highly unsteady aerodynamic forces and moments. it is noted that over the past several years, there has been an increased effort to extend the usable operating range of stall regulated wind turbines. the concepts of circulation control through trailing edge blowing, or coanda-jets, then came into view. for this purpose, in this particular work we will focus on a particular problem, i.e. the basic airflow idealization over a two-dimensional airfoil in subsonic flow. two specific airfoils will be considered. the first is an airfoil that has already been investigated thoroughly, for benchmarking. for this purpose the naca 2412 airfoil has been chosen. tangler et al. [20] argue that over the past decades, commonly used airfoil families for horizontal axis wind turbines suffer noticeable performance degradation from roughness effects resulting from leading-edge contamination. considerations are also taken on the notion that annual energy losses due to leading-edge roughness are greatest for stall-regulated rotors. the loss is largely proportional to the reduction in maximum lift coefficient ( maxl c ) along the blade. high blade-root twist helps reduce the loss by keeping the blade's angle-of attack distribution away from stall which delays the onset of maxl c . new series of blades suitable for wind-turbine applications have been developed at nrel [20]. because of the economic benefits provided by these airfoils, they are recommended for retrofit blades and most new wind turbine designs [20]. in order to obtain results that can be well assessed, especially with reference to extensive research carried out as described in [16-19], s809 airfoil [20] is considered in the present work. 2. problem formulation circulation control wing (ccw) technology is known to be beneficial in increasing the bound circulation and hence the sectional lift coefficient of airfoil. this technology has been extensively investigated both experimentally and numerically [1-19] over many years. circulation control is implemented by tangentially blowing a small high-velocity jet over a highly curved surface, such as a rounded trailing edge. this causes the boundary layer and the jet sheet to remain attached along the curved surface due to the coanda effect (a balance of the pressure and centrifugal forces) and causing the jet to turn without separation. the rear stagnation point location moves toward the lower airfoil surface, producing additional increase in circulation around the entire airfoil. the outer irrotational flow is also turned substantially, leading to high value of lift coefficient comparable to that achievable from conventional high lift systems, as indicated in fig. 1(b). tongchitpakdee [17-18] observed that early circulation controlled wing designs typically had a large-radius rounded trailing edge to maximize the lift benefit. these iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 22 (a) (b) fig. 1: illustration of coanda-jet like circulation control: (a) circulation control wing-upper surface blowing stol aircraft configuration, from [2, 15]; (b) coanda-effect jet tangential blowing over trailing edge surface for lift enhancement, from [3]. designs, however, also result in high drag penalty when the jet is turned off. one way to reduce this drag is to make the lower surface of the trailing edge a flat surface, while keeping the upper surface highly curved. this curvature on the upper surface produces a large jet turning angle, leading to high lift. in this conjunction, the ability of circulation control technology to produce large values of lift advantageous for wind turbine design since any increase in the magnitude of the lift force (while keeping drag small, and l/d high) will immediately contribute to a corresponding increase in induced thrust and torque will be taken into consideration. numerical simulation carried out by previous investigator (tongchitpakdee [17,18]) looked into two approaches of introducing coanda jet, i.e. , at the appropriately chosen point in the vicinity of the trailing as well as leading edge. a leading edge blowing jet was found to be helpful in increasing power generation at leading edge separation cases,while atrailing edge blowing jet otherwise. with such background the present work is aimed at the search for favorable coanda-jet lift enhanced configuration for windmill designs. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 23 for this purpose, a rigorous review of coanda-jet circulation control airfoil in twodimensional subsonic flow is performed. numerical simulation using commercially available navier-stokes cfd codes is carried out and critically analyzed. results obtained from recent researches will be utilized for validation. tongchitpakdee [18] found that best lift enhancing effect could be facilitated by designing the lower part of the trailing edge surface to be flat and this finding is also incorporated in the present numerical investigation. the case studies performed here use normalized dimension: airfoil chord length of 1m. these correspond to a reynolds number of the order of 106, which is considered to be a typical situation. 3. objectives in the combined theoretical and numerical analyses, one is lead to come up with desired logical cause and effect laws as well as to find ways to carry out optimization schemes to arrive at desired design configurations. it is with such objectives in mind that parametric studies may offer some clues on relevant parameters which may be utilized in a multi-variable optimization (and to a larger scale, multi-disciplinary optimization). in this conjunction, the present work will address the following aspects: a) the influence and the effectiveness of the coanda enhanced lift for a comprehensive series of configurations, for axial thrust (lift), mass flow rate or torque producing mode; the corresponding gain or changes in lift, drag (or l/d ratio) will be assessed. b) parametric study for obtaining optimum configuration of the coanda effect lift enhanced airfoil. c) the feasibility and practicability of coanda configured airfoil for wind-turbine applications. 4. methodology, computational set-up and validation 4.1 bases of numerical analysis in this approach, two-dimensional unsteady compressible reynolds-averaged navierstokes equations are solved in integral form on a computational grid surrounding a reference airfoil using the finite volume method. the cfd code utilized for this purpose is comsol®1. prior to its utilization, various baseline cases have been tried out, with favorable results. as a case in point, for benchmarking purposes the code has been applied to calculate the liftslope characteristics of naca2412 airfoil. the results as shown in fig. 2 demonstrated its applicability for the present investigation. all computations in the present study were performed on a laptop computer with a 2.00 ghz intel core duo processor, 1 gb of ram, and 32-bit operating system. typical computation time for the computation of the flow characteristics around a two dimensional airfoil is 115.565 seconds with 62243 degrees of freedom by using stationary segregated 1 made available for our present work for trial purposes by i-math co., singapore. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 24 solver in k  turbulent model analysis. with such computational environment, which in consequence limits the computational grids, the present work will seek and adopt appropriate cfd numerical procedures. simplified theoretical analysis is carried out prior to the modeling and numerical computation, while further theoretical analysis will be carried out in evaluating the computational results. fig. 2: comparison of lift-curve slope of naca2412 airfoil from cfd computation using comsol code and experimental values [22, 28]. an objective review and analysis of the application of the first principle in the numerical computation will be carried out prior to the utilization of commercially available cfd codes for the present study. for this purpose some baseline validation is made. the comprehensive results as addressed in the objective of the work will be assessed to establish key findings that will contribute to the physical basis of coanda jets for lift enhancement in aerodynamic lifting surfaces. an analysis based on physical considerations will be carried out with reference to their application in propeller (or helicopter rotor) and wind-turbine blade configuration for design purposes. 4.2 computational grid in the present work, all calculations were performed by free mesh parameter grid generation using an algebraic grid generator. the meshing was carried out using free mesh parameter grid generator and varies from extremely coarse grid up to extremely fine grid. however, for the s809 airfoil case, near the surface of the airfoil, boundary-layer based meshing is carried out throughout. grid sensitivity study on the lift force per unit span for clean airfoil at zero angle of attack were plotted as depicted in fig. 3 and table 1 which defines and indicates the range of free mesh parameter. figure 3 shows that the slope of the line starting from normal meshing grid size becomes stable after fine grid is generated. therefore, the present analysis can be assumed to have an acceptable grid size with the choice of grid size in the range of normal up to extremely fine grid size since within this range the lift force does not change appreciably. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 25 fig. 3: grid sensitivity study on lift force per unit span for clean airfoil at zero degree angle of attack. table 1: the range of free mesh parameters. the grid generator is sufficiently general so that one can easily vary the jet slot location and size. grid spacing and clustering can have significant effects on wind turbine load and performance predictions, as reported in benjanirat [27]. in this conjunction, grid spacing and clustering have been considered carefully here, adjusted and verified following considerations depicted by fig. 3 and table 1. the computational domain and the grid in the vicinity of the airfoil surface and coanda-jet slot are exhibited in fig. 4. 4.3 turbulencemodeling considerations based on results established in the literature, the menter’s shear stress transport (sst) k- turbulent model [23] will be adopted as the baseline in the present investigation. the application of such model and its acceptability in view of the objectives set up above should be assessed, in particular with the application of menter’s sst k- or the spalart-almaras (sa) turbulent model. the turbulent model is used to define the wall function y+, which is widely employed to model the near-wall region. the idea is to place the first computational node outside the viscous sub layer, and make suitable assumptions about how the near-wall velocity profile behaves, in order to obtain the wall shear stress. wall functions use empirical laws to circumvent the inability of the k- model to predict a logarithmic velocity profile near a wall. with these laws it is possible to express the mean velocity parallel to the wall and turbulence quantities outside the viscous sub layer in terms of the distance to the wall and wall conditions such as wall shear stress and pressure gradient, among others. hence, the wall iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 26 functions can be used to provide near-wall boundary conditions for the momentum and turbulence transport equations, rather than conditions at the wall itself, so that the viscous sub layer does not have to be resolved and the need for a very fine mesh is circumvented.the y+ values obtained using a chosen turbulent model are used as reference in the selection of gridsize near the airfoil surface and assessing the validity of the present computational results using comsol ®, since the coanda-jet thickness studied may be in the order of the local boundary layer thickness. figure 5 illustrates the state of affairs. (a) (b) fig. 4: (a) computational grid around a typical airfoil, shown here for s809 airfoil; (b) detail of a typical flow field in the vicinity of the coanda-jet near the trailing edge. in the utilization of the comsol® cfd code for the numerical experiments, careful considerations have been given in the appropriateness of the turbulence model adopted, in order to justify the numerical results obtained in the coanda-jet configured airfoil in the vicinity of the trailing edge. for this purpose the following review and analysis provide relevant information as a basis for the plausibility of the computational procedure adopted. the dimensionless, sub-layer scaled, distance in the boundary layer, signifying viscoussublayer length scale plays significant role in assessing the turbulence model utilized and the computation of flow characteristics associated with turbulent flow. similar to local reynolds number, the wall y+ is often used in cfd to describe how coarse or fine a mesh is for a particular flow. it is the ratio between the turbulent and laminar influences in a cell. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 27 (a) (b) fig. 5: (a) typical y+ values in the turbulent boundary layer from [24]; (b) velocity profiles in wall units for subsonic flow over flat plate, m = 0.2, rel = 1 × 106, medium grid [23, 24]. these data are used as reference in assessing the validity of the present computational results using comsol ®. 1 2 w y u y y v v           (1) iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 28 very close to the wall, viscous damping reduces the tangential velocity fluctuations, while kinematic blocking reduces the normal fluctuations. towards the outer part of the nearwall region, however, the turbulence is rapidly augmented by the production of turbulent kinetic energy due to the large gradients in mean velocity. accurate presentation of the flow in the near-wall region determines successful prediction of wall-bounded turbulent flows. however, the comsol® cfd software does not have the provision of utilizing menter’s shear stress transport k  turbulent model, which was intended for appropriate selection of the computational grid near the airfoil surface as well as validity check on the computational procedure for further use in the parametric study. therefore, resort is made to an earlier wilcox’s k  turbulent model [24]. applying the present cfd code for the case of flat plate in similar conditions for re = 1x106 like those considered by rumsey and spalart [25], the velocity profile is given in fig. 6(a) (also placed as an insert in fig. 6(b)). comparing these results to fig.5, taken from [23, 26], one may conclude that the present procedure to predict velocity profile near the wall can be justified for the present reynolds number value and if there are no separation, but need further refinement for higher reynolds numbers where boundary layer separation may ensue. (a) (b) fig. 6: velocity profiles in wall units for subsonic flow over flat plate, 6re 1 10  , medium grid (as a basis for justification of the present numerical simulation) [23, 26]. the inset is the computational verification result using comsol and wilcox k   turbulence model. 4.4 baselinevalidation another study is carried out to compare the present computational results for the pressure distribution on naca2412 airfoil with results obtained using airfoil 2.1® code, which only uses navier-stokes equation for laminar boundary layer, as exhibited in fig. 7. taking into account that the present study is carried out within limited range of reynolds number and flow without separation, it may be surmised that for the parametric study of coanda-jet effects on the l/d performance of a two-dimensional airfoil, the utilization of the present procedure and comsol® cfd code can carried out within such limitation. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 29 fig. 7: comparison of pressure distribution curve on naca2412 airfoil at 6re 1 10  as compared to that obtained by using aerofoil 2.1® cfd software (demo-version). fig. 8: construction of rounded trailing edge; note the flat surface at the lower side of the airfoil in the vicinity of the trailing edge (dimension in meter). 4.5 boundaryconditions nonreflecting boundary conditions are applied at the outer boundaries of the computation domain. the jet is set to be tangential to the blade surface at the coanda-jet nozzle location. the jet velocity profile is specified to be uniform at the jet exit.on the airfoil surface, except at the jet exit, no-slip boundary conditions are applied. to gain benefits, the jet velocity should be designed to be larger than the potential flow velocity at the vicinity of the outer edge of the boundary layer. in addition, the thickness of the coanda jet is designed to be less than the local boundary layer thickness. 4.6 computationalstudies on airfoil for wind-turbine application a thorough review has been made in the computational procedure adopted by the cfd code in the present numerical experiments, in the sense that first principles of mass, momentum and energy conservation have been followed closely, as well as that appropriate boundary conditions have been applied for the particular problem considered. validation of the outcome of these procedures are exemplified by critical assessment of baseline cases, such as that illustrated by fig. 2. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 30 in order to assess by numerical means the lift enhancing effect of coanda-jet, baseline study will first be carried out on naca2412, which is considered to be typical for wind turbine application. the free-stream velocity and the chord-length of the airfoil chosen for the study are taken to be commensurate with typical wind-turbine situation for reynolds number of 106 (one million). a coanda-jet configuration will then be developed, by modifying its trailing edge to be rounded, adding a back step in the vicinity of the rounded trailing edge and assuring continuous and smooth upper surface curve, and then choose the coanda-jet (hence back-step) thickness and its velocity. in the parametric study carried out, the jet velocity is chosen to be the same or larger than the local velocity at the outer edge of the boundary layer. from these parametric studies, some impression on the best configuration could be obtained. based on the information gained from there, similar parametric study is then carried out for s809 airfoil, which is a typical airfoil specifically designed and utilized for hawt’s applications [20] and investigated in [16-19]. (a) (b) (c) fig. 9: (a) velocity field, naca 2412; (b) pressure distribution, naca 2412; (c) velocity streamlines near the trailing-edge of naca 2412 airfoil. 5. resultsand discussion 5.1 designstudy results for baseline airfoil initial assessment on the effect of adding a coanda jet on an airfoil in enhancing the lift using naca2412 should be accompanied by introducing rounded trailing edge.figure 10 describes the approach taken in this direction to arrive at rounded trailing edge configuration, taking into account that for best effect of coanda-jet configuration the lower surface near the trailing edge should be flat, as suggested by tongchitpakdee[17,18]. further assessment follows. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 31 (a)(b) (c) fig. 10: (a) velocity profile, naca 2412 with coanda-jet; (b) pressure distribution, naca 2412 with coanda-jet; (c) velocity streamlines near naca 2412 te, with coanda-jet. 5.2 computationalresults for naca2412 airfoil 5.2.1 computational results for clean (baseline) naca2412 airfoil in the analysis and assessment of airfoil in propeller and wind-turbine configurations, a comprehensive review will be carried out to assess its performance in a series of configurations, for axial thrust (lift), mass flow rate or torque producing mode; the corresponding gain or changes in lift, drag and moment will be assessed. figures 11a-12b typify the fluid property fields for flow around naca2412 airfoil in clean (baseline configuration), where v=10m/sec, chord length c=1m and reynolds number of 106.2notice the detail of the flow field exhibited there. 2 the reynolds number of 106 was chosen since we are looking at a medium size wind-turbine, for which such value would be typical. in the cfd work using comsol, for the naca2412 airfoil, reynolds number of 106was obtained by having assumed the approximate density and viscosity values of air to be =1 kg/m3 and =10-5 kg/m-sec, while for s809 actual typical values taken were =1.225 kg/m3 and =1.789x10-5.kg/m-sec. correspondingly, the appropriate velocity for the free-stream is 14.6 m/sec. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 32 (a) (b) fig. 11: (a) influence of coanda-jet location (naca 2412); (b) influence of back-step angle (naca 2412) iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 33 (a) (b) fig. 12: (a) influence of jet thickness (naca 2412); (b) influence of coanda jet influx velocity (naca 2412) 5.2.2 computationalresults for coanda-jet configured naca2412 airfoil figures 10a-12b typify the fluid property fields for flow around coanda-jet configured naca2412 airfoil, where v=10m/sec, chord-length c=1m and reynolds number of 106. the trailing edge rounding has been carried out through parametric study by varying its radius, following the procedure illustrated in fig. 8, and a reasonable (optimum in first inspection sense) round-off radius rte = 10mm is set. the effect of varying the coanda-jet nozzle location, back-step angle (with respect to local normal), coanda-jet thickness and velocity are exhibited in figures 11a-12b. the ensuing lift or l/d ratio could be set as the deciding variable for the choice of coanda-jet configuration. in summary, the introduction of coandaiium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 34 jet has resulted in increased (favorable) lift or l/d ratio, which can be tailored following the design objectives set. 5.3 computationalresults for s809 airfoil next, we would like to investigate the influence of specifically designed airfoil geometry for wind turbine application, and for this purpose a typical s809, in clean and coanda-jet equipped configurations. s809 airfoil represents one of a new series of airfoils which are specifically designed for hawt applications [17]. for the present study, the free-stream velocity v=14.6m/sec was assumed, while the chord-length c=1m and reynolds number of 106. the baseline for assessing the advantage of coanda-jet is the clean airfoil. for s809 the l/d for the clean configuration at zero angle of attack was found to be 6.78. in hawt optimum design, the wind-turbine blade may comprise different airfoil profiles at different radial sections. cfd computation for coanda-jet tailored s809 airfoil without coanda-jet is first carried out, and then followed by its corresponding coanda-jet configuration. 5.3.1computationalresults for coanda-jet configured s809 airfoil figures 13(a)-15(b) typify the fluid property fields for flow around coanda-jet configured s809 airfoil. appropriate (optimum by inspection) trailing edge rounding radius has also determined through parametric study for flow around s809 airfoil with back-step without coanda-jet. starting from the clean wing, the trailing-edge rounding and the positioning of the back-step is determined by carrying out parametric study by varying the trailing-edge rounding off radius rte. by varying this radius from 20 to 50mm, the l/d value varies as shown in fig. 13(a). the lower curve exhibits the computational result without coanda-jet. the determination of the optimum round-off radius at trailing-edge (lower-blue curve) is based on l/d as a criterion. based on this result, a radius of rte = 40mm was selected, since larger radii results in lower l/d values. when the coanda-jet is activated (upper-red curve), significant enhanced l/d performance is obtained with a shift in the optimum position. this result (and the following one) are commensurate with the rounding-off procedure such that a smooth upper surface always prevails (if the back-step height degenerates to zero), as depicted in figure 13(b). the placement of the back-step for coanda-jet blowing follows the procedure schematically depicted by fig. 8. further movement upstream gives less l/d, and it is not possible to move it further downstream. figure 14(a) shows the effect of coanda-jet nozzle location, i.e. the back-step, to l/d performance and indicated that the best back-step position is directly at the end of the quarter circle describing the rounding-off trailing-radius and tangent to it. figure 14(b) shows the influence of the back-step angle to l/d performance of the coanda-jet configured airfoil. the computation was carried out for back-step location at 85.9% (tangential), 85%, 75% and 70% of chordline measured from le. the optimum back-step angle with respect to the local vertical was found to be within 30 to 45 degree. further computation was then carried out using optimum configuration thus obtained. figures 15(a) and (b) exhibit parametric study results for coanda-jet thickness and velocity, respectively, which can be used to determine desirable design values from l/d ratio considerations. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 35 (a) (b) fig. 13: (a) parametric study to determine the optimum round-off radius at trailing-edge (lower-blue curve) using l/d as a criterion (s809); (b) illustration of the location of the back-step for coanda-jet for optimum results (s809) 5.4 analysis and discussion 5.4.1cfd results for coanda-jet configured naca2412 and s809 airfoils from the cfd numerical computations of the flow-field around two-dimensional airfoils naca2412 and s809, the introduction of coanda-jet as configured in the present work results in enhanced l/d, which depend on the jet velocity. in the present work, parametric study carried out started with uniform jet velocity with the same magnitude as the free stream velocity, and varied it until about twice as much. within this range, taking note of the particular rounding-off radius and back-step geometry, s809 results show monotonous increase of l/d, as shown in fig. 15f, while for naca2412, the introduction of coanda-jet may not give the desired effect for the jet velocity above a certain value (fig. 12b). iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 36 (a) (b) fig. 14: (a) influence of back-step location (s809); (b) influence of back-step angle; the backstep angle is measured from the local vertical to the chord at the backstep position (s809). iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 37 5.4.2 effect of coanda-jet3 it should be noted that for the purposes of the present work, a uniform jet velocity profile has been adopted, which could be readily modified for more realistic situation. numerical results indicate that there exists an optimum coanda-jet configuration, which has been the subject of parametric study as exhibited in fig.12 (naca2412) and fig. 15 (s809) in section 5.3. (a) (b) fig. 15: (a) influence of coanda-jet thickness (s809); (b) influence of coanda-jet velocity (s809). 3the present work is devoted only to two-dimensional airfoil performance studies through cfd numerical experiments, and has been motivated by works related to coanda-jet circulation control for improved performance of wind-turbines (in particular but not exclusively hawt). some discussions on the comparison of the application of coanda jet for airfoil in propeller configuration is elaborated in an earlier work [28]. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 38 following the investigation carried out in [2, 4], the coanda-jet (jet slot) boundary condition is specified by the momentum coefficient of the jet, c , which for our twodimensional modeling an equivalent constant *c can be defined as: 2 * 2 21 1 2 2 coanda jet coanda jet coanda jet ref airfoil mv v t c v a v c             (2) assuming that the density of the coanda-jet is the same as the density of the ambient air. this expression shows that for a given constant *c , changing the thickness of the coanda-jet will affects *c favorably. for the three-dimensional configuration, there is a physical relationship between the wind-turbine shaft torque (which is a direct measure of the shaft power extracted) with c , and in the actual three-dimensional case, the wind-turbine rotor yaw angle [17, 18]. tongchitpakdee [18] indicated that for the baseline unblown case, which here corresponds to the clean airfoil configuration, the turbine shaft torque cannot exceed the value given by theoretical betz limit of, 28 27betz wind turbine rotor p a v    (3) where v is the wind speed, but with the introduction of coanda-jet, this limit can be exceeded. in this conjunction, with the present numerical results gained thus far, it can be surmised that circulation control, which in this particular case obtained by utilizing trailing-edge coanda-jet, through the l/d increase and hence the increased value of *c given by equation (2), increases the torque generated. however, the betz limit as given by equation (3), may not be exceeded, since the input energy for the coanda-jet should also be considered. to justify the results of the present study, and to give us a physical explanation of the effect of coanda-jet, one may attempt to carry out simple calculation using first principle and kutta-joukowski law for potential flow. in this conjunction, the lift of the coanda-jet configured airfoil is equal to the lift of the clean one obtained using comsol® cfd code and lift contributed by the coanda-jet, and is given by  coanda configured airfoil clean airfoil coanda jet coanda jetl l v v h       (4) where coanda jeth  is the moment arm of the coanda-jet with respect to the airfoil aerodynamic center. one then arrives at a very good conclusion on the contribution of the coanda-jet to the lift (surprisingly, using comsol® cfd results for the l values, the accuracy obtained by iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 39 using equation (4) was in the order of 1.39%). however, care should be exercised to insure valid modeling for comparison. 6. conclusion and further work the cfd numerical experiments carried out in this work serves as a first step towards better understanding of the characteristics of coanda-jet lift enhanced airfoil configuration and how it can be best utilized. the studies carried out thus far have shown that the effect of coanda-jet is effective in producing enhanced lift. by physical reasoning and extension to three-dimensional case, enhanced sectional lift could then contribute to increased torque for wind turbine application, and increased axial thrust for propeller application. noting how one can tailor the coanda-jet configuration, which in the present case has been configured in the vicinity of the trailing edge, the present results are encouraging and can be further pursued for extended parametric studies and design oriented applications. rounding-off of the trailing edge for introducing coanda-jet seems to be more convenient and effective in gaining l/d increase for wind turbine specifically designed airfoil, here exemplified by s809. such result may be due to the relatively large trailing edge angle of the wind turbine specifically designed airfoil, and may lead to better aerodynamic performance of such airfoil compared to the reference airfoil used as the baseline (see fig. 13a). the results thus far obtained are computed for two-dimensional airfoil configuration, and their effects in modifying aerodynamic performance in general agree with those obtained for three-dimensional results of tongchitpakdee [17-18]. hence, the two-dimensional numerical study can be used to extend further utilization of the cfd computational procedure to the three-dimensional wind-turbine blade studies and design optimization. numerical results presented have been confined to zero angle-of-attack case, which has been considered to be very strategic to exhibit the merit of coanda-jet as lift enhancer. the numerical studies could be extended to increasing angle of attack to obtain more comprehensive information, for which the choice of turbulence model will be more crucial. based on the work and results thus far obtained, further computational studies and design optimization of wind-turbine blades, comparison of coanda-jet lift enhanced airfoil with other related configurations such as gurney flap or jet flap (which is beyond the scope of the present study) could be readily carried out. power requirements and power performance index (which should be carefully and objectively defined) should also be studied for practical design requirements. acknowledgement the work reported here has been carried out as part of the research carried out within the university putra malaysia research university grant scheme (rugs) no. 05-02-10-0928ru initiated in april 2010. the authors would like to thank dr.abdul aziz of upm for stimulating discussions, in particular for turbulent modeling, dr. faizal mustapha for facilitating the research and i-math co. for making available comsol software for our trial iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 40 runs. the corresponding author would like to thank university putra malaysia (upm) and universitas al-azhar indonesia for the opportunity to carry out this research. references [1] lan, c. edward and campbell,james f. , “theoretical aerodynamics of upper-surface blowing jet-wing interaction”, nasa tn d-7936, november 1975. [2] harris, michael j., “investigation of the circulation control wing/ upper surface blowing high-lift system on a low aspect ratio semispan model”, report dtnsrdc/ased-81/10, david taylor naval ship rand center, aviation and surface effects department, bethesda, maryland, may 1981. [3] englar, r. j., smith, m. j., kelley, s. m., and rover, r. c. iii., “application of circulation control to advanced subsonic transport aircraft, part i: airfoil development”, journal of aircraft, vol. 31, no. 5, sep. 1994, pp. 1160-1168. [4] englar, r. j., smith, m. j., kelley, s. m., and rover, r. c. iii., “application of circulation control to advanced subsonic transport aircraft, part ii: transport application”, journal of aircraft, vol. 31, no. 5, sep. 1994, pp. 1169-1177. [5] zhulev, yu. g. and inshakov, s. i., “on the possibility of enhancing the efficiency of tangential blowing of a slit jet from an airfoil surface”, fluid dynamics, vol. 31, no. 4, plenum publishing corporation, 1996, translated from izvestiya rossiiskoi akademii nauk, mekhanika zhidkosti gaza, no. 4, pp. 182-186, july-august, 1996. [6] gad-el-hak, mohamed, “modern developments in flow control”, in applied mechanics reviews, vol. 49, pp. 365–379, 1996. [7] englar, robert j., “advanced aerodynamic devices to improve the performance”, economics, handling and safety of heavy vehicles, sae technical paper series 2001-01-2072. [8] liu, y., sankar, l. n., englar, r.j., and ahuja, k., “numerical simulations of the steady and unsteady aerodynamic characteristics of a circulation control wing”, aiaa 2001-0704, 39th aiaa aerospace sciences meeting, reno, nv. [9] liu, y., “numerical simulations of the aerodynamic characteristics of circulation control wing sections”, phd dissertation, georgia institute of technology, may 2003, www.ae.gatech.edu/~lsankar/nasa_ccwuth. [10] wu, jingshu, sankar, lakshmi and kondor, shayne, “numerical modelling of coanda jet controlled nacelle configuration”, paper aiaa-2004-0228, 42nd aiaa aerospace science meeting and exhibit, reno, nevada, 58 jan 2004. [11] mamou, m. and khalid, m., “steady and unsteady flow simulation of a combined jet flap and coanda jet effects on a 2d airfoil aerodynamic performance”, revue des energies renouvelables cer’07 oujda (2007) 55 – 60. [12] shojaefard, m.h., noorpoor, a.r., avanesians, a. and ghaffarpour, m., “numerical investigation of flow control by suction and injection on a subsonic airfoil”, american journal of applied sciences 2 (10): 14741480, 2005. [13] sinha, sumonk., “optimizing wing lift to drag ratio enhancement with flexible-wall turbulence control”, http://sinhatech.com/ aiaa-2007-101apa21-draft.pdf. [14] radespiel, r., pfingsten, k.-c. and jensch, c., “flow analysis of augmented high-lift systems”, tu braunschweig, institut für strömungsmechanik, bienroder weg 3, d-38108 braunschweig, germany, hermann schlichting – 100 years memorial volume, nnfm 102, pp. 168–189, springerlink.com, © springer-verlag berlin heidelberg 2009. iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 41 [15] day, terry, “the coanda effect and lift”, copyright 2008. terry@vortex-dynamics.com.au; http://www.newfluidtechnology.com.au/the_coanda_effect_and_lift.pdf. [16] xu, guanpeng, and sankar, l. n., “computational study of horizontal axis wind turbines”, uasme journal of solar energy engineering, vol. 122, no. 1, february 2000, pp. 35-39. [17] tongchitpakdee, chanin, benjanirat, sarun and sankar, lakshmi n., “numerical studies of the effects of active and passive circulation enhancement concepts on wind turbine performance”, journal of solar energy engineering, transactions of the asme, vol. 128, november 2006, pp. 432-444. [18] tongchitpakdee, chanin, “computational studies of the effects of active and passive circulation enhancement concepts on wind turbine performance”, phd dissertation, georgia institute of technology, august 2007. [19] xu, g., “computational studies of horizontal axis wind turbines”, phd dissertation, school of aerospace engineering, georgia institute of technology, atlanta, ga, 2001. [20] tangler, j., et al., “seri advanced wind turbine blades”, international solar energy society conference, denver, colorado, 1991. [21] sommers d.m. and tangler, j.l., “wind-tunnel tests of two airfoils for wind turbines operating at high reynolds numbers”, nrel report, june 2000. [22] anderson, john d., jr., “introduction to flight”, mcgraw-hill international edition, singapore, 2005. [23] menter, florian r., “advances in turbulence modelling of unsteady flows”, ansys, germany, © 2009 ansys, inc, 2009; also menter shear stress transport model, http://turbmodels.larc.nasa.gov/sst.html. [24] wilcox, d.c., “turbulence modeling for cfd”, dcw industries inc., 1998. [25] rumsey, christopher l. and spalart,philippe r., “turbulence model behavior in low reynolds number regions of aerodynamic flow fields”, 38th aiaa fluid dynamics conference and exhibit, seattle, wa, june 23 – 26, 2008. [26] salim, salim m. and cheah, s.c., “wall y+ strategy for dealing with wall-bounded turbulent flows”, proceedings of the international multi-conference of engineers and computer scientists 2009 vol. ii, imecs 2009, hong kong, march 18 20, 2009. [27] benjanirat, sarun, “computational studies of horizontal axis wind turbines in high wind speed condition using advanced turbulence models”, phd thesis, georgia institute of technology, december 2006. [28] abdul hamid, m.f., djojodihardjo, h., suzuki, s. and mustapha, f., “numerical assessment of coanda effect as airfoil lift enhancer in wind-turbine configuration”, paper rcmeae-131, proceedings, regional conference on mechanical and aerospace technology, bali, february 910, 2010. nomenclature cfd computational fluid dynamic ccw circulation control wing hawt horizontal axis wind turbine m mach number l/d lift over drag ratio iium engineering journal, special issue, mechanical engineering, 2011 djojodihardjoet al. 42 coanda jeth  moment arm of coanda-jet with respect to airfoil aerodynamic center te trailing edge stol short takeoff landing y dimensionless wall distance for a wall-bounded flow v wind speed m/sec rte trailing edge radius mm c airfoil chord length m l lift force n d drag force n h coanda jet thickness mm rte trailing-edge rounding off radius m u friction velocity m/sec y distance to the nearest wall m v kinematic viscosity m2/s w wall shear stress n/m 2  density kg/m3 microsoft word 4_vol17_no1_2016_(compiledversion_4).docx iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 127 harmonic components estimation in power system using bacterial foraging optimization algorithm and stochastic gradient algorithm with variable forgetting factor ahmad mohammadzadeh, jalil sadati*, and behrooz rezaie department of electrical & computer engineering, babol university of technology, babol, iran. ahmad.mohammadzade7@gmail.com; *j.sadati@nit.ac.ir; and brezaie@nit.ac.ir (received: 11 may. 2015; accepted: 15 sept. 2015; published on-line: 30 apr. 2016) abstract: in this paper, a hybrid configuration algorithm called stochastic gradient method with variable forgetting factor (sgvff) is proposed to better estimate unknown parameters in a power system such as amplitude and phase of harmonics using variable forgetting factor following the bacterial foraging optimization algorithm (bfo). it must be mentioned that harmonic estimation is a nonlinear problem and using linear optimization algorithms for solving this problem reduces the convergence speed. thus, bfo algorithm is used for initial estimation. in this paper, first, using little information and by applying bfo algorithm in an off-line procedure initial value for sgvff algorithm is achieved and then sgvff algorithm is gained in an on-line procedure. in the hybrid algorithm applied in this paper, amplitudes and phases are estimated simultaneously. simulation results indicate that the proposed method has faster convergence speed, better performance and higher accuracy in a noisy system in comparison with recursive least squares variable forgetting factors algorithm (rlsvff). this proves the superiority of the proposed method. abstrak: dalam kertas ini, algoritma konfigurasi hibrid yang dipanggil stokastik kaedah kecerunan dengan faktor lupaan berubah-ubah (sgvff) dicadangkan untuk anggaran parameter yang tidak diketahui lebih baik dalam sistem kuasa seperti amplitud dan fasa harmonik menggunakan faktor lupaan pembolehubah diikuti dengan algoritma pengoptimuman mencari makan bakteria (bfo). harus dinyatakan bahawa anggaran harmonik adalah masalah bukan linear dan menggunakan algoritma pengoptimuman linear untuk menyelesaikan masalah ini mengurangkan kelajuan penumpuan. oleh itu, algoritma bfo digunakan untuk anggaran awal. pertama, dengan menggunakan sedikit maklumat dan algoritma bfo dalam prosedur luar talian, nilai awal untuk algoritma sgvff dicapai dan kemudian algoritma sgvff diperolehi dalam prosedur dalam talian. dalam algoritma hibrid yang digunakan dalam kertas kerja ini, amplitud dan fasa dianggarkan secara serentak. hasil simulasi menunjukkan kaedah yang dicadangkan mempunyai kelajuan penumpuan lebih pantas dengan nilai sebenar, prestasi yang lebih baik dan ketepatan yang lebih tinggi dalam sistem yang bising berbanding dengan algoritma rekursif kuasa dua terkecil pembolehubah faktor lupaan (rlsvff). ini menunjukkkan keunggulan kaedah yang dicadangkan. keywords: power system harmonic; bfo algorithm; sgvff method; rlsvff method iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 128 1. introduction nonlinear loads such as power-electronic devices, induced furnaces, computers, compact fluorescent lamp, etc. cause harmonics and disturbances in power systems. some devices such as computers and upss are very sensitive to harmonics. the current and voltage of harmonics increase the power loss, transient voltages, transformers saturations and longevity of sensitive electronic devices. unfavorable effects of harmonics in the network clarify the necessity of studying about harmonic involving modeling measuring and estimating amplitude and phase of harmonic components. thus, use of an effective method is essential for measuring frequency in the presence of noise and high order harmonics. the effects of harmonics in power systems can be decreased by using harmonic filters and harmonic suppressors [1-3]. before designing such filters, the amplitudes and phases of harmonics generated in power systems must be known. thus, estimation of harmonics is an important problem in power systems. a wide range of techniques applied in such problems is discussed: estimating the phase angle and measuring bus voltage and high order harmonics in a noisy system using kalman filter are explained in [4].these results are useful in studying harmonic distortions. in [5-7], a kalman filter is applied for analysis of harmonics in power system. the kalman filter introduces observation error equation by statistical investigation of signal for estimation and linearization. this is used for analysis of power systems with harmonics of order 5, 7, 11 and 13 and signal-to-noise ratio (snr) of 400 with a gaussian noise of 0.01 in ordinary condition and sudden changes of frequency. in [8-10], the newton method is used for estimation of harmonics in power systems. however, large computational effort is a disadvantage of this method. in [11], the least square method (ls) is proposed for harmonic estimation. the method is proposed together with fft methods and the kalman filter. simulation methods verify that estimation of harmonic components using the ls method has many advantages with respect to other methods due to fewer required computations. in [12], three methods such as the discrete fourier transform (dft), least absolute value (lav) and least square (ls) method are used to estimate the harmonics. among these methods, lav leads to better results in harmonic estimation. in [13], the least mean square algorithm is presented for harmonic estimation in power systems. the weakness of this algorithm is in convergence speed. in [14], the adaptive linear neuron (adaline) method is used to estimate harmonics of time variant and time invariant signals. in [15], estimation of harmonics is divided into two sections. first, amplitude is estimated using the ls method then phase component of harmonics is estimated by the adaline method. fast convergence, short processing time and little computation are advantages of this method. in [16], stochastic gradient (sg) algorithm is explained. in [1720], properties of multi-innovation stochastic gradient (misg) algorithm is described and the strength and weakness of the method are investigated. in [21], bfo algorithm is defined and in [22] a hybrid method called bfo-rls algorithm is applied to estimate the amplitude and phase of power signal. the advantage of the mentioned method is the accuracy of the tracking error. in [23], estimation of harmonics that are integer multiplication of the principal frequency is performed using least square method and genetic algorithm. in [24], robust harmonic estimation of a time variable signal is investigated using rlsff method. in [25, 26], rls algorithm with variable forgetting factor is explained. the main problem in harmonic estimation is based on this fact that harmonic generating loads exist in power systems naturally and their amplitudes are also different. thus, a method is required that needs fast measurement and accurate estimation of harmonic signals. even though, estimation of higher order harmonics in time variable signals using rlsff method involves few computations; it involves large initial estimation error and slow convergence; since iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 129 harmonic estimation is a nonlinear problem and using linear optimization methods to solve such problems make the convergence speed slow, consequently we use a heuristic optimization method. experimentation with several benchmark functions reveal that bfo possesses a good convergence speed and final accuracy[27-29] as compared to other naturally inspired optimization techniques like the genetic algorithm (ga) [30] particle swarm optimization (pso) [31] and differential evolution (de) [32]. therefore, this paper uses bfo algorithm for initial estimation in an off-line stage on a few data smples. the bfo method is used to estimate unknown parameters based on minimization of a cost function, which is used as an initial value of the parameters for sgvff. the sgvff method is then applied on-line and recursively for reminded data. first, bfo estimates unknown parapeters of system (off-line), then sgvff updates it recursivly (on-line) weight updating using (sgvff) +output error input desired output power system (plant) fig. 1: structure of sgvff-bfo estimation scheme. the proposed method enhances the performance and reduces overall convergence speed. figure 1 shows the proposed estimation scheme of employing the bfo-sgvff combined algorithm. first, a little input signal is fed to the bfo algorithm. unknown parameters (weight vectors before initialization) are optimized using the bfo algorithm. optimized output of bfo is taken as the initial values of weights for sgvff. then weights of sgvff are updated using a recursive rule.in the applied hybrid method, the amplitudes and phases of the principal component of the harmonic is estimated from the output of sgvff algorithm simultaneously.the rest of the paper is organized as follows: in section 2, harmonic estimation of power systems is presented. in section 3, the bfo optimization algorithm is explained and in section 4, a description of the sgvff algorithm is investigated. in section 5, rlsvff and sgvff algorithms are compared. in section 6, bfo-sgvff hybrid algorithm is proposed for estimation of harmonics. in section 7, simulation results are shown and conclusion is presented in section 8. 2. harmonic estimation of power system first, it is assumed that the voltage and current waveform of the power system is with an angular frequency of ω as a principal and known harmonic and as a sum of harmonics with unknown amplitude and phase. the disturbed power signal is modeled as: iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 130 (1) y(t) = sin( ω + ) + ( ) where is the number of harmonics and = 2 and is the principal frequency and ( ) is an additive gaussian white noise. if equation (1) is written in discrete form: (2) y = a sin(ω kt + φ ) + = : angular velocity : phase of nth harmonic : amplitude of nth harmonic : sample time : white guassian noise with zero mean and variance of equation (2) can be written as a linear regression problem as follows: (3) ( ) = x (k) ( ) where: (4) x(k) = [sin( ), cos( ) , … , sin( ), ( )] (5) ( ) = [ cos( ), sin( ), . . , cos( ), sin( )] where the regression ( ) is a vector of known data and ( ) is the vector of unknown parameters. ( ) is achieved by solving an optimization problem (assuming = ( ) ) and then the amplitude parameter and the phase parameter correspond with the nth harmonic are calculated as follow: (6) = + (7) φ = tan ( ) where is the order of the harmonic. 3. bacterial foraging optimization method in this section, a brief description of the bfo algorithm is presented [21, 22]. the concept of bacterial foraging optimization algorithm is based on the fact that in nature, animals with a low sense of foraging are more probably extinct in comparison with animals with high sense of foraging. through many of generations, animals with low sense of foraging are extinct or transformed to better forms. the e. coli bacteria that lives in human iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 131 intestines has a four-step foraging method. these steps are chemotactic, swarming, reproduction and elimination and dispersal (for detail see [21, 22]). bfo algorithm can be described in the following steps: iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 132 fig. 2: flow chart of bfo-sgvff algorithm. 4. description of algorithm (sgvff) stochastic gradient algorithm with variable forgetting factor is widely used in signal processing and parameter estimation in adaptive control [16-20]. the advantages of this algorithm are fewer computations, fast estimation and high convergence in time variable systems. consider the following linear regression model: (8) ( ) = ( ) + ( ) where ( ) ∈ is the system output, ( ) ∈ r is the system information vector (input, output), ( ) ∈ is a gaussian white noise with zero mean and θ is the estimation of θ at time k. assume ( ) = 0, ( ) = 0 and ( ) = 0 for ≤ 0. { ( ), ( )} is the available measured information. for simplicity, it is assumed that k is the present time, thus ( ) and ( ) are the present information. using stochastic gradient principal (sg), recursive sg identification algorithm is defined as follows: iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 133 (9) e(k) = y(k) − (k)θ(k) ∈ r matrix ( ) and output ( ) is as follow: (10) x(k) = [x(k), x(k − 1), … , x(k − p + 1)] ∈ r (11) y(k) = [y(k), y(k − 1), . , y(k − p + 1)] ∈ r stochastic gradient algorithm is defined as follows [26]: (12) θ(k) = θ(k − 1) + (k) r(k) e(k) (13) e(k) = y(k) − x (k)θ(k − 1) (14) r(k) = λ r(k − 1) + ‖ (k)‖ , (0)˃0 λ = λ + (1 − λ ) × log ( / ) where is the forgetting factor and is defined as a variable, is an arbitrary constant value. (15) (k) = [ (k), (k − 1), … , (k + 1)] ∈ r (16) ( ) = [ ( ), ( − 1), … , ( + 1)] ∈ 5. comparison of rlsvff and sgvff algorithm in this section comparison of sgvff and rlsvff algorithms is shown in table 1. table 1: comparison of sgvff and rlsvff algorithms siso system system ( ) = ( )θ + ( ) ( ) ∈ r و ( ) ∈ r ( ) ∈ r θ و ∈ r initial value procedure of the algorithm from equation(17-20) parameter estimation vectorθ(k) ∈ r : gain vector: l(k) = p(k) ( ) ∈ r error vector: e(k) = y(k) − (k − 1)θ(k) ∈ r covariance matrix: p(k) ∈ r × rlsvff algorithm procedure of the algorithm from equation(9-14) gain vector: l(k) = ( ) ( ) ∈ r error vector: e(k) = y(k) − (k −)θ(k) ∈ r variable forgetting factor: = + (1 − ) × ( / ) sgvff algorithm iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 134 6. hybrid configuration of the proposed bfo-sgvff algorithm for harmonic estimation the flowchart of the proposed harmonic estimation method is briefly shown in fig. 1 and is briefly illustrated in fig. 2. in this method, an initial signal with limited information is first introduced to bfo algorithm and unknown parameter namely is estimated by this method.optimal output of bfo algorithm is considered as an initial value of the unknown parameter namely (0) in sgff algorithm. then the updated ( ) is used through the procedure of sgff algorithm. also, estimation of harmonic component namely amplitude of based on updated ( ) is obtained from the output of sgvff algorithm according to some equations. using mentioned hybrid configuration is due to this fact that in estimation by sgvff method the convergence trend is highly sensitive to the initial guess. as a result, first by applying little and limited information through an off-line procedure using bfo algorithm, initial value of the parameters for sgvff algorithm is obtained and after calculation of this estimation, sgvff is applied in an on-line procedure. 7. simulation in this section, a power signal with time variable amplitude is considered for high, third and fifth order harmonic estimation. (17) ( ) = 1.5 + ( ) sin + 6 + 0.5 + ( ) sin 3 + 3 + 0.2 + ( ) sin 5 + 4 + ( ) where (18) ( ) = 0.15 2 + 0.05 2 ( ) = 0.05 2 + 0.02 2 ( ) = 0.025 2 + 0.005 2 and ( ) is a white gaussian noise with variance =0.1. equation (4) is rewritten for estimating the amplitude and phase: then, signal is transformed to a parametric form: (20) ( ) = [sin( ) cos( ) (3 ) (3 ) (5 ) (5 )] also, (19) ( ) = x (k) ( ) iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 135 (21) θ(k) = ⎣ ⎢ ⎢ ⎢ ⎢ ⎢ ⎡ cos( ) ( ) cos( ) sin( ) cos( ) sin( )⎦ ⎥ ⎥ ⎥ ⎥ ⎥ ⎤ where the vector of signal parameters is achieved as follows: (22) θ(k) = ⎣ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎡ 1.5 + ( ) cos 1.5 + ( ) sin 0.5 + ( ) cos 1.5 + ( ) sin 0.2 + ( ) cos 0.2 + ( ) sin ⎦ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎤ by assuming θ = ( ) ∈ and after updating unknown parameters, the main amplitude and phase and the third and the fifth harmonic is achieved as follows: (23) = + (24) = + (25) = + (26) φ = tan ( ) (27) φ = tan ( ) (28) φ = tan ( ) where , , and , , are the amplitudes and the phases estimation parameters respectively. as is described in section5, first by bfo algorithm and considering little information (here only first twenty samples of signal) initial estimation of the unknown parameters is achieved, then sgvff algorithm with variable forgetting factor is applied. meanwhile, = 0.2, = 100 and = 500. the principal power signal following with the estimated and reconstructed power signal by the proposed and rlsvff methods are depicted in fig. 3. estimation of parameters , and which are the amplitudes of the first, third and fifth harmonic respectively are depicted in fig.4, fig. 5 and fig. 6. also, estimation of parameters , and which are the phases of the first, the third and the fifth harmonic iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 136 respectively are depicted in fig. 7, fig. 8 and fig. 9. as can be seen from these figures, the proposed method provides better performance by appropriate initial estimation and then by fast convergence in comparison with the rlsvff method. fig. 3: estimation of reference signal. fig. 4: amplitude estimation of the first harmonic. fig. 5: amplitude estimation of the third harmonic. 0 0.05 0.1 0.15 0.2 0.25 0.3 -1.5 -1 -0.5 0 0.5 1 1.5 time(s) a m pl itu de (p u) actual bfosgvff rlsv-ff 0 0.05 0.1 0.15 0.2 0.25 0.3 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 time(s) a m pl itu de (p u) actual bfosgv-ff rlsv-ff 0.01 0.02 0.03 1.4 1.5 1.6 1.7 0 0.05 0.1 0.15 0.2 0.25 0.3 0 0.2 0.4 0.6 0.8 1 1.2 time(s) a m pl itu de (p u) actual bfosgv-ff rlsv-ff 0.01 0.015 0.02 0.5 0.52 0.54 0.56 iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 137 fig. 6: amplitude estimation of the fifth harmonic. fig. 7: phase estimation of the first harmonic. fig. 8: phase estimation of the third harmonic. 0 0.05 0.1 0.15 0.2 0.25 0.3 0 0.2 0.4 0.6 0.8 1 1.2 time(s) a m pl itu de (p u) actual bfosgv-ff rlsv-ff 0.01 0.02 0.03 0.1 0.2 0.3 0 0.05 0.1 0.15 0.2 0.25 0.3 0 10 20 30 40 50 60 70 time(s) p ha se (d eg ) actual bfosgv-ff rlsv-ff 0.01 0.02 0.03 28 30 32 0 0.05 0.1 0.15 0.2 0.25 0.3 -30 -20 -10 0 10 20 30 40 50 60 70 time(s) p ha se (d eg ) actual bfosgv-ff rlsv-ff 0.03 0.04 0.05 0.06 55 60 65 iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 138 fig. 9: phase estimation of the fifth harmonic. to show the performance of the proposed method, four criteria are used. these are the mean square value of the error (mse or variance), mean absolute value of the error (mae), error in percentage, and standard deviation. in equations (29) to (32), ( ) is the reference signal and ( ) is the estimated signal for kth sample that are used for comparison of the wave form achieved from applying bfo-sgvff and rlsvff methods on the components of power system harmonics the mean square value of error (mse): (29) = 1 [ ( ) − ( )] the mean absolute value of the error (mae) (30) = 1 | ( ) − ( )| error in percentage: (31) % = 1 [ ( ) − ( )] ( ( )) × 100 standard deviation: (32) = 1 [ ( ) − ( )] the results achieved from the above methods were presented in tables 2-5. the simulation results achieved for mse criteria were shown in table 2. table 3 is correspondent with mae criteria, table 4 is correspondent with the criteria of error in 0 0.05 0.1 0.15 0.2 0.25 0.3 -60 -40 -20 0 20 40 time(s) p ha se (d eg ) actual bfosgv-ff rlsv-ff 0.01 0.02 0.03 0.04 30 40 50 iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 139 percentage and finally table 5 shows the standard deviation. these tables show that the proposed method in all four mentioned criteria is better than rlsvff. also, fig. 10 and fig. 11 correspond with the comparison between the proposed method and rlsvff method in terms of harmonic amplitudes and phases. figures 12 and 13 correspond with mae criteria of the amplitude and phase. figures 14 and 15 are the error percentage of the amplitude and phase of the power system harmonic. figures 16 and 17 show the standard deviation of amplitude and phase estimation. the achieved results denote that the results of the proposed method are closer to the reference signal and is more applicable in comparison to rlsvff method. in addition, the convergence speed in our proposed method is faster than rlsvff method. table 2: comparison of the (mse) of bfo-sgvff with rlsvff phase amplitude method 5th harmonic 3rd harmonic 1st harmonic 5th harmonic 3rd harmonic 1st harmonic 7.414 0.156 0.0273 0.0001 0.0002 0.0003 bfo-sgvff 59.404 90.645 12.155 0.0012 0.0014 0.0094 rlsvff table 3: comparison of the (mae) of bfo-sgvff with rlsvff phase amplitude method 5th harmonic 3rd harmonic 1st harmonic 5th harmonic 3rd harmonic 1st harmonic 1.0446 0.5608 0.2037 0.117 0.0223 0.0275 bfo-sgvff 8.194 4.808 1.514 0.323 0.355 0.428 rlsvff table 4: comparison of the (%error) of bfo-sgvff with rlsvff phase amplitude method 5th harmonic 3rd harmonic 1st harmonic 5th harmonic 3rd harmonic 1st harmonic 4.46×10-3 1. 53×10-2 9.27×10-4 7.4417×10-5 1.133×10 4 1.963×10 -4 bfo-sgvff 27.68 15.67 2.73 5.63×10-4 5.36×10-3 1.43×10-2 rlsvff table 5: comparison of thestandard deviation ( ) of bfo-sgvff with rlsvff phase amplitude method 5th harmonic 3rd harmonic 1st harmonic 5th harmonic 3rd harmonic 1st harmonic 5.443 0.9737 0.239 0.0085 0.0031 0.0037 bfo-sgvff 11.093 8.985 3.8313 0.449 0.0488 0.3066 rlsvff iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 140 fig. 10: mse of amplitude harmonic estimation. fig. 11: mse of phase harmonic estimation. 1 2 3 4 5 6 7 8 9 0 1 2 mse amplitude estimation 1st harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 0.1 0.2 mse amplitude estimation 3rd harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 0.02 0.04 mse amplitude estimation 5th harmonic bfo sgvff rlsvff 2 4 6 8 2 4 x 10 -3 2 4 6 8 0.5 1 1.5 2 x 10 -3 2 4 6 8 0 5 10 x 10 -4 1 2 3 4 5 6 7 8 9 0 200 400 600 mse phase estimation of 1st harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 500 1000 mse phase estimation of 3rd harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 1000 2000 mse phase estimation of 5th harmonic bfo sgvff rlsvff 2 4 6 8 0 5 10 15 2 4 6 8 0 20 40 2 4 6 8 0 10 20 30 iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 141 fig. 12: mae of amplitude harmonic estimation. fig. 13: mae of phase harmonic estimation. 1 2 3 4 5 6 7 8 9 0 0.5 1 1.5 mae amplitude estimation of the 1st harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 0.5 1 mae amplitude estimation of 3rd harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 0.1 0.2 mae amplitude estimation of 5th harmonic bfo sgvff rlsvff 2 4 6 8 0.02 0.04 0.06 2 4 6 8 0.02 0.04 2 4 6 8 0.01 0.02 0.03 1 2 3 4 5 6 7 8 9 0 10 20 mae phase estimation of 1st harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 10 20 30 mae phase estimation of 5th harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 10 20 mae phase estimation of 3rd harmonic bfo sgvff rlsvff 2 4 6 8 1 2 3 2 4 6 8 2 4 6 8 2 4 6 8 2 4 6 8 iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 142 fig. 14: % error of amplitude harmonic estimation. fig. 15: % error of phase harmonic estimation. 1 2 3 4 5 6 7 8 9 0 0.5 1 error amplitude estimation of 1st harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 0.1 0.2 error amplitude estimation of 3rd harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 0.02 0.04 error amplitude estimation of 5th harmonic bfo sgvff rlsvff 2 4 6 8 0.4 0.6 0.8 2 4 6 8 0.015 0.02 0.025 0.03 0.035 2 4 6 8 2 4 x 10 -3 1 2 3 4 5 6 7 8 9 0 0.5 1 1.5 error phase estimation of 1st harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 2 4 6 error phase estimation of 3rd harmonic bfo sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 1 2 3 error phase estimation of 5th harmonic bfo sgvff rlsvff 2 4 6 1 1.5 2 x 10 -3 2 4 6 0.8 1 1.2 1.4 1.6 x 10 -3 2 4 6 1.5 22.5 33.5 x 10 -4 iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 143 fig. 16: standard deviation ( )of amplitude estimation. fig. 17: standard deviation ( ) of phase estimation. 2 3 4 5 6 7 8 9 0 10 20 standard deviation () of phase estimation: 1st harmonic sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 10 20 30 standard deviation () of phase estimation: 3rd harmonic sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 20 40 standard deviation () of phase estimation: 5th harmonic sgvff rlsvff 2 4 6 8 0.5 1 2 4 6 8 0 1 2 2 4 6 8 10 15 1 2 3 4 5 6 7 8 9 0 0.5 1 standard deviation () of amplitude estimation: 1st harmonic sgvff rlsvff 1 2 3 4 5 6 7 8 9 0.2 0.4 0.6 standard deviation () of amplitude estimation: 3rd harmonic sgvff rlsvff 1 2 3 4 5 6 7 8 9 0 0.1 0.2 0.3 standard deviation () of amplitude estimation: 5th harmonic sgvff rlsvff 2 4 6 8 0.01 0.02 0.03 2 4 6 8 0.06 0.08 0.1 0.12 2 4 6 8 0.015 0.020.025 0.03 0.035 iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 144 8. conclusion the main problem in harmonic estimation is due to the existence of harmonic loads in power systems and the amplitude of produced harmonics being different from one another. thus, a method is required that can measure and estimate harmonic signals as fast as possible. in this paper, a hybrid intelligent algorithm bfo-sgvff is proposed for the first time to estimate amplitudes and phases of the harmonic simultaneously in a noisy power system signal. enhancing the performance, the technique of variable forgetting factor is used. using this technique is more effective according to the time variability of the reference signal. the proposed hybrid algorithm is used since in estimation by recursive methods such as rlsvff, the convergence trend is highly dependent to the initial guess of the solution. thus in the proposed method, the initial value of the parameters for sgvff algorithm is achieved by first using little and limited information through an off-line procedure using the bfo algorithm. after this initial estimation, sgvff algorithm is applied in an on-line procedure. in fact, the output of bfo algorithm is used as an initial guess of the parameters in sgvff algorithm. the simulation results verify superior performance of this algorithm in comparison with rlsvff algorithm. references [1] tang, y., loh, p. c., wang, p., choo, f. h., gao, f., & blaabjerg, f. (2012) generalized design of high performance shunt active power filter with output lcl filter. industrial electronics, ieee transactions, 59(3):1443-1452. [2] bai, z., ma, h., xu, d., wu, b., fang, y., & yao, y. (2014) resonance damping and harmonic suppression for grid-connected current-source converter. industrial electronics, ieee transactions, 61(7):3146-3154. [3] hinduja, m., rathi, m., jaya christa, s. t., & prabha, n. r. (2015) pi control of multi-level inverter based shunt active power filter for harmonic mitigation in three phase systems. circuit, power and computing technologies (iccpct), international conference on ieee. [4] beides hm, heydt gt. (1991) dynamic state estimation of power system harmonics using kalman filter methodology. ieee transactions on power delivery, 6(4):1663-1670. [5] kennedy k, lightbody g, yacamini r. (2003) power system harmonic analysis using the kalman filter. ieee power engineering society general meeting, 2:752-757. [6] routray a, pradhan ak, rao kp. (2002) a novel kalman filter for frequency estimation of distorted signals in power system,” ieee trans. instrum. meas., 51(3):469-479. [7] costa, f. f., cardoso, a. j. m., & fernandes, d. a. (2007). harmonic analysis based on kalman filtering and prony's method. in power engineering, energy and electrical drives, 2007. powereng 2007. international conference on (pp. 696-701). ieee. [8] yang j, xi h, guo w. (2007) robust modified newton algorithm for adaptive frequency estimation. ieee trans signal process lett, 14(11):879-882. [9] xue sy, yang sx. (2009) power system frequency estimation using supervised gauss– newton algorithm. measurement, 42(1):28-37. [10] terzija vv, stanojevic v. (2007) two stage improved recursive newton-type algorithm for power-quality indices estimation. ieee trans power delivery, 22(3):1351-1359. [11] jiang x, king j, emadi a. (2004) a power harmonics detection approach based on least squares energy minimization principle. 30th annual conference of the ieee industrial electronics society, busan, korea, pp.2934-2938. [12] abu al-feilat ea, el amin i, bettayeb m. (1994) power system harmonic estimation and comparative study. elect. power syst. res., 29:91-97. [13] pradhan ak, routray a, basak a. (2005) power system frequency estimation using least mean square technique. ieee trans. power del., 20(3):1812-1816. iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 145 [14] dash pk, swain dp, routray a, liew ac. (1996) harmonic estimation in a power system using adaptive perceptrons. ieee procgener. transm. distribut., 143(6):565-574. [15] joorabian m, mortazavi ss, khayyami aa. (2009) harmonics estimation in a powersystem using a novel-hybrid least square–adaline algorithm. electric power system research, 79(1):107-116. [16] lai tl, wei cz. (1982) least squares estimates in stochastic regression models with applications to identification and control of dynamic systems. annals of statistics, 10(1): 154166. [17] ding f, xie xm, fang cz. (1996) multi-innovation identification methods for time-varying systems. acta automatica sinica, 22(1):85-91. [18] ding, f., ding, t., yang, j., & xiao, d. (2001). performance of multi-innovation identification for attenuating excitation of stochastic systems. journal-tsinghua university, 41(9), 115-117. [19] ding f, chen t. (2007) multi-innovation stochastic gradient identification methods. proceedings of the 6th world congress on intelligent control and automation (wcica2006), june 21–23, 2006, dalian, china. [20] ding f, chen h, li m. (2007) multi-innovation least squares identification methods based on the auxiliary model for miso systems. journal name??, 186(1)184-192. [21] passino km. (2002) bio-mimicry of bacterial foraging for distributed optimization and control. ieee contr. syst. mag., 22(3):52-67. [22] ray, p. k., & subudhi, b. (2012). bfo optimized rls algorithm for power system harmonics estimation. applied soft computing, 12(8), 1965-1977. [23] bettayeb, m., & qidwai, u. (2003). a hybrid least squares-ga-based algorithm for harmonic estimation. power delivery, ieee transactions on, 18(2), 377-382. [24] sahoo, h. k., sharma, p., & rath, n. p. (2011, december). robust harmonic estimation using forgetting factor rls. in india conference (indicon), 2011 annual ieee (pp. 1-5). ieee. [25] park, d. j., jun, b. e., & kim, j. h. (1991). fast tracking rls algorithm using novel variable forgetting factor with unity zone. electronics letters, 27(23), 2150-2151. [26] wang j. (2009) a variable forgetting factor rls adaptive filtering algorithm. ieee conference, beijing. 27-29 oct., pp1127-1130. [27] mishra s. (2005) a hybrid least square-fuzzy bacterial foraging strategy for harmonic estimation. ieee transactions on evolutionary computation, 9(1):61-73. [28] mishra s, bhende cn. (2007) bacterial foraging technique based optimized active power filter for load compensation. ieee transactions on power delivery, 22(1):457-465. [29] biswas, a., dasgupta, s., das, s., & abraham, a. (2007). a synergy of differential evolution and bacterial foraging optimization for faster global search. international journal on neural and mass-parallel computing and information systems-neural network world, 17(6), 607626. [30] holland jh. (1975) adaptation in natural and artificial systems. university of michigan press, ann arbor, usa. [31] kennedy j, eberhart r. (1995) particle swarm optimization. proceedings of ieee international conference on neural networks, pp1942-1948. [32] storn r, price k. (1997) differential evolution – a simple and efficient heuristic for global optimization over continuous spaces. journal of global optimization, 11(4):341-359. iium engineering journal, vol. 17, no. 1, 2016 mohammadzadeh et al. 146 ahmad mohammadzade was born in noor, mazandaran, iran in 1982.he received b.sc. in power engineering from islamic azad university of noor in 2012. he is currently is m.sc. student in control engineering in babol universit y of technology, babol, iran. his research interests is system identification, heuristic optimization algorithms, and harmonic estimation in power system. jalil sadati, was born in behshahr, mazandaran. he received m.sc. degree in ferdowsi university of mashhad, and ph.d. degree in control engineering from university of mazandaran, iran in 2005 and 2011, respectivly. he is assistant professor of control engineering in the department of electrical and computer engineering of babol university of technology from 2011. his research interests are fractional-order control, time delay systems, nonlinear control, adaptive systems, and model predictive control. behrooz rezaie was born in kermanshah in 1974. he received m.sc. degree and ph.d. degree in control engineering from iran university of science and technology, tehran, iran in 2001 and 2009, respectively. he is assistant professor of control engineering in the department of electrical and computer engineering of babol university of technology from 2010. his research interests are hybrid and complex nonlinear systems, and control theory and applications especially intelligent, adaptive and predictive control methods. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 3d collision avoidance system for unmanned aerial vehicle (uav) with decentralized approach mohamad haniff harun1,2,3*, shahrum shah abdullah1, mohd shahrieel mohd aras3, mohd bazli bahar1,3 and fariz ali@ibrahim3 1 department of electronic system engineering, malaysia-japan international institute of technology, utm kl campus, jalan sultan yahya petra, 54100 kuala lumpur, malaysia 2 faculty of electric and electronic engineering technology, universiti teknikal malaysia melaka, hang tuah jaya, 76100 durian tunggal, melaka, malaysia 3 underwater technology research group (uterg), center for robotics and industrial automation (ceria), faculty of electrical engineering, universiti teknikal malaysia melaka, 76100 durian tunggal, melaka, malaysia. * corresponding author: haniff@utem.edu.my (received: 23 march 2023; accepted: 20 may 2023; published on-line: 4 july 2023) abstract: unmanned aerial vehicles uavs have been developed and refined for decades. using an integrated software system, autonomous unmanned aerial vehicles (uavs) perform missions automatically and return to a pre-programmed point. malaysia has a lot of unoccupied airspace, yet autonomous uav applications and research are still rare. in critical conditions, autonomous uavs must deal with a variety of environmental and flight issues. this project involves a decentralized 3d collision avoidance system for an autonomous uav. ultrasonic, infrared, and laser rangefinders were chosen for the 3d collision avoidance system. the uav's obstacle recognition and collision avoidance performance are also tested in four experiments. in various flight conditions, the 3d collision avoidance system can identify several material types and opacities by integrating selected rangefinders. finally, the 3d collision avoidance system quickly reacts to obstacles in the x, y, and z axes. abstrak: kenderaan udara tanpa pemandu (uav) telah dibangunkan dan diperhalusi selama beberapa dekad. menggunakan sistem perisian bersepadu, kenderaan udara tanpa pemandu (uav) autonomi melaksanakan misi secara automatik dan kembali ke titik pradiprogramkan. malaysia mempunyai banyak ruang udara yang tidak berpenghuni, namun aplikasi dan penyelidikan uav autonomi masih jarang berlaku. dalam keadaan kritikal, uav autonomi mesti menangani pelbagai isu alam sekitar dan penerbangan. projek ini melibatkan sistem pengelakan perlanggaran 3d terpencar untuk uav autonomi. pencari jarak ultrasonik, inframerah dan laser telah dipilih untuk sistem pengelakan perlanggaran 3d. prestasi pengecaman halangan dan pengelakan perlanggaran uav juga diuji dalam empat eksperimen. dalam pelbagai keadaan penerbangan, sistem pengelakan perlanggaran 3d boleh mengenal pasti beberapa jenis bahan dan kelegapan dengan menyepadukan pencari jarak terpilih. akhir sekali, sistem pengelakan perlanggaran 3d bertindak balas dengan cepat terhadap halangan dalam paksi x, y dan z. keywords: decentralized 3d collision avoidance; unmanned aerial vehicle; rangefinder 373 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 1. introduction the ir 4.0 is increasing interest in autonomous uavs. a uav is an aerial vehicle that may be piloted from a distance [1]. uavs are of use in military and civilian/commercial applications due to their wide range, inexpensive maintenance, quick deployment, mobility, and ability to hover [2]. the military uses uavs for border security surveillance, reconnaissance, and target removal. unmanned aerial vehicles are also used for search and rescue, parcel delivery, precision horticulture, and pharmaceutical transport. multi-rotor drones, fixed-wing drones, single-rotor helicopters, and fixed-wing vertical take-off and landing (vtols) are the four main drone types, as shown in fig. 1. the fact remains that each key drone type has its own benefits and drawbacks. for example, multi-rotor drones may hover due to their vertical direction drive framework, while single-rotor helicopters can hover and rotate due to their vertical direction drive framework. to put it another way, this type of aerial vehicle has slow movement speeds and requires extra energy to fulfil tasks [3]. however, fixed-wing drones and fixed-wing hybrid vtols can travel long distances due to their propulsion system and aerodynamic surfaces. fixed-wing vtols (vertical takeoff and landing) can launch and land vertically without a runway [3]. however, fixed-wing drones have many drawbacks. fixed-wing aircraft require a lot of airspace to maneuver and direct themselves. other than that, the aerodynamic wing surfaces produce lifting power through air impacts. uavs have both military and commercial uses. they must be built to work in difficult settings, such as huge open spaces, dense tree clusters, or rocky mountain slopes [4]. as a result, uavs will struggle to achieve their missions in these hostile environments. outdoor operation of uavs is even more problematic due to gps errors, poor communication, and bad weather [5]. sensors enable uavs to scan their surroundings and avoid collisions. collecting accurate environmental data is important to avoiding crashes and completing the mission. due to the increasing utilization of multi-uav cooperative operations, 3d collision avoidance is crucial. when functioning centrally, an unmanned aerial vehicle assesses all colleagues' inputs and outputs to avoid collisions. while a central communication hub is beneficial, it is difficult to expand [6-8]. decentralized systems can also handle more uav teams in congested situations. these are more stable and robust. malaysia is believed to be falling behind in aerial vehicle research and development compared to countries like the us, china, and iran. limitations include lack of aeronautical knowledge, high sensor and communication system costs, and limited airspace. to boost malaysia's aeronautics industry, aerial vehicle research and development must continue. currently, only a few malaysian aerospace companies are researching and developing autonomous uavs to solve industrial and military concerns. in many situations, rapid deployment of aerial vehicles can change a crisis situation into a non-critical situation since they can gather information faster than humans. wildfires, medication delivery, crime fighting, and search and rescue are examples [9]. wildfires, like the 2019 amazon rainforest fires, can erupt at any time throughout the dry season [10]. also, the amazon rainforest covers 5.5 million km2, making human patrolling and scouting impractical. using flying vehicles to monitor the amazon rainforest could help limit the damage and mortality caused by wildfires. 374 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 fig. 1: types of drones. 2. theoretical background numerous theories and principles must be explored and incorporated into the design and development of the unmanned aerial vehicle with decentralized 3d collision avoidance system. aerodynamic forces, center of gravity (cg), and time of flight (tof) are all significant theories and principles of flight. 2.1 aerodynamic force all aircraft in flight are subjected to the forces of thrust, drag, lift, and weight. understanding how these forces interact and utilizing power and flight controls to manage them is critical for flight. thrust, drag, lift, and weight are the four forces that act on an airplane in level, unaccelerated flight [11]. these are the terms that are used to describe them: a) thrust—the force applied forward by the engine/propeller or rotor. it opposes or overcomes drag. by and large, it acts perpendicular to the longitudinal axis. b) drag—a rearward, retarding force created by the wing, rotor, fuselage, and other projecting items disrupting airflow. drag, on the other hand, opposes thrust and acts in the opposite direction of the relative wind. c) lift—is a force generated by the dynamic action of the air on the airfoil that acts perpendicular to the flight path through the center of lift (cl) and perpendicular to the lateral axis. lift opposes the downward force of weight in level flight. d) weight—the total weight of the aircraft, crew, fuel, and cargo or baggage. weight is a force that acts as a drag on the aircraft due to the force of gravity. it acts vertically downward through the aircraft's center of gravity (cg) and opposes lift. the sum of these opposing pressures is always zero in steady flight. according to newton's third law, there can be no unbalanced forces in steady, straight flight, because every action or force has an equal but opposing response or force. this is true regardless of whether you are flying level or ascending or descending. this is not to say that the four forces are equal. this signifies that the opposing forces are equivalent to one another and hence cancel out their effects. in fig. 2(a), the thrust, drag, lift, and weight force vectors appear to be identical in magnitude. the conventional explanation claims (without specifying) that thrust equals drag and weight equals lift. while this statement is true, it might be misleading. it should be known that the opposing 375 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 lift/weight forces are equal in straight, level, unaccelerated flight. additionally, they are greater than the opposing thrust/drag forces, which are equal only to one another. this revision of the conventional "thrust equals drag; lift equals weight" formula explains that during climbs and slow flight, a component of force is directed upward and functions as lift, while a piece of weight is directed backward in the opposite direction of flight and acts as drag. in sluggish flight, thrust is directed upward. however, because the aircraft is in level flight, weight has no effect on drag, as illustrated in fig. 2(b). (a) (b) fig. 2: (a) relationship of forces acting on an aircraft (b) force vectors during a stabilized climb. 2.2 centre of gravity (cg) a body in a gravitational field has an unlimited number of particles of varying sizes, each with its own weight. the total weight of the body is the resultant parallel force system created by those weights [12]. moreover, when the gravitational field is uniform over a body, the center of gravity is also the center of mass. the uav's center of gravity influences the uav's balance while in flight. to improve overall flying performance and minimize any instability issues, the uav's center of gravity must be on the same horizontal plane as the propellers. 2.3 vibration vibration is the oscillating motion of a system or body of attached bodies [13]. free vibration and forced vibration are the two main types of vibration. forced vibration is created by an external periodic or intermittent force, whereas free vibration is caused by gravitational or elastic restoring forces. a uav's vibrations come from its aerodynamic, mechanical, and flying motions. due to electronic components like flight controllers, inertial measurement units (imus), and sensors are susceptible to vibrations, multirotor uavs have motor-propeller produced vibrations. it is also vital to consider vibrations because a built uav vibrating at its normal frequency would be disastrous. so, it is critical to isolate electrical components from vibrations and limit uav vibrations as much as feasible. 2.4 time of flight (tof) the time-of-flight concept measures the distance between a sensor and an item by the time it takes for a signal to travel from the sensor to the object and back. the time-of-flight principle works with several signals (carriers), the most prevalent being sound and light [14]. light is the carrier for teraranger sensors because it combines speed, range, weight, 376 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 and eye-safety. as a result, infrared sensors perform better than other distance sensors of similar size and weight. (a) (b) fig. 3: (a) direct tof (b) indirect tof. time-of-flight (tof) sensors detect distances by measuring the time it takes photons to travel from the sensor's emitter to a target and back. as illustrated in fig. 3, both indirect and direct tof have particular advantages. both can measure a pixel's intensity and distance. direct tof sensors give out nanosecond-long light pulses and time how long it takes for some of the light to return. indirect tof sensors use continuous modulated light to calculate the distance to objects. the object distance from the sensor can be calculated using eq. 1, where d is the object distance and c is the sound or light speed. 𝑑 = 𝑐 × 𝑇𝑜𝐹 2 (1) 3. methodology this section contains a mechanical description and the concerns related to the design of the fuselage, landing gear, and propulsion system are described in detail. the electrical and electronic description includes in-depth discussions of the thought processes behind and justifications for the choice of components including the power supply, esc, flight controller, rc transmission, and range finder. finally, the experimental procedures are presented, including the setup of all four experiments. 3.1 mechanical part fuselage solidworks is used to design the multirotor fuselage. the fuselage design defines the type of multirotor aircraft, such as the hexa-copter depicted in fig. 4(a). thus, multirotor aircraft have 6 motors and 6 propellers for propulsion. the extra two motors in the hexa x rotor arrangement provide more lift force. a hexa-copter has higher stability and can continue to fly even if one of its motors fails. also, the bare fuselage design is more convenient and versatile for research and development. these motor mounts are colored differently from the other motor mounts to show the multirotor aircraft's heading. the fuselage is also constructed such that the motor arms may be stored and transported easily. the multirotor aircraft also features a cargo mechanism at the bottom for extra electronics or sensors. to build the multirotor aircraft, the solidworks file of the bottom plate is exported as a drawing exchange format (dxf) file. this ensures the bottom plate is accurate and closely 377 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 matches the drawing. the carbon fiber tube is cut to the desired length using a grinder, where the intended motor-to-motor length is 685 mm. 3.2 mechanical part landing gear similarly, solidworks is used to design the multirotor aircraft landing gear, which is shown in fig. 4(b). this style of landing gear also allows for extra cargo area. the landing gear must be designed to support the overall weight of the multirotor aircraft plus any additional payloads. the landing gear can also be retracted horizontally for storage and transit. similar to the fuselage, the landing gear is made from carbon fiber plates and tubes, as seen in fig. 4(b). the desired payload height clearance from the ground is 180 mm. (a) (b) fig. 4: (a) fuselage design (b) landing gear. 3.3 mechanical part propulsion system the mechanical components of a multirotor aircraft propulsion system include bldc motors and propellers. bldc motors and propellers for multirotor aircraft must be chosen based on the above requirements and the aircraft's overall takeoff weight. the weight of the multirotor aircraft is the key element impacting the bldc motor choices. to reach the 2:1 thrust to weight ratio, the motors' total thrust must be at least twice the aircraft's entire takeoff weight [15]. the required motor thrust can also be determined using eq. 2 from [16]. 𝑇ℎ𝑟𝑢𝑠𝑡 = (𝑇𝑜𝑡𝑎𝑙 𝑡𝑎𝑘𝑒𝑜𝑓𝑓 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑎𝑖𝑟𝑐𝑟𝑎𝑓𝑡) × 2 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑡𝑜𝑟𝑠 (2) the datasheet for a bldc motor frequently includes the motor's thrust. important information such as kv ratings (rpm per supplied volt) and current ratings (maximum current drawable safely) are also included in the datasheet [17]. additionally, to maximize motor efficiency, most bldc motors recommend a propeller size and design. the multirotor aircraft constructed for this project is expected to weigh 3 kg in total. tarot 4108 brushless dc was finally selected. six lithium-ion batteries (25.2 v), a 380 kv motor with 1 kg of torque, and 1355 carbon fiber propellers were also selected. the uav is 13 inches in diameter and has a 5.5-degree pitch. therefore, the multirotor should include axial propulsion, puller configuration, and two-blade propellers for better performance. 378 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 3.4 electrical and electronic part – power supply a multirotor aircraft's power supply is chosen to meet the propulsion system's voltage and current needs before being stepped down to meet the electronics components' voltage and current requirements. after settling on the motors and propellers, the series and parallel configuration of battery cells can be estimated. this is because one 18650 li-ion cell delivers 4.2 v when completely charged and may safely draw up to 20 a (depending on the model). for example, to provide 24 v for the motors, at least 6 cells must be connected in series. batteries are rated in mah and c, where mah is the maximum power stored and c is the rate of discharge relative to maximum capacity. according to eqs. 3 and 4 from [18], a 2000 mah li-ion cell at 10 c may discharge at 20 a for 6 minutes. 𝐼 = 𝑄 × 𝐶 (3) 𝐷𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 𝑡𝑖𝑚𝑒 (𝑚𝑖𝑛𝑢𝑡𝑒𝑠) = 𝐼 𝐶 × 60 (4) hence, the multirotor aircraft power supply will be lg hg2 3000 mah 20 c 18650 liion batteries (6s4p) as shown in fig. 5(a) with a total capacity of 12000 mah and a maximum voltage of 25.2 v. with this li-ion battery combination, the motors can run for 12 minutes at maximum discharge current of 20 a. because the motor can only draw 12.4 a at full throttle, the multirotor aircraft can only fly for 20 minutes. nickel strips are used to spot weld the li-ion cells into 6s4p arrangement. 3.5 electrical and electronic part – electronic speed control (esc) the esc controls the motor speed of the multirotor aircraft, affecting the thrust force generated. the key problem in selecting an esc is that it can handle the voltage and current draw from the power supply to the bldc motors at full throttle. as indicated in fig. 5(b), the multirotor aircraft esc chosen is the hobbywing xrotor-40a. a safety factor larger than 2 means the esc's continuous current rating is substantially higher than the motors' maximum current demand. 3.6 electrical and electronic part – flight controller the flight controller of a multirotor aircraft receives input signals and converts them to output signals for the motors. so, one way to find a good flight controller is to look at its specs. the pixhawk 2/cube flight controller was chosen for the multirotor aircraft since it is open source and popular among uav developers. the cube also has a double redundant microprocessor, triple redundant imu, and can accommodate up to three gps modules. the cube's (i/o) ports are also attached to a carrier board that can integrate with the intel® edison single board computer. it also includes 14 pwm pins, 8 of which have a failsafe and manual override. thus, redundant components in the cube ensure that the flight controller does not fail. the carrier board also allows for easy attachment of sensors and other electronic components to the flight controller. because pixhawk 2 is an osh, the dimensions and cad model of the flying controller depicted in fig. 5(c) are simply obtained. so, the flight controller may be exactly positioned in the multirotor center to ensure accurate imu and accelerometer data. 3.7 electrical and electronic part – dc transmission the multirotor aircraft uses rc transmission to receive radio signals from the transmitter. the transmission range and frequency are important factors to consider when 379 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 choosing an rc transmission system. the ttsrc x9 remote control 2.4 g 9ch transmitter with receiver x9d is chosen for manual mode since it has a transmission range up to 1 km and runs at 2.4 ghz. in autonomous mode, the 3dr 100 mw radio telemetry is chosen due to its 1.5 km transmission range and 915 mhz transmission frequency, as seen in fig. 5(d) and 5(e). moreover, both transmitting frequencies are legal. fig. 5: (a) li-ion battery (b) esc xrotor-40a (c) pixhawk 2 cad model (d) ttsrc x9 (e) 3dr radio telemetry 3.8 electrical and electronic part – rangefinder the primary purpose of rangefinders is to determine the distance between an object and the rangefinder, but they are also utilized in this project to identify obstacles and avoid collisions. table 1 compares several types of rangefinders. table 1: comparison between rangefinders parameters ultrasonic sensor infrared sensor lidar sensor manufacturer wavgat sharp benewake model gy-us42v2 gp2y0a710k0f tfmini medium ultrasound infrared laser communication interface serial uart analog serial uart distance measuring range 20 cm ~ 720 cm 100 cm ~ 550 cm 30 cm ~ 1200 cm to construct the decentralized 3d collision avoidance system, all of the rangefinders listed in table 1 will be employed for sensor fusion, allowing the advantages of each rangefinder to outweigh the shortcomings of the others. additionally, several simulations 380 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 and experiments will be undertaken to determine each rangefinder's performance in a variety of different environments. 3.9 electrical and electronic circuit diagram figure 6(a) illustrates the relationships between electrical components that are necessary for the building of the multirotor aircraft circuit diagram depicted in fig. 6(b). the circuit schematic is created using fritzing software to aid in the rapid and exact production of the electrical and electronic system. fig. 6: (a) electronic components relations, (b) multirotor aircraft circuit diagram. multiple gpio pins are available on microcontrollers and single-board computers to read analogue and digital inputs from sensors and to output analogue and digital voltage signals. this is to respond to the mobile robot's continually changing electrical requirements. the 381 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 microcontroller is used to read data from ultrasonic sensors that generate and receive digital signals. additionally, through universal asynchronous receiver and transmitter (uart) connectivity, the single-board computer receives gps coordinates from the gps module. additionally, single-board computers are utilized to get photographs of railway track defects and video recordings of the railway track from cameras using serial connection protocol. c++ and python will be used to program the microcontroller and single-board computer, respectively. 3.10 experimental procedures various experiments are conducted to obtain the required results to achieve the project's objectives. the results are based on the specific performance index to determine the success of the research. one of them is the percentage rate of obstacle detection based on the sensor fusion algorithm. this parameter is essential to show how quickly the system detects obstacles and the percentage of successful detection. the other parameter is the reaction time for the system to perform collision avoidance when an obstacle is detected. the reaction time is vital to ensure the system's robustness in all situations. four experiments will be conducted to evaluate all the performance parameters for the system. a. experiment 1: obstacle detection on multiple type and opacity of material test objective : to measure and determine the capabilities for obstacle detection on multiple type of material based on lidar, sonar, and ir sensors parameters : manipulated variable: type of rangefinder and material responding variable: detection of obstacle apparatus : white polystyrene, cotton hoodie, clear plastic, translucent plastic, wooden plank, black box and rangefinders procedure : 1. ultrasonic, laser, and infrared rangefinders are positioned at a fixed distance from the wooden plank. 2. the microcontroller controlling the rangefinders is programmed to obtain the distance between the rangefinders and obstacle. 3. the distance obtained is recorded and compared with the fixed distance set between the rangefinders and obstacle. 4. step 1 to 3 is repeated by changing the type of material to wooden plank, cotton hoodie, clear plastic, translucent plastic, white polystyrene and black box. 5. the results obtained are tabulated in table form. b. experiment 2: obstacle detection range in different environments test objective : to verify and evaluate the obstacle detection range for each type of rangefinder in various environments. 382 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 parameters : manipulated variable: flight environment. responding variable: obstacle detection range of rangefinder apparatus : wooden plank, rangefinders, and multirotor aircraft procedure : 1. ultrasonic, infrared, and laser rangefinders are mounted at the same position on the multirotor aircraft. 2. multirotor aircraft is set up in a sunny environment. 3. the wooden plank is positioned at a fixed distance of 10m from the multirotor aircraft. 4. the distance between the wooden plank and multirotor aircraft is decreased to 9 m, 8 m, 7 m, 6 m, 5 m, 4 m, 3 m, 2 m, and 1 m. 5. the readings of the rangefinders are recorded. 6. step 2 to 6 is repeated by setting up the multirotor aircraft in a cloudy environment and a night environment. 7. the results obtained are tabulated in table form. c. experiment 3: collision avoidance reaction time test objective : to measure and study the reaction time of the multirotor aircraft on collision avoidance. parameters : manipulated variable: velocity of incoming multirotor aircraft responding variable: reaction time of multirotor aircraft apparatus : rangefinders, radio controller, telemetry, laptop, and multirotor aircraft procedure : 1. multirotor aircraft with rangefinders mounted at forward facing position is set up at an empty and open field. 2. mission planner is launched on laptop and the flight path of the multirotor aircraft is planned. 3. the flight controller is configured to record the velocity of multirotor aircraft, rangefinder readings, and throttle level of each bldc motor. 4. the multirotor aircraft took off manually in position hold mode using a radio controller and was controlled to move at a direction parallel to the surface obstacle at a speed of 2 m/s. 5. the data logged in graph form is tabulated in table form. 6. step 4 to 6 is repeated by changing the speed of the multirotor aircraft to 4 m/s and 6 m/s. 383 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 d. experiment 4: 3d collision avoidance test objective : to evaluate and demonstrate the capability of the multirotor aircraft on 3d collision avoidance. parameters : manipulated variable: position of obstacles. responding variable: collision avoidance of multirotor aircraft apparatus : wooden plank, rangefinders, telemetry, laptop, and multirotor aircraft procedure : 1. multirotor aircraft with mounted rangefinders is set up at an empty and open field. 2. mission planner is launched on laptop and the flight path of the multirotor aircraft is planned. 3. the multirotor aircraft took off in autonomous mode and executed the flight path planned. 4. wooden plank is introduced along x-axis, y-axis and zaxis of the multirotor aircraft. 5. the reaction of the multirotor aircraft is observed and recorded. 6. the observations obtained are tabulated in table form. 4. results and discussions results are based on the design of the multirotor aircraft and the 4 real experiments are conducted using the proposed multirotor aircrafts throughout this research. 4.1 design of multirotor aircraft as seen in fig. 7(a) and 7(b), the built multirotor aircraft includes the following characteristics: hexa x, typical fixed skid landing gear, two blade propellers, puller arrangement, and axial propulsion. due to the cylindrical form of the motor arm, motor mount, and landing gear, clamping is needed to secure them in place; drilling a hole through the carbon fiber tube will reduce its strength. silicon rubber dampers are installed on the carbon fiber tube that will come into touch with the ground to absorb impact forces on the landing gear system. the 6s4p 18650 li-ion battery pack is arranged in fig. 7(c), and it is designed to be sealed using a non-conductive waterproof sealing tape. these dimensions are critical because they reflect the multirotor aircraft's virtual cylinder dimension for 3d collision avoidance. thus, the width of the multirotor aircraft with propellers and the height of the multirotor aircraft with battery pack are utilized to establish the proportions of the virtual cylinder for 3d collision avoidance. as a result, the virtual cylinder has a diameter of 1014.7 mm and a height of 300.36 mm as shown in table 2, which is used to construct a 3d collision avoidance system. 4.2 obstacle detection on multiple types and opacity of material test the performance of the collision avoidance system for multirotor aircraft is directly affected by the performance of the several rangefinder types on identifying multiple types 384 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 and opacity of material. this experiment will also assess each rangefinder's ability to detect obstacles. table 2 lists the findings. as shown in table 3, ultrasonic sensors can successfully detect all materials used. also, both laser and infrared rangefinders can detect all materials except transparent materials like clear plastic where incorrect readings occur. contrary to expectations, ultrasonic sensors were able to detect soft materials like cotton hoodies with ease. however, humans typically wear cotton-based clothes, thus it is critical that the rangefinder utilized can detect it. fig. 7: (a) multirotor aircraft frame design, (b) modelling of multirotor aircraft design, (c) modelling of 18650 li-ion battery pack. table 2: dimension of multirotor aircraft dimension length (mm) motor to motor length 684.50 breadth (without propellers) 669.77 width (without propellers) 761.45 height (without battery pack) 229.00 breadth (with propellers) 922.99 width (with propellers) 1014.70 height (with battery pack) 300.36 because laser and infrared rangefinders use light to measure distance between objects and the rangefinder, they have trouble identifying transparent materials. light does not reflect from clear plastic since it is transparent and has low reflectivity. however, when using translucent materials such as translucent plastic, both the laser and infrared rangefinder may detect it due to the material's reflection. thus, the advantages of the ultrasonic rangefinder over laser and infrared rangefinder can be exploited to overcome the disadvantages. however, ultrasonic rangefinders have drawbacks including loud readings and limited obstacle detection range that can be overcome by laser and infrared rangefinders. 385 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 table 3: obstacle detection on multiple type and opacity of material test type of material material used type of rangefinder (rf) ultrasonic rf infrared rf laser rf detection observation detection observation detection observation hard wooden plank √ good √ good √ good soft cotton hoodie √ good √ good √ good transparent clear plastic √ good x bad x bad translucent translucent plastic √ good √ good √ good bright white polystyrene √ good √ good √ good dark black box √ good √ good √ good table 4: obstacle detection range in different flight environments test using ultrasonic, infrared and laser rangefinder flight environment detection range (m) ultrasonic rf infrared rf laser rf 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 sunny √ √ √ √ √ √ √ x x x √ √ √ x x x x x x x √ √ √ √ √ √ x x x x cloud √ √ √ √ √ √ √ x x x √ √ √ x x x x x x x √ √ √ √ √ √ √ √ x x night √ √ √ √ √ √ √ x x x √ √ √ x x x x x x x √ √ √ √ √ √ √ √ √ √ 386 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 4.3 obstacle detection range in different environments test while an ultrasonic rangefinder is generally unaffected by its environment (such as illumination, brightness, and weather), it is tested to confirm its function in a variety of conditions. the infrared and laser rangefinders' functionality will be impacted by the illumination conditions in the environment. in bright flight situations, the average illuminance on the surface of the obstacle is between 32 klux and 100 klux, whereas in cloudy flight environments, the average illuminance on the surface of the obstacle is between 1 klux and 20 klux. needless to add, the average value of illuminance on the surface of obstacles during night flight conditions is less than 1 lux. table 4 summarizes the findings. according to table 3, the ultrasonic rangefinder can detect obstacles from 1m to 7m in various flight situations. also, because ultrasonic rangefinders use air to measure distances between themselves and obstacles, the weather does not affect their effectiveness. the performance of the laser rangefinder varies with flight conditions since the surface of the barrier is illuminated differently in different flight situations. the laser rangefinder has a 6 m obstacle detection range in sunny conditions, 8 m in overcast conditions, and 10 m in night flight. the obstacle detection ranges of a laser rangefinder increase with decreasing surface illuminance. nevertheless, the laser rangefinder's obstacle detection range in table 1 matches its performance during night flight. the infrared rangefinder's performance does not match the criteria in table 1, which only identifies obstacles 1 to 3 meters away. surprisingly, the degree of illuminance does not impact the infrared rangefinder's effectiveness in sunny, overcast, or night flight conditions. this is true for this particular infrared rangefinder device. the chosen ultrasonic and laser rangefinders are suited for obstacle identification in the xand y-axis of the multirotor aircraft frame because they can identify obstacles at a distance. the ultrasonic rangefinder also offers a larger obstacle detecting area, increasing the success rate of the collision avoidance system. due to the design of the multirotor aircraft's frame, the infrared rangefinder can be employed for obstacle detection in the z-axis. the z-axis multirotor aircraft outermost components are the battery and landing gear, whereas the xand y-axis outermost components are the propellers. 4.4 collision avoidance reaction time test the reaction time of a multirotor aircraft is the time it takes to avoid an obstacle. preventing collisions requires quick response from multirotor aircraft when obstacles are detected. this experiment is designed to estimate the reaction time of a multirotor aircraft so that it can react quickly when an obstruction is detected. table 5 shows the results. table 5 shows that when travelling at 2 m/s, the multirotor aircraft reacts promptly when an obstruction is detected. however, at 4 m/s, the multirotor aircraft made evasive maneuvers 30 milliseconds after recognizing the obstruction. the multirotor aircraft also experienced a 35 milliseconds delay before performing evasive moves when going at 6 m/s. when an obstruction is detected, the multirotor aircraft's reaction time is sufficient to avoid it. rangefinders also read distances at 100 hz, or 10 milliseconds each reading. as a result, the reaction time for the multirotor aircraft is 0–35 milliseconds. that's because the laser rangefinder's maximum obstacle detection range in diverse flight conditions is 6 meters, so the multirotor maximum speed is limited. it will also be unable to avoid a collision with an obstruction if it exceeds 6 m/s. 4.5 3d collision avoidance test the multirotor aircraft should be able to avoid obstacles on the x, y, and z axes. figure 8 (a) shows the intended autonomous mission flight path with an impediment noted in red. the 387 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 multirotor aircraft must also avoid an impediment at waypoint 3 on the map upon landing. the mission speed for the multirotor aircraft is set to 1 m/s and the altitude to 2.5 m. table 6 contains the results seen in fig. 8(b)–(d). table 5: collision avoidance reaction time test results velocity of multirotor aircraft (m/s) reaction time of multirotor aircraft (1 x 10-3 s) 2 0 4 30 6 35 fig. 8: (a) autonomous mission flight path with obstacle position marker (b) roll and pitch angle data logged of multirotor aircraft (c) yaw angle data logged of multirotor aircraft (d) rangefinders data logged of multirotor aircraft table 6: 3d collision avoidance test results position of obstacle observation along x-axis successful avoidance along y-axis successful avoidance along z-axis successful avoidance figure 8(b) and 8(c) show the multirotor aircraft's attitude and heading reference system data logged during the autonomous mission. moreover, positive pitch indicates forward motion, while positive roll indicates rightward motion. also, the multirotor yaw angle shows the multirotor heading. on the other hand, fig. 8(d) shows the rangefinder data logged during the autonomous mission, with d0 being the forward rangefinder reading, d45 the northeast 388 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 rangefinder reading, d90 the east rangefinder reading, and d315 the northwestern rangefinder reading. also, dup is the rangefinder reading for upwards and cdis is the rangefinder reading for downwards. the multirotor aircraft avoided collisions along the x, y, and z-axis in table 6. to get from waypoint 0 to 1, the multirotor aircraft first pitches forward. the program for this experiment makes the multirotor aircraft conduct evasive maneuvers when it detects a forward obstruction. the forward barrier is between waypoints 0 and 1. also, when a multirotor aircraft detects a forward obstruction, it will roll to the right until it no longer detects the barrier and then proceed forward. the multirotor aircraft then yaws 90° and pitches forward to move from waypoint 1 to 2. the back obstacle is also parallel to the path from waypoint 1 to 2. when a multirotor aircraft detects a rear obstacle, it is programmed to roll away from it and pitch ahead. to proceed from waypoint 2 to waypoint 3, the multirotor aircraft must yaw for roughly 120° and pitch forward. also, when the multirotor aircraft reaches waypoint 3, it immediately enters land mode. an obstacle is positioned at waypoint 3 underneath the multirotor aircraft, which will undertake evasive maneuvers, such as pitching backward, until the object is not spotted, then land. thus, the multirotor aircraft can avoid obstacles on the x, y, and z axes. 5. conclusions the 3d uav collision avoidance system has been built and tested. the 3d collision avoidance system can also detect several material types and opacities in varied flight environments by combining selected rangefinders. finally, the 3d collision avoidance algorithm can react quickly to obstructions in the x, y, and z axes. in the future, the hexa-rotor design can be improved with better obstacle detection systems such as 360° lidar and solid-state lidar, or vision-based obstacle detection systems such as stereo cameras and depth sensors. as obstacle detection coverage and performance improve, better collision avoidance algorithms can be built. suitable filters should also be attached to the obstacle detection system to eliminate inconsistent readings owing to electrical disturbances and sensor interference. acknowledgments the authors would like to thank ministry of higher education (mohe) for sponsoring this work under the grant no. frgs/1/2022/tk07/utem/02/19. we wish to express our gratitude to honorable university, universiti teknikal malaysia melaka (utem) and ministry of higher education (mohe). special appreciation and gratitude especially for universiti teknologi malaysia (utm) kl campus, malaysia-japan international institute of technology (mjiit), fakulti teknologi kejuruteraan elektrik dan elektronik (ftkee) and underwater technology research group (uterg), center for robotics and industrial automation (ceria) and ministry of higher education (kpt) for supporting this research. references [1] shokirov r, abdujabarov n, jonibek t, saytov k, bobomurodov s. (2020) prospects of the development of unmanned aerial vehicles (uavs). tech. sci. innov., 2020(3): 4-8. doi: 10.51346/tstu-01.20.3-77-0069. [2] shakhatreh h, sawalmeh ah, al-fuqaha a, dou z, almaita e, khalil i, othman ns, khreishah a, guizani m. (2019) unmanned aerial vehicles (uavs): a survey on civil applications and key research challenges. ieee access, 7:48572–48634. doi: 10.1109/access.2019.2909530. 389 iium engineering journal, vol. 24, no. 2, 2023 harun et al. https://doi.org/10.31436/iiumej.v24i2.2803 [3] ke y, wang k, chen bm. (2018) design and implementation of a hybrid uav with modelbased flight capabilities. ieee/asme trans. mechatronics, 23(3): 1114-1125. doi: 10.1109/tmech.2018.2820222. [4] magree d, mooney jg, johnson en. (2014) monocular visual mapping for obstacle avoidance on uavs. j. intell. robot. syst. theory appl., 74(1-2): 17-26. doi: 10.1007/s10846-013-9967-7. [5] ferrera e, alcántara a, capitán j, castaño ar, marrón pj, ollero a. (2018) decentralized 3d collision avoidance for multiple uavs in outdoor environments. sensors (basel), 18(12): 1-20. doi: 10.3390/s18124101. [6] eduardo ferrera pjm, capitan j, castano ar. (2017) decentralized safe conflict resolution for multiple robots in dense scenario. rob. auton. syst., 91: 179-193. [7] harun mh, abdullah ss, aras msm, bahar mb. (2022) sensor fusion technology for unmanned autonomous vehicles (uav): a review of methods and applications. ieee international conference on underwater system technology: theory and applications (usys), 2020:1-8. [8] harun mh, abdullah ss, aras msm, bahar mb. (2021) collision avoidance control for unmanned autonomous vehicles (uav): recent advancements and future prospects. indian journal of geo marine sciences, 50(12): 873-883. [9] sarin p. (2013) digitallab course project ep 315, 1–22. [10] hughes r. (2019) amazon fires: what’s the latest in brazil?, bbc (oct, 2019). [11] administration fa. (2000) aerodynamics of flight, pilot handbook aeronautic knowledge. [12] hibbeler rc. (2013) engineering mechanics statics, thirteenth edition. [13] hibbeler rc. (2012) engineering mechanics dynamics, thirteenth edition. [14] pikalov s, azaria e, sonnenberg s, ben-moshe b, azaria a. (2021) vision-less sensing for autonomous micro-drones. sensors, 21(16):5293. [15] hamaza s, georgilas i, heredia g, ollero a, richardson t. (2020) design, modeling, and control of an aerial manipulator for placement and retrieval of sensors in the environment. j. f. robot., 37(7):1224–1245. [16] suprapto by, heryanto ma, suprijono h, muliadi j, kusumoputro b. (2018) design and development of heavy-lift hexacopter for heavy payload. international seminar on application for technology of information and communication (isemantic), 2018-january:242–246. doi: 10.1109/isemantic.2017.8251877. [17] ahmed mdf, mohanta jc, zafar mn. (2018) development of smart quadcopter for autonomous overhead power transmission line inspections. materials today: proceedings, 51:261-268. [18] zhao t. (2018) propulsive battery packs sizing for aviation applications. master theses. 390 microsoft word vol11_no1_final iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 28 fast zerox algorithm for routing in optical multistage interconnection networks t. d. shahida, *m. othman and m. k. abdullah dept. of communication technology and network, university putra malaysia, 43400 upm serdang, selangor darul ehsan, malaysia. {dian, mothman}@fsktm.upm.edu.my abstract : based on the zerox algorithm, a fast and efficient crosstalk-free time domain algorithm called the fast zerox or shortly fastz_x algorithm is proposed for solving optical crosstalk problem in optical omega multistage interconnection networks. a new pre-routing technique called the inverse conflict matrix (icm) is also introduced to map all possible conflicts identified between each node in the network as another representation of the standard conflict matrix commonly used in previous zero-based algorithms. it is shown that using the new icm, the original zerox algorithm is simplified, thus improved the algorithm by reducing the time to complete routing process. through simulation modeling, the new approach yields the best performance in terms of minimal routing time in comparison to the original zerox algorithm as well as previous algorithms tested for comparison in this paper. keywords : optical multistage interconnection networks (omins), zero-based routing algorithm, heuristics sequential increase algorithm and time domain approach. 1. introduction emerging of multicore systems has witnessed the trend towards powerful machines with higher computing power available at the reach of fingertips. future telecommunication systems are expected to provide seamless support for higher transmission capacity and faster switching technology to connect these high-end systems, in line with the explosive growth of the internet. interconnection networks (ins) is faced with greater challenge as the direction in computing systems is fast moving towards advanced architectures such as chip multiprocessors (cmps), systems on chip (soc) and network on chip (noc) [1]. multistage interconnection networks (mins) have been proposed as interconnecting structures in various types of communication applications ranging from parallel systems [2], switching architectures [3], to multicore systems [4]. advances in optical technologies have drawn the interest for optical implementation in mins to achieve high bandwidth capacity at the rate of terabits per second. optical mins (omins) are an attractive solution that offers a combination of high bandwidth, low error probability, and large transmission capacity [5]. * the author is also an associate researcher at the lab of computational science and informatics, institute of mathematical science and research (inspem), university putra malaysia; http://www.upm.edu.my/~mothman/ iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 29 however, omins introduce optical crosstalk, which results from coupling two signals within a switching element (se). optical crosstalk degrades the performance of omins in terms of reduced signal-to-noise ratio and limits the size of the network [6]. limited by the properties of optical signals, it is not possible to route more than one message simultaneously, without optical crosstalk, over a switching element in an omin. reducing the effect of optical crosstalk has been a challenging issue considering trade-offs between aspects i.e. performance, hardware and software complexity. the three common approaches by which the effect of crosstalk can be reduced are through network dilation in either the space, time or wavelength domain [6]. in this paper, our interest is on the time domain approach for solving optical crosstalk in the optical omega network, a class of self-routable networks, topologically equivalent to many other topologies i.e. the baseline, butterfly, and cube networks [7]. 1.1 optical crosstalk in optical omega networks an omega network connects n input to n output nodes using n stages, where n = log2n with each stage containing 2 n-1 switching elements (ses). figure 1(a) shows an example of a permutation connection when n = 16. permutation refers to the one-to-one mapping of an input to an arbitrary output port in the omega network. (b) 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 stage 0 stage 1 stage 2source destinationstage 3 0 1 3 2 5 4 6 7 6 0 3 4 15 13 7 12 8 9 11 10 13 12 14 15 1 11 5 10 8 14 2 9 (a) source destination fig. 1: (a) a 16 x 16 permutation, and (b) routing the permutation in an optical omega network. to route an optical packet from an input to an output port, the routing path is set according to its destination address. in the omega network, each optical packet must go through a number of switching stages before reaching to their destination. each of the ses iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 30 in the network can be of two logical states; either straight or cross connection. to utilize the available network bandwidth, it is a practical approach to route permutation simultaneously. figure 1(b) illustrates routing the permutation in a 16 x 16 omega network. it is clear in fig. 1(b) that there is optical crosstalk contribution in most of the ses when more than one link is active in the se. depending on the amount of voltage at the junction of the two waveguides that carry two input signals into the se, a portion of either of the two optical signals can be detected at either of the two outputs signals. figure 2(a) shows the two types of logic states of an se while fig. 2(b) shows the an illustration of the optical crosstalk occurrence within the se connected with straight logic state. consequently, the input signal will be distorted at the output due to loss and crosstalk accumulated along the connection path. fig. 2: (a) straight or cross logic state of a 2x2 se, and (b) optical crosstalk effect in an electro-optic se. 1.2 time domain approach among the three approaches to avoid optical crosstalk, the space domain approach duplicates and combines an min to avoid crosstalk within individual se. using this approach, an n x n network is dilated into a network that is essentially equivalent to a 2n x 2n network, but only half of the input and output ports used for routing. based on this idea, a dilated benes network has been proposed [8], where up to n connections can be established without sharing any se. however, it uses more than double of the number of switches required for the same connectivity, in the original benes network. the wavelength domain [9] implements an approach where, the crosstalk between two signals passing through the same se is suppressed by ensuring two wavelengths to be far apart by routing [10] or by using wavelength converters [11], which limits the efficiency of bandwidth utilization and/or increases cost and complexity [5]. time-domain approach tackles the crosstalk problem by allowing only one input and output link to be active at a time within each se in the architecture. a set of permutation connection is partitioned into several groups or passes, called semi-permutations in such a way that the elements within each group are crosstalk-free [11]. then, each independent group is routed to its corresponding destination in a different time slot. in this paper, the focus is on how to efficiently realize permutations using the time domain approach in iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 31 order to avoid crosstalk in optical omega network. figure 3 shows the general framework of the time-domain approach. fig. 3: time-domain approach framework. in permutation decomposition phase, the primary goal is to identify conflicts among all messages in the network. the arbitrary source and destination address of the permutation is first combined to build a combination matrix. then, based on the combination matrix, conflicts are checked using a pattern-checking method i.e. the window method (wm). finally, messages with conflicting path between them are listed and mapped into an array representing the conflicts. in the following message routing phase, once the conflicts are discovered, it will be mapped into some array using one of the conflict mapping techniques. based on the array of conflict generated, the messages are then sorted and selected for scheduling into crosstalk-free groups before routed to the intended destination one group per time slot. 2. previous time-domain algorithms unlike electronic mins where the main concern is merely avoiding path conflicts in the network, a different set of crosstalk avoiding algorithms have been proposed specifically for use in omins. from the literature, among the previous routing and scheduling algorithms that is based on the time domain approach are the four heuristic algorithms i.e. sequential increasing, sequential decreasing, degree ascending and degree descending [13], simulated annealing (sa) [8], genetic algorithm (ga) [15], ant colony optimization (aco) [16], remove last pass (rlp) [17], zero algorithms [4] and bitwise algorithms [18]. each algorithm has the same pattern that is to select an input and an output pair from the permutation for the current pass according to some order, and if no crosstalk occurs, the pair is scheduled in the current pass; otherwise, schedule the iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 32 pair in the next pass. it is only in the order of which message to be scheduled that these algorithms primarily differ from each other. in terms of performance wise, there exist trade-offs between the total number of passes generated and the time taken to completely route a permutation. the execution time is calculated beginning from generating conflict-free groups to routing all messages in the permutation. previous researches have shown that the sa, ga, aco and rlp algorithms give best results in the average number of passes produced for an arbitrary permutation connection. alternatively, the four heuristic algorithms, zero algorithms and bitwise algorithms performs best in the average execution time achieved by each algorithm. in this paper, the main objective is to design and develop conflict-free routing algorithms with better performance in terms of the execution time. from the literature, zero algorithms is one of the algorithms that have been shown to perform best in execution time. the bitwise algorithms have also been developed based on the zero algorithms called the bitwise improved zero (biz) algorithms [19]. 3. the fast zerox algorithm recent research has demonstrated that crosstalk may still occur when routing using the original zerox algorithm. in [16] the improved zerox (iz_x) algorithm is proposed to solve the problem, yet crosstalk is found to occur for some permutation. for example, consider the permutation for n = 8 as shown in fig. 4. fig. 4: an 8 x 8 source to destination permutation. based on the iz_x algorithm, the messages will be scheduled in three passes including messages 000, 011, 101 and 110 for the first pass, messages 001, 010 and 100 for the second pass, and message 111 for the last pass. in the first pass, routing input messages 101 and 110 simultaneously will result in optical crosstalk since destination 101 and 100 for each respective input message is connected to the same switching element in the network. throughout this section, the fastz_x algorithm is shown to eliminate the abovementioned crosstalk completely. we describe the algorithm in two subsections with the first subsection explaining permutation decomposition methods followed by the algorithm in the second. iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 33 3.1 permutation decomposition because routing messages simultaneously causes optical crosstalk, it is important to make sure a permutation is decomposed in a crosstalk-free order. permutation decomposition involves finding messages that may cause conflicts in the network and mapping these conflicts into some array before it can be selected for scheduling. the bitwise window method (bwm) [18] is used to check conflicts between messages in the network. in bwm, each (n-1)-bit binary optical window where (n = log2n) and n is network size, is simplified and converted into equivalent decimal representation using bitwise operations. as a result, the number of columns in each optical window is reduced to n, instead of 2*n for an n x n omin. once the conflicts are identified, it can be mapped into the conflict graph [20] or the conflict matrix [4] to alleviate the scheduling procedure. in this paper, we introduce a new pre-routing technique called the inverse conflict matrix (icm) to map conflicts discovered using bwm. the icm for the permutation in fig. 4 can be constructed as in fig. 5. the idea in icm is extended from the conflict matrix used in previous zero-based algorithms [4, 18], only that the icm provides a more complete mapping of all conflicts in the network. using icm, scheduling is made simple and straightforward without prior column summation of the conflict matrix, which is a mandatory step in original zerox algorithm. fig. 5: the inverse conflict matrix. 3.2 the algorithm figure 6 shows the framework of the fast z_x algorithm. as indicated by its name, the algorithm is developed to optimally minimize the execution time of zerox algorithms. based on our analysis, it is concluded that the original and iz_x algorithm involves a lot of iterative procedures in the algorithm’s functions for the summation of rows or columns, finding the intersections to refine the conflict matrix, multiple conflict-checking to ensure no conflicts when adding successful intersections to a group, reducing the matrix and calculating new summation for the reduced matrix. the advantage of the fastz_x algorithm over the original algorithm is that based on the icm a message can be determined whether it has conflicts and should not be scheduled in the same group directly iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 34 without prior column summation compulsory in zerox algorithm. without the summation of the conflict matrix, the unique case and refine functions in zerox algorithm were removed. furthermore, the icm need not be reduced to smaller matrix size since the icm provides all the information needed for scheduling. in terms of crosstalk avoidance, the fastz_x algorithm successfully avoids crosstalk for any given permutation. let the permutation as in fig. 4. after the icm in fig. 5 is obtained, we select the first message 000 and scheduled it in the first pass for initialization. then, to schedule the next message 001, check from the icm, the intersection between messages 000 and 001. if the intersection has the value equals 0, then add message 001 to the current pass consisting message 000. otherwise, if the intersection value equals 1, then go to the next pass and check the intersection value again but with the current entries in the pass. the process is repeated for the rest of the messages until all messages are scheduled. iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 35 fig. 6: fast zerox algorithm framework. in contrast to the results from the iz_x algorithm discussed previously, applying the fastz_x algorithm to the same permutation results in three conflict-free passes. the first pass contains messages 000, 011 and 101, the second pass contains messages 001, 010 and 100, and the third pass contains messages 110 and 111. the number of passes maybe the same but the messages that will be routed differs to avoid optical crosstalk in the new fastz_x algorithm. iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 36 4. performance analysis we present the test results for fastz_x algorithm in this section. fastz_x algorithm is then compared with previous zero-based algorithms as well as the heuristic’s sequential increase algorithm since equal routing results can be obtained between all algorithms under test. each algorithm is run 10,000 times and the results are presented in terms of the average number of passes as well as the average execution time. the results of the zerox algorithm presented in this paper refers to the result of a modified version of the algorithm, called the modified zerox (mz_x) algorithm developed for comparative analysis purposes. this is due to the fact that crosstalk may still occur in both the original and iz_x algorithms. therefore, in this paper the mz_x will be regarded as the original zerox algorithm as we want the original algorithm to be crosstalk-free. the mz_x algorithms further extends the work in iz_x algorithms and solved the optical crosstalk that occurs as a result from the algorithm’s unique case function. to avoid the optical crosstalk, the mz algorithms implemented two modifications to the function. first, the next entry that equals to zero in the same row or column of the group’s unique entry, be checked for conflicts before it can be added to the group when the unique case function is executed. second, the number of entries that can be added to the group is no longer limited to three entries only. in fact, a maximum of n/2 entries can be added to the group, where n is the size of the network. the rest of the mz_x algorithms follows the framework of iz_x algorithms i.e. the refine function. fig. 7: average passes for fastz_x algorithm. figure 7 presents the average number of passes or conflict-free groups required to route a permutation between all algorithms. it is clear from the figure that there is almost no difference in the average number of passes realized by all the algorithms being tested. the slight difference shown is a result most probably due only to the different random source and destination of the permutation generated in each run. otherwise, the number of passes realized is the same because the messages are selected based on the same order for scheduling starting from message 0 to message n where n is the size of the network. iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 37 in terms of the execution time, fastz_x algorithm has shown consistent improvement in the average execution time compared to that of the original zerox algorithm (mz_x algorithm) with 42% improvement as shown in fig. 8. furthermore, as can be seen, the larger the network size, the more significant the improvement in speed. compared to the other previous algorithms such as the biz_x and sequential increase algorithm, fastz_x outperforms all the algorithms with the best execution time achieved and an average of 16% improvement for both biz_x and sequential increase algorithms. fig. 8: average execution time for fastz_x algorithm. the advantage of the fastz_x algorithm is that scheduling decisions is made directly based on the icm simply by checking the intersections value between the message to be scheduled and the existing entries of the current pass. through the use of icm, the refine and unique case function in the zerox algorithm is also removed in fastz_x algorithm. furthermore, as stated before, since the icm provides the complete mapping of all conflicts in the network, prior summation of all columns in the conflict matrix is no longer necessary in the fastz_x algorithm. 5. conclusions throughout this paper, we have presented the fast zerox algorithm, a new algorithm to improve the performance of scheduling and routing in omins without crosstalk. we also proposed the inverse conflict matrix or icm to manage conflict mapping effectively. through simulation modeling, fastz_x algorithm was proven to significantly reduce the average execution time with the same number of crosstalk-free groups obtained using the original zerox algorithm. the new algorithm was also shown to achieve the best in execution time compared to other previous algorithms tested. as for future considerations, the icm approach can be applied to other zero-based algorithms as well as other time domain algorithms to reduce the execution time. the rlp algorithm can also be integrated with fastz_x algorithm to improve the number of passes needed for routing based on the time-domain approach. iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 38 references [1] j. d. owens, w. j. dally, r. ho, d. n. jayasimha, s. w. keckler and l. s. peh, “research challenges for on-chip interconnection networks”. ieee micro, vol. 27, no. 5, pp. 96-108, 2007. [2] y. yang, j. wang and y. pan, “routing permutations with link-disjoint and node-disjoint paths in a class of self-routable interconnects”. ieee transactions on parallel and distributed systems, vol. 14, no. 4, pp. 383-393, 2003. [3] d. tustch and g. hommel, “mlmin: a multicore processor and parallel computer network topology for multicast”. computers and operations research journal, elsevier, vol. 35, no. 12, pp. 3807-3821, 2008. [4] m. a. al-shabi and m. othman, “a new algorithm for routing and scheduling in optical omega network”. international journal of the computer, the internet and management, vol. 16, no. 1, pp. 26-31, 2008. [5] e. lu and s. q. zheng, “high-speed crosstalk-free routing for optical multistage interconnection networks”. proceedings of the 12th international conference on computer communications and networks, pp. 249-254, 2003. [6] s. c. chau, t. xiao and a. w. c. fu, “routing and scheduling for a novel optical multistage interconnection networks”. euro-par 2005 parallel processing, lecture notes in computer science, vol. 3648, pp. 984-993, 2005. [7] c. l. wu, and t. y. feng, “on a class of multistage interconnection networks”. ieee transactions on computers, vol. 29, no. 8, pp. 694-702, 1980. [8] k. padmanabhan and a. n. netravali, “dilated networks for photonic switching”. ieee transactions on communications, vol. 35, no. 12, pp. 1357-1365, 1987. [9] m. m. vaez and c. t. lea, “space-wavelength tradeoff in the design of nonblocking directional-coupler-based networks under crosstalk constraint”. journal of lightwave technology, vol. 8, no. 16, pp. 1373-1379, 1998. [10] j. sharony, k. w. cheung, and t. e. stern, “the wavelength dilation concept in lightwave networks – implementation and system considerations”. journal of lightwave technology, vol. 11, no. 5/6, pp. 900-907, 1993. [11] x. qin and y. yang, “permutation capacity of wdm switching networks with limitedrange wavelength conversion”. ieee proceedings of 2001 international conference on parallel processing workshops on optical networks, pp. 271-276, 2001. [12] y. yang, j. wang and y. pan, “permutation capability of optical multistage interconnection networks”. journal of parallel and distributed computing, vol. 60, no. 1, pp. 72-91, 2000. [13] . d. shahida, m. othman and m. khazani, “routing algorithms in optical multistage interconnection networks: revisited”. proceedings of the 3rd world engineering congress, pp. 63-70, 2007. [14] a. k. katangur, y. pan and m. d. fraser, “message routing and scheduling in optical multistage networks using simulated annealing”. proceedings of the international parallel and distributed processing symposium, pp. 201-208, 2002. iium engineering journal, vol. 11, no. 1, 2010 shahida et al. 39 [15] t. w. manikas and j. t. cain, “genetic algorithms vs. simulated annealing: a comparison of approaches for solving the circuit partitioning problem”. technical report 96-101, department of electrical engineering, university of pittsburgh, 1996. [16] a. k. katangur, s. akkaladevi, y. pan and m. d. fraser, “applying ant colony optimization to routing optical multistage interconnection networks with limited crosstalk”. proceedings of the 18th international parallel and distributed processing symposium, pp. 163-170, 2004. [17] s. c. chau, and t. xiao, “a new algorithm for routing and scheduling in optical multistage interconnection networks”. proceedings of the 4th iasted international multiconference on wireless and optical communications, banff, canada, pp. 749-755, 2004. [18] f. abed and m. othman, “fast method to find conflicts in optical multistage interconnection networks”. international journal of the computer, the internet and management, vol. 16, no. 1, pp. 18-25, 2008. [19] x. qin and y. yang, “permutation capacity of wdm switching networks with limitedrange wavelength conversion”. ieee proceedings of 2001 international conference on parallel processing workshops on optical networks, pp. 271-276, 2001. [20] m. abdullah, m. othman and r. johari, “an efficient approach for message routing in optical omega network”. international journal of the computer, the internet and management, vol. 14, no. 1, pp. 50-60, 2006. microsoft word vol 6-2p4v2-press.doc iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 37 investigation on laf3/si structure as lightaddressable potentiometric fluoride (f‾) sensor abu bakar md. ismail1,2, rezaul islam1, koji furuichi2, tatsuo yoshinobu2, hiroshi iwasaki2 1department of applied physics and electronics, rajshahi university rajshahi 6205, bangladesh. tel: 880-721-750041/4101, fax: 880-721-750064, e-mail: ismail@ru.ac.bd; and ismail_abm@lycos.com 2the institute of scientific and industrial research, osaka university, 8-1 mihogaoka, ibaraki, osaka 567-0047, japan. 8404 e-mail: iwasaki@sanken.osaka-u.ac.jp abstract: in this article laf3 films in laf3/si structure have been investigated for the measurement of fluoride ions in aqueous solution with higher accuracy using lightaddressable potentiometric sensing technique. laf3 films were directly grown on si by vacuum evaporation. the effects of laf3-thickness and annealing on the fluoridesensitivity of the laf3/si structures have been studied. accordingly four different laf3/si structures with various thickness of laf3 (5/50/150nm) layer were fabricated. the structures are annealed at 400ºc for 10 minutes. the un-annealed laf3/si structures show very poor fluoride sensitivity. as predicted in the theoretical study structures with thinner laf3 offer better steepness of the photocurrent characteristics that indicates better accuracy in fluoride concentration measurement. among the annealed structures, the one prepared with 150nm laf3 layer shows the best fluoride sensitivity of ≈ 54.5mv/pf in the range of pf1-pf4. experimental results show a good promise for laf3/si structure as a light-addressable potentiometric sensor that can be used for the sensing and imaging the distribution of fluoride ion in aqueous medium with higher accuracy. keywords: light-addressable potentiometric sensor (laps), fluoride sensor, capacitive eis structure 1. introduction in recent years, new scientific evidence has emerged which suggests that there are significant risks and negligible benefits from ingesting low levels of fluoride [1]. fluoridation of water supplies is harmful to bone, while providing negligible benefits when swallowed. therefore, monitoring of fluoride has become very important for the environmental and the industrial processes. generally detection of fluorine and fluorides are done by electrochemical cells [2]. almost all of them have a liquid electrolyte, which iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 38 is considered as their main disadvantage. recently there are reports on the ionic conductor laf3 thin-film as the sensitive layer in solidstate sensors for both fluorine and oxygen sensing. researchers have investigated laf3 in details for its various attributes such as its crystal structure, ionic conductivity and dielectric properties. as a candidate electrolyte for measuring oxygen gas concentration at room temperature use of laf3 has been studied thoroughly [3-9] by some researchers. most of these studies involved the laf3 in polycrystalline form or chunks of single crystal. in those works laf3 have been deposited with various deposition techniques as an epitaxial layer directly, or with additional insulating layer of sio2 and/or si3n4, on semiconductor. the interface between epitaxially grown laf3 on silicon or gallium arsenide [10-12] has also been studied to obtain a heterostructure of low density of surface states. development of fluoride sensitive field-effect transistors (pf-fet) have been carried out by moritz [13], hentsche et al. [14]. baccar et al. [15] also investigated ion sensitive field-effect transistor (isfet) and electrolyte-oxide-semiconductor (eos) structure with a fluoride ion sensitive membrane obtained by fluoride and lanthanum ion implantation into the silica insulator layer. an overview of the above reports suggests that epitaxially grown laf3 on si <100> would give an interesting structure to be used for fluoride sensing. apart from the choice of sensor materials, the choice of sensing technique is also important. recently sensors based on light-addressable potentiometric sensing (laps technique has become popular [16-18] due to some of its advantages, such as selection of measurement point by a scanning light beam and spatial resolution. in our previous work [19] we first reported a fluoride sensor using si/laf3 structure as light-addressable potentiometric sensor (laps). for potentiometric sensors high precision measurement is necessary since 1 mv in the potential shift corresponds to an error in concentration of 4% (exchange of one electron) [20]. therefore the steepness of the laps iv characteristics is of great importance for achieving accurate measurements. this article presents the investigation on vacuum evaporated laf3 on si in a heterostructure of laf3/si/au to be a high-accuracy fluoridesensitive laps devices. the possibility of obtaining high accuracy in fluoride sensing is first theoretically studied, and then experimentally it is verified. 2. sensor fabrication and experimental setup the sensor chips were obtained from small pieces of silicon cut from an n-type silicon wafer having a diameter of 8 cm, resistivity  of 1-10 ω-cm and surface of (100) orientation. the back surface (unpolished) of silicon chips was first coated with ausb (99.5%-au and 0.5%-sb) to establish the back metal contact of the sensor. the abovementioned wafer was first degreased ultrasonically in acetone and deionized water. the pieces were briefly dipped in very dilute (2 %) hf solution to remove the native oxide just before insertion into the evaporation chamber. the laf3 films were deposited in a homeassembled vacuum-coating unit. laf3 anhydrous 99.99% purity was purchased from kishida chemical co. ltd., japan, and was used without further purification. the vacuum pressure was maintained in the range of 10-8 torr. the deposition rate was 5 nm/min. in this way, 5 nm (sensor 2), 50 nm(sensor 3), 150 nm (sensor 4) -thick laf3 layers were deposited on the bulk si. the thicknesses were monitored in-situ as well as confirmed by ellipsometric measurements. the sensors (2, 3 and 4) thus constructed were annealed at 400ºc for 10 min. iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 39 3. theoretical consideration theoretically it appears that the optimization of heterostructure of laf3/si to be used as a laps might provide the steeper photocurrent response and thereby provide better accuracy in the measurement of fluoride concentration. the electrical equivalent circuit of the laf3/si structure to be used as laps can be given [21] as shown in fig. 1. fig. 1: ac equivalent circuit of laps device. the measured current is given by 1 ( ) j c rii i p j r c ci d      (1) where, ip = current due to light induced minority carriers i = measured photocurrent cd = depletion capacitance ci = insulator capacitance r = depletion resistance  = angular frequency of ac photocurrent the term [2r(ci + cd)]-1 is defined as the cutoff frequency for the laps. the measured current, at a frequency below the cutoff, is given by i pi j c ri (2) above the cutoff frequency the measured current is given by i p i d c i i c c   (3) v ir c c iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 40 equations (2) and (3) show that, at a frequency below or above the cutoff frequency, the measured current can be increased by increasing the insulator capacitance ci ( 1/d), and hence decreasing the thickness (d) of the insulating layer. conventionally the insulating layer of laps is a combination sio2 and si3n4, as such the insulator capacitance of ci(laf3) >> ci(sio2+si3n4) therefore, using very thin laf3 layer as the insulating layer in laps the measured photocurrent and hence the steepness of the i-v response can be increased. the steepness of the i-v characteristics is of great importance for achieving better resolution. the steepness of the photocurrent response is defined as the change of photocurrent for the unit change in surface potential, at the linear region of the photocurrent response characteristics around the inflexion point of the i-v characteristics. 4. results and discussion for the investigation of laf3 material as the fluoride ion sensitive material in the laps, sensors with two conditions, namely, as deposited (without annealing, sensor 1) and, annealed at 400°c (sensor 2, 3 and 4), were studied. the test solutions used in the characterization were prepared in the laboratory. the composition of the solutions was 2% tris (hydroxymethyl)-aminomethane solutions in distilled water, at a fixed ph value of 7.2. constant ionic strength was maintained at 0.4 m of kno3. analytical grade kf was added to the solution in a concentration range of 10-1m to 10-7m to obtain the experimenting solutions having pf values from 1 to 7. as shown in fig 2, the response for a particular solution is obtained by plotting the photocurrent for the corresponding bias. the typical response of the sensors for a pf2 solution is shown in fig. 3. fig. 2: experimental set-up for the laps measurement. iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 41 fig. 3: typical laps response of the 50nm-laf3/si structure for pf4 solution. as shown in fig. 3, the photocurrent for the laf3/si structures start flowing when the depletion region is created in the si by the applied bias plus the surface potential at the insulator/electrolyte interface which corresponds to the nernstian voltage of laf3 for pf4 solution. the saturation level of the photocurrent is observed at the highly depleted (inverted) condition. as the bias is further decreased towards less positive values the photocurrent starts decreasing and then becomes nearly constant. the responses of various thickness laf3/si structures used as the fluoride-laps are compared for a particular solution (pf4) and are shown in fig. 4. as the theory predicts the amplitude of the photocurrent as well as the steepness of the response characteristics for the laf3-based laps depends on the laf3 thickness. fig. 4: photocurrent response of annealed-laf3/si structures for various thickness of laf3. figure 5 shows the linear portion of the photocurrent characteristics around the inflexion points. this plot is used to calculate the steepness of the photocurrent characteristics. the steepness is calculated as the change of photocurrent for unit change in surface potential. for our experimental setup, since we used a preamplifier to convert 0 0.1 0.2 0.3 0.4 0.5 -1.5 -1 -0.5 0 0.5 1 1.5 2 un-annealed annealed p ho to cu rr en t [ a. u] bias [v] a b linear region 0 0.2 0.4 0.6 0.8 1 1.2 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 50nm laf 3 150nm laf 3 5nm laf 3 p ho to cu rr en t [ a. u] bias [v] iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 42 the photocurrent into voltage by a factor of 106, the steepness of the photocurrent response is defined as, )( )/(10)( 6 vbiasinchange avxantphotocurreinchange steepness  fig. 5. linear portion around the inflexion point of the photocurrent characteristics of various thickness annealed structures. figure 6 shows the calculated-stpeeness versus the laf3 thickness for the annealed structures corresponding to the pf4 solution. the steepness of the annealed structures was always higher than the un-annealed structures. this is evident from the fig. 3. thus, we will focus on the behavior of annealed structures. as predicted theoretically, the steepness of the photocurrent characteristics was inversely proportional to the thickness of the laf3 layer on si. fig. 6. steepness versus laf3 thickness for the annealed-structures. figure 7 shows the typical photocurrent response of the annealed structures for varied concentration fluoride solutions in the range of pf1 to pf7. here, each i-v curve is normalized at its peak value. the un-annealed (as-deposited) sensor showed indistinguishable or very low fluoride sensitivity. therefore, the response of the annealed sensors will be discussed further. 0.1 0.15 0.2 0.25 0.3 0.35 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 5nm 150nm 50nm p ho to cu rr en t a ro un d th e ifl ex io n po in t [ a. u] bias [v] 0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3 . 0 3 . 1 3 . 2 s te e p n e s s laf3 iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 43 a) un-annealed laf3/si structure b) annealed laf3/si structure fig. 7. photocurrent response for varied concentration of fluoride solution. as can be seen in fig. 7(b), the photocurrent response for the pf5, pf6 and pf7 solution appears to be overlapping which suggests a loss in fluoride sensitivity when the sensor is subjected to pf solution beyond pf4. the inflexion points for the photocurrent responses of various pf solutions are found by equating the second derivative of the response for each buffer to zero, and are plotted as shown in fig. 8 for the annealed structures. the un-annealed structures did not show distinguishable inflexion voltages for various fluoride concentrations and are not plotted for simplicity in fig. 8. the 50nmlaf3/si structure shows quite linear response for pf1 to pf5 whereas 5 nm-laf3/si and 150 nm-laf3/si structures show linear responses for pf1 to pf4 value of the solution. fig. 8. thickness dependency of the inflexion potentials. figure 9 shows the plot of the fluoride sensitivity against the thickness of the sensor. we didn't find any ordered relationship between thickness of the laf3 layer and fluoride sensitivity. this is may be due to the fact that the fluoride sensitivity of laf3 layer -500 0 500 1000 0 1 2 3 4 5 6 7 8 150nm laf 3 50nm laf 3 5nm laf 3 in fle xi on v ol ta ge [m v ] pf 49.2mv/pf 53.3mv/pf 54.6mv/pf 12.635mv/pf 20.365mv/pf 1 . 6 1 . 4 1 . 2 1 . 0 0 . 8 0 . 6 0 . 4 0 . 2 0 . 0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 n o rm a li z e d p h o to c u rr e n t [a .u ] b i a s v o l t a g e [ v ] p f 1 p f 2 p f 3 p f 4 p f 5 0 . 8 0 . 6 0 . 4 0 . 2 0 . 0 0 . 2 0 . 4 0 . 0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 n o rm a li z e d p h o to c u rr e n t [a .u ] b i a s v o l t a g e [ v ] p f 1 p f 2 p f 3 p f 4 p f 5 p f 6 p f 1 iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 44 depends on the number of surface sites, which binds the fluoride ion and does not depend on the thickness of the layer. the minimum average sensitivity of 49.2 mv/pf was observed in this experiment with the 5 nm-laf3/si. the highest sensitivity of 54.6 mv/pf was obtained with 150nm-laf3/si. the minimum average sensitivity of the sensors was more than that obtained by baccar et al. [15] for their sensor prepared with ion implantation technique (44 mv/pf). the detection limit for 5 nm-laf3/si structure was also higher than that obtained by baccar et al (pf 2 4). but the detection limit of 50 nmlaf3/si and 150 nm-laf3/si structures is quite similar to that of what baccar et a.l obtained. 49 50 51 52 53 54 55 0 20 40 60 80 100 120 140 160 pf s en si tiv ity [m v /p f ] thickness [nm ] fig. 9. thickness versus sensitivity plot. 5. conclusion vacuum-evaporated laf3 layer as fluoride-sensitive material in a heterostructure of si/laf3 as a sensor in a laps device has been investigated for obtaining fluoride measurement with higher accuracy. the sensor those were annealed at 400°c after the deposition of laf3, show good average fluoride sensitivity in their first use. but, the sensor not annealed hardly shows fluoride sensitivity. the thinner laf3 layer provides better steepness of the photocurrent response hence better accuracy of fluoride measurement. observing the performance of this simple structure, it can be concluded that very thin layer of epitaxial-laf3 on si heterostructure can be used for fluoride ion measurement with higher accuracy as an laps device. references [1] m. diesendorf, j colquhoun, b j spittle, d n everingham and f w clutterbuck, "new evidence on fluoridation," fluoride, vol. 30, no. 3, pp. 179-185, august 1997. [2] t. ichichi, m. shoichi, m. ishizuka (riken keiki), "potentiostatic electrolytic acid gas sensor," japanese patent 07, 55,768, march 3, 1995. iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 45 [3] t. katsube, m. hara, and i. serizawa, " mos-type micro-oxygen sensor using laf3 workable at room temperature," jap. j. appl. phys., vol. 29, no. 8, pp. l-1392-1395, august 1990. [4] n. yamazoe and n. miura, “solid-state electrochemical oxygen sensors for operation at room temperature,” trends anal. chem., vol. 9, no. 5, pp. 170-175, may 1990. [5] j. lukaszewicz , n. miura and n. yamazoe, “a laf3-based oxygen sensor with perovskitetype oxide electrode operative at room temperature,” sensors & actuators b, vol. 1, no. 1-6, pp. 195-198, january 1990. [6] yamazoe n. et al., “potentiometric solid-state oxygen sensor using lanthanum fluoride operative at room temperature,” sensors & actuators, vol. 12, no. 4, pp. 415-423, november –december 1987. [7] n. miura, j. hisamoto, n. yamazoe, s. kuwata, " laf3 sputtered film sensor for detecting oxyzen at room temperature," appl. surface sci., vol. 33-34, pp. 1253-1259, september 1988. [8] n. miura, j. hisamoto, n. yamazoe, s. kuwata, and j. salardenne, " solid-state oxygen sensor using sputtered laf3 film," sensors & actuators, vol. 16, no. 4, pp. 301-310, april 1989. [9] s. harke, h. d. wiemhöfer and w. göpel, " investigation of electrodes for oxygen sensor based on lanthanum trifluoride as solid electrolyte," sensors & actuators b, vol. 1, no. 1-6, pp. 188-194, january 1990. [10] s. sinharoy, r. a. hoffman, j. h. rieger, w. j. takei, and r. f. c. farrow, “epitaxial growth of lanthanide trifluorides by mbe,” j. vac. sci. technol., vol. 3, no. 2, pp. 722 – 723, march 1985. [11] s. sinharoy, r. a. hoffman, a. rohatgi, r. f. c. farrow, j. h. rieger, " epitaxial growth of laf3 on gaas(111)," j. appl. phys. vol. 59, no. 1, pp. 273-275, january 1986. [12] r. strümpler, d. guggi and h. lüth, “the structure of thin epitaxial laf3 films on si(111),” thin solid films, vol. 198, no. 1-2, pp. 221-232, march 1991. [13] w. moritz, i. meierhofer and l. müller, “fluoride-sensitive membrane for isfets,” sensors & actuators, vol. 15, no. 3, pp. 211-219, november 1988. [14] r. hintsche, i. dransfeld and f. schellerm. t. pham, w. hoffmann and j. huellerw. moritz, “integrated differential enzyme sensors using hydrogen and fluoride ion sensitive multigate fets,” biosensors bioelectron.,vol. 5, no. 4, pp. 327-334, 1990. [15] z. m. baccar, n. jaffrezic-renault, c. martelet, " new fluoride-sensitive membranes prepared through an ion implantation process," jour. mater. sci., vol. 32, no. 16, pp. 42214225, january 1997. [16] m. nakao, t. yoshinobu, and h. iwasaki, " scanning-laser-beam semiconductor ph-imaging sensor", sensors & actuators b, vol. 20, no. 2-3, pp 119-123, june 1994. [17] g. gehring, d. l. patterson, and s. tu, " use of a light-addressable potentiometric sensor for the detection of escherichia colio157:h7," anal. biochem., vol. 258, no. 2, pp. 293-298, may 1998. [18] a. b. m. ismail, t. harada, t. yoshinobu, h. iwasaki, m. j. schoening, and h. lueth, " investigation of pulsed laser-deposited al2o3 as a high ph sensitive layer for laps-based biosensing applications," sensors and actuators b, vol. 71, no. 3, pp. 169-172, december 2000. iium engineering journal, vol. 6, no. 2, 2005 a. ismail et al. 46 [19] a. b. m. ismail, k.furuichi, t. yoshinobu and h. iwasaki, " light-addressable potentiometric fluoride(f-) sensor," sensors and actuators b, vol. 86, no. 1, pp. 94-97, august 2002. [20] t. gabusjan, l. bartholomäus, w. moritz, " improved ion-conducting layer replacing the insulator in a capacitive chemical semiconductor sensor," sensors materials, 10(5), 263-273, (1998). compiled journal vol 12 no 2.pdf                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           iium engineering journal, vol. 16, no. 1, 2015 okhunov et al. 81 normalization of wave function of the band states abdurahim a. okhunov1, gulbadanbegim sh. mamathonova2, torla hj hassan1, mohammad jahangir alam3 and mukhtorjon x. ismoilov2 1department of science in enginering, faculty of engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur, malaysia. 2department of of natural science, margilan academic lyceum, margilan, uzbekistan. 3department of physics, faculty of science, international islamic university malaysia, jalan sultan ahmad shah, bandar indera mohkota, 25200 kuantan, pahang, malaysia. abdurahimokhun@iium.edu.my (received 17 march 2014; accepted 21 march 2015; published on line 29 may 2015) abstract:low – lying band states are one of the most fundamental excitation modes in the energy spectra of deformed nuclei. this paper presents a theoretical analysis of the properties of a deformed nuclei within the phenomenological model [1]. the normalization of the wave functions of low – lying excited band states are also calculated. abstrak: keadaan jalur aras rendah merupakan mod pengujaan paling asas dalam tenaga spekrum nuklei berbunga. adanya kertas kerja yang menganalisa secara teori ciriciri nuklei berbunga dalam model fenomenologis [1]. penormalan fungsi gelombang pada keadaan jalur teruja aras rendah telah dihitung. keywords: energy; band states; nuclei; angular momentum; quantum number 1. introduction at the present time, it is observed that there is increased use of nuclear isotopes in the fields of medicine, energy and agriculture. this in turn has increased the demand for nuclear engineers. however, a more in-depth study of the structure of wave functions of nucleus and its energy states is still required. substantial research and development of nuclear energy is still ongoing. the description of rotational states is one of the oldest, yet not fully solved, problem in nuclear structure physics. there have been intensive experimental [2] and theoretical [3, 4] research on the structure of deformed nucleo. it is possible to note some general structure peculiarity of even–even deformed nuclei which have defined a theoretical direction to the description of experimental data. the state property of ground  gr ,    and    rotational bands in even–even deformed rare–earth nuclei are influenced by the coriolis admixtures of the states of 1k   bands [5]. the cases of existence of several rotational bands with negative and positive parity are located in a very narrow interval of excited energy. this creates a prerequisite for mixing adiabatic states with the fixed values of projections of angular momentum k, to the symmetry axis of nuclei. with growth of the angular moment i, performance of the law ( ) ~ ( 1)e i i i  is violated. it can be connected iium engineering journal, vol. 16, no. 1, 2015 okhunov et al. 82 with a change to the moment of inertia at a change of rotational frequency, and with forming of an internal excited angular momentum with a different nature. 2. wave functions in the generalized model of the nucleus it is assumed that the complete nuclearhamiltonian consists of two parts:   '2 int int, where k k k k h h r h h b b     (1) where  2h r describes the rotational energy of the nucleus and is a function of the rotational angular momentum  r r i j  . the second term is the internal part of the hamiltonian, which we write out by introducing phonon operators  k kb b which create (annihilate) excited states of positive parity, and k  are the values of the principal band energies. from [1], the equation for a wave function that takes into account the influence coriolis interactions, is given as:         ' ' ' ' ', , ,02, ' , ' ,, ,0 2 1 2 16 1 1 i i i i m k gr k mk k k i i kk k i i k k kkk k k k i imk d d b d b                         (2) by the theory of indignations it is possible to receive analytical expressions for the amplitude mixture ', i k k  in eq.1. the hamiltonian model possesses transformation properties such that the state in eq.1 can be classified by a quantum number, the signature 1   , which imposes constraints on the values of the angular momentum  1 1i   . this leads to a significant difference on the mixing of states with a different signature. here we shall write the rotational part of the hamiltonian in eq.1 as the taylor expansion with the power of j . keeping only the zeros and first order terms, we obtain the hamiltonian            ' ' ' '' 2 , , , , 1, ˆ , rot k k k rot xk k k k k kk k h h i h i h i i j i k             (3) matrix elements from the operator corh in eq.3 is not diagonal by basis of wave functions, while other parts of the full hamiltonian in eq.1 is a diagonal. the small values of angular momentum i represent the small amendment to the indignant operator. in the basis state of a hamiltonian in eq.3, of bands with quantum numbers 0 , 2 and 1k       , we define amendments of the first and second order full wave functions systems with the following formula: , , , ,1 ,1 i m k gr imgr im im im                       (4) iium engineering journal, vol. 16, no. 1, 2015 okhunov et al. 83 where , k is an amendment for states th bands. this amends have following type: for the ground bands  gr          1 1 2 2 , 12 , 1 , 22 , 1 , ,1 1 2 , 1 , 1 1 1 1 1 1 1 1 . gr gr x x gr rot gr x x gr rot gr x rotgr x x gr rot gr j gr j i j gr j i j gr i j gr j i                                (5) for the 1 bands  1          1 1 1 1 1 1 2 1 2 1 1 1 1 1 1 12 , 1, , 1 22 , 1, , 1 ,1 1, 12 , 1, , 1 1 1 1 1 1 1 1 . x x gr rot x x rot x rot x x rot j j gr i j j i j i j j i                                               (6) for the 2 bands  2          2 2 2 2 1 2 1 2 2 2 2 2 2 2 2 22 , 1, 2 12 , 1, , , 2 ,1 1, 22 , 1, , 1 1 1 1 1 1 1 1 . x x gr rot x x rot x rot x x rot j j gr i j j i j i j j i                                               (7) iium engineering journal, vol. 16, no. 1, 2015 okhunov et al. 84 for the  bands          2 , 1, 2 , 1, , ,1 1, , 1 1 1 1 1 1. x x gr rot x x rot x rot j j gr i j j i j i                                       (8) where ,       and ˆ1 xj k – matrix elements of coriolis mixture of states 0 , 2k     and 1  band. taking into account normalizations for coriolis interactions we have  2,, ,, i ki i i i n n            l l (9) we can see from the formulas in eq.5 to eq.8, if a value of matrix element is large (table 1) and headband levels are located close, there is a hybridization of a band, which is strongly shown in values of probabilities of transitions (feature work). table 1: the matrix elements of the coriolis interaction   , 'x k kj for isotopes 170,172,174yb correspondingly a   ,1x grj   1,1xj    2 ,1xj    3 ,1xj    1,1xj  170yb 0.1864 0.3936 0.6586 0.9081 0.7278 172yb 0.2457 0.9777 0.7176 0.1100 0.3250 174yb 0.1850 0.4000 0.2500 0.1500 0.0850 3. results the coriolis mixture coefficients ', i k k  for the states of the ground band state,    ,    and 1  bands for isotope 170yb is illustrated in fig. 1, taken by the description energy of spectra states. we see that even in a low value of spin 1  and 1  there is a strong mixture of components in 1  band states. this is observed from the closely arranged energy bands, which shows that the value lies within the probability of electromagnetic transitions. from fig. 2 we can see that there is a strong mixture in the  1 20k  and  1 22k  band state in 170yb, and also  2 30k  and  1 22k  band state in 172yb , even for low spin values of i. iium engineering journal, vol. 16, no. 1, 2015 okhunov et al. 85 fig. 1 the mixture coefficients of 170yb isotope. fig. 2 the mixture coefficients of 172yb isotope. 4. conclusion a theoretical framework was introduced in the paper. to understand structure properties of states, we use the phenomenological model [1], which clearly describes large number of experimental data by the deviation properties of the positive parity in even-even deformed nuclei from the role of adiabatic theory. the mixture components of the band states are analyzed for the , ,gr       and 1k   rotational bands of the isotopes 170,172,174yb respectively. acknowledgement the work here is supported by grant edw13–034–0919, international islamic university malaysia and the margilan academic lyceum. iium engineering journal, vol. 16, no. 1, 2015 okhunov et al. 86 references [1] usmanov p.n, okhunov a.a, salikhbaev u.s, vdovin a. i. (2010) analysis of electromagnetic ttransitions in nuclei 176,178hf. phys. part. nucl., 7(3):185-191 [2] leander ga. (1985) in nuclear structure, eds. broglia ra, hagemann gb, herskind b, north–holland, amsterdam, pp. 249. [3] mikhaylov in, usmanov ph.n, okhunov aa, briancon sh. (1992) quadruple electrical transitions in isotopes 156,158,160,162,164dy. izv as ussr, ser. fiz., 56(1):121-128. [4] gromov kya, usmanov ph.n, xolmatov a.x, butabaev yu.s, niyazov r. a. (1993) nonadiabaticity of monopole and quadrupole transitions of 156gd yadernay fizika, 56(12): p.28 [5] bohr a, mottelson b. (1997) nuclear structure, vvol. 1,2 (new york: benjamin) [6] usmanov ph.n, mikhailov in. (1997) effects of nonadiabaticity of collective motion in even–even deformed nuclei. phys. part. nucl. 28(4):348–373 [7] fahlander c, varnestig b, bäcklin f., svensson l.e., disdier d., kraus l., linck i., schulz n. pedersen j. (1992) coulomb excitation of 172yb. nucl. phys., a147:157-172 nomenclature i) greek letters β nuclear bands (energy level band)  nuclear bands (energy level band) φ wave function ii) subscript i angular momentum k quantum number h hamiltonian microsoft word vol11_no1_final iium engineering journal, vol. 11, no. 1, 2010 al-khateeb and al-khateeb 41 design and performance analysis of vco for standard gsm using mems khalid a. s. al-khateeb* and wajdi f. al-khateeb department of electrical and computer engineering, kulliyah of engineering, international islamic university malaysia, p.o. box 10, kuala lumpur, 50728, malaysia *e-mail: khalid@iiu.edu.my abstract: the design of a prototype monolithic micro electro-mechanical systems (mems) electronic circuits, namely the voltage controlled oscillators (vcos) is presented. the components can achieve the stringent requirements of wireless communication applications such as gsm cellular telephony. the vco meets the low phase noise specifications of -136 dbc/hz at large offset frequency of 3mhz, over the appropriate frequency range. the model of the monolithic vco is based on the topology of the colpitts oscillator. it is relatively less complicated, which facilitates the practical integration of the mems components into the configuration. the variable capacitor and the monolithic 3-d coil inductor are suitable for low phase-noise and low power consumption at the application frequencies. a pspice simulation model was developed with mems switching devices that can be integrated into the system. the model helps in determining the design parameters, which affect the performance and operation reliability of the rf transceiver system, for which a prototype has been tested and proved successful. keywords : mems; electronic circuits; vco; gsm; phase noise. 1. introduction mobility and portability are features, which have a strong driving force in the miniaturization process of wireless communication interfaces. they have raised much interest in single-chip applications. the integration of passives devices such as variable capacitors and inductors, typically involves some trade-offs between noise, power consumption, linearity, frequency range, gain and supply voltage. higher q-factors and lower insertion losses however, may mitigate some of the trade-offs. a low phase noise vco operating at radio frequency (rf) can be designed by integrating a variety of suitable mems components. other applications that may involve mems capacitive switches are output-stage audio amplifiers, which should satisfy the gsm specifications. the important design parameters however, have to be identified before the implementation of such circuits. mems can be used to replace standard variable capacitors (varicaps) and inductors. both of these passive components can be fabricated on silicon substrates and thus are amenable to monolithic integration by standard ic processes. the mems technology is attractive for the implementation of on-chip high-quality rf variable capacitors and inductors, especially in low noise power amplifiers, matching networks, iium engineering journal, vol. 11, no. 1, 2010 al-khateeb and al-khateeb 42 and monolithic low-noise vcos. in fact, the q-factor of these components may ultimately determine the phase noise performance, which is critical in high performance communication systems [1]. the introduction of mems in rf systems increases the functionality and improves the performance. the challenge however remains in how to minimize the phase noise while maintaining lowest possible power consumption.. 2. the phase noise the requirements of a versatile vco are low phase noise, low power consumption, wide tuning range and a high power output. however, to achieve these characteristics all at once is a challenging task, because of trade-offs. much of the research is aimed at reducing the phase noise, which is a rapid short term random fluctuation. it can be expressed in terms of signal to noise power ratio in unit bandwidth. the expression, which can be used to calculate the noise power at the offset frequency fm, is based on the classical leeson’s model [2]: …… ………… ( 1 ) where; f is the excess noise factor, k boltzmann constant, t the absolute temperature, ao the amplitude of oscillation, q the resonator loaded quality factor, rp is the parallel resistance to model losses in the resonator, and δf1 / f 3 is the corner frequency in the phase noise spectrum. for an ideal oscillator, the shape of the spectrum is an impulse at a resonant frequency, ωo. however, in actual oscillators, a skirt shape is formed around ωo. figure 1(a) shows the single spike of energy at the center carrier frequency, ωo and figure 1(b) shows the skirts around ωo due to phase noise. actually, the phase noise is expressed as the power at particular offset, ωm from ωo. the signal power is measured in a 1 hz bandwidth at ωm [3]. the unit of phase noise is dbc/hz represented as decibels below the carrier per hertz. (a) (b) fig. 1: (a) output spectra of ideal oscillator, (b) output spectra of practical noisy oscillator. iium engineering journal, vol. 11, no. 1, 2010 al-khateeb and al-khateeb 43 in the prototype mems oscillator, there is an additional noise source due to the mechanical thermal vibration, which is included instead of thermal and flicker noise. in practice, this kind of additional noise is due to the vibrations of the suspended plate which cause variation in the capacitance and affect the overall output of the phase noise [1]. 3. mems passive devices in vco there are two approaches to design and fabricate a vco using mems passive devices. the first is to replace the mos capacitors with mems, which is good for a wide tuning range. the second is to use a monolithic 3-d coil inductor. the high q varicap is a key element in a low phase noise vco. the mems varicap also enables a complete monolithic fabrication of rf vco for on-chip ic compatible devices, with lower loss, larger tuning range and higher linearity [4]. the high-q variable capacitor can be realized by a surface micro-machined all aluminum microstructure. the top and cross-section are shown in fig. 2. it consists of 1 µm-thick aluminum plate suspended in air 1.5 µm above the bottom layer and anchored with four folded beam suspensions acting as springs. aluminum sheet resistance is low, which is critical to minimize the ohmic losses, and the fabrication temperature of 150ºc [1] is also low. the plate size of 200 µm by 200 µm and 1.5 µm nominal air gap results in a nominal capacitance value of approximately 200 pf. thus, large capacitance can be obtained by parallel connection [5]. in rf transceivers, the dc tuning voltage is typically limited to 3.3 v or less. thus with a 1.5 μm air gap and a 200 μm square plate it requires 3.8 n/m for a 3.3 v operation. this corresponds to a mechanical resonant frequency of 30 khz [1]. each of the suspension four folded beams is 100 μm long and 20 μm wide as in fig. 2. fig. 2: micro-machined variable capacitor. a high q inductor is another key element in low phase noise vco, since the inductors produced by silicon processes cannot provide high q factors, due to ohmic loss in the thin metal layers and eddy-currents [6]. several methods have been proposed. however, the bond-wires types are chosen as an attractive alternative because the q values are at least an order of magnitude higher than the on-chip spiral inductors. they have been iium engineering journal, vol. 11, no. 1, 2010 al-khateeb and al-khateeb 44 implemented in rf vcos and high efficiency power amplifiers. the 3-d microstructure also minimizes the capacitive coupling and eddy current loss, leading to larger q-factor at higher frequencies. bigger inductors and smaller capacitors allow operation with less power [6]. in a high q inductor every mm of bond-wire contributes about 1 nh. therefore, a few nh requirement for wireless applications can be provided readily, with a lead frame of a standard ic package [1]. fig. 3: 3-d coil inductor. the 3-d coil inductor, shown in fig. 3, consists of two 5 μm thick turns, 50μm wide copper traces electroplated around an insulating core with a 650µm by 500µm crosssection. the core is alumina, which has negligible loss tangent, which is another key parameter to ensure high q. a core width of 500µm is found experimentally to be the minimum that avoids tilting during attachment. the fabrication process is described in details elsewhere [8]. 4. the design procedure of the vco there are many types of oscillator topologies which can be used to construct an rf vco for frequencies below 1 mhz. for frequencies above 1 mhz however, lc feedback oscillators are normally used. due to the frequency limitations of most op-amps, transistor amplifiers are used as the gain elements. thus, a popular topology, which proved successful in many commercial modules, is the colpitts oscillator (fig. 4), due to its simplicity, robustness and wide range of operating frequencies, from if to rf [8]. the frequency is determined by the resonant frequency of the feedback network, which is a parallel resonant tank circuit, in which any change in the inductor or capacitor will change the oscillation frequency, fo given by: ………………….. ( 2 ) 1 2 t f l c    iium engineering journal, vol. 11, no. 1, 2010 al-khateeb and al-khateeb 45 where, ct = cv + c12, cv = (cvar x co)/(cvar + co), and c12 = (c1 x c2) / (c1 + c2) (note: the above equation is accurate only if the lc circuit has a high q). fig. 4: colpitts circuit topology for vco. fig. 5: the actual circuit design of the vco. considering the colpitts vco (fig. 5), which uses parallel-mode lc tank configuration, the analysis is straightforward. the fet is a medium power amplifier as compared to a bipolar transistor. it may provide double the power for a given frequency or double frequency for a given power. in fact, fet can be used up to 30 ghz. at 10 ghz, the fet itself may actually provide several watts of output power [9]. in the simulation model however, the vco operates at a frequency fo of approximately 1 ghz. iium engineering journal, vol. 11, no. 1, 2010 al-khateeb and al-khateeb 46 the task for phase noise performance analysis is to reconfigure the colpitts oscillator as an amplifier with positive lc feedback, as in fig. 5. hence a readily available set of design equations can be used, which are clear and convenient. instead of only analyzing the phase noise, this model can also be useful in calculating the loop gain and the amplitude of the oscillation [9]. the factors that affect the accuracy of phase noise simulation and measurement are many. it may be possible addressed these factors accurately with a prudent selection of the passive components and proper resonator modeling. for an acceptable level of simulation accuracy of a vco that operates at rf and above, all components in the linear network such as transmission lines and discontinuities must be accurately characterized over several harmonics of the fundamental oscillation frequency. this is important because the accuracy of the oscillation signal affects the noise analysis, and the noise analysis itself depends on the linear network. this means that any inaccuracy in the network characterization will affect the quality of the phase noise simulation. the simulation accuracy of the vco will ultimately determine the parameters of all the fabricated parts, including the dimensions of the circuit board, material properties, and component models of any parasitic behavior [10]. 5. analysis of the vco design microwave office is a software, which can be useful in simulating many circuit designs. therefore it has been for the simulation of the vco. it also enables the prediction of the performance characteristics. the analysis can either be performed in the frequency domain using the harmonic balance technique, or in the time domain using transient simulators such as spice and spectre. the simulation method involves three main steps. first, it attempts to locate the start-up frequency with respect to the well-known loop gain criterion. when the loop gain saturates to a magnitude of 1 in the large-signal steady state, the simulator will step the probe voltage in an attempt to detect loop gain saturation. then, the neighborhood of gain saturation is used as the starting point for the analysis. then the voltage and frequency of the probe are adjusted in a way that results in zero probe-current. after setting all the requirements, as in fig. 6, the simulation begins to perform the analysis automatically. the analysis uses a special device called oscillator probe that allows fast and robust oscillator simulations, even for the case of extremely high resonator q. the oscillator probe refers to the combination of the source and the ideal impedance element. in the microwave office simulator, the oscillator probe is denoted as oscaprobe, as shown in fig. 7. the most significant probe parameters are fstart and fend. these parameters indicate the range of search for start-up frequency. another parameter is the fsteps, which refers to the number of steps used in the search for start-up frequency and rarely needs to be changed from default. however, in extremely high-q cases, fsteps may be increased or the frequency range is narrowed. the recommended location of the oscillation probe is at a node connecting the resonator and the active device. iium engineering journal, vol. 11, no. 1, 2010 al-khateeb and al-khateeb 47 oscnoise id=ns1 ofstart=1e-8 ghz ofend=0.1 ghz ofsteps=5 swptype=log harm={1,2} fig. 6: flow chart of the analysis. fig. 7: schematic symbol of oscaprobe. the main objective of simulating the vco is to measure the phase noise performance, then to compare it with the values of a real prototype vco at the offset frequency of 3mhz. the oscnoise simulator shown in fig 8 was employed to determine the phase noise performance of the vco. the results are shown in fig. 9. the phase noise is measured in db/hz offset from the carrier and is plotted on a log frequency scale. in this simulation, the ofstart and ofend parameters were set to 1e-008 ghz and 0.1 ghz respectively. fig. 8: schematic symbol of oscnoise. it is shown that at an offset frequency of approximately 3mhz, the value of the phase noise is -138.05 dbc/hz, which is in good agreement with the actual value for the prototype -136 dbc/hz. the noise components in conventional lc tuned oscillators are; electrical thermal noise, flicker noise (l/f noise), supply voltage noise, and the noise contribution from the substrate. in practical mems tuned lc oscillators however, additional phase noise is introduced by the mechanical thermal vibration of the variable capacitors. the vibration of the suspended plates causes variation in the capacitance value, which results in phase noise or jitter in the output frequency [1]. the noise power spectral density due to plate displacement can be expressed as follows: oscaprobe id=x1 fstart=1 ghz fend=2 ghz fsteps=200 vsteps=40 iium engineering journal, vol. 11, no. 1, 2010 al-khateeb and al-khateeb 48 fig. 9: plot of the simulated phase noise. …. …. …. …. ( 3 ) where k is boltzmann constant, t is the absolute temperature, b is damping coefficient due to the surrounding gas ambient and internal dissipation of the system, ωn is the mechanical resonant frequency of the capacitor, km is the structure compliance and qm is the mechanical quality factor. additional phase noise can be further expressed as given below: … … … … … ( 4 ) where xo is the nominal air gap of the capacitor, n is the number of parallel-connected devices and α is the ratio between the nominal tank tunable capacitance and its parasitics, fo and fm are the oscillation and the offset frequencies, respectively. these two equations enable the phase noise induced by the brownian motion to be determined at various offset frequencies. for a typical design condition in which xo = 1.5μm, qm ≅ 1 at 1 atm, ωn = 2π (30 khz), n = 4, α ≅ 0.5, and fo = 1ghz, the phase noise at offset frequencies fm of 10khz, 100khz, and 3 mhz are respectively [1] 64dbc/hz, -105dbc/hz, and -136dbc/hz, typical wireless communication applications specify low phase noise requirement at relatively large offset frequency, for example –136 iium engineering journal, vol. 11, no. 1, 2010 al-khateeb and al-khateeb 49 dbc/hz at 3 mhz offset for gsm. in order to fulfill these norms, the vco phase noise must be maintained better than –135 dbc/hz at 3 mhz offset over the appropriate frequency range of 855 mhz to 863 mhz. 6. conclusion mems tunable vco is a viable proposition for gsm applications. it can provide superior performance characteristics over other types of vco. it is expected to make large impact in many applications, especially in wireless mobile telephony. the phase noise analysis performed by simulation and described explicitly in this work is one of the most important aspects of vco design. the microwave office software tool can be very useful in designing such circuits and predicting their performance. it is a powerful tool for simulation and design analysis of linear and nonlinear circuits and for measurements carried out under specifically set conditions. the practical application of the vco simulation model was the fabrication using real mems passive devices i.e. the high-q variable capacitors and 3-d coil inductors. the prototype in which mems constitute the frequency determining components of low phase-noise with low power consumption may prove to be commercially attractive, as it meets the stringent performance requirements of gsm at the application frequencies. references [1] d. j. young, v. malba, a. f. bemhardt, and b. e. boser, “a micromachined rf low phase noise voltage-controlled oscillator for wireless communications”, iedm dig. tech. papers, pp. 285-300, 24 april 2001. [2] d.b. lesson, “a simple model of feedback oscillator noise spectrum”, proc. ieee, 54 (2), pp. 329-330, 1996. [3] v. k. saraf, “low power wide tuning range lc-vco using rf mems passives”, master thesis, univ. of carnegie mellon, pittsburgh, pa, august 2004. [4] b. s. darade and t. a. parmar, “low phase noise fully integrated vco”, 18th intl. conference on vlsi design, jan 2005. [5] d. j. young and b. e. boser, “a micromachined variable capacitor for monolithic low-noise vcos”, solid-state sensor and actuator workshop, dig. tech. papers, pp. 86-89, june 1996. [6] e. c. park, y. s. choi, j. yoon, s. hong and e. yoon, “fully integrated low phasenoise vcos with on-chip mems inductors”, ieee transactions on microwave theory and techniques, vol. 51, no. 1, january 2003. [7] d. j. young, v. malba, j. j. ou, a. f. bemhardt and b. e. baser, “monolithic highperformance three-dimensional coil inductors for wireless communication applications”, iedm dig. tech. papers, pp. 67-70, december 1997. [8] r. h. berube, “computer simulated experiments for electronic devices using electronic workbench”, prentice-hall, inc., 2000. [9] c.o’connor, “develop a trimless voltage-controlled oscillator”, microwaves & rf magazine, pp. 94-105, 2000. [10] d.vye, “improving vco phase noise performance through enhanced characterization”, high frequency electronics magazine, pp. 56-60, 2004. 496 iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 81 the cauchy problem for the system of equations of thermoelasticity in e n i.e. niyozov and o.i. makhmudov department of mechanics and mathematics, samarkand state university boulevard 15, 103004, samarkand, uzbekistan.. iqboln@mail.ru, olimjan@yahoo.com abstract: in this paper, we consider the problem of analytical continuation of solutions to the system of equations of thermoelasticity in a bounded domain. that is, we make a detailed analysis of the cauchy problem regarding the values of thermoelasticity in bounded regions and the associated values of their strains on a part of the boundary of this domain. abstrak: di dalam kajian ini, kami menyelidiki masalah keselanjaran analitik bagi penyelesaian-penyelesaian terhadap sistem persamaan-persamaan termoelastik di dalam domain bersempadan berdasarkan nilai-nilainya dan nilai tegasannya bagi sebahagian daripada sempadan domain tersebut, iaitu kami mengkaji masalah cauchy. keywords: cauchy problem; system theory of elasticity; elliptic system; ill-posed problem; carleman matrix; regularization 1. introduction in this paper, we consider the problem of analytical continuation of the solution of the system equations of the thermoelasticity in spacious bounded domain from its values and values of its strains on part of the boundary of this domain, i.e., we study the cauchy problem. since, in many actual problems, either a part of the boundary is inaccessible for measurement of displacement and tensions or only some integral characteristics are available. therefore, it is necessary to consider the problem of continuation for the solution of elasticity system of equations to the domain by values of the solutions and normal derivatives in the part of boundary of domain. the system of equations of thermoelasticity is elliptic. therefore, the cauchy problem for this system is ill-posed. for ill-posed problems, one does not prove the existence theorem: the existence is assumed a priori. moreover, the solution is assumed to belong to some given subset of the function space, usually a compact one [1]. the uniqueness of the solution follows from the general holmgren theorem [2]. on establishing uniqueness in the article studio of ill-posed problems, one comes across important questions concerning the derivation of estimates of conditional stability and the construction of regularizing operators. our aim is to construct an approximate solution using the carleman function method. let x = (x1, ….., xn) and y = (y1, ….., yn) be points of the n-dimensional euclidean space e n , d a bounded simply connected domain in e n , with piecewise-smooth boundary consisting of a piece ∑ of the plane yn = 0 and a smooth surface s lying in the half-space yn > 0. iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 82 suppose ))(),(),...,((=)( 11 xuxuxuxu nn + is a vector function which satisfies the following system of equations of thermoelasticity in d [3]: 0,=)(),( xub x ω∂ (1) where ,),(=),( 1)(1)( +×+ ∂∂ nn xjkx bb ωω and ,1,...,=,,)()(=),( 2 2 njk xx b jk jkxjk ∂∂ ∂ +++∆∂ µλρωµδω ,1,...,=,=),( 1)( 1)( nk x b n xnk + + ∂ ∂ −∂ γω ,1,...,=,=),( 1)( nj x ib j xjn ∂ ∂ ∂ + ωηω ,=),( 1)(1)( θ ω ω i b xnn +∆∂ ++ δij is the kronecker delta, ω is the frequency of oscillation and λ, µ, ρ, θ its coefficients which characterize the medium, satisfying the conditions 0.>0,>0,>0,>230,> η γ θρµλµ + the system (1) may be written in the following manner:     ++∆ +−++∆ 0,= 0=)( 2 divuiv i v ugradvdivugradu ωη θ ω ρωγµλµ where ))(),((=)( xvxuxu . this system is elliptic, since, its characteristic matrix is , 1000 0)()()( 0)()()( =)( 2 2 1= 2 212 121 2 1= 2 1 λ λλλλλ λ λ ni n i ni n i ξξµαξµξµλξξµα ξξµαξξµαξµξµλ ξχ ++++ ++++ ∑ ∑ and for arbitrary ),...,(= 1 n ξξξ with real components satisfying the conditions 1,= 2 1= i n i ξ∑ we have 0.)(=)( 2 ≠+ µλµξχdet statement of the problem. find a regular solution u of the system (1) in the domain d by using its cauchy data on the surface s: iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 83 ,),(=)())(,(),(=)( syygyuyryfyu y ∈∂ ν (2) where ))(,( yr y ν∂ is the stress operator, i.e., =)),(,(=))(,( 1)(1)( +×+ ∂∂ nn ykjy yryr γνν �� ���� � � ���… … … … … … …… … … … . . ����0 0 … … … � ��, ,),(=),(= nxn yjky ttt νν ∂∂ ,1,...,=,, )( )()(=),( njk yy y y t jk k j j kykj ν δλµνµνλν ∂ ∂ ++ ∂ ∂ + ∂ ∂ ∂ ))(),...,((=)( 1 yyy n ννν is the unit outward normal vector on d∂ at a point y, ),,,(= 11 +n fff κ ),,(= 11 +n ggg κ are given continuous vector functions on s. 2. construction of the carleman matrix and approximate solution for the cap type domain it is well known that any regular solution )( xu of the system (1) is specified by the formula −∂−ψ∫∂ )}())(,(){,((=)(2 yuyryxxu yd νω ,,))()},( ~ ))(,( ~ { * dxdsyuxyyr yy ∈−ψ∂− ων (3) where the symbol − * means the operation of transposition, ψ is the matrix of the fundamental solutions for the system of equations of steady-state oscillations of thermoelasticity: given by ,),(=),( 1)(1)( +×+ ψψ nn jk xx ωω +         ∂∂ ∂ −−−ψ ++∑ jk lnl kj njnk l jk xx x 2 1)(1)( 3 1= 2 ))(1[(1=),( αδ πµ δ δδω , || )||(exp ])(1)(1 1)(1)(1)(1)(1)(1)( x xi xx i l lnjnk k nknj j njnkl λ γδδδγδδωηδβ ++++++ +         ∂ ∂ −− ∂ ∂ −+ 0,=1,2,3;=, 2))(2(2 )((11)( = 3 1= 2 3 2 1 2 2 21 11 l l lll l l l i α πρω δ λλµλπ δδλωθ α ∑− −+ +−− −− 0,=1,2,3;=, ))(2(2 )(1)( = 3 1= 2 1 2 2 21 l l ll l l l β λλµλπ δδ β ∑ −+ +− ,)2(=0,=1,2,3;=, )(2 ))((1)( = 122 1 3 1= 2 1 2 2 21 2 1 2 − + − +−− ∑ µλρωγ λλπ δδλ γ kl k l l lll l l iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 84 ),,(=),( ~ ,),( ~ =),( ~ 1)(1)( ωωωω xxxx kjkjnnkj −ψψψψ +×+ ππ =))(,( ~ yr y ν∂ �� ����� � � ����… … … … … … …… … … … . . �����0 0 … … … � ��. definition. by the carleman matrix of the problem (1),(2) we mean an (n+1)×(n+1) matrix π(y,x,ω,τ) depending on the two points y,x and a positive numerical number parameter τ satisfying the following two conditions: ),,,(),(=),,,(1) τωτω xygyxxy +−ψπ where the matrix g(y,x,τ) satisfies system (1) with respect to the variable y on d, and ψ(y,x) is a matrix of the fundamental solutions of system (1); ),(|)),,,(),(||),,,((|2) \ τετωντω ≤π∂+π∫∂ yysd dsxyrxy where 0,)( →τε as ;∞→τ here || π is the euclidean norm of the matrix ,||=|| 1)(1)( +×+ ππ nnji i.e., .|=| 2 1 2 1 1=,       ππ ∑ + ji n ji in particular, .|=| 2 1 2 1 1=       ∑ + m n m uu from the definition of carleman matrix it follows that. theorem 1. any regular solution u(x) of system (1) in the domain d is specified by the formula −∂π∫∂ )}(),(){,,,((=)(2 yurxyxu yd ντω ,,))()},,,(),( ~ { * dxdsyuxyr yy ∈π∂− των (4) where π(y,x,ω,τ) is the carleman matrix. using this matrix, one can easily conclude the estimated stability of solution of the problem (1), (2) and also indicate effective method decision this problem as in [4 6]. with a view to construct an approximate solution of the problem (1), (2) we construct the following matrix: ,),,(=),,( 1)(1)( +×+ ππ nn kj xyxy ωω (5) +         ∂∂ ∂ −−−π ++∑ jk lnl kj njnk l kj xx xy 2 1)(1)( 3 1= 2 ))(1[(1=),,( αδ πµ δ δδω ),,,(])(1)(1 1)(1)(1)(1)(1)(1)( llnjnk k nknj j njnkl kxy xx i φ+         ∂ ∂ −− ∂ ∂ −+ ++++++ γδδδγδδωηδβ where , )()( =),,()( 22 2 0 su duku xysui ysuik imkxyxkc nn n n n +        −++ ++ φ ∫ ∞ ψ (6) iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 85    ≥+ ≥ 1,1,2=,cos 1,,2=),( =)( 0 mmnku mmnkuuj kuψ )(0 uj -bessel's function of order zero, 2 11 2 11 )(...)(= −− −++− nn xyxys and    +−−⋅− −−⋅− − − 1.2=,1)!(2)(21)( 2=,2)!(2)(21)( =,2= 2 mnmn mnmn cc n nm n nm n πω πω π k(ω),ω = u + iv (u, v are real), is an entire function taking real values on the real axis and satisfying the conditions: ,<)( ∞∞≠ uforuk 0,=)( /uk .,0,...,=,<),(|=)(exp|sup 1)( 1 rumpupmkimk p v ∈∞ ≥ ων the following theorem was proved in [7]. lemma 1. for function φ(y,x,k) the following formula is valid |,=|),,,()(=),,( xyrkxygikrkxyc nnn −+φ ϕ where n ϕ are fundamental solutions of the helmholtz equation, gn(y,x,k) is a regular function that is defined for all y and x satisfies the helmholtz equation: 0.=)( 2 nny gkg −∂∆ in (6) we put )(exp=)( τωωk . then ),,(=),,( kxykxy −φφ τ su duku xysui xysui im s kxyc nn nn m m n +        −++ −++ ∂ ∂ −φ ∫ ∞ − − 22 2 01 1 )()(exp =),( ψτ τ ,)( sin )(cos)(exp= 2 2 22 01 1 duku su su xyu s xy nnm m nn ψ τ αττ         + + −++− ∂ ∂ − ∫ ∞ − − (7) .=),( τ τ τ ∂ φ∂ −φ′ kxy ,)( sin )(exp=),( 2 2 01 1 duku su su s xykxyc m m nnn ψ τ τ τ + + ∂ ∂ −−φ ′ ∫ ∞ − − ),,()(exp=),( 1 1 sk s xykxyc m m nnn ττ ψτ ′ ∂ ∂ −−φ′ − −        − −′ kksj mnks k >),)(( 2 1 2=,)(cos <0, = 22 0 22 ττπ τ τ ψ τ iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 86 now, in formulas (5) and (6) we set ),(=),,( kxykxy −φφ τ and construct the matrix ),,,(=),,( τωω xyxy ππ from lemma 1 we obtain, lemma 2. the matrix π(y,x,ω,τ) given by (5) and (6) is carleman's matrix for problem (1), (2). indeed by (5), (6) and lemma 1 we have ),,,(),,(=),,,( τωτω xygxyxy +ψπ where ,),,(=),,( ττ xygxyg kj +         ∂∂ ∂ −−− ++∑ jk lnl kj njnk l jk xx xyg 2 1)(1)( 3 1= 2 ))(1[(1=),,( αδ πµ δ δδτ +         ∂ ∂ −− ∂ ∂ −+ ++++ k nknj j njnkl xx i )(1)(1 1)(1)(1)(1)( δγδδωηδβ 1.1,...,=,),,,,(] 1)(1)( ++ ++ njkkxyg lnlnjnk τγδδ by a straightforward calculation, we can verify that the matrix g(y,x,τ) satisfies the system (1) with respect to the variable y everywhere in d. by using (5), (6) and (7) we obtain ),(exp)(|),),,,(),(||),,,((| 1\ n m yysd xxcdsxyrxy τττωντω −≤π∂+π∫∂ (8) where c1(x) is a bounded function inside of d. let us set .))()},,,(),( ~ {)}(),(){,,,((=)(2 * yyys dsyuxynryurxyxu τωντω τ π∂−∂π∫ (9) the following theorem holds. theorem 2. let u(x) be a regular solution of the system (1) in d such that .\,|)(),(||)(| sdymyuryu y ∂∈≤∂+ ν (10) then for 1≥τ the following estimate is valid: ).(exp)(|)()(| 2 n m xxmcyuyu ττ τ −≤− by formulas (4) and (9) we have .))()},,,(),( ~ {)}(),(){,,,((|=)()(|2 * \ yyysd dsyuxyryurxyxuxu τωνντω τ π∂−∂π− ∫∂ now on the basis of (8) and (10) we obtain the required estimate. next we write out a result that allows us to calculate u(x) approximately if, instead of u(y) and ),(),( yur y ν∂ its continuous approximations )( yf δ and )( yg δ are given on the surface s: iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 87 1.<<0,|)()(),(|max|)()(|max δδν δδ ≤−∂+− ygyuryfyf y ss (11) we define a function )(xu δτ by setting ,))()},,,(),( ~ {)(),,,((=)(2 * yys dsyfxyrygxyxu δδδτ τωντω π∂−π∫ (12) where 0.>,max=, 1 = 0 0 nn d n n xxx m ln x δ τ then the following theorem holds: theorem 3. let u(x) be a regular solution of the system (1) in d satisfying the condition (10). then the following estimate is valid: .,)(|)()(| 0 3 dx m lnxcxuxu m n x n x ∈      ≤− δ δ δτ from all of the above results we immediately obtain a stability estimate. theorem 4. let u(x) be a regular solution of the system (1) in d satisfying the conditions: sdymyuryu y \,|)(),(||)(| ∂∈≤∂+ ν and .1,<<0,|)(),(||)(| syyuryu y ∈≤∂+ δδν then ,)()(|)(| 0 4 m n x n x m lnxcxu       ≤ δ δ where cds yx cxc ynd ~ , || 1~ =)( 4 − ∫∂ is a constant depending on λ, µ , ω. corollary 1. the limits )(=)(lim),(=)(lim 0 xuxuxuxu δτ δ τ τ →∞→ hold uniformly on each compact subset of .d 3. regularization of solution of the problem (1), (2) for a cone type domain let ),,(= 1 n xxx κ and ),,(= 1 n yyy κ be points in ρ de n , be a bounded simply connected domain in n e whose boundary consists of a cone surface 1>0,>, 2 =,=,=: 2 1 2 1 2 11 ρ ρ π τατα ρρ nnn ytgyyy − ++σ κ and a smooth surface s lying in the cone. assume ρdxx n ∈)(0,...0,=0 . iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 88 we construct carleman matrix. in formula (5), (6) we set ( )[ ] 1.>0,>,=)( ρτωτω ρ n xek − then 0>),,(=),,( kkxykxy −φφ τ su duku xysui xysuie im s kxyc nn nn m m n +        −++ −++ ∂ ∂ −φ ∫ ∞ − − 22 2 01 1 )())(( =),( ψτρ τ (13) .=),( τ τ τ ∂ φ∂ −φ′ kxy [ ]{ } ,)((=),( 2 2 01 1 su duku xysuieim s kxyc nnm m n + −++′ ∂ ∂ −φ′ ∫ ∞ − − ψ τ ρτ where eρ(w) is mittag-löffer`s entire function [8]. for the functions ),( kxy −φτ hold lemma 1 and lemma 2. further, we may show similar estimate for uτ (x) and uτδ (x) (in cone case) defined in (9) and (12), as theorems 1, 2, 3, and 4. for the simplicity let us consider n = 3, since the other cases are considered analogously. suppose that dρ is a bounded simple connected domain in e 3 with boundary consisting of part ∑ of the surface of the cone 0,>1,>, 2 =,= 3 2 3 2 2 2 1 ytgyyy ρ ρ π ττ ρρ + and of a smooth part of the surface s lay inside the cone. assume ρ dxx ∈)(0,0,= 30 . we construct carleman`s matrix. in formulas (5), (6) we take , cos)( )(4 1 =),,( 2 33 2 1 0 3 1 2 su duku xysui we im xe kxy +−++ φ ∫ ∞ ρ ρ ρ ρ τ τ τπ (14) where 3 2 = ysuiw ++ . for the functions ),,( kxy τ φ holds lemma 1. it follows from the properties of eρ(w) that for σ∈y and ∞<<0 u the function ),,( kxy τ φ defined by (13) its gradient and the second partial derivatives 1,2,3,=,, ),,( 2 jk yy kxy jk ∂∂ φ∂ τ tends to zero as ∞→τ , for a fixed . ρ dx ∈ then from (5) we find that the matrix π(y,x,ω,τ) and its stresses ),,,(),( των xyr y π∂ also converge to zero as ∞→τ for all ,σ∈y i.e., π(y,x,ω,τ) is the carleman matrix for the domain ρd and the part σ of the boundary. iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 89 if u(x) is a regular solution of the system (1) then the following integral formula .))()},,,(),( ~ {)}(),(){,,,((=)(2 * yyy d dsyuxyryurxyxu τωνντω ρ π∂−∂π∫∂ holds. for ρ dx ∈ we denote by )(xu τ the following: .))()},,,(),( ~ {)}(),(){,,,((=)(2 * yyys dsyuxyryurxyxu τωνντω τ π∂−∂π∫ (15) then the following theorem holds. theorem 5. let u(x) be a regular solution of the system (1) in dρ such that .,|)(),(||)(| σ∈≤∂+ ymyuryu y ν (16) then for 1≥τ the following estimate is valid: ),(exp)(|)()(| 3 3 000 ρ ρτ ττ xxmcxuxu −≤− where 0,>,)(0,0,= 330 xdxx ρ ∈ .|,=|, 1 =)( 003 0 0 constantcxyrds r cxc y −−∫σ ρρρ let us take continuous approximations fδ(y) and gδ(y) of u(y) and )(),( yur y ν∂ , respectively, i. e., 1<<0,|)()(),(|max|)()(|max δδν δδ ≤−∂+− ygyuryfyu y ss and define the following function ,))()},,,(),( ~ {)(),,,((=)(2 * yys dsyfxyrygxyxu δδδτ τωντω π∂−π∫ then the following theorem holds. theorem 6. let u(x) be a regular solution of the system (1) in the domain dρ satisfying the condition (16), then ,)()(|)()(| 3 000 δ δ ρδτ m lnxcxuxu q ≤− where ,)(max=,)(= 3 ρρρ ρ δ ττ ysirer m lnr s + − . 11 =)(,)(= 4 0 3 0 0 3 y ds rr cxc r x q       +∫σρρ ρ the theorem is proved analogously as theorems 3 and 4. corollary 2. the limits )(=)(lim),(=)(lim 0 xuxuxuxu δτ δ τ τ →∞→ hold uniformly on each compact subset of . ρ d iium engineering journal, vol. 15, no. 1, 2014 niyozov and makhmudov 90 references [1] lavrent'ev, m. m. “some ill-posed problems of mathematical physics.” , springerverlag, (1967). [2] petrovskii, i. g. “lectures on partial differential equations [in russian].”, fizmatgiz press, moscow(1962). [3] kupradze, v. d., burchuladze, t. v., gegeliya, t. g. “three-dimensional problems of the mathematical theory of elasticity [in russian]”, nauka press, moscow(1968). [4] makhmudov, o. i., niyozov, i. e. “the cauchy problem for the lame system in infinite domains in rm. journal of inverse and ill-posed problems, 14(2006):905-24. [5] makhmudov, o. i., niyozov, i. e. “regularization of a solution to the cauchy problem for the system of thermoelasticity.” contemporary mathematics. ams, primary, 382(2005):35-72. [6] makhmudov, o. i., niyozov, i. e., tarkhanov, n. “the cauchy problem of couple-stress elasticity.” contemporary mathematics. ams, 455(2008):207-310. [7] yarmukhamedov, sh. ya. “cauchy problem for the laplace equation.” journal. dokl.acad.nauk sssr [soviet math.dokl.], 357(1997):320-357. [8] dzharbashyan, m. m. “integral transformations and representations of functions in a complex domain [in russian],”nauka press, moscow. (1966) microsoft word modified 79-3 pagee1-14.doc iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 1 anti-windup scheme for practical control of positioning systems wahyudi, tarig faisal and abdulgani albagul department of mechatronics engineering, international islamic university, malaysia, jalan gombak, 53100 kuala lumpur, malaysia e-mail: wahyudi@iiu.edu.my, tarig_2@hotmail.com, albagul@iiu.edu.my abstract: positioning systems generally need a good controller to achieve high accuracy, fast response and robustness. in addition, ease of controller design and simplicity of controller structure are very important for practical application. for satisfying these requirements, nominal characteristic trajectory following controller (nctf) has been proposed as a practical point-to-point (ptp) positioning control. however, the effect of actuator saturation can not be completely compensated for due to the integrator windup as the plant parameters vary. this paper presents a method to improve the nctf controller for overcoming the problem of integrator windup using simple and classical tracking anti-windup scheme. the improved nctf controller is evaluated through simulation using a rotary positioning system. the results show that the improved nctf controller is adequate to compensate for the effect of integrator windup. keywords: positioning, point-to-point, integrator windup, compensation, controller, robustness. 1. introduction motion control systems play important roles in industrial process such as machine tools, semiconductor manufacturing systems and robotic systems. one type of motion control systems is the point-to-point (ptp) positioning system, which is used to move a plant from one point to another. the positioning systems generally need a good controller to satisfy some stringent requirements such as high accuracy, fast response and robustness. up to now many types of controllers have been proposed and evaluated for positioning systems; for example the model following type controller such as controllers with disturbance observer [1-4], time-optimal controllers [5-8] and sliding mode controllers [9,10]. these controllers would give good positioning performance in cases an expert in motion control system designs the controller using the exact model and value of its parameters. in general, advanced controllers tend to be complicated and require deep knowledge of controller theory. however, in practical applications, engineers who are not expert in control system often need to design controller. in addition, exact modeling and parameter identifications are generally troublesome and time consuming tasks. hence,  correspondence author iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 2 ease of controller design and simplicity of controller structure are very important in practical application. in order to overcome these problems, nominal characteristic trajectory following (nctf) controller has been proposed as a practical controller for point-to-point (ptp) positioning systems [11]. it has been shown that, the nctf control system has a good positioning performance and robustness [12, 13]. the nctf controller is also effective in compensating the effect of the friction which is a source of positioning inaccuracy [14]. however, the effect of actuator saturation can not be completely compensated for due to integrator windup as a result of the variation of the plant parameters [15]. the nctf controller gives an excessive overshoot when both actuator saturation and parameter variations (especially inertia variation) occur in the positioning systems. this paper describes a method to improve the nctf controller for overcoming the degradation of the positioning performance due to the integrator windup. first, nctf control concept and its controller design procedure are introduced. then, an improved compensator for overcoming the integrator windup is described. finally, the effectiveness of the improved nctf controller is examined by simulation. 2. nctf control concepts the structure of the nctf control system is shown in fig. 1. the nctf controller consists of a nominal characteristic trajectory (nct) and a compensator. the nctf controller works under the following two assumptions: a dc or an ac servomotor is used as an actuator of the plant. ptp positioning systems are chosen, so r is constant and 0 r . here, the objective of the nctf controller is to make the plant motion follows the nct and end at the origin of the phase plane ( , e e ). figure 2 shows an example of a plant motion controlled by the nctf controller. the motion comprises two phases. the first one is the reaching phase whilst the other one is the following phase. in the reaching phase, the compensator forces the plant motion to reach the nct as fast as possible. however, in the following phase the compensator controls the plant motion so as to follow the nct and end at the origin. the plant motion stops at the origin, which represents the end of the positioning motion. thus, in the nctf control system, the nct governs the positioning response performance. the nctf controller is designed based on a simple open-loop experiment of the plant as follows: open-loop-drive the plant with stepwise inputs and measure the displacement and velocity responses of the plant. iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 3 plant + compensatore up e nominal characteristic e  )e,e(p  dt d controller o trajectory (nct) r upu fig. 1: nctf control system. plant motion nct o rp : reaching phase fp : following phase fp rpe error e e rr or ra te fig. 2: nct and plant motion. figure 3(a) shows the stepwise inputs, and the velocity and displacement responses due to the stepwise inputs. in this paper, the rated input to the actuator ur is used as the height of the stepwise inputs. construct the nct by using the plant responses. the velocity and displacement responses are used to determine the nct. since the main objective of ptp system is to stop the plant at a certain position, a deceleration process is used, see curve a, fig. 3(a). the h in fig. 3 represents the maximum velocity. from the curve in the area a and h in fig. 3(a), the nct in fig. 3(b) is determined. since the nct is constructed based on the actual responses of the plant, the nct includes nonlinearity effects such as friction and saturation. the important nct information, which will be used to design the compensator, are nct inclination m near the origin and maximum error rate of h. in this case, from the relationship between plant dynamics of eq. (1) and fig. 3(b), it is clear that the inclination near origin m and the maximum error rate h relate with parameters of the plant as follows [12,15]: iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 4   r h k u (1)   m (2) design the compensator based on the nct information. u r h h (b) nominal characteristics trajectory (nct) aa input velocity displacement in pu t, d is pl ac em en t,v el oc ity time h o error e e e rr or r at e a a (a) stepwise inputs and responses h m fig. 3: nct determination. here, the following pi compensator is adopted due to its simplicity:   p p i pu k u k u dt (3) where kp and ki are proportional and integral gains respectively. using the pi compensator parameters kp and ki, and the nct characteristic near the origin (see fig. 3(b)), the transfer function of the closed-loop positioning system controlled by the nctf controller can be approximated as follows [11-15]: 1 2 ( ) ( ) ( ) ( ) ( )    r s g s g s g s s (4) where iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 5 1( )     g s s (5a) 2 2 2 2 2 ( ) 2         n n n n g s s (5b) 2   npk k (5c) 2   nik k (5d) when  and n are large enough, g(s) becomes nearly equal to g1(s), which represent the condition when the plant motion follows the nct as the objective of the nctf control system. moreover, large  and n also make the closed-loop system robust to friction or inertia variation of the plant in continuous systems [9]. finally, by using  and n as design parameters and considering eqs. (2) and (3), the pi compensator parameters are designed as follows: 2  n rp u k mh (6) 2  n ri u k mh (7) here, n and  are design parameters which should be decided by the designer. generally speaking, a higher  and a larger  are preferable in the design of pi compensator parameters. however digital implementation of the nctf controller limits the design parameters to maintain the closed-loop stability. detailed discussion on the theoretical background of the nctf control system can be seen in [12, 15]. due to the fact that the nct and the compensator are constructed from a simple openloop experiment of the plant, the exact model including the friction characteristic and the identification task of the plant parameters are not required to design the nctf controller. therefore, the controller design is simple and easy to implement in practical situation. 3. compensator improvement since the nctf controller uses pi compensator to force plant motion so that it follows the nct, the integrator windup up may occur in connection with large position reference. as discussed in [15], in the case of no parameter variations, there is no significant integrator windup due to the effect of the saturation. the effect of the saturation is successfully compensated for using nctf controller. however, the integrator windup becomes a problem when the parameters vary [15]. iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 6 to overcome the problem of integrator windup, the pi compensator is improved by adopting an anti-windup scheme. hence an anti-windup pi compensator is proposed to be used instead of a pure pi compensator. here, a simple and classical tracking anti-windup is used [16]. the structure of the anti-windup pi compensator is illustrated in fig. 4(a), where kt is called the tracking gain. based on fig. 4(a), once pi compensator output u(s) exceeds the actuator limits, a feedback signal is generated from the difference of the saturated and the unsaturated signals. this signal is used to reduce the integrator input. mathematically, the output of the anti-windup pi compensator is      ( )         i t p p s k k u s k u s u s u s s s (8) where kp and ki are proportional and integral gains obtained from section ii. kp ki kt up(s) us(s) + + kt u(s) (a) standard structure of anti-windup pi compensator (b) alternative structure of anti-windup pi compensator um -um + + u(s) s 1 kp ki up(s) + + + s 1 fig. 4: proposed anti-windup pi compensator. the anti-windup pi compensator, shown in fig. 4(a), may be replaced by the structure shown in fig. 4(b) where the unsaturated signal is used as input to the dead zone so that the feedback signal is generated. the dead zone range from –um to um represents the linear range of the actuator. furthermore, the dead zone gain b relates with integral gain ki and tracking gain kt as follows: iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 7  t i k b k (9) a rule of thumb for the setting of kt is often kt = ki which corresponds to b = 1, but a higher values may give a further improvement in performance [16]. 4. results 4.1 system description the nctf controller with anti-windup pi compensator is examined using a dynamic model of the experimental rotary positioning system as shown in fig. 5. the positioning system consists of an ac servomotor, a driver and an inertia mass (spindle). for examining the positioning performance, the detailed model of fig. 6 is used. its parameters are shown in table i. the positioning performance is examined under two conditions namely normal plant and increased inertia plant. normal plant has the nominal plant parameters described in table 1, while increased inertia plant has about 10 times spindle inertia than that of normal plant. fig. 5: experimental rotary positioning system. cjs 1 rls 1  s 1 + su velocity controller current controller friction model vk bk tkspk s k k cicp  )(s)(s+ + + + fig. 6: detailed model of rotary positioning system. iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 8 table i: parameters of the plant. parameter value inertia load, j 1.17 x 10-3 kgm2 motor resistance, r 1.2  motor inductance, l 8.7 mh motor torque constant, kt 0.57 nm/a back-emf constant, kb 0.57 vs/rad viscous friction, c 1.67 x 10-3 nms/rad frictional torque, f 0.215 nm proportional current gain, kcp 26.2 v/a integral current gain, kci 3.62 x 103 v/as proportional velocity gain, ksp 8.60 x 10-2 as/rad input voltage range, ur  6 volt 4.2 controllers design first, the nctf controller is designed based on the normal plant. figure 7 shows the nct as a result of a simulated experiment. according to fig. 7, the inclination m and maximum error rate of h of the nct are 67.4 rad and 240 rad/s respectively. the compensator parameters are designed by using h and m of the nct. for designing the pi compensator, design parameters  and n are chosen as 13 and 29 rad/s respectively [15]. table ii shows the value of the compensator parameters calculated with (2). -15 -10 -5 0 5 10 15 -200 -100 0 100 200 m = -67.4 h = -240 e rr or r at e ra d/ s error rad fig. 7: nominal characteristic trajectory (nct). the performance of the positioning system controlled by nctf controller is compared with that controlled by pid controller. the pid controller is designed so that it has a similar bandwidth with the nctf control system [15]. in this paper, the pid controller iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 9 tuned with ziegler-nichols rule is not discussed again since it gives a bad robustness to parameter variations [15]. the pid controller parameters are also shown in table ii. 4.3 the effect of the tracking gain kt on positioning performance the crucial problem for anti-windup pi compensator is the value of the tracking gain kt. although it is stated that a rule of thumb for the setting of kt is often kt = ki which corresponds to b = 1, but a higher value may give a further improvement in performance [16]. therefore, in order to find the appropriate value of kt, a simulation study has been carried out for different values of b which represent the ratio between tracking gain kt and integral gain ki. simulations have been done based on increased inertia plant and large step input references (i.e. 5 rad and 10 rad step inputs) so that a saturation can occur. moreover, the positioning performance is evaluated based upon maximum overshoot and 2 % settling time. figure 8 shows the effect of the tracking gain kt on the positioning performance. figure 8(a) clearly shows that the overshoot can be reduced by using anti-windup pi compensator. in addition, a larger gain tracking results in a smaller overshoot. as shown in fig. 8(b), however, the settling time may become longer when a larger tracking gain kt is used. therefore, the tracking gain should be decided based on the compromise between the overshoot and settling time. by considering a small enough overshoot and a shortest settling time, the gain ratio b = 12 is selected to set the tracking gain kt. 0 5 10 15 20 25 30 0.0 0.2 0.4 0.6 0.8 1.0  r = 5 rad  r = 10 rad o ve rs ho ot % s et tli ng ti m e s gain ratio b=k t /k i 0 5 10 15 20 25 30 0 20 40 60  r = 5 rad  r = 10 rad (a) overshoot (b) settling time gain ratio b=k t /k i fig. 8: effect of tracking gain on positioning performance. iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 10 4.4 comparison with pid controller in this section, the performance of the positioning system controlled by the nctf (nctf-2) controller with anti-windup pi compensator is compared with that of the normal nctf (nctf-1) and pid controllers. figure 9 shows the step responses to 0.5 rad step input when the controllers are used to control normal plant. the positioning performance is summarized in table iii. as shown in fig. 9(b), the 0.5-rad step input does not cause the saturation of the control signal. here, it is clear that all controllers produce a similar response due to a similar bandwidth. hence, in terms of overshoot and settling time, all the controllers produce similar performance. 0.0 0.5 1.0 -4 -2 0 2 4 6 8 0.0 0.5 1.0 0.00 0.25 0.50 0.75 (b) control signal nctf nctf-2 pid c on tro l s ig na l v time s (a) step responses to a 0.5-rad step input nctf-1 nctf-2 pid d is pl ac em en t r ad time s fig. 9: comparison of response to a 0.5-rad step input, normal plant. moreover, in order to evaluate the robustness of the control systems to inertia variation, all the controllers are implemented on an increased inertia plant. figure 10 shows the step responses to a 0.5-rad step input when all the controllers are implemented for controlling increased inertia plant. table iii shows the positioning performance resulting from all the controllers. figure 10 and table iii show that both nctf controllers are more robust to inertia variation than the pid controller. both nctf controllers give similar results since there is no significant saturation of the actuator as shown fig. 10(b). the result confirms that the use of anti-windup pi compensator does not affect the positioning performance when there is no saturation of the actuator. iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 11 0.0 0.5 1.0 -4 -2 0 2 4 6 8 0.0 0.5 1.0 0.00 0.25 0.50 0.75 (b) control signal nctf-1 nctf-2 pid c on tr ol s ig na l v time s (a) step responses to a 0.5-rad step input nctf-1 nctf-2 pid d is pl ac em en t r ad time s fig. 10 comparison of response to a 0.5-rad step input, increased inertia plant. next, simulation is done for a larger step input so that the actuator is saturated. figure 11 shows the step responses to a 5 rad step input when all the controllers are implemented for controlling increased inertia plant. table iv shows the positioning performance resulting from all the controllers. the saturation of the actuator occurs as shown in fig. 11(b). the saturation of the actuator causes an integrator windup when the positioning system is controlled by both nctf-1 and pid controller. however, fig. 11(a) and table iv show that the positioning performance of the positioning system with nctf-1 is worse than that of pid controller. hence the nctf-1 becomes less robust to inertia variation when the saturation occurs in comparison with that with pid controller. on the other hand, nctf-2 which uses anti-windup pi compensator can successfully compensate the effect of integrator windup due to actuator saturation. as the results show, the improved nctf controller (nctf-2) gives a smaller overshoot and a shorter settling time than the other controllers. hence it can be concluded that the improved nctf controller which uses antiwindup pi compensator can maintain the robustness to parameter variation even if the actuator of the plant saturates. iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 12 0.0 0.5 1.0 -6 -4 -2 0 2 4 6 0.0 0.5 1.0 0.0 2.5 5.0 7.5 (b) control signal nctf-1 nctf-2 pid c on tr ol s ig na l v time s (a) step responses to a 0.5-rad step input nctf-1 nctf-2 pid d is pl ac em en t r ad time s fig. 11: comparison of response to a 5-rad step input, increased inertia plant. furthermore, another simulation is done to compare the improved nctf controller with anti-windup pid controller. for this purpose, an anti-windup scheme described in section iii which is similar to that of nctf controller is used. two gain ratios for b are used. the first anti-windup pid controller (pid-1) uses a gain ratio b of 1, in which the gain tracking is equal to integral gain of pid controller. while, the second anti-windup pid controller (pid-2) uses a gain ratio of 12, which is the same as the improve nctf controller. figure 12 shows the step responses to a 5-rad step input when all of the controllers are implemented for controlling increased inertia plant. table iv shows the positioning performance resulting from all of the controllers. figure12 and table iv show that although the use of anti-windup pid controllers improves the robustness to inertia variation as compared to the normal pid controller, they are still less robust to inertia variation when compared to the improved nctf controller. hence, it can be concluded that the improved nctf controller is much more robust than anti-windup pid controllers. 5. conclusions this paper has documented the improvement of the nctf controller for overcoming the effect of windup due to actuator saturation. an anti-windup pi compensator is used as compensator of the nctf controller instead of a conventional pi compensator. through simulation, using rotary positioning system, the effectiveness of the nctf controller with iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 13 anti-windup pi compensator is evaluated. the results confirm that the use of anti-windup pi compensator is effective in overcoming the problem that arises from the integrator windup. moreover, the obtained results also show that the nctf control system with antiwindup pi compensator is much more robust to inertia variation than that of conventional pi compensator and the pid controllers. 0.0 0.5 1.0 -6 -4 -2 0 2 4 6 0.0 0.5 1.0 0.0 2.5 5.0 7.5 (b) control signal pid-1 nctf-2 pid-2 c on tro l s ig na l v time s (a) step responses to a 0.5-rad step input pid-1 nctf-2 pid-2 d is pl ac em en t r ad time s fig. 12: comparison of response to a 5-rad step input, increased inertia plant. references [1] k. umeno, t. kanoko and y. hori, "robust servosystem design with two degree of freedom and its applications to novel motion control of robot manipulators", ieee trans. on industrial electronics, 40 (5), pp. 473-485, 1993. [2] s. endo, h. kobayashi, c.j. kempf, s. kobayashi, m. tomizuka and y. hori, “robust digital tracking controller design for high-speed positioning systems”, control engineering practice, 4(4), pp. 527-536, 1996. iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 14 [3] m. tomizuka, “robust digital motion controllers for mechanical systems”, robotics and autonomous systems, 19, pp. 143-149, 1996. [4] c. kempf and s. kobayashi, “disturbance observer and feedforward design for a highspeed direct-drive positioning table”, ieee trans. on control systems technology, 7(5), pp. 513-526, 1999. [5] s. wu and j. fu, “time-optimal control of servo systems using pd algorithms”, jsme international journal: series c, 41(3), pp. 384-390, 1998. [6] m.h. park and c.y. won, “time optimal control for induction motor servo system”, ieee trans. on power electronics, 6(3), pp. 514-524, 1991. [7] m.l. workman, r.l. kosut and g.f. franklin, “adaptive proximate time-optimal servomechanisms: continuous time case”, proceedings of the american control conference, minneapolis, usa, pp. 589-594, 1987. [8] c.j. kempf, “step and settle positioning algorithm for electro-mechanical system with damping”, proceedings of the 4th international workshop on advanced motion control, tsukuba, japan , pp. 47-52, 1996. [9] s. sankaranarayanan and f. khorrami, “adaptive variable structure control and applications to friction compensations”, proceedings of the 36th ieee conference on decision & control, san diego, usa , pp. 4159-4164, 1997. [10] y. fujimoto and a. kawamura, “robust servo-system based on two-degree-of-freedom control with sliding mode”, ieee trans. on industrial electronics 42(3), pp. 272-280, 1995. [11] wahyudi, “new practical control of ptp positioning systems”, ph.d thesis, tokyo institute of technology, 2002. [12] wahyudi, k. sato and a. shimokohbe, "robustness evaluation of new practical control method for ptp positioning systems", proceeding of 2001 ieee/asme international conference on advanced intelligent mechatronics, pp. 843-848, 2001. [13] wahyudi, k. sato and a. shimokohbe, "new practical control method for ptp positioning systems: robustness evaluation", proceeding of 10th international conference on precision engineering, pp. 774-778, 2001. [14] wahyudi, “robustness evaluation of two control methods for friction compensation of ptp positioning systems”, proceeding of 2003 ieee conference on control applications, pp. 1454-1458, 2003. [15] wahyudi, k. sato and a. shimokohbe, “characteristics of practical control for point-topoint (ptp) positioning systems: -effect of design parameters and actuator saturation on positioning performance”, precision engineering, vol. 27, pp. 157-169, 2003. [16] c. bohn and d.p. atherton, “a simulink package for comparative studies of pid antiwindup strategies”, proceeding of ieee/ifac joint symposium on computer-aided control system design, pp. 447-452, 1994. biographies wahyudi was born in indonesia in july 1970. he received his b.eng and msc degrees in mechanical engineering from institute of technology bandung, indonesia in 1994 and 1997 , respectively and his ph.d. in precision machinery systems from tokyo institute of technology, tokyo, japan, in 2002. he is currently an assistant professor at the mechatronics engineering department, international islamic university malaysia. his iium engineering journal, vol. 5, no. 2, 2004 wahyudi et al. 15 research fields are motion control, mechatronics and intelligent systems. dr. wahyudi is a member of ieee. tarig faisal was born in khartoum, sudan 1978. he received his b.sc. degree in electronic engineering from the university of jazeera in 2001. he joined nor al eyon company as a control engineer in 2001. currently, he is a master student at mechatronics engineering department, international islamic university malaysia. his primary research interests are design, analysis and performance evaluation of intelligent as well as industrial control systems. abdulgani albagul received his b.sc. degree in electronic engineering from the higher institute of electronics in baniwalid, libya in 1989, msc, in control engineering from university of bradford in 1993 and ph.d. in engineering from university of newcastle upon tyne in 2001. he is currently an assistant professor at the department of mechatronics engineering, faculty of engineering at the international islamic university malaysia. his research interests are control systems, system dynamics and modeling, smart sensor and instrumentation, robotics and automation. he is a member of ieee and he has several publications. microsoft word 4-83 page 55-64.doc iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 55 characterization of fairness of information distribution in a mobile agent based adaptive information system iftikhar ahmed and jafar sadiq department of electrical & computer engineering, international islamic university malaysia, 53100 kuala lumpur, malaysia email: a.iftikhar@iiu.edu.my, jsadiq@iiu.edu.my abstract: the information age is now passing through an evolutionary phase. as the capacity of networks is increasing to handle and process huge volume of information traffic, the management of such information systems is becoming a trivial issue. the internet being the largest source of information provision is heterogeneous in nature with constantly evolving environment. new information services are added whereas some are modified or removed. user’s demands and interests also change constantly. in such a dynamic environment it is very difficult to maintain a coherent picture of the information services. a novel technique proposed recently employs autonomous mobile agents in faded information field architecture to facilitate information provision and servicing in this new era of information age. the architecture is decentralized in nature whereby both the service provider and information seeker communicate through mobile agents. however, the degree of fairness of information distribution and access is still a problem to be addressed. this paper investigates the issue of fairness among information users for access to information in a networked environment that uses mobile agent technology and faded information field architecture to service the system. a number of algorithms were simulated and their effectiveness is discussed in the paper. simulation results are presented that show a lot of potential to address the issue of fairness in information systems. keywords: mobile agents, information systems, intelligent systems. 1. introduction information in today’s business environment has become the prime ingredient of a successful business enterprise. the rapid advances in information and communication technologies (ict) have given new impetus to the way business is conducted on the internet with information being the key element of a successful business enterprise. the traditional paradigms of business, learning and other essential services are undergoing an evolution. the internet is a huge data repository that is expanding without a central authority. the number of worldwide internet users is predicted to exceed one billion by the end of 2005 [1]. moreover 300 terabytes of information is published online every year [2]. iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 56 as the performance demands of the internet and its usage increase exponentially, the emphasis is shifting from platform centric computing to network centric computing. information systems have to be designed that are distributed, dynamic and have high assurance and fault tolerance to meet the heterogeneous demands of users. as ict advances, the dynamics of e-commerce tend to be more data intensive and complex. the traditional business to customer paradigm is encompassing the business to business transactions as well. companies have to comprehend the trends and demands of the users quickly in order to survive in the competitive environment of today. the expectations of users and customers have soared high and they seek the provision of a flawless any time any where service. the traditional information services based on the client-server model therefore cannot cope with the rising demand placed by the complexities of data intensive heterogeneous computing. it is therefore imperative to employ new techniques to address these problems in order to reduce the network traffic and improve user’s access time to services. information fading technique was reported recently which is based on demand-oriented service architecture [3]. the architecture balances the cost of information provision and utilization on the network by employing push and pull mobile agents to service user requests and conduct the business of information provision on the network. in the faded information field (fif) the service provider distributes the most demanded and popular information contents closer to its vicinity on various nodes. the volume of information is inversely proportional to the distance of information storing node from the service provider. thus the fif permits the fairness of information distribution to unspecified users with equal access time. 2. information service system performance requirements the wide area network services are gradually creeping into our daily lives with the number of users of these services constantly on the rise. the information systems now involve a constantly changing environment where stringent performance demands are placed on the network. the businesses are taking advantage of the wide area network facility to offer bargains and put various items on sales and special promotions resulting in the users having much more flexibility and choice available making the process of information provision and utilization a complex matter to deal with on the network. it is thus imperative for an information system to respond to both user needs and service provider (sp) requirements to respond in time to these needs in a rapidly changing environment. the main desirable attributes of such a system therefore should be flexibility, reliability and quick reaction time. only a system with these properties can successfully satisfy both users and sps in the current setting of information age. the traditional data retrieval methodologies on the optimization of digging in a huge data base to satisfy a search request. however, the fif employs the concept of autonomous provision and utilization of information based on mobile agents. the amount of information to be faded away from sp is a function of network conditions like iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 57 congestion, popularity of information contents and any other criteria programmed into mobile agents [3]. 2.1 the fif architecture the information in a fif is distributed on various nodes in the system. the information pattern in the filed is analogous to the electromagnetic radiation radiated from an antenna, high in intensity near the antenna and low in intensity away from the antenna. the sp fades away the information contents to the nodes in the field with the richness in information contents inversely proportional to the distance of the node from the sp through push mobile agents (mas). the user on the other hand sends out pull mas seeking the desired information [3-4]. the general schematic of fif architecture is depicted in fig. 1. fig. 1: the layout of fif architecture. 2.2 fif system components the system essentially consists of logically connected nodes through which users and service providers correspond. mobile agents are used by both parties to acquire and provide information respectively, under evolving/changing situation. the mobile agents (ma) generated by service providers are termed as push mobile agents (push mas). push mas carry out the function of autonomous coordination and negotiation with other nodes for information fading according to network situation and the level of importance attached to the information. the level of importance of particular information content is based on its popularity, determined from a high hit rate of query by the information seeker on the network. the pull mobile agents (pull mas) are generated by users and they autonomously navigate in search of the required information on the network nodes in a step by step fashion. once the required information is located, these agents report back to the source. the push and pull mas have no direct correspondence with each other. information volume fif network information fading information gradient information field outer boundary pull ma push ma iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 58 the third important subsystem of a fif is the node itself. it is a platform for both storage of information and program execution. it monitors the local information-based system conditions and autonomously makes decisions for allocation requests by the sp. it determines the upper directions to the information service in addition to response times on its upper directions. the upper directions or stages of information eventually point to the sp node whereas the lower directions to the information service lead to the outer nodes away from the sp. each subsystem is autonomous in terms of control to execute its operations and coordination with other nodes under evolving network conditions. 2.3 communication format in the fif the conventional communications techniques cannot cope with the evolving conditions in a heterogeneous network environment where the state of nodes, the status of the sps, and the stability of connections are highly unpredictable as the user demand to access the information is dynamic in nature. fif therefore employs a different technique referred to as content code communication technique [3]. an example of content code communication is depicted in fig.3 where the information about a university is structured according to the degree of importance. sp1 specifies the university name followed by cm1 indicating the location of university with respect to country and city. cm2 depicts the programs offered by the university. the message format components thus lead to the breakdown of the principal source of information available on the sp into its uniquely defined characteristic codes (cms). push mas are sent out in the fif by sps specifying content codes (cms) of information to the nodes using the message format shown in fig. 3. the selection of information storage/allocation is autonomously carried out by the nodes based on cms. similarly the pull mas sent out by the users search for the required information based on cms. fig. 2: the message format in a fif architecture. s p1 c m1 c m2 c m3 c m4 university location program fee start date iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 59 3. a survey of mobile agents a distributed environment is most suitable for the employment of mobile agents. the details of such applications in a distributed environment can be found elsewhere [5-7]. only, a brief introduction of mobile agents and their role in a network based information system will be discussed. the term mobile agent is often context-dependent and has two separate and distinct concepts: mobility and agency. the term agency implies having the same characteristics as that of an agent. these are self-contained and identifiable computer programs that can move within the network from node to node and act on behalf of a user or other entity. these can halt execution from a host without human interruption [8]. the current distributed network environment is based on the traditional client-server paradigm. in case of mobile agents employed in a network, the service provision and utilization can be distributed in nature and is dynamically configured according to the changing network performance metrics like congestion and user demand for service provision [3]. the two network environments are depicted in fig. 3 both for client-server and mobile agents. mobile agents are typically suited to applications requiring structuring and coordinating wide area network and distributed services involving a large number of remote real time interactions [9]. fig. 3: a mobile agent is a network aware program that can conserve bandwidth in a complex adaptive information system environment. request response client/server communication mobile agent communication request server server client client mobile agent wide area network shell response iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 60 4. fairness of information distribution and utilization simulation the purpose of information fading in a network is twofold:  congestion reduction – the server hosting a popular site is highly likely to get congested. the information provider could employ additional machines (child nodes) to which the original server would distribute or fade its information contents. a pull ma entering the network of the parent server could then access any of the child nodes, (may be referred to as an sp cluster) which would service the agent’s request for the desired information and therefore reduce the service request traffic load on the parent server (sp) in the network.  fairness of access – service providers (whether commercial or non-commercial) would like their information contents to be easily accessible by the users on the network. the established and renowned service providers stand out compared to new competitors as their search details are already indexed by search engines. not only the new service providers suffer a long delay in getting their nomenclature indexed by a search engine, but they are the tail enders on the search engine index. this particular scheme of indexing by search engine creates disparity among service providers on the network. a faded information field system therefore can aid in creating fairness among various contenders of information provision and utilization on the network. for congestion reduction, the service provider must use its own resources to create the field because the congestion reduction benefits only the provider. however, for advertising, each information provider cannot be expected to have the resources to create a field for themselves. in such a scenario, it is possible that each server participates in the faded information field as being part of the field in addition to being a source of information. thus, no one is the owner of the faded information field resources, and there is neither prohibition nor delay in becoming a member of the field. for the sake of localization (prioritizing a nearby service provider over a distant one), information should be faded in a geographic area as close as possible around the server. the faded information distance away from the sp was approximated in the simulations using propagation delays of information on the network. for the sake of fairness, the field size of all sps should be equal. this is taken to be the number of nodes that constitute the field. several possible algorithms exist for creating similar field sizes, these are outlined below:  sorting. the service provider maintains a list of nodes sorted by delay (as a substitute for physical distance). it can thus determine how “far” it needs to send its push-mas to create the standard field size, and imposes a travel restriction beyond the envisaged perimeter of its field. the push-mas will be required to keep updating the field until they reach the boundary of the sps field. alternatively the push-mas can be multicast to the required nodes in the field. sorting technique is resource intensive since it must be employed to account for cost update in the system as and when it occurs. iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 61  step size. the service provider determines the average step distance (d) from each server from the closest to the furthest. the approximate distance that the sp envisages to cover in its fif is given by the relation s = d x n where n is the number of nodes on the network constituting the fif of the sp where the information contents will be distributed. the step size must be recomputed every time there is an update in the system. during the course of simulation, it was discovered that for 50 servers, this procedure was twice as fast as the sorting strategy discussed earlier.  averaged step size. in order to account for skewing of sps’ distances, an average distance is computed for each server that is used to determine the step size instead. for a total of 50 servers simulated, its time to execute was not significantly different from the step size algorithm.  modified averaged step size. the averaged step size algorithm still gets affected by the skewing of data. the algorithm was modified by computing the average step size of all the costs excluding the minimum and maximum costs of system information updates. a simulation engine was programmed that mimicked a wide area network environment. the performance of each of the aforementioned algorithms was tested by simulation using the programmed simulation engine with randomly distributed servers connected to randomly distributed gateways. the simulation involved 50 servers and 200 routers/gateways. djikstra’s algorithm [10] was used to determine the server-to-server costs. under a standard policy used in the simulations, each server was allowed to maintain a field size of 10 nodes. figure 4 demonstrates the field size distribution for this wide area network. 0 5 10 15 20 25 30 35 40 45 0 5 10 15 size of field n um b er o f s er ve rs step size averaged mod. average sorting fig. 4: field size distribution versus the number of nodes in the network. iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 62 it was observed that the sorting algorithm gave the closest approximation to the required distribution. however, the step size method failed to give the required distribution when it was required to provide a field size of 10 nodes. the averaged step size method faired a little better. it gave better field distribution since the distances are skewed to the higher end thus diminishing the field size below the required size. however, the modified average method gave a very good average of 10.8 nodes per faded information field but the servers did not all have equal numbers of nodes in their fields in this case. in order to account for skewing, a multiplier was introduced into the algorithms for step size and averaged step size. the step size algorithm was set to produce a field size of 15 nodes and the averaged step size algorithm a field size of 16 nodes. the results are shown in fig. 5. 0 5 10 15 20 25 30 35 40 45 0 5 10 15 size of field n um be r o f s er ve rs step size averaged mod. average sorting fig. 5: compensation for skewing. it can be seen that the field sizes are better distributed with no processing overhead. the averaged step size results finally show a significant improvement over the normal step size results, as expected. in the second simulation run, the sorting algorithm had an average field size of 10.2 nodes per information provider, the step size algorithm had 10.3, the averaged step size had 10.5 and the modified average had 10.8 nodes respectively. also, the averaged step size algorithm gave a fair distribution of field size, with most of the servers within a certain range. the simulation was repeated using 150 routers instead of 200 to determine the effect of network size on the field size. the number of servers was kept the same. figure 6 shows the field size without any multiplier and fig. 7 depicts the field size with a multiplier. again, the sorting and modified average algorithms both produced the required field size, whereas the other two algorithms did not. the step size algorithm this time needed only a multiplier of 1.2 to give an acceptable average, but the average step size algorithm still iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 63 needed a multiplier of 1.6. the latter produced a decent distribution of field size. and further simulation is required to determine the effects of network size on the above algorithms, as well as the effect of required field size. the preliminary simulations demonstrated that the sorting algorithm gives the best distribution of field size. without a multiplier, the modified average algorithm gives the best performance, whereas, with a multiplier, the averaged step size algorithm gives the best distribution among the three non-sorting algorithms. fig. 6: field size without a multiplier. fig. 7: field size with a multiplier. 0 5 10 15 20 25 30 0 5 10 15 size of field n u m b er o f s er ve rs step size averaged mod. average sorting 0 5 10 15 20 25 30 0 5 10 15 size of field n um b er o f s er ve rs step size averaged mod. average sorting iium engineering journal, vol. 6, no. 1, 2005 i. ahmed and j. sadiq 64 5. conclusion faded information filed concept has been reviewed in addition to a survey of mobile agents. a faded information field was simulated by programming a network simulation engine. a number of algorithms were tested on the simulation engine to characterize the network behavior with respect to fairness of information distribution by various service providers on the network. the simulation provided a comparative analysis of algorithms to achieve this goal in addition to discovering a need to introduce a multiplicative factor to fine tune the performance of the algorithms evaluated for the purpose. it was discovered that without a multiplier, the modified average algorithm gave the best performance. but with a multiplier, the averaged step size algorithm turned out to be the best in distributing the information fairly distribution among the three non-sorting algorithms. these results indicate that the faded information technique can be used to provide equal access rights to the information seekers and equal information distribution rights to the service providers on the network thus creating fairness of information provision and utilization. references [1] l. g. roberts,” beyond moore’s law: internet growth trends,” ieee computer, vol. 33, no. 1, p.117, 2000. [2] p. lyman and h. r. varian, “how much information” journal of electronics publishing, vol. 6, issue 2, december 2000. [3] h. f. ahmad, h. arfaoui and k. mori, “autonomous information fading by mobile agents for improving user’s access time and fault tolerance,” proceedings, 5th international symposium on autonomous decentralized systems, p. 279-283, 2001. [4] h. arafoui and k. mori,” autonomous navigation architecture for load balancing user demands in distributed information systems,” ieice transactions on communications, e84b(10), p.1085-1093, 2001. [5] a. karmouch and v. a. pham, “mobile software agents: an overview,” ieee communications magazine, vol. 36, no. 7, july 1998. [6] m. k. perdikeas et al, “mobile agents standards and available platforms,” comp.net., vol. 31, no. 19, 1999, p. 1999-2016, august 1999. [7] d. b. lange and m. oshima, “seven good reasons for mobile agents,” communications of the acm, vol. 42, no. 3, march 1999, p. 88-89, march 1999. [8] j. cao, g. h. chan, w. jia, and t. dillon, “check-pointing and rollback of wide-area distributed applications using mobile agents,” proceedings international parallel and distributed processing symposium. san francisco: ieee computer society press, april 2001. [9] s. funfrocken,” integrating java-based mobile agents into web servers under security concerns,” proceedings 31st hawaii international conference on system sciences, p.34-43, january. 1998. [10] marta steenstrup,” routing in communications network,” prentice hall new jersey, usa, p.143-144, 1995. 524 iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 1 aeroelastic flutter analysis of supersonic wing with multiple external stores nur azam and erwin sulaeman department of mechanical engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728, kuala lumpur, malaysia. esulaeman@iium.edu.my abstract: flutter may be considered to be one of the most dangerous aeroelastic failure phenomenon. the flutter characteristic differs for each aircraft type, and depends on the wing geometry as well as its operational region of subsonic, transonic or supersonic speeds. prior to performing a flight flutter test, extensive numerical simulations and ground vibration tests should be conducted where the structural finite element modes and the experimentation results should be matched, otherwise the numerical simulation model must be rejected. in this paper, the analysis of simulation of a supersonic wing equipped with external missiles loaded on the wing is presented. the structural mode shapes at each generated frequency are also presented. the analysis is carried out using msc nastran fem software. the wing flutter with the external stores was simulated at different altitudes. the result shows that the flutter velocity is sensitive to the flight altitude. for this reason, the flutter analysis is conducted also for a negative altitude. the negative altitude is obtained by considering the constant equivalent speedmach number rule at the flutter speed boundary which is a requirement in standard transport aircraft regulations. abstrak: salah satu fenomena kegagalan aeroelastik yang paling membahayakan adalah kipasan (flutter). ciri-ciri kegagalan kipasan (flutter) adalah berbeza untuk setiap jenis pesawat bergantung pada geometri sayap dan regim operasi sama ada subsonik, transonic atau supersonik. sebelum melakukan ujian penerbangan kipasan ,simulasi berangka luas dan ujian getaran peringkat bawahan (darat) perlu dijalankan di mana struktur mod unsure terhingga dan keputusan eksperimen harus dipadankan, sebaliknya model simulasi berangka boleh ditolak. dalam kertas kerja ini, simulasi sayap supersonic dilengkapi dengan beban luaran peluru berpandu di sayap telah dianalisis di daerah supersonic tinggi. bentuk mod struktur pada setiap mod frekuensi yang dihasilkan juga dipersembahkan secara visual. analisis ini dilakukan dengan menggunakan perisian “fem” msc nastran. kepakan sayap dengan kedai-kedai luar telah disimulasikan pada ketinggian yang berbeza. hasil kajian menunjukkan bahawah alajukipasan(flutter) sensitive terhadap ketinggian penerbangan. atas sebabini, analisis flutter dilakukan juga untuk ketinggian negatif. ketinggian negative diperoleh dengan mempertimbangkan tetap bersamaan kelajuan mach beberapa peraturan pada kelajuan sempadan debar sebagai keperluan dalam peraturan piawaiaan pesawat pengangkutan. keywords: aeroelasticity; flutter; finite element method; external store; mode shape; supersonic wing 1. introduction aeroelasticity can be defined as a branch of aeromechanics that deals with the interaction among inertial, aerodynamic and structural stiffness effects in air vehicle iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 2 design [1]. flutter is a type of aeroelastic instability in which the structure extracts energy from the air stream and unstable self-excited oscillation results in catastrophic structural failure. there are several types of mathematical models used to represent the aircraft structure and it’s mass in aeroelasticity. these include the “beam like” model, “box like’ model, and“box like condensed to a beam like” model [2]. in this paper, the model used for the wing structure is the “box like” representation where structural detail is explored and analyzed accordingly. the present flutter analysis is conducted based on certification standards for military fighter aircraft such as mil-a-8861[3] which put the aeroelastic requirement under subpart 3: construction, material and design and mil-a-8870 at section 6.4 [4]. to determine the initial sizing of wing structure, a maximum aerodynamic load distribution during pitch up maneuver is assumed and a finite element approach has been used to set up the structural stiffness for the wing by recognizing its detailed ‘box like’ construction. the present wing structure data should be validated further by comparing to ground vibration test (gvt) results where the main frequencies and mode shapes of the numerical model should be in agreement with the gvt results [5]. external stores can be defined as any object such as missiles, gun, and fuel tank which are attached to the wing outside the wing box model. since the stores are attached to the wing, the missile launcher is designed based on the missile’s weight and there should be a clearance of at least 8 cm if the missiles are mounted near to each other [6]. each external store center of gravity must be placed as far forward as possible with respect to the elastic axis to delay the occurrence of flutter, while satisfying other design constraints [7]. for this paper, the analysis is performed at varying altitudes where the flow is supersonic and the external stores attached to the wing are two types of missiles. the technical data for the missiles were taken from [8] and [9]. the aeroelastic simulation model used in the present work consists of two parts: structural model and aerodynamic model. the structural model of the wing box skin is modeled using quadrilateral shell elements, while the external store and launcher are modeled using bar elements. the analyses take into account the in-plane membrane characteristics as well as lateral bending and shear deformation of the shell element. the material used for the wing box is aluminum which is used as a base line data for future work where the wing box skin is designed as a composite structure. the aerodynamic model of the wing for the supersonic region is based on the boundary element method where the unsteady aerodynamics is modeled using the zona51 method of msc nastran [10]. for the subsonic region, the doublet lattice method of msc nastran is used [12]. the wing lifting surface is divided into chordwise and spanwise directions using a number of trapezoidal panel elements. it is noted that even though the present wing is designed for the supersonic region, the flutter analysis is required to be conductedinthe subsonic region as well to ensure the instability does not occur in the complete flight design envelope. to ensure compatibility between the structural finite element and aerodynamic boundary element model, a surface spline is used such that the 6 degrees of freedom structural deformations at each point is related to each aerodynamic trapezoidal panel inclination angle. there are several methods to analyze the flutter speed based on frequency matching such as the k method and the pk method [10]. this paper presents the flutter speed results using the pk method. based on [2], the pkmethod is used to determine the aerodynamic stiffness and damping matrices as a function of reduced frequency. iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 3 the sol 103 module of msc nastran is used to simulate the normal modes of each frequency. the sol 145 module is developed to obtain the damping and reduced frequency variation as a function of velocity. from this latter module, the flutter speed can be determined when the graph of velocity versus damping factor is plotted. this paper presents the first 10 fundamental normal modes of sol 103 and determines the flutter speed of this supersonic wing with external stores by considering the variation of altitudes. 2. structural analysis 2.1 supersonic wing characteristics the present work utilizes a wing platform with an aspect ratio of 5 and taper ratio of 0.5. the wing leading edge swept back angle is 30°. the airfoil of this supersonic wing is a double wedge shape as shown in fig. 1. the wedge angle of the airfoil is 10°. along the wing span, the airfoil is divided into three parts which are the main wing box and two control surfaces at the leading and trailing edge. the portions of the leading and trailing edge have been specified as 15% and 20% of the chord length, respectively. the performance of the selected airfoil uses the characteristics provided by [11] for higher supersonic region analysis. the present wing design is used as a baseline for further work where the wing geometry as well as wing composite structure is set as the sensitivity parameter to obtain an optimum supersonic wing design. fig. 1: double wedge airfoil. for the external store, fig. 2 shows the configuration of the loaded missile on the wing. the external stores for each station of wing are specified in table 1. there are two types of missiles used which are amraam and sidewinder. fig. 2: external stores configuration of the wing. iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 4 table 1: external stores technical data. station missile type length [m] diameter [m] mass [kg] 1 aim-9m 2.85 0.128 86.0 2 aim-120 a 3.66 0.178 157.89 3 aim-120 a 3.66 0.178 157.89 2.2 wing loading based on [3], the load factor for the fighter aircraft is set atnz = 5.5. the load for this wing, as shown in fig. 3, is assumed to be an elliptic load acting along the wing span wise (y-axis) direction and symmetric quadratic load along chord wise (x-axis) direction. with this load assumption, the sizing of the wing box can be conducted. fig. 3: wing loading estimation equation. the formula to calculate the load factor is given by eq. (1) in which l is the lift and w is the weight of one side of the aircraft wing based on [11]; nz � lw (1) here the lift can be calculated using eq. (1) l � n�w (2) the span wise elliptic load can be formulated as: � y a� 2 �z bb � 2 � 1 (3) where the value of parameter a is half the span length since it is the length of the major axis, and parameter b is the minor axis.the value of b can be calculated using (6). the chord wise quadratic load distribution is given by: � � �� ��� ���� (4) iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 5 the area of the quadratic load in chord wise direction can be calculated by integrating eq. (4) acting along the x axis. aquadratic � � zb �1‐ �xe�2# e ‐e dx (5) then, the volume of the elliptic load can be found by integrating eq. (5) along the y axis in eq. (3) v� 43 � zb'y(e'y(dy a 0 (6) to find the minor axis of the elliptic equation, eq. (3), equation (2) is divided by 2 since this is only applicable for the half wing, equal to the volume found in eq. (3). this expression can be written as: v� l2 (7) the wing can be assumed as a beam along y axis to find the shear force q and moment m of each section as denoted in eq. (8) and eq. (9), respectively. q'y(� � dq (8) m'y(� � dm (9) 2.3 wing sizing to calculate the skin thickness of the overall wing, the wing is divided into 4 regions along the span and the thickness in each region is calculated based on the maximum load in the respective region as shown in fig. 4 and fig. 5. fig. 4: top view of skin thickness division region. iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 6 fig. 5: skin thickness segment in a region. the moment of inertia formula is given as: i� � h2 da (10) the moment of inertia for the front and rear spar are calculated as a vertical segment in (11): ixx� 112 th3 (11) the moment of inertia for the inclined segments which has an inclination angle of θ, can be derived using eq. (10). this can be done by setting the limit for integration along z axis starting from 0 to the end of each inclination segment denoted as./. the final formula is given by eq. (12): i � tcosθ � ' h2 xtanθ(2dz b' 0 (12) by assuming the thickness to be constant at every skin and spar, equation (12) reduces to form an equation to find the thickness in any region based on the associated moment macting in that region as shown in eq. (13): σy � m h middlei't( (13) where 7 is calculated based oneq. (9), 89:;;<= is the height of the inclination for the front spar of the wing only and >'?( is the summation moment of inertia of the wing box in terms of t as given in eq. (11) and eq. (12). 2.4 safety factor the safety factor fs for the structural strength analysis in the present work is set at 1.5. the shear stress at any location in any region in the y direction is denoted as @a and is calculated using eq. (14) with q as the shear force in that region calculated using eq. (8). the fs can be computed using eq. (15) or eq. (16). τy� qsb i (14) iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 7 τallowτy e f. s (15) σallowσy e f. s (16) 3. unsteady aerodynamics for the prediction of flutter, unsteady aerodynamicloadacting on the wing surface, which is oscillating according to the structural dynamic mode shapes, is estimated using the boundary element method. for the subsonic region, the unsteady aerodynamic loads are calculated using the doublet lattice method (dlm). while for the supersonic region, a constant pressure method of zona51 is used. for both methods, the wing is modeled as a flat lifting surface and is discretized into a number of trapezoidal elements. following [10], a set of aerodynamic influence coefficients in the form of a matrix equation is generated. the fundamental relationships between the lifting pressure and the dimensionless normal velocity induced by the inclination of the surface to the air stream can be formulated as in [10]: hwjj�kajjlmfj/qp (17) where w is the normal wash velocity, f is the aerodynamic pressure, q is the dynamic pressure and a is the aerodynamic influence coefficient matrix. the substantial differentiation matrix of the structural deflections to obtain the downwash is given by eq.(18): hwjj�kdjk1 i k djk2 lmukp mwjgp (18) where k is the reduced frequency. the integration of the pressure to obtain forces and moments yields, mpkp�kskjlmffp (19) the three matrices in eqs. (17), (18) and (19) can be combined to give the aerodynamic influence coefficient matrix in eq. (20): uqkkv�kskjlkajjl‐1udjk1 ikdjk2 v (20) the zona51 and dlm theories compute the a matrix. then, the matrix decomposition forward and backward substitutions are used in the computation of the q matrix. since this wing will be operating in the supersonic region, the zona51 of nastran had been used. for this part, the nastran coding development in view of aerodynamics will consider the outer part of the wing box structure including the control surface as shown in fig. 1. 4. pk method of flutter solution following [10] the pk equation for modal flutter analysis can be formulated as in eq. (21) iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 8 wmhh p2 ybhh‐ 14 ρc\vqhhik ] p ^khh‐ 12 ρv2qhhr `a muhp � 0 (21) where the circular frequency ω and the reduced frequency k are related to p as k� ω c / 2v (22) p � ω ' 2 g i( (23) the flutter solution is rewritten in the state space form as in eq. (24) where a is complex . ua ‐ p ivmuhp� 0 (24) the eigen solution of eq. (24) is in the form of a complex eigen value p for each mode, which in turn will give the structural damping g for the real part and frequency ω for the imaginary part. note that the result is computed for each velocity which is embedded in the damping and stiffness matrix terms of eqn. (21). 5. results 5.1 normal modes – sol 103 of msc nastran for the fem data, the boundary condition at the wing root is rigidly fixed, i.e. no deflection and no rotation in the x, y,and z directions at the front, middle and rear spars of the wing box. the first 8 normal modes of the wing structure are shown in fig. 6 and fig. 7. note that the rigid body mode is not included in the list. the frequency and its associated shape are recorded in table 2. fig. 6: normal mode 1 to 4. iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 9 fig. 7: normal mode 5 to 8. table 2: flutter velocity and flutter mach number at mode 5. altitude [ft] flutter speed [m/s] flutter mach number flutter frequency [hz] -7943 518.5 1.48 9.289 0 581.5 1.71 9.282 10000 677.5 2.06 9.272 20000 799.5 2.53 9.261 30000 954.5 3.15 9.249 5.2 flutter solution – sol 145 of msc nastran sol 145 simulation is further carried out at different mach numbers to find the match point velocity at 0 ft (sea level). the graph of structural damping versus velocity of every mode at 0 ft is plotted in fig. 8. besides that, a graph of velocity versus frequency at 0 ft in fig. 9 is also plotted to show the rapid changes of frequency of the flutter mode. the flutter dominant mode most likely occurs at mode 5 since the graph in fig. 8 shows that the structural damping becomes zero when it approaches a velocity of 581.5 m/s. this is the match point for the graph since at this speed it gives the result of mach number 1.71. the simulation for this solution is repeated for different altitudes. the flutter velocity and flutter mach number for this variation is shown in table 2. the result shows that the present wing flutter is sensitive to altitude. for this reason, the calculation is performed also for a negative altitude where hneg = 7,943 ft. this negative altitude is derived analytically in [13] for transport aircraft and military uav (unmanned air vehicle) [14] as the result of all combinations of altitudes and speeds encompassed by the vdive or mdive versus altitude envelope enlarged at all points by an increase of 15 percent in equivalent airspeed at both constant mach number and constant altitude. iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 10 fig. 8: v-gplot at 0 ft. fig. 7: v-f plot at 0 ft. fig .8: v-gplot at various altitudes. iium engineering journal, vol. 15, no. 2, 2014 azam and sulaeman 11 6. conclusion the present work establishes a procedure for the design of wings based on flutter analysis. the results show that the external stores have a significant effect on wing flutter. it is found that flutter speed of the present wing-external store configuration is sensitive to the flight altitude. the present result is used as a baseline for further work where aeroelastic tailoring is performed to find an optimum composite structure for the main wing box in order to find higher flutter speed and lighter wing structure. acknowledgement special thanks to the science and technology research institute for defense (stride), malaysia for allowing the authors to use msc nastran and msc patran in their facilities. the present research is funded by a research grant from the ministry of education malaysia (grant no. frgs13-020-0261). references [1] erwin hj.(1997)msc developments in aeroelasticity.the macneal-schwendler corporationaerospace users' conference proceedings (california, usa): 1-9. [2] wright jr, cooper je. (2007)aircraft aeroelasticity and loads. john wiley & sons ltd. manchester, united kingdom. [3] mil-a-m8861b(a) (1986) military specification :airplane strength and rigidity flight loads. lakehurst, new jersey: naval air engineering center, systems engineering and standardization. [4] mil-a-8870c(as) (1993)military specification: airplane strength and rigidity vibration, flutter, divergence. lakehurst, new jersey: commanding officer, naval air warfare center aircraft division. [5] peeters b, climent h, diego rd, alba jd, ahlquist jr, carreño jm, wim h, alain r, gonzalo g, jeroen d, jan d.(2008)modern solutions for ground vibration testing of large aircraft. proceeding of 26 th international modal analysis conference (imac 26orlando, usa) 1(4):110-123. [6] raymer dp. (1999)aircraft design: a conceptual approach. reston: american institute of aeronautics and astronautics, inc. [7] janardhan s, grandhi rv, eastep f, sanders b. (2005) parametric studies of transonic aeroelastic effects of an aircraft wing/tip store.journal of aircraft42:253-263. [8] approved navy trainning system plan for the aim-120 advanced medium range air to air missile. nevada: naval strike and air warfare center (nsawc), 1988. [9] aim -9 sidewinder. retrieved on may 2013 from operation guide: www.vojenskeletectvi.cz [10] willian pr, erwin hj. (2004)msc.nastran version 68:aeroelastic analysis user’s guide. msc.software corporation, california usa. [11] motte ed (2012) gripen: when logic is part of the equation. farnborough, uk: gripen export, saab aeronautics. [12] yukh, djojodihardjo h, kadarman h. (2011) acoustic effects on binary aeroelasticity model. iium engineering journal 12(2):123-126. [13] sulaeman e. (2012) on the evaluation of negative altitude requirement for flutter speed boundary of transport aircraft and uav. applied mechanics and materials225:397-202 [14] uav systems airworthiness requirements (usar) for north atlantic treaty organization (nato) military uav systems – standard agreement stanag 4671 (edition 1), 2009. microsoft word vol 6-2p5v2-press.doc iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 47 mems electromagnetic micro relays overview and design considerations zuraini dahari, thurai vinay and dinesh sood school of electrical and computer engineering rmit university, gpo box 2476v, melbourne, australia s3047454@student.rmit.edu.au abstract : miniature electromagnetic relay matrices capable of switching currents up to one ampere range are widely used in commercial applications such as instrumentation and telecommunication. traditionally these devices have been fabricated from a number of discrete components, however in recent years the emergence of micro electro mechanical system (mems) technology has opened up the possibility for batch fabrication of microrelays at much reduced unit cost. while several electromagnetic microrelay designs have been successfully developed and commercialized for use as individual units, development work on electromagnetic microrelay matrices where individual relays can be selectively switched on and off have been fewer and less successful. due to inherent limitations of the micromachining processes, significant dimensional and material property variations occur among individual relays in a matrix. these variations severely limit the tolerance window and hence the reliability of operation of the device. after reviewing existing designs of electromagnetic microrelays, a set of desirable design features that would make the electromagnetic microrelay more robust are identified. a novel design incorporating these features is proposed and preliminary results of ansys1 simulation studies are presented. keywords: mems, microrelay and electromagnetic 1. introduction recent trend in the world market shows a continuing demand for the miniaturization of devices. this trend has triggered the emergence of microelectromechanical systems (mems) technology in the past few decades. mems technologies such as silicon micromachining, bulk micromachining and liga (german acronym for lithographie, galvano-formung, abformung) offer significant advantages in size reduction without sacrificing device performance. some of the motivating factors are reduced cost, weight and power consumption. mems technology is multidisciplinary with its applications ranging from optics, transportation, aerospace, robotics, chemical analysis, and biotechnologies. comprehensive details on mems technology could be referred to madou [1], senturia [2] and pelesko [3]. mems pressure sensors, accelerometers are now established commercialized products [4]. electromechanical microrelay is amongst the predicted mems-based products to be commercialized in the next five years [5]. iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 48 the commercial need for relays up to 2a is projected to be 1 billion units annually. despite the rapid advances of the semiconductor, the electromechanical relays (emr) still serves about ninety percent (90%) of the market needs compared to ten percent (10%) by solid state relays (ssr). the major reasons of the continuing use of electromechanical relays are due to its robustness and reliability in harsh environments. in addition, they have large switching range from µv and µa, could handle both dc and ac signals, have low contact resistance (mω) and high insulation resistance (mω) [6]. figure 1 shows the miniaturization trend in manufacturing relays during the past 40 years. as can be seen from fig. 1, the predicted board space for the next generation would be about 30 mm2, the volume about 100 mm2. through mems technology, micro sized electromechanical relay, termed microrelay which integrates the merits of both ssr and emr could be manufactured. mems technology offers possibility for exceptional miniaturization of relays, extremely low power consumption and high shock resistance. fig. 1: ongoing miniaturization of telecom relays during the past 40 years [6] pioneered by petersen [7], realization of microrelay using mems technologies has attracted interests of a number of researchers in both academic and industrial field. relay operation requires sufficient contact force to provide stable contact, reliable opening which involves a lift-off force which exceeds the adherence of sticking contacts and the highest possible breakdown voltage to assure electrical insulation between the open contacts and driving circuit. the basic requirements for microrelay design can be derived as 300 µn contact force to achieve contact resistance less than 100 mω, lift-off force greater than 300 µn to overcome adherence, and contact gap in the range of 100 to 250 µm to have a breakdown voltage greater than 500 v [8]. these key parameters are dependable on the contact material, actuation means and mechanical design. from a report by schimkat [8], auni5 is reported as a well suited contact material for microrelays due to relatively high contact force and lower adhesion force. table 1 summarized the experimental results of the characteristics of several contact materials. various actuation methods have been demonstrated successfully; such as electrostatic [9,10,11], thermal [12, 13,14] and electromagnetic [15,16]. the most typical method is electrostatic due to its simplicity, small size and the versatility of integration with the standard integrated circuit (ic) technologies. however, the basic design requirements mentioned above are beyond the operating range of typical electrostatic microrelay. recently, electromagnetic actuation has generated considerable interest. the feasibility of iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 49 magnetic materials in mems technologies are discussed thoroughly by busch-vishniac [17], g. reyne [18] and d. niarchos [19]. table 1: characteristics contact data for microrelays [8]. au auni5 rh minimum contact force for stable contact, fmin (mn) <0.1 0.3 0.6 maximum adherence force, fad (mn) 2.7 0.3 < 0.1 contact resistance, rc at fmin (mω) <30 <100 <1000 though some improvement in magnetic materials properties and compatibility with ic processing still remains a challenge, electromagnetic actuation has been the preferred choice in microrelay applications where larger contact force (few millinewtons) is required to achieve stable electrical contact [20]. besides, it is also possible to achieve latching by adding permanent magnet or semi-hard magnetic material thereby minimising power consumption [21]. in the case of microrelay matrices, where individual relays will have to be switched on and off selectively, reliability of operation remains an issue owing to the difficulty in achieving sufficient dimensional uniformity among individual relays in the matrix during their manufacture. authors’ research is concerned with the development of a robust design for the microrelay that will be more tolerant to mems fabrication imperfections. a novel design of the electromagnetic microrelay is proposed and analysed using ansys finite element analysis software. 2. electromagnetic microrelays traditionally electromagnetic relays have been fabricated from a number of discrete components which include an armature made of soft magnetic material, elastic spring, electromagnetic coil, a magnetic core, and special metal contacts [22]. for applications requiring the switch to remain open or closed for relatively long periods of time, a permanent magnet is incorporated into the magnetic circuit to maintain the switch in the closed position even when the control signal is removed. implementation of magnetic actuation schemes at the micro scale is quite challenging. the most problematic is the design and fabrication of the excitation coil that would provide sufficient ampere-turns. deposition of magnetic materials and their subsequent patterning and treatment to impart desirable characteristics to them are also difficult in a micro fabrication environment [19]. micromachined electromagnetic relays reported in early publications [23-26] are simply adaptations of the conventional relay design to suit the microfabrication environment. planar magnetic coil and flat cantilever spring element have been common features in all of them. 2.1 principle of operation of the electromagnetic microrelay most magnetic microactuators that are reported in publications depend on the attractive force that can be generated between an armature made of ferromagnetic material and a iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 50 current-carrying coil [27], as shown in fig. 2. related to the above microactuators are devices that use a permanent magnet instead of the magnetisable armature as shown in fig. 3. these devices have the advantage that the actuator can generate both attractive and repulsive forces. more importantly, the relay could be held in its closed state even after the control current is removed. fig. 2: magnetization-type actuator. fig. 3: planar magnetic microactuator. the operation of the latching electromagnetic microrelay can best be understood by considering the variations in magnetic, and restoring spring forces with air gap. the relative positions of the spring and magnetic force characteristics for three different states of the relay, namely, unactuated (in either closed or open state), on the verge of closing from the open state, and on the verge of opening from the closed state are shown in fig. 4, 5 and 6 respectively. here the spring characteristic is assumed to be linear. previous studies suggest that the dependence of the magnetic force on the air gap can roughly be described by a power law f  gn with an exponent n in the range -1.4 to -2 [28]. when there is no coil current, the magnetic force will be solely due to the permanent magnet. depending on the direction of current flow in the coil, the magnetic force can be either enhanced or reduced by the electromagnet. in fig 4, fs0 = kg0, fm0 = rkg0 (say) are the spring and magnetic forces respectively when the air gap, g is zero, k is the spring stiffness, g1 and g2 are the air gaps corresponding to the two intersection points of the force characteristics, g0 is the air gap when the spring is unstressed, and r is the ratio fm0/ fs0. note that g1 is a stable equilibrium point whereas g2 is an unstable equilibrium point. in the unactuated case, either the relay remains open with air gap g1 or remains closed with contact force fm0 fs0. figure 5 shows the effect of increasing the magnetic force by applying a coil current. the spring force line is shown to touch the magnetic force curve at the air gap, gt. any further increase in the coil current will cause the relay to close. figure 6 shows the effect of reducing the magnetic force by applying coil current in the opposite direction. here the magnetic force curve is shown to meet the spring force line at g = 0. any further increase in the coil current will cause the relay to open. iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 51 fig. 4: spring and magnetic forces as functions of air gap. fig. 5: relative position of force characteristics. fig. 6: relative position of force characteristics of microrelay on the verge of latching of microrelay on the verge on unlatching. iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 52 when a current pulse of sufficient amplitude and duration is passed through the electromagnetic coil, the induced magnetic field due to the permanent magnet and the electromagnet in the relay will create sufficient force on the armature to pull the relay closed. the relay will stay closed due to the field from the permanent magnet, which is not strong enough to pull the relay closed by itself, but will hold it there when the air gap becomes small and the flux becomes stronger. to reset the relay, current pulse is applied in the opposite direction which will reduce the resultant flux in the air gap sufficiently so that the beam can spring back to the open position. another important practical consideration is the ability of the microrelay to withstand ambient shock and vibration [29]. it can be shown that greater the area of the closed region between the spring and magnetic force characteristics (between g1 and g2) in fig 4, the greater will be the resistance of the microrelay to shock and vibration. thus the following four design rules can be formulated for the microrelay.  for latching to occur, the entire magnetic force characteristics for the case of full positive electromagnetic actuation should be below the spring force line.  minimum contact force requirement must be satisfied. that is, the magnitude at zero air gap of the spring force must be less than the magnitude at zero air gap of the magnetic force due to the permanent magnet alone by the minimum contact force required.  for the switch to unlatch, the magnitude at zero air gap of the spring force must be greater than the magnitude at zero air gap of the magnetic force for the case of full negative electromagnetic excitation.  the area enclosed by the spring and magnetic force characteristics must be sufficiently large so as to alleviate the detrimental effects of shock and vibration. parameters of the spring (k and g0), magnetic circuit (n), permanent magnet (fm0), and electromagnetic coil (ampere-turns) should be carefully matched to achieve optimum performance. however, manufacturing imperfections associated with mems processes are likely to result in significant variations in the values of these parameters and severely limit the tolerance window of the final product. 2.2 microrelay matrices while several electromagnetic microrelay designs have been successfully developed and commercialized for use as individual units, development work on electromagnetic microrelay matrix arrays have been fewer and less successful although many commercial applications await them. by combining such relay matrices with electronics, it would be possible to perform multiplexing and to reduce the number of electrical lines required to switch individual relays in the matrix; an 88 array for instance would require 16 control lines, as opposed to 64 control lines when the relays are packaged separately without the multiplexing electronics. such relay arrays have great potential in the telecommunication industry. iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 53 while individual microrelays can be made to operate reliably, making micro relay matrix arrays in which individual relays need to be selectively and reliably switched on and off by an appropriate multiplexing scheme presents many challenges. the major problem is the difficulty in achieving the degree of uniformity in the structural dimensions among the individual relays in the matrix. it is difficult to achieve close dimensional tolerances of micro relay structures when cost effective mems fabrication methods are used. due to the inherent limitations of the micromachining processes, significant variations in the dimensions of the micro relay occur across the wafer. for example, each individual microrelay may not have the same thickness of cantilever beam and the initial air gap. besides, stiction problem, which occurs when two nominally flat surfaces are placed in contact also contribute to unreliability of the switching action [30]. due to these reasons, each individual relay in a matrix will have varying electrical, magnetic and mechanical properties, and as a result the strength of the control signals required for switching the relays on and off is bound to vary widely. a small variation of +5% in the thickness of the cantilever, for instance, would result in +15% variation in the spring parameter k. this could cause serious switching errors in the relay matrix. experience of two of the authors of this paper suggests that micro relay matrix arrays based on microrelay designs outlined in section 2.2 is bound to have very narrow tolerance window and hence very low reliability. 2.3 alternative design concepts the most interesting of all electromagnetic microrelay designs that have been reported to date is maglatchtm which has been commercialised by magfusion [31]. the major advantage of this relay is the latching mechanism to maintain the non-volatile state without requiring constant current supply. the device is based on preferential magnetization of a permalloy cantilever in a permanent external magnetic field. switching between two stable states is achieved by sending a short current pulse through an integrated coil underneath the cantilever. however, suitability of this design for the fabrication of integrated microrelay arrays with viable, cost effective row and column addressing scheme is yet to be demonstrated. a major drawback of the conventional design discussed in section 2.1 is the variability associated with the initial air gap and thickness of the cantilever. any stress induced in the cantilever beam during the electroplating process is likely to cause some initial deflection in the cantilever and variable air gap. the stiffness of the cantilever spring varies as the cube of its thickness, implying that the stiffness variation would be about three times the thickness variation. as the heavier armature at the end of the cantilever is not fixed when the relay is in the off state, resistance of the device to shock and vibration is bound to be low. to alleviate these problems, roshen et al. [32] proposed a micromachined electromagnetic switch with fixed on and off positions using two soft magnets and one permanent magnet as shown schematically in fig. 7(a). two soft magnets situated in fixed positions above and below a permanent magnet toggles between two fixed positions by the application of current in an actuator coil for a brief period. the permanent magnet is attached to a micromachined hinge or spring which moves under the action of a net force, thereby opening or closing the switch. current in the actuator coil changes the relative iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 54 strength of the magnetic forces due to the soft magnets. in the absence of current in the actuator coil, the switch is kept in the open or closed position by the attractive magnetic force between the permanent magnet and either the upper or lower soft magnet, whereby the stronger force is exercised between the permanent magnet and the nearest soft magnet. in the conventional electromagnetic microrelay design, the strain energy stored in the spring when the relay is in the closed state is not gainfully utilised. when the relay is switched open from its closed state, the stored energy is transformed into kinetic energy and manifests as oscillations which eventually dies down due to damping. (a) fixed on-off position switch (b) bistable switch fig. 7: schematic designs of bistable, latching, electromagnetic switch. tabat et al. [33] proposed a novel design, shown schematically in fig. 7(b) that utilises the stored energy in the switch for changing its state. bistable operation is obtained using a single coil and a magnetic core with a gap. a plunger having two magnetic heads is supported for back and forth linear movement with respect to the gap in the core. the single electrical coil is coupled to the core and is provided with electrical current to attract one of the heads toward the core by reluctance action and drive the plunger to the limit of travel in one direction. the current is then cut off and the plunger returns by spring action toward the gap, where after the current is reapplied to the coil to attract the other head of the plunger to its limit of travel. this process can be repeated at a time when switching of the actuator is required. while the above two novel concepts have significant merits and are worth pursuing, one has to bear in mind the difficulties of micromachining such devices. to the authors’ knowledge, an economically viable design utilizing one or more of these two concepts that is amenable to micromachining remains to be developed. 3. discussion of ongoing research at rmit university a group of researchers at rmit university are attempting to develop a robust design for an electromagnetic microrelay that can form the building block of microrelay array matrices. the main focus is to develop a relay structure with the following features: easily manufacturable by standard mems processes with minimum cost, has fixed on and off positions so that resistance to shock and vibration can be enhanced, utilizes the strain iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 55 energy stored in the spring for switching from one state to the other resulting in a more positive switching action, uses a permanent magnet to achieve latching as well as pushpull action during switching. 3.1 proposed design of electromagnetic micro relay the proposed design under study is shown schematically in fig. 8(a) and (b). a relatively thick and rigid beam is attached at two points to the free ends of two thin cantilever beams as in fig. 8(c). these can be made of silicon or a low permeability material such as electroplated nickel. an important feature of this mechanical arrangement is that the elastic support provided by the pair of cantilever beams is very stiff for pure vertical movements of the rigid beam (due to axial stiffening of the cantilever beams), but quite flexible for tilting movements as shown in fig 8(d). furthermore, in the tilted position the mechanical system once again becomes quite stiff if the lower end of the rigid beam is held against a mechanical stop, as in fig. 8(e). two permanent magnets are attached to the ends of the rigid beam and magnetized in a vertical direction as shown. the electromagnet is formed by a number of planar parallel wires all carrying current in the same direction (normal to the plane of the paper). the permalloy strip is placed underneath the wires to increase the magnetic flux due to the current carrying wires. it is to be noted that, even without the two permanent magnets, bistable operation similar to the device of fig. 8(b) is possible with this design. when a current pulse is applied to the coil (in a direction along the outward normal to the paper), the rhs permalloy pole piece will be polarized n and the other s, attracting the lhs end of the rigid beam while repelling the rhs end, and causing the beam to tilt counter clockwise. when the coil current is switched off, the magnetic attraction between the lhs permanent magnet and the lhs permalloy pole piece will be able to hold the rigid beam to remain in the tilted position. a current pulse in the opposite direction will cause the rigid beam tilt to the opposite side. fig. 8: schematic of the proposed mechanical system iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 56 3.2 finite element analysis (fea) to realistically study the mechanical system, a simple linear analysis will not suffice; nonlinear effect of stiffening of the beam caused by deflection will have to be accounted for. using ansys software, a nonlinear finite element analysis is carried out to determine the force-deflection characteristics of the proposed structure. figure 9 gives the normalized force – deflection characteristics of the lhs end of the rigid beam when the rhs end of the beam is held down against a normalized dead stop distance, dn below the undeflected position of the beam. at positive normalized forces (upward), the graph demonstrates for higher values of dn, the characteristics display a very flat region which implies the increasing stiffness of the system. however, beyond a certain threshold values of the applied force, the deflection steadily increases with force. for example, for dn = 0.042, the graph is nearly constant between the normalized force of 0.00 to 0.02, but when it reached the threshold value at around 0.03, the deflection increase significantly. it appears that buckling of the cantilever beams occur beyond this threshold. this trend repeats for the negative forces (downward forces) at small value of dn for example, dn =0.008. generally, the fea results show flat regions in terms of normalized deflection which demonstrates high degree of stiffness when downward forces are applied. it can therefore be concluded that within the limits set be the threshold, the mechanism offers significant disturbance immunity. some preliminary analysis of the magnetic circuit of the microrelay has also been done performed to determine the force generated on the rigid beam by the electromagnet at various positions of the rigid beam. the magnetic circuit simulated is shown in fig. 10(a). in this analysis the permanent magnets are left out and the rigid beam is assumed to be made up of a high permeable material such as electroplated permalloy. the objective is to see whether bistable operation is possible with such an arrangement. the element type plane13 is used to model the magnetic circuit, cantilever beam, air gap and the coil, while two-dimensional four node boundary elements, infin110, are used to simulate an infinite extension of the surrounding air. the flux patterns for initial horizontal beam position and for a tilted position are shown in fig. 10(b) and fig. 10(c). effect of the tilt angle on the resultant force and its point of application are analysed and the results presented in table 2. it can be seen from table 1 that as the angle of tilt of the rigid beam increases the point of application of the resultant magnetic force moves further to the right of the beam centre. the normalized force and the tilting moment also increase with the angle of tilt. graph in fig. 11 demonstrates that bistable operation under electromagnetic excitation is feasible provided the spring force line lies below the magnetic force line. table 1: magnetic force on beam at tilted angle tilted angle, θ normalised force (fθ/f0) normalised offset (e/l) normalised tilting moment (fθe/ f0l) 0 1.00 0.00 0 5 1.04 0.17 0.1768 10 1.22 0.33 0.4026 15 1.78 0.54 0.9612 iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 57 fig. 9: force – deflection characteristics of the lhs end when rhs end is pressed down against a dead stop distance d below the undeflected position of rigid beam. (a ) (b) (c) fig. 10: fea of magnetic circuit and the magnetic flux patterns for horizontal and tilted position iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 58 fig. 11: tilting moment at different angle 4. summary because of their narrow tolerance window, existing designs of electromagnetic microrelays are proving to be problematic for fabricating microrelay matrices where individual relays are required to be selectively switched on and off by row and column multiplexing. a novel design incorporating a number of desirable features to improve switching robustness is proposed. ansys simulation studies are being pursued to demonstrate the advantages of the proposed design. a prototype is to be built and evaluated in the near future. references [1] m. j. madou, fundamentals of microfabrication: the science of miniaturization, crc press. 2nd edition, 2002. [2] s. d. senturia, microsystem design, springer, 2004. [3] j. a. pelesko and d. h. bernstein, modeling mems and nems, crc press, 2002. [4] h. f. schlaak, “potential and limits of micro-electromechanical systems for relay and switches”, in proc. 21st international conference on electrical contacts, zurich, pp. 19-30, 912 sep, 2002. [5] r. h. grace, “commercialization issues of mems/mst/micromachines, an updated industry report card on the barriers to commercialization”, in proc. of sensors expo & conference, boston, 23-26 sep, 2002. [6] w. johler, “ switching contacts for low level applications-an overview”, in proc. 21st international conference on electrical contacts, zurich, pp. 19-30, 9-12 sep, 2002. [7] k. e. petersen, “microelectromechanical membrane switches on silicon. ibm j. res. dev., 24, pp. 376-385, 1979. [8] j. schimkat, “contact materials for microrelays” in proc. the eleventh annual international workshop on mems 98, pp. 190-194, 25-29 jan, 1998. [9] g. b chong et al., “simulations based design for a large displacement electrostatically actuated microrelay”. analog integrated circuits and signal processing, 32, pp. 37-46, 2002. iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 59 [10] h. s. lee, “integrated microrelays: concept and initial results”, journal of microelectromechanical systems. vol 11, no.2, pp. 147-153, 2002. [11] j. kim, “a micromechanical switch with electrostatically driven liquid-metal droplet”. sensors and actuators a , vol. 97-98, pp. 672-679, 2002. [12] j. qiu et al. “ a high-current electrothermal bistable mems relay”, n proc. of micro electro mechanical systems, 2003. mems-03 kyoto. ieee the sixteenth annual international conference, pp. 64-67, 19-23 jan. 2003. [13] y. wang et al., “a micromachined rf microrelay with electrothermal actuation”, sensors and actuators a: physical, vol. 103, issues 1-2, pp. 231-236, 2003. [14] t. moulton and g. k. ananthasuresh, “micromechanical devices with embedded electrothermal-compliant actuation”, sensors and actuators a: physical, vol. 90, issues 1-2, pp. 38-48, 2001. [15] g. d. gray, jr. and p. a kohl, “magnetically bistable actuator: part 1. ultra-low switching energy and modelling”. sensors and actuators a: physical, vol. 119, issue 2, pp. 489-501, 2005. [16] j. w. judy, “batch-fabricated ferromagnetic microactuators with silicon flexures”. doctoral dissertation, university of california, berkeley, 1996. [17] i. j. busch-vishniac, “the case of magnetically driven microactuators”, sensor and actuators, vol 33, pp. 207-220, 1992. [18] g. reyne, “electromagnetic actuation for moems, examples, advantages and drawbacks of magmas”, journals of magnetism and magnetic materials, vol. 242-245, pp. 1119-1125, 2002. [19] d. niarchos, “magnetic mems: key issues and some applications,” sensors and actuators a, vol. 109, pp. 166-173, 2003. [20] l. k. lagorce, o. brand and m. g. allen, “ magnetic microactuators based on polymer magnets”, ieee journals of microelectromechanical systems, vol. 8, no.1, 1999. [21] h. hosaka, h. kuwano and k. yanagisawa, “electromagnetic microrelays: concept and fundamental characteristics”, in proc. ieee microelectromechanical sys. conf., fort lauderdale, pp. 41-47, 1993. [22] j.a wright and y. c. tai, “ micro-miniature electromagnetic switches fabricated using mems technology”, proceedings: 46th annual relay conference: narm ’98, illinois, pp. 13-1 to 13-4, april, 1998. [23] h. hosaka and h. kuwano, “design and fabrication of miniature relay matrix and investigation of electromechanical interference in multi-actuator systems” mems '94, proceedings, ieee workshop, pp. 313 – 318, 25-28 jan. 1994. [24] w. p. taylor and m.g. allen, “integrated magnetic microrelays: normally open, normally closed, and multi-pole devices”, in transducers ’97, international conference on solid-state sensors and actuators, chicago, pp.1149-1152, 16-19 jan, 1997. [25] e. fullin et al., “a new basic technology for magnetic micro-actuators”, micro electro mechanical systems, 1998. mems 98. proceedings., the eleventh annual international workshop , pp.143–147, 25-29 jan.1998. [26] h.a. c. tilmans et al. “ fully-packaged electromagnetic microrelay”, micro electro mechanical systems, 1999, twelfth ieee international conference on mems '99, pp. 25 30, 17-21 jan. 1999. [27] t. masood, “microactuators : electrical, magnetic, thermal, optical, mechanical, chemical & smart structures”, boston : kluwer academic, 1998. [28] w.p. taylor, o. brand and m.g. allen, “fully integrated magnetically actuated micromachined relays”, journal of microelectromechanical systems, vol. 7, no. 2, june 1998. iium engineering journal, vol. 6, no. 2, 2005 z. dahari et al. 60 [29] k. persson, “fundamental requirements on mems packaging and reliability”, 8th international symposium on advanced packaging materials”, 2002. [30] a. witrouw, h.a.c tilmans and i.de wolf, “material issues in the processing, the operation and the reliability of mems”, microelectronic engineering, vol. 76, pp. 245-257, 2004. [31] http://www.magfusion.com [32] us patents, 05475353. [33] us patents, 5,808,384. application of digital cellular radio for mobile location estimation iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 117 smart portable cryotherapy system rephrased i.e. with controlled thermoelectric cooling modules for medical applications abbas rahmani1, reza hassanzadeh pack rezaee2 and naser kordani3* 1 department of electrical engineering, islamic azad university, science and research branch, tehran, iran 2 department of electrical engineering, university of guilan, guilan, iran 3* department of mechanical engineering, college of engineering, university of mazandaran, babolsar, iran * corresponding author: naser.kordani@umz.ac.ir (received: 27th dec 2016; accepted: 17th oct 2017; published on-line: 1st june 2018) https://doi.org/10.31436/iiumej.v19i1.791 abstract: when a person suffers from an injury, there are specific methods of treatment which are recommended according to the type of injury. one of these methods involves cryotherapy, in which the part of the affected body is exposed to cooling for decreasing the temperature. the aim of this therapeutic method is to decrease cellular metabolism, increase cellular survival, decrease inflammation and reduce pain and spasm. the system designed in the present study involves the possibility of “smart” treatment using portable thermoelectric cooling devices based on electronic hardware, software and digital control techniques. in the proposed system, all stages of treatment have been performed automatically by using arduino as the microcontroller to controlling temperature in cryotherapy methods. this research focus on usage of thermoelectric effect with peltier module for smart electronic cooling and does not involve the usage of chemicals or cooling materials e.g. ice. smart cooling methods have significant advantages that they are highly accurate and allow precise timing of the treatment especially for the athletes, and for whom the recovery time from injuries is critical. this approach can be fundamentally important for practical investigations relating to the timing of cryotherapy for any type of users. abstrak: apabila seseorang mengalami kecederaan, terdapat kaedah rawatan khas yang disyorkan berdasarkan jenis kecederaan. salah satu kaedah ini melibatkan krioterapi, di mana sebahagian kawasan badan yang terlibat didedahkan kepada kesejukan untuk megurangkan suhu badan. tujuan kaedah terapeutik ini adalah bagi mengurangkan metabolisme sel, menambah sel selamat, mengurangkan radang dan mengurangkan sakit dan sentakan. sistem yang direka dalam kajian ini berkemungkinan melibatkan rawatan bijak yang menggunakan alat penyejuk termoelektrik mudah alih melibatkan peranti elektronik, perisian dan teknik kawalan digital. dalam sistem cadangan ini, kesemua peringkat rawatan telah dilaksanakan secara automatik menggunakan arduino sebagai alat mikro-kawalan bagi mengawal suhu dalam kaedah krioterapi. fokus kajian ini adalah dengan menggunakan kesan termo-elektrik dengan modul peltier untuk penyejuk elektronik bijak dan tidak melibatkan penggunaan bahan kimia dan bahan penyejuk seperti ais. kaedah penyejuk bijak ini mempunyai faedah ketara seperti sangat tepat dan memberi masa rawatan yang jitu terutama untuk atlet, dan iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 118 kepada sesiapa yang tempoh masa pemulihan kecederaan amat penting untuknya. pendekatan ini boleh menjadi asas penting bagi penyelidikan praktikal berkaitan masa krioterapi untuk pelbagai jenis pengguna. keywords: cryotherapy; thermoelectric effect; medical devices; microprocessor controls 1. introduction given the type of damage that occurs in tissues, e.g. in a sprain, strain or muscle-pull or tear, suitable primary measures have been suggested for treatment through the price approach which is an acronym for protection, rest, ice, compression and elevation. this method begins with the protection of the affected members against further damage and harmful movements and actions. this involves, for example, the use of bandages, splints and immobilisation by means of special coatings which can protect the injured member against damage or deterioration. resting is the next step and, at this time, the affected member must be prevented from moving and this stage is important to prevent increasing the level of inflammation. in the next part of the therapy, the member must be cooled, since cooling the damaged member reduces inflammation. cooling should, ideally, be started from the first minute of injury and, depending on the extent and severity of injury, the cooling period should last between 48 and 72 hours [1]. this usually involves putting an ice pack on the affected area. the next step is to apply pressure to the injury which prevents further inflammation in the damaged tissue. this lowers the level of inflammation of the member and is effective in producing a more rapid improvement. pressure on the vulnerable area by means of a bandage or the use of elastic bands may also be helpful. in the final treatment, the damaged member is supported to reduce the pressure on it [2, 3]. in this paper, novel structures and algorithms have been proposed for developing optimal cryotherapy effective time for different users based on the most wellknown therapeutic methods. we suggest the use of a “smart” cryotherapy device to replace the use of ice within the price system. this involves placing an electronic device on the ordinary ice packs. with cooling liquid within it, the system is based on new programmable cryotherapy methods which are suitable for all kinds of users (human & animal). 1.1 cryotherapy there are various common methods for cooling injured members within the price system in connection with rehabilitation therapy to reduce inflammation and pain relief. cooling has been accepted as a treatment of choice for acute soft tissue injury [4, 5]. in this case, part of the patient's body or his/her whole body is exposed to reduce temperatures and therefore the cooling effects reduces the physiological changes that lead to negative effects in both muscle and other tissues [6-11]. this kind of cryotherapy can be performed using a number of different methods, namely, immersion in cold water, ice massage and use of a gel ice pack, an instant ice pack and a spray or a cooling device [1216]. in the proposed approach mentioned in this paper a smart treatment based on thermoelectric cooling (tec) device has been used for ice pack temperature adjustment. in this system, the temperature of tec device being controlled by means of a processor and a temperature sensor which is connected to a microcontroller. 1.2 thermoelectric cooling (tec) device in a tec system, the electronic element is located so that the parts that must be cooled are positioned up against the cold side, with a heat sink positioned appropriately iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 119 as shown in fig. 1 [17, 18]. when a dc voltage is applied to a thermoelectric system of the type shown in fig. 1, thermal energy is transferred from the one layer (the cold end) and this is released at the other side (the hot end). thus the cold part of the electronic element becomes colder and heat naturally flows from the system. the hot side and cold side temperature formulae for the thermoelectric device are: th = tamb + o .qh (1) qh = qc + pin (2) fig. 1: schematic of thermoelectric cooler. in these equations th is the temperature of the hot side and tamb is the second temperature level, the parameter o is the system thermal resistance (° c / watt). the quantity qh is the heat released (watts) and qc is the heat that is absorbed (watts). the quantity pin is the thermoelectric power input (watts). the parameters σp, σn, λp, and λn represent the electrical and thermal conductivities of the p and n legs and involve a block of length l. the index i refers to either p or n, the thermal conductance k is given by [19]: ki = λi. ai/li (3) the total thermal conductance k for n elements is given by [19]: k=kp.kn=n[λp ap/lp+ λn.an/ln] (4) the quantities kp and kn are the thermal conductance of the two side of the tec. we need also to determine the electrical resistance as calculated by [20]: r=rp+rn=n((σp.ap/lp) -1+(σn.an/ln) (5) here rp and rn are the electrical resistances of the two side of the tec. for calculating qh and qc, we need to know the coefficient for the two junctions calculated from: a ̅=( 1 tc−th ) ∫ (αp − αn) th tc dt (6) the quantity a ̅is the coefficient for the two junctions. then the magnitudes of the heat input and output are [21]: iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 120 qh=h.a ̅.th.i+k.∆t-1/2.i 2r (7) qc=h.a ̅.tc.i+k.∆t-1/2.i 2r (8) hence we can now see a direct relationship between k and the temperature coefficient (a ̅) and resistance (r) and the current flow. to reduce the temperature, it is necessary to reduce the temperature by an amount (δt) at the hot side of the thermoelectric module and we can use the heat sink and fan for this purpose. to enhance the process of reducing the temperature of the ice packs and also accelerate the decreasing of temperature without increasing the power consumption, we used a larger heat sink than the system required but it should be noted that in this treatment method the required temperature is 5 °c. we do not need to make use of the full capabilities of the thermoelectric module. the use of feedback control of the temperature of inside of the ice pack ensures that the desired temperature can be maintained throughout the treatment period. compared with other technologies thermoelectric cooling has a number of advantages. for example, the cooling equipment involves no moving parts and so requires less care and maintenance and has an extended lifetime which may be as much as one hundred thousand hours of stable working. unlike cooling systems containing chlorofluorocarbon materials that need to be constantly filled up, thermoelectric systems require relatively little routine attention. temperature control of the component parts of a system of this kind is recognized as being generally good and an approach of this kind can provides a cooling environment which is of the right size and sensitivity for medical applications [22]. based on the problems mentioned above, in this paper, the aim is to provide smart and programmable methods of water-cooling based on the use of a thermoelectric system that is suitable for a wide range of medical applications. 2. materials and methods 2.1 hardware design and manufacture of the system according to fig. 2 the hardware components for installation on the ice pack include a tec with four centimeters width and four centimeters length, 12 volt effective voltage, 15.2 volt maximum permissible voltage, 6 amperage maximum consumption current and 70 centigrade of maximum temperature difference of both sides that involving a cold plate, a heat exchanger, a fan for the cooling part of system and an electronic board. the electronic sub-system consists of an internal part and an external part. the internal part receives feedback from temperature sensors inside the ice pack and transmits the ice pack temperature to an atmega32 processor for controlling the cryotherapy mechanism. the external part of the electronic board involves a microprocessor sub-system that controls the process of cryotherapy and also sends data through the com port for “smart” process control operations. parts of the system in direct contact with the ice pack and must be completely waterproof. we used plastic meld for this part which allowed easy insertion of the main components of the cold side of the system, such as peltier device, the fan and the lm35 temperature sensor [23]. the heat sink and fan within the heating side of the system are located on the exterior of the device whereas. the lm35 temperature sensors are located on the inside of the device and are isolated from the water using varnish. according to fig. 2 the hardware components for installation on the ice pack include a tec with four centimeters width and four centimeters length, 12 volt effective voltage, 15.2 volt maximum permissible voltage, 6 amperage maximum consumption current and iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 121 70 oc of maximum temperature difference of both sides that involving a cold plate, a heat exchanger, a fan for the cooling part of system and an electronic board. the electronic sub-system consists of an internal part and an external part. the internal part receives feedback from temperature sensors inside the ice pack and transmits the ice pack temperature to an atmega32 processor for controlling the cryotherapy mechanism. the external part of the electronic board involves a microprocessor sub-system that controls the process of cryotherapy and also sends data through the com port for “smart” process control operations. parts of the system in direct contact with the ice pack and must be completely waterproof. we used plastic meld for this part which allowed easy insertion of the main components of the cold side of the system, such as peltier device, the fan and the lm35 temperature sensor [23]. the heat sink and fan within the heating side of the system are located on the exterior of the device whereas. the lm35 temperature sensors are located on the inside of the device and are isolated from the water using varnish. fig. 2: computer-based 3-d visualization of the component parts of the system [20]. one of the biggest advantages of this approach to design and manufacture is that the system can be coupled, with no change in its structure, to a conventional ice pack. different parts of the circuit diagram are shown in fig. 3 and each section of this is discussed separately. fig. 3: schematic diagram of the electronic board. iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 122 the temperature sensor (lm35), analog to digital converter and inverter provide analog temperature information for feedback of temperature in the ice pack to the controller. the max232, com port and usb port (ft232) send all data to an external pc or some other external programmed system for any special application. the drive circuit provides the required electrical supplies for the peltier device and all fans within the system. lcd and led displays are used to provide system status information to the user. figure 4 shows the complete assembled system. fig. 4: assembled systems for use in cryotherapy applications. 2.2 performance of the system the biggest advantage of the system is its programmable capability for a variety of different applications. the system operation, according to the microprocessor flowchart in fig. 6 are as follows: 1. system on or reset; 2. sensing of the ice pack temperature; 3. system control for the cryotherapy; 4. feedback of the system temperature for comparison with the desired equilibrium temperature ; 5. controlled cryotherapy by means of the microprocessor program to perform the required operation for a specific period and then stop after that specified period (e.g. in 48 hours); 6. system off. the procedures for the cryotherapy operation outlined above are not the only aspects of system performance that may have to be specified. however the approach based on microprocessor control allows flexibility and permits the designer to incorporate a programmable system which can be tailored according to user’s requirements. appropriate algorithms can be selected by the user. this allows specialist applications such as those for rehabilitation following sports injuries or applications involving animals, such as horses, to be undertaken using the same hardware. in terms of its basic operations, the atmega32a [24] processor receives feedback from the temperature sensors (lm35) inside the cryotherapy system and compares it with the desired temperature for the cryotherapy process. but it must be notified that practical algorithm structures are different from the investigative ones and there is no need to measure the body temperature from the skin, but in investigative sample it can be done by two sensors. this system is not limited to one particular algorithm and is based on the microprocessor and allows the user to select suitable algorithms for each application and also allows use of the output of the serial port iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 123 to receive and process data from sensors. it should be noted that the hardware system, firstly, should have a very small size and, secondly, it must be understood that it does not fundamentally change the system based on ice packs. the temperature sensor and the vibrator are introduced into the bag structure to move the water and get feedback of temperature values for use in the temperature control algorithm. in fig. 4, the final assembled structure is shown, including the ice packs, the dc electrical power supply, control system, temperature sensors and peltier module also are parts of this final assembly. the system provides direct connection to a personal computer via a serial port which allows data to be saved which relates to the performance of the system. this is of potential value for research purposes. in terms of the duration of the therapy, the standard used in previous research involving ice was 15 to 20 minutes of ice every two hours for continuous treatment [25]. previous studies [26, 27] have suggested that the state and duration of cryotherapy should involve an intermittent protocol that reduces skin temperature to 5 °c immediately after treatment. the process should also involve rest and compression, which reduces swelling and reduces the potential risk of injury [28]. for certain skin conditions and to prevent skin damage, a special program is required for each patient and may involve an algorithm intended for operation over a 48-hour time period. in general terms, it should be noted that the thermal feedback system stabilizes and the system is turned on at 5 °c to prevent damage and goes off after 48 hours. this program, as shown in the flowchart of fig. 6 is a comprehensive program but because it is also a programmable system it allows more accurate planning for any type of patient, avoiding possible harm to humans or animals. fig. 5: ice packs cooling performance charts smart cryotherapy system. figure 5 shows results comparing the performance of the smart cryotherapy approach with those obtained using a standard ice pack with 1024 gram weight and in 20 centigrade for the sample with ice and water over a period of 200 minutes. it is evident from these results that it takes some time for the tec system to reach the desired temperature but then the system continues to operate without any difficulty and the desired temperature is maintained. on the other hand, the temperature of the system involving only the ice pack tends to rise significantly towards the end of the 200 minutes period. it should be noted that the thermoelectric cooling treatment involves a portable piece of hardware that does not require any large structural change in the icepack. the system sends data to a computer for processing. the electronic system involves microprocessor-control and is iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 124 based upon use of the atmega32a [24] processor to control the system and also provides additional the programming possibilities. the treatment process can be performed automatically using cooling and the system performance can also be observed and evaluated during treatment. with the use of the electronic cooling method instead of a simple physical cooling system using ice packs, it is easier to treat elderly patients, children and animals because the system responds to disturbances and maintains the required temperature automatically with reduced sensitivity to uncertainties and patient-topatient variations. it takes some time for the tec system to reach the desired temperature but then the system continues to operate without any difficulty and the desired temperature is maintained. on the other hand, the temperature with the ice pack tends to rise significantly towards the end of the 200 minutes period. fig. 6: flow chart showing microprocessor algorithms during cryotherapy. figure 6 shows the flow chart for the microprocessor-based control and indicates how requirements can be changed according to the type of user. for example in the specific flowchart shown in fig. 6, the system was controlled so that it worked in an on-off mode and with a period of 15 minutes. 2.4 software design for controlling the process iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 125 the main aim of system is about vigilant the cryotherapy process and make the system adjustable to use for finding the effective time of protocol for different medical applications. according to the adjustable structure of macro controller, using a suitable program will fulfill all targets. paper sampling of ice bag temperature and controlling the cooling process are the important parts of providing design's target. this part is provided by microcontroller analog part that it's server's code in 2.4.2 and the other part is about a comparison of time schedule which is provided by a micro counter timer, is mentioned in 2.4.2 effective voltage of the whole controllable system which is contain of micro controller and some 5 voltage sensors and the sample frequency are provided by the 32.67 k external crystal, that change the system to a clock so it can control the cooling process all the time and does a current comparison among differences of temperature and time of cooling process. for controlling the microcontroller, we use code vision avr software for programming the processor and controlling the cryotherapy process. the software consists of several parts: 2.4.1 code for measuring the value of the temperature from inside the ice pack admux=adc_input | (adc_vref_type & 0xff); delay us(10); adcsra|=0x40; while ((adcsra & 0x10)==0); adcsra|=0x10; t=((adcw*2.56)/1023)*100; while (1){t0=read_adc(0)}; 2.4.2 code for introducing the time for the course of treatment interrupt [tim2_ovf] void timer2_ovf_isr (void) {if(second==59) {second=0; if(minute==59) {minute=0; if(hour==24) hour=0; else hour++;}else minute++;}else second++;} 2.4.3 start of cryotherapy involving algorithm in while loop control of the cryotherapy process is in accordance with the following: if (5<=t) {portd.7=1; portd.5=1; portd.6=0;} if (t<5) {portd.7=0; portd.6=1; portd.5=0;} even though all controlled items, for the best temperature transferring in the ice bag a vibrator is used to help the pack to achieve the exact temperature sooner. besides two sensors are used in the systems, so in investigator samples one of them is used for skin feedback temperature and the other one is used inside the ice bag. in reality the average of sensors temperature can be used for controlling the process in micro. this is sample program for a normal working system. this allows the users to make different patterns for different subjects. this is one of the biggest advantages that can reduce the duration of treatment for special categories of subjects such as professional athletes and the elderly or for animals such as race horses. 2.4.4 displaying information about the treatment and time of cryotherapy iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 126 sprintf(lcd_buff,"time=%d:%d:%d\nt:%i'c",hour, minute, second,t); lcd_clear(); lcd_puts(lcd_buff); delay_ms(100); this code just shows all result of timing in display. on/off control is just for controlling cooling system. 2.4.5 end of treatment and shut-down of system in this section cryotherapy is ended and the device is switched off. the program shown above is a sample program for operation of the cryotherapy system and provides an illustration of how the time of cryotherapy could be established for any other type of subject. as shown in fig. 7 the smart cryotherapy system is suitable for use as part of an emergency first aid kit. the system is portable and can be powered from the electrical systems in a car or from a mains electrical supply. fig. 7: smart cryotherapy system in physiotherapy centers and emergency ambulance service. 3. conclusions this paper outlines the design of a “smart” system for cryotherapy as fig. 7 instead of using the systems based on simple ice packs or chemicals that are currently available. it also provides a platform for investigating new procedures for cryotherapy. the designed prototype has smaller size and lighter weight compared to existing products and traditional designs. the system gets feedback of the temperature of the icepack water and the environment and this allows it to reach the required temperature of 5 ° c through the use of suitable and flexible algorithms. the objective of the system outlined in this paper is to make it possible to perform cryotherapy treatment using a portable charging the system by battery or charging it with automobile charger and programmable system which can be used for a wide range of human patients and for animals. results presented in the paper show that this has been achieved. this paper has been suggested new device that can find new temperature and time for different type of users and also work fundamentally. iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 127 acknowledgement the writing of this paper would not have been possible without the support of one person and i wish to take this opportunity to express my profound gratitude and deep regards to professor david j. murray-smith, honorary senior research fellow, school of engineering, university of glasgow, scotland, u.k. for his guidance, mentoring and constant encouragement during the writing of this paper. the blessing, help and guidance given by him from time to time shall carry me a long way in the journey of life on which i am about to embark. references [1] angelina f, amilton v, gracielle vr, rita de cm, tania de fs, gustavo op & joao lqd. (2016) multiple cryotherapy applications attenuate oxidative stress following skeletal muscle injury. redox report, pp 1-7. [2] elizabeth q. (2011) first aid for soft tissue injuries start with the price protocol price first aid guidelines protection, rest, ice, compression and elevation. medical review board. [3] chris mb, seán o, mark at, laurence gr, domnhall cm and suzanne m. (2011) design of a randomised controlled trial comparing standard versus cryokinetic ice applications in the management of acute ankle sprain. isrctn, 39-46. [4] bleakley cm, mcdonough sm, macauley dc. (2006) cryotherapy for acute ankle sprains: a randomized controlled study of two different icing protocols. br j sports med., 640:700705. [5] huang a, mccall jm, weston md, mathur p, quinn h,henderson dc, allen-mersh tg. (2002) phase i study of percutaneous cryotherapy for colorectal liver metastasis. br j surg 89(3):303310. [6] hardy m, woodall w, j hand t. (1998) therapeutic effects of heat, cold, and stretch on connective tissue. 11:148-156. [7] knight kl. , il (1995) human kinetics, champaign cryotherapy in sport injury management. [8] kellett j. (1986) acute soft tissue injuries: a review of the literature. med sci sports exerc., 18:489-500. [9] myrer jw, measom g, fellingham gw. j athl t. (1998) temperature changes in the human leg during and after two methods of cryotherapy. 33:25-29. [10] swenson c, sward l, karlsson j. scand j. (1996) cryotherapy in sports medicine. med sci sports, 6:193-200. [11] enwemeka cs, allen c, avila p, bina j, konrad j, munns s. (2002) clinical sciences: clinically relevant. soft tissue thermodynamics before, during, and after cold pack therapy. medicine & science in sports & exercise, 34(1):45-50. [12] hanley j, mckernan a, creagh md, classey s, mclaughlin p, goddard n, briggs pj, frostick s, giangrande p, wilde j, thachil j, chowdary p. (2017) musculoskeletal working party of the ukhcdo guidelines for the management of acute joint bleeds and chronic synovitis in haemophilia. haemophilia. doi:10.1111/hae.13201. [13] chris mb, seán o, mark at, laurence gr, domnhall cm and suzanne m. (2007) design of a randomised controlled trial comparing standard versus cryokinetic ice applications in the management of acute ankle sprain. isrctn, 1390: 39-46. [14] browne gj, and barnett, p. lj. (2016) common sports-related musculoskeletal injuries presenting to the emergency department. journal of paediatrics and child health, 52:231236. doi:10.1111/jpc.13101. [15] hotfiel t, carl h. d, grim c, engelhardt m. (2016) management of injured athletes at the field, foot and ankle sports orthopedics. doi 10.1007/978-3-319-15735-1_8. iium engineering journal, vol. 19, no. 1, 2018 rahmani et al. 128 [16] brison rj, day ag., pelland l, pickett w, johnson ap, aiken a et al. (2016) effect of early supervised physiotherapy on recovery from acute ankle sprain: randomised controlled trial. bmj. 355-i5650. [17] ni, liang h. (2007) zhejiang university (people's republic of china): synthesization and properties of bi2te3 based nanocomposite thermoelectric materials, proquest llc. h445368. [18] michael jn. (2016) the effectiveness of water vapor sealing agents when used in application with thermoelectric cooling modules, te technology, inc., 1590 keane drive, traverse city, mi 49686. [19] gao m, rowe dm. (1992) optimisation of thermoelectric module geometry for waste heat electric power generation. journal of power sources, 38:253-259. [20] abbas r, (2012) smart cryotherapy active system by controlling thermoelectric cooling modules. iran invention reg office: 77326, date of invention. [21] decher r, (1997) direct energy conversion – fundamentals of electric power production” oxford university press, inc., 198 madison avenue, new york. isbn 0-19-509572-3. [22] dolan mg. thornton rm, fish dr. mendel fc. (1997) effects of cold water immersion on edema formation acler blunt injury lo the hind limbs of rats. j arht train., 32(3):233-237. [23] http://www.ti.com/product/lm35. [24] http://www.atmel.com/products/microcontrollers. [25] kerr km, daily l, booth l. (1982) guidelines for the management of soft tissue (musculoskeletal) injury with protection, rest, ice, compression and elevation (price) during the first 64 hours. london: chartered society of physiotherapy, mcmaster wc. cryotherapy. physician sportsmed. 10(11):112-119. [26] knight kl, brucker j, stoneman pd, rubley md. (2000) muscle injury management with cryotherapy. athl ther today. 5(4):26-30. [27] carol f. (2012) the use of ice in patient management – a brief review the evidence. [28] haynes dh, monaghan wp. (1984) blood storage and transport in the field using a portable thermoelectric refrigerator: assessment of potential use. military medicine. 149(4):184-188. 462 iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 87 a study on health monitoring system: recent advancements atika arshad, sheroz khan, ahm zahirul alam, fadzil ismail ahmad and rumana tasnim department of electrical and computer engineering, faculty of engineering, international islamic university malaysia, p.o. box 10, 50728, kuala lumpur, malaysia. atikaarshad@hotmail.com abstract: a proliferating interest has been observed over the past years in the development of an accurate system for monitoring continuous human activities in the health care sectors, especially for the elderly. this paper conducts a survey of the various techniques and methods that are proposed to monitor the movements and activities of the elderly people. these techniques promise a useful and dependable detection system to give support and lessen the medical expenses of health care for the elderly. the detection approaches are divided into five main categories: wearable device based, wireless based, ambience device based, vision based and floor sensor / electric field sensors based. these techniques have focused on the pros and cons of the existing methods for recognizing the prospective scope of research in the domain of health monitoring systems. apart from highlighting and analyzing the features of the existing techniques, perspectives on probable future studies have been detailed. abstrak: dewasa ini, pembangunan sistem yang tepat untuk memantau aktiviti berterusan terutamanya dalam sektor kesihatan warga tua mula mendapat tempat. kaji selidik telah dijalankan dengan pelbagai teknik dan kaedah untuk meninjau pergerakan dan aktiviti golongan warga tua. kaedah-kaedah ini memberikan sistem pengesanan yang berguna dan dipercayai untuk memberikan sokongan serta mengurangkan kos perubatan kesihatan bagi golongan tua. pendekatan pengesanan dibahagikan kepada lima kategori utama; alatan yang dapat dipakai, alatan tanpa wayar, alatan berdasarkan persekitaran, alatan berasaskan penglihatan dan alatan berdasarkan pengesan pada lantai / medan elektrik. teknik-teknik ini memfokuskan kepada pro dan kontra kaedah yang sedia ada untuk mengenalpasti skop prospektif penyelidikan dalam domain sistem pengawasan kesihatan. selain daripada mengetengah dan menganalisa ciri-ciri teknik yang sedia ada, perspektif kajian akan datang juga diperincikan. keywords: health monitoring; elderly; wearable device; wireless device; ambience device, vision analysis; floor sensors 1. introduction according to a survey on ageing population by united nation in 2005 [1], the world population of the elderly is expected to double from the year 2010 to 2050 from 350 million to 1500 million. as such, with technological advancement, increasing research effort has expended in the field of elderly health care. the growing aging population will lead into several challenges for the health care system as well as for the society. an example is the increase in alzheimer’s or parkinson’s disease for which presently there is no cure. increase in health care costs such as for hospitalization, travelling, and daily check-ups are also expected to increase. due to lack of caregivers, high number of iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 88 dependencies, and individuals who will be unable to live independently, will cause economic concerns to increase on society. considering the fact that 89% of the elder people like to be in their homes, and looking into the expenses of nursing home care [2], it is essential to make some advancements in the technologies that assist elder people to age in their place. this paper is organized as follows. in section 2, different types of monitoring technologies are introduced. five different categories of monitoring approaches are discussed. finally, section 3 concludes the paper with future directions of the research. fig. 1: world population forecasts over the years [1]. 2. approaches and principles of health monitoring detection system in recent years, researchers have developed a variety of health monitoring technologies to assist elderly citizens. in this work, different categories of detection systems are first identified and then a classification of detection methods is build according to their use and principles for better understanding of the existing approaches. this work further contributes toward a detailed discussion on the strength and limitations of the existing detection methods for health monitoring. existing health monitoring approaches can be explained and categorized into five different classes to distinguish different detection methods. the monitoring approaches can be divided roughly into five categories: wearable device based, wireless based, ambience device based, vision based and floor sensor / electric field sensors based. a classification of detection methods is built in fig. 2. fig. 2: different approaches and techniques of detection methods for health monitoring systems. iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 89 2.1 wearable device based approaches the key to wearable device based approach is connecting some device or wearing garments with embedded miniaturized electronic sensors, attached by a wireless or wired body area network to data processing and communication devices which will be embedded in the user’s clothes as part of the clothing or an accessory. this health monitoring device is able to monitor the wearer’s vital signs like blood pressure; cardiac activity, respiration, sleeping patterns and social interactions continually. in most prototypes of wearable systems, microelectronics and electrical sensors are integrated in body-worn devices such as in patients’ clothing, gloves, wrist-worn or an armband devices, finger rings, earlobe devices and patches [3]. a number of these wearable systems have demonstrated an increased efficiency in health monitoring. healthgear [4] is a product of microsoft research. it is basically a real-time wearable system for monitoring, visualizing and analyzing physiological signals. it uses a blood oximeter to monitor patients’ blood oxygen level (spo2), heart rate and pulse while sleeping. this implementation is carried out using bluetooth technology via cell phone. the physiological data obtained, is then further analyzed on a home pc at a later time. bodymedia [5] developed an armband that has multiple sensors (galvanic skin response, skin and near-body temperature, two-axis accelerometer and heat flux) to continuously collect physiological data for a few days at a time. once the data is downloaded to a pc, a proprietary software derives what they call “lifestyle” information, such as energy expenditure, duration of physical activity, number of steps, etc. however, in all cases the physiological data is analyzed on a home pc at a later time. traditionally, personal medical monitoring systems, such as holter monitors, have been used only to collect data for offline processing. one of the most popular remote health systems perhaps is the amon (advanced medical monitor) [6] system, a wearable (wristworn) medical monitoring device for high-risk cardiac/respiratory patients. the system includes continuous collection and evaluation of multiple vital signs, intelligent multi parameter medical emergency detection, and a cellular connection to a medical centre, hence minimizing the effect of the devices on the user’s lifestyle. the vital jacket [7] is a wearable vital signs monitoring system, which intelligently monitors electrocardiogram (ecg) waves and heart rate for different scenarios, such as in sports, security and medical applications. here data is sent via bluetooth to a pda and stored in a memory card at the same time. ewatch [8] is a wearable sensing and notification platform developed for contextaware-computing-research built into a wrist watch making it highly available and instantly viewable. the bluetooth technology is used in order to connect to cellular phones or computers. ewatch provides visual, audio, and tactile notification while sensing and recording light, motion, sound and temperature. nguyen et al. [9] proposed a mobile waist mounted device which can notify caregivers during an emergency case. a tri-axial accelerometer and a cdma standalone modem is used to detect falls and a 3 channel ecg circuit to determine heart rate. nguyen also proposes a simple threshold algorithm to increase the accuracy of the system. if an emergency event happens, ecg and acceleration data will be sent to a remote server via cdma module. the data is not processed locally, hence the response time is larger as compared to systems where data is processed locally. iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 90 those who wear devices at their wrist are reported to have comparatively less sensitivity than those who wear it on the waist [10]. lindemann et al. [11], claimed that those who wear an accelerometer behind the ear had better sensitivity in simulated falls. they also argued that the fall detector’s position on the head would permit the device to be worn at night when a bigger risk of falls remains when the patient is not in the bed [1213]. vivometrics [14-15] developed a ‘lifeshirt system’, a lightweight, machine washable, non-invasive shirt with embedded sensors for continuous ambulatory monitoring, a system that can ascertain pulmonary, cardiac, respiration, posture, movement and other physiologic data during a person’s daily routine. respiratory function sensors are woven into the shirt around the patient’s chest and abdomen. a three-lead, single channel ecg measures heart rate, and a three-axis accelerometer records subject posture and activity level. an external pda stores the data and extracts the vital parameters, allowing researchers to correlate the physiologic parameters measured. however, the lifeshirt system is no longer available for sale. because of the cumbersome recorder and peripheral attachment to be carried around it is not recommended for prolonged and incessant monitoring. after identifying the disadvantages of the first prototype in the area of sensorized garments, researchers focussed on smart textiles. smart textiles have been proved to be successful in the applications of materials and nanotechnology research (in the case of health monitoring). the smart textile method of sensatex, i.e., the smartshirt, has been developed and patented primarily by researchers at georgia institute of technology. this receives analog signals via conductive fiber sensors and transmits them via a conductive fiber grid, which is knitted in the t-shirt [16]. health-shirt (h-shirt) [17-18] is a wearable device that is made of electrodes from etextile materials. the h-shirt is intended to monitor blood pressure cufflessly and continuously by simultaneously recording ecg and ppg signs. the ecg is taken from the two wrists, with a reference electrode placed on the forearm to evade respiration induced noise. another such system which uses textile (micro-sensing device) for monitoring human body falls was suggested by lin et al. [19]. micro-mercury switch and optical sensors were embedded into a coat and a processor was used to processes data from the sensors in order to identify the status of the wearer. lee and chung [20] likewise proposed a smart shirt, which measures ecg (electro cardio gram), and acceleration signals for continuous and real-time monitoring of health. the shirt was made up of conductive fabrics to acquire the body signal. the observed and measured data are transmitted in an ad-hoc network for remote monitoring. wearable device approaches are advantageous as well as disadvantageous in some aspects. the prime benefit is the cost effectiveness of wearable devices. also the installation and setup of the design is quite easy. the devices are comparatively easier to function and detect the primary signs of health worsening. the drawbacks consist of intrusion and fixed relative relations with the subject, which makes the device disengaged. such drawback makes wearable devices a critical option for the elder people. the drawback of the wearable device is that it is invasive. the practicing doctors commented that most of the patients do not wish to wear device for the detection of fall because they feel well before any fall. in accordance with the research and studies, the elderly user iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 91 wearing sensor can be challenging especially when the user has a cognitive injury or dementia, in that they have to wear the device and use it as well. another unavoidable fact is that it can be uncomfortable to the patients, since it maybe huge for some patients. in addition, batteries are required to be replaced very often. to resolve such battery troubles, patients can wear rfid tags [21]. the stated review demonstrates that these kinds of systems can be used for normal living atmospheres. most of the techniques are advantageous over the computer vision and acoustic & ambience sensors based techniques. the primary advantage is that a person can leave his/her house and yet the monitoring continues. noise interference is not there too. these systems are cost effective since no infrastructure is required. nevertheless these approaches have some limitations as well. these approaches offer an obtrusive method of monitoring. moreover, for designing such kind of stand-alone systems, the battery life is also a key concern. the weight is also a vital part to consider. 2.2 wireless technology based approaches the wireless body area network (wban), was first introduced by van dam et. al. [22] and latre et. al. [23], to fully exploit the benefits of wireless technologies in telemedicine and mobile health. this is a wireless sensor network. internet, intranet, or satellite communication is used for distant monitoring of patients’ vital signs. wban technology provides the automatic real-time acquisition of vital signs to ensure flexibility and keep up patient mobility. in general, for helping patients who necessitate urgent aid in surgical and intensive care units of modern hospitals, such technology is used. wban makes use of wearable sensor devices and actuators, mobile devices and wireless network devices to deal with physical health conditions of patients. the health conditions are usually predicted through signals like body temperature, body weight, waistline, blood pressure (bp), pulse rate (pr), oxygen saturation (spo2), blood sugar electrocardiogram (ecg), electroencephalograph (eeg), and electromyography (emg) without any emphasis on geographical locations of patients. the sensors and actuator devices distantly gather signs for diagnosing patients’ health conditions in real-time. zigbee and the bluetooth standards are usually used for radio interface in wban systems. interestingly wban is not suitable due to lack of an appropriate wireless technology (such as bluetooth, zigbee, gprs and wi-fi) that will satisfy all the requirements of the wbans. chavez-santiago et al. [24] illustrated that the suitability of zigbee and bluetooth for healthcare applications is to be examined, since zigbee has high exposure to interference, bluetooth has scalability problem and both zigbee and bluetooth support low data rate communication, therefore they are not suitable for wireless medical applications. moreover, chavez-santiago et al. [24] suggested the use of uwb since they are of low power consumption, less complex. the uwb signals do not cause significant interference to other systems operating in the vicinity. hence they do not create a threat to patient’s security because they protect the transmission of patient’s data by reducing the probability of detection. this therefore, rescinds the need for health data encryption that results in lower complexity of the electronics and smaller size of the devices. in the area of wireless sensor networks, the mobihealth [25] project supported by the european commission is one of the projects that integrates the wearable sensor devices namely pda’s mobile phones and verifies that a person keep it with them. it allows patients to be monitored continuously by measuring and transmitting the video recordings along with the physiological data to health service providers who provide very consistent distant aid in the time of accidents, hence enabling prediction and detection state of the iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 92 patients. mobihealth [25] proposes the convergence of various network systems namely ban, pan and wan to facilitate personalized and mobile healthcare. codeblue [26] is a hardware and software platform developed-based research project at harvard university, intended for deployment in emergency medical applications. the hardware design part consists of the design and development of a mote-base pulse oximeter, two-lead ecg, along with a motion analysis sensor board. the software architecture is based on publish/subscribe model for data delivery.it is design to work across various network densities and for a wide range of wireless medical devices in an ad hoc routing protocol, allowing sensing nodes to publish streams of data (vital sign, location and identities) to pdas or pcs which can be accessed by physicians and nurses who are subscribed. the system specifies and collects patient’s data for each step in case of any accident, starting from the place of accident to the hospital environment. a research by advanced health and disaster aid network (aid-n) [27] came up with a radical design of wearable biomedical system (to be used in wrist devices) to facilitate the patient’s monitoring by collecting the data for imperative signs and location, storing this acquired data in record. it offers triage status tracking that enables the runtime monitoring. this system was designed as part of the codeblue [26] project in collaboration with aid-n [27]. the implemented design consists of a gps receiver, blood pressure sensor, a pulse oximeter and an electronic triage tag to signal the danger level of a subject, an led and a buzzer to indicate about alert conditions. the device has a capability of running for five to six days continuously. the onkonet [28], a mobile agents-based architecture is used to tackle the difficulty of accessing to medical care services by consumers via mobile devices. the onkonet architecture can maintain a knowledge intensive cooperation between people and software agents to produce, convey, maintain and consume medical care services in virtual communities maintaining the assistance of actors indulged in diagnosing cancer as well as therapy. the onkonet can also allow local and mobile access as well as attain better incorporation of patients and medical care practitioners. the architecture ensures the support of community oriented medical care arrangement which reduces the cost and does not incorporate into grids to maintain accessibility as well as service provisioning quality. the ubiquitous healthcare system (uhs) [29] includes critical signs devices as well as environment sensor devices to gain context information for continuously observing and maintaining health condition of patients. the framework is aimed at the advancement of four healthcare applications containing self-diagnosis, distant monitoring, exercise management and crucial services. nonetheless, the framework is actually not solely based upon virtual community. it also does not integrate into grids to ensure quality and ubiquitous services at minimum cost. researchers at the mit media lab have developed and prototype mithril [30], a technique for human-computer interaction for body-worn applications. it is basically a cloth integrated design which allows sensing and networking. presently research on a wearable application of mithril for human behavior recognition and to create contextaware computing interfaces, is being conducted. another health monitoring application was demonstrated in [31], a health-wear system with sensors that can continuously monitor the user’s vital signs, daily activity, social interactions, sleep patterns, and other health indicators. based on the data obtained by the system a personalized profile of the patients physiological performance record can be generated which will help the patient in future. iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 93 the smart medical home [32] makes use of infrared sensors, computers, bio-sensors, and video cameras, which provides medical services to patients and health care experts. moreover it also provides motion and activity monitoring, pathogen detection and skin care, and personal health care recording for consumer-provider decision support. the ubimon ubiquitous monitoring [33] is from the department of computing, imperial college, london. the project aims at the development of wearable and implantable sensors for distributed mobile monitoring. it is also aimed at investigating mobile monitoring, using sensors and real-time biomedical data collection for long time trend analyses. juyng and lee [34], proposed a reliable data transmission health monitoring device based on zigbee control mechanism to monitor physiological signals. the work develokped wrist, chest belt, shoulder, and necklace devices. in their work it was seen that the devices required only a small battery for power supply and it also showed that the devices was lightweight and small hence easy to carry around, moreover the device could function properly for at least six hours without being recharged or replaced. however the batteries life spam should be improved for longer hour’s operation. recently, bluetooth has gained more attention than zigbee because of its widespread availability. qureshi and tounsi [35] implemented their first work on mobile intelligent remote-access healthcare management system (mirhms) based on mobile healthcare system using bluetooth to generate patients’ data for obtaining case-specific advice on a mobile device hence able to monitor patients. the same authors proposed an extension of their work [36] based on a remote healthcare system using bluetooth enabled smart phones with wap technology. the system proposed would be able to identify and diagnose remotely located patients thus reducing the frequent visits to healthcare service provider. the proposed system uses bluetooth channel for acquiring data into the patients’ mobile devices, from bluetooth enabled medical measurement devices. the received data is directly transferred to a solver subsystem which integrates an intelligent medical expert system through wireless access protocol (wap) over the existing cellular link (gsm) or (gprs). gaddi blumrosen et al. [37] proposed a uwb technology to monitor/assist tremor symptoms which includes neurological disorders such as parkinson’s disease (pd), midbrain tremor, etc. the author stated that the common approach used in the assessment of tremors were by using motion capture devices and video tracking systems. however gaddi demonstrated a novel approach based on uwb sensor node for the transmission of a wideband electromagnetic signal. in his approach multiple sensor nodes were placed in different locations in a home, the sensor node is used as a small radar system to capture tremor in one axis. the raw data obtained from the sensors are then sent to a uwb hub for further analysis. then the data can be further relayed by an internet gateway to a health care center for monitoring and for continuously assess and report tremor conditions during daily life activities. akyildiz [38] illustrated a health care delivery of multimedia content in wireless multimedia sensor networks (wmsns). two types of architecture have been proposed, namely cross-layer communication architecture based on the time-hopping impulse and ultra wide band (uwb) technology. the uwb technology showed to be a better choice, in that it enables low power consumption and high data rate communications. wireless technology monitoring has had a major impact on the average human lifestyle. it ensures ease and flexibility in using internet services and different iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 94 communication applications. this is one of the main advantages about the wireless system. in this system patients who stay in distant places from the hospital can receive instant and emergency treatment. a key concern on wireless means of sending data however is security and privacy. the government has formulated strict regulations to assure the security and privacy of patients’ personal health information (phi); for instance, hipaa [39]. nevertheless, when an observer knows that a patient sends his/her phi to a particular doctor, the observer has a high probability to guess the patient’s disease. three kinds of threats are stated in [40]. these are: un-authorized access, misuse of patient identities, and alteration of phi in the health monitoring system. a protection scheme of patient privacy in wireless health monitoring system is needed. the main advantage of wireless health monitoring system is in the countryside areas, since it offers cost effective and quality healthcare services to individuals via mobile devices. in contrast, there are custom developed wireless sensors which can be unobtrusive and can also have natural activity patterns. nevertheless, lack of proper standard and development enhances the time of designing and system cost [41]. according to [42], the advantages of wireless technology include convenience, portability, installation ease, and cost effectiveness. the networks may help residents and their caregivers by offering continuous monitoring service, controlling home appliances, enhancing memory, accessing to medical data, and making urgent communication. continuous monitoring will enhance diagnosis of urgent conditions in the early hours and also offer an extensive range of healthcare services for people with different degrees of physical and cognitive disabilities [43]. 2.3 ambient devices / environmental sensors based approaches ambience sensor based approach consists of a device using multiple sensors installed in a closed room / area and a dedicated pc to collect the relevant data of a person such as walking or falling based on their vibration patterns when the person is in close vicinity to the sensors installed. the pc is based on certain conditions and thresholds, which decides on the detection of an event. sixsmith et al. [44] developed a system known as smart inactivity monitor using array-based detectors (simbad). this system is based on pyroelectric ir sensor array installed on the wall for detecting the activity of a person. the system’s infrared sensor array can locate and track a thermal target within sensor’s field of view, that is only the warm moving objects are seen and not the static background. this array collects the location, size of velocity of the moving warm objects. a processor then detects the activity through analyzing the collected data. this system is proposed to be low-cost; however this system has limited application due to limited range of infrared sensors. outdoor monitoring is also not possible at all. zhuang et al. [45] proposed a detection approach using the audio signal from a single far-field microphone. a gaussian mixture model (gmm) was proposed in his work, when a movement (fall) occurrs a super-vector was created to model each fall as noise segments. the difference between the audio segments determines the occurrence of the falls. alwan et al. [46] proposed a detection scheme based on floor vibration, which is completely passive and unobtrusive to the resident. the system uses a special piezoelectric sensor coupled to the floor surface by means of a mass and spring arrangement. these sensors detect the occupancy at any moment. a processor identifies a fall by analyzing the location data thus a successful differentiation between the vibration patterns of a human fall from others can be obtained. iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 95 most ambient device based techniques make use of pressure sensors to detect a subject to track. the working principle of a pressure sensor depends on the idea of sensing high pressure of the subject due to the subject’s weight for detection and tracking purposes. it is a less expensive but useful and less invasive for implementing surveillance systems. nevertheless, it has a drawback of sensing pressure of everything in and around the subject and creating fake alarms for fall detection, which results in less accuracy for detection purposes. the trouble of such techniques is that monitoring is done only at places where the sensors are installed. additionally, these techniques assume that the subject of interest is the only one doing these events.this kind of technique also has less accuracy and high rate of fake alarms. another drawback of this method is that they cannot be confirmed by the caregiver [47]. one benefit of this method is the comparatively plain and inexpensive hardware compared to the computer vision based techniques. furthermore, systems based on these sensors have a passive and unobtrusive nature. this technique also reduces the risk attributed to privacy issues that some people may have with the computer vision based techniques. more than one person can be monitored with such techniques although more studies are required for this development. 2.4 vision based approaches camera based systems [48] use image processing which are considered to be one of the best way for human tracking. image processing usually necessitates extorting required information from data offered by an imaging sensor which gets its information from tv, camera or an infrared camera. camera based systems gives a precise and promising identification on positioning due to the use of stereo vision, however there are several deficiencies, they are expensive to install since multiple cameras are need to be installed in a single room, hence takes lots of space also the systems are susceptible to shadows, and reflections, also require more computing power. furthermore they also face the line-ofsight issue. one major disadvantage is the issue on privacy generally people do not prefer to install camera in private places like their homes. 2.5 floor sensor based approaches the integration of detectors into a user’s floor has been taken as an alternative. aud et al. [49] present the development of a ‘‘smart carpet’’, whereby a fall detector device is installed in a floor covering. the sensor within the floor coverage area may detect issues like whether someone is walking on the carpet, or whether someone is lying flat on the floor. the smart carpet has advantages in that it does not require the user to remember to maintain the batteries, as it uses ‘‘energy scavenging sensors’’, which is able to harvest energy (namely light, thermoelectric and vibrational energy) from the neighbouring environment. moreover, aud et al. [49] revealed that participants found no significant dissimilarities between walking on a standard carpet and walking on the smart carpet and, proposing that this feature would increase the suitability of the fall detector. the upcoming research area is field trials on the smart carpet [49]. however, noury et al. [50] identify the problem faced by floor sensors not being able to detect falls when it does not occur on the ground, for instance the fall may occur on furniture. a recent study explored the use of electric near-field imaging (nfi) in floor sensors [51]. the human body conductivity can be sensed by this system through emitting a lowfrequency electrical field. by a matrix of planar electrodes under the floor surface the field is produced and sensed. these electrodes are etched on aluminum foil which is laminated iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 96 between thin pet plastic films [51]. the nfi system is being used in a nursing home in finland where it detects residents falling, getting out of bed, leaving rooms, and entering the toilet [51]. the disadvantage of this system can be said as its’ incapability to recognize the person or object which has been positioned. during the time when falls occur or patients suffering from dementia leave their rooms, this system proved advantageous. furthermore, nurses can benefit from the identification characteristics as they could receive context-related information, such as patient records, or acknowledge nfi alarms by entering a room. it was also found that the system was not accurate when people fell to their knees, only detecting 20 per cent of such falls [51]. 3. conclusion and future work in this review, a study on the existing products of the health monitoring detection methods are presented in literature, focusing on identifying the approaches and principles of the existing methods. a class categorization of the detection methods has also been presented. methodologies of five different types of technologies for health monitoring and detection system has been surveyed and discussed. the techniques focuses on wearable devices, wireless based, computer vision and video analysis based, ambient based sensors and floor based sensing techniques. in summary, wearable-based devices are considered to be obtrusive and troublesome during continuous use. from the view point of an elderly patient, these techniques are not practical or user-friendly because one must pay attention to the device and remember to carry it at all times, otherwise monitoring does not take place. furthermore if the devices are battery powered, regular charging is required or batteries need to be replaced from time to time. wireless based technology has shown to improve the lifestyle of people by providing early detection, convenience and flexibility. hence people who live far from hospitals, immediate and quick treatment during an emergency can be obtained. however the major drawback in this technique is the security and privacy of transferring data. camera / vision-based techniques are considered to be one of the best ways for human monitoring. camera based systems give a precise and promising identification on positioning due to the use of stereo vision, however there are several deficiencies, they are expensive to install since multiple cameras are needed to cover a single room. considerable space is required. furthermore such systems are susceptible to shadows, and reflections, also require more computing power. furthermore, they also face the line-ofsight issue. a major disadvantage is the issue of privacy. generally patients do not prefer to have installed cameras in private places like their homes, whereas they are best suited for monitoring large groups of people in an unobtrusive manner. the ambience sensor based techniques, which use vibrations or sounds for monitoring are also restricted to indoor use and the signals obtained from the sensors are easily influenced by the excessive noise from the environments which degrades the signal received from the sensors. they are, however, very suitable for a group of people and are also unobtrusive, like the camera / vision based approach. the floor-based approach has the most potential for future advancements for indoor monitoring. it involves detection and monitoring of people more conveniently, the person being monitored does not have to carry or attach any device to their body or clothing. the floor sensors are mostly embedded under the ground / above the celling allowing patients to feel free to move around comfortably and not worry that they are being watched, unlike iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 97 when using cameras. hence the floor sensor based approach is considered to be better among the rest for the application in elderly care centres because of its cost effectiveness, portability, robustness, and reliability. the study reported in this work will allow researchers to set a platform for them to design a monitoring system according to the requirements of the current health services in care centres or at home, hence motivating the elderly population to live in their own environment. moreover, this platform will allow patients, clinicians, managers and even researchers to make better-informed decisions, leading to better patient outcomes and fewer mistakes. references [1] helpage internationalhttp://www.helpage.org/ [2] n. a., centers for disease control and prevention, “the state of aging and health in america 2007,” on an aging society, 2007, available: http://www.raytron.co.jp [3] teng xf, zhang yt, poon ccy, and bonato p. (2008). wearable medical systems for phealth. ieee reviews in biomedical engineering 1:62-74. [4] oliver nm, and fernando fm, (2006). healthgear: a real-time wearable system for monitoring and analyzing physiological signals. international workshop on wearable and implantable body sensor networks, pp. 64 [5] bodymedia. healthwear armband, bodybugg. http://www.bodymedia.com. [6] anliker u, ward ja, lukowics p, troster g, dolveck f, baer m, keita f, schenker eb, catarsi f, coluccini l, belardinelli a, shklarski d, menachem a, hirt e, schmid r, and vuskovic m., (2004). amon: a wearable multiparameter medical monitoring and alert system. ieee trans. information technology in biomedicine 8(4):415-427. [7] vital jacket , http://limserver.com/vitaljacket/index.php [8] maurer u, rowe a, smailagic a, siewiorek p. (2006). ewatch: a wearable sensor and notification platform. proceedings of international workshop on bsn, wearable and implantable body sensor networks, pp. 144-145. [9] nguyen t, cho m, lee t. (2009). automatic fall detection using wearable biomedical signal measurement terminal. 31st annual international conference of the ieee embs, minneapolis, minnesota, usa, september 2-6. [10] degen t, jaeckel h, rufer m, and wyss m. (2003), “speedy: a fall detector in a wrist watch,” seventh ieee international symposium on wearable computers, pp. 184-187. [11] lindemann u, hock a, stuber m, keck w, and becker c. (2005). evaluation of a fall detector based on accelerometers: a pilot study. medical & biological engineering & computing 43(5): 548-551. [12] tinetti me, doucette jt, claus eb. (1995). the contribution of predisposing and situational risk factors to serious fall injuries. journal of the american geriatrics society 43(11): 12071213. [13] y. depeursinge. (2001). device for monitoring the activity of a person and/or detecting a fall, us patent 6, 2012, 476 b1. [14] lifeshirt vivometrics, 2008 [online]. available: http://www.vivometrics. com/ [15] grossman p. (2004) the lifeshirt: a multi-function ambulatory system monitoring health, disease, and medical intervention in the real world. stud. health technol. inform. 108:133– 141. [16] sensatex, “http://www.sensatex.com” 2007 [17] zhang yt, poon ccy, chan ch, tsang mmw, wu kf. (2006) a healthshirt using e-textile materials for the continuous and cuffless monitoring of arterial blood pressure. proc. 3rd ieee-embs int. summer school symp. med. devices biosensors, cambridge, ma, pp. 86–89 [18] chan ch, zhang yt. (2008) continuous and long-term arterial blood pressure monitoring by using h-shirt. proc. 5th int. conf. inf. technol. appl. biomed. conjunction 2nd int. symp. summer school biomed. health eng., shenzhen, china, pp.267–269. iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 98 [19] lin cs, hsu hc, lay yl, chiu cc, chao cs. (2007) wearable device for real-time monitoring of human falls. measurement 40(9-10):831-840. [20] lee yd, chung wy. (2009) wireless sensor network based wearable smart shirt for ubiquitous health and activity monitoring. sensors and actuators b: chemical 140:390-395. [21] lin cc, lin py, lu pk, hsieh gy, lee wl, lee rg. (2008) a healthcare integration system for disease assessment and safety monitoring of dementia patients. ieee transactions on information technology on biomedicine 12(5):579-586. [22] van dam k, pitchers s, barnard m. (2001) body area networks: towards a wearable futures. proceedings of wwrf kick off meeting, munich germany. [23] latre b, braem b, moerman i, blondia c, demeester p. (2010). a survey on wireless body area networks. wireless networks manuscript. url: www.pats.ua.ac.be/content/publications/2010/bbraem10wbansurvey.pdf [24] chavez-santiago r, khaleghi a, balasingham j, ramstad ta. (2009) architecture of an ultra wideband wireless body area network for medical applications. proceedings of 2nd ieee intl. symp. on applied sciences in biomedical and communication technology (isabel 2009), pp 1 – 6. [25] katarzyna w, bults rb, beijnum v, bert-jan jf, ing w, jones v, konstantas d, vollenbroek-hutten m, hermens hj. (2009) mobile patient monitoring: the mobihealth system. annual international conference of the ieee engineering in medicine and biology society (embc 2009), pp 1238 – 124. [26] malan d, jones tf, welsh m, moulton s. (2004). codeblue: an ad hoc sensor network infrastructure for emergency medical care. proc. of the mobisys 2004 workshop on applications of mobile embedded systems (wames 2004), pp. 12-14. [27] gao t, massey t, selavo l, crawford d, chen b, lorincz k, shnayder v, hauenstein l, dabiri f, jeng j, chanmugam a, white d, sarrafzadeh m, welsh m. (2007) the advanced health and disaster aid network: a light-weight wireless medical system for triage. ieee transactions on biomedical circuits and systems 1(3):203-216. [28] ubiquitous healthcare: the onkonet mobile agents architecture. proceeding workshop on mobile computing in medicine, 105–118. [29] jung j, ha k, lee j, kim y, kim d. (2008) wireless body area network in a ubiquitous healthcare system for physiological signal monitoring and health consulting. international journal of signal processing, image processing and pattern recognition 1(1):47-54. [30] devaul, r.w., sung, m., gips, j., and pentland, s. (2003). mithril 2003: applications and architecture. in proceedings of iswc 2003. [31] pentland s. (2004) healthwear: medical technology becomes wearable. ieee computer, 37(5):42-49. [32] smart medical home, http://www.futurehealth.rochester.edu/smart_home. [33] jason wp, ng bpl, lo, oliver wells, morris sloman, nick peters, ara darzi, chris toumazou, and yang gz. (2004). ubiquitous monitoring environment for wearable and implantable sensors (ubimon). in proceedings of 6th international conference on ubiquitous computing (ubicomp’04). [34] juyng j, and lee j, “zigbee device access control and reliable data transmission in zigbee based health monitoring system”, 10th international conference on advanced communication technology, vol. 1, pp.795 – 797, 17-20 feb. 2008. [35] b. qureshi, and m. tounsi. (2006). a wireless sensor based intelligent mobile system for remote healthcare monitoring in saudi arabia" proceedings of 1st nits: bridging the digital. [36] b. qureshi, m. tounsi, “a bluetooth enabled mobile intelligent remote healthcare monitoring system in saudi arabia: analysis and design issues”, national computer conference [37] blumrosen, gaddi; uziel, moshe; rubinsky, boris; porrat, dana. “tremor acquisition system based on uwb wireless sensor network”. international conference on body sensor networks (bsn), 2010, page(s): 187 – 193 iium engineering journal, vol. 15, no. 2, 2014 arshad et al. 99 [38] akyildiz, i.f. “novel communication architectures for wireless multimedia sensor networks” 8th ieee international conference on advanced video and signal-based surveillance (avss), 2011, page(s): 204 [39] ] health insurance portability accountability act (hipaa) [40] p. dixon, “medical identity theft: the information crime that can kill you,” the world privacy forum, may 2006. available at http://www.worldprivacyforum.org/pdf/wpf_medicalidtheft2006.pdf [41] e. jovanov, a. milenkoviü, c. otto, p. de groen, b. johnson, s. warren, and g. taibi, "a wban system for ambulatory monitoring of physical activity and health status: applications and challenges", ieee engineering in medicine and biology 27th annual conference shanghai, china, september 1-4, 2005 [42] edward teaw, guofeng hou, michael gouzman, k. wendy tang, amy kesluk' "a wireless health monitoring system ", ieee international conference on information acquisition. june 27 july 3, 2005, [43] hande alemdar, cem ersoy, “wireless sensor networks for healthcare: a survey”, elsiver, computer networks 54 (2010) 2688–2710 [44] a. sixsmith, n. johnson, "a smart sensor to detect the falls of the elderly," ieee pervasive computing, vol. 3, no. 2, pp. 42-47, 2004 [45] x. zhuang, j. huang, g. potamianos, m. hasegawa-johnson, acoustic fall detection using gaussian mixture models and gmm super-vectors, ieee international conference on acoustics, speech and signal processing (icassp)(2009) 69–72. [46] m. alwan, p. rajendran, s. kell, d. mack, s. dalal, m. wolfe, r. felder – “a smart and passive floor-vibration based fall detector for elderly”, information and communication technologies, 2(1), 2006 , pages, 10031007 [47] mei jiang, yuyang chen, yanyun zhao, anni cai. (2013). a real-time fall detection system based on hmm and rvm. visual communications and image processing (vcip), pp. 1-6. [48] m. harville, (2004), “stereo person tracking with adaptive plan-view templates of height and occupancy statistics,” image and vision computing, statistical methods in video processing, vol. 22, no. 2, pp. 127-142. [49] aud, m.a., abbott, c.c., tyrer, h.w., neelgund, r.v., shriniwar, u.g., mohammed, a. and devarakonda, k.k. (2010), ‘‘smart carpet: developing a sensor system to detect falls and summon assistance’’, journal of gerontological nursing, vol. 36 no. 7, pp. 8-12 [50] noury, n., fleury, a., rumeau, p., bourke, a.k., laighin, g.o., rialle, v. and lundy, j.e. (2007). fall detection-principles and methods. conference proceedings: annual international conference of the ieee engineering in medicine and biology society, pp. 1663-6. [51] rimminen, h., linnavuo, m., & sepponen, r. (2008). human tracking using near field imaging. in 2nd international conference on pervasive computing technologies for healthcare. microsoft word 1-80 page 1-22.doc iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 1 designing framework of a segmented rubber tracked vehicle for sepang peat terrain in malaysia ataur rahman, azmi yahaya, mohd. zohadie, desa ahmad and wan ishak faculty of engineering, university putra malaysia, 43400, serdang, selangor, malaysia abstract: the focus of this paper is to present the designing framework of an off-road special segmented rubber tracked vehicle that may be required to run on low bearing capacity peat terrain. to complete this study: firstly, mechanical properties of the peat terrain were first determined by using different type of apparatus. direct shear test was performed using a wykeham farrance 25402 shear box apparatus to determine the internal friction angle, cohesiveness and shear deformation modulus of the peat sample. load-sinkage test was performed using a specially made bearing capacity apparatus to determine the stiffness values of surface mat and underlying peat. secondly, substantiate the validity of the mathematical model and finally design parameters of the special segmented rubber tracked vehicle were optimized by simulation. keywords: tracked vehicle, peat terrain, tractive performance. 1. introduction in malaysia, new requirements for greater mobility over a wide range of peat terrain, and growing demands for environmental protection and collection-transportation goods by vehicles on unprepared peat terrain constitute a significant part of the overall transportation activities. this has led to the necessity of developing segmented rubber tracked vehicle and establishing mathematical models for the vehicle-peat terrain systems, that will enable design engineers, as well as users, to evaluate a wide range of options for the selection of an optimum configuration for a given mission and environment. various organizations in malaysia are introduced different type of machines for performing several tasks on peat land. the machines suitabilities were justified based on the mechanical properties [2] of sepang peat land. it was found that the engine power of all the machines are quite reasonable based on their carrying capacity. however, the tractive performances is severely affected due to the higher ground pressure distribution.  corresponding author iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 2 2. materials and methods the feasibility of the land locomotion of the tracked vehicle operating on the weak peat terrain is discussed from the perspective of the terramechanics. figure 1 shows the processes for designing a segmented tracked vehicle. this paper presents the discussion until the design parameter optimization technique. fig. 1: flow chart for the processes of designing a segmented tracked vehicle. 2.1 mechanical properties of peat terrain to properly identify the mechanical properties of peat from a vehicle mobility viewpoint, measurement has been taken under loading conditions similar to those exerted by a vehicle on the peat terrain. field tests were carried out at sepang peat area, located about 45 km from kuala lumpur malaysia for determining the mechanical properties of peat terrain including moisture content, bulk density, cohesiveness, internal friction angle, shear deformation modulus, vane shearing strength, surface mat stiffness, and underlying stiffness of peat. the mechanical properties of sepang peat terrain including the terrain moisture content , bulk density d, peat surface mat stiffness mm, underlying stiffness of peat kp, cohesiveness c, internal frictional angle , and shear deformation modulus kw that are found from an earlier work [2] are given in table 1. segmented track vehicle operating terrainpeat mechanical properties of peat developed algorithm algorithm validity engine power requirement design parameters selection and optimization hydraulic power estimation basic design parameters identification auto cad design construction field test iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 3 table 1. peat terrain parameters. parameters un-drained drained mean value sd mean value sd , (%) 83.51 79.58 d, (kn/m3) 1.53 0.59 1.82 0.78 c, kn/m2) 1.36 0.21 2.73 0.39 , (degree) 23.78 4.56 27.22 2.19 kw, (cm) 1.19 0.10 1.12 0.17 mm,(kn/m3) 27.07 13.47 41.79 13.37 kp, (kn/m3) 224.38 52.84 356.8 74.27 notification: sd-standard deviation, source [2]. 2.2 mathematical model consider a rigid link segmented rubber track vehicle of weight w, track size including track ground contact length l, width b, pitch tp, and grouser height h, radius of the front idler rfi , rear sprocket rrs, and road-wheel rw, and height of center of gravity (c.g) hcg, which is traversing under traction on a peat terrain at a constant speed of vt and applied a driving torque q at the rear sprocket by the hydraulic motor as in fig. 10. if the pressure distribution in the track-terrain interface is assumed to be non-uniform by locating vehicle c.g rearward of the track mid point, the vehicle will traverse on the specified terrain by making an angle ti. consequently, the track entry and exit angles at the front idler fi and rear sprocket rs, the reaction pressure at the front idler pfi, main straight part po, and rear sprocket prs, and the sinkage of the front idler zfi, main straight part zmp, and rear sprocket zrs and tangential force reveal different values due to the different amount of slippage at each of the grouser positions of the rigid link tracks at the bottom track elements of the front idler ifi, main straight parts imp , and rear sprocket irs as shown in fig. 2. fig. 2: force acting on the track system of the vehicle during traversing on peat terrain with a slippage of 10%. iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 4 the following assumptions were made in order for the equation used in the mathematical modelling to be valided: i. vehicle theoretical speed was considered to be 10 km/hr on zero slope terrain based on various off-road operations asae d497.3 nov96, asae standard (1996). ii. vehicle total weight was considered to be 19.62 kn with payload of 9.81kn based on the in-field maximum fresh bunches collection practiced. iii. vehicle’s track critical sinkage was considered to be 0.1m based on experimental data on sepang peat terrain [2]. iv. aerodynamic resistance was neglected, due to the low operating speed. v. vehicle’s belly drag was considered to be zero since the vehicle hull was not in contact with the terrain. vi. vehicle speed fluctuation was considered to be 2.75% based on wong [7]. vii. road-wheel spacing was considered to be 0.245m to ensure good drawbar performance based on wong [7]. 2.2.1 slippage slippage is one of the functional parameters for the vehicle traction mechanism. it reveals different value at the bottom track part of front idler, main straight part, and rear sprocket if the vehicle traverses on unprepared peat terrain with non-uniform ground pressure distribution. therefore, it is important to compute the slippage of the front idler, track main straight part, and rear sprocket separately to determine the vehicle performance over the peat terrain. for the slippage of the ground contact track of front idler, the relationship between the front idler slippage ifi , the entry angle of the track at front idler fi , the track trim angle ti, the slippage ratio i and front idler radius rfi can be modeled by the following equation [5].      titififi fifi fi fi il r i  sinsin1          (1) where, the slip ratio, t at v vv i   , track trim angle,   arcsinti rs fiz z l   , and track entry angle  fifitifi rz  cosarccos and  tifififi rl   . for the slippage of the ground contact track of rear sprocket, the relationship between the slippage of rear sprocket irs and front idler ifi, rear sprocket radius rrs, the track entry iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 5 angle fi,, the track trim angle ti, and exit angle rs can be modeled by the following equation of ataur et al.[5] :     titirsrs rs rsrs firs il r l l iii  sinsin1                 (2) where, track exit angle                      2 222 arccosarcsin firsrs rsfirs rs zzr r l zz  , sinkage of the front idler, 2 44 2                       m fihfi m hfip m hfip fi m pd m dk m dk z , sinkage of the rear sprocket, 2 44 2                       m rshrs m hrsp m rshp rs m pd m dk m dk z , hydraulic diameter of the terrain due to front idler,  bl bl d fib fib hfi   2 4 , rear sprocket,  bl bl d rsb rsb hfi   2 4 and  tirsrsrs rl   . 2.2.2 tractive effort the tractive effort is denveloped not only on the ground contact part of the track but also on the side parts of the ground contact track grouser and on parts of front idler and rear sprocket. the initial track tension 12% of the total vehicle weight is assumed to be constant in every point of the track system in order to avoid the track deflection apparently between consecutive road-wheels. 2.3 ground contact part of the track the traction mechanics of the track bottom part of the front idler, road-wheels, and rear sprocket are different due to its different angle of entry and exit. it is also different due to the different sinkage of the track front idler, main straight part, and rear sprocket when the vehicle traverses on the unprepared peat terrain with non-uniform ground pressure distribution. therefore, it is important to compute the traction of the individual components bottom track segment, separately. for the tractive effort developed at the track ground contact length of the front idler, the relationship between the tractive effort fb developed at the ground contact track, track ground contact length l, track width b, terrain cohesiveness c, normal stress , shear stress , shear deformation modulus kw, and slippage ratio of the track-terrain interfaces i can be modeled by the following equation of ataur et al.[5]:                            wfi fibfi fibfi wfi fibfi wfi fibfib k li li k li ke cblf 1exp1tan2 1  (3) iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 6 with  tifififib rl   the tractive effort of the track main straight part and rear sprocket ground contact track was computed by eq. (3). 2.4 side of the ground contact track wong [7] suggested that the traction mechanics of the track at the side of the grouser is highly significant on the development of vehicle traction if the vehicle sinkage is more than the grouser height. in this study, it was assumed that the sinkage of the vehicle was more than the grouser height of the vehicles track. for the tractive effort developed at the side of the ground contact length of the front idler track, the relationship between the tractive effort fs developed at the side of the track ground contact part, track grouser height h, track ground contact length l, terrain cohesiveness c, normal stress , shear stress , shear deformation modulus kw, and slippage i of the vehicle track-terrain interfaces can be modeled by the following equation of ataur et al. [5]:                            wfi fibfi fibfi wfi fibfi wfi fibfis k li li k li ke chlf 1exp1costan4 1  (4) with             b h cotarctan the tractive effort at the side of the track main straight part and rear sprocket ground contact track was computed using eq. (4). 2.5 motion resistance when the same vehicle as shown in fig. 2, traverses on the peat terrain with nonuniform pressure distribution, the vehicle individual components such as front idler, main straight part, and rear sprocket reveal different values of motion resistances due to the different sinkages. therefore, it is important to compute the motion resistance of the individual component for understanding the vehicle performance. for the motion resistance of the vehicle due to terrain compaction rc, the ground contact length l, track width b, sinkage of the vehicle z, stiffness of peat surface mat mm and underlying peat kp can be modeled by equation of ataur et al. [5]:                                                                3 2 3 2 3 2 3 4 2 3 4 23 4 2 2 rsm hrs rsprs mpm hmp mppmp fim fih fipfi c zm d zk l l zm d zk l l zm d zk l l br (5) iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 7 where  bl bl d fi fi hfi   2 4 ,  bl bl d mp mp hmp   2 4 , and  bl bl d rs rs hrs   2 4 for the motion resistance of the vehicle due to bull dozing effect, the relationship between the motion resistance of the vehicle due to bull dozing effect rb, the bulk density of the terrain d, the internal frictional angle , track width b, and terrain cohesiveness c can be modeled by the following general equation of wong [7]:                    2 45tan 2 45tan2 22   czzbr db (6) the total external motion resistance of the rubber track vehicle rtm, can be computed as the sum of the individual motion resistance components by: etm fic msc rsc fib msb rsbr r r r r r r      (7) 2.6 sprocket torque when torque is applied at the sprocket, it starts driving the track and the vehicle starts moving. a frictional torque appears in the bearings of moving elements of the track system, resisting the vehicle motion. the forces appear at the track interface due to the terrain compaction and vehicle bulldozing effect, resisting the vehicle motion. therefore, the vehicle needs to develop sufficient tractive effort after developing shear stress at the track-terrain interface in order to move forward and overcoming all of the motion resistance. the tension in each track segment does not affect the torque of the vehicle motion since it was assumed to be constant due to the geometrical arrangement of the road-wheel and initial tension equals to 12% of the total weight of the vehicle. for the torque of the sprocket, the relationship between the torque of the sprocket q, vehicle total tractive effort ftt, total motion resistance rtm, sprocket radius rrs, track grouser height h, vehicle total weight w, and vehicle normal reaction force fn and track ground contact length l can be modeled by using the following equation:        tintirscgrsp ewflrhwhrdq  cos5.0sin  (8) where ti titt n fw f   cos sin  2.7 vehicle steerability the force system assumed to be acting on a tracked vehicle in general planar motion is shown in fig. 3 and fig. 4. in these figures, fot and fit are the thrusts on the outer and inner tracks. rlnot and rlnit are the longitudinal forces exerted by the terrain to per unit length of the outer and inner track, fr and l are the coefficients of the longitudinal and iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 8 lateral motion resistance, respectively, bstc is the vehicle tracks tread, fcent is the centrifugal force and  is the slip angle. fig. 3: force acting on the track during turning at 6 km/hr. fig. 4. force acting on the track during turning at 10 km/hr. during a turn, centrifugal force appears at the mass centre of the vehicle. when the vehicle turns at a traveling speed of 6 km/hr with locating c.g at the middle of the track system, the slip angle of the vehicle is assumed to be zero due to negligible effect of centrifugal forces. the lateral motion resistance assumed to be equally distributed around the c.g of the vehicle and represented by equal triangles f1 to f4 as shown in fig. 3. when the vehicle turns at a traveling speed of 10km/hr with locating c.g at 0.20 m rearward from the middle point of the track system, the slip angle of the track system  is considered significant higher value and significantly affect the vehicle stability and iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 9 steerability. therefore, the lateral force distributions on the track system to be congruent are represented by the triangles f1 to f4 as shown in fig. 4. the vehicle must have rotated about an instantaneous center point o located at a distance of d ahead of the vehicle c.g for the dynamic equilibrium. this force is generated by a shift to the point o ahead of c.g and the vehicle will be oriented by an slip angle , which can be computed as       lg l  4arctan 2 , the yaw velocity  of the vehicle can be computed as           r r itotrs 2  ,where, rrs is the radius of the sprocket. the vehicle follows the dashed trajectory, turning to the right around the instantaneous centre point o with turning radius r. 2.8 dynamic load on the tracks from the slippage equations of the outer and the inner track it can be identified that when the loading condition of the vehicle changes, as the vehicle is accelerating, the slippages of the vehicle track changes. therefore, in order to adjust the vehicle slippage on given terrain it is necessary to estimate the proper loading condition for getting the high steerability of the vehicle the centrifugal force of the vehicle that will develop during turning at speed of 10km/hr can be computed as 2 coscentf w r g  , which causes lateral load transfer. the weight transfer from the inner track to the outer track is mainly due to the centrifugal force. if the centrifugal force is taken into consideration the dynamic loads of the outside and inside track will be different. for the dynamic load of the vehicle outer and inner track, the relationship between the dynamic load of outside and inside track wot and wit, yaw movement of the vehicle , turning radius r, slip angle  and acceleration due to gravity g, can be modeled using the following equations of ataur et al.[3]: cos 2 2 gb rwhw w stc cg ot   (9) cos 2 2 gb rwhw w stc cg it   (10) where        r d arctan drawbar pull the drawbar power is referred to as the potential productivity of the vehicle, that is, the rate at which productive work may be done. it is computed using the following equation: apd vdp  (11) with tmttp rfd  iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 10 tractive efficiency tractive efficiency is used to characterize the efficiency of the track vehicle in transforming the engine power to the power available at the drawbar. it is defined by the following equation: e d d p p  (12) 3. mathematical model validation the drawbar pull and the tractive efficiency of light peat prototype kubota carrier rc20p track vehicle having track width of 0.43 m, track ground contact length of 1.85 m, total weight of 2645 kg including payload 1000 kg and three pneumatic road-wheels on each track, operating on a peat terrain were predicted through simulation. basic parameters of the reference vehicle that used in the study are shown in table 2. table 2. basic parameters of kubota carrier rc20p track vehicle. parameters symbol values vehicle parameters machine weight, kn w 1645 max. loading capacity, kn wl 1000 rated power, kw@rpm p 8.2@3200 track parameters ground contact length, m l 1.85 width, m b 0.43 grouser height, m h 0.05 machine parameters length, m lt 2.98 width, m bt 1.76 height, m ht 1.45 ground clearance, m gc 0.27 source: ooi [6] table 3 shows that the regression model is highly significant at a significance level of pr0.01. in the regression model, t values of 11.74 for i and –7.84 for i2 are higher than t*16 (0.01)=2.69. hence, the null hypothesis is rejected. this implies that the slippage of the vehicle has significant effect on the drawbar pull of the vehicle. a standard error value of 0.032 for i and 0.00067 for i2 are concluded that both of the predicted and measured drawbar pull is pretty tightly bunched together. the variability of the predicted and measured drawbar pulls of the vehicle has the less variability around the best fitted regression line,   )(005.0385.0916.0 2iidp  where, dp is the drawbar pull of the vehicle in kn and i is the slippage of the vehicle in percentage. therefore, based on the iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 11 vehicle estimated standard error of 0.032 and the r-square values of 0.967, it can be concluded that the predicted and the measured drawbar pull are strongly correlated. table 3: regression analysis on the drawbar pull of kubota carrier rc20p track vehicle. source df ss f value p value r square model 2 99.97650 49.98825 0.0001 0.9667 error 16 4.52226 0.28264 c total 18 104.49876 estimated parameter coefficient t for h0: parameter=0 standard error pr t intercept i i2 0.916190 0.385447 -0.005228 3.431 11.794 -7.842 0.26699892 0.03268138 0.00066673 0.0034 0.0001 0.0001 table 4 shows that the slippage of the vehicle significantly (pr 0.01) affects the vehicle drawbar pull. while, the non-significant value of treatments (predicted and measured drawbar pull) indicates that there is no significant difference between the treatments. therefore, the close agreement between the predicted and measured drawbar pull of the vehicle substantiates the validity of the simulation model. table 4: anova on the drawbar pull of kubota carrier rc20p track vehicle slippage 18 201.47489383 143.21 0.0001 treatment 1 0.14455325 1.85 0.1906 error 18 1.40688027 total 37 203.02632735 table 5 shows that the regression model is highly significant at significance level of pr0.01. in the regression model, t values of 2.91 for i and -3.81 for i2 are higher than t*35(0.01) = 2.67. hence, the null hypothesis is rejected. this implies that the slippage of the vehicle has significant effect on the tractive efficiency of the vehicle. the standard error values of 0.23 for i and 0.0087 for i2 concluded that both of the predicted and measured drawbar pull are pretty tightly bunched together. the variability of the predicted and measured drawbar pulls of the vehicle have less variability around the best fitted regression line,  20034.0)(25.161.56 iit  where, t is the tractive efficiency of the vehicle in percentage and i is the slippage of the vehicle in percentage. therefore, based on the standard error estimated values of the vehicle of 0.23 and the r-square value of 0.79, it can be concluded that the predicted and the measured drawbar pulls are strongly correlated. iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 12 table 5: regression analysis on the tractive efficiency of kubota carrier rc20p track vehicle. source df ss f value p value model 2 2604.69 13.31 0.000 1 0.79 3 error 35 3426.12 c total 37 6030 estimate d coefficien t t for h0: standar d error prt intercept 56.61 15.83 3.51 0.0001 table 6 shows that the slippage of the vehicle significantly (pr 0.01) affects the tractive efficiency of the vehicle. the non-significant value of treatments (predicted and measured tractive efficiency) indicates that there is no significant difference between the treatments on the model. therefore, the closed agreement between the predicted and measured tractive efficiency of the vehicle substantiates the validity of the simulation model. table 6: anova on the tractive efficiency of kubota carrier rc20p track vehicle. source df ss f value p value slippage 18 6153.59 2556.23 0.0001 treatment 1 0.006 0.05 0.83 error 18 2.28 total 37 203.026 4. vehicle design parameters optimization tractive performance of the rigid link segmented rubber tracked vehicle has been computed with the computer simulation method based on the new mathematical model for undrained peat terrain. it appeared that the engine size and tractive performance of the vehicle on peat terrain vary with: the variation of vehicle weight, track size including track ground contact length, width, pitch and grouser height track entry and exit angle, idler diameter and location, sprocket diameter and location, road-wheel diameter, spacing and geometrical arrangement, and location of center of gravity. therefore, for the selection and optimization design parameters of the vehicle track size, idler diameter and location, sprocket diameter and location, number of road-wheel, road-wheel diameter, spacing and geometrical arrangement, ratio of the road wheel spacing to track pitch, ratio of the sprocket diameter to track pitch, and the location of the center of gravity are taken into account. the optimization design parameters of the vehicle have been performed by using the microsoft excel software with performing calculations, analyzing information and managing lists in spreadsheets. iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 13 4.1 track width and ground contact length the length of the track in contact with the ground and the level of pressure within the ground are the most important factors that influenced tracked vehicle tractive performance. to evaluate the effects of track system configuration on the vehicle ground pressure distribution and surface mat stiffness, it is important to study track ground contact length and width. figures 5(a) and 5(b) show that the vehicle ground pressure distribution decreases with increasing vehicle track ground contact length and width. the vehicles under consideration are traversing on a zero slope terrain with a travel speed of 10 km/hr. from the field experiment on sepang, it was found that the bearing capacity for the undrained peat terrain was 17 kn/m2. it appears that if a ground contact pressure of the 19.62 kn vehicle, with a moderate payload of 5.89 kn, is limited to 16.35 kn/m2 by designing a track with ground contact area of 30x2000 mm2 then the sinkage and external motion resistance of the vehicle will be low and tractive effort will be high, yielding a desired travel speed of 10 km/hr and vehicle productivity. 5 10 15 20 25 0.2 0.25 0.3 0.35 0.4 0.45 0.5 track w idth,m g ro un d co nt ac t p re ss ur e, kn /m 2 11.77kn vehicle 17.65kn vehicle 21.52 5 10 15 20 25 30 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 track ground contact length,m g ro un d co nt ac t p re ss ur e, k n /m 2 11.77kn vehicle 17.65kn vehicle 21.52kn vehicle fig. 5: variation of ground pressure distribution with (a) variation of track width at constant track ground contact length of 200 cm and (b) variation of track ground contact length at constant track width of 30 cm. figures. 6 (a) and 6(b) show that the sinkage of the vehicle decreases with increasing track width and track ground contact length. if the track size of the vehicles is limited to 300 x 2000 mm2, then the sinkage of the 11.77 kn, 17.65 kn, and 21.52 kn vehicles will be 61, 81.8, and 110 mm, respectively. from the field experiment, it was found that the surface mat thickness of the sepang peat terrain was 100 mm, which will support the maximum load of the vehicle during static and dynamic as well. therefore, if the vehicle sinkage is more than 100 mm the vehicle will sink rather than traverse. if the vehicle total weight is considered to 19.62 kn and the track ground contact area to 300x2000 mm2, the vehicle will traverse on the peat terrain with sinkage of 90 mm or 10 % less than the sepang peat terrain surface mat thickness and exit ground pressure of 16 kn/m2 or 6 % less than the worst condition sepang peat terrain bearing capacity. based on the 19.62 kn vehicle sinkage and ground contact pressure, it may be conclude that the vehicle will not iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 14 in risk to traverse on peat terrain if the vehicle used the track ground contact area of 300x2000 mm2. 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 track width,m s in ka ge ,m 11.77kn vehicle 17.65kn vehicle 21.52kn vehicle 0 2 4 6 8 10 12 14 16 18 20 120 130 140 150 160 170 180 190 200 210 track ground contact length,cm s in ka ge ,c m vehic le weight, 11.77kn vehic le weight,17.65kn vehic le weight, 21.52kn fig. 6: variation of vehicle sinkage with (a) variation of track width at constant track ground contact length of 200 cm and (b) variation of track ground contact length at constant track width of 30 cm. therefore, the best choice is to select a vehicle track ground contact area of 300x2000 mm2 for the vehicle to produce an effective tractive performance. the conclusion is further supported by the relation between the track size and motion resistance with keeping option either track width or track ground contact length could increase to adjust the track ground contact area for getting the desired vehicle ground contact pressure. figures 7(a) and 7(b) show that the motion resistance coefficient of the vehicle increases with increasing track width and decreases with increasing track ground contact length. figure 7(a) shows that the motion resistance coefficient increased 18.12 % for 13.73 kn vehicle, 16.99 % for 17.65 kn vehicle and 24.12 % for 21.58 kn vehicle with increasing the track width from 0.2 to 0.4m when the track ground contact length considered to keep in constant at 2.0m. whereas, fig. 7(b) shows that the vehicle motion resistance coefficient of the vehicle decreased 21.09 % for 13.73 kn vehicle, 24.07% for 17.65 kn vehicle and 24.5 % for 21.58 kn vehicle with increasing the track ground contact length from 1.3 to 2.2m when the track width considered to keep in constant at 0.3m. from the justification of vehicle motion resistance coefficient based on vehicle track width and track ground contact length, it could be noted that the vehicle track ground contact length should be considered to increase instead of increase the track width in order to get the vehicle lower ground contact pressure of 16 kn/m2 on sepang peat terrain. therefore, it was found that for a given overall dimension of 300x2000 mm2 track system, the maximum motion resistance coefficient of the 19.62 kn vehicle is 5.4 %, which could be good enough for a track vehicle on soft terrain [7]. iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 15 5 10 15 20 25 0.2 0.25 0.3 0.35 0.4 0.45 0.5 track width,m m ot io n re si st an ce c oe ff ic ie nt ,% 11.77kn vehicle 17.65kn vehicle 21.52kn vehicle 15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 track ground contact length,m m ot io n r es is ta nc e co ef fic ie nt ,% 11.77kn vehicle 17.65kn vehicle 21.52kn vehicle fig. 7: effect of track size on vehicle tractive performance (a) track width and (b) track ground contact based on figs. 8(a) and 8(b), it could be pointed out that if the 19.62 kn vehicle track size is considered to be 300x2000 mm2, the vehicle ground pressure exit on track-terrain interfaces is 16 kn/m2 with sinkage of 90mm and motion resistance coefficient of 5.4%. therefore, the 19.62 kn vehicle track system overall dimension can be optimized by selecting track width of 300 mm and ground contact length of 2000 mm. 65 70 75 80 85 90 0.25 0.29 0.33 0.37 0.41 0.45 0.49 0.53 idler diameter,m tr ac k en try a ng le ,d eg re e 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 s in ka ge ,m track entry angle, degree sinkage,m fig. 8: relationship between track entry angle, sinkage and idler diameter. 4.2 track grouser size to fully utilize the shear strength of the peat surface mat for generating tractive effort, the use of grouser on tracks would be required. from the field experiment on sepang, it was found that the shear strength of the peat surface mat is considerably higher than that of the underlying peat deposit and that there is well defined shear-off point beyond which the resistance to shearing is significantly reduced. this would, however, considerably iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 16 increase the risk of tearing off the surface mat unless the slip of the track is properly controlled. thus, the use of aggressive grouser on vehicles for use in organic terrain does not appear to be desirable from traction as well as environmental viewpoints. the surface mat thickness of sepang peat terrain was found to be about 0.1m. in order to fully utilize the shear strength of the surface mat and to increase the traffic ability of the terrain the grouser height of the track is considered to be 0.06 m. 4.3 sprocket location and size the location of drive sprocket has a noticeable effect on the vehicle tractive performance. wong et al. [6] (1986) reported that in forward motion, the top run of the track is subjected to higher tension when the sprocket is located at the front than when the sprocket is located at the rear. thus, with a front sprocket drive, a larger proportion of the track is subjected to higher tension and the overall elongation and internal losses of the track will be higher than with a rear sprocket drive. with higher elongation, more track length is available for deflection and the track segments between road-wheels take fewer loads and the vibration of the track increase, which will cause the fluctuation of the track. consequently, the sinkage and motion resistance will be higher and the mobility of the vehicle will be affected severely on the unprepared peat terrain. therefore, the sprocket could be considered to locate at the rear part of the track system configuration in order to distribute the vehicle normal pressure to the track-terrain interfaces uniformly. the center point of the sprocket is considered the (0,0) coordinate system of the vehicle. generally, it could be mentioned that the sprocket is the most important component of the vehicle track system, which propels the vehicle with sufficient torque, control the vehicle speed fluctuation and maintain the vehicle tractive performance. therefore, the size of the sprocket can be determined from the relationship between the relationship between the sprocket torque, vehicle speed fluctuation, and vehicle turning radius. from the simulation result, it was found that the ratio of the sprocket diameter to track pitch have significant effect on the vehicle tractive performance. therefore, the ratio of the sprocket pitch diameter to track pitch should be a value which will stand to meet the field requirement. further support to optimize the sprocket size of the vehicle track system, the following equation on vehicle speed fluctuation can be considered. for the relation of vehicle speed fluctuation and the ratio of the vehicle sprocket pitch diameter to tract pitch the following mathematical model of wong [7]can be used: 2 1 1 1 p r s pd t               (13) where  is the speed fluctuation in percentage, pprs td is the sprocket pitch diameter to track pitch in proportion. using pprs td equals to 4.00, the computed value of  is 3.17%. according to wong [7], the industrial and agricultural track vehicle speed fluctuation should be in the range of 3.72 to 2.75%. since the speed fluctuation of the vehicle was found of 3.17%, the ratio of iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 17 the vehicle sprocket pitch diameter to track pitch can be optimized at 4.00. consequently, the sprocket pitch diameter was optimized at 400mm by using the track pitch of 100mm. 4.4 idler location and size idler is located at –2.0 m front of the track system. it was earlier reported that the surface mat thickness of sepang peat terrain in the ranged of 100 to 250 mm which is considered the supporting platform of the vehicle. it could be noted that if the sinkage of any vehicle on the sepang peat terrain is more than 100mm will cause the vehicle to bog down. furthermore, from the simulation it was found that the track entry angle was significantly affect the vehicle front idler size and tractive performance. therefore, from the relationship between the vehicle sinkage, track entry angle and idler diameter, the idler diameter can be identified. figure 8 shows that the vehicle track entry angle at front idler and sinkage decreases with increasing vehicle front idler diameter. if the vehicle critical sinkage of the vehicle is considered to 100 mm, the corresponding front idler diameter and track entry angle were found 400 mm and 78, respectively. this conclusion can be further supported from the relationship between the track entry angle, slippage and vehicle tractive performance. figure 9 shows that the relationship between the vehicle track entry angle, slippage, and tractive efficiency. at track entry angle 78, the vehicle slippage and tractive efficiency were found 18% and 70.5%, respectively, which was found at sprocket pitch diameter of 400mm. therefore, the front idler diameter 400mm can be optimized at 400mm for getting the tractive efficiency of the vehicle 70.5% and high productivity. 0 10 20 30 40 50 60 70 80 90 88 84 81 79 77 76 75 74 73 71 track entry angle,degree t ra ct iv e ef fic ie nc y, % 0 5 10 15 20 25 30 35 s lip pa ge , % tractive efficiency,% slippage,% fig. 9: track entry angle, tractive performance and slippage. 4.5 roadwheel diameter, track pitch, and number of roadwheel wong [7] reported that the ratio of road wheel spacing to track pitch is a significant parameter that affects the tractive performance of tracked vehicle, particularly on soft terrain. the decrease in the track motion resistance coefficient with the increase of the number of road wheels was primarily due to the reduction in the peak pressures and iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 18 sinkage under the road wheels. the longer track pitch would lead to an improvement in tractive performance over soft terrain. but, it may cause a wider fluctuation in vehicle speed and higher associated vibration. consequently, a proper compromise between tractive performance and smoothness of operation must be struck. road-wheel diameter can be predicted based on the following equation: g dd sr  22 21 (14) where, sr is the road-wheel spacing in mm, d1 is the first road-wheel diameter in mm, d2 is the second road-wheel diameter in mm and g is the gap between consecutive roadwheel is assumed to be 5mm for avoiding the track deflection between the consecutive road-wheel. in the track system all the road-wheel dimension (d1 = d2=------= d7) are considered as equal size. if the roadwheel spacing equals to 225mm, the gap between two consecutive road-wheel on the track system equals to 5 mm, the computed value of roadwheel diameter equals to 220 mm. figure 10 shows that the vehicle drawbar pull increases with increasing the ratio roadwheel spacing to track pitch and tractive efficiency increases with increasing the ratio of road-wheel spacing to track pitch until 2.1 and then decreases with further increasing of the ratio of road-wheel spacing to track pitch. if the ratio of road-wheel spacing to track pitch is considered to be 2.25, the tractive efficiency of the vehicle is found 70.5%. whereas, the tractive efficiency of the vehicle is found 70.5% for the optimum sprocket pitch diameter of 400 mm and idler diameters of 400 mm. therefore, the ratio of roadwheel spacing to track pitch should be 2.25 if the optimum sprocket pitch diameter and idler diameters each is limited to 400 mm. by using sr/tp equals to 2.25 and sr equals to 225mm, the computed value of tp equals to 100 mm. the number of road-wheels can be computed based on fig. 2 by the following equation [5]:      ( ) 2r s f i r r l d d n d g     (15) where, l is the total ground contact length in mm, drs is the outside diameter of the sprocket in mm , dfi and dr are the diameter of the front idler and road-wheel in mm and nr is the number of road-wheel. the outside diameter of the sprocket (i.e, 2hdd prsrs  ) is considered to 460mm based on the grouser height. by using l equals to 200 mm, drs equals to 460 mm, dfi equals to 400 mm, dr equals to 220 mm, g equals to 5mm, the computed value of nr is 7. therefore, total number of roadwheel seven with diameter of 220 mm on the 19.62 kn vehicle track system would significantly reduce vehicle vibration during traversing on the unprepared peat terrain by making zero deflection of the track between two consecutive road-wheel. iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 19 4.6 center of gravity location center of gravity of a tracked vehicle is a most important design parameter for getting the high tractive performance. figure 10 shows that the tractive efficiency of the vehicle increases steeply with increasing the slippage of the vehicle until a certain value and then start to decrease with increasing the slippage of the vehicle. the vehicle under consideration with total weight 19.62 kn including payload of 5.89 kn is traversing on a zero slope terrain with traveling speed of 10 km/hr. figure 11 shows the maximum tractive efficiency of 79.8% at 11% slippage for the vehicle with center of gravity located at 300 mm rearward from the mid-point of the track ground contact length and 70.5% at 12% slippage for the vehicle with center of gravity located at the mid-point of the track ground contact length. 58 60 62 64 66 68 70 72 74 1.5 1.65 1.8 1.95 2.1 2.25 2.4 2.55 2.7 2.85 3 ratio of roadw heel spacing to track pitch t ra ct iv e ef fic ie nc y, % 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 12.5 d ra w ba r pu ll, kn tractive efficiency,% drawbar pull,kn fig. 10: relationship between tractive efficiency, drawbar pull and the ratio of the road-wheel spacing to track pitch 50 55 60 65 70 75 0 5 10 15 20 25 30 35 40 slippage, % t ra ct iv e ef fic ie nc y, % center of gravity at midpoint of track center of gravity at 0.2m rearward track middle fig. 11: relationship between tractive efficiency and slippage. iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 20 from the comparison of the vehicle based on the location of center of gravity, it is found that the tractive efficiency of the vehicle with center of gravity is located at 200 mm rearward from the mid point of the track ground contact length is 13.2% higher than the tractive efficiency of the vehicle with the center of gravity is located at the mid-point of the track ground contact length. the variation of tractive efficiency is found between the vehicle with the locations of center of gravity due to the difference of external motion resistance. it could be pointed out that the vehicle with location of center of gravity at 200mm rearward from the mid point of the track ground contact length reveals lower sinkage at the frontal part of the track ground contact part causes the lower external motion resistance and the vehicle consume lower engine power for developing effective tractive effort in order to traverse the vehicle easily on the low bearing capacity peat terrain. whereas, the vehicle with location of center of gravity at the midpoint of the track ground contact length reveals the equal sinkage to all over the ground contact part causes the higher external motion resistance and vehicle consume maximum engine power for developing the required tractive effort in order to traverse the vehicle on the low bearing capacity peat terrain. therefore, the vehicle center of gravity location of 300mm rearward from the mid-point of the track ground contact length could be optimized the center of gravity location for the vehicle. the basic design parameters of the vehicle found from the simulation study are shown in table 7 table 7. basic design parameters of the special segmented rubber tracked vehicle vehicle parameters total weight including 9.81kn payload, kn w 19.62 vehicle traveling speed, km/hr vt 10 center of gravity, x coordinate, m xcg -0.80 centre of gravity, y coordinate,m ycg 0.45 sprocket pitch diameter , m drs 0.40 idler diameter, m dfi 0.40 idler center, x coordinate, m xcfi -2.0 idler center, y coordinate, m ycfi 0 number of road-wheels (each side) n 7 road-wheel diameter, m dr 0.22 road-wheel spacing, m sr 0.225 number of supporting rollers (each side) ns 3 supporting rollers diameter, m ds 0.20 track parameters track total length (each side), m lc 5.90 track pitch, m tp 0.10 track width, m b 0.30 track ground contact length, m l 2.00 road-wheel spacing to track pitch sr/tp 2.25 vehicle speed fluctuation, percentage  3.17 grouser height, m h 0.06 note: coordinates origin is at the center of the sprocket. positive x and y coordinates are to the rear and top, respectively. iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 21 5. conclusion the following conclusions were made based on the analysis of this paper: based on the results of mechanical properties of peat in the area studied, the mean values for moisture content of 79.58 %, bulk density of 1.53 kn/m3, cohesiveness of 1.36kn/m3, internal friction angle of 26.22, shear deformation modulus of 11.2 mm, surface mat stiffness of 13.6 kn/m3, and underlying peat stiffness of 171.54 kn/m3. based on the results of detailed study on vehicle parameters, an optimized track system configuration for the 19.62 kn vehicle has seven roadwheels with diameter of 0.24 m, a track pitch of 0.1m, a ratio of the initial track tension to vehicle weight of 12 %, a location of center of gravity at 30cm rearward of the mid-point of the track ground contact length ensure the vehicle to develop the maximum tractive efficiency of 74 % during traversing at 10km/hr on the specified peat terrain. based on the simulation study, it was found that the track pitch, number of road wheels, and location of centre of gravity have noticeable effects on the tractive performance of the vehicle. the maximum tractive efficiency of the vehicle is in the range of 74 to 72 % and 50 to 48% with the slip range of 9 to12 % when the vehicle traveled at 10km/hr without payload and with payload, respectively. furthermore, the tractive efficiency of the vehicle with center of gravity located at 300mm rearward of the mid-point of track ground contact length are 10% higher than the vehicle center of gravity located at the mid-point of track ground contact length. acknowledgement this research project is classified under rm7 irpa project no. 01-02-04-0135. the authors are very grateful to the ministry of science, technology and the environment of malaysia for granting the financial assistance. references [1] asae, agricultural engineers yearbook of standards, american society of agricultural engineers, michigan,1996. [2] r. ataur, y. azmi, m. zohadie, a. desa, w. ishak, and a. kheiralla, ” mechanical properties in relation to vehicle mobility of sepang peat terrain in malaysia”, journal of terramechanics, 41(1), pp24-45, 2004. [3] r. ataur, y. azmi, m. zohadie, d. ahmad, and w. ishak, “simulated steerability of a segmented rubber tracked vehicle during turning on sepang peat terrain in malaysia”, int. j. of heavy vehicle systems (ijhvs), inderscience publisher, uk: vol.12, no. 2, pp. 139-168, 2005a. [4] r. ataur, y. azmi, m. zohadie, d. ahmad, and w. ishak “ design and development of a segmented rubber tracked vehicle for sepang peat terrain in malaysia”, int. j. of heavy vehicle systems (ijhvs), inderscience publisher, uk: vol.12 no.3, 2005b iium engineering journal, vol. 6, no. 1, 2005 a. rahman et al. 22 [5] ataur, r., azmi, y., zohadie, m. ishak, w and ahmad, d. “design parameters optimization simulation of a segmented rubber tracked vehicle for sepang peat in malaysia”, american journal of applied science, science publications, new york, usa: vol.2(3), pp.655-671, 2005c. [6] h.s. ooi “performance of modified kubota carrier rc20p and porter p6-121 on peat soil”, mardi report no.110, 1986. [7] j.y. wong “optimization of design parameters of rigid-link track systems using an advanced computer aided method”, proc. instn. mech. engrs, 208(d), pp153-167, 1998. 469 iium engineering journal, vol. 15, no. 1, 2014 hashim et al. 55 analysis of chemical compounds of agarwood oil from different species by gas chromatography mass spectrometry (gcms) yumi z.h-y. hashim and n.i. ismail and p. abbas department of biotechnology engineering, faculty of engineering, international islamic university malaysia, po box 10, 50728, kuala lumpur, malaysia. yumi@iium.edu.my abstract: agarwood oil is a highly prized type of oil due to its unique aroma. the oil is extracted from the fragrant resin found in the agarwood tree (trunk). the unique aroma and quality of agarwood resin and oil are contributed by the presence of certain chemical compounds. in this work, analysis and comparison of the chemical compounds of agarwood oil from a. malaccensis, a. sub-integra and a mixture of both were conducted. the essential oils were diluted in hexane (5%) prior to gas chromatography mass spectrometry (gcms) analysis performed using agilent gcms 7890a coupled with msd quadrupole detector 5975 c. separation of analytes by gas chromatography was carried out using a hewlett packard hp-5ms silica capillary column (30 m x 0.25 mm x 0.25 mm). a total of 107 compounds were identified from the three samples of agarwood oils. fifty-five (55) components were identified in a. malaccensis sample which contributes to the largest portion of the total compounds. about 20% of the compounds identified were aromatic and sesquiterpenes, which have been revealed to be the main active compounds of agarwood oils which also give the aroma and pleasant odour of agarwood. different compositions or profile of chemical components were found in agarwood oils from the two different species. two compounds were commonly identified in all three samples, namely 3-phenyl-2-butanone and alpha-cubebene. further studies are needed to refine the results which later can be used to assist detection and authentication of agarwood as well as its scientific-based grading. abstrak: minyak gaharu merupakan sejenis minyak beraroma unik yang mendapat permintaan tinggi dan mahal. minyak ini diekstrak daripada resin beraroma yang terbentuk di dalam batang pokok gaharu. keunikan aroma dan kualiti resin dan minyak gaharu ini bergantung kepada kehadiran bahan kimia tertentu. penyelidikan ini menjurus kepada analisis dan perbandingan bahan-bahan kimia yang terdapat dalam minyak gaharu daripada spesis a. malaccensis, a. subintegra dan campuran kedua-duanya. minyak gaharu dilarutkan di dalam 5% heksana sebelum dianalisis menggunakan kromatografi gas agilent gcms 7890a berserta spektormetri jisim (msd quadrupole detector 5975 c). kolum kapilari silika hewlet packard hp-5ms (30 m x 0.25 mm x 0.25 mm) digunakan untuk pemisahan bahan-bahan kimia tersebut. sejumlah 107 kompaun dikenalpasti dalam ketiga-tiga sampel minyak gaharu tersebut dengan 55 kompaun didapati di dalam sample a. malaccensis. ini merupakan bahagian terbesar daripada keseluruhan kompaun. sebanyak 20 % daripada keseluruhan kompaun yang dikenalpasti adalah daripada kumpulan seskuiterpena dan bersifat aromatik, juga merupakan kumpulan yang bertanggungjawab memberi aroma yang unik kepada minyak gaharu. setiap spesis didapati mempunyai komposisi atau profil bahan kimia yang tersendiri. dua kompaun iaitu 3-phenyl-2butanone dan alpha-cubebene ditemui dalam ketiga-tiga sample yang dianalisis. kajian lanjut adalah perlu untuk memurnikan dapatan hasil penyelidikan yang berpotensi bagi membantu pengenalpastian gaharu berserta pembangunan penggredan gaharu yang lebih saintifik. iium engineering journal, vol. 15, no. 1, 2014 hashim et al. 56 keywords: agarwood oil; a. malaccensis; a. sub-integra; chemical compounds, gcms 1. introduction agarwood oil is a highly prized type of oil due to its unique aroma. the oil is extracted from the fragrant resin found in the agarwood tree trunk. the formation of resin can be stimulated through natural infection of a consortium of microorganisms, chemical induction and or artificial wounding. since the formation of resin through natural infection is a long process with very low yield, this lends to its high price. the unique aroma and quality of the agarwood resin and oil are contributed by the presence of certain chemical compounds. sesquiterpenes have been reported to be the main active components that play important roles in giving the aroma and pleasant odor of agarwood [1, 2]. however, there are many other chemical compounds in the agarwood resin and oil; some of which have medicinal values. earlier studies have focused on identification of the chemical compounds found in specific species of agarwood. for instance, sesquiterpenes were reported to be found in a. agallocha [3, 4]. there are fifteen species in the aquilaria genus and eight are known to produce agarwood [5]. in theory, all members in aquilaria genus can produce agarwood; however, until recently it was primarily produced from aquilaria malaccensis. other members of the genus that are usually harvested are a. crassna, a. sub-integra, a. agallocha and a. sinensis [6, 7]. in this work, analysis and comparison the chemical compounds of agarwood oil from a. malaccensis and a. sub-integra were conducted. the former is a local species found in malaysia; which has connotation with superior quality of resin and oil [6]. meanwhile, the latter, with characteristic of faster growth, is more common in thailand and cambodia where the species have been commercially cultivated in plantations. the characteristics of aroma between species may help in identification and authentication of agarwood as well as determination of its quality. 2. materials and methods 2.1 sample preparation three types of agarwood oils produced using hydrodistillation technique were obtained from different sources. the samples were labeled sample a (a. malaccensis from malaysia), sample b (a. sub-integra from thailand) and sample c (mixture of a. malaccensis and a. sub-integra from malaysia, grade c) respectively. the essential oils were diluted in hexane (5%) prior to gcms analysis. 2.2 gas chromatography mass spectrometry (gcms) analysis gcms analysis was performed with a gas chromatography system; agilent 7890a (agilent technologies) coupled with msd quadrupole detector 5975 c. separation of analytes by gas chromatography was carried out using a hewlett packard hp-5ms silica capillary column (30 m x 0.25 mm x 0.25 mm). the analytical conditions for gcms are listed in table 1. the peaks from gcms were detected based on the total ion chromatography (tic) and mass chromatograms; and further identified using national institute of standards and technology (nist) 2008 mass spectral library. iium engineering journal, vol. 15, no. 1, 2014 hashim et al. 57 table 1: analytical conditions for gcms analysis (based on [6]). program conditions oven program 80 °c for 2 min, then 10 °c/min to 250°c for 10 min carrier gas helium gas flow 2 ml/min split ratio 1:50 injection volume 1 µ l mode splitless interface temperature 250 °c electron impact (emission current) 70 ev scan range 32 to 500 amu 3. results and discussion examination of three samples of agarwood oils from different sources showed some variations in gc profile and chemical components. the variations of gc profiles are shown in fig. 1 (a-c). (a) 1 2 iium engineering journal, vol. 15, no. 1, 2014 hashim et al. 58 (b) (c) fig. 1: total ion chromatogram (tic) for agarwood oil from different species. (a) sample a (a. malaccensis from malaysia), (b) sample b (a. sub-integra from thailand) and (c) sample c (mixture for a. malaccensis and a. sub-integra from malaysia, grade c). labeled peaks are 3-phenyl-2-butanone (1), alpha-cubebene (2), and globulol (3). 1 2 3 1 2 3 iium engineering journal, vol. 15, no. 1, 2014 hashim et al. 59 a total of 107 compounds were identified from the three samples of agarwood oils. fifty five components were identified in sample a which contributes to the largest portion of the total compounds. in sample b and sample c, there were 35 and 37 compounds identified respectively. about 20% of the compounds identified were aromatic and sesquiterpenes which have been revealed to be the main active compounds of agarwood oils. these main active components play important roles in giving the aroma and pleasant odor of agarwood [1, 2]. two compounds were commonly identified in all three samples which are 3-phenyl2-butanone and alpha-cubebene, a waxy herbal odor type with medium odor strength. common occurrence of 3-phenyl-2-butanone, was observed in all agarwood oil (a. malaccensis) obtained from different sources in peninsular malaysia [8]. in an earlier study, benzylacetone was also found to be major compounds found in a. malaccensis [9]. similar compound named 1,1,4,7-tetramethyldecahydro-1h-cyclopropa[e]azulen-4ol (also known as globulol) was identified to be present in sample b and sample c. there were 11 similar compounds identified from sample a and sample c but not sample b. most of these compounds were sesquiterpenes such as alpha-caryophyllene (alphahumulene), alpha-calacorene. to this end, this suggests that the compounds could be potential characteristic compounds of each agarwood species. nevertheless, further studies are needed to refine and validate these early findings. there are several factors that may result in different chemical compositions of agarwood essential oil which include (a) species/origin of the agarwood tree, (b) methods of stimulation of agarwood resin, and (c) extraction method of agarwood oil. our results showed that different species have different composition of chemical compounds. in another study, several sesquiterpenes were found in five different types of chinese eaglewood essential oil [10]. the quality of agarwood oil is also affected by the stimulation method to produce the resin. resin production can be stimulated either through natural infection, chemical induction or artificial screw techniques which wounded the trunk (nail inserting, holing and trunk breaking). several studies have been done to compare the quality of the mantreated and wild agarwood. chen et al. [1] investigated the chemical compositions of agarwood oil originating from resin stimulated by chemical methods. meanwhile, bhuiyan et al. [11] examined the difference in composition of oil obtained from naturally infected tree and artificially inoculated eaglewood (a. agallocha robx.) by gcms. the composition of inoculum, natural variant and specific host-pathogen relationship also play great role in inducing the resin production in agarwood [11] which relates to the quality and differential composition of chemical compounds in its resin and oil. further, extraction method of agarwood oil also influences the quality and chemical composition of the oil. various techniques have been used for agarwood oil extraction: water distillation (hydrodistillation), steam distillation, solvent extraction and supercritical fluid extraction [12]. each technique has its own advantages and disadvantages. in a study done by pornpunyapat et al. [13], extraction of agarwood oil was performed by hydrodistillation at different temperature: 80°c, 100°c and 120°c. in their findings, hydrodistillation of essential oil at high temperature (120°c) gave the maximum oil yield and have better physical properties and attributes. meanwhile, there was significant difference in the quantity of each composition and types of major components of agarwood oil extracted using supercritical fluid extraction as compared to distillation method [2]. iium engineering journal, vol. 15, no. 1, 2014 hashim et al. 60 4. conclusion in conclusion, using gcms, we have identified different compositions of chemical components in agarwood oils from different species namely a. malaccensis and a. subintegra with two compounds commonly identified in all three samples which are 3phenyl-2-butanone and alpha-cubebene. further studies are needed to refine the results which later can be used to assist detection and authentication of agarwood as well as its scientific-based grading. acknowledgement this research was jointly funded by iium special grant and kayu gaharu (m) sdn. bhd. we would like to thank everyone who contributed to this research. references [1] chen, h., yang, y., xue, j., wei, j., zhang, z., chen, h. “comparison of compositions and antimicrobial activities of essential oils from chemically stimulated agarwood, wild agarwood and healthy aquilaria sinensis (lour.) gilg trees.” molecules 16.6 (2011): 488496. [2] wetwiyaklung, p., thavanapong, n., charoenteeraboon, j. “chemical constituents and antimicrobial activity of essential oil and extracts of heartwood of aquilaria crassna obtained from water distillation and supercritical fluid carbon dioxide extraction.” silpakorn u science & tech journal, 3.1(2009):25-33. [3] ishihara, m., tsuneya, t., uneyama, k. guaiane sesquiterpenes from agarwood. phytochemistry, 30.10(1991):3343-347. [4] nakanishi, t., yamagata, e., yoneda, k., nagashima, t., kawasaki, i., yoshida, t., mori, h., miura, i. three fragrant sesquiterpenes of agarwood. phytochemistry, 23.9(1984):206667. [5] eurlings, m.c.m., gravendeel, b. trnl-trnf sequence data imply paraphyly of aquilaria and gyrinops (thymelaeaceae) and provide new perspectives for agarwood identification. pl. syst. evol., 254(2005):1-12. [6] ng, l.t., chang, y.s., azizol, a.k. a review on agar (gaharu) producing aquilaria species. j. trop. forest products, 2.2(1997):272-85. [7] burkill, i.h. a dictionary of the economic products of the malay peninsula. ministry of agriculture, kuala lumpur. 1(1966):198-206. [8] nor azah ma., chang, ys., mailina j., abu said a., abd majid j., saidatul husni s., nor hasnida h., nik yasmin ycomparison of chemical profile of selected gaharu oils from peninsular malaysia. the malaysian journal of analytical sciences. 12.2(2008):338-40. [9] yaacob, k.b., joulain, d. volatile constituents from infected wood of aquilaria malaccensis benth. sains malaysiana, 29(2000):197-200. [10] mei, wen-li., zeng, yan-bo., wu, j., cui, hai-bin., dai, hao-fu. chemical composition and anti-mrsa activity of the essential oil from chinese eaglewood. journal of chinese pharmaceutical sciences, 17(2008):225-29. [11] bhuiyan, m.n.i., begum, j., bhuiyan, m.n.h. analysis of essential oil of eaglewood tree (aquilaria agallocha roxb.) by gas chromatography mass spectrometry. bangladesh j pharmacol, 4(2009):24-28. [12] naef, r. the volatile and semi-volatile constituents of agarwood, the infected heartwood of aquilaria species: a review. flavour frag j., 26(2011):73-87. [13] pornpunpayat, j., chetpattananondh, p., tongurai, c. mathematical modeling for extraction of essential oil from aquilaria crassna by hydrodistillation and quality of agarwood oil. bangladesh j pharmacol, 6(201):18-24. microsoft word vol11_no1_final iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 15 forward masking threshold estimation using neural networks and its application to parallel speech enhancement t. s. gunawan1, o. o. khalifa1, e. ambikairajah2 1electrical and computer engineering department, international islamic university malaysia, p.o. box 10, kuala lumpur, 50728, malaysia 2school of electrical engineering and telecommunications, university of new south wales, sydney, nsw 2052, australia e-mail: tsgunawan@iiu.edu.my abstract: forward masking models have been used successfully in speech enhancement and audio coding. presently, forward masking thresholds are estimated using simplified masking models which have been used for audio coding and speech enhancement applications. in this paper, an accurate approximation of forward masking threshold estimation using neural networks is proposed. a performance comparison to the other existing masking models in speech enhancement application is presented. objective measures using pesq demonstrates that our proposed forward masking model, provides significant improvements (5-15 %) over four existing models, when tested with speech signals corrupted by various noises at very low signal to noise ratios. moreover, a parallel implementation of the speech enhancement algorithm was developed using matlab parallel computing toolbox. keywords: human auditory system, forward masking, speech enhancement, pesq, parallel algorithm. 1. introduction forward masking is a time domain phenomenon in which a masker precedes the signal in time. forward masking psychoacoustic data depends on four dimensions, i.e. frequency, masker level, time difference between masker and maskee, and masker signal duration [1]. the current forward masking models do not fully take into account all the four dimension of forward masking data. functional models of the forward masking effect of the human auditory system have recently been used with success in speech and audio coding to provide more efficient signal compression [2, 3]. furthermore, forward masking has been used for speech enhancement [4] using the speech boosting technique [5]. instead of focusing on suppressing the noise, the speech boosting technique increases the relative power of the speech, thus acting as a speech booster. it is only active when speech is present, and remains idle when noise is present. jesteadt’s forward masking model [6] provides a reasonable approximation to the forward masking effect. strope et al. [7] extended the jesteadt experiment to 120 ms. in iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 16 jesteadt's and najafzadeh's forward masking models [6, 8], only masker level and delay have been taken into account. while in [9], gunawan and ambikairajah have refined the model to reflect forward masking data more accurately by averaging several parameters across frequencies. currently, the majority of these works focus on formulating mathematical models of the forward masking. such models are often too general. further refinement of the model requires software that can do curve-fitting of multi-dimensional data. nevertheless, for this purpose, we utilise neural network to better approximate forward masking threshold. to evaluate the performance of our forward masking model, five speech enhancement algorithms were implemented: spectral subtraction [10], spectral subtraction with minimum statistics [11], speech boosting [5], speech boosting using forward masking model 1 [4] and forward masking model 2 [9]. the perceptual evaluation of speech quality or pesq (itu-t p.862) measure was used here to benchmark the various methods. speech enhancement algorithm exploiting temporal masking properties of human auditory system has a very high computation requirement, especially when the noisy speech signal is long or the number of subbands is high. recent advances in multi-core system make it a natural choice and viable option for solving high computation requirements of the speech enhancement algorithm. therefore, the objective of this paper is two-folds: to evaluate the performance of our forward masking model in terms of enhanced speech quality and to implement and evaluate parallel speech enhancement algorithm on a multi-core system. the rest of the sections are organized as follows: section 2 discusses the development of forward masking models using neural networks. section 3 describes the sequential speech enhancement algorithm while section 4 discusses the parallel implementation of speech enhancement algorithm. experimental results and analyses are discussed in section 5 for the sequential and parallel algorithms. finally, section 6 concludes this paper. 2. forward masking models using neural networks neural network has been applied for various applications within the following broad categories: function approximation (or regression analysis), classification, and data processing (filtering, clustering, blind source separation, etc). brown et al. [12] applied non-recurrent neural networks for simultaneous masking modelling. in this paper, neural networks is employed to approximate the forward masking threshold for the three input parameters, including frequency, masker level, and delay. by taking into account the threshold in quiet ( tiq ) the absolute threshold of forward masking ( fm ) can be calculated using the equation we have developed below:      ssm tftiqtlmfmttlffm ,,,,,,  (1) as stated in [13], the threshold in quiet is a function of frequency and signal duration. by curve-fitting a set of 120 data points compiled from [13], we approximated the threshold in quiet to be as follows: iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 17   stftiq , for signal with long duration ( 500st ms) can be approximated as (f in khz):        43.36.08.0 001.05.664.3500, 2 feftftiq fs   (2)   stftiq , for signal with duration 500ts ms, can be approximated as        sss tftftiqtftiq   500log105.653.7500,, 10313 (3) the amount of forward masking  tlmfm ,, can be approximated using feed forward neural network as shown in fig. 1. fig. 1: amount of forward masking modelled by neural networks. the network configuration as shown in fig. 1 with 1 hidden layer could approximate any function [14]. to avoid over-fitting to the training data, the bayesian regularization as proposed in [15] was used. figure 2 shows the amount of forward masking against lm and t at frequency of 500hz using neural network. similar plots can be obtained for various frequencies, thus providing a more accurate estimation of forward masking data. iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 18 fig. 2: amount of forward masking estimation at 500hz. 3. speech enhancement this section presents the incorporation of our model to fit the speech enhancement algorithm developed in [4]. speech that has been contaminated by noise can be expressed as      nvnsnx  (4) where  nx is the noisy speech,  ns is the clean speech signal and  nv is the additive noise, all of which are in the discrete time domain. the objective in speech enhancement is to suppress the noise, thus resulting in an output signal  ny that has a higher signal-tonoise ratio (snr). the speech enhancement algorithm that incorporates forward masking [4] is shown in fig. 3. by filtering the input signal  nx using a bank of m analysis filters, the signal is divided into m subbands, each denoted by  nxm , where m is the subband index. this filtering operation can be described in the time domain as      nhnxnx mm * where .,,1 mm  and  nhm is the impulse response of the mth filter. the global forward masking threshold (gfm) and the forward masking threshold in each subband ( mfm ) are calculated from the noisy speech signal  nx and subband signal  mxm , respectively. the gfm and mfm are used to calculate the gain ( m ) in each subband. the gain, m , is a weighting function that amplifies the signal in band m during speech activity. iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 19 1 2 m 1 2 m  zh 2 zh 1  zhm  zg1  zg 2  zgm fm1 fm2 fmm gfm      nvnsnx   ny  nx1  nx2  nxm  ny1  ny2  nym dc rejection filter pesq measure  ns pesq score  nxm  nym fig. 3: speech enhancement using forward masking. the enhanced speech,  ny , is then obtained by applying the synthesis filters,  ng m , and compensating the delay ( m ) in each subband as follows:           m m mmmmm m m mm ngnxnyny 11 (5) our objective is now to find a gain function, m , that weights the input signal subbands,  nxm , based on forward masking threshold to noise ratio (mnr). the mnr in each subband can be calculated by using the ratio of a short-term average forward masking threshold,  npm , and an estimate of the noise floor level,  nqm as given in eqn (8). the short-term average temporal masking threshold in subband m is calculated as        nfmnpnp mmmmm   11 (6) iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 20 where m is a small positive constant (i.e. mm  ,0042.0 ) controlling the sensitivity of the algorithm to changes in forward masking threshold, and acts as a smoothing factor. the slowly varying noise floor estimate for the m-th subband,  nqm , is calculated as                      npnqnp npnqnq nq mmm mmmm m 1, 1,11  (7) where m is a small positive constant (i.e. mm  ,05.0 ) controlling how fast the noise floor level estimate in the m-th subband adapts to changes in the noise environment. the variables  npm ,  nqm ,  nfm m and  ngfm m are combined in a novel manner in order to calculate the gain function  nm as follows,            nq np ngfm nfm n m m m m mm   1 (8) where 10  m , i.e. mm  ,9.0 , is a positive constant controlling the contribution of the forward masking threshold ratio and the short term mnr. since the calculation of  nm involves a division, care must be taken to ensure that the quotient does not become excessively large due to a small  nqm . in a situation with a very high mnr,  nm will become very large if no limit is imposed on this function. therefore, a limiter can be applied on  nm as follows:           mmm mmm m cc cn n , (9) where 23529.0  mcm db provides a suitable limiter for the gain function. 4. parallel speech enhancement algorithm the design of an efficient parallel speech enhancement algorithm can be a challenging task. first step in the parallelization of any sequential code is to identify which part of code that takes the longest execution time. using matlab profiling tool, it was identified that the calculation of forward masking threshold and gain calculation for each subband (see eqn 5 to 9) were taking the longest execution time. in this paper, we will utilize the matlab parallel computing toolbox. the hardware used was an amd quad core 2.5 ghz system with 2 gbytes of memory. master-slave paradigm is used in the parallelization. to achieve a scalable parallel implementation of speech enhancement algorithm, we used the data-parallel or single program multiple data (spmd) programming model. a single program was written for both master and slave processes that asynchronously execute on each node. in particular, iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 21 all processes will work on different piece of data. there are two data partition schemes available in speech enhancement algorithm, time partition and frequency (subband) partition. in time partition a long noisy speech file is partitioned into smaller time and processed individually. while in frequency or subband partition, the total number of subbands is divided and distributed into a number of slaves. as the calculation of temporal masking requires the information from previous frames, it is obvious that subband partition is more appropriate for parallelization. hence, it will be used in our implementation. fig. 4: flowchart of parallel speech enhancement algorithm. figure 4 shows the flowchart of parallel speech enhancement algorithm that can be implemented on multi-core system and/or cluster system. initially, the parallel program starts with initialization at every node. of the two communication schemes available in iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 22 matlab parallel computing toolbox, i.e. distributed array and message passing, we will use message passing scheme as it provides more flexible communication scheme. then, a noisy speech signal is partitioned (using subband partition) and distributed to coren configured in master-slave fashion. after that, each slave is then filtered the noisy speech signal accordingly, calculates the forward masking threshold, determines the gain for each subband, and applies the gain for each subband signal. after obtaining denoise speech signal for each subband, each slave then sends the results to the master node. finally, speech reconstruction and pesq evaluation are applied at the master node. 5. performance evaluation in this section, the performance of sequential code, in terms of subjective and objective quality of the enhanced speech, was evaluated. furthermore, the performance of parallel code, in terms of speedup for various numbers of cores, was presented. 5.1 subjective and objective quality in order to assess the performance of the new forward masking model in enhancing speech signals, a large number of simulations were performed. six speech files were taken from ebu sqam data set including english female and male speakers, french female and male speakers, and german female and male speakers. the length of the files was between 17 and 20 seconds. the sampling frequency was 8 khz, and the frame size was 256 samples (32 ms). several algorithms were implemented and compared, including spectral subtraction, ss[10], spectral subtraction with minimum statistics, ssms[11], speech boosting, sb[5], speech boosting using forward masking model 1, sbfm1[4], speech boosting using forward masking model 2, sbfm2[9], and speech boosting using the developed neural networks forward masking model, sbfm3. different types of background noises from the noisex-92 and aurora database have been used including car, white noise, pink noise, f16, factory, babble, airport, exhibition, restaurant, street, subway and train noise. the variance of noise has been adjusted to obtain -5 db, 0 db, 5 db, and 10 db snrs. the pesq (perceptual evaluation of speech quality, itu-t p.862) measure [16] was utilised for the objective evaluation. note that, the pesq has a 93.5% correlation with subjective tests [16]. to evaluate the performance of the speech enhancement algorithms, we developed a new measure to assess the improvement achieved. suppose that we have refpesq which is the pesq score for the reference clean speech,  ns , and the corrupted speech,  nx . the pesq score of the enhanced speech,  ny , was also measured and denoted as procpesq . therefore, we can derive a new value,  , which measures the pesq improvement achieved by the algorithm as follows: %100   ref refproc pesq pesqpesq  (10) iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 23 a total of 288 data sets from six speech files, twelve noises, and four snrs for each method were simulated. the average quality improvement,  , achieved by various speech enhancement methods is shown in figure 4. note that the  results for various speech files and noises were averaged for -5, 0, 5, and 10 db snrs. from these results, the speech boosting technique incorporating neural networks forward masking model outperforms other methods for all snrs. fig. 5: average  (%) for various algorithms. in order to analyse the performance of our proposed method in more detail, the average of quality improvement at -5, 0, 5, and 10 db snrs for various noises is shown in table 1. the best  result for each type of noise condition is shown in bold, from which it can be seen that our method using neural networks forward masking model provides a better pesq improvement than the five other methods tested. table 2 shows the average of quality improvement at -5, 0, 5 and 10 db snrs for various speech files. the best  result for each individual speech file is shown in bold. the table shows that more accurate forward masking threshold calculation leads to a better and enhanced speech quality. furthermore, informal listening test confirm that the speech processed with the proposed algorithm sounds more pleasant to a human listener than those obtained by other algorithms. iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 24 table 1: average pesq improvement  (%) for various noise types. noise types ss ssms sb sbfm1 sbfm2 sbfm3 car 19.88 18.16 11.80 21.04 22.09 23.30 white 17.50 28.33 15.81 21.58 34.25 33.67 pink 22.73 28.90 16.93 27.41 37.28 37.32 f16 16.48 18.81 13.62 23.59 29.92 30.43 factory 18.28 12.47 13.79 25.65 31.75 32.07 babble 2.61 1.65 7.14 13.76 18.12 19.76 airport 6.16 3.73 7.83 12.77 16.59 17.67 exhibition 11.64 5.54 11.79 18.30 30.10 30.72 restaurant 5.02 2.06 4.34 10.54 17.78 17.96 street 8.59 9.45 12.82 18.63 15.86 17.06 subway 4.29 7.49 11.57 20.18 34.42 34.51 train 14.92 15.57 13.20 19.88 20.74 21.99 table 2: average pesq improvement  (%) for different speech files. speech files ss ssms sb sbfm1 sbfm2 sbfm3 english male 6.24 4.32 5.57 12.37 24.24 24.74 english female 8.79 9.08 9.61 15.65 26.00 26.23 french male 15.17 15.67 11.67 21.94 28.38 29.11 french female 10.83 11.46 9.36 14.69 19.31 19.73 german male 21.89 27.35 21.27 36.03 34.75 36.33 german female 11.13 8.20 12.84 16.00 21.76 22.08 5.2 parallel performance the computing environment used in this research was amd phenom quad-core processor 2.5 ghz system with 2 gbytes of memory. this section is intended to analyse the parallel performance of the speech enhancement algorithms in terms of parallel execution time and speed up. iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 25 table 3: parallel execution time and speedup for various number of processors. number of processor parallel execution time speedup 1 430 seconds 1 2 217 seconds 1.98 3 145 seconds 2.97 4 109 seconds 3.95 table 3 shows the performance of the parallel speech enhancement algorithm for 1, 2, 3, and 4 processor. for the evaluation purposes, we used female speech signal with various noises and various snrs and take the average of parallel execution time and speedup. the parallel speech enhancement algorithm achieves almost linear speedup indicating the high efficiency on parallelization. moreover, this could be due to the fast communication scheme between processor in which it did not affect the parallel performance. when the number of nodes is high, the communication time will affect the speedup, especially in a cluster system. therefore, it will be interesting if we evaluated our parallel speech enhancement algorithms on a cluster system with higher number of nodes. 6. conclusions in this paper, a new forward masking model using neural networks has been proposed and incorporated into a speech enhancement algorithm. the performance of our speech enhancement algorithm employing new forward masking model was compared with five other speech enhancement methods (two other functional models of forward masking) over twelve different noise types and four snrs. pesq results reveal that the proposed algorithm outperforms the other algorithms by 5-15% depending on the snr. hence, it appears that the proposed forward masking model has good potential for speech enhancement applications across many types and intensities of environmental noise. on a quad core system, the parallel speech enhancement algorithm developed was very efficient in which almost linear speedup was achieved. references [1] j. m. buchholz, a computational model of auditory masking based on signal-dependent compression, phd thesis, universitat bochum, 2002. [2] t. s. gunawan, e. ambikairajah, and d. sen, "comparison of temporal masking models for speech and audio coding applications," in international symposium on digital signal processing and communication systems, pp. 99-103, 2003. [3] f. sinaga, t. s. gunawan, and e. ambikairajah, "wavelet packet based audio coding using temporal masking," in int. conf. on information, communications and signal processing, singapore, pp. 1380-1383, 2003. iium engineering journal, vol. 11, no. 1, 2010 gunawan et al. 26 [4] t. s. gunawan and e. ambikairajah, "speech enhancement using temporal masking and fractional bark gammatone filters," in 10th international conference on speech science & technology, sydney, pp. 420-425, 2004. [5] n. westerlund, applied speech enhancement for personal communication, thesis, blekinge institute of technology, 2003. [6] w. jesteadt, s. p. bacon, and j. r. lehman, "forward masking as a function of frequency, masker level, and signal delay," journal of acoustic society of america, vol. 71, pp. 950962, 1982. [7] b. strope and a. alwan, "a model of dynamic auditory perception and its application to robust word recognition," ieee transactions on speech and audio processing, vol. 5, pp. 451-464, 1997. [8] h. najafzadeh, h. lahdidli, m. lavoie, and l. thibault, "use of auditory temporal masking in the mpeg psychoacoustics model 2," in the 114th convention, audio engineering society, pp., 2003. [9] t. s. gunawan and e. ambikairajah, "a new forward masking model and its application to speech enhancement," in ieee international conference on acoustics, speech and signal processing, pp. 149-152, 2006. [10] s. f. boll, "suppresion of acoustic noise in speech using spectral subtraction," ieee transactions on acoustics, speech and signal processing, vol. 27, pp. 113-120, 1979. [11] r. martin, "spectral subtraction based on minimum statistics," in europe signal processing conference, edinburgh, scotland, pp. 1182-1185, 1994. [12] e. brown, d. ros, c. bruscianelli, and b. mila de la roca, "non-recurrent neural networks for auditory perceptual modelling," in ieee international conference on devices, circuits and systems, pp. 139-143, 1995. [13] m. florentine, h. fastl, and s. buus, "temporal integration in normal hearing, cochlear impairment, and impairment simulated by masking," journal of acoustic society of america, vol. 84, pp. 195-203, 1988. [14] h. simon, neural networks: a comprehensive foundation, prentice hall ptr, 1994. [15] f. d. foresee and m. t. hagan, "gauss-newton approximation to bayesian regularization," in international joint conference on neural networks, pp. 1930-1935, 1997. [16] itu, "itu-t p.862, perceptual evaluation of speech quality (pesq), an objective method for end-to-end speech quality assessment of narrow-band telephone networks and speech codecs," international telecommunication union, geneva 2001. 504 iium engineering journal, vol. 15, no. 1, 2014 sulaeman and ahmed 71 approximate function for unsteady aerodynamic kernel function of aeroelastic lifting surfaces erwin sulaeman and layeeq ahmed department of mechanical engineering, faculty of engineering, international islamic university malaysia, po box 10, 50728, kuala lumpur, malaysia. esulaeman@iium.edu.my abstract: prediction of unsteady aerodynamic loads is still the most challenging tasks in flutter aeroelastic analysis. generally, the numerical estimation of steady and unsteady aerodynamics of thin lifting surface is conducted based on an integral equation relating aerodynamic pressure and normal wash velocity. the present work attempts to increase the accuracy of the prediction by using an approximate approach to evaluate kernel function occurring in the integral equation in the form of cylindrical function. following previous approximation approaches by other researchers to solve the cylindrical function for planar lifting surfaces, this paper extends such approaches to non planar lifting surfaces. to increase the accuracy of the method, the integration region of the kernel function is divided into two parts – near and far regions, where a nonlinear regression curve fitting technique is adapted to estimate the denominator part of the cylindrical function of each region. abstrak: penelahan daya aerodinamik tidak stabil merupakan satu tugas yang mencabar dalam menganalisis getaran aeroanjalan. umumnya, anggaran berangka untuk daya aerodinamik stabil dan tidak stabil pada permukaan mengangkat yang nipis, adalah berdasarkan kepada persamaan kamiran di antara tekanan aerodinamik dan halaju aliran udara pada garis normal yang terhasil di bawah sayap pesawat. kajian ini adalah bertujuan untuk menghasilkan penelahan daya aerodinamik yang lebih tepat dengan menggunakan pendekatan kira hampir untuk menilai fungsi kernel yang terdapat dalam persamaan kamiran dalam bentuk fungsi silinder. dengan menggunakan pendekatan kira hampir yang digunakan oleh penyelidik sebelumnya untuk menyelesaikan fungsi silinder pada permukaan mengangkat satah, kajian ini mengembangkan pendekatan tersebut kepada permukaan mengangkat tak sesatah. untuk meningkatkan lagi ketepatan penelahan, kawasan pengamiran fungsi kernel dibahagikan kepada dua bahagian, kawasan hampir dan kawasan jauh, di mana penyuaian lengkung regresi tak linear digunakan untuk kiraan hampir penyebut pada fungsi silinder pada setiap kawasan. keywords: aeroelasticity; unsteady aerodynamics; kernel function; cylindrical function; lifting surface 1. introduction investigations are in progress for the improvement of accuracy and efficiency of the load prediction methods for countless types of aerodynamic configurations ranging from simple two dimensional airfoils to complicated full scale aircrafts [1]. since its derivation in 1940, küssner’s governing formulation is the origin of most aerodynamic load formulations for thin lifting surfaces [2,3]. the fundamental part in the küssner integral equation is the so-called kernel function which relates aerodynamic pressure and normal wash velocity. several forms of the kernel function have been proposed in the past, including the formulation of watkins et al. [4], laschka [5], yates [6], landahl [7], and iium engineering journal, vol. 15, no. 1, 2014 berman et al. [8]. the effect of acoustic [9]. the widely accepted formulation of the kernel function is due to landahl where the formula is used in aeroelastic analysis tool of msc formulations contain a hyper whose solutions are not readily available in commercial software. most of the literatures use approximation methods to solve the incomplet function [3, 8]. the first approximate method was adopted by watkins et al. used in unsteady aerodynamic doublet lattice method of ref. 8. laschka both analytical and numerical similar numerical approximation of series of fraction with constant numerators was offered by dat and malfois [13,14] in order to minimize the error in the approximation. ueda expansion series to solve analytically the problem. however, the ueda series requires a large number of steps for a large number of arguments of oscillating fun [2]. to increase the accuracy of the kernel function evaluation, an analytical separation of singular and regular functions occurring in the incomplete cylindrical function is proposed in [16] by modifying the expansion series. another a bismarck-nasr [17] based on extension of the kernel function formulation to transonic flow and separated flow. and bliss [2] suggested an approximation to th dividing the regions of integration into two parts which are near and far fields. their work in ref. 2 is presented for the planar lifting surfaces. following the epstein in the present work such approac accuracy is increased by adding more terms to the approximation functio fig. 2. governing equation the küssner integral equation relating in the unsteady potential derivation is written as [3]: ol. 15, no. 1, 2014 sulaeman 72 l. [8]. the effect of acoustics in the integral equation is formulated by yu et al. the widely accepted formulation of the kernel function is due to landahl where the eroelastic analysis tool of msc nastran software. all of these formulations contain a hyper-geometric function of incomplete cylindrical function type solutions are not readily available in commercial software. most of the literatures use approximation methods to solve the incomplet the first approximate method was adopted by watkins et al. used in unsteady aerodynamic doublet lattice method of ref. 8. laschka [11 both analytical and numerical solutions for the kernel function with three digit accuracy. similar numerical approximation of series of fraction with constant numerators was offered by dat and malfois [12]. least square technique is suggested by desmarais in order to minimize the error in the approximation. ueda [15] expansion series to solve analytically the problem. however, the ueda series requires a large number of steps for a large number of arguments of oscillating functions as shown in [2]. to increase the accuracy of the kernel function evaluation, an analytical separation of singular and regular functions occurring in the incomplete cylindrical function is proposed by modifying the expansion series. another analytical solution is presented by based on differential equation approach. [18] described possible extension of the kernel function formulation to transonic flow and separated flow. and bliss [2] suggested an approximation to the incomplete cylindrical function by dividing the regions of integration into two parts which are near and far fields. their work in ref. 2 is presented for the planar lifting surfaces. following the epstein-bliss approach, in the present work such approach is extended to non planar lifting surfaces and the accuracy is increased by adding more terms to the approximation function. fig. 1: surface and panel (box) geometry. governing equation the küssner integral equation relating the pressure and the normal wash distribution in the unsteady potential derivation is written as [3]: sulaeman and ahmed the integral equation is formulated by yu et al. the widely accepted formulation of the kernel function is due to landahl where the nastran software. all of these geometric function of incomplete cylindrical function type most of the literatures use approximation methods to solve the incomplete cylindrical the first approximate method was adopted by watkins et al. [10] which is 11] presented solutions for the kernel function with three digit accuracy. similar numerical approximation of series of fraction with constant numerators was . least square technique is suggested by desmarais presented an expansion series to solve analytically the problem. however, the ueda series requires a ctions as shown in [2]. to increase the accuracy of the kernel function evaluation, an analytical separation of singular and regular functions occurring in the incomplete cylindrical function is proposed nalytical solution is presented by described possible extension of the kernel function formulation to transonic flow and separated flow. epstein e incomplete cylindrical function by dividing the regions of integration into two parts which are near and far fields. their work bliss approach, h is extended to non planar lifting surfaces and the the pressure and the normal wash distribution iium engineering journal, vol. 15, no. 1, 2014 sulaeman and ahmed 73 �� � � � ∆� �, , �, �, �, �, �, �� 8� �� � � �� �� (1) where w is the normal wash velocity at the control point (x,y,z) on the lifting surface as shown in fig. 1, u is the free stream velocity of the unperturbated flow assumed in the x axis direction; and �� is the nonstationary aerodynamic pressure difference at point � , � , �� along the line of doublets of each trapezoidal aerodynamic model box shown in fig. 1. the free stream dynamic pressure is denoted by q and is equal to ρu 2 /2 where ρ is the free stream air density. the kernel function of the integral k is a function of relative position, the free stream mach number m, and the reduced frequency k. the relative position between the control point and the doublet pressure location can be expressed as: �� � � � � � � � � �� � � � � and the reduced frequency k is defined as � � � � where l is the reference length. 2.1 planar surfaces the kernel function k given in epstein[2] for planar lifting surface is written as ! �� , �, �, �" � # $%&'( �# $%&) *√,� � � . �, �, ,� (2) where b is the incomplete cylindrical function formulated according to landahl [7] and ueda [15] as . �, �, �� � / # %&0 � � 1��2� ) $3 �1 � 1� � / #%&56 1 7��2� �7 ∞ $)5 (3) and the modified distance r , r and x are defined as � � 8 � ��� � | �| * � :��� ;�� � , � �� � �*;� � � ;� � 1 � �� separating the real and imaginary terms [2] from eqn (3) yields . �, �, ,� � .5 < .% � 1�� / cos ��7� 1 7��2� ∞ $)5 <� � / sin ��7� 1 7��2� ∞ $)5 (4) iium engineering journal, vol. 15, no. 1, 2014 sulaeman and ahmed 74 and integrating the equation by parts gives . �, �, ,� � 1� � !v"$|)/5|∞ � ��� � / # %&56 d 7��7 ∞ $)5 (5) where the term v represents the non-integral term e � #%&56 � 7√1 7� � 1� � ��# $%&56 f�7 81 7�g (6) and the function f(u) is defined by d 7� � �7 81 7� (7) in the present work, a simple curve fitting technique is utilized to approximate f(u) as follows: d 7� h i 7� � j ik 7� for 7 n 1.5 iq 7� for 7 r 1.5 s (8) where fa (u) and fb (u) are defined as ik 7� � t u% 7% v %w� (9a) iq 7� � t x% 7$% y %wz (9b) and the coefficients ai and bi are defined in table 1. table 1: coefficients ai and bi of eqn (8) and (9). i ai bi 0 0.99999933 - 1 -0.99968242 0.49998705 2 0.49488907 0.00017800315 3 0.0303999182 -0.12594842 4 -0.21413252 0.00099707005 5 0.13894299 0.071073596 6 -0.041028643 -0.032656364 7 0.0048280266 - the accuracy of the present approximation is demonstrated in fig. 2 and fig. 3. in fig. 2, the plot of f(u) resembles the target function f(u). the plot of the error representing the difference between f(u) and f(u) is presented in fig. 3. the maximum error for the present approximation is 3.5 x 10 -6 at u = 1.4. figure 3 also presents the plot of the error if the approximation of epstein-bliss [2] is used. the maximum error of their error is 0.015 which occurs at u = 0.5. therefore, the present approximation provides much better accuracy compare to the approximation of ref. 2. note that the plot for the epstein-bliss iium engineering journal, vol. 15, no. 1, 2014 sulaeman and ahmed 75 approximation in fig. 3 is multiplied by 10 -3 whereas for the present approach is multiplied by 10 -6 in order to show the sensitivity changes in the error. fig. 2: comparison between the present approach f(u) and the target function f(u). fig. 3: comparison between the error of the present approach f(u) and the epstein-biss approach with respect to the target function. figure 4 shows comparison of br(k,r,x) between the exact analytical solution of series expansion [14, 15] and the present approximation. figure 5 shows comparison of bi(k,r,x) between the exact and the present approximation. to show the accuracy of the present approximation, the error or the difference between the analytical solution and the present approximation is plotted in figs. 6 and 7 for br and bi respectively. both figures also present the error for br and bi calculated using epstein-bliss approximation which demonstrates the improvement of the present approximation. figure 6 shows that the maximum error of the epstein-bliss approximation for br is 0.0127 whereas the present approximation gives the maximum error of 0.00047. in fig. 7, the maximum difference for bi using the epstein-bliss approximation is 0.0094. but the new approximation plot shows the accuracy of 0.0000667 which increases the applicability of the new approximation to a good extent in solving the incomplete cylindrical function in the kernel function. 0 0.2 0.4 0.6 0.8 1 1.2 0 1 2 3 4 5 f (u ) u exact present approx -20 -15 -10 -5 0 5 0 2 4 6 8 10 e rr o r (e x a c t a p p ro x ) u epstein-bliss ( x 10-3) present approx. ( x 10-6) iium engineering journal, vol. 15, no. 1, 2014 sulaeman and ahmed 76 2.2 nonplanar surfaces rodemich [19] derived an expression in 1965 for the kernel function of nonplanar lifting surfaces as follow: � # $[%\'(] ^ z_z �_��/�z� (10) where _z � `ab cd � c5 � _� � 1�z� �� `ab cd � � b<e c5 � �� `ab c5 � � b<e cd � z � fz ���z* � # $%&g6g 1 7z�� z� � � �3f� � # $%&g6g 1 7z�� z� i<�z � � �z� *� s s� ��z * j 1 7z��;��z� *� 2 ��z7z * lm where the incomplete cylindrical functions are given as fz � / # $%&g6 1 7z�� 2� 3 6g �7 � �z�.z (11) f� � / # $%&g6 1 7z�� n� 3 6g �7 � �zo .� (12) where �z � �� ��� �z/� 7z � �* � ��;��z �z � ��z� the incomplete cylindrical function for nonplanar surfaces i2 can be further separated into real and the imaginary parts as follows f� � f�5 -f�% � / `ab �z7� 1 7z�� n� ∞ 6g �7 < / b<e �z7� 1 7z�� n� ∞ 6g �7 (13) the above given approximations in eqn (8) and eqn (9) could be utilized for nonplanar conditions. the solution will be extended towards the derivation of the function f(u). figure 8 shows comparison of br with the exact analytical solution of the series expansion method [15]. the accuracy is quite considerable where it is shown in the fig. 9 which shows the maximum error of 1.15 x 10 -6 . in fig. 10 the comparison of the bi is compared with that of the expansion series method and the accuracy can be read in fig. 11 which shows the maximum differences of 9 x 10 -6 for the range until x = 10. iium engineering journal, vol. 15, no. 1, 2014 sulaeman and ahmed 77 fig. 8: comparison of br (nonplanar) between the present method and the series expansion method for k = 1.0 and r = 1.0. fig. 9: difference of br (nonplanar) with the analytical solution for k = 1 and r = 1. -0.2 0 0.2 0.4 0.6 0.8 1 1.2 -4 -3 -2 -1 0 1 2 3 4 br new approx. br analytical x b r (k ,r ,x ) -0.5 -0.3 -0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3 0 2 4 6 8 10 e rr o r o f b r ( x 1 0 -6 ) x iium engineering journal, vol. 15, no. 1, 2014 sulaeman and ahmed 78 fig. 10: comparison of bi (nonplanar) between the present method and the series expansion method for k = 1.0 and r = 1.0. fig. 11: difference of bi (nonplanar) with the analytical solution for k = 1 and r = 1. 3. conclusion in the present method the solution to the incomplete cylindrical function is derived to a certain extent and the non-oscillatory part of the integrand is approximated using a simple curve fitting technique. the accuracy is appreciable with the comparison of analytical series expansion method. the applicability of the presented approximation to planar and non-planar configurations is augmented due to its plainness and the precision. acknowledgement the authors would like to acknowledge the financial support rendered by the ministry of education (moe) malaysia, under an frgs grant (13-020-0261). -0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 -4 -3 -2 -1 0 1 2 3 4 bi new approx. bi analytical x b i (k ,r ,x ) -6 -4 -2 0 2 4 6 8 10 12 0 2 4 6 8 10 e rr o r o f b i ( x 1 0 -6 ) x iium engineering journal, vol. 15, no. 1, 2014 sulaeman and ahmed 79 references [1] ahmed, l., sulaeman, e. “alternate approximate function for kernel function of planar oscillation lifting surfaces.” in selected topics in aerospace engineering, kuala lumpur: iium press, (2011). [2] epstein, r.j., bliss, d.b. “alternative solution of the kernel function in subsonic unsteady lifting surface theory.” aiaa journal, 33 (1995):2228-30. [3] sulaeman, e. formulation of kernel function for aerodynamic loading on air vehicle. in selected topics in aerospace engineering, kuala lumpur: iium press. (2011) [4] watkins, c.e., runyan, h.l., woolston, d.s. on the kernel function of the integral equation relating the lift and downwash distribution of oscillating finite wings in subsonic flow. .naca-1234. national aeronautics and space administration hampton va langley research center, 1955. [5] laschka, b“das potential und das geschwindigkeitsfeld der harmonisch schwin-genden tragenden flache bei unterschallanstromung.” z. angew. math. mech. 43(1963):325-333. [6] yates, e.c. jr (“a kernel function for nonplanar oscillating surfaces in subsonic flow. aiaa journal, 5(1966):1486-88. [7] landahl, m.t‘”kernel function for nonplanar oscillating surfaces in a subsonic flow.” aiaa journal, 4(1967):1045-46. [8] berman, h.j., shyprykevich, p., smedfjeld, j.b. “subsonic nonplanar kernel function for surfaces inclined to the freestream.” journal of aircraft 7(1970):188-190. [9] yu kh, djojodihardjo h, kadarman ak. “acoustic effects on binary aeroleasticity model.” iium engineering journal, 12.2(2011):123-129. [10] watkins, c.e., woolston, d.s., cunningham, h.j. “a systematic procedure for determining aerodynamics forces on oscillating or steady finite wings at subsonic speed”. in ." nasa 19980227841 (1959). [11] laschka, b. zur theorie der harmonisch schwingenden tragenden flache bei unterschallanstromung. z. flugwissenschaften, 11.7(1963):265-292. [12] dat, r., malfois, j.p. “sur le calcul du noyau de l’equation integrale de la surface postante en ecoulement subsonique instationnaire.” la recherche aerospatiale, 5(1970):251-259. [13] desmarais, r.n. “accurate numerical evaluation of modified struve functions occurring in unsteady aerodynamics.” journal of aircraft, 16.7(1979):441-47. [14] albano, e., rodden, w.p.) “a doublet lattice method for calculating lift distribution on oscillation surfaces in subsonic flow.” aiaa journal, 7.2(1969):279-85. [15] ueda, t. “expansion series of integral functions in unsteady aerodynamics.” journal of aircraft, 19(1982):345-47. [16] brendel, m., sulaeman, e. “improved doublet lattice formulation for calculating aerodynamic loads on lifting surface in unsteady subsonic flow.” aiaa paper 19941890, 12th aiaa applied aerodynamic conference, colorado. (1994) [17] bismarck–nasr, m.n. “kernel function occuring in subsonic unsteady potential flow.” aiaa journal, 29(1991):878-79. [18] sulaeman, e., djojodihardjo, h. “an expansion series for solving improper cylindrical functions occuring in subsonic, supersonic and transonic kernel formulations.” in contemporary research in engineering sciences, springer verlag, berlin. (1995). [19] vivian, h.t., andrew, l.v. “unsteady aerodynamic for advanced configurations.” part iapplications of the subsonic kernel function to nonplanar lifting surfaces, rdl-tdr-152, airforce flight dynamics lab, dayton, oh. (1965). microsoft word 4_vol17_no1_2016_(compiledversion_4).docx iium engineering journal, vol. 17, no. 1, 2016 abid 41 energy audit of a textile mill – a case study muhammad abid interdisciplinary research center, comsats institute of information technology, wah cantt, pakistan. drabid@ciitwah.edu.pk (received: 18 may. 2015; accepted: 14 dec. 2015; published on-line: 30 apr. 2016) abstract: the textile industry plays a pivotal role in pakistan’s economy. the industry‘s share for overall manufacturing activity is 46%; in the export sector it is 68%; in value addition it is 9% of gdp and in providing employment it is 38%, in addition to the foreign exchange earnings, investment and contribution to the value added industry. in spite of this major contribution, the textile industry is at a severe risk due to hefty increases in energy costs. keeping in view of these challenges in order to technically support the textile industry, energy audit of a textile mill ihas been carried out and areas of energy wastage are identified with an estimated cost saving of almost rs. 6.8 million. finally recommendations are given for cost effective measures for efficient energy usage, estimation of implementation costs and payback periods. abstrak: industri tekstil mempunyai peranan yang penting dalam ekonomi pakistan. saham industri tekstil untuk aktiviti pembuatan keseluruhan adalah 46 %; eksport adalah 68 %; nilai tambah adalah 9 % daripada kdnk dan penyediaan pekerjaan adalah 38%, sebagai tambahan kepada pendapatan tukaran asing, pelaburan dan sumbangan kepada industri nilai tambah. walaupun sumbangan besar ini , industri tekstil adalah atas risiko yang teruk disebabkan oleh peningkatan besar dalam kos tenaga. tetap melihat cabarancabaran ini bagi menyokong industri tekstil teknikal, audit tenaga kilang tekstil dijalankan dan bidang pembaziran tenaga dikenal pasti dan penjimatan kos yang dianggarkan hampir rs. 6.8 juta selesai. akhir sekali cadangan yang diberikan adalah untuk langkah yang berkesan kos untuk penggunaan tenaga yang cekap, penganggaran kos pelaksanaan dan tempoh bayar balik. keywords: energy; audit; loss; consumption; economy 1. introduction in any industry, the three major operating costs include energy (electrical and thermal), labor and materials. among these, the cost of energy is rated at the top [1-4]. considering the current power crisis in pakistan; the importance of the energy management function increases manifold. energy audit provides a bench-mark and basis for more effective planning for the use of energy in any organization [5-11]. textile industry is the major role player for country’s economy [12-17]. in pakistan, textile industry shares for overall manufacturing activity is 46%; export is 68%; value addition is 9% of gdp and employment provision is 38%, in addition to the foreign exchange earnings, investment and contribution to the value added industry [18-21] . in this paper energy audit of a textile industry in pakistan is presented. areas of energy losses are identified; suggestions for cost effective measures to establish efficient energy use and estimation of implementation costs and payback periods are calculated and discussed. process layout of a textile mill is shown in iium engineering journal, vol. 17, no. 1, 2016 abid 42 fig. 1. different types of cotton are mixed in mixing section; fibres made are sent to blow room to clean, blend, remove micro dusts and to provide uniform feed to the carding machine; which separates and cleans cotton fibers for spinning. in spinning, yarn is made from cotton fibers by drawing out and twisting into a thin strand. finally, cloth made is wound on the rolls for the required lengths. fig. 1: textile industry layout. for energy audit, a survey was conducted regarding energy distribution, energy consumption, energy conversion and energy management system in the above mentioned sections of a textile mill [4,15,16,18]. based on the survey, four energy resources i.e. gas, diesel oil, lesco (electricity from lahore electric supply company) used in the textile mill are identified. 2. data analysis and discussion from detailed survey and analysis, it was observed that 4 gas engines each of capacity of 1 mw used in the textile mill provide 80% of the energy needs with 64% of the total bill of the textile mill; therefore, these engines are focused to determine potential energy savings. the highest cost of energy was observed of lesco; hence gas is recommended to be used mostly. percentage distribution of cost and energy per year is shown in fig. 2. (a) (b) fig. 2: percentage distribution per year: (a) cost, (b) energy. during production, loads on the engines are distributed to provide necessary energy for the industry and average consumption of each engine is adjusted according to each engine’s efficiency. the engine with the highest efficiency is recommended to be used for the maximum power generation, and vice versa. this leads to the reduction of annual gas consumption and will translate into savings in monetary terms. average annual efficiency of 33.3, 34.1, 33.9, 34.3 is calculated for gas engines 1, 2, 3, 4 respectively. hence, in this case engine 4 should be used more and engine 1 should be used least. regarding load distribution, maximum consumptions is observed in the months of february and march because higher temperature is needed to be maintained as the lesco 33% gas 64% diesel 3% gas 80% diesel 1% lesco 19% iium engineering journal, vol. 17, no. 1, 2016 abid 43 temperatures outside is observed less (fig. 3a). in addition, the maximum energy consumption is observed in the spinning units 1&2 (fig. 3b). power quality analyzer was used to measure output power of each equipment in the respective department [4]. based on the total load distribution across each department, line losses from the input and the output were determined for spin 1 and 2 of 4.84% and in spin 3 of 2.12%. spin 1 and 2 is old and spin 3 is the new mill, therefore percentage loss of the new mill is observed comparatively less than the old mill. a constant loss of 174.11 kw is calculated based on input and output of different sections and equipment used for spin 1 and 2 and monthly percentage of energy consumption (gas, diesel and lsco), corresponding rates of energy sources, and cost of the monthly and yearly losses is summarized in table 1. (a) (b) fig. 3: monthly load distribution for departments; (a) energy (kwh), (b) percentage. 3. sources of major energy losses from equipment in order to determine sources of energy losses during consumption, data was collected from the major equipment i.e. compressors, capacitors, motors, and fans and are discussed below in detail [4,15,16,18]. compressors are an essential part of a textile industry and are used to run the different pneumatic machinery, movement of cotton in the ducts and for cleaning purposes. five screw type compressors used in the textile mill were analyzed and a total energy loss of 15 kw with equivalent energy loss of 10800 kwh per month was calculated. mainly three types of motors are used in a textile mills. 4 motors of rated power 15 kw are used for cooling water, 4 motors of rated power 5.5 kw are used for cooling tower and 7 motors of 7.5 kw are used for engine exhaust fans. for these motors total energy loss calculated is 2.55 kw and total energy loss per month calculated is 1836 kwh. power factor and power losses for each capacitor due to unnecessary high power consumption by the capacitors were calculated [15,16,18]. a benchmark value of 1.2 kw power recommended for the best conditioned capacitors based on the energy audit of several textile mills was used. power losses were calculated by subtracting the total power consumed by a capacitor bank from the bench mark value of 1.2 kw. all three phase ccapacitors of frequency 50hz each were analysed in different sections i.e. lt-1 (qty = 12), lt-2 (qty = 12), lt-3 (qty = 8), lt-4 (qty = 16, 12 were operational), lt-dying (qty = 0 500000 1000000 1500000 2000000 2500000 ja n fe b m ar a pr m ay ju n ju ly a ug se p o ct n ov e ne rg y co ns um pt io n (k w h) months spin 1&2 spin 3 twisting dyeing terry power house colony 0 10 20 30 40 50 60 70 80 sp in 1 & 2 sp in 3 tw is tin g d ye in g t er ry po w er h ou se c ol on y pe rc en ta ge c on su m pt io n textile mill sections iium engineering journal, vol. 17, no. 1, 2016 abid 44 10, 6 were operational). energy loss of 2.81, 3.59, 2.7, 2.0, 2.7 were observed in lt-1, lt2, lt-3, lt-4, and lt-dying respectively and total energy loss calculated was 13.8 kw. total losses per day and per annum calculated were 331.2 kwh/day and 120,888 kwh/year respectively. table 1: total loss for one year for spin 1&2 month percentage consumption cost (rs/kwh) monthly losses monthly losses gas diesel lesco gas diesel lesco (kwh) (rs) oct 83.46 1.33 15.21 3.42 15.30 3.56 125359 451170 nov 91.93 0.33 7.73 3.38 13.70 3.54 125359 429586 dec 69.26 0.00 30.74 3.36 0.00 3.62 125359 431225 jan 26.07 5.23 68.70 3.35 14.23 3.85 125359 534342 feb 86.80 2.90 10.30 3.44 12.51 3.58 125359 466011 mar 91.38 0.07 8.54 3.46 9.62 3.58 125359 435581 apr 89.16 0.27 10.58 3.48 12.28 3.60 125359 440768 may 73.74 0.26 26.00 3.54 11.30 2.81 125359 422489 jun 87.01 0.29 12.69 3.60 8.35 3.60 125359 453028 july 73.91 0.43 25.66 3.61 17.33 3.68 125359 462161 aug 88.39 0.60 11.01 3.44 7.31 3.62 125359 436635 sep 97.08 0.11 2.81 3.32 11.50 3.55 125359 418133 total yearly losses in rs 5381133 air conditioning for maintaining a certain temperature and humidity level plays an important role in a textile mill [15,16,18]. the fiber requires humidity to get their strength and require supply of warm humid air. this is where the role of supply fans comes into play. then there is also the need for the recirculation of the warm air as induction of fresh air in every cycle would mean a high load on the heating coils. also the suspended cotton fibers in the air cause irritation if swallowed, thus a mechanism is required to throw them out of the system. this is what return fans are used for. they suck the air from the process room along with these suspended fibers and other particles and circulate them through a filter and back to the supply fans and into the process room. the use of fans on a scale of significant magnitude meant that they formed a substantial part of the total load of the textile mill and thus required special attention during audit. results of total power consumed and percentage power savings are summarized in table 2. discharge or flow rate of each fan was calculated using averaged air velocity and area of the fan. total discharge or flow rate for a particular process room was calculated by adding the flow rates of all fans. specific power consumption was calculated by dividing the flow rate of each fan to the power consumed by that fan. the highest value of specific power consumption for a fan in a particular process room was set as a standard. total power consumed at maximum specific power of all the fans of a particular process room was calculated by dividing the total discharge or flow rate by the maximum specific power consumption. iium engineering journal, vol. 17, no. 1, 2016 abid 45 table 2: supply and return fans savings fan type department total power consumed at maximum specific power (kw) total actual power consumption (kw) power saving per kw power saving/year (kwh) saving %age supply fans blow, card room 10.19 25.33 15.14 132626 60% ring 1 & 2 46.03 96.03 50 438000 52% return fans blow, card room, drawing, simplex, comber 19.73 24.78 5.05 44238 20% ring 1 & 2 64.76 84.72 19.96 174850 24% 4. energy loss calculations finally, monthly energy losses of all equipment of a textile mill calculated are summarized in table 3 [12-15]. losses for the month = (gas percent consumption × monthly loss × monthly gas rate) + (diesel percent consumption × monthly loss × monthly diesel rate) + (lesco percent consumption × monthly loss × lesco rate) 5. recommendations regular inspections to identify the faulty capacitors should be done and written logs for maintenance schedule history should be maintained. in compressors, use of cool air intake, flows rate regulation as per requirement, highest volumetric efficiency, air compression to lower pressure level to reduce loading and unloading time for lesser power input, proper covering of exhausts should be ensured. for fans, belt inspection, motor and fan replacement as required after identification, bearing lubrications and predictive maintenance of fans must be ensured. use of proper capacity and number of electric motors, better quality windings, anti-scaling agents for water softening for smooth operation of pumps and hcl for cleaning the nozzles for eliminating the pressure losses and hence to reduce the power input be ensured. in addition regular and timely checkup of alignment, belts and bearings is strongly recommended. replacement of tungsten bulbs with fluorescent lamps and reduction of number of lamps by local lighting compared to the global lighting results in considerable cost savings. for steam transportation over long distances, high pressure and small diameter of pipes is desired, with pressure reducing valves placed as necessary to regulate the steam pressure at the point of use, thereby curbing heat losses. pressure losses around bends are great; it is desirable to make their radii large. to prevent steam leaks from joints due to the thermal expansion of the pipe, expansion joints should be placed where required. to maintain the temperature inside the valve, tank and treatment tank as well as the piping, it is necessary to install them heat-insulated, using appropriate heat insulating materials, so as to efficiently use steam while preventing heat losses. a constant check of housekeeping must be made from time to time and proper masks to workers for their health safety should be provided. iium engineering journal, vol. 17, no. 1, 2016 abid 46 table 3: monthly data: percent consumption, energy loss and financial loss percent consumption cost/kwh total constant monthly energy loss (kwh) monthly financial losses (pak rs) m on th g as d ie se l l e sc o g as d ie se l l e sc o su pp ly f an s r et ur n f an s c ap ac it or b an ks c om pr es so rs l in e l os se s m ot or l os se s e ng in e l os se s su pp ly f an s r et ur n f an s c ap ac it or b an ks c om pr es so rs l in e l os se s l in e l os se s l in e l os se s o ct 83 .4 6 1. 33 15 .2 1 3. 42 15 .3 0 3. 56 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 16 87 96 64 80 8 35 77 3 38 88 3 25 35 32 66 10 90 44 n ov 91 .9 3 0. 33 7. 73 3. 38 13 .7 0 3. 54 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 16 07 21 61 70 7 34 03 2 36 99 1 24 14 03 62 88 86 11 d ec 69 .2 6 0. 00 30 .7 4 3. 36 0. 00 3. 62 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 16 13 34 61 94 3 34 17 8 37 15 0 24 23 24 63 16 86 44 ja n 26 .0 7 5. 23 68 .7 0 3. 35 14 .2 3 3. 85 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 19 99 1 76 75 5 42 36 2 46 04 6 30 02 70 78 28 10 71 1 fe b 86 .8 2. 90 10 .3 0 3. 44 12 .5 1 3. 58 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 17 43 49 66 94 0 36 93 67 40 14 8 26 18 72 68 25 93 41 m ar 91 .3 8 0. 07 8. 54 3. 46 9. 62 3. 58 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 16 29 64 62 56 8 34 52 7 37 52 9 24 47 71 63 80 87 31 a pr 89 .1 6 0. 27 10 .5 8 3. 48 12 .2 8 3. 60 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 16 49 05 63 31 4 34 96 4 38 00 4 24 76 86 64 61 88 35 m ay 73 .7 4 0. 26 26 .0 0 3. 54 11 .3 0 2. 81 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 15 80 66 60 68 8 33 47 4 36 38 5 23 74 15 61 85 84 69 ju n 87 .0 2 0. 29 12 .6 9 3. 60 8. 35 3. 60 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 16 94 92 65 07 5 35 90 2 39 02 5 25 45 76 66 34 90 81 ju l 73 .9 2 0. 43 25 .6 6 3. 61 17 .3 3 3. 68 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 17 29 09 66 38 7 36 64 5 39 83 1 25 97 08 67 71 92 64 a ug 88 .3 9 0. 60 11 .0 1 3. 44 7. 31 3. 62 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 16 33 58 62 72 0 34 60 8 37 61 7 24 53 64 63 95 87 52 se p 97 .0 8 0. 11 2. 81 3. 32 11 .5 0 3. 55 46 90 1 18 00 7 99 36 10 80 0 70 44 5 18 36 25 13 15 64 36 60 06 3 33 14 8 36 03 0 23 49 67 61 25 83 81 20 13 25 0 77 29 72 42 65 48 46 36 40 30 23 89 3 78 81 9 10 78 63 6886983 iium engineering journal, vol. 17, no. 1, 2016 abid 47 6. conclusions based on the detailed energy audit, it is observed that the highest cost of energy was observed of lesco; hence gas is recommended to be used. an average annual efficiency of 33.3, 34.1, 33.9, and 34.3% is calculated for gas engines 1, 2, 3, and 4 respectively; hence, engine 4 is recommended to be used more and engine 1 the least. regarding load distribution, maximum consumption is observed in the months of february and march. maximum energy consumption is observed in the spinning units 1&2. total energy loss per month from motors, capacitors, compressors is calculated as 10,074kwh, 1,836 kwh and 10,800 kwh respectively. power saving of 570,626 kwh from supply fans and 219,088kwh from return fans is observed. acknowledgement author acknowledges the support of hira textile mills limited lahore, pakistan for their full support and help in completing this study. references [1] pradeep c. (1996) sustainable energy supply in asia. proceedings of the international conference, asia energy vision 2020, november 15-17, 1996. concept publishing company, india. [2] albert t. (1989) plant engineers and managers guide to energy conservation, 4th edn. fairmont publishing. [3] hartungi r, jiang l. (2012) energy efficiency and conservation in an office building: a case study. intl. j. of energy sector management. 6(2):175-188. [4] mcmullan jt, morgan r. (2007) a device for recording electrical information. intl. j. of energy res., 4(1):11-17. [5] balasubramanian p. (2004) energy auditing made simple. bala consultancy services, mylapore, india. [6] chanda rs. (2014) on energy auditing: an experience with a jute mill. intl. j. on recent innov. trends comp. comm., 2(10):3134-3137. [7] chase j, lucas njd, murgatroyd w, wilkins bc. (2007) industrial energy use-ii: energy use in a light engineering factory. intl. j. of energy res., 2(4):375-388. [8] jouni k, iikka s. (2001) cleaner energy production in industrial recycling networks. ecomanagement and auditing, 8(2):144-153. [9] virginia wj, william sj, joann cj. (2007) impact of energy audits on home energy consumption. intl. j. of consumer studies, 11(1):21-38. [10] paul oc. (1993) energy management. mcgraw-hill professional publishing. [11] tyagi ak. (2000) handbook on energy audits and management. teri, india. [12] earle ap. (1985) a case history: energy conservation in the primary textile industry in canada. national technical conference of aatcc, pp. 215. [13] dhayaneswaran y, ashokkumar l. (2013) a study on energy conservation in textile industry. j. inst. eng. india ser. b. 94(1):53-60. doi: 10.1007/s40031-013-0040-5. [14] palanichamy c, nadarajan c, naveen p, babu ns, dhanalakshmi. (2001) budget constrained energy conservation an experience with a textile industry. ieee trans. energy conversion, 16(4):340-345. [15] prakasam r, chandran kr. (2013) sitra energy audits for textile mills. textile magazine, 44(8): p 69. [16] hasanbeigi a, hasanabadi a, abdorrazaghi m. (2011) energy efficiency technologies and comparing the energy intensity in the textile industry. aceee summer study on energy efficiency in industry, 1:34-46. iium engineering journal, vol. 17, no. 1, 2016 abid 48 [17] şekkeli m, keçecioğlu of. (2012) scada based energy saving approach to operation of stenter machine in a textile plant using waste heat recovery system. journal of textile & apparel / tekstil ve konfeksiyon, 22(3):248-257. [18] masood a k, muhammad s, iftikhar s, altaf h, wasi u, shabbir f. (2015) energy efficiency in textile sector of pakistan: analysis of energy consumption of air-conditioning unit. intl. j. of env. sci. dev., 6(7): 1-11. [19] http://www.ems-textile.net [20] http://www.ptj.com.pk [21] http://textilemagazine.awardspace.com microsoft word 5-77 page 65-74.doc iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 65 solid state culture conditions for composting sewage sludge n.a. kabbashi1, a. fakhru’l-razi2 and k.b. ramachandran 3 1 department of biotechnology engineering, international islamic university malaysia, jalan gombak, 53100 kuala lumpur. malaysia. 2 department of chemical & environmental engineering, university putra malaysia, 43400 upm serdang, malaysia. 3 department of chemical engineering, university of malaya, 50602, kuala lumpur, malaysia. e-mail: alkabbashi@yahoo.com abstract: composting is applied to treat sewage sludge from treatment plants to enhance its quality and suitability for agricultural use. in this work the optimal conditions for composting sewage sludge from domestic wastewater treatment plants in a horizontal drum bioreactor (hdb) were investigated. this study investigated the physico-chemical conditions affecting the use of filamentous fungi in composting. the average number of faecal coliforms was 2.3  107 bacteria/g waste dry weight at the beginning of the composting process, and decreased considerably to 8.2  103, 8.1  103, 8.5  103, 8.0  103,and 8.4  103 bacteria/g, respectively for experiments t1 to t5. this decrease was presumably the result of raising temperature. the phase of hygienisation was marked by a very significant decrease in the number of e. coli cells (1.8  107, to 3.7  103, 3.8  103, 3.3  103, 3.2  103, and 3.6  103 bacteria/g) for t1 to t5 experiments, respectively: a second aspect was the investigation of a possible reduction of hazardous pollutants. the highest concentration was for fe and the lowest for pb, showing that fe is the most loosely bound to the sewage sludge organic matrix and pb the most strongly bound, the cd reduction b y composting was more than 50%. keywords: sewage sludge, compost, horizontal drum bioreactor, hazardous. 1. introduction the development of appropriate strategies for treatment and disposal of sewage sludge is a major problem in all countries throughout the world. sludge treatment and disposal not only represents about half of the total costs of municipal wastewater collection, but it is also strongly regulated, more so than almost any other form of waste, and readily attracts adverse media and public attention. thus, the challenge for wastewater authorities is to find affordable, sustainable and safe approaches to sludge management, which are also publicly accepted [1]. iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 66 in its untreated form, wastewater cannot be disposed off for several reasons. first, the biological decomposition of the organic materials in wastewater consumes oxygen and thus reduces the quantity available in the receiving waters for the aquatic life. the decomposition also produces large quantities of malodorous gases. secondly, the numerous pathogenic or disease causing microorganisms in untreated wastewater are health hazards to human beings. third, its toxic compounds, especially heavy metals, can be dangerous to both plants and animals, and finally the presence of phosphates and nitrogen may lead to uncontrolled growth of aquatic plants [2]. din and hamid[3] studied the history of wastewater treatment plant of kuala lumpur city, malaysia, which provided a good illustration of the above case. the annual sludge volume produced currently is estimated to be 3 million cubic meters and requires some 600,000-tanker trips to transport the sludge to designated treatment and disposal sites. by the year 2020, the volume is estimated to increase to 7 million cubic meters, which will require almost 1.4 million tanker trips to manage. the volume of sludge generated depends on the level and process of wastewater treatment. there may also be seasonal variability due to rain and runoff entering the sewers or in sewage treatment plants (stps) that serve tourist centers and schools, which cater to a variable population density, throughout the year. sludge production quantities can be estimated from the stps design capacity and treatment process. composting is becoming a more acceptable alternative for the treatment of sewage sludge in many municipalities due to the potential use of the composting product for land application [4]. it has become a well-established process for adding value to a large and growing number of organic byproducts. even so, composting systems and uses for compost are still evolving. design, operation and control issues remain key factors leading to the success or failure of the process. environmental issues, product quality and utilization strategies have not yet been fully optimized for many applications to allow the use of composting process on a sustainable and economic basis. recent advances in the design, construction and operation of municipal, industrial and agricultural facilities have brought significant improvements to this field. new techniques for monitoring microbial diversity, specific pathogens and beneficial microorganisms have led to a better understanding of the composting process. 2. materials the sewage sludge used in this study was collected from taman sri nanding and taman koperasi indah water konsortium (iwk) treatment plants, malaysia. to characterize the sludge, they were analyzed for moisture content, electrical conductivity, ph, organic carbon, nutrients (n, p, k, ca, and mg) and heavy metal content. each analysis was replicated three times. table 1 gives the characteristics of the raw sludge along with that of sawdust. sawdust was used as a bulking agent in this study. the sludge had a high moisture content around 80% to 82% and a low c/n ratio of 7 to 8.5. both sludges had more or less similar characteristics. however the ph of sludge from taman sri nanding was lower than that of taman koperasi; in addition, heavy metal content of the sludges showed some differences. sawdust had low moisture content of 17% and a high c/n ratio of 184. hence sawdust was homogenized with the sludge to increase the iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 67 c/n ratio of the sludge. this also reduced the moisture content to the optimal level for composting. the sewage sludge and sawdust was analyzed for the following parameters: moisture content (105 c for 24 h) using gravimetric method [5]; ph (dilution 1:25 w/v) using a ph electrode; electrical conductivity (dilution 1:10 w/v) using a conductivity electrode [6]; organic matter and ash content (550 c for 6 h); the total organic carbon c was estimated from the organic matter value using the factor of 1.82, which is often used for municipal solid waste [7]; the theoretical total n concentration of the sewage sludge was calculated by adding the kjeldahl nitrogen with the (no3+ no2-)-n [8]; the c/n ratio was then computed based on the concentration of total organic c and n. trace elements (cd, fe, cu, zn, pb, cr, ca, mg, mn and k); in addition to potassium, calcium, and magnesium content were determined by using the (dry digestion method), and water-extractable (1:10 w/v) (atomic absorption spectrophotometer); and evaluation of microbiological parameter performed as recommended in standard methods. three efficient cellulolytic cultures were used in this study. the first two mucor hiemalis and trichoderma harzianum were isolated and screened at universiti putra malaysia biochemical engineering laboratory and the third was phanerochaete chrysosporium atcc 24725. the strains used are non-toxic and do not produce any toxic by product during fermentation processes. they are capable of utilizing lignin, grow on lignocellulosic materials, and degraded oil. the microbial collection was obtained from upm and the indian agricultural research institute, new delhi, india. the mean and standard deviation of the three replicated were reported for all parameters measured. to compare the variations in composting at different positions, oneway analysis of variance (anova) statistical testing was performed [11]. 2.1 faecal coliforms dunnigan and dick [12] mentioned that raw sewage water contains many microorganisms such as bacteria, viruses and parasitic protozoa, which may be pathogenic. pathogen removal or reduction before land application is therefore necessary to minimize the potential risk on human and animal [13]. based on jenkins [14], pathogen reduction can occur by either dehydration or biodegradation. 3. experimental methods 3.1 composition studies a control experiment and six other experiments were carried out to determine the optimal operating conditions and operational strategies to compost the sewage sludge from treatment plant (table 2). the objective of the control was to find out the changes that would occur during composting of sewage sludge from treatment plant and compare them with other experiments, while experiments t2 to t6 were to study the effect of inoculating various microorganisms on the progress of composting and to determine the best and most efficient inoculum. iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 68 table 1: characteristics of sewage sludge, sawdust and soil. parameters sewage sludge taman koperasi sewage sludge taman sri nanding bulking agent (sawdust) typical value in soil * moisture content (%) 82  0.32a 80.2  0.057 10-20 na ph 7.27  0.012 4.29  0.0057 4.5 0.058 5.0 ec (dsm-1) 1.83 0.015 1.8  0.015 0.02  0.003 0.1 carbon (%) 40.39  0.0466 52.47 0.029 57 – 58.33 3.9 c/n ratio 7.21  0.038 8.5  0.0577 166.6 285 11 total solids (%) 22.12  0.015 19.78  0.122 85.6  0.058 nd macro nutrients n (%) p (%) k (%) ca (%) mg (%) 5.6 0.058 1.6  0.058 0.09  0.011 0.15 7.64x 10-3 0.03 2.88 x10-3 6.2 0.1 1.52  0.009 0.05  0.02 0.89 0.06 0.07 4.619 0.2 – 0.35 1.17  0.017 0.0194  5.5 x 10-4 0.0158  2.19 x 10-4 0.0039  x10-3 0.4 0.05-0.2 0.04-3 0.7-50 0.06-6 micro elements cu (ppm) cd (ppm) zn (ppm) mn (ppm) cr (ppm) fe (ppm) pb (ppm) ni (ppm) 111.4 0.058 10.2  0.24 511.8 0.0577 606.0 0.58 27.0 1.5 3586.0 0.88 51.7 0.153 497.6 0.01 49.83 0.15 1.13 0.015 2893.53 0.19 315.53 0.5 73.76 0.12 4930.0 1 55.2 0.088 na 4.8 0.058 6.5  0.115 8.2 0.145 4.6 0.5 14.6 0.0577 402.9 0.0577 16.0 0.115 293.8 0.0577 2-100 0.01-7 10-300 100-4000 5-3000 700-5500 na na * soil (adriano et al., 1980) [21] na = not analyzed ec= electrical conductivity a mean standard error iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 69 table 2: evolution during the composting process (faecal coliform and e. coli). experiment before composting e. coli (bacteria/g) after composting e. coli (bacteria/g) before composting faecal coliform (bacteria/g) after composting faecal coliform (bacteria/g) ss 1.8  107 1.8  107 2.3  107 2.3  107 control 1.8  107 1.8  107 2.3  107 2.3  107 t1 1.8  107 3.7  103 2.3  107 8.2  103 t2 1.8  107 3.8  103 2.3  107 8.1  103 t3 1.8  107 3.3  103 2.3  107 8.5  103 t4 1.8  107 3.2  103 2.3  107 8.0  103 t5 1.8  107 3.6  103 2.3  107 8.4  103 sewage sludge solid wastes were collected over a period from the towns of taman koperasi and taman sri nanding, malaysia. its moisture was estimated to be around 8082%. first the sludge was dewatered for two weeks prior to composting to moisture content of around 20-30%. the partially dried material was sieved and cleaned before starting the composting operation. furthermore, sawdust as an amendment was added to the dewatered sludge since the water content of the raw material for compost should not exceed 60% and typically should be between 50% and 60%, in order to operate the system adequately. if the water content of the sludge was less than the optimal, due to the addition of sawdust, required amount of water was added to raise the water content to the optimal level. the organic raw materials were then transferred into the horizontal drum bioreactor (hdb) of 300l. the hdb is a totally enclosed vessel of 300 l capacit y and made of pvc frame and clear pvc with a discharge window. the rotating drum unit consists of a cylinder of 0.7 m diameter and 1 m long and a working height of 1.5 m with rotation bearings on both sides. refuse is fed in the middle of the drum. the retention time in the drum is usually 2 to 30 days after which the material is discharged. these materials are turned once every 4 hours. air is usually supplied by blowing through holes. water sprayer nozzles were placed above to adjust the moisture content and to prevent the material from becoming too dry. agitation was provided by horizontal rotating arms. mixture of sewage and sawdust for seven experiments (control and t1 to t6) of weight 24 kg, 25 kg, 35 kg, 27 kg, 29 kg and 26.5 kg were prepared and composted for exactly 30, 27, 24, 21, 32 and 30 days respectively in the hdb with a closed system to monitor the changes in temperature, ph, and moisture content. the composting mass was aerated every 4 hours by air supplied through a compressor at 0.6 l/min/kg. moisture content was monitored throughout the composting period. duplicate samples of 150 g each were removed every day iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 70 during the experiments to analyze for ph, moisture content and electrical conductivity measurement, and at days 0, 3, 6, 9, 12, 15, 18, 21, up to 32 days for chemical analysis. 4. results and discussion the presence of coliform bacteria is often used as an indicator of the overall sanitary quality of soil and water environments [15]. use of an indicator such as coliforms, as opposed to the actual disease-causing organisms, is advantageous as the indicators generally occur at higher frequencies than the pathogens and are simpler and safer to detect. the average number of faecal coliforms was 2.3  107 bacteria/g waste dry weight at the beginning of the composting process, and decreased considerably to 8.2  103, 8.1  103, 8.5  103, 8.0  103,and 8.4  103 bacteria/g, respectively for experiments t1 to t5. this decrease was presumably the result of raising temperature from 26 to 42, 46, 47, 49 and 47 c, for the experiments t1, t2, t3, t4, and t5, respectively. it was observed that the changes in faecal coliforms during the composting process followed a pattern typical of other composting systems [15, 16]. for the control experiment, there was no reduction, as the composting could not proceed in the raw sludge. the results of experiments t1 to t5 show that the sludge from sewage plants can be made safe by composting. 4.1 escherichia coli le minor [17], reported that e. coli has been found to be the most representative bacterium in the group of faecal coli evolution. the number of e. coli cells showed a similar evolution (table 3) to that of faecal coliforms. the phase of hygienisation was marked by a very significant decrease in the number of e. coli cell (1.8  107, to 3.7  103, 3.8  103, 3.3  103, 3.2  103, and 3.6  103 bacteria/g for t1, t2, t3, t4, and t5 experiments respectively). 4.2 effects of composting on heavy metals composting has become a more acceptable alternative for the treatment of sewage sludge in many municipalities due to the potential use of the composting product for land application. the major limitation in general use of sewage municipal sludge compost is the high heavy metals content in the compost [4]. accumulation of heavy metal contents such as zn and cu in plant tissues and soils following the application of sewage sludge compost is not an uncommon experience [18]. it should be used only for the production of non-food crops or non-leafy foods such as grains, fruits, or nuts, because fruiting parts of these plants usually contain lower metal concentrations than do vegetative parts [19]. the present study was conducted to evaluate the effect of composting process on the heavy metal content of the sewage sludge. table 3 shows the effect of composting on heavy metal contents. the table also includes the standards acceptable in various countries. total heavy metals contained in nitric-perchloric digestion extracts and those extractable with 0.005 m dtpa (diethylene-triamine-pentaacetic acid), 0.5 m cacl2 and h2o as mentioned in materials and experimental method sections, were measured by iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 71 atomic absorption spectrometry. it can be seen from the figures, that there is a general reduction in the metal content after composting. in experiment t4, where p. chrysosporium and tichoderma harzianum were used, the cd reduction by composting is more than 50%. their reduction meets the requirement set by spain but fails to meet the standards set by other countries because the sources of sewage sludge differ from other countries and the standards they use also differ. similar trends were observed for other metals. no such standards are available for malaysia. the high amount of zn extracted in experiment t2 and t5 made this most dangerous of all metals studied. this shows the danger of sewage sludge exposed to contamination by soluble metal salts. lead and cadmium were lower at the end time of composting for all experiments. they have the least amount left for experiments t3 and t4. the amount of zn tended to be constant throughout the experiments, except t4 where it is of lower amount. this lower amount can be attributed to the drop in ph level at the end of experiment. as expected, the contaminated sewage sludge showed the highest levels for those metals added as metallic salts, during waste treatment process. the highest concentration was for fe and the lowest for pb, showing that fe is the most loosely bound to the sewage sludge organic matrix and pb the most strongly bound. it is clear from the results of metals extracted, compared with the total metal content that composting renders part of the metal insoluble so that less passes into the most soluble extracts. this means that when the wastes have been composted there is less risk of the metals in the wastes being added to soils being used by plants. 5. conclusion a medium scale bioreactor (hdb) was developed and operated for the ssf of sewage sludge. the horizontal drum bioreactor is a promising equipment for growth of microorganisms (p. chrysosporium, trichderma harzianum, and mucor hiemalis) in ssf and is worthy of further investigation, such as inducing auto-sterilization with a relatively high temperature (60-70 c) to rapid changing in biodegradation. for a successful composting process in a hdb, the main problem for a small treatment plant is to dewater the sludge sufficiently. one possibility to deal with this is to mix the sludge with sawdust. sawdust has low moisture content of 17% and high c/n ratio 184. as dry bulking material it is the kind that degrades at the same rate as the sludge and is incorporated into the compost, no screening will be necessary. a mixture of various materials is possible, but the amount of sawdust should be at least 1:1.7 of the total volume. the best microorganism for composting was found to be trichoderma harzianum and a mixture of p. chrysosporium and trichoderma harzianum. the sanitation control program covered investigations of microbial community, bacteria and parasites in the composting material. the result was acceptable for escherichia coli and faecal coliform. heavy metal co ncentration was low and below the limit values. all parameters are lower than the regulations for sewage sludge for various countries. the concentration of hazardous organic substances in the compost was smaller than in average sewage sludge from treatment p lants. the results presented in this work were statistically significant and compared favorably to those reported for ssf bioreactors used for mesophilic microorganisms [20]. similarly, the moisture content variations were also significant. iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 72 table 4: heavy metals content (g/kg) in compost, from hdb experiments parameter g/kg untreated sludge standard (spain)* standard (france) standard (germany) standard (italy) standard (austria) compost t1 compost t2 compost t3 compost t4 compost t5 cd 0.47  0.0115a 0.4 0.008 0.015 0.015 0.004 0.29  0.00577 0.26  0.00577 0.23  0.00577 0.2  0.00577 0.27  0.00577 fe 19.7  0.252 40 nd nd nd nd 12.1  0.1 14  0.98 11.2  0.12 8.98  0.057 9.89  0.008 cu 0.604  0.023 1.75 nd 0.1 0.3 0.4 0.49  0.00577 0.334  0.0008 0.548  0.015 0.22  0.0057 0.500  0.0057 zn 1.84  0.115 4.0 nd 0.4 0.5 1.0 0.275  0.0008 1.11  0.0088 1.028  0.0005 0.98  0.008 1.5  0.0577 cr 0.317  8.819x10-4 nd nd nd nd nd 0.25  0.011 0.192  0.0014 0.1 0.0115 0.08  0.0001 0.217  0.0008 pb 0.300  0.0577 1.2 0.8 0.15 0.14 0.5 0.28  0.00577 0.195  0.0014 0.189  0.0015 0.175  0.0012 0.200  0.0014 ca 16.5  0.2887 nd nd nd nd nd 15.2  0.172 14.3  0.088 13.2  0.145 12.3  0.088 13.6  0.173 (william, 2001) [22] a mean standard error nd=not determined iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 73 for better rotation and passing air for more active biooxidative phase, direct current (dc) motor on different intervals recommends rotating slowly the hdb. no turning is required during the mesophilic phase. air inlet and outlet are supposed to be placed at opposite positions for better aeration of the ssf. the aeration required is provide by a blower operated in the positive mode at 0.6 l/min/kg and the air blowing stops in the maturation phase to allow the compost maturation. heavy metal concentration was low and below the limit values of the various countries regulation after composting. to the author’s knowledge, there is no standard specification for compost maturity. refrerence [1] e. jeremy, hall, and a. zmyslowska. “development of sludge treatment and disposal strategies for large conurbation: case study”. warsaw journal of water science and technology. 1998, 36 (11), 291-298. [2] g. t. chobanoglous. “wastewater engineering, treatment, disposal and reuse”. tata mcgraw-hill. new delhi: 1987; 119-123. [3] a. din, and m. hamid. “the management of municipal wastewater sludge in malaysia”, paper presented at iem talk on sewage sludge management issues, 18th august 1998, petaling jaya 1-11. [4] j. m. fang; c. w. wong; x. g. li; and h. m. wong. “changes in biological parameters during co-composting of sewage sludge and coal ash residues”. bioresource technology 1998, 64, 55-61. [5] l. t. richard. “composting strategies for high moisture manures”. manure management in harmony with the environment and society conference. the soil and water conservation society, february 10-12. 1996; 135-138. west north central region, ames, ia. [6] j. m. fang; and c. w. wong. “effects of lime amendment on availability of heavy metals and maturation in sewage sludge composting”. environmental pollution. 1999, 106, 83-89. [7] t. r. guar, and a.l. haug. “sludge composting: a discussion of engineering principles”. compost science. 1978, 10-14. [8] standard method for the examination of water and wastewater. 15th edition apha awwa. wpci, 1980; 383-385. [9] j. l. sikora, m. ramirez; and t. troeschel. “laboratory composure for simulation studies”. j. environmental quality. 1983, 12, 219-224. [10] r. hachica, n. jedidi; and a. hassen. “aspects hygieniques de la fermentation aerobies des dechets urbains dans le contexte tunisien”. arch. ins. pasteur tunis 1993, 70, 13-20. [11] h. j. zar. “biostatistical analysis”, prentice hall international, englewood cliffs, nj; 1996. [12] p. e. dunnigan, and p.r. dick. “nutrients and coliform losses in runoff from fertilized and sewage sludge treated soil”. journal of environmental quality. 1980, 9, 243-250. [13] c. a. bruggerman, and mostaghimi. “sludge application effects on runoff, infiltration and water quality”. water resource bull. 1993, 29, 15-26. [14] j. jenkins. “the humanure”, 2nd ed. jenkins publishing, grove city, pa. 1999; 15-19. [15] a. hassen; k. belguith; n. jedidi; a. cherif. and m. b. cherif. “microbial characterization during composting of municipal solid waste”. journal of bioresource technology. 2001, 80, 217-225. iium engineering journal, vol. 6, no. 1, 2005 n.a. kabbashi et al. 74 [16] j. c. hay. “pathogen destruction and biosolids composting”. journal of biocycle. 1996, 6776. [17] l. le minor. “escherichia coli. bacteriologie medicale”. flammarion medicine sciences. paris. 1984, 240-253. [18] t. j. sims, and s. j. kline. “chemical fractionation and plant uptake of heavy metals in soil amended with co-composted sewage sludge”. journal of environmental quality. 1991, 20, 387-395. [19] j. jing; and j. t. logan. “effects of sewage sludge cadmium concentration on chemical extractability and plant uptake”. journal of environmental quality. 1992, 21, 73-81. [20] e. kalogeris, g. fountoukides, d. kekos. and j. b. macris. “design of a solid-state bioreactor for thermophilic microorganisms”. bioresource technology. 1999, 67, 313-315. [21] c. d. adriano, l. a. page, a. a. alseewi, c. a. chang, and i. straughan. “utilization and disposal of fly ash and other residues in terrestrial ecosystem: a review”. j. environmental quality. 1980, 9, 333-334. [22] f. william, and brinton. “an international look at compost standards. journal of biocycle”. 2001, 74-76. 450 iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 191 a voltage stabilizer for a microgrid system with two types of distributed generation resources m. mahzarnia, a. sheikholislami and j. adabi noshirvani university of babol, babol, iran. maedehmahzarnia@yahoo.com abstract: microgrids are used as controllable units connected to power grid, in which the electrical distances between reactive power sources and the loads that need the reactive compensation are small. thus, a coordinated compensation of reactive sources has to be implemented to avoid a fast voltage collapse by proposing a microgrid voltage stabilizer (mgvs). this stabilizer is desirable to improve the dynamic voltage profile and is tested at a 21-bus ieee microgrid system. in order to verify the performance of this stabilizer, three distributed generation (dg) resources are utilized in this microgrid (two pv resources which are categorized as power-electronic converter based on dg and a diesel generator which is known as synchronous machine also based on dg). at first, the mentioned resources and all of their needed equipments are modeled. then, a control model of the stabilizer with appropriate parameters for the proposed microgrid is presented. voltage deficiency of the system is the input of the stabilizer, and the output signal of the stabilizer is divided between the dgs in order to provide required reactive power. the dynamic voltage profile of buses in the presence of mgvs and its absence has been compared by implying disturbances. simulation results in matlab/simulink show that the dynamic voltage profile of the buses improves satisfactorily with the addition of mgvs. abstrak:grid mikro digunakan sebagai unit kawalan yang disambungkan kepada grid kuasa, di mana jarak elektrikal antara sumber kuasa reaktif dan bebanan yang memerlukan kompensasi reaktif tidak terlalu besar. dengan itu, kompensasi yang selaras dengan sumber reaktif perlu diimplimentasikan untuk mengelak kegagalan voltan pantas dengan menggunakan grid mikro penstabil voltan (microgrid voltage stabilizer mgvs). penstabil ini sesuai digunakan untuk meningkatkan profil voltan dinamik dan telah diuji ke atas sistem mikro grid 21-bus ieee. untuk memastikan keupayaan penstabil ini, tiga sumber penjanaan agihan (distributed generation dg) telah digunakan (dua sumber pv yang dikategorikan sebagai pengubah kuasa elektronik berdasarkan dg dan penjana diesel yang dikenali sebagai mesin segerak berasaskan dg). mulanya, semua sumber dan alatan yang diperlukan, diilustrasikan. kemudian, satu model penstabil kawalan bersama parameter yang sesuai dengan mikro grid yang dikemukakan. ketakcukupan voltan dalam sistem merupakan input penstabil, isyarat keluaran penstabil kemudiannya dibahagikan antara kesemua dg agar ia dapat menyalurkan kuasa reaktif yang diperlukan. profil voltan dinamik setiap bus dengan kehadiran mgv dan ketidakhadirannya dibandingkan denganmengimplikasikan gangguan. keputusan simulasi menggunakan matlab/simulink menunjukkan bahawa profil voltan dinamik setiap bus meningkat pada kadar yang memuaskan dengan kehadiran mgvs. keywords: microgrid; voltage stabilizer; photovoltaic resource; diesel generator; dc-bus-voltage-controlled inverter; closed loop dc-dc boost converter. iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 192 1. introduction considering restructuring the electricity market in recent years, power systems move toward the application of distributed generation (dg) recourses. widespread application of dgs in power system caused challenges related to stability and reliability of power system. therefore, a new structure is suggested for grid called microgrid, which is a controllable unit that works in parallel with main grid. microgrid is composed of dgs, loads, and controllers and in black out and disturbance situation can change into islanding mode through a static switch, hence power accessibility is remained in an agreeable level and overall black out is prevented [1]. regarding above-mentioned descriptions, it can be mentioned that microgrids prevent voltage instability due to sudden change of load in main gridand improve stability and reliability of the power system. on the other hand, presence of weak microgrids can leads to extreme voltage drop or overvoltage and even voltages collapse of the system. proper dynamic reactive capability is required for preventing fast voltage drop. in fact, a coordinated effort amongthe reactive sources increases the efficiency of these resources. in microgrids, electrical distances between reactive sources and loads that require reactive compensation are not too much. in addition, some loads may be sensitive to voltage variations and all dgs have not the capability of reactive power compensation in dynamic mode. therefore, a coordinated compensation between reactive sources should be performed to enhance dynamic voltage stability of the microgrid and improving voltage profile of the buses [2-4]. some researches are carried out for voltage stability in microgrids using different methods. for instance, a dstatcom is presented at [5] to enhance the stability of the system. during power imbalance in the microgrid, the dstatcom holds the microgrid voltage for few cycles and allows the protection system to shed load and stabilize the system. a rapid detection of the load shedding requirement is very crucial for the success of this scheme. if the load is not shed within 2-3 cycles, the system voltage will collapse even in the presence of dstatcom. another drawback of this strategy is increasing the cost of the system due to use of power electronics devices in stabilizer circuit instead of using control devices.also [6] presented a stability-type algorithm suitable for the analysis of an inverter dominated lv microgrid. the stability approach is adapted so that it can be applied to inertia-less systems, where sources are interfaced to the network via inverters. presented research activities did not proposed any approach for the microgrids containing synchronous machine based dgs and inverter-based dgs together.in [7], the small-signal model of the supercapacitor energy storage (ses) has been established and the control strategies to enhance the voltage stability of the microgrid, is presented. besides using expensive ses, an optimal placement should be considered which in turn adds more complexity to the system.in [8], a control strategy for stability enhancement of microgrid is proposed based on sliding mode control (smc). although this controller is very practical for microgrids but it can be used only in microgrids with synchronous dgs. therefore, proposing a method is essential to overcome these problems. hence, a microgrid voltage stabilizer (mgvs) has been designed by presenting a control model in this paper. main objective of this paper is to apply the mgvs in microgrids containing distributed generation resources with two types of ac and variable dc outputs. type 1 is a photovoltaic resource, that is a kind of power electronic converter based dg, and type 2 is diesel generator resource, that is known as a kind of synchronous machine based dg. the ieee 21-bus microgrid is considered as a test case. the suggested dynamic model of microgrid and controller are simulated in matlab/simulink. in this analysis, the applied dynamic disturbances to the grid are three-phase short circuit and iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 193 load switching fault. the simulation results are compared in two modes (with and without mgvs). in next section, models of dgs that are used in the test case microgrid and all of their elements are discussed in detail. in section 3, the suggested mgvs, for such a microgrid is investigated. simulation results and conclusion are presented in section 4 and 5, respectively. 2. modeling the microgrid including two types of dg; photovoltaic and diesel generator resources as mentioned before, the under survey microgrid contains two types of dg which are photovoltaic (pv) resource and diesel generator. model of each resource and its elements, are given in sections 2-1 and 2-2. 2.1modeling the pv distributed generation resource and its important elements in this section, elements model of photovoltaic systems including closed-loop dc-dc boost converter, dc-bus-voltage-controlled inverter, batteries and etc. are presented. it should be noted that main reason for the use of mentioned type of inverter is its appropriation for the microgrid voltage stabilizer that has been explained in section 2.1.1 in detail. in general, the different parts of a pv system can be classified as follows [7]: a) solar cells section (solar modules or panels) b) consumer or electric load c) medium section or desired power section figure1 shows equivalent circuit of a pv cell in which i is module current, v module voltage, iph photo current, m number of series cell in a module, rs series resistance of cell and rp shunt resistance of poly-crystalline cell. many of these cells in a solar module are connected in series in order to achieve higher level of voltage. photovoltaic source in this research consists of six cells which are connected to each other in series to form a module with an approximate voltage of 100 volts. the specifications of each cell and the derived module are given in appendix. in medium sectionor desired power section, electric energy of pv systems is managed in proportion to the demand of consumer. these devices are usually formed by storage and support system (battery), charge control, inverter and etc. fig. 1: simple equivalent circuit of pv cell. iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 194 2.1.1 closed-loop dc-dc boost converter and inverter model appropriate for mgvs output power of the solar panels is in the dc form and should be converted to ac power via inverter in order to inject this power to the grid. figure 2 shows schematic view of inverters connection to the pv systems. as shown in this figure, dc output of the solar cell should be increased using a step-up dc-dc converter and then regarding to the type of system performance it is connected to ac grid through a typical inverter. fig. 2: inverters connection to the pv systems. generally speaking, since output of dc-dc converter has ripple, this issue affects the accuracy of the results. hence, closed-loop dc-dc converter has to be used in order to deliver a smooth dc output (or with minimum ripple) to the inverter [8-9]. figure 3 shows simulated sample of this converter in matlab/simulink. fig.4 shows a schematic ofinverter appropriate for mgvs, which is an average model and "dc-bus-voltagecontrolled" type of inverter [10]. fig. 3: simulation of "closed-loop dc-dc boost converter" in matlab/simulink. when the microgrid is connected to the main grid, the inverter is controlled to inject a given active and reactive power. this mode is known as pq mode control. however, the under-study microgrid is considered in the islanded mode of operation, in which the iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 195 inverter control mode deviates from pq controllermode and switches to voltage and frequency control mode [11-12]. hence, the utilized inverter should primarily be capable to control active and reactive power. if so, regarding the "frequency active power" and "voltage reactive power" droop curves, the frequency and voltage can be controlled too, in the islanded microgrid. it should be mentioned that three phase symmetrical voltage and current are considered for operation of the proposed inverter. as a result, their zero components are zero. therefore, if the reference frame of dq is selected in a manner which rotates synchronized to the microgrid voltages then we would have vq=0 and active and reactive powers equations could be shortened as eqn. (1) and eqn. (2). � � �� �� (1) � � ��� �� (2) therefore, having reference values of active and reactive power and also regarding to equations (1) and (2) and voltage measurementof bus-bar, related to connecting the inverter to the microgrid, in each instant, the reference values of d and q axis currents could be derived as eqn. (3) and eqn. (4). ��, � � � �� �� (3) ��, � � � � �� �� (4) as a result, generated active and reactive power could be controlled by controlling the inverter's d and q axis currents. as it would be explained in detail in section 3, the output of the proposed voltage stabilizer is distributed between the dgs located in the microgrid, but that part of the output which is related to pv resource (or each power electronic converter based resources) should be applied on its inverter. since the signal type of this controller output is voltage, the control section of the employed inverter should have the capability to deal with output voltage of pv, reference voltage and also output voltage of mgvs, as three input signals, in addition to active and reactive power control (by id and iq control). therefore, as it shown in fig.4, the employed inverter is a "dc-bus-voltage-controlled" type inverter, which, in turn, is a kind of "average model" inverters. in this case, the share of pv resource from stabilizer output, should be added to the collector block, located in the control section of the inverter and prior to "dc bus regulator" block(that in fact a pi controller block ), as the 3 rd input 2.1.2 energy storage system (battery) the last section of pv systems is energy storage section, which is required due to limitation of solar energy. the storage process is performed through electrochemical batteries in pv power-plants. batteries increase the service time and electricity supply in nights or in hours that solar light cannot provide required power for consumers [13]. these storage elements should compensate the effects of sudden changes of pv power-plants. thus the capacity of storage system could be calculated by computing the maximum variations, on the basis of system parameters.figure 5 shows how to connect a battery to the photovoltaic system. iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 196 fig. 4: dc-bus-voltage-controlled inverter schematic. fig. 5: connection a battery to photovoltaic system. 2.2modeling of the diesel-generator and its elements diesel generator resource is known as a synchronous machine based distributed generation resource, and as it has seen in fig.6, the electrical part of it, is a synchronous generator equipped by the excitation system, and its mechanical part, is containing governor and turbine. fig. 6: synchronous generator with its exciter and governor. iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 197 2.2.1 governor modeling governors adjust turbine waste gate in a manner that enable the frequency to return to its nominal or planned value. governors are equipped with specifications to let them decrease speed by increasing load in order to distribute the load between two or more parallel units in a stable manner. as shown in fig.7, speed droop specification could be put into practice by adding a feedback loop of steady state to integrator turn. this figure shows the governor's model used in simulation analysis and fig.8 shows the simplified model of it. parameter "r" in these two figures, is the ratio of speed deviation (∆⍵r) or frequency deviation (∆f) to turbine waste gate displacement (∆y) or output power (∆p). fig. 7: the model of governor. fig. 8: simplified model of governor. 2.2.2 turbine modeling turbines convert the initial mechanical energy to the electrical one, in synchronous generators. since the turbines of the synchronous machine based resources are low dynamic equipments, the turbine model could be considered as a transfer function with time constant (see fig.9). in the simulation, tt is equal to 0.3. fig. 9: the turbine model. 2.2.3 modeling of the "secondary control of frequency" in the studied microgrid, in addition to governor we need a loop to recover the frequency due to the fact that the diesel generator resource is responsible for the secondary control of frequency (returning frequency to its nominal value in microgrid in islanded mode of operation) and to model it as exhibited in fig.10, an integrator with a time constant of ti was used. it should be mentioned that the time constant of the integrator is usually selected a large value in order to enable the performing of the secondary control after the initial control of frequency when rotor fluctuations are damped. also, it should be mentioned that parameter of tg in this figure is � �� . iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 198 fig. 10: the perfect exhibition of governor system, turbine and the loop of secondary control of frequency. 2.2.4 excitation system modeling output voltage of synchronous generator is remained constant using an excitation system. in fact, the main task of the excitation system is to supply required excitation current of synchronous machine within the allowable range of generator and adjust it automatically in order to adjust the terminal voltage of the machine at a constant value. figure 11 shows the model of excitation system used in the synchronous machine based resource. in the simulation of this research, ta=0.1, tb=0.2, te=0.2 and k=180 is considered. fig. 11: model of excitation system related to synchronous machine based dg. 3. modeling of "microgrid voltage stabilizer" and applying it to microgrid in every system, bus voltages are considered as important performance factors which should lie within a specific range. different disturbances could result in voltage drop. on the other hand, in microgrids, electrical distances between resources and loads are not too much and reactive power could be transferred from resource to load, therefore, a stabilizer which acts on this basis could be used in microgrids. "microgrid voltage stabilizer" (mgvs), works similar to pss (power system stabilizer) in traditional power systemsand its main purpose is to ensure that the voltage remains within the set point values by adjusting reactive power generated or consumed. for example, at the time of voltage drop, this controller provides more reactive power for microgrid and so prevents any voltage collapse [14-15]. at the input of this controller, the terminal voltages are compared with the reference voltage and the error voltage, that is the difference value between them, is filtered using a low pass filter and multiplied by a gain constant and so the "droop control" is obtained in this way. moreover, with respect to the "reactive power-voltage" droop curve, the injected + y ∆ ∆p + 1 1 + � ! 1 1 + � " �1 � # $" ∆f ∆ω& 1 + ' ( 1 + ' ) * 1 + ' efd +vref vin vm,rms +vaux iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 199 reactive power required by distributed generation resources, to adjust terminal voltage at a set point value, could be estimated from output signal of this controller. corresponding differential equations that indicate the performance of mgvs are given in eqn. (5) and eqn. (6): 78 9:; � � � !< 79:; + =9!<>!?; !< ? ∆� (5) �@a�b9:; � 79:; + * !? !< ∆� (6) model of mgvs that formed by a lead-lag block, is shown in fig.12, but for easy implementation in matlab/simulink, the equivalent block diagram of it, can be used (fig.13).input of mgvs is a fractional of system voltage in dynamic mode. per unit difference (∆vierr) between ideal voltage (vides) and dynamic voltage (vidyn) is calculated for all load buses (eqn. (7)). ∆� c= vdes i-vdyn i vdes i , d � 1,2, … . . h (7) then, for determination of total fractional voltage, according to eqn. (8), weighted average (∆verr) is carried out on fractional voltage of all load buses. ∆� � i<∆�� <ji?∆�� ?jk…..il∆�� m i<ji?jk…..il (8) fig. 12: model of "microgrid voltage stabilizer". fig. 13: simplified model of "microgrid voltage stabilizer". weighting factor of each bus is defined based on importance of that bus (for example induction motor loads comparing to resistive loads are more sensitive to disturbances). for i=1 to i=l load buses, their termed as α1,α2,…,αl and their values for the test-case microgrid are given in table1. ∆� �@a�b k 1 + o' 1 + �s 1t 2t st t tt 1 1 21 1 + − k mcvsv errv∆ + + iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 200 table 1: weighting factors for load buses. α21 α19 α15 α13 α11 α7 α3 0.073 0.216 0.302 0.096 0.119 0.094 0.1 as shown in fig.13, ∆verr is supplied by a lead-lag block with gain constant k and time constants t1 and t2. the values of t1, t2 and k for the under-study microgrid (contains two pv resources and one diesel generator), that resulted by the use of eigen values method, are given in table2. table 2: mgvs control parameters k t1 t2 10 1.5 0.2 output of mgvs i.e. vmgvs is distributed between dgs based on generation reserve, nature of dgs and closeness of them to the voltage sensitive loads. equation (9) shows how of this distribution on the basis of weighting factors. these factors for generator buses (1 to g), are β1,β2,…, βg and their values are given in table3. �@a�bc � qc �@a�b ,d � 1,2, … . . r (9) table 3: weighing factors for generator buses β1 β2 β3 0.3581 0.3663 0.2756 in the tested microgrid, �@a�b� and �@a�bo are shares of mgvs output which should be applied on two pv resource. as explained in section 2-1-1, they are added as the 3 rd input to the control part of the inverters of first and second pv resources, respectively. furthermore, �@a�bs is a share of �@a�b , which is related to diesel generator. it is added to the excitation system of third resource, as per the fig.14. fig. 14: addition of mgvs output signal to excitation system of diesel generator resource. 4. simulation results before fault occurrence,the difference between desired voltage and real voltage of the load buses (∆v) that is the input of mgvs is zero. therefore, the stabilizer does not operate.during fault, ∆v has a non-zero valueand the operation of mgvs starts at this time.output voltage signal of mgvs is applied to the pq controlled inverters of dgs and then according to "voltage reactive power" droop curve, the required reactive power have iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 201 been injected to the microgrid. therefore, the voltage profile will be enhanced proportional to the rate of reactive power injection. after fault clearance, ∆v is changed to zero again and mgvs has not any signal in its output to apply to the inverter. therefore, reactive power values of pv resources return to their previous values. due to this gradual reduction of reactive power, the value of voltage will be reduced gently and the magnitude of voltage will reaches at its pre-fault value. an ieee 21-bus microgrid in islanded mode of operation is considered as test system of this paper (see fig.18). simulations are carried out in matlab/simulink. two types of faults (a three-phase short circuit fault and a load switching fault applied to bus 15) are investigated in this analysis. the applied three-phase fault in this simulation, starts at 15 th cycle (t=0.25) and continues to the end of cycle 70 th (t= 1.167).the improvement rate of dynamic voltage profile by the use of mgvs is investigated in this analysis.during short-circuit fault, flowing of large currents from generator buses to faulted load bus results in the drop of the voltage of other buses. at this time, mgvshelps the microgrid to use the reactive power reserve efficiently and improve the dynamic voltage stability. simulation results related to load buses are shown in fig.15. comparison of the dynamic voltages of load buses in the systems with and without mgvs shows that the dynamic voltage profile is improved satisfactorily by the use of mgvs.in addition, fig.16 contains two sample figures that exhibit comparison of reactive power generation related to microgrid resources, in the presence of stabilizer and its absence. a) voltage profile of bus 11 b) voltage profile of bus 15 (faulted bus) c) voltage profile of bus 19 d) voltage profile of bus 21 fig.15: comparison of load bus voltages for a 3-phase short circuit fault at bus 15, with mgvs and without it. iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 202 a) reactive power generation of resource 1. b) reactive power generation of resource 3. fig.16: comparison of reactive power generation for a 3-phase short circuit fault at bus 15, with mgvs and without it. iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 203 a) voltage profile of bus 19. b) voltage profile of bus 15 (faulted bus). fig. 17: comparison of load bus voltages for a 30% load increase at bus 15, with mgvs and without it. 5. conclusion disturbances that occur in microgrids cause variations in buses voltage. these variations are sometimes very intensive so that they could likely result in the collapse of microgrid if the fault lasts more. hence, a voltage stabilizer is used that improves voltage profiles of the microgrid buses in this investigation. this stabilizer is formed by a set of control blocks and its output is a voltage signal that would be divided between the dgs in the microgrid. indeed, output signal of mgvs is effective to coordinate the dgs reactive power generation and supply the lost generation. therefore, since the generated reactive power of resources depends on voltage, each resource generates an amount of reactive power causing to improve the dynamic voltage of the load buses in the microgrid. in this paper, a microgrid containing two types of dgs, photovoltaic (pv) resource and diesel generator is tested. regarding the obtained results, it can be concluded that utilizing microgrid voltage stabilizer with proper control parameters, improves dynamic voltage profile of buses in any types of microgrids (containing power electronic converter based dg or synchronous generator based dg or combination of them). iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 204 fig.18: test systemieee 21bus microgrid in islanded mode. references [1] l. robertr, a. akhil, m. chris, s. john, d. jeff, g. ross, a. s. sakis, y. robert and e. joe, “integration of distributed energy resources: the certs microgrid concept,” ." lawrence berkeley national laboratory (2002). [2] b. a. robbinsy, a. d. domínguez-garcíay, c. n. hadjicostisz, “control of distributed energy resources for reactive power support,” north american power symposium (naps), 2011. ieee,2011. [3] p.kundur, “power system stability and control,” mcgraw-hill, inc.1994. [4] j. a. peças lopes, c. l. moreira and a. g. madureira, “defining control strategies for analysing microgrids islanded operation,” ieee transactions on power systems, (21 (2006). [5] r. majumder,a.ghosh, g. ledwich, & f. zare, “enhancing the stability of an autonomous microgrid using dstatcom,”international journal of emerging electric power systems, (2009). [6] n. l.soultanis, s. a.papathanasiou, n. d.hatziargyriou, “a stability algorithm for the dynamic analysis of inverter dominated unbalanced lv microgrids,”ieee transactions onpower systems, 22: 294-304. [7] m. s. zabihi, e. a. soleimani, s.farhangi, “photovoltaic manufacturing, system design and application trend in iran,” elsevier science, renewable energy, [8] the mathworks inc. (2009) matlab help. help document. [9] a. kalirasu, s. sekar dash, “simulation of closed loop controlled boost converter for solar instalation,” serbian journal of electrical engineering, 7.1 (2010): 121-30. iium engineering journal, vol. 14, no. 2, 2013 mahzarnia et al. 205 [10] z. ye, r. walling, l. garces, r. zhou, l.li, and t.wang, “study and development of antiislanding control for grid-connected inverters,” general electric global research center niskayuna, new york 2004:21. [11] j. a. peças lopes, c. l. moreira, a. g. madureira, f. o. resende, x. wu, “control strategies for microgrids emergency operation,” international conference on future power systems, nov. 2005. [12] r. m. kamel, a. chaouachi, k. nagasaka, “detailed analysis of micro-grid stability during islanding mode under different load conditions,”engineering journals of scirp, may 2011. [13] a. engler, “control of parallel operating battery inverters,” in pv hybrid power system, kassel, (2000):1-4. [14] h. laaksonen, p. saari, and r. komulainen, “voltage and frequency control of inverter based weak lv network microgrid,” in international conference on future power systems, amsterdam, (2005): 1-6. [15] p. l. jeffrey, “modeling of dynamic loads for voltage stability studies,” tennessee technological university, cookeville, ms thesis, (2007). nomenclature dg distributed generation mgvs micro-grid voltage stabilizer pss power system stabilizer appendix table 4: the specifications of each photovoltaic cell and the derived module. module photovoltaic cell v pv ppv v o.c is.c voltage at pmax p 103.2 510.8 22.2 5.45 17.2 85.14 microsoft word vol11_no1_final iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 106 optimization of the selective catalytic reduction of no in diesel exhaust over cuzn/zsm-5 catalyst using central composite design ahmad zuhairi abdullah*, hamidah abdullah, subhash bhatia babak salamatinia and noraini razali school of chemical engineering, engineering campus, universiti sains malaysia, 14300 nibong tebal, penang, malaysia. *e-mail : chzuhairi@eng.usm.my abstract : the optimization of the operating conditions in nitric oxide (no) selective catalytic reduction (scr) process over cu-zn/zsm-5 bimetallic catalyst using combined response surface methodology (rsm) and central composite design (ccd) is reported. a bimetallic catalyst containing 6 wt. % cu and 8 wt. % zn was prepared through a combined impregnation and ionexchange process. the process conditions investigated were temperature (300 400 c), no concentration (900-2,000 ppm) and iso-butane (reductant) concentration (900 2,000 ppm). the weight hourly space velocity (whsv) was fixed at 13,000 h-1. cu-zn/zsm-5 catalyst proved its potential for the scr process. statistical analyses showed that the no reduction was affected by all the operating conditions with the temperature as the most dominant one. based on the experimental design, a second order mathematical model was successfully developed and satisfactory fitting to the experimental data was demonstrated. interactions between variables were also analyzed at 99.99 % confidence level. the optimum conditions obtained were 624 ppm for the no concentration, 2,440 ppm for the iso-butane concentration and 389 °c for the reaction temperature to give a corresponding no reduction of 96.13 %. keywords: scr; gases; catalysis; zeolite; central composite design; optimization. 5. introduction diesel-powered engines always offer better fuel economy than stoichiometric gasoline engines because of the lean-burn conditions at high pressure that yield higher combustion temperatures [1-3]. however, diesel engine exhaust has many adverse environmental effects, particularly due to the emission of nitrogen oxides (nox). nox directly involve in the formation of irritating ground level ozone. their reactions with other chemicals present in the air also lead to the formation of other toxic chemicals such as nitrate particles and acid aerosols [4]. the lean-burn conditions also produce an exhaust containing high concentration of oxygen. such an oxidative environment complicates conventional approaches to chemically reduce nox to environmentally benign nitrogen gas [5]. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 107 the pioneering works by iwamoto et al. [5, 6] prove the plausibility of selective catalytic reduction (scr) technique with hydrocarbons as the reducing agents for the removal of nox. in this method, the unburned hydrocarbons in the exhaust in combination with added ones are used to reduce nox by means of a suitable catalyst. many catalysts have been investigated and zeolites-based catalysts produced very convincing results [3, 4, 7]. in this respect, zsm-5 recently gained attention in environmental catalysis, especially in reduction of nox emission [3, 8, 9]. witzel et al. [1] reported that three-dimensional structure of zsm-5 zeolite enabled reactant molecules to detour via adjacent channels whenever one of the channels was completely filled up by the reactant gases. this material was also found to be resistant to soot that is usually encountered in diesel exhaust [10]. among metals studied as the active components of the catalysts are cu [4, 5, 7], pt [11], pd [12] and co [2, 4]. by reviewing the results, cu should have the advantage on the basis of sufficiently high activity, high stability, low toxicity and low cost. therefore, it was used in this study. recently, bimetallic catalysts have created particular interest due to the promotional effects between metal species [11]. the second metal should allow the first metal in the active state. however, when one of the metals is easily reduced, the other should stay in a low oxidation state [13, 14]. the bimetallic catalysts generally have higher resistance towards metal sintering that will usually lead to the loss of contact between the metal and the support. the second metal could also prevent active metal migration in the supports and improve metal dispersion [13, 14]. in this respect, zn is reported to improve the activity of rh/tio2 catalysts [15] and co/zsm-5 [2]. the desired chemical effect was mainly attributed to the retardation of the oxidation of reluctant in the exhaust during the scr process. besides focusing on the catalyst itself, the optimum operating conditions in a nox reduction process are also critical in order to minimize the operating costs while ensuring highest possible removal efficiency. usually, a reaction temperature of between 300 and 400 c is needed to achieve sufficiently high catalytic activity. this range occurs within the normal operating temperature of most diesel engine exhausts. lower and higher temperature would result in low reaction rate and excessive oxidation of the reductant, respectively. excessive addition of hydrocarbons may lead to a decrease in the nox reduction because the exothermic reaction could raise the temperature to exceed the optimum value for nox reduction [7]. apart from that, the ratio of nox and hydrocarbon is also critical. while the reductant is required for the scr reaction, too high concentration of nox in the mixture would prevents the adsorption and activation of hydrocarbon. consequently, the overall reaction rate is adversely affected. this has been proven by bueno-lopez et al. [16] who observed that for a constant no concentration, an increase in c3h6 concentration increased the maximum no reduction only up to a c3h6 concentration of 2,500 ppm. meanwhile, an increase in the nox concentration usually has a negative effect on the nox conversion. therefore, the process variables should be optimized for the sake of obtaining the most efficient scr process. it is always advisable that a certain design of experiment (doe) to be employed to achieve the objective as limited number of experimental runs would be needed. however conclusions with high statistical significance could still be generated. besides, interactions between the critical process variables could be simultaneously analyzed. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 108 in the present work, a bimetallic cu-zn/zsm-5 catalyst was used for the scr of nitric oxide (no) in a synthetic diesel exhaust. the preparation method for the catalyst had been optimized through a series of studies [17]. no was used as the model nox compound while iso-butane (i-c4h10) was used as the reductant. this reductant was successfully used for scr reaction in our earlier works [7, 11]. the main objective of this work was to achieve the maximum no reduction at optimum conditions consisting of the reaction temperature, the no and iso-butane concentrations. for this purpose, combined response surface methodology (rsm) with central composite design (ccd) was employed to simultaneously study the effects of the three reaction variables on the no reduction. a mathematical model was developed to correlate the no reduction with the reaction conditions and the possible interactions between the variables demonstrated and analyzed. whereas the exhaust conditions are dictated by many external factors such as speed, the way the engine is driven etc., the result in this study would be of great assistance if a catalytic nox abatement system were to be optimally designed and operated. in addition, highly stable catalytic activity was observed throughout the study. 2. materials and methods 2.1 bimetallic catalyst preparation nh4-zsm-5 (zeolyst international, usa, si/al=40) was first converted to its h-zsm5 form by calcination at 600 °c for 5 h. the first active metal (cu) was then loaded into the h-zsm-5 using a conventional impregnation method. it was performed by mixing a 2.0 m cu (no3)2 solution with h-zsm-5. the amount of aqueous solution per gram of zeolite used was as reported by nejar and gomez [18] to produce a cu loading of 6 wt. % in the catalyst. the slurry was then placed in a rotary evaporator until it was free flowing. it was subsequently dried at 105 ºc for 24 h and then calcined at 600 ºc. then, it was kept under vacuum at 100 ºc for 2 h until the slurry became completely dry and free flowing. zn as the second metal was incorporated into the cu/zsm-5 catalyst using an ionexchange method. it was performed by mixing the cu/zsm-5 catalyst with 2.0 m of zn (no3)2 solution whereby the amount of aqueous solution used per gram of zeolite used was as reported by de lucas et al. [4]. the mixture was then continuously stirred at room temperature for 24 h. subsequently, the suspension was filtered and dried at 100 ºc for 24 h, followed by calcination at 600 ºc for 2 h. the ion-exchange process was repeated until the catalyst contained 8 wt. % of zn. the cu-zn/zsm-5 catalyst in powder form was then pelletized, crushed and sieved to produce particles in a size range between 250 and 350 µm. the catalysts were characterized using a micromeritic asap 2000 surface analyzer. 2.2 catalytic activity study the no reduction experiments were carried out in a continuous flow system. the same system as used by deeng et al. [7] was used in this study. in brief, the set-up consisted of a gas feed system for each component with individual flow control by mass flow meters, a catalytic reactor heated by a tubular furnace and an exit gas flow meter equipped with gas analysis system. the reactor was packed with 0.2 g of the catalyst. in this study, catalyst particles in the size range of 250 and 350 µm were used as our previous iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 109 study showed that the system would operate in a reaction-controlling regime with the catalyst in this size range under the experimental conditions used [11]. to better simulate the conditions in the diesel engine exhaust, the nitrogen gas was saturated with water vapor prior to mixing with other gas components. the feed gas at a total flow rate of 150 ml/min with a corresponding weight hourly space velocity (whsv) of 13,000 h-1 was allowed to flow into the reactor containing the catalyst for about 30 min at the reaction temperature. the concentration of inlet and outlet gases was determined by means of a chemiluminescence gas analyzer (kane-may 900, england). the temperature of the catalyst bed which was measured using a k-type thermocouple installed in contact with the catalyst bed was taken as the reaction temperature. 2.3 design of experiment a design of experiment was used to evaluate the effects of significant parameters and to obtain the optimum value of important variables in the selective catalytic reduction of no with iso-butane as the reducing agent. for this purpose, response surface methodology (rsm) was used to obtain the optimum conditions (no concentration, isobutane concentration and reaction temperature). rsm is a collection of mathematical and statistical techniques which is useful for modeling and problem analysis purposes. the highest no reduction was targeted in this optimization study. the effects of three input variables i.e. reaction temperature, feed no and feed isobutane concentrations towards no reduction were investigated according to a central composite design (ccd) experiment. the optimization of no conversion was carried out by three chosen independent process variables using 23 factorial experiments design with six star points (α=2) and 6 replicates at center points. table 1 lists the ranges and levels of the three independent variables studied. the design led to 20 sets of experiment as given in table 2. these parameter ranges were used based on a reported result by deeng et al. [7]. all variables at zero level were used as the center points while the variables at the lowest (-2.0) or highest (+2.0) level formed the axial points. the experimental runs were conducted in a random order to minimize the effects of the uncontrolled factors. table 1: levels of the reaction variables used in this study. reaction variable code unit level -2 -1 0 1 2 temperature a ºc 25 0 30 0 35 0 40 0 45 0 feed no b ppm 35 0 90 0 1,4 50 2,0 00 2,5 50 feed i-c4h10 c ppm 35 0 90 0 1,4 50 2,0 00 2,5 50 iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 110 table 2: matrix of the experimental design. run point type variables response a b c r1 temperature (ºc) no concentration (ppm) iso-butane concentration (ppm) no conversion (%) 1 fact 300.00 900.00 900.00 30.0 2 fact 400.00 900.00 900.00 87.5 3 fact 300.00 2000.00 900.00 29.0 4 fact 400.00 2000.00 900.00 70.6 5 fact 300.00 900.00 2000.00 70.0 6 fact 400.00 900.00 2000.00 95.0 7 fact 300.00 2000.00 2000.00 55.0 8 fact 400.00 2000.00 2000.00 72.4 9 axial 250.00 1450.00 1450.00 10.0 10 axial 450.00 1450.00 1450.00 69.0 11 axial 350.00 350.00 1450.00 93.0 12 axial 350.00 2550.00 1450.00 46.8 13 axial 350.00 1450.00 350.00 50.0 14 axial 350.00 1450.00 2550.00 76.6 15 center 350.00 1450.00 1450.00 70.0 16 center 350.00 1450.00 1450.00 76.2 17 center 350.00 1450.00 1450.00 69.1 18 center 350.00 1450.00 1450.00 65.1 19 center 350.00 1450.00 1450.00 71.0 20 center 350.00 1450.00 1450.00 69.3 the predictive effects of the factors influencing the no reduction and iso-butane conversion were to be obtained through a quadratic model shown by equation (1). y= β0 + β1a+ β2b+ β3c+ β11a 2+ β22b 2+ β33c 2+ β12ab + β13ac+ β23bc (1) where, y is the response calculated by the model while a, b, c are the coded variables corresponding to the reaction temperature, no concentration and iso-butane concentration, respectively. the constant β0 refers to the intercept coefficient and β1, β2, β3 are the terms for the single variable effects. the β11, β22, β33 coefficients predict the double actions of the each factor while the β12 β13 β23 coefficients indicate the extent of interactions between the variables studied. the regression data obtained in this study was analyzed by the rsm. the evaluation of a second order model equation was then performed using a fisher’s test and the proportion of variance in the model was evaluated on the basis of the multiple coefficient of determination (r2). the graphical and numerical analyses provided by a software (designexpert 6.0.7, usa) were employed to predict the optimum conditions for the no reduction. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 111 3. results and discussion 3.1 characteristics of the bimetallic catalyst table 3 shows the surface characteristics of cu-zn/zsm-5 catalyst as compared to its h-zsm-5 support. the support had a bet surface area of 402 m2/g and more than half of this was contributed by micropores. despite being theoretically microporous material, mesoand macropores contributed significantly to the overall surface area of the cuzn/zsm-5 catalyst. they were ascribed to the interstices between the zeolite particles, between the extra-framework species as well as that formed between the metal crystallites. it was found that the catalyst preparation procedure unsed in this study resulted in about 13 % and 15 % loss in bet surface area and micropores, respectively. a surface area of 348 m2/g with a pore volume of 0.27 ml/g were generally sufficient for an effective heterogeneous catalyst. table 3: characteristics of cu-zn/zsm-5 catalyst as compared to the h-zsm-5 support. characteristics h-zsm-5 cu-zn/zsm-5 bet surface area (m2/g) 402 348 micropore area (m2/g) 215 182 total pore volume (ml/g) 0.26 0.27 cu loading (wt. %) 6 zn loading (wt. %) 8 3.2 regression models the no conversions obtained in table 2 were correlated with the three variables studied by means of a multiple regression analysis. at first, the suggested model was in a quadratic form. however, the model was modified by excluding the insignificant terms which were identified by fisher’s test to assure the significant level of the model. the test results were analyzed by comparing the calculated f and theoretical f values based on 99.99 % confidence level for the first order of all variables and second order of term a (temperature). the other model term remained showed acceptable level of significance (99.70 %). the calculated f values should be higher than the theoretical values to make the term significant or in other words, the null-hypothesis should be rejected. the final model (significant level> 99.99%) in terms of coded value after excluding the insignificant terms (identified using fisher’s test) is given in equation (2). the significance of each coefficient in the eq. 2 was determined by student’s t-test and p-values. the t-test is a statistical hypothesis test in which the test statistic follows a student's t-distribution if the null hypothesis is true. meanwhile, the p-value is the probability of obtaining a test statistic at least as extreme as the one that was actually observed, assuming that the null hypothesis is true. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 112 no conversion (r1) =69.51 + 16.22 a 9.24 b + 8.03 c 7.17 a2 7.09 a c (2) the positive sign in front of the terms indicates a synergic effect, while the negative sign indicates an antagonistic effect [7]. the quality of the model developed could be evaluated from their coefficients of correlation. the value of r2 for equation (2) is 0.9504. it implies that 95.04 % of the total variation in the no conversion was attributed to the experimental variables studied. the remaining (4.96 % of no conversion) was therefore, explicated by the residues. on the other hand, the value of r2 which is very close to 1 suggests that the predicted data from the model are comparable with experimental data with sufficient degree of accuracy (as shown in fig. 1). r2=0.9504 fig. 1: parity plot between the predicted and actual data for the no reduction reaction. as suggested by eq. 2, the coefficient value for a is the highest, indicating the dominant effect of this variable in the scr of no. but the effect on the no conversion was in a quadratic pattern. next, it was the reductant concentration to be influencial while no concentration between 900 and 2,000 ppm was not so influencial on the no removal percentage. an increase in no concentration in the feed between 900 to 2,000 ppm as used in the present study was detrimental to the fraction of no removal. on the other hand, increasing iso-butane concentration generally increased the no removal. interaction between the temperature (a) and reductant concentration (c) was also detected in this reaction system. this interaction suggests the differrent patterns of no removal when moving from the lower limit to the higher limit of these variables. whereas this interaction is deemed to have minimal effect on the variable a, the significance impact on variable c could result. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 113 3.3 model adequacy in order to check for the adequacy of the model developed to represent the reaction system, an analysis of variance (anova) was performed and the results are shown in table 4. the anova was basically required to test the significance and adequacy of the model at the confidence level of 95 %. the anova of the model developed demonstrates that the model is highly significant (99.99 %) for no conversion as the computed f value (53.66) is much higher than the theoretical f0.05 (5, 14) value. apart from that, each term in the model is also found to be significant at a >99.7 % confidence level as the the computed f value for each term is higher than the theoritical f0.05 (1, 14) value. values of prob > f less than 0.0500 indicate model terms are significant. in this case terms a, b, c, a2, ac are significant model terms. values greater than 0.1000 indicate the model terms are not significant. if there are many insignificant model terms (not counting those required to support hierarchy), model reduction may improve your model. the "lack of fit f-value" of 3.21 implies the lack of fit is not significant relative to the pure error. there is a 10.59 % chance that a "lack of fit f-value" this large could occur due to noise. non-significant lack of fit is good. the "pred r-squared" of 0.8750 is in reasonable agreement with the "adj r-squared" of 0.9327. "adeq precision" measures the signal to noise ratio. according to the software manual a ratio greater than 4 is desirable. the ratio of 26.207 indicates an adequate signal. table 4: analysis of variance (anova) for the 23 full ccd of the no reduction process. source sum of squares dfa mean square f-value prob > f model 8407.484 5 1681.497 53.66467 < 0.0001 significant residual 438.6677 14 31.33341 lack of fit 373.9994 9 41.55548 3.21297 0.1059 not significant pure error 64.66833 5 12.93367 corr. total 8846.152 19 r2= 0.9504, cvb=8.78 % adegree of freedom bcoefficient of variance from these statistical tests, it was found that the model was adequate for predicting the no conversion within the range of the variables studied. therefore, the model developed for no conversion in equation (2) is valid for present study. in agreement with discussion in section 3.2, the reaction temperature (a) had the largest effect on the no conversion with the highest f value followed by the no concentration (b) and reductant concentration (c). the descrepancy between this result and that given in the equation (2) with respect to the significance order of variable b and c is attributed to the ac interaction. the quadratic term (a2) also significantly affects the no conversion as compared to the interaction between variables (ac). iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 114 the interaction between the reaction temperature and the reductant concentration was associated with the selectivity of the reductant to undergo oxidation in the presence of oxygen and no. the reaction between iso-butane and oxygen led to the formation of carbon dioxide while that between iso-butane and no led to the formation of nitrogen (or in other words, the reduction of no was achieved). the preference for these two reactions differed at different temperature and the reactions could either occur in the gas phase or on the surface of the catalyst. low temperature was found to favor no reduction while higher than optimum temperature accelerated the mineralization of the organic [11]. this was based on the fact that the combustion of iso-butane involves the breaking of many c-c bonds while the reduction of no only requires the extraction of oxygen atom from the single nitrogen atom. the high enthalpy of combustion for the iso-butane (hc = -2,869 kj/mol) reflects the stability of the hydrocarbon to render higher preference towards no reduction. 3.4 effects of process variables the result in table 2 shows that the process variables have great effect on the no conversion. as the model developed in this work showed no maximum no conversion within the experimental domain examined, the optimum conditions were defined as those that resulted in the highest no conversion. thus, the model developed was used to construct response surfaces to facilitate a straight forward examination of the effects by the process variables on the no conversion. response surfaces can also be visualized as two-dimensional plots that present the response as a function of two variables, while keeping the third one constant. figure 2 demonstrates the response surface for the effect of interactions between every two of the process variables i.e. temperature, no concentration and iso-butane concentration, respectively. figure 2 (a) shows the effects of temperature and feed no on no conversion. it can be seen that with an increase in reaction temperature up to approximately 390 °c the no conversion increases while a slight drop is seen afterwards. the iso-butane concentration was fixed at 1,450 ppm at the center point. it is noted that at lower temperature, a relatively more rapid increase in the conversion is observed and then it stabilizes at higher temperature. a linear moderate decrease could be observed by the increase in no feed which can be also observed clearly in fig. 2 (c). from fig. 2 (a) it can be noticed that high feed of no (> 2000 ppm) at low temperatures (<260 oc) no conversion happens. figure 2 (b) demonstrates the response surface of no conversion with varying temperature and i-c4h10 concentration. the no feed was fixed at 1450 ppm at its center point. no conversion decreased with an increase in iso-butane concentration obvious in fig. 2 (c) as well. in fig. (c) the increase or decrease trend follows a relatively linear pattern as compared to that observed in fig. 2 (a) and (b). a higher concentration of no in the mixture prevented the adsorption and activation of hydrocarbon and, consequently, the overall reaction rate was adversely affected [16]. a similar trend for all parameters was achieved by deeng et al. [7] in their study using a structured catalyst. thus, similar mechanism could be assumed regardless of the type of catalyst used. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 115 fig. 2: influences of (a) reaction temperature (b) no concentration and (c) iso-butane (i-c4h10) concentration on the no conversion (other variables were set at their respective center points). meanwhile, the increase in the iso-butane concentration was proven to be beneficial to the scr of no as it acted at the reductant to this highly polluting oxide. figure 3 shows the changes in no conversion with varying temperature at 900 ppm and 2,000 ppm of iso-butane concentration. no concentration in the feed was kept constant at 1,450 ppm. at low temperature, a significantly lower conversion of no was iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 116 achieved when the iso-butane concentration was 900 ppm as compared to that observed with 2000 ppm of iso-butane. however, it increased more rapidly with an increase in the temperature until it ended up with almost the same conversion at 400 ºc. thus, the benefit of having higher reductant concentration was only enjoyed at lower temperature. it is also noted in the figure that the no conversion decreased if the reaction temperature was increased beyond 400 c. the loss of the activity at high temperature was associated with the onset of the oxidation of iso-butane by oxygen as reported by guzman-vargas et al. [8] and de lucas et al. [4]. furthermore, cu has been found to be sufficiently active in the oxidation of organics at high temperature [19]. fig. 3: effects of iso-butane (i-c4h10) concentration and temperature on no conversion shown in an interaction plot iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 117 fig. 3: effects of iso-butane (i-c4h10) concentration and temperature on no conversion shown in an interaction plot figure 2(b) shows the three-dimension response surface plot of the effect of iso-butane concentration and temperature on no conversion. it is clearly noted that at high temperature, the no conversion is high in the range of reductant concentration tested. this observation shows that increasing iso-butane concentration did not significantly influence the no conversion at high reaction temperature. the promotional effect was only significant at lower temperature. thus, over usage of the reductant could be avoided if the concentration of the reductant could be set at the optimum level base on the reaction temperature used. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 118 3.5 optimization analysis as the exact optimum conditions could not be obtained within the range of process variables studied, the optimization was then attempted using numerical optimization feature of design expert 6.0.7 software. the primary objective was to search for a combination of factors that could simultaneously satisfy the requirements placed on each of the process variable and response. table 5 shows the constraints used to obtain the optimum value for process variables. the goal was set to maximize the no reduction while the temperature should be in the range between 2500 and 450 °c while no and ic4h10 concentrations should be in the range of 350 to 2,550 ppm. table 5: constraints used to obtain the optimum conditions for the reaction. name goal lower limit upper limit temperature in range 250 450 no concentration in range 350 2550 i-c4h10 concentration in range 350 2550 no reduction maximize 10 95 table 6: selected optimum conditions generated by the doe. temperature (°c) no concentration (ppm) i-c4h10 concentration (ppm) no reduction (%) 389 624 2,440 96.13 the doe result proposed 10 possible sets of solution. by default, the solutions are sorted from the best to the worst. thus, the first set of solution which is given in table 6 was taken as the best solution to be used for further confirmatory process studies. for that, 5 additional experimental runs were carried out in the laboratory to determine the accuracy of the optimum conditions obtained from doe. these experiments were carried out at 389 ºc with a total feed gas flow rate of 150 ml/min (624 ppm no, 2,440 ppm iso-butane, 3 v/v % o2 and balance n2). the purpose was to evaluate the applicability of the model in predicting the optimum conditions of the scr of no process on the basis of statistics. table 7 shows the results from the 3 experiments conducted at the optimum conditions. the values of no reduction obtained from experiment were compared with the one predicted by the doe. the average no reduction efficiency obtained was 95.2 % which was 0.93 % lower as compared to the simulated value of 96.13 %. there is an error of ± 0.06 % for the no reduction value. thus, the null hypothesis saying that there is no significant difference between the two mean values should be accepted. it means, the proposed statistical model is adequately accurate and reliable in predicting the no reduction for the reaction system. in this study, only the activity of fresh catalyst was iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 119 table 7: results of verification experiments conducted at optimum conditions as obtained from doe. run no conc. (ppm) no reduction (%) aerror mean error bstandard deviation (cno)in (cno)out (xno)exp (xno)doe 1 624 32 94.9 96.13 -1.23 2 624 23 96.31 96.13 0.18 0.606 0.588 3 624 29 95.35 96.13 -0.77 a= error = (xno)exp (xno)doe b= σ = √(nσx2 – (σx)2)/n(n-1) evaluated and modeled. it is of great interest to learn whether the same model can also be used to represent the performance of the deactivated catalyst after few hours on stream. similarly, the use of other type of catalyst or reductant is also expected to cause some degree of deviation from the values predicted by the statistical model. all these topics should be properly addressed to prove the robustness of the statistical model to accurately predict the behavior of the process under various conditions. 4. conclusion cu-zn/zsm-5 bimetallic catalyst was successfully synthesized and it demonstrated high activity for the scr of no in diesel exhaust. through combined application of response surface methodology (rsm) and central composite design (ccd), the optimization of the operating conditions in the no selective catalytic reduction (scr) process over the catalyst was successfully performed. based on analysis of variance (anova), no reduction was significantly affected by all the operating conditions but the effect of temperature was the most dominant. a second order mathematical model was successfully developed and satisfactory fitting to the experimental data was demonstrated. interaction between the reaction temperature and iso-butane concentration were also detected at 99.99 % confidence level. the optimum process were achieved with 624 ppm of the no concentration, 2,440 ppm of the iso-butane concentration and a reaction temperature of 389 °c to give a corresponding no reduction of 96.13 %. acknowledgements a short term research grant and research university (ru) grant from universiti sains malaysia to support this study are gratefully acknowledged. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 120 references [1] f. witzel, g.a. sill and w.k. hall. “reaction studies of the selective reduction of no by various hydrocarbons.” j. catal., 149, 229-237, 1994. [2] l. ren, t. zhang, d. liang, c. xu, j. tang and l. lin. “effect of addition of zn on the catalytic activity of a co/hzsm-5 catalyst for the scr of nox with ch4.” appl. catal. b, 35, 317-321, 2002. [3] v.g. komvokis, e.f. iliopoulou, i.a. vasalos, k.s. triantafyllidis and c.l. marshall. “development of optimized cu-zsm-5 denox catalytic materials both for hc-scr applications and as fcc catalytic additives.” appl. catal. a, 325, 345352, 2007. [4] a. de lucas, j.l. valverde, f. dorado, a. romero and i. asencio. “influence of the ion exchange metal (cu, co, ni and mn) on the selective catalytic reduction of nox over mordenite and zsm-5.” j. molec. catal. a, 225, 47-58, 2005. [5] h. iwamoto, h. yahiro, s. shundo, y. yuu and n. misono. “influence of sulfur dioxide on catalytic removal of nitric oxide over copper ion-exchanged zsm-5 zeolite.” appl. catal., 69, 15-19, 1991a. [6] m. iwamoto, h. yahiro, s. shundo, y. yuu and n. mizuno. “cu-zsm-5 zeolite as highly active catalyst for removal of nitrogen monoxide from emission of diesel engines.” appl. catal., 70, 15-20, 1991b. [7] k.d. deeng, a.r. mohamed and s. bhatia. “process optimization studies of structured cu-zsm-5 zeolite catalyst for the removal of no using design of experiments (doe).” chem. eng. j., 103, 147-157, 2004. [8] a. guzman-vargas, g. delahay, b. coq, e. lima, p. bosch and j.c. jumas. “influence of the preparation method on the properties of fe-zsm-5 for the selective catalytic reduction of no by n-decane.” catal. today, 107-108, 94-99, 2005. [9] a. shichi, t. hattori and a. satsuma. “involvement of nco species in promotion effect of water vapor on propane-scr over co-mfi zeolite.” appl. catal. b, 77, 9299, 2007. [10] a.z. abdullah, h. abdullah and s. bhatia. “improved loose contact diesel soot oxidation by synergic effects between metal oxides in k2o-v2o5/zsm-5 catalyst.” catal. comm., 6 (31), 1196-1200, 2008. [11] m.s. ismail, a.r. mohamed and s. bhatia. “activity and characterization of bimetallic zsm-5 for the selective catalytic reduction of nox.” j. molec. catal. a, 189, 241-250, 2002. [12] c.m. de correa and f.c. castrillon. “supported bimetallic pd–co catalysts: characterization and catalytic activity.” j. molec. catal. a, 228, 267–273, 2005. [13] l. guczi and i. kiricsi. “zeolite supported monoand bimetallic systems: structure and performance as co hydrogenation catalysts.” appl. catal., 186, 375-394, 1999. [14] f. figueiredo. “synergistic effect between pt and k in the catalytic reduction of no and n2o.” appl. catal. b, 62, 181-192, 2006. [15] y. hesegawa, m. haneda, y. kintaichi and h. hamada. “zn-promoted rh/sio2 catalyst for the selective of no with h2 in the presence of o2 and so2.” appl. catal. b, 60 (1-2), 41-47, 2005. [16] a. bueno-lopez, m.j. illan-gomez and c. salinas-martinez. “effect of nox and c3h6 partial pressures on the activity of pt-beta-coated cordierite monoliths for denox c3h6-scr.” appl. catal. a, 302, 244-249, 2006. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 121 [17] h. abdullah. “bimetallic monolithic catalyst for selective catalytic reduction if nox in diesel engine exhaust.” msc. thesis, universiti sains malaysia, 2008. [18] n. nejar and m.j. illan-gomez. “potassium-copper and potassium-cobalt catalysts supported on alumina for simultaneous nox and soot removal from simulated diesel engine exhaust.” appl. catal. b, 70, 261-268, 2007. [19] a.z. abdullah, m.z.a. bakar and s. bhatia. “combustion of chlorinated volatile organic compounds (vocs) using bimetallic chromium-copper supported over modified h-zsm-5 catalysts.” j. hazard. mater., 129, 39-49, 2006. iium engineering journal, vol. 11, no. 1, 2010 abdullah et al. 122 nomenclature symbol definition unit whsv weight hourly space velocity h-1 α central composite design factor value dimensionless βo constant coefficient dimensionless βi coefficients for the linear effects dimensionless βii coefficients for the quadratics effects dimensionless βij coefficients for the interactions effects dimensionless y the response calculated by the model % microsoft word vol 6-2p6v2-press.doc iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 61 thermal shock in periodic edge-cracked plate supported by elastic foundation abd el-fattah a. rizk department of science in engineering,faculty of engineering, international islamic university malaysia, p.o. box 10, 50728, kuala lumpur, malaysia e-mail: abdelfattah@iiu.edu.my abstract: the study of the transient thermal stress problem for a periodic edge cracks in an elastic plate on an elastic foundations is investigated. this study may also be applied for circumferentially periodic cracked hollow cylinder under transient thermal stresses. based on previous studies, the cylindrical shell may be modeled by a plate on an elastic foundation. the thermal stresses are generated due to sudden convective cooling on the boundary containing the edge cracks while the other boundary is insulated. the superposition technique is utilized to solve the problem. the perturbation problem is formulated by using the thermal stresses obtained from uncracked problem with opposite sign on the crack surfaces as the only external loading. this leads to hypersingular integral equation with the crack surface displacement as the only unknown function. the main output of this study is the transient stress intensity factors that are evaluated numerically. the parametric studies based on time (fourier number), crack length, coefficient of heat transfer (biot number), periodic crack spacing and the stiffness of elastic foundation are investigated. keywords: fracture mechanics, thermal stresses, periodic crack, stress intensity factor. 1. introduction the transient thermal stress problem in an elastic plate has been wide investigated since it can be found in many engineering applications. it is well understood that, the thermal shock due to sudden cooling of the surface can result in very high tensile stresses near the surface. these stresses may be occurred catastrophic failure especially in presence of preexisting surface flaws. many studies have been investigated for a single crack in a semi-infinite and finite plate under thermal shock (see [1-6]). the analyses of thermal stress problems for multiple cracks are also considered in the literature. the problem of a periodic edge cracks with equally spaced in a long strip due to quenching using the boundary element method is investigated by bahr et al [7]. wang et al. [8] examined the multiple crack problem in functionally graded materials under thermal loading. the study of periodic cracking in a half plane under convective cooling using the principle of superposition is given by rizk [9]. also, the analysis of a periodic array of cracks in an infinite elastic strip under surface cooling and heating are investigated by rizk [10, 11]. the problem of periodic array of cracks in fully constrained infinite strip under thermal shock is also considered by rizk [12]. iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 62 in the present work the studying of periodic array of edge crack in an infinite plate on an elastic foundation is investigated. this study will also be useful to investigate the cylindrical shell having circumferentially periodic array of edge cracks under thermal shock. according to previous studies [13], the cylindrical shell can be modeled by a plate on an elastic foundation that may make the shell problem analytically tractable. in this analysis, it is assumed that the problem is linear. so, the superposition technique is utilized, i.e. the solution of the thermal problem is considered to be the sum of two solutions. the first solution is evaluated for the transient thermal stress problem without cracks. the second solution is obtained for the isothermal periodic crack problem in which the crack surface tractions that are equal and opposite to the thermal stresses obtained from the first solution are the only external loads. in addition, the transient thermal problem is assumed to be quasi-static (i.e. the inertia effects are neglected), and all thermoelastic coupling effects and the temperature dependence of the thermoelastic constants are neglected. note that, since the cracks are in x direction, they will not disturb the temperature and the stress distributions. by defining the unknown function in terms of crack surface displacement, the perturbation problem will be reduced to hypersingular integral equation. the expansion method is adopted and the principle of finite-part integral developed by kaya and erdogan [14, 15] are used for numerical solution. the important parameter that needs to predict mechanical failure in the subcritical crack growth is the stress intensity. so, the main results of this work are the variation of the stress intensity factor as a function of time (fourier number), coefficient of heat transfer (boit number), crack length, periodic crack spacing and the stiffness of elastic foundation. 2. mathematical formulation consider the plane strain problem for an elastic infinite strip of thickness h at initial temperature ot with periodic cracks of length )( ab  spaced out by c2 is elastically supported with coefficient  as shown in fig. 1. the edge crack case will be considered by taking 0a . the surface containing the edge cracks )0( x is suddenly exposed to convective cooling at temperature at with heat transfer coefficient h . the other surface )( hx  that is supported by elastic foundation is assumed to be insulated. the thermal stresses for the transient thermal stress uncracked problem can be set up by solving first the diffusion equation with proper boundary conditions using lapalce transform technique to obtain the transient temperature distribution as developed in [5] and it is given by 2 1 *** 2sin5.0 )1(cossin 2 ),(),( n n nn nn ao a o e x tt txtx               (1) iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 63 fig.1: periodic crack geometry where, hxx /*  , 2/ htd (fourier number), d is the thermal diffusivity and n is the roots of the equation binn  tan , where bi is the biot number that is defined by '/ khhbi  , and 'k is the material thermal conductivity. the thermal stresses for elastically supported plate can be obtained by observing that the plate will remain flat under self-equilibrating transient thermal stresses, i.e. the plate undergoes uniform strain over the thickness h . following [16] the transient thermal stresses as a result of the transient temperature attxttx  ),(),( are given by           ),(),( 1 )1( ),( 0 txdxtx h e tx h t yy    (2) where e is the young’s modulus,  is the poisson’s ratio and  is the coefficient of linear thermal expansion. by substituting equation (1) into equation (2), the transient thermal stresses would be in the form 2 2 1 * 1 2* 2sin5.0 )1(cossin 2 )2sin5.0( sin 2 )( )1)(,( n n e x e tte x n nn nn n nnn n ao t yy                                  (3) the analysis of the circumferential cracked problem in a cylindrical shell may be approximated by a plate supported by elastic foundation under plane strain conditions. previous studies showed the validity of this assumption [13] and the stiffness of the elastic foundation is given by iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 64 2 nr eh  (4) where e is young’s modulus, h is the thickness of the cylinder )( io rr  , or is the outer radius, ir is the inner radius, and nr is the mean radius of the cylinder. the plane strain problem shown in fig. 1 may be formulated by solving the following governing differential equations 0)(2)1( 2 2 2 2        yx v x u u (5) 0)(2)1( 2 22 2        y v yx u v (6) where )43(   for plane strain, )1/()3(   for plane stress, and vu, are the x and y components of the displacement vector. because of periodicity, the local perturbation problem is considered, i.e. cy 0 , and the problem should be solved under the following homogeneous and mixed boundary conditions: 0)0,( xxy , 0),( cxxy , 0),( cxv , hx 0 (7) 0),0( yxx , 0),0( yxy , cy 0 (8) ),(),( yhuyhxx   , 0),( yhxy , cy 0 (9)       )(,),()0,( )(,0,0)0,( bbxatxx ahxbaxxv t yyyy  (10) where ),,( yxjiij  are the stresses,  is the stiffness of the elastic foundation and ),( txtyy is the thermal stress obtained from the uncracked problem. the solution of the mixed boundary value problem described by equations (5)-(10) may be obtained by expressing the displacement components in terms of sums of finite and infinite fourier transform [17]:     deypyxfyxu ix n nn       ),( 2 1 cos),(),( 0 (11)     deyqyxgyxv ix n nn       ),( 2 1 sin),(),( 1 (12) iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 65 where cnn /  . by substituting equations (11) and (12) into equations (5) and (6), and by solving ordinary differential equations, the displacements vu, may be expressed as             deeyddd eyddd i yexccexccyxu ixy y n nx n nx                  )( )( 2 1 cos])()[(),( 443 221 43 0 21 (13)             deeyddeydd yexccc excccyxv ixyy n nx n n nx n               )()( 2 1 sin)( )[(),( 4321 443 1 221 (14) where the unknown functions )4,3,2,1( idi and )4,3,2,1( ici are functions of the transform variables  and n respectively. using the stress-strain relations, the straindisplacement relations and equations (13) and (14), the stress components xx , yy , xy may be given by                  deeyddd eyddd yecxcc ecxccyx ixy y n nx nn n nx nnxx                        ) 2 3 ( ) 2 3 ( 2 1 cos]) 2 1 ( ) 2 1 [(),( 2 1 443 221 443 1 221 (15) iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 66                  deeyddd eyddd yecxcc ecxccyx ixy y n nx nn n nx nnyy                        ) 2 1 ( ) 2 1 ( 2 1 cos]) 2 3 ( ) 2 3 [(),( 2 1 443 221 443 1 221 (16)                  deeyddd eydddi yecxcc ecxccyx ixy y n nx nn n nx nnxy                        ) 2 1 ( ) 2 1 ( 2 1 sin]) 2 1 ( ) 2 1 [(),( 2 1 443 221 443 1 221 (17) where )1(2/   e is the shear modulus. seven of these unknown functions can be eliminated by the conditions (7-9). by defining the new function )0,()( xvx  and using the mixed boundary condition (10), the problem will be reduced to the following singular integral equation for the unknown function )( x     b a t yy y txdsssyxksyxk ),( 4 )1( )()],,(),,([ 21 0 lim     (18) where the kernels 1k , 2k are given by           0 22 24 1 )1( ])12()1[( ),,(    c ycc e eecyey syxk     dxs e eyeyc c yc )cos( )1( )]1()12[( 22 2              1 2 cos][2 1 ),,( n n yiiimc syxk   iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 67 nhxs nn nhxs nnn nhxs nnnn nhxs nnn exs esxsx ehxshsxhhhsx ehxhssxhi         )4(2 )4(32 )2(432 )2(3(2 )](26[ ]4)(610[ )](8)(12)10(26[ )])((4)2(610[          nhxsnn nhxs nnn nhxs nnn nhxs nn n exs esxsx exhssxh esxh            )4(2 )4(32 )2(32 )2(2 )](26[ ]4)(610[ )]2(4)2(610[ )]2(26[ 2 1 2           nhxs nnn nhxs nn nxs nnn nhxs nnnn exhshsxh exs esxsx ehsxhhsxhhxsii         )2(32 )4(2 )(32 )2(432 )])((4)2(612[ )](26[ ]4)(610[ )](8)(12)10(26[          nhxsnn nhxs nn nhxs nnn nxs nnn n exs esxh eshxsxh esxxs            )4(2 )2(2 )2(32 )(32 )](26[ )]2(26[ )]2(4)2(610[ ]4)(610[ 2 1 2           )41( 2 1 2 )42(1 424222 hnhnn n hnhn n eheeehm           the singular terms must be separated from the kernels 1k and 2k before solving the integral equation (18). by examining the asymptotic behavior of 1k for  , 0)(  xs and taking the limit 0y , it is found that ),( )( 1 ),,( 121 0 lim sxk xs syxk f y     (19) where ),(1 sxk f is bounded term and it is given by     dxs e ece sxk c cc f )cos( )1( )12(22 ),( 0 22 24 1              (20) iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 68 the kernel 2k is bounded for embedded crack ),0( hba  , and as the crack approaches the boundary )0( a some terms will be unbounded and the asymptotic behavior of 2k for n and 0)(  xs would be ),(),(),,(lim 2220 sxksxksyxk a f y    (21) where ),(2 sxk f is bounded term and ak 2 is unbounded term that is given by yesxxs c sxk n n nxs nnn y a    cos]2)(35[lim),( 1 )(32 0 2        (22) after summing the series and taking the limit, the generalized singular terms may also be separated i.e. ),(),(),( 222 sxksxksxk s a f aa   (23) where 4 2 322 )( 12 )( 12 )( 1 ),( xs x xs x xs sxk sa        (24) then the singular integral equation (18) may be expressed as ),( 4 )1( )(),( )( )( 2 txdsssxkds xs s t yy b a b a          (25) where ),(),(),(),(),( 2221 sxksxksxksxksxk s a f a ff  the solution of the integral equation would be based on the behavior of the unknown function )(s that can be obtained by following muskhelishvili technique [18] and the concept of finite part-integral described by kaya and erdogan [14, 15]. let )(s will be in the form 21 )())(()(  sbassfs  (26) where the unknown function )(sf is bounded with 0)( af , 0)( bf , and 21 , would depend on the location of the crack tip. it can be shown that for an impeded crack 2/121   ),0( hba  , and for an edge crack ),0( hba  2/1,0 21   . by defining the stress intensity factor at the crack tip b as iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 69 )(2 )0,( 1 4 )0,()(2)( limlim xb xv xbxbk bx yy bx       (27) and since xbxfxv  )()0,( for an edge crack, the stress intensity factor at the edge b becomes 2 )( 1 4 )( bf bk     (28) 3. numerical solution to evaluate the stress intensity factor given by equation (28), it is required to solve the singular integral equation (25) for the unknown function )(sf . first it is normalized by the following variables 22 ab r ab x     , 22 abab s      (29) )( 2 )(         ab s , ),( 2 ),( 2 sxk ab rh        (30) giving     1 1 1 1 2 )(),( )( )(    drhd r ),( 4 )1( trtyy    , 11  r (31) also from equations (26) and (29), )( may be written as 21 )1()1)(()(    f (32) where )(f is the new unknown function that may be approximated by truncated series as n n n naf     0 )( (33) where na are )1( n unknown coefficients to be determined. after substituting equations (32) and (33) into equation (31), we end up with )1( n linear equations that are solved at certain collocation points which are selected to be to the zeros of chebychev polynomial of order )1( n , i.e. 1,...,2,1, )1(2 )12( cos     nj n j r j  (34) iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 70 x/h 0.00 0.20 0.40 0.60 0.80 1.00  yyt ( x* , ) ( 1  ) / e  (t a t o ) -0.40 -0.20 0.00 0.20 0.40 0.60 0.80 1.00 0.001= 0.01 bi = 8 0.1 0.5 1.0 x/h 0.00 0.20 0.40 0.60 0.80 1.00  yyt ( x* , ) ( 1 ) / e  (t a t o ) -0.4 -0.2 0.0 0.2 0.4 0.6 0.8  = 0.001 0.01 0.1 0.5 1.0 bi= 20 following the technique developed by kaya and erdogan [14,15], the unknown coefficients na can be determined and then the stress intensity factors can be evaluated. 4. results figure 2 shows sample results of the normalized transient thermal stresses versus normalized distance hx / calculated from equation (3) for two values of biot number 20,bi and different values of normalized time (fourier number) 001.0 , 01.0 , 1.0 , 5.0 , 0.1 . from the stress profiles it can be observed that, for bi which corresponds to the unit step function temperature change on the boundary leads to highest transient thermal stresses compared to the values obtained for 20bi . at any instant of time the thermal stresses is tensile in the region near the cooled surface and compressive in region near the insulated surface which satisfy zero resultant force at any cross section of the plate. also the effect of the time (fourier number) on thermal stresses can be seen in the figure. the gradient of the thermal stresses is decreasing as the time increases and reaching zero value for large time. fig. 2: transient thermal stresses for bi and 20bi iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 71 time,  0.001 0.01 0.1 1 k (b ) ( 1 ) / e  (t o t a ) b 1/ 2 0.0 0.1 0.2 0.3 0.4 0.5 h/e= 0.00238 0.01108 0.08163 1.0 8 0.00238, 0.01108 0.08163 1.0 8 0.00238 0.01108 0.08163 1.0 8 0.05= 0.1 0.3 =h/e h/e= b/2c the influence of the normalized stiffness of the elastic foundation eh / on the normalized stress intensity factors defined by bttebk ao )(/)1)((   is given in fig. 3 for different values of 00238.0/ eh , 01108.0 , 08163.0 , 0.1 ,  which are corresponding to 20/ hri , 9 , 3 , 5.0 respectively, except for eh / which is related to fully constrained boundary as given by rizk [12]. . the results are obtained for normalized crack length 3.0/ hb , biot number bi , which is the most severe case, and three values of normalized periodic crack spacing 05.02/ cb , 1.0 , 3.0 . infact, the values of 3/ hri and 5.0 represent thick hollow cylinders which can not be modeled by a plate on an elastic foundation. the figure shows great effect of the normalized stiffness eh / on the normalized stress intensity factors especially for small normalized periodic crack spacing )05.02/( cb . as the normalized stiffness increases the normalized stress intensity factors decrease and the smallest values would be for the case of fully constrained boundary eh / . the effect of the normalized crack spacing )2/( cb on the normalized stress intensity factors is also exposed in the figure. if the numbers of the cracks increase per unit length ( cb 2/ increases) the normalized stress intensity factors are decreasing consequently and the effect of the normalized stiffness becomes less. for 1.02/ cb the values of the normalized stress intensity factors for 00238.0/ eh , 01108.0 ( 20/ hri , 9 ) are almost the same. for 3.02/ cb the values of the normalized stress intensity factors are approximately equal for all given values of 00238.0/ eh , 01108.0 , 08163.0 , 0.1 ,  and they are represented in the figure by one curve which corresponds to the fully constrained boundary problem. so the elastic foundation will perform as a fully constrained boundary when the cracks become closer to each other. fig. 3: stress intensity factors for different values of eh / , 3.0,1.0,05.02/ cb , 3.0/ hb , bi the variation of the normalized stress intensity factors versus time is represented in fig. 4 for varying values of normalized periodic crack spacing 0.02/ cb , 1.0 , 2.0 , 3.0 , 5.0 . the results are shown for 4.0/ hb , bi and two values of normalized iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 72 stiffness  ,01108.0/ eh . it can be seen that the normalized stress intensity factors decrease as the normalized periodic spacing increases ( c decreases) and the most dangerous case would occur for 0.02/ cb which is related to single crack problem. for large normalized periodic crack spacing ( 5.02/ cb ) the variation of the normalized stress intensity factors for  ,01108.0/ eh are almost identical and they would approach the fully constrained boundary case ( eh / ). also for large cb 2/ the normalized stress intensity factors start to be negative while they are always positive for single crack ( 0.02/ cb ). the negative values of the normalized stress intensity factors are meaningless because crack closure occur, or it is meaningful only when these results are used in a superposition and the stress intensity factors are positive. fig. 4: stress intensity factors for different values of cb 2/ ,  ,01108.0/ eh , 4.0/ hb , bi figure 5 displays the variation of the normalized stress intensity factors versus normalized time for varying normalized crack length 05.0/ hb , 1.0 , 2.0 3.0 , 4.0 , 5.0 . the calculations are based on 1.02/ cb , bi and two values of normalized stiffness  ,01108.0/ eh . as expected, the largest normalized stress intensity factors would occur for small crack which lies completely in the tensile region and as the normalized crack length increases the normalized stress intensity factors decrease due to the increasing effect of the compressive stresses in the interior of the plate. noted that, for small crack ( 05.0/ hb , 1.0 ), the normalized stiffness has weak effect on the normalized stress intensity factors while it has great effect for large crack ( 5.0,4.0/ hb ). tim e,  0 .00 1 0 .01 0 .1 1 k (b ) ( 1  ) / e  (t o t a ) b 1/ 2 -0.1 0 .0 0 .1 0 .2 0 .3 0 .4 0 .5 b/2c= 0.0 0.1 0.2 0.3 0.5 =h /e0.01108 8 iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 73 time,  0.001 0.01 0.1 1 k (b ) ( 1 ) / e  (t o t a ) b 1/ 2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 =b/h0.05 0.1 0.2 0.3 0.4 0.5 =h/e0.01108 8 fig. 5: stress intensity factors for different values of hb / ,  ,01108.0/ eh , 1.02/ cb , bi finally, fig. 6 shows the effect of the biot number on the normalized stress intensity factors for different values of 1bi , 5 , 10 , 20 ,  and two values of normalized crack length 1.0/ hb , 5.0 . the results are obtained for 1.02/ cb and 01108.0/ eh . it is clear that the normalized stress intensity factors are reducing by decreasing the biot number due to the decreasing in the thermal stresses and the most severe case will be for unit step function temperature change on the boundary (  ). the effect of the normalized crack length on the normalized stress intensity factors is also shown in the figure by reducing it as the hb / increases. time,  0.001 0.01 0.1 1 k (b ) ( 1  ) / e  (t o t a ) b 1/ 2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 bi= 8 20 10 5 bi= 1 = b/h0.1 0.5 fig. 6: stress intensity factors for different values of bi , 5.0,1.0/ hb , 01108.0/ eh , 1.02/ cb . iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 74 5. conclusion in this paper, the effect of the stiffness of elastic foundation ( eh / ), the periodic crack spacing ( cb 2/ ), the heat transfer coefficient (biot number, bi ), the crack length ( hb / ) and the time (fourier number, 2/ htd ) on the stress intensity factors are investigated. the stiffness of the elastic foundation has quit effect on the stress intensity factors especially for large crack and large periodic crack spacing ( cb 2/ small) by reducing the normalized stress intensity factors as the normalized stiffness increases. for small crack the elastic foundation has very small effect on the stress intensity factors. by increasing the crack length the normalized stress intensity factors decrease accordingly. the periodic crack spacing has a great effect on the stress intensity factors. as cb 2/ increases ( c decreases), the crack interaction will reduce the the normalized stress intensity factors and the effect of the stiffness of the elastic foundation will approach the fully constrained boundary case. in addition the increasing hb / and cb 2/ the normalized stress intensity factors started to be negative leading to the crack surfaces to be in contact along certain contact length from the edge crack b . also it is shown that the normalized stress intensity factors would be reduced with decreasing the biot number. references [1] h.f. nied, "thermal shock in an edge-cracked plate," journal of thermal stresses, vol.1, pp. 217-227, 1983. [2] h.-a. bahr, h. balke, m. kuna, and h. liesk, "fracture analysis of a single edge cracked strip under thermal shock," theoretical applied fracture mechanics, vol. 8, pp. 33-39, 1987. [3] a.a. rizk and s.f. radwan, "transient thermal stress problem for a cracked semi-infinite medium, "journal of thermal stresses, vol. 15, pp. 451-468, 1992. [4] x. fan and s. yu, “thermal shock in a surface-cracked plate”, engineering fracture mechanics, vol. 41, 1992. [5] a.a. rizk, "edge-cracked plate with one free and one constrained boundary subjected to sudden convective cooling," journal of thermal stresses, vol. 1, pp. 455-471, 1994. [6] a.a rizk, ”fracture of shells and plates on an elastic foundation under convective cooling”, alexandria engineering journal, vol. 33, no. 3, pp. 121127, 1994. [7] h.a. bahr, h.j. weiss, h.g. maschke, and f. meissner, "multiple crack propagation in a strip caused by thermal shock," theoretical and applied fracture mechanics, vol. 10, pp. 219-226, 1988. [8] b.l., wang, j.c. han, s.y du, "thermoelastic fracture mechanics for nonhomogenous material subjected to unsteady thermal load," asme journal of applied mechanics, vol. 67, pp. 87-95, 2000. [9] a.a. rizk, "transient stress intensity factors for periodic array of cracks in a half-plane due to convective cooling, " journal of thermal stresses, vol. 26, pp. 443-456, 2003. [10] a.a. rizk, "peiodic array of cracks in a strip subjected to surface heating," international journal of solids and structures, vol. 41, pp. 4685-4696, 2004. [11] a.a. rizk, “convective thermal shock of an infinite plate with periodic edge cracks”, journal of thermal stresses, vol.28, pp. 103-119, 2005. iium engineering journal, vol. 6, no. 2, 2005 a. a. rizk 75 [12] a.a. rizk, ”periodic edge cracks in fully constrained infinite elastic strip under thermal shock”, 8th international conference on production engineering, design, and control (pedac’2004), alexandria university, alexandria, egypt, 27-29 dec. 2004. [13] a.p. boresi and r.j. schmidt, “advanced mechanics of materials”, 6th edition, john wiley, 2003. [14] a.c. kaya and f. erdogan, "on the solution of integral equations with strongly singular kernels," quarterly of applied mathematics, xlv, pp. 105-122, 1987. [15] a.c. kaya, and f. erdogan, "on the solution of integral equations with generalized cauchy kernel," quarterly of applied mathematics, xlv, pp.455-469, 1987. [16] b.a. boley and j.h weiner, "theory of thermal stresses", john wiley, 1960. [17] g.w. schulze and f. erdogan, "periodic cracking of elastic coatings," international journal of solids and structures, vol. 35, pp. 3615-3634 , 1998. [18] n.i. muskhelishvili, "singular integral equations," noordhoff, groningen, the netherlands, 1953. microsoft word 3_v17no2_compiled_v3_26nov16.docx iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 169 novel control strategy for gridconnected photovoltaic arrays reza noroozian*1 and goverg b. gharehpetian2 1department of electrical engineering, faculty of engineering, university of zanjan, p.o. box 45371-38791, zanjan, iran. 2faculty of electrical engineering, amirkabir university of technology, tehran, iran. *corresponding author: noroozian@znu.ac.ir (received: 10t h jul. 2013; accepted: 13th mar. 2016; published on-line: 30th nov. 2016) abstract: pv generation systems have received much attention in recent years due to their suitable properties which offer important economic benefits. however, they are developing increasingly fast as a renewable energy resource. in this work, the configuration of pv generation systems, a dynamic model for pv modules, and their power electronic interfacing have been presented. a novel control strategy for the dcdc converter has been developed in order to extract the maximum amount of power from the pv array. also, a novel control strategy, which is based on a d – q rotating reference frame, has been proposed for the dc-ac converter. the proposed controllers have been used to transfer the pv output power and synchronize the interfacing power converters with the ac grid. the controller designs for different operating conditions of dc-ac converter, using the average large signal model, have been presented. based on the dynamic models, a simulation model for the pv generation systems has been developed using pscad/emtdc. simulation studies have been carried out to verify the dynamic performance of grid-connected pv systems under different operating conditions. the simulation results show that the novel control structure can transfer dc energy from the pv array, compensate the power factor of the ac grid, and improve the dynamic behavior of the grid-connected pv system. the simulation results show the effectiveness of the suggested control systems in grid-connected mode. abstrak: sistem penjanaan pv mendapat perhatian di dalam tahun kebelakangan ini kerana sifatnya yang sesuai dan ia menawarkan faedah ekonomi yang penting. ia semakin pesat berkembang sebagai sumber tenaga yang boleh diperbaharui. kajian ini membentangkan konfigurasi bagi sistem penjanaan pv, model dinamik untuk modul pv dan pengantaramukaan elektronik kuasa. satu strategi kawalan baru untuk penukar dcdc telah dibina untuk mengekstrak jumlah kuasa maksima daripada pelbagai pv. juga, strategi kawalan baru yang berdasarkan kepada rangka rujukan berputar d – q, telah dicadangkan untuk penukar dc-ac. alat kawalan yang dicadangkan telah digunakan untuk memindahkan kuasa output pv dan menyegerakkan pengantaramukaan penukar dengan grid ac. reka bentuk alat kawalan untuk keadaan operasi penukar dc-ac yang berbeza telah dibentangkan dengan menggunakan purata model signal besar. berdasarkan model dinamik, model simulasi bagi sistem penjanaan pv telah dibina dengan menggunakan perisian pscad/emtdc. kajian simulasi telah dijalankan untuk mengesahkan prestasi dinamik sistem pv tersambung grid di dalam keadaan operasi yang berbeza. keputusan simulasi menunjukkan bahawa struktur kawalan baru boleh memindahkan tenaga dc dari tatasusunan pv, mengimbangi faktor kuasa ac grid dan memperbaiki tingkah laku dinamik sistem pv tersambung grid. keputusan simulasi menunjukkan keberkesanan sistem kawalan yang dicadangkan dalam mod tersambung grid. keywords: grid-connected pv system; power electronic interface; modeling; control iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 170 1. introduction solar energy has great potential to supply energy for the future with minimum impact on the environment since solar energy is clean, pollution-free, and inexhaustible. with the decrease in the price of photovoltaic (pv) modules and the increase in the price of conventional petrochemical fuels for energy generation, the application of the pv generation system becomes more practical, feasible, and realizable [1, 2]. pv cells are normally connected together to make up modules, which can be combined into pv arrays as required. therefore, power electronic circuits are an enabling technology that is necessary to convert direct current (dc) electrical power generated by a pv array into usable alternating current (ac) power for grid support or supplying special loads [1-5]. the pv array is interfaced with the utility network via boost dc-dc converters and a three-phase pulse-width modulation (pwm) dc-ac converter. the dc voltage generated by a pv array varies widely but is generally low in magnitude. therefore, a boost dc-dc converter is necessary to generate a regulated higher dc voltage for desired converter input voltage. generally, the grid connected pv systems extract maximum power from the pv arrays. the maximum power point tracking (mppt) technique is usually associated with dc–dc converters. the dc-ac voltage source converter (vsc) is employed to interface pv array energy systems with the utility grid under both on-grid and off-grid operations [1, 3]. the dc–ac converter injects sinusoidal current into the grid, controlling the power factor [1-5]. many different topologies of power inverter for grid connected pv systems have been used. the parallel inverter with a common dc bus has optimal operation strategy [6]. in this topology, the power inverter converts the dc output of the pv modules into an ac output. the control strategy of the dc-ac converter should be able to deliver a preset amount of active and reactive power to the grid or supply an isolated unbalanced ac load by balanced ac voltage with constant magnitude and frequency. therefore, the dc-ac converter controller in on-grid mode controls the active and reactive power flows to the utility grid. in [7-11], a novel and simple control system based on instantaneous power control strategy has been developed for dc-ac converters. this paper presents a dynamic model of a pv array and its power electronic interfacing. a novel control strategy of the dc-dc converter has been developed, too, in order to extract the maximum amount of power from the pv array. also, a new control strategy based on a d – q rotating reference frame has been presented for the dc-ac converter. this system is capable of transferring energy from the pv power plant to a threephase ac system with control of active and reactive power and without injecting harmonic currents. reactive power compensation at the point of common coupling (pcc) is investigated, too. also, the injected reactive power can be dynamically controlled. the effectiveness of the proposed system has been verified by simulations. the simulation results show that the novel control structure can adjust the dc energy, compensate for the power factor of the utility grid and improve the dynamic behavior of the grid-connected pv system. this paper is organized as follows: the grid-connected pv system configuration is described in section 2. in section 3, the dynamic models for the pv module are introduced. the proposed power control converters are presented section 4. sections 5 and 6 discuss the simulation results and conclusion, respectively. iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 171 2. grid-connected pv system configuration figure 1 shows the block diagram of the grid-connected pv generation system analyzed in this paper. a validated 200 w pv module is used to model the pv power plant [12]. the pv power plant consists of five pv modules connected in parallel. the dc-dc boost converters drain the energy from the photovoltaic module and feed the dc bus capacitor with mppt control. the dc-dc converter is used to boost the low dc voltage. in this paper, the dc bus voltage (dc-dc converter output) is vdc = 750 v. the proposed control structure for each dc-dc converter is designed to keep this dc bus voltage within a specified limit (i.e., ±5%). the dc-ac converter is a three-phase six-switch vsc current controlled with neutral clamped dc capacitors, that interfaces the dc bus with a utility 220 v / 240 vac grid. an lc filter has been used at the output of the converter to filter the switching frequency harmonics. the dc-ac converter controller controls the active and reactive power delivered from the pv generation system to the utility grid. supercapacitors or battery banks are connected to the dc bus to provide energy storage capability under different operating conditions. dc ac bank battery or capacitors -super filter lc meter current and voltage hz 50 kv 0.4 gridutility signals control signals reference bus dc signals actual vsc dc dc #1converter boost #1 module pv ag at signal control controller dc/dc meter voltage signals actual meter current and voltage dc dc #5converter boost ag at meter current and voltage plantpower pv controller converter dc/ac signals actual signals actual #5 module pv fig. 1: block diagram of the grid-connected pv generation system. 3. dynamic models for the pv module in an array, several pv modules have been connected in a series and parallel to obtain a suitable power rating. also, the pv cells are connected in series and parallel in a module. the most commonly used model for a pv cell is the dc current source (il) with a diode connected in parallel as shown in fig. 2 [13, 14]. the dc source current depends on ambient temperature (ta) and solar irradiation (ga). the resistance rs represents the losses and voltage drop in the circuit. also, the resistance rp represents the reverse of the diode. in this paper, the pv dynamic model, reported in [15], has been used to model the pv arrays. the pv array can be modeled by temperature and irradiation dependent v – i characteristic. it is important to use the pv system near its maximum power point to increase the efficiency of the photovoltaic array. therefore, the optimal operating voltage has to be applied to achieve maximum power. this can be realized using a mppt algorithm [4, 5]. in this study, a suitable voltage-based mppt controller for the optimum iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 172 operation of the pv modules has been used. the parameters of a 200-w pv data (spr200-blk [12]) have been used for pv array simulations. the output characteristics curves for the pv array subjected to varying solar irradiance are shown fig. 3. as can be seen in fig. 3, variations of solar irradiance have a great impact on the pv array’s generated power [16-18]. fig. 2: model of a single pv cell. fig. 3: characteristic curves of the pv array with different solar irradiations. 4. proposed control of power converters the current controller for the power converter can be a closed loop pwm scheme, such as hysteresis current control (hcc), linear pwm, predictive controllers, optimized controllers, neural networks, and fuzzy logic controller systems [7-11]. in comparison to open loop pwm techniques, closed loop pwm schemes have several considerable advantages, such as extremely good dynamics, instantaneous peak current control, and prevention of overload and pulse dropping problems [7-11]. hcc has stability, which is provided by maintaining the current errors within the hysteresis band. thus, hcc has been selected in this paper. the power converters’ controller provides the reference current for the hcc. its instantaneous power regulation has a much faster response when compared to average power regulation [16]. therefore, instantaneous power regulation has been used for the converter in this paper. as a result, the reference currents for the closed loop pwm sr dili ag at i v   pr iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 173 scheme of the converter are calculated using the instantaneous active and reactive powers concept. the instantaneous powers can be expressed in either a synchronous or a stationary reference frame. in this paper, a synchronously rotating frame is used for the converter reference current generation. 4.1 control system of boost converters the proposed control strategy of the dc-dc boost converter is shown in fig. 4. this system specifies the reference current, reffpvi for the hcc scheme. the hcc system regulates the boost converter inductor current, ifpv, within the hysteresis band. the converter manages the amount of the current injected to the dc bus. fig. 4: proposed control system for each boost converter. in this control structure, the reference active power, ppv is obtained by the mppt control algorithm. the reference current, reffpvi , is expressed as: pv pvref fpv v p i  (1) the comparison of the calculated reference currents, reffpvi , with the actual current generated by the boost converter, ifpv will result in an error signal, which is fed to the hcc system in order to determine the switching pattern of the dc-dc boost converter. the inductor of each boost converter is designed to make its current track the reference current within the hysteresis band. thus, the inductor l for each boost converter is obtained by the following equation [7]: max,. 4 s ref dc fh v l  (2) where, h is the hysteresis band and fs,max is the maximum switching frequency of the boost converter. 4.2 control structure of the dc-ac converter the dc-ac voltage source converter must act as a power controller between the utility grid and the dc bus. the grid-connected (or on-grid) operation allows the converter to operate parallel to the grid, providing grid support. the average large signal model of the dc-ac converter is shown in fig. 5. this converter has been modeled with three pwm hcc meter current meter current voltage bus dc pvipvv max pvi ref fpvi fpvi l converterboost c min pvi array pv ag at controller current reference mppt pvp iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 174 current sources reffai , ref fbi and ref fci . the converter manages the current injected into the utility. since the current generated from the converter can be controlled independently from the ac voltage, the active and reactive power controls are decoupled. as can be seen in fig. 5, the input signals of the dc-ac converter are source phase voltages, (vsa, vsb, and vsc), the source phase currents, (isa, isb and isc), three-phase output currents for this converter (ifa, ifb and ifc), the dc bus voltage (vdc), the reference of the dc bus voltage ( refdcv ), and the output active power of the pv power plant (ppvs). lf is the inductance of the converter filter. rg and lg are the resistance and inductance of the ac grid, respectively. this controller uses the hcc switching technique. as can be seen in fig. 5, we have:                      fc fb fa sc sb sa i i i i i i (3) fig. 5: average large signal model of the dc-ac converter. figure 6 shows the dc-ac converter control system in the grid-connected operation. in this paper, a novel control strategy has been designed based on the instantaneous power control strategy. using d – q reference frames, the coupled dynamics of the current tracking problem have been transformed into decoupled dynamics. applying the park transformation, the source currents and voltages are converted from the three-phase coordinates to a synchronously rotating frame by eqs. (4) and (5), where θ is the instantaneous angle of the network voltage vector, which is obtained from the phase locked loop (pll) circuit.                 sc sb sa dq sq sd v v v t v v (4)                 sc sb sa dq sq sd i i i t i i (5) dci fav fbv fcv fai fbi fci fl sav sbv scv sai sbi sci gl gr ref fci ref fai ref fbi controller converter dc/ac sa v sbv scv fai fbi fci hz 50 kv 0.4 grid ac   1c 2c pvsp refdcv saisbiscidcv dcv iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 175          )120sin()120sin()sin( )120cos()120cos()cos( 3 2   ttt ttt tdq   in these equations, vsd and vsq are the d – q components of the source voltages, in the synchronously rotating frame, respectively. isd and isq are the d – q components of the source currents. the instantaneous active power is given as follows: sqsqsdsd ivivppp  ~ (6) the superscripts (-) and (~) in eq. (6) denote the average and oscillatory components of the instantaneous active power, respectively. p is the average value of the instantaneous active power (p). this is the energy per time unit transferred from the source to the load, in a balanced way through 3 phases. p~ is the oscillating term of the instantaneous active power. it is the energy per time unit, which is exchanged between the power source and the load, through 3 phases. in this paper, the instantaneous active power components, which will be injected by the dc-ac converter to the ac grid, (pref), include the undesired power quality problems (harmonics, unbalance and reactive power) and the energy available in the pv generating system, i.e.: pppp regpvsref ~ (7) fig. 6: control system of the dc-ac converter. in fig. 6, the power obtained by the mppt controller, ppvs corresponds to the output power available from the pv arrays. the instantaneous active power is passed through the high pass filter (hpf), which removes the low frequency components of the active power. this filtered signal is used for the dc-ac converter, which compensates the harmonics and unbalancing. controller current hysteresis ref sqi ref sdi filter lc bus dc meter current meter current & voltage g ri d a c ref fci ref fbi ref fai fabci sabcv      transform inverse qd   transform qd  lqvldvsqisdi p sabcihpf refp p~ lqv ref dcv dcv pi lpf ev meter voltage pll    regp transform qd  pvsp  iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 176 the dc bus voltage regulator determines the power preg. the dc bus voltage passes through a pi controller and then it is subtracted from ppvs. this power balance and switching losses can decrease the dc bus capacitor. let the voltage error, ve between the reference dc bus voltage and the measured dc capacitors voltages be defined as follows: dcvrefdc vev  , (8) adjusting the gains of the pi compensators, a fast tracking and zero steady state errors can be achieved. the voltage error has been regulated by a proportional-integral (pi) controller, then, we have:  te vkevkreg p ip d (9) the transformation of the balanced source voltages d – q axis of the synchronously rotating frame results in the following equation: 0sdv and 3 2 4.0sqv (10) substituting the eq. (6) into eq. (10) yields: sq sq v p i  (11) using eq. (11), the reference current of the dc-ac converter in q axis can be expressed by the following equation: q refref sq v p i  (12) where, refsqi is the direct component of the reference current of the converter. this component is also responsible for feeding the losses in both the converter and the capacitor. the resultant d component is responsible for the reactive power flow through the utility network. to compensate for the reactive component, the quadrature component of the reference current of the dc-ac converter can be equal to the quadrature component of the source current: sd ref sd ii  (13) considering the reactive power generation limit of the pv plant and the size of dcac converter, a limiter can be used for refsdi to represent the permissible range. the d – q inverse transformation block, shown in fig. 6, calculates the three-phase current references to be fed into the hcc scheme. thus:                  ref sq ref sd abc ref sc ref sb ref sa i i t i i i (14) iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 177               )120sin()120cos( )120sin()120cos( )sin()cos(   tt tt tt tabc                         ref sc ref sb ref sa ref fc ref fb ref fa i i i i i i (15) hcc is a closed loop control for the current of dc-ac converter. the comparison of the calculated reference currents and the actual compensator currents generated by the dc-ac converter will result in an error signal, which controls the switches of the converter. when the error reaches the upper limit of the hysteresis comparator, igbts are switched to increase the current, and when the error reaches the lower limit, the current is forced to decrease. this procedure leads to the fast dynamic response that characterizes hcc among other current control techniques. the range of the error signal, h, directly controls the amount of ripples in the output current of the dc-ac converter and is called the hysteresis band. the current is forced to stay within these limits even while the reference current is changing. 5. simulation results in this paper, to evaluate the performance of the pv generation system, the proposed control structure and the on-grid operating condition have been modeled and simulated by psacd/emtdc. the simulation results show the ability of the proposed system to transfer dc energy from the pv unit to the ac grid with high power quality under on-grid operating conditions. the novel control strategy of the dc-ac converter with neutral clamped dc capacitors has been studied in on-grid operation modes. in the simulations, the rated power for each pv unit is assumed to be 25 kw. the ambient temperature (ta) is assumed to be 25 oc. it is also assumed that the reference dc voltage is 750 v and the nominal droop is 5 percent. 5.1 solar radiation changes in this section, the evolution of some characteristics of the grid-connected pv system during daytime and nighttime modes in solar radiation has been studied. the solar irradiance, ga is shown in fig. 7(a). as shown in fig. 7(a), the irradiance has been changed from 0.8cos(2πt) kw/m2 to zero at t = 2.25 s and then from zero to 0.8cos(2πt) kw/m2 at t = 2.75 s. when 1.75 < t < 2.25 s and 2.75 < t < 3.25 s, the all pv units are operated in daytime mode. when 1.50 < t < 1.75 s, 1.25 < t < 1.75 s and 3.25 < t < 3.50 s, all pv units are operated in nighttime mode. figure 7(b) shows the instantaneous active power, p, and the power of the pv plant (ppvz). as can be seen in fig. 7(b), the active power injected into the ac grid has changed nighttime and daytime operating conditions. it is obvious that the pv generation system delivers active power to the grid that matches the solar irradiance variations. it is also clear that the system can control the power injected into the grid and the system has an excellent dynamic performance. also, the suggested control strategy for the dc-ac converters provides a reasonable response. iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 178 fig. 7: (a) solar irradiance, and (b) active power delivered to grid and power of pv plant. fig. 8: output voltage and current of each pv module. figure 8 depicts the output voltage and current of each pv module. as shown in fig. 8, the pv module current is severely affected by the solar radiance variation. however, the mppt controller is operating well since the required results for the pv generating system have been obtained. iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 179 figure 9 depicts the active power injected into the dc bus and the voltage of the dc bus (vdc). figure 9(a) depicts the active power injected into the dc bus. as shown in fig. 9(a), the active power injected into the dc bus, using the pv power plant, increases and reaches to its reference value, which matches the above mentioned solar radiation changes. according to fig. 9(b), the voltage of the dc bus experiences a swell while the pv power generated has been increased and returns to the nominal dc voltage. it is also clear that when the pv power generated has been decreased, the dc bus voltage experiences a sag phenomena. as can be seen, the dc bus voltages (vdc) follow the dc voltage (vdc,ref), which match together. therefore, the real power extracted from the pv power plant can pass through the grid. it is also clear that when the pv power generated has been decreased, the dc network voltage experiences a sag phenomena. fig. 9: (a) output power from the dc bus and (b) dc bus voltage. figure 10 shows the grid-side phase voltage and the line current of the dc-ac converter. the three-phase voltages and currents are shown only for phase a. similar wave-forms can be plotted for phases b and c. the line current changes with power reference variations, which flows into the utility grid. therefore, the converter can deliver the pv generation system power to the grid with a low harmonic current. this verifies the effectiveness of the proposed control system. as can be seen in this figure, there is no phase leading-lagging between the grid-side line current and the voltage. they are in phase and sinusoidal. as a result, the proposed control system is capable of controlling the current injected into the grid at unity power factor by changing the dc-ac converter injected reactive power dynamically. 5.2 voltage dip in the ac grid in this section, the effect of the grid fault on the operation of the pv system has been studied. a three-phase fault at the ac grid has been simulated to model a voltage dip during the time period of t = 3.0 s till t = 3.1 s. figure 11(a) and 11(b) indicate the phase to neutral voltage and the line current for three phases. according to fig. 11(c), the phase to neutral voltage and line current (phase a) is in phase. this verifies the effectiveness of the novel control strategy for the dc-ac converter. iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 180 fig. 10: grid voltage and injected current for a step change from 1000 to 300 w/m2 and from 300 to 800 w/m2. fig.11: (a) grid three phase voltage, (b) grid injected currents and (c) grid voltage and injected current. iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 181 fig. 12: (a) output power from the dc bus and (b) dc bus voltage. figure 12(a) shows the active power injected into the dc bus. considering fig. 12(a), the voltage dip does not have an influence on the maximal power provided by the dc-dc converter. this is due to the dc bus capacitor, which acts as a buffer. figure 12(b) shows the regulation of the dc bus voltage, which matches the grid connected conditions and is constant (750 v). thereby, the real power extracted from the pv power plant can pass through the grid. 5.3 frequency variation of the grid voltage the aim of this section is to study the effect of the network frequency variation on the grid-connected operation condition. the frequency variation has been applied to ac grid at t = 2.8 s (50.2 hz) and at t = 3.0 s (50 hz), which means a frequency variation of 0.2 hz in 0.2 s. figure 13(a) and 13(b) show the phase to neutral voltage and the line current for three phases. according to fig. 13(c), the phase to neutral voltage and the line current (phase a) is in phase. this figure verifies the effectiveness of the novel control strategy for the dc-ac converter. figure 14 depicts the mppt performance of the dc-dc converter and the dc bus voltage controllers. both figures are independent of the frequency variation. 6. conclusion this paper presents a new control structure for a pv generation array in on-grid operation mode. the dynamic model of the pv modules and its power electronic interfaces has been presented. also, a novel control strategy for grid-connected dc-ac converters with power factor control has been suggested. the current and dc voltage controllers have been used to transfer the pv power and synchronize the output converters with the grid. the controller designs for different operating conditions of the dc-ac converter have been presented using the average large signal model. the novel control structure, which is based on instantaneous power control strategy, has been used to control iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 182 fig. 13: frequency variation effect on (a) grid three phase voltage, (b) grid injected currents and (c) grid voltage and injected current. fig. 14: frequency variation effect on (a) output power from the dc bus and (b) dc bus voltage. the active and reactive power delivered from the pv generation system to the utility grid. the simulation results based on pscad/emtdc software demonstrate the effectiveness of the suggested control systems in grid-connected mode. also, simulation results show that the proposed control strategies can control the power factor and regulate the reactive power for pv generating systems. in the simulations, the mppt controller has been used to extract the optimal power from the pv array, while the dc bus voltage remains within acceptable limits. iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 183 references [1] hassaine l, olias e, quintero j, haddadi m. (2009) digital power factor control and reactive power regulation for grid-connected photovoltaic inverter. renewable energy, 34:315-321. [2] hamrouni n, jraidi m, cherif a. (2008) new control strategy for 2-stage grid-connected photovoltaic power system. renewable energy, 33:2212-2221. [3] barbosa pg, rolim lgb, watanabe eh, hanitsch r. (1998) control strategy for gridconnected dc-ac converters with load power factor correction. iee proceedingsgeneration, transmission and distribution,145:487-492. [4] koutroulis e, kalaitzakis k, voulgaris nc. (2001) development of a microcontroller-based, photovoltaic maximum power point tracking control system. ieee tran. power electronics, 16:46-54. [5] hua c, shen c. (1998) study of maximum power tracking techniques and control of dcdc converters for photovoltaic power system. proceedings of the 29th annual ieee power electronics specialists, 1:86-93. [6] hassaine l, olias e, quintero j, salas v. (2014) overview of power inverter topologies and control structures for grid connected photovoltaic systems. renewable and sustainable energy reviews, 30:796-807. [7] noroozian r, gharehpetian gb, abedi m, mahmoodi m. (2010) grid-tied and standalone operation of distributed generation modules aggregated by cascaded boost converters. j. power electronics, 10:97-105. [8] mahmoodi m, gharehpetian gb, abedi m, noroozian r. (2006) novel and simple control strategy for fuel cell converters in dc distribution systems. proceedings of ieee pecon, 1:358-362. [9] mahmoodi m, gharehpetian gb, abedi m, noroozian r. (2006) a suitable control strategy for source converters and a novel loadgeneration voltage control scheme for dc voltage determination in dc distribution systems. proceedings of ieee pecon, 1:363-367. [10] mahmoodi m, gharehpetian gb, abedi m, noroozian r. (2006) control systems for independent operation of parallel dg units in dc distribution systems. proceedings of ieee pecon, 1:220-224. [11] noroozian r, abedi m, gharehpetian gb, hosseini sh. (2010) distributed resources and dc distribution system combination for high power quality. int. j. electrical power and energy systems, 32:769-781. [12] sun power corporation [www.sunpowercorp.com]: residential pv nodule spr-200-blk datasheet. dec. 2004. [13] patel mr. (1999) wind and solar power systems. crc press, u.s. merchant marine academy, kings point, new york. [14] gow ja, manning cd. (1999) development of a photovoltaic array model for use in power electronic simulation studies. iee proceedings on electric power applications, 146:193200. [15] hansen ad, sorensen p. (2000) models for a stand-alone pv system. riso national laboratory: roskilde, denmark. [16] hassaine l, olias e, quintero j, salas v. (2014) overview of power inverter topologies and control structures for grid connected photovoltaic systems. renewable and sustainable energy reviews, 30:796–807. [17] molina mg, espejo ej. (2014) modeling and simulation of grid-connected photovoltaic energy conversion systems. int. j. hydrogen energy, 39:8702-8707. [18] ali sm, pattanayak p, sanki p, sabat rr. (2012) modeling and control of grid-connected hybrid photovoltaic distributed generation system. int. j. eng. sci. emerging tech., 4:125132. iium engineering journal, vol. 17, no. 2, 2016 noroozian & gharehpetian 184 abbreviations pwm pulse-width modulation pv photovoltaic mppt maximum power point tracking vsc voltage source converter pcc point of common coupling hcc hysteresis current control pll phase locked loop hpf high pass filter lpf low pass filter igbt insulated gate bipolar transistor 420 iium engineering journal, vol. 14, no. 2, 2013 chattopadhyay and sengupta 153 harmonic distortion assessment by area based approach at single phasing of an induction motor surajit chattopadhyay and samarjit sengupta 1 dept of electrical engineering, mckv institute of engineering, (west bengal university of technology), 243 gt road (n), howrah, west bengal, india 2 dept of applied physics, prof. and head, university of calcutta, apc road 92, kolkata, 700009, west bengal, india; surajitchattopadhyay@gmail.com; samarsgp@rediffmail.com abstract: this paper presents harmonic distortion assessment by area based approach at single phasing of an induction motor. this has been achieved by assessing voltage and current signals using area based approach. some specific reference signals have been defined, after which, the real power system data are plotted with this reference signal and areas. formed by the real power system data with the reference signal, the reference signal and areas have been calculated, where the contributions of fundamental waveform and the harmonic components in real and reactive powers are being assessed separately. single phasing is done on induction machine as well as the total harmonic distortion factors have been calculated afterwards. moreover, the significant change is observed in harmonic distortion due to single phasing. abstrak: kertas kerja ini membentangkan penilaian herotan harmonik menggunakan kaedah keluasan kawasan pada pemfasaan tunggal motor aruhan. menggunakan kaedah keluasan kawasan, penilaian terhasil dengan memantau isyarat arus dan voltan. sesetengah isyarat rujukan tertentu dikenal pasti, di mana, data sistem kuasa sebenar diplotkan berdasarkan isyarat rujukan ini. kawasan kemudiannya dibentuk dengan adanya data sistem kuasa sebenar dengan menggunakan pengiraan isyarat rujukan. pengiraan ini memberikan bentuk gelombang asas dan komponen harmonik sebenar di mana kuasa reaktif ditentukan secara berasingan. pemfasaan tunggal ditentukan menggunakan mesin aruhan dan faktor jumlah herotan harmonik diambil kira .perubahan yang ketara dikenal pasti dalam herotan harmonik yang disebabkan oleh pemfasaan tunggal. keywords: area based approach; harmonics; single-phasing. 1. introduction maintaining the near sinusoidal waveform of power distribution bus voltages and currents at rated magnitude and frequency is important for good quality of electric power in respect of harmonics. harmonics are generated from various types of sources like actual loads, equipment and components, subsystems of transmission and distribution systems, etc. with the increasing use of solid state control devices, power converter, nonlinear loads like switch-mode-power-supplier and phase control rectifiers in distribution and transmission networks, the amount of such disturbances is also increasing. different type of faults occurred in electrical machine also contribute in harmonic distortion. it leads iium engineering journal, vol. 14, no. 2, 2013 chattopadhyay and sengupta 154 catastrophic consequences such as long production downtimes, mal-function of devices and shortened equipment life. use of induction motor has increased and it demands an early and accurate determination of motor fault for its reliable operation. single phasing is one common fault often observed in industrial application. research work is going on to study the sources and effects of faults. a detail review on measurement of harmonic contribution in impedances and different issues of their practical implementation has been done [1]. modeling is done for large load areas considering harmonics in distributions networks [2]. modeling is also done for assessing harmonics and inter-harmonic distortion in multi-converter system [3]. measurement technique is introduced for determination of harmonic/ inter-harmonics of time varying frequencies [4]. different passive models are introduced for motor control [5-11]. a critical impedance based method has been developed for identifying harmonic sources [5]. passivity-based control system is developed for euler-lagrange systems [7]. a lot of experimental investigations have been done on the passivity based induction motor control [8-10]. modeling of adjustable speed drives for power system harmonic analysis [11] has been done. for this purpose different electric quantities under sinusoidal, non sinusoidal, balanced or unbalanced conditions [12] have been defined. for motor control and fault diagnosis, analysis of air-gap flux, current and vibration signals as a function of the combination of static and dynamic air-gap eccentricity in 3-phase induction motors [13] has been done. for fault diagnosis, use of motor current signature analysis (mcsa) [14] [15] has become very popular. condition monitoring of induction motor is also being done by mcsa [15]. a detail review of induction motor signature analysis as a medium for fault detection has been provided in [16]. some online diagnosis of induction motors using mcsa [14, 17, 18] have been introduced. wavelet and psd are being used as fault detection technique [19]. induction motor stator faults diagnosis has been achieved by a current concordia pattern-based fuzzy decision system [20]. fault detection and diagnosis in an induction machine drive is done using pattern recognition approach based on concordia stator mean current vector [21]. monitoring and diagnosis of induction motor electrical faults using a current park's vector pattern approach [22-25]. current concordia based assessment of single phasing of an induction motor by feature pattern extraction method and radar analysis [26] has been introduced. assessment of crawling of an induction motor has also been done by stator current concordia analysis [27]. in this paper, stator current of induction motor at single phasing are assessed by area based approach. some specific reference signals having sinusoidal nature and different frequencies have been defined. areas formed by the real power system data with the reference signal have been calculated. mathematical relations have been established between those areas with amplitude and phase angles of voltage and current wave forms wherefrom contributions of fundamental waveform and harmonic components have been assessed separately. active power, reactive power and total harmonic distortion factors have been measured. distortion factors of obtained from normal and fault condition have been compared. 2. area based approach for harmonic assessment 2.1 power in terms of area consider v(t) be the voltage and i(t) be the current in a power system. in presence of harmonics, these waveforms can be written as follows iium engineering journal, vol. 14, no. 2, 2013 chattopadhyay and sengupta 155 )sin()( ,.....3,2,1 n nn n tnvtv v ϕω −= ∑ = (1) )(sin)( ,......3,2,1 n nn n tniti i θω −= ∑ = (2) where, n denotes order of harmonics, nv and ni be the highest order of harmonics present in voltage waveform and current waveform respectively. fundamental frequency (ω) is assumed to be constant in single complete cycle. if these waveforms are plotted in voltage – current plane (v-i plane), covered area can be written as follows ∑∫ == − n nnn iv total invkvdia φsin 1 (3) where, ωθϕφ 1.01 =−= kandnnn from (1), iv total n nn n nn aknqinv − = == ∑∑ 1 ,......3,2,1 2 1 )(sin 2 1 φ (4) where, 1 1 1 k k = if voltage and current are plotted in vi-t plane, covered area can be written as follows ∑∫ ∑∑∫ =−−== == − n nnnn n nn n n tvi total ivkdttnitnvvidta φθωϕω cos)(sin)sin( 2 ,......3,2,1,......3,2,1 (5) where, tconsaiskand nnn tan 2 θϕφ −= from (5), tvi total n nn n nn akpiv − = == ∑∑ 2 ,......3,2,1 2 1 )(cos 2 1 φ (6) where, 2 2 1 k k = fundamental and harmonic components of same order, which are present in both voltage and current waveform, contribute to the active and reactive power (4, 6). equation (3) shows that area in v-i plane contains the information of sine of angle between the voltage and current wave form whereas, (5) shows that the area under the curve formed by vi in vi-t plane gives the information of cosine of the phase angle difference between voltage and current waveform. in the proposed scheme, a reference signal (m) of sinusoidal nature has been defined and voltage (v) and current (i) signals have been plotted with the reference signal (m) in v-m, vm-t, i-m and im-t planes respectively, areas have been calculated wherefrom amplitude and phase angles of voltage and current signals of fundamental as well as harmonic components have been isolated. iium engineering journal, vol. 14, no. 2, 2013 chattopadhyay and sengupta 156 2.2 reference signals for assessment of distortion factor, contribution of fundamental and harmonic components should be isolated. to extract powers contributed only by fundamental waveform a reference signal of unity amplitude is defined with the following properties ttm 11 sin)( ω= (7) here ω1 is frequency of the reference signal. the frequency of the reference signal ω1 should be equal to the fundamental frequency ω of the real signal collected from the power system, which is initially an unknown quantity. to select the value of ω1, first take, ωω ∆±= 50 1 , where, ω∆ is a small incremental value. if this signal is plotted against any one of the signals which have been derived from the real power system data, then the starting and ending point will not meet each other. there will be a finite gap between these two points as shown in fig. 1. fig. 1 curves formed by m1 and voltage having unequal fundamental frequency. if ω1 is changed gradually by changing ω∆ in such a way that the starting and ending points come closer to each other then, it can be said that ω1 is approaching towards ω. when starting and ending points come at minimum distance from each other, ideally zero, then it can be said that ω1= ω. then the reference signal will become ttm ωsin)(1 = (8) it should be noted that the reference signal does not consist of harmonic components which may be in the real data. as a result of this, area formed by reference and real signals will not depend on any other frequency except fundamental. real voltage and current signals are plotted with the reference signal (8) and the areas covered by the curve in one complete cycle have been calculated wherefrom amplitude and phase angle of fundamental component, have been derived for assessment of contribution of iium engineering journal, vol. 14, no. 2, 2013 chattopadhyay and sengupta 157 fundamental component in distortion. similarly, reference signal for assessment of harmonic component is defined as tntm n ωsin)( = (9) 2.3 fundamental component in phase r covered by vr and m1 waveforms in vr –m1 plane can be written as follows 1111 sin rr mv r vka ϕ= − mv rrr akvor − = 1111 sin, ϕ (10) covered area in vr m1 -t can be written as follows: 1121 cos rr tvm r vka ϕ= − tvm rrr akvor − = 1211 cos, ϕ (11) from (10) and (11), ( ) ( )212 2 111 tvm r mv rr akakv −− += (12)         = − − − tvm r mv r r ak ak 12 111 1 tanϕ (13) covered area in ir – m1 plane can be written as follows: 1111 sin rr mi r ika θ= − mi rrr akior − = 1111 sin, θ (14) covered area in ir m1 -t plane can be written as follows: 1121 cos rr tim r ika θ= − tim rrr akior − = 1211 cos, θ (15) from (14) and (15), ( ) ( )212 2 111 tim r mi rr akaki −− += (16)         = − − − tim r mi r r ak ak 12 111 1 tanθ (17) 2.4 harmonic component in phase r covered area by curve vr and mn waveforms in vr –mn can be written as follows: rnrn mv rn vka ϕsin1= − mv rnrnrn akvor − = 1sin, ϕ (18) covered area in vr mn -t can be written as follows: rnrn tvm rn vka ϕcos2= − tvm rnrnrn akvor − = 2cos, ϕ (19) from (18) and (19), ( ) ( )22 2 1 tvm rn mv rnrn akakv −− += (20) iium engineering journal, vol. 14, no. 2, 2013 chattopadhyay and sengupta 158         = − − − tvm rn mv rn rn ak ak 2 11 tanϕ (21) covered area in ir – mn plane can be written as follows rnrn mi rn ika θsin1= − mi rnrnrn akior − = 1sin, θ (22) covered area formed in ir mn -t plane can be written as follows rnrn tim rn ika θcos2= − tim rnrnrn akior − = 2cos, θ (23) from (22) and (23), ( ) ( )22 2 1 tim rn mi rnrn akaki −− += (24)         = − − − tim rn mi rn rn ak ak 2 11 tanθ (25) 2.5 harmonic distortion in phase r harmonics distortion is expressed in terms of total harmonic distortion factor. for phase r, using (12), (16), (20) and (24) distortion factors can be written as follows: ( ) ( ) ( ) ( )212 2 11 ,....4,3,2 2 2 2 1 1 .,.........3,2 2 )( tvm r mv r n tvm rn mv rn r n rn rv akak akak v v thd −− = −− = + + == ∑∑ (26) ( ) ( ) ( ) ( )212 2 11 ,....4,3,2 2 2 2 1 1 ,........3,2 2 )( tim r mi r n tim rn mi rn r n rn ri akak akak i i thd −− = −− = + + == ∑∑ (27) 3. experimentation block diagram for experimentation is shown in fig. 2. an induction motor (ventwell corporation make, 415 volts, 3 phase, 50 hz, squirrel cage, 1 hp, 1425 rpm) is fed by balanced supply and is run at no-load. the line currents are stepped down with current transformers (ct) and voltages are stepped down by potential transformer. they are then sampled and digitized and captured thorough data acquisition system (das). each phase is connected through separate switch. suddenly one phase (in fig. 2 it is phase b) is switched off and single phasing is done. voltage and current signals of healthy phases are observed for analysis. iium engineering journal, vol. 14, no. 2, 2013 chattopadhyay and sengupta 159 fig. 2: block diagram for experimentation. 4. results the motor is first run at normal condition and harmonics distortions are measured. then, three cases single phasing are done by switching off phase r, phase y and phase b respectively. for each case harmonics distortions of healthy phase are measured using area based approach. the result is compared with the normal value as presented in table 1. significant rise of harmonics distortions are observed. table 1:distortions factors at normal and fault condition. condition current distortion in healthy phase voltage distortion in healthy phase normal 1.1586 1.1592 single phasing at phase r 16.4655 8.3450 single phasing at phase y 16.4620 8.2550 single phasing at phase b 16.5685 8.6575 accuracy increases with the increase of sampling rate of the data acquisition system. the same technique may be extended in clarke plane which will reduce the computational effort. 5. conclusion in this approach fundamental frequency (ω) has been assumed constant only for one complete cycle and may change in next cycle, which is more advantageous in real system analysis than other methods where (ω) is to be constant throughout the process. small error of the method strengthens the acceptability of the above methods. single phasing has shown significant rise of harmonics distortion that has been detected by area based approach. this is done by capturing voltage and current signals. some specific reference signals are defined, then, real power system data are plotted with this reference signal and areas are then calculated wherefrom contributions of fundamental waveform and harmonic components in real and reactive powers have been assessed separately. single phasing is done on induction machine in each phase and harmonic distortion factors are calculated. significant change of distortion is observed due to single phasing. the application area may be extended in clarke plane for less computational effort. iium engineering journal, vol. 14, no. 2, 2013 chattopadhyay and sengupta 160 references [1] w. xu, e. ahmed, and x. zhang, "measurement of harmonic impedances: practical implementation issues and solutions", ieee transaction. on power delivery, 17.1 (2002):210-16. [2] r. lamedica, a. prodenzi, e. tironi, d. zaninelli, “a model of large load areas for harmonic studies in distributions networks”, ieee transactions on power delivery, 12.1 (1997) [3] r. carbone, d. menniti, r. e. morison. and a. testa, “harmonics and inter-harmonic distortion modeling in multi-converter system,” ieee transaction on power delivery, 10.3(1995):1685-92. [4] m. k. ghartemani, m. r. iravani, “measurement of harmonic/ inter-harmonics of time varying frequencies”, ieee transaction on power delivery, 20.1(2005):23-31. [5] c. li, w. xu, t. tayjasanant, “a critical impedance based method for identifying harmonic sources”, ieee transaction. on power delivery,. 19.2(2004). [6] c. li, w. xu and t. tayjasanant, "interharmonics: basic concepts and techniques for their detection and measurement", electric power systems research,. 66.1(2003):39-48. [7] r. ortega, a. loria, p. j. nickasson, and h. sira-ramyrez. “passivity-based control of euler-lagrange systems”, communications and control engineering. springer-verlag, berlin, (1998). [8] c. cecati. “experimental investigation of the passivity based induction motor control”. industrial electronics, 1998. [9] . gokdere, levent u., and marwan a. simaan. " “a passivity-based method for induction motor control”.. industrial electronics, ieee transactions on 44.5 (1997): 688-95. [10] p. j. nicklasson, r. ortega, and g. espinosa. “passivity based control of a class of blondelpark transformable machines”. automatic control, ieee transactions on 42.5 (1997): 629647. [11] w. xu, h.w. dommel, and m. b. hughes, "modeling of adjustable speed drives for power system harmonic analysis", ieee transaction. on power delivery,. 14.2(1999):595-601. [12] “definitions for the measurement of electric quantities under sinusoidal, non sinusoidal, balanced or unbalanced conditions”, ieee std. 1459-2000, jan. 2000d. [13] g. dorrel, w. t. thomson and s. roach, “analysis of airgap flux, current and vibration signals as a function of the combination of static and dynamic airgap eccentricity in 3-phase induction motors”, ieee transaction. on industry. applications ,. 33(1997):24-34. [14] jee-hoon jung, jong-jae lee and bong-hwan kwon, “online diagnosis of induction motors using mcsa”, ieee transactions on industrial electronics, 53.6(2006):1842-52. [15] neelam mehla and ratna dahiya, “an approach of condition monitoring of induction motor using mcsa”, international journal of systems applications, engineering and development 1.1(2007):13-17. [16] benbouzid, m.e.h., “a review of induction motor signature analysis as a medium for fault detection”, ieee transaction industrial. electron., 47.5(2000):984-993. [17] jordi cusido, luis romeral, juan a. ortego, javier a. rosero and antonio garefa espinosa, “fault detection in induction machines using power spectral density in wavelet decomposition”, ieee transactions on industrial electronics, 55.2 (2008):633-643. [18] jee-hoon jung, jong-jae lee and bong-hwan kwon, “online diagnosis of induction motors using mcsa”, ieee transactions on industrial electronics, 53.6(2006):1842-52. [19] j. cusido, a. jornet, l. romeral, j.a. ortega and a. garcia, “wavelet and psd as a fault detection technique”, itmc 2006-instrumentation and measurement technology conference, proceeding of ieee, sorrento, italy, 24-27 april 2006.. 1397(2006). [20] fatiha zidani, mohamed el hachemi benbouzid, demba diallo, and mohamed saïd naïtsaïd, “induction motor stator faults diagnosis by a current concordia pattern-based fuzzy decision system”, ieee transaction on energy conversion, 18.4(2003):469-75. [21] demba diallo, mohamed el hachemi benbouzid, denis hamad, and xavier pierre, “fault detection and diagnosis in an induction machine drive: a pattern recognition approach iium engineering journal, vol. 14, no. 2, 2013 chattopadhyay and sengupta 161 based on concordia stator mean current vector”, ieee transaction on energy conversion,. 29.3(2005):512-19. [22] m. e. h. benbouzid “monitoring and diagnosis of induction motor electrical faults using a current park's vector pattern approach”, proceeding. of ieee international. conference. on electrical machines and drives, seattle, wa, (1999): 275 – 77. [23] h. nejjari “monitoring and diagnosis of induction motors electrical faults using a current park’s vector pattern learning approach”, ieee transaction. industrial. application., 36.3(2000):730-35. [24] s. chattopadhyay, m. mitra, and s. sengupta: “harmonic analysis in a three-phase system using park transformation technique”, international journal on modeling, measurement and control of general physics and electrical applications, amse, . 80.3 (2007):42-58. [25] chattopadhyay, surajit, madhuchhanda mitra, and samarjit sengupta “electric power quality”, springer, 2011. [26] s chattopadhyay, s karmakar, m mitra, s sengupta, “symmetrical components and current concordia based assessment of single phasing of an induction motor by feature pattern extraction method and radar analysis”, international journal of electrical power and energy systems,. 37.1(2012):43-49. [27] s chattopadhyay, s karmakar, m mitra, s sengupta, “assessment of crawling of an induction motor by stator current concordia analysis”, iet electronic. letters. -. 48.14(2012):841-42. microsoft word vol 6-2p1v2-press.doc iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 1 fuzzy logic based controller for maintaining human comfort within intelligent building system nasrodin t. mustapha, momoh j. e. salami, nazim m. nasiri department of mechatronics engineering, kulliyyah of engineering international islamic university malaysia, p.o. box 10, 50728, kuala lumpur, malaysia abstract:this paper presents an intelligent control approach for air handling unit (ahu) which is an integral part of heat, ventilation, and air conditioning (hvac) system. in the past years various control design for hvac have been proposed as this system remarkably consumes very high energy. but most of the proposed designs were focused on the control flow of heat-transfer medium such as chilled or heated water while the importance of the efficient mixture of outdoor and indoor enthalpies is sometimes ignored. these enthalpies invariably determine the best strategy to overcome thermal load in a controlled environment to satisfy human comfort, hence a control design strategy must be able to efficiently regulate the flow and mixture of outdoor and indoor enthalpies by a proper control of ahu dampers and fans. this approach requires sensors to measure temperature and relative humidity of both outdoor and indoor environments. however, unpredictable level of disturbances coming from many sources including heat generated by occupants, electrical items and air leaking and the continuous changes of outdoor enthalpy makes it difficult to model the process. consequently, conventional controllers are not suitable, hence the use of fuzzy logic controller (flc) is proposed in this paper. this proposed controller operates in a master and slave control loop so as to control the ahu dampers and fans with adjustable output membership function whilst at the same time a scaling-factor method is used to drive the master operation. to implement the proposed system, a small scale prototype has been designed and fabricated. this prototype is an ahu model which consists of ductwork, temperature and humidity sensors, dampers, air cooling and heating systems. a small box is used as a conditioning space in which a room temperature is measured. the control algorithm is programmed using national instrument (ni) labview and executed using ni fieldpoint. experimental results reveal that proper control of ahu dampers and fans is an effective and practical means to satisfy human comfort with minimum energy consumption. keywords: human comfort, intelligent control, air handling unit, adaptive fuzzy logic control 1. intoduction heat, ventilation and air conditioning (hvac) system has nowadays become an integral part of building services. this system comprises several subsystems such as the cooling and heating units, air handling unit (ahu), dedicated digital controllers (ddc) iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 2 and the list could continue. the main function of hvac is to maintain indoor air quality and comfort level which are services that require high energy consumption. many studies [1-10] have shown that about 50-70% of the energy is consumed for the above purposes. however, employing advance and more flexible control technique reduces energy consumption and optimize the performance of the hvac regardless of thermal loads acting upon the system. ahu plays the major task in mechanical regulation of the air coming in and out of the building; and the way the air is conditioned by cooling or heating. this unit is designed to cope with the wide range of the system operating condition as weather and building occupants’ activities change significantly and periodically from day to night and from season to season 1. its primary function is achieved by having mixing dampers in the ahu properly modulated (position) as a function of the three main parameters namely the fluid energy or enthalpy (temperature and moisture) at the ahu discharge (supply air to the zones), outside and the return air. maximizing indoor quality is a process of eliminating contaminants from the air and allowing appropriate amount of air moisture. this process also is handled by mixing dampers. positioning the dampers can be achieved by sending fixed signal to their actuators based on enthalpies measured as mentioned earlier. however, the magnitude of the fixed signal can only be useful with system whose mathematical representation could be formulated. in actual situation ahu cannot easily be modeled as it characterizes highly nonlinear system as result of continuous thermal load from various sources acting on both the conditioned space and the (ahu) unit. for this reason, conventional controller such as pid would not produce desirable results. this paper proposes fuzzy logic controller for air handling unit. it is implemented by taking into accounts the temperatures of supply, outside, return and the mixed air to maintain a zone temperature at the presence of thermal load from various sources. studies have suggested that if outside, supply and return air relative humidity variables are considered for an ahu control, better performance can be expected. however, having more inputs into the ahu controller will further complicate the systems computational task and thus will contribute to the degradation of the control performance. this is avoided by considering only the return and the supply relative humidity as they can sufficiently provide information on an account of moisture level required in the conditioned space. to achieve the best performance of a controller, its parameters must be tuned. however, a system with a nonlinear operating environment cannot rely on a tuning alone as the changes in the process have a great effect in its performance. to overcome this problem an adaptive mechanism must be incorporated into an flc design. adaptive flc is capable of updating its parameters against the changes in the process. this paper proposes the use of adaptive flc which is implemented using scaling-factor method. the adaptive mechanism tunes the flc by adjusting the universal discourse of the output membership function by a factor g0. this method maintains a good performance of the flc. iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 3 2. system description to implement the proposed system, ahu prototype is designed and fabricated as shown in fig. 1. this prototype comprises four dampers actuated by dc motors, temperature and relative humidity sensors, cooling and heating unit, and fans. a cooling unit is linked to the ahu ductwork to supply cold air; and a heater is placed at the discharge point to speed up heating process when required. small box is constructed as a conditioning space where room temperature is measured. this temperature is the reference for all actuating signals as function of the outdoor and indoor enthalpies (temperature + relative humidity). indoor temperature is the variable that is being controlled by properly modulating the mixing dampers oad, ead, and rad and fans saf and raf shown fig. 2. there are times where the outside air is more economical to condition than the return air. during this period an economizer control mode is enabled in which fans and cooling equipments are turned off. figure 2 shows the schematic diagram of the ahu prototype. oats, and mats are jtype thermocouples are used to measure the outside, mixed return and supply temperature respectively; sahs and rahs humidity sensors (with built-in temperature sensor) are used for measuring the temperature and relative humidity of the return and supply air, respectively. saf and raf are supply and boosters fans; oad, ead, rad, and sad are dampers actuated by dc motors. cooled air is supplied to the ahu ductwork denoted as ca, and rhc is a heater. the control algorithm is programmed using ni labview and executed in ni fieldpoint. the controller is designed in such a way that the ahu behaves as a hybrid system which intermittently becomes variable volume or constant volume systems. fig. 1: air handling unit prototype (a) ahu ductwork, (b) fieldpoint and motor relay switches, (c) conditioning space, (d) damper and motor iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 4 saf raf ea – exhaust air oad – outside air damper oa – outside air ead – exhausted air damper oats – outside air temperature sensor rad – returned air damper mats – mixed air temperature sensor oad – outside air damper sats – supply air temperature sensor sad – supply air damper rats – returned air temperature sensor ra – returned air sats supply air temperature sensor sa – supply air rahs – returned air humidity sensor ca – cold air sahs – supply air humidity sensors rhc – reheat coil fig. 2: air handling unit schematic diagram 3. fuzzy controller design fuzzy logic controller (flc) has been used for years in many applications. some of its advantages over the conventional controller are: (i) it is robust than pid since it can cover a much wider range of operating condition than pid, and can operate with noise and disturbances of different natures (ii) it is cheaper to develop than model-based controller or other controller to do the same operation (iii) it is customizable since it is easier to understand and modify their rules, which use human operator’s strategy and are expressed in natural language (iv) it is capable to handle multi-input and vague information. the relationship between fuzzy logic controller inputs and outputs are governed by if-then rules which are characterized by membership function. these rules serve to describe, in linguistic terms, qualitative relationship between these variables. processing those rules provides mechanism to compute response to a given controller input. fuzzy controller usually contains many rules, and if one of them is applied there is a computed degree of iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 5 match between crisp input and the fuzzy sets, which describe the meaning of the antecedent part of the rules, and then ‘clipping’ the fuzzy set describing the meaning of the consequent part of the rule, to the degree to which the antecedent part has been matched by the crisp input. the proposed fuzzy logic controller has two components namely slave and master components. the slave fuzzy logic controller (sflc) consists of six fuzzy control loops intermediately controlling four dampers and two fans. the sflcs are two-input singleoutput controllers. the inputs are the temperature setpoint error, e(t), and the rate of change of this error, δe(t), and the output, u(t), is damper position or fan speed, see fig. 3. the initial rules and input/output membership functions of these controllers are heuristically created and is established based on observation made to capture the behavior of the system. since this approach can be used only for approximating the process identification, we need to iteratively tune the sflc during the design stage which is subject to stability analysis criteria using lyapunov method 10. this tuning process has been carried out manually based on the observation of the system performance such as rise time, overshoot and steady state. the center and slopes of the input membership functions in each region is adjusted so that the corresponding rule provides an appropriate control action. there is need to modify the output membership function as well to adjust the rules governing the output universe of discourse. after the tuning is done, the initial flc parameters namely the input and output membership functions, and the rules are established. nonlinearity is caused by the effect of process dynamics and induced disturbances into the system. the performance of a well-tuned controller degrades when this problem is encountered and therefore the controller must be kept tuned at all the time to adapt to the changes in the process. to overcome this problem an adaptive fuzzy controller is proposed. this is implemented by tuning the output membership functions using scaling-factor method 11. this method is implemented by introducing gain g0 between the fuzzy controller and the controlled devices (dampers and fans). the structure of this fuzzy controller is shown in fig. 4 where fuzzy control adaptive mechanism (fcam) is the master component that adjusts the gain factor g0. the value of this gain is equal to 1 for the original choice of the membership function and therefore when the value of this gain changes is not equal to one the value of control signal instantaneously changes. with the presence of various sources of thermal load in the conditioned space as well as in the ahu itself, the controller provides appropriate command signal to the damper motors and the fans for a desirable system response. but since the system is nonlinear in nature the input-output relationship of the controller must be updated all the time. this is achievable using the adaptive mechanism fcam. the main objective is to optimize the cooling or heating process by a proper mixture of fresh and return air. when the room temperature exceeds a threshold, the mixing dampers and fans are modulated in order to keep the temperature close to its setpoint without sacrificing the required relative humidity level. when the outside air temperature is lower than the return air temperature, it is more economical to condition the outside air and invariably cooling unit reduces its cooling load hence energy usage is lowered. consequently, this approach makes use of the temperatures of the outside, mixed, return and supply air as the parameters to use for the cooling/heating process control. the required amount of outside air entering the air handling unit depends on the three components namely the outside air, return and mixed air temperatures. this amount is expressed in percentage: iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 6 100 )( )( (%) x oatrat matrat oa    (1) where: oa(%) – percentage of outside air (volume) currently entering the air handling duct work rat – return air temperature mat – mixed air temperature oat – outside air temperature fig. 3: sflc structure fig. 4: slfc with adaptive mechanism 4. elements of fuzzy controller (i) fuzzification to perform control operation, the fuzzy control collects data as input from the sensors through the ni fieldpoint input modules and the magnitude of these inputs are subtracted from their reference (setpoint) values to provide error signals which are then converted into a corresponding set of membership functions of seven and five linguistic fuzzy subsets for the error e(t) and δe(t) as shown in fig. 5 and 6, respectively. iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 7 fig. :5 membership function of the sflc for input e(t) fig. 6: membership function of the sflc for input δe(t) (ii) inference engine the control action for the dampers and fans are governed by the error and rate of error of the controlled variable, indoor temperature. for instance, if oad is modulated with respect to the indoor temperature, rt, and the aim is to maintain a desired level then the rule “if (rtsp rt) is lp and the rate of change of (rtsp rt) is sn then control action is mp” provides the membership function of mp (µmp) as: (2) where µlp is the degree of error (rtsp rt) which belongs to the fuzzy subset entitled lp and µsn is the degree of error rate of change (rtsp rt) belonging to the fuzzy subset entitled sn. (iii) defuzzification ln mn sn z sp mp -5 -4 -3 -2 -1 0 1 2 3 4 5 e(t) δe(t) -.5 -0.25 0 0.25 .5 bn sn z sp bp              t rtrt rtrt sp snsplpmp    ,min iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 8 the output membership functions consist of seven and five linguistic fuzzy subsets for mds and fans respectively. the required actuating signals must be in crisp form therefore, the fuzzy controller output must be defuzzified as it is not a precise quantity but rather a logical union of two or more fuzzy membership functions defined on the universe discourse of the output variable. center of gravity has been chosen as the defuzzification method in the proposed fuzzy control so that (3) where z* is the output crisp value fig. 7: center of gravity defuzzification method (iv) fuzzy adaptive scaling factor procedure figure 4 shows the structure of the developed flc with adaptive mechanism. fuzzy control adaptive mechanism fcam updates the range of the universal discourse of the sflc input membership functions by a factor g0. the inputs to the fcam are the same as that of the sflc and the output is the “gain-updating factor”. the membership function of the fcam output variable is shown in fig. 8. fig. 8: membership function of gain-updating factor x(t) 0 0.2 0.5 0.8 1 z s m b vb    dzz zdzz z c c ).( ).( * ~ ~   iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 9 5. experimental results and analysis two cases are considered to study performance of the proposed system. in the first case, the ahu was controlled directly by a fuzzy controller without using the tuning mechanism whereas adaptive mechanism. the effect of disturbances from many sources has been observed in the second case. in case 1, there are two experimental results to compare between first and second tests as shown in fig. 9a and 9b, respectively. in the first test, the room temperature was reset from 22.7oc down to 22.5oc. the room temperature reaches the setpoint in approximately 6 minutes and 4 seconds. this is achieved by increasing the speed of the return air fan from 20% to 40% of its full speed while the rest of the controlled elements are: saf speed is 40%, oad is in 10% open, ead is fully closed and rad and sad are fully open. in the second test, the temperature reaches the setpoint in approximately 4 minutes and 3 seconds from 23.5oc to 23oc. this has been achieved by closing the 10%-opened oad towards the minimum position, saf with constant 60% of full speed, raf with 20% speed and the rest of the controlled elements remain in their original position. in the second test the consumed energy for the fans is less as compared to the first test. this can be seen by the following calculation: test 1: saf speed + raf speed = 40 + 40 = 80, time lapsed, 364 seconds test 2: saf speed + raf speed = 60 + 20 = 80, time lapsed, 243 seconds eventually the new position of the oad has made the difference while the outside air temperature remains constant. these practical and logical results can prove that an ahu that can operate as a combination of cvs and vvs mode can save energy while maintaining the desired indoor environment. in case 2, comparison of the results is shown in fig. 9c and d. the former shows the lapsed time to be 4 minutes 23 seconds while the latter is 4 minutes and 33 seconds before the temperatures rise from 22.6oc to 23.5oc and from 22.5oc to 23oc, respectively. however it can be seen that the temperature gradually increased in fig. 9d, before the step input (new setpoint) is fed to the system. this temperature increase is due to some disturbances. these different responses can be analyzed based on the position and the speed of dampers and fans respectively. in the first observation, only the supply air fan speed has been altered from 40% to 30% where the rest of the controlled elements are: raf is 40%, oad is at its minimum position, ead is fully closed and rad and sad are fully open. on the other iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 10 room temperature 21.6 21.8 22 22.2 22.4 22.6 22.8 23 23.2 0 9:3 7:1 1 0 9:3 7:5 6 0 9:3 8:4 2 0 9:3 9:2 7 0 9:4 0:1 3 0 9:4 0:5 8 0 9:4 1:4 4 0 9:4 2:2 9 0 9:4 3:1 5 0 9:4 4:0 0 9:4 4:4 6 0 9:4 5:3 1 0 9:4 6:1 7 0 9:4 7:2 time t em pe ra tu re (d eg c el ci us ) rt rt setpoint (a) room temperature 21.5 22 22.5 23 23.5 24 0 9:4 7:1 8 0 9: 47 :4 8 0 9: 48 :1 8 0 9: 48 :4 8 0 9: 49 :1 9 0 9: 49 :4 9 0 9: 50 :20 0 9: 50 :5 0 0 9: 51 :20 0 9: 51 :5 1 0 9: 52 :2 1 0 9: 52 :5 1 0 9: 53 :2 2 0 9: 53 :5 2 0 9: 54 :2 2 0 9: 54 :5 3 0 9: 55 :2 3 0 9: 55 :5 4 0 9: 56 :2 4 time te m p er at u re s (d eg c el ci us ) rt rt setpoint (b) room temperature 21.8 22 22.2 22.4 22.6 22.8 23 23.2 23.4 23.6 23.8 9:5 6: 39 0 9:5 7:2 5 0 9:5 8: 10 0 9:5 8: 56 0 9:5 9: 41 10 :0 :27 1 0:1 :12 10 :1: 58 10 :2 :43 10 :3 :29 1 0:4 :14 1 0:5 :0 10 :5 :45 10 :6 :31 10 :7: 16 10 :8: 2 time te m p er at ur e (d eg c el ci us ) rt rt setpoint (c) room temperature 22 22.2 22.4 22.6 22.8 23 23.2 10 :5 9:0 7 10 :5 9:5 2 11 :0 0:3 8 11 :01 :23 11 :0 2:0 9 11 :0 2:5 4 11 :0 3:4 0 11 :04 :25 11 :0 5:1 1 11 :0 5:5 6 11 :0 6:4 2 11 :07 :28 11 :0 8:1 3 11 :0 8:5 8 11 :0 9:4 4 time te m pe ra tu re (d eg c el cu is ) rt rt setpoint (d) fig. 9: experimental results (a) case 1, test 1 (b) case 1, test 2 iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 11 (c) case 2, test 1 (d) case 2, test 2 relative humidities 0 10 20 30 40 50 60 70 9: 56 :3 9 09 :5 7:2 5 09 :5 8:1 0 09 :5 8:5 6 09 :5 9:4 1 10 :0 :27 10 :1 :12 10 :1 :58 10 :2 :43 10 :3 :29 10 :4 :14 1 0:5 :0 10 :5 :45 10 :6 :31 1 0:7 :16 1 0:8 :2 time s a _r h & r a _r h sa_rh ra_rh relative humidities 0 10 20 30 40 50 60 70 10 :5 9:0 7 10 :5 9:5 2 11 :0 0:3 8 11 :0 1:2 3 11 :0 2:0 9 11 :02 :54 11 :0 3:4 0 11 :04 :25 11 :0 5:1 1 11 :05 :56 11 :0 6:4 2 11 :07 :28 11 :0 8:1 3 11 :08 :58 11 :0 9:4 4 time r el at iv e h um id iti es sa_rh ra_rh (a) (b) fig. 10: relative humidity (a) case 2, test 1 (b) case 2, test 2 hand, in the second observation the saf speed and oad position were altered from 55% open to 0 (shut off) and 10% open to fully open, respectively. results have shown that the first experiment is less effective and practical as the relative humidity, shown in fig. 10a, varies with time whereas in the second observation, the relative humidity is almost constant with time. this is achieved by resetting the gain-factor g0 to a value less than 1 which consequently makes the oad controller to provide higher output signal than it does when it was normalized value (i.e g0 = 1). finally, the results obtained here have provided substantial proof that the use of adaptive fuzzy logic controller is effective and practical in regulating ahu dampers position and fans in order to save energy while achieving a desired indoor environment. 6. conclusion in this paper, a new control approach to maintain human comfort is presented. a fuzzy logic controller is developed for air handling unit which is an integral part of hvac system. flc has been successfully applied in solving many problems in industry especially systems or processes which are either nonlinear in nature or affected by disturbance (perturbation) and system parameter changes. an adaptive mechanism has been used to tune the ahu fuzzy logic controller in order to improve the dynamic response of the closed-loop system. in addition, this can be used to minimize the tracking error due to the disturbances and the continuous changes in the process. it is envisaged that the future use of the enhanced flc for optimizing the hvac operation would be more appealing, especially as the technologies that support it are becoming more advanced and cheaper. the utilities will be easier to use in the design and therefore becomes more attractive and more powerful control techniques can be developed. this paper has demonstrated the effectiveness and feasibility of the flc-based controller for ahu dampers and fans which can be used to satisfy a desired controlled environment with minimum energy consumption. iium engineering journal, vol. 6, no. 2, 2005 mustafa et al 12 references [1] p.y guo, z.h.guang, z. bein, y.g. taejon, “a simple fuzzy adaptive control method and application in hvac”, ieee, 1998 [2] j.s.r jang, c.t. sun, e. mizutani, “ neuro-fuzzy and soft computing’, pentice-hall, inc. 1997. [3] h.b verbruggen, h.-j. zimmermann, r. babuska, “fuzzy algorithms for control”, kluwer academic publisher, 1999 [4] t.y sun, “air handling system design”, mcgraw-hill, inc. 1994. [5] f.c. mcquiton, e.d parker, e.d spiler, “heating, ventilating, and air conditioning, analysis and design “, 5th ed, john wiley & sons, 2000. [6] v. bradshaw, “ building control system”, 2nd ed, john wiley & sons, 1993. [7] t. horan, “ control systems and application for hvac/r”, prentice-hall, inc. 1997. [8] d.v. chadderton, “building services engineering”, 2nd ed, e & fn spon, 1998. [9] c,-t. lin and c.s g. lee, 1996, “ neural fuzzy systems: a neuro-fuzzy synergism to intelligent systems”, prentice hall. [10] k.m passino, s. yurkovich, “fuzzy control”, 1998, addision wesly longman, inc [11] l. song and m. liu, 2004, “optimal outside airflow control of an integrated air-handling unit system for large office buildings”, journal of solar energy engineering, volume 126, issue 1, pp. 614-619 507 iium engineering journal, vol. 15, no. 2, 2014 azram and zaman 101 couette flow problem for an unsteady mhd third-grade fluid with hall currents mohammad azram 1 and haider zaman 2 1 department of science in engineering, faculty of engineering, international islamic university malaysia, po box 10, 50728, kuala lumpur, malaysia. 2 faculty of numerical sciences, islamia college university 25120, peshawar 25000, pakistan. azram50@hotmail.com abstract: in this work, we analyze couette flow problem for an unsteady mangnetohydrodynamic (mhd) third-grade fluid in the presence of a pressure gradient and hall currents. existing literature on the topic shows that the effecs of hall current on couette flow of an unsteady mhd third-grade fluid with a pressure gradient has not yet been investigated. the arising non-linear problem is solved by the homotopy analysis method (ham) and the convergence of the obtained complex series solution is carefully analyzed. the effects of pressure number, hartmann number and hall parameter on unsteady velocity are discussed via analysis of plots. abstrak: kajian dijalan untuk menganalisa masalah aliran couette bagi bendalir mhd gred ketiga dan arus hall. bagi topik ini kesan arus hall terhadap aliran couette dalam bendalir mhd gred ketiga tak mantap dengan kecerunan tekanan, belum pernah dikaji selidik. masalah tak linear berbangkit diselesaikan dengan kaedah analisis homotopi (ham) dan ketumpuan solusi rangkaian kompleks dianalisa dengan teliti. kesan nilai tekanan, nombor hartmann dan parameter hall terhadap halaju tak mantap diperbincangkan melalui plot yang dianalisis. keywords: couette flow; hall currents; unsteady flow; third-grade fluid; ham 1. introduction in fluid mechanics, everyone is familiar with the couette flow problem, the flow between two parallel plates in which bottom plate is fixed and upper plate is initially at rest and is suddenly set into motion in its own plane with a constant velocity, is termed as couette flow [1,2]. bhaskara and bathaiah [3] have analyzed the couette flow problem with hall effects for flow through a porous straight channel. ganapathy [4] has written a note on the oscillatory couette flow in a rotating system. erdogan [5] solved unsteady couette flow for viscous fluid by the laplace transform method. stokes and couette flows due to an oscillating wall have been discussed by khaled and vafai [6]. hayat et al. [7] used the laplace transform method to determine the analytic solutions of couette flows of a second grade fluid. oscillatory couette flow has been studied by singh [8]. guria [9] discussed the couette flow problem for rotating and oscillatory flow. couette flow of an unsteady third-grade fluid with variable magnetic field has been investigated by hayat and kara [10], where the fluid is in an annular region between two coaxial cylinders. the axial couette flow problem of an electrically conducting fluid in an annulus has been examined by hayat et al. [11]. das et al. [12] studied unsteady couette flow problem in a rotating system. recently, zaman et al. [13] presented a solution for unsteady couette flow iium engineering journal, vol. 15, no. 2, 2014 azram and zaman 102 problem for the eyring-powell model. when a strong magnetic field is applied in an ionized gas of low density, the conductivity normal to the magnetic field is decreased by free spiraling of electrons and ions about the magnetic lines of force before suffering collisions. this phenomenon is known as the hall effect and a current induced in a direction normal to the electric and magnetic fields is called the hall current [14]. the study of the effects of hall currents on flow of non-newtonian fluids [15-23] is important because of its applications in power generators and pumps, hall accelerators, refrigeration coils, electric transformers, in flight mhd, electronic system cooling, cool combustors, fiber and granular insulation, oil extraction, thermal energy storage, and flow through filtering devices. in order to understand the interaction of electric, magnetic, and hydrodynamic forces in the unsteady third-grade fluid, we considered a simple flow problem, known as the couette flow. the effects of a pressure gradient and hall current on the flow are also taken in to account. the complex analytical solution for the non-linear problem is found by using the homotopy analysis method (ham) [2431]. this solution is valid for all values of time in the whole spatial domain 10 <≤ η . the convergence of the analytic solution is ensured with the help of the ħ-curve. the effect of pressure number, hartmann number, hall parameter, second-grade parameter and thirdgrade parameters on the unsteady velocity are illustrated through plots. also, the effects of the pertinent parameters on the local skin friction co-efficient at the surface of the wall are presented numerically in tabular form. 2. formulation of the problem and its analytic solution consider the unsteady flow of an electrically conducting incompressible third-grade fluid between two parallel flat plates, subjected to a uniform transverse magnetic field. we assume that the bottom plate is fixed and the top plate is stationary when t < 0 and at t = 0, the top plate starts moving impulsively in its own plane with a constant velocity u and a pressure gradient is also applied. the flow here is maintained by the motion of the top plate. the cauchy stress tensor t for a third-grade fluid is given as [32] 1) 2 1 (3)1221(231 2 12211 atraaaaaaaaapit βββααµ +++++++−= (1) where p is the scalar pressure, i is the identity tensor, µ is the co-efficient of viscosity iα , jβ , (i = 1, 2 and j = 1, 2, 3) are the material parameters of third-grade fluid, and ai (i = 1, 2, 3) are the first three rivlin-ericksen tensors defined by [32] a1 = (grad v) + (grad v) t (2) .2,1,)()(1 =++=+ nna t vgradvgradna dt nda na (3) the equations governing the magneto-hydrodynamic flow with hall effects are: velocity field: v = [u (y; t) , 0, 0] (4) iium engineering journal, vol. 15, no. 2, 2014 azram and zaman 103 continuity equation: div v = 0 (5) equation of motion: )()( bjtdiv dt dv ×+=ρ (6) maxwell equations: t b ecurljmbcurlbdiv ∂ ∂ −=== )(,)(,0)( µ (7) generalized ohm’s law: )( bvebj ob eewj ×+=×+ σ τ (8) where u( y; t) is the velocity component in the x-direction, t is time, b (= b0 + b) is the total magnetic field, b0 is the applied magnetic field, b is the induced magnetic field, j is the current density, σ is the electrical conductivity of the fluid, e is the electric field, µ m is the magnetic permeability, ρ is the fluid density, we and τe are the cyclotron frequency and collision time of the electrons respectively. we assume that, the quantities ρ, µ m and σ are constants throughout the flow field, the magnetic field b is normal to the velocity vector v and the induced magnetic field is neglected compared with the imposed magnetic field, so that the magnetic reynolds number is small [33]. we also suppose that weτe ~ o (1) and wiτi << 1 (where wi and τi are the cyclotron frequency and collision time for ions respectively). continuity eqn. (5) is identically satisfied by the velocity taken in eqn. (4). under the aforementioned assumptions the unsteady couette flow problem with hall currents become; ���� � � �� � � � � � ��� � ��� ����������� � � � ��� ����� �� � ��� ����� �� � ��� ����� ������ � ��� (9) 0 � � 1# $%$&, (10) the boundary and initial conditions are ��&, (� � 0, )( & � 0, *+, ( 0, (11) ��&, (� � �. � /, )( & � 0, *+, ( 1 0, ��&, (� � 0, )( ( � 0, *+, 0 2 & 3 0 where ν is the kinematic viscosity, � �� 45 65 � is the hall parameter, u is the velocity of the upper plate and h is the distance between two parallel plates and it will be considered as a length scale of the flow, eqn. (10) shows that p is independent of y. in order to non-dimensionalize the problem let us introduce the similarity transformations, � � /*�7, 8�, 7 � �9 , 8 � :�9 , (12) where *�7, 8� is the dimensionless velocity function, η is the dimensionless distance from the bottom wall and ξ is the dimensionless time. eqn. (9) and eqn. (11) become *" � < �="�> � ? � ="�> � @���������� � * � a*b *" � �=�> � c � 0 (13) *�0, 8� � 0, *�1, 8� � 1, *+, 8 0, (14) iium engineering journal, vol. 15, no. 2, 2014 azram and zaman 104 *�7, 0� � 0, *+, 0 2 7 3 1, where prime denotes differentiation with respect to 7, <�� <�/#0 � is dimensionless second-grade parameter, ?�� ?��/#0e�, a �� ��� ����f �:9 � are dimensionless third-grade fluid material parameters, c �� 9 �fg h h � is the dimensionless pressure number and i��jkl 0 /#�� is the dimensionless modified hartmann number [33]. the local skin friction coefficient or fractional drag coefficient on the surface of the moving wall is m= � n opqrqst��u , (15) now using equations (1), (2), (3), (4) and (12) the eqn. (15) can be written in dimensionless variables as v5 w m= � 2y* z n�1, 8� � < ��> * z�1, 8� � ? � =[��,>��> � �\ a�* z�1, 8��\] (16) where v5 �� /0/^� is the reynolds number. the boundary conditions (14) lead us to take base functions for velocity *�7, 8� as y7_ n8` /, a 1 0, b 1 0] (17) the velocity *�7, 8� can be expressed in terms of base functions as *�7, 8� � ∑ ∑ ωefg̀hlg_hl 7_ 8` (18) to start with the homotopy analysis methods, due to the boundary conditions (14) it is reasonable to choose the initial guess approximation *l�7, 8� � 7�1 � 8 � 78�, 8 0 (19) and the auxiliary linear operator i�*� � ��=�j,>��j� , (20) following the ham and trying higher iterations with the unique and proper assignment of the results converge to the exact solution: *�7, 8� k *l�7, 8� � *��7, 8� � *��7, 8� � * �7, 8� � l � *m �7, 8� (21) at �� 0.1, n=0.1, <=0.1, ?=0.1, a=0.1, p= 0.1 using the symbolic computation we obtained *��7, 8� � 7�1 � 8 � 78� � 3p7810 � 3p7 810 � p78 15 � p7 8 10 � p7 \8 6 � 13p7815 \ � 11p7\10 � 3p7\8\10 � p7 e8\15 � s 2271515 � u606v p78e � p7 8e20 iium engineering journal, vol. 15, no. 2, 2014 azram and zaman 105 � s 5303 � u606v p7\8e � p7 e8e12 � � 5606 � u1212�p78w � � w\l\ � ��l�� p7\8w � � w�l� � �� � � p7e8w, (22) similarly * �7, 8�, *\�7, 8�, *e�7, 8� and so on are calculated. the obtained values of *l, *�, * , ----lead us to take *m �7, 8� � x x ωm,_` 7_ \m�\y_ `hl m� _hl 8` . (23) the total complex analytic solution in compact form is as *�7, 8� � x *m �7, 8� � lim}~g � x x ωm,l` 7_ \m�\ `hl } mhl 8` �g mhl (24) where from initial guess in eqn. (19) we obtain ωl,�l � 1, ωl,�� � 1, ωl, � � �1 (25) ωl,_` � 0, �b � 0,1,2,3�, �a � 0,1,2� all other unknown constants can be determined by utilizing eqn. (25) and using the recurrence relations, which we have calculated but it is not possible to write here due to their length. we know that the auxiliary parameter p gives the convergence region and rate of approximation for the homotopy analysis method. from p-curve in fig.1 we note that the range for the admissible value for p is -1.5 < p < 0. our calculations depict that the series of the dimensionless velocity in eqn. (25) converges in the whole region of η and ξ for p = -0.5. 3. graphs, tables and discussion the discussion of emerging parameters on the dimensionless velocity f ( η, ξ ) is as follows: figures 2 to 7 are plotted in the absence of hall currents and in fig. 8 the hall current is taken into account. figure 2 presents the velocity profile f for various values of ξ. this figure shows that with the passage of time the velocity of the fluid increases due to continuous motion of the upper plate. the boundary layer thickness decreases with the passage of time and shear thinning is seen. figure 3 elucidates the variation of hartmann number on the velocity. it is found that the velocity increases with an increase in n and the boundary layer thickness decreases. this means that the magnetic force provides a mechanism to the control of boundary layer thickness. figure 4 illustrates the influence of a second-grade parameter on the velocity profile f. it is evident from the figure that an increase in α results in the decrease of the velocity; here boundary layer thickness increases and shear thickening is observed. iium engineering journal, vol. 15, no. 2, 2014 azram and zaman 106 fig.1: ħ-curve for f (η, ξ). fig. 2: influence of ξ on f (η, ξ). fig. 3: influence of n on f (η, ξ). fig. 4: influence of α on f (η, ξ). in fig. 5 and fig. 6 the velocity distribution is presented for the various values of third-grade parameters β and ζ. it is observed that the velocity increases by increasing the influence of β and decreases by increasing the influence of ζ. fig. 5: influence of β on f (η, ξ). fig. 6: influence of ζ on f (η, ξ). iium engineering journal, vol. 15, no. 2, 2014 azram and zaman 107 fig. 7: influence of p on f (η, ζ). fig. 8: influence of ε on abs {f (η, ξ)}. figure 7 depicts the variation of the pressure number on the velocity. it is observed that the velocity increases with an increase in p, which is consistent with what is expected. due to the hall current velocity field becoming complex, the absolute value of the velocity profile is plotted in fig. 8. it is observed that with an increase in the hall parameter ε, the absolute value of the velocity increases and boundary layer thickness decreases. it is observed from table 1 that for fixed values of α, β, ζ, ħ, p and ε with increase in hartmann number n, the absolute value of the skin friction co-efficient re × cf given in equation (16) increases for all values of the time ξ. also with an increase in the hall current ε, the absolute value of the skin friction co-efficient decreases for all values of the time ξ. for fixed values of n, ħ, α, β, ζ, p and ε with increase in dimensionless time ξ the absolute value of the skin friction co-efficient decreases at all points. table 2 displays the variation of the skin friction co-efficient with the pressure number p. it is observed from table 2 that increase in the pressure leads to an increase in the shear stress at the wall at all points which is consistent with our expectation. table 1: absolute values of the skin friction co-efficient re × cf with α = 0.1, β = 0.1, ζ = 0.1, p = 0.1, ħ = 0.5. ξ ε = 0.1 ε = 0.1 ε = 0.1 n = 0.1 n = 0.1 n = 0.1 n = 0.1 n = 0.3 n = 0.5 ε = 0.2 ε = 0.3 ε = 0.5 0.2 1.98649 1.99305 1.99961 1.98639 1.98625 1.98586 0.4 1.89823 1.92579 1.95333 1.89783 1.89722 1.89559 0.6 1.80866 1.87047 1.93679 1.80777 1.80641 1.80276 0.8 1.74278 1.84279 1.93615 1.74147 1.73924 1.73350 1 1.74219 1.84016 1.93205 1.74139 1.73920 1.73325 table 2: absolute values of the skin friction co-efficient re × cf with α = 0.1, β = 0.1, ζ = 0.1, ξ = 0.1, ħ = 0.5. p ε = 0.1 ε = 0.1 ε = 0.1 n = 0.1 n = 0.1 n = 0.1 n = 0.1 n = 0.3 n = 0.5 ε = 0.2 ε = 0.3 ε = 0.5 0.2 2.02849 2.03009 2.03168 2.02847 2.02844 2.02834 0.4 2.03078 2.03237 2.03396 2.03076 2.03072 2.03063 0.6 2.03306 2.03465 2.03624 2.03304 2.03300 2.03291 0.8 2.03535 2.03694 2.03853 2.03532 2.03529 2.03519 1.0 2.03763 2.03922 2.04081 2.03761 2.03757 2.03748 iium engineering journal, vol. 15, no. 2, 2014 azram and zaman 108 4. conclusion the couette flow between two parallel plates filled with mhd unsteady third-grade fluid is studied analytically. the effects of the pressure and hall current are also incorporated. a non-linear third-grade model for the fluid is used. the model is invoked into the governing equations and the resulting one dimensional equation for unsteady mhd flow is derived. this equation is solved by ham in general to study the sensitivity of the flow to the parameters that are used in the third-grade model. the various dimensionless parameters seem to affect the velocity a lot. the velocity profile and local skin friction co-efficient are greatly influenced by the hall parameter, pressure and hartmann numbers. references [1] schlichting h. (1968) boundary layer theory, sixth ed., mcgraw-hill, new york. [2] white fm. (1991) viscous fluid flow, mcgraw-hill, new york, u.s.a. [3] bhaskara r, bathaiah nd. (1982) hall effects on mhd couette flow through a porous straight channel. def. sci. j. 32:313-326. [4] ganapathy r. (1994) a note on oscillatory couette flow in a rotating system. asme j. appl. mech. 61:208. [5] erdogan me. (2002) on the unsteady unidirectional flows generated by impulsive motion of a boundary or sudden application of a pressure gradient. int. j. non-linear mech. 37:1091-1106. [6] khaled ara, vafai k. (2004) the effect of the slip condition on stokes and couette flows due to an oscillating wall: exact solutions. int. j. non-linear mech. 39:795-809. [7] hayat t, khan m, ayub m, siddiqui am. (2005) the unsteady couette flow of a second grade fluid in a layer of porous medium. arch. mech. 57(5):405-416. [8] singh kd, gorla mg, raj h. (2005) a periodic solution of oscillatory couette flow through porous medium in rotating system. indian j. pure appl. math. 36:151-159. [9] guria m, jana rn, ghosh sk. (2006) unsteady couette flow in a rotating system. int. j. non-linear mech. 41:838-843. [10] hayat t, kara ah. (2006) couette flow of a third-grade fluid with variable magnetic field. math. comp. modelling. 43:132-137. [11] hayat t, momoniat e, mahomed fm. (2008) axial couette flow of an electrically conducting fluid in an annulus. int. j. modern phys. b 22:2489-2500. [12] das s, maji sl, guria m, jana rn. (2009) unsteady mhd couette flow in a rotating system. math. comp. modelling. 50:1211-1217. [13] zaman h, shah ma, ibrahim m. (2013) unsteady incompressible couette flow problem for the eyring-powell model with porous walls. amer. j. of comput. math 3:313-325. [14] sato h. (1961) the hall effects in the viscous flow of ionized gas between parallel plates under transverse magnetic field. j. phys. soc. japan 16:1427-1433. [15] katagiri m. (1969) the effect of hall currents on the magnetohydrodynamic boundary layer flow past a semi-infinite flat plate. j. phys. soc. japan 27:1051-1059. [16] pop i, soundalgekar vm. (1974) effects of hall current on hydromagnetic flow near a porous plate. acta mech. 20:315-318. [17] gupta as. (1975) hydromagnetic flow past a porous flat plate with hall effects. acta mech. 22:281-287. [18] debnath l, ray sc, chatterjee ak. (1979) effects of hall current on unsteady hydro magnetic flow past a porous plate in a rotating fluid system. z. angew. math. mech. 59:469471. [19] khan m, asghar s, hayat t. (2009) hall effect on the pipe flow of a burgers’ fluid: an exact solution. nonlinear analysis: real world applications 10:974-979. iium engineering journal, vol. 15, no. 2, 2014 azram and zaman 109 [20] hayat t, zaman h, ayub m. (2010) analytic solution of hydromagnetic flow with hall effect over a surface stretching with a power law velocity. numerical methods for partial differential equations 27(4):937-959. [21] ahmad m, zaman h, rehman n. (2010) effects of hall current on unsteady mhd flows of a second grade fluid. cent. eur. j. phys. 8(3):422-431. [22] ayub m, zaman h, ahmad m. (2010) series solution of hydromagnetic flow and heat transfer with hall effect in a second grade fluid over a stretching sheet. cent. eur. j. phys. 8(1):135-149. [23] zaman h. (2013) hall effects on the unsteady incompressible mhd fluid flow with slip conditions and porous walls. applied mathematics and physics 1(2):31-38. [24] liao sj. (2003) beyond perturbation: introduction to homotopy analysis method, chapman and hall, crc press, florida. [25] liao sj. (1992) the proposed homotopy analysis technique for the solution of nonlinear problem. ph.d. thesis. shanghai jiao tong university. [26] liao sj. (2012) homotopy analysis method in nonlinear differential equations, higher education press, beijing, springer-verlag berlin heidelberg. [27] liao sj. (2013) advances in the homotopy analysis method, world scientific publishing company, isbn : 978-981-4551-24-3. [28] liao sj. (2009) notes on the homotopy analysis method: some definitions and theorems. comm. non-linear sci. numer. simm. 14(4):983-997. [29] ayub m, zaman h, sajid m, hayat t. (2008) analytical solution of stagnation-point flow of a viscoelastic fluid towards a stretching surface. comm. nonlinear sci. and numer. simul. 13:1822-1835. [30] zaman h, ayub m. (2010) series solution of unsteady free convection flow with mass transfer along an accelerated vertical porous plate with suction. cent. eur. j. phys. 8(6):931939. [31] zaman h, hayat t, ayub m, gorla rsr. (2011) series solution for heat transfer from a continuous surface in a parallel free stream of viscoelastic fluid. numerical methods for partial differential equations 27(6):1511-1524. [32] rivlin rs, ericksen jl. (1955) stress deformation relations for isotropic materials, j. rational mech. anal. 4:323-425. [33] sutton gw, sherman a. (1965) engineering magnetohydrodynamics, mcgraw-hill, new york. microsoft word vol11_no1_final iium engineering journal, vol. 11, no. 1, 2010 islam et al. 71 prediction of signal attenuation due to duststorms using mie scattering md. rafiqul islam, zain elabdin, omer elshaikh, othman o. khalifa, ahm zahirul alam, sheroz khan and a. w. naji wireless communication and signal processing research group, kulliyyah of engineering, international islamic university malaysia p.o. box 10, kuala lumpur, 50728, malaysia. e-mail: rafiq@iiu.edu.my abstract: the present trend in radio design calls for the use of frequencies above 40 ghz for short links carrying wide-band digital communication signals. in order to utilize the new frequency band efficiently, signal attenuation studies due to duststorms is needed urgently for desert areas. this paper presents a mathematical model which has been developed to predict the signal attenuation due to duststorm. the proposed model enables the convenient calculation of the signal path attenuation based on mie solution of maxwell's equations for the scattering of electromagnetic wave by dust particles. the predicted values from the proposed mathematical model are compared with the measured values observed in saudi arabia and sudan and show relatively close agreement. keywords: signal attenuation, duststorm, mathematical model, duststorm visibility. 1. absorption and scattering by the atmosphere when microwaves pass through the medium containing precipitations like rain, snow or dust particles, the signals get attenuated through two phenomena [1]. a) absorption of energy by these particles. b) scattering of energy out of the beam by these particles. microwaves suffer absorption and scattering by the atmosphere especially at higher frequencies where the scattering effects become more severe [2]. the knowledge of these characteristics is essential to design reliable communications. 1.1 theory of single-particle scattering the basic theory underling mathematical model for attenuation is the theory for single particle scattering [3]. the characteristics of these two phenomena, scattering and absorption, can be expressed most conveniently by assuming an incident plane wave. the total electromagnetic field around the scattering object is split into an incident and a scattered field as shown in fig. 1 [4]: iium engineering journal, vol. 11, no. 1, 2010 islam et al. 72 fig. 1: scattering configuration. the total amplitude of the fields at any point on the surface of the sphere can be given as [5]: i s h h h  (1) i se e e  (2) where, ei and hi denote the incident electric and magnet field, and es and hs denote corresponding scattered fields. 1.2 the total cross-section efficiency factors the power density of the incident wave is uniform in space. therefore, the power loss of the incident wave can be calculated by multiplying the uniform power density with a cross-section, having the dimension of the area. the total power removed from the incident field by absorption and scattering can be represented by the total or extinction cross-section [4]. when the problem is concerned with the flow of energy, poynting vector must be used. so the power density is represented by the averaged poynting vector s . this poynting vector can be splitted into separate terms using the separation of the total field into the incident and scattered field (eq. (1) and eq. (2)), resulting in [4]: i s ds s s s   (3) where, 1 re( *) 2i i i s e h  (4) 1 re( *) 2s s s s e h  (5) 1 re( * *) 2d i s s i s e h e h    (6) ei (r) e s (r) ε (r) u i r u s iium engineering journal, vol. 11, no. 1, 2010 islam et al. 73 and where, ei and hi denote the incident electric and magnet field, whereas es and hs denote corresponding scattered fields. the net power flow through the surface of this sphere can be calculated by integrating the radial component of s over the sphere. if the scatterer is a lossless dielectric, the power flow will be zero. if it is lossy (permittivity is complex), the net power flow will represent the absorption rate pa of energy by the scatterer as shown in fig. 2 and can be written as: a i s dp p p p    (7) where pa represents the integral of the radial component of s . u n u n r p s p a p i u i fig. 2: scattering points. the medium surrounding the particle is assumed to be lossless, so the net flow of the energy of the incident field is zero for every closed surface (pi = 0), and thus: a s dp p p   (8) and from eq. 6; 1 re ( * *) 2a s d i s s i n s p p p e h e h u ds         (9) where un is the unit vector normal to the surface s and directed outwards and the dot represent the inner product as shown in fig. 2. using maxwell equation the sum of absorbed and scattered energy can be expressed as [4]:   1 22 im ( , )a s i e s ip p e u f u u k            (10) where, k : wave number ( (2 )k      ). iium engineering journal, vol. 11, no. 1, 2010 islam et al. 74 1 2        : characteristic impedance of the medium. ue : unit vector defining the polarization of the wave. f (us, ui): the scattering amplitude function; it is a function of the direction of propagation ui of the incident field and of the direction us from the object to the observation point. the ratio of the rate of removal of energy (pa + ps) to the rate of the incident energy (pi) on a unit cross-sectional area of the scatterer is defined as the extinction or total crosssection efficiency factors [4]:  4 im ( , )a st a s e s i i p p u f u u p k           (11) 2. analytical models for scattering two models have been presented for an analytical solution of maxwell's equations for the scattering of electromagnetic wave by dielectric spherical particles, rayleigh approximation and mie solution. 2.1 rayleigh approximation the assumption for rayleigh approximation is that (ka < 1), meaning that the radius a of the particle is small compared with the wavelength. for a dielectric sphere that is small compared with wavelength, the field inside the particle is chosen to be the solution of the equivalent dielectric electrostatic problem. in the rayleigh approximation, the field inside the scattering particle is not modeled properly. for an exact solution the scattered field reflects all the properties of the object which is no longer true for an approximation solution [5]. the extinction or total cross-section efficiency factors by rayleigh approximation expressed as [6]:     2 42 2 2 2 8 '' 1 12 3 ( ' 1) ( '') 2 t s a a ka a ka                      (12) where, a : the particle radius k : the wavenumber (k =2π / λ) ε' , ε'' : the real and imaginary contributions of the relative dielectric constant of the particles iium engineering journal, vol. 11, no. 1, 2010 islam et al. 75 2.2 mie solution mie solution is a complete analytical solution of maxwell's equations for the scattering of electromagnetic wave by dielectric spherical particles. in contrast to rayleigh scattering mie solutions to scattering embraces all possible ratios of diameter to wavelength [7]. mie solutions unlike rayleigh scattering do not depend upon any such limitation and can be utilized to predict attenuation in microwave wave band with high reliability especially at higher frequencies used by new systems with larger bandwidth. the extinction or total cross-section efficiency factors by mie solutions can be expressed as [6]:        2 3 2 3 1 2 3 2 t ka c c ka c ka       (13) where, a : the particle radius k : the wavenumber (k =2π / λ) λ : the wavelength, and c1, c2 and c3: constants whose values depend on real (ε') and imaginary part (ε'') of the dielectric constant of the particles as:   1 2 2 6 2 c         (14)     2 2 2 22 22 2 6 7 7 4 20 1 5 5 152 3 2 3 4 c                                    (15)          2 4 3 22 2 1 2 2 1 2 94 3 2 c                                  (16) 3. signal attenuation due to duststorm the theory of attenuation due to sand and duststorm can be explained in terms of scattering and absorption cross section of a single particle. the methods to predict the signal attenuation due to rain effects can be applied for duststorm because the general model for scattering in sand and dust particle populations is essentially the same as that for a population of hydrometeors; both of them are discrete random medium [3]. iium engineering journal, vol. 11, no. 1, 2010 islam et al. 76 the signal attenuation due to duststorm is estimated generally by solving the forward scattering amplitude function of a single particle [8,9,10]. the solution may be carried out using the rayleigh approximation or mie solutions. the method depends largely on the wave number and particle radius. the attenuation of electromagnetic radiation (at) over a path of extent l through precipitating particles may be written as [11]: 0 l t pa a dx  [db] (17) where ap(db/km) is the specific attenuation characterizing the precipitating particles. the following expression has been used to calculate the attenuation due to rain [11,12,13]:    max min 34.343 10 a p ta a a n a da   [db/km]. (18) where, n(a)da : the particles number per unit volume of air with particles radius between a and a+da, σt : the total attenuation cross section efficiency factors of particle of radius a. 3.1 duststorm predicted model starting from the above, we can expressed the attenuation of electromagnetic radiation (at) over a path of extent l through duststorm as: 0 l t da a dx  [db] (19) where ad is the s pecific attenuation characterizing the duststorm which can be expressed as:    max min 34.343 10 a d ta a a n a da   [db/km]. (20) and where, n(a)da : the dust particles number per unit volume of air with dust particles radius between a and a+da, σt : the total attenuation cross section efficiency factors of dust particle of radius a. iium engineering journal, vol. 11, no. 1, 2010 islam et al. 77 a. using rayleigh approximation goldhirsh [14], in using the rayleigh approximation expression for the total crosssection efficiency factor (σt), expressed the specific attenuation due to duststorm ad as:   3 2 2 2.317 10 1 2 a v                  [db/km] (21) where, v : the visibility in kilometer, λ : the wavelength in meter, γ : constants that depend on the type of land from which the storm originated as well as the climatic conditions, ε' , ε'' : the real and imaginary part of the dielectric constant of the dust particles. goldhirsh formulation is applicable at wavelengths for which the rayleigh condition is applicable which is equal to 48 ghz as a maximum frequency [14]. b. using mie solution in order to derive a mathematical model that can predict the signal attenuation due to duststorm at higher frequencies, the mie expression for total cross-section efficiency factors (σt) that appear in eq. (13) was selected for substitution in eq. (20). so the duststorm attenuation (ad) can be written as:         max min 2 3 2 33 1 2 34.343 10 2 a d a a ka c c ka c ka n a da        [db/km] (22) i. dependence on visibility to calculate the attenuation by eq. (22) requires data for the number of particles of dust n, which is difficult to measure accurately. on the other hand, statistical information on duststorm visibility is available. goldhirsh [14] expresses the visibility in term of the particle density and the radius as: 4 2 5.5 10 ( ) e v km na   (23) where, n : the dust particles number per unit volume, ae : the equivalent particle radius in meters. iium engineering journal, vol. 11, no. 1, 2010 islam et al. 78 by solving n in the above formula we can express the particle density in term of the visibility and the radius as: 4 2 5 .5 1 0 e n v a   (24) ii. general formula by substituting the particle density expression which appear in eq. (24) into eq. (22), the specific attenuation characterizing the duststorm (ad ) may alternately be expressed as:       max min 2 4 3 2 33 1 2 3 2 5.5 10 4.343 10 2 a d a e a ka c c ka c ka da v a              [db/km]. (23) a further approximation can be made in these calculations, assuming that every dust particle in a real storm may be replaced by an equivalent particle (ae) whose radius is the mean radius for all dust particle. by this assumption the value of equivalent particle radius (ae) considered as constant value and eq. (23) may alternately be expressed as an algebraic expression:        2 4 3 2 33 1 2 3 2 5.5 10 4.343 10 2 d e e e e a ka c c ka c ka v a              [db/km]. (24) and can be simplified to:   2 3 5 3 6 4 1 2 3 0.38 d e e ea c k a c k a c k a v     [db/km]. (25) by substituting k = 2π / λ in eq. (25): 3 5 6 3 4 1 2 33 4 0.38 8 32 64 d e e ea c a c a c a v               [db/km]. (26) which can be simplified to: 3 4 1 2 33 4 94.3 3721.2 23381e e ed a a a a c c c v v v         [db/km]. (27) finally, we can express the specific attenuation due to duststorm ad (db/km) as: 3 4 3 4 e e e d x a y a za a v v v      [db/km]. (28) where, ae : the equivalent particle radius in meters, iium engineering journal, vol. 11, no. 1, 2010 islam et al. 79 v : the visibility in kilometer, λ : the wavelength in meter and; x, y and z: constants whose values depend on real (ε') and imaginary part (ε'') of the dielectric constant of the dust particles as:  2 2 565.8 2 x         (29)     2 2 3 22 22 2 6 7 7 4 20 1 5 3.7 10 5 152 3 2 3 4 y                                      (30)          2 4 4 22 2 1 2 2 1 2 9 3.12 10 2 z                                   (31) iii. the formula in term of frequencies (f) in ghz for more simplification of eq. (31) it is better to express the wavelength (λ) in term of frequencies (f) in ghz which is easier to use by microwave network engineers. so the specific attenuation of duststorm ad (db/km) can be expressed as: 3 3 4 4 3 4(0.3) (0.3) (0.3) e e e d x a f y a f za f a v v v    [db/km]. (32) and can be simplified to:  2 2 3 3ed e e a f a x ya f za f v    [db/km]. (33) where, ae : the equivalent particle radius in meters, v : the visibility in kilometer, f : the frequency in ghz, and x, y and z: constants whose values depend on real (ε') and imaginary part (ε'') of the dielectric constant of the dust particles as: iium engineering journal, vol. 11, no. 1, 2010 islam et al. 80  2 2 1886 2 x         (34)     2 2 3 22 22 2 6 7 7 4 20 1 5 137 10 5 152 3 2 3 4 y                                      (35)          2 4 4 22 2 1 2 2 1 2 9 379 10 2 z                                   (36) 3.2 determination of attenuation at different bands a further simplification can be made in this general formula (eq. (33)) to more effective and become easier for use by microwave network designers and engineers. this can be achieved by subdividing the general formula into several formulas, each one can deal with specific microwave band suitable to calculate the signal attenuation due to dust particles at every microwave bands. it is clear from the general formula that the signal attenuation due to dust particles depends on visibility, frequency, dust particles radius and dielectric constant. the dielectric constant values of dust particles are important components in the determination of attenuation. a number of investigators have measured the refractive index of sand and dust samples [9, 15, 16]. a further approximation can make in the new subdivided formulas, assuming that a single value of the refractive index can be fitted for all frequencies range in specific microwave band. i. attenuation at s-band for s-band which is in the range between 2 – 4 ghz, the dielectric constants measured were ε'= 4.56, ε''= 0.251 [15]. the specific attenuation of duststorm ad (db/km) can be expressed as: 3 3 4 4 511 433 2.46 10e e eds a f a f a f a v v v       [db/km]. (37) figure 3 showed the signal attenuation (db/km) versus frequency plot at s-bands for four different values of visibility at equivalent particle radius of 50 μm. iium engineering journal, vol. 11, no. 1, 2010 islam et al. 81 signal atte nuation due to dus tstorm with visibility (10 -500 m) at 50 μm dus t particle radius in s-band. 0 0.05 0.1 0.15 0.2 0.25 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 s-band frequency (2 4 ghz). s ig n a l a tt en u a ti o n (d b /k m ). v=500m v=100m v=50m v=10m fig. 3: signal attenuation (db/km) versus frequency at s-band. ii. attenuation at x-band for x-band which is in the range between 8 – 12 ghz, the dielectric constants measured were ε' = 5.73, ε''= 0.415 [8]. the specific attenuation of duststorm ad (db/km) can be expressed as: 3 3 4 4 513 702 2.5 10e e edx a f a f a f a v v v       [db/km]. (38) the signal attenuation (db/km) versus frequency plot at x-bands for four different values of visibility at equivalent particle radius of 50 μm is shown in fig. 4. signal atte nuation due to dus tstorm with vis ibility (10 -500 m) at 50 μm dust particle radius in x-band. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 8 8.5 9 9.5 10 10.5 11 11.5 12 x-band frequency (8 12 ghz). s ig n a l a tt en u a ti o n ( d b /k m ). v=500m v=100m v=50m v=10m fig. 4: signal attenuation (db/km) against frequency at x-band. iium engineering journal, vol. 11, no. 1, 2010 islam et al. 82 iii. attenuation at ku-band for ku-band which is in the range between 12 – 18 ghz, the dielectric constants measured were ε' = 5.5, ε''= 1.3 [16]. the specific attenuation of duststorm ad (db/km) can be expressed as: 3 3 4 4 542 2806 2.4 10e e edku a f a f a f a v v v       [db/km]. (39) figure 5 showed the signal attenuation (db/km) versus frequency plot at ku-bands for four different values of visibility at equivalent particle radius of 50 μm. signal atte nuation due to dus ts torm with vis ibility (10-500 m) at 50 μm dus t particle radius in ku-band. 0 0.5 1 1.5 2 2.5 3 3.5 4 12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 ku-band frequency (12 18 ghz). s ig n a l a tt en u a ti o n ( d b /k m ). v=500m v=100m v=50m v=10m fig. 5: signal attenuation (db/km) vs frequency at ku-band. iv. attenuation at k-band for k-band which in the range between 18 – 26.5 ghz, the dielectric constants measured were ε' = 5.1, ε''= 1.4 [16]. the specific attenuation of duststorm ad (db/km) can be expressed as: 3 3 4 4 550 3368 2.38 10e e edk a f a f a f a v v v       [db/km]. (40) the signal attenuation (db/km) versus frequency plot at k-bands for four different values of visibility at equivalent particle radius of 50 μm is shown in fig. 6. iium engineering journal, vol. 11, no. 1, 2010 islam et al. 83 signal atte nuation due to dus tstorm with visibility (10 -500 m) at 50 μm dust particle radius in k-band. 0 1 2 3 4 5 6 7 8 18 18.5 19 19.5 20 20.5 21 21.5 22 22.5 23 23.5 24 24.5 25 25.5 26 26.5 k-band frequency (18 26.5 ghz). s ig n a l a tt en u a ti o n ( d b /k m ) v=500m v=100m v=50m v=10m fig. 6: signal attenuation (db/km) vs frequency at k-band. v. attenuation at ka-band for ka-band which in the range between 26.5 – 40 ghz, the dielectric constants measured were ε' = 4, ε''= 1.325 [16]. the specific attenuation of duststorm ad (db/km) expression can be written as: 3 3 4 4 566 3712 2.2 10e e edka a f a f a f a v v v       [db/km]. (41) figure 7 showed the signal attenuation (db/km) versus frequency plot at ka-bands for four different values of visibility at equivalent particle radius of 50 μm. signal atte nuation due to dus ts torm with visibility (10-500 m) at 50 μm dus t particle radius in ka-band. 0 2 4 6 8 10 12 14 26.5 28 29.5 31 32.5 34 35.5 37 38.5 40 ka-band frequency (26.5 -40 ghz). s ig n a l a tt en u a ti o n ( d b /k m ). v=500m v=100m v=50m v=10m fig. 7: signal attenuation (db/km) against frequency at ka-band. iium engineering journal, vol. 11, no. 1, 2010 islam et al. 84 vi. attenuation at w-band for w-band which in the range between 56 – 100 ghz, the dielectric constants measured were ε' = 3.5, ε''= 1.64 [16]. the specific attenuation of duststorm ad (db/km) expression is; 3 3 4 4 594 6232 2.1 10e e edw a f a f a f a v v v       [db/km]. (42) the signal attenuation (db/km) versus frequency plot at w-bands for four different values of visibility at equivalent particle radius of 50 μm is shown in fig. 8. signal atte nuation due to dus ts torm with vis ibility (10 -500 m) at 50 μm dus t particle radius in w-band. 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 w -ban d fre qu e n cy (56 100 ghz ). s ig n a l a tt en u a ti o n ( d b /k m ). v=500m v=100m v=50m v=10m fig. 8: signal attenuation (db/km) versus frequency at w-band. 4. validity of the mathematical model in order to verify the validity of the proposed mathematical model for prediction of signal attenuation due to duststorm, a comparison run between the results obtained from the mathematical model and field measurements were made. at the same time a comparison run between the proposed model and one of the current models was also investigated. 4.1 saudi arabia measurements during the course of measurements, alhaider and ali recorded several duststorms during 1987 in the city of riyadh, saudi arabia [17]. the duststorm was observed both by the meteorological sensors and by the radio links. visibility reduction was measured by using the known marked distance method. for most of the events, the cell size of the storm exceeded 20 km. the measurements run over 14 km microwave link at 40 ghz (ka-band). the millimeter wave transmitters and receivers are placed at 100 m and 25 m above ground, respectively. iium engineering journal, vol. 11, no. 1, 2010 islam et al. 85 4.2 sudan measurements measurement in khartoum-sudan on september 1, 2007 shows attenuation 0.67 db per kilometer observed by the author on 15 km link at 13 ghz (ku band) [18]. the duststorm produced a visibility smaller than 5 m. the predicted value found by proposed model using the ku-band specific attenuation formula is 0.55 db per kilometer for the same visibility which is quite close to measured value of 0.67 db/km. 4.3 comparison of measured and calculated values calculated attenuation values for different values of visibility at 40 ghz are given in table 1 together with attenuation measured values observed in saudi arabia. the predicted values calculated by the proposed ka-band specific attenuation formula (eq. 41) and goldhirsh model (eq. 21). the following values are considered in calculation:  visibility from less than 1 km to more than 5 km.  equivalent dust particle radius (ae) = 30 μm.  the dielectric constants (ε'=4, ε''=1.325).  frequency = 40 ghz. table 1: result of measurements and calculations of signal attenuation due to duststorm for different value of visibility at 40 ghz. calculated value (db/km) measured value (db/km) a c (goldhirsh model) a c (proposed model) a m visibility (km) 0.02 0.13 0.14 0.625 0.01 0.064 0.1 1.25 0.007 0.06 0.071 1.42 0.003 0.021 0.05 3.75 0.002 0.014 0.036 5.56 the signal attenuation (db/km) versus different values of visibility plot at frequency equal to 40 ghz for measured and calculated values is shown in fig. 9. unlike the predicted values from goldhirsh model the attenuation values calculated by the proposed model show close agreement to measurements. iium engineering journal, vol. 11, no. 1, 2010 islam et al. 86 comparison of measured and calculated values of attenuation at 40ghz. 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 5.56 3.75 1.42 1.25 0.625 visibility (km) a tt e n u a ti o n ( d b /k m ) measured value goldhirsh model(ray) proposed model (mie) fig. 9: comparison between measured and calculated attenuation. 5. conclusion a model has been developed to predict microwave attenuation due to dust particles using mie solution of maxwell's equations for the scattering of electromagnetic wave. in this proposed model the term visibility (v) is applied to denote the degree of duststorm density instead of total number of dust particles (n). the predictions show that the attenuation varies from 13 db/km to 0.2 db/km at 40 ghz for dust particle radius equal to 50 μm and the visibility varies from 10 m to 500 m. at higher frequency of 100 ghz, the attenuation varies from 47 db/km to 2db/km for dust particle radius equal to 50 μm and the visibility varies from 10 m to 500 m. the predicted values from the mathematical model are compared with the measured values observed in saudi arabia and sudan. the proposed model predicts the measured data more accurately than existing model. the accurate prediction is useful to design higher frequency links at areas affected by duststorms. references [1] r. k. crane, propagation phenomena affecting satellite communication systems operating in the centimeter and millimeter wavelength bands, proc. ieee, 59(2), 173-88, 1971. [2] k. williams and r. greeley, radar attenuation by sand: laboratory measurements of radar transmission, ieee transactions on geoscience and remote sensing, vol. 39, no. 11, nov 2001. [3] g. brussaard and p.a. watson, atmospheric modelling and millimeter wave propagation (ghapman & hall, uk 1995). iium engineering journal, vol. 11, no. 1, 2010 islam et al. 87 [4] ishimaru, wave propagation and scattering in random media (ieee, n.y. 1997). [5] b.r. vishvakarma and c.s. rai, limitations of rayleigh scattering in the prediction of millimeter wave attenuation in sand and dust storms, geoscience and remote sensing symposium, ieee intr., 1993. [6] collin r., e., antenna & radiowave propagation (mcgraw-hill international edition, singapore, 1985). [7] v. e. cachorro, new improvements for mie scattering calculations, eprintarxiv:physics/0103052, march 2001. [8] s. i. ghobrial and s. m. sharief, microwave attenuation and cross polarization in dust storms, ieee trans. antennas propagat., v. ap-35, pp. 418–425, apr. 1987. [9] t. s. chu, "effects of sandstorms on microwave propagation." bell sys. tech. j.. v. 58, no. 2, feb. 1979. [10] j. goldhirsh, a parametric review and assessment of attenuation and backscatter properties associated with dust storms over desert regions in the frequency range of 1 to 10 ghz, ieee trans. antennas propagation, vol. ap-30, no. 6, pp. 1121-1127, 1982. [11] r. r. rogers, statistical rainstorm models: their theoretical and physical foundations, ieee trans. on antennas and propagation, july 1976. [12] r. l. olsen et al., the arb relation in the calculation of rain attenuation, ieee trans. on antennas and propagation, vol. ap-26, no. 2, mar. 1978. [13] oguchi, electromagnetic wave propagation and scattering in hydrometeors, proceedings of the ieee, vol.71,no.9, sep 1983. [14] j. goldhirsh, “attenuation and backscatter from a derived two-dimensional duststorm model” ieee trans. antennas propagation, v. 49, no. 12, pp. 1703-1711, 2001. [15] s. i. ghobrial, the effect of sand storms on microwave propagation, proc. nat. telecommun. conf., houston, tx. vol. 2, proc. no. ch1539-6/80/0000-0216, pp. 43.5.1-43.5.4, 1980. [16] y. ruike, w. zhensen, and y. jinguang, the study of mmw and mw attenuation considering multiple scattering effect in sand and dust storms at slant paths, international journal of infrared and millimeter waves, vol. 24, no. 8, aug 2003. [17] alhaider, m.a. ali, a.a., experimental studies on millimeterwave and infrared propagation in arid land: the effect of sand storms, sixth international conference on antennas and propagation icap, 1989. [18] zain elabdin omer elshaikh, md. rafiqul islam, othman o. khalifa and momoh jimoh e salami, duststorm measurements for the prediction of attenuation on microwave signals in sudan, submitted to international conference on computer and communication engineering 2008 (iccce‘08) kuala lumpur, may 2008. microsoft word 2_v17no2_compiled_v2_24nov16.docx iium engineering journal, vol. 17, no. 2, 2016 abid et al. 137 stamina of a gasketed bolted flanged pipe joint under dynamic loading muhammad abid1, atta ur rehman shah*2 and hafiz abdul wajid3,4 1interdisciplinary research center, comsats institute of information technology, wah cantt, pakistan. 2department of mechanical engineering, hitec university, taxila, pakistan. 3department of mathematics, comsats institute of information technology, lahore, pakistan. 4department of electrical engineering, islamic university medina, kingdom of saudi arabia. *corresponding author: atta85@engineer.com (received: 1st jun. 2015; accepted: 25th mar. 2016; published on-line: 30th nov. 2016) abstract: gasketed bolted flange joints are the most critical components in pipelines for their sealing and strength under operating conditions. most of the work available in literature is under static loading, whereas in industry, cyclic loads are applied due to the vibrating machinery such as motors, pumps, sloshing in offshore applications and in the ships etc. in this study a three dimensional finite element analysis of a gasketed joint is carried out using a spiral wound gasket under bolt up and dynamic operating conditions (internal pressure, axial and bending) singly and in combination. the cyclic axial loads are concluded relatively more challenging for both the sealing and strength of the joint. higher magnitudes of loads and frequencies are also observed more challenging to the joints performance. abstrak: sendi bebibir yang bergasket dan bolt adalah komponen paling kritikal dalam saluran paip bagi pengedapan dan kekuatan mereka di dalam keadaan operasi. kebanyakan kajian yang sedia ada dalam sastera adalah di bawah pembebanan statik, sedangkan dalam industri, beban kitar digunakan untuk jentera bergetar seperti motor, pam, sloshing dalam aplikasi luar pesisir dan dalam kapal dan lain-lain. dalam kajian ini analisis elemen finite tiga dimensi bagi sendi bergasket dijalankan menggunakan gasket bergelendong spiral dalam keadaan operasi yang dinamik (tekanan dalaman, bersama paksi dan lentur) secara tunggal dan dalam kombinasi. beban paksi kitaran diselesaikan dalam keadaan lebih mencabar bagi pengedapan dan kekuatan sendi. magnitud yang tinggi dari beban dan frekuensi juga didapati lebih mencabar kepada prestasi sendi. keywords: grid-connected pv system; power electronic interface; modeling; control 1. introduction gasketed pipe flange joints are widely used to connect pipe-to-pipe or pipe-to-otherequipment in industries including nuclear, petrochemical, processing, pressure vessels, and piping industries etc. these joints are considered to be the weakest elements (in terms of sealing and strength) in many industrial applications. most of the previous work is limited to bolt up, internal pressure, and static external loading only, but the actual conditions of the industry are dynamic in nature. these dynamic loads may be applied by various vibrating machinery like pumps, motors, and gear machinery. vibrations may also be due to sloshing effects and offshore applications. these dynamic conditions are the actual risk to the strength and sealing capability of the pipe joints. a limited amount of work is iium engineering journal, vol. 17, no. 2, 2016 abid et al. 138 available in literature [1-10] focusing on the dynamic behavior of gasketed bolted pipe joints but no research has yet been observed to address these issues. in a gasketed pipe flange joint, problems of strength, bolt scatter, bolt bending, and joint relaxation are observed even during bolt-up; resulting in the flange rotation and gasket crushing. under applied operating conditions, the performance worsens under bolt-up plus harmonic axial loading. in the present study, a three dimensional finite element analysis of a gasketed pipe flange joint is carried out using a spiral wound gasket (swg) under bolt-up, internal pressure, and harmonically applied external loads (axial and bending); these are given in table 1. variable loading magnitudes applied are selected based on the steady state analysis given in reference [11]. frequencies of loads applied are chosen on the basis of available pumps [12]. a flange joint of four-inch 900# class is used in the present study. table 1: loading conditions sr. # loading type of loading load 1 bolt-up asme bolt up strategy torque=700 nm 2 harmonic loadings harmonic axial loading only al=100~650 kn frq=30~60 hz harmonic bending loading only bl=10~25 knm frq=30~60 hz design pressure plus harmonic axial loadings dp=15.3 mpa al=100~650 kn frq=30~60 hz design pressure plus harmonic bending loadings dp=15.3 mpa bl=10~25 knm frq=30~60 hz design pressure plus combined harmonic axial plus bending loadings dp=15.3 mpa al=525 kn bl=10~20 knm frq=30~60 hz 2. finite element modeling, meshing 2.1 modeling and meshing a complete 360-degree model of the flange joint, developed by [11], is modified and used as shown in fig. 1. due to the symmetry of the geometry and loading conditions, half the thickness of the gasket is modeled. a pipe of 330 mm length is modeled with the flange. keeping in view the symmetry of the joint, only one side of the joint is used. commercial fea software ansys [13] is used during the analysis. a solid45 structural element is used to model the flange, bolt, gasket and pipe; three-dimensional ‘surface-to-surface’ conta174 contact elements, in combination with targe170 target elements are used between the flange face and gasket, bolt shank and flange hole, the top of the flange, and the bottom of the bolt in order to simulate contact distribution for both structural and thermal models. a 3-d interface element inter195 is used as a special gasket element for meshing of the spiral wound gasket, which is compatible with solid45 structural elements. the gasket meshing requires two faces i.e. iium engineering journal, vol. 17, no. 2, 2016 abid et al. 139 source and target faces. the source face which is the top area of the gasket is meshed with shell 63 elements. the fe model used is already validated by [11] under static internal pressure loading. fig. 1: modeling and meshing of flange, bolt and gasket. 2.2 material properties allowable stresses and material properties for the flange, pipe, and bolt are given in table 2 [14]. bilinear elastoplastic material is used for the flange and bolts. non-linear material behavior of the spiral wound gasket is defined using a simplified approach [15]. table 2: material properties 3. boundary conditions bolt-up: bolts are constrained in the radial and tangential directions and are free to elongate in the axial direction. during bolt tightening, displacement is applied at the bottom of the bolts to achieve target stress. asme bolt-up strategy is used to tighten the bolts [16]. the variable loading magnitudes applied are selected based on the steady state analysis given in reference [11]. contact initiation: the contact is initiated between the flange face and the bottom of the bolt and between the flange raised face bottom and the gasket top surface by applying a sufficiently small displacement at the bottom of the bolts (uy= -0.01 mm) such that it must not produce stress in the joint components. pre-stress or bolt-up: target stress in the bolts is achieved by applying a second value of displacement in sequence at the bottom of the bolts. parts as per code young’s modulus (mpa) poisson’s ratio allowable stress (mpa) flange/pipe astm a350 lf2 173058 0.3 248.2 (2/3rd σy) bolt astm sa193 b7 168922 0.3 723.9 iium engineering journal, vol. 17, no. 2, 2016 abid et al. 140 harmonic axial loading: after bolt-up, external axial loads (100~650 kn) with different cyclic frequencies (30~60 hz i.e. 1800~3600 rpm) are applied to analyze the joint behavior. internal pressure plus harmonic axial loading: after bolt-up, static design pressure is applied and then harmonic axial loads (100~650 kn) with different cyclic frequencies (30~60 hz) are applied. harmonic bending loading: after bolt-up, harmonic bending loads (10~25 knm) with different cyclic frequencies (30~60 hz) are applied to analyze the joint behavior. internal pressure plus harmonic bending loading: after bolt-up, static design pressure is applied and then harmonic bending loads (10~25 knm) with different cyclic frequencies (30~60 hz) are applied. internal pressure plus combination of harmonic axial loading plus harmonic bending loading: after bolt-up, static design pressure is applied and then combined harmonic axial loading (525 kn) plus harmonic bending loads (10~20 knm) with different cyclic frequencies (30~60 hz) are applied. applied boundary conditions are shown in fig. 2(a). (a) (b) fig. 2: (a) boundary conditions (b) flange quarter model showing different locations of stress measurement. iium engineering journal, vol. 17, no. 2, 2016 abid et al. 141 4. results and discussions results are taken at different locations in the joint including the pipe, hub center, hubflange fillet, bolts and gasket. some of the locations are tagged in fig. 2(b). 4.1 pipe and hub center stress variation at the pipe and hub center is observed within the yield limit of the pipe and flange material at all locations under all loadings and frequencies. 4.2 hub flange fillet the hub flange fillet is a critical location since principal stress and stress intensity values have exceeded the yield stress limit of the flange material even at bolt-up. 4.2.1 harmonic axial loading only figure 3 shows stress results at the hub flange fillet location under harmonic axial loading. axial stress has crossed the yield limit of the flange material at 400 kn and 525 kn axial loads at 30 hz and 60 hz frequencies respectively. the value of the stress is observed to be increasing with increase in harmonic axial loading. the maximum axial stress at the hub-flange fillet has increased from 228 mpa at bolt-up to 262mpa (15%) and 279 mpa (22%) at maximum axial load of 650 kn acting with a harmonic frequency of 30 hz and 60 hz respectively. the maximum value of stress intensity at the hub-flange fillet has increased from 269 mpa at bolt-up to 310 mpa (15%) and 322 mpa (20%) at maximum axial load of 650 kn acting with a harmonic frequency of 30 hz and 60 hz respectively. increase in the value of sy and sint at 650 kn axial load, is respectively 7% and 5% greater with the cyclic frequency of 60 hz rather than 30 hz. the increase in cyclic frequency has some effects on the stresses value at the hub flange fillet location while the increase in magnitude of the axial load is causing significant increase in the stresses. fig. 3: stresses (sy and sint) results at the hub flange fillet under bup and harmonic axial loading (100~650 kn) of frequency: (a) 30 hz, (b) 60 hz. 4.2.2 internal pressure plus harmonic axial loading figure 4 shows stress results at the hub flange fillet location under combined design pressure and harmonic axial loading. axial stress has crossed the yield limit of the flange 190 210 230 250 270 290 310 330 350 b u p 10 0 20 0 30 0 40 0 52 5 65 0 b u p 10 0 20 0 30 0 40 0 52 5 65 0 b u p 10 0 20 0 30 0 40 0 52 5 65 0 b u p 10 0 20 0 30 0 40 0 52 5 65 0 st re ss (m p a) bup + al(kn) ht-hf hs-hf hs-hf hb-hf sy (a) (b) (a) (b) sint iium engineering journal, vol. 17, no. 2, 2016 abid et al. 142 material at 400 kn at both the frequencies. the value of the stress is observed to be increasing with the application of design pressure and with the increase in harmonic axial loading and frequencies. the maximum axial stress at hub-flange fillet has increased from 228 mpa at bolt-up to 272 mpa (19.2%) and 273 mpa (19.7%) at maximum axial load of 650 kn acting with harmonic frequency of 30 hz and 60 hz respectively. the maximum value of the stress intensity at the hub-flange fillet has increased from 269 mpa at bolt-up to 317 mpa (18%) and 319 mpa (18.5%) at maximum axial load of 650 kn acting with harmonic frequency of 30 hz and 60 hz respectively. the increase in the value of sy and sint at 650 kn axial load is 0.5% greater with the cyclic frequency of 60 hz rather than 30 hz. the increase in the cyclic frequency has negligible effect on the results in this case because the static internal pressure provides damping to the structure, whereas the increase in magnitude of the axial load significantly caused an increase in the stresses. fig. 4: stresses (sy and sint) results at the hub flange fillet under bup, dp and harmonic axial loading (100~650 kn) of frequency: (a) 30 hz, (b) 60 hz. fig. 5: stresses (sy and sint) results at the hub flange fillet under bup and harmonic bending loading (10~25 knm) of frequency: (a) 30 hz, (b) 60 hz. 4.2.3 harmonic bending loading only figure 5 shows the stress results at the hub flange fillet location under harmonic bending loading. with the application of harmonic bending loading, some layers at the hub flange fillet location came under compression and others in tension. values of stress at this location are already very high at bolt-up, so even after compression, no value of stress is 200 220 240 260 280 300 320 340 b u p d p 10 0 20 0 30 0 40 0 52 5 65 0 b u p d p 10 0 20 0 30 0 40 0 52 5 65 0 b u p d p 10 0 20 0 30 0 40 0 52 5 65 0 b u p d p 10 0 20 0 30 0 40 0 52 5 65 0 st re ss ( m p a) bup + dp + al(kn) ht-hf hs-hf hs-hf hb-hf sy (a) (b) (a) (b) sint 190 210 230 250 270 290 b u p 10 13 20 25 b u p 10 0 20 0 30 0 40 0 b u p 10 0 20 0 30 0 40 0 b u p 10 0 20 0 30 0 40 0 st re ss (m p a) bup + bl(kn) ht-hf hs-hf hs-hf hb-hf sy (a) (b) (a) (b) sint iium engineering journal, vol. 17, no. 2, 2016 abid et al. 143 negative. at 25 knm bending load, the axial stress at the top node of the hub-flange fillet has decreased from 228 mpa at bolt-up to 219 mpa and at the bottom node of the hubflange fillet, axial stress has increased from 221 mpa at bolt-up to 229 mpa. variation in the values of the resulting stresses due to change in the frequencies of the applied bending loads is negligibly small. stress intensity at the top node of the hub-flange fillet decreased from 270 mpa at bolt-up to 259 mpa and at bottom node of hub-flange fillet, the principal stress increased from 260 mpa at bolt-up to 271 mpa. stress intensity at all nodes of the hub flange fillet is above the yield limit of the flange material. summarizing, an increase in the magnitude of bending load has a small effect on the resulting stresses while increase in the cyclic frequencies of these loads has no prominent effect in this case. 4.2.4 internal pressure plus bending loading figure 6 shows the stress results at the hub flange fillet location under design pressure plus harmonic bending loading. initially, with the application of internal pressure, the hub flange fillet came under tension but after the harmonic bending loading some of the layers at the hub flange fillet location came under compression. at 25knm bending load, the axial stress has increased from 221mpa at bolt-up to 233mpa. variation in the values of the resulting stresses due to change in the frequencies of the applied bending loads is negligibly small. stress intensity at hub-flange fillet has increased from 260mpa at bolt-up to 283mpa. stress intensity at all nodes of hub flange fillet is above yield limit of the flange material. summarizing, an increase in the magnitude of harmonic bending load after internal pressure has a small effect on the resulting stresses while increase in the cyclic frequencies of these loads has no prominent effect in this case. fig. 6: stresses (sy and sint) results at the hub flange fillet under bup, dp and harmonic bending loading (10~25 knm) of frequency: (a) 30 hz, (b) 60 hz. 4.2.5 internal pressure plus combined harmonic axial loading plus harmonic bending loading figure 7 shows the stress results at the hub flange fillet location under combined internal pressure plus harmonic axial (525 kn) plus harmonic bending loading (10~20 knm). axial stress has crossed the yield limit of the flange material at dp + 525 kn external load. the value of the stress further increased with the application of internal pressure and harmonic axial loading. further application of the combined internal pressure with harmonic axial and bending loadings has a very small effect on the resulting stress values. the maximum axial stress at the hub-flange fillet has increased from 263 mpa and 265 mpa at dp+525 kn to 267 mpa (1%) and 268 mpa (1%) at the maximum external 200 220 240 260 280 300 320 b u p d p 10 13 20 25 b u p d p 10 13 20 25 b u p d p 10 13 20 25 b u p d p 10 13 20 25 st re ss ( m p a) bup + dp + bl(knm) ht-hf hs-hf hs-hf hb-hf sy (a) (b) (a) (b) sint iium engineering journal, vol. 17, no. 2, 2016 abid et al. 144 load of dp + 525 kn + 20 knm acting with a harmonic frequency of 30 hz and 60 hz respectively. the maximum value of the stress intensity at hub-flange fillet has increased from 311 mpa and 312 mpa at bolt-up to 312 mpa and 313 mpa at maximum external load of dp + 525 kn + 20 knm acting with a harmonic frequency of 30 hz and 60 hz respectively. under combined external loadings, an increase in the values of the resulting stress is hardly 1% of those of dp + 525 kn. the increase in cyclic frequency has almost no effects on the stress values under all combined loadings. fig. 7: stresses (sy and sint) results at the hub flange fillet under bup, dp, harmonic axial loading (100~650 kn) and harmonic bending loading (10~25 knm) of frequency: (a) 30 hz, (b) 60 hz. 4.3 bolt stress variation 4.3.1 harmonic axial loading only figure 8 shows the average axial stress results at the mid node gauge of each bolt under bup and axial loads (100~650 kn) acting harmonically with two different frequencies 30 hz and 60 hz. the values of axial stress in bolts increase linearly with the increase in magnitude of axial load and cyclic frequency of the loads. however all resulting stresses are under the yield limit of the bolt material. at an axial load of 650 kn acting harmonically with frequency 30 hz and 60 hz, the average increase in axial stress at each bolt of the joint is almost 45% and 65% more than the bup respectively. 4.3.2 internal pressure plus harmonic axial loading figure 9 shows the average axial stress results at the mid node gauge of each bolt under bup, dp and axial loads (100~650 kn) acting harmonically with two different frequencies of 30 hz and 60 hz. at an axial load of 650 kn acting harmonically with frequencies of 30 hz and 60 hz, the average increase in axial stress at each bolt of the joint is almost 59% and 60% more than the bup respectively. 4.3.3 harmonic bending loading only figure 10 shows the average axial stress results at the mid node gauge of each bolt under bup and bending loads (10~25 knm) acting harmonically with two different frequencies 30 hz and 60 hz. overall four bolts (bolt 1, 2, 3 and 8) came under tension while remaining four bolts (bolt 4, 5, 6 and 7) came under compression. the value of axial 200 230 260 290 320 350 b u p d p d p+ 52 5 d p+ 52 5+ 10 d p+ 52 5+ 20 b u p d p d p+ 52 5 d p+ 52 5+ 10 d p+ 52 5+ 20 b u p d p d p+ 52 5 d p+ 52 5+ 10 d p+ 52 5+ 20 b u p d p d p+ 52 5 d p+ 52 5+ 10 d p+ 52 5+ 20 st re ss ( m p a) bup + dp + al(kn) + bl(knm) ht-hf hs-hf hs-hf hb-hf sy (a) (b) (a) (b) sint iium engineering journal, vol. 17, no. 2, 2016 abid et al. 145 stress in the bolts either increased or decreased linearly with the increase in magnitude of the harmonic bending load. at bending load of 25 knm acting harmonically with any frequency, the variation in axial stress at bolts is 0 to 5% of bup values. fig. 8: average bolt stress variation under bolt-up and harmonic axial loading (100~650 kn) at frequency of: (a) 30 hz, (b) 60 hz. fig. 9: bolt average stress variation under bup, dp and harmonic axial loading (100~650 kn) at frequency of: (a) 30 hz, (b) 60 hz. fig. 10: bolt average stress variation under bolt-up and harmonic bending loading (10~25 knm) at frequency of: (a) 30 hz, (b) 60 hz. 4.3.4 internal pressure plus harmonic bending loading figure 11 shows the average axial stress results at mid node gauge of each bolt under bup, internal pressure and bending loads (10~25 knm) acting harmonically with two 120 170 220 270 320 370 420 b u p 10 0 20 0 30 0 40 0 52 5 65 0 b u p 10 0 20 0 30 0 40 0 52 5 65 0 st re ss ( m p a) b1 b2 b3 b4 b5 b6 b7 b8 (a) (b) 120 170 220 270 320 370 420 b u p 10 0 20 0 30 0 40 0 52 5 65 0 b u p 10 0 20 0 30 0 40 0 52 5 65 0 st re ss (m p a) b1 b2 b3 b4 b5 b6 b7 b8 (a) (b) 120 140 160 180 200 220 240 260 280 b u p 10 13 20 25 b u p 10 13 20 25 st re ss ( m p a) b1 b2 b3 b4 b5 b6 b7 b8 (a) (b) iium engineering journal, vol. 17, no. 2, 2016 abid et al. 146 different frequencies of 30 hz and 60 hz. after the application of internal pressure all bolts came in tension but the after the application of harmonic bending loading, overall four bolts (bolt 1, 2, 3 and 8) come under tension while remaining four bolts (bolt 4, 5, 6 and 7) come under compression. at a bending load of 25 knm acting harmonically with any frequency, the variation in axial stress at the bolts is almost 1 to 12% of that of bup values. fig. 11: bolt average stress variation under bup, dp and harmonic bending loading (10~25 knm) of frequency: (a) 30 hz, (b) 60 hz. 4.3.5 internal pressure plus combined harmonic axial loading plus harmonic bending loading figure 12 shows the average axial stress results at the mid node gauge of each bolt under internal pressure plus combined harmonic axial (525 kn) loading plus harmonic bending loading (10~20 knm). initially, values of axial stress in bolts increase linearly with the increase in magnitude of axial load and cyclic frequency of the loads. but after applying bending loads in combination to the harmonic axial loads, the increase in axial stress has become calmer. at combined loads of dp + 525 kn + 20 knm acting harmonically with any frequency; the average increase in axial stress at any bolt of the joint is up to 2% of dp + 525 kn. fig. 12: bolt average stress variation under bup, dp, harmonic axial loading (100~650 kn) and harmonic bending loading (10~25 knm) at frequency of: (a) 30 hz, (b) 60 hz. 120 140 160 180 200 220 240 260 280 300 b u p d p 10 13 20 25 b u p d p 10 13 20 25 st re ss ( m p a) b1 b2 b3 b4 b5 b6 b7 b8 (a) (b) 120 170 220 270 320 370 420 b u p d p 52 5 d p+ … d p+ … b u p d p 52 5 d p+ … d p+ … st re ss (m p a) b1 b2 b3 b4 b5 b6 b7 b8 (a) (b) iium engineering journal, vol. 17, no. 2, 2016 abid et al. 147 4.4 gasket stress variation nodes on the gasket (outer and inner) sealing ring corresponding to the bolt location are selected to study the contact stress variation with the tightening of each bolt and observe the effect of bolt scatter on the sealing performance. 4.4.1 harmonic axial loading only figures 13 and 14 show gasket stress variation at inside and outside sealing ring diameter respectively, under bup and axial loading (100~650 kn) acting harmonically at two different frequencies of 30 hz and 60 hz. at both the locations, under bup and almost all axial loads and frequencies, the minimum gasket stress is observed at g6 (location of gasket near bolt number 6). an interesting behavior is seen in the gasket under harmonic axial loads. initially, with the increase in axial harmonic loads, the compressive stress in the gasket decreased, but after increasing the load beyond 300 kn with 30 hz and 200 kn with 60 hz the compressive stresses in gasket started to increase. this is because the yielding started at the hub flange fillet location at 200 kn load, and then the reverse loadings produced residual stresses in the gasket. it crushed the gasket, which was more dangerous for the sealing capability of the joint. the minimum compressive stress in the gasket at the inner sealing ring and outer sealing ring was -94 mpa and -117 mpa respectively. the seating stress recommended by the supplier was -68 mpa [17], which apparently shows the joint was safe against leakage, but actually the gasket might have been crushed and too weak to oppose leakage. due to the increase in the cyclic frequency, the stress variation was about 0 to 15 mpa from bolt-up. fig. 13: gasket contact stress variation at inner sealing ring under bolt-up and harmonic axial loading (100~650 kn) at a frequency of: (a) 30 hz, (b) 60 hz. fig. 14: gasket contact stress variation at outer sealing ring under bolt-up and harmonic axial loading (100~650 kn) at a frequency of: (a) 30 hz, (b) 60 hz. 4.4.2 internal pressure plus harmonic axial loading figures 15 and 16 show gasket stress variation at the inside and outside sealing ring diameter respectively, at bup, dp and axial loading (100~650 kn) acting harmonically at two different frequencies of 30 hz and 60 hz. at both locations, the minimum gasket stress was observed at g6 (location of gasket near bolt number 6). with the increase in axial harmonic loads the compressive stress in the gasket was decreasing but at some loads (e.g. 300 kn and 400 kn with 30 hz and 60 hz frequencies respectively) the compressive stress was increasing at some gasket locations because the residual stresses induced reverse loading. it may have crushed the gasket, which was more dangerous for the sealing -130 -120 -110 -100 -90 -80 -70 -60 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss ( m p a) bup dp 100kn 200kn 300kn 400kn 525kn 650kn (a) (b) -160 -150 -140 -130 -120 -110 -100 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss (m p a) bup dp 100kn 200kn 300kn 400kn 525kn 650kn (a) (b) iium engineering journal, vol. 17, no. 2, 2016 abid et al. 148 capability of the joint. the minimum compressive stress in the gasket at the inner sealing ring and outer sealing ring was -92 mpa and -122 mpa respectively. variation of stress by varying cyclic frequency was between 0 mpa to 12 mpa. fig. 15: gasket contact stress variation at inner sealing ring under bolt-up and harmonic axial loading (100~650 kn) at a frequency of: (a) 30 hz, (b) 60 hz. fig. 16: gasket contact stress variation at outer sealing ring under bolt-up and harmonic axial loading (100~650 kn) at a frequency of: (a) 30 hz, (b) 60 hz. 4.4.3 harmonic bending loading only figures 17 and 18 show gasket stress variation at the inside and outside sealing ring diameter respectively, at bup and bending loading (10~25 knm) acting harmonically at two different frequencies of 30 hz and 60 hz. at the inner sealing ring diameter, the minimum gasket stress was observed at g2 and g6 (gasket locations near bolts number 2 & 6). at the outer sealing ring, the minimum gasket stress was observed at g6 and g8 (gasket locations near bolts number 6 & 8). variation of gasket contact stress was small with increase in bending loads and their frequencies. the minimum compressive stress in the gasket at the inner and outer sealing rings was -105 mpa and -133 mpa respectively. hence the joint was almost safe against leakage. fig. 17: gasket contact stress variation at inner sealing ring under bup and harmonic bending loading (10~25 knm) at a frequency of: (a) 30 hz, (b) 60 hz. fig. 18: gasket contact stress variation at outer sealing ring under bup and harmonic bending loading (10~25 knm) at a frequency of: (a) 30 hz, (b) 60 hz. -130 -120 -110 -100 -90 -80 -70 -60 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss ( m p a) bup dp 100kn 200kn 300kn 400kn 525kn 650kn (a) (b) -160 -150 -140 -130 -120 -110 -100 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss (m p a) bup dp 100kn 200kn 300kn 400kn 525kn 650kn (a) (b) -115 -110 -105 -100 -95 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss (m p a) bup 10knm 13knm 20knm 25knm (a) (b) -155 -150 -145 -140 -135 -130 -125 -120 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss (m p a) bup 10knm 13knm 20knm 25knm (a) (b) iium engineering journal, vol. 17, no. 2, 2016 abid et al. 149 4.4.4 internal pressure plus harmonic bending loading figures 19 and 20 show gasket stress variation at the inside and outside sealing ring diameters respectively, at bup, dp and harmonic bending loading (10~25 knm) with frequencies 30~60 hz. at the inner sealing ring diameter, the minimum gasket stress was observed at g6 (gasket location near bolt number 6). at the outer sealing ring, the minimum gasket stress was observed at g8 (gasket location near bolt number 8). in contrast to the results of previous case (only harmonic bending loading), the gasket stress values in this case were sufficiently below bup and the main reason for this was the application of internal pressure. variation of the gasket stress under different harmonic bending loads was again very small. the minimum compressive stress in the gasket at the inner and outer sealing rings was -102 mpa and -130 mpa respectively. hence the joint was almost safe against leakage. fig. 19: gasket contact stress variation at inner sealing ring under bup, dp and harmonic bending loading (10~25 knm) at a frequency of: (a) 30 hz, (b) 60 hz. fig. 20: gasket contact stress variation at outer sealing ring under bup, dp and harmonic bending loading (10~25 knm) at a frequency of: (a) 30 hz, (b) 60 hz. fig. 21: gasket contact stress variation at inner sealing ring under bup, dp, harmonic axial loading (100~650 kn) and harmonic bending loading (10~25 knm) at a frequency of: (a) 30 hz, (b) 60 hz. fig. 22: gasket contact stress variation at outer sealing ring under bup, dp, harmonic axial loading (100~650 kn) and harmonic bending loading (10~25 knm) at a frequency of: (a) 30 hz, (b) 60 hz. 4.4.5 internal pressure plus combined harmonic axial loading plus harmonic bending loading figures 21 and 22 show the gasket stress variation at the inside and outside sealing ring diameter respectively, at bup, dp and combined harmonic axial (525 kn) and -115 -110 -105 -100 -95 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss (m p a) bup dp 10knm 13knm 20knm 25knm (a) (b) -150 -145 -140 -135 -130 -125 -120 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss (m p a) bup dp 10knm 13knm 20knm 25knm (a) (b) -150 -145 -140 -135 -130 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss ( m p a) bup dp dp+525kn dp+525kn+10knm dp+525kn+20knm (a) (b) -150 -145 -140 -135 -130 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 g 1 g 2 g 3 g 4 g 5 g 6 g 7 g 8 st re ss ( m p a) bup dp dp+525kn dp+525kn+10knm dp+525kn+20knm (a) (b) iium engineering journal, vol. 17, no. 2, 2016 abid et al. 150 bending loading (10~20 knm) acting at two different frequencies of 30hz and 60hz. at the inside sealing ring diameter, under all loadings and frequencies, the minimum gasket stress was observed at g6 (gasket location near bolt number 6), while at the outside diameter, the minimum stress was observed at g8 (gasket location near bolt number 8). more contact stress was found under higher combined loads. the reason for this was that the plasticity started at the flange. this stress was dangerous for the gasket and crushed it. the minimum compressive stress in the gasket at the inside and outside sealing ring diameter was -102 mpa and -131 mpa respectively. outwardly, it looked safe for the seal on the basis of seat stress, but actually, the gasket was crushed, increasing the chances of leakage. the variation of the stress by varying cyclic frequency was very small. 4.5 displacement versus time at flange the graph is plotted for a time of 5 seconds when the joint was under external vibration loads only. the plots are typical sinusoidal curves showing the vibration behavior of the flange. higher axial loads and higher cyclic frequencies have resulted in maximum amplitudes. 4.5.1 harmonic axial loading only figure 23 shows the displacement history of the flange innermost location during vibrating axial loads (100~650 kn) with two different cyclic frequencies (30~60hz). the flange joint was under continuous tension and compression loads, but the tension was dominant. the amplitude of the curve was changing in every other cycle and the reason was that the plasticity started at the flange. maximum amplitude in case of 30 hz cyclic frequency was -0.25516 mm (at time step 4.5) and in case of 60 hz cyclic frequency was -0.24764 mm (at time step 2.5), which was initially -0.4 mm at bup. the behavior of the flange displacement under harmonic loads was the fatigue phenomenon which may cause failure at any time step later on. generally, the maximum values found under harmonic axial loads had little difference to those found under equivalent static loads but the actual problem was the fluctuation of stresses and displacements with time under harmonic loads which is called fatigue and therein lies the real challenge. fig. 23: flange raised face displacement versus time under harmonic axial loading (100~650 kn) at a frequency of: (a) 30 hz, (b) 60 hz. -0.5 -0.45 -0.4 -0.35 -0.3 -0.25 -0.2 0 0. 5 1 1. 5 2 2. 5 3 3. 5 4 4. 5 5 0 0. 5 1 1. 5 2 2. 5 3 3. 5 4 4. 5 5 u y (m m ) time (sec) 100kn 200kn 300kn 400kn 525kn 650kn (a) (b) iium engineering journal, vol. 17, no. 2, 2016 abid et al. 151 4.5.2 internal pressure plus harmonic axial loading figure 24 shows the displacement history of the flange innermost location at dp and during the vibrating axial loads (100~650 kn) with two different cyclic frequencies (30~60 hz). higher axial loads and higher cyclic frequencies resulted in maximum amplitudes. maximum amplitude in the case of 30 hz cyclic frequency was -0.26494 mm (at time step of 3.5 seconds) and in case of 60 hz cyclic frequency it was -0.26274 mm (at time step of 1.5 seconds), which was initially -0.4 mm at bup plus dp. again, tension was dominant over compression and the maximum amplitude was in the form of tension. plasticity produced in the flange was the reason for the difference in the amplitude of different cycles. fig. 24: flange raised face displacement versus time under dp and harmonic axial loading (100~650 kn) at a frequency of: (a) 30 hz, (b) 60 hz. 4.5.3 harmonic bending loading only figure 25 shows the displacement history of the flange innermost location during the vibrating bending loads (10~25 knm) with two different cyclic frequencies (30~60 hz). maximum amplitude under both frequencies was almost same but the trend during the time of vibration was different, which showed the effect of frequency change during the fatigue period. the overall amplitude of the displacement was too low in this case in comparison to the previous two cases of axial loading. the maximum amplitude in case of 30 hz cyclic frequency was -0.39978 mm (at time step of 4.5 sec) and in case of 60 hz cyclic frequency was -0.39913 mm (at time step of 0.4 sec), which was initially -0.403 mm at bup. the behavior of the flange displacement under harmonic loads was the fatigue phenomenon, which may cause failure of at any time step later on. 4.5.4 internal pressure plus harmonic bending loading only figure 26 shows the displacement history of the flange innermost location at dp during the vibrating bending loads (10~25 knm) with two different cyclic frequencies (30~60 hz). maximum amplitude under both frequencies was almost same but the trend during the time of vibration was different, which showed the effect of frequency change during the fatigue period. the overall amplitude of displacement was too low in this case -0.5 -0.45 -0.4 -0.35 -0.3 -0.25 0 0. 5 1 1. 5 2 2. 5 3 3. 5 4 4. 5 5 0 0. 5 1 1. 5 2 2. 5 3 3. 5 4 4. 5 5 u y (m m ) time (sec) 100kn 200kn 300kn 400kn 525kn 650kn (a) (b) iium engineering journal, vol. 17, no. 2, 2016 abid et al. 152 fig. 25: flange raised face displacement versus time under harmonic bending loading (10~25 knm) at a frequency of: (a) 30 hz, (b) 60 hz. fig. 26: flange raised face displacement versus time under dp and harmonic bending loading (100~650 kn) at a frequency of: (a) 30 hz, (b) 60 hz. in comparison to the axial loading cases. maximum amplitude in the case of 30 hz cyclic frequency was -0.38558 mm (at time step of 1.5 sec) and in case of 60 hz cyclic frequency was -0.38586 mm (at time step of 2.5 sec) which was initially -0.389mm after the application of internal pressure. the behavior of the flange displacement under harmonic loads was the fatigue phenomenon, which may cause failure of at any time step later on. 4.5.5 internal pressure plus combined harmonic axial loading plus harmonic bending loading figure 27 shows the displacement history of the flange innermost location under dp and combined dp and harmonic axial (525 kn) and bending loadings (10~20 knm) with two different cyclic frequencies (30~60 hz). combined dp plus harmonic axial and bending loadings had almost the same resulting displacement values as those of dp plus -0.42 -0.415 -0.41 -0.405 -0.4 -0.395 -0.39 b u p 0. 4 0. 8 1. 2 1. 6 2 2. 4 2. 8 3. 2 3. 6 4 4. 4 4. 8 0 0. 5 1 1. 5 2 2. 5 3 3. 5 4 4. 5 5 u y (m m ) time (sec) 10knm 13knm 20knm 25knm (a) (b) -0.42 -0.415 -0.41 -0.405 -0.4 -0.395 -0.39 b u p 0. 4 0. 8 1. 2 1. 6 2 2. 4 2. 8 3. 2 3. 6 4 4. 4 4. 8 0 0. 5 1 1. 5 2 2. 5 3 3. 5 4 4. 5 5 u y (m m ) time (sec) 10knm 13knm 20knm 25knm (a) (b) iium engineering journal, vol. 17, no. 2, 2016 abid et al. 153 harmonic axial loading. it showed that the combined internal pressure plus harmonic axial and bending loadings have no more effect than the combined dp plus axial loading. maximum amplitude in the case of 30 hz cyclic frequency was -0.29132 mm (at time step 3.5 sec) and in case of 60 hz cyclic frequency was -0.28736 mm (at time step 1.5 sec) which was initially -0.38 mm at dp. the behavior of the flange displacement under harmonic loads was the fatigue phenomenon which may cause failure at any time step later on. fig. 27: flange raised face displacement versus time under harmonic axial loading (100~650 kn) at a frequency of: (a) 30 hz, (b) 60 hz. 5. conclusion  in harmonic analysis, axial loadings are concluded to be more critical over bending loadings in addition to internal pressure. at the hub flange fillet location, stress values have exceeded the yield limit (250 mpa) of flange material, which is a risk to the mechanical strength of the joint. reverse loadings after the yield limit are producing residual stress in the gasket, which crushes the gasket and increases the chances of leakage.  in the case of harmonic axial loads plus internal pressure, the stress values increase about 19% at the hub flange fillet location, and 60% at the bolts, which is a sign of risk to the joint strength.  combinations of harmonic loads and internal pressure produce lesser stresses and displacements in comparison to single harmonic loads. this is because combined loads damp out each other’s effects.  higher amplitudes of harmonic loads and higher frequencies result in more stresses and displacements, hence a greater risk to the joint strength and sealing capability. on the other hand, lower frequencies cause a greater number of fatigue cycles in the same vibration time interval, which is also a risk for sealing.  in all cases, the gasket stresses were above the recommended seating stress of -68 mpa, which showed that the gasket was crushed and this would affect the sealing capability of the joint. -0.5 -0.45 -0.4 -0.35 -0.3 -0.25 -0.2 0 0. 5 1 1. 5 2 2. 5 3 3. 5 4 4. 5 5 0 0. 5 1 1. 5 2 2. 5 3 3. 5 4 4. 5 5 u y (m m ) time (sec) dp+525kn dp+525kn+10knm dp+525kn+20knm (a) (b) iium engineering journal, vol. 17, no. 2, 2016 abid et al. 154  in the case of harmonic axial loads plus internal pressure, an average maximum displacement of -0.26 mm was produced at the flange raised face, which was initially -0.4 mm at bup plus internal pressure. this change in displacement showed flange rotation, which is responsible for producing a gap between the two flanges at the contact faces. hence, there was a chance of leakage. references [1] gaul l, lenz j. (1997) nonlinear dynamics of structures assembled by bolted joints. acta mechanica, 125(1–4):169-181. [2] ibrahim ra, pettit cl. (2005) uncertainties and dynamic problems of bolted joints and other fasteners. j. sound and vibration, 279:857-936. [3] jalali h, ahmadian h, mottershead je. (2007) identification of nonlinear bolted lap-joint parameters by force-state mapping. int. j. solids and structures, 44:8087-8105. [4] khan nb. (2009) stamina of gasketed pipe flange joint under combined loading: 3d fea study. ms thesis, gik institute of engineering sciences and technology. topi, pakistan. [5] lina t, lia r, long h, ou h. (2006) three-dimensional transient sealing analysis of the bolted flange connections of reactor pressure vessel. nuc. eng. design, 236(24):2599-2607. [6] luan y, guan z, cheng g. (2010) the study on nonlinear dynamic behaviors of the structures with bolted-flange joint. iop conf. series: materials science and engineering, 112. [7] miller hl. (2001) piping vibration involving control valves. int. joint generation conference and exposition asme international power division, 1-11. [8] ouyang h, oldfield mj, mottershead je. (2006) experimental and theoretical studies of a bolted joint excited by a torsional dynamic load. int. j. mechanical sciences, 48:14471455. [9] semkea wh, bibel gd, jerath s, guravb sb, webster al. (2006) efficient dynamic structural response modelling of bolted flange piping systems. int. j. pressure vessels and piping, 83:767-776. [10] tanlak n, sonmez f, talay e. (2010) detailed and simplified models of bolted joints under impact loading. the j. strain analysis for engineering design, 46(3):213-225. [11] abid m. (2000) experimental and analytical studies of conventional (gasketed) and uncoventional (non gasketed) flanged pipe joints (with special emphasis on the engineering of 'joint strenght' and 'sealing'). phd thesis, university of strathclyde, glasgow, uk. [12] wilcoxon research. pump monitoring with wilcoxon piezoelectric accelerometers. http://www.wilcoxon.com. 2009. [13] ansys inc. (2011), ansys elements manual, 13th edition, ansys inc. [14] american society of mechanical engineering (1998) asme boiler and pressure vessel code section viii, part d. new york, usa. [15] nagata s, shoji y, toshiyuki s. (2002) a simplified modeling of gasket stress-strain curve for fem analysis in bolted flange joint design. asme international pvp conference, bc canada, 53-58. [16] abid m, hussain s. (2007) bolt preload scatter and relaxation behavior during tightening a 4 in-900# flange joint with spiral wound gasket. proc. imech, 222(part e), j. process mechanical engineering, 123-134. [17] asme pcc-1-2000. (2002) guidelines for pressure boundary bolted flange joint assembly. an american national standard. nomenclature hf hub flange hb hub bottom hs hub side iium engineering journal, vol. 17, no. 2, 2016 abid et al. 155 ht hub top bup bolt up sy bending stress sint stress intensity dp design pressure al axial loading bl bending loading frq frequency 452 iium engineering journal, vol. 15, no. 1, 2014 mohamed et al. 33 comparison of two total rna extraction protocols from cho-k1 cells for rt-pcr: cutoff cost for researchers vasila p. mohamed, yumi z.h-y. hashim, a. amid and m. mel bioprocess and molecular engineering research unit (bpmeru), department of biotechnology engineering, faculty of engineering, international islamic university malaysia, po box 10, 50728, kuala lumpur, malaysia. yumi@iium.edu.my abstract: various methods have been described to extract rna from adherent mammalian cells. rna isolation in conjunction with reverse transcription polymerase chain reaction (rt-pcr) is a valuable tool used to study the gene expression profiling. this approach is now being used in mammalian cell bioprocessing for helping to understand and improve the system. the objective of this study was to compare and determine the most suitable rna extraction method for cho-k1 cells in a setting where a relatively large amount of samples were involved. total rna was extracted using total rna purification kit (without dnase treatment; norgen, canada) and rneasy mini kit (with dnase treatment; qiagen, usa) respectively. the extracted rna was then reverse transcribed, and the cdna was subjected to pcr-amplifying 18s. yield from rneasy kit was significantly higher (0.316 ± 0.033 µ g/µl; p=0.004) than total rna purification kit (0.177 ± 0.0243 µ g/µ l). however, the rna purity of both methods was close to 2.0 and there was no significant difference between the methods. the total rna purification kit is less expensive than rneasy kit. since there is no dnase treatment step in the former, extraction time for rna is shorter. when the extracted rna was subjected to rt-pcr, both methods were able to show detection of 18s at 219 bp. therefore, this study demonstrates that both protocols are suitable for rna extraction for cho-k1 cells. rneasy mini kit (qiagen) is recommended if higher yields is the primary issue and the total rna purification kit (norgen) is recommended if time and cost are concerned. abstrak: pelbagai kaedah telah digunakan untuk mengekstrak rna daripada sel mamalia lekat. pemencilan rna dengan menggunakan reaksi rantai polimerase transkripsi berbalik (rt-pcr) merupakan kaedah penting yang digunakan dalam mengkaji pernyataan gen berprofil. pendekatan ini kini digunakan dalam pemprosesan bio sel mamalia untuk memahami dan menambah baik sistem. tujuan kajian dijalankan adalah untuk menentukan dan membandingkan kaedah ekstraksi rna yang paling sesuai bagi sel cho-k1 di persekitaran di mana kadar sampel yang agak besar terlibat. jumlah rna diekstrak menggunakan kit penulenan jumlah rna (tanpa rawatan dnase; norgen, canada) dan kit mini rneasy (dengan rawatan dnase; qiagen, usa). rna yang diekstrak kemudiannya diterbalikkan transkripsi, dan cdna menjalani penguat pcr 18s. hasil daripada kit rneasy adalah lebih tinggi (0.316 ± 0.033 µ g/µ l; p=0.004) berbanding dengan kit penulenan jumlah rna (0.177 ± 0.0243 µ g/µl). walaupun begitu, kaedah penulenan rna untuk kedua-duanya hampir 2.0 dan tidak terdapat perbezaan yang ketara antara keduanya. kit penulenan jumlah rna adalah lebih murah berbanding dengan kit rneasy. memandangkan tidak ada langkah rawatan dnase dengan penggunaan kit jumlah rna, tempoh ekstrak rna nya lebih pendek. apabila rna yang telah diekstrak menjalani rt-pcr, kedua-dua kaedah berjaya mengesan 18s pada 219 bp. kesimpulannya, kajian ini menunjukkan kedua-dua kaedah sesuai untuk mengekstrak rna bagi sel cho-k1. kit mini rneasy (qiagen) lebih sesuai jika hasil iium engineering journal, vol. 15, no. 1, 2014 mohamed et al. 34 yang tinggi diinginkan dan kit penulenan jumlah rna (norgen) pula ideal, jika kos dan masa berkepentingan. keywords: cho-k1; rna extraction; reverse transcription polymerase chain reaction (rt-pcr) 1. introduction chinese hamster ovary (cho) cells have been widely used in the large scale production of protein. in the biotechnology industry, cho is among the most common cell line used in biomedical research and the pharmaceutical industry for production of recombinant proteins [1]. the origin of rna (e.g. from human, animal or plant), sampling procedures (biopsy material, single cell sampling, laser micro-dissection, tissue) as well as the method of rna isolation (total rna or polyadenylated rna methods) often differs from one laboratory to another [2]. various methods have been described to extract rna from adherent mammalian cells, some of which are provided in protocols accompanying various commercially available kits and reagents. these protocols are based on specific principles. some involve extra steps such as dnase treatment [3] which normally increase the cost. nevertheless, it is always important to ensure that the rna extracted is of good quality with sufficient amount in order to successfully perform other downstream techniques in gene expression profiling. specifically, dna-microarray and quantitative reverse transcriptase polymerase chain reaction (qrt-pcr) are two powerful techniques widely used in functional genomics for the analysis of gene expression profiles [4]. reverse transcriptasepcr (rtpcr) allows the amplification and the quantification of previously undetectable amounts of mrna [5]. therefore, the objective of this study was to compare two methods to extract total rna from cho-k1 cells to be used for rt-pcr. this study is part of our work to optimize media for optimal cell proliferation with emphasis on change at specific gene expression level. this study involves relatively large amount of samples which require rna extraction protocols. as such, an efficient, time and cost-effective method is of paramount importance to ensure successful and meaningful interpretation of gene expression profiles. 2. materials and methods 2.1 supplies rneasy mini kit and nuclease-free water were obtained from qiagen (usa). total rna purification kit was obtained from norgen (canada). all plastics and nuclease-free plastics tubes were obtained from orange scientific (belgium). agarose powder was obtained from promega (usa). the dna ladder was purchased from fermentas (canada). 2.2 cho-k1 cell line cho-k1 cells (atcc ccl – 61 tm ) were obtained from american type culture collection (atcc). the cell line was maintained in a rpmi 1640 medium (mediatech, usa) supplemented with 10% (v/v) fetal bovine serum (fbs) at 5% co2/ 37°c. t-75 flasks were used for cell cultivation. all cultures were initiated at a viable cell concentration 2.0 x 10 5 cells/ml. at 70 80% confluence level, cells were counted and pelleted by centrifugation (3 minutes at 1200 rpm). the cells were resuspended in 0.5 ml iium engineering journal, vol. 15, no. 1, 2014 mohamed et al. 35 phosphate buffer saline (pbs) and centrifuged at 2000 rpm for 5 minutes. after the second wash, the supernatant was discarded and cell pellet was stored in -80˚c until required. 2.3 rna extraction two different methods to extract total rna were applied. the following commercially available kits were used: total rna purification kit (norgen, canada) and rneasy mini kit (qiagen, usa). total rna was extracted according to manufacturer’s instructions [6, 7]. the rna samples were stored at -80°c until further analysis. for the rna study, three technical replicates were used. 2.4 rna quantity, purity and quality measurements the total rna quantification and purity were determined using a nanophotometer tm pearl (implen, canada). the rna yield was evaluated by measuring the extinction at 260 nm. additionally, the od260/230 and the od260/280 ratio showing rna purity were examined. the issue of rna quality was assessed by calculating the a260/280 ratio to rule out dna and protein contamination. obtained values were submitted to student’s t-test analysis. for total rna quality determination, traditional method by gel electrophoresis was used. the integrity of total rna was assessed on the basis of visualization of 28s and 18s ribosomal rna subunits under gel documentation system. 2.5 rt-pcr of rna from cho-k1 cells the reverse transcription (rt) reaction was carried out in a final volume of 20 µl rna samples using superscript iii reverse transcriptase kit (invitrogen, usa), according to the manufacturer’s instructions. 2.6 polymerase chain reaction (pcr) primers for amplification of regions of the 18s gene sequences were designed and chosen using ncbi, primer bank [8] and primer 3 [9] databases. sequences of primers used in this study appear in table 1. primers were synthesized by first base (1 st base, malaysia). each amplification reaction comprised of 1x reaction buffer; 0.2 mm dntps mix; 2.5 u taq dna polymerase; 2.0 mm mgcl2 (invitrogen, usa) and 0.3 mm of each primer (1 st base, malaysia). cdna template of samples and rnase free water were used as negative controls for the amplifications. amplification profile is depicted as table 2. analysis of amplified cdna fragments were electrophoresed on 2.0% agarose gels in 1x tae buffer, and bands were visualized by ethidium bromide staining and uv transillumination. 2.7 statistical analysis mean rna yield (µ g/µl) and purity (a260/280 ratios) between different rna extraction methods were compared using spss software (t-test). the level of significance was set at p<0.05. table 1: primers for 18s gene. gene sequence accession number 18s f 5’-aggtcggtgtgaacggatttg-3’ nm_008084 r 5’-tgtagaccatgtagtggtca-3’ note: f=forward and r= reverse the accession number is given for only one representative matching sequence on the ncbi database (http://www.ncbi.nlm.nih.gov/). iium engineering journal, vol. 15, no. 1, 2014 mohamed et al. 36 table 2: amplification profile for 18s gene. steps temperature (ºc) duration cycle pre-denaturation 94 2 min 1 denaturation 94 30 s 35 annealing 61.0 30 s extension 72.0 1 min final extension 72.0 10 min 1 3. results and discussion 3.1 cho-k1 rna yield rna yields from cho-k1 cells obtained through both protocols are summarized in table 3. the yield was found to be approximately 1.8 times higher for all rneasy (qiagen, usa) samples when compared to total rna purification (norgen, canada) method. rna extracted with rneasy produced the highest amount of rna (total of 0.316 µ g/µl). the overall yields seemed to be comparable to those reported for rneasy and total rna purification kit manufacturers. table 3: summary of results from rna extractions. method total rna purification (norgen) rneasy (qiagen) sample cho-k1 frozen (cell pellet) cho-k1 frozen (cell pellet) rna yield, µg/µl (average ± sd; n=3) 0.177 ± 0.024 *0.316 ± 0.033 reported rna yield up to 101.5 µg total rna per sample up to 100 µg total rna per sample a260/a280 ratio (average ± sd; n=3) 2.007 ± 0.035 2.056 ± 0.027 dnase treatment no yes estimated extraction time of rna (hr) 0.2 0.4 estimated bench time (hr) 1.7 1.9 cost (rm) 990.00 1515.00 note: * p=0.004 estimated bench time (hr) is the total time to include rna extraction, dnase treatment if needed and analysis by spectrophotometry. estimated extraction time of rna (hr) is the total time to extract total rna only. 3.2 rna quality the issues of rna quality was assessed by calculating the a260/280 ratio to rule out possible dna and protein contamination. the total rna was first extracted using rneasy kit with and without dnase treatment. the results show that the rna yield were 0.062 for sample with and 0.080 µ g/µ l without dnase treatment with rna purity of 1.84 and 1.96 respectively. since the rna yield and purity results for with and without dnase treatments were very similar, therefore the rneasy kit with dnase treatment was decided to be further used for this study to serve as control. the total rna purification without iium engineering journal, vol. 15, no. 1, 2014 mohamed et al. 37 dnase treatment and rneasy with dnase treatment were then used to extract total rna and the range of ratios for all types of samples examined was from 1.976 to 2.086 with mean for both methods were close to 2, which is indicative of pure rna (table 3). the quality of rna was inspected by agarose gel electrophoresis to determine the rna integrity (fig. 1). all samples showed bands typical of non-degraded rna with high intensity of 28s and 18s fragments. in this regard, it is interesting to note that both methods have their own advantages on providing good quality of rna for further analysis. the yield of isolated rna using rneasy was significantly higher than total rna purification method (p = 0.004). however, there is no significant difference between purity of rna in the methods compared. fig. 1: rna integrity check for samples extracted from norgen and qiagen rna extraction kit (n=2). lane 1: sample 1a; (norgen), 2: sample 1b ; (norgen), 3: sample 2a; (qiagen), and 4: sample 2b ; (qiagen). 3.3 bench time and cost the extraction time required by both protocol was slightly different. total rna purification method required shorter time due its shorter incubation period in the steps compared to rneasy method (table 3). accurate determination of total rna concentration is particularly important for absolute quantification of mrna levels where mrna copy numbers are best normalized against total rna and any significant dna contamination will result in inaccurate quantification [3]. thus, when time is reduced per sample, it can reduce time for many samples which is good for large number of samples. this would ensure the high quality of samples retained since samples can be processed quickly. in terms of cost, rneasy kit was more expensive when compared to total rna purification method (fig. 2). fig. 2: comparison of rna yield, purity and estimated cost (rm) between rneasy and total rna purification method. *p = 0.004 iium engineering journal, vol. 15, no. 1, 2014 mohamed et al. 38 3.4 rt-pcr of rna from cho-k1 cells for further analysis, the utility of the isolated rna from cho-k1 cells was tested by performing reverse-transcriptase pcr (rt-pcr) using supercript iii to build the first strand cdna. figure 3 showed the detection of 18s gene at 219 base pairs. rna isolated through both methods was suitable for rt-pcr. fig. 3: amplifiction of 18s cdna fragments on 2 % agarose gel in 1x tae buffer. lane 1: 100bp dna ladder, 2: sample 1a; (norgen), 3: sample 1b ; (norgen), 4: sample 2a; (qiagen), 5: sample 2b ; (qiagen), 6: rt-con; rt control is without rt enzyme and 7: pcr-con; pcr control is without cdna template. 4. conclusion in this study, both protocols were found to be suitable for rna extraction from chok1 cell lines. however, total rna purification method is recommended if simplicity, time and cost are a concern while rneasy method can be used if high yield of rna is desired. specifically, since total rna purification method gave comparable result to rneasy when applied in rt-pcr, use of the former protocol may save overall time and cost as well as maintain the same sample standard through minimizing the cycle time for each sample. this is particularly important when dealing with large number of biological samples. acknowledgements this project is funded by the ministry of education (moe), malaysia grant frgs 0409110 and supported by nano life quest sdn. bhd. references [1] jayapal, k.p., wlaschin, k.f., hu, w.s., yap m.g.s. “recombinant protein therapeutics from cho cells – 20 years and counting.” chemical engineering progress 103.10 (2007): 40. [2] nour, a. m. a., barbour, e. k., depint, f. dooms, m., niang, k., dulac, a., niamba, c. n., chayaa, g., pouillart, p. r. “comparison of five rna extraction methods from rabbit’s blood.” agriculture and biology journal of north america, 1.4(2010):448-50. [3] bustin, s. a. “quantification of mrna using real-time reverse transcription pcr (rtpcr): trends and problems.” journal of molecular endocrinology, 29(2002):23-39. [4] muyal, j. p., muyal, v., kaistha, b. p., seifart, c., fehrenbach, h. “systemic comparison of rna extraction techniques from frozen and fresh lung tissues: checkpoint towards gene expression studies.” diagnostic pathology. 4.9(2009):1-8. [5] liedtke, w., battistini, l., brosnan, c. f. “a comparison of methods for rna extraction from lymphocytes for rt-pcr.” genome res., 4.(1994):185-87. [6] norgentotal rna purification kit. thorold: biotek corporation.(2010) norgen qiagen rt-con pcr-con iium engineering journal, vol. 15, no. 1, 2014 mohamed et al. 39 [7] qiagen. rneasy® mini handbook. usa: qiagen.(2010) [8] wang, x., seed, b. “a pcr primer bank for quantitative gene expression analysis.” nucleic acids research, 31.24(2003):154. [9] rozen, s., skaletsky, h.j. “primer3 on the www for the general users and for biologist programmers.”). bioinformatics methods and protocols: humana press, totowa, nj., 1999. 365-86.